Carbon molecular sieve (CMS) membranes are microporous amorphous structures that are able to effectively separate gas mixtures at a molecular level and simultaneously possess very high thermal, chemical, and (when adequately supported) mechanical stability. The combination of those advantages makes CMS membranes promising candidates to tackle difficult, energy-intensive separations such as natural gas purification or treatment of some high-value petrochemical streams. Successful implementation of CMS membranes into large-scale chemical processes requires, however, fabrication of defect-free and sufficiently permeable membranes. 

In this contribution, we will present a detailed study on the fabrication of thin-film composite CMS membranes based on a polyimide of intrinsic microporosity (PIM-PI) precursor and supported by cost-effective stainless steel tubular supports. The chosen PIM-PI CMS precursor is unique because it undergoes two micropore evolution events: thermal rearrangement (400 – 450 °C) and pyrolysis (>600 °C). As a consequence, the resulting CMS membranes possess high gas permeances and moderate/high selectivities despite the avoidance of excessively thin selective layers.

In addition, we will discuss our research in a broader context of the somewhat surprising, generally detrimental effects related to an excessive reduction of thickness in materials that possess ultra-high free volume or microporosity (PIMs, CMS).