JPH1147568A - Inorganic separating membrane and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a silica inorganic separating membrane provided with superior characteristics such as permeability and permeability coefficient ratio when specified components are separated from respective mixed fluids, which can be formed into a thin membrane easily and among others, is provided with heat resistance suitable for separating with priority carbon dioxide and oxygen, particularly high temperature carbon dioxide, from atmosphere or various kinds of combustion exhaust gas or reaction gas. SOLUTION: Composite alkoxide composed of alkoxide of silicon partially hydrolyzed in an alcohol solvent, alkoxide of silicon having an organic functional group directly bonded with Si atoms and alkoxide of zironium is prepared, and a precursor sol prepared by hydrolyzing composite alkoxide is applied on an inorganic porous body, and then dried and burnt at a temperature of 350-600 deg.C to produce an inorganic separating membrane.

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 characteristics of transmittance and transmission coefficient ratio when separating a specific component from a mixed fluid of various gas mixtures and is easily formed into a thin film, and a method for producing the same. those with, especially carbon dioxide from within or various combustion exhaust gas or a reactive gas atmosphere (CO ₂₎ and oxygen (O ₂₎ separating, in particular separation efficiently carbon dioxide (CO ₂₎ even after exposure to high temperatures 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, specific pore size, etc. of the material used to form the inorganic porous material. It has been clarified that properties such as affinity and reactivity with substances are greatly affected.

Therefore, as a method of realizing the required performance of the inorganic porous material, for example, a silica film is formed by a sol-gel method or a C method.
Various production methods such as VD method and hydrothermal synthesis method can be adopted,
Among them, the sol-gel method using a metal alkoxide as a raw material does not require an expensive production apparatus, and many studies have been made since an inorganic porous body can be produced relatively easily.

However, the inorganic porous material is safe and simple in the field of gas separation using, for example, a porous membrane, and its application range is widened, and the technology for separating and concentrating specific gas components includes various combustion engines. , Food industry, medical equipment, and even in the field of waste disposal,
Simply controlling the pore size of the inorganic porous material for the purpose of separating a specific gas component does not provide a stable and large separation efficiency, and does not completely satisfy the requirements of the industrial field.

In order to satisfy such requirements, for example, a specific silane coupling agent is reacted on the surface of the porous glass, or a basic compound such as an amino compound is further reacted, so that the transmittance is large and the separation efficiency is high. And a polysulfone-based graft copolymer having a structure in which a part of hydrogen on an aromatic ring is substituted with a specific polyorganosiloxane chain.
₂ ) and an organic-inorganic composite membrane such as a separation membrane excellent in the separation of carbon dioxide (CO ₂ ) has been proposed (JP-A-1-90).
015, Japanese Patent Publication No. 6-92483).

[0008]

However, since all of the above separation membranes are reacted at a relatively low temperature of from room temperature to several tens of degrees Celsius to form an organic-inorganic composite membrane containing an organic functional group, the above-mentioned reaction is difficult. Although it exhibits excellent characteristics to separate specific components from a mixed fluid in a relatively low temperature range below the temperature, it is exposed to an environment of 100 ° C. or more, such as various combustion exhaust gases or reaction gases, A high temperature alters the microporous structure, such as the silicon-alkyl group bond being oxidized and rearrangement of the siloxane bond. As a result, stable gas separation characteristics cannot be obtained after exposure to an environment of 100 ° C or higher. There was a problem that.

[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 provide a method for separating a specific component from a mixed fluid of various gas mixtures, which is excellent in both characteristics of a transmittance and a transmission coefficient ratio, and has a thin film. Of carbon dioxide (C) from the atmosphere and various combustion exhaust gases or reaction gases.
Efficient separation of O ₂ ) and oxygen (O ₂ ), especially a gas separation membrane with excellent heat resistance that can preferentially separate carbon dioxide (CO ₂ ) even after exposure to a high temperature environment An object of the present invention is to provide a suitable siliceous inorganic separation membrane 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, the general formula was obtained.

