Membrane Heat Treatment Method

Abstract

This method for heat-treating a film comprises a step (step S21) for raising the temperature of a film to an intermediate heating temperature, a step (step S22) for maintaining the film at the intermediate heating temperature and heating the film for a prescribed time, a step (step S23) for raising the temperature of the film to an actual heating temperature that is higher than the intermediate heating temperature, and a step (step S24) for maintaining the heating film at the actual heating temperature and heating the film for a prescribed time. A first recovery amount R1, which is the difference between the transparency performance of the film after step S22 and that before step S21, is 50-95% of a second recovery amount R2, which is the difference between the transparency performance of the film after step S24 and that before step S21. This makes it possible to remove adsorbed substances while preventing damage to the film and suppressing coking of the film.

Description

[Technical Field]

[0001] The present invention relates to a film heating method for heating a film having an adsorbate adsorbed in its pores. [Reference to Related Application] This application claims the benefit of priority from Japanese Patent Application JP2021-011579, filed on January 28, 2021, the entire disclosure of which is incorporated herein by reference. [Background technology]

[0002] Currently, various research and development efforts are being conducted on the separation of specific molecules using separation membranes such as zeolite membranes. For example, a separation device is known in which a mixed gas containing multiple substances is supplied to a zeolite membrane, and highly permeable substances are separated from the mixed gas by passing them through the pores of the zeolite membrane.

[0003] When a zeolite membrane that has been stored in an atmospheric environment is used in the separation device, the separation performance of the zeolite membrane may be reduced due to adsorption of adsorptive molecules in the atmosphere into the pores of the zeolite membrane during storage and blocking the pores. Also, in the separation device, the separation performance of the zeolite membrane may be reduced due to adsorption of adsorptive molecules in the mixed gas into the pores of the zeolite membrane and blocking the pores.

[0004] Separation membranes with reduced separation performance must be heat-treated to remove substances adsorbed in the pores (i.e., adsorbates) and restore their separation performance. For example, Japanese Patent Laid-Open Publication No. 2016-175063 (Reference 1) discloses a heat-treatment technique in which a DDR-type zeolite membrane used in the separation process of a mixed fluid is heated to a predetermined temperature (100°C to 500°C) at a predetermined heating rate and maintained at that temperature for a predetermined holding time (1 hour to 50 hours). Furthermore, Japanese Patent No. 6325450 (Reference 2) discloses a heat-treatment technique in which a zeolite membrane, after being exposed to water or air with a humidity of 10% to 90%, is heated in an air atmosphere at a temperature lower than the oxidative thermal decomposition temperature of the structure-directing agent used in the formation of the zeolite membrane.

[0005] International Publication No. 2018 / 180210 (Document 3) discloses a technology for heat-treating a zeolite membrane used in the separation of a hydrocarbon mixture by heating it under an inert gas atmosphere. Japanese Patent Application Laid-Open No. 2013-34969 (Document 4) discloses a technology for heat-treating a water separation membrane in a dehydration system for separating water from a fluid to be treated by supplying a hot gas such as nitrogen gas to the water separation membrane and allowing it to permeate.

[0006] However, when the substance adsorbed in the pores of a separation membrane (i.e., the adsorbate) is organic, the heat treatment may cause the adsorbate to react (e.g., carbonize) in the pores, resulting in coking. On the other hand, if the heat treatment is performed at a low temperature at which the adsorbate does not react in order to prevent coking, the time required to remove the adsorbate by heating (i.e., the time required for the heat treatment) will be long. Furthermore, heat treatment at a low temperature may not be able to sufficiently remove the adsorbate from the pores, resulting in insufficient recovery of the separation membrane's performance.

[0007] The adhesion of organic matter to the pores during the heat treatment may be accelerated by the catalytic reaction of zeolite. Furthermore, if the oxygen concentration in the pores is high, the amount of heat generated by the oxidation reaction (i.e., combustion reaction) of the organic matter increases, which may cause the separation membrane to become locally hot and be damaged. Summary of the Invention

[0008] The present invention is directed to a membrane heat treatment method for heating a membrane having adsorbates adsorbed in its pores, and aims to remove the adsorbates while suppressing coking and preventing damage to the membrane.

[0009] A preferred embodiment of the present invention provides a membrane heat treatment method comprising: a) heating a membrane; The whole of b) heating the film to an intermediate heating temperature; The whole of c) heating the film at the intermediate heating temperature for a predetermined time; The whole of to a main heating temperature higher than the intermediate heating temperature; and d) heating the film. The whole of and a step of heating the substrate for a predetermined period of time while maintaining the substrate at the main heating temperature. The steps a) to d) are carried out in a heat treatment atmosphere that is a low-oxygen atmosphere having an oxygen concentration lower than that of the air. The steps a) to d) are carried out continuously, and the temperature of the film is not lowered between the steps b) and c). Regarding the permeability of the membrane, the first recovery amount, which is the difference between the permeability after the step b) and the permeability before the step a), is 50% or more and 95% or less of the second recovery amount, which is the difference between the permeability after the step d) and the permeability before the step a).

[0010] According to the present invention, it is possible to remove adsorbates while suppressing coking and preventing damage to the membrane.

[0011] Preferably, the permeability of the membrane after the decrease in permeability and after steps a) through d) are repeated n+1 times is 95% or more of the permeability of the membrane after the decrease in permeability and after steps a) through d) are repeated n times, where n is an integer greater than or equal to 1 and less than or equal to 2000.

[0012] Preferably, the intermediate heating temperature is 60°C or higher and 180°C or lower.

[0013] Preferably, the main heating temperature is 150°C or higher and 450°C or lower.

[0014] Preferably, the membrane is a zeolite membrane.

[0015] Preferably, the maximum number of ring members in the zeolite constituting the membrane is 8 or less. Preferably, the oxygen concentration in the heat treatment atmosphere is 10% by volume or less, and more preferably, the oxygen concentration in the heat treatment atmosphere is 5% by volume or less.

[0016] The above and other objects, features, aspects and advantages will become more apparent from the following detailed description of the invention which proceeds with reference to the accompanying drawings. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view of a separation membrane composite according to one embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing a part of the separation membrane composite. [Figure 3] FIG. [Figure 4] FIG. 1 is a diagram showing the flow of separation of a mixed substance. [Figure 5] FIG. 1 is a diagram showing the flow of a film heat treatment method. [Figure 6] FIG. 10 is a diagram showing temperature changes of a separation membrane in a membrane heat treatment method. [Figure 7] 1 is a graph showing the recovery of the permeation performance of a separation membrane by a membrane heat treatment method. [Figure 8] 1 is a graph showing the recovery of the permeation performance of a separation membrane by a membrane heat treatment method. [Figure 9] FIG. 10 is a diagram showing temperature changes of a separation membrane in a membrane heat treatment method. DETAILED DESCRIPTION OF THE INVENTION

[0018] Fig. 1 is a cross-sectional view of a separation membrane composite 1 according to one embodiment of the present invention. Fig. 2 is a cross-sectional view showing an enlarged portion of the separation membrane composite 1. The separation membrane composite 1 includes a support 11 and a separation membrane 12. In Fig. 1, the separation membrane 12 is depicted with a thick line. In Fig. 2, the separation membrane 12 is depicted with parallel diagonal lines to make it appear thicker than it actually is.

[0019] The support 11 is a porous member that is permeable to gas and liquid. In the example shown in FIG. 1, the support 11 is a one-piece, continuous, approximately columnar member that is molded integrally. The support 11 is provided with a plurality of through holes 111 that each extend in the longitudinal direction. In other words, the support 11 is a so-called monolithic member. The outer shape of the support 11 is, for example, approximately cylindrical. The cross section perpendicular to the longitudinal direction of each through hole 111 (i.e., cell) is, for example, approximately circular. In FIG. 1, the diameter of the through holes 111 is drawn larger than in reality, and the number of through holes 111 is drawn smaller than in reality.

[0020] The length of the support 11 (i.e., the length in the left-right direction in FIG. 1) is, for example, 10 cm to 200 cm. The outer diameter of the support 11 is, for example, 0.5 cm to 30 cm. The distance between the central axes of adjacent through holes 111 is, for example, 0.3 mm to 10 mm. The surface roughness (Ra) of the support 11 is, for example, 0.1 μm to 5.0 μm, and preferably 0.2 μm to 2.0 μm. The shape of the support 11 may be, for example, a honeycomb shape, a flat plate shape, a tubular shape, a cylindrical shape, a columnar shape, or a polygonal pillar shape. When the shape of the support 11 is tubular or cylindrical, the thickness of the support 11 is, for example, 0.1 mm to 10 mm.

[0021] The material of the support 11 can be various substances (for example, ceramic or metal) as long as they are chemically stable in the process of forming the separation membrane 12 on the surface. In this embodiment, the support 11 is formed of a ceramic sintered body. Examples of ceramic sintered bodies that can be selected as the material of the support 11 include alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide. In this embodiment, the support 11 contains at least one of alumina, silica, and mullite.

[0022] The support 11 may contain an inorganic binder, which may be at least one of titania, mullite, sinterable alumina, silica, glass frit, clay minerals, and sinterable cordierite.

