JPH04690B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a selective gas permeable membrane, mainly a blend membrane, which has good gas separation properties and excellent gas permeability. Configuration of conventional examples and their problems Recently, the progress of separation technology using membranes has been remarkable.
It has already been put to practical use on an industrial scale in some fields, such as seawater desalination and factory wastewater treatment. On the other hand, separation of mixed gases using organic polymer membranes has problems such as the low selectivity of the membrane, making it difficult to selectively obtain high-purity gases, and the inability to produce large amounts of gas due to the small amount of permeation. For this reason, there are few practical examples of gas separation using membranes. However, there are many fields where high purity gas is not necessarily required for the end use of gas. For example, in the case of oxygen, high purity oxygen is not required for combustion, medical breathing, etc. On the contrary, when high-purity oxygen is used for combustion, the combustion temperature becomes too high, causing damage to the furnace and the danger of flames. Furthermore, even in the case of medical use, high purity oxygen often causes disadvantages such as blindness in premature infants. Therefore, gas separation methods using membranes are advantageous in such fields. In the separation of oxygen from air by membranes, it is difficult to obtain air with high purity of oxygen in one stage of separation, but moderately oxygen-enriched air can be obtained relatively easily. In other words, in the membrane separation method, the oxygen concentration is approximately 25%.
It is possible to produce ~50% oxygen-enriched air directly from air, and there is no need to handle mixers or cylinders, making it a simple and economically advantageous method.
However, as has already been pointed out in several documents and patent publications regarding mixed gas separation using polymer membranes, in this case, the permeability coefficient of the polymer membrane for gases and the Mechanical strength and film thinning techniques are important issues. Among the currently reported polymer materials, natural rubber, synthetic rubber such as polybutadiene, polyolefin, and even more excellent silicone rubber are known to have relatively excellent gas permeability. Silicone rubber is better against almost all gases than any other polymeric material. However, the separation ratio of each gas becomes small, and when used to enrich air with oxygen, only low-concentration oxygen-enriched air of about 23% to 30% can be obtained. Therefore, in order to obtain oxygen-enriched air of 30% or more, a material with a higher separation ratio is required. One of them is a gas separation membrane mainly composed of polyolefin or diene polymer, which is disclosed in Japanese Patent Application Laid-open No. 56-92925. Poly 4-methylpentene-1, one of the materials shown in this publication, has an oxygen permeability coefficient of approximately 2.5×10 ^-9 cc・cm/cm ²・sec・cmHg
However, it is reduced to less than one-tenth that of silicone rubber.
The separation coefficient between oxygen and nitrogen increases to approximately 4.0.
Furthermore, polyphenylene oxide (hereinafter referred to as PPO) disclosed in US Pat. No. 3,350,844 also has comparable performance. Therefore, when these materials are used for oxygen enrichment, approximately 40% oxygen enriched air can be easily obtained. However, since the permeability coefficient is small, if the film thickness is the same as that of silicone rubber, the permeation flow rate will be less than one-tenth. In other words, when using such materials, it is important to reduce the film thickness in order to increase the permeation flow rate. Several proposals have already been made for this purpose. However, poly-4-methylpentene-
In the case of No. 1, the solubility in organic solvents is poor and film forming properties are extremely poor. On the other hand, PPO has good solubility and
It was found that the film forming properties were also good. but
Film formation using PPO alone has poor affinity with the support,
Because of the difficulty, the inventors filed Japanese Patent Application No. 57-107231.
It was possible to obtain certain characteristics by using the Sanderch-type composite membrane shown in the specification. Figure 1 shows the results and the permeation flow rate is 2.2×10 ^-2 cc/sec・cm ²・
Atm, the separation ratio α' of oxygen and nitrogen was 3.0. The permeation flow rate shown here can be used if the device is small-scale, but if the oxygen production cost is to be further reduced or the scale is increased, the device will become larger and the membrane properties will need to be further improved. As mentioned above, polymers with better separability than silicone rubber or silicone copolymers generally also have lower gas permeability coefficients. Therefore, when attempting to increase the gas permeation flow rate, thinning the film becomes even more important than in the case of silicone rubber or silicone copolymer. In the case of silicone rubber, it is necessary to add a filler or undergo vulcanization treatment to form a solid film, and it is said that the limit for obtaining a homogeneous film is about 10 μm. On the other hand, in the case of silicone copolymer, it is possible to achieve a thickness of about 0.1 μm since it does not require the same treatment as silicone rubber. The gas permeation flow rate corresponding to this latter silicone copolymer is reduced by using a polymer with high gas separation properties, such as poly-4-
If you try to obtain it with methylpentene-1, polyphenylene oxide, etc., it will be necessary to make it an ultra-thin film of about 0.01 μm. It is technically very difficult to produce such an ultra-thin and homogeneous polymer film. Purpose of the Invention The present invention has been made in view of the above points, and aims to obtain a selective gas permeable membrane that has high gas separation properties, a large permeation flow rate, and excellent film formation properties. be. Structure of the Invention The present invention uses a solution obtained by blending a condensation polymer containing a phenyl group in its main chain and a crosslinked silicone copolymer, and develops it on the water surface. It is a permeable membrane. Description of Examples Examples of the present invention will be described in detail below. The present inventors blended condensed polymers containing phenyl groups in their main chains, such as polyurethane, polysulfone, polycarbonate, and polyester, which are polymers with good gas separation properties, and a certain type of silicone copolymer. We have discovered that when fabricated by expansion, a composite membrane with extremely excellent permeability and high selectivity can be obtained. The condensation polymer containing a phenyl group in the main chain used here has the general formula (However, X is

