Separation method and separation device

Abstract

The separation method of mixed gas separation includes the following steps: supplying a mixed gas containing a first gas, a second gas, water vapor, and a third gas which is a polar gas lower in polarity than water vapor to an inorganic membrane, i.e., a separation membrane (step S11); and separating the first gas from the mixed gas by permeation through the separation membrane (step S12). Accordingly, water vapor adsorption to the separation membrane, which leads to a decrease in permeation performance, can be suppressed.

Description

Technical Field

[0001] This invention relates to a technique for separating mixed gases.

[0002] [Reference to relevant applications]

[0003] This application claims priority to Japanese Patent Application JP2024-55863, filed on March 29, 2024, the entire disclosure of which is incorporated herein by reference. Background Technology

[0004] Previously, techniques such as pressure swing adsorption and chemical absorption were used to separate a portion of gases from a mixture containing multiple gases. However, the regeneration of the adsorbent and absorbent in pressure swing adsorption and chemical absorption methods involves significant energy consumption. Therefore, in recent years, membrane separation methods using separation membranes such as zeolite membranes have attracted considerable attention for the separation of mixed gases.

[0005] However, when the mixed gas supplied to the separation membrane contains water vapor, water molecules adsorb onto the surface of the separation membrane, hindering the permeation of the gas to be separated, and the permeation rate may decrease. In particular, in separation membranes with hydroxyl (-OH) groups on the surface, water adsorption is more likely to occur, and the decrease in permeation rate is also greater.

[0006] Therefore, Japanese Patent Application Publication No. 2023-150373 (Document 1) proposes the following technology: when a mixed gas containing hydrogen and water vapor is supplied to a zeolite membrane to separate hydrogen, the effect of water adsorption on the zeolite membrane is reduced by heating the temperature of the gas passing through the zeolite membrane to above 80°C.

[0007] However, the apparatus in Reference 1 requires a heating device to heat the mixed gas supplied to the zeolite membrane, which may lead to a larger apparatus or a more complex apparatus structure. Summary of the Invention

[0008] This invention relates to a separation method for separating mixed gases, the purpose of which is to suppress water vapor adsorption on the separation membrane, which would lead to a decrease in permeability.

[0009] The invention of Scheme 1 is a separation method for separating mixed gases, comprising the following steps: a) supplying a mixed gas containing a first gas, a second gas, water vapor, and a third gas, which is less polar than water vapor, to an inorganic membrane, i.e., a separation membrane; and b) separating the mixed gas by allowing the first gas to permeate through the separation membrane.

[0010] Therefore, it is possible to suppress the adsorption of water vapor on the separation membrane, which would lead to a decrease in permeability.

[0011] The invention of Scheme 2 is based on the separation method of Scheme 1, wherein the concentration of the third gas in the mixed gas is more than 0.5 times the concentration of water vapor in the mixed gas.

[0012] The invention of Scheme 3 is based on the separation method of Scheme 1 (which can be Scheme 1 or 2), wherein the dipole moment of the third gas is less than 1.8D.

[0013] The invention of Scheme 4 is based on the separation method of Scheme 1 (which may be any one of Schemes 1 to 3), and further includes, before step a), a step of supplying a pretreatment gas containing the third gas and free of water vapor to the separation membrane.

[0014] The invention of Scheme 5 is based on the separation method of Scheme 1 (which can be any one of Schemes 1 to 4), wherein the temperature of the mixed gas is below 100°C.

[0015] The invention of Scheme 6 is based on the separation method of any one of Schemes 1 to 5, wherein the separation membrane has hydroxyl groups on its surface.

[0016] The invention of Scheme 7 is a separation device for separating mixed gases, comprising: a supply unit that supplies a mixed gas containing a first gas, a second gas, water vapor, and a third gas, which is less polar than water vapor; and a separation membrane, which is an inorganic membrane that separates from the mixed gas by allowing the first gas to permeate through.

[0017] The above-mentioned objectives, as well as other objectives, features, solutions, and advantages, will become clear from the following detailed description of the invention with reference to the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a diagram illustrating the configuration of a separation device according to one embodiment.

[0019] Figure 2 This is a cross-sectional view of the separation membrane complex.

[0020] Figure 3 This is a magnified cross-sectional view showing a portion of the separation membrane complex.

[0021] Figure 4 This is a diagram illustrating the separation process of a mixed gas.

[0022] Figure 5 This is a diagram showing a part of the separation process of a mixed gas. Detailed Implementation

[0023] Figure 1 This is a diagram illustrating the configuration of a separation device 2 according to one embodiment of the present invention. Figure 2This is a cross-sectional view showing the separation membrane composite 1 of the separation device 2. Figure 3 This is a cross-sectional view showing a portion of the separation membrane composite 1.

[0024] In the separation device 2, a mixture containing multiple gases (hereinafter also referred to as "mixed gas") is supplied to the separation membrane composite 1, causing highly permeable substances in the mixed gas to permeate through the separation membrane composite 1, thereby separating them from the mixed gas. The separation in the separation device 2 can be performed, for example, to extract highly permeable substances (hereinafter also referred to as "highly permeable substances") from the mixed gas, or to concentrate substances with low permeability (hereinafter also referred to as "lowly permeable substances").

[0025] The separation membrane composite 1 comprises a support 11 and a separation membrane 12. Figure 2 In the middle, the separation membrane 12 is drawn with thick lines. Figure 3 In the diagram, parallel oblique lines are marked on the separation membrane 12 to depict its thickness as thicker than it actually is.

