Spiral membrane element and membrane separation system

Abstract

The present invention provides a spiral membrane element that is suited to suppressing reductions in the permeation speed (or the permeation flux) of a permeated fluid from a separation membrane. This spiral membrane element 10 comprises a center tube 21, a membrane leaf 11 that has a separation membrane 12 and a permeation spacer 14 and is wound around the center tube 21, and a channel spacer 15 that is connected to the permeation spacer 14 and is wound around the center tube 21 closer to the center tube 21 side than the membrane leaf 11. The pressure loss P1 of the channel spacer 15 as measured by means of a prescribed test is lower than the pressure loss P2 of the permeation spacer 14.

Description

[Technical Field]

[0001] This invention relates to a spiral-type membrane element and a membrane separation system. [Background technology]

[0002] Membrane separation is a method developed to separate acidic gases, such as carbon dioxide, from gas mixtures containing them. Compared to absorption methods, which separate acidic gases by having an absorbent absorb them, membrane separation can efficiently separate acidic gases while keeping operating costs down.

[0003] For example, spiral membrane elements are used in membrane separation methods. A spiral membrane element comprises a central tube and membrane leaves wound around the central tube. The membrane leaves have a separation membrane and a permeation spacer. Spiral membrane elements are suitable for increasing the membrane area of ​​the separation membrane in the membrane element.

[0004] The spiral membrane element further includes, for example, a flow channel spacer wrapped around the central tube on the central tube side of the membrane leaves (for example, Patent Document 1). The flow channel spacer allows the permeate fluid from the membrane leaves to be easily delivered to the central tube. When the spiral membrane element is manufactured, the presence of the flow channel spacer allows the membrane leaves to be easily wrapped around the central tube. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 4650921 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In spiral membrane elements, the permeation rate of the fluid permeating from the separation membrane tends to be lower than that of the same fluid permeating from a flat membrane. In other words, when a separation membrane is applied to a spiral membrane element, the permeation rate of the fluid permeating from the separation membrane tends to decrease. This tendency is particularly pronounced in a system where the spiral membrane element is operated under reduced pressure inside the central tube (reduced pressure system).

[0007] Therefore, the present invention aims to provide a spiral membrane element suitable for suppressing a decrease in the permeation velocity (or permeation flux) of the permeating fluid from a separation membrane. [Means for solving the problem]

[0008] As a result of diligent research, the inventors have newly discovered that the decrease in the permeation rate of the permeating fluid in a spiral membrane element is due to pressure loss in the spacer, particularly the flow channel spacer. Based on this finding, the inventors further investigated and completed the present invention.

[0009] The present invention The central tube, It has a separation membrane and a permeable spacer, and a membrane leaf wrapped around the central tube, A flow channel spacer connected to the permeable spacer and wrapped around the central tube on the central tube side of the membrane leaf, Equipped with, The present invention provides a spiral membrane element in which the pressure loss P1 of the flow channel spacer, as measured by the following test, is smaller than the pressure loss P2 of the permeable spacer, as measured by the following test. Test: A test specimen is prepared by laminating a rectangular spacer measuring 150 mm in length and 47 mm in width (the flow channel spacer or the permeable spacer) onto a polyethylene terephthalate film. Nitrogen gas is introduced into the space adjacent to the film of the test specimen so that the pressure in the space is 0.1 MPa, and nitrogen gas is also introduced into the spacer at a flow rate of 2.5 L / min. The pressure loss caused by the movement of nitrogen gas in the longitudinal direction of the spacer within the spacer is measured.

[0010] Furthermore, the present invention provides a membrane separation system comprising the spiral membrane element described above and a decompression device for decompressing the inside of the central tube.

[0011] Furthermore, the present invention [[ID=!3]] provides a spiral membrane element comprising a central tube, a membrane leaf having a separation membrane and a permeation spacer and wound around the central tube, and a flow path spacer connected to the permeation spacer and wound around the central tube on the central tube side of the membrane leaf, wherein the pressure loss P1 of the flow path spacer measured by the following test is 30 kPa or less. Test: Prepare a test piece in which a strip-shaped flow path spacer with a length of 150 mm and a width of 47 mm is laminated on a polyethylene terephthalate film. Nitrogen gas is sent into the space so that the pressure in the space adjacent to the film of the test piece becomes 0.1 MPa, and nitrogen gas is sent to the flow path spacer at a flow rate of 2.5 L / min. Measure the pressure loss generated by the movement of nitrogen gas in the longitudinal direction of the flow path spacer within the flow path spacer.

Advantages of the Invention

[0012] According to the present invention, a spiral membrane element suitable for suppressing a decrease in the permeation rate (or permeation flux) of a permeated fluid from a separation membrane can be provided.

Brief Description of the Drawings

[0013] [Figure 1] It is a developed perspective view schematically showing a spiral membrane element according to an embodiment of the present invention. [Figure 2] It is a schematic cross-sectional view of a spiral membrane element. [Figure 3] It is a schematic cross-sectional view showing an example of a measuring device for measuring the pressure loss of a spacer. [Figure 4A] ​​It is a schematic cross-sectional view showing an example of a separation membrane included in a spiral membrane element. [Figure 4B] It is a schematic cross-sectional view showing a modified example of the separation membrane included in the spiral membrane element. [Figure 5] It is a diagram for explaining a method of manufacturing a spiral membrane element. [Figure 6] It is a diagram for explaining a method of manufacturing a spiral membrane element. [Figure 7] It is a configuration diagram of a membrane separation system including a spiral membrane element.

Embodiments for Carrying out the Invention

[0014] Hereinafter, the details of the present invention will be described, but the following description is not intended to limit the present invention to specific embodiments.

[0015] <Embodiments of Spiral Membrane Element> FIGS. 1 and 2 show a spiral membrane element 10 (hereinafter referred to as "separation membrane element 10") according to an embodiment of the present invention. The separation membrane element 10 includes a central tube 21 and a laminate 22. The laminate 22 is wound around the central tube 21 and is disposed around the central tube 2i. Inside the laminate 22, a supply fluid flow path and a permeate fluid flow path are formed.

[0016] The supply fluid is supplied into the separation membrane element 10 from one end face of the laminate 22 and flows through the supply fluid flow path in parallel with the longitudinal direction of the central tube 21. In the separation membrane element 10, the supply fluid is separated to generate a permeate fluid and a non-permeate fluid. The permeate fluid is led to the outside through the central tube 21. The non-permeate fluid is discharged to the outside of the separation membrane element 10 from the other end face of the laminate 22.

[0017] The feed fluid to be processed by the separation membrane element 10 may be a gas or a liquid. As an example, the feed fluid may be a gas mixture containing acidic gases, particularly a gas mixture containing carbon dioxide and nitrogen. As another example, the feed fluid may be a liquid mixture containing volatile organic compounds, particularly a liquid mixture containing alcohol (e.g., isopropanol) and water.

[0018] The separation membrane element 10 further includes a flow channel spacer 15. The flow channel spacer 15 is located between the central tube 21 and the laminate 22, and is wrapped around the central tube 21 on the side of the laminate 22 that is closer to the central tube 21. The flow channel spacer 15 ensures a space between the laminate 22 and the central tube 21 that serves as a permeable fluid channel.

[0019] The separation membrane element 10 may further comprise a shell that surrounds the laminate 22. The shell may be made of FRP (fiber-reinforced plastic). End face members may be positioned on both sides of the laminate 22 to protect the end faces of the laminate 22 and to prevent the laminate 22 from stretching telescopically.

[0020] As shown in Figures 1 and 2, the laminate 22 has a plurality of membrane leaves 11. Each membrane leaf 11 has a separation membrane 12 and a permeable spacer 14. In detail, each membrane leaf 11 has two separation membranes 12. The two separation membranes 12 are overlapped and sealed on three sides to form a bag-like structure. For sealing the two separation membranes 12, an adhesive layer 26 containing an adhesive is used, for example. A permeable spacer 14 is positioned between the two separation membranes 12 so as to be located inside the bag-like structure. The open end of the membrane leaf 11 is connected to a flow channel spacer 15, thereby connecting the permeable spacer 14 to the flow channel spacer 15. The permeable spacer 14 secures space between the two separation membranes 12 as a permeable fluid channel. The number of membrane leaves 11 in the laminate 22 is not particularly limited and is, for example, 2 to 30.

