Production method for acidic hypochlorous acid water

Abstract

To provide a method for industrially and stably producing acidic hypochlorous acid water having a stable pH.SOLUTION: A production method for acidic hypochlorous acid water includes an ion exchange step of passing an aqueous sodium hypochlorite solution having an effective chlorine concentration of 0.5 mass% or more through a column packed with a weakly acidic cation-exchange resin. The weakly acidic cation-exchange resin has a water retaining capacity of 60% or less. Product collection is started from a time point when the pH of passing liquid at a column outlet reaches 2.5, and the collection is stopped at a time point when the pH reaches 5.5 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for inexpensively and stably producing a highly concentrated acidic hypochlorous acid solution having excellent storage stability. [Background technology]

[0002] Conventionally, hypochlorite solutions adjusted to basicity, such as sodium hypochlorite, have been widely used for sterilization purposes. Under basic conditions, hypochlorous acid mainly converts into hypochlorite ions (ClO - On the other hand, under acidic conditions, it exists as hypochlorous acid (HClO), which is known to have a higher bactericidal effect than hypochlorite ions. For this reason, there is a demand for acidic hypochlorous acid water for sterilization.

[0003] On the other hand, it is known that acidic hypochlorous acid water is inferior to hypochlorite solutions of the same concentration in terms of storage stability. Specifically, acidic hypochlorous acid water has the property of being easily decomposed by heat, ultraviolet light, and changes over time. It is known that the decomposition speed varies depending on the amount of impurities contained in the liquid, and the higher the purity, the more difficult it is to decompose (see Patent Document 1).

[0004] As a method for producing high-purity acidic hypochlorous acid water, a three-chamber electrolysis method is known (see Patent Document 2). The three-chamber electrolysis method is a method for recovering acidic hypochlorous acid water from the anode side by applying a voltage to pure water present in a portion sandwiched between ion exchange resins. Although this method can produce high-purity acidic hypochlorous acid water, the problem is that the device configuration is complicated and only dilute acidic hypochlorous acid water of about several tens of ppm can be produced, which requires storage and transportation costs, making the resulting product acidic hypochlorous acid water expensive.

[0005] Also, a method is known in which the cations of a hypochlorite solution are exchanged with an ion exchange resin to obtain acidic hypochlorous acid water. This method is a method for obtaining high-concentration and high-purity acidic hypochlorous acid water at a lower cost, since the target acidic hypochlorous acid water can be obtained simply by contacting the raw hypochlorite solution with an ion exchange resin. For example, Patent Document 3 discloses a method for obtaining high-concentration acidic hypochlorous acid water with a pH of 3.0 to 5.5 by stirring and mixing a hypochlorite solution and a weakly acidic cation exchange resin in a reaction tank. This method has a problem in that the operation of adding and separating the raw materials, especially the ion exchange resin, is complicated.

[0006] For this reason, a method has been widely studied that simplifies the operation of loading and unloading raw materials by filling a column with ion exchange resin and passing the raw materials through it. For example, Patent Document 4 discloses a method of obtaining acidic hypochlorous acid water by passing a hypochlorous acid solution through a column filled with ion exchange resin so that the hypochlorous acid solution has a pH range of 3.0 to 7.5. However, the present inventors' study revealed that the method of Patent Document 4 may cause large fluctuations in pH of the obtained acidic hypochlorous acid water. This leaves room for improvement from the viewpoint of the need to ensure the same quality when making it into an industrial or commercial product. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 7164767 [Patent Document 2] Patent No. 4216892 [Patent Document 3] International Publication No. WO2019 / 225599 [Patent Document 4] International Publication No. WO2011 / 056940 Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, in the conventional manufacturing method, although it is possible to obtain high purity acidic hypochlorous acid water, there is still room for improvement in terms of industrially and stably obtaining the same quality acidic hypochlorous acid water.Therefore, the object of the present invention is to provide a method for industrially and stably producing the acidic hypochlorous acid water with stable pH. [Means for solving the problem]

[0009] The present inventors have conducted intensive research in view of the above-mentioned problems. By passing a hypochlorite aqueous solution through a column filled with the ion exchange resin described in the above-mentioned Patent Documents 3 and 4, and focusing on the pH of the solution passing through, in the method for producing acidic hypochlorous acid water by cation exchange, the inventors have found that by obtaining acidic hypochlorous acid water in a pH range lower than the pH described in the Patent Documents, the pH fluctuation can be suppressed and high-concentration acidic hypochlorous acid water can be obtained.

