Method and apparatus for producing sodium hypochlorite solution

Abstract

To provide a method and a device of producing a sodium hypochlorite solution, capable of producing sodium hypochlorite solution of a high effective chlorine concentration, by an on-site facility at a low cost.SOLUTION: The method of producing a sodium hypochlorite solution including a primary saline water preparation step of dissolving industrial salt G comprising sodium chloride as a main component into purified water B and a chelating step of chelating the primary saline water to prepare secondary saline water A, is characterized by keeping a salt decomposition ratio in a range from 80 to 95%, upon producing a sodium hypochlorite solution by feeding secondary saline water, i.e., an aqueous solution of sodium chloride to an anode chamber 2 in an electrolytic tank 10 separated into the anode chamber 2 and a cathode chamber 3 by an ion exchange membrane 1, and introducing an anolyte and resulting chlorine gas present in the anode chamber and a resulting aqueous solution of sodium hydroxide present in the cathode chamber after electrolysis into a reaction tank 20, to produce a sodium hypochlorite solution by the reaction of the anolyte, chlorine gas, and the catholyte, namely the resulting aqueous solution of sodium hydroxide in the reaction tank.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and an apparatus for producing a sodium hypochlorite solution (hereinafter also simply referred to as the "production method" and "production apparatus"). More specifically, the present invention relates to a technology for obtaining higher-concentration sodium hypochlorite in a method and apparatus for producing a sodium hypochlorite solution on-site by using an ion exchange membrane as a diaphragm in an electrolytic cell and mixing, in a reaction cell, electrolysis products excluding hydrogen produced in the electrolytic cell. [Background technology]

[0002] Sodium hypochlorite is used in various fields as a typical bleaching agent and disinfectant, such as in the treatment of water and sewage systems and wastewater treatment. Common methods for producing sodium hypochlorite include a method in which chlorine obtained by electrolysis of brine is reacted with an aqueous sodium hydroxide solution in a reaction tank, and a method in which an aqueous sodium chloride solution is electrolyzed in a diaphragm-less electrolytic cell to directly produce sodium hypochlorite in the diaphragm-less electrolytic cell.

[0003] In the latter method, since the electrolytic cell is membraneless, the produced sodium hypochlorite is reduced to salt on the cathode, and the produced sodium hypochlorite is anodized and converted into sodium chlorate, which has no effective oxidizing power, making it difficult to obtain a high-concentration sodium hypochlorite solution. Therefore, the applications of sodium hypochlorite produced by this production method are generally those that do not require a high concentration, such as heat exchange water in power plants, shaft cooling water for rotating machinery, prevention of the growth and adhesion of organisms in seawater in ballast water treatment, water supply and sewage treatment, and wastewater treatment.

[0004] On the other hand, a typical application of the former manufacturing method is the general manufacturing method of high-concentration sodium hypochlorite in a brine electrolysis plant. In a brine electrolysis plant, in order to maintain stable and highly efficient plant operation, a brine purification system that highly removes metal impurities and unnecessary anions contained in the raw salt and raw water, and a system that decomposes and removes hypochlorous acid and chloric acid contained in the brine after electrolysis and repurifies it in order to reuse the brine whose concentration has decreased after electrolysis, are essential, and the facilities required are large-scale.

[0005] The primary purpose of chlor-alkali electrolysis plants is not to produce sodium hypochlorite, but rather to produce sodium hydroxide and chlorine gas, which have many industrial uses. These plants are often part of petrochemical complexes and are often large-scale plants with annual production of tens of thousands to hundreds of thousands of tons of sodium hydroxide. The number of chlor-alkali electrolysis plants is overwhelmingly small compared to the number of water supply facilities that require high-concentration sodium hypochlorite. Therefore, the chlorine gas or sodium hypochlorite required for water sterilization must be transported to and stored at the water supply. This creates a constant risk of human injury and environmental damage due to leaks from storage facilities. In particular, chlorine gas has been involved in serious traffic accidents involving tanker trucks used for transport, resulting in the release of chlorine gas into the environment, leading to active efforts to tighten laws regarding the transport of chlorine gas.

[0006] Under these circumstances, an on-site method for producing high-concentration sodium hypochlorite has been proposed, in which a small electrolytic device for producing sodium hypochlorite is installed at a sodium hypochlorite-using facility such as a water supply plant, and the required amount of sodium hypochlorite is produced when needed.

[0007] For example, Patent Document 1 describes a technology in which an electrolytic cell having a cation exchange membrane provided between an anode and a cathode is used, electrolysis is performed while adding an alkaline chloride solution to the anode chamber and water to the cathode chamber, and the anolyte discharged from the electrolytic cell, the catholyte which is a caustic alkaline solution, and chlorine gas are mixed to produce an alkaline hypochlorite solution having a predetermined effective chlorine concentration.

[0008] Furthermore, Patent Document 2 describes a technology in which an electrolytic cell is partitioned into an anode chamber and a cathode chamber by an ion exchange membrane, an alkali metal chloride aqueous solution is supplied to the anode chamber, and pure water is supplied to the cathode chamber to perform electrolysis, and the anolyte and generated chlorine gas in the anode chamber after electrolysis, and the alkali metal hydroxide aqueous solution in the cathode chamber are introduced into a reaction tank to produce sodium hypochlorite, in which an ion exchange membrane for generating high-concentration caustic alkali for salt or potassium chloride electrolysis is used as the ion exchange membrane, and water is added to the anolyte or the alkali metal hydroxide aqueous solution before being introduced into the reaction tank, or to a mixture of the anolyte, chlorine gas, and alkali metal hydroxide aqueous solution introduced into the reaction tank. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 61-18495 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-96001 Summary of the Invention [Problem to be solved by the invention]

[0010] In a typical brine electrolysis plant, sodium hypochlorite is produced by reacting sodium hydroxide with chlorine gas obtained by electrolyzing brine. Brine, which serves as the anolyte, circulates between the anode chamber and the anolyte reservoir of the electrolytic cell, while secondary brine purified in a brine purifier is supplied to the anode chamber, the anolyte circulation pipe, or the anolyte reservoir. A sodium hydroxide aqueous solution, which serves as the catholyte, circulates between the cathode chamber and the catholyte reservoir of the electrolytic cell, while purified water is supplied to the cathode chamber, the catholyte circulation pipe, or the catholyte reservoir. The reaction in the electrolytic cell is represented by the following formula: 2NaCl + 2H2O = 2NaOH + Cl2 + H2 Meanwhile, a sodium hypochlorite solution is produced in the reaction tank by the reaction between the sodium hydroxide produced in the electrolytic tank and chlorine gas. The reaction in this reaction tank is represented by the following formula: 2NaOH+Cl2= NaClO+NaCl+H2O

