Chlorine producers

Most of the chlorine produced is used in the manufacture of chlorinated compounds for sanitation, pulp bleaching, disinfectants, and textile processing. Further use is in the manufacture of chlorates, chloroform, carbon tetrachloride, and in the extraction of bromine. 

Chlorination of the azobenzene complex 463 with chlorine produces mono-chloroazobenzene with regeneration of PdCN. Then complex formation takes place again with the chlorinated azobenzene. By this sequence, finally tetra-chloroazobenzene (503) is obtained using a catalytic amount of PdCT. The reaction, carried out by passing chlorine gas into an aqueous dioxane solution of azobenzene and PdCf for 16 h, gives a mixture of polychlorinated azoben-zenes[455]. 

In the United States, 76% of the chlorine produced is from diaphragm cells. Production is equally divided between bipolar and monopolar electroly2ers. 

Other Chlorine Production Processes. Although electrolytic production of CI2 and NaOH from NaCl accounts for most of the chlorine produced, other commercial processes for chlorine are also in operation. 

The spray dried MgCl2 powder is melted ia large reactors and further purified with chlorine and other reactants to remove magnesium oxide, water, bromine [7726-95-6], residual sulfate, and heavy metals (27,28). The molten MgCl2 is then fed to the electrolytic cells which are essentially a modification of the LG. Farben cell. Only a part of the chlorine produced is required for chlorination, leaving up to 1 kg of chlorine per kg of magnesium produced. This by-product chlorine is available for sale. 

The residue, which contains Ir, Ru, and Os, is fused with sodium peroxide at 500°C, forming soluble sodium mthenate and sodium osmate. Reaction of these salts with chlorine produces volatile tetroxides, which are separated from the reaction medium by distillation and absorbed into hydrochloric acid. The osmium can then be separated from the mthenium by boiling the chloride solution with nitric acid. Osmium forms volatile osmium tetroxide mthenium remains in solution. Ruthenium and osmium can thus be separately purified and reduced to give the metals. 

Chlorination of thick lime slurry at 40—45°C forms large crystals of hemibasic calcium hypochlorite. The fine crystals obtained under 30°C are difficult to filter and since they invariably contain occluded mother Hquor, they have frequently been incorrectly referred to as monobasic or two-thirds basic (187,188). The isolated hemibasic crystals are suspended in a thin chlorinated lime slurry and chlorinated, producing laminar crystals of Ca(OCl)2 2H20, which are filtered and dried. Mother Hquors are treated with a lime slurry to recover the dibasic crystals, which are then suspended in a Hquor of lower CaCl2 content and chlorinated to form the neutral salt (188—190). 

In another process, hypochlorite filtrate is treated with lime slurry to precipitate dibasic crystals that are filtered. The filtrate is mixed with strong caustic, chlorinated, and filtered to remove NaCl crystals. The filtrate containing Na and Ca hypochlorite is mixed with dibasic crystals and chlorinated producing a slurry of Ca(OCl)2 is filtered the cake goes to a dryer and the filtrate to the dibasic crystallizer (195). 

Oxidation. Atmospheric oxidation of 1,2-dichloroethane at room or reflux temperatures generates some hydrogen chloride and results in solvent discoloration. A 48-h accelerated oxidation test at reflux temperatures gives only 0.006% hydrogen chloride (22). Addition of 0.1—0.2 wt. % of an amine, eg, diisopropylamine, protects the 1,2-dichloroethane against oxidative breakdown. Photooxidation in the presence of chlorine produces monochloroacetic acid and 1,1,2-trichloroethane (23). 

Two variables of primary importance, which are interdependent, are reaction temperature and ch1orine propy1ene ratio. Propylene is typically used ia excess to act as a diluent and heat sink, thus minimising by-products (eqs.2 and 3). Since higher temperatures favor the desired reaction, standard practice generally involves preheat of the reactor feeds to at least 200°C prior to combination. The heat of reaction is then responsible for further increases in the reaction temperature toward 510°C. The chlorine propylene ratio is adjusted so that, for given preheat temperatures, the desired ultimate reaction temperature is maintained. For example, at a chlorine propylene molar ratio of 0.315, feed temperatures of 200°C (propylene) and 50°C (chlorine) produce an ultimate reaction temperature of approximately 500°C (10). Increases in preheat temperature toward the ultimate reactor temperature, eg, in attempts to decrease yield of equation 1, must be compensated for in reduced chlorine propylene ratio, which reduces the fraction of propylene converted and, thus aHyl chloride quantity produced. A suitable economic optimum combination of preheat temperature and chlorine propylene ratio can be readily deterrnined for individual cases. 

There have been a number of cell designs tested for this reaction. Undivided cells using sodium bromide electrolyte have been tried (see, for example. Ref. 29). These have had electrode shapes for in-ceU propylene absorption into the electrolyte. The chief advantages of the electrochemical route to propylene oxide are elimination of the need for chlorine and lime, as well as avoidance of calcium chloride disposal (see Calcium compounds, calcium CHLORIDE Lime and limestone). An indirect electrochemical approach meeting these same objectives employs the chlorine produced at the anode of a membrane cell for preparing the propylene chlorohydrin external to the electrolysis system. The caustic made at the cathode is used to convert the chlorohydrin to propylene oxide, reforming a NaCl solution which is recycled. Attractive economics are claimed for this combined chlor-alkali electrolysis and propylene oxide manufacture (135). 

Commercially, hydrogen chloride is obtained either as a by-product in the manufacture of salt cake from sodium chloride, or by allowing chlorine produced as a by-product in electrolytic processes to react with hydrogen in the presence of activated charcoal. It is also formed as a byproduct in the manufacture of phenol. 

