Overblog Suivre ce blog
Editer l'article Administration Créer mon blog
27 novembre 2011 7 27 /11 /novembre /2011 09:38

Compression and liquefaction

Several methods of compression may be used: liquid ring, reciprocating, or centrifugal. The chlorine gas is compressed at this stage and may be further cooled by inter- and after-coolers.Sony VAIO VGN-FW93JS Battery

After compression it flows to the liquefiers, where it is cooled enough to liquefy. Non condensible gases and remaining chlorine gas are vented off as part of the pressure control of the liquefaction systems. These gases are routed to a gas scrubber, producing sodium hypochlorite, or used in the production of hydrochloric acid (by combustion with hydrogen) or ethylene dichloride (by reaction with ethylene).Sony VAIO VGN-FW93XS Battery

Storage and loading

Liquid chlorine is typically gravity-fed to storage tanks. It can be loaded into rail or road tankers via pumps or padded with compressed dry gas.

Caustic handling, evaporation, storage and loading

Caustic, fed to the cell room flows in a loop that is simultaneously bled off to storage with a part diluted with deionized water and returned to the cell line for strengthening within the cells. Sony VAIO VGN-FW94FS Battery

The caustic exiting the cell line must be monitored for strength, to maintain safe concentrations. Too strong or too weak a solutionmay damage the membranes. Membrane cells typically produce caustic in the range of 30% to 33% by weight. The feed caustic flow is heated at low electrical loads to control its exit temperature. Sony VAIO VGN-FW94GS Battery

Higher loads require the caustic to be cooled, to maintain correct exit temperatures. The caustic exiting to storage is pulled from a storage tank and may be diluted for sale to customers who require weak caustic or for use on site. Another stream may be pumped into a multiple effect evaporator set to produce commercial 50% caustic. Sony VAIO VGN-FW94HS Battery

Rail cars and tanker trucks are loaded at loading stations via pumps.

Hydrogen handling

Hydrogen produced may be vented unprocessed directly to the atmosphere or cooled, compressed and dried for use in other processes on site or sold to a customer via pipeline, cylinders or trucks.Sony VAIO VGN-G118CN Battery

Some possible uses include the manufacture of hydrochloric acid or hydrogen peroxide, as well as desulfurization of petroleum oils, or use as a fuel in boilers or fuel cells. For example, in Porsgrunn the byproduct is used for the hydrogen fueling station at Hynor.Sony VAIO VGN-G118GN/B Battery

Energy consumption

Production of chlorine is extremely energy intensive.[11] Energy consumption per unit weight of product is not far below that for iron and steel manufacture[12] and greater than for the production of glass[13] or cement.Sony VAIO VGN-G118GN/T Battery

Since electricity is an indispensable raw material for the production of chlorine, the energy consumption corresponding to the electrochemical reaction cannot be reduced. Energy savings arise primarily through applying more efficient technologies and reducing ancillary energy use.Sony VAIO VGN-G118TN/B Battery

Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water. Water which has been treated with chlorine is effective in preventing the spread of waterborne disease.Sony VAIO VGN-G118TN/S Battery

The chlorination of public drinking supplies was originally met with resistance, as people were concerned about the health effects of the practice. The use of chlorine has greatly reduced the prevalence of waterborne disease as it is effective against almost all bacteria and viruses, as well as amoeba.Sony VAIO VGN-G11VN/T Battery

Chlorination is also used to sanitize the water in swimming pools and as a disinfection stage in sewage treatment.

Shock chlorination is a process used in many swimming pools, water wells, springs, and other water sources to reduce the bacterial and algal residue in the water. Sony VAIO VGN-G11VN/TC Battery

Shock chlorination is performed by mixing a large amount of sodium hypochlorite, which can be in the form of a powder or a liquid such as chlorine bleach, into the water. Water that is being shock chlorinated should not be swum in or drunk until the sodium hypochlorite count in the water goes down to three ppm or less.Sony VAIO VGN-G11XN/B Battery

The first scientists to suggest disinfecting water with chlorine were Louis-Bernard Guyton de Morveau (in France) and William Cumberland Cruikshank (in England), both around the year 1800.

