Gas separation device and gas separation method

Abstract

A gas separation device (3) comprises a gas supply part (36), a first separation membrane (310), and a second separation membrane (320). The gas supply part (36) supplies a mixed gas. In the first separation membrane (310), the permeability of a third gas is higher than the permeability of a first gas and a second gas. The first separation membrane (310) causes the third gas, from the mixed gas supplied from the gas supply part (36), to permeate therethrough and removes the third gas. In the second separation membrane (320), the permeability of the first gas is higher than the permeability of the second gas. The second separation membrane (320) is supplied with a first non-permeated gas, from the mixed gas, that has not permeated through the first separation membrane (310). The second separation membrane (320) cause the first gas, from the first non-permeated gas, to permeate therethrough and separates the first gas. As a result, it is possible to suppress increases in the size of facilities related to the separation of a mixed gas.

Description

Gas separation device and gas separation method

[0001] The present invention relates to a technique for separating mixed gases. [Reference to Related Applications] This application claims the benefit of priority from Japanese Patent Application JP2024-51751, filed on March 27, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] Conventionally, pressure swing adsorption, chemical absorption, and other methods have been used to separate a portion of a gas from a mixed gas containing multiple gases. However, pressure swing adsorption and chemical absorption require a large amount of energy for regeneration of the adsorbent and the absorption solution. For this reason, membrane separation using a separation membrane such as a zeolite membrane has recently attracted attention.

[0003] However, the above-mentioned mixed gas often contains impurities such as water. When attempting to separate such mixed gas by membrane separation, the impurities may be adsorbed into the pores of the separation membrane, inhibiting the permeation of the gas to be separated and reducing the separation performance. WO 2018 / 180210 (Document 1) discloses a technology for regenerating a separation membrane whose separation performance has been reduced due to contact with a hydrocarbon mixture by exposing the membrane to an inert gas atmosphere and raising the temperature of the inert gas atmosphere, thereby improving the separation performance.

[0004] Furthermore, in the carbon dioxide separation and capture system disclosed in Japanese Patent Laid-Open No. 2012-236134 (Document 2), a mixed gas is first introduced into an impurity remover (i.e., pretreatment equipment) equipped with an adsorbent such as zeolite, where impurities in the mixed gas are removed. The mixed gas from which the impurities have been removed is then introduced into a primary carbon dioxide separator equipped with a zeolite membrane for carbon dioxide separation, where carbon dioxide is separated, and further introduced into a secondary carbon dioxide separator using an amine absorption method or a pressure swing adsorption method, where carbon dioxide is separated. This suppresses contamination and deterioration of the zeolite membrane for carbon dioxide separation by impurities.

[0005] In addition, Japanese Patent No. 6,351,508 (Document 3), Japanese Patent No. 6,400,017 (Document 4), Japanese Patent Application Laid-Open No. 2011-184,283 (Document 5), Japanese Patent Application Laid-Open No. 7,365,453 (Document 6), and Japanese Patent Application Laid-Open No. 2020-163,250 (Document 7) propose a technique in which multiple separation membrane modules are connected in series and each separation membrane module separates and recovers the target gas (e.g., carbon dioxide, methane, helium, etc.) contained in the mixed gas from the mixed gas. Even in these technologies, if impurities are contained in the mixed gas, the impurities must be removed from the mixed gas using pretreatment equipment such as an impurity remover as described in Document 2 before the mixed gas is introduced into the multiple separation membrane modules.

[0006] However, the separation membrane regeneration method described in Reference 1 requires the use of an inert gas and heating for the regeneration process, which increases the running costs required for separating mixed gases. Furthermore, if the recovery rate of membrane performance through the regeneration process decreases over time, the separation membrane must be replaced.

[0007] In the carbon dioxide separation and capture system of Document 2, it is necessary to install pretreatment equipment such as an impurity remover upstream of the primary carbon dioxide separator and the secondary carbon dioxide separator, which may result in the system becoming larger. In addition, the adsorbent in the impurity remover needs to be replaced or regenerated periodically, which increases the running costs required for carbon dioxide separation and capture. The same is true in Documents 3-7, which also require the installation of pretreatment equipment such as an impurity remover, as mentioned above.

[0008] The present invention is directed to a technology for separating mixed gases, and aims to prevent the size of facilities for separating mixed gases from increasing.

[0009] A first aspect of the invention is a gas separation device that separates a mixed gas containing at least a first gas, a second gas, and a third gas that is a polar gas, and includes a gas supply unit that supplies the mixed gas; a first separation membrane that has a higher permeability for the third gas than the permeabilities for the first gas and the second gas, and that allows the third gas to permeate and be removed from the mixed gas supplied from the gas supply unit; and a second separation membrane that has a higher permeability for the first gas than the permeability for the second gas, and that allows the first gas to permeate and be separated from the non-permeated gas that did not permeate the first separation membrane when the non-permeated gas from the mixed gas is supplied.

[0010] According to the present invention, it is possible to prevent the size of facilities involved in the separation of mixed gases from increasing.

[0011] A second aspect of the present invention is the gas separation device of the first aspect, wherein the ratio of the silicon content to the aluminum content in the first separation membrane is 100 or less.

[0012] A third aspect of the present invention is the gas separation device of the first aspect (or may be the first or second aspect), wherein the ratio of the silicon content to the aluminum content in the second separation membrane is greater than 100.

[0013] The invention of aspect 4 is the gas separation apparatus of aspect 1 (which may be any one of aspects 1 to 3), wherein the concentration of the third gas in the mixed gas supplied from the gas supply unit is 1 volume % or less.

[0014] A fifth aspect of the invention is the gas separation apparatus of the first aspect (which may be any one of the first to fourth aspects), in which the third gas is water or ammonia.

[0015] A sixth aspect of the invention is the gas separation device of the first aspect (which may be any one of the first to fifth aspects), wherein the first gas and the second gas each have a kinetic molecular diameter of less than 0.4 nm.

[0016] A seventh aspect of the present invention is the gas separation apparatus of the sixth aspect, wherein the first gas has a kinetic molecular diameter of less than 0.3 nm.

[0017] An eighth aspect of the present invention is the gas separation apparatus according to any one of the first to seventh aspects, wherein the first separation membrane is a zeolite membrane.

[0018] A ninth aspect of the invention is a gas separation method for separating a mixed gas containing at least a first gas, a second gas, and a third gas that is a polar gas, comprising: a) a step of supplying the mixed gas to a first separation membrane having a higher permeability for the third gas than the permeabilities for the first gas and the second gas, and allowing the third gas to permeate and remove it; and b) a step of supplying a non-permeating gas of the mixed gas that has not permeated through the first separation membrane to a second separation membrane having a higher permeability for the first gas than the permeability for the second gas, and allowing the first gas to permeate and separate it from the non-permeating gas.

[0019] 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.

[0020] FIG. 1 is a diagram showing the configuration of a separation device according to one embodiment. FIG. 2 is a cross-sectional view showing the configuration of a first separation membrane module. FIG. 3 is a cross-sectional view of a separation membrane composite. FIG. 4 is a cross-sectional view showing an enlarged portion of the separation membrane composite. FIG. 5 is a cross-sectional view showing the configuration of a second separation membrane module. FIG. 6 is a diagram showing the separation flow of a mixed gas. FIG. 7 is a diagram showing the configuration of a separation device. FIG. 8 is a diagram showing the configuration of a separation device.

[0021] Fig. 1 is a diagram showing the configuration of a gas separation apparatus 3 according to one embodiment of the present invention. Fig. 1 schematically illustrates each component of the gas separation apparatus 3. The gas separation apparatus 3 is an apparatus that separates the first gas from a mixed gas containing a first gas, a second gas, and a third gas after removing the third gas, which is a polar gas.

[0022] The first gas and the second gas are the main components of the mixed gas. The first gas and the second gas are, for example, non-polar gases. The kinetic molecular diameter of the first gas is, for example, less than 0.4 nm, preferably less than 0.3 nm. The kinetic molecular diameter of the second gas is, for example, less than 0.4 nm. The third gas is a polar gas. The concentration of the third gas in the mixed gas is greater than 0.0 vol% and, for example, 1 vol% or less. The first gas and / or the second gas may be a polar gas. The mixed gas may contain at least the first gas, the second gas, and the third gas, and may also contain gases other than the first gas, the second gas, and the third gas.

[0023] The mixed gas may contain, for example, carbon dioxide (CO ２ ) as the second gas, and methane (CH ４ ) and water (H ) as a third gas. ２ Alternatively, the mixed gas may contain hydrogen (H ２ ) as the second gas, and nitrogen (N ２ ) and water (H ) as a third gas. ２ O) and / or ammonia (NH ３ The first gas, the second gas, and the third gas are not limited to the above examples, and may be changed in various ways.

