Stripping. Rectification, and Fractionation

Vapor leaving a distillation stage is richer than the feed in the more-volatile components. Liqnid leaving the stage is richer than the feed in the less-volatile components. In order to improve the separation, multiple stages are used. 

Stripping stages (Fig. 2.3a) concentrate the lees-volatile components in a liquid stream. A vapor recycle vaporizes ( strips ) the more-volatile components from the liquid. To generate the vapor recycle, heat is supplied to vaporize a portion of the bottom-stage liquid. This vapor recycle is termed boUup. 

Rectifying stages (Fig. 2.36) concentrate the more-volatile components in a vapor stream. A liquid recycle condenses the less-volatile components from the rising vapor. To generate the liquid recycle, cooling is applied to condense a portion of the overheed vapor. The liquid recycle is termed reflux. 

The stripping and rectifying stages shown in Fig. 2.3a and 6 can be combined into a single separation process with internal recycle (Fig 2.3c). This process is termed fractionation. 

In a single-feed fractionator, stages above the feed are rectifying 

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