Reactions in solid particles—A reappraisal of models

Kancharla Shashidhara Reddy and Akkihebbal K. SureshDept. of Chemical Engineering, IIT Bombay, Powai, Mumbai 400076, IndiaDOI 10.1002/aic.13721Published online January 13, 2012 in Wiley Online Library (wileyonlinelibrary.com).Models such as the Ishida–Wen, or even more commonly the shrinking core models (Ginstling–Brounshtein being animportant example), have long been used in the analyses of reactions in particles, particularly in solid–solid systems. Therehave been a few analyses of the validity of the assumptions made in these models, but to date, no comparison has beenundertaken of these models against a general model to delineate their regions of applicability in the parameter space. Inthis article, we present a general unsteady-state model that subsumes the earlier models as special cases.Nondimensionalization leads to the identification of two governing parameters in the model, a diffusion-reactionparameter, and a relative abundance parameter. By solving the general model and comparing the solutions with those of theapproximate models in the parameter space, conditions under which the approximate models apply, and the errors thatresult from their application in other situations, have been identified.