Gas separation system and method for separating mixed gas

Abstract

The present invention provides a gas separation system suitable for efficiently separating a mixed gas. A gas separation system 100 according to the present invention is provided with: a separation membrane unit 10 for separating a mixed gas 70 into a permeation gas 80 and a non-permeation gas 81; and a sweep gas supply path 36 for supplying a part of the non-permeation gas 81 as a sweep gas 75 to a permeation space of the separation membrane unit 10. The gas separation system 100 recovers a recovery gas 85, which contains the permeation gas 80 and the sweep gas 75.

Description

Gas separation system and method for separating mixed gases

[0001] The present invention relates to a gas separation system and a method for separating a mixed gas.

[0002] In chemical plants that manufacture chemical products, mixed gases containing, for example, carbon dioxide and hydrogen are emitted. From the perspective of environmental regulations and the effective use of resources, it is desirable to separate and recover each component of the mixed gas.

[0003] Membrane separation has been developed as a method for separating individual components from mixed gases. Compared to absorption methods, which separate specific components in mixed gases by absorbing them into an absorbent, membrane separation methods can efficiently separate individual components while reducing operating costs.

[0004] In membrane separation, the driving force is the partial pressure difference between the components to be separated in the supply space and the permeation space of the separation membrane unit. Methods for increasing this partial pressure difference include supplying a pressurized mixed gas to the supply space (pressurization method), depressurizing the permeation space (depressurization method), and supplying a sweep gas with a low content of the components to be separated to the permeation space (sweep method). Patent Document 1 discloses a membrane separation method using the sweep method.

[0005] Special Publication No. 2015-536814

[0006] The sweep method is suitable for improving the recovery rate of the components to be separated without significantly increasing the membrane area of ​​the separation membrane provided in the separation membrane unit. However, according to the studies of the present inventors, there is room for further improvement in the conventional sweep method from the viewpoint of efficiently separating mixed gases.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a gas separation system suitable for efficiently separating mixed gases.

[0008] The present invention provides a gas separation system comprising: a separation membrane unit that separates a mixed gas into a permeate gas and a non-permeate gas; and a sweep gas supply path for supplying a portion of the non-permeate gas as a sweep gas to a permeate space of the separation membrane unit; and recovering a recovered gas containing the permeate gas and the sweep gas.

[0009] The present invention further provides a method for separating a mixed gas, comprising: supplying a mixed gas to a separation membrane unit and separating the mixed gas into a permeate gas and a non-permeate gas; supplying a portion of the non-permeate gas as a sweep gas to a permeate space of the separation membrane unit; and recovering a recovered gas containing the permeate gas and the sweep gas.

[0010] According to the present invention, a gas separation system suitable for efficiently separating mixed gases can be provided.

[0011] 1 is a schematic configuration diagram of a gas separation system according to one embodiment of the present invention; FIG. 2 is a schematic cross-sectional view showing an example of a separation membrane unit; FIG. 3 is a cross-sectional view showing an example of a separation membrane; FIG. 4 is a cross-sectional view showing an example of another separation membrane; FIG. 5 is a schematic cross-sectional view showing an example of a separation membrane unit; and FIG. 6 is a schematic configuration diagram for explaining a conventional gas separation system.

[0012] A gas separation system according to a first aspect of the present invention comprises: a separation membrane unit that separates a mixed gas into a permeate gas and a non-permeate gas; and a sweep gas supply path for supplying a portion of the non-permeate gas as a sweep gas to a permeate space of the separation membrane unit; and recovers a recovery gas containing the permeate gas and the sweep gas.

[0013] In a second aspect of the present invention, for example, in the gas separation system according to the first aspect, the flow rate (m 3 / h) to the flow rate (m 3 / h) is 6.0% or more.

[0014] In a third aspect of the present invention, for example, in the gas separation system according to the first or second aspect, the flow rate (m 3 / h) to the flow rate (m 3 / h) is 19% or more.

[0015] In a fourth aspect of the present invention, for example, in the gas separation system according to any one of the first to third aspects, the mixed gas contains gas A, and the permeable gas has a higher content of gas A than the non-permeable gas.

[0016] In a fifth aspect of the present invention, for example, in the gas separation system according to the fourth aspect, the content of the gas A in the mixed gas is 30 vol % or less.

[0017] In a sixth aspect of the present invention, for example, in the gas separation system according to the fourth or fifth aspect, the recovery rate of the gas A by the recovered gas is 70% or more.

[0018] In a seventh aspect of the present invention, for example, in the gas separation system according to any one of the fourth to sixth aspects, the gas A is carbon dioxide or hydrogen.

[0019] In an eighth aspect of the present invention, for example, in the gas separation system according to any one of the first to seventh aspects, the content of water vapor in the recovered gas is 1 vol % or less.

[0020] In a ninth aspect of the present invention, for example, the gas separation system according to any one of the first to eighth aspects further comprises an exhaust path connected to the separation membrane unit for exhausting the non-permeate gas from the separation membrane unit, and the sweep gas supply path branches off from the exhaust path.

[0021] In a tenth aspect of the present invention, for example, the gas separation system according to any one of the first to ninth aspects further comprises a recovery section that recovers the recovered gas, and a recovery path that is connected to the separation membrane unit and the recovery section and that sends the recovered gas to the recovery section.

[0022] In an eleventh aspect of the present invention, for example, a gas separation system according to any one of the first to tenth aspects further includes a mixed gas supply path connected to the separation membrane unit for supplying the mixed gas to the separation membrane unit, and a pressure device for pressurizing the mixed gas is disposed in the mixed gas supply path.

[0023] In a twelfth aspect of the present invention, for example, in the gas separation system according to any one of the first to eleventh aspects, the separation membrane unit includes a separation membrane, and the separation membrane has a separation functional layer containing a polyether block amide resin or an ionic liquid.

[0024] A mixed gas separation method according to a thirteenth aspect of the present invention includes: supplying a mixed gas to a separation membrane unit and separating the mixed gas into a permeate gas and a non-permeate gas; supplying a portion of the non-permeate gas as a sweep gas to a permeate space of the separation membrane unit; and recovering a recovery gas containing the permeate gas and the sweep gas.

[0025] The present invention will be described in detail below, but the following description is not intended to limit the present invention to a specific embodiment.

[0026] 1, a gas separation system 100 of this embodiment includes a separation membrane unit 10 and a sweep gas supply path 36. The separation membrane unit 10 has a separation membrane 11 and is a membrane separation device that performs membrane separation on a mixed gas using the separation membrane 11. The separation membrane 11 allows the mixed gas to be separated into a permeate gas and a non-permeate gas.

[0027] The sweep gas supply path 36 is a path for supplying a portion of the non-permeable gas (specifically, the non-permeable gas discharged from the separation membrane unit 10) as a sweep gas to the permeate space of the separation membrane unit 10. Specifically, the sweep gas supply path 36 is connected to the sweep gas inlet (inlet 14 a) of the separation membrane unit 10.

[0028] As described above, in the gas separation system 100, a portion of the non-permeate gas is used as a sweep gas through the sweep gas supply path 36. With this configuration, by recovering a recovery gas containing the permeate gas and the sweep gas, it is possible to easily improve the recovery rate of the components to be separated contained in the mixed gas without significantly increasing the membrane area of ​​the separation membrane 11. In this way, the gas separation system 100 of this embodiment is suitable for efficiently separating mixed gases.

[0029] In this embodiment, the mixed gas contains gas A as a component to be separated. Specifically, the mixed gas contains gas A and gas B different from gas A. Gas A is preferably carbon dioxide or hydrogen. In one preferred embodiment, the mixed gas contains carbon dioxide as gas A and nitrogen as gas B. In another preferred embodiment, the mixed gas contains hydrogen as gas A and methane as gas B.

