Huge improved gas separation performance of carbon molecular sieve membranes by incorporating polyimide COF into a linear polyimide precursor

Abstract

Most of polyimide based carbon molecular sieve membranes (CMSM) are constrained by an inherent trade-off effect between CO₂ permeability and CO₂/CH₄ selectivity. In this work, a simple approach was developed to enhance the CO₂/CH₄ separation property of CMSMs by incorporating a triazine-containing polyimide-based covalent organic framework (PI–COF) into a linear polyimide precursor (PI). This incorporation induced the formation of a cross-linked structure within the PI matrix, followed by carbonization, to simultaneously achieve high CO₂ permeability and improved CO₂/CH₄ selectivity. The porous PI-COF particles were well dispersed in the carbon matrix and matched well with the matrix during pyrolysis. PI-550-C5 derived from the PI containing 5 % PI-COF exhibits higher S_BET (557 vs. 495 m²/g) and d-spacing (10.47 vs. 9.97 Å than pure PI-550. The CO₂ permeability of PI-550-C5 increased by 122 % (5962 vs. 2680 Barrer) compared to that of PI-550 and the CO₂/CH₄ selectivity was also increased by 39 %, coupled with excellent anti plasticization and mixed gas separation properties. The CO₂ permeability of PI-550-C5 was only 14 % less than pristine PI-550 membrane after 120 days and CO₂/CH₄ selectivity was increased 77 %. PI-550-C5 surpassed the Robeson Upper bounds for CO₂/CH₄, O₂/N₂ (2008, 2019) and CO₂/CH₄ (2018) in single- and mixed-gas tests, respectively, demonstrating exceptional permeability and selectivity. This work provides a potential approach to fabricate PI-based high performance CMSM with PI-COF filler for excellent gas separation performance.