Gas separation method and gas separation apparatus

Abstract

To improve the selection performance of carbon dioxide in a separation membrane.SOLUTION: A gas separation device (2) comprises: a separation membrane composite (1) where a separation membrane (12) having pores having an average pore diameter of 1 nm or less is formed on a porous support (11); and a gas supply part (26) for supplying a mixed gas containing CO2 and other gases from the separation membrane (12) side to the separation membrane composite (1). CO2 in the mixed gas is separated from the mixed gas by permeating the separation membrane (12) and the support (11) in a state that a temperature of at least a part of a permeation side surface (113) exhausting a gas permeated the separation membrane (12) is lower by 10°C or more than a temperature of the mixed gas before being supplied to the separation membrane composite (1) in the support (11). Consequently, the selection performance of CO2 in the separation membrane (12) can be improved.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas separation method and a gas separation apparatus. [Background technology]

[0002] Conventionally, gases such as carbon dioxide (CO2) have been separated from combustion exhaust gas from thermal power plants and the like. For example, Patent Document 1 and Patent Document 2 propose a technique for separating CO2 from mixed gases using a zeolite membrane. Patent Document 3 proposes a technique for separating CO2 using a facilitated transport membrane.

[0003] Patent Document 4 proposes that in multiple carbon dioxide separation membranes arranged in sequence in a gas flow path, water vapor passes through the upstream carbon dioxide separation membrane, causing a decrease in the relative humidity of the gas supplied to the downstream carbon dioxide separation membrane and a decrease in carbon dioxide permeability, by lowering the temperature of the gas supplied to the downstream carbon dioxide separation membrane below the temperature of the gas supplied to the upstream carbon dioxide separation membrane, thereby increasing the relative humidity of the gas supplied to the downstream carbon dioxide separation membrane. Patent Document 4 states that a decrease in the temperature of the carbon dioxide separation membrane causes a decrease in carbon dioxide permeability.

[0004] On the other hand, Patent Document 5 proposes a technique for separating a feed mixture containing multiple types of hydrocarbons using a porous membrane with a pore size of 5 nm to 250 nm. In Patent Document 5, the temperatures of the porous membrane and the permeate are maintained lower than the temperature of the feed mixture, thereby inducing capillary condensation of the mixture components in the pores of the porous membrane. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-159518 A [Patent Document 2] JP 2015-044162 A [Patent Document 3] International Publication No. 2009 / 093666 [Patent Document 4] JP 2017-154120 A [Patent Document 5] Special Publication No. 2018-514385 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when CO2 is separated and captured from combustion exhaust gas using a zeolite membrane as in Patent Documents 1 and 2, it is difficult to increase the concentration of CO2 in the gas that has permeated the zeolite membrane because the partial pressure of CO2 in the combustion exhaust gas is relatively low. In the case of a nonporous facilitated transport membrane as in Patent Document 3, the separation performance is likely to decrease when the moisture content in the facilitated transport membrane decreases, making it difficult to continue stable separation over the long term.

[0007] Patent Document 4 describes that, regarding the temperatures of gas supplied to multiple carbon dioxide separation membranes, the gas temperature on the downstream side is lower than the gas temperature on the upstream side. However, because the carbon dioxide permeability of the carbon dioxide separation membrane decreases with decreasing temperature, it is difficult to imagine cooling each carbon dioxide separation membrane (i.e., a single carbon dioxide separation membrane) so that the temperature of the separation membrane becomes lower than the temperature of the gas supplied to the separation membrane.

[0008] Patent Document 5 discloses the separation of hydrocarbons, but does not disclose the separation of CO2. In addition, the pore size of the porous membrane in Patent Document 5 is relatively large, at 5 nm or more, so it is difficult to use the porous membrane for CO2 separation.

[0009] The present invention is directed to a gas separation method for separating carbon dioxide from a mixed gas, and aims to improve the carbon dioxide selectivity of the separation membrane in order to increase the concentration of carbon dioxide in the gas that has permeated the separation membrane. [Means for solving the problem]

[0010] A gas separation method according to one preferred embodiment of the present invention comprises the steps of: a) preparing a separation membrane composite in which a separation membrane having pores with an average pore size of 1 nm or less is formed on a porous support, and placing the composite in a single external cylinder; and b) supplying a mixed gas containing carbon dioxide and other gases from a gas supply unit connected to the external cylinder into the internal space of the external cylinder and supplying the mixed gas to the separation membrane composite from the separation membrane side, and allowing the carbon dioxide in the mixed gas to permeate the separation membrane and the support, thereby obtaining a permeated gas. The separation membrane composite is The moisture content of the mixed gas is more than 3000 ppm. Moisture content is 3000ppm or less In the case of , the carbon dioxide permeation rate is It is said to be large For the separation membrane composite installed in the outer cylinder, step b) is performed in a state in which the temperature of at least a part of the permeate side surface of the support of the separation membrane composite, from which the permeate gas is discharged, is 10° C. or more lower than the temperature of the mixed gas before it is supplied to the separation membrane composite.

[0011] Preferably, the average pore size of the separation membrane is 0.2 nm or more and 1 nm or less.

[0012] Preferably, in the step b), the temperature of the entire permeate side surface of the support is at least 10° C. lower than the temperature of the mixed gas before it is supplied to the separation membrane composite.

[0013] Preferably, in the step b), the temperature of at least a portion of the permeate side surface of the support is at least 15° C. lower than the temperature of the mixed gas before it is supplied to the separation membrane composite.

[0014] Preferably, the pressure of the mixed gas before being supplied to the separation membrane composite in step b) is 1 MPa or more.

[0015] Preferably, the separation membrane is an inorganic membrane. More preferably, the separation membrane is a zeolite membrane. Even more preferably, the maximum number of rings in the zeolite constituting the separation membrane is 8 or less.

[0016] Preferably, the water content of the mixed gas before being supplied to the separation membrane composite in step b) is 3000 ppm or less.

[0017] Preferably, in step b), the temperature of the non-permeating gas of the mixed gas that is discharged without permeating the separation membrane and the support is higher than the temperature of the permeate side surface of the support and lower than the temperature of the mixed gas before it is supplied to the separation membrane composite.

[0018] Preferably, the other gases include one or more of hydrogen, helium, nitrogen, oxygen, carbon monoxide, nitrogen oxides, ammonia, sulfur oxides, hydrogen sulfide, sulfur fluoride, mercury, arsine, hydrogen cyanide, carbonyl sulfide, C1 to C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes.

