Abstract
Analysis of singleβpore behavior in a porous pellet of reactant is used to develop a new model for predicting the conversionβtime relationship for gasβsolid noncatalytic reactions. The model accounts for the influence of pore diffusion, diffusion through the product layer which builds upon the pore walls, and surface reaction. By focusing attention on one pore, it is possible to include the effects of the changes in pore geometry that occur during reaction. Thus, both poreβmouth clocure and uniform deposition of product throughout the pellet can be predicted by using appropriate values for the diffusional and physical properties of the reaction system. The key parameters of the model are the effective pore length and effective diffusivity in the product layer. Numerical values of these quantities can be approximated from measurements of the pore volume and surface are of the unreacted and reacted forms of the pellet, or they may be evaluated from a limited amount of conversion vs. time data. The use of the model for predicting conversionβtime curves is illustrated with available data for the reduction of nickel oxide pellets with carbon monoxide and for the reaction of sulfur dioxide with calcium carbonate.