[0030] The separation membrane 11 included in the separation membrane unit 10 allows gas A contained in the mixed gas to permeate preferentially. Therefore, the permeable gas separated by the separation membrane 11 has a higher content of gas A than the mixed gas and a lower content of gas B than the mixed gas. On the other hand, the non-permeable gas has a lower content of gas A than the mixed gas and a higher content of gas B than the mixed gas.

[0031] The gas separation system 100 may further include a mixed gas supply path 30. The mixed gas supply path 30 is connected to the mixed gas inlet (inlet 13a) of the separation membrane unit 10 and is a path for supplying the mixed gas to the separation membrane unit 10 from a tank (not shown) or the like that stores the mixed gas. The mixed gas supply path 30 may be directly connected to a mixed gas generation source, or may be configured to continuously supply the mixed gas from the generation source to the separation membrane unit 10. A pressure device 40 that pressurizes the mixed gas may be disposed in the mixed gas supply path 30. Examples of the pressure device 40 include a compressor, a blower, and a back pressure valve. The pressure device 40 can pressurize the supply space of the separation membrane unit 10 by pressurizing the mixed gas.

[0032] A heat exchanger (not shown) may be disposed in the mixed gas supply path 30 between the pressurizing device 40 and the separation membrane unit 10. The heat exchanger can, for example, cool the mixed gas pressurized by the pressurizing device 40. The heat exchanger is, for example, a gas-liquid heat exchanger that causes heat exchange between a cooling medium such as antifreeze and the mixed gas, and may typically be a fin-tube heat exchanger.

[0033] The gas separation system 100 may further include a discharge path 32. The discharge path 32 is connected to the non-permeate gas outlet (outlet 13b) of the separation membrane unit 10 and is a path for discharging the non-permeate gas from the separation membrane unit 10. The discharge path 32 may be formed with an opening (discharge port 44) for discharging the non-permeate gas from the discharge path 32. In the gas separation system 100, the non-permeate gas that is not used as the sweep gas may be discarded without being recovered through the discharge port 44. However, the discharge path 32 may be connected to a recovery section (not shown), and the non-permeate gas may be recovered in the recovery section. A specific example of this recovery section is a tank that can store the non-permeate gas.

[0034] The sweep gas supply path 36 preferably branches off from the discharge path 32 at a branch position 42. In this case, at the branch position 42, a portion of the non-permeate gas is sent to the sweep gas supply path 36 as a sweep gas. A three-way valve capable of adjusting the flow rate of the non-permeate gas (sweep gas) sent to the sweep gas supply path 36 may be disposed at the branch position 42. The sweep gas supply path 36 does not have to branch off from the discharge path 32. As an example, if the gas separation system 100 includes a recovery unit that recovers the non-permeate gas, the sweep gas supply path 36 may be connected to the recovery unit.

[0035] A pressure reducing device and a heat exchanger (not shown) may be disposed in the discharge path 32. The pressure reducing device may be located between the separation membrane unit 10 and the branching position 42, or between the branching position 42 and the discharge port 44. The pressure reducing device can reduce the pressure of the non-permeate gas to atmospheric pressure in the external environment (e.g., 101 kPa). Examples of pressure reducing devices include a pressure reducing valve. The heat exchanger is preferably located between the pressure reducing device and the discharge port 44. The heat exchanger can heat the non-permeate gas reduced in pressure by the pressure reducing device. The heat exchanger is, for example, a gas-liquid heat exchanger that causes heat exchange between a heat medium such as hot water and the non-permeate gas, and may typically be a fin-tube heat exchanger.

[0036] The gas separation system 100 may further include a recovery path 34 and a recovery section 20. The recovery path 34 is connected to the recovered gas outlet (outlet 14b) of the separation membrane unit 10 and the inlet of the recovery section 20, and is a path for sending the recovered gas from the separation membrane unit 10 to the recovery section 20. The recovery section 20 can recover the recovered gas sent from the separation membrane unit 10 and store the recovered gas. A specific example of the recovery section 20 is a tank that can store the recovered gas.

[0037] Unless otherwise specified, each of the paths of the gas separation system 100 is made up of, for example, metal or resin piping.

[0038] Gas separation system 100 may further include a controller (not shown) that controls each component of gas separation system 100. The controller is, for example, a DSP (Digital Signal Processor) that includes an A / D conversion circuit, an input / output circuit, an arithmetic circuit, a storage device, etc. The controller stores a program for appropriately operating gas separation system 100.

[0039] The gas separation system 100 of this embodiment is, for example, a continuous system. In this specification, a continuous system refers to a system that can continuously process a mixed gas without closing the paths that make up the gas separation system 100 using an on-off valve or the like. In this way, the gas separation system 100 of this embodiment is capable of continuous operation. The gas separation system 100 that functions as a continuous system is suitable for applications in which a mixed gas is continuously supplied, treatment of exhaust gas, and the like.

[0040] [Separation Membrane Unit] As shown in Fig. 2, the separation membrane unit 10 includes a separation membrane 11 and a tank 12. The tank 12 has a first chamber 13 and a second chamber 14. The space within the first chamber 13 corresponds to the supply space, and the space within the second chamber 14 corresponds to the permeation space. The separation membrane 11 is disposed inside the tank 12. Inside the tank 12, the separation membrane 11 separates the first chamber 13 and the second chamber 14. The separation membrane 11 extends from one to the other of a pair of wall surfaces of the tank 12.

[0041] The first chamber 13 has an inlet 13a and an outlet 13b, and the second chamber 14 has an inlet 14a and an outlet 14b. The inlet 13a of the first chamber 13 is an opening for supplying the mixed gas 70 to the separation membrane unit 10. The outlet 13b of the first chamber 13 is an opening for discharging the mixed gas 70 (non-permeate gas 81) that has not permeated the separation membrane 11 from the separation membrane unit 10. The inlet 14a of the second chamber 14 is an opening for supplying a sweep gas 75 to the separation membrane unit 10. The outlet 14b of the second chamber 14 is an opening for discharging a recovered gas 85 containing the sweep gas 75 and the permeate gas 80 obtained by permeating the mixed gas 70 through the separation membrane 11 from the separation membrane unit 10. The inlet 13a, the outlet 13b, the inlet 14a, and the outlet 14b are each formed, for example, on a wall surface of the tank 12.

[0042] 2 , the direction from the inlet 13 a to the outlet 13 b in the first chamber 13 is opposite to the direction from the inlet 14 a to the outlet 14 b in the second chamber 14. In this case, inside the separation membrane unit 10, the sweep gas 75 (recovered gas 85) moves in the opposite direction to the movement direction of the mixed gas 70. However, the direction from the inlet 13 a to the outlet 13 b in the first chamber 13 may coincide with the direction from the inlet 14 a to the outlet 14 b in the second chamber 14, or the sweep gas 75 may move in the same direction as the movement direction of the mixed gas 70.

[0043] The separation membrane unit 10 is suitable for a continuous membrane separation method, but may also be used for a batchwise membrane separation method.

[0044] (Separation membrane) The separation membrane 11 allows gas A contained in the mixed gas 70 to preferentially permeate. Below, a separation membrane 11 for when gas A is carbon dioxide, that is, a separation membrane 11 that preferentially allows carbon dioxide to permeate, will be described. In this specification, a separation membrane that preferentially allows carbon dioxide to permeate may be referred to as a "carbon dioxide permeable membrane."

[0045] 3A , a separation membrane 11 serving as a carbon dioxide permeable membrane includes, for example, a separation function layer 1. The separation membrane 11 may further include a porous support 3 that supports the separation function layer 1, and an intermediate layer 2 disposed between the separation function layer 1 and the porous support 3. The intermediate layer 2 is in direct contact with, for example, both the separation function layer 1 and the porous support 3.

[0046] <<Separation functional layer>> The separation functional layer 1 is a layer that allows carbon dioxide to pass preferentially, and is typically a dense layer (non-porous layer) in which no pores can be seen when observed at a magnification of 5000 times using a scanning electron microscope (SEM).

