INFLUENCE OF PORE STRUCTURE AND CHEMICAL-PROPERTIES OF SUPPORTED MO CATALYSTS ON THEIR PERFORMANCE IN UPGRADING HEAVY COAL LIQUIDS

In the hydroprocessing of solvent-refined coals, both the pore structure and the chemical properties of the catalysts affect the conversion of the heavy materials. Increasing median pore diameter (MPD) of unimodal Ni-Mo/Al2O3 catalysts in the relatively small pore region (up to 150 angstrom) enhanced the conversion of both asphaltene and preasphaltene, but further increasing the MPD up to 730 angstrom mainly promoted preasphaltene conversion. In the runs of the isolated fractions, however, conversions increased with MPD up to 290 angstrom for asphaltene and up to 730 angstrom for preasphaltene. Comparative examination suggests that when a large-pore Ni-Mo/Al2O3 catalyst is used, the presence of preasphaltene materials inhibits the catalytic conversion of asphaltene. The observed conversions of heavy fractions and their increasing extents with MPD are higher for the runs of isolated heavy fractions, especially asphaltene. The degree of heteroatom removal is also influenced by MPD. There exist preferable pore size ranges for hydrodeoxygenation. Two MO/SiO2 and several carbon-coated Ni-Mo/Al2O3 catalysts with different MPD and a commercial Ni-Mo supported on silicated Al2O3 were also comparatively examined. The increasing MPD Of SiO2-supported Mo catalysts increased the conversion of preasphaltene materials. MO/SiO2 catalysts are more effective than Ni-Mo supported on Al2O3 and silicated Al2O3 for converting preasphaltene materials, while the latter two are more active for conversion of asphaltene into oil. Another interesting observation is that, for a given MPD range, the carbon-coated Ni-Mo/Al2O3 catalysts gave higher preasphaltene conversions than fresh ones. These results point to the conclusion that larger pore and less acidic hydrogenation catalysts are more effective for preasphaltene conversion, but efficient conversion of asphaltene into oil is facilitated by mild hydrocracking catalysts having appropriate pore size ranges.