[0010] On the other hand, since the ion exchange resin used in the production can be regenerated to the original ion type by cation exchange, we investigated the regeneration and reuse of the ion exchange resin. However, when the process of producing acidic hypochlorous acid water and regenerating the ion exchange resin was repeated, it was found that the storage stability of acidic hypochlorous acid water produced using a nearly new ion exchange resin was inferior to that of acidic hypochlorous acid water produced using a repeatedly used ion exchange resin. Furthermore, when the production and regeneration process was repeated about 20 times, the ion exchange resin was crushed and deteriorated, and it was also found that the column packed with the ion exchange resin was clogged and liquid could not be passed through.

[0011] Therefore, by using various weakly acidic cation exchange resins, the inventors have studied the production of acidic hypochlorous acid water, and found that, depending on the type of weakly acidic cation exchange resin, the deterioration of the product caused by repeated use can be suppressed.As a result of further study, the inventors have found that by selecting a weakly acidic cation exchange resin with a specific range of water retention capacity, the ion exchange resin can be suppressed from being crushed or deteriorated even after repeated use, and thus completed the present invention.

[0012] That is, the present invention relates to a method for producing acidic hypochlorous acid water, which includes an ion exchange step of passing an aqueous sodium hypochlorite solution having an effective chlorine concentration of 0.5% by mass or more through a column packed with a weakly acidic cation exchange resin, characterized in that the water retention capacity of the weakly acidic cation exchange resin is 60% or less, and recovery of the effluent as a product is started after the pH of the effluent at the column outlet becomes 2.5, and recovery is stopped when the pH becomes 5.5 or less.

[0013] In the above-mentioned production method of the present invention, it is preferable to stop the collection before the pH of the passing liquid at the outlet of the column reaches 3.5. It is also preferable that the available chlorine concentration C [mass%] of the aqueous sodium hypochlorite solution and the space velocity SV [1 / h] when passing the aqueous sodium hypochlorite solution through the column satisfy the following relational formula (1), and it is more preferable to pass the solution at SV×C of 15 or less. 0.1 ≦ SV × C ≦ 20 (1)

[0014] Furthermore, it is preferable to pass a regenerant through a column packed with the weakly acidic cation exchange resin that has been subjected to the ion exchange process to regenerate the weakly acidic cation exchange resin, and then pass an aqueous sodium hypochlorite solution having an effective chlorine concentration of 0.5 mass% or more through the column packed with the regenerated weakly acidic cation exchange resin.

[0015] Furthermore, the weakly acidic cation exchange resin is preferably a resin in which polyacrylic acid is crosslinked with divinylbenzene. Effect of the Invention

[0016] According to the method of the present invention, it is possible to produce high-concentration acidic hypochlorous acid water with little pH fluctuation.In addition, the weakly acidic cation exchange resin used in the production method of the present invention can be repeatedly used in the production method of the present invention by regenerating, and can produce acidic hypochlorous acid water industrially and stably for a long period of time. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a flow diagram depicting an exemplary embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic diagram of a device for measuring water retention capacity. [Diagram 3] FIG. 2 is a diagram showing the transition of producible amounts in Examples and Comparative Examples. [Figure 4] FIG. 2 is a graph showing the change in swelling ratio over time in the examples and comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention is characterized in that in a method for producing acidic hypochlorous acid water, which includes an ion exchange step of passing an aqueous solution of sodium hypochlorite through a column filled with a weakly acidic cation exchange resin, a weakly acidic cation exchange resin having a specific water retention capacity is used and the product is recovered in a specific pH range. Hereinafter, the embodiment of the present invention will be described in detail. However, the present invention is not limited to these embodiments. In this specification, unless otherwise specified, the notation "A to B" for numerical values ​​A and B means "A or more and B or less". In such notation, when a unit is added only to numerical value B, the unit is also applied to numerical value A.

[0019] <Sodium hypochlorite> In the production method of the present invention, the aqueous sodium hypochlorite solution used as a raw material can be any known solution without particular limitation, and since it is commercially available for various applications, any of these can be used.

[0020] Most aqueous sodium hypochlorite solutions generally contain sodium chloride because they are produced by the reaction of aqueous sodium hydroxide solution with chlorine gas as shown in the following formula. In addition, they are usually alkaline with a pH of 8 or higher, and most have a pH of 10 or higher. 2NaOH aq + Cl2 → NaClO aq + NaCl + H2O Here, the effective chlorine concentration of sodium hypochlorite or acidic hypochlorous acid means the concentration of the oxidizing power of hypochlorous acid converted into the equivalent amount of chlorine, and is expressed as the mass concentration of the chlorine molecules in an amount equivalent to that of the hypochlorous acid contained.The effective chlorine concentration can be measured by iodometric titration.

