How Does chlorine dioxide liquid Work?
Chlorine dioxide - Wikipedia
- Chlorine dioxide
- Chlorine(IV) oxide
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- InChI=1S/ClO2/c2-1-3 YKey: OSVXSBDYLRYLIG-UHFFFAOYSA-N Y
- InChI=1/ClO2/c2-1-3Key: OSVXSBDYLRYLIG-UHFFFAOYAC
- O=[Cl]=O
- O=Cl[O]
constant (kH) 4.01×10−2 atm m3 mol−1 Acidity (pKa) 3.0(5) Thermochemistry Std molar
entropy (S⦵298) 257.22 J K−1 mol−1 Std enthalpy of
formation (ΔfH⦵298) 104.60 kJ/mol Hazards Occupational safety and health (OHS/OSH): Main hazards Highly toxic, corrosive, unstable, powerful oxidizer GHS labelling: Danger H271, H300+H310+H330, H314, H372 P210, P220, P260, P264, P271, P280, P283, P284, P301+P310, P304+P340, P305+P351+P338, P306+P360, P371+P380+P375, P403+P233, P405, P501 NFPA 704 (fire diamond) Lethal dose or concentration (LD, LC): LD50 (median dose) 94 mg/kg (oral, rat)[4] LCLo (lowest published) 260 ppm (rat, 2 hr)[5] NIOSH (US health exposure limits): PEL (Permissible) TWA 0.1 ppm (0.3 mg/m3)[3] REL (Recommended) TWA 0.1 ppm (0.3 mg/m3) ST 0.3 ppm (0.9 mg/m3)[3] IDLH (Immediate danger) 5 ppm[3] Safety data sheet (SDS) Safety Data Sheet Archive. Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y (what is YN ?) Chemical compound
Chlorine dioxide is a chemical compound with the formula ClO2 that exists as yellowish-green gas above 11 °C, a reddish-brown liquid between 11 °C and −59 °C, and as bright orange crystals below −59 °C. It is usually handled as an aqueous solution. It is commonly used as a bleach. More recent developments have extended its applications in food processing and as a disinfectant.
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Structure and bonding
[edit]The molecule ClO2 has an odd number of valence electrons, and therefore it is a paramagnetic radical. It is an unusual "example of an odd-electron molecule stable toward dimerization" (nitric oxide being another example).[6]
ClO2 crystallizes in the orthorhombic Pbca space group.[7]
History
[edit]Chlorine dioxide was first prepared in by Sir Humphry Davy.[8]
In , Lawrence O. Brockway, a graduate student of Linus Pauling, proposed a structure that involved a three-electron bond and two single bonds.[9] However, Pauling in his General Chemistry shows a double bond to one oxygen and a single bond plus a three-electron bond to the other. The valence bond structure would be represented as the resonance hybrid depicted by Pauling.[10] The three-electron bond represents a bond that is weaker than the double bond. In molecular orbital theory this idea is commonplace if the third electron occupies an anti-bonding orbital. Later work has confirmed that the highest occupied molecular orbital is indeed an incompletely filled antibonding orbital.[11]
Preparation
[edit]The reaction of chlorine with oxygen under conditions of flash photolysis in the presence of ultraviolet light results in trace amounts of chlorine dioxide formation.[12]
- Cl2 + 2 O2 → UV {\displaystyle {\ce {->[{\ce {UV}}]}}} 2 ClO2 ↑
Chlorine dioxide can decompose 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.
