JP3336177B2 - 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 including organic materials have been used for various filtration separation membranes or permeable membranes, but impact resistance, abrasion resistance, chemical resistance, heat resistance and the like have been used. As demands on gender etc. increase, mechanical,
Attention has been focused on various inorganic porous materials having excellent thermal and chemical stability.

The performance of such a porous inorganic separation membrane having excellent heat resistance, pressure resistance and chemical resistance is affected by the pore diameter, pore volume and pore diameter distribution of the material used to form the membrane. For example, although the Al ₂ O ₃ porous film can be relatively easily prepared by the sol-gel method, the obtained Al ₂ O ₃ porous film has relatively small pores having a diameter of about several nm. Becomes

However, even a porous membrane having the above-mentioned pore diameter has too large a pore diameter for application as a separation membrane for separating a specific component from a mixed fluid such as various gas mixtures, and therefore, sufficient separation is required. Efficiency cannot be achieved.

[0005] Therefore, it called modifying narrowing the pore diameter by increasing the pore inner walls of the Al ₂ O ₃ film manufactured by the sol-gel method as described above, other pore inner walls of the Al ₂ O ₃ film As a means for partially or entirely coating the same material or the same substance, a CVD method using the vapor pressure of various metal alkoxides, or a method of impregnating aluminum alkoxides or chelates in pores of an Al ₂ O ₃ film Have been proposed (see JP-A-1-254212 and JP-A-60-180979).

[0006]

However, the aforementioned A
In the CVD method for modifying the inner walls of the pores of the l ₂ O ₃ film, it is necessary to use a vapor pressure of various metal alkoxides at a high temperature and under a reduced pressure condition. A large-scale device such as a device and a gas introduction unit is required.

If the conditions such as temperature and pressure are not strictly controlled, not only the inner walls of the pores of the Al ₂ O ₃ film are modified, but also the pores themselves are closed, and oxides formed by various metal alkoxides are formed. And the like may be deposited on the Al ₂ O ₃ film, and many of the metal alkoxides to be used are easily hydrolyzed even by moisture in the air, so that the handling is extremely troublesome. there were.

On the other hand, a method of impregnating the the Al ₂ O ₃ film of pores in the aluminum alkoxide or chelate is of aluminum the Al ₂ O ₃ film of pores having a pore diameter of nm class alkoxide or chelate the impregnated, etc. after hydrolysis, a method of firing a change in the Al ₂ O ₃ itself γ-Al ₂ O ₃ formed by firing the alkoxide or chelate of aluminum used for modification of the pore inner wall In such a case, a structure having a pore diameter of the order of nanometers results in a problem that the efficiency is not good when a specific component is separated from the mixed fluid as described above.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and generally, when a membrane modified as described above is used as a separation membrane, the transmittance of the coexisting component or the specific component is reduced. If a membrane with a high separation coefficient can be obtained, the permeation amount as a membrane module can be improved by changing various conditions such as membrane area and pressure. The present invention provides a method for producing an inorganic separation membrane in which the inner wall of the pores can be modified by treatment at room temperature and the specific component has a high transmittance with respect to the coexisting components forming the mixed fluid, that is, a high separation coefficient of the specific component. The purpose is to do so.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above problems, and as a result, obtained by hydrolyzing an alkoxide of aluminum on the outer surface of an α-Al ₂ O ₃ porous tube. Attach AlOOH sol, 400-700 ° C
Γ-Al ₂ O ₃ film is fixed by firing at a temperature of
As a method for modifying the inner wall of the pore of the l ₂ O ₃ membrane, γAl ₂ O ₃
While depressurizing the inside of the porous tube to which the membrane is fixed , one of alkali metals and rare earth elements having low reactivity with water is mixed with aluminum.
By immersing the composite alkoxide with uranium or an alkoxide of Si in an alcohol solution, it is possible to modify the inner wall of the pores in the air and at room temperature, and to improve the separation coefficient of the specific component. I found it.

[0011] Among them, an alcoholic solution of the complex alkoxide <br/> used for modification, the composite alkoxides, alkali metal
Any of the genus Na, Rb, or the rare earth element La
It has been found that an alcohol solution containing a compound which is one type of complex alkoxide of aluminum and which reduces the reactivity to water is most desirable.

