Gas separation membrane and paint for forming gas separation membranes

Abstract

To provide a gas separation membrane that can improve gas permeability without impairing gas selectivity. [Solution] The gas separation membrane comprises a base polymer, silica fine particles, and a dispersant containing an amide, wherein the content of the amide-containing dispersant is 5 parts by weight or more per 100 parts by weight of the silica fine particles.

Description

Technical Field

[0001] The present invention relates to a gas separation membrane and a paint for forming a gas separation membrane, and more particularly to a gas separation membrane for separating carbon dioxide from other gases and a paint for forming a gas separation membrane.

Background Art

[0002] As a common long-term goal regarding climate change countermeasures, the Paris Agreement states that efforts should be made to keep the global average temperature rise well below 2°C compared to pre-industrial levels and to limit it to 1.5°C. In Japan, it has also been declared that carbon neutrality will be achieved by 2050.

[0003] For the realization of carbon neutrality, technologies for recovering carbon dioxide and performing storage or recycling are being developed. As technologies for separating and purifying carbon dioxide, absorption methods, adsorption methods, membrane separation methods, etc. have been proposed. In particular, the membrane separation method has advantages such as lower equipment investment costs and running costs compared to absorption methods and adsorption methods, and easier maintenance. The membrane separation method also has the advantage of being able to miniaturize equipment, making it possible to install separation equipment in ventilation equipment for buildings and exhaust equipment for factories, etc. to separate carbon dioxide.

[0004] As a gas separation membrane used for recovery, the use of an organic-inorganic hybrid material in which an inorganic filler is added to an organic compound has been studied. In an organic-inorganic hybrid material, it is expected that properties such as heat resistance of an inorganic compound can be imparted while maintaining properties such as flexibility of an organic compound, and a material having properties that cannot be obtained with each compound alone can be created.

[0005] Japanese Patent No. 6967230 discloses a gas separation membrane containing deformed silica nanoparticles. This gas separation membrane is characterized by containing polymer-added deformed silica nanoparticles in which a hyperbranched polymer or dendrimer polymer is added to the surface of the deformed silica nanoparticles and a matrix resin.

Prior Art Documents

[0006] [Patent Document 1] Patent No. 6967230 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In gas separation membranes made of organic-inorganic hybrid materials, gas permeation and separation occur through voids (pores) of approximately 1 nm or less in size that are formed at the interface between the organic and inorganic compounds. On the other hand, if micron-sized defects occur within the membrane, such as at the interface between the organic and inorganic compounds, the gas will pass through these defects, significantly reducing the separation performance.

[0008] The gas separation membrane described in Japanese Patent Publication No. 6967230 exhibits extremely high carbon dioxide permeability. However, the manufacturing process for the gas separation membrane described in the same publication is complex, as it requires pretreatment of the irregularly shaped silica nanoparticles with a silane coupling agent or the like in order to attach hyperbranched polymers or dendrimer polymers to the surface of the irregularly shaped silica nanoparticles.

[0009] The object of the present invention is to provide a gas separation membrane and a coating for forming a gas separation membrane that can improve gas permeability without impairing gas selectivity. [Means for solving the problem]

[0010] A gas separation membrane according to one embodiment of the present invention comprises a base polymer, silica fine particles, and a dispersant containing an amide, wherein the content of the amide-containing dispersant is 5 parts by weight or more per 100 parts by weight of the silica fine particles.

[0011] A coating for forming a gas separation membrane according to one embodiment of the present invention comprises a base polymer, silica fine particles, an amide-containing dispersant, and a solvent, wherein the content of the amide-containing dispersant is 5 parts by weight or more per 100 parts by weight of the silica fine particles. [Effects of the Invention]

[0012] According to the present invention, a gas separation membrane and a coating for forming a gas separation membrane can be obtained that can improve gas permeability without impairing gas selectivity. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a scanning electron microscope image of a cross-section of the gas separation membrane in Example 2. [Figure 2] Figure 2 is a scanning electron microscope image of a cross-section of the gas separation membrane of Comparative Example 3. [Modes for carrying out the invention]

[0014] The inventors conducted various studies on a gas separation membrane made of an organic-inorganic hybrid material in which silica nanoparticles are dispersed in a base polymer (an organic polymer that serves as a substrate). As a result, they found that by adding a predetermined amount or more of a dispersant containing an amide (hereinafter referred to as "amide-based dispersant"), the gas permeability of the gas separation membrane can be improved without impairing gas selectivity, as described below.

