Spiral membrane element and membrane separation system

Abstract

The present invention provides a spiral membrane element suitable for suppressing a decrease in the speed of permeation of a permeating fluid from a separation membrane. A spiral membrane element according to the present invention comprises: a central tube; a membrane leaf which has a separation membrane and a permeate spacer and which is wound around the central tube; and a channel spacer which is connected to the permeate spacer and which is wound around the central tube on the central tube side relative to the membrane leaf. The channel spacer has an initial tensile elastic modulus of 100 N / mm2 or greater. A pressure gradient ΔPA1 obtained from a test A1 is 5.0 kPa / m or less.

Description

Spiral membrane element and membrane separation system

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

[0002] Membrane separation methods have been developed as a way to separate volatile organic compounds from solutions containing them. Membrane separation methods are suitable for efficiently separating organic compounds while keeping operating costs down.

[0003] For example, spiral membrane elements are used in membrane separation methods. Patent Document 1 discloses an example of a spiral membrane element. The spiral membrane element comprises a central tube and membrane leaves wound around the central tube, with the membrane leaves having a separation membrane and a permeation spacer.

[0004] A 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. The flow channel spacer allows the permeating fluid from the membrane leaves to be easily directed to the central tube. The presence of the flow channel spacer when fabricating the spiral membrane element makes it easier to wrap the membrane leaves around the central tube.

[0005] Patent No. 4650921

[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 separation membrane in a flat membrane configuration. 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 systems 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-type membrane element suitable for suppressing the decrease in the permeation rate of the permeating fluid from the separation membrane.

[0008] The present invention comprises a central tube, a membrane leaf having a separation membrane and a permeable spacer and wrapped around the central tube, and a flow path spacer connected to the permeable spacer and wrapped around the central tube on the central tube side of the membrane leaf, wherein the initial tensile modulus of the flow path spacer is 100 N / mm². 2 The above provides a spiral membrane element in which the differential pressure gradient ΔPA1 determined by the following test A1 is 5.0 kPa / m or less. Test A1: A test piece is prepared by laminating the permeable spacer, which is shaped like a strip of 150 mm in length and 47 mm in width, onto a polyethylene terephthalate film. Nitrogen gas is sent into the space adjacent to the film of the test piece so that the pressure in the space is 0.1 MPa, and nitrogen gas is also sent in the longitudinal direction of the permeable spacer at a flow rate of 1.0 L / min. At this time, the differential pressure gradient ΔPA1 that occurs in the longitudinal direction of the permeable spacer is determined.

[0009] Furthermore, the present invention provides a membrane separation system comprising the spiral membrane element described above and a depressurization device for reducing the pressure inside the central tube.

[0010] According to the present invention, a spiral-type membrane element suitable for suppressing the decrease in the permeation rate of the permeating fluid from the separation membrane can be provided.

[0011] This is a schematic exploded perspective view showing a spiral membrane element according to one embodiment of the present invention. This is a schematic cross-sectional view of the spiral membrane element. This is a schematic cross-sectional view showing an example of a measuring device for measuring the pressure loss of a spacer. This is a schematic cross-sectional view of the separation membrane provided by the spiral membrane element. This is a diagram illustrating the manufacturing method of the spiral membrane element. This is a diagram illustrating the manufacturing method of the spiral membrane element. This is a configuration diagram of a membrane separation system equipped with a spiral membrane element.

[0012] A spiral membrane element according to a first aspect of the present invention comprises: a central tube; a membrane leaf having a separation membrane and a permeable spacer, wound around the central tube; and a flow channel spacer connected to the permeable spacer and wound around the central tube on the central tube side of the membrane leaf, wherein the initial tensile modulus of the flow channel spacer is 100 N / mm². 2 The above is true, and the differential pressure gradient ΔPA1 determined by the following test A1 is 5.0 kPa / m or less. Test A1: A test specimen is prepared by laminating the permeable spacer, which is 150 mm long and 47 mm wide, onto a polyethylene terephthalate film. Nitrogen gas is sent 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 sent in the longitudinal direction of the permeable spacer at a flow rate of 1.0 L / min. At this time, the differential pressure gradient ΔPA1 that occurs in the longitudinal direction of the permeable spacer is determined.

[0013] In a second embodiment of the present invention, for example, in the spiral film element according to the first embodiment, the tensile modulus is 300 N / mm². 2 The following applies:

[0014] In a third embodiment of the present invention, for example, in a spiral membrane element according to the first or second embodiment, the differential pressure gradient ΔPA2 (kPa / m) determined by the following test A2 is greater than the differential pressure gradient ΔPA1 (kPa / m). Test A2: A test piece is prepared by laminating the strip-shaped flow channel 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 piece so that the pressure in the space is 0.1 MPa, and nitrogen gas is also introduced in the longitudinal direction of the flow channel spacer at a flow rate of 1.0 L / min. At this time, the differential pressure gradient ΔPA2 generated in the longitudinal direction of the flow channel spacer is identified.

[0015] In a fourth embodiment of the present invention, for example, in the spiral membrane element according to the third embodiment, the differential pressure gradient ΔPA2 is 20 kPa / m or less.

[0016] In the fifth aspect of the present invention, for example, in the spiral membrane element according to any one of the first to fourth aspects, the permeate spacer has an opening, and the opening area of the opening is 2.5 mm 2 or more.

[0017] In the sixth aspect of the present invention, for example, in the spiral membrane element according to any one of the first to fifth aspects, the opening ratio of the permeate spacer is 65% or more.

[0018] In the seventh aspect of the present invention, for example, in the spiral membrane element according to any one of the first to sixth aspects, the thickness of the permeate spacer is 0.35 mm or more.

[0019] In the eighth aspect of the present invention, for example, in the spiral membrane element according to any one of the first to seventh aspects, the permeate spacer is a net.

[0020] In the ninth aspect of the present invention, for example, in the spiral membrane element according to any one of the first to eighth aspects, the membrane leaf comprises two of said separation membranes, and the two separation membranes are superimposed on each other and sealed so as to have a bag-shaped structure.

[0021] In the tenth aspect of the present invention, for example, in the spiral membrane element according to the ninth aspect, the permeate spacer is disposed between the two separation membranes.

[0022] In the eleventh aspect of the present invention, for example, the spiral membrane element according to any one of the first to tenth aspects further comprises a feed spacer laminated on the membrane leaf.

[0023] In the twelfth aspect of the present invention, for example, in the spiral membrane element according to any one of the first to eleventh aspects, the central tube is provided with a through hole, and the flow path spacer is in contact with the through hole.

[0024] In the thirteenth aspect of the present invention, for example, in the spiral membrane element according to any one of the first to twelfth aspects, the separation membrane is a pervaporation membrane.

[0025] In a fourteenth aspect of the present invention, for example, a spiral membrane element according to any one of the first to thirteenth aspects is used to separate a volatile organic compound from a solution containing the organic compound.

[0026] A membrane separation system according to the 15th aspect of the present invention comprises a spiral membrane element according to any one of the 1st to 14th aspects, and a depressurization device for reducing the pressure inside the central tube.