[0021] By the way, acidic hypochlorous acid water with an effective chlorine concentration in the range of about 10 to 600 ppm is usually used, but producing it at such a low concentration and storing it for a long period of time until shipping or moving it to another location is not preferable in terms of storage costs and transportation efficiency, so it is more economical to produce it at as high a concentration as possible and dilute it as necessary for shipping, bottling, etc.

[0022] Therefore, in the manufacturing method of the present invention, the aqueous sodium hypochlorite solution used as the raw material has an effective chlorine concentration of 0.5% by mass or more, preferably 0.8% by mass or more, more preferably 1.0% by mass or more, and particularly preferably 1.1% by mass or more.

[0023] The concentration of sodium hypochlorite can be calculated from the above available chlorine concentration using the following formula. C NaClO = Available chlorine concentration × M NaClO ÷ M Cl2 C NaClO : Sodium hypochlorite concentration M NaClO : Molecular weight of sodium hypochlorite (74.44) M Cl2 Molecular weight of chlorine (70.90)

[0024] On the other hand, the hypochlorous acid water produced by the production method of the present invention has good storage stability even at high concentration, but the lower the concentration, the better the storage stability.Therefore, the upper limit is not particularly limited, but considering the balance between the above-mentioned storage efficiency and transport efficiency, it is preferable to make it 5.0 mass% or less, and more preferably 2.0 mass% or less.In addition, in the production method of the present invention, the effective chlorine concentration at the time of passing through a column filled with an ion exchange resin described below and discharging from the column is practically equal to the effective chlorine concentration of the raw material introduced into the column.In other words, the effective chlorine concentration in the obtained hypochlorous acid water is almost determined by the effective chlorine concentration of the raw material.

[0025] Various concentrations of sodium hypochlorite aqueous solution are commercially available, but if the concentration of the sodium hypochlorite aqueous solution obtained is higher than desired, it can be diluted with water before use.As the dilution water, the water generally used can be used without any restrictions, but since impurities such as metal ions contained in water may reduce the storage stability of acidic hypochlorous acid water, it is preferable to use pure water such as ion-exchanged water, distilled water, RO water, etc., and in particular, it is preferable to use ion-exchanged water from the viewpoint of the balance between impurity amount and economic efficiency, and if storage stability is more important, it is preferable to use ultrapure water.

[0026] <Weakly acidic cation exchange resin> In the present invention, the above-mentioned aqueous sodium hypochlorite solution is passed through a column packed with a weakly acidic cation exchange resin to obtain acidic hypochlorous acid water.In the production method of the present invention, a part of the cations such as sodium ions contained in the raw material aqueous sodium hypochlorite solution, which is basic, is exchanged with hydrogen ions to make the pH within the above range, and a weakly acidic cation exchange resin is used for this exchange.As the weakly acidic cation exchange resin to be used, one having a carboxyl group as an ion exchange group is preferably used.Such an ion exchange resin is generally obtained by three-dimensionally crosslinking an unsaturated organic acid such as acrylic acid or methacrylic acid or its ester with divinylbenzene, and further hydrolyzing the ester.

[0027] Such a weakly acidic cation exchange resin can exchange sodium ions of weak acid salts such as sodium hypochlorite, but cannot decompose strong acid salts such as sodium chloride, so the treatment solution does not become extremely acidic, and the decomposition of hypochlorous acid into chlorine, which proceeds vigorously under strong acidity, can be suppressed.

[0028] On the other hand, from the viewpoint of the storage stability of the acidic hypochlorous acid water described later, in order to achieve the preferred pH of 3.5 or less, it is preferable to use a resin in which polyacrylic acid is crosslinked with divinylbenzene as a weakly acidic cation exchange resin, which has a high degree of acid dissociation and can easily lower the pH of the raw material.

[0029] In addition, the ion exchange resin may be of a porous type, a gel type, a macroporous type, etc., and any structure may be used as the weakly acidic cation exchange resin used in the present invention without any restrictions. From an economical viewpoint, it is preferable to use an acrylic macroporous type ion exchange resin that is generally used for water treatment.

