TW201524894A - Production processes of high-purity sodium hypochlorite pentahydrate and aqueous sodium hypochlorite solution - Google Patents

Abstract

The present invention provides a method of efficiently producing aqueous sodium hypochlorite solution with high-purity in high yield. The disclosed method is characterized in containing the following steps: a chlorination step of introducing the chlorine into the aqueous sodium hydroxide solution to perform the chlorination reaction, a separation step (1) of separating the by-product raw sodium chloride in the chlorination step from the reaction solution to obtain the filtrate 1, a crystallization step (1) of cooling the filtrate 1 and precipitating the crystal 1 of high-purity sodium hypochlorite pentahydrate, a separation step (2) of separating and recycling the crystal 1 from the reaction solution passed through the crystallization step (1) and obtaining filtrate 2, a crystallization step (2) of cooling filtrate 2 under existence of the sodium hypochlorite pentahydrate seed crystal and precipitating the crystal 2 of high-purity sodium hypochlorite pentahydrate, and a separation step (3) of separating and recycling the crystal 2 from the reaction solution passed through the crystallization step (2) and synchronously obtaining the filtrate 3.

Description

Method for producing high-purity sodium hypochlorite pentahydrate and sodium hypochlorite aqueous solution

The present invention relates to a method for producing high-purity sodium hypochlorite pentahydrate (NaClO‧5H ₂ O) and a method for producing an aqueous sodium hypochlorite solution, and more particularly to industrially and efficiently producing sodium chloride or other impurities as impurities in high yield. A method of low-purity, high-purity sodium hypochlorite aqueous solution.

In the sodium hypochlorite aqueous solution, when the effective chlorine concentration is 10% by mass or more, the sodium chloride concentration exceeds 4% by mass. On the other hand, the low-salt sodium hypochlorite aqueous solution generally has a sodium chloride concentration of 4% by mass or less, and has an advantage of reducing transportation cost, suppressing clogging due to precipitated salts, and low decomposability. In addition, in recent years, it is required to have a high-quality, high-purity sodium hypochlorite aqueous solution having a low impurity concentration when used in the sterilization, disinfection, and the like of the water supply. In particular, in the use of sterilization, disinfection, etc. of the waterway, it is required that the concentration of sodium chloride is not as high as 2% by mass in an aqueous solution having an effective chlorine concentration of 12% by mass or more. Aqueous sodium chlorate solution.

Further, a method of producing a high-purity sodium hypochlorite aqueous solution having an extremely low impurity concentration and having a specific effective chlorine concentration is known. The method of crystallizing in the form of sodium hypochlorite pentahydrate and dissolving the crystal of the obtained sodium hypochlorite pentahydrate in water is known.

There are various known methods for producing high-purity sodium hypochlorite pentahydrate. However, in the industry, a chlorine gas is introduced into a high-concentration aqueous solution of sodium hydroxide to carry out a chlorination reaction represented by the following formula.

2NaOH+Cl ₂ → NaClO+NaCl+H ₂ O

When the three components of NaClO-NaCl-H ₂ O exceed a certain area, the by-product sodium chloride starts to precipitate from the reaction liquid. After the completion of the reaction, the precipitated NaCl was removed by solid-liquid separation to obtain a high concentration aqueous sodium hypochlorite solution. Next, when the obtained sodium hypochlorite aqueous solution is cooled, crystals of sodium hypochlorite pentahydrate are precipitated, so that the precipitated crystals are subjected to solid-liquid separation and taken out.

Further, in Patent Document 1, a method for producing sodium hypochlorite pentahydrate is described as "a method for producing sodium hypochlorite pentahydrate, which is characterized in that chlorine is introduced into a 38 to 60% by weight aqueous sodium hydroxide solution in a chlorination step and is The reaction temperature is chlorinated at 25 to 30 ° C, and the precipitated by-produced sodium chloride crystal is separated and recovered, and a sodium perchlorate aqueous solution having a sodium hypochlorite concentration of 30 to 38% by weight is recovered, and in the crystallization step, the cooler and the crystallizer are used. In the integrated crystallization tank, the high-concentration sodium hypochlorite aqueous solution is cooled to a cooling temperature of 10 to 22 ° C in the presence of a seed crystal of sodium hypochlorite pentahydrate to precipitate sodium hypochlorite pentahydrate, followed by solid-liquid separation to obtain sodium hypochlorite pentahydrate. .

