Aqueous solution manufacturing apparatus, electrolytic cell unit and manufacturing method

Abstract

To provide a production device capable of attaining the optimization of the service life of electrodes and an electrolytic tank by effectively cooling the electrolytic tank, and stably producing an aqueous solution within the range of target properties in a normal electrolytic operation.SOLUTION: A production device of an aqueous solution comprises: an electrolytic tank; plural electrodes provided at the inside of the electrolytic tank; one or more unit cells respectively formed between the electrodes in the electrolytic tank; and a solution feed passage for feeding a raw material solution into the electrolytic tank. The production device further comprises: a water feed passage for feeding cooling water into each of the one or more unit cells, independently of the raw material solution; an exhaust port for exhausting an electrolytic solution produced by the electrolysis of the raw material solution from the one or more unit cells; and a power supply device for flowing an electric current to a space between the plural electrodes.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an apparatus for producing an aqueous solution, an electrolytic cell unit, and a production method. More specifically, the present disclosure relates to an apparatus for producing an aqueous solution by electrolyzing a solution containing chloride ions, an electrolytic cell unit used for producing the aqueous solution, and a production method for producing the aqueous solution. [Background technology]

[0002] A technique is known in which a solution containing chlorine ions, such as hydrochloric acid alone or a mixed solution of hydrochloric acid and sodium chloride or potassium chloride, is electrolyzed under predetermined conditions and diluted to produce an aqueous solution containing free hypochlorous acid.The aqueous solution produced has free hypochlorous acid acting as a bactericidal component and exhibiting bactericidal effect against a wide range of microorganisms, and is therefore used in a wide range of fields.Among the aqueous solutions containing free hypochlorous acid mentioned above, the slightly acidic hypochlorous acid water produced from hydrochloric acid or an aqueous solution prepared by adding sodium chloride aqueous solution to hydrochloric acid is also designated for sterilization of food additives, and is known to have many excellent features.

[0003] Due to its many excellent characteristics, slightly acidic hypochlorous acid water is used in an extremely wide range of fields, including food processing (milk and dairy products, beverages, alcoholic beverages, confectionery, prepared foods, seafood processing, agricultural and livestock processing, etc.), medical care, sports and leisure facilities, agriculture and fisheries (paddy rice cultivation, fruit orchards, vegetable cultivation factories, livestock and poultry farming, aquaculture, etc.), and is used as a safe and effective disinfectant in hygiene management in ordinary households.

[0004] Slightly acidic hypochlorous acid water is produced by electrolyzing a solution containing chlorine ions such as hydrochloric acid in a membraneless electrolytic cell and diluting the resulting electrolyte with water. In this technology for producing slightly acidic hypochlorous acid water, the required points include stable electrolysis operation of the production equipment, stable production of slightly acidic hypochlorous acid water with an effective chlorine concentration and pH within a predetermined range, and the life of the electrodes and electrolytic cell.

[0005] However, in certain fields, there are cases where high concentrations of available chlorine are required, and there are an increasing number of cases where users place a heavy load on the equipment and subject it to continuous stress, which means that conventional electrolysis designs are no longer sufficient.

[0006] For example, in the past, under certain conditions depending on the quality of the raw water and usage conditions, malfunctions such as unstable operation due to abnormal electrolysis, deviations from the target ranges of available chlorine concentration and pH, and shortened lifespans of electrodes and electrolytic cells could occur.

[0007] One of the physical conditions that affects the lifespan of the electrodes and electrolytic cell mentioned above is the heat generated by electrolysis. Minimizing the temperature rise around the electrodes is beneficial for the lifespan of the electrodes.

[0008] Japanese Patent Publication No. 2019-198820 (Patent Document 1) is known in relation to electrodes that generate heat. Patent Document 1 discloses a technology aimed at providing a method for producing an aqueous solution that prevents electrode deterioration due to electrolytically generated hydrogen and heat and enables the safe discharge of hydrogen. The prior art of Patent Document 1 discloses a method for producing an aqueous solution containing at least free hypochlorous acid, which includes a step of mixing a gas with a chloride ion-containing solution in a mixing chamber. The mixed gas agitates the solution in the electrolytic cell, and the heat of vaporization generated by the vaporization of some of the liquid into the bubbles cools the interior of the electrolytic cell. This absorbs heat generated by the electrodes and suppresses temperature rise of the electrodes. Furthermore, prior art, including the aforementioned Patent Document 1, uses a double-shell electrolytic cell consisting of an inner tank and an outer tank, and cools the inner tank where electrolysis occurs using raw water stored in the outer tank. Summary of the Invention [Problem to be solved by the invention]

[0009] Even with the above-mentioned conventional technology, the inside of the electrolytic cell can be cooled to a certain extent by the raw water flowing through the outer tank of the double-shell electrolytic cell. After extensive research into the above-mentioned problems, the inventors discovered that cooling the core of the electrolytic cell using raw water from the outer tank of a double-shell electrolytic cell may not be sufficient under certain conditions, resulting in problems such as unstable operation due to abnormal electrolysis and a shortened lifespan of the electrodes or electrolytic cell due to an increase in internal temperature. Furthermore, the design lowered the internal temperature and alleviated high-temperature conditions by partially backflowing raw water into each unit cell from an outlet connected to the outer tank. However, there remained issues that needed improvement in terms of maintaining and stabilizing the specified properties under certain conditions. The inventors identified this problem and devised a method to stabilize it.

[0010] The present disclosure has been made in consideration of the above points, and aims to provide a manufacturing apparatus, an electrolytic cell unit, and a manufacturing method that can effectively cool the electrolytic cell, optimize the lifespan of the electrodes and the electrolytic cell, and stably produce an aqueous solution within a target property range through normal electrolysis operation. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have found that by providing a path for supplying cooling water to each unit cell of the electrolytic cell independently of the raw material solution, it is possible to efficiently cool the inside of the electrolytic cell, including the central portion, thereby enabling stable production of an aqueous solution within target property ranges through normal electrolysis operation and preventing shortening of the lifespan of the electrodes and the electrolytic cell, and have arrived at the present invention.

[0012] That is, in order to solve the above-mentioned problems, the present invention provides an apparatus for producing an aqueous solution having the following characteristics. The apparatus includes an electrolytic cell, a plurality of electrodes provided in the electrolytic cell, and one or more unit cells formed between the electrodes in the electrolytic cell. The apparatus also includes a solution supply path for supplying a raw material solution to the electrolytic cell, an outlet for discharging an electrolytic solution produced by electrolysis of the raw material solution from the one or more unit cells, and a power supply device for passing an electric current between the multiple electrodes. The apparatus further includes a water supply path for supplying cooling water to each of the one or more unit cells, independent of the raw material solution.

[0013] In a preferred embodiment, the manufacturing apparatus further includes a solution supply pump connected to the solution supply channel and a water supply pump connected to the water supply channel and operating asynchronously with the solution supply pump. In a more preferred embodiment, the water supply pump supplies cooling water intermittently or continuously at a fixed rate, and the manufacturing apparatus further includes a control device that controls the operation of the solution supply pump based on a current measurement value from the power supply device. The control device can also cause the water supply pump to supply cooling water during electrolysis, excluding a stage in which the voltage of the power supply device is increased based on a current measurement value from the power supply device, starting from the start of electrolysis. The water supply pump can preferably supply cooling water through the solution supply channel at a flow rate that results in an average residence time of 750 seconds or less per unit cell.