[0011] This method of producing a sodium hypochlorite solution by contacting sodium hydroxide with chlorine gas can easily produce a sodium hypochlorite solution with a high effective chlorine concentration and a low salt concentration, compared to the techniques described in Patent Documents 1 and 2. The salt decomposition rate is approximately 40%. The brine discharged from the anode chamber, after the salt has been consumed by electrolysis, is reused after undergoing a dechlorination process. The dechlorination process uses large amounts of chemical solutions, such as hydrochloric acid, aqueous sodium hydroxide solution, and sodium sulfite, and requires a large amount of equipment, such as tanks and pumps, to handle these. Therefore, when this equipment is applied to an on-site sodium hypochlorite production facility, there are problems with the footprint, initial costs, and running costs.

[0012] According to the technology described in Patent Document 1, it is possible to produce an alkaline hypochlorite solution with an available chlorine concentration of 2 to 6 mass% by mixing an anolyte, which is an alkaline chloride solution discharged from an electrolytic cell using a cation exchange membrane, a catholyte, which is a caustic alkaline solution, and chlorine gas. Since the anolyte is mixed with the alkaline hypochlorite solution together with the catholyte and chlorine gas, a dechlorination process is not required. However, with this method, the sodium hypochlorite solution is diluted by the anolyte, and the concentration of the aqueous sodium hydroxide solution produced at the cathode is low, making it impossible to increase the available chlorine concentration in the sodium hypochlorite solution.

[0013] Furthermore, according to the technology described in Patent Document 2, it is possible to produce sodium hypochlorite by reacting chlorine gas, anolyte, and catholyte discharged from an anode chamber and a cathode chamber separated by an ion exchange membrane in a reaction tank. This method, like Patent Document 1, also does not require a dechlorination treatment step. This method produces a high concentration of aqueous sodium hydroxide solution at the cathode, producing a sodium hypochlorite solution with a higher available chlorine concentration than Patent Document 1. However, because brine discharged from the anode chamber after consuming salt during electrolysis flows into the reaction tank, it is not possible to produce a sodium hypochlorite solution with a low salt concentration. Furthermore, because chloric acid contained in the anolyte is also mixed with the sodium hypochlorite solution, this method has the drawback of only producing a sodium hypochlorite solution with a high chloric acid concentration, compared to the method of contacting chlorine gas with an aqueous sodium hydroxide solution.

[0014] In the section on sodium hypochlorite for water supply in the Japan Water Works Association standard (JWWA K120:2008), the grade of sodium hypochlorite solution is defined by the concentrations of effective chlorine, free alkali, bromate, chlorate, and salt. Grade 3 sodium hypochlorite, which has an effective chlorine concentration of 12% or more, is specified as having a salt concentration of 12.5% ​​or less. Therefore, when a user requires sodium hypochlorite equivalent to Grade 3, the method shown in Patent Document 2 is unable to meet this requirement, which is an issue.

[0015] Increasing the available chlorine concentration in the sodium hypochlorite solution reduces the solubility of salt. When generating a high-concentration sodium hypochlorite solution or when the generated sodium hypochlorite solution is cold, there is a risk that salt will precipitate, causing problems such as pipe blockage. While it is possible to reduce the salt concentration by centrifuging the sodium hypochlorite solution while cooling it, this would require excessively large equipment, increasing the footprint and cost, making it undesirable to incorporate this into on-site equipment.

[0016] Therefore, an object of the present invention is to provide a method and apparatus for producing a sodium hypochlorite solution that can solve the above problems and produce a sodium hypochlorite solution with a high effective chlorine concentration at low cost using on-site facilities. [Means for solving the problem]

[0017] To address the above problem, it is conceivable to reduce the salt concentration in the sodium hypochlorite solution by increasing the salt decomposition rate as much as possible. However, simply increasing the salt decomposition rate would result in a decrease in the salt concentration in the anolyte, which would cause other problems: an increase in the cell voltage and blister formation on the ion exchange membrane, making continuous stable operation difficult. Furthermore, since the salt decomposition rate also affects the amount of water moving through the ion exchange membrane, the water balance in the system would also change significantly from conventional processes, making it difficult to apply conventional knowledge as is.

[0018] Furthermore, the brine supplied to the anolyte also contains impurities originating from the raw salt. Typical impurities, such as calcium and magnesium, can be removed using a brine purifier. However, for example, bromine contained in raw salt cannot be removed using a brine purifier and is contaminated into the anolyte and even the sodium hypochlorite solution as carcinogenic bromate. Therefore, the Japan Water Works Association standard (JWWA K120:2008) also sets a standard value for sodium hypochlorite for water supply. Therefore, selecting the appropriate raw salt is also an issue in increasing the salt decomposition rate.

[0019] In view of the above, the present inventors have conducted extensive research and have found that it is possible to produce a highly concentrated sodium hypochlorite solution by improving the process of producing an aqueous sodium chloride solution from raw salt and increasing the salt decomposition rate when producing a sodium hypochlorite solution in a reaction tank by the reaction of an anolyte obtained by electrolysis, chlorine gas, and an aqueous sodium hydroxide solution, and have thus completed the present invention.

[0020] That is, the method for producing a sodium hypochlorite solution of the present invention comprises supplying secondary brine, which is an aqueous sodium chloride solution, to an anode chamber of an electrolytic cell partitioned into an anode chamber and a cathode chamber by an ion exchange membrane, introducing the anolyte and generated chlorine gas in the anode chamber after electrolysis, and the aqueous sodium hydroxide solution in the cathode chamber into a reaction tank, and producing a sodium hypochlorite solution by reaction of the anolyte, chlorine gas, and the aqueous sodium hydroxide solution that is the catholyte in the reaction tank, as follows: As a process for producing the secondary brine from raw salt, (1) a primary brine production step in which the raw salt, the main component of which is sodium chloride, is dissolved in purified water to produce primary brine; (2) a chelation treatment step of performing a chelation treatment on the primary brine to remove calcium ions and magnesium ions derived from the raw salt from the primary brine to produce the secondary brine, The decomposition rate of sodium chloride during electrolysis is set to 80-95%. Purified water is introduced into the reaction tank, and the available chlorine concentration of the sodium hypochlorite solution produced in the reaction tank is adjusted to 8% or more.

