Method for preparing aqueous hypochlorous acid solution and method for regenerating weakly acidic cation exchanger

Abstract

Provided is a method for preparing a hypochlorous acid aqueous solution by which a weakly acidic hypochlorous acid aqueous solution having a pH of about 3.5-7 can be obtained without substantially generating chlorine gas even immediately after regeneration or even with a new weakly acidic cation exchange resin.　In a method for preparing a hypochlorous acid aqueous solution wherein an aqueous solution of hypochlorite is brought into contact with a weakly acidic cation exchanger to exchange cations constituting the hypochlorite with hydrogen ions to increase the concentration of hypochlorous acid in the aqueous solution, a neutral salt solution of a strong acid and a strong base in an amount that may obtain the hypochlorous acid aqueous solution having a pH of at least 3.5 when the hypochlorite aqueous solution is brought into contact with the weakly acidic cation exchanger is brought into contact, prior to the contact between the hypochlorite aqueous solution and the weakly acidic cation exchanger, with a weakly acidic cation exchanger that has been regenerated or has not been substantially subjected to cation exchange.

Description

[Technical field]

[0001] The present invention relates to a method for preparing an aqueous hypochlorous acid solution and a method for regenerating a weakly acidic cation exchanger, and more specifically to a method for preparing an aqueous hypochlorous acid solution using a weakly acidic cation exchanger, and a method for regenerating a weakly acidic cation exchanger used for similar purposes. [Background technology]

[0002] 2. Description of the Related Art Hypochlorous acid has been widely used in the past for its bactericidal effect in a wide variety of fields, such as for sterilizing tap water and food manufacturing equipment.

[0003] The bactericidal action of hypochlorous acid comes from the hypochlorite ions (ClO) that are generated when hypochlorites such as sodium hypochlorite (NaClO) are dissolved in water. - ) or reacts with an acid to produce hypochlorite ions (ClO - ) and hydrogen ions (H + It is produced by the combination of the two compounds to form molecular hypochlorous acid (HClO).

[0004] When hypochlorous acid is used for sterilization purposes, it is generally known that the most effective sterilization is achieved when hypochlorous acid is in the undissociated molecular form, i.e., in the HClO state. It is also known that the sterilization effect of a hypochlorite solution prepared by dissolving hypochlorite in water or other aqueous solvents varies significantly depending on the pH of the solution.

[0005] At alkaline pH levels, hypochlorous acid exists as hypochlorite ions and has a low bactericidal effect, whereas at highly acidic pH levels below 3.5, the bactericidal effect is low and chlorine gas is generated.

[0006] It is believed that hypochlorous acid is present in a high proportion in its undissociated molecular form when the pH is approximately 3.5 to 6.5.

[0007] On the other hand, the sodium hypochlorite aqueous solution is an alkaline solution. Even if this sodium hypochlorite aqueous solution is diluted to, for example, 50 to 100 ppm, which is a concentration generally used as sterilizing water, the pH only drops to about 8.5 to 9.5. When using hypochlorous acid for sterilization purposes, it is desirable to lower the pH to a level that exhibits a higher sterilizing effect.

[0008] The method of lowering the pH of sodium hypochlorite aqueous solution includes, for example, electrolysis and two-liquid method.However, electrolysis requires an apparatus equipped with an electrolytic cell, so the maintenance cost is expensive, and the electrode also deteriorates with use, so the cost of replacing parts is also required.In addition, electrolysis has the problem that it can only produce low-concentration hypochlorous acid.

[0009] On the other hand, the two-liquid method is a method in which the pH is adjusted to the acidic side by mixing an acid solution such as hydrochloric acid with a sodium hypochlorite aqueous solution. However, this two-liquid method has a major safety problem because it uses an acid solution such as hydrochloric acid to adjust the pH.

[0010] That is, when the acid liquid is mixed with sodium hypochlorite, chlorine gas is generated, which makes the work dangerous.

[0011] In this regard, several methods have been proposed to lower the pH of an aqueous sodium hypochlorite solution by using an ion exchange resin instead of an acid solution.

[0012] In particular, the present inventors have discovered and previously proposed a method for producing an aqueous hypochlorous acid solution without using an acid such as hydrochloric acid and without lowering the pH to a value that would generate chlorine gas, by using a weakly acidic ion exchanger that has a buffering effect at a pH level equal to or higher than the pH level at which chlorine gas is generated.

[0013] In particular, this method includes a step of treating the hypochlorite solution with a weakly acidic ion exchanger that has a buffering effect at a pH higher than the pH at which chlorine gas is generated, making it possible to extremely safely obtain a weakly acidic aqueous hypochlorous acid solution with a pH of about 3.5 to 7 without substantially generating chlorine gas (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0014] [Patent Document 1] JP 2014-043392 A Summary of the Invention [Problem to be solved by the invention]

[0015] Weakly acidic cation exchange resins are resins that have carboxylic acid groups (-COOH) as exchange groups and exhibit weak acidity similar to acetic acid, etc. Therefore, weakly acidic cation exchange resins can exchange bases such as NaOH and salts of weak acids such as NaHCO3.

[0016] In addition, the carboxylic acid group (-COOH), which is the exchange group of the weak acid cation exchange resin, does not dissociate in an acidic environment. Therefore, in theory, the weak acid cation exchange resin cannot decompose neutral salts such as NaCl and Na2SO4, which are salts of strong acids and strong bases, but it can exchange bases such as NaOH and salts of weak acids such as NaHCO3.

[0017] In addition, ion exchange resins theoretically have ion exchange capacity at a pH of about 3.5 to 5 or higher depending on the acidity of the exchange group. Therefore, the pH of a solution after ion exchange with an ion exchange resin will theoretically never be lower than about 3.5 to 5.

[0018] However, the present inventors have now found that a weakly acidic cation exchange resin may exhibit properties similar to those of a strongly acidic cation exchange resin at the start of ion exchange.

[0019] To be more specific, as described above, in theory, when a sodium hypochlorite solution is treated with a weakly acidic cation exchange resin, a hypochlorous acid solution with a pH of about 3.5 to 5 or more is produced, and it is impossible for the pH to fall below 3.

