Hydrogen sulphide (H₂S)

Small amounts of hydrogen sulphide occur in crude petroleum, but natural gas can contain up to 90%. Volcanoes and some hot springs (as well as cold springs) emit some H₂S, where it probably arises via the hydrolysis of sulphide minerals, i.e. MS + H₂O → MO + H₂S. Hydrogen sulphide can be present naturally in water, often as a result of the action of sulphate-reducing bacteria. About 10% of total global emissions of H₂S is due to human activity. The largest industrial emission of H₂S is from petroleum refineries. The hydrodesulphurization process liberates sulphur from petroleum by the action of hydrogen. The resulting H₂S is converted to elemental sulphur by partial combustion via the Claus process, which is a major source of elemental sulphur. Hydrogen sulphide arises from anywhere where elemental sulphur comes in contact with organic material, especially at high temperatures.