[0014] In certain embodiments, one outlet may be provided for each unit cell. In other certain embodiments, multiple outlets may be provided for each unit cell, and the manufacturing apparatus may further include a common outlet flow path for collecting the electrolyte solution from the outlets of one or more unit cells and a common outlet for discharging the collected electrolyte solution in the electrolytic cell. In addition, in certain embodiments, the water supply path may supply cooling water to the inlet of each of the one or more unit cells independently of the solution supply path, or may be independent of the solution supply path up to a stage upstream of the inlet of each of the one or more unit cells and share a portion of the flow path with the solution supply path at that stage.

[0015] In a preferred embodiment, the manufacturing apparatus may further include a dilution tank that is provided outside the electrolytic cell so as to surround the electrolytic cell, is connected to the electrolytic cell, dilutes the electrolytic solution discharged from the electrolytic cell with raw water, and cools the electrolytic cell with the raw water, and an outlet for removing the diluted aqueous solution from the dilution tank.

[0016] In a specific embodiment, the plurality of electrodes may each be plate-shaped, and the electrolytic cell may be a bipolar electrolytic cell in which the plurality of electrodes are arranged in parallel, the two outermost electrodes are connected to power feed wires, and at least one non-powered electrode is arranged in parallel between the two outermost electrodes that are connected to power feed wires, and a raw material solution may be supplied to each unit cell, and an electrolytic solution may be discharged from each unit cell.

[0017] In a specific embodiment, the plurality of electrodes comprises a substrate comprising titanium or an alloy containing titanium, and the raw material solution is a chloride ion-containing solution in which one or more substances selected from the group consisting of hydrogen chloride, sodium chloride, and potassium chloride are dissolved.

[0018] Furthermore, according to an embodiment of the present invention, an electrolytic cell unit having the following characteristics can be provided. The electrolytic cell unit includes an electrolytic cell, a plurality of electrodes provided in the electrolytic cell, one or more unit cells formed between the electrodes in the electrolytic cell, a solution supply channel for supplying a raw material solution to each of the one or more unit cells, a water supply channel for supplying cooling water to each of the one or more unit cells independently of the raw material solution, and an outlet provided in each of the one or more unit cells for discharging an electrolytic solution produced by electrolysis of the supplied raw material solution. In a preferred embodiment, the water supply channel and the solution supply channel may be connected to a water supply pump and a solution supply pump, respectively, that operate asynchronously with each other.

[0019] Furthermore, according to an embodiment of the present invention, it is possible to provide a method for producing an aqueous solution having the following characteristics. The production method includes a step of supplying a raw material solution to each of one or more unit cells provided in an electrolytic cell via a solution supply channel. The production method further includes a step of passing a current between multiple electrodes provided in the electrolytic cell to electrolyze the raw material solution supplied to each unit cell, thereby producing an electrolytic solution. The production method also includes a step of supplying cooling water to each of the one or more unit cells via a water supply channel, independently of the raw material solution. The production method includes a step of discharging the electrolytic solution from each unit cell, and a step of diluting the discharged electrolytic solution with raw water.

[0020] In a preferred embodiment, the step of supplying cooling water is performed by a water supply pump that is controlled asynchronously with a raw material pump that supplies the raw material solution through the solution supply path. [Effects of the Invention]

[0021] The above-described configuration makes it possible to effectively cool the electrolytic cell, optimize the lifespan of the electrodes and the electrolytic cell, and stably produce an aqueous solution within the target property range through normal electrolysis. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is an overall configuration diagram of a slightly acidic hypochlorous acid water producing apparatus according to the present embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the detailed structure of the double-shell electrolytic cell according to the present embodiment. [Figure 3] FIG. 2 is a top view of the double-shell electrolytic cell according to the present embodiment. [Figure 4] 5A and 5B are diagrams illustrating how to attach the electrolytic cell unit to the outer cell according to the present embodiment. [Figure 5] FIG. 2 is a perspective view of an electrolytic cell unit according to the present embodiment. [Figure 6] 1 is a flowchart showing an embodiment of a method for producing slightly acidic hypochlorous acid water. [Figure 7] 1 is a flowchart showing the acclimation process at the start of electrolysis performed in a specific embodiment. [Figure 8] 4 is a chart illustrating pump operation according to a preferred embodiment. [Figure 9] Graph showing temperature changes measured at the electrolyte and gas outlets of a rectangular electrolytic cell. [Figure 10] 1 is a graph showing the change over time in current value when electrolysis is restarted after being stopped during stable operation. [Figure 11] Graph showing the time changes in available chlorine concentration and pH when electrolysis is restarted after being stopped during continuous operation. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, the present invention will be described with reference to the drawings, showing embodiments thereof, but the present invention is not limited to the specific embodiments shown in these drawings.

[0024] FIG. 1 is an overall configuration diagram of a manufacturing apparatus 50 for producing slightly acidic hypochlorous acid water (hereinafter simply referred to as a manufacturing apparatus) according to this embodiment.

[0025] The manufacturing apparatus 50 shown in FIG. 1 includes a double-shell electrolytic cell 40, which includes an inner cell 20 and an outer cell 32 that is provided outside the inner cell 20 and configured to surround the inner cell 20.

[0026] The inner tank 20 functions as an electrolytic tank for producing an electrolyte solution containing hypochlorous acid by electrolysis of the raw material solution. The electrolyte solution containing a relatively high concentration of hypochlorous acid produced in the inner tank 20 is discharged from an opening 28 provided in the ceiling of the inner tank 20 into the space inside the outer tank 32 located outside the inner tank 20.

[0027] The outer tank 32 is connected to the inner tank 20 via an opening 28 and serves as a dilution tank for diluting the produced electrolyte solution. The outer tank 32 is filled with water (hereinafter referred to as raw water) for diluting the produced electrolyte solution and cooling the inner tank 20. The outer tank 32 is provided with a raw water supply port 33, and raw water 34 supplied from the raw water supply port 33 dilutes the electrolyte solution while cooling the inner tank 20 immersed in the outer tank 32. The upper part of the outer tank 32 is sealed with an outer tank lid 39, and the outer tank lid 39 is provided with an outlet 35 for removing the diluted aqueous solution from the outer tank 32. The diluted electrolyte solution has an available chlorine concentration within a predetermined range and a pH within a predetermined range, and is discharged from the outlet 35 to the outside of the double-shell electrolytic cell 40 as slightly acidic hypochlorous acid water 36.

[0028] Here, the slightly acidic hypochlorous acid water is a kind of hypochlorous acid water (aqueous solution containing hypochlorous acid as a main component, obtained by electrolyzing hydrochloric acid or sodium chloride aqueous solution), and refers to an aqueous solution obtained by electrolyzing a raw material solution adjusted to an appropriate concentration by adding hydrochloric acid and, if necessary, sodium chloride aqueous solution in a membraneless electrolytic cell. The effective chlorine concentration of the slightly acidic hypochlorous acid water is in the range of 10 to 80 mg / L, and the pH range is 5.0 to 6.5.

