Improved CO2/CH4 Separation in Carbon Molecular Sieve Membranes via Copolymerization of Long-Chain Flexible Structures

Carbon molecular sieve (CMS) membranes demonstrate considerable advantages and significant potential in the separation of CO₂ and CH₄. Nevertheless, current research predominantly emphasizes the enhancement of CMS membranes through the incorporation of rigid structures and chain spatial stacking. The role of flexible structures in this context remains inadequately understood. To address this gap, we introduced long-chain polydimethylsiloxane (PDMS) and copolymerized it to synthesize polyimide that combines rigid and flexible frameworks. This approach enabled us to investigate the impact of flexible structures on the structure and properties of carbon membranes by varying the PDMS content. The findings indicated that flexible PDMS significantly influenced the thermal decomposition behavior of polyimide and facilitated in situ silicon doping within the carbon membranes, thereby modifying the pore characteristics of the carbon film. Specifically, with a 10% addition of PDMS, the CO₂ permeability of the CMS membrane reached 9556 Barrer, representing an enhancement of 103.9% and surpassing the 2019 upper bound for CO₂/CH₄ separation. Furthermore, the effect of pyrolysis temperature was also examined. Ultimately, this study offers a novel perspective on regulating the structural and performance characteristics of carbon membranes through the integration of long-chain flexible structures.