Gas separation system and separation method of mixed gas

Abstract

Provided is a novel gas separation system suitable for efficiently separating a mixed gas. This gas separation system (100) is provided with: a first separation membrane (11) that separates a mixed gas (70) into a first permeate gas (80) and a first impermeable gas (81); and a second separation membrane (21) that separates the first impermeable gas (81) into a second permeate gas (90) and a second impermeable gas (91). The mixed gas 70 contains a gas A and a gas B different from the gas A. The first separation membrane (11) can preferentially permeate the gas (A). The second separation membrane (21) can preferentially permeate the gas (B). The separation coefficient [alpha] 1 of the first separation membrane and the separation coefficient [alpha] 2 of the second separation membrane satisfy the following relational expressions (1) and (2). [alpha] 1 / [alpha] 2 > = 1.9 (1) [alpha] 2 < = 50 (2).

Description

Technical Field

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

[0002] Chemical plants that produce chemicals, for example, discharge mixed gases containing carbon dioxide, hydrogen, etc. From the perspectives of environmental control and effective resource utilization, it is desirable to separate and recover the individual components of the mixed gases.

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

[0004] In membrane separation methods, a gas separation system composed of a combination of multiple separation membranes is sometimes used. For example, Patent Document 1 discloses a methane concentrator that uses two separation membranes that preferentially permeate carbon dioxide to concentrate methane gas.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2008-260739 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] There is a need for new gas separation systems suitable for efficiently separating mixed gases.

[0010] Means for solving problems

[0011] The inventors of the present application have conducted intensive research and have come to the following new understanding: when combining two separation membranes that preferentially permeate different types of gases, if the separation coefficients α of the two separation membranes are appropriately adjusted, mixed gases can be separated at a sufficiently high recovery rate and purity, even if the separation coefficient α of one separation membrane is a small value of 50 or less (particularly 20 or less). Based on this understanding, the inventors of the present application have conducted research and completed the present invention.

[0012] The present invention provides a gas separation system comprising:

[0013] a first separation membrane for separating the mixed gas into a first permeated gas and a first non-permeated gas;

[0014] a second separation membrane for separating the first non-permeated gas into a second permeated gas and a second non-permeated gas,

[0015] The mixed gas includes gas A and gas B which is different from gas A.

[0016] The first separation membrane is capable of preferentially permeating the gas A.

[0017] The second separation membrane can preferentially permeate the gas B.

[0018] The separation coefficient α1 of the gas A to the gas B of the first separation membrane obtained by the following experiment and the separation coefficient α2 of the gas B to the gas A of the second separation membrane obtained by the following experiment satisfy the following relations (1) and (2):

[0019] Test: A test piece is prepared using the first separation membrane or the second separation membrane; a test gas obtained from the gas A and the gas B is supplied to a space adjacent to one side of the test piece, and the space adjacent to the other side of the test piece is depressurized; the separation coefficient α1 or the separation coefficient α2 is determined based on the result of the operation; wherein, in the operation, the content of the gas A in the test gas is 50 vol% (volume %) under standard conditions, the test gas supplied to the space adjacent to the one side has a temperature of 30° C. and a pressure of 0.1 MPa, and the space adjacent to the other side is depressurized in such a manner that the pressure in the space is reduced by 0.1 MPa relative to the atmospheric pressure in the measurement environment.

[0020] α1 / α2≥1.9 (1)

[0021] α2≤50 (2).

[0022] In addition, the present invention also provides a method for separating a mixed gas, comprising:

[0023] a first separation step of separating a mixed gas containing gas A and gas B different from gas A into a first permeated gas and a first non-permeated gas via a first separation membrane that allows gas A to preferentially permeate; and

[0024] a second separation step of separating the first non-permeated gas into a second permeated gas and a second non-permeated gas via a second separation membrane that allows the gas B to preferentially permeate;

[0025] The separation coefficient α1 of the gas A to the gas B of the first separation membrane obtained by the following test and the separation coefficient α2 of the gas B to the gas A of the second separation membrane obtained by the following test satisfy the following equations (1) and (2):

[0026] Test: A test piece is prepared using the first separation membrane or the second separation membrane; a test gas obtained from the gas A and the gas B is supplied to a space adjacent to one side of the test piece, and the space adjacent to the other side of the test piece is depressurized; the separation coefficient α1 or the separation coefficient α2 is determined based on the result of the operation; wherein, in the operation, the content of the gas A in the test gas is 50 vol% under standard conditions, the test gas supplied to the space adjacent to the one side is at a temperature of 30° C. and a pressure of 0.1 MPa, and the space adjacent to the other side is depressurized in such a manner that the pressure in the space is reduced by 0.1 MPa relative to the atmospheric pressure in the measurement environment.

[0027] α1 / α2≥1.9 (1)

[0028] α2≤50 (2).

[0029] Effects of the Invention

[0030] According to the present invention, a new gas separation system suitable for efficiently separating mixed gases can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] [ Figure 1 ] is a schematic diagram of the gas separation system according to one embodiment of the present invention.

[0032] [ Figure 2 ] is a schematic cross-sectional view showing an example of the first separation membrane unit.

[0033] [ Figure 3 ] is a cross-sectional view schematically showing an example of the first separation membrane.

[0034] [ Figure 4 ] is a schematic cross-sectional view showing an example of the second separation membrane unit.

[0035] [ Figure 5 ] is a cross-sectional view schematically showing an example of the second separation membrane.

[0036] [ Figure 6 ] is a perspective view schematically showing another example of the first separation membrane unit.

[0037] [ Figure 7 ] is a schematic structural diagram showing a modified example of the gas separation system.

[0038] [ Figure 8 ] is a diagram for explaining the structure of the gas separation system used in Calculation Example 9. DETAILED DESCRIPTION

[0039] A gas separation system according to a first aspect of the present invention includes:

[0040] a first separation membrane for separating the mixed gas into a first permeated gas and a first non-permeated gas;

[0041] a second separation membrane for separating the first non-permeated gas into a second permeated gas and a second non-permeated gas,

[0042] The mixed gas includes gas A and gas B which is different from gas A.

[0043] The first separation membrane is capable of preferentially permeating the gas A.

[0044] The second separation membrane can preferentially permeate the gas B.

[0045] The separation coefficient α1 of the gas A to the gas B of the first separation membrane obtained by the following experiment and the separation coefficient α2 of the gas B to the gas A of the second separation membrane obtained by the following experiment satisfy the following relations (1) and (2):

[0046] Test: A test piece is prepared using the first separation membrane or the second separation membrane; a test gas obtained from the gas A and the gas B is supplied to a space adjacent to one side of the test piece, and the space adjacent to the other side of the test piece is depressurized; the separation coefficient α1 or the separation coefficient α2 is determined based on the result of the operation; wherein, in the operation, the content of the gas A in the test gas is 50 vol% under standard conditions, the test gas supplied to the space adjacent to the one side is at a temperature of 30° C. and a pressure of 0.1 MPa, and the space adjacent to the other side is depressurized in such a manner that the pressure in the space is reduced by 0.1 MPa relative to the atmospheric pressure in the measurement environment.

[0047] α1 / α2≥1.9 (1)

[0048] α2≤50 (2).

[0049] In a second aspect of the present invention, for example, in the gas separation system of the first aspect, the separation coefficient α2 is 20 or less.

[0050] In a third aspect of the present invention, for example, in the gas separation system of the first or second aspect, the gas A is hydrogen, and the gas B is carbon dioxide.

[0051] 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 first permeated gas and the second permeated gas are recovered separately.

[0052] In a fifth aspect of the present invention, for example, in the gas separation system according to any one of the first to fourth aspects, the membrane area of the first separation membrane is larger than the membrane area of the second separation membrane.

[0053] In the sixth aspect of the present invention, for example, in the gas separation system of any one of the first to fifth aspects, the content of the gas A in the first permeated gas is 85 vol% or more, and the recovery rate of the gas A based on the first permeated gas is 70 wt% (weight %) or more.

[0054] In the seventh aspect of the present invention, for example, in the gas separation system of any one of the first to sixth aspects, the content of the gas B in the second permeated gas is 85 vol% or more, and the recovery rate of the gas B based on the second permeated gas is 80 wt% or more.

[0055] In the 8th aspect of the present invention, for example, in the gas separation system of any one of the 1st to 7th aspects, in the mixed gas, the ratio of the volume of the gas A to the total volume of the gas A and the volume of the gas B is 20 to 80 vol%.

[0056] In the 9th embodiment of the present invention, for example, the gas separation system of any one of the 1st to 8th embodiments further comprises: a first separation membrane unit that accommodates the first separation membrane; a mixed gas supply path that is connected to the first separation membrane unit and is used to supply the mixed gas to the first separation membrane unit; and a pressurizing device that is arranged in the mixed gas supply path to increase the pressure of the mixed gas.

[0057] In the tenth embodiment of the present invention, for example, the gas separation system of any one of the first to ninth embodiments further comprises: a first separation membrane unit that accommodates the first separation membrane; a first recovery section that recovers the first permeated gas; and a first recovery path that is connected to the first separation membrane unit and the first recovery section and is used to transport the first permeated gas to the first recovery section.