[0024] The gas separation device 3 includes a first separation membrane module 31, a second separation membrane module 32, a first recovery section 33, a second recovery section 34, a third recovery section 35, and a gas supply section 36. The gas separation device 3 also includes a first permeable gas flow path 311, a first non-permeable gas flow path 312, a second permeable gas flow path 321, and a second non-permeable gas flow path 322.

[0025] The gas supply unit 36 ​​is connected to the first separation membrane module 31. The gas supply unit 36 ​​supplies the mixed gas to the first separation membrane module 31. The gas supply unit 36 ​​includes a pressure-feeding mechanism such as a blower or a pump that pressure-feeds the mixed gas toward the first separation membrane module 31. 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 first separation membrane module 31.

[0026] The first separation membrane module 31 and the first recovery section 33 are connected by a first permeable gas flow path 311. The first separation membrane module 31 and the second separation membrane module 32 are connected by a first non-permeable gas flow path 312. The second separation membrane module 32 and the second recovery section 34 are connected by a second permeable gas flow path 321. The second separation membrane module 32 and the third recovery section 35 are connected by a second non-permeable gas flow path 322.

[0027] The first separation membrane module 31 includes a first separation membrane 310. The specific structure of the first separation membrane module 31 will be described later. ２ The permeability of the first gas (e.g., H O ) to the first separation membrane 310 is ２ ) permeability to the first separation membrane 310 and the second gas (e.g., N ２ ) is higher than the permeability of the first separation membrane 310. The first separation membrane 310 selectively allows the third gas, which is contained in the mixed gas supplied from the gas supply unit 36 ​​to the first separation membrane module 31, to pass therethrough, thereby removing the third gas, which is an impurity, from the mixed gas. In the first separation membrane module 31, the first separation membrane 310 may remove substantially all of the third gas from the mixed gas, or may remove only a portion of the third gas from the mixed gas.

[0028] The third gas / first gas selectivity of the first separation membrane 310 is preferably 10 or more, and more preferably 50 or more. The third gas / first gas selectivity is the permeation rate ratio obtained by dividing the permeation rate (permeance) of the third gas per unit membrane area and unit pressure difference by the permeation rate of the first gas per unit membrane area and unit pressure difference. The upper limit of the third gas / first gas selectivity of the first separation membrane 310 is not particularly limited, but considering a realistic range, it is 10,000 or less. Note that the permeation rates of the third gas and the first gas through the first separation membrane 310 are those when the partial pressure difference between the supply side and permeation side of the first separation membrane 310 is 0.1 MPa.

[0029] Of the mixed gas supplied to the first separation membrane module 31, the gas that permeates the first separation membrane 310 is guided to the first recovery section 33 via the first permeate gas flow path 311. In the following description, the gas that permeates the first separation membrane 310 is also referred to as the "first permeate gas." The first permeate gas is mainly composed of the third gas. The first permeate gas may also contain gases other than the third gas (e.g., the first gas and / or the second gas). The first recovery section 33 is a storage container that stores the first permeate gas, or a blower or pump that transports the first permeate gas.

[0030] Of the mixed gas supplied to the first separation membrane module 31, the gas that does not permeate the first separation membrane 310 is supplied to the second separation membrane module 32 via the first non-permeate gas flow path 312. In the following description, the gas that does not permeate the first separation membrane 310 is also referred to as the "first non-permeate gas." The first non-permeate gas is a gas obtained by removing some or all of the third gas contained in the mixed gas supplied to the first separation membrane module 31 by the gas supply unit 36. The first non-permeate gas is mainly composed of the first gas and the second gas, which are the main components of the mixed gas. The first non-permeate gas may also contain a gas other than the first gas and the second gas (e.g., a third gas that did not permeate the first separation membrane 310). The concentration of the third gas in the first non-permeate gas is lower than the concentration of the third gas (e.g., 1% by volume or less) in the mixed gas delivered from the gas supply unit 36 ​​to the first separation membrane module 31.

[0031] The second separation membrane module 32 includes a second separation membrane 320. The specific structure of the second separation membrane module 32 will be described later. ２ The permeability of the second gas (e.g., N ２ The second separation membrane 320 selectively allows the first gas to permeate out of the first non-permeating gas supplied from the first separation membrane module 31 to the second separation membrane module 32, thereby separating the first gas from the first non-permeating gas.

[0032] The first gas / second gas selectivity of the second separation membrane 320 is preferably 50 or more, and more preferably 100 or more. The first gas / second gas selectivity is the permeation rate ratio obtained by dividing the permeation rate of the first gas per unit membrane area and unit pressure difference by the permeation rate of the second gas per unit membrane area and unit pressure difference. There is no particular upper limit to the first gas / second gas selectivity of the second separation membrane 320, but considering a realistic range, it is 10,000 or less. Note that the permeation rates of the first gas and the second gas through the second separation membrane 320 are those when the partial pressure difference between the supply side and permeation side of the second separation membrane 320 is 0.1 MPa.

[0033] Of the first non-permeable gas supplied to the second separation membrane module 32, the gas that permeates the second separation membrane 320 (mainly the first gas) is guided to the second recovery section 34 via the second permeable gas flow path 321. Of the gas supplied to the second separation membrane module 32, the gas that does not permeate the second separation membrane 320 (mainly the second gas) is guided to the third recovery section 35 via the second non-permeable gas flow path 322.

[0034] Of the first non-permeable gas supplied to the second separation membrane module 32, the gas that permeates the second separation membrane 320 is guided to the second recovery section 34 via the second permeable gas flow path 321. In the following description, the gas that permeates the second separation membrane 320 is also referred to as the "second permeable gas." The second permeable gas is mainly composed of the first gas. The second permeable gas may also contain gases other than the first gas (e.g., the second gas and / or the third gas). The second recovery section 34 is a storage container that stores the second permeable gas, or a blower or pump that transports the second permeable gas.

[0035] Of the first non-permeate gas supplied to the second separation membrane module 32, the gas that does not permeate the second separation membrane 320 is guided to the third recovery section 35 via the second non-permeate gas flow path 322. In the following description, the gas that does not permeate the second separation membrane 320 is also referred to as the "second non-permeate gas." The second non-permeate gas is the first non-permeate gas supplied from the first separation membrane module 31 to the second separation membrane module 32, with some or all of the first gas removed. The second non-permeate gas is primarily composed of the second gas, or the first gas and the second gas. The second non-permeate gas may also contain a gas other than the first gas and the second gas (e.g., a third gas). The concentration of the first gas in the second non-permeate gas is lower than the concentration of the first gas in the first non-permeate gas delivered from the first separation membrane module 31 to the second separation membrane module 32.

[0036] Next, an example of a specific structure of the first separation membrane module 31 will be described with reference to Figures 2 to 4. Figure 2 is a cross-sectional view showing the configuration of the first separation membrane module 31. Figure 3 is a cross-sectional view of the separation membrane composite 1 of the first separation membrane module 31. Figure 4 is a cross-sectional view showing an enlarged portion of the separation membrane composite 1.

[0037] The first separation membrane module 31 includes a separation membrane composite 1, a sealing unit 21, a housing 22, and two sealing members 23. The separation membrane composite 1, the sealing unit 21, and the sealing members 23 are housed in the internal space of the housing 22.

[0038] The separation membrane composite 1 includes a porous support 11 and a first separation membrane 310 formed on the support 11. In Fig. 3, the first separation membrane 310 is depicted with a thick line. In Fig. 4, the first separation membrane 310 is depicted with parallel diagonal lines. In Fig. 4, the thickness of the first separation membrane 310 is depicted thicker than it actually is.

[0039] The support 11 is a porous member that is permeable to gas. In the example shown in FIG. 2, the support 11 is a monolithic support having a single, continuous columnar body formed integrally with the support 11, and a plurality of through-holes 111 extending in the longitudinal direction (i.e., the left-right direction in FIG. 2). In the example shown in FIGS. 2 and 3, the support 11 is substantially cylindrical. The cross section perpendicular to the longitudinal direction of each through-hole 111 (i.e., cell) is, for example, substantially circular. In FIGS. 2 and 3, the diameter of the through-hole 111 is drawn larger than in reality, and the number of through-holes 111 is drawn smaller than in reality. The first separation membrane 310 is formed on the inner surface of the through-hole 111 and covers the inner surface of the through-hole 111 over substantially the entire surface.

[0040] The length of the support 11 (i.e., the length in the left-right direction in FIG. 2 ) 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 columnar 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.

[0041] The material of the support 11 can be various substances (e.g., ceramic or metal) as long as they are chemically stable during the process of forming the first separation membrane 310 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 includes at least one of alumina, silica, and mullite.

[0042] 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.

