CHEMCAD 7 Thermophysical

The Standard Component Database Page 1 of 89The Standard Component Database The standard CHEMCAD database maintains properties for a number of pure components. You can access all the components, or limit access only to certain classes of compounds such as alcohols or aldehydes. Along with standard physical property data, the program keeps a database of about 6000 pairs of binary interaction parameters for use with the NRTL, UNIQUAC, Margules, Wilson, and Van Laar activity coefficient methods. This data can be accessed directly by any simulation. Optionally, you can view or print the data's individual components or groups of compounds. Data stored in the standard database can be accessed in read-only mode. That is, you can print it or use it as a part of a simulation, but you cannot change it in any way. You can, however, copy a component to a user database and then change any parameter you want. Accessing Property Data To access the CHEMCAD component database, select Thermophysical > Component Database. The options on this sub-menu enable you to add new components to the user database or edit properties for existing compounds. Please note that you cannot change any values in the CHEMCAD database directly; you can, however, duplicate a component and then edit the copy to create a user-defined component. Note: Most of the data for CHEMCAD is for the Library equations. However, the program also keeps other data for alternate methods for items such as vapor pressure and liquid density. User-added Components CHEMCAD allows you to add components to the database. This permits you to save data for compounds that are not in the database or if you wish to change individual properties for some of the standard components. Additional components can be added to the pool or corporate database. Editing Components View/Edit Use this command to edit User Added components directly. The main difference between the use of this command on standard components and user components is that, while editing standard components, all the numeric fields are for display only. When editing a user component, the fields become editable. Before being able to edit a standard component, you must first use the Copy command to make it a user (editable) component. Clone Component The Clone Component command enables you to make a copy of an existing component. The component to be copied may be either a library component or one that you defined previously. The default name for the new component will be Clone [Component name]. Delete Component This command erases a component from the list of user defined components. When you select this option, the program will give you a list of the User Added components in the library. It will not present you with ALL the components in the database as you are not allowed to erase components from the Chemstations database. You can select the components by ID number, by formula, or by typing in its synonym (if available). It will then ask you to confirm the deletion. Adding New Components New Component You can define new component properties for CHEMCAD in three ways. They can be estimated from correlations suited for hydrocarbon pseudo-components, estimated by the Modified Lydersen method, or entered by the user from the keyboard. In any case, a minimum of data may be entered. Defining A Pure Component (Group Contribution) The UNIFAC / Modified Lydersen method estimates the physical properties of individual components from their molecular weight and molecular structure. It may be used to estimate properties for all kinds of compounds, whether they are hydrocarbon, chemical, polar or non polar. It is necessary that the functional groups in the molecule be in the CHEMCAD database. The required input is the molecular weight and the compound molecular structure. It is recommended that you input the normal boiling point and specific gravity. This method can estimate these two properties, but other properties generated by the program will be more accurate if you can supply them. After invoking the New Component command, follow this procedure to create a new compound. 1. Select either Group Contribution or Pseudo-component method. For our example, select Group contribution and click OK. 2. Fill out the Group Assignment forms (using the tabs to access each form) to include all the functional groups and quantities of each group found in this molecule. Note that there are hydrocarbon groups listed for both ring or straight chain molecules. Example: Ethyl Alcohol is composed of 1 Methyl group ( CH3), 1 Methylene (>CH2) group, and 1 hydroxy group ( OH). Each of these would have a 1 in each field. 3. Click OK. CHEMCAD now allows you to name & optionally provide Boiling point, specific gravity, or API gravity data. 4. Use the Edit Component menu to review data generated by the program and to change estimated data with any available experimental values. Defining A Pure Component (Manual input) When entering data manually, you must satisfy the minimum system requirements. Each component must have molecular weight, critical temperature, and pressure, specific gravity, acentric factor, and the coefficients for the ideal gas heat capacity. You can enter as much data as you have available. Defining a Hydrocarbon Pseudocomponent The hydrocarbon pseudo-component method is used for estimating properties for pseudocomponents that may be constituents of pure hydrocarbon mixtures. This method is specifically for hydrocarbons in the form of lumped components. The method is empirical and requires only a minimal amount of information to generate reasonable properties for fractions. Only the average boiling point and specific gravity of the mixture are required input. Follow this procedure after selecting New Component from the menu. 1. Select pseudo-component and click OK. 2. The Component Name, Normal Boiling Point, and either the Specific Gravity or API Gravity must be entered. 3. Choose the correlation for estimating molecular weight. Select from: Chemstations [Default] Old API New API Lee Kesler 4. Choose the Critical Properties Method. Select from: Cavett [Default] file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 2 of 89 API Lee Kesler 5. Click OK to save data and the program will generate the properties and automatically call up the Edit Component menu. 6. Use the Edit Component menu to review data generated by the program and to change estimated data with any available experimental values. Component Property Regression The CHEMCAD regression package lets you fit experimental data to obtain properties for pure compounds. The available regression options are: · Antoine vapor pressure · Heat of vaporization · Library ideal gas heat capacity · Library vapor pressure · Liquid density · Liquid heat capacity · Liquid surface tension · Liquid thermal conductivity · Liquid viscosity · Polynomial ideal gas heat capacity · Vapor thermal conductivity · Vapor viscosity To use the regression package with any of these properties, follow the steps outlined in the CHEMCAD User Guide. Data from Distillation Curves Sometimes the material data available is in the form of a distillation curve. In this case, CHEMCAD allows you to enter the whole curve and will break it into a set of pseudo-components that covers the entire distillation range. You access this option from the Thermophysical menu by selecting the Distillation Curve command. This command allows you to enter a distillation curve. This distillation curve permits the program to break the material into pseudo-components based on boiling range. These are also known as fractions. Once the material has been divided into pseudo components, these fractions can be treated as pure components. In turn, you can calculate the properties and vapor liquid equilibrium constants for them as with the pure compounds. The first time you use this command, the program will take you from one step to the next. On subsequent uses, it will give you an editing menu that allows you to choose each command individually. Entering a crude assay: 1. First, define any pure compounds in the flowsheet. If the curve is going to be used in a problem where steam is used for distillation, then Water (62) must be in the component list. Other light hydrocarbons, the "light ends", are commonly present. You must also select these components. 2. Select Thermophysical > Pseudocomponent Curves. The first time you use the command, the program will display a screen prompting you for ID numbers of streams to be characterized. If more than one stream number is entered, the properties of both streams can be blended by CHEMCAD to create a common set of pseudocomponents (see 5 below). 3. Select which correlation to use for estimating molecular weight and critical properties of the pseudocomponents. Molecular Weight Method · Chemstations [default] · New API · Old API · Lee Kesler Critical Properties Method · Cavett [default] · API · Lee Kesler ASTM D86-TBP Interconversion Method · Chemstations · New API [default] Liquid Viscosity Model · Abbott · API [default] · Twu 4. The next screen will ask you to enter the temperature cut range. The range of the cut and the number of cuts determines the "width" of a boiling range in each pseudocomponent. The default ranges will be shown in the input screen. For example, the default range shows that there are four points in the range between 1200 and 1600 °F. Each pseudocomponent in that range will be 100 degrees wide. 5. Select Edit curve data to enter the bulk properties for the whole material. · Distillation Curve Type: Specify the type of distillation curve you are using. · Pressure: Enter the pressure if the selected curve type (above) requires a specified pressure. · Gravity type: Choose the type of bulk gravity to be used. Select either specific gravity or API gravity. · Bulk gravity: Input the bulk gravity for the curve. · Total flow units: Select flow units to use for the feed rate. · Total flow rate: Enter the total flow rate in the units specified above. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 3 of 89 · Water flow rate: If water is being carried with the oil, then enter the flow in the rate units specified above. · Light ends flow unit: Select the flow basis in which the data is presented. Options include: Volume %, Weight %, Mole/hr, Mass/hr · Distillation Curve: Select the units for the distillation curve (volume % or weight %). · Blend distillation curves/Do not blend distillation curves: Designate whether the program is to blend two curves and generate fewer components. If blending is not performed, each curve will contain more cuts and be more precise. · Viscosity: If you have viscosity data, you can enter it to improve the accuracy of your pseudocomponent curve. To do this, you must check this option, which causes CHEMCAD to display the Viscosity Data dialog box. 6. An input form is now displayed that allows you to enter the actual distillation curve. 7. The next screen allows you to input a gravity curve for the whole curve. If you have entered a bulk gravity, then this data is optional. However, if you provide both the bulk gravity and this gravity curve, the program will adjust the gravity curve to match the bulk gravity. 8. Next, the Light Ends Analysis input screen appears. This screen is displayed only when water or light hydrocarbons are present in the feed. 9. Finally, the Viscosity Data dialog box appears, if you checked the Viscosity option above. 10. Use the Edit Curve Data option to go back and change any data for the assay. 11. Click Save and Exit to start calculations. After proceeding through the characterization step, CHEMCAD will show a report of the pseudocomponents and properties calculated. You may also plot this data by selecting Plot > Pseudocomponent Curves. CHEMCAD and Solids The process of crystallization, fusion, and melting are too complex to approach with general rules. For most systems, only an empirical model is accurate. As such, process simulators do not inherently address solids. CHEMCAD provides two approaches to dealing with solids. A third approach is recommended as an analog model that is often used as a workaround Defining Solids Select Thermophysical > Solids > Identify Solid Components to define a component as a solid. The vapor pressure of solid components is ignored for flash calculations. In separation units, the solid components will always leave with the heavy liquid stream. Heat capacity data is taken for the solid, if present. Select Thermophysical > Solids > Particle Size Distribution to specify the particle size distribution (PSD) of the solid. The various solids handling unit operations can be used with defined solids. Several solid separation UnitOps in CHEMCAD use the PSD for solid separation. Neutral File Import of Component Properties This section describes how to import physical properties for one or more components into CHEMCAD using a special text file called a neutral file. The Neutral File Format The neutral file is an ASCII file in which each line is terminated by a carriage-return line-feed pair of bytes. The following sections describe the format and syntax for the neutral file. The very last line of a neutral file should contain the ENDF keyword, indicating the end of the file. Lines beginning with the keyword COMM can be located anywhere in the file; all information trailing a COMM keyword is treated as a comment and ignored during the import process. The file can contain physical properties for several components. The data for each component comprises a group of lines, one keyword per line. The STRC keyword indicates the start of a new component, and the ENDC keyword indicates the end of the component. Between these keywords are the lines specifying physical properties data for the component. The file NEUTRAL.KWF, stored in the CHEMCAD system directory, is an ASCII file containing a list of all valid keywords and a brief description of each. This file must NOT be changed; it is used by CHEMCAD during the import process. A sample neutral file named EXAMPLE.NF is stored in the system directory. Physical properties keywords fall into various categories. These categories and the keywords comprising each category are described in the following sections. Descriptive Keywords Use of keywords in this group is optional. GUID {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} The GUID keyword is the unique identifier for the component in the CHEMCAD component database. If you leave this keyword blank, CHEMCAD will generate a new component and assign a unique ID. If you specify a GUID keyword, CHEMCAD will either create a new component with that number or update the component that matches that GUID. NAME (e.g., NAME  Glycerol) The name you specify here is used for all data entry screens and reports. A name consists of up to 16 characters; any characters can be used, including spaces. CLS (e.g., CLS  Alcohol) You can assign your component to any one of the following classes. Classes are used while selecting components for editing or for including in a flowsheet simulation. These classes are listed in the CLASSES.SF file stored in the CHEMCAD system directory: Misc Alcohol Aldehyde Amine CarbAcid Ester Ether Halogen HC Ketone Nitrile Phenol Solid file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 4 of 89 Electrolyte True Species FRM (e.g., FRM  C3H6COOH, FRM  CH2OHCHOHCH2OH) You can specify one or more formulae for each component. Formulae are used while selecting components for editing or for including in a flowsheet simulation. If you specify a component formula, you will be able to select the component by typing its formula rather than its ID or synonym (see below). Upper- and lower-case alphanumerics and the digits 0 through 9 can be used in formulae; all other characters are discarded. SYN (e.g., SYN  1,2,3-Propanetriol) You can specify one or more synonyms for each component. Synonyms are used while selecting components for editing or for including in a flowsheet simulation. If you specify a component synonym, you will be able to select the component by typing its synonym rather than its ID or formula (see above). A synonym consists of up to 48 characters; any characters can be used, including spaces. Non-Dimensional Data All keywords in this group pertain to physical property data which are either non-dimensional or which must be specified in units compatible with CHEMCAD. Lines consist of the keyword followed by a value. WM e.g. WM 92.095 Molecular weight (note WM, not MW) WI e.g. WI 1.3196 Acentric factor STEL Stiel polar factor PP Polar parameter EPK EPS/K HSD Molecular diameter (always angstroms) UOPK Watson factor API API gravity SG Specific gravity at 60 F ZRA e.g. ZRA 0.28 Rackett constant MAF Modified acentric factor UAP e.g. UAP 3.0599 UNIQUAC area parameter UVP e.g. UVP 3.5857 UNIQUAC volume parameter WMV e.g. WMV 73.19 Wilson molar volume VW e.g. VW 10.56 Liquid volume constant (always cc/mol) ECHARGE Electrolyte charge ESTATE Electrolyte state (0 through 3) 0 = Aqueous 1 = Solid 2 = Gas 3 = Liquid ETYPE Electrolyte type (0 through 4) 0 = Molecule 1 = Simple cation 2 = Simple anion 3 = Oxy anion 4 = Acid oxy anion COMM The following keywords pertain to Environmental Impact Factors ODP Ozone Depletion Potential GWP Global Warming Potential SFP Smog Formation Potential ARP Acid Rain Potential HTA Human Toxicity - in Air HTW Human Toxicity - in Water HTS Human Toxicity - in Soil EEAQ Environmental Effects - in Aqueous Media EETER Environmental Effects - in Terrestrial Media Dimensional Data Each keyword in this group is associated with one of the following tables of units. A value can be specified in any of the units listed in its corresponding table. Each line must include a keyword followed by the units ID taken from the appropriate table followed by the value. For example, to specify a critical temperature of 723 Kelvin and a critical pressure of 40 bar, your neutral file would include the two lines: TC 1 723 PC 4 40.0 TABLE 1 - Temperature 0 R 1 K 2 F 3 C TABLE 2 - Pressure 0 psia 1 atm file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 5 of 89 2 psig 3 mmHg 4 bar 5 kPa 6 MPa 7 Pa 8 kg/cm2 9 bar gauge 10 kg/cm2 gauge 11 torr 12 inches of water 13 mm of water TABLE 3 - Specific Volume 0 ft3/lbmol 1 gal/lbmol 2 bbl/lbmol 3 m3/kmol 4 litre/kmol 5 cc/mol 6 litre/mol 7 Imp gal/lbmol TABLE 4 - Specific Enthalpy 0 Btu/lbmol 1 J/mol 2 J/kmol 3 cal/mol 4 kcal/mol 5 Btu/lb 6 kJ/kg 7 J/kg 8 kcal/kg 9 kcal/g NOTE: If you use entries 5 through 9 above for any of your values, you must first specify a molecular weight (refer to the WM keyword above). TABLE 5 - Solubility 0 (cal/cc)**0.5 1 (J/m3)**0.5 TABLE 6 - Dipole Moment 0 debyes 1 C.m TABLE 7 - Specific Heat 0 Btu/lbmol-F 1 J/mol-K 2 J/kmol-K 3 cal/mol-C 4 kcal/mol-C 5 Btu/lb-F 6 kJ/kg-K 7 J/kg-K 8 kcal/kg-C 9 kcal/g-C NOTE: If you use entries 5 through 9 above for any of your values, you must first specify a molecular weight (refer to the WM keyword above) TABLE 8 - Density 0 lb/ft3 1 lb/gal 2 lb/bbl 3 kg/m3 4 kg/litre 5 g/cc 6 g/litre 7 lb/Imp gal NOTE: If you specify a table of liquid density data for regression (see the EDY keyword in a later section), you must first specify a molecular weight (refer to the WM keyword above) file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 6 of 89 TABLE 9 - Viscosity 0 cP 1 g/cm-sec 2 kg/m-s 3 lbm/ft-sec 4 lbf-sec/ft2 5 lbm/ft-hr 6 Pa-sec 7 N-s/m2 8 mPa-sec TABLE 10 - Thermal Conductivity 0 Btu/hr-ft-F 1 W/m-K 2 cal/sec-cm-C 3 lbf/sec-F 4 lbm-ft/sec3-F 5 kcal/h-m-C 6 cal/h-mm-C TABLE 11 - Surface Tension 0 dyne/cm 1 J/m2 2 N/m 3 lbf/ft TC Table 1 Critical temperature MP Table 1 Melting point TBOL Table 1 Normal boiling point BPM Table 1 Mean average boiling point PC Table 2 Critical pressure VC Table 3 Critical volume LMV Table 3 Liquid molar volume HFOR Table 4 Ideal gas heat of formation HGIB Table 4 Ideal gas Gibbs heat of formation SHF Table 4 Solid heat of formation SGF Table 4 Solid Gibbs heat of formation HVP Table 4 Standard heat of vaporization NHV Table 4 API net heating value (heat of combustion) GHV Table 4 API gross heating value LSHF Table 4 Liquid standard heat of formation LSGF Table 4 Liquid standard Gibbs heat of formation SOL Table 5 Solubility parameter DPM Table 6 Dipole moment LSE Table 7 Liquid standard entropy ISHC Table 7 Ion standard heat capacity Tables 8 through 11 are referred to by a later section. Library Equation Coefficients CHEMCAD provides general-purpose library equations which can be used for calculating various temperature-dependent properties. The following is a list of keywords for each of the physical properties that can be modeled using the library equations. Physical Property Keywords Library solid density DSD#, DSDL, DSD1, DSDU, DSD2, DSDA, DSDB, DSDC, DSDD, DSDE Library liquid density DEN#, DENL, DEN1, DENU, DEN2, DENA, DENB, DENC, DEND, DENE Library vapor pressure VP#, VPL, VP1, VPU, VP2, VPA, VPB, VPC, VPD, VPE Library heat of vaporization HV#, HVL, HV1, HVU, HV2, HVA, HVB, HVC, HVD, HVE Library solid heat capacity CPS#, CPSL, CPS1, CPSU, CPS2, CPSA, CPSB, CPSC, CPSD, CPSE file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 7 of 89 Library liquid heat capacity CPL#, CPLL, CPL1, CPLU, CPL2, CPLA, CPLB, CPLC, CPLD, CPLE Library ideal gas heat capacity DIG#, DIGL, DIG1, DIGU, DIG2, DIGA, DIGB, DIGC, DIGD, DIGE Library liquid viscosity DLV#, DLVL, DLV1, DLVU, DLV2, DLVA, DLVB, DLVC, DLVD, DLVE Library vapor viscosity DVV#, DVVL, DVV1, DVVU, DVV2, DVVA, DVVB, DVVC, DVVD, DVVE Library liquid thermal conductivity DLC#, DLCL, DLC1, DLCU, DLC2, DLCA, DLCB, DLCC, DLCD, DLCE Library vapor thermal conductivity DVC#, DVCL, DVC1, DVCU, DVC2, DVCA, DVCB, DVCC, DVCD, DVCE Library surface tension DST#, DSTL, DST1, DSTU, DST2, DSTA, DSTB, DSTC, DSTD, DSTE The following are examples of how these keywords work for specifying liquid density and heat of vaporization: COMM Liquid Density coefficients DEN# 105 DENL 291.33 DEN1 13.688 DENU 723 DEN2 3.7905 DENA 0.9439 DENB 0.249 DENC 723 DEND 0.1541 COMM Heat of Vaporization coefficients HV# 106 HVL 291.33 HV1 8.9203e+7 HVU 563.15 HV2 6.6128e+7 HVA 1.042e+8 HVB 0.3013 The DEN# and HV# keywords specify which Library equation is to be used for calculating the temperature-dependent property. The next four keywords in each group specify the lower and upper bounds for each equation. These four values are optional; if specified, they can be used to check your neutral file input. The DENA, DENB, DENC, and DEND values are the four coefficients to be used with equation 105 to calculate liquid density. The HVA and HVB values are the two coefficients to be used with equation 106 to calculate heat of vaporization. Non-Library Equation Coefficients Coefficients can be specified for various specific-purpose equations used by CHEMCAD to calculate temperature-dependent properties. Each coefficient has its own keyword. A line must include both the keyword and the value. Coefficients must be specified in units compatible with the equation as noted. ANTA, ANTB, ANTC Constants for the Antoine Vapor Pressure equation: Ln(Psat) = ANTA - ANTB/(T + ANTC) where Psat is in mmHg and T is in Kelvin APH, BETT, GAMM, DTAA, EPSS, ETAA Constants for the Ideal Gas Heat Capacity equation: Cp = APH + BETT*T + GAMM*T2 + DTAA*T3 + EPSS*T4 + ETAA*T5 where Cp is in cal/mol-K and T is in Kelvin VISA, VISB Constants for the Liquid Viscosity equation: Log10(Visc) = VISA * (1/T - 1/VISB) where Visc is in cP and T is in Kelvin SURA, SURB Constants for the Surface Tension equation: ST = SURA * (1 - (T/Tcrit))**SURB where ST is in Nm, and T and Tcrit are in Kelvin B1, B2, B3, B4 Henry's constants for the equation: Ln(H) = B1/T + B2*Ln(T) + B3*T + B4 where H is in psia/mole fraction and T is in degrees Rankin file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 8 of 89 SRKM, SRKN Modified SRK parameters. Binary Interaction Parameters (BIPs) You can load BIP data into your user database via the neutral file. The format of each BIP line is: BIP type sec-ID BIP-A, [BIP-B, BIP-C, BIP-D, etc] The BIP type must be one of the following: NRTL PR (Peng-Robinson) SRK (Soave-Redlich-Kwong) UNIQUAC WILSON BWRS ESD SAFT Valid names are listed in the BIPNAMES.SF file in the system directory. The BIP sec-ID is the secondary ID for this BIP data. Associated with each set of BIP values are, of course, two components; the primary component and the secondary component. The BIP keyword must be included somewhere between a pair of STRC and ENDC keywords. The STRC and ENDC keywords define a group of lines pertaining to the same component and it is assumed that this component is the primary component. The BIP sec-ID is the secondary ID associated with this BIP data and is the CHEMCAD ID number for the secondary component. You can specify any secondary ID so long as it is numerically less than the primary ID. For example, the following BIP line specifies values for WILSON BIPs between a user-added component and water (CHEMCAD ID for water is 62). BIP WILSON 62 -52.605 620.63 If the current group of lines in your neutral file pertains to component 8001 and you include the following line in this group, it would be discarded because the secondary ID is greater than the primary ID: BIP WILSON 8005 -52.605 620.63 [invalid data] The order in which you specify the BIP parameters is important. You must specify at least one BIP parameter. The maximum number of parameters depends on which BIP type you are specifying. The BIPNAMES.SF file in the system directory includes the maximum number of parameters that can be specified for each BIP type. The order in which you specify BIP parameters is also important. The following list indicates the correct ordering for each BIP type: BIP NRTL secID Bij, Bji, alphaIJ, Aij, Aji [maximum of 5 parameters] BIP PR secID Bij [1 parameter only] BIP SRK secID Bij [1 parameter only] BIP UNIQUAC secID Aij, Aji, Uij, Uji [maximum of 4 parameters] BIP WILSON secID Aij, Aji [maximum of 2 parameters] BIP BWRS secID Kij [1 parameter only] BIP ESD secID Kij, KTij, KaLin, dHLin, KaBin, dHBin [maximum of 6 parameters] BIP SAFT secID Kij, KTij, KaLin, dHLin, KaBin, dHBin [maximum of 6 parameters] UNIFAC/UNIQUAC Sub-Group Contributions IDG1, NGI1, IDG2, NGI2, IDG3, NGI3, IDG4, NGI4, etc. These keywords are used to specify the UNIFAC/UNIQUAC sub-group IDs and their frequencies. Up to 8 sub-groups can be specified for a component and each specification must include a pair of lines, one line for the sub-group ID keyword (IDG?) and one line for the fequency keyword (NGI?). For example, the following lines specify that a component is made up of three UNIFAC sub-groups. There are 2 type 2 sub-groups (CH2), 1 type 3 sub-group (CH), and 3 type 15 sub-groups (OH): IDG1 2 NGI1 2 IDG2 3 NGI2 1 IDG3 15 NGI3 3 Values to be Regressed You can generate temperature-dependent coefficients for a variety of equations used by CHEMCAD by including data tables in your neutral file. These tables are regressed automatically as part of the neutral file import process. The sample neutral file EXAMPLE.NF, stored in the CHEMCAD system directory, contains several examples of regression tables. Each table of data contains a header line followed by a set of lines containing the values to be regressed. The values to be regressed must be specified in pairs, one line per pair. The first value is the temperature (independent value) and the second value is the dependent value at this temperature. The header line has the following format: regtype T-units dep-units table-size · The regtype value must be one of the following keywords: Keyword Units From Meaning EVPL Table 2 Library vapor pressure file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 9 of 89 EPST Table 2 Antoine vapor pressure EDHV Table 4 Library heat of vaporization ECPL Table 7 Library liquid heat capacity ECPV Table 7 Ideal gas heat capacity EDY Table 8 Library liquid density EVIS Table 9 Library liquid viscosity (not ELVIS) EVV Table 9 Library vapor viscosity ELTC Table 10 Library liquid thermal conductivity EVTC Table 10 Library vapor thermal conductivity ESUR Table 11 Library surface tension EHRY Table 2 Henry’s vapor pressure · The T-units value is the units ID taken from the Temperature units table (Table 1), corresponding to the temperature units used in the regression table. · The dep-units value is the units ID for the dependent values included in the regression table, taken from the appropriate units table. · The table-size value is the number of entries included in the table, i.e., the number of lines following the header line. The following table is an example of eight vapor pressure values in which temperature is specified in Kelvin and vapor pressure is specified in mmHg: EPST 1 3 8 124.02 0.0704 149.55 2.96 175.08 35.5 200.62 209 226.15 786 251.68 2200 277.22 5010 302.75 9820 Loading a Neutral File Into CHEMCAD To access the neutral file import facility, select Thermophysical > Component Database > Neutral File Import. In the Open dialog box, browse to the neutral file and select it. Click Open to begin the import process. The neutral file can be located anywhere on your computer or on a remote LAN drive. Only read access is needed. The bottom line of the screen displays progress messages while your neutral file is being imported. Warnings and error messages also appear on this line. After each warning or error message, you must press a key to continue processing. If your neutral file contains errors, you should exit CHEMCAD and correct these errors and then return to this option again. A neutral file can be imported several times if necessary. However, please read the following notes regarding importing the same neutral file more than once. NOTE: If your neutral file contains component data for which no component ID is specified (refer to the NID keyword above), an ID is automatically assigned to your data during the import process. Typically, the next available ID number is used and your data is appended to the end of your database. For this reason, you should view your component data, using Thermophysical > Component Database > View/Edit Component, and update your neutral file with any pre-assigned component IDs before importing the same neutral file a second time. NOTE: Whereas physical properties data included in a neutral file replace any existing data, formulae (refer to the FRM keyword above) and synonyms (refer to the SYN keyword above) do not. If your neutral file includes FRM and SYN keywords and you import the same neutral file a second time, your components will end up having twice as many formulae and synonyms! Therefore, we suggest that you initially exclude FRM and SYN keywords from your neutral file until you are sure it contains no errors. Alternatively, you can build a separate neutral file containing only your FRM and SYN specifications (with the associated STRC, NID, and ENDC keywords, of course) and then make sure you import this file only once. Physical Properties To view or edit the physical properties of a component, select Thermophysical > Component Database > View/Edit Component. Select a component to bring up the View/Edit Component Data menu. Options here include the following: · Synonyms · Formulas · Minimum Required Data · Basic Data · Other Data · Electrolyte Data · Density Data · Vapor Pressure and HoV Data · Heat Capacity Data file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 10 of 89 · Viscosity Data · Therm. Cond. and Surf. Tens Component Synonyms Clicking Synonyms on the View/Edit Component Data menu displays the standard component name and all available synonyms. The standard component name is used for display purposes. For user-added components, you can enter as many synonyms as you need. Component Formulas Clicking Formulas on the View/Edit Component Data menu displays one or more structural formulas for standard compounds. For example, ethanol may be CH3CH2OH or C2H6O or C2H5OH. Do not use parentheses or punctuation marks. Note that CHEMCAD will attempt to calculate the molecular weight of a component based on its formula, but does not require you to accept the calculated molecular weight. Minimum Required Data Clicking Minimum Required Data on the View/Edit Component Data menu displays the minimum data required for a component. For a user-created component, these values are initially estimated from the input (molecular weight, boiling point, SG, UNIFAC groups, etc.) using literature- based correlations. It is recommended that you update these values with reliable values, if available. Molecular Weight Weight of one unit mole of the component. Critical T The highest temperature at which the pure component may form a liquid. Critical P The highest pressure at which the pure component may form a vapor. Acentric factor The acentric factor is used in equations of state such as SRK. SG at 60F Specific gravity at 60° F, usually used in lieu of the API gravity. Polynomial Ideal Gas Heat Capacity (cal/mol-K) Temperature (T) is in Kelvin. Coefficients A through F are constants for the equation in the form. Basic Data Clicking Basic Data on the View/Edit Component Data menu displays basic physical constants for a component. Several of the properties displayed here are duplicated on the Minimum Required Data dialog box. Molecular Weight Weight of one mole of the component. Critical T The highest temperature at which the pure component may form a liquid. Critical P The highest pressure at which the pure component may form a vapor. Critical V Volume of one mole of the component at critical point. Acentric factor The acentric factor is used in equations of state such as SRK. Normal boiling point The temperature of boiling for the pure component at 1 atm. Melting point The temperature at which the component will melt under 1atm. Not used in simulation. Enter either ideal gas or solid data Heat of formation Enter the heat of formation of the component at standard state. Note that the value is adjusted for a theoretical vapor phase if the component is a liquid at these conditions. Gibbs of formation The ideal Gibbs Energy of formation of the component at standard state. Note that the value is adjusted for a theoretical vapor phase if the component is a liquid at these conditions. Solubility parameter Used to calculate activity coefficients by VLE models Regular and Flory-Huggins. Dipole moment The dipole moment is used in the Chapman-Enskog equation for gas viscosity. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 11 of 89 Other Component Properties Misc. Data Tab Clicking Other Data on the View/Edit Component Data menu displays several constants which are typically used to estimate transport properties when library equation coefficients are not available. Mean avg. boiling point Used only for hydrocarbon fractions. Molecular diameter Term used for gas viscosity equation if available. Heat of vaporization Value at normal boiling point. Only used if library equation coefficients not available. API net heating value Nominal net heating value for the compound. API gross heating value Nominal gross heating value for the compound. Liquid volume constant Empirical constant used to estimate liquid density. Modified acentric factor Modification of the Acentric factor for use with MSRK. UNIQUAC area parameter See the UNIQUAC discussion for an explanation. UNIQUAC vol. parameter See the UNIQUAC discussion for an explanation. WILSON molar volume No longer used by CHEMCAD. Stiel polar factor Used in the internal gas viscosity equation. Rackett constant A constant used in hydrocarbon density calculations. If unknown, it will be approximated from the critical compressibility factor. Polar parameter Used in the gas viscosity correlation. Eps/K Used in the gas viscosity equation. Eps is the characteristic energy. K is the Boltzmann constant Watson factor Also known as the UOP K, used only for hydrocarbon fractions. API gravity Usually of a hydrocarbon fraction. SG at 60 F Specific gravity at 60 °F, usually used in lieu of the API gravity. Parametric Data Tab Antoine Vapor Pressure (mmHg) The following equation is used if the program does not find coefficients for the Library/DIPPR Vapor Pressure equation (P is in mmHg; T is in Kelvin). To make use of the above equation, you must enter data for more than three parameters. If you enter data for only the first three parameters, CHEMCAD's legacy equation will be used to calculate Antoine Vapor Pressure, as follows: Liquid Viscosity (cP) Coefficients The following equation yields liquid viscosity in Cp. Temperature is in Kelvin. This equation is used if the program doesn't find coefficients for the Library/DIPPR Liquid Viscosity equation. Surface Tension (N/m) Coefficients In the expression below, Tr is the reduced temperature.ln This equation is used if the program doesn't find coefficients for the Library/DIPPR Surface Tension equation. MSRK Coefficients Parameters for the Modified SRK equation of state (MSRK). Henry’s Constant Coeff. These are the constants used for the Henry's Gas Law Correlation. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 12 of 89 Electrolyte Data Clicking Electrolyte Data on the View/Edit Component Data menu displays electrolyte parameters for the selected component. Electrolyte state Defines the state of the species. Options are: · Aqueous (default) · Solid · Gas · Liquid Electrolyte type Defines the type of electrolyte for the compound. Options are: · Molecule (default) · Simple cation · Simple anion · Oxy anion · Acid oxy anion Molecular weight The molecular weight for the species. Electrostatic charge The electrostatic charge for the compound. Std heat of formation The standard heat of formation at 25 C in BTU/Lbmole. Std Gibbs of formation The standard Gibbs free energy of formation at 25 C in BTU/Lbmole. Std entropy The standard entropy for the component at 25 C in BTU/Lbmole F. Std heat capacity The standard heat capacity of the component at 25 C in BTU/Lbmole. Library Equations The system of units for all Library equations is SI. T is always in Kelvin, and the coefficients used must be compatible with the SI form of the equation. The following table lists the physical properties that can be modeled using these library equations and the units in which they are calculated. Temperature-dependent Property Units Solid density kmol/m3 Liquid density kmol/m3 Vapor pressure Pa Heat of vaporization J/kmol Solid heat capacity J/kmol-K Liquid heat capacity J/kmol-K Ideal gas heat capacity J/kmol-K Liquid viscosity Pa-sec Vapor viscosity Pa-sec Liquid thermal conductivity W/m-K Vapor thermal conductivity W/m-K Surface Tension N/m Note that for these equations: τ=1-T r  T r = T / TC Y is the property value. You do not always need to specify all coefficients (A through G). The number of coefficients that you can specify is noted for each file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 13 of 89 equation. Equation 100 Specify any number of coefficients, from 1 to 5. Equation 101 Specify either 2, 3, or 5 coefficients. Equation 102 Specify either 2, 3, or 4 coefficients. Equation 103 You must specify all 4 coefficients. Equation 104 Specify either 2, 3, 4, or 5 coefficients. Equation 105 You must specify all 4 coefficients. Equation 106 Specify either 2, 3, 4, or 5 coefficients. You must also specify the critical temperature for this component. Equation 107 file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 14 of 89 Specify either 3 or 5 coefficients. Equation 114 Specify either 2, 3, or 4 coefficients. You must also specify the critical temperature for this component. Equation 116 Specify either 2, 3, 4, or 5 coefficients. Equation 119 Specify either 2. 3, 4, 5, 6, or 7 coefficients. Equation 124 Specify either 2, 3, 4, or 5 coefficients. Equation 127 Specify either 3, 5, or 7 coefficients. Component Density Clicking Density Data on the View/Edit Component Data menu brings up the Library Density Data dialog box. Library equations are used by CHEMCAD to calculate values of temperature-dependent transport properties. To regress data for a user component, select Thermophysical > Component Database > Component Property Regression. Liquid Density (kmol /m3) Number of moles of a substance per unit volume in the liquid state. The equation and coefficients are used to calculate liquid density as a function of temperature. The range of applicability and values at Tmin and Tmax are file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 15 of 89 shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 105 Coefficients: A, B, D; C=Tc if adequate data is available. Liquid Density may be calculated by various models. The default model is the Library equation, if coefficients are available. To change the model go to the Thermophysical menu and choose Transport Properties. Solid Density (kmol /m3) Number of moles of a substance per unit volume in the solid state. The equation and coefficients are used to calculate solid density as a function of temperature. The range of applicability and values at Tmin and Tmax are shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 100 Coefficients: As appropriate Vapor Pressure and Heat of Vaporization Clicking Vapor Pressure and HoV Data on the View/Edit Component Data menu brings up the Library VP and HoV Data dialog box. Library equations are used by CHEMCAD to calculate values of temperature dependent transport properties.To regress data for a user component, select Thermophysical > Component Database > Component Property Regression. Vapor Pressure (Pascals) Vaporization pressure for liquid-vapor equilibrium. The equation and coefficients are used to calculate Vapor Pressure as a function of temperature. The range of applicability and values at Tmin and Tmax are shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 101 Coefficients: 5 Note that the vapor pressure equation is not used by all VLE K models. Check the documentation of your selected K value to verify calculation of Vapor Pressure. Heat of Vaporization (J/kmol) Difference between the enthalpies of a unit mole of a saturated vapor and saturated liquid of a pure component at any temperature and corresponding vapor pressure. The equation and coefficients are used to calculate Heat of Vaporization as a function of temperature. The range of applicability and values at Tmin and Tmax are shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 106 Coefficients: 4 Component Heat Capacity Clicking Heat Capacity Data on the View/Edit Component Data menu brings up the Library Heat Capacity Data dialog box. Library equations are used by CHEMCAD to calculate values of temperature dependent transport properties. To regress data for a user component, select Thermophysical > Component Database > Component Property Regression. Ideal Gas Heat Capacity (J/kmol-K) The amount of energy required to change the temperature of a unit mole of vapor one degree when the vapor is ideal. The equation and coefficients are used to calculate ideal gas heat capacity as a function of temperature. The range of applicability and values at Tmin and Tmax are shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 107 Coefficients: 3; 2 if data is sparse, 5 if data is extensive Ideal Gas Heat capacity may be calculated by the library equation or the ideal gas heat capacity polynomial (minimum data). The model can be selected using the Enthalpy command on the Thermophsical menu. Liquid Heat Capacity (J/kmol-K) The amount of energy required to change the temperature of a unit mole of liquid one degree at constant pressure. The equation and coefficients are used to calculate liquid heat capacity as a function of temperature. The range of applicability and values at Tmin and Tmax are shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 100 Coefficients: 2-3; use 4-5 if warranted by data Solid Heat Capacity (J/kmol-K) The amount of energy required to change the temperature of a unit mole of solid one degre. The equation and coefficients are used to calculate liquid heat capacity as a function of temperature. The range of applicability and values at Tmin and Tmax are shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 100 Coefficients: as appropriate for data Component Viscosity Clicking Viscosity Data on the View/Edit Component Data menu brings up the Library Viscosity Data dialog box. Library equations are used by CHEMCAD to calculate values of temperature dependent transport properties. To regress data for a user component, select Thermophysical > Component Database > Component Property Regression. Vapor Viscosity (Pascal-sec) The shear stress per unit area at any point in a confined Newtonian vapor divided by the velocity gradient in the direction perpendicular to the direction of flow. The equation and coefficients are used to calculate vapor viscosity as a function of temperature. The range of applicability and values at Tmin and Tmax are shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 102 Coefficients: 2 to 4, as appropriate Vapor Viscosity may be calculated by various models. The default model is the Library equation, if coefficients are available. To change the model go to the Thermophysical menu and choose Transport Properties. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 16 of 89 Liquid Viscosity (Pascal-sec) The shear stress per unit area at any point in a confined Newtonian liquid fluid divided by the velocity gradient in the direction perpendicular to the direction of flow. The equation and coefficients are used to calculate liquid viscosity as a function of temperature. The range of applicability and values at Tmin and Tmax are shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 101 Coefficients: 3; 2 if data is sparse, 5 if data is extensive Liquid Viscosity may be calculated by various models. The default model is the Library equation, if coefficients are available. To change the model go to the Thermophysical menu and choose Transport Properties. Thermal Conductivity and Surface Tension Clicking Therm. Cond. and Surf. Tens on the View/Edit Component Data menu brings up the Library TC and ST Data dialog box. Library equations are used by CHEMCAD to calculate values of temperature dependent transport properties.To regress data for a user component, select Thermophysical > Component Database > Component Property Regression. Vapor Thermal Conductivity (W/m-K) The value is the ratio of energy flux per unit time divided by the temperature change per unit distance in the substance. The equation and coefficients are used to calculate Vapor Thermal Conductivity as a function of temperature. The range of applicability and values at Tmin and Tmax are shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 102 Coefficients: 2-4 Thermal Conductivity may be calculated by various models. The default model is the Library equation, if coefficients are available. To change the model go to the Thermophysical menu and choose Transport Properties. Liquid Thermal Conductivity (W/m-K) The proportionality constant in Fourier’s law of heat conduction which describes the rate at which heat flows through a liquid.. The equation and coefficients are used to calculate Liquid Thermal Conductivity as a function of temperature. The range of applicability and values at Tmin and Tmax are shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 100 Coefficients: 2-3 Thermal Conductivity may be calculated by various models. The default model is the Library equation, if coefficients are available. To change the model go to the Thermophysical menu and choose Transport Properties. Surface Tension (N/m) Inherent force in the plane of the surface of a gas-liquid interface per unit length of surface which tends to minimize the surface area. The equation and coefficients are used to calculate Surface Tension as a function of temperature. The range of applicability and values at Tmin and Tmax are shown. The values predicted by a library equation may not be valid outside the temperature range of applicability. Recommended Equation: 106 Coefficients: 2 To view this dialog go to the Thermophysical menu, select View/Edit, and choose a component. Select Thermal Conductivity from the options. Surface Tension may be calculated by various models. The default model is the Library equation, if coefficients are available. To change the model go to the Thermophysical menu and choose Transport Properties. Thermodynamics Guidelines to Selecting Thermodynamic Methods If the state of chemical engineering technology was advanced enough, we could provide one equation to describe the phase equilibrium of all components and all mixtures of components under all conditions. Unfortunately, this is not the case and all that is available to us today are "partial" models which apply to specific classes of components and mixtures. It is our job, as a simulation service, to provide you with the optimum selection of these models. And your job, as a process engineer, to select the appropriate model when you are creating the flowsheet. As you can see from the list above, CHEMCAD provides an extensive array of the most up-to-date methods for performing heat and material balances. These techniques cover applications ranging from straight hydrocarbon applications, to chemical models, to a wide variety of special applications involving electrolytes, salt effects, amines, sour water, to other specialty chemical applications. These methods have been field tested over a period of years and have been demonstrated to give highly accurate results. To achieve accurate results, however, it is necessary to select the proper method for a given application. This section of the manual provides guidelines for making these selections. It should be noted, however, that the guidelines we will be discussing are for the selection of K-value (phase equilibrium) and enthalpy methods only. The selection of physical property is not considered important to this discussion. You may refer to the end of this section for a more complete discussion of properties techniques. The Basics To understand why a particular equation is preferable in a given application, you must understand some basic definitions and relationships. · Fugacity · Activity · Equilibrium The Thermodynamics Wizard For those users who would like assistance, CHEMCAD provides an advice system for the selection of K-value and enthalpy methods. Briefly explained, the system works like this: 1. First, it looks at the component list and decides what general type of model is required, i.e., equation-of-state, activity model, etc. 2. Next, it looks at the temperature and pressure ranges input by the user and decides which equation within a given category is best at the limits of those ranges. 3. If the method is an activity model, the program then looks at the BIP database to see which model has the most data sets for the current problem. It then calculates the fractional completeness of the BIP matrix. If that fraction is greater than the BIP threshold parameter, it uses the chosen activity method; if not, it uses UNIFAC. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 17 of 89 The Thermodynamics Wizard is no replacement for engineering judgment. The wizard makes uses an algorithm based on general rules and may not always be correct. The suggested model may not be the ‘best’ model for the system. Example of how the Thermodynamics Wizard may be incorrect: Choose water, carbon dioxide, and hydrocarbons as the components in a job. The Thermodynamic Wizard will choose UNIFAC because this is the ‘best’ model for a mixture of water, gas and hydrocarbons in certain situations. The wizard did not know that water is the utility for your heat exchangers and doesn’t mix with process streams, or it would have chosen SRK. Conclusions and Recommendations for Thermodynamic Models Generally speaking, the primary consideration when selecting a thermodynamic method for your simulation is to ask yourself what is happening in the liquid phase. We classify liquid solutions into five categories, as discussed in Types of Solutions.: ideal, regular, polar (highly non-ideal), electrolytes, and special. The recommendations for specific systems are summarized in the following table: Hydrocarbons Soave-Redlich-Kwong (SRK) High - moderate P & T API SRK High - moderate P & T Peng-Robinson High - moderate P & T Benedict-Webb-Ruben-Starling High - moderate P & T Grayson-Streed Moderate P & T ESSO (Maxwell-Bonnell K- Low pressure, heavy material charts) ESD Hydrocarbon-water; hydrocarbon-gases SAFT Hydrocarbon-water; hydrocarbon-gases Chemicals UNIFAC T = 275K - 475K; P = 0-4 atm.; two liquid phases; non-ideal; group contribution; predictive Wilson Highly non-ideal Vapor Pressure Ideal solutions NRTL Highly non-ideal and 2 liquid phases UNIQUAC Highly non-ideal and 2 liquid phases Margules Highly non-ideal and 2 liquid phases. (4 suffix) T. K. Wilson Highly non-ideal and 2 liquid phases Hiranuma (HRNM) Highly non-ideal and 2 liquid phases Regular Solution Moderately non-ideal (predictive) Van Laar Moderately non-ideal Modified SRK (4 parameter) Polar compounds in regular solutions Predictive SRK Polar compounds in non-ideal solutions; better than UNIFAC at high pressures Wilson Salt Non-ideal solutions with salts dissolved in them Special Techniques Henry's Gas Law Gases dissolved in water Amine (MEA DEA) Gas sweetening Sour Water Acid gases and NH3 dissolved in H2O K Tables User Ks Polynomial User Ks User-Added Subroutine User Ks TSRK Methanol system; particularly with light gases PPAQ General, but electrolyte systems is most common application TEG Dehydration of hydrocarbon streams using tri- ethylene-glycol FLOR Flory-Huggins method for polymers file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 18 of 89 UPLM UNIFAC for polymers ACTX User-specified activity coefficients ESD Hydrogen bonding; hydrogen bonding at high pressure SAFT Hydrogen bonding; hydrogen bonding at high pressure For the selection of enthalpy methods, we make the following general recommendations: K-Value Model Recommended Enthalpy Model PR PR BWRS BWRS SRK, APIS, MSRK, VAP SRK REGU, SOUR, TEG, TSRK SRK ESD, SAFT SRK Grayson-Streed, ESSO Lee-Kesler NRTL, UNIF, UNIQ, WILS, VANL, LATE MARG, HRNM, T. K. Wilson, PSRK, FLOR, UPLM, ACTX AMIN AMIN PPAQ SRK or LATE w/HTSL Thermodynamic Settings K-value Models Tab Global K-value Option Choose the K-value to use for this flowsheet. K-values are the expressions that relate liquid and gas phase vapor liquid equilibrium (VLE). You can use local K-values on UnitOps to override the global K-value setting. Ethane/Ethylene, Propane/Propylene Use special binary interaction parameters for ethane/ethylene and propane/propylene systems. This option is only valid when the SRK or Peng-Robinson method is used for K-values. Typically, the special BIPs will give the best results near the critical points. Vapor Phase Association Certain compounds, especially carboxylic acids, have the tendency to dimerize or even polymerize in the vapor phase. Selecting this option accounts for this vapor phase association. Note that this option will activate the Poynting correction. Vapor Fugacity/Poynting Correction This method is a correction for pressure of the vapor phase fugacity when using activity coefficient methods. If this option is selected, the vapor fugacity will be calculated using the SRK equation of state. Typically, it is safe to ignore this correction at lower operating pressures. This option may only be used with a liquid activity coefficient method and is recommended when pressure is above 3 atm. This option also turns on the HF hexamerization when HF is present and activity coefficient models have been selected. SRK/PR Alpha function For SRK and Peng-Robinson EOS models, you are allowed to choose either the standard alpha function or the newer Boston-Mathias alpha function. The default is the standard alpha function. Boston-Mathias is reccomended for temperatures above critical. Global Phase Option Instructs the program to make all flashes three-phase flashes (LLV) or two-phase flashes (LV). This can only be used with K-value methods capable of performing three-phase flashes: MARG, NRTL, UNIF, UNIQ, etc. Water/Hydrocarbon Solubility Change the immiscibility status of water. Water immiscibility may be invoked for any method, except for liquid activity coefficient methods; for those options, water is always considered to be miscible. When water is immiscible for applicable models, the K-value of water will be calculated by a special routine that accounts for the solubility of water in the hydrocarbons. If the miscible setting is chosen, the global K-value is used for water. Wilson model salt Account for the effect of dissolved salts on the vapor-liquid equilibrium of the solvents. This option may only be used with the Wilson equation. No. of BIP sets CHEMCAD allows you to have up to ten (10) sets of BIPs for each activity coefficient method. This gives you the flexibility of using one set of BIPs in one section of a flowsheet and a different set in another. A typical use of this would be when you know that two liquid phases exist in the condenser of a distillation column. You can choose to use NRTL LLE BIPs in the condenser and NRTL VLE for the rest of the column. Default BIP set Defines the set to be used globally by the program. Default value is 1. Other sets are treated as local sets. Clear all local K models/BIPs If selected, allows you to clear your local K-value options. The entire flowsheet will be reset to use the global K model. Clear all tray BIPs file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 19 of 89 If selected, allows you to clear all tray BIPs. Set local K models/BIPs If selected, upon exiting the K-value screen, the program will go into selection mode and allow you to choose one or more units from the flowsheet. It will then present you with an input screen where you can define what K-value model or BIP set is applicable to the particular unit operation. Set tray BIPs If selected, upon exiting the K-value screen, the program will go into selection mode and allow you to choose one or more distillation towers from the flowsheet. It will then present you with an input screen where you can enter a range of tray numbers and the BIP set that applies to that range. Set Henry components Select which components are to be modeled by Henry’s Gas Law K-values. All others will be modeled using the global K-value method. If checked, a upon exiting the K Value dialog a select Henry’s Component dialog appears. This option applies only when activity models are being used. Enthalpy Models Tab Global Enthalpy Option Select the enthalpy model for global use on the flowsheet. Separate enthalpy models may be assigned locally to specific Unit Operations. Ideal gas heat capacity CHEMCAD calculates ideal gas heat capacity, either from a polynomial equation with calculated parameters or from a DIPPR library equation with empirical parameters. When library parameters exist (within CHEMCAD) for a component, the polynomial equation is recalculated to reflect the data. The default selection is DIPPR. The following options may be used in combination with the selected enthalpy model. Use heat of solution file A heat of solution file is an ASCII file which contains heat correction data for compositions of mixtures of components. Use electrolyte enthalpy The electrolytes model contains an enthalpy model to compensate for heat of dissociation. This check box allows the user to turn off enthalpy effects of dissociation if an electrolytes model is in use. This setting has no effect on non-electrolytes models. Heat of Mixing by Gamma The enthalpy of liquids can be adjusted for heats of mixing, based on gamma. Clear all local H models If selected, allows you to clear your local enthalpy models. All units will be reset to use the global enthalpy option. Specify local H models If selected, prompts you to select units at which you will define a "local" enthalpy model. Transport Properties Tab Liquid density model Select the liquid density method used during the simulation from one of four methods: the API method, the Cavett equation, the Library equation, or the Rackett equation The Library method is the default. If the Library method coefficients are not available in the database, the program uses the API method. Since this method requires the specific gravity at 60° F, if the specific gravity (60/60) is not available, the Cavett equation is used. API Lu's method is based on Figure 6A2.21, and Procedures 6A2.21 and 6A2.22 of the API databook. The correlation is based on the relationship C1/d1 = C2/d2 = constant, where d1 and d2 represent two densities and C1 and C2 represent the corresponding density correlation factors. Where this relation holds, any density may be expressed as a function of one known density: where: d = is the density in units of weight per volume, and C = represents an empirical density correlation factor (explained below) C = A(0) + A(1) Tr + A(2)Tr2 + A(3) Tr3 Each coefficient in the above equation is determined by: where Tr = reduced temperature i = 0 --> 3 Pr = reduced pressure The coefficients are as follows: i B0(i) B1(i) B2(1) B3(i) B4(i) 0 1.6368 -0.04615 2.1138(10-3) -0.7845(10-5) -0.6923(10-6) 1 -1.9693 0.21874 - 8.0082e-3 (10-3) -8.2328(10-5) 5.2604(10-6) 2 2.4638 -0.36461 12.8763(10-3) 14.8059(10-5) -8.6895(10-6) 3 -1.5841 0.25136 -11.3805(10-3) 9.5672(10-5) 2.1812(10-6) C1 is stored in the database as the specific gravity at 60° F (item 42). d1 equals d at 60o F. d2 is then determined by evaluating C2 and applying it to the above ratio. The average error in estimating the density of a pure hydrocarbon is 1 percent. However, errors up to 10 percent can be expected at reduced temperatures greater than 0.95. The Cavett equation has the form: liquid volume = Vol Con * (5.7 + 3Tr) where liquid volume is in cc/gmole VolCon is the liquid mole volume constant (item 9 in the databank) Tr is the reduced temperature file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 20 of 89 Equation of state predicts liquid density using an equation of state. The default model for liquid density will be SRK, except where the selected K-value model is one of the following equations of state: · BWRS · PR · PRSV · ESD · SAFT The Library equation has the following form: where: Density is in kgmoles/m3 Temperature is in degrees Kelvin. A, B, C, D are component specific coefficients stored in the database (items 26 through 29). The modified Rackett equation, which was developed by Rackett and later modified by Spencer and Danner, is used to estimate saturated volumes: ZRA is a unique constant for each compound. Liquid viscosity model The primary method for computing liquid viscosities of a pure component is to use the DIPPR equation which has the following form: where: μ = the liquid viscosity in Pascal seconds A,B,C,D,E = DIPPR coefficients for liquid viscosities If the DIPPR data is absent, the following two-term equation is used: where: μ = the liquid viscosity in centipoise A and B = DIPPR coefficients stored in the database (terms 30 and 31) If coefficients for methods 1 and 2 are not available, the method of Letsou and Stiel is used. where: where: Tc = critical temperature x = Tc0.166 M -0.5 Pc-0.67 MW = molecular weight w = the acentric factor For pseudocomponents, CHEMCAD uses the method of ASME for liquid viscosity estimation. The following mixing rule is used for the liquid-mixture viscosities: xi = mole fraction component i An optional mass-based mixing rule may be selected for liquid mixture viscosities. This rule is sometimes used for polymer viscosities. xi = mass fraction component i Liquid Viscosity pressure correction Check this box to activate the liquid viscosity pressure correction model. The high pressure model is based on API 11A5.1 and 11A5.7. Vapor Viscosity model The primary method for computing gas viscosities of a pure component is to use the DIPPR equation which has the form: where: μg = gas viscosity in Pascal seconds A,B,C,D = DIPPR coefficients for gas viscosities For low pressure gas, the Chapman-Enskog relation is used: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 21 of 89 where: M = Molecular weight R = Gas law constant T = Temperature P = Pressure O = Molecular diameter Ωv = Collision integral Mp = Dipole moment For non-polar gases the method of Neufeld is used to evaluate Ωv: where: T* = kT/e A = 1.16145 B = 0.14874 C = 0.52487 D = 0.77320 E = 2.16178 F = 2.43787 For polar compounds, Ωv is evaluated using the method of Brokaw: where: Ωv(LJ) = The Leonard-Jones collision integral d = The polar parameter T* = kT/e k = Boltman's constant e = Th energy potential parameter If c/K and d are unavailable in the database, an alternative method for evaluating gas viscosity is the method of Thodos: For gases: where: Tr = Reduced temperature x = Tc0.166 M-0.5 Pc-0.67 The viscosities of gas mixtures are evaluated using the method of Wilke: where: μi = The pure component viscosity Mi = The pure component molecular weight The method of Dean and Stiel is used for the effect of pressure on the viscosity of gas mixtures. Dean-Stiel pressure correction Check this box to use the Dean-Stiel correction for high-pressure vapor viscosity. Liquid Surface tension model Select a model from the drop-down list. The library model will not show the mixing effect at low temperatures which can sometimes occur. Liquid thermal conductivity model/Vapor thermal conductivity model/Vapor conductivity correlation (>1 atm) For thermal conductivity, both for gases and liquids, CHEMCAD uses the DIPPR equation to evaluate pure component thermal conductivities. For gases: where: lv = the gas thermal conductivity in w/m.K A, B, C, and D = DIPPR coefficients file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 22 of 89 T = temperature in Kelvin The Stiel-Thodos method is used for high-pressure correction. For liquids: where: lL = the liquid thermal conductivity in w/m.K A, B, C, and D = DIPPR coefficients T = temperature in Kelvin For gases where the DIPPR data is absent, CHEMCAD uses the API procedure (12B1.5) to estimate component thermal gas conductivities. API procedure 12B4.1 is used for high pressure correction, and API procedure 12B2.1 is used for mixing rules for gas mixtures. For liquids where the DIPPR data is absent, the following methods are used: · API procedure 12A1.2 for pressure < 500 psia and TR < 0.8. · API Figure 12A3.1 for hydrocarbon fractions. · API Figure 12A4.1 for high pressure correction. · API procedure 12A1.3 if the methods above do not apply. · API procedure 12A2.1 is used as the mixing rule. Electrolyte Std Liquid CHEMCAD normally uses the specific gravity (SG) of the components to calculate the Standard liquid (StdL) volume rates for a mixture. For a strong electrolyte system, this method uses the poor assumption that molar volumes (from SG) are