Industrial electrolysis processes

Modern industry could not function in its present form without electrolysis reactions. A number of elements are produced almost exclusively by electrolysis—for example, aluminum, magnesium, chlorine, and fluorine. Among chemical compounds produced industrially by electrolysis are NaOH, K2Cr2, KMn04, Na2S20g, and a number of organic compounds. 

In electroplating, one metal is plated onto another, often less expensive, metal by electrolysis. This procedure is done for decorative purposes or to protect the underlying metal from corrosion. Silver-plated flatware, for example, consists of a thin coating of metallic silver on an underlying base of iron. In electroplating, the item to be plated is the cathode in an electrolytic cell. The electrolyte contains ions of the metal to be plated, which are attracted to the cathode, where they are reduced to metal atoms. 

An example of electrosynthesis in organic chemistry is the reduction of acrylonitrile, CH2=CH—C=N, to adiponitrile, N=C(CH2)4C=N, at a lead cathode (chosen because of the high overpotential of H2 on lead). Oxygen is released at the anode. 

The commercial importance of this electrolysis is that adiponitrile can be readily converted to two other compounds hexamethylenediamine, H2NCH2(CH2)4CH2NH2, and adipic acid, HOOCCH2(CH2)2CH2COOH. These two compounds are the monomers used to make the polymer Nylon 66 (page 1313). 

On page 901 we described the electrolysis of NaCl(aq) through the reduction half-cell reaction (19.30) and the oxidation half-cell reaction (19.31). 

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The synthesis of chlorine by the electrolysis of brine is attributed to Cruikshank in 1800, but it took almost 90 years before the electrolytic method was used successfully on a commercial scale. Although the laws that govern the electrolysis of aqueous solutions were formulated by Faraday in 1833, electrochemical processes could not develop through the nineteenth century because of a lack of electrical generation capacity. The development of the dynamo (around 1865) allowed Edison, Siemens, Varley, Wheatstone and others to invent generators of electricity with large capacity and high efficiency. This in turn opened the way to industrial electrolysis processes,... 

Industrial Electrolysis Processes—Electrolysis has many industrial applications, including electroplating, refining of metals, and production of substances such as NaOH(aq), H2(g),and Cl2(g). 

The electrolysis of NaCl brine for the production of chlorine and caustic soda is one of the oldest and certainly one of the most important industrial electrochemical processes (22—26). The overall reaction is... 

The development of electrical power made possible the electrochemical industry. Electrolysis of sodium chloride produces chlorine and either sodium hydroxide (from NaCl in solution) or metallic sodium (from NaCl fused). Sodium hydroxide has applications similar to sodium carbonate. The ad vantage of the electrolytic process is the production of chlorine which has many uses such as production of polyvinyl chloride. PVC, for plumbing, is produced in the largest quantity of any plastic. 

At present about 77% of the industrial hydrogen produced is from petrochemicals, 18% from coal, 4% by electrolysis of aqueous solutions and at most 1% from other sources. Thus, hydrogen is produced as a byproduct of the brine electrolysis process for the manufacture of chlorine and sodium hydroxide (p. 798). The ratio of H2 Cl2 NaOH is, of course, fixed by stoichiometry and this is an economic determinant since bulk transport of the byproduct hydrogen is expensive. To illustrate the scde of the problem the total world chlorine production capacity is about 38 million tonnes per year which corresponds to 105000 toimes of hydrogen (1.3 x I0 m ). Plants designed specifically for the electrolytic manufacture of hydrogen as the main product, use steel cells and aqueous potassium hydroxide as electrolyte. The cells may be operated at atmospheric pressure (Knowles cells) or at 30 atm (Lonza cells). 

The electrolysis of molten sodium chloride is an important industrial reaction. Figure 11.15 shows the large electrolytic cell used in the industrial production of sodium and chlorine. You will meet other industrial electrolytic processes later in this chapter. 

Tantalum metal is prepared from potassium fluotantalate or tantalum pen-toxide produced from the ore concentrate by solvent extraction or fractional crystallization as described. The metal is produced industrially by Balkes electrolysis process. Fused potassium fluotantalate is electrolyzed at 900°C in a cast iron pot. While the latter serves as a cathode, a graphite rod is used as the anode. A small amount of tantalum oxide is added to the melt. The unreduced potassium fluotantalate is separated from the tantalum metal produced by leaching with water. Impurities are removed from the metal by acid wash. 

The industrial Nalco process for the production of 11a and 11b was conducted in mixtures of 53 with THF, at 35-40 °C or 40-50 °C and about 2 kg cm pressure, in a cell divided by porous diaphragms and with current densities of 1.5-3.0 A dm at 15-30 V. However, production details are beyond the scope of this Chapter. Effective methods of recovery of 11 from mixtures after or during the electrolysis were elaborated . Of... 

