Zero-gap type cation exchange membrane method salt electrolysis cell

Abstract

To provide an electrolysis cell that can be operated at a particularly low electrolysis voltage and has a large power-saving effect in a cation exchange membrane method electrolysis cell capable of obtaining high-purity caustic alkali in so-called chlor-alkali electrolysis for electrolyzing salt water to obtain sodium hydroxide and chlorine.SOLUTION: In a zero-gap type cation exchange membrane method salt electrolysis cell according to the present invention, an electrode base material of an anode is a roll-pressed product of expanded metal, an apparent thickness P of the roll-pressed product is 1.1 t or more and 2 t or less, and a cathode is a nickel mesh obtained by plain-weaving nickel wires having a wire diameter of 0.06 to 0.16 mm. A pitch of the cathode is 1 / 2 or less of SW of the anode.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to electrolysis that enables electrolysis with minimal power consumption in a zero-gap cation exchange membrane method for producing chlorine from the anode and hydrogen and sodium hydroxide from the cathode by electrolyzing mainly brine. [Background technology]

[0002] Currently, the cation exchange membrane method is commonly used in chloralkali electrolysis, and in order to minimize the electrical resistance in the electrolysis, the so-called zero-gap method, in which the anode and cathode are closely attached to a cation exchange membrane (a diaphragm), is widely used.

[0003] In the early days of cation exchange membrane chloride electrolysis, there were problems with the quality of the cation exchange membrane itself, and the anode side of the cation exchange membrane would become strongly alkaline due to the return of alkali from the cathode chamber. This would reduce the efficiency of chlorine generation at the anode and cause corrosion of the titanium substrate that makes up the anode due to alkali, so people took the trouble to avoid contact between the anode and the cation exchange membrane by inserting a PTFE mesh between the anode and the cation exchange membrane.

[0004] Later, with the improvement and development of cation exchange membranes, especially when carboxylic acid membranes were put into practical use instead of the conventional sulfonic acid membranes, the problem of alkali returning to the anode side was solved, and there were no problems even if the anode was in contact with the cation exchange membrane, and the electrical resistance of the electrolyte due to the close contact between the anode and the cation exchange membrane was reduced, and a drop in voltage was achieved.In addition, with the current use of composite membranes, the cathode is also in close contact with the cation exchange membrane during electrolysis, and with the implementation of the zero-gap method, it has become possible to operate at a lower electrolysis voltage.

[0005] However, in the case of a conventional electrolytic cell, in addition to the pressure from the cathode side to the anode side through the cation exchange membrane due to the difference in specific gravity between the caustic alkali used as the catholyte and the saline used as the anolyte, pressure fluctuations caused by bubbles generated within the electrolytic cell require the anode itself to have great physical strength, and optimization of the shape itself has been difficult.

[0006] On the other hand, on the cathode side, which is hardly affected by pressure fluctuations, even if the anode, cation exchange membrane, and cathode are initially in close contact with each other, the cation exchange membrane is pushed toward the anode by the caustic soda solution used as the catholyte, causing the cathode and cation exchange membrane to separate, making it difficult to achieve a perfect zero gap.

[0007] Subsequently, improvements were made to the electrolytic cell to eliminate pressure fluctuations within the cell, and special processing was carried out to make the surface of the cation exchange membrane hydrophilic, minimizing the liquid resistance caused by the electrolyte. This led to the so-called zero gap electrolysis, in which the anode and cathode are constantly in contact with the surface of the cation exchange membrane by applying pressure to the cathode surface to make it tightly attached.

[0008] There is a technique for using a perforated plate as an electrode plate, where the perimeter of the hole is specified to be 2 m or more for an effective flat electrode plate unit size of 100 x 100 mm (see, for example, Patent Document 1).

[0009] There is a technology that uses an expanded metal with a thickness of 0.05 mm to 0.3 mm as the anode (see, for example, Patent Document 2). It has been shown that by using such a thin anode and placing the anode as close as possible to the cation exchange membrane, it is possible to operate the cell at a low voltage.

[0010] There is a zero-gap electrolysis technology in which the expanded metal anode is completely smoothed to the thickness of the original plate so that it adheres closely to the cation exchange membrane (see, for example, Patent Document 3). This reduces the electrolysis voltage by bringing the anode into close contact with the cation exchange membrane.

[0011] There is a technology that uses an electrode structure made of expanded metal that is very thin, has small pores, and has an extremely small aperture ratio (see, for example, Patent Document 4). In this case, the plate thickness is 0.5 to 1.2 mm, which is close to the electrode base material that is currently commonly used.

[0012] There is a technology in which an expanded metal is used as the anode, the plate thickness is 0.1 to 0.5 mm, and the shape of the formed mesh is SW / LW = 0.45 to 0.55 (see, for example, Patent Document 5). This technology has a relatively large mesh opening, but the plate thickness of the mesh used is thin.

[0013] Regarding water electrolysis cells, there is a technique in which the partition walls are provided with irregularities, and electrodes are fitted to these irregularities, and a cushion mat is used as an elastic body to hold down the electrodes (see, for example, Patent Document 6).

[0014] Regarding water electrolysis, there is a technology using a metal wire mesh containing nickel as the cathode and forming an electrode active material on its surface (see, for example, Patent Document 7). The mesh size is disclosed as a plain weave of 20 to 60 meshes with a wire diameter of 0.05 mm or more and 1.0 mm or less. An expanded metal is described as the anode, and it is shown to have a zero gap, particularly in relation to the diaphragm and cation exchange membrane. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Publication No. 56-146884 [Patent Document 2] Japanese Patent Application Publication No. 58-130286 [Patent Document 3] Japanese Patent No. 4453973 [Patent Document 4] WO2018 / 131519 publication [Patent Document 5] WO2015 / 108115 publication [Patent Document 6] Japanese Patent No. 7323299 [Patent Document 8] WO2018 / 151228 publication Summary of the Invention [Problem to be solved by the invention]

[0016] While this zero-gap method makes it possible to minimize the electrical resistance of the electrolyte between the anode and cathode, there has been little discussion regarding the reduction of the electrical resistance of the cation-exchange membrane itself, which is only about 0.1–0.2 mm thick and has a voltage loss of 200 mV or more. To reduce the electrical resistance of the cation-exchange membrane, the membrane resistance itself remains constant; therefore, it is necessary to equalize the current flowing across the entire membrane surface and achieve a uniform current density within the membrane. This typically requires specifying the morphological relationship between the anode and cathode sandwiching the cation-exchange membrane. However, although various anode and cathode structures have been studied, no prior literature was found that directly addressed the size and shape relationship between the anode and cathode facing each other across the cation-exchange membrane.

[0017] Regarding the anode and cathode, the shape of the anode has been made finer, and a fine electrode structure has been given to make the current density in the cation exchange membrane uniform. However, in reality, specifying the electrode shape, including removing the bubbles that occur, is a major problem.

[0018] Patent Document 1 does not disclose the shape of the perforated plate. This would mean that a plate with cutouts could be used as the substrate, but in that case, there would be no escape route for the gas generated on the cation exchange membrane side. Therefore, the technology included would make it impossible to maintain a low voltage.

[0019] Regarding Patent Document 2, although the operating conditions may differ from those of the present, when the actual electrode area is taken into consideration, the cross-sectional electrode area is small due to the thinness of the plate, and it is clear that this is completely incompatible with the present electrolysis conditions that require high current density. Also, it is likely that if there is no physical protection on the back side of the anode, the anode will be more likely to deform due to pressure from the cathode chamber side.

[0020] Patent Document 4 imposes restrictions on the relationship between the opening size and the aperture ratio of the expanded metal, and applying this restriction results in a small mesh size. This makes it difficult to vent gas generated on the cation exchange membrane side of the anode to the back side of the anode, except under special conditions, and at the same time, there is a possibility that the supply of electrolyte to this area will be insufficient, which is a problem.

[0021] In Patent Document 5, the thin expanded metal plate allows gas generated on the electrolytic surface in contact with the cation exchange membrane to escape relatively easily to the side of the electrode opposite the cation exchange membrane, i.e., the back side of the electrode. However, because the expanded metal plate is thin, when considered three-dimensionally, the electrode surface area is inevitably small, which increases the current density on the electrode surface, raising the electrode potential and potentially shortening the electrode life, which is problematic, particularly for large current densities.

[0022] Patent Document 6 does not describe the combination of a cathode and an anode, but only the cathode. Although there is no indication of the cathode, it suggests a plain woven mesh as the cathode, and it is preferable that the wire diameter is 0.05 mm or more and 1.0 mm or less, and the mesh number is 5 to 70, which indicates an extremely wide range. There is no description of how such a cathode should be related to an anode or a cation exchange membrane.

[0023] In Patent Document 7, the shapes of the anode and cathode are described as expanded metal and plain woven mesh, but the relationship between their sizes is not disclosed at all.

[0024] In other words, in the past, much effort was made to reduce the electrical resistance of the electrolyte, which has a relatively high electrical resistance. However, the cation exchange membrane itself has another large electrical resistance. Although its apparent thickness is only about 100 microns, it is difficult to reduce the electrical resistance at the commonly used electrolysis current density of 0.5 A / cm. 2Even at this level, it is said that there is an electrical resistance of about 0.2 V or more. Under these circumstances, the basic technology for achieving the so-called zero gap is widely known, but little is known about the technology relating to the relationship between the electrodes and the cation exchange membrane. This is probably because, in order to solve the problems of bubble generation and liquid resistance at the anode and cathode, the anode and cathode have been considered in relation to the closely attached cation exchange membrane, and little consideration has been given to the relationship between the anode and cathode, that is, the problem of electrical resistance within the cation exchange membrane, with the focus being on the cation exchange membrane.