[0019] The present invention is also directed to a gas separation device for separating carbon dioxide in a mixed gas. A gas separation device according to one preferred embodiment of the present invention comprises a separation membrane composite in which a separation membrane having pores with an average pore size of 1 nm or less is formed on a porous support, a single outer cylinder that houses the separation membrane composite in its internal space, and a gas supply unit that is connected to the outer cylinder and supplies a mixed gas containing carbon dioxide and other gases to the internal space of the outer cylinder and supplies the mixed gas to the separation membrane composite from the separation membrane side. The separation membrane composite comprises: The moisture content of the mixed gas is more than 3000 ppm. Moisture content is 3000ppm or less In the case of , the carbon dioxide permeation rate is It is said to be large With respect to the separation membrane composite installed in the outer cylinder, carbon dioxide in the mixed gas is separated from the mixed gas by permeating through the separation membrane and the support in a state in which the temperature of at least a part of the permeation side surface of the support of the separation membrane composite, from which gas that has permeated the separation membrane is discharged, is 10° C. or more lower than the temperature of the mixed gas before it is supplied to the separation membrane composite. With this gas separation device, the selectivity of the separation membrane to carbon dioxide can be improved. Preferably, the average pore size of the separation membrane is 0.2 nm or more and 1 nm or less. Effect of the Invention

[0020] According to the present invention, the selectivity of the separation membrane for carbon dioxide can be improved. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 shows a gas separation apparatus. [Diagram 2] FIG. 2 is a cross-sectional view of a separation membrane composite. [Diagram 3] FIG. 2 is an enlarged cross-sectional view of the separation membrane composite. [Figure 4] FIG. 2 is a diagram showing the flow of separation of a mixed gas. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] FIG. 1 is a diagram showing a schematic structure of a gas separation apparatus 2 according to an embodiment of the present invention. In FIG. 1, the parallel oblique lines in the cross section of a part of the configuration are omitted. The gas separation apparatus 2 is an apparatus that separates carbon dioxide (CO2) from a mixed gas containing carbon dioxide and other gases. The mixed gas is, for example, a combustion exhaust gas from a thermal power plant.

[0023] The gas separation device 2 includes a separation membrane composite 1, a sealing section 21, an outer cylinder 22, two sealing members 23, a gas supply section 26, a first gas recovery section 27, a second gas recovery section 28, and a cooling section 29. The separation membrane composite 1, the sealing section 21, and the sealing members 23 are housed in the internal space of the outer cylinder 22. The gas supply section 26, the first gas recovery section 27, and the second gas recovery section 28 are disposed outside the outer cylinder 22 and connected to the outer cylinder 22. In the example shown in FIG. 1, the cooling section 29 is disposed outside the outer cylinder 22 and covers the outer surface of the outer cylinder 22.

[0024] Fig. 2 is a cross-sectional view of the separation membrane composite 1. Fig. 3 is a cross-sectional view showing an enlarged portion of the separation membrane composite 1. The separation membrane composite 1 includes a porous support 11 and a separation membrane 12 formed on the support 11. In Fig. 2, the separation membrane 12 is drawn with a thick line. In Fig. 3, the separation membrane 12 is drawn with parallel diagonal lines. Furthermore, in Fig. 3, the thickness of the separation membrane 12 is drawn thicker than it actually is.

[0025] The support 11 is a porous member that allows gas to pass through. In the example shown in FIG. 2, the support 11 is a monolithic support having a single continuous columnar body that is molded integrally and has a plurality of through holes 111 that extend in the longitudinal direction (i.e., the vertical direction in FIG. 2). In the example shown in FIG. 2, 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 FIG. 1 and FIG. 2, the diameter of the through hole 111 is drawn larger than the actual diameter, and the number of the through holes 111 is drawn smaller than the actual number. The separation membrane 12 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.

[0026] The length of the support 11 (i.e., the length in the vertical 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 column shape. When the shape of the support 11 is a tubular or cylindrical shape, the thickness of the support 11 is, for example, 0.1 mm to 10 mm.

[0027] Various substances (for example, ceramics or metals) can be used as the material of the support 11, so 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 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.

[0028] 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.

[0029] The average pore diameter of the support 11 near the surface where the separation membrane 12 is formed is preferably smaller than the average pore diameter of other parts of the support 11. To realize 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 each layer may be the same or different. The average pore diameter of the support 11 can be measured by a mercury porosimeter, a perm porometer, a nanoperm porometer, or the like.

[0030] The average pore size of the support 11 is, for example, 0.01 μm to 70 μm, and preferably 0.05 μm to 25 μm. The average pore size 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. With regard to the distribution of pore sizes throughout the support 11, including the surface and the 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 in the vicinity of the surface on which the separation membrane 12 is formed is, for example, 25% to 50%.

[0031] The separation membrane 12 is a porous membrane having pores. The separation membrane 12 is a gas separation membrane that separates CO2 from a mixed gas containing a plurality of types of gases by utilizing a molecular sieve action. The mixed gas contains other gases that are less likely to permeate the separation membrane 12 than CO2. In other words, the mixed gas contains other gases that have a lower permeation rate than the permeation rate of CO2 through the separation membrane 12. In addition to CO2, the mixed gas contains one or more gases selected from the group consisting of hydrogen (H2), helium (He), nitrogen (N2), oxygen (O2), carbon monoxide (CO), nitrogen oxides, ammonia (NH3), sulfur oxides, hydrogen sulfide (H2S), sulfur fluoride, mercury (Hg), arsine (AsH3), hydrogen cyanide (HCN), carbonyl sulfide (COS), C1 to C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes. Note that separating CO2 refers to allowing at least a portion of the CO2 in the mixed gas to permeate through the separation membrane 12 and the support 11, regardless of the gas concentration. In the following description, the gas that has permeated through the separation membrane 12 and the support 11 is also referred to as the "permeated gas."

[0032] Nitrogen oxides are compounds of nitrogen and oxygen. Examples of the above-mentioned 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 The gas is called NOX.

[0033] Sulfur oxides are compounds of sulfur and oxygen. The above-mentioned sulfur oxides include, for example, sulfur dioxide (SO2), sulfur trioxide (SO3), and other SO X The gas is called SOXX.

[0034] Sulfur fluoride is a compound of fluorine and sulfur. The above-mentioned sulfur fluoride is, for example, disulfur difluoride (FSSF, S = SF2), sulfur difluoride (SF2), sulfur tetrafluoride (SF4), sulfur hexafluoride (SF6) or disulfur decafluoride (S2F 10 ) etc.

