Industrial processes chloralkali industry

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... 

In the profiles of the core from the industrial area, mercury displays the highest accumulation. Mercury in this area, close to the industrial district, has probably derived from a large chloralkali plant which has employed mercury cathodes since the fifties. Whereas, at present, very severe measures are taken to prevent mercury spills into the Lagoon, in the past, polluted waters and solid materials were discharged almost untreated. In the most superficial strata a marked decrease in the accumulations is, in fact, recorded. Lead and Cd accumulations are lower here by a factor of 5-10. The presence of cadmium in the sediments of the Lagoon has been referred to sphalerite (ZnS) processing on the basis of a strict concomitant... 

A mixture of hydrogen and chlorine gas, eventually in combination with air, can be very explosive if one of the components exceeds certain limits. In chlorine production plants, based on the electrolysis of sodium chloride solutions, there is always a production of hydrogen. It is, therefore, essential to be aware of the actual hydrogen content of chlorine gas process streams at any time. There are several places in the chlorine production process where the hydrogen content in the chlorine gas can accumulate above the explosion limits. Within the chloralkali industry, mainly two types of processes are used for the production of chlorine—the mercury- and the membrane-based electrolysis of sodium chloride solutions (brine). 

There is a need for accurate in-line hydrogen monitor in individual electrolyzers in chloralkali industry that will provide huge cost savings in chlorine manufacturing processes. Again, an in-line process monitor that can be installed in individual electrolyzers is highly desired. 

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"... 

Several industrial processes use mercury in large amounts, and the resulting potential for spills and loss to the environment is great. One of the largest is the chloralkali industry, in which mercury is used as an electrode for the electrolysis of brine to form chlorine gas and sodium hydroxide ... 

Hydrogen is also formed in large quantities as a byproduct in petrochemical processes, refineries, coking plants (coke oven gas) and in chemical and electrochemical processes e.g. chloralkali-electrolysis. Other processes such as the photochemical production of hydrogen or thermal dissociation of water are only used in special applications and are currently industrially unimportant. 

Mercury compounds continue to have numerous commercial uses. Besides its use as a preservative, mercury is used in the manufacture of many technical and medical instruments including blood pressure measurement devices, manometers, thermometers, and barometers. Mercury is also used in production of certain types of fluorescent lamps and in the chloralkali industry, where chlorine and caustic soda are produced using brine electrolysis in mercury cells. Metallic mercury is used in the production of precious metals such as gold and silver. As part of the production process, metallic mercury can be used to concentrate gold from... 

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... 

Based on samples from museum collections, it was demonstrated that mercury content in feathers from fish-eating birds were comparatively low in the years 1815 through 1940. However, since 1940, or the advent of the chlo-ralkali industry (wherein mercury is used as a catalyst in the process to produce sodium hydroxide and chlorine gas from sodium chloride and water, with significant loss of mercury to the biosphere), mercury concentrations in feathers were eight times higher on average. Mercury levels were also elevated in feathers and tissues of aquatic and fish-eating birds from the vicinity of chloralkali plants these increased levels of mercury were detectable up to 300 km from the chloralkali plant. 

Both the nature and amount of R D carried out varies significantly across the various sectors of the chemical industry. In sectors which involve large-scale production of basic chemicals and where the chemistry, products and technology change only slowly because the processes are mature, R D expenditure is at the lower end of the range for the chemical industry. Most of this will be devoted to process improvement and effluent treatment. Examples include ammonia, fertilizers and chloralkali production (section 10.5) from the inorganic side, and basic petrochemical intermediates such as ethylene (sections 12.3.1-3) from the organic side. 

In addition to electrochemical energy conversion in fuel cells, the reaction has applications in energy storage in metal-air batteries, in several industrial processes as the chloralkali electrolysis, and it causes corrosion of metals and alloys in the presence of air. That is why the efforts have been focused on elucidating the mechanism of this reaction and developing proper catalysts. 

Of the industrial activities under the heading of process engineering the chloralkali industry is probably the most important. Chlorine world capacity in 1985 was estimated as 43 million metric tons and total world production in 1983 as 31 million tons. Over 80% of the chlorine produced is used to produce other chemicals. Large-tonnage products associated with chlorine include caustic soda and soda ash (anhydrous sodium carbonate). 

We mentioned in Section 1.3 some important industrial applications of electrolysis—in the chloralkali industry, metal winning and refining, and organic electrosynthesis. As indicated in Section 1.2, we do not intend to describe electrochemical processes in detail, since there are many books on electrochemical technology. We will discuss the design of individual reactors, with emphasis on modularized, general purpose flow electrolyzers. We will classify reactors by their mode of operation. 

Occupational exposure to mercury vapor occurs in a variety of industries such as chloralkali plants, thermometer factories, gold extraction process, and mercury mining. Dentists and dental assistants are also exposed to mercury vapor during insertion, polishing, and removal of amalgam fillings. 

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

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