JPH0543344A - Production of alumina-based porous body - Google Patents

Abstract

PURPOSE:To obtain an alumina-based porous body, capable of providing a body having a high specific surface area by burning without reducing its specific surface even in use at a temperature as high as 1200 deg.C and suitable for use as high-temperature reaction catalysts or their carriers. CONSTITUTION:This is a method for producing an alumina-based porous body characterized as follows: An alumina-based wet gel synthesized from an aluminum compound, preferably an aluminum alkoxide or a mixture containing the aluminum compound is treated at >=100 deg.C in water or a solution containing water or a water-containing atmospheric gas under >=2kgf/cm<2> pressure and the solvent is then replaced with an organic solvent. The resultant body is further dried.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an alumina-based porous material which, when used as a catalyst used at high temperature or a carrier constituting the catalyst, can maintain a high specific surface area even at high temperature.

[0002]

2. Description of the Related Art Conventional catalysts used in various chemical processes have a low reaction temperature in those chemical processes, so long as they can withstand temperatures up to about 600.degree. Since there was no particular hindrance to the chemical process, even if a ceramics catalyst is generally used as a catalyst, the characteristics of the ceramics possessed by the ceramics catalyst can be sufficiently dealt with, and especially the heat resistance Was not a problem, but in recent years equipment with high temperature thermochemical processes, especially catalytic combustors,
Applications such as gas turbines, boilers and jet engines are expected, and ceramics resistant to a high temperature environment of about 1000 ° C. have come to be used due to demands for reduction of NOx generation and improvement of combustion efficiency.

Such ceramics are produced, for example, by appropriately mixing and mixing powders of various metal oxides and the like to obtain a desired composition and shape, molding, and firing. However, in this method, since the starting material powder itself has a low specific surface area, the specific surface area is further reduced by the high temperature calcination, and a highly efficient catalyst cannot be obtained. Therefore, the wet precipitation method is used to produce ceramics with a higher specific surface area, and since it is still insufficient, the metal alkoxide is hydrolyzed to obtain a sol, which is gelled and then baked (sol-gel method). Law) has been proposed. In the latter method, ceramics are manufactured by a sol-gel method using metal alkoxides alone or a mixture thereof as a raw material. For example, in the case of manufacturing alumina ceramics, aluminum alkoxides may be used as the alumina source, or other materials may be mixed. The component of does not have to be a metal alkoxide,
It is said that a metal salt may be used. An alumina-based gel (hereinafter referred to as “alumina-based wet gel”) that has been hydrolyzed and wetted is obtained, and this is dried and then fired to obtain a porous alumina-based ceramics body having a large specific surface area.

[0004]

However, even in the alumina-based porous body produced from the metal alkoxide as described above, the combustion catalyst used in the catalytic combustor is most commonly exposed to a reaction temperature of 1200 ° C. In the vicinity, the specific surface area was as small as 50 to 60 g / m ² at most, and it could not be said that the specific surface area was sufficiently large. An object of the present invention is to solve the above-mentioned drawbacks, and to provide a method for producing an alumina-based porous ceramic having a high specific surface area at a high temperature by a sol-gel method or a precursor thereof, that is, an alumina-based porous body. To do.

[0005]

The present invention was able to achieve the above object by the following means. (1) Alumina-based wet gel synthesized from an aluminum compound or a mixture containing aluminum compound in water or a solution containing water or an atmospheric gas containing water at a temperature of 100 ° C. or higher, 2 kg
A method for producing an alumina-based porous body, which comprises treating at a pressure of f / cm ² or more, then substituting the solvent with an organic solvent and drying. (2) The method for producing an alumina-based porous body according to the item (1), wherein the aluminum compound or a mixture containing the aluminum compound is mainly a metal alkoxide and / or a derivative thereof. The "alumina-based" of the alumina-based porous body produced in the present invention is a composite of two or more components of alumina alone and alumina and other inorganic oxides (mainly metal oxides) such as alumina-silica and alumina-magnesia. It is a system.

In the present invention, the alumina-based wet gel as a starting material of the production method is synthesized from an aluminum compound or a mixture containing the aluminum compound. When producing a porous body made of alumina alone, the raw material may be an aluminum compound alone. As the aluminum compound, any compound can be used as long as it can form an alumina-based wet gel by hydrolysis or the like, and various compounds such as sulfate, chloride, sodium aluminate, and aluminum alkoxide are used. However, an aluminum alkoxide is preferable in order to obtain high porosity. The aluminum alkoxide used in the present invention has the general formula (RO)
₃ Al (R: alkyl group), specifically, R is methyl, ethyl, n-propyl, iso-
Examples include propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl and the like. Further, an aluminum alkoxide derivative can be used in place of the aluminum alkoxide, and the aluminum alkoxide derivative is obtained by chelating the aluminum alkoxide with ethyl acetoacetate, diethanolamine, or the like, for example, a part of the -OR group or another functional group. , For example, an alkyl group (CxHy).

