JPH07267633A - Production of boehmite sol and production of porous alumina by using the same sol - Google Patents

Abstract

PURPOSE:To produce porous alumina 'having a fine pore size and a sharp pore size distribution and boehmite sol as its precursor. CONSTITUTION:After adding an organic solvent and a compound capable of reducing the reactivity of an alkoxide with water, e.g. a carboxylic acid anhydride, an acetoacetic acid ester, a dicarboxylic acid ester, a beta-diketone or ethanolamine to an aluminum alkoxide, the alkoxide is hydrolyzed with water of >=80 deg.C. An acid is further added thereto after filtering the precipitate or without filtering it according to demand and the resultant mixture is subjected to peptization at >=80 deg.C to form boehmite sol. The formed boehmite sol is dried and calcined to give the objective porous alumina having a sharp pore size distribution.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carrier of a functional material such as a catalyst or an enzyme, a membrane for filtration / separation, an electrolytic partition, an absorbent / adsorbent,
Preparation method of boehmite sol as a precursor suitable for producing an alumina porous body having pores of very small size, such as a desiccant and a filler for germanography, and a porous body using the same The present invention relates to a manufacturing method of.

[0002]

2. Description of the Related Art Performance of a carrier of a functional material such as a general catalyst or enzyme, a membrane for filtration / separation, an electrolytic partition, an absorbent / adsorbent, a desiccant, and a filler for germanography depends on the surface of the material used. It is significantly affected by the size of the pore size and the pore size distribution. Much research has been done since Yoldas reported that an alumina-based porous material can be prepared relatively easily by the sol-gel method. Jordas
It was shown that γ-alumina with an average pore size of 100 Å or less can be produced by hydrolyzing aluminum alkoxide with a large amount of water heated to 80 ° C or higher, and then deflocculating with an acid and then firing, but the pore size distribution is relatively wide. However, even if it was tried to apply to the various uses mentioned above, sufficient performance could not be obtained as it was. The size of the pore size of alumina,
As a method of controlling the pore size distribution, aluminum alkoxide is hydrolyzed with water at 80 ° C. or lower, then peptized at 80 ° C. or higher and fired to produce γ-alumina having an average pore size of 22Å and a relatively narrow pore size distribution. Method (JP-A-5-238845) or by adding β-diketone to an alcohol solution of aluminum alkoxide, followed by hydrolysis to obtain a bulk gel body, followed by drying and firing to obtain a pore size of 10 to 500 Å. A method for producing an alumina porous body (Japanese Patent Laid-Open No. 2-196076) has been proposed.

[0003]

Problems to be Solved by the Invention
When aluminum alkoxide is hydrolyzed with water below ℃, there is a problem that bayerite that cannot be deflocculated is generated, and in order to avoid it, it is necessary to remove the generated bayerite by a centrifugation method or the like, which makes the operation procedure complicated. There is a problem that becomes. In addition, the method of adding a β-diketone to produce an alumina porous body via a bulk gel body has a problem that the pore size distribution is wide. An application example using a porous body having a fine pore size is a gas separation membrane. As the characteristics of the separation membrane, the ratio of separating the target gas from the mixed gas, that is, the separation coefficient, and the permeation flow rate of the gas are important. The gas molecules permeate through the pores having a size less than the mean free path by the Knudsen flow, and the permeation flow rate Q at that time is given by the following equation 1 when converted into the standard state.

[0004]

[Equation 1]

In the above formula 1, M is the molecular weight of the permeable molecule, R is the gas constant, T is the absolute temperature, r is the pore radius, L is the thickness of the separation membrane, and ΔP is the pressure between the upstream and downstream of the separation membrane. It is the difference. When this separation membrane is used for filtering a virus having a diameter of 10 nm existing in a gas, not only the average pore diameter but also the maximum pore diameter needs to be 10 nm or less. If the pore size distribution of the separation membrane is wide, the average pore size must be considerably smaller than 10 nm. However, it can be seen that if the pore diameter is reduced to, for example, 1/2, the permeation flow rate drops to 1/8 from Equation 1. That is, in order to produce a separation membrane excellent in separation coefficient and permeation flow rate, it is necessary to design a structure having a sharp pore size distribution.