【formula】

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【formula】

[Formula], and Y is selected from divalent or higher alcohol residues. ), the general formula for polyurethane is (However, Z is

【formula】

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Selected from [Formula]. R is selected from a hydrogen atom, a halogen atom, an alkyl group, and a halogenated alkyl group, and may be the same or different. ), the general formula is (However, Z is the same as above) or the general formula is (However, Z is the same as above). Silicone copolymers are disclosed in Japanese Patent Application Laid-Open No. 56-24019 by the present inventors,
-26506 Publication, JP-A-56-28605 Publication, Patent Application Sho
A crosslinked silicone copolymer having a structure containing a polyorganosiloxane chain or a phenol nucleus as shown in Nos. 56-112456 to 112460 is used. Generally, when blending two types of polymers, those with similar structures or properties have good compatibility, but other types of polymers usually have very poor compatibility. It is. However, despite having different molecular structures and different properties, the silicone copolymer and the condensation type polymer having phenyl groups in the main chain are highly compatible, and are compatible up to a silicone copolymer content of approximately 40%. dissolve A blend film of these polymers was prepared on a uniform glass plate by a casting method, and its gas permeation properties were measured by a low vacuum method. As a result, the gas permeability coefficient of the blend membrane prepared in this way increases as the silicone copolymer content increases, but on the contrary, the oxygen and nitrogen separation coefficient decreases, and at a silicone content of 30%, the gas permeability coefficient increases. It decreases to approximately α≒2.5. However, surprisingly, a film was formed on the water surface (Langmiure method) using a blend solution of the same composition by the method shown in JP-A-56-26506.
When composited with a support and measured its properties, it was found that the gas separation property was significantly increased to α≈3.4. This is presumed to be because the film structure differs significantly between the casting method and the Langmire method due to the difference in solvent evaporation rate during film formation. Further, the film forming properties at this time were very good, and the effective film thickness could be easily adjusted to about 500 Å. Hereinafter, specific examples of the present invention will be described in more detail together with comparative examples. Comparative example 1 The structural formula of condensation polymer A is 0.2 silicone copolymer obtained by reaction-polymerizing α, ω-2 functional polysiloxane to a mixture of 0.5 g of polysulfone (Mw≒42000) shown by , a phenolic resin having an aromatic ring in the main chain, and a terminal functional polymer. g
was dissolved in 40 ml of toluene, and a 180 μm blend film was created on a uniform glass plate using a casting method. As a result of measuring this gas permeation property using a low vacuum method, the oxygen permeability coefficient Po ₂ ≒3.5×10 ^-9 cc・cm/cm ²・sec・cmHg,
The separation coefficient α for oxygen and nitrogen was approximately 2.7. Example 1 A film was formed by Langmiur method using a solution having the same composition as in Comparative Example 1, and Jyuragard 2400 (manufactured by Polyplastics Co., Ltd.) was used as a support. When forming a composite between the support and the blend membrane, due to poor adhesion between the blend membrane and the support and to prevent pinholes in the blend membrane, as shown in Fig. 2, between the blend membrane 1 and the support 3. Then, silicone copolymer layers 2 and 4 were provided on the blend membrane 1 to form a composite of the support 3 and the blend membrane 1. At that time, the gas separation characteristics were significantly improved, and the permeation flow rate ratio of oxygen and nitrogen was α′ = 3.54.