Oxidation of chlorite
[edit]In the laboratory, ClO2 can be prepared by oxidation of sodium chlorite with chlorine:[13]
NaClO2 + 1⁄2 Cl2 → ClO2 + NaClTraditionally, chlorine dioxide for disinfection applications has been made from sodium chlorite or the sodium chlorite–hypochlorite method:
2 NaClO2 + 2 HCl + NaOCl → 2 ClO2 + 3 NaCl + H2Oor the sodium chlorite–hydrochloric acid method:
5 NaClO2 + 4 HCl → 5 NaCl + 4 ClO2 + 2 H2Oor the chlorite–sulfuric acid method:
4 ClO−2 + 2 H2SO4 → 2 ClO2 + HClO3 + 2 SO2−4 + H2O + HClAll three methods can produce chlorine dioxide with high chlorite conversion yield. Unlike the other processes, the chlorite–sulfuric acid method is completely chlorine-free, although it suffers from the requirement of 25% more chlorite to produce an equivalent amount of chlorine dioxide. Alternatively, hydrogen peroxide may be efficiently used in small-scale applications.[1]
Addition of sulfuric acid or any strong acid to chlorate salts produces chlorine dioxide.[10]
Reduction of chlorate
[edit]In the laboratory, chlorine dioxide can also be prepared by reaction of potassium chlorate with oxalic acid:
KClO3 + H2C2O4 → 1⁄2 K2C2O4 + ClO2 + CO2 + H2Oor with oxalic and sulfuric acid:
KClO3 + 1⁄2 H2C2O4 + H2SO4 → KHSO4 + ClO2 + CO2 + H2OOver 95% of the chlorine dioxide produced in the world today is made by reduction of sodium chlorate, for use in pulp bleaching. It is produced with high efficiency in a strong acid solution with a suitable reducing agent such as methanol, hydrogen peroxide, hydrochloric acid or sulfur dioxide.[1] Modern technologies are based on methanol or hydrogen peroxide, as these chemistries allow the best economy and do not co-produce elemental chlorine. The overall reaction can be written as:[14]
chlorate + acid + reducing agent → chlorine dioxide + by-productsAs a typical example, the reaction of sodium chlorate with hydrochloric acid in a single reactor is believed to proceed through the following pathway:
ClO−3 + Cl− + H+ → ClO−2 + HOCl ClO−3 + ClO−2 + 2 H+ → 2 ClO2 + H2O HOCl + Cl− + H+ → Cl2 + H2Owhich gives the overall reaction
ClO−3 + Cl− + 2 H+ → ClO2 + 1⁄2 Cl2 + H2O.The commercially more important production route uses methanol as the reducing agent and sulfuric acid for the acidity. Two advantages of 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.[1]
The variant process using sodium chlorate, hydrogen peroxide and sulfuric acid has been increasingly used since for water treatment and other small-scale disinfection applications, since it produce a chlorine-free product at high efficiency, over 95%.[citation needed]
Other processes
[edit]Very pure chlorine dioxide can also be produced by electrolysis of a chlorite solution:[15]
NaClO2 + H2O → ClO2 + NaOH + 1⁄2 H2High-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:[15]
NaClO2 + 1⁄2 Cl2 → ClO2 + NaClHandling properties
[edit]Chlorine dioxide is very different from elemental chlorine.[1] One of the most important qualities of chlorine dioxide is its high water solubility, especially in cold water. Chlorine dioxide does not react with water; it remains a dissolved gas in solution. Chlorine dioxide is approximately 10 times more soluble in water than elemental chlorine[1] but its solubility is very temperature-dependent.
At partial pressures above 10 kPa (1.5 psi)[1] (or gas-phase concentrations greater than 10% volume in air at STP) of ClO2 may explosively decompose into chlorine and oxygen. The decomposition can be initiated by light, hot spots, chemical reaction, or pressure shock. Thus, chlorine dioxide is never handled as a pure gas, but is almost always handled in an aqueous solution in concentrations between 0.5 and 10 grams per liter. Its solubility increases at lower temperatures, so it is common to use chilled water (5 °C, 41 °F) when storing at concentrations above 3 grams per liter. In many countries, such as the United States, chlorine dioxide may not be transported at any concentration and is instead almost always produced on-site.[1] In some countries,[which?] chlorine dioxide solutions below 3 grams per liter in concentration may be transported by land, but they are relatively unstable and deteriorate quickly.