However, in the method described in Patent Document 1, or a method in which the filtrate from which the sodium chloride is removed from the reaction liquid in which the chlorination step is removed is cooled, and the crystal of sodium hypochlorite pentahydrate is precipitated, the problem is based on The concentration of sodium hypochlorite before crystallization and the cooling temperature determine the yield and yield of the obtained crystal. Further, when the filtrate recovered by solid-liquid separation of sodium hypochlorite pentahydrate is recycled to the chlorination step, since the impurities are concentrated, it is practically impossible to increase the yield of the crystallization by circulating the filtrate. On the other hand, there is a problem that in order to increase the amount of crystallization of sodium hypochlorite pentahydrate and increase the amount of feed, the yield of the filtrate which is simultaneously formed by crystallization increases.

Another method of increasing the crystal yield of sodium hypochlorite pentahydrate generally provides a means to further increase the concentration of sodium hypochlorite prior to cooling, or to further reduce the cooling temperature. Here, in order to increase the concentration of the sodium hypochlorite aqueous solution before cooling, it is necessary to increase the concentration of sodium hydroxide in the chlorination step. However, in the case of producing a high concentration of sodium hypochlorite, a sodium hydroxide aqueous solution of 30 to 48% is generally used. Therefore, in order to achieve a sodium hydroxide concentration or higher, it is necessary to use solid sodium hydroxide or the like, and as a result, the operation is complicated. Further, when the cooling temperature is lowered, since the concentration of the slurry is increased, it is likely to cause fouling or the like, so that the operation is difficult, and a large freezer is required, which is uneconomical.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2000-290003

SUMMARY OF THE INVENTION An object of the present invention is to provide a process for producing an aqueous solution of a high-purity sodium hypochlorite which can be industrially and efficiently produced in a high yield.

As a result of a positive review by the present inventors, it was found that two chlorine gases were introduced into a sodium hydroxide aqueous solution to carry out a chlorination reaction, and after the separation of the by-produced sodium chloride from the reaction liquid, high-purity sodium hypochlorite pentahydrate was precipitated from the obtained filtrate. The present invention can be solved by the step of crystallizing and recovering, and using the recovered crystals of high-purity sodium hypochlorite pentahydrate to solve the above problems. The present invention relates to the following matters.

[1] A method for producing high-purity sodium hypochlorite pentahydrate, which comprises the steps of: introducing a chlorine gas into an aqueous sodium hydroxide solution to carry out a chlorination step of a chlorination reaction, and separating a precipitate which is precipitated in the chlorination step from the reaction liquid. The separation step (1) of obtaining the filtrate 1 by the production of sodium chloride, the crystallization step (1) of crystal 1 in which the filtrate 1 is cooled to precipitate high-purity sodium hypochlorite pentahydrate, and the reaction from the crystallization step (1) The liquid crystal is separated and recovered, and the separation step (2) of the filtrate 2 is obtained, and the crystallization step of cooling the precipitate 2 to precipitate the crystal 2 of the high-purity sodium hypochlorite pentahydrate in the presence of the seed crystal of sodium hypochlorite pentahydrate (2) And separating the crystal 2 from the reaction liquid having passed through the crystallization step (2), and simultaneously obtaining the separation step (3) of the filtrate 3.

[2] The method for producing high-purity sodium hypochlorite pentahydrate according to [1], wherein the chlorine gas is introduced by diluting with an inert gas.

[3] High purity sodium hypochlorite pentahydrate as described in [1] or [2] The production method wherein the chlorination reaction is carried out in the range of 18 to 50 °C.

[4] The method for producing high-purity sodium hypochlorite pentahydrate according to any one of [1] to [3] wherein the cooling temperature in the crystallization step (1) is in the range of 5 to 25 °C.

[5] The method for producing high-purity sodium hypochlorite pentahydrate according to any one of [1] to [4] wherein the cooling temperature in the crystallization step (2) is in the range of 0 to 15 °C.

