TWI635044B - Production process of aqueous sodium hypochlorite solution - Google Patents

Abstract

The present invention provides a process for producing a low salt sodium hypochlorite aqueous solution in high yield.

The method for producing a low-salt sodium hypochlorite aqueous solution according to the present invention comprises the steps of: supplying a 30-60% by mass aqueous sodium hydroxide solution to a reaction tank (1), and introducing a chlorine gas diluted with an inert gas to be supplied thereto. The step (2) of performing a chlorination reaction in the sodium hydroxide aqueous solution of the reaction tank at a reaction temperature of 20 ° C to 50 ° C, and separating and removing the by-produced sodium chloride precipitated in the above step (2) from the reaction liquid Step (3) of an aqueous solution of sodium hypochlorite.

Description

Method for producing sodium hypochlorite aqueous solution

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

Sodium hypochlorite (NaClO) is known to have excellent bactericidal action or bleaching effect, and is generally widely used as a general industrial drug in the form of an aqueous solution, as a sterilization application for swimming pools, water pipes, sewers, and households, or as a paper industry or a fiber industry. Such as bleaching or drainage treatment.

A sodium hypochlorite aqueous solution is generally commercially available, and a sodium hypochlorite aqueous solution widely used for sodium chloride containing about 10% by mass of a reaction by-product is used, and a sodium salt of sodium hypochlorite having a sodium chloride concentration of 4% by mass or less is used. Aqueous solution.

As a method for producing a low-salt sodium hypochlorite aqueous solution, Patent Document 1 proposes to use an aqueous solution of caustic soda having a concentration of 34 to 38% by weight, and react the caustic soda with chlorine gas while maintaining the reaction temperature at 24 to 29 ° C to produce an effective chlorine concentration. 26.5~29% by weight of high concentration sodium hypochlorite In the aqueous solution, the salt precipitated in the high-concentration sodium hypochlorite aqueous solution is separated and diluted with water to obtain 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. A method of aqueous sodium hypochlorite solution. Further, the mg/L unit in Patent Document 1 indicates the concentration of chloric acid when 100 mg of sodium hypochlorite is added to 1 liter of tap water, and the aqueous solution of sodium hypochlorite corresponds to 2000 wtppm based on the concentration of chloric acid.

Here, since chlorination is an exothermic reaction and the crystal of by-product sodium chloride is formed, the higher the reaction temperature, the lower the energy applied by the heat removal can be suppressed, and the scaling of the salt crystal to the cooling coil can be prevented. However, when the reaction temperature is high, the amount of decomposition of sodium hypochlorite is increased, and in particular, the decomposition is rapidly performed at 40 ° C or higher, so that the original unit is greatly deteriorated (see Non-Patent Document 1). Further, Patent Document 1 mainly describes that sodium hypochlorite is rapidly decomposed at a temperature of 30 ° C or higher. In other literatures, there are also examples in which sodium hypochlorite is obtained in a yield of more than 90% at a reaction temperature higher than 30 ° C, especially a reaction temperature higher than 35 ° C.

Patent Document 2 discloses a method for producing an aqueous sodium hypochlorite solution by using purified purified chlorine gas. In paragraph 0044, it is described that "the reaction of chlorine gas with an aqueous sodium hydroxide solution is preferably at 15 to 45 ° C, more preferably at 20 to 40 ° C, and further It is preferably carried out at 25 to 30 ° C. By setting the reaction temperature to 15 to 45 ° C, a sodium hypochlorite aqueous solution having a low salt concentration can be stably produced. However, the inventors of the present invention conducted an experiment of reacting chlorine gas with an aqueous sodium hydroxide solution at a reaction temperature of 40 ° C by the method of Patent Document 2, and confirmed that a side reaction or a decomposition reaction was carried out to greatly reduce the original unit.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2009-132583

[Patent Document 2] Japanese Patent No. 4300810

[Non-patent literature]

[Non-Patent Document 1] Japanese Sooda Industry Association, Soda Handbook Editing Working Group, "Soda Technical Handbook 2009", issued by Japan Soda Industry Association, page 212

SUMMARY OF THE INVENTION An object of the present invention is to provide a process for producing a low-salt sodium hypochlorite aqueous solution at a high reaction temperature, preferably at a reaction temperature of 30 ° C or higher.