[0020] However, in reality, it has been found that when a sodium hypochlorite solution is treated with a weakly acidic cation exchange resin, in the initial stage of the reaction, particularly immediately after the regeneration of the ion exchange resin, or when a new resin that has not been substantially subjected to cation exchange is first used, a treated solution with a pH of 2 or less is produced by reaction with the sodium hypochlorite solution. In the following description, this phenomenon is referred to as the "initial reaction pH drop phenomenon."

[0021] This means that there is a risk that the pH of the hypochlorous acid solution will drop to 2 or less, resulting in the generation of chlorine gas. Although this is only at the initial stage of the reaction with the weakly acidic cation exchange resin, it is not possible to obtain a weakly acidic aqueous hypochlorous acid solution having a pH of about 3.5 to 7 without substantially generating chlorine gas. Therefore, a method for solving this problem has been sought.

[0022] The present invention has been made in view of the above circumstances, and provides a method for preparing an aqueous hypochlorous acid solution, which can obtain an aqueous hypochlorous acid solution having a pH of about 3.5 to 7 without substantially generating chlorine gas, even when using a weakly acidic cation exchange resin immediately after regeneration or a new weakly acidic cation exchange resin.

[0023] In addition, in cases where the physical properties of a substance contained in a solution, regardless of whether it is hypochlorous acid or a salt thereof, are lost due to the phenomenon of a decrease in pH during the initial reaction of a weakly acidic cation exchanger, it would be desirable to have a method for regenerating a weakly acidic cation exchanger that can suppress this phenomenon as much as possible in order to maintain the physical properties.

[0024] Therefore, the present invention also provides a method for regenerating a weakly acidic cation exchanger, which can suppress as much as possible the phenomenon of a decrease in pH during the initial reaction of the weakly acidic cation exchanger. [Means for solving the problem]

[0025] In order to solve the above-mentioned problems, the method for preparing a hypochlorous acid aqueous solution according to the present invention comprises the steps of: (1) contacting an aqueous solution of hypochlorite with a weakly acidic cation exchanger to exchange the cations constituting the hypochlorite with hydrogen ions and increase the concentration of hypochlorous acid in the aqueous solution; The method comprises contacting a neutral salt solution of a strong acid and a strong base in an amount sufficient to obtain the aqueous hypochlorous acid solution having a pH of 3.5 or higher when the aqueous hypochlorite solution is contacted with a regenerated or weakly acidic cation exchanger that has not been substantially subjected to cation exchange prior to contacting the aqueous hypochlorite solution with the weakly acidic cation exchanger.

[0026] In addition, the regeneration method for a weakly acidic cation exchanger according to the present invention is (2) a regeneration method for a weakly acidic cation exchanger for removing cations from a solution to be treated containing cations and a substance that loses its target physical property in a predetermined pH range lower than the pH range of the solution to be treated described below, and includes an exchange capacity recovery treatment step in which an acid solution is contacted with the weakly acidic cation exchanger that has been subjected to cation exchange to liberate and remove the cations trapped in the exchange groups, and a neutral salt solution contacting step in which a neutral salt solution of a strong acid and a strong base is contacted with the weakly acidic cation exchanger that has been subjected to the exchange capacity recovery treatment step in an amount such that a treated solution having a pH higher than the predetermined pH range and in which the substance exhibits the target physical property when subjected to cation exchange in the solution to be treated is obtained. Effect of the Invention

[0027] According to the method for preparing a hypochlorous acid aqueous solution of the present invention, in the method for preparing a hypochlorous acid aqueous solution, an aqueous solution of hypochlorite is contacted with a weakly acidic cation exchanger to exchange cations constituting the hypochlorite with hydrogen ions to increase the concentration of hypochlorous acid in the aqueous solution. A neutral salt solution of a strong acid and a strong base in an amount that gives a hypochlorous acid aqueous solution of pH 3.5 or more when the aqueous solution of hypochlorite is contacted with a regenerated or weakly acidic cation exchanger that has not been substantially subjected to cation exchange prior to contacting the aqueous solution of hypochlorite with a weakly acidic cation exchanger, a method for preparing a hypochlorous acid aqueous solution that can obtain a weakly acidic hypochlorous acid aqueous solution of pH 3.5 to 7 without substantially generating chlorine gas, even if the weakly acidic cation exchange resin is immediately after regeneration or is new, can be provided.

[0028] Furthermore, according to the regeneration method for a weakly acidic cation exchanger of the present invention, there is provided a method for removing cations from a solution to be treated that contains cations and a substance that loses its desired physical property in a predetermined pH range lower than the pH range of the solution to be treated described below, and the method comprises an exchange capacity recovery treatment step in which an acid solution is contacted with the weakly acidic cation exchanger that has been subjected to cation exchange to liberate and remove the cations trapped in the exchange groups, and a neutral salt solution contacting step in which a neutral salt solution of a strong acid and a strong base is contacted with the weakly acidic cation exchanger that has been subjected to the exchange capacity recovery treatment step in an amount such that a treated solution having a pH higher than the predetermined pH range and in which the substance exhibits the desired physical property when subjected to cation exchange in the solution to be treated is obtained. Therefore, a regeneration method for a weakly acidic cation exchanger that can suppress the initial pH drop phenomenon during the reaction of the weakly acidic cation exchanger as much as possible can be provided. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is an explanatory diagram showing the results of a pH confirmation test. [Diagram 2] FIG. 1 is an explanatory diagram showing the results of a pH confirmation test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The present invention provides a method for preparing an aqueous hypochlorous acid solution, which comprises contacting an aqueous hypochlorite solution with a weakly acidic cation exchanger to exchange cations constituting the hypochlorite with hydrogen ions to increase the concentration of hypochlorous acid in the aqueous solution, and which can obtain an aqueous hypochlorous acid solution having a pH of about 3.5 to 7 without substantially generating chlorine gas, even when using a weakly acidic cation exchange resin immediately after regeneration or a new weakly acidic cation exchange resin.

