Electrodialysis stack arrangement

Figure 5.3 Exploded view of a sheet-flow-type electrodialysis stack arrangement indicating the individual cells and the spacer gaskets containing the manifold for the distribution of the different flow streams.

Figure 10.2 Schematic diagram of a plate-and-frame electrodialysis stack. Alternating cation- and anion-permeable membranes are arranged in a stack of up to 100 cell pairs...

Stack design in bipolar membrane electrodialysis The key component is the stack which in general has a sheet-flow spacer arrangement. The main difference between an electrodialysis desalination stack and a stack with bipolar membranes used for the production of acids and bases is the manifold for the distribution of the different flow streams. As indicated in the schematic diagram in Figure 5.10 a repeating cell unit in a stack with bipolar membranes is composed of a bipolar membrane and a cation- and an anion-exchange membrane and three flow streams in between, that is, a salt... 

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... 

Stack, and a potential difference sufficient to force current through the stack is applied between the two electrodes placed at each end of the stack. For current to pass between the electrodes, ions must be transported through each of the membranes. By arranging the feeds to the various intermembrane compartments, it is possible to force ionic salts to pass from the dilute stream to the concentrated stream. In this way, a salt can also be split into its acid and base components. By combination of several cell pairs that comprise an anion- and a cation-selective membrane sheets in parallel, a stream concentrated in the original salts may be prepared. This configuration is the common method for industrial use, in which electrodialysis gives broadly the same result as reverse osmosis and has found very similar applications to general water treatment. 

Electrodialysis involves the use of a selectively permeable membrane, but the driving force is an electrical potential across the membrane. Electrodialysis is useful for separating inorganic electrolytes from a solution, and can therefore be used to produce freshwater from brackish water or seawater. Electrodialysis typically consists of many cells arranged side by side, in a stack. Figure 9.12 illustrates a two-cell stack. 

An electrodialysis (ED) stack is composed of several flow chambers separated by imi exchange membranes and superimposed by an electric field. In most cases, an alternating arrangement... 

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