CN1304059C - Device for catalytic purifying air and water by vaccum ultraviolet light action - Google Patents

Abstract

The invention discloses a vacuum ultraviolet photocatalytic purification device for air and water. The device for purifying air and water by vacuum ultraviolet photocatalysis of the present invention comprises a low-pressure mercury lamp capable of emitting 185nm ultraviolet rays, a photocatalyst, a filter screen, a fan, and a reactor. The device of the present invention combines the effects of both vacuum ultraviolet photolysis and photocatalysis, and has both vacuum ultraviolet photolysis and photocatalysis in the reaction process, and has a higher reaction rate than separate vacuum ultraviolet photolysis and photocatalysis. Under the same energy consumption, there is a better purification effect, which can improve efficiency and reduce costs. The device of the invention can be used for purifying air and water, especially indoor air and drinking water, to remove particles, various organic pollutants and pathogenic microorganisms in the air and water, and has important practical application value.

Description

A device for vacuum ultraviolet photocatalytic purification of air and water

technical field

The invention relates to a device for purifying air and water, in particular to a device for catalytically purifying air and water with vacuum ultraviolet light.

Background technique

Particulate matter, pathogenic microorganisms, volatile organic compounds and other pollutants in indoor air are harmful to people's health. The indoor air purification methods currently used mainly include filtration, adsorption, electrostatic dust removal, ozone oxidation disinfection, negative oxygen ions, and photocatalytic methods.

Filtration is effective in removing particulate matter, smoke, dust, and more. High-efficiency filter material (HEPA) has the characteristics of high temperature resistance, corrosion resistance, waterproof, and mildew resistance. It can effectively capture inhalable particles, smoke, dust, bacteria, etc. above 0.3 μm, and the filtration efficiency is over 99.97%. However, the disadvantage of the HEPA filtration method is that it cannot remove volatile organic compounds in the air. The high-voltage electrostatic precipitator can ionize and adsorb pollutants in the air, and its dust removal efficiency mainly depends on the electric field strength, dust particle size, air velocity and the residence time of dust particles in the dust collection section.

Adsorption is a widely used indoor air purification method at present, which has the characteristics of broad spectrum and high efficiency. The main disadvantage of the adsorption method is that it has adsorption saturation, and the porous adsorption material needs to be replaced regularly. The air volume and the concentration of harmful substances directly affect its working life and adsorption efficiency.

The ozone oxidation method can effectively disinfect, deodorize and degrade organic matter, but the toxicity of ozone is high, and people cannot enter the site during the ozone disinfection process. When the ozone concentration is high (> 1ppm), it is easy to cause discomfort such as coughing. Higher concentrations of ozone Bring more serious harm to human health, so the pure ozone air purifier has no application value. The U.S. Environmental Protection Agency has banned ozone generators as air cleaning devices. In addition, ozone oxidation is selective and has no degradation effect on many volatile organic compounds (such as toluene).

Photocatalysis is a new technology developed in the 1970s, which can remove organic pollutants in water and air, and has the functions of sterilization and disinfection. Photocatalytic technology generally uses ultraviolet light sources (such as low-pressure mercury lamps emitting 254nm ultraviolet rays, black light lamps emitting 365nm ultraviolet rays, etc.) to irradiate semiconductor catalysts with photocatalytic activity, such as titanium dioxide (TiO ₂ ), zinc oxide (ZnO), tungsten trioxide (WO ₃ ), etc., the electrons in the valence band of the semiconductor catalyst jump to the conduction band after being excited by ultraviolet light, an electron with strong reducing ability is generated in the conduction band, and a hole with strong oxidative property appears in the valence band.

The hydroxyl radicals formed by the holes generated by the semiconductor excited by ultraviolet light and migrated to the surface of the semiconductor and captured by water or hydroxyl groups have a strong oxidizing ability, which can oxidize and degrade most pollutants in air and water, such as volatile organic compounds. , disinfection by-products, endocrine disruptors and other organic pollutants, and can kill various bacteria, viruses, etc., so it can purify air and water. Different from activated carbon adsorption, it does not simply transform pollutants from one phase to another, or simply concentrate pollutants, but a purification technology that can completely remove pollutants, and also has the function of sterilization effect. However, the current photocatalyst activity is not high, the efficiency of photocatalytic purification of air and water is low, the treatment time is long, the energy consumption is high, and catalyst deactivation may also occur. Therefore, how to improve the efficiency of photocatalysis, improve the economics of photocatalysis technology, and avoid the deactivation of photocatalysts are the problems that need to be solved in the practical application of photocatalysis.

