Pure- and mixed-gas transport properties of a microporous Tröger's Base polymer (PIM-EA-TB)

Abstract

Polymers of intrinsic microporosity (PIMs) offer tantalizing combinations of high selectivity and permeability in initial gas permeation measurements. Here, we report characterization of pure- and mixed-gas permeation properties of a thick (∼80 μm) PIM consisting of Tröger's Base (TB) and Ethanoanthracene (EA) films. The effects of feed pressure and temperature on pure-gas permeabilities of CH4, N2, O2, H2, and CO2 were investigated. The physical aging behavior of the thick film was tracked via pure-gas O2, N2, and CH4 permeability at 35 °C. Gas permeability decreased noticeably and selectivity increased as aging time increased. Particular attention was given to mixed-gas measurements of CO2 and CH4 (50/50) permeabilities at 35 °C and fugacities ranging from 2 to 18 atm to explore whether the rigid, bridged, bicyclic TB and EA units could resist CO2-induced plasticization. These results are presented along with pure-gas CO2 and CH4 results for membrane samples aged at different times. PIM-EA-TB aged for ∼24 h did not show signs of plasticization across the fugacity range considered. Dual-mode competitive sorption presumably caused the CO2/CH4 mixed-gas selectivity to be slightly higher than its corresponding pure-gas selectivity. However, as aging time increased, aged films underwent progressively more rapid and extensive CO2-induced plasticization with increasing fugacity, suggesting a systematic relationship between physical aging and plasticization in PIMs. Consequently, physical aging caused less improvement in mixed-gas CO2/CH4 selectivity than it did in pure-gas selectivity, due mainly to plasticization effects.