JP2020128304A - Alumina porous body and manufacturing method thereof - Google Patents

Abstract

To provide a method for producing an alumina porous body having a sharp pore size distribution and a large porosity with those parameters adjustable.SOLUTION: A raw material liquid comprising an aluminum-containing colloid having good dispersibility is obtained by adding a carboxylic acid and an alkali to an aluminum salt aqueous solution. Porous alumina particles are obtained by spray pyrolysis of the raw material liquid. An alumina porous body is obtained by firing a molding material comprising the particle material. The pore characteristics of the porous alumina particles are adjusted by raw material liquid preparation conditions and the like, and the pore characteristics, porosity and the like of the alumina porous body highly reflect the pore characteristics of the porous alumina particles, and are further adjusted by molding and firing conditions.SELECTED DRAWING: Figure 8

Description

The present specification relates to an alumina porous body and a method for producing the same.

Alumina (Al ₂ O ₃ ) which is an oxide of aluminum is useful as a carrier for a polishing material, various heat resistant materials, toughness materials, heat shock resistant materials, catalysts for automobile exhaust gas purification catalysts and the like. Among them, a porous sintered body of alumina is suitable for such applications.

There are various methods for producing a porous alumina body. For example, a method of forming alumina particles having a predetermined particle diameter and firing them to form pores as particle gaps to form a porous body, and an alumina formed body containing a pore source material such as a foam material or a burnout material. There is known a method of firing and removing the pore source material in the process of firing to obtain a porous body (Non-Patent Document 1).

National Science Museum, 12th Report of Systematization Survey on Technology, p. 183-p. 187

However, even though the above method is disclosed, it is difficult to control the pore characteristics such as the porosity, the pore diameter, the communication rate, and the specific surface area of the alumina porous body. Therefore, until now, it has been difficult to produce an alumina porous body that is suitable for use as a catalyst carrier or the like.

The present specification provides an alumina porous body having excellent pore characteristics, a method for producing the same, and the like.

The present inventors examined the preparation of a raw material liquid using a carboxylic acid as a quenching agent (disintegrating agent) and a dispersant when producing an alumina porous body by a spray pyrolysis method. As a result, they have found that by devising the method of preparing the raw material liquid, it is possible to produce the alumina porous particles having good porosity and specific surface area by the spray pyrolysis method. Furthermore, the present inventors have found that when a sintered body is manufactured using such alumina porous particles, it is possible to obtain an alumina porous body in which the median diameter and porosity are controlled with extremely high accuracy. The present specification provides the following means based on these findings.

The present specification describes a raw material liquid preparing step of preparing a raw material liquid which is an aluminum-containing colloid containing a carboxylic acid, a manufacturing step of an alumina porous particle material in which droplets of the raw material liquid are heated to form particles, and And a step of sintering a molding material containing an alumina porous particle material at 1000° C. or more and less than 1400° C. to obtain an alumina porous body, the method for producing an alumina porous body.

Further, the present specification provides a porous alumina body containing crystalline alumina and having a median diameter of 0.02 μm or more and less than 0.2 μm. Further, the present specification provides a porous alumina body having a median diameter of 0.02 μm or more and 0.2 μm or less and an open porosity of 50% or more.

For example, this specification can provide the means of the following aspect.

[1] A method for manufacturing a porous alumina body,
A raw material liquid preparing step of preparing a raw material liquid which is an aluminum-containing colloid containing a carboxylic acid,
A step of producing an alumina porous particle material for heating the droplets of the raw material liquid to form particles,
A sintering step of sintering a molding material containing the porous alumina particle material to obtain an alumina porous body at 1000° C. or higher and less than 1400° C.;
Comprising a method.
[2] The method according to [1], wherein the raw material liquid preparation step is a step of adding a carboxylic acid to an aluminum salt aqueous solution and then adding an alkali to prepare the raw material liquid.
[3] The method according to [1], wherein the raw material liquid preparation step is a step of adding an alkali to an aluminum salt aqueous solution and then adding a carboxylic acid to prepare the raw material liquid.
[4] The method according to [3], wherein the raw material liquid preparation step is a step of preparing the raw material liquid by adding a carboxylic acid to a dispersion liquid containing insoluble aluminum hydroxide.
[5] The method according to [4], wherein the aluminum hydroxide is gel aluminum hydroxide.
[6] The method according to any one of [3] to [5], wherein the raw material liquid preparation step includes adjusting the pH of a liquid in which an aluminum salt is dissolved to precipitate aluminum hydroxide.
[7] The method according to any one of [1] to [6], wherein the raw material liquid preparing step includes adding the carboxylic acid to aluminum in a molar ratio of 1 or more and 2 or less.
[8] The method according to any one of [1] to [7], wherein the carboxylic acid is one or more selected from the group consisting of acetic acid, citric acid, oxalic acid and malic acid.
[9] The method according to any one of [1] to [8], wherein the carboxylic acid is citric acid.
[10] In any one of [1] to [9], further comprising a step of calcining the alumina porous particle material at 600° C. or higher and 950° C. or lower after the generation step and prior to the firing step. The described method.
[11] The method according to [10], further comprising a crystallization step of converting at least a part of the alumina porous particle material into a γ-alumina phase after the calcination step and before the firing step.
[12] The method according to [10], further comprising a crystallization step of converting at least a part of the alumina porous particle material into an α-alumina phase after the calcination step.
[13] A method for producing an alumina porous particle material for producing an alumina porous body,
A raw material liquid preparing step of preparing a raw material liquid which is an aluminum-containing colloid containing a carboxylic acid,
A step of producing an alumina porous particle material for heating the droplets of the raw material liquid to form particles,
A calcining step of calcining the alumina porous particle material at 600° C. or higher and 950° C. or lower;
Comprising a method.
[14] A porous alumina body containing crystalline alumina, having a median diameter of 0.02 μm or more and 0.2 μm or less and an open porosity of 50% or more.
[15] A porous alumina body containing crystalline alumina and having a median diameter of 0.02 μm or more and less than 0.2 μm.
[16] The alumina porous body according to [14] or [15], which has a total porosity of 55% or more.
[17] The alumina porous body according to [14] or [15], which has an open porosity of 55% or more.

