A comparative review of extractive desulfurization using designer solvents: Ionic liquids & deep eutectic solvents

Background: Hydrodesulfurization (HDS) is extensively used for the exclusion of carcinogenic compounds from liquid fuels. Although less reactive refractory compounds including Dibenzothiophene (DBT), and a few alkyl DBTs such as 4, 6-Dimethyldibenzothiophene are difficult to be separated due to steric hindrance. In addition, the production of ultra-low-sulfur diesel consumes a significant quantity of hydrogen and requires severe operating conditions; hence, reducing the efficiency of HDS. Methods: Ionic Liquids have been the most researched area in the recent decade owing to their green nature and volatile properties. Furthermore, deep eutectic solvents (DESs) have also been found to be reliable and economical solvents for desulfurization. This review highlights the comparison of Extractive Desulfurization (EDS) over traditional desulfurization techniques and a cogent summary of interesting outcomes highlighting the complexity, challenges, and outlooks of such modern approaches using DESs/ILs. Significant findings: The extractive desulfurization has been found to be one of the most effective way for desulfurization of the liquid fuels. The major aspects which affects the desulfurization are the temperature, oilIL/DES mass ratio, extraction time, initial S Content, mutual solubilities, multiple cycles and regeneration of the used solvents in the EDS process. The results of this work will be significant in deciding the solvent selection and setting up the criteria for EDS process.