A new approach has been developed to analyse the kinetics of heterogeneous gas-solid reactions. The solid reactant is considered as consisting of reactant species having different overall reaction rate constants and thus a rate constant distribution is associated with the solid. This distribution arises due to chemical heterogeneity of the material, availability of varying amounts of gaseous reactants at various locations within the particle due to its microstructural effects, and other physical phenomena which offer resistance to the reaction. Appropriate mathematics has been developed to express the reaction kinetics in terms of this rate constant distribution. The problem of evaluating the distribution is recognized to be equivalent to the problem of finding the inverse of the Laplace transform. A numerical method, based on non-linear optimization, has been used to carry out inversion of the Laplace transform and the rate constant distribution evaluated employing specified kinetic data. The applications of this new concept are illustrated using the kinetic data for reduction of hematite with hydrogen, and gasification of carbon with carbon dioxide. Effects of some of the operating parameters, e.g., temperature, particle size, porosity, gas flow rate and gas composition on the reaction kinetics are discussed in terms of this new concept.
