Method for producing a gas separation membrane and gas separation membrane

Abstract

The present invention provides a method for manufacturing a gas separation membrane, which includes: a step of allowing a dispersion liquid obtained by mixing zeolite microcrystals composed of MFI zeolite and graphene oxide with pure water to stand still, and coating the periphery of the zeolite microcrystals with the graphene oxide; a step of drying the dispersion liquid after standing still and pulverizing it; a step of subjecting the powder to a reduction treatment of the graphene oxide by heating; and a step of pressure-molding the powder after the reduction treatment into a film shape.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a gas separation membrane and to the gas separation membrane itself. Background Technology

[0002] As a method for manufacturing zeolite films using zeolite microcrystals, Patent Document 1 describes a method for precipitating zeolite films on a porous support such as alumina using a hydrothermal synthesis method or a gas-phase method with silica and alumina as starting materials. Patent Document 2 describes a method for forming zeolite films on a support using zeolite microcrystals as seed crystals.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2003-210950

[0006] Patent Document 2: Japanese Patent Application Publication No. 2016-174996 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] This disclosure was made in view of the above circumstances, and its object is to provide a method for manufacturing a gas separation membrane with improved gas separation performance and a gas separation membrane.

[0009] Methods for solving problems

[0010] To achieve the above objectives, one method for manufacturing a gas separation membrane disclosed herein includes: a step of allowing a dispersion formed by mixing zeolite microcrystals composed of MFI zeolite and graphene oxide with pure water to stand, and then coating the zeolite microcrystals with the graphene oxide; a step of drying the standing dispersion and pulverizing it; a step of reducing the graphene oxide in the powder by heating; and a step of pressing the reduced powder to form a membrane.

[0011] According to the above-described method for manufacturing a gas separation membrane, a dispersion containing zeolite microcrystals and graphene oxide is allowed to stand. After coating the zeolite microcrystals with graphene oxide, the mixture is pulverized and then reduced by a reduction treatment. The reduced powder is then pressed and molded into a membrane to obtain the gas separation membrane. This method produces a gas separation membrane where adjacent zeolite microcrystals are appropriately filled with graphene, thus improving gas separation performance.

[0012] Here, the following method can be adopted: after the aforementioned reduction treatment of graphene oxide and before forming the aforementioned film, a step is further performed: heating treatment at a temperature higher than the heating temperature in the aforementioned reduction treatment to form a nanowindow in the reduced graphene.

[0013] Prior to the process of forming a film, a process involving the formation of nanowindows in graphene is used to create nanowindows in the graphene surrounding the coated zeolite microcrystals. This significantly improves gas selectivity based on molecular size, thereby further enhancing separation performance.

[0014] The dispersion can be allowed to stand with the pH adjusted to a range of 3.6-11.0 using a pH adjuster. As described above, by adjusting the pH of the dispersion using a pH adjuster, the coating of graphene oxide around the zeolite microcrystals can be increased.

[0015] The following method can be used: the aforementioned pH adjuster is ammonium chloride, and the pH of the aforementioned dispersion is adjusted to the range of 3.6-4.0 using the aforementioned pH adjuster.

[0016] A sheet-like gas separation membrane is formed by pressing together the aforementioned zeolite microcrystals whose surfaces are coated with graphene, and the aforementioned zeolite microcrystals are bonded to each other via the aforementioned graphene. The sheet-like gas separation membrane is formed by pressing together the aforementioned zeolite microcrystals whose surfaces are coated with the aforementioned graphene, and the spaces between adjacent aforementioned zeolite microcrystals are filled with the aforementioned graphene.

[0017] In the aforementioned gas separation membrane, zeolite microcrystals coated with graphene are pressurized to form a membrane in which graphene is embedded between adjacent zeolite microcrystals. Because the graphene is appropriately embedded between adjacent zeolite microcrystals in the aforementioned gas separation membrane, gas separation performance can be improved.

[0018] The following approach can be adopted: the aforementioned graphene has nanowindows. By forming nanowindows in graphene, the selectivity of gases based on molecular size can be improved, thereby further enhancing the separation performance.

[0019] In addition, the method for manufacturing a gas separation membrane according to other embodiments of the present disclosure includes: a step of standing a dispersion formed by mixing apatite microcrystals composed of hydroxyapatite and graphene oxide with pure water, and coating the surrounding area of ​​the apatite microcrystals with the aforementioned graphene oxide; a step of drying the aforementioned dispersion after standing and pulverizing it; a step of performing a reduction treatment of the aforementioned graphene oxide on the aforementioned powder by heating; and a step of pressing the aforementioned reduced powder to form a membrane.

[0020] According to the above-described method for manufacturing a gas separation membrane, a dispersion containing apatite microcrystals and graphene oxide is allowed to stand. After coating the apatite microcrystals with graphene oxide, the mixture is pulverized and then reduced using a reduction treatment. The reduced powder is then pressed and molded into a membrane to obtain the gas separation membrane. By using this method to manufacture the gas separation membrane, a gas separation membrane in which graphene is appropriately embedded between adjacent apatite microcrystals can be obtained, thus improving gas separation performance.

[0021] Here, the following method can be adopted: after the aforementioned step of reducing graphene oxide and before the aforementioned step of forming a film, there is also a step of heating the graphene at a temperature higher than the heating temperature in the aforementioned reduction process to form a nano-window in the reduced graphene.

[0022] Prior to the process of forming the film, there is a step of forming nanowindows in the graphene, thus allowing nanowindows to be set in the graphene surrounding the coated apatite microcrystals. This, in particular, improves the selectivity of gases based on molecular size, thereby further enhancing separation performance.

[0023] The dispersion can be allowed to stand with the pH adjusted to a range of 3.6-11.0 using a pH adjuster. As described above, by adjusting the pH of the dispersion with a pH adjuster, the coating of graphene oxide around the apatite microcrystals can be increased.

[0024] The following method can be used: the aforementioned pH adjuster is ammonium chloride, and the pH of the aforementioned dispersion is adjusted to the range of 6.0-9.3 using the aforementioned pH adjuster.

[0025] A sheet-like gas separation membrane is formed by pressing together the aforementioned apatite microcrystals whose surfaces are coated with graphene and whose surfaces are made of hydroxyapatite. The graphene is used to fill the spaces between adjacent apatite microcrystals.

[0026] In the aforementioned gas separation membrane, graphene-coated apatite microcrystals are pressurized to form a membrane in which graphene is embedded between adjacent apatite microcrystals. Because the graphene is appropriately embedded between adjacent apatite microcrystals in this gas separation membrane, gas separation performance can be improved.

[0027] The following approach can be used: the aforementioned graphene has nanowindows. By forming nanowindows in graphene, the selectivity for gases based on molecular size can be improved, thus further enhancing the separation performance.

[0028] Invention Effects

[0029] According to this disclosure, a method for manufacturing a gas separation membrane with improved gas separation performance and a gas separation membrane can be provided. Attached Figure Description

[0030] Figure 1 A diagram illustrating the structure of a gas separation membrane according to one aspect of this disclosure.