[0026] The support 11 is a porous component that is permeable to gas. Figure 2 In the example shown, the support 11 is a one-piece, integrally connected, generally cylindrical component. Multiple through holes 111 extending along the length direction are provided in the support 11. That is, the support 11 is a so-called integral component. The shape of the support 11 is, for example, generally cylindrical. The cross-section of each through hole 111 (i.e., compartment) perpendicular to the length direction is, for example, generally circular. Figure 2 In the diagram, the diameter of the through hole 111 is depicted as larger than it actually is, and the number of through holes 111 is depicted as fewer than it actually is.

[0027] The length of the support 11 (i.e., Figure 2 The length (in the left-right direction) of the support 11 is, for example, 10cm to 200cm. The outer diameter of the support 11 is, for example, 0.5cm to 30cm. The distance between the central axes of adjacent through holes 111 is, for example, 0.3mm to 10mm. The surface roughness (Ra) of the support 11 is, for example, 0.1μm to 5.0μm, preferably 0.2μm to 2.0μm. It should be noted that the shape of the support 11 can be, for example, honeycomb, flat, tubular, cylindrical, prismatic, or polygonal. When the shape of the support 11 is tubular or cylindrical, the thickness of the support 11 is, for example, 0.1mm to 10mm.

[0028] The material of the support 11 only needs to be chemically stable during the process of forming the separation film 12 on the surface, and various substances (such as ceramics or metals) can be used. In this embodiment, the support 11 is formed from a ceramic sintered body. Examples of ceramic sintered bodies selected as the material of the support 11 include: alumina, silicon dioxide, andalusite, zirconium oxide, titanium dioxide, yttrium oxide, silicon nitride, silicon carbide, etc. In this embodiment, the support 11 includes at least one of alumina, silicon dioxide, andalusite.

[0029] The support 11 may contain an inorganic binder. As an inorganic binder, at least one of the following can be used: titanium dioxide, andalusite, easily sinterable alumina, silica, glass frit, clay minerals, and easily sinterable cordierite.

[0030] The average pore size of the support 11 is, for example, 0.01 μm to 70 μm, preferably 0.05 μm to 25 μm. The average pore size of the support 11 near the surface to which the separation membrane 12 is to be formed is 0.01 μm to 1 μm, preferably 0.05 μm to 0.5 μm. The average pore size can be measured, for example, using a mercury porosimeter, a pore size distribution measuring instrument, or a nanoscale pore size distribution measuring instrument. Regarding the overall pore size distribution of the support 11, including the surface and interior, D5 is, for example, 0.01 μm to 50 μm, D50 is, for example, 0.05 μm to 70 μm, and D95 ​​is, for example, 0.1 μm to 2000 μm. The porosity of the support 11 near the surface to which the separation membrane 12 is to be formed is, for example, 20% to 60%.

[0031] The support 11 may be a multilayer structure formed by stacking multiple layers with different average pore sizes in the thickness direction. The average pore size and sintered particle size in the surface layer, including the surface on which the separation membrane 12 is to be formed, are smaller than those in the layers other than the surface layer. The average pore size of the surface layer of the support 11 is, for example, 0.01 μm to 1 μm, preferably 0.05 μm to 0.5 μm. When the support 11 has a multilayer structure, the material of each layer can be the material described above. The materials of the multiple layers forming the multilayer structure may be the same or different.

[0032] The separation membrane 12 is a generally cylindrical thin film disposed on the inner surface of the through hole 111 of the support 11, covering approximately the entire inner surface. The separation membrane 12 is a dense porous membrane with micropores. The separation membrane 12 separates a specific substance from the gas mixture. Other substances are less likely to permeate through the separation membrane 12 compared to the specific substance. In other words, the permeation rate of the other substances through the separation membrane 12 is lower than that of the specific substance.

[0033] 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. If the separation membrane 12 is thickened, the separation performance is improved. If the separation membrane 12 is thinned, the permeation rate is increased. 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 more preferably 0.5 μm or less.

[0034] The separation membrane 12 is an inorganic membrane formed using inorganic materials. For example, the separation membrane 12 has hydroxyl groups (-OH groups) on its surface (i.e., the inner surface facing the aforementioned through-hole 111). The separation membrane 12 is, for example, a zeolite membrane. This zeolite membrane is defined as a membrane obtained by forming zeolite in a film-like form on at least the surface of the support 11, etc., excluding membranes obtained simply by dispersing zeolite particles in an organic membrane. When the separation membrane 12 is a zeolite membrane, it may contain two or more types of zeolite with different structures or compositions. It should be noted that the separation membrane 12 may be a carbon membrane composed of carbon and / or carbides, or a porous membrane other than a zeolite membrane or a carbon membrane.

[0035] When the separation membrane 12 is a zeolite membrane, the pore size of the zeolite crystals contained in the separation membrane 12 (hereinafter also referred to as "pore size of the separation membrane 12") is 0.2 nm or more and 0.8 nm or less, more preferably 0.25 nm or more and 0.7 nm or less, and even more preferably 0.28 nm or more and 0.45 nm or less. When the pore size of the separation membrane 12 is less than 0.2 nm, the amount of gas permeating through the separation membrane 12 may sometimes be less, and when the pore size of the separation membrane 12 is greater than 0.8 nm, the selectivity of the separation membrane 12 for the gas may sometimes be insufficient. The pore size of the separation membrane 12 refers to the diameter (i.e., the minor axis) of the pores in a direction substantially perpendicular to the maximum diameter of the pores of the zeolite crystals constituting the separation membrane 12 (i.e., the major axis as the maximum distance between oxygen atoms). The pore size of the separation membrane 12 is smaller than the average pore size at the surface of the support 11 on which the separation membrane 12 is disposed.

