Gasket and ion dialysis tank formed by laminating ion exchange membrane and gasket

Abstract

Provided are: a gasket laminated together with an ion exchange membrane, which is capable of suppressing internal leakage and liquid leakage occurring beside a flow distribution unit; and an ion dialysis tank comprising a laminate in which the ion exchange membrane and the gasket are laminated. The gasket is provided with: a processing unit that forms a space for ion exchange in a fastening-type ion exchange dialysis tank and forms a space for diffusion or dialysis in a fastening-type diffusion dialysis tank; and a gasket frame surrounding the treatment unit, in which a flow distribution unit for connecting the treatment unit and a communication hole formed in the ion exchange membrane laminated on the gasket is formed in the gasket frame, a flow distribution plate having a mesh structure is disposed in the flow distribution unit, and the aperture ratio of the mesh structure constituting the flow distribution plate is 26-90%. The thickness of the flow distribution plate is made to be 103%-128% of the thickness of the gasket frame.

Description

Technical Field

[0001] The present invention relates to a gasket laminated together with an ion exchange membrane in an ion dialysis cell, which is a fixed-type ion exchange dialysis cell or a fixed-type diffusion dialysis cell, and an ion dialysis cell formed by laminating the ion exchange membrane and the gasket. Background Art

[0002] Ion dialysis cells are known that are composed of a stacked portion comprising a laminated body including an ion exchange membrane and a gasket. These ion dialysis cells include at least an ion exchange dialysis cell, in which ionic substances in a solution are desalinated, concentrated, purified, or recovered by electrodialysis through electrical interaction with the ion exchange membrane; and a diffusion dialysis cell, in which acid or alkali is recovered from waste liquid by utilizing the concentration difference between the liquids on both sides of the ion exchange membrane, rather than relying on electrical interaction.

[0003] Electrolyte solution desalination technology using ion exchange dialysis cells and electrodialysis was first developed in the 1950s for the desalination of brine. Since then, it has been used in a variety of fields, including seawater concentration for salt production, desalination of soy sauce and whey, streamlining various chemical manufacturing processes, wastewater treatment, and separation of impurities from wine.

[0004] As a typical electrodialysis device using an ion exchange dialysis cell such as the one described above, a known fixed-type ion exchange dialysis cell utilizes a stacking unit in which a plurality of ion exchange membranes (anion exchange membranes and cation exchange membranes) and gaskets are stacked between a pair of electrodes, with the anion exchange membranes and cation exchange membranes alternately positioned between adjacent gaskets, and the stacked bodies are pressed from both ends of the stacking direction. Each gasket is provided with a processing unit sandwiched between the anion exchange membranes and the cation exchange membranes to function as an ion exchange chamber for ion exchange, and a gasket frame surrounding the processing unit. The gasket frame is provided with a flow distribution unit connecting the processing unit to a communication hole formed in the ion exchange membrane (see, for example, Patent Document 1).

[0005] As a fastened ion exchange dialysis cell capable of performing electrodialysis, in addition to the above-mentioned structure of stacking multiple anion exchange membranes, cation exchange membranes and gaskets to form a stacked portion for ion exchange, there are also known structures: an ion exchange membrane (bipolar membrane) having a structure consisting of an anion exchange layer and a cation exchange layer bonded together is stacked in combination with the anion exchange membrane, cation exchange membrane and gasket to form a stacked portion for ion exchange; a structure in which the bipolar membrane is stacked in combination with an anion exchange membrane and a gasket to form a stacked portion for ion exchange; and a structure in which the bipolar membrane is stacked in combination with a cation exchange membrane and a gasket to form a stacked portion for ion exchange.

[0006] In addition, when recovering acid from waste liquid using a fastened diffusion dialysis cell having a stacking portion formed by pressing a stacked body from both ends in its stacking direction, an anion exchange membrane and a gasket are stacked to form a stacking portion, and when recovering alkali from waste liquid, a cation exchange membrane and a gasket are stacked to form a stacking portion. In a treatment portion having the same structure as the gasket of the above-mentioned fastened ion exchange dialysis cell, a chamber for supplying waste liquid and water of acid or alkali is formed and waste liquid or water is supplied to the treatment portion, so that the acid or alkali contained in the waste liquid moves toward the water side through the anion exchange membrane or cation exchange membrane under the action of the concentration difference, thereby recovering the acid or alkali (for example, refer to patent document 2). Similar to the gasket used in the above-mentioned fastened ion exchange dialysis cell, the gasket used in the fastened diffusion dialysis cell also forms a processing portion that is clamped by an anion exchange membrane or a cation exchange membrane and functions as a chamber for diffusion, etc., and a gasket frame surrounding the processing portion, and a distribution portion is formed in the gasket frame that connects the processing portion and the connecting hole formed in the ion exchange membrane (anion exchange membrane or cation exchange membrane).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-14776