[0031] Figure 2 A diagram illustrating a method for manufacturing a gas separation membrane according to one aspect of this disclosure.

[0032] Figure 3 A graph showing the relationship between pH and graphene coating amount in the manufacturing process of a gas separation membrane (zeolite separation membrane).

[0033] Figure 4 This is a SEM image of a gas separation membrane (zeolite separation membrane).

[0034] Figure 5 (a) and Figure 5 (b) A graph showing the nitrogen adsorption isotherm of the gas separation membrane (zeolite separation membrane).

[0035] Figure 6 The graph shows the TG curves of powder samples from examples and comparative examples of the gas separation membrane (zeolite separation membrane).

[0036] Figure 7 A diagram illustrating the apparatus used to evaluate gas separation performance.

[0037] Figure 8 A graph illustrating the results of the permeability measurement.

[0038] Figure 9 A graph showing the evaluation results of gas separation performance.

[0039] Figure 10 A graph showing the evaluation results of the gas permeability of the gas separation membrane (zeolite separation membrane).

[0040] Figure 11 This is a SEM image of a gas separation membrane (apatite separation membrane).

[0041] Figure 12 (a) and Figure 12 (b) is a graph showing the nitrogen adsorption isotherm of the gas separation membrane (apatite separation membrane).

[0042] Figure 13 A graph showing the evaluation results of the gas permeability of the gas separation membrane (apatite separation membrane). Detailed Implementation

[0043] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. It will be noted that in the description of the drawings, the same reference numerals are used to denote the same elements, and repeated descriptions are omitted.

[0044] <First Embodiment: Zeolite Separation Membrane>

[0045] (Zeolite separation membrane)

[0046] As a first embodiment, a zeolite separation membrane will be described. The zeolite separation membrane of this embodiment is a gas separation membrane that utilizes the microporous structure of zeolite crystals to separate various gases. The types of gases to be separated are not limited; as an example, the zeolite separation membrane described in this embodiment can be used for the separation of hydrogen and methane or hydrogen and carbon monoxide. Other applications include the separation of hydrogen and oxygen, carbon dioxide and nitrogen, and methane and nitrogen. The zeolite separation membrane is a sheet-like membrane formed by coating the surface of zeolite microcrystals with graphene, thereby binding the zeolite microcrystals together via the graphene.

[0047] Figure 1 A diagram illustrating the structure of a zeolite separation membrane is shown. The gas separation membrane 1 is configured to contain zeolite microcrystals 10 and graphene 20. Furthermore, the gas separation membrane 1 can be used while supported by a support 30 or the like.

[0048] The gas separation membrane 1 is, for example, a sheet-like membrane with a thickness of about 10 μm to 50 μm. Furthermore, the size (diameter) of the main surface can be, for example, about 500 μm to 13 mm. The gas separation membrane 1 has a structure in which the main component is a plurality of zeolite microcrystals 10, and a plurality of graphene 20 are arranged to cover their periphery. There is no particular limitation on the shape of the main surface of the gas separation membrane 1; for example, it can be a polygonal shape such as a quadrilateral, or a circle.

[0049] Zeolite microcrystals 10 are MFI zeolite crystals. Various zeolites with different framework structures are known. The zeolite used in the zeolite separation membrane described in this embodiment is MFI zeolite (ZSM-5), with the chemical formula Na₂SO₄ per unit lattice. n Al n Si 96- n O 192 • 16H₂O (0 < n < 27). It should be noted that the framework structure of MFI zeolite is specified by the International Zeolite Society. MFI zeolite can be synthesized to a particle size of approximately several μm, but the size (particle size) of the zeolite microcrystals 10 used in this embodiment is set to a range of 50 nm to 150 nm. It should be noted that in the gas separation membrane 1, the zeolite microcrystals 10 are approximately spherical, but... Figure 1 In the diagram, it is schematically shown in a polygonal (hexagonal) shape.

[0050] Furthermore, the surface of the zeolite microcrystal 10 has multiple micropores derived from its structure. The diameter of the micropores in the zeolite microcrystal 10 is 0.54 nm to 0.56 nm. As an example, MFI zeolite (MFI zeolite manufactured by Mitsubishi Chemical Corporation) with a crystal particle size of less than 100 nm and a micropore diameter of about 0.55 nm can be used as the zeolite microcrystal 10.

[0051] Graphene 20 is disposed in a manner that connects adjacent zeolite microcrystals 10. Furthermore, graphene 20 covers the area surrounding the zeolite microcrystals 10. However, "covering the area surrounding the zeolite microcrystals 10" does not mean that the entire surface of the zeolite microcrystals 10 is covered by graphene 20; a portion of the zeolite microcrystals 10 may be exposed. Graphene 20 is a sheet-like material with a thickness of a single atom, where carbon atoms are firmly bonded into benzene rings.

[0052] like Figure 1 As shown, in the gas separation membrane 1, multiple zeolite microcrystals 10 are each coated with multiple graphene 20 and bonded to adjacent zeolite microcrystals 10 via the graphene 20. Therefore, for example, there may be a case where zeolite microcrystals 10 are present on both sides of a single graphene 20. Furthermore, the graphene 20 is arranged in a manner that fills the spaces between adjacent zeolite microcrystals 10. Therefore, when viewed from above, fine pores penetrating between adjacent zeolite microcrystals 10 are not formed; instead, graphene 20 is disposed between adjacent zeolite microcrystals 10.

[0053] It should be noted that the size of graphene 20 (the size of the main face of the sheet-like structure) is smaller than the particle size of zeolite microcrystal 10, for example, it can be set in the range of 5 nm to 50 nm. Therefore, the surface of zeolite microcrystal 10 is coated with multiple layers of graphene 20. Graphene 20 can be coated on zeolite microcrystal 10 as a single layer, or it can be coated on zeolite microcrystal 10 in a multilayer state (multilayer state). It should be noted that in Figure 1 The graphene 20 is not shown as a multilayer structure, but rather schematically shown as a plurality of graphene 20 in a state where a single layer of zeolite microcrystals 10 is coated.

[0054] Multiple nanowindows (fine pores with a diameter of approximately 0.3 nm to 1.5 nm) are formed in graphene 20. By incorporating these nanowindows, the selectivity in gas separation performance can be further improved, particularly.

[0055] In the gas separation membrane 1, the mass ratio of zeolite microcrystals 10 to graphene 20 can be set to approximately 6:100 to 20:100. This mass ratio can be determined using thermogravimetric analysis (TG). For example, the percentage of mass reduction can be confirmed from the TG curve obtained using TG analysis in air. From this result, the mass ratio of zeolite microcrystals 10 to graphene 20 in the gas separation membrane 1 can be determined.

[0056] While the gas separation membrane 1 described above can be used as a single unit, it can, as an example, be used in a state supported by a support 30. There are no particular limitations as long as the support 30 is a support capable of supporting the gas separation membrane 1 and has an opening with a pore size sufficiently larger than the pores of the zeolite microcrystals 10. The support 30 can be, for example, a frame material supporting the outer periphery of the gas separation membrane 1.

