Gas transport properties of solution-cast perfluorosulfonic acid ionomer films containing ionic surfactants

Abstract We have made solution-cast films of perfluorosulfonic acid ionomer (PFSA) that included ionic surfactants in the casting solution. Gas transport measurements were made, using mixtures of CO 2 and CH 4 , through both solution-cast and commercial PFSA films that contained either NA + or HEDA + (monoprotonated ethylenediamine) counterions. The HEDA + provides facilitated transport of CO 2 at low partial pressures. For all the films with the NA + counterion the difference in permeability was greater at lower feed total pressures than at the higher pressures (∼11 MPa). We interpret this result as a mechanical pressure effect on the free volume around the ionic clusters. Additional observations include a “hindering” effect of the HEDA + counterion on both CO 2 and CH 4 permeation rates but more so for the CO 2 . We discuss these results in the context of separate diffusional paths for the two solutes. In general, all of these membranes exhibit CO 2 /CH 4 separation factors that are economically attractive at all the pressures studied. However, the permeability of the membranes was below economic targets by a factor of 100 considering the fact that they are 30 μm thick.