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2016-221507 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] In any of the above-mentioned fastening type ion exchange dialysis cells, there is provided one or more stacking sections formed by a stack of ion exchange membranes and gaskets, and a press machine is used to press the stacking section from the side to apply pressing force to maintain the stacking section, and a space is formed for the processing section and the distribution section based on the gasket to allow the liquid to be processed to flow and implement ion exchange, diffusion or dialysis.

[0013] In order to ensure space for the flow and treatment of the liquid to be treated, a sheet-like member is provided in the treatment section and the flow distribution section of the gasket sandwiched between the ion exchange membranes. The sheet-like member is composed of a sheet with a mesh structure, so that the raw liquid, acid, and alkaline waste liquid to be treated by desalination, supplied to the treatment section, can flow through the treatment section and the flow distribution section.

[0014] Typically, the thickness of the ion exchange membrane is thinner than that of the gasket. When a plurality of ion exchange membranes and gaskets are stacked to form a stacked portion, and a raw liquid, acid waste liquid, alkaline waste liquid, or the like to be subjected to desalination treatment is supplied to the treatment unit while maintaining the stacked portion in a state where a pressing force is applied by a press, the ion exchange membrane stacked on the gasket may sometimes be recessed toward the flow distribution portion formed on the gasket frame, creating a gap between the adjacent gaskets sandwiching the ion exchange membrane in the flow distribution portion. As a result, the flow distribution portion cannot be formed, and liquid flowing in the treatment portion of the adjacent gasket may leak between the gasket frame and the ion exchange membrane of the adjacent gasket, where liquid is not normally expected to flow (hereinafter referred to as "internal leakage"). In a fixed ion exchange dialysis cell, liquids from independent circulation systems (e.g., concentrate and desalted liquid) that would not normally mix mix, resulting in a problem of reduced efficiency of the ion dialysis cell.

[0015] In order to avoid the dents in the ion exchange membrane that could cause the aforementioned internal leakage, one approach is to install a mesh sheet with a small opening ratio and sufficient thickness relative to the gasket in the flow distribution section formed in the gasket frame. However, even if this can suppress the aforementioned internal leakage, the seal between the ion exchange membrane and the gasket near the flow distribution section will be insufficient, resulting in liquid leakage near the flow distribution section (the mating surface between the ion exchange membrane and the gasket). In the case of an electrodialysis cell, this also poses the problem of the ion exchange membrane burning and degrading under the action of electricity (stray current) flowing in the area where the liquid leaks, resulting in irreversible damage.

[0016] In order to prevent the aforementioned internal leakage and liquid leakage occurring next to the distribution section, it is necessary to appropriately manage the thickness of the mesh-structured sheet (hereinafter referred to as the "distribution plate") provided in the distribution section. The distribution plate is constructed of a mesh cloth structure or a woven cloth structure formed from strands of molten plastic of a resin, such as polyethylene, polyolefin, or other polypropylene, formed into a filamentary shape. The thickness of the distribution plate is determined by the thickness of the intersection of two strands, i.e., the diameter of the two strands multiplied by 2. When such a distribution plate is provided in the distribution section of a gasket and the ion exchange membrane and the gasket are stacked, the distribution plate of the distribution section formed in an overlapping position when viewed in the stacking direction is stacked together with the gasket frame and the ion exchange membrane. However, the intersection of the strands that determine the thickness of the distribution plate is not necessarily located in the same position between the two adjacent distribution plates. In this case, the effect of preventing the aforementioned internal leakage and liquid leakage occurring next to the distribution section is not fully achieved. That is, since the gasket frame is also generally formed of a soft resin material as described later, if the gasket frame and ion exchange membrane located between the two adjacent distribution plates are not clamped from both sides at the intersection of each distribution plate, their support will become uneven. In the gap portion of the mesh structure constituting the distribution plate on one side, the pressure from the intersection portion of the distribution plate on the other side will be applied to the ion exchange membrane via the elastic force of the gasket frame, causing a local depression. Moreover, when the number of stacked layers increases, this depression will become more pronounced, causing problems such as the aforementioned internal leakage. In this context, how to set the thickness of the distribution plate provided in the distribution portion and the opening ratio of the mesh structure to eliminate the aforementioned internal leakage and liquid leakage occurring next to the distribution portion has not yet been fully studied.