[0023] The average pore diameter of the support 11 is, for example, 0.01 μm to 70 μm, and preferably 0.05 μm to 25 μm. The average pore diameter of the support 11 in the vicinity of the surface on which the separation membrane 12 is formed is 0.01 μm to 1 μm, and preferably 0.05 μm to 0.5 μm. The average pore diameter can be measured, for example, by a mercury porosimeter, a perm-po Lome Data or NanoPerm LomeThe pore size distribution throughout the support 11, including the surface and interior, is such that D5 is, for example, 0.01 μm to 50 μm, D50 is, for example, 0.05 μm to 70 μm, and D95 ​​is, for example, 0.1 μm to 2000 μm. The porosity of the support 11 near the surface where the separation membrane 12 is formed is, for example, 20% to 60%.

[0024] The support 11 has a multilayer structure in which, for example, multiple layers with different average pore sizes are stacked in the thickness direction. The average pore size and sintered grain size in the surface layer, including the surface on which the separation membrane 12 is formed, are smaller than the average pore size and sintered grain size in the layers other than the surface layer. The average pore size in the surface layer of the support 11 is, for example, 0.01 μm to 1 μm, and preferably 0.05 μm to 0.5 μm. When the support 11 has a multilayer structure, the materials described above can be used for each layer. The materials of the multiple layers forming the multilayer structure may be the same or different.

[0025] The separation membrane 12 is a substantially cylindrical thin film provided on the inner surface of the through-hole 111 of the support 11, covering substantially the entire inner surface. The separation membrane 12 is a dense porous membrane having micropores. The separation membrane 12 is capable of separating a specific gas from a mixed gas containing multiple types of gases by utilizing its molecular sieve action.

[0026] The separation membrane 12 is, for example, an inorganic membrane, and in this embodiment, is a zeolite membrane. A zeolite membrane is at least a membrane of zeolite formed on the surface of a support 11, and does not include an organic membrane in which zeolite particles are simply dispersed. As described above, a zeolite membrane can be used as a separation membrane for separating a specific substance from a mixture of substances. Other substances are less likely to permeate a zeolite membrane than the specific substance. In other words, the amount of other substances that permeate a zeolite membrane is smaller than the amount of the specific substance that permeates the zeolite membrane. Note that a zeolite membrane may contain two or more types of zeolites with different structures and compositions.

[0027] The thickness of the separation membrane 12 is, for example, 0.05 μm to 30 μm, preferably 0.1 μm to 20 μm, and more preferably 0.5 μm to 10 μm. Increasing the thickness of the separation membrane 12 improves separation performance. Reducing the thickness of the separation membrane 12 increases the permeation rate. The surface roughness (Ra) of the separation membrane 12 is, for example, 5 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and even more preferably 0.5 μm or less.

[0028] The pore diameter of the zeolite crystals contained in the separation membrane 12 (hereinafter simply referred to as the "pore diameter of the separation membrane 12") is 0.2 nm or more and 0.8 nm or less, more preferably 0.3 nm or more and 0.7 nm or less, and even more preferably 0.3 nm or more and 0.45 nm or less. If the pore diameter of the separation membrane 12 is less than 0.2 nm, the amount of gas permeating the separation membrane 12 may be reduced, and if the pore diameter of the separation membrane 12 is greater than 0.8 nm, the gas selectivity of the separation membrane 12 may be insufficient. The pore diameter of the separation membrane 12 is the diameter of the pore in a direction approximately perpendicular to the maximum diameter of the pores of the zeolite crystals constituting the separation membrane 12 (i.e., the major axis, which is the maximum distance between oxygen atoms). The pore diameter of the separation membrane 12 is smaller than the average pore diameter on the surface of the support 11 on which the separation membrane 12 is disposed.

[0029] When the maximum number of rings in the zeolite constituting the separation membrane 12 is n, the minor axis of the n-membered ring pore is defined as the pore diameter of the separation membrane 12. When the zeolite has multiple types of n-membered ring pores with the same n, the minor axis of the n-membered ring pore with the largest minor axis is defined as the pore diameter of the separation membrane 12. Note that an n-membered ring refers to a portion in which the number of oxygen atoms constituting the skeleton forming the pore is n, and each oxygen atom is bonded to a T atom (described below) to form a ring structure. Note that an n-membered ring refers to a ring that forms a through-hole (channel), and does not include a ring that does not form a through-hole. An n-membered ring pore is a pore formed by an n-membered ring. From the viewpoint of improving selectivity, the maximum number of rings in the zeolite contained in the separation membrane 12 is preferably 8 or less (for example, 6 or 8).

[0030] The pore size of the separation membrane 12, which is a zeolite membrane, is uniquely determined by the skeletal structure of the zeolite.<URL:http: / / www.iza-structure.org / databases / > The values ​​can be obtained from the values ​​disclosed in

[0031] The type of zeolite constituting the separation membrane 12 is not particularly limited, and examples thereof include AEI, AEN, AFN, AFV, AFX, BEA, CHA, DDR, ERI, ETL, FAU (X, Y), GIS, IHW, LEV, LTA, LTJ, MEL, MFI, MOR, PAU, RHO, SOD, and SAT types of zeolite. When the zeolite is an eight-membered ring zeolite, examples thereof include AEI, AFN, AFV, AFX, CHA, DDR, ERI, ETL, GIS, IHW, LEV, LTA, LTJ, RHO, and SAT types of zeolite.

[0032] The zeolite constituting the separation membrane 12 contains, for example, aluminum (Al) as a T atom (i.e., an atom located at the center of an oxygen tetrahedron (TO4) constituting the zeolite). Zeolites constituting the separation membrane 12 may include zeolites in which the T atom is silicon (Si) only or contains Si and Al, AlPO-type zeolites in which the T atom is Al and phosphorus (P), SAPO-type zeolites in which the T atom is Si, Al, and P, MAPSO-type zeolites in which the T atom is magnesium (Mg), Si, Al, and P, and ZnAPSO-type zeolites in which the T atom is zinc (Zn), Si, Al, and P. Some of the T atoms may be substituted with other elements.

[0033] Separation membrane 12 contains, for example, Si. Separation membrane 12 may contain, for example, any two or more of Si, Al, and P. Separation membrane 12 may contain an alkali metal. The alkali metal is, for example, sodium (Na) or potassium (K). When separation membrane 12 contains Si atoms and Al atoms, the Si / Al ratio in separation membrane 12 is, for example, 1 or more and 100,000 or less. The Si / Al ratio is the molar ratio of Si elements to Al elements contained in separation membrane 12. The Si / Al ratio is preferably 5 or more, more preferably 20 or more, and even more preferably 100 or more, and the higher the Si / Al ratio, the better. The Si / Al ratio in separation membrane 12 can be adjusted by adjusting the compounding ratio of the Si source and the Al source in the raw material solution, which will be described later.

[0034] In the separation membrane composite 1, the separation membrane 12 may include a membrane other than a zeolite membrane in addition to the zeolite membrane. Alternatively, the separation membrane 12 may be an inorganic membrane other than a zeolite membrane, or may be a membrane other than an inorganic membrane (for example, an organic membrane).

[0035] Next, separation of a mixed substance using the separation membrane complex 1 will be described with reference to Figures 3 and 4. Figure 3 is a diagram showing the separation device 2. Figure 4 is a diagram showing the flow of separation of a mixed substance by the separation device 2.

[0036] In the separation device 2, a mixed substance containing multiple types of fluids (i.e., gases or liquids) is supplied to the separation membrane composite 1, and highly permeable substances in the mixed substance are separated from the mixed substance by permeating through the separation membrane composite 1. Separation in the separation device 2 may be performed, for example, for the purpose of extracting highly permeable substances (hereinafter also referred to as "highly permeable substances") from the mixed substance, or for the purpose of concentrating lowly permeable substances (hereinafter also referred to as "lowly permeable substances").

[0037] The mixed substance (i.e., mixed fluid) may be a mixed gas containing multiple types of gases, a mixed liquid containing multiple types of liquids, or a gas-liquid two-phase fluid containing both gas and liquid.

[0038] The mixture of substances may include, for example, one or more of hydrogen (H), helium (He), nitrogen (N), oxygen (O), water (H), water vapor (H), carbon monoxide (CO), carbon dioxide (CO), nitrogen oxides, ammonia (NH), sulfur oxides, hydrogen sulfide (H), sulfur fluoride, mercury (Hg), arsine (AsH), hydrogen cyanide (HCN), carbonyl sulfide (COS), C to C hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes. The highly permeable substance may, for example, be one or more of H, N, O, H, CO, and H.

[0039] Nitrogen oxides are compounds of nitrogen and oxygen. Examples of the nitrogen oxides include nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (also called dinitrogen monoxide) (N2O), dinitrogen trioxide (N2O3), dinitrogen tetroxide (N2O4), dinitrogen pentoxide (N2O5), etc. X It is a gas called NOX.

[0040] Sulfur oxides are compounds of sulfur and oxygen. Examples of sulfur oxides include sulfur dioxide (SO2), sulfur trioxide (SO3), and other sulfur compounds. X It is a gas called SOX.

[0041] Sulfur fluoride is a compound of fluorine and sulfur. The sulfur fluoride may be, for example, disulfur difluoride (FSSF, S=SF), sulfur difluoride (SF), sulfur tetrafluoride (SF), sulfur hexafluoride (SF), or disulfur decafluoride (SF). 10 ) etc.