The technique of purification of drinking water by use of compressed liquefied chlorine gas was developed in 1910 by U.S.Sony VAIO VGN-G1AAPS Battery

Army Major (later Brig. Gen.) Carl Rogers Darnall (1867–1941), Professor of Chemistry at the Army Medical School.[2] Shortly thereafter, Major (later Col.) William J. L. Lyster (1869–1947) of the Army Medical Department used a solution of calcium hypochlorite in a linen bag to treat water.Sony VAIO VGN-G1AAPSA Battery

For many decades, Lyster's method remained the standard for U.S. ground forces in the field and in camps, implemented in the form of the familiar Lyster Bag (also spelled Lister Bag). Darnall's work became the basis for present day systems of chlorination of municipal water supplies, which were perfected in the 1930s and widely established in the United States by World War II.Sony VAIO VGN-G1AAPSB Battery

Chemistry in water

When chlorine is added to water, it reacts to form a pH dependent equilibrium mixture of chlorine, hypochlorous acid and hydrochloric acid  :

Cl2 + H2O ? HOCl + HCl

Depending on the pH, hypochlorous acid partly dissociates to hydrogen and hypochlorite ions:Sony VAIO VGN-G1AAPSC Battery

HOCl ? H+ + ClO-

In acidic solution, the major species are Cl2 and HOCl while in alkaline solution effectively only ClO- is present. Very small concentrations of ClO2-, ClO3-, ClO4-are also found.Sony VAIO VGN-G1ABNS Battery

Drawbacks

Disinfection by chlorination can be problematic, in some circumstances. Chlorine can react with naturally occurring organic compounds found in the water supply to produce compounds known as disinfection byproducts (DBPs). The most common DBPs are trihalomethanes (THMs) and haloacetic acids (HAAs). Sony VAIO VGN-G1KAP Battery

Due to the potentialcarcinogenicity of these compounds, drinking water regulations across the developed world require regular monitoring of the concentration of these compounds in the distribution systems of municipal water systems. The World Health Organization has stated that the "Risks to health from DBPs are extremely small in comparison with inadequate disinfection."Sony VAIO VGN-G1KBN Battery

There are also other concerns regarding chlorine, including its volatile nature which causes it to disappear too quickly from the water system, and aestheticconcerns such as taste and odour.

Alternatives

Chlorine in water is more than three times more 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.Sony VAIO VGN-G1KBNA Battery

Several alternatives to traditional chlorination exist, and have been put into practice to varying extents. Ozonation is used by many European countries and also in a few municipalities in the United States. Due to current regulations, systems employing ozonation in the United States still must maintain chlorine residuals comparable to systems without ozonation.Sony VAIO VGN-G1LAP Battery

Disinfection with chloramine is also becoming increasingly common. Unlike chlorine, chloramine has a longer half life in the distribution system and still maintains effective protection against pathogens. The reason chloramines persist in the distribution is due to the relatively lower redox potential in comparison to free chlorine. Sony VAIO VGN-G1LBN Battery

Chloramine is formed by the addition of ammonia into drinking water to form mono-, di-, and trichloramines. Whereas Helicobacter pylori can be many times more resistant to chlorine than Escherichia coli, both organisms are about equally susceptible to the disinfecting effect of chloramine.Sony VAIO VGN-G218LN/T Battery

Water treated by filtration may not need further disinfection; a very high proportion of pathogens are removed by materials in the filter bed. Filtered water must be used soon after it is filtered, as the low amount of remaining microbes may proliferate over time.Sony VAIO VGN-G218N/B Battery

The advantage of chlorine in comparison to ozone is that the residual persists in the water for an extended period of time. This feature allows the chlorine to travel through the water supply system, effectively controlling pathogenic backflow contamination.Sony VAIO VGN-G21XP/B Battery

In a large system this may not be adequate, and so chlorine levels may be boosted at points in the distribution system, or chloramine may be used, which remains in the water for longer before reacting or dissipating.

Another method which is gaining popularity is UV disinfection. UV treatment leaves no residue in the water due to use of light instead of chemical disinfectants. Sony VAIO VGN-G2AANS Battery

However, this method alone (as well as chlorination alone) will not remove bacterially produced toxins, pesticides, heavy metals, etc. from water. Often, multiple steps are taken in commercially sold water.

An organochloride, organochlorine, chlorocarbon, chlorinated hydrocarbon, or chlorinated solvent is an organic compound containing at least one covalently bonded chlorine atom.Sony VAIO VGN-G2AAPS Battery

Their wide structural variety and divergent chemical properties lead to a broad range of applications. Many derivatives are controversial because of the effects of these compounds on the environment and on human and animal health.

