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Membrane gas separation possesses the advantages of energy-saving, simple operation, environmental friendliness, and economic efficiency compared to traditional separation processes. Carbon molecular sieve (CMS) membranes have attracted increasing interest due to their superior chemical resistance and thermal stability compared to polymer membranes, as well as their ability to overcome the limitations of the trade-off between permeability and selectivity commonly present in polymer membranes. Specifically, polyimides (PIs) and polymers of intrinsic microporosity (PIMs), which have the intrinsic advantages of designable structures, superior gas separation performances, and good thermal and mechanical strength, serve as excellent precursors for making CMS membranes. Although significant progress has been achieved in the study of PI- and PIM-derived CMS membranes in the past few decades, there is still a lack of systematic research on their pyrolysis protocols. Herein, the current work reviewed the research progress in PI- and PIM-derived CMS membranes in the field of CO2 separation (CO2/CH4, CO2/N2 and CO2/H2) and olefin/paraffin separation, as well as the process simulation and techno-economic analysis of CMS membrane based gas separation processes. In particular, the effect of pyrolysis protocols including pyrolysis temperature, ramping rate, pyrolysis atmosphere and soaking time on the pore structure and gas separation performance of PI- and PIM-derived CMS membranes were systematically summarized and discussed. In addition, similar to CMS membranes made via other precursors, PI and PIM precursors also play an important role in the final CMS membrane separation performance. Generally, CMS membranes fabricated from PI and PIM precursors with higher free volume exhibited better gas separation performance. Overall, PIs and PIMs have been proven to be promising candidate precursors for CMS membrane fabrication. In addition, this review also offers perspectives and future research directions for next-generation PI- and PIM-derived CMS membranes for various gas separation applications. [ABSTRACT FROM AUTHOR]

Membrane materials exhibiting high CO2 permeability and selectivity are needed for CO2 capture to mitigate global climate change. In this study, Nafion is dissolved in and cast from N-methylpyrrolidone to generate membranes that are subsequently immersed in liquid water to promote nanostructural rearrangement of this amphiphilic polyelectrolyte. Gas permeability results confirm that the CO2 permeability and CO2/N2 selectivity of the membrane both increase significantly (to 472 Barrer and 61, respectively) after such rearrangement and thus exceed the 2008 Robeson upper bound. Transmission electron microscopy and small-angle X-ray scattering reveal that the nanostructure of Nafion is affected by the different processing routes utilized here. In addition, the influence of water vapor on the permeability of a CO2/N2 mixture at different relative humidity levels has been examined. These results confirm that the morphology and permeability of Nafion membranes are sensitive to water (as vapor or liquid), which enhances CO2 transport. Moreover, our findings indicate that (non)solvent-induced nanostructural rearrangement of amphiphilic polyelectrolytes constitutes a largely unexplored, but facile and effective, strategy with broad prospects to improve the CO2-separation efficacy of carbon-capture polymer membranes. [ABSTRACT FROM AUTHOR]