Hollow fiber membrane element and hollow fiber membrane module

Abstract

This axial flow-type hollow fiber membrane element comprises: a core material; a hollow fiber membrane group formed of a plurality of hollow fiber membranes arranged around the core material; and a solid fiber that is radially wound on the core material and that binds the hollow fiber membrane group together. In the hollow fiber membrane group, the main direction of the flow of a liquid outside the plurality of hollow fiber membranes is the axial direction of the core material.

Description

Hollow fiber membrane element and hollow fiber membrane module

[0001] The present invention relates to a hollow fiber membrane element and a hollow fiber membrane module.

[0002] For example, a hollow fiber membrane module, which is formed by assembling hollow fiber membranes (hollow fiber semipermeable membranes) and housing them in a pressure vessel, is used in membrane separation processes. Although the hollow fiber membrane module does not have a large permeate amount per unit membrane area compared to a spiral-wound membrane module, it has the advantage of being able to provide a large membrane area per membrane module volume, resulting in a large permeate amount for the entire module and very high volumetric efficiency, and is also excellent in compactness.

[0003] In hollow fiber membrane modules, for example, a radial flow system (cross flow system) is used, in which the flow in the outer region of the hollow fiber membranes, generated from multiple holes in the core tube, is approximately perpendicular to the flow in the inner region (hollow portion) of the hollow fiber membranes. In a radial flow system hollow fiber membrane module, the liquid flowing in the outer region of the hollow fiber membranes is discharged from multiple holes in the core tube (distribution pipe) at the center of the hollow fiber membrane group and flows dispersedly in the radial and longitudinal directions of the hollow fiber membrane module. Therefore, if the flow rate of the liquid passing through the outer region of the hollow fiber membranes decreases, the flow velocity (flow velocity in the longitudinal direction of the hollow fiber membrane module) also decreases, which has the disadvantage of making concentration polarization more likely to occur on the outer surface of the hollow fiber membranes.

[0004] To overcome these drawbacks, axial flow hollow fiber membrane modules have been proposed, which guide the flow in the outer region of the hollow fiber membranes along the length (axis) of the hollow fiber membrane module. For example, Japanese Patent Publication No. 6565898 (Patent Document 1), Japanese Patent Publication No. 7379835 (Patent Document 2), and International Publication No. 2023 / 036944 (Patent Document 3) disclose hollow fiber membrane modules in which a liquid flows in the longitudinal (axial) direction of the module from an opening provided only at one end of a core tube (supply tube) located at the radial center of the module, through the outer region of the hollow fiber membranes, and toward an outlet at the other end. In such axial flow hollow fiber membrane modules, the flow rate in the outer region of the hollow fiber membranes is increased, thereby suppressing concentration polarization that occurs on the outer surface of the hollow fiber membranes.

[0005] Japanese Patent No. 6565898 Japanese Patent No. 7379835 International Publication No. 2023 / 036944

[0006] However, in an axial flow hollow fiber membrane module, the water flow distance is long and the cross-sectional area of ​​the flow path is small, which increases pressure loss and makes it prone to drift. Drift drift can potentially hinder the overall separation efficiency. This is because the concentration polarization on the membrane surface caused by water penetration is not resolved in the stagnant areas caused by drift drift, resulting in a significant decrease in separation efficiency and the creation of dead spaces that do not contribute to separation, making it impossible to effectively use the membrane.

[0007] Furthermore, when a high-pressure liquid is passed outside a hollow fiber membrane to perform an OARO method, an RO method, or the like, the hollow fiber membrane shrinks in the radial direction due to compaction over time, which increases the space outside the hollow fiber membrane over time, potentially causing the initial balance to be lost and resulting in a decrease in membrane separation performance.

[0008] Furthermore, when the hollow fiber membrane element is wrapped in an impermeable sheet 6 to prevent the axial flow from being deflected (see Figure 6), the impermeable sheet 6 covering the hollow fiber membrane bundle will swell over time due to the pressure of the liquid, causing uneven spaces between the hollow fiber membranes (outside the hollow fiber membranes). This can lead to problems such as a decrease in membrane separation performance due to uneven flow caused by areas where the liquid flow concentrates.

[0009] Therefore, an object of the present invention is to suppress uneven flow of liquid outside the hollow fiber membranes in an axial flow type hollow fiber membrane module in which the liquid outside the hollow fiber membranes flows mainly in the axial direction of the module.

[0010] [1] An axial flow type hollow fiber membrane element comprising: a core material; a hollow fiber membrane group consisting of a plurality of hollow fiber membranes arranged around the core material; and a solid fiber wound in the radial direction of the core material to restrain the hollow fiber membrane group, wherein in the hollow fiber membrane group, the main direction of liquid flow outside the plurality of hollow fiber membranes is the axial direction of the core material.

[0011] [2] The hollow fiber membrane element according to [1], wherein the plurality of hollow fiber membranes are spirally wound around the core material so as to cross each other.

[0012] [3] The hollow fiber membrane element according to [1] or [2], wherein the solid fiber is wound spirally in a plan view seen from the axial direction of the core material.

