Incorporating organic macrocyclic cavitands into polyimide to fabricate high-performance hybrid carbon molecular sieve membranes for gas separation

Abstract

Precisely controlling the pore structure of carbon molecular sieve (CMS) membranes is essential for optimizing their gas separation performance. In the present work, 4-sulfocalix[4]arene (SC), an organic macrocyclic cavitands (OMC), was incorporated into polyimide (PI) to modulate the pore structure and enhance the gas separation performance of CMS membranes. The results indicated that SC molecules formed multiple disconnected PI-SC chain network regions within the PI matrix, providing additional short-distance rapid transport pathways for CO₂ and He, thereby enhancing their permeability. Moreover, the inclusion of SC increased the sp² C content in the CMS membrane, leading to a more ordered graphite-like carbon structure that enhanced the molecular sieving ability. In addition, by adjusting the content of SC and the carbonization temperature, the resulting PI/SC CMS membranes exhibited enhanced permeability for CO₂ and He, along with high gas selectivity. Under optimized conditions, the CO₂ and He permeabilities of the PI/SC-5-550 CMS membrane were significantly increased compared to the pure PI precursor membrane (P_CO2: 257.2 Barrer vs 1665.9 Barrer; P_He: 260.4 Barrer vs 2578.9 Barrer). Furthermore, the selectivity for CO₂/CH₄ and He/CH₄ increased by approximately 247 % and 378 %, respectively, both surpassing the latest Robeson upper bounds.