[0058] In the 11th embodiment of the present invention, for example, the gas separation system of the 10th embodiment further comprises: a second separation membrane unit that accommodates the second separation membrane; and a discharge path that is connected to the second separation membrane unit and is used to discharge the second non-permeable gas from the second separation membrane unit, wherein the discharge path merges with the first recovery path at a confluence position.

[0059] In the 12th aspect of the present invention, for example, the gas separation system of any one of the 1st to 11th aspects further comprises: a second separation membrane unit for accommodating the second separation membrane; a second recovery section for recovering the second permeated gas; and a second recovery path connected to the second separation membrane unit and the second recovery section, for transporting the second permeated gas to the second recovery section.

[0060] In a thirteenth aspect of the present invention, for example, in the gas separation system according to any one of the first to twelfth aspects, the first separation membrane includes a resin layer containing a resin or a metal layer containing a metal as the separation function layer.

[0061] In a fourteenth aspect of the present invention, for example, in the gas separation system according to any one of the first to thirteenth aspects, the second separation membrane includes a separation functional layer containing a polyether block amide resin or an ionic liquid.

[0062] A fifteenth aspect of the present invention is a method for separating a mixed gas, comprising:

[0063] a first separation step of separating a mixed gas containing gas A and gas B different from gas A into a first permeated gas and a first non-permeated gas via a first separation membrane that allows gas A to preferentially permeate; and

[0064] a second separation step of separating the first non-permeated gas into a second permeated gas and a second non-permeated gas via a second separation membrane that allows the gas B to preferentially permeate;

[0065] The separation coefficient α1 of the gas A to the gas B of the first separation membrane obtained by the following test and the separation coefficient α2 of the gas B to the gas A of the second separation membrane obtained by the following test satisfy the following equations (1) and (2):

[0066] Test: A test piece is prepared using the first separation membrane or the second separation membrane; a test gas obtained from the gas A and the gas B is supplied to a space adjacent to one side of the test piece, and the space adjacent to the other side of the test piece is depressurized; the separation coefficient α1 or the separation coefficient α2 is determined based on the result of the operation; wherein, in the operation, the content of the gas A in the test gas is 50 vol% under standard conditions, the test gas supplied to the space adjacent to the one side is at a temperature of 30° C. and a pressure of 0.1 MPa, and the space adjacent to the other side is depressurized in such a manner that the pressure in the space is reduced by 0.1 MPa relative to the atmospheric pressure in the measurement environment.

[0067] α1 / α2≥1.9 (1)

[0068] α2≤50 (2).

[0069] Hereinafter, the present invention will be described in detail, but the following description is not intended to limit the present invention to specific embodiments.

[0070] <Gas Separation System>

[0071] like Figure 1 As shown, the gas separation system 100 of this embodiment includes a first separation membrane 11 and a second separation membrane 21. Specifically, the gas separation system 100 includes a first separation membrane unit 10 housing the first separation membrane 11 and a second separation membrane unit 20 housing the second separation membrane 21. The first separation membrane unit 10 is a membrane separation device that performs membrane separation on a mixed gas using the first separation membrane 11. The first separation membrane 11 can separate the mixed gas into a first permeated gas and a first non-permeated gas. The second separation membrane unit 20 is a membrane separation device that performs membrane separation on the first non-permeated gas discharged from the first separation membrane unit 10 using the second separation membrane 21. The second separation membrane 21 can separate the first non-permeated gas into a second permeated gas and a second non-permeated gas.

[0072] The mixed gas processed by the first separation membrane unit 10 includes a gas A and a gas B different from gas A. Examples of gas A and gas B include hydrogen and carbon dioxide. In one example, gas A is hydrogen and gas B is carbon dioxide. However, depending on the circumstances, gas A may also be carbon dioxide and gas B may be hydrogen.

[0073] The first separation membrane 11 preferentially permeates gas A. Therefore, the first permeated gas separated by the first separation membrane 11 has a higher gas A content and a lower gas B content than the mixed gas. On the other hand, the first non-permeated gas has a lower gas A content and a higher gas B content than the mixed gas.

[0074] The second separation membrane 21 allows gas B to preferentially permeate. Therefore, the second permeated gas separated by the second separation membrane 21 has a higher gas B content than the first non-permeated gas, and a lower gas A content than the first non-permeated gas. On the other hand, the second non-permeated gas has a lower gas B content than the first non-permeated gas, and a higher gas A content than the first non-permeated gas.

[0075] In the gas separation system 100, the separation coefficient α1 of gas A relative to gas B of the first separation membrane 11 obtained by the following experiment and the separation coefficient α2 of gas B relative to gas A of the second separation membrane 21 obtained by the following experiment satisfy the following relationship equations (1) and (2).

[0076] Test: A test piece is prepared using the first separation membrane 11 or the second separation membrane 21. An operation (separation operation) is performed in which a test gas obtained by gas A and gas B is supplied to a space adjacent to one side of the test piece, and the space adjacent to the other side of the test piece is depressurized. Based on the result of the separation operation, the separation coefficient α1 or the separation coefficient α2 is determined. In the separation operation, the content of gas A in the test gas is 50 vol% under standard conditions, the temperature of the test gas supplied to the space adjacent to one side is 30°C and the pressure is 0.1 MPa, and the space adjacent to the other side is depressurized in such a way that the pressure in the space is reduced by 0.1 MPa relative to the atmospheric pressure in the measurement environment.

[0077] α1 / α2≥1.9 (1)

[0078] α2≤50 (2)

[0079] In the above test, the test piece can be prepared by, for example, cutting the first separation membrane 11 or the second separation membrane 21 into a disk shape with a diameter of 20 mm. The size of the disk-shaped test piece can be 20 mm or more in diameter.

[0080] The separation operation of the above test can be performed, for example, by the following method. First, the test piece is placed in a metal chamber and sealed with an O-ring to prevent leakage. Next, the test gas is injected into the space (supply space) in the metal chamber in such a manner that the test gas contacts the main surface of one side of the test piece (for example, the main surface 11a or 21a described later). As described above, the content of gas A in the test gas injected into the supply space is 50 vol% under standard conditions (0°C, 101 kPa). The temperature of the test gas is 30°C and the pressure is 0.1 MPa. It should be noted that in this specification, "pressure" refers to absolute pressure unless otherwise specified.

[0081] Next, a vacuum pump is used to depressurize the space (permeation space) within the metal cell adjacent to the other main surface of the test piece (e.g., main surface 11b or 21b, described later). At this time, the permeation space is depressurized so that the pressure within the space is reduced by 0.1 MPa relative to the atmospheric pressure in the measurement environment. Thus, a permeated fluid that has permeated the test piece is obtained in the permeation space. The separation coefficient α of the test piece can be calculated based on the weight of the permeated fluid and the volume ratio of gas A and gas B in the permeated fluid. Specifically, by performing the above separation operation using a test piece made from the first separation membrane 11, the separation coefficient α1 (Gas A / Gas B) of the first separation membrane 11 can be calculated. By performing the above separation operation using a test piece made from the second separation membrane 21, the separation coefficient α2 (Gas B / Gas A) of the second separation membrane 21 can be calculated.

[0082] Specifically, the separation coefficient α can be calculated according to the following formula. When calculating the separation coefficient α1 (gas A / gas B) of the first separation membrane 11, in the following formula, X A and X B are the volume ratios of gas A and gas B in the test gas, and Y A and Y B are the volume ratio of gas A and the volume ratio of gas B in the permeated fluid that has permeated the test piece. On the other hand, when calculating the separation coefficient α2 (gas B / gas A) of the second separation membrane 21, in the following formula, X A and X B are the volume ratio of gas B and gas A in the test gas, Y A and Y B These are the volume ratio of gas B and the volume ratio of gas A in the permeating fluid that has permeated the test piece. These volume ratios are values under standard conditions (0° C., 101 kPa).

[0083] Separation coefficient α=(Y A / Y B ) / (X A / X B )

[0084] In the gas separation system 100, by satisfying the relationship (1) (α1 / α2 ≥ 1.9), even when the separation coefficient α2 of the second separation membrane 21 is a small value of 50 or less (particularly 20 or less), there is a tendency to be able to separate the mixed gas at a sufficiently high recovery rate and recovery purity. In particular, in a separation membrane that preferentially permeates carbon dioxide, there is a tendency to be difficult to adjust the separation coefficient of carbon dioxide to a high value. According to the gas separation system 100, by using a separation membrane that preferentially permeates carbon dioxide as the second separation membrane 21, there is a tendency to be able to separate the mixed gas at a sufficiently high recovery rate and recovery purity even without adjusting the separation coefficient of the separation membrane to a high value.

[0085] The ratio of the separation coefficient α1 to the separation coefficient α2 (α1 / α2) may be 2.0 or greater, 2.3 or greater, 2.5 or greater, 2.8 or greater, 3.0 or greater, 3.5 or greater, or even 4.0 or greater. The upper limit of the ratio (α1 / α2) is not particularly limited, and may be, for example, 10.0 or less, or 8.0 or less.

[0086] The separation coefficient α1 of the first separation membrane 11 is not particularly limited as long as it satisfies the above-mentioned relational expression (1), and may be, for example, 5 or more, 10 or more, 15 or more, 20 or more, 25 or more, 30 or more, 40 or more, 50 or more, 60 or more, 70 or more, or even 80 or more. The upper limit of the separation coefficient α1 is, for example, 200 or less, 150 or less, or 100 or less.

