3 years ago

Ultraselective Carbon Molecular Sieve Membranes with Tailored Synergistic Sorption Selective Properties

Ultraselective Carbon Molecular Sieve Membranes with Tailored Synergistic Sorption Selective Properties
Chen Zhang, William J. Koros
Membrane-based separations can reduce the energy consumption and the CO2 footprint of large-scale fluid separations, which are traditionally practiced by energy-intensive thermally driven processes. Here, a new type of membrane structure based on nanoporous carbon is reported, which, according to this study, is best referred to as carbon/carbon mixed-matrix (CCMM) membranes. The CCMM membranes are formed by high-temperature (up to 900 °C) pyrolysis of polyimide precursor hollow-fiber membranes. Unprecedentedly high permselectivities are seen in CCMM membranes for CO2/CH4, N2/CH4, He/CH4, and H2/CH4 separations. Analysis of permeation data suggests that the ultrahigh selectivities result from substantially increased sorption selectivities, which is hypothetically owing to the formation of ultraselective micropores that selectively exclude the bulkier CH4 molecules. With tunable sorption selectivities, the CCMM membranes outperform flexible polymer membranes and traditional rigid molecular-sieve membranes. The capability to increase sorption selectivities is a powerful tool to leverage diffusion selectivities, and has opened the door to many challenging and economically important fluid separations that require ultrafine differentiation of closely sized molecules. Carbon/carbon mixed-matrix membranes are formed by pyrolyzing polyimide precursors. Unprecedentedly high permselectivities are achieved owing to substantially increased sorption selectivities, which are enabled by ultramicropores and micropores that selectively exclude bulkier penetrants. The capability to increase sorption selectivities is a powerful tool to leverage diffusion selectivities, and opens the door to many challenging separations requiring ultrafine discrimination of closely sized molecules.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adma.201701631

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