[0012]

According to the method for producing an inorganic separation membrane of the present invention, α-
An AlOOH sol obtained by hydrolyzing an alkoxide of aluminum is adhered to the outer surface of the Al ₂ O ₃ porous support tube, and calcined at a temperature of 400 to 700 ° C. to obtain γ-Al ₂ O ₃
Fixed as a membrane, while further reducing the pressure the γ-Al ₂ O ₃ film α-Al ₂ O ₃ porous tube which is fixed to the surface, is immersed in an alcohol solution of low reactivity various composite alkoxide to water Drying and baking, the alkali gold
Alcohol solution of a complex alkoxide of one of the genus and rare earth elements and aluminum has an inner wall of pores of the γ-Al ₂ O ₃ film having an affinity for a specific component, and calcined by an alcohol solution of alkoxide of Si. Since the subsequent film has fine pores, the inner walls of the pores of the γ-Al ₂ O ₃ film have finer pores, and the separation coefficient of the specific component gas component is improved. .

[0013]

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.

The present invention, α-Al ₂ O ₃ on the outer surface of the porous tube to form a γ-Al ₂ O ₃ film, the atmosphere, various composite alkoxide solution or while reducing the pressure thereof porous tube at room temperature
Dipped in an alkoxide solution of Si to form the γ-Al ₂ O ₃
By impregnating the inside of the pores of the membrane and baking it, the inner wall of the pores is modified to obtain an inorganic separation membrane having an improved separation coefficient for a target specific component.

[0015] In the present invention, as a method of modifying the pore inner walls of the γ-Al ₂ O ₃ film, seal the end of the γ-Al ₂ O ₃ film was formed α-Al ₂ O ₃ porous tube There is a method in which the porous tube is immersed in an alcohol solution of various metal alkoxides while impregnating the porous tube from the other end while reducing the pressure in the porous tube using a simple decompression device such as an aspirator or a vacuum pump, and then dried and fired.

[0016] The alcoholic solution of the complex alkoxide, alkali metal Na as a composite alkoxide,
Rb, Li, K, Cs, or rare earth element La,
Y, Ce, Pr, Nd, using a composite alkoxide of any one of aluminum and aluminum, the composite alkoxide is diluted with an organic solvent such as ethanol, propanol, butanol, 2-methoxyethanol, and 2-ethoxyethanol; Further, it is prepared by adding a compound that reduces the reactivity of the alkoxide with water.

[0017] The composite alkoxide, from the viewpoint of high affinity for the acid gases such as CO ₂ or NO _2, the composite alkoxide with any one of aluminum alkali metal Na, Rb or rare earth elements La, Is preferred.

The compound that reduces the reactivity of the alkoxide with water, ie, the stabilizer, is R ₁ R ₂
Ethanolamine represented by NCH ₂ CH ₂ OH (wherein R ₁ or R ₂ is any one of H, CH ₃ , C ₂ H ₅ , CH ₃ CH ₂ OH), or β-diketone; Acetic anhydride, acetoacetic acid ester, dicarboxylic acid ester, etc., and from the viewpoint that workability and the reactivity are reduced to such an extent that modification is possible at room temperature in the air, ethanolamine, β-diketone, acetoacetic acid Esters are preferred.

If the amount of the stabilizer is less than 0.1 mol relative to 1 mol of aluminum alkoxide, the effect as a stabilizer is substantially small, so that the amount is desirably 0.1 mol or more.

As described above, alkali metals and rare earth elements
Affinity for acidic gases such as CO ₂ and NO ₂ by modifying the inner wall of the pores of the γ-Al ₂ O ₃ film using a complex alkoxide of any one and aluminum, drying and firing And the surface diffusion mechanism makes it possible to efficiently separate these gases from a mixed gas containing these gases.

Further, the most suitable alkoxide alcohol solution is one prepared by diluting Si alkoxide with an organic solvent such as ethanol, propanol, butanol, 2-methoxyethanol and 2-ethoxyethanol.

