JPH11244676A - Inorganic separation membrane and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the heat resistance, or the like of a separation membrane by hydrolyzing a multiple alkoxide consisting of a silicone alkoxide, a silicone alkoxide having an org. functional group comprising a hydrocarbon represented by a specified formula and a zirconium alkoxide and firing the resultant precursor sol. SOLUTION: A multiple alkoxide consisting of a silicone alkoxide, a silicone alkoxide having an org. functional group comprising a hydrocarbon bonding directly to two Si atoms represented by formula I and a zirconium alkoxide represented by formula II is hydrolyzed and the resultant precursor sol is dried and fired at 350-600 deg.C to obtain the objective zirconia-contg. siliceous inorg. separation membrane excellent in both permeability and selectivity when a specified component is separated from a mixed fluid of various gaseous mixtures. The thickness of the membrane is easily reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inorganic separation membrane which is excellent in both the transmittance and the selectivity when separating a specific component from a mixed fluid of various gas mixtures and is easy to be made into a thin film, and a method for producing the same. Especially hydrogen (H ₂ ), methane (CH ₄ ), or oxygen (O ₂ ) from the atmosphere or from various combustion exhaust gas, fuel raw material gas or reaction gas
TECHNICAL FIELD The present invention relates to a siliceous inorganic separation membrane suitable for a gas separation membrane having excellent heat resistance and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a thin film for filtering and separating a specific component from a mixed fluid of various gas mixtures, a carrier for a functional material such as a catalyst, an electrolytic partition, various fillers, and the like include organic materials. Porous bodies made of various materials have been used.

However, as the demand for durability of the porous body, such as heat resistance, chemical resistance, impact resistance, and abrasion resistance, becomes higher, various types of materials having better mechanical, thermal, and chemical stability have been developed. Inorganic porous bodies have received particular attention and have been studied in various ways.

As a result, when the inorganic porous material is applied to various uses, its performance depends on the pore size, pore volume, pore size distribution, pore size distribution, etc. of the material used to form the inorganic porous material itself. It has been clarified that properties such as affinity and reactivity with a substance are greatly affected.

In order to achieve the required performance of the inorganic porous material, for example, for a silica film, various production methods such as a sol-gel method, a CVD method, and a hydrothermal synthesis method can be adopted. The sol-gel method using an alkoxide as a raw material does not require an expensive production apparatus and can produce an inorganic porous material relatively easily, and thus much research has been conducted.

However, the inorganic porous material is widely used in the field of gas separation using a porous membrane, for example, because it is safe and simple. Institutions, food industries and medical equipment, as well as attention in the field of waste treatment, but for the purpose of separating specific gas components, it is stable only by controlling the pore size of the inorganic porous material Large separation efficiencies cannot be obtained and the requirements of the industrial field are not completely satisfied.

In order to satisfy such requirements, for example,
A porous gas separation membrane with high transmittance and high separation efficiency, which is obtained by reacting a specific silane coupling agent on the surface of porous glass or further reacting a basic compound such as an amino compound, or an aromatic ring An organic-inorganic composite such as a separation membrane excellent in separability of oxygen (O ₂ ) or the like, particularly composed of a polysulfone-based graft copolymer having a structure in which a part of the above hydrogen is substituted with a specific polyorganosiloxane chain A membrane has been proposed (see JP-A-1-90015 and JP-B-6-92483).

[0008]

However, each of the separation membranes is formed by reacting at a relatively low temperature of room temperature to several tens of degrees Celsius to form an organic-inorganic composite membrane containing an organic functional group. Exhibits excellent properties for separating specific components from a mixed fluid in a relatively low temperature range below the reaction temperature, but must be exposed to an environment of 100 ° C or higher, such as various combustion exhaust gases or reaction gases. As a result, the silicon-alkyl group bond is oxidized and siloxane bond rearrangement occurs, and the micropore structure is altered by high temperature. As a result, stable gas separation characteristics are obtained after exposure to an environment of 100 ° C. or more. There was a problem that it could not be obtained.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to separate a specific component from a mixed fluid of various gaseous mixtures, thereby being excellent in both characteristics of transmittance and selectivity, and having a thin film. It is particularly easy to separate hydrogen (H ₂ ), methane (CH ₄ ), or oxygen (O ₂ ) from the atmosphere or from various combustion exhaust gases, raw material gases for fuels or reaction gases, especially in high-temperature environments. An object of the present invention is to provide a siliceous inorganic separation membrane suitable for a gas separation membrane having excellent heat resistance and capable of efficiently separating even after exposure, and a method for producing the same.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies on the above-mentioned problems, and as a result, have found that the alkoxide of silicon and the general formula