[0017] The present invention is made in view of the above facts, and its main technical problem is to provide a gasket stacked together with an ion exchange membrane, which can suppress the above-mentioned internal leakage and liquid leakage generated next to the distribution part, and an ion dialysis cell comprising a stacked body formed by stacking the ion exchange membrane and the gasket.

[0018] Solutions for solving problems

[0019] In order to solve the above-mentioned main technical problems, according to the present invention, a gasket is provided, which is stacked together with an ion exchange membrane in an ion dialysis cell which is a tight-fitting ion exchange dialysis cell or a tight-fitting diffusion dialysis cell, wherein the gasket comprises: a processing portion which forms a space for ion exchange in the tight-fitting ion exchange dialysis cell and a space for diffusion or dialysis in the tight-fitting diffusion dialysis cell; and a gasket frame which surrounds the processing portion, wherein a distribution portion is formed in the gasket frame for connecting the processing portion and a connecting hole formed in the ion exchange membrane stacked on the gasket, and a distribution plate with a mesh structure is provided in the distribution portion, so that the opening rate of the mesh structure constituting the distribution plate is formed to be 26% to 90%, and the thickness of the distribution plate is formed to be 103% to 128% of the thickness of the gasket frame.

[0020] In order to solve the above-mentioned main technical problems, an ion dialysis cell is provided, wherein the ion dialysis cell includes a stacked body formed by stacking one or more ion exchange membranes and the above-mentioned gaskets, and the number of stacked gaskets of the distribution plate stacked at the same position in the stacking direction of the ion exchange membranes and the gaskets is more than 30.

[0021] Effects of the Invention

[0022] The gasket of the present invention is stacked together with an ion exchange membrane in an ion dialysis cell which is a fastened ion exchange dialysis cell or a fastened diffusion dialysis cell, wherein the gasket comprises: a processing portion which forms a space for ion exchange in the fastened ion exchange dialysis cell and a space for diffusion or dialysis in the fastened diffusion dialysis cell; and a gasket frame which surrounds the processing portion, wherein a distribution portion is formed in the gasket frame to connect the processing portion and a connecting hole formed in the ion exchange membrane stacked on the gasket, and a distribution plate with a mesh structure is provided in the distribution portion, so that the opening rate of the mesh structure constituting the distribution plate is formed to be 26% to 90%, and the thickness of the distribution plate is formed to be the thickness of the gasket frame. The thickness is 103% to 128% of the thickness of the gasket, so it can prevent internal leakage such as liquid flowing in the processing part of the adjacent gasket from leaking into the space between the gasket frame and the ion exchange membrane of the adjacent gasket where liquid should not normally flow, and can eliminate the problem that liquids of independent circulation systems that would not mix originally (such as concentrated liquid and desalted liquid) are mixed, thereby reducing the efficiency of the ion dialysis cell, and can eliminate the following problem: when liquid leakage occurs next to the distribution part (the mating surface of the ion exchange membrane and the gasket) and it is an electrodialysis cell, the ion exchange membrane is burned and degraded under the action of electricity (stray current) flowing in the part where the liquid leakage occurs, resulting in irreversible damage.

[0023] In addition, the ion dialysis cell of the present invention includes a stacked body formed by stacking more than one ion exchange membrane and the above-mentioned gasket, and the number of stacked gaskets of the distribution plate stacked at the same position in the stacking direction of the ion exchange membrane and the gasket is more than 30. Therefore, in the ion dialysis cell, internal leakage such as liquid flowing in the treatment part of the adjacent gasket can be prevented from leaking between the gasket frame and the ion exchange membrane of the adjacent gasket where liquid should not normally flow. The problem of mixing liquids of independent circulation systems that would not originally be mixed (such as concentrated liquid and desalted liquid) thereby reducing the efficiency of the ion dialysis cell can be eliminated, and the following problem can be eliminated: when liquid leakage occurs next to the distribution part (the mating surface of the ion exchange membrane and the gasket) and it is an electrodialysis cell, the ion exchange membrane is burned and degraded under the action of electricity (stray current) flowing in the part where the liquid leakage occurs, resulting in irreversible damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic side view of a fixed-type ion exchange dialysis cell constituting the electrodialysis device of this embodiment.

