Effects of Supercritical CO2 Conditioning on Cross-Linked Polyimide Membranes

The effects of supercritical CO 2 (scCO 2 ) conditioning on high-performance cross-linked polyimide membranes is examined through gas permeation and sorption experiments. Under supercritical conditions, the cross-linked polymers do not exhibit a structural reorganization of the polymer matrix that was observed in the non-cross-linkable, free acid polymer. Pure gas permeation isotherms and mixed gas permeabilities and selectivities show the cross-linked polymers to be much more stable to scCO 2 conditioning than the free acid polymer. In fact, following scCO 2 conditioning, the mixed gas CO 2 permeabilities of the cross-linked polymers increased while the CO 2 /CH 4 separation factors remained relatively unchanged. This response highlights the stability and high performance of these cross-linked membranes in aggressive environments. In addition, this response reveals the potential for the preconditioning of cross-linked polymer membranes to enhance productivity without sacrificing efficiency in practical applications which, in effect, provides another tool to “tune” membrane properties for a given separation. Finally, the dual mode model accurately describes the sorption and dilation characteristics of the cross-linked polymers. The changes in the dual mode sorption model parameters before and after the scCO 2 exposure also provide insights into the alterations in the different glassy samples due to the cross-linking and scCO 2 exposure.