Carbon dioxide separation membrane and production method for carbon dioxide separation membrane

Abstract

Provided is a carbon dioxide separation membrane that has good gas separation performance and excellent durability when rolled into a roll shape.　This carbon dioxide separation membrane has a separation layer and a porous layer adjacent to the separation layer, has a resin component mainly composed of a cellulose-based resin, and contains 5-50 mass% of at least one type of fine particles with respect to the whole of the resin component and the fine particles. The separation layer and the porous layer are the same matrix. The cellulose-based resin preferably has a substituent with 3 or more carbon atoms, and the fine particle content in the separation layer is preferably 10-40 mass%, inclusive.

Description

Carbon dioxide separation membrane and method for manufacturing a carbon dioxide separation membrane

[0001] This disclosure relates to a carbon dioxide separation membrane and a method for manufacturing a carbon dioxide separation membrane. More specifically, this disclosure relates to a carbon dioxide separation membrane that has good gas separation performance and excellent durability when wound into a roll, and a method for manufacturing such a carbon dioxide separation membrane.

[0002] Carbon dioxide (CO2) is a greenhouse gas. ２ The development of technologies for efficiently separating and recovering carbon dioxide (CO2) is a critical industrial and environmental challenge. One known CO2 separation and recovery technology is membrane separation using resin. In CO2 separation using resin membranes, carbon dioxide is first adsorbed onto the surface of the resin. The adsorbed carbon dioxide is thought to dissolve inside the resin and then pass through the gaps in the resin's molecular chains. Because the ease of adsorption and dissolution on the resin surface differs depending on the type of gas, there is a difference in permeability between carbon dioxide and other gases, allowing them to be separated.

[0003] It is generally known that there is a trade-off between the selective separation and permeability of carbon dioxide in a separation membrane. A pressure difference is required to permeate carbon dioxide, and energy is needed for pressurization. Higher permeability means less energy is needed for pressurization. Therefore, from the perspective of reducing the total cost of carbon dioxide separation and recovery, permeability is more important than selective separation in order to reduce the energy required for pressurization.

[0004] The thinner the separation membrane, the higher its permeability. However, if the separation membrane is too thin, it becomes difficult to handle. Therefore, a method has been devised in which a thin gas separation functional layer is coated onto a porous support to form a composite membrane. By making the separation membrane a laminate of a porous support layer and a thin gas separation functional layer, it is possible to increase permeability while maintaining mechanical strength.

[0005] One method for forming a laminate consisting of a porous support layer and a thin gas separation functional layer is to form an asymmetric porous membrane from a resin solution using a phase separation method. This asymmetric porous membrane has a dense layer that contributes to separation and a porous layer that functions as a support layer responsible for mechanical strength.

[0006] In recent years, techniques have been disclosed to further improve permeability by adding fine particles to carbon dioxide separation membranes (see, for example, Patent Documents 1 and 2).

[0007] Japanese Patent Publication No. 2015-160205 Japanese Patent Publication No. 2013-027520

[0008] On the other hand, carbon dioxide separation membranes are usually transported and stored in a rolled state. However, when conventional carbon dioxide separation membranes are stored in a rolled state, there is a problem in that the gas separation performance of the carbon dioxide separation membrane deteriorates due to pressure, tension, and even minute vibrations during storage.

[0009] This disclosure has been made in view of the above-mentioned problems and circumstances. The problem to be solved by this disclosure is to provide a carbon dioxide separation membrane that has good gas separation performance and excellent durability when wound into a roll shape, and a method for manufacturing such a carbon dioxide separation membrane.

[0010] The Discloser has conducted thorough investigations to solve the above problems. As a result, the Discloser has found that the above problems can be solved by forming a carbon dioxide separation membrane having a separation layer on the surface side and a porous layer on the substrate side through a drying shrinkage operation of a web containing a cellulose resin, a good low-boiling point solvent, a poor high-boiling point solvent, and fine particles, and has made this disclosure. In other words, the above problems related to this disclosure are solved by the following means.

[0011] 1. A carbon dioxide separation membrane having a separation layer and a porous layer adjacent to the separation layer, having a resin component mainly composed of a cellulose resin, containing at least one type of fine particles in an amount of 5 to 50% by mass relative to the total amount of the resin component and the fine particles, wherein the separation layer and the porous layer are the same matrix.

[0012] 2. The carbon dioxide separation membrane according to item 1, wherein the cellulose resin has substituents having 3 or more carbon atoms.

[0013] 3. The carbon dioxide separation membrane according to paragraph 1, wherein the content of the fine particles in the separation layer is 10% by mass or more and 40% by mass or less.

[0014] 4. A method for producing a carbon dioxide separation membrane, comprising: a coating step of applying a liquid composition containing a cellulose resin, a good solvent, a poor solvent, and fine particles to a substrate to form a web; a drying step of vaporizing the good solvent and the poor solvent from the web to form a carbon dioxide separation membrane having a separation layer and a porous layer adjacent to the separation layer; and a winding step of winding up the carbon dioxide separation membrane, wherein the ratio of the mass of the poor solvent to the total mass of the good solvent and the poor solvent in the liquid composition is 20 to 60%, the good solvent has a lower boiling point than the poor solvent, and the drying step is a step of vaporizing the good solvent and the poor solvent to dry and shrink the web, forming a carbon dioxide separation membrane having the separation layer on the surface side and the porous layer on the substrate side, with the separation layer and the porous layer being the same matrix.

[0015] 5. The method for producing a carbon dioxide separation membrane according to paragraph 4, wherein the temperature difference between the boiling point of the poor solvent and the boiling point of the good solvent is 50°C or more.

[0016] 6. The method for producing a carbon dioxide separation membrane according to paragraph 4, wherein the in-plane shrinkage rate when the web is dried and shrunk is 10% or more.

[0017] 7. The method for producing a carbon dioxide separation membrane according to item 4, wherein the cellulose resin has substituents having 3 or more carbon atoms.

[0018] 8. The method for producing a carbon dioxide separation membrane according to item 4, wherein the content of the fine particles in the separation layer is 10% by mass or more and 40% by mass or less.

[0019] The carbon dioxide separation membrane of this disclosure is a carbon dioxide separation membrane that has good gas separation performance and excellent durability when wound into a roll. The method for manufacturing the carbon dioxide separation membrane of this disclosure can be used to manufacture such a carbon dioxide separation membrane.

[0020] Although the mechanism of action or mechanism of the effects of this disclosure is not clearly defined, it is presumed to be as follows.