[0025] Figure 2 It contains the components Figure 1 An exploded perspective view of a unit of a fastened ion exchange dialysis cell is shown, showing a gasket, an anion exchange membrane, a gasket, a cation exchange membrane, and a gasket stacked on the cation exchange membrane.

[0026] Figure 3(a) shows the Figure 2 FIG3(b) is a front view showing an enlarged portion of a region of the gasket where the flow distribution portion is formed, and FIG3(a) is a front view showing a further enlarged portion of the front view shown in FIG3(a).

[0027] Description of Reference Numerals

[0028] 1. Fastened ion exchange dialysis cell; 10a, anode chamber; 10b, cathode chamber; 12, 14, fastening plate; 20, spacer; 30, distribution plate; 31, 32, strands; A, anion exchange membrane; K, cation exchange membrane; G1, G2, gasket; G1a, processing unit; G1b, gasket frame; G1c, distribution unit; G1d, connecting hole; G2a, processing unit; G2b, gasket frame; G2c, distribution unit; G2d, connecting hole; N1, N2, electrode diaphragm. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of a gasket laminated together with an ion exchange membrane and an ion dialysis cell including a laminated body including the ion exchange membrane and the gasket, which are constructed according to the present invention, will be described in detail with reference to the accompanying drawings.

[0030] Hereinafter, with reference to the accompanying drawings, embodiments of an ion dialysis cell constructed in accordance with the present invention, comprising a gasket laminated together with an ion exchange membrane in an ion dialysis cell as a fixed-type ion exchange dialysis cell or a fixed-type diffusion dialysis cell, and an ion dialysis cell comprising a laminated body formed by laminating one or more ion exchange membranes and the gasket, will be described in detail. Furthermore, the ion dialysis cell described below is an example of a fixed-type ion exchange dialysis cell that desalinates or concentrates ionic substances in a solution through electrical interaction with the ion exchange membrane. However, the present invention is not limited to this embodiment and can also be applied to fixed-type diffusion dialysis cells that utilize a concentration difference between liquids sandwiching an ion exchange membrane, rather than relying on electrical interaction, to recover acids or bases from wastewater.

[0031] Figure 1 : This is a schematic side view of the fastening type ion exchange dialysis cell 1 of the present embodiment. For the convenience of explanation, it is a diagram showing the fastening type ion exchange dialysis cell 1 in a decomposed manner. The fastening type ion exchange dialysis cell 1 shown in the figure constitutes a so-called filter press type electrodialysis device. The fastening type ion exchange dialysis cell 1 is formed by stacking a plurality of ion exchange membranes and gaskets between the anode chamber 10a containing the anode plate and the cathode chamber 10b containing the cathode plate. More specifically, as shown in the figure, the gaskets G1 and G2 are arranged in a plurality of overlapping manners, and between these gaskets, cation exchange membranes K and anion exchange membranes A as ion exchange membranes are alternately arranged. As such cation exchange membranes K and anion exchange membranes A, known exchange membranes can be used. As shown in the figure, the gasket G1, anion exchange membrane A, gasket G2, and cation exchange membrane K surrounded by dotted lines are formed into a unit U, and the unit U is stacked in a plurality of ( Figure 1 (omitted in the figure) to form a stacking part S. At both ends of the stacking part S and between the anode chamber 10a and the cathode chamber 10b, electrode diaphragms N1 and N2 composed of ion exchange membranes are provided. Figure 1 The stacking portion S is held by a pair of fastening plates 12 and 14, and a pressing force is applied from a horizontal direction by a pressing device (not shown). Figure 1 This is a schematic side view of the fixed ion exchange dialysis cell 1 , not showing all the components, and including flow paths for the raw solution, concentrate, and desalted solution, pumps, and other components not shown.