[0021] In the production method of the present invention, it is preferable to use a two-layer membrane composed of a sulfonic acid layer and a carboxylic acid layer as the ion exchange membrane.

[0022] Furthermore, in the production method of the present invention, it is preferable to provide a first switching device between the anode chamber and the reaction tank, which switches whether or not the anolyte is introduced from the anode chamber to the reaction tank, and to produce a sodium hypochlorite solution without introducing a part or all of the anolyte into the reaction tank; it is also preferable to provide a second switching device between the anode chamber and the reaction tank, which switches whether or not the chlorine gas is introduced from the anode chamber to the reaction tank, and to produce a sodium hypochlorite solution while supplying a part or all of the chlorine gas to a chlorine gas-using facility.

[0025] Furthermore, the production method of the present invention preferably includes a cation exchange step in which raw water is treated with a cation exchange resin to produce the purified water.

[0028] Furthermore, in the production method of the present invention, it is also preferable that an anolyte reservoir tank for storing the anolyte and a catholyte reservoir tank for storing the catholyte are provided near the electrolytic cell, bottoms of the anolyte reservoir tank and the catholyte reservoir tank are disposed higher than a position that is half the height of the electrolytic cell, and the anolyte and the catholyte are circulated between the anolyte reservoir tank and the anode chamber, and between the catholyte reservoir tank and the cathode chamber, respectively, by difference in gravity.

[0029] The apparatus for producing a sodium hypochlorite solution of the present invention comprises an electrolytic cell divided into an anode chamber and a cathode chamber by an ion exchange membrane, and supplied with secondary brine, which is an aqueous sodium chloride solution; and a reaction tank into which products from the anode chamber and the cathode chamber after electrolysis are introduced, and is an apparatus for producing a sodium hypochlorite solution by a reaction in the reaction tank, a brine production unit for producing the secondary brine from raw salt; The salt water production unit (1) a primary brine generating unit that dissolves the raw salt, the main component of which is sodium chloride, in purified water to generate primary brine; (2) a chelating treatment unit that performs a chelating treatment on the primary brine to remove calcium ions and magnesium ions derived from the raw salt from the primary brine to produce the secondary brine, The decomposition rate of sodium chloride during electrolysis is kept within the range of 80-95%. a first switching means provided between the anode chamber and the reaction tank, for switching whether or not the anolyte in the anode chamber is introduced from the anode chamber to the reaction tank; a purified water inlet channel for introducing purified water into the reaction tank; an automatic control device that operates the first switching means by switch operation or an external signal, The automatic control device is characterized in that it controls the first switching means so that a sodium hypochlorite solution having an available chlorine concentration of 8% or more is produced in the reaction tank.

[0030] In the production apparatus of the present invention, the ion exchange membrane is preferably a two-layer membrane composed of a sulfonic acid layer and a carboxylic acid layer.

[0031] In addition, in the production apparatus of the present invention, it is also preferable to provide a second switching means between the anode chamber and the reaction tank, which switches whether or not chlorine gas generated in the anode chamber is introduced from the anode chamber to the reaction tank.

[0034] Furthermore, the production apparatus of the present invention preferably includes a cation exchange treatment section that treats raw water with a cation exchange resin to produce the purified water.

[0037] Furthermore, in the production apparatus of the present invention, it is preferable that an anolyte reservoir tank for storing anolyte and a catholyte reservoir tank for storing catholyte are further included near the electrolytic cell, and that bottoms of the anolyte reservoir and the catholyte reservoir tank are located higher than a position that is half the height of the electrolytic cell. [Effects of the Invention]

[0038] According to the present invention, it is possible to provide a method and an apparatus for producing a sodium hypochlorite solution that can produce a sodium hypochlorite solution having a high available chlorine concentration at low cost using on-site facilities. [Brief explanation of the drawings]

[0039] [Figure 1] FIG. 1 is a diagram showing an example of an apparatus for producing a sodium hypochlorite solution used in the present invention. [Figure 2] FIG. 1 is a schematic diagram illustrating another embodiment of the apparatus for producing a sodium hypochlorite solution used in the present invention. [Figure 3]1 is a graph showing the relationship between the salt consumption rate and the salt decomposition rate in the present invention, based on a sodium hypochlorite solution manufacturing apparatus having a dechlorination treatment step. DETAILED DESCRIPTION OF THE INVENTION

[0040] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.

[0041] Fig. 1 is a diagram showing an example of an apparatus for producing a sodium hypochlorite solution used in the present invention. Fig. 2 is a diagram showing an apparatus for producing a sodium hypochlorite solution used in the present invention.

[0042] The present invention relates to an improved method and apparatus for producing sodium hypochlorite solution on-site near a facility where the solution is used. In the present invention, a secondary brine, which is an aqueous sodium chloride solution, is supplied to the anode chamber of an electrolytic cell partitioned into an anode chamber and a cathode chamber by an ion exchange membrane, and the anolyte and chlorine gas produced in the anode chamber after electrolysis, and the aqueous sodium hydroxide solution produced in the cathode chamber, are introduced into a reaction tank, where a high-concentration sodium hypochlorite solution is produced by reaction of the anolyte, chlorine gas, and the aqueous sodium hydroxide solution produced as the catholyte in the reaction tank.

[0043] In the present invention, the salt decomposition rate is set to a range of 80 to 95%, and secondary brine to be supplied to the anode chamber is produced from raw salt by dissolving raw salt, the main component of which is sodium chloride, in purified water to produce primary brine (primary brine production step), and then subjecting this primary brine to chelation treatment to produce secondary brine (chelation treatment step).This makes it possible to produce sodium hypochlorite solution with a high available chlorine concentration at low cost using on-site facilities.

[0044] In the present invention, the salt decomposition rate when producing a sodium hypochlorite solution must be in the range of 80 to 95%, and preferably 82 to 93%. If the salt decomposition rate is less than 80%, it becomes difficult to produce a high-concentration sodium hypochlorite solution when producing sodium hypochlorite by introducing anolyte into a reaction vessel without discharging it. Furthermore, as described in detail below, if the salt decomposition rate is less than 80%, economic viability cannot be ensured when producing sodium hypochlorite while discharging anolyte. On the other hand, if the salt decomposition rate exceeds 95%, the voltage of the electrolytic cell increases significantly, regardless of whether the anolyte is introduced into the reaction vessel or discharged, making it virtually impossible to continue operation.

