JP3346704B2 - Method for producing inorganic separation membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an inorganic separation membrane suitable for separating a specific component from a mixed fluid such as various mixed gases.

[0002]

2. Description of the Related Art Conventionally, porous bodies made of various materials such as organic materials have been used for various filtration separation membranes or permeable membranes. However, heat resistance, chemical resistance, impact resistance,
As the demand for wear resistance and the like has increased, various inorganic porous materials having excellent thermal, chemical stability and mechanical properties have been attracting attention.

The performance of such a porous inorganic separation membrane having excellent heat resistance, chemical resistance and pressure resistance is affected by the pore diameter, pore volume and pore diameter distribution of the material used to form the membrane. Yes, for example, H ₂ and N ₂ , H ₂ and C
When separating O and the like, it is necessary to control the pore diameter of the porous membrane to about several tens of degrees to several hundreds of degrees so that Knussen diffusion is dominant, while CO ₂ having a small difference in molecular weight is required.
When separating N ₂ and N ₂ , it is necessary to control the pore diameter of the porous membrane to 10 ° or less so that the surface diffusion is dominant.

[0004] Specifically, Al produced by a sol-gel method is used.
_{The 2} O ₃ membrane is formed by attaching a sol obtained by hydrolyzing an alkoxide with a large amount of water to the outer surface of a porous support tube, drying the sol,
By baking and applying, a porous film can be relatively easily prepared, and the obtained Al ₂ O ₃ porous film has relatively small pores having a diameter of about several tens of degrees.

[0005] Films such as SiO ₂ and TiO ₂ can be easily formed on a substrate having a smooth surface such as a glass substrate by using a sol obtained by hydrolyzing an alkoxide in an alcohol solvent. Can be produced, and the film also has pores of about several Å (Japanese Patent Laid-Open No.
117053, JP-A-7-313853).

[0006]

However, the aforementioned A
The l ₂ O ₃ membrane has a pore diameter of about several tens of degrees, and the problem that the pore diameter of the Al ₂ O ₃ membrane is too large to be applied for separating a gas mixture having a small difference in molecular weight based on the surface diffusion control. was there.

On the other hand, the film of SiO ₂ , TiO _2, etc.
Even if dip coating is performed on a porous substrate using a sol obtained by hydrolyzing an alkoxide in an alcohol solvent, a film is not formed due to penetration into the substrate, or even if a film is formed, a crack is formed. , Peeling and the like were observed.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a porous support having a fine pore diameter without cracks or peeling having a pore diameter of 10 mm or less.
An object of the present invention is to provide a method for producing an inorganic separation membrane capable of forming a porous membrane having a high permeability of a specific gas component, that is, a high separation coefficient of a specific component.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above problems, and as a result, have found that an aluminum alkoxide and a silicon
A partially hydrolyzed sol is complexed in an alcohol solvent, and the sol obtained by hydrolysis is diluted, adhered, dried, and then fired, and a series of operations are repeated to cause cracks and peeling. No Al ₂ O ₃ -S
It has been found that an iO ₂ composite membrane can be produced, and that the membrane has an improved separation coefficient for specific gas components.

That is, the method for producing an inorganic separation membrane of the present invention comprises:
And aluminum alkoxide, partial hydrolysis of the silicon obtained silicon alkoxide and partial hydrolysis
A sol is compounded in an alcohol solvent to prepare a composite alkoxide.
A composite sol was prepared by hydrolysis with a solution in which 5 to 100 mol of water and an alcohol were mixed with each other, and the composite sol was diluted , attached to the outer surface of a porous ceramic support tube, and dried. Thereafter, it is applied by firing at a temperature of 400 to 700 ° C.