[0015] When silica nanoparticles are added to the base polymer without an amide-based dispersant, the strength of the base polymer is significantly reduced by the addition of the silica nanoparticles, making it difficult to form a self-supporting film. Furthermore, when a silane coupling agent is used instead of an amide-based dispersant, numerous silica aggregates approximately 100 μm in size are generated in the film, and cracks several hundred μm in size develop around these aggregates, making it difficult to achieve gas separation performance.

[0016] The inventors have discovered that by adding an amide-based dispersant to the base polymer, the formation of sub-millimeter-sized silica aggregates can be suppressed, and a self-supporting membrane with gas separation capabilities can be formed. Furthermore, the inventors have found that by increasing the amount of amide-based dispersant added, the gas permeability of the gas separation membrane can be improved.

[0017] In a gas separation membrane in which silica nanoparticles and an amide-based dispersant were added to a base polymer, numerous pores approximately 100 nm in size, which are not observed in conventional gas separation membranes, were formed at the interface between the base polymer and the silica nanoparticles. Furthermore, increasing the amount of amide-based dispersant added increased the number of these pores. From this, it is thought that in a gas separation membrane in which silica nanoparticles and an amide-based dispersant are added to a base polymer, gas permeability is improved by increasing the number of these pores without significantly impairing gas selectivity. It should be noted that the amide-based dispersant alone did not have the effect of improving gas permeability, and when only the amide-based dispersant was added to the base polymer without adding silica nanoparticles, the gas permeability of the gas separation membrane decreased.

[0018] The present invention was completed based on the above findings. Below, a gas separation membrane and a paint for forming a gas separation membrane according to one embodiment of the present invention will be described.

[0019] [Gas separation membrane] A gas separation membrane according to one embodiment of the present invention comprises a base polymer, silica fine particles, and a dispersant containing an amide, wherein the content of the dispersant containing the amide is 5 parts by weight or more per 100 parts by weight of the silica fine particles.

[0020] The gas separation membrane according to this embodiment is a gas separation membrane for separating carbon dioxide and other gases. More specifically, the gas separation membrane according to this embodiment is a gas separation membrane that selectively permeates carbon dioxide. The gas separation membrane according to this embodiment preferably has an ideal separation factor (the ratio of the permeation coefficient of carbon dioxide to the permeation coefficient of nitrogen) of 10 or more, more preferably 20 or more, and particularly preferably 26 or more.

[0021] (Base polymer) The base polymer is an organic polymer that serves as the substrate (matrix) of the gas separation membrane. The type of the base polymer is not particularly limited, and various ones can be selected from the organic polymers generally used in this field according to the environment of the equipment where the gas separation membrane is installed and the like. Examples of the organic polymers that can be used as the base polymer include, but are not limited to, polyimide, polysulfone, polyether, polydimethylsiloxane, poly-substituted acetylene, poly-4-methylpentene, natural rubber, and the like.

[0022] Among the above-mentioned organic polymers, the base polymer is preferably polyimide, and particularly preferably soluble polyimide. Among polyimides, those having a bulky substituent (such as a benzene ring, tetracarboxylic acid, fatty acid, etc.) in the polymer backbone and having a multi-branched structure are preferred.

[0023] (Silica fine particles) The silica fine particles exist in a dispersed state in the base polymer. The silica fine particles may be either dry silica or wet silica. The silica fine particles are preferably amorphous silica (silica with a non-uniform particle shape). The silica fine particles are preferably dry silica, and particularly preferably fumed silica.

[0024] The size of the silica nanoparticles is not particularly limited, but if they are extremely large, they may not function as a gas separation membrane. The size of the silica nanoparticles is, for example, 1 nm to 5 μm in average primary particle diameter (particle diameter calculated from BET specific surface area). The average primary particle diameter of the silica nanoparticles is preferably 1 nm to 1 μm, more preferably 1 to 500 nm, particularly preferably 1 to 100 nm, and most preferably 1 to 50 nm.

