Membrane separation device and membrane separation method

Abstract

To perform membrane separation of target gas included in gaseous starting material with high separation efficiency.SOLUTION: According to a first embodiment, a membrane separation device is provided, performing membrane separation of mixed gas including first gas and second gas, the membrane separation device comprises: a constant temperature bath which keeps temperature in the inside thereof at -196°C or higher and 0°C or lower; and a separation membrane which is positioned in a space inside the constant temperature bath, and performs membrane separation of the mixed gas. According to a second embodiment, a membrane separation device is provided which performs membrane separation of mixed gas including first gas and second gas, and comprises: a constant temperature bath which keeps an internal space at a temperature above 0°C; and a separation membrane which is positioned in the space, and performs membrane separation of the mixed gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, membrane separation has been used as a method for separating and recovering a desired gas from a mixed gas that is a mixture of multiple gases.

[0003] Specifically, for example, in Patent Document 1, helium is separated and purified from a gas containing low concentrations of helium using membrane separation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2021 / 0402345 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above conventional technology, when separating the target gas, helium, from a raw material gas containing a low concentration of helium, a separation membrane that allows the low concentration component, helium, to permeate is used, and therefore the separation efficiency is low.

[0006] Therefore, there was a demand for a technology that could perform membrane separation with high separation efficiency of the target gas contained in the raw gas. [Means for solving the problem]

[0007] The present inventors have newly discovered that even when membrane separation is performed using the same separation membrane, the permeability tendency of gases may differ between room temperature and low temperature; specifically, when membrane separation of a mixed gas containing a first gas and a second gas having a larger permeability coefficient than the first gas at room temperature is performed, the second gas may have a smaller permeability coefficient when the membrane separation is performed at a low temperature.

[0008] That is, the present invention aims to advantageously solve the above problems, and [1] the membrane separation device of the present invention is a membrane separation device that performs membrane separation of a mixed gas containing a first gas and a second gas, and is characterized in that it includes a thermostatic chamber that keeps the internal space at a temperature of -196 ° C or higher and 0 ° C or lower, and a separation membrane that is located in the space and performs membrane separation of the mixed gas. In this way, by providing a thermostatic chamber that keeps the internal space at a low temperature of -196 ° C or higher and 0 ° C or lower, membrane separation can be performed at low temperatures with a permeation tendency different from that at room temperature. Therefore, by using the membrane separation device according to the concentration of the target gas contained in the mixed gas and the permeation coefficient at room temperature, it is possible to perform membrane separation of the target gas with high separation efficiency.

[0009] The present invention also aims to advantageously solve the above problems, and [2] the membrane separation device of the present invention is a membrane separation device that performs membrane separation of a mixed gas containing a first gas and a second gas, and is characterized in that it includes a thermostatic chamber that makes the internal space above 0°C, and a separation membrane that is located in the space and performs membrane separation of the mixed gas. In this way, by providing a thermostatic chamber that makes the internal space above 0°C, membrane separation can be performed with the same permeation tendency as at room temperature, so that by using different membrane separation devices depending on the concentration of the target gas contained in the mixed gas and the permeation coefficient at room temperature, it is possible to perform membrane separation of the target gas with high separation efficiency.

[0010] Furthermore, the present invention aims to advantageously solve the above problems, and [3] the membrane separation device of the present invention is a membrane separation device that performs membrane separation of a mixed gas containing a first gas and a second gas in multiple stages, and is characterized in that it comprises a first thermostatic chamber that keeps the internal space at -196°C or higher and 0°C or lower, a first membrane separation unit having a first separation membrane located in the space of the first thermostatic chamber, a second thermostatic chamber that keeps the internal space above 0°C, and a second membrane separation unit having a second separation membrane located in the space of the second thermostatic chamber. In this way, by performing membrane separation in multiple stages using the first membrane separation unit and the second membrane separation unit, it is possible to perform membrane separation of the target gas contained in the mixed gas with high separation efficiency.

[0011] [4] In the membrane separation device described in the above [1] or [2], the separation membrane preferably has a layer made of a hydrophobic material. [5] In the membrane separation device described in [3] above, it is preferable that the first separation membrane and the second separation membrane each have a layer made of a hydrophobic material.

[0012] [6] In the membrane separation device according to any one of the above [1] to [5], it is preferable that the first gas is oxygen, and the second gas is a rare gas or hydrogen.

[0013] The present invention also aims to advantageously solve the above problems, and the membrane separation method of the present invention is a membrane separation method for separating a mixed gas containing a first gas and a second gas, characterized in that it includes a step of separating the mixed gas at a temperature of -196°C or higher and 0°C or lower. In this way, by separating the mixed gas at a temperature of -196°C or higher and 0°C or lower, membrane separation can be performed at low temperatures with a different permeation tendency than at room temperature. Therefore, by using different membrane separation methods depending on the concentration of the target gas contained in the mixed gas and the permeation coefficient at room temperature, it is possible to separate the target gas with high separation efficiency.

[0014] Furthermore, the present invention aims to advantageously solve the above problems, and [8] the membrane separation method of the present invention is a membrane separation method for separating a mixed gas containing a first gas and a second gas, characterized in that it includes a step of separating the mixed gas at a temperature above 0° C. In this way, if the mixed gas is separated by membrane at a temperature above 0° C., the membrane separation can be performed with the same permeation tendency as at room temperature, so that by using different membrane separation methods depending on the concentration of the target gas contained in the mixed gas and the permeability coefficient at room temperature, it is possible to separate the target gas by membrane with high separation efficiency.

[0015] The present invention also aims to advantageously solve the above problems, and the membrane separation method of the present invention is a membrane separation method for performing multi-stage membrane separation of a mixed gas containing a first gas and a second gas, characterized in that it includes a first membrane separation step of performing membrane separation of the membrane-separated gas at a temperature of -196°C or higher and 0°C or lower, and a second membrane separation step of performing membrane separation of the membrane-separated gas at a temperature higher than 0°C. In this way, by performing multi-stage membrane separation by carrying out the first membrane separation step and the second membrane separation step, it becomes possible to perform membrane separation of the target gas contained in the mixed gas with high separation efficiency.

[0016]

[10] In the membrane separation method according to any one of the above [7] to [9], it is preferable that the first gas is oxygen, and the second gas is a rare gas or hydrogen.

[0017]

[11] In the membrane separation method according to any one of the above [7] to

[10] , the membrane separation is preferably carried out using a separation membrane having a layer made of a hydrophobic material.

[0018]

[12] In the membrane separation method according to any one of the above [7] to

[11] , it is preferable that the membrane separation is carried out so that the pressure of the permeating component is 0.01 to 1 times the pressure of the gas to be separated by the membrane. Effect of the Invention

[0019] According to the present invention, it is possible to perform membrane separation of a target gas contained in a raw material gas with high separation efficiency. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is an explanatory diagram showing a configuration of an example of a membrane separation device of the present invention. [Diagram 2] FIG. 2 is an explanatory diagram showing the configuration of another example of a membrane separation device of the present invention. [Diagram 3] FIG. 1 is a cross-sectional view illustrating a schematic configuration of a membrane module that can be used in an example of a membrane separation device of the present invention. [Figure 4]FIG. 4 is a cross-sectional view showing an example of the configuration of a separation unit applicable to the membrane module shown in FIG. [Diagram 5] 1 is an enlarged cross-sectional photograph of an example of a separation membrane that can be used in the membrane separation device of the present invention. [Figure 6] FIG. 1 is a schematic diagram showing an example of an inorganic material having a crosslinked structure of siloxane bonds, where (a) shows the structure of a bridged-type organosilica, and (b) shows the structure of a side-chain-type organosilica. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention will be described in detail below. Here, the membrane separation apparatus and the membrane separation method of the present invention can be used when subjecting a mixed gas containing a first gas and a second gas to membrane separation.