[0030] Weakly acidic cation exchange resins with spherical particles having an average particle diameter of about 0.1 mm to 1.0 mm are used for water treatment applications and for purifying antibiotics and amino acids, and such particles can also be suitably used in the present invention. Small particle diameters tend to increase the pressure loss in ion exchange resin columns, so particles with an average particle diameter of 0.4 to 0.8 mm are preferred.

[0031] Of course, since this is used to exchange sodium ions for hydrogen ions, the weak acid cation exchange resin used is in the RH form (also called acid form, hydrogen form, proton form, etc.).

[0032] <Water retention capacity of weakly acidic cation exchange resin> The manufacturing method of the present invention is characterized by using a weakly acidic cation exchange resin with a water retention capacity of 60% or less. Here, the water retention capacity of an ion exchange resin is expressed as the mass fraction of water in the ion exchange resin when the water is in a saturated equilibrium state inside the pores of the ion exchange resin in the standard ion form, RH form in the case of a cation exchange resin. In other words, it is an index showing the amount of water that the pores in the ion exchange resin can retain.

[0033] A small water retention capacity means that the size of the pores in the resin is small on average. Large ions are less likely to participate in the ion exchange reaction, and the ion exchange rate tends to slow down. On the other hand, the amount of ions that can be exchanged per unit volume of the ion exchange resin tends to increase because the non-pore portion per unit volume, i.e., the components that contribute to ion exchange, increases.

[0034] By using such a weakly acidic cation exchange resin, it is possible to stably produce a high-concentration acidic hypochlorous acid water with little pH fluctuation, and the weakly acidic cation exchange resin can be repeatedly reused. Although the details are unclear, the present inventors speculate as follows.

[0035] As already mentioned, general weakly acidic cation exchange resin is an organic substance with unsaturated organic acid as the main chain structure.In addition, when acidic hypochlorous acid water contacts with a substance that is easily oxidized such as organic matter, it essentially oxidizes the substance that is easily oxidized.Due to this property, in the manufacturing method of the present invention, during the manufacturing of acidic hypochlorous acid water, weakly acidic cation exchange resin is always exposed to the oxidizing action of the acidic hypochlorous acid water that is the product, and is constantly degraded.

[0036] It is believed that the weakly acidic cation exchange resin collapses due to deterioration caused by oxidation, and a part of the collapsed ion exchange resin is mixed into the produced acidic hypochlorous acid water, which reduces the purity, thereby deteriorating the storage stability of the acidic hypochlorous acid water obtained as a product. In addition, it is believed that the powdering of the resin due to deterioration increases the pressure loss of the column filled with the ion exchange resin, making it impossible to pass the liquid through the column. It is presumed that the above-mentioned problem is caused by this phenomenon. Therefore, it is presumed that a resin with a low water retention capacity and few pores is less likely to collapse structurally and can repeatedly and stably produce acidic hypochlorous acid water.

[0037] From the viewpoint of ion exchange capacity and stability in repeated reuse, the water retention capacity is preferably 30 to 60%, more preferably 35 to 52%, and even more preferably 40 to 50%. The water retention capacity of the weakly acidic cation exchange resin can be determined by allowing the cation exchange resin to retain a sufficient amount of water to reach an equilibrium state, then drying the resin, and measuring the ratio of the mass difference between the weakly acidic cation exchange resin before and after drying to the mass of the weakly acidic cation exchange resin at the equilibrium state.

[0038] <Column packed with weakly acidic cation exchange resin> In the production method of the present invention, the raw material, an aqueous sodium hypochlorite solution, is passed through a column packed with the above-mentioned weakly acidic cation exchange resin (hereinafter also referred to as an "ion exchange resin column" or simply as "column") to continuously contact the resin.

[0039] A known packing container can be used without limitation for the column packed with ion exchange resin. In order to prevent corrosion by hypochlorous acid or the regenerant (acid) described later, a resin container is preferable, and in particular, materials that are highly durable against hypochlorous acid, such as vinyl chloride, polypropylene, polyethylene, AS resin, ABS resin, PFA, and PTFE, are preferable. In addition, in order to increase the strength of the column, it is also a preferred embodiment to install an exterior made of FRP or metal.

[0040] There is no particular limit to the height at which the ion exchange resin is packed in the ion exchange resin column, but if the column diameter is large and the packed height is too low, the treatment liquid will not be uniformly treated. Although it depends on the treatment scale, it is generally desirable to determine the column diameter so that the packed height of the resin is preferably 10 cm or more, more preferably 30 cm or more. On the other hand, if the column diameter is small and the packed height is too high, the pressure loss in the column is large and the workability of removing the column for replacing the ion exchange resin is deteriorated, so it is desirable to determine the column diameter so that the packed height of the resin is preferably 200 cm or less, more preferably 100 cm or less.

