A simple treatment for obtaining the Solution of single isothermal gas-solid non-catalytic reactions is presented. The model is formulated under a local volumetric approach and permits to incorporate non-linear chemical kinetics and the change in porous structure during conversion. The methodology developed in this work is based on the quantize method for decoupling the solid and gas equations and on perturbation and matching techniques for approximating the gas conservation equation. With this strategy, the calculation of gas concentration and solid conversion at any time and position are reduced to the solution of two coupled algebraic equations. The model compares favourably with the exact (numerical) solution for a variety of cases. This procedure provides an effective and general tool for obtaining the solution of gas-solid reactions with minor calculations. (c) 2006 Elsevier Ltd. All rights reserved.