Chlorine

GENERALITY :
Chlorine (gas phase) is the result of combining two chlorine Cl atoms, or the formula Cl₂.
Molecular weight: 70.906 g mol-1.

Chemical compound of the family of halogens, chlorine is a yellowish-green gas with suffocating smell very unpleasant and it is extremely toxic.
Chlorine has the highest electron affinity and the fourth highest electronegativity of all the reactive elements. For this reason, chlorine is a strong oxidizing agent. Free chlorine is rare on Earth, and is usually a result of direct or indirect oxidation by oxygen.

The high oxidizing potential of elemental chlorine led commercially to free chlorine's bleaching and disinfectant uses, as well as its many uses of an essential reagent in the chemical industry. Chlorine is used in the manufacture of a wide range of consumer products, about two-thirds of them organic chemicals such as polyvinyl chloride, as well as many intermediates for production of plastics and other end products which do not contain the element. As a common disinfectant, elemental chlorine and chlorine-generating compounds are used more directly in swimming pools to keep them clean and sanitary.

Properties.
non-flammable gas (but supports combustion in the air).
It is a heavier-than-air gas = 3.2 kg m3^-1 (0 °C, 101.325 kPa).
Boiling point = -34.04 °C (239.11 K).
Liquid density at b.p. = 1.5625 g·cm3.
Melting point = -101.5 °C (171.6 K).
Critical point = 416.9 K, 7.991 MPa.
Triple Point is located at T = - 101.00 ° C (172 K) and P = 14 hPa (0.014 bar)
Heat of fusion (Cl₂) = 6.406 kJ·mol^-1.
Heat of vaporization (Cl2) = 20.41 kJ·mol^-1.

Chlorine gas is normally carried in the liquid state, in pressurized steel cylinders.

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Chlorine phase diagram:

(Sources : Air Liquide)

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Some features::

• Gas phase:
  • Density (1013.25 hPa, at 15 °C ) : 3.04 kg m3^-1
  • Equivalent gas / liquid (1013.25 hPa 15 °C) : 1 m3 as gas (3.04 kg) > 0.001919 m3 as liquid
  • Specific volume (1013.25 hPa, 21 °C ) : 0.336 m3 kg^-1
  • Specific heat at constant pressure (Cp) (1013.25 hPa at 25 °C) : 33 J/(mole.K)
  • Viscosity (1013.25 hPa, at 0 °C ) : 0.0001245 Poise
  • Thermal Conductivity (1013.25 hPa, at 0 °C ) : 7.91 mW/(m.K)
    
  • Solubility in water (1013.25 hPa, at 0 °C ) : 4.61 vol/vol.
    Note: 10 ° C, 1 liter of water dissolved 3.10 liters of chlorine, and 1.77 liter at 30 ° C.
     
• Liquid phase:
  • Density (1013.25 hPa, at boiling point) : 1562.5 kg m3^-1
  • Equivalent gas / liquid (1013.25 hPa at 15 °C) : 521 vol/vol ( 1 m3 as liquid chlorine > 521 m3 as gas [1583.839 kg] )
  • Boiling point (1013.25 hPa) : -34.1 °C (239.05 K)
  • Latent heat of vaporization (1013.25 hPa, at boiling point) : 287.79 kJ kg^-1
  • Vapor pressure (21 °C) : 0.695 MPa (6.95 bar).
    
• Solid phase (ice):
  • Melting point : -100.84°C (172.31 K)
  • Latent heat of fusion (1013.25 hPa, triple point ) : 90.374 kJ kg^-1 ---------------------------

Standardization.
Standard products used for the production of drinking water : bulletin officiel - Chlore : NF EN 937.

Uses.

• Production of industrial and consumer products.
  Principal applications of chlorine are in the production of a wide range of industrial and consumer products. For example, it is used in making plastics, solvents for dry cleaning and metal degreasing, textiles, agrochemicals and pharmaceuticals, insecticides, dyestuffs, household cleaning products, etc.
  
  Many important industrial products are produced via organochlorine intermediates. Examples include polycarbonates, polyurethanes, silicones, polytetrafluoroethylene, carboxymethyl cellulose, and propylene oxide. Like the other halogens, chlorine participates in free-radical substitution reactions with hydrogen-containing organic compounds. When applied to organic substrates, reaction is often—but not invariably—non-regioselective, and, hence, may result in a mixture of isomeric products. It is often difficult to control the degree of substitution as well, so multiple substitutions are common. If the different reaction products are easily separated, e.g., by distillation, substitutive free-radical chlorination (in some cases accompanied by concurrent thermal dehydrochlorination) may be a useful synthetic route. Industrial examples of this are the production of methyl chloride, methylene chloride, chloroform, and carbon tetrachloride from methane, allyl chloride from propylene, and trichloroethylene, and tetrachloroethylene from 1,2-dichloroethane.
  
