Ozone decomposition filter manufacturing method and ozone decomposition filter

Abstract

An ozone decomposition filter manufacturing method comprising a step for thermal spraying, onto a base material, a thermal spray material which contains a metal oxide, and forming, on a surface of the base material, a thermal-sprayed film substantially comprising the metal oxide, wherein the metal oxide contains a metal oxide having an ozonolysis capacity.

Description

Ozone decomposition filter manufacturing method and ozone decomposition filter

[0001] The present invention relates to a method for producing an ozone decomposition filter and to an ozone decomposition filter.

[0002] Ozone is used in many applications, including wastewater treatment, deodorization, decolorization, and COD removal. Also, trace amounts of ozone are generated from copying machines and electronic devices. Ozone has strong oxidizing power, making it highly reactive and potentially harmful to the human body. Therefore, excess or generated ozone must be decomposed as quickly as possible.

[0003] Generally, methods for decomposing ozone into oxygen include catalytic methods, activated carbon methods, chemical treatment methods, and thermal decomposition methods. Of these, activated carbon methods are often used to decompose low-concentration ozone, but this method has difficulty in stably decomposing high-concentration ozone. Thermal decomposition methods are often used to decompose high-concentration ozone, but in this method, in order to achieve a high decomposition rate, it is necessary to maintain the ozone-containing gas at a high temperature of, for example, 300°C or higher for 2 seconds or more. On the other hand, catalytic methods can decompose even high-concentration ozone at room temperature, and are therefore used in many situations.

[0004] As filters used in catalytic methods, Patent Document 1 reports a filter in which a composition in which activated carbon is added to a metal oxide such as manganese is supported on a carrier, Patent Document 2 reports a filter in which a composition containing amorphous manganese dioxide and zeolite is supported on an integrated honeycomb carrier, and Patent Document 3 reports a filter in which a compound mainly composed of nickel oxide is supported on the skeletal surface of a porous ceramic carrier (three-dimensional, honeycomb).

[0005] Japanese Patent Application Laid-Open No. 2006-231324 Japanese Patent Application Laid-Open No. 04-007038 Japanese Patent Application Laid-Open No. 2006-150290

[0006] In all of the above patent documents, the catalyst component is supported on the carrier by immersing the carrier in a slurry containing a catalytically active compound (catalytic component) and drying it. However, when attempting to increase the cell density of the honeycomb to accommodate high SV (Space Velocity) conditions, for example, this immersion method results in the cells being clogged with the catalyst component, preventing the filter from functioning satisfactorily. In addition, if the slurry contains an organic binder component, the catalyst component is covered by the organic binder component, and the desired ozone decomposition performance may not necessarily be achieved.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing an ozone decomposition filter that has excellent ozone decomposition performance even under high SV conditions. Another object of the present invention is to provide an ozone decomposition filter that has excellent ozone decomposition performance even under high SV conditions.

[0008] An aspect of the present invention is as follows, for example. [1] A method for producing an ozone decomposition filter, comprising the step of spraying a spray material containing a metal oxide onto a substrate to form a thermal spray coating consisting essentially of the metal oxide on the surface of the substrate, wherein the metal oxide includes a metal oxide having ozone decomposition properties. [2] The production method according to [1], wherein the thermal spraying is atmospheric pressure plasma spraying, low pressure plasma spraying, or suspension plasma spraying. [3] An ozone decomposition filter, comprising a substrate and a thermal spray coating consisting essentially of a metal oxide formed on the surface of the substrate, wherein the metal oxide includes a metal oxide having ozone decomposition properties. [4] The ozone decomposition filter according to [3], wherein the metal oxide having ozone decomposition properties includes at least one selected from the group consisting of manganese oxide, a composite oxide of copper oxide and manganese oxide, a composite oxide of iron oxide and manganese oxide, a composite oxide of cobalt oxide and manganese oxide, and a composite oxide of nickel oxide and manganese oxide. [5] The metal oxide having ozone decomposition properties includes manganese oxide, and the BET specific surface area of ​​the thermal spray coating is 1 m ２[6] The ozone decomposition filter according to [3] or [4], wherein the substrate is a porous substrate having a cell density of 1000 cpsi or more, and the amount of the metal oxide capable of decomposing ozone supported on the substrate is 20 g / m ２ [7] The ozone decomposition filter according to any one of [3] to [6], wherein the porous substrate is a metal mesh.

