JPH0419891B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a composite membrane for gas separation. More specifically, the present invention relates to a composite membrane for gas separation that is effective for obtaining oxygen-enriched air from air by a membrane separation method. (Prior Art) In recent years, gas separation by membrane methods, particularly methods for obtaining oxygen-enriched air by membrane separation, have attracted attention. A membrane that can be practically used for this membrane separation must satisfy the conditions of high gas separation performance and high gas permeation performance. Therefore, the form of the membrane needs to be a composite membrane in which a thin membrane material with high gas separation performance is combined on a porous support. However, when the thin film is directly composited onto a porous support, there is a drawback that the thin film peels off when the composite film is handled due to poor adhesion. In order to solve this problem, as described in US Pat. No. 3,874,986, a thin film of polyphenylene oxide (PPO) with high gas separation performance and a porous support were used.
Composite membranes have been proposed in which thin films of polycarbonate/polydimethylsiloxane (PC-PDMS) copolymers are interposed, which have high adhesion and high film-forming properties. However, the PC-PDMS copolymer has low gas permeability due to its polycarbonate copolymer component, which plays a role in improving thin film formation. The drawback was that it degraded performance. It is also possible to use crosslinked polydimethylsiloxane instead of the PC-PDMS copolymer. However, despite the materials having high adhesive properties and high gas permeability, those cross-linked with conventionally known trifunctional or less cross-linking agents cannot be made into thin films, and the gas permeability of composite membranes is said to be low. There were flaws. (Problems to be Solved by the Invention) The object of the present invention is to solve the above-mentioned drawbacks, and to provide a composite material for gas separation that does not peel off the thin film layer from the porous support membrane and has excellent gas separation performance and gas permeation performance. The purpose is to provide a membrane. (Means for solving the problems) In order to achieve the above object, the present invention has the following configuration:
That is, between the porous support A and the ultrathin film B made of a polymer having high gas separation properties, a polyorganosiloxane made of polyorganosiloxane crosslinked with a tetrafunctional or more functional silane crosslinking agent or a tetrafunctional or more functional siloxane crosslinking agent is provided. This is a composite membrane for gas separation in which an ultra-thin membrane C is interposed. The porous support A in the present invention may be anything that supports a thin film, and includes Japanese paper, nonwoven fabric, synthetic paper, filter paper, cloth, wire mesh, filtration membrane, ultrafiltration membrane, etc. Ultrafiltration membranes are preferred because smooth surfaces and smaller pores are preferred for reinforcement. Specific examples of ultrafiltration membranes include polysulfone porous support membranes, polyethersulfone porous support membranes, polypropylene porous support membranes, polytetrafluoroethylene porous support membranes, and the like. The shape of these porous supports A is
It may be in the form of a sheet, a tube, a fiber, etc., but is not particularly limited. Next, the ultrathin film B made of a polymer having high gas separation property in the present invention has high gas separation property,
Any polymer may be used as long as it has relatively good gas permeability, but the following polymers are preferable in terms of the balance of thin film forming property, gas separation property, and gas permeability. Vinyl polymers of poly(4-methylpentene-1), polyethylene/propylene copolymers, and polyvinyltrimethylsilane. The general formula is (However, m is an integer of 1, 2, 3. R ₁ is −CH ₃ , −
selected _from the group consisting of alkyl groups _{of C2H5} , _-C3H7 , _{-C4H9 ,} and _{-C5H11 ;} ), or the general formula is (However, R ₃ and R ₄ are

[Formula] −C ₂ H ₄ −, −C ₃ H ₆ −, −C ₄ H ₈ −, −C ₅ H ₁₀ −R ₂ is −
C ₂ H ₄ O−, (−C ₂ H ₄ O)− ₂ , (−C ₃ H ₆ O)−, (−C ₄ H ₈ O
)−, (−C ₅ H ₁₀ O)−. ), or the general formula is (However, R ₅ is