additive. A strong dissociating electrolyte is dissolved in water; it does not add its volume to the mixture. The Based on actual volume option allows CHEMCAD to calculate actual liquid volume of the mixture at Standard Conditions. The Based on components option calculates StdL from the SG of the components. This method was left in CHEMCAD to prevent existing flowsheets from changing. Note that if you are defining a feed stream as StdL, CHEMCAD will calculate the mass flow rate of the stream from your specification. Fugacity It can be shown that where: G = Gibbs free energy S = Entropy T = Temperature V = Volume P = Pressure For a pure component at constant T, (5-1) Now let's consider the implications of this for an ideal gas. An ideal gas, you will remember, is a gas made up of infinitesimally small spheres which are completely elastic in their collisions. Thus, these spheres occupy no volume and have no intermolecular forces between them. Operating from these assumptions and using the laws of statistical mechanics, we can derive the following relationship for one mole of gas: (5-2) which is the ideal gas law. Combining 5-1 and 5-2 we get: (5-3) This is a useful relationship since we can measure T and P for real gases. However, equation 5-3 is not for real gases; it is for ideal gases. Therefore, let us define a new quantity, fugacity, which would make Equation 5-3 true for real gases and try to relate fugacity to measurable quantities like P, V, and T. Thus, by definition: (for a pure component) (5-4) This is only a partial definition since it only permits us to determine relative values of fugacity. To complete our definition, let us relate it to an ideal gas. From Equations 5-3 and 5-4, for an ideal gas: integrating, we get or Now define C = 1 to relate fugacity to ideal gas pressures. Since all materials behave like ideal gases as pressure approaches zero, we have: (5-5) A simple analysis for components in solution will yield us the following relations: (5-6) file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 23 of 89 (5-7) We still have to relate fugacity to measurable quantities like P, V, and T. Therefore, let us define two new useful concepts: · The fugacity coefficient, (for a pure component) (5-8) (for a component in solution) (5-9) · The compressibility factor, Z (5-10) We can combine Equation 5-1 and Equation 5-4 to get: (5-11) now (5-12) Similarly, for solutions: (5-13) Since we have equations-of-state which relate P, V, and T to Z, we can solve for Z and FFi. It merely remains now to relate FF to phase equilibrium. Activity The above approach for computing fugacity is effective only if the equation-of-state we use is adequate for the computation of Φi. This may not be true for two reasons. First, the equation may not adequately represent the compound itself, even in the pure state. Secondly, the mixing rules of the equation may not adequately represent or quantify what happens to a molecule when it is in solution. This can be for many reasons but frequently it is due to the failure to adequately model intermolecular forces. In such a case, an alternative approach is taken. Define activity, αi, as follows: (5-14) where = the fugacity of the component in solution = the fugacity of the component at some arbitrarily defined standard state Also define the activity coefficient, γ , so that: (5-15) thus (5-16) From the Gibbs-Duhem relation, it can be demonstrated that for one mole of solution: (5-17) where file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 24 of 89 The difference between the Gibbs free energy of the component in solution and the Gibbs free energy of the component in the standard state, called the excess Gibbs free energy. The term 1 is the change in excess Gibbs free energy for the entire solution. We can thus approach γi, by relating it to the excess Gibbs free energy of solution, ≅GE. However, since ≅GE cannot be directly measured, this is virtually always taken as a theoretical framework or starting point. In the final analysis, the value of γi, must be directly correlated over narrow data ranges. This is done through the use of binary interaction parameters or BIPs. CHEMCAD provides a BIP database, as well as a data regression facility through which these BIPs can be directly correlated from phase equilibrium data. Thus, activity coefficients are a function not only of the component for which they are computed, but also of the nature and quantity of the other components in the solution. In addition, the activity coefficients themselves are computed semi-empirically, i.e., the approach has a theoretical basis but the application is dependent on parameters correlated over specific data ranges. Equilibrium At equilibrium, all net driving forces are zero and, thus, all thermodynamic properties such as U (free energy), A (Hemholtz free energy), G (Gibbs free energy), etc., are minimized. Mathematically, for any quantity, the first derivative of that quantity equals zero at either a maximum, a minimum, or an inflection point. Since the second law of thermodynamics tells us that energy always flows downhill, we know we are looking for a minimum, i.e., we are seeking to minimize the free energy functions U, A, and G. (5-18) Now we have some options: Since dU = TdS - PdV, if S and T are fixed (i.e., known, measured), we can minimize U. Since dA = -PdV - SdT, if V and T are fixed, we can minimize A. Since dG = VdP - SdT, if P and T are fixed, we can minimize G. For our purposes it is best to attempt to minimize G because T and P are easily measured. For a closed two-phase system, For any given phase: Therefore: Conservation of mass requires that dn1 = - dn2. Therefore, (5-19) In order for Equation 5-19 to be generally valid, it cannot depend on any particular choice of the dni. Thus the total Gibbs free energy will be a minimum (dG = 0) for an arbitrary choice of the dni only if (5-20) for all components. Thus at equilibrium the partial molar Gibbs free energy of each component must be the same in each phase present in the system. In other words, (5-21) Although developed above for a two-phase system, the above analysis can be equally applied to multi-phase systems. Thus, (5-22) Using previously developed concepts, we can express Equation 5-22 in a variety of ways: (5-23) If we assume that phase one is a liquid and phase two is a vapor and we denote the vapor mole fractions with a yi instead of an xi, we can rearrange Equation 5-23 into its most commonly used forms: namely, (5-24) where: Ki = The vapor-liquid equilibrium constant or K-value. If we can compute values of ggli, FFvi 2 and 3 we have a method for determining vapor-liquid equilibrium. In practice, this depends upon two factors: 1. The nature of the molecules under consideration 2. The type of solutions they form Types of Components You will remember that an ideal gas is one composed of infinitesimally small spheres that exert no intermolecular forces on one another. The farther away from these two assumptions a component gets, the less accurately the ideal gas law will model the fluid. Therefore, more complex equations-of-state have been developed to account for deviations from these premises. Some equations, such as the van der Waals' equation of state: (5-25) attempt to explicitly account for these deviations. In the above equation, the term b is meant to account for the finite size of the molecules and is sometimes referred to as the "molecular volume". Its value depends on the size and nature of the molecules. The term is a correction which was meant to account for the attractive forces that exist between molecules. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 25 of 89 Other equations-of-state, although attempting to account for the same phenomena, are not so explicit in assigning physical significance to their parameters. It is generally true, however, that greater levels of complexity are required as we move away from the ideal gas assumptions, i.e., to accurately model behavior, equations tend to become more complex (add parameters and constants) as follows: · The molecules get bigger. · The molecules get more complex. · The molecules get more polar. This is true even when discussing the pure component. When evaluating mixtures, these issues become even more important until attempts to build predictive models break down all together. Types of Solutions Ideal Solutions For some systems, the partial molar volume of a component is nearly the same as the molar volume of the pure component. A mixture of benzene and toluene at ambient temperature and pressure is an example of a liquid system for which this is true. It is also approximately true for certain gas mixtures even at high pressures. The treatment of the thermodynamic properties of such systems is greatly simplified, with respect to the general case, and a pronounced simplification is effected in the solution of phase equilibrium problems. Systems which exhibit this behavior are called ideal solutions, and the term signified that for such a solution, the partial molar volume of each component in solution is equal to its pure component volume at the same temperature and pressure. We can conclude the following about ideal solutions: 1. They will follow the Lewis-Randall rule: (5-26) where fi is the fugacity of the pure component in the same phase and at the same temperature and pressure as the mixture. Since gaseous mixtures at low to moderate pressures typically obey the Lewis-Randall rule, it is possible to use Equation 5-26 to evaluate partial fugacities in these systems. 2. Since by definition there is no volume change in these solutions, we can write: (5-27) 3. An ideal gas will always behave as an ideal solution, but a system need not conform to the ideal gas law to behave as an ideal solution. 4. If the liquid phases are ideal solutions and the vapor phase is an ideal gas, we can deduce: (5-28) where: Pi = Partial pressure V*Pi = Vapor pressure at saturation P = System pressure This is Raoult's law. The most critical assumption is that the liquid phase is an ideal solution. This is not likely to be even approximately valid unless the system is made up of species of similar molecular size and chemical nature as in the case of benzene and toluene or n-hexane and n-heptane. Regular or Normal Solutions The treatment of VLE would be simple if all systems followed Raoult's law because, in this event, no information about the mixtures which made up the phases would be required. In actual fact, deviations from Raoult's law are usually observed. Fundamentally, the failure of Raoult's law is due to differences in molecular size and in the molecular forces of the components. The differences vanish only when the components become identical; where they are appreciable, the underlying assumptions are invalid. The considerations are usually not important with respect to a vapor phase at low pressure, where ideal gas behavior is approached. However, in the liquid phase, the intermolecular distances are small and the molecular interactions, based both on force fields and on volume differences (packing considerations), determine the departure from ideal solution behavior. These liquid phase non-idealities are of primary importance and usually must be taken into account. At higher pressures, deviation from ideal gas behavior of the vapor phase must also be considered. We can speculate that these non-idealities are attributable to either physical or chemical intermolecular forces. Physical forces would be those due simply to collisions between the molecules. They would be affected primarily by the size and shape of the molecules. Chemical forces would be electromagnetic type forces at the molecular level which tend to cause the molecules to group or associate in a non-random fashion. The latter kind of force tends to be the more difficult to account for and, where it predominates, more empirical approaches are required. Where the non-idealities tend to stem predominantly from physical interactions and are in general not too large, we can define a new class of solutions called regular solutions. The strict definition of a regular solution is one where the excess entropy of mixing is zero. This most generally occurs in systems where the components are non-polar and do not differ appreciably in size, shape, and chemical behavior. Systems of this type can be modeled using modern equations-of-state such as Soave-Redlich-Kwong and Peng-Robinson. The following considerations are relevant: 1. These equations should be applied to systems with different size molecules but these differences should not be too large, such as the differences between monomers and polymers. The difference between straight chained hydrocarbons, such as nC4 and nC12 can be handled by these equations. 2. The equation-of-state selected should be applicable to the components being set up for straight-chained and ring hydrocarbons. Their accuracy tends to diminish as branch chains are added and other molecules, such as nitrogen, sulfur, and oxygen, are added. This is especially so if the compound is polar. Certain extensions have been made to the SRK equation to make it more accurate for branch chained, polar, and other hydrocarbon chemical compounds. The extension has been incorporated into CHEMCAD in the form of the MSRK option (MSRK = Modified SRK). This modification extends the three- parameter SRK equation to a four-parameter equation by dropping the use of the acentric factor and incorporating two new factors, m and n, which must be correlated against data. In CHEMCAD the m and n are available for approximately 300 components. 3. The mixing rules of the equations-of-state have a significant bearing on how accurately they handle mixtures. The mixing rules for the equations-of-state currently available do not account for interactions between unlike pairs of molecules if they are greatly different from the interactions between like pairs. To overcome this limitation, a binary interaction parameter, Kij, has been added to the mixing rules of these equations. Even this, however, has been found to be capable only of improving the accuracy between molecules of unlike sizes, to quote Peng-Robinson: "It was found that the optimum binary interaction coefficients were negligibly small for components with moderate differences in molecular size. However, systems involving components having relatively large differences in molecular size required the use of a non-trivial interaction coefficient in order to get good agreement between predicted and experimental bubble point pressures." Polar or Highly Non-Ideal Solutions For systems where the non-idealities derive from chemical or intermolecular forces of attraction or repulsion, the predictive methods described above are generally inadequate. For these situations, it is necessary to use methods based upon the excess Gibbs free energy, that is, to use activity coefficient file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 26 of 89 methods. For these methods, the K-value takes the form: where: γI = Component i liquid activity coefficient = The standard state fugacity for component i P = System pressure = The fugacity coefficient of component i in the vapor mixture Note the following: 1. In CHEMCAD the standard state fugacity, 4, is defined in one of two ways. In the default condition, the vapor phase is taken to be ideal and the standard state is the pure component vapor pressure. In this event, the standard state liquid fugacity equals the vapor pressure of the components, the vapor phase fugacity equals one, and: An alternate approach assumes the vapor phase is a regular solution and defines the standard state as follows: where: i = The vapor pressure of component i = The fugacity coefficient of the pure component i at saturation = The volume of the pure component i at T and VPi This is the fugacity of the pure component at the temperature and pressure of the system. The fugacity coefficients in the above equations are calculated using the SRK equation. The vapor phase, therefore, is not assumed to be ideal, but rather it is assumed to be a non-ideal gas in a regular (non- associating) solution. Use the Poynting Correction option on the K-value screen to switch back and forth between these two standard states. 2. The gamma term in the above equation may be calculated using any of the following equations: · UNIFAC · UNIQUAC · NRTL · WILSON, T. K. WILSON, HRNM WILSON, WILSON SALT · VAN LAAR · MARGULES · REGULAR · GMAC For all of the above, except the UNIFAC and REGULAR equations, system dependent binary interaction parameters must be supplied in order to produce reliable results. Within CHEMCAD, these BIPs can come from any of four sources: · They can be correlated or "regressed" from experimental data. This is the preferred and most frequently used method. · The user can input them directly using the BIP command. This obviously requires obtaining them from an outside source, such as the literature. · The data can be estimated using the UNIFAC equation and then regressed to produce the required BIPs. This method is discussed under the UTIL menu and is useful for generating BIPs for secondary pairs, i.e., pairs not critical to the separation. · The BIPs can be obtained from the CHEMCAD database. CHEMCAD supplies a database of BIPs for VLE calculations. If the system in question is in the database, these will be automatically retrieved and used unless overridden by one of the above methods. The user is cautioned that the BIPs in the database were all regressed from data taken at one atmosphere and, therefore, should be used with caution at system pressure significantly different from this value. 3. The UNIFAC and REGULAR equations are predictive methods not requiring BIPs. The REGULAR equation is an old technique which applies only to regular solutions. These are better handled by equations-of-state these days, so the REGULAR equation is not generally used anymore. The UNIFAC equation is based upon the group contribution method for estimating activity coefficients. It has the following advantages and disadvantages: · Parameters almost independent of temperature. · Size and binary interaction parameters available for many functional groups. · Temperature range of 275 - 425 ºK (35-305 ºF). · Pressures to a few atmospheres. · Extensive comparisons with experimental data. · Not as accurate as Wilson, NRTL, or UNIQUAC methods. · Cannot be used where data on functional groups is not available. 4. The PSRK equation is also a predictive model in the same sense that any equation-of-state is (PSRK stands for Predictive Soave-Redlich-Kwong). It attempts to combine the best features of the UNIFAC and SRK methods. The PSRK equation, therefore, can handle non-ideal as well as regular solutions, including two liquid phases. Its accuracy for non-ideal solutions at low pressure is approximately the same as UNIFAC but at high pressures it is substantially better. 5. In practice, the number of adjustable constants per binary is typically two or three, but it may be as high as five (for NRTL). The larger the number of constants, the better the representation of the data but, at the same time, the larger the number of reliable experimental data points required to determine the constants. Extensive and highly accurate experimental data are required to justify more than three empirical constants for a binary mixture at a fixed temperature. 6. For many moderately non-ideal binary mixtures, all equations for GE containing two (or more) binary parameters give good results; there is little reason to choose one over another except a user may have more experience with the older ones (Margules, Van Laar). For strongly non-ideal binary mixtures (e.g., file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 27 of 89 solutions of alcohols with hydrocarbons), the equation of Wilson is probably the most useful because, unlike the NRTL equation, it contains only two adjustable parameters and is mathematically simpler than the UNIQUAC equation. For such mixtures, the Margules equation and the Van Laar equation are likely to represent the data with significantly less success, especially in the region dilute with respect to alcohol where the Wilson equation is particularly suitable. The four-suffix (three-parameter) Margules equation has no significant advantages over the three-parameter NRTL equation. 7. The Wilson equation is not applicable to a mixture which exhibits a miscibility gap; it is inherently unable, even qualitatively, to account for phase splitting. Nevertheless, Wilson's equation may be useful even for those mixtures where miscibility is incomplete, provided attention is confined to the one-phase equation. A number of modifications have been developed to extend the Wilson equation to the liquid-liquid region. Two of these are included in the program: T. K. Wilson and Hiranuma (HRNM) methods. 8. Unlike Wilson's equation, the NRTL and UNIQUAC equations are applicable to both vapor-liquid and liquid-liquid equilibria. Therefore, mutual solubility data can be used to determine NRTL or UNIQUAC parameters. While UNIQUAC is mathematically more complex than NRTL, it has three advantages: (1) it has only two (rather than three) adjustable parameters, (2) UNIQUAC's parameters often have a smaller dependence on temperature, and (3) the primary concentration variable is a surface fraction (rather than mole fraction). UNIQUAC is applicable to solutions containing small or large molecules, including polymers. Special Types of Solutions The above discussions cover the types of general solutions which CHEMCAD can handle, i.e., ideal, regular, and polar. There are a wide variety of special systems, however, which CHEMCAD also addresses. These are discussed briefly below and are described fully later in this chapter. 1. Electrolytes: Electrolyte solutions are mixtures in which one or more of the molecules breaks up into its constituent atoms or ion radicals. Generally, this occurs with non-hydrocarbon molecules dissolved in water. They are called electrolytes because such solutions are capable of carrying electrical currents. CHEMCAD has two generalized models for handling these solutions: The Pitzer method and the MNRTL method. These are discussed in the Electrolytes Section of this manual. There is, however, an additional, highly useful technique for handling certain specific situations which are frequently found in petrochemical plants. These situations have the following characteristics: · There is a single electrolyte component dissolved in water. · This single electrolyte solution is in the presence of other non-electrolyte materials which have limited solubility in water. This method is called the PPAQ model and some common examples of its application are columns absorbing hydrochloric acid and ammonia absorption systems. The approach PPAQ takes to solve this type of problem is empirical. The user sets up two tables: One contains data for the partial pressures of the solute and of water over the solution over a range of temperatures and concentrations; the second stores the integral heat of solution as a function of solute concentration. During the simulation, CHEMCAD interpolates these tables to calculate the K and H values of the solute and water. Other components are handled either by Henry's Gas Law method, MSRK, or SRK. The PPAQ method is described in detail later in this section. 2. Dissolved gases: There are two specialty methods for handling non-condensible gases dissolved in some solute. These are Henry's Gas Law method and the TSRK method. The first is generally used for light gases dissolved in water and the second is for light gases dissolved in methanol. Both are basically empirical methods and both are described later in this section. 3. Reactive systems: There are two special methods within CHEMCAD designed to model systems in which reactions are occurring in the liquid phase. These are the Amine System and the Sour Water System. The first, AMIN, is for the removal of sour gases from hydrocarbon streams using MEA, MDEA or DEA. The second, SOUR, is for modeling systems with CO2, NH3, H2S, and other compounds dissolved in water. Both are empirical systems which model a set of reactions between specific constituents occurring in the vapor phase. The reaction data is stored in the form of a temperature dependent polynomial. The reaction equilibrium is computed first, then the vapor-liquid equilibrium constant is calculated. 4. Physical Solvent: A special method for the dehydration of hydrocarbon streams using Tri-Ethylene Glycol is also available within the program. The method is semi-empirical and is called TEG. 5. Polynomial K-values: You can input the coefficients for a temperature dependent polynomial for the computation of K and H values if desired. 6. Tabular K-values: You can set up a table of K and H values which the program will interpolate during simulation. 7. User-Added Subroutines: You can link your own subroutine for the computation of K and/or H values if so desired. Vapor Phase Solutions This discussion has thus far focused primarily on the nature and modeling of liquid solutions. The assumption has been that the vapor phase solution is ideal to moderately regular. Actually, this is not always true. There are certain vapor phase solutions where some of the molecules associate and, therefore, behave as non-ideal solutions. This almost always occurs when certain molecules dimerize, trimerize, etc., i.e., when they combine with other like molecules. Carboxylic acids are the most common example of these types of systems. In CHEMCAD, the following methods are applicable: 1. If both the vapor and liquid phase form ideal solutions, Raoult's law should be used (the VAP method). 2. If both phases form regular solutions, use an equation of state. 3. If the liquid phase solution is non-ideal and the vapor phase solution is regular, use Poynting's correction. 4. If the liquid phase solution is non-ideal and the vapor phase solution is ideal, do not use Poynting's correction. 5. If the liquid phase solution is non-ideal and the vapor phase solution is non-ideal, i.e., association occurs in the vapor phase, use the vapor phase association option. Invoking the vapor phase association model on the K-value screen changes the way that the vapor phase fugacity, Φvi, coefficient and the liquid fugacity coefficient in the standard state, Φvi, are calculated. Under vapor phase association, the fugacities of the associating compounds are calculated by actually reacting them in the equation: where: Ca = the compound Ca2 = the dimer The solution of this reaction is achieved by solving the equation: where: The As and Bs for the dimerization of carboxylic acids are included in the program. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 28 of 89 Conclusions and Recommendations Generally speaking, the primary consideration when selecting a thermodynamic method for your simulation is to ask yourself what is happening in the liquid phase. We classify liquid solutions into five categories: ideal, regular, polar (highly non-ideal), electrolytes, and special. For these classifications, we make the following distinctions and qualifications: 1. Ideal solutions are systems where the vapor phase behaves essentially as an ideal gas (low pressure) and all the molecules in the liquid phase are of virtually the same size. In addition, no intermolecular forces of attraction exist. For these systems, you can use the Ideal Vapor Pressure model for K- values and SRK for enthalpies. Vapor-liquid equilibria will be determined using Raoult's law: where VPi is calculated using the selected vapor pressure equation. 2. Regular solutions are systems where the non-idealities stem from moderate physical interactions, i.e., from differences in the size and shape of the molecules. Intermolecular associations are assumed to be minimal. These systems are best modeled using equations of state such as Peng-Robinson, SRK, API SRK, BWRS, CS/GS, and MSRK. It is recommended that you use Peng-Robinson and SRK for all hydrocarbon systems except for certain wide boiling-range units where CS/GS is advised, and for units dealing specifically with heavy materials at low pressures where ESSO (really a vapor pressure approach) is suggested. For chemicals that form regular solutions, such as branch-chained hydrocarbons, halogenated hydrocarbons, some polar compounds, etc., we recommend the MSRK equation. In all of these cases, both the vapor and the liquid phases are assumed to form regular (i.e., mildly non-ideal) solutions, and K-values are calculated as follows: 3. Polar (highly non-ideal) solutions are systems where the liquid phase non-idealities arise predominantly from molecular associations. These systems must be modeled using activity coefficient methods which generally require BIPs for accuracy. The vapor phase is taken to be a regular solution, therefore: where: The equations that fall into this category are: NRTL, UNIFAC, UNIQUAC, Wilson, T. K. Wilson, Hiranuma, Van Laar, Margules, and GMAC. Wilson, NRTL, and UNIQUAC are the recommended methods. UNIFAC may be used where data is absent. 