JP2000015040A - Gas separation membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas separation membrane for separating oxygen from nitrogen or carbon dioxide from nitrogen and usable in environments requiring high heat resistance. SOLUTION: An independent membrane containing polysiloxane, which consists of network composing units having a formula: RnSiO(4-n)/2 (wherein R is selected from methyl, ethyl, n propyl, isopropyl, phenyl, and vinyl; n satisfies 0.5<=n<=1.5) and repeatedly bound as to form a three-dimensional mesh structure, and having 10 μm or thicker thickness is used as this gas separation membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a symmetrical separation membrane for separating a mixed gas composed of independent membranes obtained by a sol-gel method, and more particularly to an air separation membrane used in an environment where heat resistance is required. Oxygen / nitrogen separation membrane and carbon dioxide / nitrogen separation membrane for oxygen enrichment.

[0002] Conventionally, reduction of nitrogen oxides in exhaust gas has been regarded as important as a measure against environmental problems, and high-purity oxygen and oxygen-enriched gas have been used for combustion. Also, in the medical field, technologies such as oxygen enrichment are required. For enrichment up to an oxygen concentration of 35%, the membrane separation method is said to be the most economical. Also, from the viewpoint of environmental issues, there is a need for a technique for collecting and storing carbon dioxide in exhaust gas. Therefore, carbon dioxide with high separation performance
A nitrogen separation membrane is needed.

As a separation membrane, a so-called asymmetric membrane in which a porous substrate is generally coated with a thin film having a separation function has been studied and partially put to practical use. Until now, organic polymer films, silicone films and composite films thereof have been studied. Polydimethylsiloxane (silicone rubber) has a high permeability coefficient of oxygen gas, but has a separation coefficient of 2 between oxygen and nitrogen.
Is not enough. On the other hand, the organic polymer membrane has a disadvantage that the separation coefficient is high but the oxygen permeability coefficient is low.
Further, it is said that organic polymers are excellent in film-forming ability, but silicone rubber is difficult to form a film. Further, the organic polymer film has a drawback of poor heat resistance, and is difficult to use in an environment where heat resistance is required.

Therefore, copolymers of polyorganosiloxane and various organic polymers have been studied (for example, Japanese Patent Application Laid-Open No. 54-40868). In addition, as an attempt to reduce the film thickness in order to increase the permeation speed, a method of developing a membrane on the liquid surface, laminating this on a porous support, and obtaining a separation membrane with a high permeation speed has been studied (for example, JP-A-61-6
No. 8106).

Japanese Patent Application Laid-Open No. 56-26508 discloses a selective gas permeable membrane containing a copolymer of a polyorganosiloxane having a crosslinked structure and a linear polyorganosiloxane as a main component. Also, Japanese Patent Application Laid-Open No. 7-213
No. 877 discloses an asymmetric separation membrane of inorganic xerogel for carbon dioxide / nitrogen separation.

[0006]

The separation membrane containing the above-mentioned conventional organic polymer has insufficient heat resistance even though it is an inorganic-organic composite. In particular, a high-performance separation membrane that can be used in a high-temperature environment has not yet been developed. Therefore, a separation membrane having a developed inorganic network and a perfect inorganic network having good separation characteristics has been desired. Further, in the formation of the asymmetric separation membrane, there is a problem of generation of pinholes derived from defects in the porous substrate. If the film thickness is increased to solve this problem, problems such as cracks and warpage occur. Further, the inorganic xerogel film disclosed in Japanese Patent Application Laid-Open No. 7-213877 has a disadvantage that the surface OH groups are considerably left, so that the influence of moisture is large. Therefore, a symmetric separation membrane having no pinholes, having excellent mechanical strength and heat resistance, and having few surface OH groups has been desired.