[0013] [4] The hollow fiber membrane element according to any one of [1] to [3], wherein the core material is a core tube having a hole only near a first end, which is one end of the core material in the axial direction.

[0014] [5] The hollow fiber membrane element according to any one of [1] to [4], wherein the radial periphery of the hollow fiber membrane group, excluding the periphery near the second end, which is the end opposite the first end, is covered with an impermeable sheet.

[0015] [6] The hollow fiber membrane element according to any one of [1] to [5], which is for osmotic pressure-assisted reverse osmosis or reverse osmosis.

[0016] [7] A hollow fiber membrane module comprising the hollow fiber membrane element according to any one of [1] to [6] and a container in which at least one hollow fiber membrane element is loaded.

[0017] According to the present invention, in an axial flow type hollow fiber membrane module in which the liquid outside the hollow fiber membranes flows mainly in the axial direction of the module, it is possible to suppress uneven flow of the liquid outside the hollow fiber membranes, thereby improving the membrane separation performance of the axial flow type hollow fiber membrane module.

[0018] FIG. 1 is a schematic diagram showing an example of a hollow fiber membrane element of an embodiment. FIG. 2(a) is a schematic diagram showing the arrangement of hollow fiber membranes and solid fibers in an example of a hollow fiber membrane element of an embodiment. FIG. 2(b) is a schematic diagram showing the arrangement of hollow fiber membranes in an example of a conventional hollow fiber membrane element. FIG. 3 is a schematic diagram showing the winding process of hollow fiber membranes and solid fibers in an example of a hollow fiber membrane element of an embodiment. FIG. 4 is a cross-sectional schematic diagram showing the winding process of hollow fiber membranes and solid fibers in an example of a hollow fiber membrane element of an embodiment. FIG. 5 is a graph showing the water permeability performance of hollow fiber membrane elements of Examples and Comparative Examples. FIG. 6 is a cross-sectional schematic diagram showing an example of a hollow fiber membrane module of an embodiment. FIG. 7 is a cross-sectional schematic diagram showing a modified example of a hollow fiber membrane module of an embodiment. FIG. 8 is a cross-sectional schematic diagram showing a modified example of a hollow fiber membrane module of an embodiment. FIG. 9 is a cross-sectional schematic diagram showing a modified example of a hollow fiber membrane module of an embodiment. FIG. 10 is a cross-sectional schematic diagram showing a modified example of a hollow fiber membrane module of an embodiment. Fig. 11 is a cross-sectional view showing a modified example of the hollow fiber membrane module of the embodiment. Fig. 12 is a cross-sectional view showing a modified example of the hollow fiber membrane module of the embodiment. Fig. 13 is a cross-sectional view showing details of an example of a hollow fiber membrane module similar to Fig. 6.

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals denote the same or corresponding parts.

[0020] 1, 6 and 13, the hollow fiber membrane element of this embodiment includes a core material 20, a hollow fiber membrane group 22, and a solid fiber 7. The hollow fiber membrane group is made up of a plurality of hollow fiber membranes 21 arranged around the core material 20 (so as to surround the periphery of the core material 20). The solid fiber 7 is wound radially around the core material 20 and restrains the hollow fiber membrane group 22. The hollow fiber membrane element has, for example, a cylindrical shape.

[0021] The hollow fiber membrane element (hollow fiber membrane module) of this embodiment is of an axial flow type. In an axial flow type, the direction of the liquid flow outside the plurality of hollow fiber membranes 21 in the hollow fiber membrane element (the region where the hollow fiber membrane group 22 is arranged outside the core material 20) is mainly in the axial direction of the core material. In other words, when the direction of the liquid flow outside the hollow fiber membranes 21 is divided into a component in the radial direction of the core material and a component in the axial direction of the core material, the component in the axial direction of the core material is more prevalent overall than the component in the radial direction of the core material.

[0022] Thus, an axial flow hollow fiber membrane element (hollow fiber membrane module) has a configuration for guiding the flow in the outer region of the hollow fiber membranes 21 in the longitudinal (axial) direction of the hollow fiber membrane module (hollow fiber membrane element, core material 20). An example of such a configuration is shown in FIG. 13 . In the hollow fiber membrane element (hollow fiber membrane module) shown in FIG. 13 , the fluid flowing in through the supply port 13 is dispersed in the radial direction of the hollow fiber membrane element near the resin wall 42, then flows along the outer side 3 of the hollow fiber membrane in the axial direction of the element (core material 20), passes through the holes 20a in the core material 20, and is discharged from the discharge port 10. In an axial flow hollow fiber membrane element, the flow velocity of the fluid on the outer side (outer surface) 3 of the hollow fiber membranes 21 can be increased, thereby sufficiently reducing concentration polarization on the outer surface of the hollow fiber membrane, resulting in high membrane separation performance (membrane separation efficiency).

[0023] In the axial flow type hollow fiber membrane module of this embodiment, the flow directions on the outside 3 and inside of the hollow fiber membrane 21 may be opposite (countercurrent) or may be the same (parallel), but it is preferable to perform a countercurrent separation operation as shown in the figure (see Figure 13). When performing membrane separation treatment by the OARO method, the countercurrent flow is considered to have higher membrane separation performance because the osmotic pressure difference between the liquid inside and the liquid outside at each point of the hollow fiber membrane is smaller (the osmotic pressure difference is relatively uniform throughout the entire length of the hollow fiber membrane).