[0029] The raw material solution is stored in a raw material tank 1, and a raw material supply port 30 is provided in an outer tank lid 39 that seals the outer tank 32. The raw material solution is supplied from the raw material supply port 30 to the inner tank 20 inside the outer tank 32 via a raw material supply pipe 2 using a raw material solution supply pump 3. In this embodiment, the main component of the raw material solution is a hydrogen chloride solution. In a specific embodiment, the raw material solution is stored in the raw material tank 1 at a desired hydrochloric acid concentration and can be supplied directly to the double-shell electrolytic cell 40. In another specific embodiment, the raw material solution is stored in the raw material tank 1 at a predetermined concentration and can be diluted with raw water to the desired hydrochloric acid concentration before being supplied to the double-shell electrolytic cell 40. Hereinafter, the entire path or a portion thereof that supplies the raw material solution from the raw material tank 1 through the raw material supply pipe 2 to the inside of the inner tank 20 (more specifically, to the unit cells in the inner tank 20, which will be described in detail later) will be referred to as a solution supply path.

[0030] The manufacturing apparatus 50 according to this embodiment further includes a path for supplying cooling water 4 from a water source to the interior of the inner tank 20 (more specifically, to the unit cells within the inner tank 20, as will be described in detail later), independent of the raw material solution. A cooling water supply port 37 is provided in the outer tank lid 39. The cooling water 4 is supplied from a water faucet, a water storage tank, or the like as a water source, via a water supply pump 6, through the cooling water supply port 37 via a water supply pipe 5, and into the inner tank 20. Hereinafter, the entire path for supplying cooling water from the water source through the water supply pipe 5 to the interior of the inner tank 20 (more specifically, to the unit cells within the inner tank 20, as will be described in detail later) and a portion thereof will be referred to as a water supply channel.

[0031] The manufacturing apparatus 50 shown in FIG. 1 further includes a power supply unit 41, a current measurement unit 42, and a control unit 43. Two power supply terminals 29 are provided on the outer tank lid 39. The power supply unit 41 is electrically connected to the two power supply terminals 29 provided on the outer tank lid 39, and passes a direct current between multiple electrodes of the inner tank 20 inside the double-shell electrolytic tank 40. The value of the current flowing between the two power supply terminals 29 is measured by the current measurement unit 42. The current value measured by the current measurement unit 42 is provided to the control unit 43.

[0032] The control device 43 controls the operation of the raw material solution supply pump 3 based on the measured current value, and manages the supply of raw material solution to the inner tank 20. For example, a range of measured current values ​​is set in advance in the control device 43, and when the measured current value falls below the lower limit of the range, the control device operates the raw material solution supply pump 3 to start supplying raw material. When the measured current value exceeds the upper limit of the range, the control device stops the raw material solution supply pump 3, thereby stopping the supply of raw material.

[0033] The control device 43 also controls the voltage applied between the two power supply terminals 29. In certain embodiments, the control device 43 may include a mode in which the voltage is adjusted based on the measured current value at the start of electrolysis (hereinafter referred to as acclimation mode, and the process or treatment performed in the acclimation mode is referred to as acclimation or acclimation treatment). In the acclimation mode, the control device 43 attempts to increase the voltage from the initial voltage until the measured current value reaches the target value. Once the measured current value reaches the target value, the control device 43 reduces the voltage at a predetermined rate to the normal set voltage (a voltage suitable for chlorine generation) while repeatedly operating and stopping the raw solution supply pump 3 based on the upper and lower current limits, as in the normal operation described above. Note that if the measured current does not reach the target value even after the set maximum voltage is reached, the control device 43 simply starts operating the raw solution supply pump 3. This acclimation mode makes it easier to ensure a normal current at the start of electrolysis, even when the electrodes or inner tank 20 are beginning to show signs of deterioration.

[0034] In an embodiment in which the raw solution is diluted with raw water before being supplied to the double-shell electrolytic cell 40, the control device 43 may be configured to control a dilution pump (not shown) in synchronization with the raw solution supply pump 3, mix the raw solution with raw water, and supply the diluted raw solution from the raw material supply port 30.

[0035] The control device 43 according to this embodiment further controls the feed water pump 6 asynchronously with the raw material solution supply pump 3 to supply the cooling water 4 to the inner tank 20. In a preferred embodiment, the feed water pump 6 can supply the cooling water 4 intermittently or continuously and at a fixed amount to the inside of the inner tank 20 (more specifically, to the unit cells in the inner tank 20, which will be described in detail later). It is also preferred that the control device 43 controls the feed water pump 6 asynchronously with the pump that supplies the raw water 34 to supply the cooling water 4 to the inner tank 20.

[0036] Although the internal structure of the inner bath 20 is omitted in Fig. 1, this will be described later with reference to Figs. 2 to 5. The unit including the inner bath 20 shown in Fig. 1 will hereinafter be referred to as an electrolytic bath unit 60 in this embodiment.

[0037] The electrolytic cell unit 60 (inner cell 20) in the manufacturing apparatus 50 according to this embodiment will be described in more detail below with reference to FIGS.

[0038] 2(A) and 2(B) are cross-sectional views showing the structure of a double-shell electrolytic cell 40 according to this embodiment, including the interior of the inner cell 20. FIG. 3 is a top view of the double-shell electrolytic cell 40 according to this embodiment. FIG. 2(A) shows the view from the arrow A in FIG. 3, and FIG. 2(B) shows the view from the arrow B in FIG. 3. FIGS. 2(A) and 2(B) show cross-sectional views of the inner cell 20 taken along a cut surface perpendicular to the electrode surfaces of the electrodes provided in the inner cell 20. In FIG. 3, the outline of the rectangular inner cell 20 housed in the cylindrical outer cell 32 is shown by a dashed line.

[0039] As shown in Figures 2(A) and 2(B), a plurality of electrodes 24 are arranged in parallel with their surfaces facing each other in the inner cell 20, which is an electrolytic cell. The two outermost electrodes 24 are connected to power feed wires and are supplied with electrolytic current from the power supply device 41 shown in Figure 1 via power feed terminals 29, forming a bipolar membraneless electrolytic cell in which a plurality of plate-like electrodes are arranged in parallel.

[0040] At least one unconnected electrode plate is arranged parallel to the two outermost electrodes that are connected to power feed wires. By applying a DC current to the outermost plate electrodes in this configuration, one side of each of the unconnected middle plate electrodes among the plurality of plate electrodes 24 functions as an anode and the other side as a cathode, forming a unit cell 31 between them. In the embodiment described below, the electrodes 24 are assumed to be flat electrodes, but as long as they are parallel and can form a uniform electric field, the electrodes 24 are not limited to flat plates and may have a shape forming parallel curved surfaces.

[0041] The electrode 24 includes an electrode substrate. Examples of the electrode substrate include a material containing titanium or a titanium alloy. The anode surface of the electrode substrate may be coated with iridium oxide, ruthenium or osmium oxide, platinum, or the like. The electrode 24 may also contain a trace amount of tantalum as a binder. The cathode surface of the electrode substrate may be the electrode substrate itself without any treatment, or may be coated with a material containing a platinum group metal. However, from the perspective of reducing the manufacturing and maintenance costs of the electrode and the inner tank 20, the coating with a material containing a platinum group metal may be omitted.

[0042] The inner tank 20, together with the bottom 20b and ceiling 20a, forms an insulating frame structure that tightly surrounds the entire peripheral end surfaces of the electrodes 24 in order to secure the multiple electrodes 24 arranged in parallel at equal intervals. The inner tank 20 holds the side edges of the electrodes 24 and also isolates the electrolyte from the raw water. The inner tank 20 is not particularly limited, but is typically formed using a resin such as polyvinyl chloride.