[0009] According to the present invention, it is possible to provide a method for producing an ozone decomposition filter that has excellent ozone decomposition performance even under high SV conditions. The present invention has advantages such as the ability to directly form a thermal spray coating containing a catalytic metal oxide on the surface of a substrate without using an organic binder, thereby achieving high catalytic performance, the ability of the formed thermal spray coating to adhere strongly to the substrate, and the ability to form a thermal spray coating on a flexible substrate such as a metal mesh without clogging. Furthermore, according to the present invention, it is possible to provide an ozone decomposition filter that has excellent ozone decomposition performance even under high SV conditions.

[0010] Preferred embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0011] <Method for manufacturing ozone decomposition filter> The method for manufacturing an ozone decomposition filter includes a step of spraying a spray material containing a metal oxide onto a substrate to form a sprayed coating substantially consisting of a metal oxide on the surface of the substrate.

[0012] (Substrate) Examples of the substrate include porous substrates such as mesh (netting). Materials constituting the porous substrate may be metal, ceramic, resin, etc. Examples of metal include stainless steel, zinc plating, copper, aluminum, etc. Examples of ceramic include alumina, silicon carbide, cordierite, etc. Examples of resin include polyethylene, nylon, etc. From the viewpoint of heat resistance and flexibility, metal mesh (wire mesh) is preferred as the substrate, and stainless steel mesh (SUS mesh) is particularly preferred.

[0013] The weaving method of the mesh includes plain weave, twill weave, plain tatami weave, twill tatami weave, etc. Also, a mesh with diamond-shaped mesh can be used.

[0014] The cell density of the porous substrate is preferably 1000 cpsi (cells per square inch) or more, more preferably 5000 cpsi or more, and even more preferably 10000 cpsi or more. A cell density of 1000 cpsi or more makes it easier to obtain sufficient ozone decomposition performance. The cell density of the porous substrate is preferably 90000 cpsi or less, and more preferably 50000 cpsi or less. A cell density of 90000 cpsi or less makes it easier to suppress pressure loss.

[0015] The thickness of the substrate may be adjusted appropriately depending on the application of the filter, but from the viewpoint of ozone decomposition performance, it is preferably 0.01 mm or more, and more preferably 0.15 mm or more, while from the viewpoint of pressure loss and flexibility, it is preferably 0.35 mm or less, and more preferably 0.2 mm or less. The thickness of the substrate is measured using a vernier caliper or the like.

[0016] Various aspects of the substrate can be appropriately adjusted in consideration of the balance between pressure loss and ozone decomposition performance.

[0017] (Thermal Spray Material) The thermal spray material includes a metal oxide, and the metal oxide includes a metal oxide having ozone decomposition properties. Examples of metal oxides that can be thermally sprayed and have ozone decomposition properties include powders of manganese oxide, composite oxides of copper oxide and manganese oxide, composite oxides of iron oxide and manganese oxide, composite oxides of cobalt oxide and manganese oxide, composite oxides of nickel oxide and manganese oxide, and the like, or powders of mixtures of two or more of these. Among these, from the viewpoint of ozone decomposition properties, at least one powder selected from the group consisting of manganese oxide, composite oxides of copper oxide and manganese oxide, composite oxides of iron oxide and manganese oxide, and composite oxides of cobalt oxide and manganese oxide is preferred, and manganese oxide powder is more preferred. Examples of the crystal system of manganese oxide having ozone decomposition properties include amorphous, α-type, β-type, δ-type, and ε-type, and in particular, those having a BET specific surface area of ​​40 to 300 m２ / g can be suitably used. These metal oxide powders have the function of acting as a catalyst for ozone to promote ozone decomposition, and can therefore be called ozone decomposition catalyst powders. In addition to the above metal oxides having ozone decomposition ability, the metal oxide may also contain other metal oxides such as silica.

[0018] The average particle size (D50) of the metal oxide (spray material) to be thermal sprayed is preferably 1 to 100 μm from the viewpoint of transportability when used as a powder, and preferably 0.01 to 10 μm from the viewpoint of dispersibility when used as a dispersion in a solvent. The average particle size is the particle size (D50; median diameter) at which the cumulative value is 50% on a volume basis when particle size distribution is measured by a laser diffraction / scattering method.

