JP6190718B2 - Method for producing sodium hypochlorite aqueous solution - Google Patents

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.

  In general, sodium hypochlorite is obtained by reacting sodium hydroxide and chlorine. For example, in Patent Document 1, when an aqueous sodium hydroxide solution and chlorine are reacted to produce an aqueous sodium hypochlorite solution, an opening position of the chlorine introduction pipe is provided above the final liquid level of the reaction liquid in the reaction tank, It has been proposed to carry out the chlorination reaction while sufficiently stirring the reaction solution.

In the lower right column on page 2 of Patent Document 1, “the less agitation, the longer the time for the reaction solution to locally contact with chlorine, so the decomposition reaction of the generated sodium hypochlorite is accelerated. As a result, sodium chlorate is undesirable as a by-product, and a certain amount of stirring is necessary. However, since this reaction is performed quickly, vigorous stirring is not necessary. ” Is about 60 rpm for a 10 m ³ reaction tank, which is not much different from normal reaction agitation. ”Furthermore,“ If it is too fast, the reaction liquid droplets adhere to the upper part of the reaction tank. "It is costly and has no merit." As described above, in Patent Document 1, although the stirring speed is described as the stirring condition in the production of the sodium hypochlorite aqueous solution, the shape and size of the stirring blade and the balance with the stirring tank are described as “stirring speed”. The optimum condition may be set as appropriate based on the design of the reaction liquid material, the shape of the stirring blade, etc. ”.

  In Examples 1 and 2 of Patent Document 1, the yields of sodium hypochlorite are 86% and 88%, both being less than 90%, and in Example 3, the yield is 94%. However, the concentration of sodium hypochlorite in the obtained sodium hypochlorite aqueous solution is as low as 29%, and even if this sodium hypochlorite aqueous solution is diluted, a low salt sodium hypochlorite aqueous solution can be obtained. Can not.

Here, the reaction for obtaining sodium hypochlorite from sodium hydroxide and chlorine is represented by the following reaction formula.
2NaOH + Cl ₂ → NaClO + NaCl + H ₂ O
However, in this reaction, sodium chloride and chloric acid are by-produced by decomposition or side reaction represented by the following formula, for example.
_{6NaOH + 3Cl 2 → NaClO 3 +} 5NaCl + 3H 2 O

  Thus, when a side reaction represented by the above formula occurs, sodium chloride and chloric acid are by-produced, so that the sodium hypochlorite concentration decreases and the sodium chloride and chloric acid concentrations increase. As a result, there is a problem that the salt concentration and chloric acid concentration in diluted sodium hypochlorite after dilution increase.

  In addition, chlorination is an exothermic reaction, and crystals of sodium chloride are by-produced. Therefore, the higher the reaction temperature, the lower the energy required for heat removal, which prevents scaling of salt crystals to the cooling coil. it can. 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).

JP 59-182204

Japan Soda Industry Association Soda Handbook Editorial Working Group, “Soda Technology Handbook 2009”, published by Japan Soda Industry Association

  An object of this invention is to provide the method of manufacturing the sodium hypochlorite aqueous solution with little content of impurities, such as chloric acid and sodium chloride, with a high yield.

  As a result of intensive studies, the present inventors have conducted the chlorination reaction while stirring under specific stirring conditions in the method for producing a sodium hypochlorite aqueous solution in which chlorine gas is introduced into the sodium hydroxide aqueous solution. As a result, the present invention has been completed. That is, the present invention relates to the following matters.

[1] Step (1) of supplying 30 to 60% by mass of an aqueous sodium hydroxide solution to the reaction vessel, and introducing chlorine gas into the aqueous sodium hydroxide solution supplied to the reaction vessel to react at a reaction temperature of 20 ° C. to 50 ° C. A step (2) for carrying out a chlorination reaction at 0 ° C., and a step (3) for obtaining a sodium hypochlorite aqueous solution by separating and removing the by-product sodium chloride precipitated in the step (2) from the reaction solution; In the step (2), the required power for stirring per unit volume is 0.1 to 15 kW / m ³ , and the ratio (Np / Nq) of the required power number Np and the circulating flow rate Nq is 0.5. A process for producing a low-sodium sodium hypochlorite aqueous solution, which is carried out with stirring under the conditions of -8.

