Electrodialysis with bipolar membranes for extraction of organic acids

Electrodialysis is an electrochemical membrane process, by which the 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 step with the electrodialytically forced water dissociation on bipolar membranes, aqueous ionogenic solutions are transferred into the respective inorganic or organic acid and base.

The inherent advantage of this technique lies in the avoidance of otherwise useless neutral salts, which opens a wide field of applications for the bipolar membrane technique.

Applications for bipolar electrodiaysis in downstream processing, e.g. in biotechnology and food technology

• Separation and purification of organic acids and amino acids from fermentation broths by combined electro-dialysis and e.g. crystallization, distillation, and nanofiltration (experiences in: acetic acid, formic acid, citric acid, malic acid, fumaric acid, itaconic acid, succinic acid, gluconic acid, galacturonic acid, glycine, alanine, glutamic acid, methionine)
• Separation of amino acids from racemic mixtures
• Pasteurization of hydrous solutions at room temperature
• Combined deacidification of fruit juices and recovery of the organic acid
• Gentle adjustment of the pH value of aqueous solutions without increasing the ion potential, e.g. flavor enhancing
• Partial inversion of sucrose or inversion of potato starch

Further applications of bipolar electrodialysis are the recovery of process chemicals and the saving of chemicals in manufacturing industries, e.g. for the recovery of EDTA from electroless copper plating bath, for the recycling and regeneration of battery acid or the recovery of exhausted alkali from process solutions for the manufacture of nickel-cadmium batteries.

Bipolar electrodialysis is used for the recovery of lactic acid in a process, developed at the IGB, for the production of lactic acid from acid whey, which is a residual material of milk processing. In the first step of this process a selected strain of lactic acid bacteria produces lactic acid from lactose with high efficiency. After the fermentation the organisms are removed by cross-flow-filtration (cell recycle), and the lactate ions are separated from the fermentation broth and converted to free lactic acid by bipolar electrodialysis. The product can be used as a renewable raw material in chemical industry – e.g. for the synthesis of biologically degradable polymers (PLA).