[0036] When the maximum number of rings in the zeolite constituting the separation membrane 12 is n, the short axis of the n-membered ring pores is set as the pore diameter of the separation membrane 12. Furthermore, when the zeolite has multiple n-membered ring pores of equal size, the short axis of the n-membered ring pore with the largest short axis is set as the pore diameter of the separation membrane 12. It should be noted that an n-membered ring refers to a portion where the number of oxygen atoms constituting the framework forming the pores is n, and each oxygen atom is bonded to T atoms (described later) to form a ring structure. Additionally, an n-membered ring refers to the case where a through-hole (channel) is formed, excluding cases where no through-hole is formed. An n-membered ring pore refers to a pore formed using an n-membered ring. From the viewpoint of improving selectivity, the maximum number of rings in the zeolite contained in the separation membrane 12 is preferably 10 or less (e.g., 10, 8, or 6).

[0037] The pore size of the separation membrane 12 is uniquely determined by the zeolite skeleton structure that constitutes the separation membrane 12, and can be solved according to the values ​​published in the "Database of Zeolite Structures" of the International Zeolite Society [online], URL: http: / / www.iza-structure.org / databases / >.

[0038] The type of zeolite constituting the separation membrane 12 is not particularly limited, and can include, 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, IHW type, LEV type, LTA type, LTJ type, MEL type, MFI type, MOR type, MTN type, PAU type, RHO type, SOD type, SAT type, etc. The preferred zeolite constituting the separation membrane 12 is CHA type, DDR type, LTA type, MFI type, or MTN type zeolite.

[0039] In the zeolite constituting the separation membrane 12, the T atom (i.e., the atom located at the center of the oxygen tetrahedron (TO4) constituting the zeolite) may contain, for example, aluminum (Al). The zeolite constituting the separation membrane 12 may include: zeolites with T atoms consisting only of silicon (Si), zeolites with T atoms consisting of both Si and Al, AlPO-type zeolites with T atoms consisting of Al and phosphorus (P), SAPO-type zeolites with T atoms consisting of Si, Al, and P, MAPSO-type zeolites with T atoms consisting of magnesium (Mg), Si, Al, and P, ZnAPSO-type zeolites with T atoms consisting of zinc (Zn), Si, Al, and P, etc. A portion of the T atoms may be replaced by other elements.

[0040] The separation membrane 12 may contain, for example, Si. The separation membrane 12 may contain any two or more of Si, Al, and P. The separation membrane 12 may contain an alkali metal, such as sodium (Na) or potassium (K). When the separation membrane 12 contains both Si and Al 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 the molar ratio of Si to Al contained in the separation membrane 12. This Si / Al ratio is preferably 5 or more, more preferably 20 or more, and even more preferably 100 or more; the higher the ratio, the better. The Si / Al ratio in the separation membrane 12 can be adjusted by adjusting the proportions of the Si source and Al source in the feed solution, as described later.

[0041] Figure 1The separation device 2 shown includes: a separation membrane composite 1, a sealing part 21, a housing 22, two sealing components 23, a supply part 26, a first recovery part 27, and a second recovery part 28. The separation membrane composite 1, the sealing part 21, and the sealing components 23 are housed within the housing 22. The supply part 26, the first recovery part 27, and the second recovery part 28 are disposed outside the housing 22 and connected to the housing 22.

[0042] The sealing part 21 is: installed in the longitudinal direction of the support 11 (i.e., Figure 1 The sealing portion 21 is a component that seals the two ends of the support body 11 in the left-right direction and covers and seals the two end faces of the support body 11 in the longitudinal direction and the outer surfaces near the two end faces. The sealing portion 21 prevents gas and liquid from flowing in and out relative to the two end faces of the support body 11. The sealing portion 21 is, for example, a plate-shaped or film-shaped component made of glass or resin. The material and shape of the sealing portion 21 can be appropriately changed. It should be noted that the sealing portion 21 is provided with multiple openings that coincide with the multiple through holes 111 of the support body 11 in the longitudinal direction. Therefore, the two ends of each through hole 111 of the support body 11 in the longitudinal direction are not covered by the sealing portion 21. Therefore, gas and liquid can flow in and out from the two ends through the through holes 111.

[0043] The shape of the outer casing 22 is not particularly limited; for example, it may be a generally cylindrical cylindrical component. The outer casing 22 is formed of, for example, stainless steel or carbon steel. The length direction of the outer casing 22 is generally parallel to the length direction of the separation membrane composite 1. At one end of the length direction of the outer casing 22 (i.e., Figure 1 A supply port 221 is provided at the left end of the housing 22, and a first discharge port 222 is provided at the other end. A second discharge port 223 is provided on the side of the housing 22. A supply section 26 is connected to the supply port 221. A first recovery section 27 is connected to the first discharge port 222. A second recovery section 28 is connected to the second discharge port 223. The internal space of the housing 22 is a sealed space isolated from the space surrounding the housing 22.

[0044] Two sealing components 23 are arranged circumferentially between the outer surface of the separation membrane composite 1 and the inner surface of the housing 22 near both ends along the length of the separation membrane composite 1. Each sealing component 23 is a generally annular component formed of a gas- and liquid-impermeable material. For example, the sealing component 23 is an O-ring formed of a flexible resin. The sealing components 23 are tightly fitted circumferentially to the outer surface of the separation membrane composite 1 and the inner surface of the housing 22. Figure 1 In the example shown, the sealing member 23 is sealed to the outer side of the sealing part 21 and indirectly sealed to the outer side of the separation membrane composite 1 by sandwiching the sealing part 21. The sealing member 23 is sealed between the outer side of the separation membrane composite 1 and the inner side of the housing 22, so that gas and liquid can hardly or completely pass through.