[0024] The core material 20 is, for example, a core tube. The core tube has a hole 20a only near a first end 4a, which is one end in the axial direction of the core material 20 (hollow fiber membrane element). The opening on the first end 4a side of the core tube is connected to the outlet 10, and the opening on the second end 4b, which is the end opposite the first end 4a (outlet 10), of the core tube is closed by a member. In Figure 6, a plug 20b is filled inside the portion of the core tube where no hole 20a is provided, but the plug 20b is not necessary.

[0025] As shown, the first end 4a on the side where the holes 20a are provided is preferably located downstream of the flow of liquid outside the hollow fiber membrane (indicated by the white arrow in Fig. 1 and the black arrow in Fig. 6). In this case, the outside of the impermeable sheet 6 is filled with liquid having a high pressure close to the pressure of the liquid on the supply port 13 side, so the impermeable sheet 6 is less likely to bulge outward, and it is thought that drift is less likely to occur.

[0026] The hollow fiber membrane element may include resin walls 41, 42 that fix the core material 20 and the hollow fiber membrane group 22 (plurality of hollow fiber membranes 21) at both ends thereof.

[0027] At least a portion of the radial periphery of the hollow fiber membrane group 22 may be covered with a (cylindrical) impermeable sheet 6. Here, as shown in FIGS. 1( b), 6, and 13, it is preferable that the radial periphery of the hollow fiber membrane group 22, excluding the periphery near the second end 4b, which is the end opposite the first end 4a, is covered with the impermeable sheet 6. On the first end 4a side, the impermeable sheet 6 may be fixed with resin (resin walls 41, 42) together with the core material 20 and the plurality of hollow fiber membranes 21 (hollow fiber membrane group 22). By covering the hollow fiber membrane group 22 with the impermeable sheet 6 in this way, the occurrence of short-circuiting flow through the gap between the hollow fiber membrane group 22 and the vessel 1 is suppressed, and the feed liquid can be efficiently used as an axial flow between the hollow fiber membranes 21.

[0028] The plurality of hollow fiber membranes 21 are preferably spirally wound around the core material 20 so as to intersect with each other.

[0029] Referring to FIG. 1(a), in this embodiment, a plurality of hollow fiber membranes 21 (a plurality of hollow fiber membrane bundles 22a, 22b) are spirally wound around a core material 20 so as to intersect with one another. In FIG. 1(a), the hollow fiber membrane bundle 22a is depicted by a thick line, and the hollow fiber membrane bundle 22b is depicted by a thin line. "Spiral wound" means, in other words, that the arrangement of the hollow fiber membranes 21 (hollow fiber membrane bundles 22a, 22b) is wound so as to form an angle (excluding 90°) with the axis of the core material 20. The angle in this case is, for example, 3 to 60°.

[0030] By arranging the plurality of hollow fiber membranes 21 (plurality of hollow fiber membrane bundles 22a, 22b) so that they intersect with one another, regular gaps are formed in a cross point group 24 including a plurality of crossing points (cross points 23) of the hollow fiber membranes. Due to the presence of these regular gaps, the fluid flowing on the outer side 3 of the hollow fiber membranes 21 is less likely to drift, and pressure loss is also small. Furthermore, undissolved components, particulate components, and the like in the fluid flowing on the outer side 3 of the hollow fiber membranes 21 are less likely to be trapped between the hollow fiber membranes 21, so an increase in pressure loss is less likely to occur.

[0031] In Figure 13, solid fibers are omitted to show the details of the liquid flow, and the hollow fiber membranes 21 are simply drawn parallel to the core material 20. In this way, multiple hollow fiber membranes 21 may be arranged parallel to the core material 20. However, if the hollow fiber membranes are arranged parallel to the core material (especially if they are not closely packed), the gaps between the hollow fiber membranes are likely to vary, and fluid is likely to flow only in areas with low pressure loss, resulting in drift. For this reason, the hollow fiber membranes 21 (hollow fiber membrane bundles 22a, 22b) are preferably wound spirally around the core material 20 so that the multiple hollow fiber membrane bundles 22a, 22b intersect with each other. In a hollow fiber membrane element (hollow fiber membrane wound body) in which multiple hollow fiber membranes 21 are arranged in a crossing pattern, the gaps between the multiple hollow fiber membranes 21 are less likely to vary, and drift is less likely to occur.

[0032] In the hollow fiber membrane element (hollow fiber membrane wound body), the number of windings (winding number) of the hollow fiber membrane is not particularly limited, but is, for example, 1.0 to 2.0. The winding number is the number of times (number of rotations) that the hollow fiber membrane (bundle) is wound around the core material from one end to the other end in the axial direction of the hollow fiber membrane element.

