Remarkable gas separation performance of a thermally rearranged membrane derived from an alkynyl self-crosslinkable precursor

Abstract

One critical problem confronted with gas separation industrial is membrane with high permeability, selectivity, mechanical strong and reliability. Here, we reported a high performance thermally rearranged polymer (EBAP-TR) membrane that partially fulfills the above objects, which was formed by a novel ortho-hydroxyl functionalized polyimide (EBAP-OH) containing an alkynyl group in the repeat unit. The acetylene groups in EBAP-OH are first cross-linked at ∼350 °C via a Diels - Alder reaction to form a fully aromatic special reticulated polymer (EBAP-CR), and then, thermally rearranged at 450 °C to form EBAP-TR. The CR and TR processes opened the polymer chains with larger d-spacing, lower density and higher BET surface area (35 times). The resulting EBAP-TR membrane exhibits a remarkable CO2 permeability (6455 Barrer) and CO2/CH4 selectivity (40) among the reported PBO membranes, which outperforms the newest 2019 CO2/CH4 trade off line. Besides, the EBAP-TR also shows good anti-plasticization properties and mixed-gas CO2/CH4 separation performances. When the upstream pressure is 30 bar, the PCO2 in CO2/CH4 mixed-gas still reaches 4055 Barrer and CO2/CH4 selectivity of 23.7. The above high performance of EBAP-TR is caused by its very large activation energy difference (ΔEp) between gas pairs. This Diels-Alder alkynyl crosslinking method to make TR membrane provides an effective way to develop high performance membrane in CO2-based separation applications.