(350f) Catalytic Oxidative Desulfurization of Model Diesel

An analysis of heterogeneous oxidation catalysts was performed to determine activities and optimal operating conditions for the multiphase oxidative desulfurization (ODS) reactions, using a model number 2 diesel. Catalysts studied included well-characterized Pd on Al2O3, SiO2 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, DBT) 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 (70-90ºC, 0.8-1.8 MPa, feed vol/wt cat. =100 mL/g) of this model diesel, Pd/C and Mo2C/C showed the best selectivity for oxidizing the S- and N-heterocycles vs. the alkylaromatics. Increasing the pressure increased the reaction rates of the S- and N-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. Initial analysis of reaction products by mass spectroscopy indicated the oxidation products: DBT sulfoxide, nitroso-compounds, methylquinoline, acetophenone, and naphthalenecarboxaldehyde. The absence of sulfones, along with the disappearance of thiophene and DBT, indicated that these products remained adsorbed onto the surfaces of the catalysts. 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 piston-oscillating reactor, which can eliminate the diffusion limitations and provide a uniform hydrodynamic environment. *dooley@lsu.edu