[0025] The silica nanoparticle content is not particularly limited, but for example, it is 0.1 to 70% by weight relative to the entire gas separation membrane. The higher the silica nanoparticle content, the greater the interface between the base polymer and the silica nanoparticles, and the more the gas permeability tends to improve. On the other hand, if the silica nanoparticle content is too high, the properties of the base polymer may be lost. The lower limit of the silica nanoparticle content is preferably 0.5% by weight, more preferably 1.0% by weight, more preferably 2.0% by weight, more preferably 5.0% by weight, more preferably 10.0% by weight, and more preferably 15.0% by weight. The upper limit of the silica nanoparticle content is preferably 60% by weight, more preferably 50% by weight, more preferably 40% by weight, and more preferably 30% by weight.

[0026] (Amide-based dispersants) Dispersants containing amides (hereinafter referred to as "amide-based dispersants") promote the dispersion of silica nanoparticles in the base polymer and suppress the aggregation of silica nanoparticles. Furthermore, amide-based dispersants form submicron-sized voids at the interface between the base polymer and the silica nanoparticles and within the aggregates, thereby improving the gas permeability of the gas separation membrane.

[0027] Examples of amide-based dispersants include Noptex E-D053 from Sunopco, Inc., BYK-W 996 and BYK-W 980 from BYK (BYK-Chemie GmbH), Disparon 1850, Disparon 1860, and Disparon DA-1401 from Kusumoto Chemical Co., Ltd., Amizole CME, Amizole SME, and Amizole PLME-A from Kawaken Fine Chemical Co., Ltd.

[0028] The gas separation membrane according to this embodiment contains 5 parts by weight or more of amide-based dispersant per 100 parts by weight of silica fine particles. By increasing the content of amide-based dispersant to 5 parts by weight or more per 100 parts by weight of silica fine particles, excellent gas permeability can be obtained.

[0029] In this embodiment, as described above, an amide-based dispersant is included in the gas separation membrane not only to disperse the silica nanoparticles, but also to form submicron-sized pores at the interface between the base polymer and the silica nanoparticles and within the aggregates. This amount of "5 parts by weight or more per 100 parts by weight of silica nanoparticles" is excessive for the purpose of dispersing silica nanoparticles in the base polymer. If the sole purpose is to disperse silica nanoparticles, the amount of amide-based dispersant should depend on the particle size of the silica nanoparticles, but 3 parts by weight per 100 parts by weight of silica nanoparticles would be sufficient. In this embodiment, the gas permeability of the gas separation membrane is improved by including an amount of amide-based dispersant that exceeds the amount normally added as a dispersant.

[0030] The higher the content of the amide-based dispersant, the greater the number of pores, and the better the gas permeability of the gas separation membrane. The lower limit of the amide-based dispersant content is preferably 10 parts by weight, more preferably 15 parts by weight, and even more preferably 20 parts by weight, per 100 parts by weight of silica fine particles. The amount of amide-based dispersant added to silica can be any amount, but if the content of amide-based dispersant relative to silica fine particles is extremely high, it may become difficult to produce an independent membrane. The upper limit of the amide-based dispersant content is preferably 200 parts by weight, more preferably 100 parts by weight, and particularly preferably 50 parts by weight, per 100 parts by weight of silica fine particles. However, if an independent membrane can be formed due to the structure of the base polymer, more amide-based dispersant may be added.

[0031] (vacancies, etc.) The gas separation membrane according to this embodiment has submicron-sized voids at the interface between the base polymer and the silica fine particles. In the gas separation membrane according to this embodiment, submicron-sized voids may also be formed inside the aggregate. In the gas separation membrane according to this embodiment, gas permeation and separation occur through these voids. If the voids are too large, permeability improves, but gas selectivity decreases significantly. If the voids are too small, the target gas cannot permeate, which is undesirable. The size of the voids is preferably 1 to 500 nm. The lower limit of the void size is more preferably 5 nm, and even more preferably 10 nm. The upper limit of the void size is more preferably 200 nm, and even more preferably 100 nm. Here, the size of the voids in the gas separation membrane is the average value of the equivalent circle diameter of the voids in a field of view of approximately 3 μm × 4 μm when observing the cross-section of the gas separation membrane at a magnification of approximately 3000x.

