Carbon Molecular Sieve Membranes from Acenaphthenequinone-Biphenyl Polymer; Synthesis, Characterization, and Effect on Gas Separation and Transport Properties.

A rigid, high temperature-resistant aromatic polymer, poly(1,1'-biphenyl)-6,8a-dihydroacenaphthylene-1(2H)-one (BDA) comprising acenaphthenequinone and biphenyl was successfully synthesized by superacid catalyzed polymerization. BDA has a high decomposition temperature (T = 520 °C) that renders it a viable candidate for carbon molecular sieve membranes (CMSM) formation. BDA precursor pyrolysis at 600 °C (BDA-P600) leads to a carbon turbostratic structure formation with graphene-like amorphous strands in a matrix with micropores and ultramicropores, resulting in a carbon structure with higher diffusion and higher selectivity than dense BDA. When the BDA pyrolysis temperature is raised to 700 °C (BDA-P700), the average stacking number of carbon layers increases, along with an increase in the crystallite thickness stacking , and layer plane size , leading to a more compact structure. Pure gas permeability coefficients are between 3 and 5 times larger for BDA-P600 compared to the BDA precursors. On the other hand, there is a decrease between 10 and 50% for O and CO between CMSM BDA-P600 and BDA-P700, while the large kinetic diameter gases N and CH show a large decrease in permeability of 44 and 67%, respectively. It was found that the BDA-P700 WAXD results show the emergence of a new peak at 2θ = 43.6° (2.1 Å), which effectively hinders the diffusion of gases such O, N, and CH. This behavior has been attributed to the formation of new micropores that become increasingly compact at higher pyrolysis temperatures. As a result, the CMSM derived from BDA precursors pyrolyzed at 700 °C (BDA-P700) show exceptional O/N gas separation performance, significantly surpassing baseline trade-off limits.