Spiral membrane element

Abstract

This invention provides a spiral-type membrane element that improves the durability of the bonding joint between the membrane leaf and the central tube, while also facilitating the separation and recovery of the central tube during recycling. [Solution] A spiral membrane element E comprising a plurality of membrane leaves L having permeable channels between opposing separation membranes, and a perforated central tube 5 around which the membrane leaves L are wound with supply channels interposed between the membrane leaves L, wherein both ends of the inner circumference side of the membrane leaves L in the axial direction A1 are bonded to the central tube 5, and in at least a portion of the area of ​​the bonded channel 13, the outer circumference surface of the central tube 5 has a tapered portion 5b that widens toward the center in the axial direction A1.

Description

Technical Field

[0001] The present invention relates to a spiral membrane element having a structure advantageous for recycling (hereinafter sometimes abbreviated as "membrane element").

Background Art

[0002] A spiral membrane element is manufactured, for example, by winding a plurality of membrane leaves with a permeate water spacer interposed between opposing separation membranes around a central tube, together with a feed water spacer, and applying FRP (fiber reinforced plastic) to its outer periphery. An ATD (Anti-telescoping device) attached to both ends is integrated when applying FRP. A U packing is attached to the ATD to prevent a bypass flow from occurring in the gap between the element and the inner surface of the vessel. The membrane leaves are made liquid-tight by sealing three sides, and have a permeate side flow path between the opposing separation membranes.

[0003] Due to the use of a spiral membrane element, deterioration over time and membrane surface contamination progress, so it is inevitable that the performance decreases over time. Regarding membrane surface contamination, it is possible to physically wash away contaminants by increasing the flow rate on the feed water side called flushing cleaning, or chemically clean by chemical cleaning, and a certain degree of recovery is possible, but that will also reach its limit someday and the element itself needs to be replaced. The used membrane element after replacement may be reused for another purpose that does not require high performance, but most are disposed of. Disposal methods include landfill disposal and incineration disposal.

[0004] The treatment method of used membrane elements is a major issue. Landfill disposal has the problem that the volume of the treatment site where treatment is possible is limited, and since membrane elements are mostly made of plastic materials and are not decomposed underground, they will remain in the ground semi-permanently, so it is not a sustainable treatment method. On the other hand, when incineration disposal is carried out, CO2, which is a greenhouse gas, is emitted, so there is an issue from the perspective of the global environment.

[0005] Therefore, it is desirable to recycle as much of the used membrane element as possible. For example, Patent Document 1 proposes a method for reusing a used spiral-type membrane element of a conventional structure, in which the separation functional layer of the RO membrane element is removed with an acidic aqueous solution or the like, and the resulting UF membrane is regenerated as a porous support.

[0006] Furthermore, methods for recycling a portion of the used membrane elements have also been proposed. For example, as a technology for reusing the central tube (material recycling), Patent Document 2 proposes a fluid separation element in which a membrane unit including a separation membrane, a permeate flow channel material, and a raw liquid flow channel material is formed around a central tube, and an outer casing is formed on the outside of the membrane unit, with a separator interposed between the central tube and the membrane unit. This separator is attached to the membrane unit and simply adheres to the outer surface of the central tube, so that the central tube can be easily pulled out and disassembled from the membrane unit and separator. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-156169 [Patent Document 2] Japanese Patent Application Publication No. 11-267467 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, in the membrane element described in Patent Document 2, a separator is interposed between the membrane leaf and the central tube, making it difficult to ensure sufficient durability against forces applied in the axial direction. There are concerns that displacement may cause deformation of the membrane leaf, leading to damage to the sealing portion.

[0009] Furthermore, Patent Document 2 discloses that a tapered section is provided in the central tube, where the outer diameter increases from the upstream side to the downstream side, in order to prevent displacement due to forces in the direction of the raw liquid flow. However, since opposing forces are generated at the bonding section between the sealing section on the downstream side of the membrane leaf and the central tube, such a tapered section may promote displacement of the separator. In other words, the outside of the membrane leaf during operation is under high pressure due to the operating pressure, while the inside is under low pressure on the permeation side. Therefore, a force resulting from this pressure difference acts on the bonding section, and since this force acts on the central side in the axial direction of the central tube, it is in opposite directions on the upstream and downstream sides.

