Extraction of sulfur compounds from middle distillate fuels using ionic liquids and deep eutectic solvents: A critical review

Abstract

Desulfurization of commercial fuel is essential due to various problems, including catalyst deactivation and environmental problems such as acid rain. Due to the limitations of the conventional sulfur removal methods such as HDS methods, the development of alternative or complementary methods such as extractive desulfurization (EDS) is essential. In recent years, ionic liquids (ILs) and deep eutectic solvents (DESs) have been applied in the extractive desulfurization of fuels. While a wide range of ILs and DESs have been examined in the sulfur removal from model fuels, a few numbers of studies reported the application of these solvents in the sulfur removal from real hydrocarbon fuels. Therefore, it is required to analyze the reported results for the real fuel cases to address the research gaps in the field and suggesting new research directions. In this study, various aspects of the EDS process using ILs and DESs such as physical and chemical properties of solvents, the structure of solvents, the role of oxidants and catalysts in the process, and experimental conditions are investigated. Regeneration of ILs and DESs compared to traditional organic solvents is discussed, as well. Finally, the challenges and associated problems using ILs, and DES in the EDS process are discussed and research gaps are addressed for future studies.