[0043] The average pore size of the support 11 near the surface where the first separation membrane 310 is formed is preferably smaller than the average pore size in other parts of the support 11. To achieve such a structure, the support 11 has a multilayer structure. When the support 11 has a multilayer structure, the materials for each layer can be those described above, and the layers may be the same or different. The average pore size of the support 11 can be measured using a mercury porosimeter, a perm porometer, a nanoperm porometer, or the like.

[0044] 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 near the surface where the first separation membrane 310 is formed is 0.01 μm to 1 μm, and preferably 0.05 μm to 0.5 μm. With regard to the pore diameter distribution throughout the support 11, including the surface and interior, 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 first separation membrane 310 is formed is, for example, 25% to 50%.

[0045] The first separation membrane 310 is a porous membrane having pores. As described above, the first separation membrane 310 is a gas separation membrane that separates a third gas from a mixed gas containing multiple types of gases by allowing it to permeate. Note that separating the third gas means allowing at least a portion of the third gas in the mixed gas to permeate through the first separation membrane 310 and the support 11, regardless of the concentration of the third gas in the first permeated gas.

[0046] The thickness of the first separation membrane 310 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 first separation membrane 310 improves selectivity. Increasing the thickness of the first separation membrane 310 increases the permeation rate. The surface roughness (Ra) of the first separation membrane 310 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.

[0047] The average pore diameter of the first separation membrane 310 is 1 nm or less. This can improve the selectivity of the first separation membrane 310 for the third gas. The lower limit of the average pore diameter of the first separation membrane 310 is not particularly limited as long as the third gas can permeate through it, but can be, for example, 0.2 nm or more. The average pore diameter of the first separation membrane 310 is preferably 0.2 nm or more and 0.8 nm or less, more preferably 0.3 nm or more and 0.6 nm or less, and even more preferably 0.3 nm or more and 0.5 nm or less. Reducing the average pore diameter of the first separation membrane 310 improves the selectivity. Increasing the average pore diameter of the first separation membrane 310 increases the permeation rate. The average pore diameter of the first separation membrane 310 is smaller than the average pore diameter on the surface of the support 11 on which the first separation membrane 310 is disposed.

[0048] The first separation membrane 310 is preferably an inorganic membrane, and in this embodiment is a zeolite membrane (i.e., a zeolite membrane). A zeolite membrane is at least a membrane of zeolite formed on the surface of the support 11 or the like, and does not include an organic membrane in which zeolite particles are simply dispersed. The zeolite membrane may contain two or more types of zeolite with different structures or compositions, or may partially contain substances other than zeolite through surface treatment or the like.

[0049] The zeolite constituting the first separation membrane 310 is an oxygen tetrahedron (TO ４ Zeolites in which the atom (T atom) located at the center of the zeolite (T atom) is composed of only Si or Si and Al, AlPO zeolites in which the T atoms are composed of Al and P, SAPO zeolites in which the T atoms are composed of Si, Al, and P, MAPSO zeolites in which the T atoms are composed of magnesium (Mg), Si, Al, and P, and ZnAPSO zeolites in which the T atoms are composed of zinc (Zn), Si, Al, and P can be used. Some of the T atoms may be substituted with other elements.

[0050] When the maximum number of rings in the zeolite constituting the first separation membrane 310 is n, the average pore size is the arithmetic mean of the minor and major axes of the n-membered ring pores (the same applies to the second separation membrane 320). An n-membered ring pore is a pore in which the number of oxygen atoms in the portion where an oxygen atom is bonded to a T atom to form a ring structure is n. When a zeolite has multiple n-membered ring pores with the same n, the average pore size of the zeolite is the arithmetic mean of the minor and major axes of all the n-membered ring pores. In this way, the average pore size of a zeolite membrane is uniquely determined by the skeletal structure of the zeolite, and can be obtained from values ​​disclosed in the International Zeolite Society's "Database of Zeolite Structures" [online] on the Internet at <URL: http: / / www.iza-structure.org / databases / >.

[0051] The type of zeolite constituting the first separation membrane 310 is not particularly limited, and may be, for example, AEI type, AEN type, AFN type, AFV type, AFX type, BEA type, CHA type, DDR type, ERI type, ETL type, FAU type (X type, Y type), GIS type, LEV type, LTA type, MEL type, MFI type, MOR type, PAU type, RHO type, SAT type, SOD type, or other zeolite. From the viewpoint of increasing the permeation rate of the third gas and improving selectivity, the maximum number of rings in the zeolite is preferably 8 or less (e.g., 6 or 8). The first separation membrane 310 is, for example, an LTA type zeolite. In other words, the first separation membrane 310 is a zeolite membrane composed of a zeolite with the structure code "LTA" defined by the International Zeolite Association. In this case, the zeolite constituting the first separation membrane 310 has an intrinsic pore size of 0.41 nm×0.41 nm, and an average pore size of 0.41 nm.

[0052] The first separation membrane 310 contains, for example, silicon (Si). The first separation membrane 310 may contain, for example, any two or more of Si, aluminum (Al), and phosphorus (P). The first separation membrane 310 may contain an alkali metal. The alkali metal is, for example, sodium (Na) or potassium (K).

[0053] When the first separation membrane 310 contains Si and Al, the ratio of the Si content to the Al content in the first separation membrane 310 (hereinafter also referred to as the "Si / Al ratio") is, for example, 100 or less, preferably 50 or less, and more preferably 30 or less. This increases the polarity of the first separation membrane 310 and the hydrophilicity of the first separation membrane 310. As a result, the third gas, which is a polar gas, is more easily adsorbed by the first separation membrane 310, and the permeation rate of the third gas through the first separation membrane 310 can be increased. The Si / Al ratio in the first separation membrane 310 is, for example, 1 or more.

[0054] The Si / Al ratio in the first separation membrane 310 can be adjusted, for example, by adjusting the compounding ratio of the Si source and the Al source in the raw material solution when forming the first separation membrane 310 by hydrothermal synthesis (the same applies to the Si / Al ratio of the second separation membrane 320).

[0055] The sealing portion 21 is attached to both longitudinal end portions of the support 11 (i.e., the left-right direction in FIG. 2 ) 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 from flowing in and out from these end faces of the support 11. The sealing portion 21 is, for example, a plate-like member formed 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 with the multiple through holes 111 of the support 11, and therefore both longitudinal ends of each through hole 111 of the support 11 are not covered by the sealing portion 21. Therefore, gas can flow in and out of the through holes 111 from these ends.

[0056] The housing 22 is a substantially cylindrical tubular member. The housing 22 is made of, for example, stainless steel or carbon steel. The longitudinal direction of the housing 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 housing 22 (i.e., the left end in FIG. 2 ), and a first discharge port 222 is provided at the other end. A second discharge port 223 is provided on the side of the housing 22. A gas supply unit 36 ​​is connected to the supply port 221. The second separation membrane module 32 is connected to the first discharge port 222 via a first non-permeate gas flow path 312. The second discharge port 223 is connected to the first recovery unit 33 via a first permeate gas flow path 311. The interior space of the housing 22 is a sealed space isolated from the space surrounding the housing 22.

[0057] The two seal members 23 are disposed around the entire periphery of the separation membrane composite 1, near both longitudinal ends of the separation membrane composite 1, between the outer surface of the separation membrane composite 1 (i.e., the outer surface of the support 11) and the inner surface of the housing 22. Each seal member 23 is a substantially annular member made of a gas-impermeable material. The seal members 23 are, for example, O-rings made of a 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 housing 22 around the entire periphery. In the example shown in FIG. 2 , 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 housing 22, so that gas hardly or completely passes through.

[0058] Figure 5 is a cross-sectional view showing an example of a specific structure of the second separation membrane module 32. In this embodiment, the structure of the second separation membrane module 32 is substantially the same as the structure of the first separation membrane module 31 shown in Figure 2, except that a second separation membrane 320 is provided in place of the first separation membrane 310 in the separation membrane composite 1. In Figure 5, the same reference numerals are used to designate components of the second separation membrane module 32 that correspond to the components of the first separation membrane module 31.

[0059] Similar to the first separation membrane 310, the second separation membrane 320 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 second separation membrane 320 is a porous membrane having pores. As described above, the second separation membrane 320 is a gas separation membrane that separates the first gas from the first non-permeable gas by allowing it to permeate. Note that separating the first gas means allowing at least a portion of the first gas in the first non-permeable gas to permeate through the second separation membrane 320 and the support 11, regardless of the concentration of the first gas in the second permeable gas.

[0060] The thickness of the second separation membrane 320 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 second separation membrane 320 improves selectivity. Increasing the thickness of the second separation membrane 320 increases the permeation rate. The surface roughness (Ra) of the second separation membrane 320 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.