[0032] exist Figure 2 In FIG, a perspective view of a gasket G1, an anion exchange membrane A, a gasket G2 and a cation exchange membrane K constituting one unit U of the above-mentioned fastened ion exchange dialysis cell 1 is shown. Similar units U are stacked before and after the illustrated unit U. Figure 2, the gasket G1 of the adjacent unit U stacked with the cation exchange membrane K of the unit U is also shown. The gasket G1, which is sandwiched between the above-mentioned cation exchange membrane K (or the electrode diaphragm N1 composed of an ion exchange membrane) and the anion exchange membrane A, includes a processing portion G1a for performing ion exchange and a gasket frame G1b surrounding the processing portion G1a. In the gasket frame G1b, distribution portions G1c are formed in a total of four locations, one above the other, that connect the processing portion G1a to the connecting holes of the ion exchange membrane stacked on the gasket G1, more specifically, the connecting holes Ab of the anion exchange membrane A. In addition, in the gasket frame G1b, connecting holes G1d, which are independent of the processing portion G1a and connected to the connecting holes Aa of the anion exchange membrane A stacked on the gasket G1, are also formed in a total of four locations, one above the other.

[0033] The gasket G2, which is stacked on the above-mentioned gasket G1 with an anion exchange membrane A interposed therebetween and is sandwiched between the anion exchange membrane A and the cation exchange membrane K, comprises: a processing section G2a, which forms a space (desalination chamber) for generating a desalted solution from a raw solution through ion exchange; and a gasket frame G2b, which surrounds the processing section G2a. In the gasket frame G2b, flow distribution sections G2c are formed in a total of four locations, top and bottom, connecting the processing section G2a with the connecting holes Aa and Ka formed in the anion exchange membrane A and the cation exchange membrane K sandwiching the gasket G2. Furthermore, in the gasket frame G2b, connecting holes G2d, which are independent of the processing section G2a and connect the connecting holes Ab and Kb formed in the anion exchange membrane A and the cation exchange membrane K sandwiching the gasket G2, are also formed in a total of four locations, top and bottom. In the gasket G2, a gasket G1, which constitutes adjacent units U, similar to the gasket G1, is stacked with the cation exchange membrane K interposed therebetween. Thus, the fixed ion exchange dialysis cell 1 of this embodiment is formed by stacking a plurality of units U each including a gasket G1, an anion exchange membrane A, a gasket G2, and a cation exchange membrane K. Furthermore, the processing portion G1a of the gasket G1, which is sandwiched between the cation exchange membrane K and the anion exchange membrane A, forms a space (concentration chamber) for generating a concentrated solution through ion exchange.

[0034] like Figure 2 As shown, a mesh-structured spacer 20 is provided in the processing portion G1a of gasket G1 and the processing portion G2a of gasket G2, and a mesh-structured distribution plate 30 is provided in the distribution portion G1c of gasket G1 and the distribution portion G2c of gasket G2. That is, the mesh-structured distribution plates 30 provided in the distribution portion G1c of gasket G1 and the distribution portion G2c of gasket G2 are stacked at the same position in the stacking direction of the units U, for the same number of units U.

[0035] FIG3(a) shows an enlarged front view of the gasket G1 in which the flow distribution portion G1c is formed. Figure 2As can be understood from FIG3(a), the spacer 20 is formed throughout the entire region of the processing section G1a. Rather than weaving strands of a resin, such as molten plastic of a polyolefin such as polyethylene or polypropylene, into a filamentary shape, the spacer 20 is formed using a single mesh sheet having a biaxial mesh structure. The provision of this spacer 20 allows the formation of a concentrating chamber in the processing section G1a without contact between the opposing ion exchange membranes.

[0036] As can be understood from FIG3(a), the distribution plate 30 is sized to correspond to the widthwise dimension of the distribution section G1c indicated by arrows X1-X2. It is also sized to extend from the boundary between the processing section G1a and the distribution section G1c to the communication holes Kb and Ab (indicated by dashed lines) of the cation exchange membrane K and anion exchange membrane A sandwiching the gasket G1. This plate is inserted to ensure a space between the cation exchange membrane K and anion exchange membrane A in the distribution section G1c sandwiching the gasket G1, allowing liquid to flow in the direction indicated by arrows Y1-Y2. Similar to the spacer 20, the distribution plate 30 is formed from a single sheet of mesh structure, not from strands of woven molten plastic of a resin, such as a polyolefin such as polyethylene or polypropylene, but rather from a biaxial mesh structure formed from these strands.