[2] The method for producing a low-sodium sodium hypochlorite aqueous solution according to item [1], wherein the chlorine gas is diluted with an inert gas and introduced.
[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, since a complicated operation is not required, a low-sodium sodium hypochlorite aqueous solution can be produced in a high yield, advantageously in terms of cost and equipment maintenance.

It is the figure which showed typically the reaction tank used by the Example and the comparative example. FIG. 3 is a diagram schematically showing a stirring blade used in Example 1. In the stirring blade, the upper and lower blades intersect at 45 degrees, and both ends of the lower blade are bent in the direction opposite to the rotation direction. 6 is a diagram schematically showing a stirring blade used in Example 2. FIG. The stirring blade is a typical disk turbine blade, and six teeth are evenly arranged on one side (lower side) of the disk. It is the figure which showed typically the stirring blade used in the comparative example 1. FIG. The stirring blade is a typical paddle blade.

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 into the aqueous sodium hydroxide solution supplied to the reaction vessel 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,
In the step (2), the required power for stirring per unit volume is 0.1 to 15 kW / m ³ , and the ratio (Np / Nq) of the required power number Np and the circulating flow rate Nq is 0.5 to 8 It is characterized by being carried out with stirring under conditions.

  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 40-48 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 step (2) is usually 20 ° C to 50 ° C, preferably 25 ° C to 50 ° C, more preferably 25 ° 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, for example, as described in JP 2009-132583 A, it is said that the reaction temperature needs to be maintained at 26 to 29 ° C. 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 decomposes naturally, 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 the knowledge found by the present inventors, in the present invention, in order to suppress the above-described local perchlorination, the chlorination reaction is performed while stirring under a condition where the power required for stirring per unit volume is large. I do. Here, the “power required for stirring per unit volume” is obtained by dividing the stirring power [kW] required to rotate the stirring blade at an arbitrary speed by the volume [m ³ ] of the reaction solution, and the unit is [ kW / m ³ ]. The value of the stirring power can be obtained, for example, by measuring the electric power of the motor during stirring.

The stirring power per unit volume, which is the stirring condition in the step (2), is usually 0.1 to 15 kW / m ³ , preferably 0.2 to 10 kW / m ³ , more preferably 0.3 to 5 kW / m. ³ . In order to achieve a condition where the required stirring power per unit volume is large, energy is required, which is not preferable from the viewpoint of cost. Moreover, even if the stirring power per unit volume is made larger than the above range, the yield improvement obtained thereby is low.

  Further, the present inventors have exceeded the shear force, that is, the action of dispersing the blown chlorine bubbles and the reaction liquid, rather than the action of crushing the blown chlorine bubbles finely even at the same stirring power. It was found that it is very effective for suppressing chlorination. Therefore, the lower the ratio (Np / Nq) of the power required for stirring Np and the circulation flow rate Nq, the more local perchlorination reaction can be suppressed. It can be obtained in a high yield.

  Np / Nq which is the stirring conditions in the step (2) is usually 0.5 to 8, preferably 1 to 7.5, more preferably 1.5 to 6. By stirring under these conditions, an aqueous sodium hypochlorite solution having a high yield and low salt and low chloric acid concentration can be obtained. Under conditions where Np / Nq is higher than the above range, since the discharge force is low, it tends to be difficult to efficiently suppress the perchlorination reaction by stirring. On the other hand, when Np / Nq is lower than the above range, the shearing force is too low and sufficient effects tend not to be obtained.

