Synthesis of Ionic-Liquid-Based Deep Eutectic Solvents for Extractive Desulfurization of Fuel

Deep eutectic solvents (DESs) have been widely applied in organic synthesis, extraction processes, electrochemistry, enzymatic reactions, and many others. However, the research of DESs on extractive desulfurization of fuel is only in its infancy. Here, a new class of DESs, ionic liquid-based DESs, was synthesized and characterized, where ionic liquid was produced in situ. Among the three DESs prepared from 1-methylimidazole (MIM) and diethanolamine as hydrogen bond acceptors and propanoic acid (PA) and nitric acid as hydrogen bond donors, MIM/PA showed the highest extractive efficiency and the sulfur partition coefficient (KN) reached 2.31. The viscosity of MIM/PA is much lower than other DESs and the low-viscosity ionic liquids in the literature, which is of benefit to mass transfer. The extraction mechanism was discussed by 1H nuclear magnetic resonance, and the activity differences among aromatic sulfur compounds were explained by density functional theory calculations. The addition of p-xylene and cyclohexene in model oil has no obvious effect on extraction of dibenzothiophene, meaning that the extractive desulfurization with DESs may also be suitable for the actual fuel. Finally, the free-sulfur fuel can be obtained after 5 times extraction.