[0011]

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An alkoxide of silicon having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms represented by the following formula:

[0013]

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By baking the precursor sol prepared by hydrolyzing the complex alkoxide with the alkoxide of zirconium represented by the formula (1) under a certain condition, the separation characteristics are improved and the heat resistance as a separation membrane is improved. Found to improve.

That is, the inorganic separation membrane of the present invention comprises a silicon alkoxide made of silica containing zirconia and a general formula:

[0016]

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An alkoxide of silicon having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms represented by the following formula:

[0018]

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It is a fired body of a precursor sol prepared from a composite alkoxide with a zirconium alkoxide represented by the formula:

In particular, the silicon alkoxide has the general formula

[0021]

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More preferably, it is a partially hydrolyzed silicon alkoxide represented by the formula:

Further, the method for producing an inorganic separation membrane of the present invention comprises the steps of: forming an alkoxide of silicon in an alcohol solvent;

[0024]

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An alkoxide of silicon having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms represented by the formula:
After compounding to be within the range of ~ 0.5 equivalents, the general formula further

[0026]

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The alkoxide of zirconium represented by the formula (1) is added in the range of 0.1 to 0.5 times the molar amount of the total silicon to form a composite, and the obtained composite alkoxide is hydrolyzed to form a precursor sol. It is characterized in that it is applied to an inorganic porous body, dried, and then fired at a temperature of 350 to 600 ° C.

In particular, in the method for producing an inorganic separation membrane of the present invention, the silicon alkoxide has a general formula

[0029]

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More preferably, it is a partially hydrolyzed silicon alkoxide represented by the formula:

[0031]

According to the inorganic separation membrane and the method for producing the same of the present invention, a composite of a silicon alkoxide, a silicon alkoxide having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms, and a zirconium alkoxide. Since it is a calcined body of a precursor sol obtained by hydrolyzing alkoxide, that is, a composite inorganic separation membrane made of silica containing zirconia, its properties deteriorate even when exposed to a high temperature environment of 100 ° C. or more. The resulting separation membrane has high heat resistance.

Further, by the heat treatment at 350 to 600 ° C., the obtained inorganic separation membrane has a pore size of the order of 対 応 corresponding to the size of the organic functional group. Hydrogen (H ₂ ), methane (CH ₄ ), or oxygen (O ₂ )
₂ ) can be separated efficiently.

Further, γ having pores of several nm on the surface of a porous α-alumina support having a pore diameter of submicron
-By coating the alumina film, when applying the precursor sol, it is possible to obtain a very thin film without cracking or peeling, and to obtain a separation membrane having a high transmittance. Becomes possible.

[0034]

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

The present invention relates to an alkoxide of silicon having the general formula

[0036]

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An alkoxide of silicon having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms represented by the following formula is compounded in an alcoholic solvent,

[0038]

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The alkoxide of zirconium represented by the formula (1) is added to form a complex, and the complex alkoxide is hydrolyzed with water to obtain a homogeneous and stable precursor sol. By calcining, a silica-based inorganic separation membrane made of silica containing zirconia is obtained.

The inorganic separation membrane of the present invention has a pore structure formed by preventing siloxane bonds from excessively progressing in the above-mentioned calcination process due to steric hindrance of the organic functional groups dispersed in the precursor sol. is there.

Accordingly, in order to form a network structure of continuous pores, it is necessary to sufficiently disperse the organic functional groups at the time of preparing the precursor sol.