[0021] Conventionally, carbon dioxide separation membranes were manufactured by dissolving a resin in a liquid composition using only a good solvent, coating it onto a porous support to form a film, and then drying it to form a separation layer. In this method, the solvent is vaporized while the liquid composition is constrained (adhered) to the porous support, which suppresses shrinkage due to drying and generates stress in the carbon dioxide separation membrane. When the liquid composition contains fine particles, stress concentrates at the interface between the resin and the fine particles, making it easy for cracks ranging in size from a few micrometers to several hundred micrometers to form from this point. Hereafter, the size of a few micrometers to several hundred micrometers may be referred to as a size of approximately a micrometer. These cracks of approximately a micrometer size can also be called interface cracks. These cracks are even more likely to occur when the carbon dioxide separation membrane is rolled up, due to the pressure and tension applied to the membrane, as well as minute vibrations during storage. Thus, conventional carbon dioxide separation membranes had poor durability when rolled up. Furthermore, if a cracked membrane is used for gas separation, all gases, regardless of type, will permeate the membrane uniformly through the crack. In other words, a membrane in this condition leaks gas and has poor gas separation performance. As described above, conventional porous supports, along with the separation layer, were components of carbon dioxide separation membranes.

[0022] In contrast, when a carbon dioxide separation membrane is prepared from a liquid composition containing a cellulose resin, a good solvent with a low boiling point, a poor solvent with a high boiling point, and fine particles, by vaporizing the good solvent and the poor solvent, it is presumed that a carbon dioxide separation membrane with good gas separation properties and excellent durability when wound into a roll can be obtained in the following manner.

[0023] Since the poor solvent contained in the liquid composition does not dissolve the resin, the liquid composition forms a sea-island structure in which particles of the poor solvent are dispersed within the resin. Here, the liquid composition is applied to a substrate to form a film-like structure, which then becomes a web. At this time, it is preferable that the substrate is a flat surface that maintains its horizontal orientation. The web is then heated and dried on the substrate, and further dried in a drying process until a predetermined solvent content is reached, thereby forming a carbon dioxide separation membrane.

[0024] When the web is heated and dried, a good solvent with a low boiling point moves to the surface of the web, increasing the concentration of the good solvent near the surface, and then vaporizing from there. Therefore, it is presumed that a separation layer without pores is formed on the surface of the web as the good solvent vaporizes. Here, when we refer to the surface side of a film or web, we mean the side of the film or web that is opposite to the side that is in contact with the substrate. In this specification, even after the film has been peeled from the substrate, the side opposite to the side that was attached to the substrate may also be referred to as the surface side of the film.

[0025] Then, as the poor solvent primarily vaporizes, the poor solvent forming the island portions of the sea-island structure is removed, and pores are formed in those island portions. It is presumed that the formation of these pores creates a porous layer on the substrate side. As the web dries, the separation layer and porous layer described above are formed, so it is presumed that a carbon dioxide separation membrane is formed that has a separation layer on the surface side and a porous layer on the substrate side.

[0026] Thus, in the process of forming a carbon dioxide separation membrane from a liquid composition via a web, a porous layer is formed on the substrate side of the web. As a result, the pores in the porous layer formed at the interface with the substrate become depressions that do not come into contact with the substrate at that interface. This reduces the contact area between the substrate and the web. Therefore, it is presumed that the frictional force between the substrate and the web decreases, and the web dries while shrinking in plane without adhering to the substrate.

[0027] Furthermore, as described above, the web does not adhere to the substrate but shrinks in plane while drying, making it less likely for stress to be generated in the resulting carbon dioxide separation membrane. It is also presumed that no stress remains in the separation layer containing the fine particles. Therefore, it is presumed that when the carbon dioxide separation membrane is rolled up, the occurrence of cracks of approximately micrometer size in the separation layer containing the fine particles can be suppressed. This is presumed to result in a carbon dioxide separation membrane with excellent durability when rolled up. Here, when we say that the web or membrane shrinks in plane, it means that the web or membrane shrinks so that its surface area becomes smaller.

[0028] Furthermore, in the method for manufacturing a carbon dioxide separation membrane according to this disclosure, a porous layer is formed on one side of a single membrane (web), and a separation layer is formed on the other side. As a result, the separation layer and the porous layer are dried and shrunk simultaneously. This is a completely different method from conventional separation membranes, which involve applying a liquid composition to the surface of a dried porous membrane and drying it to obtain a separation membrane. Therefore, it is presumed that no stress is generated between the separation layer and the porous layer, and no stress remains within either the separation layer or the porous layer. This is presumed to result in a carbon dioxide separation membrane with excellent durability when rolled up. Here, when referring to a single membrane or a single web as described above, it means a membrane or web composed of a single continuous matrix. Such a matrix is ​​a matrix without an interface.

[0029] Thus, the carbon dioxide separation membrane of this disclosure has an asymmetric porous membrane, in which a separation layer is formed on one side and a porous layer is formed on the other side during the process of forming a single membrane. This is a different structure from a separation membrane with a structure in which multiple membranes are bonded together (including membranes with a structure of two or more layers formed by coating a dry membrane with a liquid composition and drying it). Separation membranes with a structure in which multiple membranes are bonded together include membranes with a structure of two or more layers formed by coating a dry membrane with a liquid composition and drying it.

[0030] Furthermore, the separation layer contains fine particles because the liquid composition contains fine particles. In the carbon dioxide separation membrane of this disclosure, a gap of several angstroms to several hundred angstroms in size is formed at the interface between the resin contained in the separation layer and the fine particles, and is small enough not to cause gas leakage. Hereinafter, a size of several angstroms to several hundred angstroms may be referred to as a size of approximately angstroms. It is presumed that the carbon dioxide permeability and gas separation performance of the carbon dioxide separation membrane of this disclosure are improved by this gap. Furthermore, when the web shrinks in plane, a force acts on the fine particles to align in the thickness direction of the web. As a result, the fine particles are arranged to align in the thickness direction of the resulting carbon dioxide separation membrane. Therefore, the gap of approximately angstroms in size formed at the interface between the resin and the fine particles is formed to extend in the thickness direction of the carbon dioxide separation membrane. It is presumed that this can further improve the carbon dioxide permeability and gas separation performance of the carbon dioxide separation membrane of this disclosure.

[0031] This is a schematic cross-sectional view showing a portion of the cross-section of one embodiment of the carbon dioxide separation membrane according to this disclosure. This is a flowchart showing one embodiment of the method for manufacturing the carbon dioxide separation membrane according to this disclosure. This is a schematic diagram showing a manufacturing apparatus used in one embodiment of the method for manufacturing the carbon dioxide separation membrane according to this disclosure.

[0032] The following describes specific forms for implementing this disclosure. However, this disclosure is not limited to the following embodiments, and it should be understood that appropriate design modifications, improvements, etc., may be made based on the ordinary knowledge of a person skilled in the art, without departing from the spirit of this disclosure.

[0033] In this specification, "~" is used to mean that the numbers before and after it are included as the lower and upper limits, respectively.

[0034] 1. Carbon Dioxide Separation Membrane One embodiment of the carbon dioxide separation membrane of this disclosure is an asymmetric porous carbon dioxide separation membrane 10 having a separation layer 11 and a porous layer 12 adjacent to the separation layer. The carbon dioxide separation membrane 10 of this embodiment has a resin component mainly composed of a cellulose resin. The carbon dioxide separation membrane 10 of this embodiment contains at least one type of fine particles in an amount of 5 to 50% by mass relative to the resin component and the total amount of fine particles. The separation layer 11 and the porous layer 12 are the same matrix. Figure 1 is a schematic cross-sectional view schematically showing a part of one embodiment of the carbon dioxide separation membrane according to this disclosure.