[6] The method for producing high-purity sodium hypochlorite pentahydrate according to any one of [1] to [5], further comprising the step of diluting the filtrate 3 with water to obtain an aqueous sodium hypochlorite solution.

[7] A method for producing a high-purity sodium hypochlorite aqueous solution, which comprises dissolving crystal 1 and crystal 2 of high-purity sodium hypochlorite pentahydrate obtained by the production method according to any one of [1] to [6] The steps in the water.

[8] The method for producing a high-purity sodium hypochlorite aqueous solution according to [7], wherein the high-purity sodium hypochlorite aqueous solution has an effective chlorine concentration of 5 to 20% by mass.

[9] The method for producing a high-purity sodium hypochlorite aqueous solution according to [7] or [8], wherein the sodium chloride concentration of the high-purity sodium hypochlorite aqueous solution is less than 2% by mass.

[10] A method for producing an aqueous sodium hypochlorite solution having an effective chlorine concentration of 5 to 20% by mass and a sodium chloride concentration of 2 to 20% by mass, which comprises the steps of: introducing chlorine into an aqueous sodium hydroxide solution for chlorine a chlorination step of the reaction, separating the by-produced sodium chloride precipitated in the chlorination step from the reaction liquid to obtain a separation step (1) of the filtrate 1, and cooling the filtrate 1 to precipitate a crystal of high-purity sodium hypochlorite pentahydrate The crystallization step (1), separating and recovering the crystal 1 from the reaction liquid having passed through the crystallization step (1), obtaining the separation step (2) of the filtrate 2, and allowing the filtrate to be present in the presence of a seed crystal of sodium hypochlorite pentahydrate 2 crystallization step (2) of crystal 2 in which high-purity sodium hypochlorite pentahydrate is precipitated, and the above-mentioned crystal 2 is separated and recovered from the reaction liquid having passed through the crystallization step (2), and a separation step (3) of the filtrate 3 is obtained, The step of diluting the aforementioned filtrate 3 with water.

According to the present invention, a high-quality sodium hypochlorite aqueous solution having a low impurity concentration can be efficiently obtained in a high yield, so that an industrially advantageous method for producing an aqueous sodium hypochlorite solution can be provided.

A1‧‧‧Low salt sodium hypochlorite solution

A2‧‧‧Low salt sodium hypochlorite solution

A3‧‧‧ Sodium hypochlorite aqueous solution (general product)

B1‧‧‧High purity sodium hypochlorite solution

Figure 1 is a graph showing the saturation solubility curve of sodium chloride relative to sodium hypochlorite concentration.

Fig. 2 is a view showing a eutectic line of a three-component system of NaClO-NaCl-H ₂ O.

Fig. 3 is a view showing the manufacturing steps of an example of the manufacturing process of the present invention.

Hereinafter, the method for producing high-purity sodium hypochlorite pentahydrate of the present invention, the method for producing a high-purity sodium hypochlorite aqueous solution, and the method for producing a sodium hypochlorite aqueous solution (general product) will be described in detail.

[Method for producing high-purity sodium hypochlorite pentahydrate]

The method for producing high-purity sodium hypochlorite pentahydrate of the present invention, as shown in FIG. 3, comprises the steps of: introducing a chlorine gas into an aqueous sodium hydroxide solution to carry out a chlorination step of chlorination, and separating the chlorination step from the reaction liquid. a separation step (1) of obtaining the filtrate 1 by the precipitation of the by-product sodium chloride, and a crystallization step (1) of crystal 1 in which the filtrate 1 is cooled to precipitate high-purity sodium hypochlorite pentahydrate, since the crystallization step ( 1) The reaction liquid is separated and recovered, and the separation step (2) of the filtrate 2 is obtained, and the filtrate 2 is cooled in the presence of a seed crystal of sodium hypochlorite pentahydrate to precipitate a crystal of high purity sodium hypochlorite pentahydrate crystal 2 The step (2) is carried out, and the crystal 2 is separated and recovered from the reaction liquid having passed through the crystallization step (2), and the separation step (3) of the filtrate 3 is obtained.