[0087] The separation coefficient α2 of the second separation membrane 21 is not particularly limited as long as it satisfies the above-mentioned equations (1) and (2), and may be, for example, 40 or less, 30 or less, 25 or less, 20 or less, 15 or less, or even 10 or less. The lower limit of the separation coefficient α2 is, for example, greater than 1, and may be 2 or more, 3 or more, 4 or more, or even 5 or more.

[0088] It should be noted that the permeation rate T1 of the gas A passing through the first separation membrane 11 is not particularly limited, and may be, for example, 1 GPU or more, 5 GPU or more, 10 GPU or more, 50 GPU or more, or even 100 GPU or more. The upper limit of the permeation rate T1 is not particularly limited, and may be, for example, 1000 GPU or less. Here, GPU refers to 10 -6 cm 3 (STP) / (sec·cm 2 cmHg). 3 (STP) refers to the volume of gas under the conditions of 1 atmosphere and 0° C. The permeation rate T1 can be calculated based on the results of the above-mentioned separation operation using a test piece prepared using the first separation membrane 11 .

[0089] The permeation rate T2 of gas B passing through the second separation membrane 21 is not particularly limited, and may be, for example, 1 GPU or greater, 5 GPU or greater, 10 GPU or greater, 50 GPU or greater, or even 100 GPU or greater. The upper limit of the permeation rate T2 is not particularly limited, and may be, for example, 1000 GPU or less. The permeation rate T2 can be calculated based on the results of the above-described separation operation using a test piece prepared using the second separation membrane 21.

[0090] The gas separation system 100 of the present embodiment further includes a mixed gas supply path 30. The mixed gas supply path 30 is connected to the mixed gas inlet (inlet 13a) of the first separation membrane unit 10, and is a path for supplying a mixed gas from a tank (not shown) storing the mixed gas to the first separation membrane unit 10. The mixed gas supply path 30 can be directly connected to a source of mixed gas, or can be a structure that continuously supplies mixed gas from the source to the first separation membrane unit 10. For example, a pressurizing device 40 for increasing the pressure of the mixed gas is provided in the mixed gas supply path 30. Examples of the pressurizing device 40 include a compressor, a blower, and a back pressure valve. The pressurizing device 40 can pressurize the supply side space of the first separation membrane unit 10 by increasing the pressure of the mixed gas.

[0091] In the mixed gas supply path 30, a heat exchanger (not shown) may be disposed between the pressurizing device 40 and the first separation membrane unit 10. The heat exchanger cools, for example, the mixed gas pressurized by the pressurizing device 40. The heat exchanger is, for example, a gas-liquid heat exchanger that exchanges heat between a cooling medium such as antifreeze and the mixed gas, and is typically a fin-tube heat exchanger.

[0092] The gas separation system 100 further includes a non-permeable gas supply path 32. The non-permeable gas supply path 32 is connected to the non-permeable gas outlet (outlet 13b) of the first separation membrane unit 10 and the non-permeable gas inlet (inlet 23a) of the second separation membrane unit 20, and is used to supply the first non-permeable gas from the first separation membrane unit 10 to the second separation membrane unit 20. The non-permeable gas supply path 32 does not need to include a tank such as a trap for collecting the first non-permeable gas or an on-off valve for opening and closing the path. With this configuration, the first non-permeable gas discharged from the first separation membrane unit 10 can be continuously supplied to the second separation membrane unit 20, making it easy to increase the amount of mixed gas processed per unit time. As an example, the non-permeable gas supply path 32 can also be composed solely of piping.

[0093] The gas separation system 100 further includes a first recovery path 34 and a first recovery section 42. The first recovery path 34 is connected to the permeated gas outlet (outlet 14a) of the first separation membrane unit 10 and the inlet of the first recovery section 42, and is a path for transporting the first permeated gas from the first separation membrane unit 10 to the first recovery section 42. The first recovery section 42 recovers the first permeated gas transported from the first separation membrane unit 10 and can, for example, store the first permeated gas. The first recovery section 42 is, for example, a tank for storing the first permeated gas.

[0094] The gas separation system 100 further includes a second recovery path 36 and a second recovery section 44. The second recovery path 36 is connected to the permeated gas outlet (outlet 24a) of the second separation membrane unit 20 and the inlet of the second recovery section 44, and is a path for transporting the second permeated gas from the second separation membrane unit 20 to the second recovery section 44. The second recovery section 44 recovers the second permeated gas transported from the second separation membrane unit 20 and can, for example, store the second permeated gas. The second recovery section 44 is, for example, a tank for storing the second permeated gas.

[0095] The gas separation system 100 further includes a discharge path 38. The discharge path 38 is connected to the non-permeated gas outlet (outlet 23b) of the second separation membrane unit 20 and is a path for discharging the second non-permeated gas from the second separation membrane unit 20. The discharge path 38 merges with the first recovery path 34, for example, at a merging position 35. By merging the discharge path 38 with the first recovery path 34, the first permeated gas and the second non-permeated gas can be mixed in the first recovery path 34. As a result, for gas A, there is a tendency to further improve the recovery rate without significantly reducing the recovery purity. It should be noted that in the gas separation system 100, when the pressure of the mixed gas supplied to the first separation membrane unit 10 is high, there is a tendency for the pressure of the second non-permeated gas to also be high. By mixing the first permeated gas and the second non-permeated gas of high pressure, a gas (recovered gas) having a higher pressure than the first permeated gas can be obtained.

[0096] It should be noted that the exhaust path 38 may not merge with the first recovery path 34. The exhaust path 38 may also be directly connected to the first recovery part 42. A pressure reducing device and a heat exchanger (not shown) may also be arranged on the exhaust path 38. The pressure reducing device can be used to reduce the pressure of the second non-permeable gas to the atmospheric pressure (e.g., 101 kPa) in the external environment. As the pressure reducing device, a pressure reducing valve can be cited, for example. The heat exchanger is located, for example, between the pressure reducing device and the merging position 35. The heat exchanger heats the second non-permeable gas after the pressure is reduced by the pressure reducing device. The heat exchanger is, for example, a gas-liquid heat exchanger that generates heat exchange between a heat medium such as warm water and the second non-permeable gas, and is typically a fin-tube heat exchanger.

[0097] Unless otherwise specified, each path of the gas separation system 100 is composed of a pipe made of metal or resin, for example.

[0098] The gas separation system 100 may further include a controller (not shown) for controlling the various components of the gas separation system 100. The controller is, for example, a DSP (Digital Signal Processor) that includes an A / D converter circuit, input / output circuits, arithmetic circuits, a storage device, and the like. The controller stores a program for properly operating the gas separation system 100.

[0099] The gas separation system 100 of the present embodiment is, for example, a continuous system. In this specification, the so-called continuous system refers to a system that can continuously process a mixed gas without closing the path constituting the gas separation system 100 using an on-off valve or the like. In other words, the gas separation system 100 can process the mixed gas using the first separation membrane unit 10, and the first non-permeable gas obtained in the first separation membrane unit 10 is directly processed using the second separation membrane unit 20 without being captured in a tank or the like. In this way, the gas separation system 100 of the present embodiment can achieve 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, for processing exhaust gas, and the like.

[0100] [First separation membrane unit]

[0101] like Figure 2 As shown, the first separation membrane unit 10 includes a first 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-side space, and the space within the second chamber 14 corresponds to the permeate-side space. The first separation membrane 11 is disposed within the tank 12. Within the tank 12, the first separation membrane 11 separates the first chamber 13 from the second chamber 14. The first separation membrane 11 extends from one side of a pair of walls of the tank 12 to the other side.

[0102] The first chamber 13 has an inlet 13a and an outlet 13b. The second chamber 14 has an outlet 14a. The inlet 13a of the first chamber 13 is an opening for supplying the mixed gas 70 to the first separation membrane unit 10. The outlet 14a of the second chamber 14 is an opening for discharging the first permeated gas 80 obtained by the mixed gas 70 permeating through the first separation membrane 11 from the first separation membrane unit 10. The outlet 13b of the first chamber 13 is an opening for discharging the mixed gas 70 that has not permeated the first separation membrane 11 (first non-permeated gas 81) from the first separation membrane unit 10. The inlet 13a, outlet 13b, and outlet 14a are each formed, for example, on the wall surface of the tank 12.

[0103] (First separation membrane)

[0104] In the gas separation system 100 of this embodiment, the membrane area M1 of the first separation membrane 11 is preferably greater than the membrane area M2 of the second separation membrane 21. The ratio M1 / M2 of the membrane area M1 of the first separation membrane 11 to the membrane area M2 of the second separation membrane 21 can be, for example, greater than 1.0, 1.3 or greater, 1.5 or greater, 1.8 or greater, or even 2.0 or greater. The upper limit of the ratio M1 / M2 is not particularly limited and can be, for example, 10 or less, or 5.0 or less.

[0105] As described above, the first separation membrane 11 allows gas A contained in the mixed gas 70 to preferentially permeate. Below, the first separation membrane 11 is described when gas A is hydrogen, i.e., the first separation membrane 11 preferentially permeates hydrogen. In this specification, a separation membrane that preferentially permeates hydrogen is sometimes referred to as a "hydrogen permeable membrane." It should be noted that the first separation membrane 11 may also be a separation membrane other than a hydrogen permeable membrane (for example, a carbon dioxide permeable membrane described later).