[0021] The laminate 22 further includes supply spacers 13. The supply spacers 13 are located outside the bag-like structure described above and are laminated on the membrane leaves 11. In detail, the laminate 22 has a plurality of supply spacers 13, and in the laminate 22, the plurality of supply spacers 13 and the plurality of membrane leaves 11 are alternately laminated. The supply spacers 13 secure space between the membrane leaves 11 as a supply fluid channel.

[0022] The central tube 21 plays the role of collecting the permeable fluid that has permeated through each separation membrane 12 and guiding it to the outside of the separation membrane element 10. The central tube 21 is provided with openings 21h that connect the internal space of the central tube 21 to the external space. The openings 21h are, for example, through holes formed in the wall surface of the central tube 21. In detail, the central tube 21 is provided with a plurality of openings 21h at predetermined intervals along the direction in which the central tube 21 extends. The number of rows of the plurality of openings 21h provided along the direction in which the central tube 21 extends is not particularly limited, and is, for example, 1 or 2. The central tube 21 may be provided with two rows of the plurality of openings 21h facing each other. A flow path spacer 15 is in contact with each of the plurality of openings 21h. This allows the permeable fluid to flow from the flow path spacer 15 into the interior of the central tube 21 through the plurality of openings 21h. The outer diameter of the central tube 21 is, for example, 10 to 100 mm, preferably 12 to 50 mm.

[0023] In this embodiment, the pressure loss P1 (kPa) of the flow channel spacer 15 is smaller than the pressure loss P2 (kPa) of the permeable spacer 14. The pressure loss P1 can be measured using the measuring device 30 shown in Figure 3 by the following method. First, a strip-shaped spacer 15a measuring 150 mm in length and 47 mm in width is prepared. The spacer 15a has the same shape as the flow channel spacer 15 before it is wrapped around the central pipe 21, except for its length and width. The longitudinal direction of the spacer 15a coincides with the direction in which the flow channel spacer 15 is wrapped around the central pipe 21. Next, a polyethylene terephthalate film 41 is laminated onto the spacer 15a to prepare a test piece 40. The film 41 is, for example, PET100SG2 manufactured by Panac Co., Ltd.

[0024] Next, the test specimen 40 is set in the measuring device 30. The measuring device 30 comprises, for example, a holder 31, a lid member 35, and a sealing member 34. More specifically, the test specimen 40 is set in the holder 31 of the measuring device 30 such that the spacer 15a of the test specimen 40 is positioned below the film 41. Openings 32 and 33 are formed in the wall surface of the holder 31. Each of the openings 32 and 33 communicates with the spacer 15a of the test specimen 40. The openings 32 and 33 are positioned so that when nitrogen gas is introduced into the holder 31 from one opening 32, the nitrogen gas moves in the longitudinal direction X of the spacer 15a and is discharged from the other opening 33. The openings 32 and 33 may or may not face each other.

[0025] The lid member 35 is fastened to the holder 31 above the holder 31 using fasteners (not shown). The lid member 35 has an opening 36 for supplying nitrogen gas to the space 37 adjacent to the film 41 of the test piece 40. The sealing member 34 is located between the holder 31 and the lid member 35 and prevents air from venting inside and outside the measuring device 30 in areas other than the openings 32, 33, and 36. The sealing member 34 is, for example, a circular cross-section sealing ring (O-ring) made of an elastic material. Figure 3 shows the sealing member 34, which is a sealing ring, in a compressed state.

[0026] Next, nitrogen gas is introduced into the space 37 adjacent to the film 41 of the test piece 40 through the opening 36 of the lid member 35 so that the pressure in the space 37 becomes 0.1 MPa, and nitrogen gas is also introduced into the spacer 15a at a flow rate of 2.5 L / min through the opening 32 of the holder 31. The temperature of the nitrogen gas introduced into the measuring device 30 is, for example, 23°C. The nitrogen gas introduced through the opening 32 moves within the spacer 15a in the longitudinal direction X of the spacer 15a and is discharged from the opening 33. The difference (differential pressure D1) between the pressure of the nitrogen gas introduced into the opening 32 and the pressure of the nitrogen gas discharged from the opening 33 is measured. Next, the differential pressure D0 is measured in the same manner as the differential pressure D1, except that the spacer 15a is absent. Based on the differential pressures D0 and D1, the pressure loss due to the spacer 15a is calculated. The calculated value can be considered as the pressure loss P1 caused by the movement of nitrogen gas within the spacer 15a in the longitudinal direction X of the spacer 15a.

[0027] The pressure loss P2 can be measured in the same way as the pressure loss P1, except that a spacer 14a, which corresponds to the permeable spacer 14, is used instead of spacer 15a. Spacer 14a has the same shape as the permeable spacer 14 before it is wrapped around the central pipe 21, except for its length and width.

[0028] The relationship between pressure drops P1 and P2 measured by the above test method is in good agreement with the relationship between the pressure drop in the flow path spacer 15 and the pressure drop in the permeation spacer 14 during operation of the separation membrane element 10.

[0029] The separation membrane element 10 typically has a plurality of permeation spacers 14. In this embodiment, the pressure loss P1 of the flow channel spacer 15 only needs to be smaller than the pressure loss P2 of at least one permeation spacer 14 selected from the plurality of permeation spacers 14. As long as this condition is met, the separation membrane element 10 may include permeation spacers 14 that exhibit a pressure loss P2 equal to or smaller than the pressure loss P1. For example, the pressure loss P1 of the flow channel spacer 15 may be equal to the pressure loss P2 of one of the plurality of permeation spacers 14, and smaller than the pressure loss P2 of all the other permeation spacers 14. Preferably, the pressure loss P1 of the flow channel spacer 15 is smaller than the pressure loss P2 of all the permeation spacers 14.

[0030] The value obtained by subtracting the pressure loss P1 from the pressure loss P2 (P2-P1) is not particularly limited, but is, for example, 5 kPa or more, preferably 10 kPa or more, and more preferably 20 kPa or more. The upper limit of the value (P2-P1) is not particularly limited, but is, for example, 50 kPa. The ratio of pressure loss P1 to pressure loss P2 (P1 / P2) is not particularly limited, but is, for example, 0.8 or less, preferably 0.5 or less, and more preferably 0.2 or less. The lower limit of the ratio (P1 / P2) is not particularly limited, but is, for example, 0.01.

[0031] The pressure loss P1 is, for example, 30 kPa or less, preferably 20 kPa or less, more preferably 10 kPa or less, and even more preferably 6 kPa or less. The lower limit of the pressure loss P1 is not particularly limited, and is, for example, 0.1 kPa. The pressure loss P1 may, in some cases, be greater than 30 kPa.

[0032] From another aspect, the present invention The central tube 21 and It has a separation membrane 12 and a permeable spacer 14, and a membrane leaf 11 wrapped around a central tube 21, A flow channel spacer 15 is connected to the permeable spacer 14 and is wrapped around the central tube 21 on the central tube 21 side of the membrane leaf 11, Equipped with, The present invention provides a spiral membrane element 10 in which the pressure loss P1 of the flow channel spacer 15, as measured by the above test, is 30 kPa or less.

[0033] The pressure loss P2 is, for example, greater than 30 kPa and 50 kPa or less. In some cases, the pressure loss P2 may be 30 kPa or less.

[0034] Examples of flow channel spacers 15 include nets, meshes, wire fabrics, fiber fabrics, nonwoven fabrics, grooved sheets, and corrugated sheets. Examples of materials for the flow channel spacer 15 include resin materials such as polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyamide, polyphenylene sulfide (PPS), ethylene-chlorotrifluoroethylene copolymer (ECTFE), epoxy resin, and urethane resin; natural polymers; rubber; and metals.

[0035] The thickness of the flow channel spacer 15 is not particularly limited, but is, for example, 300 μm or more, preferably 400 μm or more, more preferably 500 μm or more, and even more preferably 600 μm or more. The greater the thickness of the flow channel spacer 15, the lower the pressure loss P1 of the flow channel spacer 15 tends to be. The upper limit of the thickness of the flow channel spacer 15 is not particularly limited, but from the viewpoint of ensuring a sufficient membrane area of ​​the separation membrane 12 within the separation membrane element 10, it is, for example, 2000 μm.