[0011]

According to the method for producing an inorganic separation membrane of the present invention, an aluminum alkoxide and a silicon alkoxide are partially hydrolyzed on the outer surface of a porous ceramic support tube.
The obtained partially hydrolyzed sol is compounded in an alcohol solvent, and the water content is 5 to 100 m with respect to 1 mol of the larger of the aluminum and silicon alkoxides.
The sol obtained by hydrolysis by adding at a ratio of ol is attached, dried and calcined, so that almost all of the alkoxyl groups, which are the reactive groups of the existing alkoxide, have sufficient water to react with water. , Polycondensation develops three-dimensionally, a sol having a strong network structure is obtained , and a complex sol is diluted.
In order to reduce the thickness of the film component applied at one time, an Al ₂ O ₃ —SiO ₂ composite film free from cracks and peeling can be obtained even after drying and firing.
The pores of the membrane have a pore size of の order,
As a result, the separation coefficient of the specific component can be improved.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for producing an inorganic separation membrane of the present invention will be described in detail.

According to the present invention, a composite sol prepared by combining aluminum and silicon alkoxides in an organic solvent such as alcohol on the outer surface of a ceramic porous support tube and hydrolyzing the composite alkoxide is diluted. rear
After the attached matter is dried by immersion or the like and dried, and then baked in the air, it is possible to produce a composite membrane having a fine pore diameter, and the permeation efficiency for a specific gas component is improved. An inorganic separation membrane is obtained.

In the present invention, the complexation of each alkoxide of aluminum and silicon can be produced by heating and refluxing each alkoxide in an alcohol solution. However, since there is a great difference in the reaction rate of hydrolysis of each alkoxide, Mixing and stirring a partially hydrolyzed sol prepared by partially hydrolyzing a tetraalkoxysilane such as tetraethoxysilane in an alcohol solution using an inorganic acid such as hydrochloric acid and a trialkoxyaluminum such as aluminum secondary butoxide. Is important
You .

Further, for an aluminum alkoxide having a higher hydrolysis reaction rate, it is preferable to add a compound that reduces the reactivity of the alkoxide to water in an alcohol solution of the aluminum alkoxide.

The compound that reduces the reactivity of the alkoxide with water is R ₁ R ₂ NCH ₂ CH ₂ OH
(Wherein R ₁ or R ₂ is H, CH ₃ , C ₂
H _5, CH ₃ CH ₂ OH or one) represented by ethanolamine or β- diketones, acetic anhydride, acetoacetate esters, dicarboxylic acid esters and the like.

If the amount of the compound, that is, the stabilizer, is less than 0.1 mol, the effect of the stabilizer is not substantially obtained. It is preferably at least 1 mol.

On the other hand, the alcohol solution of each alkoxide of aluminum or silicon includes a monohydric alcohol such as ethanol, propanol, butanol, 2-methoxyethanol and 2-ethoxyethanol or a dihydric alcohol such as ethylene glycol and propylene glycol. Alcohol is used.

As described above, an alcohol solution of a complex alkoxide in which aluminum and silicon alkoxides are complexed is mixed with an alcohol solution of aluminum or silicon, whichever is greater, in order to hydrolyze it.
By dropping a mixed solution of 5 to 100 mol of water and alcohol with respect to 1 liter, a composite sol can be prepared.

The reason why the amount of the water is limited to 5 to 100 mol per 1 mol of aluminum or silicon alkoxide, whichever is larger, is to adhere the prepared composite sol to the outer surface of the ceramic porous support tube. When the amount of the water is less than 5 mol, the polycondensation of the sol does not develop three-dimensionally, the structure of the sol itself is weak, and the sol is directly adhered to the outer surface of the porous support tube and dried and fired. It is virtually impossible to avoid the occurrence of cracks and peeling due to shrinkage in those processes,
When the amount exceeds 1, the obtained sol becomes a colloidal sol,
This is because the pore diameter increases, or the sol concentration substantially decreases, so that the penetration of the sol into the porous ceramic support tube increases, and film formation becomes difficult.

As the porous ceramic support tube used in the present invention, an α-Al ₂ O ₃ porous tube is generally used. In addition, ZrO ₂ , SiO ₂ , Si
₃ N _4, it is possible to use various ceramic support tube, such as glass, its pore size 0.01 to 10 [mu] m, is preferably preferably 0.05 to 2 [mu] m.

