Method for producing acidic hypochlorous acid water

Abstract

To provide a production method for industrially and stably producing acidic hypochlorous acid water having a stable pH, and for safely resuming production of acidic hypochlorous acid water after production of acidic hypochlorous acid water has been interrupted for some reason.SOLUTION: A method for producing acidic hypochlorous acid water comprises an ion exchange step of making a sodium hypochlorite aqueous solution pass through a column filled with weakly acidic cation exchange resin and a stop step of stopping passage of the sodium hypochlorite aqueous solution. The method for producing acidic hypochlorous acid water further comprises a water passage step of making water pass through the column before resuming the ion exchange step after the stop step.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] For disinfection purposes, hypochlorite solutions adjusted to basicity, such as sodium hypochlorite, are widely used. Under basic conditions, hypochlorous acid mainly converts into hypochlorite ions (ClO - ) Under acidic conditions, it exists as hypochlorous acid (HClO), which is known to have a higher bactericidal effect than hypochlorite ions. For this reason, acidic hypochlorous acid water is in demand for sterilization.

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

[0004] One known method for producing highly pure acidic hypochlorous acid water is to exchange cations in a hypochlorite solution with an ion exchange resin to obtain acidic hypochlorous acid water. This method allows the target acidic hypochlorous acid water to be obtained simply by contacting the raw hypochlorite solution with an ion exchange resin, making it possible to inexpensively obtain highly concentrated, highly pure acidic hypochlorous acid water. For example, Patent Document 2 discloses a method for obtaining highly concentrated acidic hypochlorous acid water with a pH of 3.0 to 5.5 by stirring and mixing a hypochlorite solution with a weakly acidic cation exchange resin in a reaction vessel. This method has the problem of requiring complicated operations for adding and separating raw materials, particularly the ion exchange resin.

[0005] For this reason, methods have been widely studied that simplify the operation of loading and unloading raw materials by filling a column with an ion exchange resin and passing the raw material through it. For example, Patent Document 3 discloses a method for obtaining acidic hypochlorous acid water by passing a hypochlorous acid solution through a column filled with an ion exchange resin so that the pH is in the range of 3.0 to 7.5. However, studies by the present inventors have revealed that the method of Patent Document 3 can result in large fluctuations in the pH of the obtained acidic hypochlorous acid water. This leaves room for improvement in terms of the need to ensure the same quality when producing industrial and commercial products.

[0006] In addition, hypochlorous acid water is usually used with an effective chlorine concentration in the range of about 10 to 600 ppm, but producing it at such a low concentration and storing it for a long period of time before shipping or moving it to another location is not desirable 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 needed when shipping, bottling, etc. On the other hand, it has traditionally been thought that acidic hypochlorous acid water with a low concentration and a high pH has better storage stability, and it has been thought that it is difficult to achieve both cost, efficiency, and storage stability.

[0007] Therefore, the inventors conducted research and found that the storage stability of high-concentration hypochlorous acid water is closely related to pH, and that the lower the pH, the better the stability (see Patent Document 4). Further research was conducted into a method for reproducibly and efficiently producing hypochlorous acid water with such a pH, and the inventors found that the above-mentioned problem can be solved by applying a method using a column packed with an ion exchange resin as described in Patent Document 3, and further setting the raw material concentration and the flow rate through the column within specific ranges. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 7164767 [Patent Document 2] International Publication No. WO2019 / 225599 [Patent Document 3] International Publication No. WO2011 / 056940 [Patent Document 4] International Publication No. WO2023 / 248640 Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, in the past studies of the inventors, it has become possible to industrially obtain high-purity and high-concentration acidic hypochlorous acid water stably and with the same quality.Specifically, when the pH of the resulting effluent is between 2.5 and 5.5, the following four steps can be repeated: a step of passing a sodium hypochlorite solution through a column to recover acidic hypochlorous acid water; a step of rinsing the column with water after stopping the recovery; a step of regenerating the ion exchange resin with a regenerant such as hydrochloric acid; and a step of rinsing the regenerant with water, thereby continuously producing and recovering acidic hypochlorous acid water.

