| Summary: | 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.
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