Coking of Hydroprocessing Catalyst by Residue Fractions of Bitumen

The deposition of organic material, or coke, on hydroprocessing catalyst was studied using Athabasca bitumen vacuum residue (ABVB) and narrow fractions of ABVB, prepared by supercritical fluid extraction (SCFE) with n -pentane. The feed materials were diluted in a low-sulfur gas oil and hydroprocessed over a commercial NiMo/γ-Al 2 O 3 catalyst in a 1 L continuous-stirred tank reactor at 440 °C. The coked catalysts were Soxhlet extracted with methylene chloride; then, carbon content, surface area, pore volume, and pore size were measured. Hydrodesulfurization activity was then measured using bitumen and dibenzothiophene as reactants.The SCFE fractions that contained only saturates, aromatics, and resins gave a low yield of carbon on the catalyst (<7.5 wt %). The asphaltene-rich fraction gave higher coke yields, both on the catalyst and in the reactor, and a lower H/C ratio than the lighter fractions. In the worst case with asphaltene-rich feed, over half of the surface area and pore volume of catalyst was lost due to coke deposition on the catalyst. HDS activity of the spent catalyst decreased monotonically with increasing carbon content on the catalyst. A portion of the carbonaceous material, or coke, on the catalyst was mobile and reactive at the conditions used for hydroprocessing of bitumen. The data suggested that this mobile adsorbed material had a significant impact on the observed activity of the catalyst.