Page 206 - Separation process engineering

is a saturated liquid, and CMO can be assumed. Find the side-stream concentration and the
distillate concentration. Data are given in Table 2-7.
E3.* A distillation column with at total condenser and a total reboiler is separating ethanol from

water. Reflux is returned as a saturated liquid, and boilup is returned as a saturated vapor. CMO
can be assumed. Assume that the stages are equilibrium stages. Column pressure is 1 atm. A
saturated liquid feed that is 32 mol% ethanol is fed to the column at 1000 kmol/h. The feed is to
be input on the optimum feed stage. We desire a distillate composition of 80 mol% ethanol and a
bottoms composition that is 2 mol% ethanol. A liquid side stream is removed on the eighth stage
from the top of the column at a flow rate of S = 457.3 kmol/h. This liquid is sent to an intermediate
reboiler and vaporized to a saturated vapor, which is returned to the column at its optimum feed
location. The external reflux ratio is L /D = 1.86. Find the optimum feed locations of the feed and
0
of the vapor from the intermediate reboiler. Find the total number of equilibrium stages required.
Be very neat! Data are in Table 2-1.
E4. A distillation column is separating methanol and water at a pressure of 1 atm. Feed rate of the
mixture is 100 kmol/h. The feed is 25 mol% methanol and 75 mol% water. The feed is a
subcooled liquid. To heat the feed to the boiling point, one mole of vapor condenses on the feed
stage for every 10 moles of feed. We desire a distillate mole fraction that is 90 mol% methanol
and a bottoms mole fraction that is 2.5 mol% methanol. We operate with a boilup ratio of 1.0. The
column is operated with two reflux streams. The reflux to the first stage operates with a flow rate
of L = 21.4 kmol/h. Sufficient reflux (L ) is returned to stage 2 for the column to operate. Both
0
R
reflux streams are saturated liquids. The column has a total condenser and a partial reboiler.
Assume CMO. Equilibrium data are in Table 2-7.

a. Find D and B (distillate and bottoms flow rates).
b. Determine the reflux rate to stage 2 (L ) in kmol/h.
R
c. Find the optimum feed plate location and the total number of stages.

E5. A distillation column is separating a feed that is 30 mol% acetone and 70 mol% ethanol. The
column has a partial condenser. Operation is at p = 1 atm. The feed flow rate is 1000 kmol/day,
the feed is a saturated liquid, and feed is input at the optimum location. We desire a distillate that
is 90 mol% acetone and a bottoms that is 10 mol% acetone. Use a boilup ratio of /B = 1.25. On
the fourth stage above the partial reboiler, a vapor sidestream with flow rate S = 200 kmol/day is
withdrawn and then condensed to a saturated liquid, which is returned to the column as feed at the
optimum location. Assume CMO. Find the mole fraction of vapor side stream y , optimum feed
s
location, optimum location to input saturated liquid from intermediate condenser, and total number
of equilibrium stages. Equilibrium data are in Problem 4.D7.