[0022] (Gas Mixture) The mixed gas to be separated by the membrane separation apparatus and method of the present invention contains a first gas and a second gas, and may optionally further contain a gas other than the first gas and the second gas.

[0023] Here, without being particularly limited, the second gas may have a larger permeability coefficient through the separation membrane at a temperature of 30° C. than the first gas. The first gas and the second gas preferably satisfy at least one of the following conditions (1) to (3), more preferably satisfy condition (1) or (2), and even more preferably satisfy both conditions (1) and (2). This is because when at least one of the following conditions (1) to (3) is satisfied, the permeation tendency of the gas is likely to be significantly different between at room temperature and at low temperatures. (1) The first gas is more easily adsorbed by the separation membrane than the second gas. (2) The second gas diffuses faster than the first gas. (3) The molecular diameter of the second gas is smaller than the molecular diameter of the first gas.

[0024] Among these, the combination of the first gas and the second gas is preferably such that the first gas is oxygen (O2) and the second gas is a rare gas (helium, neon, argon, krypton, xenon, radon) or hydrogen (H2), more preferably such that the first gas is oxygen and the second gas is a rare gas, and even more preferably such that the first gas is oxygen and the second gas is helium.

[0025] Furthermore, the concentrations of the first gas and the second gas in the mixed gas are not particularly limited and can be any concentration, but the total concentration of the first gas and the second gas in the mixed gas is preferably 50 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and may be 100 mol%.

[0026] (separation membrane) In addition, the separation membrane used in the membrane separation apparatus and the membrane separation method of the present invention is not particularly limited, and any separation membrane can be used. Among them, the separation membrane is preferably a separation membrane having a layer made of a hydrophobic material, and more preferably a separation membrane made of a laminated membrane of an active separation layer and an intermediate layer made of a hydrophobic material. The hydrophobic material is preferably an inorganic material having a siloxane bond, and the active separation layer is preferably a layer made of an inorganic material having a cross-linked structure of a siloxane bond. The separation membrane is not particularly limited, and can be used for membrane separation of a mixed gas in the form of a membrane module including a separation section having a separation membrane on a support layer made of a porous substrate.

[0027] Here, Fig. 5 is an enlarged cross-sectional photograph showing a separation membrane 10 according to one embodiment of the present invention. In Fig. 5, the separation membrane 10 is provided on a support layer 7 made of a porous substrate.

[0028] As shown in FIG. 5, separation membrane 10 is a laminated membrane of intermediate layer 8 and active separation layer 9 supported on support layer 7 .

[0029] The intermediate layer 8 is located on the support layer 7 and supports the active separation layer 9. By providing the intermediate layer 8 between the support layer 7 and the active separation layer 9, the difference in average pore diameter between the adjacent layers can be reduced. In this case, the intermediate layer 8 has an average pore diameter smaller than that of the support layer 7 and larger than that of the active separation layer 9.

[0030] The intermediate layer 8 is a layer made of a hydrophobic material. Examples of hydrophobic materials include inorganic materials having a siloxane bond (-Si-O-Si-), carbon materials made of carbon, etc. Among these, it is preferable to use inorganic materials having a siloxane bond from the viewpoint of low temperature resistance.

[0031] Here, when a hydrophilic material is used for the intermediate layer 8, moisture that cannot be completely removed remains in the membrane pores even after high-temperature baking using an inert gas. Therefore, when the temperature drops to a low temperature of 0°C or lower, the moisture remaining in the membrane pores freezes, causing physical blockages and inhibiting gas permeation. In contrast, in the separation membrane 10, the intermediate layer 8 is a layer made of a hydrophobic material, so that no moisture remains in the membrane pores after high-temperature firing, and even at low temperatures below 0°C, blockage due to freezing of the remaining moisture does not occur, and gas permeation is not hindered.

[0032] Examples of inorganic materials having siloxane bonds include sols prepared from organoalkoxysilanes, sols prepared from tetraethoxysilanes, etc. Among these, it is preferable to use sols prepared from organoalkoxysilanes from the viewpoint of controlling the pore size.

[0033] Examples of organoalkoxysilanes include one or more precursors selected from 1,2-bis(triethoxysilyl)methane (BTESM), 1,2-bis(triethoxysilyl)ethane (BTESE), 1,2-bis(triethoxysilyl)propane (BTESP) and 1,2-bis(triethoxysilyl)benzene (BTESB), and one or more sols obtained from their hydrolyzates. Among these, BTESM or BTESE crosslinked with at least C3 components, preferably with C2 or lower components, is preferred from the viewpoint of exhibiting properties similar to those of inorganic materials.

[0034] Examples of the gel structure formed by firing a sol prepared from an organoalkoxysilane include a bridged organosilica represented by the following general formula (1) and a side chain organosilica represented by the following general formula (2). [ka] [ka]

[0035] In the above general formula (1), the linking group X located between silicon atoms (Si) is an unsaturated hydrocarbon having an unsaturated bond between carbon atoms. The number of carbon atoms in the unsaturated hydrocarbon is 1 to 8, preferably 1 to 3. The above-mentioned linking group X also includes a structure in which some of the hydrogen atoms are substituted with a simple metal ion or a compound such as a metal oxide. Examples of the metal species constituting the metal ions or metal oxides include Ag, Cu, Fe, Ni, Co, Al, Ti, Zr, etc. Note that the metal species listed here are merely examples and are not limited to these metals.

[0036] In the above general formula (1), the organic group R is a hydrogen atom or an unsaturated hydrocarbon having an unsaturated bond between carbon atoms and having from 1 to 10 carbon atoms. The organic group R also includes a structure in which some of the hydrogen atoms are substituted with a compound such as a simple metal ion or a metal oxide. Examples of the metal species constituting the metal ions or metal oxides include Ag, Cu, Fe, Ni, Co, Al, Ti, Zr, etc. Note that the metal species listed here are merely examples and are not limited to these metals.

[0037] In the above general formula (2), the organic group R can be the same as that in the above general formula (1). In addition, in the above general formula (2), OR' is a side chain (pendant) hanging from the siloxane bond, and examples of the organic group R' include CH3 and C2H5.

[0038] Examples of the side chain type organosilica represented by the above general formula (2) include methyltriethoxysilane (MTES) and methyltrimethoxysilane (MTMS).

[0039] An example of a carbon material made of carbon is a carbon film.

[0040] The average pore diameter of the intermediate layer 8 is not particularly limited as long as it is smaller than the average pore diameter of the support layer 7 and larger than the average pore diameter of the active separation layer 9. It is particularly preferable that the average pore diameter of the intermediate layer 8 is about 2 nm or less. If the average pore diameter of the intermediate layer 8 is too large, the selectivity during gas separation decreases. If the average pore diameter of the intermediate layer 8 is too small, the gas permeability decreases.

[0041] The thickness of the intermediate layer 8 is not particularly limited as long as it can cover the irregularities on the upper surface of the support layer 7 and flatten the active separation layer 9. Such a thickness can be 10 nm or more and 500 nm or less, preferably 50 nm or more and 400 nm or less, and more preferably 100 nm or more and 200 nm or less.

[0042] The active separation layer 9 is located on the intermediate layer 8, and is a layer that selectively separates any component from the raw gas mixture. The material of the active separation layer 9 is not particularly limited as long as it can selectively separate any component from the mixed gas. Examples of such materials include inorganic materials having a cross-linked structure of siloxane bonds with organoalkoxysilane as a precursor; and inorganic materials composed of oxides of metals such as zirconia, titanium, and iron. Among these, it is preferable to use inorganic materials having a cross-linked structure of siloxane bonds with organoalkoxysilane as a precursor from the viewpoint of pore size control and hydrophobicity.

[0043] Examples of inorganic materials having a crosslinked structure of siloxane bonds include sols prepared from organoalkoxysilanes and sols prepared from tetraethoxysilanes. Among these, it is preferable to apply a sol prepared from organoalkoxysilanes from the viewpoint of controlling the pore size. By controlling the pore size, it is also possible to apply the sol to the separation of gases with high diffusion coefficients such as helium and hydrogen.