[0011]

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A partially hydrolyzed silicon alkoxide represented by the following formula, and an organic functional silicon alkoxide represented by the general formula:

[0013]

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It has been found that by calcining a precursor sol prepared by hydrolyzing a complex alkoxide of zirconium alkoxide represented by the formula (1) under a certain condition, the heat resistance as a separation membrane is improved as compared with the prior art.

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

[0016]

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The partially hydrolyzed silicon alkoxide represented by the formula and the silicon alkoxide having an organic functional group are represented by the following general formula:

[0018]

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It is characterized in that it is a calcined product of a precursor sol prepared from a complex alkoxide of zirconium alkoxide represented by the formula:

Among them, the alkoxide of silicon having an organic functional group has a general formula

[0021]

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More preferably,

Further, the production method is such that a alkoxide of silicon partially hydrolyzed in an alcohol solvent and an alkoxide of silicon having one organic functional group directly bonded to a Si atom are mixed in a molar ratio of 90:10 to 50. The composite alkoxide was hydrolyzed by adding the alkoxide of zirconium in the range of 0.1 to 0.5 mol based on 1 mol of total silicon, and hydrolyzing the obtained composite alkoxide to form the precursor. A body sol is applied to an inorganic porous body, dried, and fired at a temperature of 350 to 600 ° C.

In particular, the silicon alkoxide having an organic functional group has a general formula

[0025]

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More preferably, the precursor sol is obtained by hydrolyzing with 1 to 20 times the molar amount of water to the total alkoxide.

[0027]

According to the inorganic separation membrane and the method for producing the same of the present invention, a precursor sol obtained by hydrolyzing a composite alkoxide of partially hydrolyzed silicon alkoxide, silicon alkoxide having an organic functional group, and zirconium alkoxide is used. Since it is a fired body, that is, a composite inorganic separation membrane made of silica containing zirconia, carbon dioxide can be preferentially separated from the atmosphere or from various combustion exhaust gases and reaction gases, and at 100 ° C. A separation membrane with high heat resistance, whose characteristics do not deteriorate even when exposed to the above high temperature environment.

Further, by the heat treatment at 350 to 600 ° C., the obtained inorganic separation membrane has a pore size of Å order, and a part of the organic functional groups remains. When activated, CO ₂ gas permeation by the surface diffusion mechanism occurs preferentially.

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, a very thin film can be obtained without applying cracks or peeling when the precursor sol is applied, and a separation film having high transmittance can be obtained. It becomes possible.

[0030]

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.

According to the present invention, a partially hydrolyzed silicon alkoxide and a silicon alkoxide having an organic functional group directly bonded to a Si atom are compounded in an alcohol solvent, and then a zirconium alkoxide is added to form a compound. By hydrolyzing the composite alkoxide with water, a homogeneous and stable precursor sol is obtained. After drying the sol, the precursor sol is calcined at a temperature of 350 to 600 ° C. to produce a siliceous silica containing zirconia. An inorganic separation membrane is obtained.

The inorganic separation membrane of the present invention has a pore structure formed by preventing excessive progression of siloxane bonds in the calcination process due to steric hindrance of the organic functional groups dispersed in the precursor sol. .

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, and for this purpose, the partially hydrolyzed silicon alkoxide and the organic It is more desirable that the alkoxide of silicon having a functional group is uniformly compounded.

Further, the compound alkoxide of silicon and the alkoxide of zirconium are uniformly compounded so that the characteristics do not deteriorate 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 compounding of the silicon alkoxide with the silicon alkoxide having an organic functional group and the compounding of the silicon alkoxide with the zirconium alkoxide are necessary to ensure the compounding. And the general formula is

[0036]

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It is necessary to use a silicon alkoxide which has been partially hydrolyzed in advance and represented by the following formula:

The partially hydrolyzed silicon alkoxide is added to an alcohol solution of silicon alkoxide in the presence of an alcohol by adding 1 to 3 moles of water and a small amount of acid to 1 mole of the silicon alkoxide. It can be manufactured by the following.

