A random pore model for fluid‐solid reactions: II. Diffusion and transport effects

The prior random pore model for kinetically controlled fluid‐solid reaction (Bhatia and Perlmutter, 1980) is generalized to include transport effects arising from boundary layer, intraparticle, and product layer diffusion. Numerical solutions are presented for a variety of conditions. The results show that the rate and surface area maxima predicted in the kinetic regime are shifted to lower conversions as intraparticle or product layer diffusional resistances increase. In addition, with increasing temperature a decrease in the overall reaction surface is predicted, in agreement with experimental findings (Kawahata and Walker, 1962). For reactions accompanied by an increase in the volume of the solid phase, it is shown that incomplete conversion may be expected, the ultimate conversion decreasing with an increase in the intrapellet diffusional resistance. Optimal temperatures for such reactions are also identified.