Gas separation processes and gas separators

Abstract

Gas separation process for separating carbon dioxide in a mixed gas, comprising: a) Production of a separation membrane complex (1) in which a separation membrane (12) with pores having a mean pore diameter of less than or equal to 1 nm is formed on a porous support (11); and b) Supplying a mixed gas containing carbon dioxide and another gas from one side of the separation membrane (12) to the separation membrane complex (1) and obtaining a permeated gas by causing the carbon dioxide in the mixed gas to penetrate the separation membrane (12) and the support (11), wherein process b) is carried out in a state in which at least a part of a penetration surface (113) of the support (11) from which the permeated gas is expelled is cooled to have a temperature at least 10 °C lower than a temperature of the mixed gas before it is supplied to the separation membrane complex (1).

Description

[Technical field]

[0001] The present invention relates to a gas separation process and a gas separator. [Technical background]

[0002] The separation of gases, such as carbon dioxide (CO2), from combustion exhaust gas emitted by a thermal power plant or other similar facility has been carried out using conventional methods. For example, Japanese patent publication JP 2003-159518 A (Document 1) and Japanese patent publication JP 2015-044162 A (Document 2) propose methods for separating CO2 from a mixed gas using a zeolite membrane. International publication WO 2009 / 093666 A1 (Document 3) proposes a method for separating CO2 using a membrane for facilitated transport.

[0003] Japanese patent application JP 2017-154120 A (Document 4) proposes that in multiple carbon dioxide separation membranes arranged sequentially in a gas flow path, the temperature of a gas supplied to a carbon dioxide separation membrane on the downstream side is set lower than the temperature of a gas supplied to a carbon dioxide separation membrane on the upstream side. This increases the relative humidity of the gas supplied to the downstream carbon dioxide separation membrane, thus addressing the problem that water vapor penetrating the upstream carbon dioxide separation membrane reduces the relative humidity of the gas supplied to the downstream carbon dioxide separation membrane and consequently decreases the permeability to carbon dioxide. Document 4 describes how the permeability to carbon dioxide decreases as the temperature of the carbon dioxide separation membrane decreases.

[0004] Meanwhile, the unexamined Japanese patent application (published Japanese translation of a PCT application) JP 2018-514385 A (Document 5) proposes a method for separating a fed mixture containing several types of hydrocarbons using a porous membrane with pore diameters ranging from 5 nm to 250 nm. According to Document 5, the porous membrane and the substances through which it is penetrated are maintained at temperatures below that of the fed mixture to induce capillary condensation of the mixture components in the pores of the porous membrane.

[0005] Furthermore, when CO2 is separated and collected from combustion exhaust gas using a zeolite membrane, as described in Documents 1 and 2, it is difficult to increase the concentration of CO2 in the gas that has passed through the zeolite membrane, since CO2 has a relatively low partial pressure in the combustion exhaust gas. With a non-porous, facilitated-transport membrane, as described in Document 3, it is difficult to maintain stable separation over a long period, as separation capabilities deteriorate rapidly with decreasing moisture content in the facilitated-transport membrane.

[0006] Document 4 deals with the temperatures of gases fed to multiple carbon dioxide separation membranes and points out that the temperature of a gas on the downstream side is lower than the temperature of a gas on the upstream side. However, since the permeability of the carbon dioxide separation membranes to carbon dioxide decreases with decreasing temperature, it is difficult to conceive of cooling each carbon dioxide separation membrane (i.e., an individual carbon dioxide separation membrane) to have a lower temperature than that of a gas fed to that separation membrane.

[0007] Document 5 discloses the separation of hydrocarbons but not the separation of CO2. Furthermore, the pores in the porous membrane according to Document 5 have relatively large pore diameters of more than or equal to 5 nm. Therefore, it is difficult to use this porous membrane for CO2 separation. Further relevant prior art is provided by DE 11 2019 000 832 T5. It describes a gas separation device comprising a gas supply section and a zeolite membrane. The gas supply section provides a mixed gas at a pressure greater than or equal to 10 atm and less than or equal to 200 atm. The mixed gas contains at least CH4, CO2, and N2. The water content of the mixed gas is adjusted to less than or equal to 3000 ppm. The zeolite membrane allows CO2 and N2 to pass through the mixed gas in order to separate CO2 and N2 from CH4. [Description of the invention]

[0008] The present invention relates to a gas separation process for separating carbon dioxide in a mixed gas and it is an object of the present invention to improve the carbon dioxide selectivity in a separation membrane in order to increase the concentration of carbon dioxide in a gas that has passed through the separation membrane.

[0009] A gas separation process according to a preferred embodiment of the present invention comprises a) producing a separation membrane complex, in which a separation membrane with pores having a mean pore diameter of less than or equal to 1 nm is formed on a porous support, and b) supplying a mixed gas containing carbon dioxide and another gas from one side of the separation membrane to the separation membrane complex and obtaining a permeated gas by causing the carbon dioxide in the mixed gas to permeate the separation membrane and the support. Operation b) is carried out in a condition in which at least a portion of a permeation surface of the support from which the permeated gas is expelled is cooled to have a temperature at least 10 °C lower than the temperature of the mixed gas before it is supplied to the separation membrane complex. This gas separation process improves the carbon dioxide selectivity in a separation membrane.

[0010] Preferably, the carbon dioxide concentration in the permeated gas obtained in process b) is higher than the carbon dioxide concentration in the mixed gas.

[0011] Preferably in process b) the entire penetration surface of the support has a temperature at least 10 °C lower than the temperature of the mixed gas before it is fed to the separation membrane complex.

[0012] Preferably in process b) at least a part of the penetration surface of the support has a temperature at least 15 °C lower than the temperature of the mixed gas before it is fed to the separation membrane complex.

[0013] Preferably in process b) the mixed gas has a pressure greater than or equal to 1 MPa before it is fed to the separation membrane complex.

[0014] Preferably, the separating membrane is an inorganic membrane. More preferably, the separating membrane is a zeolite membrane. Even more preferably, the maximum number of segmented rings in a zeolite of the separating membrane is less than or equal to 8.

[0015] Preferably in process b) the mixed gas has a moisture content of less than or equal to 3000 ppm before it is fed to the separation membrane complex.

[0016] Preferably in process b) an unpermeated gas contained in the mixed gas and expelled without penetrating the separating membrane and the support has a temperature that is higher than the temperature of the penetration surface of the support and lower than the temperature of the mixed gas before it is fed to the separating membrane complex.

[0017] Preferably, the other gas contains one or more types of gases including hydrogen, helium, nitrogen, oxygen, carbon monoxide, nitric oxide, ammonia, sulfur oxide, hydrogen sulfide, sulfur fluoride, mercury, arsine, hydrogen cyanide, carbonyl sulfide, C1 to C8 hydrocarbons, organic acid, alcohol, mercaptans, esters, ethers, ketones and aldehydes.

