Separation of Amino Acids by Electrodialysis with Ion-Exchange Membranes

The selective separation of amino acids, glutamic acid, methionine and lysine, from their solution mixture was examined by electrodialysis with ion-exchange membranes, SELEMION-CMV and SELEMION-AMV, under conditions of pH 1 to 12 and current densities of 0 to 15 A/m2. The amino acids were almost completely separated from each other under the conditions studied: Only glutamic acid is transported across the anion-exchange membrane; only lysine across the cation-exchange membrane; and methionine is not transported at all. Their fluxes across the membranes have maxima in the neutral pH range, increasing almost linearly with current density. A model for explanation of the experimental results has been proposed considering solution equilibrium, ion-exchange equilibrium and diffusion in the membranes. Successful simulation has confirmed the amino acid transport mechanism which was proposed in the model. The diffusivities of ionic species, model parameters, have been determined. Moreover the role of each ionic species in carrying current and the effect of water splitting are also discussed.