Gasket and ion dialysis tank in which ion exchange membrane and gasket are laminated

Abstract

To provide a gasket laminated together with an ion exchange membrane capable of suppressing internal leakage or liquid leakage occurring on the side of a distribution part, and an ion dialysis tank in which the ion exchange membrane and the gasket are laminated.SOLUTION: This gasket comprises: a processing unit that forms a space in which ion exchanging is executed in a fastening-type ion exchange dialysis tank and forms a space in which diffusion or dialysis is executed in a fastening-type diffusion dialysis tank; and a gasket frame surrounding the processing unit. In the gasket frame, a distribution part for connecting the processing unit and a communication hole formed in the ion exchange membrane laminated on the gasket is formed. A distribution plate of a network structure is distributed at the distribution part. The numerical aperture of the network structure constituting the distribution plate is 26-90%. The thickness of the distribution plate is 103-128% with respect to the thickness of the gasket frame.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a gasket to be laminated together with an ion exchange membrane in an ion dialysis cell that is a clamping type ion exchange dialysis cell or a clamping type diffusion dialysis cell, and to an ion dialysis cell in which an ion exchange membrane and the gasket are laminated. [Background technology]

[0002] Ion dialysis cells composed of a stack including a laminate of ion exchange membranes and gaskets are known. These ion dialysis cells include at least two types: ion exchange dialysis cells that use ion exchange membranes and electricity to perform electrodialysis to demineralize, concentrate, purify, and recover ionic substances in a solution, and diffusion dialysis cells that recover acids or alkalis from waste liquids by utilizing the concentration difference between the liquids on either side of an ion exchange membrane, without relying on electricity.

[0003] The technology for desalination of electrolyte solutions by electrodialysis using ion exchange dialysis cells was first developed in the 1950s for the purpose of desalination of brine. Since then, it has been used in a variety of fields, including concentrating seawater to produce table salt, desalination of soy sauce and whey, streamlining various chemical manufacturing processes, wastewater treatment, and separation of impurities in wine.

[0004] A typical electrodialysis device using the above-described ion exchange dialysis cell is a clamping-type ion exchange dialysis cell, which has a plurality of ion exchange membranes (anion exchange membranes and cation exchange membranes) and gaskets stacked between a pair of electrodes, with anion exchange membranes and cation exchange membranes alternately positioned between adjacent gaskets, and which is used by pressing the stack from both ends in the stacking direction. Each gasket has a treatment section that functions as an ion exchange chamber sandwiched between the anion exchange membrane and the cation exchange membrane and where ion exchange takes place, and a gasket frame surrounding the treatment section, and the gasket frame has a distribution section that connects the treatment section to communication holes formed in the ion exchange membranes (see, for example, Patent Document 1).

[0005] As clamping type ion exchange dialysis cells that enable electrodialysis, in addition to the configuration in which a stack is formed by laminating a large number of the above-mentioned anion exchange membranes, cation exchange membranes, and gaskets to perform ion exchange, other known configurations include a configuration in which a stack is formed by laminating an ion exchange membrane (bipolar membrane) having a structure in which an anion exchange layer and a cation exchange layer are bonded together with the above-mentioned anion exchange membrane, cation exchange membrane, and gasket, and the like to perform ion exchange; a configuration in which a stack is formed by laminating a bipolar membrane, an anion exchange membrane, and gasket, and the like to perform ion exchange; and a configuration in which a stack is formed by laminating a bipolar membrane, an anion exchange membrane, and gasket, and the like to perform ion exchange.

[0006] Furthermore, when recovering acid from waste liquid using a clamping diffusion dialysis tank in which a stack is formed by compressing the laminate from both ends in the stacking direction, anion exchange membranes and gaskets are stacked to form a stack, and when recovering alkali from waste liquid, cation exchange membranes and gaskets are stacked to form a stack. A treatment section having a configuration similar to that of the gasket in the clamping ion exchange dialysis tank described above is provided with a chamber for supplying acid or alkaline waste liquid and water. By supplying the waste liquid or water to this treatment section, the acid or alkali contained in the waste liquid permeates the anion or cation exchange membrane and migrates to the water side due to the difference in concentration, thereby recovering the acid or alkali (see, for example, Patent Document 2). Similar to the gasket used in the clamping ion exchange dialysis tank described above, the gasket used in this clamping diffusion dialysis tank also has a treatment section sandwiched between anion or cation exchange membranes and functioning as a chamber for diffusion, etc., and a gasket frame surrounding the treatment section. The gasket frame has a distribution section connecting the treatment section to a communication hole formed in the ion exchange membrane (anion or cation exchange membrane). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-14776 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-221507 Summary of the Invention [Problem to be solved by the invention]

