Highly Selective and Permeable Microporous Polymer Membranes for Hydrogen Purification and CO₂ Removal from Natural Gas

This paper reports a new macromolecular design that incorporates hierarchical triptycene unit into thermally rearranged polybenzoxazole (TR-PBO) structures for highly selective and permeable gas separation membranes with great potential for H₂ purification and CO₂ removal from natural gas. We demonstrate that triptycene moieties not only effectively disrupt chain packing enabling microporous structure for fast mass transport, but also introduce ultrafine microporosity via the unique internal free volume intrinsic to triptycene unit that allows for superior molecular sieving capability in resulting PBO membranes. Consequently, these triptycene-based polybenzoxazole (TPBO) membranes display among the highest gas selectivities for H₂ separations (i.e., α(H₂/N₂) = 96; α(H₂/CH₄) = 203) and CO₂ removal from natural gas (i.e., α(CO₂/CH₄) = 68) among existing glassy polymeric membranes. It is also demonstrated that microporous structure and gas transport properties of TPBO films are highly tailorable by adjusting the triptycene content and the ortho-functionality of the precursors. The highly diverse tunability, along with the excellent resistance toward membrane plasticization and physical aging, render the TPBO membranes with extremely versatile separation capability applicable for a wide range of important industrial processes to get clean or low carbon fuels and reduce carbon footprint.