[0047] In a preferred embodiment, the separation functional layer 1 contains a resin. Examples of resins contained in the separation functional layer 1 include polyether block amide resins, polyamide resins, polyether resins, polyimide resins, cellulose acetate resins, silicone resins, and fluororesins. The separation functional layer 1 preferably contains a polyether block amide resin. In this embodiment, the separation functional layer 1 preferably consists essentially of a resin. In this specification, "consisting essentially of" means excluding other components that alter the essential characteristics of the referenced material, and means, for example, that 95 wt % or more, or even 99 wt % or more is composed of the material.

[0048] In another preferred embodiment, the separation functional layer 1 contains an ionic liquid. The ionic liquid is a salt (ionic compound) that is liquid at 25°C. The separation functional layer 1 may have a double-network gel containing an ionic liquid. The double-network gel is a gel having two types of network structures that are independent of each other. The double-network gel includes, for example, a first network structure mainly composed of an organic material, a second network structure mainly composed of an inorganic material, and an ionic liquid. The second network structure may be mainly composed of an organic material different from the first network structure. In this specification, "mainly composed" means that 50 wt% or more, or even 70 wt% or more, of the material in question is composed.

[0049] The organic material for forming the first network structure includes a polymer such as polyacrylamide (particularly, polydialkylacrylamide such as polydimethylacrylamide). The polymer contained in the organic material has structural units derived from an acrylamide derivative and may further include a crosslinked structure. A polymer including a crosslinked structure can be produced by a known method. For example, first, a prepolymer having a structural unit with an N-hydroxysuccinimide ester group is prepared. The structural unit with an N-hydroxysuccinimide ester group is derived from, for example, N-acryloxysuccinimide. Next, a polymer including a crosslinked structure can be obtained by reacting the prepolymer with an amine-based crosslinking agent. The amine-based crosslinking agent is a compound having two or more primary amino groups, such as ethylene glycol bis(3-aminopropyl) ether.

[0050] The second network structure may include a network of a plurality of particles. The network of a plurality of particles may be formed, for example, by a plurality of particles bonded to each other by hydrogen bonds. The particles included in the second network structure may be particles exemplified as nanoparticles, which will be described later. As an example, the particles included in the second network structure are silica particles.

[0051] In this embodiment, specific examples of the ionic liquid include an ionic liquid having imidazolium, pyridinium, ammonium, or phosphonium and a substituent having one or more carbon atoms.

[0052] In the ionic liquid having an imidazolium and a substituent having one or more carbon atoms, examples of the substituent having one or more carbon atoms include an alkyl group having from 1 to 20 carbon atoms, a cycloalkyl group having from 3 to 14 carbon atoms, and an aryl group having from 6 to 20 carbon atoms, which may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group, or the like (for example, a hydroxyalkyl group having from 1 to 20 carbon atoms).

[0053] Examples of the alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group, an n-eicosadecyl group, an Examples of the alkyl group include an alkyl group, an i-propyl group, a sec-butyl group, an i-butyl group, a 1-methylbutyl group, a 1-ethylpropyl group, a 2-methylbutyl group, an i-pentyl group, a neopentyl group, a 1,2-dimethylpropyl group, a 1,1-dimethylpropyl group, a t-pentyl group, a 2-ethylhexyl group, and a 1,5-dimethylhexyl group, which may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group, or the like.

[0054] The alkyl group may be substituted with a cycloalkyl group. The number of carbon atoms in the alkyl group substituted with a cycloalkyl group is, for example, 1 or more and 20 or less. Examples of the alkyl group substituted with a cycloalkyl group include a cyclopropylmethyl group, a cyclobutylmethyl group, a cyclohexylmethyl group, and a cyclohexylpropyl group, which may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group, or the like.

[0055] Examples of the cycloalkyl group having from 3 to 14 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclododecyl group, a norbornyl group, a bornyl group, and an adamantyl group, which may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group, or the like.

[0056] Examples of the aryl group having 6 to 20 carbon atoms include a phenyl group, a toluyl group, a xylyl group, a mesityl group, an anisyl group, a naphthyl group, and a benzyl group, which may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group, or the like.

[0057] The imidazolium and the compound having a substituent having one or more carbon atoms may further have a substituent such as an alkyl group, and may form a salt with a counter anion. Examples of the counter anion include alkyl sulfate, tosylate, methanesulfonate, acetate, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, thiocyanate, dicyanamide, tricyanomethanide, tetracyanoborate, hexafluorophosphate, tetrafluoroborate, and halide. From the viewpoint of gas separation performance, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, dicyanamide, tricyanomethanide, and tetracyanoborate are preferred.

[0058] Specific examples of the ionic liquid having an imidazolium and a substituent having one or more carbon atoms include 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium tetrachloroferrate, 1-butyl-3-methylimidazolium iodide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate ...bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium tetrachloroferrate, 1-butyl-3-methylimidazolium iodide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoro(trifluoromethyl)borate, 1-butyl-3-methylimidazolium tribromide, 1,3-dimesitylimidazolium chloride, 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride, 1,3-diisopropylimidazolium tetrafluoroborate, 1,3-di-tert-butylimidazolium tetrafluoroborate, 1,3-dicyclohexylimidazolium tetrafluoroborate, 1,3-dicyclohexylimidazolium chloride, 1,2-dimethyl-3-propylimidazolium iodide, 1-hexyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium bromide, 1-methyl-3-propylimidazolium iodide, 1-methyl-3-n-octylimidazolium bromide, 1-methyl-3-n-octylimidazolium Examples of suitable imidazolium compounds include 1-methyl-3-n-octylimidazolium hexafluorophosphate, 1-methyl-3-[6-(methylsulfinyl)hexyl]imidazolium p-toluenesulfonate, 1-ethyl-3-methylimidazolium tricyanomethanide, 1-ethyl-3-methylimidazolium tetracyanoborate, and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0059] Among these, from the viewpoint of gas separation performance, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMI][FSI]), 1-ethyl-3-methylimidazolium dicyanamide ([EMI][DCA]), 1-ethyl-3-methylimidazolium tricyanomethanide ([EMI][TCM]), 1-ethyl-3-methylimidazolium tetracyanoborate ([EMI][TCB]), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][TF2N]), and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2OHim][TF2N]) are particularly preferred.

[0060] The method for producing the double network gel is not particularly limited, and for example, the method disclosed in E. Kamio et al., Adv. Mater, 29, 1704118 (2017) can be used.

[0061] The ionic liquid content in the double-network gel is, for example, 50 wt% or more, preferably 60 wt% or more, more preferably 70 wt% or more, and even more preferably 80 wt% or more. The higher the ionic liquid content, the more preferentially carbon dioxide contained in the mixed gas can pass through the separation functional layer 1. The upper limit of the ionic liquid content is not particularly limited and is, for example, 95 wt%.

[0062] The content of the first network structure in the double-network gel, which is primarily made of organic material, is, for example, 1 wt% or more, preferably 5 wt% or more, and more preferably 10 wt% or more. The upper limit of the content of the first network structure is, for example, 15 wt%. From the viewpoint of improving the strength of the double-network gel, the content of the second network structure in the double-network gel, which is primarily made of inorganic material, is, for example, 1 wt% or more. The upper limit of the content of the second network structure is, for example, 5 wt%. The ratio of the total weight of the first network structure and the second network structure to the weight of the double-network gel is, for example, 2 wt% or more, preferably 5 wt% or more, and more preferably 10 wt% or more. This ratio is preferably 20 wt% or less. In this embodiment, the separation functional layer 1 preferably consists essentially of a double-network gel.

[0063] As described above, in the separation membrane 11 serving as a carbon dioxide permeable membrane, the separation functional layer 1 preferably contains a polyether block amide resin or an ionic liquid.

[0064] The thickness of the separation functional layer 1 is, for example, 50 μm or less, preferably 25 μm or less, and more preferably 15 μm or less. In some cases, the thickness of the separation functional layer 1 may be 10 μm or less, 5.0 μm or less, or 2.0 μm or less. The thickness of the separation functional layer 1 may be 0.05 μm or more, or 0.1 μm or more.