Accordingly, the present invention provides an OH comprising an inorganic polymer having a polysiloxane network having no pinhole.
It is an object of the present invention to develop a stable symmetric separation membrane having a small number of groups and to achieve both a high oxygen and carbon dioxide permeability coefficient and a high separation coefficient.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have used an independent membrane having a thickness of 10 μm or more containing a polysiloxane of a specific composition as a gas separation membrane. With no pinholes and high separation characteristics, the present invention was completed based on this finding. Further, they have found a gas separation method using these membranes. The present inventors have already invented a method for producing an inorganic polymer film on an aqueous solution or a substrate (JP-A-9-77509, JP-A-9-30971).
No. 7). The present invention intends to apply the independent membrane produced according to the invention of the present inventors to separation of oxygen and nitrogen or separation of carbon dioxide and nitrogen.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The present invention has the formula: R _n SiO _{(4-n) / 2}
(0.5 ≦ n ≦ 1.5) (R is a methyl group, an ethyl group, n
-A propyl group, an isopropyl group, a phenyl group, and an organic group selected from a vinyl group) having a film thickness of 10 μm or more containing polysiloxane that is repeatedly bonded to form a three-dimensional network structure. It is a gas separation membrane composed of an independent membrane.

R _n SiO _{(4-n) / 2} (0.5 ≦ n ≦ 1.
The reason why n ≧ 0.5 in 5) is that if n is less than 0.5, it becomes difficult to make the thickness of the independent film 10 μm or more. The reason for setting n ≦ 1.5 is that if n exceeds 1.5, it is difficult to form a three-dimensional network structure and mechanical strength is poor. Further, the value of n is more preferably 0.8 ≦ n ≦ 1.4. By setting n ≧ 0.8, the strain in the gel can be more reliably reduced in the drying stage,
It becomes easier to obtain a thick film. By setting n ≦ 1.4, a material having more excellent mechanical properties can be obtained. In other words, it has an intermediate property between a crosslinked silica polymer having SiO ₂ as a constitutional unit and a polyorganosiloxane elastomer having R ₂ SiO as a constitutional unit. In the gas separation membrane of the present invention, both oxygen and carbon dioxide are 2 × 10 ⁻¹² at 110 ° C.
It preferably has a transmission coefficient of cc · cm · cm ⁻² · s ⁻¹ · Pa ⁻¹ or more. 2 × 1 transmission coefficient at 110 ° C.
If it is less than 0 ^-12 cc · cm · cm ⁻² · s ⁻¹ · Pa ⁻¹ , a large-area separation membrane is required, which is economically disadvantageous. The separation coefficient (oxygen / nitrogen) is preferably 2 or more, and the separation coefficient (carbon dioxide / nitrogen) is preferably 4 or more. If the separation factor is less than 2 and less than 4, respectively, many steps are required to obtain a high concentration of the desired gas, which is not practical.

In the production of the gas separation membrane of the present invention, tetraalkoxysilanes such as tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS) are used as raw materials.
Methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), ethyltrimethoxysilane (ETMS), phenyltriethoxysilane (PhTE
S), trialkoxysilanes such as vinyltriethoxysilane (VTES), n-propyltrimethoxysilane (n-PrTMS), and isopropyltrimethoxysilane (iso-PrTMS); dimethyldiethoxysilane (D
MDE), diphenyldimethoxysilane (DPhDM)
And the like. Further, trialkoxysilane may be used alone. Further, in order to improve the mechanical properties of the material, silica, alumina, zirconia, zeolite or the like can be added in an amount of 50% by weight or less in terms of solid content. These components may be added as an organosol in which the dispersion medium is alcohol or the like. Alumina and zirconia may be added with an alkoxide as a starting material.

[0012] The above raw materials are given as follows: 1.4 ≦ H ₂ O / Si ≦ 4.0
(Molar ratio), it is preferable to add water so as to carry out a hydrolysis / polycondensation reaction. If H ₂ O / Si <1.4 (molar ratio), unreacted alkoxy groups remain, and the material strength may be degraded. Conversely, when H ₂ O / Si> 4.0 (molar ratio), when the organoalkoxysilane is contained in a large amount, phase separation is particularly likely to occur, making it difficult to obtain a uniform material. More preferably, the amount of water added is 1.4 ≦ H ₂ O / Si ≦ 2.5 (molar ratio).

