Mass Transfer II - October1998
Part A(20 X 2 = 40)
Part B(5 X 12 = 60)
(ii) Describe with a neat sketch the working of a batch distillation unit and state its fields of application. (8)
Or
(b) (i) Derive Rayleigh's equation. (3)
(ii) A feed of 50 mole % hexane and 50 mole % octane is fed into a pipe still through a pressure reducing valve and then into a flash disengaging chamber. The vapor and liquid leaving the chamber are assumed to be in equilibrium. If the fraction of the feed converted to the vapor is 0.5, find the compositions of the top and bottom products. The following table gives the equilibrium data for this system. (9)
Mole fractions of hexane in liquid X |
1.00 |
0.69 |
0.40 |
0.192 |
0.045 |
0.00 |
Mole fractions of hexane in vapour Y |
1.00 |
0.932 |
0.78 |
0.538 |
0.1775 |
0.00 |
(ii) Explain the effect of quality of feed in distillation calculation. (3)
Or
(b) A continuous fractionating column operating at atmospheric pressure is to separate a feed containing 30% CS_{2} and 70% CC1_{4} into an overhead product of 95 % CS_{2} and a bottom product of 95 mole % CC1_{4}. The feed enters as a liquid at its boiling point. Assuming an overall plate efficiency of 70% and a reflux ratio of 3:1 estimate the number of plates needed. All the compositions are in mole %.
Equilibrium data:
x |
0.0296 |
0.0615 |
0.258 |
0.39 |
0.532 |
0.663 |
0.758 |
0.86 |
y |
0.0823 |
0.1555 |
0.494 |
0.634 |
0.747 |
0.830 |
0.880 |
0.932 |
(ii) What are the types of packing? Explain them with suitable examples.
Or
(b) If an air- ammonia mixture containing 5% ammonia by volume is absorbed in water using a packed tower at 20^{o}C and 1 atm pressure to recover 98% ammonia and the inert gas flow rate is 1200 kg/hr.m2, Determine
(i) minimum mass velocity of liquid and
(ii) number of transfer units using 1.25 times the minimum liquid flow rate. The equilibrium relationship for the system is given by y =1.154 x where x and y are expressed in mole fraction units.
wt % of dioxane in water (100 x) |
5.1 |
18.9 |
25.2 |
wt % of dioxane in benzene (100 y) |
5.2 |
22.5 |
32.0 |
Determine the number of stages required if the solvent rate is 1.5 times the minimum benzene is used Benzene is free from dioxane.
Or
(b) (i) Describe the Bollmann extractor used in leaching operation.
(ii) Write briefly about selection of solvent liquid -liquid extraction.
(i) dialysis and
(ii) Reverse osmosis.
Or
(b) (i) Distinguish between the two types of adsorption phenomena out their essential features. (6)
(ii) Explain briefly the following: adsorption isotherm and adsorption hysterisis. (6)