Cyclodextrin-based deep eutectic solvents for efficient extractive and oxidative desulfurization under room temperature

A promising green solvent, deep eutectic solvents (DESs), has received much attention in extraction combined with oxidative desulfurization (EODS) of fuel oil. However, the catalytic activity of DES and the mechanism of the desulfurization performance remain challenging issues. In this study, DESs with high catalytic property based on cyclodextrins (CDs) are designed and synthesized, which are employed as extractants and catalysts at the same time for EODS. Under optimal conditions (T = 30 °C, O/S = 3), the sulfur removal can reach 99.6% in the presence of methyl-β-cyclodextrin/3 formic acid (MBCD/3FA) DES. Experiments, characterizations, and density functional theory (DFT) calculations are combined to study the desulfurization mechanism. The results reveal that peroxy-compounds are the predominant active species, and the excellent catalytic performance of DESs based on CDs can decrease 81% of the reaction barrier in the EODS process. In addition, the structural deformation of DBT is confirmed by observing the vibration of the interaction between DES and DBT. Significantly, this work can provide a way to efficient EODS under room temperature and low O/S molar ratio.