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27 novembre 2011 7 27 /11 /novembre /2011 09:36

Chlorine : atomic number 17 and symbol Cl

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine. Sony VAIO VGN-CS120J/Q Battery

It has the highest electron affinity and the third highestelectronegativity of all the elements; for this reason, chlorine is a strong oxidizing agent.

The most common compound of chlorine, sodium chloride, has been known since ancient times; however, around 1630, chlorine gas was obtained by the Belgian chemist and physician Jan Baptist van Helmont.Sony VAIO VGN-CS120J/R Battery

The synthesis and characterization of elemental chlorine occurred in 1774 by Swedish chemist Carl Wilhelm Scheele, who called it "dephlogisticated muriatic acid air," having thought he synthesized the oxide obtained from the hydrochloric acid. Because acids were thought at the time to necessarily contain oxygen,Sony VAIO VGN-CS190JTB Battery

a number of chemists, including Claude Berthollet, suggested that Scheele's dephlogisticated muriatic acid air must be a combination of oxygen and the yet undiscovered element, and Scheele named the supposed new element within this oxide as muriaticum. The suggestion that this newly discovered gas was a simple element was made in 1809 by Joseph Louis Gay-Lussac and Louis-Jacques.Sony VAIO VGN-CS190JTP Battery

This was confirmed by Sir Humphry Davy in 1810, who named it chlorine, from the Greek word ?????? (chl?ros), meaning "green-yellow."

Chlorine is a component of various compounds, including table salt. It is the second most abundant halogen and 21st most abundant chemical element in Earth's crust.Sony VAIO VGN-CS190JTQ Battery

The great oxidizing potential of chlorine led it to its bleaching and disinfectant uses, as well as uses of an essential reagent in the chemical industry. As a common disinfectant, chlorine compounds are used in swimming pools to keep them clean and sanitary.Sony VAIO VGN-CS190JTR Battery

In the upper atmosphere, chlorine-containing molecules such as chlorofluorocarbons have been implicated in ozone depletion. Elemental chlorine is extremely dangerous and poisonous for all lifeforms; however, chlorine is necessary to most forms of life, including humans, in form ofchloride ions.Sony VAIO VGN-CS190JTW Battery

Physical characteristics

Chlorine, liquefied under a pressure of 8 bar at room temperature. The liquid column size is ca. 0.3×3 cm.

At standard temperature and pressure, two chlorine atoms form the diatomic molecule Cl2. This is a yellow-green gas that has its distinctive strong smell, the smell of bleach.Sony VAIO VGN-CS190NAB Battery

The bonding between the two atoms is relatively weak (only 242.580 ±0.004 kJ/mol), which makes the Cl2 molecule highly reactive. The boiling point at regular atmosphere is around ?34 ?C, but it can be liquefied at room temperature with pressures above 8 atmospheres.Sony VAIO VGN-CS190NAC Battery

Chemical characteristics

Along with fluorine, bromine, iodine, and astatine, chlorine is a member of the halogen series that forms the group 17 (formerly VII, VIIA, or VIIB) of the periodic table. Chlorine forms compounds with almost all of the elements to give compounds that are usually called chlorides. Sony VAIO VGN-CS190NAD Battery

Chlorine gas reacts with most organic compounds, and will even sluggishly support the combustion of hydrocarbons.

Hydrolysis

At 25 °C and atmospheric pressure, one liter of water dissolves 3.26 g or 1.02 L of gaseous chlorine. Solutions of chlorine in water contain chlorine (Cl2), hydrochloric acid, and hypochlorous acid:Sony VAIO VGN-CS190NBB Battery

Cl2 + H2O   HCl + HClO

This conversion to the right is called disproportionation, because the ingredient chlorine both increases and decreases in formal oxidation state. The solubility of chlorine in water is increased if the water contains dissolved alkali hydroxide, and in this way, chlorine bleach is produced.Sony VAIO VGN-CS190NCA Battery

Cl2 + 2 OH– ? ClO– + Cl– + H2O

Chlorine gas only exists in a neutral or acidic solution.

Compounds

Chlorine exists in all odd numbered oxidation states from ?1 to +7, as well as the elemental state of zero and four in chlorine dioxide (see table below, and also structures in chlorite).Sony VAIO VGN-CS190NCB Battery

Progressing through the states, hydrochloric acid can be oxidized using manganese dioxide, or hydrogen chloride gas oxidized catalytically by air to form elemental chlorine gas.

