Electrodialysis is an electrochemical
membrane process where charged particles of an electrolyte solution
(ions) are separated from a crude solution in an electrical field using
ion-selective membranes. Through the combination of the product
separation with the electrodialytically forced water dissociation on
bipolar membranes, aqueous ion-ogenic solutions are transferred into the
respective inorganic or organic acid and base. The advantage is that
usage of neutral salts is not needed in this technique. This opens a
wide field of applications for using the bipolar membrane technique.
Applications of bipolar membrane technique:
Bipolar electrodialysis is used for the recovery of lactic acid during the production of lactic acid. A selected strain of lactic acid bacteria produces lactic acid from lactose with high efficiency in the fermentation.
After the fermentation the organisms are removed by cross-flow-filtration (cell recycle). The lactate ions are then separated from the fermentation broth and converted to free lactic acid using the bipolar electrodialysis technique.
AEM: Anion Exchange Membrane
The outline of the bipolar
electrodialysis uses the three-chamber stack as illustrated above. The
mechanism behind this transfer reaction can be demonstrated using sodium
chloride solution to hydrochloric acid and caustic soda as an example.
Similarly caustic soda recombines on the anion selective side of the BM and an ion-depleted diluate remains in the neighboring feed solution chamber.