[0043] In the described embodiment, each rectangular parallelepiped space is surrounded by a frame structure consisting of two adjacent electrodes, the walls of the inner tank 20, the ceiling 20a, and the bottom 20b, and each unit cell 31 is formed between two adjacent electrodes 24 within the inner tank 20. For convenience of explanation, FIG. 2 illustrates an example in which three unit cells 31 are formed for four electrodes. However, the number of electrodes and the corresponding number of unit cells are not limited to four and three, and may be any number of electrodes (n) and a corresponding number of cells (n-1). For example, in a specific implementation, five electrodes may be connected in series to form four cells, and in another specific implementation, any configuration may be used depending on production capacity, such as 10 electrodes with nine cells or 12 electrodes with 11 cells.

[0044] The voltage applied per unit cell can be set to preferably 0.5 V or more and 6.0 V or less, more preferably 1.5 V or more and 5.0 V or less, from the viewpoints of increasing the efficiency of chlorine generation and preventing deterioration in quality due to the generation of by-products. The current density is preferably 0.05 mA / mm 2 from the viewpoints of preventing a decrease in the amount of electrolysis per unit area, preventing an increase in the size of the device, and suppressing electrode wear. 2 More than 1.2mA / mm 2 Less than or equal to 0.2 mA / mm 2 More than 1.00mA / mm 2 More preferably, 0.7 mA / mm 2 More than 0.95mA / mm 2 The electrode spacing can be preferably 0.5 mm or more and 10 mm or less, more preferably 1 mm or more and 8 mm or less, from the viewpoint of facilitating separation of bubbles generated during electrolysis and preventing deterioration of power efficiency.

[0045] The bottom 20b of the frame structure is provided with two connectors 30c, 37c for connecting pipes. The first connector 30c is for connecting the pipes to a flow path inside the bottom 20b. The electrolytic cell unit 60 (inner cell 20) has one end connected to the first connector 30c on the bottom 20b and the other end connected to a raw material supply port 30a provided on the outer cell lid 39, and is equipped with a first pipe 30b for supplying raw material solution from outside the double-shell electrolytic cell 40 to the inside of the inner cell 20. The second connector 37c is also for connecting pipes to a flow path inside the bottom 20b, and the electrolytic cell unit 60 has one end connected to the second connector 37c on the bottom 20b and the other end connected to a cooling water supply port 37a provided on the outer cell lid 39, and is equipped with a second pipe 37b for supplying cooling water from outside the double-shell electrolytic cell 40 to the inside of the inner cell 20. To improve safety, a check valve may be provided upstream (in terms of the normal flow) of the connecting portions 30c and 37c in a direction that blocks the liquid flow from the unit cell 31.

[0046] The bottom 20b of the frame structure is provided with, as internal structures, a first internal flow path 30d connected to the first connecting portion 30c and individual raw material supply paths 30e communicating with the first internal flow path 30d for individually supplying the raw material solution to each rectangular parallelepiped space of the inner tank 20. The bottom 20b of the frame structure is further provided with, as internal structures, a second internal flow path 37d connected to the second connecting portion 37c and individual cooling water supply paths 37e communicating with the second internal flow path 37d for individually supplying cooling water to each rectangular parallelepiped space of the inner tank 20.

[0047] First piping 30b, first connection part 30c, first internal flow path 30d, and individual raw material supply path 30e for each unit cell constitute a solution supply path that supplies raw material solution to each of one or more unit cells 31 included in electrolytic cell unit 60. Similarly, second piping 37b, second connection part 37c, second internal flow path 37d, and individual cooling water supply path 37e for each unit cell constitute a water supply path that supplies cooling water to each of one or more unit cells 31 included in electrolytic cell unit 60, independently of the raw material solution.

[0048] In a preferred embodiment, the water supply channel for supplying cooling water is preferably provided independently of the solution supply channel described above up to the inlet of each unit cell 31 (the opening of each individual cooling water supply channel 37e on the unit cell 31 side), as exemplified in Fig. 2. This is because it becomes possible to supply cooling water into the unit cell completely independently of the raw material solution, which is advantageous in terms of control.

[0049] However, the present invention is not limited to this preferred embodiment, and a partially independent configuration is also possible in which the water supply channel for supplying cooling water is independent from the solution supply channel up to the upstream of the inlet of each unit cell 31 and shares a portion of the flow path with the solution supply channel upstream of the inlet. For example, second internal flow path 37d connected to second connecting portion 37c may be connected to first internal flow path 30d connected to first connecting portion 30c, or internal flow paths 30d, 37d and individual flow paths 30e, 37e to unit cell 31 may be shared. On the other hand, if the flow paths are partially shared, raw material solution remaining in the shared flow path will be pushed into unit cell 31 together with the supply of cooling water, even during a period when raw material solution supply pump 3 is stopped and only feedwater pump 6 is operating.

[0050] In the present disclosure, supplying cooling water to each of one or more unit cells 31 independently of the raw material solution means that when the feedwater pump 6 is operating while the raw material solution supply pump 3 is stopped, cooling water is predominantly supplied into the unit cells 31. In other words, the flow path portion common to the solution supply path and the water supply path is allowed, provided that the volume of this common flow path (the maximum volume that the remaining raw material solution can be pushed out) is such that the average flow rate of the feedwater pump 6 (the flow rate averaged over the on and off periods) results in an average residence time (the time required for the common flow path to be completely replaced with cooling water due to the inflow of cooling water) of 2 to 12 seconds.

[0051] The diameters of the individual raw material supply passages 30e and the individual cooling water supply passages 37e are not particularly limited, and the number thereof may be one or more per unit cell. Generally, however, the number and size of each passage can be set so that the total opening area is a predetermined percentage of the effective one-side area of ​​the electrode.

[0052] An individual electrolyte outlet 26 for discharging the electrolyte generated by electrolysis is provided for each unit cell 31 in the ceiling portion 20a of the frame structure. The diameter and number of the individual electrolyte outlets 26 are not particularly limited, but depending on certain conditions, it is preferable to have only one individual electrolyte outlet 26 per unit cell. The individual electrolyte outlets 26 may be provided with a structure (electrolyte collection / discharge structure) for uniformly discharging the electrolyte from each outlet. The predetermined conditions regarding the number of individual electrolyte outlets 26 described above relate to the electrolyte collection / discharge structure. If no electrolyte collection / discharge structure is provided, it is preferable to provide one individual electrolyte outlet 26 per unit cell. In this case, the individual electrolyte outlet 26 for each unit cell serves as an opening 28 directly communicating with the outer tank.

[0053] Furthermore, when multiple individual electrolyte outlets 26 are provided per unit cell, it is preferable to provide an electrolyte collection and discharge structure to uniformly discharge the electrolyte from each outlet 26. The embodiment shown in FIG. 2 illustrates a case where an electrolyte collection and discharge structure 28a is provided. The electrolyte collection and discharge structure 28a includes a common discharge flow path 28b for collecting the electrolyte from the individual electrolyte outlets 26 and an opening (common outlet) 28 for discharging the collected electrolyte. When multiple individual electrolyte outlets 26 are provided, while the electrolyte is discharged to the outer tank 32 through one outlet, raw water from the outer tank 32 is likely to backflow from another outlet. This backflow of raw water may affect the properties of the resulting slightly acidic hypochlorous acid water 36. Therefore, the electrolyte collection and discharge structure 28a is provided to effectively reduce the backflow of raw water from the outer tank 32 to the inner tank 20, even when multiple individual electrolyte outlets 26 are provided.

