Influence of the cationic form of an ion-exchange membrane in the permeability and solubility of methanol/water mixtures

• Permeability has been obtained at different temperatures for different cationic forms.
• Solubility by different cationic forms has been found as function of the temperature.
• Activation energy of permeation and the enthalpy of sorption have been determined.
• The obtained results have been interpreted in terms of membrane microstructure.

The influence on the substitution of the cationic form of a Nafion®117 membrane was investigated by means of swelling and permeation measurements. This effect was studied in terms of the permeability and the solubility of a mixture of methanol and water through membranes substituted by Li+, Na+, K+, Rb+ and Cs+. It was found that both, permeability and solubility decrease with increasing the ionic radius of the substituted cation. The dependence of permeability and solubility on the temperature was studied by measurements at different temperatures. This allowed to determine the activation energy of permeation and the enthalpy of sorption by numerical fitting of experimental data. The trend in activation energy of permeation and the enthalpy of sorption did not appear to be related to the ionic radius of the cation. The increase of differences in permeability of the different cation forms, when the temperature was increased, has been related with the results obtained for solubility.