Alumina porous body, and production method of alumina porous body

Abstract

To provide an alumina porous body that can effectively collect impurities in fluids and is difficult to break.SOLUTION: An alumina porous body 10 has a spherical shape and the ratio of the volume of pores 10A to the total volume is 40% or more and 60% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a porous alumina body and a method for producing a porous alumina body. [Background technology]

[0002] Patent Document 1 discloses a technique for producing a porous alumina body by mixing alumina powder, bentonite as a clay mineral, an organic substance that forms pores in the porous body, and an organic binder, and then using a rolling granulation method. The porous alumina body is formed by sintering a mixture of the alumina powder, bentonite, the organic substance, and the organic binder that are combined and granulated by the rolling granulation method. The porous alumina body has a configuration with a plurality of pores. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-270782 Summary of the Invention [Problem to be solved by the invention]

[0004] The pores of porous alumina have the function of capturing impurities contained in fluids. To increase the amount of impurities captured by porous alumina, it is conceivable to form pores with larger diameters. However, forming pores with larger diameters raises concerns that the porous alumina itself may become brittle. Furthermore, using organic materials with large outer diameters to form pores with larger diameters raises concerns that the alumina powder, bentonite, organic materials, and organic binders may not bond well together during tumbling granulation. For this reason, organic binders with high adhesive strength are used to bind organic materials with large outer diameters together, or the organic binder is dissolved in water and sprayed onto the powder for granulation. However, organic binders with high adhesive strength may also bond the granulated porous alumina together, which could result in agglomerations of the porous alumina particles or a poor spherical shape, potentially preventing the desired performance. Furthermore, in the method of Patent Document 1 in which an organic binder is dissolved in water and sprayed onto powder, the intermediate particles bond together to form agglomerates.

[0005] The first invention has been made to solve at least one of the above-mentioned problems, and aims to provide an alumina porous body that can effectively capture impurities contained in a fluid and is not easily broken.

[0006] The second invention has been made to solve at least one of the above-mentioned problems, and aims to provide a method for producing an alumina porous body that can effectively capture impurities contained in a fluid, is not easily broken, and has a uniform outer diameter. [Means for solving the problem]

[0007] The alumina porous body according to the first aspect of the present invention comprises: It has a spherical shape, and the ratio of pore volume to the total volume is 40% or more and 60% or less.

[0008] The method for producing a porous alumina body according to the second invention comprises the steps of: a granular pore-forming material; Alumina powder, a powdered organic binder; A powdered clay mineral having water absorption properties is used, A rolling granulation method is carried out in which intermediate granules are granulated while water is sprayed onto them. [Effects of the Invention]

[0009] According to the first aspect of the present invention, it is possible to obtain a porous alumina body that can effectively capture impurities contained in a fluid and is not easily broken.

[0010] Since intermediate granules are formed by binding multiple granular pore-forming materials, a highly adhesive organic binder is required. However, if the organic binder absorbs too much water and becomes too adhesive, the intermediate granules tend to bond together during granulation, forming agglomerates, or the outer diameters of the intermediate granules tend to vary greatly. Therefore, according to the second invention, by using a water-absorbent powdered clay mineral, it is possible to prevent the organic binder from absorbing too much water, suppressing adhesiveness and binding the pore-forming material together, thereby making it possible to granulate intermediate granules with a uniform outer diameter. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of the porous alumina body of this example. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 3 is a schematic diagram showing an outline of an apparatus for measuring the amount of trapped impurities. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Example> An embodiment of the present invention will be described with reference to FIGS. 1 to 3. As shown in FIG. 1, the porous alumina body 10 of this embodiment is a roughly spherical granule with an outer diameter of approximately 3 mm to 20 mm. The porous alumina body 10 is composed primarily of Al2O3 and SiO2. The porous alumina body 10 has a plurality of pores 10A. The pores 10A are roughly spherical and are evenly distributed throughout the porous alumina body 10 (see FIGS. 1 and 2). Adjacent pores 10A are connected to each other via communicating holes 10B (see FIG. 2). In other words, the pores 10A form an open-cell structure. As a result, when the porous alumina body 10 is immersed in liquid, the liquid reaches the center of the porous alumina body 10 via the pores 10A.

[0013] For example, by placing a mesh basket or the like containing a plurality of porous alumina bodies 10 in a flow path through which water flows, impurities such as dust mixed in the water can be captured and removed by the pores 10A. In other words, the porous alumina body 10 functions as a filter.

