METHOD AND APPARATUS FOR PRODUCING A SODIUM HYPOCHLORITE SOLUTION

Abstract

To provide a method and production apparatus for a sodium hypochlorite solution that can produce a sodium hypochlorite solution with a high concentration of available chlorine at low cost using an on-site installation. In the production of a sodium hypochlorite solution, secondary saltwater, as an aqueous sodium chloride solution, is fed into an electrolyzer 10 divided into an anode chamber 2 and a cathode chamber 3 by an ion-exchange membrane 1. Following electrolysis, an anolyte and chlorine gas generated in the anode chamber, and an aqueous sodium hydroxide solution generated in the cathode chamber, are introduced into a reaction tank 20 to allow the anolyte, chlorine gas, and the aqueous sodium hydroxide solution generated as a catholyte to react in the reaction tank.A primary saltwater generation step consisting of dissolving salt feedstock G containing sodium chloride as the main component in purified water B to generate primary saltwater, and a chelation step consisting of chelating the primary saltwater to generate secondary saltwater A are included, wherein the salt decomposition rate varies from 80 to 95%.

Description

[Document Title] DESCRIPTION [Title of the invention] METHOD FOR PRODUCING AND APPARATUS FOR PRODUCING SODIUM HYPOCHLORITE SOLUTION [Technical field]

[0001] The present invention relates to a method for producing a sodium hypochlorite solution and an apparatus for producing a sodium hypochlorite solution (hereinafter also referred to as the “production method” and “production apparatus”). Specifically, the present invention relates to a technique for obtaining a high-concentration sodium hypochlorite solution in a method and apparatus that produce a sodium hypochlorite solution in situ by using an ion-exchange membrane for a diaphragm of an electrolytic tank and mixing an electrolysis product, other than hydrogen, generated in the electrolytic tank into a reaction tank. [Previous technique]

[0002] Sodium hypochlorite is used as a bleaching or disinfecting agent in various settings, such as water and sewage treatment and wastewater treatment. Methods for producing sodium hypochlorite generally include one method by reacting chlorine with an aqueous sodium hydroxide solution obtained by electrolysis of ordinary salt water in a reaction tank, and another method for directly producing sodium hypochlorite in a diaphragm-less electrolyzer by electrolyzing an aqueous sodium chloride solution.

[0003] In the latter method, obtaining a high-concentration sodium hypochlorite solution is difficult because the electrolyzer lacks a diaphragm. Consequently, the generated sodium hypochlorite is reduced to common salt at the cathode, and the resulting sodium hypochlorite is anodized and converted to sodium chlorate, which lacks effective oxidizing power. Therefore, applications for sodium hypochlorite produced using this method are generally those where high concentration is not required, such as heat exchange water in power plants, well cooling water in rotary equipment, and preventing the growth / adhesion of living organisms in seawater during ballast water treatment, as well as in water and sewage treatment and wastewater treatment.

[0004] On the other hand, one application to which the aforementioned production method is applied is representative of a common method for producing high-concentration sodium hypochlorite in a salt electrolysis plant. A salt electrolysis plant necessarily includes a saltwater purification system to remove a high degree of metallic impurities and unnecessary anions contained in the salt and water feedstocks to maintain stable and highly efficient plant operation, and a repurification system to decompose and remove hypochlorous and chloric acids contained in the saltwater after electrolysis in order to recycle the reduced-concentration saltwater produced after electrolysis. The facilities are scaled up as the plant scales up.

[0005] A primary objective of a salt electrolysis plant is to produce sodium hydroxide and chlorine gas, which have various industrial applications, rather than sodium hypochlorite. These plants are typically part of a petrochemical complex and are usually large-scale operations, producing tens of thousands to hundreds of thousands of tons of sodium hydroxide annually. The number of salt electrolysis plants is relatively small compared to the number of water treatment plants and similar facilities that require high-concentration hypochlorite. 1786733 of 21. Therefore, the need arises to transport chlorine gas or hypochlorite, necessary for the sterilization of clean water, to a water treatment plant and for storage. Consequently, hazards, such as human-caused disasters and environmental destruction due to leaks or similar incidents from a storage facility, are always present. In particular, a road accident involving a tanker truck used for transporting chlorine gas could lead to a serious incident where chlorine gas is released into the environment. This could occur in various countries, prompting a movement to strengthen legislation on the transport of chlorine gas.

[0006] Under these circumstances, a method for the in situ production of high concentration sodium hypochlorite is proposed, in which a small electrolytic apparatus for the production of sodium hypochlorite is deposited in a physical plant that uses sodium hypochlorite, such as a water treatment plant, and a necessary quantity of sodium hypochlorite is produced when required.

[0007] For example, Patent Document 1 describes a technique for producing an alkaline hypochlorite solution with a predetermined available chlorine concentration, by electrolysis with the addition of an alkaline chlorine solution to an anode chamber and water to a cathode chamber, through the use of an electrolyte with a cation exchange membrane between an anode and a cathode, and the mixture of an anolyte discharged from the electrolyte, a catholyte such as a caustic alkaline solution, and chlorine gas.

[0008] Patent Document 2 describes a technique in which, when sodium hypochlorite is produced by electrolysis in an electrolyzer divided into an anode chamber and a cathode chamber with an ion exchange membrane, with the feeding of an aqueous alkaline metal chloride solution to the anode chamber and the feeding of pure water to the cathode chamber, and the introduction of an anolyte and chlorine gas generated in the anode chamber and an aqueous alkaline metal hydroxide solution in the cathode chamber, after electrolysis, into a reaction tank, an ion exchange membrane for the generation of high concentration caustic alkalis for the electrolysis of a common salt or potassium chloride is used as the ion exchange membrane, and water is also added to the anolyte or the aqueous alkaline metal hydroxide solution before introduction into the reaction tank, or to a mixture of the anolyte,Chlorine gas and aqueous alkaline metal hydroxide solution after introduction into the reaction tank. [Related technical documents] [Patent Documents]

[0009] [Patent Document 1] JPS61-18495A [Patent Document 2] JP2013-096001A [Summary of the invention] [Problems to be solved through the invention]

