Binary and Three-Component Azeotropic Mixtures

In the discussed examples, synthesis of separation flowsheets is carried out automatically on the basis of formal rules. In more comphcated cases, in the process of synthesis there can be no other variants other than variants of obtaining azeotropes as some products. These cases are discussed in the following section. 

After identification of several preferable sequences, choosing among the optimum sequences, taking into consideration possible thermodinamic improvements and thermal integration of columns, arises. This task is similar to the synthesis of separation flowsheets of zeotropic mixtures (see Section 8.3), and it should be solved by the same methods (i.e., by means of comparative estimation of expenditures on separation). The methods of design calculation, described in Chapters 5 7 for the modes of minimum reflux and reflux bigger than minimum, have to be used for this purpose. In contrast to zeotropic mixtures, the set of alternative preferable sequences for azeotropic mixtures that sharply decreases the volume of necessary calculation is much smaller. 

Some examples of separation of three-component mixtures using curvature of separarix fines are described in Chapter 3. Examples of the application of entrainers forming heteroazeotropes and of columns with decanters for het-eroazeotropic and heteroextractive distillation are given in Chapter 6. 

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