<chlorination step>

The chlorination step is carried out by introducing chlorine gas into an aqueous sodium hydroxide solution to carry out a reaction of the following formula to obtain an aqueous solution of sodium hypochlorite.

2NaOH+Cl ₂ → NaClO+NaCl+H ₂ O

When introducing chlorine into an aqueous sodium hydroxide solution, it is based on suppressing side reactions caused at high temperatures or suppressing sodium hypochlorite pentahydrate caused at low temperatures. From the viewpoint of the precipitation of the compound, the temperature of the aqueous sodium hydroxide solution is preferably maintained at 18 to 50 ° C, more preferably maintained at 20 to 35 ° C, and more preferably maintained at 25 to 32 ° C. Further, the concentration of the aqueous sodium hydroxide solution is preferably from 30 to 60% by mass, more preferably from 30 to 48% by mass, even more preferably from 40 to 48% by mass, from the viewpoint of obtaining a desired salt concentration and sodium hypochlorite concentration or adjusting easily. %.

The chlorine gas may be diluted with an inert gas such as nitrogen. The 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. When the chlorine gas is diluted, it is preferable because the effect of suppressing the decomposition of sodium hypochlorite or the formation of impurities is obtained. The concentration of chlorine gas is preferably from 10 to 75% by volume, more preferably from 25 to 60% by volume.

When the above reaction is carried out, the by-produced sodium chloride crystals are precipitated. For example, as shown in the dissolution curve (NaClO-NaCl-H ₂ O) of Fig. 1, in the region where the concentration of sodium hypochlorite is high, since the solubility of sodium chloride is lowered, the sodium chloride component crystallizes in a region exceeding the saturated solubility (region 1). It is precipitated in the reaction liquid.

<Separation step (1)>

The separation step (1) separates sodium chloride precipitated in the above chlorination step from the reaction liquid to obtain an aqueous sodium hypochlorite solution (filtrate 1). The concentration of sodium hypochlorite in the filtrate 1 obtained is preferably from 25 to 45% by mass, more preferably from 30 to 40% by mass, even more preferably from 30 to 36% by mass.

The separation method is not particularly limited, and a conventional method such as use can be employed. A method of a solid-liquid separation device such as a centrifugal separator or a filtration device.

<Cleavage Step (1)>

In the crystallization step (1), the crystal 1 of the high-purity sodium hypochlorite pentahydrate is precipitated by cooling the filtrate 1 to lower the solubility of sodium hypochlorite.

The cooling temperature can be determined within the range in which the impurities are not eutectic, or can be determined from the desired filtrate composition. For example, as shown in the eutectic line (NaClO-NaCl-H ₂ O) of Fig. ₂ , in the region where sodium hypochlorite precipitates but sodium chloride does not precipitate (in the region 2 on the left side of the thick solid line, for example, at 15 ° C in the ratio The crystallization operation is carried out in the region of the upper side of the curve of 15 ° C, and only sodium hypochlorite pentahydrate can be precipitated. In fact, impurities such as chlorate ions are contained in addition to sodium chloride, and the eutectic concentration is also based on the impurity concentration other than sodium chloride. The specific cooling temperature is preferably 5 to 25 ° C, more preferably 10 to 20 ° C, and even more preferably 4 to 18 ° C.

The method of cooling the filtrate 1 is not particularly limited, and a conventional method can be used. The sodium hypochlorite aqueous solution (filtrate 1) is introduced into a cooler, and is cooled to a temperature range below the saturation temperature of sodium hypochlorite and the saturation temperature of sodium chloride, and the cooled solution is sent, as described in JP-A-56-22604. Into the crystallization tank. A sodium hypochlorite pentahydrate slurry is previously placed in the crystallization vessel, and crystals are crystallized by adding the cooled sodium hypochlorite (filtrate 1). Alternatively, as described in Patent Document 1, the filtrate 1 may be cooled by using a crystallization tank in which a cooler and a crystallizer are integrated.