[0010] Incidentally, membrane elements are made from plastic materials derived from crude oil, a valuable fossil resource, and used membrane elements can also be considered a valuable carbon resource, thus requiring recycling into plastic materials (chemical recycling).

[0011] The central tube, which serves as the water collection pipe, is primarily in contact with the permeate, and therefore remains relatively uncontaminated even after use, making it suitable for recycling. However, because it is bonded and fixed to the membrane leaves near both ends, removing it is time-consuming and costly. For this reason, there is a need for a method and structure that allows for easy removal of the central tube from used membrane elements.

[0012] Therefore, the object of the present invention is to provide a spiral membrane element that improves the durability of the adhesive joint between the membrane leaf and the central tube, while also facilitating the separation and recovery of the central tube during recycling. [Means for solving the problem]

[0013] The above objective can be achieved by the present invention as described below.

[0014] [1] A spiral membrane element comprising a plurality of membrane leaves having permeable channels between opposing separation membranes, and a perforated central tube in which the membrane leaves are wound while interposing supply channels between the membrane leaves, The inner circumferential end of the membrane leaf has adhesive portions where both ends in the axial direction are bonded to the central tube. A spiral membrane element having a tapered portion in at least a portion of the adhesive portion, where the outer surface of the central tube widens toward the axial center.

[0015] According to the spiral membrane element of the present invention, in at least a portion of the adhesive area, the outer surface of the central tube has a tapered portion that widens towards the axial center. Therefore, the force caused by the differential pressure between the operating pressure and the permeation pressure, i.e., the force applied to the center of the central tube, becomes a force that presses against the tapered surface, thus reducing the risk of the adhesive portion peeling off due to the differential pressure. Furthermore, because of the tapered portion, the adhesive portion can be easily detached by applying a striking force or the like from the opposite end of the central side of the central tube, making it easier to separate and recover the central tube during recycling. As a result, it is possible to provide a spiral membrane element that improves the durability of the adhesive portion between the membrane leaf and the central tube while making it easier to separate and recover the central tube during recycling.

[0016] [2] The spiral membrane element according to [1], wherein the outer surface of the central tube has a tapered portion in which the diameter expands toward the axial center in the entire area of ​​the adhesive portion.

[0017] In the entire area of ​​the adhesive joint, the outer surface of the central tube has a tapered section that widens towards the axial center, thereby improving the durability of the adhesive joint between the membrane leaf and the central tube in the entire adhesive joint, both upstream and downstream, while also making it easier to separate and recover the central tube during recycling.

[0018] [3] The spiral membrane element according to [1] or [2], wherein the gradient θ of the tapered portion satisfies tanθ = 0.005 to 0.1.

[0019] When the gradient θ of the tapered section satisfies tanθ = 0.005 to 0.1, there is no need to change the shape of the conventional membrane leaf, and the effect of the tapered section can be fully realized while maintaining a sufficient effective membrane area of ​​the packed separation membrane.

[0020] [4] The spiral membrane element according to any one of [1] to [3], wherein the central tube has a structure that can be divided on the central side of the bonding portion.

[0021] When the central tube has a structure that can be divided on the central side of the bonding portion, for example, when cutting off the end seals of the membrane leaf in the recycling process, by cutting the membrane leaf around the central tube while leaving the central tube, the end side of the central tube can be separated and recovered from the central part of the central tube without cutting the central tube. Therefore, by reconnecting etc. to the central part of the central tube again, it becomes possible to reuse (recycle) the central tube on the end side.

Advantages of the Invention

[0022] According to the spiral membrane element of the present invention, it is possible to provide a spiral membrane element that improves the durability of the bonding portion between the membrane leaf and the central tube and makes it easier to separate and recover the central tube during recycling.