[0019] The thermal spray material is, for example, in powder form. When the thermal spray material is in powder form, it may be substantially composed of metal oxide (containing 90% or more by mass of metal oxide). The content of the metal oxide having ozone decomposing ability contained in the entire metal oxide can be 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more (the metal oxide is substantially composed of metal oxide having ozone decomposing ability). The thermal spray material is, for example, in slurry form. When the thermal spray material is in slurry form, in addition to the metal oxide (solid content), the thermal spray material may contain one or more dispersants selected from water and organic solvents as a dispersion medium, and may further contain a dispersant. The content of the metal oxide having ozone decomposing ability contained in the entire metal oxide can be 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more (the metal oxide is substantially composed of metal oxide having ozone decomposing ability).

[0020] (Thermal Spraying) In this process, plasma spraying, flame spraying, and the like can be used as the spraying method for the spray material. Of these, plasma spraying is preferred because it is suitable for spraying metal oxides and can minimize heat input to the substrate when a metal mesh is used as the substrate. Plasma spraying involves applying a voltage between a cathode and an anode placed inside a spray gun to generate a DC arc, which ionizes a working gas using the arc to generate a plasma jet, which is used as a heat source. Depending on the type of spray material and the spraying environment (atmospheric pressure or vacuum pressure), plasma spraying can be classified into atmospheric plasma spraying (APS), vacuum plasma spraying (VPS), suspension plasma spraying (SPS), and the like.

[0021] The plasma spraying conditions can be adjusted as appropriate within the range in which a desired coating can be formed on the substrate. For example, argon (Ar) is generally used as the working gas for generating plasma, and helium (He) or nitrogen (N ２ ) or hydrogen (H ２ ) can also be used in combination. Each spraying method is explained in detail below. Atmospheric pressure plasma spraying: A plasma spraying method performed under atmospheric pressure. The temperature and flow rate of the plasma jet can be easily adjusted depending on the operating conditions (type and flow rate of working gas, power output, etc.), making it highly versatile and easy to work with, and the most widely used method. Reduced pressure plasma spraying: A plasma spraying method performed inside a vacuum chamber. Although it has a lower heating capacity than atmospheric plasma spraying, it has the advantage of being less likely to alter the material. Suspension plasma spraying: A plasma spraying method that uses a slurry in which powder is dispersed in a dispersant as the spraying material, rather than powder. It has the advantage of being able to use powder with a small particle size, making it easy to create a sprayed coating with a large specific surface area.

[0022] <Ozone decomposition filter> The ozone decomposition filter includes a substrate and a thermal spray coating formed on the surface of the substrate and consisting essentially of a metal oxide. Details of the substrate and the metal oxide are as described above. In particular, a filter substrate having a mesh shape can be referred to as a mesh catalyst.

[0023] Because the thermal spray material does not need to contain resin components such as organic binders, the thermal spray coating formed can also be substantially free of these components. Therefore, the thermal spray coating can be said to be substantially composed of metal oxides (containing 90% by mass or more of metal oxides). In this case, the content of the metal oxides with ozone decomposition capabilities contained in the entire metal oxide can be 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more (the metal oxide is substantially composed of metal oxides with ozone decomposition capabilities). Although a thermal spray coating substantially composed of metal oxides can be said to be substantially free of resin components as described above, it may contain unavoidable impurities.

[0024] For example, the mechanism of ozone decomposition by manganese oxide is considered to be as follows: 1: M (catalyst) + O ３ →M-O+O ２ 2: M-O+O ３ →M+2O ２ In conventional methods using wash coating, the slurry contains organic binders, dispersants, etc., making it difficult to obtain a coating that can fully demonstrate the ozone decomposition properties of manganese oxide, and the organic binder may burn, making it difficult to use the coating under high-temperature conditions. On the other hand, this method using thermal spraying can be made binderless, making it easy to obtain a coating that can fully demonstrate the ozone decomposition properties of manganese oxide, and the coating can be used under high-temperature conditions.

[0025] The thickness of the thermal spray coating is preferably 1 μm or more, more preferably 5 μm or more, from the viewpoint of ozone decomposition performance, while from the viewpoint of pressure loss and adhesive strength, the thickness is preferably 100 μm or less, more preferably 30 μm or less. The thickness of the thermal spray coating is measured, for example, with a micrometer.

