The hydrodesulfurization (HDS) of a straight-run diesel fraction of a Cold Lake crude was investigated using ammonium tetrathiomolybdate (ATTM) and phosphomolybdic acid (PMA) as dispersed catalysts. The experiments were performed in an autoclave at 340 °C using different hydrotreating media such as H2, H2/H2O, and H2 generated in situ from CO/H2O via the water gas shift reaction (WGSR). The external supply of molecular hydrogen proved to be the most effective medium for HDS with both catalysts, while similar levels of sulfur removal were achieved using either the H2/H2O or the CO/H2O medium. Desulfurization using molecular H2 was thus apparently inhibited by the addition of water to the feed, while H2 generated in situ proved to be at least as efficient at removing sulfur from diesel as using molecular H2 in the presence of water. Under our reaction conditions, ATTM exhibited greater activity for HDS and for the WGSR than PMA. This work demonstrates that Mo-based dispersed catalysts and partial oxidation flue gases containing CO, H2O, CO2, and H2 can be used to achieve satisfactory levels of sulfur removal from an industrial-type feedstock, as well as the feasibility of using dispersed catalysts and recycle streams for the treatment of heavy oil emulsions.

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