[0010] In a general common salt electrolysis plant, sodium hypochlorite is produced by the reaction of chlorine gas and sodium hydroxide obtained from the electrolysis of common salt water. Salt water, as the anolyte, is circulated between an anode chamber in an electrolyzer and an anolyte reservoir. Simultaneously, purified secondary salt water, from a salt water purifier, is introduced into the anode chamber, anolyte circulation lines, or the anolyte reservoir. Additionally, an aqueous sodium hydroxide solution, as the catholyte, is circulated between an anode chamber in the electrolyzer and a... 1786733 of 21 catholyte reservoir, and at the same time, purified water is introduced into the cathode chamber, catholyte circulation pipes, or the catholyte reservoir. The reaction in the electrolyzer is represented by the following formula: 2NaCl + 2H2O = 2NaOH + Cl2+ H2 In this context, a reaction between sodium hydroxide and chlorine gas generated in the electrolyzer produces a sodium hypochlorite solution in a reaction tank. This reaction in the reaction tank is represented by the following formula: 2NaOH + Cl2 = NaClO + NaCl + H2O

[0011] This method for generating a sodium hypochlorite solution by contacting sodium hydroxide and chlorine gas can easily produce a sodium hypochlorite solution with a high concentration of available chlorine and a low concentration of common salt, compared to the techniques described in Patent Document 1 and Patent Document 2. The salt decomposition rate is approximately 40%. The saltwater discharged from the anode chamber, where the common salt is consumed by electrolysis, is recycled through a dechlorination treatment step. This dechlorination treatment step uses large quantities of liquid chemicals such as hydrochloric acid, an aqueous sodium hydroxide solution, and disodium sulfite, and also requires various instruments such as a tank and pump for these liquids.Therefore, the area occupied, the initial cost, and the execution cost increase when this installation is applied to an in situ type sodium hypochlorite production site.

[0012] According to the technique described in Patent Document 1, an alkaline hypochlorite liquid with an available chlorine concentration of 2 to 6% by mass can be produced by mixing an anolyte, such as an alkaline chlorine solution discharged from the electrolyzer with the cation exchange membrane, a catholyte, such as a caustic alkaline solution, and chlorine gas. The anolyte, catholyte, and chlorine gas are mixed together in the alkaline hypochlorite solution, and therefore, no dechlorination treatment step is required. However, this method, in which not only is a sodium hypochlorite solution diluted with the anolyte, but the concentration of the aqueous sodium hydroxide solution generated at the cathode is also low, does not allow for an increase in the available chlorine concentration in the sodium hypochlorite solution.

[0013] According to the technique described in Patent Document 2, sodium hypochlorite can be produced by a reaction of chlorine gas, an anolyte, and a catholyte discharged from the anode and cathode chambers separated by the ion-exchange membrane, in the reaction tank. This method also eliminates the dechlorination treatment step required in the case of Patent Document 1. Although this method allows for a high concentration of aqueous sodium hydroxide solution generated at the cathode and a higher concentration of available chlorine in the sodium hypochlorite solution than that produced in Patent Document 1, it cannot produce a sodium hypochlorite solution with a low concentration of common salt because the saltwater discharged from the anode chamber, in which the common salt is consumed by electrolysis, flows into the reaction tank.Furthermore, chloric acid included in the anolyte is also mixed with the sodium hypochlorite solution, and therefore a disadvantage appears which is that only the sodium hypochlorite solution with a high concentration of chloric acid can be generated compared to a method for the contact of chlorine gas and an aqueous sodium hydroxide solution.

[0014] The grade of a sodium hypochlorite solution is defined by the concentration of available chlorine and the concentrations of free alkalis, bromic acid, chloric acid, and sodium chloride in the sodium hypochlorite section of the Japan Water Works Association Standard (JWWA K120: 2008). The third grade to which 1786733 of 21 refers to sodium hypochlorite with an available chlorine concentration of 12% or more, designated as one comprising a salt concentration of 12.5% ​​or less. Therefore, if the sodium hypochlorite corresponding to the third grade is what the user requires, the problem will be that the method mentioned in Patent Document 2 will not be able to satisfy this requirement.

[0015] An increase in the concentration of available chlorine in a sodium hypochlorite solution leads to a decrease in the solubility of the salt. When a high-concentration sodium hypochlorite solution is generated, or when the generated sodium hypochlorite solution is at a low temperature, there is also a risk of creating problems such as pipe blockages due to common salt deposits. A reduction in the concentration of common salt can be achieved by centrifuging a sodium hypochlorite solution under cooling, but this requires extensive equipment and increases the footprint and cost, and therefore is not preferred for on-site installations.

[0016] An objective of the present invention is to solve the aforementioned problems and provide a method and apparatus for producing a sodium hypochlorite solution that can in turn produce a sodium hypochlorite solution with a high concentration of available chlorine at low cost and in the on-site installation. [Means to solve the problems]

[0017] Although increasing the salt decomposition rate as much as possible to reduce the salt concentration in a sodium hypochlorite solution is also considered a solution to the aforementioned problems, another issue arises: even if the salt decomposition rate is simply increased, the concentration of common salt in the anolyte is reduced, leading to an increase in the electrolyzer voltage and blistering on an ion-exchange membrane. This makes stable and continuous operation difficult to maintain. The salt decomposition rate also influences the amount of water transferred through an ion-exchange membrane, and therefore the water balance in the system undergoes significant changes compared to a conventional process. As a result, conventional findings are difficult to apply in their current state.

[0018] Furthermore, impurities from the salt raw material are also present in the saltwater entering the anolyte. Typical impurities such as calcium and magnesium can be removed using a saltwater purifier. However, bromide, for example, cannot be removed by a saltwater purifier and is incorporated as bromic acid, a carcinogenic substance, into the anolyte and also into a sodium hypochlorite solution. Therefore, the standard value is also established in the section on sodium hypochlorite in municipal water in the Japan Water Works Association Standard (JWWA K120: 2008). Consequently, selecting an appropriate salt raw material is also a factor in increasing the salt decomposition rate.

