Facile synthesis of Bi-functionalized intrinsic microporous polymer with fully carbon backbone for gas separation application

Abstract Membrane technology is considered as one of the most efficient methods to capture CO2 economically. In which, functionalized PIMs are attracting more and more attention due to their superior gas separation properties in both high permeability and selectivity; however, one of the biggest challenges is their high cost. Herein, a novel bi-functionalized PIM with fully carbon main chain was synthesized efficiently by a simple one-step Friedel-Craft polycondensation reaction. The HSBI-NO2 polymer bearing two functional groups (–OH and –NO2) derived from two cheap raw materials is easy scale up, which showed high molecular weight of 94 KDa, good solubility in most conventional solvents, and high thermal stability with on-site decomposition temperature above 344 °C. There is no glass transition temperature below 300 °C that confirmed the rigidity of this polymer backbone. It also showed modest microporosity with BET surface area of ∼ 288 m2 g−1 and strong mechanical strength of 65 Mpa. The HSBI-NO2 membrane demonstrated an over 3-fold improved CO2 permeability than previously reported analogue without sacrificing its CO2/CH4 selectivity due to the bulky and rigid spirobisindane contortion center. Temperature dependent gas separation analysis indicated that the gas permeation in HSBI-NO2 was attributed to its diffusion, as confirmed by its much higher activation energy of diffusion (Ed) than heat of adsorption (-ΔHs). HSBI-NO2 also showed good anti-plasticization properties, aging resistance, and CO2/CH4 mixed-gas separation performance. Even under the upstream CO2 partial pressure of 10 bar, the permeability of CO2 is 52.3 Barrer and the CO2/CH4 selectivity is still 20. The convenient in synthesis, cheap raw materials, good physical properties, and modest to high separation performance make this HSBI-NO2 polymer extremely cost-effectiveness and great potential in practical gas separation applications.