The pyridinium-based ionic liquids (ILs) N-butylpyridinium tetrafluoroborate ([BPy][BF 4 ]), N-hexylpyridinium tetrafluoroborate ([HPy][BF 4 ]), and N-octylpyridinium tetrafluoroborate ([OPy][BF 4 ]) were found to be effective for the selective removal of aromatic heterocyclic sulfur compounds from diesel at room temperature. The results suggested that the structure and size of the cation greatly affect the extractive performance of ILs. The extractive performance using pyridinium-based ILs followed the orderand for the IL, the sulfur removal selectivity of sulfur compounds followed the order thiophene (TS) < benzothiophene (BT) < dibenzothiophene (DBT) under the same conditions. The pyridinium-based ILs would not contaminate the diesel due to their insolubility. On the other hand, diesel has a certain solubility in pyridinium-based ILs, varying from 0.49 wt % for [BPy][BF 4 ] to 1.97 wt % for [OPy][BF 4 ]. According to the results, [HPy][BF 4 ] and [OPy][BF 4 ] might be used as promising solvents for the extractive desulfurization of diesel.

The Brønsted acidic ionic liquids 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM][HSO 4 ]) and N-butylpyridinium hydrogen sulfate ([C 4 Py][HSO 4 ]) were used as extractant and catalyst for desulfurization of diesel. The results show that [BMIM][HSO 4 ] is better as extractant and catalyst than [C 4 Py][HSO 4 ] during the desulfurization process. The sulfur removal of dibenzothiophene (DBT) in n-octane was 99.6% in 90 min under the conditions of V model oil /V IL = 2 : 1 and H 2 O 2 /DBT molar ratio at 5 (O/S = 5), at room temperature. The sulfur removal of four sulfur compounds by extraction and catalytic oxidation process followed the order of DBT > benzothiophene (BT) > thiophene (TS) > 4,6-dimethyldibenzothiophene (4,6-DMDBT). Moreover, the [BMIM][HSO 4 ] can be recycled for at least 6 times with a little decrease in the desulfurization activity. The sulfur removal of diesel fuel containing sulfur content of 97 ppm is 85.5%, which was much better than desulfurization performance by simple extraction with IL (11.0%). In this extraction and oxidative desulfurization process, DBT was oxidized to corresponding sulfone by H 2 O 2 with Brønsted acidic IL [BMIM][HSO 4 ] which served as not only extractant but also catalyst.

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