A model is proposed to study the reaction between a porous solid and a reactant gas resulting in solid and gaseous products. The model describes the reacting solid as a sphere made up of a distribution of randomly oriented open pores. The evolution of the pore-size distribution is followed by use of a population balance, using a combination of the independent variables of time and location first presented by Dudukovic (1976). The macroscopic properties of the solid are obtained by integrating over the pore size distribution. The results of the population balance are used with a mass balance on the reacting gas to obtain rate and conversion data.
The results of the model are compared to experimental data obtained for the sulfation of limestone (Ulerich et al., 1977). Both rate vs. conversion as well as conversion vs. time plots are presented, which serve as a more strenuous test of the model than either type of plot alone.