[0045] When the anolyte is discharged without being introduced into the reaction tank, the temperature of the discharged anolyte is 50°C to 80°C, the pH is 4 to 5, and chlorine gas is dissolved therein. It is not preferable to send the anolyte directly to a wastewater treatment facility in terms of the heat resistance of the facility and the generation of a chlorine odor. Therefore, when discharging the anolyte, it must be aerated to expel chlorine, and then subjected to processes such as cooling and pH adjustment before being sent to the wastewater treatment facility. Therefore, from an economic perspective, it is preferable to increase the salt decomposition rate and reduce the amount of wastewater.

[0046] If a dechlorination process is included, the anolyte that has been dechlorinated is reused to dissolve salt, thereby reducing the salt consumption rate. On the other hand, as described above, the dechlorination process uses large amounts of chemicals, such as hydrochloric acid, aqueous sodium hydroxide solution, and sodium sulfite. Therefore, when installing equipment for the dechlorination process, a large number of devices, such as tanks and pumps, are required. Therefore, when this equipment is applied to an on-site sodium hypochlorite production facility, the footprint increases, and the initial and running costs become high. Since the present invention does not use a dechlorination process, the associated equipment and chemicals are not used, reducing the footprint, initial, and running costs. However, the salt contained in the anolyte is mixed into the sodium hypochlorite solution (product) or is discharged outside the system by being discharged, resulting in a high salt consumption rate.

[0047] A detailed comparison of the cost-saving effect of eliminating the dechlorination process and reducing the amount of chemical solution used with the disadvantages of increased salt consumption and increased costs associated with treating the anolyte when it is discharged revealed that, from the standpoint of cost effectiveness, it is preferable to keep the salt consumption rate at 25% or less compared to a system with a dechlorination process. Figure 3 is a graph showing the relationship between the salt consumption rate and the salt decomposition rate in the present invention, based on a sodium hypochlorite solution manufacturing system with a dechlorination process. According to Figure 3, in order to keep the increase in salt consumption rate at 25% or less compared to a system with a dechlorination process, the salt decomposition rate needs to be 80% or more.

[0048] Furthermore, the secondary brine of the present invention can be produced by providing a brine production unit for producing secondary brine from raw salt adjacent to the main part of the sodium hypochlorite solution production apparatus, thereby making it possible to create a compact production plant that can be used on-site. Specifically, the brine production unit of the present invention basically comprises a primary brine production section that produces primary brine by dissolving raw salt, the main component of which is sodium chloride, in purified water, and a chelating treatment section that performs a chelating treatment on the primary brine to produce secondary brine.

[0049] [Primary brine generation process] As described above, in the present invention, when producing secondary brine A, raw salt G, which is mainly composed of sodium chloride, is first dissolved in purified water B to produce primary brine H, which is saturated brine at room temperature. The dissolution of raw salt G in purified water B can be carried out in the salt dissolution tank 30.

[0050] Either solar salt or rock salt may be used as the raw salt G. It is more preferable to use purified salt obtained by further refining the raw salt G as a raw material and removing metal impurities such as calcium ions and magnesium ions to a certain extent. Because calcium and magnesium, which are typical impurities in brine, reduce the performance of ion exchange membranes, it is preferable to purify the brine supplied to the anode chamber and reduce the impurity concentration to a level that meets the ion exchange membrane usage standards. Note that chelating resins may be used to remove cations such as calcium and magnesium. Furthermore, since bromine contained in the raw salt is mixed into the sodium hypochlorite solution produced as bromate, it is preferable to keep the bromine ion concentration in the raw salt below 100 mg / kg, particularly about 69 mg / kg or less, from the perspective of obtaining a sodium hypochlorite solution having a bromate concentration equivalent to Class 1 as specified in JWWA K120:2008.

[0051] Furthermore, purified water B may be typically used industrial purified water, or purified water B produced from raw water I in an on-site facility may be used by providing a cation exchange treatment unit 40 that produces purified water by treating raw water with a cation exchange resin prior to the primary brine production unit. That is, the present invention may include a cation exchange step that produces purified water by treating raw water I with a cation exchange resin prior to the primary brine production step. This cation exchange step adsorbs and removes calcium ions, magnesium ions, and other heavy metal ions contained in the raw water and replaces them with sodium ions and hydrogen ions, thereby producing purified water B, which is softer and has a lower hardness than raw water I.

[0052] As the raw water I used in the cation exchange step, tap water, well water (groundwater), industrial water, etc. available at an on-site production site near the facility where the sodium hypochlorite solution is used can be used.

[0053] The cation exchange resin used in the cation exchange step is not particularly limited, and may be either Na-type or H-type.

[0054] In the present invention, a water softener using a cation exchange resin may be used as the cation exchange treatment unit 40 for carrying out the cation exchange step, instead of using only a cation exchange resin. When a cation exchange resin deteriorates, it may be regenerated by replacing the deteriorated cation exchange resin with a new cation exchange resin. However, when a water softener is used, it may be regenerated using a regeneration mechanism and salt attached to the water softener.

[0055] [Chelate treatment process] In the present invention, the primary brine H obtained in the above process is subjected to a chelation treatment to produce secondary brine A. By subjecting the primary brine H to a chelation treatment, calcium ions and magnesium ions carried over from the raw salt G can be removed from the primary brine, producing pure secondary brine A. The chelation treatment of the primary brine H can be carried out in a brine purifier 50.

[0056] Next, the manufacturing process of a sodium hypochlorite solution in the present invention will be described. First, in the manufacturing apparatus shown in FIG. 1, electrolysis is performed by supplying the secondary brine A produced above to the anode chamber 2 of an electrolytic cell 10 partitioned into an anode chamber 2 and a cathode chamber 3 by an ion exchange membrane 1, and supplying purified water B to the cathode chamber 3. Thereafter, the anolyte C and the produced chlorine (Cl) gas D in the anode chamber 2 after electrolysis, and the produced aqueous sodium hydroxide solution E in the cathode chamber 3, are introduced into a reaction vessel 20, and a sodium hypochlorite solution F is produced by a reaction between the anolyte C, the chlorine gas D, and the aqueous sodium hydroxide solution E in the reaction vessel 20. Here, the anolyte C is brine whose concentration has been reduced to, for example, less than 100 g / liter after electrolysis.

