Ozone physical properties:
Ozone (O3), also known as superoxide, is an allotrope of oxygen (O2), which is a gas with a “special smell“ at normal temperature. Ozone is mainly distributed in the stratospheric atmosphere at a height of 10 to 50 km. At normal temperature and pressure, low concentration of ozone is a colorless gas, when the concentration reaches 15%, it shows a pale blue color.
Ozone chemical properties:
Ozone is very unstable, the half-life of decomposition is about 20 to 30 minutes. As the temperature increases, the decomposition rate increases. When the temperature exceeds 100 °C, the decomposition is very intense. When the temperature reaches 270 °C, it can be converted into oxygen immediately. Ozone decomposes faster in water than in air. In water containing impurities, ozone can be rapidly decomposed into oxygen.
Ozone has a strong oxidizing ability, which is only lower than fluorine. This property is mainly used in its application. Ozone supports combustion. When combustibles are put into ozone gas ambient, combustion is more intense than in oxygen.
Ozone reduction reaction
A, Ozone reduction reaction with inorganic substances
Ozone reacts with ferrous iron, Mn2+, sulfide, thiocyanide, cyanide, chlorine, etc.
Such as:
B, Ozone reaction with organic matter
The reaction of ozone with organic matter in water is extremely complicated.
(1) Reaction of ozone with olefinic compounds
Ozone readily reacts with olefinic compounds having double bonds, and the final product of the reaction may be a mixture of monomeric, polymeric, or staggered ozonides. Ozone oxides decompose into aldehydes and acids.
(2) Reaction of ozone with aromatic compounds
The reaction between ozone and aromatic compounds is slow, the oxidation sequence of ozone with the following is :benzene <naphthalene < phenanthrene.
(3) Reacts with nuclear protein (amino acid) and organic ammonia
The oxidation sequence of ozone in the following mixtures is
Alkenes > Amines > Phenols > Polycyclic Aromatic Hydrocarbons > Alcohols > Aldehydes > Paraffins
Toxicity and corrosivity
Ozone is a harmful gas. When the concentration is 6.25×10-6mol/L (0.3mg/L), it has a stimulating feeling to the eyes, nose and throat. Concentration (6.25-62.5)×10-5mol/L (3～30mg/ L), will cause headache and local paralysis of the respiratory organs; concentration 3.125 × 10-4 ~ 1.25 × 10-3mol / L (15 ~ 60mg / L), it is harmful to the human body. The toxicity is also related to the contact time. For example, long-term exposure to ozone concentration 1.748×10-7mol/L (4ppm) can cause permanent heart disease, but exposure to ozone below 20ppm does not exceed 2h, there is no permanent harm to the human body. Therefore, the allowable value of the ozone concentration is 4.46 × 10-9 mol / L (0.1 ppm) 8 h. Since the smell of ozone is very concentrated, when concentration is 4.46 × 10-9 mol / L (0.1 ppm), people feel it easily. Therefore, even ozone in the world has been used for more than a hundred years, but there is no report of death due to ozone poisoning.
Ozone is highly oxidizing, in addition to gold and platinum, ozonized air has a corrosive effect on almost all metals. Aluminum, zinc, lead and ozone are strongly oxidized, but chrome-containing alloys are substantially free of ozone corrosion. therefore, chrome-iron alloy (stainless steel) is often used in production to manufacture parts of ozone generating equipment and filling equipment that are in direct contact with ozone.
Safe ozone concentration
According to the book “Ozone Technology Application Collection” edited by Tsinghua University, the concentration of ozone in application is classified to safe concentration in air, applied concentration, water application concentration, environmental concentration and perceived concentration.
◎ Ozone industry hygiene standards: International Ozone Association: 0.1 ppm, exposure for 10 hours; United States, Germany, France, Japan: 0.1 ppm, exposure for 8 hours, China: 0.15 ppm, exposure for 8 hours
◎ The ozone leakage by the household ozone disinfection cabinet shall not exceed 0.2 mg/m3 (refer to 1.5 meters away), and the residual concentration after disinfection for one cycle shall not exceed 0.3 mg/m3.
Air application concentration
◎ Air purification require ozone concentration is between 1 mg/m3 to 10 mg/m3.
◎ Ozone is more active in low temperature and high humidity environment, if relative humidity is lower than 45%, the ozone has almost no killing effect on the suspended microorganisms in the air, while Its effect gradually increases at 60% and reaches a maximum at 95% humidity.
◎ Ozone disinfection for food processing workshop, 0.5 ~ 1.0 ppm can kill 80% of the natural bacteria in the air.
◎ Cold storage disinfection requires an ozone concentration of 6 to 10 ppm, After treated by ozone and close the storage room for 24 hours, the bacterial killing rate is about 90% and the mold killing rate is about 80%.
◎ During the storage of fruits, 2 to 3 ppm of ozone can inhibit the growth of mold, and extend the storage period.
Ozone concentration in water application
◎ Tap water ozone purification, the international standard is 0.4 mg/L(0.4ppm) contact time: 4 minutes.
◎ The dissolved ozone level maintained at 0.1-0.5 mg/L for 5-10 minutes for common disinfection purposes.
◎ Ozone in water disinfection and sterilization is rapid, the bacteria are killed within 0.5 to 1 minute. At a concentration of 4 mg/L, the hepatitis B virus inactivation killing rate is 100% in 1 minute.
◎Herbold reports: At 20 ° C, 0.43 mg/L(0.43ppm) ozone concentration, can kill E. coli by 100%, and only 0.36 mg/L (0.36ppm) ozone concentration required at 10 ° C.
◎ When the ozone concentration is 0.25 to 38 mg/L, it takes only a few seconds to completely inactivate the hepatitis A virus (HAV).
◎ Mineral water disinfection need an ozone concentration of 0.4~0.5mg/L, it can meet the sterilization and quality requirements.
◎ Bottled water treatment should reach the ozone concentration of 0.3~0.5mg/L.
Post time: May-14-2019