MASS TRANSFER AND SEPARATION Question Papers (Regular, November 2007, RR)

SET :1
1. Develop expressions for the estimation of flux in Gaseous systems for ‘A’ through stagnant ‘B’. [16]

2. (a) Distinguish between Eddy and Molecular Diffusion?
(b) Explain Penetration Theory versus Two Film Theory? [8+8]

3. A solution of CCl4 and CS2 containing 50% wt each is to be continuously fractionated at 1 atm at the rate of 4000 kg/hr. Distillate product is to contain 95% wt CS2 and residue 0.5%. The feed will be 30% mole vapourised before it enters the tower. Total condenser will be used and reflux returned at bubble point. Determine
(a) Product rates.
(b) Theoretical trays for a reflux ratio of twice the minimum. The equilibrium data is as follows. [8+8]
X 0.11 0.26 0.39 0.53 0.66 0.76 0.86
Y 0.27 0.49 0.63 0.75 0.83 0.88 0.93

4. A Blend of 50% Toluene liquid and 50% Benzene liquid volume is being separated by fractionation into an over head product that has 10 mole percent Toluene and a bottom product that has 0.5 mole percent Benzene. The blend is fractionated at the rate of 10000 gal/day. How many gallons of each product is produced, if the reflux ratio is 4. A sample of vapour from one of the trays above the feed tray was taken and found to contain 20% Toluene. What was the composition of the liquid from the tray along the point of which the sample of vapour was taken? [16]

5. Explain the terms constant and variable under flow conditions? [16]

6. Explain the method of leaching vegetable oil seeds for extraction of Oil? [16]

7. Explain multistage counter current adsorption. Give some applications. [10+6]

8. (a) Explain types of flow in gas permeation.
(b) In what way pervaporation is different from other membrane separations, explain. [8+8]


SET :2

1. Obtain an expression for the steady state Equimolal counter diffusion of two gases starting from fundamentals? [16]

2. It is desired to estimate the mass transfer coefficient KG in kg mol/m2s p.a for water vapour in air at 338.6 k and 101.32 Kpa flowing in a large duct past different geometry solids. The velocity of the duct is 3.66 m/s. The water vapour concentration in the air is transferred to the solids. Do this for the following geometries.
(a) A single 25.4 mm - diameter sphere.
(b) A packed bed of 25.4 mm sphere with ε = 0.35 [8+8]

3. A liquid feed consisting of 1200 kg moles of mixture containing 30% Naphthalene and 70% Dipropylene Glycol is differentially distilled at 100 mm Hg pressure and final distillate contains 55% of Naphthalene. The VLE data are
X 8.4 11.6 2.8 50.6 68.7 80.6 88
Y 22.3 41.1 62.9 74.8 80.2 84.4 88
(a) Determine the amount of distillate.
(b) Determine the concentration of Naphthalene in residue and distillate? [8+8]

4. A rectification column is fed 100 kg mol/h of a mixture of 50 mol% Benzene and 50 mol% Toluene at 101.32 Kpa abs pressure. The feed is liquid at the boiling point. The distillate is to contain 90 mol% Benzene and the bottoms 10 mol% Benzene. The reflux ratio is 4.52:1. Calculate the kg mol/h distillate, kg mol/h bottoms and the number of theoretical trays needed using Mc Cabe Thiele Method. [16]

5. (a) What is a plait point?
(b) Draw the flow diagram for continuous counter current multistage extraction operation. [6+10]

6. Seeds containing 20 percent by weight of oil are extracted in a counter current plant and 90 percent of the oil is recovered in a solution containing 50 percent by weight of oil. If the seeds are extracted with fresh solvent and 1 kg of solution is removed in the underflow in association with every 2 kg of insoluble matter, how many ideal stages are required? [16]

7. (a) Explain in detail break through curve and its significance?
(b) Indicate how rate of adsorption in fixed beds is estimated. [8+8]

8. Explain the Ultrafiltration, microfiltration and Reverse Osmosis with examples. [4+4+4+4]


SET :3

1. Obtain an expression for the steady state Equimolal counter diffusion of two gases starting from fundamentals? [16]

2. (a) Distinguish between Eddy and Molecular Diffusion?
(b) Explain Penetration Theory versus Two Film Theory? [8+8]

3. A solution of CCl4 and CS2 containing 50% wt each is to be continuously fractionated at 1 atm at the rate of 4000 kg/hr. Distillate product is to contain 95% wt CS2 and residue 0.5%. The feed will be 30% mole vapourised before it enters the tower. Total condenser will be used and reflux returned at bubble point. Determine
(a) Product rates.
(b) Theoretical trays for a reflux ratio of twice the minimum. The equilibrium data is as follows. [8+8]
X 0.11 0.26 0.39 0.53 0.66 0.76 0.86
Y 0.27 0.49 0.63 0.75 0.83 0.88 0.93

