Extraction and oxidative desulfurization of diesel fuel catalyzed by a Brønsted acidic ionic liquid at room temperature

Abstract

The Brønsted acidic ionic liquids 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM][HSO₄]) and N-butylpyridinium hydrogen sulfate ([C₄Py][HSO₄]) were used as extractant and catalyst for desulfurization of diesel. The results show that [BMIM][HSO₄] is better as extractant and catalyst than [C₄Py][HSO₄] 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 H₂O₂/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][HSO₄] 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 H₂O₂ with Brønsted acidic IL [BMIM][HSO₄] which served as not only extractant but also catalyst.