[0031] As generally recognized by those skilled in the art, an aqueous solution of hypochlorite refers to a solution containing any salt of hypochlorite, such as sodium hypochlorite (NaClO), potassium hypochlorite (KClO), and calcium hypochlorite (Ca(ClO)2), in an aqueous solvent.

[0032] The hypochlorite may be a commercially available material or a material produced by a method known to those skilled in the art. The solution may be in any solution, including water and an aqueous solution containing a predetermined component such as any additive described below. The solution may also be in a buffer solution. The hypochlorite solution may further include any additive. For example, the hypochlorite solution may include any weak acid salt such as sodium bicarbonate and calcium lactate.

[0033] By including such an additive, the hypochlorite solution can be adjusted to a pH level that provides greater bactericidal activity.

[0034] Hypochlorite can be either sodium hypochlorite, potassium hypochlorite or calcium hypochlorite.Hypochlorite can be a single type or a mixture of multiple types.Furthermore, hypochlorite solution can be used alone, or hypochlorite solutions with different types of hypochlorite, presence or absence and types of additives, and their concentrations can be mixed.

[0035] In the method of the present invention, the hypochlorite solution can be used at any concentration. For example, a commercially available 12% sodium hypochlorite solution can be diluted and used at a concentration of 1 to 120000 ppm or more, for example, 10, 100, 200, 500, 1000, 10000 and 120000 ppm.

[0036] For example, the hypochlorite solution can be 500 ppm or more. According to the method of the present invention, hypochlorous acid of a concentration of 10,000 ppm, which cannot be produced by conventional methods, can be produced. In addition, hypochlorous acid of a concentration of 50 to 1,000 ppm, which is the concentration actually used for sterilization, can be directly produced.

[0037] The hypochlorite solution can also be prepared during the practice of the production method of the present invention. In addition to salts that are produced as a solution, such as sodium hypochlorite, solid salts can also be used. For example, a hypochlorite solution can be prepared by adding a solid, such as calcium hypochlorite, to water.

[0038] The weakly acidic cation exchanger used is one that is theoretically capable of ion exchange at about pH 3.5 or higher, for example, 4 to 7 or higher. The weakly acidic cation exchanger can be, for example, an ion exchanger having a carboxylic acid group (-COOH) as an exchange group.

[0039] The weakly acidic cation exchanger can also exchange ions of bases such as NaOH. In the method of the present invention, the weakly acidic cation exchanger can be any weakly acidic cation exchanger known to those skilled in the art.

[0040] The weakly acidic ion exchanger can be a weakly acidic cation exchange resin such as a methacrylic acid-based weakly acidic cation exchange resin and an acrylic acid-based weakly acidic cation exchange resin. For example, it can be a weakly acidic cation exchange resin known to those skilled in the art, such as Amberlite IRC-76 (Organo Corporation) and acrylic Diaion (registered trademark) WK40L (Mitsubishi Chemical Corporation). In addition to the weakly acidic cation exchange resin, any material having an ion exchange function, such as silica gel, ceramics, and natural ores, can be used as the weakly acidic cation exchanger.

[0041] Furthermore, the weakly acidic cation exchanger can be used in any amount, and the method of the present invention allows the use of an excess amount of the weakly acidic cation exchanger without adjusting the amount.

[0042] The contact between the aqueous solution of hypochlorite and the weakly acidic cation exchanger can be carried out, for example, by passing the aqueous solution of hypochlorite through a column packed with the weakly acidic cation exchanger. It is also possible to carry out the contact by the same method as the contact between the weakly acidic cation exchanger and the neutral salt solution described below.

[0043] Then, the aqueous solution of hypochlorite is brought into contact with a weakly acidic cation exchanger to measure the amount of cations constituting the hypochlorite, for example, sodium ions (Na + ) for hydrogen ions, the concentration of hypochlorous acid in the aqueous solution increases, depending on the pH of the aqueous solution.

[0044] Here, the characteristic of the method for preparing the hypochlorous acid aqueous solution according to this embodiment is that a neutral salt solution in an amount that will give the hypochlorous acid aqueous solution of pH 3.5 or more when the aqueous solution of hypochlorite is contacted with a weakly acidic cation exchanger that has been regenerated or has not been substantially subjected to cation exchange, prior to contacting the aqueous solution of hypochlorite with the weakly acidic cation exchanger.

[0045] Here, the neutral salt contained in the neutral salt solution is a water-soluble salt that is a salt of a strong acid and a strong base. Such a neutral salt can be, for example, table salt (NaCl), sodium sulfate (Na2SO4), calcium chloride (CaCl2), etc. The neutral salt can also be a mixture of multiple neutral salts. The neutral salt solution can be prepared as an aqueous solution of such neutral salts.

[0046] The step of contacting the neutral salt solution with the weakly acidic cation exchanger can be carried out in any manner, where contacting means that the neutral salt solution is applied to the weakly acidic cation exchanger in such a way as to allow physical contact between the exchange groups of the weakly acidic cation exchanger and the neutral salt solution.

[0047] Therefore, the step of contacting the neutral salt solution with the weakly acidic cation exchange resin may be carried out, for example, by a batch process in which the weakly acidic cation exchanger is placed in a vessel containing the neutral salt solution, or the neutral salt solution may be contacted by passing it through a column packed with the weakly acidic cation exchanger.

[0048] For example, in the case of contact using a column, a pump inlet is connected to one end of the column and a pump outlet is connected to the other end of the column, and a neutral salt solution can be added to the circulation system to bring the neutral salt solution into contact with the weakly acidic cation exchanger.

[0049] Furthermore, when the neutral salt solution is passed through a column packed with a weakly acidic cation exchanger, for example, the neutral salt solution is contacted with the neutral salt solution until the pH of the solution after passing through the column is at least pH 5, at least pH 4.5, at least pH 4, at least pH 3.5, or at least pH 3. When circulating, since the pH of the solution after passing through is lowered, a base such as NaOH may be added to the solution after passing through to raise the pH and generate a neutral salt solution again, which may then be circulated through the column again.

