Organic fouling of anion-exchange and bipolar membranes during the separation of amino acid and sucrose by electrodialysis

The article presents a study of the behaviour of the MA-41 anion-exchange membrane and MB-2 bipolar membrane during the electrodialysis of a solution containing tyrosine and sucrose. It establishes changes in current-voltage, transport, and structural characteristics of ion-exchange membranes. The study of the evolution of membrane characteristics during a prolonged contact with solutions containing an aromatic amino acid and disaccharide is aimed at providing a deeper understanding of and finding solutions to the problem of organic fouling of membranes, which complicates the electromembrane separation of components of the solution during microbiological synthesis of amino acids. It was found that the fluxes of tyrosine and sucrose through the MA-41 membrane measured after its operation during 50-hour electrodialysis reach higher values than during the first hours of operation after the system reaches a steady state. However, it was noted that when the membrane continues to be used, the flux of components through the MA-41 membrane decreases. What is more, this change is pronounced with a high current density. This decrease in mass transport, an increased voltage drop on the MB-2 and MA-41 membranes, and lower values for the effective ОН- ion transport number for the MA-41 membrane are associated with the phenomenon of organic fouling confirmed by revealed structural changes in the ion-exchange material, which become significant after a prolonged contact (more than 60 hours) with a mixed solution of tyrosine and sucrose. These changes are associated with the accumulation of an amino acid and its oxidation product, 3,4-dihydroxyphenylalanine, in the membrane phase, as well as with a decrease in the content of sucrose absorbed by the membrane