[0008] In any of the clamping-type ion exchange dialysis cells described above, one or more stacks each formed as a laminate of ion exchange membranes and gaskets are disposed, and a pressing machine presses the stack from the side to apply a pressing force to hold the stack in place. At the same time, a space is formed by the treatment section and the distribution section of the gasket, through which the liquid to be treated flows, thereby carrying out ion exchange, diffusion, or dialysis.

[0009] In the treatment section and distribution section of the gasket sandwiched between the ion exchange membranes, a sheet-like member is disposed to ensure a space for the liquid to be treated to flow and be treated. This sheet-like member is made of a mesh-structured sheet so that the raw liquid to be desalted, acid or alkaline waste liquid, etc., supplied to the treatment section can flow through the treatment section and distribution section.

[0010] Generally, the thickness of an ion exchange membrane is thinner than that of a gasket. When a stack of multiple ion exchange membranes and gaskets is formed and the stack is held in place by applying pressure with a press, a raw liquid to be desalted, an acid waste liquid, an alkaline waste liquid, or the like is supplied to the treatment section. The ion exchange membrane stacked on the gasket may sag toward the distribution section formed in the gasket frame, creating a gap between the adjacent gaskets across the ion exchange membrane. This can result in leakage of liquids flowing through the treatment section of the adjacent gasket (hereinafter referred to as "internal leakage") between the gasket frame and the ion exchange membrane of the adjacent gasket, through which no distribution section is formed and through which liquids normally do not flow. This can cause intermixing of liquids in separate circulation systems (e.g., concentrated liquid and desalted liquid) in a clamping-type ion exchange dialysis tank, reducing the efficiency of the ion exchange dialysis tank.

[0011] In order to avoid the collapse of the ion exchange membrane, which causes the internal leakage, it is conceivable to provide a mesh-structured sheet with a small opening ratio and sufficient thickness relative to the gasket in the distribution section formed in the gasket frame. However, in this case, even if the internal leakage is suppressed, the seal between the ion exchange membrane and the gasket near the distribution section will be insufficient, causing leakage of liquid at the side of the distribution section (the mating surface between the ion exchange membrane and the gasket). In the case of an electrodialysis cell, electricity (stray current) flowing through the leaking section can burn and deteriorate the ion exchange membrane, resulting in irreversible damage.

[0012] To prevent the internal leakage and leakage around the sides of the distribution section, it is necessary to properly control the thickness of the mesh-structured sheet (hereinafter referred to as "distribution plate") disposed in the distribution section. Here, the distribution plate is a woven or braided structure made of strands of molten plastic resin, such as polyolefins like polyethylene and polypropylene, formed into threads. The thickness is determined by the thickness at the intersection of two strands, i.e., twice the diameter of the two strands. When such a distribution plate is disposed in the distribution section of a gasket and an ion exchange membrane and a gasket are stacked, the distribution plates of the distribution section, which are formed at overlapping positions in the stacking direction, are stacked together with the gasket frame and the ion exchange membrane. However, the intersections of the strands, which determine the thickness of the distribution plate, do not necessarily coincide with each other on adjacent plates. In such cases, the effectiveness of preventing internal leakage and leakage around the sides of the distribution section is not fully achieved. That is, because the gasket frame is typically made of a soft resin material, as described below, the gasket frame and ion exchange membrane located between the two adjacent flow distribution plates must be sandwiched from both sides at the intersections of the flow distribution plates, resulting in uneven support. Pressure from the intersections of the flow distribution plates on one side of the mesh structure is applied to the ion exchange membrane through the elastic force of the gasket frame in the gaps of the mesh structure of the flow distribution plate on the other side, causing partial sagging. As the number of stacked bodies increases, this sagging becomes more pronounced, leading to problems such as internal leakage. Given this background, sufficient consideration has not been given to how to set the thickness of the flow distribution plates disposed in the flow distribution section and the aperture ratio of the mesh structure to eliminate the above-mentioned internal leakage and liquid leakage occurring around the side of the flow distribution section.

