Anodic depolarizers

Cl- and S042+ leakage (DI). Anodic depolarization, leading to depassivation and corrosion... 

A cathodic depolarizer is reduced in preference to solvent. For oxidation reoctions. anodic depolarizers include N2H4 (hydrazine) and NH2OH (hydroxylamine)... 

Classical anodic depolarization reactions (25) of mercury were successfully used for the determination of sulfides, thiosulfate and sulfite in coal conversion process streams (18,19). The relevant electrode reactions are... 

The latter class is by far the larger. It can again be subdivided into two groups, the cathodic and the anodic depolarizers. It is very seldom that a body acts simultaneously as a cathodic and anodic depolarizer. More often a cathodic (or anodic) depolarizer, by reacting with the cations (or anions), acquires the faculty of now depolarizing anodically (or cathod-Ically). Thus, for example, an easily reducible body may be changed by cathodic reduction into one easily oxidized, i.e. accessible to the action of the anions. However, it is more conducive to clearness to adhere to the division into cathodic and anodic depolarizers and to determine the nature of the possible reactions. 

Anodic Depolarizers.—The conditions are somewhat more complicated at the anode. All the anodic depolarizers are oxidizable, it is true, even reducing substances which destroy the negative charges-. But the reaction-picture is more varied at the anode than at the cathode—due to the individual variety of the anions. If the action consists merely in a withdrawal of hydrogen and an addition of oxygen, or both, it is called oxidation. 

The electrolysis of aromatic acids by no means offers results which are comparable to those obtained by the electrolysis of aliphatic acids. In so far as the aromatic acids, or their salts, act as electrolytes, a regeneration of the acid from the anion RCOO and water, with evolution of oxygen, occurs almost exclusively. A splitting off of carbonic acid, which makes possible the manifold reactions of aliphatic acids, almost never occurs here. The results obtained with aromatic acids are, therefore, only of a more general interest so far as the acids, by substitutions in the benzene nucleus, can act as cathodic or anodic depolarizers, and can in this way exert reduction and oxidation effects. 

There are several problems associated with hydrogen production however, some of them are really a side product associated inconvenience, such as oxygen formation in the course of electrolysis. The use of new anode depolarizers seems to be one of the solutions to avoid the large overpotentials associated with the anodic process. All these anodes are patent protected, but some of them are not new material, but only a product of a side process with lower activation energy. The Westinghouse thermo(electro)chemical hybrid process for hydrogen production is an example [25] with 45% of... 

Demonstrate the concept of using natural gas as anode depolarizer to reduce the electrical energy consumption. 

Our approach to decrease the electrical energy input requirements for electrolysis is to use natural gas as an anode depolarizer. This approach... 

It is advisable to protect T1 from surface oxidation by coating it with a layer of paraffin or storing it under glycerol or petroleum. II. Brown and McGlynn report preparation of a good, smooth, cohesive electrolytic deposit of metallic T1 from a thallium perchlorate bath containing peptone as an anodic depolarizer and cresol as a further additive. Current densities of 0.5 to 1.8 amp./ 100 cm. are used. 

Again, difficulties sometimes arise in chloride media because chlorine is generated at the anode and some platinum may dissolve. Both cause difficulties at the cathode, the first by reoxidizing copper and the second by depositing platinum so hydrazine is often added as an anodic depolarizer since it is easily oxidized to nitrogen ... 

In conclusion, still other methods may be mentioned. Sulfhydryl groups can also be determined polarographically by the anodic depolarization wave, and disulfidic groups by the reduction wave. Although catalytic reactions (such as that of BrdiJka and the pre-sodium wave method) are most sensitive for examinations of proteins, the former methods were... 

The early attempts to use an undivided cell were based on the addition of an organic anode depolarizer such as isopropanol. It was thought that the reaction... 

These studies together showed that it was possible to run the process effectively with low acrylonitrile and tetraalkylammonium ion concentrations. In such circumstances the anode depolarizer would seem unnecessary and, indeed, Phillips have run a pilot plant with an undivided cell, lead cathode and steel anode, and a very simple electrolyte consisting of dipotassium hydrogen phosphate (1.5 m), acrylonitrile (6%) and a tetrabutylammonium salt (0.03%) in water the anode reaction is again oxygen evolution. The yield of adiponitrile is over 90% and the major byproducts were propionitrile and trimer. 

Copper and lead in brasses and bronzes. Nitric acid treatment of brass leads to chemical separation of tin as SnOi XH2O after filtration and an ignition procedure, the tin can be gravimetrically determined. Thereafter, the analysis is based upon cathodic deposition of Cu and anodic deposition of PbOi. If copper alone is to be determined, deposition from a pH 4 tartrate medium with hydrazine as the anodic depolarizer gives separation from most common metals. If lead is also to be determined, one uses a concentrated nitric acid medium, from which PbOi is deposited... 

Controlled-current coulometry (coulometric titration) can be utilized to determine not-easily oxidizable (or reducible) analytes of different applications via acid-base, precipitation, com-plexation titrations, etc. Furthermore, it benefits short analysis time and small amount determination [2]. Dzudovic et al. [21] reviewed some studies employing acid-base titrations for the determinations of non-aqueous or water-insoluble compounds (organic and inorganic). Typically, acidimetric titrations were undertaken coulometrically based on the EF liberated by the oxidation of the introduced H2O. Coulometric titrations of bases in nonaqueous solvent were performed using anodic depolarizers (titrants) to generate as a source. On the other hand, coulometrically atkalimetric... 

In general, restrictions on electrolyte composition are not severe and each of the articles quoted contains recipes which seem to work satisfactorily. Electrolysis is usually carried out in a slightly acid solution of HCl or H SO containing an anodic depolarizer (hydrazine sulfate or hydrochloride are the beet, although hydroxylamine hydrochloride may also be used), hydrolyzable elements are present, complexing agents such as citrate, tartrate, or oxalate may be added to keep the solution clear and improve the nature of the final deposits. 

By the mid 1970s it was clear that the hydrodimcrizalion of acrylonitrile could be run very effectively with only a low concentration ortctraalkylammoniurn ion and that a saturated solution of acrylonitrile in an aqueous buffer was an appropriate medium. In such circumstances, it seemed likely that the electrolysis could be run jn an undivided cell without the additional complication of an anode depolarizer. Such a system was first reported by Phillips Petroleum. They ran a pilot plant with an undivided cell consisting of a lead cathode and a steel anode a very simple electrolyte, 6% acrylonitrile and 0,03% tetrabutylaminon-ium salt in aqueous dipotassium hydrogen phosphate was employed and the anode reaction was oxygen evolution. The yield of adiponitrile remained above 90% and the chief by-products were propioniirile and trimer. No base-initiated chemistry was observ due to the use of an effective buffer. 

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