In order to attach the composite sol to the outer surface of such a porous ceramic support tube, the ceramic support tube is immersed in the composite sol, dried and fired to form Al ₂ O ₃ —S.
An iO ₂ composite membrane can be provided.

The immersion in the Al ₂ O ₃ —SiO ₂ composite sol and the lifting from the sol can be carried out by using a constant speed motor, followed by drying at room temperature and then 400-700. Firing at a temperature of about 0.5 to 10 hours.

It is preferable to repeat the above-described series of operations a plurality of times because a thick film component applied at one time cannot avoid cracks and peeling due to shrinkage generated during drying and firing. By diluting the sol with an alcohol or the like used as a solvent for the composite sol,
It is necessary to thin the film component applied at one time.

[0025]

The method for producing an inorganic separation membrane of the present invention will be described in detail below.

(Example 1) 0.25 mol of aluminum secondary butoxide was added to 0.7 of 2-methoxyethanol.
5 mol dissolved in ethyl silicate 2 mol
Methoxyethanol 4mol, water 1mol and nitric acid 0.0
A mixed alkoxide was prepared by adding a partially hydrolyzed sol prepared by adding a solution obtained by mixing 7 mol with 7 mol.

Next, 15 m of water was added to the composite alkoxide.
After a mixed solution of 3 mol of ol and 2 methoxyethanol was dropped to prepare a composite sol, 15 mol of 2 methoxyethanol as a solvent was further added and diluted to prepare a composite sol for film formation.

Using the thus obtained composite sol for film formation, α-Al ₂ O ₃ having a porosity of 39% and a pore diameter of 0.3 μm was used.
An operation of depositing the composite sol for film formation on the outer surface of the porous support tube by an immersion method, drying at room temperature, and sintering at 500 ° C. was repeated 15 times to obtain an Al ₂ O ₃ —SiO ₂ composite film. It was prepared -al ₂ O ₃ porous support tube.

On the other hand, the amount of water in the mixed solution dropped to the composite alkoxide was reduced to 1 mol, and α-Al ₂ O ₃ porous was prepared in the same manner as described above except that 2 methoxyethanol for dilution was not added after the preparation of the composite sol. A film formed on the outer surface of the porous support tube 10 times was used as a comparative example.

The Al ₂ O of the present invention prepared as described above
_{The 3-} SiO ₂ composite film has a thickness of about 1 μm and has no defects such as cracks and peeling, whereas the composite film of the comparative example has a thickness of about 1 μm, but covers the entire film surface. A crack has occurred.

For each of the Al ₂ O ₃ —SiO ₂ composite films, the permeation rates (permeability) of CO ₂ and N ₂ gas and the CO ₂ / N ₂ separation coefficient (permeation coefficient ratio) were measured at room temperature. However, in the Al ₂ O ₃ —SiO ₂ composite film of the present invention, the CO ₂ transmission rate is 2.5 × 10 ⁻⁹ mol / (m ²
Pa · sec), N ₂ transmission speed is 1.4 × 10 ⁻⁹ mo
1 / (m ² · Pa · sec), and the CO ₂ / N ₂ separation coefficient is 1.79, whereas the CO ₂ permeation rate in the comparative example is 3.0 × 10 ⁻⁹ mol / (m ²・ Pa ・ se
c), the N ₂ permeation rate is 3.7 × 10 ⁻⁹ mol / (m ^2.
Pa · sec), and the CO ₂ / N ₂ separation coefficient is 0.8
It was 0.

Example 2 Next, 1 mol of aluminum secondary butoxide was added to 3 mol of 2-methoxyethanol.
to a mixed solution prepared by adding 1 mol of triethanolamine as a stabilizer, a mixed solution of 0.25 mol of ethyl silicate, 1 mol of 2 methoxyethanol, 0.25 mol of water and 0.0175 mol of nitric acid is added. A composite alkoxide was prepared by adding the partially hydrolyzed sol prepared by the addition.