Therefore, the present invention provides a method for producing a boehmite sol suitable for producing an alumina-based porous body having a fine pore size and a sharp pore size distribution by a simple operation, and a method for producing the alumina-based porous body. It is intended to provide.

[0007]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that as a method for producing a boehmite sol, firstly, aluminum alkoxide is soluble in water. Second, a method of adding a solution obtained by adding a simple organic solvent and a compound that reduces the reactivity of the alkoxide to water to water at 80 ° C. or higher, and secondly,
A solution of an aluminum alkoxide in which a water-soluble organic solvent and a compound that reduces the reactivity of the alkoxide with respect to water are added is added to water at 80 ° C. or higher for hydrolysis, and then an inorganic acid or an inorganic acid is added to the solution. Add organic acid,
Method of peptizing at 80 ° C or higher, Thirdly, a solution obtained by adding an organic solvent soluble in water to aluminum alkoxide and a compound that reduces the reactivity of the alkoxide to water is added to water at 80 ° C or higher. After that, the formed precipitate is suction filtered and washed with water, and then the precipitate is dispersed again in pure water, and an inorganic acid or an organic acid is added to the dispersion solution, and the mixture is heated to 80 ° C.
The method for deflocculating is as described above, and the method for producing the alumina-based porous body is as follows. The boehmite sol obtained by any one of the above first to third is used, dried at 80 ° C. or lower, and then oxidized. It has been found that a porous alumina-based sintered body having a small pore system distribution can be obtained by firing at a temperature of 400 to 1000 ° C. for 0.1 to 10 hours in a neutral atmosphere.

When the compound that reduces the reactivity of the alkoxide with water is selected from carboxylic acid anhydrides, acetoacetic acid esters, and dicarboxylic acid esters, the first and second methods are used, and the compound is β-. In the case of a diketone, the second method is used, in which the compound is

[0009]

[Chemical 1]

In the case of ethanolamine represented by, it is desirable to adopt the third method.

The present invention will be described in detail below. First, in the method for producing boehmite sol (AlOOH) of the present invention, as the aluminum alkoxide used as a starting material, isopropoxide, butoxide, 2-butoxide and the like can be used, and among them, the solubility in an organic solvent is high. 2-Butoxide is preferred. Further, as an organic solvent that is uniformly mixed and soluble in water, ethanol, isopropanol, 2-butanol, 2-methoxyethanol,
Alcohols such as 2-ethoxyethanol can be used.

[0012] Examples of the compound that reduces the reactivity of alkoxide with water include carboxylic acid anhydrides such as acetic anhydride and maleic anhydride, acetoacetic acid esters such as methyl acetoacetate, ethyl acetoacetate and propyl acetoacetate, and malonic acid. Dicarboxylic acid esters such as dimethyl, diethyl malonate and dipropyl malonate, β-diketones such as acetylacetone and N, N ′ dimethyl monoethanolamine, N, N ′ diethyl monoethanolamine, monoethanolamine, diethanolamine, triethanolamine, etc. Ethanolamines can be used, but they must be used properly as described below because of their different chemical properties. Therefore, the method for producing the boehmite sol in the present invention will be described using the above various chemicals.

First, as the first method, an organic solvent that is uniformly mixed and soluble in water and a compound that reduces the reactivity of the alkoxide with water are added to the aluminum alkoxide. As the compound that reduces the reactivity of the alkoxide with water at this time, at least one selected from the group consisting of carboxylic acid anhydrides, acetoacetic acid esters and dicarboxylic acid esters is adopted.
These are 0.1 to aluminum alkoxide
It is added at a rate of 0.5 mol%. Then, after mixing them sufficiently, this solution is heated to 80 ° C. or higher, particularly 80 to 9
Add to water at 5 ° C and stir to hydrolyze. When adding this solution to water, it is desirable to gradually add it under vigorous stirring. This is to generate fine nuclei of boehmite sol by efficiently dispersing the raw material alkoxide in water. The reason for limiting the temperature during the addition to 80 ° C or higher is that once the temperature is lower than 80 ° C, an amorphous hydrate is formed, and then it is changed to vialite which cannot be peptized.