[0045] The supply unit 26 supplies the mixed gas into the internal space of the outer casing 22 via the supply port 221. The supply unit 26 may include, for example, a pressure conveying mechanism such as a blower or pump that pressurizes the mixed gas toward the outer casing 22. This pressure conveying mechanism may include, for example, a temperature regulating unit and a pressure regulating unit that respectively regulate the temperature and pressure of the mixed gas supplied to the outer casing 22. The first recovery unit 27 and the second recovery unit 28 may include, for example, a storage container for storing the gas discharged from the outer casing 22 or a blower or pump for transferring the gas.

[0046] The mixed gas supplied by the supply unit 26 includes a first gas, a second gas, a third gas, and water vapor. The first gas, the second gas, and the third gas are all different types of gases. The first gas, the second gas, and the third gas are each one or more gases other than water vapor. The first gas and the second gas are the main components of the mixed gas. The total concentration of the first gas and the second gas in the mixed gas (i.e., the sum of the concentrations of the first gas and the second gas) is, for example, 90% to 99.9% by volume. The first gas is the aforementioned highly permeable substance, and the second gas is the aforementioned low-permeability substance. The first gas and the second gas are preferably non-polar gases. It should be noted that the first gas and the second gas may also be polar gases.

[0047] The third gas is a polar gas with a lower polarity than water vapor (i.e., H2O). The dipole moment of the third gas is, for example, 1.8D (Debye) or less. The lower limit of the dipole moment of the third gas is greater than 0.0D, but there is no particular limitation; for example, it is 0.3D or more. The concentration of the third gas in the gas mixture is, for example, 0.5 times or more the concentration of water vapor in the gas mixture, preferably 1 times or more. The upper limit of the concentration of the third gas in the gas mixture is not particularly limited, but to ensure that the combined concentration of the first and second gases in the gas mixture is not too low, it is preferably, for example, less than 2 times the concentration of water vapor in the gas mixture. It should be noted that the gas mixture may include the first gas, the second gas, the third gas, and gases other than water vapor.

[0048] The first gas and the second gas each contain, for example, one or more substances selected from hydrogen (H2), helium (He), nitrogen (N2), oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides, ammonia (NH3), sulfur oxides, hydrogen sulfide (H2S), sulfur fluoride, mercury (Hg), arsine (AsH3), hydrogen cyanide (HCN), carbonyl sulfide (COS), C1-C8 hydrocarbons, organic acids, alcohols, thiols, esters, ethers, ketones, and aldehydes. The first gas may be, for example, one or more substances selected from H2, He, N2, O2, CO2, NH3, and H2S.

[0049] Nitrogen oxides refer to compounds of nitrogen and oxygen. Examples of nitrogen oxides include nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (also known as dinitrogen monoxide) (N2O), dinitrogen trioxide (N2O3), dinitrogen tetroxide (N2O4), and dinitrogen pentoxide (N2O5), all collectively referred to as NO. X (NOx) gas.

[0050] Sulfur oxides are compounds of sulfur and oxygen. Examples of sulfur oxides include sulfur dioxide (SO2) and sulfur trioxide (SO3), collectively referred to as SO42-SO ... X (Sox) gas.

[0051] Sulfur fluoride refers to compounds of fluorine and sulfur. Examples of sulfur fluoride mentioned above include disulfur difluoride (F-S-S-F, S=SF2), sulfur difluoride (SF2), sulfur tetrafluoride (SF4), sulfur hexafluoride (SF6), or disulfur decafluoride (S2F). 10 )wait.

[0052] Hydrocarbons with C1 to C8 carbon atoms are defined as hydrocarbons with one or more but fewer than eight carbon atoms. Hydrocarbons with C3 to C8 carbon atoms can be any of the following: straight-chain compounds, side-chain compounds, and cyclic compounds. Additionally, hydrocarbons with C2 to C8 carbon atoms can be any of the following: saturated hydrocarbons (i.e., hydrocarbons without double or triple bonds in the molecule) and unsaturated hydrocarbons (i.e., hydrocarbons with double and / or triple bonds in the molecule). Examples of hydrocarbons with C1 to C4 carbon atoms include methane (CH4), ethane (C2H6), ethylene (C2H4), propane (C3H8), propylene (C3H6), n-butane (CH3(CH2)2CH3), isobutane (CH(CH3)3), 1-butene (CH2=CHCH2CH3), 2-butene (CH3CH=CHCH3), or isobutene (CH2=C(CH3)2).

[0053] The organic acids mentioned above are carboxylic acids or sulfonic acids, etc. Examples of carboxylic acids include formic acid (CH2O2), acetic acid (C2H4O2), oxalic acid (C2H2O4), acrylic acid (C3H4O2), or benzoic acid (C6H5COOH), etc. Examples of sulfonic acids include ethanesulfonic acid (C2H6O3S), etc. These organic acids can be chain compounds or cyclic compounds.

[0054] The alcohols mentioned above include, for example, methanol (CH3OH), ethanol (C2H5OH), isopropanol (2-propanol) (CH3CH(OH)CH3), ethylene glycol (CH2(OH)CH2(OH)) or butanol (C4H9OH), etc.

