Sodium chlorate, formation solution

Sodium chlorate, formation of, in preparation of chlorine (I) oxide in carbon tetrachloride solution, 5 159n. 

In Eq. (18.1), sodium hypochlorite is produced by feeding chlorine into a 30% aqueous caustic solution in a circulating reactor/cooler system. To avoid sodium chlorate formation, the reaction temperature is kept below 30°C and NaOH concentration is kept below 1 g/liter. Typical reaction temperature is 5 °C132. 

The pH of the chlorine dioxide reaction mixture must be maintained in the 2.8—3.2 pH range, otherwise decreased conversion yields of chlorite to chlorine dioxide are obtained with by-product formation of chlorate. Generator efficiencies of 93% and higher have been demonstrated. A disadvantage of this system is the limited storage life of the sodium hypochlorite oxidant solution. 

Perchlorates, Concentrated solutions of sodium chlorate are electrolyzed to produce sodium perchlorate [7601 -89-0] NaClO (see Perchloric ACID AND perchlorates). The electrolytic cells for perchlorate production are usually simple tank electrolyzers. Anode materials are limited to platinum, platinum-clad titanium, or lead dioxide on graphite or titanium. The cathodes are generally mild steel. Cell feed solutions may contain 600 g/L of NaClO. Production of very high (1000 g/L or more) concentrations of NaClO is achieved by resaturating partially converted electrolyte with NaQO and continuing the electrolysis to minimum final NaClO concentrations. A mechanism of perchlorate formation has been proposed involving the reaction of chlorate ion and an absorbed active oxygen species at the anode (38,39). 

A typical specification for sodium chlorate in bleach is 1,500 mgpl. It cannot practically be removed from a solution but must be controlled by proper reaction and handling. Production at lower temperature, lower final product strength, and the proper pH limits the in-process formation of chlorate. The use of high-purity ingredients also contributes to this. Finally, prompt use of the product limits its gradual deterioration by reactions (32) and (34). 

For example, with nickel-abased alloys, the formation of a nickel oxide film seems to be pre- requisite for obtaining a polished surface a finish of this quality, of 0.2 ym Ra, has been claimed for a Nimonic (nickel alloy) machined in saturated sodium chloride solution. Surface finishes as fine as 0.1 ym Ra have been reported when nick el- chromium steels have been machined in sodium chlorate solution. Again, the formation of an oxide film on the metal surface has been considered to be the key to these conditions of polishing. 

Sodium hypochlorite is most commonly produced by a continuous process in which dilute caustic soda solution and chlorine are fed into a specially designed, cooled reactor. Control of rate of chlorine addition is by monitoring of Redox potential. Temperature is controlled to below 38°C to avoid chlorate formation. Alternately, a batch process may be used in which chlorine is passed slowly into a cold 20°C NaOH solution through a sparge tube near the bottom of a tank. Air agitation is used and chlorine feed rate is kept low to minimise temperature rise. 

Important chemicals, such as sodium hydroxide and sodium chlorate(i) (bleach) are made by the electrolysis of hrine (saturated salt solution). The electrolysis of brine results in the formation of chlorine, hydrogen and sodium hydroxide, which are all useful raw materials for a variety of industrial processes (Figure 19.16). 

The industrial production of Prussian blue is based on the reaction in aqueous solution of sodium hexacyanoferrate(n), Na4Fe(CN)6, with iron(n) sulfate, FeS04-7H20 in the presence of an ammonium salt, which results initially in the formation of the colourless insoluble iron(n) hexa-cyanoferrate(n) (Berlin white). Prussian blue is generated by subsequent oxidation with a dichromate or chlorate. 

Thermal. Heating the solution to 60-80°C decomposes the sodium hypochlorite, albeit slowly. If the temperature is too high then this leads to the formation of chlorates via Equation 26.2. Therefore, care is required not to overheat the solution. The consequent requirement for large holding tanks and process safety issues mean that this approach is generally not favoured. 

A normal solution of sodium hypochlorite is prepared as follows in a 5-I. round-bottom flask are placed 1800 g. of sodium hydroxide solution (300 g. of sodium hydroxide to 1500 g. of water) and 1500 g. of ice. Chlorine gas is then passed into the solution until it has gained in weight approximately 213 g. During this addition, the solution must be kept thoroughly cooled with ice, in order that chlorates will not be formed. After all the chlorine has been passed in, it is necessary to be certain that the mixture is slightly alkaline, since any excess of free chlorine in the solution prevents the formation of hydrazine. 

Bromides and iodides give rise to the free halogens, which yield colourless solutions with sodium hydroxide if the ratio of iodide to chloride exceeds 1 15, the chromyl chloride formation is largely prevented and chlorine is evolved.J Fluorides give rise to the volatile chromyl fluoride, Cr02F2, which is decomposed by water, and hence should be absent or removed. Nitrites and nitrates interfere, as nitrosyl chloride may be formed. Chlorates must, of course, be absent. 

Powdered chromium is slowly attacked by mercuric chloride in solution, with the formation of chromic chloride. Though unattacked by fused sodium carbonate, fused potassium nitrate and chlorate oxidise it vigorously. Pyrophoric chromium (see p- 11) combines with nitrogen on heating. ... 

The formation of bromate in hypobromite solutions is about one hundred times as fast as that of chlorate in hypochlorite solutions and occurs readily in slightly alkaline solution, because of the greater hydrolysis of the sodium hypobromite. The velocity of iodate formation in hypoiodite solution proceeds at a much greater rate, about 3,000,000 times that for the chlorate. Hence, hypoiodite solutions are stable only in very low concentration or in the presence of a very small excess of alkali. An increase in temperature increases the rate of iodate formation. Ethanol will react readily with a cold solution of iodine in alkali with the... 

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