Since the Si alkoxide itself has low reactivity with water, it is not necessary to add a compound that reduces the reactivity with water as described above, that is, a stabilizer.

In the inorganic separation membrane modified with the above-mentioned alcohol solution of alkoxide of Si, since the SiO ₂ obtained after firing has fine pores of the angstrom class, the inner wall of the pores of the γ-Al ₂ O ₃ membrane Is most desirable because it has more micropores, the capillary condensation and the surface diffusion mechanism function effectively, and the gas of a specific component can be efficiently separated.

The modification of the γ-Al ₂ O ₃ film formed on the outer surface of the α-Al ₂ O ₃ porous tube is performed by the above-mentioned composite alkoxide.
Or in order to efficiently modify the pore inner wall with an alcohol solution of Si alkoxide , immersion under reduced pressure, drying,
It is desirable to repeat the firing operation.

In the present invention, the γ-Al ₂ O ₃ film is formed by hydrolyzing an aluminum alkoxide in hot water and then peptizing with an acid.
A sol-gel method of dipping, drying and baking the IOOH sol is used. Preferably, alkoxide of aluminum is converted to propanol, butanol, 2-methoxyethanol,
-An AlOOH sol prepared by diluting with an organic solvent such as ethoxyethanol, adding the compound that reduces the reactivity of the alkoxide to the alkoxide solution, and then hydrolyzing and peptizing the alkoxide is preferred.

The α-Al ₂ O ₃ porous support tube is immersed in the AlOOH sol prepared as described above, and the operation of drying and firing is repeated to form an α-Al ₂ O ₃ porous support tube on the α-Al ₂ O ₃ porous support tube. A γ-Al ₂ O ₃ film having a finer pore structure than the pores of the γ-Al ₂ O ₃ film can be produced.

[0027]

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

First, aluminum secondary butoxide is added to hot water at 80 ° C. at a ratio of 100 mol of water to 1 mol of aluminum secondary butoxide to hydrolyze.

Thereafter, nitric acid is added at a ratio of 0.07 mol of nitric acid to 1 mol of the aluminum secondary butoxide, deflocculated while keeping the temperature at 85 ° C. or higher, and subsequently refluxed for 16 hours to prepare an AlOOH sol.

Next, the porosity is 39% and the pore size is 0.3 μm.
m α-Al ₂ O ₃ porous tube was immersed and adhered in the AlOOH sol, dried at room temperature, and fired at a temperature of 500 ° C.

This operation was repeated five times to obtain γ-Al ₂ O ₃
An α-Al ₂ O ₃ porous support tube having a membrane fixed to its outer surface was prepared.

[0032] One end of the obtained porous support tube is sealed,
The porous support tube was immersed in various metal alkoxide solutions while reducing the pressure, dried, and fired at a temperature of 500 ° C. to modify the inner walls of the pores of the γ-Al ₂ O ₃ film.

In this embodiment, the above modification operation is repeated 1 to 3 times, and the CO ₂ and N ₂ transmittances and the CO ₂ / N ₂ separation coefficient are measured each time. He is introduced inside, while C is added outside the porous support tube.
O ₂ / N ₂ was filled with a mixed gas of CO ₂ and N ₂ of 1/9, and the gas composition and the permeated amount in the porous tube passed through the separation membrane and the porous support tube were analyzed and measured by gas chromatography.

The time, the membrane area of each gas, and the permeation amount per partial pressure difference between the inside and outside of the porous tube are defined as the transmittance, and the ratio of the transmittance of CO ₂ and N ₂ is referred to as the separation coefficient. The higher the value, the higher the separation performance.

Further, for the γ-Al ₂ O ₃ film before modification, the transmittance and the separation coefficient were similarly measured to confirm the effect of the repetitive operation, and the results are shown in FIGS.

FIG. 1 shows that 2-methoxyethoxide of Na.
091mol and aluminum secondary butoxide 1
mol in 7 mol of 2 methoxyethanol,
The result of modification with a Na-Al complex alkoxide solution prepared by adding 1 mol of NN dimethylaminoethanol is shown.