Vacuum ultraviolet light is ultraviolet light with a wavelength below 200nm. There are two common vacuum ultraviolet light sources: one is a low-pressure mercury lamp, which emits 185nm vacuum ultraviolet light in addition to 253.7nm far ultraviolet light; the other is an excimer The light source, for example, a xenon excimer light source can emit 172nm vacuum ultraviolet rays. Since 185nm vacuum ultraviolet rays will photolyze oxygen in the air to generate ozone and cause harm, when using a low-pressure mercury lamp as a photocatalytic light source, a low-pressure mercury lamp that does not emit 185nm is usually used, for example, doping titanium dioxide into the quartz used as a lamp tube Can make the low-pressure mercury lamp not emit 185nm ultraviolet rays.

When a low-pressure mercury lamp capable of emitting 185nm ultraviolet rays is used as a light source, the main light emitted by this lamp is 253.7nm and a small amount of 185nm ultraviolet rays. When 185nm ultraviolet rays irradiate air and water, the following effects will occur:

(1) Directly photolyze pollutants in air and water or kill pathogenic microorganisms. However, because the 185nm vacuum ultraviolet rays emitted by the low-pressure mercury lamp are relatively weak, this effect is very limited, and the contribution to the degradation of pollutants is small.

(2) Hydroxyl radicals (OH·) are formed by photolysis of water molecules and oxygen through the following reactions:

In water, because the content of oxygen is less than that of water, the vacuum ultraviolet rays are mainly absorbed by water at the beginning, and the water decomposes to generate strong oxidizing hydroxyl radicals (OH·). In the air, the concentration of water vapor is much lower than that of oxygen, so the way of oxygen photolysis to form hydroxyl is more important. Since water and oxygen have a strong absorption of 185nm ultraviolet rays, 185nm ultraviolet rays are completely absorbed within a short optical path. The hydroxyl radicals and active oxygen atoms formed by the photolysis of water and oxygen molecules can quickly and effectively degrade pollutants.

If the oxygen atoms produced by oxygen photolysis do not fully react with pollutants or water, they will react with oxygen to form ozone:

Excessive ozone generation is harmful and undesirable.

Invention content

The purpose of the present invention is to provide a vacuum ultraviolet photocatalytic purification device for air and water, which can remove pollutants in air and water more economically and effectively.

The vacuum ultraviolet photocatalytic purifying device for air and water provided by the invention comprises a low-pressure mercury lamp capable of emitting 185nm ultraviolet rays and a photocatalyst.

In order to improve the effect of the purification device, the device also includes a filter screen and a fan, and may also include a reactor.

Wherein, the photocatalyst can be a semiconductor catalyst with photocatalytic activity, such as titanium dioxide, zinc oxide, tungsten trioxide and the like. The photocatalyst can be made in the form of a net or a plate catalyst, and can be fixed on the inner wall of the reactor, or coated on a metal sheet close to the inner wall of the reactor.

The device for purifying air and water by vacuum ultraviolet photocatalysis of the present invention uses a low-pressure mercury lamp capable of emitting 185nm ultraviolet rays as a light source for photocatalysis. The main light emitted by this lamp is 253.7nm and a small amount of 185nm ultraviolet rays, which can be used in combination with photocatalysts. The following advantages:

(1) 253.7nm ultraviolet light can be used as a light source for photocatalysts to produce photocatalysis without additional light sources; while 185nm vacuum ultraviolet rays are absorbed in a short distance and generally do not irradiate the surface of photocatalysts, so usually Will not be a light source for photocatalysis.

(2) Ozone produced by photolysis of 185nm vacuum ultraviolet rays can be used as an electron trap in the photocatalytic process, thereby improving the efficiency of the photocatalytic reaction. In the air, the presence of photocatalyst can also play a role in reducing the concentration of ozone.

(3) 185nm vacuum ultraviolet rays can directly degrade pollutants and hydroxyl radicals generated by photolysis of water or oxygen can degrade pollutants.

The invention cleverly combines the functions of vacuum ultraviolet photolysis and photocatalysis, that is, there are both vacuum ultraviolet photolysis and photocatalysis in the reaction process, and the ozone generated by vacuum ultraviolet light exciting air and water promotes photocatalysis The effect of avoiding or reducing the shortcomings of a single reaction, that is, the reaction rate of a large amount of ozone generated by vacuum ultraviolet photolysis and photocatalysis is low. At the same time, the device of the present invention is not a simple superposition of vacuum ultraviolet photolysis and photocatalysis, it has a higher reaction speed than separate vacuum ultraviolet photolysis and photocatalysis, and has a better purification effect under the same energy consumption. Improve efficiency and reduce costs. The device of the invention can be used for purifying air and water, especially indoor air and drinking water, and can remove various organic pollutants and pathogenic microorganisms in the air and water, and has important practical application value.