[0061] The average pore diameter of the second separation membrane 320 is 1 nm or less. This allows the selectivity of the second separation membrane 320 to the first gas to be improved. The lower limit of the average pore diameter of the second separation membrane 320 is not particularly limited as long as the first gas can permeate through it, but can be, for example, 0.2 nm or more. The average pore diameter of the second separation membrane 320 is preferably 0.2 nm or more and 0.8 nm or less, more preferably 0.3 nm or more and 0.6 nm or less, and even more preferably 0.3 nm or more and 0.5 nm or less. Reducing the average pore diameter of the second separation membrane 320 improves the selectivity. Increasing the average pore diameter of the second separation membrane 320 increases the permeation rate. The average pore diameter of the second separation membrane 320 is smaller than the average pore diameter on the surface of the support 11 on which the second separation membrane 320 is disposed.

[0062] The second separation membrane 320 is preferably an inorganic membrane, and in this embodiment, is a zeolite membrane. The zeolite constituting the second separation membrane 320 is, similarly to the first separation membrane 310, a zeolite-containing oxygen tetrahedron (TO) constituting the zeolite. ４Zeolites in which the atom (T atom) located at the center of the zeolite (T atom) is Si only or is composed of Si and Al, AlPO zeolites, SAPO zeolites, MAPSO zeolites, ZnAPSO zeolites, etc. can be used.

[0063] The type of zeolite constituting the second separation membrane 320 is not particularly limited, but may be, for example, AEI type, AEN type, AFN type, AFV type, AFX type, BEA type, CHA type, DDR type, ERI type, ETL type, FAU type (X type, Y type), GIS type, LEV type, LTA type, MEL type, MFI type, MOR type, MTN type, PAU type, RHO type, SAT type, SOD type, or other zeolite. From the viewpoint of increasing the permeation rate of the first gas and improving selectivity, the maximum number of rings in the zeolite is preferably 8 or less (e.g., 6 or 8). The second separation membrane 320 is, for example, a DDR type zeolite. In this case, the intrinsic pore diameter of the zeolite constituting the second separation membrane 320 is 0.36 nm × 0.44 nm, and the average pore diameter is 0.40 nm.

[0064] The second separation membrane 320 contains, for example, silicon (Si). The second separation membrane 320 may contain, for example, any two or more of Si, aluminum (Al), and phosphorus (P). The second separation membrane 320 may contain an alkali metal. The alkali metal is, for example, sodium (Na) or potassium (K).

[0065] When the second separation membrane 320 contains Si and Al, the Si / Al ratio in the second separation membrane 320 is, for example, greater than 100, preferably 150 or greater, and more preferably 200 or greater. This reduces the polarity of the second separation membrane 320 and increases the hydrophobicity of the second separation membrane 320. Therefore, even if a third gas, which is a polar gas, remains in the first non-permeating gas, adsorption of the third gas to the second separation membrane 320 can be suppressed. As a result, a decrease in the permeation performance of the second separation membrane 320 due to adsorption of the third gas (e.g., a decrease in the permeation rate of the first gas through the second separation membrane 320) can be suppressed.

[0066] The mixed gas may be, for example, hydrogen (H ２), helium (He), nitrogen (N ２ ), oxygen (O ２ ), carbon monoxide (CO), carbon dioxide (CO ２ ), nitrogen oxides, ammonia (NH ３ ), sulfur oxides, hydrogen sulfide (H ２ S), sulfur fluoride, mercury (Hg), arsine (AsH ３ ), hydrogen cyanide (HCN), carbonyl sulfide (COS), C1-C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes.

[0067] Nitrogen oxides are compounds of nitrogen and oxygen. Examples of the nitrogen oxides include nitric oxide (NO), nitrogen dioxide (NO ２ ), nitrous oxide (also called dinitrogen monoxide) (N ２ O), dinitrogen trioxide (N ２ O ３ ), dinitrogen tetroxide (N ２ O ４ ), dinitrogen pentoxide (N ２ O ５ ) etc. Ｘ It is a gas called NOX.

[0068] Sulfur oxides are compounds of sulfur and oxygen. Examples of the sulfur oxides include sulfur dioxide (SO ２ ), sulfur trioxide (SO ３ ) and other SOs Ｘ It is a gas called SOX.

[0069] Sulfur fluoride is a compound of fluorine and sulfur. The above-mentioned sulfur fluoride is, for example, disulfur difluoride (FS-SF, S=SF ２ ), sulfur difluoride (SF ２ ), sulfur tetrafluoride (SF ４ ), sulfur hexafluoride (SF ６ ) or disulfur decafluoride (S ２ F １０ ) etc.

[0070] 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 either saturated hydrocarbons (i.e., those without double and triple bonds in the molecule) or unsaturated hydrocarbons (i.e., those with double and / or triple bonds in the molecule). C1-C4 hydrocarbons include, for example, methane (CH ４ ), ethane (C ２ H ６ ), ethylene (C ２ H ４ ), propane (C ３ H ８ ), propylene (C ３ H ６ ), normal butane (CH ３ (CH ２ ) ２ CH ３ ), isobutane (CH(CH ３ ) ３ ), 1-butene (CH ２ =CHCH ２ CH ３ ), 2-butene (CH ３ CH=CHCH ３ ) or isobutene (CH ２ =C(CH ３ ) ２ )

[0071] The organic acid is a carboxylic acid or a sulfonic acid. The carboxylic acid is, for example, formic acid (CH ２ O ２ ), acetic acid (C ２ H ４ O ２ ), oxalic acid (C ２ H ２ O ４ ), acrylic acid (C ３ H ４ O ２ ) or benzoic acid (C ６ H ５ COOH), etc. Sulfonic acids include, for example, ethanesulfonic acid (C ２ H ６ O ３S) and the like. The organic acid may be a chain compound or a cyclic compound.

[0072] The alcohols mentioned above include, for example, methanol (CH ３ OH), ethanol (C ２ H ５ OH), isopropanol (2-propanol) (CH ３ CH(OH)CH ３ ), ethylene glycol (CH ２ (OH)CH ２ (OH)) or butanol (C ４ H ９ OH) and the like.

[0073] Mercaptans are organic compounds with hydrogenated sulfur (SH) at the end, and are also called thiols or thioalcohols. Examples of the above-mentioned mercaptans include methyl mercaptan (CH ３ SH), ethyl mercaptan (C ２ H ５ SH) or 1-propanethiol (C ３ H ７ SH), etc.

[0074] The esters mentioned above are, for example, formates or acetates.

[0075] The above-mentioned ethers include, for example, dimethyl ether ((CH ３ ) ２ O), methyl ethyl ether (C ２ H ５ OCH ３ ) or diethyl ether ((C ２ H ５ ) ２ O) etc.

[0076] The above-mentioned ketones can be, for example, acetone ((CH ３ ) ２ CO), methyl ethyl ketone (C ２ H ５ COCH ３ ) or diethyl ketone ((C ２ H ５ ) ２ CO), etc.

[0077] The aldehydes mentioned above include, for example, acetaldehyde (CH ３ CHO), propionaldehyde (C ２ H ５ CHO) or butanal (butyraldehyde) (C ３ H ７ CHO) etc.

[0078] 6 is a diagram showing the flow of mixed gas separation by the gas separation apparatus 3. As described above, in the gas separation apparatus 3, first, the gas supply unit 36 ​​supplies the mixed gas to the internal space of the housing 22 via the supply port 221 of the first separation membrane module 31 (see FIG. 2). The pressure of the mixed gas supplied to the first separation membrane module 31 is, for example, 0.1 MPaG to 10 MPaG, and preferably 0.3 MPaG or higher. The temperature of the mixed gas is, for example, 10°C to 250°C.

[0079] The first gas, the second gas, and the third gas contained in the mixed gas are, for example, H ２ , N ２ and H ２ The concentration of the first gas in the mixed gas is, for example, 20% by volume to 80% by volume. The concentration of the second gas in the mixed gas is, for example, 80% by volume to 20% by volume. The total concentration of the first gas and the second gas in the mixed gas is, for example, 99% by volume to 99.9% by volume. The concentration of the third gas in the mixed gas is, for example, 0.001% by volume to 1% by volume.

[0080] The mixed gas supplied from the gas supply unit 36 ​​into the housing 22 of the first separation membrane module 31 is supplied to the separation membrane composite 1 as shown by arrow 251, and is introduced into each through-hole 111 of the support 11 from the left end of the separation membrane composite 1 in FIG. 2. ２The first permeable gas, which is mainly composed of fluorine-containing oxygen (CO), permeates through the first separation membrane 310 provided on the inner surface of each through-hole 111 and the support 11, and is discharged from the outer surface of the support 11. As a result, the third gas in the mixed gas is separated from the mixed gas and removed as an impurity (step S11). The first permeable gas is guided to the first recovery section 33 via the second discharge port 223 and the first permeable gas flow path 311, as indicated by arrow 253, and is recovered in the first recovery section 33. The third gas in the first permeable gas recovered in the first recovery section 33 may be returned to the gas supply section 36, discarded, or used for various purposes, for example.