[0057] (Manufacturing method of zeolite separation membrane)

[0058] Zeolite separation membranes are formed by coating zeolite microcrystals with graphene oxide, allowing them to bond together. Therefore, as... Figure 2 As shown, the method for manufacturing a zeolite separation membrane includes: a step of preparing a dispersion containing zeolite microcrystals and graphene oxide (step S01); a step of adjusting the dispersion to a specified pH and placing it for a specified time (step S02); a step of freeze-drying (step S03); a step of reducing the dispersion by heating (step S04); a step of preparing a nano-window (step S05); and a step of pressing and molding (step S06).

[0059] In step S01, a dispersion is prepared by mixing zeolite microcrystals and graphene oxide in pure water. As the zeolite microcrystals, MFI zeolite with a particle size in the range of 50 nm to 150 nm and a pore size of 0.54 nm to 0.56 nm, as described above, is used.

[0060] Furthermore, graphene oxide is used for the purpose of bonding zeolite microcrystals together. Graphene oxide has a structure formed by the oxidation of graphene and contains hydroxyl, carboxyl, and epoxy groups. Graphene oxide used in the manufacture of zeolite separation membranes, for example, uses graphene oxide with 5 or fewer layers and a particle size of approximately 5 nm to 50 nm. When graphene oxide is separated into single layers or has a small number of layers, coating with zeolite microcrystals and bonding between the zeolite microcrystals can be appropriately performed. It should be noted that there are no particular limitations on the properties of the graphene oxide when added to the dispersion.

[0061] A dispersion of zeolite microcrystals and graphene oxide can be prepared by mixing zeolite microcrystals and graphene oxide in pure water. Regarding the mixing amounts of zeolite microcrystals and graphene oxide with pure water, for example, relative to 10 ml of pure water, approximately 10 mg to 20 mg of zeolite microcrystals and approximately 0.6 mg to 4.0 mg of graphene oxide can be used. Furthermore, the mixing ratio of zeolite microcrystals to graphene oxide, by mass, can be approximately 6:100 to 20:100.

[0062] In step S02, the pH of the dispersion of zeolite microcrystals and graphene oxide is adjusted. This promotes the electrostatic interaction between the zeolite microcrystals and graphene oxide in the dispersion. As a result, the surface of the zeolite microcrystals is coated with graphene oxide. According to the results of the investigation on the surface charge density of graphene oxide, the surface charge density hardly changes within a pH range of approximately 2 to 10. On the other hand, regarding the zeolite microcrystals, since the surface charge density changes with pH, ​​the ionic strength between the zeolite microcrystals and graphene oxide can be altered by adjusting the pH of the dispersion.

[0063] The target pH for adjusting the dispersion varies depending on the type of pH adjuster added. For example, when using salts such as ammonium chloride to adjust the pH, the target pH is set to around 3.6 to 4.0.

[0064] It should be noted that, in addition to ammonium chloride, ammonium bicarbonate, ammonium nitrate, etc., can also be used as salts for pH adjustment. On the other hand, when using a weak base such as ammonia to adjust the pH, the target pH is set to approximately 3.6 to 11.0. Besides ammonia, tetramethylammonium hydroxide, etc., can also be used as a weak base for pH adjustment.

[0065] The pH of the dispersion is adjusted to the aforementioned range using a pH adjuster, and then allowed to stand for several hours to tens of hours. This allows the zeolite microcrystals to be coated with graphene oxide through electrostatic interaction with the graphene oxide. By allowing the dispersion, adjusted to a specified pH, to stand for a specified time, the interaction between the zeolite microcrystals and graphene oxide in the dispersion proceeds. The standing time is not particularly limited as long as it allows sufficient interaction to occur in the dispersion. For example, it was confirmed that by allowing a dispersion adjusted to pH 4.6 using ammonium chloride to stand for 24 hours, sufficient interaction between the zeolite microcrystals and graphene oxide in the dispersion occurs. Whether the interaction is sufficient can be confirmed, for example, by separating the phase into a colloidal dispersion containing zeolite particles and an aqueous phase without them.

[0066] It should be noted that a pH-adjusted dispersion can also be formed by mixing zeolite microcrystals and graphene oxide into a pre-adjusted pH liquid. That is, steps S01 and S02 can be performed simultaneously. For example, when a 0.05M ammonium chloride aqueous solution is prepared, and 9.2 mg of zeolite microcrystals and 0.8 mg of graphene oxide are mixed into this aqueous solution, a dispersion adjusted to pH 4.6 can be obtained. This sequence can also be used to prepare a pH-adjusted dispersion.

[0067] In step S03, the above dispersion is dried to produce a powder of zeolite microcrystals coated with graphene oxide. As an example, the dispersion is dried in a vacuum freeze dryer at a temperature of -40°C to -30°C (233K to 243K) and a pressure of 5Pa to 20Pa to remove moisture and obtain a powder of zeolite microcrystals coated with graphene oxide. It should be noted that heating drying can also be used instead of vacuum freeze drying to obtain a powder of zeolite microcrystals coated with graphene oxide.

[0068] In step S04, the powder of zeolite microcrystals coated with graphene oxide is heated. This reduces the graphene oxide coated with zeolite microcrystals (thermal reduction).

[0069] The heat treatment is performed, for example, at a temperature range of 220°C to 300°C (493K to 573K) for approximately 10 minutes to 6 hours. There is no upper limit to the heating temperature and time; by heating under the above conditions, the reduction of graphene oxide can be fully achieved. For example, an argon atmosphere can be used as the atmosphere for the heat treatment. As an example, when the mass of zeolite microcrystals coated with graphene oxide is approximately 20 mg, the microcrystals are heated to 573K at a heating rate of 1K / min in an argon atmosphere furnace and held at that temperature for 30 minutes, then cooled to below 333K to reduce the graphene oxide. By performing the heat treatment under the above conditions, the graphene oxide surrounding the zeolite microcrystals is reduced to graphene. This results in the zeolite microcrystals being coated with graphene. It should be noted that by completely reducing the graphene oxide, the performance as a gas separation membrane can be fully utilized.

[0070] By allowing the thermal reduction treatment to proceed to a certain extent, the adhesion between the zeolite microcrystals and graphene is improved. Therefore, the separation membrane, as described later, can be stably formed.

[0071] In step S05, the reduced graphene is further heated to form nano-windows (fine pores with a diameter of about 0.3 nm to 1.5 nm) in the graphene.

[0072] The heat treatment used to form nanowindows is, for example, carried out in a temperature range of 200°C to 600°C (473K to 873K) for approximately 5 minutes to 50 hours. The atmosphere used for the heat treatment can be, for example, atmospheric air. As an example, with approximately 20 mg of zeolite microcrystals coated with graphene, heating to 623K at a heating rate of 1K / min in an atmospheric furnace and holding the temperature for 10 minutes, followed by cooling to below 333K, allows the formation of fine pores in the graphene. It should be noted that the higher the heating temperature, the larger the pore size of the nanowindows.

