JP2004358469A - Method and apparatus for removing harmful gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which is easy of handling, compact, and inexpensive and can effectively remove a harmful gas containing NOx even in the atmosphere and an apparatus for the method. <P>SOLUTION: In the method for removing the harmful gas 3 containing NOx in the atmosphere, the gas 12, after being contacted with a photocatalyst support 8 in which a photocatalyst is supported on the uneven surface of a light-transmitible support while the inside of the light-transmitible support is irradiated with light 9, is passed through a nitric acid catching filter. The irradiation can be carried out in an electric field. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

The prior art will be described by taking toxic gases such as NOx, SOx, and tobacco odor in various industries and industries.
First, regarding the emission of exhaust gas from various industries and industries and the exhaust gas from automobiles to the atmosphere, legal and other regulatory measures have been taken from the viewpoint of pollution prevention. In particular, for nitrogen oxides and sulfur oxides, Its emission as a causative agent of acid rain and photochemical smog is severely restricted. Many techniques have been proposed for treating nitrogen oxides (NOx) and sulfur oxides (SOx) in exhaust gas, which are subject to emission regulations, but there are various problems in practice. For example, as a conventional exhaust gas denitration technique, a reduction method by adding ammonia, a reduction method using a catalyst, a radiation irradiation method, and the like have been proposed.

  Each of these conventional methods has the following problems. (A) Reduction method by adding ammonia: the denitration effect is low. (B) Reduction method using a catalyst: When used continuously, catalyst performance is reduced. Since metals and precious metals are used as catalysts, they need to be reviewed from the viewpoint of resource saving. Susceptible to dust acidic substances. (C) Irradiation method: Since secondary products such as ammonium nitrate and ammonium sulfate are generated 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. In addition, it is necessary to review the use of ammonia and resource saving.

Also, once these harmful gases are released into the atmosphere, it is difficult to remove them, and a new method and apparatus capable of removing them in the atmosphere are expected.
Next, harmful gases (including odorous gases) containing NOx generated by smoking in homes and offices will be described. These substances are generally regarded as a so-called tobacco odor, and their harmfulness (eg, carcinogenicity) as well as the odor has increased the demand for collection and removal in recent years. For the collection and removal of these, there are proposed methods and apparatuses using various removal materials such as those using activated carbon or vegetable essential oil, but all of these removal materials have insufficient performance, and new methods have been proposed. -Appearance of devices 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 an apparatus for removing harmful gases containing NOx which are easy to handle, compact and inexpensive, and are effective even in the atmosphere. .

In order to solve the above problems, the present invention provides a method for removing a harmful gas containing NOx in a gas, wherein the gas is a photocatalyst in which a photocatalyst is supported on a surface of a light-transmitting support having an uneven surface. After contacting the support with the light-transmissive support under light irradiation, the support is passed through a filter for collecting nitric acid.
In the removal method, light irradiation is preferably performed in an electric field.
Further, according to the present invention, in a device for removing a harmful gas containing NOx in a gas, a photocatalyst carrier in which a photocatalyst is carried on a surface of a light-transmissive support having an uneven surface in contact with the gas; A light source for irradiating light to the inside of the light-transmitting support, and a filter for collecting nitric acid through which the gas is provided after contact with the photocatalyst support are provided.
In the above device, the light source is provided at the center of the device and provided so that light can be applied to the inside of the light-transmitting support.