[0050] More preferably, the contact is carried out until the pH of the resulting aqueous hypochlorous acid solution becomes higher than the pH at which chlorine gas is generated when the contact step between the neutral salt solution and the weakly acidic cation exchanger is completed and then the aqueous hypochlorite solution is contacted with the weakly acidic cation exchanger.

[0051] The pH higher than the pH at which chlorine gas is generated is the pH range at which chlorine gas is not substantially generated when the pH of the hypochlorite solution is lowered. In this specification, weak acidity includes the pH range at which chlorine gas is not substantially generated when the pH of an alkaline hypochlorite solution is lowered. For example, weak acidity refers to the range from weak acidity to neutrality, the pH range of about 3.5 to 7.5, particularly the range of 4.0 to 7.0.

[0052] "Not substantially generating chlorine gas" refers to not substantially generating chlorine gas at a level dangerous to living organisms, or not substantially confirming the generation of chlorine bubbles from the solution when the pH of the hypochlorite solution is lowered, or not substantially exhibiting the bleaching effect of chlorine when the pH of the hypochlorite solution is lowered. One of the criteria is that even if the generated hypochlorous acid aqueous solution is put into a cup or the like and directly smelled, the pungent odor peculiar to chlorine is hardly felt. In the technical field, it is generally considered that even at pH 4.0, chlorine gas is not substantially generated, and chlorine gas is not generated up to about pH 3.5. Therefore, the pH at which chlorine gas is generated includes the pH range below such a pH.

[0053] The amount of neutral salt solution to be brought into contact with the weakly acidic cation exchanger varies depending on the concentration of the neutral salt, the type of salt, the contacting method, etc., but is such that the pH of the resulting aqueous hypochlorous acid solution is higher than the pH at which the above-mentioned chlorine gas is generated.

[0054] As an example, the contact is carried out in an amount, for a time, and under conditions sufficient to exchange the H of a part of the exchange group of the weakly acidic cation exchanger, which has properties similar to those of a strongly acidic cation exchange resin, with the cations of the neutral salt solution. Appropriate conditions will depend on the weakly acidic ion exchanger used, and can be easily selected by one skilled in the art.

[0055] For example, the step of contacting the neutral salt solution with the weakly acidic cation exchanger can be carried out at room temperature. The contact of the neutral salt solution with the weakly acidic cation exchanger can be carried out for, for example, 10 minutes or more, 30 minutes or more, 1 hour or more, 2 hours or more, 3 hours or more, 5 hours or more, or 24 hours or more. The concentration of the neutral salt solution can be, for example, 1% or more, 2% or more, 3% or more, 5% or more, or 10% or more.

[0056] The weakly acidic cation exchanger to be contacted with the neutral salt solution is a regenerated weakly acidic cation exchanger that has not been substantially subjected to cation exchange.

[0057] Weakly acidic cation exchangers that have undergone ion exchange can be regenerated by treating them with an acid solution such as hydrochloric acid. For example, a weakly acidic cation exchanger that has been contacted with sodium hypochlorite undergoes ion exchange to produce the R-COONa type, but the exchange groups can be regenerated to the R-COOH type by treating with hydrochloric acid.

[0058] In addition, the H of the hydrochloric acid can be absorbed by the weakly acidic cation exchanger by contacting the hydrochloric acid generated by contacting a weakly acidic cation exchanger with sodium hypochlorite and contacting the hydrochloric acid with an R-COONa type weakly acidic cation exchanger that has already been ion-exchanged.

[0059] In addition, the weakly acidic cation exchanger is contacted with the neutral salt solution prior to the contact of the aqueous hypochlorite solution with the weakly acidic cation exchanger. In other words, the weakly acidic cation exchanger is pretreated before the actual production process of hypochlorous acid water.

[0060] After the step of contacting the weakly acidic cation exchanger with the neutral salt solution, the column can be washed with a solution such as water to flush out the neutral salt solution and the resulting strong acid solution. For example, a pump can be connected to a column to circulate the salt solution through the column packed with the weakly acidic cation exchanger, and then water can be flushed through the column to flush out the remaining salt solution and the resulting hydrochloric acid.

[0061] The thus treated weakly acidic cation exchanger has an ion exchange capacity, for example, in the weakly acidic to neutral range, that is, in the pH range of about 3.5 to 7.5, particularly in the pH range of 4.0 to 7.0.

[0062] Therefore, the pH of the solution after treatment with the weakly acidic cation exchange resin becomes weakly acidic or higher, for example, pH 3.5 or higher, so there is no risk of chlorine gas being generated and the sterilizing effect is high.

[0063] In addition, when such an ion exchange resin with a buffering effect adsorbs excess hydrogen ions, it does so while releasing the adsorbed sodium ions and calcium ions, so that the pH does not drop even partially below the pH at which chlorine gas is generated. In the reaction between the hypochlorite solution and the ion exchange resin with a buffering effect, the effect of lowering the pH is carried out by this ion exchange resin.

[0064] Therefore, the weakly acidic cation exchange resin used in the present invention does not temporarily or partially become lower than the pH that generates chlorine gas when lowering the pH of hypochlorite solution.When using an acid such as hydrochloric acid to lower the pH of hypochlorite solution as in the conventional method for producing hypochlorous acid, the acid with a pH that generates chlorine gas is mixed with the hypochlorite solution, so that the pH of the solution is temporarily or locally lowered to the pH that generates chlorine gas during the mixing process, and chlorine gas is generated.However, by using a weakly acidic cation exchange resin as in the present invention, chlorine gas is not generated.

[0065] In addition, the present application provides a regeneration method for a weakly acidic cation exchanger, which removes cations from a solution to be treated that contains a substance that loses its target property in a predetermined pH range lower than the solution to be treated described below and cations, and which can suppress the initial pH drop phenomenon of the reaction of the weakly acidic cation exchanger as much as possible.Note that the regeneration method for a weakly acidic cation exchanger according to this embodiment has a common concept with the above-mentioned method for preparing an aqueous hypochlorous acid solution, and the description of the overlapping parts may be omitted.