[0065] <<Intermediate Layer>> The intermediate layer 2 may contain a resin and may further contain nanoparticles dispersed in the resin (matrix). The nanoparticles may be spaced apart within the matrix or may be partially aggregated. The material of the matrix is ​​not particularly limited, and examples thereof include silicone resins such as polydimethylsiloxane; fluororesins such as polytetrafluoroethylene; epoxy resins such as polyethylene oxide; polyimide resins; polysulfone resins; polyacetylene resins such as polytrimethylsilylpropyne and polydiphenylacetylene; and polyolefin resins such as polymethylpentene. The matrix preferably contains a silicone resin.

[0066] The nanoparticles may contain an inorganic material or an organic material. Examples of inorganic materials contained in the nanoparticles include silica, titania, alumina, etc. Preferably, the nanoparticles contain silica.

[0067] The thickness of the intermediate layer 2 is not particularly limited and is, for example, less than 50 μm, preferably 40 μm or less, and more preferably 30 μm or less. The lower limit of the thickness of the intermediate layer 2 is not particularly limited and is, for example, 1 μm. The intermediate layer 2 is, for example, a layer having a thickness of less than 50 μm.

[0068] <Porous Support> The porous support 3 supports the separation function layer 1 via the intermediate layer 2. Examples of the porous support 3 include nonwoven fabrics, porous polytetrafluoroethylene, aromatic polyamide fibers, porous metals, sintered metals, porous ceramics, porous polyesters, porous nylons, activated carbon fibers, latex, silicone, silicone rubber, polyvinyl fluoride, polyvinylidene fluoride, polyurethane, polypropylene, polyethylene, polystyrene, polycarbonate, polysulfone, polyether ether ketone, polyacrylonitrile, polyimide, and polyphenylene oxide. Permeable (porous) polymers containing at least one selected from the group consisting of metal foams having open or closed cells, polymer foams having open or closed cells, silica, porous glass, and mesh screens. The porous support 3 may be a combination of two or more of these.

[0069] The porous support 3 has an average pore size of, for example, 0.01 to 0.4 μm. The thickness of the porous support 3 is not particularly limited and is, for example, 10 μm or more, preferably 20 μm or more, and more preferably 50 μm or more. The thickness of the porous support 3 is, for example, 300 μm or less, preferably 200 μm or less, and more preferably 150 μm or less.

[0070] <<Method for Producing Separation Membrane>> The separation membrane 11 can be produced by the following method. First, a coating solution containing the material for the intermediate layer 2 is prepared. Next, the coating solution containing the material for the intermediate layer 2 is applied onto the porous support 3 to form a coating film. The method for applying the coating solution is not particularly limited, and for example, a wire bar or the like can be used. The thickness of the formed intermediate layer 2 can be adjusted by adjusting the wire diameter of the wire bar and the concentration of the material for the intermediate layer 2 in the coating solution. The coating film may also be formed by immersing the porous support 3 in the coating solution. Next, the coating film is dried to form the intermediate layer 2. The drying of the coating film can be performed, for example, under heating conditions. The heating temperature of the coating film is, for example, 50°C or higher. The heating time of the coating film is, for example, 1 minute or more, and may be 5 minutes or more.

[0071] If necessary, an adhesion-improving treatment may be applied to the surface of the intermediate layer 2. The adhesion-improving treatment may include surface treatment such as application of a primer, corona discharge treatment, or plasma treatment.

[0072] Next, a coating liquid containing the material for the separation functional layer 1 is prepared. The coating liquid containing the material for the separation functional layer 1 is applied onto the intermediate layer 2 to obtain a coating film. This coating film is dried to form the separation functional layer 1. The coating method and drying conditions for the coating liquid can be the same as those described above for the intermediate layer 2. The coating liquid containing the material for the separation functional layer 1 may also be applied by spin coating. This results in a separation film 11.

[0073] The method for producing the separation membrane 11 is not limited to the above method, and the separation membrane 11 can also be produced by the following method. First, a coating liquid containing the material for the separation functional layer 1 is applied onto a transfer film to obtain a coating film. The coating film is dried to form the separation functional layer 1. Next, a coating liquid containing the material for the intermediate layer 2 is applied onto the separation functional layer 1 and dried to form the intermediate layer 2. The laminate of the intermediate layer 2 and the separation functional layer 1 is transferred to the porous support 3. In this way, the separation membrane 11 is obtained.

[0074] <Characteristics of Separation Membrane> The permeation rate of carbon dioxide permeating through the separation membrane 11 is not particularly limited. As an example, the permeation rate T CO2 is, for example, 5 GPU or more, and may be 10 GPU or more, 50 GPU or more, 100 GPU or more, 300 GPU or more, or even 500 GPU or more. CO2 The upper limit of the number of GPUs is not particularly limited, and is, for example, 1000 GPUs. -6 ·cm 3 (STP) / (sec cm 2 cm 3 (STP) means the volume of a gas at 1 atmosphere and 0°C.

[0075] Transmission rate T CO2 can be calculated by the following method. First, a mixed gas consisting of carbon dioxide and nitrogen is supplied to a space adjacent to one surface of the separation membrane 11 (for example, the main surface 11a of the separation membrane 11 on the separation functional layer side), and the space adjacent to the other surface of the separation membrane 11 (for example, the main surface 11b of the separation membrane 11 on the porous support side) is depressurized. As a result, a permeated gas that has permeated the separation membrane 11 is obtained in the space adjacent to the other surface of the separation membrane 11. The composition and weight of the permeated gas are measured. From the measurement results, the permeation rate T CO2In the above operation, the concentration of carbon dioxide in the mixed gas is 50 vol% under standard conditions (0°C, 101 kPa). The mixed gas supplied to the space adjacent to one side of the separation membrane 11 has a temperature of 30°C and a pressure of 0.1 MPa. The space adjacent to the other side of the separation membrane 11 is decompressed so that the pressure in the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment.

[0076] The permeation rate T CO2 Under the measurement conditions, the separation coefficient α of carbon dioxide relative to nitrogen of the separation membrane 11 CO2 is, for example, 20 or more, and may be 30 or more, 40 or more, or even 50 or more. CO2 The upper limit of the separation factor α is not particularly limited and is, for example, 100. CO2 can be calculated from the following formula: A and X B are the volume ratios of carbon dioxide and nitrogen in the mixed gas, respectively. A and Y B are the volume ratio of carbon dioxide and the volume ratio of nitrogen in the permeation gas that has permeated the separation membrane 11, respectively. CO2 = (Y A / Y B ) / (X A / X B )

[0077] (Modified Example of Separation Membrane) The separation membrane 11 is not limited to the carbon dioxide permeable membrane described above. Below, a separation membrane 11 for when gas A is hydrogen, that is, a separation membrane 11 that preferentially allows hydrogen to permeate, will be described. In this specification, a separation membrane that preferentially allows hydrogen to permeate may be referred to as a "hydrogen permeable membrane."

[0078] As shown in FIG. 3B , the separation membrane 11 serving as a hydrogen-permeable membrane includes, for example, a separation functional layer 5. Examples of the separation functional layer 5 include a resin layer containing a resin and a metal layer containing a metal. The separation membrane 11 may further include a support 7 that supports the separation functional layer 5 and a coating layer 6 that coats the separation functional layer 5. The separation functional layer 5 is disposed, for example, between the coating layer 6 and the support 7 and is in direct contact with both the coating layer 6 and the support 7. However, an adhesive may be disposed between the separation functional layer 5 and the support 7. Another support may also be disposed between the separation functional layer 5 and the coating layer 6.

[0079] <<Separation Functional Layer>> The separation functional layer 5 is a layer that allows hydrogen to permeate preferentially. When the separation functional layer 5 is a resin layer, examples of the resin contained in the resin layer include polyamide resin and polyimide resin. The resin layer is preferably made essentially of resin.

