Study on extraction of thiophene from model gasoline with brønsted acidic ionic liquids

Brønsted acidic ionic liquids (ILs), N-methylimidazole hydrogen sulfate ([HMIm]HSO₄) and N-methylpyrrolidone hydrogen sulfate ([HNMP]HSO₄), are synthesized and employed as extractants to extract thiophene from model gasoline (thiophene dissolved in noctane). The effect of extraction temperature, extraction time and volume ratio of ILs to model gasoline on desulfurization rates is investigated. Then, the optimal desulfurization conditions are obtained: the ratio of ILs to model gasoline is 1:1, extraction temperature is 50°C for [HMIm]HSO₄ and 60°C for [HNMP]HSO₄, extraction time is 60 min. Meanwhile, the desulfurization rate of [HNMP] HSO₄ for model gasoline is 62.8%, which is higher than that of [HMIm]HSO₄ (55.5%) under optimal conditions. The reason is discussed on the basis of the interaction energy between thiophene and ILs at the B3LYP/6-311 ++ G(d,p) level. Furthermore, the total desulfurization rate of [HNMP]HSO₄ and [HMIm]HSO₄ reaches 96.4% and 94.4%, respectively, by multistage extraction. Finally, the used ILs can be reused by vacuum drying, and their desulfurization rates are not significantly decreased after recycling 7 times in single-stage desulfurization.