[0066] The regeneration method according to this embodiment is characterized in that it comprises an exchange capacity recovery process in which an acid solution is brought into contact with a weakly acidic cation exchanger that has been subjected to cation exchange to liberate and remove the cations trapped in the exchange groups, and a neutral salt solution contact process in which a neutral salt solution of a strong acid and a strong base is brought into contact with the weakly acidic cation exchanger that has been subjected to the exchange capacity recovery process in an amount such that a treated solution having a pH higher than the specified pH range and in which the substance exhibits the desired physical property when subjected to cation exchange in the treated solution is obtained.

[0067] The invention relating to the method for preparing the hypochlorous acid aqueous solution described above, and in particular the method for regenerating the weakly acidic cation exchanger, is based on the discovery that a weakly acidic cation exchange resin has properties similar to those of a strongly acidic cation exchange resin in the early stages of the reaction, and that, as a means for eliminating such properties, the weakly acidic cation exchange resin can be adjusted to have the theoretically expected reactivity by treating the weakly acidic cation exchange resin with a neutral salt solution of a strong acid and a strong base.

[0068] In other words, the applicants have discovered that even when a weakly acidic cation exchange resin that has been ion-exchanged into the R-COONa type is regenerated into the R-COOH type using a strong acid such as hydrochloric acid, it retains the properties of a strongly acidic cation exchange resin in the initial stage of the reaction, as described above, and have thus completed the present invention.

[0069] In theory, when a neutral salt is brought into contact with a strongly acidic cation exchange resin, it undergoes ion exchange to produce an acid, but when it is brought into contact with a weakly acidic cation exchange resin, it does not undergo ion exchange. However, in the method of the present invention, by bringing a weakly acidic cation exchange resin into contact with a neutral salt, in the early stage of the reaction, the part that has properties similar to those of the strongly acidic cation exchange resin is exchanged with the cations of the neutral salt solution. A weakly acidic cation exchange resin has a complex three-dimensional structure. For this reason, it is believed that there are areas where the ion exchange group (-COOH) is locally dense. It is presumed that the strong acidic properties arise in such areas where the ion exchange group (-COOH) is dense.

[0070] In the method of the present invention, after the portion having the properties of the strong acid cation exchange resin has been exchanged with the cations of the neutral salt solution, the weak acid cation exchange resin does not exchange with the cations of the neutral salt solution, as expected from the theory. Therefore, even if an excess amount of the neutral salt solution is brought into contact with the weak acid cation exchange resin, the treatment capacity of the weak acid cation exchange resin is not reduced.

[0071] The regeneration method for a weakly acidic cation exchanger according to this embodiment is a regeneration method applied to a weakly acidic cation exchanger that removes cations from a treatment solution that contains a predetermined substance and cations.

[0072] Here, the predetermined substance is a substance that loses its target property in a predetermined pH range lower than the pH of the solution to be treated.A typical example of such a substance is the preparation of hypochlorous acid aqueous solution using the above-mentioned aqueous solution of hypochlorite, in which the predetermined substance is hypochlorous acid or hypochlorite ion, and in a predetermined pH range lower than the pH of the solution to be treated, that is, under low pH such as pH 3.5 or below pH 3, hypochlorous acid decomposes and loses the strong bactericidal action characteristic of hypochlorous acid as the target property.

[0073] Of course, in the method for regenerating a weakly acidic cation exchanger according to this embodiment, the substance is not limited to hypochlorous acid, etc., and any substance that meets the situation in which some of the desired physical properties are lost, such as in the above-mentioned case, can be applied.

[0074] Specifically, the exchange capacity recovery treatment step can be realized by the same method as the regeneration treatment of the weakly acidic cation exchanger described above.

[0075] The neutral salt solution contact step is a step in which a neutral salt solution is brought into contact with the weakly acidic cation exchanger that has been subjected to the exchange capacity recovery treatment step.

[0076] The neutral salt solution is the same as described above, and is provided in an amount according to the concentration and mode of use so as to obtain a treated solution having a pH higher than the predetermined pH range at which the substance exhibits the desired physical property.

[0077] The predetermined pH range is a pH range lower than that of the solution to be treated and is a pH range in which the predetermined substance loses its target physical property. In the neutral salt solution contact step, the pH range in which the weakly acidic cation exchanger performs ion exchange is adjusted to a pH range higher than the predetermined pH range in which the aforementioned predetermined substance can exhibit its target physical property.

[0078] The solution after the neutral salt solution contact step may be contacted with a weakly acidic cation exchanger that has already been subjected to ion exchange.

[0079] By contacting a weakly acidic cation exchanger with a neutral salt, the part that has properties similar to those of a strongly acidic cation exchange resin is exchanged with the cations in the neutral salt solution, producing a strong acid. For example, when a weakly acidic cation exchange resin is contacted with saline solution, the part that has properties similar to those of a strongly acidic cation exchange resin is exchanged with the sodium ions in the saline solution, producing hydrochloric acid. The hydrochloric acid produced is highly reactive and dangerous, so it must be disposed of appropriately.

[0080] On the other hand, weakly acidic cation exchangers that have been ion-exchanged can be regenerated by treating them with hydrochloric acid. For example, a weakly acidic cation exchanger that has been contacted with sodium hypochlorite undergoes ion exchange to produce the R-COONa type, but can be regenerated to the R-COOH type by treating it with hydrochloric acid.

[0081] Therefore, by contacting the hydrochloric acid generated by contacting a weakly acidic cation exchanger with sodium hypochlorite with an R-COONa type weakly acidic cation exchanger that has already been ion-exchanged, the H of the hydrochloric acid can be absorbed by the weakly acidic cation exchanger.

[0082] In addition, when the resulting strong acid solution is brought into contact with a weakly acidic cation exchanger that has already been ion-exchanged, not only is the H of the strong acid exchanged, but on the other hand, the weakly acidic cation exchanger that has already been ion-exchanged is regenerated to the R-COOH type.

