Topic: Distillation
Question 1: Chloroform-Benzene Distillation
A mixture of 30 mol.% chloroform in benzene is to be separated by distillation so that an overheads product containing 85 mol.% chloroform is obtained. The feed is introduced into the column as saturated liquid and the mole ratio of liquid reflux to distillate product is controlled at R = 20 by a reflux divider in the condensate stream from a partial condenser. How many ideal plates must be used if the bottoms composition is to be maintained at 5 mol.% chloroform? What is the recovery of chloroform from this column? What are the liquid and vapour flow rates in the two sections of the column? Use a basis of 100 kmol/h of feed. Equilibrium data is provided in the table below.
EQUILIBRIUM DATA: CHLOROFORM--BENZENE AT 760 mm Hg
| Liquid |
0 |
8 |
15 |
22 |
29 |
36 |
44 |
54 |
66 |
79 |
100 |
| Vapor |
0 |
10 |
20 |
30 |
40 |
50 |
60 |
70 |
80 |
90 |
100 |
| Temperature, 'C |
80.6 |
79.8 |
79 |
78.2 |
77.3 |
76.4 |
75.3 |
74 |
71.9 |
68.9 |
61.4 |
Question 2: Ammonia-Water Distillation
Refer to the ammonia-water system at 100 psis. Ammonia and water, in a saturated liquid state at 150 °F, arc to be separated using a distillation column consisting of three equilibrium stages, with the distillate mol fraction of ammonia at 0.90 and with the exit waste mol fraction of ammonia set at 0.02. Determine the required reflux ratio, and the required internal flows through the column on both sides of the feed entry position. Assume the feed enters in the middle of the vessel and that the feed rate is 1000 lcmoVh. The equilibrium diagram is provided over the page.
Q1) no additional information needed Allocations of Marks
How many ideal plates must be used if the bottoms composition is to be maintained at 5 mol% chloroform?
Students need to provide a sketch of the system showing the internal and external flows. Students need to provide the basic calculations to support the graphical construction and then prepare a graph and correctly step off the correct number of stages.
What is the recovery of chloroform from this column? 12 marks Provide the correct set of calculations.
What are the liquid and vapour flow rates in the two sections of the column? 13 marks Provide the correct set of calculations.
Q2) Students need to provide a sketch of the system showing the internal and external flows, using symbols.
Students need to correctly specify the feed operating line, based on the enthalpy concentration diagram.
Students need to provide the basic calculations to support the graphical construction. They should then show the final graph. They should explain the approach used to obtain the Reflux Ratio.
They should then provide the internal liquid flows.