[0044] Examples of organoalkoxysilanes include one or more precursors selected from 1,2-bis(triethoxysilyl)methane (BTESM), 1,2-bis(triethoxysilyl)ethane (BTESE), 1,2-bis(triethoxysilyl)propane (BTESP) and 1,2-bis(triethoxysilyl)benzene (BTESB), as well as one or more sols obtained from their hydrolysates. Among these, from the viewpoint of exhibiting properties similar to those of inorganic materials, those in which the organic group R has 3 or less carbon atoms (BTESM, BTESE, BTESP) are preferred. This reflects the finding that as the organic group R has a larger carbon number, it begins to exhibit the properties of organic materials.

[0045] Examples of the structure of the gel formed by firing the sol prepared from the organoalkoxysilane include the bridged organosilica represented by the following general formula (3) and the side chain organosilica represented by the following general formula (4). [ka] [ka]

[0046] In the above general formula (3), the linking group X located between silicon atoms (Si) is an unsaturated hydrocarbon having an unsaturated bond between carbon atoms. The number of carbon atoms in the unsaturated hydrocarbon is 1 to 8, preferably 1 to 3. The above-mentioned linking group X also includes a structure in which some of the hydrogen atoms are substituted with a simple metal ion or a compound such as a metal oxide. Examples of the metal species constituting the metal ions or metal oxides include Ag, Cu, Fe, Ni, Co, Al, Ti, Zr, etc. Note that the metal species listed here are merely examples and are not limited to these metals.

[0047] In the above general formula (3), the organic group R is a hydrogen atom or an unsaturated hydrocarbon having an unsaturated bond between carbon atoms and having from 1 to 10 carbon atoms. The organic group R also includes a structure in which some of the hydrogen atoms are substituted with a compound such as a simple metal ion or a metal oxide. Examples of the metal species constituting the metal ions or metal oxides include Ag, Cu, Fe, Ni, Co, Al, Ti, Zr, etc. Note that the metal species listed here are merely examples and are not limited to these metals.

[0048] In the above general formula (4), the organic group R can be the same as that in the above general formula (3). In addition, in the above general formula (4), OR' is a side chain (pendant) hanging from the siloxane bond, and examples of the organic group R' include CH3 and C2H5.

[0049] Examples of the side chain type organosilica represented by the above general formula (4) include methyltriethoxysilane (MTES) and methyltrimethoxysilane (MTMS).

[0050] FIG. 6 is a schematic diagram showing an example of an inorganic material having a crosslinked structure of siloxane bonds, where (a) shows the structure of a bridged-type organosilica, and (b) shows the structure of a side-chain-type organosilica. As the active separation layer 9, it is preferable to use a gel in which the siloxane bond is replaced with a linking group X, as shown in FIG. 6(a). The linking group X is not particularly limited and can be appropriately selected depending on the type of gas to be separated, etc. Examples of the linking group X include an alkyl group having 1 to 8 carbon atoms and an aromatic group such as a phenyl group.

[0051] Inorganic materials composed of metal oxides such as zirconia, cobalt, nickel, aluminum, and iron include, for example, composites of precursors such as TEOS and metal nitrates. Among these, it is preferable to use cobalt or nickel from the viewpoint of water vapor resistance. Depending on the object to be separated and the separation environment, it can also be applied to the separation of hydrocarbon gases such as hydrogen and propane / propylene.

[0052] The average pore size of the active separation layer 9 is preferably 1 nm or less, more preferably 0.1 nm or more and 0.8 nm or less, and particularly preferably 0.2 nm or more and 0.6 nm or less.

[0053] The thickness of the active separation layer 9 is not particularly limited as long as it can selectively separate any component from the mixed gas. Examples of such a thickness include 50 nm to 300 nm, preferably 50 nm to 200 nm, and more preferably 50 nm to 100 nm.

[0054] <Membrane manufacturing method> The above-mentioned separation membrane can be produced, for example, as follows.

[0055] First, a porous alumina tube (average pore size: 1 μm, porosity: approximately 50%) is used as a support layer 7, and an intermediate layer 8 is formed on the surface of the support layer 7.

[0056] It is preferable to form the intermediate layer 8 after first homogenizing the surface of the support layer 7. The material used for homogenization is preferably fine particles of the same material as the porous substrate used as the support layer 7. For example, when alumina is used as the porous substrate, alumina fine particles of the same material are supported on the surface of the porous substrate and homogenized. The alumina fine particles can be supported on the porous substrate by using a sol of the same material as that used to form the intermediate layer 8 as a binder (for example, a sol obtained from organoalkoxysilane), dispersing the alumina fine particles in the binder, applying the binder to the surface of the porous substrate, and drying and firing the binder. It is preferable to homogenize the surface of the porous substrate by carrying out the above process multiple times, and in this case, it is preferable to gradually reduce the size of the alumina fine particles dispersed in the binder.

[0057] An intermediate layer 8 is formed on the homogenized support layer 7. The intermediate layer 8 may be formed by a hot coating method as described below. In the hot coating method, the porous substrate is heated in advance to about 170°C to 180°C, and a dilute solution of a sol obtained from an organoalkoxysilane is applied to the surface of the porous substrate, followed by baking to form the intermediate layer 8. Note that the above steps may be repeated multiple times to obtain an intermediate layer 8 of a desired thickness.

[0058] Next, the active separation layer 9 is formed on the surface of the intermediate layer 8. Specifically, the active separation layer 9 can be formed by condensation polymerization of organoalkoxysilane by the sol-gel method. First, hydrochloric acid or nitric acid is added as an acid to a 50°C ethanol solution in which the water / silica ratio has been adjusted, and the mixture is stirred for about one hour. Next, the obtained sol is applied onto the intermediate layer that has been preheated in advance to form a thin film, and sintered. After that, it is baked at 300°C under a nitrogen atmosphere to obtain a gel in which the siloxane bond is replaced with a linking group X (see FIG. 6).

[0059] (Membrane module) The membrane module using the above-mentioned separation membrane is not particularly limited, and examples thereof include a membrane module body in which a separation section having a separation membrane in an inner space is located, a raw material inlet section for introducing a mixed gas into the membrane module body, a permeated component outlet section for extracting components that permeate the separation section from the module body, and a non-permeated component outlet section for extracting components that do not permeate the separation section from the module body.

[0060] Specifically, one example of a membrane module using a separation membrane is not particularly limited, but is roughly configured to include a membrane module body 2, a separation unit 3, a raw material introduction section 4, a permeated component discharge section 5, and a non-permeated component discharge section 6, as shown in cross section in FIG. 3.

[0061] The membrane module body 2 is a cylindrical container having a sealed space 2A inside. The membrane module body 2 is provided with a raw material introduction section 4 at one end and a permeated component discharge section 5 at the other end. The membrane module body 2 also has a non-permeated component discharge section 6 in its cylindrical trunk. Furthermore, a separation unit 3 is located in the space 2A inside the membrane module body 2.

[0062] 3 and 4, the separation unit 3 extends in the axial direction of the membrane module main body 2 and is a hollow tubular member with a closed end on the raw material introduction section 4 side and an open end on the permeated component discharge section 5 side. The separation unit 3 has a separation section 3A and a support section 3B.

[0063] The separation section 3A is located near the end of the separation unit 3 on the side of the raw material introduction section 4. The separation section 3A also has a separation membrane 10 on a support layer 7 for separating a mixed gas.

[0064] The support layer 7 is a hollow tubular member that supports the separation membrane 10. By supporting the separation membrane 10 on the support layer 7, the mechanical strength of the separation section 3A can be increased.