Interhalogen compounds

Chlorine oxidizes bromide and iodide salts to bromine and iodine, respectively. Sony VAIO VGN-CS190NCC Battery

However, it cannot oxidize fluoride salts to fluorine. It makes a variety of interhalogen compounds such as the chlorine fluorides, chlorine monofluoride (ClF), chlorine trifluoride (ClF3), chlorine pentafluoride (ClF5). Chlorides of bromine and iodine are also known.Sony VAIO VGN-CS50B/W Battery

Organochlorine compounds

Chlorine is used extensively in organic chemistry in substitution and addition reactions. Chlorine often imparts many desired properties to an organic compound, in part due to its electronegativity. Some organochlorine compounds are also serious pollutants, either as side products of industrial processes or as persistent pesticides.Sony VAIO VGN-CS51B/W Battery

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. Sony VAIO VGN-CS52JB/W Battery

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. Sony VAIO VGN-CS60B/P Battery

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,Sony VAIO VGN-CS60B/Q Battery

methylene chloride, chloroform, and carbon tetrachloride from methane, allyl chloride from propylene, and trichloroethylene, and tetrachloroethylene from 1,2-dichloroethane.

Like the other halides, chlorine undergoes electrophilic addition reactions, the most notable one being the chlorination of alkenes and aromatic compounds with aLewis acid catalyst. Sony VAIO VGN-CS60B/R Battery

Organic chlorine compounds tend to be less reactive in nucleophilic substitution reactions than the corresponding bromine or iodine derivatives, but they tend to be cheaper. They may be activated for reaction by substituting with a tosylate group, or by the use of a catalytic amount of sodium iodide.Sony VAIO VGN-CS61B/P Battery

Chlorides

Chlorine combines with almost all elements to give chlorides. Compounds with oxygen, nitrogen, xenon, and krypton are known, but do not form by direct reaction of the elements.Chloride is one of the most common anions in nature.Sony VAIO VGN-CS61B/Q Battery

Hydrogen chloride and its aqueous solution, hydrochloric acid, are produced on megaton scale annually both as valued intermediates but sometimes as undesirable pollutants.

Occurrence

In nature, chlorine is found primarily as the chloride ion, a component of the salt that is deposited in the earth or dissolved in the oceans — about 1.9% of the mass of seawater is chloride ions. Sony VAIO VGN-CS61B/R Battery

Even higher concentrations of chloride are found in the Dead Sea and in underground brine deposits. Most chloride salts are soluble in water, thus, chloride-containing minerals are usually only found in abundance in dry climates or deep underground. Sony VAIO VGN-CS62JB/P Battery

In the Earth's crust, chlorine is present at average concentrations of about 126 parts per million, predominantly in such minerals as halite (sodium chloride), sylvite (potassium chloride), andcarnallite (potassium magnesium chloride hexahydrate). Over 2000 naturally occurring organic chlorine compounds are known.Sony VAIO VGN-CS62JB/Q Battery

In the interstellar medium, chlorine is produced in supernovae via the r-process.

Isotopes

Chlorine has a wide range of isotopes. The two stable isotopes are 35Cl (75.77%) and 37Cl (24.23%). Together they give chlorine an atomic weight of 35.4527 g/mol. Sony VAIO VGN-CS62JB/R Battery

The half-integer value for chlorine's weight caused some confusion in the early days of chemistry, when it had been postulated that atoms were composed of even units of hydrogen (see Proust's law), and the existence of chemical isotopes was unsuspected.

Trace amounts of radioactive 36Cl exist in the environment, in a ratio of about 7x10?13 to 1 with stable isotopes.Sony VAIO VGN-CS71B/W Battery

36Cl is produced in the atmosphere by spallationof 36Ar by interactions with cosmic ray protons. In the subsurface environment, 36Cl is generated primarily as a result of neutron capture by 35Cl or muon capture by40Ca. 36Cl decays to 36S and to 36Ar, with a combined half-life of 308,000 years. Sony VAIO VGN-CS72JB/W Battery

The half-life of this hydrophilic nonreactive isotope makes it suitable for geologic dating in the range of 60,000 to 1 million years. Additionally, large amounts of 36Cl were produced by irradiation of seawater during atmospheric detonations ofnuclear weapons between 1952 and 1958. Sony VAIO VGN-CS90HS Battery