4. Electrolytes are described elsewhere in this Help file. 5. Special systems are provided for the simulation of common applications that do not lend themselves to the above approaches. Hydrocarbons · Soave-Redlich-Kwong (SRK): High to moderate P & T · API Soave General HC: High to moderate P & T · Peng-Robinson: High to moderate P & T · Benedict-Webb-Ruben-Starling: High to moderate P & T · Grayson-Streed: Moderate pressures and temperatures · ESSO (Maxwell-Bonnell K-charts): Low pressure, heavy material · ESD: Hydrocarbon-water; hydrocarbon-gases · SAFT: Hydrocarbon-water; hydrocarbon-gases Chemicals · UNIFAC: T = 275K - 475K; P = 0-4 atm.; two liquid phases; non-ideal; group contribution; predictive · Wilson: Highly non-ideal · Vapor Pressure: Ideal solutions · NRTL: Highly non-ideal and 2 liquid phases · UNIQUAC: Highly non-ideal and 2 liquid phases · Margules: Highly non-ideal and 2 liquid phases (four-suffix) · T. K. Wilson: Highly non-ideal and 2 liquid phases · Hiranuma (HRNM): Highly non-ideal and 2 liquid phases · Regular Solution: Moderately non-ideal; predictive · Van Laar: Moderately non-ideal · Modified SRK (four-parameter): Polar compounds in regular solutions · Predictive SRK: Polar compounds in non-ideal solutions; better than UNIFAC at high pressures · Wilson Salt: Non-ideal solutions with salts dissolved in them Special Techniques · Henry's Gas Law: Gases dissolved in water · Amine (MEA DEA): Gas sweetening · Sour Water: Acid gases and NH3 dissolved in H2O · K Table: User Ks · Polynomial K: User Ks file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 29 of 89 · USRK: User Ks · TSRK: Methanol system; particularly with light gases · PPAQ: General, but electrolyte systems is most common application · TEG: Dehydration of hydrocarbon streams using tri-ethylene-glycol · FLOR: Flory-Huggins method for polymers · UPLM: UNIFAC for polymers · ACTX: User specified activity coefficients · ESD: Hydrogen bonding; hydrogen bonding at high pressure · SAFT: Hydrogen bonding; hydrogen bonding at high pressure For the selection of enthalpy methods, we make the following general recommendations: If the K-value method is: Use this for enthalpy: Peng-Robinson (PR) Peng-Robinson (PR) BWRS BWRS SRK, API SRK, MSRK, Ideal Vapor Pressure, SRK Regular Solution, Sour Water, TEG Dehydration, TSRK, ESD, SAFT Grayson-Streed, ESSO Lee-Kesler NRTL, UNIF, UNIQ, WILS, VANL, MARG, HRNM, Latent Heat T.K. Wilson, PSRK, FLOR, UPLM, ACTX Amine Amine PPAQ SRK or Latent Heat w/HTSL Overview of BIPs in CHEMCAD Binary interaction parameters (BIPs) in CHEMCAD can come from a variety of sources: · The built-in CHEMCAD component database includes BIP data for hundreds of component pairs, and more are added with each CHEMCAD release. · CHEMCAD users can create their own BIPs for pairs of components within a simulation. · Users can also regress experimental VLE (vapor/liquid equilibrium) and LLE (liquid/liquid equilibrium) data for binary, ternary, and quaternary systems. · BIPs that other users have created or regressed can be made available through shared BIP databases in a networked CHEMCAD environment. Default BIPs For any component pair that has multiple BIPs in the CHEMCAD database, the program must have a way of determining which BIP will be used by default. If more than one BIP exists between two components, CHEMCAD chooses which BIP to assign by checking a field called Priority on all available BIPs. The higher the priority number, the higher the priority CHEMCAD will give that BIP. The standard priority for VLE BIPs in the CHEMCAD database is 5; the standard priority for LLE BIPs is 4. Users creating their own BIPs can assign a higher number to give preference to those BIPs. Note that if the Priority field is left blank at BIP creation, CHEMCAD enters a priority of 0. Regardless of priority, a user can always elect to use a different BIP than the one that is assigned by default. Maintaining the BIP Database Creating a New Database BIP You can create a new BIP or copy an existing BIP. Viewing and Editing an Existing BIP You can view or edit detailed parameter data for user-defined BIPs, or view CHEMCAD's built-in BIPs. Using BIPs in a Simulation Viewing Available BIPs From within a simulation, you can view a listing of all BIPs available for use with a particular component pair Selecting a Different BIP for Use in a Simulation You can select any available BIP for use with a given component pair. Handling Suggestions for New BIPs In certain situations, CHEMCAD suggests BIPs to add to the current simulation. Regressing BIPs from Experimental Data You can create new BIPs for the current simulation by regressing experimental data. Editing BIPs When you select Thermophysical > Edit BIPs, CHEMCAD displays your first (or only) set of BIP parameters. This dialog box lists all of the BIPs currently being used in the simulation. If you have specified multiple BIP sets under Thermophysical Settings, then you will see this dialog box display once for each BIP set. The title of the dialog file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 30 of 89 box indicates which BIP set you are currently viewing. How are default BIPs assigned? If more than one BIP exists between any two components, CHEMCAD chooses which BIP to assign by checking the priority of all available BIPs. The higher the priority number, the higher the priority CHEMCAD will give that BIP. The standard priority for VLE BIPs in the CHEMCAD database is 5; the standard priority for LLE BIPs is 4. When you create your own BIPs, you can assign a higher number to give preference to those BIPs. Note that if you leave the Priority field blank, CHEMCAD will enter a priority of 0. Selecting a Different BIP Should you want to use a different BIP than the one currently assigned to a component pair, you can choose any available BIP or alter an existing one. To see available BIPs for a given component pair, find the BIP pair in the list and then click the ellipsis (...) button to the left of the I column. This brings up the Select Database BIP dialog box, where you can select any available BIP for the pair in question. Editable Fields Component I, Component J These columns display the components for the various BIPs. Subtype This column displays the thermo method subtype for each BIP currently in use. Note that the subtype is used only as a descriptor, and does not affect the simulation. The available options are as follows: · VLE (vapor-liquid equilibrium) · LLE (liquid-liquid equilibrium) · VLLE (vapor-liquid-liquid equilibrium) · SLE (solid-liquid equilibrium) · Infinite dilution · User (for situations where none of the above apply) Comment This field displays any text entered at the time of the BIP's creation, for example a literature reference. If you change a system BIP, the Comment field will display a "Modified by" message, which you can overwrite if you choose. Note that you can change the Comment field for a system BIP only after you have made one or more parameter changes; for a user-created BIP, you can change this field at any time. Valid Temperature Range (Min/Max) This field displays the minimum and maximum temperature values for this BIP. Source This field displays the name of the database where the BIP resides. Fill Matrix Option In the bottom left corner of the dialog box is a drop-down list of three options: · Fill matrix by UNIFAC VLE · Fill matrix by UNIFAC LLE · Fill matrix by modified UNIFAC You can use one of these options to have CHEMCAD automatically regress any missing BIPs for component pairs in the simulation. Simply select a method and click Go. CHEMCAD creates equilibrium data based on your selection, then regresses that data into your current thermo method, creating a BIP for each component pair. Selecting Database BIPs The Select Database BIP dialog box displays a list of all available BIPs for a specified pair of components. You can view the detailed parameters for a given BIP by selecting it in the list and then clicking View. To use a different BIP than the one currently assigned, select it and then click OK. Type This column displays the name of the thermo method used for each BIP. Subtype This column displays the thermo method subtype used for each BIP. This field is used only as a descriptor, and does not affect the simulation. The available options are as follows: · VLE (vapor-liquid equilibrium) · LLE (liquid-liquid equilibrium) · VLLE (vapor-liquid-liquid equilibrium) · SLE (solid-liquid equilibrium) · Infinite dilution · User (for situations where none of the above apply) Priority This column displays the priority assigned to each BIP. If more than one BIP exists between two components, CHEMCAD chooses which BIP to assign by checking the Priority field on all available BIPs. The higher the priority number, the higher the priority CHEMCAD will give that BIP. The standard priority for VLE BIPs in the CHEMCAD database is 5; the standard priority for LLE BIPs is 4. When you create your own BIPs, you can assign a higher number to give preference to those BIPs. Note that if you leave the Priority field blank, CHEMCAD will enter a priority of 0. Description This column displays any text used to reference the source of each BIP. If you create new BIPs, you can enter any text here that you like, for example a file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 31 of 89 literature reference. Valid Temp Range This column displays the valid temperature range for each BIP. Source This column displays the name of the database where each listed BIP resides. Select a BIP to View or Edit To view or edit the detailed parameters of a BIP, select Thermophysical > Component Database > Database BIPs. This brings up the Select Components dialog box. Add the two components for this BIP to the Selected Components list at right, using the methods described here, and then click OK. The View/Edit Database BIPs dialog box now appears, listing all available BIPS for the selected component pair. Type This column displays the name of the thermo method used for each BIP. Subtype This column displays the thermo method subtype used for each BIP. This field is used only as a descriptor, and does not affect the simulation. The available options are as follows: · VLE (vapor-liquid equilibrium) · LLE (liquid-liquid equilibrium) · VLLE (vapor-liquid-liquid equilibrium) · SLE (solid-liquid equilibrium) · Infinite dilution · User (for situations where none of the above apply) Priority This column displays the priority assigned to each BIP. If more than one BIP exists between two components, CHEMCAD chooses which BIP to assign by checking the Priority field on all available BIPs. The higher the priority number, the higher the priority CHEMCAD will give that BIP. The standard priority for VLE BIPs in the CHEMCAD database is 5; the standard priority for LLE BIPs is 4. When you create your own BIPs, you can assign a higher number to give preference to those BIPs. Note that if you leave the Priority field blank, CHEMCAD will enter a priority of 0. Description This column displays any text used to reference the source of each BIP. If you create new BIPs, you can enter any text here that you like, for example a literature reference. Valid Temp Range This column displays the valid temperature range for each BIP. Source This column displays the name of the database where each listed BIP resides. View/Edit Select a BIP from the list and then click this button to bring up the BIP's detailed parameter information. Note that when you select a built-in CHEMCAD BIP, this button changes to read View,because system BIPs cannot be changed. New Click this button to begin creating a new BIP that will be stored in the BIP database that you choose. Delete Select a BIP from the list and then click this button to remove the BIP from the BIP database. Copy Select a BIP from the list and then click this button to create a new BIP based on your selection. The BIP copy will initially have the same data as the selected BIP, and you can change any data as needed to make a discrete BIP for the same component pair. Selecting a Thermo Method for a New BIP Type Select the thermo method to use for the new BIP. Subtype Select a method subtype to use for the new BIP. This field is used only as a descriptor, and does not affect the simulation. The available options are as follows: · VLE (vapor-liquid equilibrium) · LLE (liquid-liquid equilibrium) · VLLE (vapor-liquid-liquid equilibrium) · SLE (solid-liquid equilibrium) · Infinite dilution · User (for situations where none of the above apply) Editing BIPs in the Database Whenever you edit, copy, or create a new database BIP, you will see the same dialog box. Note: For new or copied BIPs, this dialog box will be followed by a prompt to select a destination database for your BIP. You can choose Simulation to store the BIP only within the current simulation, or select User to view a list of available user databases where you can store the BIP for use in other simulations. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 32 of 89 Component I, Component J The components for this BIP display here. Priority If more than one BIP exists between two components, CHEMCAD chooses which BIP to assign by checking the Priority field on all available BIPs. The higher the priority number, the higher the priority CHEMCAD will give that BIP. The standard priority for VLE BIPs in the CHEMCAD database is 5; the standard priority for LLE BIPs is 4. When you create your own BIPs, you can assign a higher number to give preference to those BIPs. Note that if you leave the Priority field blank, CHEMCAD will enter a priority of 0. Regardless of priority, a user can always elect to use a different BIP than the one that is assigned by default. Subtype This field indicates the thermo method subtype used for the BIP. This field is used only as a descriptor, and does not affect the simulation. The available options are as follows: · VLE (vapor-liquid equilibrium) · LLE (liquid-liquid equilibrium) · VLLE (vapor-liquid-liquid equilibrium) · SLE (solid-liquid equilibrium) · Infinite dilution · User (for situations where none of the above apply) Comment This field displays any text entered at the time of the BIP's creation, for example a literature reference. Valid Temperature Range (Min/Max) These fields indicate the minimum and maximum temperature values for this BIP. BIP Parameters The I,J and J,I areas of the dialog box list the detailed parameters of this BIP for components I and J. Accepting or Rejecting New BIPs The New BIPs Available dialog box appears whenever CHEMCAD identifies potentially useful BIPs for the current simulation. You will see this dialog box whenever: · You have added one or more components that have BIPs with each other or existing components in your simulation. · You have loaded a simulation for which new BIPs have been added to a database to which you are connected, in cases where you did not previously have BIPs for one or more component pairs. Whenever you see this screen, you should first decide which of the suggested BIPs you want to accept. Then make sure the boxes adjacent to the desired BIPs are checked; simply click a box to turn the check mark on or off. When you have finished, click OK to add the selected BIPs to the current simulation. If you choose not to accept a given BIP, you will not be prompted with that BIP in the future. To obtain the BIP at a later time, you can simply add it using the Thermophysical > Edit BIPs command. BIP Regression This utility allows you to regress experimental data and generate binary interaction parameters (BIP) for mixtures. The CHEMCAD regression facility only calculates BIPs for the widely used equations. If you select an equation which CHEMCAD does not support, you will receive an error message. This regression utility lets you regress experimental VLE (vapor/liquid equilibrium) and LLE (liquid/liquid equilibrium) data for binary, ternary, and quaternary systems. There is also a special case where BIPs can be regressed from the UNIFAC method for systems where no experimental data is available. Regress from UNIFAC VLE: The purpose of this function is to let you obtain binary interaction parameters for other activity coefficient methods where you have no experimental data. As an illustration, say that you have a system of three highly polar compounds but only have experimental data for one pair of compounds. You can use this experimental data to get NRTL BIPs for that binary pair. However, because the other two pairs are missing BIPs you cannot adequately model the system. What then can be done? One option is to model the whole system using the UNIFAC method. A better way is to use the experimental data available and use it with activities derived from UNIFAC. CHEMCAD will regress the UNIFAC generated activities and thereby calculate a set of NRTL BIPs. The experimental BIPs and those regressed from UNIFAC can then be used to solve the problem. Note: UNIFAC is only applicable to binary mixtures. Unlike the other methods shown here, it cannot be used for multicomponent regression. Regress TPxy, Pxy, Txy VLE data: CHEMCAD will take experimental data entered into the data entry dialog box and generate BIPs for the K-value option that is currently set. The program will warn you if you are trying to generate BIPs for a method that does not require them. In general, when there are three or more components present, it is more accurate to regress from ternary (3 components) than from binary data. CHEMCAD will also allow you to use quaternary (4 component) data if available. The calculation of the BIPs is an optimization process. There is no unique set of BIPs, only a best fit within a given region. For this option, the program attempts to match the bubble point temperatures (or pressures in the case of PXY data) and vapors compositions to the liquid compositions. When regressing VLE data, the following nomenclature applies: x1,x2,x3 = Mole fractions of components 1, 2, and 3 in the liquid phase. y1,y2,y3 = Mole fractions of components 1, 2, and 3 in the vapor phase. A binary system would make use of x1 and y1. A ternary system x1, x2, y1, y2. A quaternary system would use all three. CHEMCAD will adjust the input dialog boxes depending on how many components you choose. Regress TPx VLE data: Sometimes you get experimental data where only the liquid phase compositions are known. In this case, the regression utility accepts the temperatures, pressure, and liquid compositions. CHEMCAD will try to match up bubble point temperatures and liquid compositions. In this situation, the program uses x1, x2, and x3 as the compositions in the liquid phase for components 1, 2, and 3, respectively. Regress Txx LLE data: If you need to calculate BIPs from liquid/liquid equilibrium data, then you would use this option. It lets you enter any experimental liquid/liquid equilibrium data. For a liquid/liquid system, the following nomenclature applies: x1,1,x2,1,x3,1 = Mole fractions of components 1, 2, and 3 in the first liquid phase. x1,2,x2,2,x3,2 = Mole fractions of components 1, 2, and 3 in the second liquid phase. In the case of a binary system, CHEMCAD will use x1,1 and x2,1. A ternary system would also include x1,1, x2,1, x1,2 and x2,2. The quaternary system would include all three pairs. The program will change the data entry dialog box depending on the number of components regressed. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 33 of 89 Regress Gamma data: With this option, you can compute BIPs from the direct regression of liquid activity coefficient data. You can regress from binary up to quaternary data. Regression of coefficients at infinite dilution is a special case for this method. For this option, you would follow the nomenclature. x1,x2,x3 = Mole fractions of components 1, 2, and 3, respectively. g1,g2,g3,g4 = Activity coefficients for components 1 through 4. When regressing the activity coefficients, you enter x1 and g1,g2 for a binary regression. Enter x1,x2 and g1,g2,g3 for ternary systems. A quaternary system would require you to enter x1, x2, x3, g1, g2, g3, and g4 data. Regress from UNIFAC LLE: This option is identical to "Regress from UNIFAC" except that the UNIFAC LLE group interaction parameters are used instead of the UNIFAC VLE group interaction parameters. Using the BIP Regression Utility Entering data and running the regression utility follows the same procedure regardless of which option you select. The only difference comes when using regression from UNIFAC (because it does not require entry of experimental data) and regressing Gamma Data (because you enter actual activity coefficients instead of mole fractions). 1. Set your thermodynamic options on the Thermodynamic Settings dialog box. You must use either SRK, Peng-Robinson, BWRS, ESD, SAFT, or one of the activity coefficient methods. 2. Select Thermophysical > Regress BIPs. 3. Choose one of the regression options based on the type of data that you have available. 4. Pick up to four components from the component selection list. The number of components you select will define whether the regression is to be for a binary, ternary, or quaternary system. Note: The components you select in this step here are essentially independent of those selected for the problem. This gives you the flexibility to use the regression utility to examine many systems without having to define a new job. However, if the components selected here are the same as any found in the problem component list, the BIPs calculated for them will be loaded into the BIP matrix for this problem subject to user confirmation. 5. CHEMCAD displays an input dialog box where you enter initial estimates, upper and lower bounds for the BIPs. 6. The next dialog box lets you set convergence parameters for the regression step. Change these values or skip this screen to accept the defaults. 7. The main data entry dialog box is next. It will display existing data if you have done a regression on this set of data before. Otherwise, the screen will be blank. Enter/edit your experimental data in the following fields: · Weight Factor: Lets you apply an arbitrary weight factor to individual data points. This allows you to use higher weight factors to regions of higher interest. The default is 1 which means that all points are weighted equally. · Temperature: Enter the temperature for the data point in system units. If you wish to do the regression at a constant temperature, you only need to enter the temperature for the first point. The remaining points will use the same temperature. · Pressure: Enter the pressure for the data point in system units. If you wish to do the regression at a constant pressure, you only need to enter the pressure for the first point. The remaining points will use the same pressure. · x1,x2,x3: These are the mole fractions in the liquid phase for components 1, 2, and 3, respectively. Enter only x1 for binary regression. x1,x2 are used for ternary regression. All three parameters, x1,x2,x3, are used for quaternary systems. · y1,y2,y3: These are the mole fractions in the vapor phase for components 1, 2, and 3, respectively. Enter only y1 for binary regression. y1,y2 are used for ternary regression. All three parameters, y1,y2,y3, are used for quaternary systems. 8. After you have entered all the points, click OK to save the data. Click Cancel if you decide not to save the data. If you have made changes, CHEMCAD will ask if you want to save changed data. 9. The regression analysis will start immediately. When the analysis converges the program displays a screen that contains calculation messages and the resulting BIPs. If the analysis fails to converge or if the program is unable to minimize the objective function, you will get a message describing the problem. 10. When the regression is finished, CHEMCAD asks into which BIP set you want to save the calculated BIPs. Enter the desired set number in the field provided, then click OK. Using the BIP Regression from UNIFAC Follow steps 1 through 6 above. The regression analysis will start after you exit the Convergence Parameters screen. When the analysis converges, the program will display a screen that contains calculation messages and the resulting BIPs. If the analysis fails to converge or if the program is unable to minimize the objective function, you will get a message describing the problem. If the components you regressed are in the current component list, CHEMCAD will ask into which BIP set you want to save the calculated BIPs. Enter the correct set number in the field provided, then click OK. If the regressed components are not in the current component list, you will have to write down the results for later entry into a job BIP matrix. Equation of State BIPs The mixing rules of the equations-of-state have a significant bearing on how accurately they handle mixtures. The mixing rules for the equations-of-state currently available do not account for interactions between unlike pairs of molecules if they are greatly different from the interactions between like pairs. To overcome this limitation, a binary interaction parameter, Kij, has been added to the mixing rules of these equations. Even this, however, has been found to be capable only of improving the accuracy between molecules of unlike sizes. The binary interaction parameter (kij) for an equation of state may be expressed as a temperature dependent function. where: T is temperature in degrees Kelvin. Kij is the binary interaction parameter between component i and j. By definition: · kij=kji , kii=kjj=0 · Aij = Aji · Bij = Bji · Cij = Cji For user-added components, you can edit the constants (A, B, C) from the CHEMCAD interface. BIP Conversion file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 34 of 89 The primary source of VLE and LLE data reporting and analysis is the DECHEMA data series. To use such parameters, you must be aware of the parameter units. The following table defines the parameter units for both DECHEMA and CHEMCAD, and provides the required conversions. Conversion of DECHEMA Parameters to CHEMCAD Model DECHEMA aij Units CC aij Units DECHEMA to CHEMCAD UNIQ(VLE) (Uij-Ujj), cal/mol Same None NRTL(VLE) (Gij-Gjj), cal/mol (Gij-Gjj) /R, deg K /R WILS(VLE) (Λij-Λjj), cal/mol Same None UNIQ(LLE) (Uij-Ujj) /R, deg K (Uij-Ujj), cal/mol *R NRTL(LLE) (Gij-Gjj) /R, deg K Same None R = 1.98721 cal/mol/deg K If you are using parameters from sources other than DECHEMA, be aware of the parameter units and apply an appropriate conversion. How to Check Outside Data Occasionally literature data regressions are misprinted or otherwise in error. Such fits may be checked by regressing the reported data and constraining the parameters to the reported values. The parameters may be constrained by setting minimums and maximums to the reported values. If the parameters are good, the regression will converge in one iteration. For this check to be useful, the fit of the vapor pressure equation in the range of data must be good. If you choose, you can create user components and use the literature form of either the Antoine or DIPPR equation. Techniques for Unusual Cases If a regression will not converge, there can be many reasons and approaches to the problem. Consider the following techniques as they seem appropriate: · Plot the model fit with the data points. Note whether the data points form a reasonable curve. The plot should show data entry errors or discrepant (non-smooth) data points. · If using NRTL, the third parameter, alpha, could be clamped by setting both the minimum and maximum allowable values. The value is normally 0.2 - 0.4. · If the model looks good but a better fit is required, reduce the relative and absolute tolerances and note the reduction in FERR (error term). At some point, FERR cannot be further lowered. Even though you see a not converged message, the fit as good as can be obtained within the current range of parameters. ESSO The ESSO K-value model uses the Maxwell-Bonnell vapor pressure equation to calculate K-values. The ESSO K model predicts K-values for heavy hydrocarbon materials effectively at pressures below 100 psia. This model can be used to model vacuum towers. Summary equations of: where: where: Tb12 = normal boiling point corrected to K = 12 in degrees Rankine T = absolute temperature in degrees Rankine DDT = Tb - Tb12 = 2.5 f (K - 12) log p * /14.7 where: Tb = normal boiling point, in degrees Rankine f = correction factor. For all subatmospheric vapor pressures and for all substances having normal boiling points greater than 400 F, f = 1. For substances having normal boiling points less than 200 F, f = 0. For super atmospheric vapor pressures of substances having normal boiling points between 200 F and 400 F, f is given by: K = Watson characterization factor The average error for pure hydrocarbons is 8% for p* > 1 mmHg, and 30% for p* between 10E-6 and 1 mmHg according to the API Technical Data Book, file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 35 of 89 Volume 1. Reference: API Technical Data Book, Volume 1. Vapor Pressure Model (Ideal Solution) In the vapor pressure model, both vapor and liquid are treated as ideal. The K-value is defined as where: Pi = the vapor pressure of component i at system temperature P = system pressure The program checks the critical temperature and · If Tr>1 and B4 (the last Henry's Gas Law constant) is non-zero, then the program uses the Henry's Gas Law model for the K-value of that component. · If Tr>1 and B4 is zero, then CHEMCAD looks to see if the DIPPR Vapor Pressure constants are present. If they are, the DIPPR equation is used to calculate the component VP. If the DIPPR constants are zero, then ANTOINE is used to calculate the component VP. · If Antoine is the equation used and if Tr>2, the program sets the upper bound on the VP of VP = VP at T = 2*T (critical) The lower bound is VP at T = 0.05 * T (critical) These changes produce better results above the critical point. Water-Gas Henry's Constants Henry’s Gas Law is used to correct for liquid fugacity of gases dissolved in water. For a given component i, vapor pressure is calculated using the equation: ƒi = xi * Hi where: ƒi = fugacity of component i (apparent vapor pressure), psia Hi = Henry's constant for component i, psia per unit mole fraction of gas xi = liquid mole fraction of component i The following equation is used to calculate Henry's constants for gases in water at low pressures: ln(H) = A / T + B * ln(T) + C * T + D where: H = Henry's constant, in psia per unit mole fraction of gas T = system temperature in degrees Rankine A, B, C, D are the coefficients. Note that the Henry’s Gas constants are systems where the gas is dissolved in liquid water at 1 atm. The API Technical Data Book references alternative sources for techniques to use for systems of gas dissolved in gas, or gas in water at high pressure. Henry's constant coefficients are available in CHEMCAD for the gases listed below: Ammonia Hydrogen sulfide Argon Iodine Bromine Methane Carbon dioxide Neon Carbon monoxide Nitrogen Chlorine Nitrous oxide Ethane Oxygen Ethylene Propane Hydrogen Sulfur dioxide Helium-4 Where Henry's constant coefficients are available, they are stored in the component's database entry. To see whether a given component includes these coefficients, or to view the coefficients being used, bring up the View/Edit Component Data menu for that component and select Other Data. Then click the Parametric Data tab to view Henry's constant coefficients A through D. In scientific literature, Henry’s constants are most often expressed as a single value H. To use this value for a component that does not yet have Henry's constant coefficients in CHEMCAD, simply specify coefficient D as equal to the log of H, resulting in a constant temperature coefficient. Bear in mind that Henry’s constants are given in many different unit sets, so you may need to convert your constant to psia/mole fraction of gas. Soave-Redlich-Kwong (SRK) The Soave-Redlich-Kwong equation is very effective for predicting K-values for hydrocarbon systems at medium to high pressures. Good results have been obtained by using this method for demethanizers, de-ethanizers, depropanizers, debutanizers, wellhead processes, etc. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 36 of 89 The compressibilities and mixture fugacity coefficients for both vapor and liquid phases are derived from the Soave-Redlich-Kwong equation of state. The binary interaction parameters are included for several hydrocarbons and non-condensible gases. User supplied data is usually not required for this method. However, the binary interaction parameters can be modified or supplied by editing them in the CHEMCAD BIP databases. Summary of Equations where: Fugacity Coefficient where: The K-values Boston-Mathias Extrapolation Boston and Mathias developed an alternative alpha function to the one above for temperatures exceeding critical. The Boston-Mathias extrapolation may be used with SRK. The alpha function used by SRK and Peng-Robinson gives unrealistic results for light gases at high reduced temperatures. Boston and Mathias developed an alternative alpha function to the one above for temperatures exceeding critical. The following equations will be used for the alpha function, if Boston-Mathias is selected. where: Mixing Rules The equation of state binary interaction parameter, kij, may be specified as a temperature dependent equation. Binary interaction parameters (BiPs) extend cubic equations of state beyond systems with only modest deviation from ideal gas. References 1. Soave, G., Chem. Eng. Sci., 27, 1197 (1972). 2. Gundersen, T., Computer and Chem. Eng., 3, 245 (1982). Grayson-Streed Modified Chao-Seader (GS) The Grayson-Streed modified Chao-Seader model is primarily applicable to systems of non-polar hydrocarbons. It is good for modeling hydrocarbon units, depropanizers, debutanizers, or reformer systems. The approximate range of its applicability is as follows: Temperature Range Pressure Range 0 °F to 800 °F < 3000 psia (-18 °C to 430 °C) (< 20000 KPA) The correlation can also be applied down to the lower temperature limit of the original Chao-Seader work (Tr = 0.5 for hydrocarbons except methane) and down to -100 F for hydrogen and methane. Hydrocarbon liquid solutions are considered to be regular solutions in this correlation. The liquid phase pure species fugacities are derived from Grayson- file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 37 of 89 Streed's corresponding state option. Vapor phase mixture fugacity coefficients as well as vapor compressibilities are based on the Redlich-Kwong equation of state. Correlation of Liquid Fugacity Coefficient where the coefficient Ai is represented as the following table: Simple Fluid Methane Hydrogen A0 2.05135 1.36822 1.50709 A1 -2.10899 -1.54831 2.74283 A2 0. 0. -0.02110 A3 -0.19396 0.02889 0.00011 A4 0.02282 - 0.01076 0. A5 0.08852 0.10486 0.008585 A6 0. -0.02529 0. A7 -0.00872 0. 0. A8 -0.00353 0. 0. A9 0.00203 0. 