The Four- and Multicomponent Mixtures

We now examine the four-component mixture for = 2 (Fig. 6.9a). The conditions of joining of section trajectories at a set flow rate of the entrainer in the mode of minimum reflux in the cases of top or bottom control feed do not differ from the conditions for three-component mixtures discussed above. In the case of bottom 

With the top feed for the control one, Xe-i = N+ and Xe = N+. The equations of material balance (6.4) (6.7) should be valid in both cases. 

For four-component mixtures at nim = 3 and at two components in the bottom product (Fig. 6.9b), the conditions of joining in the case of bottom control feed are defined by the dimensionality of trajectory bundles N - Sm(d = 1) and (d = 1) and are similar to those of joining of sections trajectories of two-section column in the mode of minimum reflux at intermediate split (see Section 5.6). Point X/-1 should lie on the separatrix min-reflux region Re (N - Sm) and point Xf should lie on the separatrix min-reflux region Re ( - N ). 

It is shown below that such a joining variant of sections trajectories at arbitrary compositions of the top product and of the pseudoproduct is unfeasible. Joining is feasible if point Xe-i belongs to working trajectory bundle of top section Reg. (Sr - N+). In other words, the top feed cannot be the control one. 

We now examine the general case of separation of a multicomponent mixture by means of sharp extractive distillation in a column with two feeds at a set flow rate of entrainer in the mode of minimum reflux. The conditions of sections joining are similar to the conditions of sections joining of the two-section column and depend on the number of components in the product or in the pseudoproduct of each section (trir, trim, and tits) (i.e., on the dimensionality of the working and separatrix bundles of the sections). 

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