Evaluation of concentration-dependent diffusivity with uptake curve

Abstract

A theoretical approach to concentration-dependent diffusion has been proposed based on the constant diffusivity diffusion theory. The uncertainty function F_t was introduced to describe the diffusion process. Linear relationships have been deduced for evaluation of the diffusion coefficients at different diffusion times from the uptake curve. The diffusivity variation during the diffusion process could be represented by the time-dependent diffusivity, D_t. The applicability of the theoretical model has been tested in zeolitic adsorption systems. As an example of the applications, the diffusion of hexane, heptane and octane in NaZSM-5 zeolite has been studied.