Description of drawings

Figure 1 is a flow chart of a vacuum ultraviolet photocatalytic air purification device

Figure 2 is a flow chart of the vacuum ultraviolet photocatalytic air purification device

Fig. 3 is a graph showing the relationship between the degradation rate and concentration of n-hexane in the air

Fig. 4 is a graph showing the relationship between n-hexane degradation rate and time in the air

Fig. 5 is the graph of relationship between toluene degradation rate and concentration in the air

Fig. 6 is the curve graph of toluene degradation rate and time in the air

Detailed ways

Example 1: Vacuum ultraviolet photocatalytic air purification device

The vacuum ultraviolet photocatalytic air purification device of the present invention is shown in Fig. 1, comprises filtering device 1, mesh catalyst titanium dioxide 2, low-pressure mercury lamp 3 emitting 185nm ultraviolet light, mesh catalyst titanium dioxide 4 and fan 5. The fan 5 extracts the air to be purified, first passes through the filter device 1 to remove particulate matter in the air, and after being catalyzed and purified by the mesh catalyst titanium dioxide 3, it reaches the low-pressure mercury lamp 3 for ultraviolet photolysis, which is also the ozone generating layer, and passes through the mesh again. Catalytic purification of titanium dioxide 4, a catalyst, removes ozone generated by vacuum ultraviolet photolysis, and also removes organic pollutants and pathogenic microorganisms in the air, thereby achieving the effect of purifying the air.

Example 2: Vacuum ultraviolet photocatalytic air purification device

The vacuum ultraviolet photocatalytic air purification device of the present invention is shown in FIG. 2 , including a filter device 1 , a fan 2 , a low-pressure mercury lamp 3 emitting 185nm ultraviolet light, and a plate-shaped photocatalyst tungsten trioxide 4 . The fan 2 extracts the air to be purified and first passes through the filter device 1 to remove particulate matter in the air. After passing through the fan, it reaches the low-pressure mercury lamp 3 for ultraviolet photolysis. The ozone produced by vacuum ultraviolet photolysis also removes organic pollutants and pathogenic microorganisms in the air, thereby achieving the effect of purifying the air.

Embodiment 3, degrade n-hexane in the air with the device of the present invention

n-Hexane is a typical VOC in indoor air and is recommended as a model pollutant for testing indoor air purifiers. The degradation of n-hexane is carried out in a cylindrical device with a volume of 1.44 liters. A 15W low-pressure mercury lamp capable of emitting 185nm ultraviolet rays is placed in the center of the cylindrical reactor, and a titanium dioxide photocatalyst is placed close to the inner wall of the cylindrical reactor. Aluminum sheet, the air containing n-hexane flows in from one end of the reactor, and the treated gas flows out from the other end. When performing vacuum ultraviolet photolysis, no titanium dioxide-loaded aluminum sheet is placed; when performing photocatalytic degradation, a 15W low-pressure mercury lamp that does not emit 185nm is used as the photocatalytic light source. Under various conditions, the effect of VUV photocatalytic degradation of n-hexane is much better than VUV degradation and photocatalysis.

The results are shown in Figure 3. Under the condition that the flow rate is 12L/min and the relative air humidity is 35%, no matter whether the concentration of n-hexane is high or low, the removal rate of n-hexane by vacuum ultraviolet photocatalysis is higher than that by vacuum ultraviolet photolysis. About 15-20 percentage points out, and 18-25 percentage points higher than photocatalysis.

Under the conditions of n-hexane concentration of about 3ppm and relative humidity of 35%, regardless of the length of treatment time, the removal rate of n-hexane by vacuum ultraviolet photocatalysis is about 7-12 percentage points higher than that of vacuum ultraviolet photolysis, which is higher than that of photocatalytic The removal rate was about 15-20 percentage points higher, and the results are shown in Figure 4.

Embodiment 4: Degrade toluene in the air with the device of the present invention

Toluene is a common pollutant in indoor air and one of the model pollutants for testing the performance of air purifiers. The degradation of toluene is carried out in a cylindrical device with a volume of 1.44 liters. A 15W low-pressure mercury lamp capable of emitting 185nm ultraviolet rays is placed in the center of the cylindrical reactor, and an aluminum alloy loaded with titanium dioxide photocatalyst is placed close to the inner wall of the cylindrical reactor. The air containing toluene flows in from one end of the reactor, and the treated gas flows out from the other end. When performing vacuum ultraviolet photolysis, no titanium dioxide-loaded aluminum sheet is placed; when performing photocatalytic degradation, a 15W low-pressure mercury lamp that does not emit 185nm is used as the photocatalytic light source. Under various conditions, the effect of VUV photocatalytic degradation of toluene is much better than that of VUV degradation and photocatalysis.

