Characteristics of separation processes

The subject of separation processes is so extensive that the scope of this section must be extremely limited. We shall therefore concentrate on the general characteristics of separation processes and only examine simple distillation in any detail. Several excellent textbooks on the subject are available. 

Separation usually involves the formation of more than one phase by the addition of the separating agent. The components of a mixture will be distributed unequally between the phases. Separation of phases of different density is easily accomplished by mechanical means. For example, a liquid feed is passed through a pressure-reducing valve into a vessel (flash drum) where it separates into two phases of different composition. Vapour is taken off at the top of the drum and liquid at the bottom. The separating agent is energy— introduced as work of compression of the feed. 

The driving force for interphase mass transfer is always the thermodynamic 

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