JP2000007306A - Production of porous inorganic film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for easily producing a porous inorganic film having high characteristics and uniform pore size using an alkoxysilane solution as a main agent even in a case that the solution contains other metallic materials. SOLUTION: This production process comprises a coating film formation process to apply an inorganic material composition composed mainly of an alkoxysilane solution containing water and a catalytic amount of an acid, incorporated with a metal salt soluble in the solvent of the solution and having a molar ratio of water to an alkoxysilane (H2O/Si) of <=4 and a pH of 1-2.5 to a porous inorganic substrate and dry the applied composition to form an amorphous coating film and a heating process to heat the amorphous coating film under a low-temperature normal-pressure condition not to cause the crystallization of the film by hydrolysis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing an inorganic porous membrane.

[0002]

2. Description of the Related Art Conventionally, inorganic porous membranes have been known to be strongly acidic,
Or, under strong alkaline conditions, after hydrothermal synthesis of zeolite, molded into a thin film and used as an inorganic porous membrane,
Alternatively, a porous glass material is applied on a support, solidified into a thin film, and formed into an inorganic porous film.

[0003]

Among the above-mentioned conventional inorganic porous membranes, hydrothermal synthesis, which is one of the production techniques for forming zeolite into a thin film, requires expensive equipment,
Because of the need for high-temperature, high-pressure, high-energy supply and the like, it has to be said that this is a very expensive synthesis method. In addition, although the obtained zeolite crystals individually have uniform `` pores '' having a small diameter, since zeolite is obtained in a polycrystalline state, even if the pore diameter of the pores is appropriate and Even if the particles are uniform and uniform in size, a non-uniform “gap” larger than the pores is generated between the crystal grains, so that the inorganic particles having dense pores uniformly are formed as a whole. It is not a porous membrane and must be unsuitable for applications requiring a high degree of separation ability (characteristics of pores), for example, as a molecular sieve for gas separation. In addition, in order to form a porous glass material into a thin film, uniform fine pores having a small diameter are difficult to form, and it is also difficult to apply the porous glass material to applications that require a high degree of pore characteristics. Was. In particular, in the technique of coating the porous glass material on a support and solidifying the material into a thin film, depending on the surface condition of the support, pinholes and cracks are likely to occur in the formed thin film. Even if uniform pores could be formed,
There was a fact that a porous film having "unevenness" which was not uniform as a whole had to be obtained.

Therefore, an inorganic material composition containing an alkoxysilane solution as a main component is coated on an inorganic porous support.
A coating film forming step of drying to form an amorphous coating film, and
There has been proposed a method for producing an inorganic porous membrane in which a heating step is performed in which the amorphous coating film is subjected to a heat treatment at a low temperature and a normal pressure so as not to be crystallized by the hydrolysis. However, when the inorganic material composition contains only alkoxysilanes as a main component, durability such as water resistance and chemical resistance is not sufficient, and there is a demand to improve the durability. It is conceivable that the amorphous coating contains an alkoxide of another metal in order to improve the durability, but when forming a film by hydrolyzing a plurality of types of alkoxides as described above, The hydrolysis rate differs between the alkoxides, and it is often difficult to form a film as a uniform composition. More specifically, another metal alkoxide having a high reaction rate is first hydrolyzed to form a precipitate, and the problem that the reaction with alkoxysilane cannot be efficiently performed tends to occur. In such a case, it is necessary to add various additives to the inorganic material composition to form a film while suppressing the reaction rate. There is a problem in practicality, for example, it is difficult to appropriately control the reaction rate for each metal material.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for forming a uniform pore size even when other metal materials are contained when an alkoxysilane solution is used as a main component. An object of the present invention is to provide a method for easily producing an inorganic porous membrane having high characteristics.

[0006]

In order to achieve this object, a feature of the present invention is that an alkoxysilane solution containing water and a catalytic amount of an acid is used as a main material, and a metal salt soluble in the solvent is used. And the molar ratio of water to alkoxysilanes (H ₂ O / Si) is 4
The following inorganic material composition having a pH of 1 to 2.5 is applied on an inorganic porous support, and a coating film forming step of drying to form an amorphous coating film, and the amorphous coating film Low temperature and normal pressure not causing crystallization by hydrolysis, specifically, for example, 150 ° C to 700 ° C, preferably 300 ° C to 500 ° C
Wherein the metal salt is preferably a zirconium salt, and the heat treatment is preferably performed at 500 ° C. for 2 hours or more, and the inorganic material composition at least one templating agent selected from ammonium ion phosphonium ion amines, specifically tetra-n- butylammonium ion _{((n-C 4 H 9} ) 4 n +), tetra-n- propylammonium ion ((n- ^{_{C 3 H 7) 4 n +}} ), tetraethylammonium ion _{((C 2 H 5) 4} n +), tetramethylammonium ion ^{_{((CH 3) 4 n +}} ), n- propyl trimethyl ammonium ion ((n-C ₃ H ₇₎ (CH _3)
3 N ⁺ ), benzyltrimethylammonium ion ((C _{7
H 7) (CH 3) 3} N +), tetra-n- butyl phosphonium ion _{((n-C 4 H 9} ) 4 P +), benzyl triphenyl phosphonium ion _{((C 7 H 7) (} C 6 H 5) ₃ P ⁺ ), 1,4-dimethyl-1,4-diazobicyclo (2,2,2) octane, pyrrolidine, n-propylamine (nC ₃ H ₇ NH)
₂ ) and methylquinuclidine may be added, and the molar ratio (Si: M (M is a metal)) between the alkoxysilanes and the metal salt in the inorganic material composition is 0. .95: 0.05 to 0.3: 0.7.