[0026] The BET specific surface area of ​​the thermal spray coating is 1 m from the viewpoint of ozone decomposition performance. ２ / g or more, and ２ On the other hand, the BET specific surface area is not particularly limited from the viewpoint of ozone decomposition performance, but it is preferable that the BET specific surface area is 250 m / g or more in consideration of various aspects of the manufacturing process (for example, the viscosity of the slurry when the thermal spray material is in a slurry state). ２ The BET specific surface area is a specific surface area measured in accordance with JIS Z8830.

[0027] The amount of metal oxide with ozone decomposing ability supported on the substrate is 1 g / m from the viewpoint of ozone decomposition performance. ２ It is preferable that the content is 20 g / m or more. ２ More preferably, the adhesive strength is 300 g / m or more. ２ It is preferable that the weight is 90 g / m or less. ２ The amount of the metal oxide having ozone decomposing ability supported can be calculated from the weight of the substrate before and after the thermal spraying step using, for example, an electronic balance.

[0028] The ozone decomposition filter can be installed, for example, perpendicular to the air flow in the piping, or attached to the wall of the piping or the wall of the device. In addition, pleating the ozone decomposition filter can increase the geometric surface area and improve the ozone decomposition performance.

[0029] The present invention will be described in more detail by the following examples, but the present invention is not limited to these examples.

[0030] <Preparation of Ozone Decomposition Filter> Ozone decomposition filters of the comparative example and the example were prepared according to the following procedure.

[0031] (Comparative Example A) Powder containing α-type manganese oxide (BET specific surface area: 200 m ２ / g, average particle size (D50): 5 μm), silica sol (Snowtex manufactured by Nissan Chemical Industries, Ltd., particle size 12 nm), an organic binder, and other additives were dispersed in pure water to prepare a slurry. The contents of each component in the slurry were 84 mass % manganese oxide, 6 mass % silica particles, 8 mass % organic binder, and 2 mass % additives.

[0032] The slurry was coated onto an aluminum honeycomb (cell density: 750 cpsi) using a washcoat method (W / C), and then dried at 150° C. to form a film containing manganese oxide powder on the surface of the aluminum honeycomb. The amount of manganese oxide supported was 84 g / L.

[0033] (Example A) Powder containing α-type manganese oxide (BET specific surface area: 200 m ２ / g, average particle size (D50): 9.5 μm) was sprayed in turn onto each side of a stainless steel mesh (SUS mesh) having a cell density of 10,000 cpsi (100 mesh) and a thickness of 0.25 mm by atmospheric pressure plasma spraying (APS), to form a sprayed coating with a thickness of 8 to 13 μm on both sides of the stainless steel mesh. The sprayed coating thus formed consisted essentially of manganese oxide. The film thickness was measured at two locations on each of the front and back surfaces (four locations in total).

[0034] (Example B) Powder containing α-type manganese oxide (BET specific surface area: 200 m ２ / g, average particle size (D50): 9.5 μm) was sprayed in turn onto each side of a stainless steel mesh having a cell density of 90,000 cpsi (300 mesh) and a thickness of 0.1 mm by atmospheric plasma spraying (APS), to form a sprayed coating with a thickness of 8 to 13 μm on both sides of the stainless steel mesh. The sprayed coating thus formed consisted essentially of manganese oxide.

[0035] (Example C) Powder containing ε-type manganese oxide (BET specific surface area: 250 m ２ / g, average particle size (D50): 1.7 μm) was sprayed in turn onto each side of a stainless steel mesh having a cell density of 10,000 cpsi (100 mesh) and a thickness of 0.25 mm by low-pressure plasma spraying (VPS), to form a sprayed coating with a thickness of 7 μm on both sides of the stainless steel mesh. The sprayed coating thus formed consisted essentially of manganese oxide.

[0036] (Example D) Powder containing ε-type manganese oxide (BET specific surface area: 250 m ２ / g, average particle size (D50): 1.7 μm) was sprayed in turn onto each side of a stainless steel mesh having a cell density of 90,000 cpsi (300 mesh) and a thickness of 0.1 mm by low-pressure plasma spraying (VPS), to form a thermal spray coating with a thickness of 7 μm on both sides of the stainless steel mesh. The thermal spray coating thus formed consisted essentially of manganese oxide.