It is a figure which shows an example of the manufacturing process of the alumina porous particle material disclosed in this specification. FIG. 3 is a diagram showing a manufacturing process of an alumina porous particle material in Example 1. It is a figure which shows the pore distribution of an alumina porous body by calcination at 1050 degreeC for 2 hours. It is a figure which shows the fine pore distribution of the alumina porous body by 1100 degreeC and 0 hour baking. It is a figure which shows the fine pore distribution of the alumina porous body by baking at 1200 degreeC for 0 hour. It is a figure which shows the fine pore distribution of the alumina porous body by 1300 degreeC and 0 hour baking. It is a figure which shows the fine pore distribution of the alumina porous body by 1400 degreeC and 0 hour baking. It is a figure which shows the pore distribution of an alumina porous body by baking at 1400 degreeC for 2 hours. It is a figure which shows the relationship between the calcination temperature of various alumina porous bodies, and a median diameter, and the calcination temperature and an open porosity.

The present specification relates to an alumina porous body, a method for producing the same, and the like. According to the method for producing an alumina porous body (hereinafter, also simply referred to as the present porous body) disclosed herein (hereinafter, also simply referred to as the present production method), the following steps may be provided. it can. First, an alumina porous particle material (hereinafter also referred to as the present particle material) having pores inside and on the surface thereof is obtained. Further, a molded body containing the present particle material is fired under constant conditions. By including these steps, the present porous body having excellent pore characteristics can be obtained.

When the molded body of the present particle material is fired under the above-mentioned conditions, the present particle materials come close to each other and are bonded to each other, whereby sintering proceeds. At this time, along with the growth of the contacting portions (neck) of the respective main particle materials, the pores on the surface and inside of the combined main particle materials communicate with each other. As a result, the present porous body has at least communication holes formed by communicating the pores inside or on the surface of the present particle material. On the other hand, since the firing conditions are relaxed, the progress of sintering is controlled, neck growth and grain growth are suppressed, and further connection and expansion of communication holes are suppressed. Therefore, it is possible to obtain a porous body in which the median diameter is suppressed, in which the porosity originally possessed by the present particle material is reflected. In addition, the present particle material may have pores derived from the voids between the present particle materials.

As described above, according to the present production method, the porosity of the present particle material (for example, it is clear from the tap (bulk) density and the particle internal voids observed by electron microscope observation) is highly reflected. It is possible to obtain a porous body having the specified pore characteristics. That is, according to the present production method, the particle size characteristics of the present particle material can be obtained by obtaining the porous particle material excellent in particle size characteristics such as particle size characteristics with high homogeneity and adopting the above firing conditions. It is possible to obtain a porous body having a small median diameter by reflecting the porosity and the porosity. In addition, it is possible to obtain the present porous body having high open porosity and total porosity and/or excellent uniformity of pore diameter.

Note that the above operation is an inference and does not necessarily bind the disclosure in this specification. Heretofore, it has been difficult to obtain a porous alumina body having high porosity and uniform pore size.

Hereinafter, various embodiments of the present particle material production method, the present particle material, the present porous body, the present production method, the present porous body, and the like, which are also a part of the present production method, will be described with reference to the drawings as appropriate. FIG. 1 is a diagram showing an outline of a method for producing the present particle material.

(Method for producing porous alumina particle material)
The method for producing the present particulate material can include a raw material liquid preparation step that is an aluminum-containing colloid, and a production step in which droplets of the raw material liquid are heated to form particles. Further, if necessary, the present particle material manufacturing method can include a crystallization step of heating (calcining) the particles to promote crystallization.

The present particle material manufacturing method uses a powder synthesis method called a so-called spray pyrolysis method. That is, a solution or dispersion liquid containing the raw material of the powder to be obtained is formed into droplets by an appropriate means, and the droplets are heated to evaporate the liquid and at least partially thermally decompose the raw material. This is a method of forming particles. The application of the spray pyrolysis method to this manufacturing method will be described in detail later.

(Raw material liquid preparation process)
The raw material liquid preparation step is a step of preparing a raw material liquid which is an aluminum-containing colloid containing a carboxylic acid. The raw material liquid can be produced, for example, in two steps. Hereinafter, a case will be described in which the first raw material liquid is first prepared, and then the second raw material liquid is prepared and subjected to spray pyrolysis. That is, in the present particle material manufacturing method, the raw material liquid can be manufactured by sequentially adding the carboxylic acid and the alkali such as ammonia to the liquid containing the aluminum salt. The order of adding the carboxylic acid and the alkali may be first alkali and then carboxylic acid, or first carboxylic acid and then alkali.

(First mode of preparation of raw material liquid)
(First raw material liquid)
The first raw material liquid can be a liquid containing aluminum hydroxide as an insoluble material. The first raw material liquid can be prepared by various methods. For example, aluminum hydroxide (Al(OH) ₃ ) is generally insoluble in water, but may be water prepared by adding aluminum hydroxide to water.

Further, the first raw material liquid may be prepared by adjusting the pH of a liquid in which an aluminum salt is dissolved and precipitating aluminum hydroxide. This first raw material liquid contains aluminum hydroxide as a gel-like precipitate. Furthermore, the first raw material liquid may be prepared by adding separately prepared aluminum hydroxide gel to water or the like, or an aluminum hydroxide gel powder prepared in advance so as to gel when added to water or the like. (Commercially available) may be poured into water to prepare.

Considering the operability and the subsequent preparation of the second raw material liquid, the first raw material liquid preferably contains gelled aluminum hydroxide produced from an aluminum salt. By including such an aluminum hydroxide, it is possible to form an aluminum-containing colloid suitable for forming porous particles by the spray pyrolysis method by adding a carboxylic acid, and to make the carboxylic acid content as a disappearing agent porous. Since it is possible to disperse in various forms, and relatively large colloidal particles can be formed, it is easy to control the porosity and/or the specific surface area.

The liquid that holds or disperses aluminum hydroxide in the first raw material liquid is, for example, a mixed liquid of water or an organic solvent compatible with water. Examples of the organic solvent include lower alcohols having about 1 to 4 carbon atoms such as methanol and ethanol, acetonitrile, DMSO and the like. The mixed liquid preferably contains water as a main component, that is, contains more than 50% by volume of water, for example, 60% by volume or more, or, for example, 70% by volume or more, and for example, 80% by volume or more, Further, for example, it may be 90% by volume or more, and further, for example, 95% by volume or more.

The concentration of aluminum hydroxide (Al(OH) ₃ ) contained in the first raw material liquid is not particularly limited, but can be 0.05M or more and 5M or less, and, for example, 0.05M or more and 2M or less. You can Further, for example, it can be 0.1 M or more and 1.5 M or less.