[0073] In step S06, a zeolite separation membrane is formed by pressurizing a mixture of zeolite microcrystals treated with nano-window fabrication and graphene. Up to this stage, the zeolite microcrystals are coated with graphene, and by promoting the bonding of graphene with each other, a separation membrane is formed in which the zeolite microcrystals are nearly aligned with each other via graphene. Specifically, a pressure of 5 MPa to 40 MPa is applied during compression molding to form a membrane. For example, a tablet forming device can be used when forming the membrane. Thus, a zeolite separation membrane can be obtained. By setting the pressure during pressurization to 5 MPa or higher, a sheet-like separation membrane can be formed. On the other hand, by setting the pressure to 40 MPa or lower, damage to the pores of the zeolite microcrystals (pore fracture) accompanying the pressurization can be prevented. It should be noted that when the pressure during pressurization is, for example, 10 MPa to 20 MPa, a separation membrane with increased membrane strength and suppressed pore damage of the zeolite microcrystals can be obtained.

[0074] By going through the above-mentioned pressure molding process, a zeolite separation membrane in which the graphene surrounding the coated zeolite microcrystals is firmly bonded together can be obtained.

[0075] The zeolite separation membrane obtained by the above sequence is, for example, obtained by using... Figure 1 The support shown, such as the support body 30, can be used to support the gas separation membrane, which can be used to improve rigidity.

[0076] (Characteristics of zeolite separation membranes)

[0077] The gas separation membrane 1 described in this embodiment can separate mixed gases with different molecular sizes by utilizing a plurality of fine pores 11 provided in the zeolite microcrystals 10. Specifically, molecules with small molecular diameters can pass through the fine pores of the zeolite microcrystals 10 and therefore can pass through the gas separation membrane 1. On the other hand, molecules with large molecular diameters cannot pass through the fine pores of the zeolite microcrystals 10 and therefore cannot pass through the gas separation membrane 1. In the gas separation membrane 1, the gas mixture can be separated with good precision by utilizing the difference in molecular diameter of the molecules constituting such a mixed gas. It should be noted that when adjusting the pore size of the gas separation membrane 1, the gas to be separated in the zeolite separation membrane can be selected.

[0078] Specifically, the gas separation membrane 1 described in this embodiment can be used for the separation of methane and hydrogen. When a mixture of methane and hydrogen is passed through the gas separation membrane 1, the hydrogen passes through the gas separation membrane 1, while the methane cannot pass through it. Therefore, by using the gas separation membrane 1, methane and hydrogen can be appropriately separated. Furthermore, the gas separation membrane 1 is characterized by a faster gas separation rate than conventional gas separation membranes.

[0079] As described above, the method for manufacturing a gas separation membrane according to this embodiment includes: a step of allowing a dispersion formed by mixing zeolite microcrystals composed of MFI zeolite and graphene oxide with pure water to stand, and then coating the area around the zeolite microcrystals with graphene oxide; a step of drying the stood dispersion and pulverizing it; a step of performing a reduction treatment on the powder using heat to obtain graphene oxide; and a step of pressing the reduced powder to form a membrane. By manufacturing a gas separation membrane using the above method, a gas separation membrane in which graphene is appropriately embedded between adjacent zeolite microcrystals can be obtained, thereby improving gas separation performance.

[0080] Furthermore, after the reduction treatment of graphene oxide and before the film formation process, a heating treatment at a higher temperature than that in the reduction treatment is performed. During the process of forming nanowindows in the reduced graphene, nanowindows are formed in the graphene surrounding the coated zeolite microcrystals. This further improves separation performance, particularly enhancing the selectivity for gases based on molecular size.

[0081] The dispersion can be allowed to stand with the pH adjusted to a range of 3.6-11 using a pH adjuster. As mentioned above, adjusting the pH of the dispersion with a pH adjuster can increase the coating of graphene oxide around the zeolite microcrystals. Specifically, the pH can be adjusted to a range of 3.6-4 using ammonium chloride as the pH adjuster.

[0082] A sheet-like gas separation membrane is a sheet-like gas dispersion membrane consisting of multiple zeolite microcrystals made of MFI zeolite with their surfaces coated with graphene and the zeolite microcrystals bonded to each other via graphene. The zeolite microcrystals coated with graphene are formed by pressing them together, and the spaces between adjacent zeolite microcrystals are filled with graphene.

[0083] In the aforementioned gas separation membrane, zeolite microcrystals coated with graphene are pressurized to form a membrane in which graphene is embedded between adjacent zeolite microcrystals. Because the graphene is appropriately embedded between adjacent zeolite microcrystals in this gas separation membrane, gas separation performance can be improved.

[0084] This can be achieved by using graphene with nanowindows. By forming nanowindows in graphene, the selectivity for gases based on molecular size can be improved, thus further enhancing separation performance.

[0085] Several embodiments have been described above, but this disclosure is not limited to the embodiments described above. Furthermore, the descriptions of the above embodiments are applicable to each other.

[0086] <Second Embodiment: Apatite Separation Membrane>

[0087] (Apatite separation membrane)

[0088] As a second embodiment of the gas separation membrane, an apatite separation membrane in which zeolite microcrystals are replaced with apatite microcrystals will be described. The apatite microcrystals used in the apatite separation membrane of the second embodiment differ from zeolite microcrystals in that they do not have a microporous structure. However, regarding the apatite separation membrane, the same gas separation performance as the zeolite separation membrane can be obtained by coating the surface of the apatite microcrystals with graphene. That is, the apatite separation membrane described in this embodiment can also be used for the separation of hydrogen and methane or hydrogen and carbon monoxide, the separation of hydrogen and oxygen, the separation of carbon dioxide and nitrogen, the separation of methane and nitrogen, etc. The apatite separation membrane also has the same gas separation performance as the zeolite separation membrane. Figure 1 The structure of the zeolite separation membrane shown is the same. However, as mentioned above, apatite microcrystals do not have pores, which is a difference from the zeolite separation membrane.

[0089] It should be noted that in the second embodiment, the difference between the apatite separation membrane and the zeolite separation membrane is explained, but the parts of the apatite separation membrane that are not described are the same as those of the zeolite separation membrane.

[0090] The apatite microcrystals used in the apatite separation membrane are hydroxyapatite crystals. The chemical formula is Ca5(PO4)3(OH). It should be noted that hydroxyapatite has a hexagonal crystal system. The size (particle size) of the apatite microcrystals used in this embodiment is set to be in the range of 2 μm to 3 μm. It should be noted that in gas separation membrane 1, the hydroxyapatite microcrystals are plate-shaped.

[0091] In apatite separation membrane, with Figure 1 Similarly, the gas separation membrane 1 shown also applies to multiple apatite microcrystals (corresponding to...) Figure 1 The zeolite microcrystals 10 shown are coated with a plurality of graphene 20 and bonded to adjacent apatite microcrystals via the graphene 20. As a result, they have the same shape as the zeolite separation membrane of the first embodiment.

[0092] It should be noted that the same applies to the formation of multiple nanowindows (pores with a diameter of about 0.3 nm to 1.5 nm) in graphene 20.