[0032] The gas separation membrane according to this embodiment preferably has a carbon dioxide permeability coefficient of 40 Barrer or higher. More preferably, the carbon dioxide permeability coefficient is 45 Barrer or higher, even more preferably 50 Barrer or higher, and even more preferably 55 Barrer or higher.

[0033] [Method for manufacturing gas separation membranes and paint for forming gas separation membranes] Next, an example of a method for manufacturing the gas separation membrane described above will be explained. The method for manufacturing the gas separation membrane according to this embodiment is not limited to this method.

[0034] First, the base polymer, silica fine particles, and amide-based dispersant described above are mixed with a solvent to produce a paint for forming gas separation membranes (hereinafter sometimes simply referred to as "paint").

[0035] The solvent can be any solvent that can dissolve or disperse the base polymer. The choice of solvent depends on the type of base polymer, but examples include water, lactams such as NMP, alcohols, ethers, ketones, hydrocarbons, and aromatic hydrocarbons. Depending on the type of base polymer, a solvent with good handling properties in terms of viscosity and solubility should be selected. If the viscosity is too high, it will be difficult to disperse the silica particles in subsequent processes; if it is too low, it will be difficult to adjust the paint composition. The amount of solvent should be adjusted as needed to achieve the appropriate viscosity of the paint.

[0036] The base polymer, silica nanoparticles, amide dispersant, and solvent may all be mixed at once, but it is preferable to first thoroughly mix the base polymer, silica nanoparticles, and solvent, and then add and mix the amide dispersant. Alternatively, the solvent, silica nanoparticles, and base polymer may be added as needed during the mixing process. These mixtures can be carried out using a general-purpose stirrer or mixer.

[0037] The manufactured paint is applied to the substrate and dried. Vacuum drying is preferred. This removes the solvent from the paint, yielding a gas separation membrane containing the base polymer, silica fine particles, and amide-based dispersant.

[0038] The gas separation membrane according to this embodiment does not require the silica fine particles to be surface-treated with a silane coupling agent or the like beforehand, and can be manufactured in a single-step dispersion process.

[0039] The gas separation membrane and gas separation membrane forming coating according to one embodiment of the present invention have been described above. According to this embodiment, a gas separation membrane and a gas separation membrane forming coating can be obtained that can improve gas permeability without impairing gas selectivity. [Examples]

[0040] The present invention will be described more specifically below with reference to examples. The present invention is not limited to these examples.

[0041] [Example 1] A coating for forming gas separation films was prepared containing 0.5 g of silica fine particles, 15.0 g of soluble polyimide varnish (2.0 g solids) as a base polymer, 0.14 g of amide-based dispersant (0.07 g solids), and 2.6 g of NMP as a solvent.

[0042] The silica nanoparticles used were dry silica manufactured by Tokuyama Corporation, Rheoroseal®, HG-09 (average primary particle size 22 nm).

[0043] For the soluble polyimide varnish, we used Spixeria HR-003, a polyimide varnish manufactured by Somar.

[0044] For the amide-based dispersant, we used BYK-W 996 manufactured by BYK Corporation.

[0045] A 120 μm thick layer of the manufactured gas separation membrane-forming coating was applied to a 250 μm thick PET film substrate. After drying at 80°C for 1 hour, the membrane was removed from the substrate. The removed membrane was fixed in a stainless steel frame and further dried at 120°C for 10 minutes, 180°C for 30 minutes, and 300°C for 1 hour to produce a gas separation membrane.

[0046] [Example 2] A gas separation membrane was manufactured in the same manner as in Example 1, except that the content of the amide-based dispersant was changed to 0.25 g (solid content 0.125 g).

[0047] [Comparative Example 1] A 120 μm thick layer of soluble polyimide varnish was applied to a 250 μm thick PET film substrate and dried at 80°C for 1 hour. The film was then removed from the substrate. The removed film was fixed in a stainless steel frame and further dried at 120°C for 10 minutes, 180°C for 30 minutes, and 300°C for 1 hour to produce a gas separation membrane.

[0048] [Comparative Example 2] A gas separation membrane was manufactured in the same manner as in Example 1, except that silica nanoparticles were not added.

[0049] [Comparative Example 3] A gas separation membrane was manufactured in the same manner as in Example 1, except that the content of the amide-based dispersant was changed to 0.03 g (solid content 0.015 g).

