How does petroleum refining convert foul-smelling thiols into less offensive disulfides?

In petroleum refining, the process of converting foul-smelling thiols (also known as mercaptans) into less offensive disulfides is called "sweetening."12

This process relies on oxidation to transform the thiols, which are responsible for the characteristic rotten-egg or skunky odors in crude oil and fuel products. The conversion typically involves the following steps:12

• Catalytic Oxidation: The oil is heated and agitated in the presence of air, which provides the oxygen necessary for the reaction. Catalysts are used to facilitate the oxidation of mercaptans into disulfides.1
• Process Evolution: Historically, the "doctor process" used a solution of lead oxide in caustic soda as a catalyst, but this required the addition of elemental sulfur, which increased the total sulfur content of the product. Modern refineries have largely replaced this with the copper chloride process, which utilizes a slurry of copper chloride and fuller’s earth.1
• Refinement: After the reaction, the slurry is separated for reuse, and the oil is water-washed and dried to remove any remaining traces of the catalyst.1

By converting these compounds into disulfides, refineries reduce the objectionable odors and mitigate the corrosive effects that thiols have on equipment and catalysts.13