[0033] (Solid Fiber) The hollow fiber membrane element of this embodiment includes solid fibers 7 wound radially around the core material 20 (hollow fiber membrane element) and restraining the hollow fiber membrane group 22. The hollow fiber membrane group 22 is restrained by these solid fibers 7 so as not to expand radially of the core material 20. This makes it possible to prevent the hollow fiber membrane group 22 from expanding radially of the core material 20, thereby preventing the occurrence of drift (deterioration of membrane separation performance).

[0034] When the solid yarn 7 is wound radially around the core material 20, the solid yarn 7 may be disposed in a substantially radial direction (wound without moving in the length direction of the core material 20), or may be disposed offset from the radial direction (wound while moving in the length direction of the core material 20). However, in the latter case, in order to enable the solid yarn 7 to restrain the hollow fiber membranes 21, the moving speed in the length direction of the core material 20 when winding the solid yarn is set to be slower than the moving speed in the length direction of the core material 20 when winding the hollow fiber membranes (bundle).

[0035] Although a single solid fiber 7 may be used, as shown in Figures 1, 2(a), and 3, it is preferable that a plurality of solid fibers 7 are wound radially around the core material 20 at multiple locations in the longitudinal direction of the core material 20 to restrain the hollow fiber membrane group 22. In this case, it is possible to more reliably prevent the occurrence of drift caused by the hollow fiber membrane group 22 expanding in the radial direction of the core material 20. Note that Figure 2(b) shows the arrangement of hollow fiber membranes 21 in a conventional hollow fiber membrane element. In this cross-shaped arrangement of hollow fiber membranes 21, a plurality of solid fibers 7 restrain the hollow fiber membrane group 22.

[0036] When multiple solid fibers are used, the thickness of each solid fiber may be the same or different, for example, the thickness of each solid fiber may be adjusted (varied) so as to provide a uniform space between the hollow fiber membranes throughout the hollow fiber membrane group.

[0037] The solid yarn 7 is preferably wound spirally in a plan view seen from the axial direction of the core material 20 (see FIG. 1( c)). For example, as shown in FIG. 3, the solid yarn 7 may be wound simultaneously with the hollow fiber membranes 21 (hollow fiber membrane bundles 22a, 22b) being wound around the core material 20. This allows the solid yarn 7 to be wound spirally as described above. In this way, by arranging the solid yarn 7 at multiple locations from the inside to the outside in the radial direction of the core material 20 (hollow fiber membrane element), the outer hollow fiber membranes 21 and the inner hollow fiber membranes 21 can be constrained with a uniform constraining force. This allows the hollow fiber membranes 21 to be constrained uniformly in the radial direction of the core material 20, more reliably suppressing the occurrence of drift.

[0038] The solid yarn 7 is not particularly limited, and examples thereof include rubber yarn and resin yarn. In this embodiment, it is preferable to use a solid yarn having conformability (stretchability and flexibility), such as rubber yarn. In this case, the constraint of the solid yarn 7 prevents the interior (hollow portion) of the hollow fiber membrane 21 from being crushed, and the occurrence of drift of the liquid flowing inside the hollow fiber membrane 21 (deterioration of membrane separation performance) can be prevented.

[0039] The solid fibers 7 are preferably made of an impermeable material that does not have water permeability, because if the solid fibers 7 have water permeability, this may affect the balance of the membrane separation process using the hollow fiber membrane module.

[0040] (Method for manufacturing hollow fiber membrane element) The hollow fiber membrane element of this embodiment can be produced, for example, by spirally winding hollow fiber membranes around a core material 20, arranging the hollow fiber membranes 21 in a crosswise manner, and winding the solid fibers 7 radially around the core material 20, sealing both ends of the hollow fiber membrane winding body with resin, and then cutting part of the resin (resin walls 41, 42) to open both ends of the hollow fiber membranes 21.

[0041] First, as shown in Figures 3 and 4, the hollow fiber membranes 21 (hollow fiber membrane bundles 22a, 22b) are traversed while rotating the core tube (core material 20) around its axis, and are wound spirally around the core tube, thereby arranging the hollow fiber membranes in a cross-like configuration. It is preferable that no tension is applied to the hollow fiber membranes (bundle) when winding them. For example, if the hollow fiber membranes 21 are thin and do not have sufficient strength, the hollow fiber membrane bundles 22a, 22b, each consisting of a plurality of hollow fiber membranes 21, may be wound cross-like to arrange the hollow fiber membranes 21 in a cross-like configuration.

[0042] Simultaneously with the winding of the hollow fiber membranes (bundle), the core tube (core material 20) is rotated about its axis, while the multiple solid fibers 7 are traversed and wound approximately radially around the core tube. Both longitudinal ends of the thus obtained assembly of hollow fiber membranes 21 (hollow fiber membrane group 22) are fixed by potting with epoxy resin, and then both ends of the resin portion are cut to open the hollow portions of the hollow fiber membranes, thereby producing a hollow fiber membrane element.

[0043] In the illustrated hollow fiber membrane element, both ends of the multiple hollow fiber membranes are open. Such a hollow fiber membrane module can be used for membrane separation processes such as osmotic-assisted reverse osmosis (OARO), forward osmosis (FO), pressure-retarded osmosis (PRO), and reverse osmosis (RO). However, one end of the hollow fiber membrane may be open and the other end may be closed. Such a hollow fiber membrane module can be used for membrane separation processes such as RO (reverse osmosis).