The pH of the reaction solution is preferably 7.0 or less as an initial value immediately after preparation of the reaction solution. Under the condition of pH> 7.0,
The desired reaction hardly proceeds. More preferably, an acid catalyst is added to accelerate the progress of the reaction, and the initial pH of the reaction solution is adjusted to 5.0 or less. The acid catalyst to be used is not particularly limited, and an inorganic acid catalyst such as nitric acid and hydrochloric acid and an organic acid catalyst such as acetic acid are used according to a conventional method.

Further, particularly when a large amount of methyltrialkoxysilane is used as a raw material, as described in JP-A-8-165114,
It is preferable to add a soluble metal chelate compound to this raw material. Examples of the metal chelate compound satisfying the above conditions include metal chelates of β-diketones (compounds having a 1,3-dioxopropylene chain) and metal chelates of macrocyclic polyether compounds.

The type of metal ion is not particularly limited,
It is necessary to select one having a large complex formation constant with the ligand. As a specific example, tris (acetylacetonato)
Aluminum (III), tris (ethylacetoacetato) aluminum (III), tris (diethylmalonato) aluminum (III), bis (acetylacetonato) copper (II), tetrakis (acetylacetonato) zirconium (IV), Tris (acetylacetonato) chromium (III), tris (acetylacetonato) cobalt (II)
I) and titanium (II) oxide acetylacetonate [C
Β-diketone metal chelates such as H ₃ COCHCOCH ₃ ) ₂ TiO], β-diketone metal chelates of rare earth metals, 18-crown-6-potassium chelate compound salts, 12-crown-4-lithium chelate compound salts,
Metal chelates such as metal chelates of macrocyclic polyether compounds such as 15-crown-5-sodium chelate compound salts.

The amount of addition is from 0.001 to 5 mol% based on methyltrialkoxysilane depending on the effect.
It is preferable to add in the range. If the amount is less than 0.001 mol%, it is difficult to obtain the effect of suppressing crystal precipitation. Conversely 5
If more than mol% is added, there is a possibility that a chelate compound is precipitated or the properties of the film are affected. For such a metal chelate compound, a ligand component and a metal component may be separately added to the reaction system and chelated in situ. The addition amount of the metal chelate compound is more preferably 0.01 to 1 mol% based on methyltrialkoxysilane.

The above-mentioned chelate compound controls the polycondensation reaction and makes it easier to form a linear polymer at the beginning of the reaction.
No precipitation occurs. As a result, it works advantageously for the formation of a film. When methyltrialkoxysilane is not included in the starting material, no precipitate is formed even if the chelate compound is not added. However, in order to facilitate formation of a film, it is preferable to similarly add the above chelate compound.

When a large amount of tetraalkoxysilane is used as a raw material, it is preferable to add an alcohol as a solvent in order to obtain a uniform sol.

As a method for producing a film, various known molding methods used for sheet molding can be applied. The substrate can be used as long as it has good releasability from the gel film. For example,
By an organic material which is not bonded to a silanol group contained in the gel film, that is, an organic material which does not have a functional group such as a carbonyl group, an imide group and a cyano group, or a glass, plastic or metal whose surface is coated with the organic material , Preferably a formed substrate. If the surface of the substrate is formed of a material capable of hydrogen bonding with a silanol group in the sol, for example, a metal oxide, polymethyl methacrylate, or the like, it may be difficult to peel off the target film. From this point, as the organic material to be used, polyethylene, polypropylene, polystyrene, polytetrafluoroethylene, silicone, polyvinyl chloride and the like are preferable.

The film thickness is adjusted by an air knife, a bar coater,
It can be performed using a doctor blade, a metering roll, a doctor roll, or the like, and a film having a thickness of 10 to 250 μm can be easily obtained. Under these manufacturing conditions,
A uniform and smooth sheet can be obtained without generating pinholes.

