Objectives of distillation column control

Objectives of distillation column control

The basic objective of distillation is to take a liquid mixture and separate it into two or more streams which have compositions different to the feed stream. In a basic distillation column a feed stream enters in the middle of the column and two streams leave, one at the top and one at the bottom. 

Components with lower boiling points are concentrated in the stream leaving the top while components with higher boiling points are concentrated in the stream leaving the bottom.

Separation is achieved by controlling the column temperature and pressure profiles to take advantage of differences in the relative volatility of the mixture components and therefore tendency to change phase. 

The lighter, lower boiling point components evaporate and travel up the column to form the top product and the heavier, higher boiling point components condense and travelling down the column to form the bottom product.