Desulfurization by oxidation combined with extraction using acidic room-temperature ionic liquids

Abstract

Room-temperature ionic liquids (ILs) are commonly used for desulfurization by extraction for their unique solvent characteristics. In this study, 1-ethyl-3-(4-sulfobutyl)imidazolium bis(trifluoromethanesulfonyl)imide ([EimC₄SO₃H]NTf₂) was used as catalyst and extractant for desulfurization of DBT in n-octane. The results show that dibenzothiophene (DBT) could be removed from the oil phase effectively by this process, and that the sulfur content in a model oil could be decreased from 1600 ppm to less than 20 ppm. The extraction efficiency of the IL was greatly influenced by the structure of the anions and cations. The order of extraction capability of ILs was [EimC₄SO₃H]NTf₂ > [EimC₄SO₃H]HSO₄ > [C₄Py]NTf₂ > [Bmim]NTf₂ > [Bmim]PF₆. Experiments on the recycling and reuse of the room-temperature IL were also performed, and we found that [EimC₄SO₃H]NTf₂ could be recycled 5 times without significant decrease in the desulfurization activity. The extraction mechanism was also probed in detail, and we found that DBT was oxidized to its corresponding sulfone by H₂O₂ and NaClO, which was then extracted by the IL phase. However, different extraction mechanisms are at work with different oxidants.