Absorption

Absorption is one of many unit operations used in process industries. It is a separation process that involves a mass transfer from a gas to a liquid. The solute which is absorbed is called absorptive and the solvent which absorbs solute is referred as absorbent. The reversed process (mass transfer from a liquid to a gas) is desorption.

These are the applications of (physical) absorption:

1) Air purification
2) Odor control
3) Purification in refinery and petro-chemical industry

Meanwhile desorption is sometimes used in:

1) Regenerating of loaded absorbent
2) Removing of solved components from liquids

There are some similarities between distillation and absorption:

1) Both involve two phases, liquid and gas
2) Both phases are normally saturated

With that being said absorption differs from distillation in many ways:

1) Feed in distillation is mostly liquid, vapour is sometimes generated as a part of the liquid feed
2) The operating temperature for absorption is normally lower than that for distillation
3) Liquid to gas ratio in absorption is mostly lower than that in distillation

Physical absorption and chemical absorption:

a) Physical absorption: where absorbed solute does not react with the aqueous solution
b) Chemical absorption: solute is absorbed and then reacts with the aqueous solution

Physical absorption is normally preferred at high pressure while at low pressure chemical absorption works best. However the regeneration in case of chemical absorption is really challenging.