ENHANCEMENT OF RESIDUE HYDROPROCESSING CATALYSTS BY DOPING WITH ALKALI-METALS

Alkali metal nitrates and hydroxides were added to Ni/Mo on gamma-alum ina hydroprocessing catalysts in order to neutralize surface acidity, thereby reducing coke deposition on the catalyst and enhancing activit y. The initial activity of the catalysts was tested by hydroprocessing Athabasca bitumen in microbatch reactors and a 1 L continuous-feed st irred reactor. Addition of nitrate salts was not effective. Addition o f 0.26 mmol alkali metal hydroxide/g of catalyst was sufficient to red uce the concentration of very acidic sites in the catalyst, as measure d by thermal desorption of pyridine. At this level of addition, coke d eposition was reduced and hydrodesulfurization was increased. Experime nts in a batch reactor showed that Li and Na were similar in activity, giving 80% sulfur removal compared to 63% with the untreated commerci al catalyst. Coke content was reduced, with carbon concentration decre asing from 17.3% in the untreated catalyst to 14.4% with Li or Na at 2 6 to 28 mmol/g. The Na-doped catalyst gave a 40% increase in the hydro desulfurization rate constant over the untreated catalyst in a continu ous-feed stirred reactor during a 6 h experiment, consistent with the batch results. Asphaltene removal was also improved, while hydrodenitr ogenation, microcarbon residue conversion, and residue conversion were unaffected.