[0054] Furthermore, the amount of cooling water supplied to one or more unit cells 31 can be set to an average flow rate that results in an average residence time (the time required for the inflow of cooling water to completely replace the inside of the unit cell with cooling water) of 200 to 750 seconds per unit cell, preferably an average residence time of 600 seconds or less, and more preferably an average residence time of 550 seconds or less, from the viewpoint of sufficient cooling. Note that the range of the amount of cooling water described above indicates a preferred range from the viewpoint of stably producing electrolyzed water with predetermined properties from the time of restart and preventing electrode deterioration at high temperatures, but is not limited to this range. Even a small amount of cooling water supply, such as an average residence time of about 3000 seconds, can be expected to have a certain degree of effect on electrode deterioration. Depending on conditions such as hardness, an average residence time of less than 200 seconds may also be sufficient. Therefore, cooling water can be supplied at any average residence time as long as conditions permit.

[0055] The number of millimoles of pure hydrogen chloride supplied per unit volume of a unit cell per unit time (amount of hydrogen chloride supplied) is preferably 0.0006 mMol / hmm from the viewpoint of preventing a decrease in power efficiency due to power loss and a decrease in the conversion rate of chlorine. 3 More than 0.013mMol / hmm 3 or less, more preferably 0.0013 mMol / hmm 3 More than 0.0063mMol / hmm 3 It can be as follows:

[0056] The raw material solution supplied to each unit cell 31 via the individual raw material supply path 30e is electrolyzed while moving vertically upward through the unit cell 31, and the electrolyte that has passed through each unit cell 31 is discharged from the individual electrolyte outlet 26. Chloride ions contained in the raw material are electrolyzed while passing through each unit cell 31, and are ultimately converted into hypochlorous acid HOCl and a small amount of hydrogen chloride HCl.

[0057] In an embodiment in which the electrolyte collection and discharge structure 28a is provided, the multiple individual electrolyte discharge ports 26 are formed in their upper portions and communicate with a common discharge flow path 28b that is connected to the opening 28, and the electrolyte that has passed through the gaps is discharged from the opening 28. The electrolyte is discharged through this common discharge flow path 28b from an opening 28 formed in the inner tank 20 with a larger area than the individual electrolyte discharge ports 26 to the portion of the outer tank 32 through which raw water flows. In contrast, in an embodiment in which the electrolyte collection and discharge structure 28a is not provided, the multiple individual electrolyte discharge ports 26 discharge the electrolyte that has passed through the gaps directly into the portion of the outer tank 32 through which raw water flows.

[0058] The electrolyte is discharged into outer tank 32 through opening 28 and mixed with the raw water flowing down there. After being diluted with the raw water in outer tank 32, the electrolyte is discharged from outlet 35 as slightly acidic hypochlorous acid water 36.

[0059] The bipolar electrode described above has the advantage that it is possible to provide appropriate electrolysis characteristics at the anode and cathode while simplifying the electrode structure, thereby improving the electrolysis efficiency and improving the efficiency of producing slightly acidic hypochlorous acid water.

[0060] FIG. 4 is a diagram illustrating how the electrolytic cell unit 60 according to this embodiment is attached to the outer tank 32. FIG. 5 is a perspective view of the electrolytic cell unit 60 according to this embodiment. Note that the viewing directions of FIGS. 5(A) and 5(B) are different, as indicated by the arrangement of the arrows A and B. As shown in FIGS. 4 and 5, the electrolytic cell unit 60 includes the inner tank 20, two power supply wirings 29a attached to the upper surface of the inner tank 20, and pipes 30b and 37b connected to the inner tank 20 via connectors 30c and 37c, respectively. As shown in FIG. 4, the electrolytic cell unit 60 is fitted into the outer tank 32 through its upper opening, and is then covered and sealed with an outer tank lid 39 equipped with various terminals and supply ports.

[0061] Hereinafter, a method for producing slightly acidic hypochlorous acid water using the double-shell electrolytic cell 40 according to the embodiment described above will be described with reference to Fig. 6. The control shown in Fig. 6 corresponds to a case where acclimation is not performed. Fig. 6(A) shows the control flow on the raw solution supply pump 3 side, and Fig. 6(B) shows the control flow on the water supply pump 6 side, which is performed asynchronously with the raw solution supply pump 3.

[0062] 6 starts from step S100, and in step S101, the control device 43 opens the raw water supply valve. In step S102, the control device 43 energizes the power supply device and starts applying an electrolytic current between the electrodes.

[0063] In step S103, the control device 43 determines whether the pump start condition is satisfied. For example, the control device 43 can determine whether the pump start condition is satisfied by reading the measured current value measured by the current measurement unit 42 and determining whether the measured current value is less than a preset lower limit value. If it is determined in step S103 that the pump start condition is not satisfied (NO), for example, because the current value exceeds the lower limit value, the control device 43 loops step S103. On the other hand, if it is determined in step S103 that the pump start condition is satisfied (YES), for example, because the current value is less than the lower limit value, the control device 43 proceeds to step S104. In step S104, the control device 43 starts the raw material solution supply pump 3 and, if necessary, the dilution pump (if the raw material solution is diluted in advance) to start supplying the raw material solution.

[0064] In step S105, the control device 43 determines whether the pump stop condition is met and waits until it is met (during the NO state). For example, the control device 43 can determine whether the pump stop condition is met by reading the current measurement value measured by the current measurement unit 42 and determining whether the measurement value exceeds a preset upper limit. If it is determined in step S105 that the pump stop condition is met, for example, because the current exceeds the preset upper limit (YES), control proceeds to step S106. In step S106, the control device 43 stops the raw material solution supply pump 3 and, if necessary, the dilution pump (if the raw material solution is diluted in advance), stops the supply of the raw material solution, and returns to step S103.

[0065] Focusing on the electrolyte, the following process is performed by the operation of the raw solution supply pump 3 described above. The pump operation supplies the raw solution to unit cells 31 between multiple electrodes 24 arranged facing each other in the inner tank 20. While the raw solution passes through the unit cells 31, a current is applied between the multiple electrodes 24, causing chlorine ions in the raw material to be electrolytically oxidized at the anode surfaces of the electrodes 24 and hydrogen gas to be generated at the cathode surfaces. The electrolytic solution mixed with the electrolytically generated hydrogen gas is discharged from the unit cells 31 between the electrodes 24 and diluted with dilution water in the outer tank 32. The generated slightly acidic hypochlorous acid water 36 is discharged from the double-shell electrolytic cell 40 via the outlet 35, with excess gas separated.

[0066] Furthermore, on the side of the water supply pump 6, which operates asynchronously with the raw material solution supply pump 3, control is performed according to steps S200 to S203 shown in FIG. 6(B).

[0067] In step S201, the control device 43 determines whether the cooling water supply condition is satisfied. Here, the cooling water supply condition can be first conditioned on the fact that electrolysis is in progress. As described above, acclimation may be performed at the start of electrolysis. During acclimation, a voltage increase period is included in which the applied voltage is increased when the measured current is low, creating a more favorable electrolysis state. Meanwhile, supplying cooling water not only cools the space surrounding the unit cell 31 but also dilutes the raw material solution in the unit cell 31, resulting in a side effect of lowering the conductivity. Therefore, during acclimation boosting, it is undesirable to supply cooling water, which has the side effect of making it more difficult for the current to flow. Therefore, it is preferable that the cooling water supply condition be conditioned on the fact that acclimation boosting is not in progress. That is, the control device 43 preferably controls the feedwater pump 6 to supply cooling water during electrolysis, except for the stage (during acclimation boosting) in which the voltage of the power supply device 41 is increased based on the measured current from the power supply device 41, which begins at the start of electrolysis.