[0018] The present invention further relates to a gas separator for separating carbon dioxide in a mixed gas. A gas separator according to a preferred embodiment of the present invention comprises a separation membrane complex in which a separation membrane with pores having a mean pore diameter of less than or equal to 1 nm is formed on a porous support, and a gas supply section which supplies a mixed gas containing carbon dioxide and another gas to the separation membrane complex from one side of the separation membrane.This causes the carbon dioxide in the mixed gas to penetrate the separation membrane and the support and be separated from the mixed gas in a state in which at least part of a penetration surface of the support, from which a gas is expelled after penetrating the separation membrane, is cooled to have a temperature at least 10 °C lower than the temperature of the mixed gas before it is fed to the separation membrane complex. This gas separator improves the carbon dioxide selectivity in a separation membrane. [Brief description of the drawings] Fig. Figure 1 is a diagram illustrating a gas separator. Fig. Figure 2 is a cross-sectional view of a separation membrane complex. Fig. Figure 3 is an enlarged cross-sectional view of the separating membrane complex. Fig. Figure 4 is a diagram illustrating a process for separating a mixed gas. [Description of the embodiments]

[0019] Fig. Figure 1 is a diagram illustrating a schematic structure of a gas separator 2 according to an embodiment of the present invention. Fig. 1. Cross-hatching is omitted in the sections of some components. The gas separator 2 is a device that separates carbon dioxide (CO2) from a mixed gas containing carbon dioxide and other gases. For example, the mixed gas is combustion exhaust gas emitted by a thermal power plant.

[0020] The gas separator 2 comprises a separating membrane complex 1, sealing material 21, an outer cylinder 22, two sealing elements 23, a gas supply section 26, a first gas collection section 27, a second gas collection section 28, and a cooler 29. The separating membrane complex 1, the sealing material 21, and the sealing elements 23 are located inside the outer cylinder 22. The gas supply section 26, the first gas collection section 27, and the second gas collection section 28 are located outside the outer cylinder 22 and connected to it. Fig. In the illustrated example 1, the cooler 29 is arranged outside the outer cylinder 22 and covers the outer surface of the outer cylinder 22.

[0021] Fig. Figure 2 is a cross-sectional view of the separating membrane complex 1. Fig.Figure 3 is a cross-sectional view illustrating a portion of the separation membrane complex 1 in enlarged dimensions. The separation membrane complex 1 comprises a porous support 11 and a separation membrane 12 formed on the support 11. Fig. Figure 2 illustrates the separating membrane 12 with thick lines. Fig. 3 is the separating membrane 12 cross-hatched. The thickness of the in Fig. The separation membrane 12 shown in the illustration is larger than its actual thickness.

[0022] The support 11 is a porous element that is permeable to gases. In the Fig. In the illustrated example 2, the support 11 is a monolithic support in which several through holes 111 are located, each in a longitudinal direction (i.e. an upward-downward direction in Fig. 2) extend, formed in a single-piece, column-like body. In the Fig.In the illustrated example 2, the support 11 generally has a column-like shape. Each through-hole 111 (i.e., cell), for example, generally has a circular shape in section perpendicular to the longitudinal direction. In the illustration in Fig. 1 and Fig. 2. The diameter of the through holes 111 is larger than the actual diameter, and the number of through holes 111 is less than the actual number. The separating membrane 12 is formed on the inner surfaces of the through holes 111 and covers approximately the entire inner surface of the through holes 111.

[0023] The support 11 has a length (i.e., length in the upward-downward direction in Fig.2) from, for example, 10 cm to 200 cm. The support 11 has an outer diameter of, for example, 0.5 cm to 30 cm. The distance between the center axes of adjacent through holes 111 is, for example, in the range of 0.3 mm to 10 mm. The surface roughness (Ra) of the support 11 is, for example, in the range of 0.1 µm to 5.0 µm and preferably in the range of 0.2 µm to 2.0 µm. Alternatively, the support 11 can have a different shape, such as a honeycomb shape, a flat plate shape, a tubular shape, a cylindrical shape, a columnar shape, or a polygonal prism shape. If the support 11 has a tubular or cylindrical shape, the thickness of the support 11 is, for example, in the range of 0.1 mm to 10 mm.

[0024] Various substances (e.g., ceramic or metal) can be used as the material for the support 11, provided they are chemically stable during the step of forming the zeolite membrane 12 on the surface of the support. In the present embodiment, the support 11 is formed from a ceramic sintered body. Examples of the ceramic sintered body selected as the material for the support 11 include aluminum oxide, silicon dioxide, mullite, zirconium dioxide, titanium dioxide, yttrium, silicon nitride, and silicon carbide. In the present embodiment, the support 11 contains aluminum oxide, silicon dioxide, and / or mullite.

[0025] The carrier 11 may contain an inorganic binder. The inorganic binder may be titanium dioxide, mullite, readily sinterable aluminum oxide, silicon dioxide, glass frit, clay minerals and / or readily sinterable cordierite.

[0026] The mean pore diameter of the support 11 in the vicinity of the surface where the separation membrane 12 is formed is preferably smaller than the mean pore diameter of the support 11 in the other sections. To achieve this structure, the support 11 has a multilayered structure. If the support 11 has a multilayered structure, the material for each layer can be any of the materials described above, and each layer can be made of the same material or different materials. The mean pore diameter of the support 11 can be measured using a device such as a mercury porosimeter, a permporosimeter, or a nanopermporosimeter.

[0027] The mean pore diameter of the support 11 is, for example, in the range of 0.01 µm to 70 µm, and preferably in the range of 0.05 µm to 25 µm. The mean pore diameter of the support 11 in the vicinity of the surface where the separating membrane 12 is formed is in the range of 0.01 µm to 1 µm, and preferably in the range of 0.05 µm to 0.5 µm. In a pore size distribution of the entire support 11, including the surface and the interior of the support 11, D5 is, for example, in the range of 0.01 µm to 50 µm, D50 is, for example, in the range of 0.05 µm to 70 µm, and D95 ​​is, for example, in the range of 0.1 µm to 2000 µm. For example, the porosity of the support 11 in the vicinity of the surface where the separating membrane 12 is formed is in the range of 25% to 50%.

[0028] The separation membrane 12 is a porous membrane with small pores. The separation membrane 12 is a gas separation membrane that separates CO2 from a mixed gas consisting of several types of gases using a molecular sieve function. This mixed gas contains other gases that are less likely to pass through the separation membrane 12 than CO2. In other words, the mixed gas contains other gases that have lower permeances than the CO2 permeance of the separation membrane 12. In addition to CO2, the mixed gas contains one or more types of gases, including hydrogen (H2), helium (He), nitrogen (N2), oxygen (O2), carbon monoxide (CO), nitric oxide, ammonia (NH3), sulfur oxide, 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.The separation of CO2 refers to causing at least some CO2 in the mixed gas to pass through the separation membrane 12 and the support 11, and the gas concentration is not discussed here. In the following description, a gas that has passed through the separation membrane 12 and the support 11 is also referred to as a "permeated gas".