[0065] The material of the support layer 7 is not particularly limited as long as it is a porous substrate that is permeable to the gas contained in the mixed gas. The porous substrate may be either an inorganic porous body or an organic porous body, and preferably has a strength sufficient for industrial use. In addition, in order to increase the permeability of the separation membrane 10, it is preferable that the pore size and porosity of the porous substrate are large. The average pore size of the porous substrate is preferably 0.05 μm or more and 10 μm or less, more preferably 0.1 μm or more and 5 μm or less, and particularly preferably 0.5 μm or more and 3 μm or less. If the pore size is too large, the difference with the pore size of the separation membrane becomes too large, and if the pore size is too small, the permeability decreases.

[0066] Examples of the porous substrate include ceramics made of alumina (α-Al2O3 (α-alumina), γ-Al2O3 (γ-alumina)), mullite, zirconia, titania, or composites of these. Among these, ceramics mainly composed of α-alumina are preferred because they are inexpensive, easily available, and have excellent chemical resistance, heat resistance, and strength.

[0067] The shape of the support layer 7 is not particularly limited, but is preferably cylindrical or plate-like. More specifically, the support layer 7 may be a porous alumina tube (average pore size: 1 μm, porosity: about 50%).

[0068] The support section 3B is a hollow tubular member. The space inside the support section 3B, together with the space inside the support layer 7 constituting the separation section 3A, serves as a flow path for the component (permeating gas) that permeates the separation section 3A.

[0069] The material of the support portion 3B is not particularly limited as long as it is impermeable to the gas contained in the mixed gas. Examples of such materials include a non-porous alumina tube and a Pyrex (registered trademark) glass tube. Among these, it is preferable to use a non-porous alumina tube in consideration of the pressure resistance at the operating pressure of the membrane separation device and use at extremely low temperatures.

[0070] In the separation unit 3, the separation part 3A and the support part 3B are fixed to each other with an intermediate material (not shown) sandwiched therebetween. The material of the intermediate material is not particularly limited as long as it reduces the difference in thermal expansion coefficient between the separation part (support layer 7) 3A and the support part 3B. An example of such a material is glass frit.

[0071] The shape of the separation unit 3 is not particularly limited as long as it has a cylindrical space inside, and can be appropriately selected depending on the area and application of the separation membrane 10. Examples of the shape of the separation unit 3 include a cylindrical shape and a square prism shape.

[0072] 3, the raw material introducing part 4 is located at one end of the membrane module main body 2. The raw material introducing part 4 is a gas component inlet for introducing a mixed gas into the inner space 2A of the membrane module main body 2.

[0073] The permeate component outlet 5 is located at the other end of the membrane module main body 2. The permeate component outlet 5 is a gas component outlet that outlets the component (permeate gas) that permeates through the separation section 3A of the separation unit 3 (i.e., the separation membrane 10) from the membrane module main body 2.

[0074] The permeate component discharge section 5 is connected in a sealed state to the open end of the separation unit 3, and communicates with the space inside the support section 3 that constitutes the separation unit 3. This allows the components (permeate gas) that permeate through the separation section 3A of the separation unit 3 to be discharged from the permeate component discharge section 5 to the outside of the membrane module body 2.

[0075] The non-permeated component discharge portion 6 is located in the trunk portion of the membrane module main body 2. The non-permeated component discharge portion 6 is a gas component discharge port that discharges components (non-permeated gases) that do not permeate the separation portion 3A of the separation unit 3 (i.e., the separation membrane 10) from the inner space 2A of the membrane module main body 2.

[0076] (Membrane separation device and membrane separation method) The membrane separation apparatus and the membrane separation method of the present invention using the above-mentioned separation membrane will be described in detail below.

[0077] <First membrane separation device and first membrane separation method> The first membrane separation method according to the present invention includes a step of membrane separating a mixed gas at a temperature of -196°C or more and 0°C or less, and optionally further includes a step of post-treating the obtained gas. The first membrane separation method is not particularly limited, and can be performed using the first membrane separation device according to the present invention. The first membrane separation device includes a thermostatic chamber that keeps the internal space at a temperature of -196°C or more and 0°C or less, and a separation membrane that is located in the internal space of the thermostatic chamber and separates the mixed gas by membrane separation.

[0078] The first membrane separation apparatus and the first membrane separation method are preferably used in the case where membrane separation is performed using a second gas in a mixed gas as the target gas, and the second gas has a larger permeability coefficient at room temperature (e.g., a temperature of 30°C) than the first gas but a lower concentration in the mixed gas, and are further preferably used in the case where the second gas has a larger permeability coefficient at room temperature (e.g., a temperature of 30°C) than the first gas but a lower concentration in the mixed gas of 50 mol% or less. In particular, when the separation membrane used is a separation membrane having a layer made of the above-mentioned hydrophobic material, the first membrane separation apparatus and the first membrane separation method are preferably used for membrane separation of a mixed gas containing oxygen as a first gas and helium having a lower concentration than oxygen as a second gas, and are more preferably used for membrane separation of a mixed gas containing oxygen as a first gas with a concentration of 50 mol % or more and helium as a second gas with a concentration of 50 mol % or less.

[0079] In general, when the concentration of the second gas having a large permeability coefficient at room temperature is low, it is difficult to obtain a driving force for the second gas to permeate to the permeation side when performing membrane separation of a mixed gas at room temperature. If the pressure on the secondary side (permeation side) of the separation membrane is lowered to maximize the driving force, the pressure of the obtained permeation component is lowered, so that the permeation component needs to be recompressed when it is recovered and filled into a container. However, when membrane separation is performed at a low temperature of -196°C or higher and 0°C or lower, a high-density layer of the first gas is formed in the pores of the separation membrane, so that the permeation tendency is reversed and the first gas has a larger permeation coefficient. Therefore, according to the first membrane separation device and the first membrane separation method, the second gas having a low concentration can be treated as a non-permeation component, and the first gas having a large driving force can be treated as a permeation component. Therefore, membrane separation can be performed with high separation efficiency without lowering the pressure on the secondary side (permeation side) of the separation membrane.

[0080] In the first membrane separation device and the first membrane separation method, since membrane separation is performed under conditions of -196°C or higher and 0°C or lower, it is preferable that the mixed gas does not contain components that solidify in the above temperature range, such as water and carbon dioxide. In particular, the mixed gas to be separated only needs to have a dew point of -50°C or lower, preferably -70°C or lower, and more preferably -100°C or lower.

[0081] In the first membrane separation method, membrane separation of the mixed gas is performed at a temperature of −196° C. or higher and 0° C. or lower, preferably −196° C. or higher and −30° C. or lower, more preferably −196° C. or higher and −50° C. or lower, and even more preferably −196° C. or higher and −100° C. or lower. When membrane separation is performed within the above-mentioned temperature range, the membrane separation can be performed with high separation efficiency with a permeation tendency different from that at room temperature.

[0082] In the first membrane separation method, the pressure of the mixed gas supplied to the separation membrane (i.e., the pressure on the primary side) is not particularly limited as long as the temperature is above the dew point so that the raw gas is not liquefied, but the pressure on the primary side of the membrane is preferably higher than atmospheric pressure and is preferably 2000 kPaG or less. If the pressure on the primary side is set to be equal to or higher than the above-mentioned lower limit, the driving force of membrane separation can be made sufficiently large. Also, if the pressure on the primary side is set to be equal to or lower than the above-mentioned upper limit, it is easy to ensure the pressure resistance strength of the equipment used in membrane separation.

[0083] Furthermore, in the first membrane separation method, the pressure on the secondary side is not particularly limited, but from the viewpoint of sufficiently increasing the driving force of the membrane separation, it is preferably 50 kPaG or less, more preferably 10 kPaG or less, and even more preferably 0 kPaG (atmospheric pressure).

[0084] In addition, from the viewpoint of making the driving force of membrane separation sufficiently large, the pressure on the secondary side (pressure of the permeating component) is preferably 0.01 to 1 times the pressure on the primary side (pressure of the gas to be separated by membrane).

