Development of High-Functioned Fixed Carrier Membrane by Control of Membrane Morphology

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The facilitated transport of ethyl ester of docosahexaenoic acid (DHA-Et) was studied through the thin solution-cast perfluorosulfonated ionomer membranes. The carrier of DHA-Et was Ag^+ and was immobilized in the support ionomer membrane by electrostatic force. In this system, the feed phase, membrane phase and receiving phase had the same solvent. This system was already proved to be highly stable in our previous work. When ethanol with 15vol% water was used as the solvent, the DHA-Et permeance in the cast membrane, which is defined as the flux divided by the solute concentrations the feed phase, was about 4 times higher thatn that in the commercial Nafion^<<encircledR>> 117 membrane due to thinner membrane thickness. In the case of acetone solvent, the high selectivity of DHA-Et to ethyl ester of oleic acid of 42 and the high facilitation factor of 153, which is defined as the ratio of facilitated transport rate to physical transport rate, were obtained. These membrane performances were superior to those by Nafion^<<encircledR>> 117 membrane. The effects of membrane preparation conditions such as the annealing temperature and kinds of the polar solvents added to the ionomer solution before the annealing on the membrane performances were investigated in detail. Furthermore, small angle X-ray scattering (SAXS) measurement was carried out to study the membrane structure. The experimental result suggested that the lower crystallinity in the cast membrane than in Nafion^<<encircledR>> 117 membrane.