Ionic liquids based on imidazolium tetrafluoroborate for the removal of aromatic sulfur-containing compounds from hydrocarbon mixtures

Abstract

Two ionic liquids 1-methyl-3-butylimidazolium (BMImBF₄) tetrafluoroborate and 1-methyl-3-octylimidazolium (OMImBF₄) tetrafluoroborate were studied from the viewpoint of removing aromatic sulfur-containing compounds from hydrocarbon mixtures using transition metal ions as complexing centers. The values of distribution coefficients (D) indicate that OMImBF₄ absorbs benzothiophene (BT) and dibenzothiophene (DBT) better than BMImBF₄, which corresponds to the increasing absorption ability of the IL due to the presence of a longer hydrocarbon (octyl) chain in the third position of the imidazolium ring. The influence of additives of various complexes of cobalt(II) on the extraction of BT and DBT was studied in the system OMImBF₄–heptane. The planar complex of the Na-salt of 4,5-dicarboxyphthalocyanine of cobalt was found to be the most efficient for the extraction of both substances. The electrochemical approach enables one to purify the IL from BT and DBT by electrochemical oxidation or reduction. This result can be used for searching ways to increase the degree of extraction of BT and DBT in hydrocarbon–IL systems.