When the first raw material liquid is prepared from an aluminum salt, the aluminum salt is not particularly limited, and a water-soluble aluminum salt can be used. Examples thereof include aluminum chloride, aluminum nitrate, aluminum sulfate, aluminum lactate, aluminum acetate, aluminum oxalate, and aluminum phosphate, as well as aluminum secondary butyrate and aluminum isopropylate. The concentration of the aluminum salt can be such that the molar concentration of aluminum hydroxide described above can be obtained.

When the first raw material liquid is prepared from aluminum salt, the pH of the aluminum salt solution can be adjusted to about 4 or more and 11 or less by using alkali such as ammonia. By doing so, a gel-like precipitate of aluminum hydroxide can be deposited. The addition amount of alkali such as ammonia is not particularly limited. For example, when adding ammonia to aluminum salt (aluminum), the amount of ammonia can be about 2 mol or more and 8 mol or less with respect to 1 mol of aluminum. Further, for example, the amount may be 3 mol or more and 6 mol or less.

(Second raw material liquid)
The second raw material liquid can be prepared as a colloidal solution in which carboxylic acid is added to the first raw material liquid to disperse insoluble aluminum hydroxide as colloidal particles. In the second raw material liquid, the carboxylic acid is adsorbed on the aluminum hydroxide formed as a gel-like precipitate, and as a result, a repulsive force is generated between the particles and the particles can be dispersed as colloidal particles. In addition, the carboxylic acid contains various dispersoids (colloidal particles) including an aluminum-containing compound in which hydroxide ions are partially substituted.

In addition, the carboxylic acid can disappear by heating and form pores in the particles. Therefore, preparing an aluminum-containing colloid using a carboxylic acid for aluminum hydroxide particles formed as an insoluble material can produce comparatively large aluminum hydroxide colloid particles and eliminates aluminum ions and disappearance. Since it can be dispersed in various forms with the agent, it is possible to prepare a raw material liquid suitable for spray pyrolysis for producing the alumina porous particle material.

A large number of such aluminum-containing colloidal particles are formed in the second raw material liquid. Therefore, the droplets formed from the second raw material liquid can contain the carboxylic acid in a high concentration and in various forms, which can contribute to increase the porosity and specific surface area of the obtained alumina particles. ..

As the carboxylic acid, formic acid, acetic acid, propionic acid, monocarboxylic acids such as lactic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, dicarboxylic acids such as malic acid, citric acid, Examples thereof include tricarboxylic acids such as aconitic acid and α-hydroxycarboxylic acids such as lactic acid, malic acid and citric acid. Alternatively, it may be EDTA or a salt thereof. Preferably, α-hydroxycarboxylic acid can be used. More preferred is α-hydroxytricarboxylic acid such as citric acid.

The formation of the aluminum hydroxide colloid can be confirmed by adding the carboxylic acid to the first raw material liquid and disappearing the gel-like precipitate to gradually clear the liquid. Although not particularly limited, it is preferable to add the carboxylic acid until the gel-like precipitation is almost eliminated and the liquid becomes almost clear to clear.

The amount of carboxylic acid also affects porosity and specific surface area. According to this production method, since aluminum hydroxide is made into a colloid with carboxylic acid, aluminum hydroxide can be dispersed in the second raw material liquid together with a large amount of carboxylic acid. Therefore, the degree of freedom in designing the porosity and the specific surface area is improved.

The addition amount of the carboxylic acid is not particularly limited, and generally depends on the type of the carboxylic acid used, the intended porosity and/or the specific surface area, but is generally based on the aluminum (aluminum salt) in the first raw material liquid. The equivalent ratio can be about 1 or more and 4 or less. Alternatively, for example, the number may be 1 or more and 3 or less. Since aluminum is trivalent, the carboxylic acid having an equivalent ratio of 1 to 1 mol of aluminum is 3 mol for acetic acid and 1 mol for citric acid.

The second raw material liquid thus prepared is an aluminum-containing colloid containing colloidal particles of various aspects as described above. For this reason, the second raw material liquid contains aluminum and carboxylic acid well dispersed in the second raw material liquid.

The aluminum-containing colloid is a colloid obtained by adding a carboxylic acid to insoluble aluminum hydroxide. Therefore, this colloid is considered to have colloidal particles (dispersoids) having a relatively large particle size.

In addition to colloidal particles in which carboxylic acid is adsorbed to Al(OH) _{3 with} respect to aluminum hydroxide, for example, Al(OH) ₂ (R(COOH) ₃ ) _1/3 , Al(OH)(R(COOH) ₃ ) _2/3 , Al(R(COOH) ₃ ) _3, etc. Al(OH) ₂ (RCOOH) _1- Al(OH) ₁ (RCOOH) _2- Al(RCOOH) It is considered that the dispersoid, which is an aluminum-containing compound in various embodiments, is included depending on the type of carboxylic acid such as ₃ .

By evaporating and thermally decomposing the second raw material liquid, which is the aluminum-containing colloid of this aspect, as droplets, the progress of sintering on the droplet surface and inside is suppressed, and voids are formed on the droplet surface and inside the droplet. It is considered that the formation of the

(Second mode of preparation of raw material liquid)
(First raw material liquid)
The first raw material liquid can be a solution (liquid) containing an aluminum salt. The first raw material liquid can be prepared by various methods. For example, in general, the water-soluble aluminum salt described above can be prepared by dissolving it in water. The concentration of the aluminum salt contained in the first raw material liquid of the second aspect is not particularly limited, but can be 0.05 M or more and 5 M or less, and can be, for example, 0.05 M or more and 2 M or less. .. Further, for example, it can be 0.1 M or more and 1.5 M or less.

When the first raw material liquid is prepared from an aluminum salt, the aluminum salt is not particularly limited, and a water-soluble aluminum salt can be used. Examples thereof include aluminum chloride, aluminum nitrate, aluminum sulfate, aluminum lactate, aluminum acetate, aluminum oxalate, and aluminum phosphate, as well as aluminum secondary butyrate and aluminum isopropylate. The concentration of the aluminum salt may be such that the molar concentration of aluminum hydroxide described above is finally obtained.

The first raw material liquid of the second aspect contains a carboxylic acid. Carboxylic acid also produces an aluminum-containing compound in which the carboxylate salt is partially replaced. The carboxylic acid can be used in the same manner (type, concentration) as in the first aspect.

(Second raw material liquid)
The second raw material liquid can be prepared by supplying an alkali such as ammonia to the first raw material liquid of the second aspect to the extent that an aluminum-containing colloid is formed. The alkali can be used in the same manner (type, concentration, etc.) as in the first aspect.

