1. Physical and chemical properties of chlorine dioxide

Chlorine dioxide is a yellow-green or orange-red gas at room temperature, with a pungent odor similar to chlorine, and is a dark red liquid when cooled to -40 °C, and an orange-yellow solid when cooled to -59 °C.

Chemical formula:_CLO2, there are two isomers OCLO and CLOO, the former is stable, and the latter is easy to decompose. Molar mass: 67.45 Melting Point: -59 °C Boiling Point: 11 °C Specific gravity: 2.4 (air 1.0) Heat of formation: 104.6KJ/moL

 

2. Solubility of chlorine dioxide

Chlorine dioxide is easily soluble in water, and the solubility of chlorine dioxide in water is 2.9 g/L at 20 °C and 30 mmHg partial pressure. The solubility of chlorine dioxide in water is 11.5 g/L at 5 °C and 60 mmHg partial pressure. When dissolved, a yellow-green solution is formed, and chlorine dioxide exists in water as a stable chlorine dioxide molecule, unlike other chlorine-containing disinfectants that produce hypochlorous acid in water.

3. Chlorine dioxide is explosive

Chlorine dioxide is explosive when the concentration in water exceeds 10% or the volume concentration in air exceeds 10%, and when it explodes, it decomposes into chlorine and oxygen, and at the same time releases heat. Wang Xiuli's master's thesis from North University of China studied the explosion characteristics of gas chlorine dioxide, and the conclusion was that the lower explosion limit of gas chlorine dioxide was 9.5% (volume percentage), and there was no upper explosion limit. When the concentration of gas chlorine dioxide is 90%, the maximum explosion pressure is 0.6406MPa, and the explosion pressure is different with the increase of gas chlorine dioxide concentration, and the time for the maximum explosion pressure to occur is shorter and shorter with the increase of gas chlorine dioxide concentration. It is said that chlorine dioxide can decompose at 30 °C and may decompose explosively at 50 °C. Personal experience: In the presence of organic matter, the chlorine dioxide explosion intensifies.

4. Chlorine dioxide toxicity

Concentration mg/m3	Effect
15	Irritation of the respiratory organs
51	The smell is very pronounced
135	It causes damage to the eyes and throat and irritates coughing
450	Animals died in 40 minutes
1050	Animals die quickly

The U.S. Institute of Occupational Health and Safety has set an 8-hour weighted average limit of 0.3 mg/m³ for chlorine dioxide. When we disinfect the air with gas chlorine dioxide, the upper limit of the spatial concentration should be less than 0.3mg/^m3.

When chlorine dioxide is used for drinking water disinfection, GB5749-2006 stipulates that the dosage limit of water plant is 0.8mg/L, the residual amount of factory water is ≥0.1mg/L, and the maximum limit of chlorite and chlorate by-products of disinfection is 0.7mg/L. When chlorine dioxide is used for drinking water disinfection, about 50%-70% is converted into chlorite, and studies have shown that drinking high concentration chlorite water will cause hemolysis and affect growth and development. In foreign experiments on human volunteers, drinking 5mg/L (0.036mg/kg/d) every day for 84 consecutive days, most of them had no abnormalities, and some people found changes in deaminase and serum, and drinking less than 2mg/L water was found to be abnormal.

5. Oxidation of chlorine dioxide

 

Chlorine dioxide is a strong oxidant, and the standard electrode potential of common oxidants is ozone_O3 (2.07) chlorine dioxide CLO₂ (1.511) oxygen_O2 (1.23); dichromate H2Cr2O7 (1.33), chlorine_Cl2(1.358); perchloric acid (perchloric acid) HClO4 (1.39); HClO3 chloric acid (1.47), hypochlorous acid HClO (1.61); chlorite HClO2(1.645); Permanganic acid (permangantic acid) HMnO4 (1.679).

 

Chlorine oxide is also very corrosive, can react with zn, Ca, Mg, Ni and other forms of corresponding chlorite, chlorine dioxide corrosion-resistant materials include platinum, tantalum, titanium, zirconium, nickel, quartz products, glass, acid-resistant ceramics, polyvinyl chloride, polyester, fluorine resin, etc. Studies have shown that 304 stainless steel has poor corrosion resistance in 8g/L chlorine dioxide solution at 60 °C, pH of 4.8g/L and 10g/L, pH of 2.4g/L and 8g/L at 60 °C, and pH of 6 at 60 °C. 316L stainless steel is not corrosion-resistant metal at 60 °C, pH 4, concentration 8g/L, 10g/L, 60 °C, pH 2.4g/L and 8g/L, 316L stainless steel belongs to the corrosion-resistant monk corrosion-resistant series under other research processes. In addition to the passivation tendency in the alkaline chlorine dioxide solution, 316L stainless steel also has a passivation tendency under the acidic conditions of low concentration and low temperature. Except for the chlorine dioxide solution at 60 °C, the concentration of 8g/L and 10g/L, and the pH less than 4, which is still corrosion-resistant, titanium belongs to the corrosion-resistant series under other conditions; Titanium exhibits good passivation characteristics in chlorine dioxide solution.