In addition to being the most widely used disinfectant for water treatment, chlorine is extensively used in a variety of products, including paper products, dyestuffs, textiles, petroleum products, pharmaceuticals, antiseptics, insecticides, foodstuffs, solvents, paints, and other consumer products. Most chlorine produced is used in the manufacture of chlorinated compounds for sanitation, pulp bleaching, disinfectants, and textile processing. It is also used in the manufacture of chlorates, chloroform, and carbon tetrachloride and in the extraction of bromine. Among other past uses, chlorine served as a war gas during World War I. 

Oxidation of phenols with chlorine dioxide or chlorine produces chlorinated aromatic intermediates before ring rupture. Oxidation of phenols with either chlorine dioxide or ozone produces oxidized aromatic compounds as intermediates which undergo ring rupture upon treatment with more oxidant and/or longer reaction times. In many cases, the same nonchlorinated, ringruptured aliphatic products are produced using ozone or chlorine dioxide. 

The successive substitution of methane hydrogens with chlorine produces a mixture of four chloromethanes ... 

As current is passed through the cells shown in Figure 14-2, the oxygen produced in the first cell is collected and its volume is compared with the volume of chlorine produced in the center cell (the volumes being compared at identical temperatures and pressures). The volume of chlorine is found to be exactly double that of oxygen. Applying Avogadro s Hypothesis, explain how this result shows that electricity can count atoms. 

The magnesium metal is thus recovered for repeated use in reaction (7). Chlorine produced in reaction (5) is also put to use in the manufacture of TiCh, the other reactant in reaction (7). 

Parazol was used in Europe during the early days of WWI for filling projectiles. According to Davis (Ref 6), this was done because of a shortage of toluene, necessary for the manuf of TNT an abundance of chlorine, produced during... 

FIGURE 14.17 A diaphragm cell tor the electrolytic production of sodium hydroxide from brine (aqueous sodium chloride solution), represented by the blue color. The diaphragm (gold color) prevents the chlorine produced at the titanium anodes from mixing with the hydrogen and the sodium hydroxide formed at the steel cathodes. The liquid (cell liquor) is drawn off and the water is partly evaporated. The unconverted sodium chloride crystallizes, leaving the sodium hydroxide dissolved in the cell liquor. 

An inorganic contaminant that is relatively common in waste HBr streams and can be volatilized by the vaporizer is HCl. Separate studies (ref. 19) with the HBr oxidation catalyst have shown that conversion of HCl to chlorine is possible, but high conversion requires temperature near 400°C. In the presence of HBr, any chlorine produced by oxidation of HCl will oxidize the HBr to bromine (eqn. 6). 

Complete phase-out of chlorinated compounds is being resisted not only by chlorine producers, but also by the many industries that use chlorine compounds in the manufacture of products from paper to pharmaceuticals. Meanwhile, chemists seek ways to degrade dioxins to nontoxic substances. 

Transformation of the widely used over-the-counter analgesic acetaminophen (paracetamol) during chlorination produced the toxic 1,4-benzoquinone via the A-acetylquinone-imine and minor amounts of products from chlorination of the phenolic ring (Bedner and Maccrehan 2006). 

Bedner M, WA Maccrehan (2006) Transformation of acetaminophen by chlorination produces the toxicants 1,4-benzoquinone and iV-acetyl-/)-benzoquinone imine. Environ Sci Technol 40 516-522. 

Bromine was being added in portions to acrylonitrile with ice cooling, with intermediate warming to 20°C between portions. After half the bromine was added, the temperature increased to 70°C then the flask exploded. This was attributed either to an accumulation of unreacted bromine (which would be obvious) or to violent polymerisation [1], The latter seems more likely, catalysed by hydrogen bromide formed by substitutive bromination. Chlorine produces similar phenomena, even if the flask stays intact. The runaway is preceded by loss of yellow colouration and accompanied by formation of 3-chloroacrylonitrile and derivatives. It can be suppressed by presence of bases [2],... 

Baumann [197] collected the chlorine produced in the reaction in excess potassium iodide solution and back titrated against standard sodium thiosulfate to obtain the necessary correction for chloride. 

In the first experiment, 2.18 g of sodium produces 5.54 g of sodium chloride. In the second experiment, 2.10 g of chlorine produces 3.46 g of sodium chloride. The amount of sodium contained in this second sample of sodium chloride is given by mass of sodium = 3.46 g sodium chloride -2.10 g chlorine = 1.36 g sodium We now have sufficient information to determine the % Na in each of the samples of sodium chloride. 

Energy costs should gradually be lowered for many chlorine producers. Less predictable are the interference of governments and the imposition of taxes in the guise of climate change. The UK government got very near to imposing such a tax, which would have shut down a considerable part of the industry. 

While participating in the European Union programme on risk assessment of existing chemicals, Euro Chlor (representing all major European chlorine producers), recognised the need to carry out a detailed risk evaluation on chemicals linked to the production of chlorine. In view of concerns about specific risks of organohalogen compounds to the marine environment as a sink for all watercourses, Euro Chlor focused on this environmental compartment, with emphasis on the North Sea. This sea area has been extensively studied and is controlled by the Oslo and Paris Convention for the Prevention of Marine Pollution (OSPARCOM). For a series of chemicals on lists of concern adopted by the North Sea Conference (1990), risk assessments are being carried out to demonstrate their variable environmental profiles. 

B-l has already been licensed to eight chlorine producers since 1997. The total capacity of these B-l plants has exceeded 440000 metric tonnes per year (caustic... 

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