Downs process chlorine produced

K.18 The industrial production of sodium metal and chlorine gas makes use of the Downs process, in which molten sodium chloride is electrolyzed (Chapter 12). Write a balanced equation for the production of the two elements from molten sodium chloride. Which element is produced by oxidation and which by reduction ... 

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. 

In the Downs process, molten sodium chloride is electrolyzed to produce sodium. A valuable byproduct is chlorine. Write equations representing the processes taking place at the anode and at the cathode in the Downs process. 

About 75 percent of the caustic produced is concentrated. The remainder is used directly as alkaline cell liquor—as, for example, in the conversion of propylene to propylene oxide by the chlorhydrin process. Similarly, there is some chlorine produced by methods that do not produce caustic, as shown in Table 12.18. Fused chloride salt electrolysis produces chlorine in the manufacture of magnesium metal by the Dow process, and of sodium metal in the Downs cell. The only other process of note is the Kel-Chlor process. This process converts by-product HCl to chlorine by oxidation with NO2 through the intermediates NOCl and HNSO5. 

Shell Chlorine Process. The Shell process produces CI2 from the HCl usiag air or O2 ia the preseace of cupric and other chlorides on a siUcate carrier (71). The reaction proceeds at an optimal rate ia the temperature range of 430—475°C at an efficiency of 60—70%. A manufactuting unit was built by Shell ia the Netherlands (41,000 t/yr) and another ia ladia (27,000 t/yr). Both plants have been closed down. 

Sodium Hydroxide. Before World War 1, nearly all sodium hydroxide [1310-93-2], NaOH, was produced by the reaction of soda ash and lime. The subsequent rapid development of electrolytic production processes, resulting from growing demand for chlorine, effectively shut down the old lime—soda plants except in Eastern Europe, the USSR, India, and China. Recent changes in chlorine consumption have reduced demand, putting pressure on the price and availabiHty of caustic soda (NaOH). Because this trend is expected to continue, there is renewed interest in the lime—soda production process. EMC operates a 50,000 t/yr caustic soda plant that uses this technology at Green River it came onstream in mid-1990. Other U.S. soda ash producers have aimounced plans to constmct similar plants (1,5). 

Over 90% of the HCl produced ia the United States origiaates as a coproduct from various chlorination processes direct generation of HCl from and CI2 accounts for only about 8% of the total production. Table 11 describes the production contribution of HCl from significant sources through the period 1980 to 1992 (72). Figure 6 illustrates the historical production growth of HCl ia the United States (73). The growth rate, about 5—6% from 1955 to 1975, slowed to - 1% because of disparity between supply and demand (see Table 12). The production capacity ia 1993 was about 2.92 million metric tons, down 9.6% from the 1992 production of 3.24 million metric tons (74). 

Many processes have been used to produce tetrachloroethylene. One of the first was chlorination of acetylene (C2H2) to form tetrachloroethane, followed by dehydrochlorination to trichloroethylene. If tetrachloroethylene was desired, the trichloroethylene was further chlorinated to pentachloroethane and dehydrochlorinated. This process is no longer used in the United States Hooker Chemical closed down the last plant in 1978. 

The double arrow in the chemical equation above indicates that the reaction is reversible. This means that while some hydrochloric acid molecules are breaking down into hydrogen and chlorine ions, some ions are also combining to produce hydrochloric acid. The same ongoing, continuous process also occurs to the ammonia molecules. Some ammonia molecules accept a hydrogen ion to become an ammonium ion while some ammonium ions give up a hydrogen ion to become an ammonia molecule. 

Configurations used include tubes, plate-and-frame arrangements and spiral wound modules. Spiral wound modules should be treated to remove particles down to 20 to 50. im, while hollow fiber modules require particles down to 5 im to be removed. If necessary, pH should be adjusted to avoid extremes of pH. Also, oxidizing agents such as free chlorine must be removed. Because of these restrictions, reverse osmosis is only useful if the wastewater to be treated is free of heavy contamination. The concentrated waste material produced by membrane processes should be recycled if possible but might require further treatment or disposal. 

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. 

Sodium is produced by an electrolytic process, similar to the other alkali earth metals. (See figure 4.1). The difference is the electrolyte, which is molten sodium chloride (NaCl, common table salt). A high temperature is required to melt the salt, allowing the sodium cations to collect at the cathode as liquid metallic sodium, while the chlorine anions are liberated as chlorine gas at the anode 2NaCl (salt) + electrolysis —> Cl T (gas) + 2Na (sodium metal). The commercial electrolytic process is referred to as a Downs cell, and at temperatures over 800°C, the liquid sodium metal is drained off as it is produced at the cathode. After chlorine, sodium is the most abundant element found in solution in seawater. 

Practically all of the sodium produced in the United States involves the use of the Downs electrolytic cell, which consists of a massive graphite anode surrounded by two or more iron cathodes. The electrolyte is an aqueous solution of sodium choloride. The NaCl salt is continuously added. As electric current is passed between the electrodes, chlorine gas is collected in a hood over the graphite anode and piped off to further processing for marketing. The electrolysis of sodium chloride proceeds as follows ... 

The liquid phase processes resembled Wacker-Hoechst s acetaldehyde process, i.e., acetic acid solutions of PdCl2 and CuCl2 are used as catalysts. The water produced from the oxidation of Cu(I) to Cu(II) (Figure 27) forms acetaldehyde in a secondary reaction with ethylene. The ratio of acetaldehyde to vinyl acetate can be regulated by changing the operating conditions. The reaction takes place at 110-130°C and 30-40 bar. The vinyl acetate selectivity reaches 93% (based on acetic acid). The net selectivity to acetaldehyde and vinyl acetate is about 83% (based on ethylene), the by-products being CO2, formic acid, oxalic acid, butene and chlorinated compounds. The reaction solution is very corrosive, so that titanium must be used for many plant components. After a few years of operation, in 1969-1970 both ICI and Celanese shut down their plants due to corrosion and economic problems. 

Downs cell An industrial apparatus that electrolyzes molten NaCl to produce sodium and chlorine. (718) dynamic equilibrium In a chemical or physical change, the condition at which the forward and reverse processes are taking place at the same rate, so there is no net change in the amounts of reactants or products. (353)... 

Sodium hydroxide is produced commercially simultaneously with chlorine gas by the electrolysis of a sodium chloride solution. In this process, an electric current breaks down sodium chloride into its component elements, sodium and chlorine. The chlorine escapes as a gas, while the sodium metal form reacts with water to form sodium hydroxide ... 

This synthesis has the disadvantage of introducing chlorine into the molecule. Chlorinated organic materials are not desirable and the removal of chlorine from the product must be assured. It is very difficult to remove trace organochlorine components down to the detection threshold as is required and this therefore adds to the process costs. However, one advantage of this route lies in its potential contribution to sustainability. Isoprene is normally produced from petrochemicals... 

Apart from the variety of possible agent fills, there are several other reasons why unusual compounds might be present in recovered munitions. Special formulations of agents and industrial chemicals were sometimes used to achieve certain effects. For instance, tin tetrachloride was encountered in phosgene rounds treated in the Porton Down tests of the EDS-1. This chemical was added to facilitate the penetration of gas masks and to produce a smoke that aided in spotting where rounds had landed. Chlorobenzene, possibly used as a solvent or stabilizer, was found in the mustard rounds processed at Porton Down (Table 2-1). Chlorinated rubber was used as a thickener in some mustard formulations. In addition, unusual compounds or sludges may result from chemical reactions such as corrosion and polymerization that may occur among the components over a period of decades. 

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