[0035] C1-C8 hydrocarbons are those with 1 to 8 carbon atoms. C3-C8 hydrocarbons may be straight-chain compounds, side-chain compounds, or cyclic compounds. C2-C8 hydrocarbons may be saturated hydrocarbons (i.e., those with no double or triple bonds in the molecule) or unsaturated hydrocarbons (i.e., those with double or triple bonds in the molecule). C1-C4 hydrocarbons are, for example, 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), or isobutene (CH2=C(CH3)2).

[0036] The organic acid may be a carboxylic acid or a sulfonic acid. The carboxylic acid may be, for example, formic acid (CH2O2), acetic acid (C2H4O2), oxalic acid (C2H2O4), acrylic acid (C3H4O2), or benzoic acid (C6H5COOH). The sulfonic acid may be, for example, ethanesulfonic acid (C2H6O3S). The organic acid may be a chain compound or a cyclic compound.

[0037] The above-mentioned alcohols are, for example, methanol (CH3OH), ethanol (C2H5OH), isopropanol (2-propanol) (CH3CH(OH)CH3), ethylene glycol (CH2(OH)CH2(OH)) or butanol (C4H9OH).

[0038] Mercaptans are organic compounds that have hydrogenated sulfur (SH) at the end, and are also called thiols or thioalcohols. Examples of the mercaptans mentioned above include methyl mercaptan (CH3SH), ethyl mercaptan (C2H5SH), and 1-propanethiol (C3H7SH).

[0039] The esters mentioned above are, for example, formates or acetates.

[0040] The above-mentioned ethers are, for example, dimethyl ether ((CH3)2O), methyl ethyl ether (C2H5OCH3) or diethyl ether ((C2H5)2O).

[0041] The above-mentioned ketones are, for example, acetone ((CH3)2CO), methyl ethyl ketone (C2H5COCH3) or diethyl ketone ((C2H5)2CO).

[0042] The above-mentioned aldehydes are, for example, acetaldehyde (CH3CHO), propionaldehyde (C2H5CHO) or butanal (butyraldehyde) (C3H7CHO).

[0043] 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. The thicker the separation membrane 12, the higher the selectivity. The thinner the separation membrane 12, the higher 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. The average pore size of the separation membrane 12 is 1 nm or less. This allows the separation membrane 12 to have high selectivity for CO2. The lower limit of the average pore size of the separation membrane 12 is not particularly limited as long as it allows CO2 to permeate, but can be, for example, 0.2 nm or more. The average pore size of the separation membrane 12 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. The selectivity improves when the average pore diameter of the separation membrane 12 is reduced. The permeation rate increases when the average pore diameter of the separation membrane 12 is increased. The average 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.

[0044] The separation membrane 12 is preferably an inorganic membrane, and in this embodiment, it is a zeolite membrane (i.e., a membrane-like zeolite). As the zeolite constituting the separation membrane 12, a zeolite in which the atom (T atom) located at the center of the oxygen tetrahedron (TO4) constituting the zeolite is only Si or is composed of Si and Al, an AlPO type zeolite in which the T atom is composed of Al and P, a SAPO type zeolite in which the T atom is composed of Si, Al and P, a MAPSO type zeolite in which the T atom is composed of magnesium (Mg), Si, Al and P, a ZnAPSO type zeolite in which the T atom is composed of zinc (Zn), Si, Al and P, or the like can be used. A part of the T atoms may be substituted with other elements.

[0045] When the maximum number of rings in the zeolite constituting the separation membrane 12 is n, the average pore diameter is the arithmetic average of the short diameter and long diameter of the n-membered ring pores. An n-membered ring pore is a pore in which the number of oxygen atoms in a portion in which 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 arithmetic average of the short diameter and long diameter of all the n-membered ring pores is the average pore diameter of the zeolite. In this way, the average pore diameter of a zeolite membrane is uniquely determined by the skeletal structure of the zeolite, and is calculated based on the arithmetic average of the short diameter and long diameter of all the n-membered ring pores in the "Database of Zeolite Structures" [online] of the International Zeolite Society, the Internet, and the like.<URL:http: / / www.iza-structure.org / databases / > The values ​​can be obtained from the values ​​disclosed in the

[0046] The type of zeolite constituting the separation membrane 12 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, PAU type, RHO type, SAT type, SOD type, or other zeolite. From the viewpoint of increasing the permeation rate of CO2 and improving the selectivity performance described later, it is preferable that the maximum number of rings of the zeolite is 8 or less (for example, 6 or 8). The separation membrane 12 is, for example, a DDR type zeolite. In other words, the separation membrane 12 is a zeolite membrane composed of a zeolite whose structure code is "DDR" as defined by the International Zeolite Society. In this case, the intrinsic pore size of the zeolite constituting the separation membrane 12 is 0.36 nm x 0.44 nm, and the average pore size is 0.40 nm.

[0047] When the separation membrane 12 is a zeolite membrane, the separation membrane 12 contains, for example, silicon (Si). The separation membrane 12 may contain, for example, any two or more of Si, aluminum (Al), and phosphorus (P). The separation membrane 12 may contain an alkali metal. The alkali metal is, for example, sodium (Na) or potassium (K). When the separation membrane 12 contains Si atoms, the Si / Al ratio in the separation membrane 12 is, for example, 1 or more and 100,000 or less. 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 ratio, the more preferable it is. The Si / Al ratio in the separation membrane 12 can be adjusted by adjusting the mixing ratio of the Si source and the Al source in the raw material solution described later.

[0048] The CO2 permeation amount (permeance) of the separation membrane 12 at -50°C to 300°C is, for example, 50 nmol / m 2 s Pa or more. The ratio of the CO2 permeation amount / CH4 leakage amount (permeance ratio) of the separation membrane 12 at -50°C to 300°C is, for example, 30 or more. The permeance and permeance ratio are those when the partial pressure difference of CO2 between the supply side and permeation side of the separation membrane 12 is 1.5 MPa.

[0049] The sealing portion 21 is a member attached to both ends of the support 11 in the longitudinal direction (i.e., the left-right direction in FIG. 1) and covers and seals both longitudinal end faces of the support 11 and the outer side faces 112 near the both end faces. The sealing portion 21 prevents the inflow and outflow of gas from the both end faces of the support 11. The sealing portion 21 is, for example, a plate-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 a plurality of openings that overlap with the plurality of 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 both ends.