In 1800. William Nicholson and Anthony Carlisle decomposed water into hydrogen and oxygen by an electric current supplied by a voltaic pile. Whereas Volta had pruduced electricity from chemical action these experimenters reversed the process and utilized electricity to produce chemical changes. In 1807. Sir Humphry Davy discovered two new elements, potassium and sodium, by the electrolysis of ihe respective solid hydroxides, utilizing a voltaic pile as the source of electric power. These electrolytic processes were the forerunners of the many industrial electrolytic processes used today to obtain aluminum, chlorine, hydrogen, or oxygen, for example, or in die electroplating of metals such as silver or chromium. 

Electrolytic reduction. Although perhaps not properly classified as a smelting process, the production of metals by electrolysis may be included at this juncture. Examples of the production of active metals by the electrolysis of either fused salts or aqueous solutions are included in the discussion of industrial electrochemical processes earlier in this chapter. 

Although current industrial production is via chemical reduction, the electrolysis process is convenient for small quantities of HOOH. 

The direct electrochemical methoxylation of furan derivatives represents another technically relevant alkoxylation process. Anodic treatment of furan (14) in an undivided cell provides 2,5-dimethoxy-2,5-dihydrofuran (15). This particular product represents a twofold protected 1,4-dialdehyde and is commonly used as a C4 building block for the synthesis of N-heterocycles in life and material science. The industrial electroorganic processes employ graphite electrodes and sodium bromide which acts both as supporting electrolyte and mediator [60]. The same electrolysis of 14 can be carried out on BDD electrodes, but no mediator is required The conversion is performed with 8% furan in MeOH, 3% Bu4N+BF4, at 15 °C and 10 A/dm2. When 1.5 F/mol were applied, 15 is obtained in 75% yield with more or less quantitative current efficiency. Treatment with 2.3 F/mol is rendered by 84% chemical yield for 15 and a current efficiency of 84% [61, 62]. In contrast to the mediated process, furan is anodically oxidized in the initial step and subsequently methanol enters the scene (Scheme 7). 

The use of electrochemistry in industry is affected by the price of electricity and its ease of supply, principally in cases where there is an alternative production method. For this reason large-scale energy-intensive electrolysis processes such as metal extraction have developed where electricity can be generated at low cost. This criterion is more... 

Castner, Hamilton Young — (Sep. 11, 1858, Brooklyn, New York, USA - Oct. 11,1899, Saranac Lake, New York, USA) Castner studied at the Brooklyn Polytechnic Institute and at the School of Mines of Columbia University. He started as an analytical chemist, however, later he devoted himself to the design and the improvement of industrial chemical processes. He worked on the production of charcoal, and it led him to investigate the Devilles aluminum process. He discovered an efficient way to produce sodium in 1886 which made also the production of aluminum much cheaper. He could make aluminum on a substantial industrial scale at the Oldbury plant of The Aluminium Company Limited founded in England. However, - Hall and - Heroult invented their electrochemical process which could manufacture aluminum at an even lower price, and the chemical process became obsolete. Castner also started to use electricity, which became available and cheap after the invention of the dynamo by - Siemens in 1866, and elaborated the - chlor-alkali electrolysis process by using a mercury cathode. Since Karl Kellner (1851-1905) also patented an almost identical procedure, the process became known as Castner-Kellner process. Cast-... 

D. H. Smith, Industrial water electrolysis, in Industrial Electrochemical Processes, edited by A. T. Kuhn, Elsevier Publishing Company, 1971, pp. 127-157. 

Of all aluminum electrolyte systems, to our knowledge type 3 is today the technically most accepted. This type of electrolyte was discovered and intensely studied by Ziegler and Lehmkuhl [118, 217, 218, 221]. The companies Siemens AG, HGA, MBB, SEDEC, Interatom, and ALU 2000 have developed the industrial scale process (Sigal Process = Siemens galvanoaluminum). The used electrolytes consist of aluminumalkyls as well as alkali metal halides or quaternary onium salts, which are dissolved in aromatics (i.e., toluene). Electrolysis is carried out at temperatures around 90-100°C. Electrolytes of this kind have demonstrated their high produc-... 

Because of gas evolving in the gravity field, the industrial two-phase electrolysis processes generally use vertical electrodes to promote bubble detachment and avoid gas accumulation. This is the reason why the present work focuses upon vertical electrodes. 

In Chapter 4 by Popov et al., the aspects of the newest developments of the effect of surface morphology of activated electrodes on their electrochemical properties are discussed. These electrodes, consisting of conducting, inert support which is coated with a thin layer of electrocatalyst, have applications in numerous electrochemical processes such as fuel cells, industrial electrolysis, etc. The inert electrodes are activated with electrodeposited metals of different surface morphologies, for example, dendritic, spongy-like, honeycomblike, pyramid-like, cauliflower-like, etc. Importantly, the authors correlate further the quantity of a catalyst and its electrochemical behavior with the size and density of hemispherical active grain. 

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