[0042]

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More preferably, the partially hydrolyzed silicon alkoxide represented by the formula and the silicon alkoxide having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms are uniformly compounded. Things.

Furthermore, the composite alkoxide of silicon and the alkoxide of zirconium are uniformly compounded so that the characteristics are not deteriorated even under various conditions when operating as a separation membrane, especially at a high temperature of 100 ° C. or more. Is more desirable.

In the present invention, the alkoxide of silicon is combined with the alkoxide of silicon having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms, and the alkoxide of zirconium is combined with the alkoxide of zirconium. As described above, it is more preferable to use a silicon alkoxide that has been partially hydrolyzed in advance, in order to reliably perform the composite.

The partially hydrolyzed silicon alkoxide can be obtained by adding 1 to 3 times the molar amount of water and a small amount of an acid to the silicon alkoxide alcohol solution in the presence of the alcohol. Can be made.

The silicon alkoxide and the S
Complexation of a silicon alkoxide and a zirconium alkoxide having an organic functional group consisting of a hydrocarbon directly bonded to two i atoms can also be prepared by heating and refluxing all of these alkoxides in an alcohol solution. Subsequently, the whole may be hydrolyzed to form a precursor sol.

The composite ratio of the partially hydrolyzed silicon alkoxide and the silicon alkoxide having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms may be such that both alkoxides coexist. On the other hand, a complex is formed in an alcohol solvent such that the organic functional group is in the range of 0.05 to 0.5 equivalent, then an alkoxide of zirconium is added to form a complex, and the obtained complex alkoxide is hydrolyzed to form a precursor. After preparing the body sol, the precursor sol is applied to an inorganic porous support, dried, and then calcined at a temperature of 350 to 600 ° C. to obtain an inorganic separation membrane. In particular, from the viewpoint of separation characteristics, The organic functional group is more preferably in the range of 0.1 to 0.3 equivalent.

The ratio of the addition of the alkoxide of zirconium to the composite alkoxide of silicon is 0.1 to 0.5 times the total silicon in terms of heat resistance and film forming property. It is necessary to be within the range of the amount, particularly from the separation characteristics of the inorganic separation membrane, 0.1 to 0.3
A molar range is desirable.

Si atom 2 used in the composite alkoxide 2
The alkoxide of silicon having an organic functional group consisting of a hydrocarbon directly bonded to an alkoxide is an alkoxide such as Si (OR) ₄ or a compound represented by the general formula:

[0051]

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As compared with the alkoxide having an organic functional group consisting of one Si atom represented by the formula, the organic functional group is less likely to be burned off by heat treatment and remains in the fired body up to several hundred degrees Celsius, so that the size of the organic functional group A pore of the order of さ corresponding to the size is formed.

Accordingly, the film formed using the alkoxide can be used to convert hydrogen (H ₂ ), methane (C
H ₄ ) or oxygen (O ₂ ) can be selectively separated.

On the other hand, the amount of the organic functional group contained in the alkoxide of silicon having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms is 0.1% of the total silicon.
In the range of 0.5 to 0.5 equivalents, the selectivity tends to increase as the content increases, but when the content exceeds 0.5 equivalents, the proportion of the alkoxide having an organic functional group increases. This is probably because the film forming property is reduced and minute defects are generated on the film surface, but the selectivity tends to decrease.

Further, examples of the silicon alkoxide in the present invention include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane and the like.

The silicon alkoxide of the present invention having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms includes bis (triethoxysilyl) methane, bis (triethoxysilyl) ethane, and bis (triethoxysilyl) ethane. Triethoxysilyl) ethylene, bis (triethoxysilyl)
Hexane, 1,4-bis (triethoxysilylethyl)
Benzene or those obtained by substituting an alkoxyl group of a compound thereof with a methoxy group may be mentioned.

On the other hand, examples of the zirconium alkoxide of the present invention include tetraethoxyzirconium, tetrapropoxyzirconium, and tetrabutoxyzirconium.