[0081] The concentration of the third gas in the first permeable gas is higher than the concentration of the third gas in the mixed gas. The concentrations of the first gas and the second gas in the first permeable gas are lower than the concentrations of the first gas and the second gas in the mixed gas, respectively. The concentration of the third gas in the first permeable gas is, for example, 90% by volume to 100% by volume, and preferably 95% by volume or more. The concentration of the first gas in the first permeable gas is, for example, 0% by volume to 10% by volume. The concentration of the second gas in the first permeable gas is, for example, 0% by volume to 10% by volume. The pressure of the first permeable gas is, for example, -0.09 MPaG to 1 MPaG.

[0082] The recovery rate of the third gas by the first separation membrane 310 is, for example, 50% to 90%, and preferably 70% or more. The recovery rate of the third gas by the first separation membrane 310 is determined by dividing the mass of the third gas that has permeated the first separation membrane 310 in the first separation membrane module 31 (i.e., the mass of the third gas in the first permeated gas) by the mass of the third gas in the mixed gas supplied from the gas supply unit 36 ​​(i.e., (mass of the third gas in the first permeated gas) / (mass of the third gas in the mixed gas)).

[0083] The first non-permeate gas that does not permeate the first separation membrane 310 in the first separation membrane module 31 passes through each through hole 111 of the support 11 from left to right in Figure 2 and is supplied to the second separation membrane module 32 via the first discharge port 222 and the first non-permeate gas flow path 312, as shown by arrow 252.

[0084] The concentrations of the first gas and the second gas in the first non-permeable gas are higher than the concentrations of the first gas and the second gas in the mixed gas, respectively. The concentration of the third gas in the first non-permeable gas is lower than the concentration of the third gas in the mixed gas. The concentration of the first gas in the first non-permeable gas is, for example, 20% to 80% by volume. The concentration of the second gas in the first non-permeable gas is, for example, 80% to 20% by volume. The concentration of the third gas in the first non-permeable gas is, for example, 0.001% to 0.1% by volume. The pressure of the first non-permeable gas is, for example, 0.1 MPaG to 10 MPaG.

[0085] The first non-permeate gas supplied from the first separation membrane module 31 into the housing 22 (see FIG. 5) through the supply port 221 of the second separation membrane module 32 is supplied to the separation membrane composite 1 as shown by arrow 251, and is introduced into each through-hole 111 of the support 11 from the left end of the separation membrane composite 1 in FIG. 5. ２ The second permeable gas, which is mainly composed of the first non-permeable gas (the first non-permeable gas), permeates through the second separation membrane 320 provided on the inner surface of each through-hole 111 and the support 11, and is discharged from the outer surface of the support 11. As a result, the first gas in the first non-permeable gas is separated from the first non-permeable gas (step S12). The second permeable gas is led to the second recovery section 34 via the second discharge port 223 and the second permeable gas flow path 321, as indicated by arrow 253, and is recovered in the second recovery section 34. The first gas in the second permeable gas recovered in the second recovery section 34 can be used for various purposes.

[0086] The concentration of the first gas in the second permeable gas is higher than the concentration of the first gas in the first non-permeable gas. The concentration of the second gas in the second permeable gas is lower than the concentration of the second gas in the first non-permeable gas. The concentration of the first gas in the second permeable gas is, for example, 90% by volume to 100% by volume, and preferably 95% by volume or more. The concentration of the second gas in the second permeable gas is, for example, 0% by volume to 10% by volume. The pressure of the second permeable gas is, for example, 0 MPaG to 1 MPaG.

[0087] The second non-permeate gas that does not permeate the second separation membrane 320 in the second separation membrane module 32 passes through each through-hole 111 of the support 11 from left to right in FIG. 5 and is led to the third recovery section 35 via the first discharge port 222 and the second non-permeate gas flow path 322 as indicated by arrow 252, and is recovered in the third recovery section 35. The second gas in the second non-permeate gas recovered in the third recovery section 35 can be used for various purposes. Alternatively, the second non-permeate gas recovered in the third recovery section 35 may be led to the supply port 221 (see FIG. 2 ) of the first separation membrane module 31 and supplied into the housing 22 of the first separation membrane module 31.

[0088] As described above, the gas separation device 3 is a device that separates a mixed gas containing at least a first gas, a second gas, and a third gas that is a polar gas. The gas separation device 3 includes a gas supply unit 36, a first separation membrane 310, and a second separation membrane 320. The gas supply unit 36 ​​supplies the mixed gas. The first separation membrane 310 is a separation membrane that has a higher permeability for the third gas than the permeability for the first gas and the second gas. The first separation membrane 310 permeates and removes the third gas from the mixed gas supplied from the gas supply unit 36. The second separation membrane 320 is a separation membrane that has a higher permeability for the first gas than the permeability for the second gas. A non-permeating gas (i.e., a first non-permeating gas) from the mixed gas that did not permeate through the first separation membrane 310 is supplied to the second separation membrane 320. The second separation membrane 320 separates the first gas from the first non-permeating gas by allowing it to permeate.

[0089] In the gas separation device 3, the third gas is removed from the mixed gas by the first separation membrane 310, thereby reducing the concentration of the third gas in the first non-permeate gas supplied to the second separation membrane 320. This makes it possible to suppress or prevent a decrease in the permeability of the second separation membrane 320 (e.g., the permeation rate of the first gas through the second separation membrane 320) due to, for example, adsorption of the third gas onto the second separation membrane 320. As a result, separation of the first gas by the second separation membrane 320 can be performed favorably. Furthermore, deterioration over time of the permeability of the second separation membrane 320 can be suppressed.

[0090] Furthermore, in the gas separation apparatus 3, by removing the third gas (i.e., impurities) from the mixed gas using the first separation membrane 310, it is no longer necessary to provide pretreatment equipment such as an impurity remover equipped with an adsorbent upstream of the gas separation apparatus 3, as was conventionally the case, and this makes it possible to prevent the size of the equipment involved in separating the mixed gas from increasing. Furthermore, since there is no need to replace or regenerate the adsorbent, which is required in the pretreatment equipment, it is also possible to reduce the frequency of maintenance of the equipment involved in separating the mixed gas.

[0091] As described above, the ratio of the Si content to the Al content in the first separation membrane 310 (i.e., the Si / Al ratio) is preferably 100 or less. This increases the polarity of the first separation membrane 310, and the hydrophilicity of the first separation membrane 310. As a result, the third gas, which is a polar gas, is more easily adsorbed by the first separation membrane 310, and the permeation rate of the third gas through the first separation membrane 310 can be increased. Therefore, the third gas can be suitably removed from the mixed gas.

[0092] As described above, the first gas and the second gas are preferably non-polar gases. This makes it possible to prevent the first gas and the second gas from permeating the first separation membrane 310 for separating the third gas, which is a polar gas. As a result, the third gas can be separated favorably by the first separation membrane 310. Furthermore, the amount of the first gas separated and recovered by the second separation membrane 320 can be increased.

[0093] As described above, the ratio of the Si content to the Al content in the second separation membrane 320 (i.e., the Si / Al ratio) is preferably greater than 100. This reduces the polarity of the second separation membrane 320, thereby increasing the hydrophobicity of the second separation membrane 320. Therefore, even if a third gas, which is a polar gas, remains in the first non-permeating gas, adsorption of the third gas to the second separation membrane 320 can be suppressed. As a result, a decrease in the permeation performance of the second separation membrane 320 due to adsorption of the third gas (e.g., a decrease in the permeation rate of the first gas through the second separation membrane 320) can be suppressed.

[0094] As described above, the concentration of the third gas in the mixed gas supplied from the gas supply unit 36 ​​is preferably 1% by volume or less. Even such a small amount of impurity can be suitably removed by providing the first separation membrane 310 in the gas separation device 3.

[0095] As described above, the gas separation apparatus 3 can effectively remove the polar third gas from the mixed gas while suppressing an increase in the size of the equipment involved in separating the mixed gas, and therefore the gas separation apparatus 3 is particularly suitable when the third gas is water or ammonia. The gas separation apparatus 3 can suppress or prevent a decrease in the permeability of the second separation membrane 320 due to adsorption of water or ammonia to the second separation membrane 320.

[0096] As described above, the kinetic molecular diameters of the first gas and the second gas are preferably each less than 0.4 nm. In the gas separation device 3, even when the kinetic molecular diameters of the first gas and the second gas are relatively small, the third gas is removed in advance by the first separation membrane 310, so that the first gas can be suitably separated by the second separation membrane 320.