[0044] In the OARO method, a semipermeable membrane module has a semipermeable membrane (hollow fiber membrane) and first and second chambers separated by the semipermeable membrane. A high-pressure target solution is passed through the first chamber, and a low-pressure auxiliary solution (such as the target solution) is passed through the second chamber, causing the solvent (such as water) contained in the target solution in the first chamber to migrate through the semipermeable membrane to the auxiliary solution in the second chamber, thereby discharging a concentrated target solution (concentrated solution) from the first chamber and a diluted auxiliary solution (diluted solution) from the second chamber. The OARO method makes it possible to reduce the energy required for membrane separation (concentration) processing using the RO method and to obtain a more highly concentrated concentrate, among other things.

[0045] When a high-pressure liquid is passed outside the hollow fiber membrane to carry out the OARO method, RO method, or the like, problems such as uneven flow due to compaction of the hollow fiber membrane 21 over time and swelling of the impermeable sheet 6 over time are likely to occur, resulting in a deterioration in membrane separation performance. However, by using the hollow fiber membrane element and hollow fiber membrane module of this embodiment, these problems can be resolved and the deterioration of membrane separation performance can be suppressed.

[0046] When the OARO method, RO method, or the like is carried out using a hollow fiber membrane module, it is preferable to flow a pressurized liquid in the region outside 3 of the hollow fiber membrane 21. Even if the solution flowing inside the hollow fiber membrane is pressurized, there are cases where the pressure loss becomes large and it is difficult to pressurize the solution sufficiently, and further, although hollow fiber membranes generally easily maintain their structure against external pressure, there is a possibility that the hollow fiber membranes may be damaged if the internal pressure becomes too high.

[0047] Hereinafter, the respective constituent members of the hollow fiber membrane element and hollow fiber membrane module of this embodiment will be described in detail.

[0048] (Hollow fiber membrane) A hollow fiber membrane is a semipermeable membrane in the form of a hollow fiber. Hollow fiber membranes are advantageous in that they have a smaller membrane thickness than flat membranes, and can have a larger membrane area per module, thereby increasing permeation efficiency.

[0049] Examples of semipermeable membranes constituting the hollow fiber membrane include semipermeable membranes called reverse osmosis membranes (RO membranes), forward osmosis membranes (FO membranes), nanofiltration membranes (NF membranes), and ultrafiltration membranes (UF membranes). The semipermeable membrane is preferably a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane. When a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane is used as the semipermeable membrane, the pressure of the liquid (target solution) in the first chamber is preferably 0.5 to 10.0 MPa.

[0050] Typically, RO membranes and FO membranes have pore sizes of approximately 2 nm or less, and UF membranes have pore sizes of approximately 2 to 100 nm. NF membranes have a relatively low rejection rate for ions and salts compared to RO membranes, and typically have pore sizes of approximately 1 to 2 nm. When an RO membrane, FO membrane, or NF membrane is used as the semipermeable membrane, the salt rejection rate of the RO membrane, FO membrane, or NF membrane is preferably 90% or higher.

[0051] The material constituting the semipermeable membrane is not particularly limited, but examples thereof include cellulose-based resins, polysulfone-based resins, polyamide-based resins, etc. The semipermeable membrane is preferably made of a material containing at least one of a cellulose-based resin and a polysulfone-based resin.

[0052] The cellulose-based resin is preferably a cellulose acetate-based resin. Cellulose acetate-based resins are resistant to chlorine, a disinfectant, and have the characteristic of being able to inhibit the growth of microorganisms. The cellulose acetate-based resin is preferably cellulose acetate, and from the viewpoint of durability, more preferably cellulose triacetate.

[0053] The polysulfone-based resin is preferably a polyethersulfone-based resin. The polyethersulfone-based resin is preferably a sulfonated polyethersulfone.

[0054] A specific example of a hollow fiber membrane is a membrane with a single layer structure composed entirely of a cellulose-based resin. However, the single layer structure referred to here does not necessarily mean a membrane with a uniform layer throughout; for example, it may be a membrane that is non-uniform in the thickness direction. Specifically, the membrane may have a dense layer on the outer surface, which serves as a separation active layer that essentially determines the pore size of the hollow fiber membrane, and the inner surface side may have a lower density than the dense layer. Since the dense layer essentially serves as a separation active layer that determines the pore size of the hollow fiber membrane, when the solution outside the hollow fiber membrane is pressurized, having a dense layer on the outer surface of the hollow fiber membrane allows for more accurate control of the movement of molecules from the outside to the inside of the hollow fiber membrane.

[0055] Another specific example of a hollow fiber membrane is a two-layer membrane having a dense layer of a polyphenylene resin (e.g., sulfonated polyethersulfone) on the outer surface of a support layer (e.g., a layer made of polyphenylene oxide). Another example is a two-layer membrane having a dense layer of a polyamide resin on the outer surface of a support layer (e.g., a layer made of polysulfone or polyethersulfone).

