Mercaptans (RSH) occur naturally in crude oils and are also generated from other sulfur compounds during crude fractionation and cracking processes. Mercaptans are undesirable in gasoline because of their obnoxious odor and their tendency to hydrolyze, forming toxic and corrosive hydrogen sulfide. The classic tests for mercaptan presence are the "Doctor" test and odor threshold.

The Sulfrex and sweetening processes eliminate mercaptans by extraction or by their conversion into less aggressive compounds thereby protecting equipment or downstream units such as hydrotreaters as well as meeting fuel specifications.

The extractive Sulfrex process both sweetens and reduces the total sulfur concentration. With its moderate operating conditions of pressure and ambient temperature, this continuous process is ideal for C3, C4, LPG, light gasoline and NGL feeds.