The compounding of an alkoxide of silicon with a compound alkoxide of silicon having an organic functional group and an alkoxide of zirconium can also be produced by heating and refluxing all these alkoxides in an alcohol solution. The whole may be hydrolyzed to form a precursor sol.

The compounding ratio of the partially hydrolyzed silicon alkoxide and the silicon alkoxide having an organic functional group may be such that both alkoxides coexist. 90 to 1 in ratio
It must be in the range of 0 to 50:50, and in particular, the range of 90:10 to 70:30 is more preferable from the viewpoint of separation characteristics.

The ratio of the addition of the alkoxide of zirconium to the composite alkoxide of silicon is 0.1 to 0.5 mol per 1 mol of total silicon in view of the heat resistance and film formability of the inorganic separation membrane. Is required, and in particular, the range of 0.1 to 0.3 mol is desirable from the viewpoint of the separation characteristics of the inorganic separation membrane.

The silicon alkoxide having an organic functional group directly bonded to a Si atom used in the composite alkoxide is compared with an alkoxide such as Si (OR) ₄ .
Organic functional groups hardly burn off due to heat treatment, remain in the fired body up to several hundred degrees Celsius, form pores of the order of Å, and activate OH groups on the surface of the pores. From exhaust gas and reaction gas, carbon dioxide (C
This is indispensable for producing a separation membrane capable of preferentially separating O ₂ ) and the like.

On the other hand, when the amount of the organic functional group contained in the alkoxide of silicon having the organic functional group is in the range of 10 to 40% of the total alkoxide, the transmission coefficient ratio tends to increase as the content increases. However, when the content exceeds 40%, the proportion of the alkoxide having an organic functional group is increased, and it is considered that the film-forming property is reduced and minute defects are generated on the film surface. Conversely, it tends to decrease.

The alkoxide of silicon in the present invention includes tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane and the like. The alkoxide of silicon having an organic functional group includes phenyl, vinyl, amino Examples include trimethoxysilane and triethoxysilane each having a propyl group, and the other alkoxides of zirconium include tetraethoxyzirconium, tetrapropoxyzirconium, and tetrabutoxyzirconium.

Particularly, from the viewpoint of the drying property of the gel film and the economy of the raw material, the alkoxide of silicon is tetramethoxysilane or tetraethoxysilane, and the alkoxide of silicon having an organic functional group is trimethoxysilane having the respective functional groups. Silane or triethoxysilane
The alkoxide of zirconium is preferably tetraethoxyzirconium or tetrapropoxyzirconium.

Examples of the alcohol in the mixed solvent of each alkoxide include methanol, ethanol, propanol, butanol, 2-methoxyethanol, and 2-ethoxyethanol.
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. More preferably, it is in the range of 1 to 20 moles.

In other words, when the amount of water for hydrolysis is in the range of 1 to 20 moles, siloxane bonds are sufficiently developed by firing after film formation, and a film having sufficient mechanical strength is easily obtained. However, no defects such as film cracking and film peeling occurred,
The obtained precursor sol is also stable, and the sol does not become cloudy or precipitate.

The hydrolysis may be carried out simultaneously after complexing each alkoxide. However, preferably, only the alkoxide of silicon is partially hydrolyzed first, and then the silicon having an organic functional group is hydrolyzed. It is better to form a precursor sol by complexing an alkoxide and then a zirconium alkoxide and then hydrolyzing the whole.

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

The inorganic separation membrane of the present invention has a thickness of 1 μm or less, particularly 0.1 to 0.5 μm, in order to satisfy required transmittance and transmission coefficient ratio and have practical strength. The degree is desirable, and it is desirable to use together with the 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 having no defects such as cracks. Even if a film having no 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 support in which a γ-alumina film having a controlled pore diameter and surface roughness is carried on an α-alumina porous material as an intermediate layer.