[0027] A spiral membrane element according to a sixteenth aspect of the present invention comprises: a central tube; a membrane leaf having a separation membrane and a permeable spacer, wound around the central tube; and a flow channel spacer connected to the permeable spacer and wound around the central tube on the central tube side of the membrane leaf, wherein the initial tensile modulus of the flow channel spacer is 100 N / mm². 2 The above is true, and the pressure loss PB1 of the permeable spacer measured by the following test B1 is 10 kPa or less. Test B1: A test specimen is prepared by stacking the permeable spacer, which is shaped like a strip 178 mm in length and 44 mm in width, on a porous support (manufactured by Nitto Denko, RS-50). Nitrogen gas is sent into the space adjacent to the porous support of the test specimen so that the pressure in the space becomes 0.1 MPa, and nitrogen gas is also sent to the permeable spacer at a flow rate of 4.0 L / min. The pressure loss caused by the movement of nitrogen gas in the longitudinal direction of the permeable spacer is measured.

[0028] In the 17th aspect of the present invention, for example, in the spiral membrane element according to the 16th aspect, the tensile modulus is 300 N / mm 2 The following applies:

[0029] In the eighteenth aspect of the present invention, for example, in the spiral membrane element according to the sixteenth or seventeenth aspect, the pressure loss PB2 of the flow channel spacer measured by the following test B2 is greater than the pressure loss PB1. Test B2: A test specimen is prepared by stacking the flow channel spacer, which is shaped like a strip 178 mm in length and 44 mm in width, on a porous support (manufactured by Nitto Denko, RS-50). Nitrogen gas is sent into the space adjacent to the porous support of the test specimen so that the pressure in the space is 0.1 MPa, and nitrogen gas is also sent to the flow channel spacer at a flow rate of 4.0 L / min. The pressure loss caused by the movement of nitrogen gas in the longitudinal direction of the flow channel spacer within the flow channel spacer is measured.

[0030] In the 19th embodiment of the present invention, for example, in the spiral membrane element according to the 18th embodiment, the pressure loss PB2 is 70 kPa or less.

[0031] In a 20th embodiment of the present invention, for example, in a spiral membrane element according to any one of the 16th to 19th embodiments, the permeable spacer has an opening, and the opening area of ​​the opening is 2.5 mm². 2 That's all.

[0032] In the 21st aspect of the present invention, for example, in the spiral membrane element according to any one of the 16th to 20th aspects, the aperture ratio of the permeable spacer is 65% or more.

[0033] In the 22nd aspect of the present invention, for example, in a spiral membrane element according to any one of the 16th to 21st aspects, the thickness of the permeable spacer is 0.35 mm or more.

[0034] In the 23rd aspect of the present invention, for example, in a spiral membrane element according to any one of the 16th to 22nd aspects, the permeable spacer is a net.

[0035] In a 24th embodiment of the present invention, for example, in a spiral membrane element according to any one of the 16th to 23rd embodiments, the membrane leaf has two of the separation membranes, and the two separation membranes are overlapped and sealed to form a bag-like structure.

[0036] In a 25th embodiment of the present invention, for example, in the spiral membrane element according to the 24th embodiment, the permeable spacer is positioned between the two separation membranes.

[0037] In a 26th aspect of the present invention, for example, a spiral membrane element according to any one of the 16th to 25th aspects further comprises a supply spacer laminated on the membrane leaf.

[0038] In the 27th aspect of the present invention, for example, in a spiral membrane element according to any one of the 16th to 26th aspects, the central tube is provided with a through hole, and the flow path spacer is in contact with the through hole.

[0039] In the 28th aspect of the present invention, for example, in a spiral membrane element according to any one of the 16th to 27th aspects, the separation membrane is a permeable vaporization membrane.

[0040] In a 29th aspect of the present invention, for example, a spiral membrane element according to any one of the 16th to 28th aspects is used to separate a volatile organic compound from a solution containing the organic compound.

[0041] A membrane separation system according to the 30th aspect of the present invention comprises a spiral membrane element according to any one of the 16th to 29th aspects, and a depressurization device for reducing the pressure inside the central tube.

[0042] The details of the present invention will be described below, but the following description is not intended to limit the present invention to any particular embodiment.

[0043] <Embodiment of a Spiral-Type Membrane Element> Figures 1 and 2 show a spiral-type membrane element 10 (hereinafter referred to as "separation membrane element 10") according to one embodiment of the present invention. The separation membrane element 10 comprises a central tube 21 and a laminate 22. The laminate 22 is wrapped around the central tube 21 and arranged around the central tube 21. A supply fluid channel and a permeable fluid channel are formed inside the laminate 22.

[0044] 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 channel parallel to the longitudinal direction of the central pipe 21. In the separation membrane element 10, the supply fluid is separated to produce a permeable fluid and an impermeable fluid. The permeable fluid is guided to the outside through the central pipe 21. The impermeable fluid is discharged to the outside of the separation membrane element 10 from the other end face of the laminate 22.

[0045] The supply fluid to be processed by the separation membrane element 10 may be a liquid or a gas. As an example, the supply fluid may be a solution containing a volatile organic compound.

[0046] The separation membrane element 10 further includes a flow path spacer 15. The flow path 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 path spacer 15 secures a space between the laminate 22 and the central tube 21 that serves as a permeable fluid flow path.

[0047] 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.

[0048] 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. More specifically, 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, for example, an adhesive layer 26 containing an adhesive is used. 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 50.

[0049] 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. More specifically, 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 to serve as supply fluid channels.

[0050] The central tube 21 plays the role of collecting the permeate 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 through holes 21h that connect the internal space of the central tube 21 to the external space. In detail, the central tube 21 is provided with a plurality of through holes 21h at predetermined intervals along the direction in which the central tube 21 extends. The number of rows of the plurality of through holes 21h provided along the direction in which the central tube 21 extends is not particularly limited, and is, for example, 1 to 15. The central tube 21 may be provided with two rows of the plurality of through holes 21h facing each other. A flow path spacer 15 is in contact with each of the plurality of through holes 21h. As a result, the permeate fluid can flow into the interior of the central tube 21 from the flow path spacer 15 through the plurality of through holes 21h. The outer diameter of the central tube 21 is, for example, 10 to 100 mm, preferably 12 to 50 mm.

[0051] [Spacer] In the present embodiment, the initial tensile modulus of elasticity of the flow path spacer 15 is 100 N / mm 2 or more, and for the permeation spacer 14, the differential pressure gradient ΔPA1 determined by Test A1 described later is 5.0 kPa / m or less. According to the separation membrane element 10 in which such a permeation spacer 14 and such a flow path spacer 15 are combined, a decrease in the permeation rate of the permeated fluid from the separation membrane 12 can be sufficiently suppressed.

