Upgrading polyetherimide-derived carbon molecular sieve membrane via co-pyrolysis for gas separation applications

Abstract

Composite membrane technology offers a scalable and efficient approach for fabricating membranes suitable for large-scale production. It involves a selective thin film supported by a porous substrate, enabling highly efficient separation processes. However, achieving a uniformly coated selective layer on porous substrates remains a major challenge in developing high-performance gas separation membranes. Therefore, establishing strong interfacial compatibility between the selective layer and the substrate is essential for improving coating quality. An important yet often overlooked step in composite membrane preparation is polishing the inorganic substrate layer. This process effectively removes surface impurities and modifies surface roughness preparing the substrate for subsequent layer deposition. The resulting surface characteristics may also contribute to the formation of an asymmetric substrate, enhancing adhesion and coating performance, particularly for molecular sieving gas separation membranes.

Carbon molecular sieve membranes (CMSM) have been extensively studied as promising candidates for industrial gas separation and purification owing to their molecular sieving mechanism, which enables high gas permeance, tailored selectivity, and stability under corrosive and high-temperature conditions. Polyetherimide (PEI) is commonly used as a carbon precursor due to its low cost, thermal stability, and industrial compatibility. However, the relatively low gas permeability of PEI-derived CMS membranes limits their industrial application. To enhance the porous structure of PEI-based carbon membranes, thermally stable dopants—metal-based 2,6-bis(2-benzimidazolyl) pyridine (MtBBP)—have been introduced. These metal–ligand complexes incorporate gas-facilitating moieties, acting as functional dopants within the PEI matrix to improve gas transport and membrane porosity.