[0019] The present inventors have carried out intensive studies in view of these circumstances and, as a result, have discovered that a high concentration sodium hypochlorite solution can be produced by improving a step in generating an aqueous sodium chloride solution from salt raw material and increasing the rate of salt decomposition in the production of a sodium hypochlorite solution by a reaction of an anolyte, chlorine gas, and an aqueous sodium hydroxide solution obtained by electrolysis, in a reaction tank, leading to the completion of the present invention. 1786733 of 21

[0020] In other words, the method for producing a sodium hypochlorite solution of the present invention includes, in the production of a sodium hypochlorite solution by introducing secondary salt water as an aqueous sodium chloride solution into an electrolyzer divided into an anode chamber and a cathode chamber by means of an ion exchange membrane, into the anode chamber and, after electrolysis, introducing an anolyte and chlorine gas generated in the anode chamber and an aqueous sodium hydroxide solution generated in the cathode chamber into a reaction tank to allow the anolyte, chlorine gas, and aqueous sodium hydroxide solution generated as a catholyte to react in the reaction tank, a primary salt water generation step consisting of dissolving water feed containing sodium chloride as the main component in purified water to generate primary salt water,and a chelating step to chelate the primary salt water, thus generating secondary salt water, which is characterized by a salt composition rate ranging from 80 to 95%.

[0021] In the production method of the present invention, a bilayer membrane configured from a sulfonic acid layer and a carboxylic acid layer is preferably used as the ion exchange membrane.

[0022] Furthermore, in the production method of the present invention, it is preferable to provide a first alternating means that alternates between introducing or not introducing the anolyte from the anode chamber into the reaction tank between the anode chamber and the reaction tank, to produce a sodium hypochlorite solution without introducing a part or the total amount of the anolyte into the reaction tank, and it is also preferable to provide a second alternating means that alternates between introducing or not introducing chlorine gas from the anode chamber into the reaction tank between the anode chamber and the reaction tank, to carry out the production of a sodium hypochlorite solution with the introduction of a part or the total amount of chlorine gas into an installation where chlorine gas is used.

[0023] Furthermore, in the production method of the present invention, two or more electrolyzers can be used to introduce the chlorine gas obtained from one or more electrolyzers into an installation where chlorine gas is used, and a sodium hypochlorite solution can be produced using the chlorine gas obtained from one or more electrolyzers.

[0024] Furthermore, in the production method of the present invention, it is preferable to introduce purified water into the reaction tank to adjust the concentration of the sodium hypochlorite solution. In the production method of the present invention, the available chlorine concentration of a sodium hypochlorite solution generated in the reaction tank can be 8% or higher.

[0025] Furthermore, in the production method of the present invention, it is preferable to include a cation exchange step to treat raw water with a cation exchange resin to generate purified water. In this case, it is also preferable to use a water softener in the cation exchange step.

[0026] 1786733 of 21 Furthermore, in the production method of the present invention, the first alternation means and / or the second alternation means can be activated by an alternation operation or an external signal based on an instruction from an automatic control apparatus communicable with the outside of a production facility.

[0027] Furthermore, in the production method of the present invention, a sodium hypochlorite solution can be produced in situ in the vicinity of a facility where a sodium hypochlorite solution is used.

[0028] Furthermore, in the production method of the present invention, it is also preferable that an anolyte reservoir that stores the anolyte and a catholyte reservoir that stores the catholyte be provided in the vicinity of the electrolyzer, and that the lower parts of the anolyte reservoir and the catholyte reservoir be arranged above a position halfway up the electrolyzer, so that the anolyte and catholyte respectively circulate between the anolyte reservoir and the anode chamber and between the catholyte reservoir and the cathode chamber due to the difference in gravity.

[0029] The sodium hypochlorite solution production apparatus of the present invention comprises an electrolyzer divided into an anode chamber and a cathode chamber by an ion exchange membrane and supplied with secondary salt water as an aqueous sodium chloride solution, and a reaction tank into which the products from the anode and cathode chambers are introduced after electrolysis, and produces a sodium hypochlorite solution by means of a reaction in the reaction tank, characterized in that the apparatus comprises a primary salt water generation section that dissolves water-based feedstock containing sodium chloride as the main component in purified water to generate primary salt water, and a chelating section for carrying out the chelation of the primary salt water to generate secondary salt water, and the apparatus is operated at a salt decomposition rate ranging from 80 to 95%.

[0030] In the production apparatus of the present invention, the ion exchange membrane is preferably a bilayer membrane configured from a sulfonic acid layer and a carboxylic acid layer.

[0031] Furthermore, in the production apparatus of the present invention, it is preferable to provide a first alternating means that alternates between the fact that the anolyte in the anode chamber is introduced from the anode chamber to the reaction tank between the anode chamber and the reaction tank, and it is also preferable to provide a second alternating means that alternates between the fact that the chlorine gas generated in the anode chamber is introduced from the anode chamber to the reaction tank between the anode chamber and the reaction tank.

[0032] Furthermore, the production apparatus of the present invention may comprise two or more electrolyzers, and a chlorine gas inlet path for introducing chlorine gas obtained from one or more electrolyzers into an installation where chlorine gas is used.

[0033] 1786733 of 21 Furthermore, the production apparatus of the present invention preferably has a purified water introduction path for introducing purified water into the reaction tank. The production apparatus of the present invention is appropriately used for the production of a sodium hypochlorite solution with an available chlorine concentration of 8% or more.

[0034] Furthermore, the production apparatus of the present invention preferably comprises a cation exchange treatment section that treats water raw material with a cation exchange resin to generate purified water. In this case, the cation exchange treatment section also preferably includes a water softener.

[0035] Furthermore, in the production apparatus of the present invention, the first alternation means and / or the second alternation means can be configured to be operated by an alternation operation or an external signal through an automatic control apparatus communicable with the outside of a production facility.

[0036] Furthermore, the production apparatus of the present invention is appropriately located in the vicinity of a facility where sodium hypochlorite is used and is used for the production of a sodium hypochlorite solution in situ.

[0037] Furthermore, in the production apparatus of the present invention, it is preferable that the apparatus have an anolyte reservoir that stores anolyte and a catholyte reservoir that stores catholyte in the vicinity of the electrolyzer, and the lower parts of the anolyte reservoir and the catholyte reservoir are arranged above a position at half the height of the electrolyzer. [Effects of the invention]

[0038] According to the present invention, it is possible to provide a method of production and a production apparatus for a sodium hypochlorite solution, in which the sodium hypochlorite solution with a high concentration of available chlorine can be produced at low cost in an on-site facility. [Brief description of the drawings]

[0039] Fig. 1 is an apparatus configuration diagram illustrating an example of an apparatus for producing a sodium hypochlorite solution for use in the present invention. Fig. 2 is an apparatus configuration diagram that schematically illustrates another mode of an apparatus for producing a sodium hypochlorite solution for use in the present invention. Fig. 3 is a graph that represents a relationship between a salt consumption rate and the salt decomposition rate in the present invention, as a function of a sodium hypochlorite solution production apparatus with a dechlorination treatment step. [Method for carrying out the invention]

[0040] 1786733 of 21 From here on, embodiments of the present invention will be described with reference to the drawings; however, the present invention is not limited to them.