[0057] According to the present invention, the above-mentioned configuration enables a sodium hypochlorite solution having a high effective chlorine concentration to be produced stably, efficiently, and at low cost in a compact on-site production facility, and makes it possible to easily produce sodium hypochlorite at the site where sodium hypochlorite is consumed.

[0058] When anolyte C is introduced into the reaction vessel 20, the resulting sodium hypochlorite solution is diluted, making it impossible to increase the available chlorine concentration. Therefore, it is necessary to increase the concentration of the catholyte (sodium hydroxide aqueous solution E) to reduce the amount of water in the reaction vessel 20 and increase the concentration of the sodium hypochlorite solution. When anolyte C is introduced into the reaction vessel 20 and the salt decomposition rate is set to 80 to 95%, a sodium hydroxide aqueous solution concentration of at least 22% by mass is required to obtain an available chlorine concentration of 12%. Because on-site facilities are sometimes installed in cold regions, freezing of the sodium hydroxide aqueous solution during shutdown must also be considered. A sodium hydroxide aqueous solution with a concentration exceeding 30% by mass freezes at temperatures above 0°C. While it is possible to dilute the sodium hydroxide aqueous solution by supplying purified water before shutdown, this increases the amount of purified water used and requires appropriate management of the amount of purified water added. For this reason, the concentration of the sodium hydroxide aqueous solution when anolyte C is introduced into the reaction vessel 20 is preferably set to 22 to 30% by mass.

[0059] On the other hand, when the salt decomposition rate was 80 to 95% without introducing anolyte C into the reaction vessel 20, the concentration of the aqueous sodium hydroxide solution had to be at least 16% by mass to obtain an available chlorine concentration of 12%. Increasing the concentration of the aqueous sodium hydroxide solution allows for a higher concentration of sodium hypochlorite solution. However, if the concentration of the aqueous sodium hydroxide solution exceeds 23% by mass, salt may precipitate in the sodium hypochlorite solution. For this reason, the concentration of the aqueous sodium hydroxide solution when introducing anolyte C into the reaction vessel 20 is preferably in the range of 16 to 23% by mass.

[0060] In the present invention, as shown in the figure, it is preferable to provide a first switching means 4 between the anode chamber 2 and the reaction chamber 20, which switches whether or not the anolyte C is introduced from the anode chamber 2 to the reaction chamber 20. This makes it possible to produce a sodium hypochlorite solution without introducing a part or all of the anolyte C into the reaction chamber 20. By providing the first switching means 4 that can control the introduction of the anolyte C in this way, it becomes possible to select and produce sodium hypochlorite solutions with different salinity and chloric acid concentrations according to demand.

[0061] Furthermore, in the present invention, a second switching means 5 for switching whether or not chlorine gas D is introduced from the anode chamber 2 to the reaction tank 20 can be provided between the anode chamber 2 and the reaction tank 20, thereby making it possible to produce a sodium hypochlorite solution while supplying a part or all of the chlorine gas D to a chlorine gas-using facility. By providing the second switching means 5 capable of controlling the introduction of chlorine gas D in this way, it becomes possible to produce a sodium hypochlorite solution while supplying chlorine gas D to a chlorine-using facility on demand.

[0062] The first and second switching means 4, 5 may be configured as manual valves, motorized valves, air-operated valves, or the like. For example, if the first and second switching means 4, 5 are configured as motorized valves or air-operated valves, they may be configured to be operable by switch operation or external signal based on instructions from an automatic control device capable of communicating with the outside of the production facility. Examples of such automatic control devices include, but are not limited to, the MELSEC-Q series manufactured by Mitsubishi Electric Corporation and the SIMATIC S7 manufactured by SIEMENS. For example, when producing sodium hypochlorite solution as part of a water treatment plant such as a water purification plant, the automatic control device may be operated based on an external signal from the central control system of the water treatment plant. Furthermore, the first switching means 4 may be operated by an on-site operator using an on-site switch or the like depending on the measurement results of the sodium hypochlorite solution and salt concentration, and the second switching means 5 may be operated depending on whether chlorine gas is injected into the treated water.

[0063] In addition, in the present invention, it is preferable to provide a purified water inlet passage for introducing purified water B into the reaction tank 20. This allows the concentration of the sodium hypochlorite solution to be adjusted by supplying purified water B to the reaction tank 20 when producing the sodium hypochlorite solution in the reaction tank 20. For example, to produce a sodium hypochlorite solution with an available chlorine concentration of 15%, the concentrations of the anolyte C and the catholyte sodium hydroxide aqueous solution E can be combined and purified water B can be supplied to achieve an available chlorine concentration of 8%. A high available chlorine concentration increases the amount of chloric acid produced by its decomposition. In high-temperature regions or during the summer, where sodium hypochlorite decomposes quickly, diluting the sodium hypochlorite solution is effective in suppressing an increase in chloric acid concentration. When producing a sodium hypochlorite solution with an available chlorine concentration of 1 to 8%, a single-layer ion exchange membrane composed of a sulfonic acid layer, which is highly resistant to impurities in brine, can be used. Using purified salt with few impurities can simplify the brine purification process.

[0064] According to the present invention, a sodium hypochlorite solution having an available chlorine concentration of 8% or more, particularly 12 to 15%, can be easily produced in the reaction tank 20.

[0065] In the present invention, as shown in the drawing, an anolyte reservoir 6 that stores anolyte C and a catholyte reservoir 7 that stores sodium hydroxide aqueous solution E as a catholyte are preferably provided near the electrolytic cell 10, with bottoms 6b, 7b of the anolyte reservoir 6 and the catholyte reservoir 7 being located higher than a position that is half the height of the electrolytic cell 10. In such an arrangement, by providing communication between the anolyte reservoir 6 and the anode chamber 2 and between the catholyte reservoir 7 and the cathode chamber 3 via piping, the anolyte C and the sodium hydroxide aqueous solution E can be circulated between the anolyte reservoir 6 and the anode chamber 2 and between the catholyte reservoir tank 7 and the cathode chamber 3 by gravity, without providing a flow device such as a pump. Flow devices such as pumps may also be provided between the anolyte reservoir 6 and the anode chamber 2 and between the catholyte reservoir tank 7 and the cathode chamber 3, and are not limited thereto.

