Page 199 - Separation process engineering

plate to cool 5 moles of feed to a saturated vapor, what is the value of q? What is the slope of
the feed line?
D5.* A distillation column is operating with a subcooled reflux. The vapor streams have an enthalpy of

H = H = 17,500 Btu/lbmol, while the saturated liquid h = 3100 Btu/lbmol. Enthalpy of the
2
1
1
reflux stream is h = 1500 Btu/lbmol. The external reflux ratio is set at L /D = 1.1. Calculate the
0
0
internal reflux ratio inside the column, L /V .
1 2
D6. We are separating a mixture of acetone and ethanol in a distillation column operating at one
atmosphere pressure. The column has a total condenser and a partial reboiler. The distillate is 90
mol% acetone, and the bottoms is 10 mol% acetone. The reflux is returned as a saturated liquid.
Use a boilup ratio of /B = 2.0. Two feeds are fed to the column. The first feed has a flow rate of

75 kmol/h, it is a saturated liquid, and it is 60 mol% acetone. The second feed has a flow rate of
100 kmol/h, it is a two-phase mixture that is 60% vapor, and it is 40 mol% acetone. Use the
optimum feed location for each feed. Assume CMO. Equilibrium data are in Problem 4.D7.
a. Find the distillate and bottoms flow rates, D and B.

b. Plot the two feed lines and the three operating lines.
c. Step off stages and find the optimum feed location for each feed stream and the total number of
equilibrium stages required.

D7.*
a. A distillation column with a total condenser is separating acetone from ethanol. A distillate

concentration of x = 0.90 mole fraction acetone is desired. Since CMO is valid, L/V =
D
constant. If L/V is equal to 0.8, find the composition of the liquid leaving the fifth stage below
the total condenser.
b. A distillation column separating acetone and ethanol has a partial reboiler that acts as an

equilibrium contact. If the bottoms composition is x = 0.13 mole fraction acetone and the
B
boilup ratio /B = 1.0, find the vapor composition leaving the second stage above the partial
reboiler.

c. The distillation column in parts a and b is separating acetone from ethanol and has x = 0.9, x B
D
= 0.13, L/V = 0.8, and /B = 1.0. If the feed composition is z = 0.3 (all concentrations are mole
fraction of more volatile component), find the optimum feed plate location, total number of
stages, and required q value of the feed. Equilibrium data for acetone and ethanol at 1 atm
(Perry et al., 1963, pp. 13–4) are

D8.* For Problem 4.D7c for separation of acetone from ethanol, determine:

a. How many stages are required at total reflux?

b. What is (L/V) min ? What is (L/D) min ?
c. The L/D used is how much larger than (L/D) min ?

d. If E MV = 0.75, how many real stages are required for L/V = 0.8?

D9. A distillation column with two feeds is separating ethanol (E) and water at a pressure of 1.0 atm.
The column has a total condenser with saturated liquid reflux and a partial reboiler. Feed 1 is a
saturated liquid and is 42 mol% ethanol. Feed 2 flow rate is F = 100 kmol/h. Feed 2 is 18 mol%
2
ethanol and is a two-phase mixture that is 30% vapor. The external reflux ratio is L/D = 1/2, and