Sodium hypochlorite electrolytic

Diacetone-L-sorbose (DAS) is oxidized at elevated temperatures in dilute sodium hydroxide in the presence of a catalyst (nickel chloride for bleach or palladium on carbon for air) or by electrolytic methods. After completion of the reaction, the mixture is worked up by acidification to 2,3 4,6-bis-0-isoptopyhdene-2-oxo-L-gulonic acid (2,3 4,6-diacetone-2-keto-L-gulonic acid) (DAG), which is isolated through filtration, washing, and drying. With sodium hypochlorite/nickel chloride, the reported DAG yields ate >90% (65). The oxidation with air has been reported, and a practical process was developed with palladium—carbon or platinum—carbon as catalyst (66,67). The electrolytic oxidation with nickel salts as the catalyst has also... 

Oxidative surface treatment processes can be gaseous, ie, air, carbon dioxide, and ozone Hquid, ie, sodium hypochlorite, and nitric acid or electrolytic with the fiber serving as the anode within an electrolytic bath containing sodium carbonate, nitric acid, ammonium nitrate, ammonium sulfate, or other electrolyte. Examples of electrolytic processes are described in the patent Hterature (39,40)... 

Hypohalite ions, XO, are formed when a halogen is added to the aqueous solution of a base. Sodium hypochlorite, NaClO, is produced from the electrolysis of brine when the electrolyte is rapidly stirred, and the chlorine gas produced at the... 

When chlor-alkali electrolysis is conducted in an undivided cell with mild-steel cathode, the chlorine generated anodically will react with the alkali produced cathodically, and a solution of sodium hypochlorite NaClO is formed. Hypochlorite ions are readily oxidized at the anode to chlorate ions this is the basis for electrolytic chlorate production. Perchlorates can also be obtained electrochemically. 

To summarize the production of sodium hypochlorite is favoured by (i) Neutral cone. soln. of sodium chloride (ii) Low temp. (iii) High anodic current density (iv) The presence of potassium bichromate and (v) An adequate circulation of the electrolyte. G. E. Cullen and R. S. Hubbard have studied the best... 

Although NaI04 or KI04 are the secondary oxidants used in the vast majority of cases in which alcohols are oxidized with catalytic Ru04, the employment of sodium hypochlorite (NaOCl),31 sodium bromate (NaBrOj )32 or Cl+, electrolytic-ally generated by oxidation of chloride ion,33 have also been reported. 

Mercury represents a serious environmental risk, and the study of removal of mercury from wastewater has received considerable attention in recent years. Mercury concentration was usually reduced by deposition on a cathode with high surface area. Removal of mercury is studied using extended surface electrolysis which reduces the level of mercury to below acceptable concentrations of 0.01 ppm in wastes by employing a Swiss roll cell with a cadmium-coated, stainless-steel cathode. An industrial cell with a fluidized bed electrode has also been studied. Graphite, as an efficient porous electrode, has been used to remove traces of mercuric ions form aqueous electrolyte solutions. In order to apply the electrochemical method for some effluents, it is necessary to use sodium hypochlorite to convert elemental mercury and less soluble mercury compounds to water-soluble mercuric-chloride complex ions. 

What chemical reaction takes place at each electrode m the electrolytic preparation of sodium hypochlorite from sodium chloride W ould a well stirred solution become more acidic or more basic during the course of this electrolysis ... 

Sodium hypochlorite, used commercially in cotton bleaching, is made by the electrolysis of brine, the electrolyte being agitated to mix the anode and cathode products. At the cathode, 2H+ + 2e -> Hg increases the concentration of OH , while at the anode, 2C1 CI2 + 2e releases chlorine. These combine ... 

Sludges result from the pretreatment of resaturated brine for removal of impurities, and from brine to be discharged, which was occasionally necessary because of water buildup in the brine circuit. These sludges contain 8-15 mg/g (dry basis) mercury as a complex mixture of compounds. To recover the mercury, most of the water is removed, and then the sludge is resuspended in aqueous sodium hypochlorite. The hypochlorite oxidizes the sulfide and any elemental mercury present (Eqs. 8.46 and 8.51) in order to produce a concentrated aqueous stream of dissolved mercury salts. Insoluble components are then removed by filtration, and the solution is then returned to the brine circuit. When this reaches the electrolyzer, electrolytic reduction recovers the dissolved mercury present (Eq. 8.52). 