When crystallization 1 is precipitated, it is preferably in the sodium hypochlorite pentahydrate. It is carried out in the presence of a crystal. As the crystal of sodium hypochlorite pentahydrate used as a seed crystal, a crystal having a length in the range of 500 to 5000 μm and a width in the range of 100 to 2000 μm is preferably used. The crystal size can be measured by an optical microscope.

The amount of the crystal to be added is preferably from 0.005 to 20% by mass, more preferably from 0.01 to 10% by mass, even more preferably from 0.1 to 5% by mass, based on the theoretical amount of sodium hypochlorite pentahydrate. When the amount of addition of the crystal is too small, the addition effect is not observed and the amount of impurities mixed increases, and it is uneconomical when the amount of addition is too large.

<Separation step (2)>

The separation step (2) is carried out by separating the crystal 1 from the reaction liquid (the slurry containing the crystal 1 described above) through the liquid phase separation device such as a centrifugal separator or a filter, and recovering the sodium hypochlorite aqueous solution. (filtrate 2). The recovered crystal 1 is a high-purity sodium hypochlorite pentahydrate having a sodium hypochlorite concentration of preferably 35 to 46% by mass, more preferably 40 to 46% by mass, and even more preferably 42 to 46% by mass. In other words, the concentration of sodium hypochlorite pentahydrate is preferably 77 to 100% by mass, more preferably 88 to 100% by mass, and still more preferably 93 to 100% by mass of high purity sodium hypochlorite pentahydrate.

The concentration of sodium hypochlorite of the obtained filtrate 2 varies depending on the crystallization temperature, but is preferably from 20 to 40% by mass, more preferably from 23 to 35% by mass, even more preferably from 25 to 33% by mass.

<Cleavage Step (2)>

In the crystallization step (2), the filtrate 2 is cooled in the presence of a seed crystal of sodium hypochlorite pentahydrate, whereby the solubility of sodium hypochlorite is lowered to precipitate crystal 2 of high-purity sodium hypochlorite pentahydrate.

The cooling temperature is in the range of the region where the sodium chloride does not precipitate in the eutectic line of Fig. 2 (region 2), preferably 0 to 15 ° C, more preferably 0 to 10 ° C, and even more preferably 4 to 8 ° C.

The method of cooling the filtrate 2 is not particularly limited, and a conventional method can be used. For example, it can be carried out in the same manner as the method of cooling the filtrate 1 described above, and a crystallization tank in which a cooler and a crystallizer are integrated can be used as described in JP-A-2000-290003 (Patent Document 1).

As the crystal of sodium hypochlorite pentahydrate used as a seed crystal, a crystal having a length in the range of 1000 to 5000 μm and a width in the range of 300 to 2000 μm is preferably used. When the length and width of the crystal are less than the above range, the filtrate may be entrained in the sodium hypochlorite crystal or the amount of adhesion may be increased to deteriorate the quality.

The theoretical amount of the added amount of the crystal is preferably from 0.005 to 20% by mass, more preferably from 0.01 to 10% by mass, even more preferably from 0.1 to 5% by mass, based on the theoretical amount of sodium hypochlorite pentahydrate. When the amount of addition of the crystal is too small, the addition effect is not observed and the amount of precipitation of sodium chloride is increased, and it is not economical when the amount of the seed crystal is excessively added.

<Separation step (3)>

The separation step (3) is carried out using, for example, a centrifugal separator, a filter, or the like. In the liquid separation apparatus, the crystal 2 is separated and recovered from the reaction liquid (the slurry containing the crystal 2 described above) in the crystallization step (2), and an aqueous sodium hypochlorite solution (filtrate 3) is obtained. The recovered crystal 2 sodium hypochlorite concentration is preferably 35 to 46% by mass, more preferably 40 to 46% by mass, and more preferably 42 to 46% by mass of high purity sodium hypochlorite pentahydrate.

The concentration of sodium hypochlorite of the obtained filtrate 3 varies depending on the crystallization temperature, but is preferably from 10 to 35 mass%, more preferably from 15 to 30 mass%, still more preferably from 20 to 25 mass%.

<other steps>

The method for producing high-purity sodium hypochlorite pentahydrate of the present invention may include other steps than those described above without departing from the effects of the present invention. Examples of other steps are shown below.