[0042] C1-C8 hydrocarbons are hydrocarbons with one or more carbon atoms and eight or less. C3-C8 hydrocarbons may be straight-chain compounds, branched-chain compounds, or cyclic compounds. C2-C8 hydrocarbons may be saturated hydrocarbons (i.e., those without double or triple bonds in the molecule) or unsaturated hydrocarbons (i.e., those with double and / or triple bonds in the molecule). Examples of C1-C4 hydrocarbons include methane (CH4), ethane (C2H6), ethylene (C2H4), propane (C3H8), propylene (C3H6), normal butane (CH3(CH2)2CH3), isobutane (CH(CH3)3), 1-butene (CH2=CHCH2CH3), 2-butene (CH3CH=CHCH3), and isobutene (CH2=C(CH3)2).

[0043] The organic acid may be a carboxylic acid or a sulfonic acid. Examples of the carboxylic acid include formic acid (CHO), acetic acid (CHO), oxalic acid (CHO), acrylic acid (CHO), or benzoic acid (CHCOOH). Examples of the sulfonic acid include ethanesulfonic acid (CHOS). The organic acid may be a chain compound or a cyclic compound.

[0044] The alcohols mentioned above are, for example, methanol (CH3OH), ethanol (C2H5OH), isopropanol (2-propanol) (CH3CH(OH)CH3), ethylene glycol (CH2(OH)CH2(OH)) or butanol (C4H9OH).

[0045] Mercaptans are organic compounds with hydrogenated sulfur (SH) at the end, also known as thiols or thioalcohols. Examples of the mercaptans include methyl mercaptan (CHSH), ethyl mercaptan (CHSH), and 1-propanethiol (CHSH).

[0046] The esters mentioned above are, for example, formates or acetates.

[0047] The above-mentioned ethers are, for example, dimethyl ether ((CH3)2O), methyl ethyl ether (C2H5OCH3) or diethyl ether ((C2H5)2O).

[0048] The ketone may be, for example, acetone ((CH3)2CO), methyl ethyl ketone (C2H5COCH3), or diethyl ketone ((C2H5)2CO).

[0049] The aldehydes mentioned above are, for example, acetaldehyde (CH3CHO), propionaldehyde (C2H5CHO) or butanal (butyraldehyde) (C3H7CHO).

[0050] In the following description, it is assumed that the mixed substance separated by the separation device 2 is a mixed gas containing multiple types of gases.

[0051] The separation device 2 includes a separation membrane composite 1, a sealing unit 21, an outer cylinder 22, two sealing members 23, a supply unit 26, a first recovery unit 27, and a second recovery unit 28. The separation membrane composite 1, the sealing unit 21, and the sealing members 23 are housed within the outer cylinder 22. The supply unit 26, the first recovery unit 27, and the second recovery unit 28 are disposed outside the outer cylinder 22 and connected to the outer cylinder 22.

[0052] The sealing portion 21 is attached to both ends of the support 11 in the longitudinal direction (i.e., the left-right direction in FIG. 3 ) and is a member that covers and seals both longitudinal end faces of the support 11 and the outer surfaces near these end faces. The sealing portion 21 prevents gas and liquid from flowing in and out from these end faces of the support 11. The sealing portion 21 is, for example, a plate-like or film-like member made of glass or resin. The material and shape of the sealing portion 21 may be changed as appropriate. Note that the sealing portion 21 has multiple openings that overlap the multiple through holes 111 of the support 11 in the longitudinal direction, and therefore both longitudinal ends of each through hole 111 of the support 11 are not covered by the sealing portion 21. Therefore, gas and liquid can flow in and out of the through holes 111 from these ends.

[0053] The shape of the outer cylinder 22 is not particularly limited, but for example, it is a substantially cylindrical tubular member. The outer cylinder 22 is formed of, for example, stainless steel or carbon steel. The longitudinal direction of the outer cylinder 22 is substantially parallel to the longitudinal direction of the separation membrane composite 1. A supply port 221 is provided at one longitudinal end of the outer cylinder 22 (i.e., the left end in FIG. 3 ), and a first discharge port 222 is provided at the other end. A second discharge port 223 is provided on the side of the outer cylinder 22. A supply unit 26 is connected to the supply port 221. A first collection unit 27 is connected to the first discharge port 222. A second collection unit 28 is connected to the second discharge port 223. The internal space of the outer cylinder 22 is a sealed space isolated from the space surrounding the outer cylinder 22.

[0054] The two seal members 23 are disposed around the entire circumference between the outer surface of the separation membrane composite 1 and the inner surface of the outer cylinder 22 near both longitudinal ends of the separation membrane composite 1. Each seal member 23 is a substantially annular member made of a material impermeable to gases and liquids. The seal members 23 are, for example, O-rings made of flexible resin. The seal members 23 are in close contact with the outer surface of the separation membrane composite 1 and the inner surface of the outer cylinder 22 around the entire circumference. In the example shown in FIG. 3 , the seal member 23 is in close contact with the outer surface of the sealing portion 21 and indirectly in close contact with the outer surface of the separation membrane composite 1 via the sealing portion 21. A seal is formed between the seal member 23 and the outer surface of the separation membrane composite 1, and between the seal member 23 and the inner surface of the outer cylinder 22, so that gases and liquids can hardly or not pass through at all.

[0055] The supply unit 26 supplies the mixed gas to the internal space of the outer cylinder 22 via the supply port 221. The supply unit 26 includes a pressure-feeding mechanism such as a blower or a pump that pressure-feeds the mixed gas toward the outer cylinder 22. The pressure-feeding mechanism includes, for example, a temperature adjustment unit and a pressure adjustment unit that respectively adjust the temperature and pressure of the mixed gas supplied to the outer cylinder 22. The first recovery unit 27 and the second recovery unit 28 include, for example, a storage container that stores the gas delivered from the outer cylinder 22, or a blower or pump that transfers the gas.

[0056] When separating a mixed gas, first, a separation membrane composite 1 is prepared (FIG. 4: step S11). Specifically, the separation membrane composite 1 is attached inside the outer casing 22. Next, a mixed gas containing multiple types of gases with different permeabilities to the separation membrane 12 is supplied into the inside of the outer casing 22 by the supply unit 26, as indicated by arrow 251. For example, the main components of the mixed gas are CO2 and CH4. The mixed gas may contain gases other than CO2 and CH4. The pressure of the mixed gas supplied from the supply unit 26 to the inside of the outer casing 22 (i.e., the supply-side pressure, which is the gas pressure on the primary side of the separation membrane 12) is, for example, 0.1 MPaG to 20.0 MPaG. The temperature of the mixed gas supplied from the supply unit 26 is, for example, 10°C to 250°C.

[0057] The mixed gas supplied from the supply unit 26 to the outer cylinder 22 is introduced into each of the through-holes 111 of the support 11 (i.e., the inside of the approximately cylindrical separation membrane 12) from the left end of the separation membrane composite 1 in the drawing. Highly permeable gases, which are gases with high permeability in the mixed gas, permeate through the separation membranes 12 provided on the inner surfaces of the through-holes 111 and the support 11, and are discharged from the outer surface of the support 11. In this way, the highly permeable gases (e.g., CO2) are separated from the low-permeability gases (e.g., CH4) in the mixed gas (step S12).

[0058] The gas discharged from the outer surface of support 11 (hereinafter referred to as "permeation gas") is introduced to second recovery section 28 via second discharge port 223 as indicated by arrow 253, and is recovered by second recovery section 28. The pressure of the gas recovered by second recovery section 28 (i.e., the permeation side pressure, which is the gas pressure on the secondary side of separation membrane 12) is, for example, 0.0 MPaG. In other words, the difference between the supply side pressure and the permeation side pressure is, for example, 0.1 MPa to 20.0 MPa. In addition to the high permeation gases described above, the permeation gas may also include low permeation gases that have permeated through separation membrane 12.

[0059] Furthermore, of the mixed gas, gas other than the gas that has permeated the separation membrane 12 and the support 11 (hereinafter referred to as "non-permeated gas") passes through each through-hole 111 of the support 11 from left to right in the figure and is recovered by the first recovery section 27 via the first discharge port 222, as indicated by arrow 252. The pressure of the gas recovered by the first recovery section 27 is, for example, approximately the same as the supply-side pressure. In addition to the low-permeability gas described above, the non-permeable gas may also include a high-permeability gas that has not permeated the separation membrane 12. The non-permeable gas recovered by the first recovery section 27 may be circulated to the supply section 26, for example, and supplied again into the outer casing 22.

[0060] In the separation membrane composite 1 described above, substances contained in the atmosphere may be adsorbed into the pores of the separation membrane 12 while the composite is stored in the atmosphere. The substances (i.e., adsorbates) adsorbed into the pores of the separation membrane 12 are, for example, HO and / or volatile organic compounds (VOCs) contained in the atmosphere. Examples of adsorbates of volatile organic compounds include hydrocarbons with three or more carbon atoms (C). Examples of adsorbates of volatile organic compounds include acetone, isopropyl alcohol, methyl ethyl ketone, ethyl acetate, n-butanol, methyl isobutyl ketone, butyl acetate, toluene, m-xylene, p-xylene, o-xylene, 1,3,5-trimethylbenzene, decane, n-butane, isobutane, n-hexane, n-pentane, cis-2-butene, and undecane. Furthermore, in the separation membrane composite 1, substances contained in a mixed gas may be adsorbed into the pores of the separation membrane 12 while the composite is being used to separate the mixed gas in the separation device 2.