As a result of the active review by the inventors of the present invention, it has been found that the above-described problem can be solved by diluting chlorine gas with an inert gas such as nitrogen gas in a method for producing a sodium hypochlorite aqueous solution in which a chlorine gas is introduced into an aqueous sodium hydroxide solution. That is, the present invention relates to the following items.

[1] A method for producing a low-salt sodium hypochlorite aqueous solution, characterized by comprising the steps of: dissolving 30 to 60% by mass of sodium hydroxide in water; The step of supplying the liquid to the reaction tank (1), introducing chlorine gas diluted with an inert gas into the sodium hydroxide aqueous solution supplied to the reaction tank, and performing the chlorination reaction at a reaction temperature of 20 ° C to 50 ° C (2) And removing the by-product sodium chloride precipitated in the above step (2) from the reaction liquid to obtain the sodium hypochlorite aqueous solution (3).

[2] The method for producing a low-salt sodium hypochlorite aqueous solution according to [1], wherein the concentration of the chlorine gas diluted with the inert gas is 5 to 95% by volume.

[3] The method for producing a low-salt sodium hypochlorite aqueous solution according to [1] or [2], wherein a molar ratio of sodium hydroxide to chlorine (NaOH/Cl ₂ ) introduced in the chlorination reaction is 2.0. ~2.5.

[4] The method for producing a low-salt sodium hypochlorite aqueous solution according to any one of [1] to [3] wherein the reaction temperature in the step (2) is 30 to 50 °C.

[5] The method for producing a low-salt sodium hypochlorite aqueous solution according to any one of [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.

[6] The method for producing a low-salt sodium hypochlorite aqueous solution according to any one of [1] to [5] wherein the chlorinated ion concentration of the sodium hypochlorite aqueous solution obtained in the step (3) is 1.5% by mass or less.

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

[8] A method for producing a thin aqueous solution of sodium hypochlorite, which The characteristic system comprises the step of diluting the low-salt sodium hypochlorite aqueous solution obtained by the production method according to any one of [1] to [7] with water to a specific effective chlorine concentration.

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

According to the present invention, the low-salt sodium hypochlorite aqueous solution can be produced in a high yield at a high temperature reaction temperature which is advantageous on the cost surface and the equipment preparation surface.

Hereinafter, the method for producing the sodium hypochlorite aqueous solution of the present invention will be described in detail.

The method for producing a low-salt sodium hypochlorite aqueous solution according to the present invention comprises the steps of: supplying a 30-60% by mass aqueous sodium hydroxide solution to a reaction tank (1), and introducing a chlorine gas diluted with an inert gas to be supplied thereto. The step (2) of performing a chlorination reaction in the sodium hydroxide aqueous solution of the reaction vessel at a reaction temperature of 20 ° C to 50 ° C, and separating the by-produced sodium chloride precipitated in the above step (2) from the reaction liquid to obtain Step (3) of an aqueous solution of sodium hypochlorite.

Raw material sodium hydroxide water supplied to the reaction tank in the step (1) The concentration of the solution is usually from 30 to 60% by mass, preferably from 35 to 55% by mass, more preferably from 40 to 50% by mass. When the concentration of the raw material aqueous sodium hydroxide solution is less than the above range, there is a tendency that it is difficult to produce a sodium hypochlorite aqueous solution having a desired low salt concentration. On the other hand, when the concentration of the raw material aqueous sodium hydroxide solution is higher than the above range, in order to adjust the sodium hydroxide aqueous solution of a specific concentration, complicated operation such as distillation is required.

The reaction temperature in the chlorination reaction in the step (2) is usually from 20 ° C to 50 ° C, preferably from 30 ° C to 50 ° C, more preferably from 30 ° C to 40 ° C. When the reaction temperature is lower than the above range, the cooling coil is likely to cause scale formation. On the other hand, when the reaction temperature is higher than the above range, the decomposition rate of sodium hypochlorite is accelerated, and the tendency of the original unit is lowered.

