Diaphragm cells cell liquor

Since current leakage through an electrolyte depends on the existence of a continuous path, another technique for the prevention of leakage currents is the use of current breakers at the cells. Their purpose is to physically break the electrolyte stream in order to interrupt the electrical path. Figure 8.10 shows the design used with some diaphragm cells. The liquor from each cell is collected in a cup (C). The demister... 

FIGURE 14.17 A diaphragm cell tor the electrolytic production of sodium hydroxide from brine (aqueous sodium chloride solution), represented by the blue color. The diaphragm (gold color) prevents the chlorine produced at the titanium anodes from mixing with the hydrogen and the sodium hydroxide formed at the steel cathodes. The liquid (cell liquor) is drawn off and the water is partly evaporated. The unconverted sodium chloride crystallizes, leaving the sodium hydroxide dissolved in the cell liquor. 

Fig. 14.1 Suppliers and cell-liquor clients of the Diaphragm Electrolysis Plant at Delfzijl, The Netherlands.

Solution-mined brine is used for salt production, and is also the feed for the diaphragm electrolysis and soda-ash production. The cell-liquor derived from the electrolysis is also used for soda-ash production after pre-carbonation. 

The anolyte is evaporated to increase the chloride concentration from 75-250 gdm and cobalt, and most of the iron, is then extracted by the organic solvent. The nickel containing raffinate is diluted by condensate from the evaporation and returned to the Ni-cathode compartments in the diaphragm electrolytic cells for precipitation of nickel. Stripping of cobalt from the organic solvent is performed with the weakly acidic condensate. The strip liquor is fed to the Co-cathode compartment in the electrolytic cells. 

The 50 per cent caustic solution obtained by evaporation of the diaphragm cell liquor meets the current industrial requirements. For the manufacture of rayon, one of the foremost industries today, the salt content of the diaphragm... 

The cell liquor flowing from the cathode compartment of each cell is collected for evaporation to 50 percent product caustic. The diaphragm cell liquor contains 10-12 percent NaOH, 14-16 percent NaCl, 0.1—0.5 percent Na2S04, 0.O2-O.O4 percent Na2C03, and 0.01-0.2 percent NaC103. The evaporation is carried out in nickel-lined quadruple-effect evaporator systems. The salt content of membrane cell effluent is so low that only a simple flash evaporator is required. This represents a considerable reduction in investment versus diaphragm caustic plants. Because of the high... 

The catliolyte from diaphragm cells typically analyzes as 9—12% NaOH and 14—16% NaQ. This cell liquor is concentrated to 50% NaOH in a series of steps primarily involving three or four evaporators. Membrane cells, on the other hand, produce 30—35% NaOH which is evaporated in a single stage to produce 50% NaOH. Seventy7 percent caustic containing very little salt is made directly in mercury cell production by reaction of the sodium amalgam from the electrolytic cells with water in denuders. 

In the case of diaphragm cells, the cell liquor (10-12 wt% sodium hydroxide and 16-18 wt% unreacted sodium chloride) is concentrated in multieffect evaporators to 50% NaOH. The sodium chloride then is salted out and must be removed, only 1-1.5 wt% remain in the solution. Depending on customers requirements further purification steps will follow, for example, adsorption of salt, chlorate, and carbonate by liquid ammonia or removal of metal impurities by cathodic deposition [18]-... 

Anode and cathode materials are equivalent to those used in the diaphragm process. The pH-value of the cell liquor is adjusted from 10 to 12. Low temperatures near ambient values suppress the disturbing reaction (7). 

One of the most common industrial methods for the production of sodium hydroxide depends on the electrolysis of brine in a diaphragm cell. The products of the electrolysis are chlorine, hydrogen, and cell liquor, which is a solution of sodium hydroxide and sodium chloride. A large fraction of the cost of commercial sodium hydroxide results from the concentration, separation, and purification of the alkali. The sodium hydroxide required in the sea water descaling process need... 

The diaphragm cell produces caustic soda containing 11% caustic soda and 15% salt, with a low concentration of sodium chlorate. This solution, called cell liquor, is evaporated to produce 50% caustic soda. During evaporation, salt crystallizes as the caustic concentration increases. About 1 % salt is present in the 50% caustic soda solution. 

Generally, the feed brine to the diaphragm cells and the exiting caustic liquor do not contain any active chlorine species. However, if these species (i.e., Cl2< HCK 1, OCl ) are present in the feed brine or cell liquor, the material balance can easily be modified to account for their presence. 

A major differentiator among the various chlor-alkali cells is the quality of their product caustic solutions. Diaphragm cells produce a liquor containing about 11% NaOH and... 

Dechlorination of depleted brine treatment of diaphragm cell liquor automatic flushing of membrane cells upon loss of power... 

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