In particular, from the viewpoint of the drying property of the gel film and the economical efficiency of the raw material, tetramethoxysilane or tetraethoxysilane may be used as the alkoxide of silicon.
Alkoxides of silicon having an organic functional group consisting of a hydrocarbon directly bonded to two i atoms include bis (triethoxysilyl) ethane, bis (triethoxysilyl) ethylene, bis (triethoxysilyl) hexane, and the like. What substituted the alkoxyl group of the compound with a methoxy group, on the other hand, the alkoxide of zirconium,
Tetraethoxyzirconium or tetrapropoxyzirconium is preferred.

Examples of the alcohol in the mixed solvent of each alkoxide include methanol, ethanol, propanol, butanol, 2-methoxyethanol and 2-ethoxyethanol, and the like.
From the viewpoint of solubility of raw materials, lower alcohols such as methanol and ethanol are most suitable.

The method of hydrolyzing the composite alkoxide is not particularly limited, and any known or well-known means can be used. The amount of water to be added may be a large amount. A range of 1 to 20 times the molar amount is more desirable.

In other words, when the amount of water for hydrolysis is in the range of 1 to 20 times the molar amount, siloxane bonds are sufficiently developed by firing after film formation, and a film having sufficient mechanical strength is easily obtained. Defects such as cracking of the film and peeling of the film do not occur at all under any conditions, and the obtained precursor sol is stable, and the sol does not become cloudy or precipitate.

The above-mentioned hydrolysis may be carried out simultaneously after complexing each alkoxide. However, preferably, only the alkoxide of silicon is partially hydrolyzed first, and then the two alkoxides are directly bonded to two Si atoms. It is better to form a precursor sol by complexing the alkoxide of silicon having an organic functional group made of a hydrocarbon, and then complexing the alkoxide of zirconium, and then hydrolyzing the whole.

Next, the method for forming the inorganic separation membrane on the inorganic porous support is not particularly limited, and various known or well-known means can be applied. After diluting to a predetermined concentration with the solvent used for preparing the sol, a porous α-alumina support previously coated with a γ-alumina film is immersed in the diluent, pulled up and applied, or applied to the support. It may be produced by directly applying, drying, and then firing at a temperature of 350 to 600 ° C.

The inorganic separation membrane of the present invention must satisfy the required transmittance and selectivity and have a practical strength.
The thickness of the membrane is desirably 1 μm or less, particularly about 0.1 to 0.5 μm, and is desirably used with an inorganic porous support.

On the other hand, the inorganic porous support is not particularly limited, but has sufficient strength to support the separation membrane and does not react with the precursor sol even during firing.
Any material may be used as long as it is a porous material having sufficient heat resistance at least in the range of the firing temperature of the film.

For example, porous ceramics and glass,
Metals and the like are listed, and porous ceramics such as α-alumina are particularly preferable in terms of heat resistance, chemical resistance, and the like.However, when porous α-alumina itself is used as a support, its large pore size and Due to the surface roughness, it is difficult to produce a film without defects such as cracks. Even if a film without defects can be produced, a film thickness of several μm is required, resulting in a significant decrease in transmittance.

Therefore, it is optimal to employ a γ-alumina film having a controlled pore diameter and surface roughness as an intermediate layer and a support supported on an α-alumina porous material.

If the firing temperature after the application of the precursor sol is lower than 350 ° C., the alkoxyl groups in the dried gel film cannot be completely removed, and the siloxane bond cannot be further strengthened. If the temperature exceeds sintering,
Since the pores required for the separation disappear, 350 to 600
The temperature is limited to a temperature range of 400C, and the temperature is more preferably 400 to 500C in view of permeation performance and separation characteristics.

Further, in order to prevent defects of the film, it is more preferable to repeat a series of operations of coating, drying and firing of the precursor sol several times.

The inorganic separation membrane of the present invention can be used as a mixed fluid to be separated and concentrated, for example, a mixture of hydrogen (H ₂ ), nitrogen (N ₂ ), oxygen (O ₂ ), methane (CH ₄ ), etc. However, as long as it does not react with or dissolve in the separation membrane, any of them can be applied, and it goes without saying that it can be applied to the separation of a mixture containing them and an inorganic substance such as dust.