[0085] Furthermore, the first membrane separation device equipped with a thermostatic chamber and a separation membrane is not particularly limited, and may be equipped with the separation membrane in the form of a membrane module, and may optionally further include a compressor for compressing the mixed gas, a pretreatment device for pretreating the mixed gas, a heat exchanger, etc.

[0086] Specifically, an example of the first membrane separation apparatus is generally configured to include a thermostatic bath 20, a membrane module 1, a heat exchanger 30, a raw material introduction path L1, a permeated component discharge path L2, and a non-permeated component discharge path L3, as shown in Fig. 2. This membrane separation apparatus 101 separates an arbitrary component from a mixed gas by membrane separation using the membrane module 1.

[0087] The thermostatic bath 20 can block heat from entering from the outside and can maintain a constant temperature inside the bath at a temperature between -196° C. and 0° C. The heat exchanger 30 and the membrane module 1 are disposed inside the space inside the thermostatic bath 20. The space inside the thermostatic bath 20 may also be provided with a temperature adjustment mechanism (not shown) such as a cooler. The temperature of the inner space of the thermostatic chamber 20 can be preferably −196° C. or higher and −30° C. or lower, more preferably −196° C. or higher and −50° C. or lower, and even more preferably −196° C. or higher and −100° C. or lower. If membrane separation is performed within the above-mentioned temperature range, it becomes possible to perform membrane separation with high separation efficiency with a permeation tendency different from that at room temperature.

[0088] The heat exchanger 30 is located in the thermostatic bath 20, and performs heat exchange between one or more hot fluids and one or more cold fluids, thereby cooling the hot fluids and heating the cold fluids. In the membrane separation device 101, the raw material introduction path L1 is a hot fluid, and the permeated component discharge path L2 and the non-permeated component discharge path L3 are cold fluids, and heat exchange is performed between them. That is, the heat exchanger 30 cools the mixed gas flowing through the raw material introduction path L1 to, for example, -196°C or higher and 0°C or lower. In addition, a hot fluid and a cold fluid (not shown) may also be circulated through the heat exchanger 30.

[0089] The membrane module 1 is located within a thermostatic chamber 20, and separates the introduced mixed gas into a component that permeates (hereinafter referred to as the "permeating component") and a component that does not permeate (hereinafter referred to as the "non-permeating component") by a separation section 3A having a separation membrane.

[0090] The raw material introduction path L1 is a flow path for introducing a mixed gas to be subjected to membrane separation into the membrane module 1. The raw material introduction path L1 is connected to the raw material introduction part 4 of the membrane module 1 (see FIG. 3).

[0091] In the raw material introduction path L1, a compressor 40 that compresses the mixed gas to a required pressure, a pretreatment device 50 that removes impurities such as moisture and hydrocarbons contained in the mixed gas, and a heat exchanger 30 are arranged in this order. That is, in the mixed gas supply path, the membrane module 1 is located on the secondary side of the heat exchanger 30. Thereby, the mixed gas from which impurities have been removed and whose temperature and pressure have been increased to the required temperature and pressure is introduced into the membrane module 1.

[0092] The permeate component discharge path L2 is a flow path that discharges, from the membrane module 1, a component that permeates through a separation section 3A having a separation membrane, out of the mixed gas introduced into the membrane module 1. The permeate component discharge path L2 is connected to a permeate component discharge section 5 of the membrane module 1 (see FIG. 3).

[0093] The non-permeated component discharge path L3 is a flow path that discharges, from the membrane module 1, a component of the raw gas that does not permeate through the separation section 3A having a separation membrane, out of the membrane module 1. The non-permeated component discharge path L3 is connected to the non-permeated component discharge section 6 of the membrane module 1 (see FIG. 3).

[0094] According to the membrane separation apparatus 101, a mixed gas introduced into the membrane module 1 is separated into a permeated component and a non-permeated component by a separation section 3A having a separation membrane, and each component is discharged from the membrane module 1. The permeated component and the non-permeated component discharged from the membrane module 1 can be recovered as products after cold energy is recovered by a heat exchanger 30.

[0095] Specifically, for example, by subjecting a mixed gas containing a first gas and a second gas having a permeability coefficient at room temperature (e.g., a temperature of 30°C) greater than that of the first gas to membrane separation in membrane separation device 101, a permeated component enriched in the first gas and a non-permeated component enriched in the second gas can be obtained.

[0096] <Second Membrane Separation Apparatus and Second Membrane Separation Method> The second membrane separation method according to the present invention includes a step of membrane separating a mixed gas at a temperature above 0°C, and optionally further includes a step of post-treating the obtained gas. The second membrane separation method is not particularly limited, and can be performed using the second membrane separation device according to the present invention. The second membrane separation device includes a thermostatic chamber that keeps the internal space above 0°C, and a separation membrane that is located in the internal space of the thermostatic chamber and separates the mixed gas by membrane separation.

[0097] The second membrane separation apparatus and the second membrane separation method are preferably used when membrane separation is performed using a second gas in a mixed gas as the target gas, and the second gas has a higher permeability coefficient at room temperature (e.g., a temperature of 30°C) than the first gas and a higher concentration in the mixed gas, and are even more preferably used when the second gas has a higher permeability coefficient at room temperature (e.g., a temperature of 30°C) than the first gas and a higher concentration in the mixed gas of 50 mol% or more. In particular, when the separation membrane used is a separation membrane having a layer made of the above-mentioned hydrophobic material, the second membrane separation apparatus and the second membrane separation method are preferably used for membrane separation of a mixed gas containing oxygen as a first gas and helium having a higher concentration than oxygen as a second gas, and are more preferably used for membrane separation of a mixed gas containing oxygen as a first gas with a concentration of 50 mol % or less and helium as a second gas with a concentration of 50 mol % or more.

[0098] According to the second membrane separation device and the second membrane separation method, the second gas, which has a high concentration and can provide a large driving force, can be used as the permeating component, so that membrane separation can be performed with high separation efficiency.

[0099] In the second membrane separation method, membrane separation of the mixed gas is performed at a temperature above 0° C., preferably above 0° C. and not higher than 500° C., more preferably from 10° C. to 400° C., and particularly preferably from 30° C. to 300° C. If the membrane separation is performed within the above-mentioned temperature range, the membrane separation can be performed with high separation efficiency.

[0100] In the second membrane separation method, the pressure of the mixed gas supplied to the separation membrane (i.e., the pressure on the primary side) is not particularly limited as long as it is at a temperature above the dew point so that the raw gas is not liquefied, but the pressure on the primary side of the membrane is preferably higher than atmospheric pressure and is preferably 2000 kPaG or less. If the pressure on the primary side is set to be equal to or higher than the above-mentioned lower limit, the driving force of membrane separation can be made sufficiently large. Also, if the pressure on the primary side is set to be equal to or lower than the above-mentioned upper limit, it is easy to ensure the pressure resistance strength of the equipment used in membrane separation.

[0101] Furthermore, in the second membrane separation method, the pressure on the secondary side is not particularly limited, but from the viewpoint of sufficiently increasing the driving force of the membrane separation, it is preferably 50 kPaG or less, more preferably 10 kPaG or less, and even more preferably 0 kPaG (atmospheric pressure).

[0102] In addition, from the viewpoint of making the driving force of membrane separation sufficiently large, the pressure on the secondary side (pressure of the permeating component) is preferably 0.01 to 1 times the pressure on the primary side (pressure of the gas to be separated by membrane).

[0103] The second membrane separation apparatus equipped with a thermostatic bath and a separation membrane is not particularly limited, and may be a membrane separation apparatus having the same configuration as the first membrane separation apparatus described above, except that a thermostatic bath capable of heating the inner space to above 0° C., preferably above 0° C. and below 500° C., more preferably from 10° C. to 400° C., and particularly preferably from 30° C. to 300° C., is used as the thermostatic bath. In the second membrane separation apparatus, the heat exchanger may cool or heat the mixed gas flowing through the raw material introduction path L1.