[0056] The outer diameter of the hollow fiber membrane is not particularly limited, but is, for example, 120 to 400 μm. If the outer diameter is small, the inner diameter will inevitably be small as well, which may increase the flow pressure loss of the fluid flowing through the hollow portion of the hollow fiber membrane. On the other hand, if the outer diameter is large, it will be impossible to increase the membrane area per unit volume in the module, which may impair the compactness that is one of the advantages of hollow fiber membrane modules.

[0057] As described in Japanese Patent No. 3591618, for example, a cellulose acetate hollow fiber membrane can be produced by discharging a membrane-forming solution consisting of cellulose triacetate, ethylene glycol (EG), and N-methyl-2-pyrrolidone (NMP) from a three-division nozzle, passing through an airborne section, and immersing the hollow fiber membrane in a coagulation solution consisting of water / EG / NMP, followed by washing the hollow fiber membrane with water and heat-treating it. Alternatively, a copolymerized polyamide obtained by low-temperature solution polymerization from terephthalic acid dichloride, 4,4'-diaminodiphenyl sulfone, and piperazine is purified, and then coagulated with CaCl ２ and diglycerin to form a membrane-forming solution, which is then discharged from a three-division nozzle through an airborne part into a coagulation liquid, and the resulting hollow fiber membrane is washed with water and then heat-treated to produce a polyamide-based hollow fiber membrane.

[0058] The hollow fiber membranes obtained as described above are incorporated into hollow fiber membrane elements by conventionally known methods. As described, for example, in Japanese Patent Nos. 4412486, 4277147, 3591618, and 3008886, 45 to 90 or more hollow fiber membranes are assembled into a hollow fiber membrane assembly, and then multiple hollow fiber membrane assemblies are arranged horizontally to form a flat hollow fiber membrane bundle, which is then wound around a core material in a traversing manner. The length and rotation speed of the core material and the traversing speed of the hollow fiber membrane bundle are adjusted to form intersections on the circumferential surface of the wound body at specific positions. Next, the length and intersection positions of the wound body are adjusted, and the wound body is cut at the predetermined positions. Thereafter, an impermeable sheet is placed on the outer periphery of the hollow fiber wound body, leaving the side opposite to the hole in the core tube, and both ends of the wound body are adhered, after which both sides are cut to form openings in the hollow fiber membrane, thereby producing a hollow fiber membrane element.

[0059] (Impermeable Sheet) The impermeable sheet 6 is not particularly limited as long as it is a film material that is substantially impermeable to the fluid (liquid to be treated) flowing outside the hollow fiber membrane or that causes a large pressure loss when the fluid passes through. Examples of impermeable sheets that can be used include rubber sheets, resin films, and fine-mesh cloths. In this embodiment, it is preferable to use an impermeable sheet that has conformability (stretchability, flexibility), such as a rubber sheet. In this case, it is possible to prevent the occurrence of drift (deterioration of membrane separation performance) due to the interior (hollow portion) of the hollow fiber membrane being crushed by covering the impermeable sheet.

[0060] To enable the impermeable sheet 6 to withstand the pressure loss of the fluid flowing outside the hollow fiber membranes, a support member may be wrapped around the outside of the impermeable sheet. The support member may be a linear or woven material made of natural fiber, synthetic polymer fiber, inorganic fiber, or the like, or may be one to which an adhesive is attached. The support member maintains the pressure difference between the inside and outside of the hollow fiber membrane assembly.

[0061] In order to prevent the impermeable sheet 6 from swelling over time, the above-mentioned solid yarn may be further wound around the outside of the impermeable sheet.

[0062] In the hollow fiber membrane element of the present invention, in order to improve the uniformity of the axial flow of the fluid flowing outside the hollow fiber membranes, a flow straightening member 61 such as a spacer (mesh member, etc.) or a flow straightening plate may be provided to radially divide the hollow fiber membrane group 22 into multiple layers (see Figure 8). For example, an impermeable sheet may be provided as a flow straightening member so as to cover the radially inner portion of the hollow fiber membrane group 22 (not just the outermost layer of the hollow fiber membrane group 22).

[0063] The outer diameter of the hollow fiber membrane wound body is preferably 130 to 420 mm. If the outer diameter is too large, operability during maintenance such as membrane replacement may be impaired. If the outer diameter is too small, the membrane area per unit membrane element decreases, resulting in a smaller throughput, which is undesirable from an economic standpoint.

[0064] <Hollow Fiber Membrane Module> The hollow fiber membrane module shown in Figs. 6 and 13 comprises at least the above-described hollow fiber membrane element and a vessel 1 in which at least one hollow fiber membrane element is loaded.

[0065] The vessel 1 is not particularly limited, but may be, for example, a pressure vessel having pressure resistance capable of withstanding the operating pressure.

[0066] This hollow fiber membrane module has a supply port 13 and a discharge port 10 (discharge port 10 connected to core tube 20) that communicate with the outside of hollow fiber membrane 21, and a supply port 11 and a discharge port 12 that communicate with the inside of hollow fiber membrane 21. Note that supply port 13 communicates with the outside of hollow fiber membrane 21 via a portion near second end 4b that is not covered by impermeable sheet 6, and is provided on the side surface of vessel 1. These are fixed by wall members 14, 15, 51, and 52. Wall members 51 and 52 are fixed liquid-tight to the inner wall of vessel 1 by O-rings 51a and 52b.

