Caustic-chlorine plant

The Chlorohydrin process involves the reaction of propylene with chlorine and water to produce propylene chlorohydrin. The propylene chlorohydrin is then dehydrochlorinated with lime or caustic to yield propylene oxide and a salt by-product. The chemistry is very similar to the chlorohydrin route from ethylene to ethylene oxide which was eventually replaced by the direct oxidation process. There are two major problems with the chlorohydrin route which provided the incentive for developing an improved process. There is a large water effluent stream containing about 5-6% calcium chloride or 5-10% sodium chloride (depending on whether lime or caustic is used for dehydrochlorination) and trace amounts of chlorinated hydrocarbon by-products that must be treated before disposal. Treatment of these by-products is expensive. The only practical way to handle it is to use caustic so that sodium chloride is produced and then integrate the effluent stream with a caustic-chlorine plant so that it can be recycled to the caustic plant. This, however, is also expensive because recovery of sodium chloride from this relatively dilute stream has a high energy cost. 

CHLORINE. CI2. In laboratory tests, aqueous solutions containing 25,50, and 100 ppm chlorine caused moderate attack of 1100 and 6( 1 alloys at ambient temperature. Diy chlorine gas does not attack aluminum alloys, but in the presence of water is corrosive. Aluminum alloy bus bar has been used in caustic-chlorine plants. Hot chlorine gas has been cooled in aluminum alloy heat exchangers. See also Ref (1) p. 129, (2) p. 167, (3) pp. 36, 247, (7) p. 57. 

The principal source of chlorine-containing gas in caustic-chlorine plants is the liquefaction step where noncondensables are vented from chlorine condensers as sniff gas containing 30 to 40% chlorine by weight. Dilute gas may be collected at other points in the operation this gas also requires purification before it can be vented to the atmosphere. A number of processes have been developed to recover the chlorine from the vent-gas streams, including its use for the manufacture of bleach. Where the demand for bleach does not justify this operation, a regenerative recovery system is neces.sary, and one of the simplest of these involves absorption in water. The absorption of chlorine gas in water is also an important step in the manufacture of certain types of wood pulp. In this application, the process is intended primarily to provide a source of concentrated bleaching solution however, design data which have been obtained for the absorption step are equally applicable to gas-purification or chlorine-recovery operations. 

Rgure 6-21. Simplified diagram of water-absorption process for removing chlorine from waste gases of electrolytic caustic chlorine plants. Hooka-Bectrochemh Cmpeny process (Anon., 1957)... 

E. H. Cook and M. P. Grotheer, Energy S avingDevelopments for Diaphragm Cells and Caustic Evaporators, 23rd Chlorine Plant Manager s Seminar, New Orleans, The Chlorine Institute, Inc., Feb. 6, 1980. 

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). 

Since 1960, about 95% of the synthetic ammonia made in the United States has been made from natural gas worldwide the proportion is about 85%. Most of the balance is made from naphtha and other petroleum Hquids. Relatively small amounts of ammonia are made from hydrogen recovered from coke oven and refinery gases, from electrolysis of salt solutions, eg, caustic chlorine production, and by electrolysis of water. In addition there are about 20 ammonia plants worldwide that use coal as a hydrogen source. 

Krupp Uhde has more than 40 years of experience in the design and construction of chlorine/caustic soda plants [1]. The company s 150 plants throughout the world have an overall production capacity of approximately 8 million metric tonnes per year of NaOH (100%) and thus make Krupp Uhde unique in its field. 

Shaw BP, Sahu A, Panigrahy AK. 1986. Mercury in plants, soil, and water from a caustic chlorine industry. Bull Environ Contam Toxicol 36 299-305. 

A 100 tonne/day electrolytic chlorine plant, complete with caustic soda facilities costs about 12 million dollars. 

Recent phosgene plants constructed in the Gulf Coast of the United States obtain their CO from synthesis gas by low-temperature fractionation [8]. Early units derived their raw material from coal, directly or indirectly. Most phosgene plants have their own caustic chlorine facilities. Since most phosgene is consumed captively, the hydrogen chloride is recovered in an oxidation unit. 