[0106] like Figure 3 As shown, the first separation membrane 11 as a hydrogen permeable membrane, for example, comprises a separation functional layer 1. As the separation functional layer 1, a resin layer comprising a resin, a metal layer comprising a metal, etc. can be cited. In other words, the first separation membrane 11 comprises a resin layer comprising a resin or a metal layer comprising a metal as the separation functional layer 1. The first separation membrane 11 may further comprise a support 3 for supporting the separation functional layer 1, and a coating 2 for coating the separation functional layer 1. The separation functional layer 1 is, for example, arranged between the coating 2 and the support 3, and is directly in contact with the coating 2 and the support 3, respectively. However, an adhesive may also be arranged between the separation functional layer 1 and the support 3. Other supports may also be arranged between the separation functional layer 1 and the coating 2. The first separation membrane 11 has a main surface 11a on the coating 2 side, and a main surface 11b on the support 3 side.

[0107] Separation Functional Layer

[0108] The separation functional layer 1 is a layer that preferentially allows hydrogen to permeate. When the separation functional layer 1 is a resin layer, examples of the resin contained in the resin layer include polyamide resins and polyimide resins. The resin layer is preferably formed substantially of the resin. In this specification, the phrase "formed substantially of" excludes other components that alter the essential characteristics of the material in question, and for example, means that the material is composed of at least 95 wt%, or more preferably at least 99 wt%.

[0109] When the separation functional layer 1 is a metal layer, the metal contained in the metal layer is not particularly limited as long as it is a metal that has a hydrogen permeability function in its simple form or by alloying. 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.

[0110] The metal layer is preferably an alloy layer comprising a Pd alloy. The other metals forming the Pd alloy are not particularly limited, but are preferably Group 11 elements, more preferably at least one selected from the group consisting of Au, Ag and Cu. The metal layer preferably comprises 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%, further preferably 30 to 60 mol%, and particularly preferably 40 to 60 mol%. An alloy layer comprising a Pd-Ag alloy having an Ag content of 20 mol% or more, a Pd-Cu alloy having a Cu content of 30 mol% or more, or a Pd-Au alloy having an Au content of 20 mol% or more has the following tendency: even in a low temperature range of about 60°C or less, it is not easily embrittled by hydrogen. The Pd alloy may also contain metals of Group IB and / or Group IIIA.

[0111] The Pd alloy may not be an alloy of the two components mentioned above, but an alloy of three or more components. 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 value of the Au content in the alloy and the content of the other metals is preferably 55 mol% or less, more preferably 50 mol% or less, further preferably 45 mol% or less, and particularly preferably 40 mol% or less.

[0112] The metal layer is substantially formed of metal, for example.

[0113] The metal layer can be produced by, for example, rolling, sputtering, vacuum evaporation, ion plating, or plating. Rolling is suitable for producing a thicker metal layer, while sputtering is suitable for producing a thinner metal layer.

[0114] The rolling method can be hot rolling or cold rolling. The rolling method is a method of using one or more pairs of rollers to stretch the metal into a film while applying pressure. 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 thickness of the metal layer 5 μm or more, the generation of pinholes or cracks during production can be suppressed, and deformation when hydrogen is absorbed can be suppressed. By making the thickness of the metal layer 50 μm or less, for the metal layer, it is possible to suppress production costs and achieve sufficient hydrogen permeability.

[0115] The sputtering method can be performed by the following method using a sputtering device such as a parallel plate type, a monolithic type, a through type, a DC sputtering device and an RF sputtering device. First, a substrate is mounted on a sputtering device provided with a metal target. Next, the sputtering device is vacuum-exhausted and the Ar gas pressure is adjusted to a specified value. A specified sputtering current is passed through the metal target to form a metal film on the substrate. The metal film is peeled off from the substrate, thereby obtaining a metal layer. As a metal target, one or more targets can be used depending on the composition of the metal layer to be produced. As substrates used in the sputtering method, for example, glass plates, ceramic plates, silicon wafers, metal plates containing aluminum, stainless steel, etc. can be cited. It should be noted that, according to the sputtering method, a metal layer can also be formed directly on the support 3.

[0116] The thickness of the metal layer obtained by sputtering is preferably 0.01 to 5 μm, more preferably 0.05 to 2 μm. By making the thickness of the metal layer 0.01 μm or more, the generation of pinholes during production can be suppressed, and sufficient mechanical strength can be obtained. If the thickness of the metal layer is 0.01 μm or more, it is not easy to be damaged when peeled from the substrate, and there is a tendency for easy handling after peeling. When the thickness of the metal layer is 5 μm or less, the metal layer can be produced in a short time, which can suppress manufacturing costs.

[0117] "coating"

[0118] The material of the coating 2 is not particularly limited, and examples thereof include fluorine-based compounds, rubber-based polymers, silicone-based polymers, urethane-based polymers, polyester-based polymers, etc., and preferably at least one selected from the group consisting of fluorine-based compounds, rubber-based polymers, and silicone-based polymers.

[0119] As fluorine-based compounds, for example, compounds containing fluoroalkyl groups such as fluoroalkyl carboxylates, fluoroalkyl quaternary ammonium salts, and fluoroalkyl ethylene oxide adducts can be cited; compounds containing perfluoroalkyl groups such as perfluoroalkyl carboxylates, perfluoroalkyl quaternary ammonium salts, and perfluoroalkyl ethylene oxide adducts; fluorine-based polymers such as tetrafluoroethylene / hexafluoropropylene copolymers, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene polymers, vinylidene fluoride / tetrafluoroethylene copolymers, vinylidene fluoride / hexafluoropropylene copolymers, fluorine-containing (meth)acrylate polymers, fluorine-containing (meth)acrylate alkyl ester polymers, and copolymers of fluorine-containing (meth)acrylates and other monomers; fluorine-containing (meth)acrylates, etc. As fluorine-based compounds, the "DURASURF" series manufactured by Harves, the "OPTOOL" series manufactured by Daikin Industries, Ltd., and the "KY-100" series manufactured by Shin-Etsu Chemical Co., Ltd. can be used.

[0120] Examples of the rubber polymer 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, and ethylene-vinyl acetate copolymer rubber. Examples of the rubber polymer include the "ELEP COAT" series manufactured by Nitto Shinko Corporation.

[0121] Examples of the silicone polymer include polydimethylsiloxane, alkyl-modified polydimethylsiloxane, carboxyl-modified polydimethylsiloxane, amino-modified polydimethylsiloxane, epoxy-modified polydimethylsiloxane, fluorine-modified polydimethylsiloxane, and (meth)acrylate-modified polydimethylsiloxane.

[0122] The coating layer 2 can be formed, for example, by applying a composition containing the material of the coating layer 2 onto the separation functional layer 1 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, rod coating, knife coating, die coating, inkjet coating, and gravure coating.

[0123] The solvent contained in the composition can be appropriately selected according to the raw material of the coating 2. When a fluorine-based compound is used as the material of the coating 2, the solvent can be one of a fluorine-based solvent, an alcohol solvent, an ether solvent, an ester solvent, a hydrocarbon solvent, or the like, or a mixture of two or more thereof. Among these solvents, it is preferred to use a non-flammable and rapidly volatile fluorine-based solvent alone or in a mixture with other solvents.

[0124] Examples of the fluorine-based solvent include hydrofluoroether, perfluoropolyether, perfluoroalkane, hydrofluoropolyether, hydrofluorocarbon, perfluorocyclic ether, perfluorocycloalkane, hydrofluorocycloalkane, xylenehexafluoride, hydrofluorochlorocarbon, and perfluorocarbon.

[0125] The thickness of the coating layer 2 is not particularly limited, but is preferably 0.1 μm or greater, more preferably 0.3 μm or greater, further preferably 0.5 μm or greater, and particularly preferably 1.0 μm or greater. The thickness of the coating layer 2 is, for example, 80 μm or less, preferably 50 μm or less, more preferably 30 μm or less, further preferably 20 μm or less, particularly preferably 10 μm or less, and particularly preferably 5 μm or less. The thickness of the coating layer 2 can be adjusted by the solid content concentration of the composition comprising the material of the coating layer 2 and the number of times the composition is applied. The coating layer 2 is preferably non-porous.

[0126] Supporting Body

[0127] The support 3 is not particularly limited as long as it has hydrogen permeability and supports the separation functional layer 1. For example, it can be a porous body. However, the support 3 can also be non-porous. The support 3 can also be a fabric, a non-woven fabric, etc. Examples of the material of the support 3 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; polyimides, etc., preferably chemically and thermally stable polysulfones or polytetrafluoroethylene.

[0128] The support 3 is preferably a porous body with an average pore diameter of 100 μm or less. This porous body has sufficient surface smoothness, making it easy to form a metal layer of uniform thickness when directly forming the metal layer on the porous body using a sputtering method or the like. This also helps prevent the formation of pinholes and cracks in the metal layer. The thickness of the support 3 is not particularly limited, but is, for example, 5 to 1000 μm, preferably 10 to 300 μm.

