EXTRACTIVE DESULFURIZATION OF LIQUID FUELS USING QUATERNARY AMMONIUM SALTS BASED DEEP EUTECTIC SOLVENTS

Abstract

Air pollution is increasing day by day owing to the combustion of fuels in vehicles. SOx emission occurs due to the combustion of organic sulfur compounds present in fuels. It is quite challenging for oil refineries to achieve a mandatory reduction of fuel impurities, which is required to obtain ultra-low sulfur fuels. Environmental issues have forced countries to impose strict regulations to reduce the sulfur content in hydrocarbon fuels. The presence of sulfur also creates processing difficulties such as catalyst inhibition and corrosion of pipelines and equipment. The sulfur content of crude oils varies from under 0.05 to > 10 wt.%; however, commonly, that is in the range of 1-4 wt.%. In India, the sulfur content for on-road diesel and gasoline has also been limited to 10 ppm according to the Bharat stage-VI (BS-VI) standards, implemented in April 2020. Various conventional and newer treatment techniques, which include hydrodesulfurization (HDS), adsorptive desulfurization (ADS), biodesulfurization (BDS), oxidative desulfurization (ODS), oxidative catalytic extractive desulfurization (OCEDS), and extractive desulfurization (EDS) have been reported in the literature for the sulfur removal from the liquid fuel. HDS is the most widely used method to remove sulfur from fuels. However, aromatic sulfur compounds such as dibenzothiophene (DBT) and its alkyl derivatives are highly stable compounds. They require a very high amount of hydrogen and severe conditions in terms of temperature and pressure for their removal. Organosulfur compounds abound in crude oil, including thiols (R-S-H), sulfides (R-S-R), and aromatics containing sulfur: thiophene and its alkyl derivatives, etc. However, extractive desulfurization (EDS) can remove thiophene and its alkyl derivatives from liquid fuels. Many researchers have reported the desulfurization study using ionic liquids (ILs). The issue with ILs, when used in desulfurization, is that it is very difficult to recycle and regenerate for further use in the EDS. Therefore, it is necessary to check other solvents or green solvents so-called deep eutectic solvents (DES) which can be easily recyclable and reusable for further use.