That is, in the second raw material liquid of the second aspect, by adding an alkali, “a variety of aluminum dispersoids containing an aluminum-containing compound in which carboxylate ion of aluminum carboxylate is partially replaced by hydroxide ion It is possible to produce an aluminum-containing colloid in which "(colloid particles)" are uniformly dispersed together with a carboxylic acid. That is, the aluminum-containing colloid in this raw material liquid is Al(OH) ₂ (R(COOH) ₃ ) _1/3 , Al(OH)(R(COOH) ₃ ) _2/3 , Al(R(COOH) ₃ ) _{3 and the} like, Al(OH) ₂ (RCOOH) _{1 to} Al(OH) ₁ (RCOOH) _{2 to} Al(RCOOH) _{3, and the} like, including dispersoids that are aluminum-containing compounds in various embodiments depending on the type of carboxylic acid. It is thought to be coming out. Therefore, since aluminum ions and carboxylic acid that is a quencher can be dispersed in various forms, it is possible to prepare a raw material solution suitable for spray pyrolysis for producing a porous alumina particle material.

A large number of such aluminum-containing colloidal particles are formed in the second raw material liquid. Therefore, the droplets formed from the second raw material liquid can contain the carboxylic acid in a high concentration and in various forms, which can contribute to increase the porosity and specific surface area of the obtained alumina particles. ..

(Generation process)
In the production step, the raw material liquid, more specifically, the droplets of the second raw material liquid can be heated to be granulated. In the producing step, the second raw material liquid is formed into droplets by an appropriate droplet forming means, the droplets are heated to evaporate the liquid, and the raw material in the second raw material is thermally decomposed to form particles containing alumina. Can be generated. The production step can be carried out according to, for example, a so-called conventional spray pyrolysis method.

The droplets obtained from the second raw material liquid are aluminum-containing colloids that are relatively large and contain colloidal particles of various aspects. That is, since the aluminum-containing colloid of the second raw material liquid has various aspects, therefore, it depends on various conditions such as temperature, gas flow rate, atomization in the production process and temperature conditions in the subsequent firing process. The degree of freedom in controlling the desired specific surface area and relative density is large. In addition, the second raw material liquid of the first aspect is better than the aluminum-carboxylic acid chelate (second raw material liquid according to the second aspect) obtained by supplying a carboxylic acid to a water-soluble aluminum salt. It tends to be large particles. For this reason, the degree of freedom in controlling the particle characteristics is higher.

The droplet forming means used in the production step is not particularly limited, and a means applied to a known spray pyrolysis method can be used. Therefore, without particular limitation, a spray nozzle, an ultrasonic atomizing means, an electrostatic atomizing means, or the like can be appropriately selected and used. Preferably, it is an ultrasonic atomizing means or the like.

Further, in the production step, a heating furnace using various heat sources can be used. The heating furnace is also not particularly limited, and various heating furnaces such as an infrared heating furnace, a microwave heating furnace, and a resistance heating furnace applied to a known spray pyrolysis method can be appropriately used.

In addition to the raw material concentration in the second raw material liquid in the production step, the temperature, the type of gas, the gas flow rate, etc. can be appropriately set from the viewpoints of particle size control, composition control, particle structure control, and productivity. For example, the temperature may be a constant temperature, but the temperature can be gradually raised from the introduction part to the discharge part of the heating furnace. Typically, a temperature setting intended for the drying to thermal decomposition of the droplets can be used. A temperature of about 200° C. to 600° C. can be set for drying the droplets. Moreover, for example, for the thermal decomposition, a temperature of about 600° C. to 1600° C. can be set.

As an example, the heating furnace as a whole is heated in a range of 200° C. to 1000° C., for example, 200° C. to 800° C., and these temperature ranges are set to 2 or more, more preferably 3 or more. More preferably, it is preferable to arrange and heat a controlled heat source at 4 or more different temperatures (for example, 200° C., 400° C., 600° C. and 800° C.).

As the gas, an oxidizing gas containing oxygen, typically air, can be used from the viewpoint of alumina generation. The flow rate can be set according to a known spray pyrolysis method, but can be appropriately set in the range of, for example, 2 L/min to 10 L/min, or 3 L/min to 7 L/min. ..

The particles obtained by the producing step can include alumina particles at least in part. Further, at least a part thereof is porous or hollow particles due to the disappearance of carboxylic acid. For example, the particles obtained by the production process are generally porous, and may typically have one or more pores inside and also pores on the surface. Alumina may be amorphous or crystalline. Generation of alumina, its type (crystallinity, crystal type), and porosity can be appropriately controlled by the temperature conditions and gas flow conditions in the generation step.

The particles obtained in the production step are appropriately captured by a known capturing means. As such a trapping means, a trapping means generally used in the spray pyrolysis method can be appropriately adopted.

(Firing process)
For the particles obtained in the production step, an additional firing step is preferably performed in order to further control or ensure the particle characteristics such as the crystallinity and crystal form of alumina, the porosity and the specific surface area. The firing step may be carried out, for example, as a crystallization step of heating the particles obtained in the production step to promote the crystallization of alumina, or to completely eliminate the carboxylic acid and improve the porosity. It may be carried out as a step (calcination step) of adjusting (decreasing or increasing) the specific surface area.

For example, in order to suppress the median diameter of the porous material, in an oxidizing atmosphere, for example, 400°C or higher and 1000°C or lower, or 600°C or higher and 950°C or lower, or 800°C or higher and 900°C or lower, for example. You can do it for as long as you need. Further, for example, it can be performed at a temperature of 400° C. or higher and 800° C. or lower, for example, 500° C. or higher and 700° C. or lower, and for example, about 550° C. or higher and 650° C. or lower for a required time. The time is, for example, 2 hours or more and 10 hours or less, or, for example, 4 hours or more and 8 hours or less, or, for example, 5 hours or more and 7 hours or less. By carrying out such a calcination step, it is possible to improve the sinterability in the subsequent step of firing the molded body, increase the open porosity, and suppress the median diameter.

For example, when carrying out the crystallization step, the firing temperature can be set according to the crystal form of the alumina to be obtained. For example, in the present particle material, when γ-alumina is the main crystal form, the temperature can be, for example, 800° C. or higher, or, for example, 850° C. or higher and lower than 1100° C. Further, in the present particle material, when α-alumina is the main crystal form, for example, 1050° C. or higher, or 1100° C. or higher, or 1100° C. or higher and 1400° C. or lower, or more preferably 1150° C. or lower. The temperature can be set to about not lower than 1200C and not higher than 1200C. Further, the firing time can be set as appropriate, but for example, it can be set to about 1 hour to 3 or 4 hours or less, typically within 2 to 3 hours. Preferably, a firing step for converting γ-alumina is carried out.