[0013] The present invention has been made in view of the above facts, and its main technical object is to provide a gasket that is laminated together with an ion exchange membrane, which can suppress the above-mentioned internal leakage and liquid leakage that occurs beside a distribution section, and an ion dialysis cell including a laminate in which an ion exchange membrane and the gasket are laminated. [Means for solving the problem]

[0014] In order to solve the above-mentioned main technical problem, the present invention provides a gasket to be laminated together with an ion exchange membrane in an ion dialysis cell that is a clamping type ion exchange dialysis cell or a clamping type diffusion dialysis cell, the gasket comprising: a treatment section that forms a space where ion exchange takes place in a clamping type ion exchange dialysis cell, or a space where diffusion or dialysis takes place in a clamping type diffusion dialysis cell; and a gasket frame surrounding the treatment section, wherein the gasket frame is formed with a distribution section that connects the treatment section with communicating holes formed in the ion exchange membrane laminated to the gasket, and a mesh-structured distribution plate is disposed in the distribution section, the mesh structure constituting the distribution plate 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.

[0015] In order to solve the above-mentioned main technical problem, there is provided an ion dialysis cell which includes a laminate in which one or more types of ion exchange membranes and the above-mentioned gaskets are laminated, and in which the number of stacked gaskets is 30 or more, and the flow distribution plates are stacked at the same position in the stacking direction of the ion exchange membranes and gaskets. [Effects of the Invention]

[0016] The gasket of the present invention is a gasket to be laminated together with an ion exchange membrane in an ion dialysis cell that is a clamping type ion exchange dialysis cell or a clamping type diffusion dialysis cell, and the gasket comprises a treatment section that forms a space where ion exchange takes place in a clamping type ion exchange dialysis cell, or a space where diffusion or dialysis takes place in a clamping type diffusion dialysis cell, and a gasket frame that surrounds the treatment section, and the gasket frame has a flow distribution section that connects the treatment section with communication holes formed in the ion exchange membrane laminated on the gasket, and a mesh-structured distribution plate is disposed in the flow distribution section, and the mesh structure that constitutes the distribution plate has an opening rate of 26 to 90%, and the thickness of the distribution plate is 26 to 90% of the opening rate of the gasket frame. Because the gasket is formed to a thickness that is 103 to 128% of the original thickness, internal leakage, such as liquid flowing through the processing section of an adjacent gasket, is prevented from occurring between the gasket frame and ion exchange membrane of an adjacent gasket, where liquid would not normally flow, thereby eliminating the problem of liquids in independent circulation systems (for example, concentrated liquid and desalted liquid) that would not normally mix mixing together, reducing the efficiency of the ion dialysis cell.It also eliminates the problem of liquid leakage at the side of the distribution section (the joint between the ion exchange membrane and the gasket frame) and, in the case of an electrodialysis cell, the electricity (stray current) flowing in the part where the liquid leakage has occurred, burning and deteriorating the ion exchange membrane and causing irreversible damage.

