Polyethersulfone-modulated Matrimid®-derived carbon molecular sieve membranes for enhanced C3H6/C3H8 separation

Abstract

Polymer-derived carbon molecular sieve (CMS) membranes hold significant potentials for propylene/propane (C₃H₆/C₃H₈) separation; however, further enhancement of their molecular sieving properties remains a critical challenge. In this study, we present a novel approach to regulating the pore structure of CMS membranes by incorporating the rubbery polyethersulfone (PES) into the Matrimid® precursor to fabricate CMS membranes. The incorporation of PES during pyrolysis creates voids between Matrimid® molecular chains, increasing the chain d-spacing and the content of ultramicropores, significantly enhancing the C₃H₆/C₃H₈ separation performance of the CMS membranes. As the PES content in the precursor membrane increases, the rising content of ultramicropores leads to improved C₃H₆/C₃H₈ selectivity, along with a minor increase in gas permeability. Notably, the 60 %Matrimid®+40 %PES-550 CMS membrane displays a C₃H₆ permeability of 70.3 Barrer with a C₃H₆/C₃H₈ selectivity of 21.4, representing increases of 194 % and 188 %, respectively, compared to Matrimid®-550 and exceeding the C₃H₆/C₃H₈ separation upper bound. Furthermore, under mixed gas separation conditions with a 50/50 (mol%) C₃H₆/C₃H₈ feed, this membrane exhibited a C₃H₆ permeability of 47.6 Barrer with a C₃H₆/C₃H₈ selectivity of 18.3, also surpassing the mixed gas upper bound for C₃H₆/C₃H₈ separation. The design principle of CMS membranes in this work provides a new approach for the preparation of high-performance CMS membranes, with the potential for separating the challenging C₃H₆/C₃H₈ mixture.