[0052] The initial tensile modulus of elasticity of the flow path spacer 15 can be measured by the following method. First, a rectangular test piece with a long side of 150 mm and a short side of 15 mm is cut out from the flow path spacer 15. At this time, the long side of the test piece is aligned with the MD direction (Machine Direction) of the flow path spacer 15. This test piece is set in a tensile tester, and a tensile test is performed under the conditions of a temperature of 23°C, a humidity of 50% RH, an initial chuck distance of 100 mm, and a tensile speed of 100 mm / min. The amount of change in stress and the amount of change in strain when the test force applied to the test piece is in the range of 5 N to 10 N are calculated, and the tensile modulus of elasticity is calculated by the following formula. The obtained calculated value can be regarded as the initial tensile modulus of elasticity of the flow path spacer 15. Tensile modulus of elasticity [N / mm 2 = amount of change in stress [N / mm 2 / amount of change in strain [-]

[0053] The initial tensile modulus of elasticity of the flow path spacer 15 is 100 N / mm as described above 2 or more, 110 N / mm 2 or more, 120 N / mm 2 or more, 130 N / mm 2 or more, or even 135 N / mm 2 or more. When the flow path spacer 15 having an initial tensile modulus of elasticity of 100 N / mm 2 or more is wound around the central tube 21, its shape does not tend to change significantly even when tension is applied. Specifically, this flow path spacer 15 tends not to easily stretch in the direction in which it is wound around the central tube 21. According to this flow path spacer 15, the separation membrane element 10 tends to be easily produced. The upper limit of the initial tensile modulus of elasticity is, for example, 300 N / mm 2 or less, 250 N / mm 2Below, 200N / mm 2 Below, 180N / mm 2 Furthermore, 150 N / mm 2 The following is also acceptable.

[0054] The differential pressure gradient ΔPA1 can be determined by the following test A1. Test A1: A test specimen is prepared by laminating a strip-shaped permeable spacer 14, measuring 150 mm in length and 47 mm in width, onto a polyethylene terephthalate (PET) film. Nitrogen gas is introduced into the space so that the pressure in the space adjacent to the film of the test specimen becomes 0.1 MPa, and nitrogen gas is also introduced in the longitudinal direction of the permeable spacer 14 at a flow rate of 1.0 L / min. At this time, the differential pressure gradient ΔPA1 that occurs in the longitudinal direction of the permeable spacer 14 is determined.

[0055] The differential pressure gradient ΔPA1 can be determined in detail using the measuring device 30 shown in Figure 3 by the following method. First, a strip-shaped permeable spacer 14a measuring 150 mm in length and 47 mm in width is prepared. The permeable spacer 14a may also be a rounded rectangle. Except for its length and width, the permeable spacer 14a has the same shape as the permeable spacer 14 before it is wrapped around the central tube 21. The longitudinal direction of the permeable spacer 14a coincides with the direction in which the permeable spacer 14 is wrapped around the central tube 21. Next, a polyethylene terephthalate film 41 is laminated onto the permeable spacer 14a to produce a test piece 40. The film 41 and the permeable spacer 14a may be fixed with tape or the like. The film 41 is, for example, Diafoil T100-100 manufactured by Mitsubishi Chemical Corporation.

[0056] Next, the test specimen 40 is set in the measuring device 30. The measuring device 30 includes, 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 permeable spacer 14a of the test specimen 40 is located 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 permeable spacer 14a 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 permeable spacer 14a and is discharged from the other opening 33. The openings 32 and 33 may or may not face each other.

[0057] 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. Two ports (not shown) for differential pressure measurement are formed on the bottom surface of the holder 31, perpendicular to the permeable spacer 14a. Specifically, one port is formed on the bottom surface of the holder 31 near the opening 32, and the other port is formed on the bottom surface of the holder 31 near the opening 33. The holder 31 and the lid member 35 may be made of stainless steel (SUS) or of a resin such as acrylic.

[0058] 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.

[0059] 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 permeable spacer 14a through the opening 32 of the holder 31 at a flow rate of 1.0 L / min. 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 in the longitudinal direction X of the permeable spacer 14a within the permeable spacer 14a and is discharged from the opening 33. The differential pressure ΔP (kPa) of the nitrogen gas is measured from the two ports. The differential pressure gradient ΔPA1 (kPa / m) can be obtained by dividing the differential pressure ΔP by the distance (m) between the two ports.

[0060] The differential pressure gradient ΔPA1 is 5.0 kPa / m or less as described above, but may also be 4.5 kPa / m or less, 4.0 kPa / m or less, 3.5 kPa / m or less, 3.0 kPa / m or less, or even 2.5 kPa / m or less. The lower the differential pressure gradient ΔPA1, the more effectively the decrease in the permeation rate of the permeating fluid from the separation membrane 12 can be suppressed. The lower limit of the differential pressure gradient ΔPA1 is, for example, 0.1 kPa / m or more, but may also be 0.5 kPa / m or more, or even 1.0 kPa / m or more.

[0061] The separation membrane element 10 typically has a plurality of permeation spacers 14. In this embodiment, it is sufficient that the differential pressure gradient ΔPA1 of at least one permeation spacer 14 selected from the plurality of permeation spacers 14 is 5.0 kPa / m or less. As long as this condition is met, the separation membrane element 10 may include permeation spacers 14 whose differential pressure gradient ΔPA1 exceeds 5.0 kPa / m. In this embodiment, it is preferable that the differential pressure gradient ΔPA1 of all permeation spacers 14 provided in the separation membrane element 10 is 5.0 kPa / m or less.

[0062] In this embodiment, the pressure loss PB1 of the permeable spacer 14 measured by the following test B1 may be 10 kPa or less. Test B1: A test specimen is prepared by stacking strip-shaped permeable spacers 14 measuring 178 mm in length and 44 mm in width on a porous support (manufactured by Nitto Denko, RS-50). Nitrogen gas is introduced into the space so that the pressure in the space adjacent to the porous support of the test specimen becomes 0.1 MPa, and nitrogen gas is also introduced into the permeable spacer 14 at a flow rate of 4.0 L / min. The pressure loss caused by the movement of nitrogen gas in the longitudinal direction of the permeable spacer 14 is measured.

[0063] The pressure loss PB1 can be measured in detail using the measuring device 30 shown in Figure 3 by the following method. First, a strip-shaped permeable spacer 14a with a length of 178 mm and a width of 44 mm is prepared. The permeable spacer 14a may be a rounded rectangle or a roughly elliptical shape. Except for its length and width, the permeable spacer 14a has the same shape as the permeable spacer 14 before it is wrapped around the central tube 21. The longitudinal direction of the permeable spacer 14a coincides with the direction in which the permeable spacer 14a is wrapped around the central tube 21. Next, a porous support 41 (manufactured by Nitto Denko, RS-50) is laminated onto the permeable spacer 14a to prepare a test piece 40. RS-50 is an ultrafiltration membrane made by laminating a PVDF porous layer and a PET nonwoven fabric. In the test piece 40, the permeable spacer 14a is in contact with the PET nonwoven fabric of the porous support 41.

[0064] Next, the test specimen 40 is set in the measuring device 30. The measuring device 30 can be the one described above for the differential pressure gradient ΔPA1. Next, nitrogen gas is sent into the space 37 adjacent to the porous support 41 of the test specimen 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 sent to the permeable spacer 14a at a flow rate of 4.0 L / min through the opening 32 of the holder 31. The temperature of the nitrogen gas sent into the measuring device 30 is, for example, 23°C. The nitrogen gas sent through the opening 32 moves in the longitudinal direction X of the permeable spacer 14a within the permeable spacer 14a and is discharged from the opening 33. The difference (differential pressure D1) between the pressure of the nitrogen gas sent to 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 way as the differential pressure D1, except that the permeable spacer 14a is not present. Based on the differential pressures D0 and D1, the pressure loss due to the permeable spacer 14a is calculated. The calculated value can be considered as the pressure loss PB1 caused by the movement of nitrogen gas in the longitudinal direction X of the permeable spacer 14a within the permeable spacer 14a.

