A general asymptotic analytical solution for non‐catalytic gas‐solid reactions

The reaction between a porous solid pellet and a gas is analyzed in the asymptotic region of the effectiveness factor. The solid consumption is divided in two stages. The influences of effective diffusivity and surface area profiles are taken into account for both stages through a correction modulus of the effectiveness factor. The conversion — time relationship can be calculated for a selected model of porous structure and any reaction order for the gaseous reactant. The results are extended to non‐equimolar counterdiffusion and a non‐isothermal situation with external heat and mass transfer resistances.