Systematic investigation of the extractive desulfurization of fuel using deep eutectic solvents from multifarious aspects

Deep eutectic solvents (DESs) have attracted increasing attention as promising solvents for the ecofriendly and effective extractive desulfurization (EDS) of fuel oil. Herein, various aspects of DESs were examined using systematically designed experiments. Seven tetraalkylammonium bromide salts (C2-C8) as hydrogen bond acceptors (HBAs) and four alkyl diols (C2-C5) as hydrogen bond donors (HBDs) were combined to produce 28 DESs, and their physicochemical properties were characterized, including melting point, viscosity, density, and polarity. The mutual solubility of the DESs with a model oil was tested, and their sulfur removal efficiency was evaluated for thiophene, benzothiophene, and dibenzothiophene. The price and recyclability of the DESs using water as the anti-solvent were considered. The effects of the DES components on these aspects were simultaneously evaluated using a multilevel factorial design in which the HBA and HBD were considered categorical variables, and a desirability function was used to select the optimal solvent. Several facets important to the practical application of DESs in EDS, including multistage extraction for deep desulfurization, extraction capacity, and regeneration, were investigated for the suggested solvent. In particular, three readily applicable solvent regeneration methods, the addition of water as an anti-solvent, back-extraction using diethyl ether, and adsorption to granular activated carbon, were tested, and the anti-solvent strategy was found to fully recover the extraction capacity. This study provides useful insights and strategy to further examine DESs as the extraction solvent in the EDS system.