JP2015124110A - Process for preparing sodium hypochlorite aqueous solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for preparing in high yield a low-salt sodium hypochlorite aqueous solution.SOLUTION: The process for preparing a low-salt sodium hypochlorite aqueous solution is characterized in comprising steps of: (1) feeding a 30 to 60 mass% sodium hydroxide aqueous solution into a reaction vessel; (2) introducing a chlorine gas diluted with inert gas, into the sodium hydroxide aqueous solution fed into the reaction vessel, and carrying out a chlorination reaction at reaction temperature of 20°C to 50°C; and (3) obtaining a sodium hypochlorite aqueous solution by separating and removing the by-product sodium chloride crystallized in the step (2), from the reaction mixture.

Description

  The present invention relates to a method for efficiently producing an aqueous sodium hypochlorite solution having a low sodium chloride concentration and a low chloric acid concentration.

  Sodium hypochlorite (NaClO) is known to have an excellent bactericidal action and bleaching action, and is generally in the form of an aqueous solution, as a general industrial chemical, for pools, waterworks, sewers, households, etc. It is widely used as a sterilizing application, or as a bleaching application or wastewater treatment chemical in the paper industry, textile industry, and the like.

  As the sodium hypochlorite aqueous solution, generally, a general-purpose sodium hypochlorite aqueous solution containing about 10% by mass of sodium chloride as a reaction by-product based on an effective chlorine concentration of 12% by mass, and a sodium chloride concentration Is commercially available with a low sodium hypochlorite aqueous solution of 4% by mass or less.

  As a method for producing a low-sodium sodium hypochlorite aqueous solution, Patent Document 1 uses a caustic soda aqueous solution having a concentration of 34 to 38% by weight, and maintains the reaction temperature at 24 to 29 ° C. while maintaining the caustic soda and chlorine gas. To produce a high concentration sodium hypochlorite aqueous solution having an effective chlorine concentration of 26.5 to 29% by weight, and then separating the salt precipitated in the high concentration sodium hypochlorite aqueous solution and diluting with water Thus, a method of obtaining an aqueous sodium hypochlorite solution having an effective chlorine concentration of 12% by weight or more, a salt concentration of 4% by weight or less, and a chloric acid concentration of 0.2 mg / L or less has been proposed. In addition, the mg / L unit in patent document 1 represents the chloric acid concentration when 100 mg of sodium hypochlorite is added to 1 liter of tap water, and the chloric acid concentration of the sodium hypochlorite aqueous solution is It corresponds to 2000wtppm.

  Here, since chlorination is an exothermic reaction and sodium chloride crystals are by-produced, the higher the reaction temperature, the lower the energy required for heat removal, and the prevention of scaling of the salt crystals to the cooling coil. Can do. However, when the reaction temperature is high, the amount of decomposition of sodium hypochlorite increases, and particularly at 40 ° C. or higher, the decomposition proceeds rapidly, so that the basic unit is greatly deteriorated (see Non-Patent Document 1). Patent Document 1 describes that sodium hypochlorite is rapidly decomposed at a temperature of 30 ° C. or higher. In other literatures, there is no example of obtaining sodium hypochlorite in a yield exceeding 90% at a reaction temperature higher than 30 ° C., particularly at a reaction temperature higher than 35 ° C.

  Patent Document 2 discloses a method for producing a sodium hypochlorite aqueous solution by using washed purified chlorine gas, and its 0042 paragraph describes that "the reaction between chlorine gas and sodium hydroxide aqueous solution is Preferably it is 15-45 degreeC, More preferably, it is 20-40 degreeC, More preferably, it is 25-30 degree C. By making reaction temperature 15-45 degreeC, sodium hypochlorite aqueous solution with low salt concentration is stabilized. It is possible to manufacture the system in a standard manner. " However, when the present inventors conducted an experiment in which chlorine gas and an aqueous sodium hydroxide solution were reacted at a reaction temperature of 40 ° C. by the method of Patent Document 2, side reactions and decomposition reactions proceeded, and the basic unit was greatly reduced. It was confirmed that it would decrease.