[0029] Nitrogen oxide is a compound of nitrogen and oxygen. The aforementioned nitrogen oxide is, for example, a gas called NOₓ. X names such as nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (also called dinitrogen monoxide) (N2O), nitrous trioxide (N2O3), nitrous tetroxide (N2O4) or nitrous pentoxide (N2O5).

[0030] Sulfur oxide is a compound of sulfur and oxygen. The sulfur oxide mentioned earlier is, for example, a gas called SO₂. X is called, for example, sulfur dioxide (SO2) or sulfur trioxide (SO3).

[0031] Sulfur fluoride is a compound of fluorine and sulfur. Examples of sulfur fluoride include difluorodisulfane (FSSF, S=SF2), sulfur difluoride (SF2), sulfur tetrafluoride (SF4), sulfur hexafluoride (SF6), and disulfur decafluoride (S2F). 10 ).

[0032] C1 to C8 hydrocarbons are hydrocarbons containing one or more and eight or fewer carbon atoms. C3 to C8 hydrocarbons can each be a linear-chain compound, a side-chain compound, or a cyclic compound. C2 to C8 hydrocarbons can each be either a saturated hydrocarbon (i.e., the absence of a double bond and a triple bond in a molecule) or an unsaturated hydrocarbon (i.e., the presence of a double bond and / or a triple bond in a molecule). Examples of C1 to C4 hydrocarbons include methane (CH4), ethane (C2H6), ethylene (C2H4), propane (C3H8), propylene (C3H6), normal butane (CH3(CH2)2CH3), isobutane (CH(CH3)3), 1-butene (CH2=CHCH2CH3), 2-butene (CH3CH=CHCH3), or isobutene (CH2=C(CH3)2).

[0033] The aforementioned organic acid can be, for example, a carboxylic acid or a sulfonic acid. The carboxylic acid could be, for example, formic acid (CH₂O₂), acetic acid (C₂H₄O₂), oxalic acid (C₂H₂O₄), acrylic acid (C₃H₄O₂), or benzoic acid (C₆H₅COOH). The sulfonic acid could be, for example, ethanesulfonic acid (C₂H₆O₃S). The organic acid can be, for example, either a chain-like compound or a cyclic compound.

[0034] The aforementioned alcohol can be, for example, methanol (CH3OH), ethanol (C2H5OH), isopropanol (2-propanol) (CH3CH(OH)CH3), ethylene glycol (CH2(OH)CH2(OH)) or butanol (C4H9OH).

[0035] Mercaptans are organic compounds with a terminal sulfur hydride (SH) group and are also substances known as thiols or thiol alcohols. Examples of mercaptans mentioned above include methyl mercaptans (CH3SH), ethyl mercaptans (C2H5SH), and 1-propanethiols (C3H7SH).

[0036] The aforementioned ester could be, for example, formic acid ester or acetic acid ester.

[0037] The aforementioned ether can be, for example, dimethyl ether ((CH3)2O), methyl ethyl ether (C2H5OCH3) or diethyl ether ((C2H5)2O).

[0038] The aforementioned ketone can be, for example, acetone ((CH3)2CO), methyl ethyl ketone (C2H5COCH3) or diethyl ketone ((C2H5)2CO).

[0039] The aforementioned aldehyde can be, for example, acetaldehyde (CH3CHO), propionaldehyde (C2H5CHO) or butanal (butyraldehyde) (C3H7CHO).

[0040] The separating membrane 12 has a thickness of, 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 separating membrane 12 improves the selectivity. Decreasing the thickness of the separating membrane 12 increases the permeance. The surface roughness (Ra) of the separating membrane 12 is, for example, less than or equal to 5 µm, preferably less than or equal to 2 µm, more preferably less than or equal to 1 µm, and even more preferably less than or equal to 0.5 µm. The separation membrane 12 has a mean pore diameter of less than or equal to 1 nm. This improves the CO2 selectivity through the separation membrane 12. There are no specific restrictions on the lower limit of the mean pore diameter of the separation membrane 12, as long as CO2 can pass through the separation membrane; however, the lower limit can be set to more than or equal to 0.2 nm.The mean pore diameter of the separation membrane 12 is preferably greater than or equal to 0.2 nm and less than or equal to 0.8 nm, more preferably greater than or equal to 0.3 nm and less than or equal to 0.6 nm, and even more preferably greater than or equal to 0.3 nm and less than or equal to 0.5 nm. Decreasing the mean pore diameter of the separation membrane 12 improves the selectivity. Increasing the mean pore diameter of the separation membrane 12 increases the permeance. The mean pore diameter of the separation membrane 12 is smaller than the mean pore diameter in the surface of the support 11 where the separation membrane 12 is provided.

[0041] The separating membrane 12 is preferably an inorganic membrane and, in the present embodiment, a zeolite membrane (i.e., a zeolite in membrane form). Examples of the zeolite of the separating membrane 12 include zeolite in which atoms (T atoms) located at the center of an oxygen tetrahedron (TO4) constituting the zeolite are composed solely of Si or of Si and Al; an AlPO-type zeolite in which the T atoms are composed of Al and P; a SAPO-type zeolite in which the T atoms are composed of Si, Al, and P; a MAPSO-type zeolite in which T atoms are composed of magnesium (Mg), Si, Al, and P; and a ZnAPSO-type zeolite in which T atoms are composed of zinc (Zn), Si, Al, and P. Some of the T atoms can be replaced by other elements.

[0042] If n represents a maximum number of ring-shaped structures in the zeolite of the separation membrane 12, then an arithmetic mean of the major and minor axes of an n-membered ring pore is assumed to be the mean pore diameter. The n-membered ring pore, as used herein, refers to a pore whose number of oxygen atoms bonded to T atoms and forming a ring structure is n. If the zeolite has multiple n-membered ring pores, where n is the same number, then an arithmetic mean of the major and minor axes of all n-membered ring pores is assumed to be the mean pore diameter of the zeolite. In this way, the mean pore diameter of the zeolite membrane is uniquely determined by the framework structure of the zeolite and can be obtained from the "Database of Zeolite Structures" [online] of the International Zeolite Association on the Internet. <URL:http: / / www.iza-structure.The revealed value can be obtained from org / databases / >.

[0043] There are no specific restrictions on the type of zeolite used in the separation membrane 12, and the zeolite can be any of the following types, including: 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, and SOD type. From the perspective of increasing CO2 permeance and improving CO2 selectivity, which will be described later, the maximum number of segmented rings in the zeolite is preferably less than or equal to 8 (e.g., 6 or 8). For example, the separation membrane 12 is a DDR-type zeolite. In other words, the separation membrane 12 is a zeolite membrane composed of a zeolite with a framework type code “DDR” assigned by the International Zeolite Association.In this case, the zeolite of the separation membrane 12 has an intrinsic pore diameter of 0.36 nm × 0.44 nm and a mean pore diameter of 0.40 nm.

