Method for producing gas separation membrane

Abstract

This method for producing a gas separation membrane comprises: a step wherein a dispersion liquid, which is obtained by mixing graphene oxide and a zeolite microcrystalline body formed of MFI zeolite with pure water, is left at rest so that the periphery of the zeolite microcrystalline body is covered by the graphene oxide; a step wherein the dispersion liquid after being left at rest is dried and powderized; a step wherein the powder is subjected to a reduction treatment of the graphene oxide by means of heating; and a step wherein the powder after the reduction treatment is subjected to press molding so as to be formed into the shape of a membrane.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a gas separation membrane and a gas separation membrane.

Background Art

[0002] As a method for manufacturing a zeolite membrane using zeolite microcrystals, Patent Document 1 describes a method of depositing a zeolite membrane on a porous support such as alumina by a hydrothermal synthesis method or a vapor phase method using silica and alumina as starting materials. Further, Patent Document 2 describes a method of forming a zeolite membrane on a support using zeolite microcrystals as seed crystals.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present disclosure has been made in view of the above, and an object thereof is to provide a method for manufacturing a gas separation membrane and a gas separation membrane having enhanced gas separation performance.

Means for Solving the Problems

[0005] To achieve the above object, a method for manufacturing a gas separation membrane according to one embodiment of the present disclosure includes a step of allowing a dispersion liquid obtained by mixing zeolite microcrystals made of MFI zeolite and graphene oxide with pure water to stand, and covering the periphery of the zeolite microcrystals with the graphene oxide; a step of drying and powdering the dispersion liquid after standing; a step of performing a reduction treatment of the graphene oxide by heating on the powder; and a step of pressure-molding the powder after the reduction treatment into a film shape.

[0006] According to the above method for manufacturing a gas separation membrane, a dispersion containing zeolite microcrystals and graphene oxide is allowed to stand. After covering the periphery of the zeolite microcrystals with graphene oxide, it is powdered, and the graphene oxide is reduced by a reduction treatment. Then, the powder after the reduction treatment is pressure-molded into a film shape to obtain a gas separation membrane. By manufacturing a gas separation membrane by such a method, a gas separation membrane in which the space between adjacent zeolite microcrystals is appropriately filled with graphene can be obtained, so that the gas separation performance can be enhanced.

[0007] Here, after the step of performing the reduction treatment of the graphene oxide and before the step of forming the film shape, a heat treatment is performed at a temperature higher than the heating temperature in the reduction treatment to form nano-windows in the reduced graphene, and an embodiment may further include this step.

[0008] By having the step of forming nano-windows in the graphene before the step of forming the film shape, nano-windows are provided in the graphene covering the periphery of the zeolite microcrystals. Thereby, since the selectivity of the gas based on the molecular diameter is particularly enhanced, the separation performance can be further enhanced.

[0009] The dispersion can be allowed to stand in a state where the pH is adjusted to the range of 3.6 - 11.0 by a pH adjuster. As described above, by adjusting the pH of the dispersion with a pH adjuster, the coating amount of graphene oxide around the zeolite microcrystals can be increased.

[0010] The pH adjuster is ammonium chloride, and the pH of the dispersion can be adjusted to the range of 3.6 - 4.0 by the pH adjuster.

[0011] A sheet-like gas separation membrane in which the surfaces of a plurality of zeolite microcrystals made of MFI zeolite are coated with graphene, and the zeolite microcrystals are bonded to each other through the graphene. By pressure-molding the zeolite microcrystals whose surfaces are coated with the graphene, the spaces between adjacent zeolite microcrystals are filled with the graphene.

[0012] In the above gas separation membrane, the zeolite microcrystals coated with graphene are formed into a membrane in which the spaces between adjacent zeolite microcrystals are filled with graphene by pressure molding. In the above gas separation membrane, since the spaces between adjacent zeolite microcrystals are appropriately filled with graphene, the gas separation performance can be enhanced.

[0013] The graphene can be in a form having nano-windows. Since the formation of nano-windows in the graphene enhances the selectivity of gases based particularly on the molecular diameter, the separation performance can be further enhanced.

[0014] Moreover, a method for manufacturing a gas separation membrane according to another aspect of the present disclosure includes a step of allowing a dispersion liquid obtained by mixing apatite microcrystals made of hydroxyapatite and graphene oxide with pure water to stand still to cover the periphery of the apatite microcrystals with the graphene oxide, a step of drying and pulverizing the dispersion liquid after standing still, a step of performing a reduction treatment of the graphene oxide by heating on the powder, and a step of pressure-molding the powder after the reduction treatment into a membrane shape.

[0015] According to the above method for manufacturing a gas separation membrane, a dispersion liquid containing apatite microcrystals and graphene oxide is allowed to stand still, and after covering the periphery of the apatite microcrystals with graphene oxide, it is pulverized, and the graphene oxide is reduced by a reduction treatment. Then, by pressure-molding the powder after the reduction treatment into a membrane shape, a gas separation membrane can be obtained. By manufacturing a gas separation membrane by such a method, a gas separation membrane in which the spaces between adjacent apatite microcrystals are appropriately filled with graphene can be obtained, so that the gas separation performance can be enhanced.

[0016] Here, after the step of performing the reduction treatment of the graphene oxide and before the step of forming the film, a heat treatment is performed at a temperature higher than the heating temperature in the reduction treatment to form nano-windows in the reduced graphene. An aspect can be further provided that includes this step.

[0017] By having a step of forming nano-windows in the graphene before the step of forming the film, nano-windows are provided in the graphene covering the periphery of the apatite microcrystals. Thereby, since the gas selectivity based on the molecular diameter is particularly enhanced, the separation performance can be further improved.

[0018] The dispersion can be in a state where it is adjusted to a pH range of 3.6 - 11.0 with a pH adjuster and then allowed to stand. As described above, by adjusting the pH of the dispersion with a pH adjuster, the coating amount of graphene around the apatite microcrystals can be increased.

[0019] The pH adjuster is ammonium chloride, and the pH of the dispersion can be adjusted to a range of 6.0 - 9.3 with the pH adjuster.

[0020] A sheet-like gas separation membrane in which the surfaces of a plurality of apatite microcrystals made of hydroxyapatite are coated with graphene and the apatite microcrystals are bonded to each other through the graphene. By pressure-molding the apatite microcrystals whose surfaces are coated with the graphene, the spaces between adjacent apatite microcrystals are filled with the graphene.

[0021] In the above gas separation membrane, the apatite microcrystals coated with graphene are formed into a membrane in which the spaces between adjacent apatite microcrystals are filled with graphene by pressure molding. In the above gas separation membrane, since the spaces between adjacent apatite microcrystals are appropriately filled with graphene, the gas separation performance can be enhanced.