[0055] Thiols are organic compounds with hydrogenated sulfur (SH) at their terminals, also known as Thiol or Thioalcohol. Examples of thiols include methanethiol (CH3SH), ethanethiol (C2H5SH), and 1-propanethiol (C3H7SH).

[0056] The esters mentioned above are, for example, formate esters or acetate esters.

[0057] The ethers mentioned above are, for example, dimethyl ether ((CH3)2O), methyl ethyl ether (C2H5OCH3), or diethyl ether ((C2H5)2O), etc.

[0058] The ketones mentioned above include acetone ((CH3)2CO), methyl ethyl ketone (C2H5COCH3), or diethyl ketone ((C2H5)2CO), etc.

[0059] The aldehydes mentioned above include acetaldehyde (CH3CHO), propionaldehyde (C2H5CHO), or butylaldehyde (C3H7CHO).

[0060] The third gas is, for example, one or more substances selected from NH3, alcohols such as ethanol, and hydrocarbons such as toluene (C6H5CH3). The dipole moments of NH3, ethanol, and toluene are 1.42D, 1.69D, and 0.36D, respectively. In addition, the dipole moment of water vapor is 1.85D.

[0061] Next, refer to Figure 4 The separation of a mixed gas using the separation membrane composite 1 will be explained. Figure 4 This is a diagram illustrating the separation process of a mixed gas based on separation device 2. In separating the mixed gas, firstly, the separation membrane composite 1 is... Figure 1 It is installed inside the housing 22 as shown and is ready for use. Next, the above-mentioned mixed gas is supplied to the inside of the housing 22 through the supply port 221 as shown by arrow 251 using the supply unit 26 (step S11).

[0062] The pressure of the mixed gas supplied from the supply section 26 to the interior of the housing 22 (i.e., the gas pressure on the primary side of the separation membrane 12, i.e., the supply-side pressure) is, for example, 0.1 MPaG to 20.0 MPaG. The temperature of the mixed gas supplied from the supply section 26 is, for example, 10°C to 250°C. In this embodiment, the temperature of the mixed gas is 100°C or less.

[0063] The mixed gas supplied from the supply unit 26 to the housing 22 is introduced from the left end of the separation membrane composite 1 in the figure into each through hole 111 of the support 11 (i.e., the inner side of the generally cylindrical separation membrane 12). The highly permeable substance in the mixed gas, namely the first gas, permeates through the separation membrane 12 provided on the inner side of each through hole 111 and the support 11 and is discharged from the outer side of the support 11. Thus, the first gas is separated from the mixed gas (step S12). In other words, the first gas and the second gas (i.e., the low-permeability substance) in the mixed gas are separated.

[0064] The gas exiting from the outer surface of the support 11 (hereinafter referred to as "permeable gas") is guided to the second recovery section 28 via the second outlet 223 as shown by arrow 253, and recovered by the second recovery section 28. The pressure of the gas recovered by the second recovery section 28 (i.e., the gas pressure on the secondary side of the separation membrane 12, i.e., the permeable side pressure) is, for example, 0.0 MPaG. In other words, the difference between the supply side pressure and the permeable side pressure is, for example, 0.1 MPa to 20.0 MPa. In addition to the first gas, the permeable gas may contain a second gas, a third gas, and / or water vapor that has permeated from the separation membrane 12.

[0065] Additionally, the gas in the mixed gas other than the gas that has permeated through the separation membrane 12 and the support 11 (hereinafter referred to as "non-permeable gas") passes from left to right in each through hole 111 of the support 11 as shown by arrow 252, and is recovered by the first recovery unit 27 via the first outlet 222. The pressure of the gas recovered by the first recovery unit 27 is, for example, approximately the same as the supply side pressure. The non-permeable gas may contain the first gas that has not permeated through the separation membrane 12, in addition to the second gas, the third gas, and water vapor. The non-permeable gas recovered by the first recovery unit 27 can, for example, be recycled to the supply unit 26 and supplied again to the housing 22.

[0066] In the separation of the mixed gas in the separation device 2, a third gas contained in the mixed gas is adsorbed onto the surface of the separation membrane 12. As mentioned above, the third gas is a polar gas; however, its polarity is lower than that of water vapor, therefore, its adsorption force on the surface of the separation membrane 12 is weaker than that of water vapor. Thus, the molecules of the third gas repeatedly adsorb onto and detach from the surface of the separation membrane 12. In other words, the third gas repeatedly undergoes reversible adsorption and detachment relative to the surface of the separation membrane 12. As a result, it prevents water vapor in the mixed gas from adsorbing onto the surface of the separation membrane 12. Water vapor has a higher polarity than the third gas; therefore, once adsorbed onto the surface of the separation membrane 12, it is difficult to detach, potentially reducing the permeability of the separation membrane 12. In the separation device 2, by reversibly adsorbing and detaching the third gas from the separation membrane 12, the adsorption of water vapor is prevented, thereby suppressing the reduction in the permeability of the separation membrane 12.

[0067] When the separation membrane 12 described above is a zeolite membrane, the separation membrane composite 1 is manufactured as follows. First, the support 11 is immersed in a solution containing dispersed seed crystals, causing the seed crystals to adhere to the support 11. The seed crystals are, for example, powder of zeolite synthesized by hydrothermal synthesis or a substance obtained by pulverizing the powder. It should be noted that the adhesion of the seed crystals to the support 11 can be performed using methods other than those described above.

