Extractive Desulfurization of Fuel Using 3-Methylpyridinium-Based Ionic Liquids

3-Methylpyridinium-based ionic liquids (ILs) were demonstrated to be effective for the selective removal of aromatic heterocyclic sulfur compounds from diesel at room temperature. The results indicated that the extractive performance using 3-methylpyridinium-based ILs followed the order of 1-octyl-3-methylpyridinium tetrafluoroborate ([C(8)(3)Mpy][BF4]) > 1-hexyl-3-methylpyridinium tetrafluoroborate ([C(6)(3)Mpy][BF4]) > 1-butyl-3-methylpyridinium tetrafluoroborate ([C(4)(3)Mpy][BF4]). For a given IL, the sulfur removal selectivity of sulfur compounds followed the order of dibenzothiophene (DBT) > benzothiophene (BT) > thiophene (TS) > 4,6-dibenzothiophene (4,6-DMDBT) under the same conditions, except for [C(8)(3)Mpy][BF4] IL, which followed the order of DBT > BT > 4,6-DMDBT > TS. The 3-methylpyridinium-based ILs are insoluble in diesel, while diesel has a certain solubility in 3-methylpyridinium-based ILs, with the content varying from 6.1 wt % for [C(4)(3)Mpy][BF4] to 9.5 wt % for [C(8)(3)Mpy][BF4]. The spent IL saturated sulfur compounds could be regenerated by a water dilution process. Considering these results, ILs studied in this work are more competitive and feasible for extractive desulfurization applications. Moreover, the extractive desulfurization using 3-methylpyridinium-based ILs could be used at least as a complementary process to hydrodesulfurization (HDS).