A novel pore diffusion model in combination with a homogeneous reaction in the bulk solution is proposed to model the kinetic behavior of conversion of acetic acid during its esterification with methanol using ion exchange resin catalyst. The model parameters are determined based on the experimental data of a batch reactor with reactant quantities in stoichiometric ratio. Experimental kinetic data of conversion of acetic acid is obtained for various ranges of parameters such as catalyst loading in g/cc of reactant mixture volume, temperature in the range of 323.15-353.15 K, average diameter of catalyst particle varied from 425 pm to 925 mu m and RPM of magnetic stirrer. A multi time scale model is adopted in updating the conversion of acetic acid in the bulk liquid where the measurement is carried out. Since the homogeneous part of catalytic esterification is slow reaction, a large time step is used for updating bulk concentration or conversion, whereas a small time step is used to find the concentration distribution and inward flux of acetic acid inside the catalyst particle in a quasi steady state mode. This multi time scale approach leads to utilizing only the initial time kinetics of reaction for predicting two reaction constants namely k(f1), the forward reaction rate constant for homogeneous reaction in bulk solution and k(f2), the forward reaction rate constant for reaction inside the catalyst particle. The equilibrium conversion data provides the reaction equilibrium constant. The model predicts the overall kinetics of heterogeneous esterification reaction accurately. (C) 2013 Elsevier Ltd. All rights reserved.