Solvent-Free Desulfurization System to Produce Low-Sulfur Diesel Using Hybrid Monovacant Keggin-Type Catalyst.

Two quaternary ammonium catalysts based on the monovacant polyoxotungstate ([PW11O39]7-, abbreviated as PW11) were prepared and characterized. The desulfurization performances of the PW11-based hybrids (of tetrabutylammonium and trimethyloctadecylammonium, abbreviated as TBA[PW11] and ODA[PW11], respectively), the corresponding potassium salt (K7PW11O39, abbreviated as KPW11) and the peroxo-compound (TBA-PO4[WO(O2)2], abbreviated as TBA[PW4]) were compared as catalysts for the oxidative desulfurization of a multicomponent model diesel (2000 ppm S). The oxidative desulfurization studies (ODS) were performed using solvent-free systems and aqueous H2O2 as oxidant. The nature of the cation in the PW11 catalyst showed to have an important influence on the catalytic performance. In fact, the PW11-hybrid catalysts showed higher catalytic efficiency than the peroxo-compound TBA[PW4], known as Venturello compound. TBA[PW11] revealed a remarkable desulfurization performance with 96.5% of sulfur compounds removed in the first 130 min. The reusability and stability of the catalyst were also investigated for ten consecutive ODS cycles without loss of activity. A treated clean diesel could be recovered without sulfur compounds by performing a final liquid/liquid extraction diesel/EtOH:H2O mixture (1:1) after the catalytic oxidative step.