Intraparticle diffusivity reduction during hydrotreatment of coal-derived liquids

Abstract

Measurements of effective intraparticle diffusivity were made by using aged catalysts withdrawn at various times from coal liquefaction expanded-bed hydrotreaters. Artifically 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.

Effects of solvent and solute configuration on restrictive diffusion in hydrotreating catalysts

“…Hydrotreating of high molecular weight feeds, e.g., petroleum residua, coal, or coal-derived liquids, can be significantly influenced by pore diffusion in catalysts (Guin et al, 1986). Diffusion of large molecules in relatively small catalyst pores results in a lowering of the diffusion rate due to steric exclusion and wall effects (Beck and Schultz, 1970).…”

Effects of Solute Adsorption on Hindered Diffusion Uptake Rates in Finite Bath Experiments

“…This basic technique has been used by a number of investigators (Guin et al, 1986;Lee et al, 1991;Limbach and Wei, 1990 in a magnetically stirred glass diffusion cell containing a wire screen basket for holding catalyst particles. Temperature was controlled at 303 and 308 K for quinoline and polystyrene systems, respectively.…”

“…Generally, in studies of this type, properties of the porous solid are considered to be: uniform throughout the particle during adsorptive diffusion process (Guin et al, 1986;Lee et al, 1991;Limbach and Wei, 1990). This assumption is valid if the adsorbed layers of solute do not significantly change the pore diameter, e.g., small solute molecules and/or low amounts of adsorption.…”

“…Many investigators have observed intrapore diffusion effects, and several mathematical diffusion models have been applied to describe the diffusion process (Guin et al, 1986;Lee et al, 1991;Limbach and Wei, 1990;Haynes, 1988). Hindered diffusion effects include both steric exclusion and hydrodynamic restriction phenomena (Deen, 1987).…”

Effect of restrictive diffusion on hydrodesulfurization of heavy residue oils over CoMo/Al2O3

“…These heteroatoms contribute to the problems of air pollution. Therefore, residue hydrotreating is strongly influenced by pore diffusion limitation since the dimension of the reactant molecules is comparable to that of the catalyst pores (Guin et al, 1986). Hydrotreating is normally used for the primary upgrading step, using catalysts such as Co-Mo, Ni-Mo, or Ni-W supported on alumina or silica-alumina (Stanislaus et al, 1986).…”