[0022] The graphene can be in a form having nano-windows. Since the formation of nano-windows in the graphene enhances the selectivity of gases based particularly on the molecular diameter, the separation performance can be further improved.

Advantages of the Invention

[0023] According to the present disclosure, there are provided a method for manufacturing a gas separation membrane with enhanced gas separation performance and a gas separation membrane.

Brief Description of the Drawings

[0024]

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Mode for Carrying Out the Invention

[0025] Hereinafter, embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are assigned to the same elements, and duplicate descriptions are omitted.

[0026] <First Embodiment: Zeolite Separation Membrane> (Zeolite Separation Membrane) As a first embodiment, a zeolite separation membrane will be described. The zeolite separation membrane according to one embodiment is a gas separation membrane having a function of separating multiple types of gases by utilizing the microporous structure of zeolite crystals. 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 separating hydrogen and methane or hydrogen and carbon monoxide. As other applications, it can also be used for separating hydrogen and oxygen, carbon dioxide and nitrogen, methane and nitrogen, etc. The zeolite separation membrane is formed into a sheet-like membrane in which zeolite microcrystals are bonded via graphene by coating graphene on the surface of the zeolite microcrystals.

[0027] Fig. 1 is a diagram for explaining the structure of the zeolite separation membrane. The gas separation membrane 1 includes a zeolite microcrystal 10 and graphene 20. Further, the gas separation membrane 1 can be used in a state supported by a support 30 or the like.

[0028] The gas separation membrane 1 is, for example, a sheet-like membrane with a thickness of about 10 μm to 50 μm. Also, 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 graphenes 20 are arranged so as to cover the periphery thereof. The shape of the main surface of the gas separation membrane 1 is not particularly limited, and can be, for example, a polygonal shape such as a quadrilateral, a circular shape, or the like.

[0029] The zeolite microcrystal 10 is a crystal of MFI zeolite. There are many zeolites with different framework structures known. The MFI zeolite (ZSM-5) is used for the zeolite separation membrane described in this embodiment, and the chemical formula of the unit cell is Na n Al n Si 96-n O 192 ·16H2O (0 < n < 27). The framework structure of the MFI zeolite is defined by the International Zeolite Association. Although it is possible to synthesize MFI zeolite with a particle size of about several μm, the size (particle diameter) of the zeolite microcrystal 10 used in this embodiment is in the range of 50 nm to 150 nm. In the gas separation membrane 1, the zeolite microcrystal 10 is substantially spherical, but in FIG. 1, it is schematically shown as a polygonal shape (hexagonal shape).

[0030] Also, the zeolite microcrystal 10 has a large number of pores derived from its structure on its surface. The pores in the zeolite microcrystal 10 have a diameter of 0.54 nm to 0.56 nm. As an example, MFI zeolite (MFI zeolite manufactured by Mitsubishi Chemical Corporation) with a crystal particle diameter of 100 nm or less and a pore diameter of about 0.55 nm can be used as the zeolite microcrystal 10.

[0031] Graphene 20 is provided to connect adjacent zeolite microcrystals 10. Further, graphene 20 covers the periphery of zeolite microcrystals 10. However, "covering the periphery of zeolite microcrystals 10" does not mean that the entire surface of zeolite microcrystals 10 is covered by graphene 20, and a part of zeolite microcrystals 10 may be exposed. Graphene 20 is a sheet-like substance having a single-atom thickness with carbon atoms strongly bonded in a benzene ring shape.

[0032] As shown in FIG. 1, in the gas separation membrane 1, each of the plurality of zeolite microcrystals 10 is covered by a plurality of graphenes 20 and is bonded to adjacent zeolite microcrystals 10 via graphene 20. Therefore, for example, zeolite microcrystals 10 may exist on both main surfaces of a pair of a single graphene 20. Further, graphene 20 is arranged to fill the space between adjacent zeolite microcrystals 10. Therefore, pores penetrating between adjacent zeolite microcrystals 10 in a plan view are not formed, and graphene 20 is provided between adjacent zeolite microcrystals 10.

[0033] Note that the size of graphene 20 (the size of the main surface of the sheet-like structure) is smaller than the particle diameter of zeolite microcrystals 10, and is, for example, in the range of 5 nm to 50 nm. Therefore, the surface of zeolite microcrystals 10 is covered by a plurality of graphenes 20. Graphene 20 may cover zeolite microcrystals 10 with a single layer, or may cover zeolite microcrystals 10 in a state where a plurality of graphenes 20 overlap (a multi-layer state). Note that FIG. 1 does not show a structure in which graphene 20 forms a multi-layer, and schematically shows a state in which a plurality of graphenes 20 cover zeolite microcrystals 10 with a single layer.

[0034] A large number of nano-windows (pores having a pore diameter of about 0.3 nm to 1.5 nm) are formed in graphene 20. By providing this nano-window, the selectivity among the gas separation performances is further enhanced.

[0035] In the gas separation membrane 1, the mass ratio of the zeolite microcrystals 10 to the graphene 20 is, for example, about 6:100 to 20:100. The mass ratio of the zeolite microcrystals 10 to the graphene 20 can be determined by thermogravimetric analysis. For example, in the TG curve obtained by thermogravimetric analysis in air, the rate of mass reduction can be confirmed. From this result, the mass ratio of the zeolite microcrystals 10 to the graphene 20 in the gas separation membrane 1 can be determined.

[0036] The above gas separation membrane 1 can be used alone, but as an example, it can be used while being supported by a support 30. The support 30 is not particularly limited as long as it can support the gas separation membrane 1 and has an opening sufficiently larger than the pore diameter of the pores of the zeolite microcrystals 10. The support 30 may be, for example, a frame material that supports the outer periphery of the gas separation membrane 1.

[0037] (Method for manufacturing a zeolite separation membrane) The zeolite separation membrane is formed by generally coating the surface of zeolite microcrystals with graphene oxide and then bonding them to each other. Therefore, as shown in FIG. 2, the method for manufacturing a zeolite separation membrane includes a step of preparing a dispersion liquid containing zeolite microcrystals and graphene oxide (step S01), a step of adjusting the dispersion liquid to a predetermined pH and leaving it for a predetermined time (step S02), a step of performing freeze-drying (step S03), a step of heating and performing a reduction treatment (step S04), a step of producing nano-windows (step S05), and a step of performing pressure molding (step S06).

[0038] In step S01, zeolite microcrystals and graphene oxide are mixed in pure water to prepare a dispersion liquid. As the zeolite microcrystals, MFI zeolite having a particle diameter in the range of 50 nm to 150 nm and a pore diameter of 0.54 nm to 0.56 nm as described above is used.