JP 2009-132583 A Japanese Patent No. 4308810

Japan Soda Industry Association Soda Handbook Editing Working Group, “Soda Technology Handbook 2009”, Japan Soda Industry Association, page 212

  An object of the present invention is to provide a method for producing a low-sodium sodium hypochlorite aqueous solution at a relatively high reaction temperature, preferably at a reaction temperature of 30 ° C. or higher, and in a high yield.

  As a result of intensive studies, the present inventors have solved the above problem by diluting chlorine gas with an inert gas such as nitrogen in a method for producing a sodium hypochlorite aqueous solution in which chlorine gas is introduced into a sodium hydroxide aqueous solution. The inventors have found that this can be solved, and have completed the present invention. That is, the present invention relates to the following matters.

  [1] A step (1) of supplying a 30-60 mass% sodium hydroxide aqueous solution to the reaction vessel, and introducing chlorine gas diluted with an inert gas into the sodium hydroxide aqueous solution supplied to the reaction vessel A step (2) of performing a chlorination reaction at a reaction temperature of 20 ° C. to 50 ° C., and separating and removing the by-product sodium chloride precipitated in the step (2) from the reaction solution, thereby removing an aqueous sodium hypochlorite solution. And a step (3) for obtaining a low-sodium sodium hypochlorite aqueous solution.

[2] The method for producing a low-sodium sodium hypochlorite aqueous solution according to item [1], wherein the concentration of chlorine gas diluted with the inert gas is 5 to 95% by volume.
[3] The item [1] or [2], wherein in the chlorination reaction, a molar ratio (NaOH / Cl ₂ ) between sodium hydroxide and chlorine gas introduced is 2.0 to 2.5. A method for producing a low-sodium sodium hypochlorite aqueous solution.

[4] The method for producing a low-sodium sodium hypochlorite aqueous solution according to any one of items [1] to [3], wherein the reaction temperature in the step (2) is 30 to 50 ° C.
[5] The low salt according to any one of Items [1] to [4], wherein the sodium hypochlorite aqueous solution obtained in the step (3) has a sodium chloride concentration of 5.0% by mass or less. Manufacturing method of sodium hypochlorite aqueous solution.

  [6] The low value according to any one of items [1] to [5], wherein the sodium hypochlorite aqueous solution obtained in the step (3) has a chlorate ion concentration of 1.5% by mass or less. A method for producing a sodium hypochlorite aqueous solution.

  [7] The sodium hypochlorite concentration in the aqueous sodium hypochlorite solution obtained in the step (3) is 30 to 40% by mass, according to any one of items [1] to [6]. A method for producing a low-sodium sodium hypochlorite aqueous solution.

  [8] including a step of diluting the low-sodium sodium hypochlorite aqueous solution obtained by the production method according to any one of items [1] to [7] with water to a predetermined effective chlorine concentration A method for producing a dilute aqueous sodium hypochlorite solution characterized by

  [9] The method for producing a diluted aqueous sodium hypochlorite solution according to item [8], wherein the effective chlorine concentration is 1 to 20% by mass.

  According to the present invention, a low-sodium sodium hypochlorite aqueous solution can be produced in a high yield at a high reaction temperature advantageous in terms of cost and equipment maintenance.

Hereinafter, the manufacturing method of the sodium hypochlorite aqueous solution which concerns on this invention is demonstrated in detail.
The method for producing the low-sodium sodium hypochlorite aqueous solution of the present invention comprises:
Supplying a 30-60 mass% aqueous sodium hydroxide solution to the reaction vessel (1);
A step (2) of introducing a chlorine gas diluted with an inert gas into a sodium hydroxide aqueous solution supplied to the reaction tank to cause a chlorination reaction at a reaction temperature of 20 ° C. to 50 ° C .;
A step (3) of obtaining a sodium hypochlorite aqueous solution by separating and removing the by-product sodium chloride precipitated in the step (2) from the reaction solution.

  The density | concentration of the raw material sodium hydroxide aqueous solution supplied to a reaction tank at a process (1) is 30-60 mass% normally, Preferably it is 35-55 mass%, More preferably, it is 40-50 mass%. When the concentration of the raw material sodium hydroxide aqueous solution is lower than the above range, it tends to be difficult to produce a desired sodium chloride aqueous solution having a low salt concentration. On the other hand, when the concentration of the raw material sodium hydroxide aqueous solution is higher than the above range, a complicated operation such as distillation may be required to adjust the sodium hydroxide aqueous solution having a predetermined concentration.