After the completion of the above addition, a nearly transparent solution is obtained by stirring the mixture at a temperature of 80 ° C. or higher for 0.5 to 72 hours under normal stirring, and a boehmite (AlOOH) sol is obtained. Can be made.

As a second method, when β-diketone is used as a compound that reduces the reactivity of alkoxide with water, an inorganic acid or an organic acid is added to the dispersion solution and the temperature is kept at 80 ° C. or higher for a certain time. Need to peptize. Therefore, a compound that reduces the reactivity of the alkoxide with water is added to the aluminum alkoxide in the same manner and in the same amount as in the first method, and the solution is added to water at 80 ° C. or higher under vigorous stirring to add water. After decomposition, an inorganic acid such as hydrochloric acid, nitric acid or perchloric acid, or an organic acid such as acetic acid, trichloroacetic acid or oxalic acid is added to the solution, and the temperature is kept at 80 ° C. or higher, particularly 80 to 95 ° C. .5
It may be peptized while stirring for about 72 hours. At this time, the addition amount of the inorganic acid or the organic acid is appropriately 3 to 100 mol% with respect to the alkoxide.

In the second series of production methods, any one of carboxylic acid anhydrides other than β-diketones, acetoacetic acid esters, and dicarboxylic acid esters is used as a compound that reduces the reactivity of alkoxide with water. Of course, these compounds are hydrolyzed by themselves in water at 80 ° C. or higher to generate an organic acid, so that it is not always necessary to newly add an acid for peptization of the gel.

As a third method, when ethanolamine having an organic base as shown in the above chemical formula 1 is used as a compound that reduces the reactivity of alkoxide with water, it is directly hydrolyzed to the solution. Even if an inorganic acid or an organic acid is added, a neutralization reaction occurs and the peptization cannot be effectively performed. Therefore, in this case, when a solution obtained by adding a compound that reduces the reactivity of the alkoxide to water to the aluminum alkoxide is added to water under vigorous stirring in the same manner as in the first method, the aggregated boehmite precipitates. Occurs. This precipitate is suction filtered, washed with water, dispersed again in pure water, and the above-mentioned inorganic acid or organic acid is added to the dispersed solution, and the temperature is adjusted to 80 ° C. or higher and 80 to 95 ° C.
A boehmite sol can be prepared by peptizing for 5 to 72 hours.

The boehmite sol thus obtained is a colorless and transparent sol solution in which fine boehmite particles are uniformly dispersed and which does not substantially contain aggregates.

In order to produce an alumina porous body using the boehmite sol obtained as described above, first the obtained boehmite sol is dried at a temperature of 80 ° C. or lower, particularly 60 ° C. or lower, and then A powder (gel) can be obtained by calcining the dried product at a temperature of 400 to 1000 ° C., particularly 500 to 600 ° C. for about 0.1 to 10 hours in an oxidizing atmosphere such as air.

In order to obtain a bulk body as a porous body, the dried boehmite is formed into a desired shape by a desired forming means such as a die press, a cold isostatic press and an extrusion forming method. After that, firing may be performed under the above conditions. Further, in the case of obtaining a sheet body or a membrane body, the boehmite sol as it is, or after adding a thickener such as polyethylene glycol, this is applied to any substrate by a method such as a doctor blade method or a dip coating method. It can be obtained by applying it on the surface, drying it, and then firing it under the same firing conditions as above.

The reason for limiting the drying temperature to 80 ° C. or lower is that aggregated particles are likely to be produced when the temperature exceeds 80 ° C. Further, the temperature during firing is limited to 400 to 1000 ° C., because the crystallization to γ-alumina is not sufficient when it is lower than 400 ° C., and the phase transition to α-alumina occurs when it exceeds 1000 ° C. Is sharply reduced.

The alumina-based porous body thus obtained has an average pore diameter of 40 Å or less, particularly 30 to 40 Å
The fine pores are uniformly formed, and the distribution of the pore size thereof has a very sharp distribution as will be apparent from the examples described later.

