JP4082516B2 - Method and apparatus for removing harmful gases - Google Patents

Description

  The present invention relates to a method and apparatus for removing harmful gases in gas, and more particularly, to a method and apparatus for removing harmful gases containing NOx in the atmosphere.

The conventional technology will be described by taking harmful gases such as NOx, SOx and tobacco odor in various industries and industries as examples.
First, regarding the release of exhaust gases from various industries and industries and the exhaust gases of automobiles into the atmosphere, legal and other regulatory measures have been taken from the viewpoint of pollution prevention, especially for nitrogen oxides and sulfur oxides, Its emission is severely limited as a causative agent of acid rain and photochemical smog. Many methods for treating nitrogen oxide (NOx) and sulfur oxide (SOx) in exhaust gas, which are subject to emission regulations, have been proposed in the past, but there are various problems in practical use. For example, as a conventional denitration technology for exhaust gas, a reduction method by adding ammonia, a reduction method using a catalyst, a radiation irradiation method, and the like have been proposed.

  These conventional methods have the following problems, respectively. (A) Reduction method by adding ammonia: Denitration effect is low. (B) Reduction method using a catalyst: When continuously used, the catalyst performance decreases. Since metals and precious metals are used as catalysts, it is necessary to review from the viewpoint of resource saving. Susceptible to the acidic substance of dust. (C) Radiation irradiation method: Since secondary products such as ammonium nitrate and ammonium sulfate are produced in large quantities, it is necessary to separately treat by-products. In addition, since ammonia is added in any of these methods, ammonia that is not consumed in the denitration reaction is discharged as leaked ammonia, resulting in secondary pollution. Moreover, it is necessary to review from the viewpoint of the use of ammonia and resource saving.

Moreover, once these harmful gases are released into the atmosphere, it is difficult to remove them, and new methods and devices that can be removed even in the atmosphere are expected to emerge.
Next, harmful gas (including odorous gas) containing NOx generated by smoking in a home or office will be described. These substances are generally regarded as a problem as a so-called tobacco odor, and the demand for collection / removal has increased particularly in recent years due to their harmfulness (eg, carcinogenicity) as well as odor. For the collection and removal of these, there are proposals for methods and devices that use various removal materials such as those using activated carbon and plant essential oils, but these removal materials are all inadequate in performance.・ Appearance of equipment is expected.

  An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a method and apparatus for removing harmful gas containing NOx that is easy to handle, is compact and inexpensive, and is effective even in the atmosphere. .

In order to solve the above-mentioned problems, in the present invention, in a method for removing harmful gas containing NOx in the atmosphere on a road, a wall on which light is irradiated in the atmosphere is provided on the road, and the surface is provided on the wall. There to name an uneven, deploying a light transmissive support having supported thereon a photocatalyst, it is obtained by a method of removing harmful gas, characterized in Rukoto to irradiate light to the support.
In the present invention, an apparatus for removing harmful gas containing NOx in the atmosphere on the road, on the road, a wall light in air is irradiated provided, the front surface forms an uneven shape on the wall surface deploying a light transmissive support is obtained by a device for removing noxious gases light of the light transmissive support is characterized in that by supporting an uneven surface in the photocatalyst is irradiated.

According to the present invention, the use of the light-transmitting glass material having an uneven surface as the support for the photocatalyst has the following effects.
(A) Since it is an uneven support, the area of photoreaction (irradiation) increased. Moreover, since light was scattered on the uneven surface, it was effectively absorbed by the photocatalyst.
As a result, the processing efficiency of the harmful gas was improved and the processing was effectively performed.
(B) Since the support is a glass material, the photocatalyst can be irradiated with ultraviolet light and / or visible light directly from the back surface of the photocatalyst without passing through the treated material. It is possible to effectively select a large degree of freedom.
Moreover, sunlight can also be utilized suitably by this.
That is, in the case of irradiation from only the conventional surface, when a solid substance or the like adheres to the surface of the photocatalyst over time, the portion becomes a dead space and performance deteriorates. In addition, since the conventional method is irradiated through the processed material, the performance is affected by the processed material, and depending on the processed material, the processed material absorbs light, and the light cannot be effectively used.
(C) Normally, NOx is a substance that is difficult to process, and if it is processed using NOx as an indicator, other coexisting harmful zuka can be processed at the same time, so that it is practically easy to control and manage.
In the present invention, as described above, the performance could be stably maintained for a long time regardless of the processed material.

