Dehydration of nitric acid using perfluoro carboxylate ionomer membranes

Investigations determined the feasibility of using perfluoro carboxylate ionomer films for the dehydration of nitric acid. Motivation for this effort was the speculation of improved water selectivity (nitrate rejection) for the carboxylate film when compared to the dehydration using perfluoro sulfonate or sulfonate/carboxylate composite films. The methodology used was to generate solution cast perfluoro carboxylate ionomer films, characterize the film and to assess the filmʹs aqueous transport performance. Experimental results suggest that the cast films had a reduction in ion-exchange capacities when compared to “as received” films by as much as 56% due to the generation of an ester form of the ionomer during the dissolution/casting process. Nitric acid pervaporation experiments showed that permeate fluxes were two orders of magnitude smaller for the cast films when compared to ionomer sulfonate films of similar thickness (sulfonated Nafion™ 111). Water separation efficiencies (α) were demonstrated to be one order of magnitude higher for the carboxylate cast films when compared to sulfonated Nafion™ 111.