[0093] In addition, in the apatite separation membrane, the mass ratio of apatite microcrystals to graphene is set to approximately 4:100 to 20:100.

[0094] (Manufacturing method of apatite separation membrane)

[0095] The apatite separation membrane is formed by coating the surface of apatite microcrystals with graphene oxide and then bonding them together. This is similar to the zeolite separation membrane. Therefore, the manufacturing method of the apatite separation membrane is the same as the manufacturing method of the zeolite separation membrane described in the first embodiment. The manufacturing method of the zeolite separation membrane is as follows: Figure 2 As shown, the method includes: a step of preparing a dispersion containing zeolite microcrystals and graphene oxide (step S01); a step of adjusting the dispersion to a specified pH and allowing it to stand for a specified time (step S02); a step of freeze-drying (step S03); a step of reducing the dispersion by heating (step S04); a step of preparing nano-windows (step S05); and a step of pressing and molding (step S06). By changing the zeolite microcrystals used in each step to apatite microcrystals, a method for manufacturing an apatite separation membrane can be obtained.

[0096] It should be noted that the apatite microcrystals used in step S01 are hydroxyapatite with a particle size ranging from 2 μm to 3 μm, as described above. Furthermore, in the step of adjusting the dispersion to a predetermined pH and allowing it to stand for a predetermined time (step S02), the pH of the dispersion prepared by mixing the apatite microcrystals and graphene oxide in pure water is approximately 9.3, which differs from the pH of the dispersion of zeolite microcrystals and graphene oxide. Therefore, for example, when using salts such as ammonium chloride to adjust the pH, the target pH is set to approximately 6.0 to 9.3.

[0097] In the gas separation membrane of the second embodiment described above, graphene-coated apatite microcrystals are pressurized and molded, resulting in a membrane in which graphene is embedded between adjacent apatite microcrystals. In this gas separation membrane, since graphene is appropriately embedded between adjacent apatite microcrystals, gas separation performance can be improved.

[0098] This can be achieved by using graphene with nanowindows. By forming nanowindows in graphene, the selectivity for gases based on molecular size can be improved, thus further enhancing separation performance.

[0099] Several embodiments have been described above, but this disclosure is not limited to the embodiments described above. Furthermore, the descriptions of the above embodiments are applicable to each other.

[0100] Example

[0101] The present disclosure will now be described in more detail with reference to the embodiments and comparative examples. However, the present disclosure is not limited to the embodiments described below.

[0102] 1. Zeolite separation membrane

[0103] (Research on pH adjustment)

[0104] In the gas separation membrane manufacturing method described in this embodiment, as described above, the zeolite microcrystals 10 are coated with graphene oxide by adjusting the pH of the dispersion and allowing it to stand. The relationship between the pH at this time and the amount (by weight) of graphene oxide coating is investigated. The results are shown below. Figure 3 .

[0105] Prepare a dispersion containing 2.0 mg of graphene oxide (Hummer process graphene oxide synthesized by Shinshu University, Japan) and 20 mg of MFI zeolite microcrystals (Mitsubishi Chemical Corporation, particle size 100 nm, pore size 0.55 nm) in 10 ml of pure water. Use ammonium chloride aqueous solution (1 M concentration) to prepare the dispersion. Figure 3 Solutions at various pH values ​​(pH 3.40, pH 3.45, pH 3.50, pH 3.55, pH 3.60, pH 3.65, pH 3.70, pH 3.75, pH 3.80, pH 3.85, pH 3.90, pH 3.95, pH 4.00) were shown. These solutions were allowed to stand at 25°C for 24 hours. The lower layer of the solution, which had separated into two phases, was then recovered using a micropipette and evaporated to dryness. The resulting powder was subjected to thermogravimetric analysis in air, and a TG curve was prepared. In the obtained TG curve, the weight reduction at 750–800 K was assumed to be the weight of graphene, and the proportion of graphene (mass %) was estimated.

[0106] exist Figure 3 In the figure, the pH of the dispersion (preparation solution) is used as the horizontal axis, and the graphite coating ratio (the amount of graphite contained in the dry powder: mass%) is used as the vertical axis.

[0107] (Example 1)

[0108] A dispersion containing 1.6 mg of graphene oxide (Hummer process graphene oxide synthesized by Shinshu University, Japan) and 18.4 mg of MFI zeolite microcrystals (Mitsubishi Chemical Corporation, particle size 100 nm, pore size 0.55 nm) was prepared in 10 ml of 0.05 M ammonium chloride aqueous solution. The pH of the dispersion was 4.6. The solution, which had been allowed to stand at 25 °C for 24 hours, was then placed in a vacuum freeze dryer and dried at 223 K and 10 Pa to obtain 20 mg of zeolite microcrystal powder coated with graphene oxide.

[0109] The obtained powder was placed in a quartz boat and placed in a furnace under an argon atmosphere. Heating was carried out in an argon flow at a heating rate of 1 K / min, maintained at 573 K for 30 minutes, and then allowed to cool naturally. The argon flow was stopped when the furnace cooled to below 333 K, and the quartz boat was removed from the furnace. The mass of the powder obtained after heating was 14 mg.

[0110] Next, the powder removed from the heating furnace was placed in a quartz boat and placed in an electric furnace. It was heated in air at a heating rate of 1 K / min, held at 623 K for 10 minutes, and then allowed to cool naturally. The quartz boat was removed from the furnace when the temperature inside cooled to below 333 K. The mass of the powder obtained after heating was 13.8 mg.

[0111] The powder removed from the electric furnace was pressurized into a film using a tablet former. The pressure during pressurization was set to 15 MPa. As a result, the zeolite separation membrane of Example 1 was obtained. The zeolite separation membrane of Example 1 is a circle with an outer diameter of 8 mm when viewed from above. It should be noted that the thickness of the zeolite separation membrane of Example 1 was estimated to be 90 nm based on density calculations. An SEM image of the zeolite separation membrane of Example 1 is shown below. Figure 4 .

[0112] (Comparative Example 1: MFI zeolite)

[0113] 18.4 mg of MFI zeolite (manufactured by Mitsubishi Chemical Corporation, particle size 100 nm, pore size 0.55 nm) was prepared and pressurized into a membrane using a tablet former. The pressure during pressurization was set to 15 MPa to obtain the separation membrane of Comparative Example 1.

[0114] (Comparative Example 2: Graphene Oxide)

[0115] 10 mg of graphene oxide (Hummer process graphene oxide prepared by Shinshu University, Japan) was prepared and pressurized into a membrane using a tablet former. The pressure during pressurization was set to 15 MPa to obtain the separation membrane of Comparative Example 2.

[0116] (Comparative Example 3)

[0117] A dispersion containing 1.6 mg of graphene oxide (Hummer process graphene oxide synthesized by Shinshu University, Japan) and 18.4 mg of MFI zeolite microcrystals (100 nm particle size, 0.55 nm pore size manufactured by Mitsubishi Chemical Corporation) was prepared in 10 ml of 0.05 M ammonium chloride aqueous solution. The pH of the dispersion was 4.6. The dispersion was allowed to stand at 25 °C for 24 hours and then filtered through an alumina filter (100 nm pore size). This resulted in a membrane of MFI zeolite coated with graphene oxide stacked on the alumina filter. The membrane was then dried in a dryer at 110 °C to remove residual moisture.