When the flow rate is 12L (that is, the treatment time is 7.2s) and the relative humidity is 35%, vacuum ultraviolet photocatalysis has a high removal rate for various concentrations of toluene, for example, the removal rate of toluene with an initial concentration of 0.55ppm 63%, while photocatalysis is only 34%. At other concentrations, the removal rate of toluene by VUV photocatalysis is also 25-30 percentage points higher than that of photocatalysis. Vacuum ultraviolet photocatalysis also has a higher removal rate than vacuum ultraviolet photolysis, which is 4-25 percentage points higher. The result is shown in Figure 5.

When the toluene is 1ppm and the relative humidity is 35%, the VUV photocatalysis has a higher removal rate of toluene in a shorter treatment time. For example, the removal rate of treatment 4.6s is 37%, the removal rate of treatment 5.4s is 49%, and the removal rate of treatment 17.3s is 75.6%. The removal rates after vacuum ultraviolet and photocatalytic treatment for 4.6s were 18.7% and 15.2%, respectively; the removal rates after 17.3s treatment were 65.5% and 65.1%, respectively, which were much lower than those of vacuum ultraviolet photocatalysis. Because indoor air purification is carried out at a large flow rate (that is, a very short processing time), the advantages of vacuum ultraviolet photocatalysis will be more obvious at a large flow rate. The result is shown in Figure 6.

Embodiment 5: purify pollutants in water with the device of the present invention

The vacuum ultraviolet photocatalytic water purification device of the present invention includes a reactor 1, a low-pressure mercury lamp 2 with a quartz sleeve that emits 185nm ultraviolet light, a photocatalyst coated on the inner wall of the reactor or a coated light placed close to the inner wall of the reactor. Catalyst metal flakes3. The effect of vacuum ultraviolet photocatalytic purification of pollutants in water was tested in a cylindrical reactor with a volume of 0.8L. A low-pressure mercury lamp with a quartz sleeve is placed in the middle of the reactor, and the catalyst is fixed on the inner wall of the reactor, or coated on a metal sheet, and the metal sheet is placed close to the inner wall of the reactor. When performing vacuum ultraviolet photocatalytic degradation, use a 15W low-pressure mercury lamp that can emit 185nm ultraviolet light as the light source; when performing vacuum ultraviolet photolysis, there is no catalyst, and still use a 15W low-pressure mercury lamp that can emit 185nm ultraviolet light A lamp is used as the light source; when performing photocatalytic degradation, a low-pressure mercury lamp that cannot emit 185nm ultraviolet light is used as the light source.

The degradation of various pollutants such as 4-chlorophenol, 2,4-dichlorophenol, p-nitrophenol, hydroquinone, and 4-chlorobenzoic acid were tested. It has a better degradation effect and can speed up the reaction rate. For example, for 4-chlorophenol, the first-order reaction rate constant of VUV photocatalytic degradation is 1.183min ^-1 , while VUV photolysis and photocatalysis are 0.815min ^-1 and 0.677min ^-1 , respectively, an increase of 45% and 75% %; 2,4-dichlorophenol's vacuum ultraviolet photocatalytic reaction rate constant is 0.7229min ^-1 , while the photocatalytic reaction rate constant is only 0.0669min ^-1 , an increase of 9.8 times; the reaction rate of hydroquinone vacuum ultraviolet photocatalytic reaction is also 6 times of photocatalysis, 30% higher than vacuum ultraviolet photolysis; the vacuum ultraviolet photocatalytic reaction rate constant of 4-chlorobenzoic acid is 50% higher than vacuum ultraviolet photolysis rate constant. The results are shown in Table 1.

Table 1 The first-order reaction rate constants (1/min) of VUV photocatalytic degradation of pollutants Pollutants vacuum ultraviolet photocatalysis vacuum ultraviolet photolysis Photocatalytic 4-Chlorophenol 1.183 0.815 0.677 2,4-Dichlorophenol 0.7229 - 0.0669 Quinol 0.606 0.466 0.099 4-Chlorobenzoic acid 0.725 0.484 -

Claims (8)

1, the device of a kind of VUV light catalytic purifying air and water, it comprises can launch 185nm ultraviolet low pressure mercury lamp and photocatalyst as the photocatalysis light source.

2, device according to claim 1 is characterized in that: described device also comprises defecator and blower fan.

3, device according to claim 1 is characterized in that: described device also comprises reactor.

4, according to claim 1 or 2 or 3 described devices, it is characterized in that: described photocatalyst is the semiconductor catalyst with photocatalytic activity.

5, device according to claim 4 is characterized in that: described photocatalyst is titanium dioxide, zinc oxide or Tungstic anhydride..

6, device according to claim 4 is characterized in that: described photocatalyst is done and is reticulated or tabular form.

7, device according to claim 4 is characterized in that: described photocatalyst is fixed on the inwall of reactor.

8, device according to claim 4 is characterized in that: described photocatalyst coating is being close on the foil of reactor wall.

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