[0080] When the separation functional layer 5 is a metal layer, the metal contained in the metal layer is not particularly limited as long as it has hydrogen permeability either alone or when alloyed together. Examples of such metals include Pd, Nb, V, Ta, Ni, Fe, Al, Cu, Ru, Re, Rh, Au, Pt, Ag, Cr, Co, Sn, Zr, Y, Ce, Ti, Ir, Mo, and alloys containing two or more of these metals.

[0081] The metal layer is preferably an alloy layer containing a Pd alloy. The other metal forming the Pd alloy is not particularly limited, but is preferably a Group 11 element, more preferably at least one selected from the group consisting of Au, Ag, and Cu. The metal layer preferably contains a Pd—Au alloy. The content of the Group 11 element in the Pd alloy is preferably 20 to 65 mol%, more preferably 30 to 65 mol%, even more preferably 30 to 60 mol%, and particularly preferably 40 to 60 mol%. Alloy layers containing a Pd—Ag alloy with an Ag content of 20 mol% or more, a Pd—Cu alloy with a Cu content of 30 mol% or more, or a Pd—Au alloy with an Au content of 20 mol% or more tend to be less susceptible to embrittlement by hydrogen even at low temperatures below approximately 60°C. The Pd alloy may contain a metal from Group IB and / or Group IIIA.

[0082] The Pd alloy may be an alloy of three or more components, rather than the above-mentioned two-component alloy. Examples of alloys of three or more components include Pd—Au—Ag, Pd—Au—Cu, and Pd—Au—Ag—Cu. For example, in the case of a multi-component alloy containing Pd, Au, and other metals, the total content of Au and the other metals in the alloy is preferably 55 mol% or less, more preferably 50 mol% or less, even more preferably 45 mol% or less, and particularly preferably 40 mol% or less.

[0083] The metal layer preferably consists essentially of metal. The metal layer can be formed by, for example, rolling, sputtering, vacuum deposition, ion plating, plating, or the like. The rolling method is suitable for forming a relatively thick metal layer. The sputtering method is suitable for forming a relatively thin metal layer.

[0084] The rolling method may be hot rolling or cold rolling. The rolling method is a method in which a pair or multiple pairs of rolls are used to stretch a metal into a film while applying pressure to the metal. The thickness of the metal layer obtained by the rolling method is preferably 5 to 50 μm, more preferably 10 to 30 μm. By making the metal layer thickness 5 μm or more, it is possible to suppress the occurrence of pinholes or cracks during production, and further to suppress deformation when hydrogen is absorbed. By making the metal layer thickness 50 μm or less, it is possible to achieve sufficient hydrogen permeability for the metal layer while suppressing production costs.

[0085] Sputtering can be performed using a sputtering apparatus, such as a parallel plate type, a single wafer type, a pass-through type, a DC sputtering type, or an RF sputtering type, as follows: First, a substrate is attached to the sputtering apparatus with a metal target set therein. Next, the sputtering apparatus is evacuated and the Ar gas pressure is adjusted to a predetermined value. A predetermined sputtering current is passed through the metal target to form a metal film on the substrate. A metal layer can be obtained by peeling the metal film from the substrate. One or more metal targets can be used depending on the composition of the metal layer to be produced. Examples of substrates used in sputtering include glass plates, ceramic plates, silicon wafers, and metal plates containing aluminum or stainless steel. Furthermore, sputtering can also be used to form a metal layer directly on a support 7.

[0086] The thickness of the metal layer obtained by sputtering is preferably 0.01 to 5 μm, more preferably 0.05 to 2 μm. When the metal layer is 0.01 μm or thicker, the occurrence of pinholes during fabrication can be suppressed, and sufficient mechanical strength can be obtained. When the metal layer is 0.01 μm or thicker, it is less likely to be damaged when peeled off from the substrate, and tends to be easier to handle after peeling. When the metal layer is 5 μm or thicker, it can be produced in a short time, and manufacturing costs can be reduced.

[0087] <Coating Layer> The material of the coating layer 6 is not particularly limited and may be, for example, a fluorine-based compound, a rubber-based polymer, a silicone-based polymer, a urethane-based polymer, or a polyester-based polymer, and at least one selected from the group consisting of a fluorine-based compound, a rubber-based polymer, and a silicone-based polymer is preferred.

[0088] Examples of fluorine-based compounds include fluoroalkyl group-containing compounds such as fluoroalkyl carboxylates, fluoroalkyl quaternary ammonium salts, and fluoroalkylethylene oxide adducts; perfluoroalkyl group-containing compounds such as perfluoroalkyl carboxylates, perfluoroalkyl quaternary ammonium salts, and perfluoroalkylethylene oxide adducts; tetrafluoroethylene / hexafluoropropylene copolymers, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene polymers, vinylidene fluoride / tetrafluoroethylene copolymers, vinylidene fluoride / hexafluoropropylene copolymers, fluorine-containing (meth)acrylic acid ester polymers, fluorine-containing (meth)acrylic acid alkyl ester polymers, and copolymers of fluorine-containing (meth)acrylic acid esters and other monomers; and fluorine-containing (meth)acrylic acid esters. Examples of fluorine-based compounds that may be used include the "Durasurf" series manufactured by Harves, the "Optoo" series manufactured by Daikin Industries, Ltd., and the "KY-100" series manufactured by Shin-Etsu Chemical Co., Ltd.

[0089] Examples of rubber-based polymers include natural rubber, styrene butadiene rubber, acrylonitrile butadiene rubber, chloroprene rubber, polyisoprene rubber, polybutadiene rubber, ethylene propylene rubber, ethylene-propylene-diene terpolymer rubber, chlorosulfonated polyethylene rubber, ethylene-vinyl acetate copolymer rubber, etc. As the rubber-based polymer, the "Elepcoat" series manufactured by Nitto Shinko Corporation, etc. may be used.

[0090] Examples of silicone polymers include polydimethylsiloxane, alkyl-modified polydimethylsiloxane, carboxyl-modified polydimethylsiloxane, amino-modified polydimethylsiloxane, epoxy-modified polydimethylsiloxane, fluorine-modified polydimethylsiloxane, and (meth)acrylate-modified polydimethylsiloxane.

[0091] The coating layer 6 can be formed, for example, by applying a composition containing the material of the coating layer 6 onto the separation functional layer 5 and curing the composition. The method for applying the composition is not particularly limited, and examples thereof include roll coating, spin coating, dip coating, spray coating, bar coating, knife coating, die coating, inkjet coating, and gravure coating.

[0092] The solvent contained in the composition can be appropriately selected depending on the raw material of the coating layer 6. When a fluorine-based compound is used as the material of the coating layer 6, the solvent can be a fluorine-based solvent, an alcohol-based solvent, an ether-based solvent, an ester-based solvent, a hydrocarbon-based solvent, or the like, which can be used alone or in combination with two or more other solvents. Of these solvents, it is preferable to use a non-flammable, rapidly volatilizing fluorine-based solvent alone or in combination with other solvents.

[0093] Examples of fluorine-based solvents include hydrofluoroethers, perfluoropolyethers, perfluoroalkanes, hydrofluoropolyethers, hydrofluorocarbons, perfluorocycloethers, perfluorocycloalkanes, hydrofluorocycloalkanes, xylene hexafluoride, hydrofluorochlorocarbons, and perfluorocarbons.

[0094] The thickness of the coating layer 6 is not particularly limited, and is preferably 0.1 μm or more, more preferably 0.3 μm or more, even more preferably 0.5 μm or more, and particularly preferably 1.0 μm or more. The thickness of the coating layer 6 is, for example, 80 μm or less, preferably 50 μm or less, more preferably 30 μm or less, even more preferably 20 μm or less, particularly preferably 10 μm or less, and especially preferably 5 μm or less. The thickness of the coating layer 6 can be adjusted by the solids concentration of the composition containing the material of the coating layer 6 and the number of times the composition is applied. The coating layer 6 is preferably non-porous.

