Sulfonic Membrane Sorption and Permeation Properties: Complementary Approaches to Select a Membrane for Pervaporation

In this contribution, the physical and chemical properties of the dense sulfonic membrane IonClad R4010 in the lithium form were studied to evaluate its potential application in pervaporation. To develop new membrane materials, it is necessary to know the influence of the membrane structure on the membrane equilibrium and transport properties. For this purpose, the sorption and permeation measurements of water and methanol in the liquid and vapor states were performed and correlated to the ion pairs/solvent interactions analyzed by the infrared spectroscopy. The IonClad R4010 equilibrium and transport properties were found to be quite different depending on the permeant nature. The sorption and diffusion behavior of water and methanol was well described by means of the type II sorption model (BET theory). The swelling capacity of the IonClad R4010 membrane in methanol was found to be much lower than that in liquid water. In contrast to methanol, the total dissociation of the ion pairs in the IonClad R4010 membrane was obtained in the presence of water but only at high activity (∼0.8). Besides, the dispersion of the water molecules in the membrane was found to be homogeneous. The infrared spectroscopy results revealed that the methanol molecules had weaker interactions with the sulfonic groups of IonClad R4010 in agreement with the sorption data. The permeation properties were investigated by means of the sweeping gas and gravimetric methods in order to evaluate the membrane performance for pervaporation. The permeation results are in accordance with those obtained by sorption, thus confirming the complementariness of the two approaches.