[0023]

According to the present invention, in the process of producing the boehmite sol, first, the aluminum alkoxide is diluted with an organic solvent, which lowers the viscosity of the alkoxide and facilitates efficient dispersion when added to water, As a result, minute nuclei of boehmite sol are generated.

When a compound which reduces the reactivity of the alkoxide with water is added to the above solution, the highly reactive aluminum alkoxide is hydrolyzed before it can be sufficiently dispersed in water, resulting in a boehmite sol having a large particle size. You can prevent it from making a nucleus. When a β-diketone such as acetylacetone is used as the compound, it is necessary to add an inorganic acid or an organic acid to the dispersion solution and peptize at a temperature of 80 ° C. or higher for a certain period of time. When any of the dicarboxylic acid esters is used, the compounds themselves hydrolyze in water at 80 ° C. or higher to produce an organic acid,
It is not always necessary to add new acid for peptization of the gel. When an organic base such as ethanolamine is used as the above compound, it is directly hydrolyzed into the solution,
Even if an inorganic acid or an organic acid is added, a neutralization reaction occurs and the deflocculation cannot be effectively performed.Therefore, the formed boehmite precipitate is filtered once, the organic base is removed by washing, and then dispersed again in pure water. Alternatively, it is necessary to add an organic acid for peptization.

Ultimately, the size of the boehmite particles is determined by the conditions under which the alkoxide undergoes hydrolysis, that is, how the amorphous hydroxide initially formed is converted into boehmite particles in the solution. It is determined by whether it is highly dispersed. Therefore, it is necessary to add a compound that reduces the reactivity of the alkoxide with water. In addition, since the size of the boehmite primary particles once formed does not change in the subsequent peptization step, the conditions at the time of hydrolysis of the alkoxide depend on the fineness of the alumina porous body obtained by drying and firing the boehmite sol. The size of the pore size and the pore size distribution will be determined.

Therefore, according to the present invention, since a boehmite sol in which boehmite is uniformly dispersed can be prepared, even when an alumina porous body is prepared using this, fine crystal particles are uniformly arranged. Therefore, it is possible to obtain a porous body having a sharp distribution of the pore size of the porous body.

As a result, a highly accurate filter can be produced even when applied to a virus filter or the like.

[0028]

【Example】

Example 1 In a well-dried glove box, 0.1 mol of aluminum secondary butoxide (Al (sec-Bu) ₃ ) was placed in a 100 ml round-bottomed flask, and 0.3 mol of 2-methoxyethanol (MeO-CH) was added thereto. _2- CH
₂ -OH) and 0.01 mole of acetylacetone _{((CH 3 CO) 2 CH} 2) was added taken out from the glove box was thoroughly mixed, water 180 heated to 85 ° C.
It was added to ml (10 mol) with vigorous stirring. Thirty
After the addition, 0.007 mol of nitric acid was added to the reaction solution, the temperature of the solution was adjusted to 95 ° C., and the mixture was refluxed for 16 hours to obtain an almost colorless and transparent boehmite sol. The result of X-ray diffraction measurement after drying this sol is shown in FIG.

The sol was sufficiently dried at 60 ° C. for 3 days and calcined in the air at 500 ° C. for 1 hour. As a result, a porous powder having a BET specific surface area of 333 m ² / g and an average pore size of 33Å was obtained. The pore distribution of the obtained powder was measured by Asapps 2000 manufactured by Shimadzu Micromeritex Co., Ltd., and the results are shown in FIG. As is clear from FIG. 2, it had a very sharp pore distribution.

Example 2 In a well-dried glove box, a 100 ml round-bottomed flask was charged with 0.1 mol of aluminum secondary butoxide, to which 0.3 mol of 2-methoxyethanol and 0.01 mol of acetic anhydride (( CH ₃ CO) ₂ O)
Was thoroughly mixed and then taken out from the glove box and added to 180 ml (10 mol) of water heated to 85 ° C. with vigorous stirring. After 30 minutes, add 0.0 to the reaction solution.
07 mol of nitric acid was added, the solution temperature was adjusted to 95 ° C., and the mixture was refluxed for 16 hours to obtain an almost colorless and transparent boehmite sol. This sol is dried at 60 ° C. for 3 days, and is dried in the air at 50
It was baked at 0 ° C. for 1 hour. As a result, the BET specific surface area is 30
Alumina porous powder having a pore size of 4 m ² / g and an average pore size of 35 Å was obtained.

