Unified treatment of structural effects in fluid-solid reactions

Abstract

By considering reaction and diffusion through a product layer and concomitant movement of pore and reaction surfaces, a general rate equation is derived for fluid-solid reactions. Application to the random pore model extends the prior results (Bhatia and Perlmutter, 1980, 1981a) to account for nonlinear concentration gradients in the product layer, by assuming that the product is deposited as overlapping cylindrical annulae. For the Petersen (1957) model, new results are derived which account for product layer diffusion. A comparison of numerical conversion-time predictions from the grain model (Szekely et al., 1976), the Petersen model, and the random pore models suggests that they are more strongly affected by the representation of the reaction surface than by that of the pore surface. The model is applied to the data of Borgwardt (1970) on the SO₂-lime reaction, and the results are compared with a previous interpretation using a linear concentration gradient approximation.