JPH04281018A - Production of porous yarn of silica alumina - Google Patents

Abstract

PURPOSE:To obtain the title yarn useful for high-temperature catalyst carrier, etc., having excellent productivity by blending an aluminum alkoxide and an active hydrogen-containing compound with a specific silicon alkoxide, forming a sol, spinning, treating with steam and calcining. CONSTITUTION:In a method of producing silica alumina yarn from an aluminum alkoxide and a silicon alkoxide, a reaction mixture of an aluminum alkoxide and an active hydrogen-containing compound such as monoethanolamine (preferably 0.6-2.7 mols of active hydrogen based on 1mol aluminum alkoxide) is blended with a silicon alkoxide and/or a derivative thereof in an amount to give <=30wt.% silica content in ceramics after calcining, and the blend is hydrolyzed to form a sol, the sol is spun to give a gel yarn, which is treated with steam and then the gel yarn treated with steam is calcined to give the objective yarn.

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 porous silica-alumina fibers that can maintain a high specific surface area even at high temperatures and are suitable for use as high-temperature catalyst carriers. More specifically, in a method for obtaining silica-alumina fibers by chemically modifying aluminum alkoxide and firing gel fibers obtained from silicon alkoxide or its derivatives,
The present invention relates to a method for producing porous silica alumina fibers by subjecting gel fibers to steam treatment before firing.

0002

[Prior Art] Conventionally, ceramic catalysts have been commonly used as catalysts that have been used in chemical processes because they do not cause any problems in normal chemical processes as long as they can withstand temperatures below 600°C. However, in recent years, equipment involving high-temperature chemical processes, especially catalytic combustors, are expected to be applied to gas turbines, boilers, jet engines, etc., and NOx
1,000 in response to requests for reducing emissions and improving combustion efficiency, etc.
Ceramics that can withstand high-temperature environments of ℃ or higher are being used.

[0003] Such ceramics are manufactured, for example, by appropriately mixing powders of various metal oxides, molding, and firing in order to obtain a desired composition and shape. However, in this method, since the starting raw material powder itself has a low specific surface area, the specific surface area is further reduced by high-temperature calcination, and the catalyst cannot be said to be highly efficient.

Therefore, in order to produce ceramics with a higher specific surface area, a sol-gel method has been developed in which a gel formed by mixing and hydrolyzing a metal alkoxide, such as aluminum alkoxide or barium alkoxide, is fired instead of powder as the starting material. , INTERNATIONAL SYM
POSIUM ON FINE CERAMICS A
It is described in a document by Hiromichi Arai entitled "Development of heat-resistant catalyst materials for high-temperature catalytic combustion" in RITA '87.

[0005]

[Problems to be Solved by the Invention] However, in the above-mentioned gel-sol method, reformation is necessary in order to integrate the product into a powder, and the temperature at which it is most commonly used as a combustion catalyst is The specific surface area at around 1200° C. 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.

[0006] The present invention solves the above problems and
The object of the present invention is to provide a method for producing porous silica alumina fibers that have a high specific surface area at high temperatures using a gel method, are fibrous, have a large geometric surface area, and can be easily modularized.

[0007] In addition, conventionally known ceramic fibers for catalyst carriers have low specific surface areas, and even if they have high specific surface areas, it is difficult to maintain the specific surface area at high temperatures. there were. The present invention also intends to solve this problem.

[0008]

[Means for Solving the Problems] The present invention provides a method for producing silica-alumina fibers from aluminum alkoxide and silicon alkoxide, in which the silica content in ceramics after firing a reaction mixture of aluminum alkoxide and a compound having active hydrogen. mixed with silicon alkoxide and/or its derivative in an amount of 30% by weight or less, hydrolyzing the mixture to form a sol, spinning the sol into gel fibers, and then treating with steam,
This method of producing porous silica alumina fibers is characterized in that the steam-treated gel fibers are then fired, thereby solving the above problem.

[0009] In the present invention, a sol produced by hydrolyzing a mixture containing a metal alkoxide having the above composition is spun and then subjected to steam treatment to generate and maintain porosity in the gel fiber. Even after firing, the porosity of the gel state can be maintained, and silica-alumina porous fibers with a high specific surface area can be obtained.

[0010] The mixture to be hydrolyzed contains at least both metal alkoxides, which are the constituent metals of the sol produced from aluminum alkoxide and silicon alkoxide, and a compound having active hydrogen to produce a reaction mixture with aluminum alkoxide. If contained, other arbitrary components such as organic solvents, water, arbitrary additives, catalysts such as inorganic acids such as hydrochloric acid, other sol composition metal materials, crystal control agents, etc. can be contained. .