[0036] The opening ratio of the flow channel spacer 15 is not particularly limited, but is, for example, 30% or more, preferably 40% or more, and more preferably 50% or more. The higher the opening ratio of the flow channel spacer 15, the lower the pressure loss P1 of the flow channel spacer 15 tends to be. The upper limit of the opening ratio of the flow channel spacer 15 is not particularly limited, but is, for example, 80%.

[0037] The aperture ratio of the flow channel spacer 15 can be determined by the following method. First, the flow channel spacer 15 is placed on the film, and the surface of the flow channel spacer 15 is observed with a scanning electron microscope (SEM). From the obtained electron microscope image, the surface area A1 of the flow channel spacer 15 and the area A2 (area of ​​the gap formed in the flow channel spacer 15) through which the film can be seen via the flow channel spacer 15 are calculated by image processing. The ratio of area A2 to area A1 can be determined as the aperture ratio of the flow channel spacer 15.

[0038] Table 1 below shows specific examples of the flow path spacer 15. The flow path spacer 15 is preferably made of PE30.

[0039] [Table 1]

[0040] Examples of permeable spacers 14 include nets, meshes, wire fabrics, fiber fabrics, nonwoven fabrics, grooved sheets, and corrugated sheets. The materials for the permeable spacer 14 are those described above for the flow channel spacer 15.

[0041] The thickness of the permeation spacer 14 is not particularly limited, and is, for example, less than 300 μm, preferably 250 μm or less. The smaller the thickness of the permeation spacer 14, the easier it is to arrange a sufficient number of membrane leaves 11 within the separation membrane element 10. In other words, a sufficient membrane area can be easily secured for the separation membrane 12 within the separation membrane element 10. The lower limit of the thickness of the permeation spacer 14 is not particularly limited, and is, for example, 100 μm. The thickness of the permeation spacer 14 may, in some cases, be 300 μm or more.

[0042] The aperture ratio of the permeable spacer 14 is not particularly limited, and is, for example, less than 30%, preferably 25% or less, and more preferably 20% or less. The lower the aperture ratio of the permeable spacer 14, the more likely it is to suppress the deterioration of the performance of the separation membrane 12 caused by a portion of the separation membrane 12 entering the gap of the permeable spacer 14 during operation of the separation membrane element 10. The lower limit of the aperture ratio of the permeable spacer 14 is not particularly limited, and is, for example, 10%. The aperture ratio of the permeable spacer 14 may be 30% or more in some cases. The aperture ratio of the permeable spacer 14 can be determined by the method described above for the flow channel spacer 15.

[0043] A specific example of the permeable spacer 14 is #1000E (material: PET, aperture ratio: 22%, thickness: 250 μm, pressure loss P2: 33.6 kPa). In some cases, the permeable spacer 14 may be one of those exemplified in Table 1.

[0044] In this embodiment, the permeation spacer 14 is fundamentally different from the flow channel spacer 15. However, in the separation membrane element 10, at least one permeation spacer 14 selected from the plurality of permeation spacers 14 may be the same as the flow channel spacer 15. For example, one of the plurality of permeation spacers 14 may be the same as the flow channel spacer 15, and all the other permeation spacers 14 may be different from the flow channel spacer 15. More specifically, one of the plurality of permeation spacers 14 may be PE30, and all the other permeation spacers 14 may be #1000E.

[0045] The supply spacer 13 is not particularly limited, and for example, the permeable spacer 14 or the flow path spacer 15 described above can be used as appropriate.

[0046] [Separation membrane] The separation membrane 12 may be a separation membrane that can preferentially permeate acidic gases contained in the gas mixture (gas separation membrane), or it may be a separation membrane that can preferentially permeate volatile organic compounds contained in the liquid mixture (liquid separation membrane). Below, the separation membrane 12 as a gas separation membrane will be described.

[0047] As shown in Figure 4A, the separation membrane 12A, as a gas separation membrane, comprises, for example, a separation functional layer 1 and a porous support 3 that supports the separation functional layer 1, and may further comprise an intermediate layer 2 disposed between the separation functional layer 1 and the porous support 3. The intermediate layer 2 is, for example, in direct contact with the separation functional layer 1 and the porous support 3, respectively.

[0048] (separation functional layer) The separation functional layer 1 is, for example, a layer that can preferentially permeate acidic gases contained in a gas mixture. In a preferred embodiment, the separation functional layer 1 includes a resin. Examples of resins included in the separation functional layer 1 include polyether block amide resins, polyamide resins, polyether resins, polyimide resins, cellulose acetate resins, silicone resins, and fluororesins. The separation functional layer 1 preferably includes a polyether block amide resin. In this embodiment, the separation functional layer 1 preferably consists substantially of a resin. In this specification, "substantially consisting of" means excluding other components that alter the essential characteristics of the material mentioned, for example, that 95 wt% or more, and more precisely 99 wt% or more, is composed of the material.

[0049] In another preferred embodiment, the separation functional layer 1 comprises an ionic liquid. The separation functional layer 1 comprises, for example, a double network gel comprising an ionic liquid. The double network gel is a gel comprising two independent network structures. The double network gel comprises, for example, a first network structure composed mainly of organic material, a second network structure composed mainly of inorganic material, and an ionic liquid. In this specification, "composed mainly of" means that 50 wt% or more, and more specifically 70 wt% or more, of the material is composed of the said material.

[0050] The organic material for constituting the first network structure includes, for example, polymers such as polyacrylamide (particularly polydialkylacrylamide such as polydimethylacrylamide). The polymer contained in the organic material has structural units derived from acrylamide derivatives and may further contain crosslinked structures. Polymers containing crosslinked structures can be prepared by known methods. For example, first, a prepolymer having structural units having N-hydroxysuccinimide ester groups is prepared. Structural units having N-hydroxysuccinimide ester groups are derived, for example, from N-acrylooxysuccinimide. Next, a polymer containing crosslinked structures can be obtained by reacting the prepolymer with an amine-based crosslinking agent. The amine-based crosslinking agent is a compound having two or more primary amino groups, for example, ethylene glycol bis(3-aminopropyl) ether.

[0051] The second network structure may include a network of multiple particles. This network of particles is formed, for example, by multiple particles being bonded to each other by hydrogen bonds. The particles included in the second network structure may be particles exemplified as nanoparticles, as described later. As an example, the particles included in the second network structure are silica particles.

[0052] In this embodiment, specific ionic liquids include, for example, ionic liquids having imidazolium, pyridinium, ammonium, or phosphonium and substituents having one or more carbon atoms.

[0053] In an ionic liquid having imidazolium and a substituent having 1 or more carbon atoms, examples of substituents having 1 or more carbon atoms include alkyl groups having 1 to 20 carbon atoms, cycloalkyl groups having 3 to 14 carbon atoms, and aryl groups having 6 to 20 carbon atoms. These may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc. (for example, hydroxyalkyl groups having 1 to 20 carbon atoms).

[0054] Examples of alkyl groups 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, and n-eicosadecyl. Examples include hydroxyl groups, i-propyl groups, sec-butyl groups, i-butyl groups, 1-methylbutyl groups, 1-ethylpropyl groups, 2-methylbutyl groups, i-pentyl groups, neopentyl groups, 1,2-dimethylpropyl groups, 1,1-dimethylpropyl groups, t-pentyl groups, 2-ethylhexyl groups, and 1,5-dimethylhexyl groups, which may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc.

[0055] The alkyl groups described above may be substituted with cycloalkyl groups. The number of carbon atoms in the alkyl groups substituted with cycloalkyl groups is, for example, 1 to 20. Examples of alkyl groups substituted with cycloalkyl groups include cyclopropylmethyl group, cyclobutylmethyl group, cyclohexylmethyl group, and cyclohexylpropyl group, which may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc.

[0056] Examples of cycloalkyl groups 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, or monovalent ether groups.

[0057] Examples of aryl groups having 6 to 20 carbon atoms include phenyl, toluyl, xylyl, mesityl, anisyl, naphthyl, and benzyl groups, which may be further substituted with hydroxyl, cyano, amino, or monovalent ether groups.

