Absorption (chemistry)

In chemistry, absorption is a process by which a substance incorporated in one state is transferred into another substance of a different state (e.g., gases being absorbed by a liquid or liquids being absorbed by a solid). As an industrial process, the most commonly encountered use of absorption is for the separation and/or purification of a gas mixture by the absorption of part of the mixture in a solvent.

Types of absorption

Absorption may be either a physical or a chemical process:

Physical absorption of a gas or part of a gas mixture in a liquid solvent involves the mass transfer that occurs at the interface between the gas and the liquid and the rate at which the gas diffuses into the liquid.

An example of physical absorption of a gas into a liquid is the absorption of ammonia (NH₃) into water (H₂). Another example is the separation of low molecular weight gases such as propane (C₃H₈) and butane (C₄H₁₀) from a hydrocarbon gas mixture of methane (CH₄), ethane (C₂H₆), propane and butane by absorbing the propane and butane in a solvent that is a mixture of much higher molecular weight hydrocarbon liquids.