[0050] The outer cylinder 22 is a tubular member having a substantially cylindrical shape. 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 gas supply port 221 is provided at one end of the outer cylinder 22 in the longitudinal direction (i.e., the end on the left side in FIG. 1), and a first gas discharge port 222 is provided at the other end. A second gas discharge port 223 is provided on the side of the outer cylinder 22. A gas supply unit 26 is connected to the gas supply port 221. A first gas recovery unit 27 is connected to the first gas discharge port 222. A second gas recovery unit 28 is connected to the second gas discharge port 223. The internal space of the outer cylinder 22 is a sealed space isolated from the space around the outer cylinder 22.

[0051] The two seal members 23 are disposed around the entire circumference between the outer surface 112 of the separation membrane composite 1 (i.e., the outer surface 112 of the support 11) and the inner surface of the outer tube 22 near both ends of the separation membrane composite 1 in the longitudinal direction. Each seal member 23 is a substantially annular member made of a material that is gas impermeable. The seal member 23 is, for example, an O-ring made of a flexible resin. The seal member 23 is in close contact with the outer surface 112 of the separation membrane composite 1 and the inner surface of the outer tube 22 around the entire circumference. In the example shown in FIG. 1, 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 112 of the separation membrane composite 1 via the sealing portion 21. The gap between the seal member 23 and the outer surface 112 of the separation membrane composite 1 and the gap between the seal member 23 and the inner surface of the outer tube 22 are sealed, and gas is hardly or completely unable to pass through.

[0052] The gas supply unit 26 supplies a mixed gas containing CO2 and other gases (e.g., nitrogen (N2)) to the internal space of the outer cylinder 22 via the gas supply port 221. The gas supply unit 26 is, for example, a blower or a pump that pressure-feeds the mixed gas toward the outer cylinder 22. The blower or pump includes a pressure adjustment unit that adjusts the pressure of the mixed gas supplied to the outer cylinder 22.

[0053] The mixed gas supplied from the gas supply unit 26 to the inside of the outer cylinder 22 is introduced into each through-hole 111 of the support 11 from the left end of the separation membrane composite 1 in the figure, as shown by arrow 251. CO2 in the mixed gas permeates through the separation membrane 12 provided on the inner surface of each through-hole 111 and the support 11, and is discharged from the outer surface 112 of the support 11, and is recovered by the second gas recovery unit 28 through the second gas discharge port 223, as shown by arrow 253. In other words, the gas supply unit 26 supplies the above-mentioned mixed gas to the separation membrane composite 1 from the separation membrane 12 side, and separates CO2 in the mixed gas from the mixed gas by permeating the separation membrane 12 and the support 11 and discharging it from a substantially cylindrical surface-shaped region (hereinafter referred to as the "permeation side surface 113") between the two seal members 23 of the outer surface 112 of the support 11. The permeate side surface 113 does not include the area of ​​the outer side surface 112 of the support 11 that is covered by the plug 21. The second gas recovery section 28 is, for example, a storage container that stores the permeate gas such as CO2 that has permeated through the separation membrane 12 and the support 11 and been discharged from the outer cylinder 22, or a blower or pump that transports the permeate gas.

[0054] Furthermore, gases other than the above-mentioned permeable gas (hereinafter referred to as "non-permeable gas") in the mixed gas pass through each through-hole 111 of the support 11 from left to right in the figure, and are recovered by the first gas recovery section 27 via the first gas discharge port 222, as shown by arrow 252. The first gas recovery section 27 is, for example, a storage container that stores the non-permeable gas discharged from the outer cylinder 22, or a blower or pump that transfers the non-permeable gas.

[0055] The cooling section 29 cools the outer cylinder 22 by directly or indirectly contacting the outer surface of the outer cylinder 22. The cooling section 29 is, for example, a substantially cylindrical cooling jacket provided around the outer cylinder 22. In this case, the outer cylinder 22 is cooled by continuously flowing a refrigerant such as cooling water inside the cooling section 29. In FIG. 1, the refrigerant in the cooling section 29 is indicated by parallel diagonal lines. The length of the cooling section 29 in the longitudinal direction described above is, for example, substantially the same as or longer than the longitudinal distance between the two seal members 23. In the example shown in FIG. 1, both ends of the cooling section 29 are located at substantially the same positions in the longitudinal direction as the two seal members 23.

[0056] In the gas separation device 2, the cooling unit 29 cools the outer casing 22, thereby also cooling the separation membrane composite 1 facing the inner surface of the outer casing 22. In detail, the cooling unit 29 cools the outer casing 22, thereby cooling the gas present between the inner surface of the outer casing 22 and the outer surface 112 of the support 11, and the support 11 is cooled over almost the entirety from the outer surface 112 side in contact with the gas. As a result, the separation membrane 12 in contact with the support 11 is also cooled over almost the entirety.

[0057] Next, with reference to FIG. 4, an example of the flow of mixed gas separation by the gas separation apparatus 2 will be described. When mixed gas separation is performed, first, a separation membrane 12 is produced on a support 11 to prepare a separation membrane composite 1 (step S11). To specifically explain step S11, first, seed crystals to be used in manufacturing the separation membrane 12 (i.e., a zeolite membrane) are prepared. For example, a powder of DDR-type zeolite is produced by hydrothermal synthesis, and the seed crystals are obtained from the powder of the zeolite. The powder of the zeolite may be used as it is as the seed crystals, or the seed crystals may be obtained by processing the powder by pulverization or the like.

[0058] Next, the porous support 11 is immersed in the solution in which the seed crystals are dispersed, and the seed crystals are attached to the support 11. Alternatively, the solution in which the seed crystals are dispersed is brought into contact with a portion of the support 11 where the separation membrane 12 is to be formed, thereby attaching the seed crystals to the support 11. In this way, a seed crystal-attached support is produced. The seed crystals may be attached to the support 11 by other techniques.

[0059] The support 11 to which the seed crystal is attached is immersed in the raw material solution. The raw material solution is prepared by dissolving and dispersing, for example, a Si source and a structure-directing agent (hereinafter also referred to as "SDA") in a solvent. The composition of the raw material solution is, for example, 1.0SiO2:0.015SDA:0.12(CH2)2(NH2)2. Water or an alcohol such as ethanol may be used as the solvent for the raw material solution. The SDA contained in the raw material solution is, for example, an organic substance. For example, 1-adamantanamine can be used as the SDA.

[0060] Then, DDR-type zeolite is grown by hydrothermal synthesis using the seed crystals as nuclei, thereby forming a separation membrane 12, which is a DDR-type zeolite membrane, on the support 11. The temperature during the hydrothermal synthesis is preferably 120 to 200° C., for example, 160° C. The hydrothermal synthesis time is preferably 10 to 100 hours, for example, 30 hours.

