Carbon-Silica Hybrid Microporous Membranes for Gas Separations

Membrane-based gas separation requires highly delicate engineering of molecular structures for the desired separation performance. For instance, natural gas processing including CO₂/CH₄ and N₂/CH₄ separations or olefin/paraffin separation involves a minimal molecular size difference of less than 0.5 Å. However, the extent of improvement in separation performance via engineering the chemical structure of polymeric membranes is very limited due to the trade-off relationship between permeability and selectivity. Moreover, most polymeric membranes are susceptible to condensable gas-induced plasticization at high pressures, suffering from significant selectivity loss. Carbon molecular sieve (CMS) membranes are promising molecular sieving candidates to overcome the intrinsic drawbacks of polymeric membranes including the limited separation performance and weak plasticization resistance. Recently, our group proposed a new approach to engineering the selective micropore structure of CMS membranes for various gas separations, including CO₂/CH₄, N₂/CH₄, or C₃H₆/C₃H₈ separation by pyrolyzing homogeneous blends of polyimide and ladder-structured polysilsesquioxanes. In particular, the SiOx phases in a carbonaceous matrix contributed to enhancing the molecular sieving ability of the resultant carbon-silica hybrid microporous membranes for various gas separations. In addition, our newly proposed approach enabled the formation of asymmetric CMS hollow fiber membranes with an excellent separation performance owing to the enhanced thermal stress resistance.