The filtrate 1 can be extracted as a part thereof, and if necessary, diluted with water to form a low-salt sodium hypochlorite aqueous solution (A1) having a specific effective chlorine concentration of 4% or less of sodium chloride.

Similarly, the filtrate 2 can be extracted as a part thereof, and if necessary, diluted with water to form a low-salt sodium hypochlorite aqueous solution (A2) having a specific effective chlorine concentration of 4% or less of sodium chloride.

The filtrate 3 may be diluted with water as needed to form a sodium hypochlorite aqueous solution (A3) having a specific effective chlorine concentration.

Since the crystal 1 and the crystal 2 described above have a small content of impurities, it is suitable for producing a high-purity sodium hypochlorite aqueous solution (B1) for use in applications such as sterilization and disinfection of water channels.

[Method for Producing High Purity Sodium Hypochlorite Solution (B1)]

The method for producing a high-purity sodium hypochlorite aqueous solution (B1) according to the present invention is characterized by comprising the step of dissolving the above-mentioned high-purity sodium hypochlorite pentahydrate (crystal 1 + crystal 2) in water.

The effective chlorine concentration of the high-purity sodium hypochlorite aqueous solution (B1) obtained by the method of the present invention is preferably from 5 to 20% by mass, more preferably from 10 to 17% by mass, still more preferably from 12 to 15% by mass, and the sodium chloride concentration is higher. It is less than 2% by mass, more preferably 0.01 to 1.5% by mass, and even more preferably 0.1 to 1% by mass.

[Sodium hypochlorite aqueous solution (A3)]

The method for producing the sodium hypochlorite aqueous solution (A3) of the present invention is characterized by the step of diluting the filtrate 3 with water as needed. The sodium hypochlorite aqueous solution (A3) obtained by the above method corresponds to a so-called general product, and the effective chlorine concentration thereof is preferably from 5 to 20% by mass, more preferably from 10 to 17% by mass, still more preferably from 12 to 15% by mass, of chlorine. The sodium concentration is preferably from 2 to 20% by mass, more preferably from 4 to 15% by mass, even more preferably from 5 to 10% by mass.

Accordingly, according to the present invention, high-purity sodium hypochlorite pentahydrate and a high-purity sodium hypochlorite aqueous solution produced using the high-purity sodium hypochlorite pentahydrate can be efficiently produced, and an aqueous sodium hypochlorite solution equivalent to a general product can be efficiently produced.

[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]

The chlorination step is carried out in a reaction tank (capacity: 11 m ³ ) equipped with a stirrer, a coil cooler, and an external circulation type cooler, and a 48 mass% sodium hydroxide aqueous solution as a raw material is charged at 1520 kg/Hr, and the residual alkali concentration is simultaneously made. In a mode of 1% by mass, chlorine gas was introduced while adjusting the supply amount, and chlorination was performed while cooling at a temperature of 32 °C. At this time, the residence time in the reaction tank was about 100 minutes.

The separation step (1) is such that the reaction slurry extracted from the reaction tank of the chlorination step at 2270 kg/Hr is subjected to solid-liquid separation by a centrifugal separator, thereby obtaining precipitated sodium chloride 570 kg/Hr, and sodium hypochlorite concentration of 32.9 mass%. The sodium hypochlorite aqueous solution (filtrate 1) having a sodium chloride concentration of 5.4% by mass was 1700 kg/Hr.

The crystallization step (1) is carried out in a crystallization tank (capacity: 25 m ³ ) equipped with a stirrer, a coil cooler, and an external circulation type cooler, and the filtrate 1 is charged at 1700 kg/Hr, and the length of the seed crystal is 500. In the range of ~5000 μm and 10 kg of sodium hypochlorite pentahydrate having a width in the range of 100 to 2000 μm, it was cooled to 15 ° C for crystallization. At this time, the residence time in the crystallization tank was about 5 hours.

The separation step (2) is to carry out solid-liquid separation of the slurry from the crystallization tank of the crystallization step 1 by overflowing with a centrifugal separator, thereby obtaining high-purity sodium hypochlorite pentahydrate (crystal 1) 560 kg/Hr, and sodium hypochlorite. The sodium hypochlorite aqueous solution (filtrate 2) having a concentration of 27.7% by mass and a sodium chloride concentration of 7.6% by mass was 1140 kg/Hr.