[0037] (Example E) Powder containing ε-type manganese oxide (BET specific surface area: 250 m ２ / g, average particle size (D50): 1.7 μm) was dispersed in pure water to prepare a slurry. This slurry was sprayed in turn onto each side of a stainless steel mesh having a cell density of 10,000 cpsi (100 mesh) and a thickness of 0.25 mm by suspension plasma spraying (SPS), forming sprayed coatings with thicknesses of 9 to 13 μm on both sides of the stainless steel mesh. The sprayed coatings thus formed were essentially composed of manganese oxide.

[0038] (Example F) Powder containing ε-type manganese oxide (BET specific surface area: 250 m ２A slurry was prepared by mixing a 10000 cpsi (100 mesh) stainless steel mesh with a cell density of 10,000 cpsi (100 mesh) and a thickness of 0.25 mm (Snowtex) in a dry mass ratio of 80:20 and dispersing the mixture in pure water. This slurry was sprayed sequentially onto each side of a stainless steel mesh with a cell density of 10,000 cpsi (100 mesh) and a thickness of 0.25 mm by suspension plasma spraying (SPS), forming a thermal spray coating with a thickness of 9 to 13 μm on both sides of the stainless steel mesh. The thermal spray coating thus formed was essentially composed of metal oxides and contained 73 mass% manganese oxide and 27 mass% silica.

[0039] <Measurement of Specific Surface Area of ​​Film> The BET specific surface area of ​​the film of the ozone decomposition filter obtained in each example was measured in accordance with JIS Z 8830. The results are shown in Table 1.

[0040] The amount of catalyst (metal oxide having ozone decomposing ability) carried on the ozone decomposition filter obtained in each example was calculated from the weight of the substrate before and after the catalyst was carried on the filter. The results are shown in Table 1.

[0041] <Evaluation of Ozone Decomposition Performance> The ozone decomposition performance of the ozone decomposition filter obtained in each example was evaluated. The evaluation conditions were as follows. The results are shown in Table 1. Apparatus: fixed-bed flow-type reactor. Test conditions: SV = 5,200,000, temperature 20°C, humidity dry, ozone concentration 1 ppm, after 10 minutes. Ozone decomposition rate: calculated as ((inlet ozone concentration - outlet ozone concentration) / inlet ozone concentration) x 100%.

[0042]

[0043] The above test results revealed the following: The thermal spraying method makes it possible to form a film of catalytic components on a substrate with a high cell density, which is impossible with the washcoat method. The higher the cell density of the substrate, the higher the ozone decomposition performance. The BET specific surface area of ​​the thermal spray coating can be adjusted by changing the thermal spraying method, and the values ​​tend to increase in the order APS < VPS < SPS. The ozone decomposition performance tends to increase as the BET specific surface area of ​​the thermal spray coating increases. From this perspective, VPS and SPS are more suitable than APS for forming a film of catalytic components. Example D exhibits particularly excellent ozone decomposition performance, which is presumably due to the use of a substrate with a high cell density and the fact that VPS is less likely to alter the sprayed material.

Claims

1. A method for manufacturing an ozone decomposition filter, comprising a step of spraying a spray material containing a metal oxide onto a substrate to form a spray coating substantially consisting of the metal oxide on the surface of the substrate, wherein the metal oxide includes a metal oxide having ozone decomposition ability.

2. The manufacturing method according to claim 1, wherein the thermal spraying is atmospheric pressure plasma spraying, low pressure plasma spraying, or suspension plasma spraying.

3. An ozone decomposition filter comprising a substrate and a thermal spray coating formed on the surface of the substrate, the thermal spray coating consisting essentially of a metal oxide, the metal oxide including a metal oxide having ozone decomposition ability.

4. The ozone decomposition filter according to claim 3, wherein the metal oxide having ozone-decomposing ability comprises at least one selected from the group consisting of manganese oxide, a composite oxide of copper oxide and manganese oxide, a composite oxide of iron oxide and manganese oxide, a composite oxide of cobalt oxide and manganese oxide, and a composite oxide of nickel oxide and manganese oxide.

5. The metal oxide having ozone decomposition properties contains manganese oxide, and the BET specific surface area of the thermal spray coating is 1 m ２ 5. The ozonolysis filter of claim 4, wherein the ozonolysis coefficient is 1 / g or more.

6. The substrate is a porous substrate having a cell density of 1000 cpsi or more, and the amount of the metal oxide having ozone decomposition ability supported on the substrate is 20 g / m ２ 5. The ozone decomposition filter according to claim 3 or 4.

7. The ozone decomposition filter of claim 6, wherein said porous substrate is a metal mesh.

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