[0058] Compounds having imidazolium and substituents with one or more carbon atoms may further have substituents such as alkyl groups and may form salts with counter anions. Examples of counter anions include alkyl sulfates, tosylates, methanesulfonates, acetates, bis(fluorosulfonyl)imides, bis(trifluoromethanesulfonyl)imides, thiocyanates, dicyanamides, tricyanomethanides, tetracyanoborates, hexafluorophosphates, tetrafluoroborates, and halides. From the viewpoint of gas separation performance, bis(fluorosulfonyl)imides, bis(trifluoromethanesulfonyl)imides, dicyanamides, tricyanomethanides, and tetracyanoborates are preferred.

[0059] Ionic liquids having imidazolium and substituents with one or more carbon atoms include, specifically, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium trifluoromethanephosphate, 1-butyl-3-methylimidazolium tetrachloroferate, 1-butyl-3-methylimidazolium iodide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, and 1-butyl-2,3-dimethylimidazolium tetrafluorophosphate. Lafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-2,3-dimethylimidazolium 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-dimesitylyimidazolium 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 Examples include methyl-3-n-octylimidazolium chloride, 1-methyl-3-n-octylimidazolium hexafluorophosphate, 1-methyl-3-[6-(methylsulfinyl)hexyl]imidazolium p-toluenesulfonate, 1-ethyl-3-methylimidazolium tricyanomethanide, and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0060] In particular, from the viewpoint of gas separation performance, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMI][FSI]), 1-ethyl-3-methylimidazolium dicyanamide ([EMI][DCA]), 1-ethyl-3-methylimidazolium tricyanomethanide ([EMI][TCM]), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][TF2N]), and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2OHim][TF2N]) are especially preferred.

[0061] The method for preparing 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.

[0062] The ionic liquid content in the double network gel is, for example, 50 wt% or more, preferably 60 wt% or more, more preferably 70 wt% or more, and even more preferably 80 wt% or more. The higher the ionic liquid content, the more preferentially the separation functional layer 1 can permeate the acidic gas contained in the mixed gas. The upper limit of the ionic liquid content is not particularly limited, and is, for example, 95 wt%.

[0063] The content of the first network structure, which is mainly composed of organic material, 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 network structure is, for example, 15 wt%. The content of the second network structure, which is mainly composed of inorganic material, in the double network gel is, for example, 1 wt% or more, from the viewpoint of improving the strength of the double network gel. The upper limit of the content of the second network structure is, for example, 5 wt%. The ratio of the total weight of the first network structure and the second network structure to the weight of the double network gel is, for example, 2 wt% or more, preferably 5 wt% or more, and more preferably 10 wt% or more. This ratio is preferably 20 wt% or less. In this embodiment, the separation functional layer 1 preferably consists substantially of a double network gel.

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

[0065] (Middle class) The intermediate layer 2 may, for example, contain a resin and further contain nanoparticles dispersed in the resin (matrix). The nanoparticles may be spaced apart from each other in the matrix or partially aggregated. The material of the matrix is ​​not particularly limited and includes, for example, 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; polyolefin resins such as polymethylpentene; and polyurethane resins. The matrix preferably contains at least one selected from the group consisting of silicone resins and polyurethane resins, and more preferably contains both silicone resins and polyurethane resins.

[0066] Nanoparticles may contain inorganic materials or organic materials. Examples of inorganic materials that can be included in nanoparticles include silica, titania, and alumina. It is preferable that the nanoparticles contain silica.

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

[0068] (porous support) The porous support 3 supports the separation functional layer 1 via the intermediate layer 2. Examples of the porous support 3 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; permeable (porous) polymer containing at least one selected from the group consisting of polyvinyl fluoride, polyvinylidene fluoride, polyurethane, polypropylene, polyethylene, polystyrene, polycarbonate, polysulfone, polyetheretherketone, polyacrylonitrile, polyimide, and polyphenylene oxide; metal foam having open or closed cells; polymer foam having open or closed cells; silica; porous glass; mesh screen, etc. The porous support 3 may be a combination of two or more of these.

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

[0070] [Method for manufacturing separation membranes] The separation membrane 12A can be manufactured, for example, by the following method. First, a coating solution containing the material for the intermediate layer 2 is prepared. Next, the coating solution containing the material for the intermediate layer 2 is applied to the porous support 3 to form a coated film. The method of applying the coating solution is not particularly limited, and for example, spin coating, dip coating, gravure coating, etc., can be used. The coating solution may also be applied using a wire bar or the like. The thickness of the formed intermediate layer 2 can be adjusted by adjusting the concentration of the material for the intermediate layer 2 in the coating solution. Next, the coated film is dried to form the intermediate layer 2. Drying of the coated film can be carried out, for example, under heating conditions. The heating temperature of the coated film is, for example, 50°C or higher. The heating time of the coated film is, for example, 1 minute or more, and may be 5 minutes or more.

[0071] The surface of the intermediate layer 2 may be treated to facilitate adhesion as needed. This may include surface treatments such as the application of a primer, corona discharge treatment, or plasma treatment.

[0072] Next, a coating solution containing the material for the separation functional layer 1 is prepared. The coating solution containing the material for the separation functional layer 1 is applied onto the intermediate layer 2 to obtain a coating film. This coating film is dried to form the separation functional layer 1. The coating method and drying conditions for the coating solution can be the same as those described above for the intermediate layer 2. This yields a separation film 12A.

[0073] The method for producing the separation membrane 12A is not limited to the method described above. For example, the separation membrane 12A can also be produced by the following method. For example, a coating solution containing the material for the separation functional layer 1 is applied onto a transfer film to obtain a coating film. The separation functional layer 1 is formed by drying the coating film. Next, an intermediate layer 2 is formed by coating a coating solution containing the material for the intermediate layer 2 onto the separation functional layer 1 and drying it. The laminate of the intermediate layer 2 and the separation functional layer 1 is transferred onto a porous support 3. This yields the separation membrane 12A.

[0074] [Differential examples of separation membranes] As described above, the separation membrane 12 may be a separation membrane (liquid separation membrane) that can preferentially permeate volatile organic compounds contained in the mixed liquid. The separation membrane 12 as a liquid separation membrane is, for example, a permeation vaporization membrane that produces a permeable fluid of the above-mentioned organic compounds by permeation vaporization. The separation membrane 12 as a liquid separation membrane will be described below.

[0075] As shown in Figure 4B, the separation membrane 12B, as a liquid separation membrane, comprises, for example, a separation functional layer 5 and a porous support 6 that supports the separation functional layer 5. The separation membrane 12B may further include a protective layer (not shown) that protects the separation functional layer 5. The separation functional layer 5 is in direct contact with, for example, the porous support 6.

[0076] (separation functional layer) The separation function layer 5 is, for example, a layer that can preferentially permeate volatile organic compounds contained in the mixed liquid. The separation function layer 5 includes, for example, a silicone resin such as polydimethylsiloxane (PDMS) or a polyolefin resin such as polypropylene, which is a hydrophobic material. It is preferable that the separation function layer 5 includes a silicone resin as the hydrophobic material. The separation function layer 5 may contain a hydrophobic material as its main component, or it may be composed substantially only of a hydrophobic material. "Main component" means the component that is present in the largest amount by weight in the separation function layer 5.

[0077] The separation functional layer 5 may include a matrix containing a hydrophobic material and fillers dispersed in the matrix. The fillers are embedded within the matrix. Within the matrix, all fillers may be spaced apart from each other or partially aggregated.

[0078] The filler includes, for example, an inorganic material such as zeolite. Preferably, the zeolite included in the filler is a high-silica zeolite with a high silica-to-alumina ratio. High-silica zeolites are suitable for applications involving the separation of water-containing liquids due to their excellent hydrolysis resistance. Examples of high-silica zeolites that can be used include HSZ (registered trademark) from Tosoh Corporation, HiSiv (registered trademark) from Union Showa Co., Ltd., USKY from Union Showa Co., Ltd., and Zeoal (registered trademark) from Nakamura Choko Co., Ltd.