It is preferable to perform a heat treatment to promote the polycondensation of silanol groups in the film. When a large amount of silanol remains in the membrane, a problem arises in that moisture in the air is adsorbed and the separation characteristics become unstable. By setting the heat treatment temperature of the film to 100 ° C. or more, particularly 120 to 250 ° C.,
Since the amount of silanol remaining in the membrane is reduced, it is less affected by moisture in the air, and stable separation characteristics can be obtained.

The gas separation method using the separation membrane according to the present invention comprises:
It is preferable to carry out at a temperature of 0 to 300 ° C. When the temperature is lower than 40 ° C., the separation coefficients of oxygen and nitrogen and carbon dioxide and nitrogen do not change much. Conversely, if the temperature exceeds 300 ° C,
Organic groups in the siloxane film are gradually decomposed, and the film is deteriorated. The mixed gas separation method using the separation membrane of the present invention is more preferably performed at a temperature of 100 to 250 ° C.

The gas separation apparatus using the separation membrane of the present invention comprises:
A pair of separation membranes is disposed on the opposing surface of the first spacer member, and a membrane envelope is used in which the peripheral edges thereof are hermetically sealed. The membrane envelope has an arbitrary contour such as a rectangle, an ellipse, or the like. For example, a pair of separation membranes is formed on a facing surface of a spacer member formed of a gas-permeable porous plate of, for example, sintered metal, glass, or ceramic. Is disposed, and the periphery of the separation membrane that protrudes from the contour of the spacer member is hermetically sealed by, for example, bonding. Alternatively, the periphery may be sealed using a gasket, or the periphery of the spacer member may have a dense structure, and the periphery of the separation membrane may be bonded to the dense portion to form an envelope.

A module is formed by alternately laminating the plurality of membrane envelopes thus formed and the plurality of second spacer members. The second spacer member may be made of the same material as the first spacer member. One specific example of such a module is shown schematically in FIG. The apparatus includes a housing for housing the module therein, a source gas passage in the housing including an inlet and an outlet, and an outlet for the separation gas passing through the separation membrane and into the envelope. The apparatus also comprises means for maintaining the pressure of the feed gas in the housing at a level higher than the pressure of the separation gas. This can be achieved by connecting the source gas inlet to a pump and increasing the pressure, or connecting a suction pump to the separation gas outlet and reducing the pressure.

In operation, the feed gas entering the housing passes through the second spacer and exits the feed gas outlet through the outlet. Meanwhile, due to the preferential permselectivity and pressure difference of the separation membrane to oxygen gas or carbon dioxide,
The gas rich in oxygen or carbon dioxide that has passed through the separation membrane enters the inside of the envelope and exits from a separation gas outlet different from the source gas outlet.

[0026]

EXAMPLES The permeability coefficients of oxygen, carbon dioxide and nitrogen were measured by using a cell having a diameter of 12 cm and applying 10 atm. The flow rate permeating through the membrane is a gas flow meter (Sect. SEC42) having a sensitivity of 0.001 cc / min.
00). Each transmission coefficient p [cc · cm
· Cm ^-2 · s ^-1 · Pa ^-1 ].

[0027]

(Equation 1)

Here, F is the gas flow rate [cc · s ⁻¹ ], t
Is the thickness of the separation membrane [cm], S is the area of the membrane [cm ² ], Δ
P is a pressure difference [Pa]. The separation coefficient is represented by the ratio of the transmission coefficients.