[0065] The pressure loss PB1 of the permeation spacer 14 may be 10 kPa or less as described above, or it may be 9 kPa or less, 8 kPa or less, 7 kPa or less, or even 6 kPa or less. The lower the pressure loss PB1 of the permeation spacer 14, the more effectively the decrease in the permeation rate of the permeating fluid from the separation membrane 12 can be suppressed. The lower limit of the pressure loss PB1 of the permeation spacer 14 is, for example, 0.1 kPa or more, or it may be 1.0 kPa or more, or even 3.0 kPa or more.

[0066] The separation membrane element 10 typically has a plurality of permeation spacers 14. In this embodiment, the pressure loss PB1 of at least one permeation spacer 14 selected from the plurality of permeation spacers 14 may be 10 kPa or less. The separation membrane element 10 may include permeation spacers 14 with a pressure loss PB1 exceeding 10 kPa. In this embodiment, it is preferable that the pressure loss PB1 of all permeation spacers 14 provided in the separation membrane element 10 is 10 kPa or less.

[0067] (Flow channel spacer) Examples of flow channel spacers 15 include nets, meshes, knitted fabrics, wire woven fabrics, fiber woven fabrics, nonwoven fabrics, grooved sheets, corrugated sheets, etc., with knitted fabrics (especially tricot knitted fabrics) being preferred. 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.

[0068] The flow channel spacer 15 has, for example, an opening. The opening is typically a through hole that penetrates in the thickness direction of the flow channel spacer 15. Preferably, the flow channel spacer 15 has a plurality of openings.

[0069] In the flow channel spacer 15, the opening area of ​​one opening is, for example, 2.5 mm². 2 The following is 2.0 mm 2 Below, 1.5mm 2 Below, 1.0mm 2 Below, 0.5mm 2 Below, and even 0.45 mm 2 The following may also be used: The above-mentioned opening area is, for example, 0.1 mm². 2 That's all, 0.3 mm 2 The above is also acceptable. In the flow path spacer 15, it is preferable that the opening area of ​​each opening satisfies the above range.

[0070] The opening ratio of the flow channel spacer 15 is not particularly limited and may be, for example, 30% or more, 40% or more, or even 50% or more. The upper limit of the opening ratio of the flow channel spacer 15 is not particularly limited and may be, for example, 80% or less, or 70% or less.

[0071] The opening 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 microscope. From the obtained 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 opening ratio of the flow channel spacer 15.

[0072] The thickness of the flow channel spacer 15 is not particularly limited, and may be, for example, 0.1 mm or more, and even more so, 0.2 mm or more. The upper limit of the thickness of the flow channel spacer 15 is not particularly limited, but from the viewpoint of ensuring sufficient membrane area of ​​the separation membrane 12 within the separation membrane element 10, it may be, for example, 2.0 mm or less, and even 1.0 mm or less. In this specification, the thickness of spacers such as the flow channel spacer 15 can be measured using a dial gauge.

[0073] For the flow channel spacer 15, it is preferable that the differential pressure gradient ΔPA2 (kPa / m) obtained by the following test A2 is greater than the differential pressure gradient ΔPA1 (kPa / m) obtained by the above test A1 for the permeable spacer 14. Test A2: A test specimen is prepared by laminating a strip-shaped flow channel spacer 15 measuring 150 mm in length and 47 mm in width onto a polyethylene terephthalate (PET) film. Nitrogen gas is introduced into the space so that the pressure in the space adjacent to the film of the test specimen becomes 0.1 MPa, and nitrogen gas is also introduced in the longitudinal direction of the flow channel spacer 15 at a flow rate of 1.0 L / min. At this time, the differential pressure gradient ΔPA2 generated in the longitudinal direction of the flow channel spacer 15 is determined.

[0074] The differential pressure gradient ΔPA2 can be determined in the same way as the differential pressure gradient ΔPA1, except that a strip-shaped flow path spacer 15a with a length of 150 mm and a width of 47 mm is used instead of the permeable spacer 14a.

[0075] Furthermore, the relationship between the differential pressure gradients ΔPA1 and ΔPA2 identified by the above tests A1 and A2 closely matches the relationship between the differential pressure gradient due to the permeation spacer 14 and the differential pressure gradient due to the flow path spacer 15 during operation of the separation membrane element 10.

[0076] As described above, the separation membrane element 10 usually has a plurality of permeable spacers 14. In this embodiment, it is preferable that the differential pressure gradient ΔPA2 due to the flow channel spacer 15 is greater than the differential pressure gradient ΔPA1 due to at least one permeable spacer 14 selected from the plurality of permeable spacers 14. The separation membrane element 10 may include permeable spacers 14 that exhibit a differential pressure gradient ΔPA1 that is the same value as the differential pressure gradient ΔPA2, or a value greater than the differential pressure gradient ΔPA2. For example, the differential pressure gradient ΔPA2 due to the flow channel spacer 15 may be the same value as the differential pressure gradient ΔPA1 due to one of the plurality of permeable spacers 14, and greater than the differential pressure gradient ΔPA1 of all other permeable spacers 14. It is preferable that the differential pressure gradient ΔPA2 due to the flow channel spacer 15 is greater than the differential pressure gradient ΔPA1 of all permeable spacers 14.

[0077] The value obtained by subtracting the differential pressure gradient ΔPA1 from the differential pressure gradient ΔPA2 (ΔPA2 - ΔPA1) is not particularly limited and may be, for example, 3.0 kPa / m or more, 5.0 kPa / m or more, 8.0 kPa / m or more, or even 10 kPa / m or more. The upper limit of the value (ΔPA2 - ΔPA1) is not particularly limited and may be, for example, 100 kPa / m or less, 50 kPa / m or less, or even 30 kPa / m or less. The ratio of the differential pressure gradient ΔPA1 to the differential pressure gradient ΔPA2 (ΔPA1 / ΔPA2) is not particularly limited and may be, for example, 0.8 or less, 0.5 or less, or even 0.2 or less. The lower limit of the ratio (ΔPA1 / ΔPA2) is not particularly limited and may be, for example, 0.01 or more, or even 0.1 or more.

[0078] The differential pressure gradient ΔPA2 due to the flow path spacer 15 may be greater than, for example, 5.0 kPa / m, and may be 8.0 kPa / m or more, or even 10 kPa / m or more. The upper limit of the differential pressure gradient ΔPA2 may be, for example, 100 kPa / m or less, and may be 80 kPa / m or less, 50 kPa / m or less, 40 kPa / m or less, or even 30 kPa / m or less.

[0079] The pressure loss PB2 of the flow channel spacer 15 is preferably greater than the pressure loss PB1 of the permeable spacer 14. The pressure loss PB2 of the flow channel spacer 15 is measured by the following test B2. Test B2: A test specimen is prepared by stacking strip-shaped flow channel spacers 15, measuring 178 mm in length and 44 mm in width, on a porous support (manufactured by Nitto Denko, RS-50). Nitrogen gas is introduced into the space adjacent to the porous support of the test specimen so that the pressure in that space becomes 0.1 MPa, and nitrogen gas is also introduced into the flow channel spacer 15 at a flow rate of 4.0 L / min. The pressure loss caused by the movement of nitrogen gas in the longitudinal direction of the flow channel spacer 15 is measured.

