Hypochlorite redox potential

When there is a peak flow of chlorine in the feed-stream the redox potential decreases and the amount of caustic that is dosed increases automatically. Caustic is fed to the jet-loop and its flow is regulated by the measurement of the redox potential. When the lead time is long there is a shortage of caustic, which results in a lower level of free caustic that leads to a higher chlorine concentration. This chlorine subsequently reacts with the chlorite in the hypochlorite solution to form chlorine dioxide. The absorption of chlorine dioxide by the caustic is then very limited in step one and is hardly absorbed at all in the caustic present in step two of the production and is emitted with the inert gas stream. 

The two-electron reduction of Compound I to Fe(III) and the one electron reduction of Compound I to Compound II and Compound II to Fe(III) have been estimated by different methods. These methods will be described in the next section, but they differ in the strategy to estimate the redox potential. Two of them rely on spectral determination of equilibrium between redox species [63-65], whereas a third one proposes the use of catalytic measurements [53]. The values obtained with the different methods are shown in Table 4.4. It should be noted these are not standard values. As expected, one of the more oxidant enzymes is the versatile peroxidase, which is able to catalyze the oxidation of Mn(II) to Mn (III) ( 0,=1.5 V). MPO has the highest two-electron redox potential, supporting the fact that only this enzyme is able to catalyze the oxidation of chloride to hypochlorite at neutral pH [72, 73], whereas eosinophil peroxidase performs better at acidic pH [74]. 

The reaction of sodium hydroxide with chlorine is strongly exothermic (AH = 103 kJ/mol). Production can be carried out discontinuously and is monitored by redox potential measurements. Since hypochlorite is easily converted to chlorate at high temperatures, the reaction temperature must be kept below 40°C, for which coolers constructed of titanium are used. The chlorination is generally carried out in such as way that a slight excess of alkali is retained so as to increase the stability of the... 

Mn" porphyrins may be electrochemically oxidized in non-aqueous media to yield Mn " cation radicals and dications as the probable products." The redox potentials depend on the nature of the solvent, counter ion present, of any axially-bound ligands as well as on the basicity of the porphyrin ring involved. Water-soluble Mn " porphyrins are oxidized by a range of oxidants in aqueous alkaline solution to the corresponding Mn porphyrins which appear to exist as fx-oxo dimers using hypochlorite as oxidant, a second oxidation step also occurs. In this case the product has been postulate to be a Mn 0x0 porphyrin. The Mn and Mn porphyrins show only limited stability in water and revert to the stable Mn" porphyrin upon standing in the dark for several... 

At millimolar levels of molecular chlorine, the reaction goes to 99% completion in a matter of a few seconds. Above pH 4.4, essentially no molecular chlorine remains in aqueous solution. Hypochlorous acid is a weak acid (pKa approximately 7.5) and thus, near neutrality, both the protonated form and the anion occur at appreciable levels. HCl-free solutions may be prepared by adding salts such as sodium hypochlorite (NaOCl, commercially available as a stabilized 5.25% [0.7 M] solution as a fabric bleach). Either chlorine gas or hypochlorite solutions can be used in large-scale water chlorination applications. In addition to water treatment, chlorine is also used as a disinfectant for beef, pork, and poultry carcasses and also as a bleaching agent for paper pulp and cake flour (Wei et al., 1985). The disinfecting ability of aqueous chlorine is closely associated with its vigorous oxidant character the redox potential for the reactions... 

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. 

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