[0061] When the hydrothermal synthesis is completed, the support 11 and the separation membrane 12 are washed with pure water. After washing, the support 11 and the separation membrane 12 are dried, for example, at 80° C. When the support 11 and the separation membrane 12 are dried, the separation membrane 12 is subjected to a heat treatment to almost completely burn off the SDA in the separation membrane 12 and penetrate the micropores in the separation membrane 12. In this way, the above-mentioned separation membrane composite 1 is obtained.

[0062] When step S11 is completed, the gas separation device 2 shown in FIG. 1 is assembled (step S12). The separation membrane composite 1 is installed in the outer casing 22. Then, the separation membrane composite 1 is cooled by the cooling unit 29 through the outer casing 22. Specifically, the cooling unit 29 cools a portion of the outer casing 22 between the two seal members 23, and the gas present between the inner surface of the outer casing 22 and the outer surface 112 of the support 11 between the two seal members 23 is cooled. Furthermore, the permeation side surface 113, which is a region of the support 11 that contacts the gas, is cooled, and the support 11 is cooled almost entirely, and the separation membrane 12 is also cooled almost entirely (step S13). The cooling of the separation membrane composite 1 by the cooling unit 29 is continued, for example, until the gas separation process by the gas separation device 2 is completed.

[0063] Next, the gas supply unit 26 supplies a mixed gas containing CO2 and other gases to the internal space of the outer casing 22 (step S14). In this embodiment, the main components of the mixed gas are CO2 and N2. The mixed gas may contain gases other than CO2 and N2. Since it is possible to suppress a decrease in the permeation rate of CO2 caused by the moisture in the mixed gas inhibiting the adsorption of CO2 into the pores of the separation membrane 12, the moisture content of the mixed gas in the internal space of the outer casing 22 before being supplied to the separation membrane composite 1 is preferably 3000 ppm or less in volume ratio (i.e., molar ratio), more preferably 1000 ppm or less, further preferably 500 ppm or less, and particularly preferably 100 ppm or less. When the moisture content in the mixed gas is greater than 3000 ppm, a mixed gas whose moisture content has been reduced to 3000 ppm or less by a dehydrator or the like can be used.

[0064] The gas introduction pressure, which is the pressure of the mixed gas supplied from the gas supply unit 26 to the internal space of the outer casing 22, is preferably 0.5 MPa or more, more preferably 1 MPa or more, and further preferably 2 MPa or more. The gas introduction pressure is, for example, 20 MPa or less, typically 10 MPa or less. The temperature of the mixed gas supplied from the gas supply unit 26 to the internal space of the outer casing 22 is, for example, −50° C. to 300° C., and in this embodiment, about 10° C. to 150° C. In the internal space of the outer casing 22, the pressure and temperature of the mixed gas before being supplied to the separation membrane composite 1 (i.e., the mixed gas immediately before being supplied to the separation membrane 12) are approximately the same as the pressure and temperature of the mixed gas supplied from the gas supply unit 26 to the internal space of the outer casing 22.

[0065] The mixed gas supplied into the outer cylinder 22 is introduced into each through-hole 111 of the separation membrane composite 1. Then, CO2 in the mixed gas permeates through the separation membrane 12 and the support 11 of the separation membrane composite 1 and is discharged from the permeate side surface 113 of the support 11, thereby being separated from the mixed gas (step S15).

[0066] As described above, the support 11 is cooled by the cooling section 29. Therefore, the temperature of the support 11 is lower than the temperature of the mixed gas before being supplied to the separation membrane composite 1 (i.e., the mixed gas that moves from the gas supply port 221 toward the separation membrane 12 and is about to be supplied to the separation membrane 12). Specifically, the temperature of at least a part of the permeation side surface 113 of the support 11 is lower than the temperature of the mixed gas by 10° C. or more. Note that since the temperature of the permeation side surface 113 of the support 11 and the temperature of the gas immediately after permeating the support 11 are almost the same, when it is difficult to directly measure the temperature of the permeation side surface 113 of the support 11, it can be said that the temperature of at least a part of the permeation side surface 113 of the support 11 is lower than the temperature of the mixed gas by 10° C. or more when the temperature of the gas immediately after permeating the support 11 is lower than the temperature of the mixed gas before being supplied to the separation membrane composite 1.

[0067] When the gas separation device 2 contains multiple separation membrane composites, in at least one separation membrane composite 1 among the multiple separation membrane composites, the temperature of at least a portion of the permeate side surface 113 of the support 11 of the separation membrane composite 1 is 10°C or more lower than the temperature of the mixed gas immediately before it is supplied to the separation membrane 12 of the separation membrane composite 1.

[0068] Preferably, the temperature of the entire permeate side surface 113 of the support 11 is 10° C. or more lower than the temperature of the mixed gas before it is supplied to the separation membrane composite 1. The temperature of the permeate side surface 113 does not necessarily have to be 10° C. or more lower than the temperature of the mixed gas over the entire surface, and it is also preferable that the temperature of at least a portion of the permeate side surface 113 is 15° C. or more lower than the temperature of the mixed gas. More preferably, the temperature of the entire permeate side surface 113 of the support 11 is 15° C. or more lower than the temperature of the mixed gas before it is supplied to the separation membrane composite 1.

[0069] As described above, in the gas separation apparatus 2, the temperature of at least a part of the permeation side surface 113 of the support 11 is at least 10° C. lower than the temperature of the mixed gas before it is supplied to the separation membrane composite 1. This allows CO2 to be efficiently adsorbed into the pores of the separation membrane 12, and increases the ratio of the permeation rate of CO2 to the permeation rate of N2 and the like through the separation membrane 12. In other words, the selectivity of CO2 through the separation membrane 12 is improved. Preferably, the concentration of CO2 in the permeation gas that has permeated through the separation membrane 12 and support 11 is increased more than the concentration of CO2 in the mixed gas.

[0070] The permeable gas that has permeated the separation membrane composite 1 is recovered by the second gas recovery section 28. The pressure in the second gas recovery section 28 (i.e., the permeation side pressure) can be set arbitrarily, and is, for example, about 1 atmosphere (0.101 MPa). The permeable gas recovered by the second gas recovery section 28 may contain gases other than CO2.