[0041] <Passing an aqueous solution of sodium hypochlorite through a column packed with a weakly acidic cation exchange resin> When sodium hypochlorite aqueous solution is passed through a column packed with a weakly acidic cation exchange resin, the initial pH of the passing liquid is low, and the pH increases as the passage continues. The storage stability (maintenance rate of effective chlorine concentration during storage) of concentrated acidic hypochlorous acid water is closely related to pH, and when the pH exceeds 5.5, the storage stability is significantly deteriorated. On the other hand, when the pH is less than 2.5, the presence of molecular chlorine (Cl2) increases, and concentrated hypochlorous acid may be dangerous. Therefore, from the viewpoint of obtaining good storage stability for a long period of time, the pH is preferably less than 3.5, more preferably 3.4 or less, and particularly preferably 3.3 or less. The lower limit of pH is preferably 2.8 or more, particularly preferably 2.9 or more.

[0042] In the manufacturing method of the present invention, in order to reliably obtain the acidic hypochlorous acid water in the above-mentioned pH range, the pH of the effluent is 2.5 or more, and the recovery is stopped when the pH is 5.5 or less. By carrying out the recovery in this range, the pH of the recovered acidic hypochlorous acid aqueous solution is necessarily 2.5 or more and 5.5 or less. Furthermore, the treated liquid (column effluent) with a pH of less than 2.5 has a low effective chlorine concentration because hypochlorous acid is partially decomposed, and for this reason, it is not recovered as a product but is discarded.

[0043] Although recovery may be started at any time as long as the pH of the effluent is 2.5 or higher, for the reasons mentioned above, it is preferable to set the timing for starting recovery at or after the pH reaches 2.7, and more preferably at or after the pH reaches 2.8. On the other hand, if the start is too late, the production efficiency decreases, so it is preferable to start before the pH reaches 3.1, and more preferably before the pH reaches 3.0.

[0044] On the other hand, since the lower the pH, the better the storage stability, it is preferable to set the timing for stopping recovery at or before the pH reaches 4.5, more preferably at or before the pH reaches 3.5, and even more preferably at or before the pH reaches 3.4. Also, from the viewpoint of production efficiency, it is preferable to set the timing for stopping recovery at pH 3.2 or higher.

[0045] In addition, as the liquid passes through the column (as the ion exchange resin changes to R-Na type), the pH gradually increases. Although it depends on other conditions, in many cases, when the pH exceeds 3.5, the pH rise rate increases, and when it exceeds 4.5, it becomes even more rapid. From this point of view, it is preferable to stop passing the liquid through the column (or switch the flow path, etc.: hereinafter, also referred to as "stop collection") when the pH of the column passing through the column reaches the above pH, preferably 4.5, more preferably 3.5, in order to reliably obtain hypochlorous acid water with excellent storage stability.

[0046] The pH of the liquid passing through the column can be easily monitored by installing a pH meter near the outlet of the column. It is also preferable that the pH meter has a temperature compensation function.

[0047] The production method of the present invention is characterized by making the raw material concentration and space velocity SV within a specific range.By producing within such range, the acidic hypochlorous acid water in the above pH range can be obtained as much as possible and stably in one pass.

[0048] Specifically, it is preferable that the available chlorine concentration C [mass%] of the aqueous sodium hypochlorite solution and the spatial velocity SV [1 / h] when passing the aqueous sodium hypochlorite solution through the column are within the range of the following formula (1). 0.1 ≦ SV × C ≦ 20 (1)

[0049] When the spatial velocity SV × concentration C becomes larger than a certain value, the pH of the liquid passing through the column tends to increase in proportion to that value. Therefore, when SV × C is greater than 20, it becomes difficult to set the conditions to keep the pH below 5.5 even if other factors are adjusted. In other words, although there are many cases where conditions such as resin particle size and reaction temperature need to be set from the viewpoint of factors other than pH, there are advantages such as increased freedom in setting these factors if SV × C is set to 20 or less.

[0050] In addition, the spatial velocity SV changes depending on the amount of liquid passing through, that is, the amount of liquid introduced into the column, but even if this amount of liquid introduced is controlled, it is inevitable that it will fluctuate slightly due to various factors.In addition, in the region where the spatial velocity SV is large, the pH of the obtained acidic hypochlorous acid water is sensitive to the change in the SV, and in this respect, it is preferable that SV×C is small.