The reaction time in the chlorination reaction in the step (2) is preferably from 10 to 200 minutes, more preferably from 50 to 150 minutes, most preferably from 70 to 130 minutes.

In the chlorination reaction of the step (2), the introduced molar ratio of sodium hydroxide to chlorine (NaOH/Cl ₂ ) is preferably from 2.0 to 2.5, more preferably from 2.01 to 2.30, still more preferably from 2.02 to 2.20. When the molar ratio of sodium hydroxide to chlorine is less than the above range, perchlorination becomes easy. On the other hand, when the ratio is higher than the above range, the concentration of sodium hydroxide remaining in the aqueous sodium hypochlorite solution becomes high, so that the quality is higher. Not good.

In the step (2), a chlorine gas is introduced into an aqueous sodium hydroxide solution to carry out a reaction of the following formula to produce sodium hypochlorite.

2NaOH+Cl ₂ → NaClO+NaCl+H ₂ O

In the chlorination reaction, a chlorine such as sodium hypochlorite is formed. Sodium (salt) is used, but when a sodium hydroxide aqueous solution having the above concentration is used as a raw material, sodium chloride having a low solubility is crystallized. A high concentration of sodium hypochlorite aqueous solution having a low salt concentration is obtained by removing it.

Here, according to the tap water method, as the impurity of the sodium hypochlorite aqueous solution, the restriction on the above-mentioned sodium chloride and p-chlorous acid tends to be strong. In order to reduce the chloric acid, for example, it is necessary to maintain the reaction temperature at 26 to 29 ° C as described in Patent Document 1. This is because of the "natural decomposition" and "side reaction" described below due to the formation of chloric acid.

The "natural decomposition" is a phenomenon in which sodium hypochlorite is naturally decomposed, and is particularly rapidly decomposed at 40 ° C or higher (see Non-Patent Document 1). This decomposition is represented by the following reaction, whereby sodium chlorate (NaClO ₃ ) is produced.

NaClO → NaCl+O

2NaClO → NaCl+NaClO ₂

NaClO+NaClO ₂ → NaCl+NaClO ₃

The "side reaction" is a side reaction caused by the reaction of sodium hydroxide with chlorine, and refers to the reaction by-product sodium chlorate shown below.

6NaOH+3Cl ₂ → NaClO ₃ +5NaCl+3H ₂ O

Such natural decomposition and side reactions reduce the original chlorine unit relative to sodium hypochlorite in any reaction system. That is, the formation of sodium chlorate reduces the original unit, and inhibition of the formation of sodium chlorate means an increase in the original unit.

These two phenomena are unavoidable reactions, and in particular, in the high temperature state which is advantageous in terms of the cost surface and the equipment preparation surface, since the natural decomposition is rapidly performed, the formation of chloric acid is suppressed, and it is considered that the yield is good. It is very difficult to obtain an aqueous solution of sodium hypochlorite.

However, after the inventors of the present invention conducted a positive review, it was found that the method of blowing chlorine gas by stirring the sodium hydroxide aqueous solution with stirring agitation means that neither the "natural decomposition" nor the "side reaction" generates chloric acid and the original unit is lowered. main reason. In other words, it is considered that in addition to "natural decomposition" and "side reaction", there is a reaction that causes chloric acid to form and lower the original unit.

Therefore, the inventors of the present invention have focused on "perchlorination". In the above-mentioned "perchlorination", according to Non-Patent Document 1, when the chlorination reaction is completed and the caustic soda is lost, the following decomposition reaction occurs in the chain, and all the sodium hypochlorite is rapidly decomposed.