The residence time of 36Cl in the atmosphere is about 1 week. Thus, as an event marker of 1950s water in soil and ground water, 36Cl is also useful for dating waters less than 50 years before the present. 36Cl has seen use in other areas of the geological sciences, including dating ice and sediments.Sony VAIO VGN-CS90NS Battery

The most common compound of chlorine, sodium chloride, has been known since ancient times; archaeologists have found evidence that rock salt was used as early as 3000 BC and brine as early as 6000 BC. Around 1630, chlorine was recognized as a gas by the Belgian chemist and physician Jan Baptist van Helmont.Sony VAIO VGN-CS90S Battery

Elemental chlorine was first prepared and studied in 1774 by Swedish chemist Carl Wilhelm Scheele, and, therefore, he is credited for its discovery. He called it "dephlogisticated muriatic acid air" since it is a gas (then called "airs") and it came from hydrochloric acid (then known as "muriatic acid").Sony VAIO VGN-CS91HS Battery

However, he failed to establish chlorine as an element, mistakenly thinking that it was the oxide obtained from the hydrochloric acid (see phlogiston theory). [22] He named the new element within this oxide as muriaticum. Regardless of what he thought, Scheele did isolate chlorine by reacting MnO2 (as the mineral pyrolusite) with HCl:Sony VAIO VGN-CS91NS Battery

4 HCl + MnO2 ? MnCl2 + 2 H2O + Cl2

Scheele observed several of the properties of chlorine: the bleaching effect on litmus, the deadly effect on insects, the yellow green color, and the smell similar to aqua regia. Sony VAIO VGN-CS91S Battery

At the time, common chemical theory was: any acid is a compound that contains oxygen (still sounding in the German and Dutch names of oxygen: sauerstoff or zuurstof, both translating into English as acid stuff), so a number of chemists, including Claude Berthollet, suggested that Scheele's dephlogisticated muriatic acid air must be a combination of oxygen and the yet undiscovered element, muriaticum.Sony VAIO VGN-CS92DS Battery

In 1809, Joseph Louis Gay-Lussac and Louis-Jacques Thénard tried to decompose dephlogisticated muriatic acid air by reacting it with charcoal to release the free element muriaticum (and carbon dioxide).They did not succeed and published a report in which they considered the possibility that dephlogisticated muriatic acid air is an element, but were not convinced.Sony VAIO VGN-CS92JS Battery

In 1810, Sir Humphry Davy tried the same experiment again, and concluded that it is an element, and not a compound. He named this new element as chlorine, from the Greek word ?????? (chl?ros), meaning green-yellow. The name halogen, meaning salt producer, was originally defined for chlorine (in 1811 by Johann Salomo Christoph Schweigger), Sony VAIO VGN-CS92XS Battery

and later in 1842, at a suggestion by Jöns Jakob Berzelius, this term was applied to the rest of the elements in this family.[29][30] In 1823,Michael Faraday liquefied chlorine for the first time, and demonstrated that what was then known as "solid chlorine" had a structure of chlorine hydrate (Cl2·H2O).Sony VAIO VGN-FW11E Battery

Chlorine was first used by Claude Berthollet to bleach textiles in 1785. In 1826, silver chloride was used to produce photographic images for the first time. Chloroform was first used as an anesthetic in 1847. An elemental chlorine solution in water (which was expensive),Sony VAIO VGN-FW11L Battery

then the less expensive chlorine gas dissolved in lime-water (calcium hypochlorite) was first used as an antiseptic to prevent the spread of puerperal fever in the maternity wards of Vienna General Hospital in Austria in 1847,. In 1850, chlorine in lime-water was used by John Snow to purify the water supply in London after an outbreak of cholera. Sony VAIO VGN-FW11M Battery

(Both uses preceded the germ theory of disease, and were based on destruction of odors and "putrid matter").

The US Department of Treasury called for all water to be disinfected with chlorine by 1918. Polyvinyl chloride (PVC) was invented in 1912, initially without a purpose.Sony VAIO VGN-FW11S Battery

Chlorine gas was first introduced as a weapon on April 22, 1915, at Ypres by the German Army, and the results of this weapon were disastrous because gas masks had not yet been invented.