[0017] Furthermore, the ion dialysis cell of the present invention includes a laminate comprising one or more types of ion exchange membranes and the above-described gaskets, and the number of stacked gaskets is 30 or more, with the distribution plates stacked at the same position in the stacking direction of the ion exchange membranes and gaskets. Therefore, in the ion dialysis cell, internal leakage, such as leakage of liquid flowing through the processing section of an adjacent gasket, between the ion exchange membrane and the gasket frame of an adjacent gasket, through which liquid would not normally flow, is prevented. This eliminates the problem of mixing of independent circulating liquids (e.g., concentrated liquid and desalted liquid) that would not normally mix, resulting in a decrease in the efficiency of the ion dialysis cell. It also eliminates the problem of liquid leakage at the side of the distribution section (the mating surface between the ion exchange membrane and the gasket frame) and, in the case of an electrodialysis cell, burning and deterioration of the ion exchange membrane due to electricity (stray current) flowing through the leaking part, resulting in irreversible damage, of the ion exchange membrane. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic side view of a clamping-type ion exchange dialysis cell constituting the electrodialysis apparatus of the present embodiment. [Figure 2] FIG. 2 is an exploded perspective view showing a gasket, an anion exchange membrane, a gasket, and a cation exchange membrane that constitute a unit constituting the clamping type ion exchange dialysis cell shown in FIG. 1, as well as a gasket laminated on the cation exchange membrane. [Figure 3] 3(a) is an enlarged front view of the gasket shown in FIG. 2 in which a flow distribution portion is formed, and FIG. 3(b) is a further enlarged front view of a portion of the front view shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of a gasket laminated together with an ion exchange membrane configured according to the present invention, and an ion dialysis cell including a laminate in which an ion exchange membrane and the gasket are laminated, will be described in detail with reference to the accompanying drawings.

[0020] Hereinafter, embodiments of a gasket laminated together with an ion exchange membrane in an ion dialysis cell that is a clamping type ion exchange dialysis cell or a clamping type diffusion dialysis cell constructed according to the present invention, and an ion dialysis cell including a laminate in which the gasket and one or more types of ion exchange membranes are laminated, will be described in detail with reference to the accompanying drawings. Note that the ion dialysis cell described below is an example of a clamping type ion exchange dialysis cell that desalinates and concentrates ionic substances in a solution using the action of an ion exchange membrane and electricity. However, the present invention is not limited to this, and can also be applied to a clamping type diffusion dialysis cell that recovers acid or alkali from waste liquid by utilizing the concentration difference between the liquids on either side of the ion exchange membrane, without relying on the action of electricity.

[0021] FIG. 1 is a schematic side view of a clamp-type ion exchange dialysis cell 1 according to this embodiment, and for ease of explanation, the clamp-type ion exchange dialysis cell 1 is shown exploded. The illustrated clamp-type ion exchange dialysis cell 1 constitutes a so-called filter press-type electrodialysis device. This clamp-type ion exchange dialysis cell 1 is formed by stacking multiple ion exchange membrane and gasket laminates between an anode chamber 10a containing an anode plate and a cathode chamber 10b containing a cathode plate. More specifically, as shown in the figure, multiple gaskets G1 and G2 are stacked, and ion exchange membranes, cation exchange membrane K and anion exchange membrane A, are alternately disposed between these gaskets. Well-known cation exchange membranes K and anion exchange membrane A are used as these membranes. As shown in the figure, a gasket G1, an anion exchange membrane A, a gasket G2, and a cation exchange membrane K, each surrounded by a dashed line, are formed as a unit U, and a stack S is formed by stacking multiple units U (not shown in FIG. 1). Electrode diaphragms N1 and N2 made of ion exchange membranes are disposed at both ends of the stack S, between the anode chamber 10a and the cathode chamber 10b. The stack S is sandwiched between a pair of clamping plates 12 and 14 shown in Fig. 1 and is held in place by applying a horizontal pressing force using a press device (not shown). Note that Fig. 1 is a side view showing an outline of a clamping-type ion exchange dialysis cell 1 and does not show the entire configuration. Components other than those shown, including flow paths for the raw solution, concentrated solution, and desalted solution, pumps, and the like, have been omitted as appropriate.

[0022] FIG. 2 shows a perspective view of the gasket G1, anion exchange membrane A, gasket G2, and cation exchange membrane K that constitute one unit U of the clamping-type ion exchange dialysis tank 1. Similar units U are stacked before and after the illustrated unit U, and FIG. 2 also shows the gasket G1 of an adjacent unit U that is stacked on the cation exchange membrane K of the unit U. The gasket G1, sandwiched between the cation exchange membrane K (or electrode diaphragm N1 made of an ion exchange membrane) and the anion exchange membrane A, includes a processing section G1a where ion exchange occurs and a gasket frame G1b that surrounds the processing section G1a. The gasket frame G1b has four flow distribution sections G1c formed at the top and bottom that connect the processing section G1a to the through-holes of the ion exchange membranes stacked on the gasket G1, more specifically, the through-holes Ab of the anion exchange membrane A. The gasket frame G1b also has four communication holes G1d formed at the top and bottom, which are independent from the processing section G1a and communicate with the communication holes Aa of the anion exchange membrane A laminated on the gasket G1.

