Electrolysis chlor-alkali process

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. 

The chlor-alkali process,34 in which seawater is electrolyzed to produce Cl2 and NaOH, is the second most important commercial electrolysis, behind production of aluminum. 

Ion-exchange membranes are currently used not only for more or less conventional separation processes like membrane electrolysis (mainly the chlor-alkali process), electrodialysis, dialysis or electro-ultrafiltration (cf. Table 2.1), but also in various... 

The largest scale synthesis based on electrolysis is the chlor-alkali process. Sodium ions in a salt brine migrate... 

Relatively pure solid NaOH is recovered from the aqueous solution, and the regenerated mercury is then pumped back to the electrolysis cell. This process, called the chlor-alkali process, has often resulted in significant mercury contamination of the environment the waste solutions from this process are now carefully treated to remove mercury. 

Energy Consumption. Electric power consumption of electrolysis is the major part of the energy consumption in a chlor-alkali process. The power consumption of the membrane process has recently been greatly reduced by various improvements. The latest performance of Asahi Chemical s membrane process realized at a commercial plant and also in an industrial scale cell is shown in relation to current density in Figure 13 (82). 

Chlorine gas, CI2, is prepared industrially by the electrolysis of molten NaCl (see Section 19.8) or by the chlor-alkali process, the electrolysis of a concentrated aqueous NaCl solution (called brine). Chlor denotes chlorine and alkali denotes an alkali metal, snch as sodium.) Two of the common cells nsed in the chlor-alkali process are the mercnry cell and the diaphragm cell. In both cells the overall reaction is... 

Electrolysis of Aqueous Salt Solutions Overvoltage and the Chlor-Alkali Process... 

Understand the basis of an electrolytic cell describe the Downs cell for the production of Na, the chlor-alkali process and the importance of overvoltage for the production of CF, the electrorefining of Cu, and the use of cryolite in the production of Al know how water influences the products at the electrodes during electrolysis of aqueous salt solutions ( 21.7) (SP 21.8) (EPs 21.63-21.75,21.82)... 

The largest electrolysis process using an ion exchange membrane is the chlor-alkali process to produce caustic soda, chlorine gas and hydrogen gas. The production capacity of caustic soda in the world was about 56.4 million ton/year in 2001 (demand was about 45.1 million ton/year in 2001).117... 

Figure 6.20 Principle of electrolysis of sodium chloride solution (chlor-alkali process).

This means that the electrical energy required for electrolysis is reduced by about 56%. It has been reported that the voltage drop between electrodes attains 1.93-1.95 V at a current density of 30 A dm-2 in a semi-commercial electrolyzer.126 Further energy saving is possible in the chlor-alkali process. 

In practice, we remain far from meeting these apparently trivial requirements so-called inert electrodes have a finite lifetime due to corrosion and physical wear while it is common, even normal, to accept an overpotential of several hundred millivolts. Only in the chlor-alkali process and, to a lesser extent, in water electrolysis has significant progress towards improved electrode materials been made. Generalizations concerning electrode materials are probably unwise and the choice of electrodes for particular industrial processes will be discussed in... 

For small-scale electrolysis units, energy consumption will be much less important than in a chlor-alkali process ease of operation with a minimum of maintenance and replacement of components and the initial cost of the total unit will more often determine the choice of the cell. As a result, for example, while the cathode will generally be steel, a wide range of anode materials including graphite, lead dioxide and platinized titanium have been used as well as dimension-ally stable anodes. Hence the quoted energy consumptions of hypochlorite cells lie in the range 4.5—7.0 kWh kg , considerably above those for a chlor-alkali cell. 

Abstract Ion-conducting materials are used as cell separators in electrolysis cells for the double purpose of carrying electric charges between electrodes and separating the products formed at each electrode. The purpose of this chapter is to provide an overview of chlor-alkali technology and associated cell separators. After a brief historical review of the chlor-alkali process, the main reaction characteristics (thermodynamics, cell reactions and kinetics) are detailed in Section 9.1. Main chlor-alkali technologies are described in Section 9.2. Main cell separators are described in Section 9.3 (diaphragm materials) and in Section 9.4 (membrane materials). Some improved electrolysis concepts are described in Section 9.5. 

Calcium was first isolated by Sir Humphry Davy in 1808. Davy produced calcium amalgam by electrolyzing an aqueous solution of the chloride, CaCl, using a liquid-mercury cathode such as in the chlor-alkali process employing a mercury cathode. After distilling mercury from the amalgam formed, he obtained the pure calcium metal. His discovery showed lime to be an oxide of calcium. Later, Moissan reduced the calcium diiodide with sodium. The first industrial production of calcium metal was reported in 1904 and attributed to Brochers and Stockem, who prepared it by electrolysis of the molten chloride. This process was discontinued in 1940 and replaced by aluminothermic reduction of the oxide. 

In membrane electrol sis an electrolysis process is combined w ilh a membrane separation process. The classical example is the chlor-alkali process in which sodium chloride is converted into chlorine and caustic soda. Other examples are the electrolytic recovery of (hea 7) metals and the production of acid and base from the corresponding salts. 

The diaphragm process is the oldest version of chlor-alkali electrolysis which started up 1885 in Germany, soon after electrical energy was available due to the invention of electric generators for power stations. The diaphragm process was by far the most applied chlor-alkali process until some years ago, especially in the USA, and also today it remains important. 

Hydrogen evolution reaction (her) is one of the most frequently occurring cathodic reactions in industrial cell processes. Hydrogen is formed as a by-product in the chlor-alkali process and in the chlorate production, which are the major industrial electrochemical processes [1], but it is the desired reaction in water electrolysis. Traditional cathode materials for industrial applications have long been iron and mild steel. But, with the increasing cost of electrical power and especially... 

The chlor-alkali process produces annually about 40 million tonnes of chlorine gas by electrolysis of sodium chloride ... 

Electrolysis of Aqueous Salt Solutions Overvoltage and the Chlor-Alkali Process Aqueous salt solutions are mixtures of ions and water, so we have to compare the various electrode potentials to predict the electrode products. 

For small-scale electrolysis units, energy consumption will be much less important than in a chlor-alkali process ease of operation with a minimum of... 

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