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13.4.2 Rules (Heuristics) and Examples
In this subsection, some examples are presented along with the relevant
rules that apply. Some important formulas are presented first:
Number of separating columns ¼ Number of components 1 ð1Þ
The number of sequences S is related to the number of components c by
the relationship
½2ðc 1Þ!
S ¼ ð2Þ
c!ðc 1Þ!
Example 1 (Introductory Example)
Find the possible technical sequences for separating a mixture of BTX
(benzene, toluene, xylene).
Solution
First, applying Eq. (1), the number of columns to be used is two. Similarly,
solving Eq. (2),
½2ð2Þ!
S ¼
ð3 2 1Þð2 1Þ
4 3 2 1
¼ ¼ 2
3 2 2
The number of feasible sequences is found to be 2. However, in Figure 8,
four sequences are shown; but not all of them are feasible. Both
arrangements (b) and (c) are excluded because the former does not produce
pure products and the latter employs three columns. Thus, arrangements (a)
and (b) are both feasible and equivalent.
Statement of Rules
Rule 1: All other things being equal, aim to separate the more
plentiful components early.
Rule 2: Difficult separations are best saved last.
Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.