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-propyl, n-butyl,
Examples include iso-butyl, sec-butyl, and tert-butyl.

[0012] Compounds with active hydrogen to be reacted with aluminum alkoxide generally have hydrogen atoms in organic compounds bonded to heteroatoms such as oxygen, nitrogen, sulfur, etc., and are more reactive than ordinary hydrogen-carbon bonds. It is characterized by strong The active hydrogen-containing compound referred to in the present invention is one that satisfies the above-mentioned conditions and is reactive with aluminum alkoxide, which is a starting material.D. C. Bradley, R. C. Meh
rotra and D. P. “Matal” by Gaur
Compounds listed in "Alkoxides" p. 149-298 correspond.

Specifically, alkanolamine compounds represented by monoethanolamine, mono-n-propanolamine, mono-iso-propanolamine, diethanolamine, di-iso-propanolamine, triethanolamine, and tri-iso-propanolamine; β represented by acetylacetone and ethyl acetoacetate
- Diketone compounds; glycol compounds represented by ethylene glycol and diethylene glycol; other examples include organic acids, phenols, thiols, amines, etc.
From the viewpoint of adjusting the hydrolysis rate, alkanolamine compounds and β-diketone compounds are particularly preferred. Furthermore, among these, triethanolamine is particularly preferred as the alkanolamine compound, and β-ketonic acid esters such as ethyl acetoacetate are particularly preferred as the β-diketone compound.

The amount of this active hydrogen-containing compound used is:
For other than β-diketone compounds, the number of moles of active hydrogen per mole of aluminum alkoxide is 0.6 ~
Use within a range of 2.7 moles. β-diketone compounds such as acetylacetone and ethyl acetoacetate are enol-type and participate in the reaction, so the number of active hydrogens is counted as one per molecule; however, β-diketone compounds, especially β-ketone acids such as ethyl acetoacetate, In the case of esters, they have an excellent ability to stabilize aluminum alkoxides, and the number of moles of active hydrogen,
That is, a sufficient effect can be obtained in an amount of 0.2 to 1.5 moles of molecules.

Since the hydrogen atom of the hydroxyl group of alkanolamines participates in the reaction with aluminum alkoxide,
The number of active hydrogens in one molecule is 1 for monoalkanolamines, 2 for dialkanolamines, and 3 for trialkanolamines. When the amount of the compound having active hydrogen is within the above range, the hydrolysis rate of aluminum alkoxide can be sufficiently adjusted during hydrolysis, and a sol having a viscosity suitable for spinning operations can be obtained.

[0016] If the amount of the compound having active hydrogen is less than the above range, the hydrolysis rate of aluminum alkoxide will not be sufficiently adjusted, and the reaction will proceed rapidly during hydrolysis, resulting in the precipitation of powdery precipitates. However, it is impossible to synthesize a sol with a viscosity suitable for spinning operations. On the other hand, if the amount used is larger than the above range, a viscous sol will be obtained after removing the hydrolyzed alcohol and organic solvent from the system, but the gelation rate will be low because it is stable against hydrolysis even after the spinning operation. This is extremely slow and makes it difficult to maintain the shape of the gel fiber, making it impractical.

[0017] The reaction between aluminum alkoxide and a compound having active hydrogen can be carried out by mixing the two at room temperature or under heating. Preferably, it is carried out in the presence of However, the reaction is possible even in the absence of an organic solvent. The organic solvent used here is preferably one that dissolves aluminum alkoxide, specifically alcohols represented by iso-propanol, sec-butanol, etc., aromatic hydrocarbons represented by toluene, benzene, xylene, etc. , tetrahydrofuran, dimethylformamide, carbon tetrachloride, etc., but alcohols are preferred from the viewpoint of solubility.

On the other hand, the silicon alkoxide to be mixed with the above reaction mixture is represented by the general formula (RO) 4 Si (R: alkyl group), and specifically R is methyl, ethyl, n-propyl, n-butyl, iso-
There are butyl, sec-butyl, tert-butyl, etc. Derivatives of silicon alkoxide include those obtained by partially hydrolyzing the above-mentioned silicon alkoxide with water in an amount not more than 4 times the mole of silicon alkoxide, and oligomers which have undergone a polycondensation reaction in advance.