[0035] In this specification, "matrix" refers to the continuous phase formed by resin components that constitute a membrane or web. The carbon dioxide separation membrane of this disclosure has a structure in which fine particles and pores are scattered within the continuous phase matrix. The statement that the separation layer and the porous layer are the same matrix means that the resin components (matrix) filling the spaces between multiple fine particles in the separation layer and the resin components (matrix) surrounding the pores in the porous layer are composed of the same material. This is because a single resin composition is separated into two layers with the same composition but different shapes due to the influence of solvents with different properties during the drying process after coating. Therefore, the composition of the separation layer (dense layer) and the porous layer can be analyzed using commonly used chemical analysis methods, and their identity can be determined at a level of instrumental accuracy. For example, infrared spectroscopy (IR), nuclear magnetic resonance (NMR), and pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) are used to analyze the resin composition. Thermogravimetric analysis (TG-DTA) is also used as a method to determine the identity of different samples. Therefore, in this disclosure, the same resin component (matrix) is continuously present from the separation layer to the porous layer, and there is no interface. The fact that the matrix is ​​continuous from the separation layer to the porous layer and there is no interface can be confirmed by SEM imaging. Furthermore, the statement that the separation layer and the porous layer are the same matrix can also be said to mean that the carbon dioxide separation membrane formed from a single matrix as a whole has a structure in which the separation layer and the porous layer are located inside.

[0036] Further, a carbon dioxide separation membrane in which the separation layer and the porous layer are formed of the same matrix is generally formed from a liquid composition via a web into a single carbon dioxide separation membrane by a single coating application. As a result, the entire carbon dioxide separation membrane is formed of one continuous matrix as a whole. Accordingly, the porous layer and the dense non-porous layer (separation layer) are formed of the same matrix. As used herein, the term "dense layer" is a concept encompassing not only layers that are entirely dense, but also layers that have dense regions contributing to gas separation while containing pores and are capable of gas separation as a whole. Furthermore, the term "dense" means dense to a degree that contributes to gas separation.

[0037] As used herein, the statement that the separation layer and the porous layer are adjacent means that there is no intermediate layer, adhesive layer or the like between the separation layer and the porous layer, and the separation layer and the porous layer are in direct contact with each other.

[0038] It can also be stated that the carbon dioxide separation membrane of the present embodiment is an asymmetric porous membrane. An asymmetric porous membrane is a membrane in an asymmetric porous state. As used herein, the term "asymmetric porous membrane" means a membrane that comprises a porous layer and a dense non-porous layer, wherein the porous layer and the dense layer are formed of the same matrix. The carbon dioxide separation membrane of the present disclosure is composed of a single matrix for the entire membrane, where one surface side is a non-porous separation layer and the other surface side is a porous layer, thereby being asymmetric in the thickness direction.

[0039] As used herein, the porous layer is a layer having pores. The average pore diameter of the pores is, for example, 0.005 to 10 µm, preferably 0.01 to 1 µm. The porosity (void fraction) is 20 to 90%, preferably 30 to 80%. The pore diameter and porosity can be determined, for example, by image analysis from a cross-sectional photograph (SEM) of the separation membrane.

[0040] Furthermore, the separation layer, which is a dense non-porous layer, is a layer capable of selectively permeating carbon dioxide contained in a mixed gas, and thus refers to a region other than the porous layer in the asymmetric membrane in the case of the present disclosure.

[0041] The carbon dioxide separation membrane of the present embodiment has the configuration as described above, and therefore is a carbon dioxide separation membrane that has favorable gas separation performance and is excellent in durability when wound into a roll.

[0042] The carbon dioxide separation membrane of the present embodiment may be composed only of a separation layer and a porous layer.

[0043] From the viewpoint of handleability, the thickness of the carbon dioxide separation membrane is preferably 10 to 500 μm, and more preferably 30 to 250 μm.

[0044] (Cellulose-based resin) The carbon dioxide separation membrane of the present embodiment includes a resin component containing a cellulose-based resin as a main component. Here, the term "main component" refers to a component that is contained in an amount of 60% by mass or more based on the entire resin component. The cellulose-based resin is preferably a cellulose ester resin. The cellulose-based resin is contained in the carbon dioxide separation membrane as a resin component, and these resin components constitute a matrix.

[0045] The cellulose ester resin preferably has a structure represented by the following general formula (1).

[0046]

[0047] In general formula (1), R １ , R ２ and R ３ are each independently a hydrogen atom or an acyl group. n represents the degree of polymerization.

[0048] The degree of polymerization n is the number of each repeating structure, and is, for example, about 20 to 500, preferably about 81 to 500, more preferably about 85 to 400, and particularly preferably about 90 to 250. R in each repeating structure １ , R ２ and R ３ may be the same or different.

[0049] In the cellulose ester resin represented by the above general formula (1), R １ , R ２ and R ３At least one of the groups is preferably an acyl group having three or more carbon atoms. Examples of acyl groups having three or more carbon atoms include propionyl group, butyryl group, pentanoyl (valeryl) group, hexanoyl group, heptanol group, octanoyl group, nonanoyl group, decanoyl group, undecanoyl group, dodecanoyl group, etc. Of the acyl groups having three or more carbon atoms, propionyl group or butyryl group is preferred.

[0050] Specific examples of cellulose ester resins include diacetylcellulose, triacetylcellulose, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate.

[0051] The carbon dioxide separation membrane of this embodiment may contain, as a resin component other than cellulose-based resin, cycloolefin resin, polyester resin, polyimide resin, polyamide resin, polystyrene resin, acrylic resin, polysulfone resin, polyethylene resin, polypropylene resin, cellophane, vinyl resin, polycarbonate resin, polyarylate resin, polyetherketone resin, polyetherketoneimide resin, fluororesin, etc.

[0052] Examples of polyester resins include polyethylene terephthalate resin and polyethylene naphthalate resin.

[0053] Examples of acrylic resins include polymethyl methacrylate resin.

[0054] Polysulfone resin contains polyethersulfone.

[0055] Examples of vinyl resins include polyvinylidene chloride resin, polyvinyl alcohol resin, ethylene vinyl alcohol resin, syndiotactic polystyrene resin, cycloolefin resin, and polymethylpentene resin.

[0056] In addition to the resin components described above, the carbon dioxide separation membrane of this embodiment may also contain organosilicon compounds (silicone) in the matrix to improve the smoothness of the dense layer surface. Furthermore, small amounts of nano-sized fibrous compounds, such as cellulose nanofibers, may be included to improve the mechanical strength of the dense layer and porous layer.

