Industrial electrolysis electrolyzer

More than 400 industrial water electrolyzers were in operation by the beginning of the nineteenth century. In 1939, the first large water electrolysis plant of 10,000 Nm3 H2/h capacity went into operation and in 1948, Zdansky/Lonza built the first pressurized industrial electrolyzer [1],... 

Both Italy and Switzerland have work in progress on advanced alkaline electrolyzers. The DeNora Corporation and Brown Boveri of Italy and Switzerland, respectively, have built some of the largest industrial electrolysis plants and are each supporting in-house R D efforts, as well as working on contracts from their respective governments. 

All the above material confirm that the problem of industry electrolysis of pure hydrochloric acid is solved in general. Waste HCl from several chlororganic productions (for example, the chloromethane production [18] ) can be electrolyzed as well. Electrolysis of such acid cause no difficulties unless an organic phase appears, as its presence sharply reduces the diaphragm lifetime. Chlorine, the main purpose product, contains only tetraolorooarbon - the final product of methane chlorination. 

Initially, Nafion-type membranes had been developed for the needs of the chlorine industry. Chlorine electrolyzers with such membranes were widely introduced. Apart from chlorine, they yield alkali that is very pure as the second major electrolysis product. Soon after the advent of these membranes, work on fuel cells that would include them started. Fuel cells with such membranes had lifetimes two to three orders of magnitude longer. 

One important technical evaluation criterion for electrolytic processes is the efficiency, i.e. the cost-benefit ratio for an industrial electrolysis system. When determining the efficiency, it is expedient to utilize the heating value (3.54 kWh Nm ) or the thermoneutral voltage Vth = 1.48 V because in commercial electrolysis systems for alkaline and PEM electrolysis, water is added in its liquid state. As such, the efficiency referring to the heating value of hydrogen specifies how efficiently the electrolyzer or the entire electrolysis system with all auxiliary components can be operated. 

Industrial scale electrolyzers were developed early in the 20th century for the manufacture of chlorine and caustic soda from brine, and for the commercial production of hydrogen used in ammonia synthesis. Large water-electrolysis plants were constructed in Norway and Canada in the 1930 s, based on cheap hydroelectric power, and the hydrogen so produced was used in fertilizer manufacture. With the advent of natural gas and low cost petroleum, hydrogen production moved toward catalytic steam-reforming of hydrocarbons, and water electrolysis became less significant. 

You have already seen that chlorine gas can be made by the electrolysis of molten sodium chloride. In industry, some chlorine is produced in this way using the Downs cell described earlier. However, more chlorine is produced in Canada using a different method, called the chlor-alkali process. In this process, brine is electrolyzed in a cell like the one shown in Figure 11.32. Brine is a saturated solution of sodium chloride. 

In alkaline electrolyzers, Ni is the only elemental cathode that can be used. It is generally considered as a fairly good electrocatalyst, but in facts it exhibits two shortcomings (i) its activity decreases with time [cf. the AVtterm in Equation (7.16)] especially under conditions of intermittent electrolysis and (ii) shutdown of industrial cells (for maintenance) leads to Ni dissolution at the cathode since this electrode is driven to more positive potentials by short-circuit with the anode. These shortcomings can be alleviated if Ni cathodes are activated, that is, if they are coated with a thin layer of more active and more stable materials. Activation has been attempted with a variety of materials from sulfides to oxides, from alloys to intermetallic compounds. 

For a long time, conventional alkaline electrolyzers used Ni as an anode. This metal is relatively inexpensive and a satisfactory electrocatalyst for O2 evolution. With the advent of DSA (a Trade Name for dimensionally stable anodes) in the chlor-alkali industry [41, 42[, it became clear that thermal oxides deposited on Ni were much better electrocatalysts than Ni itself with reduction in overpotential and increased stability. This led to the development of activated anodes. In general, Ni is a support for alkaline solutions and Ti for acidic solutions. The latter, however, poses problems of passivation at the Ti/overlayer interface that can reduce the stability of these anodes [43[. On the other hand, in acid electrolysis, the catalyst is directly pressed against the membrane, which eliminates the problem of support passivation. In addition to improving stability and activity, the way in which dry oxides are prepared (particularly thermal decomposition) develops especially large surface areas that contribute to the optimization of their performance. 

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. 

If the final product desired is tellurium metal, excess free caustic soda is required in the sodium tellurite solution. The solution is electrolyzed in a cell using stainless steel anodes to produce tellurium metal (20). This technology is used at the CCR Division of Noranda Metalluigy Inc., Canada, and at Pacific Rare Metals Industries Inc., the Philippines. Typical electrolysis conditions are given in Table 2. 

On the other hand, application of alkali metal amalgam permits the slowing down of the reaction of metals with alcohols, which is used in the industrial production of alkali metals alkoxides. Production of NaOR by Mathieson Alkali Works is based, for instance, on the reaction of sodium amalgam (formed as a result of the electrolysis of aqueous NaCl solution with the mercury cathode) with alcohol NaOR ROH is isolated from the solutions. Na residue in the amalgam is hydrolyzed, the obtained mixture is returned to the electrolyz-... 

Electrolysis of water — This is a process of electrochemical decomposition of water into -> hydrogen and -> oxygen. Apart from alkaline electrolyzers using 25% KOH solution [i], devices with polymer, or ceramic ion-conducting -> membranes have been developed for industrial applications [ii]. 

Electrolyzers are today commercially viable only in selected industrial gas applications (excepting various noncommercial military and aerospace applications). Commercial applications include the previously mentioned remote fertilizer market in which natural gas feedstock is not available. The other major commercial market for electrolysis today is the distributed, or merchant, industrial hydrogen market. This merchant market involves hydrogen delivered by truck in various containers. Large containers are referred to as tube trailers. An industrial gas company will deliver a full tube trailer to a customer and take the empty trailer back for refilling. Customers with smaller-scale requirements are served by cylinders that are delivered by truck and literally installed by hand. 

The same high sensitivity that makes measurements so convenient causes great difficulty in the electrolytic industry. Thus, it takes 9.65x10 C or 26.8 A h to generate one equivalent of a product formed by electrolysis. A cylinder of compressed contains about a pound of the gas. It would take a water electrolyzer running at 10 A about 12 hours to produce this small amount of hydrogen ... 

Manufacture. At first sodium chlorate is prepared by the electrolysis of industrial salt or the milk of lime process described in (2). The sodium chlorate is further electrolyzed to produce sodium perchlorate, and when potassium chloride is added to cause double decomposition, crude potassium perchlorate is obtained. This is recrystallized and crushed to powder. It is impossible to obtain potassium perchlorate by the direct electrolysis of potassium chlorate, because of the low solubility of potassium. perchlorate in water. 

Industrial electrolyzers use electrodes and gas collection schemes optimized to produce the maximum amount of hydrogen using the minimum size equipment and minimum quantity of electric energy. Their basic principle of operation is an extension of the simple process described above. Equipment for the industrial scale production of hydrogen by electrolysis is available from a number of manufacturers. Some of these are ... 

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