(646d) High-Performance Intrinsically Microporous Dihydroxyl-Functionalized Triptycene-Based Polyimide for Natural Gas Separation

A novel polyimide of intrinsic microporosity (PIM-PI) was synthesized from a 9,10-diisopropyl-triptycene-based dianhydride (TPDA) and dihydroxyl-functionalized 4,6-diaminoresorcinol (DAR). The unfunctionalized TPDA-m-phenylenediamine (mPDA) polyimide derivative was made as a reference material to evaluate the effect of the OH groups in TPDA-DAR on its gas transport properties. Pure-gas permeability coefficients of He, H₂, N₂, O₂, CH₄, and CO₂ were measured at 35 °C and 2 atm. The BET surface area based on nitrogen adsorption of dihydroxyl-functionalized TPDA-DAR (308 m²Â g^â??1) was 45% lower than that of TPDA-mPDA (565 m²Â g^â??1). TPDA-mPDA had a pure-gas CO₂ permeability of 349 Barrer and CO₂/CH₄ selectivity of 32. The dihydroxyl-functionalized TPDA-DAR polyimide exhibited enhanced pure-gas CO₂/CH₄ selectivity of 46 with a moderate decrease in CO₂ permeability to 215 Barrer. The CO₂ permeability of TPDA-DAR was â?¼30-fold higher than that of a commercial cellulose triacetate membrane coupled with 39% higher pure-gas CO₂/CH₄ selectivity. The TPDA-based dihydroxyl-containing polyimide showed good plasticization resistance and maintained high mixed-gas selectivity of 38 when tested at a typical CO₂ natural gas wellhead CO₂ partial pressure of 10 atm