[0083] As mentioned above, it is possible to maintain a constant pH even when an excessive amount of weakly acidic cation exchange resin is used. However, since weakly acidic cation exchange resin also has the property of adsorbing mineral components such as calcium and magnesium in the solution, it is also possible to prevent whitening due to mineral components occurring in the device by leaving the weakly acidic cation exchange resin in the hypochlorous acid solution without removing it after lowering the pH of the hypochlorite solution by the method according to the present embodiment.

[0084] On the other hand, the strength of adsorption of weakly acidic cation exchange resins to various ions generally increases selectivity for ions with higher valences, but weakly acidic cation exchange resins are characterized by their extremely high selectivity for H ions in particular. Therefore, after H ions are exchanged for other cations, they can be easily returned to the R-COOH form using chemicals such as hydrochloric acid or sulfuric acid aqueous solutions. This makes them easy to regenerate when used repeatedly, and regeneration is possible with an amount of chemical slightly more than the theoretical chemical equivalent.

[0085] In addition, the bleaching power of sodium hypochlorite is considered to be due to the chlorination reaction caused by dissolved chlorine. In addition, the order of the factors that contribute to the bleaching power is considered to be dissolved chlorine>sodium hypochlorite>hypochlorous acid. According to the method of the present invention, hypochlorous acid can be produced without substantially generating dissolved chlorine, so hypochlorous acid with a low bleaching effect can be obtained. In addition, as described above, since dissolved chlorine is not substantially generated, chlorination reaction does not occur.

[0086] When there is a large amount of dissolved chlorine, the odor becomes very strong. However, according to the method of the present invention, hypochlorous acid can be produced without substantially generating dissolved chlorine, and therefore the odor due to chlorine is minimal.

[0087] Hereinafter, the method for preparing an aqueous hypochlorous acid solution and the method for regenerating a weakly acidic cation exchanger according to this embodiment will be described with reference to test results and the like.

[0088] [1. Construction of ion exchange unit] We filled a specified container with weakly acidic cation exchange resin to construct an ion exchange unit. We created a total of eight ion exchange units, four of each type with different capacities, large and small.

[0089] The container used was an ion exchange cylinder, which is a container consisting of a cylinder body with a bottom and a screw-top opening at the top, and a lid body with a water inlet and outlet that is screwed onto the screw-top opening to seal the inside of the cylinder, and is configured so that when the solution to be treated is supplied from the water inlet, it comes into contact with the ion exchange resin filled in the cylinder body and undergoes ion exchange, and the treated solution is discharged from the water outlet.

[0090] The cover is also provided with a straight water collection tube. This water collection tube is a tube that is disposed in the approximate center of the cylinder interior space from the cover to near the bottom of the cylinder body when the cover is screwed closed, and a trap is provided at the bottom end to prevent ion exchange resin from flowing out together with the discharged water, and the cover end is connected to the aforementioned water outlet. Therefore, the solution to be treated that reaches the upper part of the cylinder body space from the water inlet at a predetermined supply pressure permeates downward from the upper part of the ion exchange resin bed, weaving through the gaps in the ion exchange resin and being led out from the bottom through the water collection tube, so that the solution to be treated that has been in sufficient contact with the ion exchange resin can be obtained as a treated solution.

[0091] Weakly acidic cation exchange resin was Diaion acrylic weakly acidic cation exchange resin WK40L manufactured by Mitsubishi Chemical Corporation. Eight ion exchange cylinders were filled with weakly acidic cation exchange resin swollen with water to create an ion exchange unit. Of the eight ion exchange units created, four were filled with 10 L of weakly acidic cation exchange resin, and the other four were filled with 20 L of weakly acidic cation exchange resin.

[0092] 2. Creation of a regenerated ion exchange unit Next, in order to compare with an ion exchange unit using a new weakly acidic cation exchange resin, an ion exchange unit packed with the regenerated weakly acidic cation exchange resin was produced.

[0093] First, the ion exchange capacity of two of the four ion exchange units filled with 10 L and two of the four ion exchange units filled with 20 L was temporarily reduced by performing ion exchange with a sufficient amount of sodium hypochlorite aqueous solution.

[0094] Next, a predetermined amount of hydrochloric acid of a predetermined concentration was supplied to and passed through the four ion exchange units with reduced ion exchange capacity to release and remove the sodium trapped in the exchange groups, thereby performing an exchange capacity recovery process to create regenerated ion exchange units (a total of four units: two 10 L units and two 20 L units).

[0095] [3. Neutral salt solution contact treatment] Next, in order to compare the results with and without neutral salt solution treatment, an ion exchange unit that had been subjected to neutral salt solution treatment was prepared.

[0096] Specifically, a neutral salt solution contact treatment was performed on each of the following ion exchange units (4 units in total): an ion exchange unit filled with 10 L of weakly acidic cation exchange resin that had not been regenerated (new), an ion exchange unit filled with 10 L of weakly acidic cation exchange resin that had been regenerated, an ion exchange unit filled with 20 L of weakly acidic cation exchange resin that had not been regenerated (new), and an ion exchange unit filled with 20 L of weakly acidic cation exchange resin that had been regenerated. After the neutral salt solution contact treatment, sodium chloride was removed by passing water through each unit.

