Electrodialysis water splitting

Mani KN (1991) Electrodialysis water splitting technology, J Membr Sci 58 117 Chem Abstr 115 (1991) 52408b... 

Pourcelly G, Gavach C (2000) Electrodialysis water splitting - application of electrodialysis with bipolar membranes. In Kemperman AJB (ed) Handbook of bipolar membrane technology. Twenty University Press, Enschede... 

FIG. 22-61 Electrodialysis water dissociation (water splitting) membrane inserted into an ED stack. Starting with a salt, the device generates the corresponding acid and base by supplying and OH" from the dissociation of water in a bipolar membrane. CouHesy Elsevier.)... 

Separations research has resulted in the development of a two-stage desalting and water-splitting electrodialysis system that concentrates, purifies, and acidifies the succinic acid. The base is recycled back to the fermentation, where it is used for neutralization, eliminating the generation of gypsum salt, an unwanted neutralization byproduct that must be disposed of or sold (38). 

Water Splitting A modified electrodialysis arrangement is used as a means of regenerating an acid and a base from a corresponding salt. For instance, NaCl may be used to produce NaOH and HCl. Water splitting is a viable alternative to disposal where a salt is produced by neutralization of an acid or base. Other potential applications include the recovery of organic acids from their salts and the treating of effluents from stack gas scrubbers. The new component required is a bipolar membrane, a membrane that splits water into H and OH . At its simplest, a bipolar membrane may be prepared by... 

Hwang, G.-J., Onuki, K., Nomura, M., Kasahara, S., and Kim, J.-W., Improvement of the thermochemical water-splitting IS (iodine-sulfur) process by electro-electrodialysis, Journal of Membrane Science, 220, 129-136, 2003. 

A composite membrane prepared, e.g., by lamination of a cation exchange membrane with an anion exchange membrane, called a bipolar ion exchange membrane, shows interesting properties, for example water splitting to generate hydrogen ions and hydroxide ions at the interface of both membranes in electrodialysis, or a rectifier effect.110 When the current is passed from one direction. 

Rubinstein, A. Warshawsky, L. Schechtman and O. Kedem, Elimination of acid-base generation ( water-splitting ) in electrodialysis. Desalination, 1984, 51, 55-60. 

The solutions were 0.01N KC1 or 0.01N NaCl. The membrane was supplied by T.N.O., The Hague, Netherlands. Its exposed area was about 1 sq. cm. and the current density in the different experiments was varied up to 25 ma. per sq. cm. The experiments were carried out at room temperature without stirring. Under these conditions concentration polarization and water splitting may be expected to occur to a larger extent and hence be more readily observed than in a flow compartment of an electrodialysis stack. 

Electrochemical regeneration of the mixed-bed ion-exchange resin can take place in both desalination and concentration chambers of electrodialysis apparatus. Withdrawal of ions from desalination chambers would be responsible for the resin regeneration in this chamber. Ion desorption on the C A contact points and water splitting on the A C contact points would carry out the regeneration in the concentration compartment. In all cases the current efficiency will increase as the current density grows. 

The water-splitting electrodialysis products still contained small amounts of impurities, and aliquots of them were further purified by using different polishing schemes to evaluate the efficacy of each scheme. Table II shows the impurity profiles of purified succinic acid products obtained from different polishing schemes. 

Figure 17.18 Process for the recovery of SA from fermentation broth by electrodialysis coupled with water-splitting electrodialysis.

Water-splitting electrodialysis can be improved by using a supersaturated solution of the fi-ee acid. Sodium acetate inhibits crystallization of succinic acid, but free acetic acid, which is produced by water-splitting electrodialysis, promotes crystallization of succinic acid (Berglund et al. 1991). 

The costs of separation of succinic acid will be a critical component in economical production of this acid. As acids are neutralized in the fermentation to maintain an appropriate pH for the microorganism, the salts formed must eventually be removed and can be a waste generation problem. Promising separation technology is the use of liquid-liquid extraction and water-splitting electrodialysis. Key also to lowering separation costs is the development of microorganisms that produce as few by-products as possible which need to be removed from the final product stream. 

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