4. A rectification column is fed 100 kg mol/h of a mixture of 50 mol% Benzene and 50 mol% Toluene at 101.32 Kpa abs pressure. The feed is liquid at the boiling point. The distillate is to contain 90 mol% Benzene and the bottoms 10 mol% Benzene. The reflux ratio is 4.52:1. Calculate the kg mol/h distillate, kg mol/h bottoms and the number of theoretical trays needed using Mc Cabe Thiele Method. [16]

5. With the help of neat sketches, explain briefly the various types of commercial extraction equipment. [16]

6. Soyabean flakes containing 22 wt% oil are to be leached in a counter current multistage to contain 0.8 kg oil/ 100 kg inert solid. Using fresh and pure hexane solvent.For every 1000 kg soyabeans, 1000 kg Hexane is used. Experiments give the following retention of solution with the solids in the underflow, where N is kg inertsolid/ kg solution retained and YA is wt. fraction of oil in solution.
N 1.73 1.52 1.43
YA 0 0.20 0.30
Calculate the exit flows and compositions and the number of theoretical stages required? [16]

7. Explain Freundlich equation and its application. Explain fixed bed adsorption? [8+8=16]
8. A liquid containing solute A at a concentration C1 = 3 ×10−2 kg mol/m3 is flowing rapidly by a membrane of thickness L=3.0×10−5 m. The distribution coefficient K′=1.5 and DAB = 7.0×10−11m2/s in the membrane. The solute diffuses through the membrane and its concentration on the other side is C2 = 0.50×10−2kgmol/m3. The mass transfer coefficient KC1 is large and can be considered as infinite and KC2=2.02 ×10−5 kmol/m2s mol fraction. Calculate the flux and the concentrations at the membrane interfaces? [16]


SET :4

1. Obtain an expression for the steady state Equimolal counter diffusion of two gases starting from fundamentals? [16]

2. (a) Distinguish between Eddy and Molecular Diffusion?
(b) Explain Penetration Theory versus Two Film Theory? [8+8]
3. An equimolar mixture of A and B is flash distilled such that 65% of the feed is in product distillate of the total moles fed. Compute the composition of the distillate and residue. Vapour liquid equilibrium data is as follows.
X (mole) % 8 10 20 30 40 50 70 80 95
Y (mole) % 37 42 58 67 73 78 87 96 98
x and y represent the composition of A in liquid and vapour phase respectively.[16]

4. A Methanol - water solution containing 36 mole% Methanol at 26.70C is to be continuously rectified at 1 std atmosphere at a rate of 5000 kg/hr to provide distillate containing 91.5 mole% Methanol and a residue containing 99.5 mole% of water. The feed is introduced at its boiling point. The distillation is totally condensed and the reflux is returned at its bubble point. A reflux ratio of 1.5 times the minimum is used. Determine using enthalpy-concentration diagram.
(a) Quantity of products in kg/hr.
(b) Minimum Reflux ratio.
(c) Number of Ideal Plates.
Mole fraction Enthalpies Saturated liquid KJ/Kmol Saturated Vapour
0 8000 48000
1 7500 39000


Mole% of Methanol in liquid X 4 10 20 30 40 50 60 70 80 90 95
Mole%ofMethanol invapour Y 23 42 58 66 73 78 82 87 91 96 98
[5+5+6]

5. A 25% (weight%) solution of dioxane in water is to be continuously extracted in counter current fashion with Benzene to remove 95% of the dioxane in feed. If the feed rate is 1000 kg/hr estimate the
(a) Minimum solvent required and
(b) Theoretical stages needed if 900 kg/hr of solvent is used
Wt% Dioxane in water 5.1 18.9 25.2
Wt% Dioxane in Benzene 5.2 22.5 32.0[8+8]

6. Seeds containing 20 percent by weight of oil are extracted in a counter current plant and 90 percent of the oil is recovered in a solution containing 50 percent by weight of oil. If the seeds are extracted with fresh solvent and 1 kg of solution is removed in the underflow in association with every 2 kg of insoluble matter, how many ideal stages are required? [16]

7. (a) Explain in detail break through curve and its significance?
(b) Indicate how rate of adsorption in fixed beds is estimated. [8+8]

8. A liquid containing solute A at a concentration C1 = 3 ×10−2 kg mol/m3 is flowing rapidly by a membrane of thickness L=3.0×10−5 m. The distribution coefficient K′=1.5 and DAB = 7.0×10−11m2/s in the membrane. The solute diffuses through the membrane and its concentration on the other side is C2 = 0.50×10−2kgmol/m3. The mass transfer coefficient KC1 is large and can be considered as infinite and KC2=2.02 ×10−5 kmol/m2s mol fraction. Calculate the flux and the concentrations at the membrane interfaces? [16]