[0071] In addition, the non-permeable gas (i.e., the gas of the mixed gas that did not permeate the separation membrane 12 and the support 11) passes through each through hole 111 in the longitudinal direction and is discharged from the outer casing 22 through the first gas discharge port 222. The non-permeable gas passing through the through hole 111 of the separation membrane composite 1 is cooled by the separation membrane composite 1, which has a lower temperature than the mixed gas. Therefore, the temperature of the non-permeable gas immediately after passing through the through hole 111 is lower than the temperature of the mixed gas before being supplied to the separation membrane composite 1 (i.e., the mixed gas that moves from the gas supply port 221 toward the separation membrane 12 and is immediately before being supplied to the separation membrane 12). The temperature of the non-permeable gas immediately after passing through the through hole 111 is preferably higher than the temperature of the permeable side surface 113 of the support 11. In addition, the temperature of the non-permeable gas immediately after passing through the through hole 111 is preferably higher than the temperature of the permeable gas immediately after permeating the separation membrane composite 1. The temperature of the non-permeable gas immediately after passing through the through hole 111 is approximately the same as the temperature of the non-permeable gas discharged from the first gas discharge port 222.

[0072] The impermeable gas discharged from the outer cylinder 22 is recovered by the first gas recovery section 27. The pressure in the first gas recovery section 27 is, for example, substantially the same as the pressure of the mixed gas supplied by the gas supply section 26. The impermeable gas recovered by the first gas recovery section 27 may contain CO2 that did not permeate through the separation membrane composite 1.

[0073] Next, with reference to Table 1, the relationship between the temperature difference between the mixed gas immediately before being supplied to separation membrane 12 and permeation side surface 113, and the pressure of the mixed gas immediately before being supplied to separation membrane 12, and the CO2 permeation flow rate and selectivity will be described for the gas separation method shown in steps S11 to S15 described above. Examples 1 to 5 and Comparative Examples 1 and 2 in Table 1 differ in the temperature difference ΔT (°C) between the mixed gas immediately before being supplied to separation membrane 12 and permeation side surface 113, and the pressure P (MPa) of the mixed gas immediately before being supplied to separation membrane 12. The temperature difference ΔT (°C) is calculated by subtracting the temperature of the lowest temperature region of permeation side surface 113 from the temperature of the mixed gas.

[0074] Although not shown in Table 1, in Examples 1 to 5 and Comparative Examples 1 and 2, the separation membrane 12 is a DDR type zeolite membrane. The composition ratio (excluding moisture) of the mixed gas supplied from the gas supply unit 26 to the gas separation device 2 is 50 vol% CO2 and 50 vol% N2. The moisture content of the mixed gas is 3000 ppm. The temperature of the mixed gas immediately before being supplied to the separation membrane 12 is 30°C. The pressure of the second gas recovery unit 28 (i.e., the permeation side pressure) is 1 atmosphere.

[0075] The permeation flow rate and selectivity of CO2 in Table 1 were obtained as follows. First, the flow rate and composition of the permeating gas permeating the separation membrane composite 1 were measured using a mass flow meter and gas chromatography, respectively. Next, the permeation rates of CO2 and N2 were obtained for the separation membrane 12 from the measured values ​​of the flow rate and composition of the permeating gas. Furthermore, the permeation rates (Permeance) of CO2 and N2 per unit area, unit time, and unit pressure difference were obtained, and the value obtained by dividing the permeation rate of CO2 by the permeation rate of N2 was taken as the selectivity of CO2. That is, the selectivity of CO2 in Table 1 is the ratio of the permeation rate of CO2 to N2, and the larger the value in Table 1, the higher the selectivity of CO2 and the higher the ratio (vol%) of CO2 in the permeating gas.

[0076] [Table 1]

[0077] As shown in Table 1, in Examples 1 to 3 in which the temperature difference ΔT was 10°C, the selectivity of CO2 was 30.9 or more, and the CO2 permeation flow rate increased as the mixed gas pressure increased. In Examples 2, 4, and 5 in which the mixed gas pressure was 1.0 MPa, the CO2 permeation flow rate was almost the same, and the CO2 selectivity improved as the temperature difference ΔT increased. In Examples 2 to 5 in which the mixed gas pressure was 1.0 MPa or more, the CO2 permeation flow rate was 22.4 L (liters) / min or more. On the other hand, when comparing Comparative Examples 1 and 2 in which the temperature difference ΔT was less than 10 ° C. with Example 1 in which the mixed gas pressure was the same, the CO2 permeation flow rate was almost the same, but the CO2 selectivity was 60.7 in Example 1, 49.8 in Comparative Example 1, and 44.3 in Comparative Example 2.

[0078] In addition, in Examples 1 to 5, when the moisture content of the mixed gas was made less than 3000 ppm, the CO2 permeation rate and selectivity were equivalent to or greater than the results shown in Table 1. In Examples 1 to 5, the temperature of the impermeable gas (i.e., the temperature of the impermeable gas immediately after passing through the through hole 111) was lower than the temperature of the mixed gas before being supplied to the separation membrane composite 1 (i.e., the mixed gas immediately before being supplied to the separation membrane 12) and higher than the temperature of the permeate side surface 113 of the support 11.

[0079] Although not shown in Table 1, when the separation membrane 12 was changed from the DDR-type zeolite membrane to a CHA-type zeolite membrane or a Y-type (FAU-type) zeolite membrane, the selectivity for CO2 was improved by setting the temperature difference ΔT to 10° C. or more as described above. Furthermore, when a DDR-type zeolite membrane or a CHA-type zeolite membrane made of a zeolite with a maximum number of rings of 8 was used as the separation membrane 12, the selectivity for CO2 was further improved than when a Y-type zeolite membrane made of a zeolite with a maximum number of rings of 12 was used. When the separation membrane 12 was changed to a carbon membrane or a silica membrane, which is an inorganic membrane other than a zeolite membrane, the selectivity for CO2 was improved by setting the temperature difference ΔT to 10° C. or more as described above.

[0080] As described above, the gas separation method for separating CO2 from a mixed gas includes a step (step S11) of preparing a separation membrane composite 1 in which a separation membrane 12 having pores with an average pore size of 1 nm or less is formed on a porous support 11, and a step (step S14) of supplying a mixed gas containing CO2 and other gases to the separation membrane composite 1 from the separation membrane 12 side and permeating the CO2 in the mixed gas through the separation membrane 12 and support 11 to obtain a permeated gas. Step S14 is performed in a state in which the temperature of at least a part of the permeation side surface 113 of the support 11, from which the permeated gas is discharged, is 10° C. or more lower than the temperature of the mixed gas before it is supplied to the separation membrane composite 1.