[0039] In addition, graphene oxide is used for the purpose of binding zeolite microcrystals to each other. Graphene oxide has a structure in which graphene is oxidized and contains hydroxyl groups, carboxyl groups, epoxy groups, etc. As the graphene oxide used for the production of the zeolite separation membrane, for example, those having 5 or less layers of stacked layers and a particle diameter of about 5 nm to 50 nm are used. When the graphene oxide is separated into a single layer or the number of stacked layers is small, the coating of the zeolite microcrystals and the binding of the zeolite microcrystals to each other can be appropriately performed. Note that the properties of the graphene oxide when introduced into the dispersion are not particularly limited.

[0040] The dispersion of zeolite microcrystals and graphene oxide can be prepared by mixing the zeolite microcrystals and graphene oxide in pure water. The mixing amount of the zeolite microcrystals, graphene oxide and pure water can be, for example, about 10 mg to 20 mg of zeolite microcrystals with respect to 10 ml of pure water, and about 0.6 mg to 4.0 mg of graphene oxide. Further, the mixing ratio of the zeolite microcrystals and graphene oxide can be, for example, about 6:100 to 20:100 as a mass ratio.

[0041] In step S02, the pH of the dispersion of zeolite microcrystals and graphene oxide is adjusted. Thereby, the electrostatic interaction between the zeolite microcrystals and graphene oxide in the dispersion is promoted. As a result, a state in which the surface of the zeolite microcrystals is coated with graphene oxide is formed. According to the result of examining the surface charge density of graphene oxide, the surface charge density hardly changes in the range of about pH 2 to 10. On the other hand, since the surface charge density of the zeolite microcrystals changes when the pH changes, the ionic strength between the zeolite microcrystals and graphene oxide can be changed by adjusting the pH of the dispersion.

[0042] The target pH for adjusting the dispersion varies depending on the type of pH adjuster added for adjusting the pH of the dispersion. For example, when adjusting the pH with salts such as ammonium chloride, the target pH for adjustment is about 3.6 to 4.0.

[0043] In addition, as the salts used for the above pH adjustment, in addition to ammonium chloride, ammonium hydrogen carbonate, ammonium nitrate, etc. are used. On the other hand, when adjusting the pH with a weak base such as aqueous ammonia, the target pH for adjustment is set to about 3.6 to 11.0. As the weak base used for pH adjustment, in addition to aqueous ammonia, tetramethylammonium hydroxide, etc. are used.

[0044] Using a pH adjuster to adjust the pH of the dispersion to the pH within the above range, and then allowing it to stand for several hours to several tens of hours, the electrostatic interaction between the zeolite microcrystals and graphene oxide causes the periphery of the zeolite microcrystals to be covered by graphene oxide. By allowing the dispersion adjusted to a predetermined pH to stand for a predetermined time, the interaction between the zeolite microcrystals and graphene oxide in the dispersion proceeds. The standing time is not particularly limited as long as the interaction in the dispersion can proceed sufficiently. As an example, it has been confirmed that by allowing a dispersion adjusted to pH 4.6 with ammonium chloride to stand for 24 hours, the interaction between the zeolite microcrystals and graphene oxide in the dispersion proceeds sufficiently. Whether the interaction has proceeded sufficiently can be confirmed, for example, by separating the phase of the colloidal dispersion containing zeolite particles from the phase of the aqueous solution not containing them.

[0045] Note that a dispersion in which pH adjustment is performed may be formed by mixing zeolite microcrystals and graphene oxide with the liquid whose pH has been adjusted previously. That is, steps S01 and S02 may be performed simultaneously. For example, when preparing a 0.05 M aqueous ammonium chloride solution and mixing 9.2 mg of zeolite microcrystals and 0.8 mg of graphene oxide with this aqueous solution, a dispersion adjusted to pH 4.6 can be obtained. A dispersion in which pH adjustment is performed by such a procedure may be prepared.

[0046] In step S03, by drying the above dispersion liquid, a powder of zeolite microcrystals coated with graphene oxide is produced. As an example, by drying the dispersion liquid in a vacuum freeze dryer under the conditions of a temperature of -40°C to -30°C (233K to 243K) and a pressure of 5 Pa to 20 Pa, the moisture in the dispersion liquid is removed, and a powder of zeolite microcrystals coated with graphene oxide can be obtained. Note that instead of vacuum freeze drying, a powder of zeolite microcrystals coated with graphene oxide may be obtained by heat drying.

[0047] In step S04, heat treatment is performed on the powder of zeolite microcrystals coated with graphene oxide. Thereby, reduction (thermal reduction) of the graphene oxide covering the zeolite microcrystals is performed.

[0048] The heat treatment is performed, for example, in a temperature range of 220°C to 300°C (493K to 573K) for about 10 minutes to 6 hours. There is no upper limit on the heating temperature and heating time, but by heating under the above conditions, the reduction of graphene oxide can be sufficiently performed. As the atmosphere during the heat treatment, for example, an argon atmosphere can be used. As an example, when the mass of the zeolite microcrystals coated with graphene oxide is about 20 mg, in a heating furnace under an argon atmosphere, it is heated to 573K at a heating rate of 1K / min, the temperature is maintained for 30 minutes, and then cooled to 333K or lower, whereby the graphene oxide is reduced. By performing the heat treatment under the above conditions, the graphene oxide around the zeolite microcrystals is reduced to graphene. Thereby, the periphery of the zeolite microcrystals is covered with graphene. Note that when the graphene oxide is completely reduced, the performance as a gas separation membrane can be sufficiently exhibited.

[0049] As the thermal reduction treatment progresses to a certain extent, the adhesion between the zeolite microcrystals and graphene increases. Therefore, a separation membrane can be stably formed after forming the separation membrane described later.

[0050] In step S05, by further performing heat treatment on the reduced graphene, nanopores (pores with a pore diameter of about 0.3 nm to 1.5 nm) are formed in the graphene.

[0051] The heat treatment for forming the nanopores is performed, for example, in a temperature range of 200°C to 600°C (473 K to 873 K) for about 5 minutes to 50 hours. As the atmosphere during the heat treatment, for example, air can be used. As an example, when the mass of the zeolite microcrystals coated with graphene is about 20 mg, in a heating furnace under an air atmosphere, it is heated to 623 K at a heating rate of 1 K / min, the temperature is maintained for 10 minutes, and then cooled to 333 K or lower, whereby pores can be formed in the graphene. Note that the larger the heating temperature, the larger the pore diameter of the nanopores can be.

