SHRINKING-CORE MODEL FOR SYSTEMS WITH FACILE HETEROGENEOUS AND HOMOGENEOUS REACTIONS

The shrinking-core equation for pore diffusion control has been extend ed to the case of a facile heterogeneous reaction coupled to a facile homogeneous reaction occurring within the pores of the product layer a nd in the bulk solution. The model considered is very general in that the simultaneous transport of all reacting species is included. The re sulting equation is identical to the standard one for diffusional cont rol by a single species except that the parabolic rate constant k(d) i s considerably more complex and contains useful information concerning the system. Analysis of its dependence on the system parameters yield s important criteria that determine the identity of the rate-controlli ng species and the direction of the heterogeneous reaction. Depending upon the relative values of the equilibrium constants of the two react ions, the dependence of k(d) on the bulk reactant concentration can va ry significantly from the linearity expected from the standard model. Copyright (C) 1996 Elsevier Science Ltd