Next, each configuration of the present invention will be described in detail.
In the present invention, ultraviolet light and / or visible light can be used as irradiation light, and it may be sunlight or artificial light.
The photocatalyst used in the present invention is used while being supported on the surface of a light-transmitting support having a rough surface (roughened). By so doing, the reaction rate by the photocatalyst is significantly improved by irradiating the catalyst carrier with light. Here, the light irradiation is preferably performed by irradiating the photocatalyst coated on the surface of the support from the back surface with respect to the light introduced into the support, that is, the coated catalyst.
The reason why the action of the photocatalyst is effective is due to the following two effects.
One is that the photoreactive area is further increased by the surface irregular support in the present invention as compared to the case of using a smooth surface support. The other is that the light is scattered by the irregularities on the surface, so that it is effectively absorbed by the semiconductor as the photocatalyst.

  Any material can be used as the material for the light-transmitting support as long as it has a high transmittance for ultraviolet light and / or visible light. In particular, quartz glass, Pyrex (registered trademark) glass, and soda having excellent light resistance. A glass material such as lime glass can be preferably used. As the shape, a plate shape, a sheet shape, a curved surface shape, a columnar shape, a rod shape, a linear shape, a net shape, a lattice shape, a fiber shape and the like can be used. The thinner or thinner the light-transmitting support is, the better. However, in terms of strength, it is desirable that the thickness is 0.1 mm or more, or φ0.1 mm or more. Further, although there is no upper limit, the photoreaction efficiency per volume of the fiber decreases as the thickness increases and the thickness increases, but even about 10 mm can be used depending on the application.

The method for roughening the surface of the light-transmitting support is not particularly limited, and chemical etching using an HF aqueous solution and physical abrasion using an abrasive may be used. The uneven dimension needs to be about 200 nm or more in order to scatter ultraviolet light and / or visible light. However, if the uneven size is too large, the reaction surface area becomes small, and the efficiency is lowered. As a result, the upper limit is desirably 0.1 mm.
The type of the photocatalyst supported on the uneven light-transmitting support can be selected in consideration of the target harmful gas, the type of the light source, and the like. Because of its high photocatalytic activity and chemical stability, the most widely used photocatalyst at present is TiO ₂ and can be suitably used in the present invention. However, the photocatalyst used in the present invention is not limited to this, and any known photocatalyst can be used.

Usually, semiconductor materials are preferable because they are effective, easily available, and have good workability.
From the aspect of effect and economy, Se, Ge, Si, Ti, Zn, Cu, Al, Sn, Ga, In, P, As, Sb, C, Cd, S, Te, Ni, Fe, Co, Ag, Any of Mo, Sr, W, Cr, Ba, and Pb, or a compound, alloy, or oxide thereof is preferable. These are used alone or in combination of two or more.
For example, the elements Si, Ge, Se, AlP as compounds, AlAs, GaP, AlSb, GaAs , InP, GaSb, InAs, InSb, CdS, CdSe, ZnS, MoS 2, WTe 2, Cr 2 Te 3, MoTe , Cu ₂ S, WS ₂ , oxides include TiO ₂ , Bi ₂ O ₃ , CuO, Cu ₂ O, ZnO, MoO ₃ , InO ₃ , Ag ₂ O, PbO, SrTiO ₃ , BaTiO ₃ , Co ₃ O _4. , Fe ₂ O ₃ , NiO, and the like.

