Ultra-deep Desulfurization Of Diesel By Selective Oxidation-Extraction In Emulsion System

In the last decade, much attention has been paid to the deep desulfurization of fuel oils due to more stringent environmental regulations. Oxidative desulfurization(ODS) combined with extraction is considered to be one of the most promising processes and the refractory compounds, such as, 4, 6-dimethyldibenzothiophens can be oxidized relatively easily under mild reaction conditions.The oxidation of sulfur-containing compounds (benzothiophene, dibenzothiophene and their derivatives) in diesel was conducted in emulsion oxidative system (water in oil, W/O) composed of diesel, 30 wt% hydrogen peroxide and an amphiphilic catalyst [C₁₈H₃₇N(CH₃)₃]₄[H₂NaPW₁₀O₃₆] under mild conditions. The catalyst [C₁₈H₃₇N(CH₃)₃]4[H₂NaPW₁₀O₃₆] in the W/O emulsion system demonstrates very high catalytic activity that all sulfur-containing compounds in either model or actual diesel were selectively oxidized into their corresponding sulfones using nearly a stoichiometric amount of hydrogen peroxide as an oxidant. The catalytic oxidation reactivity of sulfur containing compounds was found to be in the following order: 4,6-dimethyldibenzothiophene > dibenzothiophene > 5-mthylbenzothiophene > benzothiophene. Although benzothiophene was relatively difficult to be oxidized, it can be also efficiently oxidized into sulfone in the emulsion system. The oxidized products, sulfones were readily separated from diesel using an extractionprocess. The sulfur level of a pre-hydrotreated diesel was lowered from 500 ppm to 0.1 ppm, while the sulfur level of a straight-run diesel was decreased from 6000 ppm to 30 ppm, using oxidation-extraction in emulsion system.In addition, the oxidation of dibenzothiophene (DBT) with molecular oxygen in the emulsion oxidative system (acetonitrile in decalin, W/O) was conducted by using polyoxometalate anion [C₁₈H₃₈N(CH₃)₃]₅[PV₂Mo₁₀O₄₀ and aldehyde as catalyst and sacrificial material under mild condition. It was found that the dibenzothiophene can be oxidized to corresponding sulfoxide and sulfone in the emulsion system under mild conditions. This possibly opens a new route for ultra-deep desulfurization of diesel using molecular oxygen as the oxidant.