Common basic knowledge and common values of ozone
1. The specifications of the ozone generator are divided according to the amount of ozone produced. The unit of ozone production is mg/h or g/h (mg/hour or gram/hour), that is, how many weight units of ozone can be produced by the ozone generator working for one hour.
2. The unit of concentration of ozone in the air is ppm or mg/m3; the unit of concentration of ozone in water is ppm or mg/L. Conversion method: 1ppm﹦2 mg/m3 in air; 1ppm﹦1mg/L when in water.
3. When ozone reaches a certain concentration in the atmosphere, it will cause environmental pollution. Our country stipulates: In the residential environment, when the ozone concentration exceeds 0.1mg/m3, it constitutes air pollution; in the workplace, when the ozone concentration exceeds 0.2mg/m3, it constitutes pollution.
4. When the ozone concentration in the air reaches 0.01-0.02mg/m3, people can smell it.
5. When disinfecting food factories, cosmetics factories, production workshops, warehouses and other places, the ozone concentration in the air must reach 10-20 mg/m3, and it must be sealed for 30 minutes. No one can be on site during disinfection.
6. Under normal pressure mixing conditions, when bottled pure water is disinfected with ozone, usually 1m3/h water needs to use 3g ozone, and the ozone concentration in the water needs to be ≥0.3mg/L; when bottled mineral water is ozone disinfected, usually 1m3/h water 6g ozone is required, and the ozone concentration in the water must be ≥0.5mg/L.
Ozone is an unstable gas with a pungent and special smell, and its molecular structure is shown in the figure. It can be synthesized photochemically in the stratosphere of the earth, but only exists in a very low concentration on the ground level.
1.1 General physical properties
At room temperature, ozone is a blue gas, but at room temperature, the blue color is not obvious unless it is a fairly thick gas. The main physical properties of ozone are listed in Table 1-1, and the liquid density and vapor pressure are listed in Table 1-2.
1-1 The physical properties of pure ozone
Melting point (760mmHg)/℃ -192.5±0.4 Gas density (0℃)/(g/L) 2.144
Boiling point (760mmHg)/℃ -111.9±0.3 Evaporation heat (-112℃)/(J/L) 316.8
Critical temperature /℃ -12.1 Critical density /(g/ml) 0.437
Critical pressure /atm 54.6 Solid ozone density (77.4K)/(g/cm 3) 1.728
Critical volume (cm 3 /mol) 111 Liquid heat capacity (90～105K)/(cal/k) 0.425+0.0014×(T-9)
Viscosity of liquid ozone 77.6K(Pa•s)
0.00156 Heat of vaporization
Surface tension (cyn/cm)①
38.4 Heat of generation
Ideal gas (0k) 142.98
Isotonic specific volume (90.2K) 75.7 Free energy of formation (gas, 298.15k) 162.82
Dielectric constant (liquid state 90.2k) 4.79 Dipole moment /Debye 0.55
Magnetic susceptibility (cm-g-s unit) gas/liquid 0.002×10 -6
①1dyn=10 -3 N/m; 1atm=101.325Pa; 1cal=4.18J.
Table 1-2 Liquid density and vapor pressure of ozone
Temperature /℃ Liquid density
/(G/cm 3) liquid vapor pressure
/MmHg temperature /℃ liquid density / (g/cm3) liquid vapor pressure
-183 1.574 0.11 -140 1.442 74.2
-180 1.566 0.21 -130 1.410 190
-170 1.535 1.41 -120 1.318 427
-160 1.504 6.75 -110 1.347 865
-150 1.473 24.3 -100 1.316 1605
1.2 Solubility of ozone
Ozone is slightly soluble in water. Under standard pressure and temperature (STP), its solubility is 13 times greater than oxygen (see Table 1-3) and 25 times greater than air.
Table 1-3 The solubility of ozone in water (gas partial pressure is 10 5 Pa) /(ml/L)
Gas Density (g/L) Temperature /℃
0 10 20 30
O 2 1.492 49.3 38.4 31.4 26.7
O 3 2.143 641 520 368 233
Air 1.2928 28.8 23.6 18.7 16.1
By passing ozone into distilled water, the solubility of ozone in water at different temperatures and pressures can be measured. Figure 2-2 is the relationship curve between the solubility of pure ozone in water and the temperature when the pressure is 1atm. From Figure 2-2, when the temperature is 0℃, the solubility of pure ozone in water can reach 2.858×10 -2 mol/L (1372mg/L).
Like other gases, the solubility of ozone in water conforms to Henry’s law, that is, at a certain temperature, the mass of any gas dissolved in a known liquid will be proportional to the partial pressure of the gas acting on the liquid, and the size of Henry’s constant It’s just a function of temperature, and has nothing to do with concentration.
C=K H P (1-1)
where C-the solubility of ozone in water, mg/L;
P －Partial pressure of ozone in ozonized air, kPa;
K H-Henry’s constant, mg/(L•kPa).
From equation (1-1), since most of the ozonized air is used in actual production, the partial pressure of ozone is very small, so the solubility of ozone is much lower than the data in Table 1-3. For example, in the ozonized air produced by the ozone generator using air as the raw material, ozone only accounts for 0.6% to 1.2% (volume). According to the gaseous equation and Dalton’s law of partial pressure, the partial pressure of ozone is only 0.6% to 1.2% of the pressure of ozonized air. Therefore, when the water temperature is 25℃, the solubility of ozone is only (0.625 ~ 1.458) × 10 -4 mol/L (3 ~ 7mg/L) when this ozonized air is added to the water.
Table 1-4 Solubility of low-concentration ozone in water /(mg/L)
gas mass percentage content /% temperature /℃
0 5 10 15 20 25 30
1 8.31 7.39 6.5 5.6 4.29 3.53 2.7
1.5 12.47 11.09 9.75 8.4 6.43 5.09 4.04
2 16.64 17.79 13 11.19 8.57 7.05 5.39
3 24.92 22.18 19.5 16.79 12.86 10.58 8.09
In general water treatment, the ozone concentration is low, so the solubility in water is not large. At lower concentrations, the solubility of ozone in water basically satisfies Henry’s law. The solubility of low-concentration ozone in water is shown in Table 1-4.