Ternary nonazeotropic mixtur

We have seen in Section 8.1.1.3 that continuous operation of a distillation column with countercurrent flow of vapor and liquid can separate a binary mixture only. If we have a multicomponent nonazeotropic mixture as feed, then only one of the two product streams can have one species with sufficient purity the other product stream will contain aU other species in quantities reflecting their feed concentration. This stream has to be fed to another distillation column that can produce two product streams, where each product stream will have sufficient purity with respect to one of the two remaining species for a ternary feed to the first distillation column. Similarly, if the feed to the first column has four components, in general, we will need three columns to obtain four product streams, each product stream being sufficiently purified in one of the species. In general, to separate n species in the feed by distillation in simple distillation columns of the type shown in Figure 8.1.19(b), we will need n - 1) distillation columns. 

Figure 9.2.1. Number of possible column sequences in multicomponent distillation of nonazeotropic mixture using simple distillation columns. Ternary mixture of species A, B and C (a) direct sequence (b) indirect sequence.

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