[0037] Here, the electrodialysis device has a commercially practical size, that is, the area of ​​the treatment section G1a (effective current-carrying area) is 50 to 14,000 cm 2 , more preferably 55 to 6000 cm 2 In the case of the above-mentioned embodiment, the dimension of the distribution section G1c in the width direction indicated by the arrow X1-X2 is generally 0.5 to 10 cm, preferably 0.8 to 5 cm. The dimension of the distribution section G1c in the length direction (the length from the boundary between the processing section G1a and the distribution section G1c to the connecting holes Ab and Kb indicated by the single-dot chain line) is generally 1.5 to 5.5 cm, preferably 1.7 to 5.0 cm. In addition, the material of the gasket frame is not particularly limited, but a soft resin material can usually be used, in particular, a soft resin with a hardness (JIS A) of about 60 to 90 degrees is preferred. Specifically, thermoplastic resins such as polyolefins and polyvinyl chloride, or rubbers such as styrene-butadiene rubber and ethylene-propylene rubber, as well as thermoplastic elastomers mixed with thermoplastic resins and rubbers can be used. In addition, the thickness of the gasket frame is generally 0.4 to 1.0 mm, and when used in an electrodialysis device, 0.5 to 1.0 mm is preferably used.

[0038] Here, the applicant arranges the distribution plate 30 in the distribution parts G1c and G2c to form gaskets G1 and G2, so that the gasket G1, the anion exchange membrane A, the gasket G2 and the cation exchange membrane K form a unit U. Figure 1 As shown, a stack portion S is formed by stacking a plurality of the units U. At both ends of the stack portion S and between the anode chamber 10a and the cathode chamber 10b, electrode diaphragms N1 and N2 composed of ion exchange membranes are provided. Figure 1 The stack S is clamped by a pair of fastening plates 12 and 14, and a pressing device (not shown) is used to apply a pressing force from the horizontal direction to maintain the stack S, thereby forming a fastened ion exchange dialysis cell 1. The pressing force acts only on the gasket frame surface of the stack, and the appropriate fastening pressure is generally 0.6N / mm 2 ±0.1N / mm 2 .

[0039] The structure of the distribution plate 30 will be described in more detail with reference to FIG3(b) in addition to FIG3(a) above. FIG3(b) shows an enlarged view of the area indicated by the dashed line R in the distribution plate 30 shown in FIG3(a). In FIG3(b), the direction indicated by the arrows Y1-Y2 represents the flow direction of the liquid in the distribution section G1c, and the direction indicated by the arrows X1-X2 represents the width of the distribution section G1c. As shown in FIG3(b), the distribution plate 30 is a sheet having a mesh structure, formed by welding so that strands 31, 31 tilted to the left and strands 32, 32 tilted to the right intersect. Openings P1', P2', P3', and P4' are formed by points P1', P2', P3', and P4' within the quadrilateral P1P2P3P4 formed by the intersection points P1, P2, P3, and P4 of strands 31 and 32. In this embodiment, in the openings P1'P2'P3'P4' shown in the figure, the spacing a in the liquid flow direction indicated by the arrow Y1-Y2 (= openings P1'P3') is formed to be longer than the spacing b in the width direction indicated by the arrow X1-X2 orthogonal to the liquid flow direction (= openings P2'P4'), but the present invention is not limited to this.

[0040] The aperture ratio formed by the distribution plate 30 can generally be described using the ratio of the area of ​​the openings P1'P2'P3'P4' relative to the area of ​​the quadrilateral P1P2P3P4 formed by the intersections of the strands 31, 31 and the strands 32, 32 shown in Figure 3(b). Therefore, assuming that the positions of the intersections P1, P2, P3, and P4 between the strands 31 and 32 remain unchanged, if the diameters of the strands 31 and 32 are increased (thickened), the aperture ratio decreases, and if the diameters are decreased (thinned), the aperture ratio increases. In addition, even if the diameters of the strands 31 and 32 are not changed, the aperture ratio can be changed by moving the intersections P1, P2, P3, and P4 between the strands 31 and 32 closer or further away. The wires 31 and 32 forming the mesh structures of the spacer 20 and the manifold 30, respectively, typically have a diameter of 0.25 to 0.55 mm, more preferably 0.28 to 0.45 mm. The thickness of the manifold 30 is set to correspond to the thickness of the gasket. The thickness of the manifold 30 is determined by the thicknesses at the intersection points P1, P2, P3, and P4 of the two wires when the manifold 30 is formed.