Example 1 Methyltriethoxysilane (LS-18, Shin-Etsu Chemical Co., Ltd.)
90) 22.5 g of aqueous nitric acid solution was added to 178 g.
The aqueous nitric acid solution was prepared by mixing 10 wt% of a 0.1 mol / l aqueous nitric acid solution and 90 wt% of distilled water.
After stirring at room temperature for 2 days to react, 92 g of ethanol produced by the reaction was distilled off by an evaporator to obtain 108 g of an oligomer solution. 0.32 to this oligomer solution
g of tris (acetylacetonato) aluminum (III
) And 9 g of distilled water. The mixture was stirred at 50 ° C. to form a clear solution, and then allowed to stand at 40 ° C. for 22 hours. Using the obtained liquid, a film was formed with a doctor blade. It was dried in air at 120 ° C. for 1 hour and peeled from the sheet to obtain a 50 μm-thick CH ₃ SiO _3/2 independent film. The permeation rate of nitrogen, oxygen and carbon dioxide at 110 ° C. of this film was 2.2 × 10 ⁻¹² cc · cm · cm, respectively.
^-2 · s ^-1 · Pa ^-1 , 6.2 × 10 ^-12 cc · cm · cm
^-2 · s ^-1 · Pa ^-1 and 2.1 × 10 ^-11 cc · cm · c
m ^-2 · s ^-1 · Pa ^-1 . The separation coefficients are 2.
8 (O ₂ / N ₂ ) and 9.5 (CO ₂ / N ₂ ).

Example 2 Methyltriethoxysilane (LS-18, Shin-Etsu Chemical Co., Ltd.)
90) 178 g, tetraethoxysilane (Shin-Etsu Chemical Co., Ltd., LS-2430) 41 g and ethanol 50 g were mixed, and 27 g of nitric acid aqueous solution was added. The aqueous nitric acid solution includes 10 wt% of a 0.1 mol / l aqueous nitric acid solution,
It was prepared by mixing 90 wt% of distilled water. After stirring at room temperature for 2 days to react, ethanol 140
g was distilled off with an evaporator to obtain 152 g of an oligomer solution. To this oligomer solution was added 0.32 g of tris (acetylacetonato) aluminum (III) and 14 g
Of distilled water was added. This mixed solution was stirred at 50 ° C. to form a clear solution, and then allowed to stand at 40 ° C. for 8 hours. Using the obtained liquid, a film was formed with a doctor blade. Dried 1 hour at 120 ° C. in air, it is peeled off from the sheet, to obtain a 17SiO ₂ · 83CH ₃ SiO _3/2 independent film having a thickness of 80 [mu] m. The permeation rates of nitrogen and oxygen at 110 ° C. of this film were 2.0 × 10 ⁻¹² cc · cm · cm ⁻² · s ^−1.
Pa ^-1 and 5.6 × 10 ^-12 cc · cm · cm ^-2 · s ^-1
-It was Pa- ¹ . The separation factor (O ₂ / N ₂ ) was 2.8.

Example 3 Methyltriethoxysilane (LS-18, Shin-Etsu Chemical Co., Ltd.)
178 g of 90) and 29 g of dimethyldiethoxysilane (Shin-Etsu Chemical Co., Ltd., LS-1370) were mixed, and 27 g of an aqueous nitric acid solution was added. The nitric acid aqueous solution is 0.1 mol /
It was prepared by mixing 10% by weight of a 1% aqueous nitric acid solution and 90% by weight of distilled water. After stirring at room temperature for 2 days to react, 110 g of ethanol produced by the reaction was distilled off by an evaporator to obtain 122 g of an oligomer solution. To this oligomer solution was added 0.32 g of tris (acetylacetonato) aluminum (III) and 11 g of distilled water. This mixed solution was stirred at 50 ° C. to form a clear solution, and then allowed to stand at 40 ° C. for 8 hours. Using the obtained liquid, a film was formed with a doctor blade. Dry in air at 120 ° C. for 1 hour, peel off from the sheet, and use 83C with a thickness of 30 μm.
An H ₃ SiO ₃ / _2.17 (CH ₃ ) ₂ SiO independent film was obtained. The permeation rates of nitrogen and oxygen at 110 ° C. of this film were 2.5 × 10 ⁻¹² cc · cm · cm ⁻² · s ⁻¹ · Pa, respectively.
^-1 and 6.8 × 10 ^-12 cc · cm · cm ^-2 · s ⁻¹ · P
a- ¹ . The separation factor (O ₂ / N ₂ ) was 2.7.