[0061] In this way, when the adsorbate is adsorbed into the pores of the separation membrane 12, the pores may be blocked, potentially reducing the permeation performance of the separation membrane 12. Therefore, a membrane heating treatment is performed to remove (i.e., desorb) the adsorbate from the pores of the separation membrane 12 and restore the permeation performance of the separation membrane 12.

[0062] Fig. 5 is a diagram showing the flow of a membrane heat treatment method for heating a separation membrane 12 having an adsorbate adsorbed in its pores. Fig. 6 is a diagram showing the temperature change (i.e., the temperature profile) of separation membrane 12 in the membrane heat treatment method. In Fig. 6, the regions corresponding to steps S21 to S25 shown in Fig. 5 are denoted by the symbols S21 to S25.

[0063] In this membrane heat treatment method, first, the separation membrane composite 1 is set in a heating device. For example, the separation membrane composite 1 is removed from the outer casing 22 of the separation device 2 and placed in a heating device such as a dryer. Various devices other than a dryer can be used as the heating device as long as they can heat the separation membrane composite 1 to a desired temperature, which will be described later.

[0064] When the separation membrane composite 1 is placed in the heating device, the atmosphere inside the heating device is set to the desired atmosphere (hereinafter also referred to as the "heat treatment atmosphere"). The heat treatment atmosphere is, for example, a low-oxygen atmosphere with an oxygen concentration lower than that of the atmosphere. The oxygen concentration in the heat treatment atmosphere is, for example, 10% by volume or less, and preferably 5% by volume or less. This makes it possible to suppress a rapid combustion reaction of the adsorbate when the separation membrane composite 1 is heated as described below, and to prevent damage to the separation membrane 12 due to a localized and rapid temperature rise.

[0065] In the heating device, an inert gas such as nitrogen (N2) is supplied to the interior to create a low-oxygen atmosphere. Alternatively, carbon dioxide (CO2) may be supplied to the interior of the heating device. The gas supplied to the interior of the heating device is preferably the above-mentioned highly permeable substance that easily permeates the separation membrane 12. This prevents or suppresses clogging of the pores of the separation membrane 12 by substances contained in the heat treatment atmosphere. Furthermore, when the separation membrane composite 1 is heated as described below, the heated atmosphere easily permeates the pores of the separation membrane 12, allowing the separation membrane 12 to be heated evenly. Furthermore, by using N2 or CO2 as the gas supplied to the heating device, the cost required for the membrane heat treatment method can be reduced. The gas supplied to the heating device as the heat treatment atmosphere may be only one type of substance or a mixed gas containing multiple types of substances.

[0066] In the heating device, the internal space containing the separation membrane composite 1 may be filled with the heat treatment atmosphere and sealed, and then the following membrane heating treatment of the separation membrane 12 may be performed. Alternatively, the membrane heating treatment may be performed while the heat treatment atmosphere is flowing through the internal space (i.e., while the heat treatment atmosphere is continuously supplied). Depending on the flow state of the heat treatment atmosphere in the internal space of the heating device, a pressure difference may occur between the spaces on both sides of the separation membrane 12, and the membrane heating treatment may be performed while a portion of the heat treatment atmosphere is continuously permeating the separation membrane 12. The heat treatment atmosphere is preferably maintained inside the heating device until the membrane heating treatment is completed.

[0067] Once the internal space of the heat treatment is set to the above-described heat treatment atmosphere, the separation membrane composite 1 is heated by the heating device, and the separation membrane composite 1 (i.e., the support 11 and the separation membrane 12) is heated from room temperature (e.g., 20°C) to a predetermined intermediate heating temperature (step S21: pre-heating step). The intermediate heating temperature is, for example, 60°C or higher and 180°C or lower, preferably 70°C or higher and 160°C or lower, and more preferably 80°C or higher and 150°C or lower. The intermediate heating temperature is appropriately set based on the type of adsorbate and separation membrane 12. When the zeolite constituting the separation membrane 12 functions as a catalyst to promote the carbonization reaction of the adsorbate, the intermediate heating temperature is, for example, a temperature lower than the catalytic reaction temperature of the zeolite.

[0068] The temperature increase rate in step S21 (hereinafter also referred to as the "preliminary temperature increase rate") is, for example, 5°C / h or more, and preferably 10°C / h or more. This prevents the temperature increase time in step S21 from becoming too long. There is no particular upper limit to the temperature increase rate in step S21, but from the viewpoint of preventing the occurrence of thermal stress in the separation membrane composite 1, the temperature increase rate is, for example, 200°C / h or less, and preferably 100°C / h or less.

[0069] Once the temperature of the separation membrane composite 1 has been raised to the intermediate heating temperature, the separation membrane 12 is heated by the heating device for a predetermined time while maintaining the temperature of the separation membrane 12 at the intermediate heating temperature (step S22: intermediate heating step). In the following description, the heating time at the intermediate heating temperature in step S22 is also referred to as the "intermediate heating time." The intermediate heating time is, for example, 1 hour to 48 hours. By heating the separation membrane 12 in step S22, some of the adsorbates adsorbed within the pores of the separation membrane 12 are desorbed from the pore surfaces by the heat and removed from the pores. This restores the permeability of the separation membrane 12 to at least a predetermined level, as described below.

[0070] The intermediate heating temperature and intermediate heating time may be set appropriately based on the type of adsorbate, the adsorptive power of the adsorbate to separation membrane 12, the degree of deterioration in the permeability of separation membrane 12, and the like. For example, if the adsorbate is highly reactive with separation membrane 12 and the adsorbate is likely to carbonize, the carbonization reaction of the adsorbate can be suppressed by setting the intermediate heating temperature low and the intermediate heating time long. Furthermore, for example, if the adsorptive power of the adsorbate to separation membrane 12 is relatively low and the degree of deterioration in the permeability of separation membrane 12 is also relatively small, the time required for membrane heating treatment of separation membrane 12 can be shortened by setting the intermediate heating time short.

[0071] If the intermediate heating temperature is excessively low, the degree of recovery of the permeability of the separation membrane 12 at the end of step S22 may be insufficient, or it may take a long time to restore the permeability to a predetermined level or higher. Therefore, the intermediate heating temperature is, for example, 60°C or higher, preferably 70°C or higher, and more preferably 80°C or higher. On the other hand, if the intermediate heating temperature is excessively high, the adsorbate may be carbonized in step S22 and adhere to the pores of the separation membrane 12, causing coking. Therefore, the intermediate heating temperature is, for example, 180°C or lower, preferably 160°C or lower, and more preferably 150°C or lower.

[0072] Furthermore, if the intermediate heating time is excessively long, it is not suitable for practical membrane heating treatment, and there is also a possibility that the separation membrane 12 may be deteriorated due to the thermal history. Therefore, the intermediate heating time is, for example, 48 hours or less, preferably 24 hours or less, and more preferably 16 hours or less. On the other hand, if the intermediate heating time is excessively short, there is a possibility that the degree of recovery of the permeability of the separation membrane 12 at the end of step S22 may be insufficient. Therefore, the intermediate heating time is, for example, 1 hour or more, preferably 2 hours or more.

[0073] In step S22, the temperature of separation membrane 12 is preferably maintained strictly constant at the intermediate heating temperature, but may fluctuate slightly (for example, vibrate slightly) around the intermediate heating temperature. Alternatively, in step S22, due to temperature fluctuations in separation membrane 12, the temperature at the end of the intermediate heating step may be slightly higher or slightly lower than the temperature at the start of the intermediate heating step. Either of these cases is included in the state in which the temperature of separation membrane 12 is maintained at the intermediate heating temperature.

[0074] In step S22, if the temperature at the end of the intermediate heating step is different from the temperature at the start of the intermediate heating step, the absolute value of the difference between the temperatures at the end of the intermediate heating step and the start of the intermediate heating step divided by the intermediate heating time is less than the heating rate in step S21 (i.e., the initial heating rate), and preferably 50% or less of the initial heating rate. In this case, the absolute value of the difference between the temperatures at the end of the intermediate heating step and the start of the intermediate heating step divided by the intermediate heating time is less than the heating rate in step S23 (hereinafter also referred to as the "post-heating rate"), which will be described later, and preferably 50% or less of the post-heating rate.

[0075] When the intermediate heating time has elapsed and step S22 (intermediate heating step) is completed, the temperature of separation membrane 12 is raised from the intermediate heating temperature to a predetermined main heating temperature by the heating device (step S23: post-heating step). The main heating temperature is higher than the intermediate heating temperature, for example, 150°C or higher and 450°C or lower, preferably 160°C or higher and 400°C or lower, and more preferably 160°C or higher and 380°C or lower. The main heating temperature is set appropriately based on the type of adsorbate and separation membrane 12.

[0076] The temperature increase rate in step S23 (hereinafter also referred to as the "post-heat increase rate") is, for example, 5°C / h or more, and preferably 10°C / h or more. This prevents the temperature increase time in step S23 from becoming too long. There is no particular upper limit to the temperature increase rate in step S23, but from the viewpoint of preventing the occurrence of thermal stress in the separation membrane composite 1, the temperature increase rate is, for example, 200°C / h or less, and preferably 100°C / h or less.