[0010] On the other hand, in actual operation, situations are anticipated in which the flow of liquid through the column will be interrupted and stopped midway through each of the four steps due to the need for equipment maintenance and inspection, adjustment of product production volume, and emergency shutdown in the event of an abnormality. The inventors' studies have shown that if the recovery of acidic hypochlorous acid water is interrupted and the column is immersed in a high-concentration sodium hypochlorite solution for a long period of time, for example, approximately 10 hours or more, when product recovery is resumed, many bubbles are observed in the liquid obtained from the column outlet, and the liquid's available chlorine concentration and pH drop are observed. When concentrated acidic hypochlorous acid water has a pH below 2.5, molecular chlorine (Cl2) is present in large amounts, generating chlorine gas, which may pose a manufacturing hazard. Furthermore, chlorine has the property of corroding metals and tends to be so corrosive that it rusts metal parts of nearby items that are not used as parts directly contacting the hypochlorous acid solution. Furthermore, when a pump is used to circulate the liquid through the column, gas can be generated in the flow path of the liquid extracted from the column, which can cause cavitation and accelerate the deterioration of the pump, which may cause problems in the operation of the manufacturing equipment.

[0011] Therefore, an object of the present invention is to provide a method for industrially and stably producing acidic hypochlorous acid water having a stable pH, and to safely resume the production of acidic hypochlorous acid water after the production of acidic hypochlorous acid water has been interrupted for some reason. [Means for solving the problem]

[0012] The present inventors have conducted extensive research in light of the above-mentioned problems. They have hypothesized that the occurrence of bubbles in the liquid obtained from the outlet of the column and the decrease in the effective chlorine concentration of the liquid observed when the production of acidic hypochlorous acid water is interrupted and then resumed are due to the decomposition of hypochlorous acid and the generation of chlorine gas.

[0013] Therefore, further study the method of suppressing the decomposition of hypochlorous acid and the generation of chlorine gas.As a result, find that after the production of acidic hypochlorous acid water is stopped, ion-exchanged water is passed through column, then sodium hypochlorite is passed through column, and the production of acidic hypochlorous acid water is resumed, so that the decomposition of hypochlorous acid and the generation of chlorine gas can be suppressed, and the present invention is completed.

[0014] That is, the present invention provides a method for producing acidic hypochlorous acid water, which includes an ion exchange step of passing an aqueous sodium hypochlorite solution through a column packed with a weakly acidic cation exchange resin, and a discontinuation step of discontinuing the passage of the aqueous sodium hypochlorite solution, and further includes a water passing step of passing water through the column before resuming the ion exchange step after the discontinuation step.

[0015] In the production method of the present invention, it is preferable to pass water in the water passing step until the available chlorine concentration of the water discharged from the column falls within the range of 0 to 3000 ppm. Furthermore, in the ion exchange step, it is preferable to start recovering the product after the pH of the effluent at the column outlet reaches 2.5, and to stop recovery when the pH reaches 5.5 or less, and it is more preferable to stop recovery before the pH of the effluent at the column outlet reaches 3.5.

[0016] In the ion exchange step, it is preferable to pass an aqueous sodium hypochlorite solution having an available chlorine concentration of 0.5% by mass or more.

[0017] Furthermore, the effective chlorine concentration C [mass%] of the sodium hypochlorite aqueous solution and the space velocity SV [1 / h] when the sodium hypochlorite aqueous solution is passed through the column are expressed by the following relational expression (1): 0.1 ≦ SV×C ≦ 20 (1) It is preferable that the following be satisfied. [Effects of the Invention]

[0018] According to the method of the present invention, can produce high-concentration acidic hypochlorous acid water with little pH fluctuation.In addition, even when the flow of sodium hypochlorite solution is temporarily interrupted due to operational reasons, after the sodium hypochlorite solution is passed through the column packed with weakly acidic cation exchange resin again, the generation of bubbles in the distillate obtained from the outlet of the column and the decrease in the effective chlorine concentration of the distillate can be suppressed, and can safely and stably produce acidic hypochlorous acid water. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a flow diagram illustrating an exemplary embodiment of the present invention. [Figure 2] FIG. 1 is a graph showing the transition of pH in Examples and Comparative Examples. [Figure 3] FIG. 1 is a graph showing the transition of the available chlorine concentration in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention is characterized in that in the method for producing acidic hypochlorous acid water, comprising an ion exchange step of passing sodium hypochlorite aqueous solution through a column packed with weakly acidic cation exchange resin, after the flow of sodium hypochlorite solution is stopped, before resuming, water is passed through this column.By carrying out this operation, after resuming the flow of sodium hypochlorite solution through the column packed with weakly acidic cation exchange resin, the generation of bubbles in the distillate obtained from the outlet of the column and the decrease in the effective chlorine concentration of the distillate can be suppressed, and acidic hypochlorous acid water can be stably produced.