[0044] If the separation membrane 12 is a zeolite membrane, the separation membrane 12 contains, for example, silicon (Si). For example, the separation membrane 12 can contain any two or more atoms of Si, aluminum (Al), and phosphorus (P). The separation membrane 12 can contain alkali metal. The alkali metal is, for example, sodium (Na) or potassium (K). If the separation membrane 12 contains Si atoms, the Si / Al ratio in the separation membrane 12 is, for example, greater than or equal to 1 and less than or equal to 100,000. The Si / Al ratio is preferably greater than or equal to 5, more preferably greater than or equal to 20, and even more preferably greater than or equal to 100. The ratio is preferably as high as possible. The Si / Al ratio in the separation membrane 12 can be adjusted, for example, by adjusting the composition ratio of a Si source and an Al source in a starting material solution, which will be described later.

[0045] The CO2 permeance of the separation membrane 12 at temperatures from -50 °C to 300 °C is, for example, more than or equal to 50 nmol / m². 2 ·s·Pa. The ratio (permeance ratio) between the CO2 permeance and the CH4 permeance (leakage) of the zeolite membrane 12 at temperatures from -50 °C to 300 °C is, for example, greater than or equal to 30. The permeance and the permeance ratio are values ​​for the case in which a difference in the partial pressure of CO2 between the supply side and the penetration side of the zeolite membrane 12 is 1.5 MPa.

[0046] The sealing means 21 are elements that are located on the opposite ends of the support 11 in the longitudinal direction (i.e., right-left direction). Fig.1) are attached and cover and seal the opposite end faces of the support 11 in the longitudinal direction and the outer surface of the support 11 in the vicinity of the opposite end faces. The sealing elements 21 prevent the inflow and outflow of gases from the opposite end faces of the support 11. The sealing elements 21 are, for example, plate-like elements made of glass or resin. The material and shape of the sealing elements 21 can be appropriately modified. The sealing elements 21 have several openings that overlap several through-holes 111 of the support 11, and therefore the opposite ends in the longitudinal direction of each through-hole 111 of the support 11 are not covered by the sealing elements 21. Accordingly, the gas can flow in and out through the through-holes 111 from the opposite ends.

[0047] The outer cylinder 22 is a generally cylindrical, tubular element. The outer cylinder 22 is made, for example, of stainless steel or carbon steel. The longitudinal direction of the outer cylinder 22 is approximately parallel to the longitudinal direction of the separating membrane complex 1. The outer cylinder 22 has a gas supply port 221 at one end in the longitudinal direction (i.e., left end in Fig. 5) and a first gas outlet port 222 at the other end. The outer cylinder 22 also has a second outlet port 223 on its side surface. The gas supply port 221 is connected to the gas supply section 26. The first gas outlet port 222 is connected to the first gas collector section 27. The second gas outlet port 223 is connected to the second gas collector section 28. An interior of the outer cylinder 22 is a closed space that is isolated from the space surrounding the outer cylinder 22.

[0048] The two sealing elements 23 are arranged longitudinally around the entire circumference between the outer surface 112 of the separating membrane complex 1 (i.e., the outer surface 112 of the support 11) and the inner surface of the outer cylinder 22 in the vicinity of opposite ends of the zeolite membrane complex 1. Each sealing element 23 is generally annular and made of a gas-impermeable material. For example, the sealing elements 23 are O-rings made of a flexible resin. The sealing elements 23 are in intimate contact with the outer surface 112 of the separating membrane complex 1 and the inner surface of the outer cylinder 22 around the entire circumference. Fig.In the illustrated example 1, the sealing elements 23 are in close contact with the outer surfaces of the sealing means 21 and are indirectly in close contact via the sealing means 21 with the outer surface 112 of the separating membrane complex 1. A space between the sealing elements 23 and the outer surface 112 of the separating membrane complex 1 and a space between the sealing elements 23 and the inner surface of the outer cylinder 22 are sealed in such a way that they almost or completely block the passage of gases.

[0049] The gas supply section 26 supplies a mixed gas containing CO2 and other gases (e.g., nitrogen (N2)) through the gas supply port 221 into the interior of the outer cylinder 22. For example, the gas supply section 26 is a blower or a pump that delivers the mixed gas under pressure to the outer cylinder 22. This blower or pump has a pressure regulator that controls the pressure of the mixed gas supplied to the outer cylinder 22.

[0050] The mixed gas supplied from the gas supply section 26 to the interior of the outer cylinder 22 is guided from the left end of the separating membrane complex 1 in the drawing into each through-hole 111 of the support 11, as indicated by arrow 251. CO2 is carried out of the outer surface 112 of the support 11 in the mixed gas as it passes through the separating membrane 12, which is provided on the inner surface of each through-hole 111, and the support 11, and is collected by the second gas collecting section 28 through the second gas outlet port 223, as indicated by arrow 253.In other words, the gas supply section 26 delivers the aforementioned mixed gas from the side of the separating membrane 12 to the separating membrane complex 1 and separates the CO2 in the mixed gas from the mixed gas by causing the CO2 to penetrate the separating membrane 12 and the support 11 and be expelled from a generally cylindrical region of the outer surface 112 of the support 11, located between the two sealing elements 23 (hereinafter referred to as a "penetration surface 113"). It should be noted that the penetration surface 113 does not include any region of the outer surface 112 of the support 11 that is covered with the sealing materials 21.The second gas collection part 28 can, for example, be a container for storing a permeated gas, such as CO2, which is led out of the outer cylinder 22 as it passes through the separating membrane 12 and the support 11, or it can be a blower or a pump that conveys the permeated gas.

[0051] In the mixed gas, a gas other than the aforementioned permeated gas (hereinafter referred to as "an unpermeated gas") flows through each through-hole 111 of the support 11 from the left side to the right side in the drawing and is collected by the first gas collecting section 27 through the first gas discharge port 222, as indicated by an arrow 252. For example, the first gas collecting section 27 may be a container for storing an unpermeated gas that is discharged from the outer cylinder 22, or it may be a blower or pump that conveys the unpermeated gas.

[0052] The cooler 29 is in direct or indirect contact with the outer surface of the outer cylinder 22 and cools the outer cylinder 22. For example, the cooler 29 is a generally cylindrical cooling jacket provided around the outer cylinder 22. In this case, the outer cylinder 22 is cooled as a result of a cooling medium, such as cooling water, flowing continuously through the interior of the cooler 29. Fig. 1 The cooling medium in the cooler 29 is cross-hatched. The length of the cooler 29 in the aforementioned longitudinal direction corresponds, for example, approximately to the longitudinal distance between the two sealing elements 23 or may be longer than this distance. In the Fig. In the illustrated example 1, the opposite ends of the cooler 29 are located in approximately the same positions in the longitudinal direction as the positions of the two sealing elements 23.

[0053] In the gas separator 2, the separating membrane complex 1, which faces the inner surface of the outer cylinder 22, is cooled as a consequence of the outer cylinder 22 being cooled by the cooler 29. More precisely, the gas present between the inner surface of the outer cylinder 22 and the outer surface 112 of the support 11 is cooled as a consequence of the outer cylinder 22 being cooled by the cooler 29, and approximately the entire support 11 is cooled from the side of the outer surface 112 that is in contact with the gas. Consequently, approximately the entire separating membrane 12, which is in contact with the support 11, is also cooled.