[0080] The pressure loss PB2 can be measured in the same manner as the pressure loss PB1, except that a strip-shaped flow path spacer 15a measuring 178 mm in length and 44 mm in width is used instead of the permeable spacer 14a.

[0081] Furthermore, the relationship between pressure losses PB1 and PB2 measured by the above tests B1 and B2 closely matches the relationship between the pressure loss in the permeation spacer 14 and the pressure loss in the flow path spacer 15 during operation of the separation membrane element 10.

[0082] As described above, the separation membrane element 10 usually has a plurality of permeation spacers 14. In this embodiment, it is preferable that the pressure loss PB2 of the flow channel spacer 15 is greater than the pressure loss PB1 of at least one permeation spacer 14 selected from the plurality of permeation spacers 14. The separation membrane element 10 may include permeation spacers 14 that exhibit a pressure loss PB1 that is the same value as the pressure loss PB2, or a value greater than the pressure loss PB2. For example, the pressure loss PB2 of the flow channel spacer 15 may be the same value as the pressure loss PB1 of one of the plurality of permeation spacers 14, and greater than the pressure loss PB1 of all the other permeation spacers 14. It is preferable that the pressure loss PB2 of the flow channel spacer 15 is greater than the pressure loss PB1 of all the permeation spacers 14.

[0083] The value obtained by subtracting the pressure loss PB1 from the pressure loss PB2 (PB2 - PB1) is not particularly limited and may be, for example, 5 kPa or more, 10 kPa or more, or even 20 kPa or more. The upper limit of the value (PB2 - PB1) is not particularly limited and may be, for example, 100 kPa or less, 80 kPa or less, or even 50 kPa or less. The ratio of pressure loss PB1 to pressure loss PB2 (PB1 / PB2) is not particularly limited and may be, for example, 0.8 or less, 0.5 or less, or even 0.2 or less. The lower limit of the ratio (PB1 / PB2) is not particularly limited and may be, for example, 0.01 or more, or even 0.1 or more.

[0084] The pressure loss PB2 of the flow path spacer 15 may be greater than, for example, 10 kPa, and may be 20 kPa or more, or even 30 kPa or more. The upper limit of the pressure loss PB2 may be, for example, 100 kPa or less, and may be 80 kPa or less, 70 kPa or less, 60 kPa or less, or even 50 kPa or less.

[0085] (Permeable Spacer) Examples of permeable spacers 14 include nets, meshes, knitted fabrics, wire woven fabrics, fiber woven fabrics, nonwoven fabrics, grooved sheets, corrugated sheets, etc., with nets being preferred. Examples of materials for the permeable spacer 14 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.

[0086] The permeable spacer 14 has, for example, an opening. The opening is typically a through hole that penetrates in the thickness direction of the permeable spacer 14. Preferably, the permeable spacer 14 has a plurality of openings. If the permeable spacer 14 is a net, the shape of the opening is preferably rhombic.

[0087] In the permeable spacer 14, the opening area of ​​one opening is, for example, 0.5 mm². 2 That is all, 1.0 mm 2 Above, 2.0 mm 2 Above, 2.5 mm 2 Furthermore, 3.0 mm 2 The above may also be acceptable. A permeable spacer 14 with a large opening area tends to have a low pressure loss PB1. The above opening area is, for example, 10 mm 2 The following is 8.0 mm 2 Below, and furthermore, 5.0 mm 2 The following is also possible. In the permeable spacer 14, it is preferable that the opening area of ​​each opening satisfies the above range. If the permeable spacer 14 is a net and the shape of the opening is rhombus, the opening area of ​​the opening can be calculated using the following formula based on one diagonal L1 and the other diagonal L2 of the opening. Opening area [mm²] 2 ] = diagonal L1 [mm] × diagonal L2 [mm] / 2

[0088] The aperture ratio of the permeable spacer 14 is, for example, 50% or more, and may be 60% or more, 65% or more, or even 70% or more. The upper limit of the aperture ratio of the permeable spacer 14 is not particularly limited, and may be, for example, 90% or less, and may be 80% or less.

[0089] The opening ratio of the permeable spacer 14 can be measured for the flow channel spacer 15 using the method described above. Furthermore, if the permeable spacer 14 is a net and the opening is rhombic in shape, the opening ratio of the permeable spacer 14 can be calculated using the following formula, based on the opening area, the diagonal L1 and L2 of the opening, and the width (thread width) of the frame surrounding the opening: Opening ratio [%] = Opening area [mm²] 2 ] / ((diagonal L1 [mm] + thread width [mm]) × (diagonal L2 [mm] + thread width [mm]) / 2) × 100

[0090] The thickness of the permeable spacer 14 is not particularly limited and may be, for example, 0.3 mm or more, 0.35 mm or more, 0.4 mm or more, or even 0.45 mm or more. The upper limit of the thickness of the permeable spacer 14 is not particularly limited, but from the viewpoint of ensuring sufficient membrane area of ​​the separation membrane 12 within the separation membrane element 10, it may be, for example, 2.0 mm or less, or 1.0 mm or less.

[0091] The permeable spacer 14 has an initial tensile modulus of 100 N / mm². 2 Preferably less than 50 N / mm 2 Below, 30N / mm 2 Furthermore, 10 N / mm 2 The following may also be true: The lower limit of the initial tensile modulus of the permeable spacer 14 is, for example, 1.0 N / mm². 2 That concludes the explanation. The initial tensile modulus of the permeable spacer 14 can be measured for the flow channel spacer 15 using the method described above.

[0092] 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, while all the other permeation spacers 14 may be different from the flow channel spacer 15.

[0093] (Supply spacer) The supply spacer 13 is not particularly limited, and for example, the permeable spacer 14 and the flow path spacer 15 described above can be used as appropriate.

[0094] [Separation Membrane] As shown in Figure 4, the separation membrane 12 comprises, for example, a separation functional layer 1 and a porous support 2 that supports the separation functional layer 1. The separation functional layer 1 is in direct contact with, for example, the porous support 2. The separation membrane 12 is preferably a membrane that preferentially allows organic compound C to permeate from a solution S containing volatile organic compound C, and is typically a permeable vaporization membrane. If the separation membrane 12 is a permeable vaporization membrane, the separation membrane 12 may further comprise a protective layer (not shown) that protects the separation functional layer 1.

[0095] (Separation Functional Layer) The separation functional layer 1 is a layer that, for example, can preferentially allow organic compound C to pass through from the above solution S. Typically, it is a dense layer (non-porous layer) in which no pores can be observed when viewed with a scanning electron microscope (SEM) at a magnification of 5000x.

[0096] The separation functional layer 1 preferably contains a hydrophobic material. In this specification, "hydrophobic material" means, for example, a material in which, when a 10 μL drop of water (at a temperature of 25°C) is dropped onto the surface of a test piece made of the material, the static contact angle of the water exceeds 90°. The static contact angle of water can be measured using a commercially available contact angle meter.

