(152bt) Porous Organic Cages-Stabilized Carbon Molecular Sieve for Efficient Gas Separation

Here we present results of gas selectivity and diffusion of different gases (C₃H₈, C₃H₆, H₂, and CO₂,) in porous organic cages (POCs) incorporated into fluorinated copolyimides polymers (FCPs). The FCPs were synthesized by the thermal and chemical imidization reaction of fluorinated dianhydrides, nonfluorinated dianhydride, and nonfluorinated diamine. Asymmetric hollow fiber membranes formed by the dry-jet/wet-quench spinning process. Once fresh FCP fibers were synthesized, they were crosslinked with POCs, vacuum dried at 90 °C. We investigated the uptake, gas selectivity and diffusion of different gases (C₃H₈, C₃H₆, CO₂, and H₂) over synthesized POC-mixed matrixed membranes (POC-MMM) at 25 °C and pressures up to 1 bar. At 1 bar and 25 °C, C₃H₈, C₃H₆ adsorption capacities reached 2.77 and 2.65 mmol/g over POC-MMM, respectively, while CO₂, and H₂ adsorption capacities of 1.48, and 0.068 mmol/g, respectively. Furthermore, stable CMS membrane was formed by pyrolysis of POC-MMMs under an inert argon atmosphere at 1 atm. To test the gas transport properties of CMS-derived POC/MMM, a lab-scale hollow fiber module with two-five fibers was constructed. The results of longer-term operation of synthesized CMS membrane that was continuously operated for 264 h (10 days) with an equimolar binary C₃H₆/C₃H₈ and H₂/CO₂, feed at 25°C and 1 bar feed pressure. The modification yielded promising results in the reduction of physical aging of CMS membranes.

This work was supported by the National Science Foundation Grant No. 2316143.