[0118] The dried membrane was placed in a furnace under an argon atmosphere. It was heated in an argon stream at a rate of 1 K / min and held at 573 K for 30 minutes, followed by natural cooling. The argon stream was stopped when the furnace cooled to below 333 K, and the membrane was removed from the furnace. This yielded the separation membrane of Comparative Example 3.

[0119] (Refer to Example 1)

[0120] The unformed graphene oxide powder used in the fabrication of the separation membrane in Comparative Example 2 was placed in a quartz boat and placed in a furnace under an argon atmosphere. Heating was performed in an argon flow at a heating rate of 1 K / min, maintained at 573 K for 30 minutes, and then allowed to cool naturally. The argon flow was stopped when the furnace cooled to below 333 K, and the quartz boat was removed from the furnace, yielding the powder of Reference Example 1. This powder is equivalent to graphene powder obtained by reducing graphene oxide.

[0121] <Comparison of Structures>

[0122] The powder used in the fabrication of the zeolite separation membrane in Example 1 (before pressure molding, powder of zeolite microcrystals in the state of being surrounded by graphene), the powder used in the fabrication of the separation membrane in Comparative Example 1 (before molding, zeolite microcrystals), and the powder (graphene powder) in Reference Example 1 were observed using SEM. Furthermore, the specific surface area of ​​each powder was measured using a specific surface area meter (Quantachrome, model: Autosorb iQ). The results are shown in Table 1.

[0123] [Table 1]

[0124] shape Specific surface area Example 1 Spherical particle coating <![CDATA[380m 2 / g]]> Comparative Example 1 Spheres with a diameter of approximately 100 nm <![CDATA[400m 2 / g]]> Reference Example 1 plate-like <![CDATA[3000m 2 / g]]>

[0125] <Nitrogen Adsorption Determination>

[0126] Nitrogen adsorption was measured on the powder (zeolite microcrystals in the state of being surrounded by graphene) used in the fabrication of the zeolite separation membrane in Example 1 and the powder (zeolite microcrystals) used in the fabrication of the separation membrane in Comparative Example 1 before pressing and molding.

[0127] For the determination, three steps are performed sequentially: "pretreatment for adsorption determination," "determination of the adsorption branch of the adsorption isotherm," and "desorption branch determination." The apparatus used is a fully automated gas adsorption capacity measuring device (manufactured by Quantachrome, model: Autosorb iQ).

[0128] In the pretreatment for adsorption determination, the powder samples of Example 1 and Comparative Example 1 were kept for 3 hours at a pressure of less than 1 MPa and a temperature of 250°C.

[0129] Next, as an adsorption branch determination, nitrogen gas was introduced into the sample cell containing the powder samples of Example 1 and Comparative Example 1 under vacuum and maintained at 77 K, thereby measuring the amount of nitrogen adsorbed sequentially starting from low pressure. Next, as a desorption branch determination, the pressure was gradually reduced starting from the pressure after the adsorption branch determination, thereby measuring the amount of nitrogen adsorbed into the powder sample sequentially starting from high pressure.

[0130] The nitrogen adsorption isotherm obtained from the above measurements is shown below. Figure 5 (a) and Figure 5 (b) Figure 5 (a) is a diagram showing the overall nitrogen adsorption isotherm. Figure 5 (b) is a magnified view of the rising section (low-pressure section). Figure 5 In the diagram, black markings represent adsorption branches, and white markings represent desorption branches. MFI zeolite, which constitutes the zeolite separation membrane, originally lacks mesopores (fine pores of 2–50 nm), therefore only a sharp increase in adsorption near the relative pressure 0 should occur, and adsorption hysteresis should not be observed. However, Figure 5 The results shown confirmed the adsorption hysteresis around a relative pressure of 0.2, indicating the presence of micropores. This is believed to be because the interparticle gaps narrow during the pressure molding process in powder manufacturing, and these gaps function as micropores. Furthermore, if a graphene coating is formed as in Example 1, the adsorption hysteresis around a relative pressure of 0.2 changes to a slightly higher pressure, thus suggesting that the aforementioned interparticle gaps function more effectively as micropores.

[0131] Thermogravimetric Analysis

[0132] Thermogravimetric analysis (TG) was performed on the powder used in the fabrication of the zeolite separation membrane in Example 1 (zeolite microcrystals in the state of being surrounded by graphene), the powder used in the fabrication of the separation membrane in Comparative Example 1 (zeolite microcrystals), the powder used in the fabrication of the separation membrane in Comparative Example 2 (graphene oxide), and ammonium chloride, and TG curves were generated. The results are shown in... Figure 6 .

[0133] Depend on Figure 6 The results confirmed that the weight of MFI-graphene (equivalent to the powder of Example 1) decreased by 8% at 750–800 K. This weight reduction is attributed to the combustion of the graphene. Therefore, it can be inferred that the MFI-graphene (equivalent to the powder of Example 1) contains 8% by mass of graphene. Furthermore, although ammonium chloride (NH4Cl) was used, Figure 6 The results show a weight reduction in the range of 500K to 570K. This confirms that ammonium chloride was removed during the heat treatment process.

[0134] <Evaluation through Sex>

[0135] Prepare Figure 7 The device 50 shown has a capacity of 100 cm³ without volume change. 3 The system includes a chamber 51, a pressure gauge 52, an inlet flow path L1 with valve V1, and an exhaust flow path L2 with valve V2. Additionally, a separation membrane M for the evaluation object is installed upstream of valve V2 on the exhaust flow path L2.

[0136] The temperature inside chamber 51 is maintained at a constant 302 K. A hydrogen (H2) to methane (CH4) mixture with a volume ratio of 1:1 is introduced into chamber 51 through inlet flow path L1 until the pressure reaches 120 kPa. At the point when the pressure inside chamber 51 reaches 120 kPa, valve V1 of inlet flow path L1 is closed. Then, valve V2 of exhaust flow path L2 is opened. In this state, the pressure change over time inside chamber 51 is measured using pressure gauge 52. In addition, the concentration ratio of the gas discharged from exhaust flow path L2 is determined using a mass spectrometer. It should be noted that in the case of the hydrogen:methane mixture, it is assumed that hydrogen passes through the gas separation membrane and methane remains in chamber 51.

[0137] exist Figure 8 The diagram illustrates the result of plotting the pressure values ​​relative to time. Also, as... Figure 7As shown, the pressure change dp / dt with respect to time can be obtained from the pressure p1 at time t1 and the pressure p2 at time t2. That is, since dp / dt is basically equal to Δp / Δt, it is considered to be basically equal to (p2-p1) / (t2-t1), and dp / dt can be calculated from this relationship. On the other hand, dp / dt can also be expressed as the following formula (1). Here, p is the pressure of the chamber (Pa), A is the permeation area of ​​the membrane, R is the gas constant, T is the temperature, V is the volume of the chamber, and N is the flux.

