ABSTRACTGas diffusion occurred when diffusion of vapor takes place from volatile liquid(organic solvent) into another gas (air). This process used same concept as mass transfer where one constituent is transported from region of higher concentration to that of a lower concentration. In this experiment, acetone is used as the organic solvent. Unit operation that used during experiment is theGas Diffusion Coefficient Apparatus (Model: BP 10).The objective of experiment is to find out the gas diffusion coefficient, D of acetone in the air by using Winkleman’s method.This experiment is conducted at a temperature of 50ºC and atmospheric pressure. The level of acetone, L is determined every 30 minutes by using a microscope with mounted sliding vernier scale alongside the thermostatic tank. A horizontal glass tube is fixed to the upper end of capillary tube and air is drawn through this by small air pump included within the unit. This arrangement allows maintenance of partial pressure difference within capillary tube between evaporating liquid surface and flowing air stream.With the level of acetone being determined, a graph oft/L+Lo (min /mm) against L-Lo (mm) is plotted and the gradient, s of the graph can be determined. With the gradient of the graph s, the diffusion coefficient, D of the experiment can be calculated by applying some mathematical derivation. Antoine equation is used to determine the partial pressure of acetone. From the resultvalue of diffusion coefficient, D calculated to be 3.937 x 102 m2/s. Several errors are made in this experiment which causes the value of diffusion coefficient todeviate which will be discussed later in discussion section. 1 3 3.0 Theory…………………………………………………………………………………4-5 4.3 Original Data Sheets…………………………………………………….6-7 5.0 Experimental Procedures………………………………………………………………7-8 6.0 Result and Discussion………………………………………………………………8-11 7.17 2 ..15 Table of Antoine Equation Constant…………………………………….0 Sample Calculation…………………………………………………………………..1 10.0 Objectives………………………………………………………………………………..TABLE OF CONTENTS Abstract …………………………………………………………………………………………..0 Conclusions and Recommendations…………………………………………………… 14 9.12-13 8.0 References ………………………………………………………………………………14 10.0 Diagram and Description of Apparatus……………………………………………….0 Introduction……………………………………………………………………………… 3 2.. 1 Table of Contents……………………………………………………………………………….2 10.0 Appendices …………………………………………………………………....16 Table of Selected Physical Property Data………………………………..14 10.. 2 1.. The transfer of the molecule through the fluid by a random molecular is called molecular diffusion. Besides that . Then .0 INTRODUCTION In process engineering . With the knowledge of that. 2.1. to investigate the relationship between time interval and the level of the acetone. The diffusivity of the vapour of a volatile liquid can be determined using Winkelmann’s method in which the liquid is contained in a vertical glass tube over the top of which stream of vapour – free gas is passed is allowed to evaporate. One such property is diffusivity. to calculate the diffusion coefficient. A water bath is provided for maintaining a steady temperature to make sure there are no eddy current in the narrow diameter vertical tube and an air stream is passed over the top of the tube to ensure that the partial pressure of the vapour transferred from the surface of the liquid to the air stream by the molecular diffusion.0 OBJECTIVES The experiment is conducted to determine the gas diffusion coefficient of acetone using established Winkelmann’s method. 3 . The mass transfer by diffusion take place when there is concentration gradient of the diffusing component. Mass transfer coefficient can be estimated from the theoretical equation . and analogies that are function of that materials properties. the diffusivity of the vapour of the volatile liquid can be calculated. correlations . determine the mass transfer equation using a Fick’s Law with a bulk flow. The travelling telescope is provided for the determining. Lastly . the knowledge of physical and chemical properties of a certain material is important because the process deal with the transformation and distribution of these materials in bulk. the partial pressure gradient and diffusion coefficiect D is deduced from the one dimensional steady state version of Fick’s Law with bulk flow(3) : N’A = D (A) : CA and CB are the molar concentration of the vapour A and air B respectively. The apparatus consist of a glass capillary tube place in a transparent – sided temperature controlled water bath. Where : D = diffusivity [ ] CA = saturation concentration of mass transfer at the interface [ L = effective distance of mass transfer [m] 4 ] . Normally .3. A horizontal glass tube is fixed to the upper end of the capillary tube and air is blown through the small pump included within the unit. is mounted on a rigid stand alongside the thermostatic bath and is