Production

In industry, elemental chlorine is usually produced by the electrolysis of sodium chloride dissolved in water.Sony VAIO VGN-FW11ZU Battery

Along with chlorine, this chloralkali processyields hydrogen gas and sodium hydroxide, according to the following chemical equation:

2 NaCl + 2 H2O ? Cl2 + H2 + 2 NaOH

The electrolysis of chloride solutions all proceed according to the following equations:

Cathode: 2 H+ (aq) + 2 e? ? H2 (g)

Anode: 2 Cl? (aq) ? Cl2 (g) + 2 e? Sony VAIO VGN-FW139E/H Battery

Overall process: 2 NaCl (or KCl) + 2 H2O ? Cl2 + H2 + 2 NaOH (or KOH) In diaphragm cell electrolysis, an asbestos (or polymer-fiber) diaphragm separates a cathode and an anode, preventing the chlorine forming at the anode from re-mixing with the sodium hydroxide and the hydrogen formed at the cathode.Sony VAIO VGN-FW140AE Battery

The salt solution (brine) is continuously fed to the anode compartment and flows through the diaphragm to the cathode compartment, where the caustic alkali is produced and the brine is partially depleted. Diaphragm methods produce dilute and slightly impure alkali but they are not burdened with the problem of preventing mercury discharge into the environment and they are more energy efficient.Sony VAIO VGN-FW140D Battery

Membrane cell electrolysis employ permeable membrane as an ion exchanger. Saturated sodium (or potassium) chloride solution is passed through the anode compartment, leaving at a lower concentration. This method is more efficient than the diaphragm cell and produces very pure sodium (or potassium) hydroxide at about 32% concentration, but requires very pure brine.Sony VAIO VGN-FW140E Battery

Laboratory methods

Small amounts of chlorine gas can be made in the laboratory by combining hydrochloric acid and manganese dioxide. Alternatively a strong acid such as sulfuric acid or hydrochloric acid reacts with sodium hypochlorite solution to release chlorine gas but reacts with sodium chlorate to produce chlorine gas and chlorine dioxide gas as well.Sony VAIO VGN-FW140E/H Battery

In the home, accidents occur when hypochlorite bleach solutions are combined with certain acidic drain-cleaners.

Production of industrial and consumer products

Principal applications of chlorine are in the production of a wide range of industrial and consumer products.Sony VAIO VGN-FW140E/W Battery

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. Quantitavely, about 63% and 18% of all chlorine are used in the manufacture of organic and inorganic chlorine compounds, respectively,[38] and about 15,000 chlorine compounds are being used commercially.Sony VAIO VGN-FW140FE Battery

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.Sony VAIO VGN-FW140N Battery

Other particularly important organochlorines are methyl chloride, methylene chloride, chloroform, vinylidene chloride, trichloroethylene, perchloroethylene, allyl chloride, epichlorohydrin,chlorobenzene, dichlorobenzenes, and trichlorobenzenes. Sony VAIO VGN-FW140N/W Battery

The major inorganic compounds include HCl, Cl2O, HOCl, NaClO3, chlorinated isocyanurates, AlCl3, SiCl4, SnCl4, PCl3, PCl5, POCl3, AsCl3, SbCl3, SbCl5, BiCl3, S2Cl2, SCl2, SOCI2, CIF3, ICl, ICl3, TiCl3, TiCl4, MoCl5, FeCl3, ZnCl2, etc.[38][43]

Purification and disinfection

Chlorine is an important chemical for water purification (such as water treatment plants), in disinfectants, and in bleach.Sony VAIO VGN-FW145E Battery

Chlorine in water is more than three times as effective as a disinfectant against Escherichia coli than an equivalent concentration of bromine, and is more than six times more effective than an equivalent concentration of iodine.