[0050] [evaluation] A gas permeability test was conducted on each of the manufactured gas separation membranes. The gas permeability test was performed using the differential pressure method (JIS K 7126-1) at 1 atmosphere and 25°C. The test results are shown in Table 1.

[0051] [Table 1]

[0052] In Table 1, the values ​​in the "Amount of Silica Fine Particles" column represent the weight ratio (weight %) of the silica fine particles to the total weight of the gas separation membrane. Furthermore, the values ​​in the "Amount of Dispersant" column for all but Comparative Example 2 represent the weight ratio of the amide-based dispersant to the weight of the silica fine particles (parts by weight of amide-based dispersant per 100 parts by weight of silica fine particles). For Comparative Example 2, the value in the "Amount of Dispersant" column represents the amount of amide-based dispersant (solid content).

[0053] As shown in Example 1, by incorporating silica microparticles and a predetermined amount or more of amide-based dispersant into the base polymer, it is possible to increase the carbon dioxide permeability coefficient while maintaining a high ideal separation coefficient (ratio of carbon dioxide permeability coefficient to nitrogen permeability coefficient) compared to cases where silica microparticles and amide-based dispersant are not included (Comparative Example 1) or where the amount of amide-based dispersant is small (Comparative Example 3). Furthermore, a comparison between Example 1 and Example 2 shows that the carbon dioxide permeability coefficient increases as the content of amide-based dispersant increases. In addition, Comparative Example 2 shows that even if only amide-based dispersant is added to the base polymer without adding silica microparticles, the carbon dioxide permeability coefficient does not increase, and is even smaller than in the case where no amide-based dispersant is added (Comparative Example 1).

[0054] Figure 1 is a scanning electron microscope image of a cross-section (a section parallel to the thickness direction) of the gas separation membrane of Example 2. In Figure 1, the black areas are voids. Figure 2 is a scanning electron microscope image of a cross-section (a section parallel to the thickness direction) of the gas separation membrane of Comparative Example 3. In Figure 1 (Example 2), there are many voids approximately 100 μm in size, whereas in Figure 2 (Comparative Example 3), there are almost no such voids.

[0055] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the invention.

Claims

1. Base polymer and Silica nanoparticles and A dispersant containing an amide, A gas separation membrane in which the amount of the dispersant containing the amide is 5 parts by weight or more per 100 parts by weight of the silica fine particles.

2. The gas separation membrane according to claim 1, having pores of size 1 to 500 nm at the interface between the base polymer and silica fine particles.

3. The gas separation membrane according to claim 1 or 2, wherein the base polymer is polyimide.

4. The gas separation membrane according to claim 1 or 2, wherein the amount of the dispersant containing the amide is 200 parts by weight or less per 100 parts by weight of the silica fine particles.

5. A gas separation membrane according to claim 1 or 2, wherein the ratio of the permeability coefficient of carbon dioxide to the permeability coefficient of nitrogen is 10 or more.

6. The gas separation membrane according to claim 1 or 2, wherein the content of the silica fine particles is 0.1 to 70% by weight of the entire gas separation membrane.

7. A gas separation membrane according to claim 1 or 2, wherein the carbon dioxide permeability coefficient is 40 Barre or more.

8. The gas separation membrane according to claim 1 or 2, wherein the average primary particle size of the silica fine particles is 1 nm to 1 μm.

9. Base polymer and Silica nanoparticles and A dispersant containing an amide, A solvent, and A paint for forming a gas separation membrane, wherein the amount of the dispersant containing the amide is 5 parts by weight or more per 100 parts by weight of the silica fine particles.

10. The gas separation film forming coating according to claim 9, wherein the amount of the dispersant containing the amide is 200 parts by weight or less per 100 parts by weight of the silica fine particles.

11. The gas separation film forming paint according to claim 9 or 10, wherein the content of the silica fine particles is 0.1 to 70% by weight of the total solid content.

12. The paint for forming a gas separation membrane according to claim 9 or 10, wherein the average primary particle size of the silica fine particles is 1 nm to 1 μm.

13. The paint for forming a gas separation membrane according to claim 9 or 10, wherein the base polymer is polyimide.

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