[0057] (Fine particles) The carbon dioxide separation membrane of this embodiment contains at least one type of fine particles in an amount of 5 to 50% by mass relative to the total resin component and fine particles. Preferably, the carbon dioxide separation membrane of this embodiment contains at least one type of fine particles in an amount of 10 to 40% by mass, and more preferably 15 to 30% by mass, relative to the total resin component and fine particles. Because the carbon dioxide separation membrane of this embodiment contains at least one type of fine particles in this range, the gas separation performance of the carbon dioxide separation membrane is good, and the durability when the carbon dioxide separation membrane is wound into a roll is excellent. If the content of the at least one type of fine particles is less than 5% by mass relative to the total resin component and fine particles, the gas separation performance of the carbon dioxide separation membrane will decrease, which is undesirable. If the content of the at least one type of fine particles is more than 50% by mass relative to the total resin component and fine particles, the gas separation performance of the carbon dioxide separation membrane will decrease, and the durability of the membrane will decrease, which is undesirable.

[0058] The fine particles contained in the carbon dioxide separation membrane of this embodiment are preferably at least one of silica particles and zeolite particles.

[0059] The fine particles may have pores. In that case, the average pore size is, for example, 0.1 nm to 5 nm. Specific examples of fine particles include silica particles such as AEROSIL® R972V from the "AEROSIL®" series manufactured by Nippon Aerosil Co., Ltd. Furthermore, an aggregate having a distinctive shape in which small amounts of silica particles are linked together, known as a pearl necklace shape, is, for example, Snowtex® PS-S from Nissan Chemical Corporation. In this disclosure, pearl necklace-shaped silica fine particles are preferable because they facilitate the creation of a channel for carbon dioxide generated at the resin-fine particle interface in the separation membrane.

[0060] The method for producing silica particles is not particularly limited and can be produced by known methods, for example, as described in "Production and Application Trends of Silica Particles" (CMC Publishing, published December 25, 2023, supervised by Mitsumasa Kimata). The method for producing olite particles is not particularly limited and can be produced by known methods, for example, as described in detail in "The Science and Engineering of Zeolites" (Kodansha Scientific Edition, published July 10, 2000, edited by Yoshio Ono and Takeaki Yashima).

[0061] The average particle size of the fine particles is preferably 5 to 200 nm, more preferably 10 to 100 nm, and particularly preferably 15 to 50 nm. By setting the average particle size of the fine particles within this range, the gas separation performance of the carbon dioxide separation membrane is improved, and the durability of the carbon dioxide separation membrane when wound into a roll is also improved. If the particle size is smaller than 5 nm, the gas separation performance of the carbon dioxide separation membrane may decrease. If the particle size is larger than 200 nm, the gas separation performance of the carbon dioxide separation membrane may decrease, as may the durability of the membrane.

[0062] The average particle size of microparticles is determined by taking a cross-sectional image of the microparticles using a transmission electron microscope (TEM) and calculating the area of ​​the identified microparticles through image processing. The diameter of the circle with the same area as the calculated area is taken as the particle size of the identified microparticles. Then, an arbitrary number of microparticles (for example, 10) are selected and their average value is considered to be the particle size of all existing microparticles.

[0063] It is preferable that the fine particles include pearl necklace-shaped particles. The inclusion of pearl necklace-shaped particles makes it easier for the fine particles to align in the thickness direction of the carbon dioxide separation membrane, thereby improving the gas separation performance of the carbon dioxide separation membrane. An example of pearl necklace-shaped particles is Snowtex®, manufactured by Nissan Chemical Corporation.

[0064] 1-1. Separation Layer The carbon dioxide separation membrane of this embodiment has a separation layer with the same matrix as the porous layer. The resin components, non-resin components, etc. contained in the separation layer are the same as the resin components, non-resin components, etc. contained in the carbon dioxide separation membrane described above.

[0065] The separation layer contains fine particles. The conditions of the fine particles contained in the separation layer are the same as those of the fine particles described above.

[0066] The thickness of the separation layer is preferably 0.05 to 5 μm, and more preferably 0.2 to 2 μm. Because the thickness of the separation layer is within this range, the carbon dioxide separation membrane of this embodiment has better gas separation performance. If the thickness of the separation layer is less than 0.05 μm, the durability of the membrane may decrease significantly. If the thickness of the separation layer is greater than 5 μm, the gas permeability of the carbon dioxide separation membrane decreases, and the processing capacity of the gas to be separated may decrease significantly.

[0067] The thickness of the separation layer is determined by taking images of the separation membrane cross-section with an electron microscope (SEM) and analyzing the images.

[0068] 1-2. Porous Layer The carbon dioxide separation membrane of this embodiment has a porous layer, which helps maintain mechanical strength and suppress damage to the separation layer.

[0069] The thickness of the porous layer is preferably 10 to 300 μm, and more preferably 20 to 200 μm. Because the thickness of the porous layer is within this range, the carbon dioxide separation membrane of this embodiment maintains its mechanical strength and can suppress damage to the separation layer. If the thickness of the porous layer is less than 10 μm, the mechanical strength of the carbon dioxide separation membrane will decrease, and the durability of the membrane may also decrease. If the thickness of the porous layer is greater than 300 μm, the gas permeability performance of the carbon dioxide separation membrane may decrease significantly. In addition, the carbon dioxide separation membrane may become too thick, making it inconvenient to handle.

[0070] 2. Method for Manufacturing a Carbon Dioxide Separation Membrane One embodiment of the method for manufacturing a carbon dioxide separation membrane according to this disclosure, as shown in Figure 2, comprises a coating step S01, a drying step S02, and a winding step S03. The coating step S01 is a step of applying a liquid composition containing a cellulose resin, a good solvent, a poor solvent, and fine particles to a substrate to form a web. The drying step S02 is a step of vaporizing the good solvent and the poor solvent from the web to form a carbon dioxide separation membrane having a separation layer and a porous layer adjacent to the separation layer. The winding step S03 is a step of winding up the carbon dioxide separation membrane. In the method for manufacturing a carbon dioxide separation membrane of this embodiment, the ratio of the mass of the poor solvent to the total mass of the good solvent and the poor solvent in the liquid composition is 20 to 60%. In the method for manufacturing a carbon dioxide separation membrane of this embodiment, the good solvent has a lower boiling point than the poor solvent. In the method for manufacturing a carbon dioxide separation membrane of this embodiment, the separation layer contains fine particles. The method for manufacturing a carbon dioxide separation membrane according to this embodiment involves a drying step S02 in which a good solvent and a poor solvent are vaporized to dry and shrink the web, thereby forming a carbon dioxide separation membrane having a separation layer on the surface side and a porous layer on the substrate side, where the separation layer and the porous layer are the same matrix. The carbon dioxide separation membrane of this embodiment can be manufactured by the method for manufacturing a carbon dioxide separation membrane according to this embodiment. Figure 2 is a flowchart showing one embodiment of the method for manufacturing a carbon dioxide separation membrane according to this disclosure.

