7HC - Mass Transfer II - October 1999

Part A (20 x 2 = 40 Marks)

  1. What is distillation?
  2. What are the limitations of distillation?
  3. Derive the expression y = ax/(1+(a-1)x)
  4. Explain Flash Vaporisation.
  5. Explain the term total reflux.
  6. What is the use of open steam and how to calculate the number of stages in case of open steam
  7. Define molecular distillation.
  8. What is the use of entrainer in azeotropic distillation?
  9. What is meant by desorption?
  10. Define the term Minimum Reflux ratio.
  11. Give the Vont Hoffs law of mobile equilibrium.
  12. Define flooding and loading in an absorber.
  13. Define the term leaching and extraction.
  14. What is distribution law?
  15. Explain the use of triangular graph for extraction.
  16. What are the different types of adsorption?
  17. Explain the process of Ion exchange.
  18. Define selectivity and distribution coefficient.
  19. Define Thermal and sweep diffusion.
  20. What are the various types of dialysis?

    Part B (5 x 12 = 60 Marks

  21. (a) (i) Explain the process of differential distillation.

    (ii) Derive Rayleigh's equation.

    (iii) Differentiate between flash and differential distillation.

    Or

    (b) A liquid feed consisting of 1200 g moles of mixture containing 30% naphthalene and 70% dipropylene glycol is differentially distilled at 100mm 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

    (i) Determine the amount of distillate

    (ii) Determine the concentration of naphthalene in residue and distillate

  22. (a) Explain the method of estimation of number of stages by Panchon-Savarit method
    Or

    (b) A continuous fractionating column has to be designed for separating a liquid mixture of 4050 kg/hr containing equimolar amounts of methanol and water into an overhead product of 95% methanol and residue containing 3% methanol. The feed is 30% vaporised. Calculate:

    (i) Molar flow rate of overhead and bottom products

    (ii) The number of actual plates assuming tray efficiency of 0.7

    (iii) Use a reflux ratio of 1.75 times the minimum reflux, locate the feed tray

    Equilibrium data:

    x

    0.1

    0.2

    0.3

    0.4

    0.5

    0.6

    0.7

    0.8

    0.9

    y

    0.417

    0.579

    0.669

    0.729

    0.78

    0.825

    0.879

    0.915

    0.959

  23. (a) Explain how the number of stages can be theoretically determined for an absorber
    Or

    (b) An effluent gas containing 12% benzene is to be scrubbed in a packed column continuously, operating in countercurrent manner at 43oC and 1 atm pressure. The column is to be designed for treating 15 m3 of entering gas per hour per square meter of the column cross section, such that the exit gas will contain 1% benzene. The solvent for scrubbing is mineral oil which will enter the top of the column at a rate of 28 kmol/hr.m2 and a benzene content of 1%. Determine the height of the column assuming height of transfer unit to be 0.75 m. The equilibrium concentration at the operating conditions may be estimated as y* = 0.263 x.

  24. (a) Explain how the number of stages can be determined for immiscible solvents in cross current extraction.
    Or

    (b) In extraction of acetic acid from an aqueous solution with benzene in a packed column of height 1.4 m and cross sectional area of 0.0045 m2, the concentration measured at the inlet and outlet of the column are:

    Acid concentration in inlet water phase = 0.690 kmol/m3

    Acid concentration in outlet water phase = 0.685 kmol/m3

    Inlet benzene phase concentration = 0.004 kmol/m3

    Outlet benzene phase concentration = 0.0115 kmol/m3

    Flow rate of benzene phase = 5.7 cm3/sec

    Determine the overall transfer coefficient and height of transfer unit.

  25. (a) A solid adsorbent is used to remove the color impurities from an aqueous solution. The original value of color on an arbitrary scale is 48. It is required to reduce this value to 10% of its original value. Using the following data find the quantity of fresh adsorbent used for 1000 kg of a solution for

    (i) Single stage

    (ii) Two stage cross current operating with the intermediate color value of 24.

    Equilibrium data:

    kg adsorbent/kg solution

    0

    0.001

    0.004

    0.008

    0.02

    0.04

    Equilibrium color

    48

    43

    31.5

    21.5

    8.5

    3.5

    Or

    (b) Write short notes on:

    (i) BET isotherm

    (ii) Gas chromatography

    (iii) Membrane separation process


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