[0051] On the other hand, when SV×C is less than 0.1, the amount of liquid passing through the column is very small compared to the size of the column, and the size of the column tends to be too large for the target production rate.

[0052] From the viewpoint of storage stability, the pH at the outlet of the ion exchange resin column is preferably less than 3.5, and therefore, the above SV×C is preferably 15 or less, and more preferably 14 or less. From the viewpoint of productivity, the SV×C is preferably 1 or more, and more preferably 3 or more.

[0053] The space velocity SV is calculated as SV=R / V, where V[L] is the volume of the packed bed of the ion exchange resin and R[L / h] is the flow rate of the treatment liquid. It is known that the volume of the packed bed of the ion exchange resin changes depending on the ion exchange state of the resin, but in the present invention, the space velocity SV is calculated based on the resin bed volume of the RH type (resin regenerated state). Furthermore, the volume can be obtained by the measuring cylinder method (tap method).

[0054] Therefore, the space velocity SV is determined by the amount of weakly acidic cation exchange resin packed in the ion exchange resin column used and the supply rate of sodium hypochlorite introduced into the column. If you want to change the space velocity SV for some reason, it is easier to change the space velocity SV by changing the supply rate of sodium hypochlorite than by changing the amount of weakly acidic cation exchange resin when using the same equipment. The supply rate can be controlled by a metering pump or the like according to a standard method.

[0055] Incidentally, sodium hypochlorite aqueous solution and hypochlorous acid water are less likely to decompose at low temperatures. Therefore, it is preferable to maintain the temperature of sodium hypochlorite aqueous solution and hypochlorous acid water in the range of 40°C or less throughout the entire reaction process (including raw material storage), and more preferably 30°C or less. As a method for satisfying such conditions, it is possible to adjust the temperature by installing a part or the whole of the manufacturing equipment, including the storage tank and piping, in a temperature-controlled space or by incorporating a cooling mechanism. Of course, it is necessary to prevent freezing, and considering the cooling cost, a temperature of 5°C or more is sufficient, or even 10°C or more. In cold regions, a heating mechanism to prevent freezing may be incorporated.

[0056] <Regeneration process of ion exchange resin column> After the pH of the liquid that has passed through the ion exchange resin column reaches a predetermined value, the weakly acidic cation exchange resin packed in the column can be regenerated, and acidic hypochlorous acid water can be produced again.

[0057] Regeneration can also be performed with the weakly acidic cation exchange resin still packed in the column. Specifically, the used ion exchange resin column can be reused by running water through it to wash it, and then passing a regenerant through it. As the regenerant, any acid stronger than the ion exchange resin can be used, and it is preferable to use an inorganic acid such as hydrochloric acid or sulfuric acid diluted to about 1 mol / L. The flow rate of the regenerant is generally 1 to 10 in SV, and the flow amount of the regenerant required for regeneration is generally about 3 to 5 times the volume of the ion exchange resin layer, but regeneration can be performed without being limited to this range. Completion of regeneration can be easily determined by the fact that the pH of the liquid at the column outlet is less than 2.

[0058] After the regeneration is completed, water is again passed through the column to wash the acid used as the regenerating agent, and then an aqueous sodium hypochlorite solution having an effective chlorine concentration within the above-mentioned range is passed through at the above-mentioned space velocity, whereby acidic hypochlorous acid water can be produced again using the same column packed with ion exchange resin.

[0059] The water used for washing the ion exchange resin in the column can be any water that is generally used without any restrictions. For the same reasons as the dilution water of the sodium hypochlorite solution, it is preferable to use pure water such as ion exchange water, distilled water, and RO water, and it is particularly preferable to use ion exchange water from the viewpoint of the balance between the amount of impurities and the economical efficiency, and it is preferable to use ultrapure water if the storage stability is more important.

[0060] In addition, the apparatus used for producing acidic hypochlorous acid water and the apparatus used for regeneration do not necessarily have to be the same. An apparatus used exclusively for producing acidic hypochlorous acid water and an apparatus used exclusively for regenerating ion exchange resin can be prepared separately, and after the production of acidic hypochlorous acid water is completed, the ion exchange resin column can be removed from the production apparatus and attached to the apparatus used for regeneration to regenerate the ion exchange resin column, and after the regeneration, the column can be used again to produce acidic hypochlorous acid water.