Chlorine is usually used (in the form of hypochlorous acid) to kill bacteria and other microbes in drinking water supplies and public swimming pools. Sony VAIO VGN-FW145E/W Battery

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 a human's hair and skin because hair and skin are made from protein.(Reaction with protein amino groups) Even small water supplies are now routinely chlorinated. Sony VAIO VGN-FW160AE Battery

It is often impractical to store and use poisonous chlorine gas for water treatment, so alternative methods of adding chlorine are used. These include hypochloritesolutions, which gradually release chlorine into the water, and compounds like sodium dichloro-s-triazinetrione (dihydrate or anhydrous), Sony VAIO VGN-FW160D Battery

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.Sony VAIO VGN-FW160E Battery

Chlorine gas, also known as bertholite, was first used as a weapon in World War I by Germany on April 22, 1915 in the Second Battle of Ypres. As described by the soldiers it had a distinctive smell of a mixture between pepper and pineapple. It also tasted metallic and stung the back of the throat and chest.Sony VAIO VGN-FW160E/H Battery

Chlorine can react with water in the mucosa of the lungs to form hydrochloric acid, an irritant that can be lethal. The damage done by chlorine gas can be prevented by a gas mask, or other filtration method, which makes the overall chance of death by chlorine gas much lower than those of other chemical weapons. Sony VAIO VGN-FW160F/E Battery

It was pioneered by a German scientist later to be a Nobel laureate, Fritz Haber of the Kaiser Wilhelm Institute in Berlin, in collaboration with the German chemical conglomerate IG Farben, who developed methods for discharging chlorine gas against an entrenched enemy. Sony VAIO VGN-FW170J/H Battery

It is alleged that Haber's role in the use of chlorine as a deadly weapon drove his wife,Clara Immerwahr, to suicide.[47] After its first use, chlorine was utilized by both sides as a chemical weapon, but it was soon replaced by the more deadly phosgeneand mustard gas.Sony VAIO VGN-FW180AE Battery

Iraq War

Chlorine gas has also been used by insurgents against the local population and coalition forces in the Iraq War in the form ofchlorine bombs. On March 17, 2007, for example, three chlorine filled trucks were detonated in the Anbar province killing two and sickening over 350.Sony VAIO VGN-FW180D Battery

Other chlorine bomb attacks resulted in higher death tolls, with more than 30 deaths on two separate occasions.[50] Most of the deaths were caused by the force of the explosions rather than the effects of chlorine, since the toxic gas is readily dispersed and diluted in the atmosphere by the blast.Sony VAIO VGN-FW180E Battery

The Iraqi authorities have tightened up security for chlorine, which is essential for providing safe drinking water for the population.

Chlorine cracking

The element is widely used for purifying water owing to its powerful oxidizing properties, especially potable water supplies and water used in swimming pools.Sony VAIO VGN-FW180E/H Battery

Several catastrophic collapses of swimming pool ceilings have occurred owing to stress corrosion cracking of stainless steel rods used to suspend them. Some polymers are also sensitive to attack, including acetal resin andpolybutene. Both materials were used in hot and cold water domestic supplies, and stress corrosion cracking caused widespread failures in the USA in the 1980s and 1990s.Sony VAIO VGN-FW180FU Battery

One example shows an acetal joint in a water supply system, which, when it fractured, caused substantial physical damage to computers in the labs below the supply. The cracks started at injection molding defects in the joint and grew slowly until finally triggered. Sony VAIO VGN-FW190EBH Battery

The fracture surface shows iron and calcium salts that were deposited in the leaking joint from the water supply before failure.

Health effects

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.Sony VAIO VGN-FW190ECH Battery

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.Sony VAIO VGN-FW190EDH Battery

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) andhypochlorous acid (HClO).Sony VAIO VGN-FW190NAH Battery

When used at specified levels for water disinfection, the reaction of chlorine with water is not a major concern for human health. However, other materials present in the water may generate disinfection by-products that can damage human health.

The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion (negatively-charged ion) Cl?. Sony VAIO VGN-FW190NBH Battery

The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water. It is an essential electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating fluid in and out of cells.Sony VAIO VGN-FW190NCH Battery

Terminology

The word chloride can also refer to a chemical compound in which one or more chlorine atoms are covalently bonded in themolecule.Sony VAIO VGN-FW190NDH Battery

This ambiguity is present in chemistry terminology, however it is important to remember that the inorganic, ionic-bond forming chloride ion is entirely different from a covalently bonded chlorine atom, and the term organo-halide, such as methyl chloride, is a terminological coincidence, resulting from the way that organic chemists name their molecules. Sony VAIO VGN-FW190NEH Battery

As an example, compare sodium chloride, NaCl, with methyl chloride, CH3Cl. NaCl is an inorganic, ionically bonded compound, while methyl chloride is an organic covalently bonded compound, which does not contain a chloride ion. Methyl chloride does not have to be named as a chloride, and its more common name is chloromethane. NaCl must be named as a chloride because it actually contains the chloride ion.Sony VAIO VGN-FW198U/H Battery