NaClO+Cl ₂ +H ₂ O → NaCl+2HClO

NaClO+2HClO → NaClO ₃ +2HCl

NaClO+2HCl → NaCl+H ₂ O+Cl ₂

The perchlorination is considered to be a violent reaction caused by the supply of the above-mentioned chlorine to the sodium hydroxide. However, the inventors of the present invention thought that local perchlorination may be caused not only in the above conditions but also in the vicinity of the chlorine gas inlet. That is, it is considered that the concentration of sodium hydroxide in the vicinity of the inlet of the chlorine gas is lowered to increase the concentration of sodium hypochlorite, thereby reacting the chlorine gas with sodium hypochlorite. If so, sodium hypochlorite is decomposed by the above reaction formula to form sodium chlorate, and chlorine is regenerated by chlorination. Further, in addition to the vicinity of the inlet of the chlorine gas, since the concentration of sodium hydroxide is sufficient, the regenerated chlorine is consumed. Therefore, all of the hypochlorite is not rapidly decomposed, but the sodium hypochlorite near the inlet is decomposed into chloric acid, resulting in a decrease in the original unit.

Based on the findings discovered by the inventors of the present invention, the present invention dilutes the introduced chlorine with an inert gas in order to suppress the above partial perchlorination. gas. Thereby, the chlorine concentration in the vicinity of the blowing inlet can be reduced, and local perchlorination can be suppressed. Moreover, the inert gas for dilution also has the effect of stirring in the reaction solution, so that the degree of dispersion in the system is improved, and the chlorination can be further suppressed.

The so-called inert gas system in the present invention is a gas which is less likely to cause a chemical reaction with chlorine or oxygen. Specifically, it is a gas of a rare gas element such as helium, neon or argon, or nitrogen gas. Further, in the present invention, air or carbon dioxide gas is also regarded as an inert gas.

The method of diluting the raw material chlorine gas is, for example, a method of adjusting the diluted chlorine to a specific concentration in advance, or a method of simultaneously blowing 100% of chlorine gas and an inert gas from a separate line and combining them in a nozzle.

The concentration of chlorine gas diluted with an inert gas is preferably from 5 to 95% by volume, more preferably from 20 to 80% by volume, most preferably from 30 to 70% by volume, based on the chlorine concentration. When the concentration of the diluted chlorine gas is higher than the above range, a sufficient effect of suppressing perchlorination may not be obtained. On the other hand, when the concentration of the diluted chlorine gas is lower than the above range, the efficiency of the chlorination reaction tends to be lowered, and it is uneconomical. Further, the reaction liquid may be scattered in the reaction tank due to the blowing of the inert gas.

In the step (3), a by-product sodium chloride precipitated in the step (2) is separated from the reaction liquid by using a solid-liquid separation device such as a centrifugal separator or a filter. Thereby, an aqueous sodium hypochlorite 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, most preferably 3.0 to 4.8% by mass.

Further, the chlorinated 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, most preferably 0.05 to 1.0% by mass. As described above, the low-salt sodium hypochlorite aqueous solution obtained by the production method of the present invention has a low impurity chloric acid concentration, and thus has a sufficient product value as a hypochlorite sodium hypochlorite aqueous solution.

The method for producing a thin aqueous solution of sodium hypochlorite according to the present invention is characterized by comprising a step of diluting a low-salt sodium hypochlorite aqueous solution obtained by the above-described method for producing a low-salt sodium hypochlorite aqueous solution of the present invention to a specific effective chlorine concentration.

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

[Examples]

Hereinafter, the present invention will be more specifically described based on examples, but the present invention is not limited by the examples.

[Example 1]

In a reaction tank equipped with a stirrer, a coil cooler, and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied as a raw material at 1514 kg/hr while stirring, and the aqueous sodium hydroxide solution was maintained at 40. At 0.25 ° C, 560 kg / hr of chlorine gas was diluted with nitrogen to 50 vol% and introduced, and the chlorination reaction was carried out in such a manner that the residence time was about 100 minutes.

The reaction slurry was taken out from the reaction tank at 2074 kg/hr, and subjected to solid-liquid separation by a centrifugal separator, thereby obtaining precipitated sodium chloride of 682 kg/hr. And the sodium hypochlorite concentration was 34.5 mass%, the sodium chloride concentration was 4.5% by mass, and the chlorate ion concentration was 0.41% by mass, and the low-salt sodium hypochlorite aqueous solution was 1390 kg/hr. The yield at this time was 95.9%. Further, the yield is a value calculated from the number of moles of sodium hypochlorite obtained based on the introduced chlorine gas (the same applies hereinafter).