  The reaction temperature in the chlorination reaction in the step (2) is usually 20 ° C to 50 ° C, preferably 30 ° C to 50 ° C, more preferably 30 ° C to 40 ° C. When the reaction temperature is lower than the above range, the cooling coil is likely to be scaled. On the other hand, when the reaction temperature is higher than the above range, the rate of progress of decomposition of sodium hypochlorite is high and the basic unit tends to decrease.

The reaction time in the chlorination reaction in step (2) is preferably 10 to 200 minutes, more preferably 50 to 150 minutes, and particularly preferably 70 to 130 minutes.
In the chlorination reaction of the step (2), the molar ratio of sodium hydroxide to chlorine gas (NaOH / Cl ₂ ) to be introduced is preferably 2.0 to 2.5, more preferably 2.01 to 2. 30, more preferably 2.02 to 2.20. When the molar ratio of sodium hydroxide and chlorine gas is lower than the above range, the perchlorination tends to proceed, while when higher than the above range, the concentration of sodium hydroxide remaining in the obtained sodium hypochlorite aqueous solution Is not preferable in terms of quality.

In step (2), by introducing chlorine gas into the aqueous sodium hydroxide solution, the reaction of the following formula proceeds to produce sodium hypochlorite.
2NaOH + Cl ₂ → NaClO + NaCl + H ₂ O

  In this chlorination reaction, sodium hypochlorite and sodium chloride (salt) in an equimolar amount are produced, but when a sodium hydroxide aqueous solution having the above concentration is used as a raw material, crystals of sodium chloride having low solubility are precipitated. By removing this, a low sodium chloride concentration and high concentration sodium hypochlorite aqueous solution is obtained.

  Here, in the water supply law, not only the above-mentioned sodium chloride but also chloric acid tends to become more restrictive as impurities in the sodium hypochlorite aqueous solution. In order to reduce this chloric acid, it is said that it is necessary to keep reaction temperature at 26-29 degreeC like patent document 1, for example. This is because the cause of the generation of chloric acid is considered to be “natural decomposition” and “side reaction” as described below.

The “spontaneous decomposition” is a phenomenon in which sodium hypochlorite is naturally decomposed, and it is said that the decomposition proceeds rapidly particularly at 40 ° C. or higher (see Non-Patent Document 1). This decomposition is represented by the following reaction, which produces sodium chlorate (NaClO ₃ ).
NaClO → NaCl + O
2NaClO → NaCl + NaClO ₂
NaClO + NaClO ₂ → NaCl + NaClO ₃

The “side reaction” is a side reaction that occurs when sodium hydroxide and chlorine are reacted. It is assumed that sodium chlorate is by-produced by the following reaction.
_{6NaOH + 3Cl 2 → NaClO 3 +} 5NaCl + 3H 2 O

  Such natural decomposition and side reaction both reduce the basic unit of sodium hypochlorite with respect to chlorine in the reaction system. In other words, the production of sodium chlorate reduces the basic unit, and suppressing the production of sodium chlorate means improving the basic unit.

  These two phenomena are unavoidable reactions, and especially at high temperatures, which are advantageous in terms of cost and equipment maintenance, spontaneous decomposition proceeds rapidly. It was considered very difficult to obtain an aqueous sodium acid solution.

  However, as a result of intensive studies by the present inventors, in a method in which chlorine gas is blown into a sodium hydroxide aqueous solution while stirring with a stirring blade, both “natural decomposition” and “side reaction” generate chloric acid to produce the raw material. It turns out that it is not the main factor which reduces a unit. That is, in addition to “natural decomposition” and “side reaction”, it is considered that a reaction causing chloric acid production and reduction of the basic unit occurs.