[0067] <Modifications> Figures 7 to 12 show modifications of the hollow fiber membrane module (hollow fiber membrane element) of the above embodiment. Below, the differences between each modification and the above embodiment shown in Figure 6 etc. will be explained. Other points are the same as those of the above embodiment.

[0068] 7, a hole is also provided on the side opposite to hole 20a of the core tube (core material 20), and no sealing material 20b is provided inside that portion of the core tube, and the interior communicates with the back side (discharge port 12 side) of wall member 52, which in turn communicates with supply port 13. With this configuration, the liquid supplied from supply port 13 not only flows from the outside of hollow fiber membrane group 22 to the region outside hollow fiber membranes 21, but also can flow from the inside of hollow fiber membrane group 22 to the region outside hollow fiber membranes 21 by passing through the back side of wall member 52 and the inside of the core tube.

[0069] In the modification shown in Fig. 8, flow straightening members 61 such as impermeable sheets and spacers (mesh members, etc.) are provided so as to divide the hollow fiber membrane group 22 into multiple layers in the radial direction, thereby further improving the uniformity of the axial flow of the fluid flowing outside the hollow fiber membranes.

[0070] In the modified example shown in FIG. 9 , the core tube (the first end 4 a side of the core material 20) is connected to a supply port 13, and liquid is supplied from the inside of the hollow fiber membrane group 22 to the outside of the hollow fiber membranes 21 through the hole 20 a of the core tube. The liquid is then discharged from an outlet 10 (located on the second end 4 b side of the core material 20) on the outside of the hollow fiber membrane group 22. In the modified example shown in FIG. 9 , the outside of the impermeable sheet 6 is filled with liquid at a low pressure close to the pressure of the liquid on the outlet 10 side, which is thought to cause the impermeable sheet 6 to bulge outward and lead to drift. However, even in this case, the above-described action of the solid fibers 7 prevents drift and prevents a decrease in membrane separation performance. In the modified example shown in FIG. 9 , the liquid inside the hollow fiber membranes 21 flows in the opposite direction to the above embodiment, so that it is countercurrent to the liquid flow outside the hollow fiber membranes 21 (see white arrows). However, the flow direction of the liquid inside the hollow fiber membranes 21 is not limited to this.

[0071] In the modified example shown in Figure 10, the position of the supply port 13 provided on the side of the container 1 is changed to the opposite side in the longitudinal direction of the core material 20. In this modified example, the liquid supplied from the supply port 13 passes through the region between the container 1 and the impermeable sheet 6 and is supplied to the outside of the hollow fiber membrane, as in Figure 6. In this case, the pressure of the liquid supplied from the supply port 13 in the region between the container 1 and the impermeable sheet 6 is higher than the pressure of the liquid outside the hollow fiber membrane, and therefore, it is expected that swelling of the impermeable sheet 6 over time will be suppressed.

[0072] 11, a supply port 13 is provided on an end surface in the longitudinal direction of the vessel 1. In this modification, the liquid supplied from the supply port 13 passes through the back side of a wall member 52 that communicates with the supply port 13 and the outside of the hollow fiber membrane, and is supplied to the outside of the hollow fiber membrane, similar to the case of FIG.

[0073] In the modification shown in Fig. 12, the position of the supply port 13 is changed to the end face in the longitudinal direction of the vessel 1, and the liquid supplied from the supply port 13 is supplied to the outside of the hollow fiber membranes as in Fig. 11. Other than that, it is the same as the modification shown in Fig. 7.

[0074] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0075] Comparative Example 1 The hollow fiber membrane of Comparative Example 1 was prepared as follows. 41 wt% cellulose triacetate (CTA, Daicel Chemical Industries, Ltd., LT35), 41.4 wt% N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical Corporation), 17.3 wt% ethylene glycol (EG, Mitsubishi Chemical Corporation), and 0.3 wt% benzoic acid (Nacalai Tesque, Inc.) were uniformly dissolved at 180°C to obtain a membrane-forming solution. The resulting membrane-forming solution was degassed under reduced pressure and then discharged at 162°C from an arc-type (three-section) nozzle into a space isolated from the outside air. After a space time of 0.03 seconds, the solution was immersed in a 10°C coagulation bath consisting of NMP / EG / water (21.9 / 9.1 / 69). Subsequently, the hollow fiber membrane was washed using a multi-stage tilted-tub water washing method and shaken off while still wet. The resulting hollow fiber membrane was immersed in 99°C water and subjected to hot water treatment for 20 minutes. The obtained hollow fiber membrane had an inner diameter of 90 μm and an outer diameter of 200 μm.

[0076] The hollow fiber membranes were placed in a cross-shaped configuration around a core tube (core material) with a hole at one end. The core tube was rotated around its axis, traversing the bundle of hollow fiber membranes and wrapping it around the core tube. Both ends of this assembly of hollow fiber membranes were then fixed by potting with epoxy resin, and both ends of the resin were cut to open the hollow fiber membranes, producing a hollow fiber membrane element. The outer periphery, excluding a section extending approximately 30 cm from the other end toward the center, was then covered with an impermeable sheet.