[0104] In the second membrane separation device, for example, a mixed gas containing a first gas and a second gas having a permeability coefficient at room temperature (e.g., a temperature of 30°C) greater than that of the first gas is subjected to membrane separation, thereby obtaining a permeated component enriched in the second gas and a non-permeated component enriched in the first gas.

[0105] <Third membrane separation device and third membrane separation method> In the third membrane separation apparatus and the third membrane separation method according to the present invention, membrane separation is performed multiple times on the mixed gas, and the mixed gas is separated in multiple stages. The third membrane separation method includes a first membrane separation step of membrane separating the membrane separated gas at a temperature of -196°C or higher and 0°C or lower, and a second membrane separation step of membrane separating the membrane separated gas at a temperature higher than 0°C, and optionally further includes a step of post-treating the obtained gas. The third membrane separation method is not particularly limited and can be performed using the third membrane separation apparatus according to the present invention. The third membrane separation apparatus includes a first thermostatic chamber that keeps the internal space at a temperature of -196°C or higher and 0°C or lower, a first membrane separation section including a first separation membrane located in the space of the first thermostatic chamber, a second thermostatic chamber that keeps the internal space at a temperature higher than 0°C, and a second membrane separation section including a second separation membrane located in the space of the second thermostatic chamber.

[0106] In the third membrane separation apparatus and the third membrane separation method, the number of times that the mixed gas undergoes membrane separation is not particularly limited as long as it is two or more times. In the third membrane separation method, the order in which the first membrane separation step and the second membrane separation step are performed is not particularly limited, and the first membrane separation step may be performed first, or the second membrane separation step may be performed first. Furthermore, in the third membrane separation apparatus, the first membrane separation section may be provided in the front stage of the second membrane separation section, or may be provided in the rear stage. The order in which the first membrane separation step and the second membrane separation step are performed, and the arrangement of the first membrane separation section and the second membrane separation section may be selected depending on the properties and concentration of the target gas contained in the mixed gas.

[0107] Specifically, the third membrane separation method in which the second membrane separation step is carried out after the first membrane separation step and the third membrane separation device in which the first membrane separation section is provided upstream of the second membrane separation section can be suitably used when membrane separation is carried out using a second gas in a mixed gas as the target gas, and the second gas has a higher permeability coefficient at room temperature (e.g., a temperature of 30°C) than the first gas but a lower concentration in the mixed gas, and can be even more suitably used when the second gas has a higher permeability coefficient at room temperature (e.g., a temperature of 30°C) than the first gas but a lower concentration in the mixed gas of 50 mol% or less. In particular, when the separation membrane used is a separation membrane having a layer made of the above-mentioned hydrophobic material, the third membrane separation method in which the second membrane separation step is carried out after the first membrane separation step and the third membrane separation device in which the first membrane separation section is provided upstream of the second membrane separation section are preferably used for membrane separation of a mixed gas containing oxygen as the first gas and helium having a lower concentration than oxygen as the second gas, and more preferably used for membrane separation of a mixed gas containing oxygen as the first gas at a concentration of 50 mol % or more and helium as the second gas at a concentration of 50 mol % or less.

[0108] In general, when the concentration of the second gas having a large permeability coefficient at room temperature is low, it is difficult to obtain a driving force for the second gas to permeate to the permeation side when the membrane separation of the mixed gas is performed at room temperature, and if the pressure on the secondary side (permeation side) of the separation membrane is lowered to maximize the driving force, the pressure of the obtained permeation component is lowered, so that the permeation component needs to be recompressed when it is recovered and filled into a container. However, when membrane separation is performed at a low temperature of -196°C or higher and 0°C or lower, the permeation tendency may be reversed, so if membrane separation of the mixed gas as the membrane separation gas is performed first in the first membrane separation step or the first membrane separation section, the second gas having a low concentration can be made the non-permeation component, and the first gas having a large driving force can be made the permeation component. Then, if the non-permeation component enriched in the second gas is used as the membrane separation gas and membrane separation is performed in the second membrane separation step or the second membrane separation section, the second gas having a high concentration and having a large driving force can be made the permeation component. Therefore, membrane separation can be performed with high separation efficiency.

[0109] Furthermore, a third membrane separation method in which the first membrane separation step is carried out after the second membrane separation step, and a third membrane separation device in which the second membrane separation section is provided upstream of the first membrane separation section, can be suitably used when membrane separation is carried out using a first gas in a mixed gas as the target gas, and the second gas has a higher permeability coefficient at room temperature (e.g., a temperature of 30°C) than the first gas and a higher concentration in the mixed gas, and can be even more suitably used when the second gas has a higher permeability coefficient at room temperature (e.g., a temperature of 30°C) than the first gas and a higher concentration in the mixed gas of 50 mol% or more. In particular, when the separation membrane used is a separation membrane having a layer made of the above-mentioned hydrophobic material, the third membrane separation method in which the first membrane separation step is carried out after the second membrane separation step and the third membrane separation device in which the second membrane separation section is provided upstream of the first membrane separation section are preferably used for membrane separation of a mixed gas containing oxygen as the first gas and helium having a higher concentration than oxygen as the second gas, and more preferably used for membrane separation of a mixed gas containing oxygen as the first gas at a concentration of 50 mol % or less and helium as the second gas at a concentration of 50 mol % or more.

[0110] If membrane separation of the mixed gas as the membrane separation gas is first performed in the second membrane separation step and the second membrane separation section, where membrane separation is performed at a temperature above 0°C, the second gas, which is highly concentrated and can provide a large driving force, can be used as the permeating component, and membrane separation can be performed with high separation efficiency. If membrane separation is then performed in the first membrane separation step or the first membrane separation section using the non-permeating component enriched in the first gas as the membrane separation gas, the first gas, which is highly concentrated and can provide a large driving force, can be used as the permeating component. Therefore, membrane separation can be performed with high separation efficiency.

[0111] In the first membrane separation step and the first membrane separation section of the third membrane separation method, the membrane separation is performed under conditions of -196°C or higher and 0°C or lower, so it is preferable that the membrane separation gas does not contain components that solidify in the above temperature range, such as water and carbon dioxide. In particular, the moisture content in the membrane separation gas to be separated may be such that its dew point is -50°C or lower, preferably -70°C or lower, and more preferably -100°C or lower.

[0112] In the first membrane separation step, the membrane separation of the membrane separation gas is carried out at a temperature of −196° C. or higher and 0° C. or lower, preferably −196° C. or higher and −30° C. or lower, more preferably −196° C. or higher and −50° C. or lower, and further preferably −196° C. or higher and −100° C. If the membrane separation is carried out within the above-mentioned temperature range, the membrane separation can be carried out with high separation efficiency with a permeation tendency different from that at room temperature.

[0113] In the second membrane separation step, the membrane separation of the membrane separation gas is carried out at a temperature higher than 0° C., preferably higher than 0° C. and not higher than 500° C., more preferably from 10° C. to 400° C., and particularly preferably from 30° C. to 300° C. If the membrane separation is carried out within the above-mentioned temperature range, the membrane separation can be carried out with high separation efficiency.

[0114] In the first and second membrane separation steps, the pressure of the membrane separation gas supplied to the separation membrane (i.e., the pressure on the primary side) is not particularly limited as long as it is at a temperature above the dew point so that the raw gas does not liquefy, but the pressure on the primary side of the membrane is preferably higher than atmospheric pressure, and is preferably 2000 kPaG or less. If the pressure on the primary side is set to be equal to or higher than the above-mentioned lower limit, the driving force of the membrane separation can be made sufficiently large. Also, if the pressure on the primary side is set to be equal to or lower than the above-mentioned upper limit, it is easy to ensure the pressure resistance strength of the equipment used in the membrane separation.

