A two-stage process used for the removal of sulphur from natural gas or crude oil. In the first, hydrogen sulphide is partially oxidized using air to form sulphur dioxide. In the second, the sulphur dioxide is reacted with the hydrogen sulphide in the presence of a catalyst at 300ºC to form elemental sulphur and water vapour:
It is named after its inventor, chemist Carl Friedrich Claus, who developed the process in 1883 while working on ways of recovering sulphur from the waste calcium sulphide produced in the Leblanc process. He originally used iron ore and later bauxite as the catalyst.