Solvent effect in homogeneous and heterogeneous reactions to remove dibenzothiophene by an oxidation-extraction scheme

In this work a study of dibenzothiophene removal by an oxidation-extraction scheme is presented. Experiments were carried out to observe the role that the solvent plays during the process, as well as the oxidizing agent and catalyst. The oxidation was carried out with hydrogen peroxide in the presence of a catalyst of tungsten supported on zirconia (WOx-ZrO2). A dibenzothiophene + n-hexadecane model mixture was employed to simulate a diesel fuel. Methanol, ethanol, acetonitrile, and gamma-butyrolactone were used as extraction solvents. Dibenzothiophene (DBT) was removed more efficiently by gamma-butyrolactone with respect to other solvents. The highest reactivity was achieved when gamma-butyrolactone was used during DBT oxidation with and without catalyst. When oxidation was carried out without catalyst, the oxidant behavior of the mixture could be explained in terms of the dissociation of hydrogen peroxide to produce strong oxidant species such as perhydroxyl ions (HO2-) by the influence of the aprotic solvents. Finally, when a catalyst was used during the oxidation, there was an additional oxidation contribution through the formation of surface peroxo-metal intermediates (W-O-O-H).