Gasification of solid substances involves complex processes that inculpates non-catalytic heterogeneous interactions. These interactions are significantly influenced by heat and mass transfer limitations resulting into large differences in actual and intrinsic rate of reaction. In the present work, a non-isothermal transient mathematical formulation, based on grain model, is developed to capture the effect of heat and mass transfer limitations for the CO2-gasification of single raintree char pellet. For kinetic rate law, conventional unreacted shrinking core model is modified by introducing a parameter that appreciated the catalytic effect of mineral content. The kinetic parameters were estimated by the non-linear regression analysis. The activation energies were estimated to be E = 122.37 kJ/mol/K and E1 = 176.94 kJ/mol/K for semi-empirical modified SCM. The total conversion time dropped by 32 min on increasing the ash content of char from 0% to 10% which is quite significant indicating that ash is highly catalytic in nature. A CFD software COMSOL Multiphysics 5.4 is used to solve the governing set of partial differential equations. The pellet model is validated by comparing the model results with the experimental results and a good agreement was realized. The experimental results are obtained by performing gasification experiments for a single char pellet at three different temperatures. The concept of effectiveness factor is explored to quantify the effect of internal mass and heat transfer limitations. The effectiveness factor was found to be more or less constant for a wide range of conversion and decreasing with increasing pellet radius.