[0021] As described above, the generation of bubbles in the distillate obtained from the outlet of the column after the flow of sodium hypochlorite solution is resumed and the decrease in the effective chlorine concentration of the distillate are presumably due to the decomposition of hypochlorous acid in the column and the generation of chlorine gas. Therefore, it is presumed that the generation of bubbles and the decrease in the effective chlorine concentration when the flow of sodium hypochlorite solution is resumed can be suppressed by passing water through the column to replace the inside of the column with water before resuming the flow of sodium hypochlorite solution through the column. Hereinafter, the embodiments 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.

[0022] <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 may be used.

[0023] 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. Furthermore, they are usually alkaline, with a pH of 8 or higher, and most often 10 or higher.

[0024] 2NaOH aq + Cl2 → NaClO aq + NaCl + HO The concentration of sodium hypochlorite or acidic hypochlorous acid is generally expressed as effective chlorine concentration. Effective chlorine concentration means the concentration converted into the equivalent chlorine of the oxidizing power of hypochlorous acid, and is expressed as the mass concentration of chlorine molecules in an amount equivalent to the molar amount of hypochlorous acid contained.

[0025] The effective chlorine concentration of acidic hypochlorous acid water is usually in the range of about 10 to 600 ppm, but as mentioned above, handling at low concentration is not preferable in terms of storage cost and transportation efficiency, so it is more economical to produce at high concentration as much as possible and dilute as necessary.Therefore, in the production method of the present invention, the effective chlorine concentration of the sodium hypochlorite aqueous solution used as raw material is 0.5 mass% or more.Preferably 0.8 mass% or more, more preferably 1.0 mass% or more, particularly preferably 1.1 mass% or more.

[0026] 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 preferably 5.0 mass% or less, more preferably 2.0 mass% or less.In addition, in the production method of the present invention, raw material is passed through a column packed with ion exchange resin as described below, and the effective chlorine concentration at the time of being discharged from this column is practically equal to the effective chlorine concentration of the raw material introduced into the column.That is, the effective chlorine concentration in the obtained hypochlorous acid water is almost determined by the effective chlorine concentration of raw material.

[0027] As sodium hypochlorite aqueous solution, various concentrations can be commercially obtained, but when the concentration of the sodium hypochlorite aqueous solution that is obtained is higher than desired concentration, it can be used by diluting with water.As this dilution water, the water that is generally used can be used without any restrictions, but the impurities contained in water such as metal ions may reduce the storage stability of acidic hypochlorous acid water, so it is preferred to use pure water such as ion-exchanged water, distilled water, RO water, etc., and especially from the viewpoint of the balance between impurity amount and economical efficiency, it is preferred to use ion-exchanged water, and if it is more important to store stability, it is preferred to use ultrapure water.

[0028] <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 basic raw material aqueous sodium hypochlorite solution is exchanged with hydrogen ions to adjust the pH to the above range, and a weakly acidic cation exchange resin is used for this exchange.As the weakly acidic cation exchange resin 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 hydrolysis in the case of ester.

[0029] Such a weakly acidic cation exchange resin can exchange sodium ions from 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 occurs vigorously under strong acidic conditions, can be suppressed.

[0030] On the other hand, from the viewpoint of the storage stability of the acidic hypochlorous acid water described below, in order to achieve a preferred pH of 3.5 or less, it is preferable to use a resin in which polyacrylic acid is cross-linked 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.

[0031] Ion exchange resins include porous, gel, and macroporous types, and any of these structures can be used as the weakly acidic cation exchange resin in the present invention without any restrictions. From an economical viewpoint, it is preferable to use an acrylic macroporous ion exchange resin, which is generally used for water treatment.

[0032] Weakly acidic cation exchange resins with spherical particles having an average particle size of approximately 0.1 mm to 1.0 mm are used for water treatment and purification of antibiotics and amino acids, and such resins can also be suitably used in the present invention. Since small particle sizes tend to increase the pressure loss in ion exchange resin columns, those with an average particle size of 0.4 to 0.8 mm are preferred.

[0033] Of course, since the resin 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.).