[0014] [Example of a method for manufacturing porous alumina] Next, an example of a method for manufacturing the alumina porous body 10 will be described. First, alumina powder, clay mineral, pore-forming material, and organic binder are placed in a pan granulator or mixer capable of performing tumbling granulation. The alumina powder, clay mineral, and organic binder are in powder form. The alumina powder is powdered Al2O3.

[0015] Clay minerals include smectite and vermiculate clay minerals, aluminosilicates, and diatomaceous earth, and specific minerals that belong to these groups include powdered bentonite, beidellite, nontronite, and saponite. Bentonite, a typical example, has the property of absorbing water (i.e., water absorption). SiO2, contained in bentonite, has a lower melting point than alumina (Al2O3), and acts as a sintering aid.

[0016] The pore-forming material is in the form of roughly spherical particles. The particle size of the pore-forming material is larger than the particle size of the alumina powder, clay mineral, and organic binder. The pore-forming material is formed from natural substances such as starch, rice husks, and walnut shells, and organic compounds such as polyethylene glycol, melamine, and acrylic. The median diameter of the pore-forming material is 400 μm or more and 1000 μm or less.

[0017] Examples of the organic binder include starch, polyvinyl alcohol, acrylic, and cellulose.

[0018] Next, while the pan granulator or mixer is rotated around its rotation axis, a mist of water is sprayed onto the alumina powder, clay mineral, pore-forming material, and organic binder charged into the pan granulator or mixer. The water-absorbent clay mineral then absorbs the water, and the organic binder simultaneously absorbs water, gradually beginning to exhibit adhesiveness. By absorbing water, the clay mineral prevents the organic binder from absorbing too much water and acts to suppress excessive adhesiveness of the organic binder. As a result, the alumina powder, clay mineral, pore-forming material, and organic binder charged into the pan granulator or mixer are bound together by the adhesiveness of the organic binder to form a plurality of intermediate granules with roughly uniform outer diameters.

[0019] For example, if intermediate granules are formed without adding an organic binder, the clay mineral simply absorbs water and increases in volume, but the pore-forming material, clay mineral, and alumina powder do not bond, and intermediate granules are not formed. In contrast, if intermediate granules are formed without adding a clay mineral, it is possible to form intermediate granules using the adhesiveness of the organic binder. However, if the organic binder absorbs water without any restrictions and exhibits excessive adhesiveness, the formed intermediate granules will bond together due to the adhesiveness of the organic binder, resulting in intermediate granules with irregular outer shapes. In other words, by using both a clay mineral and an organic binder, the organic binder can exhibit appropriate adhesiveness, thereby enabling the successful formation of intermediate granules that are uniformly spherical and have a consistent outer diameter.

[0020] After the intermediate granules are formed, the alumina powder, clay mineral, pore-forming material, and organic binder are again placed in the rotating pan granulator or mixer, and the process of spraying with water is repeated to grow the intermediate granules until they reach the desired outer diameter.

[0021] Next, the intermediate granules that have grown to the desired outer diameter are dried and then placed in a gas furnace or electric furnace for heat treatment. The heat treatment temperature is, for example, 1000°C to 1600°C. The pore-forming material and organic binder in the intermediate granules are burned out by the heat treatment. As a result, the regions within the intermediate granules where the pore-forming material was located become hollow, forming pores 10A. By subjecting the intermediate granules to heat treatment in this manner, an alumina porous body 10 having a plurality of pores 10A is completed (see FIG. 1).

[0022] [Characteristics of porous alumina] Next, the results of measurements of the pore diameter, porosity, crushing strength, and impurity capture amount for the porous alumina bodies 10 of Example 1 to Comparative Example 2, which were produced using the above-mentioned manufacturing method, are described. The pore diameter is the diameter of the pores 10A in the porous alumina body 10. The pore diameter was calculated as the circle-equivalent diameter of the pores 10A present in the porous alumina body 10 using a micrograph or SEM photograph of the cross section of the porous alumina body 10. The smaller the pore diameter, the lower the ability to capture impurities in a fluid, while the larger the pore diameter, the higher the ability to capture impurities in a fluid. Furthermore, if the pore diameter is too large, the porous alumina body 10 becomes brittle and the crushing strength decreases. Furthermore, the ratio of the diameter of the pores 10A to the maximum diameter of the porous alumina body 10 is preferably 1% or more and 20% or less. The aspect ratio of the porous alumina body 10 ((major axis - minor axis) / major axis) × 100) is 0.9 or more. That is, the porous alumina body 10 is formed in a substantially spherical shape. Therefore, the maximum diameter of the porous alumina body 10 corresponds to the major axis.