 

6. Chlorine dioxide bactericidal effect

Chlorine-containing disinfectants include liquid chlorine (Cl2), NaClO, and Ca(OCl)₂•_3H2O, sodium dichloroisocyanurate and tricyanoisocyanuric acid dissolve in water to produce HOCl, the HOCl produced is the same as liquid chlorine disinfection, and will have chlorine substitution reaction with THMS precursors in water to produce trihalomethanes and other organohalogenates that are harmful to the human body. Chlorine dioxide exists completely or almost exclusively as a monomer free atom cluster in water, and does not produce HOCL in water. Chlorine dioxide has very different properties from other chlorine preparations, and reacts with organic matter in water to produce almost no organohalogenates such as chloroform CHCl₃, which is the main reason why chlorine dioxide is recommended for drinking water disinfection. Chlorine dioxide inactivation mechanism of microorganisms: chlorine dioxide enters the microbial body to destroy the enzymes and proteins in the microbial body to achieve the purpose of inactivating microorganisms, generally water is close to neutral or alkaline, the surface of bacterial cells has a negative charge, chlorine dioxide molecules are neutral and easy to contact with bacteria, hypochlorous acid partially exists in neutral or alkaline water, hypochlorite is negatively charged and is not easy to contact with the same negatively charged bacteria, and chlorine dioxide has advantages over traditional chlorine disinfectants from the inactivation mechanism.

Chlorine dioxide almost does not form organohalides such as chloroform in drinking water disinfection, and the effect of killing bacteria, viruses, algae and zooplankton is better than that of liquid chlorine, and no mutagenic substances are produced in the process of water disinfection. The reaction of chlorine dioxide with inorganic and organic substances in water, especially organic matter, is mainly oxidized, while liquid chlorine is mainly replaced by chlorine, and chlorine gas reacts with precursors in water to form a significant amount of organohalogenates such as chloroform.

 

Chlorine dioxide is effective in killing bacteria in the pH range of 3-9; However, liquid chlorine can effectively kill bacteria only under near-neutral conditions (pH value of 6.5-8.5), and compared with liquid chlorine, chlorine dioxide requires less dosage and has a faster sterilization rate. In particular, chlorine dioxide can kill heterotrophic bacteria, iron bacteria and sulfate-reducing bacteria in water, and the effect is long-lasting. The bactericidal effect of chlorine dioxide can last for a long time and can maintain a certain residue in the pipe network system.

Chlorine dioxide has the ability to kill almost all known microorganisms. Chlorine dioxide disinfectants were identified for pure strains such as Staphylococcus aureus, Escherichia coli and Bacillus subtilis, and the results showed that the sterilization effect of these pure strains increased with the increase of disinfectant dosage, and the effect of chlorine dioxide was significantly better than that of chlorine. Chlorine dioxide has a good disinfection effect on water viruses such as polio type I, coxsackievirus B3, echovirus II, adenovirus type 7, herpes simplex virus type I, mumps virus, hepatitis B virus, and respiratory viruses; It has a good inactivating effect on algae and plankton in the water. The control of chlorine dioxide on algae is mainly due to its certain affinity for benzene rings, which can make the benzene ring change without odor. The pyrrole in chlorophyll is very similar to the benzene ring, and chlorine dioxide also acts on the pyrrole ring. In this way, chlorine dioxide oxidizes chlorophyll, plant metabolism is terminated, so that the synthesis in the protein is interrupted. The damage to plants as a result of this reaction is the hypertonic shrinkage (plasmid wall separation) caused by the dehydration of the protoplasm, an irreversible process that leads to the death of algae.

7. Bleaching and decolorization of chlorine dioxide

As an oxidant with strong oxidizing properties and few organoligen compounds in the oxidation process, chlorine dioxide has been widely used in the bleaching of the papermaking and pulp industries. Using CLO2 as a bleaching agent, compared to other bleaching powders and chlorine,_CLO2 can improve whiteness, prevent loss of fiber strength, simplify the production process, and avoid the harm of generating free chlorine and generating a large number of carcinogens. CLO₂ also kills microorganisms during the bleaching process, effectively dispersing mucus and inorganic deposits from the pulp, thereby eliminating the formation of solid lumps in the pulp and improving the quality of the paper. CLO₂ is a very effective and optional oxidizing agent for textile and wood pulp bleaching, especially when used in wood pulp bleaching to produce white, strong and smooth papers.