Example 3 In Example 2, when the amount of acetic anhydride added was 0.05 mol, a milky white sol was obtained. 60 this solution
As a result of drying at ℃ for 3 days and baking at 500 ℃ for 1 hour in the atmosphere,
A powder having a BET specific surface area of 330 m ² / g and an average pore diameter of 33Å was obtained.

Example 4 In Example 2, the amount of acetic anhydride added was 0.05 mol,
When the reflux time at 95 ° C. was set to 30 minutes, a colorless and transparent sol was obtained. This sol was dried at 60 ° C. for 3 days and calcined in the air at 500 ° C. for 1 hour. BET specific surface area is 344m
² / g, to obtain a powder having an average pore diameter 32 Å.

Example 5 In Example 4, 30 ° C. at 95 ° C. without adding nitric acid.
Upon refluxing for a minute, a colorless and transparent sol was obtained. This sol was dried at 60 ° C. for 3 days and calcined in the air at 500 ° C. for 1 hour. As a result, the BET specific surface area was 345 m ² / g and the average pore diameter was 32Å.

Example 6 When 0.05 mol of ethyl acetoacetate (CH ₃ COCH ₂ COOC ₂ H ₅ ) was used in place of acetic anhydride in Example 2, an almost colorless and transparent sol was obtained. This sol was dried at 60 ° C. for 3 days and calcined in the air at 500 ° C. for 1 hour. The BET specific surface area was 329 m ² / g, and the average pore diameter was 34Å.

Example 7 In Example 2, when 0.05 mol of dimethyl malonate (CH ₂ (COOCH ₃ ) ₂ ) was used instead of acetic anhydride, an almost colorless and transparent sol was obtained. This sol was dried at 60 ° C. for 3 days and calcined in the air at 500 ° C. for 1 hour.
BET specific surface area is 334 m ² / g, average pore size is 33Å
Met.

Example 8 In a well-dried glove box, a 100 ml round-bottomed flask was charged with 0.1 mol of aluminum secondary butoxide, to which 0.3 mol of 2-methoxyethanol and 0.05 mol of N, N 'were added. Dimethylmonoethanolamine ((CH ₃ ) ₂ NCH ₂ CH ₂ OH) was added and mixed well, then taken out from the glove box and added to 180 ml (10 mol) of water heated to 85 ° C. with vigorous stirring. After 30 minutes, the precipitate was filtered, washed three times with a small amount of water, dispersed in 180 ml of water, 0.007 mol of nitric acid was added to the solution, and the solution temperature was adjusted to 95 ° C.
The mixture was further refluxed for 16 hours, and an almost colorless and transparent sol was obtained. This sol is dried at 60 ° C. for 3 days, and then dried in air at 500
It was baked at 1 ° C for 1 hour. The BET specific surface area of the obtained powder is 3
It was 15 m ² / g and the average pore diameter was 34 Å.

Example 9 In Example 8, instead of N, N'-dimethylmonoethanolamine, diethanolamine ((HN (CH ₂ C
When H ₂ OH) ₂ ) 0.05 mol was used, an almost colorless and transparent sol was obtained. This sol was dried at 60 ° C. for 3 days and calcined in the air at 500 ° C. for 1 hour. The BET specific surface area was 338 m ² / g, and the average pore diameter was 33Å.

Comparative Example 1 0.1 mol of aluminum secondary butoxide was added to 8
It was added to 180 ml (10 mol) of water heated to 5 ° C. with vigorous stirring. After 30 minutes, 0.007 mol of nitric acid was added to the reaction solution, the temperature of the solution was adjusted to 95 ° C., and the mixture was refluxed for 16 hours to obtain a milky white sol solution. This solution was dried at 60 ° C. for 3 days and calcined in the air at 500 ° C. for 1 hour. BET specific surface area is 254 m / g, average pore size is 49
It was Å. The pore size distribution is shown in FIG. As is clear from FIG. 2, the average pore diameter was larger and the distribution was broader than that of Example 1, which was a product of the present invention.