If the firing temperature after applying the precursor sol is lower than 350 ° C., the alkoxyl groups in the dried gel film are 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 separates a mixture of, for example, carbon dioxide and oxygen, as well as hydrogen, helium, nitrogen, carbon monoxide, methane, ethane, and propane, as a mixed fluid to be separated and concentrated. As long as it does not react or dissolve with the membrane, any of them can be applied, and it goes without saying that it can also be applied to 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.

[0059]

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

First, 7.29 g of tetraethoxysilane
(Molar ratio 0.7) 23.04 g of ethanol (molar ratio 1)
0), a mixed solution of 0.63 g of water (molar ratio of 0.9) and HCl (molar ratio of 0.07) were added to prepare a partially hydrolyzed sol, and 0.72 g of phenyltriethoxysilane was added thereto.
(Molar ratio 0.3) and ethanol 23.04 g (molar ratio 1)
0) was added and stirred under a nitrogen stream, and then a mixed solution of 0.82 g (molar ratio 0.25) of zirconium alkoxide and 23.04 g (molar ratio 10) of ethanol was added. An alkoxide was prepared.

Next, 8.37 of water was added to the composite alkoxide.
g (molar ratio: 9.3) and a mixed solution of ethanol (115.18 g (molar ratio: 50)) were added, hydrolyzed, and further stirred for 3 hours to prepare a precursor sol.

Then, an inorganic porous support obtained by coating a 2 μm-thick γ-alumina on an α-alumina porous tube (porosity: 40%) having an outer diameter of 3 mm in advance was added to the precursor sol solution for 30 seconds. It was immersed, pulled up at a speed of 5 mm / sec, dried at room temperature for 1 hour, subsequently kept at the firing temperature shown in Table 1 for 1 hour, and then cooled to room temperature.

A series of operations of immersion, drying and firing were repeated four times, and a silica-based film was deposited on the γ-alumina layer to prepare a sample for evaluation.

Also, various molar ratios of the above-mentioned tetraethoxysilane and phenyltriethoxysilane, and vinyltriethoxysilane, 3-aminopropyltriethoxysilane instead of phenyltriethoxysilane,
A sample for evaluation was prepared in the same manner as described above using p-aminophenyltrimethoxysilane.

A silicon alkoxide having an organic functional group was not mixed with the alkoxide of tetraethoxysilane and tetrapropoxyzirconium, but was prepared in the same manner as described above. The alkoxide of zirconium was not mixed with tetraethoxysilane and phenyltrisilane. Those manufactured in the same manner as described above using only ethoxysilane were used as comparative examples.

Further, in Table 1, the number of moles of the alkoxide of zirconium relative to 1 mole of the total silicon is shown as a molar ratio of the zirconium alkoxide.

[0067]

[Table 1]

The sample for evaluation thus obtained was attached to a gas permeability measuring device, and 10 cc / mi was placed inside the tube of the sample.
n helium gas, and a 1/1 mixed gas of nitrogen and carbon dioxide gas at a flow rate of 100 cc / min.
While maintaining the membrane portion of the sample at 30 ° C., the ratio (permeation coefficient ratio) of nitrogen gas and carbon dioxide gas permeating the membrane is evaluated by gas chromatography, and the respective transmittances are determined from the gas flow rates at the inside and outside of the sample tube. I asked.

Thereafter, as an evaluation of heat resistance, the evaluation sample was exposed to an atmosphere at 350 ° C. for 2 hours,
After cooling to 0 ° C., the transmittance was measured in the same manner as described above,
The transmittance and the transmission coefficient ratio before and after the heat treatment of each sample were determined.

[0070]

[Table 2]

As is clear from the table, Sample Nos. 9 and 18, which are outside the scope of the present invention, exhibit high separation characteristics before heat treatment, but exhibit CO ₂ /
The properties deteriorated when the N ₂ transmission coefficient ratio was 1/5 or less before the heat treatment. Similarly, in Samples Nos. 5 and 17, the amount of alkoxide of silicon having an organic functional group was small or not contained at all. The transmission coefficient ratio is only as low as 10 or less.