[0071] The method for manufacturing a carbon dioxide separation membrane in this embodiment involves vaporizing a good solvent and a poor solvent during the drying process to form a carbon dioxide separation membrane while drying and shrinking the web. The resulting carbon dioxide separation membrane has a separation layer on the surface side and a porous layer on the substrate side, with the separation layer containing fine particles, and the separation layer and the porous layer being the same matrix. Therefore, the resulting carbon dioxide separation membrane has good gas separation performance and excellent durability when wound into a roll.

[0072] Figure 3 is a schematic diagram showing the manufacturing apparatus used in this embodiment. The carbon dioxide separation membrane manufacturing apparatus 1 of this embodiment includes a coating device 101, a drying device 102, a peeling device 103, and a winding device 105.

[0073] 2-1. Coating Process In the method for manufacturing a carbon dioxide separation membrane of this embodiment, the coating process is a process of forming a web by coating a substrate with a liquid composition containing a cellulose resin, a good solvent, a poor solvent, and fine particles, as described above. It is preferable to use a coating apparatus 101 in the coating process. When coating a substrate with a liquid composition, methods include spraying it onto the substrate or casting it onto the substrate using a casting die. On the other hand, when coating a sheet-shaped substrate, methods include using an applicator or using a spin coater to spread the coating to a certain film thickness.

[0074] (Liquid composition) In the method for producing a carbon dioxide separation membrane of this embodiment, the liquid composition contains a cellulose resin, a good solvent, a poor solvent, and fine particles. The conditions for the cellulose resin and fine particles are the same as those for the cellulose resin and fine particles in the description of one embodiment of the carbon dioxide separation membrane according to the present disclosure.

[0075] The content of cellulose-based resin in the liquid composition is preferably 2 to 30% by mass, and more preferably 5 to 15% by mass. A cellulose-based resin content within this range ensures desirable film thickness and uniformity after drying. If the cellulose-based resin content in the liquid composition is less than 2% by mass, the required film thickness may not be achieved. If the cellulose-based resin content in the liquid composition exceeds 30% by mass, a decrease in surface uniformity and film thickness distribution may occur.

[0076] The content of fine particles in the liquid composition is preferably 0.2 to 30% by mass, and more preferably 0.5 to 15% by mass. This range of fine particle content ensures a viscosity suitable for coating and a uniform film surface after drying. If the fine particle content in the liquid composition is less than 0.2% by mass, the slipperiness of the roll after drying may deteriorate. If the fine particle content in the liquid composition exceeds 30% by mass, aggregation of fine particles may occur within the resin composition, resulting in uneven coating.

[0077] The ratio of the mass of the poor solvent to the total mass of the good solvent in the liquid composition is 20 to 60%, as described above. Preferably, the ratio of the mass of the poor solvent to the total mass of the good solvent in the liquid composition is 30 to 50%, and more preferably 35 to 45%. When the ratio of the mass of the poor solvent to the total mass of the good solvent is within this range, the porous layer and the separation layer (dense layer) have a desirable film thickness. Furthermore, this forms desirable pores in the porous layer. And furthermore, this forms a uniform and smooth separation layer. If the ratio of the mass of the poor solvent is lower than 20%, the porous layer may not be formed. Also, if the ratio of the mass of the poor solvent is higher than 60%, defects may occur on the surface of the separation layer, leading to unexpected gas leakage.

[0078] A good solvent has a lower boiling point than a poor solvent. Because the good solvent has a lower boiling point than the poor solvent, the good solvent vaporizes before the poor solvent, forming a separation layer first, followed by the formation of a porous layer. As a result, the resulting carbon dioxide separation membrane can have two layers: a separation layer and a porous layer. Furthermore, it is preferable that the temperature difference between the boiling points of the poor solvent and the good solvent is 20°C or more. Preferably, the temperature difference between the boiling points of the poor solvent and the good solvent is in the range of 40°C or more, and more preferably in the range of 50°C or more. When the temperature difference between the boiling points of the poor solvent and the good solvent is 50°C or more, the poor solvent is less likely to vaporize when the good solvent vaporizes, resulting in the formation of a separation layer with suppressed pore formation. As a result, the gas separation performance of the carbon dioxide separation membrane of this embodiment is improved.

[0079] The boiling point of the good solvent is preferably 80°C or lower, and more preferably 60°C or lower. The boiling point of the poor solvent is preferably 100°C or higher, and more preferably 110°C or higher. By setting the boiling points of the good and poor solvents within the above ranges, a separation layer with excellent gas separation capabilities and a porous layer with excellent gas permeability and mechanical strength can be formed effectively. Furthermore, by setting the boiling points of the good and poor solvents within the above ranges, the thermal energy required for drying can be reduced, and consequently, carbon dioxide emissions can be reduced.

[0080] A good solvent is one that has a strong interaction with the resin being used and can dissolve the resin on its own. For example, if the resin is a cellulose-based resin, a good solvent can loosen the entanglement caused by hydrogen bonds within the cellulose-based resin molecular chains. In a good solvent, the resin molecules swell and expand, forming a stretched state, and then dissolve. When a resin is mixed with a solvent, if the cohesive force between the resin molecules is weaker than the affinity between the resin molecules and the solvent, the resin molecules will dissolve through a swelling process. Specifically, a good solvent is one in which, when a dissolution test is performed by mixing the resin to be used in a solvent to a concentration of 1% by mass and stirring for 24 hours, it can be visually confirmed that there are no solid particles remaining from the undissolved resin. If two or more types of resins are used, the ratio of each resin mixed into the solvent in the dissolution test should be adjusted to be the same as the ratio of each resin in the liquid composition used to manufacture carbon dioxide separation membranes, so that the total is 1% by mass.

[0081] A poor solvent is one that has weak interaction with the resin used, causing the resins to clump together and repel the solvent when mixed (partial separation). Specifically, a solvent is considered a poor solvent if, after mixing the resin to a concentration of 1% by mass and stirring for 24 hours, undissolved solid particles can be visually confirmed. If two or more resins are used, the ratio of each resin mixed into the solvent in the dissolution test should be adjusted to match the ratio of each resin in the liquid composition used to manufacture carbon dioxide separation membranes, so that the total concentration is 1% by mass.

[0082] The properties of a good solvent and a poor solvent vary depending on the resin used. For example, if the resin is a cellulose ester resin, the properties of a good solvent and a poor solvent change depending on the degree of acyl group substitution of the cellulose ester resin. For example, if the resin is diacetylcellulose (acetyl group substitution degree 2.4) or cellulose acetate propionate, acetone is a good solvent. For example, if the resin is triacetylcellulose (acetyl group substitution degree 2.8), acetone is a poor solvent.