[0095] <<Support>> The support 7 is not particularly limited as long as it has hydrogen permeability and supports the separation function layer 5, and is, for example, a porous body. However, the support 7 may also be non-porous. The support 7 may also be a woven fabric, a non-woven fabric, or the like. Examples of materials for the support 7 include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyarylethersulfones such as polysulfone and polyethersulfone; fluororesins such as polytetrafluoroethylene and polyvinylidene fluoride; epoxy resins; polyamides; and polyimides, among which polysulfone or polytetrafluoroethylene, which is chemically and thermally stable, is preferred.

[0096] The support 7 is preferably a porous body with an average pore size of 100 μm or less. This porous body has sufficient surface smoothness, so when a metal layer is formed directly on the porous body by a method such as sputtering, a metal layer of uniform thickness can be easily formed. At this time, the occurrence of pinholes or cracks in the metal layer can also be suppressed. The thickness of the support 7 is not particularly limited and is, for example, 5 to 1000 μm, preferably 10 to 300 μm.

[0097] <<Characteristics of Separation Membrane>> The permeation rate of hydrogen permeating through the separation membrane 11 is not particularly limited. As an example, the permeation rate T H2is, for example, 5 GPU or more, and may be 10 GPU or more, 50 GPU or more, 100 GPU or more, 300 GPU or more, or even 500 GPU or more. H2 The upper limit is not particularly limited, and is, for example, 1000 GPU.

[0098] Transmission rate T H2 can be calculated by the following method. First, a mixed gas consisting of hydrogen and methane is supplied to a space adjacent to one surface of the separation membrane 11 (for example, the main surface 11a of the separation membrane 11 on the coating layer side), and the space adjacent to the other surface of the separation membrane 11 (for example, the main surface 11b of the separation membrane 11 on the support side) is depressurized. As a result, a permeated gas that has permeated through the separation membrane 11 is obtained in the space adjacent to the other surface of the separation membrane 11. The composition and weight of the permeated gas are measured. From the measurement results, the permeation rate T H2 In the above operation, the hydrogen concentration in the mixed gas is 50 vol% under standard conditions (0°C, 101 kPa). The mixed gas supplied to the space adjacent to one side of the separation membrane 11 has a temperature of 30°C and a pressure of 0.1 MPa. The space adjacent to the other side of the separation membrane 11 is decompressed so that the pressure in the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment.

[0099] The permeation rate T H2 Under the measurement conditions, the separation coefficient α of the separation membrane 11 for hydrogen relative to methane H2 is, for example, 50 or more, and may be 100 or more, 200 or more, or even 400 or more. H2 The upper limit of the separation factor α is not particularly limited and is, for example, 1000. H2 can be calculated from the following formula: A and X B are the volume ratios of hydrogen and methane in the mixed gas, respectively. A and Y B are the volume ratios of hydrogen and methane in the permeation gas that has permeated the separation membrane 11, respectively. H2 = (Y A / Y B ) / (X A / XB )

[0100] [Method for Separating Mixed Gas] In this embodiment, the method for separating mixed gas 70 includes supplying mixed gas 70 to separation membrane unit 10 and separating mixed gas 70 into permeable gas 80 and non-permeable gas 81 (separation step), supplying a portion of non-permeable gas 81 as sweep gas 75 to the permeation space of separation membrane unit 10 (sweep gas supply step), and recovering recovered gas 85 containing permeable gas 80 and sweep gas 75 (recovery step).

[0101] The separation step can be carried out by the following method. First, the mixed gas 70 is supplied to the first chamber 13 (supply space) of the separation membrane unit 10 through the mixed gas supply path 30. The mixed gas 70 is preferably pressurized by the pressurizing device 40 and supplied to the first chamber 13. The pressure of the mixed gas 70 pressurized by the pressurizing device 40, i.e., the pressure in the supply space of the separation membrane unit 10, is, for example, 0.1 MPa or more, and may be 0.5 MPa or more, or even 0.8 MPa or more. The upper limit of the pressure of the mixed gas 70 is not particularly limited and is, for example, 10.0 MPa or less. In this specification, unless otherwise specified, "pressure" means absolute pressure.

[0102] As described above, the mixed gas 70 contains gas A as a component to be separated. Gas A is preferably carbon dioxide or hydrogen. The mixed gas 70 may be exhaust gas from a thermal power plant or exhaust gas from a chemical plant (e.g., exhaust gas produced by a shift reaction). However, gas A is not limited to carbon dioxide or hydrogen. Gas A may be an acidic gas other than carbon dioxide, a non-polar gas such as oxygen, or an inert gas such as helium. Examples of acidic gases other than carbon dioxide include hydrogen sulfide, carbonyl sulfide, and sulfur oxides (SO x ), hydrogen cyanide, nitrogen oxides (NO x ) etc.

[0103] The mixed gas 70 further contains a gas B different from the gas A. The gas B is preferably nitrogen or methane. However, in some cases, the gas B may be the same as that described above for the gas A. As described above, in a preferred embodiment, the mixed gas 70 contains carbon dioxide as the gas A and nitrogen as the gas B. In another preferred embodiment, the mixed gas 70 contains hydrogen as the gas A and methane as the gas B. The mixed gas 70 may or may not contain water vapor as the gas A or the gas B.

[0104] The content of Gas A in the mixed gas 70 is, for example, 50 vol% or less, and may be 30 vol% or less, 20 vol% or less, 10 vol% or less, or even 5 vol% or less. The lower limit of the content of Gas A in the mixed gas 70 is not particularly limited, and is, for example, 1 vol% or more. The content of Gas B in the mixed gas 70 is not particularly limited, and is, for example, 50 vol% to 99 vol%. In this specification, unless otherwise specified, "content" and "volume" refer to values ​​under standard conditions (0°C, 101 kPa).

[0105] The mixed gas 70 supplied to the first chamber 13 of the separation membrane unit 10 is separated by the separation membrane 11. As a result, a permeated gas 80 is supplied to the second chamber 14. As described above, the separation membrane 11 of the separation membrane unit 10 preferentially allows gas A contained in the mixed gas 70 to permeate. Therefore, the permeated gas 80 has a higher content of gas A than the mixed gas 70. The permeated gas 80 supplied to the second chamber 14 is mixed with a sweep gas 75 supplied in a sweep gas supply step described below. A recovered gas 85 containing the permeated gas 80 and the sweep gas 75 is discharged to the outside of the separation membrane unit 10 through the outlet 14b.

[0106] The concentration of gas A in the mixed gas 70 gradually decreases from the inlet 13a to the outlet 13b of the first chamber 13. The content of gas A in the mixed gas 70 (non-permeation gas 81) treated in the first chamber 13 is not particularly limited and may be, for example, 10 vol% or less, 5 vol% or less, 3 vol% or less, or even 1 vol% or less. The non-permeation gas 81 is discharged to the outside of the separation membrane unit 10 through the outlet 13b and sent to the discharge path 32.

[0107] In the sweep gas supply step, for example, at the branch position 42 of the discharge path 32, a portion of the non-permeate gas 81 is sent to the sweep gas supply path 36 as a sweep gas 75. The sweep gas 75 is supplied to the second chamber 14 (permeation space) of the separation membrane unit 10 through the sweep gas supply path 36. As described above, the sweep gas 75 supplied to the second chamber 14 is mixed with the permeate gas 80, thereby obtaining the recovered gas 85.

[0108] In this embodiment, the pressure of the recovered gas 85 is preferably adjusted to approximately atmospheric pressure in the surrounding environment of the gas separation system 100, but is not particularly limited thereto. The pressure of the recovered gas 85 may be lower than atmospheric pressure or higher than atmospheric pressure.

