Electrolysis drawbacks

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

Platinum is generally acknowledged as the most effective catalyst for the electroreduction of oxygen in a wide range of conditions (e.g. fuel cells). In the instance of aqueous HC1 electrolysis, the basic drawback is corrosion or deactivation of the catalyst during cell shutdown, owing to chemical attack from HC1 and chlorine that diffuse across the membrane. 

The fused salt electrolysis technique was successfully applied to the preparation, also as single crystals, of several transition metal compounds. A review on this subject was published by Wold and Bellavance (1972). A systematic treatment of several reactions and processes, was presented possibly somewhat obsolete now and with a drawback due to the presence of several impurities in the synthesis products. The preparation of the following compounds was especially discussed. 

Furthermore, the presence of pyridine in electrosynthesis reaction mixtures can disturb some couphng reactions, its nucleophilic properties being in some cases a drawback when electrophilic species are added to an electrolysis mixture. 

Lund and Iversen first showed that azobenzene was an effective probase it is reduced to radical-anion at a low potential (—0.9 V vi. Ag/AgCl) and the reduced form is sufficiently basic to deprotonate benzylphosphonium salts. Its usefulness as an alternative to conventional bases was illustrated by the near quantitative production of stilbene by electrolysis of azobenzene in the presence of benzaldehyde and benzyl-triphenylphosphonium bromide (Table 2, entry 1). However, the concomitant formation of the carcinogenic benzidene, by acidic work-up of a product mixture which contains hydrazobenzene, is a severe drawback for this system. 

This process can effectively oxidize many pollutants, however, it has the drawback of permitting the formation of chlorinated organic compounds during the electrolysis. 

Stuart cell — Monopolar water - electrolysis tank cell employing plate electrodes with those of the same polarity connected in parallel resulting in a cell voltage of 1.7-2 V. Cells are connected in series, the inherent drawbacks of cells of the filterpress design (e.g., complicated sealing and interconnect devices) are avoided. 

Although removal of organic and microbiological pollutants from waters has been thoroughly studied, less attention has been paid to the transformation of metal or metalloid ions in species of lower toxicity or more easily isolated. Metals in their various oxidation states have infinite lifetimes, and chemical or biological treatments present severe restrictions or are economically prohibitive. Removal of these species is carried out, generally, by precipitation, electrolysis, chemical oxidation, adsorption, or chelation, all of them presenting drawbacks. 

But membrane electrolysis suffers a severe drawback the high costs for the solid polymer electrolyte. If membranes being... 

Another drawback of this membrane is its rather poor chemical stability due to its tendency to be hydrolyzed during electrolysis. 

If acetylene is the raw material, the hydrochloric acid by-product can be used as an addition. In fact one mole of this acid is produced when starting with ethylene, by the decomposition of the ethylene dichloride obtained by chlorination, and per molecule of vinyl chloride. The chlorine atom in this acid was originally obtained by the electrolysis of sodium chloride. To overcome this drawback and make maximum use of an expensive reactant, it has been proposed to employ equal part mixtures of ethylene and acetylene, or to perform the oxychlorinarion of ethylene. 

Besides advantages outlined in the introduction, the reagent electrode also has some disadvantages that limit its use. The necessary conductivity of the supporting electrolyte makes preparative scale electrolyses below — 50°C difficult because of the increased resistance of the electrolyte. Sometimes the electrode surface becomes deactivated by insulating films (passivation, see Section 2.6.2.4). However, the most serious drawback is the lack of experience with the method, which makes the potential user rather take a chemical oxidant or reductant from the shelf. Therefore, the practice of electroorganic synthesis, which involves electrodes, electrolyte, elec-troanalytical investigation of the substrate and preparative scale electrolysis will be addressed briefly in the next section. 

Membrane electrolysis technology is well established and appropriate for smaller scale facilities. One application is its use as an oxygen generator in submarines, where the hydrogen is considered only a byproduct. Drawback is the high-cost membrane production [14]. 

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