Here, the required power Np for stirring is a dimensionless number represented by “Np≡P / (ρn ³ d ⁵ )”, P is the stirring power [W], and ρ is the density of the stirring liquid [kg / m ³ ], N is the rotational speed [rps], and d is the stirring blade diameter [m]. The circulation flow rate number Nq is represented by “Nq≡q / (nd ³ )”, and q is the total circulation flow rate [m ³ / s]. The circulation flow rate Nq is determined by the reaction tank type and the stirring blade type, and Np / Nq represents the characteristics of the stirring blade. Low Np / Nq can be said to be a discharge-type stirring blade having high discharge efficiency, and high Np / Nq can be said to be low-efficiency and a shear-type stirring blade. In addition, the above-mentioned “making the condition that the power required for stirring per unit volume is large” is almost synonymous with increasing only the value of Np in Np / Nq.

  The stirring blade is preferably located in the vicinity of the chlorine gas inlet. Specifically, the “distance between the chlorine gas inlet and the stirring blade (B) relative to the height of the liquid surface from the bottom of the reactor (A)” (B ) "Ratio (B / A) is preferably 0.1 to 0.8, more preferably 0.2 to 0.6.

  In the present invention, the chlorine gas introduced in step (1) may be diluted with an inert gas. 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.
In the following Examples and Comparative Examples, the chlorination reaction was performed using a reaction tank as shown in FIG. The material of the reaction tank 1 and the stirring blade 5 is titanium, and the material of the sodium hydroxide supply pipe 2 and the chlorine gas introduction pipe 3 is vinyl chloride. The reactant slurry can be extracted from the extraction port 4. The curve shown near the center in the vertical direction of the reaction tank in FIG. 1 represents the liquid level during operation. In the reaction tank of FIG. 1, the ratio (B / A) of “distance between chlorine gas inlet and stirring blade (B)” to “height of liquid level from bottom of reactor (A)” is 0.54. [= 1300 / (1050 + 1350)]. As will be described later, the stirring blades 5 used in Examples 1 and 2 and Comparative Example 1 have different shapes, and the distance (B) between the chlorine gas inlet and the stirring blade is the lowest end of the stirring blade. It is calculated from the position of

[Example 1]
A stirring tank as shown in FIG. 2 is used in a reaction vessel as shown in FIG. 1 equipped with a stirrer, a coil cooler and an external circulation type cooler, and the required power for stirring per unit volume is 0.41 kW / While stirring at a ratio of m ³ and the required power number Np of stirring and the ratio of circulation flow rate Nq (Np / Nq) of 2.5, 45 mass% sodium hydroxide aqueous solution was fed at 1491 kg / hr as a raw material, While maintaining this sodium hydroxide aqueous solution at 30 ° C., chlorine gas was introduced at 560 kg / hr to carry out a chlorination reaction so that the average residence time was about 100 minutes. The stirring power P = 2.22 kW, the reaction liquid density ρ = 1500 kg / m ³ , the rotational speed n = 1.30 rps, the stirring blade diameter d = 0.67 m, the total circulation flow rate q = 0.351 m ³ / s. Therefore, Np = 5 and Nq = 2 were calculated from Np≡P / (ρn ³ d ⁵ ) and Nq≡q / (nd ³ ).

  Next, 2051 kg / hr of the reactant slurry was extracted from the reaction tank, and solid-liquid separation was performed using a centrifugal separator. A low-sodium sodium hypochlorite aqueous solution 1419 kg / hr having a sodium concentration of 4.8% by mass and a chlorate ion concentration of 0.68% by mass was obtained. The yield at this time was 94.9%. 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 1.9% by mass and a chlorate ion concentration Was 0.27 mass%.

[Example 2]
A stirring vessel as shown in FIG. 3 is used in a reaction tank as shown in FIG. 1 equipped with a stirrer, a coil cooler and an external circulation type cooler, and the required power for stirring per unit volume is 0.41 kW / While stirring under the condition of m ³ and Np / Nq of 7.1, 45 mass% sodium hydroxide aqueous solution was supplied at 1442 kg / hr as a raw material, and while maintaining this sodium hydroxide aqueous solution at 30 ° C., chlorine Gas was introduced at 552 kg / hr, and the chlorination reaction was performed so that the average residence time was about 100 minutes. The stirring power required P = 2.22 kW, the reaction liquid density ρ = 1500 kg / m ³ , the rotational speed n = 1.30 rps, the stirring blade diameter d = 0.67 m, and the total circulation flow rate q = 0.27 m ³ / s. Therefore, Np = 5 and Nq = 0.7 were calculated from Np≡P / (ρn3d5) and Nq≡q / (nd3).