[0066] In the present invention, any ion exchange membrane 1 may be used in the electrolytic cell 10, but it is preferable to use a two-layer membrane composed of a sulfonic acid layer (anode side) and a carboxylic acid layer (cathode side). By using such a two-layer membrane, the carboxylic acid layer suppresses the diffusion of hydroxide ions diffusing from the cathode side, enabling highly efficient production. Examples of such two-layer membranes include Nafion (registered trademark) N2050 manufactured by Chemours, Flemion (registered trademark) F-9010 manufactured by AGC, and Aciplex (registered trademark) F7001 manufactured by Asahi Kasei Corporation.

[0067] In the production apparatus used in the present invention, the anode chamber 2 of the electrolytic cell 10 partitioned by the ion exchange membrane 1 can be provided with an anode made of a metal substrate such as titanium coated with an electrode catalyst material containing an oxide of a platinum group metal. On the other hand, the cathode chamber 3 can be provided with a cathode made of nickel, stainless steel, or titanium, or made of these metals coated with a cathode active material that reduces hydrogen overvoltage and has excellent long-term durability.

[0068] In the present invention, the aqueous sodium hydroxide solution E can be supplied to the electrolytic cell 10 while controlling its concentration and flow rate according to the target production amount of sodium hypochlorite solution. Furthermore, when purified water B is introduced into the electrolytic cell 10, the flow rate of purified water B can also be controlled similarly according to the target production amount and concentration of sodium hypochlorite solution.

[0069] The produced aqueous sodium hydroxide solution E and hydrogen gas K are extracted from the top of the cathode chamber 3, and of these, the aqueous sodium hydroxide solution E, which serves as a catholyte, is supplied to the reaction vessel 20, while the hydrogen gas K is discharged to the outside. In addition, from the top of the anode chamber 2, an anolyte C, which is an aqueous sodium chloride solution whose concentration has been reduced by electrolysis, and chlorine gas D are extracted and supplied to the reaction vessel 20 via first and second switching means 4 and 5, respectively.

[0070] In the reaction tank 20, chlorine and sodium hydroxide react to produce a sodium hypochlorite solution F. Here, the sodium hypochlorite solution F removed from the reaction tank 20 is taken out as a product, and is also supplied by a pump to a cooling device 8 using cooling water L for cooling, and then circulated to the reaction tank 20. This prevents the temperature of the electrolytic cell 10 from rising and also prevents the decomposition of the produced sodium hypochlorite.

[0071] 2 is a schematic diagram of another embodiment of the apparatus for producing a sodium hypochlorite solution used in the present invention. As shown in the figure, in the present invention, two or more electrolytic cells, two electrolytic cells 10A and 10B in the illustrated example, are arranged, and chlorine gas D obtained from one or more of these, one electrolytic cell 10A in the illustrated example, is supplied to a chlorine gas-using facility, and chlorine gas D obtained from the remaining one or more, one electrolytic cell 10B in the illustrated example, can be used to produce a sodium hypochlorite solution. That is, by providing a chlorine gas supply line for supplying chlorine gas obtained from some of the multiple electrolytic cells to the chlorine gas-using facility, the supply of chlorine gas to the chlorine gas-using facility and the production of a sodium hypochlorite solution can be carried out in parallel.

[0072] For example, in the facility shown in FIG. 2 , when producing a sodium hypochlorite solution from the products obtained in electrolytic cells 10A and 10B, chlorine gas produced in anode chamber 2A and anode chamber 2B and aqueous sodium hydroxide solution E produced in cathode chamber 3A and cathode chamber 3B are mixed in reaction tank 20 to produce the sodium hypochlorite solution. While producing a sodium hypochlorite solution with an available chlorine concentration of 12% or more, second switching means 5 composed of an automatic valve can be operated to remove chlorine gas D produced in electrolytic cell 10A from the system. At this time, a switching means (not shown) for selecting whether or not to introduce catholyte can be installed between cathode chamber 3A and reaction tank 20 and operated, and the aqueous sodium hydroxide solution E produced in cathode chamber 3A can be removed from the system and stored. The chlorine gas D removed from the system in this way can be directly injected into treated water at a water purification plant or the like. [Example]

[0073] The present invention will be described in more detail below with reference to examples.

[0074] A sodium hypochlorite solution was produced in the apparatus shown in Figure 1. The electrolysis area of ​​the electrolytic cell was 8000 cm 2 The electrolysis current was 2400 A. The ion exchange membrane of the electrolytic cell was F-9010 manufactured by AGC, which is a two-layer membrane composed of a sulfonic acid layer and a carboxylic acid layer.

[0075] A raw salt with a bromine ion concentration of 50 mg / kg was dissolved in purified water to produce primary brine, and the resulting primary brine was then subjected to a chelate treatment to produce secondary brine. When the raw salt had a bromine ion concentration of 50 mg / kg, the bromate concentration in the sodium hypochlorite solution in Example 1 (described below) was 15 mg / kg, and the bromate concentration in the sodium hypochlorite solution in Example 2 (described below) was 18 mg / kg, both of which were below the 50 mg / kg standard value for Grade 1 sodium hypochlorite for water supply use in the Japan Water Works Association standard (JWWA K120:2008). Bromine ions are anions, so they cannot be removed by the chelating resin used in brine purification.

[0076] The pH of the brine, prepared by dissolving raw salt in purified water, was 7.8 before purification. The brine was purified using Diaion (registered trademark) CR11, an iminodiacetic acid-type chelating resin manufactured by Mitsubishi Chemical Corporation. The calcium and magnesium concentrations in the brine before purification were 16 mg / L, and those in the purified brine were 10 μg / L.

[0077] After charging the purified secondary brine into the anode chamber and 25% by mass of aqueous sodium hydroxide solution into the cathode chamber, operation was initiated. The temperature of the electrolyte during operation was 75°C, and purified water was supplied to the cathode chamber to adjust the concentration of the aqueous sodium hydroxide solution in the cathode chamber. The amount of aqueous sodium hydroxide solution supplied to the reaction tank was adjusted so that the concentration of the aqueous sodium hydroxide solution in the sodium hypochlorite solution was 1%. The reaction tank was cooled to a temperature of 30°C. Tests of each example and comparative example were conducted by providing a first switching means between the anode chamber and the reaction tank for switching whether or not the anolyte was introduced from the anode chamber to the reaction tank, and by switching between introducing and discharging the anolyte into and from the reaction tank using an automatic valve and simultaneously adjusting the amount of purified water supplied to the cathode chamber.