Therefore, the inventors focused on “perchlorination”. According to Non-Patent Document 1, the term “perchlorination” means that when the chlorination reaction is completed and the caustic soda disappears, the following decomposition reaction occurs in a chain, and all the sodium hypochlorite is rapidly decomposed. It is a phenomenon that does.
NaClO + Cl ₂ + H ₂ O → NaCl + 2HClO
NaClO + 2HClO → NaClO ₃ + 2HCl
NaClO + 2HCl → NaCl + H ₂ O + Cl ₂

  This perchlorination is considered to be a runaway reaction that occurs when chlorine is supplied to sodium hydroxide more than necessary, but the present inventors are not limited to such conditions, but near the chlorine gas inlet. It was thought that perchlorination occurred locally. That is, it is thought that chlorine gas is reacting with sodium hypochlorite by decreasing the sodium hydroxide concentration and increasing the sodium hypochlorite concentration near the chlorine gas inlet. Then, according to the above reaction formula, sodium hypochlorite is decomposed to produce sodium chlorate, and chlorine is regenerated by perchlorination. In addition, since the sodium hydroxide concentration is sufficient outside the vicinity of the chlorine gas inlet, the regenerated chlorine is consumed. Therefore, although all sodium hypochlorite does not decompose rapidly, sodium hypochlorite in the vicinity of the inlet is decomposed into chloric acid, resulting in a decrease in basic unit.

  Based on such knowledge found by the present inventors, in the present invention, the introduced chlorine gas is diluted with an inert gas in order to suppress the above-mentioned local perchlorination. Thereby, the chlorine concentration in the vicinity of the blowing port decreases, and local perchlorination can be suppressed. Moreover, since the inert gas for dilution also has the effect of stirring the reaction solution, it is possible to increase the degree of dispersion in the system and further suppress perchlorination.

  The inert gas in the present invention is a gas that hardly causes a chemical reaction with chlorine or oxygen. Specific examples include rare gas elements such as helium, neon, and argon, and nitrogen gas. In the present invention, air and carbon dioxide are also considered as inert gases.

  As a method of diluting the chlorine gas of the raw material, for example, a method of adjusting chlorine diluted to a predetermined concentration in advance, a method of combining 100% chlorine gas and inert gas from different lines into the same blowing nozzle, etc. Is mentioned.

  The concentration of chlorine gas diluted with an inert gas is preferably 5 to 95% by volume, more preferably 20 to 80% by volume, and particularly preferably 30 to 70% by volume as the chlorine concentration. When the concentration of the diluted chlorine gas is higher than the above range, a sufficient perchlorination suppressing effect may not be obtained. On the other hand, if the concentration of the diluted chlorine gas is lower than the above range, the efficiency of the chlorination reaction tends to be reduced, and it is not economical. Further, the reaction liquid is scattered in the reaction tank by blowing out the inert gas. There is.

  In the step (3), by-product sodium chloride precipitated in the step (2) is separated and removed from the reaction solution using a solid-liquid separation device such as a centrifuge or a filter. Thereby, a sodium hypochlorite aqueous solution having a sodium hypochlorite concentration of preferably 30 to 40% by mass, more preferably 32 to 38% by mass is obtained.

  The sodium chloride concentration of the sodium hypochlorite aqueous solution obtained in the step (3) is preferably 5.0% by mass or less, more preferably 1.0 to 5.0% by mass, and particularly preferably 3.0 to 4.%. 8% by mass.

  Moreover, the chlorate ion concentration of the sodium hypochlorite aqueous solution obtained in the step (3) is preferably 1.5% by mass or less, more preferably 0.01 to 1.2% by mass, and particularly preferably 0.05. It is -1.0 mass%. Thus, since the low salt sodium hypochlorite aqueous solution obtained by the manufacturing method of this invention has the low concentration of chloric acid which is an impurity, it is fully product worth as a low sodium chlorite hypochlorite aqueous solution.

  A method for producing a dilute aqueous sodium hypochlorite solution of the present invention is obtained by diluting a low-sodium sodium hypochlorite aqueous solution obtained by the above-described method for producing a low-sodium sodium hypochlorite aqueous solution with water. The method includes the step of setting the effective chlorine concentration.

  The effective chlorine concentration is preferably 1 to 20% by mass, more preferably 2 to 17% by mass, and particularly preferably 3 to 15% by mass.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to these Examples at all.
[Example 1]
To a reaction vessel equipped with a stirrer, a coil cooler, and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied at 1514 kg / hr as a raw material while stirring, and this sodium hydroxide aqueous solution was brought to 40 ° C. While maintaining, 560 kg / hr of chlorine gas was diluted with nitrogen gas to 50 volume% and introduced, and the chlorination reaction was performed so that the residence time was about 100 minutes.