Comparative Example 2 In a well-dried glove box, 0.1 mol of aluminum secondary butoxide was placed in a 100 ml round-bottomed flask, 0.3 mol of 2-methoxyethanol was added thereto, mixed well, and then taken out from the glove box. ,
To 180 ml (10 mol) of water heated to 85 ° C. was added with vigorous stirring. After 30 minutes, 0.007 mol of nitric acid was added to the reaction solution, the temperature of the solution was adjusted to 95 ° C., and the mixture was refluxed for another 16 hours to obtain an almost colorless and transparent sol. This sol was dried at 60 ° C. for 3 days and calcined in the air at 500 ° C. for 1 hour. The BET specific surface area of the obtained powder was 274 m ² / g,
The average pore size was 45Å.

[0040]

As described above, according to the method of the present invention, it is possible to prepare a boehmite sol in which uniform and fine particles are dispersed. As a result, an alumina porous material having a fine pore size and a sharp pore size distribution is obtained. A body can be produced. This makes it possible to exhibit excellent properties when applied to a carrier of a functional material such as a catalyst or an enzyme, an electrolytic partition wall, an absorbent / adsorbent, a desiccant, a filler for germanography and the like. Furthermore, the method of the present invention has a feature of passing through the sol state, and the shape of the alumina porous membrane can be imparted by immersing or coating the porous support in the sol state. Therefore, the present invention can be expected to have excellent properties when applied to a filtration membrane having a fine pore diameter and a narrow pore size distribution, a separation membrane for liquid or gas, and a permeable membrane.

[Brief description of drawings]

FIG. 1 is a view showing a chart by an X-ray diffraction measurement of a boehmite sol produced in Example 1.

FIG. 2 is a diagram showing a pore size distribution of an alumina porous body in Example 1 and Comparative Example 1.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C04B 38/00 304 B

Claims (8)

[Claims] 1. A solution obtained by adding a water-soluble organic solvent to an aluminum alkoxide and a compound that reduces the reactivity of the alkoxide with water to water at 80 ° C. or higher for hydrolysis. And method of making boehmite sol. 2. The method for producing a boehmite sol according to claim 1, wherein the compound that reduces the reactivity of the alkoxide with water is at least one selected from the group consisting of carboxylic acid anhydrides, acetoacetic acid esters and dicarboxylic acid esters. . 3. A solution obtained by adding a water-soluble organic solvent to an aluminum alkoxide and a compound that reduces the reactivity of the alkoxide with water to water at 80 ° C. or higher for hydrolysis. A method for producing a boehmite sol, which comprises adding an inorganic acid or an organic acid to this solution and peptizing at 80 ° C or higher. 4. The boehmite according to claim 3, wherein the compound that reduces the reactivity of the alkoxide with water is at least one selected from the group consisting of β-diketones, carboxylic acid anhydrides, acetoacetic acid esters and dicarboxylic acid esters. Method of making sol. 5. A solution obtained by adding a water-soluble organic solvent to an aluminum alkoxide, and a compound which reduces the reactivity of the alkoxide to water to water at 80 ° C. or higher to cause hydrolysis, Preparation of a boehmite sol characterized in that the precipitate is suction filtered and washed with water, the precipitate is dispersed again in pure water, and an inorganic acid or an organic acid is further added to the dispersion solution to peptize at 80 ° C or higher. Law. 6. A compound which reduces the reactivity of the alkoxide with water is represented by the following chemical formula 1. The method for producing a boehmite sol according to claim 5, which is ethanolamine represented by: 7. The boehmite sol obtained by the method according to any one of claims 1, 2 and 5 is dried at 80 ° C. or lower, and then 400 to 1 in an oxidizing atmosphere.
A method for producing an alumina-based porous body, which comprises firing at a temperature of 000 ° C. 8. The method for producing an alumina porous body according to claim 7, wherein the average pore diameter is 40 Å or less.