[0052] In step S06, a zeolite separation membrane is formed by pressure-molding a mixture of the zeolite microcrystals and graphene after the treatment for producing the nanopores has been performed. Up to this stage, the zeolite microcrystals are covered with graphene, but by promoting the bonding between the graphenes, a separation membrane is formed in a state where the zeolite microcrystals are arranged in proximity to each other via the graphene. As a specific procedure, a pressure of 5 MPa to 40 Mpa is applied by compression molding to form a film. When forming the film, for example, a tablet press can be used. Thereby, a zeolite separation membrane can be obtained. By setting the pressure during pressurization to 5 MPa or more, a sheet-like separation membrane is formed. On the other hand, by setting the pressure to 40 MPa or less, breakage (collapse of pores) of the pores of the zeolite microcrystals due to pressurization can be prevented. Note that when the pressure during pressure molding is, for example, 10 MPa to 20 MPa, a separation membrane with increased strength as a film and suppressed breakage of the pores of the zeolite microcrystals can be obtained.

[0053] By going through the above-described process of pressure molding, a zeolite separation membrane can be obtained in which the graphenes covering the periphery of the zeolite microcrystals are firmly bonded to each other.

[0054] The zeolite separation membrane obtained by the above procedure can be used as a highly rigid gas separation membrane by being supported, for example, by a support 30 shown in FIG. 1.

[0055] (Properties of Zeolite Separation Membrane) The gas separation membrane 1 described in this embodiment can separate a mixed gas having different molecular sizes by utilizing a large number of pores 11 provided in the zeolite microcrystals 10. Specifically, molecules with a small molecular diameter can pass through the pores of the zeolite microcrystals 10 and thus can pass through the gas separation membrane 1. On the other hand, molecules with a large molecular diameter cannot pass through the gas separation membrane 1 because they cannot pass through the pores of the zeolite microcrystals 10. In the gas separation membrane 1, the separation of the mixed gas can be accurately performed by utilizing the difference in the molecular diameters of the molecules constituting such a mixed gas. Note that by adjusting the pore diameter of the gas separation membrane 1, the gas to be separated in the zeolite separation membrane can be selected.

[0056] In particular, the gas separation membrane 1 described in this embodiment can be used for the separation of methane and hydrogen. When a mixed gas of methane and hydrogen is passed through the gas separation membrane 1, hydrogen passes through the gas separation membrane 1 while methane does not pass through the gas separation membrane 1. Therefore, the separation of methane and hydrogen can be suitably performed by using the gas separation membrane 1. Further, the gas separation membrane 1 also has the feature that the gas separation rate is faster than that of conventional gas separation membranes.

[0057] As described above, the method for manufacturing a gas separation membrane according to this embodiment includes a step of allowing a dispersion liquid obtained by mixing zeolite microcrystals made of MFI zeolite and graphene oxide with pure water to stand still to cover the periphery of the zeolite microcrystals with graphene oxide, a step of drying and pulverizing the dispersion liquid after standing still, a step of performing a reduction treatment of graphene oxide by heating on the powder, and a step of pressure-molding the powder after the reduction treatment into a film shape. By manufacturing a gas separation membrane by the above method for manufacturing a gas separation membrane, a gas separation membrane in which the space between adjacent zeolite microcrystals is appropriately filled with graphene can be obtained, and thus the gas separation performance can be enhanced.

[0058] Also, after the step of performing the reduction treatment of graphene oxide and before the step of forming it into a film, a heat treatment is performed at a temperature higher than the heating temperature in the reduction treatment to form nano-windows in the reduced graphene. When there is a further step, nano-windows are provided in the graphene that covers the periphery of the zeolite microcrystals. Thereby, since the gas selectivity based on the molecular diameter is particularly enhanced, the separation performance can be further enhanced.

[0059] The dispersion liquid can be in a state of being allowed to stand still after being adjusted to a range of pH 3.6 to 11 by a pH adjuster. As described above, by adjusting the pH of the dispersion liquid with a pH adjuster, the coating amount of the periphery of the zeolite microcrystals with graphene oxide can be increased. In particular, the pH adjuster is ammonium chloride, and the pH of the dispersion liquid can be adjusted to a range of 3.6 to 4 by the pH adjuster.

[0060] A sheet-like gas separation membrane in which the surfaces of a plurality of zeolite microcrystals composed of MFI zeolite are coated with graphene and the zeolite microcrystals are bonded to each other via graphene. By pressure-molding the zeolite microcrystals whose surfaces are coated with graphene, the spaces between adjacent zeolite microcrystals are filled with graphene.

[0061] In the above gas separation membrane, the zeolite microcrystals coated with graphene are formed into a membrane in which the spaces between adjacent zeolite microcrystals are filled with graphene by pressure molding. In the above gas separation membrane, since the spaces between adjacent zeolite microcrystals are appropriately filled with graphene, the gas separation performance can be enhanced.

[0062] Graphene can be in a mode having nano-windows. Since the formation of nano-windows in graphene particularly enhances the gas selectivity based on the molecular diameter, the separation performance can be further enhanced.

[0063] Although several embodiments have been described above, the present disclosure is not limited to the above embodiments in any way. Also, the description contents of the above-described embodiments can be applied to each other.

[0064] <Second Embodiment: Apatite Separation Membrane> (Apatite Separation Membrane) As the gas separation membrane according to the second embodiment, an apatite separation membrane in which zeolite microcrystals are changed to apatite microcrystals will be described. The apatite microcrystals used in the apatite separation membrane according to the second embodiment are different from zeolite microcrystals in that they do not have a minute pore structure. However, also for the apatite separation membrane, by coating the surface of the apatite microcrystals with graphene, gas separation performance similar to that of the zeolite separation membrane can be obtained. That is, the apatite separation membrane described in the present embodiment can also be used for separation of hydrogen and methane or hydrogen and carbon monoxide, separation of hydrogen and oxygen, separation of carbon dioxide and nitrogen, separation of methane and nitrogen, and the like. The apatite separation membrane also has the same structure as the structure of the zeolite separation membrane shown in FIG. 1. However, as described above, since the apatite microcrystals do not have pores, this is a different part from the zeolite separation membrane.

[0065] In the second embodiment, the differences between the apatite separation membrane and the zeolite separation membrane will be described. However, for the parts where the apatite separation membrane is not described, it is the same as the zeolite separation membrane.

[0066] The apatite microcrystals used in the apatite separation membrane are crystals of hydroxyapatite. The chemical formula is Ca5(PO4)3(OH). Note that hydroxyapatite has a hexagonal crystal structure. The size (particle diameter) of the apatite microcrystals used in the present embodiment is in the range of 2 μm to 3 μm. In the gas separation membrane 1, the hydroxyapatite microcrystals have a plate-like outer shape.