  By extracting 2074 kg / hr of the reactant slurry from the reaction vessel and performing solid-liquid separation with a centrifuge, the precipitated sodium chloride 682 kg / hr, the sodium hypochlorite concentration is 34.5% by mass, the sodium chloride concentration Was 4.5% by mass, and a low-sodium sodium hypochlorite aqueous solution 1390 kg / hr having a chlorate ion concentration of 0.41% by mass was obtained. The yield at this time was 95.9%. The yield is a value calculated from the number of moles of sodium hypochlorite obtained on the basis of the introduced chlorine gas (the same applies hereinafter).

  The dilute sodium hypochlorite aqueous solution obtained by diluting the obtained low sodium hypochlorite aqueous solution with pure water to adjust the effective chlorine concentration to 13% by mass has a sodium chloride concentration of 1.8% by mass and a chlorate ion concentration. Was 0.16% by mass.

[Example 2]
While stirring, a 45 mass% sodium hydroxide aqueous solution was supplied at 1512 kg / hr to a reaction vessel equipped with a stirrer, a coil cooler, and an external circulation type cooler. While maintaining, 560 kg / hr of chlorine gas was diluted with nitrogen gas to 50 volume% and introduced, and the chlorination reaction was performed so that the residence time was about 100 minutes.

  By extracting 2072 kg / hr of the reactant slurry from the reaction vessel and performing solid-liquid separation with a centrifuge, the precipitated sodium chloride was 680 kg / hr, the sodium hypochlorite concentration was 35.4% by mass, the sodium chloride concentration Was 4.2% by mass, and a low-sodium sodium hypochlorite aqueous solution 1390 kg / hr having a chlorate ion concentration of 0.29% by mass was obtained. The yield at this time was 97.3%.

  The dilute sodium hypochlorite aqueous solution obtained by diluting the obtained low sodium hypochlorite aqueous solution with pure water to adjust the effective chlorine concentration to 13% by mass has a sodium chloride concentration of 1.6% by mass and a chlorate ion concentration. Was 0.11% by mass.

[Example 3]
To a reaction vessel equipped with a stirrer, a coil cooler, and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied at 1513 kg / hr as a raw material while stirring, and this sodium hydroxide aqueous solution was brought to 30 ° C. While being maintained, 556 kg / hr of chlorine gas was diluted with nitrogen gas to 95% by volume and introduced, and the chlorination reaction was performed so that the residence time was about 100 minutes.

  By extracting 2069 kg / hr of the reactant slurry from the reaction vessel and performing solid-liquid separation with a centrifugal separator, 642 kg / hr of precipitated sodium chloride and a sodium hypochlorite concentration of 33.3% by mass were obtained. Was 4.4% by mass, and a low-sodium sodium hypochlorite aqueous solution 1427 kg / hr having a chlorate ion concentration of 0.84% by mass was obtained. The yield at this time was 93.1%.

  The dilute sodium hypochlorite aqueous solution obtained by diluting the obtained low sodium hypochlorite aqueous solution with pure water to adjust the effective chlorine concentration to 13% by mass has a sodium chloride concentration of 1.8% by mass and a chlorate ion concentration. Was 0.34 mass%.

[Example 4]
To a reaction vessel equipped with a stirrer, a coil cooler and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied at 1503 kg / hr as a raw material while stirring, and this sodium hydroxide aqueous solution was brought to 30 ° C. While being maintained, 556 kg / hr of chlorine gas was diluted with nitrogen gas to 80% by volume and introduced, and the chlorination reaction was performed so that the residence time was about 100 minutes.

  By extracting 2059 kg / hr of the reactant slurry from the reaction vessel and performing solid-liquid separation with a centrifuge, the precipitated sodium chloride 672 kg / hr, the sodium hypochlorite concentration is 34.5% by mass, the sodium chloride concentration Of 4.1% by mass and a low salt sodium hypochlorite aqueous solution of 1387 kg / hr having a chlorate ion concentration of 0.41% by mass was obtained. The yield at this time was 95.6%.