[0025] Thus, in alkaline water electrolysis technology, which is a form of salt water electrolysis or similar electrolysis, when an expanded metal is used as the anode and a plain-woven mesh made of nickel or nickel-containing metal wire is used as the cathode, the relationship between the shape of the anode and the shape of the cathode and their combinations have never been studied. Furthermore, the ultimate reduction in electrolysis voltage depends on how to reduce the electrical resistance when the cation exchange membrane is sandwiched between the cathode and anode in a zero-gap configuration, and measures to achieve this are needed.

[0026] Therefore, an object of the present disclosure is to provide an electrolytic cell that uses a cation exchange membrane method to obtain high-purity caustic alkali in so-called chlor-alkali electrolysis, in which sodium chloride is electrolyzed to obtain sodium hydroxide and chlorine, and that can be operated at an exceptionally low electrolysis voltage and has a significant power-saving effect. [Means for solving the problem]

[0027] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by: (1) forming an expanded metal into a roll-pressed product as an anode and then using the product as an electrode base material, and in this case, performing roll-pressing so that the apparent thickness of the roll-pressed product does not become as thin as the thickness of the sheet (hereinafter also referred to as the original sheet) before processing the expanded metal (hereinafter, a roll-pressed product that satisfies this condition will also be referred to as a weakly pressed product), (2) using a plain-woven nickel mesh as the cathode, and (3) further, setting the pitch of the cathode to be 1 / 2 or less of the SW of the anode, and have thereby completed the present invention. That is, the zero-gap type cation exchange membrane method chlor-alkali electrolyzer according to the present invention comprises a cation exchange membrane serving as a diaphragm, an anode in close contact with one surface of the cation exchange membrane, an anode chamber in which the anode is housed and filled with anolyte, a cathode in close contact with the other surface of the cation exchange membrane, and a cathode chamber in which the cathode is housed and filled with catholyte, wherein anode gas is generated at the anode and hydrogen is generated at the cathode, and the anode comprises an electrode substrate made of a perforated plate and an anode coating layer made of a hydrophilic electrode active material formed on the surface of the electrode substrate, and the electrode substrate is a roll-pressed product of expanded metal of which the perforated plate has a plate thickness of t mm, a long-side opening pitch of LW mm, a short-side opening pitch of SW mm, and strands of W mm, the aperture ratio of the perforated plate is 20% or more and 60% or less, the ratio calculated by LW / SW is 1.5 or more and 3.5 or less, the thickness t of the perforated plate is 0.5 mm or more and 1.0 mm or less, the aperture period SW of the short side is 2.0 mm or more and 5.5 mm or less, and the apparent thickness Pmm of the roll-pressed product is 1.1t or more and 2.0t or less, the cathode has a nickel mesh formed by plain weaving nickel wires having a wire diameter of 0.06 to 0.16 mm, and a cathode coating layer of a hydrophilic electrode active material formed on the surface of the nickel mesh, the pitch of the cathode being 1 / 2 or less of the SW of the anode, and the zero-gap cation exchange membrane method chlor-alkali electrolytic cell has an elastic body that applies pressure to the surface of the cathode opposite to the surface that is in close contact with the cation exchange membrane.

[0028] The zero-gap type cation exchange membrane process chlor-alkali electrolytic cell according to the present invention includes an electrolytic cell in which the expanded metal is made of pure titanium, the anolyte is a saline solution, the catholyte is a caustic soda aqueous solution, chlorine gas is produced as the anode gas, and caustic soda and hydrogen are produced in the cathode chamber.

[0029] In the zero-gap type cation exchange membrane process chlor-alkali electrolytic cell according to the present invention, it is preferable that the expanded metal is made of pure titanium, and the electrode active material of the anode coating layer is a hydrophilic composite oxide containing iridium, ruthenium, and titanium.

[0030] In the zero-gap type cation exchange membrane process sodium chloride electrolytic cell according to the present invention, the electrode active material of the cathode coating layer preferably contains a platinum group metal and / or a platinum group metal oxide.

[0031] In the zero-gap type cation exchange membrane process sodium chloride electrolytic cell according to the present invention, the electrode active material of the cathode coating layer preferably contains a composite oxide of ruthenium and cerium.

[0032] In the zero-gap type cation exchange membrane process sodium chloride electrolytic cell according to the present invention, the pitch of the nickel mesh is preferably 0.6 to 1.2 mm.

[0033] In the zero-gap type cation exchange membrane process sodium chloride electrolytic cell according to the present invention, it is preferable that the elastic body is a sponge-like mattress made of nickel wires randomly folded and bundled, and is placed between the current collector and the cathode. [Effects of the Invention]

[0034] According to the present disclosure, it is possible to provide a cation exchange membrane electrolytic cell that can minimize the electrolysis voltage and achieve extremely high energy savings when producing chlorine gas mainly from the anode side and hydrogen and alkali hydroxide from the cathode side. [Brief explanation of the drawings]

[0035] [Figure 1] 1A and 1B are schematic diagrams showing an example of the shape of an expanded metal, in which FIG. 1A shows the shape of an eye, and FIG. 1B is a schematic cross-sectional view of a bond taken along line A'. [Figure 2] Schematic diagrams showing the shape of the mesh of expanded metal, where (a) shows a diamond shape and (b) shows a tortoiseshell shape. [Figure 3] 1A and 1B are explanatory diagrams of the removal of air bubbles, in which (a) is a conventional electrode and (b) is an electrode according to this embodiment. [Figure 4] FIG. 1 is a schematic cross-sectional view of a zero-gap type cation exchange membrane method sodium chloride electrolysis cell, taken along a plane passing through the ribs of the cathode chamber. DETAILED DESCRIPTION OF THE INVENTION

[0036] Next, the present invention will be described in detail with reference to the embodiments, but the present invention is not limited to these descriptions. Various modifications of the embodiments may be made as long as the effects of the present invention are achieved.

[0037] As shown in FIG. 4, the zero-gap cation exchange membrane method sodium chloride electrolytic cell according to this embodiment includes a cation exchange membrane 12 serving as a diaphragm, an anode 10 in close contact with one surface of the cation exchange membrane 12, an anode chamber 14 in which the anode 10 is accommodated and filled with anolyte, a cathode 11 in close contact with the other surface of the cation exchange membrane 12, and a cathode chamber 13 in which the cathode 11 is accommodated and filled with catholyte. In this zero-gap cation exchange membrane method sodium chloride electrolytic cell 100, anode gas is generated at the anode 10 and hydrogen is generated at the cathode 11. The anode 10 includes an electrode substrate made of a perforated plate and an anode coating layer made of a hydrophilic electrode active material formed on the surface of the electrode substrate. The electrode substrate is made of a roll-pressed expanded metal perforated plate having a thickness of t mm, a long-side opening pitch of LW mm, a short-side opening pitch of SW mm, and strands of W mm. the open area ratio of the expanded metal is 20% or more and 60% or less, the ratio calculated by LW / SW is 1.5 or more and 3.5 or less, the plate thickness t of the perforated plate is 0.5 mm or more and 1.0 mm or less, the open area period SW of the short side is 2.0 mm or more and 5.5 mm or less, the apparent thickness P mm of the roll-pressed product is 1.1t or more and 2.0t or less, the cathode 11 has a nickel mesh obtained by plain weaving nickel wires having a wire diameter of 0.06 to 0.16 mm, and a cathode coating layer of a hydrophilic electrode active material formed on the surface of the nickel mesh, the pitch of the cathode 11 being 1 / 2 or less of the SW of the anode 10, and the zero-gap cation exchange membrane process sodium chloride electrolysis cell 100 has an elastic body 15 that applies pressure to the surface of the cathode 11 opposite to the surface that is in close contact with the cation exchange membrane 12.

[0038] Here, the anode substrate is a roll-pressed expanded metal product, which is coated with an electrode active material to form the anode, and the cathode substrate is a plain-woven mesh made by weaving nickel wires of a specific size relative to the anode substrate, with the surface of the mesh coated with the electrode active material.The cathode is sandwiched around the cation exchange membrane, and a force is applied to the cathode surface by an elastic body 15 such as a mat-like spring body made of thin nickel wire, pressing it against the cation exchange membrane from the cathode side, thereby integrating the cathode, cation exchange membrane, and anode.This successfully uniforms the current density within the cation exchange membrane, minimizes electrical resistance, and obtains the minimum electrolysis voltage.

[0039] The cathode 11 must be constantly pressed against the cation exchange membrane 12 and in close contact with it. To this end, the cathode 11 is fixed to a rib 17 via an elastic body 15 with spring properties so that it is always in close contact with the surface of the cation exchange membrane. The cathode is placed on the surface of a cathode current collector 16, which is physically strong and porous. The elastic body 15 can be a sponge-like mattress made of randomly folded and bundled fine nickel wires or a metal scrubber made of nickel wires. The cathode current collector 16 is made of nickel expanded metal or punched metal. Electric current is applied to the cathode via the cathode current collector 16 and the elastic body 15. The rib 17 is disposed in the cathode chamber 13 and attached to the electrolytic cell. The rib 17 is preferably provided with a liquid passage 19 to avoid impeding the circulation of the cathode solution in the cathode chamber 13.

[0040] In other words, conventional cation exchange membrane electrolytic cells have been designed to minimize the electrical resistance and electrolysis voltage by sandwiching an optimal anode and an optimal cathode in close contact with each other through a cation exchange membrane, with the primary focus being on minimizing the electrical resistance of the electrolyte containing bubbles generated from the anode and cathode. However, the cation exchange membrane has hardly been taken into consideration. However, although the cation exchange membrane is extremely thin, its electrical resistance is high, and minimizing its electrical resistance is essentially one of the important factors for reducing the electrolysis voltage. To achieve this, since the cation exchange membrane itself cannot be modified, it is important to make the distribution of the current flowing through the cation exchange membrane as uniform as possible in order to minimize the voltage.