[0067] Also in the apatite separation membrane, similar to the gas separation membrane 1 shown in FIG. 1, each of a plurality of apatite microcrystals (corresponding to the zeolite microcrystals 10 shown in FIG. 1) is coated with a plurality of graphenes 20 and is bonded to an adjacent apatite microcrystal via the graphenes 20. As a result, it has the same shape as the zeolite separation membrane according to the first embodiment.

[0068] Note that the same applies to the fact that a large number of nano-windows (pores having a pore diameter of about 0.3 nm to 1.5 nm) are formed in the graphene 20.

[0069] Also, in the apatite separation membrane, the mass ratio of the apatite microcrystal to the graphene is, for example, about 4:100 to 20:100.

[0070] (Method for manufacturing apatite separation membrane) The apatite separation membrane is formed by generally coating the surface of apatite microcrystals with graphene oxide and then bonding these to each other. This is the same as the zeolite separation membrane in this regard. Therefore, the method for manufacturing the apatite separation membrane is the same as the method for manufacturing the zeolite separation membrane described in the first embodiment. The method for manufacturing the zeolite separation membrane is as shown in FIG. 2, and includes a step of preparing a dispersion liquid containing zeolite microcrystals and graphene oxide (step S01), a step of adjusting the dispersion liquid to a predetermined pH and leaving it for a predetermined time (step S02), a step of performing freeze-drying (step S03), a step of heating and performing a reduction treatment (step S04), a step of creating nano-windows (step S05), and a step of performing pressure 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.

[0071] Note that, as described above, hydroxyapatite with a particle size in the range of 2 μm to 3 μm is used as the apatite microcrystals used in step S01. In the step of adjusting the dispersion liquid to a predetermined pH and leaving it for a predetermined time (step S02), the pH of the dispersion liquid prepared by mixing apatite microcrystals and graphene oxide in pure water becomes about 9.3, which is different from the dispersion liquid of zeolite microcrystals and graphene oxide. Therefore, for example, when adjusting the pH with salts such as ammonium chloride, the target pH to be adjusted is about 6.0 to 9.3.

[0072] In the gas separation membrane according to the second embodiment described above, as a result of pressure molding of apatite microcrystals coated with graphene, the space between adjacent apatite microcrystals is filled with graphene to form a membrane. In the gas separation membrane described above, since the space between adjacent apatite microcrystals is appropriately filled with graphene, the gas separation performance can be enhanced.

[0073] Graphene can be in a form having nano-windows. Since the formation of nano-windows in graphene enhances the selectivity of gases based particularly on the molecular diameter, the separation performance can be further enhanced.

[0074] As described above, several embodiments have been explained, but the present disclosure is not limited to the above embodiments in any way. Also, the explanatory content regarding the above-described embodiments can be applied to each other.

Example

[0075] Hereinafter, the content of the present disclosure will be described in more detail with reference to examples and comparative examples. However, the present disclosure is not limited to the following examples.

[0076] 1. Zeolite separation membrane (Consideration regarding pH adjustment) In the method for manufacturing a gas separation membrane described in this embodiment, as described above, after adjusting the pH of the dispersion liquid and then allowing it to stand, the periphery of the zeolite microcrystals 10 is covered with graphene. The relationship between the pH at this time and the coating amount (weight) of graphene was examined. The results are shown in FIG. 3.

[0077] A dispersion liquid was prepared by dispersing 2.0 mg of graphene (Hummer method graphene manufactured by Shinshu University) and 20 mg of MFI zeolite microcrystals (manufactured by Mitsubishi Chemical Corporation, particle size 100 nm, pore size 0.55 nm) in 10 mL of pure water. Solutions of each pH (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) shown in FIG. 3 were prepared using an aqueous ammonium chloride solution (concentration 1 M). After allowing each of these solutions to stand at 25° C. for 24 hours, the lower layer solution separated into two phases was collected with a micropipette and evaporated to dryness. Thermogravimetric analysis was performed on the powder thus obtained in air, and a TG curve was created. Assuming that the rate of weight loss at 750 to 800 K in the obtained TG curve is the weight of graphene, the ratio (mass %) of graphene was estimated.

[0078] In FIG. 3, the horizontal axis represents the pH of the dispersion liquid (preparation solution), and the vertical axis represents the coating ratio of graphite (the amount of graphite contained in the dry powder: mass %).

[0079] (Example 1) A dispersion liquid was prepared by dispersing 1.6 mg of graphene (Hummer method graphene manufactured by Shinshu University) and 18.4 mg of MFI zeolite microcrystals (manufactured by Mitsubishi Chemical Corporation, particle size 100 nm, pore size 0.55 nm) in 10 mL of a 0.05 M aqueous ammonium chloride solution. The pH of the dispersion liquid at this time was 4.6. The solution obtained by allowing this dispersion liquid to stand at 25° C. for 24 hours was placed in a vacuum freeze dryer and dried under the conditions of a temperature of 223 K and a pressure of 10 Pa to obtain 20 mg of a powder of zeolite microcrystals coated with graphene.

[0080] The obtained powder was placed in a quartz boat and installed in a heating furnace under an argon atmosphere. It was heated at a heating rate of 1 K / min in an argon stream, held at a temperature of 573 K for 30 minutes, and then naturally cooled. When the heating furnace was cooled to a temperature of 333 K or lower, the argon stream was stopped and the quartz boat was taken out of the heating furnace. The mass of the powder obtained after heating was 14 mg.

[0081] Next, the powder taken out from the heating furnace was placed in a quartz boat and installed in an electric furnace. It was heated at a heating rate of 1 K / min in air, held at a temperature of 623 K for 10 minutes, and then naturally cooled. When the temperature inside the electric furnace was cooled to a temperature of 333 K or lower, the quartz boat was taken out of the electric furnace. The mass of the powder obtained after heating was 13.8 mg.

[0082] The powder taken out from the electric furnace was pressure-molded into a film using a tablet press. The pressure during pressing was 15 MPa. As a result, a zeolite separation membrane according to Example 1 was obtained. The zeolite separation membrane according to Example 1 was circular in shape with an outer diameter of 8 mm in plan view. The thickness of the zeolite separation membrane according to Example 1 was estimated to be 90 nm by calculation based on density. The SEM image of the zeolite separation membrane according to Example 1 is shown in FIG. 4.

[0083] (Comparative Example 1: MFI zeolite) 18.4 mg of MFI zeolite (manufactured by Mitsubishi Chemical Corporation, particle size 100 nm, pore diameter 0.55 nm) was prepared and pressure-molded into a film using a tablet press. The pressure during pressing was 15 MPa to obtain a separation membrane according to Comparative Example 1.

