Modeling Transient Permeation of Binary Mixtures through Zeolite Membranes

Transient permeation of binary mixtures through zeolite membranes was modeled by Maxwell−Stefan diffusion and extended Langmuir adsorption. The permeate response of the faster-diffusing component overshoots its steady-state permeance, even when adsorption properties of the two components are identical. For zero permeate pressure and negligible support resistance, the adsorption equilibrium constants only affect the transient response by determining feed occupancies. Both higher permeate pressures and more support resistance decrease the overshoot in the permeate response of the faster-diffusing component. In some cases, molecules transport through the membranes against their concentration gradient under transient conditions because of the influence of slower-diffusing molecules. At steady-state, slower-diffusing molecules can cause faster-diffusing molecules to transport against their concentration gradient for high permeate pressures or substantial support resistance.