used to measure t inthe rate of fall of the air meniscus within capillary. A travelling microscope with sliding vernier scale .0 THEORY The diffusivity of the vapour of the acetone in this experiment can be determined by the Winkelmann’s method. The relationship between the measured molar mass rate ( ‘NA’ per unit area) . Mass transfer take place in either a gas phase or a liquid phase or in both simultaneously. B is air and A is an organic solvent such as acetone. The diffusion of vapour A from the volatile liquid into another gas B can be conveniently studied by confining a small sample of the liquid in a narrow vertical tube. pL = density of liquid [ M = molecular weight [ ] Combination of equation A and B : ( =D( )( ) The L0 is at t = 0.CT = total molar concentration ] CBM = logarithmic mean value of CB [ ] Evaporation of the liquid : N’A = (B) Where . the slope of plotting the graph of S=( )( ) The diffusivity : D= 5 against ( L – L0 ): . In water bath tank.4. capillary tube. there are some additional parts that help this experiment works such as heater W1. air pump and travelling telescope. temperature sensor. the T-shape vertical capillary tube is used with the air pump which has been attached to the one end of the T-Tube.0 DIAGRAM AND DESCRIPTION OF APPARATUS The SOLTEQ Gaseous Diffusion Coefficient Apparatus consists of water bath tank. The purpose of heater W1 is to heat up the water in the water bath to the temperature desired. Temperature controller is about controlling the temperature following the experimental temperature and water bath itself can maintain a steady temperature so that there is no eddy current in the vertical tube and mass transfer takes place from the surface by molecular diffusion alone. The travelling telescope equipped with a vernier scale is used to measure the level of the acetone meniscus within the capillary 6 . Temperature sensor is to measure the temperature by correlating the resistance of the element with the temperature. temperature controller and level switch. Next. The purpose is to allow the maintenance of a partial pressure difference within the capillary tube between the evaporating liquid surface and the flowing air stream. The water temperature was observed till it heats up to 50oC and remains constant. The main power on the control panel was switched on. 5. 4. The set-point value on the temperature controller was adjusted to 50oC.0 EXPERIMENTAL PROCEDURES 1. The capillary tube was carefully inserted through the fitting on top of the water bath cover. 2.FIGURE 1 5. 3. The heater was switched on. 7 . The capillary tube was cleaned up and partially filled with acetone to a depth about 30mm. The water bath was filled with filtered water to approximately 20mm from the top. 6. 9.L (mm) 60.1 58. t (min) 0 30 60 90 120 Level of Acetone. dL (mm) 0 1.01 5.3 55. The initial level of acetone was observed through the telescope.8 3. the air pump was switched off.2 L-LO.89 5.7. 6.8 4. After 30 minutes.52 Table 2: Calculated Data Table for Gaseous Diffusion Experiment Time.t (ks) 0 1.469 .2 3. The flexible tubing from the air pump line was connected to one end of the capillary tube.2 Level of Acetone.161 1.0 RESULTS AND DISCUSSIONS 6.500 1. The other end of the capillary tube was covered with a finger.421 1.70 5.9 8 t/dL (ks/mm) 0 1.0 56. L (cm) 6.6 5.1 RESULTS Table 1: Raw Data Table for Gaseous Diffusion Experiment Time. Step 9 was repeated at 30 minutes intervals. 10. the pump was switched on. 8. The level of acetone was observed and recorded.1 3.63 5.9 57. Then.4 7. 5019 1. 6. The partial pressure that obtained from the Antoine equation is PA1 is 9.6 1. Normally. the level of acetone was decreased when the time was increased caused by diffusion.4 0.6 0.902 kPa.5199 R² = 0. The gas diffusivity of the gas is 3.Graph t/dL versus dL 1.227x + 0.8 y = 0.937x102 m2/s.227. the volatile liquid is heated until it evaporated into free air stream.8 Linear (t/dL (ks/mm)) 0.352 kPa and PA2 is 81. the movement of molecule is from high concentration part to more less concentration gradient.2 DISCUSSION The objective of the gaseous diffusion experiment is to determine the gas diffusion coefficient of acetone using the Winkelmann’s method. In this experiment.2 0 0 1 2 3 4 5 6 FIGURE 2: Graph t/dL versus dL The slope of the graph is 0.4 1. Diffusion is process where involving the movement of component or molecules from one location to another location due to exist of concentration gradient.2 1 t/dL (ks/mm) 0. 9 . Based on the result. The rate of diffusion can be observed by the rate of decreasing of acetone level in the tube by using a telescope. The +1 means the perfect positive relationship where one variable increase another variable also increases.5019.5019. 