[0041] Figure 1 is an apparatus configuration diagram illustrating one example of an apparatus for producing a sodium hypochlorite solution for use in the present invention. Figure 2 is an apparatus configuration diagram schematically illustrating another mode of an apparatus for producing a sodium hypochlorite solution for use in the present invention.

[0042] The present invention relates to improvements of a method and apparatus for producing a sodium hypochlorite solution in situ near a physical plant where a sodium hypochlorite solution is used. In the present invention, a high-concentration sodium hypochlorite solution is produced in an electrolyzer divided into an anode chamber and a cathode chamber with an ion-exchange membrane by introducing secondary salt water as an aqueous sodium chloride solution into the anode chamber and by introducing an anolyte and generated chlorine gas into the anode chamber, and a generated aqueous sodium hydroxide solution into the cathode chamber, after electrolysis, into a reaction tank, allowing the anolyte, chlorine gas, and generated aqueous sodium hydroxide solution, as a catholyte, to react in the reaction tank.

[0043] In the present invention, when the salt decomposition rate is in the range of 80 to 95%, and the secondary saltwater entering the anode chamber is generated from salt raw material, this raw material, containing sodium chloride as its main component, is dissolved in purified water to generate primary saltwater (primary saltwater generation step). The primary saltwater is then chelated to generate secondary saltwater (chelation step). In this way, a sodium hypochlorite solution with a high concentration of available chlorine can be produced from an on-site installation at low cost.

[0044] In the present invention, the salt decomposition rate in the production of sodium hypochlorite solution shall be in the range of 80 to 95%, and preferably in the range of 82 to 93%. If the salt decomposition rate is less than 80%, it will be difficult to generate a high-concentration sodium hypochlorite solution when producing sodium hypochlorite by introducing the anolyte into the reaction tank without draining the anolyte. Furthermore, if the salt decomposition rate is less than 80% when producing sodium hypochlorite with anolyte drainage, as described in detail below, economic efficiency cannot be guaranteed.On the other hand, if the salt decomposition rate is greater than 95%, the voltage in the electrolyzer rises significantly, and no operation can be substantially continued, even in the case of introducing the anolyte into the reaction tank or even in the case of draining the anolyte.

[0045] If the anolyte is drained rather than introduced into the reaction tank, its temperature and pH range from 50°C to 80°C and 4 to 5, respectively, and chlorine gas dissolves in it. Sending the anolyte directly to the wastewater treatment plant is not preferable due to the plant's thermal resistance and the generation of chlorine odors. Therefore, when drained, the anolyte must be aerated to remove chlorine, undergo cooling, pH adjustment, and similar processes, and then be sent to a wastewater treatment plant. In this way, from an economic standpoint, it is preferable to increase the salt decomposition rate and reduce the amount drained.

[0046] 1786733 of 21 In cases where a dechlorination treatment step is included, the anolyte undergoing dechlorination is recycled for salt dissolution, thus keeping the salt consumption rate low. As previously described, liquid chemicals such as hydrochloric acid, aqueous sodium hydroxide solution, and disodium sulfite are used in large quantities in the dechlorination treatment step, consequently increasing the required equipment, such as tanks and pumps, if a dechlorination treatment system is installed. Therefore, if this system is applied to an on-site sodium hypochlorite production facility, the footprint increases, and both the initial and maintenance costs are higher.In the present invention, although neither the dechlorination treatment step nor the corresponding instruments are used, liquid chemicals are therefore used, and in this way the occupied area, the initial cost and the maintenance cost can be reduced; the salt included in the anolyte is incorporated into a sodium hypochlorite solution as a product or is drained and therefore discharged out of the system, resulting in an increased rate of salt consumption.

[0047] It has been demonstrated, as a result of a detailed comparison between the cost-reduction benefits of eliminating the dechlorination treatment step and reducing the amount of liquid chemicals used, and the disadvantages of increasing the salt consumption rate and the associated costs of anolyte drainage treatment, that the increase in the salt consumption rate is preferably 25% or less in terms of cost-effectiveness compared to the case where the dechlorination treatment step is present. Figure 3 consists of a graph representing the relationship between the original salt unit ratio and the salt decomposition rate in the present invention, based on a sodium hypochlorite solution production apparatus with a dechlorination treatment step. According to Figure 3,3, the salt decomposition rate must be 80% or more so that the amount of the increase in the salt consumption rate is 25% or less compared to the case where the facility has the dechlorination treatment step.

[0048] The generation of secondary saltwater in the present invention can be carried out by providing a saltwater production unit to produce secondary saltwater from salt feedstock, in parallel with a main section of the apparatus for producing a sodium hypochlorite solution, and a compact, site-usable production plant can be provided. Specifically, the saltwater production unit in the present invention includes a primary saltwater generation section that dissolves salt feedstock containing sodium chloride as the main component in purified water to generate primary saltwater, and a chelation section that carries out the chelation of the primary saltwater to thereby generate secondary saltwater, as a basic configuration.

[0049] [Primary saltwater generation step] As previously described, in the present invention, when generating secondary salt water A, the salt feed material G, containing sodium chloride as its main component, is first dissolved in purified water B to generate primary salt water H as saturated salt water at room temperature. This dissolution of the salt feed material G in purified water B can be carried out in a salt dissolution tank 30.

[0050] Any solar salt and rock salt can be used as raw material for salt G. It is preferable to carry out further purification with the salt G raw material and then use purified salt from which metallic impurities such as calcium and magnesium ions are removed to some extent. Because calcium and magnesium, as typical impurities in saltwater, impair the performance of the ion exchange membrane, it is preferable to purify the saltwater that will enter the anode chamber and reduce the 1786733 of 21 concentration of these impurities to a level corresponding to the standard use of the ion exchange membrane. A chelating resin may be used in this case for the removal of calcium and magnesium, which serve as cations. Because bromide is incorporated into the salt feed as bromic acid into a produced sodium hypochlorite solution, the concentration of bromide ions in the salt feed is preferably less than 100 mg / kg, particularly around 69 mg / kg or less, from the standpoint of obtaining a sodium hypochlorite solution with a bromic acid concentration corresponding to the first grade illustrated in JWWA K120:2008.