[0115] Furthermore, in the first membrane separation process and the second membrane separation process, the pressure on the secondary side is not particularly limited, but from the viewpoint of sufficiently increasing the driving force of the membrane separation, it is preferably 50 kPaG or less, more preferably 10 kPaG or less, and even more preferably 0 kPaG (atmospheric pressure).

[0116] In addition, from the viewpoint of making the driving force of membrane separation sufficiently large, the pressure on the secondary side (pressure of the permeating component) is preferably 0.01 to 1 times the pressure on the primary side (pressure of the gas to be separated by membrane).

[0117] In addition, in the third membrane separation device, the first membrane separation section and the second membrane separation section each equipped with a thermostatic bath and a separation membrane are not particularly limited, and may be equipped with a separation membrane in the form of a membrane module, and may optionally further include a compressor for compressing the mixed gas, a pretreatment device for pretreating the mixed gas, a heat exchanger, etc.

[0118] Specifically, in one example of the third membrane separation device, as shown in FIG. 1, a first membrane separation section 102 is provided upstream of a second membrane separation section 103, and non-permeated components produced when the mixed gas is membrane-separated in the first membrane separation section 102 are membrane-separated in the second membrane separation section 103.

[0119] 1 is roughly configured to include a first constant temperature bath 21, a first membrane module 1A, a first compressor 41, a first heat exchanger 51, a raw material introduction path L4, a first permeated component discharge path L6, and a first non-permeated component discharge path L5. This first membrane separation section 102 separates an arbitrary component from the mixed gas by membrane separation using the first membrane module 1A.

[0120] The first constant temperature bath 21 can block heat from entering from the outside and can maintain a constant temperature inside the bath at a temperature between -196°C and 0°C. A first heat exchanger 51 and a first membrane module 1A are disposed in the space inside the first constant temperature bath 21. A temperature adjustment mechanism (not shown) such as a cooler may also be provided in the space inside the first constant temperature bath 21. The first thermostatic chamber 21 can have an inner space preferably at −196° C. to −30° C., more preferably at −196° C. to −50° C., and even more preferably at −196° C. to −100° C. If membrane separation is performed within the above-mentioned temperature range, it becomes possible to perform membrane separation with high separation efficiency with a permeation tendency different from that at room temperature.

[0121] The first heat exchanger 51 is located in the first thermostatic bath 21, and exchanges heat between one or more hot fluids and one or more cold fluids, thereby cooling the hot fluids and heating the cold fluids. In the first membrane separation section 102, heat exchange is performed between the raw material introduction path L4 as a hot fluid and the first permeated component discharge path L6 and the second non-permeated component discharge path L8 of the second membrane separation section 103 described later as cold fluids. That is, the first heat exchanger 51 cools the mixed gas flowing through the raw material introduction path L4 to, for example, -196°C or higher and 0°C or lower. The first heat exchanger 51 may be provided with a heat medium path L9 for further circulating a hot or cold fluid.

[0122] The first membrane module 1 is located within the first thermostatic bath 21, and separates the introduced mixed gas into a component that permeates (hereinafter referred to as the "permeating component") and a component that does not permeate (hereinafter referred to as the "non-permeating component") by a separation section having a separation membrane.

[0123] The raw material introduction path L4 is a flow path for introducing the mixed gas to be subjected to membrane separation into the first membrane module 1A. The raw material introduction path L4 is connected to the raw material introduction part of the first membrane module 1 (see FIG. 3).

[0124] In the raw material introduction path L4, a first heat exchanger 51 and a first compressor 41 that compresses the mixed gas to a required pressure are arranged in this order. That is, in the mixed gas supply path, the first membrane module 1A is located on the secondary side of the first heat exchanger 51 and the first compressor 41. As a result, the mixed gas that has been heated and pressurized to the required temperature and pressure is introduced into the first membrane module 1A.

[0125] The first permeate discharge path L6 is a flow path that discharges, from the first membrane module 1A, a component that permeates through a separation section having a separation membrane, out of the mixed gas introduced into the first membrane module 1A. The first permeate discharge path L6 is connected to the permeate discharge section of the first membrane module 1A (see FIG. 3).

[0126] The first non-permeating component discharge path L5 is a flow path that discharges, from the first membrane module 1A, a component of the raw material gas that does not permeate through a separation section having a separation membrane. One end of the first non-permeating component discharge path L5 is connected to the non-permeating component discharge section of the first membrane module 1A (see FIG. 3), and the other end is connected to the second membrane separation section 103.

[0127] 1 is roughly configured to include a second constant temperature bath 22, a second membrane module 1B, a second compressor 42, a second heat exchanger 52, a first non-permeated component outlet path L5, a second permeated component outlet path L7, and a second non-permeated component outlet path L8. This second membrane separation section 103 separates an arbitrary component from the non-permeated component obtained in the first membrane separation section 102 by membrane separation using the second membrane module 1B.

[0128] The second constant temperature bath 22 can block heat intrusion from the outside and can maintain a constant temperature so that the temperature of the inner space can be above 0° C. A second heat exchanger 52 and a second membrane module 1B are disposed in the inner space of the second constant temperature bath 22. A temperature adjustment mechanism (not shown) such as a cooler may also be provided in the inner space of the second constant temperature bath 22. The second constant temperature bath 22 can have an inner space preferably heated to a temperature higher than 0°C and not higher than 500°C, more preferably 10°C or higher and not higher than 400°C, and particularly preferably 30°C or higher and not higher than 300°C.

[0129] The second heat exchanger 52 is located in the second thermostatic bath 22, and performs heat exchange between one or more hot fluids and one or more cold fluids, thereby cooling the hot fluids and heating the cold fluids. In the second membrane separation section 103, the first non-permeated component discharge path L5 serves as a cold fluid, and the second non-permeated component discharge path L8 serves as a hot fluid, and performs heat exchange between them. That is, the second heat exchanger 52 heats the membrane-separated gas (the non-permeated component obtained in the first membrane separation section 102) flowing through the first non-permeated component discharge path L5, for example, to a temperature above 0°C. Note that a hot fluid and a cold fluid (not shown) may also be circulated through the second heat exchanger 52.

[0130] The second membrane module 1B is located within the second thermostatic bath 22, and separates the introduced membrane separation gas into a component that permeates (hereinafter referred to as the "permeating component") and a component that does not permeate (hereinafter referred to as the "non-permeating component") by a separation section having a separation membrane.

[0131] The first non-permeated component discharge path L5 is a flow path for introducing the membrane-separated gas to be separated into the second membrane module 1B. The first non-permeated component discharge path L5 is connected to the raw material introduction part of the second membrane module 1B (see FIG. 3).

[0132] In the first non-permeating component discharge path L5, a second compressor 42 and a second heat exchanger 52 that compress the membrane separated gas to a required pressure are arranged in this order. That is, in the supply path of the membrane separated gas, the second membrane module 1B is located on the secondary side of the second compressor 42 and the second heat exchanger 52. As a result, the membrane separated gas that has been heated and pressurized to the required temperature and pressure is introduced into the second membrane module 1B.

[0133] The second permeate discharge path L7 is a flow path for discharging, from the second membrane module 1B, a component that permeates through a separation section having a separation membrane, out of the membrane separated gas introduced into the second membrane module 1B. The second permeate discharge path L7 is connected to the permeate discharge section of the second membrane module 1B (see FIG. 3).

[0134] The second non-permeated component discharge path L8 is a flow path for discharging, from the second membrane module 1B, a component that does not permeate through a separation section having a separation membrane, out of the membrane-separated gas introduced into the second membrane module 1B. The second non-permeated component discharge path L8 is connected to the non-permeated component discharge section of the second membrane module 1B (see FIG. 3).

