Continuous electrodialysis

Continuous electrodialysis One pass One pass Partial circulation in electrodialyzer Partial circulation in electrodialyzers One electrodialyzer (one stage) Multi-electrodialyzer (multi-stage) One electrodialyzer (one stage) Multi-electrodialyzer (multi-stage) Large scale Largest scale Small scale Small and large scale... 

Figure 6.13 Principle of continuous electrodialysis method with partial circulation.

S. Okonogi, Progress in practice of membrane separation techniques in dairy industry, Nihon Shokuhin Kougyou Gakkaishi (J. Food Ind. Jpn.), 1985, 32, 144—155 Y. Kobuchi and H. Motomura, Demineralization of whey by multistage continuous electrodialysis, International Membrane Technology Conference, Nov. 8-10 (1983), Sydney. 

Electrodialysis. In electro dialysis (ED), the saline solution is placed between two membranes, one permeable to cations only and the other to anions only. A direct electrical current is passed across this system by means of two electrodes, causiag the cations ia the saline solution to move toward the cathode, and the anions to the anode. As shown ia Figure 15, the anions can only leave one compartment ia their travel to the anode, because a membrane separating them from the anode is permeable to them. Cations are both excluded from one compartment and concentrated ia the compartment toward the cathode. This reduces the salt concentration ia some compartments, and iacreases it ia others. Tens to hundreds of such compartments are stacked together ia practical ED plants, lea ding to the creation of alternating compartments of fresh and salt-concentrated water. ED is a continuous-flow process, where saline feed is continuously fed iato all compartments and the product water and concentrated brine flow out of alternate compartments. 

Electrodialysis can be applied to the continuous-flow type of operation needed in industry. Multi-membrane stacks can be built by alternately spacing anionic- and cationic-selective membranes. Among the technical problems associated with the electrodialysis process, concentration polarization is perhaps the most serious (discussed later). Other problems in practical applications include membrane scaling by inorganics in feed solutions as well as membrane fouling by organics. 

Electrodemineralization includes a number of subset technologies, including electrodialysis (ED), electrodialysis reversal (EDR), and electrodeionization (EDI). Electrodeionization is sometimes termed continuous electrodeionization (CEDI) or continuous deionization (CDI). 

Polysaccharide formation may be endocellular, exocellular or capsular. The polysaccharide is usually a normal metabolic product, frequently a major product. Isolation and purification of a bacterial polysaccharide generally involve continued precipitations from a buffered solution, together with electrodialysis or ultrafiltration. 

In 1994, Kunz et al. studied the oxidation of sucrose in the presence of Pt/C at 307 K and neutral pH [104]. Under these conditions, the positions 6, 6, and V of sucrose were mainly oxidized and a mixture of monocarboxylic and dicarboxylic acids (56/44) has been produced. Note that when the oxidized products were continuously removed by electrodialysis in order to avoid their subsequent... 

Other pilot plant activity includes testing of solar stills at an experimental station near Daytona Beach, Fla. At the Bureau of Reclamation Laboratories in Denver, the Office of Saline Water has two electrodialysis units, one built by Ionics, Inc., Cambridge, Mass., and the other by the Central Technical Institute, T.N.O., of the Netherlands. A Japanese electrodialysis unit is on order and will be tested at the Denver Laboratories. Various types of membranes are also being tested at Denver. Distillation experiments are continuing in research facilities located at Wrightsville Beach, N. C. 

Boyaval, P., Corre, C., and Terre, S. 1987. Continuous lactic acid fermentation with concentrated product recovery by ultrafiltration and electrodialysis. Biotechnol. Lett. 9(3), 207-212. 

Electromembrane processes such as electrolysis and electrodialysis have experienced a steady growth since they made their first appearance in industrial-scale applications about 50 years ago [1-3], Currently desalination of brackish water and chlorine-alkaline electrolysis are still the dominant applications of these processes. But a number of new applications in the chemical and biochemical industry, in the production of high-quality industrial process water and in the treatment of industrial effluents, have been identified more recently [4]. The development of processes such as continuous electrodeionization and the use of bipolar membranes have further extended the range of application of electromembrane processes far beyond their traditional use in water desalination and chlorine-alkaline production. 

In this chapter only electromenbrane separation processes such as electrodialysis, electrodialysis with bipolar membranes and continuous electrodeionization will be discussed. 

Ion exchange desalination - DESAL , SIROTHERM Membrane desalination - Reverse Osmosis, Electrodialysis Continuing fixed bed counterflow development Condensate polishing systems Ion Chromatography analysis, and Pellicular resins Polymeric adsorbents... 

The ionic concentration to be treated is an overriding consideration governing the cost of plant of a given design and therefore for very high ion concentrations it is foreseeable that membrane pretreatments such as reverse osmosis and electrodialysis will continue to fulfil an important role as might a more widespread revival of continuous countercurrent ion exchange. 

Eysmondt, V.J., Vasic-Racki, D., and Wandrey, C. 1993. The continuous production of acetic acid by electrodialysis integrated fermentation. Modeling and computer simulation. Chemical and Biochemical Engineering Quarterly 7 139-148. 

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