[0023] The porosity was measured in accordance with JIS R 2205. The porosity referred to here is the apparent porosity. Here, the porosity is the ratio of the volume of pores 10A to the total volume of the alumina porous body 10. The total volume of the alumina porous body 10 is the volume of the region surrounded by the surface of the alumina porous body 10 and the imaginary curved surface, assuming that all pores 10A appearing on the surface of the alumina porous body 10 are covered by an imaginary curved surface having the same curvature as the area near each pore 10A. This volume includes the volume of the pores 10A. The diameter of the pores 10A of the alumina porous body 10 is preferably 300 μm or more and 600 μm or less.

[0024] The smaller the porosity, the lower the ability to trap impurities in a fluid, and the higher the porosity, the higher the ability to trap impurities in a fluid. Furthermore, if the porosity is too high, the alumina porous body 10 becomes brittle and its crushing strength decreases. Therefore, the porosity is preferably 40% or more and 60% or less.

[0025] The crushing strength was measured using a known Kiya-type crushing strength measuring device. When the porous alumina body 10 is filled in a container used for immersion in a fluid, the smaller the crushing strength, the more likely the porous alumina body 10 located at the bottom of the container will be crushed and damaged due to the weight of the porous alumina body 10 located at the top of the container being applied to the porous alumina body 10 located at the bottom of the container. Therefore, the crushing strength is preferably 10 kgf or more. In other words, the higher the crushing strength value, the less likely the porous alumina body 10 will be crushed. In other words, the higher the crushing strength value, the better, and there is no upper limit.

[0026] The amount of captured impurities was measured using the apparatus shown in FIG. 3. In the apparatus shown in FIG. 3, a container 30 containing 600 g of pure water Pw, 2.5 g of iron (III) oxide, and a stirrer 31 was placed on a hot stirrer 32, and the stirrer 31 was rotated by the hot stirrer 32. The iron (III) oxide was a powdered form of red rust. The particle size of the iron (III) oxide was approximately 1 μm. The iron (III) oxide was dispersed in the pure water by the rotation of the stirrer 31. Then, a mesh basket 33 containing a 15 ml volume of alumina porous body 10 was immersed in the pure water Pw in which the iron (III) oxide had been dispersed and left for a predetermined time. The mesh basket 33 was suspended by a piano wire 34. As a result, the pure water Pw and iron (III) oxide entered the pores 10A, and the iron (III) oxide was collected in the alumina porous body 10. After a predetermined time has elapsed, the mesh basket 33 containing the porous alumina body 10 is pulled up and the porous alumina body 10 is dried. The weight of the porous alumina body 10 before immersion in the pure water Pw was subtracted from the weight after immersion in the pure water Pw to determine the amount of trapped impurities.

[0027] The alumina porous body 10 of Example 1 was produced by mixing 50 wt% to 80 wt% alumina powder, 0.1 wt% to 10 wt% clay mineral, 20 wt% to 40 wt% pore-forming material with a median diameter (average particle size D50) of 650 μm, and 0.1 wt% to 5 wt% organic binder, and the mixed powder was placed in a pan-type granulator or mixer and granulated while spraying water. The intermediate granules obtained by granulation were fired in a gas furnace or electric furnace at a temperature in the range of 1000°C to 1600°C to obtain spherical alumina porous bodies with diameters of 4 mm to 6 mm.

[0028] The manufacturing conditions for the alumina porous body 10 of Example 2 were the same as those for Example 1, except that a pore-forming material with a median diameter of 480 μm was used. The manufacturing conditions for the alumina porous body 10 of Example 3 were the same as those for Example 1, except that a pore-forming material with a median diameter of 700 μm was used. The manufacturing conditions for the alumina porous body 10 of Example 4 were the same as those for Example 1, except that a pore-forming material with a median diameter of 650 μm was used in an amount of 40 wt % to 60 wt %.

[0029] The conditions for producing the alumina porous body 10 in Comparative Example 1 were the same as those in Example 1, except that no pore-forming material was added. The conditions for producing the alumina porous body 10 in Comparative Example 2 were the same as those in Example 1, except that 1 to 20 wt % of a pore-forming material having a median diameter of 250 μm was used.

[0030] [Table 1]

[0031] As shown in Table 1, the alumina porous body 10 of Example 1 had a pore diameter of 450 μm, a porosity of 47%, a crushing strength of 26.8 kgf, and an impurity capture amount of 0.315 g.