[0034] <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 weakly acidic cation exchange resin, thereby allowing continuous contact.

[0035] Any known container can be used for the column packed with the ion exchange resin without any restrictions. To prevent corrosion by hypochlorous acid or the regenerant (acid) described below, a resin container is preferred, and materials that are highly resistant to hypochlorous acid, such as vinyl chloride, polypropylene, polyethylene, AS resin, ABS resin, PFA, and PTFE, are particularly preferred. In addition, to increase the strength of the column, it is also a preferred embodiment to install an exterior made of FRP or metal.

[0036] There are no particular restrictions on the height at which the ion exchange resin is packed in an ion exchange resin column, but if the column diameter is large and the packed height is too low, the treatment liquid may not be uniformly treated. Although this depends on the treatment scale, it is generally desirable to determine the column diameter so that the resin packed height 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 reduced. Therefore, it is desirable to determine the column diameter so that the resin packed height is preferably 200 cm or less, more preferably 100 cm or less.

[0037] <Ion exchange process> In the production method of the present invention, an ion exchange step is performed in which an aqueous sodium hypochlorite solution is passed through a column packed with a weakly acidic cation exchange resin. The initial pH of the passing solution is low, and the pH increases as the solution continues to pass through. The storage stability of concentrated acidic hypochlorous acid solution (the maintenance rate of the effective chlorine concentration during storage) is closely related to the pH, and storage stability deteriorates significantly when the pH exceeds 5.5. On the other hand, when the pH is less than 2.5, the amount of molecular chlorine (Cl2) present increases, which can be dangerous if the solution is concentrated. Therefore, from the viewpoint of achieving good storage stability over a longer 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 the pH is preferably 2.8 or more, and particularly preferably 2.9 or more.

[0038] In the production method of the present invention, in order to reliably obtain the acidic hypochlorous acid water in the pH range described above, the pH of the effluent is 2.5 or later, and the recovery is stopped when the pH is 5.5 or less. By carrying out the recovery within 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 partially decomposed hypochlorous acid and has a low effective chlorine concentration, so it is not recovered as a product but is discarded.

[0039] Although recovery may be started at any time as long as the pH of the effluent is 2.5 or higher, for the reasons described above, recovery is preferably started when the pH reaches 2.7 or later, and more preferably when the pH reaches 2.8 or later. On the other hand, if the start is too late, production efficiency decreases, so recovery is preferably started before the pH reaches 3.1, and more preferably before the pH reaches 3.0.

[0040] On the other hand, since the lower the pH, the better the storage stability, the timing for stopping recovery is preferably set 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. From the viewpoint of production efficiency, the timing for stopping recovery is preferably set at pH 3.2 or higher.

[0041] In addition, as mentioned above, as the elution proceeds (as ion exchange resin changes to R-Na type), pH gradually increases.Although it depends on other conditions, in many cases, when this pH exceeds 3.5, pH rises more rapidly, and when it exceeds 4.5, it becomes even more rapid.From this point of view, it is preferable to stop collecting acidic hypochlorous acid water when the pH of the column elution liquid reaches preferably 4.5, more preferably 3.5, so as to ensure that the hypochlorous acid water with excellent storage stability is obtained.

[0042] The pH of the column-passed liquid can be easily monitored by installing a pH meter near the column outlet. The pH meter is preferably one with a temperature compensation function.

[0043] The production method of the present invention is characterized by that raw material concentration and space velocity SV are set within a specific range.By producing within such range, acidic hypochlorous acid water in the pH range can be obtained as much as possible and stably in one pass.

[0044] Specifically, it is preferable that the effective 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)

[0045] When the spatial velocity (SV) × concentration (C) increases beyond 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 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 must be set from perspectives other than pH, keeping SV × C at 20 or less offers the advantage of increasing the degree of freedom in setting these factors.

[0046] In addition, 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 spatial velocity SV is large, the pH of the obtained acidic hypochlorous acid water is sensitive to the change of this SV, and in this respect, SV × C is preferably small.

[0047] 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.

[0048] 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 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.

[0049] The space velocity SV is calculated as SV = R / V, where V [L] is the volume of the packed bed of ion exchange resin and R [L / h] is the flow rate of the treated liquid. It is known that the volume of the packed bed of ion exchange resin changes depending on the ion exchange state of the resin. In the present invention, the space velocity SV is calculated based on the resin bed volume of the RH type (resin regenerated state). Furthermore, this volume can be determined by the measuring cylinder method (tap method).