[0023] The gasket G2 is laminated on the gasket G1 with an anion exchange membrane A interposed therebetween and sandwiched between the anion exchange membrane A and the cation exchange membrane K. The gasket G2 includes a processing section G2a that forms a space (demineralization compartment) for producing a desalted solution from a raw solution by ion exchange, and a gasket frame G2b that surrounds the processing section G2a. The gasket frame G2b is formed with four distribution sections G2c (upper and lower) that connect the processing section G2a to the communicating holes Aa of the anion exchange membrane A and the communicating holes Ka of the cation exchange membrane K that sandwich the gasket G2. The gasket frame G2b also has four communication holes G2d (upper and lower) that are independent of the processing section G2a and connect the communicating holes Ab of the anion exchange membrane A and the communicating holes Kb of the cation exchange membrane K that sandwich the gasket G2. The gasket G2 is laminated with a gasket G1 that constitutes an adjacent unit U similar to that described above, with the cation exchange membrane K interposed therebetween. As described above, the clamping type ion exchange dialysis tank 1 of this embodiment is formed by stacking a plurality of units U, each of which includes a gasket G1, an anion exchange membrane A, a gasket G2, and a cation exchange membrane K. The processing section 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) in which a concentrated solution is produced by ion exchange.

[0024] 2, mesh-structured spacers 20 are disposed in the processing portions G1a of gasket G1 and G2a of gasket G2, and mesh-structured flow distribution plates 30 are disposed in the flow distribution portions G1c of gasket G1 and G2c of gasket G2. That is, the mesh-structured flow distribution plates 30 disposed in the flow distribution portions G1c of gasket G1 and G2c of gasket G2 are stacked at the same position in the stacking direction of the units U, the number of which is equal to the number of units U.

[0025] Figure 3(a) shows an enlarged front view of the gasket G1, showing the area where the flow distribution section G1c is formed. As can be seen from Figures 2 and 3(a), the spacer 20 is formed over the entire processing section G1a and is a single mesh-structured sheet made of a biaxially woven fabric of strands of molten plastic resin, such as polyethylene or polyolefin, formed into threads. By providing this spacer 20, concentration chambers can be formed in the processing section G1a without the opposing ion exchange membranes coming into contact with each other.

[0026] 3(a), the flow distribution plate 30 is formed with a size corresponding to the width dimension of the flow distribution section G1c indicated by the arrows X1-X2, and with a size extending from the boundary between the processing section G1a and the flow distribution section G1c to the through-holes Kb of the cation exchange membrane K and the through-holes Ab of the anion exchange membrane A (indicated by the dashed dotted line) that sandwich the gasket G1, and is inserted between the cation exchange membrane K and the anion exchange membrane A that sandwich the flow distribution section G1c of the gasket G1 to ensure a space for liquid to flow in the direction indicated by the arrows Y1-Y2. Like the spacer 20, the flow distribution plate 30 is formed from a single mesh-structure sheet in which strands of molten plastic resin, such as polyolefin plastics such as polyethylene and polypropylene, are formed into a filamentous shape and then woven into a biaxial fabric structure.

[0027] Here, the electrodialysis apparatus is of a commercially practical size, and the area of ​​the treatment section G1a (effective current-carrying area) is 50 to 14,000 cm 2 , more preferably 55 to 6,000 cm 2In this case, the width of the distribution section G1c indicated by the arrow X1-X2 is generally 0.5 to 10 cm, preferably 0.8 to 5 cm. The length of the distribution section G1c (the length from the boundary between the processing section G1a and the distribution section G1c to the communicating holes Ab and Kb indicated by the dashed dotted line) is generally 1.5 to 5.5 cm, preferably 1.7 to 5.0 cm. The material of the gasket frame is not particularly limited, but soft resin materials are generally used, and soft resins with a hardness (JIS A) of approximately 60 to 90 are particularly preferred. Specifically, thermoplastic resins such as polyolefins and vinyl chloride, rubbers such as styrene-butadiene rubber and ethylene-propylene rubber, and thermoplastic elastomers that are mixtures of thermoplastic resins and rubbers are used. The thickness of the gasket frame is generally 0.4 to 1.0 mm, and when used in an electrodialysis device, a thickness of 0.5 to 1.0 mm is preferably used.