0. Activity Coefficient in a Liquid Solution (using solubility parameters) Fugacity Coefficient in a Vapor Mixture - Reference Chao, K. C. and Seader, J. D., A General Correlation of Vapor-Liquid Equilibria in Hydrocarbon Mixtures, AIChE Journal, 7, No. 4 (December 1961). Peng-Robinson (PR) The Peng-Robinson equation of state is very effective for predicting K-values for hydrocarbon systems at medium to high pressures. Good results have been obtained by using this method for demethanizers, de-ethanizers, depropanizers, debutanizers, wellhead processes, etc. The Peng-Robinson equation is the best available method for cryogenic systems. The compressibilities and mixture fugacity coefficients for both vapor and liquid phases are derived from the Peng-Robinson equation of state. The binary interaction parameters are included for several hydrocarbons and non-condensible gases. User-supplied data is usually not required for this method. However, the binary interaction parameters can be modified or supplied by the user by editing them in the CHEMCAD databases. Summary of Equations where: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 38 of 89 Fugacity Coefficient where: Boston-Mathias Extrapolation Boston and Mathias developed an alternative alpha function to the one above for temperatures exceeding critical. The Boston-Mathias extrapolation may be used with Peng Robinson. Mixing Rules The equation of state binary interaction parameter, kij, may be specified as a temperature dependent equation. Binary interaction parameters (BIPs) extend cubic equations of state beyond systems with only modest deviation from ideal gas. Reference Peng, D. Y. and D. B. Robinson, Ind. Eng. Chem. Fundam., 15, 59 (1976). Volume Translated Peng-Robinson (VTPR) The VTPR model (Volume Translated Peng-Robinson) combines a very good equation of state with the Twu alpha function and a Gibbs excess mixing rule to create a very versatile method for predicting the thermodynamic properties of mixtures. VTPR builds upon PSRK's success in predicting gas solubilities, but is better able to predict liquid densities, infinite dilution activity coefficients, and heats of mixing. The Gibbs excess mixing rule used in VTPR is an improvement over the GE used in PSRK, owing to the use of temperature-dependent parameters. This method has had good performance in both polar and non-polar systems, where data is available. Summary of Equations The VTPR equation of state is defined as follows: where the mixing rule for the attractive parameter is given by: The quadratic mixing rule for parameter b is: Translation parameter c is determined by a linear mixing rule: If c is not in the database for a given component, we estimate c using the following: The Twu alpha multiplier ac,i is a component of the attractive parameter, and is calculated as follows: The Twu alpha function itself is calculated as follows: Calculation of the attractive parameter a(T) includes the Gibbs excess mixing rule: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 39 of 89 where: The following temperature function for group interaction parameters is the same as that used for modified UNIFAC: Reference Schmid, B., Schedemann, A., and Gmehling, J., Extension of the VTPR Group Contribution Equation of State: Group Interaction Parameters for Additional 192 Group Combinations and Typical Results, Ind. Eng. Chem. Res. 2014, 53, 3393-3405. Gmehling, J., Kolbe, B., Kleiber, M., Rarey, J., Chemical Thermodynamics for Process Simulation, John Wiley & Sons, 2012. VTPR Group Specifications The Subgroup number is the number to assign to a component for the given subgroup. Subgroup Main Group Subgroup number Example component Groups for Example Component CH2 CH3 1 butane 2 CH3, 2 CH2 CH2 2 butane 2 CH3, 2 CH2 CH 3 i-butane 3 CH3, 1 CH C 4 2,2-dimethylpropane 4 CH3, 1 C C=C CH2=CH 5 1-hexene 1 CH3, 3 CH2, 1 CH2=CH CH=CH 6 2-hexene 2 CH3, 2 CH2, 1 CH=CH CH2=C 7 2-methyl-1- butene 2 CH3, 1 CH2, 1 CH2=C CH=C 8 2-methyl-2- butene 3 CH3, 1 CH=C C=C 70 2,3-dimethylbutene 4 CH3, 1 C=C Allene 97 =CHCH= 98 =CCH= 99 H2C=CH2 250 ACH ACH 9 benzene 6 ACH AC 10 styrene 1 CH2=CH, 5 ACH, 1 AC ACCH2 ACCH3 11 toluene 5 ACH, 1 ACCH3 ACCH2 12 ethylbenzene 1 CH3, 5 ACH, 1 ACCH2 ACCH 13 cumene 2 CH3, 5 ACH, 1 ACCH OH OH(p) 14 1-propanol 1 CH3, 2 CH2, 1 OH(p) OH(s) 81 2-propanol 2 CH3, 1 CH, 1 OH(s) OH(t) 82 tert-butanol 3 CH3, 1 C , 1 OH (t) CH3OH CH3OH 15 methanol 1 CH3OH H2O H2O 16 water H2O ACOH ACOH 17 phenol 5 ACH, 1 ACOH Ketone CH2CO CH3CO 18 2-butanone 1 CH3, 1 CH2, 1 CH3CO file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 40 of 89 CH2CO 19 3-pentanone 2 CH3, 1 CH2, 1 CH2CO Aldehyde CHO CHO 20 acetaldehyde 1 CH3, 1 CHO Esters CCOO CH3COO 21 butyl acetate 1 CH3, 3 CH2, 1 CH3COO CH2COO 22 butyl propanoate 2 CH3, 3 CH2, 1 CH2COO CHCOO 129 CCOO 180 HCOO HCOO 23 ethyl formate 1 CH3, 1 CH2, 1 HCOO Ether CH2O OCH3 24 dimethyl ether 1 CH3, 1 CH3O OCH2 25 diethyl ether 2 CH3, 1 CH2, 1 CH2O OCH 26 diisopropyl ether 4 CH3, 1 CH, 1 CH-O Amine CH2NH2 CH3NH2 28 methylamine 1 CH3NH2 CH2NH2 29 n-propylamine 1CH3, 1 CH2, 1 CH2NH2 CHNH2 30 isopropylamine 2 CH3, 1 CHNH2 CNH2 85 tert-butylamine 3 CH3, 1 CNH2 CH2NH CH3NH 31 dimethylamine 1 CH3, 1CH3NH CH2NH 32 diethylamine 2 CH3, 1 CH2, 1 CH2NH CHNH 33 diisopropylamine 4 CH3, 1 CH, 1CHNH (C)3N CH3N 34 trimethylamine 2 CH3, 1 CH3N CH2N 35 triethylamine 3 CH3, 2 CH2, 1 CH2N ACNH2 ACNH2 36 aniline 5 ACH, 1 ACNH2 AR-CNC C2H2N 37 C2HN 38 C2N 39 CH2CN CH3CN 40 CH2CN 41 COOH COOH 42 acetic acid 1 CH3, 1 COOH CCl CH2Cl 44 1-chlorobutane 1 CH3, 2CH2, 1CH2Cl CHCl 45 2-chloro-propane 2 CH3, 1 CHCl CCl 46 2-chloro-2-methyl propane 3 CH3, 1 CCl CH3Cl 252 CCl2 CH2Cl2 47 dichloromethane 1 CH2Cl2 CHCl2 48 1,1-dichloroethane 1 CH3, 1 CCl2 CCl2 49 2,2-dichloropropane 2 CH3, 1 CCl2 CCl3 CCl3 51 1,1,1-trichloroethane 1 CH3, 1 CCl3 CCl4 CCl4 52 carbon tetrachloride 1 CCl4 ACCl ACCl 53 chlorobenzene 5 ACH, 1 ACCl CNO2 CH3NO2 54 nitromethane 1 CH3NO2 CH2NO2 55 1-nitropropane 1 CH3, 1 CH2, 1 CH2NO2 CHNO2 56 2-nitropropane 2 CH3, 1 CHNO2 ACNO2 ACNO2 57 nitro-benzene 5 ACH, 1 ACNO2 CS2 CS2 58 carbon disulfide 1 CS2 CH3SH CH3SH 59 methanethiol 1 CH3SH CH2SH 60 ethanethiol 1 CH3, 1 CH2SH CHSH 185 Furfural furfural 61 furfural 1 furfural furfur-C 187 DOH DOH 62 1,2-ethanediol 1 DOH I I 63 iodoethane 1 CH3, 1 CH2, 1 I Br Br 64 bromomethane 1 CH3, 1 Br C=-C CH=-C 65 1-hexyne 1 CH3, 3 CH2, 1 CH=-C C=-C 66 2-hexyne 2 CH3, 2 CH2, 1 C=-C HC=-CH 251 file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 41 of 89 DMSO DMSO 67 dimethyl sulfoxide 1 DMSO Acrylonitrile Acrylonitrile 68 acrylonitrile 1 acrylonitrile ClCC Cl-(C=C) 69 ACF ACF 71 hexafluorobenzene 6 ACF DMF DMF 72 N,N-dimethylformamide 1 DMF HCON(CH2)2 73 N,N-diethylformamide 2 CH3, 1 HCON(CH2)2 CF3 74 perfluorohexane 2 CF3, 4 CF2 CF2 75 perfluorohexane 2 CF3, 4 CF2 CF 76 perfluoromethylcyclohexane 1 CF3, 5 CF2, 1 CF COO COO 77 methyl acrylate 1 CH3, 1CH2=CH, 1 COO CY-CH2 CY-CH2 78 CY-CH 79 CY-C 80 CY-CH2O THF 27 CY-CH2O 83 1,1,3,3-tetramethyldisiloxane 4 CH3, 1 SiHO, 1 SiH Trioxan 84 octamethylcyclotetrasiloxane 8 CH3, 4 SiO HCOOH HCOOH 43 formic acid 1 HCOOH CHCl3 CHCl3 50 chloroform 1 CHCl3 CY-CON-C NMP 86 N-methylpyrrolidone 1 NMP NEP 87 NIPP 88 NTBP 89 Amide CON(AM) AMH2 91 acetamide 1 CH3, 1 CONH2 AMHCH3 92 N-methylacetamide 1 CH3, 1 CONHCH3 AMHCH2 100 N-ethylacetamide 2 CH3, 1 CONHCH2 CONHC 183 N-tert-Butyl-Acetamide 4 CH3, 1 CONHC CONR2 AM(CH3)2 101 N,N-dimethylacetamide 1 CH3, 1 CON(CH3)2 AMCH3CH2 102 N,N-methylethylacetamide 2 CH3, 1 CONCH3CH2 AM(CH2)2 103 N,N-diethylacetamide 3 CH3, 1 CON(CH2)2 HCONR HCONHCH3 93 N-Methyl-formamide 1 HCONHCH3 HCONHCH2 94 N-Ethyl-formamide 1 CH3,1 HCONHCH2 ACCN ACCN 95 Benzonitrile 5 ACH, 1 ACCN NCO NCO 96 Butylisocyanate 1 CH3, 2 CH2, 1 NCO ACS AC2H2S 104 thiophene 2 ACH, 1 AC2H2S AC2HS 105 2-methylthiophene 1 CH3, 2 ACH, 1 AC2HS AC2S 106 2,5-dimethylthiophene 2 CH3, 2 ACH, 1 AC2S Epoxide Epoxy H2COCH 107 propylene oxide 1 H2COCH, 1 CH3 COCH 108 2-methyl, 2,3-butylene oxide 1 HCOC, 3 CH3 HCOCH 109 2,3-epoxybutane 1 HCOCH, 2 CH3 H2COCH2 119 ethylene oxide 1 H2COCH2 H2COC 153 2-methyl propylene oxide 1 H2COC, 2 CH3 Anhydride OC-O-CO 90 Carbonate (CH3)2CB 112 (CH2)2CB 113 CH2CH3CB 114 CHCH2CB 115 Sulfone (CH2)2SU 110 sulfolane 1 (CH2)2SU, 2 CH2 CH2SUCH 111 2,4-dimethylsulfolane 1 CH2SUCH, 2 CH3, 1 CH2, 1 CH AC-CHO AC-CHO 116 AC-COOH AC-COOH 117 AC-COO AC-COO 118 OCCOH C2H5O2 120 2-ethoxyethanol 1 CH3, 1 CH2, 1 C2H5O2 C2H4O2 121 2-ethoxy-1-propanol 2 CH3, 1 CH2, 1 C2H4O2 file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 42 of 89 CH2S CH3S 122 dimethylsulfide 1 CH3, 1 CH3S CH2S 123 diethylsulfide 2 CH3, 1 CH2, 1 CH2S CHS 124 diisopropylsulfide 4 CH3, 1 CH, 1 CHS CYCONH-C CYCONH-C 125 n-isopropylpyrrolidone 1 CY-CON-CH, 3 CY-CH2, 2 CH3 CY-COO-C CY-COO-C 126 g-butyrolactone 2 CH2, 1 cy-COO-C -O-O- -O-O- 127 di-tert-butylperoxide 6 CH2, 2 C, 1 -O-O- -O-OH 128 tert-butylhydroperoxide 3 CH2, 1 C, 1 -O-OH CFH CFH3 130 R41 1 CFH3 CFH2 131 R161 1 CH3, 1 CFH2 CFH 132 R225BB 1 CFCl, 1 CF2H, 1 CF2Cl CFCl CFClH2 133 R31 1 CFClH2 CFClH 134 CFCl 135 R225BB 1 CFCl, 1 CF2H, 1 CF2Cl CH2BrCl 186 CFCl2 CFCl2H 136 CFCl2 137 CFCl3 138 CF2H CF2H2 139 R32 1 CF2H2 CF2H 140 R134 2 CF2H CF2ClH CF2ClH 141 CF2Cl2 CF2Cl 142 CF2Cl2 143 CF3Br 148 CF3H CF3H 144 R23 1 CF3H (CH3)CF3 147 R143A 1 CH3, 1 (CH3)-CF3 CF3Cl CF3Cl 145 CF2ClBr 149 R13B1 1 CF3Br CF4 CF4 146 R14 CF4 Acetals O-CH2-O 150 Dimethoxymethane 2 CH3, 1 O-CH2-O O-CH-O 151 1,1-Dimethoxyethane 3 CH3, 1 O-CH-O O-C-O 152 2,2-Dimethoxypropane 4 CH3, 1 O-C-O ACNR2 ACN(CH3)2 154 N,N-Dimethylaniline 5 ACH, 1 ACN(CH3)2 ACN(CH2)2 155 N,N-Diethylaniline 2 CH3, 5 ACH, 1 ACN(CH2)2 ACNCH3CH2 156 N-Ethyl-N-methylaniline 1 CH3, 5 ACH, 1 ACNCH3CH2 ACNHR ACNHCH3 157 N-Methylanilin 5 ACH, 1 ACNHCH3 ACNHCH2 158 N-Ethylanilin 1 CH3, 5 ACH, 1 ACNHCH2 Furan AC2H2O 159 Furan 2 ACH, 1 AC2H2O AC2HO 160 2-Methylfuran 1 CH3, 2 ACH, 1 AC2HO AC2O 161 2,5-Dimethylfuran 2 CH3, 2 ACH, 1 AC2O CY-C-NH CYCH2-NH 162 CYCH-NH 163 CYC-NH 164 CY-C-NR CY-CNCH3 165 CY-CNCH2 166 CY-CNCH 167 CY-CNC 168 SiH2 SiH3 169 methylsilane 1 CH3, 1 SiH3 SiH2 170 diethylsilane 2 CH3, 2 CH2, 1 SiH2 SiH 171 heptamethyltrisiloxane 7 CH3, 2 SiO, 1 SiH Si 172 hexamethyldisiloxane 6 CH3, 1 SiO, 1 Si SiO H2SiO 173 1,3-dimethylsiloxane 2 CH3, 1 SiH2O, 1 SiH2 HSiO 174 1,1,3,3-tetramethyldisiloxane 4 CH3,1 SiHO, 1 SiH SiO 175 octamethylcyclotetrasiloxane 4 CH3, 1 SiHO, 1 SiH file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 43 of 89 Oxime HCNOH 176 propionaldehydoxime 1 HCNOH, 1 CH3, 1 CH2 CNOH 177 acetoneoxime 1 CNOH, 2 CH3 ACCO ACCOCH3 181 ACCOCH2 182 Imidazol C3H2N2+ 178 C3H3N2+ 184 BTI BTI- 179 NH3 NH3 300 CO2 CO2 306 CH4 CH4 307 O2 O2 308 Ar Ar 305 N2 N2 304 H2S H2S 303 H2 H2 302 D2 D2 309 CO CO 301 SO2 SO2 310 NO NO 311 N2O N2O 312 SF6 SF6 313 He He 314 Ne Ne 315 Kr Kr 316 Xe Xe 317 HF HF 318 HCl HCl 319 HBr HBr 320 HI HI 321 COS COS 322 F2 F2 326 Cl2 Cl2 327 Br2 Br2 328 HCN HCN 329 NO2 NO2 330 CF4 CF4 331 O3 O3 332 ClNO ClNO 333 Hg Hg 345 Benedict-Webb-Rubin-Starling Model (BWRS) The Benedict-Webb-Rubin-Starling BWRS) equation is very effective at predicting K-values for hydrocarbon systems and is generally considered to be more accurate for light normal paraffins than the other equations of state. Binary interaction parameters are provided for various hydrocarbons and non-condensible gases. User-supplied data is not required to use BWRS but BIPs may be modified or supplied by editing them in the CHEMCAD databases. Summary of Equations It can be rewritten for z = pv/RT as a function of temperature and molal volume: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 44 of 89 The 11 pure component coefficients Ao, Bo, Co, Do, Eo, a, b, c, d, aa and gg can be expressed as functions of Tc, rrc and ww The 2 sets of 11 constants A j and Bj were determined by simultaneous fitting to PVT, enthalpy and vapor pressure data of normal paraffin hydrocarbons. j= 1 0.443690 0.115449 2 1.28438 - 0.920731 3 0.356306 1.70871 4 0.544979 -0.270896 5 0.528629 0.349261 6 0.484011 0.754130 7 0.0705233 -0.044448 8 0.504087 1.32245 9 0.0307452 0.179433 10 0.0732828 0.463492 11 0.006450 -0.022143 The coefficients for mixtures are found with 11 mixing rules: The binary interaction parameters kij are zero when i equals j (pure fluid interaction); for unequal pairs i ¹¹ j, the value of k ij can be determined by fitting to file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 45 of 89 available binary VLE data. Fugacity Coefficient The fugacity fi of each component i in the mixture can be calculated as follows: K-values References 1. Starling, K. E., Fluid Thermodynamics Properties of Light Petroleum Systems, Gulf Publishing Company, 1973. 2. Benedict, M., Webb, R. B., Rubin, L. C., J. Chem. Phys. 8, 1940. API Soave-Redlich-Kwong The API Soave-Redlich-Kwong option is similar to the Soave-Redlich-Kwong option and is very effective for predicting K-values for hydrocarbon systems at medium to high pressures. Good results have been obtained by using this method for demethanizers, de-ethanizers, depropanizers, debutanizers, wellhead processes, etc. The compressibilities and mixture fugacity coefficients for both vapor and liquid phases are derived from the API modification of the Soave-Redlich-Kwong equation of state. The binary interaction parameters are included for several hydrocarbons and non-condensable gases published in the API Technical Data Book, Volume 1. User-supplied data is usually not required for this method. However, the binary interaction parameters can be modified or supplied by the user by editing them in the CHEMCAD databases. Summary of Equations where: Fugacity Coefficient where: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 46 of 89 References 1. API Technical Data Book, Volume 1. 2. Gundersen, T., Computer and Chem. Eng., 3, 245 (1982). Modified Soave-Redlich-Kwong (MSRK) The modified SRK (MSRK) differs from the original only in the functional form of the temperature-dependent energy attraction term, (Tr). The Alpha (T) expression gives a better representation of polar systems in terms of two parameters, m and n, in addition to Tc and Pc. Parameters m and n are unique to the component of interest, and must be determined with empirical data fit. This contrasts with the original SRK alpha which uses only one fitted parameter, the acentric factor. Parameters m and n for approximately 200 compounds are stored in the CHEMCAD database. Summary of Equations where: Fugacity Coefficient where: References Sandarusi, J. A., Kidnay, A. J., and Yesavage, V. F., Industrial Engineering Chemical Process Design Development, 1986, Vol. 25, No. 4, 957-963. Extended Soave-Redlich-Kwong (TSRK) The TSRK method extends the SRK method to methanol systems with light gases and/or water. The method is taken from the work of Chang, Rosseau, and Ferrell and is described below: Summary of Equations SRK Equation For any pure component, the constants a and b are found at the critical point to be file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 47 of 89 Soave expressed aa as a function of temperature and held b constant so that where the quantity aa is a function of temperature. An expression used here is given by Mathias as The first and second terms on the right side of this equation were introduced by Soave to correlate m as a function of the acentric factor and reproduce the vapor pressure of nonpolar hydrocarbons. Graboski and Daubert used a regression program to evaluate m based on a large API vapor pressure data set for hydrocarbons and gases to obtain Although use of the Soave aa temperature function calculates vapor pressures of hydrocarbons and gases accurately, it can not do the same for vapor pressure of polar compounds such as water and alcohols. Mathias introduced the third term for this purpose; it uses a correction term p that is obtained by fitting the equation to the vapor pressure data of the system component. This polar correction factor uses only one temperature-independent parameter and enables accurate calculation of the vapor pressures of the polar compounds. The extended Soave-Redlich-Kwong equation can be applied to mixtures using the mixing rules: and where the cross parameters are given by: and Kij and Cij are interaction parameters. In a previous study (Chang et al., 1983), Kij was expressed as a function of temperatures for systems containing methanol: Mathias has suggested that Cij should also be expressed as a function of temperature: The evaluation of fugacity coefficients from the SRK equation of state is made easier with the definitions: The SRK equation then can be written as: Reference "Vapor-Liquid Equilibria of Constituents from Coal Gasification in Refrigerated Methanol"; Te Chang, R. M. Rousseau, and J. K. Ferrell; North Carolina University; NTIS, EPA/600/7-87/004. Predictive Soave-Redlich-Kwong (PSRK) The PSRK equation serves as a supplementary model for predicting vapor-liquid-equilibria or gas solubilities and is not designed to replace well known and useful methods like UNIFAC. The PSRK equation is a group contribution equation-of-state which combines the SRK and UNIFAC models. This concept makes use of recent developments and has the main advantage that vapor-liquid-equilibria (VLE) can be predicted for a large number of systems without introducing new model parameters that must be fitted to experimental VLE-data. The PSRK equation of state can be used for VLE-predictions over a much larger temperature and pressure range than the UNIFAC gg-ff- approach and is easily extended to mixtures containing supercritical compounds. Additional PSRK parameters, which allow the calculation of gas/gas and gas/ alkane phase equilibria are provided by the program. The PSRK Equation of State The PSRK equation is based on the modified Soave-Redlich-Kwong equation of state, which yields good results for vapor-liquid-equilibria (VLE) of nonpolar or slightly polar mixtures: (1) Two modifications are necessary to obtain an equation of state for predicting vapor-liquid-equilibria of polar as well as nonpolar mixtures. The first modification concerns the temperature dependence of the pure component parameter aa, which was originally expressed by Soave in terms of the acentric factor ww. (2) This temperature dependence yields sufficiently accurate vapor pressure data for nonpolar substances, but improvements are still necessary for polar components. Therefore, the expression proposed by Mathias and Copeman is used in the PSRK equation: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 48 of 89 (3) The use of the three adjustable parameters especially improves the description of the pure component vapor pressures for polar components. The second modification concerns the mixing rule for the parameter aa. Recent developments of Heidemann and Kokal and Michelsen lead to simple, density independent mixing rules, which link the mixture parameter aa to the excess Gibbs energy gE0. In contrast to mixing rules involving the excess Gibbs energy at infinite pressure (Huron and Vidal, Tochigi, et al.) a recalculation of existing parameter tables is not necessary. Michelsen proposed a mixing rules based on the zero pressure reference state and a first- and second-order approximation. The simplest first-order approximation is used in the PSRK equation: (4) Michelsen recommends a value of A1 = -0.593. This value is changed to A1 = -0.64663 in the PSRK equation, which yields better results at higher pressures. Therefore, the PSRK equation is especially suited for conditions, where the use of an gg-ff-approach is difficult (i.e. when the real behavior of the vapor phase is unknown and not negligible) or inadequate (i.e. when supercritical components are present). Equation (4) is used together with the UNIFAC model (Fredenslund et al.) and with the linear mixing rule for the parameter b: (5) Experimental data on gas / alkane systems was used to regress UNIFAC interaction parameters. The data covers a larger temperature range than the UNIFAC model covers, so temperature dependent parameters are introduced into the UNIFAC expression: is replaced by: Estimation of New PSRK Parameters The main advantage of equations of state in comparison with gg-ff-approaches is their ability to calculate phase equilibria of systems containing supercritical components. Therefore, the UNIFAC interaction parameter table was extended. Light gases were included and parameters for alkane/gas and gas/gas phase equilibria predictions are now available. The missing van der Waals volumes rk and surface areas qk are summarized below and were estimated using Bondi's method. In some cases, slight changes were found useful to improve VLE predictions. Van der Waals properties for PSRK equation of state were added for the following subgroups. The table lists CHEMCAD components which use these subgroups for PSRK calculations. Subgroup        Component                ID Number CO2 Carbon Dioxide 49 CH4 methane 2 N2 nitrogen 46 H2S Hydrogen Sulfide 50 H2 hydrogen 1 CO carbon monoxide 48 H2C=CH2 ethylene 22 CH ºCH acetylene 65 NH3 ammonia 63 Ar argon 98 O2 oxygen 47 SO2 sulfur dioxide 51 NO nitric oxide 108 N2O nitrous oxide 110 SF6 sulfur hexafluoride 953 He Helium 212 Kr Krypton 971 Xe Xenon 994 HCl Hydrogen Chloride 104 HBr Hydrogen Bromide 209 HF Hydrogen Fluoride 210 HI Hydrogen Iodide 106 COS carbonyl sulfide 219 CHSH, CSH (mercaptans) 1266,1295,716,1698,838 H2COCH (epoxy rings) 707,129,1792,444 HCOCH HCOC H2COCH2 H2COC COC References Th. Holderbaum, J. Gmehling, "PSRK: A Group Contribution Equation of State Based on UNIFAC," Fluid Phase Equilibria 70, 251-265 (1991) K. Fischer, J. Gmehling; "Further Development, Status and Results of the PSRK- Method for the Prediction of Vapor-Liquid Equilibria and Gas Solubilities," Fluid Phase Equilibria 121, 185 (1996) file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 49 of 89 K. Fischer, J. Gmehling; "Further Development, Status and Results of the PSRK- Method for the Prediction of Vapor-Liquid Equilibria and Gas Solubilities II," Fluid Phase Equilibria 141, 113-127 (1997) S. Horstmann, K. Fischer, J. Gmehling; "PSRK group contribution equation of state: Revision and Extension III," Fluid Phase Equilibria 167, 173-186 (2000) The SAFT Equation The implementation of SAFT applied by CHEMCAD is based on the specifications of Huang and Radosz (1991). The SAFT equation of state (Chapman et al., 1990; Huang and Radosz, 1990,1991) is similar to perturbed hard chain equations like those of Beret and Prausnitz (1978) or Donohue and coworkers (cf. Ikonomou and Donohue, 1988) equation for hydrocarbons and gases, but provides accuracy competitive with UNIQUAC, NRTL, or Wilson’s equation for hydrogen bonding mixtures. It also provides high accuracy for hydrogen bonding mixtures at high pressure like the interpolation methods of Dahl et al. (1991), Schwartzentruber and Renon (1989), and Wong et al. (1992). It can provide accuracy for hydrocarbon+water mixtures that is comparable with that of the adaptation of the Soave equation by Kabadi and Danner (1986) method (e.g. Suresh and Beckman, 1994). Unlike the interpolation methods, the SAFT equation is based on treating the hydrogen bonding interactions as chemical reactions in accordance with the formalism developed by Wertheim (1986). In this sense, the SAFT equation is similar to the ESD equation of Elliott et al. (1990). Substantial experience with polymer solutions has been obtained with the SAFT equation (Hasch et al., 1996; Chen et al., 1995), especially for supercritical polymer solutions. Generally, the SAFT equation derives its size, shape, and dispersion energy parameters by optimizing the representation of liquid density as well as vapor pressure, but it ignores the experimental value for the critical point. Matching the experimental critical point may be important for high pressure applications like supercritical extraction, but it should be possible by limiting the range of conditions to develop specific pure component parameters that provide sufficient accuracy for any particular application that the user may have. The treatment of the association thermodynamics applied here is restricted to linear Acceptor-donor association like alcohols and water and binary associations like carboxylic acids. This restriction permits an increase in computational efficiency of about 100-fold relative to the completely general formulation (Elliott, 1996). Evaluations for mixtures containing ethers, esters, and ketones, as well as aldehydes, amines, and glycols have shown little or no reduction in the accuracy as a result of this restriction. Summary of Equations (1) where: (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 50 of 89 (14) XiA = the fraction of linear proton acceptor sites not bonded XiC = the fraction of binary (carboxylic) bonding sites not bonded The procedure for determining the fractions of bonding is given by Elliott (1996). t=0.74058; C, e, Dij are general constants given by Huang and Radosz (1990) si, mi, and uio/k are adjustable pure-component parameters Elliott-Suresh-Donohue (ESD) The ESD equation (Elliott, Suresh, and Donohue, 1990) is similar to conventional cubic equations of state like the Soave (1972) equation or Peng-Robinson (1976) equation for hydrocarbons and gases, but provides accuracy competitive with UNIQUAC, NRTL, or Wilson’s equation for hydrogen bonding mixtures. It also provides high accuracy for hydrogen bonding mixtures at high pressure like the interpolation methods of Dahl et al. (1991), Schwartzentruber and Renon (1989), and Wong et al. (1992). It also provides accuracy for hydrocarbon+water mixtures that is comparable with that of the adaptation of the Soave equation by Kabadi and Danner (1986). Unlike the interpolation methods, the ESD equation is based on treating the hydrogen bonding interactions as chemical reactions in accordance with the formalism developed by Wertheim (1986). In this sense, the ESD equation is similar to the SAFT equation of Chapman et al. (1990). The ESD and SAFT equations are also similar in their ability to treat polymer components by straightforward application of the basic equations. One difference between the ESD equation and the SAFT equation is the way that the pure-component parameters are determined.The ESD equation uses the critical properties and acentric factor to estimate the pure-component parameters when no parameters are listed in the database. Parameters estimated in this way are based on neglecting self-association. For associating compounds, the ESD equation still matches the experimental critical temperature, but adjusts the size and shape parameters to obtain an optimal representation of vapor pressure data. Matching the experimental critical point may be important for high pressure applications like supercritical extraction, but the ESD equation is not recommended for predicting liquid densities. If the accuracy is insufficient for any particular application, it should be possible by limiting the range of conditions to develop specific pure component parameters that provide sufficient accuracy. Accuracy of VLE correlations by the ESD equation has been studied for a wide range of mixtures by Puhala and Elliott (1993). Their findings are briefly summarized in the table below. Treatment of binary experimental data can also be optimized by the ESD regression option on the BIP tab of the Databank menu. The treatment of the association thermodynamics applied here is restricted to linear Acceptor-donor association like alcohols and water and binary associations like carboxylic acids. This restriction permits an increase in computational efficiency of about 100-fold relative to the completely general formulation (Elliott, 1996). Evaluations to date for mixtures containing ethers, esters, and ketones, as well as alcohols, aldehydes, amines, and glycols have shown little or no reduction in accuracy as a result of this restriction. Summary of Equations (1) where: (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) XiA = the fraction of linear proton acceptor sites not bonded XiC = the fraction of binary (carboxylic) bonding sites not bonded The procedure for determining the fractions of bonding is given by Elliott (1996). bi, ci, and eii/k are adjustable pure-component parameters Summary of Results for the ESD EOS with Optimal Binary Interaction Coefficients file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 51 of 89 Type of System Number of Total Number Bubble Pressure (1) Binary of Data Points Error with Optimal Systems kij Optimized Methane 19 1256 5.36% Hydrogen Sulfide 17 594 4.82% Nitrogen 12 510 6.45% Carbon 6 184 2.62% Monoxide Carbon Dioxide 27 1033 3.99% Hydrogen 17 521 8.73% Water 8 1594 6.33% Methanol 22 1249 3.77% Ethanol 10 677 2.07% UNIFAC In the UNIFAC K model, the liquid phase activity coefficients for each species are calculated from the UNIFAC group contribution method. The limitations of UNIFAC are temperature range from 275 K to 425 K and pressure up to a few atmospheres. Also this UNIFAC reads the group contribution parameter stored in the VLE database. Because UNIFAC is a Gibbs excess model, it is theoretically capable of predicting a second liquid phase. In practice, however, liquid-liquid behavior cannot be adequately predicted from VLE data. It is recommended that you use UNIFAC LLE to model a two-liquid-phase system with the UNIFAC models. UNIFAC Equation where: } and where: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 52 of 89 The UNIFAC Group Specifications chart provides a list of all the UNIFAC groups for which data is provided within CHEMCAD. The chart indicates which groups are applicable to the various UNIFAC models (UNIFAC, UNIFAC LLE, Modified (Do.) UNIFAC). UNIFAC LLE As the UNIFAC model is a Gibbs excess energy model, it can theoretically predict Liquid-Liquid Equilibria (LLE). In practice, binary interaction parameters regressed from VLE data are insufficient to predict LLE behavior. CHEMCAD provides an alternate UNIFAC model which uses binary interaction parameters regressed from LLE data. The UNIFAC VLE model equations are used without change. Group interaction parameter values differ from the UNIFAC VLE model. The LLE parameters were regressed between 10 and 40° C. The model may not be applicable outside this range. Typically a second liquid phase will not be a concern outside this range. It was necessary to develop additional subgroups for 1-propanol (P1), 2-propanol (P2), diethylene glycol (DEOH), trichloroethylene (TCE), methylformamide (MFA), and tetramethylenesulfone (TMS). These additional subgroups are only for the UNIFAC LLE model. The LLE subgroups use regressed values of Q and R which differ from UNIFAC VLE subgroups. The subgroup assignment in the component databank does not use the additional LLE subgroups. You need to manually specify the additional subgroup for a component. For example, to use 1-propanol in a UNIFAC LLE model the user would need to copy component 146 (1-propanol) and edit the copy to use (1) contribution of subgroup P2. The matrix of group interaction parameters is not full. The LLE interaction parameters are not available for all binary combinations. The model will default to VLE parameters when LLE parameters are not available. Refer to the UNIFAC Group Specifications chart to determine if LLE groups exist for the system you are modeling, or if CHEMCAD is defaulting to VLE groups. If no group interactions (VLE or LLE) exist in the databank for a pair of groups, CHEMCAD issues a warning. Reference Magnussen, Rasmussen, Fredenslund, "UNIFAC Parameter Table for Prediction of Liquid-liquid Equilibria," 20, pp331-339, Ind.Eng.Chem.Processs Des. Dev, 1981. Modified UNIFAC (Dortmund) The Modified UNIFAC model (Dortmund) introduces temperature dependent interaction parameters. This allows a more reliable description of phase behavior as a function of temperature. The modified UNIFAC (Dortmund) method also uses van der Waals (Q and R) properties which are slightly different than those used in the original UNIFAC method. For Original UNIFAC: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 53 of 89 For Modified UNIFAC (Do): The Modified UNIFAC (Do.) model uses different component group and subgroup matrices than the original UNIFAC. Published interaction parameters have been included in CHEMCAD. Unpublished parameters can be added into CHEMCAD if your company has access to them. As with the original, the Modified UNIFAC model has the activity coefficient as the sum of a combinatorial and residual part: The combinatorial term in Modified UNIFAC has changed, to allow it to deal with compounds of very different sizes. where V’i is calculated from relative van der Waals volumes Rk of the different groups. The Modified (Do.) UNIFAC model has several groups which do not correspond to the original UNIFAC groups. Components in the databank use the original UNIFAC group assignment. To use modified UNIFAC groups you need to manually specify the subgroup for a component. Where groups do exist in both models, no action is necessary. For example, to use subgroup OH(s) for a secondary alcohol, you will need to change the subgroup contribution for the alcohol from 15 to 3000. References Gmehling, Li, Schiller; "A modified UNIFAC Model. 2. Present Parameter Matrix and Results for Different Thermodynamic Properties,",Ind.Eng.Chem.Res., 1993, v32, 178-193. Gmehling, Lohmann, Jakob, Li, Joh; "A Modified UNIFAC (Dortmund) Model. 