Intraparticle diffusivity reduction during hydrotreatment of coal-derived liquids

Measurements of effective intraparticle diffusivity were made by using aged catalysts withdrawn at various times from coal liquefaction expanded-bed hydrotreaters. Artificially aged catalysts from the laboratory were also used. Depending on the feed properties and the catalyst age, the effective intraparticle diffusivities were reduced, by up to 2 orders of magnitude, as compared to the corresponding values with the fresh catalyst. The data suggest a significant increase in catalyst pellet tortuosity because of deposition of materials inside pores during hydroprocessing activities, indicating a contributing factor to catalyst deactivation. The intraparticle diffusivity values could be partially restored through controlled oxidative regeneration.