Determination of diffusion coefficients from sorption kinetic measurements considering the influence of nonideal gas expansion

The influence of gas-phase kinetics on sorption kinetic measurements under constant volume/variable concentration conditions was investigated by theoretical means. Therefore, an analytical solution of Fick's law under appropriate boundary conditions was developed taking into account the finite rate of gas expansion in real experiments. This equation allows us to predict the influence of the valve effect on sorption kinetic curves. Reasonable criteria for the applicability of sorption kinetic methods are derived. The equation is suitable for the evaluation of experimental curves with respect to Fickian diffusivity.