Further, in Sample Nos. 8 and 12, it was confirmed from the electron microscopic observation of the film surface that fine cracks were generated. Therefore, before and after the heat treatment, the transmission coefficient ratio was as low as less than 2. Has become.

Similarly, Sample No. 13 had a low firing temperature, the siloxane bond of the film was not strong, and Sample No. 16
On the contrary, the baking temperature is high, the film densification progresses, and CO ₂
/ N ₂ permeability coefficient ratio is only a value close to 0.8, which is the theoretical permeability coefficient ratio when there is no interaction between the pore wall and the permeated gas, that is, the permeability coefficient ratio by Knudsen diffusion.

On the other hand, in the present invention, a very large value of 21 or more was obtained even when exposed to a 350 ° C. high temperature atmosphere in which the CO ₂ / N ₂ permeability coefficient ratio exceeded 100 ° C.
This is considered to be because the inorganic separation membrane of the present invention has a very narrow pore size distribution of 1 nm or less due to the use of alkoxide of silicon containing an organic functional group, and thus showed high CO ₂ selectivity. It is considered that the addition of the alkoxide of zirconium resulted in an inorganic separation membrane having high heat resistance.

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

[0076]

As described above, according to the inorganic separation membrane and the method for producing the same of the present invention, a partially hydrolyzed silicon alkoxide, a silicon alkoxide having an organic functional group and a zirconium alkoxide are combined. After drying the precursor sol obtained by hydrolyzing the composite alkoxide, it is a zirconia-added siliceous inorganic separation membrane produced by firing at a temperature of 350 to 600 ° C.
Due to the high burning temperature of the organic functional groups, excessive progress of siloxane bonds in the vicinity is suppressed, and a fine pore structure of 1 nm or less is maintained.

Accordingly, in separating a specific component from a mixed fluid such as various gas mixtures, both characteristics of the transmittance and the transmission coefficient ratio are excellent.
Even when exposed to a high-temperature atmosphere of 00 ° C. or higher, no deterioration in characteristics is observed, and a gas separation membrane having high heat resistance can be obtained.

Further, the inorganic separation membrane of the present invention can be easily formed into a thin film. Particularly, it separates carbon dioxide (CO ₂ ) and oxygen (O ₂ ) from the atmosphere or various combustion exhaust gases or reaction gases, particularly at 100 ° C. It is suitable for a gas separation membrane that preferentially separates the above high-temperature carbon dioxide (CO ₂ ).

Claims (5)

[Claims] An alkoxide of silicon, an alkoxide of silicon having an organic functional group and an alkoxide of zirconium are compounded in an alcohol solvent, and the alkoxide of the precursor is obtained by hydrolyzing the compound alkoxide. An inorganic separation membrane characterized by the above-mentioned. 2. The alkoxide of silicon having an organic functional group has a general formula: The inorganic separation membrane according to claim 1, wherein: 3. A partially hydrolyzed silicon alkoxide and a silicon alkoxide having an organic functional group directly bonded to a Si atom in a molar ratio of 90:10 to 50:50.
In an alcohol solvent, and then the alkoxide of zirconium is added in an amount of 0.1 to 1 mol of total silicon.
After adding and complexing within a range of 1 to 0.5 mol, a precursor sol is prepared by hydrolyzing the obtained composite alkoxide, and then the precursor sol is applied to an inorganic porous support and dried, Then, the method is fired at a temperature of 350 to 600 ° C. 4. The general formula of the silicon alkoxide having an organic functional group is as follows: The method for producing an inorganic separation membrane according to claim 3, wherein 5. When hydrolyzing the composite alkoxide,
The method for producing an inorganic separation membrane according to claim 3, wherein water is added in an amount of 1 to 20 times the molar amount of all alkoxides.