Efficient non-catalytic oxidative and extractive desulfurization of liquid fuels using ionic liquids

Oxidative desulfurization (ODS) is one of the promising alternative and heavily researched desulfurization technologies. This is partly due to its ability to preferentially oxidize and ease the removal of refractory sulfur compounds with the aid of a suitable solvent. Despite its long list of advantages, challenges in different research areas within ODS technology still exist. In this work, an effort was made to bridge the gap that exists in terms of the selection of suitable oxidant and strategy. A preliminary kinetic modeling of the experimental data showed that the non-catalytic conversion of dibenzothiophene (DBT) and benzothiophene (BT) to their corresponding sulfones using the electrophilic meta-chloroperoxybenzoic acid (mCPBA) can be considered a bimolecular and a trimolecular reaction respectively. Using an ionic liquid (IL) as an extraction solvent in a simultaneous oxidation and extraction setup (EODS), >78% BT was removed at optimum experimental conditions. Using the post-oxidation extractive desulfurization setup (OEDS), 99% removal of BT was achieved at milder optimum experimental conditions. Also using the OEDS strategy, >99% of DBT removal was achieved after only 15 min at 60 °C, with a mass fraction of ≥0.5 and O/S of 3/1 for all the ILs tested. Finally, the sulfur content of a commercial diesel fuel was reduced to 15.6 ppm using the OEDS strategy with tetrabutylphosphonium methanesulfonate as a suitable extraction solvent, which can be readily regenerated.