Brief Description of the Drawings

[0023] [Figure 1A] It is a perspective view showing an example of the membrane element of the present invention with a part disassembled. [Figure 1B] It is a perspective view showing a main part with a part of an example of the membrane element of the present invention cut away. [Figure 2] It is a side view cross-sectional view showing an example of the membrane element of the present invention. [Figure 3A] It is a perspective view showing an example of the manufacturing process of the membrane element of the present invention. [Figure 3B] It is a perspective view showing an example of the manufacturing process of the membrane element of the present invention. [Figure 4A] It is a plan view showing an example of the process of cutting off the both-side seals. [Figure 4B] It is a developed view showing an example of the process of cutting off the both-side seals, and shows one membrane leaf developed. [Figure 5] It is a longitudinal cross-sectional view showing an example of the process of separating and recovering the central tube from the cut-off both-side seals. [Figure 6A] This is a side cross-sectional view showing another example of the film element of the present invention. [Figure 6B] This is a longitudinal cross-sectional view showing another example of the process of separating and recovering the central tube from the excised bilateral sealing portions. [Figure 7A] This is a perspective view showing another example of the central tube of a membrane element. [Figure 7B] This is a perspective view showing another example of the central tube of a membrane element. [Figure 7C] This is a perspective view showing another example of the central tube of a membrane element. [Figure 8] This is a side cross-sectional view showing another example of the film element of the present invention. [Modes for carrying out the invention]

[0024] (Spiral-type membrane element) As shown in Figures 1A to 1B, the spiral membrane element E of the present invention comprises a plurality of membrane leaves L having permeation-side channels between opposing separation membranes 1, and a perforated central tube 5 in which the membrane leaves L are wound while interposing supply-side channels between the membrane leaves L. Typically, the permeation-side channels are formed by permeation-side spacers 3, and the supply-side channels are formed by supply-side spacers 2. Furthermore, the membrane leaves L generally have a structure in which three sides are sealed together with the permeation-side spacers 3.

[0025] Therefore, in this embodiment, an example of a used membrane element E is shown, comprising a permeable-side spacer 3 interposed between opposing separation membranes 1, a plurality of membrane leaves L having both side sealing portions 11 and outer peripheral sealing portion 12 that seal both side ends and outer peripheral ends in the axial direction A1, a supply-side spacer 2 interposed between the membrane leaves L, and a perforated central tube 5 around which the membrane leaves L and the supply-side spacer 2 are wound.

[0026] The membrane element E of the present invention has a structure that is advantageous for recycling the central tube 5 when it becomes a used membrane element E, and during operation, it is possible to improve the durability of the adhesive portion 13 between the membrane leaf L and the central tube 5.

[0027] Therefore, we will also explain examples of anticipated recycling methods. In the examples of recycling methods described later, methods are shown that allow for the recycling of not only the central tube 5 but also the permeable spacer 3 and other components included in the membrane leaf L. However, the present invention is not limited to membrane elements E that can be used only with such recycling methods.

[0028] Furthermore, the spiral membrane element E of the present invention may sometimes be described as a used membrane element E, but the two are the same. A used membrane element E is one in which, for example, even if chemical cleaning is performed, recovery of its function as a membrane element E cannot be expected.

[0029] In this specification, the membrane leaf L wound around the central tube 5 and the supply-side spacer 2 are referred to as the winding body R, and the membrane element E generally has an outer covering material 15 on the outer circumference of the winding body R, as shown in Figure 1A.

[0030] In this embodiment, the membrane element E is provided with two side sealing portions 11 and an outer peripheral sealing portion 12 as sealing portions to prevent mixing of the supply side flow path and the permeate side flow path. As shown in Figure 1B, of the sealing portions, the two side sealing portions 11 are formed by sealing the ends of two sides on both sides of the membrane leaf L in the axial direction A1 with adhesive. The outer peripheral sealing portion 12 is formed by sealing the end of the outer peripheral tip of the membrane leaf L with adhesive. The region enclosed by the opposing separation membrane 1, the two side sealing portions 11, and the outer peripheral sealing portion 12 becomes the permeate side flow path, which is structured to communicate with the opening 5a of the central tube 5.