The sodium chloride sodium hypochlorite aqueous solution obtained by diluting the obtained low-salt sodium hypochlorite aqueous solution with pure water was adjusted to have an effective chlorine concentration of 13% by mass, and the sodium chloride concentration was 1.8% by mass, and the chloric acid ion concentration was 0.16% by mass.

[Embodiment 2]

In a reaction tank equipped with a stirrer, a coil cooler, and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied as a raw material at 1512 kg/hr while stirring, and the aqueous sodium hydroxide solution was maintained at 35. At 0.25 ° C, 560 kg / hr of chlorine gas was diluted with nitrogen to 50 vol% and introduced, and the chlorination reaction was carried out in such a manner that the residence time was about 100 minutes.

The reaction slurry was taken out from the reaction tank at 2072 kg/hr, and subjected to solid-liquid separation by a centrifugal separator, thereby obtaining precipitated sodium chloride 680 kg/hr, sodium hypochlorite concentration of 35.4% by mass, sodium chloride concentration of 4.2% by mass, and chlorine. The low-salt sodium hypochlorite aqueous solution having an acid ion concentration of 0.29% by mass was 1390 kg/hr. The yield at this time was 97.3%.

The sodium chloride sodium hypochlorite aqueous solution obtained by diluting the obtained low-salt sodium hypochlorite aqueous solution with pure water was adjusted to have an effective chlorine concentration of 13% by mass, and the sodium chloride concentration was 1.6% by mass, and the chloric acid ion concentration was 0.11% by mass.

[Example 3]

In a reaction tank equipped with a stirrer, a coil cooler, and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied as a raw material at 1513 kg/hr while stirring, and the aqueous sodium hydroxide solution was maintained at 30. At ° C, 556 kg/hr of chlorine gas was diluted with nitrogen to 95% by volume and introduced, and the chlorination reaction was carried out in such a manner that the residence time was about 100 minutes.

The reaction slurry was extracted from the reaction tank at 2069 kg/hr, and subjected to solid-liquid separation by a centrifugal separator, thereby obtaining precipitated sodium chloride of 642 kg/hr, sodium hypochlorite concentration of 33.3% by mass, sodium chloride concentration of 4.4% by mass, and chlorine. The low-salt sodium hypochlorite aqueous solution having an acid ion concentration of 0.84% by mass was 1427 kg/hr. The yield at this time was 93.1%.

The sodium chloride sodium hypochlorite aqueous solution having an effective chlorine concentration of 13% by mass was adjusted to have a sodium chloride concentration of 1.8% by mass and a chlorate ion concentration of 0.34% by mass.

[Example 4]

In a reaction tank equipped with a stirrer, a coil cooler, and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied as a raw material at 1503 kg/hr while stirring, and the aqueous sodium hydroxide solution was maintained at 30. At ° C, 556 kg/hr of chlorine gas was diluted with nitrogen to 80% by volume and introduced, and the chlorination reaction was carried out in such a manner that the residence time was about 100 minutes.

The reaction slurry was extracted from the reaction tank at 2059 kg/hr, and subjected to solid-liquid separation by a centrifugal separator, thereby obtaining precipitated sodium chloride 672 kg/hr, sodium hypochlorite concentration of 34.5% by mass, and sodium chloride concentration of 4.1 mass. %, a low-salt sodium hypochlorite aqueous solution having a chloric acid ion concentration of 0.41% by mass was 1387 kg/hr. The yield at this time was 95.6%.

The aqueous sodium hypochlorite solution obtained by diluting the obtained low-salt sodium hypochlorite aqueous solution with pure water was adjusted to have an effective chlorine concentration of 13% by mass, and the sodium chloride aqueous solution had a sodium chloride concentration of 1.6% by mass and a chloric acid ion concentration of 0.16% by mass.