[0028] Here, the applicant arranges the above-mentioned flow distribution plates 30 in the flow distribution sections G1c and G2c to form gaskets G1 and G2, and the gasket G1, the above-mentioned anion exchange membrane A, the gasket G2, and the above-mentioned cation exchange membrane K are formed into one unit U. Next, as shown in FIG. 1, a plurality of the units U are stacked to form a stack S. Electrode diaphragms N1 and N2 made of ion exchange membranes are arranged at both ends of the stack S, between the anode chamber 10a and the cathode chamber 10b. Furthermore, the stack S is sandwiched between a pair of clamping plates 12 and 14 shown in FIG. 1, and is held in place by applying a horizontal pressing force using a press device (not shown), thereby forming a clamping-type ion exchange dialysis cell 1. The pressing force is applied only to the gasket frame surface of the stack, and the appropriate clamping pressure is 0.6 N / mm. 2 ±0.1N / mm 2 is common.

[0029] The configuration of the flow distribution plate 30 will be described in more detail with reference to FIG. 3(b) in addition to FIG. 3(a). FIG. 3(b) shows an enlarged view of the area enclosed by the dashed line R in the flow distribution plate 30 shown in FIG. 3(a). In FIG. 3(b), the direction indicated by the arrows Y1-Y2 is the direction of liquid flow in the flow distribution section G1c, and the direction indicated by the arrows X1-X2 is the width direction of the flow distribution section G1c. As shown in FIG. 3(b), the flow distribution plate 30 is a sheet having a woven structure formed by welding strands 31, 31 slanting to the left in the figure and strands 32, 32 slanting to the right. Openings P1'P2'P3'P4' are formed by points P1', P2', P3', and P4' inside a rectangle P1P2P3P4 formed by intersections P1, P2, P3, and P4 of strands 31 and 32. In this embodiment, the illustrated openings P1'P2'P3'P4' are formed so that the pitch a in the liquid flow direction indicated by arrows Y1-Y2 (= openings P1'P3') is longer than the pitch b in the width direction indicated by arrows X1-X2 perpendicular to the liquid flow direction (= openings P2'P4'), but the present invention is not limited to this.

[0030] The aperture ratio formed by the flow distribution plate 30 can generally be explained as the ratio of the area of ​​the apertures P1', P2', P3', and P4' to the area of ​​the rectangle P1, P2, P3, and P4 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 of the strands 31 and 32 do not change, increasing (thickening) the wire diameter of the strands 31 and 32 decreases the aperture ratio, and decreasing (thinning) the wire diameter increases the aperture ratio. Furthermore, the aperture ratio can also be changed by moving the intersections P1, P2, P3, and P4 of the strands 31 and 32 closer to or farther apart without changing the wire diameter of the strands 31 and 32. The wire diameter of the strands 31, 32 forming the mesh structures of the spacer 20 and the flow distribution plate 30 is generally 0.25 to 0.55 mm, and more preferably 0.28 to 0.45 mm. The thickness of the flow distribution plate 30 is set to correspond to the thickness of the gasket, and is determined by the thickness at the intersections P1, P2, P3, and P4 of two strands when forming the flow distribution plate 30.

[0031] Here, when constructing the clamping-type ion exchange dialysis tank 1, the applicant varied the aperture ratio of the flow distribution plate 30, the thickness of the flow distribution plate 30, the thickness of the gaskets, and the number of units U constituting the stack S in various ways to verify whether internal leakage, such as leakage of liquid flowing through the treatment sections of adjacent gaskets, occurred between the gasket frames G1b, G2b of the adjacent gaskets G1, G2 and the ion exchange membranes (anion exchange membrane A and cation exchange membrane K) in the areas near the flow distribution sections G1c, G2c, where liquid would not normally flow, and whether liquid leakage occurred at the sides of the flow distribution sections G1c, G2c (at the mating surfaces between the ion exchange membranes and the gasket frames). The verification results are described below.