Corrosion

The presence of chlorides, e.g. in seawater, significantly aggravates the conditions for pitting corrosion of most metals (including stainless steels and high-alloyed materials) by enhancing the formation and growth of the pits through an autocatalytic process.Sony VAIO VGN-FW260J/B Battery

Uses

Chloride is used to form salts that can preserve food such as sodium chloride. Other salts such as calcium chloride,magnesium chloride, potassium chloride have varied uses ranging from medical treatments to cement formation. Sony VAIO VGN-FW280J/H Battery

An example is table salt, which is sodium chloride with the chemical formula NaCl. In water, it dissociates into Na+ and Cl?ions.

Examples of inorganic covalently bonded chlorides that are used as reactants are:

  • phosphorus trichloride, phosphorus pentachloride, and thionyl chloride, all three of which reactive chlorinating reagents that have been used in a laboratory  Sony VAIO VGN-FW290JRB Battery
  • disulfur dichloride (S2Cl2), used for vulcanization of rubber.

A chloride ion is also the prosthetic group present in the amylase enzyme.

Another example is calcium chloride with the chemical formula CaCl2. Calcium chloride is a salt that is marketed in pellet form for removing dampness from rooms. Sony VAIO VGN-FW290JTB Battery

Calcium chloride is also used for maintaining unpaved roads and for sanite fortifying roadbases for new construction. In addition, Calcium chloride is widely used as a deicer since it is effective in lowering the melting point when applied to ice.

In the petroleum industry, the chlorides are a closely monitored constituent of the mud system.Sony VAIO VGN-FW290JTH Battery

The increase of the chlorides in the mud system could indicate the possibility of drilling into a high-pressure saltwater formation. Its increase can also indicate the poor quality of a target sand.

Chloride is also a useful and reliable chemical indicator of river / groundwater fecal contamination, as chloride is a non-reactive solute and ubiquitous to sewage & potable water. Sony VAIO VGN-FW290JTW Battery

Many water regulating companies around the world utilize chloride to check the contamination levels of the rivers and potable water sources.

Human Health

Chloride is a chemical the human body needs for metabolism (the process of turning food into energy). It also helps keep the body's acid-base balance. The amount of chloride in the blood is carefully controlled by the kidneys.Sony VAIO VGN-FW355J/H Battery

Gas extraction

Chlorine can be manufactured by electrolysis of a sodium chloride solution (brine). The production of chlorine results in the co-products caustic soda (sodium hydroxide, NaOH) and hydrogen gas (H2). Sony VAIO VGN-FW373J/B Battery

These two products, as well as chlorine itself, are highly reactive. Chlorine can also be produced by the electrolysis of asolution of potassium chloride, in which case the co-products are hydrogen and caustic potash (potassium hydroxide). There are three industrial methods for the extraction of chlorine by electrolysis of chloride solutions, all proceeding according to the following equations:Sony VAIO VGN-FW30B Battery

Cathode: 2 H+ (aq) + 2 e? ? H2 (g)

Anode: 2 Cl? (aq) ? Cl2 (g) + 2 e?

Overall process: 2 NaCl (or KCl) + 2 H2O ? Cl2 + H2 + 2 NaOH (or KOH) Sony VAIO VGN-FW50B Battery

Mercury cell electrolysis

Mercury cell electrolysis, also known as the Castner-Kellner process, was the first method used at the end of the nineteenth century to produce chlorine on an industrial scale. The "rocking" cells used have been improved over the years.Sony VAIO VGN-FW51B/W Battery

Today, in the "primary cell", titanium anodes (formerly graphite ones) are placed in a sodium (or potassium) chloride solution flowing over a liquid mercury cathode. When a potential difference is applied and current flows, chlorine is released at the titanium anode and sodium (or potassium) dissolves in the mercury cathode forming an amalgam. Sony VAIO VGN-FW51MF Battery

This flows continuously into a separate reactor ("denuder" or "secondary cell"), where it is usually converted back to mercury by reaction with water, producing hydrogen and sodium (or potassium) hydroxide at a commercially useful concentration (50% by weight). The mercury is then recycled to the primary cell.Sony VAIO VGN-FW51MF/H Battery

The mercury process is the least energy-efficient of the three main technologies (mercury, diaphragm and membrane) and there are also concerns about mercuryemissions.

