Enhancement of Residue Hydroprocessing Catalysts by Doping with Alkali Metals

Abstract

Alkali metal nitrates and hydroxides were added to Ni/Mo on γ-alumina hydroprocessing catalysts in order to neutralize surface acidity, thereby reducing coke deposition on the catalyst and enhancing activity. The initial activity of the catalysts was tested by hydroprocessing Athabasca bitumen in microbatch reactors and a 1 L continuous-feed stirred reactor. Addition of nitrate salts was not effective. Addition of 0.26 mmol alkali metal hydroxide/g of catalyst was sufficient to reduce the concentration of very acidic sites in the catalyst, as measured by thermal desorption of pyridine. At this level of addition, coke deposition was reduced and hydrodesulfurization was increased. Experiments in a batch reactor showed that Li and Na were similar in activity, giving 80% sulfur removal compared to 63% with the untreated commercial catalyst. Coke content was reduced, with carbon concentration decreasing from 17.3% in the untreated catalyst to 14.4% with Li or Na at 26 to 28 mmol/g. The Na-doped catalyst gave a 40% increase in the hydrodesulfurization rate constant over the untreated catalyst in a continuous-feed stirred reactor during a 6 h experiment, consistent with the batch results. Asphaltene removal was also improved, while hydrodenitrogenation, microcarbon residue conversion, and residue conversion were unaffected.