Physical properties

Chloride substituents modify the physical properties of organic compounds in several ways. Sony VAIO VGN-G2AAPSA Battery

They are typically denser than water due to the presence of high atomic weight of chlorine. Chloride substituents induce stronger intermolecular interactions than hydrogen substituents. The effect is illustrated by trends in boiling points: methane (-161.6 °C), methyl chloride (-24.2 °C), dichloromethane (40 °C), chloroform (61.2 °C), and carbon tetrachloride (76.72 °C). Sony VAIO VGN-G2AAPSB Battery

The increased intermolecular interactions is attributed to the effects of both van der Waals and polarity.

Natural occurrence

Although rare compared to non-halogenated organic compounds, many organochlorine compounds have been isolated from natural sources ranging from bacteria to humans.Sony VAIO VGN-G2AAPSC Battery

Chlorinated organic compounds are found in nearly every class of biomolecules including alkaloids, terpenes, amino acids, flavonoids, steroids, andfatty acids. Organochlorides, including dioxins, are produced in the high temperature environment of forest fires, and dioxins have been found in the preserved ashes of lightning-ignited fires that predate synthetic dioxins.Sony VAIO VGN-G2KAN Battery

In addition, a variety of simple chlorinated hydrocarbons including dichloromethane, chloroform, and carbon tetrachloride have been isolated from marine algae. A majority of the chloromethane in the environment is produced naturally by biological decomposition, forest fires, and volcanoes.Sony VAIO VGN-G2KANA Battery

The natural organochloride epibatidine, an alkaloid isolated from tree frogs, has potent analgesic effects and has stimulated research into new pain medication.

From chlorine

Alkanes and arylalkanes may be chlorinated under free radical conditions, with UV light. However, the extent of chlorination is difficult to control. Sony VAIO VGN-G2KBNA Battery

Aryl chlorides may be prepared by the Friedel-Crafts halogenation, using chlorine and a Lewis acid catalyst.

The haloform reaction, using chlorine and sodium hydroxide, is also able to generate alkyl halides from methyl ketones, and related compounds. Chloroform was formerly produced thus.

Chlorine adds to the multiple bonds on alkenes and alkynes as well, giving di- or tetra-chloro compounds.Sony VAIO VGN-NR160E/S Battery

Reactions

Alkyl chlorides are versatile building blocks in organic chemistry. While alkyl bromides and iodides are more reactive, alkyl chlorides tend to be less expensive and more readily available. Alkyl chlorides readily undergo attack by nucleophiles.Sony VAIO VGN-NR160E/T Battery

Heating alkyl halides with sodium hydroxide or water gives alcohols. Reaction with alkoxides or aroxides give ethers in the Williamson ether synthesis; reaction withthiols give thioethers. Alkyl chlorides readily react with amines to give substituted amines. Sony VAIO VGN-NR160E/W Battery

Alkyl chlorides are substituted by softer halides such as the iodide in the Finkelstein reaction. Reaction with other pseudohalides such as azide, cyanide, and thiocyanate are possible as well. In the presence of a strong base, alkyl chlorides undergo dehydrohalogenation to give alkenes or alkynes.Sony VAIO VGN-NR180E/S Battery

Alkyl chlorides react with magnesium to give Grignard reagents, transforming an electrophilic compound into a nucleophilic compound. The Wurtz reaction reductively couples two alkyl halides to couple with sodium.

Vinyl chloride

The largest application of organochlorine chemistry is the production of vinyl chloride. The annual production in 1985 was around 13 billion kilograms, almost all of which was converted into polyvinylchloride (PVC).Sony VAIO VGN-NR180E/T Battery

Chloromethanes

Most low molecular weight chlorinated hydrocarbons such as chloroform, dichloromethane, dichloroethene, and trichloroethane are useful solvents. These solvents tend to be relatively non-polar; they are therefore immiscible with water and effective in cleaning applications such as degreasing and dry cleaning. Sony VAIO VGN-NR290E/S Battery

Several billion kilograms of chlorinated methanes are produced annually, mainly by chlorination of methane:

CH4 + x Cl2 ? CH4-xClx + x HCl

The most important is dichloromethane, which is mainly used as a solvent. Chloromethane is a precursor to chlorosilanes and silicones. Sony VAIO VGN-NR290E/T Battery

Historically significant, but smaller in scale is chloroform, mainly a precursor to chlorodifluoromethane (CHClF2) and tetrafluoroethene which is used in the manufacture of Teflon.

Pesticides

Many pesticides contain chlorine. Notable examples include DDT, dicofol, heptachlor, endosulfan, chlordane, aldrin, dieldrin, endrin, mirex, and pentachlorophenol.Sony VAIO VGN-NR298E/S Battery

These can be either hydrophilic or hydrophobic depending on their molecular structure. Many of these agents have been banned in various countries, e.g. mirex, aldrin.

Insulators

Polychlorinated biphenyls (PCBs) were once commonly used electrical insulators and heat transfer agents. Sony VAIO VGN-NR460E/L Battery

Their use has generally been phased out due to health concerns. PCBs were replaced by polybrominated diphenyl ethers (PBDEs), which bring similar toxicity and bioaccumulation concerns.

Toxicity

Some types of organochlorides have significant toxicity to plants or animals, including humans. Sony VAIO VGN-NR460E/P Battery

Dioxins, produced when organic matter is burned in the presence of chlorine, and some insecticides such as DDT are persistent organic pollutants which pose dangers when they are released into the environment. For example, DDT, which was widely used to control insects in the mid 20th century, also accumulates in food chains, and causes reproductive problems (i.e., eggshell thinning) in certain bird species. Sony VAIO VGN-NR498E/L Battery

When chlorinated solvents, such as carbon tetrachloride, are not disposed of properly, they accumulate in groundwater. Some highly reactive organochlorides such asphosgene have even been used as chemical warfare agents.

However, the presence of chlorine in an organic compound does not ensure toxicity. Sony VAIO VGN-NR498E/S Battery

Many organochlorides are safe enough for consumption in foods and medicines. For example, peas and broad beans contain the natural chlorinated plant hormone 4-chloroindole-3-acetic acid (4-Cl-IAA); and the sweetener sucralose (Splenda) is widely used in diet products. Sony VAIO VGN-NR498E/T Battery

As of 2004, there were at least 165 organochlorides approved worldwide for use as pharmaceutical drugs, including the natural antibiotic vancomycin, the antihistamine loratadine (Claritin), the antidepressant sertraline (Zoloft), the anti-epileptic lamotrigine (Lamictal), and the inhalation anesthetic isoflurane.Sony VAIO VGN-NR498E/W Battery

Rachel Carson brought the issue of DDT pesticide toxicity to public awareness with her 1962 book Silent Spring. While many countries have phased out the use of some types of organochlorides such as the US ban on DDT, persistent DDT, PCBs, and other organochloride residues continue to be found in humans and mammals across the planet many years after production and use have been limited. In Arctic areas, particularly high levels are found in marine mammals. Sony VAIO VGN-NR50 Battery

These chemicals concentrate in mammals, and are even found in human breast milk. Males typically have far higher levels, as females reduce their concentration by transfer to their offspring through breast feeding.

Chlorine dioxide is a chemical compound with the formula ClO2. This yellowish-green gas crystallizes as bright orange crystals at ?59 °C. Sony VAIO VGN-NR50B Battery

As one of several oxides of chlorine, it is a potent and useful oxidizing agent used in water treatment and in bleaching.

The molecule ClO2 has an odd number of valence electrons and it is therefore aparamagnetic radical. Its electronic structure has baffled chemists for a long time because none of the possible Lewis structures are very satisfactory. Sony VAIO VGN-NR51 Battery

In 1933 L.O. Brockway proposed a structure that involved a three-electron bond. Chemist Linus Pauling further developed this idea and arrived at two resonance structures involving a double bond on one side and a single bond plus three-electron bond on the other.Sony VAIO VGN-NR51B Battery

In Pauling's view the latter combination should represent a bond that is slightly weaker than the double bond. In molecular orbital theory this idea is commonplace if the third electron is placed in an anti-bonding orbital. Later work has confirmed that the HOMO is indeed an incompletely-filled orbital.Sony VAIO VGN-NR52 Battery

Preparation

Chlorine dioxide is a highly endothermic compound that can decompose extremely violently when separated from diluting substances. As a result, preparation methods that involve producing solutions of it without going through a gas phase stage are often preferred. Arranging handling in a safe manner is essential.Sony VAIO VGN-NR52B Battery

In the laboratory, ClO2 is prepared by oxidation of sodium chlorite:

2 NaClO2 + Cl2 ? 2 ClO2 + 2 NaCl

Over 95% of the chlorine dioxide produced in the world today is made from sodium chlorate and is used for pulp bleaching. Sony VAIO VGN-NR71B Battery

It is produced with high efficiency by reducing sodium chlorate in a strong acid solution with a suitable reducing agent such asmethanol, hydrogen peroxide, hydrochloric acid or sulfur dioxide. Modern technologies are based on methanol or hydrogen peroxide, as these chemistries allows the best economy and does not co-produce elemental chlorine. Sony VAIO VGN-NR71B2 Battery

The overall reaction can be written;

Chlorate + Acid + reducing agent ? Chlorine Dioxide + By-products

The reaction of sodium chlorate with hydrochloric acid in a single reactor is believed to proceed via the following pathway:Sony VAIO VGN-NR72B Battery

HClO3 + HCl ? HClO2 + HOCl

HClO3 + HClO2 ? 2 ClO2 + Cl2 + 2 H2O

HOCl + HCl ? Cl2 + H2O

The commercially more important production route uses methanol as the reducing agent and sulfuric acid for the acidity. Sony VAIO VGN-NS10E/S Battery

Two advantages by not using the chloride-based processes are that there is no formation of elemental chlorine , and that sodium sulfate, a valuable chemical for the pulp mill, is a side-product. These methanol-based processes provide high efficiency and can be made very safe.Sony VAIO VGN-NS10J/S Battery

A much smaller, but important, market for chlorine dioxide is for use as a disinfectant. Since 1999 a growing proportion of the chlorine dioxide made globally for water treatment and other small scale applications has been made using the chlorate, hydrogen peroxide and sulfuric acid method which can produce a chlorine free product at high efficiency. Sony VAIO VGN-NS10L/S Battery

Traditionally, chlorine dioxide for disinfection applications has been made by one of three methods using sodium chlorite or the sodium chlorite - hypochlorite method:

2 NaClO2 + 2 HCl + NaOCl ? 2 ClO2 + 3 NaCl + H2O

or the sodium chlorite - hydrochloric acid method:Sony VAIO VGN-NS110E/L Battery

5 NaClO2 + 4 HCl ? 5 NaCl + 4 ClO2 + 2 H2O

All three sodium chlorite chemistries can produce chlorine dioxide with high chlorite conversion yield, but unlike the other processes the chlorite-HCl method produces completely chlorine free chlorine dioxide but suffers from the requirement of 25% more chlorite to produce an equivalent amount of chlorine dioxide. Sony VAIO VGN-NS110E/S Battery

Alternatively, hydrogen peroxide may efficiently be used also in small scale applications.

Very pure chlorine dioxide can also be produced by electrolysis of a chlorite solution:

2 NaClO2 + 2 H2O ? 2 ClO2 + 2 NaOH + H2

High purity chlorine dioxide gas (7.7% in air or nitrogen) can be produced by the Gas:Solid method, which reacts dilute chlorine gas with solid sodium chlorite.Sony VAIO VGN-NS110E/W Battery

2 NaClO2 + Cl2 ? 2 ClO2 + 2 NaCl

These processes and several slight variations have been reviewed.

Handling properties

At gas phase concentrations greater than 30% volume in air at STP (more correctly: at partial pressures above 10 kPa [7]), ClO2 may explosively decompose into chlorine and oxygen. Sony VAIO VGN-NS115N/S Battery

The decomposition can be initiated by, for example, light, hot spots, chemical reaction, or pressure shock. Thus, chlorine dioxide gas is never handled in concentrated form, but is almost always handled as a dissolved gas in water in a concentration range of 0.5 to 10 grams per liter. Sony VAIO VGN-NS11ER/S Battery

Its solubility increases at lower temperatures: it is thus common to use chilled water (5 °C or 41 °F) when storing at concentrations above 3 grams per liter. In many countries, such as the USA, chlorine dioxide gas may not be transported at any concentration and is almost always produced at the application site using a chlorine dioxide generator.Sony VAIO VGN-NS11E/S Battery

In some countries, chlorine dioxide solution below 3 grams per liter in concentration may be transported by land, but are relatively unstable and deteriorate quickly. The use of chlorine dioxide generators is steadily falling out of fashion in industry as these systems generally require the use of strong acids to work and can take several hours to reach their full yield with poor efficiency.Sony VAIO VGN-NS11J/S Battery

The requirement to store the hazardous gas in a pressurized chamber poses a risk some sites prefer not to take. Newer dosing systems have proven to provide a safer alternative producing ClO2 in solution and offering a huge leap in efficiency converting around 95% instantly only requiring the use of weak FDA approved acids offering a much safer method of producing ClO2 as there is no storage which proves a more effective Chlorine Dioxide Water Treatment. Sony VAIO VGN-NS11L/S Battery

Uses

Chlorine dioxide is used primarily (>95%) for bleaching of wood pulp, but is also used for the bleaching of flour and for the disinfection of municipal drinking water.  The Niagara Falls, New York water treatment plant first used chlorine dioxide for drinking water treatment in 1944 for phenoldestruction.Sony VAIO VGN-NS11MR/S Battery