According to the present invention, the following effects are achieved by using a light-transmissive glass material having an uneven surface as a support for a photocatalyst.
(A) The area of the photoreaction (irradiation) is increased due to the uneven support. In addition, since light was scattered on the uneven surface, it was effectively absorbed by the photocatalyst.
Thereby, the processing efficiency of the harmful gas was improved, and the processing was effective.
(A) Since the support is made of 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 a processed material. It is possible to effectively select a large degree of freedom.
In addition, sunlight can be appropriately used.
That is, in the case of irradiation only from the conventional surface, when a solid substance or the like adheres to the surface of the photocatalyst with the passage of time, the portion becomes a dead space and the performance is deteriorated. Further, in the conventional method, since the irradiation is performed through the processing object, the performance is affected by the processing object, and depending on the processing object, the processing object absorbs light, and the light cannot be used effectively.
(C) Normally, NOx is a substance that is difficult to treat, and if it is treated using NOx as an index, other coexisting harmful gases can be treated at the same time, so that control and management are practically easy.
In the present invention, as described above, the performance can 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 sunlight or artificial light may be used.
The photocatalyst used in the present invention is used by being supported on the surface of a light-transmitting support whose surface is uneven (roughened). By doing so, the reaction speed 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 with light introduced into the support, that is, the coated catalyst from the back.
The reason why the action by the photocatalyst is effective is due to the following two effects.
One is that, in the present invention, the photoreactive area is further increased by the uneven surface support, as compared with the case of using a smooth surface support. Another is that light is effectively absorbed by the semiconductor as a photocatalyst because the light is scattered by the irregularities of the surface.

  As the material of the light-transmitting support, any material can be used as long as it has a high transmittance of ultraviolet light and / or visible light. Particularly, quartz glass, Pyrex (registered trademark) glass, and soda having excellent light resistance are used. A glass material such as lime glass can be suitably used. The shape may be a plate, a sheet, a curved surface, a column, a bar, a line, a net, a lattice, a fiber, or the like. The thickness or thickness of the light-transmitting support is preferably as thin or thin as possible, but is desirably 0.1 mm or more in thickness or 0.1 mm or more in terms of strength. Although there is no upper limit, the photoreaction efficiency per volume of the fiber decreases as the thickness and the thickness of the fiber increase.

The method for roughening the surface of the light-transmitting support is not particularly limited, and chemical etching with an HF aqueous solution, physical polishing with an abrasive, or the like may be used. The dimension of the unevenness needs to be about 200 nm or more in order to scatter ultraviolet light and / or visible light. However, if the size of the concavities and convexities is too large, the reaction surface area is reduced, and the efficiency is reduced. As a result, the upper limit is desirably 0.1 mm.
The type of the photocatalyst to be supported on the uneven light-transmitting support can be selected in consideration of the type of the target harmful gas and the light source. From height and chemical stability of the photocatalytic activity, photocatalyst currently most widely used is TiO _2, it can be suitably used in the present invention. However, the photocatalyst used in the present invention is not limited to this, and any of those conventionally known as photocatalysts can be used.

Generally, semiconductor materials are preferable because they are effective, easily available, and have good workability.
From the viewpoint 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, and 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 , and oxides such as TiO ₂ , Bi ₂ O ₃ , CuO, Cu ₂ O, ZnO, MoO ₃ , InO ₃ , Ag ₂ O, PbO, SrTiO ₃ , BaTiO ₃ , and Co ₃ O ₄ , Fe ₂ O ₃ , NiO and the like.

If the thickness of the photocatalyst film is too small, light cannot be sufficiently absorbed. On the other hand, if it is too thick, the photocarriers generated in the film cannot diffuse to the surface, and the catalytic activity decreases. Therefore, there is an optimum value. The value varies depending on the type of photocatalyst used, but is in the range of several nm to several μm.
In the use of the above-mentioned photocatalyst, it is effective to carry out under 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 wire, a net, a rod, or a lattice in the vicinity of the photocatalyst and applying a voltage between the photocatalyst and the shape of the photocatalyst or the electrode material. Preliminary tests can be conducted as appropriate to select appropriate conditions.
The type and thickness of the photocatalyst, the presence or absence of an electric field, and the strength of the photocatalyst should be determined by conducting appropriate preliminary tests 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 be.

Next, the light source will be described.
Any light source may be used as long as it has a wavelength that excites the photocatalyst. 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 the light source, and the shape of the device. Usually, it is preferable to install a light source at the center of the reactor because all the light radially emitted from the light source is effectively used.
Further, depending on the place of use, it can be used in combination with a well-known harmful gas removing means. Well-known harmful gas removing means include activated carbon, activated carbon fiber, zeolite, ion exchange filters (fibers), and organic polymer polymers (organic polymer beads).