[0097] Examples of hydrophobic materials include compounds having siloxane bonds (Si-O-Si bonds), olefin polymers, oils, and fluorinated compounds. The separation functional layer 1 preferably contains a compound having siloxane bonds as a hydrophobic material. Compounds having siloxane bonds are typically silicone polymers. Silicone polymers may be solid or liquid at 25°C. Specific examples of silicone polymers include polydimethylsiloxane (PDMS). Specific examples of olefin polymers include polyethylene and polypropylene. Examples of oils include hydrocarbon oils such as liquid paraffin. Examples of fluorinated compounds include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Hydrophobic materials can be used individually or in combination of two or more.

[0098] The separation functional layer 1 may contain a hydrophobic material as its main component, or 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 functional layer 1.

[0099] The separation functional layer 1 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.

[0100] The filler includes, for example, inorganic materials such as zeolite, silica, and bentonite. The zeolite included in the filler is preferably high-silica zeolite, which has a high silica-to-alumina ratio. High-silica zeolite is suitable for applications involving the separation of water-containing solutions S due to its excellent hydrolysis resistance. Examples of high-silica zeolite 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.

[0101] The filler may contain a metal-organic framework (MOF). The metal-organic framework is also called a porous coordination polymer (PCP). The metal-organic framework is preferably hydrophobic. The metal-organic framework contains, for example, a metal ion and an organic ligand. Examples of metal ions include Zn ions. Examples of organic ligands include aromatic rings. Examples of aromatic rings included in the organic ligand include imidazole rings. Examples of organic ligands include 2-methylimidazole. A specific example of a metal-organic framework is ZIF-8.

[0102] 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 1 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 sizes of any number (at least 50) of fillers are calculated, and the average of the calculated values ​​is considered to be the average particle size of the filler.

[0103] The filler content in the separation functional layer 1 is, for example, 10 wt% or more, preferably 30 wt% or more, and more preferably 40 wt% or more. The upper limit of the filler content in the separation functional layer 1 is not particularly limited, but is, for example, 70 wt%. The matrix content in the separation functional layer 1 is not particularly limited, but is, for example, 30 wt% to 90 wt%.

[0104] The thickness of the separation functional layer 1 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 1 may be 1.0 μm or more, 10 μm or more, or 30 μm or more.

[0105] (Porous support) Examples of porous support 2 include nonwoven fabrics; porous polytetrafluoroethylenes; aromatic polyamide fibers; porous metals; sintered metals; porous ceramics; porous polyesters; porous nylons; activated carbon fibers; latex; silicones; silicone rubbers; permeable (porous) polymers 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 foams having open or closed cells; polymer foams having open or closed cells; silica; porous glass; mesh screens, etc. The porous support 2 may be a combination of two or more of these.

[0106] The porous support 2 has an average pore diameter of, for example, 0.01 to 0.4 μm. The thickness of the porous support 2 is not particularly limited, but is, for example, 10 μm or more, preferably 50 μm or more, and more preferably 100 μm or more. The thickness of the porous support 2 is, for example, 300 μm or less, and preferably 200 μm or less.

[0107] (Protective layer) The protective layer covers the surface of the separation functional layer 1, for example. 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 or different from the material of the matrix of the separation functional layer 1.

[0108] The thickness of the protective layer is not particularly limited, but is, for example, 0.5 μm or more, preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. The thickness of the protective layer is, for example, 100 μm or less, preferably 50 μm or less, and more preferably 30 μm or less.

[0109] [Method for Manufacturing a Separation Membrane] The separation membrane 12 can be manufactured, for example, by forming a separation functional layer 1 on a porous support 2. Specifically, first, a coating solution containing the material for the separation functional layer 1 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 compound having a siloxane bond, the coating solution may further contain a catalyst for curing the compound. Next, a coating film is obtained by applying the coating solution onto the porous support 2. The separation functional layer 1 is formed by drying the coating film.

[0110] [Method for Manufacturing a Spiral-Type Membrane Element] 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.

[0111] 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 path 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 can be, for example, 2 to 50. Note that the uppermost separation membrane unit U does not need to have a permeation spacer 14.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] [Characteristics of Spiral Membrane Element] 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, and membrane separation of the supply fluid by the separation membrane 12 proceeds. Therefore, if pressure loss occurs within the separation membrane element 10, the above pressure difference decreases, and the permeation rate of the permeate fluid from the separation membrane 12 decreases. In particular, in the method of operating the separation membrane element 10 by reducing the pressure inside the central tube 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 reduction in pressure difference due to pressure loss is large.

[0116] As described above, the separation membrane element 10 of this embodiment uses a permeation spacer 14 with a low differential pressure gradient ΔPA1, which tends to suppress the decrease in the pressure difference. With the separation membrane element 10, by suppressing the decrease in the pressure difference, the decrease in the permeation velocity of the permeating fluid from the separation membrane 12 can be sufficiently suppressed.

[0117] As an example, when a mixed liquid consisting of isopropanol (IPA) and water is used as the supply fluid, and both the separation membrane element 10 and the flat separation membrane 12 are operated under reduced pressure, the permeation flux F1 (kg / m) of IPA from the flat separation membrane 12 is 2 The permeation flux F2 (kg / m) of IPA from the separation membrane element 10 relative to / hr 2 The ratio R of ( / hr) is, for example, 50% or more, and may be 60% or more, 70% or more, 80% or more, or even 85% or more. In this specification, the ratio R may be referred to as element efficiency.

[0118] The permeation flux F1 described above can be determined in detail by the following method. First, a flat separation membrane 12 is cut to a size of 75 mm in diameter to make a test specimen. This test specimen is set in a metal cell and sealed with an O-ring to prevent leakage. Next, the supply fluid is filled into the metal cell so that the supply fluid comes into contact with the main surface of the separation functional layer on the test specimen. As described above, a mixed liquid consisting of IPA and water is used as the supply fluid. The mixed liquid has a temperature of 40°C and an IPA content of 10 wt%.

[0119] Next, a vacuum pump is used to reduce the pressure in the space adjacent to the main surface of the porous support side of the test specimen to 30 hPa. This causes the mixed liquid to permeate the test specimen, yielding a gaseous permeate fluid. In other words, separation by permeation vaporization proceeds under reduced pressure operation. The gaseous permeate fluid is liquefied by cooling it with liquid nitrogen (-196°C), and the composition of the resulting liquid permeate fluid is analyzed. Composition analysis can be performed using gas chromatography or the like. Based on the results obtained, the permeate flux F1 of IPA can be determined.

[0120] The permeation flux F2 described above can be determined in detail by the following method. First, the separation membrane element 10 is operated under the same conditions as for the permeation flux F1. At this time, the supply flow rate of the supply fluid is set to an appropriate value according to the size of the separation membrane element 10. By operating the separation membrane element 10, the mixed liquid permeates through the separation membrane 12 in the separation membrane element 10, thereby obtaining a gaseous permeable fluid. The permeable fluid is liquefied in the same manner as for the permeation flux F1, and its composition is analyzed. Based on the obtained results, the permeation flux F2 of IPA can be determined.