In addition, the inorganic separation membrane of the present invention can be used in a wide temperature range from room temperature to 100 ° C. or higher.
From the viewpoint of heat resistance and durability of the separation membrane, a temperature range from room temperature to 400 ° C. can be more preferably used.

[0072]

Next, the inorganic separation membrane of the present invention and the method for producing the same were evaluated as follows.

First, as an example, 23.04 g of ethanol was added to 4.17 g (molar ratio 0.4) of tetraethoxysilane.
A mixed solution consisting of 0.36 g (molar ratio 0.4) of water containing HCl (molar ratio 10) and HCl (molar ratio 0.07) was added to prepare a partial hydrolysis sol, and bis (triethoxy) was added thereto. A mixed solution of 5.32 g (molar ratio 0.3) of silyl) ethane and 23.04 g (molar ratio 10) of ethanol was added, and the mixture was stirred under a nitrogen stream, and then 0.82 g of tetra-n-propoxyzirconium ( A mixed solution of a molar ratio of 0.25) and 23.04 g of ethanol (molar ratio of 10) was added to prepare a composite alkoxide.

Next, 8.6 of water was added to the composite alkoxide.
A mixed solution of 4 g (mole ratio: 9.6) and 115.18 g (mole ratio: 50) of ethanol was added to hydrolyze, and the mixture was further stirred for 3 hours to prepare a precursor sol.

Thereafter, the precursor sol solution is added to the precursor sol solution having an outer diameter of 3 μm.
mm in porosity α-alumina porous tube with a porosity of 40%
An inorganic porous support previously coated with μm γ-alumina was immersed for 30 seconds, pulled up at a speed of 5 mm / second, dried at room temperature for 1 hour, and subsequently heated at a firing temperature of 500 ° C. for 1 hour.
Hold for a time and then cool to room temperature.

The series of operations of immersion, drying, and firing are performed in four steps.
The process was repeated twice to deposit a siliceous film on the γ-alumina layer to prepare a sample for evaluation.

In the same manner as in the above-mentioned example, those obtained by changing the molar ratio of the above-mentioned tetraethoxysilane, bis (triethoxysilyl) ethane and tetra-n-propoxyzirconium, setting the firing temperature variously, and adding bis ( A sample for evaluation was prepared in the same manner as described above except that bis (triethoxysilyl) ethylene and bis (triethoxysilyl) hexane were used instead of triethoxysilyl) ethane.

As the alkoxide of silicon having an organic functional group, one using ethyl triethoxy silane, one using vinyl triethoxy silane, one using hexyl triethoxy silane, or silicon using an organic functional group Prepared in the same manner as above using only tetraethoxysilane and tetra-n-propoxyzirconium without mixing the alkoxide of the above, and further using only tetraethoxysilane and bis (triethoxysilyl) ethane without mixing the alkoxide of zirconium. Each of those manufactured in the same manner as above was used as a comparative example.

[0079]

[Table 1]

The evaluation sample thus obtained was attached to a gas permeability measuring device, and 10 cc / mi was placed inside the sample tube.
n helium gas, hydrogen (H ₂ ), nitrogen (N
₂ ), oxygen (O ₂ ) and methane (CH ₄ ) gas were flowed at a rate of 100 cc / min each,
While maintaining the temperature at 0 ° C., the concentrations of the respective gases passing through the membrane were measured by gas chromatography, and the gas flow rates and selectivities of the respective gases were determined by measuring the flow rates of the gas inside and outside the sample tubes.

[0081]

[Table 2]

Thereafter, as an evaluation of heat resistance, the evaluation sample was exposed to a helium atmosphere heated to 350 ° C. for 2 hours, and then the evaluation sample was cooled to 30 ° C.
The transmittance was measured in the same manner as described above, and the transmittance and the selectivity of each sample before and after the heat treatment were obtained.