Uses
[edit]Chlorine dioxide is used for bleaching of wood pulp and for the disinfection (called chlorination) of municipal drinking water,[16][17]: 4–1 [18] treatment of water in oil and gas applications, disinfection in the food industry, microbiological control in cooling towers, and textile bleaching.[19] As a disinfectant, it is effective even at low concentrations because of its unique qualities.[1][17][19]
Bleaching
[edit]Chlorine dioxide is sometimes used for bleaching of wood pulp in combination with chlorine, but it is used alone in ECF (elemental chlorine-free) bleaching sequences. It is used at moderately acidic pH (3.5 to 6). The use of chlorine dioxide minimizes the amount of organochlorine compounds produced.[20] Chlorine dioxide (ECF technology) currently is the most important bleaching method worldwide. About 95% of all bleached kraft pulp is made using chlorine dioxide in ECF bleaching sequences.[21]
Chlorine dioxide has been used to bleach flour.[22]
Water treatment
[edit]The water treatment plant at Niagara Falls, New York first used chlorine dioxide for drinking water treatment in for destroying "taste and odor producing phenolic compounds."[17]: 4–17 [18] Chlorine dioxide was introduced as a drinking water disinfectant on a large scale in , when Brussels, Belgium, changed from chlorine to chlorine dioxide.[18] Its most common use in water treatment is as a pre-oxidant prior to chlorination of drinking water to destroy natural water impurities that would otherwise produce trihalomethanes upon exposure to free chlorine.[23][24][25] Trihalomethanes are suspected carcinogenic disinfection by-products[26] associated with chlorination of naturally occurring organics in raw water.[25] Chlorine dioxide also produces 70% fewer halomethanes in the presence of natural organic matter compared to when elemental chlorine or bleach is used.[27]
Chlorine dioxide is also superior to chlorine when operating above pH 7,[17]: 4–33 in the presence of ammonia and amines,[28] and for the control of biofilms in water distribution systems.[25] Chlorine dioxide is used in many industrial water treatment applications as a biocide, including cooling towers, process water, and food processing.[29]
Chlorine dioxide is less corrosive than chlorine and superior for the control of Legionella bacteria.[18][30] Chlorine dioxide is superior to some other secondary water disinfection methods, in that chlorine dioxide is not negatively impacted by pH, does not lose efficacy over time, because the bacteria will not grow resistant to it, and is not negatively impacted by silica and phosphates, which are commonly used potable water corrosion inhibitors. In the United States, it is an EPA-registered biocide.
It is more effective as a disinfectant than chlorine in most circumstances against waterborne pathogenic agents such as viruses,[31] bacteria, and protozoa – including the cysts of Giardia and the oocysts of Cryptosporidium.[17]: 4-20–4-21
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 part per million in drinking water in the USA.[17]: 4–33 This EPA standard limits the use of chlorine dioxide in the US to relatively high-quality water, because this minimizes chlorite concentration, or water that is to be treated with iron-based coagulants, because iron can reduce chlorite to chloride.[32] The World Health Organization also advises a 1ppm dosification.[27]
Use in public crises
[edit]Chlorine dioxide has many applications as an oxidizer or disinfectant.[1] Chlorine dioxide can be used for air disinfection[33] and was the principal agent used in the decontamination of buildings in the United States after the anthrax attacks.[34] After the disaster of Hurricane Katrina in New Orleans, Louisiana, and the surrounding Gulf Coast, chlorine dioxide was used to eradicate dangerous mold from houses inundated by the flood water.[35]
In addressing the COVID-19 pandemic, the U.S. Environmental Protection Agency has posted a list of many disinfectants that meet its criteria for use in environmental measures against the causative coronavirus.[36][37] Some are based on sodium chlorite that is activated into chlorine dioxide, though differing formulations are used in each product. Many other products on the EPA list contain sodium hypochlorite, which is similar in name but should not be confused with sodium chlorite because they have very different modes of chemical action.
