Absorption is a mass transfer operation in which a soluble gaseous component is removed from a gas stream by dissolving in a liquid. Absorption can be used to recover valuable gaseous components such as hydrocarbons or to remove unwanted gaseous components such as hydrogen sulfide from a stream. A valuable solute can be separated from the absorbing liquid and recovered in a pure, concentrated form by distillation or stripping (desorption). The absorbing liquid is then used in a closed circuit and is continuously regenerated and recycled. Examples of regeneration alternatives to distillation or stripping are removal through precipitation and settling; chemical destruction through neutralization, oxidation, or reduction; hydrolysis; solvent extraction; and liquid adsorption. Absorption is one of the main methods of separation used in the chemical processing industry. Accompanied by chemical reaction between the absorbed component and a reagent in the absorbing fluid, absorption can become a very effective means of separation. Absorption can also be used to remove an air pollutant like an acid gas from stream. Then, the system could be a simple absorption in which the absorbing liquid is used in a single pass and then disposed of while containing the absorbed pollutant.