Structural effects of ion‐exchange membrane on the separation of L ‐phenylalanine ( L ‐Phe) from fermentation broth using electrodialysis

The effects of membrane structure on the separation of L ‐phenylalanine ( L ‐Phe) by electrodialysis from a fermentation broth and on the fouling tendency were investigated in this study. Two anion‐exchange membranes (Neosepta AFX and AM‐1, Tokuyama, Japan) were selected and characterized using the chronopotentiometry method. For a fresh membrane, AFX showed a lower electrical resistance and a lower permselectivity than AM‐1. After being fouled with humic acid, however, the electrical resistance of AFX was higher than that of AM‐1. The L ‐Phe selectivities for both membranes were lower than those of the fresh membranes. The result may be attributed to the structural difference between AFX and AM‐1 membranes. AFX has a lower repulsion force against the co‐ion and could be more strongly affected by the foulants than AM‐1 because AFX has a more porous structure than AM‐1. Experiments on the separation of L ‐Phe from the fermentation broth were carried out using two different stack configurations, ie desalting electrodialysis and water‐splitting electrodialysis. It was observed that the recovery efficiency of L ‐Phe through electrodialysis for 100 min reached 95% for AFX and 85% for AM‐1. In the desalting configuration of electrodialysis, the solution pH must be adjusted to alkaline conditions to recover the L ‐Phe through the anion‐exchange membrane. On the contrary, it was possible to recover the L ‐Phe without adjustment of the solution pH in the water‐splitting electrodialysis because OH − generated from the bipolar membrane converted neutral L ‐Phe into an anion. © 2002 Society of Chemical Industry