[0129] Shape of the first separation membrane

[0130] In this embodiment, the first separation membrane 11 is typically a flat membrane. However, the first separation membrane 11 may be in a shape other than a flat membrane, for example, a hollow fiber membrane.

[0131] [Second separation membrane unit]

[0132] like Figure 4 As shown, the second separation membrane unit 20 includes a second separation membrane 21 and a tank 22. The tank 22 has a third chamber 23 and a fourth chamber 24. The space within the third chamber 23 corresponds to the supply-side space, and the space within the fourth chamber 24 corresponds to the permeate-side space. The second separation membrane 21 is disposed within the tank 22. Within the tank 22, the second separation membrane 21 separates the third chamber 23 from the fourth chamber 24. The second separation membrane 21 extends from one side of a pair of walls of the tank 22 to the other side.

[0133] The third chamber 23 has an inlet 23a and an outlet 23b. The fourth chamber 24 has an outlet 24a. The inlet 23a of the third chamber 23 is an opening for supplying the first retentate gas 81 to the second separation membrane unit 20. The outlet 24a of the fourth chamber 24 is an opening for discharging the second permeated gas 90 obtained by the first retentate gas 81 permeating through the second separation membrane 21 from the second separation membrane unit 20. The outlet 23b of the third chamber 23 is an opening for discharging the first retentate gas 81 (second retentate gas 91) that has not permeated the second separation membrane 21 from the second separation membrane unit 20. The inlet 23a, outlet 23b, and outlet 24a are each formed on a wall surface of the tank 22, for example.

[0134] (Second separation membrane)

[0135] As described above, the second separation membrane 21 preferentially permeates the gas B contained in the first non-permeated gas 81. Below, the second separation membrane 21 is described when the gas B is carbon dioxide, i.e., the second separation membrane 21 that preferentially permeates carbon dioxide. In this specification, a separation membrane that preferentially permeates carbon dioxide may sometimes be referred to as a "carbon dioxide permeable membrane." It should be noted that the second separation membrane 21 may also be a separation membrane other than a carbon dioxide permeable membrane (for example, the aforementioned hydrogen permeable membrane).

[0136] like Figure 5 As shown, the second separation membrane 21, which is a carbon dioxide permeable membrane, includes, for example, a separation functional layer 5. The second separation membrane 21 may further include a porous support 7 supporting the separation functional layer 5, and an intermediate layer 6 disposed between the separation functional layer 5 and the porous support 7. The intermediate layer 6 is, for example, directly in contact with the separation functional layer 5 and the porous support 7, respectively. The second separation membrane 21 has a main surface 21a facing the separation functional layer 5 and a main surface 21b facing the porous support 7.

[0137] Separation Functional Layer

[0138] The functional separation layer 5 is a layer that preferentially allows carbon dioxide to permeate. In one preferred embodiment, the functional separation layer 5 comprises a resin. Examples of the resin contained in the functional separation layer 5 include polyether block amide resins, polyamide resins, polyether resins, polyimide resins, cellulose acetate resins, silicone resins, and fluororesins. The functional separation layer 5 preferably comprises a polyether block amide resin. In this embodiment, the functional separation layer 5 is preferably formed substantially of a resin.

[0139] In another preferred embodiment, the separation functional layer 5 contains an ionic liquid. An ionic liquid is a salt (ionic compound) that is liquid at 25° C. Thus, in the second separation membrane 21 , the separation functional layer 5 may contain a polyether block amide resin or an ionic liquid.

[0140] The separation functional layer 5 may comprise a double network gel containing an ionic liquid. A double network gel is a gel having two independent network structures. For example, a double network gel comprises a first network structure primarily composed of an organic material, a second network structure primarily composed of an inorganic material, and an ionic liquid. It should be noted that the second network structure may also be primarily composed of an organic material different from that of the first network structure. In this specification, "primarily composed of" means that the material constitutes at least 50 wt%, and further, at least 70 wt%.

[0141] The organic material used to constitute the first mesh structure includes, for example, polymers such as polyacrylamide (especially polydialkyl acrylamide such as polydimethylacrylamide). The polymer contained in the organic material has a structural unit derived from an acrylamide derivative and may also include a cross-linked structure. The polymer containing a cross-linked structure can be made by a known method. For example, first, a prepolymer containing a structural unit having an N-hydroxysuccinimide ester group is prepared. The structural unit having an N-hydroxysuccinimide ester group is derived from, for example, N-acryloyloxysuccinimide. Next, a polymer containing a cross-linked structure can be obtained by reacting the prepolymer with an amine cross-linking agent. The amine cross-linking agent is a compound having two or more primary amino groups, for example, ethylene glycol bis(3-aminopropyl) ether.

[0142] The second mesh structure may also include a network of multiple particles. The network of multiple particles is formed, for example, by multiple particles being bonded to each other via hydrogen bonds. The particles included in the second mesh structure may be particles exemplified as nanoparticles described later. As an example, the particles included in the second mesh structure are silica particles.

[0143] In the present embodiment, specific examples of the ionic liquid include ionic liquids having imidazolium, pyridinium, ammonium, or phosphonium, and a substituent having 1 or more carbon atoms.

[0144] In the ionic liquid having an imidazolium group and a substituent having 1 or more carbon atoms, examples of the substituent having 1 or more carbon atoms include an alkyl group having 1 or more carbon atoms and 20 or less, a cycloalkyl group having 3 or more carbon atoms and 14 or less carbon atoms, and an aryl group having 6 or more carbon atoms and 20 or less carbon atoms. These may be further substituted with a hydroxyl group, a cyano group, an amino group, a monovalent ether group, or the like (for example, a hydroxyalkyl group having 1 or more carbon atoms and 20 or less carbon atoms).

[0145] Examples of the alkyl group having 1 to 20 carbon atoms include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, n-eicosyl, isopropyl, sec-butyl, isobutyl, 1-methylbutyl, 1-ethylpropyl, 2-methylbutyl, isopentyl, neopentyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl, tert-pentyl, 2-ethylhexyl, and 1,5-dimethylhexyl. These groups may be further substituted with a hydroxyl group, a cyano group, an amino group, a monovalent ether group, or the like.

[0146] The above-mentioned alkyl groups may be substituted with cycloalkyl groups. The number of carbon atoms of the alkyl group substituted with cycloalkyl groups is, for example, 1 or more and 20 or less. Examples of the alkyl group substituted with cycloalkyl groups include cyclopropylmethyl, cyclobutylmethyl, cyclohexylmethyl, and cyclohexylpropyl groups, which may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, and the like.

[0147] Examples of the cycloalkyl group having 3 to 14 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclododecyl, norbornyl, bornyl, and adamantyl groups, which may be further substituted with hydroxyl, cyano, amino, monovalent ether groups, and the like.

[0148] Examples of the aryl group having 6 to 20 carbon atoms include phenyl, tolyl, xylyl, mesityl, methoxyphenyl, naphthyl, and benzyl groups, which may be further substituted with hydroxyl, cyano, amino, or monovalent ether groups.

[0149] The compound having an imidazolium and a substituent having 1 or more carbon atoms may further have a substituent such as an alkyl group, and may also form a salt with a counter anion. As the counter anion, alkyl sulfate, toluenesulfonate, methanesulfonate, acetate, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, thiocyanate, dicyanamide, tricyanomethane anion, tetracyanoborate, hexafluorophosphate, tetrafluoroborate, halide, etc. may be mentioned. From the viewpoint of gas separation performance, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, dicyanamide, tricyanomethane anion, tetracyanoborate are preferred.

[0150] Specific examples of the ionic liquid having imidazolium and a substituent having 1 or more carbon atoms include 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium dicyanamide, 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-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide 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-dimesityl imidazolium 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 chloride, 1-methyl-3-n-octylimidazolium hexafluorophosphate, 1-methyl-3-[6-(methylsulfinyl)hexyl]imidazolium p-toluenesulfonate, 1-ethyl-3-methylimidazolium tricyanomethane tricyanomethanide), 1-ethyl-3-methylimidazolium tetracyanoborate, 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, etc.

[0151] Among them, from the viewpoint of gas separation performance, particularly preferred are 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMI][FSI]), 1-ethyl-3-methylimidazolium dicyanamide ([EMI][DCA]), 1-ethyl-3-methylimidazolium tricyanomethane ([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]).

[0152] 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.

[0153] The ionic liquid content in the double network gel is, for example, 50 wt% or greater, preferably 60 wt% or greater, more preferably 70 wt% or greater, and even more preferably 80 wt% or greater. The higher the ionic liquid content, the more the separation functional layer 5 can preferentially permeate carbon dioxide contained in the mixed gas. The upper limit of the ionic liquid content is not particularly limited, but is, for example, 95 wt%.

[0154] The content of the first mesh structure mainly composed of organic materials in the double network gel 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 mesh structure is, for example, 15 wt%. From the perspective of improving the strength of the double network gel, the content of the second mesh structure mainly composed of inorganic materials in the double network gel is, for example, 1 wt% or more. The upper limit of the content of the second mesh structure is, for example, 5 wt%. The ratio of the total weight of the first mesh structure and the weight of the second mesh 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 5 is preferably substantially formed by the double network gel.

