Catalytic oxidative desulfurization of a model diesel

An analysis of heterogeneous oxidation catalysts was performed to determine the activities and optimal operating conditions for the multiphase oxidative desulfurization (ODS) reactions, using a model diesel. Catalysts studied included well-characterized Pd on Al2O3 and activated carbon supports, and carbon-supported Mo2C and W2C, which were prepared by temperature programmed reaction. Several other typical oxidation catalysts were also examined. The model diesel consisted of ~1 wt% sulfur compounds (thiophene and dibenzothiophene) with appropriate amounts of aliphatic, alkylaromatic and N-heterocyclic compounds to simulate a raw number 2 diesel. With oxygen as the oxidant in ODS reactions of this model diesel (70-90ºC, 0.8-1.8 MPa, feed vol/wt cat. = 100 mL/g), Pd/C and Mo2C/C showed the best selectivity for oxidizing the N- and S-heterocycles vs. the alkylaromatics. Increasing the pressure increased the reaction rates of the N- and S-heterocycles. Except for thiophene, there was only a small dependence of observed rates on temperature, which suggests the reactions were partially diffusion (of O2) controlled. The optimal ODS catalysts (carbides and 5%Pd/MPT-5) also showed high activity for the conversion of N-heterocycles. Current work includes further investigations of the better catalysts, full characterization of the products by GC-MS, and kinetics measurements using catalyst monoliths in a pistonoscillating reactor, which can eliminate the diffusion limitations and provide a uniform hydrodynamic environment