Cascades for multicomponent mixture separation via distillation

Using this equation, the number of different configurations for ra = 2, 3, 4 and 5 are, respectively, 1, 2, 5 and 14. As n increases, the number of different configurations increases at an astounding rate. 

Considerable research has been carried out to facilitate the selection of desirable configurations. A few simple heuristics are generally employed to guide the selection of a few sequences, which may be subjected to detailed analysis (King, 1980 Doherty and Malone, 2001). Consideration of the energy required for separation is very important in these deliberations. (An elementary introduction to the energy required for separation in distillation is provided in Sections 10.1.3, 10.1.4.2, 10.2.2.1 and 10.2.2.2.) We list a few simple sequencing heuristics below the rest 

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