[0050] 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 feed rate of sodium hypochlorite introduced into the column.If you want to change the space velocity SV for some reason, and if you use the same equipment, it is easier to change the space velocity SV by changing the feed rate of sodium hypochlorite than by changing the amount of weakly acidic cation exchange resin.The feed rate can be controlled using a metering pump or the like according to standard methods.

[0051] Note that 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 the sodium hypochlorite aqueous solution and hypochlorous acid water in the range of 40°C or less throughout the entire reaction process (including storage of raw materials), and 30°C or less is even more preferable. Methods for satisfying these conditions include installing part or all of the manufacturing equipment, including the storage tank and piping, in a temperature-controlled space or by incorporating a cooling mechanism to control the temperature. Of course, it is necessary to prevent freezing, and considering cooling costs, a temperature of 5°C or higher is sufficient, or even 10°C or higher. In cold regions, a heating mechanism may be incorporated to prevent freezing.

[0052] <Cancelled process> The production method of the present invention includes a discontinuation step of discontinuing the passage of the aqueous sodium hypochlorite solution after the ion exchange step. The discontinuation step in the production method of the present invention refers to the interval between the stopping of the passage of the aqueous sodium hypochlorite solution through the column and the resumption of the passage of the aqueous sodium hypochlorite solution through the column without carrying out the regeneration step of the ion exchange resin column described below.

[0053] <Water flow process> The manufacturing method of the present invention is characterized by comprising the water passing step of passing water through the column packed with this weakly acidic cation exchange resin before restarting the ion exchange step after the stopping step.As mentioned above, it is presumed that the generation of bubbles in the distillate obtained from the outlet of the column after restarting the flow of sodium hypochlorite solution and the decrease in the effective chlorine concentration of the distillate are caused by the decomposition of hypochlorous acid in the column and the generation of chlorine gas.Therefore, it is presumed that by passing water through the column before restarting the flow of sodium hypochlorite solution through the column, the generation of bubbles and the decrease in the effective chlorine concentration can be suppressed when restarting the flow of sodium hypochlorite solution through the column.

[0054] The water flowing step in the production method of the present invention may be carried out before the ion exchange step is resumed. Specifically, the water flowing step may be carried out immediately after the ion exchange step is completed, and then the ion exchange step may be resumed after the suspension step. Alternatively, the ion exchange step may be completed, the water flowing step may be carried out after the suspension step, and then the ion exchange step may be resumed. From the viewpoint of suppressing the generation of chlorine gas, it is more preferable to carry out the water flowing step immediately after the ion exchange step is completed. When the ion exchange step is resumed, the method of passing the sodium hypochlorite solution may be the same as that described in the ion exchange step.

[0055] In this case, from the viewpoint of suppressing the generation of chlorine gas, the lower the available chlorine concentration due to sodium hypochlorite in the column, the better. It is most desirable that the available chlorine concentration of the liquid sampled from the column after substitution is measured be below the lower detection limit of the measurement.

[0056] On the other hand, when performing water replacement in a column, if the concentration of the liquid remaining in the column is reduced too much, the amount of water required for water replacement and the amount of waste liquid generated during water replacement will increase. Therefore, from an operational standpoint, it is also necessary to set the control value for the available chlorine concentration of the liquid removed from the column after water replacement to a relatively high value within an acceptable range.

[0057] From the above viewpoint, when replacing the water in the column after interrupting the flow of the sodium hypochlorite solution, it is desirable to continue until the available chlorine concentration of the liquid extracted from the column after replacement is 0 to 3000 ppm, more preferably 2500 ppm or less, and even more preferably 1000 ppm or less.

[0058] As the water used for substitution, any commonly used water can be used without any restrictions.For the same reasons as those mentioned for the water used for diluting the sodium hypochlorite solution, pure water such as ion-exchanged water, distilled water, RO water, etc. is preferred, and in particular, from the viewpoint of the balance between the amount of impurities and economic efficiency, it is preferred to use ion-exchanged water, and if the storage stability of the obtained product is more important, it is preferred to use ultrapure water.

