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4.3 WORKSHOPS
Workshop 4.1
The separation of ethanol from water by heterogeneous azeotropic
distillation is carried out by two distillation columns, each with its own overhead
condensor but sharing a common decanter, as shown in Figure 4.5. The first col-
umn has two feeds, one of fresh material and one containing the water-rich phase
recycled from the decanter. The bottoms product of this column is primarily water.
The fresh ethanol-rich feed is composed of 1000 lb/hr of ethanol and 9000 lb/hr
of water. The overhead product of this column is condensed and sent to the shared
decanter.
The decanter has a fresh cyclohexane feed of 1 lb/hr, which represents the makeup
of cyclohexane lost in the products of both columns. The feed to the second column is
the organic product of the decanter, which contains primarily ethanol and cyclohexane.
The bottoms product of this column is primarily ethanol. The overheads product is
condensed and sent to the shared decanter. All fresh feeds are saturated liquids. All
operations are at 1 atmosphere pressure with negligible pressure drops within the
equipment. The two distillation columns are to be simulated with Sep2 blocks and
the decanter with a Sep block. Solve using the material-balance-only option and use
Wegstein's default method for convergence.
The performance specifications of the unit operations are given in Table 4.1. For
both columns the fraction of the feed of each component leaving with the respective
bottoms product is given. For the decanter, the fraction of the feed of each component
leaving with the organic phase is given.
a. Why may one assume that the system can be represented by ideal thermodynam-
ics for the vapor and liquid phases?
b. Has Aspen Plus chosen the best tear streams?
D
C
G
G
DECANT
DIST1
DIST2
F
A
E
H
B
Figure 4.5
Heterogeneous azeotropic distillation.