[0051] The purified water B used herein may be industrially purified water, or it may be purified water B generated from water raw material I in an on-site facility by providing a cation exchange treatment section 40 that treats the water raw material with a cation exchange resin to generate purified water, prior to the primary saltwater generation section. In other words, the present invention may include a cation exchange step for treating water raw material I with a cation exchange resin to generate purified water, prior to the primary saltwater generation step.This cation exchange step can obtain purified water B as a soft water with lower hardness than water raw material I by adsorbing and removing calcium ions, magnesium ions, and other heavy metal ions contained in the water raw material and exchanging these ions with sodium ions or hydrogen ions.

[0052] The raw water material I for use in the cation exchange step can be drinking water, well water (groundwater), industrial water or similar available at an on-site production site in close proximity to a facility where a sodium hypochlorite solution is used.

[0053] The cation exchange resin for use in the cation exchange step is not particularly limited, and can be of the Na type or the H type.

[0054] In the present invention, the cation exchange treatment section 40 used to carry out the cation exchange step can also be a water softener that utilizes the cation exchange resin, instead of the cation exchange resin itself. If the cation exchange resin deteriorates, regeneration can be achieved by a method involving the exchange of the deteriorated cation exchange resin with a new cation exchange resin, or by a regeneration method with a regeneration mechanism attached to the water softener, and salt in the case of using the water softener.

[0055] [Chelation step] In the present invention, the primary salt water H obtained in the step is chelated to generate secondary salt water A. The primary salt water H can be chelated to remove calcium ions and magnesium ions brought from the salt raw material G from the primary salt water, and thus generate clean secondary salt water A. The primary salt water H can be chelated in a salt water purifier 50.

[0056] The following describes a process for producing a sodium hypochlorite solution according to the present invention. First, electrolysis is carried out in the production apparatus illustrated in Fig. 1, by introducing the previously generated secondary salt water A into an anode chamber 2 and introducing the purified water B into a chamber of 1786733 of 21 cathode 3 in an electrolyzer 10 divided into anode chamber 2 and cathode chamber 3 by means of an ion exchange membrane 1. From here on, an anolyte C and chlorine gas (Cl2) D generated, in anode chamber 2, and an aqueous sodium hydroxide solution E generated, in cathode chamber 3, after electrolysis, are introduced into a reaction tank 20, and the anolyte C, chlorine gas D, and aqueous sodium hydroxide solution E react in reaction tank 20, to thereby produce a sodium hypochlorite solution F. The anolyte C in this case is salt water reduced in concentration to, for example, a concentration less than 100 g / L after electrolysis.

[0057] According to the present invention, the above configuration allows a high concentration of stable chlorine sodium hypochlorite solution to be produced stably and efficiently at low cost in a compact on-site production facility, and allows the production of sodium hypochlorite in a simple manner at a location where this sodium hypochlorite is consumed.

[0058] In the case where anolyte C is introduced into reaction tank 20, it dilutes the generated sodium hypochlorite solution, thus not increasing the available chlorine concentration. Therefore, it is necessary to increase the concentration of the aqueous sodium hydroxide solution E as a catholyte, thereby decreasing the amount of water in reaction tank 20 and increasing the concentration of the sodium hypochlorite solution. When anolyte C is introduced into reaction tank 20 and the salt decomposition rate is 80 to 95%, the concentration of the aqueous sodium hydroxide solution must be at least 22% by mass or higher to obtain an available chlorine concentration of 12%. Because an on-site installation may also be located in a cold region, the solidification of the aqueous sodium hydroxide solution during operation must also be considered.Aqueous sodium hydroxide solution, when its concentration exceeds 30% by mass, solidifies at 0°C or higher. Although the aqueous sodium hydroxide solution can be diluted by adding purified water before the start of the operation, a disadvantage is that the amount of purified water used decreases, and an appropriate amount of additional purified water will also need to be managed. Therefore, the preferred concentration range for the aqueous sodium hydroxide solution when introducing anolyte C into reaction tank 20 is 22 to 30% by mass.

[0059] On the other hand, when the salt decomposition rate is 80 to 95% without the introduction of anolyte C into reaction tank 20, the concentration of the aqueous sodium hydroxide solution should be at least 16% by mass or higher to obtain an available chlorine concentration of 12%. If the concentration of the aqueous sodium hydroxide solution increases, the concentration of the sodium hypochlorite solution can also be increased. However, if the concentration of the aqueous sodium hydroxide solution exceeds 23% by mass, salt may settle in the sodium hypochlorite solution. Therefore, the preferred range for the concentration of the aqueous sodium hydroxide solution when introducing anolyte C into reaction tank 20 is 16 to 23% by mass.

[0060] Furthermore, in the present invention, a first switching means 4 that alternates between introducing the anolyte C or not from the anode chamber 2 into the reaction tank 20 is preferably provided between the anode chamber 2 and the reaction tank 20, as illustrated, and thus a sodium hypochlorite solution can be produced without introducing some or all of the quantity of anolyte C into the reaction tank 20. The first switching means 4 that can control the introduction of the anolyte C can be provided in this way, thereby allowing the selection and production of a sodium hypochlorite solution with different concentrations of common salt and chloric acid according to the requirements.

[0061] 1786733 of 21 Furthermore, in the present invention, a second switching means 5, which alternates between introducing or not introducing chlorine gas D from the anode chamber 2 into the reaction tank 20, can be provided between the anode chamber 2 and the reaction tank 20, thereby allowing the production of a sodium hypochlorite solution with the introduction of part or all of the quantity of chlorine gas D into an installation where chlorine gas is used. The second switching means 5, capable of controlling the introduction of chlorine gas D, can thus be provided to allow the production of a sodium hypochlorite solution with the introduction of chlorine gas D into a physical plant according to the requirements.