[0068] If it is determined in step S201 that the cooling water supply conditions are met (YES), control proceeds to step S202. In step S202, the control device 43 operates the water supply pump 6, and after an appropriate waiting time, returns control to step S201. On the other hand, if it is determined in step S201 that the cooling water supply conditions are not met (NO), the process branches to step S203. In step S203, the control device 43 stops the water supply pump 6, and after an appropriate waiting time, returns control to step S201.

[0069] The above-mentioned acclimation process at the start of electrolysis will be described below with reference to Fig. 7. The control shown in Fig. 7 shows a control flow on the raw solution supply pump 3 side, which is performed asynchronously with the water supply pump 6 side.

[0070] 7 starts from step S300, and in step S301, the control device 43 opens the raw water supply valve. In step S302, the control device 43 energizes the power supply device 41 and starts applying an electrolytic current between the electrodes. In step S303, the control device 43 measures the flow rate of the raw water at the timing when the power supply device 41 is energized, and calculates the target current value, upper limit current value, and lower limit current value during acclimation.

[0071] In step S304, the control device 43 initiates a voltage increase process that gradually increases the voltage applied to the power supply device 41 at regular intervals. In step S305, the control device 43 determines whether the measured current value has reached the target current value and continues increasing the voltage until the target current value is reached (NO). If it is determined in step S305 that the target current value has been reached (YES), the control proceeds to step S306. The period from when the voltage increase begins in step S304 until it is determined in step S305 that the target current value has been reached is the acclimation voltage increase period. Note that, as shown in FIG. 7, while it is determined in step S305 that the target current value has not been reached (NO), the control may proceed to step S314 to determine whether the set maximum voltage has been reached. If the set maximum voltage has been reached but the target current value has not yet been reached (YES in S314), the control may proceed to step S306.

[0072] In step S306, the control device 43 determines whether the measured current value is below the upper limit current value. If it is determined in step S306 that the measured current value is below the upper limit current value (YES), control proceeds to step S307. In step S307, the control device 43 starts the raw material solution supply pump 3 and maintains the voltage constant. In step S308, the control device 43 determines whether the measured current value exceeds the upper limit current value and waits until it exceeds the upper limit current value (during NO). If it is determined in step S308 that the measured current value exceeds the upper limit current value (YES), control proceeds to step S309. In step S309, the control device 43 stops the raw material solution supply pump 3 and starts decreasing the voltage at a predetermined rate, and control proceeds to step S311. On the other hand, if it is determined in step S306 that the measured current value is not below the upper limit current value (NO), processing proceeds to step S310. In step S310, the control device 43 starts decreasing the voltage at a predetermined rate without starting the raw material solution supply pump 3, and then proceeds to step S311.

[0073] In step S311, the control device 43 determines whether the currently applied voltage has reached a predetermined set voltage. If it is determined in step S311 that the set voltage has not been reached (NO), control proceeds to step S312. In step S312, the control device 43 determines whether the measured current value is below the lower limit current value, and loops back to step S311 until it falls below the lower limit current value (while NO is returned). On the other hand, if it is determined in step S312 that the measured current value is below the lower limit current value (YES), control returns to step S307, where the raw material pump is started and the voltage is maintained. In this manner, starting the raw material solution supply pump 3 and maintaining the voltage, and stopping the raw material solution supply pump 3 and dropping the voltage are repeated. If it is determined in step S311 that the set voltage has been reached (YES), normal operation is resumed in step S313. Note that overcurrent detection is not performed until normal operation is resumed.

[0074] Although not shown in Figure 7, in the acclimatization voltage drop process, when the condition that the measured current value exceeds the set current value at a constant voltage and is maintained for a set time or more is satisfied, control may be performed to further step down the voltage.

[0075] As described above, the raw solution supply pump 3 is controlled based on the current measured by the power supply device 41. Therefore, if cooling water is supplied in synchronization with the raw solution supply pump 3, the supply of cooling water will result in the side effect of diluting the raw solution supply pump 3, which makes it difficult for the current to flow, even though the raw solution supply pump 3 is operated in response to a decrease in the current measured by the power supply device 41. Therefore, it is desirable that the operation of the feedwater pump 6 be asynchronous with the operation of the solution supply pump. Furthermore, from the viewpoint of steadily cooling the interior of the inner tank 20 with cooling water while performing electrolysis, it is preferable that the feedwater pump 6 supply cooling water intermittently at a constant interval or continuously at a fixed rate. Note that the feedwater pump 6 is not particularly limited, but from the viewpoint of intermittently supplying cooling water, a diaphragm pump with a single pump head or the like can be used.

[0076] FIG. 8 is a chart showing the control signals for the raw material solution supply pump 3 and the feedwater pump 6 according to a preferred embodiment. For reference, FIG. 8 also shows the control signal for the dilution pump, which operates in synchronization with the raw material solution supply pump 3. As shown in FIG. 8, the raw material solution supply pump 3 and the dilution pump are turned on and off at any timing in response to the measured current values. Meanwhile, in a preferred embodiment, the feedwater pump 6 is driven intermittently for an on period T2 with a cycle T1, as shown in FIG. 8.

[0077] Hereinafter, with reference to FIGS. 9 to 11, the advantages of the above-described method of supplying cooling water to the unit cell 31 independently of the raw material solution will be described.

[0078] FIG. 9 is a graph showing the temperature change measured at the outlet of the electrolyte (gas) of the rectangular electrolytic cell.

[0079] Here, we briefly explain how we came to measure the temperature. Under certain conditions, depending on the raw water quality and usage conditions, problems such as unstable operation due to abnormal electrolysis, deviations from the target ranges for available chlorine concentration and pH, and shortened electrode (and ultimately electrolytic cell) lifespans (deterioration symptoms appearing earlier than expected) have occurred. In particular, in electrolytic cells with multiple outlets per unit cell and the electrolyte collection and discharge structure 28a, abnormal electrolysis has been associated with unstable operation, particularly an overcurrent state in which the set current continues unintentionally even after the acclimation process, resulting in shortened electrode lifespans. Electrode deterioration, as detailed below, manifests itself in the form of a failure to obtain the expected current (the current value before electrolysis was stopped) when electrolysis is temporarily stopped and then resumed after a period of time, as shown by the dashed-dotted line in Figure 9 (without water added). In such cases, acclimation is typically performed. The above-mentioned unintentionally continuing overcurrent state is an event in which an attempt to pass current causes an excessive supply of raw material solution, and after the set value is reached, the current does not decrease even when the supply is stopped, and an overcurrent is detected, causing an error.

[0080] On the other hand, while removing the electrolyte collection and discharge structure 28a from the electrolytic cell somewhat alleviates the unintended continuous overcurrent state and shortened electrode life, it can affect the properties of the slightly acidic hypochlorous acid water produced under certain conditions. In particular, when a high effective chlorine concentration is targeted, the pH of the resulting slightly acidic hypochlorous acid water can be lower than expected. Conversely, when trying to keep the pH of the slightly acidic hypochlorous acid water within the appropriate range, it can be difficult to raise the effective chlorine concentration to the target level.