FIG. 2 shows the isopropoxide of La 0.0
91mol and aluminum secondary butoxide 1m
ol in 7 mol of 2 methoxyethanol and mixed with N 2
The result of modification with a La-Al complex alkoxide solution prepared by adding 1 mol of N-dimethylaminoethanol is shown.

FIG. 3 shows that 1 mol of ethoxide of Si
ol diluted in 2 methoxyethanol
The result of modification with an alkoxide solution is shown.

As a comparative example, FIG. 4 shows the results of modification with an Al alkoxide solution prepared by mixing 1 mol of aluminum secondary butoxide in 7 mol of 2 methoxyethanol, and 1 mol of aluminum secondary butoxide in 7 mol of 2 methoxyethanol. FIG. 5 shows the results of modification with an Al alkoxide solution prepared by mixing and adding 1 mol of NN dimethylaminoethanol.

As apparent from FIGS. 1 to 5, in FIGS. 4 and 5 of the comparative examples, the transmittance and the separation coefficient are not changed even when the modification is performed with an alcohol solution of aluminum alkoxide as shown in FIG. Almost no change is observed, and even if a compound that reduces the reactivity to water is added as shown in FIG. 5, it is recognized that the inner wall of the pore is modified because the transmittance is certainly reduced. However, no improvement was observed in the separation coefficient.

On the other hand, the alkali metal of the present invention ,
FIG. 1 shows the result of modification with an alcohol solution of a complex alkoxide of aluminum and any one of rare earth elements .
FIG. 3 shows that in all cases, the transmittance is reduced, the inner wall of the pore is modified, and the improvement of the separation coefficient of CO ₂ with respect to N ₂ is extremely remarkable.

[0042]

As described above, according to the method for producing an inorganic separation membrane of the present invention, the inner wall of the pores of a γ-Al ₂ O ₃ membrane is modified by using a metal alkoxide solution having low reactivity to water. The inner wall of the pores can be modified by treating it in the air at room temperature by a simple method, and the inner wall of the pores of the γ-Al ₂ O ₃ film has an affinity for a specific component, It becomes possible to improve the separation coefficient of the gas component of the specific component, the transmittance of the specific component to the coexisting components forming a mixed fluid such as various mixed gas is high, that is, the specific component An inorganic separation membrane having a high separation coefficient can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the modification conditions of a separation membrane modified with a Na—Al composite alkoxide solution, transmittance, and separation coefficient.

FIG. 2 is a diagram showing a relationship between a modification condition of a separation membrane modified with a La-Al composite alkoxide solution, a transmittance, and a separation coefficient.

FIG. 3 is a diagram showing a relationship between a modification condition of a separation membrane modified with a Si alkoxide solution, a transmittance, and a separation coefficient.

FIG. 4 is a diagram showing a relationship between a modification condition, a transmittance, and a separation coefficient of a separation membrane modified with an Al alkoxide solution of a comparative example.

FIG. 5 is a diagram showing the relationship between the modification conditions, the transmittance, and the separation coefficient of a separation membrane modified with an Al alkoxide solution to which a stabilizer of a comparative example has been added.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/22 B01D 67/00-71/82 510

Claims (2)

(57) [Claims] 1. The method according to claim 1, wherein an aluminum alkoxide is hydrolyzed on an outer surface of the α-Al ₂ O ₃ porous support tube.
After adhering an OOH sol and baking at a temperature of 400 to 700 ° C. and fixing it as a γ-Al ₂ O ₃ film, while reducing the pressure in the porous support tube, the inside of the pores of the γ-Al ₂ O ₃ film is reduced. One of alkali metals and rare earth elements with low reactivity to water
Alkoxide of aluminum and aluminum
A method for producing an inorganic separation membrane, comprising impregnating an alcohol solution of coxide , drying, and firing at a temperature of 400 to 700 ° C. 2. The method according to claim 1, wherein the alkali metal is Na or Rb,
The method for producing an inorganic separation membrane according to claim 1 , wherein the earth element is La, and the alcohol solution of the complex alkoxide of these elements and aluminum contains a compound that reduces the reactivity to water.