The crystallization step (2) is carried out in a crystallization tank (capacity: 17 m ³ ) equipped with a stirrer, a coil cooler, and an external circulation type cooler, and the filtrate 2 is supplied at 1140 kg/Hr, and the length of the crystal is included as a seed crystal. In the range of 1000 to 5000 μm and 5 kg of sodium hypochlorite pentahydrate having a width in the range of 300 to 2000 μm, it is cooled to 5 ° C for crystallization. At this time, the residence time in the crystallization tank was about 5 hours.

The separation step (3) is to perform solid-liquid separation of the slurry from the crystallization tank of the crystallization step 2 by overflowing with a centrifugal separator, thereby obtaining high-purity sodium hypochlorite pentahydrate (crystal 2) 360 kg/Hr, and sodium hypochlorite. The sodium hypochlorite aqueous solution (filtrate 3) having a concentration of 22.0% by mass and a sodium chloride concentration of 11.0% by mass was 780 kg/Hr.

The sodium hypochlorite aqueous solution (filtrate 3) obtained in the step (3) was diluted with water to obtain an aqueous sodium hypochlorite solution (A3) of 1430 kg/Hr having an effective chlorine concentration of 13% by mass and a sodium chloride concentration of 6.0% by mass.

Further, the high-purity sodium hypochlorite pentahydrate (crystal 1) obtained in the separation step (2) and the high-purity sodium hypochlorite pentahydrate (crystal 2) obtained in the separation step (3) are diluted with water to obtain an effective chlorine concentration of 13% by mass. The high-purity sodium hypochlorite aqueous solution (B1) having a sodium chloride concentration of 0.5% by mass was 3030 kg/Hr. The production yield of the obtained high-purity sodium hypochlorite aqueous solution (B1) was about 70%. The above production yield is a ratio of the amount of sodium hypochlorite contained in the sodium hypochlorite in the crystallization tank of the first stage, which is obtained by obtaining a high-purity sodium hypochlorite aqueous solution. For the first embodiment, it is as follows Calculated.

The concentration of the sodium hypochlorite aqueous solution introduced into the crystallization tank of the first stage was 32.9 mass%, and the supply amount was 1700 kg/hr, so sodium hypochlorite (calculated as NaClO) was 1700 x 0.329 = 559.3 kg/Hr. Next, the concentration of the obtained high-purity sodium hypochlorite aqueous solution was 13% by mass, and the yield was 3030 kg/Hr. Therefore, sodium hypochlorite (calculated as NaClO) was 3030 × 0.13 = 393.9 kg / Hr. Therefore, the yield was calculated to be 393.9 / 559.3 = 70%. The same is calculated below.

[Embodiment 2]

In the same manner as in Example 1, a high-purity sodium hypochlorite pentahydrate (crystal 1, crystal 2) and a high-purity sodium hypochlorite aqueous solution were produced in the same manner as in Example 1 except that the chlorine gas was supplied in the chlorination step, and the same volume of nitrogen was mixed with chlorine gas. (B1) and sodium hypochlorite aqueous solution (A3).

In the chlorination step, a slurry of 2280 kg/Hr was obtained, and in the separation step (1), sodium chloride 560 kg/Hr, sodium hypochlorite concentration was 34.3% by mass, and sodium chloride concentration was 4.8% by mass aqueous sodium hypochlorite solution (filtrate 1) 1720 kg. /Hr. In the crystallization step (1) and the separation step (2), a high-purity sodium hypochlorite pentahydrate (crystal 1) 680 kg/Hr, a sodium hypochlorite concentration of 27.8% by mass, and a sodium chloride concentration of 7.5% by mass aqueous sodium hypochlorite solution (filtrate) were obtained. 2) 1040kg/Hr. In the crystallization step (2) and the separation step (3), a high-purity sodium hypochlorite pentahydrate (crystal 2) 320 kg/Hr, a sodium hypochlorite concentration of 22.0% by mass, and a sodium chloride concentration of 10.9% by mass of a sodium hypochlorite aqueous solution (filtrate) are obtained. 3) 710 Kg/Hr.