[0054] Next, an example of the process for separating a mixed gas, which is carried out by the gas separator 2, will be given with reference to Fig.As described in section 4, to separate a mixed gas, the separation membrane complex 1 is first produced by forming the separation membrane 12 on the support 11 (step S11). Step S11 is described in more detail, and seed crystals are first prepared for use in the production of the separation membrane 12 (i.e., the zeolite membrane). For example, the seed crystals are obtained from DDR-type zeolite powder synthesized by hydrothermal synthesis. The zeolite powder can be used unchanged as the seed crystals or processed into seed crystals by pulverization or other methods.

[0055] The porous support 11 is then immersed in a solution containing dispersed seed crystals to deposit the seed crystals onto the support 11. Alternatively, a solution containing dispersed seed crystals can be brought into contact with a section of the support 11 on which the separation membrane 12 is desired to form, in order to deposit the seed crystals onto the support 11. In this way, a support on which seed crystals have been deposited is prepared. The seed crystals can then be deposited onto the support 11 by the other methods.

[0056] The support 11 with the seed crystals deposited on it is immersed in a starting material solution. The starting material solution is prepared, for example, by causing substances such as a silicon source and a structure-controlling agent (hereinafter also referred to as an "SDA") to dissolve or disperse in a solvent. The starting material solution has a composition of, for example, 1:0.15:0.12 of SiO₂:SDA:(CH₂)₂(NH₂)₂. The solvent in the starting material solution can be, for example, water or alcohol, such as ethanol. The SDA in the starting material solution can be, for example, an organic compound. For example, 1-adamantanamine can be used as the SDA.

[0057] Using the seed crystals as nuclei, the DDR-type zeolite is then grown by hydrothermal synthesis to form a DDR-type zeolite membrane, i.e., the separation membrane 12, on the support 11. The temperature of the hydrothermal synthesis is preferably in the range of 120 to 200 °C and is, for example, 160 °C. The time of the hydrothermal synthesis is preferably in the range of 10 to 100 hours and is, for example, 30 hours.

[0058] Once the hydrothermal synthesis is complete, the support 11 and the separation membrane 12 are rinsed with demineralized water. After rinsing, the support 11 and the separation membrane 12 are dried, for example, at 80 °C. After drying, the separation membrane 12 is subjected to heat treatment to almost completely burn off and remove the SDA in the separation membrane 12 and to create micropores in the separation membrane 12. In this way, the aforementioned zeolite membrane complex 1 is obtained.

[0059] Once step S11 has been completed, the following will be Fig.Figure 1 illustrates the assembly of the gas separator 2 (step S12). The separating membrane complex 1 is installed in the outer cylinder 22. The cooler 29 then cools the separating membrane complex 1 via the outer cylinder 22. Specifically, the cooler 29 cools the section of the outer cylinder 22 located between the two sealing elements 23, so that in the section between the two sealing elements 23, the gas present between the inner surface of the outer cylinder 22 and the outer surface 112 of the support 11 is cooled. Furthermore, the penetration surface 113 of the support 11, which is the area in contact with the gas, is cooled, and approximately the entire support 11 and the separating membrane 12 are also cooled (step S13). The cooling of the separating membrane complex 1 by the cooler 29 continues until the gas separator 2 completes the gas separation process.

[0060] Subsequently, the gas supply section 26 introduces a mixed gas containing CO2 and other gases into the interior of the outer cylinder 22 (step S14). In the present embodiment, the mixed gas consists mainly of CO2 and N2. The mixed gas may also contain gases other than CO2 and N2. Moisture in the mixed gas inhibits the adsorption of CO2 into the pores of the separating membrane 12 and suppresses a reduction in the CO2 permeance. Therefore, the moisture content in the mixed gas inside the outer cylinder 22, before it is introduced to the separating membrane complex 1, is preferably less than or equal to 3000 ppm, corresponding to the volume ratio (i.e., molar ratio), more preferably less than or equal to 1000 ppm, even more preferably less than or equal to 500 ppm, and most preferably less than or equal to 100 ppm.If the moisture content in the mixed gas is higher than 3000 ppm, it is possible to use a mixed gas obtained by reducing the moisture content to less than or equal to 3000 ppm using a dehydrator.

[0061] The pressure of the mixed gas supplied from the gas supply section 26 to the interior of the outer cylinder 22, i.e., the initial gas pressure, is preferably more than or equal to 0.5 MPa, more preferably more than or equal to 1 MPa, and even more preferably more than or equal to 2 MPa. The outlet gas pressure is, for example, less than or equal to 20 MPa and typically less than or equal to 10 MPa. The temperature of the mixed gas supplied from the gas supply section 26 to the interior of the outer cylinder 22 is, for example, in the range of -50 °C to 300 °C and, in the present embodiment, approximately in the range of 10 °C to 150 °C. In the interior of the outer cylinder 22, the mixed gas has, before it is supplied to the separating membrane complex 1 (i.e.,mixed gas, immediately before it is supplied to the separating membrane 12), at approximately the same pressure and temperature as the pressure and temperature of the mixed gas supplied to the interior of the outer cylinder 22 by the aforementioned gas supply part 26.

[0062] The mixed gas supplied to the outer cylinder 22 is guided to each through-hole 111 of the separating membrane complex 1. Then, CO2 in the mixed gas penetrates the separating membrane 12 and the support 11 of the separating membrane complex 1, is guided out of the penetration surface 113 of the support 11 and separated from the mixed gas (step S15).

[0063] As described above, the support 11 is cooled by the cooler 29. Therefore, the temperature of the support 11 is lower than the temperature of the mixed gas before it is fed to the separating membrane complex 1 (i.e., the mixed gas that has flowed from the gas supply port 221 to the separating membrane 12 and that is fed to the separating membrane 12 immediately beforehand). In particular, the temperature of at least a portion of the penetration surface 113 of the support 11 is at least 10 °C lower than the temperature of the mixed gas. It should be noted that the temperature of the penetration surface 113 of the support 11 and the temperature of the gas immediately after it has penetrated the support 11 are approximately the same.Thus, if it is difficult to directly measure the temperature of the penetration surface 113 of the support 11, it can be concluded from the fact that the temperature of the gas immediately after it has penetrated the support 11 is at least 10 °C lower than the temperature of the mixed gas before it is supplied to the separation membrane complex 1 that the temperature of at least a part of the penetration surface 113 of the support 11 is at least 10 °C lower than the temperature of the mixed gas.

[0064] If the gas separator 2 has several separation membrane complexes in at least one of the separation membrane complexes 1, the temperature of at least a part of the penetration surface 113 of the support 11 in the separation membrane complex 1 is at least 10 °C lower than the temperature of the mixed gas immediately before it is supplied to the separation membrane 12 in the separation membrane complex 1.