It became. Also, the oxygen permeation flow rate is 4.12×10 ^-2
It showed high permeability of cc/seccm ² ×atm. Comparative Example 2 Polyurethane whose structural formula is shown below (Mw≒25000) 0.6g and the repeating unit is R-
0.3 g of a silicone copolymer of polyorganosiloxane obtained by polymerizing trifunctional organosiloxane, which is SiO _3/2 , was dissolved in 50 ml of toluene, and a blend film of 200 μm was prepared on a uniform glass plate by a casting method. The gas permeation characteristics were measured by a low vacuum method, and the oxygen permeability coefficient Po ₂ was approximately 7.32×10 ^-9 cc·cm/cm ² ·sec·cmHg, and the oxygen and nitrogen separation coefficient α was approximately 2.75. Example 2 A composite membrane was obtained in the same manner as in Example 1 using the solution of Comparative Example 2. As a result, the oxygen permeation flow rate is 5.7
At cc/sec·cm ² ·atm, the separation property was α'≈3.10 in terms of the permeation flow rate ratio of oxygen and nitrogen, and as in Example 1, the composite membrane had improved separation property and exhibited high gas permeability. In Example 1, the properties were shown for polysulfone, and in Example 2, the properties were shown for a blend film of polyurethane and silicone copolymer, but the properties were also shown for other condensation polymers containing phenyl groups in the main chain, such as polycarbonate and polyester. Similar properties are obtained. Effects of the Invention As described above, the present invention is a blend film produced by spreading on water surface using a solution obtained by blending a condensation polymer containing a phenyl group in the main chain and a crosslinked silicone copolymer. It is possible to obtain a selective gas permeable membrane that has a large gas permeation flow rate and a large separation coefficient between oxygen and nitrogen, and has excellent film formability.

[Brief explanation of drawings]

Figure 1 is a gas permeation characteristic diagram of a composite membrane of PPO and silicone copolymer according to the inventors' earlier application;
FIG. 2 is a sectional view showing the structure of a selective gas permeable membrane according to the present invention. 2, 4...Silicone copolymer, 3...Support.

Claims (1)

[Scope of Claims] 1. A selective gas permeable membrane mainly comprising a blend membrane produced by water surface development from a solution of a blend of a condensed polymer containing a phenyl group in its main chain and a crosslinked silicone copolymer. 2 Condensation type polymer has a general formula (However, X is selected from the group consisting of [Formula][Formula] [Formula][Formula] Selective gas permeable membrane according to scope 1. 3 Condensation type polymer has a general formula (However, X is selected from the group consisting of: [Formula] [Formula] [Formula] [Formula] The selective gas permeable membrane according to claim 1, which is a polycarbonate represented by: 4 General formula for condensation polymers (However, X is selected from the group consisting of: [Formula] [Formula] [Formula] [Formula] The selective gas permeable membrane according to claim 1, which is a polysulfone represented by: 5. The selective gas permeable membrane according to claim 1, wherein the crosslinked silicone copolymer contains a polyorganosiloxane chain or a phenol nucleus. 6. Claim 1, in which a multilayer film in which a blend film is sandwiched between silicone copolymers is formed on a support.
Selective gas permeable membranes as described in Section.