A structural model for gas-solid reactions with a moving boundary—III: A general dimensionless representation of the irreversible reaction between a porous solid and a reactant gas

Abstract

A general structural model is developed for the description of non-catalytic gas-solid reactions; which allows for spherical and flat plate like pellets, made up of spherical or flat plate-like grains. The numerical solution of the dimensionless form of the governing equations results in a plot of the dimenionless time to achieve complete reaction against a gas-solid reaction modulus, which is valid for all the geometries considered. The use of this plot could be useful for the planning of experiments or for the interpretation of experimental data, in terms of structural models, without the need for digital computation. It is shown that for extreme values of the gas-solid reaction modulus, the results of the model reduce to the asymptotic solutions corresponding to the “shrinking core” and the “uniform reacting pellet” models respectively. Thus the “gas-solid reaction modulus” is helpful for the quantitative definition of the range of these asymptotic regimes, in terms of the chemical and structural parameters of the system.