CO2 separation using thin film composite membranes of acid-hydrolyzed PIM-1

Abstract

The polymer of intrinsic microporosity PIM-1 was synthesized with different topologies and negligible network content. A more rapid heating rate from room temperature yielded a predominantly di-substituted PIM-1 (D-PIM-1), whereas a marginally lower heating rate produced a more branched structure (B-PIM-1). Both polymers were acid-hydrolyzed to give carboxylic acid functionalization (cPIM-1), as indicated by FT-IR, 1H NMR, and elemental analysis. Both PIM-1 and cPIM-1 were processed into self-supported membranes and into thin film composite (TFC) membranes on a polyacrylonitrile support. For a 70% hydrolyzed polymer (D-cPIM-1-70%), the initial CO2 permeance reached 7700 GPU, with ideal selectivity of 56 for CO2/N2 and 37 for CO2/CH4. D-PIM-1 and D-cPIM-1-70% showed 85% and 52% CO2 permeance drop after 60 days’ aging, respectively. B-PIM-1, with initial CO2 permeance of 3100 GPU and ideal selectivity of 19 for CO2/N2 and 11 for CO2/CH4, showed only a 65% decrease. Polymer that was both branched and hydrolyzed (B-cPIM-1-73&81%), with CO2 permeance of 3200 GPU and selectivity of 64 for CO2/N2 and 45 for CO2/CH4, showed no decrease of CO2 permeance after 60 days. The branched structure is crucial for reducing membrane aging. Plasticization gave rise to reduced selectivity in mixed gas experiments, but nevertheless TFC membranes prepared from B-cPIM-1-81% were able to concentrate CO2 to 38% from a 10% CO2/90% N2 mixture at 4.8 bar.