In addition, the means (JP-A-6-205930 and JP-A-6-194895) using the composite oxide catalyst already proposed by the present inventors can be appropriately used depending on the application field. As a method of using them, when the harmful gas to be treated is relatively high or when there are many kinds of treatment gases, the harmful gas is removed to some extent by these means in advance and then removed by the means of the present invention. As a result, the gas to be treated having a high concentration or a complex harmful gas of a multi-component system can be treated with high efficiency, and an ultra-clean gas or space can be effectively obtained.
The present invention is effective for treating NOx. NOx is the most stable of other harmful gases and is difficult to treat by conventional methods. Since NOx can be easily treated in the present invention, other harmful gases coexisting with NOx, for example, NH ₃ , organic Cl compounds, hydrocarbons, tobacco odor, musty odor components, etc. can be easily treated.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.
Example 1
FIG. 1 shows a basic configuration diagram of the harmful gas removing device of the present invention, and air purification in a hospital will be described with reference to FIG.
In FIG. 1, fine particles (particulate matter) and harmful gases (including odorous gases, for example, aldehydes, ketones, pyridines, pyrroles, nitriles, nitrogen oxides, ammonia, etc.) resulting from smoking 2 and the like. 3 has occurred.

The air purification is performed by a pretreatment filter 4, an electrostatic filter 5, an activated carbon 6, an ion exchange filter 7, and a photocatalyst carrier 8 carrying a photocatalyst of the present invention, an ultraviolet lamp 9, The operation is performed by the air purifier 11 including the fan 10.
The photocatalyst carrier 8 is formed by coating a large number of rod-shaped (rod) quartz glass having irregularities on the surface with TiO ₂ , and the ultraviolet light from the ultraviolet lamp 9 passes through the rod-shaped quartz glass to pass through the TiO ₂ on the quartz glass surface. 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 purified by the air purifier 11.

In the air purifier 11, coarse particles that are caused by smoking or the like are first removed by the pretreatment filter 4, and then the remaining particles are removed by the electrostatic filter 5. On the other hand, as for the harmful gas caused by smoking, first, activated carbon 6 mainly removes neutral substances and acidic substances such as aldehydes and ketones. Next, an alkaline substance such as ammonia is mainly 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. (Examples: 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 to nitric acid and removed by being fixed.

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 a filter (collection material) for collecting nitric acid, which is a product, for example, an ion-exchange fiber (anion type), activated carbon, activated carbon fiber, or glass fiber is appropriately provided in the rear, the effect of the photocatalyst is maintained, and Since it can be collected even when it flows backward, it is preferable depending on the type of equipment, the concentration of the harmful gas to be treated, the type of material for removing 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 harmful gas to an extremely low concentration or below the detection limit concentration. For this reason, if the treatment is carried out to a low concentration in advance by a known method as in this example and the final treatment is carried out with a photocatalyst, the treatment can be practically and effectively performed.
The air purifier 11, air 12 containing cigarette smell odor concentration (value of sensory test) 50 to 1,000, the odor concentration 10 or less, and NOx as a harmful gas 5ppb or less, NH ₃ becomes less 10 ppb, Clean air 13 is obtained.

Example 2
FIG. 2 is a schematic configuration diagram of air cleaning using the removal apparatus of the present invention for removing trace harmful gases in a clean room in a semiconductor factory.
In FIG. 2, NOx, NH _3, and fine particles 22 are generated as harmful gases by a work 21 in a clean room 20 of class 1,000 (the number of particles having a particle size of 0.1 μm or more). (Non-methane hydrocarbon) is present at 0.8-1.0 ppm. Since these contaminants (the gaseous pollutants and fine particles) contaminate raw materials, products and semi-finished products of the semiconductor factory, an air purifier 11 is installed to collect and remove the harmful gases and fine particles. Has been done.