[0083] Examples of solvents that can be used in this disclosure include methyl formate, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, propyl acetate, methyl ethyl ketone (2-butanone), methyl isobutyl ketone, acetone, N-methylpyrrolidone, dimethylformamide, dioxane, dioxolane, dioxolane derivatives, organic halogen compounds such as dichloromethane, chloroform, tetrachloroethane, dimethyl sulfoxide, and methylene chloride, as well as tetrahydrofuran, cyclohexanone, and 2,2,2-trifluorocarbon. Examples of suitable propane sources include ethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, alcohols with 1 to 8 carbon atoms, monochlorobenzene, benzene, cyclohexane, methyl cellulose, ethylene glycol monomethyl ether, and water. Examples of alcohols with 1 to 8 carbon atoms include methanol, ethanol, n-propanol (1-propanol), iso-propanol (2-propanol), n-butanol (1-butanol), sec-butanol (2-butanol), and tert-butanol (2-methyl-2-propanol). Water can also be used.

[0084] The liquid composition may contain poor solvents and good solvents as solvents, as well as other components other than the cellulose resin, such as plasticizers.

[0085] (Substrate) The substrate 2 is unwound from the roll-shaped substrate 100, passes through the roll 106, and is supplied to the coating device 101. Many commonly used materials can be used as substrates to which the liquid composition is applied, such as polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE). Among these, PET is preferred as the substrate.

[0086] The thickness of the substrate is not particularly limited, but is preferably in the range of 20 to 500 μm, and more preferably in the range of 40 to 200 μm. This thickness allows the substrate to be used in general manufacturing processes without causing significant problems.

[0087] The size of the substrate is not particularly limited and can be appropriately determined according to the specifications of the carbon dioxide separation membrane to be manufactured and the plant using the carbon dioxide separation membrane.

[0088] 2-2. Drying Process The drying process involves vaporizing a good solvent and a poor solvent from the web to form a carbon dioxide separation membrane having a separation layer and a porous layer adjacent to the separation layer. Furthermore, the drying process involves vaporizing the good solvent and the poor solvent to dry and shrink the web, forming a carbon dioxide separation membrane having a separation layer on the surface side and a porous layer on the substrate side, where the separation layer and the porous layer are the same matrix. The drying process is carried out by a drying apparatus 102.

[0089] In the drying process, first, a liquid composition is applied to the substrate to form a web, and then the substrate with the web formed on its surface is transported to a drying apparatus. Then, the web formed on the surface of the substrate is heated while standing in the drying apparatus to vaporize the good solvent and poor solvent from the web and form a carbon dioxide separation membrane. This makes it possible to obtain a carbon dioxide separation membrane that is stable, has excellent gas separation performance and excellent durability when wound into a roll.

[0090] Alternatively, the drying process may involve continuously forming a web while moving the substrate, vaporizing a good solvent and a poor solvent from the web, and continuously winding up the resulting carbon dioxide separation membrane.

[0091] In the drying process, it is preferable to heat the web from both the "substrate side" and the "surface side opposite to the substrate side." This makes it easier to control the formation of the separation layer and the porous layer.

[0092] During the heating process in the drying step, the heating temperature may be constant, but it is preferable to gradually increase the heating temperature. This allows for the formation of the separation layer and the porous layer well while achieving the desired solvent content in a short time. The solvent content in the carbon dioxide separation membrane is preferably in the range of 0.5% by mass or less, and more preferably in the range of 0.1% by mass or less. By having the solvent content in the carbon dioxide separation membrane within this range, it is possible to suppress initial performance fluctuations when the gas separation membrane is first put into use.

[0093] In this disclosure, a heating temperature of 100°C or higher is preferably used, but 120°C or higher is more preferable in terms of productivity.

[0094] Methods for heating the substrate side of the web include heating with a medium such as water, heating with heated air, and heating with an infrared heater. Methods for heating the surface side of the web include heating with heated air and heating with an infrared heater.

[0095] During the drying process, the web does not adhere easily to the substrate and shrinks on the substrate so that only the web deforms. In addition, the pores formed within the porous layer become slightly smaller as they evaporate into the solvent during the drying process. In this disclosure, it is presumed that this plastic deformation during the drying process allows the web to deform without being subjected to force from the substrate, thus preventing stress and strain from remaining within the web. The reason the web does not adhere easily to the substrate is thought to be because the presence of pores reduces the contact area between the web and the substrate.

[0096] In this disclosure, the in-plane shrinkage rate when the web is dried is preferably 10% or more, but it is more preferably in the range of 15 to 30%. By having an in-plane shrinkage rate of 10% or more, it is possible to suppress the occurrence of slight distortions and defects that tend to remain inside the film during the drying process. The shrinkage rate is the shrinkage rate over area.

[0097] The content of fine particles in the separation layer of the resulting carbon dioxide separation membrane is the same as the content of fine particles in the separation layer described in the description of the separation membrane in the carbon dioxide separation membrane of this embodiment.

[0098] 2-3. Peeling Step In the method for manufacturing a carbon dioxide separation membrane according to this embodiment, a peeling step may be included before the winding step. The method for manufacturing a carbon dioxide separation membrane according to this embodiment does not have to include a peeling step. The peeling step can be performed by a peeling device 103. In the peeling step, the substrate 2 on which the carbon dioxide separation membrane is formed on its surface is separated into the carbon dioxide separation membrane and the substrate 2. Then, the carbon dioxide separation membrane peeled from the substrate 2 is wound up by the winding device 105. In this case, it is preferable that the substrate 2 is also wound up separately to form a roll (not shown) made of the substrate 2.

[0099] 2-4. Winding Process In the method for manufacturing a carbon dioxide separation membrane of this embodiment, the winding process is a process of winding the obtained carbon dioxide separation membrane 4. The winding process is preferably carried out by a winding device 105. In the winding process, the carbon dioxide separation membrane 4 may be wound together with the base material 2. Alternatively, in the winding process, after separating the carbon dioxide separation membrane 4 and the base material 3 in the peeling process described above, only the carbon dioxide separation membrane 4 may be wound. In the winding process, it is preferable to wind the carbon dioxide separation membrane 4 onto a winding core to the required length. When winding, it is preferable to cool the carbon dioxide separation membrane 4 to room temperature to prevent scratches, loosening, etc., due to shrinkage after winding. The winding method is not particularly limited, and examples include the constant tension method, constant torque method, tapered tension method, and programmed tension control method with constant internal stress. The winding machine used is not particularly limited and can be a commonly used one.

[0100] 3. Manufacturing apparatus for carbon dioxide separation membranes The manufacturing apparatus 1 shown in Figure 3 comprises a coating device 101, a drying device 102, a peeling device 103, and a winding device 105, as described above. The manufacturing apparatus used in one embodiment of the method for manufacturing carbon dioxide separation membranes according to this disclosure is not limited to this.

[0101] The coating apparatus 101 is used in the coating process. The substrate 2 is supplied to the coating apparatus 101 by being fed out from a roll-shaped substrate 100. In the coating apparatus 101, a liquid composition is applied to the substrate 2 by a die coater to form a web.

