Chemically cross-linkable polyimide membranes for improved transport plasticization resistance for natural gas separation

Abstract

A series of cross-linkable membrane materials based on the 6FDA-DAM:DABA (3:2) polyimide with enhanced transport plasticization resistance were synthesized to separate CO2 from CH4. Glycidol was used as a cross-linking agent to modify 6FDA-DAM:DABA (3:2) efficiently and form a transesterification reaction-based cross-linking. The conversion was calculated by solution 1H NMR. These materials were also characterized via density, glass transition temperature, permeation, and sorption measurements. Pure (CO2, CH4) and mixed gas (CO2/CH4) permeation was studied on dense films of these materials up to 700 psia (1000 psia) for pure CO2 (50%:50% CO2:CH4 mixed gas) feed. Compared to the 6FDA-DAM:DABA (3:2) membrane, CO2-induced plasticization resistance for cross-linked membranes was enhanced in aggressive feed streams. Under CO2 feed conditions at 35 °C, plasticization for the 41% glycidol-modified cross-linked membrane was not observed up to approximately 450 psia. Glycidol-induced cross-linking offers an excellent balance of selectivity, permeability, and plasticization resistance. The glycidol-modified 6FDA-DAM:DABA (3:2) is competitive with the earlier reported 1,3-propanediol modified materials. Possible issues such as resistance to contaminants may be final determinants in choice of approach; however, this topic was beyond the scope of the current study.