Chloralkali process

Chloralkali process Combustion of coal and oil Electrical and electronic Explosives Paints... 

Sodium hydroxide, NaOH, is a soft, waxy, white, corrosive solid that is sold commercially as lye. It is an important industrial chemical because it is an inexpensive starting material for the production of other sodium salts. The amount of electricity used to electrolyze brine to produce NaOH in the chloralkali process (Section 12.13) is second only to the amount used to extract aluminum from its ores. The process produces chlorine and hydrogen gases as well as aqueous socFinn hydroxide (Fig. 14.17). The net ionic equation for the reaction is... 

Self-Test 14.5A Use Table 12.1 to determine the minimum potential difference that must be applied under standard conditions to carry out the chloralkali process. 

Explosives Batteries Photographic Scientific instruments Chloralkali process Paints... 

Figure 7-29 Salt electrolysis to produce CI2 gas and NaOH solution in a chloralkali process. This is the process by which most alkali and chlorine are produced The reactor operates continuously with brine solution flowing into the cell and NaOH and Q2 gas flowing out.

Sodium chloride is plentiful as rock salt, but the solid does not conduct electricity, because the ions are locked into place. Sodium chloride must be molten for electrolysis to occur. The electrodes in the cell are made of inert materials like carbon, and the cell is designed to keep the sodium and chlorine produced by the electrolysis out of contact with each other and away from air. In a modification of the Downs process, the electrolyte is an aqueous solution of sodium chloride. The products of this chloralkali process are chlorine and aqueous sodium hydroxide. 

Rappe C, Kjeller LO, Kulp SE, de Wit C, Melin A (1990), Chemosphere 20 1701-1706.. .Levels of PCDDs and PCDFs in products and effluent from the Swedish pulp and paper industry and chloralkali process"... 

The best known anhydrous oxides are listed in Table 18-E-2 the tetraoxides of Ru and Os are discussed later (Section 18-F-l). The oxides, generally rather inert to aqueous acids, are reduced to the metal by hydrogen, and dissociate on heating. There are mixed metal oxides, e.g., BaRu03, and platinum and palladium bronzes of formula MlPt304 (x = 0-1). Some oxides like MnPt306 have Pt—Pt bonds. Mixed oxides are used for electrodes in H2—02 fuel cells and in the chloralkali process. 

The possibility of activation of the electrocatalysis for Hj evolution at various materials by introduction of depositable transition metal salts has been recognized for some time. Some practical applications refer to depolarization of amalgam electrodes in the old Hg cell chloralkali process. This procedure can be applied to various other substrates, for example, graphite, Fe, Ni steel, and Ti (164-167). 

In 2000, 45 Mt of CI2 was manufactured by the chloralkali process this represents 95% of the global supply. The main producers are the US, Western Europe and Japan. Whereas the Japanese chloralkali industry operates almost entirely with the membrane cell, the US favours use of the diaphragm cell, and just over half of the Western European industry retains use of the mercury cell. On environmental grounds, the chloralkali industry is being pressured to replace mercury and diaphragm cells by the membrane cell. This is not the only environmental concern facing the industry demand for CI2 has fallen in the pulp and paper industry and in the production of chlorofluorocarbons, the latter being phased out as a result of the Montreal Protocol for the Protection... 

The hydroxides are formed by electrolysis of aqueous brines as part of the chloralkali process. The metal formed at the cathode immediately reacts with water to produce the hydroxide and hydrogen gas. 

Figure 9.24 The chloralkali process (a) membrane cell (b) the membrane is permeable only to Na" " ions, leading to segregation of Cr and OH in the anode and cathode compartments...

The chloralkali process, which involves the electrolysis of brine, is widely used for the production of sodium hydroxide and chlorine gas. During electrolysis it is necessary to keep the sodium hydroxide separate from the chlorine, to prevent the formation of sodium hypochlorite, NaOCl, and this determines cell design. In older processes, the cathode used was flowing mercury. At this electrode, sodium is formed, and this dissolves in the mercury to form a sodium amalgam. The sodium amalgam is removed continually from the cell and reacted with water to produce hydrogen gas and... 

The low melting point (234 K) of Hg results in its being a unique metal. Its high thermal expansion coefficient makes it a suitable liquid for use in thermometers, and it has widespread application in barometers, dilfusion pumps and in Hg switches in electrical apparatus. The use of mercury cells in the chloralkali process is gradually being phased out (see Box 11.4). Some other metals dissolve in mercury to give amalgams their uses are varied, for example ... 

What are the two products of the chloralkali process Name two common uses for each of the products. 

Fedkiw Jr PS. Preparing in situ electrocatalytic films in solid polymer electrolyte membranes, composite microelectrode structures produced thereby and chloralkali process utilizing the same. United States patent US 4959132. 1990 Sep 25. 

Using the chloralkali process, common salt and water are broken down into chlorine, hydrogen, and sodium hydroxide. All three resulting products are considered hazardous materials. Hydrogen is a flammable gas, chlorine is a poisonous gas, and sodimn hydroxide is a corrosive. 

CaCl2 is added to reduce the operating temperature to about 870 K, since pure NaCl melts at 1073 K (see Section 9.12). The design of the electrolysis cell (Fig. 11.2) is critical to prevent reformation of NaCl by recombination of Na and CI2. Although the Downs process is the major manufacturing process for Na, the CI2 produced contributes only 5% of the world s supply. The remaining 95% is produced by the chloralkali process which involves the electrolysis of aqueous NaCl (see Box 11.4). 

Dichlorine is one of the most important industrial chemicals in the world, and is manufactured by the chloralkali process... 

Caustic soda electrolysis (better known as the chloralkali process) uses salt water (brine) to produce chlorine (CI2), caustic soda (NaOH) and hydrogen (H2). The anodic and cathodic reactions are respectively Cl —> %Cl2 + e and Na + H2O + e NaOH + V2H2. 

A current industrial application of ionomers is their use as permselective membranes for the chloralkali process. The ionomers used in these membranes are based on a poly(tetrafluoroethylene) backbone containing occasional ether linkages with ionic side groups. These are based upon either sulfonate or carboxylate salts. 

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