[0102] In the coating apparatus 101, the heating temperature on the surface side and the heating temperature on the substrate side of the web formed by coating with the liquid composition may be set to be the same, but it is preferable to set them to be different. This makes it easier for the ratio of poor solvent to good solvent to change in the thickness direction of the web, and facilitates the formation of an asymmetric porous film. Therefore, it is preferable for the heating temperature on the substrate side to be lower than the temperature on the surface side.

[0103] The drying apparatus 102 is used in the drying process. The drying apparatus 102 comprises a drying box 102a and a plurality of conveying rolls installed inside the drying box 102a for conveying the web. The drying box 102a has an intake port for taking in drying air and an exhaust port for discharging the gas inside (not shown). The drying apparatus 102 can vaporize a good solvent and a poor solvent, causing the web to dry and shrink, and form a carbon dioxide separation membrane having a separation layer on the surface side and a porous layer on the substrate side, with the separation layer and the porous layer being the same matrix.

[0104] The drying temperature in the drying apparatus 102 can be appropriately determined considering the formation state of the separation layer and porous layer, the amount of residual solvent, drying time, shrinkage uniformity, and the stability of expansion and contraction. For example, 100 to 150°C is preferred. By setting the temperature within this range, the separation layer and porous layer of the resulting carbon dioxide separation membrane can be formed well. In addition, a drying temperature of 100°C or higher makes it easier to sufficiently remove the solvent. A drying temperature of 150°C or lower reduces the energy required for drying and reduces carbon dioxide emissions. The drying temperature may be constant or may be divided into several stages, for example, 2 to 4 stages.

[0105] The peeling device 103 is a device that separates the carbon dioxide separation membrane 4 from the substrate 2, which has a carbon dioxide separation membrane 4 formed on its surface, by sandwiching the substrate 2 between two rolls. The manufacturing apparatus 1 may or may not have the peeling device 103.

[0106] The winding device 105 is used in the winding process. The winding device 105 winds the carbon dioxide separation membrane 4, which is the dried web, onto a winding core to the required length. The conditions for winding are the same as those for the winding process described above.

[0107] The present disclosure will be specifically described below with reference to examples, but the present disclosure is not limited to these examples. In the following examples, unless otherwise specified, the operations were carried out at room temperature (25°C). In the following examples, unless otherwise specified, "%" and "parts" mean "mass%" and "parts by mass," respectively.

[0108] The following resins were used: • Cellulose resin A (cellulose acetate propionate, acetyl group substitution degree 1.6, propionyl group substitution degree 0.9, total acyl group substitution degree 2.5, number average molecular weight (Mn) 64000) • Cellulose acetate propionate CAP-482-20 (manufactured by Eastman) • Cellulose acetate butyrate CAB-381-20 (manufactured by Eastman) • Cellulose acetate CA394-60LF (manufactured by Eastman) • Cellulose acetate L-70 (manufactured by Daicel) • Resin A / CA394 (a mixture of cellulose resin A and cellulose acetate CA394-60LF in a "1:1" mass ratio)

[0109] (Sample 101) Cellulose resin A and fine particles R972V manufactured by Nippon Aerosil Co., Ltd. were mixed. At this time, the amount of fine particles was set to 20% of the total solid content of the mixture of cellulose resin A and fine particles. Furthermore, 54 g of methyl acetate as a good solvent and 36 g of 1-butanol as a poor solvent were added to the mixture and heated to dissolve. Furthermore, 0.1 g of KP-341 (manufactured by Shin-Etsu Chemical Co., Ltd.) was added as a leveling improver to prepare a resin composition with a solid content concentration of 10% by mass. At this time, the ratio of good solvent to total solvent was 60%, and the ratio of poor solvent to total solvent was 40%. Cellulose ester resin A is sometimes referred to as resin A.

[0110] Next, the prepared resin composition was applied to a 180 μm thick PET film (Toray Industries, Ltd., Therapeutic® PJ101) that had been treated for mold release, to a thickness of 350 μm using an applicator. After standing for 5 minutes, the sample 101 of an asymmetric porous membrane (carbon dioxide separation membrane) was dried at 130°C for 30 minutes, resulting in a partially porous structure. In this asymmetric porous membrane, a porous layer was formed on the substrate side. Each sample was an asymmetric porous membrane, and the absence of an interface between the separation layer and the porous layer in the matrix was confirmed by cross-sectional SEM images. From the SEM images and the manufacturing method, it can be seen that the separation layer and the porous layer in the obtained samples are in the same matrix.

[0111] At this time, the width and length of resin A were measured and marked before drying. After drying, the marked positions were measured again. This allowed us to determine the area of ​​the rectangle with width and length before and after drying. The shrinkage rate (%) was then calculated as ((area before drying - area after drying) / area before drying) × 100.

[0112] Furthermore, the prepared samples were peeled off the PET film substrate after drying and then evaluated.

[0113] The obtained sample 101 was subjected to the following tests to evaluate permeability, selective separation, and separation durability. The results are shown in Table 2. The dense layer thickness (μm), porous layer thickness (μm), and shrinkage rate (%) are also shown in Table 2.

[0114] (Samples 102 to 125) Asymmetric porous membranes (carbon dioxide separation membranes) for Samples 102 to 125 were prepared in the same manner as for Sample 101, except that the resin, solvent, and fine particles were changed as shown in Table 1. In Table 1, "Butanol / Water A" in the "Poor Solvent" column is a mixed solvent prepared by mixing 1-butanol and water in a ratio of "1-butanol:water = 87:13". Also in Table 1, "Butanol / Water B" in the "Poor Solvent" column is a mixed solvent prepared by mixing 1-butanol and water in a ratio of "1-butanol:water = 74:26". The obtained Samples 102 to 125 were subjected to the following tests to evaluate permeability, selective separation, and separation durability. The results are shown in Table 2. The dense layer thickness (μm), porous layer thickness (μm), and shrinkage rate (%) are also shown in Table 2.

[0115] The details of each type of microparticle are as follows: R972V: Silica (AEROSIL® R972V manufactured by Nippon Aerosil Co., Ltd., average particle size 15 nm to 18 nm) 4A: Zeolite (Zeoal® 4A manufactured by Nakamura Choko Co., Ltd., average particle diameter 50 nm, average pore diameter 0.4 nm) ZSM-5: Zeolite (Zeoal® ZSM-5 manufactured by Nakamura Choko Co., Ltd., average particle diameter 100 nm, average pore diameter 0.55 nm) PS-S: Pearl necklace-shaped silica (Snowtex® PS-S manufactured by Nissan Chemical Corporation, silica particles with an average particle size of 10 to 15 nm bonded together, length 80 to 120 nm, slurry with 18% solid content)

[0116] (Samples 201-204) The resin compositions of Samples 101, 102, and 119 were applied to a polyester nonwoven fabric (film thickness 130 μm) (05TH-100S, manufactured by Hirose Paper Co., Ltd.) and dried to create a film consisting of an asymmetric porous membrane on the nonwoven fabric. Polyester nonwoven fabric was used as the substrate.