The most common source of pure hydrogen in small amounts is as a byproduct from caustic-chlorine electrolysis plants. A typical 100-ton/day chlorine plant would produce around one millon scfd of pure hydrogen, that is far in excess of the needs of a typical small consumer of hydrogen such as a fats and oils hydrogenation unit. 

Two processes are currently used for the production of propylene oxide. About 50% is produced by the chlorohydrin process and the other 50% by the peroxidation process. The chlorohydrin process is the older technology and it is slowly being replaced by the more economical and environmentally acceptable peroxidation route. There are environmental issues associated with the large aqueous by-product stream of calcium chloride and chlorinated hydrocarbon by-products from the chlorohydrin process. The only producers that will continue to operate chlorohydrin plants are highly integrated caustic-chlorine producers who have chlorine production facilities which can handle the calcium chloride by-product and chlorinated hydrocarbons [9]. 

Provide induced draught fans and scrubbers for necessary equipments to suck out any toxic and inflammable vapours in working areas (e.g. electrolysis cells for chlorine/caustic soda plants). 

Comparative economics of the forms of carbonate value available to a plant will determine the best choice. Providing the option to use direct CO2 adds some flexibility to the operation and allows more variation in the caustic/chlorine ratio in the plant s output. By consuming some of the caustic, it can make possible the production of more chlorine during times when sales of caustic are slack. 

Vinyl Esters. These resins include chemical features of both epoxies aud polyesters. Vinyl ester resins offer better chemical resistance, somewhat higher temperature limits, aud better solvent resistance than ordinary polyesters but generally do not compare to epoxies in these properties. Vinyl ester resins are preferred over polyesters because they are more chemical-resistant than the isophthalics and less brittle than the bisphenol A fumarates. Typical services are in fertilizer plants (acid lines), chlorine plants (chlorine-saturated briue hues), and paper mills (caustic and black-hquor lines). 

Chlorine Plant—Caustic Fusion Pots.. Chlorine Plant—Caustic Fusion Pots.. Clothing Renovating Plant-Heating Ventilating. 

Hypochlorites are made by electrolysis in small plants where sea water is used as brine. On a large scale, it is made by dissolving chlorine in caustic soda in a plant adjacent to, but separate from, the chlorine plant. 

Electrolytic plant producing caustic soda, chlorine, and hydrogen from brine. 

Benzene Chlorination. In this process, benzene is chlorinated at 38—60°C in the presence of ferric chloride catalyst. The chlorobenzene is hydrolyzed with caustic soda at 400°C and 2.56 kPa (260 atm) to form sodium phenate. The impure sodium phenate reacts with hydrochloric acid to release the phenol from the sodium salt. The yield of phenol is about 82 mol % to that of the theoretical value based on benzene. Plants employing this technology have been shut down for environmental and economic reasons. 

Heavy metals on or in vegetation and water have been and continue to be toxic to animals and fish. Arsenic and lead from smelters, molybdenum from steel plants, and mercury from chlorine-caustic plants are major offenders. Poisoning of aquatic life by mercury is relatively new, whereas the toxic effects of the other metals have been largely eliminated by proper control of industrial emissions. Gaseous (and particulate) fluorides have caused injury and damage to a wide variety of animals—domestic and wild—as well as to fish. Accidental effects resulting from insecticides and nerve gas have been reported. 

In the membrane process, the chlorine (at the anode) and the hydrogen (at the cathode) are kept apart by a selective polymer membrane that allows the sodium ions to pass into the cathodic compartment and react with the hydroxyl ions to form caustic soda. The depleted brine is dechlorinated and recycled to the input stage. As noted already, the membrane cell process is the preferred process for new plants. Diaphragm processes may be acceptable, in some circumstances, but only if nonasbestos diaphragms are used. The energy consumption in a membrane cell process is of the order of 2,200 to 2,500 kilowatt-hours per... 

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