Modeling Transient Permeation of Binary Mixtures through Zeolite Membranes

Abstract

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.

Zeolite membranes – a review and comparison with MOFs

“…The models proposed in the literature are well established and incorporate flux through the Knudsen and bulk diffusion and viscous flow. 144,193,194 The sweep gas is introduced to carry away the species on the permeate side and thus increase the driving force for permeation. In most of the modeling studies, the effect of sweep gas is incorporated by assuming zero partial pressure of the species on the permeate side.…”

A transient method for mass‐transfer characterization through supported zeolite membranes: Extension to two components

“…The confinement effect that can induce a strong loading influence on the Maxwell‐Stefan approach (MS) diffusivities has also been studied by simulation . A parametric study for binary mixtures has been provided in relation with transient experiments . The slowing‐down and speeding‐up effect in binary mixtures have also been studied in the case of polar organic components diffusion through MFI composite tubular membranes …”

A model for the performance of microporous mixed matrix membranes with oriented selective flakes

“…The Maxwell-Stefan model for diffusion provides such a treatment. This model has been widely applied to the analysis and prediction of diffusive transport within zeolites and other microporous materials [16][17][18][19]. It uses chemical potential gradients as the driving force for diffusion, and it contains diffusion coefficients with clear physical meanings.…”