EVALUATION OF CONCENTRATION-DEPENDENT DIFFUSIVITY WITH UPTAKE CURVE

A theoretical approach to concentration-dependent diffusion has been p roposed based on the constant diffusivity diffusion theory. The uncert ainty function F-t was introduced to describe the diffusion process. L inear relationships have been deduced for evaluation of the diffusion coefficients at different diffusion times from the uptake curve. The d iffusivity variation during the diffusion process could be represented by the time-dependent diffusivity, D-t. The applicability of the theo retical model has been tested in zeolitic adsorption systems. As an ex ample of the applications, the diffusion of hexane, heptane and octane in NaZSM-5 has been studied.