[0031] As shown in Figures 1B and 2, the membrane element E of the present invention has adhesive portions 13 where both ends of the inner circumference side (base end) of the membrane leaf L in the axial direction A1 are bonded to the central tube 5, thereby sealing the central tube 5 and the base end of the membrane leaf L. In this example, the membrane leaf L and the supply-side spacer 2 are wound around the central tube 5 via such adhesive portions 13, forming a wound body R. The adhesive used for sealing is not particularly limited, and any conventionally known adhesive, such as a urethane-based adhesive or an epoxy-based adhesive, can be used.

[0032] In a typical membrane element E, as shown in Figure 1A, an upstream end member 10, such as a seal carrier, is provided on the upstream side of the winding body R, and a downstream end member 20, such as an anti-telescopic material, is provided on the downstream side. These upstream end members 10 and downstream end members 20 may be integrated with the winding body R by winding FRP, which will be the outer periphery of the winding body R, around the winding body R.

[0033] In a typical 8-inch diameter spiral membrane element E, approximately 15 to 30 membrane leaves L are wound around it. When using the membrane element E, it is housed in a pressure vessel, and the supply fluid 7 is supplied from one end face of the membrane element E.

[0034] As shown in Figure 1A, the supplied feed liquid 7 flows along the supply-side spacer 2 in a direction parallel to the axial direction A1 of the central tube 5 and is discharged as concentrated liquid 9 from the other end face of the membrane element E. In addition, the permeate 8 that has permeated the separation membrane 1 as the feed liquid 7 flows along the supply-side spacer 2 flows along the permeate-side spacer 3 and then flows into the interior of the central tube 5 through the opening 5a and is discharged from the end of the central tube 5.

[0035] As shown in Figure 2, the central tube 5 in the present invention has an opening 5a, and in at least a portion of the adhesive portion 13, the outer surface of the central tube 5 has a tapered portion 5b that widens toward the center in the axial direction A1. In the illustrated example, the adhesive portion 13 is present on both the upstream and downstream sides, but it can be provided on at least one of the upstream or downstream sides. In either case, the total area of ​​the tapered portion 5b is preferably 10 to 200%, more preferably 50 to 150%, and even more preferably 80 to 120% of the total area of ​​the adhesive portion 13.

[0036] In this embodiment, an example is shown in which the outer circumferential surface of the central tube 5 has a tapered portion 5b that widens towards the center in the axial direction A1 over the entire area of ​​the adhesive portion 13. In other words, an example is shown in which the total area of ​​the tapered portion 5b is 100% or more of the total area of ​​the upstream and downstream sides of the adhesive portion 13.

[0037] The gradient θ of the tapered portion 5b is preferably such that tanθ = 0.005 to 0.1, and more preferably such that tanθ = 0.01 to 0.035. Note that the gradient θ refers to the angle θ made between the surface of the tapered portion 5b and the axial direction A1 in a cross section that crosses the axial direction A1.

[0038] The outer surface of the tapered portion 5b is not limited to having a straight cross-sectional shape; it may also be a broken line or a curve made up of multiple line segments. However, from the viewpoint of improving the durability of the adhesive portion 13 and the ease of separating and recovering the central tube 5 during recycling, a straight cross-sectional shape is preferable.

[0039] Furthermore, if the cross-sectional shape of the outer surface of the tapered portion 5b is a broken line or a curve, it is preferable that the angle of inclination increases monotonically in the direction of diameter expansion. Also, if the cross-sectional shape of the outer surface of the tapered portion 5b is a broken line or a curve, it is preferable that the gradient θ of the straight line connecting the start and end points of the tapered portion 5b satisfies tanθ = 0.005 to 0.1, and more preferably tanθ = 0.01 to 0.035.

