Structural effects of ion-exchange membrane on the separation ofL-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