For example, when the present particle material contains γ-alumina in a crystalline form, it is possible to employ a calcination temperature at which α-alumina is obtained in the subsequent step of calcination of the molded body. In that case, the phase change from γ to α can be used as an element for controlling the pore diameter and homogeneity of the present porous body, and it may be easier to obtain the intended alumina porous body.

In addition, such a firing process can be performed in an oxidizing atmosphere. That is, it may be carried out in an oxygen atmosphere or an air atmosphere, or may be carried out in a reducing atmosphere such as argon gas or nitrogen, but an oxidizing atmosphere is preferable.

For example, the firing step for improving the porosity and the firing step for γ-aluminization or α-alumination can be performed in this order. Further, for example, these two types of firing steps can be continuously performed. Preferably, a firing step for converting γ-alumina is carried out.

According to this production method, the second raw material liquid, which is an aluminum-containing colloid containing aluminum and carboxylic acid, can be prepared in various modes. Therefore, particles having excellent porosity and/or specific surface area can be obtained from the second raw material liquid, that is, the droplets of the second raw material liquid. Accordingly, it is suitable for making porous and/or specific surface areas of alumina porous particle materials, such as the alumina porous particle materials disclosed herein below, ie, of desired porosity and/or specific surface area. It can be

In addition, in this manufacturing method, you may implement the disintegration process of the particle for canceling the aggregation state of the obtained particle in any stage after a production|generation process. Such a crushing step may be ultrasonic crushing in a liquid phase in addition to usual crushing.

(Alumina porous particle material)
The alumina porous particle material disclosed herein contains crystalline alumina and can have a specific surface area of 20 m ² /g or more and 90 m ² /g or less and a relative density of 60% or more and 80% or less. .. This is because according to the present production method, the porosity and the specific surface area can be adjusted by controlling the concentration of aluminum salt such as aluminum hydroxide or the concentration of carboxylic acid.

The alumina porous particle material disclosed in the present specification can include, for example, γ-alumina and include porous alumina particles having a relative density of 60% or more and 98% or less. Further, for example, it is 60% or more and 95% or less, or, for example, 60% or more and 90% or less, or for example, 60% or more and 85% or less, or for example, 60% or more and 80% or less. Such materials are suitable for conventional alumina applications. In particular, it tends to be useful for materials that require specific surface area and porosity, such as catalyst carriers.

The present particulate material can have, for example, γ-alumina (phase). γ-Alumina can be confirmed by an X-ray diffraction spectrum. Further, the present particle material has a relative density of 60% or more and 80% or less. Within such a relative density range, the pore structure (porosity, hollowness, etc.) of the porous alumina particles of the present particle material is suitable. Further, for example, the relative density may be 60% or more and 70% or less. In the present specification, the relative density is obtained from the pore volume (Vp (cm ³ /g)) derived from the nitrogen adsorption isotherm of the present particle material with respect to the true density of alumina (3.7 g/cm ³ ). It can be calculated as a ratio of the density of the present particle material (ρ=1/((1/3.7)+Vp) (g/cm ³ )) obtained from the density of the particle material and the true density of alumina.

The specific surface area of the present particle material may be, for example, 5 m ² /g or more, or may be 10 m ² /g or more, for example, 15 m ² /g or more. And may be, for example, 20 m ² /g or more, and may be, for example, 40 m ² /g or more, and may be, for example, 50 m ² /g or more, and, for example, 60 m ² /g It is also possible to set the above, and for example, it can be set to 80 m ² /g or more. Although not particularly limited, when the non-surface area is 40 m ² /g or more, or 50 m ² /g or more, or 60 m ² /g or more, or 80 m ² /g or more, a catalyst carrier or a solid oxide fuel cell It can be said that it has a sufficient surface area to be used for such purposes. The specific surface area can be measured by using nitrogen as a gas and an adsorption isotherm measuring device (Bell Soap Mini, made by Nippon Bell) as a device, and measuring at 0.1 to 0.5 kPa at 5 points. it can. That is, the value of the specific surface area can be obtained from the slope by linearly extrapolating to these points. Note that other measurement conditions tend to be measurable with the default settings of the device used.

Other alumina porous particle materials disclosed herein may also contain α-alumina. α-Alumina can be confirmed by an X-ray diffraction spectrum. Also, this material can have the same relative density as in the case of containing γ-alumina. Although not particularly limited, the relative density is preferably 60% or more and 80% or less, for example. Further, for example, it may be 60% or more and 70% or less. Furthermore, this material may have a specific surface area of, for example, 5 m ² /g or more, for example, 10 m ² /g or more, and for example, 15 m ² /g or more, Further, it may be, for example, 20 m ² /g or more, and may be, for example, 40 m ² /g or more, or 50 m ² /g or more, or 60 m ² /g or more. The larger the specific surface area, the more the reaction area and the supporting area can be secured, so that high performance can be exhibited.

In addition, since the alumina porous particle material disclosed in this specification is synthesized by the spray pyrolysis method, each particle can take the form of a true spherical particle in appearance. The average particle size of the obtained particulate material can be appropriately adjusted by adjusting the mist diameter in spray pyrolysis, controlling the temperature, and the like. For example, according to the spray pyrolysis method using a mist using ultrasonic waves, the average particle size of the present particle material can be 0.5 μm or more and 3 μm or less. Further, according to the spray pyrolysis method, the bulk density of the particles obtained by adjusting the concentration of the raw material solution can be adjusted. For example, the present particle material in the range of 0.3 g/cm ³ or more and 1 g/cm ³ or less can be obtained. According to the present particulate material obtained by the spray pyrolysis method, the open porosity and the total porosity are respectively high, and the ratio of open porosity/total porosity is, for example, 80% or more, or, for example, 85% or more, or For example, it becomes easy to obtain the present porous body of 90% or more, 95% or more, and 98% or more, for example.

The average particle diameter of the present particle material is obtained by measuring two diameters measured from two directions with respect to 10,000 randomly selected secondary particles (which is the present particle material) from the SEM observation image, and calculating the average value. It can be adopted as the average particle size. Such a particle size can be measured by an image analysis device of Morphologi series manufactured by Malvern Panalytical.