It is estimated that there are still around 100 mercury-cell plants operating worldwide. Sony VAIO VGN-FW51ZF Battery

In Japan, mercury-based chloralkali production was virtually phased out by 1987 (except for the last two potassium chloride units shut down in 2003). In the United States, there will be only five mercury plants remaining in operation by the end of 2008.Sony VAIO VGN-FW51ZF/H Battery

In Europe, mercury cells accounted for 43% of capacity in 2006 and Western European producers have committed to closing or converting all remaining chloralkali mercury plants by 2020.

Diaphragm cell electrolysis (Bipolar)

In diaphragm cell electrolysis, an asbestos (or polymer-fiber) diaphragm separates a cathode and an anode, preventing the chlorine forming at the anode from re-mixing with the sodium hydroxide and the hydrogen formed at the cathode.Sony VAIO VGN-FW52JB Battery

This technology was also developed at the end of the nineteenth century. There are several variants of this process: the Le Sueur cell (1893), the Hargreaves-Bird cell (1901), the Gibbs cell (1908), and the Townsend cell (1904). The cells vary in construction and placement of the diaphragm, with some having the diaphragm in direct contact with the cathode.Sony VAIO VGN-FW54FB Battery

The salt solution (brine) is continuously fed to the anode compartment and flows through the diaphragm to the cathode compartment, where the caustic alkali is produced and the brine is partially depleted. As a result, diaphragm methods produce alkali that is quite dilute (about 12%) and of lower purity than do mercury cell methods.Sony VAIO VGN-FW70DB Battery

Diaphragm cells are not burdened with the problem of preventing mercury discharge into the environment; they also operate at a lower voltage, resulting in an energy savings over the mercury cell method, but large amounts of steam are required if the caustic has to be evaporated to the commercial concentration of 50%.Sony VAIO VGN-FW71DB/W Battery

Membrane cell electrolysis

Development of this technology began in the 1970s. The electrolysis cell is divided into two "rooms" by a cation permeable membrane acting as an ion exchanger. Saturated sodium (or potassium) chloride solution is passed through the anode compartment, leaving at a lower concentration.Sony VAIO VGN-FW72JGB Battery

Sodium (or potassium) hydroxidesolution is circulated through the cathode compartment, exiting at a higher concentration. A portion of the concentrated sodium hydroxide solution leaving the cell is diverted as product, while the remainder is diluted with deionized water and passed through the electrolysis apparatus again.Sony VAIO VGN-FW73JGB Battery

This method is more efficient than the diaphragm cell and produces very pure sodium (or potassium) hydroxide at about 32% concentration, but requires very pure brine.

Other electrolytic processes

Although a much lower production scale is involved, electrolytic diaphragm and membrane technologies are also used industrially to recover chlorine from hydrochloric acid solutions, producing hydrogen (but no caustic alkali) as a co-product.Sony VAIO VGN-FW74FB Battery

Furthermore, electrolysis of fused chloride salts (Downs process) also enables chlorine to be produced, in this case as a by-product of the manufacture of metallicsodium or magnesium.

Other methods

Before electrolytic methods were used for chlorine production, the direct oxidation of hydrogen chloride with oxygen or air was exercised in the Deacon process:Sony VAIO VGN-FW81HS Battery

4 HCl + O2 ? 2 Cl2 + 2 H2O

This reaction is accomplished with the use of copper(II) chloride (CuCl2) as a catalyst and is performed at high temperature (about 400 °C). The amount of extracted chlorine is approximately 80%. Due to the extremely corrosive reaction mixture, industrial use of this method is difficult and several pilot trials failed in the past. Sony VAIO VGN-FW81NS Battery

Nevertheless, recent developments are promising. Recently Sumitomo patented a catalyst for the Deacon process using ruthenium(IV) oxide (RuO2).

