Deep Desulfurization of Light Oil through Extraction and Oxidation Processes using H2O2/Tungstophosphoric Acid in Room‐temperature Ionic Liquids

In this research, using room-temperature ionic liquids (RTILs) as the solvents to combine solvent extraction and chemical oxidation processes in one-pot operation for the desulfurization of fuel oil was pursued. In this solvent extraction and chemical oxidation desulfurization (SECOD), RTILs as media are immiscible with oil; sulfur compounds in oil are extracted into RTILs and oxidized thereafter to the corresponding sulfones by H2O2/TPA (tungstophosphoric acid). During SECOD, these high polar sulfones partition mainly in the ionic liquid phase. Hence, it results in their continuous removal from oil, which leads to deep desulfurization. To study the SECOD, we employed dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in hexadecane as model oil systems and compared the effects of RTILs on the removal of DBT and 4,6-DMDBT. The desulfurization rates followed the order OMIM+PF6− > BMIM+PF6− > BMIM+BF4−. Both OMIM+PF6− and BMIM+PF6− are water-immiscible and form three-phase (oil–water–ionic liquid) reaction systems; these three-phase systems offer higher removal efficiencies of sulfur compounds from oil. Under the optimized conditions, SECOD process reduced the sulfur content of diesel light oil from 897 to 42 ppm (i.e., 95% desulfurization efficiency) in a one-batch operation.