[0077] When the temperature of the separation membrane composite 1 is raised to the main heating temperature, the temperature increase of the separation membrane 12 is stopped. Then, the separation membrane 12 is heated for a predetermined time by the heating device while maintaining the temperature of the separation membrane 12 at the main heating temperature (step S24: main heating step). In the following description, the heating time at the main heating temperature in step S24 is also referred to as the "main heating time." The main heating time is, for example, 1 hour to 48 hours. By heating the separation membrane 12 in step S24, any adsorbates remaining in the pores of the separation membrane 12 are removed from the pores. If the adsorbate is, for example, an organic compound, the adsorbate may be removed by being oxidized. This restores the permeation performance of the separation membrane 12.

[0078] The main heating temperature and main heating time described above may be set appropriately based on the type of adsorbate, the adsorptive power of the adsorbate to separation membrane 12, the degree of deterioration in the permeability of separation membrane 12, and the like. For example, if the adsorbate is highly reactive with separation membrane 12 and the adsorbate is likely to carbonize, the main heating temperature can be set low and the main heating time can be set long, thereby suppressing the carbonization reaction of the adsorbate. Furthermore, for example, if the adsorptive power of the adsorbate to separation membrane 12 is relatively low and the degree of deterioration in the permeability of separation membrane 12 is also relatively small, the main heating time can be set short, thereby shortening the time required for the membrane heating treatment of separation membrane 12.

[0079] If the main heating temperature is excessively low, a large amount of adsorbate may remain in the pores of the separation membrane 12, or it may take a long time to remove the adsorbate. Therefore, the main heating temperature is, for example, 150°C or higher, and preferably 160°C or higher. On the other hand, if the main heating temperature is excessively high, the separation membrane 12 may be damaged by thermal stress or the like. Therefore, the main heating temperature is, for example, 450°C or lower, preferably 400°C or lower, and more preferably 380°C or lower.

[0080] Furthermore, if the main heating time is excessively long, it is not suitable for practical membrane heating treatment and there is also a possibility that the separation membrane 12 may be altered due to the thermal history. Therefore, the main heating time is, for example, 48 hours or less, preferably 24 hours or less, and more preferably 16 hours or less. On the other hand, if the main heating time is excessively short, there is a possibility that the permeation performance of the separation membrane 12 may not be fully recovered. Therefore, the main heating time is, for example, 1 hour or more, preferably 2 hours or more.

[0081] In step S24, the temperature of separation membrane 12 is preferably maintained strictly constant at the main heating temperature, but may fluctuate slightly (for example, vibrate slightly) around the main heating temperature. Alternatively, in step S24, due to temperature fluctuations in separation membrane 12, the temperature at the end of the main heating step may be slightly higher or slightly lower than the temperature at the start of the main heating step. Either of these cases is included in the state in which the temperature of separation membrane 12 is maintained at the main heating temperature.

[0082] In step S24, if the temperature at the end of the main heating step is different from the temperature at the start of the main heating step, the absolute value of the difference between the temperatures at the end of the main heating step and the start of the main heating step divided by the main heating time is less than the initial heating rate, preferably 50% or less of the initial heating rate. In this case, the absolute value of the difference between the temperatures at the end of the main heating step and the start of the main heating step divided by the main heating time is less than the post-heating rate, preferably 50% or less of the post-heating rate.

[0083] When the main heating time has elapsed and step S24 (main heating step) is completed, the temperature of the separation membrane 12 is lowered from the main heating temperature (step S25: temperature lowering step). The temperature of the separation membrane 12 in step S25 is lowered, for example, by controlling the temperature lowering rate using the heating device. Alternatively, the separation membrane composite 1 may be removed from the heating device and left in the atmosphere, etc., to allow the separation membrane 12 to cool naturally.

[0084] The temperature decrease rate in step S25 is, for example, −5° C. / h or less, and preferably −10° C. / h or less. This prevents the temperature decrease time in step S25 from becoming too long. There is no particular lower limit to the temperature decrease rate in step S25, but from the viewpoint of preventing the occurrence of thermal stress in the separation membrane composite 1, the temperature decrease rate is, for example, −200° C. / h or more, and preferably −100° C. / h or more.

[0085] After the temperature is lowered and the membrane heating treatment is completed, the separation membrane composite 1 is reattached to the outer cylinder 22 of the separation device 2. In the membrane heating treatment, the main heating temperature in step S24 is the highest temperature during the treatment.

[0086] Figure 7 is a graph that schematically illustrates the recovery of the permeability of the separation membrane 12 by the membrane heat treatment method described above. The horizontal axis in Figure 7 represents the passage of time, and the vertical axis represents the permeability of the separation membrane 12. Note that the length of the horizontal axis is not proportional to the actual length of elapsed time. Also, the permeability in each region described below is shown as a straight line, but in reality it may be a curved line. The same applies to Figure 8 described below.

[0087] In this embodiment, the permeation performance is defined as the N2 permeation rate when a gas containing N2 is supplied to the separation membrane composite 1 under predetermined supply conditions in the separation device 2. The permeation rate is measured, for example, by supplying a gas consisting essentially of N2 to the separation device 2 at a supply temperature of 20°C to 30°C, a supply-side pressure of 0.1 MPaG to 0.5 MPaG, and a permeation-side pressure of 0 MPaG to 0.1 MPaG. The permeation rate is determined by measuring the permeated gas recovered in the second recovery section 28 of the separation device 2 using a flow measurement device such as a mass flow meter (MFM). Measurement conditions such as the supply temperature, supply-side pressure, and permeation-side pressure may be set arbitrarily, but the permeation rate measurement conditions in each region described below are the same. Furthermore, when the above-described membrane heating treatment is performed multiple times, the permeation rate measurement conditions are the same each time. The permeation performance of the separation membrane 12 may also be evaluated based on the permeation rate of a gas other than N2 (preferably the highly permeable substance described above, such as CO2) supplied to the separation membrane composite 1.

[0088] Region 81 on the horizontal axis of Figure 7 indicates the period during which the permeability of the separation membrane 12 is maintained approximately constant. Region 82 indicates the period during which the adsorbate adsorbed in the pores of the separation membrane 12 gradually increases and the permeability of the separation membrane 12 gradually decreases during storage and use of the separation membrane composite 1. Regions 83 and 84 indicate the periods during which the above-mentioned membrane heating treatment is performed. Region 83 corresponds to the above-mentioned step S21 (pre-heating step) and step S22 (intermediate heating step). Region 84 corresponds to the above-mentioned step S23 (post-heating step) and step S24 (main heating step).

[0089] Region 820 between regions 82 and 83 is a convenient region provided to make the boundary between regions 82 and 83 easier to understand. There is no period that actually corresponds to region 820, and region 820 corresponds to the state immediately before step S21 (pre-heating step) of the film heating process is started. Region 830 between regions 83 and 84 is a convenient region provided to make the boundary between regions 83 and 84 easier to understand. There is no process that actually corresponds to region 830 in the above-mentioned film heating process, and region 830 corresponds to the state immediately after step S22 (intermediate heating step) is completed. Region 840 after region 84 is a convenient region provided to make the end point of region 84 easier to understand. There is no process that actually corresponds to region 840 in the above-mentioned film heating process, and region 840 corresponds to the state immediately after step S24 (main heating step) is completed. In regions 820, 830, and 840, the permeability of the separation membrane 12 is depicted as being constant.

[0090] Note that the actual period corresponding to regions 81-82 may usually be longer than the actual period corresponding to regions 83-84. Furthermore, although the graph showing the permeation performance in region 82 is drawn as a substantially straight line, in reality, it varies depending on the type of adsorbate and separation membrane 12. The same is true for regions 83 and 84. Furthermore, although the slope of the graph showing the permeation performance in region 83 and the slope of the graph showing the permeation performance in region 84 are drawn as substantially the same in FIG. 7, they may be different.

[0091] In the following description, the value obtained by subtracting the permeability of the separation membrane 12 in region 820 from the permeability of the separation membrane 12 in region 830 in FIG. 7 is referred to as the "first recovery amount," and is denoted by the symbol R1 in FIG. 7. Furthermore, the value obtained by subtracting the permeability of the separation membrane 12 in region 820 from the permeability of the separation membrane 12 in region 840 is referred to as the "second recovery amount," and is denoted by the symbol R2 in FIG. 7. In other words, the first recovery amount R1 is the difference in the permeability of the separation membrane 12 between after step S22 (intermediate heating step) and before step S21 (pre-heating step). Furthermore, the second recovery amount R2 is the difference in the permeability of the separation membrane 12 between after step S24 (main heating step) and before step S21 (pre-heating step).

[0092] In the above-described membrane heating process, the first recovery amount R1 is set to 50% or more and 95% or less of the second recovery amount R2. In other words, R1 / R2 (hereinafter also referred to as the "recovery rate after intermediate heating") is 50% or more and 95% or less. In the membrane heating process, mainly in step S22, a relatively large amount of the adsorbates in the pores of the separation membrane 12 is removed at a relatively low intermediate heating temperature at which carbonization of the adsorbates does not substantially occur, so that the first recovery amount R1 is set to 50% or more of the second recovery amount R2. Therefore, the amount of remaining adsorbates to be removed from the pores in step S24 is relatively small. Therefore, when removing the adsorbates at a relatively high main heating temperature, it is possible to rapidly remove almost all or most of the remaining adsorbates while suppressing coking due to carbonization of the adsorbates. In the membrane heating treatment, for example, most of the adsorbates of organic compounds that cause coking are removed at the intermediate heating temperature, and the remaining adsorbates of organic compounds and adsorbates such as HO that do not cause coking are removed at the main heating temperature.

