Page 291 - Separation process engineering

distillate. A 99.2% recovery of n-butane is desired in the bottoms. Use the optimum feed stage.
Use DePriester chart. Assume relative volatility is constant at value calculated at the bubble point
temperature of the feed.

a. Find N min from the Fenske equation.

b. Find (L/D) min from the Underwood equation.
c. Use L/D = 1.2 (L/D) min and estimate N and N Feed from Gilliland correlation.

D8.* We wish to separate a mixture of 40 mol% benzene and 60 mol% ethylene dichloride in a
distillation column with a partial reboiler and a total condenser. The feed rate is 750 mol/h, and
feed is a saturated vapor. We desire a distillate product of 99.2 mol% benzene and a bottoms
product that is 0.5 mol% benzene. Reflux is a saturated liquid, and CMO can be used. Equilibrium

data can be approximated with an average relative volatility of 1.11 (benzene is more volatile).
a. Find the minimum external reflux ratio.
b. Use the Fenske equation to find the number of stages required at total reflux.

c. Estimate the total number of stages required for this separation, using the Gilliland correlation
for L/D = 1.2(L/D) min .

D9. We are separating a mixture of ethanol and water in a distillation column with a total condenser
and a partial reboiler. Column is at 1.0 atm. pressure. The feed is 30.0 mol% ethanol. The feed is
a two-phase mixture that is 80 % liquid. Feed rate is 100.0 kmol/h. We desire a bottoms
concentration of 2.0 mol% ethanol, and a distillate that is 80.0 mol% ethanol.

Do this problem by using McCabe-Thiele diagram for parts a and b and the Gilliland correlation
for part c. Equilibrium data are given in Table 2-1.
D10. A distillation column is separating ethane, propane, and n-butane at 5 atm. Operation is at total

reflux. We want a 98.9% recovery of ethane in the distillate and a 99.8% recovery of n-butane in
the bottoms. Propane is a sandwich component (e.g., in between light and heavy keys). F = 100
kmol/h and is 30 mol% ethane, 33 mol% propane and 37 mol% n-butane. Feed is a saturated
liquid. Assume relative volatilities are constant, α = 13.14, and α = 3.91.
PB
EB
a. At total reflux find N min .

b. At total reflux find the fractional recovery of propane in the distillate.
c. At total reflux find distillate flow rate D.

D11. A distillation column with a total condenser and a partial reboiler is separating a mixture of
propane (P), n-butane (B), and n-hexane (H). The feed (a saturated vapor) is 20 mol% propane,
35 mol% n-butane, and 45 mol% n-hexane. Feed rate is F = 100 kmol/h. We desire a 99%
recovery of the n-butane in the distillate and a 98% recovery of n-hexane in the bottoms. CMO can
be assumed to be valid. If we choose butane as the reference, the average relative volatilities are
α = 2.04, α = 1.0, α HB = 0.20. Calculate the distillate flow rate D assuming all propane is in
PB
BB
the distillate, and find the minimum external reflux ratio, (L/D) min .
D12.* a. A distillation column with a partial reboiler and a total condenser is being used to separate a
mixture of benzene, toluene, and cumene. The feed is 40 mol% benzene, 30 mol% toluene and 30
mol% cumene. The feed is input as a saturated vapor. We desire 99% recovery of the toluene in

the bottoms and 98% recovery of the benzene in the distillate. The reflux is returned as a saturated