[0068] Next, the support 11 with seed crystals attached is immersed in the raw material solution for hydrothermal synthesis. Zeolite is grown from the seed crystals, forming a separation membrane 12 (i.e., a zeolite membrane) on the support 11. The raw material solution is prepared by dissolving or dispersing raw materials such as Si source and a structure-directing agent (hereinafter also referred to as "SDA") in a solvent (e.g., water). The hydrothermal synthesis temperature is, for example, 110°C to 200°C, and the hydrothermal synthesis time is, for example, 5 hours to 200 hours.

[0069] After hydrothermal synthesis, the support 11 and separation membrane 12 are cleaned and dried, and then subjected to heat treatment in an oxidizing gas atmosphere. Through this heat treatment, SDA and impurities in the separation membrane 12 are burned off. As a result, a separation membrane composite 1 with interconnected micropores is obtained. The aforementioned oxidizing gas atmosphere is an atmosphere containing oxygen, such as atmospheric air. The temperature during the aforementioned heat treatment is, for example, 200°C to 800°C. Furthermore, the heat treatment time is, for example, 10 hours to 200 hours.

[0070] When the separation membrane 12 described above is a carbon membrane, the separation membrane composite 1 is manufactured as follows. First, a precursor solution is allowed to flow into the through-hole 111 of the support 11, and the precursor solution is brought into contact with the inner surface of the through-hole 111, thereby forming a membrane of the precursor solution on the inner surface. The precursor solution is obtained by mixing or dissolving the precursor of the carbon membrane in a solvent. The precursor is, for example, a thermosetting resin such as phenolic resin, melamine resin, urea resin, furan resin, polyimide resin, or epoxy resin, a thermoplastic resin such as polyethylene, polyphenylene ether, or polyetherimide, a cellulose resin, or an inherently porous polymer (PIM). Alternatively, the precursor can be a precursor material of these resins. The solvent described above is, for example, an organic solvent such as methanol, ethanol, acetone, tetrahydrofuran, NMP (N-methyl-2-pyrrolidone), or toluene, or water. It should be noted that the precursors and solvents contained in the precursor solution are not limited to the examples above and can be modified in various ways.

[0071] Next, the support 11 of the membrane on which the precursor is disposed is dried, and the dried support 11 is subjected to heat treatment to harden the precursor membrane. This heat treatment is performed, for example, by heating the support 11 to 90°C to 500°C using a dryer and holding it for 0.5 hours to 60 hours. It should be noted that the supply of the precursor solution and the above-mentioned heat treatment can be repeated multiple times during the formation of the precursor membrane. Afterwards, the support 11 of the membrane on which the precursor is disposed is subjected to carbonization treatment. As a result, a separation membrane 12 (i.e., a carbon membrane) is formed on the surface of the support 11 (i.e., the inner surface of the through-hole 111) by the precursor membrane, obtaining a separation membrane composite 1 having the separation membrane 12. In this carbonization treatment, for example, the support 11 is placed in an electric furnace and heated to 400°C to 1200°C. This carbonization treatment is preferably performed in a non-oxidizing atmosphere. A non-oxidizing atmosphere refers to an atmosphere in which the precursor is not oxidized when carbonized within the above-mentioned temperature range. The non-oxidizing atmosphere is specifically a non-reactive gas atmosphere such as nitrogen or argon, or a vacuum atmosphere.

[0072] Next, referring to Table 1, embodiments and comparative examples related to the separation of mixed gases based on separation device 2 will be described.

[0073] [Table 1]

[0074]

[0075] In Examples 1-9, the permeability was verified by changing conditions such as the type of the third gas added to the gas mixture. Additionally, in Comparative Examples 1-3, the permeability was verified when no third gas, which is a polar gas, was added to the gas mixture. In the following description, gases added to the gas mixture other than the first gas, the second gas, and water vapor (e.g., the third gas) will be referred to as "added gases." The gas mixture substantially does not contain any gases other than the first gas, the second gas, the added gas, and water vapor.

[0076] In Examples 1-9 and Comparative Examples 1-3, as described in steps S11-S12 above, a mixed gas containing H2 and CH4 as the first gas and water vapor as the second gas was supplied to the separation device 2, and the permeation rate (permeate flow) of H2 per unit membrane area and unit pressure difference permeating through the separation membrane 12 was measured. Furthermore, the permeation rate of H2 10 hours after the start of use of the separation membrane composite 1 in the separation device 2 was divided by the permeation rate of H2 at the start of use of the separation membrane composite 1 (i.e., the initial permeation rate), and 1 was subtracted to obtain the permeation performance reduction rate (%). In the above measurements in the separation device 2, the pressure and temperature of the mixed gas supplied from the supply section 26 of the separation device 2 were 0.3 MPaG and 25°C, respectively. Additionally, the permeate-side pressure of the separation membrane 12 was 0.0 MPaG. The concentration of the first gas in the mixed gas supplied from the supply section 26 was 20% by volume, and the concentration of the second gas was 80% by volume.

[0077] In Example 1, the separation membrane 12 is a DDR-type zeolite membrane. DDR-type zeolite membranes have hydroxyl groups on their surface. In Example 1, the additive gas added to the mixed gas is a polar gas, i.e., a third gas, specifically ammonia (NH3). The dipole moment of ammonia is 1.42D as described above. The concentration of the additive gas in the mixed gas supplied to the separation membrane composite 1, divided by the concentration of water vapor (hereinafter also referred to as the "additive gas / water vapor ratio"), is 1. The temperature of the mixed gas supplied to the separation membrane composite 1 (hereinafter also referred to as the "supply temperature") is 60°C. In Example 1, the permeability reduction rate is 52%.