[0084] (Comparative Example 2: Graphene oxide) 10 mg of graphene oxide (Hummer method graphene oxide manufactured by Shinshu University) was prepared and pressure-molded into a film using a tablet press. The pressure during pressing was 15 MPa to obtain a separation membrane according to Comparative Example 2.

[0085] (Comparative Example 3) 10 mL of a 0.05 M aqueous ammonium chloride solution was prepared with a dispersion liquid in which 1.6 mg of graphene oxide (Hummer method graphene oxide manufactured by Shinshu University) and 18.4 mg of MFI zeolite microcrystals (manufactured by Mitsubishi Chemical Corporation, particle diameter 100 nm, pore diameter 0.55 nm) were dispersed. The pH of the dispersion liquid at this time was 4.6. The dispersion liquid was allowed to stand at 25°C for 24 hours, and the solution was filtered through an alumina filter (pore diameter 100 nm). As a result, a film-like body in which MFI zeolite coated with graphene oxide was laminated was obtained. This film-like body was dried in a dryer at 110°C to remove the moisture remaining in the film-like body.

[0086] The dried film-like body was placed in a heating furnace in an argon atmosphere. It was heated at a heating rate of 1 K / min in an argon stream, held at a temperature of 573 K for 30 minutes, and then naturally cooled. When the heating furnace was cooled to a temperature of 333 K or lower, the argon stream was stopped and it was taken out from the heating furnace. As a result, the separation membrane according to Comparative Example 3 was obtained.

[0087] (Reference Example 1) The powder before molding (graphene oxide powder) used for producing the separation membrane according to Comparative Example 2 was placed in a quartz boat and installed in a heating furnace in an argon atmosphere. It was heated at a heating rate of 1 K / min in an argon stream, held at a temperature of 573 K for 30 minutes, and then naturally cooled. When the heating furnace was cooled to a temperature of 333 K or lower, the argon stream was stopped, the quartz boat was taken out from the heating furnace, and the powder according to Reference Example 1 was obtained. This powder corresponds to graphene powder in which graphene oxide has been reductively treated.

[0088] <Comparison of Structures> The powder before pressure molding (powder of zeolite microcrystals in a state where graphene covers the surroundings) used for producing the zeolite separation membrane according to Example 1 above, the powder before molding (zeolite microcrystals) used for producing the separation membrane according to Comparative Example 1, and the powder according to Reference Example 1 (graphene powder) were observed by SEM. Also, the specific surface area of each powder was measured using a specific surface area meter (manufactured by Quantachrome Corporation, model number: Autosorb iQ). The results are shown in Table 1.

[0089]

Table 1

[0090] <Nitrogen adsorption measurement> Nitrogen adsorption measurement was performed on the powder before pressure molding used in the production of the zeolite separation membrane according to Example 1 above (powder of zeolite microcrystals with graphene covering the surroundings) and the powder before molding used in the production of the separation membrane according to Comparative Example 1 (zeolite microcrystals).

[0091] The measurement was carried out in the following three steps in this order: "pretreatment for adsorption measurement" to remove moisture and the like adsorbed on the powder of the sample, "measurement of the adsorption branch of the adsorption isotherm", and "measurement of the desorption branch". The apparatus used was a fully automatic gas adsorption measurement apparatus (manufactured by Quantachrome Corporation, model number: Autosorb iQ).

[0092] In the pretreatment for adsorption measurement, each of the powder samples according to Example 1 and Comparative Example 1 was held at a temperature of 250 °C under a pressure of 1 mPa or less for 3 hours.

[0093] Next, as the adsorption branch measurement, with the sample cell containing the powder samples according to Example 1 and Comparative Example 1 evacuated and maintained at 77 K, nitrogen gas was introduced, and the amount of nitrogen adsorbed was measured in order from low pressure. Next, as the desorption branch measurement, starting from the pressure after the adsorption branch measurement, the pressure was gradually decreased, and the amount of nitrogen adsorbed on the powder sample was measured in order from high pressure.

[0094] The nitrogen adsorption isotherms obtained from the results of the above measurements are shown in FIGS. 5(a) and 5(b). FIG. 5(a) is a diagram showing the entire nitrogen adsorption isotherm, and FIG. 5(b) is an enlarged view of the rising part (low pressure part). In FIG. 5, the black marks indicate the adsorption branch, and the white marks indicate the desorption branch. Since the MFI zeolite that constitutes the zeolite separation membrane originally has no mesopores (pores of 2 to 50 nm), there should be only a sharp rise in the adsorption amount near a relative pressure of 0, and no adsorption hysteresis should be observed. However, in the results shown in FIG. 5, adsorption hysteresis was confirmed near a relative pressure of 0.2, which suggests the presence of pores. This is presumably because the gap between particles becomes narrow due to pressure molding during powder production, and this gap between particles serves as pores. Furthermore, when the coating with graphene was formed as in Example 1, the result was that the adsorption hysteresis near a relative pressure of 0.2 changed to a slightly higher pressure. Therefore, it is considered that the above-mentioned gap between particles acts more effectively as pores.

[0095] <Thermogravimetric analysis> For the powder before pressure molding used in the production of the zeolite separation membrane according to Example 1 (powder of zeolite microcrystals with graphene covering the surroundings), the powder before molding used in the production of the separation membrane according to Comparative Example 1 (zeolite microcrystals), the powder before molding used in the production of the separation membrane according to Comparative Example 2 (graphene oxide), and ammonium chloride, thermogravimetric analysis was performed in air, and TG curves were created. The results are shown in FIG. 6.

[0096] From the results shown in FIG. 6, it was confirmed that at 750 to 800 K, the weight of MFI-Graphene (powder corresponding to Example 1) decreased by 8%. This weight loss is considered to be due to the combustion of graphene. Therefore, it can be inferred that MFI-Graphene (powder corresponding to Example 1) contains 8 mass% of graphene. Also, although ammonium chloride (NH4Cl) was used, it was confirmed from the results shown in FIG. 6 that the weight decreased in the range of 500 K to 570 K. From this, it was confirmed that ammonium chloride is removed during the heat treatment process.

[0097] <Evaluation of Permeability> The apparatus 50 shown in Fig. 7 was prepared. The apparatus 50 has a chamber 51 with a volume of 100 cm 3 that does not change in volume, a pressure gauge 52, an introduction flow path L1 having a valve V1, and an exhaust flow path L2 having a valve V2. Further, a separation membrane M to be evaluated is attached upstream of the valve V2 on the exhaust flow path L2.