【formula】

【formula】

【formula】

【formula】

[Formula] Selected from the group consisting of -CH ₂ , -C ₂ H ₄ -, -C ₃ H ₆ -, -C ₄ H ₈ -. Here, m is an integer of 1, 2, or 3. ) It was a polysulfone represented by Among these, particularly preferred are poly(4methylpentene-1) and polyvinyltrimethylsilane. The thickness of the ultra-thin film B is preferably 0.01 μm or more and 0.3 μm or less. If the film thickness does not exceed 0.01μ, pinholes will occur and gas separation performance will decrease.
If it exceeds 0.3μ, the gas permeation resistance increases and the gas permeation performance of the composite membrane decreases, which is not preferable. In the present invention, a tetrafunctional or higher functional silane crosslinking agent or a tetrafunctional or higher functional siloxane crosslinking agent is a tetrafunctional or higher functional condensed silane crosslinking agent or a tetrafunctional or higher functional condensed siloxane crosslinking agent that reacts with the terminal silanol group of polyorganosiloxane. It is about. Among these, the types of silane crosslinking agents with tetrafunctionality or higher are:
Acetoxy-based silanes such as tetraacetoxysilane, oxime-based silanes such as tetradimethyloxime silane, alkoxy-based silanes such as ethyl orthosilicate and propyl orthosilicate, and alkenyloxy-based silanes such as tetrakisisopropenyloxysilane. These include silane, amide silane, and amino silane. Preferred are acetoxy-based silanes, oxime-based silanes, alkoxy-based silanes, and alkenyloxy-based silanes because of their high crosslinking speeds. Particularly preferred among these are tetraacetoxysilane, tetradimethyloxime silane, and ethyl orthosilicate. In addition, as tetrafunctional or higher functional siloxane crosslinking agents, cohydrolyzed condensates of trifunctional silanes and tetrafunctional silanes, partial hydrolyzed condensates of each tetrafunctional silane, and cohydrolyzed condensates of difunctional silanes and trifunctional silanes. Alternatively, there are tetrafunctional or higher functional condensates produced by hydrolysis of polyfunctional silanes, such as co-hydrolyzed condensates of bifunctional silanes and tetrafunctional silanes. Among these, preferred are cohydrolyzed condensates of trifunctional silanes and tetrafunctional silanes, and partial hydrolyzed condensates of each tetrafunctional silane. Other siloxanes are not preferred because of their slow crosslinking speeds. Preferred concrete tetrafunctional or higher functional siloxane crosslinking agents include ethyl polysilicate, pentadimethyloxime siloxane, hexadimethyloxime siloxane, and hexaacetoxysiloxane. The polyorganosiloxane in the present invention is a polymer in which all the terminal groups are silanol groups, preferably at least 50 mol% or more, preferably 80 mol% or more of the number of terminal groups. If less than 50 mol% of the terminal groups are silanol groups, the crosslinking rate will drop significantly due to the presence of uncrosslinked polyorganosiloxane, which is undesirable as thin film forming properties will deteriorate. The molecular weight of polyorganosiloxane is over 1000
300,000 or less, preferably 10,000 or more and 100,000 or less. If the molecular weight is less than 1000, the crosslinking density is too high and it becomes brittle, making it difficult to obtain an extremely thin film without pinholes, which is not preferable. Furthermore, if the molecular weight exceeds 300,000, it is not preferable because thin film forming properties are significantly impaired due to a decrease in crosslinking density and a decrease in crosslinking speed. The chemical structure of polyorganosiloxane is shown by the following formula. (However, R ₁ and R ₂ are −CH ₃ , −C ₂ H ₅ , −NH ₂ , −CH
= _{CH2 , -C6H5} . ), but preferably both R ₁ and R ₂ are −CH ₃ ,
Other substituents are not preferred because they have low gas permeability and poor thin film forming properties. The thickness of this ultra-thin polyorganosiloxane film is
It is preferably 0.01μ or more and 1.0μ or less. If the film thickness is less than 0.01μ, pinholes are likely to occur, which is undesirable. If the film thickness exceeds 1.0 μm, the gas permeability of the composite film will significantly decrease, which is undesirable. The method for manufacturing the laminated composite membrane for gas separation of the present invention will be explained. A solution is prepared in advance in which a tetrafunctional or higher functional silane crosslinking agent or a tetrafunctional or higher functional siloxane crosslinking agent, a polyorganosiloxane, and a catalyst are dissolved in a water-immiscible solvent. The concentration of polyorganosiloxane is preferably 0.01 wt% or more and 5.0 wt% or less.
