Anions and cations membrane

Electrodialysis units are constructed using a plate-and-frame technique similar to filter presses. Alternating sheets of anionic and cationic membranes are placed between two electrodes. The plating or rinse solution to be recovered (electrolyte) circulates past the system s electrodes. Hydrogen and oxygen evolve. Positive ions travel to the negative terminal and negative ions travel to the... 

The ED stack is the unit holding together anionic and cationic membranes assembled in parallel as in a filter press between two electrode-end blocks in such a manner that the stream undergoing ion depletion (i.e., the diluate or diluting stream) is kept separated from the other solution (concentrate or concentrating stream) undergoing ion enrichment. Figure 4 shows an exploded view of it. 

Lindstrand et al. (2000) investigated the effect of different organic fou-lants, such as octanoic acid, sodium octonate, and sodium dodecylbenzene sulfonate, on anionic and cationic membranes by monitoring the increase in the membrane resistance (Rm) with time. 

Current-voltage tests to determine the limiting current intensity (/lim), ion transport numbers (ta, tc+), and surface resistances (ra, rc) in anionic and cationic membranes, as well as solute mass transfer coefficient (Am). 

As far as the overall potential drop (E) is concerned, the contribution of solute polarization, namely the electric resistance (R ) and junction potential difference (TTj) across any boundary layer, may be neglected. On the contrary, the Donnan potential difference (Eu) in any cell pair, which behaves as a DC generator with inverted polarities with respect to those of the external DC generator (Figure 9), has to be accounted for as the solute concentration difference at both sides of the anionic and cationic membranes increases ... 

Bipolar membranes consist of an anionic and a cationic membrane laminated together [13]. When placed between two electrodes, as shown in Figure 10.19, the interface between the anionic and cationic membranes becomes depleted of ions. The only way a current can then be carried is by the water splitting reaction, which liberates hydrogen ions that migrate to the cathode and hydroxyl ions that... 

A number of chambers called diluting and concentrating cells are separated by alternating anion and cation membranes and are arranged between two electrodes. This is shown in Figure 36-8, p. 426. 

A commercially available ED stack with bipolar, anion and cation membranes was used by the author to generate 1 N HCl and NaOH from NaCl. A current density of 100 mA/cm2 was maintained with an applied potential of 2V/cell. 

The basic building block of an electrodialysis unit is the array of alternating anion and cation membranes (with interposed water-carrying spacers) called the membrane stack. The characteristics of an Ionics Mark III stack are described in Table IV. 

Eignre 12.4 shows a simple electrodialysis cell, consisting of two compartments, separated by alternating anion and cation membranes. The difference in potential at the electrode terminals... 

The first indnstrial electrodialysis nnit with a 45 m membrane surface went into operation in 1996. Its resnlts, consistent with those of the many earlier pilot tests, showed that electrodialysis can be applied on an industrial scale for the tartrate stabilization of wine. The optimnm effectiveness of this techniqne is subject to choosing a pair of (anion and cation) membranes that best preserve the wine s natnral balance, and combining it with an antomatic testing system to restrict the treatment to the minimum required to achieve tartrate stability. 

The filter-press type configurations are made up of a set of modules which are arranged in alternating anionic and cationic membranes. The thin intermembrane compartments contain spacers to improve the hydrodynamic conditions. High-pressure pumps push the fluids inside the hydraulic circuits so as to overcome any drops in pressure that may occur along the flow line. 

To conclude, one should note that the mass balances can also be modified by using permselective or specific membranes in some industrial processes. A good example of such applications includes the use of anionic and cationic membranes to desalinate sea water or other methods of separation or purification. 

Anionic and cationic membranes electric field Electric fluid... 

---