[0041] Here, the applicants have verified whether, while varying the combinations of the opening ratio of the distribution plate 30, the thickness of the distribution plate 30, the thickness of the gaskets, and the number of units U constituting the stacked portion S when constructing the aforementioned fastened ion exchange dialysis cell 1, they have verified whether internal leakage occurs in the vicinity of the distribution portions G1c and G2c, such as liquid flowing in the processing portions of adjacently arranged gaskets leaking between the gasket frames G1b and G2b and the ion exchange membranes (anion exchange membrane A and cation exchange membrane K), where liquid is not normally expected to flow, and whether liquid leakage occurs adjacent to the distribution portions G1c and G2c (at the mating surface between the ion exchange membranes and the gasket frames). The verification results are described below.

[0042] It was confirmed that when the mesh structure constituting the distribution plate 30 has an opening ratio of 26% to 90% and the thickness of the distribution plate is 103% to 128% of the thickness of the gasket frame, the aforementioned internal leakage and liquid leakage that can cause stray current are less likely to occur. An opening ratio of less than 26% can suppress ion exchange membrane depression, but excessive pressure loss increases, hindering the flow of liquid in the distribution sections G1c and G2c, making this undesirable. In addition, it was found that when the opening ratio is greater than 90%, although the pressure loss of the distribution parts G1c and G2c is reduced, when multiple distribution plates 30 are stacked, the probability that the intersection points P1, P2, P3, and P4 in adjacent distribution plates 30 do not overlap in the stacking direction will inevitably increase. In the gap portion of the mesh structure constituting the distribution plate on one side, the ion exchange membrane pressed from the intersection portion of the distribution plate on the other side through the elastic force of the gasket frame will be locally recessed, thereby easily causing the above-mentioned internal leakage.

[0043] Furthermore, it was discovered that even when the opening ratio is set as described above, if the thickness of the distribution plate 30 is less than 103% relative to the thickness of the gasket frames G1b and G2b, the intersection points P1, P2, P3, and P4 of adjacent distribution plates 30 are not completely aligned, as described above. Consequently, localized depressions of the ion exchange membranes can occur within the interstices of the mesh structure of the distribution plate 30, easily leading to the aforementioned internal leakage. This problem becomes more pronounced with increasing opening ratios. Furthermore, when the thickness of the distribution plate 30 exceeds 128% of the thickness of the gasket frames G1b and G2b, the excess thickness of the distribution plate 30 leads to insufficient sealing between the ion exchange membranes (anion exchange membrane A, cation exchange membrane K) and the gasket frames G1b and G2b, causing liquid leakage near the distribution plate 30 and reducing the efficiency of the ion dialysis cell. This problem becomes more pronounced with decreasing opening ratios. The above-mentioned effects are not limited by the number of stacked units U, but it has been confirmed that a greater effect can be obtained when the number of units U is 30 or more, more preferably 35 to 400.

[0044] In addition, when the number of stacked units U is greater than 30, it is preferred that the opening rate of the mesh structure constituting the above-mentioned distribution plate 30 is formed to be 30-85% and the thickness of the distribution plate 30 is formed to be 108-119% of the thickness of the gasket frames G1b and G2b. It is more preferred that when the number of stacked units U is greater than 35 and less than 400, the opening rate of the mesh structure constituting the above-mentioned distribution plate 30 is formed to be 40-80%, and the thickness of the distribution plate 30 is formed to be 109-115% of the thickness of the gasket frames G1b and G2b. It is further preferred that when the number of units U is greater than 40 and less than 350, the opening rate of the mesh structure constituting the above-mentioned distribution plate 30 is formed to be 50-80%, and the thickness of the distribution plate 30 is formed to be 109-113% of the thickness of the gasket frames G1b and G2b. In addition, in this embodiment, the number of the above-mentioned units U is consistent with the number of gaskets stacked on the distribution plate at the same position in the stacking direction of the ion exchange membrane and the gasket, and the number of the above-mentioned units U has the same meaning as the number of stacked gaskets stacked on the distribution plate at the same position in the stacking direction of the ion exchange membrane and the gasket.

