In this work, the physicochemical properties of spent Ni-Mo/Al2O3 catalysts which were used in the hydrotreating of deasphalted vacuum bottoms were investigated. Catalysts were taken from the last stage of operation of a typical run of an industrial reactor belonging to a Colombian refinery. Spent catalysts were sampled from different locations along the catalytic bed. Six heights (h from 1 to 6) and three samples per height (θ = 0°, 90° and 180°) were taken to characterize their porosity, surface and bulk chemical composition. Porosity was analyzed by acquiring N2 physisorption isotherms at 77 K. Surface area was calculated by the BET method and pore size distributions using DFT. In general, the adsorption-desorption N2 isotherm showed important changes in the porous structure (hysteresis loops) depending on the location of the spent catalysts. An 8% reduction in the microporous area was found for samples taken from θ orientation equal to 0° as compared to samples taken at θ = 90° and 180°. Changes in surface area were also observed. This suggests that hydrodynamic problems, wall effect or packed bed channeling are present during normal reactor operation. The surface chemical composition was obtained by X-ray photoelectron spectroscopy and the bulk chemical composition, by inductively coupled plasma – optical emission spectroscopy. Surface and bulk chemical composition showed similar trends. Though, according literature, coke accumulation should be increase and metal accumulation decrease from the top to the bottom of industrial hydrotreating units, in this case, a remarkably higher amount of metals and coke in the middle of the catalytic bed was observed. The presence of metal and coke deposits agreed with trends in surface area. Particularly, when residual metals from hydrometallization reactions and coke from hydrocarbon transformations were at their highest, surface area was lowest.

Characterization of spent catalysts from an industrial hydrotreating unit give insight upon catalyst life evolution

255th National Meeting (2018)

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