UNIVERSITITEKNOLOGì P ETRONAS FINAL EXAMINATION SEPTEM BER 2012 SEM ESTER COURSE : CCB2053 MASS TRANSFER DESIGN DATE TIME 29th DECEMBER 2012 (SATURDAY) : : 9.00 AM - 12.00 NOON (3 HOURS) INSTRUCTIONS TO CANDIDATES 1. 2. 3. 4. Answer ALL questions from the Questions Booklet. Begin EACH answer on a new page in the Answer Booklet. lndicate clearly answers that are cancelled, if any. Where applicable, show clearly steps taken in arriving at the solutions and indicate ALL assumptions. 5. 6. Do not open this Question Booklet until instructed. Engineering Data Formulae Booklet is provided. Note : There are ELEVEN (11) pages in this Question Booklet including the cover page and Appendix. Universiti Teknologi PETRONAS Calculate the flux of NH3 in kgmol/s. [4 marks] b. ì.066 atm. a. [3 marks] . Ammonia (NHs) gas is diffused through a layer of nitrogen (N2) gas at 298 K and 1 atm pressure. Repeat part (i) assuming Nz also diffuses and the flux eq is uimolar cou nterdiffusion. [3 marks] iii. The diffusivity of the mixture is 2. Explain TWO (2') types of mass transfer and gives TWO (2) examples for each type of mass transfer.133 atm and at the other point 20 mm away it is 0. Based on the mass flux obtained in part (i) and (ii).30 x 10-5 m2ls. The partial pressure of ammonia at one point is 0.m2 with non-diffusing Nz at one boundary. which conditions give the highest flux? Explain your answer.CCB 2053 1. [4 marks] ii. F zi TF Pf L xi TL P. FIGURE Q1: Adibatic Equilibrium Flash Separator Compute the degrees of freedom using the Gibbs phase rule. indicates all variables in each stream.CCB 2053 FIGURE Q1 shows an adiabatic equilibrium flash separator which c. [3 marks] il What variables might be specified to solve the above problem? [3 marks] . 5 1.08 55.80 80.00 89.85 78.7 39.1 89.22 79.75 84 1 16.7 23.99 78. TABLE Q3: Equilibrium data of ethanol in ethanol-water system Temperature Molpercent of Molpercent of ("c) ethanol in the liquid ethanol in the gas phase.65 61. Equilibrium data for ethanolwater system at 1 atm are given in TABLE e3.43 78.66 43.0 0.00 100. y 100.43 89.3 100. A continuous distillation column operating at 1 atm is to be designed for separating an ethanol-water mixture.00 95. Give THREE (3) reasons why an economic tradeoff exists between the number of trays and the reflux ratio.00 0.89 82.63 73.ccB2053 a. The feed is 20 mol% ethanol and the feed flow rate is 1000 kgmol/h of saturated liquid.37 54.0 7.00 .98 65.91 86. The reflux ratio is 5/3. A distillate composition of 80 mol% ethanol and bottoms composition of not more than 2 mol% ethanol is desired.7 51.7 9.7 67. [3 marks] b.21 38.45 82. x phase.3 26.90 17.6't 50. determinethe number of theoretical stages required. [3 marks] iv. [4 marks] . calculate the amount of distillate and bottom products in kgmol/h. By using the graphical McCab-e-Thiele method. lf the feed condition changes to saturated vapour condition. [4 marks] ii. [6 marks] iii.ccB2053 i. Estimate the minimum reflux ratio. discuss the differences in the number of theoretical stages. CCB 2053 Using a suitable diagram.68x for this dilute stream.3 kPa. Determine the HETP for the above absorption proÇess. [4 marks] A packed tower 4. ill y'/. Justify your answers. [4 marks] I Using the analytical equations.a moP/o alcohot and the exit concentration is 0. Show the relationship between the number of theoretical trays obtained ín part (ii) and the number of transfer unit obtained in part (iii) by using suitable graphical explanation. [4 marks] tv. Calculate the mol fraction of ethyl alcohol in the exít liquid. The equilibrium relation is y i. calculate the theoretical trays. The total gas stream flowrate of 100 kgmol/h contains 2. : mx : 0.20 mol%. show the operating line for minimum liquid a.0 m tall is used to absorb ethyl alcohol from an b. flow of absorption process and the operating line for minimum gas flow of a stripping process. [4 marks] . inert gas by 90 kgmol/h of pure water at 303K and 101. 