If the concentration is less than 0.01 wt%, it will be difficult to form a pinhole-free thin film, and if it exceeds 5.0 wt%, it will be difficult to obtain a thin film of less than 1.0 μm, which is not preferred. The amount of the tetrafunctional or more functional silane crosslinking agent or the tetrafunctional or more functional siloxane crosslinking agent is preferably 2 times or more and 20 times or less the number of terminal silanol groups of the polyorganosiloxane.
This is not preferable because gelation progresses and the crosslinking rate becomes slow. Catalysts are added to increase the crosslinking rate, and include dibutyltin diacetate, dibutyltin dioctoate, stannath octoate, and the like.
Preferably, the solvent is immiscible with water. If it is not miscible with water, water, which is a reaction initiator for the crosslinking reaction, will be included in the solvent, so crosslinking will proceed in the solution, making handling inconvenient and undesirable. These solvents include cyclohexane, ethyl ether, chloroform, pentane, dioxane, Freon solvents,
Examples include hexamethyldisiloxane. This solvent must not soak the porous support, and must be selected in combination with the porous support. The solution prepared in this manner is thinly and uniformly applied to a porous support and dried with hot air to produce a composite membrane. Next, a polymer having high gas separation properties is dissolved in a solvent such as benzene, toluene, xylene, dichloromethane, dichloroethane, cyclohexane, cycloxene, or tetrachloroethane to prepare a membrane forming solution B'. The appropriate concentration was 0.01 to 5.0 wt%, particularly preferably 0.03 to 2.0 wt%. The membrane-forming solution B' prepared in this manner is dropped onto the water surface, spread to form a thin film, and supported on the thin film surface of a polyorganosiloxane composite membrane prepared in advance to create a composite membrane for gas separation. Note that the evaluation criteria for characteristics in the present invention are as follows. (1) Gas permeability, gas separation property The composite membrane for gas separation of the present invention is separated, and the pressure on the primary side is 2 atm and the pressure on the secondary side is 1 atm, and the gas (oxygen or nitrogen) that has permeated through the composite membrane is permeated. Speed Precision Membrane Flowmeter SF-101 (Standard)
(manufactured by Technology Co., Ltd.). The oxygen permeability was defined as the gas permeation performance, and the separation coefficient, which is the ratio of the oxygen permeation rate to the nitrogen permeation rate, was used as the evaluation standard for the gas separation performance. (2) Adhesiveness A separately prepared porous support was placed on the surface of the ultrathin film B of the composite membrane for gas separation of the present invention, and the porous support was bonded with a pressure of 2 g/cm ² . The membrane was peeled off. The gas (oxygen or nitrogen) permeation rate of the composite membrane for gas separation after peeling was measured in the same manner as above,
The oxygen permeation rate and separation coefficient were evaluated based on the difference between before and after adhesion and peeling. (Example) Next, embodiments of the present invention will be described based on Examples. Example 1 9.5 parts by weight of polydimethylsiloxane (number average molecular weight of approximately 50,000) having silanol groups at both ends, 0.4 parts by weight of ethyl orthosilicate, and 0.1 parts by weight of Stanas 2-ethylhexoate were dissolved in cyclohexane to reduce the solid content. Adjust to 0.5wt%. This dilute solution was applied to a polysulfone porous support and heated to 120°C.
After drying by heating for 1 minute at room temperature, a composite membrane was prepared by drying at room temperature for 10 minutes. Next, poly(4-methylpentene-1) (trade name TPX-MX001, manufactured by Mitsui Petrochemicals) is dissolved in cyclohexene to adjust to 0.1 part by weight. This solution was spread on the water surface to form a thin film, and this thin film was supported on the thin film surface of a polydimethylsiloxane composite membrane prepared in advance to prepare a composite membrane for gas separation. The thickness of the poly(4-methylpentene-1) film was approximately 0.02 μm, and the thickness of the polydimethylsiloxane thin film was approximately 0.1 μm. Table 1 shows the results of measuring the oxygen permeation rate and oxygen/nitrogen separation coefficient of this composite membrane for gas separation. Despite the presence of a polydimethylsiloxane thin film, high gas permeability and high gas separation performance were achieved. Example 2 Polyphenylene oxide (weight average molecular weight approximately 50,000) is dissolved in benzene to prepare a 0.5 wt% solution. This solution is spread on the water surface to form a thin film. A polydimethylsiloxane composite membrane prepared by the same method as in Example 1 was supported on the surface of the thin film to prepare a composite membrane for gas separation. The thickness of the polyphenylene oxide thin film was approximately 0.04μ, and the thickness of the polydimethylsiloxane thin film was approximately 0.1μ. Table 1 shows the results of measuring the oxygen permeation rate and oxygen/nitrogen separation coefficient of this composite membrane for gas separation. Both gas permeability and gas separation are excellent. Example 3 A polysulfone porous support was applied to the thin film surface of the composite membrane for gas separation prepared in Example 1 at a pressure of 2 g/cm ²