[0041] To make the current density in the cation exchange membrane uniform, it is desirable to make both the anode and cathode plates, but in reality, as electrolysis progresses on both the cathode and anode, bubbles are generated, and electrolyte must be supplied to those areas. Electrolysis generates bubbles, and the generated bubbles must escape (be removed) from the electrode part of the electrical resistor, and electrolyte must be supplied at the same time.

[0042] To achieve this, an electrode shape that matches the characteristics of the bubbles that are generated is essential, and this is also related to the surface characteristics of the cation exchange membrane. In other words, the cation exchange membranes used in salt electrolysis may come into contact with highly oxidizing chlorine gas, so highly corrosion-resistant fluororesin-based cation exchange membranes are used. However, fluororesin is highly water-repellent, which makes it difficult for bubbles generated in the electrolysis reaction to separate, or the bubbles, which are insulators, may grow large, increasing electrical resistance and potentially increasing the electrolysis voltage.

[0043] In cation exchange membrane brine electrolysis, the specific gravity of the sodium hydroxide (usually about 32%) produced in the cathode chamber is greater than that of the anolyte (salt solution) of approximately 200 g / liter, so the cation exchange membrane adheres closely to the anode due to the difference in specific gravity. Chlorine gas generated on the surface of the anode by electrolysis naturally grows while adhering to the cation exchange membrane to which it is attached, but on a water-repellent surface, the bubbles of chlorine gas generated do not separate until they grow large. Naturally, since the bubbles are insulators, the electrolysis voltage becomes extremely high. To avoid this, the surface of recent cation exchange membranes has been specially treated to be highly hydrophilic.

[0044] On the other hand, the anode, which is in close contact with the cation exchange membrane, may become water-repellent depending on the electrode active material and manufacturing conditions, causing bubbles to grow on the anode surface, increasing electrical resistance and the electrolysis voltage. Furthermore, when the bubbles grow in this way, it becomes difficult for gas generated at the contact surface between the cation exchange membrane and the anode to escape to the back side of the electrode.

[0045] On the other hand, the porous body on the anode surface is used in close contact with the cation exchange membrane, which has an extremely high electrical resistance, and in order to ensure a uniform current distribution in the cation exchange membrane, it is desirable that the porous body of the anode be as fine as possible and uniform across the entire surface, which naturally makes it impossible to provide large pores for removing air bubbles, and therefore, since it is necessary to remove the air bubbles before they grow, it is essential to maintain the anode surface, i.e., the electrode coating, as hydrophilic. Naturally, in addition to this, it is also necessary for the anode to have as many fine pores as possible, and to ensure that the air bubbles, being light, can escape upwards quickly.

[0046] For this reason, it is necessary to make the current distribution on the anode side as uniform as possible on the cation exchange membrane surface. On the other hand, the chlorine gas bubbles generated by electrolysis are much larger than the hydrogen gas bubbles generated from the cathode, so the anode structure must be adapted to this in order to quickly extract the chlorine gas generated from the anode that is in close contact with the cation exchange membrane to the rear.

[0047] In the case of chloralkali electrolysis, the electrode active materials of the anode are iridium and ruthenium, and the anode is an oxide containing a stabilizer.

[0048] The same expanded mesh, plain woven mesh, or perforated plate is also used for the cathode, but what must be considered here is that the anode and cathode must be combined in such a way that the current density within the surface of the cation exchange membrane, which has a high electrical resistance, is made as uniform as possible.

[0049] However, the problem with industrial electrolytic cells is that they are typically large, measuring 1.2m x 2.4m, making it impossible to control the relative positions of the anode and cathode relative to the cation exchange membrane surface. For example, if it were possible to fix the relative positions of cathodes made of expanded metal of the same shape while maintaining a certain relationship, it would be possible to achieve an almost ideal relative position, but in reality, it is virtually impossible to control the relative positions on the order of millimeters in an electrolytic cell that is on the order of meters. The only possibility seems to be to use expanded metal with the same mesh size, or an integer multiple or fraction of that, and rotate them 90 degrees relative to each other, which would allow for an approach to the ideal relative position.

[0050] However, while this may be possible for expanded metal with a relatively large mesh and thickness, in the case of fine mesh, there is a limit to the size of the original titanium and nickel plates used to make the expanded metal, making it very difficult to freely rotate them by 90 degrees, and there is also the problem that it becomes difficult to make the mesh of the expanded metal finer.

[0051] Because of its electrical conductivity, the anode side titanium can be made finer by using either a punched plate or expanded metal. However, considering economic efficiency and manufacturing methods, it was found that the most effective electrode is one in which a titanium plate of a certain thickness is made into fine expanded metal, and then roll-pressed to create a fine mesh, with the expanded metal having a slightly tilted electrode mesh as the base material so that the generated bubbles can be more effectively and quickly removed to the rear, and this is coated with a hydrophilic electrode active material so that the bubbles generated by electrolysis are separated from the base material before they can grow large.

[0052] On the other hand, when combining the cathode with the expanded metal anode, as mentioned above, nickel expanded metal has a high possibility of causing current imbalance within the cation exchange membrane due to its similar shape. Therefore, a woven mesh made of nickel is required, which is easy to adjust in size and has a completely different shape. Furthermore, it was found that the mesh size should be less than half that of the expanded metal anode. In other words, it was found that the metal-to-metal distance between the anode and cathode is almost the same throughout. This means that the current density flowing within the cation exchange membrane is uniform throughout, and therefore the voltage consumed by the cation exchange membrane is minimized. Furthermore, when expanding metal is combined with a fine plain-woven mesh, the mesh openings sandwiching the anode / cathode cation exchange membrane do not coincide in position, but remain nearly uniform regardless of the positional relationship. Furthermore, by making the pitch size of the plain-woven mesh less than half that of the expanded metal openings (specifically, the SW), no change in voltage is observed, and it is minimized, even when the relative positions are changed. As a result, although the current distribution within the cation exchange membrane is not ideal, it becomes uniform within a practical range, and it is found that the resistance loss when the cation exchange membrane is sandwiched between the cathode and anode in a zero-gap configuration is minimized and uniform.

[0053] Here, the pitch is the value obtained by dividing 1 inch (25.4 mm) by the number of meshes, in other words, the distance between the central axis of a nickel wire and the central axis of an adjacent nickel wire, or the sum of the wire diameter of the nickel wire and the width of the space surrounded by the nickel wire and the adjacent nickel wire.

[0054] That is, the cathode is a fine-meshed nickel porous body, i.e., a nickel mesh made by plain weaving nickel wires with a wire diameter of 0.06 to 0.16 mm, preferably a plain weave of nickel wires with a wire diameter of 0.08 to 0.14 mm. The cathode is a mesh substrate with a pitch of 1 / 2 or less, preferably 2 / 5 or less, of the anode SW, and the same hydrophilic electrode active material as the anode is provided on the surface. For example, when the SW is 2 mm and the plain weave mesh pitch is 30 mesh, the ratio is 2 / 5. The lower limit of the nickel mesh pitch relative to the anode SW is, for example, 1 / 3. For example, when the SW is 2 mm and the plain weave mesh pitch is 40 mesh, the ratio is 1 / 3. This shows that even if the relative positions of the anode and cathode across the cation exchange membrane are arbitrarily determined, the electrical resistance during electrolysis when the cation exchange membrane is sandwiched between the cathode and anode in a zero-gap configuration remains almost unchanged and is at a minimum.

[0055] In this embodiment, the pitch of the nickel mesh is preferably 0.6 to 1.2 mm. If the pitch is less than 0.6 mm, depending on the current density, the mesh size may be insufficient, causing bubbles to concentrate in the mesh areas, resulting in a shortage of effective cathode area, resulting in a high voltage and increased current resistance. Alternatively, increasing the nickel wire diameter may reduce current resistance, but increase the mesh thickness, resulting in a decrease in effective electrode area. On the other hand, if the pitch exceeds 1.2 mm, the mesh size of the cathode itself may be large, causing the cathode itself to create a current density distribution in the cation exchange membrane.

[0056] In the zero-gap type cation exchange membrane process chlor-alkali electrolysis cell according to the present invention, the electrode active material of the cathode coating layer preferably contains a platinum group metal and / or a platinum group metal oxide, which reduces the electrode overpotential by 300 mV or more compared to a case without the cathode coating layer, i.e., reduces the electrolysis voltage by 300 mV or more, and also improves the wettability of the electrode surface, allowing generated bubbles to quickly leave the electrode surface, thereby enabling a stable maintenance of a lower electrolysis voltage.

[0057] In the zero-gap type cation exchange membrane process chlor-alkali electrolytic cell according to the present invention, the electrode active material of the cathode coating layer preferably contains a composite oxide of ruthenium and cerium, which is not only hydrophilic but also the most active of platinum group metals and platinum group metal oxides, and can maintain its activity and stability for a long period of time.

[0058] In this embodiment, an anode made of expanded metal that meets certain conditions is brought into close contact with the surface of the cation exchange membrane. Then, electrolysis occurs at the contact area, generating chlorine gas on the hydrophilic electrode surface. Then, bubbles separate before the chlorine gas develops significantly. The chlorine gas passes through the slightly outward-facing electrode surface of the expanded metal and immediately escapes to the side of the electrode opposite the cation exchange membrane. This allows electrolysis with minimal electrolyte resistance.