[0093] In this way, in the membrane heating treatment, coking can be suppressed without increasing the oxygen concentration in the pores in step S24 (main heating step), and therefore excessive heat generation during the oxidation of the adsorbate can be prevented. Therefore, damage to the separation membrane 12 can be prevented. Furthermore, by setting the first recovery amount R1 to 95% or less of the second recovery amount R2, the intermediate heating time in step S22 can be prevented from becoming long, and the time required for the membrane heating treatment can be shortened. From the viewpoint of efficiently removing the adsorbate while suppressing coking and preventing damage to the separation membrane 12 as described above, it is more preferable that the first recovery amount R1 be 70% or more and 95% or less of the second recovery amount R2.

[0094] FIG. 8 is a graph schematically illustrating the degradation of the permeability of the separation membrane 12 due to adsorption of adsorbates into the pores, and the recovery of the permeability of the separation membrane 12 when the above-mentioned membrane heating treatment is repeated multiple times. In FIG. 8, the subscript "n" is added to the regions 81 to 84, 820, 830, and 840 relating to the nth membrane heating treatment. The same applies to the n+1th and subsequent membrane heating treatments. In FIG. 8, the membrane heating treatment on the left is the nth membrane heating treatment, and the membrane heating treatment on the right is the n+1th membrane heating treatment. Note that n is an integer greater than or equal to 1 and less than or equal to 2000.

[0095] In the following description, the area 840 in FIG. n The permeability of the separation membrane 12 in this case is called the "reference permeability" and is indicated by the symbol P n That is, the standard transmission performance P n is the permeation performance of the separation membrane 12 after the decrease in permeation performance of the separation membrane 12 due to adsorption of the adsorbate and the above-mentioned membrane heating treatment (steps S21 to S25) are repeated n times. n+1 The permeability of the separation membrane 12 is indicated by the symbol P n+1 Permeability P n+1 is the reference transmission performance P n After the measurement, the permeability of the separation membrane 12 decreases again, and the permeability is the permeability after the membrane heating treatment is performed once. In other words, the permeability P n+1 is the permeation performance of the separation membrane 12 after the permeation performance reduction and membrane heating treatment have been repeated n+1 times.

[0096] In this membrane heating treatment, the permeability P n+1 is the reference transmission performance P n That is, P n+1 / P n The P value is 95% or more. As described above, the membrane heating treatment can efficiently remove adsorbates while suppressing coking, so that even if the membrane heating treatment is repeated multiple times, the permeation performance of the separation membrane 12 can be favorably restored and maintained at a high level. n+1 / P n is the reference transmission performance P nAfter the measurement, the value indicates the degree to which the permeation performance is maintained after one membrane heating treatment (i.e., the performance maintenance rate).

[0097] Next, with reference to Tables 1 and 2, the relationship between the recovery rate R1 / R2 after intermediate heating and the performance maintenance rate in the above-mentioned film heat treatment method will be described.

[0098] [Table 1]

[0099] [Table 2]

[0100] "Membrane type" in Table 1 indicates the type of zeolite that constitutes the separation membrane 12. In the separation membrane composites 1 of Examples 1 to 7 and Comparative Examples 1 and 2, the separation membrane 12 is composed of DDR-type zeolite.

[0101] The separation membrane composites 1 of Examples 1 to 7 and Comparative Examples 1 and 2 were produced by the following method. First, a monolithic alumina support 11 with a diameter of 30 mm and a length of 160 mm was prepared. Next, 7.329 g of ethylenediamine (manufactured by Wako Pure Chemical Industries, Ltd.) was placed in a fluororesin bottle, and then 1.153 g of 1-adamantanamine (manufactured by Aldrich Chemical Co.) was added and dissolved so that no 1-adamantanamine precipitate remained. In a separate bottle, 115.97 g of water was placed, and 97.55 g of 30% by mass silica sol (Snowtex S: manufactured by Nissan Chemical Industries, Ltd.) was added and gently stirred. The above-mentioned solution of 1-adamantanamine dissolved in ethylenediamine was then added, and the mixture was stirred and mixed for about 1 hour until completely dissolved, producing a raw material solution.

[0102] The raw material solution was then placed in a stainless steel pressure vessel equipped with a fluororesin inner cylinder, and the support 11 with the DDR zeolite seed crystals attached was immersed in the raw material solution to perform hydrothermal synthesis. The hydrothermal synthesis was carried out at 120°C for 84 hours. As a result, a DDR zeolite separation membrane 12 was formed on the inner surface of the through-holes 111 (see FIG. 1 ) of the support 11. The support 11 with the separation membrane 12 formed thereon was then washed with water and dried. Thereafter, the support 11 with the separation membrane 12 formed thereon was heated in an electric furnace in the atmosphere to 500°C at a rate of 0.1°C / min, held at that temperature for 50 hours, and then cooled to room temperature at a rate of 0.5°C / min, thereby obtaining a separation membrane composite 1.

[0103] The "Performance Degradation Conditions" in Table 1 indicate the conditions under which the permeation performance of the separation membrane 12 was reduced by adsorbing an adsorbate into the pores of the separation membrane 12. In Examples 1 to 6 and Comparative Examples 1 and 2, the separation membrane composite 1 was left indoors in the air for two weeks, thereby reducing the permeation performance of the separation membrane 12. In Example 7, the separation membrane composite 1 was left outdoors in the air for two weeks, thereby reducing the permeation performance of the separation membrane 12. In all cases, substances in the air (e.g., organic compounds, HO, etc.) adsorbed into the pores of the separation membrane 12 as adsorbates, thereby reducing the permeation performance of the separation membrane 12. Note that in this case, the adsorbates did not substantially contain sulfur (S). In Examples 1 to 7, the separation membrane 12 with reduced permeation performance was subjected to the membrane heating treatment (steps S21 to S25) under different heating conditions (i.e., heating temperature and heating time). The same applies to Comparative Examples 1 and 2.

[0104] "Intermediate heating conditions" indicate the intermediate heating temperature and intermediate heating time in step S22 (intermediate heating step). "Post-intermediate heating recovery rate R1 / R2" indicates the ratio of the first recovery amount R1 to the second recovery amount R2 (see FIG. 7).

[0105] "Main heating conditions" in Table 2 indicate the main heating temperature and main heating time in step S24 (main heating step). "Performance retention rate P2 / P1 after second heating treatment" is the value obtained by dividing the permeation performance P2 of the separation membrane 12 after the series of treatments, i.e., performance degradation treatment and membrane heating treatment, on the separation membrane composite 1 is repeated twice by the reference permeation performance P1. The reference permeation performance P1 is the permeation performance after the series of treatments, i.e., performance degradation treatment and membrane heating treatment, is performed once. The permeation performance was measured using a method similar to the measurement method described in the explanation for FIG. 7.

[0106] Performance maintenance rate after 11 heat treatments 11 / P1" is the permeation performance P of the separation membrane 12 after a series of treatments, namely, the performance degradation treatment and the membrane heating treatment, have been repeated 11 times. 11 is the value obtained by dividing the reference transmission performance P1. 11 In the "Evaluation of / P1", "◎" is P 11 / P1 is 90% or more, and "○" indicates P 11 / P1 is 80% or more and less than 90%, and "×" indicates P 11 / P1 is less than 80% or more.

[0107] In Example 1, the intermediate heating temperature and the intermediate heating time were 120°C and 8 hours, respectively. The recovery rate R1 / R2 after intermediate heating was 80%. The main heating temperature and the main heating time were 180°C and 10 hours, respectively. The performance retention rate P2 / P1 after the second heating treatment was 99%. The performance retention rate P 11 / P1 was high at 96% (rating: ◎).

[0108] In Example 2, the intermediate heating conditions and main heating conditions were changed from those in Example 1. In Example 2, the intermediate heating temperature and the intermediate heating time were 180°C and 4 hours, respectively. The recovery rate R1 / R2 after the intermediate heating was 93%. The main heating temperature and the main heating time were 450°C and 4 hours, respectively. The performance retention rate P2 / P1 after the second heating treatment was 100%. In addition, the performance retention rate P 11 / P1 was high at 99% (rating: ◎).

[0109] In Example 3, the intermediate heating conditions and main heating conditions were changed from those in Example 1. In Example 3, the intermediate heating temperature and the intermediate heating time were 60°C and 12 hours, respectively. The recovery rate R1 / R2 after intermediate heating was 50%. The main heating temperature and the main heating time were 150°C and 12 hours, respectively. The performance retention rate P2 / P1 after the second heating treatment was 95%. In addition, the performance retention rate P 11 / P1 was relatively high at 88% (rating: ○).