[0078] Regarding Example 2, the ratio of added gas to water vapor in the mixed gas was set to 2; otherwise, it was the same as in Example 1. In Example 2, the permeability reduction rate was 16%.

[0079] Regarding Example 3, the ratio of added gas to water vapor in the mixed gas was set to 3; otherwise, it was the same as in Example 1. In Example 3, the permeability reduction rate was 16%.

[0080] Regarding Example 4, the ratio of added gas to water vapor in the mixed gas was set to 0.5; otherwise, it was the same as in Example 1. In Example 4, the permeability reduction rate was 63%.

[0081] Regarding Example 5, the supply temperature of the mixed gas was set to 30°C; otherwise, it was the same as in Example 1. In Example 5, the permeability reduction rate was 64%.

[0082] Regarding Example 6, the supply temperature of the mixed gas was set to 80°C; otherwise, it was the same as in Example 1. In Example 6, the permeability reduction rate was 9%.

[0083] Regarding Example 7, ethanol was used instead of NH3 as the third gas; otherwise, it was the same as in Example 1. The dipole moment of ethanol was 1.69D as described above. In Example 7, the permeability reduction rate was 37%.

[0084] Regarding Example 8, toluene was used instead of NH3 as the third gas; otherwise, it was the same as in Example 1. The dipole moment of toluene was 0.36D as described above. In Example 8, the permeability reduction rate was 65%.

[0085] In Example 9, a carbon membrane was used as the separation membrane 12, and otherwise it was the same as in Example 1. The carbon membrane did not have hydroxyl groups on its surface. In Example 9, the permeability reduction rate was 35%.

[0086] In Comparative Example 1, no additional gas was added; otherwise, it was the same as in Example 1. The gas mixture in Comparative Example 1 essentially contained only the first gas, the second gas, and water vapor, and did not contain the polar gas, i.e., the third gas. Therefore, the added gas / water vapor ratio was 0. In Comparative Example 1, the permeability reduction rate was 73%.

[0087] In Comparative Example 2, hexane (CH3(CH2)4CH3), a non-polar gas, was used as the additive gas; otherwise, it was the same as in Example 1. The gas mixture in Comparative Example 2 essentially contained only the first gas, the second gas, water vapor, and hexane, and did not contain the polar gas, i.e., the third gas. The additive gas / water vapor ratio was 1. In Comparative Example 2, the permeability reduction rate was 73%.

[0088] In Comparative Example 3, no additional gas was added; otherwise, it was the same as in Example 9. The gas mixture in Comparative Example 3 essentially contained only the first gas, the second gas, and water vapor, and did not contain the polar gas, i.e., the third gas. Therefore, the added gas / water vapor ratio was 0. In Comparative Example 3, the permeability reduction rate was 59%.

[0089] As described above, in Examples 1 to 8, the mixed gas contained not only the first gas, the second gas, and water vapor, but also a polar gas, namely the third gas, resulting in a permeability reduction rate of 9% to 65%. On the other hand, in Comparative Examples 1 and 2, where the mixed gas did not contain the third gas, the permeability reduction rate was as high as 73%. Furthermore, in Example 9, where the mixed gas contained the third gas, the permeability reduction rate was 35%, while in Comparative Example 3, where the mixed gas did not contain the third gas, the permeability reduction rate was as high as 59%. Therefore, it can be seen that by adding a polar gas, namely the third gas, to the mixed gas, the reduction in the permeability of the separation membrane 12 can be suppressed.

[0090] Comparing Examples 1 to 4, from the viewpoint of reducing the permeation performance by 52% or less, the gas / water vapor ratio is preferably 1 or more. Furthermore, in Examples 2 and 3, considering that the permeation performance reduction rate is the same, from the viewpoint of preventing the total concentration of the first and second gases in the mixed gas from being too low and thus suppressing the reduction in the permeation performance of the separation membrane 12, the gas / water vapor ratio is preferably 2 or less.

[0091] Comparing Examples 1, 7, and 8, from the viewpoint of reducing the permeability by less than 52%, the dipole moment of the third gas is preferably 1.42D or more.

[0092] In the separation device 2 described above, before supplying and separating the mixed gas as shown in steps S11 to S12, as follows: Figure 5 As shown, the pretreated gas can be supplied to the separation membrane 12 (step S21). The pretreated gas and the mixed gas are supplied from... Figure 1 The supply unit 26 shown is supplied to the interior of the housing 22 and to the separation membrane 12 of the separation membrane composite 1. The pretreatment gas is a gas containing the aforementioned third gas and substantially free of water vapor. The concentration of water vapor in the pretreatment gas is, for example, 10 ppm or less by volume. The pretreatment gas may contain gases other than the third gas. By supplying the pretreatment gas to the separation membrane 12 before steps S11 to S12, reversible adsorption of the third gas onto the separation membrane 12 can occur in advance, further hindering the adsorption of water vapor onto the separation membrane 12 when the mixed gas is supplied. As a result, the adsorption of water vapor onto the separation membrane 12, which would otherwise reduce permeability, can be further suppressed.

[0093] As explained above, the separation method for separating mixed gases includes the following steps: supplying a mixed gas containing a first gas, a second gas, water vapor, and a third gas with a polarity lower than that of water vapor to an inorganic membrane, i.e., separation membrane 12 (step S11); and separating the first gas from the mixed gas by allowing it to permeate through the separation membrane 12 (step S12). Accordingly, as described above, it is possible to suppress the adsorption of water vapor on the separation membrane 12, thereby preventing a decrease in permeation performance.