[0081] To investigate the cause of electrode degradation, we investigated the deterioration of the electrode surface (iridium oxide and platinum coatings were worn away at the feedstock solution inlet and electrolyte outlet, and dissolution of the titanium substrate was occurring). Furthermore, we suspected that the electrode wear was accelerated by localized current concentration due to asymmetric hydrochloric acid concentrations, given that the electrolyte outlet was constantly in contact with a harsh liquid—a mixture of chlorine gas, hypochlorous acid, and hydrochloric acid. Therefore, we created a single-electrode transparent electrolytic cell and attempted to measure the current distribution and hydrochloric acid concentration within the cell. Results indicated no bias in current density that would affect the entire cell, that current was uniformly distributed across the entire electrode plate, and that the measured internal hydrochloric acid concentration was not extremely high. However, we also found that the sides of the electrolytic cell were warmer than expected. Based on the above findings, we focused on the temperature at the center of the electrolytic cell and conducted experiments to measure the temperature of the electrolytic cell and verify the effects of adding cooling water.

[0082] The temperature change graph in Figure 9 was obtained using a rectangular electrolytic cell (inner cell) made by Bitanken Co., Ltd., with a thermocouple installed near the electrolyte and gas outlets. Electrolysis was performed with the rectangular electrolytic cell removed from the outer cell and placed outside the water tank, and submerged in the water tank. Cooling water and 9% hydrochloric acid (raw material solution) were supplied to the internal flow path of the electrolytic cell via separate outlets, and power was applied to the power supply, recording the thermocouple output and current values. The experimental conditions were changed over time, and the outlet temperature values ​​at the time the temperature stabilized are shown in Figure 9, along with the thick vertical lines indicating the stable points for each condition.

[0083] The electrolysis conditions were all set voltage 33V and set current 5A. The cooling water temperature was 20°C. In condition 1, no cooling water was added to the unit cell, and the rectangular electrolytic cell was placed outside the water tank and electricity was applied. In condition 2, a moderate amount of cooling water was added, and the rectangular electrolytic cell was placed outside the water tank and electricity was applied. In condition 3, a large amount of cooling water was added, and the rectangular electrolytic cell was placed outside the water tank and electricity was applied. In condition 4, similar to condition 3, a large amount of cooling water was added, and the rectangular electrolytic cell was submerged in the water tank and electricity was applied. In condition 5, no cooling water was added, and the rectangular electrolytic cell was submerged in the water tank and electricity was applied.

[0084] As shown in Figure 9, the measurements yielded the following results: 79°C under condition 1, 64°C under condition 2, 57°C under condition 3, 46°C under condition 4, and 55°C under condition 5. Condition 1 above can be considered to correspond to the cell temperature in the center of a multi-layer electrolytic cell with no heat exchange. Conditions 2 and 3 above show the cooling effect of adding cooling water, and condition 4 shows the effect of jacket cooling compared to condition 3. Condition 5 corresponds to the condition of jacket cooling in the outer cell of a conventional double-shell electrolytic cell without adding cooling water.

[0085] What is noteworthy in Figure 9 is that it suggests that the temperature at the center of the cell may reach approximately 79°C, and that jacket cooling is effective in cooling the electrolyte to approximately 66°C. The inside of the electrolytic cell contains a mixture of chlorine, hydrochloric acid, and hypochlorous acid, which has high oxidizing and dissolving power, and this, combined with the temperature condition, has been found to be prone to accelerating the deterioration of the electrode materials described above.

[0086] On the other hand, when the electrolyte collection and discharge structure 28a, which is installed for the purpose of uniformity, is removed, the occurrence of the above-mentioned unintentional continuous overcurrent state and electrode deterioration is suppressed, but it has been found that the reason properties such as pH are affected is that the raw water that flows back from the outer tank into the electrolytic cell cools the inside of the electrolytic cell, changes the state of the solution inside the unit cell 31, and, combined with the feedback control of the raw solution supply pump 3 according to the current value, affects the electrolysis state.

[0087] Furthermore, by installing the above-mentioned electrolyte collection and discharge structure 28a (or by providing a single discharge outlet) to prevent backflow of raw water into the electrolytic cell, and by providing a path for supplying cooling water to each unit cell of the electrolytic cell independently of the raw solution, it has become possible to efficiently cool the inside of the electrolytic cell, including the central part, and it has been found that it is possible to stably produce an aqueous solution within the target property range through normal electrolysis operation, and that the lifespan of the electrodes and electrolytic cell can be optimized.

[0088] Figure 10 is a graph showing the change in current over time when electrolysis was restarted after stopping during stable operation. Figure 10 corresponds to the case without acclimatization. Using 9% hydrochloric acid as the feedstock solution, HOCL 0.96t manufactured by Bitanken Co., Ltd. was operated continuously for 2 hours at 5A. Once the internal temperature stabilized, electrolysis was stopped, held for 30 minutes, and then restarted. The change in current over time was recorded. The electrolytic cell had 12 cells, with a volume of 22.8 ml per cell. When no cooling water was added (i.e., "no water added"), the current could not be maintained at the level immediately before stopping and tended to gradually increase over several minutes. During electrolysis, the cathode side was in a reducing state, which is thought to prevent oxidation reactions from progressing. However, it is believed that oxidation or other degradation of the titanium base material occurred during the shutdown at high temperatures. This tendency worsened particularly when the electrolysis was left overnight (12 hours).

[0089] On the other hand, when cooling water was added ("weak water" and "strong water"), the current recovered to the level just before shutdown more quickly, and the stronger the water addition, the better. In the graph in Figure 10, "weak water" refers to the water addition conditions (Welco pump (WPX1-P3.2M4-WM4-B) set at 16V) where the cycle time T1 is 10 seconds and the on-duration T2 is 5 seconds, as shown in Figure 8, resulting in an average residence time of approximately 720 seconds per cell. "strong water" refers to the water addition conditions (Welco pump (WPX1-P3.2M4-WM4-B) set at 16V) where the cycle time T1 is 10 seconds and the on-duration T2 is 5 seconds, as shown in Figure 8, resulting in an average residence time of approximately 540 seconds per cell. Under the "strong water" condition, the set current of 5.5A was reached immediately after restart (approximately 10 seconds later), whereas under the "weak water" condition, the set current of 5.5A was reached slightly later. Meanwhile, under the "no water" condition, the restart response was even worse. Although the "high water addition" setting tended to cause an overcurrent, the current subsequently decreased (after 35 seconds) due to the addition of cooling water, and the operation returned to normal. With the other settings, the current value did not return to normal, but returned to the set current value due to the supply of hydrochloric acid by the raw solution supply pump. With the "low water addition" setting, the current only recovered to about 4.5A within the time range shown in Figure 10, but in reality, the current gradually increased and generally reached the set current of 5.5A.

[0090] The flow rate of "Strong water addition" in Figure 10 is converted to 1800 ml / hr, and if added to the raw solution in synchronous operation, it is equivalent to diluting it 7 times, which is too low a concentration and it is not possible to expect to obtain the required current. Therefore, it is preferable to have separate flow paths for the raw solution (hydrochloric acid) and the cooling water.

[0091] It was confirmed that even if the above-mentioned electrode degradation occurs once, by performing electrolysis again while adding cooling water, the behavior returns to the same as when there is no degradation, without interrupting the set current maintained before restarting. In other words, this indicates that electrode degradation can be recovered, and it is expected that a stable current can be ensured without performing the acclimation treatment that is performed when the above-mentioned electrodes are deteriorated.

