From first principal study to continuum modeling: competitive gas adsorption in microporous PIM membranes

With the increasing demand for hydrogen (H₂) as a clean energy source, the use of efficient methods for its purification has become increasingly important, especially due to the presence of carbon dioxide (CO₂) as one of the main impurities in the hydrogen production process. In this study, a combined approach including molecular simulation and Maxwell-Stefan modeling was used to analyze the transport behavior of CO₂ and H₂ in P-HAB-6FDA membranes. The simulation results show a significant difference between pure gas and mixed gas conditions. While hydrogen has a higher permeability in pure gas conditions, in mixed gas systems, carbon dioxide takes over the adsorption process and practically prevents the adsorption and transport of hydrogen. Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations were used to determine the adsorption and diffusion coefficients, and the Maxwell-Stefan model was used to predict the gas permeability and selectivity. Also, under mixed gas conditions, the permeability of CO₂ exceeds that of H₂, which is in contrast to the behavior under pure gas conditions and is due to the strong adsorption tendency of CO₂. Lower temperature improves membrane performance by simultaneously increasing CO₂ adsorption and facilitating hydrogen diffusion. These findings highlight the significant difference between the transport mechanisms under pure and mixed gas conditions and confirm the efficiency of 6FDA-based membranes in selective hydrogen purification and CO₂ separation; and advance our understanding of the development of membrane-based gas separation technologies.