Large-ScaleComputational Screening of Metal OrganicFramework (MOF) Membranes and MOF-Based Polymer Membranes for H2/N2 Separations

摘要

Several thousands of metal organic frameworks (MOFs) have been reported to date, but the information on H2/N2 separation performances of MOF membranes is currently very limited in the literature. We report the first large-scale computational screening study that combines state-of-the-art molecular simulations, grand canonical Monte Carlo (GCMC) and molecular dynamics (MD), to predict H2 permeability and H2/N2 selectivity of 3765 different types of MOF membranes. Results showed that MOF membranes offer very high H2 permeabilities, 2.5 × 10³ to 1.7 × 10⁶ Barrer, and moderate H2/N2 membrane selectivities up to 7. The top 20 MOF membranes that exceed the polymeric membranes’ upper bound for H2/N2 separation were identified based on the results of initial screening performed at infinite dilution condition. Molecular simulations were then carried out considering binary H2/N2 and quaternary H2/N2/CO2/CO mixtures to evaluate the separation performance of MOF membranes under industrial operating conditions. Lower H2 permeabilities and higher N₂ permeabilities were obtained at binary mixture conditions compared to the ones obtained at infinite dilution due to the absence of multicomponent mixture effects in thelatter. Structure–performance relations of MOFs were also exploredto provide molecular-level insights into the development of new MOFmembranes that can offer both high H₂ permeability andhigh H₂/N₂ selectivity. Results showed thatthe most promising MOF membranes generally have large pore sizes (>6Å) as well as high surface areas (>3500 m²/g) andhigh pore volumes (>1 cm³/g). We finally examined H₂/N₂ separation potentials of the mixed matrix membranes(MMMs) in which the best MOF materials identified from our high-throughputscreening were used as fillers in various polymers. Results showedthat incorporation of MOFs into polymers almost doubles H₂ permeabilities and slightly enhances H₂/N₂ selectivities of polymer membranes, which can advance the currentmembrane technology for efficient H₂ purification.