[0092] Figure 11 is a graph showing the time course of the available chlorine concentration and pH upon restart after stopping electrolysis during continuous operation. The continuous operation time was 2 hours, with a 15-minute shutdown period before restart. As shown in Figure 11, without water addition, excessive hydrochloric acid was supplied due to insufficient current during restart, resulting in the production of slightly acidic hypochlorous acid water with a high chlorine concentration and low pH over a 20-minute period. Meanwhile, without cooling, the temperature rose. As the temperature increased, the conductivity increased, allowing for easier current flow (the electrolysis was stopped at this state, and the conductivity subsequently decreased due to the drop in electrolyte temperature). This reduced the amount of raw hydrochloric acid supplied. This resulted in a lower concentration of chlorine and an increase in pH. In contrast, with the addition of cooling water, sufficient hydrochloric acid was supplied, stabilizing the pH at 6.3. Cooling by adding water (which maintained a sufficient electrolyte concentration in the electrolytic cell immediately after restart) resulted in the production of stable chlorine gas and a sufficient available chlorine concentration.

[0093] According to the embodiments described above, it is possible to provide a manufacturing apparatus, an electrolytic cell unit, and a manufacturing method that can effectively cool the electrolytic cell, optimize the lifespan of the electrodes and the electrolytic cell, and stably produce an aqueous solution within the target property range through normal electrolysis operation.

[0094] Furthermore, the supply of cooling water not only provides cooling but also acts as a brake when the current becomes too large. By suppressing the temperature rise through cooling, the conductivity can be maintained constant, the concentration of the raw material hydrochloric acid can be maintained constant, and a decrease in the chlorine concentration can be prevented.

[0095] In the above-mentioned embodiment, the case of using the aqueous solution of hydrogen chloride and hydrochloric acid as the solution containing chlorine ions as raw material is illustrated, but it is not limited to hydrochloric acid, and can be the solution of sodium chloride, potassium chloride, etc., or their mixture, and can use the solution containing chlorine ions that one or more substances selected from the group consisting of hydrogen chloride, sodium chloride and potassium chloride are dissolved.In addition, although the production of hypochlorous acid water is described, it can be extended to the aqueous solution that contains at least free hypochlorous acid.

[0096] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above-described embodiments, and any embodiment that can be conceived by a person skilled in the art is included in the scope of the present invention as long as it exhibits the functions and effects of the present invention. [Explanation of symbols]

[0097] 1...raw material tank, 2...raw material supply pipe, 3...raw material solution supply pump, 4...cooling water, 5...water supply pipe, 6...water supply pump, 20...inner tank, 24...electrode, 26...individual electrolyte outlet, 28...opening, 29...power supply terminal, 30...raw material supply port, 31...unit cell, 32...outer tank, 33...raw water supply port, 34...raw water, 35...outlet, 36...slightly acidic hypochlorous acid water, 37...cooling water supply port, 39...outer tank lid, 40...double-shelled electrolytic cell, 41...power supply unit, 42...current measurement unit, 43...controller, 50...manufacturing equipment, 60...electrolytic cell unit [Prior art documents] [Patent documents]

[0098] [Patent Document 1] Japanese Patent Application Publication No. 2019-198820

Claims

1. an electrolytic cell; A plurality of electrodes provided in the electrolytic cell; one or more unit cells formed between electrodes in the electrolytic cell; a solution supply channel for supplying a raw material solution to each of the one or more unit cells; a water supply line for supplying cooling water to each of the one or more unit cells, at least to the inside of the electrolytic cell, independently of the solution supply line; an outlet for discharging an electrolytic solution generated by electrolysis of the raw material solution from the one or more unit cells; a power supply device that applies current between the plurality of electrodes; a control device that determines whether or not a first condition that electrolysis is in progress and a second condition that the voltage of the power supply device is not yet at a stage of being increased based on a measurement value of a current by the power supply device starting from the start of electrolysis are satisfied, and controls a feed water pump connected to the feed water passage when it is determined that the first condition and the second condition are satisfied so as to supply the cooling water at a flow rate that results in an average residence time per unit cell of 750 seconds or less; wherein the cooling water supplied to each of the one or more unit cells dilutes the raw material solution in each of the one or more unit cells.

2. a solution supply pump connected to the solution supply path; the water supply pump; The manufacturing apparatus according to claim 1 , further comprising: a water supply pump that operates asynchronously with the solution supply pump.

3. 3. The manufacturing apparatus of claim 2, wherein the water supply pump supplies the cooling water intermittently or continuously at a fixed amount, and the control device further controls the operation of the solution supply pump based on a measured value of current from the power supply device.

4. The outlet is provided for each of the unit cells, or 4. The manufacturing apparatus according to claim 1, wherein a plurality of the discharge ports are provided for each of the unit cells, and the manufacturing apparatus further comprises, in the electrolytic cell, a common discharge flow path for collecting the electrolytic solution from the discharge ports of the one or more unit cells, and a common discharge port for discharging the collected electrolytic solution.

5. 5. The manufacturing apparatus according to claim 1, wherein the water supply channel supplies the cooling water to the inlet of each of the one or more unit cells independently of the solution supply channel.

6. A manufacturing apparatus described in any one of claims 1 to 4, wherein the water supply channel is independent of the solution supply channel up to the stage preceding the inlet of each of the one or more unit cells, and has a flow path portion that shares a portion of the flow path with the solution supply channel at the stage preceding the inlet, and the flow path portion has a volume such that the average residence time is 2 to 12 seconds at the average flow rate of the water supply pump.

7. a dilution tank provided outside the electrolytic cell so as to surround the electrolytic cell, in communication with the electrolytic cell, for diluting the electrolytic solution discharged from the electrolytic cell with raw water and for cooling the electrolytic cell with the raw water; an outlet for taking out the diluted aqueous solution from the dilution tank; The manufacturing apparatus according to any one of claims 1 to 6, further comprising:

8. supplying the raw material solution to each of one or more unit cells provided in the electrolytic cell via a solution supply path; a step of causing a current to flow between a plurality of electrodes provided in the electrolytic cell to electrolyze the raw material solution supplied to each of the one or more unit cells to produce an electrolytic solution; a step of determining whether or not a first condition that electrolysis is in progress and a second condition that the stage is not yet at which the voltage of the power supply device is being boosted based on a measurement value of the current by the power supply device starting from the start of electrolysis are satisfied; when it is determined that the first condition and the second condition are satisfied, supplying cooling water to each of the one or more unit cells by a water supply pump through a water supply path independent of the solution supply path at least into the electrolytic cell at a flow rate that results in an average residence time per unit cell of 750 seconds or less, and diluting the raw material solution in each of the one or more unit cells with the cooling water supplied to each of the one or more unit cells; discharging the electrolyte from each of the one or more unit cells; A process of diluting the discharged electrolyte with raw water; A method for producing an aqueous solution, comprising:

9. The step of supplying cooling water includes:

9. The manufacturing method according to claim 8, wherein the method is performed by the water supply pump, which is controlled asynchronously with a solution supply pump that supplies the raw material solution through the solution supply path.

10. The water supply channel is supplying the cooling water to the inlet of each of the one or more unit cells independently of the solution supply path; or 10. The manufacturing method according to claim 8 or 9, wherein a flow path portion is provided that is independent from the solution supply path up to a stage upstream of an inlet of each of the one or more unit cells and that shares a part of a flow path with the solution supply path in the stage upstream, and the flow path portion has a volume such that an average residence time is 2 to 12 seconds at an average flow rate of the feed water pump.

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