[0059] On the other hand, hydrogen gas generated at the cathode has bubbles less than 10 microns in size and simply diffuses into the electrolyte. Unless there is a large liquid flow in the electrolyte, the cathode is surrounded by bubbles. This electrical resistance can cause the effective surface area to constantly change, leading to instability, especially in the case of a zero-gap expanded metal membrane with a thickness of 0.5 mm or more. While the cause of this is unclear, it is known that during electrolysis, sodium ions from the anode side typically flow toward the cathode side along with their entrained water. This stable liquid flow creates a fast liquid flow in the thinner portion (less than 0.5 mm). This is thought to remove bubbles and ensure stable electrolysis. However, thicker expanded metal membranes within this range can result in instability due to ineffective use of the backside of the expanded metal. Therefore, the use of an extremely thin plain-weave mesh is essential, which was also appropriate in this case.

[0060] The problems with using expanded metal as the cathode are related to the anode / cathode mentioned above. However, as mentioned above, hydrogen gas bubbles generated at the cathode are less than 10 microns in size and therefore hardly move without electrolyte flow. Furthermore, an elastic material is required to press the cathode mesh against the cation exchange membrane, which impedes the liquid flow and disrupts it. Therefore, the flow of the catholyte is mostly due to migration water passing through the cation exchange membrane. Fast liquid flow can remove hydrogen bubbles, and current can effectively flow only about 0.2 to 0.3 mm from the surface of the cation exchange membrane. Therefore, a plain weave knitted mesh is effective, but the wire diameter of the mesh must be 0.16 mm or less. To maximize the surface area, the mesh must be made of thick wires 0.06 mm or thicker.

[0061] As mentioned above, the fine knitted mesh has a completely different shape from the anode-side expanded metal, with smaller meshes than the anode expanded metal. The differently shaped, fine plain-weave knitted mesh substrate is extremely effective in achieving a nearly uniform current distribution across the entire membrane surface. To achieve a uniform current density across the cation exchange membrane, the knitted mesh must have a mesh size that matches the anode mesh but is significantly smaller than that. As mentioned above, the pitch of the knitted mesh must be less than half the size of the anode SW. The surface of such a knitted mesh must be coated with an electrode active material that is more hydrophilic and has catalytic properties that minimize hydrogen overvoltage.

[0062] For example, if the SW of the anode is 2 mm, the line spacing of the plain weave mesh of the cathode must be 1 mm or less, i.e., 25.4 mesh or more. In the case of the above 25.4 mesh, which is considered with a wire diameter of 0.1 mm, the repeat area is 1 mm. 2 The surface area of ​​the nickel wire in the wire is 2 x 0.1 x π = 0.2π, which is almost the same as the surface of the expanded metal, but is finer and has better in-plane uniformity. It was found that this combination produces the best results.

[0063] [anode] The anode is an electrode for cation exchange membrane chloralkali electrolysis having an electrode substrate made of a perforated plate made of pure titanium and a hydrophilic electrode active material coating layer formed on the surface of the electrode substrate, wherein the electrode substrate is a roll-pressed product of expanded metal, the perforated plate having a thickness of t mm, a long-side opening period of LW mm, a short-side opening period of SW mm, and strands of W mm, the open area ratio of the expanded metal being 20% ​​to 60%, and the ratio calculated by LW / SW being 1.5 to 3.5, the perforated plate having a thickness t of 0.5 mm to 1.0 mm, the short-side opening period SW being 2.0 mm to 5.5 mm, and the roll-pressed product having an apparent thickness P mm of 1.1t to 2t.

[0064] In cation exchange membrane chloralkali electrolysis, the main reaction at the anode is the chlorine generation reaction, and the chlorine gas generated by electrolysis is electrically resistive because the bubbles themselves are not conductive. Therefore, it is important to consider how quickly the bubbles can be removed from the periphery of the anode, thereby keeping the periphery of the electrode constantly filled with liquid, which is a requirement for stable continuation of electrolysis at a low electrolysis voltage.

[0065] In this embodiment, it is preferable to use an expanded metal made of pure titanium as the base material of the electrode, and expanded metal has the advantages that it can be produced relatively easily when making a perforated plate for the electrode, and that, although it is a perforated plate, it has a high titanium utilization rate of 100% compared to other base materials such as punched plates, and is relatively inexpensive. Here, it is preferable that the pure titanium be JIS Class 1 or JIS Class 2 titanium.

[0066] The thickness of the base plate, i.e., the thickness t of the perforated plate, is 0.5 mm to 1.0 mm. If the plate thickness is less than 0.5 mm, the cross-sectional area of ​​the perforations within the electrode surface area effective for electrolysis is reduced, resulting in a smaller overall actual surface area of ​​the electrode. This increases the actual current density, resulting in a slight increase in electrode overvoltage and a shortened electrode life. Furthermore, the physical strength may be insufficient. On the other hand, if the base plate thickness is greater than 1.0 mm, the titanium weight increases, making it more expensive, and it becomes difficult to achieve a smaller mesh size. Furthermore, current tends to concentrate on the front side of the electrode, i.e., the cation exchange membrane side, preventing the back side from being used effectively, potentially reducing the effective actual surface area. For these reasons, the thickness t of the electrode substrate base plate is 0.5 mm to 1.0 mm, preferably 0.6 mm to 0.9 mm, and more preferably 0.7 mm to 0.8 mm.

[0067] When the expanded metal is made, the outer dimensions of the expanded metal expand by the number of holes that are made porous, and the rate at which the plate expands is its opening ratio. If the length of the barrel is 2000 mm, the aperture ratio is (2000-1000) / 2000=0.5, or 50%. If the aperture ratio is 30%, and the length of the perforated plate is x, then x can be expressed by the following equation (1). (Number 1)x=0.3x+1000 From (Equation 1), we can calculate that x is approximately 1429 (mm).

[0068] The mesh size of this expanded metal is determined by the repeating period in the direction of expansion, SW, and the repeating period in the perpendicular direction, LW. In other words, a small mesh has smaller LW and SW, and the expanded metal has a larger number of repeating periods per unit size. Also, as the ratio of LW to SW, LW / SW, increases, the opening of the holes in the porous portion becomes elongated, and as LW / SW decreases, that is, approaches 1, the holes become closer to a square.

[0069] For such meshes, it is desirable to have a uniform current distribution within the cation exchange membrane, which has a relatively high electrical resistance, and to achieve this, it is better to have small meshes in the expanded metal. However, in reality, the bubbles generated by electrolysis need to be expelled through the openings, i.e., the meshes of the expanded metal, and for this to happen, a certain degree of pore size is essential. Furthermore, even if there are openings, it is difficult for the bubbles to escape if the gaps are too narrow, such as with thin mesh. After careful consideration of this issue, it was found that it would be sufficient to keep the relationship between the opening rate and the pore size of the expanded metal within a certain range.

[0070] Figure 2 shows specific examples of preferred mesh shapes for expanded metal. Figure 2(a) shows a diamond shape, and (b) shows a tortoiseshell shape.

[0071] The aperture ratio of the expanded metal used here is 20% to 60%, preferably 22% to 55%, more preferably 25% to 50%, and even more preferably 35% to 40%. If the aperture ratio is less than 20%, the titanium area per surface, i.e., the electrode area, increases. However, the gaps within the expanded metal become smaller, making it difficult for generated bubbles to escape to the opposite side of the cation exchange membrane, i.e., to the back side of the electrode. Therefore, when forming the expanded metal, it is desirable to increase the gaps even slightly by making it three-dimensional. It is also desirable to make the apparent thickness thicker than the original sheet thickness. This increases the effective electrode area and makes it possible for bubbles to escape to the opposite side of the cation exchange membrane more effectively. On the other hand, if the aperture ratio exceeds 60%, the effective electrode area decreases, resulting in a problem of increased voltage. The stretching ratio of the expanded metal used during production is 1.25 to 2.50 times the length of the original sheet, preferably 1.28 to 2.22 times, more preferably 1.33 to 2.00 times, and even more preferably 1.54 to 1.67 times.

[0072] That is, ordinary expanded metal is produced by expanding a plate to form a porous body, and then roll-pressing the porous body until it has the same thickness as the original plate to form a porous body with a smooth surface. In contrast, in this embodiment, roll-pressing is performed as follows. That is, the original plate (thickness t mm) is expanded to form a porous body. The apparent thickness of the porous body before roll-pressing is T mm. The porous body is then roll-pressed to a thickness 1.1 to 2.0 times that of the original plate. That is, the apparent thickness P mm of the roll-pressed product is set to 1.1 t or more and 2 t or less. The roll-pressed product is not pressed to the same thickness as the original plate, so it can be said to be a weakly pressed product.

[0073] Here, we will consider an example of a porous body made by expanding a plate. Figure 1 shows a schematic diagram of a porous body made by expanding a plate. As shown in Figure 1, the thickness of the plate before expanding a plate and the thickness of the porous body are the same, and are denoted as t (mm). The opening period of the long side of the porous body is denoted as LW (mm), the opening period of the short side is denoted as SW (mm), and the strand is denoted as W (mm). The apparent thickness of the expanded metal before roll pressing is denoted as T (mm). In this case, T is expressed by Equation 2. (Equation 2) T = 2W / SW·{t + √(SW 2 -4W 2 )}

[0074] As shown in Figure 1(b), the manufacturing conditions for expanded metal usually determine the apparent thickness T, which is determined by the original plate thickness (t) and the plate feed width (strand (W)) when manufacturing the expanded metal, and the metal portion is tilted relative to the flat plate, making it significantly thicker than the original plate. When expanded metal is used, its opening ratio is given by the strand and the repeating period in the extension direction, SW.

[0075] If the measured apparent thickness of the expanded metal before roll pressing is K, K has the relationship of (Equation 3) with the calculated apparent thickness T of the expanded metal obtained by (Equation 2). (Math 3)K=α·T Here, 0.7≦α≦1.0 α is a correction coefficient, and the actual measured value tends to be slightly smaller than the calculated value due to rounding and distortion of the edges of the metal parts during actual expanded metal processing.