Sodium hypochlorite has virtually replaced bleaching powder. It is more constant in composition and is supplied as a concentrated solution in carboys or tanks ready for use. Chlorine is produced in large quantities as a by-product in the electrolytic manufacture of sodium hydroxide. A solution of salt is electrolysed, with the result that chlorine collects at the anode and sodium at the cathode. The sodium reacts with the water immediately to form sodium hydroxide, and the electrolytic cell is so constructed that the chlorine formed at the anode escapes before it has had an opportunity to come into contact with the sodium hydroxide. 

By contrast the electrolytic oxidation at 8°C and a current of 0.7A with a graphite anode and a stainless steel cathode of a solution of mesitytene in aqueous sulphuric acid/acetonitrile (4 1) gave, over 5.5 hours, a 43% yield of the same product, namely 4-hydroxy-2,4,6-trimethylcyclohexa-2,5-dienone (ref.25) as obtained with the oxidants chlorine, manganese dioxide or sodium hypochlorite. 

Equation (128) was proposed as one of the causes of the (aesence of O2 in electrolytic sodium chlorate operations using graphite anodes. However, there-is no evidence for its participation in chlor-alkali cells because (1) the anolyte pH in these cells is ca. 3-5 whoB hypochlorite is not a major species and (2) the anode potentials are much lower dian that required for reaction (128) to take place at any measurable rate. 

Development of small but sophisticated systems for electrochemical generation of hypochlorite from very dilute solutions of NaCl is of present interest. In recent years, electrochemical synthesis of extra-pure sodium hypochlorite solutions for medical use has received growing attention [84,85]. The electrolytic solution is an isotonic physiological salt solution containing 0.89% NaCl. Another application is the disinfection of drinking water that contains only 10-100 mg NaCl per liter [86,87]. Reviews of onsite generation of hypochlorite for water treatment and of the sterilization of water and wastewater include those of Michalek and Leitz [56] and, more recently, Scott [88]. 

Tin recovery from sludge [28]. In the electrodeposition of tin from a fluoroborate electrolyte, a sludge containing approximately 50% tin is formed. The tin can be recovered by electrodeposition of a leachate of the sludge obtained by reacting with concentrated hydrochloric acid. After dilution of the leachate to give a Sn(IV) ion concentration of 50 g dm , the tin can be electrodeposited onto steel plate in tank elec-trolysers. The anode reaction in this process is chlorine gas evolution which is absorbed in sodium hydroxide solution to form sodium hypochlorite which is used in another part of the plant. Tin is recovered as a 3 mm thick compact deposit with a current efficiency >90%. 

In the process the Ni-Cd batteries are first shredded and leached of the metal components in concentrated hydrochloric acid. This leachate consists of a solution of the dissolved metals, mainly Fe, Ni, Cd with small amounts of Co, Cu and Hg at a pH of approximately 0. The Cd is extracted with a commercial metal ion extractant, then stripped into an aqueous electrolyte solution from which cadmium is electrowon. After extraction of the cadmium, the leachate is contacted with sodium hypochlorite, at pH 4, to oxidise Fe(II) to Fe(III) and induce precipitation of ferric hydroxide. The filtrate now contains mainly Ni which is recovered by electrodeposition. The processing of 1000 kg of batteries will produce 200 kg of Ni metal and 159 kg of Cd metal and 500 kg of ferro-nickel scrap. An alternative process [33], is operated in China for the recovery of Ni and Cd from Ni/Cd batteries. 

Sodium hypochlorite did not dominate hypochlorite markets until about 1930. Electrolytic production of chlorine did not begin until 1890, and liquid chlorine could not be shipped before 1909. Before this, bleaching powder was essentially the only form of hypochlorite, or even chlorine, that was marketed. ... 

Electrolytic cells are also used in a variety of devices - and appliances " to produce dilute solutions of electrolyzed water for cleaning and sanitization. Miniature, battery-powered cells are used to generate hypochlorite in handheld sprayers and small portable water disinfection devices. " " The brine may be saturated or have 1-5 g L of salt. An acidic solution of chlorine, hypochlorous acid, and possibly chlorine dioxide is obtained from the anode of a divided cell. It typically has 10-100 mg L of available chlorine and pH values of 2-4. Its stability is poor, and the volatile oxidants are rapidly lost from open solutions. A neutral solution of hypochlorous acid and sodium hypochlorite is dispensed from undivided cells or by combining effluents from the anode and cathode. It typically has 80-100 mg L of available chlorine and pH 5-8. Devices to make 500-1000 mg L" of available chlorine are also available. Neutral solutions made using larger versions of these devices are bottled and sold in some regions. 

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