The apparatus 11 is mainly pre-processing filter 4, the fan 10, the ion exchange filter (cationic form) 7, ULPA filter _{5 -1, 5 -2,} and is composed of a photocatalyst carrying member 8 and the ultraviolet lamp 9. FIG. 2B is a cross-sectional view taken along the line BB ′ of FIG. The air to be treated 12 containing harmful gas is sucked by the fan 10, and the treated clean air is discharged in the direction of arrow 13.
Each configuration will be described.
The pretreatment filter 4 is a filter mainly composed of glass fibers having a low air resistance, and first, coarse particles (particles having a relatively large particle diameter) in the suction air 12 are removed.

Ion exchange filter 7 is a filter for removing the NH ₃ in the clean room, such as NH ₃ generated by the work 21, which the present inventors have already proposed (above) can be appropriately used, thereby NH ₃ Is removed to 10 ppb or less.
ULPA filter _{5 -1} is a particulate removal filter in a clean room, such as particles generated by the work 21. Thereby, the fine particles in the clean room of class 1,000, the fine particles generated by the operation 21 and the fine particles generated by the operation of the fan 10 are removed to class 10 or less.

The photocatalyst carrier 8 mainly removes NOx generated by the operation 21 and decomposes hydrocarbons that increase the contact angle. The TiO ₂ is coated on a large number of fibrous quartz glass having an uneven surface. Things.
Ultraviolet lamp 9 passes through the inside of the quartz glass coated with TiO _2, the TiO ₂ coated on the surface of the quartz glass irradiated, is intended to act as a photocatalyst. Thereby, NOx in the clean room and NOx generated by the operation 21 are removed to 5 ppb or less. Also, hydrocarbons are converted to a stable form that does not affect the increase in contact angle.
ULPA filters _5-2 is a filter for removing generated particles from the photocatalyst and its vicinity, is usually unnecessary, are installed to define emergency.

As a result, clean air 13 having a NOx concentration of 5 ppb or less, a non-methane hydrocarbon of 0.2 ppm or less, an NH ₃ concentration of 10 ppb or less, and a fine particle concentration class of 10 or less can be obtained.
When harmful gas is generated in the clean room, it adheres to products and semi-finished products, increases the contact angle, and lowers the yield (decreases productivity). Is important in management.
The order of combination of the photocatalyst and the known harmful gas removing means in the embodiment is not limited at all, and can be appropriately determined by performing a preliminary test.
The contact angle is an index indicating the degree of contamination of the solid surface.If the solid surface is contaminated, the contact angle of water reflects the state of contamination well, and if the degree of contamination is large, the contact angle increases. Conversely, if the degree of contamination is small, the contact angle is small.

Example 3
The deodorizing effect and NOx removal performance using the air purifier of FIG. 1 are shown below.
The volume of the waiting room 1 in which the air purifier was installed was about 30 m ³ , and the air flow rate in the purifier was 100 liter / min. When 10 cigarettes are smoked at a position about 1 m immediately below the pretreatment filter 4, tobacco smoke is visually observed in the sample air collected at the position 12 immediately before the filter, and the odor concentration is determined by a sensory test (three-point comparison method). ) Was 500.
When NOx and NH ₃ were measured, they were 2 ppm and 2 ppm, respectively. The measuring method is a chemiluminescence method.

As a light-transmitting support, a surface-polished quartz rod (diameter: 5.0 mm) having a polished surface was prepared, and the surface was sanded with polished sand to roughen the surface.
28.39 g of titanium (IV) propoxide was added to 18.43 g of absolute ethanol, and the mixture was stirred at room temperature for about 3 minutes, and then cooled with ice (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 added dropwise 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 baked at 500 ° C. for 10 minutes to obtain a photocatalyst carrier of the present invention. FIG. 3 shows a schematic view of the obtained TiO ₂ -coated quartz rod as the photocatalyst carrier.