[0081] This allows the temperature of separation membrane 12 to be lower than the temperature of the mixed gas, and allows CO2 to be efficiently adsorbed into the pores of separation membrane 12. As a result, it is possible to improve the selectivity of CO2 in separation membrane 12. Furthermore, according to this gas separation method, the amount of energy required for cooling can be reduced compared to when the entire mixed gas is cooled before being supplied to separation membrane 12.

[0082] In the above-described gas separation method, the carbon dioxide concentration in the permeable gas obtained in step S14 is higher than the carbon dioxide concentration in the mixed gas, thereby facilitating separation of CO2 in the separation membrane 12.

[0083] In the above-described gas separation method, preferably, in step S14, the temperature of the entire permeation side surface 113 of the support 11 is at least 10° C. lower than the temperature of the mixed gas before it is supplied to the separation membrane composite 1. This can further improve the selectivity of CO2 in the separation membrane 12.

[0084] In the above-described gas separation method, in step S14, the temperature of at least a part of the permeate side surface 113 of the support 11 is preferably at least 15° C. lower than the temperature of the mixed gas before it is supplied to the separation membrane composite 1. This can further improve the CO2 selectivity of the separation membrane 12.

[0085] In the above-described gas separation method, in step S14, the pressure of the mixed gas before being supplied to the separation membrane composite 1 is preferably 1 MPa or more. This makes it possible to increase the permeation flow rate of CO2 through the separation membrane 12.

[0086] As described above, it is preferable that the separation membrane 12 is an inorganic membrane. This makes it possible to preferably increase the CO2 permeation rate and improve the CO2 selectivity in the separation membrane 12, as described above. Examples of inorganic membranes include zeolite membranes, silica membranes, and carbon membranes.

[0087] More preferably, separation membrane 12 is a zeolite membrane. In this way, by using a zeolite membrane having a specific pore size as separation membrane 12, it is possible to further improve the selectivity of CO2 in separation membrane 12. Note that the zeolite membrane is at least a membrane of zeolite formed on the surface of support 11, and does not include a membrane in which zeolite particles are simply dispersed in an organic membrane.

[0088] More preferably, the maximum number of ring members in the zeolite constituting the separation membrane 12 is equal to or less than 8. This makes it possible to further improve the selectivity of the separation membrane 12 for CO2.

[0089] In the above-described gas separation method, the moisture content of the mixed gas before being supplied to the separation membrane composite 1 in step S14 is preferably 3000 ppm or less. This makes it possible to suppress inhibition of adsorption of CO2 into the pores of the separation membrane 12 by moisture in the mixed gas. As a result, it is possible to further increase the permeation rate of CO2 through the separation membrane 12 and further improve the selectivity for CO2.

[0090] In the above-mentioned gas separation method, in step S14, the entire mixed gas is not cooled before being supplied to separation membrane 12, but the permeate gas is cooled by contacting it with separation membrane 12. Therefore, according to this gas separation method, the amount of energy required for cooling can be reduced compared to when the entire mixed gas is cooled before being supplied to separation membrane 12. Furthermore, in the above-mentioned gas separation method, in step S14, the temperature of the non-permeate gas that is discharged from the mixed gas without permeating separation membrane 12 and support 11 is preferably higher than the temperature of permeate side surface 113 of support 11 and lower than the temperature of the mixed gas before being supplied to separation membrane composite 1. This suppresses cooling of the non-permeate gas, thereby further reducing the amount of energy required for cooling.

[0091] As described above, the gas separation method can improve the selectivity of CO2 in the separation membrane 12. Therefore, the gas separation method is particularly suitable for separating CO2 from a mixed gas of CO2 and other gases (a gas containing at least one or more of hydrogen, helium, nitrogen, oxygen, carbon monoxide, nitrogen oxides, ammonia, sulfur oxides, hydrogen sulfide, sulfur fluoride, mercury, arsine, hydrogen cyanide, carbonyl sulfide, C1-C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes).

[0092] The gas separation device 2 described above includes a separation membrane composite 1 in which a separation membrane 12 having pores with an average pore size of 1 nm or less is formed on a porous support 11, and a gas supply unit 26 that supplies a mixed gas containing CO2 and other gases to the separation membrane composite 1 from the separation membrane 12 side. Then, in a state in which the temperature of at least a part of a permeation side surface 113 of the support 11, from which the gas that has permeated the separation membrane 12 is discharged, is 10°C or more lower than the temperature of the mixed gas before being supplied to the separation membrane composite 1, CO2 in the mixed gas is separated from the mixed gas by permeating through the separation membrane 12 and the support 11.

[0093] As a result, as described above, the temperature of the separation membrane 12 can be made lower than the temperature of the mixed gas, and CO2 can be efficiently adsorbed into the pores of the separation membrane 12. As a result, it is possible to improve the selectivity of CO2 in the separation membrane 12. Furthermore, according to the gas separation device, the amount of energy required for cooling can be reduced compared to when the entire mixed gas is cooled before being supplied to the separation membrane 12.

[0094] The above-described gas separation apparatus 2 and gas separation method can be modified in various ways.

[0095] For example, the gas other than CO2 contained in the mixed gas may contain a gas other than the gases exemplified in the above description, or may be composed only of a gas other than the gases exemplified in the above description.

[0096] The moisture content of the mixed gas before being supplied to the separation membrane 12 may be greater than 3000 ppm. In addition, the pressure of the mixed gas may be less than 1 MPa, as described above.

[0097] The temperature of the impermeable gas immediately after passing through the through holes 111 may be approximately the same as the temperature of the mixed gas before being supplied to the separation membrane composite 1 (i.e., the mixed gas immediately before being supplied to the separation membrane 12). In addition, the temperature of the impermeable gas may be approximately the same as the temperature of the permeate side surface 113 of the support 11.

[0098] When separation membrane 12 is a zeolite membrane, the maximum number of rings of the zeolite constituting the zeolite membrane may be smaller than 8 or larger than 8. As described above, separation membrane 12 is not limited to a zeolite membrane, and may be an inorganic membrane formed of an inorganic substance other than zeolite. Separation membrane 12 may also be a membrane other than an inorganic membrane.

[0099] Furthermore, although the separation membrane composite 1 includes the separation membrane 12 formed on the support 11, it may further include a functional membrane or a protective membrane laminated on the separation membrane 12. Such functional membranes and protective membranes may be inorganic membranes such as a zeolite membrane, a silica membrane, or a carbon membrane, or may be organic membranes such as a polyimide membrane or a silicone membrane. Furthermore, a substance that easily adsorbs CO2 may be added to the functional membrane or protective membrane laminated on the separation membrane 12.

