Transport and reaction in evolving, disordered composites-II. Coke deposition in a catalytic pellet

Abstract

We present a model for transient diffusion and reaction occurring in a single, spherical pellet undergoing deactivation by coke deposition. The assumption and limitations are similar to those of Part I. The solid morphology is assumed to be completely disordered throughout the process and is represented by a site-percolation model. The emphasis of this work is on the pore-plugging phenomenon, although the active-site poisoning is accounted for in conventional terms. We study the influence of process parameters, such as Damköhler number and selectivity, on the pore plugging process for both the parallel and series mechanisms. Special attention is paid to the effect, on the same process, of various morphological parameters such as accessible void area fraction, accessible void volume fraction, accessible intermaterial area density and the effective diffusivity factor. Some of these morphological features are critical in the modeling of catalyst deactivation under diffusion control.