  The obtained sodium hypochlorite aqueous solution prepared by diluting the low-sodium sodium hypochlorite aqueous solution with pure water to adjust the effective chlorine concentration to 13% by mass has a sodium chloride concentration of 1.6% by mass and a chlorate ion concentration. It was 0.16 mass%.

[Example 5]
To a reaction vessel equipped with a stirrer, a coil cooler and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied at 1505 kg / hr as a raw material while stirring, and this sodium hydroxide aqueous solution was brought to 30 ° C. While maintaining, 552 kg / hr of chlorine gas was introduced after being diluted to 67 volume% with nitrogen gas, and the chlorination reaction was performed so that the residence time was about 100 minutes.

  By extracting 2057 kg / hr of the reactant slurry from the reaction tank and performing solid-liquid separation with a centrifuge, the precipitated sodium chloride of 649 kg / hr, the sodium hypochlorite concentration is 34.2% by mass, the sodium chloride concentration Was 4.2% by mass, and a low-sodium sodium hypochlorite aqueous solution 1408 kg / hr having a chlorate ion concentration of 0.37% by mass was obtained. The yield at this time was 96.8%.

  The obtained sodium hypochlorite aqueous solution prepared by diluting the low sodium hypochlorite aqueous solution with pure water to adjust the effective chlorine concentration to 13% by mass has a sodium chloride concentration of 1.7% by mass and a chlorate ion concentration. It was 0.15 mass%.

[Example 6]
To a reaction vessel equipped with a stirrer, a coil cooler and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was fed at 1484 kg / hr as a raw material while stirring, and this sodium hydroxide aqueous solution was brought to 30 ° C. While being maintained, 556 kg / hr of chlorine gas was diluted with nitrogen gas to 50% by volume and introduced, and the chlorination reaction was performed so that the residence time was about 100 minutes.

  By extracting 2040 kg / hr of the reactant slurry from the reaction vessel and performing solid-liquid separation with a centrifuge, the precipitated sodium chloride was 630 kg / hr, the sodium hypochlorite concentration was 36.2% by mass, and the sodium chloride concentration Was 4.2% by mass, and a low-sodium sodium hypochlorite aqueous solution 1410 kg / hr having a chlorate ion concentration of 0.17% by mass was obtained. The yield at this time was 98.7%.

  The obtained sodium hypochlorite aqueous solution prepared by diluting the low-sodium sodium hypochlorite aqueous solution with pure water to adjust the effective chlorine concentration to 13% by mass has a sodium chloride concentration of 1.6% by mass and a chlorate ion concentration. It was 0.06 mass%.

[Comparative Example 1]
To a reaction vessel equipped with a stirrer, a coil cooler and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied at 1520 kg / hr as a raw material while stirring, and this sodium hydroxide aqueous solution was brought to 40 ° C. While maintaining, chlorine gas was introduced at 560 kg / hr, and the chlorination reaction was performed so that the residence time was about 100 minutes.

  From the reaction tank, 2080 kg / hr of the reactant slurry was extracted and subjected to solid-liquid separation using a centrifuge, so that 624 kg / hr of precipitated sodium chloride and the sodium hypochlorite concentration were 28.9% by mass. A sodium hypochlorite aqueous solution 1456 kg / hr having a concentration of 6.3% by mass and a chlorate ion concentration of 2.04% by mass was obtained. The yield at this time was 81.5%.

  The diluted sodium hypochlorite aqueous solution obtained by diluting with pure water to adjust the effective chlorine concentration to 13% by mass has a sodium chloride concentration of 3.0% by mass and a chlorate ion concentration of 0%. It was 96 mass%.

[Comparative Example 2]
To a reaction vessel equipped with a stirrer, a coil cooler and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied at 1516 kg / hr as a raw material while stirring, and this sodium hydroxide aqueous solution was brought to 35 ° C. While maintaining, chlorine gas was introduced at 560 kg / hr, and the chlorination reaction was performed so that the residence time was about 100 minutes.