The amount of silicon alkoxide and/or its derivative used is such that the silica content in the fired ceramic is 30% by weight or less. If the amount of silica used exceeds 30% by weight in the ceramic after firing, the heat resistance of the resulting silica-alumina fibers will decrease significantly, and the ability to maintain a high specific surface area at high temperatures as described below will result. becomes difficult. Furthermore, in the case of a pure alumina-based material without the addition of a silica source, crystal transition to α-alumina and grain growth occur at relatively low temperatures, making it difficult to maintain a high specific surface area at high temperatures.

[0020] The amount of water used when hydrolyzing a mixture of a reaction mixture of aluminum alkoxide and a compound having active hydrogen mixed with silicon alkoxide and/or its derivatives is as follows:
Silicon alkoxide, as described below, including other metal alkoxides, is 0.0% per mole of all alkoxides.
It is used in a range of 5 to 2.0 moles. Even when using an oligomer that has undergone a polycondensation reaction as a silicon alkoxide derivative, the oligomer is treated as one molecule and water within the above range is used. In addition, when using a derivative of silicon alkoxide that has been partially hydrolyzed with water that is less than 4 times the mole of silicon alkoxide, calculate the amount of water used for this partial hydrolysis. Water is added so that the amount of hydrolyzed water is within the above range per mole of all alkoxides such as aluminum alkoxide and silicon alkoxide as a starting material.

If the amount of water used is less than 0.5 mol, a viscous sol is obtained after the removal of the hydrolyzed alcohol and, if an organic solvent is used in the system, after its removal. However, it becomes difficult to maintain the shape of the gel fiber after the spinning operation, making it impractical. On the other hand, if the amount of water used is more than 2.0 moles, the reaction will proceed rapidly during hydrolysis, and a powdery precipitate may be deposited, or even if a viscous sol is obtained, gelation will be rapid and the spinning will be difficult. The available conditions and time are extremely short, making it unsuitable for synthesizing a sol with a viscosity suitable for spinning operations. Further, from the above viewpoint, the amount of water used for hydrolysis is more preferably in the range of 0.5 to 1.5 moles per mole of total alkoxide.

Methods for hydrolyzing the mixture include hydrolysis by adding a mixture of water and an organic solvent that has an appropriate solubility in water or dissolves water, and using moisture in the air. Examples include hydrolysis, hydrolysis using blowing gas containing water vapor, and the like. Monoethanolamine as a compound with active hydrogen,
When acetylacetone is used, it is preferable to use a hydrolysis method using moisture in the air or a hydrolysis method using blowing gas containing water vapor. In this case, when hydrolysis is performed by adding a mixture of water and an organic solvent that has a suitable solubility in water or dissolves water, the concentration of water must be kept at an extremely low concentration, otherwise powder-like substances will be formed during hydrolysis. A precipitate forms, making it unsuitable for industrial synthesis of a sol with a viscosity suitable for spinning operations. When triethanolamine or ethyl acetoacetate is used as a compound having active hydrogen, there are no particular limitations on the hydrolysis method. From this point of view, these two compounds can be said to be particularly preferable compounds.

Further, this hydrolysis is preferably carried out in the presence of an organic solvent for the same reason as mentioned for the reaction of aluminum alkoxide with a compound having active hydrogen. An organic solvent for this purpose may be added during this hydrolysis step, but aluminum alkoxide and a compound having active hydrogen must be already mixed and reacted in the presence of an organic solvent, or silicon alkoxide must be partially hydrated. When decomposition is carried out in the presence of an organic solvent, a mixture of silicon alkoxide and/or its derivatives containing the organic solvent may be directly subjected to the hydrolysis reaction.

[0024] The order in which the aluminum alkoxide, the compound having active hydrogen, the silicon alkoxide and/or its derivative, and water used in the present invention are mixed is that the aluminum alkoxide and the compound having active hydrogen are mixed before the addition of water. There are no particular limitations as long as the conditions are right for the reaction and for silicon alkoxide and/or its derivatives to coexist in the reaction mixture.

A silica-alumina precursor sol is obtained by the above hydrolysis. This sol has a certain degree of viscosity,
Although it has spinnability, its concentration is low and insufficient for spinning, so by carrying out an appropriate concentration operation, a viscous sol that can be spun is obtained. This concentration operation may be either normal pressure distillation or reduced pressure distillation. Using this concentrated viscous sol, spinning can be performed by an appropriate known method.