Chlorine dioxide was introduced as a drinking water disinfectant on a large scale in 1956, when Brussels, Belgium, changed from chlorine to chlorine dioxide.[12] Its most common use in water treatment is as a pre-oxidant prior to chlorination of drinking water to destroy natural water impurities that produce trihalomethanes on exposure to free chlorine.Sony VAIO VGN-NS11M/S Battery

Trihalomethanes are suspect carcinogenic disinfection by-products associated with chlorination of naturally occurring organics in the raw water. Chlorine dioxide is also superior to chlorine when operating above pH 7, in the presence of ammonia and amines  and/or for the control of biofilms in water distribution systems.Sony VAIO VGN-NS11SR/S Battery

Chlorine dioxide is used in many industrial water treatment applications as a biocide including cooling towers, process water and food processing.

Chlorine dioxide is less corrosive than chlorine and superior for the control of legionella bacteria.Sony VAIO VGN-NS11S/S Battery

Chlorine dioxide is superior to some other secondary water disinfection methods in that chlorine dioxide: 1) is an EPA registered biocide, 2) is not negatively impacted by pH 3) does not lose efficacy over time (the bacteria will not grow resistant to it) and 4) is not negatively impacted by silica and phosphate, which are commonly used potable water corrosion inhibitors.Sony VAIO VGN-NS11ZR/S Battery

Some unscrupulous biocide manufacturers will state that their product is EPA registered as a biocide. All EPA registered biocides must have a product label that is supplied with the product. This label will contain specifications as far as the product's EPA registration. Sony VAIO VGN-NS11Z/S Battery

EPA will register certain products as a general biocide, but others will have specifications for what bacteria the product can protect against. For instance, although chlorine dioxide is a registered biocide, it is not registered to protect against Legionella. If a biocide is sold without an EPA approved biocide label that is because the product is not registered as an EPA approved biocide.Sony VAIO VGN-NS12M/S Battery

It is more effective as a disinfectant than chlorine in most circumstances against water borne pathogenic microbes such as viruses, bacteria and protozoa – including the cysts of Giardia and the oocysts of Cryptosporidium.

The use of chlorine dioxide in water treatment leads to the formation of the by-product chlorite which is currently limited to a maximum of 1 ppm in drinking water in the USA.Sony VAIO VGN-NS12M/W Battery

This EPA standard limits the use of chlorine dioxide in the USA to relatively high quality water or water which is to be treated with iron based coagulants (Iron can reduce chlorite to chloride).

It can also be used for air disinfection,  and was the principal agent used in the decontamination of buildings in the United States after the 2001 anthrax attacks.Sony VAIO VGN-NS12S/S Battery

After the disaster of Hurricane Katrina in New Orleans, Louisiana and the surrounding Gulf Coast, chlorine dioxide has been used to eradicate dangerousmold from houses inundated by the flood-water.

Chlorine dioxide is used as an oxidant for phenol destruction in waste water streams, control of zebra and quagga mussels in water intakes and for odor control in the air scrubbers of animal byproduct (rendering) plants.Sony VAIO VGN-NS21M/P Battery

"Stabilized chlorine dioxide" is used in an oral rinse to treat oral disease and malodor. This term is a misnomer, referring simply to sodium chlorite, not chlorine dioxide.

Safety

On July 30, 2010 and again on October 1, 2010, the United States Food and Drug Administration warned against the use of the product "Miracle Mineral Supplement" or "MMS", Sony VAIO VGN-NS21M/W Battery

which when made up according to instructions produces chlorine dioxide. MMS has been marketed as a treatment for a variety of conditions, including HIV, cancer, and acne. The FDA warning informed consumers that this industrial bleach can cause serious harm to health, including severe dehydration, nausea and diarrhea.Sony VAIO VGN-NS21S/S Battery

There have been no reported deaths from use of MMS; however the FDA has received numerous reports of nausea, severe vomiting, and life-threatening low blood pressure caused by dehydration.

Polymer degradation is a change in the properties—tensile strength, colour, shape, etc.—of a polymer or polymer-based product under the influence of one or more environmental factors such as heat, light or chemicals such as acids, alkalis and some salts. Sony VAIO VGN-NS21S/W Battery

These changes are usually undesirable, such as cracking and chemical disintegration of products or, more rarely, desirable, as in biodegradation, or deliberately lowering the molecular weight of a polymer for recycling. The changes in properties are often termed "aging".Sony VAIO VGN-NS21Z/S Battery

In a finished product such a change is to be prevented or delayed. Degradation can be useful for recycling/reusing the polymer waste to prevent or reduce environmental pollution. Degradation can also be induced deliberately to assist structure determination.