[0138]

[0139] Based on the relationship shown in formula (1), the permeability P can be calculated by the following formula (2).

[0140]

[0141] For the separation membranes shown in Example 1 and Comparative Examples 1 to 3, the hydrogen permeability was calculated based on the above formula. Permeability can be used as an indicator of the rate at which gas separation occurs in the gas separation membrane.

[0142] Figure 9 The measurement results of each gas separation membrane in Example 1 and Comparative Examples 1 to 3 are plotted with hydrogen permeability as the horizontal axis and selectivity as the vertical axis. In the case of a hydrogen:methane mixture, hydrogen passes through the gas separation membrane, and methane remains in chamber 51. Therefore, the concentration of hydrogen relative to methane in the discharged gas is plotted.

[0143] right Figure 9 When the experimental results shown (above figure) were analyzed using a model, the following conclusions were drawn: Regarding the mechanism of gas permeation through a graphene-coated zeolite microcrystalline membrane, Knudsen diffusion is the dominant mechanism. Knudsen diffusion refers to a diffusion mechanism in which the mean free path of the diffusing molecules (in this case, the molecules permeating the membrane) is sufficiently large, resulting in almost no collisions between molecules; the permeating molecules pass through the pores only by colliding with the walls of the pores they wish to permeate.

[0144] In this Knudsen diffusion process, since there is no deceleration of the permeation velocity due to collisions between molecules, the diffusion rate is greater than that of ordinary molecular diffusion (where the mean free path is small and molecules diffuse while colliding with each other). When the size of the zeolite crystallite is around 100 nm, this is comparable to the mean free path of molecules under normal pressure (approximately 70 nm).

[0145] Furthermore, it is believed that the pores of zeolite microcrystals are cylindrical in shape with a diameter of approximately 0.55 nm and penetrate through the zeolite. Therefore, molecules passing through the gas separation membrane only pass through the cylindrical pores along this straight line. Thus, it is believed that molecules pass through zeolite particles with almost no collision with the pore walls and with almost no deceleration.

[0146] <Gas permeability>

[0147] use Figure 7 The apparatus 50 shown evaluates the permeability of a gas. The temperature inside chamber 51 of apparatus 50 is maintained at a constant 303 K. A mixed gas mixture of hydrogen (H2), methane (CH4), and sulfur hexafluoride (SF6) in a volume ratio of 1:1:1 is introduced into chamber 51 through inlet flow path L1 until the pressure reaches 120 kPa. At the point when the pressure in chamber 51 reaches 120 kPa, valve V1 of inlet flow path L1 is closed. Then, valve V2 of exhaust flow path L2 is opened. In this state, pressure gauge 52 is used to measure the pressure change over time in chamber 51. The pressure change relative to time is shown in the figure. Figure 10 .Depend on Figure 10 The results shown indicate a transmittance of 6.02 × 10⁻⁶. -7 mol / m 2 sPa.

[0148] 2. Apatite separation membrane

[0149] (Example 2)

[0150] A dispersion containing 0.99 mg of graphene oxide (Hummer process graphene oxide synthesized by Shinshu University, Japan) and 50 mg of hydroxyapatite microcrystals (Sigma-Aldrich, particle size 2.5 μm) was prepared in 100 ml of 0.01 M ammonium chloride aqueous solution. The pH of the dispersion was 7.63. The solution, which had been allowed to stand at 25 °C for 24 hours, was then placed in a vacuum freeze dryer and dried at 223 K and 10 Pa to obtain 51 mg of apatite microcrystal powder coated with graphene oxide.

[0151] The obtained powder was placed in a quartz boat and placed in a furnace under an argon atmosphere. Heating was carried out in an argon flow at a heating rate of 1 K / min, maintained at 573 K for 30 minutes, and then allowed to cool naturally. The argon flow was stopped when the furnace cooled to below 333 K, and the quartz boat was removed from the furnace. The mass of the powder obtained after heating was 48 mg.

[0152] Next, the powder removed from the heating furnace was placed in a quartz boat and placed in an electric furnace. It was heated in air at a rate of 1 K / min, held at 623 K for 10 minutes, and then allowed to cool naturally. The quartz boat was removed from the furnace when the temperature inside cooled to below 333 K. The mass of the powder obtained after heating was 47.2 mg.

[0153] The powder removed from the electric furnace was pressurized into a film using a tablet former. The pressure during pressurization was set to 15 MPa. This resulted in the apatite separation membrane of Example 2. The apatite separation membrane of Example 2 is a circle with an outer diameter of 8 mm when viewed from above. Note that the thickness of the apatite separation membrane of Example 2 was estimated to be 90 nm based on density calculations. SEM images of the apatite separation membrane of Example 2 are shown below. Figure 11 .

[0154] (Comparative Example 4: Hydroxyapatite)

[0155] 18.4 mg of hydroxyapatite (Sigma-Aldrich, particle size 2.5 μm) was prepared and pressurized into a membrane using a tablet press. The pressure during pressurization was set to 15 MPa to obtain the separation membrane of Comparative Example 4.

[0156] <Nitrogen Adsorption Determination>

[0157] Similar to the evaluation of the zeolite separation membrane, nitrogen adsorption was measured on the powder (powder of apatite microcrystals in the state of being surrounded by graphene) used in the fabrication of the apatite separation membrane in Example 2 above, and the powder (apatite microcrystals) used in the fabrication of the separation membrane in Comparative Example 4 before molding. The order of operation was the same as that in Example 1 and Comparative Example 1 above.

[0158] The nitrogen adsorption isotherm obtained from the above measurements is shown below. Figure 12 (a) and Figure 12 (b) Figure 12 (a) is a diagram showing the overall nitrogen adsorption isotherm. Figure 12 (b) is a magnified view of the rising section (low-pressure section). Figure 12 In the diagram, black markings represent adsorption branches, and white markings represent desorption branches. It was confirmed that the apatite microcrystals of Comparative Example 4, lacking pores within the crystals and particles, exhibited no adsorption hysteresis and a small adsorption capacity in the low-to-medium pressure range (around 0.1 to 0.7). Furthermore, it was confirmed that adsorption capacity increased significantly and adsorption hysteresis occurred starting from a relative pressure exceeding approximately 0.8. This indicates the presence of interparticle gaps that act as pores. It should be noted that since adsorption hysteresis exists on the high-pressure side relative to MFI zeolite, it can be inferred that the pore size of these gaps is larger than that of the MFI zeolite gaps.

[0159] As confirmed by the above measurement results, the specific surface area of ​​the powder (powder of apatite microcrystals in the state surrounding graphene coating) used in the fabrication of the apatite separation membrane in Example 2 before pressure molding was 110 m². 2 / g. On the other hand, it was confirmed that the specific surface area of ​​the powder (apatite microcrystals) used in the fabrication of the separation membrane in Comparative Example 4 was 100 m². 2 / g.