  Quantitatively, about 63% and 18% of all elemental chlorine produced is used in the manufacture of organic and inorganic chlorine compounds, respectively,. About 15,000 chlorine compounds are being used commercially.The remaining 19% is used for bleaches and disinfection products. The most significant of organic compounds in terms of production volume are 1,2-dichloroethane and vinyl chloride, intermediates in the production of PVC. Other particularly important organochlorines are methyl chloride, methylene chloride, chloroform, vinylidene chloride, trichloroethylene, perchloroethylene, allyl chloride, epichlorohydrin, chlorobenzene, dichlorobenzenes, and trichlorobenzenes. The major inorganic compounds include HCl, Cl2O, HOCl, NaClO3, chlorinated isocyanurates, AlCl3, SiCl4, SnCl4, PCl3, PCl5, POCl3, AsCl3, SbCl3, SbCl5, BiCl3, S2Cl2, SCl2, SOCI2, ClF3, ICl, ICl3, TiCl3, TiCl4, MoCl5, FeCl3, ZnCl2, etc
  
  Public sanitation, disinfection, and antisepsis.
  Bleach (water chlorination).
  
  Combating putrefaction.
  In France (as elsewhere) there was a need to process animal guts in order to make musical instrument strings, Goldbeater's skin and other products. This was carried out in "gut factories" (boyauderies) as an odiferous and unhealthy business. In or about 1820, the Société d'encouragement pour l'industrie nationale offered a prize for the discovery of a method, chemical or mechanical, that could be used to separate the peritoneal membrane of animal intestines without causing putrefaction. It was won by Antoine-Germain Labarraque, a 44 year-old French chemist and pharmacist who had discovered that Berthollet's chlorinated bleaching solutions ("Eau de Javel") not only destroyed the smell of putrefaction of animal tissue decomposition, but also retarded the decomposition process itself.
  Labarraque's research resulted in chlorides and hypochlorites of lime (calcium hypochlorite) and of sodium (sodium hypochlorite) being employed not only in the boyauderies but also for the routine disinfection and deodorisation of latrines, sewers, markets, abattoirs, anatomical theatres and morgues. They were also used, with success, in hospitals, lazarets, prisons, infirmaries (both on land and at sea), magnaneries, stables, cattle-sheds, etc.; and for exhumations, embalming, during outbreaks of epidemic illness, fever, blackleg in cattle, etc.
  
  Water treatment.
  Chlorine is usually used (in the form of hypochlorous acid) to kill bacteria and other microbes in drinking water supplies and public swimming pools. In most private swimming pools, chlorine itself is not used, but rather sodium hypochlorite, formed from chlorine and sodium hydroxide, or solid tablets of chlorinated isocyanurates. The drawback of using chlorine in swimming pools is that the chlorine reacts with the proteins in human hair and skin (Hypochlorous acid, see bleach). Once the chlorine reacts with the hair and skin, it becomes chemically bonded. Even small water supplies are now routinely chlorinated.
  
  It is often impractical to store and use poisonous chlorine gas for water treatment, so alternative methods of adding chlorine are used. These include hypochlorite solutions, which gradually release chlorine into the water, and compounds like sodium dichloro-s-triazinetrione (dihydrate or anhydrous), sometimes referred to as "dichlor", and trichloro-s-triazinetrione, sometimes referred to as "trichlor". These compounds are stable while solid and may be used in powdered, granular, or tablet form. When added in small amounts to pool water or industrial water systems, the chlorine atoms hydrolyze from the rest of the molecule forming hypochlorous acid (HOCl), which acts as a general biocide, killing germs, micro-organisms, algae, and so on.
  

Health effects of the free element and hazards :

• Chlorine is a toxic gas that irritates the respiratory system. Because it is heavier than air, it tends to accumulate at the bottom of poorly ventilated spaces. Chlorine gas is a strong oxidizer, which may react with flammable materials.
  Chlorine is detectable with measuring devices in concentrations of as low as 0.2 parts per million (ppm), and by smell at 3 ppm. Coughing and vomiting may occur at 30 ppm and lung damage at 60 ppm. About 1000 ppm can be fatal after a few deep breaths of the gas. Breathing lower concentrations can aggravate the respiratory system, and exposure to the gas can irritate the eyes. The toxicity of chlorine comes from its oxidizing power. When chlorine is inhaled at concentrations above 30 ppm, it begins to react with water and cells, which change it into hydrochloric acid (HCl) and hypochlorous acid (HClO).
  When used at specified levels for water disinfection, the reaction of chlorine with water is not a major concern for human health. Other materials present in the water may generate disinfection by-products that are associated with negative effects on human health, however, the health risk is far lower than drinking undisinfected water.
  
  High exposure to chlorine can cause induced asthma : Reactive Airways Dysfunction Syndrome or RADS is a term proposed by Stuart M. Brooks M.D. and colleagues in 1985 to describe an asthma-like syndrome developing after a single exposure to high levels of an irritating vapor, fume, or smoke. It involves coughing, wheezing, and dyspnea. It can also manifest in adults with exposure to high levels of chlorine, ammonia, acetic acid or sulphur dioxide, creating symptoms like asthma. The severity of these symptoms can be mild to fatal, and can even create long-term airway damage depending on the amount of exposure and the concentration of chlorine. Some experts classify RADS as occupational asthma. Those with exposure to highly irritating substances should receive treatment to mitigate harmful effects.
  
  Toxicity:

(Source : INERIS - 03DR002.doc/Septembre2003)

Link (Canadian Centre for Occupational Health and Safety).

> Sources (link) : BELGOCHLOR (BelgoChlor, Diamant Building, Bd A.Reyers 80, 1030 Bruxelles)

Download Technical MSDS AL (pdf files > over there ).

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