Chlorine electrochemical production

HCIO4, one of the strongest of the mineral acids. The perchlorates are more stable than the other chlorine oxyanions, ie, chlorates, CIO chlorites, CIO or hypochlorites, OCf (3) (see Chlorine oxygen acids and salts). Essentially, all of the commercial perchlorate compounds are prepared either direcdy or indirectly by electrochemical oxidation of chlorine compounds (4—8) (see Alkali and chlorine products Electrochemical processing). 

Several industries are highly dependent on cheap electric power. These include the aluminum industry, the Portland cement industry, electrochemical industries such as plating and chlorine production, the glass industry, and the pulp and paper industry. Other industries such as the petrochemical industry, which is highly competitive, depend on low priced power. About two-thirds of the cost of producing ammonia is electrical cost. 

The first systematic study of the reaction of chlorine with toluene was carried out in 1866 by Bedstein and Geitner. During the next 40 years, many studies were performed to isolate and identify the various chlorination products (1). During the early 1930s, Hooker Electrochemical Co. (Hooker Chemicals Plastics Corp.) and the Heyden Chemical Corp. (Tenneco) began the manufacture of chlorotoluenes. Hooker Electrochemical Co. was later acquired by Occidental Petroleum Corp. and became the Occidental Chemical Corp. In the mid-1970s, Heyden exited chlorotoluenes production Occidental thus is the sole U.S. producer of chlorotoluenes. 

Electrochemical processes require feedstock preparation for the electrolytic cells. Additionally, the electrolysis product usually requires further processing. This often involves additional equipment, as is demonstrated by the flow diagram shown in Figure 1 for a membrane chlor-alkali cell process (see Alkali AND chlorine products). Only the electrolytic cells and components ate discussed herein. 

Electrochemistry is widely used in industry, for example in effluent treatment, corrosion prevention and electroplating as well as in electrochemical synthesis. Electrochemical synthesis is a well-established technology for major processes such as aluminium and chlorine production there is, however, increased interest in the use of electrochemistry for clean synthesis of fine chemicals. The possible green benefits of using electrochemical synthesis include ... 

Electrochemical Processes. The reductive cleavage of azo-group-containing dyes has been applied on a full scale for the decolorization of concentrates from batch dyeing. Depending on the color, decolorization of up to 80% of the initial absorbance can be obtained. Mixed processes consist of combinations of electrochemical treatment and precipitation by use of dissolving electrodes [43,49]. Such techniques have been described in the literature and have, in part, also been tested on a full scale. Anodic processes that form chlorine from oxidation of chloride have also been proposed to destroy dyes, but care has to be taken with regard to the chlorine and chlorinated products (AOX) formed [114,115]. 

Electrochemical reduction in aqueous acid is useful in the treatment of waste liquors obtained from the formation of chloroacetic acid by chlorination of acetic acid. The liquors contain further chlorination products. These are reduced in an undivided cell at a magnetite cathode and a carbon anode to give excellent conversion to monochloroacetic acid [73]. 

A regio- and chemoselective ene-type chlorination of isoprenoids has been realized by electrolysis in a CH2C12/H20—NaCl—(Pt) two-phase system. The electrochemical chlorination of dehydrolinalyl acetate 35 forms the ene-type chlorinated product 43 in 91 % yield (Scheme 3-14)641. The product selectivity of the ene-type chlorination is... 

ELECTROCHEMICAL PROCESSES are employed in chemical production, metal finishing, and energy conversion. Electrochemical engineering encompasses the conception, design, scale-up, and optimization of such processes. The largest-scale electrolytic processes are aluminum and chlorine production together they consume... 

Own experiments in divided cells using Nation membrane separators and hypochlorite solutions in the ppm range of concentration resulted in current efficiency values for active chlorine reduction of a few percent. Shifting the pH to higher values complicated the experiments. A buffer stabilised the pH but the relatively high concentration of buffer ions hindered the electrochemical reaction. Thus, quantification is difficult. Kuhn et al. (1980) showed reduction inhibition when calcareous deposits were precipitated on the cathode, but practical experiments showed the decrease of chlorine production in this case. 

Chlorination products (mainly chlorotyrosine) are measured by HPLC (Fig. 8) or gas chromatography-mass spectrometry. Also, 3-nitrotyrosine can be detected in protein hydrolysates by HPLC in combination with various detection systems, including UV and electrochemical detection (Cl7, C20, L23, L24, 04, S26), gas chromatography, gas chromatography-mass spectrometry (J2), electrospray mass spectrometry, and Western blotting or ELISA using antinitrotyrosine antibodies (H20, T2, V6). 

The Production of Sodium and Chlorine. Many electrochemical processes depend for their success on ingenious devices for securing the purity of the product. As illustration we may consider a cell used for making metallic sodium and elementary chlorine from sodium chloride. 

Salt was first electrochemically decomposed by Cruickshank in 1800, and in 1808 Davy confirmed chlorine to be an element. In the 1830s Michael Faraday, Davy s laboratory assistant, produced definitive work on both the electrolytic generation of chlorine and its ease of liquefaction. And in 1851 Watt obtained the first English patent for an electrolytic chlorine production cell (11). 