[0032] It has been 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 above-mentioned internal leakage and liquid leakage that causes stray currents are relatively unlikely to occur. If the opening ratio is less than 26%, sagging of the ion exchange membrane can be suppressed, but pressure loss increases excessively, which is undesirable because it hinders the flow of liquid in the distribution sections G1c and G2c. Furthermore, when the opening rate is greater than 90%, the pressure loss in the distribution sections G1c and G2c is reduced; however, when multiple distribution plates 30 are stacked, the probability that the intersections P1, P2, P3, and P4 of adjacent distribution plates 30 will not overlap in the stacking direction increases significantly, and the ion exchange membrane, pressed from the intersection of the distribution plate on one side by the elastic force of the gasket frame, partially falls into the gaps in the mesh structure that makes up the distribution plate on the other side, making the above-mentioned internal leakage more likely to occur.

[0033] Furthermore, even when the aperture ratio was set as described above, if the thickness of the distribution plate 30 relative to the thickness of the gasket frames G1b and G2b was less than 103%, the intersections P1, P2, P3, and P4 of adjacent distribution plates 30 did not completely coincide, as described above. This resulted in partial depression of the ion exchange membrane in the gaps of the mesh structure constituting the distribution plate 30, making the internal leakage more likely to occur. This problem became more pronounced as the aperture ratio increased. Furthermore, if the thickness of the distribution plate 30 relative to the thickness of the gasket frames G1b and G2b exceeded 128%, the distribution plate 30 became too thick, resulting in insufficient sealing between the ion exchange membrane (anion exchange membrane A, cation exchange membrane K) and the gasket frames G1b and G2b. This resulted in liquid leakage near the sides of the distribution plate 30, reducing the efficiency of the ion dialysis cell. This problem became more pronounced as the aperture ratio decreased. The above-mentioned effects are not limited to the number of stacked units U, but it has been confirmed that the effects are greater when the number of units U is 30 or more, more preferably 35 to 400.

[0034] Furthermore, when the number of stacked units U is 30 or more, it is preferable that the mesh structure constituting the above-mentioned distribution plate 30 has an opening rate of 30 to 85%, and that the thickness of the distribution plate 30 is 108 to 119% of the thickness of the gasket frames G1b and G2b; more preferably, when the number of stacked units U is 35 to 400, the mesh structure constituting the above-mentioned distribution plate 30 has an opening rate of 40 to 80%, and that the thickness of the distribution plate 30 is 109 to 115% of the thickness of the gasket frames G1b and G2b; and even more preferably, when the number of stacked units U is 40 to 350, the mesh structure constituting the above-mentioned distribution plate 30 has an opening rate of 50 to 80%, and that the thickness of the distribution plate 30 is 109 to 113% of the thickness of the gasket frames G1b and G2b. In this embodiment, the number of units U described above corresponds to the number of gaskets on which the flow distribution plates are stacked at the same position in the stacking direction of the ion exchange membrane and gasket, and the number of units U described above is synonymous with the number of gaskets on which the flow distribution plates are stacked at the same position in the stacking direction of the ion exchange membrane and gasket.

[0035] The above-described configuration prevents internal leakage, in which liquid flowing through the processing section of an adjacent gasket leaks out between the ion exchange membrane and the gasket frame of an adjacent gasket, through which liquid would not normally flow. This solves the problem in clamp-type ion exchange dialysis tanks where liquids in independent circulation systems (e.g., concentrated liquid and desalted liquid) that would not normally mix are mixed together, reducing the efficiency of the ion dialysis tank. It also solves the problem of liquid leakage at the side of the distribution section (the mating surface between the ion exchange membrane and the gasket frame) and, in the case of an electrodialysis tank, where electricity (stray current) flowing through the leaking part can burn and deteriorate the ion exchange membrane, resulting in irreversible damage.