Another earlier process to produce chlorine was to heat brine with acid and manganese dioxide.Sony VAIO VGN-FW81S Battery

2 NaCl + 2H2SO4 + MnO2 ? Na2SO4 + MnSO4 + 2 H2O + Cl2

Using this process, chemist Carl Wilhelm Scheele was the first to isolate chlorine in a laboratory. The manganese can be recovered by the Weldon process.Sony VAIO VGN-FW82DS Battery

Small amounts of chlorine gas can be made in the laboratory by putting concentrated hydrochloric acid in a flask with a side arm and rubber tubing attached.Manganese dioxide is then added and the flask stoppered. The reaction is not greatly exothermic. As chlorine is denser than air, it can be easily collected by placing the tube inside a flask where it will displace the air. Once full, the collecting flask can be stoppered.Sony VAIO VGN-FW82JS Battery

Another method for producing small amounts of chlorine gas in a lab is by adding concentrated hydrochloric acid (typically about 5M) to sodium hypochlorite or sodium chlorate solution.

Industrial production

Large-scale production of chlorine involves several steps and many pieces of equipment. Sony VAIO VGN-FW82XS Battery

The description below is typical of a membrane plant. The plant also simultaneously produces sodium hydroxide (caustic soda) and hydrogen gas. A typical plant consists of brine production/treatment, cell operations, chlorine cooling & drying, chlorine compression & liquefaction, liquid chlorine storage & loading, caustic handling, evaporation, storage & loading and hydrogen handling.n-fw83ds-battery-27349.htm" title="Sony VAIO VGN-FW83DS laptop battery">Sony VAIO VGN-FW83DS Battery

Brine

Key to the production of chlorine is the operation of the brine saturation/treatment system. Maintaining a properly saturated solution with the correct purity is vital, especially for membrane cells. Many plants have a salt pile which is sprayed with recycled brine. Others have slurry tanks that are fed raw salt.Sony VAIO VGN-FW83JS Battery

The raw brine is partially or totally treated with sodium hydroxide, sodium carbonate and a flocculant to reduce calcium, magnesium and other impurities. The brine proceeds to a large clarifier or a filter where the impurities are removed. The total brine is additionally filtered before entering ion exchangers to further removeimpurities. Sony VAIO VGN-FW83XS Battery

At several points in this process, the brine is tested for hardness and strength.

After the ion exchangers, the brine is considered pure, and is transferred to storage tanks to be pumped into the cell room. Brine, fed to the cell line, is heated to the correct temperature to control exit brine temperatures according to the electrical load. Sony VAIO VGN-FW90HS Battery

Brine exiting the cell room must be treated to remove residual chlorine and control pH levels before being returned to the saturation stage. This can be accomplished via dechlorination towers with acid and sodium bisulfiteaddition. Failure to remove chlorine can result in damage to the cells.Sony VAIO VGN-FW90NS Battery

Brine should be monitored for accumulation of both chlorate anions and sulfate anions, and either have a treatment system in place, or purging of the brine loop to maintain safe levels, since chlorate anions can diffuse through the membranes and contaminate the caustic, while sulfate anions can damage the anode surface coating.Sony VAIO VGN-FW90S Battery

Cell room

The building that houses the many electrolytic cells is usually called a cell room or cell house, although some plants are built outdoors. This building contains support structures for the cells, connections for supplying electrical power to the cells and piping for the fluids. Sony VAIO VGN-FW91NS Battery

Monitoring and control of the temperatures of the feed caustic and brine is done to control exit temperatures. Also monitored are the voltages of each cell which vary with the electrical load on the cell room that is used to control the rate of production. Monitoring and control of the pressures in the chlorine and hydrogen headers is also done via pressure control valves.Sony VAIO VGN-FW91S Battery

Direct current is supplied via a rectified power source. Plant load is controlled by varying the current to the cells. As the current is increased, flow rates for brine and caustic and deionized water are increased, while lowering the feed temperatures.Sony VAIO VGN-FW92DS Battery

Cooling and drying

Chlorine gas exiting the cell line must be cooled and dried since the exit gas can be over 80°C and contains moisture that allows chlorine gas to be corrosive toiron piping. Cooling the gas allows for a large amount of moisture from the brine to condense out of the gas stream.Sony VAIO VGN-FW92JS Battery

Cooling also improves the efficiency of both thecompression and the liquefaction stage that follows. Chlorine exiting is ideally between 18°C and 25°C. After cooling the gas stream passes through a series of towers with counter flowing sulfuric acid. These towers progressively remove any remaining moisture from the chlorine gas. Sony VAIO VGN-FW93DS Battery

After exiting the drying towers the chlorine is filtered to remove any remaining sulfuric acid.

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