[0079] The shape of the filler is, for example, particulate. In this specification, "particulate" includes spherical, ellipsoidal, flaky, and fibrous. The average particle size of the filler is not particularly limited, but is, for example, 50 μm or less, preferably 20 μm or less, and more preferably 10 μm or less. The lower limit of the average particle size of the filler is, for example, 0.01 μm. The average particle size of the filler can be determined, for example, by the following method: First, a cross-section of the separation functional layer 5 is observed with a transmission electron microscope. In the obtained electron microscope image, the area of ​​a specific filler is calculated by image processing. The diameter of a circle having the same area as the calculated area is considered to be the particle size (diameter of the particle) of that specific filler. The particle size of any number (at least 50) of fillers is calculated, and the average of the calculated values ​​is considered to be the average particle size of the filler.

[0080] The filler content in the separation functional layer 5 is, for example, 10 wt% or more, preferably 20 wt% or more. The upper limit of the filler content in the separation functional layer 5 is not particularly limited, but is, for example, 70 wt%. The matrix content in the separation functional layer 5 is not particularly limited, but is, for example, 30 wt% to 90 wt%.

[0081] The thickness of the separation functional layer 5 is, for example, 200 μm or less, preferably 100 μm or less, and more preferably 80 μm or less. The thickness of the separation functional layer 5 may be 1.0 μm or more, 10 μm or more, or 30 μm or more.

[0082] The separation functional layer 5 may have a microporous structure with an average pore diameter of less than 0.01 μm, but it may also be a dense layer without pores on its surface.

[0083] (porous support) As the porous support 6, the one described above for the separation membrane 12A can be used.

[0084] (protective layer) The protective layer, for example, covers the surface of the separation function layer 5. The material of the protective layer is not particularly limited, and examples include silicone resin. The material of the protective layer may be the same as the material of the matrix of the separation function layer 5. The thickness of the protective layer is not particularly limited, and is, for example, 5 μm or more, preferably 10 μm or more, and more preferably 20 μm or more. The thickness of the protective layer is, for example, 100 μm or less, and preferably 50 μm or less.

[0085] [Method for manufacturing separation membranes] The separation membrane 12B can be fabricated, for example, by forming a separation functional layer 5 on a porous support 6. Specifically, first, a coating solution containing the material for the separation functional layer 5 is prepared. The coating solution may contain a filler along with a dispersant for dispersing the filler in the coating solution. If the coating solution contains a silicone resin, the coating solution may further contain a catalyst for curing the silicone resin. Next, a coating film is obtained by applying the coating solution onto the porous support 6. The separation functional layer 5 is formed by drying the coating film.

[0086] [Manufacturing method for spiral membrane elements] Next, an example of a method for manufacturing the separation membrane element 10 will be described with reference to Figures 5 and 6. First, as shown in Figure 5, the separation membrane 12 is folded in half so that the separation functional layer 1 of the separation membrane 12 is located on the inside. A supply spacer 13 is placed between the two folded separation membranes 12, and a permeable spacer 14 is placed on top of the separation membrane 12. Furthermore, adhesive 26a is applied to three sides of the outer circumference of the permeable spacer 14. This gives rise to the separation membrane unit U. At this point, the adhesive 26a is in an uncured state.

[0087] Next, as shown in Figure 6, a central tube 21, a spacer 16, and a plurality of separation membrane units U are prepared. The spacer 16 has, for example, a first portion 16a that is directly wrapped around the central tube 21 and a second portion 16b that is stacked with the separation membrane units U. The first portion 16a of the spacer 16 corresponds to the flow channel spacer 15, and the second portion 16b corresponds to the permeation spacer 14. The material, thickness, etc. of the first portion 16a may be the same as or different from that of the second portion 16b. The plurality of separation membrane units U are arranged in a stepped manner on the second portion 16b of the spacer 16. The number of the plurality of separation membrane units U is not particularly limited, and is, for example, 2 to 30. Note that the uppermost separation membrane unit U does not have to have a permeation spacer 14.

[0088] Next, the first portion 16a of the spacer 16 is wrapped around the central tube 21. The number of turns of the first portion 16a is not particularly limited, and is, for example, 1 to 15, preferably 2 to 10.

[0089] Next, multiple separation membrane units U are wrapped around the central tube 21. At this time, the uppermost separation membrane unit U is stacked with the second portion 16b of the spacer 16. After the separation membrane units U are wrapped around the central tube 21, the adhesive 26a hardens to form an adhesive layer 26, and a bag-shaped membrane leaf 11 is formed. This gives rise to an assembly including the central tube 21 and the laminate 22.

[0090] Note that the spacer 16 is not limited to the shape shown in Figure 6. For example, the spacer 16 may have a third portion (not shown) connected to the second portion 16b and extending from the second portion 16b to the side opposite to the central tube 21. The third portion is wrapped around the central tube 21 on the outside of the laminate 22 formed by wrapping the separation membrane unit U around the central tube 21. That is, the third portion can cover the laminate 22 on the outside of the laminate 22. A film (for example, Lumirror 38E20 manufactured by Panac Co., Ltd.) may be placed between the laminate 22 and the third portion so that the supply spacer 13 of the laminate 22 does not come into contact with the third portion. The material, thickness, etc. of the third portion may be the same as or different from that of the first portion 16a.

[0091] [Characteristics of spiral-type membrane elements] In the separation membrane element 10, the difference between the pressure of the supply fluid and the pressure of the permeate fluid (pressure difference) is used as the driving force for membrane separation of the supply fluid by the separation membrane 12. Therefore, if pressure loss occurs within the separation membrane element 10, the above pressure difference decreases, and the permeation velocity and permeation flux of the permeate fluid from the separation membrane 12 decrease. In particular, in the method of operating the separation membrane element 10 by reducing the pressure inside the central pipe 21 (reduced pressure method), the pressure difference tends to be smaller compared to the method of operating the separation membrane element 10 by pressurizing the supply fluid (pressurized method), so the effect of the decrease in pressure difference due to pressure loss is greater.

[0092] According to the inventors' studies, pressure loss tends to occur particularly significantly in the flow path spacer 15 where the permeate fluid from each membrane leaf 11 concentrates. In the separation membrane element 10 of this embodiment, the reduction in the above-mentioned pressure difference is efficiently suppressed by setting the pressure loss P1 of the flow path spacer 15 to be smaller than the pressure loss P2 of the permeate spacer 14. With the separation membrane element 10 of this embodiment, by suppressing the reduction in the pressure difference, the decrease in the permeation velocity and permeation flux of the permeate fluid from the separation membrane 12 can be sufficiently suppressed.

[0093] (Characteristics of spiral membrane elements in relation to carbon dioxide) As an example, when carbon dioxide is used as the supply fluid and a separation membrane element 10 equipped with a separation membrane 12 (specifically separation membrane 12A) and a flat membrane separation membrane 12 (specifically separation membrane 12A) are operated under a pressurized system, the ratio R of the carbon dioxide permeation rate T2 (GPU) from the separation membrane element 10 to the carbon dioxide permeation rate T (GPU) from the flat membrane separation membrane 12 is, for example, 90% or more, preferably 95% or more. Here, in the pressurized operation to determine the ratio R, the supply fluid supplied to the separation membrane element 10 or the flat membrane separation membrane 12 is at a temperature of 23°C and a pressure of 0.2 MPa. In the pressurized system, the pressure in the space where the permeate fluid is obtained (the space in the permeate fluid flow path) matches the atmospheric pressure in the measurement environment (e.g., 101 kPa). Note that GPU is 10 -6 ·cm 3 (STP) / (sec·cm 2 This means cmHg. 3 (STP) refers to the volume of carbon dioxide at 1 atmosphere and 0°C.

[0094] When carbon dioxide is used as the supply fluid and the flat membrane separation membrane 12 is operated under reduced pressure, the ratio R1 of the carbon dioxide permeation rate T1 (GPU) from the flat membrane separation membrane 12 to the carbon dioxide permeation rate T2 (GPU) from the separation membrane element 10 when the separation membrane element 10 is operated under pressurized conditions is, for example, 85% or more, preferably 90% or more, and more preferably 95% or more. The permeation rate T1 can be measured under the conditions described later. The permeation rate T2 is the same as the ratio R described above.