[0036] Furthermore, as described above, the pitch a of the openings P1', P2', P3', and P4' in the liquid flow direction (the direction of the arrows Y1-Y2) in the flow distribution section G1c is preferably longer than the pitch b in the width direction X1-X2 perpendicular to the liquid flow direction Y1-Y2 in the flow distribution section G1c. If the pitch a is shorter than the pitch b, the smoothness of the flow in the flow distribution section G1c is impaired, undesirably increasing the pressure loss in the flow distribution section G1c. Therefore, the pitch a is preferably at least 1.1 times longer than the pitch b, more preferably 1.1 to 2.2 times, even more preferably 1.3 to 2.2 times, and particularly preferably 1.5 to 2.2 times. Note that the pitch a is generally 0.25 to 0.55 mm, and more preferably 0.28 to 0.45 mm, when the strands forming the network structure have the typical wire diameters described above.

[0037] The present invention is not limited to the above-described embodiment and includes various modifications. In the above-described embodiment, an example was shown in which a laminate of an ion exchange membrane and a gasket constructed according to the present invention was applied to a clamping-type ion exchange dialysis cell capable of electrodialysis. However, for example, the present invention can be applied to a configuration in which an ion exchange membrane (bipolar membrane) having a structure in which an anion exchange layer and a cation exchange layer are bonded together with the above-described anion exchange membrane, cation exchange membrane, and gasket are combined and laminated to form a stack for ion exchange, a configuration in which the bipolar membrane, an anion exchange membrane, and a gasket are combined and laminated to form a stack for ion exchange, a configuration in which the bipolar membrane, a cation exchange membrane, and a gasket are combined and laminated to form a stack for ion exchange, and even an ion exchange membrane and a gasket are stacked to form a stack for diffusion dialysis. That is, the present invention is effective in an ion dialysis cell including a laminate in which one or more types of ion exchange membranes and the above-mentioned gasket are laminated, and more preferably, the present invention is more effective when the number of stacked gaskets, in which the flow distribution plates are stacked at the same position in the stacking direction of the ion exchange membranes and gaskets, is 30 or more (the number of units U is 30 or more), which is the number that is commercially practical in ion dialysis cells.

[0038] In the above-described embodiment, the ion exchange membranes (anion exchange membrane A, cation exchange membrane K) have a total of four communicating holes (Aa, Ab, Ka, Kb) formed on the top and bottom, respectively. However, the present invention is not limited to this; other numbers may be used, and their sizes may be set as needed. In the above-described embodiment, the communicating holes Aa, Ab, Ka, Kb of the anion exchange membrane A and cation exchange membrane K have a substantially rectangular shape. However, the present invention is not limited to this; they may have a circular shape. Even if the communicating holes Aa and Ka have a circular shape, the present invention can achieve the same effects as the above-described embodiment. [Explanation of symbols]

[0039] 1: Clamp-type ion exchange dialysis tank 10a:Anode chamber 10b: Cathode chamber 12, 14: Clamping plate 20: Spacer 30: Distribution plate 31, 32: Strand A: Anion exchange membrane K: Cation exchange membrane G1, G2: Gasket G1a: Processing section G1b: Gasket frame G1c: Distribution area G1d: Communication hole G2a: Processing section G2b: Gasket frame G2c: Distribution section G2d: Communication hole N1, N2: Electrode diaphragm

Claims

1. A gasket to be laminated together with an ion exchange membrane in an ion dialysis cell that is a clamping type ion exchange dialysis cell or a clamping type diffusion dialysis cell, the gasket comprises a treatment section which forms a space where ion exchange takes place in a clamping type ion exchange dialysis cell, and a space where diffusion or dialysis takes place in a clamping type diffusion dialysis cell, and a gasket frame which surrounds the treatment section; a flow distribution section that connects the processing section and a communication hole formed in the ion exchange membrane laminated on the gasket is formed in the gasket frame; A mesh-structured flow distribution plate is disposed in the flow distribution section, The mesh structure constituting the flow distribution plate has an opening ratio of 26 to 90%, and the thickness of the flow distribution plate is 103 to 128% of the thickness of the gasket frame.

2. 10. An ion dialysis tank comprising a laminate of one or more types of ion exchange membranes and the gasket according to claim 1, wherein the number of stacked gaskets is 30 or more, and the flow distribution plates are stacked at the same positions in the stacking direction of the ion exchange membranes and the gaskets.

Images