Research Progress of Phase Transfer Catalysts Used in Oxidative Desulfurization of Fuel Oil

The removal of sulfur compounds from fuel oil has been a major concern of the fuel industry. Hydrodesulfurization (HDS) is the most common desulfurization method currently used in oil refineries. However, HDS requires high temperature and high pressure conditions, consumption of hydrogen, and the removal effect of thiophene sulfides is not ideal. In view of defects of HDS, nonhydrodesulfurization technologies have been developed. Oxidative desulfurization (ODS) is regarded as the most potential desulfurization technology to replace HDS in industry because of mild operating conditions and high desulfurization efficiency. However, most ODS reactions are performed in heterogeneous systems. The common problem is that the oxidant and sulfur-containing compounds cannot contact effectively. Phase Transfer Catalysts (PTCs) are a class of catalysts that can assist in the transfer of reactants, thereby increasing mass transfer and accelerating the reaction rate of the heterogeneous ODS system. In this review, we divide PTCs applied to ODS into quaternary ammonium salts PTCs, ILs PTCs, polymers PTCs, supported PTCs and reaction-controlled PTCs, and will systematically introduce and summarize the research progress of PTCs used in ODS system. It is pointed out that reaction-controlled PTCs have a broad prospect in ODS system. In addition, the synthesis and recovery of PTCs will be briefly described.