A new method to obtain the rate constant and activation energy independent of a kinetic model is proposed and evaluated for thermochemical conversion, specifically in the steam and CO2 gasification of coal and biomass. Recent works on gas solid reactions are based on single-step chemical reaction models that have been increasing in complexity through the use of more regression parameters to fit experimental data. These models fit better; however, sometimes their kinetic parameters are inconsistent, resulting in an incorrect interpretation of the reaction mechanism. The proposed method, which does not require any assumed kinetic model, is useful in calculating the parameters of the Arrhenius equation using cumulative variables obtained from the experimental data, i.e. conversion and residence time. For this reason, the uncertainty is reduced compared to conventional methods. The new method could be used as a consistency test between different kinetic models by comparing their kinetic parameters with those obtained with the proposed free-model method. The procedure has been applied to our previous experimental work and other authors' information on CO2 and steam gasification, verifying that the random pore model is not the best kinetic model to represent gasification and partial oxidation of coal and biomass. The new procedure can be used as a tool for chemical reaction engineering analysis in a broad range of thermochemical reactions under isothermal consideration. (c) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.