  By extracting 2076 kg / hr of the reactant slurry from the reaction vessel and performing solid-liquid separation with a centrifuge, the precipitated sodium chloride 621 kg / hr, the sodium hypochlorite concentration was 30.9% by mass, the sodium chloride concentration Was 5.4% by mass, and a sodium hypochlorite aqueous solution 1455 kg / hr having a chlorate ion concentration of 1.84% by mass was obtained. The yield at this time was 85.1%.

  The sodium hypochlorite aqueous solution obtained by diluting the obtained sodium hypochlorite aqueous solution with pure water to adjust the effective chlorine concentration to 13% by mass has a sodium chloride concentration of 2.4% by mass and a chlorate ion concentration of 0.2%. It was 81 mass%.

[Comparative Example 3]
To a reaction vessel equipped with a stirrer, a coil cooler, and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was fed at 1471 kg / hr as a raw material while stirring, and this sodium hydroxide aqueous solution was brought to 30 ° C. While maintaining, chlorine gas was introduced at 552 kg / hr, and the chlorination reaction was performed so that the residence time was about 100 minutes.

  By extracting 2023 kg / hr of the reactant slurry from the reaction vessel and performing solid-liquid separation with a centrifugal separator, 654 kg / hr of precipitated sodium chloride, the sodium hypochlorite concentration was 32.1% by mass, the sodium chloride concentration Was 4.4% by mass and an aqueous sodium hypochlorite solution of 1369 kg / hr having a chlorate ion concentration of 1.63% by mass was obtained. The yield at this time was 88.7%.

  The sodium hypochlorite aqueous solution obtained by diluting the obtained sodium hypochlorite aqueous solution with pure water to adjust the effective chlorine concentration to 13% by mass has a sodium chloride concentration of 1.9% by mass and a chlorate ion concentration of 0.8%. It was 69 mass%.

In Comparative Examples 1 to 3, the sodium hypochlorite yield decreased and the sodium chloride concentration and the sodium chlorate concentration increased because local perchlorination occurred near the chlorine gas inlet, This is probably because sodium chlorite was decomposed.
The results of the above-described examples and comparative examples are shown in Table 1 below.

Claims (9)

Supplying a 30-60 mass% aqueous sodium hydroxide solution to the reaction vessel (1);
A step (2) of introducing a chlorine gas diluted with an inert gas into a sodium hydroxide aqueous solution supplied to the reaction tank to cause a chlorination reaction at a reaction temperature of 20 ° C. to 50 ° C .;
Low sodium chloride hypochlorite comprising the step (3) of obtaining a sodium hypochlorite aqueous solution by separating and removing the by-product sodium chloride precipitated in the step (2) from the reaction solution A method for producing an aqueous solution.   The manufacturing method of the low salt sodium hypochlorite aqueous solution of Claim 1 whose density | concentration of the chlorine gas diluted with the said inert gas is 5-95 volume%. The low salt hypochlorous acid according to claim 1 or 2, wherein in the chlorination reaction, a molar ratio (NaOH / Cl ₂ ) between sodium hydroxide and chlorine gas introduced is 2.0 to 2.5. A method for producing an aqueous sodium solution.   The manufacturing method of the low salt sodium hypochlorite aqueous solution of any one of Claims 1-3 whose reaction temperature of the said process (2) is 30-50 degreeC.   The sodium chloride hypochlorite aqueous solution according to any one of claims 1 to 4, wherein the sodium hypochlorite aqueous solution obtained in the step (3) has a sodium chloride concentration of 5.0% by mass or less. Manufacturing method.   The low-sodium sodium hypochlorite according to any one of claims 1 to 5, wherein the chlorate ion concentration in the sodium hypochlorite aqueous solution obtained in the step (3) is 1.5% by mass or less. A method for producing an aqueous solution.   The low-sodium hypochlorous acid of any one of Claims 1-6 whose sodium hypochlorite density | concentration of the sodium hypochlorite aqueous solution obtained at the said process (3) is 30-40 mass%. A method for producing an aqueous sodium solution.   A dilute order comprising a step of diluting a low-sodium sodium hypochlorite aqueous solution obtained by the production method according to any one of claims 1 to 7 with water to a predetermined effective chlorine concentration. A method for producing an aqueous sodium chlorite solution.   The manufacturing method of the diluted sodium hypochlorite aqueous solution of Claim 8 whose said effective chlorine concentration is 1-20 mass%.