[0160] <Gas permeability>

[0161] use Figure 7 The apparatus 50 shown evaluates the permeability of a gas. The temperature inside chamber 51 of apparatus 50 is maintained at a constant 303 K. A mixed gas mixture of hydrogen (H2), methane (CH4), and sulfur hexafluoride (SF6) in a volume ratio of 1:1:1 is introduced into chamber 51 through inlet flow path L1 until the pressure reaches 120 kPa. At the point when the pressure in chamber 51 reaches 120 kPa, valve V1 of inlet flow path L1 is closed. Then, valve V2 of exhaust flow path L2 is opened. In this state, pressure gauge 52 is used to measure the pressure change over time in chamber 51. The pressure change relative to time is shown in the figure. Figure 10 .Depend on Figure 13 The results shown indicate a transmittance of 1.34 × 10⁻⁶. -7 mol / m 2 sPa.

[0162] Selective evaluation

[0163] use Figure 7 The apparatus 50 shown evaluates the permeability and selectivity of each gas. The temperature inside chamber 51 is kept constant at 303 K. The target gas (the gas to be separated) is introduced into chamber 51 until the pressure reaches 120 kPa. At the point when the pressure inside chamber 51 reaches 120 kPa, valve V1 of the inlet flow path L1 is closed. Then, valve V2 of the exhaust flow path L2 is opened. In this state, pressure gauge 52 is used to measure the pressure change over time inside chamber 51. From the results, the permeability of hydrogen relative to the target gas is determined.

[0164] Additionally, using apparatus 50, a 1:1 mixture of hydrogen (H2) and the target gas (the gas to be separated) is introduced from the inlet flow path L1 into chamber 51, which is maintained at a constant temperature of 303 K, until the pressure reaches 120 kPa. At the point when the pressure in chamber 51 reaches 120 kPa, valve V1 of the inlet flow path L1 is closed. Then, valve V2 of the exhaust flow path L2 is opened. In this state, pressure gauge 52 is used to measure the pressure change over time in chamber 51. Furthermore, a mass spectrometer is used to measure the gas discharged from the exhaust flow path L2, and the gas concentration ratio is determined. It is noted that when the target gas is methane, hydrogen passes through the gas separation membrane, and methane remains in chamber 51.

[0165] The kinetic diameter varies depending on the target gas. The evaluation results of selectivity and permeability for each target gas are shown in Table 2 below. The results in Table 2 confirm that, when a gas with a kinetic diameter of at least 0.35 nm is used as the target gas, the apatite separation membrane of Example 2 achieves higher performance compared to the apatite monomer separation membrane of Comparative Example 4. It should be noted that the permeability calculation method is the same as that for zeolite separation membranes.

[0166] [Table 2]

[0167]

[0168] Symbol Explanation

[0169] 1: Gas separation membrane

[0170] 10: Zeolite microcrystals

[0171] 11: Fine pores

[0172] 20: Graphene

[0173] 30: Support body

[0174] 50: Device

[0175] Room 51

[0176] 52: Pressure gauge

Claims

1. A method for manufacturing a gas separation membrane, comprising: A dispersion consisting of zeolite microcrystals composed of MFI zeolite and graphene oxide mixed with pure water is allowed to stand, and the graphene oxide is used to coat the zeolite microcrystals. The process of drying and pulverizing the dispersion after it has been allowed to stand; The process of reducing the graphene oxide powder by heating; and The process of pressing the reduced powder into a film shape. in, After the reduction treatment of the graphene oxide and before the formation of the film, the process further includes a step of heating the graphene at a temperature higher than the heating temperature in the reduction treatment to form nanowindows in the reduced graphene.

2. The method for manufacturing the gas separation membrane as described in claim 1, wherein, The dispersion was allowed to stand while the pH was adjusted to the range of 3.6-11.0 using a pH adjuster.

3. The method for manufacturing the gas separation membrane as described in claim 2, wherein, The pH adjuster is ammonium chloride, and the pH of the dispersion is adjusted to the range of 3.6-4.0 using the pH adjuster.

4. The method for manufacturing the gas separation membrane according to any one of claims 1 to 3, wherein, The heat treatment used to form nanowindows is carried out in a temperature range of 200°C to 600°C for 5 minutes to 50 hours.

5. The method for manufacturing the gas separation membrane according to any one of claims 1 to 3, wherein, In the process of forming a film by pressure molding, pressure molding is performed by applying a pressure of 5MPa to 40MPa.

6. A gas separation membrane obtained by the manufacturing method of the gas separation membrane according to claim 1, wherein the surface of a plurality of zeolite microcrystals composed of MFI zeolite is coated with graphene, and the zeolite microcrystals are bonded to each other via the graphene to form a sheet-like gas separation membrane. in, The zeolite microcrystals, whose surfaces are coated with graphene, are pressurized and shaped, thereby filling the spaces between adjacent zeolite microcrystals with graphene. The graphene has nanowindows.

7. The gas separation membrane as described in claim 6, wherein the thickness is 10 μm to 50 μm and the diameter of the main surface is 500 μm to 13 mm.

8. The gas separation membrane as described in claim 6 or 7, wherein, The size of the main facet of the graphene sheet structure is smaller than the particle size of the zeolite microcrystals.

9. The gas separation membrane as described in claim 6 or 7, wherein, The mass ratio of the zeolite microcrystals to the graphene is 6:100 to 20:

100.

10. The gas separation membrane as claimed in claim 6 or 7, wherein, The particle size of the zeolite microcrystals is 50 nm to 150 nm.

11. The gas separation membrane as claimed in claim 6 or 7, wherein, The pore size of the zeolite microcrystals is 0.54 nm to 0.56 nm.

12. The gas separation membrane as described in claim 6 or 7, wherein, The main facet of the graphene sheet structure has a size of 5nm to 50nm.

13. A method for manufacturing a gas separation membrane, comprising: The process involves allowing a dispersion of apatite microcrystals composed of hydroxyapatite and graphene oxide to stand, and then coating the area around the apatite microcrystals with the graphene oxide. The process of drying and pulverizing the dispersion after it has been allowed to stand; A process of reducing the graphene oxide powder by heating; After the reduction treatment of the graphene oxide, a heating treatment is performed at a temperature higher than the heating temperature in the reduction treatment to form nanowindows in the reduced graphene; and Following the process of forming nanowindows, the reduced powder is pressurized and molded into a film.

14. The method for manufacturing the gas separation membrane as described in claim 13, wherein, The dispersion was allowed to stand while the pH was adjusted to the range of 3.6-11.0 using a pH adjuster.

15. The method for manufacturing the gas separation membrane as described in claim 14, wherein, The pH adjuster is ammonium chloride, and the pH of the dispersion is adjusted to the range of 6.0-9.3 using the pH adjuster.

16. A gas separation membrane obtained by the manufacturing method of the gas separation membrane according to claim 13, wherein the gas separation membrane is a sheet-like gas separation membrane in which the surfaces of a plurality of apatite microcrystals composed of hydroxyapatite are coated with graphene, and the apatite microcrystals are bonded to each other via the graphene. in, The graphene has nano-windows. The apatite microcrystals whose surfaces are coated with graphene are pressurized and shaped, thereby filling the spaces between adjacent apatite microcrystals with graphene.

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