Adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or a liquid, forming a film of molecules or atoms. It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution. The term sorption encompasses both processes, while desorption is the reverse process.

Charcoal used to remove hydrocarbon vapors given off by gasoline, in a so-called vehicle “onboard” vapor recovery system, is an example of adsorption in the petroleum equipment industry.

Adsorption is present in many natural physical, biological, and chemical systems, and is widely used in industrial applications such as activated charcoal, synthetic resins, and water purification. Adsorption, ion exchange, and chromatography are sorption processes in which certain adsorbates are selectively transferred from the fluid phase to the surface of insoluble, rigid particles suspended in a vessel or packed in a column.