[0059] In systems where a pump is used to extract the product or supply sodium hypochlorite solution to the column, it is desirable to replace the liquid in the pump from sodium hypochlorite or acidic hypochlorous acid water with water. Generally, pumps selected for systems that circulate liquid containing hypochlorite ions are often designed to tolerate the effects of cavitation caused by chlorine gas generated by the decomposition of hypochlorite ions, but from the perspective of improving pump maintainability, it is preferable to operate the pump in a way that prevents gas from being generated as much as possible.

[0060] Furthermore, situations may be anticipated in which it is difficult or undesirable to use the equipment to replace the water in the column immediately after an interruption, such as after a sudden power outage or the activation of an interlock due to the detection of an equipment abnormality, and until the soundness of the equipment is confirmed. For this reason, it is preferable to configure the equipment so that the liquid in the column can be replaced manually by installing a valve or liquid receiving port that can be opened and closed manually.

[0061] <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.

[0062] Regeneration can also be performed while the weakly acidic cation exchange resin is still packed in the column. Specifically, after washing the used ion exchange resin column with water, the column can be reused by passing a regenerant through it. Any acid stronger than the ion exchange resin can be used as the regenerant; preferably, an inorganic acid such as hydrochloric acid or sulfuric acid diluted to approximately 1 mol / L is used. The regenerant flow rate is typically 1 to 10 SV, and the volume of regenerant flow required for regeneration is typically approximately 3 to 5 times the volume of the ion exchange resin layer, although regeneration can be performed without being limited to these ranges. Completion of regeneration can be easily determined by the pH of the liquid at the column outlet being less than 2.

[0063] After the regeneration is completed, water is again passed through the column to wash it and wash away the acid used as the regenerant. Then, an aqueous sodium hypochlorite solution having an effective chlorine concentration within the above-mentioned range is passed through the column at the above-mentioned space velocity. This allows the production of acidic hypochlorous acid water using the same column packed with the same ion exchange resin again.

[0064] The water used to wash the ion exchange resin in the column can be any commonly used water without any restrictions, similar to the water used to dilute sodium hypochlorite or replace water in the column. Pure water such as ion-exchanged water, distilled water, or RO water is preferred.

[0065] 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 exclusively used for producing acidic hypochlorous acid water and an apparatus exclusively used for regenerating ion exchange resins may be prepared separately, and after the production of acidic hypochlorous acid water is completed, the ion exchange resin column may be removed from the production apparatus and attached to the apparatus used for regeneration, thereby regenerating the ion exchange resin column. After being used for regeneration, the column may be used again to produce acidic hypochlorous acid water.

[0066] Repeated use of weakly acidic cation exchange resins gradually deteriorates and powders due to the oxidizing power of hypochlorous acid, which may increase the pressure loss in the column or worsen the storage stability of the resulting acidic hypochlorous acid water compared to when the resin was first used. Usually, it is preferable to replace an ion exchange resin that has been used repeatedly about 40 to 60 times with a new one. [Example]

[0067] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Measurements of various physical properties were carried out by the following methods.

[0068] 1) Measurement of available chlorine concentration An appropriate amount of sample was diluted with ion-exchanged water to about several tens to 100 ppm, and then approximately 0.5 g of potassium iodide and a 10% acetic acid solution were added. Starch was then added, and titration was carried out with sodium thiosulfate standard solution. The available chlorine concentration was measured from the volume of sodium thiosulfate standard solution and the dilution rate of the sample.

[0069] 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.

[0070] 3) Raw materials A special grade sodium hypochlorite aqueous solution for water supply (Shimada Shoten Neolux Super) with an effective chlorine concentration of 12% by mass and a salt content of 1% by mass or less 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 material solution.

[0071] 4) Ion exchange resin in the column A weakly acidic cation exchange resin (Amberlite HPR8400H manufactured by Organo Corporation) with a wet volume of 100 mL was prepared. The ion exchange resin was immersed in ion-exchange water overnight, then transferred to a measuring cylinder together with water. The wet volume was determined by measuring the amount of resin so that the scale at the top of the resin layer reached exactly 100 mL when tapped without any change in volume.

[0072] <Examples 1 and 2, Comparative Example 1> The experiment was conducted using the equipment configuration shown in Figure 1. The above ion exchange resin was packed into an ion exchange resin column (diameter 30 mm, height 650 mm). A sodium hypochlorite solution was supplied to the column, and the solution was extracted from the bottom of the column using a metering pump, allowing the sodium hypochlorite solution to flow through the ion exchange resin column. The available chlorine concentration of the solution obtained at the outlet was measured, and once it stabilized at 0.9% or higher, the sodium hypochlorite solution was passed through at SV=6, and the solution at this point was considered the product. The pH of the solution obtained at the outlet was also continuously measured. Transparent PFA tubing (diameter 6.35 mm) was used in part of the piping through which the column outlet liquid passed, allowing for confirmation of gas generation within the piping. All experiments were conducted at room temperature.