Other disinfection uses
[edit]Chlorine dioxide may be used as a fumigant treatment to "sanitize" fruits such as blueberries, raspberries, and strawberries that develop molds and yeast.[38]
Chlorine dioxide may be used to disinfect poultry by spraying or immersing it after slaughtering.[39]
Chlorine dioxide may be used for the disinfection of endoscopes, such as under the trade name Tristel.[40] It is also available in a trio consisting of a preceding pre-clean with surfactant and a succeeding rinse with deionized water and a low-level antioxidant.[41]
Chlorine dioxide may be used for control of zebra and quagga mussels in water intakes.[17]: 4–34
Chlorine dioxide was shown to be effective in bedbug eradication.[42]
For water purification during camping, disinfecting tablets containing chlorine dioxide are more effective against pathogens than those using household bleach, but typically cost more.[43][44]
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Other uses
[edit]Chlorine dioxide is used as an oxidant for destroying phenols in wastewater streams and for odor control in the air scrubbers of animal byproduct (rendering) plants.[17]: 4–34 It is also available for use as a deodorant for cars and boats, in chlorine dioxide-generating packages that are activated by water and left in the boat or car overnight.
In dilute concentrations, chlorine dioxide is an ingredient that acts as an antiseptic agent in some mouthwashes.[45][46]
Safety issues in water and supplements
[edit]Potential hazards with chlorine dioxide include poisoning and the risk of spontaneous ignition or explosion on contact with flammable materials.[47][48]
Chlorine dioxide is toxic, and limits on human exposure are required to ensure its safe use. The United States Environmental Protection Agency has set a maximum level of 0.8 mg/L for chlorine dioxide in drinking water.[49] The Occupational Safety and Health Administration (OSHA), an agency of the United States Department of Labor, has set an 8-hour permissible exposure limit of 0.1 ppm in air (0.3 mg/m3) for people working with chlorine dioxide.[50]
Chlorine dioxide has been fraudulently and illegally marketed as an ingestible cure for a wide range of diseases, including childhood autism[51] and coronavirus.[52][53][54] Children who have been given enemas of chlorine dioxide as a supposed cure for childhood autism have suffered life-threatening ailments.[51] The U.S. Food and Drug Administration (FDA) has stated that ingestion or other internal use of chlorine dioxide, outside of supervised oral rinsing using dilute concentrations, has no health benefits of any kind, and it should not be used internally for any reason.[55][56]
Pseudomedicine
[edit] Main article: Miracle Mineral SupplementOn 30 July and 1 October , the United States Food and Drug Administration warned against the use of the product "Miracle Mineral Supplement", or "MMS", which when prepared according to the instructions produces chlorine dioxide. MMS has been marketed as a treatment for a variety of conditions, including HIV, cancer, autism, acne, and, more recently, COVID-19. Many have complained to the FDA, reporting life-threatening reactions,[57] and even death.[58] The FDA has warned consumers that MMS can cause serious harm to health, and stated that it has received numerous reports of nausea, diarrhea, severe vomiting, and life-threatening low blood pressure caused by dehydration.[59][60] This warning was repeated for a third time on 12 August , and a fourth on 8 April , stating that ingesting MMS is just as hazardous as ingesting bleach, and urging consumers not to use them or give these products to their children for any reason, as there is no scientific evidence showing that chlorine dioxide has any beneficial medical properties.[61][56]
References
[edit]How Stabilised Chlorine Dioxide Works
What is Chlorine Dioxide?
Chlorine Dioxide (ClO2) is relied on by multiple industries around the world and in many everyday products to kill germs quickly, effectively, and safely. It is an extremely powerful sanitiser and antimicrobial that has been used for the past century to make public water safe to drink and to help prevent the spread of bacterial infections and disease.
Unlike other sanitisers, ClO2 is especially effective at killing tough germs that have developed a resistance to chlorine. It works by oxidation - reacting to the acid in the cell walls of microorganisms which kills them quickly.
This oxidising process is so powerful that ClO2 has the broadest efficacy against microbial organisms that include bacteria, viruses, protozoa, yeasts, fungi, mycobacteria, and bacterial spores.
Here's how DX50 stabilised Chlorine Dioxide works
Chlorine dioxide acts as an oxidising agent, but it works differently to other oxidisers like chlorine because of its unique chemical behaviour.
It penetrates the cell wall by stealing electrons from the microorganism’s vital structures (cell walls, membranes, organelles, and genetic materials) and reacts with the amino acids in the cytoplasm within the cell. This disrupts the protein function and enzyme action and kills the microorganism.