[0062] The first and second switching means 4 and 5 are configured using, for example, a manual valve, an electrically operated valve, or an air-operated valve. For instance, if the first and second switching means 4 and 5 are configured using an electrically operated valve or an air-operated valve, these means can be configured to operate via a switching mechanism or an external signal, based on an instruction from an automatic control device that communicates with the outside of a production facility. This automatic control device could be, for example, the MELSEC-Q series manufactured by Mitsubishi Electric Corporation or the SIMATIC S7 manufactured by Siemens AG, but is not limited to these.For example, if a sodium hypochlorite solution is produced at a water treatment plant, such as a water purification plant, the automatic control device can be activated based on an external signal from the plant's central control system. The first switching means 4 and the second switching means 5 can be activated by an on-site switch or similar device operated by an on-site operator, respectively, based on measurement results of, for example, the sodium hypochlorite solution and common salt concentrations, and based on the chlorine gas injection requirements for the treated water.

[0063] Furthermore, in the present invention, a purified water introduction path for introducing purified water B into reaction tank 20 is preferably provided, and in this way the concentration of the sodium hypochlorite solution can be adjusted by introducing purified water B into reaction tank 20 during the generation of the sodium hypochlorite solution in reaction tank 20. For example, when producing a sodium hypochlorite solution with an available chlorine concentration of 15%, the available chlorine concentration can be 8% by matching the concentrations of the anolyte C and the aqueous sodium hydroxide solution E as a catholyte and introducing purified water B. A high available chlorine concentration results in an increase in the amount of chloric acid generated according to the decomposition.It is effective in mitigating the increase in chloric acid concentration required to dilute sodium hypochlorite solution in hot regions or during the summer months when sodium hypochlorite decomposes rapidly. When producing a sodium hypochlorite solution with an available chlorine concentration of 1 to 8%, an ion-exchange membrane configured with a sulfonic acid layer, highly resistant to impurities in saltwater, can be used. A step in saltwater purification can be simplified by using purified salt with few impurities.

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

[0065] In the present invention, it is preferable to provide an anolyte reservoir 6 that stores the anolyte C and a catholyte reservoir 7 that stores the aqueous sodium hydroxide solution E as a catholyte in the vicinity of the electrolyzer 10, and to arrange the lower portions 6b and 7b of the anolyte reservoir 6 and the catholyte reservoir 7 above a position halfway up the electrolyzer 10, as illustrated. This arrangement allows communication between the 12 1786733 of 21 pipes between the anolyte reservoir 6 and the anode chamber 2 and between the catholyte reservoir 7 and the cathode chamber 3, in order to circulate the anolyte C and the aqueous sodium hydroxide solution E respectively between the anolyte reservoir 6 and the anode chamber 2 and between the catholyte reservoir 7 and the cathode chamber 3 due to the difference in gravity, even if a flow medium such as a pump is not provided. A flow medium such as a pump may also be provided between the anolyte reservoir 6 and the anode chamber 2 and between the catholyte reservoir 7 and the cathode chamber 3, without any limitation.

[0066] In the present invention, the ion-exchange membrane 1 used in the electrolyzer 10 can be any, and preferably is a bilayer membrane configured from a sulfonic acid layer (anode side) and a carboxylic acid layer (cathode side). This bilayer membrane is used to enable the carboxylic acid layer to inhibit the dissipation of hydroxide ions from the cathode side, thereby allowing for high-efficiency production. Examples of this bilayer membrane include Nafion (registered trademark) N2050 manufactured by Chemours, FLEMION (registered trademark) F-9010 manufactured by AGC Inc., and Aciplex (registered trademark) F7001 manufactured by Asahi Kasei Corporation.

[0067] In the production apparatus for use in the present invention, an anode obtained by forming a coating with an electrode catalyst substance containing an oxide of a platinum group metal, on a metal substrate such as titanium, can be provided in the anode chamber 2 of the electrolyzer 10 divided with the ion exchange membrane 1. Accordingly, a cathode made of nickel, stainless steel, or titanium, or obtained by forming a coating with a cathode active substance that not only results in a reduction of the excess hydrogen voltage, but is excellent in long-term durability, in said metal, can be provided in the cathode chamber 3.

[0068] In the present invention, the aqueous sodium hydroxide solution E, although controlled in terms of its concentration and flow rates based on a target amount of the generated sodium hypochlorite solution, can be introduced into the electrolyzer 10. In the case where the purified water B is introduced into the electrolyzer 10, the purified water B can also be similarly controlled in terms of its flow rate based on the target amount and concentration of the generated sodium hypochlorite solution.

[0069] Aqueous sodium hydroxide solution E and generated hydrogen gas K are drawn from the top of cathode chamber 3, where aqueous sodium hydroxide solution E is introduced as a catholyte into reaction tank 20 and hydrogen gas K is discharged to the outside. An anolyte C, comprising aqueous sodium chloride solution diluted by electrolysis, and chlorine gas D, are drawn from the top of anode chamber 2 and introduced into reaction tank 20 respectively via first and second alternating means 4 and 5.

[0070] A sodium hypochlorite solution F is generated in reaction tank 20 by a reaction of chlorine and sodium hydroxide. The sodium hypochlorite solution F extracted from reaction tank 20 in this case is not only extracted as a product, but is also introduced and cooled in a cooling unit 8 using cooling water L and from there is circulated in reaction tank 20 by means of a pump, thus not only preventing an increase in the temperature of the electrolyzer 10, but also preventing the decomposition of the generated sodium hypochlorite.

[0071] 1786733 of 21 Figure 2 is an apparatus configuration diagram schematically illustrating another mode of an apparatus for producing a sodium hypochlorite solution, for use in the present invention. As illustrated, in the present invention, two or more electrolyzers, two electrolyzers 10A and 10B in the illustrated example, are arranged, and chlorine gas D obtained from one or more electrolyzers, an electrolyzer 10A in the illustrated example, can be fed into an installation where chlorine gas is used, and also chlorine gas D obtained from one or more of the remaining electrolyzers, an electrolyzer 10B in the illustrated example, can be used to produce a sodium hypochlorite solution.In other words, a chlorine gas inlet path for introducing chlorine gas obtained from electrolyzers between several of them, to an installation where chlorine gas is used, can be provided in order to simultaneously carry out the introduction of chlorine gas to an installation where chlorine gas is used and the production of a sodium hypochlorite solution.