[0032] In the alumina porous body 10 of Example 2, the pore diameter was 350 μm, the porosity was 43%, the crushing strength was 33.3 kgf, and the amount of trapped impurities was 0.208 g.

[0033] In the alumina porous body 10 of Example 3, the pore diameter was 500 μm, the porosity was 44%, the crushing strength was 17.7 kgf, and the amount of trapped impurities was 0.445 g.

[0034] In the alumina porous body 10 of Example 4, the pore diameter was 450 μm, the porosity was 53%, the crushing strength was 20.1 kgf, and the amount of trapped impurities was 0.41 g.

[0035] The alumina porous body of Comparative Example 1 had almost no pores, so the pore size was unmeasurable, the porosity was 5%, the crushing strength was 50 kgf or more, and the amount of trapped impurities was 0.018 g.

[0036] The alumina porous body of Comparative Example 2 had a pore diameter of 80 μm, a porosity of 20%, a crushing strength of 50 kgf or more, and an amount of trapped impurities of 0.022 g.

[0037] <Actions and Effects of the Example> The alumina porous body 10 has a spherical shape, and the ratio of the volume of the pores 10A to the total volume is 40% or more and 60% or less. With this configuration, impurities contained in the fluid can be effectively captured while preventing collapse.

[0038] The ratio of the diameter of the pores 10A to the maximum diameter of the alumina porous body 10 is 1% or more and 20% or less. With this configuration, impurities contained in the fluid can be effectively captured.

[0039] The diameter of the pores 10A of the alumina porous body 10 is 300 μm or more and 600 μm or less. This configuration allows the fluid to easily permeate into the alumina porous body 10, making it easier to effectively capture impurities.

[0040] The crushing strength of the porous alumina body 10 is 10 kgf or more. With this configuration, the porous alumina body 10 can withstand external forces that may be applied to the porous alumina body 10 when it is handled, and is therefore less susceptible to crushing.

[0041] A method for producing an alumina porous body uses a granular pore-forming material, alumina powder, a powdered organic binder, and a water-absorbent powdered clay mineral, and employs a rolling granulation method in which intermediate granules are granulated while spraying water. This configuration requires the use of a highly adhesive organic binder to form intermediate granules by binding multiple granular pore-forming materials together. However, if the organic binder absorbs too much water and becomes too adhesive, the intermediate granules tend to aggregate together during granulation, or the outer diameters of the individual intermediate granules tend to vary greatly. Therefore, by using a water-absorbent powdered clay mineral, the organic binder can be prevented from absorbing too much water, reducing adhesiveness and consolidating the pore-forming material, thereby enabling the production of intermediate granules with uniform outer diameters.

[0042] In the method for producing a porous alumina body, the median diameter of the pore-forming material is 400 μm or more and 1000 μm or less. This configuration makes it possible to produce a porous alumina body 10 having pores 10A with a larger diameter than conventional ones.

[0043] <Other Examples> The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments are also included within the technical scope of the present invention. (1) Unlike Example 1, powdered PVA may be used as the organic binder. (2) Unlike Example 1, examples of clay minerals include smectite and vermiculate clay minerals, aluminosilicates, and diatomaceous earth. Powdered bentonite, beidellite, nontronite, saponite, and the like may also be used. (3) In addition to water, the porous alumina body may be used to capture impurities from fluids such as machining oil and coolant. Also, the porous alumina body may be used as a catalyst by supporting it. (4) When the outer diameter of the alumina porous body is 3 mm to 20 mm, the pore diameter may be in the range of 30 μm to 4 mm, which corresponds to 1% or more and 20% or less. [Explanation of symbols]

[0044] 10: Porous alumina 10A: Pore

Claims

1. A porous alumina body having a spherical shape, the ratio of pore volume to the total volume being 40% or more and 60% or less.

2. 2. The alumina porous body according to claim 1, wherein the ratio of the diameter of the pores to the maximum diameter is 1% or more and 20% or less.

3. 3. The alumina porous body according to claim 2, wherein the pores have a diameter of 300 μm or more and 600 μm or less.

4. 4. The alumina porous body according to claim 1, which has a crushing strength of 10 kgf or more.

5. a granular pore-forming material; Alumina powder, a powdered organic binder; A powdered clay mineral having water absorption properties is used, A method for manufacturing porous alumina by carrying out a rolling granulation method in which intermediate granules are granulated while spraying water.

6. 6. The method for producing a porous alumina body according to claim 5, wherein the pore-forming material has a median diameter of 400 μm or more and 1000 μm or less.

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