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.