Comparison of structural models for gas-solid reactions in porous solids undergoing structural changes

Abstract

In many gas-solid reactions the porous solid undergoes structural changes due to differences in molar volume between solid reactants and solid products. In this paper some new models are proposed which take into account the effects of structural changes on the reaction rate. The models differ in their geometric descriptions of the initial structure of the porous solid but they all take into consideration the decreasing diffusion rate in the growing ash layer and the decreasing gas-solid interfacial area at swelling of the solid structure during reaction. The different models are compared with each other and with previously suggested models. A model that regards the initial solid structure as an aggregate of truncated spheres in contact with each other as in the initial stage of sintering seems to be the most realistic and flexible model of those investigated. This model has been used to predict conversion-time curves for the sulfation of limestone. The predicted curves are in good agreement with experimental results reported in literature. It is also shown that a semi-empirical approach can give essentially the same results with less numerical effort.