UBC Theses and Dissertations
Catalyst recycle in slurry-phase residue upgrading Rezaei, Hooman
The application of slurry-phase hydroconversion to upgrade residue oil derived from the Canadian oilsands (CLVR) is hindered by the cost of the catalyst, in part because the catalyst is used once-through before being discarded as part of the solid product (coke). The goal of the present study was to assess the potential of recycling the slurry-phase catalyst under high residue conversion conditions and to identify the cause of catalyst deactivation during catalyst recycle. Catalyst screening in a batch reactor operated at 415 °C and 5.6 MPa initial H₂ pressure with CLVR as reactant, showed that MoS₂ prepared in reversed micelles was most active for coke suppression and liquid yield among a series of Fe- and Mo-based catalysts. Furthermore, MoS₂ derived from Mo-micelle and Mo-octoate precursors had equivalent coke yields, but were more active for coke suppression than a water-soluble ammonium heptamolybdate precursor, as measured in a semi-batch reactor under more severe hydroconversion conditions (T = 445 °C and H₂ pressure of 13.8 MPa and 900 mL(STP)/min). MoS₂ prepared using Mo-micelle and Mo-octoate precursors over a range of Mo concentrations (0 – 1800 ppm) were recycled in the semi-batch reactor to assess the activity of the recycled catalyst in terms of coke suppresion and selectivity toward different products. The MoS₂ catalyst remained active for up to 4 reaction cycles, depending on the initial concentration of Mo added to the reactor. Characterization of the coke and catalyst recovered after each recycling step showed that the coke associated with the catalyst undergoes significant chemical and morphological changes during recycle and these changes result in deactivation of the catalyst. A conceptual model of the catalyst deactivation mechanism based on the characterization results was developed and ex-situ simulation of catalyst aging validated the proposed deactivation mechanism in the semi-batch slurry-phase upgrading reactor. Finally, a kinetic model of the CLVR hydroconversion reactions was developed that included the consumption and production of coke as an important step in the overall kinetic scheme.
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