Polymeric molecules are very large (on the molecular scale), and their unique and useful properties are mainly a result of their size. Any loss in chain length lowers tensile strength and is a primary cause of premature cracking.Sony VAIO VGN-NS31M/P Battery

Commodity polymers

Today there are primarily seven commodity polymers in use: polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate or PET, polystyrene,polycarbonate, and poly(methyl methacrylate) (Plexiglass). These make up nearly 98% of all polymers and plastics encountered in daily life. Sony VAIO VGN-NS31M/W Battery

Each of these polymers has its own characteristic modes of degradation and resistances to heat, light and chemicals. Polyethylene, polypropylene, and poly(methyl methacrylate) are sensitive to oxidation and UV radiation, while PVC may discolour at high temperatures due to loss of hydrogen chloride gas, and become very brittle. Sony VAIO VGN-NS31S/S Battery

PET is sensitive to hydrolysis and attack by strong acids, while polycarbonate depolymerizes rapidly when exposed to strong alkalis.

For example, polyethylene usually degrades by random scission - that is by a random breakage of the linkages (bonds) that hold the atoms of the polymer together.Sony VAIO VGN-NS31Z/P Battery

When this polymer is heated above 450 Celsius it becomes a complex mixture of molecules of various sizes that resemble gasoline. Other polymers - like polyalphamethylstyrene - undergo 'unspecific' chain scission with breakage occurring only at the ends; they literally unzip or depolymerize to become the constituentmonomers.Sony VAIO VGN-NS31Z/S Battery

Solvolysis

Step-growth polymers like polyesters, polyamides and polycarbonates can be degraded by solvolysis and mainly hydrolysis to give lower molecular weight molecules. The hydrolysis takes place in the presence of water containing an acid or a base as catalyst.Sony VAIO VGN-NS31Z/W Battery

Polyamide is sensitive to degradation by acids and polyamide mouldings will crack when attacked by strong acids. For example, the fracture surface of a fuel connector showed the progressive growth of the crack from acid attack (Ch) to the final cusp (C) of polymer. The problem is known as stress corrosion cracking, and in this case was caused by hydrolysis of the polymer.Sony VAIO VGN-NS38M/P Battery

Cracks can be formed in many different elastomers by ozone attack. Tiny traces of the gas in the air will attack double bonds in rubber chains, with Natural rubber, polybutadiene, Styrene-butadiene rubber and NBR being most sensitive to degradation. Ozone cracks form in products under tension, but the critical strain is very small. Sony VAIO VGN-NS38M/W Battery

The cracks are always oriented at right angles to the strain axis, so will form around the circumference in a rubber tube bent over. Such cracks are dangerous when they occur in fuel pipes because the cracks will grow from the outside exposed surfaces into the bore of the pipe, and fuel leakage and fire may follow. Sony VAIO VGN-NS130E/L Battery

The problem of ozone cracking can be prevented by adding anti-ozonants to the rubber before vulcanization. Ozone cracks were commonly seen in automobile tire sidewalls, but are now seen rarely thanks to these additives. On the other hand, the problem does recur in unprotected products such as rubber tubing and seals.Sony VAIO VGN-NS130E/S Battery

Oxidation

Polymers are susceptible to attack by atmospheric oxygen, especially at elevated temperatures encountered during processing to shape. Many process methods such as extrusion and injection moulding involve pumping molten polymer into tools, and the high temperatures needed for melting may result in oxidation unless precautions are taken. Sony VAIO VGN-NS130E/W Battery

For example, a forearm crutch suddenly snapped and the user was severely injured in the resulting fall. The crutch had fractured across a polypropylene insert within the aluminium tube of the device, and infra-red spectroscopy of the material showed that it had oxidised, possible as a result of poor moulding.Sony VAIO VGN-NS140E/L Battery

Oxidation is usually relatively easy to detect owing to the strong absorption by the carbonyl group in the spectrum of polyolefins.Polypropylene has a relatively simple spectrum with few peaks at the carbonyl position (like polyethylene). Sony VAIO VGN-NS140E/S Battery

Oxidation tends to start at tertiary carbon atoms because the free radicals formed here are more stable and longer lasting, making them more susceptible to attack by oxygen. The carbonyl group can be further oxidised to break the chain, this weakens the material by lowering its molecular weight, and cracks start to grow in the regions affected.Sony VAIO VGN-NS140E/W Battery