[0121] [Applications of the spiral membrane element] The separation membrane element 10 of this embodiment is suitable for applications such as separating an organic compound C from a solution S containing a volatile organic compound C. The solution S is typically an aqueous solution containing an organic compound C. The organic compound C is not particularly limited as long as it is volatile. In this specification, "volatile organic compound" means, for example, an organic compound whose boiling point at atmospheric pressure (101.325 kPa) is 20°C to 260°C.

[0122] The number of carbon atoms in organic compound C is not particularly limited and may be, for example, 10 or less, 8 or less, 6 or less, or even 4 or less. The lower limit of the number of carbon atoms in organic compound C may be 1 or 2. Organic compound C has functional groups containing oxygen atoms, such as hydroxyl groups, carbonyl groups, ether groups, and ester groups. In organic compound C, the number of functional groups containing oxygen atoms is typically one.

[0123] Examples of organic compound C include alcohols, ketones, and esters, and are typically alcohols. The alcohol may be an alkyl alcohol composed only of an alkyl group and a hydroxyl group, or an aryl alcohol containing an aryl group and a hydroxyl group. The alkyl alcohol may be linear, branched, or cyclic. Examples of alkyl alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, isobutanol, t-butanol, and n-pentanol. Examples of aryl alcohols include phenol.

[0124] The ketone may be a dialkylketone composed only of an alkyl group and a carbonyl group. Examples of dialkylketones include methyl ethyl ketone (MEK) and acetone.

[0125] The ester may be a fatty acid alkyl ester composed solely of an alkyl group and an ester group. Examples of fatty acid alkyl esters include ethyl acetate.

[0126] Note that organic compound C is not limited to those described above. Organic compound C may also be an aromatic hydrocarbon such as benzene, toluene, or xylene.

[0127] Solution S may contain one type of organic compound C, or it may contain two or more types of organic compound C. The content of organic compound C in solution S is, for example, 0.5 wt% or more, and may be 1 wt% or more, 2 wt% or more, or even 5 wt% or more. The upper limit of the content of organic compound C is not particularly limited, but is, for example, 50 wt%.

[0128] Organic compound C may be a fermented product produced by microorganisms fermenting a carbon source, or it may be alcohol produced by microorganisms (bio-alcohol). In other words, solution S may be a fermentation liquid containing organic compound C as a fermentation product. However, solution S is not limited to a fermentation liquid, and may also be waste liquid or wastewater discharged from a chemical plant or the like.

[0129] Solution S may further contain other components besides water and organic compound C, such as microorganisms that produce fermentation products, a carbon source, a nitrogen source, and inorganic ions. Microorganisms that produce fermentation products are typically fungi. Examples of carbon sources include polysaccharides such as starch and monosaccharides such as glucose.

[0130] <Embodiment of the Membrane Separation System> As shown in Figure 7, the membrane separation system 100 of this embodiment includes the separation membrane element 10 and the depressurization device 60 described above. The depressurization device 60 can reduce the pressure inside the central tube 21 of the separation membrane element 10. In other words, the depressurization 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 depressurization 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 depressurization devices 60a and 60b.

[0131] 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 that pressurizes 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.

[0132] 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 the 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.

[0133] 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.

[0134] 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) 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.

[0135] 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.

[0136] 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 60b 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.

[0137] 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 the 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, the impermeable fluid discharged from the separation membrane element 10b can be reused.

[0138] Each of the pathways in the membrane separation system 100 is composed of, for example, metal or resin piping.

[0139] According to the membrane separation system 100 of this embodiment, the separation operation can be performed by reducing the pressure in the space within the permeable fluid path of the separation membrane element 10 using the depressurization device 60. This type of depressurization separation operation is suitable for reducing the energy required to separate the mixed fluid compared to the pressurization method.

[0140] 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.

[0141] (Example A1) ・Preparation of separation membrane A permeable vaporization membrane prepared by the following method was used as the separation membrane. First, a silicone resin composition (coating solution) was prepared by adding 2 parts by weight of a curing agent containing polyorganosiloxane (SRX212 containing platinum catalyst, manufactured by Dow-Toray) to 100 parts by weight of a silicone main component (BY24-489, manufactured by Dow-Toray), which is a polyorganosiloxane mixture. A coating film (thickness 10 μm) was obtained by applying the coating solution onto a porous support. As the porous support, CF-30S (a laminate of a microporous layer made of polysulfone and a PET nonwoven fabric) manufactured by Nitto Denko Corporation was used. The coating film was formed on the microporous layer made of polysulfone of CF-30S. Next, a separation functional layer with a thickness of 4 μm was prepared by heating the coating film at 150°C for 10 minutes to cure it. This obtained a permeable vaporization membrane.

[0142] - Fabrication of spiral membrane element Along with the fabricated separation membrane, the spacers shown in Table 1 were used as the spacer 16 (flow channel spacer 15) and other permeation spacers 14 in Figure 6, and a net with a thickness of 0.86 mm was used as the supply spacer 13, and the spiral membrane element of Example A1 was fabricated by the method described with reference to Figure 6.

[0143] (Examples A2-A5 and Comparative Examples A1-A2) The spiral membrane elements of Examples A2-A5 and Comparative Examples A1-A2 were fabricated using the same method as in Example A1, except that the flow channel spacer 15 and permeable spacer 14 were changed as shown in Table 1.

[0144] (Comparative Example A3) An attempt was made to fabricate a spiral membrane element using the same method as in Example A1, except that the flow channel spacer 15 and the permeation spacer 14 were changed as shown in Table 1. However, when winding the first portion 16a of the spacer 16 around the central tube, the first portion 16a stretched excessively, making it impossible to wind the separation membrane unit around the central tube in an appropriate shape.

[0145] [Evaluation of Spacer Properties] (Flow Channel Spacer) For the flow channel spacer used in the fabricated spiral membrane element, the differential pressure gradient ΔPA2 and the initial tensile modulus were determined using the method described above. Furthermore, the thickness of the flow channel spacer was also measured. For the measurement of the tensile modulus, a Shimadzu Autograph AGX V 10kN load cell was used. A dial gauge was used for the measurement of the thickness.

[0146] (Permeable Spacer) The differential pressure gradient ΔPA1 was determined for the permeable spacer used in the fabricated spiral membrane element using the method described above. The thickness, aperture area, and aperture ratio of the permeable spacer were also measured. A dial gauge was used to measure the thickness. Microscope images obtained using a microscope (Keyence Digital Microscope VHX-7000) were used to measure the aperture area, aperture ratio, etc.

[0147] [Element Efficiency] First, regarding the separation membrane used in the spiral membrane element, the permeation flux F1 (kg / m) of IPA in the flat membrane state was determined by the method described above. 2 The permeation flux F2 (kg / m³) of IPA was measured using a spiral membrane element in the method described above. 2 The permeation flux F1 (kg / m³) was measured. When measuring the permeation flux F2, the supply flow rate of the supply fluid supplied to the spiral membrane element was set to 773 g / min. From the obtained results, the permeation flux F1 (kg / m³) was measured. 2 Permeation flux F2 (kg / m) for / hr) 2 The ratio R (element efficiency) of / hr was calculated.

