Fine tune gas separation property of intrinsic microporous polyimides and their carbon molecular sieve membranes by gradient bromine substitution/removal

Membrane technology is attracting more and more attention in hydrogen energy and natural gas sweetening applications. One challenge remaining is advanced membranes with both high separation performance and robust. Herein, remarkable gas separation properties of carbon molecular sieve membranes (CMSMs) are obtained by debromination assisted carbonization for a series of brominated intrinsic microporous polyimides (PIM-PIs). The di-bromine substituted 6FDBPI shows over 10 times higher permeability of CO2 (2147 vs 184 Barrer) and similar CO2/N-2 selectivity (19.7 vs 22.7) than the non-bromine substituted 6FNBPI. This is due to the bromine introduction creates a large number of ultra-micropore channels. After carbonization and debromination at 550 degrees C, the CMSM-550s exhibit a smaller (4.20-4.62 vs 4.77-8.49 angstrom), more intensive (75-90% vs 5-35%) and higher percentage (similar to 80% vs 10-55%) of ultra-micropores than their pristine PIM-PIs. Consequently, the CMSM-550s show both higher permeability and selectivity than their precursors, the larger permeability originates from the higher diffusion and solubility coefficient, the higher selectivity is purely contributed by diffusion selectivity. Notably, the 6FDBPI-550 shows an unprecedented H-2 permeability of 30,943 Barrer and H-2/N-2, H-2/ CH4 selectivity of 47.5 and 46.6 that by far exceed the latest trade-off lines, coupled with excellent anti plasticization and mixed-gas separation properties. This high performance together with the bromine facilitate carbonization method provide great potential in H-2 enrichment and natural gas sweetening applications.

Automated summary

By debromination assisted carbonization, carbon molecular sieve membranes (CMSMs) with remarkable gas separation properties were obtained from a series of brominated intrinsic microporous polyimides (PIM-PIs). The CMSM-550s exhibited smaller, more intensive, and higher percentage of ultra-micropores compared to their pristine PIM-PIs, resulting in higher permeability and selectivity. The 6FDBPI-550 showed unprecedented H2 permeability and selectivity that far exceeded the latest trade-off lines.