At low concentrations, ClO2 kills microorganisms even when they are inactive, and because they die so fast the pathogens cannot become resistant. Chlorine dioxide even kills Giardia Lambia and Cryptosporidium, which are highly resistant to other disinfectants including sodium hypochlorite and chlorine.
Importantly, chlorine dioxide is a size selective antimicrobial agent that can rapidly kill microorganisms, but not larger humans and animals. This selectivity isn’t based on the different biochemistry between microbes and humans, but on the difference in size.
A flexible alternative
DX50 Water Treatment is not pH dependent and works most effectively in cold water. DX50 can also break down the protective biofilm surrounding a wide range of pathogens.
Chemical DX50® Chlorine Dioxide Chlorine - Sodium Hypochlorite Killing Power High (2.46) Moderate (1.00) Microbial Range Broad Spectrum: Effective against all Bacteria, E-coli, Virus, mould, Fungi, Algae, and spore formers Less effective against fungi & spore formers. Ineffective against viruses Dose (parts per million) 50 ppm 600ppm Killing Speed Minutes Minutes - Hours Corrosivity Negligible at use concentration High to most metals Optimal Kill Conditions 2 - 11 pH 6.8 - 7.3 pHHow was chlorine dioxide discovered?
Chlorine dioxide is a neutral chemical compound that consists of one chlorine atom and two oxygen atoms. It is a yellowish-green gas that at normal room temperature (above 11oC) is highly soluble, but it doesn’t react with water.
It was discovered in by British chemist Sir Humphrey Davy when he dropped sulfuric acid (an acidic reactor) on to potassium chlorate (the precursor to chlorine dioxide).
At temperatures between 11oC and −59oC the gas turns into a reddish-brown liquid and below −59oC it becomes bright orange crystals. Later experimentation replaced the sulfuric acid with hypochlorous acid to produce chlorine dioxide. As a gas ClO2 is unstable and potentially dangerous if inhaled, so it is normally generated in water solution by using sodium chlorite.
By , sodium chlorite became established as a commercial product for the generation of ClO2. With powerful oxidising, antimicrobial, and bleaching properties interest in ClO2 grew rapidly. Its use spread widely for treating municipal drinking water supplies.
What is chlorine dioxide used for?
In recent years the use of ClO2 has extended considerably for a variety of liquid, gas, and surface treatment applications. This includes disinfecting food processing and equipment, medical and pharmaceutical equipment, agriculture and horticultural environments, premises and vehicles, bio-medical waste, wastewater, mould eradication, microbiological control in cooling towers, air disinfection and odour control, treatment of swimming pools, dental applications, wound cleansing, and more.
The compound is favoured over other disinfectants for treating water because ClO2 is also more effective at reducing unpleasant odours, tastes, and colours, and for removing mould and algae. Plus, it helps to remove iron and manganese from untreated water.
Chlorine dioxide is also used in disaster management. It was used to decontaminate buildings after the anthrax attacks in the US, and to kill mould growing in flooded houses after Hurricane Katrina.
Nowadays, with increasing microbial resistance to traditional chemical disinfectants (such as alcohols and quaternary ammonium compounds), there is growing interest in ClO2 as a strong and effective biocide.
What’s the difference between chlorine and chlorine dioxide?
Many people confuse the term “chlorine dioxide” with a compound that acts like chlorine, which is misleading because chlorine is not in fact the active element.
Chlorine has two chlorine atoms and no oxygen (Cl₂) and works by chlorinating, whereas ClO2 has one chlorine and two oxygen atoms and works by oxidising.
While they’re both oxidisers (electron receivers), ClO2 is very different from elemental chlorine both in its chemical structure and in its behaviour. Firstly, chlorine dioxide doesn’t react (or reacts extremely slowly) with most organic compounds of a living tissue because it is size selective. What this means is it can kill micron-sized organisms fast, but it can’t do much harm to larger organisms like animals or humans, as it is unable to penetrate deeply into their living tissues.
Secondly, ClO2 has more than 2.5 times the oxidation capacity of chlorine, and it kills bacteria, viruses, and protozoa differently via an electron exchange. It can take in five electrons before it is reduced and forms a stable chloride, whereas chlorine can only absorb two electrons.