[0155] The thickness of the separation functional layer 5 is, for example, 50 μm or less, preferably 25 μm or less, and more preferably 15 μm or less. Depending on the circumstances, the thickness of the separation functional layer 5 may be 10 μm or less, 5.0 μm or less, or 2.0 μm or less. The thickness of the separation functional layer 5 may be 0.05 μm or more, or 0.1 μm or more.

[0156] The Middle Layer

[0157] Intermediate layer 6 may comprise, for example, a resin and may further comprise nanoparticles dispersed in the resin (matrix). The nanoparticles may be spaced apart from one another within the matrix or 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 comprises a silicone resin.

[0158] Nanoparticles may contain inorganic materials or organic materials. Examples of inorganic materials contained in nanoparticles include silicon dioxide, titanium dioxide, and aluminum oxide. Preferably, the nanoparticles contain silicon dioxide.

[0159] The thickness of the intermediate layer 6 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 6 is not particularly limited, and is, for example, 1 μm. The intermediate layer 6 is, for example, a layer having a thickness of less than 50 μm.

[0160] Porous Support

[0161] The porous support 7 supports the separation functional layer 5 via the intermediate layer 6. Examples of the porous support 7 include: nonwoven fabric; porous polytetrafluoroethylene; aromatic polyamide fiber; porous metal; sintered metal; porous ceramic; porous polyester; porous nylon; activated carbon fiber; latex; silicone; silicone rubber; a permeable (porous) polymer comprising at least one selected from the group consisting of polyvinyl fluoride, polyvinylidene fluoride, polyurethane, polypropylene, polyethylene, polystyrene, polycarbonate, polysulfone, polyetheretherketone, polyacrylonitrile, polyimide, and polyphenylene ether; metal foam having open or closed cells; polymer foam having open or closed cells; silica; porous glass; mesh; and the like. The porous support 7 may also be a combination of two or more of these.

[0162] The porous support 7 has an average pore diameter of, for example, 0.01 to 0.4 μm. The thickness of the porous support 7 is not particularly limited, but is, for example, 10 μm or greater, preferably 20 μm or greater, and more preferably 50 μm or greater. The thickness of the porous support 7 is, for example, 300 μm or less, preferably 200 μm or less, and more preferably 150 μm or less.

[0163] Shape of the Second Separation Membrane

[0164] In this embodiment, the second separation membrane 21 is typically a flat membrane. However, the second separation membrane 21 may be in a shape other than a flat membrane, for example, a hollow fiber membrane.

[0165] <<Method for producing the second separation membrane>>

[0166] The second separation membrane 21 can be produced, for example, by the following method. First, a coating liquid containing the material of the intermediate layer 6 is prepared. Next, the coating liquid containing the material of the intermediate layer 6 is coated on the porous support 7 to form a coating film. The coating method of the coating liquid is not particularly limited, and for example, a wire rod can be used. By adjusting the wire diameter of the wire rod and the concentration of the material of the intermediate layer 6 in the coating liquid, the thickness of the intermediate layer 6 formed can be adjusted. It should be noted that the coating film can also be formed by immersing the porous support 7 in the coating liquid. Next, the coating film is dried to form the intermediate layer 6. The drying of the coating film can be carried out, for example, under heating conditions. The heating temperature of the coating film is, for example, above 50°C. The heating time of the coating film is, for example, more than 1 minute, and can also be more than 5 minutes.

[0167] If necessary, an adhesion-facilitating treatment may be applied to the surface of the intermediate layer 6. As the adhesion-facilitating treatment, a surface treatment such as primer coating, corona discharge treatment, or plasma treatment may be applied.

[0168] Next, a coating liquid containing the material for the separation functional layer 5 is prepared. This coating liquid containing the material for the separation functional layer 5 is applied onto the intermediate layer 6 to form a coating film. This coating film is dried to form the separation functional layer 5. The coating liquid application method and drying conditions described above for the intermediate layer 6 can be employed. It should be noted that the coating liquid containing the material for the separation functional layer 5 can also be applied by spin coating. This results in the second separation membrane 21.

[0169] The method for producing the second separation membrane 21 is not limited to the method described above. For example, the second separation membrane 21 can also be produced by the following method. For example, a coating liquid containing the material for the separation functional layer 5 is applied to a transfer membrane to form a coating film. The coating film is dried to form the separation functional layer 5. Next, a coating liquid containing the material for the intermediate layer 6 is applied to the separation functional layer 5 and dried to form the intermediate layer 6. The stack of the intermediate layer 6 and the separation functional layer 5 is transferred to the porous support 7. Thus, the second separation membrane 21 is obtained.

[0170] The first separation membrane unit 10 and the second separation membrane unit 20 included in the gas separation system 100 are suitable for a flow-through (continuous) membrane separation method. However, these separation membrane units can also be used for a batch-type membrane separation method.

[0171] [Method for separating mixed gases]

[0172] In this embodiment, the method for separating the mixed gas 70 includes a first separation step using the first separation membrane 11 and a second separation step using the second separation membrane 21. The separation method may further include a recovery step for separately recovering the first permeated gas 80 obtained in the first separation step and the second permeated gas 90 obtained in the second separation step.

[0173] The first separation step can be implemented, for example, as follows. First, the mixed gas 70 is supplied to the first chamber 13 (supply side space) of the first separation membrane unit 10 via the mixed gas supply path 30. The mixed gas 70 can be pressurized by, for example, the pressurizing device 40 and supplied to the first chamber 13. The pressure of the mixed gas 70 pressurized by the pressurizing device 40, that is, the pressure in the supply side space of the first separation membrane unit 10, is, for example, 0.1 MPa or more, preferably 0.5 MPa or more, and may also be 1.0 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.

[0174] As described above, the mixed gas 70 includes gas A and gas B. As an example, gas A is hydrogen and gas B is carbon dioxide. However, depending on the situation, gas A may be carbon dioxide and gas B may be hydrogen. Typically, the mixed gas 70 is an exhaust gas from a chemical plant, such as an exhaust gas produced by a shift reaction. However, the gas separation system 100 of this embodiment can also be used to separate mixed gases 70 other than the above-mentioned composition. For example, gas A or gas B may be one gas selected from non-polar gases such as nitrogen, methane, and oxygen, inert gases such as helium, and other acidic gases other than carbon dioxide. As other acidic gases other than carbon dioxide, for example, hydrogen sulfide, carbonyl sulfide, sulfur oxides (SO x ), hydrogen cyanide, nitrogen oxides (NO x )wait.

[0175] The content of gas A in the mixed gas 70 is, for example, 10 vol% or more, or 20 vol% or more, or 40 vol% or more, or 50 vol% or more. The upper limit of the content of gas A in the mixed gas 70 is not particularly limited, and is, for example, 80 vol%. The content of gas B in the mixed gas 70 is, for example, 10 vol% or more, or 20 vol% or more, or 40 vol% or more, or 50 vol% or more. The upper limit of the content of gas B in the mixed gas 70 is not particularly limited, and is, for example, 80 vol%. The ratio of the volume of gas A to the total volume of gas A and gas B in the mixed gas 70 is not particularly limited, and is, for example, 20 to 80 vol%. In this specification, unless otherwise specified, "content" and "volume" refer to values under standard conditions (0°C, 101 kPa).

[0176] The mixed gas 70 supplied to the first chamber 13 of the first separation membrane unit 10 passes through the first separation membrane 11 and is separated into a first permeated gas 80 and a first non-permeated gas 81. The first permeated gas 80 is then supplied to the second chamber 14. The first permeated gas 80 supplied to the second chamber 14 is discharged to the exterior of the first separation membrane unit 10 through the outlet 14a. The first permeated gas 80 is conveyed to the first recovery section 42 via the first recovery path 34. The first permeated gas 80 can be recovered in the first recovery section 42.

[0177] As described above, the first separation membrane 11 of the first separation membrane unit 10 preferentially permeates Gas A contained in the mixed gas 70. Therefore, the first permeated gas 80 obtained by passing through the first separation membrane unit 10 has a higher Gas A content than the mixed gas 70. The Gas A content (recovery purity) in the first permeated gas 80 is, for example, 80 vol% or greater, but may also be 83 vol% or greater, 85 vol% or greater, 88 vol% or greater, or even 90 vol% or greater. The upper limit of the Gas A content in the first permeated gas 80 is not particularly limited, and may be, for example, 99 vol% or less, or 95 vol% or less. The recovery rate of Gas A based on the first permeated gas 80 is, for example, 70 wt% or greater, 73 wt% or greater, 75 wt% or greater, or even 78 wt% or greater. The upper limit of the Gas A recovery rate based on the first permeated gas 80 is not particularly limited, and may be, for example, 90 wt% or less, or 85 wt% or less. In this specification, the recovery rate refers to the ratio of the weight of the recovered specific gas to the weight of the gas contained in the mixed gas. It should be noted that "weight" refers to the value under standard conditions (0°C, 101 kPa).

[0178] The concentration of gas B in the mixed gas 70 gradually increases from the inlet 13a toward the outlet 13b of the first chamber 13. The content of gas B in the mixed gas 70 (first retentate gas 81) treated in the first chamber 13 is not particularly limited, but is, for example, 25 to 75 vol%. The first retentate gas 81 is discharged to the exterior of the first separation membrane unit 10 through the outlet 13b. The first retentate gas 81 is supplied to the second separation membrane unit 20 through the retentate gas supply path 32.