[0095] When carbon dioxide is used as the supply fluid and both the separation membrane element 10 and the flat membrane separation membrane 12 are operated under reduced pressure conditions, the ratio R2 of the carbon dioxide permeation rate T3 (GPU) from the separation membrane element 10 to the carbon dioxide permeation rate T1 (GPU) from the flat membrane separation membrane 12 is, for example, 80% or more, preferably 85% or more. Here, in the reduced pressure operation to determine the ratio R2, the supply fluid supplied to the separation membrane element 10 or the flat membrane separation membrane 12 has a temperature of 23°C and a pressure of 0.1 MPa. In the reduced pressure operation, a vacuum pump is used to reduce the pressure of the space where the permeate fluid is obtained (the space in the permeate fluid flow path) to about 10 kPa or less.

[0096] (Characteristics of spiral membrane elements in a mixed liquid consisting of IPA and water) As another example, when a mixed liquid consisting of isopropanol (IPA) and water is used as the supply fluid, and the separation membrane element 10 equipped with a separation membrane 12 (specifically separation membrane 12B) and the flat membrane separation membrane 12 (specifically separation membrane 12B) are operated under reduced pressure conditions, the permeation flux F1 (kg / m³) of IPA from the flat membrane separation membrane 12 is as follows: 2 F2 (kg / m³) of the permeate flux of IPA from the separation membrane element 10 relative to / hr 2 The ratio L of the permeate flow rate ( / hr) is, for example, 60% or more. The upper limit of the ratio L is not particularly limited, but is, for example, 90%. Here, in the reduced-pressure operation for determining the ratio L, the supply fluid supplied to the separation membrane element 10 or the flat membrane separation membrane 12 has a temperature of 40°C. The amount of supply fluid is set appropriately within a range that does not affect the measurement of permeate fluxes F1 and F2. As an example, in the measurement of permeate flux F2, the supply flow rate of the supply fluid sent to the separation membrane element 10 may be set to 40 g / min. The concentration of IPA in the supply fluid is 5 wt%. In the reduced-pressure method, a vacuum pump is used to reduce the pressure of the space in which the permeate fluid is obtained (the space in the permeate fluid flow path) to 1.5 kPa. In the reduced-pressure method, a gaseous permeate fluid is usually obtained. The permeate fluxes F1 and F2 can be determined by condensing the gaseous permeate fluid and analyzing the composition of the resulting liquid permeate fluid.

[0097] Furthermore, in the separation membrane element 10 of this embodiment, it is not necessary to reduce the pressure loss P2 of the permeation spacer 14 compared to the conventional design. That is, it is not necessary to increase the thickness of the permeation spacer 14, for example, in order to reduce the pressure loss P2. Therefore, the separation membrane element 10 of this embodiment has the advantage that the number of membrane leaves 11 within the separation membrane element 10 can be maintained, thereby ensuring a sufficient membrane area of ​​the separation membrane 12. However, in the separation membrane element 10 of this embodiment, a permeation spacer 14 exhibiting a smaller pressure loss P2 than the conventional design may be used.

[0098] [Applications of separation membrane elements] One example of the application of the separation membrane element 10 of this embodiment is the separation of an acidic gas from a gas mixture containing an acidic gas. Examples of acidic gases in the gas mixture include carbon dioxide, hydrogen sulfide, carbonyl sulfide, sulfur oxides (SOx), hydrogen cyanide, and nitrogen oxides (NOx), with carbon dioxide being preferred. The gas mixture contains other gases besides the acidic gas. Examples of other gases include nonpolar gases such as hydrogen and nitrogen, and inert gases such as helium, with nitrogen being preferred. The separation membrane element 10 equipped with the above-described separation membrane 12A is suitable for applications in which carbon dioxide is separated from a gas mixture containing carbon dioxide and nitrogen.

[0099] Another example of the application of the separation membrane element 10 is the separation of volatile organic compounds from a mixed liquid containing such compounds. Examples of volatile organic compounds include alcohols, typically lower alcohols. Lower alcohols are, for example, alcohols with 5 or fewer carbon atoms. Lower alcohols may be monohydric or polyhydric alcohols. Lower alcohols may be linear or branched. Examples of lower alcohols include methanol, ethanol, n-propanol, isopropanol (IPA), n-butanol, 2-butanol, isobutanol, t-butanol, and n-pentanol, with IPA being preferred. The volatile organic compound may be an alcohol other than a lower alcohol, such as phenol. The mixed liquid contains other liquids besides the volatile organic compound. The other liquid is typically water. The separation membrane element 10 equipped with the above-described separation membrane 12B is suitable for applications in which alcohol is separated from a mixed liquid containing alcohol and water.

[0100] The separation membrane element 10 of this embodiment preferably satisfies at least one of the following conditions: (i) it is used to separate carbon dioxide from a mixed gas containing carbon dioxide and nitrogen, and (ii) it is used to separate alcohol from a mixed liquid containing alcohol and water. However, the application of the separation membrane element 10 is not limited to the application described in (i) or (ii) above.

[0101] <Embodiment of a membrane separation system> As shown in Figure 7, the membrane separation system 100 of this embodiment includes the separation membrane element 10 and the pressure reducing device 60 described above. The pressure reducing device 60 can reduce the pressure inside the central tube 21 of the separation membrane element 10. In other words, the pressure reducing device 60 can create or increase a differential pressure between the space in the supply fluid flow path and the space in the permeate fluid flow path of the separation membrane element 10. A specific example of the pressure reducing device 60 is a vacuum device such as a vacuum pump. The membrane separation system 100 may also include two separation membrane elements 10a and 10b and two pressure reducing devices 60a and 60b. The membrane separation system 100 is suitable for applications in which an acidic gas is separated from a mixed gas containing an acidic gas.

[0102] The membrane separation system 100 further includes a mixed fluid supply path 50. The mixed fluid supply path 50 is connected to the mixed fluid inlet of the separation membrane element 10a and is a path for supplying the mixed fluid to the separation membrane element 10a from a tank (not shown) that stores the mixed fluid. The mixed fluid supply path 50 may or may not include a pressurizing device 64 for pressurizing the space within the supply fluid path of the separation membrane element 10a. Examples of the pressurizing device 64 include a compressor, a blower, and a back pressure valve. The pressurizing device 64 can pressurize the space within the supply fluid path of the separation membrane element 10a by, for example, increasing the pressure of the mixed fluid supplied to the separation membrane element 10a.

[0103] The membrane separation system 100 further includes a permeate fluid supply path 52. The permeate fluid supply path 52 is connected to the permeate fluid outlet of the separation membrane element 10a and the permeate fluid inlet of the separation membrane element 10b, and is a path for supplying permeate fluid from the separation membrane element 10a to the separation membrane element 10b. The permeate fluid from the separation membrane element 10a is further processed in the separation membrane element 10b. A depressurizing device 60a is located in the permeate fluid supply path 52.

[0104] The permeate fluid supply path 52 has a first portion 52a extending from the separation membrane element 10a to the pressure reducing device 60a, and a second portion 52b extending from the pressure reducing device 60a to the separation membrane element 10b. The pressure reducing device 60a can reduce the pressure of the space in the permeate fluid path of the separation membrane element 10a through the first portion 52a. The pressure reducing device 60a, for example, sucks in the permeate fluid that has passed through the first portion 52a and discharges the permeate fluid to the second portion 52b. The second portion 52b may or may not have a pressurizing device (not shown) that pressurizes the permeate fluid discharged from the pressure reducing device 60a. This pressurizing device can pressurize the space in the supply fluid path of the separation membrane element 10b. Examples of pressurizing devices include a compressor, a blower, and a back pressure valve.

[0105] The membrane separation system 100 further includes a first discharge path 54. The first discharge path 54 is connected to the impermeable fluid outlet of the separation membrane element 10a and is a path for discharging the impermeable fluid from the separation membrane element 10a. The first discharge path 54 has an opening (discharge port 72) formed therein for discharging the impermeable fluid from the first discharge path 54. The membrane separation system 100 further includes a tank (not shown) for storing the impermeable fluid, and the first discharge path 54 may be connected to this tank.

[0106] The membrane separation system 100 further includes a second discharge path 56 and a tank 70. The second discharge path 56 is connected to the permeate outlet of the separation membrane element 10b and the inlet of the tank 70, and is a path for sending the permeate from the separation membrane element 10b to the tank 70. The tank 70 can store the permeate sent from the separation membrane element 10b. A depressurizing device 60b is located in the second discharge path 56.