Galvanic action

Polymer degradation by galvanic action was first described in the technical literature in 1990.  This was the discovery that "plastics can corrode", i.e. polymer degradation may occur through galvanic action similar to that of metals under certain conditions.Sony VAIO VGN-NS190J/L Battery

Normally, when two dissimilar metals such as copper (Cu) and iron (Fe) are put into contact and then immersed in salt water, the iron will undergo corrosion, or rust. This is called a galvanic circuit where the copper is the noble metal and the iron is the active metal, i.e., the copper is the cathode or positive (+) electrode and the iron is the anode, or negative (-) electrode. Sony VAIO VGN-NS190J/S Battery

A battery is formed. It follows that plastics are made stronger by impregnating them with thin carbon fibers only a few micrometers in diameter known as carbon fiber reinforced polymers (CFRP). This is to produce materials that are high strength and resistant to high temperatures.Sony VAIO VGN-NS190J/W Battery

The carbon fibers act as a noble metal similar to gold (Au) or platinum (Pt). When put into contact with a more active metal, for example with aluminum (Al) in salt water the aluminum corrodes. However in early 1990, it was reported that imide-linked resins in CFRP composites degrade when bare composite is coupled with an active metal in salt water environments. Sony VAIO VGN-NS235J/L Battery

This is because corrosion not only occurs at the aluminum anode, but also at the carbon fiber cathode in the form of a very stron

g base with a pH of about 13. This strong base reacts with the polymer chain structure degrading the polymer. Polymers affected include bismaleimides (BMI), condensation polyimides, triazines, and blends thereof.Sony VAIO VGN-NS235J/P Battery

Degradation occurs in the form of dissolved resin and loose fibers. The hydroxyl ions generated at the graphite cathode attack the O-C-N bond in the polyimide structure. Standard corrosion protection procedures were found to prevent polymer degradation under most conditions.Sony VAIO VGN-NS235J/S Battery

Chlorine-induced cracking

Another highly reactive gas is chlorine, which will attack susceptible polymers such as acetal resin and polybutylene pipework. There have been many examples of such pipes and acetal fittings failing in properties in the US as a result of chlorine-induced cracking. Sony VAIO VGN-NS235J/W Battery

In essence, the gas attacks sensitive parts of the chain molecules (especially secondary, tertiary, or allylic carbon atoms), oxidizing the chains and ultimately causing chain cleavage. The root cause is traces of chlorine in the water supply, added for its anti-bacterial action, attack occurring even at parts per million traces of the dissolved gas. Sony VAIO VGN-NS240E/L Battery

The chlorine attacks weak parts of a product, and in the case of an acetal resin junction in a water supply system, it is the thread roots that were attacked first, causing a brittle crack to grow. Discolouration on the fracture surface was caused by deposition of carbonates from the hard water supply, so the joint had been in a critical state for many months. Sony VAIO VGN-NS290J/L Battery

The problems in the US also occurred to polybutylenepipework, and led to the material being removed from that market, although it is still used elsewhere in the world.

Biological degradation

Biodegradable plastics can be biologically degraded by microorganisms to give lower molecular weight molecules.Sony VAIO VGN-NS290J/S Battery

To degrade properly biodegradable polymers need to be treated like compost and not just left in a landfill site where degradation is very difficult due to the lack of oxygen and moisture.

Hindered amine light stabilisers (HALS) stabilise against weathering by scavenging free radicals that are produced by photo-oxidation of the polymer matrix. Sony VAIO VGN-NS50B/L Battery

UV-absorbers stabilises against weathering by absorbing ultraviolet light and converting it into heat. Antioxidants stabilize the polymer by terminating the chain reaction due to the absorption of UV light from sunlight. Sony VAIO VGN-NS50B/W Battery

The chain reaction initiated by photo-oxidation leads to cessation of crosslinking of the polymers and degradation the property of polymers.Sony VAIO VGN-NS51B/L Battery,Sony VAIO VGN-NS51B/P Battery,Sony VAIO VGN-NS51B/W Battery,Sony VAIO VGN-NS52JB/L Battery,Sony VAIO VGN-NS52JB/P Battery,Sony VAIO VGN-NS52JB/W Battery,Sony VAIO VGN-NS70B/W Battery,Sony VAIO VGN-NS71B/W Battery,Sony VAIO VGN-NS72JB/W Battery,Sony VAIO VGN-NS90HS Battery,Sony VAIO VGN-NS92JS Battery,Sony VAIO VGN-NS92XS Battery

Partager cet article

Repost 0
Published by batterys - dans Laptop Battery
commenter cet article

commentaires