[0072] For example, in the production of a sodium hypochlorite solution from products in electrolyzer 10A and electrolyzer 10B in the installation illustrated in Fig. 2, the chlorine gas generated in anode chamber 2A and anode chamber 2B, and an aqueous sodium hydroxide solution E generated in cathode chamber 3A and cathode chamber 3B are mixed in reaction tank 20 to produce a sodium hypochlorite solution. Although a sodium hypochlorite solution with an available chlorine concentration of 12% or more is produced, the second alternating means 5, configured from an automatic valve, can be operated to take chlorine gas D generated in electrolyzer 10A and remove it from the system.A switching device (not illustrated) that alternates between introducing or not introducing a catholyte may also be located and operated between cathode chamber 3A and reaction tank 20, to take an aqueous sodium hydroxide solution E generated in cathode chamber 3A and remove it from the system, and store the solution. The chlorine gas D removed from the system in this manner may be injected directly into treated water in a water purification plant or similar structure and used thereafter. [Examples]

[0073] From here on, the present invention will be described more specifically with reference to the Examples.

[0074] The production of a sodium hypochlorite solution was carried out in an apparatus with the configuration illustrated in Fig. 1. The electrolysis area was 8000 cm² and the electrolysis current was 2400 A in the electrolyzer. A bilayer membrane, F-9010, manufactured by AGC Inc., consisting of a sulfonic acid layer and a carboxylic acid layer, was used as the ion exchange membrane of the electrolyzer.

[0075] After dissolving salt raw material with a bromide ion concentration of 50 mg / kg in purified water to generate primary saltwater, the resulting primary saltwater was chelated to generate secondary saltwater. When the bromide ion concentration in the salt raw material was 50 mg / kg, the bromic acid concentration in a sodium hypochlorite solution in Example 1, described below, was 15 mg / kg, and the bromic acid concentration in a sodium hypochlorite solution in Example 2, described below, was 18 mg / kg. These values ​​were below the 50 mg / kg default value for first-grade sodium hypochlorite in city water in the Japan Water Works Association Standard (JWWA K120: 2008). Bromide ions were anions, and therefore could not be removed by a chelating resin used in the purification of salt water.

[0076] The pH before purification of the salt water, where raw salt material was dissolved in purified water, was 7.8. DIAION (brand) was used in the purification of the salt water. CR11 (registered as 1786733 of 21) manufactured by Mitsubishi Chemical Corporation, as an iminodiacetic acid type chelation resin. The concentration of calcium and magnesium in the salt water before purification was 16 mg / L, and the concentration of calcium and magnesium in the salt water after purification was 10 pg / L.

[0077] After purified secondary salt water and 25% by mass of an aqueous sodium hydroxide solution were loaded into the anode and cathode chambers, respectively, the operation was initiated. The temperature of the electrolyte solution during the operation was 75°C, and purified water was introduced into the cathode chamber to adjust the concentration of the aqueous sodium hydroxide solution. The amount of aqueous sodium hydroxide solution introduced into the reaction tank was adjusted so that the concentration of the aqueous sodium hydroxide solution in the sodium hypochlorite solution was 1%. Cooling was carried out so that the temperature of the reaction tank was 30°C.A first means of alternating between introducing or not introducing the anolyte from the anode chamber into the reaction tank was provided between the anode chamber and the reaction tank, and each test in the Examples and Comparative Examples was carried out by alternating the introduction and discharge of the anolyte into and out of the reaction tank by means of an automatic valve, and at the same time the amount of purified water introduced into the cathode chamber was adjusted.

[0078] In each of the examples, purified water was used to dissolve the salt feedstock and add it to the cathode chamber. Although ion-exchange water could have been used instead of purified water, purified water was preferred due to cost considerations. The silica concentrations in both the purified water and the secondary saltwater were 12 mg / L. In this case, electrolysis was continued for two months with intentional adjustments to maintain a silica concentration of 40 mg / L in the secondary saltwater, while the amount of chlorine generated and the voltage remained stable. Although the concentration of the aqueous sodium hydroxide solution was adjusted in this case by introducing purified water into the cathode chamber, the concentration of the sodium hypochlorite solution could also have been adjusted by introducing purified water into the reaction tank.

[0079] Pipes were connected between the anolyte reservoir and the anode chamber, and between the catholyte reservoir and the cathode chamber. No flow medium, such as a pump, was provided. The lower portions of the anolyte and catholyte reservoirs were positioned above a point halfway up the electrolyzer, allowing for favorable circulation of the anolyte and catholyte between the respective reservoirs and the electrolyzer, resulting in stable operating voltage, temperature, and pressure. Conversely, when the lower portions of the respective reservoirs were positioned below a point halfway up the electrolyzer, favorable circulation was not achieved, and the pressure was unstable.

[0080] [Example 1] A sodium hypochlorite solution was produced by introducing the anolyte into the reaction tank. When the salt decomposition rate was 80.4% and the concentration of the aqueous sodium hydroxide solution in the catholyte was 28.0% by mass, the available chlorine concentration, the concentration of common salt, and the concentration of chloric acid in the resulting sodium hypochlorite solution were 12.2% by mass, 13.5% by mass, and 0.18% by mass, respectively. The amount of anolyte drained was zero due to the operation involving the introduction of the anolyte into the reaction tank.

[0081] [Example 2] 1786733 of 21 A sodium hypochlorite solution was produced by introducing the anolyte into the reaction tank. When the salt decomposition rate was 89.4% and the concentration of the aqueous sodium hydroxide solution in the catholyte was 26.2% by mass, the available chlorine concentration, the concentration of common salt, and the concentration of chloric acid in the resulting sodium hypochlorite solution were 12.8% by mass, 13.0% by mass, and 0.17% by mass, respectively. The amount of anolyte drained was zero due to the operation involving the introduction of the anolyte into the reaction tank.

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

[0083] [Example 4] A sodium hypochlorite solution was produced by draining the anolyte. When the salt decomposition rate was 89.1% and the concentration of the aqueous sodium hydroxide solution in the catholyte was 16.0% by mass, the available chlorine concentration, the concentration of common salt, and the concentration of chloric acid in the resulting sodium hypochlorite solution were 12.0% by mass, 10.1% by mass, and 0.06% by mass, respectively. The amount of anolyte drained 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 while simultaneously draining a portion of the anolyte. The ratio of the amount of anolyte introduced into the reaction tank to the amount drained was 1:1. When the salt decomposition rate was 86.7% and the concentration of the aqueous sodium hydroxide solution in the catholyte was 17.4% by mass, the concentration of available chlorine, common salt, and chloric acid in the resulting sodium hypochlorite solution were 12.1% by mass, 11.0% by mass, and 0.08% by mass, respectively. The amount of anolyte drained was 3.7 L / hour.