[0078] In each example, purified water was used to dissolve the raw salt and to add to the cathode chamber. Ion-exchanged water can be used instead of purified water, but from a cost perspective, purified water is preferable. The silica concentration in the purified water and secondary brine was 12 mg / L. The silica concentration in the secondary brine was intentionally adjusted to 40 mg / L, and electrolysis was continued for two months, but the amount of chlorine produced and the voltage were stable. Here, purified water was supplied to the cathode chamber to adjust the concentration of the sodium hydroxide aqueous solution, but purified water may also be supplied to the reaction tank to adjust the concentration of the sodium hypochlorite solution.

[0079] Furthermore, the anolyte reservoir and the anode chamber, and the catholyte reservoir and the cathode chamber were connected by piping, and no pump or other flow means were installed. When the bottoms of the anolyte reservoir and the catholyte reservoir were positioned above half the height of the electrolytic cell, the anolyte and the catholyte circulated well between the respective reservoirs and the electrolytic cell, and the operating voltage, operating temperature, and operating pressure were all stable. On the other hand, when the bottoms of the reservoirs were positioned below half the height of the electrolytic cell, good circulation was not achieved, and the operating pressure was unstable.

[0080] [Example 1] A sodium hypochlorite solution was produced while introducing anolyte into the reaction tank. When the salt decomposition rate was 80.4% and the concentration of the sodium hydroxide aqueous solution in the catholyte was 28.0 mass%, the available chlorine concentration, salt concentration, and chloric acid concentration in the resulting sodium hypochlorite solution were 12.2 mass%, 13.5 mass%, and 0.18 mass%, respectively. Because the system was operated with anolyte introduced into the reaction tank, no anolyte was discharged.

[0081] [Example 2] A sodium hypochlorite solution was produced while introducing anolyte into the reaction tank. When the salt decomposition rate was 89.4% and the concentration of the sodium hydroxide aqueous solution in the catholyte was 26.2 mass%, the available chlorine concentration, salt concentration, and chloric acid concentration in the resulting sodium hypochlorite solution were 12.8 mass%, 13.0 mass%, and 0.17 mass%, respectively. Because the system was operated with anolyte introduced into the reaction tank, no anolyte was discharged.

[0082] [Example 3] While discharging the anolyte, a sodium hypochlorite solution was produced. When the salt decomposition rate was 81.1% and the concentration of the sodium hydroxide aqueous solution in the catholyte was 16.3 mass%, the available chlorine concentration, salt concentration, and chloric acid concentration in the resulting sodium hypochlorite solution were 12.3 mass%, 10.4 mass%, and 0.06 mass%, respectively. The discharge rate of the anolyte was 9.5 L / hour.

[0083] [Example 4] While discharging the anolyte, a sodium hypochlorite solution was produced. When the salt decomposition rate was 89.1% and the concentration of the sodium hydroxide aqueous solution in the catholyte was 16.0 mass%, the available chlorine concentration, salt concentration, and chloric acid concentration in the resulting sodium hypochlorite solution were 12.0 mass%, 10.1 mass%, and 0.06 mass%, respectively. The discharge rate of the anolyte was 6.5 L / hour.

[0084] [Example 5] A sodium hypochlorite solution was produced by introducing a portion of the anolyte into the reaction tank and simultaneously discharging a portion of the anolyte. The ratio of the amount of anolyte introduced into the reaction tank to the amount of discharged was 1:1. When the salt decomposition rate was 86.7% and the concentration of the sodium hydroxide aqueous solution in the catholyte was 17.4 mass%, the available chlorine concentration, salt concentration, and chloric acid concentration in the resulting sodium hypochlorite solution were 12.1 mass%, 11.0 mass%, and 0.08 mass%, respectively. The discharge rate of the anolyte was 3.7 L / hour.

[0085] [Comparative Example 1] A sodium hypochlorite solution was produced while introducing anolyte into the reaction tank. When the salt decomposition rate was 45.1% and the concentration of the sodium hydroxide aqueous solution in the catholyte was 32.3 mass%, the available chlorine concentration, salt concentration, and chloric acid concentration in the resulting sodium hypochlorite solution were 5.5 mass%, 18.4 mass%, and 0.12 mass%, respectively. Because the system was operated with anolyte introduced into the reaction tank, no anolyte was discharged.

[0086] In Comparative Example 1, the salt decomposition rate was lower than in Examples 1 and 2, and therefore the available chlorine concentration in the sodium hypochlorite solution was low and the salt concentration was high.

[0087] Comparative Example 2 While discharging the anolyte, a sodium hypochlorite solution was produced. When the salt decomposition rate was 47.0% and the concentration of the sodium hydroxide aqueous solution in the catholyte was 16.3 mass%, the available chlorine concentration, salt concentration, and chloric acid concentration in the resulting sodium hypochlorite solution were 12.3 mass%, 10.1 mass%, and 0.04 mass%, respectively. The discharge rate of the anolyte was 27.8 L / hour.

[0088] In Comparative Example 2, the amount of wastewater was greater than in Examples 3 and 4.

[0089] Comparative Example 3 Sodium hypochlorite solution was produced while the anolyte was being discharged. When the salt decomposition rate reached 96%, a voltage increase occurred, and operation could not be continued until the concentration of the sodium hypochlorite solution stabilized. The concentration of the sodium hydroxide aqueous solution in the catholyte when operation was stopped was 18.1 mass%. The amount of discharged water during the 30 minutes from when the salt decomposition rate reached 96% until operation was stopped was 3.5 L / hour.

[0090] In Comparative Example 3, although the amount of wastewater was small, stable operation was not possible.

[0091] Comparative Example 4 A sodium hypochlorite solution was produced while introducing anolyte into the reaction tank. When the salt decomposition rate was 77.9% and the concentration of the sodium hydroxide aqueous solution in the catholyte was 29.3 mass%, the available chlorine concentration, salt concentration, and chloric acid concentration in the resulting sodium hypochlorite solution were 11.3 mass%, 14.9 mass%, and 0.14 mass%, respectively. Because the operation was performed by introducing anolyte into the reaction tank, no anolyte was discharged.

[0092] In Comparative Example 4, the decomposition rate of salt was low, so that an available chlorine concentration of 12% in the sodium hypochlorite solution could not be obtained.

[0093] Comparative Example 5 A sodium hypochlorite solution was produced while the anolyte was being discharged. When the salt decomposition rate was 75.6% and the concentration of the sodium hydroxide aqueous solution in the catholyte was 16.5 mass%, the available chlorine concentration, salt concentration, and chloric acid concentration in the sodium hypochlorite solution were 12.1 mass%, 10.3 mass%, and 0.06 mass%, respectively. The discharge rate of the anolyte was 11.7 L / hour.