[0117] (Sample 201) The resin composition prepared in Sample 101 was applied to a nonwoven fabric to a thickness of 350 μm using an applicator and left to stand for 5 minutes. Then, Sample 201, an asymmetric film with a partially porous structure on the nonwoven fabric, was prepared by drying at 130°C for 30 minutes. In the asymmetric porous film, a porous layer was formed on the nonwoven fabric side.

[0118] (Sample 202, Sample 203) Samples 202 and 203, which are asymmetric porous membranes with a partially porous structure on a nonwoven fabric, were prepared in the same manner as Sample 201, except that the resin composition described in Table 3 was used. In the asymmetric porous membrane, a porous layer was formed on the nonwoven fabric side.

[0119] (Sample 204) A coating solution consisting of polydimethylsiloxane and a solvent (water:ethanol = 9:1 (mass ratio)) was applied to a nonwoven fabric and dried to form an intermediate layer with a thickness of 2 μm on the nonwoven fabric. Then, an asymmetric porous membrane was formed on top of it in the same manner as when sample 201 was prepared. This produced sample 204, an asymmetric porous membrane with an intermediate layer between the nonwoven fabric and the asymmetric porous membrane, and which was partially porous.

[0120] The obtained samples 201 to 204 were subjected to the following tests to evaluate permeability, selective separation, and separation durability. The results are shown in Table 3. The dense layer thickness (μm), porous layer thickness (μm), and shrinkage rate (%) are also shown in Table 3.

[0121] (Evaluation) [Permeability] The gas permeability [GPU] through the carbon dioxide separation membrane will be measured using a gas permeability measuring device (GTR-11A, manufactured by GTR Tech Co., Ltd.). The measurement will be performed in accordance with the method of JIS K 7126 Part 1 (differential pressure gas chromatography method). A mixed gas consisting of nitrogen and carbon dioxide will be used as the gas. The mixing ratio of nitrogen and carbon dioxide will be "nitrogen:carbon dioxide = 80:20". "1 GPU" is "1 × 10⁻¹⁶". －６ cm ３ (STP) / (sec・cm ２ • cmHg). GPU is an abbreviation for "Gas Permeation Unit". STP is an abbreviation for "Standard Temperature and Pressure". Transmittance [GPU] is such that a higher value indicates a better result, and a value of 20 or higher is practically acceptable.

[0122] [Selective Separation] In the permeability test described above, the ratio of the volume of carbon dioxide V1 to the volume of nitrogen V2 that permeated the carbon dioxide separation membrane, V1 / V2, was determined. A larger value of V1 / V2 indicates higher selective separation. A selective separation value of 10 or higher is considered acceptable for practical purposes.

[0123] [Separation Durability Evaluation] The sample was cut into 14 cm x 14 cm pieces, stacked in groups of 10 so that the dense layer (separation layer) and the porous layer were aligned, and sandwiched between stainless steel plates at 20 kg / cm². ２ The sample was subjected to a load and maintained that state. After 100 hours, the "selective separation" of the gas in the sample that had undergone the load history was evaluated (Selective Separability B), and the retention rate relative to the evaluated value of "Selective Separability" before load application (Selective Separability A) was shown as the evaluation result. The retention rate, which is the evaluation result, is calculated using the formula "100 × (Selective Separability B) / (Selective Separability A)" (%). Selective Separability A and B are the values ​​of V1 / V2, respectively. The closer the retention rate is to 100%, the better the result, and D and E indicate that there are practical problems. A: 95% or more B: 90% or more, less than 95% C: 70% or more, less than 90% D: 50% or more, less than 70% E: Less than 50%

[0124]

[0125]

[0126]

[0127] As shown in the evaluation results for samples 101 to 125 in Table 2, the samples of this disclosure exhibit excellent performance in both carbon dioxide permeability and selective separation. On the other hand, in samples 111 and 112, which contain only one or a small amount of solvent, carbon dioxide permeability is low, and it can be observed that the separation performance deteriorates when the separation membranes are stored in an overlapping state.

[0128] As shown in Table 3, the evaluation results for samples 201-204 demonstrate that even when an asymmetric membrane containing a porous layer is fabricated on a nonwoven fabric, the present disclosure exhibits excellent separation performance. In particular, the durability performance showed virtually no change in separation performance. Specifically, it was shown that even without an intermediate layer between the nonwoven fabric and the asymmetric porous membrane, the present disclosure can achieve performance that ensures both permeability and durability.

[0129] According to this disclosure, it is possible to provide a carbon dioxide separation membrane that has good gas separation performance and excellent durability when wound into a roll shape.

[0130] 1 Manufacturing apparatus 2 Substrate 3 Substrate with a web formed on its surface 4 Carbon dioxide separation membrane 10 Carbon dioxide separation membrane 11 Separation layer 12 Porous layer 100 Roll-shaped substrate 101 Coating apparatus 102 Drying apparatus 102a Drying box 103 Peeling apparatus 105 Winding apparatus 106 Roll S01 Coating process S02 Drying process S03 Winding process

Claims

1. A carbon dioxide separation membrane having a separation layer and a porous layer adjacent to the separation layer, having a resin component mainly composed of a cellulose resin, containing at least one type of fine particles in an amount of 5 to 50% by mass relative to the total amount of the resin component and the fine particles, wherein the separation layer and the porous layer are the same matrix.

2. The carbon dioxide separation membrane according to claim 1, wherein the cellulose resin has substituents having 3 or more carbon atoms.

3. The carbon dioxide separation membrane according to claim 1, wherein the content of the fine particles in the separation layer is 10% by mass or more and 40% by mass or less.

4. A method for producing a carbon dioxide separation membrane, comprising: a coating step of applying a liquid composition containing a cellulose resin, a good solvent, a poor solvent, and fine particles to a substrate to form a web; a drying step of vaporizing the good solvent and the poor solvent from the web to form a carbon dioxide separation membrane having a separation layer and a porous layer adjacent to the separation layer; and a winding step of winding up the carbon dioxide separation membrane, wherein the ratio of the mass of the poor solvent to the total mass of the good solvent and the poor solvent in the liquid composition is 20 to 60%, the good solvent has a lower boiling point than the poor solvent, and the drying step is a step of vaporizing the good solvent and the poor solvent to dry and shrink the web, forming a carbon dioxide separation membrane having the separation layer on the surface side and the porous layer on the substrate side, with the separation layer and the porous layer being the same matrix.

5. The method for producing a carbon dioxide separation membrane according to claim 4, wherein the temperature difference between the boiling point of the poor solvent and the boiling point of the good solvent is 50°C or more.

6. The method for producing a carbon dioxide separation membrane according to claim 4, wherein the in-plane shrinkage rate when the web is dried and shrunk is 10% or more.

7. The method for producing a carbon dioxide separation membrane according to claim 4, wherein the cellulose resin has substituents having 3 or more carbon atoms.

8. The method for producing a carbon dioxide separation membrane according to claim 4, wherein the content of the fine particles in the separation layer is 10% by mass or more and 40% by mass or less.

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