30 45.1 16.5 1.5 45. a ln general.3 97.2 0.3 25. The exit acid concentration in the aqueous phase is to contain 3 wt% acetic acid.41 wt%(A) wt%(W) wt%(E) 1.4 2.water (W).30 84. The riquid-riquid equilibrium data at 25oC and 1 atm are presented in TABLE e4. An aqueous feed of 200 kg/h containing 25 wt% acetic acid is being extracted by pure isopropyl ether at the rate of 600 kg/h in a counter-current multistage system.93 1.4 58.79 1.7 .5 11.6 46.3 4.42 91.8 98.5 0.70 58.60 31.5 99.1 1.isoproppyl ether (E) system at2SoC and 1 atm.2 0 0. TABLE Q4: Liquid-liquid equilibrium data for acetic acid (A).4 6. [2 marks] ¡i.1 1.9 4.20 10.7 98.50 71.37 0.6 0. [2 marks] b. Define the liquid-liquid extraction process and its importance I over distillation.1 48.1 13.7 36.89 95.69 98.4 6.6 0. state TWo (2) requirements for liquid-liquid extraction to be feasible. Water layer lsopropyl ether layer wt%(A) wt%(W) wt%(E) 0 98.18 0.9 0.40 37.40 21.9 93.4 3.1 99. extraction Ìs preferred over distillation for certain applications.9 1.1 9.1 3.9 84.9 71.7 1.0 97.9 2.82 1.8 15.CCB 2053 4.10 36. & . The leaching process is in the condition of constant underflow of N = 1. v¡. d. Plot the equilibrium data on a Ponchon-savarit diagram using the graph paper provided. usíng the graph in part (a). a. oír.CCB 2053 5. leaving the stream. calculate the amount of underflow slurry. ãtrd in the oveúlow. A continuous countercurrent multistage system is to be used to leach oil from a meal by benzene solvent.85 kg solid/kg solution. The leached solids are to contain ea kg oil. [4 marks] b. determine the weight fraction of leaving the stream. -END OF PAPER- I . The process is to treat 2000 kg/h of an inert solid meal (B) containing 800 kg oil (A) and also 50 kg benzene (c). L¡¡. Determine the number of stages required for the process. y¡¡y [4 marks] c. The inert flow per hour in the fresh solvent mixture contains 1310 kg benzene and 20 kg oil. (l-!o.R l'-_-r+_ ' R+l 4.-...mol EquatÍons: 1."?u--)ráls ADSorPIlon Absorption ractor i -'re ris )lwhere Y..145 cm3 barlK. General diffusion and convection No: "= Jo -cD*+..9o(*^+trr) azc D ulP n' . - InA 10 A¡. R. Absorption material balance: (constant molar flow) v ( -z'): t( {f +-)* .' l+.-_t- d* f' r ^=y-x L2 J.) 6. 3..) [l-r.qt tY . KremserEquation nl ¡¡ : I : lt t.055 cm3 atm/K. non-diffusing B (total pressure constant) : DnuP Àr " --ln RT(2.r. : :t- ffirV r.p 'l) RT(r.. ntr.-l l. 5.) Flux for equimolarcounter diffusion 2.0. T(K) = tf C) + Zts 1 atm = 760 torr = 101325 Pa = 8314 m3Pa /kg 'K'mol = 83. . . Rayleigh: 'idL: ln L' xD Jr R+l .9869 atm 1 liter = 1 dm3= 1O0O cm3 = 82..CCB 2053 APPENDIX Constants Conversion factors Gas constants.J lt.-l . Stagnant.-Zt) P-p.y.mol l bar = 1OsPa = 0. Rectifying operating line: . .CCB 2053 t'oc _ - ^/ ln{l(t -l) t All0. absorb "O: ffi 8.18-ffi 11 ...... i.kxi.. Fuller equation: lo'r'trs(l lMrrllM)'') /r _ u.kx.)l+ (t¡ l)} 7. . Extraction: Fraction of a solute. .y(y.