[0097] By carrying out this series of operations on the ion exchange unit, a new ion exchange unit (hereinafter also referred to as ion exchange unit NSn10L) was filled with 10 L of weakly acidic cation exchange resin that had not been subjected to neutral salt solution contact treatment ("S"alt) ("n"ot applied) and a new ion exchange unit (hereinafter also referred to as ion exchange unit NSn10L) that had not been subjected to neutral salt solution contact treatment ("S"alt) ("n"ot applied) were filled with 10 L of weakly acidic cation exchange resin. The ion exchange unit was packed with 20 L of weakly acidic cation exchange resin that had been regenerated (hereinafter also referred to as ion exchange unit NSn20L), the ion exchange unit was packed with 10 L of new ("N"ew) weakly acidic cation exchange resin that had been subjected to neutral salt solution contact treatment ("Sa"alt) (hereinafter also referred to as ion exchange unit NSa10L), the ion exchange unit was packed with 20 L of new ("N"ew) weakly acidic cation exchange resin that had been subjected to neutral salt solution contact treatment ("Sa"alt) (hereinafter also referred to as ion exchange unit NSa20L), and the ion exchange unit was packed with 20 L of new ("N"ew) weakly acidic cation exchange resin that had been regenerated ("Regeneration") but not subjected to neutral salt solution contact treatment ("Sa"alt) (hereinafter also referred to as ion exchange unit NSa20L). Eight types of ion exchange units were prepared for the following pH confirmation test: an ion exchange unit packed with 10 L of weakly acidic cation exchange resin that had been regenerated ("Regeneration") but not contacted with a neutral salt solution ("Sa"alt) (hereinafter also referred to as ion exchange unit RSn10L); an ion exchange unit packed with 20 L of weakly acidic cation exchange resin that had been regenerated ("Regeneration") but not contacted with a neutral salt solution ("Sa"alt) (hereinafter also referred to as ion exchange unit RSn20L); an ion exchange unit packed with 10 L of weakly acidic cation exchange resin that had been regenerated ("Regeneration") and contacted with a neutral salt solution ("Sa"alt) (hereinafter also referred to as ion exchange unit RSa10L); and an ion exchange unit packed with 20 L of weakly acidic cation exchange resin that had been regenerated ("Regeneration") and contacted with a neutral salt solution ("Sa"alt) (hereinafter also referred to as ion exchange unit RSa20L).

[0098] [4. pH confirmation test] Next, a test was conducted to confirm how the pH changed when an aqueous hypochlorite solution was passed through the ion exchange unit.

[0099] Specifically, a 200 ppm aqueous sodium hypochlorite solution was flowed at 10 L / min into ion exchange units NSn10L, NSa10L, RSn10L, and RSa10L, which were filled with 10 L of weakly acidic cation exchange resin, and a 250 ppm aqueous sodium hypochlorite solution was flowed at 10 L / min into ion exchange units NSn20L, NSa20L, RSn20L, and RSa20L, which were filled with 20 L, and the pH of the treated solution, the aqueous hypochlorous acid solution, was measured every time 20 L or 50 L was discharged.

[0100] (4-1.10L filled ion exchange unit) FIG. 1 shows the results of comparing NSn10L, an ion exchange unit packed with 10 L of new weakly acidic cation exchange resin, which has not been subjected to a neutral salt solution contact step, with NSa10L, which has been subjected to a neutral salt solution contact step.

[0101] As shown in Figure 1, the pH of the ion exchange unit NSn10L was low at 3.20 when it was first discharged, and was 3.40 when 40 L had been discharged. In addition, a strong irritating odor of chlorine was sensed from the treated solution when it was first discharged, and the irritating odor of chlorine was also sensed from the treated solution when 40 L had been discharged.

[0102] After that, 3.60 (50 L), 4.10 (100 L), 4.60 (160 L), and 4.90 (200 L) of treated solution were discharged from the ion exchange unit NSn10L, and the irritating odor of chlorine was no longer noticeable. Furthermore, there was no significant change in pH until 440 L was discharged (pH 5.10), and the irritating odor of chlorine was no longer noticeable.

[0103] In contrast, the ion exchange unit NSa10L that had undergone the neutral salt solution contact step had a pH of 6.08 from the beginning of discharge, and then discharged treated solutions of 5.92 (50L), 5.93 (100L), 5.92 (160L), and 5.91 (200L). In addition, no irritating odor due to chlorine was felt from any of the treated solutions. In addition, there was no significant change in pH until the time of discharge of 440L (pH 5.83), and no irritating odor due to chlorine was felt. In addition, the pH of the discharged treated solution changed very little from the beginning of discharge to the time of discharge of 440L, from pH 6.08 to 5.83, which showed that it was possible to produce a treated solution with a stable pH compared to when the neutral salt solution contact step had not been performed.

[0104] Although not shown in the figure, this tendency was also observed in the comparison results between RSn10L, an ion exchange unit packed with 10 L of regenerated weakly acidic cation exchange resin and not subjected to a neutral salt solution contact process, and RSa10L, which had undergone a neutral salt solution contact process.

[0105] Specifically, the pH of the ion exchange unit RSn10L was low at 3.10 when it was first discharged, and was 3.43 when 40 L had been discharged. In addition, a strong irritating odor of chlorine was sensed from the treated solution when it was first discharged, and the irritating odor of chlorine was also sensed from the treated solution when 40 L had been discharged.

[0106] After that, 3.50 (50 L) was discharged from the ion exchange unit RSn10L, and thereafter, treated solution with a pH of 3.5 or more was discharged, tending to approach approximately pH 5. In addition, after the pH reached 3.50 or more, no irritating odor of chlorine was felt.

[0107] In contrast, the ion exchange unit RSa10L, which had been through the neutral salt solution contact process, had a pH of 5.60 from the beginning of discharge, and discharged treated solutions with roughly the same pH thereafter. In addition, no irritating odor of chlorine was detected from any of the treated solutions.

[0108] (4-2.20L filled ion exchange unit) Next, Figure 2 shows the results of comparing NSn20L, an ion exchange unit packed with 20 L of new weakly acidic cation exchange resin, which has not undergone a neutral salt solution contact process, with NSa20L, which has undergone a neutral salt solution contact process.

[0109] As shown in Figure 2, the pH of the ion exchange unit NSn20L was extremely low at 3.00 at the beginning of discharge, and was 3.10 when 40 L had been discharged. This tendency for low pH was still observed even when the discharge volume reached 100 L (pH 3.40). Although clarification is awaited in future research, this phenomenon is thought to be due to an increase in the portion of the bed formed by packing the weakly acidic cation exchange resin that has properties similar to those of strongly acidic cation exchange resin compared to NSn10L, which has a smaller packing volume, causing the pH to rise more slowly.

[0110] In addition, a strong, irritating odor of chlorine was detected from the treated solution immediately after it was discharged, and the irritating odor of chlorine was still detected from the treated solution after 100 L had been discharged.

