Synthesis of triptycene-based linear polyamide membrane for molecular sieving of N₂ from the VOC mixture

In this study, triptycene-based carboxylic acid (triptycene-2,3,6,7-tetracarboxylic acid) was synthesized for polycondensation with two amino compounds to ultimately form linear polyamides with different backbone structures. Characterizations, including nuclear magnetic resonance (NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy, were performed to confirm the polycondensation, and the structural properties were determined. Solubility of the synthesized polyamides was also measured. Subsequently, these polyamides were fabricated into membranes to investigate the separation of N₂ over the VOCs, and their stability and separation performance under different operating conditions were determined. Good separation performance, such as a rejection rate above 95%, was obtained during the studied separation range for the N₂/VOC mixture, indicating that a linear polymer can also be used for the separation of a condensable gas/vapor mixture and only the rotation of polymer chains can be restricted to a certain extent by the side groups.