[0026] The fibrous sol absorbs moisture in the air,
Alternatively, gel fibers can be obtained by increasing the amount of water vapor or rapidly gelling in the presence of a gaseous catalyst that promotes gelling. If this gel fiber is fired without any treatment, only ceramic fibers with a low specific surface area will be obtained, and porous fibers that can maintain a high specific surface area at high temperatures suitable for high-temperature catalyst supports cannot be obtained.

This problem could be solved by subjecting the gel fibers to steam treatment immediately after spinning. The water vapor treatment referred to here is a process performed in a humidified atmosphere at a temperature of 40°C or higher, and in an atmosphere of 40°C and a relative humidity of 50% or higher, that is, 0.024 kg H2 in a temperature range of 40°C or higher.
Processing under an atmosphere of absolute humidity of 0/kg-dry air or higher is shown. In order to shorten the processing time, it is more preferable to use 0.091 kgH2O/in an atmosphere of a temperature of 60°C and a relative humidity of 60% or higher, that is, in a temperature range of 60°C or higher.
It is preferable to carry out the test under an atmosphere of absolute humidity of kg-dry air or higher.

Although it is naturally possible to use high-pressure steam at a temperature of 100° C. or higher for this steam treatment, treatment under a high humidity atmosphere at atmospheric pressure is sufficient. This treatment time varies depending on the type and amount of the compound having active hydrogen to be reacted with the aluminum alkoxide, but as a general tendency, the higher the silica content, the more It is necessary to lengthen the steam treatment time. Although the processing time cannot be determined uniquely because it is influenced by temperature and humidity, the higher the temperature and the higher the humidity, the shorter the processing time is possible, and the processing time of 5 minutes or more is effective.

If this treatment time is too short, the progress of hydrolysis and polycondensation in the gel fiber will be insufficient,
It becomes impossible to generate sufficient micropores. Therefore, the specific surface area of the gel fiber does not increase, and it is also impossible to maintain the specific surface area at high temperatures. There is no particular problem with this processing time being too long, and it is preferable to make it as long as possible so as not to cause any problems in the manufacturing process.

[0030] In the above steam treatment, the fibers may be treated continuously or in batches. The gel fibers subjected to steam treatment become silica-alumina porous fibers by being fired, and after the steam treatment, appropriate steps such as application of a desired chemical, for example, immersion in a catalyst solution, etc. A heat treatment step or the like at a temperature below the firing temperature can be provided.

As described above, gel fibers with a high specific surface area can be easily obtained by treating gel fibers with steam immediately after spinning, and this high specific surface area is maintained even after firing.
It becomes possible to produce a silica-alumina porous fiber suitable for a high-temperature catalyst carrier with good reproducibility and which can maintain a high specific surface area even at high temperatures.

[0032] Furthermore, for the purpose of controlling crystal transition, suppressing abnormal grain growth, etc., B2 O3, MgO, P2 O
5, CaO, Cr2O3, CuO, Fe2O3
, TiO2 and ZrO2 may also be added. These compounds include oxides, inorganic salts, organic salts,
It is also possible to add metal alkoxide or the like before or after the production of the silical alumina precursor sol and before spinning.

[0033] Furthermore, as a method for producing a high-temperature catalyst from this silica-alumina porous fiber, it is possible to apply a known method. A high-temperature catalyst carrying a catalyst component can be obtained by immersing the silica-alumina porous fibers heat-treated in a solution containing a catalyst metal component and then calcination in an oxidizing or reducing atmosphere.

[0034]

[Function] According to the present invention, gel fibers with a high specific surface area can be easily obtained by steam-treating the gel fibers immediately after spinning, and this high specific surface area is maintained even after firing, with good reproducibility, and under high temperature conditions. However, it has become possible to produce silica-alumina porous fibers suitable for high-temperature catalyst carriers that can maintain a high specific surface area.

Although the exact mechanism is unclear, it is thought to be as follows. In the synthesis of stringable sols from metal alkoxides, the amount of water used for their hydrolysis is less than the stoichiometric amount required for complete hydrolysis. Therefore, a large amount of alkoxyl groups remain in the gel fiber immediately after spinning. When this gel fiber is placed in a steam atmosphere, hydrolysis and polycondensation proceed from the surface portion, forming a thick shell. After this hard shell is formed, polycondensation further progresses inside the shell, causing the volume to contract and thus producing a large number of micropores, resulting in a gel fiber with a high specific surface area. Since the pore diameter of these micropores is relatively large, it is thought that a silica-alumina porous fiber that maintains a high specific surface area even at high temperatures and is suitable as a high-temperature catalyst carrier can be obtained.

