Page 140 - Separation process engineering

0.9999 mol% methanol. The boilup ratio = 1.5. Estimate the reboiler heat duty Q . Data
R
are available in Problem 3.E1.

D10. A distillation column operating at 2.0 atm. is separating a feed that is 55.0 mol% n-pentane and
45.0 mol% n-hexane. The feed is at 65°C, and its flow rate is 1000 kmol/h. The distillate is 99.93
mol% n-pentane, and we want a 99.50% recovery of n-pentane. The system uses a total
condenser, and reflux is a saturated liquid with an external reflux ratio of L/D = 2.8. There is a
partial reboiler. Data are available in Problem 3.D6 and in the DePriester charts. Find D, B, x ,
B
Q , Q .
c
R
E. More Complex Problems

E1. A mixture of methanol and water is being separated in a distillation column with open steam (see
figure in Problem 3.D2). The feed rate is 100 kmol/h. Feed is 60.0 mol% methanol and is at 40
°C. The column is at 1.0 atm. The steam is pure water vapor (y = 0) and is a saturated vapor.
M
The distillate product is 99.0 mol% methanol and leaves as a saturated liquid. The bottoms is 2.0
mol% methanol and, since it leaves an equilibrium stage, must be a saturated liquid. The column

is adiabatic. The column has a total condenser. External reflux ratio is L/D = 2.3.
Equilibrium data are in Table 2-7 in Problem 2.D1. Data for water and methanol is available in
Felder and Rousseau (2004) (C , λ and steam tables) and in Perry’s.
P
Find D, B, Q , and S. Be careful with units and in selecting basis for energy balance. Data:
c
λ = ΔH = 8.43 kcal/mol = 35.27 kJ/mol (at boiling point)
methanol vap
λ = ΔH = 9.72 kcal/mol = 40.656 kJ/mol
water vap
C p,w,liquid = 1.0 cal/(g °C) = 75.4 J/mol °C

C PL,Meoh = 75.86 + 0.1683T J/(gmole °C)
−5
−9
2
C p,w,vapor = 33.46 + 0.006880 T + 0.7604 × 10 T −3.593 × 10 T 3
2
−9
−5
C p,meoh,vapor = 42.93 + 0.08301 T − 1.87 × 10 T −8.03 × 10 T 3
For Vapor T is in °C, C is in J/mol °C
p
VLE data: Table 2-7. Density and MW data Problem 2.D1
E2. A mixture of methanol and water is being separated in a distillation column with open steam (see
figure in Problem 3.D2). The feed rate is 500 kmol/h. Feed is 60.0 mol% methanol and is a
saturated liquid. The column is at 1.0 atm. The steam is pure water vapor (y = 0) and is a
M
saturated vapor. The distillate product is 99.8 mol% methanol and leaves as a saturated liquid.

The bottoms is 0.13 mol% methanol and since it leaves an equilibrium stage must be a saturated
liquid. The column is adiabatic. The column has a total condenser. External reflux ratio is L/D =
3. Data for water and methanol are available in Problem 3.E1.
Find D, B, Q , and S. Be careful with units and in selecting basis for energy balance.
c

F. Problems Requiring Other Resources

F1.* A mixture of oxygen and nitrogen is to be distilled at low temperature. The feed rate is 25,000
kmol/h and is 21 mol% oxygen and 79 mol% nitrogen. An ordinary column (as shown in Figure 3-
8) will be used. Column pressure is 1 atm. The feed is a superheated vapor at 100 K. We desire a
bottoms composition of 99.6 mol% oxygen and a distillate that is 99.7 mol% nitrogen. Reflux ratio