[0098] The temperature inside the chamber 51 is kept constant at 302K. A mixed gas of hydrogen (H2):methane (CH4) with a mixing volume ratio of 1:1 is introduced into this chamber 51 from the introduction flow path L1 until the pressure reaches 120 kPa. When the pressure inside the chamber 51 reaches 120 kPa, the valve V1 of the introduction flow path L1 is closed. Then, the valve V2 of the exhaust flow path L2 is opened. In this state, the time change of the pressure inside the chamber 51 is measured by the pressure gauge 52. Also, the gas discharged from the exhaust flow path L2 is measured with a mass spectrometer to obtain the concentration ratio of the gas. In the case of a mixed gas of hydrogen:methane, it is considered that hydrogen passes through the gas separation membrane and methane remains inside the chamber 51.

[0099] Fig. 8 schematically shows the result of plotting the pressure values against time. As also shown in Fig. 7, the change in pressure 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 approximately equal to Δp / Δt, it can be calculated from this relationship considering it to be approximately equal to (p2 - p1) / (t2 - t1). On the other hand, dp / dt can also be described by the following mathematical 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.

[0100]

Equation

[0101]

Equation

[0102] For each of 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 an index indicating the rate at which gas separation proceeds in a gas separation membrane.

[0103] Figure 9 plots the measurement results of each gas separation membrane of Example 1 and Comparative Examples 1 to 3, with the hydrogen permeability on the horizontal axis and the selectivity on the vertical axis. In the case of a hydrogen:methane mixed gas, 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 was plotted.

[0104] When model-analyzing the experimental results shown in Figure 9 (the upper figure), it was concluded that the mechanism by which gas permeates through the "zeolite microcrystal membrane coated with graphene" is mainly due to Knudsen diffusion. Knudsen diffusion is a diffusion mechanism in which the mean free path of the diffusing molecules (here, the molecules permeating through the membrane) is sufficiently large, so that collisions between molecules hardly occur, and the permeating molecules permeate through the pore body while colliding only with the wall surface of the permeating pore body.

[0105] In such a Knudsen diffusion process, since the deceleration of the permeation rate due to collisions between molecules does not occur, the diffusion rate is higher than that of normal molecular diffusion (where the mean free path is small and molecules diffuse while colliding with each other). When the size of the zeolite microcrystals is about 100 nm, it is comparable to the mean free path of molecules (about 70 nm) at normal pressure.

[0106] Also, the pores of the zeolite microcrystals are considered to be approximately cylinder-shaped with a diameter of 0.55 nm and penetrate through the zeolite. Therefore, the molecules permeating through the gas separation membrane only permeate through the cylinder-shaped pores on this straight line. Therefore, it was considered that the molecules hardly collide with the pore wall surface and permeate through the zeolite particles with little deceleration.

[0107] <Gas Permeability> Using the apparatus 50 shown in Fig. 7, the permeability to gas was evaluated. The temperature inside the chamber 51 in the apparatus 50 was kept constant at 303K. A mixed gas with a volume ratio of hydrogen (H2): methane (CH4): sulfur hexafluoride (SF6) of 1:1:1 was introduced into this chamber 51 from the introduction flow path L1 until the pressure reached 120 kPa. When the pressure inside the chamber 51 reached 120 kPa, the valve V1 of the introduction flow path L1 was closed. Then, the valve V2 of the exhaust flow path L2 was opened. In this state, the time change of the pressure inside the chamber 51 was measured by the pressure gauge 52. The pressure change with respect to the time change is shown in Fig. 10. From the results shown in Fig. 10, the permeability was determined to be 6.02×10 -7 mol / m 2 sPa.

[0108] 2. Apatite separation membrane (Example 2) A dispersion was prepared by dispersing 0.99 mg of graphene oxide (Hummer method graphene oxide manufactured by Shinshu University) and 50 mg of hydroxyapatite microcrystals (manufactured by Sigma - Aldrich, particle size 2.5 μm) in 100 mL of a 0.01 M ammonium chloride aqueous solution. The pH of the dispersion at this time was 7.63. The solution obtained by allowing this dispersion to stand at 25°C for 24 hours was placed in a vacuum freeze - dryer and dried under the conditions of a temperature of 223K and a pressure of 10 Pa to obtain 51 mg of a powder of hydroxyapatite microcrystals coated with graphene oxide.

[0109] The obtained powder was placed in a quartz boat and installed in a heating furnace in an argon atmosphere. It was heated at a heating rate of 1K / min in an argon stream, held at a temperature of 573K for 30 minutes, and then naturally cooled. When the heating furnace was cooled to a temperature of 333K or lower, the argon stream was stopped and the quartz boat was taken out of the heating furnace. The mass of the powder obtained after heating was 48 mg.

[0110] Next, the powder taken out from the heating furnace was placed in a quartz boat and installed in an electric furnace. It was heated at a heating rate of 1 K / min in air, held at a temperature of 623 K for 10 minutes, and then naturally cooled. When the temperature in the electric furnace was cooled to a temperature of 333 K or lower, the quartz boat was taken out from the electric furnace. The mass of the powder obtained after heating was 47.2 mg.

[0111] The powder taken out from the electric furnace was pressure-molded into a film shape using a tablet press. The pressure during pressing was 15 MPa. As a result, an apatite separation membrane according to Example 2 was obtained. The apatite separation membrane according to Example 2 had a circular shape with an outer diameter of 8 mm in plan view. The thickness of the apatite separation membrane according to Example 2 was estimated to be 90 nm by calculation based on the density. The SEM image of the apatite separation membrane according to Example 2 is shown in Fig. 11.

[0112] (Comparative Example 4: Hydroxyapatite) 18.4 mg of hydroxyapatite (manufactured by Sigma-Aldrich, particle size 2.5 μm) was prepared and pressure-molded into a film shape using a tablet press. The pressure during pressing was 15 MPa to obtain a separation membrane according to Comparative Example 4.

[0113] <Nitrogen adsorption measurement> Similar to the evaluation of the zeolite separation membrane, nitrogen adsorption measurements were performed on the powder before pressure molding (powder of apatite microcrystals with graphene covering the surroundings) used for the preparation of the apatite separation membrane according to Example 2 above and the powder before molding (apatite microcrystals) used for the preparation of the separation membrane according to Comparative Example 4. The operation procedure was the same as the procedures according to Example 1 and Comparative Example 1 described above.