[0109] The content of gas A in the recovered gas 85 is higher than the content of gas A in the mixed gas 70, and may be, for example, 5 vol% or more, 10 vol% or more, 20 vol% or more, 30 vol% or more, 40 vol% or more, 50 vol% or more, or even 60 vol% or more. The upper limit of the content of gas A in the recovered gas 85 is not particularly limited, and may be, for example, 90 vol% or less or 80 vol% or less. In some cases, the upper limit of the content of gas A in the recovered gas 85 may be 60 vol% or less or 50 vol% or less. The ratio of the content of gas A (vol%) in the recovered gas 85 to the content of gas A (vol%) in the mixed gas 70 is not particularly limited, and may be, for example, 1.2 to 9, 1.2 to 5, or 1.2 to 3.

[0110] The recovered gas 85 may have a low water vapor content. The water vapor content in the recovered gas 85 may be, for example, 10 vol% or less, 5 vol% or less, 1 vol% or less, 0.5 vol% or less, or even 0.1 vol% or less. The recovered gas 85 may be substantially free of water vapor.

[0111] In the recovery step, recovered gas 85 is recovered by recovery unit 20. The recovery rate of gas A by recovered gas 85 is, for example, 30% or more, and may be 50% or more, 70% or more, 80% or more, 90% or more, 95% or more, or even 99% or more. In this specification, the recovery rate refers to the ratio of the weight of gas A contained in recovered gas 85 to the weight of gas A contained in mixed gas 70.

[0112] In the separation method of this embodiment, if the flow rate of the sweep gas 75 is adjusted to a large value, the recovery rate of the gas A by the recovery gas 85 can be easily adjusted to a high value. As an example, the flow rate F2 (m 3 / h) of the sweep gas 75 to the flow rate F1 (m 3 / h), is, for example, 6.0% or more, and may be 8.0% or more, 10% or more, 15% or more, 20% or more, 25% or more, or even 30% or more. The upper limit of the ratio F1 / F2 is, for example, 50% or less, or may be 35% or less, from the viewpoint of adjusting the content of gas A in the recovered gas 85 to a high value. In this specification, unless otherwise specified, the "flow rate" refers to a value under standard conditions (0°C, 101 kPa).

[0113] Furthermore, the flow rate F3 (m 3 / h) of the sweep gas 75 to the flow rate F1 (m 3 The ratio F1 / F3 of the total number of cycles (F1 / F3) is, for example, 19% or more, and may be 25% or more, 30% or more, 40% or more, 50% or more, or even 60% or more. The upper limit of the ratio F1 / F3 is, for example, 80% or less, and may be 70% or less.

[0114] In the gas separation system 100, the flow rate F4 (m ) of the non-permeable gas 81 (non-permeable gas 81 excluding the sweep gas 75) discharged from the discharge port 44 of the discharge path 32 is3 / h) of the sweep gas 75 to the flow rate F1 (m 3 The ratio F1 / F4 of the total number of cycles (F1 / F4) is, for example, 6.0% or more, and may be 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or even 90% or more. The upper limit of the ratio F1 / F4 is, for example, 120% or less, and may be 100% or less.

[0115] The flow rate F2 (m 3 / h) with respect to the flow rate F3 (m 3 The ratio F3 / F2 of the total number of cycles (hours / hour) is not particularly limited and may be, for example, 10% to 70%, or may be 15% to 70%.

[0116] FIG. 5 is a schematic diagram illustrating an example of a conventional gas separation system 200. The conventional gas separation system 200 has a configuration similar to that of the gas separation system 100 of FIG. 1 , except that the non-permeate gas is not used as a sweep gas. Specifically, the gas separation system 200 includes a separation membrane unit 210 having a separation membrane 211, a recovery section 220, a mixed gas supply path 230, a discharge path 232, a recovery path 234, and a sweep gas supply path 236. A pressurizing device 240 for pressurizing the mixed gas is disposed in the mixed gas supply path 230. The sweep gas supply path 236 is configured to supply the sweep gas to the separation membrane unit 210 from a tank (not shown) that stores the sweep gas. A pressurizing device 246 for pressurizing the sweep gas is disposed in the sweep gas supply path 236. In the gas separation system 200, a gas (e.g., air) that contains almost no gas A, the component to be separated, is used as the sweep gas.

[0117] In the conventional gas separation system 200, the non-permeate gas discharged from the separation membrane unit 210 is discarded through the outlet 244 of the discharge path 232. Therefore, in order to improve the recovery rate of gas A using the recovered gas in the gas separation system 200, it is necessary to increase the membrane area of ​​the separation membrane 211 and increase the amount of gas A that permeates the separation membrane 211.

[0118] In contrast, in the gas separation system 100 of the present embodiment, a portion of the non-permeable gas 81 is used as the sweep gas 75. With this configuration, a portion of the gas A contained in the non-permeable gas 81 is not discarded but is mixed with the permeable gas 80. This makes it possible to easily improve the recovery rate of the gas A (component to be separated) contained in the mixed gas 70 without significantly increasing the membrane area of ​​the separation membrane 11. It can be said that the gas separation system 100 of the present embodiment is more suitable for efficiently separating the mixed gas 70 than the conventional gas separation system 200.

[0119] Furthermore, in the conventional gas separation system 200, it is usually necessary to pressurize the sweep gas using a pressure device 246 in order to send the sweep gas to the separation membrane unit 210. In contrast, in the gas separation system 100 of the present embodiment, the mixed gas 70 is pressurized using a pressure device 40, so that the sweep gas 75 has a pressure that is sufficient for practical use. That is, in the gas separation system 100, it is not necessary to separately pressurize the sweep gas 75. Therefore, in the gas separation system 100 of the present embodiment, it is easier to adjust the power for recovering gas A (recovery power) to a smaller value than in the conventional gas separation system 200.

[0120] [Modifications of Separation Membrane Unit] In the gas separation system 100, the separation membrane unit 10 may be a spiral membrane element, a hollow fiber membrane element, or the like. Fig. 4 shows a spiral membrane element. The separation membrane unit 15 in Fig. 4 includes a central tube 16 and a laminate 17. The laminate 17 includes a separation membrane 11.

[0121] The central tube 16 has a cylindrical shape. A plurality of holes are formed on the surface of the central tube 16 to allow the permeation gas 80 to flow into the interior of the central tube 16. Examples of materials for the central tube 16 include resins such as acrylonitrile-butadiene-styrene copolymer resin (ABS resin), polyphenylene ether resin (PPE resin), and polysulfone resin (PSF resin); and metals such as stainless steel and titanium. The inner diameter of the central tube 16 is, for example, in the range of 20 to 100 mm.

[0122] In addition to the separation membrane 11, the laminate 17 further includes a feed-side channel material 18 and a permeate-side channel material 19. The laminate 17 is wound around a central tube 16. The separation membrane unit 15 may further include an exterior material (not shown).

[0123] As the feed-side flow path material 18 and the permeate-side flow path material 19, for example, a resin net, woven fabric, or knitted fabric made of polyethylene, polypropylene, polyethylene terephthalate (PET), polyphenylene sulfide (PPS), or ethylene-chlorotrifluoroethylene copolymer (ECTFE) can be used.

[0124] Membrane separation using the separation membrane unit 15 is performed, for example, by the following method. First, a mixed gas 70 is supplied to one end of the wound stack 17, and a sweep gas 75 is supplied into the interior of the central tube 16. The sweep gas 75 moves from the interior of the central tube 16 to a space (permeation space) in which the permeation-side flow path material 19 is present. A permeation gas 80 that has permeated the separation membranes 11 of the stack 17 is mixed with the sweep gas 75 in the permeation space. A recovery gas 85 containing the permeation gas 80 and the sweep gas 75 moves into the interior of the central tube 16 and is discharged to the outside through the central tube 16. The mixed gas 70 (non-permeation gas 81) treated in the separation membrane unit 15 is discharged to the outside from the other end of the wound stack 17.