[0179] The second separation step can be performed, for example, as follows. First, the first retentate gas 81 is supplied to the third chamber 23 (supply-side space) of the second separation membrane unit 20 via the retentate gas supply path 32. The first retentate gas 81 has, for example, a pressure approximately equal to that of the mixed gas 70 supplied to the first separation membrane unit 10. The pressure of the first retentate gas 81, i.e., the pressure within the supply-side space of the second separation membrane unit 20, is, for example, 0.1 MPa or higher, preferably 0.5 MPa or higher, and may be 1.0 MPa or higher. The upper limit of the pressure of the first retentate gas 81 is not particularly limited, but is, for example, 10.0 MPa.

[0180] The first retentate gas 81 supplied to the third chamber 23 of the second separation membrane unit 20 passes through the second separation membrane 21 and is separated into a second permeated gas 90 and a second retentate gas 91. The second permeated gas 90 is thus supplied to the fourth chamber 24. The second permeated gas 90 supplied to the fourth chamber 24 is discharged to the exterior of the second separation membrane unit 20 through the outlet 24a. The second permeated gas 90 is conveyed to the second recovery section 44 via the second recovery path 36. The second permeated gas 90 can be recovered in the second recovery section 44.

[0181] As described above, the second separation membrane 21 of the second separation membrane unit 20 preferentially permeates the gas B contained in the first retentate gas 81. Therefore, the gas B content in the second permeated gas 90 obtained by passing through the second separation membrane unit 20 is higher than that in the first retentate gas 81. The gas B content (recovery purity) in the second permeated gas 90 is, for example, 80 vol% or higher, 85 vol% or higher, 88 vol% or higher, 90 vol% or higher, 93 vol% or higher, or even 95 vol% or higher. The upper limit of the gas B content in the second permeated gas 90 is not particularly limited, but is, for example, 99 vol% or lower. The recovery rate of gas B based on the second permeated gas 90 is, for example, 70 wt% or higher, 75 wt% or higher, 80 wt% or higher, 83 wt% or higher, or even 85 wt% or higher. The upper limit of the gas B recovery rate based on the second permeated gas 90 is not particularly limited, but is, for example, 99 wt% or lower, or even 95 wt% or lower.

[0182] The concentration of Gas A in first impermeable gas 81 gradually increases from inlet 23a toward outlet 23b of third chamber 23. The content of Gas A in first impermeable gas 81 (second impermeable gas 91) processed in third chamber 23 is not particularly limited, but is, for example, 50 vol% to 90 vol%. The recovery rate of Gas A from second impermeable gas 91 is not particularly limited, but is, for example, 5 wt% to 30 wt%.

[0183] The second retentate gas 91 is discharged to the outside of the second separation membrane unit 20 through the outlet 23b. The second retentate gas 91 is transported to the first recovery path 34 through the discharge path 38. The second retentate gas 91 is mixed with the first permeated gas 80 in the first recovery path 34 and then transported to the first recovery section 42. In the gas separation system 100 of this embodiment, the second retentate gas 91 can be recovered in the first recovery section 42 together with the first permeated gas 80.

[0184] The content (recovery purity) of Gas A in the recovered gas formed by mixing the first permeated gas 80 and the second non-permeated gas 91 is, for example, 75 vol% or more, and may be 80 vol% or more, 83 vol% or more, or even 85 vol% or more. The upper limit of the content of Gas A in the recovered gas is not particularly limited, and may be, for example, 95 vol% or less, or 90 vol% or less. The recovery rate of Gas A based on the recovered gas is, for example, 80 wt% or more, and may be 85 wt% or more, 90 wt% or more, 93 wt% or more, or even 95 wt% or more. The upper limit of the recovery rate of Gas A based on the recovered gas is not particularly limited, and may be, for example, 99 wt% or less.

[0185] In the separation method of this embodiment, the first and second separation steps are performed continuously, for example. That is, the first non-permeated gas 81 separated in the first separation step is not captured in a tank or the like but is directly supplied to the second separation step. By performing the first and second separation steps continuously, the processing volume of the mixed gas 70 per unit time can be easily increased.

[0186] It should be noted that when separating mixed gases using conventional gas separation systems equipped with only a single separation membrane, achieving high recovery rates and purity requires adjusting the membrane area of the separation membrane to a very large value, significantly increasing manufacturing costs. Furthermore, in gas separation systems that treat the mixed gas with a first separation membrane and further treat the resulting permeated gas with a second separation membrane, a separate pressurizing device is required to pressurize the permeated gas, which tends to increase the power required to operate the system.

[0187] The configuration of the gas separation system 100 of this embodiment has the following tendency: it is possible to recover gas A and gas B separately at a sufficiently high recovery rate and purity while reducing the power required to operate the system, without significantly increasing the total membrane area of the first separation membrane 11 and the membrane area of the second separation membrane 21. Thus, the gas separation system 100 of this embodiment is suitable for efficiently separating mixed gases.

[0188] [Modification of the First Separation Membrane Unit]

[0189] In the gas separation system 100 , the first separation membrane unit 10 may be a spiral membrane element, a hollow fiber membrane element, or the like. Figure 6 A spiral-type membrane element is shown. Figure 6 The first separation membrane unit 15 includes a central tube 16 and a stacked body 17 . The stacked body 17 includes the first separation membrane 11 .

[0190] The center tube 16 has a cylindrical shape. A plurality of holes or slits are formed on the surface of the center tube 16 for allowing the first permeating gas 80 to flow into the center tube 16. Examples of materials for the center tube 16 include resins such as acrylonitrile-butadiene-styrene copolymer (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 center tube 16 is, for example, in the range of 20 to 100 mm.

[0191] The stack 17 includes, in addition to the first separation membrane 11, a feed-side flow path material 18 and a permeate-side flow path material 19. The stack 17 is wound around the central tube 16. The first separation membrane unit 15 may further include an outer packaging material (not shown).

[0192] As the feed side flow path material 18 and the permeate side flow path material 19, a net, woven fabric or knitted fabric made of a resin such as polyethylene, polypropylene, polyethylene terephthalate (PET), polyphenylene sulfide (PPS) or ethylene-chlorotrifluoroethylene copolymer (ECTFE) can be used.

[0193] Membrane separation using the first 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. This causes a first permeated gas 80, which has permeated the first separation membrane 11 of the stack 17, to move into the interior of the central tube 16. The first permeated gas 80 is discharged to the outside through the central tube 16. The mixed gas 70 (first non-permeated gas 81) processed by the first separation membrane unit 15 is discharged to the outside from the other end of the wound stack 17.

[0194] In the gas separation system 100 , the second separation membrane unit 20 may be a spiral membrane element, a hollow fiber membrane element, etc. As an example, the second separation membrane unit 20 may be a spiral membrane element having the same structure as the first separation membrane unit 15 .

[0195] <Modification of Gas Separation System>

[0196] Figure 7 1 is a schematic diagram showing a modified example of a gas separation system 110. Figure 7 As shown, in gas separation system 110, exhaust path 38 does not merge with first recovery path 34. Other than this, the structure of gas separation system 110 in this embodiment is identical to that of gas separation system 100. Therefore, common elements in gas separation system 100 and gas separation system 110 in this embodiment may be denoted by the same reference numerals, and their descriptions may be omitted. That is, the descriptions of each embodiment are applicable to each other as long as they do not technically conflict.

[0197] In the gas separation system 110, an opening (discharge port 46) is formed in the discharge path 38 for discharging the second non-permeated gas from the discharge path 38. The gas separation system 110, for example, does not recover the second non-permeated gas but discards it. The gas separation system 110 tends to be able to recover Gas A at a higher recovery purity.

[0198] Example

[0199] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0200] (Calculation Example 1)

[0201] Using Schlumberger's process simulation software Symmetry, the operation Figure 1 In detail, the simulation of the gas separation system shown in FIG. Figure 1 The gas separation system shown in the figure assumes that a hydrogen permeable membrane is used as the first separation membrane (using hydrogen as gas A) and a carbon dioxide permeable membrane is used as the second separation membrane (using carbon dioxide as gas B). For the hydrogen permeable membrane, the separation coefficient α1 of hydrogen to carbon dioxide is set to 20, and the membrane area M1 is set to 664m 2 For the carbon dioxide permeation membrane, the separation coefficient α2 of carbon dioxide relative to hydrogen is set to 5, and the membrane area M2 is set to 336m 2 The supply conditions of the mixed gas are set as follows: It is assumed that the mixed gas is pressurized from the atmospheric pressure (101.33 kPa) of the external environment to 0.9 MPa by a pressurizing device disposed in the mixed gas supply path.

[0202] [Mixed gas supply conditions]

[0203] Flow rate: 1016.47Nm 3 / hr

[0204] Composition (volume ratio): CO2 / H2=50 / 50

[0205] CO2 weight: 1000kg / hr

[0206] H2 weight: 45.81kg / hr

[0207] Pressure: 0.9MPa

[0208] Temperature: 25℃

[0209] Assume that the hydrogen permeable membrane in Calculation Example 1 is Figure 3The separation membrane 11 shown is shown. Specifically, a separation membrane 11 is assumed to include a resin layer containing a polyamide resin as a separation functional layer 1 and a coating layer 2 containing a silicone polymer. It should be noted that, in the calculation examples described below, unless otherwise specified, the same separation membrane as in Calculation Example 1 is assumed as the hydrogen permeable membrane.