[Effects] Alkoxysilanes containing an acid catalyst produce amorphous silicon oxide (SiO ₂ ) (hereinafter abbreviated as silica) by condensation polymerization. This silica is considered to be a chain polymer when the molar ratio of water to alkoxysilanes (H ₂ O / Si) is small. Then, the present inventors, in the state of adding the template agent, the condensation polymerization of the alkoxysilanes solution under low water content, low polymerization rate conditions, chain silica, around the template agent Gathered into an amorphous and chain-like polymer, and considered to be pores standardized by the template agent, considering various reaction conditions, and examining various reaction conditions, the inorganic material composition When the pH is 1 to 2.5, the condensation polymerization rate of the alkoxysilanes is low and the mixture is densely gelled, so that the molar ratio of water to the alkoxysilanes (H ₂
By subjecting an inorganic material composition having an O / Si) of 4 or less and a pH of 1 to 2.5 to heat treatment under low-temperature and normal-pressure conditions, an amorphous porous structure having a large number of uniform pore sizes is obtained. We have already obtained the knowledge that we can obtain.

However, from the above findings, when incorporating the other metal into the porous structure, the inorganic material composition is expected to incorporate the other metal through a hydrolysis reaction, while the other metal is incorporated. When the film forming method using the alkoxide of the above is tried, the reaction does not occur as expected when the reactivity between the alkoxides is different, and the one having excellent reactivity reacts first and precipitates. I found it. Therefore, when various forms of addition of the other metal were examined, it was found that when the other metal was added in the form of a metal salt, the silica thin film could be uniformly incorporated without causing precipitation. New knowledge was obtained.

[0009] The present invention is based on the above-mentioned new findings, and comprises, as a main material, an alkoxysilane solution containing water and a catalytic amount of an acid, and adding a metal salt soluble in the solvent to the solution. And a molar ratio of water to alkoxysilanes (H ₂ O / Si) of pH 1 or less of 4 or less.
Coating the inorganic material composition of 2.5 on an inorganic porous support and drying to form a non-crystalline coating; and crystallizing the non-crystalline coating by the hydrolysis. A non-crystalline porous film having a large number of uniform pore diameters can be synthesized with low energy by a simple method of simply performing a heating step of performing a heat treatment under low-temperature and normal-pressure conditions to prevent the formation of a porous film. Therefore, a porous membrane that could not be used conventionally, for example, a porous membrane that can be used as a molecular sieve for gas separation could be provided at low cost.

If the metal salt is a zirconium salt, the technical field using ceramics has high durability because it is known that water resistance is improved when zirconium is added to silica-based ceramics. It is expected that a porous membrane will be obtained.

The above-mentioned heat treatment conditions of 500 ° C. for 2 hours or more are suitable for synthesizing a good porous film without causing crystallization. At least one template agent selected from ammonium ion phosphonium ion amines in the inorganic material composition, specifically, tetra n-butyl ammonium ion
((nC ₄ H ₉ ) ₄ N ⁺ ), tetra n-propyl ammonium ion ((n-C ₃ H ₇ ) ₄ N ⁺ ), tetraethyl ammonium ion ((C ₂ H ₅ ) ₄ N ⁺ ), tetra Methyl ammonium ion ((CH ₃ ) ₄ N ⁺ ), n-propyltrimethyl ammonium ion ((n-C ₃ H ₇ ) (CH ₃ ) ₃ N ⁺ ), benzyltrimethyl ammonium ion ((C ₇ H ₇ ) (CH _{3) 3} N ⁺⁾
, Tetra n- butyl phosphonium ion _{((n-C 4 H 9} )
₄ P ⁺ ), benzyltriphenylphosphonium ion ((C
_{7 H 7) (C 6 H} 5) 3 P +), 1,4- dimethyl-1,4-diazabicyclo (2,2,2) octane, pyrrolidine, n
- propylamine _{(n-C 3 H 7 NH} 2), if the addition of one of at least one methyl quinuclidine, while being set to the chain-like silica, the silica was hydrolyzed more Is convenient for condensation polymerization.
Since it is easily removed from the silica by the heat treatment, many pores having a uniform diameter defined by the size of the template agent can be formed. Further, the molar ratio of water to alkoxysilanes (H ₂ O: Si) in the inorganic material composition is 0.1.
When it is 1 to 150, the silica easily grows in a chain form and is difficult to be crystallized. Further, the acid in the inorganic material composition is hydrochloric acid, and the amount of addition is 1/100 with respect to water.
When it is 10 ⁵ to 1/10, suitable polymerization conditions can be obtained, which is advantageous. However, according to the present invention, it is easy to obtain a well-controlled pore diameter without using a template agent, and it is possible to use a synthesis method that does not employ a template agent because of simple reaction conditions. .