[0097] As described above, the kinetic molecular diameter of the first gas is preferably less than 0.3 nm. In the gas separation device 3, even when the kinetic molecular diameter of the first gas is small, the first gas can be suitably separated by the second separation membrane 320 by removing the third gas in advance using the first separation membrane 310.

[0098] In the gas separation device 3, the first separation membrane 310 is preferably a zeolite membrane. Zeolite membranes have a specific pore size, which allows specific impurities (i.e., the third gas) to permeate and be removed from the mixed gas. Furthermore, the maximum number of rings in the zeolite constituting the first separation membrane 310 is more preferably 8 or less. This allows for the selective permeation of the third gas (i.e., removal from the mixed gas) to be preferably achieved even when the kinetic molecular diameter of the third gas is relatively small.

[0099] In the gas separation device 3, the second separation membrane 320 is preferably a zeolite membrane. As described above, zeolite membranes have an intrinsic pore size, which allows the first gas to permeate favorably and separate it from the first non-permeating gas. Furthermore, it is more preferable that the maximum number of rings in the zeolite constituting the second separation membrane 320 is 8 or less. This makes it possible to favorably achieve selective permeation of the first gas (i.e., separation of the first gas and the second gas) even when the kinetic molecular diameters of the first gas and the second gas are relatively small.

[0100] The gas separation method described above is a method for separating a mixed gas containing at least a first gas, a second gas, and a third gas that is a polar gas, and includes the steps of: supplying the mixed gas to a first separation membrane 310 having a higher permeability for the third gas than the first and second gases, thereby allowing the third gas to permeate and be removed (step S11); and supplying a non-permeating gas of the mixed gas that did not permeate the first separation membrane 310 (i.e., a first non-permeating gas) to a second separation membrane 320 having a higher permeability for the first gas than the second gas, thereby allowing the first gas to permeate and be separated (step S12).

[0101] As a result, similarly to the above, it is possible to suppress or prevent the third gas from being adsorbed onto the second separation membrane 320 and thereby reducing the permeability performance of the second separation membrane 320. It is also possible to suppress an increase in the size of the equipment involved in the separation of the mixed gas. Furthermore, it is also possible to reduce the frequency of maintenance of the equipment involved in the separation of the mixed gas.

[0102] Next, with reference to Tables 1 and 2, examples and comparative examples relating to the separation of mixed gases by the gas separation apparatus 3 will be described.

[0103]

[0104]

[0105] In Examples 1 to 4, mixed gases were separated using the gas separation apparatus 3 shown in Fig. 1. In Comparative Examples 1 to 3, mixed gases were separated using a gas separation apparatus of a comparative example in which the first separation membrane module 31 and the first recovery section 33 were omitted from the gas separation apparatus 3 shown in Fig. 1. In the gas separation apparatus of the comparative example, the gas supply section 36 was connected to the supply port 221 of the second separation membrane module 32 without passing through the first separation membrane module 31.

[0106] In Comparative Example 1, the first separation membrane module 31 was omitted, and a zeolite membrane made of DDR-type zeolite was used as the second separation membrane 320 in the second separation membrane module 32. The Si / Al ratio in the second separation membrane 320 was greater than 100.

[0107] A separation membrane composite 1 including a second separation membrane 320 that is a DDR-type zeolite membrane was produced by the method described in WO 2017 / 169591. First, a support 11 was immersed in a solution in which seed crystals were dispersed, and the seed crystals were attached to the support 11. Next, the support 11 with the attached seed crystals was immersed in a raw material solution to perform hydrothermal synthesis. As a result, zeolite was grown using the seed crystals as nuclei, and a second separation membrane 320 was formed on the support 11.

[0108] In Comparative Example 1, the mixed gas supplied from the gas supply unit 36 ​​to the second separation membrane module 32 contains CO as the first gas. ２ and CH as the second gas. ４ and a third gas, H ２ The composition of the mixed gas (CO ２ / CH ４ / H ２ The ratio of the mixed gas to the second permeate gas in the second separation membrane module 32 is 50% by volume, 49.6% by volume, and 0.4% by volume. The pressure and temperature of the mixed gas supplied from the gas supply unit 36 ​​are 0.5 MPaG and 30° C., respectively. The pressure of the second permeate gas in the second separation membrane module 32 is 0 MPaG.

[0109] In Comparative Example 1, as described above, the first separation membrane module 31 is omitted, and therefore the third gas is not recovered in the first separation membrane module 31. Therefore, the concentration of the third gas in the feed gas supplied to the second separation membrane module 32 is 0.4% by volume, the same as the concentration in the mixed gas described above.

[0110] In Comparative Example 1, the second gas, CH ４ is the gas to be recovered in the second separation membrane module 32 (hereinafter also referred to as "recovered gas"). Therefore, this recovered gas is recovered in the third recovery section 35 as the second non-permeate gas in the second separation membrane module 32. The "recovery rate" and "recovered gas volume" in Table 2 are calculated by the area of ​​the second separation membrane 320 required when the purity of the recovered gas in the second non-permeate gas is 95% (i.e., the concentration is 95% by volume). The "recovery rate" and "recovered gas volume" in Table 2 indicate the recovery rate and volume of the recovered gas recovered by using a second separation membrane 320 with that area. The recovered gas recovery rate (i.e., the value obtained by dividing the volume of recovered gas recovered in the third recovery section 35 by the volume of recovered gas in the mixed gas) was 86.9%. In Comparative Example 1 and Example 1, the recovered gas volume is expressed as a ratio, with the recovered gas volume in Comparative Example 1 being the reference (i.e., 1). Therefore, the recovered gas volume in Comparative Example 1 is 1.

[0111] Example 1 is the same as Comparative Example 1 except that a first separation membrane module 31 is provided. In Example 1, a zeolite membrane made of LTA-type zeolite was used as the first separation membrane 310 in the first separation membrane module 31. The Si / Al ratio of the first separation membrane 310 is 2.

[0112] The separation membrane composite 1 including the first separation membrane 310, which is an LTA-type zeolite membrane, was produced by the following procedure. Sodium hydroxide (manufactured by Sigma-Aldrich) as a Na source and sodium aluminate powder (manufactured by Sigma-Aldrich) as an Al source were mixed with pure water, and the mixture was stirred at room temperature for 1 hour. After that, colloidal silica (Snowtex-50T, manufactured by Nissan Chemical Industries, Ltd.) as a Si source was added to obtain a raw material solution. Assuming that the Si source, Al source, and Na source are all present as oxides, the SiO ２ / Al２ O ３ The molar ratio of H ２ O / Na ２ The molar ratio of O and Na ２ O / SiO ２ The molar ratios of were 4.85, 729, and 0.25, respectively. Subsequently, the raw material solution was stirred at room temperature for 12 hours. 70 minutes after the end of stirring of the raw material solution, the support 11 to which LTA zeolite seed crystals were attached was immersed in the raw material solution, and heating of the raw material solution (hydrothermal synthesis) was initiated. The hydrothermal synthesis was carried out at 80°C for 100 hours. After the hydrothermal synthesis, the support 11 and the first separation membrane 310, which was a zeolite membrane, were thoroughly washed with pure water and then dried at 80°C.

[0113] In Example 1, the mixed gas supplied from the gas supply unit 36 ​​to the first separation membrane module 31 is the same as the mixed gas supplied from the gas supply unit 36 ​​in Comparative Example 1. The pressure of the first permeate gas in the first separation membrane module 31 is −0.09 MPaG.

[0114] In Example 1, the third gas (i.e., H ２ The recovery rate of the third gas (i.e., the value obtained by dividing the amount of the third gas recovered in the first recovery section 33 by the amount of the third gas in the mixed gas) was 88.1%. The concentration of the third gas in the feed gas supplied to the second separation membrane module 32 was 0.05% by volume.

[0115] In Example 1, as in Comparative Example 1, the second gas CH ４ is the recovered gas, and is recovered in the third recovery section 35. The recovery rate of the recovered gas in Example 1 was 87.3%, which was increased compared to Comparative Example 1. The amount of recovered gas in Example 1 was 1.1, which was increased compared to Comparative Example 1. Therefore, the performance of the gas separation device 3 in Example 1 was "good", and the performance of the gas separation device in Comparative Example 1 was "poor". This difference in performance is thought to be due to the fact that the third gas in the mixed gas was removed by the first separation membrane 310, and the decrease in the permeation performance of the second separation membrane 320 due to adsorption of the third gas, etc., was suppressed, as described above.