If the photocatalyst film is too thin, it cannot absorb light sufficiently. On the other hand, if it is too thick, the photocarrier generated in the film cannot be diffused to the surface, so that the catalytic activity is lowered. Therefore, there exists an optimum value. The value varies depending on the type of photocatalyst used, but is in the range of several nm to several μm.
The use of the photocatalyst is effective when carried out in an electric field. The strength of the electric field is 1 V / cm to 10 kV / cm, usually 10 V / cm to 1 kV / cm.
The electric field can be set by installing an appropriate electrode material such as a line, net, rod, lattice, etc. in the vicinity of the photocatalyst, and applying a voltage between the photocatalyst, depending on the shape of the photocatalyst or electrode material, Appropriate conditions can be selected by conducting preliminary tests as appropriate.
The type and thickness of the photocatalyst, the presence or absence of electric field, and its strength should be determined by conducting preliminary tests as appropriate according to the application field, the type and concentration of the substance to be treated, the type of light source, the type and shape of the photocatalyst support, the required performance, etc. Can do.

Next, the light source will be described.
Any light source may be used as long as it has a wavelength that excites the photocatalyst, and a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, a xenon lamp, or the like can be used.
The position of the light source can be appropriately selected depending on the application field, the type of light source, and the device shape. Further, depending on the use destination, it can be used in combination with known harmful gas removing means as appropriate. Known harmful gas removal means include activated carbon, activated carbon fiber, zeolite, ion exchange filter (fiber), and organic polymer polymer (organic polymer beads).

Further, means using the composite oxide catalyst already proposed by the present inventors (Japanese Patent Laid-Open Nos. 6-194895 and 6-205930) can be appropriately used depending on the application field. As a method of using these, when the processing harmful gas is usually relatively high or there are many kinds of processing gases, the harmful gas is removed to some extent by these means in advance, and then removed by the means of the present invention. Thereby, the gas to be processed having a high concentration and the complex harmful gas of a multi-component system can be processed with high efficiency, and an ultra-clean gas and space can be obtained effectively.
The present invention is effective for the treatment of NOx. NOx is the most stable of other harmful gases and is difficult to process by conventional methods. Since NOx can be easily treated in the present invention, other harmful gases coexisting with NOx, such as NH ₃ , organic Cl compounds, hydrocarbons, tobacco odor, and mold odor components, are easily treated.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
Example 1
FIG. 2 shows a schematic view of incorporating a photocatalyst into the highway wall surface to remove harmful gases.
In FIG. 2, on the highway 40, NOx is discharged from the vehicle 15 traveling at high speed. The road 40 has a wall surface 16, a part of the wall surface is made of glass, and the glass surface is uneven, and is a photocatalyst carrier 8 coated with TiO ₂ .
The photocatalyst carrier 8 is irradiated with sunlight 17 from the back surface and / or front surface thereof, and NOx is removed. NOx is converted to nitric acid by the photocatalyst and adheres to the surface of the photocatalyst. However, the nitric acid is washed off from the photocatalyst by occasional rainfall, recovered from the pit 18, and separately up to N ₂ by a well-known method using a water treatment device. Reduced.
Reference numeral 19 denotes a frame that supports the highway.
Although the position of irradiation 17 on the photocatalyst by sunlight changes with time, since the present catalyst is effective for both surface irradiation and backside irradiation, sunlight can be used effectively.

Reference example 1
A basic configuration diagram of the harmful gas removal apparatus is shown in FIG. 1, and air cleaning in a hospital will be described with reference to FIG.
In FIG. 1, fine particles (particulate matter) and harmful gases (including odorous gases such as aldehydes, ketones, pyridines, pyrroles, nitriles, nitrogen oxides, ammonia, etc.) resulting from smoking 2 and the like. 3 has occurred.

The air cleaning is performed by the pretreatment filter 4, the electrostatic filter 5, the activated carbon 6, the ion exchange filter 7, and the photocatalyst carrier 8 carrying the photocatalyst of the present invention, the ultraviolet lamp 9, This is carried out by an air purifier 11 comprising a fan 10.
The photocatalyst carrier 8 is obtained by coating a large number of rod-shaped (rod) quartz glass with an uneven surface with TiO ₂ , and ultraviolet rays from the ultraviolet lamp 9 pass through the rod-shaped quartz glass, and the TiO ₂ on the surface of the quartz glass. ₂ is excited and activated as a photocatalyst. FIG. 1B is a cross-sectional view taken along the line AA ′ of FIG. Reference numeral 12 denotes a flow of contaminated air, and reference numeral 13 denotes clean air cleaned by the air purifier 11.