[0094] In Comparative Example 5, the amount of wastewater was greater than in Examples 3 and 4 due to the low salt decomposition rate.

[0095] [Table 1]

[0096] From the above, it was found that in order to produce a high-concentration sodium hypochlorite solution, whether the anolyte is introduced into the reaction tank or discharged, a salt decomposition rate of 80% or more is required. On the other hand, if the salt decomposition rate exceeds 95%, the voltage rises significantly and operation cannot be continued. Therefore, it was confirmed that from the viewpoint of operational stability, the upper limit of the salt decomposition rate must be 95%. [Explanation of symbols]

[0097] 1. Ion exchange membrane 2,2A,2B Anode chamber 3,3A,3B Cathode chamber 4. First Switching Method 5 Secondary switching method 6 Anolyte reservoir 6b Bottom of anolyte reservoir 7 Catholyte reservoir 7b Bottom of catholyte reservoir 8 Cooling device 10,10A,10B electrolytic cell 20 Reaction Tank 30 Salt dissolving tank 40 Cation exchange treatment section 50 Salt Water Purifier A Secondary brine B Purified water C Anolyte D. Chlorine gas E. Sodium hydroxide solution F. Sodium hypochlorite solution G Raw salt H Primary brine I Raw water K Hydrogen gas L Cooling water

Claims

1. In an electrolytic cell partitioned into an anode chamber and a cathode chamber by an ion exchange membrane, secondary brine, which is a sodium chloride aqueous solution, is supplied to the anode chamber, and the anolyte and generated chlorine gas in the anode chamber after electrolysis, and the sodium hydroxide aqueous solution in the cathode chamber are introduced into a reaction tank, and a sodium hypochlorite solution is produced by reaction of the anolyte, chlorine gas, and generated sodium hydroxide aqueous solution, which is the catholyte, in the reaction tank; As a process for producing the secondary brine from raw salt, (1) a primary brine production step of dissolving the raw salt, the main component of which is sodium chloride, in purified water to produce primary brine; (2) a chelation treatment step of performing a chelation treatment on the primary brine to remove calcium ions and magnesium ions derived from the raw salt from the primary brine to produce the secondary brine, The decomposition rate of sodium chloride during electrolysis is set to a range of 80 to 95%, A method for producing a sodium hypochlorite solution, characterized in that purified water is introduced into the reaction tank, and the available chlorine concentration of the sodium hypochlorite solution produced in the reaction tank is set to 8% or more.

2. 2. The method for producing a sodium hypochlorite solution according to claim 1, wherein the ion exchange membrane is a two-layer membrane composed of a sulfonic acid layer and a carboxylic acid layer.

3. 3. The method for producing a sodium hypochlorite solution according to claim 1 or 2, wherein a first switching means for switching whether or not the anolyte is introduced from the anode chamber to the reaction tank is provided between the anode chamber and the reaction tank, and the sodium hypochlorite solution is produced without introducing a part or all of the anolyte into the reaction tank.

4. The method for producing a sodium hypochlorite solution according to any one of claims 1 to 3, wherein a second switching means is provided between the anode chamber and the reaction tank, for switching whether or not the chlorine gas is introduced from the anode chamber to the reaction tank, and the sodium hypochlorite solution is produced while supplying a part or all of the chlorine gas to a chlorine gas-using facility.

5. The method for producing a sodium hypochlorite solution according to any one of claims 1 to 4, further comprising a cation exchange step of treating raw water with a cation exchange resin to produce the purified water.

6. 6. The method for producing a sodium hypochlorite solution according to claim 1, wherein an anolyte reservoir tank for storing the anolyte and a catholyte reservoir tank for storing the catholyte are provided near the electrolytic cell, bottoms of the anolyte reservoir tank and the catholyte reservoir tank are located higher than a position that is half the height of the electrolytic cell, and the anolyte and the catholyte are circulated between the anolyte reservoir tank and the anode chamber, and between the catholyte reservoir tank and the cathode chamber, respectively, by difference in gravity.

7. An apparatus for producing a sodium hypochlorite solution by a reaction in the reaction tank, the apparatus comprising: an electrolytic cell divided into an anode chamber and a cathode chamber by an ion exchange membrane, to which secondary brine, which is a sodium chloride aqueous solution, is supplied; and a reaction tank into which products in the anode chamber and the cathode chamber after electrolysis are introduced, a brine production unit for producing the secondary brine from raw salt; The salt water production unit (1) a primary brine generating unit that dissolves the raw salt, the main component of which is sodium chloride, in purified water to generate primary brine; (2) a chelating treatment unit that performs a chelating treatment on the primary brine to remove calcium ions and magnesium ions derived from the raw salt from the primary brine to produce the secondary brine, The decomposition rate of sodium chloride during electrolysis is operated in the range of 80 to 95%. a first switching means provided between the anode chamber and the reaction tank, for switching whether or not the anolyte in the anode chamber is introduced from the anode chamber to the reaction tank; a purified water inlet channel for introducing purified water into the reaction tank; an automatic control device that operates the first switching means by switch operation or an external signal, The apparatus for producing a sodium hypochlorite solution is characterized in that the automatic control device controls the first switching means so that a sodium hypochlorite solution having an available chlorine concentration of 8% or more is produced in the reaction tank.

8. 8. The apparatus for producing a sodium hypochlorite solution according to claim 7, wherein the ion exchange membrane is a two-layer membrane composed of a sulfonic acid layer and a carboxylic acid layer.

9. 9. The apparatus for producing a sodium hypochlorite solution according to claim 7 or 8, further comprising a second switching means between the anode chamber and the reaction tank for switching whether or not chlorine gas generated in the anode chamber is introduced from the anode chamber to the reaction tank.

10. The apparatus for producing a sodium hypochlorite solution according to any one of claims 7 to 9, further comprising a cation exchange treatment unit that treats raw water with a cation exchange resin to produce the purified water.

11. The apparatus for producing a sodium hypochlorite solution according to any one of claims 7 to 10, further comprising an anolyte reservoir tank for storing an anolyte and a catholyte reservoir tank for storing a catholyte, both located near the electrolytic cell, wherein bottoms of the anolyte reservoir tank and the catholyte reservoir tank are located higher than a position that is half the height of the electrolytic cell.

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