[0083]

[Table 3]

As is clear from Tables 2 and 3, in Comparative Examples Nos. 15, 16 and 17 in which no silicon alkoxide having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms was used, the heat Although the influence of the history is extremely small, the sample of the comparative example in which the transmittance or selectivity of a specific gas component is reduced, the separation characteristics are hardly exhibited, and the silicon alkoxide having an organic functional group is not contained at all. In the number 18, the transmittance is low,
In particular, CH ₄ cannot be measured, and in sample No. 19 of the comparative example containing no zirconium alkoxide,
In particular, the change due to the heat history is remarkable, the pore size increases due to the heat history, the transmittance of each gas component increases, and the selectivity of each decreases.

In Sample Nos. 3 and 7, which are out of the scope of the present invention, since the firing temperature is out of the range of the present invention, if the firing temperature is too low, a sufficient pore structure is not formed. If it is too long, sintering proceeds and the pore structure is densified, so that the transmittance is greatly reduced.If the amount of zirconium alkoxide of Sample No. 12 is too large, it is densified and the transmittance is large. On the other hand, in Sample No. 9 in which the amount of alkoxide of silicon having an organic functional group was too large, fine cracks were observed from the observation of the film surface with an electron microscope, and although the transmittance was high overall, especially H ₂ / separation characteristics as seen in the selectivity of N ₂ is not substantially observed.

On the other hand, in each of the present invention, the transmittance and the selectivity are maintained at high values even after the thermal history, and it can be seen that they are practical.

The inorganic separation membrane and the method for producing the same according to the present invention are not limited to the above embodiments.

[0088]

As described above, according to the inorganic separation membrane and the method of manufacturing the same of the present invention, silicon alkoxide and Si
A precursor sol obtained by combining a silicon alkoxide and an zirconium alkoxide having an organic functional group consisting of a hydrocarbon directly bonded to two atoms and hydrolyzing the composite alkoxide is dried, and then dried at 350 to 600
The zirconia-added siliceous inorganic separation membrane was calcined at a temperature of ° C., so that the siloxane bond in the vicinity was prevented from excessively advancing due to a high burning-off temperature of the organic functional group.
A fine pore structure of nm or less can be maintained.

Therefore, in separating a specific component from a mixed fluid such as various gas mixtures, both the transmittance and the selectivity are excellent.
Even when exposed to a high-temperature atmosphere of 0 ° C. or higher, no deterioration in characteristics is observed, and a gas separation membrane having high heat resistance can be obtained.

In addition, the inorganic separation membrane of the present invention can be easily formed into a thin film. In particular, hydrogen (H ₂ ), methane (CH ₄ ) can be obtained from the atmosphere, various combustion exhaust gas, fuel raw material gas or reaction gas. Alternatively, it is most suitable as a gas separation membrane for selectively separating oxygen (O ₂ ).

Claims (4)

[Claims] An alkoxide of silicon and a compound represented by the general formula: An alkoxide of silicon having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms represented by the formula: ## STR2 ## An inorganic separation membrane comprising a calcined body of a precursor sol obtained by hydrolyzing a complex alkoxide with a zirconium alkoxide represented by the following formula: 2. The alkoxide of silicon has a general formula: The inorganic separation membrane according to claim 1, which is a partially hydrolyzed silicon alkoxide represented by the following formula: 3. An alkoxide of silicon and a compound represented by the general formula: Alkoxide of silicon having an organic functional group consisting of a hydrocarbon directly bonded to two Si atoms represented by the following formula: And the general formula is The alkoxide of zirconium represented by is added in the range of 0.1 to 0.5 times the molar amount of the total silicon to form a composite, and the obtained composite alkoxide is hydrolyzed to prepare a precursor sol. Thereafter, the precursor sol is applied to an inorganic porous support, dried, and then fired at a temperature of 350 to 600 ° C. 4. The alkoxide of silicon has a general formula: 4. The method for producing an inorganic separation membrane according to claim 3, wherein the alkoxide is a partially hydrolyzed silicon alkoxide represented by the formula: