Ion exchange membranes in aqueous, methanolic and ethanolic electrolyte solutions

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Ion exchange membranes act as selective barriers in (electro-)dialytic separation processes, primarily used in aqueous electrolyte systems. This study explores their applicability to non-aqueous solutions by investigating the equilibrium and transport properties of commercial monopolar and bipolar membranes in aqueous, methanolic, and ethanolic sodium perchlorate solutions. It discusses how membrane performance depends on solution characteristics like relative permittivity, solute concentration, and ionic mobility, as well as membrane specifics such as functional group types and morphology. The findings highlight the significance of ion pair formation in both the solution and membrane phases, which can lead to varying degrees of membrane performance degradation. Additionally, a detailed dynamic bipolar membrane model is developed, incorporating four ionic species, solvent, electric potential, and a space charge region at the cation/anion exchange layer interface. This model accounts for non-idealities through activity coefficients and solvent dissociation based on a chemical reaction model. It successfully reproduces all observed experimental trends for both aqueous and non-aqueous solutions, providing deeper insights into the behavior of ion exchange membranes.