Unprecedented gas separation performance of a difluoro-functionalized triptycene-based ladder PIM membrane at low temperature

Abstract

Advanced membrane materials are playing increasingly important roles in solving global energy intensive separation problems. Herein, we introduce a high-performance intrinsically microporous Tröger's base-derived ladder polymer (DFTTB) as an advanced membrane material for low-temperature gas separation applications. DFTTB was obtained by design of a 2,3-difluoro-functionalized triptycene (DFTrip) building block. The resulting ladder polymer exhibited high microporosity (S_BET = 918 m² g⁻¹), good thermal and mechanical properties, and excellent gas separation performance at or above the latest 2015 permeability/selectivity trade-off curves for H₂/N₂, H₂/CH₄ and O₂/N₂ with H₂ and O₂ permeabilities of 5468 and 650 barrer coupled with H₂/N₂, H₂/CH₄ and O₂/N₂ selectivities of 50, 38 and 6.0, respectively. Furthermore, DFTTB displayed unprecedented performance at sub-ambient temperatures with an O₂/N₂ selectivity of 10.1 and O₂ permeability of 137 barrer at −30 °C. This high selectivity coupled with up to ∼100-fold higher O₂ and H₂ permeability than commercial glassy polymer membrane materials, provides new opportunities for low temperature air separation and hydrogen recovery from petrochemical process streams.