Transport properties of O2, N2, and CO2 through the CMS membranes derived from tris(4‐aminophenyl)amine‐based polyimides

Abstract Two carbon molecular sieve (CMS) membranes (XS22‐600 and XS23‐600) with closely matched pore‐size distribution were prepared via conditional pyrolysis of the hyperbranched tris(4‐aminophenyl)amine (TAPA)‐based polyimide membranes. The differentiation in their nitrogen contents comes from the dianhydride monomers, 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic (PMDA). These CMS membranes were characterized using Fourier transform infrared, XRD, XPS, and Raman analysis. XS22‐600 with larger ultra‐micropores has a lower selectivity of 3.6 than XS23‐600 (4.1), implying the molecular sieving mechanism domains in O 2 /N 2 separation. XS22‐600 with higher nitrogen content exhibits a higher selectivity of 19.1 than XS23‐600 (13.1) in CO 2 /N 2 separation. The doped nitrogen atoms exhibit a beneficial effect on CO 2 surface diffusing through the CMS membranes. This work provides empirical data for understanding the synergistic effect of selective surface diffusing and molecular sieving in CO 2 /N 2 separation.