(Method for producing porous alumina body)
The method for producing an alumina porous body disclosed in the present specification can include a step of producing the present particle material, and a step of firing the molding material containing the present particle material obtained in such an producing step. That is, the present manufacturing method includes a raw material liquid preparation step of preparing a raw material liquid containing an aluminum-containing colloid, a production step of heating droplets of the raw material liquid to form particles, and an alumina porous layer obtained in the production step. A step of firing the fine particulate material and a step of firing the molding material containing the fired alumina porous particulate material to obtain a porous alumina body can be provided (if necessary).

The steps until obtaining the present particulate material are as already described. In order to obtain the present porous body using the present particle material, for example, a calcined temporary formed body of the present particle material is produced according to a conventional method. Then, it can be obtained by firing this temporary molded body.

In obtaining the present porous body, the median diameter of the present porous body can be adjusted by appropriately selecting the firing step temperature after the spray pyrolysis of the present particulate material.

In order to obtain the present porous body, generally, the raw material for firing, the preparation of the molded body and the firing of the molded body can be carried out. A known method applied to an alumina sintered body can be applied to the preparation of the firing raw material. Although not particularly limited, for example, the present particle material alone may be used as the molding material. By using only the present particulate material as the raw material for firing, it is possible to avoid the formation of pores due to other materials, and thus it becomes easy to control the median diameter, the open area ratio, and the like. In addition, by appropriately using a dispersant such as water or an organic solvent in the present particle material, and optionally using a ball mill, a bead mill, or the like, mixing (wet mixing or dry mixing), and drying as necessary. You can also get it. Known additives such as binders and auxiliaries can be used as the raw material for firing. The raw material for firing can be in the form of powder, granules, slurry or the like, depending on the process used in the preparation of the molded body. Known dispersants, binders, auxiliaries and the like can be appropriately used. For example, a suitable molded product can be obtained by mixing about 2% by mass of polyvinyl alcohol, and the influence on the pore size control of the sintered product based on the use of the present particle material can be avoided or suppressed.

In addition, the present porous body can use only the present particle material as the ceramics, and may include other ceramic materials which can be co-sintered with alumina, in addition to the present particle material, if necessary. Good. When other ceramic materials are used, the present particle material is, for example, 90% by mass or more, or 95% by mass or more, or 98% by mass or more, or 99% by mass with respect to the total mass of the ceramic materials. % Or more, for example, 99.5% by mass or more, for example, 99.8% by mass or more, and for example, 99.9% by mass or more. The other ceramic material is not particularly limited, but examples thereof include zirconia and magnesia. As for the other ceramic materials, it is preferable to use spherical particle materials obtained by the spray pyrolysis method using mist, like the present particle material.

Various known processes can be employed to prepare an intended molded product from the raw material for firing. Although not particularly limited, for example, pressure molding such as uniaxial pressure molding and CIP, cast molding, gel cast molding, filter film formation, injection molding, rubber press, extrusion molding, doctor blade molding, tape molding, etc. are known. The molding process can be appropriately adopted. The molded body is appropriately dried if necessary.

Next, the molded body is fired. The firing temperature as the firing condition, that is, the maximum holding temperature in the firing step can be set to, for example, 1000° C. or more and less than 1400° C. The lower the firing temperature, the larger the open porosity and the smaller the median diameter. For example, at a firing temperature of 1400°C, the open porosity tends to decrease as the firing time increases (the firing level increases). Further, for example, at a calcination temperature of 1400° C., when the calcination time becomes long (the calcination level becomes high), the median diameter tends to increase, while at 1100° C. or less, the median diameter tends to largely decrease. Therefore, the firing temperature is, for example, 1000° C. or more and 1350° C. or less, or, for example, 1000° C. or more and 1300° C. or less, or, for example, 1000° C. or more and 1250° C. or less, or, for example, 1000° C. or more 1200° C. Or less, for example, 1000° C. to 1150° C. or less, or, for example, 1000° C. to 1100° C. or less, or, for example, 1000° C. or more and 1050° C. or less. Further, for example, in consideration of α-formation, it is 1050° C. or higher and lower than 1400° C., for example, 1050° C. or higher and 1350° C. or lower, for example, 1050° C. or higher and 1300° C. or lower, and for example, 1050° C. or higher and 1250° C. Or less and, for example, 1050° C. or more and 1200° C. or less, and for example, 1050° C. or more and 1100° C. or less. The α-formation promotes the bond between the particles and improves the strength.

Further, the firing time as the firing conditions, that is, the holding time at the firing temperature can be set to, for example, 0 hours or more and 4 hours or less. As described above, when the firing time becomes long, depending on the temperature conditions, the sintering proceeds, the open porosity tends to decrease, and the median diameter tends to increase. Therefore, the firing time is, for example, 0 hour or more and 3 hours or less, or, for example, 0 hour or more and 2 hours or less, or, for example, 0 hour or more and 1 hour or less, or, for example, 0 hour or more and 0. 5 hours or less.

From the above, the firing conditions are, for example, 0 hours or more and 2 hours or less when the firing temperature is less than 1100°C, and 0 when the firing temperature is, for example, 1100°C or more and less than 1400°C. The time can be 1 hour or more and 1 hour or less, and can be 0 hour or more and 0.5 hour or less, for example.

The temperature rising conditions until reaching the firing temperature are not particularly limited, but are, for example, 0.5° C./min or more and 5° C./or less, or, for example, 1° C./min or more and 3° C./or less, Further, for example, it can be set to 1.5° C./minute or more and 2° C./or less. The temperature lowering condition from the firing temperature is not particularly limited, but is, for example, 0.5° C./minute or more and 5° C./or less, or 1° C./minute or more and 3° C./or less, or, for example, 1 The temperature can be set to 0.5° C./min or more and 2° C./min or less.

The firing atmosphere may be an oxidizing atmosphere such as oxygen or air or a reducing atmosphere, but is preferably an oxidizing atmosphere.

When the molded body contains a binder or the like, in order to remove the binder in advance, at a temperature near the burning temperature of the binder and sufficiently lower than the firing temperature (for example, 200° C. or higher and 500° C. or lower), The process of maintaining for a period of time can be implemented.

A known firing process can be adopted for firing the molded body. Although not particularly limited, for example, normal pressure sintering using microwaves, gas pressure sintering, hot press sintering, hot isostatic pressing (HIP), pulse current pressure sintering, Microwave sintering or the like can be appropriately adopted.