[0135] According to the membrane separation apparatus 200, the mixed gas introduced into the first membrane module 1A of the first membrane separation section 102 is separated into a permeated component and a non-permeated component by a separation section having a separation membrane, and each component is discharged from the first membrane module 1A. The permeated component discharged from the first membrane module 1A can be recovered cold energy by the first heat exchanger 51, and then introduced again into the first membrane module 1A together with the mixed gas.

[0136] In the membrane separation apparatus 200, the non-permeated component (membrane-separated gas) discharged from the first membrane module 1A of the first membrane separation section 102 is pressurized by the compressor 42 of the second membrane separation section 103, heated by the second heat exchanger 52, and introduced into the second membrane module 1B of the second membrane separation section 103. The membrane-separated gas is then separated into a permeated component and a non-permeated component by a separation section having a separation membrane, and each component is discharged from the second membrane module 1B. The non-permeated component discharged from the second membrane module 1B may have hot heat recovered by the second heat exchanger 52, and then have cold heat recovered by the first heat exchanger 51, and then be introduced again into the first membrane module 1A together with the mixed gas.

[0137] Specifically, for example, by subjecting a mixed gas containing a first gas and a second gas having a permeability coefficient at room temperature (e.g., a temperature of 30°C) greater than that of the first gas to membrane separation in the membrane separation device 200, a permeated component enriched in the first gas and a non-permeated component enriched in the second gas can be obtained in the first membrane separation section 102. Moreover, in the second membrane separation section 103, a permeated component further enriched in the second gas can be obtained. Furthermore, in the membrane separation device 200, heat is recovered from the first permeated component discharge path L6 and the second non-permeated component discharge path L8, and the first permeated component and the second non-permeated component are reused as raw gas, thereby making it possible to perform membrane separation more efficiently.

[0138] In the above example, a membrane separation device 200 was described in which the first membrane separation section 102 is provided upstream of the second membrane separation section 103, but the third membrane separation device may also be one in which the second membrane separation section 103 is provided upstream of the first membrane separation section 102. EXAMPLES

[0139] The present invention will be described in more detail below using reference examples, but the present invention is not limited to the following descriptions.

[0140] <Reference example> A separation membrane was prepared as follows, and its permeability coefficient was measured at room temperature (30° C.) and at a low temperature (−115° C.).

[0141] [Support layer] -Porous alumina tube (average pore size: 1 μm, porosity: approx. 50%) [Middle layer] - Hydrophobic material is supported by gel using BTESE (average pore size: 10-20 nm) -Manufacturing method and conditions- -Adjust the ratio of BTESE:H2O:HCl:=1:240:0.1 in ethanol solvent. The mixture was stirred at 50℃ for 60 minutes to cause hydrolysis and condensation reactions to prepare a BTESE sol. -Film forming- Two types of α-alumina particles were coated on the surface of an α-alumina porous tube (average pore size: coarse: 1.2 μm, fine: 0.5 μm). BTESE gel was applied several times on top of the particles by hot coating and sintered at 300°C for 30 min in a nitrogen atmosphere. This process was repeated several times. [Active separation layer] · Supports sol using BTESM (average pore size: 0.7-1.2 nm) -Manufacturing method and conditions- -Adjusted to BTESM:H2O:HCl:=1:200:0.1 in ethanol solvent. The mixture was stirred at 50℃ for 60 minutes to cause hydrolysis and condensation reactions to prepare a BTESM sol. -Film forming- The BTESM gel was applied to the intermediate layer several times by hot coating, and then baked at 300°C for 30 min in a nitrogen atmosphere. This process was repeated several times.

[0142] (Measurement of the transmission coefficient) The oxygen and helium permeability coefficients of the separation membrane were measured under the following conditions. The results are shown in Table 1. Gas type: Oxygen (O2) and helium (He) mixture (He concentration: 50 mol%) Gas temperature: -115℃, 30℃ · Primary membrane pressure: 300 (kPaG) Secondary membrane pressure: Atmospheric pressure Flow rate through the membrane: 1 (L / min) External surface area of ​​membrane: 3.14×10 -3 (m 2 )

[0143] [Table 1]

[0144] From Table 1, it can be seen that the gas permeation tendency is different at room temperature (30°C) and at low temperature (-115°C). [Industrial Applicability]

[0145] According to the present invention, it is possible to perform membrane separation of a target gas contained in a raw material gas with high separation efficiency. [Explanation of symbols]

[0146] 1...Membrane module 1A…First membrane module 1B…Second membrane module 2…Membrane module body 2A…Space 3…Separation unit 3A…Separation part 3B…Support part 4...Raw material introduction section 5...Transmission component derivation section 6...Non-transparent component derivation section 7…Support layer 8. Middle class 9…Active separation layer 10...Separation membrane 20…Thermostatic oven 21...1st constant temperature bath 22...Second temperature chamber 30...Heat exchanger 40…Compressor 41…First compressor 42…Second compressor 50...Pretreatment device 51...First heat exchanger 52…Second heat exchanger 101...Membrane separation device 102...First membrane separation section 103…Second membrane separation section 200...Membrane separation equipment L1: Raw material introduction route L2: Transmission component derivation route L3: Non-transmitting component derivation route L4: Raw material introduction route L5: First non-transmitted component derivation path L6…first transmission component derivation path L7: Second transmitted component derivation path L8: Second non-transmitted component derivation route

Claims

1. A membrane separation apparatus for performing membrane separation of a mixed gas containing a first gas and a second gas, A thermostatic chamber that maintains the internal space at a temperature between -196°C and 0°C; A separation membrane located in the space for membrane separation of the mixed gas; A membrane separation device comprising:

2. A membrane separation apparatus for performing membrane separation of a mixed gas containing a first gas and a second gas, A thermostatic chamber that keeps the internal space above 0°C; A separation membrane located in the space for membrane separation of the mixed gas; A membrane separation device comprising:

3. A membrane separation apparatus that performs membrane separation of a mixed gas containing a first gas and a second gas in multiple stages, A first membrane separation unit including a first thermostatic chamber that maintains an internal space at a temperature of −196° C. or higher and 0° C. or lower, and a first separation membrane located in the space of the first thermostatic chamber; A second membrane separation unit including a second thermostatic chamber that sets the internal space at a temperature higher than 0° C. and a second separation membrane located in the space of the second thermostatic chamber; A membrane separation device comprising:

4. 3. The membrane separation device according to claim 1, wherein the separation membrane has a layer made of a hydrophobic material.

5. The membrane separation apparatus according to claim 3 , wherein the first separation membrane and the second separation membrane each have a layer made of a hydrophobic material.

6. 4. The membrane separation device according to claim 1, wherein the first gas is oxygen, and the second gas is a rare gas or hydrogen.

7. A membrane separation method for separating a mixed gas containing a first gas and a second gas, comprising: The membrane separation method includes a step of subjecting the mixed gas to membrane separation at a temperature of −196° C. or higher and 0° C. or lower.

8. A membrane separation method for performing membrane separation on a mixed gas containing a first gas and a second gas, comprising: The method for membrane separation comprises a step of subjecting the mixed gas to membrane separation at a temperature above 0°C.

9. A membrane separation method for performing membrane separation on a mixed gas containing a first gas and a second gas in multiple stages, comprising: A first membrane separation step of subjecting the membrane separation gas to membrane separation at a temperature of −196° C. or higher and 0° C. or lower; A second membrane separation step of membrane separating the membrane separated gas at a temperature higher than 0°C; The membrane separation method comprising:

10. The membrane separation method according to any one of claims 7 to 9, wherein the first gas is oxygen, and the second gas is a rare gas or hydrogen.

11. The membrane separation method according to any one of claims 7 to 9, wherein the membrane separation is carried out using a separation membrane having a layer made of a hydrophobic material.

12. The membrane separation method according to any one of claims 7 to 9, wherein the membrane separation is carried out so that the pressure of the permeating component is 0.01 to 1 times the pressure of the gas to be separated by the membrane.

Images