Electrochemical oxidation diaphragm

Electrochemical Generation of Chlorine Dioxide from Chlorite. The electrochemical oxidation of sodium chlorite is an old, but not weU-known method of generating chlorine dioxide. Concentrated aqueous sodium chlorite, with or without added conductive salts, is oxidized at the anode of an electrolytic cell having a porous diaphragm-type separator between the anode and cathode compartments (122—127). The anodic reaction is... 

It follows from the above explanation that electrolysis of alkali chlorides in an electrolyzer without a diaphragm must be interrupted before curve h which represents the concentration of hypochlorite oxygen changes into a horizontal line only under this condition is the process economical, as a prolonged electrolysis would result in a waste of current without any further increase in th<) hypochlorite content. Moreover, care should be taken to prevent the hypochlorite ions formed from being electrochemically oxidized, as this would result in lower current efficiency and lower hypochlorite concentration in the liquor produced. This process is influenced by a number of factors, e. g. brine concentration, hydrogen ion concentration, anode material, current density, temperature, and last but not least a suitable design of the electrolyzer. 

Electrochemical oxidations were carried out in a divided H-type cell with a fine porosity glass frit as the diaphragm and 1/4" graphite rods as electrodes. All oxidations were carried out with 2 mmol of 4 in 0.05 M solution with 0.75 M NaOAc as the electrolyte at constant current in the solvents indicated in Table I. Mn(OAc)2 and Cu(OAc)2 were used in the amounts indicated. Since 2 equivalents of Mn(OAc)3 are required, 0.2 equivalents is 10% of the theoretical amount. No 8 is formed in the absence of current since Mn(II) was used all the Mn(III) generated is formed electrochemically. Since 2.0 F/mol of electricity is required for two one-electron oxidations of 4, the reaction theoretically should be complete when 386 coulombs have been passed through the solution. 

An interesting system is the methylene blue catalyzed oxidation of HS by O2 in a CSTR. Oscillation occurs over a narrow range of flow rates, and a mechanism has been proposed. Oscillations have also been found in the cobalt/bromide catalyzed oxidation of cyclohexanone by O2 in the electrochemical oxidation of HCHO and HCOOH/HCOO , and in the electrodissolution of copper in acidic chloride solution, and the anodic dissolution of nickel in aqueous sulfuric acid. °° Damped oscillations are predicted for reactions in stirred diaphragm cells. ... 

Heterocyclophane 177e was also obtained on a platinum cylindrical electrode by the preparative electrochemical oxidation of podand 158e in a diaphragm (cellulose) glass electrolyzer. The electrosynthesis was carried out for 4 h. The mass spectrometric investigations of the mixture after the electrolysis showed the existence of two macrocyclic products 152e (m/z = 830), and the macrocyclic dimer (m/z = 1660). The preparative yield was 40 % (Mamedov et al. 2007). There was no starting compound in the solution. 

For forced-convection studies, the cathodic reaction of copper deposition has been largely supplanted by the cathodic reduction of ferricyanide at a nickel or platinum surface. An alkaline-supported equimolar mixture of ferri- and ferrocyanide is normally used. If the anolyte and the catholyte in the electrochemical cell are not separated by a diaphragm, oxidation of ferrocyanide at the anode compensates for cathodic depletion of ferricyanide.3... 

M. Hirita, S. Suwazono, and H. Tanigawa, Diaphragm thickness control in silicon pressure sensors using an anode oxidation etch-stop, J. Electrochem. Soc. 134, 2037, 1987. 

The electrochemical deposition of chromium upon metals is usually carried out in chromium(VI) oxide-containing baths to which ca. 1% sulfuric acid has been added. The material to be coated is used as the cathode, the anode usually being lead. A diaphragm is not necessary. The baths contain ca. 300 g/L of chromium) VI) oxide, in addition to a number of other components. The yield on the basis of electricity consumed is very poor, due to hydrogen being preferentially produced at the cathode. The energy consumption amounts to ca. 75 kWh/kg chromium. The chromium obtained is relatively pure. 

The effectiveness of many electrochemical processes is determined by the presence of a porous partition or diaphragm, which separates the electrolyzer into cathodic and anodic compartments. In processes of electrosynthesis of organic compounds the diaphragm has usually the role of separating the electrolysis products so as to prevent reverse oxidation or reduction and also to prevent mutual contamination of the products. 

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