Example 4 Methyltriethoxysilane (LS-18, Shin-Etsu Chemical Co., Ltd.)
90) 178 g and phenyltriethoxysilane (Shin-Etsu Chemical Co., Ltd., LS-4480) 48 g were mixed, and 27 g of nitric acid aqueous solution was added. The aqueous nitric acid solution is 0.1 mol
/ Wt concentration of nitric acid aqueous solution 10wt% and distilled water 90wt%
Was prepared by mixing. After stirring at room temperature for 2 days to react, 105 g of ethanol produced by the reaction was distilled off by an evaporator to obtain 146 g of an oligomer solution. To this oligomer solution was added 0.32 g of tris (acetylacetonato) aluminum (III) and 11 g of distilled water. This mixed solution was stirred at 50 ° C. to form a clear solution, and then allowed to stand at 40 ° C. for 8 hours. Using the obtained liquid, a film was formed with a doctor blade. Dry in air at 120 ° C. for 1 hour, peel off from sheet, 40 μm thick 83C
An H ₃ SiO _3/2 .17C ₆ H ₅ SiO _3/2 independent film was obtained. The permeation rates of nitrogen and oxygen at 110 ° C. of this film are 1.8 × 10 ⁻¹² cc · cm · cm ⁻² · s ⁻¹ · Pa, respectively.
^-1 and 4.7 × 10 ^-12 cc · cm · cm ^-2 · s ⁻¹ · P
a- ¹ . The separation factor (O ₂ / N ₂ ) was 2.6.

[Brief description of the drawings]

FIG. 1 is a schematic view of a specific example of a membrane module housed in a housing of a gas separation device using the separation membrane of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C01B 31/20 C01B 31/20 B (72) Inventor Yoshinori Tanigami 2-21 Hamamatsubaramachi, Nishinomiya-shi, Hyogo Prefecture No. Yamamura Glass Co., Ltd. (72) Inventor Akio Konishi 2-21 Hamamatsubara-cho, Nishinomiya City, Hyogo Prefecture Yamamura Glass Co., Ltd. F-term (reference) 4D006 GA41 JA04A MA28 MA31 MB15 MC65 4G042 BA29 BA30 BA39 BB02 4G046 JA04 JB06 JC02

Claims (7)

[Claims] The formula: R _n SiO _{(4-n) / 2} (0.5 ≦ n ≦
1.5) (R is a methyl group, an ethyl group, an n-propyl group,
An organic group selected from the group consisting of isopropyl group, phenyl group, and vinyl group) is composed of an independent film having a film thickness of 10 μm or more containing polysiloxane repeatedly bonded to form a three-dimensional network structure. A gas separation membrane characterized by the above-mentioned. 2. The gas separation membrane according to claim 1, which is used for separating oxygen and nitrogen or carbon dioxide and nitrogen. 3. An oxygen permeability coefficient at 110 ° C. of 2 × 1
The gas separation membrane according to claim 1, wherein the gas separation membrane has a separation coefficient (oxygen / nitrogen) of at least 0 ⁻¹² cc · cm · cm ⁻² −s ⁻¹ · Pa ⁻¹ . 4. The carbon dioxide permeation coefficient at 110 ° C.
2 × 10 ⁻¹² cc · cm · cm ⁻² · s ⁻¹ · Pa ⁻¹ or more,
3. The gas separation membrane according to claim 1, wherein the separation coefficient (carbon dioxide / nitrogen) is 4 or more. 5. The gas separation membrane according to claim 1, which has a heat resistance of 300 ° C. 6. A gas separation method comprising performing gas separation at a temperature of 40 to 300 ° C. using the gas separation membrane according to claim 1. 7. A plurality of membrane envelope units comprising: a pair of the gas separation membranes according to claim 1 disposed on opposing surfaces of a first air-permeable spacer member, and a peripheral edge hermetically sealed; A) a plurality of second gas permeable spacer members alternately stacked with the plurality of membrane envelope units; (c) a source gas inlet and an outlet in communication with the plurality of second spacer members; A separation gas outlet communicating with the interior of the envelope unit; and (e) means for maintaining the gas pressure at the source gas inlet side at a higher level than the gas pressure at the separation gas outlet side. Gas separation equipment.