Page 330 - Distillation theory

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304 Synthesis of Separation Flowsheets

2,3 1,2,3
a) 1 3 2 b) 1 3 c) 1 3

F 0 F 0 F 0

2,3,4 2,4 2,3,4 2,3
4 4 2 4 2
1 1 1

2,3
d) 3 2 e) 3 f) 3 2

F 0 F 0 F 0

2,3,4 2,4 2,3,4 2,3,4 2,4
4 4 2 4

1 1 1

2,3 2,3 3 2
g) 3 h) 3 i)

F 0 F 0 F 0

2,3,4 2,3,4 2,3,4 2,4 4
4 2 4 2
Figure 8.23. Sequences for distillation of the acetone(1)-benzene(2)-chloroform(3)-toluene(4)
mixture, obtained by means of automatic sequencing.

3,4, sequences in Fig. 8.23h,i) meet conditions of autoextractive separation. These
splits are also preferable.
In the given example mixture 2,3,4, that is bottom product of the first column,
is zeotropic; therefore, its separation in the second and third columns presents no
difficulty. Figure 8.23 shows nine preferable separation flowsheets for this exam-
ple, obtained by means of synthesis. All these flowsheets separate four-component
mixtures using a minimum number (three) of columns without additional entrain-
ers, but with application of autoentrainer. Component 2 or 4 or mixtures 2,4 or
3,4 are used as an autoentrainer. Therefore, each of nine separation flowsheets
contains one column with one or two feedings where recycle flow of autoentrainer
is brought in.