[0040] The outer surface of the tapered portion 5b may be surface-treated to adjust the peeling force with respect to the adhesive portion 13. For example, to reduce the peeling force, the surface of the tapered portion 5b may be modified, or a coating layer with higher release properties than the material constituting the central tube 5 may be formed. Such adjustment of the peeling force may be performed on at least a part of the tapered portion 5b, on the entire tapered portion 5b, or on the entire length of the central tube 5.

[0041] The supply-side spacer 2 generally serves to ensure a gap for evenly supplying fluid to the membrane surface. Such a supply-side spacer 2 can be made of, for example, a net, knitted fabric, or a textured sheet, and can be used as needed with a maximum thickness of approximately 0.1 to 3 mm. Spacers are installed on both sides of the separation membrane 1, but it is common to use different flow channel materials: the supply-side spacer 2 on the supply liquid side and the permeate-side spacer 3 on the permeate liquid side. It is preferable to use a coarse, thick net-like flow channel material for the supply-side spacer 2, while using a fine-mesh woven or knitted flow channel material for the permeate-side spacer 3.

[0042] The permeate-side spacer 3 is installed between opposing separation membranes 1 in the membrane leaf L, as shown in Figure 1A, when using RO membranes or NF membranes in applications such as seawater desalination and wastewater treatment. This permeate-side spacer 3 is required to support the pressure applied to the separation membrane 1 from the back of the membrane and to ensure a flow path for the permeate.

[0043] Furthermore, during operation, the outside of the membrane leaf L becomes high pressure due to the operating pressure, while the inside becomes low pressure on the permeation side. As a result, a force due to this pressure difference acts on the adhesive portion 13, and this force acts on the central side of the central tube 5 in the axial direction A1. In this invention, the downstream adhesive portion 13 also has a tapered portion 5b in that region where the outer surface of the central tube 5 expands in diameter toward the central side of the axial direction A1. Therefore, the force due to the pressure difference between the operating pressure and the permeation pressure, i.e., the force acting toward the central side of the central tube 5, becomes a force that presses against the tapered surface, thus reducing the risk of the adhesive portion 13 peeling off due to the pressure difference.

[0044] To ensure the above-mentioned functions, the permeable spacer 3 is preferably formed from a tricot knitted fabric, and more preferably from a tricot knitted fabric that has been reinforced with resin impregnation or fused after knitting.

[0045] As the separation membrane 1, various porous membranes can be used, but a composite semipermeable membrane having a separation functional layer on the surface of a porous support is preferred. As the porous support, one having a polymer porous layer on one side of a nonwoven fabric layer is preferred.

[0046] These composite semipermeable membranes are called RO (reverse osmosis) membranes, NF (nanofiltration) membranes, or FO (forward osmosis) membranes depending on their filtration performance and treatment method, and can be used for ultrapure water production, seawater desalination, brine desalination, and wastewater reuse.

[0047] Examples of exterior materials 15 include various sheets, films, tapes, etc., and fiber-reinforced plastic (FRP) may be used for reinforcement as needed. In a structure in which the upstream end member 10 and the downstream end member 20 are firmly integrated by the exterior FRP, it is difficult to dismantle and recover the upstream end member 10 and the downstream end member 20. However, by cutting off the sealing portions 11 on both sides during recycling, their separation and recovery become easier.

[0048] (Manufacturing method for spiral-type membrane elements) The membrane elements described above can be manufactured using the same manufacturing method as in the past. That is, for example, as shown in Figure 3A, multiple membrane units U are prepared by placing a permeation-side spacer 3 on top of a separation membrane 1 that has been folded in half so that the supply-side surfaces (separation functional layer sides) face each other, with a supply-side spacer 2 interposed between them, and then applying an adhesive 4 for forming the sealing portions 11 on both sides and an adhesive 6 for forming the sealing portion 12 on the outer circumference side to the permeation-side spacer 3.

