| Summary: | Previous studies of slurry phase reactors for residue oil upgrading used dispersed
metal sulfide catalysts, prepared by in situ decomposition of either FeSO4 or the
naphthenate salts of Co, Mo and Ni, that were mixed with the residue oil. However, the
size of the catalyst particles was not well established and a high dispersion of the catalysts
in the oil was not always achieved. Recent studies have shown that catalysts prepared in
reverse micelles can be well characterized and have particle sizes in the nm range. In the
present study, catalysts prepared in reverse micelles were investigated as model catalysts
for residue oil upgrading, to study the effects of metal type, particle size and dispersion on
residue oil upgrading.
Fe, Co and Mo catalysts were prepared in n-hexane/PE4LE (polyoxyethylene-4-
lauryl ether), decalin/PE4LE, toluene/DDAB (didodecyldimethylarnmonium bromide), and
tetrahydrofuran/DDAB microemulsions, using nitrate salts of Fe and Co, and MoCI5. The
metal catalysts were prepared by reduction of the metal ions with N2H4.XH2O or LiBH4.
The size of metal particles prepared in the n-hexane/PE4LE microemulsions was measured
using transmission electron microscopy (TEM). The size of the catalysts was in the range
5-8 nm and decreased in the order: Mo > Fe > Co. The size of Co particles prepared from
Co/PE4LE/n-hexane with various water/PE4LE ratios was in the range 5.1-5.9 nm, but no
trend of increased particle size with increased water/PE4LE ratio was apparent from these
measurements. The catalysts prepared in microemulsions using different solvents were
sulfided in situ in the reactor. The performance of the colloidal catalysts for residue oil
upgrading was determined in a batch reactor operated at 430°C, in 5%H2S/95%H2, at an
initial pressure of 500 psig and a reaction time of 1 h.
The dispersion of the metal catalysts in the residue oil was studied by mixing the
residue oil with the metal catalysts prepared in reverse micelles. The amount of metal
catalyst recovered in the asphaltene fraction of the residue oil was measured. A high
catalyst content of the asphaltenes was taken as a measure of good dispersion of the
catalysts in the asphaltenes. There was no significant difference in dispersion of metal
catalysts prepared in hexane, decalin, toluene or tetrahydrofuran based microemulsions.
Hence, any effect of microemulsion solvent on hydroconversion activity could be ascribed
to the chemical properties of the solvents rather than catalyst dispersion effects.
Residue oil hydroconversion using different metal catalysts prepared from different
microemulsions using different solvents, showed a significant effect of metal type and
solvent. Mo was superior to Fe and Co for suppression of coke and gas formation. Coke
yield from decalin/PE4LE microemulsions was 5.8%, 6.2%, and 7.1% for Mo, Co and Fe,
respectively. Mo provided the highest MCR and S conversions but lowest asphaltene
conversion. Hence, it was concluded that Mo was a better hydrogenolysis catalyst whereas
Fe and Co were better hydrogenation catalysts at the conditions of the present study.
Hydrogen donor ability was important for residue upgrading and the choice of
microemulsion solvent had a detectable effect on catalyst performance. Mixed CoMo and
NiMo catalysts showed lower coke yield than the Co catalyst (5.0% for CoMo and NiMo
compared to 6.2% for Co) and lower than that of Mo (5.8%). A synergistic effect of the
CoMo and NiMo catalysts was observed for MCR conversion and coke yield. Cobalt
naphthenate catalyst precursor gave higher conversions of MCR and S, and a comparable
>525°C fraction conversion but gave lower asphaltene conversion than the Fe, Co, and
Mo catalysts prepared in microemulsions. === Applied Science, Faculty of === Chemical and Biological Engineering, Department of === Graduate
|
|---|