[0111] After that, 3.50 (150 L), 3.60 (200 L), 3.80 (250 L), and 3.90 (300 L) of treated solution were discharged from the ion exchange unit NSn20L, and the irritating odor of chlorine was no longer felt. In addition, although not shown in the figure, the irritating odor of chlorine was not felt even when the discharge volume exceeded 400 L.

[0112] In contrast, the ion exchange unit NSa20L that had been through the neutral salt solution contact step had a pH of 5.54 from the beginning of discharge, and then discharged treated solutions of 5.45 (50 L), 5.38 (100 L), 5.42 (150 L), and 5.40 (200 L). In addition, no irritating odor due to chlorine was felt from any of the treated solutions. In addition, no significant change in pH was observed until the point at which 300 L was discharged (pH 5.41), or even until the discharge amount exceeded 400 L (not shown), and no irritating odor due to chlorine was felt. It is noteworthy that when comparing the ion exchange units NSa10L and NSa20L with different filling amounts, the discharged treated solution of NSa20L with a larger filling amount had an extremely small pH change from the beginning of discharge and was stable, which tends to be preferable in terms of the nature of the present invention. This is an extremely interesting result, considering that in the case of NSn10L and NSn20L, which were not treated with a neutral salt solution, the larger the volume, the more significantly and prolonged the initial pH drop in the reaction, which is undesirable.

[0113] In addition, although not shown in the figure, this tendency was also observed in the comparison results between RSn20L, an ion exchange unit packed with 20 L of regenerated weakly acidic cation exchange resin and not subjected to a neutral salt solution contact process, and RSa20L, which had undergone a neutral salt solution contact process.

[0114] Specifically, the pH of the ion exchange unit RSn20L was low at 3.10 when it was first discharged, and was 3.45 when 100 L had been discharged. In addition, a strong irritating odor of chlorine was sensed from the treated solution when it was first discharged, and the irritating odor of chlorine was also sensed from the treated solution when 100 L had been discharged.

[0115] After that, 3.50 (150 L) was discharged from the ion exchange unit RSn20L, and thereafter, treated solution with a pH of 3.5 or higher was discharged at a rate that would have exceeded pH 4. In addition, after the pH reached 3.50 or higher, no irritating odor due to chlorine was detected.

[0116] In contrast, the ion exchange unit RSa20L, which had been through the neutral salt solution contact process, had a pH of 5.60 from the beginning of discharge, and discharged treated solutions with roughly the same pH thereafter. In addition, no irritating odor due to chlorine was detected from any of the treated solutions.

[0117] Considering these test results, it was shown that the method for preparing a hypochlorous acid aqueous solution according to the present embodiment can obtain a weakly acidic hypochlorous acid aqueous solution having a pH of about 3.5 to 7 without substantially generating chlorine gas, even when using a weakly acidic cation exchange resin immediately after regeneration or a new one.

[0118] In addition, taking into account the results of the regenerated ion exchange units RSn10L, RSa10L, RSn20L, and RSa20L, it was shown that the regeneration treatment method for a weakly acidic cation exchanger according to this embodiment can minimize the decrease in pH during the initial reaction of the weakly acidic cation exchanger.

[0119] Furthermore, by carrying out the above-mentioned operations, the pH range for ion exchange of the weakly acidic cation exchanger can be adjusted to the theoretical pH value.

[0120] In other words, the present application also includes the following invention, which was made in consideration of the background that there is a need for a means to prevent a weakly acidic cation exchange resin from exhibiting ion exchange capacity below the theoretical ion exchange range, i.e., at a pH of about 3.5 to 7.0 or less. (a) A method for adjusting the pH range for ion exchange of a weakly acidic cation exchanger, comprising the step of contacting the weakly acidic cation exchanger with a neutral salt solution. (b) The method according to (a), further comprising a step of contacting the solution after the neutral salt treatment step with a weakly acidic cation exchanger that has been subjected to ion exchange. (c) The method of (a), wherein the neutral salt solution is a saline solution. (d) A method for producing a hypochlorous acid solution, comprising the steps of contacting the weakly acidic cation exchanger with a neutral salt solution and contacting the weakly acidic cation exchanger with a hypochlorite solution.

[0121] According to these inventions, the reaction pH of the weakly acidic cation exchanger can be about pH 3.5 or more. Also, according to the present invention, when producing a hypochlorous acid solution using a weakly acidic cation exchanger, the pH of the hypochlorous acid solution can be easily adjusted without lowering the pH of the solution below the pH at which chlorine is generated (i.e., less than pH 3.5).

[0122] Finally, the above-mentioned embodiments are merely examples of the present invention, and the present invention is not limited to the above-mentioned embodiments. Therefore, even if the above-mentioned embodiments are different, various modifications can be made depending on the design, etc., as long as they do not deviate from the technical idea of ​​the present invention.

Claims

1. A method for preparing an aqueous solution of hypochlorous acid, comprising contacting an aqueous solution of hypochlorite with a weakly acidic cation exchanger to exchange cations constituting the hypochlorite with hydrogen ions and thereby increasing the concentration of hypochlorous acid in the aqueous solution, A method for preparing an aqueous hypochlorous acid solution, comprising contacting a neutral salt solution of a strong acid and a strong base in an amount such that the aqueous hypochlorous acid solution has a pH of 3.5 or higher when the aqueous hypochlorite solution is contacted with a weakly acidic cation exchanger that has been regenerated or has not been substantially subjected to cation exchange prior to contacting the aqueous hypochlorite solution with the weakly acidic cation exchanger.

2. A method for regenerating a weakly acidic cation exchanger, which removes cations from a solution to be treated that contains a substance that loses a target property in a predetermined pH range lower than that of the solution to be treated, comprising the steps of: an exchange capacity recovery treatment step in which an acid solution is brought into contact with the weakly acidic cation exchanger that has been subjected to cation exchange to release and remove the cations trapped in the exchange groups; a neutral salt solution contacting step in which a neutral salt solution of a strong acid and a strong base is contacted with the weakly acidic cation exchanger that has undergone the exchange capacity recovery treatment step in an amount that results in a treated solution having a pH higher than the specified pH range and in which the substance exhibits the desired physical property when subjected to cation exchange in the treated solution.

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