Synthesis of task-specific ternary deep eutectic solvents for deep desulfurization via reactive extraction

Deep eutectic solvents (DESs) are a new type of green solvents, which have received widespread attention due to their similar nature to that of ionic liquids. They are generally composed of two or more components through physical interaction. In this work, a series of three-component DESs were synthesized by simple mixing of three components including boric acid , ethylene glycol and choline-like quaternary ammonium salt (2-hydroxyethyl)- n -alkyl-dimethylammonium chloride ([C n DMEA]Cl) with different molar ratios, where the alkyl group (C n , n  = 4, 8, 12) represented different lengths of carbon chain. The characterization results of DESs through FT-IR and 1 H NMR showed that DESs were formed by hydrogen bonding interaction. Extractive desulfurization combined with oxidation was established, where DESs were used as not only extractant but also catalysts. Compared with binary DESs, the ternary DES [C 4 DMEA]Cl/H 3 BO 3 /EG (1:3:5) showed higher catalytic activity in desulfurization of fuel, and the sulfur removal could reach up to 95.3% under optimized reaction conditions. Moreover, the high extraction efficiency of DESs was beneficial to their oxidation of the sulfur compounds. The reaction mechanism was studied by electron spin-resonance spectroscopy test and radical capture experiment.