[0110] In Example 4, the intermediate heating conditions and main heating conditions were changed from those in Example 1. In Example 4, the intermediate heating temperature and the intermediate heating time were 100°C and 6 hours, respectively. The recovery rate R1 / R2 after the intermediate heating was 75%. The main heating temperature and the main heating time were 380°C and 5 hours, respectively. The performance retention rate P2 / P1 after the second heating treatment was 98%. In addition, the performance retention rate P 11 / P1 was high at 90% (rating: ◎).

[0111] In Comparative Example 1, the intermediate heating conditions were changed from those in Example 1. In Comparative Example 1, the intermediate heating temperature and intermediate heating time were 55°C and 12 hours, respectively. The recovery rate R1 / R2 after intermediate heating was low at 45% (i.e., less than 50%). The main heating temperature and main heating time were 180°C and 10 hours, respectively, the same as in Example 1. The performance retention rate P2 / P1 after the second heating treatment was 92%, but the performance retention rate P 11 / P1 was low at 75% (rating: ×).

[0112] In Example 5, the main heating conditions were changed from those in Example 1. In Example 5, the intermediate heating temperature and the intermediate heating time were 120°C and 8 hours, respectively, as in Example 1. The recovery rate R1 / R2 after the intermediate heating was 80%. The main heating temperature and the main heating time were 140°C and 12 hours. The performance retention rate P2 / P1 after the second heating treatment was 90%. In addition, the performance retention rate P 11 / P1 was relatively high at 83% (rating: ○).

[0113] In Example 6, the intermediate heating conditions were changed from those in Example 4. In Example 6, the intermediate heating temperature and intermediate heating time were 200°C and 4 hours, respectively. The recovery rate R1 / R2 after intermediate heating was 95%. The main heating temperature and main heating time were 380°C and 5 hours, respectively, the same as in Example 4. The performance retention rate P2 / P1 after the second heating treatment was 98%. In addition, the performance retention rate P 11 / P1 was relatively high at 85% (rating: ○).

[0114] In Comparative Example 2, step S22 (intermediate heating step) was not performed. Therefore, the recovery rate R1 / R2 after intermediate heating was 0% (i.e., less than 50%). The main heating temperature and main heating time were 200°C and 12 hours, respectively. The performance retention rate P2 / P1 after the second heating treatment was 95%, but the performance retention rate P 11 / P1 was low at 70% (rating: ×).

[0115] Example 7 is the same as Example 1, except that the performance degradation conditions were changed from indoors to outdoors, and the intermediate heating time and main heating time were slightly longer. In Example 7, the intermediate heating temperature and intermediate heating time were 120°C and 10 hours, respectively. The recovery rate R1 / R2 after intermediate heating was 77%. The main heating temperature and main heating time were 180°C and 12 hours, respectively. The performance retention rate P2 / P1 after the second heating treatment was 99%. The performance retention rate P 11 / P1 was high at 94% (rating: ◎).

[0116] In Examples 1 to 7, the recovery rate after intermediate heating R1 / R2 was set to 50% or more and 95% or less, so that the performance maintenance rate P2 / P1 after the second heating treatment was high at 90% or more (specifically, 90% to 100%), and the performance maintenance rate P2 / P1 after the 11th heating treatment was 11 On the other hand, in Comparative Example 1, the recovery rate R1 / R2 after intermediate heating was 45% (i.e., less than 50%), so the performance maintenance rate P 11In Comparative Example 2, the intermediate heating step was not performed, and the recovery rate R1 / R2 after the intermediate heating was 0% (i.e., less than 50%). 11 / P1 was low at 70% (i.e., less than 80%).

[0117] Comparing Examples 1 to 4 with Example 5, in Examples 1 to 4, the main heating temperature was set to 150°C or higher and 450°C or lower, so that the performance maintenance rate P2 / P1 after the second heating treatment was 95% or higher (specifically, 95% to 100%), and the performance maintenance rate P2 / P1 after the 11th heating treatment was 95% or higher (specifically, 95% to 100%). 11 The performance retention rate P2 / P1 after the 11th heat treatment was also high, reaching 86% or more (specifically, 88% to 99%). On the other hand, in Example 5, the main heating temperature was set to 140°C (i.e., less than 150°C), and the performance retention rate P2 / P1 after the 11th heat treatment was 90% (i.e., less than 95%), which was lower than in Examples 1 to 4. 11 / P1 was also 83% (i.e., less than 86%), which was lower than in Examples 1 to 4. In Example 5, the main heating temperature was less than 150°C, which is thought to be why the adsorbate removal rate in step S24 (main heating step) was lower than in Examples 1 to 4. Therefore, the main heating temperature is preferably 150°C or higher and 450°C or lower.

[0118] Comparing Examples 1 to 4 with Example 6, in Examples 1 to 4, the intermediate heating temperature was set to 60°C or higher and 180°C or lower, so that the performance maintenance rate P2 / P1 after the second heating treatment was 95% or higher (specifically, 95% to 100%), and the performance maintenance rate P2 / P1 after the 11th heating treatment was 95% or higher (specifically, 95% to 100%). 11 On the other hand, in Example 6, the intermediate heating temperature was set to 200°C (i.e., higher than 180°C), and the performance maintenance rate P2 / P1 after the second heating treatment was as high as 98%, but the performance maintenance rate P2 / P1 after the 11th heating treatment was 11 / P1 was 85% (i.e., less than 86%), which was lower than in Examples 1 to 4. In Example 6, the intermediate heating temperature was higher than 180°C, and therefore the suppression of carbonization of the adsorbate in step S22 (intermediate heating step) was insufficient compared to Examples 1 to 4. As a result, coking occurred in step S24 (main heating step), and the performance retention rate was lower than in Examples 1 to 4. Therefore, it is preferable that the intermediate heating temperature be 60°C or higher and 180°C or lower.

[0119] Comparing Examples 1 to 4, the recovery rate after intermediate heating R1 / R2 was 80% to 93% (i.e., 80% or more) in Examples 1 and 2, 75% (i.e., 70% or more and less than 80%) in Example 4, and 50% (i.e., 50% or more and less than 70%) in Example 3. Furthermore, the performance maintenance rate P2 / P1 after the second heat treatment was 99% to 100% in Examples 1 and 2, 98% in Example 4, and 95% in Example 3. The performance maintenance rate P2 / P1 after the 11th heat treatment was 99% to 100% in Examples 1 and 2, 98% in Example 4, and 95% in Example 3. 11 With respect to / P1, it was 96% to 99% in Examples 1 and 2, 90% in Example 4, and 88% in Example 3. Therefore, the recovery rate after intermediate heating R1 / R2 is in the range of 50% or more and 95% or less, and is more preferably 70% or more, and even more preferably 80% or more.

[0120] Comparing Examples 1 to 4, the main heating temperature was 180°C to 450°C (i.e., 160°C or higher) in Examples 1 to 4, and 150°C (i.e., less than 160°C) in Example 3. Furthermore, the performance retention rate P2 / P1 after the second heat treatment was 98% to 100% in Examples 1 to 4, and 95% in Example 3. The performance retention rate P2 / P1 after the 11th heat treatment was 98% to 100% in Examples 1 to 4, and 95% in Example 3. 11 With respect to / P1, Examples 1 to 4 were 90% to 99%, and Example 3 was 88%. Therefore, the main heating temperature is more preferably 160°C or higher in the range of 150°C or higher and 450°C or lower. On the other hand, in consideration of the heat resistance of the zeolite membrane 12, the main heating temperature is more preferably 400°C or lower, and even more preferably 380°C or lower.

[0121] When Example 1 (performance degradation conditions: indoors) is compared with Example 7 (performance degradation conditions: outdoors), the recovery rate after intermediate heating R1 / R2, the performance maintenance rate after the second heating treatment P2 / P1, and the performance maintenance rate after the 11th heating treatment P 11 Regarding / P1, Example 1 was 80%, 99%, and 96% (rating: ◎), and Example 7 was 77%, 99%, and 94% (rating: ◎). In Example 7, the degree of performance degradation was considered to be slightly greater than in Example 1, so the intermediate heating time and main heating time were made slightly longer than in Example 1. As a result, the recovery rate after intermediate heating R1 / R2, the performance maintenance rate P2 / P1 after the second heating treatment, and the performance maintenance rate P after the eleventh heating treatment 11 Therefore, it is thought that the difference in the performance degradation conditions does not have a significant effect on the performance maintenance rate due to the membrane heating treatment.

[0122] In Tables 1 and 2, the permeation performance P1 of the separation membrane 12 after the permeation performance reduction of the separation membrane 12 due to adsorption of the adsorbate and the above-mentioned membrane heating treatment (steps S21 to S25) have been performed once is used as the reference permeation performance. However, the permeation performance P1 of the separation membrane 12 after the permeation performance reduction and the membrane heating treatment have been repeated n times (n is an integer of 1 or more and 2000 or less) is used as the reference permeation performance. n In this case, the performance maintenance rate P2 / P1 after the second heat treatment is calculated based on the reference permeability P n After obtaining the above, the permeation performance of the separation membrane 12 is decreased and the permeation performance P n+1 , P n Performance maintenance rate P expressed based on n+1 / P n In addition, the performance retention rate after the 11th heat treatment is P 11 / P1 is the reference transmission performance P n After obtaining the data, the permeability of the separation membrane 12 was decreased and the permeability P after the membrane heating treatment was repeated 10 times was n+10 , P n Performance maintenance rate P expressed based on n+10 / P n is equivalent to

[0123] In the separation membrane composite 1, even when n is changed between 1 and 2000, the recovery rate after intermediate heating R1 / R2 is set to 50% or more and 95% or less, so that the performance maintenance rate P n+1 / P n The performance retention rate of the nth + 10th heat treatment, P n+10 / P n The performance retention rate P n+1 / P n From a comparison between Examples 1 to 4 and Example 5, it is preferable that the ratio is 95% or more.

