Chlor-alkali

Chlor-alkali cell Chlor-alkali industry... 

Pioneer Chlor- Alkali Co., Inc. Henderson, Nev. 104.3 1942 OxyTech MDC29 diaphragm 76 1... 

Fig. 2. Operating chlor—alkali plants in the United States and Canada (5). Courtesy of the Chlorine Institute, Inc. (500 miles = 800 km.)...

Table 5. Publicly Announced Chlor—Alkali Expansions...

Table 7. Thermodynamic Decomposition Voltage of Chlor—Alkali Cells at 25°C...

Overvoltages for various types of chlor—alkali cells are given in Table 8. A typical example of the overvoltage effect is in the operation of a mercury cell where Hg is used as the cathode material. The overpotential of the H2 evolution reaction on Hg is high hence it is possible to form sodium amalgam without H2 generation, thereby eliminating the need for a separator in the cell. 

Table 8. Components of Chlor—Alkali Cell Voltages...

The unit cost of the d-c supply decreases with increasing voltage and amperage (see Fig. 4). A chlor—alkali plant is therefore most economical when as many high amperage cells as possible are connected in series. 

Table 12. Nafion 90209 Performance in Chlor-Alkali Production...

Chlorine Plant Auxiliaries. Flow diagrams for the three electrolytic chlor—alkali processes are given in Figures 28 and 29. Although they differ somewhat in operation, auxiUary processes such as brine purification and chlorine recovery are common to each. 

Removal of brine contaminants accounts for a significant portion of overall chlor—alkali production cost, especially for the membrane process. Moreover, part or all of the depleted brine from mercury and membrane cells must first be dechlorinated to recover the dissolved chlorine and to prevent corrosion during further processing. In a typical membrane plant, HCl is added to Hberate chlorine, then a vacuum is appHed to recover it. A reducing agent such as sodium sulfite is added to remove the final traces because chlorine would adversely react with the ion-exchange resins used later in the process. Dechlorinated brine is then resaturated with soHd salt for further use. 

MetaUic ions are precipitated as their hydroxides from aqueous caustic solutions. The reactions of importance in chlor—alkali operations are removal of magnesium as Mg(OH)2 during primary purification and of other impurities for pollution control. Organic acids react with NaOH to form soluble salts. Saponification of esters to form the organic acid salt and an alcohol and internal coupling reactions involve NaOH, as exemplified by reaction with triglycerides to form soap and glycerol,... 

North American Chlor—Alkali Industy Plants and Production Data Book, Pamphlet 10, The Chlorine Institute, Washington, D.C., Jan. 1989. 

J. L. Hurst, ImplementingMembrane Cell Technology Within OuyChem Manufacturing International Symposium on Chlor—Alkali Industry, Tokyo, Japan, April, 1988. 

Pefluorinated Membranesfor the Chlor—Alkali Industy, E. I. du Pont de Nemours Co., Inc., Wilmington, Del., 1983. 

D. L. Peet and J. H. Austin, Nafion Pefluorinated Membranes, Operation in Chlor—Alkali Plants, Chlorine Institute Plant Managers Seminar, Tampa, The Chlorine Institute, Feb. 1986. 

D. L. Peet, Membrane Durability in Chlor—Alkali Plants, Electrochemical Society Meeting, Honolulu, Hawaii, Oct. 1987 Proceedings of the Symposium on Electrochemical Engineering in the Chlor—Alkali and Chlorine Industries, PV. 88-2, 1988, pp. 329—336. 

Asahi Chemical Membrane Chlor—Alkali Process, Asahi Chemical Industry Co., Ltd., Tokyo, Japan, 1987. 

N. M. Pront and J. S. Moorhouse, Modem Chlor-Alkali Technology, Vol. 4, Society of Chemical Industry, Elsevier AppHed Sci., London, 1990. 

Y. Sajima, K. Sato, and H. Ukihashi, Recent Progress of Asahi Glass Membrane Chlor—Alkali Process, AICHE Symp. Ser. 82(248), 108 (1985). 

Membrane Chlor—Alkali Process, Oronzio De Nora Technologies, BV Milan, Italy and Houston, Tex., 1988. 

M. O. Coulter, Modem Chlor—Alkali Technology, Ellis Horwood, London, 1980. 

Electrolytic Preparation of Chlorine and Caustic Soda. The preparation of chlorine [7782-50-5] and caustic soda [1310-73-2] is an important use for mercury metal. Since 1989, chlor—alkali production has been responsible for the largest use for mercury in the United States. In this process, mercury is used as a flowing cathode in an electrolytic cell into which a sodium chloride [7647-14-5] solution (brine) is introduced. This brine is then subjected to an electric current, and the aqueous solution of sodium chloride flows between the anode and the mercury, releasing chlorine gas at the anode. The sodium ions form an amalgam with the mercury cathode. Water is added to the amalgam to remove the sodium [7440-23-5] forming hydrogen [1333-74-0] and sodium hydroxide and relatively pure mercury metal, which is recycled into the cell (see Alkali and chlorine products). 

Sodium was made from amalgam ia Germany duriag World War II (68). The only other commercial appHcation appears to be the Tekkosha process (74—76). In this method, preheated amalgam from a chlor—alkali cell is suppHed as anode to a second cell operating at 220—240°C. This cell has an electrolyte of fused sodium hydroxide, sodium iodide, and sodium cyanide and an iron cathode. Operating conditions are given ia Table 6. 

B. I. Fleming, "Chlorine Caustic iu Pulp Bleaching Future Trends," The 2nd World Chlor-Alkali Symposium, Washiagton, D.C., Sept. 19—21,1990. 

Electrochemical processes require feedstock preparation for the electrolytic cells. Additionally, the electrolysis product usually requires further processing. This often involves additional equipment, as is demonstrated by the flow diagram shown in Figure 1 for a membrane chlor-alkali cell process (see Alkali AND chlorine products). Only the electrolytic cells and components ate discussed herein. 

Fig. 1. Flow diagram for chlor-alkali production by a membrane cell process.

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