A mixed solution composed of 5 mol of water and 3 mol of 2-methoxyethanol was added dropwise to the composite alkoxide thus obtained to prepare a composite sol.
15 mol of methoxyethanol was added and diluted to prepare a composite sol for film formation.

Thereafter, the porosity is 39% and the pore diameter is 0.3 μm.
The composite sol for film formation was adhered to the outer surface of the α-Al ₂ O ₃ porous support tube by dipping and dried at room temperature.
The operation of firing at a temperature of 500 ° C. was repeated 15 times,
An α-Al ₂ O ₃ porous support tube provided with a ₂ O ₃ —SiO ₂ composite film was produced.

On the other hand, the amount of water in the mixed solution dropped to the composite alkoxide was reduced to 1 mol, and α-Al ₂ O ₃ porous was prepared in the same manner as described above except that 2 methoxyethanol for dilution was not added after the preparation of the composite sol. A film formed on the outer surface of the porous support tube 10 times was used as a comparative example.

The Al ₂ O of the present invention prepared as described above
_{The 3-} SiO ₂ composite film has a thickness of about 1 μm and has no defects such as cracks and peeling, whereas the composite film of the comparative example has a thickness of about 1 μm, but covers the entire film surface. A crack has occurred.

For each of the Al ₂ O ₃ —SiO ₂ composite films, the permeation speed (permeability) of CO ₂ and N ₂ gas and the CO ₂ / N ₂ separation coefficient (permeation coefficient ratio) were measured at room temperature. However, the Al ₂ O ₃ —SiO ₂ composite film of the present invention has a CO ₂ transmission rate of 1.7 × 10 ⁻⁹ mol / (m ²
Pa · sec), N ₂ transmission rate is 1.2 × 10 ⁻⁹ mo
1 / (m ² · Pa · sec), and the CO ₂ / N ₂ separation coefficient is 1.42, whereas the CO ₂ permeation rate in the comparative example is 1.8 × 10 ⁻⁹ mol / (m ²・ Pa ・ se
c), the N ₂ permeation rate is 2.3 × 10 ⁻⁹ mol / (m ²
Pa · sec), and the CO ₂ / N ₂ separation coefficient is 0.7
It was 8.

As can be seen from the results of Example 1 and Example 2, the Al ₂ O ₃ —SiO ₂ composite film of the present invention has a transmission speed almost the same as that of the comparative example having defects such as cracks. Despite the, whereas comparative example shows only the separation factor of about Knudsen diffusion, Al ₂ of the present invention
The O ₃ —SiO ₂ composite film has about twice the CO ₂ / N ₂ of the comparative example.
It can be seen that it has a separation factor.

[0039]

As described above, according to the method for producing an inorganic separation membrane of the present invention, the outer surface of the α-Al ₂ O ₃ porous support tube is
To a composite alkoxide of aluminum and silicon, a mixed solution of 5 to 100 mol of water and alcohol is added to 1 mol of the greater of each alkoxide of aluminum and silicon, and the mixture is hydrolyzed. By repeatedly forming a film after dilution, it is possible to improve the separation coefficient of gas components of specific components without defects such as cracks and peeling, and to transmit specific components to coexisting components forming a mixed fluid such as various mixed gases. High rate, ie
An inorganic separation membrane having a high separation coefficient of a specific component can be obtained.

Claims (1)

(57) [Claims] The outer surface of the 1. A ceramic porous support tube, and aluminum alkoxide, a silicon alkoxide
Partially hydrolyzed sol of silicon obtained by partial hydrolysis
And a composite sol obtained by adding a mixed solution of 5 to 100 mol of water to 1 mol of the greater of the alkoxide of aluminum and silicon, and an alcohol to a composite alkoxide obtained by complexing , After dilution, and after drying, 400-70
A method for producing an inorganic separation membrane, comprising firing at a temperature of 0 ° C.