Carbon molecular sieve membranes derived from pseudo-interpenetrating polymer networks for gas separation and carbon capture

The design of polyimide-based pseudo-interpenetrating polymer networks (IPNs) is proposed to tailor the molecular structure of polymeric precursors for fabricating carbon molecular sieve membranes (CMSMs). To demonstrate the feasibility of this concept, pseudo-IPNs comprising of poly(2,3,5,6-phenylene-2, 2′-bis(3,4-carboxylphenyl)hexafluoropropane) diimide (6FDA-TMPDA) and 2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone (azide) are used to fabricate CMSMs. The gas transport properties of CMSMs are dependent on the azide loading and heat treatment temperature. During the pyrolysis, two competing processes of pore evolution from the released gases and molecular transformation are occurring simultaneously. The creation of pores determines the structural morphology of the CMSM at a low pyrolysis temperature of 550 °C while the molecular rearrangement is the governing factor for carbonization at an elevated temperature of 800 °C. The CMSMs prepared at 550 °C display good CO₂/N₂ separation performance. The 6FDA-TMPDA/azide (90-10) CMSM pyrolyzed at 550 °C shows a CO₂ permeability of 9290 ± 170 Barrer and an ideal CO₂/N₂ selectivity of 26.0 ± 0.8. CMSMs with high CO₂/CH₄ selectivity can be fabricated by carbonization at 800 °C. The 6FDA-TMPDA/azide (70-30) CMSM prepared at 800 °C has a CO₂ permeability of 280 ± 7.0 Barrer and CO₂/CH₄ selectivity of 164 ± 6.0. The CMSMs derived from polyimide/azide pseudo-IPNs exhibit potential use in pre- and post-combustion CO₂ capture.