[0076] The unrolled expanded metal with apparent thickness K is roll-pressed to an apparent thickness P mm of 1.1 t or more and 2 t or less. At this time, there is almost no change in LW, SW, W, and t before and after roll-pressing.

[0077] For the anode in the cation exchange membrane method of chloride chlorine electrolysis, a tilted structure is rolled down to the original plate thickness (t) to form a simple perforated plate. This makes it easy to handle, but it has little effect, especially when the perforations of the perforated plate are relatively large. However, the bubbles that are generated first flow perpendicular to the cation exchange membrane in the plate thickness direction, and then flow along with the liquid flow, resulting in a problem of poor bubble removal. This is because when the plate is thin and the aperture ratio is low, the apparent perforations become small, which leads to a problem of poor bubble removal in the case of chlorine, which has much larger bubbles than hydrogen.

[0078] In this embodiment, this is pressed by roll pressing to a thickness 1.1 to 2.0 times that of the original plate, which makes the porous portion tilted, and by utilizing this tilt and tilting it upward from the cation exchange membrane side toward the back side of the electrode, air bubbles can be removed without resistance along the flow of the air bubbles.

[0079] Figure 3 shows an explanatory diagram of how bubbles escape. Smoothing the expanded metal to the same thickness as the base plate, as is done in conventional cation-exchange membrane electrolysis, maximizes the contact area between the expanded metal and the cation-exchange membrane, and one would expect this to result in the most efficient electrolysis. However, in reality, the bubbles generated by electrolysis would normally move to the opposite side of the cation-exchange membrane, i.e., the back side of the electrode, and then continue upward. However, they are obstructed by the cross section of the electrode, and must first emerge horizontally and then rise due to their own buoyancy. This resistance prevents the bubbles from escaping, and the slower their rate of ascent results in a slight increase in the amount of bubbles in the solution (see Figure 3(a)). This essentially poses the problem of increasing the electrical resistance of the electrolyte.

[0080] In this embodiment, these factors are taken into consideration, and the cation exchange membrane actually swells slightly during use. The pressure of the catholyte allows the cation exchange membrane to conform to any slight irregularities on the anode, allowing it to adhere to the surface. The ideal irregularity is preferably 1.2 to 2.0 times, and more preferably 1.2 to 1.5 times, the thickness of the pure titanium plate before processing. This minimizes resistance and prevents generated bubbles from moving horizontally, allowing them to rise diagonally upward, opposite the cation exchange membrane (see Figure 3(b)). Depending on the degree of swelling of the cation exchange membrane, the degree of electrode smoothing may need to be slightly changed to 1.4 to 2.0 times, and appropriate selection may be desirable depending on the cation exchange membrane.

[0081] The LW / SW ratio, which determines the mesh size and shape of the expanded metal, is 1.5 to 3.5, preferably 1.6 to 2.5, and more preferably 1.7 to 2.0. The LW / SW ratio shown here is related to the aspect ratio of the diamond-shaped opening of the expanded metal. As the LW / SW ratio increases, the long diameter of the diamond increases relative to the short diameter. This means that even with the same opening area, the mesh size becomes narrower, making it more difficult for air bubbles to escape. Therefore, it is desirable for the opening to have an aspect ratio close to 1:1. To achieve this, an LW / SW ratio close to 1 is desirable, but considering the workability of titanium, a ratio of around 1.5 is considered the limit; processing becomes difficult if the ratio is smaller than that. If the LW / SW ratio is greater than 3.5, depending on the mesh size, there is a high possibility that thin areas will form in the diamond-shaped opening, preventing complete escape of air bubbles.

[0082] In this embodiment, the opening period SW of the short side is 2.0 mm or more and 5.5 mm or less, preferably 2.0 mm or more and 5.0 mm or less, and more preferably 2.2 mm or more and 4.5 mm or less. The size of SW is determined by the strand (W) and opening ratio of the expanded metal, but in the case of cation exchange membrane chlor-alkali electrolysis, when manufacturing expanded metal, it is determined to be as small as possible while allowing generated bubbles to easily escape. Furthermore, in order to ensure stable production when manufacturing expanded metal, the plate thickness (t) and strand (W) are often made approximately the same size. The SW of the expanded metal is determined by these factors.

[0083] Next, a method for producing an anode according to this embodiment will be described. The method for producing an electrode for chloralkali electrolysis using a cation exchange membrane method includes the following steps.

[0084] (Process 1) Prepare an expanded metal made of pure titanium perforated plate with a thickness of t mm, a long side opening period of LW mm, a short side opening period of SW mm, strands of W mm, and an apparent thickness of K mm. (Process 2) The expanded metal is roll-pressed to form a roll-pressed product with an apparent thickness of P mm as an electrode substrate. (Step 3) A hydrophilic electrode active material coating layer is formed on the surface of the roll-pressed product.

[0085] In the roll-pressed product, the opening rate of the expanded metal is 20% or more and 60% or less, the ratio calculated by LW / SW is 1.5 or more and 3.5 or less, the plate thickness t of the perforated plate is 0.5 mm or more and 1.0 mm or less, the opening period SW of the short side is 2.0 mm or more and 5.5 mm or less, and the apparent thickness Pmm of the roll-pressed product is 1.1t or more and 2t or less.

[0086] So far, we have discussed the shape of the anode electrode substrate. The size of chlorine gas bubbles generated from the anode is typically more than 100 times larger than the size of hydrogen bubbles generated from the cathode. This size varies depending on the hydrophilicity of the electrode surface, the hydrophilicity of the cation exchange membrane, and even the unevenness of the electrode surface. The porous portions of the anode expanded metal are relatively small because they are numerous and arranged in a fine pattern. Although this embodiment improves bubble escape at an angle, it is desirable for smaller bubbles to escape from the electrode. To achieve this, a hydrophilic electrode active material coating layer is provided. Furthermore, it is preferable to process the surface of the electrode substrate.

[0087] The method for producing an anode preferably further includes, between step 2 and step 3, step 4 of subjecting the roll-pressed product obtained in step 2 to a surface blasting treatment, and step 5 of etching the surface-blasted roll-pressed product with high-temperature hydrochloric acid to remove sharp protrusions and sharp edges on the surface.

[0088] (Step 4) For this reason, it is preferable to roughen the surface of the expanded metal substrate by blasting or other methods, remove burrs, and smooth the corners and edges. Smoothing the corners is particularly important because the porous area is tilted, potentially creating areas that come into contact with the cation-exchange membrane at sharp angles, preventing damage to the membrane. For example, when sandblasting, it is preferable to use white alumina shot with an average particle size of approximately 0.5 mm as the medium and apply a pressure of approximately 0.2 to 0.5 MPa. However, this should be adjusted depending on the thickness of the titanium substrate used. Of course, it is also possible to use other media, such as SiC powder or zircon sand, if they can achieve similar properties.

[0089] Furthermore, blasting with iron grit or iron shot is sometimes used to roughen the surface, but this requires a high blasting pressure, and blasting tends to leave iron in the titanium substrate, which requires excessive etching of the substrate to remove, so although it is not impossible, its use is not recommended.

[0090] (Step 5) After blasting, the surface is preferably etched with a high-temperature hydrochloric acid solution to completely remove any remaining blast dust, smooth any sharp irregularities created by blasting, and activate the substrate surface. Hydrochloric acid is used as the etching acid because it has a strong etching effect, smoothing any sharp irregularities created by blasting and improving the desorption of bubbles generated during electrolysis, allowing them to leave the substrate surface before they grow large, resulting in small bubbles that quickly escape from the anode. Furthermore, hydrochloric acid etching produces countless fine titanium hydrides on the titanium substrate surface, which provides extremely strong adhesion when electrode coating is applied to the surface. The conditions for hydrochloric acid etching are a hydrochloric acid concentration of 18% to 25%, and a temperature of 90°C to 107°C (boiling). The treatment time is preferably 10 to 15 minutes, and the titanium weight loss is 30 to 70 g / m. 2 - A projection surface is preferable, but is not limited to this.

[0091] A composite oxide-type electrode coating is applied to the surface of the substrate prepared in this manner. At least the surface of this electrode coating must be hydrophilic. This allows for better bubble separation of the generated gas (chlorine gas), resulting in finer bubbles that are easier to remove. The hydrophilic coating used here is preferably formed by a conventional pyrolytic coating method. The solvent for the coating solution is preferably an alcohol-based solution. However, electrodes prepared in this manner have the problem of relatively rapid electrode wear. Therefore, considering durability, it is recommended that the base be coated using a conventional hydrochloric acid solvent solution, and then the surface be pyrolytically coated from the solution that will become the hydrophilic coating described here. In other words, it is possible to layer two or more types of coatings. Naturally, if necessary, a single hydrophilic coating may be used.

[0092] More specifically, step 3 preferably includes step 3-1 of applying a coating liquid consisting of a dilute hydrochloric acid solution containing ruthenium or a dilute hydrochloric acid solution containing ruthenium and iridium to the surface of the roll-pressed product and repeating thermal decomposition multiple times, and step 3-2 of applying a coating liquid containing ruthenium and mainly containing alcohol as a solvent or a coating liquid containing ruthenium and iridium and mainly containing alcohol as a solvent and performing thermal decomposition coating one or more times to make the surface of the electrode active material coating layer hydrophilic.

[0093] Although the components of the electrode coating are not specifically specified here, it is preferable that the electrode active material coating layer be an oxide coating layer consisting of ruthenium or two components, ruthenium and iridium, as the electrode active material, with titanium or tin or two components, titanium and tin, as stabilizers, and further containing other components as necessary. These can be modified versions of conventional components. However, the electrode coating on the electrode surface must be highly hydrophilic. Furthermore, when a long-life electrode is required, as is the case with current technologies, a composite oxide consisting of ruthenium and iridium as the electrode active materials and titanium as a stabilizer is desirable.

