Propionic acid-based deep eutectic solvents: synthesis and ultra-deep oxidative desulfurization activity

Abstract

Propionic acid-based deep eutectic solvents (C₃H₆O₂/X ZnCl₂, X from 0.1 to 0.6) were synthesized by stirring a mixture of propionic acid and zinc chloride at 100 °C. C₃H₆O₂/0.5 ZnCl₂ was characterized by infrared spectroscopy, electrospray ionization mass spectrometry and ¹H NMR spectroscopy. The oxidative desulfurization (ODS) of model oil and gasoline was investigated with C₃H₆O₂/0.5 ZnCl₂ DESs as an extractant and catalyst, and hydrogen peroxide (H₂O₂) as an oxidant. Some influence factors such as acidity of DESs, reaction temperature, H₂O₂ to sulfur (H₂O₂/S) molar ratio, and volume ratio of DESs to oil were studied. The results indicated that the desulfurization rates of dibenzothiophene (DBT), 4,6-dimethyl-dibenzothiophene (4,6-DMDBT), and gasoline can reach 99.42%, 98.80%, and 66.67%, respectively, under conditions of 30 °C, an H₂O₂/S molar ratio of 4, and volume ratio of DESs to oil of 0.15/1 over a period of 180 min. The desulfurization rate of DBT in model oil reached 96.31% after five recycles in the C₃H₆O₂/0.5 ZnCl₂–H₂O₂ systems.