8. Oxidation of chlorine dioxide

The oxidation of manganese by chlorine dioxide can oxidize manganese divalent to tetravalent manganese, making it insoluble in water to form manganese dioxide.

即: 2CIO 2+5Mn 2++6H₂O=5MnO ₂+12H++2Cl-

 

The oxidation of iron by chlorine dioxide can oxidize divalent iron into trivalent iron to form iron hydroxide precipitation, namely: ClO 2+5Fe(HC0₃)₂+13H2 O=5Fe(0H)3+10C0 ₃₂-+Cl-+21H+

 

Chlorine dioxide oxidizes sulfide to sulfide in the pH range of 5~9, oxidizing sulfide (S2-) to sulfate, namely:

8ClO₂+5S 2-+4H₂O=5SO₄₂-+8Cl-+8H+

 

Chlorine dioxide oxidizes cyanide to carbon dioxide and nitrogen, i.e.: 2ClO 2+2CN-=2CO 2+N₂+2Cl-

 

Chlorine dioxide oxidizes nitric oxide, which instantaneously oxidizes NO to_NO2. When chlorine dioxide is used to remove organic contaminants, it is best to experimentally determine the reaction conditions and removal effect.

 

9. Application of chlorine dioxide

Since the advent of chlorine dioxide, it has been used in paper and fiber bleaching, drinking water disinfection, food processing, sterilization and preservation of meat, fruits, vegetables and aquatic products, industrial cooling water and wastewater treatment, food packaging paper disinfection and bleaching, water injection oil recovery and oil well unplugging, disinfection and sterilization in clinical medical treatment, sanitation and epidemic prevention disinfection, oil decolorization and bleaching and sterilization in flour and rice processing, water aquaculture disinfection and disease prevention and treatment in aquaculture, algae killing in water plants and control biological pollution and pipeline siltation.

10. Chlorine dioxide industry

There are three main types of chlorine dioxide industry, one is to produce and sell chlorine dioxide disinfectants, the other is to produce small and medium-sized chlorine dioxide generators for environmental protection and water treatment, and the third is to manufacture large-scale chlorine dioxide production devices for bleaching. Among them, chlorine dioxide disinfectants are liquid, solid, liquid or solid are divided into binary and unary, chlorine dioxide generators are divided into electrolytic chlorine dioxide generators and chemical chlorine dioxide generators, chemical chlorine dioxide generators are divided into composite chlorine dioxide generators and high-purity chlorine dioxide generators according to different product purities, and large-scale chlorine dioxide generators for pulp bleaching also have comprehensive methods, R3 methods, R8 methods and R11 and other processes. Since the 80s of the last century, the chlorine dioxide industry has developed rapidly in China.

11. Current effective standards related to chlorine dioxide

CCGF 304.4-2015 Disinfectants

GB/T 26366-2010 Hygienic standard for chlorine dioxide disinfectants

GB/T 20783-2006 Stable chlorine dioxide solution

GB 1886.248-2016 National food safety standard Food additives Steady chlorine dioxide

GB 5009.244-2016 National food safety standard Determination of chlorine dioxide in food

HG 3669-2000 Food additives Steady chlorine dioxide solution

GB/T 27802-2011 Chlorine dioxide solid release agent

GB/T 27802-2011 Chlorine dioxide solid release agent

GB/T 27803-2011 Methods for the analysis of chlorine dioxide solid release agents

GB/T 20621-2006 Chemical composite chlorine dioxide generator

GB 28931-2012 Standard for safety and hygiene of chlorine dioxide disinfectant generators

HJ/T 272-2006 Technical requirements for environmental protection products Chemical chlorine dioxide disinfectant generator

HJ/T257-2006 Technical Requirements for Environmental Protection Products Electrolytic chlorine dioxide synergistic disinfectant generator

GB/T 27709-2011 Calculation method for energy balance and energy efficiency of four-stage bleaching system with chlorine dioxide

HJ 551-2016 Water quality Determination of chlorine dioxide and chlorite Continuous titration of iodine

GB/T 5750.11-2006 Standard inspection methods for drinking water - Indicators for disinfectants

epilogue

Chlorine dioxide is the best chemical disinfectant with comprehensive effect, but it is not non-toxic and not omnipotent, I hope to learn Xi understand the relevant knowledge before using chlorine dioxide.