[0049] Next, as shown in Figure 3B, for example, membrane units U are stacked on a permeable-side spacer 3, which has one end extended and fixed to the central tube 5, according to the number of membrane leaves L, to form a laminate LB, and the laminate LB is wound around the central tube 5. At this time, only the uppermost membrane unit U is left without a permeable-side spacer 3, and adhesive 4 for forming the sealing portions 11 on both sides and adhesive 6 for forming the sealing portion 12 on the outer circumference are applied to the separation membrane 1.

[0050] Furthermore, adhesive 4a is applied to each membrane unit U so that the inner circumferential ends of the adhesive 4 are continuous, and adhesive 4b is applied to both ends of the permeable spacer 3 located at the bottom so that the area where it is fixed to the central tube 5 is continuous with adhesive 4a.

[0051] After winding, the shape of the wound body R is maintained and the adhesive 4, etc., is cured to form the sealing portions 11 on both sides, the sealing portion 12 on the outer circumference, and the adhesive portion 13 that seals the outer circumference of the central tube 5. In particular, the adhesive portion 13 is mainly formed by adhesives 4a and 4b. As a result, a membrane element E is manufactured that comprises a plurality of membrane leaves L having permeable channels between opposing separation membranes 1, and a perforated central tube 5 in which the membrane leaves L are wound with supply channels interposed between the membrane leaves L.

[0052] In this invention, the central tube 5 has a tapered portion 5b, which differs from the conventional structure. However, as long as the gradient θ of the tapered portion 5b is not particularly large, there is no need to change the membrane unit U, and the conventional membrane unit U can be used as is. In that case, slight deformation of the membrane unit U may occur near the tapered portion 5b, but deformation that would impair the separation function of the separation membrane 1 is unlikely to occur. In this way, the conventional membrane unit U can be wound around the central tube 5 having the tapered portion 5b, and the adhesive 4, etc., can be cured.

[0053] Next, if necessary, an upstream end member 10 such as a seal carrier can be attached to the upstream side of the winding body R, and a downstream end member 20 such as an anti-telescopic material can be attached to the downstream side of the central pipe 5, and an outer covering material 15 can be provided on the outer circumference of the winding body R. The upstream end member 10 and the downstream end member 20 can be integrated with the winding body R by wrapping the FRP that will become the outer covering material 15 around the outer circumference of the winding body R.

[0054] (Recycling methods) Figure 4A is a plan view showing an example of the process of removing the sealing portions 11 on both sides, and Figure 4B is an unfolded view showing an example of the process of removing the sealing portions 11 on both sides, with one of the membrane leaves L unfolded.

[0055] A method for recycling the membrane element E of the present invention may include, for example, the step of removing at least the sealing portions 11 on both sides of the used membrane element E, as shown in Figures 4A to 4B. Here, the sealing portions 11 on both sides typically include opposing separation membranes 1 and a permeable-side spacer 3 interposed between them. In this step, as shown in Figure 4A, when the sealing portions 11 on both sides are removed, both ends of the supply-side spacer 2 in the axial direction A1 are removed.

[0056] This process yields a structure in which the cut membrane leaf L' and the supply-side spacer 2' are wound around the central tube 5' on the cut end side, as shown in Figure 5. Figure 5 also shows the structure after the sealing portions 11 on both sides have been removed and the upstream end member 10 or the downstream end member 20 has been removed.

[0057] In this process, it is sufficient that at least the sealing portions 11 on both sides are removed from the main body of the membrane element E, and at the same time, the ends of the central tube 5, the upstream end member 10, or the downstream end member 20 may also be removed. In other words, it is possible to leave the ends intact without cutting the central tube 5. In this embodiment, an example is shown in which the sealing portions 11 on both sides, both ends of the central tube 5, the upstream end member 10, and the downstream end member 20 are removed.

[0058] Methods for removing the double-sided sealing portions 11 include, for example, cutting along the cutting line C1 to remove both ends of the wound body R including the double-sided sealing portions 11 and both ends of the central tube 5 from the main body of the membrane element E, or cutting only the wound body R without cutting the central tube 5 to separate both ends of the wound body R including the double-sided sealing portions 11 from the main body of the membrane element E. It is also possible to remove the upstream end member 10 and the downstream end member 20 simultaneously or separately.