  Next, the reaction product slurry 2018 kg / hr is extracted from the reaction tank, and solid-liquid separation is performed using a centrifuge, so that the precipitated sodium chloride 655 kg / hr and the sodium hypochlorite concentration are 32.1 mass% A sodium hypochlorite aqueous solution 1360 kg / hr having a sodium concentration of 4.4% by mass and a chlorate ion concentration of 1.63% by mass was obtained. The yield at this time was 90.0%.

  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 1.9% by mass and a chlorate ion concentration Was 0.69 mass%.

[Comparative Example 1]
Using a stirring blade as shown in FIG. 4 in a reaction tank as shown in FIG. 1 equipped with a stirrer, a coil cooler and an external circulation type cooler, the required power for stirring per unit volume is 0.41 kW / m. ³ and Np / Nq of 12 while stirring, 45 mass% sodium hydroxide aqueous solution was supplied at 1520 kg / hr as a raw material, and the sodium hydroxide aqueous solution was maintained at 30 ° C., while chlorine gas was 560 kg. The chlorination reaction was performed so that the average residence time was about 100 minutes. The stirring power P = 2.22 kW, the reaction liquid density ρ = 1500 kg / m ³ , the rotational speed n = 0.85 rps, the stirring blade diameter d = 0.67 m, the total circulation flow rate q = 0.204 m ³ / s. Therefore, Np = 1P and Nq = 1.48 were calculated from Np≡P / (ρn ³ d ⁵ ) and Nq≡q / (nd ³ ).

  Next, 2080 kg / hr of the reactant slurry is extracted from the reaction vessel and subjected to solid-liquid separation with a centrifuge, so that 624 kg / hr of precipitated sodium chloride and the sodium hypochlorite concentration are 28.9 mass%, A low-sodium sodium hypochlorite aqueous solution 1456 kg / hr having a sodium 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 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 3.0% by mass and a chlorate ion concentration. Was 0.95 mass%.
The results of the above-described examples and comparative examples are shown in Table 1 below.

表１に示すように、撹拌所要動力が同一であるにも関わらず次亜塩素酸ナトリウムの収率が低下し、食塩濃度および塩素酸ナトリウム濃度が増大した理由は、吐出力が低いために塩素の吹込口付近で局所的な過塩素化が起こり、次亜塩素酸ナトリウムが分解されたためと考えられる。

As shown in Table 1, despite the same power required for stirring, the yield of sodium hypochlorite decreased and the concentration of sodium chloride and sodium chlorate increased. It is thought that local perchlorination occurred in the vicinity of the nozzle and sodium hypochlorite was decomposed.

DESCRIPTION OF SYMBOLS 1 Reaction tank 2 Sodium hydroxide supply pipe 3 Chlorine gas introduction pipe 4 Extraction port 5 Stirring blade

Claims (9)

Supplying a 30-60 mass% aqueous sodium hydroxide solution to the reaction vessel (1);
A step (2) of introducing a chlorine gas into the aqueous sodium hydroxide solution supplied to the reaction vessel 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,
In the step (2), the required power for stirring per unit volume is 0.1 to 15 kW / m ³ , and the ratio (Np / Nq) of the required power number Np and the circulating flow rate Nq is 0.5 to 8 A method for producing a low-sodium sodium hypochlorite aqueous solution, which is carried out with stirring under conditions.   The manufacturing method of the low salt sodium hypochlorite aqueous solution of Claim 1 which dilutes and introduce | transduces the said chlorine gas with an inert gas. 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%.

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