Description of the interactions between intrinsic kinetics and internal mass transfer is one of the central issues in chemical reaction engineering. A general model was developed, comprising the kinetic and mass transfer effects in porous particles reacting in batch reactors. The catalyst particle size distribution was included in the model. A numerical algorithm and software was developed to solve the model for simulation and parameter estimation purposes. The model was applied to an industrially relevant case of green chemistry: synthesis of peroxycarboxylic acids from carboxylic acids and hydrogen peroxide. Due to the potential industrial applications, the present study was focused on the acetic and propionic acid perhydrolysis. The concentrations in the bulk phase and inside the catalyst particles were predicted by the model. It turned out that the smallest ion-exchange resin particles operated under kinetic control, whereas the largest particles (higher than 300 mu m) are influenced by diffusional limitation. Thus the combined effect of reaction and diffusion along with the particle size distribution are essential ingredients in the model. (C) 2009 Elsevier Ltd. All rights reserved.