[0065] Preferably, the temperature of the entire penetration surface 113 of the support 11 is at least 10 °C lower than the temperature of the mixed gas before it is fed to the separation membrane complex 1. The temperature of the entire penetration surface 113 need not necessarily be at least 10 °C lower than the temperature of the aforementioned mixed gas, and it is also preferred that the temperature of at least a portion of the penetration surface 113 is at least 15 °C lower than the temperature of the mixed gas. Even more preferably, the temperature of the entire penetration surface 113 of the support 11 is at least 15 °C lower than the temperature of the mixed gas before it is fed to the separation membrane complex 1.

[0066] As described above, in the gas separator 2, at least the temperature of a portion of the penetration surface 113 of the support 11 is at least 10 °C lower than the temperature of the mixed gas before it is fed to the separation membrane complex 1. This allows CO2 to be effectively adsorbed into the pores of the separation membrane 12, thereby increasing the ratio of the CO2 permeance of the separation membrane 12 to its other permeances, such as the N2 permeance. In other words, the CO2 selectivity of the separation membrane 12 is improved. Preferably, the concentration of CO2 in the gas that has passed through the separation membrane 12 and the support 11 is made higher than the concentration of CO2 in the mixed gas.

[0067] The gas that has passed through the separation membrane complex 1 is collected by the second gas collection section 28. The pressure of the gas in the second gas collection section 28 (i.e., permeation-side pressure) can be arbitrarily set and, for example, set to a pressure of approximately one atmosphere (0.101 MPa). The gas collected by the second gas collection section 28 may also contain other gases besides CO2.

[0068] An unpermeated gas (i.e., a gas that has not passed through the separating membrane 12 and the support 11 in the mixed gas) passes through each through-hole 111 in the longitudinal direction and is expelled from the outer cylinder 22 through the first gas discharge port 222. After passing through the through-holes 111 in the separating membrane complex 1, the unpermeated gas is cooled by the separating membrane complex 1, whose temperature is lower than the temperature of the mixed gas. Therefore, the temperature of the unpermeated gas immediately after passing through the through-holes 111 is lower than the temperature of the mixed gas before it is fed to the separating membrane complex 1 (i.e., the mixed gas after it has flowed from the gas supply port 221 to the separating membrane 12 and immediately before it is fed to the separating membrane 12).The unpermeated gas, immediately after passing through the through-holes 111, is preferably higher than the temperature of the penetration surface 113 of the support 11. The temperature of the unpermeated gas immediately after passing through the through-holes 111 is also preferably higher than the temperature of the permeated gas immediately after passing through the separating membrane complex 1. It should be noted that the temperature of the unpermeated gas immediately after passing through the through-holes 111 is approximately the same as the temperature of the unpermeated gas that was expelled through the first gas discharge port 222.

[0069] The unpermeated gas expelled from the outer cylinder 22 is collected by the first gas collection section 27. For example, the pressure of the gas in the first gas collection section 27 is approximately equal to the pressure of the mixed gas supplied by the gas supply section 26. The unpermeated gas collected by the first gas collection section 27 may contain CO2 that has not passed through the separation membrane complex 1.

[0070] Next, the relationship between the temperature difference between the mixed gas immediately before it is fed to the separation membrane 12 and the penetration surface 113, the pressure of the mixed gas immediately before it is fed to the separation membrane 12, the CO2 flux, and the CO2 selectivity in the gas separation process, as described above in steps S11 to S15, is illustrated with reference to Table 1. Examples 1 to 5 and Comparative Examples 1 and 2 in Table 1 vary in the temperature difference ΔT(°C) between the mixed gas immediately before it is fed to the separation membrane 12 and the penetration surface 113, and in the pressure P (MPa) of the mixed gas immediately before it is fed to the separation membrane 12. The temperature difference ΔT(°C) is obtained by subtracting the temperature of a region of the penetration surface 113 that has the lowest temperature from the temperature of the mixed gas described above.

[0071] Although not shown in Table 1, the separation membranes 12 according to Examples 1 to 5 and Comparative Examples 1 and 2 are DDR-type zeolite membranes. The mixed gas (excluding moisture) supplied from the gas supply section 26 to the gas separator 2 has a composition of 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 it is supplied to the separation membrane 12 is 30 °C. The pressure in the second gas collection section 28 (i.e., permeation-side pressure) is set at one atmosphere.

[0072] In Table 1, the CO2 flux and CO2 selectivity were obtained as follows. First, the flow rate and composition of the gas passing through the separation membrane complex 1 were measured using a mass flow meter and gas chromatography, respectively. Then, the CO2 permeance and N2 permeance of the separation membrane 12 were determined from the measured flux and gas composition values. Furthermore, the permeance of CO2 and N2 per unit area, per unit time, and per unit pressure were calculated, and the value obtained by dividing the CO2 permeance by the N2 permeance was used to define the CO2 selectivity. This means that the CO2 selectivity in Table 1 corresponds to the ratio of the CO2 permeance to the N2 permeance. As the numerical value in Table 1 increases, the CO2 selectivity improves, and the ratio (by volume) of CO2 in the gas passing through increases. Table 1 Temperature of mixed gas Temperature of penetration surface Temperature difference ΔT Pressure of mixed gas CO2 flux CO2 selectivity °C °C °C MPa (l / min) Example 1 30 20 10 0,4 8,8 60,7 Example 2 30 20 10 1,0 22,9 42,6 Example 3 60 50 10 2,0 36,7 30,9 Example 4 30 15 15 1,0 22,6 50,7 Example 5 30 10 20 1,0 22,4 56,8 Comparative example 1 30 25 5 0,4 8,9 49,8 Comparative example 2 30 30 0 0,4 9,0 44,3

[0073] As shown in Table 1, in Examples 1 to 3, the CO2 selectivity is greater than or equal to 30.9 with a temperature difference ΔT of 10 °C, and the CO2 flux increases with increasing mixed gas pressure. In Examples 2, 4, and 5, the CO2 flux is nearly constant with a mixed gas pressure of 1.0 MPa, and the CO2 selectivity improves with increasing temperature difference ΔT. In Examples 2 to 5, the CO2 flux with a mixed gas pressure of greater than or equal to 1.0 MPa is greater than or equal to 22.4 liters (l) / min. However, when comparative examples 1 and 2 with a temperature difference ΔT of less than 10 °C are compared with example 1 with the same pressure of the mixed gas, these examples show almost the same CO2 flux and differ in CO2 selectivity, in particular 60.7 in example 1, 49.8 in comparative example 1 and 44.3 in comparative example 2.

[0074] In Examples 1 to 5, if the moisture content in the mixed gas was reduced to less than 3000 ppm, the CO2 permeance and CO2 selectivity were the same as, or improved upon, the results shown in Table 1. In Examples 1 to 5, the temperature of the unpermeated gas (i.e., the temperature of the unpermeated gas immediately after passing through the through-holes 111) was lower than the temperature of the mixed gas before it was fed to the separation membrane complex 1 (i.e., the mixed gas immediately before it was fed to the separation membrane 12) and higher than the temperature of the penetration surface 113 of the support 11.