[0036]

[Examples] The present invention will be specifically explained below with reference to Examples. However, the present invention is not limited only to these examples.

Example 1 Se per mole of aluminum sec-butoxide
6.6 mol of c-butanol and 0.33 mol of triethanolamine were mixed at room temperature for 2 hours to obtain a reaction product. To the obtained reaction product, 0.15 mol of silicon ethoxide was partially hydrolyzed with 0.15 mol of water acidified with 1N hydrochloric acid, and this was mixed with 1 mol of water and 3.3 mol of water. A mixture of molar sec-butanol is added, stirred for 12 hours, and distilled under reduced pressure at 60° C. and 100 mmHg to remove a portion of the sec-butanol. A spinnable sol is obtained, and a spinning operation is performed. As a result, transparent gel fibers were obtained.

The obtained gel fiber was subjected to steam treatment for 3 days at 70° C. and 85% relative humidity. The BET specific surface area of the gel fiber obtained was 321 m2/
g and a high specific surface area. This steam-treated gel fiber was fired in air at 1100° C. for 2 hours, resulting in a silica-alumina porous fiber with a crystalline phase of γ-alumina and a high specific surface area of 303 m 2 /g.

Comparative Example 1 The gel fiber obtained in Example 1 was fired under the same conditions as in Example 1 without steam treatment. This fiber was black and brittle due to residual carbon, and its specific surface area was as low as 0.15 m2/g.

Comparative Example 2 A gel fiber having a silica content of 54% by weight was obtained in the same manner as in Example except that the amount of silicon alkoxide used was 1 mol per mol of aluminum sec-butoxide. By treating this gel fiber with steam under the same conditions as in Example 1, a BET specific surface area of 254
A gel fiber with a high specific surface area of m2/g was obtained. As a result of firing this gel fiber under the same conditions as in Example 1,
The crystal phase is mullite and its specific surface area is 0.05m2/g
The porosity was completely lost.

Example 2 Se per mole of aluminum sec-butoxide
c-butanol 6.6 mol, ethyl acetoacetate 0.4
The moles were mixed for 2 hours at room temperature to obtain the reaction product. Silicon methoxide 0.045 mol, silicon sec
- 5 moles of butoxide, 0.045 moles of water
The mixture was mixed at 0° C. for 2 hours to obtain a silicon alkoxide derivative. The reaction product and the silicon alkoxide derivative were mixed, and a mixed solution of 1.0 mol of water and 3.3 mol of sec-butanol was added to perform a hydrolysis operation. After the addition, the mixture was stirred for 12 hours and distilled under reduced pressure at 60°C and 100 mmHg to remove a portion of the sec-butanol, to obtain a spinnable sol that could be spun, and a transparent gel fiber was obtained by performing the spinning operation. .

[0042] The obtained gel fiber was subjected to a steam treatment for 24 hours at 70°C and a relative humidity of 85%. The BET specific surface area of the gel fiber obtained was 263 m
It had a high specific surface area of 2/g. As a result of firing this steam-treated gel fiber in air at 1100°C for 2 hours,
The crystalline phase was γ-alumina, and silica-alumina porous fibers with a high specific surface area of 240 m 2 /g were obtained.

Comparative Example 3 The gel fiber obtained in Example 2 was fired under the same conditions as Example 2 without steam treatment. This fiber was black and brittle due to residual carbon, and its specific surface area was as low as 1.5 m2/g.

[0044]

Effects of the Invention According to the present invention, chemically modified aluminum alkoxide, silicon alkoxide and/or
By steam-treating gel fibers obtained from the gel fibers or their derivatives and then firing them, it becomes possible to produce porous silica-alumina fibers that can maintain a high specific surface area even at high temperatures. This is an extremely useful production method for stably producing fibers suitable as high-temperature catalyst carriers and useful as industrial materials with good reproducibility.

Claims (1)

[Claims] Claim 1: In a method for producing silica alumina fibers from aluminum alkoxide and silicon alkoxide, an amount such that the silica content in the ceramic after firing a reaction mixture of aluminum alkoxide and a compound having active hydrogen is 30% by weight or less. The mixture is hydrolyzed to form a sol, the sol is spun into gel fibers, and then treated with steam, and the steam-treated gel fibers are then mixed with silicon alkoxide and/or its derivatives. A method for producing a silica-alumina porous fiber, the method comprising firing a silica-alumina porous fiber.