[0125] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0126] (Calculation Example A1) A simulation was performed using process modeling software Symmetry manufactured by Schlumberger when the gas separation system 100 shown in FIG. 1 was operated. It was assumed that a carbon dioxide permeable membrane was used as the separation membrane provided in the separation membrane unit. In this separation membrane, the permeation rate T CO2 is set to 500 GPU, and the separation factor α of carbon dioxide relative to nitrogen is CO2was set to 30. Furthermore, in this simulation, it was assumed that a portion of the non-permeable gas was used as a sweep gas, and that a captured gas consisting of the permeable gas and the sweep gas was captured. Furthermore, the mixed gas supply conditions and the carbon dioxide capture conditions using the captured gas were set as follows. It was assumed that the mixed gas was pressurized from atmospheric pressure (101.33 kPa) in the external environment to a gauge pressure of 0.8 MPa using a pressure device arranged in the mixed gas supply path. [Mixed gas supply conditions] Flow rate: 10176 Nm 3 / h Composition (volume ratio): CO2 / N2 = 5 / 95 CO2 weight: 1000 kg / hr Pressure: Gauge pressure 0.8 MPa (absolute pressure 0.9 MPa) Temperature: 30°C [Conditions for carbon dioxide recovery using recovered gas] CO2 content in recovered gas: 10 vol% Recovery rate (ratio of CO2 weight in recovered gas to CO2 weight in mixed gas): 99.1% Recovery gas pressure: Gauge pressure 0 MPa (absolute pressure 0.1 MPa)

[0127] By the simulation of Calculation Example A1, the membrane area of ​​the separation membrane required to separate the mixed gas using the gas separation system and the carbon dioxide recovery power (the ratio of the energy (kWh) required to operate the gas separation system to the weight (kg) of recovered carbon dioxide) were calculated.

[0128] Calculation Example B1 A simulation of Calculation Example B1 was performed using the same method as Calculation Example A1, except that the gas separation system 200 shown in FIG. 5 was operated instead of the gas separation system 100. In this simulation, it was assumed that air was used as a sweep gas and that a recovery gas consisting of a permeate gas and the sweep gas was recovered. It was also assumed that the sweep gas was pressurized to a pressure suitable for supply to the separation membrane unit using a pressure device disposed in the sweep gas supply path. The air was considered to be a mixed gas of nitrogen and oxygen (N2 / O2 = 80 / 20 (volume ratio)).

[0129] (Calculation Examples A2 to A5) Simulations for calculation examples A2 to A5 were performed using the same method as calculation example A1, except that the supply conditions for the mixed gas and the conditions for recovering carbon dioxide using the recovered gas were changed as shown in Tables 1 and 2.

[0130] (Calculation Examples B2 to B5) Simulations for calculation examples B2 to B5 were performed using the same method as calculation example B1, except that the supply conditions for the mixed gas and the conditions for recovering carbon dioxide using the recovered gas were changed as shown in Tables 1 and 2.

[0131]

[0132]

[0133] As can be seen from Tables 1 and 2, when the mixed gas supply conditions and the conditions for carbon dioxide recovery using the recovery gas were the same, calculation examples A1 to A5 using the gas separation system of Figure 1 required a smaller separation membrane area and recovery power to achieve the target carbon dioxide recovery rate compared to calculation examples B1 to B5. The results in Tables 1 and 2 show that by using a portion of the non-permeable gas as a sweep gas and recovering a recovery gas containing the permeable gas and sweep gas, it is possible to easily improve the recovery rate of the components to be separated contained in the mixed gas without significantly increasing the membrane area of ​​the separation membrane, thereby enabling the mixed gas to be separated efficiently.

[0134] Example 1 In Example 1, first, a gas separation system 100 shown in FIG. 1 was actually prepared. As a separation membrane unit, a membrane element having a length of 30 cm and a carbon dioxide permeable membrane set therein was used. The carbon dioxide permeable membrane had a permeation rate of carbon dioxide alone, T CO2 is 120 GPU, and the separation coefficient α of carbon dioxide relative to air CO2 / Air was 20.

[0135] The permeation rate of carbon dioxide alone, T CO2was measured by the following method. First, carbon dioxide at a pressure of 201.33 kPa and a temperature of 25°C is supplied to a space adjacent to one side of the carbon dioxide permeable membrane. At this time, the pressure in the space adjacent to the other side of the carbon dioxide permeable membrane is adjusted to 101.33 kPa. As a result, a permeating fluid (carbon dioxide) that has permeated the carbon dioxide permeable membrane is obtained from the other side of the carbon dioxide permeable membrane. The flow rate of this permeating fluid is measured with a mass flow meter, and from the obtained results, the permeation rate T of carbon dioxide alone is calculated. CO2 Identify the GPU.

[0136] Separation factor α CO2 / Air is the permeation rate of air alone, T air (GPU) vs. carbon dioxide permeation rate T CO2 (GPU) ratio T CO2 / T air The permeation rate of air alone, T air is the permeation rate T of carbon dioxide alone, except that air at a pressure of 201.33 kPa and a temperature of 25°C is used instead of carbon dioxide. CO2 can be measured by the method described above.

[0137] Next, the mixed gas was supplied to the separation membrane unit, and the gas separation system 100 was operated. In this operation, a portion of the non-permeable gas was used as a sweep gas, and a recovered gas consisting of the permeable gas and the sweep gas was recovered. The mixed gas was a mixture of carbon dioxide and compressed air (air), and was supplied under the following supply conditions. [Mixed gas supply conditions] Flow rate: 20 NL / min Composition (volume ratio): CO2 / Air = 5 / 95 Pressure: 500 kPa absolute pressure Temperature: 25°C

[0138] The air was considered to be a mixed gas of nitrogen and oxygen (N / O = 80 / 20 (volume ratio)). In Example 1, compressed air was used, so no operation was performed to pressurize the mixed gas using a pressure device. The pressure (absolute pressure) of the recovered gas was 101.33 kPa.

[0139] The CO content of each gas, the flow rate of each gas, the CO recovery rate (the ratio of the weight of CO in the recovered gas to the weight of CO in the mixed gas), and the power (Wh) required to operate the gas separation system were determined for the operation performed in Example 1. The flow rate of each gas was measured using a flow meter installed in each path of the gas separation system 100.

[0140] Comparative Example 1 In Comparative Example 1, first, the gas separation system 200 shown in FIG. 5 was actually prepared. The same separation membrane unit as in Example 1 was used. Next, under the same conditions as in Example 1, a mixed gas was supplied to the separation membrane unit, and the gas separation system 200 was operated. In this operation, air was used as a sweep gas, and a recovered gas consisting of a permeate gas and a sweep gas was recovered. The sweep gas was pressurized to a pressure suitable for supply to the separation membrane unit using a pressure device arranged in the sweep gas supply path. The pressure (absolute pressure) of the recovered gas was 101.33 kPa.

[0141] For the operation carried out in Comparative Example 1, the CO2 recovery rate and the like were determined in the same manner as in Example 1.

[0142] Example 2 The gas separation system 100 was operated in the same manner as in Example 1, except that the composition (volume ratio) of the mixed gas was changed to CO2 / Air = 10 / 90.

[0143] Comparative Example 2 The gas separation system 200 was operated in the same manner as in Comparative Example 1, except that the composition (volume ratio) of the mixed gas was changed to CO2 / Air = 10 / 90.

[0144]

[0145]

[0146] As can be seen from Tables 3 and 4, the examples using the gas separation system of Figure 1 had a higher carbon dioxide recovery rate and required less power to operate the gas separation system than the comparative examples. The results in Tables 3 and 4 indicate that mixed gases can be separated efficiently by using a portion of the non-permeable gas as a sweep gas and recovering a recovery gas containing the permeable gas and the sweep gas.

[0147] The flow rates listed in Table 3 reflect slight errors in the measurements made by each flow meter.

[0148] The gas separation system of this embodiment is suitable for separating a mixed gas, for example, a mixed gas containing carbon dioxide or hydrogen, and is particularly suitable for treating exhaust gas from thermal power plants and chemical plants.

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