[0116] Comparative Example 2 is the same as Comparative Example 1 except that the type of second separation membrane 320 is different and the first gas in the mixed gas is different. In Comparative Example 2, a zeolite membrane composed of amorphous silica and MTN-type zeolite was used as the second separation membrane 320. The Si / Al ratio of the second separation membrane 320 is greater than 100.

[0117] A separation membrane composite 1 including a second separation membrane 320, which is a zeolite membrane composed of amorphous silica and MTN-type zeolite, was manufactured as follows. First, a support 11 manufactured in the same manner as in Comparative Example 1 was pretreated by immersing it in an aqueous solution containing silica and holding it at 50°C for 1 hour, and then dried at 100°C. The silica concentration in the aqueous solution was set to 50% by mass. Next, the pretreated support 11 was immersed in a raw material solution to perform hydrothermal synthesis, thereby forming a second separation membrane 320, which is an amorphous silica membrane containing MTN-type zeolite particles. The hydrothermal synthesis time was 8 hours, and the hydrothermal synthesis temperature was 180°C. The raw material solution was prepared by mixing 6.28 g of a 30% by mass tetramethylammonium hydroxide solution (manufactured by SACHEM) with 146.8 g of distilled water. Then, 14.8 g of approximately 30% by mass silica sol (trade name: Snowtex S, manufactured by Nissan Chemical Industries, Ltd.) was added and stirred with a magnetic stirrer (room temperature, 30 minutes) to obtain a raw material solution. The second separation membrane 320 and support 11 after hydrothermal synthesis were immersed for 1 day in a post-treatment solution prepared by mixing distilled water with sodium hydroxide to a pH of 9 or higher for post-treatment. The second separation membrane 320 and support 11 were then washed with distilled water, dried at 80°C for 12 hours, and then held at 450°C for 50 hours to burn off the SDA, thereby obtaining a separation membrane composite 1.

[0118] In Comparative Example 2, the first gas in the mixed gas was H ２ The composition of the mixed gas (H ２ / CH ４ / H ２ The ratio of the mixed gas to the second permeate gas in the second separation membrane module 32 is 50% by volume, 49.6% by volume, and 0.4% by volume. The pressure and temperature of the mixed gas supplied from the gas supply unit 36 ​​are 0.5 MPaG and 30° C., respectively. The pressure of the second permeate gas in the second separation membrane module 32 is 0 MPaG.

[0119] In Comparative Example 2, as described above, the first separation membrane module 31 is omitted, and therefore the third gas is not recovered in the first separation membrane module 31. Therefore, the concentration of the third gas in the feed gas supplied to the second separation membrane module 32 is 0.4% by volume, which is the same as the concentration in the mixed gas described above.

[0120] In Comparative Example 2, the second gas, CH ４ is the gas to be recovered in the second separation membrane module 32 (i.e., recovered gas). Therefore, this recovered gas is recovered in the third recovery section 35 as the second non-permeate gas in the second separation membrane module 32. The "recovery rate" and "recovered gas amount" in Table 2 were determined in the same manner as in Comparative Example 1. The recovery rate of the recovered gas was 75.0%. In Comparative Example 2, Example 2, and Example 3, the recovered gas amount is shown as a ratio, with the recovered gas amount in Comparative Example 2 being the reference (i.e., 1). Therefore, the recovered gas amount in Comparative Example 2 is 1.

[0121] Example 2 is the same as Comparative Example 2 except that a first separation membrane module 31 is provided. In Example 2, a zeolite membrane made of LTA-type zeolite was used as the first separation membrane 310 in the first separation membrane module 31, as in Example 1. The Si / Al ratio in the first separation membrane 310 is 2.

[0122] In Example 2, the mixed gas supplied from the gas supply unit 36 ​​to the first separation membrane module 31 is the same as the mixed gas supplied from the gas supply unit 36 ​​in Comparative Example 2. The pressure of the first permeate gas in the first separation membrane module 31 is −0.09 MPaG.

[0123] In Example 2, the third gas (i.e., H ２ The recovery rate of the third gas (O) was 88.1%. The concentration of the third gas in the feed gas supplied to the second separation membrane module 32 was 0.05% by volume.

[0124] In Example 2, as in Comparative Example 2, the second gas CH ４is the recovered gas, and is recovered in the third recovery section 35. The recovery rate of the recovered gas in Example 2 was 88.0%, which was increased compared to Comparative Example 2. The amount of recovered gas in Example 2 was 2.7, which was increased compared to Comparative Example 2. Therefore, the performance of the gas separation device 3 in Example 2 was "good", and the performance of the gas separation device in Comparative Example 2 was "poor". This difference in performance is thought to be due to the fact that the third gas in the mixed gas was removed by the first separation membrane 310, and the decrease in the permeation performance of the second separation membrane 320 due to adsorption of the third gas, etc., was suppressed, as described above.

[0125] Example 3 is the same as Example 2, except for the type of first separation membrane 310. In Example 3, a zeolite membrane made of CHA-type zeolite was used as the first separation membrane 310 in the first separation membrane module 31. The Si / Al ratio of the first separation membrane 310 was 20.

[0126] The separation membrane composite 1 including the first separation membrane 310, which is a CHA-type zeolite membrane, was produced by the following procedure. The raw material solution for the first separation membrane 310 was prepared based on the method for preparing a membrane synthesis solution described in Japanese Patent Application Laid-Open No. 2011-16123. Specifically, a mixture of silica sol ("Cataloid SI-30" manufactured by Catalysts and Chemical Industries, Ltd.) and 50% aluminum nitrate (Al(NO ３ ) ３ ) aqueous solution in such a ratio that the Si / Al ratio in the first separation membrane 310 after hydrothermal synthesis would be 20 was used as the raw material solution. Next, the support 11 to which CHA-type zeolite seed crystals had been attached was immersed in the raw material solution, and heating of the raw material solution (hydrothermal synthesis) was initiated. The hydrothermal synthesis was carried out at 120°C for 10 days. After the hydrothermal synthesis, the first separation membrane 310 and the support 11 were cooled and thoroughly washed, and then dried at 70°C for 16 hours. Then, the first separation membrane 310 and the support 11 were calcined at 550°C for 10 hours.

[0127] In Example 3, the third gas (i.e., H ２ The recovery rate of the third gas (O) was 88.1%. The concentration of the third gas in the feed gas supplied to the second separation membrane module 32 was 0.05% by volume.

[0128] In Example 3, similar to Comparative Example 2 and Example 2, the second gas CH ４ is the recovered gas, and is recovered in the third recovery section 35. The recovery rate of the recovered gas in Example 3 was 88.0%, which was increased compared to Comparative Example 2. The amount of recovered gas in Example 3 was 2.7, which was increased compared to Comparative Example 2. Therefore, the performance of the gas separation device 3 in Example 3 is "good." This is thought to be because, as described above, the third gas in the mixed gas is removed by the first separation membrane 310, and a decrease in the permeation performance of the second separation membrane 320 due to adsorption of the third gas, etc., is suppressed.

[0129] Comparative Example 3 is the same as Comparative Example 2, except that the second gas and the third gas in the mixed gas are different. In Comparative Example 3, the second gas and the third gas in the mixed gas are N ２ and N.H. ３ The composition of the mixed gas (H ２ / N ２ / NH ３ ) are 50 vol% / 49.6 vol% / 0.4 vol%. The pressure and temperature of the mixed gas supplied from the gas supply unit 36 ​​are 0.5 MPaG and 30°C, respectively. The pressure of the second permeate gas in the second separation membrane module 32 is 0 MPaG.

[0130] In Comparative Example 3, as described above, the first separation membrane module 31 is omitted, and therefore the third gas is not recovered in the first separation membrane module 31. Therefore, the concentration of the third gas in the feed gas supplied to the second separation membrane module 32 is 0.4% by volume, which is the same as the concentration in the mixed gas described above.

[0131] In Comparative Example 3, the first gas was H ２is the gas to be recovered in the second separation membrane module 32 (i.e., the recovered gas). Therefore, this recovered gas is recovered in the second recovery section 34 as the second permeate gas in the second separation membrane module 32. The "recovery rate" and "recovered gas volume" in Table 2 indicate the recovery rate and volume of recovered gas recovered by using a second separation membrane 320 with a calculated area, which is calculated when the purity of the recovered gas in the second permeate gas is 90% (i.e., the concentration is 90% by volume). The recovered gas recovery rate (i.e., the value obtained by dividing the volume of recovered gas recovered in the second recovery section 34 by the volume of recovered gas in the mixed gas) was 85.6%. In Comparative Example 3 and Example 4, the recovered gas volume is expressed as a ratio, with the recovered gas volume in Comparative Example 3 being the reference (i.e., 1). Therefore, the recovered gas volume in Comparative Example 3 is 1.