[0094] For hydrophilic coatings, it is desirable to use an alcohol-based solution such as n-butanol or iso- or n-propanol as the solvent for the coating solution containing these electrode active materials, rather than an aqueous solution, and to carry out the coating under conditions adjusted accordingly. This allows for a highly hydrophilic coating layer to be obtained. Furthermore, since the hydrophilic coating produced in this way has the characteristic of slightly greater consumption of the electrode active material compared to when dilute hydrochloric acid is used as the solvent, it is also recommended to apply an aqueous coating to the base layer and then layer a coating using an alcohol-based liquid on top of the base layer.

[0095] The electrode coating layer made from an aqueous solution system here is initially hydrophobic and has the characteristic of having a slightly high potential, but after several months to three years of electrolysis, the potential decreases and the layer becomes hydrophilic. Therefore, by using such an electrode coating with two or more layers for continuous use, it is possible to maintain a low potential and hydrophilicity over a long period of time.

[0096] This reduces the current to 6kA / m 2 to 8kA / m 2 This is extremely excellent at large current densities, and together with the low overvoltage, the influence of bubbles generated by electrolysis is minimized, that is, electrolysis at a low electrolysis voltage is possible.

[0097] [Cathode coating layer formation] When the electrode active material for the cathode coating layer contains a platinum group metal and / or platinum group metal oxide, the formation method is essentially the same as for the anode: pyrolysis. Specifically, a nickel plain-woven mesh substrate is blasted to roughen and hydrophilize the surface, followed by etching to create fine irregularities and activate the surface. However, with such a fine mesh, applying mechanical force such as blasting can cause excessive deformation, so an etching process that roughens the surface is desirable. For example, immersion for 3 to 5 minutes at room temperature in an etching solution prepared by mixing nitric acid, acetic acid, and acetone in a 1:1:1 (molar ratio) can produce a slightly matte surface and activate the surface. The desired concentration of the etching solution can be achieved by diluting it with deionized water. After the surface is roughened and activated in this manner, a coating solution containing an electrode catalyst material is applied. Spray application is preferred, but a brush or rubber roller can also be used. In plain weave applications, the applied coating solution tends to accumulate at the intersections of the nickel wires. However, with proper etching, the coating spreads due to the capillary effect present on the nickel surface, creating a coating layer of nearly uniform thickness. This coating is then dried and pyrolyzed at a predetermined temperature to form an electrode coating containing platinum group metals and / or platinum group metal oxides. Repeating this process from application to pyrolysis allows for the formation of a coating layer of the required thickness. However, compared to anode coating solutions, cathode coating solutions require a lower-viscosity solvent to improve the solution's wettability and reduce its viscosity. For example, instead of n-butanol, which is typically used for anodes, a lower-viscosity solvent, such as iso- or n-propanol, is used for cathodes.

[0098] When the electrode active material for the cathode coating layer contains a ruthenium-cerium composite oxide, the cathode substrate is degreased with a neutral detergent and then immersed in an etching solution prepared by mixing nitric acid, acetic acid, and acetone in a 1:1:1 molar ratio until the metallic luster of the surface is slightly altered. Then, cerium chloride is mixed with ruthenium chloride hydrochloride solution to achieve a metal molar ratio of 2:1, and the resulting solution is diluted with a 10% HCl solution:n-propanol solution (volume ratio of 1:1). The nickel substrate is immersed in this solution for 1 minute, and then approximately dried by blowing cold air from above to remove excess coating solution. The substrate is then dried at 40°C for 10 minutes and then thermally decomposed at 500°C to form a RuO2-SrO2 composite oxide layer. Repeating this process allows the formation of a hydrophilic coating layer with the desired coating amount.

[0099] Flexible Body The elastic body 15 is preferably a spring-like body, such as a sponge mattress made of randomly folded and bundled nickel wire, or a metal scrubber made of nickel wire. The elastic body 15 is preferably placed between the cathode current collector 16 and the cathode 11.

[0100] [Anode support] The anode 10 is supported by a support. For example, the anode 10 is directly welded to the frame of the electrolytic cell and to a rib 18 attached to the electrolytic cell. The rib 18 is preferably provided with a liquid passage hole 20 so as not to impede the circulation of the anolyte filled in the anode chamber 14.

[0101] This embodiment enables electrolysis at an extremely low electrolysis voltage in zero-gap cation exchange membrane chloralkali electrolysis, achieving excellent chlorine generation efficiency and a long and stable anode life. Specifically, by slightly tilting the meshes of the porous portion of the expanded metal slightly upward from the cation exchange membrane side toward the opposite side (back side) of the cation exchange membrane, air bubbles are more easily removed. Furthermore, by improving the electrode surface and making the electrode coating itself hydrophilic, air bubbles are more easily removed. Furthermore, the air bubbles are smaller in diameter, which improves air bubble removal from the electrode. As a result, even if the current density is increased and the air bubble ratio around the electrode is increased, the generated air bubbles remain small and escape to the rear more quickly. As a result, even when the current density is increased, the increase in voltage is minimized, and the voltage itself can be maintained low.

[0102] When electrodes with a longer life are required, a compact electrode coating is applied to the base using a coating liquid of an aqueous solvent, and then a hydrophilic electrode coating of a hydrophilic alcohol solvent is layered on the surface. This allows the cell voltage to be low from the beginning, and stable electrolysis can be performed for a long period of time. [Example]

[0103] <Test 1> As an anode, a pure titanium plate with a thickness of t = 0.8 mm was used to fabricate an expanded metal (diamond-shaped mesh) with a width of 3.0 mm, length of 5.0 mm, and an aperture ratio of 40%. The strand width (W) was approximately 0.9 mm, and the apparent thickness of the expanded metal before roll pressing was 1.8 to 1.9 mm. The expanded metal was roll-pressed to produce porous titanium bodies with varying apparent thicknesses P (also referred to as electrode thickness P in the table) as shown in Tests 1-1 to 1-7. These porous titanium bodies were then blasted at a pressure of 0.2 MPa using white alumina sand as a medium. The porous titanium bodies were then etched in a 20% hydrochloric acid solution at 95°C for 10 minutes to clean and activate the surface. The surfaces of the porous titanium bodies thus prepared were then coated with an electrode active material. The coating solution was prepared by dissolving iridium chloride, ruthenium chloride, and titanium butoxide in n-butyl alcohol. The composition of the metal components in the coating liquid was iridium:ruthenium:titanium = 16.7:33.3:50.0 in terms of metal molar ratio. This coating liquid was applied with a brush to the surface of the blasted and etched titanium porous body, dried at 60°C, and then thermally decomposed at 510°C for 10 minutes. After repeating the application, drying, and thermal decomposition process 10 times, a total amount of iridium and ruthenium of 8 g / m2 was obtained as an anode coating layer of hydrophilic electrode active material per projected surface of the titanium porous body. 2 A composite oxide coating equivalent to 1000 ppm was formed. Next, a 25-mesh plain weave mesh was prepared as the cathode by weaving pure nickel wire with a diameter of 0.12 mm. The pitch of this mesh was 1.02 mm both vertically and horizontally. The pitch / SW was 0.34. This mesh was subjected to blasting treatment with white alumina sand at a pressure of 0.15 MPa, and then the surface was etched and activated with a 20% hydrochloric acid solution at 60°C. The etched and activated mesh was then coated with a coating solution prepared by dissolving dinitrodiammine platinum and cerium chloride in a 1:1 mixture of n-propanol and pure water, and pyrolyzed at 450°C. The coating / pyrolysis process was repeated eight times to obtain a coating of platinum at 5 g / m². 2A cathode coating layer of hydrophilic electrode active material equivalent to 1000 kJ / cm2 was prepared. The anode and cathode prepared in this way were placed in an experimental zero-gap cation exchange membrane electrolytic cell, and the electrolysis voltage was measured. The operating temperature was 85°C, and the current density was 0.6 A / cm2. 2 After 10 hours of preliminary electrolysis, the electrolysis voltage was measured. The anolyte was 200 g-NaCl / L, but the pH was not adjusted. As shown in Table 1, the electrolysis voltages in Tests 1-2 to 1-6 were lower than those of the conventional expanded metal electrode (Test 1-1) in which the thickness of the substrate was achieved by pressing, and were 2.95 V or less. The electrolysis voltage in Test 1-7 exceeded 2.95 V. This was because the electrode was thick due to insufficient pressing, and the electrolysis current was concentrated more on the front side of the electrode. To change the relative positions of the cathode and anode, the cathode was rotated in 90° increments within the plane and the voltage was measured; however, there was no change at all. This indicated that the change in current density in the cation exchange membrane was negligible.

[0104] [Table 1]

[0105] <Test 2> As anodes, expanded metal plates with LW = 4.0 mm and SW = 2.5 mm were fabricated from pure titanium plates with a thickness of t = 0.6 mm. The open area ratios were varied as shown in Tests 2-1 to 2-7. The apparent thickness before roll pressing was 1.7 mm for Test 2-1 (open area ratio of 10%) and 1.0 mm for Test 2-7 (open area ratio of 70%). These expanded metal plates were roll-pressed to a thickness P of 0.9 mm, which was 1.5 times the original plate thickness. The porous titanium bodies thus obtained were used as electrode substrates, and after pretreatment, an anode coating layer of a hydrophilic electrode active material was formed. The characteristics of the anodes were measured. The porous titanium electrode substrates thus fabricated were blasted at a pressure of 0.2 MPa using SiC powder to create surface irregularities and to homogenize the surface. They were then etched for 10 minutes in a 20% hydrochloric acid solution at 90°C. This anode was prepared using the same coating solution and under the same conditions as in Test 1. The cathode used was the same activated cathode as in Test 1, consisting of a nickel plain-woven mesh surface coated with a hydrophilic cathode active material. The pitch / SW was 0.41. The same experimental zero-gap cation exchange membrane electrolytic cell was used as in Test 1, and electrolysis was performed under the same conditions. The potential and electrolysis voltage were measured. The results are shown in Table 2. In Test 2-1, with a 10% aperture ratio, the effective electrode area was indeed large, but the apertures were very small, resulting in the accumulation of air bubbles between the electrode and the cation exchange membrane, making it difficult to pass current at high current densities. The electrolysis voltage was significantly higher than 2.95 V. In Test 2-7, the effective electrode area decreased as the aperture ratio increased, resulting in an increase in electrolysis voltage (3.20 V). The cathode position on the cation exchange membrane surface was varied as in Test 1, but no change in electrolysis voltage was observed for each anode.

