[3] However, the Texas Commission on Environmental Quality has historically defined sour gas for upstream operations – which requires permitting, reporting, and possibly additional emission controls – as gas that contains more than 24 ppm by volume.
[6] Within oil refineries or natural gas processing plants, the removal of hydrogen sulfide and other organosulfur compounds is referred to as "sweetening".
The sweetened product lacks the sour, foul odors of mercaptans and hydrogen sulfide.
Before a raw natural gas containing hydrogen sulfide or carbon dioxide can be used, the raw gas must be treated to remove those impurities to acceptable levels, commonly by an amine treatment process.
In addition to utilizing an amine or Claus process, liquid redox is becoming increasingly popular.