[0075] Although not shown in Table 1, if the separation membrane 12 was changed from a DDR-type zeolite membrane to a CHA-type or Y-type (FAU-type) zeolite membrane, the CO2 selectivity further improved as a result of adjusting the temperature difference ΔT to at least 10 °C, as described above. The CO2 selectivity improved when using a DDR-type or CHA-type zeolite membrane composed of a zeolite with a maximum number of 8 segments, compared to using a Y-type zeolite membrane composed of a zeolite with a maximum number of 12 segments.Similarly, when the separating membrane 12 was replaced by an inorganic membrane, such as a carbon or silicon dioxide membrane other than a zeolite membrane, the CO2 selectivity was further improved as a result of adjusting the temperature difference ΔT to at least 10 °C, as described above.

[0076] As described above, the gas separation process for separating CO2 in a mixed gas comprises the step of producing the separation membrane complex 1, in which the separation membrane 12 with pores having a mean particle diameter of less than or equal to 1 nm is formed on the porous support 11 (step S11), and the step of supplying a mixed gas containing CO2 and other gases from the side of the separation membrane 12 to the separation membrane complex 1 and obtaining a permeated gas by causing CO2 in the mixed gas to permeate the separation membrane 12 and the support 11 (step S14). Step S14 is carried out in a condition in which the temperature of at least a portion of the permeation surface 113 of the support 11, from which the permeated gas is expelled, is at least 10 °C lower than the temperature of the mixed gas before it is supplied to the separation membrane complex 1.

[0077] This allows the temperature of the separation membrane 12 to be lower than the temperature of the mixed gas, resulting in the effective adsorption of CO2 into the pores of the separation membrane 12. Consequently, it is possible to improve the CO2 selectivity of the separation membrane 12. According to this gas separation method, it is possible to reduce the amount of energy required for cooling more significantly than in the case where the entire mixed gas is cooled before being fed to the separation membrane 12.

[0078] In the gas separation process described above, the CO2 concentration in the permeated gas obtained in step S14 is higher than the CO2 concentration in the previously mentioned mixed gas. This accelerates the separation of CO2 in the separation membrane 12.

[0079] In the gas separation process described above, it is preferred in step S14 that the temperature of the entire penetration surface 113 of the support 11 is at least 10 °C lower than the temperature of the mixed gas before it is fed to the separation membrane complex 1. This further improves the CO2 selectivity of the separation membrane 12.

[0080] In the gas separation process described above, it is preferred in step S14 that the temperature of at least a portion of the penetration surface 113 of the support 11 is at least 15 °C lower than the temperature of the mixed gas before it is fed to the separation membrane complex 1. This further improves the CO2 selectivity of the separation membrane 12.

[0081] In the gas separation process described above, it is preferred in step S14 that the pressure of the mixed gas, before it is fed to the separation membrane complex 1, is at least 1 MPa. This increases the CO2 flux in the separation membrane 12.

[0082] As described above, the separation membrane 12 is preferably an inorganic membrane. As described above, this advantageously allows for an increase in the CO2 permeance in the separation membrane 12 and an improvement in the CO2 selectivity. Examples of inorganic membranes include a zeolite membrane, a silicon dioxide membrane, and a carbon membrane.

[0083] A zeolite membrane is more preferably used for the separation membrane 12. Using a zeolite membrane with a pore diameter smaller than that of the separation membrane 12 in this way allows for a further improvement in the CO2 selectivity of the separation membrane 12. It should be noted that the zeolite membrane used herein refers to at least one membrane obtained by forming a zeolite in membrane form on the surface of the support 11, and does not include a membrane obtained by simply dispersing zeolite particles in an organic membrane.

[0084] Preferably, the maximum number of segmented rings in the zeolite of the separation membrane 12 is less than or equal to 8. This further improves the CO2 selectivity of the separation membrane 12.

[0085] In the gas separation process described above, it is preferred in step S14 that the moisture content in the mixed gas, before it is fed to the separation membrane complex 1, is less than or equal to 3000 ppm. This reduces the situation in which moisture in the mixed gas inhibits the adsorption of CO2 in the pores of the separation membrane 12. Consequently, it is possible to further increase the CO2 permeance in the separation membrane 12 and further improve the CO2 selectivity.

[0086] In step S14 of the gas separation process described above, the entire mixed gas is not cooled before being fed to the separation membrane 12, and the permeated gas is cooled by contact with the separation membrane 12. According to this gas separation process, it is therefore possible to reduce the amount of energy required for cooling more significantly than in the case where the entire mixed gas is cooled before being fed to the separation membrane 12. In step S14 of the gas separation process described above, the temperature of the unpermeated gas, which is expelled without passing through the separation membrane 12 and the support 11, is preferably higher in the mixed gas than the temperature of the penetration surface 113 of the support 11 and lower than the temperature of the mixed gas before it is fed to the separation membrane complex 1. This suppresses the cooling of the unpermeated gas and thus further reduces the amount of energy required for cooling.

[0087] As described above, the CO2 selectivity of the separation membrane 12 can be improved using the gas separation process. Accordingly, this gas separation process is particularly suitable for separating CO2 from a mixed gas consisting of CO2 and another gas (i.e., a gas containing at least one type of gas, including hydrogen, helium, nitrogen, oxygen, carbon monoxide, nitric oxide, ammonia, sulfur oxide, hydrogen sulfide, sulfur fluoride, mercury, arsine, hydrogen cyanide, carbonyl sulfide, C1 to C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes).

[0088] The gas separator 2 described above comprises the separating membrane complex 1, in which the separating membrane 12, with pores having a mean pore diameter of less than or equal to 1 nm, is formed on the porous support 11, and the gas supply section 26, which supplies a mixed gas containing CO2 and another gas to the separating membrane complex 1 from the side of the separating membrane 12. CO2 in the mixed gas is then separated from the other gas by causing the CO2 to pass through the separating membrane 12 and the support 11 in a state in which the temperature of at least a portion of the penetration surface 113, from which the gas is ejected after passing through the separating membrane 12, is at least 10 °C lower than the temperature of the mixed gas before it is supplied to the separating membrane complex 1.

[0089] As described above, this allows the temperature of the separation membrane 12 to be lower than the temperature of the mixed gas, enabling CO2 to be effectively adsorbed into the pores of the separation membrane 12. Consequently, it is possible to improve the CO2 selectivity of the separation membrane 12. According to this gas separator, it is possible to reduce the amount of energy required for cooling more significantly than if the entire mixed gas were cooled before being fed to the separation membrane 12.

[0090] The gas separator 2 and the gas separation process described above can be modified in various ways.

[0091] For example, gases contained in the mixed gas, with the exception of CO2, may contain a different gas than those listed as examples in the description above, or may simply contain a different gas than those listed as examples in the description above.

[0092] The moisture content in the mixed gas before it is fed to the separation membrane 12 can be higher than 3000 ppm. As described above, the pressure of the mixed gas can be lower than 1 MPa.