[0107] The second discharge path 56 has a first portion 56a extending from the separation membrane element 10b to the depressurization device 60b, and a second portion 56b extending from the depressurization device 60b to the tank 70. The depressurization device 60 can reduce the pressure in the space within the permeate fluid path of the separation membrane element 10b through the first portion 56a. The depressurization device 60b, for example, sucks in the permeate fluid that has passed through the first portion 56a and discharges the permeate fluid to the second portion 56b.

[0108] The membrane separation system 100 further includes a third discharge path 58. The third discharge path 58 is connected to the impermeable fluid outlet of the separation membrane element 10b and is a path for discharging impermeable fluid from the separation membrane element 10b. The third discharge path 58 may also merge with the mixed fluid supply path 50. In Figure 7, the third discharge path 58 is connected to a pressurizing device 64 and merges with the mixed fluid supply path 50 at the pressurizing device 64. By merging the third discharge path 58 with the mixed fluid supply path 50, for example, impermeable fluid containing acidic gases that could not be completely separated by the separation membrane element 10b can be reused.

[0109] Each of the pathways in the membrane separation system 100 is composed of, for example, metal or resin piping.

[0110] According to the membrane separation system 100 of this embodiment, the vacuum device 60 can be used to reduce the pressure in the space within the permeable fluid path of the separation membrane element 10 to perform the separation operation. This type of vacuum separation operation is suitable for reducing the energy required to separate the mixed fluid compared to the pressurized method. [Examples]

[0111] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0112] (Example 1) [Separation membrane fabrication] First, a coating solution containing silicone resin and polyurethane resin in a weight ratio of 9:1 was prepared. The coating solution contained water as a solvent. Next, a coating film was obtained by applying the coating solution onto a porous support using the gravure coating method. As the porous support, Nitto Denko's UF membrane (ultrafiltration membrane) RS-50 (a laminate of a porous PVDF layer and a PET nonwoven fabric) was used. An intermediate layer was formed by drying the obtained coating film. This created a laminate of the porous support and the intermediate layer.

[0113] Next, 2 g of polyether block amide (Pebax MH1657, manufactured by Arkema) was added to 98 g of a 70 wt% isopropanol aqueous solution and stirred at 80°C for 3 hours to prepare a 2 wt% Pebax solution. Then, the prepared solution was coated onto the intermediate layer using the gravure coating method. Next, the resulting coated film was dried to form a separation functional layer. This obtained a separation film.

[0114] [Fabrication of spiral-type membrane elements] A spiral membrane element of Example 1 was fabricated using the method described with reference to Figure 6, with PE30 manufactured by NBC Mesh Tech as the spacer 16 in Figure 6, #1000E manufactured by KB Seiren as the other permeable spacer 14, and 34mil manufactured by Tokyo Ink Co., Ltd. as the supply spacer 13. The first portion 16a of spacer 16 had a length of 90 mm in the direction in which it is wrapped around the central tube and a length of 280 mm in the direction in which the central tube extends. The permeable spacer 14 had a length of 290 mm in the direction in which it is wrapped around the central tube and a length of 280 mm in the direction in which the central tube extends. After spacer 16 and permeable spacer 14 were wrapped around the central tube, their ends were cut. In the spiral membrane element, the length at which these spacers function effectively in the direction in which the central tube extends was 180 mm. The outer diameter of the central tube 21 was 17.3 mm, and the outer diameter of the spiral membrane element was approximately 2 inches.

[0115] (Examples 2 and 3) The spiral-type membrane elements of Examples 2 and 3 were fabricated using the same method as in Example 1, except that the spacer 16 was changed as shown in Table 2.

[0116] (Example 4) The spiral membrane element of Example 4 was fabricated using the same method as in Example 1, except that a laminate of a porous support and an intermediate layer (the laminate before the creation of the separation functional layer) was used as the separation membrane.

[0117] (Example 5) The spiral membrane element of Example 5 was manufactured in the same manner as in Example 1, except that the length of the first portion 16a of the spacer 16 and the permeable spacer 14 in the direction in which the central tube extends was changed to 1 m, the length of the permeable spacer 14 in the direction in which it is wrapped around the central tube was changed to 400 mm, the length of the first portion 16a of the spacer 16 in the direction in which it is wrapped around the central tube was changed to 136 mm, and the outer diameter of the spiral membrane element was changed to approximately 4 inches.

[0118] (Comparative Example 1) The spiral-type membrane element of Comparative Example 1 was fabricated using the same method as in Example 1, except that #1000E manufactured by KB Seiren Co., Ltd. was used as the spacer 16.

[0119] (Comparative Example 2) The spiral-type film element of Comparative Example 2 was fabricated using the same method as in Example 4, except that #1000E manufactured by KB Seiren Co., Ltd. was used as the spacer 16.

[0120] [Evaluation of flat membrane-type separation membranes] The carbon dioxide permeation rate T1 (GPU) in the flat membrane state was measured for the separation membranes used in the spiral membrane elements of Examples 1-5 and Comparative Examples 1-2. The permeation rate T1 was measured using a differential pressure gas permeability meter (GTR-31AHND manufactured by GTR Tech Co., Ltd.) by the following method. First, the separation membrane was set in a metal cell in a flat membrane state and sealed with an O-ring to prevent leakage. The membrane area of ​​the separation membrane was 3.14 cm². 2 Next, the supply fluid (carbon dioxide) was injected into a metal cell so that it came into contact with the main surface of the separation membrane on the functional separation layer (or intermediate layer) side. The supply fluid injected into the metal cell had a temperature of 23°C and a pressure of 0.1 MPa. Next, a vacuum pump was used to reduce the pressure in the space adjacent to the main surface of the separation membrane on the porous support side to approximately 10 kPa or less. As a result, permeate fluid was obtained from the main surface of the separation membrane on the porous support side. The permeation rate T1 of carbon dioxide was calculated based on the composition and weight of the obtained permeate fluid. The composition of the permeate fluid was measured using gas chromatography (G2700T, manufactured by Yanaco Technical Sciences).

[0121] The transmission velocity T1 of the separation membrane used in Example 1 was 100 GPU. The transmission velocity T1 of the separation membrane (a laminate of a porous support and an intermediate layer) used in Example 4 was 1500 GPU.

[0122] [Evaluation of spiral membrane elements] Next, the carbon dioxide permeation rate T2(GPU) of the spiral membrane elements of Examples 1-5 and Comparative Examples 1-2 was measured when operated under a pressurized system, and the carbon dioxide permeation rate T3(GPU) was measured when the spiral membrane elements were operated under a reduced pressure system.

[0123] The permeation rate T2 was measured by the following method. First, a supply fluid (carbon dioxide) was supplied to the supply fluid channel of the spiral membrane element. The supply fluid had a temperature of 23°C and a pressure of 0.2 MPa. As a result, permeation fluid was obtained through the central tube of the spiral membrane element. The permeation rate T2 of carbon dioxide was calculated based on the flow rate of the obtained permeation fluid. The flow rate of the permeation fluid was measured using a soap membrane flow meter (manufactured by HORIBA).

[0124] The permeation velocity T3 was measured using the same method as for the permeation velocity T2, except that the pressure of the supply fluid (carbon dioxide) supplied to the supply fluid channel was changed to 0.1 MPa, and the pressure inside the central tube of the spiral membrane element was reduced to approximately 10 kPa or less using a vacuum pump.

[0125] Next, the ratio R1 of transmission velocity T2 to transmission velocity T1, and the ratio R2 of transmission velocity T3 to transmission velocity T1 were calculated. The results are shown in Table 2.

[0126] [Table 2]

[0127] As can be seen from Table 2, in the spiral membrane elements of Examples 1 to 5, where the pressure loss P1 of the flow channel spacer was smaller than the pressure loss P2 of the permeation spacer, the ratios R1 and R2 were higher than those of Comparative Examples 1 and 2, respectively. Specifically, in the spiral membrane elements of Examples 1 to 5, the ratio R1 was 83% or higher in all cases, which was higher than the ratio R1 of Comparative Examples 1 and 2. Furthermore, in the spiral membrane elements of Examples 1 to 5, the ratio R2 was 78% or higher in all cases, which was higher than the ratio R2 of Comparative Examples 1 and 2. From these results, it can be seen that the spiral membrane elements of this embodiment are suitable for suppressing the decrease in the permeation rate of the permeable fluid from the separation membrane.

