Heteropolyacids as effective catalysts to obtain zero sulfur diesel
This paper deals with the catalytic properties of different supported heteropolyacids (HPAs), both molybdenum- and tungsten-based, in the oxidative desulfurization process of diesel. We are jointly developing a new oxidative desulfurization process, aimed at reducing the sulfur content in diesel to less than 10 ppm (parts per million) using in situ produced peroxides. In this new process, high-molecular-weight organosulfur compounds, such as 4,6-dimethyl-dibenzothiophene (DMDBT), difficult to be eliminated by conventional hydrodesulfurization, are oxidized to the corresponding sulfones and subsequently removed by adsorption. Molybdenum-based HPAs, with Keggin structure, proved to be the most active and selective catalysts for oxidizing DMDBT with on-stream lifetimes exceeding 1500 h time on stream (t.o.s.).