Emerging desulfurization technologies and cutting-edge solvents for sulfur compounds removal from liquid fuels – a comprehensive review
Aman Khalid, Abdul Rafay Khalid, Ahmad Farhan, Yusra Arooj, Muhammad Zahid, Muhammad Azam Qamar, Ewa Rostek, Jarosław Serafin, Grzegorz Boczkaj
Abstract
Desulfurization technologies represent one of the most essential steps in fuel processing. This importance arises from environmental issues related to the emission of sulfur oxides (SO x ) into the atmosphere as a result of fuel combustion, which contains sulfur compounds. SO x is a significant atmospheric pollutant that causes health hazards and has a serious environmental impact. Current worldwide limitations on the total sulfur content in automotive fuels are very strict. Sulfur is present in fuels in the form of organo-sulfur compounds. A selective refining process commonly referred to as desulfurization has been developed to eliminate these S-compounds from liquid fuel, enabling effective production of high-quality, low-sulfur, environmentally friendly liquid fuels. This review explores the traditional as well as the emerging desulfurization technologies. The fundamental features of several desulfurization technologies, notably hydrodesulfurization, oxidative desulfurization, biodesulfurization, and extractive and adsorptive processes, are discussed. It highlights the reaction mechanisms, efficiency, and drawbacks of these methods. Key focus areas include process alternatives to typical hydrodesulfurization, including the catalytic systems used in oxidative desulfurization, microorganisms utilized in biodesulfurization, novel solvents employed in extractive desulfurization, and the integration of extractive-catalytic oxidative desulfurization systems (ECODS). The importance of solvents such as Deep Eutectic Solvents (DESs) and Ionic Liquids (ILs) (including porous ionic liquids, ILs combined with polyoxometalates, ionanofluid systems) in enhancing desulfurization performance has also been explored. Best processes based on DESs provide above 99 % removal of S-compounds in a time of 5 min (many other processes based on extractive or oxidative desulfurization, report the optimal time as 10–30 min). Confirming possibility of DES recycling for 50 desulfurization cycles. Biodesulfurization processes demand minimum several hours for effective process, but for many studies time of minimum 3 days was reported. Chemical oxidation of S-compounds results in formation of sulfoxides and sulfones which are polar and easily extracted from the fuel. Kodama or 4S metabolic pathway are typical mechanisms in biodesulfurization processes. 4S pathway can be named as preferred as generated by-products do not contain the sulfur atom. This review presents a comprehensive evaluation of the fundamentals, progress, recent developments, challenges, and limitations of desulfurization technologies.