Chlorine chlor-alkali process

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. 

The starting material for all industrial chlorine chemistry is sodium chloride, obtained primarily by evaporation of seawater. The chloride ion is highly stable and must be oxidized electrolytically to produce chlorine gas. This is carried out on an industrial scale using the chlor-alkali process, which is shown schematically in Figure 21-15. The electrochemistry involved in the chlor-alkali process is discussed in Section 19-. As with all electrolytic processes, the energy costs are very high, but the process is economically feasible because it generates three commercially valuable products H2 gas, aqueous NaOH, and CI2 gas. 

Celdecor A process for making paper from straw or bagasse. The fiber is digested in aqueous sodium hydroxide and bleached with chlorine. The essential feature is that the alkali and chlorine are used in the proportions in which they are made by the Chlor-Alkali process. 

PCDFs are also found in residual waste from the production of vinyl chloride and the chlor-alkali process for chlorine production. Factors favourable for the formation of PCDD/PCDFs are high temperatures, alkaline media, the presence of ultraviolet light, and the presence of radicals in the reaction mixture/chemical process (Fiedler, 1999 Hutzinger and Fiedler 1993). 

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 products of the chlor-alkali process are all useful. Sodium hydroxide is used to make soaps and detergents. It is widely used as a base in many other industrial chemical reactions, as well. The hydrogen produced by the chlor-alkali process is used as a fuel. Chlorine has many uses besides water treatment. For example, chlorine is used as a bleach in the pulp and paper industry. Chlorine is also used in the manufacture of chlorinated organic compounds, such as the common plastic polyvinyl chloride (PVC). 

Would you predict the products of the chlor-alkali process to he hydrogen and chlorine Explain. 

Chlor-alkali process the process for producing chlorine and sodium hydroxide by electrolyzing brine in a mercury cell. (11.8)... 

The method for making sodium hydroxide is called the chlor-alkali process. The name comes from the fact that both chlorine and an alkali metal (sodium) are produced at the same time. In this case, an electric current is passed through a solution of sodium chloride dissolved in water ... 

Three useful products are obtained from this reaction chlorine gas (CI2), hydrogen gas (H2), and sodium hydroxide (NaOH). The chlor-alkali process is one of the most important industrial processes used today. 

Chlor-Alkali Process", Oronzio De Nora Symposium on Chlorine Technology 15-18 May 1979, Venice, Italy. 

Seko, M., New development of the Asahi Chemical membrane chlor-alkali process, presented at the Chlorine Institute Inc., 22nd Chlorine Plant Managers Seminar, Atlanta Geogia... 

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... 

Chlorine is produced from concentrated seawater by the electrochemical chlor-alkali process. During the process, the chlorine is collected in a container that is isolated from the other products to prevent unwanted (and explosive) reactions. If a... 

Unfortunately, the products predicted from electrode potentials are not always the products that form. For gases such as H2(g) and 02(g) to form at metal electrodes, an additional voltage is required. This increment above the expected required voltage is called the overvoltage. The phenomenon of overvoltage has major practical significance in the chlor-alkali process for the industrial production of chlorine and several other chemicals, which is based on the electrolytic oxidation of Cl ion from concentrated aqueous NaCl solutions. Chlorine ranks among the top 10 chemicals produced in the United States. 

In addition to the Downs cell for sodium production and the chlor-alkali process for chlorine manufacture, industrial methods based on voltaic and electrolytic cells are used commonly to obtain metals and nonmetals from their ores or to purify them for later use. Here we focus on two key electrochemical processes. 

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... 

Chlor-alkali process the process for producing chlorine and sodium hydroxide by electrolyzing brine in a mercury cell. (18.9) Chromatography the general name for a series of methods for separating mixtures by employing a system with a mobile phase and a stationary phase. (1.9)... 

Since then, several membrane-cell technologies were developed in Japan, as a pollution-free chlor-alkali process. Japanese contributions include composite membranes and several electrolyzer designs. Japan was the first major chlorine producing country to convert entirely to membrane cell technology. As of January 2003, 35% of world production of chlorine is by membrane-cell technology, generating 52,000 metric tons caustic/day. 

Hydrochloric acid may be purchased or produced internally. It is a widely available commodity, easily obtained in good quality. HCl is available in the anhydrous form as well as in the form of aqueous acid (up to 23° Be or about 37% HCl). The use of aqueous acid is standard in the chlor-alkali industry, and we do not discuss anhydrous HCl here. Byproduct acids are available, sometimes at lower prices, and may be suitable for use in the chlor-alkali process. Their quality should be checked carefully, and testing may be advisable before use. When HCl is produced from chlorine liquefaction tail gas, the absorbing water is the most likely source of impurities. Demineralized water is the standard source when producing acid for use in a membrane-cell chlorine plant. A certain amount of chlorine tends to be present in burner acid. This can be minimized by process control, and a small bed packed with activated carbon (Section 7.5.9.3B) is a useful safeguard. Usually only the acid intended for use in the ion-exchange system need be treated in this way. 

The materials of construction used in wet chlorine service are not required for dry chlorine and may even be unsuitable. The metal of choice in dry chlorine service usually is carbon steel. Within the chlor-alkali process, the maximum service temperature is of concern only in the compression area. Section 9.1.6 describes the design precautions... 

FIGURE 10.2.9. Energy flow diagram for mercury cell chlor-alkali process. (The numbers are kWhrton" of chlorine.)... 

Chlorine and Alkali from Sodium Chloride etc. 283 Tab. 3 Advantages and disadvantages of the three chlor-alkali processes [3, p. 117]... 

---