Ageing of ion-exchange membranes used in electrodialysis: Investigation of static parameters, electrolyte permeability and tensile strength

Ion-exchange membranes (IEM), used in some food industrial electrodialysis application, were researched by measuring their static parameters, electrolyte permeability and mechanical resistance in order to evaluate their evolution during this application.Two cation-exchange membranes (CEM) of Neosepta® type and two anion- exchange membranes (AEM) of Neosepta® type as well, were considered. Each pair was composed of a new sample and an extracted sample (used membrane) from an electrodialyzer after two years of operation. For both, CEM and AEM, there was a sevenfold decrease in permeability after use in that application. The tensile strength decreased by 1.5 times for CEM and eightfold for AEM. There was also a proof of loss of mechanical resistance of the used membranes. These observations may be attributed, on the one hand, to the inhibition and disappearance of a great part of the functional sites of the membranes, and on the other hand, to the degradation of the polymer itself. The fouling by organic species present in the solution might also be a significant cause of the permeability decrease. It turned out that the AEM was more affected than the CEM.

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► Use of IEMs over long period changes almost all their characteristics.
► Permeability decreases sharply after 2 years of ED in food industrial application.
► AEM is the most affected: loss of polymer rigidity and damage in PS sulfonated chain.
► CEM is also damaged but in a lower degree than AEM.