The result of the structureal change in the solid is a feedback effect in which the chemical and porosity effects reinforce each other. The study of such reactions involves simultaneous considerations of chemical rates of reaction and structural change in the solid.
Experimental data is needed on global rates at various conversions.
The interpretation of such measurements calls for analytic models and their numerical solutions, especially to highlight critical values of parameters that produce maxima in rates or conversions. Realistic modeling of gas-solid reaction systems must allow for gaseous products as well as for the possible deposition of solid products. In the latter case, diffusion through solid layers adds an additional complication to the overall mechanism. For this purpose, random pore models have been successful in interpreting a wide range of observations in gas-solid systems related to environmental and energy problems. Specific applications have been made to coal char gasification, to removal of pollutant SO x via reaction with lime, and to dehydration of inorganic salt hydrates.