In producing a composite alumina-based porous material such as alumina-silica or alumina-magnesia,
An alumina-based wet gel is synthesized using a mixture of an aluminum compound and a compound such as a silica source as a reaction raw material. However, the silica source is not limited to the compound. Although various compounds can be used as the reaction raw materials, it is most preferable to use a mixture of the respective metal alkoxides. However, in the case of producing an alumina-silica porous body, when a silicon alkoxide is used as a silica source, a sufficiently large surface area can be obtained even if an aluminum salt is used as an aluminum compound. A derivative thereof can be used in place of the metal alkoxide.

As the mixture of the reaction raw materials, an aluminum alkoxide and an alkoxide of another metal other than aluminum (eg, Mg (OR) ₂ , Si (OR)) are used.
₄ , PO (OR) ₃ , KOR, Ca (OR) ₂ , Ti
(OR) ₄ , Sr (OR) ₂ , Y (OR) ₃ , Zr (O
R) ₄ , Ba (OR) _{2 and the} like, R is an alkyl group such as methyl and ethyl), inorganic compounds such as metal salts thereof (for example, M
gBr ₂ , a halide such as TiCl ₄ , K ₂ SO ₄ ,
Ca (NO ₃ ) _{2 and} other nitrates, sulfates, organometallic compounds other than alkoxides (eg, CH ₃ COONa,
Acetates such as (CH ₃ COO) ₂ Ca, (COON
a) ₂ , oxalates such as (COOK) ₂ , EDTA, N
Complexes with chelate compounds such as TA), and in some cases finely reactive metals and oxide fine powders (eg Ca
O, TiO ₂ , SiO ₂ , P ₂ O ₅ , ZrO _2, etc.) can be used together.

In the present invention, in order to synthesize the above-mentioned alumina-based wet gel, when a means for hydrolyzing an aluminum alkoxide or a mixture containing the same is used as a reaction raw material, the above-mentioned aluminum alkoxide is added to
It is preferable to mix one or more kinds of alkanolamine, β-keto acid ester and β-diketone compound in a 0.1 to 5 times molar amount to form an alumina precursor or a mixture thereof. The mixing of the aluminum alkoxide with the alkanolamine, β-keto acid ester, β-diketone compound (hereinafter sometimes referred to as a modifier) involves a reaction, and both can be mixed at room temperature or under heating. From the viewpoints of miscibility and uniformity of reaction, it is preferable to carry out in the presence of an organic solvent. However, mixing is possible without the presence of an organic solvent. The organic solvent used here is preferably one that dissolves aluminum alkoxide, and specifically, methanol, ethanol, n-propanol, i
Examples include alcohols typified by so-propanol, sec-butanol, etc., aromatic hydrocarbons typified by toluene, benzene, xylene, tetrahydrofuran, dimethylformamide, carbon tetrachloride, etc., but from the viewpoint of solubility. Alcohols are preferred.

The alkanolamines to be mixed and reacted with the aluminum alkoxide used in the present invention include monoethanolamine, mono-n-purpanolamine, monoiso-propanolamine, diethanolamine, diiso-propanolamine and triethanolamine. , Triiso-propanolamine and the like, β-keto acid ester also includes ethyl acetoacetate, methyl acetoacetate, ethyl malonate, diethyl malonate, and the like, and β-diketone compound includes acetylacetone and the like. ..

The alumina-based precursor mixture is, if necessary, in the presence of a base catalyst such as ammonia, pyridine, piperidine or piperazine, and the number of hydrolyzable reactive groups present in the mixture (for example, (RO) ₃ Al unreacted RO groups, and the number of reaction groups of the alkanolamine, β-keto acid ester, β-diketone compound and the RO groups, that is, the number of RO groups of the starting aluminum alkoxide, Further, the number of alkoxide groups of an added metal alkoxide other than aluminum alkoxide or a metal alkoxide produced from a simple metal can be mentioned.) 0.5 to 2 times by mole of water. In this case, if the amount of water is 0.5 times or less the gelation is difficult, and if it is 2 times or more the particles tend to be formed, and the desired homogeneous gel cannot be produced.

Even when an aluminum compound other than aluminum alkoxide, for example, an aluminum salt such as aluminum nitrate or aluminum chloride is used as the aluminum compound, the alumina wet gel can be easily synthesized by hydrolysis. The alumina-based wet gel synthesized as described above is used in water or a solution containing water, or in an atmospheric gas containing water as water vapor.
The treatment is performed at a temperature of 0 ° C. or higher and a pressure of ² kgf / cm ² or higher. Since the treatment is usually carried out in an autoclave, it is preferable to determine the treatment temperature in consideration of the pressure resistance of the autoclave. For processing purposes, the temperature is up to 150 ° C and the pressure is 5
Up to kgf / cm ² is sufficient, and the processing time is determined based on the temperature and pressure.

The porosity of the alumina-based wet gel is very large, especially when it is synthesized from a metal alkoxide (typically an aluminum alkoxide).
Although a product with a large specific surface area can be obtained, on the other hand, the strength is low and it is easy to disintegrate, but if the heat and pressure treatment is performed in the presence of water in this way, the structure of the alumina-based wet gel is strengthened. Will grow. The water-containing solution is, for example, a solution in a broad sense containing water, such as a water-alcohol mixture, and any salt solution or water-containing solution can be used.