[0148]

[0149] As can be seen from Table 1, the initial tensile modulus is 100 N / mm². 2In the spiral membrane elements of Examples A1 to A5, which combined the flow channel spacer described above with a permeation spacer having a differential pressure gradient ΔPA1 of 5.0 kPa / m or less, the element efficiency was higher than that of the comparative example. From these results, it can be said that the spiral membrane elements of Examples A1 to A5 are suitable for suppressing the decrease in the permeation rate of the permeating fluid from the separation membrane.

[0150] (Example B1) ・Preparation of separation membrane A permeable vaporization membrane prepared by the following method was used as the separation membrane. First, a silicone resin composition (coating solution) was prepared by adding 2 parts by weight of a curing agent containing polyorganosiloxane (SRX212 containing platinum catalyst, manufactured by Dow-Toray) to 100 parts by weight of a silicone main component (BY24-489, manufactured by Dow-Toray), which is a polyorganosiloxane mixture. A coating film (thickness 10 μm) was obtained by applying the coating solution onto a porous support. As the porous support, CF-30S (a laminate of a polysulfone microporous layer and a PET nonwoven fabric) manufactured by Nitto Denko Corporation was used. The coating film was formed on the polysulfone microporous layer of CF-30S. Next, a separation functional layer with a thickness of 4 μm was prepared by heating the coating film at 150°C for 10 minutes to cure it. This obtained a permeable vaporization membrane.

[0151] - Fabrication of spiral membrane element Along with the fabricated separation membrane, the spacers shown in Table 2 were used as the spacer 16 (flow channel spacer 15) and other permeation spacers 14 in Figure 6, and a net with a thickness of 0.66 mm was used as the supply spacer 13, and the spiral membrane element of Example B1 was fabricated by the method described with reference to Figure 6.

[0152] (Example B2 and Comparative Examples B1-B2) The spiral membrane elements of Example B2 and Comparative Examples B1-B2 were fabricated in the same manner as in Example B1, except that the flow channel spacer 15 and permeable spacer 14 were changed as shown in Table 2.

[0153] (Comparative Example B3) An attempt was made to fabricate a spiral membrane element using the same method as in Example B1, except that the flow channel spacer 15 and permeation spacer 14 were changed as shown in Table 2. However, when winding the first portion 16a of the spacer 16 around the central tube, the first portion 16a stretched excessively, making it impossible to wind the separation membrane unit around the central tube in an appropriate shape.

[0154] [Evaluation of Spacer Properties] (Flow Channel Spacer) The flow channel spacer used in the fabricated spiral membrane element had its pressure loss PB2 and initial tensile modulus measured using the method described above. Furthermore, the thickness of the flow channel spacer was also measured. For measuring the tensile modulus, a Shimadzu Autograph AGX V 10kN load cell was used. For measuring the thickness, a dial gauge was used.

[0155] (Permeable Spacer) The pressure loss PB1 of the permeable spacer used in the fabricated spiral membrane element was measured using the method described above. The thickness, aperture area, and aperture ratio of the permeable spacer were also measured. A dial gauge was used to measure the thickness. Microscope images obtained using a microscope (Keyence Digital Microscope VHX-7000) were used to measure the aperture area, aperture ratio, etc.

[0156] [Element Efficiency] First, regarding the separation membrane used in the spiral membrane element, the permeation flux F1 (kg / m) of IPA in the flat membrane state was determined by the method described above. 2 The permeation flux F2 (kg / m³) of IPA was measured using a spiral membrane element in the method described above. 2 The permeation flux F1 (kg / m³) was measured. When measuring the permeation flux F2, the supply flow rate of the supply fluid supplied to the spiral membrane element was set to 773 g / min. From the obtained results, the permeation flux F1 (kg / m³) was measured. 2 Permeation flux F2 (kg / m) for / hr) 2 The ratio R (element efficiency) of / hr was calculated.

[0157]

[0158] As can be seen from Table 2, the initial tensile modulus is 100 N / mm². 2 In the spiral membrane elements of Examples B1 and B2, which combined the flow channel spacer described above with a permeation spacer having a pressure loss PB1 of 10 kPa or less, the element efficiency was higher than that of the comparative example. From these results, it can be said that the spiral membrane elements of Examples B1 and B2 are suitable for suppressing the decrease in the permeation rate of the permeating fluid from the separation membrane.

[0159] The spiral membrane element of this embodiment is suitable for efficiently separating volatile organic compounds from a solution containing such compounds.

Claims

1. The apparatus comprises a central tube, a membrane leaf having a separation membrane and a permeable spacer and wrapped around the central tube, and a flow path spacer connected to the permeable spacer and wrapped around the central tube on the central tube side of the membrane leaf, wherein the initial tensile modulus of the flow path spacer is 100 N / mm². 2 The above describes a spiral membrane element in which the differential pressure gradient ΔPA1 determined by the following test A1 is 5.0 kPa / m or less. Test A1: Prepare a test specimen by laminating the aforementioned permeable spacers, which are 150 mm long and 47 mm wide, 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 in the longitudinal direction of the permeable spacer at a flow rate of 1.0 L / min. At this time, the differential pressure gradient ΔPA1 that occurs in the longitudinal direction of the permeable spacer is identified.

2. The tensile modulus is 300 N / mm². 2 The spiral membrane element according to claim 1, which is as follows:

3. The spiral membrane element according to claim 1, wherein a differential pressure gradient ΔPA2 (kPa / m) obtained by the following Test A2 is larger than the differential pressure gradient ΔPA1 (kPa / m). Test A2: Prepare a test specimen by laminating the aforementioned flow channel spacers, which are strip-shaped with a length of 150 mm and a width of 47 mm, 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 in the longitudinal direction of the flow channel spacer at a flow rate of 1.0 L / min. At this time, the differential pressure gradient ΔPA2 that occurs in the longitudinal direction of the flow channel spacer is determined.

4. The spiral membrane element according to claim 3, wherein the differential pressure gradient ΔPA2 is 20 kPa / m or less.

5. The permeable spacer has an opening, and the opening area of ​​the opening is 2.5 mm². 2 The spiral membrane element according to claim 1 is as described above.

6. The spiral membrane element according to claim 1, wherein the aperture ratio of the permeable spacer is 65% or more.

7. The spiral membrane element according to claim 1, wherein the thickness of the permeable spacer is 0.35 mm or more.

8. The spiral membrane element according to claim 1, wherein the permeable spacer is a net.

9. The spiral membrane element according to claim 1, wherein the membrane leaf has two separation membranes, and the two separation membranes are overlapped and sealed to have a bag-like structure.

10. The spiral membrane element according to claim 9, wherein the permeable spacer is positioned between the two separation membranes.

11. The spiral membrane element according to claim 1, further comprising a supply spacer laminated on the membrane leaf.

12. The spiral membrane element according to claim 1, wherein the central tube is provided with a through hole, and the flow path spacer is in contact with the through hole.

13. The spiral membrane element according to claim 1, wherein the separation membrane is a permeable vaporization membrane.

14. The spiral membrane element according to claim 1, used for separating an organic compound from a solution containing a volatile organic compound.

15. A membrane separation system comprising a spiral membrane element according to any one of claims 1 to 14, and a depressurization device for reducing the pressure inside the central tube.

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