Addition of dimethylformamide makes it possible to achieve essential increase in monoohlorobenzene yield. In this case the total current efficiency of the benzene chlorination products is 9056, 3B-33% substance yield, while the chlorobenzene current efficiency 15%. This effect mi t have been concerned with the enhancement of benzene solubility in the water phase. Furthermore dimethylformamide depresses side processes, concerned v/ith both electrochemical conversion of chlorine, formed on the electrodes and formation of dichlorobenzene. As fair as chlorination of benzene derivatives to the side oliain is concerned, the factors that influence the chemical chlorination (UV and more hard radiation, the presence of different initiators of free radicals formation) favorably affect the isolation of benzyl chloride, o-, m-, p-xylylchloric -. The current efficiency is more than 85%. 

The influence of hydrochloric acid concentration appeared to be similar to that in the case of aromatic compounds chlorination in the electrochemical system. While working with aphite electrodes in 27 - 30 hydrochloric acid solutions at the range of current density values from 1 to 4 IcA/m, and at the range of temperatures from 35 to 80°C, the dominating product of ethylene chlorination reaction was stated to be 1,2-dichloroethane. At 35°C, the yield of ethylene chlorination products is 68-8056 at rather low current densities. The increase in the temperature of chlorination process up to 50°C, at the same current densities cause the fiy-owth of the diohloroethane content in the mixture up to 77% - 92%. Though temperature growth to 65°C leads to some increase in total mixture mass of ethylene chlorination products, however, the substance yield of 1,2-diohloroethane is only 75-80%, as lateral processes take place. While temperature rises to SO C,... 

By definition, power expressed in watts is equal to amperes x volts, and energy expressed in watt-hours is equal to amperes x volts x time (in hours). Therefore, the calculation of energy consumption requires a knowledge of the overall reaction and the number of Faradays required to produce the desired product, the operating cell voltage, and the cell current efficiency, which is illustrated here for the case of electrolytic chlorine production. The main anodic electrochemical reaction during the electrolysis of brine is the discharge of the chloride ions to produce chlorine, as described by reaction (4). When the chlorine current efficiency, ci2> is 100%, one Faraday of electricity will produce... 

G. van der Heiden, Diaphragm Cells for Chlorine Production, Proc. Symp. held at the City University, London (1976), Society of Chemical Industry, London (1977), p. 33 J. Appl. Electrochem. 19, 571 (1989). 

S. Pribidevic, Brine Preparation for Chlorine Production, Chlorine Bicentennial Symposium, The Electrochemical Society, Princeton, NJ (1974). 

A typical chlorine production plant using membrane cells is pictured in Fig. 9.8. Electrolysers are operating at atmospheric pressure and 85°C.The main electrochemical characteristics of brine electrolysis cells using membranes are (i) operating current density 300-500 mA.cm (ii) cell voltage 3.0-3.6 V (iii) NaOH concentration 33-35 wt% (iv) energy consumption 2600-2800 kWh/ton Clj at 500 mA.cm (v) efficiency 50% and (vi) steam consumption for concentrating NaOH to 50% 180 kWh/ton CI2. The production of one ton of chlorine requires -1.7 tons of NaCl and less than 1 ton of water vapour. 

The production of chlorine by electrochemical oxidation of chlorides (chlor-aUcali technology, CAT) is nowadays one of the largest processes in industrial electrochemistry. The process, which spends two moles of electricity (2 F), is based on the following stoichiometric equation ... 

On-site hypochlorite or chlorine gas electrochemical generators using brine solutions have larger production capacities and are not commonly used in residential pools. 

Organic Pollutants in Water Using DSA Electrodes, In-Cell Mediated (via Active Chlorine) Electrochemical Oxidation, Fig, 5 Dependence of the electrochemical free chlorine production efficiency on the chloride content of the electrolyzed water under standard conditions using four different anode materials (iridium oxide, mixed iridium/ruthenium oxides, platinum, doped diamond) (Adapted from [26]. Reprinted with permission from Johnson Matthey Pic)... 

In 1800, Cruickshank was the first to prepare chlorine electrochemically [38] however, the process was of little significance until the development of a suitable generator by Siemens and of synthetic graphite for anodes by Acheson and Castner in 1892. These two developments made possible the electrolytic production of chlorine, the chlor-alkali process, on an industrial scale. About the same time, both the diaphragm cell process (1885) and the mercury cell process (1892) were introduced. The membrane cell process was developed much mpre recently (1970). Currently, more than 95 % of world chlorine production is obtained by the chlor-alkali process. Since 1970 graphite anodes have been superseded by activated titanium anodes in the diaphragm and mercury cell processes. The newer membrane cell process uses only activated titanium anodes. 

Other electrochemical processes in which chlorine is produced include the electrolysis of hydrochloric acid and the electrolysis of molten alkali metal and alkaline earth metal chlorides, in which the chlorine is a byproduct. Purely chemical methods of chlorine production are currently insignificant. 

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