Cell liquor

Figure 8 Effect of acid concentration on the grafting of cotton linters. [KMn04] = 0.06 N [monomer] = 1 mol/g cell liquor ratio 1 50 T = 50°C t = 1 h. (—) Oxalic acid (----) sulfuric acid.

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. 

Several chlor-alkali producers have some control over surplus caustic inasmuch as they use large quantities in-house. In some cases, if caustic is tight then the weak cell liquor can be upgraded and placed on the market. Dow s propylene oxide (PO)... 

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 chlorine liquefaction plant comprises a bromine-removal column, a compression-condensation unit and a Tetra absorption/distillation unit (Fig. 14.2). Waste streams of chlorine are absorbed in diluted cell-liquor in the chlorine destruction area. As a result, the destruction liquid contains sodium chloride and less sodium hydroxide than is usual. Bromine from the bromine-removal column is also added to the chlorine destruction unit. The hypochlorite solution that is formed contains a reasonable amount of bromine and salts. However, it is a hypochlorite of non-marketable quality. 

This process (see Fig. 14.3) was chosen because of the lowest variable and investment costs compared with the other options. This is a process without emissions - which is another great advantage. Bromide is discharged from the process by the cell-liquor. A small increase of bromide and chlorate concentrations in the cell-liquor is therefore expected. 

In the cell, chlorate and bromate are converted to chloride and bromide at the cathode by reduction with nascent hydrogen, although the chlorate reacts only partially. The chlorate remaining in the cell-liquor can be reduced with thiosulphate or another chemical reducing agent ... 

Now that the circle is closed, there is no longer any bromine-containing waste stream flowing from the destruction units. All bromide in the feed brine is returned to the cell-liquor. This is an excellent achievement for the environmental aspects of the DEP ... 

There is some increase of sodium chlorate (100 mg kg-1) and sodium bromide (40 mg kg-1) in the cell-liquor. This is a result of the chlorate that is formed in brine degassing. Therefore, more chlorate is fed to the electrolysis cells. Since not all the chlorate is reduced at the cathode, an increase in chlorate in the cell-liquor is observed (see Fig. 14.4). 

The increase of bromide in the cell-liquor is a result of recycling all of the bromine in the plant. Almost all bromine leaves the plant via the cell-liquor as bromide. The remaining quantity of sodium bromate in the cell-liquor has not changed (8 mg kg-1). 

Fig. 14.4 Sodium chlorate concentration in cell-liquor before and after recycling of hypochlorite.

The disadvantage of the hypochlorite recycling process is the small increase of chlorate and bromide concentrations in the cell-liquor. However, this is offset by higher chlorine production (0.1% more), resulting in a higher current efficiency. 

That the growing polymer extended to the cathode means that the composite polymer and cell liquor possessed the property of conductivity by what appears to be a nonionic process. 

Anhydrous perchloric acid is not sold commercially, Aqueous solutions of perchloric acid are sold at low concentrations foi analytical standard applications and at concentrations up to 70%. The price for 70% perchloric acid varies and starts at 2.70/kg, depending on the quantity and level of impurities. The U.S. domestic capacity of ammonium perchlorate is roughly estimated at 31,250 t/yr. The actual production vanes, based on the requirements for solid propellants. Environmental effects of the decomposition products, which result from using solid rocket motors based on ammonium perchlorate-containing propellants, are expected to keep increasing public pressure until consumption is reduced and alternatives are developed. Approximately 450 t/yr of NH+ClCXt-equivalent cell liquor is sold to produce magnesium and lithium perchlorate for use in the production of batteries. 

The reaction mixture is filtered. The solids containing K2Mn04 are leached, filtered, and the filtrate composition adjusted for electrolysis. The solids are gangue. The Cams Chemical Co. electrolyzes a solution containing 120—150 g/L KOH and 50—60 g/L K MnO The cells are bipolar (68). The anode side is monel and the cathode mild steel. The cathode consists of small protrusions from the bipolar unit. The base of the cathode is coated with a corrosion-resistant plastic such that the ratio of active cathode area to anode area is about 1 to 140. Cells operate at 1.2—1.4 kA. Anode and cathode current densities are about 85—100 A/m2 and 13—15 kA/m2, respectively. The small cathode areas and large anode areas are used to minimize the reduction of permanganate at the cathode (69). Potassium permanganate is continuously crystallized from cell liquors. The caustic mother liquors are evaporated and returned to the cell feed preparation system. 

The cell liquor is pumped to tanks where it is heated with steam to 90°C to destroy any hypochlorite present and the required amount of barium chloride is introduced to precipitate any chromate present. 

Cleavage of the carbon backbone is reported to be mediated by hydrolases [63]. However, there are no indications that this side-reaction proceeds enzymatically. Instead formation of retro-Claisen products 12 and 13 proceeds via GSH addition to the carbonyl center in 2. The active role of GSH was demonstrated with GSH-depleted cells. After treatment with N-ethyl maleimide (NEM) [64] no retro-Claisen product was detectable. The same applied for NEM-treated cell liquor. 

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... 

In this process, the chlorine and caustic produced in the cell react immediately, and the cell liquor is kept hot in an additional vessel that provides sufficient residence time for all the hypochlorite to disproportionate into chloride and chlorate ... 

For optimum operation, the cell temperature is maintained at 65-75°C with a pH of 6.9. Current efficiencies of over 90 percent have been reported with a power consumption of 4500-5800 kWhr per metric ton of sodium chlorate produced. Coated titanium metal anodes and steel cathodes are used, and small amounts of dichromate are added to the cell liquor to prevent the cathodic reduction of chlorate and hypochlorite. The cell liquor contains about 50 percent NaC103, which may be used as is, or evaporated to 75 percent... 

Since heat (as well as HP) causes a denaturation of the cell membranes and also liberates the PME, the divalent cations (Ca, Mg) from the cell liquor come into contact with the deesterified pectin and form Ca-bridges. Within canning, this tissue firming effect is further promoted via the addition of Ca-salts. 

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. 

Current is fed into the electrolyzer by means of anodic and cathodic end elements. The anodic compartment of each cell is joined to an independent brine feed tank by means of flanged connections. Clilorine gas leaves each cell from the top, passing through the brine feed tank and then to the cellroom collection system. Hydrogen leaves from the top of the cathodic compartment of each cell the cell liquor leaves the cathodic compartment from the bottom through an adjustable level connection. 

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). 

Both reduction processes are inhibited by addition of chromate (3-6 g L-1 sodium chromate) to the cell liquor. 

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