In addition, according to the present manufacturing method, the progress of sintering is controlled by controlling the firing conditions, and the connecting holes that make use of the particle characteristics of the present particle material are provided to provide a sharp pore size distribution and a high open porosity. The alumina porous body provided can be obtained.

(Alumina porous body)
The present process can be used to obtain the present porous body using the present particle material as a raw material. The present porous body can be a porous body having a median diameter of 0.02 μm or more and less than 0.2 μm in its pore size distribution (volume basis).

In the present specification, the median diameter is the pore diameter at a cumulative rate of 50% (D50) in the cumulative distribution of pore diameters (undersize: the side with a larger pore diameter is the zero side). The pore size can be determined by the method disclosed in the examples. The upper limit of the median diameter is, for example, less than 0.2 μm (200 nm), for example, 0.15 μm (150 nm) or less, and for example, 0.1 μm (100 nm) or less, and for example 0.05 μm. (50 nm) or less. Also, the lower limit of the median diameter is, for example, 0.03 μm (30 nm) or more, for example, 0.05 μm (50 nm) or more, and for example, 0.1 μm (100 nm) or more, and for example, It is 0.15 μm (150 nm) or more. The range of the median diameter can be set by appropriately combining these lower and upper limits, and can be set to, for example, 0.02 μm or more and 0.15 μm or less, or, for example, 0.02 μm or more and 0.1 μm or less. .. The median diameter can be determined by the method described in Examples below.

Regarding the cumulative distribution of the pore size of the present porous body, the ratio of the pore size D10 at the cumulative rate of 10% and the pore size D90 at the cumulative rate of 90%, that is, the ratio of D10/D90 is 2.0 or less. Can have It is considered that this is due to the porosity, shape, specific surface area, etc. of the individual particles of the present particle material used as a raw material, but it is an alumina porous body with a sharp pore size distribution that has never existed before.

Further, the D10/D90 ratio of the present porous body may also be, for example, 1.8 or less, also, for example, 1.6 or less, and for example, 1.5 or less. D10 and D90 in the cumulative distribution of pore sizes can also be obtained by the method disclosed in the examples.

The present porous material can have high open porosity, total porosity, and open porosity/total porosity because the raw material of the present particulate material is a true spherical particle having voids.

The present porous body can have an open porosity of 50% or more, for example. It can also have an open porosity of, for example, 52% or more, for example 53% or more, for example 54% or more, and for example 55% or more. Furthermore, the present porous body can have an open porosity of, for example, 56% or more, for example 57% or more, for example 58% or more, for example 59% or more.

Further, the present porous body has, for example, 50% or more, also, for example, 55% or more, for example, 60% or more, for example, 62% or more, for example, 63% or more, for example, 64% or more, or For example, a total porosity of 65% or more, and, for example, 66% or more, can be provided.

Further, the present porous body has, for example, an opening ratio of 80% or more, 85% or more, 90% or more, 91% or more, 92% or more, or 93% or more. It may have a porosity/total porosity ratio.

The open porosity of the present porous body can be measured by the Archimedes method. The total porosity of the present porous body can be measured by the Archimedes method.

The present porous body is an alumina porous body having a median diameter of 0.02 μm or more and less than 0.2 μm. Conventionally, it was not possible to obtain an alumina porous body having a median diameter of less than 0.2 μm, but by controlling the firing temperature and the firing time based on the present manufacturing method, it is possible to control the progress of the sintering. While the median diameter was 0.2 μm or more, the fine alumina porous body had a median diameter of less than 0.2 μm.

The present porous body contains alumina derived from the present particle material. When the present particulate material has an α-alumina phase, the present porous body can also have an α-alumina phase. Further, when the present particle material has a γ-alumina phase, it can be made into an α-alumina phase in the firing step in the present production method, and as a result, can have an α-alumina phase.

The following examples embody and describe the disclosure of the present specification, but do not limit the disclosure of the present specification.

(Synthesis of alumina porous particle material by spray pyrolysis method)
Alumina porous particle material was synthesized according to the scheme shown in FIG.

(1) using aluminum nitrate nonahydrate Preparation raw raw material solution _{(Al (NO 3) 3 ·} 9H 2 O), a solution of a concentration of 0.9M was prepared for aluminum nitrate nonahydrate, then, To 1000 ml of this solution, 1000 ml of an aqueous citric acid solution (concentration 1.8 M) and 1000 ml of ammonia water (concentration 5.4 M) were added to give a concentration of 0.3 M as aluminum nitrate, a concentration of 0.6 M as citric acid and ammonia. A transparent raw material solution having a concentration of 1.8 M was prepared.

(2) Spray pyrolysis Using a spray pyrolysis apparatus equipped with an ultrasonic atomizer, the prepared raw material solution is heated to a temperature of 200°C, 400°C, 600°C, and 800°C in order from the inlet and heated to a total length of 120 cm. Air was supplied to the furnace as a carrier gas at 5 L/min, and particles were synthesized by spray pyrolysis.

(3) Calcination After collecting each material (alumina precursor) in the collection part of the spray pyrolysis device, a part of the material is subjected to two kinds of calcination conditions shown in Table 1 under atmospheric pressure and under air. Calcination was performed (only at 600° C. for 6 hours or at 600° C. for 6 hours and 900° C. for 2 hours) to obtain an alumina porous particle material which was a porous true spherical particle.

In this example, a sintered body was produced using the alumina porous particle material synthesized in Example 1. That is, an alumina porous body (sintered body) was obtained by the following operation using the two types of porous particle materials under the calcination conditions synthesized in Example 1. That is, about 12 g of each porous particle material was mixed with 4.8 g of a 20% aqueous polyvinyl alcohol solution so as to be 8% by mass with respect to the porous particle material using an agate mortar, and then dried to obtain a raw material powder, This raw material powder was filled in a molding die having a diameter of 10 mm and pressed by primary molding (49 MPa) and CIP molding (245 Mpa) to obtain a compact having a diameter of about 10 mm and a thickness of about 2 to 3 mm. The molded body was fired under atmospheric pressure and under air under the firing conditions shown in Table 1 to obtain alumina porous bodies (sintered bodies) of Examples 1 to 4 and Comparative Examples 1 and 2.

In this example, the alumina porous body sample produced in Example 3 was evaluated. The items and evaluation methods are shown below.