As described above, the alumina-based wet gel treated at high temperature and high pressure in the presence of water is dried after the water content in the wet gel is replaced with an organic solvent. As the organic solvent used for solvent substitution, an organic solvent that can be used during hydrolysis of the above-mentioned aluminum alkoxide and the like can be used. To illustrate them,
Methanol, ethanol, n-propanol, iso-
Alcohols represented by propanol, sec-butanol, etc., aromatic hydrocarbons represented by toluene, benzene, xylene, etc., tetrahydrofuran, dimethylformamide, carbon tetrachloride, etc., but alcohols are preferable.

When the alumina wet gel to be treated is obtained by being hydrolyzed in the presence of an organic solvent, such as by hydrolysis of an aluminum alkoxide dissolved in an organic solvent, the organic wet gel is contained therein. In addition to the solvent, alcohol by-produced by hydrolysis of metal alkoxide such as aluminum alkoxide is included, so that the amount of the organic solvent used for solvent substitution can be reduced to some extent. However, the organic solvent contained in the alumina wet gel is lost to some extent by the high temperature and high pressure treatment in the presence of water.

This drying process is performed by replacing the solvent with alumina.
Be sure to remove the organic solvent contained in the system wet gel sufficiently.
However, the drying temperature should be as low as possible.
The range of -60 ° C is preferred. By the above processing, the specific surface
Alumina-based porous material with a large product and high strength was obtained.
Be done. As the alumina-based porous material obtained here, for example,
If Al₂O₃, Al ₂O₃-BaO system (BaO ・ 6Al
₂O₃), Al₂O₃-SiO₂System, Al₂O₃-Ti
O₂System, Al₂O₃-ZrO₂System, Al₂O₃-SiO
₂-MgO type (cordierite type) etc. are mentioned.

[0017]

[Operation] In the present invention, an alumina-based wet gel synthesized from an aluminum compound or a mixture containing the same (particularly when it is a metal alkoxide) has a large specific surface area but a weak structure. By the treatment below, the strength is increased probably because the tissue or structure is strengthened. This is because the unreacted —OR group completely forms the skeleton of the OH group and Al—O—Al.
Further, it is because alumina develops from an amorphous state into crystals into boehmite. When the alumina-based wet gel treated in this way is dried, the surface tension of water is so large that the holes are crushed when they come out of the porous holes, causing shrinkage and cracking. .. Therefore, the solvent can be replaced, and an organic solvent having a relatively small surface tension can be used to prevent shrinkage and cracking.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to this embodiment. Example 1 1.90 g of ethanol to 2.90 g of silicon ethoxide
0.2 g of water diluted with 1.6 g of ethanol.
6 g was added. Aluminum alkoxide 72.
It was put in 00 g and stirred. Next, ethyl acetoacetate 3
1.70 g was put and 80 ml of ethanol was further added. 16.6 of water diluted with 160 ml of ethanol
0 g was added and hydrolysis was performed to obtain a sol. This sol was kept at 60 ° C. for 1 week for gelation to obtain a silica / alumina wet gel.

This wet gel was placed in water, kept at a temperature of 150 ° C. and a pressure of 6 kgf / cm ² for 4 days, then immersed in a large amount of ethanol to replace the solvent, and then taken out at 40 ° C. It was dried for 6 hours. The dried silica / alumina was calcined at 1200 ° C. for 5 hours. When the specific surface area of this calcined silica / alumina is examined, it is 160.4 m ² /
It was g.

Comparative Example 1 The production method of Example 1 was carried out by hydrolysis without adding ethyl acetoacetate. Then, it was heated to distill off ethanol and then dried. This silica-alumina was fired at 1200 ° C. for 5 hours. The specific surface area of the obtained calcined silica / alumina product was 53.3 m ² / g.

[0021]

INDUSTRIAL APPLICABILITY According to the present invention, an alumina-based porous body having a large specific surface area and high strength can be obtained by heating and pressurizing an alumina-based wet gel in the presence of water, replacing the solvent with an organic solvent and drying. Be done. Moreover, even if this alumina-based porous body is fired at a high temperature, it is possible to obtain a fired alumina-based porous body having a large specific surface area. And since it has high heat resistance at high temperature, it is useful as a catalyst used at high temperature such as a catalytic combustor or a catalyst carrier therefor, and the specific surface area may decrease at such high temperature. Absent.

Claims (2)

[Claims] 1. An alumina-based wet gel synthesized from an aluminum compound or a mixture containing the aluminum compound in water or a solution containing water or an atmospheric gas containing water at a temperature of 100 ° C. or higher and a pressure of ² kgf / cm ² or higher. After the treatment, a method for producing an alumina-based porous body, comprising performing solvent substitution with an organic solvent and drying. 2. The method for producing an alumina-based porous body according to claim 1, wherein the aluminum compound or a mixture containing the aluminum compound is mainly a metal alkoxide and / or a derivative thereof.