3. Revision and Extension,", Ind.Eng.Chem.Res., 1998, v37,4876-4882. Gmehling, Lohmann, "From UNIFAC to Modified UNIFAC," Ind. Eng. Chem. Res., 2001,v40, 957-964. Gmehling, Lohmann, "Modified UNIFAC: Reliable Model for the Development of Thermal Separation Processes," J. Che. Eng. Jpn.,2001, v34,pp43-54. Gmehling, Wittig, Lohmann, "Vapor Liquid Equilibria and Enthalpies of Mixing,"Ind.Eng.Chem.Res., 2001,v40,5831-5838. UNIFAC Group Specifications Subgroup Listing for CHEMCAD UNIFAC Models The VLE, LLE, and Do columns represent UNIFAC VLE, UNIFAC LLE, and Modified (Dortmund) UNIFAC, respectively. The Subgroup number is the number to assign to a component for the given subgroup. Subgroup Groups for Example Main Group Subgroup number VLE LLE Do Example component Component CH2 CH3 1 X X X butane 2 CH3, 2 CH2 CH2 2 X X X butane 2 CH3, 2 CH2 CH 3 X X X i-butane 3 CH3, 1 CH C 4 X X X 2,2-dimethylpropane 4 CH3, 1 C c-CH2 3095 * - X cyclohexane 6 c-CH2 c-CH 3100 * - X methylcyclohexane 1 CH3, 5 c-CH2, 1 c-CH c-C 3105 * - X 1,1-dimethylcyclohexane 2 CH3, 5 c-CH2, 1 c-C C=C CH2=CH 5 X X X 1-hexene 1 CH3, 3 CH2, 1 CH2=CH CH=CH 6 X X X 2-hexene 2 CH3, 2 CH2, 1 CH=CH CH2=C 7 X X X 2-methyl-1- butene 2 CH3, 1 CH2, 1 CH2=C CH=C 8 X X X 2-methyl-2- butene 3 CH3, 1 CH=C C=C 9 X * X 2,3-dimethylbutene 4 CH3, 1 C=C C=C=C 3295 - - $ =CHCH= 3300 - - $ =CCH= 3305 - - $ ACH ACH 10 X X X benzene 6 ACH AC 11 X X X styrene 1 CH2=CH, 5 ACH, 1 AC ACCH2 ACCH3 12 X X X toluene 5 ACH, 1 ACCH3 ACCH2 13 X X X ethylbenzene 1 CH3, 5 ACH, 1 ACCH2 ACCH 14 X X X cumene 2 CH3, 5 ACH, 1 ACCH OH OH 15 X X X 1-propanol 1 CH3, 2 CH2, 1 OH(p) file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 54 of 89 OH(s) 3000 * * X 2-propanol 2 CH3, 1 CH, 1 OH(s) OH(t) 3005 * * X tert-butanol 3 CH3, 1 C , 1 OH (t) CH3OH CH3OH 16 X * X methanol 1 CH3OH H2O H2O 17 X X X water H2O ACOH ACOH 18 X X X phenol 5 ACH, 1 ACOH Ketone CH2CO CH3CO 19 X X X 2-butanone 1 CH3, 1 CH2, 1 CH3CO CH2CO 20 X X X 3-pentanone 2 CH3, 1 CH2, 1 CH2CO Aldehyde CHO CHO 21 X X X acetaldehyde 1 CH3, 1 CHO Esters CCOO CH3COO 22 X X X butyl acetate 1 CH3, 3 CH2, 1 CH3COO CH2COO 23 X X X butyl propanoate 2 CH3, 3 CH2, 1 CH2COO HCOO HCOO 24 X * X ethyl formate 1 CH3, 1 CH2, 1 HCOO CHCOO 144 $ * $ CCOO 145 $ * $ Ether CH2O CH3O 25 X X X dimethyl ether 1 CH3, 1 CH3O CH2O 26 X X X diethyl ether 2 CH3, 1 CH2, 1 CH2O CH-O 27 X X X diisopropyl ether 4 CH3, 1 CH, 1 CH-O fCH2O 28 X X - tetrahydrofuran 3 CH2, 1 fCH2O Amine CNH2 CH3NH2 29 X * X methylamine 1 CH3NH2 CH2NH2 30 X * X n-propylamine 1CH3, 1 CH2, 1 CH2NH2 CHNH2 31 X * X isopropylamine 2 CH3, 1 CHNH2 CNH2 3090 - - X tert-butylamine 3 CH3, 1 CNH2 CNH CH3NH 32 X * X dimethylamine 1 CH3, 1CH3NH CH2NH 33 X * X diethylamine 2 CH3, 1 CH2, 1 CH2NH CHNH 34 X * X diisopropylamine 4 CH3, 1 CH, 1CHNH (C3)N CH3N 35 X * X trimethylamine 2 CH3, 1 CH3N CH2N 36 X * X triethylamine 3 CH3, 2 CH2, 1 CH2N Tert-N TERT-N 85 X * - triethylamine 3 CH3, 3 CH2, 1 >N- ACNH2 ACNH2 37 X X X aniline 5 ACH, 1 ACNH2 (Pyridines) C5H5N 38 X X - pyridine 1 C5H5N C5HnN C5H4N 39 X X - 2-methylpyridine 1 CH3, 1 C5H4N C5H3N 40 X X - 2,3-dimethylpyridine 2 CH3, 1 C5H3N Pyridine AC2H2N 3010 - - X pyridine 1 AC2H2N, 3 ACH AC2HN 3015 - - X 2-methylpyridine 1 AC2HN, 3 ACH, 1 CH3 AC2N 3020 - - X 2,5-dimethylpyridine 1 AC2N, 3 ACH, 2 CH3 CCN CH3CN 41 X X X acetonitrile 1 CH3CN CH2CN 42 X X X propionitrile 1 CH3, 1 CH2CN COOH COOH 43 X X X acetic acid 1 CH3, 1 COOH HCOOH 44 X X X formic acid 1 HCOOH CCl CH2Cl 45 X X X 1-chlorobutane 1 CH3, 2CH2, 1CH2Cl CHCl 46 X X X 2-chloro-propane 2 CH3, 1 CHCl CCl 47 X X X 2-chloro-2-methyl propane 3 CH3, 1 CCl CCl2 CH2Cl2 48 X X X dichloromethane 1 CH2Cl2 CHCl2 49 X X X 1,1-dichloroethane 1 CH3, 1 CCl2 CCl2 50 X X X 2,2-dichloropropane 2 CH3, 1 CCl2 CCl3 CHCL3 51 X X X chloroform 1 CHCl3 CCl3 52 X X X 1,1,1-trichloroethane 1 CH3, 1 CCl3 CCl4 CCl4 53 X X X carbon tetrachloride 1 CCl4 ACCl ACCl 54 X X X chlorobenzene 5 ACH, 1 ACCl Cl(C=C) Cl(C=C) 70 X * X trichloroethene 1 CH=C, 3 Cl-(C=C) CNO2 CH3NO2 55 X X X nitromethane 1 CH3NO2 CH2NO2 56 X X X 1-nitropropane 1 CH3, 1 CH2, 1 CH2NO2 CHNO2 57 X X X 2-nitropropane 2 CH3, 1 CHNO2 file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 55 of 89 ACNO2 ACNO2 58 X X X nitro-benzene 5 ACH, 1 ACNO2 CS2 CS2 59 X * X carbon disulfide 1 CS2 CH3SH CH3SH 60 X * X methanethiol 1 CH3SH CH2SH 61 X * X ethanethiol 1 CH3, 1 CH2SH furfural furfural 62 X X X furfural 1 furfural DOH (CH2OH)2 63 X X X 1,2-ethanediol 1 (CH2OH)2 I I 64 X * X iodoethane 1 CH3, 1 CH2, 1 I Br Br 65 X * X bromomethane 1 CH3, 1 Br C<->C CH<->C 66 X * X 1-hexyne 1 CH3, 3 CH2, 1 CH<->C C<->C 67 X * X 2-hexyne 2 CH3, 2 CH2, 1 C<->C DMSO (CH3)2SO 68 X X X Dimethyl sulfoxide 1 (CH3)2SO Acrylonitrile acrylonitrile 69 X * X acrylonitrile 1 acrylonitrile ACF ACF 71 X * X hexafluorobenzene 6 ACF DMF DMF 72 X X X N,N-dimethylformamide 1 DMF HCON(CH2)2 73 X * X N,N-diethylformamide 2 CH3, 1 HCON(CH2)2 CF2 CF3 74 X * X perfluorohexane 2 CF3, 4 CF2 CF2 75 X * X perfluorohexane 2 CF3, 4 CF2 CF 76 X * X perfluoromethylcyclohexane 1 CF3, 5 CF2, 1 CF COO COO 77 X * X methyl acrylate 1 CH3, 1CH2=CH, 1 COO c-CH2O c-CH2O[CH2]½ 3075 - - X 1,3-dioxane 1 c-CH2, 2 c-CH2O[CH2](1/2) c-[CH2]½O[CH2] 3080 - - X 1,3,5-trioxane 3 c-[CH2]1/2O[CH2]1/2 ½ c-CH2OCH2 3085 - - X tetrahydrofuran 2 c-CH2, 1 c-CH2OCH2 SiH2 SiH3 78 X * - methylsilane 1 CH3, 1 SiH3 SiH2 79 X * - diethylsilane 2 CH3, 2 CH2, 1 SiH2 SiH 80 X * - heptamethyltrisiloxane 7 CH3, 2 SiO, 1 SiH Si 81 X * - hexamethyldisiloxane 6 CH3, 1 SiO, 1 Si SiO SiH2O 82 X * - 1,3-dimethyldisiloxane 2 CH3, 1 SiH2O, 1 SiH2 SiHO 83 X * - 1,1,3,3-tetramethyldisiloxane 4 CH3, 1 SiHO, 1 SiH SiO 84 X * - octamethylcyclotetrasiloxane 8 CH3, 4 SiO Chlorofluorocarbons CCl3F 86 X * $ trichlorofluoromethane 1 CCl3F CCl2F 87 X * $ tetrachloro-1,2-difluoroethane 2 CCl2F HCCl2F 88 X * $ dichlorofluoromethane 1 HCCl2F HCClF 89 X * $ 1-chloro-1,2,2,2- 1 CF3, 1 HCClF tetrafluoroethane CClF2 90 X * $ 1,2-dichlorotetrafluoroethane 2 CClF2 HCClF2 91 X * $ chlorodifluoromethane 1 HCClF2 CClF3 92 X * $ chlorotrifluoromethane 1 CClF3 CCl2F2 93 X * $ dichlorodifluoromethane 1 CCl2F2 Amide CONH2 94 X * $ acetamide 1 CH3, 1 CONH2 CONMeCH2 CONHCH3 95 X * X N-methylacetamide 1 CH3, 1 CONHCH3 CONHCH2 96 X * X N-ethylacetamide 2 CH3, 1 CONHCH2 CONHC 3183 - - $ N-tert-Butyl-Acetamide 4 CH3, 1 CONHC CONR2 CON(CH3)2 97 X * X N,N-dimethylacetamide 1 CH3, 1 CON(CH3)2 CONCH3CH2 98 X * X N,N-methylethylacetamide 2 CH3, 1 CONCH3CH2 CON(CH2)2 99 X * X N,N-diethylacetamide 3 CH3, 1 CON(CH2)2 NMP NMP 109 X * - N-methylpyrrolidone 1 NMP Pyrrolidone cy-CON-CH3 3055 - - X N-methylpyrrolidone 1 cy-CON-CH3, 3 cy-CH2 cy-CONC cy-CON-CH2 3060 - - X N-ethylpyrrolidone 1 cy-CON-CH2, 3 cy-CH2,1 CH3 cy-CON-CH 3065 - - X N-isopropylpyrrolidone 1 cy-CON-CH, 3 cy-CH2, 2 CH3 cy-CON-C 3070 - - X N-tert-butylpyrrolidone 1 cy-CON-C, 3 cy-CH2, 3 CH3 Ethoxy C2H5O2 100 X * $ 2-ethoxyethanol 1 CH3, 1 CH2, 1 C2H5O2 OCCOH C2H4O2 101 X * $ 2-ethoxy-1-propanol 2 CH3, 1 CH2, 1 C2H4O2 CH2S CH3S 102 X * $ dimethylsulfide 1 CH3, 1 CH3S CH2S 103 X * $ diethylsulfide 2 CH3, 1 CH2, 1 CH2S file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 56 of 89 CHS 104 X * $ diisopropylsulfide 4 CH3, 1 CH, 1 CHS Morpholine MORPH 105 X * - morpholine 1 Morph Thiophene C4H4S 106 X * - thiophene 1 C4H4S (CS) C4H3S 107 X * - 2-methylthiophene 1 CH3, 1 C4H3S C4H2S 108 X * - 2,3-dimethylthiophene 2 CH3, 1 C4H2S NCO NCO 1109 $ - $ Butylisocyanate 1 CH3, 2 CH2, 1 NCO Epoxide H2COCH 110 X * X propylene oxide 1 H2COCH, 1 CH3 H2COC 131 X - - 2-methyl propylene oxide 1 H2COC, 2 CH3 HCOCH 111 X * X 2,3-epoxybutane 1 HCOCH, 2 CH3 HCOC 112 X * $ 2-methyl, 2,3-butylene oxide 1 HCOC, 3 CH3 H2COCH2 113 X * $ ethylene oxide 1 H2COCH2 Thiophene AC2H2S 3040 - - X thiophene 2 ACH, 1 AC2H2S (ACS) AC2HS 3045 - - X 2-methylthiophene 1 CH3, 2 ACH, 1 AC2HS AC2S 3050 - - X 2,5-dimethylthiophene 2 CH3, 2 ACH, 1 AC2S Anhydrides OCOCO 114 $ - $ acetic anhydride 1 OCOCO, 2 CH3 Carbonates (CH3O2)2CO 3025 $ - X dimethylcarbonate (CH3O)2CO (CH2O2)2CO 3030 $ - X diethylcarbonate 1 (CH2O)2CO, 2 CH3 CH2OCH3OCO 3035 $ - X methyl-ethyl-carbonate 1 CH2OCH3OCO, 1 CH3 CHOCH2OCO 120 $ - $ Ethyl-Isopropyl-Carbonate 1 CHOCH2OCO,3 CH3 Sulfones (CH2)2Su 118 $ - $ sulfolane 1 (CH2)2SU, 2 CH2 CH2SuCH 119 $ - $ 2,4-dimethylsulfolane 1 CH2SuCH, 2 CH3, 1 CH2, 1 CH HCONR HCONHCH3 121 $ - $ N-Methyl-formamide 1 HCONHCH3 HCONHCH2 122 $ - $ N-Ethyl-formamide 1 CH3,1 HCONHCH2 ACCN ACCN 123 $ - $ Benzonitrile 5 ACH, 1 ACCN cy-CONH cy-CONH 124 $ - $ e-Caprolactam 4 CH2, 1 cy-CONH Lactone cy-COO-C 125 $ - $ g-Butyrolactone 2 CH2, 1 cy-COO-C peroxide -O-O- 126 $ - $ Di-Tert-Butylperoxide 6 CH2, 2 C, 1 -O-O- -O-OH 127 $ - $ Tert-Butylhydroperoxide 3 CH2, 1 C, 1 -O-OH Acetals O-CH2-O 128 $ - $ Dimethoxymethane 2 CH3, 1 O-CH2-O O-CH-O 129 $ - $ 1,1-Dimethoxyethane 3 CH3, 1 O-CH-O O-C-O 130 $ - $ 2,2-Dimethoxypropane 4 CH3, 1 O-C-O Aniline ACN(CH3)2 132 $ - $ N,N-Dimethylaniline 5 ACH, 1 ACN(CH3)2 ACN(CH2)2 133 $ - $ N,N-Diethylaniline 2 CH3, 5 ACH, 1 ACN(CH2)2 ACNCH3CH2 134 $ - $ N-Ethyl-N-methylaniline 1 CH3, 5 ACH, 1 ACNCH3CH2 ACNHCH3 135 $ - $ N-Methylanilin 5 ACH, 1 ACNHCH3 ACNHCH2 136 $ - $ N-Ethylanilin 1 CH3, 5 ACH, 1 ACNHCH2 ACBr ACBr 137 $ - - Brombenzene 5 ACH, 1 ACBr Oxime HCNOH 138 $ - $ Propionaldehydoxime 1 HCNOH, 1 CH3, 1 CH2 CNOH 139 $ - $ Acetoneoxime 1 CNOH, 2 CH3 ACCHO ACCHO 3200 - - $ Benzaldehyde 1 ACCHO, 5 ACH ACCOOH ACCOOH 3205 - - $ Benzoic Acid 1 ACCOOH, 5 ACH ACCOO ACCOO 3210 - - $ Benzylbenzoate 1 ACCOO, 1 ACCH2, 10 ACH ACCO ACCOCH3 3285 - - $ ACCOCH2 3290 - - $ CFH CFH3 3215 - - $ R41 1 CFH3 CFH2 3220 - - $ R161 1 CH3, 1 CFH2 CFH 3225 - - $ R225BB 1 CFCl, 1 CF2H, 1 CF2Cl CFClH2 3230 - - $ R31 1 CFClH2 CFCl 3235 - - $ R225BB 1 CFCl, 1 CF2H, 1 CF2Cl CF2H2 3240 - - $ R32 1 CF2H2 CF2H 3245 - - $ R134 2 CF2H file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 57 of 89 CF3H CF3H 3250 - - $ R23 1 CF3H (CH3)-CF3 3260 - - $ R143A 1 CH3, 1 (CH3)-CF3 CF4 CF4 3255 - - $ R14 CF4 CF3Cl CF2ClBr 3265 - - $ R13B1 1 CF3Br CF2ClBr 3270 - - $ R12B1 1 CF2ClBr Furane AC2H2O 140 $ - $ Furan 2 ACH, 1 AC2H2O AC2HO 141 $ - $ 2-Methylfuran 1 CH3, 2 ACH, 1 AC2HO AC2O 142 $ - $ 2,5-Dimethylfuran 2 CH3, 2 ACH, 1 AC2O c- Amine c-CH2NH 162 - - $ Pyrrolidine 1 c-CH2NH, 3 c-CH2 c-CHNH 163 - - $ 2-Methylpiperidine 1 c-CHNH, 1 CH3, 4 c-CH2 c-CNH 164 - - $ 2,2-Dimethylpiperidine 1 c-CNH, 2 CH3, 4 c-CH2 c-CNCH3 165 - - $ N-Methylpyrrolidine 1 c-CNCH3, 3 c-CH2 c-CNCH2 166 - - $ N-Ethylpiperidine c-CNCH2, 1 CH3, 5 c-CH2 c-CNCH 167 - - $ N-Isopropylpiperidine 1 c-CNCH, 2 CH3, 5 c-CH2 c-CNC 168 - - $ N-tert-Butylpyrrolidine 1 c-CNC, 3 CH3, 5 c-CH2 Additional Subgroups for UNIFAC LLE Model Subgroup Groups for Example Main Group Subgroup number VLE LLE Do Example component Component P1 P1 (1-propanol) 501 - X - 1-propanol 1 P1 P2 P2 (2-propanol) 502 - X - 2-propanol 2 P2 DEOH (HOCH2CH2)2O 503 - X - diethylene glycol 1 (HOCH2CH2)2O TCE CCl2=CHCl 504 - X - trichloroethylene 1 CCl2=CHCl MFA HCONHCH3 505 - X - methylformamide 1 HCONHCH3 TMS 1 (CH2)2SO 506 - X - tetramethylenesulfone 1 (CH2)2SO Additional Subgroups for PSRK Model Subgroup Groups for Example Main Group Subgroup number VLE LLE Do Example component Component CO2 CO2 1001 X - - carbon dioxide 1 CO2 CH4 CH4 1002 X - - methane 1 CH4 N2 N2 1003 X - - nitrogen 1 N2 H2S H2S 1004 X - - hydrogen sulfide 1 H2S H2 H2 1005 X - - hydrogen 1 H2 CO CO 1006 X - - carbon monoxide 1 CO H2C=CH2 H2C=CH2 1007 X - - ethene 1 CH=CH CHºCH CHºCH 1008 X - - ethyne 1 CH<->CH NH3 NH3 1009 X - - ammonia 1 NH3 Ar Ar 1010 X - - argon 1 Ar O2 O2 1011 X - - oxygen 1 O2 SO2 SO2 1012 X - - suflur dioxide 1 SO2 NO NO 1013 X - - nitric oxide 1 NO N2O N2O 1014 X - - dinitrogen monoxide 1 N2O SF6 SF6 1015 X - - sulfur hexafluoride 1 SF6 He He 1016 X - - helium 1 He Ne Ne 1017 X - - neon 1 Ne Kr Kr 1018 X - - krypton 1 Kr Xe Xe 1019 X - - xenon 1 Xe HCl HCl 1020 X - - hydrogen chloride 1 HCl HBr HBr 1021 X - - hydrogen bromide 1 HBr CHSH CHSH 1022 X - - iso-propyl mercaptan 1 CHSH, 2 CH3 CSH CSH 1023 X - - tert-butyl mercaptan 1 CSH, 3 CH3 COC COC 1025 X - - 2,3-dimethyl 2,3 butylene 1 COC, 4 CH3 oxide HF HF 1026 X - - hydrogen fluoride 1 HF HI HI 1027 X - - hydrogen iodide 1 HI COS COS 1028 X - - carbonyl sulfide 1 COS Notes file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 58 of 89 · UNIFAC / UNIFAC LLE subgroups 3000 3005 are identical to OH. · 3095, 3100, and 3105 are identical to 2, 3, and 4, respectively CH2, CH, C Legend X CHEMCAD has data for this subgroup. $ The subgroup is available to UNIFAC Consortium members in a supplement to CHEMCAD. * The optimized subgroup is not specified for this model. UNIFAC subgroup will be used as a default. - The subgroup does not exist in the model. cy Denotes a cyclic hydrocarbon. <-> Denotes a triple bond. A Indicates an aromatic ring. R Indicates a hydrocarbon branch. Me Indicates a methyl group (-CH3). UNIQUAC In the UNIQUAC K model, the liquid phase activity coefficients for each species are calculated by the UNIQUAC equation. CHEMCAD supports up to 8 parameters ( Aij, Aji, Uij-Uji, Uji-Uij, Cij, Cji, Dij, Dji) for the UNIQUAC model. UNIQUAC Equation where: ϕi = xi * ri / (Σ xj * rj) θi = xi * qi / (Σ xj * qj) τij = exp [Aij - (U ij - Ujj) / RT + Cij*Ln(T) + Dij*T ] T = Temperature in degrees Kelvin li = (z / 2) * (ri - qi) - ri + 1 z = 10 (coordination number) qi = van der Waals area parameter (Awi / (2.5E9) where Awi is the van der Waals area) ri = van der Waals volume parameter (Vwi / 15.17 where Vwi is the van der Waals volume) For comparison to DECHEMA format values aij and bij: aij + bij/T = Aij + (Uij - Ujj) / RT bij = - (Uij - Ujj)/R aij = Aij The UNIQUAC binary interaction parameters Aij, (Uij - Ujj) and (Uji - Uii) are in cal/gmol. The binary interaction parameters (BiPs) Cij and Dij are optional. Several binary interaction parameters (BiPs) are in the UNIQUAC program. The Thermophysical menu command Edit BIPs can be used to view existing BIPs for the system, if the K-value model is UNIQUAC. The UNIQUAC equation uses qi, the van der Waals area parameter, and ri, the van der Waals volume parameter. Values for qi and ri are required for each component in the mixture. Values of qi and ri stored in the databank were computed for use with the UNIQUAC model. If qi and ri are not in the databank for the component (i.e., a user- added component) they will be computed using the UNIFAC group Qk and Rk (see UNIFAC). Earlier versions of CHEMCAD (before Version 3.0) did not store values for qi and ri in the databank. Therefore, whenever UNIQUAC was used, these values were calculated by summing UNIFAC group surface and volume parameters over all of the groups in the molecule. If the user selects UNIQUAC method and wants to use the UNIFAC values Qk and Rk to calculate qi and ri, select the VLE method called UNIQUAC / UNIFAC on the K-value menu. Note When regressing BIPs for UNIQUAC in the default condition, CHEMCAD calculates only (Uij - Ujj) and (Uji - Uii). Aij and Aji are set to zero. If you want to calculate all four BIPs during the regression, simply include initial estimates for Aij and Aji during the regression analysis. UNIQUAC/UNIFAC file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 59 of 89 This method is uses the calculation methods of CHEMCAD's UNIQUAC method, but Van der Waals parameter data is taken from the UNIFAC method. The sums of the UNIFAC surface area and volume parameters (Qk and Rk) for the UNIFAC groups specified for the component are used as the UNIQUAC surface area and volume parameters (qi and ri) for the component. The remaining parameters are calculated normally using the UNIQUAC model. UNIFAC for Polymers (UPLM) The UNIFAC model is based upon a twoliquid lattice theory of liquid mixtures which does not explicitly take into account changes in free volume caused by mixing. It has now been well established that in polymer solutions free volume effects are important. In ordinary liquid mixtures remote from critical conditions, the components are, to a rough approximation, equally expanded and, therefore, freevolume effects are usually secondary. In polymersolvent solutions, however, free volume effects are far from negligible since the polymer molecules are much more tightly packed than the solvent molecules. To apply UNIFAC to polymer solvent mixtures, we write: where: c = combinational r = UNIFAC residual fv = free volume For mixture of ordinary liquids, , makes only a small contribution which is usually negligible in comparison with other approximations in UNIFAC. However, for mixtures of solvents and polymers, , is often significant. When UNIFAC without free volume correction is applied to polymer solutions, predicted solvent activities tend to be lower than those observed experimentally. CHEMCAD calculates with the following equation: Reference "Estimation of Solvent Activities in Polymer Solutions Using a Group Contribution Method"; Tokeru Oishi and John M. Prausnitz; Ind. Eng. Chem. Proc. Des. Dev.; Vol. 17, No. 3, 1978. Wilson Model The liquid phase activity coefficients are calculated by the Wilson equation. Wilson Equation where: You can provide either LLij and LLji or (llij - llii) and (llji - lljj). If the absolute value of any parameter is greater than 10, the program will assume that you are using (llij - llii)s. The Wilson parameters can be entered via the Edit BIPs menu option on the Thermophysical menu. T. K. Wilson The liquid phase activity coefficients are calculated by the T. K. Wilson equation. The T. K. Wilson equation is a modification of the Wilson equation by Tsuboka and Katayama. The primary justification for this equation is that it extends the Wilson equation to liquid-liquid equilibrium. T. K. Wilson Equation where: The infinite dilution version of the T. K. Wilson equation can be given the same mathematical form as the Wilson equation by introducing pseudo-infinite- dilution activity coefficients file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 60 of 89 Although only a few T. K. Wilson sets of parameters have been recorded, the extensive collections of Wilson parameters can be used to find them. One way to find the T. K. Wilson parameters is, first, to find the infinite dilution activity coefficients with the Wilson parameters, and, second, substitute those values into the above equation. Such T. K. Wilson parameters may be satisfactory approximations for analysis of processes where both vapor-liquid and liquid-liquid equilibrium occur. Liquid-liquid equilibrium, however, are quite sensitive to the values of the parameters; even parameters evaluated from the whole range of activity coefficients based on vapor-liquid equilibrium are sometimes not good enough. In that event, it is best to regress liquid-liquid equilibrium data. HRNM Modified Wilson Equation The liquid phase activity coefficients are calculated by the HRNM modified Wilson equation. This equation is a modification of the Wilson equation by Mitsuyasu Hiranuma. The primary justification for this equation is that it extends the Wilson equation to liquid-liquid phase equilibrium. HRNM Equation where: The practical significance of Ck is that it extends Wilson into the liquid-liquid region. Based on a detailed study of seven (7)* systems, Hiranuma concluded that c depends on the degree of hydrogen bond formation and is set as an adjustable parameter for component i, not for a system. Based on Hiranuma's recommendation, CHEMCAD uses the following values for ci: ci = 1.5 for water ci = 1.0 for alcohols ci = 1.1 for all other components The parameter ci mostly controls the size of immiscibility regions in the HRNM equation. The seven systems studied were: System No. System Components 1 benzene(1), n-heptane(2), acetonitrile(3) 2 ethanol(1), n-hexane(2), acetonitrile(3) 3 ethyl either(1), methanol(2), cyclohexane(3) 4 acetonitrile(1), water(2), ethyl acetate(3) 5 acetone(1), methyl acetate(2), water (3)) 6 acetone(1), chloroform(2), water(3) 7 ethanol(1), benzene(2), water(3) Reference "Significance and Value of the Third Parameter in the Modified Wilson Equation"; Mitsuyasu Hiranuma; Ind. Eng. Chem. Fund.; 1981; 20, 25-28. Van Laar Model Liquid phase activity coefficients are calculated by the van Laar equation. Van Laar Equation Renon NRTL Model Liquid phase activity coefficients are calculated by NRTL equation. NRTL Equation The NRTL equation has the following form: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 61 of 89 where: The most common usage of the NRTL equation is the three-parameter equation. The NRTL equation may be used either as a three-parameter (Bji, Bij, and αij only), as a five-parameter (Aji, Aij, Bji, Bij, and αij), seven-parameter (Aji, Aij, Bji, Bij, Cji, Cij, and αij), or nine-parameter equation (Aji, Aij, Bji, Bij, Cji, Cij, Dji, Dij, and αij). Converting Binary Parameters (BIPs) from Literature Many data sources use the DECHEMA equation whereas CHEMCAD divides the actual BIPs by RT. To use BIPs from a source using the alternate format, divide by R (1.97842) for the proper value and divide by T to identify the proper BIP. For example: Using data from DECHEMA, if A12 = A +B *T, then CHEMCAD BIPs are Bij= A / R and Aij = B / R. Regressing BIPs Use the Thermophysical menu command Regress BIPs. When regressing BIPs for NRTL in the default condition, CHEMCAD calculates only Bij, Bji, and αij. Aij and Aji are set to zero. If you want to calculate all five BIPs during the regression, include initial estimates for all BIPs on the Regress NRTL Parameters screen during the regression analysis. Margules Model Liquid activity coefficients are calculated by the Margules equation. Margules Equation The four-suffix binary equation by Wohl is used in the program. where: You must provide Aij, Aji and Dij. GMAC (Chien-Null) The liquid phase activity coefficients are calculated by the GMAC method (Generalized Multicomponent equation for Activity Coefficient), Chien-Null (1972). The primary justification for the GMAC equation is that it combines the Margules, Van Laar, NRTL, Scatchard-Hamer, and Fariss liquid activity models as special cases. The GMAC model permits the use of different special cases for each binary pair. In the design of processes for vapor-liquid, liquid-liquid, or solid-liquid separations, the calculation of liquid phase activity coefficients is of critical significance. There has been a proliferation of equations proposed for calculating the activity coefficient, and a surprisingly large number have survived primarily because no single equation has been proposed which can represent all types of solutions. Wohl, in a classical paper in 1964 showed how the useful equations of that time (Margules (1895; Scatchard-Hamer, 1952; van Laar, 1910) could be represented as special cases within a single framework of generalized equations, and how the binary forms could be extended to multicomponent systems. There were relatively few new equations presented after Wohl's work until 1964. Since that time there has been a flurry of equations which could not be taken as special cases of the Wohl generalized equations. The most significant of these are the Wilson equations (Wilson, 1964) and the NRTL equations of Renon and Prausnitz (1968). In spite of the availability of all these separate equations, it is still necessary occasionally to develop special equations for some systems. For example, sometimes a particular binary pair of a multicomponent system will exhibit an interior maximum activity coefficient. The Margules equations are particularly well suited to such a binary but are often unsatisfactory for the remaining binary pairs. The GMAC equations combines a set of two thermodynamically consistent equations in which two or more different binary equations could be mixed in the multicomponent computations. It includes, as special cases, the binary form of any of the Wohl three suffix equations (Margules, Scatchard-Hamer, van Laar), Fariss Equations (Null, 1970) and the NRTL equations of Renon and Prausnitz. The multicomponent form of the van Laar, Margules, and Scatchard-Hamer equations differs from the Wohl expansion and requires binary parameters only. It has been shown by Renon and Prausnitz that the NRTL equations, by the adjustment of an extra parameter, can be made to virtually reproduce the Wilson binary equations. The Fariss equations also have the ability to virtually reproduce the Wilson equation with the appropriate choice of the third parameter while reducing identically to the van Laar equations when the third constant is zero. Further, the new equations provide a means of expanding Fariss' equations to multicomponent systems. Thus, this work incorporates into a single set of equations the ability to duplicate all the more commonly used equations now available for calculating activity coefficients. Furthermore, it also provides the capability of mixing the forms. GMAC Equation file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 62 of 89 where: A = parameter for general activity coefficient equation R = parameter for general activity coefficient equation S = parameter for general activity coefficient equation V = parameter for general activity coefficient equation x = mole fraction in liquid phase γ = activity coefficient i,j,k = component index Reference "Generalized Multicomponent Equation for Activity Coefficient Calculation"' H. H. Chien and H. R. Null; AICHE Journal (Vol. 18, No. 6); November 1972. Scatchard-Hildebrand (Regular Solution) Model Liquid phase activity coefficients are calculated by the Scatchard-Hildebrand equation. For typical nonpolar mixtures, calculated and experimental results are often in good agreement. where: Solubility parameters are available for most components in the database, and you can include solubility parameters in user-specified components. Amine Model (AMINE) About the Model The Kent-Eisenberg model is a simplified way to model the reactions (and phase equilibria) in a gas sweetening system. Use the model in a system where water with one amine is used to treat gas with carbon dioxide, sulfuric acid, and/or ammonia. Components in the Amines Model The following amines are represented by reactions in the AMINES model. · Diethanolamine (DEA) · Monoethanolamine (MEA) · Methyl diethanolamine (MDEA) Reactions in the Amines Model The chemical reactions in an H2S-CO2-Amine system are described by the following reactions: 1. RR'NH2+ <-----> H+ + RR'NH K1 2. RR'NCOO + H2O <-----> RR'NH + HCO3- K2 3. CO2 + H2O <-----> HCO3- + H+ K3 4. HCO3- <-----> CO3-- + H+ K4 5. H2S <-----> HS- + H+ K5 6. HS- <-----> S-- + H+ K6 7. H2O <-----> H+ + OH- K7 where R and R' represent alcohol groups. The reaction equations are solved simultaneously to obtain the free concentration of H2S and CO2. The partial pressure of H2S and CO2 are calculated by the Henry's constants and free concentration in the liquid phase. The chemical reaction constants are calculated as: The values of A1i,...,A5i for the seven equilibrium constants are incorporated in CHEMCAD. Henry's Constants The coefficients B1i,...,B4i are stored in the database for the following gases: Hydrogen, Helium, Argon, Neon, Krypton, Xenon, Oxygen, Nitrogen, Hydrogen sulfide, Ammonia, Carbon monoxide, Carbon dioxide, Sulfur dioxide, Nitrous oxide, Chlorine, Bromine, Iodine, Methane, Ethane, Propane, Ethylene. For components heavier than C3, the program uses either the SRK equation or the UNIFAC equation to estimate K-values. If the flash calculation being performed is the two-phase flash (default) method, SRK is used. If the flash calculation being performed is a three-phase flash, then the UNIFAC method is used. For UnitOp EXTR, local K value of V/L/L, or flowsheet three-phase flash (V/L/L) option, CHEMCAD uses UNIFAC to estimate K-values for components not listed above. In all other situations, CHEMCAD uses SRK. Reference Kent, R. L. and Eisenberg, Hydrocarbon Processing, Feb. 1976, p. 87-92. Sour Water Model (SOUR) file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 63 of 89 The chemical reactions in H2S-CO2-NH3 systems are represented by the following reactions: 1. CO2 + H2O <-----> HCO3- + H+ K1 2. HCO3- <-----> CO3-- + H+ K2 3. NH3 + H+ <-----> NH4+ K3 4. NH3 + HCO3- <-----> H2NCOO- + H2O K4 5. H2S <-----> HS- + H+ K5 6. HS- <-----> S-- + H+ K6 7. H2O <-----> H+ + OH- K7 The addition of NAOH or Carbolic acid is also considered in CHEMCAD. The dissociation of Phenol and Hydrogen Cyanide is also included in the program. Chemical Reaction Constants The values of A1i,...,A5i for the seven equilibrium constants are incorporated in CHEMCAD. Henry's Constants The coefficients B1i,...,B4i are stored in the database for the following gases: Hydrogen, Helium, Argon, Neon, Krypton, Xenon, Oxygen, Nitrogen, Hydrogen sulfide, Ammonia, Carbon monoxide, Carbon dioxide, Sulfur dioxide, Nitrous oxide, Chlorine, Bromine, Iodine, Methane, Ethane, Propane For components heavier than C3, the SRK model is used to estimate K-values. Reference EPA-600/2-80-067 A New Correlation of NH2, CO2, and H2S Volatility Data from Aqueous Sour Water Systems by Grant M, Wilson EPA Grant No. R804364010. Tri-Ethylene Glycol/Water Dehydration (TEG) The TEG method is a specialized system for calculating the dehydration of hydrocarbon systems with Tri-ethylene-glycol (TEG). Thermodynamic Correlations for TEG-water System At equilibrium, the fugacities of water, fw, in the vapor and liquid phases are the same, that is: (A-1) where: The superscripts V and L stand for the vapor and liquid phases, respectively. The vapor fugacity is calculated as the product of the fugacity coefficient, FVw and the partial pressure, Pyw; the liquid fugacity is the product of the activity coefficient, gw, standard state fugacity, fw0L, liquid mole fraction, xw, and the Poynting correction } (A-2a) (A-2b) The last term in equation (A-2b) is the Poynting correction which reflects the pressure effect on the liquid fugacity. The fugacity coefficient, FVw, was calculated by a modified Soave-Redlich-Kwong equation of state. The partial molar volume of Water, Vw, was calculated by Lyckman's correlation and the activity coefficients were calculated by an empirical function proposed by Edwards et al which was modified by Won et al. (A-3) (A-4) where: (A-5) and tanh and cosh are hyperbolic tangent and cosine functions. A, B, and C are temperature-dependent coefficients: A = exp (-12.792 + 0.03293 T ) (A-6a) B = exp (0.77377 - 0.00695 T ) (A-6b) C = (0.88874 - 0.001915 T ) (A-6c) The standard state fugacity, fwoL, is the product of the saturated vapor pressure of water, PS. The saturated fugacity coefficient, FwS, and the reciprocal of the Poynting correction. To obtain the standard state fugacity as a function of the temperature we used (A-7a) where: (A-7b) In the above equations, T is in Kelvin and f is in psia. Equations (A-3) to (A-6) are applicable between 80° F - 400° F because the following data was used to obtain the constants: 1) infinite dilution activity coefficients of water between 80° F - 220° F; 2) finite concentration activity coefficients of water at 79° F and 139° F; and 3) the boiling points of aqueous TEG solutions from the TEG Product Information Bulletin of Union Carbide. The boiling point pressures were fitted up to 300° F, and the equations were used to extrapolate the temperature range to 400° F. Flory-Huggins Method (FLOR) The Flory-Huggins method is an extension to the Regular Solution Method of Scatchard and Hildebrand. Thus in Flory-Huggins: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 64 of 89 where: Vli = liquid molar volume of component i di = solubility parameter of component i dm = solubility parameter of the mixture R = gas law constant T = temperature The Flory-Huggins equation for real polymer solutions does not provide an accurate description of the thermodynamic properties of such solutions, but there is little doubt that this relatively simple theory contains most of the essential features which distinguish solutions of very large molecules from those containing only molecules of ordinary size. Tabular K-values (K table) You can input tabular K-values which CHEMCAD will then interpolate for use during calculations. The table of K-values must be set up in a separate file called jobname.KTB, where jobname is the file name for the simulation, prior to thermodynamics selection. The format of this file is as follows: NP, TU, PU Reference pressure T1, T2 . . . .Tn K1, K2 . . . .Kn for component No. 1 K1, K2 . . . .Kn for component No. 2 where: NP = number of points (Maximum = 20) TU = temperature units PU = pressure units Temperature and pressure unit codes are listed below. Unit code T unit P unit 0 R psia 1 K atm 2 F psig 3 C mm Hg 4 bar 5 Kpa 6 Mpa 7 Pa 8 Kg/cm2 9 bar G 10 Kg/cm2 G 11 Torr 12 in - H2O T1, T2 are the temperatures at points one, two, etc. K1, K2 are the corresponding K-values for a given component at the temperatures provided above. One set of K-values for each component. During the calculations, the K-values are interpolated logarithmically with temperature and are adjusted for pressure effects by assuming the K-values are inversely proportional to the reference pressure (absolute). Notes · Data must be in order of increasing temperature. · If the K-values for any components are not provided, the program will use the SRK method to calculate the K-values. Polynomial K-values (Polynomial K) The K-values are assumed to be a function of temperature in the following forms: where T is the temperature in units selected by the user. The left side may be any of the following forms: Option Function f(K) 1 f(K) = K 2 f(k) = LOG10 (K) 3 f(K) = ln (K) 4 f(K) = Square root (K) file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 65 of 89 5 f(K) = Cubic root (K) 6 f(K) = Square root (K/T) 7 f(K) = Cubic root (K/T) The coefficients a, b, c, d, and e may be entered by filling in the menu which appears at the time of K-value selection. Partial Pressures of Aqueous Mixtures K-values (PPAQ) This K-value method is for modeling the vapor-liquid equilibrium of compounds dissolved in water using partial pressures to calculate the equilibrium of the solute. This option is normally used for the modeling of ionic type compounds, such as HCl or HNO3, which dissolve in water and disassociate. The equilibrium of such systems is highly concentration dependent, that is, it is largely a function of the relative amounts of the solute and solvent present, and is not much affected by the presence of other components. As such, these mixtures do not lend themselves well to modeling by activity coefficients or other correlated procedures. When using the PPAQ method, you should generally select the Heat of Solution method for enthalpies. This will permit accounting for the heat of disassociation. To use this method, you must first prepare an external ASCII file that contains the partial pressure data. This data may be input as a table of partial pressures, or as a set of coefficients, A and B, for the relation in log PP = A-B/T. The layout of this file is given below. PU,TU,C,ID,NC,NT,D <-- General Information C1,C2,C3,...Cn <-- Concentration Points T1,T2,T3,...Tm <-- Temperature Points PP1,1,PP1,2,,...PP1,m ) Partial pressure of PP2,1,PP2,2,,...PP2,m ) solute over solution · ) if D = 0 · ) · ) PPn,1,PPn,2,,...PPn,m ) PP1,1,PP1,2,,...PP1,m ) Partial Pressure of PP2,1,PP2,2,,...PP2,m ) WATER over solution · ) if D = 0 · ) · ) PPn,1,PPn,2,...PPn,m ) or PU,TU,C,ID,NC,0,D <-- General information C1,C2,...Cn <-- Concentration Points A1,B1 ) A2,B2 ) Partial pressure · ) equation coefficients · ) or solute over · ) solution if D=1. An,Bn ) A1,B1 ) Partial pressure · ) equation coefficients · ) for water over · ) solution if D=1. An,Bn ) where PU, TU are pressure and temperature unit codes selected from the following table. Unit code T unit P unit 0 R psia 1 K atm 2 F psig 3 C mm Hg 4 bar 5 Kpa 6 Mpa 7 Pa 8 Kg/cm2 9 bar G 10 Kg/cm2 G 11 Torr 12 in - H2O file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 66 of 89 C = concentration basis, 0 = mass %, 1 = molar % ID = component ID number of solute NC = number of concentration points (maximum = 20) NT = number of temperature points (maximum = 20) D = data flag, 0 = table, 1 = formula Cn = concentration of solute in solvent in units defined by C Tm = temperature of partial pressures PPn,m = partial pressures at Tm and Cn An = partial pressure coefficient, A, at Cn Bn = partial pressure coefficient, B, at Cn This file should always be given the name jobname.PPA, where jobname is the file name for the simulation. When this K-value method is selected, CHEMCAD will always look for this file. If the file is not found, the Unable to access PP data file message will appear. Methodology When calculating K-values using this method, CHEMCAD uses the following rules and methods: · The K-value of the solute is calculated by the following equation: where: PP = the solute partial pressure, calculated by interpolating the user-provided table PT = the system pressure X = the liquid molar concentration of the solute · The K-value of water is calculated using the partial pressure data given in the .PPA file. · K-values for all other components are calculated using Henry's Gas Law. If the HGL data is not present for a given compound, the program will fall back to the MSRK method. If the MSRK parameters for a given compound are not present, the program will use the SRK method. · The program will extrapolate data. However, if it has to do so, it will alert the user by issuing the following message to the screen: % SOLUTION OUTSIDE DATA RANGE Note The partial pressure data for the HCL-Water and NH3-Water systems are stored in the program. If you are modeling these systems, you do not need to create the .PPA file unless you want to override the CHEMCAD file. User-specified Activity Coefficient Model (ACTX) The activity coefficients for each component can be specified as a function of temperature: where: T = Temperature (K) γ = Activity coefficient Water/Hydrocarbon Solubility You can set water as being miscible or immiscible with the other components. In the Thermodynamic Settings dialog box, on the K-value Models tab, select a Water/Hydrocarbon Solubility setting of either Miscible or Immiscible. The default setting is that water is immiscible for KVAL options SRK, PR, APIS, ESSO, and GS; and miscible for all other options. If water is miscible, it means that the K-values for all components, including water, are calculated by the same routine; that is, by whatever the selected K- value routine for that flowsheet on that unit is. If water is immiscible, all components except water are calculated using the selected K-value routine. The K-value for water is calculated using a special routine designed to reflect the solubility of water in hydrocarbons. The water solubility correlation is primarily for non-polar hydrocarbon systems where water and hydrocarbon form two liquid layers in the liquid phase. This model calculates the amount of water dissolved in the hydrocarbons. The amount of hydrocarbons dissolved in water is usually small and can be ignored. If two liquid layers actually form in the process, the first layer will contain the hydrocarbons with the dissolved water while the second layer will contain free water only. When water is immiscible, its K-value is calculated as follows: } where: and is found by a proprietary calculation. If two liquid layers form in the water-polar chemical system, this model should not be used. Select NRTL, Margules, or UNIQUAC models and set the phase option to vapor / liquid / liquid to predict the actual vapor-liquid-liquid equilibrium. Multi-phase Systems Whenever sufficient information is present, CHEMCAD will automatically flash a stream to completely define or initialize it. As soon as you input the file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 67 of 89 temperature, pressure, and component flow rates of a stream, CHEMCAD immediately flashes the stream and determines the remaining stream variables: enthalpy, vapor fraction, and total flow rate. CHEMCAD also performs flashes on every outlet stream from a unit. In the default conditions, these are all two-phase, i.e., vapor-liquid equilibrium flashes. Except for the cases of immiscible water, no second liquid phase is recognized. Within CHEMCAD we call these LV flashes. Solids may be present as a third or fourth phase. If the simulation is concerned with a system where a second liquid phase may be routinely forming, LV flashes are not appropriate for stream initialization or outlet flashes. In this situation you can specify these flashes to be true, rigorous three-phase flashes. Within CHEMCAD, these are known as LLV flashes. You switch back and forth between these options by selecting the appropriate global phase options. The implications of the LLV option are profound. It means that all unit operations, including distillation, may be converted to three-phase unit operations. If you want to perform a three-phase distillation, all you need to do is invoke the LLV option and set up the distillation unit (SCDS is recommended, but not required) as you normally would. CHEMCAD will determine if and where two liquid phases form. The Salt Effect The presence of a dissolved salt in a mixture of solvents can often significantly change the vapor liquid equilibrium of the system. For an azeotropic system, this may even lead to total elimination of the azeotrope. This observed phenomenon is often associated with the salting-in/salting-out of the solvent components and is the basis of the salt distillation process for separating close boiling or azeotropic systems which could not be easily purified by conventional distillation processes. A model describing the vapor liquid equilibrium of a mixture of solvents containing a dissolved salt was derived along similar basis as that used for the derivation of the Wilson equation for salt-free systems. This model, called the "salt-effect model", contains two groups of parameters - one set is the same as that defined by Wilson or solvent-solvent interaction in salt-free systems and the other set describes the salt-solvent interaction which can be easily calculated from the bubble points of the individual solvent components containing the given salt at the system pressure. Using the appropriate documented Wilson's solvent-solvent parameters for the salt-free system and the computed values of salt-solvent parameters from bubble point data, the vapor liquid equilibrium predicted by the model was found to compare satisfactorily with the experimental data for 57 different binary alcohol-water systems containing different salts at different concentrations. The criteria for salting-out of alcohol suggested by the model was shown to be consistent with the range of experimental relative volatility enhancement factors for the 57 systems examined. The exact form and approach of this method is proprietary. Be aware that to properly apply this method, three pieces of information must be supplied in addition to the normal binary interaction parameters for the Wilson: 1. The position of the salt in the component list. This is identified in the Thermo/Kvalue menu. 2. The value Asi: VP = The vapor pressure of the component in which the salt is dissolved at the bubble point temperature of the solvent and the salt at the system pressure and given composition P = The system pressure 3. The mole fraction of the salt dissolved solvent for which Asi above is provided. The procedure for determining Asi above would be: 1. Determine the bubble point temperature of the solution at the system pressure and at the salt concentrations, MFs, being considered. 2. At this temperature, determine the vapor pressure of the pure solvent, VP. 3. Divide VP by P, the system pressure to get Asi. You must then enter Asi and MFs on the solvent line of the BIP menu. For example, suppose you have a five-component system with methanol, toluene, water, acetic acid, and sodium chloride. The salt will dissolve in the methanol and water, but not in the toluene. Acetic acid is present only in small amounts. You have computed the ordinary BIPs for the Wilson equation where relevant. You have also computed the following: Marek and Standart Vapor Phase Association Correction One of the two options for vapor phase association correction in CHEMCAD is the Marek and Standart model. To use this option, open the Thermodynamic Settings dialog box and select Marek and Standart from the Vapor Phase Association drop-down list. This option should be coupled with a liquid activity method. Note that this option will also activate the Poynting correction. For all activity coefficient methods: Invoking this option changes the way that the vapor phase fugacity, fvi, coefficient and the liquid fugacity coefficient in the standard state, fvi, are calculated. Under Marek and Standart, the fugacities of the associating compounds are calculated by actually reacting them in the equation: M+M→D where: M is the monomer compound. D is the dimer of the compound. The solution of this reaction is achieved by solving the equation: where: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 68 of 89 PID is partial pressure of the pure dimer, and PIM is partial pressure of the monomer. When multiple components with dimerization constants appear in the same stream, CHEMCAD calculates the effects of cross dimerization on vapor pressures. The As and Bs for the dimerization of the following carboxylic acids are included in the program: Dimerization Constants (Pressure Unit: mm Hg) Comp. ID Component A B 223 Formic Acid CH2O2 10.743 3083. 238 Trifluoroacetic Acid C2HF3O2 10.800 3053. 439 Chloroacetic Acid C2H3CLO2 10.728 3315. 130 Acetic Acid C2H4O2 10.421 3166. 253 Acrylic Acid C3H4O2 10.843 3316. 143 Propionic Acid C3H6O2 10.843 3316. 446 Methacrylic Acid C4H6O2 10.100 3040. 154 Butyric Acid C4H8O2 10.100 3040. 283 Isobutyric Acid C4H8O2 10.100 3040. 306 Valeric Acid C5H10O2 10.005 2993. 510 Hexanoic Acid C6H12O2 9.891 2943. 819 Heptanoic Acid C7H14O2 9.807 2900. 540 Octanoic Acid C8H16O2 9.663 2852. 544 Nonanoic Acid C9H18O2 9.550 2792. 890 Decanoic Acid C10H20O2 9.436 2741. These As and Bs are stored in an ASCII file called VASS.SF stored in the CHEMCAD system directory. You can expand this file to include other dimerization reactions or even trimerization and hexamerization reaction, if so desired. The format of this file is as follows (enter one such line for each possible reaction): COMPID,NOCOMB,A,B where: COMPID is the component ID number. NOCOMB is the number of molecules combining, thus 2 is for dimerization, 3 is for trimerization, etc. A and B are the equilibrium coefficients defined above. The file is free format, so commas or blanks may be used as delimiters. Note The vapor phase association affects the vapor phase fugacity, and therefore affects the K-value calculation when using activity coefficient methods. This means that it will exert an influence of the BIPs calculated from TPXY data during a regression analysis. It is, therefore, critical that the user keep straight whatever vapor phase association assumptions are made during the calculation of the BIPs. If Marek and Standart is selected during the regression analysis, then the effect of vapor phase association will be taken into account during the regression analysis for liquid activity coefficient equation BIPs. Hayden O'Connell Vapor Phase Association Correction The Hayden O'Connell (HOC) method in CHEMCAD is implemented as a vapor phase correction using chemical theory intended primarily for dimerization of carboxylic acids. This correction is applied to the component vapor fugacities, the number of moles, and an enthalpy correction. The pure component vapor fugacities are provided by the current equation of state, or SRK in the case of an activity coefficient K-value model. To enable the HOC option, select Hayden O'Connell from the Vapor Phase Association drop-down list on the Thermodynamic Settings dialog box. Each pair of chemical components has an interaction determined by its eta parameter. The eta parameters are managed by database BIPs. CHEMCAD attempts to estimate the HOC BIPs for each interaction, based on UNIFAC group information (see O'Connell reference, below). Each BIP can be modified by editing either the simulation or the user database. The HOC chemical theory approach only considers dimers between components that have an eta greater than or equal to the eta threshold set in the thermodynamics settings dialog. The method is based on the chemical theory implementation given by Prausnitz and Andersen (see References, below). The method requires each component's critical temperature, critical pressure, dipole moment, radius of gyration, and an eta solvation/association adjustable parameter (BIP) for each component interaction (pure or mixture). The dimerization reaction equilibrium constant is defined by second virial coefficients: The enthalpy correction is derived from van 't Hoff equation: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 69 of 89 Apparent/superficial mole fraction constraint: True mole fraction constraint: Ratio of apparent/superficial moles to true moles: where: = apparent/superficial monomer vapor mole fraction of component i = Kronecker delta function = calculated true monomer vapor mole fraction of component i = calculated true dimer vapor mole fraction of component i with component j = total number of superficial moles = total number of true monomer and dimer moles Calculated values from the Hayden O'Connell method: = second virial coefficient free contribution of component i with component j = second virial coefficient metastable contribution of component i with component j = second virial coefficient bound contribution of component i with component j = second virial coefficient chemical contribution of component i with component j Note The vapor phase association affects the vapor phase fugacity, and therefore affects the K-value calculation when using activity coefficient methods. This means that it will exert an influence of the BIPs calculated from TPXY data during a regression analysis. It is, therefore, critical that the user keep straight whatever vapor phase association assumptions are made during the calculation of the BIPs. If Hayden O'Connell is selected during the regression analysis, then the effect of vapor phase association will be taken into account during the regression analysis for liquid activity coefficient equation BIPs. References Hayden, J. and O'Connell, J., A Generalized Method for Predicting Second Virial Coefficients. Ind. Eng. Chem. Process Des. Dev., 14, 209 (1975). Prausnitz, Andersen, Computer Calculations for Multicomponent Vapour-Liquid and Liquid-liquid Equilibria, Prentice Hall, 1980. O’Connell, J., AIChE Journal Vol.30, No.6, pp. 1037-1038. Hydrogen Fluoride Modeling Hydrogen fluoride hexamerizes in the vapor phase. This hexamerization is a function of temperature and pressure and must be accounted for in the phase equilibrium model. The HF equation-of-state is a model for HF and other components in a non-electrolyte system. A combined equation-of-state/vapor phase association method is used. This method is automatically switched on when under the following conditions: 1. HF is in the component list and SRK K-values are selected. 2. HF is in the component list, an activity coefficient method is selected for K-values, and, the Poynting Correction is turned on. In a "normal" equation-of-state model, it is assumed that the total number of moles in the system is constant. Because HF hexamerizes in the vapor phase, this assumption is not valid in HF systems. In this method, HF is treated as a mixture of monomer and hexamers which are in chemical equilibrium. The reaction: is modeled using the equilibrium constant, Keq, when: where: K [=] mmHg-5 T [=] degrees Kelvin q6 = the fugacity coefficient of the hexamer file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 70 of 89 q1 = the fugacity coefficient of the monomer Z6 = mole fraction of the hexamer Z1 = mole fraction of the monomer P = pressure The equation-of-state for "pure" HF then becomes: where: nr = nT/no nT = the total number of moles of the monomer and the hexamer no = the number of moles of HF that would exist in the absence of hexamerization v = VT/no VT = the volume of the total number of moles The expression for the fugacity coefficient of "pure" HF is then devised as: To solve for the compressibility factor, Z: Reference "An Equation-of-State for Hydrogen Fluoride"; Twu, C. H., Loon, J. E., Cunningham, J. R.; Fluid Phase Equilibrium; 86 (1993) 47-62. Hydrogen Hydrogen is a special component and is recognized by CHEMCAD as such. It is necessary to develop special procedures for handling hydrogen due to its very low critical temperature. In addition, the retrograde bubble-point behavior common in hydrogen-containing mixtures must be reliably predicted. The analysis of binary VLE data has made possible the determination of reliable binary interaction parameters (BIP) for the SRK and PR equations.This analysis has been extended to multi-component systems with excellent accuracy through the mixing rules. The BIPs for H2 are hard-wired into CHEMCAD; that is, they are not stored in the BIP database for SRK or PR. Therefore, when you look in these files, you will find only zeroes for H2. You can override the hard-wired BIPs by entering parameters in the appropriate location in the database. Inert Gases with Activity Models When inert gases such as CO2, N2, and H2 are present with non-ideal chemicals, they present some computational difficulties for activity models. As you will recall, the K-value, when using activity models, is calculated as follows: The problem with this formulation where inert gases are concerned is that the system is very often operating above the critical point of the pure inert gas. The standard vapor pressure correlation cannot be accurately extrapolated into this region. It is necessary, for the inert gas only, to switch to the Henry's Gas Law method for vapor pressure representation whenever the system temperature is above the critical temperature of a given compound. CHEMCAD accomplishes this task by following the procedure described below. Each time the vapor pressure is calculated, CHEMCAD compares the critical temperature of each compound to the system temperature. If the system temperature is greater than the critical temperature of one or more of the compounds, then the program will check to see if the Henry's constants are present for the components in question. If the Henry's constants are present, then, for the "inert" compounds only, CHEMCAD will represent the vapor pressure using the Henry's method. All other components will use the regular vapor pressure equation. If the Henry's constants are not present, then the program remains with the regular default vapor pressure method. In certain unusual cases, this approach can cause some numerical difficulties. If the system happens to be operating right in the vicinity of the critical point of one of the components, then it is possible that on one iteration the calculation will be above the critical temperature and on the next it will be below the critical temperature. This causes the program to switch back and forth between vapor pressure methods, causing numerical discontinuities and non-convergence. To overcome this problem, use the Henry's method globally for certain components. Enthalpy and Entropy Models With certain special exceptions, enthalpy in CHEMCAD is calculated one of two ways: · Using an equation-of-state method · Using the latent heat method The EOS approach finds real vapor and liquid enthalpies by calculating departures from the ideal gas enthalpy. It can, therefore, be considered "gas equation- based." The latent heat method integrates the liquid heat capacity equation, adds latent heat, then adds the enthalpy from integration of the ideal gas heat capacity equation. It is thus more "liquid equation based". Certain exceptions to the above two methods are sometimes used. These exceptions are as follows: · The steam tables are used to determine the enthalpy of water (if water is the only component and SRK enthalpy is selected). · A special enthalpy method for systems using DEA and MEA to absorb acid gases is provided. · You can supply your own enthalpies, either through tables or through polynomials. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 71 of 89 · Heats of solution data may be read and are used by the program. · The enthalpy of solid components is treated as a special case. · For mass balancing only, enthalpy calculations can be omitted. It should be noted that unless otherwise stated, the standard reference state for all enthalpy calculations is the ideal vapor heat of formation at 298.15°K. Enthalpy from Equations of State The enthalpy of a process stream may be calculated from an equation of state by the following equation: where: Coefficients a,...,f for each component are stored in the database. The term 7 is the enthalpy departure function. The entropy of a process stream is calculated by the following equation: where: Cp is the ideal gas heat capacity defined above. SP is the entropy departure 8 Note 1: The precise form of the enthalpy and entropy departure functions depends on the equation of state mode. Note 2: The standard reference state for all enthalpy calculations is the liquid heat of formation at 298.15° K. The departure function is calculated from whichever equation-of-state is chosen to model enthalpy. The options available in CHEMCAD are: · Soave-Redlich-Kwong · Peng-Robinson · Benedict-Webb-Rubin-Starling · Redlich-Kwong · API-SRK · Lee-Kesler Redlich-Kwong H Model The enthalpy departure function is as follows: The entropy departure function is as follows: Soave-Redlich-Kwong H Model The enthalpy departure function for the Soave-Redlich-Kwong equation of state is represented by the following equation: where: The entropy departure function is as follows: where: P0 is the reference pressure (14.696 psia). file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 72 of 89 Peng-Robinson H Model The enthalpy departure function for the Peng-Robinson equation of state is represented by the following equations: where The entropy departure function is as follows: Volume Translated Peng-Robinson (VTPR) H Model The Volume Translated Peng-Robinson (VTPR) equation of state is represented by the following. The enthalpy for a mixture is given by: The entropy of a mixture is given by: where: Reference Schmid, B., Schedemann, A., and Gmehling, J., Extension of the VTPR Group Contribution Equation of State: Group Interaction Parameters for Additional 192 Group Combinations and Typical Results, Ind. Eng. Chem. Res. 2014, 53, 3393-3405. Gmehling, J., Kolbe, B., Kleiber, M., Rarey, J., Chemical Thermodynamics for Process Simulation, John Wiley & Sons, 2012. API Soave-Redlich-Kwong H Model The enthalpy departure function for the API Soave-Redlich-Kwong equation of state is represented by the following equations: where: The entropy departure function is as follows: Lee-Kesler H Model The Lee-Kesler enthalpy model is good for hydrocarbon systems. Lee-Kesler Equation where: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 73 of 89 The constants b1,b2,...,etc. are given in the following table: Constant Simple fluids Reference fluids b1 0.1181193 0.2026579 b2 0.265728 0.331551 b3 0.154790 0.027655 b4 0.030323 0.203488 c1 0.0236744 0.0313385 c2 0.0186984 0.0503618 c3 0.0 0.016901 c4 0.042724 0.041577 d1x10e4 0.155488 0.48736 d2x10e4 0.623689 0.0740336 b 0.65392 1.226 g 0.060167 0.03754 Enthalpy Departure where: Entropy Departure where P0 is the reference pressure (14.696 psia). Reference Lee, B.I. and M.G. Kesler, AIChE J., 21, 510 (1975). Benedict-Webb-Ruben-Starling H Model The isothermal departure functions showing the effect of pressure on the properties of a fluid, pure or multicomponent can be calculated starting from the ideal gas state as the reference or standard state: Latent-heat H Model The Basic Equations This model is mostly suited to chemical systems. The enthalpies are calculated by the following equations: where: HL = the liquid enthalpy = the heat of formation of liquid at 298.15 K Cpl = the liquid heat capacity HV = the vapor enthalpy HL (bubble) = the liquid enthalpy at bubble point and system pressure HV (at bubble) = the heat of vaporization at bubble point Cpv = the heat capacity of vapor The coefficients of the HL polynomial for most chemical components are available in the database. If the coefficients are not available, this enthalpy option should not be used. The heat of vaporization at temperature T is calculated by the Library equation if the coefficients are available: where: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 74 of 89 Hv is in J/Kmol Tr is the reduced temperature If the Library coefficients are not available, the heat of vaporization at temperature T is calculated by the Watson equation: where: Tr1 and Tr2 are the reduced temperature at T1 and T2, respectively. The heat of vaporization at component normal boiling point is stored in the database. If it is not available, it is estimated by the following equation: where: Tb is the component normal boiling point. Tc is the critical temperature Pc is the critical pressure Tbr = Tb/Tc The Soave-Redlich-Kwong entropy is used for this option. Electrolytes Enthalpy Model Electrolyte chemistries involve heats of reaction (or heats of dissociation if you prefer), which should be included in the heat balance. To ensure that this happens, check the Use electrolyte enthalpy box on the Enthalpy Models tab in the Thermodynamic Settings dialog box. CHEMCAD automatically makes this entry when appropriate, but you may turn it off. The option to turn off the electrolyte enthalpy option for an electrolytes problem is permitted in order to handle those situations where the heat of reaction data is not known, and therefore other enthalpy methods may be needed. Steam Tables The steam table for the enthalpy and entropy of steam/water is used for streams containing steam/water. When water is the only component in the system, the enthalpy datum is liquid water at 32° F; therefore, the enthalpy is directly comparable to the ASME steam table. The steam table is good for pressures up to 3000 psia and temperatures up to 1200° F. Mixed Model for Enthalpy The mixed model for enthalpy enables you to use the latent heat method for some components and the SRK equation-of-state method for others. If you have selected this method on the Enthalpy Models tab in the Thermodynamic Settings dialog box, CHEMCAD opens a dialog box where you can identify which components are to be calculated using the latent head approach. The remaining components will have their enthalpies calculated using the SRK equation-of-state approach. Enthalpy Calculations Involving Solid Components CHEMCAD has solids handling features. At the present time, identifying a component as a solid simply excludes that component from the flash equilibrium (sum Kx) calculations while including them in the enthalpy balance. No transport properties other than heat capacity are calculated by the program. Therefore, when you view the properties of a stream, the Solids column will be blank. You must specifically identify a component as a solid for CHEMCAD to treat it as a solid. To do this, select Thermophysical > Solids > Identify Solid Components. When a compound is identified as a solid, its enthalpy is calculated by integrating the heat capacity equation using the latent heat method. Heat of vaporization is taken as zero. If the process involves heat of fusion, the value is entered in the appropriate process module (i.e., crystallizer). Such fusion effects are accounted for by creating distinct compound species in the solid and other (usually liquid) phase. The liquid and vapor phases may be treated in any appropriate manner, since the solids enthalpy is treated independently, then combined with the enthalpy of the liquid or vapor. Amine Enthalpy Model The vapor enthalpy is obtained from the Soave-Redlich-Kwong equation of state. The liquid enthalpy with heat of absorption of H2S and CO2 in amine solution is calculated by the method of Crynes and Maddox. No Enthalpy Option If you select the No enthalpy option on the Enthalpy Models tab of the Thermodynamic Settings dialog box, the enthalpy calculation will be ignored; that is, enthalpy will be 0 at all conditions. This option is useful if you want to perform a mass balance calculation only. Note Only the following unit operation modules are allowed for the No enthalpy option: Flash, Divider, Mixer, Component Separator, Reactor, Pump, Valve, Three- Phase Flash, Phase Generator, Stream Reference, And Shortcut Distillation. Polynomial Enthalpy Model The polynomial enthalpy for vapor and liquid are assumed to be of the form: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 75 of 89 where: H = H vapor or H liquid in units selected by the user T = temperature in units selected by the user a,...,e are the coefficients entered by the user for each component f(H) has the following forms: Option number Description 1 f(H) = H 2 f(H) = log10 H 3 f(H) = ln H 4 f(H) = Square root (H) 5 f(H) = Cubic root (H) 6 f(H) = Square root (H/T) 7 f(H) = Cubic root (H/T) The equations are set up in the Enthalpy Polynomial dialog box, which appears after you complete the Thermodynamic Settings dialog box. Tabular H-values You have the option of inputting tabular enthalpy values. During analysis, these values will be interpolated for use by the program. The tabular values must be set up in a separate file called jobname.HTB, where jobname is the file name for the simulation, prior to thermodynamics selection. The format for this file is as follows: NPVPTS, NPLPTS, TU, HU, FU TV1, TV2 . . . . TVn vapor temperature points HV1, HV2 . . . . HVn vapor enthalpy for component no. 1 HV1, HV2 . . . . HVn vapor enthalpy for component no. 2 . . . HV1, HV2 . . . . HVn for component no. M TL1, TL2 . . . . TLn liquid temperature points HL1, HL2 . . . . HLn liquid enthalpy for component no. 1 HL1, HL2 . . . . HLn liquid enthalpy for component no. 2 . . . HL1, HL2 . . . . HLn for component no. M where: NPVPTS = number of vapor points (maximum = 20) NPLPTS = number of liquid points (maximum = 20) TU = temperature units HU = enthalpy units FU = flow units Temperature and pressure unit codes are listed below: Code TU HU FU 0 R Btu lb mol 1 K KBtu K mol 2 F MMBtu mol 3 C J lb 4 KJ Kg 5 MJ g 6 Cal 7 KCal 8 MCal 9 Hp-hr 10 Kw-hr 11 Mw-hr One set of H values per component per phase. During the calculations, the H values are interpolated linearly with temperature. No adjustment is made for pressure. Heat of Solution Enthalpies (HTSL) The heat of solution enthalpy method is intended for use with the PPAQ K-value method and like that method requires an external user-created ASCII file which contains the heat of solution data as a function of solute concentration. The program uses the integral heat of solution. Up to three components can be included in the file. The name of the user file containing the heat of solution data must be jobname.HTS, where jobname is the file name for the simulation. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 76 of 89 The jobname.HTS file must be placed in the simulation folder, which only appears while the simulation in question is open in CHEMCAD. The folder is visible in Windows Explorer within the same directory where the simulation file resides. The file layout is as follows: HU,FU,NPT ID1,PH1,CF1 C1,1, H1,1 . . C1,n, H1,n ID2, PH2,CF2 C2,1, H2,1 . . C2,n, H2,n ID3,PH3,CF3 C3,1, H3,1 . . C3,n, H3,n where: HU, FU = Enthalpy and flow units (see table below) NPT = Number of data points per component ID1, 1D2, ID3 = Component ID number of solutes 1, 2, and 3 PH1, PH2, PH3 = Phase: 0 = Liquid, 1 = Vapor (for each component) CF1,CF2,CF3 = Concentration flag for each component: 0 = Moles of solvent/moles of solute 1 = Mole % of liquid solution 2 = Mass % of liquid solution Ci,X = Concentration point x of component i Hi,x = Integral heat of solution at Ci,x Code TU HU FU 0 R Btu lb mol 1 K KBtu K mol 2 F MMBtu mol 3 C J lb 4 KJ Kg 5 MJ g 6 Cal 7 KCal 8 MCal 9 Hp-hr 10 Kw-hr 11 Mw-hr The following rules should be noted regarding HTSL: 1. Heats of solution may be used with SRK enthalpies, PR enthalpies, latent heat enthalpies, etc. 2. CHEMCAD will extrapolate data if necessary. If this occurs, you will see the message OUTSIDE ENTHALPY DATA RANGE. 3. The heat of vaporization of the solute will be accounted for based upon the phase value in your .HTS file. If the solute is dissolved as a gas, temperatures will be lower than if dissolved as a liquid. Normally, this effect is only a few degrees. Note The integral heats of solution for the HCL-Water and NH3-Water systems are stored in CHEMCAD. If you are modeling these systems, you do not need to create the .HTS file unless you want to override the CHEMCAD data. Electrolytes CHEMCAD provides models and databases to solve a wide range of problems involving electrolyte processes. Typical applications involve the need to calculate the effect of ionization on solution phase behavior, the need to determine pH, precipitation or extent of ionization. These and many more problems can be solved by CHEMCAD using a variety of approaches. CHEMCAD offers the following options: · A choice of using apparent components or true components to represent the system species; · A choice of using specified or calculated reaction equilibrium constants for the solution chemistry; · A choice of using the Pitzer or MNRTL methods for calculating activities. CHEMCAD can handle single or mixed solvents; vapor, liquid and solid components, and can perform all unit operations calculations in a rigorous and stable manner. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 77 of 89 About Electrolyte Solids Electrolyte Salts Using the true species electrolytes model, you can define an electrolyte as a possible precipitate. The electrolyte model will determine whether the salt precipitates during the flash calculation of a stream. A precipitated salt follows the same behavior as a defined solid. If you have solubility data for a salt, it can be regressed into the electrolyte system. The heat of solution for an electrolyte salt may be regressed into the electrolyte system. Analog model You may have temperature-dependent solubility data for your process. Temperature vs. solubility data can be regressed into a kinetic expression. A separate component may be created as a solid; use a kinetic reactor to change component to solid component. Apparent vs. True Species In CHEMCAD, there are two approaches to represent the composition of a stream in the electrolyte model: the apparent component model and true species model. In the apparent component model, the stream composition is expressed in terms of the molecular components prior to solving the electrolyte chemical reactions. In the true species model, the stream composition is expressed in terms of the actual species (molecules + ions) which exist after solving the electrolyte chemical reactions. The user may determine which model to use by selecting the proper components to represent the model. If only the molecular components are selected in the component list, CHEMCAD will use the apparent component model. If both the molecular components and all the ions involved in the reaction are defined in the component list, CHEMCAD will use the true species model. For example, if only water and carbon dioxide are defined in the component list, it becomes the apparent component model. If water, carbon dioxide, H+, OH-, HCO3-, and CO3-- are all included in the component list, the program will use the true species approach. Note: To use the true species model, all ions involved in the reactions must be included in the component list and the molecular components must be defined in front of the ions. It is the user's personal preference to choose between the apparent component and the true species models. The only exception is that if the chemical reactions generate some volatile components, then only true species model can be used. For example: In a NH4Cl-NaOH-NH3-H2O system, mixing NH4Cl, NAOH and H2O yield the volatile component NH3, only the true species approach can be taken in this case. The differences in the approaches can be described in the following ways: Using the apparent species approach, only the molecular components from the component database are reported. Therefore, if we are looking at flashing a mixture of 80 moles H2O and 20 moles NaCl, the system would be represented as follows: H2O <---> H+ + OH- NaCl <---> Na+ + Cl- Component list: Electrolyte species list: H2O H2O NaCl NaCl H+ OH- Na+ Cl- The material balance is: Input - 80 moles H2O, 20 moles NaCl Top output - 10 moles H2O Bottom output - 70 moles H2O, 20 moles NaCl Even if the NaCl is 95% dissociated, only H2O and NaCl show up in the streams' outputs. The actual electrolyte species can be reported, but would show up in a separate stream's output for electrolytes species. If all of both the components and electrolytes species are taken from the component database, the same situation would be represented as follows: H2O <---> H+ + OH- NaCl <---> Na+ + Cl- The component list would be: H2O NaCl H+ OH- Na+ Cl- There would be no electrolytes list. At 95% NaCl dissociation, the material balance would be as follows: Input: H2O 80 moles NaCl 20 moles H+0 moles OH- 0 moles Na+ 0 moles Cl- 0 moles Top output: 10 moles H2O Bottom output: 69.5 moles H2O 1.0 moles NaCl .5 moles H+ file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 78 of 89 .5 moles OH- 19.0 moles Na+ 19.0 moles Cl- The ionic species now show up on all reports, and the H2O and NaCl are reported only in their whole molecular component form. Now Na+ and Cl- can be displayed in any way the program provides. The apparent species approach always maintains a mole balance across all unit operations. The true species maintains only an atom balance. It is not required to maintain a mole balance. This difference clearly has computational significance and it further means that in some situations, the apparent species approach is not suitable. Again, an example is probably more demonstrative of the relevant points. In the above H2O - NaCl problem it makes no difference which approach is used, so let's move on to a more complex example. Suppose we are neutralizing aqueous NaOH by adding HCl. The solution chemistry of this system would look like this: H2O <---> H+ + OH- NaOH <---> Na+ + OH- HCl <---> H+ + Cl- NaCl <---> Na+ + Cl- Notice that the last reaction involves the creation of a component which does not exist in the feed. In the apparent species approach this system would be modeled as follows: Component list: Electrolyte species list: H2O H2O NaOH H+ HCl OH- NaCl NaOH Na+ HCl Cl- NaCl Top input: 100 moles H2O 50 moles NaOH Bottom input: 50 moles HCl 0 moles NaCl Top output: 5 moles H2O Bottom output: 95 moles H2O 50 moles NaOH 50 moles HCl 0 moles NaCl But what happened to the NaCl? Even though we know it is formed and that the electrolyte models will predict it's formation, it cannot show up in the outlet streams because of the requirement that a mole balance be maintained across the flash unit. This is clearly bogus and renders the apparent species approach unusable in such cases. Now let's look at the true species approach. In the true species approach this system is handled as follows: Component List: H2O H+ OH- NaOH Na+ HCl Cl- NaCl Top Input: 100 moles H2O 50 moles NaOH Botom input: 50 moles HCl 0 moles NaCl Top output: 5 moles H2O file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 79 of 89 Bottom output: 94.9 moles H2O 0.05 moles NaOH 0.05 moles HCl 0.15 H+ 0.15 OH- 0.05 Na+ 0.05 Cl- 40 NaCl The results are much more acceptable now. The NaCl shows up in the output and the model is not forced to a poor solution. So, what's the downside? The downside to the true species approach is largely in presentation. If you are absorbing CO2 with water, you may want to see CO2 displayed as CO2 not as HCO3-. This would help you quickly conceptualize your process. The true species approach would not permit such a display, because in those cases where it is required, there is no longer a one to one correspondence between the ions and the molecules. Na+ could go to form NaOH and NaCl so how do you display the free ions as molecules? In cases where the solution chemistry is such that a one to one correspondence exists between the ions and the molecules, the true species and apparent species approaches will give the same answers. It is only when this one to one correspondence no longer exists that the apparent species method breaks down. The true species approach is computationally more stable than the apparent species approach. The apparent species approach is easier to implement. Electrolyte Models To better understand the basis for the electrolyte system, consider the formulation of a predictive model for a particular aqueous based electrolyte system. The example chosen involves water-chlorine. The reactions to be considered are: · H2O(vap) = H2O(aq) · Cl2(vap) = Cl2(aq) · Cl2(aq) + H2O = H(ion) + Cl(ion) + HClO(aq) · HClO(aq) = H(ion) + ClO(ion) · H2O(aq) = H(ion) + OH(ion) The problem is to predict the resulting phase distribution and phase compositions. Determine: · Total vapor rate, V · Rate of H2O (aq) · Vapor phase partial pressure, ph2O and pCl2. · Liquid phase concentrations, usually expressed in molality (gm moles solute per 1000 gms solvent)-H2O(aq), mHClO2(aq), mClO2(aq), mH(ion), mOH (ion), mCl(ion), mClO(ion). The problem, stated above for water-chlorine, is typical of all calculations involving electrolytes. For the water-chlorine system above, a set of ten equations is required in order to solve for the ten unknowns just described. These equations are as follows. These ten equations can, with a reasonable computer, be solved for the ten unknowns in question. What has been understated thus far is that, embedded in equations 1-5, the K equations, is the essential complexity of the electrolyte calculations. The variables, K(T,P) and g(T,P,m) are often highly nonlinear functions of the state variables shown. In CHEMCAD , the g(T,P,m) can be calculated by either Pitzer or Modified NRTL model. Equilibrium Equations Equilibrium K equations are written, one for each reaction. As we shall see, these equations are of the form: where K = The thermodynamic equilibrium constant; a function of T and P. giP', giR = Activity coefficient or, for vapors, fugacity coefficient of the ith product and reactant respectively; a function of T, P and composition. uiP', uiR = Stoichiometric coefficient of the ith product and reactant respectively. miP', miR = Molality or, for vapors, partial pressure of ith product and reactant respectively. For our H2O-Cl2 system (using ¡ for activity coefficient, a for activity, f for fugacity coefficient and p for vapor partial pressure), we thus have five such equations: Electroneutrality Equation file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 80 of 89 The electroneutrality equation states that the solution is, at equilibrium, electrically neutral. Generally stated, the equation is: or for our H2O-Cl2 system: mH(ion) = mOH(ion) + mCl(ion) + mClO(on) Material Balance Equations Four material balances are needed to make the number of equations equal to the number of unknowns. The equations are: Overall Material Vapor Phase Chlorine Hydrogen Electrolyte Methods The Pitzer and MNRTL methods actually calculate the phase equilibrium activity coefficients. They do not compute the degree of dissociation of the electrolyte reactions. For this, an ionic equilibrium model must be used. Both methods use the same approach to this portion of the problem. The stoichiometry of all electrolyte reactions is specified and the reaction equilibrium constant, Keq, is used to determine the equilibrium concentrations of all electrolyte species. Thus, in the hypothetical situation: and where ai = the activity of species i. The Keq values may be specified (or taken from the CHEMCAD database) in the following form: If left unspecified, the program computes Keq as follows: where: ΔG = change in system Gibbs free energy R = gas law constant T = temperature The Gibbs free energy of formation is stored for all electrolyte species. The Gibbs energy differences are adjusted for temperature and then summed to determine the overall Gibbs energy difference. Activities are calculated by the electrolyte model selected, either Pitzer or MNRTL. These methods compute the activity coefficients and therefore the phase equilibrium of the system. Pitzer The method revolves around calculating the equilibrium relationships for all the equations defining the electrolyte reactions. At equilibrium, the system will satisfy the minimum free energy criteria and be electrically neutral. Activity coefficients are calculated by Pitzer's method. For volatile components, the user has the normal range of choices in simulating K-values. The system is then solved by minimizing Gibbs Free Energy consistent with the constraint of electrical neutrality. The general theory, equations and numerous examples are covered in the HANDBOOK OF AQUEOUS ELECTROLYTE THERMODYNAMICS, (Zemaitis, Clark, Rafal, Scrivner; DIPPR publication (1986)). The method applies to both strong and weak electrolytes. Strong electrolytes are those which are completely ionized over a wide range of concentrations, such as HCl in water. Weak electrolytes are only partially ionized except in minute dilutions, such as acetic acid. For a strong electrolyte reaction, i.e: the equilibrium coefficient, K, may be defined as: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 81 of 89 where ai = activity of species, i. In calculating these activities, we need to define reference states and activity coefficients. We also would like to preserve the mathematical and intuitive convenience that the activity coefficient approaches unity at infinite dilution of the measurable species. Since HCl is completely ionized at infinite dilution, it behaves as two species rather than one and the activity of HCl in solution behaves as a function of the product of the ion species: However, by a simple transformation, we preserve all limiting conditions: This implies a reference state of unit molality, that is, one gram mol of solute in 1000 grams of water. It then follows that: where m = molality g± = mean ion activity coefficient The definition of mean ion activity may be generalized to account for other forms of the electrolyte equilibrium equations. Mean activity coefficients may be obtained experimentally from VLE data for volatile substances such as HCl or from electrochemical cells for non-volatile substances. For dilute solutions only, mean activity coefficients may be estimated from Debye-Hückel theory using the equation: where The Pitzer method for calculating activity coefficients, like other similar methods, is an extension of the Debye-Hückel theory moving the range of applicability into the 4+ molality area. Activity coefficients for cation C and anion A in a multicomponent solution that can be calculated with the following equations: where Af = the Debye-Huckel constant for osmotic coefficients on a log e basis b = 1.2 I = ionic strength = 0.5 SmiZi2 Zi = ionic charge mi = ionic molality a = subscript denoting anions c = subscript denoting cations and a1 = 2.0 for 1-1, 2-1, 1-2, 3-1, 4-1, 5-1 electrolytes; and 1.4 for 2-2 electrolytes a2 = 0.0 for 1-1, 2-1, 1-2, 3-1, 4-1, 5-1 electrolytes; and 12.0 for 2-2 electrolytes b1, b2, Cf, q, and j are Pitzer parameters. The first four are binary parameters; the last is a ternary parameter. b1, b2, Cf, q, and j are single numbers. b0 is a temperature dependent variable whose determination is explained in the “Physical Properties of Electrolytes” later in this chapter. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 82 of 89 The mean molal activity coefficient can be calculated by combining ionic activity coefficients: The water activity is expressed as: where the molecular weight of the water is denoted by Mw. MNRTL The electrolyte nonrandom, two-liquid (MNRTL) model uses two fundamental assumptions about the structure of electrolyte systems: 1. The local composition of cations (anions) around a central cation (anion) is zero. 2. The distribution of cations and anions around a central molecule is such that the net local ionic charge is zero. The model also determines the excess Gibbs energy to be the sum of two expressions. One expression is derived from the NRTL equation which accounts for the local interaction contribution resulting from short-range and long-range interactions that occur between all neighboring species. The method uses the Pitzer-Debye-Hückel equation to account for the long-range interaction contribution resulting from the long-range ion-ion electrostatic interactions beyond the immediate neighborhood of a central ion. These two expressions are combined to give an equation for the excess Gibbs free energy: This leads to: Long-range Interaction Contribution The Pitzer-Debye-Hückel formula, normalized to mole fractions of unity for solvent and zero for electrolytes, is used to represent the long-range interaction contribution. This leads to: Short-range Interaction Contribution The short-range interaction contribution is accounted for by the nonrandom two-liquid theory. The basic assumption of the NRTL model is that the non-ideal entropy of mixing is negligible compared to the heat of mixing. The effective local mole fractions Xji and Xii of species j and i, respectively, in the neighborhood of molecular species i are related by: where Xj = xjCj(Cj = Zj for ions and Cj = unity for molecules) Gji = exp (-aji tji) tji = (gji - gii)/RT aji = nonrandomness factor Gji and Gii are energies of interaction between j-i and i-i species, respectively. Both gji and aji are inherently symmetric (gji = gij and aji = aij). Similarly, the effective local mole fractions Xji and Xki of species j and k, respectively, in the neighborhood of ionic species i are related by: The pure component state is adopted as the reference state for the reference Gibbs energy of molecules and the hypothetical homogeneously mixed, completely dissociated liquid electrolyte mixture is adopted as the reference state for electrolytes. The reference Gibbs energies per mole are then: The excess Gibbs energy expression for aqueous multicomponent electrolyte systems is then: file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 83 of 89 The activity coefficient equation for molecular components is given by: The activity coefficient equation for cations is given by: The activity coefficient equation for anions is given by: where A molal average mixing rule is adopted for the nonrandomness factor as follows: The variable tim are computed accordingly from the Gim. Furthermore, the variables tma,ca and tmc,ac can be computed from the tim. and The nonrandomness factor, aca,m, aca,ca’, aca,c’a, and amm’, and the energy parameters, tca,m, tm,ca, tca,ca’, tca’,ca, tca,c’a, tc’a,ca, tmm’ and tm’m, are the adjustable binary parameters for the model and must be regressed from data. A facility for this is provided in the Utilities portion of CHEMCAD . Data for file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 84 of 89 about 50 systems are provided with the program. gca and gc’a are assured to be pure electrolyte quantities. Therefore, tca,c’a and tc’a,ca are calculated as follows: where q = reference temperature. a,b, and c are the binary interaction parameter. Electrolyte Regression This option is for electrolyte data regression. It allows the user to determine the best values for the adjustable parameters of the electrolyte models; that is, the BIPs, the Henry's Constants, and the Keq parameters. The following kinds of data can be regressed: · Partial pressure data · TPXY data · TPX data · Gamma (activity coefficient) data · Solid solubility data · Solution enthalpy data The following parameters can be calculated from the regression analysis: For the Pitzer Method: BO_A B1 BO_B B2 BO_C C The Henry's Constants The parameters for the electrolyte reaction equilibrium constants BO_A, BO_B, and BO_C are the Bo terms in the following equations: Therefore, the user must decide which equation form is to be used to calculate B in the "Electrolyte Edit BIP" screen. B1, B2 and C are the Pitzer parameters. Please refer to the Section on Electrolytes for a more complete explanation of the parameters. The parameters for reaction equilibrium are A, B, C, D, and E, where: The parameters for Henry's constants are A, B, C, and D given below: If Henry's constants are to be regressed, the ID1 must be entered as the component ID in the component list (NOT the species list). Example 1: Regress CO2 Henry's constants A and B. ID1 ID2 ID3 Estimation Lower bound Upper bound Henry_A 49 0 0 5 10 10 Henry_B 49 0 0 3000 3000 Example 2: Regress B0_A (Na+,Cl) for water and NaCl system. Component ID Sodium Chloride 473 Water 62 Species ID file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 85 of 89 H2O 1005 H+ 1002 OH 1004 NaCl 1206 Na+ 1198 Cl 1009 ID1 ID2 ID3 Estimation Lower bound Upper bound B0_A 1198 1009 0 0 -0.5 0.5 Note: ID3 is not used for Pitzer model. The Pitzer parameters are usually in the range of 0.5 to 0.5. Do not enter a lower or upper bound beyond the proper range. FOR THE MNRTL EQUATION: Tmca_A Tmca_B Tmca_C Aph_cam Tcam_A Tcam_B Tcam_C Tcaca_A Tcaca_B Tcaca_C Tacac_A Tacac_B Tacac_C Tmm_A Tmm_B Aph_mm Henry's Constants The parameters for the electrolyte reaction equilibrium T in the above variables stands for t in the MNRTL activity coefficient equations. See Section 12 of this help system for a full description of these equations. The subscripts m, c, and a stand for molecule (m), cation (c), and anion (a), respectively. The subscripts A, B, and C designate the BIPs themselves. Aph represents the non-randomness factors. Using this nomenclature, Tmca_A means the A BIP is used to calculate the t term representing the interactions between a molecule, a cation, and an anion. The t values are summed over all combinations and are computed as follows: {bmct IMG00491.bmp} Aph_cam represents the non-randomness factor for all the electrolyte interactions. The terms Tacac_A, Tacac_B, Tacac_C, Tcaca_A, Tcaca_B, and Tcaca_C, represent the t's for the anion-cation interactions. acac indicates a cation surrounded by anions (the MNRTL method uses a local composition model). caca is for anions surrounded by cations. A, B, and C are as indicated above. Therefore, Tacac_A represents the A BIP used to calculate the t term describing the interactions of a cation with two different anions. The Tmm_A, Tmm_B, and Aph_mm are the BIPs for the regular NRTL equation. They describe the interactions between two different molecules. The parameters A, B, C, D, and E for the electrolyte reaction equilibrium constant are exactly the same as those described for the Pitzer method above. The Henry’s Constants, A, B, C, and D, are as described above under Pitzer. The Procedure for Electrolytes Regression The electrolyte regression procedure is independent of the current flowsheet, and therefore the electrolyte chemistry and activity model selections must be made before the specific data input and regression procedures can be accessed. Therefore, the electrolytes regression procedure is as follows: 1. Select the Electrolytes option from the Util Menu off the Simulate Flowsheet Menu Bar. The Component Selection dialog box will appear. 2. Select the electrolyte and molecular species that are relevant to this regression from the databank. It is not necessary to select water since the program assumes it is present. The program will prompt you through this step, which functions in the same way an the normal component selection dialog box. 3. After selecting the species, the “Edit Electrolytes Input” menu will appear. At this point the program will have attempted to set up the electrolyte chemistry, select an appropriate activity model, and load any available data. The user now has the option to edit or add to anything the program has done. This process is described further below. 4. Upon exiting the Edit Electrolytes Input menu, CHEMCAD will take you to the “Electrolyte Data Regression” menu which has the following options: · Select Parameters · Input/Edit partial pressure data · Input/Edit TPXY data · Input/Edit TPX data · Input/Edit gamma data · Input/Edit solid solubility data · Input/Edit solution enthalpy data · Perform regression These options are described below: Select Parameters This screen is used to define exactly which parameters are to be calculated and from which type of data. If you already know the regular NRTL parameters, there may be no need to recalculate them. If you do not request that they be calculated, the program will fix them based upon the BIPs currently in the NRTL matrix. Likewise, you may want to fix one or more of the Keqs by specifying them on the electrolyte screens. In this case, you would want the program to use your values in the regression. The regression will calculate only those parameters identified in the Select Parameters dialog box. Different screens appear for Pitzer and MNRTL, whichever is the current selection. Each parameter to be calculated must be specified individually, line by line. Therefore, for each desired parameter, the user must specify: The parameter itself The component(s) involved in the interaction or reaction it is representing An estimate (optional) The upper and lower bounds (optional) Components are identified by their component ID numbers, not by their position in the stream list as in other BIP regressions. If Henry's constants are to be regressed, the ID1 must be entered as the component ID (NOT the species ID). If the MNRTL parameters are to be regressed and if the component exists in both component list and species list such as water, use the ID number in the file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 86 of 89 species list( NOT the component list). For example, use 1005 instead of 62 for water. Example: Regress Tmca_A and Tcam_A for water and NaCl system. Component ID Sodium Chloride 473 Water 62 Species ID H2O 1005 H+ 1002 OH 1004 NaCl 1206 Na+ 1198 Cl 1009 ID1 ID2 ID3 Estimation Lower bound Upper bound Tmca_A 1005 1198 1009 8 0. 15. Tcam_A 1198 1009 1005 4 15 0. Note: For Tmca, ID1 = m, ID2 = c, ID3 = a For Tcam, ID1 = c, ID2 = a, ID3 = m m = molecule; c = cation; a = anion The following table shows the suggested lower and upper bounds for some of the MNRTL parameters: Lower bound Upper bound Tmca_A 30. 30. Tcam_A 30. 30. Aph_cam 0.02 0.3 Tmca_B 3000. 3000. Tcam_B 3000. 3000. Tcaca_A 30. 30. Tcaca_B 3000 3000. Tacac_A 30. 30. Tacac_B 3000 3000. Tmm_A 10. 10. Tmm_B 3000 3000. Aph_mm 0.02 0.4 The reactions are identified by the order in which they were listed on the electrolytes screens. The second tab of the Select Parameters dialog box is where the user specifies which type of data is to be used in the analysis. Under the heading "Specify file name for each data set:" you will find a list of all types of data which can be regressed. Beside each item is a field which identifies the filename to be used to store the raw data. You must give a filename here if you are going to supply and/or regress this type of information. Please note the following: · CHEMCAD will not let you into the corresponding dialog box (on the Edit Electrolytes Input menu) if no filename is provided. · CHEMCAD is capable of including all these types of data in a single regression. If a field is left blank, CHEMCAD will not include that data set in the regression analysis. If a filename is given, CHEMCAD will look for the data in that filename and include that data in the regression analyses. Any combination of data types can be included in the analysis. With composition units, you can specify whether the data will be entered and stored in mole fractions or weight fractions. At the bottom of the screen, you can enter the maximum number of iterations, the relative tolerance, and the absolute tolerance for the analysis. Input/ partial pressure data This dialog box is used to input the partial pressure data. The variables input are: Weight factor This allows the user to give greater emphasis to some data points than to others. Temperature The temperature of the data in the displayed units. x1 ... xn-1 The liquid mole or weight fraction of all but the last of the components on the component list (not including those species from the electrolytes databank). P1 ... Pn The partial pressure of all the components in the system (excluding electrolyte species from the electrolytes databank). If the partial pressure of a component is unknown, enter zero as the partial pressure. Input/Edit TPXY data This dialog box is used to input the temperature-pressure-liquid fractions-vapor fractions data. The variables are: Weight factor - As above. Temperature - As above. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 87 of 89 x1 ... xn-1 - As above. y1 ... yn-1 - The vapor mole or weight fractions of all but the last component in the components list (not including species taken from the electrolytes database). Input/Edit TPX data This dialog box is used for input when only temperature-pressure-liquid fraction data are known. The program attempts to match the bubble point. The variables are: Weight factor - As above. Temperature - As above. x1 ... xn-1 - As above. Input/Edit Gamma Data This dialog box is used to input activity coefficient data. The program matches the gammas at the bubble point. The variables are: Weight factor - As above. Temperature - As above. x1 ... xn-1 - As above. g1 ...gn - These are the activity coefficients at T and x. Input/Edit Solid Solubility Data This dialog box is used to input the saturation solubility of solids. The program tries to match the x's at specified temperatures. The variables are: Weight factor - As above. Temperature - As above. x1 ... xn-1 - As above, but at saturation. Solids Flag 1 ...gn - This is the Component ID number of the solids components. Input/Edit Solution Enthalpy Data This dialog box is used to input the liquid enthalpies at specified compositions and temperatures. The program attempts to match the enthalpies. The variables are: Weight factor - As above. Temperature - As above. x1 ... xn-1 - As above. Enthalpy of the solution Perform regression This command executes the regression analysis based on the above input. Electrolyte Regression Example Electrolyte regression is a very time-consuming process. It may take several hours if the system and parameters are complicated. The following example shows the input procedure and some of the major input screens to regress NMRTL parameters and Henry's constants from the partial pressure data of the HCl/H2O system. 1. Select Thermophysical > Electrolytes > Electrolyte Regression. 2. Enter the component ID numbers for Hydrogen Chloride (104) and Water (62). 3. The system will automatically generate the following species list for the above components. Species ID Species 1005 H2O 1002 H+ 1004 OH 1017 HCl 1009 Cl 4. The edit electrolyte input menu pops up. You may edit the data if you wish. Select exit from the menu. 5. The electrolyte data regression menu pops up. Choose Select Parameters from the menu. Assuming the parameters to be regressed are: Tmca_A, Tcam_A, Aph_cam, Tmca_B, Tcam_B for H2O/H+/Cl molecule/cation/anion parameters. Tmm_A for H2O/HCl, HCl/H2O moleculemolecule parameters. Henry's constants A, B and C for HCl. Enter the data as the following table shows. Electrolyte Parameters Lower Upper Par type ID1 ID2 ID3 Estimation bound bound 1. Tmca_A 1005 1002 1009 10 50 2. Tcam_A 1002 1009 1005 -5 -50 3. Aph-Cam 1002 1009 1005 0.1 0.01 0.2 8. Henry-A 104 5 -20 20 9. Henry-B 104 -2000 -3000 3000 10. Henry_C 104 0.01 -3 3 23. Tmm_A 1005 1017 -5 -20 20 23. Tmm_A 1017 1005 10 -20 20 file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 88 of 89 4. Tmca_B 1005 1002 1009 -5000 5000 5. Tcam_B 1002 1009 1005 -5000 5000 Click the Page 2 tab and specify the file name for the partial pressure data set (PPHCL in this example). Use the weight fraction option as the composition unit. Set the maximum iterations to 3000 (1000 may not be enough). When finished, click OK to save the data and close the dialog box. Electrolyte Parameters Specify file name for each data set: Composition unit Partial pressure data set PPHCL Weight fractions TPXY data set Mole fractions TPX data set Mole fractions Reserved Mole fractions Gamma data set Mole fractions Solid solubility data set Mole fractions Reserved Mole fractions Solution enth. data set Mole fractions Solution density data set Mole fractions Max. iterations 3000 Relative tolerance 1e-005 Absolute tolerance 1e-005 Select "Input/Edit Partial Pressure Data" from the menu. Because HCl is defined as the first component in the component list, X1 will be the weight fraction of HCl. Enter the weight factor (1.), temperature, X1, partial pressure P1 for HCl and P2 for H2O. Partial Pressure Data Weight factor Temp C X1 P 1 atm P 2 atm 1 25 0.06 1.7237e-006 0.0286842 1 25 0.1 8.8158e-006 0.0263158 1 25 0.14 4.1579e-005 0.0236842 1 25 0.18 0.000194737 0.0202632 1 25 0.2 0.000421053 0.0185526 1 25 0.22 0.000894737 0.0165789 1 25 0.24 0.00196053 0.015 1 25 0.26 0.00421053 0.0130921 1 25 0.28 0.00927632 0.0115132 1 25 0.3 0.0198684 0.00989474 1 25 0.32 0.0427632 0.00838158 1 25 0.34 0.0901316 0.00703947 1 25 0.36 0.186842 0.00580263 1 25 0.38 0.364474 0.00473684 1 25 0.4 0.677632 0.00378947 1 50 0.06 2.1447e-005 0.113158 1 50 0.1 9.079e-005 0.105263 1 50 0.14 0.000361842 0.0947368 1 50 0.18 0.00146053 0.822369 1 50 0.2 0.0029079 0.075 When finished, click OK to save the data and close the dialog box. You will be returned to the regression menu. Select Perform Regression from the menu. The program will perform the regression and display the results on the screen. Reinitializing Streams When you see this message, it is recommended that you click Yes. This causes CHEMCAD to reflash all flowsheet streams with your new thermodynamic settings. Note that it may also result in different vapor-liquid equilibrium at streams. Clicking Yes does not run the simulation; it's recommended that you run file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018 The Standard Component Database Page 89 of 89 the simulation after reinitializing streams, to produce new results that match your new thermodynamic settings. If you click No, CHEMCAD does not reflash any flowsheet streams, nor does the simulation run. This leaves a mismatch between your new thermodynamic settings and the current stream data. CHEMCAD will flash the streams the next time you run the simulation. file:///C:/Users/t_ann/AppData/Local/Temp/~hhB512.htm 31/03/2018