Mass Transfer II - April 2000

Part A
  1. What are the advantages of distillation over absorption?
  2. Define the term relative volatility
  3. State Henry's law
  4. What is Murphree tray efficiency?
  5. What is meant by equilibrium distillation?
  6. What is absorption factor?
  7. What is molecular distillation?
  8. Sketch the operating line and equilibrium curve for an absorber and stripper
  9. What is meant by minimum liquid gas ratio?
  10. What is plait point?
  11. Explain percolation method of leaching?
  12. Define distribution coefficient and state its importance
  13. What is electrodialysis?
  14. What are the properties of solvent for extraction?
  15. What is ion retardation?
  16. Mention few industrial adsorbents
  17. What is adsorption hysteresis?
  18. Write the principle of ion-exchange
  19. What is meant by constant molal over flow?
  20. What is the role of Raoult's law in distillation?

    21. Part B
  21. (a) Write short notes on:

    (i) Azeotropic distillation

    (ii) Extractive distillation

    (iii) Rayleigh's equation

    Or

    (b) A binary mixture of benzene and toluene containing 40% of benzene is to be distilled at 1 atm pressure to recover 95% of the benzene. Estimate the molal percent of mixture to be distilled and the composition of the distillate obtained if distillation is carried out by

    (i) Equilibrium distillation

    (ii) Differential distillation, collecting all the distillate together.

    The average relative volatility of benzene to toluene is 2.5.

  22. (a) Explain in detail, the method of estimation of number of stages by Mc Cabe - Thiele method.
    23. Or

    (b) A continuous fractionator is to be designed for separating a feed mixture containing equimolar amounts of CCl4 and CS2 to get a top product containing 95% CS2 and bottom product containing 6% CS2 at 1 atm pressure. The feed is saturated vapor and fed at the rate of 5000 kg/hr. A total condenser is used and reflux is returned to the top plate as a saturated liquid. The equilibrium data is given below:

    x

    0.06

    0.11

    0.26

    0.39

    0.53

    0.66

    0.76

    0.86

    1

    y

    0.16

    0.27

    0.50

    0.63

    0.75

    0.83

    0.88

    0.93

    1

    (i) Determine the flow rate of top and bottom product

    (ii) Calculate the theoretical number of trays required if a reflux ratio of 2 times Rm is used.

    (iii) Locate the feed tray.

  23. (a) Derive an expression for the number of plates in terms of absorption factor.
    24. Or

    (b) The experimental data given below are obtained for the absorption of ammonia from air into water using a 2.5 cm diameter Rasching rings packed in a 25 cm diameter up to 2 m. The total pressure is 1 atm and the average temperature is 20oC. Air flow rate excluding ammonia is 105 m3/hr and the water flow rate is 400 kg/hr. Ammonia concentration in the gas inlet is 7% and in the outlet is 0.314%. The interfacial area of packing is 185 m2/m3. Partial pressure of ammonia at equilibrium with the solution at the bottom is 0.011 atm and at the top is zero/since pure water is used. Assuming that both equilibrium and operating line are straight, calculate:

    (i) Overall mass transfer coefficient for the system.

    (ii) The number of overall gas phase transfer unit.

    (iii) The height of overall gas phase transfer unit.

  24. (a) With neat sketch, explain the working of Bollman extractor.
    25. Or

    (b) An aqueous solution of solute C is to be extracted with pure solvent B to recover the solute. The equilibrium data in terms of weight % of solute in the two layers are given below:

    Aqueous layer

    2

    8

    15

    20

    Solvent layer

    8

    22

    35

    45

    A feed 20% by weight of solute is to be treated in two consecutive cross current cascades using aqueous solution to solvent ratio of 1.8. Calculate:

    (i) Concentration of final raffinate

    (ii) Amount of raffinate

    (iii) % recovery of solute

    (iv) Amount of solvent to be used for a single stage extraction to obtain the same final concentration.

    Water and solvent are immiscible with each other.

  25. (a) Write short notes on:

    (i) Electrodialysis

    (ii) Ultrafiltration

    (iii) Reverse osmosis

    Or

    (b) The equilibrium absorption of acetone vapor on activated carbon at 30oC is given below:

    Acetone partial pressure, in mm Hg

    2

    12

    42

    92

    Gram acetone/Gram carbon

    0.1

    0.2

    0.3

    0.35

    The vapor pressure of acetone at 30oC is 283 mm Hg. A one litre flask containing air and acetone mixture at 1 atm is fed with 2 gram of activated carbon and then sealed. Compute the final vapor concentration and the final pressure. Neglect the adsorption of air.


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