In the air purifier 11, the particulate matter resulting from smoking or the like is first removed from the coarse particulate matter by the pretreatment filter 4, and then the remaining particulate matter is removed by the electrostatic filter 5. On the other hand, harmful gases resulting from smoking are first removed mainly by activated carbon 6 from neutral substances and acidic substances such as aldehydes and ketones. Next, mainly an alkaline substance such as ammonia is removed by an ion exchange filter (cation type) 7.
As the ion exchange filter, those already proposed by the present inventors can be appropriately used. (For example, JP-A-63-12315, JP-A-63-77557, JP-A-63-97246, JP-A-2-59018)
Next, NOx that cannot be removed by these filters and the leaked harmful gas are removed by a photocatalyst. In the photocatalyst, NOx is mainly converted into nitric acid and is removed by immobilization.

The nitric acid converted from NOx on the photocatalyst of the photocatalyst carrier 8 deteriorates the performance of the photocatalyst when operated for a long time and may be scattered backward by the long-time operation. If the filter for collecting nitric acid as a product (collecting material), for example, ion exchange fiber (anion type), activated carbon, activated carbon fiber, or glass fiber is appropriately installed on the rear side, the effect of the photocatalyst is maintained, and Since it can be collected even if it flows backward, it is preferable depending on the type of apparatus, the concentration of the processing harmful gas, the type of the removal material for other harmful components used, the required performance, and the like. The installation of the collection filter can be determined by conducting a preliminary test as appropriate.
The photocatalyst is suitable for treating a low concentration of harmful gas to a very low concentration or below a detection limit concentration. For this reason, it is possible to effectively treat practically by treating to a low concentration in advance by a known method as in this example and performing the final treatment with a photocatalyst.
By the air cleaner 11, the air 12 containing a tobacco odor with an odor concentration (sensory test value) of 50 to 1,000 is an odor concentration of 10 or less, NOx as a harmful gas is 5 ppb or less, NH ₃ is 10 ppb or less, Clean air 13 is obtained.

Reference example 2
The deodorizing effect and NOx removal performance using the air cleaner of FIG. 1 are shown below.
The volume of the waiting room 1 in which the air cleaner is installed is about 30 m ³ , and the air flow rate in the cleaner is 100 liters / min. When 10 cigarettes were smoked at a position of about 1 m directly under the pretreatment filter 4, the sample air collected at the position 12 immediately before the filter was visually recognized as tobacco smoke, and the odor concentration was determined by a sensory test (three-point comparison method). ) Was 500.
In addition, it was measured NOx, NH _3, and each 2ppm, was 2ppm. The measurement method is a chemiluminescence method.

As a light-transmitting support, a smooth surface quartz rod having a polished surface (diameter: 5.0 mm) was prepared, and the surface was ground by polishing with sand.
Titanium (IV) propoxide (28.39 g) was added to 18.43 g of absolute ethanol, stirred at room temperature for about 3 minutes, and then ice-cooled (solution A). Separately, a mixed aqueous solution of ethanol (18.43 g), water (1.8 g) and hydrochloric acid (0.29 g) was prepared (Solution B). While stirring the solution A, the solution B was slowly dropped using a burette to obtain a uniform mixed solution (solution C).
After the quartz rod was immersed in the solution C, it was pulled up at a constant speed of 1.8 cm / min using a dipping device. After sufficiently drying in air, it was calcined at 500 ° C. for 10 minutes to obtain a photocatalyst carrier of the present invention. A schematic diagram of the resulting TiO ₂ -coated quartz rod as the photocatalyst carrier is shown in FIG.

