Sodium hydroxide production

Some electrochemicals are produced in very large quantity. Chlorine and sodium hydroxide production in 1991 were 10,727,000 t and 11,091,000 t, respectively (1). Aluminum was produced at the rate of 4,100,000 t/yr and had an annual market value of about 5.4 biUion. Other electrochemically produced products are required in smaller volume. The production of the metals cadmium, lithium, and nickel were at the rates of 1600 t, 2800 t, and 8400 t, respectively for 1991 (see Table 1). Electrochemical processing plants produce a variety of products in a wide range of capacities. 

Martin AD (1992) Sodium hydroxide production by the electrohydrolysis of aqueous effluent streams containing sodium salts, Inst Chem Eng Symp Series, 1992,127 (Electrochem Eng En 92), 153 Chem Abstr 117 (1992) 19458H... 

Potassium hydroxide is made by electrolysis of potassium chloride solutions in cells that are exactly analogous to sodium hydroxide production. 

A sodium hydroxide product, without separation, would react vigorously with chlorine to give sodium chloride and sodium hypochlorite (Eqs 8.3, 8.4), so that similar precautions are required with either option. 

There have been many attempts to utilize the approximately 1.8 V generated by the electrochemical reactions of the decomposer. Elowever, it has not been found possible to do this and to maintain high concentrations of sodium hydroxide and low residual sodium in the stripped mercury. The sodium hydroxide product obtained from the decomposer of a mercury cell is very pure, containing 0.001% or less sodium chloride. This product is referred to as rayon grade caustic because the high purity and low sodium chloride content makes it particularly suitable for rayon manufacture. This is achieved without the special purification steps required for the diaphragm cell product. 

Chlorine and sodium hydroxide production by the electrolysis of brine solutions necessarily locks the ratio of the two products to the theoretical ratio of the process [45, 46]. When the market for sodium hydroxide exceeds the market for chlorine, the causticization of sodium carbonate to sodium hydroxide (Section 7.3) may be used by some suppliers and consumers to supplement the available sodium hydroxide without producing large amounts of excess chlorine. Another expedient for large-scale chloralkali producers faced with this situation is to stimulate the chlorinated solvent or hydrochloric acid markets in an attempt to increase the consumption of chlorine to restore the balance. These measures are not usually rapid enough to respond over the short term unless the solvent plant is also operated by the chloralkali producer. 

As a by-product, hydrogen is also produced by electrolytic processes such as chlorine-sodium hydroxide production, catalytic reforming processes in refineries, olefin production, and recovery from ammonia plant purge gas. 

This electrochemical process is also the major industrial route for sodium hydroxide production, so essentially the only side product from this initial reaction is hydrogen gas, which is later converted to water. Once the ethylene is produced from the crude hydrocarbons, it is reacted with chlorine gas ... 

In the reaction of chloroacetic acid with fluoro-substituted phenols or trifluo-romethyl-substituted phenols in the presence of sodium hydroxide, products had low yields because of a strong electron-withdrawing nature of the substituent. However, by using the method of Brayer et al. [10], fluoro-substituted phenoxy-acetic acids and trifluoromethyl-substituted phenoxyacetic acids M4-17-M4-27 (Table 2.4) could be prepared in satisfactory yields by the reaction of fluoro-substituted phenols or trifluoromethyl-substituted phenols with ethyl bromoacetate in the presence of K2CO3 in DMSO followed by alkaline hydrolysis (Scheme 2.8, method M4-B). Thus, a series of substituted phenoxyacetic acids M4-1-M4-27 was prepared by method M4-A or M4-B. 

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