[0073] After confirming that the available chlorine concentration of the resulting liquid had stabilized to 0.9% or more, the supply of raw materials and the withdrawal of products were suspended overnight.

[0074] In Example 1, after the supply of raw materials and the extraction of products are stopped, the water replacement operation of the column is carried out, and after confirming that the effective chlorine concentration of the liquid at the column outlet is 570 ppm, the process is shifted to the stop step, and the process is left standing overnight. In Example 2, the same operation is carried out, and after confirming that the effective chlorine concentration of the liquid at the column outlet is 2500 ppm, the process is shifted to the stop step, and the process is left standing overnight. In Comparative Example 1, the water replacement operation is not carried out, and the column is left standing overnight while being immersed in the sodium hypochlorite solution.

[0075] After leaving the column to stand overnight, the supply of raw materials and the withdrawal of liquid from the column were resumed for each of Examples 1, 2, and the Comparative Example. After resumption, the presence or absence of gas generation in the outlet piping, and the pH and available chlorine concentration of the liquid were compared.

[0076] First, the presence or absence of gas generation in the outlet piping is summarized in Table 1. In Examples 1 and 2, no gas generation was observed in the piping, but in the Comparative Example, the generation of bubbles was confirmed in the outlet piping after the withdrawal of liquid was resumed. This is presumed to be chlorine gas due to the decomposition of hypochlorous acid.

[0077] [Table 1]

[0078] Next, when product collection was resumed, the degree to which the pH of the liquid obtained from the outlet varied from the pH of the liquid at the outlet at the time of interruption was compared for each case, and the results are shown in Figure 2. In Comparative Example 1, behavior that appears to be due to decomposition caused by the longer contact time between sodium hypochlorite and the cation exchange resin was observed, but this was not observed in Examples 1 and 2.

[0079] Finally, when product acquisition was resumed, the effective chlorine concentration of the liquid obtained from the outlet was compared to how it changed with the amount of product obtained after resumption. In the comparative example, assuming no decomposition occurred, the effective chlorine concentration should theoretically be consistently 0.9% or higher after resumption, but in reality, a decrease in the effective chlorine concentration was observed, which is thought to be due to decomposition. In Examples 1 and 2, the concentration in the column was diluted with water compared to the raw material, so although the initial concentration was low, the effective chlorine concentration gradually increased as the supply of raw material was resumed. [Explanation of symbols]

[0080] 1: Ion exchange resin column 2: Column outlet pH measuring device 3: Fixed volume extraction pump 4: Acidic hypochlorous acid water storage tank

Claims

1. an ion exchange step of passing the sodium hypochlorite aqueous solution through a column packed with a weakly acidic cation exchange resin; In a method for producing acidic hypochlorous acid water, the method includes a step of stopping the flow of a sodium hypochlorite aqueous solution, A method for producing acidic hypochlorous acid water, comprising a water passing step of passing water through a column packed with the weakly acidic cation exchange resin before restarting the ion exchange step after the suspension step.

2. The method for producing acidic hypochlorous acid water according to claim 1, wherein the water passing step is performed until the effective chlorine concentration of the water discharged from the column is in the range of 0 to 3000 ppm.

3. 3. The method for producing acidic hypochlorous acid water according to claim 1 or 2, wherein in the ion exchange step, recovery as a product is started after the pH of the passing liquid at the column outlet becomes 2.5, and recovery is stopped when the pH becomes 5.5 or less.

4. The method for producing acidic hypochlorous acid water according to claim 3, wherein the collection is stopped before the pH of the passing-through liquid at the column outlet reaches 3.

5.

5. 3. The method for producing acidic hypochlorous acid water according to claim 1 or 2, wherein an aqueous sodium hypochlorite solution with an effective chlorine concentration of 0.5% by mass or more is passed through the ion exchange step.

6. 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). The method for producing acidic hypochlorous acid water according to claim 1 or 2. 0.1 ≦ SV × C ≦ 20 (1)

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