The organic material selectivity and greater oxidation capacity of ClO2 makes it a stronger oxidative disinfectant than chlorine.
What about residues?
The electron exchange difference also explains why ClO2 does not form chlorinated compounds when it reacts with organic substances.
When exposed to organic matter and sunlight, ClO2 breaks down quickly and leaves minimal to no detectable chemical residues. The only by-products of chlorine dioxide’s oxidising reaction are chlorite and chloride, which at low levels is harmless to humans and animals.
Whereas when chlorine reacts, it not only accepts electrons, it also takes part in addition and substitution reactions; adding one or more chlorine atoms to the substance to form environmentally dangerous chlorinated organics, including potentially carcinogenic residues and trihalomethanes such as chloroform.
As the diagram below shows, while dosing the same concentrations, in heavily polluted water the residual concentration of ClO2 is much higher than the residual concentration of chlorine.
Therefore, disinfecting water with lower doses of ClO2 is not only more efficient and effective at killing bugs than chlorine, but safer for humans, animals, and the environment.
Is chlorine dioxide safe?
Chlorine dioxide rapidly decomposes after use and leaves no harmful by-products.
When applied in recommended doses, chlorine dioxide is safe and does not lead to health risks. The EPA’s maximum concentration for chlorine dioxide in public drinking water is 0.8 milligrams per litre (mg/L) and 1.0 mg/L for chlorite ion.
DX50 Water Treatment solution is known to be effective at an even lower ClO2 concentration of just 0.075 mg/L, which is well within acceptable limits. Applying just 50ml per L of water will safely disinfect a full water tank in just a few hours.
In its concentrate form, however, chlorine dioxide is a hazardous gas and can cause irritation if inhaled. Because it is normally used in a diluted form, and quickly breaks down. Most of us are unlikely to breathe in dangerous levels of ClO2. Similarly, most people will not be exposed to ClO2 or chlorite in amounts large enough to damage the body.
When manufactured with dry ingredients, and at high ppm (parts per million), ClO2 is potentially explosive.
But ClO2 produced as a watery solution at around 4ºC becomes a nonhazardous gaseous diluent, as it does not hydrolyse to any appreciable extent. In this state it is quite stable, and will remain so for some time, but not indefinitely if exposed to air as ClO2 will slowly dissociate into chlorine and oxygen.
To maintain its stability, aqueous ClO2 solutions like DX50 should be stored in a cool, well-sealed and dark area protected from sunlight. It is best used within a year of manufacture.
Contact us to discuss your requirements of Chlorine Dioxide Effervescent Tablet. Our experienced sales team can help you identify the options that best suit your needs.
Benefits of ClO2
- Approved by the Environmental Protection Agency as a primary drinking water disinfectant
- Five electrons produce higher oxidation capacity than chlorine
- It is highly soluble in water even in cold water - up to ten times more so than chlorine.
- Inactivates microorganisms over a broad pH range
- Superior germicidal properties
- Chlorine dioxide has the broadest efficacy against microbial organisms such as bacteria, viruses, protozoa, yeasts, fungi, mycobacteria, and bacterial spores
- Unlike other disinfectants, ClO2 is even effective against Cryptosporidium and Giardia
- Microorganisms cannot develop resistance to ClO2
- Can also be applied when a large amount of organic matter is present.
- Excellent residual disinfection action and biofilm control.
- Chlorite is the main disinfection by product of ClO2 which quickly reduces to form harmless chloride.
- Does not form chloramines and chlorogenic compounds as toxic by-products. Unlike ozone, chlorine dioxide does not oxidise bromide ions into bromate ions, which are known carcinogens. Nor does it produce large amounts of aldehydes and ketones.
- Chlorine dioxide improves water taste and odour
- It is more potent than equivalent doses of chlorine
- It destroys sulphides, cyanides, and phenols, controls algae, and neutralises iron and manganese ions
- Less chlorine dioxide is needed to obtain an active residual disinfectant than other disinfectants such as chlorine and ozone
- Less affected by nitrogenous wastes