Question

1. Explain the principle upon which separation is achieved in a distillation column. (4)

Answer 1

Distillation refers to the separation by physical means of a mixture on the basis of its difference in vapor pressure/boiling points.The simplest example of distillation is that of a 2-component system,where we can just heat the mixture and separate out the components i.e the component with lower boiling point will form vapor easily and can be later condensed whereas the component with higher boiling point will remain as residue.

In case of a distillation colum the same principle is utilised at different stages to separate multiple components or for acheiving higher purity .The stages are usually called trays or plates.Each stage in itself acts as a tray for separation of components. In normal operation, there is a certain amount of liquid on each plate, and some arrangement is made for ascending vapors to pass through the liquid and make contact with it.The fundamental principle involves the formation of equilibrium and separation into distillate and bottoms governed by the equilibrium composition curve,number of stages and the purity with which the distillate/ bottom is required.