[0132] Example 4 is similar to Comparative Example 3, except that a first separation membrane module 31 is provided. In Example 4, a zeolite membrane made of CHA-type zeolite was used as the first separation membrane 310 in the first separation membrane module 31, as in Example 3. The Si / Al ratio of the first separation membrane 310 is 20.

[0133] In Example 4, the mixed gas supplied from the gas supply unit 36 ​​to the first separation membrane module 31 is the same as the mixed gas supplied from the gas supply unit 36 ​​in Comparative Example 3. The pressure of the first permeate gas in the first separation membrane module 31 is −0.09 MPaG.

[0134] In Example 4, the third gas (i.e., NH ３ The recovery rate of the third gas was 82.5%. The concentration of the third gas in the feed gas supplied to the second separation membrane module 32 was 0.1% by volume.

[0135] In Example 4, as in Comparative Example 3, the first gas was H ２ is the recovered gas, and is recovered in the second recovery section 34. The recovery rate of the recovered gas in Example 4 was 40.2%. This is because the first gas (H ２) permeated the first separation membrane 310 and was recovered in the first recovery section 33. The recovered gas amount in Example 4 was 7.6, which was greater than that in Comparative Example 3. Therefore, the performance of the gas separation device 3 in Example 4 was "good," and the performance of the gas separation device in Comparative Example 3 was "poor." This difference in performance is thought to be due to the fact that, as described above, the third gas in the mixed gas was removed by the first separation membrane 310, and a decrease in the permeation performance of the second separation membrane 320 due to adsorption of the third gas or the like was suppressed.

[0136] The gas separation apparatus 3 and the gas separation method described above can be modified in various ways.

[0137] In the gas separation device 3 of the above example, one first separation membrane 310 and one second separation membrane 320 are provided, but a plurality of first separation membranes 310 and / or second separation membranes 320 may be provided.

[0138] For example, in the gas separation apparatus 3a illustrated in FIG. 7 , another second separation membrane module 32a having the same structure as the second separation membrane module 32 is provided between the second separation membrane module 32 and the third recovery section 35. In the gas separation apparatus 3a, two second separation membrane modules 32, 32a are connected in series. In the gas separation apparatus 3a, the second non-permeate gas discharged from the second separation membrane module 32 on the upstream side (i.e., the side closer to the first separation membrane module 31) is supplied to the second separation membrane module 32a via the second non-permeate gas flow path 322. In the second separation membrane module 32a, the first gas remaining in the second non-permeate gas is separated from the second non-permeate gas by permeating through the second separation membrane 320. The gas that permeated the second separation membrane 320 of the second separation membrane module 32a is led to the second recovery section 34 via the second permeate gas flow path 321a. On the other hand, the gas that does not permeate through the second separation membrane 320 of the second separation membrane module 32a is guided to the third recovery section 35 via the second non-permeation gas flow path 322a.

[0139] Alternatively, in a gas separation apparatus 3b illustrated in FIG. 8, another second separation membrane module 32b having the same structure as the second separation membrane module 32 is disposed in parallel with the second separation membrane module 32 between the first separation membrane module 31 and the third recovery section 35. In the gas separation apparatus 3b, the two second separation membrane modules 32, 32b are connected in parallel. In the gas separation apparatus 3b, the first non-permeate gas discharged from the first separation membrane module 31 is supplied in parallel to the second separation membrane module 32 and the second separation membrane module 32b. In the second separation membrane module 32b, similar to the second separation membrane module 32, the first gas in the first non-permeate gas is separated from the first non-permeate gas by permeating through the second separation membrane 320. The gas that permeates the second separation membrane 320 of the second separation membrane module 32b is led to the second recovery section 34 via the second permeate gas flow path 321b. On the other hand, the gas that does not permeate through the second separation membrane 320 of the second separation membrane module 32b is guided to the third recovery section 35 via the second non-permeation gas flow path 322b.

[0140] In the above-described gas separation devices 3, 3a, and 3b, the first separation membrane 310 and / or the second separation membrane 320 may be a laminated membrane in which a plurality of zeolite membranes formed from different types of zeolite are stacked in the thickness direction, or may be a zeolite membrane that has been subjected to a surface treatment. Furthermore, in the gas separation devices 3, 3a, and 3b, a membrane of a type other than a zeolite membrane (for example, an inorganic membrane other than a zeolite membrane, such as a silica membrane) may be provided on the first separation membrane 310 and / or the second separation membrane 320.

[0141] In the above-described gas separation devices 3, 3a, and 3b, the first separation membrane 310 and / or the second separation membrane 320 do not necessarily have to be a zeolite membrane, but may be various types of separation membranes (for example, inorganic membranes other than zeolite membranes, etc.).

[0142] When first separation membrane 310 is a zeolite membrane, the maximum number of membered rings of the zeolite constituting first separation membrane 310 may be greater than 8. When second separation membrane 320 is a zeolite membrane, the maximum number of membered rings of the zeolite constituting second separation membrane 320 may be greater than 8.

[0143] The Si / Al ratio in the first separation membrane 310 may be greater than 100. The Si / Al ratio in the second separation membrane 320 may be 100 or less.

[0144] The structures of the first separation membrane module 31 and the second separation membrane module 32 are not necessarily limited to the above examples and may be modified in various ways. For example, in the first separation membrane module 31, the first separation membrane 310 does not necessarily have to be supported by the support 11 and may be provided in various ways. Furthermore, in the second separation membrane module 32, the second separation membrane 320 does not necessarily have to be supported by the support 11 and may be provided in various ways.

[0145] The first separation membrane 310 and the second separation membrane 320 do not necessarily have to be housed separately in the housing 22 of the first separation membrane module 31 and the housing 22 of the second separation membrane module 32, respectively, and may be housed in a single housing.

[0146] The kinetic diameter of the first gas may be 0.3 nm or more, or 0.4 nm or more, and the kinetic diameter of the second gas may be 0.4 nm or more.

[0147] The third gas may be a polar gas other than water and ammonia. The concentration of the third gas in the mixed gas supplied from the gas supply unit 36 ​​may be higher than 1% by volume.

[0148] In the gas separation apparatus 3, for example, a pretreatment facility such as an impurity remover that adsorbs and removes a third gas from the mixed gas may be provided between the gas supply unit 36 ​​and the first separation membrane module 31 or between the first separation membrane module 31 and the second separation membrane module 32. In this case, the pretreatment facility is designed on the premise of separation and removal of the third gas in the first separation membrane module 31, and therefore the pretreatment facility can be made compact. As a result, it is possible to prevent the facility related to the separation of the mixed gas from becoming large in size.

[0149] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0150] 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.

[0151] The present invention can be used to separate various types of mixed gases.

[0152] 1 Separation membrane composite 3, 3a, 3b Gas separation device 310 First separation membrane 320 Second separation membrane 36 Gas supply unit S11 to S12 Steps

Claims

1. A gas separation apparatus for separating a mixed gas containing at least a first gas, a second gas, and a third gas that is a polar gas, comprising: a gas supply unit for supplying the mixed gas; a first separation membrane having a higher permeability for the third gas than the permeabilities of the first gas and the second gas, which allows the third gas to permeate and be removed from the mixed gas supplied from the gas supply unit; and a second separation membrane having a higher permeability for the first gas than the permeability for the second gas, which is supplied with a non-permeating gas from the mixed gas that did not permeate through the first separation membrane, and which allows the first gas to permeate and be separated from the non-permeating gas.

2. A gas separation device according to claim 1, wherein the ratio of the silicon content to the aluminum content in said first separation membrane is 100 or less.

3. A gas separation device according to claim 1, wherein the ratio of the silicon content to the aluminum content in said second separation membrane is greater than 100.

4. A gas separation apparatus according to claim 1, wherein the concentration of the third gas in the mixed gas supplied from the gas supply unit is 1% by volume or less.

5. A gas separation apparatus according to claim 1, wherein the third gas is water or ammonia.

6. The gas separation device according to claim 1, wherein the first gas and the second gas each have a kinetic molecular diameter of less than 0.4 nm.

7. A gas separation device according to claim 6, wherein the kinetic molecular diameter of the first gas is less than 0.3 nm.

8. A gas separation apparatus according to any one of claims 1 to 7, wherein the first separation membrane is a zeolite membrane.

9. A gas separation method for separating a mixed gas containing at least a first gas, a second gas, and a third gas that is a polar gas, comprising: a) a step of supplying the mixed gas to a first separation membrane having a higher permeability for the third gas than the permeabilities for the first gas and the second gas, and allowing the third gas to permeate and remove it; and b) a step of supplying a non-permeating gas from the mixed gas that has not permeated the first separation membrane to a second separation membrane having a higher permeability for the first gas than the permeability for the second gas, and allowing the first gas to permeate and separate it from the non-permeating gas.

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