[0094] As described above, the concentration of the third gas in the mixed gas is preferably 0.5 times or more the concentration of water vapor in the mixed gas. This increases the reversibility of the adsorption of the third gas onto the separation membrane 12. Consequently, the adsorption of water vapor onto the separation membrane 12 is further suppressed, thereby further suppressing the decrease in the permeation performance of the separation membrane 12.

[0095] As described above, the dipole moment of the third gas is preferably 1.8D or less. This allows for efficient and repeated adsorption and desorption of the third gas onto the separation membrane 12. Consequently, the reduction in the permeation performance of the separation membrane 12 can be effectively suppressed.

[0096] The above-described method for separating mixed gases preferably further includes, before step S11, a step of supplying a pretreated gas containing a third gas and free of water vapor to the separation membrane 12 (step S21). This further suppresses the adsorption of water vapor onto the separation membrane 12, thereby further suppressing the reduction in the permeation performance of the separation membrane 12.

[0097] According to the separation method described above, as shown in Examples 1 to 9, even when separating relatively low-temperature mixed gases, the decrease in permeability can be suppressed. Therefore, this separation method is particularly suitable for situations where the temperature of the mixed gas is below 100°C. By keeping the temperature of the mixed gas below 100°C, heating equipment that heats the mixed gas before supplying it can be omitted or miniaturized, thereby simplifying the structure of the separation device 2. In addition, the energy required for separating the mixed gas can also be reduced.

[0098] According to the separation method described above, the adsorption of water vapor onto the separation membrane 12, which would otherwise reduce the permeability, can be suppressed. Therefore, this separation method is particularly suitable for separating mixed gases using a separation membrane 12 that readily adsorbs water vapor due to the presence of hydroxyl groups on its surface.

[0099] As described above, in this separation method, a polar gas, namely a third gas, is added to the mixed gas, thereby suppressing the decrease in the permeation performance of the separation membrane 12. Therefore, the decrease in permeation performance is further suppressed when the first and second gases are non-polar gases. That is, the above separation method is particularly suitable for situations where the first and second gases are non-polar gases.

[0100] The separation device 2 described above includes a supply unit 26 and a separation membrane 12. The supply unit 26 supplies a mixture of a first gas, a second gas, water vapor, and a third gas, which is less polar than water vapor. The separation membrane 12 is an inorganic membrane that separates the first gas from the mixture. In this separation device 2, similarly to the above, it is possible to suppress the adsorption of water vapor on the separation membrane 12, which would lead to a decrease in permeation performance.

[0101] Various modifications can be made to the separation device 2 and the separation method described above.

[0102] As described above, the separation membrane 12 can be an inorganic membrane with hydroxyl groups on its surface or an inorganic membrane without hydroxyl groups on its surface.

[0103] The temperature of the mixed gas supplied to the separation membrane 12 can be higher than 100°C.

[0104] The dipole moment of the third gas only needs to be smaller than that of the water vapor, and can be greater than 1.8D.

[0105] The concentration of the third gas in the gas mixture can be less than 0.5 times the concentration of water vapor in the gas mixture.

[0106] As described above, the separation membrane 12 can be a porous membrane other than a zeolite membrane or a carbon membrane. In addition, when the separation membrane 12 is a zeolite membrane, the zeolite membrane can be a laminated membrane obtained by stacking multiple zeolite membranes formed by different types of zeolite in the thickness direction, or it can be a zeolite membrane that has undergone surface treatment.

[0107] In the separation membrane composite 1, a membrane of a different type than the separation membrane 12 (e.g., an inorganic membrane such as a silica membrane) may be provided on the separation membrane 12 (i.e., on the outer surface of the separation membrane 12 on the side opposite to the support 11).

[0108] The components in the above-described embodiments and their variations can be appropriately combined as long as they do not contradict each other.

[0109] Although the invention has been described in detail, the above description is exemplary and not limiting. Therefore, it can be said that numerous modifications and solutions can be adopted without departing from the scope of the invention.

[0110] Industrial availability

[0111] This invention can be used for the separation of various mixed gases.

[0112] Explanation of reference numerals in the attached figures

[0113] 2. Separation device

[0114] 12 Separation Membrane

[0115] 26 Supply Department

[0116] Steps S11~S12, S21

Claims

1. A separation method for separating a mixed gas, The separation method is characterized by including the following steps: a) A mixed gas comprising a first gas, a second gas, water vapor, and a third gas (a gas with a lower polarity than water vapor) is supplied to an inorganic membrane, i.e., a separation membrane; and b) Separating the first gas from the mixed gas by allowing the first gas to permeate through the separation membrane.

2. The separation method according to claim 1, characterized in that, The concentration of the third gas in the mixed gas is more than 0.5 times the concentration of water vapor in the mixed gas.

3. The separation method according to claim 1, characterized in that, The dipole moment of the third gas is less than 1.8D.

4. The separation method according to claim 1, characterized in that, Prior to step a), the process further includes a step of supplying a pretreatment gas containing the third gas and free of water vapor to the separation membrane.

5. The separation method according to claim 1, characterized in that, The temperature of the mixed gas is below 100°C.

6. The separation method according to any one of claims 1 to 5, characterized in that, The separation membrane has hydroxyl groups on its surface.

7. A separation device for separating a mixed gas, The separation device is characterized by having: The supply unit supplies a mixture of a first gas, a second gas, water vapor, and a third gas, which is less polar than water vapor; and The separation membrane is an inorganic membrane that separates from the mixed gas by allowing the first gas to pass through.

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