[0061] Even in the case of a weakly acidic cation exchange resin having a water retention capacity within the above range, repeated use gradually progresses deterioration due to oxidation, and the pressure loss of the column increases, and the storage stability of the obtained acidic hypochlorous acid water may deteriorate compared to the initial time when the resin is first used. Usually, it is preferable to replace the ion exchange resin that has been used repeatedly about 40 to 60 times with a new one. EXAMPLES

[0062] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The physical properties were measured by the following methods.

[0063] 1) Measurement of available chlorine concentration An appropriate amount of sample was diluted with ion-exchanged water to about several tens to 100 ppm, about 0.5 g of potassium iodide and a 10% acetic acid solution were added, starch was added, and titration was performed with sodium thiosulfate standard solution to measure the available chlorine concentration from the volume of sodium thiosulfate standard solution and the dilution rate of the sample.

[0064] 2) Measurement of pH A glass electrode with a temperature compensation function was used to measure the sample at a liquid temperature of 25°C.

[0065] 3) Measurement of water retention capacity About 10 mL of ion exchange resin was placed in a beaker in terms of dry volume, and ion exchange water was added to make the total volume about 50 mL. The ion exchange resin was immersed in the ion exchange water for about 30 minutes. A funnel, a suction filter, a rubber stopper, and a gas washing bottle were also prepared. Filter paper was placed in the funnel and moistened with water, and the apparatus was assembled as shown in Figure 2. Air with a relative humidity of 100% was supplied to the funnel by passing through a gas washing bottle filled with water. The degree of vacuum in the suction filter was adjusted to about 720 mmHg. The rubber stopper was removed, and about 5 g of resin was placed in the funnel and sucked to remove the excess moisture contained in the resin. Suction was continued for 10 minutes from the point when water stopped dripping from the resin. This prepared ion exchange resin in equilibrium with saturated water vapor. After that, the vacuum was stopped, the rubber stopper was removed, and the ion exchange resin was taken out.

[0066] The resin that had been moistened using the above procedure was weighed precisely into a glass container that had been previously tared. The ion exchange resin that had been removed and precisely weighed was then dried in an oven at 110°C for approximately 18 hours. After being removed from the oven, the ion exchange resin was left to cool in a desiccator for approximately 30 minutes. The ion exchange resin was removed from the desiccator, and the mass after drying was precisely weighed, and the moisture retention capacity was calculated using the following formula. Moisture retention capacity = mass difference of ion exchange resin before and after drying / mass of ion exchange resin when wet x 100

[0067] Example 1 A special grade aqueous solution of sodium hypochlorite for water use (Shimada Shoten Neolux Super) with an effective chlorine concentration of 12% by mass and salt content of less than 1% by mass was diluted with ion-exchanged water to an effective chlorine concentration of 1.1% by mass (sodium hypochlorite concentration of 1.15% by mass), and this was used as the raw solution. In addition, 35% hydrochloric acid (Wako Pure Chemical Industries, general reagent) was diluted with ion-exchanged water to 3.5%, and this was used as the regenerant. The experiment was carried out using the equipment shown in Figure 1. All tests were carried out at room temperature, except for the product storage stability test.

[0068] A weakly acidic cation exchange resin (HPR8400H manufactured by Organo Corporation, water retention capacity 46%) was prepared with a wet volume of 100 mL. The ion exchange resin was immersed in ion exchange water overnight, transferred together with water to a measuring cylinder, and the wet volume was determined by measuring the amount of resin that reached exactly 100 mL on the scale at the top of the resin layer when there was no change in volume even when tapped.

[0069] The above ion exchange resin was fed with an aqueous sodium hypochlorite solution into an ion exchange resin column (diameter 30 mm, height 650 mm), and the solution was extracted from the bottom of the column using a metering pump, so that the aqueous sodium hypochlorite solution was passed through the column. The available chlorine concentration of the solution obtained at the outlet was measured, and when it stabilized at 0.9% or more, the aqueous sodium hypochlorite solution was passed through at SV=3, and the outlet at this time was taken as the product. When the pH of the solution reached 3.5, collection was stopped, and ion exchange water was passed through the column at SV=24 to push out the sodium hypochlorite and acidic hypochlorous acid solution remaining in the column. Then, 600 mL of regenerant was passed through at SV=24 to regenerate the column. After regeneration, 1000 mL of ion exchange water was passed through at SV=24 to push out hydrochloric acid, and then the aqueous sodium hypochlorite solution was supplied. The process from passing the aqueous sodium hypochlorite solution to pushing out the regenerant was considered as one cycle (first time).