[0059] When removing the sealing portions 11 on both sides of the used membrane element E, the width is preferably 50 mm or less, based on the length A1 in the axial direction of the separation membrane 1. Furthermore, it is preferable that the length of the separation membrane 1 after removal is 87% or more of the length of the separation membrane 1 before removal, based on the length A1 in the axial direction of the separation membrane 1 before removal.

[0060] As shown in Figure 5, the cut-off end can be easily separated from the adhesive portion 13 by applying a striking force in the direction of the arrow, thereby detaching the end-side central tube 5'. Specifically, one end of the cut-off end is placed on a support base 32 with a hole 32a slightly larger in diameter than the outer diameter of the central tube 5, and a jig 31 is attached to the end-side central tube 5', with a striking force applied to the jig 31. At this time, the jig 31 only needs to have a structure that can transmit the striking force to the central tube 5', but it is preferable to have an internal fitting portion 31a that is inscribed on the inner circumferential surface of the central tube 5' in order to prevent damage to the central tube 5'.

[0061] The adhesive portion 13 is bonded to the tapered portion 5b which widens on the lower side. By applying impact force to the jig 31, a peeling force is generated at the interface between the central pipe 5' and the adhesive portion 13, allowing the interface to be easily separated. The other cut-off end can also be separated from the central pipe 5' on the end side in the same manner. The separated and recovered central pipe 5' on the end side is a petroleum resource and can be mainly used for chemical recycling.

[0062] On the other hand, after the membrane leaf L on the main body side is excised, the outer material 15 is removed, and the membrane leaf L is unfolded and the outer sealing portion 12 is excised, making it easy to separate each component, and the remaining parts of the permeable side spacer 3, supply side spacer 2, and central tube 5 can be recycled.

[0063] (Other embodiments) (1) In the above embodiment, an example was shown in which the central tube 5 does not have a divisible structure. However, in the present invention, as shown in Figure 6A, the central tube 5 may have a structure that is divisible on the central side of the adhesive portion 13. In the illustrated example, the central tube 5 has a fitting connection portion 5c that is divisible slightly on the central side of the adhesive portion 13. The position in which the divisible structure is provided is preferably on the central side of the adhesive portion 13 and outside of the openings 5a provided at both ends of the central tube 5.

[0064] If the central tube 5 has a separable structure, after cutting the sealing portions 11 on both sides slightly towards the center while leaving both ends of the central tube 5 intact, the end portion of the central tube 5' can be separated from the central portion 5* of the central tube 5. Furthermore, as shown in Figure 6B, the end portion of the central tube 5' can be separated and recovered from the cut end. This end portion of the central tube 5' can then be reconnected to the central portion 5* of the central tube, making it possible to reuse both the end portion of the central tube 5' and the central portion 5* of the central tube.

[0065] Specifically, one of the cut-off ends is placed on a support base 32 with a hole 32a that is slightly larger in diameter than the outer diameter of the central pipe 5. With the jig 31 attached to the end-side central pipe 5', the separated end-side central pipe 5' can be separated and recovered by applying a striking force to the jig 31.

[0066] The divisible structure of the central tube 5 is not particularly limited, but a fitting structure with an anti-rotation feature is preferred. Figures 7A to 7C show examples of such fitting structures for the central tube 5. In the example shown in Figure 7A, the fitting connection portion 5c of the end-side central tube 5' has a projection, and the central portion 5* of the central tube 5 has a guide groove and a recess, so the fitting connection portion 5c can be pushed in and the projection can be locked into the recess for fixation.

[0067] In the example shown in Figure 7B, the fitting connection portion 5c of the end-side central tube 5' has a projection, and the central portion 5* of the central tube 5 has an L-shaped guide groove and a recess. Therefore, by pushing and rotating the fitting connection portion 5c so that the projection follows the guide groove, the projection can be locked into the recess and fixed in place.