Table 2 shows the results of measuring the oxygen permeation rate and the separation coefficient between oxygen and nitrogen of the composite membrane for gas separation after adhering it with the membrane and then peeling it off. Example 4 The results of adhesive peeling performed on the gas separation composite membrane prepared in Example 2 in the same manner as in Example 3 are shown in the table below.
Shown in 2. In both Examples 3 and 4, the gas permeability and gas separation properties did not change before and after the adhesive was peeled off, indicating that the present invention had good adhesive properties. Comparative Example 1 Poly(4-methylpentene-
1) Spread a 0.1wt% cyclohexene solution on the water surface,
A thin film was formed. This thin film was supported on a polysulfone porous support to prepare a composite membrane for gas separation.
The thickness of the poly(4-methylpentene-1) thin film of this composite film was about 0.02μ. Table 1 shows the results of measuring the oxygen permeation rate and oxygen/nitrogen separation coefficient of this composite membrane for gas separation. It can be seen that the composite membrane for gas separation in which the polydimethylsiloxane thin film prepared in Example 1 was interposed was not inferior in terms of gas permeability. Comparative Example 2 A 0.5 wt% benzene solution of polyphenylene oxide prepared in Example 2 is spread on a water surface to form a thin film, and the thin film is supported on a polysulfone porous support membrane to prepare a composite membrane for gas separation. The thickness of the polyphenylene oxide thin film was approximately 0.04μ.
Table 1 shows the results of measuring the oxygen permeation rate and oxygen/nitrogen separation coefficient of this composite membrane for gas separation. It can be seen that the composite membrane for gas separation in which the polydimethylsiloxane thin film prepared in Example 2 was interposed was not inferior in terms of gas permeability. Comparative Example 3 A polysulfone porous support was applied to the thin film surface of the composite membrane for gas separation prepared in Comparative Example 1 at a pressure of 2 g/cm ²
The oxygen permeation rate and the separation coefficient between oxygen and nitrogen of the composite membrane for gas separation that was bonded under pressure and then peeled off were measured and are shown in Table 2. Comparative Example 4 The composite membrane for gas separation prepared in Comparative Example 2 was bonded under pressure in the same manner as Comparative Example 3, and then peeled off.
The oxygen permeation rate and the separation coefficient between oxygen and nitrogen of the composite membrane for gas separation were measured and are shown in Table 2. It can be seen that in both Comparative Examples 3 and 4, the composite membranes for gas separation without a polydimethylsiloxane thin film had poor adhesion and lost gas separation performance. As is clear from the above, the composite membrane for gas separation of the present invention is easy to handle because the thin film layer B is difficult to peel off from the porous support A, and has excellent gas permeability and gas separation performance. Recognize.

[Table] *3 α: Separation coefficient

[Table] (Effects of the invention) The composite membrane for gas separation of the present invention has a porous support A
Ultrathin membrane B made of a polymer with high gas separation properties
In between, an ultra-thin film C made of polyorganosiloxane crosslinked with a tetrafunctional or higher functional silane crosslinking agent or a tetrafunctional or higher functional siloxane crosslinking agent is interposed, so due to the excellent adhesiveness and gas permeability of polyorganosiloxane, The following excellent effects can be obtained. (1) Composite membranes are easy to handle because the thin film does not peel off during use. (2) Both gas separation performance and gas permeation performance are extremely excellent.

Claims (1)

[Claims] 1 Between the porous support A and the ultrathin membrane B made of a polymer with high gas separation properties, an ultrathin membrane made of polyorganosiloxane crosslinked with a tetrafunctional or more functional silane crosslinking agent or a tetrafunctional or more functional siloxane crosslinking agent. A composite membrane for gas separation in which C is interposed.