[Example 5]

In a reaction tank equipped with a stirrer, a coil cooler, and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied as a raw material at 1505 kg/hr while stirring, and the aqueous sodium hydroxide solution was maintained at 30. At ° C, 552 kg/hr of chlorine gas was diluted with nitrogen to 67 vol% and introduced, and the chlorination reaction was carried out in such a manner that the residence time was about 100 minutes.

The reaction slurry was extracted from the reaction tank at 2057 kg/hr, and subjected to solid-liquid separation by a centrifugal separator, thereby obtaining precipitated sodium chloride of 649 kg/hr, sodium hypochlorite concentration of 34.2% by mass, sodium chloride concentration of 4.2% by mass, and chlorine. The low-salt sodium hypochlorite aqueous solution having an acid ion concentration of 0.37 mass% was 1408 kg/hr. The yield at this time was 96.8%.

The aqueous sodium hypochlorite solution obtained by diluting the obtained low-salt sodium hypochlorite aqueous solution with pure water was adjusted to have an effective chlorine concentration of 13% by mass, and the sodium chloride aqueous solution had a sodium chloride concentration of 1.7% by mass and a chlorate ion concentration of 0.15% by mass.

[Embodiment 6]

In a reaction tank equipped with a stirrer, a coil cooler, and an external circulation type cooler, 45 mass% of hydrogen and oxygen are supplied at 1484 kg/hr while stirring. An aqueous solution of sodium hydride was used as a raw material, and while maintaining the aqueous sodium hydroxide solution at 30 ° C, 556 kg/hr of chlorine gas was diluted with nitrogen to 50 vol% and introduced, and the chlorination reaction was carried out in such a manner that the residence time was about 100 minutes. .

The reaction slurry was extracted from the reaction tank at 2040 kg/hr, and subjected to solid-liquid separation by a centrifugal separator, thereby obtaining precipitated sodium chloride 630 kg/hr, sodium hypochlorite concentration of 36.2% by mass, sodium chloride concentration of 4.2% by mass, and chlorine. The low-salt sodium hypochlorite aqueous solution having an acid ion concentration of 0.17 mass% was 1410 kg/hr. The yield at this time was 98.7%.

The sodium hypochlorite aqueous solution having an effective chlorine concentration of 13% by mass was adjusted to have a sodium chloride concentration of 1.6% by mass and a chlorate ion concentration of 0.06% by mass.

[Comparative Example 1]

In a reaction tank equipped with a stirrer, a coil cooler, and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied as a raw material at 1520 kg/hr while stirring, and the aqueous sodium hydroxide solution was maintained at 40. At ° C, chlorine gas was introduced at 560 kg/hr to carry out a chlorination reaction in such a manner that the residence time was about 100 minutes.

The reaction slurry was taken out from the reaction tank at 2080 kg/hr, and subjected to solid-liquid separation by a centrifugal separator, thereby obtaining precipitated sodium chloride 624 kg/hr, sodium hypochlorite concentration of 28.9% by mass, sodium chloride concentration of 6.3% by mass, chlorine. The sodium hypochlorite aqueous solution having an acid ion concentration of 2.04% by mass was 1456 kg/hr. The yield at this time was 81.5%.

The aqueous sodium hypochlorite solution diluted with pure water is adjusted to be effective The sodium chloride aqueous solution having a chlorine concentration of 13% by mass has a sodium chloride concentration of 3.0% by mass and a chlorate ion concentration of 0.96% by mass.

[Comparative Example 2]

In a reaction tank equipped with a stirrer, a coil cooler, and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied as a raw material at 1516 kg/hr while stirring, and the aqueous sodium hydroxide solution was maintained at 35. At ° C, chlorine gas was introduced at 560 kg/hr, and the chlorination reaction was carried out in such a manner that the residence time was about 100 minutes.

The reaction slurry was extracted from the reaction tank at 2076 kg/hr, and subjected to solid-liquid separation by a centrifugal separator, thereby obtaining precipitated sodium chloride 621 kg/hr, sodium hypochlorite concentration of 30.9 mass%, sodium chloride concentration of 5.4 mass%, and chlorine. The sodium hypochlorite aqueous solution having an acid ion concentration of 1.84% by mass was 1455 kg/hr. The yield at this time was 85.1%.