[0128] (Example 6) [Separation membrane fabrication] First, a coating solution was prepared by mixing silicone resin (YSR3022, manufactured by Momentive Performance Materials Japan), silicone curing catalyst (YC6831, manufactured by Momentive Performance Materials Japan), and high-silica zeolite (HiSiv3000, manufactured by Union Showa). Next, a coating film was obtained by applying the coating solution onto a porous support (RS-50, manufactured by Nitto Denko Corporation). A separation functional layer was fabricated by drying the coating film. This resulted in the acquisition of a separation film. In the separation functional layer, the weight ratio of silicone resin to high-silica zeolite was 50:50.

[0129] [Fabrication of spiral-type membrane elements] A spiral membrane element of Example 6 was fabricated using the method described with reference to Figure 6, with PE30 manufactured by NBC Mesh Tech as the spacer 16 in Figure 6, #1000E manufactured by KB Seiren as the other permeable spacer 14, and 34mil manufactured by Tokyo Ink Co., Ltd. as the supply spacer 13. The first portion 16a of spacer 16 had a length of 90 mm in the direction in which it is wrapped around the central tube and a length of 280 mm in the direction in which the central tube extends. The permeable spacer 14 had a length of 140 mm in the direction in which it is wrapped around the central tube and a length of 280 mm in the direction in which the central tube extends. After spacer 16 and permeable spacer 14 were wrapped around the central tube, their ends were cut. In the spiral membrane element, the length at which these spacers function effectively in the direction in which the central tube extends was 180 mm. The outer diameter of the central tube 21 was 17.3 mm, and the outer diameter of the spiral membrane element was approximately 2 inches.

[0130] (Example 7) The spiral-type membrane element of Example 7 was fabricated using the same method as in Example 6, except that the spacer 16 was changed as shown in Table 3.

[0131] (Comparative Example 3) A spiral membrane element of Comparative Example 3 was fabricated in the same manner as in Example 6, except that #1000E manufactured by KB Selen was used as the spacer 16.

[0132] [Evaluation of flat membrane separation membrane] For the separation membranes used in the spiral membrane elements of Examples 6 to 7 and Comparative Example 3, the permeation flux F1 (kg / m 2 / hr) of isopropanol (IPA) in the state of a flat membrane was measured. The measurement of the permeation flux F1 was carried out by the following method. First, the separation membrane was set in a metal cell in the state of a flat membrane and sealed with an O-ring so that no leakage occurred. The membrane area of the separation membrane was 34.2 cm 2 . Next, the supply fluid was filled in the metal cell so that the supply fluid contacted the main surface on the separation functional layer side of the separation membrane. The supply fluid was substantially composed of IPA and water. The concentration of IPA in the supply fluid was 5 wt%. The temperature of the supply fluid supplied into the metal cell was 40°C. Next, using a vacuum pump, the space adjacent to the main surface on the porous support side of the separation membrane was depressurized to 1.5 kPa. As a result, a gaseous permeate fluid was obtained from the main surface on the porous support side of the separation membrane. That is, separation by the pervaporation method (PV) proceeded by an operation in a depressurization mode. The permeate fluid was liquefied by cooling the gaseous permeate fluid using liquid nitrogen at -196°C. The composition of the liquid permeate fluid was analyzed using gas chromatography. Based on the composition of the obtained permeate fluid, the weight of the permeate fluid, etc., the permeation flux F1 of IPA was calculated.

[0133] [Evaluation of spiral membrane element] Next, the permeation flux F2 (kg / m 2 / hr) of IPA when the spiral membrane elements of Examples 6 to 7 and Comparative Example 3 were operated in a depressurization mode was measured.

[0134] The permeate flux F2 was measured by the following method. First, a supply fluid was supplied to the supply fluid channel of the spiral membrane element. The supply fluid consisted substantially of IPA and water. The concentration of IPA in the supply fluid was 5 wt%. The temperature of the supply fluid was 40°C. The supply flow rate of the supply fluid was 40 g / min. Next, the pressure inside the central tube of the spiral membrane element was reduced to 1.5 kPa using a vacuum pump. This resulted in the acquisition of a gaseous permeate fluid through the central tube of the spiral membrane element. In other words, separation by permeation vaporization (PV) proceeded under reduced pressure operation. The gaseous permeate fluid was liquefied by cooling it with liquid nitrogen at -196°C. The composition of the liquid permeate fluid was analyzed using gas chromatography. Based on the composition and weight of the obtained permeate fluid, the permeate flux F2 of IPA was calculated.

[0135] Next, the ratio L of the permeation flux F2 to the permeation flux F1 was calculated. The results are shown in Table 3.

[0136] [Table 3]

[0137] As can be seen from Table 3, in the spiral membrane elements of Examples 6 and 7, where the pressure loss P1 of the flow channel spacer was smaller than the pressure loss P2 of the permeation spacer, the ratio L was higher than that of Comparative Example 3. Specifically, in the spiral membrane elements of Examples 6 and 7, the ratio L was approximately 63%, which was higher than the ratio L of Comparative Example 3. From these results, it can be seen that the spiral membrane element of this embodiment is suitable for suppressing the decrease in permeation flux of the permeating fluid from the separation membrane, even when a liquid is used as the supply fluid. [Industrial applicability]

[0138] The spiral membrane element of this embodiment is suitable for separating acidic gases from a gas mixture containing acidic gases. In particular, the spiral membrane element of this embodiment is suitable for separating carbon dioxide from off-gases in chemical plants or thermal power plants. The spiral membrane element of this embodiment is also suitable for separating volatile organic compounds from a liquid mixture containing such organic compounds.

Claims

1. The central tube, It has a separation membrane and a permeable spacer, and a membrane leaf wrapped around the central tube, A flow channel spacer connected to the permeable spacer and wrapped around the central tube on the central tube side of the membrane leaf, Equipped with, A spiral membrane element wherein the pressure loss P1 of the flow channel spacer, as measured by the following test, is smaller than the pressure loss P2 of the permeable spacer, as measured by the following test. Test: Prepare a test specimen by laminating a strip-shaped spacer (the flow channel spacer or the permeable spacer) measuring 150 mm in length and 47 mm in width onto a polyethylene terephthalate film. Nitrogen gas is introduced into the space adjacent to the film of the test specimen so that the pressure in the space is 0.1 MPa, and nitrogen gas is also introduced into the spacer at a flow rate of 2.5 L / min. The pressure loss caused by the movement of nitrogen gas in the longitudinal direction of the spacer is measured.

2. The spiral membrane element according to claim 1, wherein the pressure loss P1 is 30 kPa or less.

3. The spiral membrane element according to claim 1 or 2, wherein the opening ratio of the flow channel spacer is 30% or more.

4. The spiral membrane element according to any one of claims 1 to 3, wherein the thickness of the flow channel spacer is 300 μm or more.

5. The membrane leaf has two of the separation membranes, The spiral membrane element according to any one of claims 1 to 4, wherein the two separation membranes are superimposed on each other and sealed to have a bag-like structure.

6. The spiral membrane element according to claim 5, wherein the permeable spacer is disposed between the two separation membranes.

7. The spiral membrane element according to any one of claims 1 to 6, further comprising a supply spacer laminated on the membrane leaf.

8. The central tube is provided with an opening, The spiral membrane element according to any one of claims 1 to 7, wherein the flow channel spacer is in contact with the opening.

9. The separation membrane is Separation functional layer, A porous support that supports the separation functional layer, A spiral membrane element according to any one of claims 1 to 8, having the following:

10. The spiral membrane element according to claim 9, wherein the separation functional layer comprises a polyether block amide resin.

11. The spiral membrane element according to claim 9, wherein the separation functional layer comprises a silicone resin.

12. A spiral membrane element according to any one of claims 1 to 11, wherein at least one of the following is fulfilled: (i) used for separating carbon dioxide from a mixed gas containing carbon dioxide and nitrogen, and (ii) used for separating alcohol from a mixed liquid containing alcohol and water.

13. A spiral membrane element according to any one of claims 1 to 12, A pressure reducing device for reducing the pressure inside the central tube, A membrane separation system equipped with [the following features].

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