[0077] The obtained hollow fiber membrane element had a winding number of 2, a length of approximately 199.5 cm, an outer diameter of 265 mm, a hollow fiber membrane filling rate of 55%, and a membrane area of ​​1000 m ２ It should be noted that no solid fiber was wound in Comparative Example 1. This hollow fiber membrane element was loaded into a vessel 1 (pressure vessel) as shown in Figure 6 to prepare a hollow fiber membrane module.

[0078] In Example 1, as shown in Fig. 3, when the hollow fiber membranes 21 (hollow fiber membrane bundles 22a, 22b) were wound around the core material 20, a plurality of (18) solid fibers 7 were simultaneously wound. As a result, the solid fibers 7 were wound in a spiral shape in a plan view seen from the axial direction of the core material 20 (see Fig. 1(c)). Otherwise, the hollow fiber membrane element and hollow fiber membrane module of Example 1 were produced in the same manner as in Comparative Example 1.

[0079] <Evaluation of Water Permeability> The hollow fiber membrane modules obtained in Example 1 and Comparative Example 1 were subjected to the following water permeation measurement. The measurements were carried out in a countercurrent state as shown in Figure 6. The test results are shown in Figure 5. Figure 5 shows the ratio of water permeation rates when the water permeation rate of Comparative Example 1 is set to 1.

[0080] (Measurement of water permeation rate) An aqueous solution (auxiliary solution) with a sodium chloride concentration of 100 g / L was supplied to a hollow fiber membrane module (see FIG. 6) from a supply port 11 using a supply pump and allowed to flow out from a discharge port 12. Meanwhile, an aqueous solution (target solution) with a sodium chloride concentration of 100 g / L was supplied to the outside of the hollow fiber membrane from a supply port 13 using a high-pressure pump and allowed to flow out from a discharge port 10. The pressure and flow rate of the target solution flowing outside the hollow fiber membrane were adjusted using a flow control valve provided on the discharge port 10 side.

[0081] For the target solution, the supply pressure is P Ｈ１ (MPa), the supply flow rate is Q Ｈ１ (L / min), the discharged water volume Q Ｈ２ (L / min), and the supply flow rate of the auxiliary solution is Q Ｌ１ (L / min), the discharge flow rate is Q Ｌ２ (L / min), and the discharge pressure is P Ｌ２ (kPa), the flow rate increment (Q Ｌ２ -Q Ｌ１ ) was measured as the water permeation rate of the hollow fiber membrane module. The temperature was adjusted to 40°C. Ｈ１ = 7.0 MPa P Ｌ２ =50kPa or less Q Ｈ１ = 30 L / min Q Ｌ１ = 15 L / min

[0082] (Discussion) From the results shown in FIG. 5, it can be seen that Example 1 (membrane element with solid fiber introduction), in which the hollow fiber membrane was restrained by winding a solid fiber, had higher water permeability (larger amount of permeated water) than Comparative Example 1 (membrane element without solid fiber introduction), in which no solid fiber was wound around the hollow fiber membrane.

[0083] 1 Container, 10, 12 Discharge port, 11, 13 Supply port, 14, 15, 51, 52 Wall member, 20 Core material (core tube), 20a Hole, 20b Sealing material, 21 Hollow fiber membrane, 22 Hollow fiber membrane group, 22a, 22b Hollow fiber membrane bundle, 23 Cross point, 24 Cross point group, 3 Outside of hollow fiber membrane, 4a First end, 4b Second end, 41, 42 Resin wall, 6 Impermeable sheet, 61 Flow straightening member, 7 Solid fiber.

Claims

1. An axial flow type hollow fiber membrane element comprising: a core material; a hollow fiber membrane group consisting of a plurality of hollow fiber membranes arranged around the core material; and a solid fiber wound radially around the core material to restrain the hollow fiber membrane group, wherein in the hollow fiber membrane group, the main direction of liquid flow outside the plurality of hollow fiber membranes is the axial direction of the core material.

2. The hollow fiber membrane element according to claim 1, wherein the plurality of hollow fiber membranes are spirally wound around the core member so as to intersect with each other.

3. A hollow fiber membrane element according to claim 1 or 2, wherein the solid fibers are spirally wound in a plan view seen from the axial direction of the core material.

4. A hollow fiber membrane element according to any one of claims 1 to 3, wherein the core material is a core tube having a hole only near a first end, which is one end of the core material in the axial direction.

5. A hollow fiber membrane element as described in claim 4, wherein the radial periphery of the hollow fiber membrane group, except for the periphery near the second end, which is the end opposite the first end, is covered with an impermeable sheet.

6. A hollow fiber membrane element according to any one of claims 1 to 5, which is for osmotic pressure assisted reverse osmosis or reverse osmosis.

7. A hollow fiber membrane module comprising the hollow fiber membrane element according to any one of claims 1 to 6 and a container in which at least one hollow fiber membrane element is loaded.

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