FIG. 3 is an explanatory view showing the action of the photocatalyst 39 of the present invention.
A photocatalytic film 32 is supported on the surface of the light-transmissive support A. The light 33 introduced from the light transmissive support A is effectively absorbed by the photocatalyst film 32 by the action of the surface of the support A that has been roughened.
When the photocatalytic film 32 absorbs light having energy greater than the width of the forbidden band, electrons are excited to the conduction band 34 and holes 37 are formed in the valence band 35. In this way, the holes 37 in the valence band 35 have an oxidizing power, and the excited electrons 36 in the conduction band 34 have a reducing power. Reference numeral 38 denotes an object to be processed, and the object to be processed is decomposed by the force of the above action.
The thickness of the coated TiO ₂ is 30 mm.
The light source is a high-pressure mercury lamp.
Size of air cleaner for performance test used: 50 × 50 × 60 cm

As a result, when this air was cleaned by operating the air purifier 11, the odor concentration of air at the position 13 of the straight line of the outlet of the purifier 11 was 10 or less at the maximum in the sensory test. In addition, no tobacco smoke was visually observed in the discharged air. The NOx and NH ₃ concentrations were 5 ppb or less, respectively.

Reference example 3
The activated carbon 6 and the ion exchange filter 7 are removed from the air purifier 11 shown in FIG. 1, and tunnel exhaust gas containing NOx is introduced into the purifier at 50 liters / min. I examined it in total.
NOx concentration: 1-3ppm
Air cleaner size: 50 × 50 × 60cm
Photocatalyst and light source: Same as in Reference Example 4.
Results The NOx concentration at the outlet of the purifier was 10 to 30 ppb.
In addition, as a comparative example, when the quartz rod was not roughened and was similarly coated with TiO ₂ and tested, the NOx concentration at the purifier outlet was 0.3 to 0.5 ppm.

Next, application fields and applications to which the present invention is applied will be described.
(1) Treatment of NOx, tobacco, mold odor, toilet odor and various chemical odors at home, office and hospital.
(2) Car exhaust gas treatment in tunnels and highways.
(3) Treatment of various harmful gases (eg, NOx, hydrocarbons) in the clean room and its surroundings in the semiconductor industry, pharmaceutical industry, food industry, agriculture and forestry industry, medical care, precision machinery industry.
(4) _NOx in the atmosphere _{(NO, NO 2, N 2} O), the processing of the SOx.
(5) Treatment of emission gas (NOx, organic Cl compound) containing NOx by stripping in a water treatment plant.

(A) is a basic block diagram of the harmful gas removal apparatus used for the air cleaning in a hospital, (b) is AA 'sectional drawing of (a). Schematic which applied this invention to the wall surface of a highway. Explanatory drawing which shows the effect | action of the photocatalyst of this invention.

Explanation of symbols

  1: Hospital waiting room 2: Cigarette 3: Hazardous gas 4: Pretreatment filter 5: Static filter 6: Activated carbon 7: Ion exchange filter 8: Photocatalyst carrier 9: UV lamp 10: Fan, 11: Air purifier, 12: Contaminated air, 13: Clean air, 15: Automobile, 16: Road wall surface, 17: Sunlight, 18: Pit, 19: Mount, 31: Uneven surface of support, 32: Photocatalyst Membrane, 33: Light, 34: Conduction band, 35: Valence band, 36: Excited electron, 37: Hole, 38: Harmful gas, 39: Photocatalyst carrier, 40: Road, A: Light transmissive support

Claims (2)

A method for removing harmful gas containing NOx in the atmosphere on the road, on the road, a wall light in air is irradiated is provided, the surface wall surfaces to name an uneven, was supported photocatalyst deploying a light transmissive support, a method of removing harmful gas, characterized in Rukoto to irradiate light to the support. An apparatus for removing harmful gas containing NOx in the atmosphere on the road, on the road, a wall light in air is irradiated provided, the front surface to the wall surface of the light transmitting substrate that forms an uneven deployed, device for removing noxious gases light of the light transmissive support is characterized in that by supporting photocatalyst on uneven surfaces to be irradiated.

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