The continuous ODS of a model fuel, catalyzed by titanium nanocrystals dispersed onto silica, was performed with <1% aqueous H2O2.

Aside from the desulfurisation, the denitrogenation of fuels is of great importance to minimze the environmental impact of transport emissions. The oxidative reaction pathway of organic nitrogen in the catalytic...

Extractive catalytic oxidative deoxygenation (ECODO) completes extractive catalytic oxidative desulfurization (ECODS) and extractive catalytic oxidative denitrogenation by removing organic oxygen from fuels. This is particularly necessary for renewable fuels to make them more stable and efficient. In ECODO, compounds such as cresol, furan, and their derivatives could be completely oxidized under oxygen at 20 bar and 120 °C using an aqueous heteropolyacid catalyst solution. The oxidation products were separated in situ in the three-phase process, either as CO 2 or CO in the gas phase or as water-soluble organic acids like formic and acetic acid as well as acetone. In the case of stable dibenzofuran (DBF), the conversion could be drastically increased from only 27% to above 50% by tuning the reaction conditions and optimizing the catalyst loading by a design of experiment. Moreover, the amount of oxygen in the gas phase could be drastically reduced from 20 to 4 bar operating in 20 bar of synthetic air without limiting the performance of the catalyst. Furthermore, it could be shown that the parallel ECODS in the presence of an oxygenate like DBF leads to better desulfurization of model gasoline than without. The ECODO therefore offers a potential alternative to the classical hydrodeoxygenation, which is not only more energy-efficient but also replaces the expensive hydrogen with cheap air and avoids additional unit operations for fuel cleaning.

The capability of extraction-coupled oxidative desulfurization (ECODS) to remove refractory sulfur compounds like dibenzothiophene from a model fuel has been investigated. Therefore, n-tetradecane was chosen as a diesel fuel matrix, and an aqueous H8[PV5Mo7O40] (HPA-5) polyoxometalate catalyst solution was used for the oxidative treatment. The oxidant of choice was molecular oxygen, and the desulfurization was conducted under moderate reaction conditions (130 °C, 20 bar O2). Thiophene and benzothiophene were found to degrade so fast into water-soluble substances that neither sulfoxides nor sulfones could be detected analytically as reaction intermediates. However, the analytical data show that the oxidation of refractory sulfur molecules, like dibenzothiophene (DBT) and its alkylated derivatives, into water-soluble products occurs via the sulfoxides and sulfones in a subsequent reaction. Furthermore, the kinetic data reveal that the degradation of the sulfone, i.e., the carbon skeleton, represents the rate-determining step in ECODS of dibenzothiophenes. The sulfoxide being formed initially is almost directly converted to the corresponding sulfone that accumulates and is only slowly transferred to water-soluble products. In contrast to thiophene and benzothiophene, DBT was found to inhibit the formation of active catalyst species. This inhibition could be reversed by adding a sacrificial substrate such as oxalic acid yielding the active catalyst species by reduction of HPA-5 from VV to VIV. Finally, the influence of organic nitrogen and oxygen compounds, which are also present in real distillation cuts, on ECODS has been studied.

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