SIMPLIFIED TREATMENT OF THE RATES OF GAS-SOLID REACTIONS INVOLVING MULTICOMPONENT DIFFUSION

An approximate analytical solution is presented which describes the rate of a gas-solid reaction involving multicomponent diffusion in the gas phase. The model obviates the numerical solution of the nonlinear Stefan-Maxwell equations by defining pseudobinary diffusivities at the diffusion boundaries which take into consideration the Stefan-Maxwell dependence of the binary diffusivities. A linear dependence on mole fraction is subsequently assumed for the pseudobinary diffusivities across the control volume. The model has been generalized to account for reversible reactions and bulk flow effects due to volume change of the gas. The approximate solution is compared with the rigorous numerical solution over a variety of conditions, and the resulting comparisons show that, even for very large differences in binary diffusivity values, good agreement is obtained between the two solutions.