CL 351 Homework # 9
No due date but solve for end-semester exam
1.
As part of applying paint, you produce a large
amount of methanol vapour. You recover
the methanol by absorbing the vapour in water, and then distilling the
water-methanol mixture in an old six-stage column plus reboiler. You have an old description of the column
which says that the Murphree efficiency of the top three stages is 50%, but
that of the bottom three and the reboiler is 100%. The man who wrote the report died last year,
only eleven months after retiring.
Company policy dictates a reflux 1.5 times the minimum. You need to process 1200 kg/hr of a 32 mole%
methanol feed. You want a distillate
that is 90% methanol. What is
concentration of the bottoms?
Equilibrium data is given below.
x(methanol) |
0 |
0.1 |
0.2 |
0.3 |
0.4 |
0.5 |
0.6 |
0.7 |
0.8 |
0.9 |
1.0 |
y(methanol) |
0 |
0.42 |
0.58 |
0.67 |
0.73 |
0.78 |
0.83 |
0.87 |
0.92 |
0.96 |
1.0 |
2.
Lemon grass is a major source of lemon
flavouring. You are extracting the lemon
grass with three well-mixed, counter-current stages, using dilute bisulphate solution
as an extraction solvent. The solvent
enters with no lemon flavour. The
extraction factor for this extraction is 0.38.
If you extract 85% of the flavour, what is the stage efficiency? (Chapter
11, Cussler)
3.
An extraction column is used to remove an impurity P
from toluene with water as the solvent.
The toluene and water may be considered to be completely
immiscible. Toluene enters the column with
20 wt% of P, and it should leave with 1.0 wt% P. Water enters the column with no P. Over the range of operation, equilibrium data
can be satisfactorily represented by
Wt. frac
of P in water = 0.75 (wt. frac of P in toluene) + 10.0 (wt. frac of P in
toluene)2
Find the number of equilibrium stages required.
4.
We are extracting acetic acid from water with
isopropyl ether at 20oC and 1 atm pressure. Equilibrium data is given below. The column has three equilibrium stages. The entering feed rate is 1000 kg/hr. The feed is 40 wt% acetic acid and 60 wt%
water. The exiting extract stream has a
flow rate of 2500 kg/hr and is 20 wt% acetic acid. The entering extract stream (which is not
pure isopropyl ether) contains no water.
Find: a) the exit raffinate concentration, b) the required entering
extract stream concentration and c) flow rates of exiting raffinate and
entering extract streams.
Equilibrium
data for water - acetic acid – isopropyl ether at 20oC and 1 atm
pressure.
Acetic acid, xA |
Water, xD |
Isopropyl ether, xs |
Acetic acid, yA |
Water, yD |
Isopropyl ether, yS |
0.69 |
98.1 |
1.2 |
0.18 |
0.5 |
99.3 |
1.41 |
97.1 |
1.5 |
0.37 |
0.7 |
98.9 |
2.89 |
95.5 |
1.6 |
0.79 |
0.8 |
98.4 |
6.42 |
91.7 |
1.9 |
1.93 |
1.0 |
97.1 |
13.3 |
84.4 |
2.3 |
4.82 |
1.9 |
93.3 |
25.5 |
71.1 |
3.4 |
11.4 |
3.9 |
84.7 |
36.7 |
58.9 |
4.4 |
21.6 |
6.9 |
71.5 |
44.3 |
45.1 |
10.6 |
31.1 |
10.8 |
58.1 |
46.4 |
37.1 |
16.5 |
36.2 |
15.1 |
48.7 |