EFFECTS OF INCORPORATION OF FLUOROCARBON AND HYDROCARBON SURFACTANTS INTO PERFLUOROSULFONIC ACID (NAFION) MEMBRANES

Significant permeability improvements can be made to perfluorinated ionomer films by incorporating sulfonated surfactants of suitable size into the membrane microstructure. A variety of 20-mum composite Nafion/surfactant membranes were prepared from DMF casting solutions containing Nafion and the sodium salts of perfluoro-1-butanesulfonic acid (perf-ButSO3Na), perfluoro-1-octanesulfonic acid (perf-OctSO3Na) and 1-octanesulfonic acid (OctSO3Na). The time required for 50% extraction of the surfactants from the membranes into water was 1 min for OctSO3Na, 5 min for perf-ButSO3Na, and approximately 3 days for perf-OctSO3Na. Extraction of perf-OctSO3Na into isooctane contacting solutions was not observable over periods of days. For membranes containing surfactants and exchanged with silver(I) ion, 3-fold permeability improvements can be obtained for the separation of 1,5-hexadiene from 1-hexene and n-hexane without any decreases in separation factors. Observed flux improvements are larger than the increase in ion-exchange site density and are attributed to increased mobility of olefins between carrier sites due to the presence of specific surfactants. Results indicate that movement of olefins in Nafion occurs primarily through an interfacial region of the film structure. The ability of a surfactant to improve transport performance is dependent on its ability to partition into the interfacial region.