[0085] [Comparative Example 1] A sodium hypochlorite solution was produced by introducing the anolyte into the reaction tank. When the salt decomposition rate was 45.1% and the concentration of the aqueous sodium hydroxide solution in the catholyte was 32.3% by mass, the available chlorine concentration, the concentration of common salt, and the concentration of chloric acid in the resulting sodium hypochlorite solution were 5.5% by mass, 18.4% by mass, and 0.12% by mass, respectively. The amount of anolyte drained was zero due to the operation involving the introduction of the anolyte into the reaction tank.

[0086] The rate of salt decomposition was low in Comparative Example 1 compared to Example 1 and Example 2, and the concentration of available chlorine in the sodium hypochlorite solution was low and the concentration of common salt in that location was high.

[0087] [Comparative Example 2] 1786733 of 21 A sodium hypochlorite solution was produced from the anolyte drainage. When the salt decomposition rate was 47.0% and the concentration of the aqueous sodium hydroxide solution in the catholyte was 16.3% by mass, the available chlorine concentration, the concentration of common salt, and the concentration of chloric acid in the resulting sodium hypochlorite solution were 12.3% by mass, 10.1% by mass, and 0.04% by mass, respectively. The amount of anolyte drained was 27.8 L / hour.

[0088] In Comparative Example 2, the amount drained was large compared to Example 3 and Example 4.

[0089] [Comparative Example 3] A sodium hypochlorite solution was produced by draining the anolyte. When the salt decomposition rate reached 96.2%, a voltage increase occurred, and no further operation could be maintained until the sodium hypochlorite solution concentration stabilized. The concentration of the aqueous sodium hydroxide solution in the catholyte during the operation was 18.1% by mass. The amount drained over 30 minutes to achieve the 96% salt decomposition rate was 3.5 L / hour.

[0090] [Comparative Example 4] A sodium hypochlorite solution was produced by introducing the anolyte into the reaction tank. When the salt decomposition rate was 77.9% and the concentration of the aqueous sodium hydroxide solution in the catholyte was 29.3% by mass, the available chlorine concentration, the concentration of common salt, and the concentration of chloric acid in the resulting sodium hypochlorite solution were 11.3% by mass, 14.9% by mass, and 0.14% by mass, respectively. The amount of anolyte drained was zero due to the operation involving the introduction of the anolyte into the reaction tank.

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

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

[0094] In Comparative Example 5, the rate of salt decomposition was low and therefore the amount drained was greater than the amounts in Example 3 and Example 4.

[0095] [Table 1] 1786733 of 21 Anolyte Salt Decomposition Rate (%) Caustic Soda Concentration (% by mass) at the Cathode Concentration (% by mass) of each component in the Sodium Hypochlorite Solution Amount (L / hour of drained anolyte) Stability Available Chlorine Concentration Common Salt Concentration Chloric Acid Concentration Example 1 Intake to Reaction Tank 80.4 28.0 12.2 13.5 0.18 0 No Voltage Increase Example 2 Intake to Reaction Tank 89.4 26.2 12.8 13.0 0.17 0 No Voltage Increase Example 3 Drainage 81.1 16.3 12.3 10.4 0.06 9.5 No Voltage Increase Example 4 Drainage 89.1 16.0 12.0 10.1 0.06 6.5 No Voltage Increase Example 5 Intake to Reaction Tank: Drainage = 1:1 86.7 17.4 12.1 11.0 0.08 3.7 No voltage increase Comparative Example 1 Introduction to reaction tank 45.1 32.3 5.5 18.4 0.12 0 No voltage increase Comparative Example 2 Drainage 47.0 16.3 12.3 10.1 0.04 27.8 No voltage increase Comparative Example 3 Drainage 96.2 18.1 - - - 3.5 Voltage increase observed; operation cannot be continued. 1786733 of 21 Example Comparative 4 Example Comparative 5 Introduction to the reaction tank Drainage 77.9 75.6 29.3 16.5 11.3 14.9 0.14 0 No voltage increase 12.1 10.3 0.06 11.7 No voltage increase 1786733 of 21

[0096] It has been discovered from the above that, even when the anolyte is introduced into or drained from the reaction tank, a salt decomposition rate of 80% or higher is necessary to produce a high-concentration sodium hypochlorite solution. Furthermore, it has been confirmed that a salt decomposition rate exceeding 95% results in a significant voltage increase, preventing the continuation of operations. Therefore, the upper limit for the salt decomposition rate needs to be 95% for operational stability. [Description of the symbols]

[0097] ion exchange membrane, 2A, 2B anode chamber, 3A, 3B cathode chamber first alternation medium second alternation medium anolyte reservoir 6b lower part of the anolyte reservoir catholyte reservoir 7b lower part of the catholyte reservoir cooling apparatus, 10A, 10B electrolyzer reaction tank salt dissolution tank cation exchange treatment section saltwater purifier Secondary saltwater B purified water Cannolite Chlorine gas E aqueous sodium hydroxide solution F sodium hypochlorite solution G raw material of salt Primary saltwater I raw material of water K hydrogen gas Cooling water

Claims

1. A method for producing a sodium hypochlorite solution; characterized in that: in the production of a sodium hypochlorite solution by introducing secondary salt water as an aqueous sodium chloride solution into an electrolyzer divided into an anode chamber and a cathode chamber by means of an ion exchange membrane, into the anode chamber and, after electrolysis, introducing an anolyte and a chlorine gas generated in the anode chamber and an aqueous sodium hydroxide solution generated in the cathode chamber into a reaction tank to allow the anolyte, the chlorine gas, and the aqueous sodium hydroxide solution generated as a catholyte to react in the reaction tank,wherein the process for producing secondary saltwater from raw salt includes: (1) a primary saltwater generation step consisting of dissolving water feed containing sodium chloride as the main component in purified water to generate primary saltwater, and (2) a chelation step for chelating the primary saltwater and subjecting it to chelation treatment to remove calcium and magnesium ions derived from the raw salt in the primary saltwater, thereby generating secondary saltwater, which is identified by the fact that the rate of sodium chloride decomposition during electrolysis varies from 80 to 95%; wherein purified water is introduced into the reaction tank to adjust the available chlorine concentration of a sodium hypochlorite solution generated in the reaction tank to 8% or more. 22 Claims follow.