10 . the y-axis of the graph is the time taken divide by the difference between the levels of acetone. The significance of this value is to show or to measure the strength of the straight line or linear relationship between two variables. In the experiment.227x + 0. This values usually ranging between -1 until +1. where the slope of the graph is 0. due to some driving forces and existing of concentration gradient.5199. it showed the Correlation coefficient R2 value is 0. the increasing the time divide by the difference between the levels of acetone. The boiling process of water was generated heat and the heat was transferred to the acetone. the x-axis of the graph is the differences between final level of acetone and the initial level of acetone.In the experiment. the molecule was move from inside the capillary tube to the surrounding air that has less concentration. Furthermore. From the calculation and the data from the table. the value of diffusivity was determined which is 3. -1 means the perfect negative relationship where one variable increase the another variable is decreasing. Based from the graph also. Meanwhile.227 in positive value. the diffusion concept can be observed by the decreasing of acetone level in the capillary tube. In addition. Based on the graph that has been plotted. This process was increased the movement of molecules in the acetone until it createsbody that has high concentration compare to surrounding. The increasing the difference between the levels of acetone. means that the relationship of the graph is moderate positive linear relationship. The equation that obtained from the graph is y=0. the trend of the graph is increased proportionally. the obtained value is 0. Meanwhile.937 x 102m2/s. the temperature controller was set up at 50. This situation can cause the problem to the experimenter to collect the data or difference of acetone level.0 ºC through along the experiment and it not been set beyond 70. the concentration of the substance is also increasing. the discrepancy from the experimental data is the value of the time divide by difference between levels of acetone between intervals is not increased constantly due to some errors such as parallax error and the initial value of the acetone in the capillary tube was not read accurately. Finally. When the partial pressure of the substance is increase. Moreover. the rate of evaporation is faster compare to temperature at the boiling point. It is because the boiling point of the acetone is at 56.0 ºC where the process where the phase of acetone change from liquid to vapor.0 ºC. P is partial pressure.The Antoine equation was used in the calculation in order to determine the partial pressure and the concentration. When the temperature exceeds 70.0 ºC. 11 . R is gas constant and T is the temperature. The relationship between the partial pressure and the concentration is directly proportional: Where the C is the concentration. 0305 12 .08 kg / mol Temperature. Absolute at 0 C = 273 K Water at 50 C = 323 K CT =CA1 + CB1 CT = CA2 + CB2 CA2 = = =C For of acetone at 50 oC .902 kPa At absolute temperature. Log10 PA2 = 7.0 SAMPLE CALCULATION Value of slope = 0.316 mmHg PA2 = 81.11714 PA2 = 614. A = 7.595 C = 229.352 kPa CA2 = = = 0.664 Log10 PA2= A Log10 PA2 = 7.Antoine Equation .7.143 mmHg PA2 = 9.11714 B = 1210.227 Molecular Weight of Acetone = 58.11714 PA1 = 70. 937 x 102 x x = 2.CTOTAL = = = 0.0377 CA2 0.0072 CA1 = 0.0305 = 0.0377 CB2 = CT = 0.937 x 102 N’A = D(CA/L)(CT/CBM) = 3.00412 CB1 = 0.0 x 103 13 .03357 CBM = CA= CA1 + CA2 D = = ( ) ( ) ( ) = 3. Retrieved June 8.0 CONCLUSION AND RECOMMENDATIONS Overall.0 APPENDICES 14 . The molecules moves from capillary tube to surrounding air due to driving forces. Secondly. at the time interval where the readings of acetone is being recorded.uk/data/cer 10. As the acetone evaporates into surrounding air the vapor concentration slowly decreased from high to low concentration.co.discoveramfield. 2013. Semester June-October 2013.mendeley.diffusion coefficient.ion. Based on the result.0 REFERENCES (1) Chemical Engineering Laboratory Manual. (2) Determination of gaseous diffusion. Retrieved June 8.d.8. every experimenter must make sure to avoid parallax error while taken the readings of level of acetone from the vernier scale because it will deviate the data and results calculated at the end of experiment. (n. the amount of acetone used should be pipette and closed from surrounding before it is drop into the capillary tube so that it will not alter the accuracy of the results. There are some recommendations for future used firstly.). experimenter must use the cap provided instead of fingers to close the end of capillary tube and the flexible tubing.com/.). from http://www. gas (3) Mass Transfer and Diffusion Coefficients. the level of acetone decreased as the time increased caused by diffusion. By using Winkelmann’s method the gas diffusion coefficient of acetone was determined. Lastly. 2013. 9.d. from http://www. the experiment produces results agreeing to theory. (n. 15 . 16 . 17 .