Page 139 - Separation process engineering

portion of mole fraction x is returned to the column as reflux. The liquid and vapor leaving the
0
partial condenser can be assumed to be in equilibrium.

A distillation column with a partial condenser and a partial reboiler is separating 100 kmol/h of a
mixture that is 30 mol% methanol and 70 mol% water and is a saturated liquid. Column pressure
is 1.0 atm. We desire a 99% recovery of the methanol in the vapor distillate and a 98% recovery
of water in the bottoms. Equilibrium data are in Table 2-7 (in Problem 2.D1), and other data are
in Problem 3.E1.

a. Find D, B, y D,M , and x B,M .
b. If L/D = 2.0, find x 0,M and L where subscript 0 refers to the reflux stream.
0
c. If L/D = 2.0, find Q and Q .
c
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2
D5.* A distillation column is separating ethanol from water at a pressure of 1 kg/cm . A two-phase
feed of 20 wt% ethanol at 93°C is input at 100 kg/min. The column has a total condenser and a

partial reboiler. The distillate composition is 90 wt % ethanol. Distillate and reflux are at 20°C.
Bottoms composition is 1 wt % ethanol. Reflux ratio is L /D = 3. A liquid side stream is
0
withdrawn above the feed stage. Side stream is 70 wt % ethanol, and side stream flow rate is 10
kg/min. Find D, B, Q , and Q . Data are in Figure 2-4.
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c
D6.* A distillation column receives a feed that is 40 mol% n-pentane and 60 mol% n-hexane. Feed
flow rate is 2500 lbmol/h, and feed temperature is 30°C. The column is at 1 atm. A distillate that
is 99.9 mol% n-pentane is desired. A total condenser is used. Reflux is a saturated liquid. The
external reflux ratio is L /D = 3. Bottoms from the partial reboiler is 99.8 mol% n-hexane. Find D,
0
B, Q , Q . Note: Watch your units on temperature.
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c

where T is in °C and C and C are
PL
PV

Source for λ and C data is Felder and Rousseau (2004).
P
D7. A continuous, steady-state distillation column is fed a mixture that is 70 mol% n-pentane and 30
mol% n-hexane. Feed rate is 1000 kmol/h. Feed is at 35°C. Column is at 101.3 kPa. The vapor
distillate product is 99.9 mol% n-pentane and the bottoms product is 99.9 mol% n-hexane. The
system has a partial condenser (thus the distillate product is a saturated vapor) and operates at an
external reflux ratio of L/D = 2.8. The reboiler is a partial reboiler. Find D, B, Q & Q . Data are
c
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given in Problem 3.D6. Use DePriester chart to determine boiling points.
D8. A distillation column with a partial condenser and a partial reboiler is separating methanol and
water. Column pressure is 1.0 atm. We desire 120 kmol/h of a bottoms product that is 0.0001
mole fraction methanol. Boilup ratio is 1.5. Equilibrium data are in Table 2-7 (in Problem
2.D1), and other data are in Problem 3.E1. Assume that all streams entering and leaving the partial
reboiler contain very little methanol. Find Q .
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D9. A distillation column is separating 500 kmol/h of a mixture that is 76 mol% methanol and 24
mol% water. The bottoms product contains 0.00002 mole fraction methanol, and the distillate is