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Carbon molecular sieve (CMS) membranes offer some of the best combinations of high selectivity and permeability for molecular separations of permanent and condensable gases available to date. In addition, the fabrication of CMS membranes benefits from the well-established solution processing methods developed for fabrication of high-performance commercial polymeric membranes. In this review, we critically evaluate the extensive data set on CMS membranes available in the peer-reviewed literature published since the 1980s. In the first part, we focus on the material perspectives and evaluate how various polymer chemistries were used as precursors for generation of CMS films. We highlight the role of fluorinated and non-fluorinated polyimides as well as polymers of intrinsic microporosity (PIMs) which tend to dominate the more recent literature. In addition, we identify the most important parameters that determine the gas separation performance of CMS membranes, such as (i) pyrolysis temperature, (ii) pyrolysis atmosphere, or (iii) pre- and post-treatments and others. We collected and evaluated the CMS membrane performance for the separation of permanent gases (He, H 2 , O 2 , N 2 , CH 4 , CO 2) and highly energy-intensive olefin/paraffin separation. In the second part, we highlight the currently available data on CMS thin-film composite and integrally-skinned asymmetric membranes, which exhibit excellent permeance and selectivity in many important industrial separations. Finally, we provide a set of recommendations for future research in the area of CMS materials and membranes based on a critical evaluation of the reported data. [Display omitted] • Comprehensive review of CMS materials and membranes since 1980s. • Detailed material-oriented perspective on the role of various CMS precursor chemistries. • Highlight of the emerging CMS precursors such as PIMs. • Insights on relevant pyrolysis parameters: temperature, atmosphere, pre-/post-treatment. • Examination of the effect of selective layer thickness in composite CMS membranes. [ABSTRACT FROM AUTHOR]

The nonideal behavior of polymeric membranes during separation of gas mixtures can be quantified via the solution-diffusion theory from experimental mixed-gas solubility and permeability coefficients. In this study, CO2-CH4 mixtures were sorbed at 35 °C in 4,4′-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA)-m-phenylenediamine (mPDA)—a polyimide of remarkable performance. The existence of a linear trend for all data of mixed-gas CO2 versus CH4 solubility coefficients—regardless of mixture concentration—was observed for 6FDA-mPDA and other polymeric films; the slope of this trend was identified as the ratio of gas solubilities at infinite dilution. The CO2/CH4 mixed-gas solubility selectivity of 6FDA-mPDA and previously reported polymers was higher than the equimolar pure-gas value and increased with pressure from the infinite dilution value. The analysis of CO2-CH4 mixed-gas concentration-averaged effective diffusion coefficients of equimolar feeds showed that CO2 diffusivity was not affected by CH4. Our data indicate that the decrease of CO2/CH4 mixed-gas diffusion, and permeability selectivity from the pure-gas values, resulted from an increase in the methane diffusion coefficient in mixtures. This effect was the result of an alteration of the size sieving properties of 6FDA-mPDA as a consequence of CO2 presence in the 6FDA-mPDA film matrix. [ABSTRACT FROM AUTHOR]