[0114] The nitrogen adsorption isotherms obtained from the results of the above measurements are shown in FIGS. 12(a) and 12(b). FIG. 12(a) is a diagram showing the entire nitrogen adsorption isotherm, and FIG. 12(b) is an enlarged view of the rising part (low-pressure part). In FIG. 12, the black marks indicate the adsorption branches, and the white marks indicate the desorption branches. Since there are no pores inside the crystals and particles of the apatite microcrystals according to Comparative Example 4, it was confirmed that there is no adsorption hysteresis in the low-pressure to medium-pressure part (around 0.1 to 0.7), and the adsorption amount is not large. And it was confirmed that the adsorption amount starts to increase significantly and there is adsorption hysteresis from around when the relative pressure exceeds 0.8. This indicates that there are gaps between the particles that act as pores. Since there is adsorption hysteresis on the high-pressure side compared to MFI zeolite, it is estimated that the pore diameter of the gaps is larger than the pore diameter of the gaps in MFI zeolite.

[0115] Incidentally, from the above measurement results, the specific surface area of the powder before pressure molding (powder of apatite microcrystals with graphene covering the surroundings) used for the production of the apatite separation membrane according to Example 2 is 110 m 2 / g was confirmed. On the other hand, the specific surface area of the powder before molding (apatite microcrystals) used for the production of the separation membrane according to Comparative Example 4 was confirmed to be 100 m 2 / g.

[0116] <Gas permeability> Using the apparatus 50 shown in FIG. 7, the permeability to gas was evaluated. The temperature inside the chamber 51 in the apparatus 50 is kept constant at 303 K. A mixed gas of hydrogen (H2): methane (CH4): sulfur hexafluoride (SF6) with a mixed volume ratio of 1:1:1 is introduced into this chamber 51 from the introduction flow path L1 until the pressure reaches 120 kPa. When the pressure inside the chamber 51 reaches 120 kPa, the valve V1 of the introduction flow path L1 is closed. Then, the valve V2 of the exhaust flow path L2 is opened. In this state, the time change of the pressure inside the chamber 51 was measured by the pressure gauge 52. The pressure change with respect to the time change is shown in FIG. 10. From the results shown in FIG. 13, the permeability was determined to be 1.34×10 -7 mol / m 2 sPa.

[0117] <Evaluation of selectivity> Using the apparatus 50 shown in Fig. 7, the permeability and selectivity for each gas type were evaluated. The temperature inside the chamber 51 was kept constant at 303K. The target gas (the gas to be separated) was introduced into this chamber 51 until the pressure reached 120 kPa. When the pressure inside the chamber 51 reached 120 kPa, the valve V1 of the introduction flow path L1 was closed. Then, the valve V2 of the exhaust flow path L2 was opened. In this state, the time change of the pressure inside the chamber 51 was measured by the pressure gauge 52. From this result, the permeability of hydrogen with respect to the target gas was obtained.

[0118] Also, using the apparatus 50, a mixed gas with a hydrogen (H2): target gas (the gas to be separated) volume ratio of 1:1 was introduced into the chamber 51 with a constant temperature of 303K from the introduction flow path L1 until the pressure reached 120 kPa. When the pressure inside the chamber 51 reached 120 kPa, the valve V1 of the introduction flow path L1 was closed. Then, the valve V2 of the exhaust flow path L2 was opened. In this state, the time change of the pressure inside the chamber 51 was measured by the pressure gauge 52. Also, the gas discharged from the exhaust flow path L2 was measured with a mass spectrometer to obtain the concentration ratio of the gas. When the target gas is methane, it is considered that hydrogen passes through the gas separation membrane and methane remains inside the chamber 51.

[0119] The kinetic diameter changes depending on the target gas. The evaluation results of selectivity and permeability for each target gas are shown in Table 2 below. From the results in Table 2, it was confirmed that when the target gas is at least a gas with a kinetic diameter of 0.35 nm or more, the apatite separation membrane according to Example 2 has higher performance compared to the separation membrane of apatite alone according to Comparative Example 4. The calculation method of permeability was the same as that for the zeolite separation membrane.

[0120]

Table 2

Explanation of symbols

[0121] 1…Gas separation membrane, 10…Zeolite microcrystal, 11…Pore, 20…Graphene, 30…Support, 50…Device, 51…Chamber, 52…Pressure gauge.

Claims

1. A step of mixing a dispersion obtained by mixing zeolite microcrystals composed of MFI zeolite and graphene oxide with pure water and allowing the dispersion to stand to cover the periphery of the zeolite microcrystals with the graphene oxide; A step of drying and pulverizing the dispersion after standing; A step of performing a reduction treatment of the graphene oxide by heating on the powder; A step of pressure-molding the powder after the reduction treatment into a film shape; characterized by comprising: After the step of performing the reduction treatment of the graphene oxide and before the step of forming the film shape, a heat treatment is performed at a temperature higher than the heating temperature in the reduction treatment to form nano-windows in the reduced graphene, and a method for manufacturing a gas separation membrane further comprising this step.

2. The method for manufacturing a gas separation membrane according to claim 1, wherein the dispersion is allowed to stand in a state adjusted to a pH range of 3.6 to 11.0 by a pH adjuster.

3. The pH adjuster is ammonium chloride, The method for manufacturing a gas separation membrane according to claim 2, wherein the pH of the dispersion is adjusted to a range of 3.6 to 4.0 by the pH adjuster.

4. The heat treatment for forming the nano-windows is performed in a temperature range of 200°C to 600°C for about 5 minutes to 50 hours, and the method for manufacturing a gas separation membrane according to any one of claims 1 to 3.

5. In the step of pressure-molding into a film shape, compression molding is performed by applying a pressure of 5 MPa to 40 MPa, and the method for manufacturing a gas separation membrane according to any one of claims 1 to 4.

6. A step of mixing a dispersion obtained by mixing apatite microcrystals composed of hydroxyapatite and graphene oxide with pure water and allowing the dispersion to stand to cover the periphery of the apatite microcrystals with the graphene oxide; A step of drying and pulverizing the dispersion after standing; A step of performing a reduction treatment of the graphene oxide by heating on the powder; A step of pressure-molding the powder after the reduction treatment into a film shape; characterized by comprising:

7. After the step of performing the reduction treatment of the graphene oxide and before the step of forming the film shape, a heat treatment is performed at a temperature higher than the heating temperature in the reduction treatment to form nano-windows in the reduced graphene, and the method for manufacturing a gas separation membrane according to claim 6 further comprising this step.

8. The method for manufacturing a gas separation membrane according to claim 6 or 7, wherein the dispersion is allowed to stand in a state adjusted to a pH range of 3.6 to 11.0 by a pH adjuster.

9. The pH adjuster is ammonium chloride, and The method for producing a gas separation membrane according to claim 8, wherein the pH of the dispersion is adjusted to a range of 6.0 to 9.3 by the pH adjuster.

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