[0045] By having the above-mentioned structure, it is possible to suppress internal leakage such as liquid flowing in the processing part of the adjacent gasket from leaking into the gasket frame and ion exchange membrane of the adjacent gasket where liquid should not normally flow. It is possible to eliminate the problem that liquids of independent circulation systems (such as concentrated liquid and desalted liquid) that would not originally mix in the fastened ion exchange dialysis cell are mixed, thereby reducing the efficiency of the ion dialysis cell. It is also possible to eliminate the following problem: when liquid leakage occurs next to the distribution part (the mating surface of the ion exchange membrane and the gasket) and it is an electrodialysis cell, the ion exchange membrane is burned and degraded under the action of electricity (stray current) flowing in the part where the liquid leakage occurs, resulting in irreversible damage.

[0046] Furthermore, as described above, the spacing a of the openings P1', P2', P3', and P4' in the direction of liquid flow at the distribution section G1c (the direction of the arrow Y1-Y2) is preferably formed to be longer than the spacing b in the width direction X1-X2, which is orthogonal to the liquid flow direction Y1-Y2 at the distribution section G1c. If the spacing a is shorter than the spacing b, the smoothness of the flow in the distribution section G1c will be impaired, and the pressure loss at the distribution section G1c will increase, which is not preferred. Therefore, the spacing a is preferably longer than the spacing b by at least 1.1 times, more preferably 1.1 to 2.2 times, more preferably 1.3 to 2.2 times, and particularly preferably 1.5 to 2.2 times. In addition, when the wire diameter of the strands forming the mesh structure is the general wire diameter, the spacing a is generally 0.25 to 0.55 mm, and more preferably 0.28 to 0.45 mm.

[0047] The present invention is not limited to the above-mentioned embodiment, but includes various modifications. In the above-mentioned embodiment, an example of applying a laminate of an ion exchange membrane and a gasket constructed based on the present invention to a fastened ion exchange dialysis cell capable of performing electrodialysis is shown. However, for example, the present invention can also be applied to a structure in which an ion exchange membrane (bipolar membrane) having a structure consisting of an anion exchange layer and a cation exchange layer bonded together is stacked together with the above-mentioned anion exchange membrane, cation exchange membrane, and gasket to form a stacked portion for ion exchange; a structure in which the bipolar membrane is stacked together with an anion exchange membrane and a gasket to form a stacked portion for ion exchange; a structure in which the bipolar membrane is stacked together with a cation exchange membrane and a gasket to form a stacked portion for ion exchange; or an ion dialysis cell in which an ion exchange membrane and a gasket are stacked together to perform diffusion dialysis. That is, the present invention is effective in an ion dialysis tank comprising a stacked body formed by stacking one or more ion exchange membranes and the above-mentioned gaskets. More preferably, a better effect can be achieved when the number of stacked gaskets of the distribution plate stacked at the same position in the stacking direction of the ion exchange membranes and the gaskets is more than 30 (the number of units U is more than 30) which is commercially practical in the ion dialysis tank.

[0048] In addition, the communicating holes (Aa, Ab, Ka, Kb) of the ion exchange membrane (anion exchange membrane A, cation exchange membrane K) in the above-mentioned embodiment are each formed with 4 in total on the top and bottom, but the present invention is not limited to this, and other numbers can be used, and their sizes can also be set as needed. In addition, in the above-mentioned embodiment, the communicating holes Aa, Ab, Ka, Kb of the anion exchange membrane A and the cation exchange membrane K are roughly quadrilateral, but the present invention is not limited to this, and circular shapes can also be used. Even if the communicating holes Aa and Ka are circular, according to the present invention, the same effects as those in the above-mentioned embodiment can be achieved.

Claims

1. A gasket stacked together with an ion exchange membrane in an ion dialysis cell that is a fixed ion exchange dialysis cell or a fixed diffusion dialysis cell, wherein: The gasket has: a processing section that forms a space for ion exchange in the fixed ion exchange dialysis cell and a space for diffusion or dialysis in the fixed diffusion dialysis cell; as well as a gasket frame surrounding the processing portion, The gasket frame is provided with a flow distribution portion that connects the processing portion and a communication hole formed in the ion exchange membrane stacked on the gasket. The distribution part is provided with a distribution plate with a mesh structure. The opening ratio of the mesh structure constituting the manifold plate is set to 26% to 90%, and the thickness of the manifold plate is set to 103% to 128% of the thickness of the gasket frame.

2. An ion dialysis cell, wherein: The ion dialysis cell comprises a stacked body formed by stacking one or more ion exchange membranes and the gasket according to claim 1, wherein the number of stacked gaskets of the distribution plate stacked at the same position in the stacking direction of the ion exchange membranes and the gaskets is 30 or more.

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