Characteristics of Multi-Component Separation

A multi-component mixture is separated in a fractionation column into an overhead or distillate product that is enriched in the lighter components and a bottoms product that is enriched in the heavier components. The product compositions depend on the extent of fractionation (or separation) taking place inside the column and on the product rates. 

Consider a feed mixture of components 1 through C with mole fractions Zj through 

Zc- It is convenient to list the components in the feed in the order of decreasing 

It may be desired to separate components i and j that are not necessarily adjacent to each other on the volatility list. Between them there may be irrelevant components with intermediate volatilities. In this case, if i is lighter than j, then i is the light key and j is the heavy key. The components in between are distributed components , they may flow either mostly with the overhead or with the bottoms. 

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