(Bulk density)
After measuring the dry mass of the sample, the sample is placed in water to impregnate the inside of the sample, and the mass of the sample in the state of being floated in water is measured. Then, the sample is taken out, only the water on the surface is removed, and then the saturated water mass is measured. (Bulk density)=(dry mass)/((saturated water mass)−(mass in water))×water density

(Open porosity)
Open porosity (%)=((saturated water mass)−(dry mass))/((saturated water mass)−(water mass))×100

(Closed porosity)
Closed porosity (%) = (total porosity)-(open porosity)

(Total porosity)
Total porosity (%)=100-(relative density)

(Relative density)
Relative density=(bulk density)/4.0×100 (the true density of α-alumina is 4.0 g/cm ³ ).

(Pore size distribution)
The mercury porosimeter method was used. Specifically, using a mercury porosimeter AutoProbe III (manufactured by Shimadzu Corporation), a porous alumina sample was placed in a container, evacuated, and then filled with mercury. The pressure was applied to mercury to introduce mercury into the pores, and the volume of the pores was measured from the relationship between the amount of mercury introduced (void volume) and the pressure at that time. Since the pore diameter that becomes smaller as the pressure increases, a graph of pore diameter-pore volume was created using the following formula. From this graph, the median diameter, which is the pore diameter of 50% of the total pore volume, was determined.
D=-4σcosθ/P
D: pore diameter, σ: mercury surface tension, θ: mercury contact angle, P: pressure

(result)
The results for the alumina porous body samples of Examples 1 to 4 and Comparative Examples 1 to 2 are shown in FIGS. 3 to 8, and the relationship between the sintering temperature and the open porosity and the relationship between the sintering temperature and the median diameter. Is shown in FIG.

As shown in Table 1 and FIGS. 3 to 9, each of the porous body samples of Examples 1 to 4 had a median diameter of 200 nm or less. Further, as shown in the numerical values of D10/D90 in Table 1 and FIGS. 3 to 6, it was found that the pore size distribution was substantially uniform and sharp. Further, the porous body samples of Examples 1 to 4 had an open porosity of 58% to 60% and a total porosity of 62 to 66%, which were high. Further, it was found that the porous body samples of Examples 1 to 4 tended to increase in median diameter and decrease in open porosity as the temperature and time of firing conditions increased. Further, it was found that the median diameter greatly changed (increased) when the firing temperature was 1050°C and 1100°C.

In addition, the porous body samples of Comparative Examples 1 and 2 have a median diameter of more than 200 nm and an open porosity of 56% to 54%, but show good uniformity and a sharp pore size distribution. .. Further, Comparative Examples 1 and 2 are different only in that the firing temperature is 1400° C. and the firing time is 0 hour and 2 hours, respectively. However, Comparative Example 2 has a median diameter in comparison with Comparative Example 1. It was found that the porosity was significantly increased and the open porosity was significantly decreased.

From the above, the firing temperature is 1000°C to 1400°C or lower, or 1000°C to less than 1400°C, and the median diameter is 200 nm or less to less than 200 nm by controlling the firing time, and the open porosity is 58% or more. It was found that a porous alumina body was obtained. It was also found that a lower median diameter (for example, 180 nm or less) and a larger open porosity (for example, 59% or more) can be obtained at a lower temperature. Among them, the firing temperature is 1000° C. to 1100° C. or less, or 1050° C. or more and 1100° C. or less, and by controlling the firing time, the median diameter (for example, 170 nm or less, or, for example, 160 nm or less, or, for example, 150 nm or less, Further, it has been found that, for example, 100 nm or less) and open porosity (for example, 59% or more, and, for example, 60% or more) can be obtained.

In addition, when the crystal phase was confirmed by X-ray diffraction spectra in Examples 1 to 4 and Comparative Examples 1 and 2, it was found to be α phase.

Claims (17)

A method for manufacturing an alumina porous body,
A raw material liquid preparing step of preparing a raw material liquid which is an aluminum-containing colloid containing a carboxylic acid,
A step of producing an alumina porous particle material for heating the droplets of the raw material liquid to form particles,
A sintering step of sintering a molding material containing the porous alumina particle material to obtain an alumina porous body at 1000° C. or higher and less than 1400° C.;
Comprising a method. The method according to claim 1, wherein the raw material liquid preparation step is a step of adding a carboxylic acid to an aluminum salt aqueous solution and then adding an alkali to prepare the raw material liquid. The method according to claim 1, wherein the raw material liquid preparation step is a step of adding an alkali to an aluminum salt aqueous solution and then adding a carboxylic acid to prepare the raw material liquid. The method according to claim 3, wherein the raw material liquid preparing step is a step of preparing the raw material liquid by adding a carboxylic acid to a dispersion liquid containing insoluble aluminum hydroxide. The method according to claim 4, wherein the aluminum hydroxide is gel aluminum hydroxide. The said raw material liquid preparation process is a method in any one of Claims 3-5 including adjusting the pH of the liquid which melt|dissolved the aluminum salt, and depositing aluminum hydroxide. The method according to claim 1, wherein the raw material liquid preparation step includes adding the carboxylic acid to aluminum in a molar ratio of 1 or more and 2 or less. The method according to claim 1, wherein the carboxylic acid is one kind or two or more kinds selected from the group consisting of acetic acid, citric acid, oxalic acid and malic acid. The method according to claim 1, wherein the carboxylic acid is citric acid. The method according to claim 1, further comprising a calcination step of calcining the alumina porous particle material at 600° C. or higher and 950° C. or lower after the generation step and prior to the firing step. .. The method according to claim 10, further comprising a crystallization step of converting at least a part of the alumina porous particle material into a γ-alumina phase after the calcination step and prior to the firing step. The method according to claim 10, further comprising a crystallization step of converting at least a part of the alumina porous particle material into an α-alumina phase after the calcination step. A method for producing an alumina porous particle material for producing an alumina porous body,
A raw material liquid preparing step of preparing a raw material liquid which is an aluminum-containing colloid containing a carboxylic acid,
A step of producing an alumina porous particle material for heating the droplets of the raw material liquid to form particles,
A calcining step of calcining the alumina porous particle material at 600° C. or higher and 950° C. or lower;
Comprising a method. A porous alumina body containing crystalline alumina, having a median diameter of 0.02 μm or more and 0.2 μm or less and an open porosity of 50% or more. A porous alumina body containing crystalline alumina and having a median diameter of 0.02 μm or more and less than 0.2 μm. The alumina porous body according to claim 14 or 15, which has a total porosity of 55% or more. The alumina porous body according to claim 14 or 15, which has an open porosity of 55% or more.