FIG. 3 is an explanatory diagram showing the operation of the photocatalyst 39 of the present invention.
On the surface of the light-transmitting support A, a photocatalyst film 32 is supported. The light 33 introduced from the light-transmitting support A is effectively absorbed by the photocatalytic film 32 by the action of the uneven surface of the support A.
When the photocatalytic film 32 absorbs light having energy equal to or greater than the width of the forbidden band, electrons are excited by the conduction band 34, and holes 37 are formed in the valence band 35. Thus, the holes 37 in the valence band 35 have oxidizing power, and the excited electrons 36 in the conduction band 34 have 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 the performance test air purifier used: 50 × 50 × 60 cm

Results When this air was cleaned by operating the air purifier 11, the odor concentration of the air at the position 13 of the straight line at the outlet of the purifier 11 was 10 or less at the maximum in the sensory test. Here, no tobacco smoke was visually observed in the discharged air. Further, NOx and NH ₃ concentrations were respectively 5ppb or less.

Example 4
The activated carbon 6 and the ion-exchange filter 7 are removed from the air purifier 11 shown in FIG. 1, and tunnel ventilation exhaust gas containing NOx is introduced into the purifier at a rate of 50 liter / min. The total was checked.
NOx concentration: 1-3 ppm
Air purifier size: 50 × 50 × 60cm
Photocatalyst and light source: Same as in Example 3.
Results The NOx concentration at the outlet of the purifier was 10 to 30 ppb.
As a comparative example, when the quartz rod was similarly coated with TiO ₂ without roughening and tested, the NOx concentration at the outlet of the purifier was 0.3 to 0.5 ppm.

Next, application fields to which the present invention is applied will be described.
(1) Treatment of NOx, tobacco, musty odor, toilet odor, and various chemical odors in homes, offices, and hospitals.
(2) Treatment of exhaust gas such as NOx and SOx from various combustion facilities.
(3) Exhaust gas treatment of automobiles in tunnels and highways.
(4) Treatment of various harmful gases (eg, NOx, hydrocarbons) in and around clean rooms in the semiconductor industry, the pharmaceutical industry, the food industry, the agriculture and forestry industry, the medical industry, and the precision machinery industry.
(5) _NOx in the atmosphere _{(NO, NO 2, N 2} O), the processing of the SOx.
(6) Treatment of released 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 of the present invention used for air purification in a hospital, and (b) is a cross-sectional view taken along line A-A 'of (a). (A) is a schematic block diagram of the removal apparatus of this invention used for the clean room of a semiconductor factory, (b) is B-B 'sectional drawing of (a). Explanatory drawing which shows the effect | action of the photocatalyst of this invention.

Explanation of reference numerals

1: hospital waiting rooms, 2: Tobacco, 3: harmful gas, 4: pre-processing filter, 5: left _filter, 5 _-1, 5 -2: ULPA filter, 6: activated carbon, 7: ion exchange filter, 8: Photocatalyst carrier, 9: ultraviolet lamp, 10: fan, 11: air cleaner, 12: contaminated air, 13: clean air, 20: clean room, 21: work table, 22: contaminated gas, 31: uneven surface of support, 32: photocatalyst film, 33: light, 34: conduction band, 35: valence band, 36: excited electron, 37: hole, 38: harmful gas, 39: photocatalyst carrier, A: light transmissive support

Claims (4)

  In the method for removing a harmful gas containing NOx in a gas, the gas is introduced into a photocatalyst carrier in which a photocatalyst is carried on a surface of a light transmissive support having an uneven surface, and into the light transmissive support. A method for removing harmful gases, comprising contacting the sample under light irradiation and passing through a filter for collecting nitric acid.   The method according to claim 1, wherein the light irradiation is performed in an electric field.   An apparatus for removing harmful gas containing NOx in a gas, comprising: a photocatalyst carrier in which a photocatalyst is carried on a surface of a light transmissive support having an uneven surface in contact with the gas; and an interior of the light transmissive support. A light source for irradiating the gas, and a filter for collecting nitric acid, which is provided after the contact with the photocatalyst carrier, and passes the gas.   The harmful gas removing apparatus according to claim 3, wherein the light source is provided at a central portion of the apparatus, and is provided so that light can be applied to the inside of the light-transmitting support.

Images