The molar ratio of the alkoxysilanes to the metal salt in the inorganic material composition (Si: M (M is a metal))
Is from 0.95: 0.05 to 0.3: 0.7, it is easy to improve the durability of the obtained inorganic porous membrane, and a porous membrane having a controlled pore diameter can be obtained.

[0013]

Embodiments of the present invention will be described below. First, an inorganic material composition 1 shown in Table 1 is prepared.
This inorganic material composition is dip-coated on the outer surface of the porous support and dried to form a coating film (coating film forming step). After the obtained coating film is dried, baking (heating step)
Then, an inorganic porous film is formed. Similarly, with respect to the inorganic material compositions 2 to 12, a coating film forming step and a heating step were performed to form an inorganic porous film. The coating film forming step and the heating step were alternately repeated.

[0014]

[Table 1] However, TEOS: tetraethoxysilane, Zr: zirconium oxychloride octahydrate, TPABr: tetrapropylammonium bromide TEABr: tetraethylammonium bromide TBABr: tetrabutylammonium bromide TMABr: tetramethylammonium bromide Values are molar ratios. Heating was performed at a heating rate of 0.5 ° C./min after drying at room temperature for 1 hour in the course of each coating.

[Adjustment of Inorganic Material Composition] A hydrous ethanol solution of zirconium oxychloride octahydrate, which also serves as an acid catalyst, is slowly dropped into an ethanol solution of alkoxysilane, and mixed so as to have a composition ratio shown in Table 1. By further stirring for one hour, a sol-like composition can be obtained.
To this, a predetermined amount of a template agent is added, and the mixture is stirred at room temperature in the air for 1 hour to obtain an inorganic material composition. If the solution to which the metal salt is added does not reach acidic conditions, hydrochloric acid or the like may be used.
In addition, a catalytic amount of an acid may be added so that the alkoxide can be hydrolyzed.

[Coating film forming step] As the porous support,
A porous alumina tube having an average pore diameter of 200 nm is used. The porous support is immersed in the inorganic material composition, and 0.5 m
The inorganic material composition is applied to the surface of the porous support by pulling up at a speed of m / sec (dip coating).
This is dried at room temperature for 1 hour to obtain a coating film.

[Heating Step] The coating film obtained by drying is 50
By heating to 0 ° C. and then heating for 2 hours, a glass-like inorganic porous film can be obtained.

[Other Embodiments] In the above-described embodiment, TPABr, TEABr, TBA
Br, was used TMABr, n- propyl trimethyl ammonium ion _{((n-C 3 H 7} ) (CH 3) 3 N +), benzyltrimethylammonium ion _{((C 7 H 7) (} CH 3) 3
N ⁺ ), tetra n-butylphosphonium ion ((n-C ₄
H ₉ ) ₄ P ⁺ ), benzyltriphenylphosphonium ion
_{((C 7 H 7) (} C 6 H 5) 3 P +), 1,4- dimethyl-1,4
- diazabicyclo (2,2,2) octane, pyrrolidine, n- propylamine _{(n-C 3 H 7 NH} 2), in which methyl quinuclidine, and the like can also be used, working template agent as cation If the halide,
It can be used in the form of a hydroxide or the like. In short, any material having at least one element selected from ammonium ions, phosphonium ions, and amines may be used. Further, as the alkoxysilanes, TEO
In addition to S, TMOS (tetramethoxysilane), tetrapropoxysilane (Si (OC ₃ H ₇ ) ₄ ), tetrabutoxy silane (Si (OC ₄ H ₉ ) ₄ ), and the like can be used, and are reduced by hydrolysis. Any material can be used as long as it can polymerize to produce silica. Further, a metal alkoxide such as an alkoxide of zirconium, aluminum, or titanium may be mixed with the alkoxysilane to such an extent that rapid hydrolysis does not occur. Further, as the metal salt, another zirconium salt may be used instead of zirconium oxychloride, and further, an aluminum salt, a titanium salt, or the like may be used. Further, the molar ratio (H ₂ O: Si) of water to alkoxysilanes is particularly preferably from 1 to 4. Under such conditions, the silica tends to be a chain polymer having a low fractal dimension. . Further, when an acid catalyst is used under such conditions, hydrochloric acid, nitric acid, acetic acid, trifluoroacetic acid, paratoluenesulfonic acid and the like can be used, but hydrochloric acid is particularly desirable, and the pH of the inorganic material composition is adjusted. When the amount is 1 to 2.5, the polymerization rate can be particularly slowed down.