[0070] The amount of product obtained in this process was the amount that could be produced in that cycle. In order to correct the error in the concentration of the diluted raw sodium hypochlorite aqueous solution due to the number of trials in the experiment, the concentration was standardized using the following formula for comparison. The results are shown in Table 1. A = t × v × (available chlorine concentration of raw material) ÷ ​​1.1 A: The amount of production that cycle can produce (mL) t: Time from the start of product collection until the pH of the outlet solution reaches 3.5 (min) v: Flow rate of sodium hypochlorite solution into the column (mL / min)

[0071] The height of the resin layer in the column was measured, and the swelling rate of the ion exchange resin observed during the cycle was calculated from the height and the column diameter. The results are shown in Table 1. Sw = 100× r 2 × π ×(h h -h l ) ÷ V Resin Sw: Swelling rate (%) r: column radius (15mm) h h: Maximum resin layer height observed during cycle (mm) h l : Minimum resin layer height observed during cycle (mm) V Resin : Initial volume of ion exchange resin (mm 3 )

[0072] The above cycle was repeated 30 times. The producible amount and swelling ratio in each cycle are shown in FIG. 3 and FIG. 4, respectively.

[0073] [Table 1]

[0074] (Example 2, Comparative Example 1) The acidic hypochlorous acid water was produced in the same manner as in Example 1, except that 100 mL of Organo Corporation's IRC76 (water retention capacity 53%, Example 2) and 50 mL of Purolite Corporation's C106 (water retention capacity 72%, Comparative Example 1) were used as the weakly acidic cation exchange resin. The results are shown in Table 1. In Example 2, the amount of production was reduced by half from the first to the fifteenth times. In addition, the collapse and crushing of the ion exchange resin increased the pressure loss of the column, and the liquid could not be passed through the column at the 27th time, making production impossible. In Comparative Example 1, the amount of production was reduced by about 70% from the first to the tenth times. In addition, after recording a swelling rate of 424% at the seventh time, the swelling rate exceeded the measurable range from the eighth time onwards, and the maximum height at the time of swelling approached the column top height (650 mm), making production impossible.

[0075] (Examples 3 and 4) Finally, the acidic hypochlorous acid water products obtained in HPR8400H (Example 1) and IRC76 (Example 2) were diluted with ion-exchanged water to an effective chlorine concentration of 760 ppm, filled into polyethylene containers, sealed, and subjected to a storage stability test at 60° C. Table 2 shows the remaining effective chlorine concentration after storage at 60° C. for 14 days.

[0076] [Table 2] [Explanation of symbols]

[0077] 1: Ion exchange resin column 2: Column outlet pH measuring device 3: Fixed volume extraction pump 4: Acidic hypochlorous acid water storage tank 5: Rubber stopper 6: Funnel 7: Aspirator or suction pump 8: Suction filtration bottle 9: Gas washing bottle

Claims

1. A method for producing acidic hypochlorous acid water, comprising an ion exchange step of passing an aqueous solution of sodium hypochlorite with an effective chlorine concentration of 0.5% by mass or more through a column packed with a weakly acidic cation exchange resin, The water retention capacity of the weakly acidic cation exchange resin is 60% or less; A method for producing acidic hypochlorous acid water, comprising starting recovery of the effluent as a product from the time when the pH of the effluent at the column outlet becomes 2.5, and stopping recovery when the pH becomes 5.5 or less.

2. The method for producing acidic hypochlorous acid water according to claim 1, characterized in that the recovery is stopped before the pH of the passing liquid at the column outlet reaches 3.

5.

3. The method for producing acidic hypochlorous acid water according to claim 1 or 2, wherein the effective chlorine concentration C [mass%] of the sodium hypochlorite aqueous solution and the spatial velocity SV [1 / h] when the sodium hypochlorite aqueous solution is passed through the column satisfy the following relational expression (1). 0.1≦SV×C≦20 (1)

4. The method for producing acidic hypochlorous acid water according to claim 3, wherein the solution is passed through the filter at a SV×C ratio of 15 or less.

5. A regenerant is passed through a column packed with the weakly acidic cation exchange resin that has been subjected to the ion exchange step to regenerate the weakly acidic cation exchange resin; 3. The method for producing acidic hypochlorous acid water according to claim 1 or 2, wherein an aqueous solution of sodium hypochlorite having an effective chlorine concentration of 0.5% by mass or more is passed through a column packed with the regenerated weakly acidic cation exchange resin.

6. The method for producing acidic hypochlorous acid water according to claim 1 or 2, wherein the weakly acidic cation exchange resin is a resin in which polyacrylic acid is crosslinked with divinylbenzene.

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