[0124] The above-described membrane heating treatment may be applied to the heating of membranes other than the separation membrane 12 provided on the support 11. The membrane to be subjected to the membrane heating treatment may be any permeable membrane that allows highly permeable substances to pass through, and may be, for example, the separation membrane 12 alone that exists independently from the support 11, or a type of membrane that is not generally called a separation membrane.

[0125] As explained above, the membrane heating method is a method of heating a membrane (separation membrane 12 in the above example) having an adsorbate adsorbed in its pores. The membrane heating method includes the steps of heating the membrane to an intermediate heating temperature (step S21), maintaining the membrane at the intermediate heating temperature for a predetermined period of time (step S22), heating the membrane to a main heating temperature higher than the intermediate heating temperature (step S23), and maintaining the membrane at the main heating temperature for a predetermined period of time (step S24). Regarding the permeability of the membrane, the first recovery amount R1, which is the difference between the permeability after step S22 and the permeability before step S21, is 50% or more and 95% or less of the second recovery amount R2, which is the difference between the permeability after step S24 and the permeability before step S21. This makes it possible to suppress coking due to carbonization reactions of the adsorbate within the membrane pores. Furthermore, in step S24 (main heating step), excessive heat of oxidation of the adsorbate can be suppressed, thereby preventing damage to the membrane due to localized high temperatures. That is, according to the above-described membrane heat treatment method, it is possible to suppress coking of the membrane and remove the adsorbate while preventing damage to the membrane. Furthermore, it is possible to prevent the intermediate heating time from becoming excessively long, thereby suppressing an increase in the time required for the membrane heat treatment and enabling efficient removal of the adsorbate. Furthermore, even if the membrane permeability deteriorates and the membrane heat treatment is repeated, it is possible to preferably recover and maintain the membrane permeability.

[0126] As described above, the decrease in the permeability of the membrane and the permeability of the membrane after steps S21 to S24 are repeated n+1 times (P n+1 ) is the decrease in the permeability of the membrane and the permeability of the membrane after steps S21 to S24 are repeated n times (P n ) is preferably 95% or more of the total permeability of the membrane, where n is an integer of 1 or more and 2000 or less. According to the membrane heat treatment method, even when the membrane permeability is repeatedly decreased and then heated, the membrane permeability can be preferably restored and maintained at a high level.

[0127] As described above, the intermediate heating temperature is preferably 60° C. or higher and 180° C. or lower. This makes it possible to suitably suppress the carbonization reaction of the adsorbate in the pores of the membrane in step S22 (intermediate heating step). As a result, coking in the pores of the membrane can be suppressed, and even when the membrane permeability degradation and membrane heating treatment are repeated, the membrane permeability can be suitably restored and maintained at a high level.

[0128] As described above, the main heating temperature is preferably 150°C or higher and 450°C or lower. This allows adsorbates to be suitably removed from the membrane pores in step S24 (main heating step). As a result, even if the membrane permeability degradation and membrane heating treatment are repeated, the membrane permeability can be suitably restored and maintained at a high level.

[0129] As described above, the membrane is preferably a zeolite membrane. By forming the membrane from zeolite crystals with a uniform molecular diameter, selective permeation of the target substance can be suitably achieved when separating a mixed substance using the membrane, and the target substance can be efficiently separated from the mixed substance.

[0130] More preferably, the maximum number of ring members in the zeolite constituting the membrane is 8 or less. This makes it possible to suitably realize selective permeation of a target substance having a relatively small molecular diameter, such as CO2, and to efficiently separate the target substance from a mixed substance.

[0131] The membrane heat treatment method and separation device 2 described above can be modified in various ways.

[0132] For example, the intermediate heating temperature in step S22 may be less than 60°C and may be higher than 180°C. The main heating temperature in step S24 may be less than 150°C and may be higher than 450°C.

[0133] The above-described step S22 (intermediate heating step) is not limited to maintaining the separation membrane 12 at one intermediate heating temperature, but may be performed at two intermediate heating temperatures t m1 ,t m2 The separation membrane 12 may be maintained at each of the intermediate heating temperatures t m2 is the intermediate heating temperature t m1 The intermediate heating temperature t m1 ,t m2 As described above, is, for example, 60°C or higher and 180°C or lower, preferably 70°C or higher and 160°C or lower, and more preferably 80°C or higher and 150°C or lower. Alternatively, in step S22, separation membrane 12 may be maintained for a predetermined time at each of three or more intermediate heating temperatures. In these cases, the difference between the permeation performance of separation membrane 12 after treatment at multiple or more intermediate heating temperatures (i.e., the permeation performance after step S22) and the permeation performance before step S21 is the above-mentioned first recovery amount R1.

[0134] Similarly, in step S24 (main heating step), separation membrane 12 may be maintained for a predetermined time at each of two or more main heating temperatures. Each of the two or more main heating temperatures is, for example, 150°C or higher and 450°C or lower, preferably 160°C or higher and 400°C or lower, and more preferably 160°C or higher and 380°C or lower.

[0135] The heating of the separation membrane 12 in steps S21 to S24 does not necessarily have to be performed after removing the separation membrane composite 1 from the separation device 2, but may be performed while the separation membrane composite 1 remains attached to the outer casing 22 of the separation device 2. For example, a substantially cylindrical electric heater in contact with the outer peripheral surface of the outer casing 22 may be provided in the separation device 2, and the separation membrane 12 may be heated by heating the outer casing 22 with the electric heater. Alternatively, heated gas may be supplied from the supply unit 26 to the inside of the outer casing 22, and the gas may pass through the through-holes 111 of the separation membrane composite 1 and permeate the separation membrane 12 and the support 11, thereby heating the separation membrane 12.

[0136] The above-mentioned permeability Pn+1 is the reference transmission performance P n It may be less than 95% of the above.

[0137] In addition to the support 11 and the separation membrane 12, the separation membrane composite 1 may further include a functional membrane or a protective membrane laminated on the separation membrane 12. Such a functional membrane or protective membrane may be an inorganic membrane such as a zeolite membrane, a silica membrane, or a carbon membrane, or an organic membrane such as a polyimide membrane or a silicone membrane.

[0138] As described above, separation membrane 12 may be an inorganic membrane other than a zeolite membrane, or may be a membrane other than an inorganic membrane (for example, an organic membrane). Furthermore, when separation membrane 12 is a zeolite membrane, the maximum number of membered rings of the zeolite constituting separation membrane 12 may be greater than eight.

[0139] In the above-described separation device 2, substances other than those exemplified in the above description may be separated from the mixed gas. Furthermore, the structure of the separation device 2 is not limited to the above example, and may be modified in various ways.

[0140] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0141] While the invention has been particularly illustrated and described, it should be understood that the foregoing description is illustrative and not restrictive, and that numerous modifications and variations are possible without departing from the scope of the invention. [Industrial Applicability]

[0142] The present invention can be used for heat treatment of membranes used for separating various fluids. [Explanation of symbols]

[0143] 12 Separation membrane Steps S11~S12, S21~S25

Claims

1. A membrane heating treatment method for heating a membrane having an adsorbate adsorbed in pores, comprising: a) raising the temperature of the entire film to an intermediate heating temperature; b) heating the entire film at the intermediate heating temperature for a predetermined period of time; c) raising the temperature of the entire film to a main heating temperature that is higher than the intermediate heating temperature; d) heating the entire film for a predetermined time while maintaining the main heating temperature; Equipped with The steps a) to d) are performed in a heat treatment atmosphere that is a low-oxygen atmosphere having an oxygen concentration lower than that of the atmosphere, the steps a) to d) are carried out continuously, and the temperature of the film is not lowered between the steps b) and c); Regarding the permeability of the membrane, a first recovery amount, which is the difference between the permeability after the step b) and the permeability before the step a), is 50% or more and 95% or less of a second recovery amount, which is the difference between the permeability after the step d) and the permeability before the step a).

2. The film heating method according to claim 1, the permeation performance of the membrane after the decrease in permeation performance of the membrane and the repetition of steps a) through d) n+1 times is 95% or more of the permeation performance of the membrane after the decrease in permeation performance of the membrane and the repetition of steps a) through d) n times, n is an integer of 1 or more and 2000 or less.

3. 3. The film heating method according to claim 1 or 2, The intermediate heating temperature is 60°C or higher and 180°C or lower.

4. 4. The film heating method according to claim 1, further comprising: The main heating temperature is 150°C or higher and 450°C or lower.

5. 5. The film heating method according to claim 1, The membrane is a zeolite membrane.

6. The film heating method according to claim 5, The maximum number of ring members of the zeolite constituting the membrane is 8 or less.

7. 5. The film heating method according to claim 1, The oxygen concentration in the heat treatment atmosphere is 10% by volume or less.

8. The film heating method according to claim 7, The oxygen concentration in the heat treatment atmosphere is 5% by volume or less.

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