The sodium hypochlorite aqueous solution diluted with pure water was adjusted to have an effective chlorine concentration of 13% by mass, and the sodium hypochlorite aqueous solution had a sodium chloride concentration of 2.4% by mass and a chlorate ion concentration of 0.81% by mass.

[Comparative Example 3]

In a reaction tank equipped with a stirrer, a coil cooler, and an external circulation type cooler, a 45 mass% sodium hydroxide aqueous solution was supplied as a raw material at 1,471 kg/hr while stirring, and the aqueous sodium hydroxide solution was maintained at 30. At ° C, chlorine gas was introduced at 552 kg/hr, and the chlorination reaction was carried out in such a manner that the residence time was about 100 minutes.

The reaction slurry was extracted from the reaction tank at 2023 kg/hr, and subjected to solid-liquid separation by a centrifugal separator, thereby obtaining precipitated sodium chloride 654 kg/hr, sodium hypochlorite concentration of 32.1% by mass, sodium chloride concentration of 4.4% by mass, and chlorine. The sodium hypochlorite aqueous solution having an acid ion concentration of 1.63 mass% was 1369 kg/hr. The yield at this time was 88.7%.

The sodium hypochlorite aqueous solution diluted with pure water was adjusted to have an effective chlorine concentration of 13% by mass, and the sodium hypochlorite aqueous solution had a sodium chloride concentration of 1.9% by mass and a chlorate ion concentration of 0.69% by mass.

In Comparative Examples 1 to 3, the yield of sodium hypochlorite was low, and the reason for the increase in the concentration of sodium chloride and the concentration of sodium chlorate was considered to cause local perchlorination in the vicinity of the chlorine gas inlet to decompose sodium hypochlorite.

The results of the above examples and comparative examples are shown in Table 1 below.

Claims (8)

A method for producing a low-salt sodium hypochlorite aqueous solution, comprising the steps of: supplying a 30-60% by mass aqueous sodium hydroxide solution to a reaction tank (1), and introducing a chlorine gas diluted with an inert gas into the supplied In the sodium hydroxide aqueous solution of the reaction tank, the step (2) of chlorination is carried out at a reaction temperature of 30 ° C to 50 ° C, and the by-produced sodium chloride precipitated in the above step (2) is separated from the reaction liquid to obtain Step (3) of an aqueous solution of sodium hypochlorite. The method for producing a low-salt sodium hypochlorite aqueous solution according to claim 1, wherein the concentration of the chlorine gas diluted with the inert gas is 5 to 95% by volume. The method for producing a low-salt sodium hypochlorite aqueous solution according to claim 1, wherein the chlorination reaction has a molar ratio of sodium hydroxide to chlorine (NaOH/Cl ₂ ) of 2.0 to 2.5. The method for producing a low-salt sodium hypochlorite aqueous solution according to any one of claims 1 to 3, wherein the sodium hypochlorite aqueous solution obtained in the step (3) has a sodium chloride concentration of 5.0% by mass or less. The method for producing a low-salt sodium hypochlorite aqueous solution according to any one of claims 1 to 3, wherein the chlorinated ion concentration of the sodium hypochlorite aqueous solution obtained in the step (3) is 1.5% by mass or less. The method for producing a low-salt sodium hypochlorite aqueous solution according to any one of claims 1 to 3, wherein the sodium hypochlorite obtained in the above step (3) is dissolved in water. The concentration of sodium hypochlorite in the liquid is 30 to 40% by mass. A method for producing a thin aqueous sodium hypochlorite solution, which comprises the step of diluting a low-salt sodium hypochlorite aqueous solution obtained by the production method according to any one of claims 1 to 6 with water to a specific effective chlorine concentration. A method for producing a thin aqueous solution of sodium hypochlorite according to claim 7, wherein the effective chlorine concentration is from 1 to 20% by mass.