Giant star mass, when on the main sequence, was below approximately , it will never reach the central temperatures necessary to fuse helium. It will therefore remain a hydrogen-fusing red giant until it runs out of hydrogen, at which point it will become a helium white dwarf. According to stellar evolution theory, no star of such low mass can have evolved to that stage within the age of the Universe. In stars above about the core temperature eventually reaches 10 K and helium will begin to fuse to carbon and oxygen in the core by the triple-alpha process. When the core is
Acid gas hydrogen sulfide and/or carbon dioxide can be used, the raw gas must be treated to reduce impurities to acceptable levels and this is commonly done with an amine gas treating process. The removed HS is most often subsequently converted to by-product elemental sulfur in a Claus process or alternatively converted to valuable sulfuric acid in a WSA Process unit. Processes within oil refineries or natural-gas processing plants that remove mercaptans and/or hydrogen sulfide are commonly referred to as 'sweetening' processes because they result in products which no longer have the sour, foul odors of mercaptans and hydrogen sulfide. Hydrogen sulfide