[0019]

Embodiments of the present invention will be described below. The separation performance of nitrogen gas and carbon dioxide gas and the separation performance of nitrogen gas and helium gas were measured using the inorganic porous membrane obtained in the above embodiment, and the results are shown in Table 2.

[0020]

[Table 2] Here, α (gas 1 / gas 2) is the ratio of the permeation speed P (gas 1) of the pure gas 1 permeating the inorganic porous membrane to the permeation speed P (gas 2) of the pure gas 2 at each temperature.

The gas permeation speed P (gas) of each gas type used in Table 2 shows the value shown in Table 3 at each temperature.

[0022]

[Table 3]

From Table 2, it can be seen that the inorganic porous membrane of the present invention shows high gas separation performance.
This suggests that the inorganic porous membrane has a controlled and uniform pore size, and is expected to exhibit suitable performance in various uses such as a catalyst and an adsorbent. Also, from Table 3, it was found that a sufficient gas permeation amount was obtained, and it was proved that the gas separation membrane exhibited sufficiently high performance. When considering the use as a gas permeable membrane, the correlation between the data in Tables 2 and 3 shows that carbon dioxide gas can be efficiently separated at a relatively high temperature. It is understood that it contributes to the reduction of carbon dioxide emission in the inside. When the amount of the template agent is examined, the gas permeability tends to increase as the amount of the template agent increases. On the other hand, if the amount of the template agent increases too much, the gas selectivity decreases. (T) is S with respect to the total amount (S) of alkoxysilanes and metal salt:
It is understood that it is preferable to add T (molar ratio) so as to be 1: 0.05 to 1: 0.5.

Continued on the front page (72) Inventor Kazuo Nagata 5-6-1 Koyodai, Ryugasaki-shi, Ibaraki F-term in Kubota Research Institute of Technology (reference) 4G042 DA01 DB11 DB23 DD02 DD11 DE09 DE14

Claims (6)

[Claims] 1. An alkoxysilane solution containing water and a catalytic amount of an acid as a main material, and a metal salt soluble in the solvent is added to the solution, and a mole of water and the alkoxysilane is mixed. A coating film forming step of applying an inorganic material composition having a pH (H ₂ O—Si) of 4 or less to pH 1 to 2.5 on an inorganic porous support and drying to form an amorphous coating film; And a method for producing an inorganic porous film, wherein a heating step of heating the amorphous coating film under low-temperature and normal-pressure conditions that does not cause crystallization by hydrolysis of the alkoxysilanes. 2. The method according to claim 1, wherein the metal salt is a zirconium salt. 3. The method for producing an inorganic porous membrane according to claim 1, wherein the heat treatment is performed at 500 ° C. for 2 hours or more. 4. The method for producing an inorganic porous membrane according to claim 1, wherein at least one template agent selected from ammonium ion phosphonium ion amines is added to said inorganic material composition. 5. The method according to claim 1, wherein the template agent is tetra-n-butylammonium ion ((nC ₄ H ₉ ) ₄ N).
^+), Tetra-n- propylammonium ion _{((n-C 3 H 7} ) 4
N ⁺ ), tetraethyl ammonium ion ((C ₂ H ₅ ) ₄ N ⁺ ), tetramethyl ammonium ion ((CH ₃ ) ₄ N ⁺ ), n-propyltrimethyl ammonium ion ((n-C ₃
H ₇ ) (CH ₃ ) ₃ N ⁺ ), benzyltrimethyl ammonium ion ((C ₇ H ₇ ) (CH
₃ ) ₃ N ⁺ ), tetra n-butylphosphonium ion ((n-C ₄ H ₉ ) ₄ P
⁺ ), Benzyltriphenylphosphonium ion ((C ₇ H ₇ ) (C
^{_{6 H 5) 3 P +)}} , 1,4- dimethyl-1,4-diazabicyclo (2,2,
2) octane, pyrrolidine, n- propylamine _{(n-C 3 H 7 NH} 2), methyl quinuclidine, a method of manufacturing at least one is of the claim 4, wherein the inorganic porous membrane. 6. The molar ratio (Si: M (M is a metal)) of an alkoxysilane to a metal salt in the inorganic material composition is 0.95: 0.05 to 0.3: 0.7. The method for producing an inorganic porous membrane according to claim 1.