[0068] In the example shown in Figure 7C, the fitting connection portion 5c of the end-side central tube 5' has a male screw structure, and the central portion 5* of the central tube 5 has a female screw structure, so the fitting connection portion 5c can be rotated and screwed together.

[0069] (2) In the above embodiment, an example was shown in which the outer diameter of the main body of the central tube 5 is larger than the outer diameter of the tip of the central tube 5. However, in the present invention, as shown in Figure 8, it is also possible to have a central tube 5 in which the outer diameter of the main body of the central tube 5 is equal to or less than the outer diameter of the tip of the central tube 5.

[0070] In that case, by providing a tapered portion 5b in the central tube 5, the increase in the outer diameter of the main body of the central tube 5 can be suppressed, and the volume for filling the separation membrane 1 can be maintained, thereby suppressing a decrease in the effective membrane area.

[0071] Specifically, as shown in Figure 8, a stepped portion is provided in which the outer diameter becomes smaller than the outer diameter of the tip of the central tube 5. A tapered portion 5b is formed starting from this point, with the outer surface expanding toward the center in the axial direction A, and at the end of the tapered portion 5b, the outer diameter is the same as or smaller than the outer diameter of the tip of the central tube 5. In other words, the central tube 5 has a tip tube portion, a stepped portion that reduces the outer diameter of the tip tube portion, a tapered portion 5b from the stepped portion where the outer surface expands toward the center in the axial direction A, and a main body portion that is continuous from the end of the tapered portion 5b and has an outer diameter the same as or smaller than the outer diameter of the tip tube portion.

[0072] Even with this structure, because the outer surface has a tapered portion 5b that widens towards the center in the axial direction A, the adhesive portion 13 can be easily peeled off by cutting the tip of the central tube 5, including the stepped portion, and then applying a striking force from the tip side of the central tube 5, making it easier to separate and recover the central tube 5 during recycling.

[0073] Furthermore, by shortening the fitting portion for attaching the interconnector that connects the membrane elements E, the thickness of the tapered portion 5b of the central tube 5 can be ensured. In that case, it is preferable that the inner circumferential surface of the tapered portion 5b of the central tube 5 also has a slope of about the same degree as the slope θ of the tapered portion 5b. [Industrial applicability]

[0074] The spiral membrane element of the present invention provides a spiral membrane element that improves the durability of the adhesive joint between the membrane leaf and the central tube, while also facilitating the separation and recovery of the central tube during recycling. The central tube can be recycled in a cut or divided state; in the case of cutting, it can be subjected to chemical recycling or material recycling, and in the case of division, it can be reused in addition to the above. In either case, the separation and recovery of the central tube becomes easier, making it a useful spiral membrane element with a structure advantageous for recycling. [Explanation of symbols]

[0075] 1: Separation membrane 2: Supply side spacer 3: Transmissive side spacer 5: Central tube 5b: Tapered section 11: Sealing section on both sides 12: Outer peripheral sealing portion 13: Adhesive part 15: Exterior materials A1: Axial direction E: Membrane element R: Coiled body L: Membrane Leaf

Claims

1. A spiral membrane element comprising a plurality of membrane leaves having permeable channels between opposing separation membranes, and a perforated central tube in which the membrane leaves are wound while interposing supply channels between the membrane leaves, The inner circumferential end of the membrane leaf has adhesive portions where both ends in the axial direction are bonded to the central tube. A spiral membrane element having a tapered portion in at least a portion of the adhesive area, where the outer surface of the central tube widens toward the axial center.

2. The spiral membrane element according to claim 1, wherein the outer surface of the central tube has a tapered portion in the entire area of ​​the adhesive portion that widens toward the center in the axial direction.

3. The spiral membrane element according to claim 1, wherein the gradient θ of the tapered portion satisfies tanθ = 0.005 to 0.

1.

4. The spiral membrane element according to claim 1, wherein the central tube has a structure that allows it to be divided on the central side of the adhesive portion.

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