Extraction Methods for Removing Sulfur and Its Compounds from Crude Oil and Petroleum Products

Sulfur is present in crude oil and petroleum products in the form of various compounds: mercaptans, hydrogen sulfide, sulfides, disulfides, thiophene derivatives, high-molecular-mass heterocyclic compounds, etc. The content of elemental sulfur in petroleum feedstock is low (up to 0.1%). Sulfur negatively affects the service and transportation properties of oil; therefore, the content of sulfur compounds in petroleum products and commercial oil is strictly limited. Numerous methods are used today for removing sulfur compounds from petroleum feedstock, such as hydrotreating, bio- and oxidative desulfurization, extraction, including supercritical fluid extraction, adsorption, alkylation, etc. This review deals with the use of extraction methods for treating petroleum feedstock to remove various sulfur-containing compounds. Particular attention is paid to papers dealing with the use of cheap and available polar organic solvents and inorganic chemicals for removing sulfur and its compounds both from model solutions and from crude oils and petroleum fractions. Also, search for new "green" solvents such as ionic liquids and eutectic mixtures, allowing removal of sulfur compounds from crude oil, shows promise. As a rule, complete removal of sulfur-containing compounds from oil samples by extraction requires a multistep extraction process.