[0093] The temperature of the unpenetrated gas immediately after passing through the through-holes 111 can be approximately the same as the temperature of the mixed gas before it is fed to the separation membrane complex 1 (i.e., the mixed gas immediately before it is fed to the separation membrane 12). The temperature of the unpenetrated gas can also be approximately the same as the temperature of the penetration surface 113 of the support 11.

[0094] If the separating membrane 12 is a zeolite membrane, the maximum number of segmented rings in the zeolite of this zeolite membrane can be less than 8 or greater than 8. As described above, the separating membrane 12 is not limited to a zeolite membrane and can be an inorganic membrane formed from inorganic substances other than zeolite. The separating membrane 12 can also be a membrane other than an inorganic membrane.

[0095] While the separation membrane complex 1 comprises the separation membrane 12 formed on the support 11, the separation membrane complex 1 can also be a functional membrane or a protective membrane coated onto the separation membrane 12. Such a functional membrane or protective membrane can be an inorganic membrane, such as a zeolite membrane, a silicon dioxide membrane, or a carbon membrane, or it can be an organic membrane, such as a polyimide membrane or a silicone membrane. Furthermore, a substance that readily adsorbs CO2 can be added to such a functional membrane or protective membrane coated onto the separation membrane 12.

[0096] The gas separator 2 can have a generally tubular or cylindrical separation membrane complex of the single-tube type instead of the previously mentioned monolithic separation membrane complex 1. A configuration is also possible in which the separation membrane is provided on the outer surface of a generally tubular or cylindrical support, and CO2, which has penetrated the separation membrane and the support, is directed out to a space located radially inside the support. Sealing means may or may not be provided. In this case, the penetration surface corresponds to the inner surface of the generally tubular or cylindrical support. As a cooler, the gas separator 2 can have a cooling tube or the like extending longitudinally in a central section of the space located radially inside the support.

[0097] The shape and structure of the cooler 29 can be modified in various ways. For example, the cooler 29 can be a tube-like cooling jacket wound spirally onto the outer surface of the outer cylinder 22. A cooling medium flowing through the cooling jacket can be a liquid or slurry other than cooling water, or it can be a cooled gas. A gas that has passed through the separating membrane complex 1 can be used as this cooled gas. Alternatively, the cooler 29 can be a Peltier unit provided on the outer surface of the outer cylinder 22.

[0098] As a method for cooling the separation membrane complex 1, the separation membrane complex 1 can be cooled by causing a low-temperature gas to flow as a purge gas into contact with the penetration surface, or the Joule-Thomson effect can be used for cooling by the gas passing through it. In this case, the cooler 29 can be omitted if it is possible to reduce the temperature of at least part of the penetration surface 113 by at least 10 °C below the temperature of the mixed gas before it is introduced into the separation membrane complex 1. Even in this case, it is possible to improve the CO2 selectivity of the separation membrane 12 in the same way as described above.

[0099] The configurations of the embodiment and variations described above can be combined accordingly, as long as there are no mutual contradictions. [Commercial Applicability]

[0100] The gas separator and the gas separation method according to the present invention are applicable for use as a device or method for separating CO2 in a combustion exhaust gas emitted by a thermal power plant or other such plant, and are also applicable for separating CO2 into a variety of other mixed gases. [List of reference symbols] 1 Separation membrane complex 2 gas separators 11 carriers 12 Separation membrane 26 Gas supply section 113 Penetration surface Step S11 to S15

Claims

[1] Gas separation process for separating carbon dioxide in a mixed gas, comprising: a) Production of a separation membrane complex (1) in which a separation membrane (12) with pores having a mean pore diameter of less than or equal to 1 nm is formed on a porous support (11); and b) Supplying a mixed gas containing carbon dioxide and another gas from one side of the separation membrane (12) to the separation membrane complex (1) and obtaining a permeated gas by causing the carbon dioxide in the mixed gas to penetrate the separation membrane (12) and the support (11), wherein process b) is carried out in a state in which at least a part of a penetration surface (113) of the support (11) from which the permeated gas is expelled is cooled to have a temperature at least 10 °C lower than a temperature of the mixed gas before it is supplied to the separation membrane complex (1). [2] Gas separation process according to claim 1, wherein a carbon dioxide concentration in the permeated gas obtained in process b) is higher than a carbon dioxide concentration in the mixed gas. [3] Gas separation process according to claim 1 or 2, wherein in process b) the entire penetration surface (113) of the support (11) has a temperature at least 10 °C lower than the temperature of the mixed gas before it is supplied to the separation membrane complex (1). [4] Gas separation process according to one of claims 1 to 3, wherein in process b) at least a part of the penetration surface (113) of the support (11) has a temperature at least 15 °C lower than the temperature of the mixed gas before it is supplied to the separation membrane complex (1). [5] Gas separation process according to any one of claims 1 to 4, wherein in process b) the mixed gas has a pressure greater than or equal to 1 MPa before it is supplied to the separation membrane complex (1). [6] Gas separation process according to any one of claims 1 to 5, wherein the separation membrane (12) is an inorganic membrane. [7] Gas separation process according to claim 6, wherein the separation membrane (12) is a zeolite membrane. [8] Gas separation process according to claim 7, wherein a maximum number of segmented rings in a zeolite of the separation membrane (12) is less than or equal to 8. [9] Gas separation process according to any one of claims 1 to 8, wherein in process b) the mixed gas has a moisture content of less than or equal to 3000 ppm before it is fed to the separation membrane complex (1). [10] Gas separation process according to any one of claims 1 to 9, wherein in process b) an unpermeated gas contained in the mixed gas and expelled without penetrating the separation membrane (12) and the support (1) has a temperature that is higher than a temperature of the penetration surface of the support (11) and lower than the temperature of the mixed gas before it is supplied to the separation membrane complex (1). [11] Gas separation process according to any one of claims 1 to 10, wherein the other gas contains one or more types of gases including hydrogen, helium, nitrogen, oxygen, carbon monoxide, nitric oxide, ammonia, sulfur oxide, hydrogen sulfide, sulfur fluoride, mercury, arsine, hydrogen cyanide, carbonyl sulfide, C1 to C8 hydrocarbons, organic acid, alcohol, mercaptans, esters, ethers, ketones and aldehydes. [12] Gas separator (2) for separating carbon dioxide in a mixed gas, comprising: a separation membrane complex (1) in which a separation membrane (12) with pores having a mean pore diameter of less than or equal to 1 nm is formed on a porous support (11); and a gas supply section which supplies a mixed gas containing carbon dioxide and another gas from one side of the separation membrane (12) to the separation membrane complex (1), wherein the carbon dioxide in the mixed gas is caused to penetrate through the separation membrane (12) and the support (11) and to be separated from the mixed gas in a state in which at least a part of a penetration surface (113) of the support (11), from which a gas is expelled after penetrating through the separation membrane (12), is cooled to have a temperature at least 10 °C lower than a temperature of the mixed gas before it is supplied to the separation membrane complex (1).

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