Carbon molecular sieve gas separation materials and membranes: A comprehensive review

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, H2, O2, N2, CH4, CO2) 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.