[0106] [Table 2]

[0107] <Comparative test> The porous titanium body of Test 2 was processed in the same manner as Tests "Test 1" to "Test 7," except that the expanded metal was pressed to the same thickness as the original plate, 0.6 mm. The surface treatment and coating were also the same, and anodes were fabricated. Electrolysis was performed on these under the same conditions as Test 2, and the electrolysis voltage was measured. The results are shown in Table 3. The pitch / SW was 0.41.

[0108] [Table 3]

[0109] As shown in Table 3, the electrolysis voltage in all cases was significantly higher than 2.95 V. This resulted in increased power consumption.

[0110] <Test 3> As anodes, 1.0 mm thick pure titanium plates with a 50% aperture ratio and a SW of 3.0 mm were used to fabricate expanded metal plates with LW = 4.0 mm, 6.0 mm, 7.0 mm, 8.0 mm, 10.0 mm, and 12.0 mm as shown in Tests 3-1 to 3-7. Among these, the LW = 4.0 mm plate in Test 3-1 could be manufactured, but cracks occurred in some areas, making it unsuitable for the intended purpose. Except for Test 3-1 with LW = 4.0 mm, the plates were processed by roll pressing to an apparent thickness P of 1.2 mm. These plates were first subjected to a hydrophobic electrode coating under the following conditions, and then a hydrophilic electrode coating was applied to the surface to fabricate anodes. A comparative example (Test 3-7) was also prepared with only a hydrophobic electrode coating. The surfaces of the expanded metal plates prepared as described above were then blasted with white alumina at a pressure of 0.25 MPa. The substrate was then etched for 10 minutes in a 20% aqueous hydrochloric acid solution maintained at 100°C. After preparation in this manner, the following pyrolytic coating was carried out. First, two types of coating liquids were prepared, each with the same composition but different raw materials. In other words, the metal components of the coating were iridium, ruthenium, and titanium, and the metal mass ratio in both compositions was iridium:ruthenium:titanium = 30:30:40 (molar ratio). Coating liquid 1 was prepared by using iridium chloride, ruthenium chloride, and an aqueous titanium tetrachloride solution as raw materials, and dissolving these in a 10% aqueous hydrochloric acid solution. Coating liquid 2 was prepared by using iridium chloride, ruthenium chloride, and orthotitanium butoxide as raw materials, and dissolving these in n-butanol. The coating conditions were 1 g / m of iridium + ruthenium per titanium surface. 2The coating was applied with a brush so that the surface would become a projection surface, dried at 60°C for 10 minutes, pyrolyzed at 480°C for 10 minutes, and then allowed to cool. This process was repeated as many times as necessary. Specifically, the coating, drying, and pyrolysis procedures for Coating Liquid 1 were repeated five times, and then Coating Liquid 2 was applied to the surface, dried, and pyrolyzed five more times to form an anode. As a comparative example, an anode was prepared by repeating the coating, drying, and pyrolysis procedures 10 times using only Coating Liquid 1 (Tests 3-7). For the cathode, a 30-mesh knitted mesh was prepared by plain weaving nickel wire with a wire diameter of 0.1 mm. This was then subjected to blasting and etching in the same manner as in Test 1, and then coated with platinum-cerium oxide to form an activated cathode. The pitch of the nickel mesh was 0.85 mm. The pitch / SW was 0.28. Using these anodes and cathodes, an electrolytic cell was assembled under the same conditions as in Test 1, and electrolysis was performed under the same conditions. The results are shown in Table 4. As shown in Table 4, when the LW / SW ratio was greater than 3.5, as in Test 3-6, the small mesh area expanded, which led to poor bubble removal and an electrolysis voltage exceeding 2.95 V. In Test 3-7, the electrolysis voltage was higher than in Test 3-5, likely due to the hydrophobic coating and the large bubbles generated by electrolysis. The cathode's position on the cation-exchange membrane surface was changed as in Test 1, but no change in voltage was observed. This indicates that changing the relative positions of the anode and cathode through the cation-exchange membrane does not substantially change the current density within the cation-exchange membrane.

[0111] [Table 4]

[0112] <Test 4> Using a 1.0 mm thick pure titanium plate with a 40% aperture ratio and a LW of 6.0 mm, expanded metal plates with SWs of 2.0 mm, 3.0 mm, 4.0 mm, and 5.0 mm were manufactured as in Tests 4-1 to 4-4. This expanded metal was roll-pressed to an apparent thickness P of 1.2 mm. These roll-pressed titanium expanded metals with the same apparent thickness P were blasted in the same manner as in Test 1, then etched in 20% hydrochloric acid held at 90°C to clean and activate the surface, after which a hydrophilic electrode active material was coated on the surface. The anode coating was an oxide system consisting of ruthenium, titanium, and tin. Specifically, a coating solution was prepared by dissolving aqueous solutions of ruthenium chloride, tin dichloride, and titanium tetrachloride in a 1:1 volumetric mixture of n-butanol and 10% hydrochloric acid. The metal molar ratio of the metal components in the coating solution was ruthenium:tin:titanium = 15:15:70. This coating solution was applied with a brush so that it was evenly distributed over the entire surface of the blasted and etched titanium expanded metal, dried at 110°C, and then thermally decomposed in a muffle furnace at 470°C in circulating air for 10 minutes. The application, drying, and thermal decomposition process was repeated 10 times, and then heat treatment was carried out in circulating air at 470°C for 1 hour to produce an electrode. This resulted in a coating amount of 1 m2 of projected surface. 2The amount of ruthenium per electrode was 10 g. The same cathode as used in Test 3 was used. The pitch / SW was 0.43 for Test 4-1, 0.28 for Test 4-2, 0.21 for Test 4-3, and 0.17 for Test 4-4. The potential and electrolysis voltage of the zero-gap cation exchange membrane electrolytic cell were measured for the electrodes prepared in this manner under the same conditions as Test 3. Observation of the bubbles emerging from the electrolysis revealed very little bubble growth on the electrode surface, confirming the electrode's hydrophilic surface. While the cation exchange membrane surface was visible to some extent on the cathode side, the area behind it was covered with white bubbles, which were uniform and showed very little movement. Table 5 shows the potential and electrolysis voltage measurements for Tests 4-1 to 4-4. As shown in Table 5, the anode potentials of Tests 4-1 to 4-3 were almost the same, including the comparative example of Test 4-4. However, in the comparative example of Test 4-4, the porous area was large, but the spacing between the holes was wide, which resulted in a higher apparent electrolysis voltage. However, as mentioned above, the cathode side of each test was apparently the same, and changes in the state of the bubbles generated at the anode were observed. As in Tests 1 to 3, the cathode was rotated on the surface of the cation exchange membrane to change the relative position of the anode and cathode. However, no change in the electrolysis voltage was observed, and no change in the current distribution within the cation exchange membrane was observed. It was also found that the change in electrolysis voltage corresponded to the change in the anode. In Test 4-4, the strands were large, and the large blind area on the surface of the cation exchange membrane likely prevented the generated bubbles from escaping, resulting in a higher electrolysis voltage.

[0113] [Table 5]

[0114] <Test 5-I> Using a pure titanium plate with a thickness of 0.5 mm, an opening ratio of 20%, an LW of 6.0 mm, and expanded metal plates with SW of 1.8 mm, 2.0 mm, 2.5 mm, 3.0 mm, and 4.0 mm were prepared as in Tests 5-1 to 5-5. These expanded metal plates were roll-pressed to an apparent thickness P of 0.9 mm. These titanium expanded metal plates with the same thickness were pretreated and coated with an electrode active material under the same conditions as in Test 4 to prepare electrodes. The amount of electrode coating was 1 m of projected surface. 2 The amount of ruthenium per electrode was 8 g. The potential and electrolysis voltage of the zero-gap cation exchange membrane electrolytic cell were measured for the electrodes prepared in this manner under the same conditions as in Test 4. The cathode was prepared as in Test 3 by plain-weaving 0.1 mm diameter nickel wire to form a 30-mesh knitted mesh. This was then subjected to blasting and etching in the same manner as in Test 1, followed by a platinum-cerium oxide coating to form a cathode coating layer of hydrophilic electrode active material. The mesh pitch was 0.85 mm. As can be seen, in Tests 5-1 to 5-5, the pitches of the cathode plain-woven nickel mesh for the anode SW were 1.8 mm, 2.0 mm, 2.5 mm, 3.0 mm, and 4.0 mm, respectively, while the pitch / SW ratios were 0.47, 0.43, 0.34, 0.28, and 0.21, respectively. The pitch / SW ratios were all less than 0.5. Perhaps for this reason, as in Test 4, the cathode was rotated on the surface of the cation exchange membrane, and the relative positions of the anode and cathode were changed, but no change in the electrolysis voltage was observed. In other words, it was found that when the size relationship between the cathode and anode is as described above, the relative positions of the anode and cathode have almost no effect. The measurement results are shown in Table 6.