[0210] Through the simulation of Calculation Example 1, the compositions of the first permeated gas, the second permeated gas, and the second non-permeated gas were calculated when a mixed gas was separated using a gas separation system. Based on the calculated results, the recovery rates and purities of hydrogen and carbon dioxide were calculated. Furthermore, the energy (compression energy) required for operating the pressurizing device (MWh) was calculated, and the compression energy per ton (MWh / t) of hydrogen contained in the recovered gas and the compression energy per ton (MWh / t) of carbon dioxide contained in the second permeated gas were determined.

[0211] (Calculation Examples 2 to 8)

[0212] The simulations for Calculation Examples 2 to 8 were performed in the same manner as in Calculation Example 1, except that the separation coefficients α1 and α2 were changed as shown in Table 1. Note that the hydrogen permeable membrane of Calculation Example 3 was assumed to be a separation membrane 11 having a metal layer as the separation functional layer 1 .

[0213] (Calculation Example 9)

[0214] Using Schlumberger's process simulation software Symmetry, the operation Figure 8 The gas separation system 200 shown in FIG. 2 is provided with a first separation membrane unit 210 housing a first separation membrane 211 and a second separation membrane unit 220 housing a second separation membrane 221. The first separation membrane 211 and the second separation membrane 221 correspond to Figure 1 The first separation membrane 11 and the second separation membrane 21 of the gas separation system 100 are shown.

[0215] The gas separation system 200 includes a mixed gas supply path 230, a non-permeated gas supply path 232, a recirculation path 234, a second recovery path 236, a second recovery section 244, a third recovery path 238, and a third recovery section 248. The mixed gas supply path 230 is a path for supplying a mixed gas to the first separation membrane unit 210. A pressurizing device 240 is disposed in the mixed gas supply path 230 to increase the pressure of the mixed gas.

[0216] The non-permeated gas supply path 232 is connected to the non-permeated gas outlet of the first separation membrane unit 210 and the non-permeated gas inlet of the second separation membrane unit 220 , and is used to supply the first non-permeated gas from the first separation membrane unit 210 to the second separation membrane unit 220 .

[0217] The recirculation path 234 is connected to the permeated gas outlet of the first separation membrane unit 210 and the mixed gas supply path 230 , and is used to return the first permeated gas from the first separation membrane unit 210 to the mixed gas supply path 230 .

[0218] The second recovery path 236 is connected to the permeated gas outlet of the second separation membrane unit 220 and the inlet of the second recovery section 244 , and is a path for conveying the second permeated gas from the second separation membrane unit 220 to the second recovery section 244 .

[0219] The third recovery path 238 is connected to the non-permeated gas outlet of the second separation membrane unit 220 and the inlet of the third recovery section 248 , and is a path for conveying the second non-permeated gas from the second separation membrane unit 220 to the third recovery section 248 .

[0220] The simulation of Calculation Example 9 was performed by the same method as Calculation Example 8 except that the gas separation system 200 was used.

[0221] (Calculation Examples 10-12)

[0222] The simulations of Calculation Examples 10 to 12 were performed in the same manner as in Calculation Example 1, except that the separation coefficients α1 and α2 were changed as shown in Table 1.

[0223] [Table 1]

[0224]

[0225] [Table 2]

[0226]

[0227] As can be seen from Tables 1 and 2, in Calculation Examples 1 to 5 and 10 of the gas separation system of this embodiment, in which the ratio of the separation coefficient α1 of the first separation membrane to the separation coefficient α2 of the second separation membrane (α1 / α2) is 1.9 or greater, even when the separation coefficient α2 of the second separation membrane is as low as 50 or less (particularly 20 or less), the mixed gas can be separated at a sufficiently high recovery rate and recovery purity compared to the other calculation examples. In particular, in Calculation Examples 1 to 5 and 10, the recovery rate of Gas B (carbon dioxide) based on the second permeated gas is high.

[0228] Industrial applicability

[0229] The gas separation system of this embodiment is suitable for separating mixed gases, for example, mixed gases containing carbon dioxide and hydrogen. In particular, the gas separation system of this embodiment is suitable for processing exhaust gas from chemical plants.

Claims

1. A gas separation system comprising: a first separation membrane for separating the mixed gas into a first permeated gas and a first non-permeated gas; a second separation membrane for separating the first non-permeated gas into a second permeated gas and a second non-permeated gas, in, The mixed gas includes gas A and gas B different from gas A, The first separation membrane is capable of preferentially permeating the gas A. The second separation membrane can preferentially permeate the gas B. The separation coefficient α1 of the gas A to the gas B of the first separation membrane obtained by the following experiment and the separation coefficient α2 of the gas B to the gas A of the second separation membrane obtained by the following experiment satisfy the following relations (1) and (2): Test: A test piece is prepared using the first separation membrane or the second separation membrane; a test gas obtained from the gas A and the gas B is supplied to a space adjacent to one side of the test piece, and the space adjacent to the other side of the test piece is depressurized; the separation coefficient α1 or the separation coefficient α2 is determined based on the result of the operation; wherein, in the operation, the content of the gas A in the test gas is 50 vol% under standard conditions, the test gas supplied to the space adjacent to the one side is at a temperature of 30° C. and a pressure of 0.1 MPa, and the space adjacent to the other side is depressurized in such a manner that the pressure in the space is reduced by 0.1 MPa relative to the atmospheric pressure in the measurement environment. α1 / α2≥1.9 (1) α2≤50 (2)。 2. The gas separation system according to claim 1, wherein: The separation coefficient α2 is 20 or less.

3. The gas separation system according to claim 1, wherein: The gas A is hydrogen, and the gas B is carbon dioxide.

4. The gas separation system according to claim 1, wherein: The first permeated gas and the second permeated gas are recovered separately.

5. The gas separation system according to claim 1, wherein: The membrane area of the first separation membrane is larger than the membrane area of the second separation membrane.

6. The gas separation system according to claim 1, wherein: The content of the gas A in the first permeated gas is 85 vol% or more, The recovery rate of the gas A based on the first permeated gas is 70 wt % or more.

7. The gas separation system according to claim 1, wherein: The content of the gas B in the second permeated gas is 85 vol% or more, The recovery rate of the gas B based on the second permeated gas is 80 wt % or more.

8. The gas separation system according to claim 1, wherein: In the mixed gas, a ratio of the volume of the gas A to the total volume of the gas A and the volume of the gas B is 20 to 80 vol%.

9. The gas separation system according to claim 1, further comprising: a first separation membrane unit accommodating the first separation membrane; a mixed gas supply path connected to the first separation membrane unit and configured to supply the mixed gas to the first separation membrane unit; and A pressurizing device is disposed in the mixed gas supply path and increases the pressure of the mixed gas.

10. The gas separation system according to claim 1, further comprising: a first separation membrane unit accommodating the first separation membrane; a first recovery unit for recovering the first permeated gas; and A first recovery path is connected to the first separation membrane unit and the first recovery section, and is used to send the first permeated gas to the first recovery section.

11. The gas separation system according to claim 10, further comprising: a second separation membrane unit accommodating the second separation membrane; and a discharge path connected to the second separation membrane unit and configured to discharge the second non-permeated gas from the second separation membrane unit; in, The discharge path merges with the first recovery path at a merging position.

12. The gas separation system according to claim 1, further comprising: a second separation membrane unit accommodating the second separation membrane; a second recovery unit for recovering the second permeated gas; and A second recovery path is connected to the second separation membrane unit and the second recovery section, and is used to send the second permeated gas to the second recovery section.

13. The gas separation system according to claim 1, wherein: The first separation membrane includes a resin layer containing a resin or a metal layer containing a metal as a separation function layer.

14. The gas separation system according to claim 1, wherein: The second separation membrane includes a separation functional layer containing a polyether block amide resin or an ionic liquid.

15. A method for separating mixed gases, comprising: a first separation step of separating a mixed gas containing gas A and gas B different from gas A into a first permeated gas and a first non-permeated gas via a first separation membrane that allows gas A to preferentially permeate; and a second separation step of separating the first non-permeated gas into a second permeated gas and a second non-permeated gas via a second separation membrane that allows the gas B to preferentially permeate; The separation coefficient α1 of the gas A to the gas B of the first separation membrane obtained by the following test and the separation coefficient α2 of the gas B to the gas A of the second separation membrane obtained by the following test satisfy the following equations (1) and (2): Test: A test piece is prepared using the first separation membrane or the second separation membrane; a test gas obtained from the gas A and the gas B is supplied to a space adjacent to one side of the test piece, and the space adjacent to the other side of the test piece is depressurized; the separation coefficient α1 or the separation coefficient α2 is determined based on the result of the operation; wherein, in the operation, the content of the gas A in the test gas is 50 vol% under standard conditions, the test gas supplied to the space adjacent to the one side is at a temperature of 30° C. and a pressure of 0.1 MPa, and the space adjacent to the other side is depressurized in such a manner that the pressure in the space is reduced by 0.1 MPa relative to the atmospheric pressure in the measurement environment. α1 / α2≥1.9 (1) α2≤50 (2)。

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