[0100] In the gas separation device 2, instead of the above-mentioned monolith-type separation membrane composite 1, a substantially tubular or cylindrical single-tube separation membrane composite may be provided. The separation membrane may be provided on the outer surface of a substantially tubular or cylindrical support, and CO2 that has permeated the separation membrane and the support may be led to a space radially inside the support. A sealing portion may or may not be provided. In this case, the permeation side surface is the inner surface of the substantially tubular or cylindrical support. In the gas separation device 2, a cooling pipe or the like extending in the longitudinal direction in the center of the space radially inside the support may be provided as a cooling portion.

[0101] The shape and structure of the cooling unit 29 may be modified in various ways. The cooling unit 29 may be, for example, a tubular cooling jacket wound in a spiral shape on the outer surface of the outer cylinder 22. The refrigerant flowing through the cooling jacket may be a liquid or slurry other than cooling water, or may be a cooled gas. The permeated gas that has permeated the separation membrane composite 1 may be used as the cooled gas. Alternatively, the cooling unit 29 may be a Peltier element provided on the outer surface of the outer cylinder 22.

[0102] As a method for cooling the separation membrane composite 1, a low-temperature gas may be flowed as a sweep gas or the like so as to come into contact with the permeate side surface, or cooling may be performed by the Joule-Thomson effect of the permeate gas. In this case, the cooling section 29 may be omitted so long as the temperature of at least a portion of the permeate side surface 113 is 10°C or more lower than the temperature of the mixed gas before it is supplied to the separation membrane composite 1. Even in this case, the selectivity of CO2 in the separation membrane 12 can be improved in the same manner as described above.

[0103] The configurations in the above-described embodiment and each of the modified examples may be combined as appropriate as long as they are not mutually inconsistent. [Industrial Applicability]

[0104] The gas separation apparatus and gas separation method of the present invention can be used as an apparatus and method for separating CO2 from combustion exhaust gas from thermal power plants, etc., and can also be used to separate CO2 from various other mixed gases. [Explanation of symbols]

[0105] 1 Separation membrane complex 2 Gas separation equipment 11 Support 12 Separation membrane 26 Gas Supply Section 113 Transmission side surface S11~S15 steps

Claims

1. A gas separation method for separating carbon dioxide from a mixed gas, comprising the steps of: a) preparing a separation membrane composite in which a separation membrane having pores with an average pore diameter of 1 nm or less is formed on a porous support, and placing the composite in a single outer cylinder; b) supplying a mixed gas containing carbon dioxide and other gases from a gas supply unit connected to the outer cylinder into an internal space of the outer cylinder and supplying the mixed gas to the separation membrane composite from the separation membrane side, and allowing the carbon dioxide in the mixed gas to permeate through the separation membrane and the support to obtain a permeated gas; Equipped with The separation membrane composite has a characteristic that the carbon dioxide permeation rate is higher when the moisture content of the mixed gas is 3000 ppm or less than when the moisture content of the mixed gas is more than 3000 ppm, The gas separation method is characterized in that the step b) is performed in a state in which the temperature of at least a portion of the permeation side surface of the support of the separation membrane composite installed in the outer cylinder, from which the permeation gas is discharged, is 10°C or more lower than the temperature of the mixed gas before it is supplied to the separation membrane composite.

2. 2. The gas separation method according to claim 1, A gas separation method, characterized in that the separation membrane has an average pore size of 0.2 nm or more and 1 nm or less.

3. The gas separation method according to claim 1 or 2, A gas separation method, wherein in the step b), the temperature of the entire permeate side surface of the support is at least 10° C. lower than the temperature of the mixed gas before it is supplied to the separation membrane composite.

4. A gas separation method according to any one of claims 1 to 3, A gas separation method, characterized in that in the step b), the temperature of at least a portion of the permeate side surface of the support is at least 15° C. lower than the temperature of the mixed gas before it is supplied to the separation membrane composite.

5. A gas separation method according to any one of claims 1 to 4, A gas separation method, wherein the mixed gas has a pressure of 1 MPa or more before being supplied to the separation membrane composite in the step b).

6. A gas separation method according to any one of claims 1 to 5, The gas separation method, wherein the separation membrane is an inorganic membrane.

7. 7. The gas separation method according to claim 6, The gas separation method, wherein the separation membrane is a zeolite membrane.

8. 8. The gas separation method according to claim 7, A gas separation method, wherein the maximum number of rings in the zeolite constituting the separation membrane is 8 or less.

9. A gas separation method according to any one of claims 1 to 8, A gas separation method, characterized in that the moisture content of the mixed gas before being supplied to the separation membrane composite in the step b) is 3000 ppm or less.

10. A gas separation method according to any one of claims 1 to 9, a temperature of the non-permeating gas discharged from the mixed gas stream without permeating the separation membrane and the support is higher than the temperature of the permeation side surface of the support and is lower than the temperature of the mixed gas before it is supplied to the separation membrane composite,

11. A gas separation method according to any one of claims 1 to 10, The other gases include one or more of hydrogen, helium, nitrogen, oxygen, carbon monoxide, nitrogen oxides, ammonia, sulfur oxides, hydrogen sulfide, sulfur fluoride, mercury, arsine, hydrogen cyanide, carbonyl sulfide, C1 to C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes.

12. A gas separation apparatus for separating carbon dioxide from a mixed gas, comprising: a separation membrane composite in which a separation membrane having pores with an average pore diameter of 1 nm or less is formed on a porous support; a single outer cylinder that accommodates the separation membrane composite in an internal space; a gas supply unit connected to the outer cylinder and configured to supply a mixed gas containing carbon dioxide and other gases to an internal space of the outer cylinder and supply the mixed gas to the separation membrane composite from the separation membrane side; Equipped with The separation membrane composite has a characteristic that the carbon dioxide permeation rate is higher when the moisture content of the mixed gas is 3000 ppm or less than when the moisture content of the mixed gas is more than 3000 ppm, A gas separation apparatus characterized in that, for the separation membrane composite installed in the outer cylinder, carbon dioxide in the mixed gas is separated from the mixed gas by permeating through the separation membrane and the support in a state in which the temperature of at least a portion of the permeation side surface of the support of the separation membrane composite, from which gas that has permeated the separation membrane is discharged, is 10°C or more lower than the temperature of the mixed gas before it is supplied to the separation membrane composite.

13. 13. The gas separation apparatus of claim 12, A gas separation device characterized in that the separation membrane has an average pore size of 0.2 nm or more and 1 nm or less.

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