[0115] [Table 6]

[0116] <Test 5-II> Pure titanium plates with a thickness of 0.5 mm were processed essentially the same as in Test 5-1, except that the aperture ratio was set to 25%. Titanium perforated plates were fabricated using different strands as in Tests 5-6 to 5-9. These were used as electrode substrates and pretreated under the same conditions as in Test 5-1. A hydrophilic electrode active material coating layer was applied to fabricate electrodes, and measurements were performed as electrodes under the same conditions as in Test 5-1. The cathodes used were also the same as in Test 5-1. The pitch of the cathode nickel mesh was 0.85 mm. The pitch / SW ratio was 0.47 in Test 5-6, 0.43 in Test 5-7, 0.34 in Test 5-8, and 0.28 in Test 5-9. The results are shown in Table 7. As in Test 5-1, the cathode was rotated on the surface of the cation exchange membrane, and the relative positions of the anode and cathode were varied, but no change in the electrolysis voltage was observed.

[0117] [Table 7]

[0118] <Test 6> A pure titanium plate with a thickness of 0.8 mm was used as the anode, and an expanded metal with a width of 2.2 mm, length of 3.5 mm, and an opening ratio of 30% was produced. The expanded metal was then roll-pressed to an apparent thickness P of 1.15 mm. This expanded metal was blasted and pickled under the same conditions as in Test 1, and electrode-coated under the same conditions as in Test 1 to produce an anode. A nickel wire with a diameter of 0.12 mm was used as the cathode, and the pitch size was changed to 1.69 mm, 1.27 mm, 1.02 mm, 0.85 mm, 0.74 mm, and 0.64 mm, as in Tests 8-1 to 8-6, to produce plain weave meshes equivalent to 15, 20, 25, 30, 35, and 40 meshes. The pitch / SW ratios were 0.77 for Test 8-1, 0.58 for Test 8-2, 0.46 for Test 8-3, 0.39 for Test 8-4, 0.34 for Test 8-5, and 0.29 for Test 8-6. These samples were pre-etched using a solution containing nitric acid, acetic acid, and acetone in a molar ratio of 1:1:1. Ruthenium chloride and cerium chloride were then dissolved in a solution containing 10% hydrochloric acid and n-propanol in a volume ratio of 1:1 to achieve a metal molar ratio of 2:1. The coating was applied by immersion in the solution, and the excess coating was blown off with a blower. Then, the samples were thermally decomposed at 550°C. This process was repeated to produce a composite oxide coating consisting of ruthenium oxide and cerium oxide. The prepared anode and cathode, or a cation exchange membrane sandwiched between them, were installed in the same electrolytic cell as in Example 1, and electrolysis was performed using a zero-gap electrolytic cell. As in Tests 1 to 5, the cathode was allowed to rotate on the surface of the cation exchange membrane to observe changes in electrical resistance within the membrane. The results are shown in Table 8. As can be seen, there were no problems with the electrolysis voltage in Tests 8-1 and 8-2, but rotating the cathode caused slight changes in the cell voltage. This was thought to be due to changes in the relative positions of the anode and cathode meshes, which changed the resistance within the membrane. It was also found that if the pitch of the cathode plain weave mesh was less than half that of the anode SW, no changes in voltage occurred, meaning that electrical resistance within the membrane would be kept to a minimum.

[0119] [Table 8]

[0120] <Test 7> A pure titanium plate with a thickness of 0.8 mm was used as the anode to fabricate an expanded metal with a SW of 2.2 mm, LW of 3.5 mm, and an aperture ratio of 30%. The fabricated expanded metal was roll-pressed to an apparent thickness P of 1.2 mm. An electrode coating was fabricated for this substrate under the same conditions as in Example 1, from pretreatment to coating. This resulted in an anode with a hydrophilic surface. For the cathodes in Tests 9-1 to 9-7, seven types of nickel wire with diameters of 0.05 mm, 0.06 mm, 0.08 mm, 0.10 mm, 0.14 mm, 0.16 mm, and 0.18 mm were used, respectively, to fabricate a plain weave mesh for each. The mesh size of the plain weave was 25 mesh, and the pitch was 1.02 mm. The pitch / SW ratio was 0.46. These plain-woven nickel meshes were used as electrode substrates. Their surfaces were blasted at 0.3 MPa using SiC powder as the blasting powder, followed by etching for 10 minutes with 20% hydrochloric acid heated to 60°C. Furthermore, a solution of dinitrodiammine platinum dissolved in isopropanolamine and pure water was diluted with a 1:1 mixture of isopropanol and HO by volume to form a coating solution. This coating solution was applied to the electrode substrate surface, dried, and then pyrolyzed at 450°C for 10 minutes. This application-pyrolysis process was repeated six times to form a cathode coating layer of electrode active material. Water droplets dropped on the cathode surface spread across the mesh, confirming its hydrophilicity. Electrolysis was performed by attaching the mesh to the zero-gap cation-exchange membrane discharge chamber used in Test 6, and electrode voltage measurements were performed for Tests 9-1 to 9-7. To determine the change in current density within the cation-exchange membrane, the cathode was rotated on the cation-exchange membrane surface and the change in electrolysis voltage was measured for Tests 9-1 to 9-7. The results are shown in Table 9. For all cathodes in Tests 9-1 to 9-7, the electrolysis voltage did not change even when the cathode was rotated, and it was found that there was almost no change in the electrical resistance within the cation exchange membrane. However, when the nickel wire diameter was 0.05 mm, it was observed that the electrolysis voltage increased, possibly due to the small cathode surface area. Furthermore, when the wire diameter was 0.18 mm, the voltage increased, although the cause is unknown. There appears to be a problem with the wire diameter and the gap between the wires, and it was found that this also increased the voltage and was not practical.

[0121] [Table 9]

[0122] The current density distribution in the cation exchange membrane, which has rarely been discussed in the past and which is a cause of large electrical resistance, can now be kept almost uniform in this example, and a low electrolysis voltage can be maintained. Furthermore, in long-term operation, the load in the cation exchange membrane is made uniform over the entire surface, resulting in no uneven load and a longer lifespan. [Industrial Applicability]

[0123] The electrolytic cell of the present invention is a so-called zero-gap type cation exchange membrane chloralkali electrolytic cell that can obtain a lower electrolysis voltage and substantially eliminates current bias in the cation exchange membrane, thereby contributing to extending the life of expensive cation exchange membranes. [Explanation of symbols]

[0124] 1 electrode 2. Cation exchange membrane 3 Flow of generated bubbles 10 Anode 11 Cathode 12 Cation exchange membrane 13 Cathode chamber 14 Anode chamber 15 Elastic Body 16 Cathode assembly 17,18 Ribs 19,20 Liquid hole

Claims

1. a cation exchange membrane that serves as a diaphragm; an anode in close contact with one surface of the cation exchange membrane; an anode chamber in which the anode is accommodated and filled with an anolyte; a cathode in close contact with the other surface of the cation exchange membrane; a cathode chamber in which the cathode is accommodated and which is filled with catholyte; In a zero-gap type cation exchange membrane process chlor-alkali electrolysis cell, anode gas is generated at the anode and hydrogen is generated at the cathode, the anode has an electrode substrate made of a perforated plate and an anode coating layer made of a hydrophilic electrode active material formed on the surface of the electrode substrate, The electrode substrate is a roll-pressed product of expanded metal, the perforated plate having a plate thickness of t mm, an opening period of long sides of LW mm, an opening period of short sides of SW mm, and a strand of W mm, The opening ratio of the expanded metal is 20% or more and 60% or less, The ratio calculated by LW / SW is 1.5 or more and 3.5 or less, The plate thickness t of the perforated plate is 0.5 mm or more and 1.0 mm or less, the opening period SW of the short side is 2.0 mm or more and 5.5 mm or less, The apparent thickness P mm of the roll-pressed product is 1.1 t or more and 2.0 t or less, The cathode has a nickel mesh formed by plain weaving nickel wires having a wire diameter of 0.06 to 0.16 mm, and a cathode coating layer made of a hydrophilic electrode active material formed on the surface of the nickel mesh, The pitch of the cathode is equal to or less than half the SW of the anode, The zero-gap type cation exchange membrane process chlor-alkali electrolyzer is characterized in that it has an elastic body that applies pressure to the surface of the cathode opposite to the surface that is in close contact with the cation exchange membrane.

2. The expanded metal is made of pure titanium, the anolyte is a saline solution; the catholyte is an aqueous caustic soda solution; Chlorine gas is produced as the anode gas, and 2. The zero-gap type cation exchange membrane process sodium chloride electrolysis cell according to claim 1, wherein caustic soda and hydrogen are produced in the cathode chamber.

3. The expanded metal is made of pure titanium, and 3. The zero-gap type cation exchange membrane process sodium chloride electrolysis cell according to claim 1, wherein the electrode active material of the anode coating layer is a hydrophilic composite oxide containing iridium, ruthenium, and titanium.

4. 3. The zero-gap type cation exchange membrane process sodium chloride electrolysis cell according to claim 1, wherein the electrode active material of the cathode coating layer contains a platinum group metal and / or a platinum group metal oxide.

5. 3. The zero-gap type cation exchange membrane process sodium chloride electrolysis cell according to claim 1, wherein the electrode active material of the cathode coating layer contains a composite oxide of ruthenium and cerium.

6. 3. The zero-gap type cation exchange membrane process sodium chloride electrolysis cell according to claim 1, wherein the pitch of the nickel mesh is 0.6 to 1.2 mm.

7. 3. A zero-gap type cation exchange membrane process sodium chloride electrolysis cell according to claim 1 or 2, characterized in that the elastic body is a sponge-like mattress made of nickel wires randomly folded and bundled, and is placed between the current collector and the cathode.

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