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

Two quaternary ammonium catalysts based on the monovacant polyoxotungstate ([PW(11)O(39)](7−), abbreviated as PW(11)) were prepared and characterized. The desulfurization performances of the PW(11)-based hybrids (of tetrabutylammonium and trimethyloctadecylammonium, abbreviated as TBA[PW(11)] and ODA[PW(11)], respectively), the corresponding potassium salt (K(7)PW(11)O(39), abbreviated as KPW(11)) and the peroxo-compound (TBA-PO(4)[WO(O(2))(2)], abbreviated as TBA[PW(4)]) 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 H(2)O(2) as oxidant. The nature of the cation in the PW(11) catalyst showed to have an important influence on the catalytic performance. In fact, the PW(11)-hybrid catalysts showed higher catalytic efficiency than the peroxo-compound TBA[PW(4)], known as Venturello compound. TBA[PW(11)] 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:H(2)O mixture (1:1) after the catalytic oxidative step.