The obtained filtrate 3 was diluted with water to obtain an aqueous sodium hypochlorite solution (A3) of 1300 kg/Hr having an effective chlorine concentration of 13% by mass and a sodium chloride concentration of 5.9% by mass.

Further, the crystal 1 and the crystal 2 were diluted with water to obtain a high-purity sodium hypochlorite aqueous solution (B1) of 3360 kg/Hr having an effective chlorine concentration of 13% by mass and a sodium chloride concentration of 0.5% by mass. The production yield of the obtained high-purity sodium hypochlorite aqueous solution (B1) was about 72%.

In the chlorination step, the chlorine gas is diluted with nitrogen to suppress the decomposition of sodium hypochlorite, thereby increasing the reaction yield, thereby also increasing the yield of high-purity sodium hypochlorite pentahydrate.

[Comparative Example 1]

High-purity sodium hypochlorite pentahydrate (crystal 1), high-purity sodium hypochlorite aqueous solution (B1), and sodium hypochlorite aqueous solution (A2) were produced in the same manner as in Example 1 except that the crystallization step (2) was not carried out.

In the crystallization step (1) and the separation step (2), a high-purity sodium hypochlorite pentahydrate (crystal 1) 560 kg/Hr, a sodium hypochlorite concentration of 27.7% by mass, and a sodium chloride concentration of 7.6% by mass aqueous sodium hypochlorite solution (filtrate) were obtained. 2) 1140kg/Hr.

The obtained filtrate 2 was diluted with water to obtain an aqueous sodium hypochlorite solution (A2) of 2574 kg/Hr having an effective chlorine concentration of 13% by mass and a sodium chloride concentration of 3.4% by mass.

And, the obtained crystal 1 is diluted with water to obtain an effective chlorine concentration of A high-purity sodium hypochlorite aqueous solution (B1) of 13 mass% and a sodium chloride concentration of 0.4 mass% was 2050 kg/Hr. The production yield of the obtained high-purity sodium hypochlorite aqueous solution (B1) was 47%, which was remarkably decreased as compared with Example 1.

Claims (10)

A method for producing high-purity sodium hypochlorite pentahydrate, which comprises the steps of: introducing a chlorine gas into an aqueous sodium hydroxide solution to carry out a chlorination step of chlorination reaction, and separating a by-product chlorination precipitated in the chlorination step from the reaction liquid. The separation step (1) of the filtrate 1 is obtained by sodium, the crystallization step (1) of crystal 1 in which the filtrate 1 is cooled to precipitate high-purity sodium hypochlorite pentahydrate, and the reaction liquid from the crystallization step (1) is separated and recovered. The crystal 1 is obtained simultaneously with the separation step (2) of the filtrate 2, and the crystallization step (2) of cooling the precipitate 2 to precipitate the crystal 2 of the high-purity sodium hypochlorite pentahydrate in the presence of the seed crystal of sodium hypochlorite pentahydrate, and The crystallization 2 is separated and recovered from the reaction liquid having passed through the crystallization step (2), and the separation step (3) of the filtrate 3 is obtained. A method for producing high-purity sodium hypochlorite pentahydrate according to claim 1, wherein the chlorine gas is introduced by diluting with an inert gas. A method for producing high purity sodium hypochlorite pentahydrate according to claim 1 or 2, wherein the chlorination reaction is carried out at a temperature of from 18 to 50 °C. The method for producing high-purity sodium hypochlorite pentahydrate according to any one of claims 1 to 3, wherein the cooling temperature in the crystallization step (1) is in the range of 5 to 25 °C. High purity sodium hypochlorite pentahydrate according to any one of claims 1 to 4 The manufacturing method, wherein the cooling temperature in the crystallization step (2) is in the range of 0 to 15 °C. The method for producing high-purity sodium hypochlorite pentahydrate according to any one of claims 1 to 5, further comprising the step of diluting the filtrate 3 with water to obtain an aqueous sodium hypochlorite solution. A method for producing a high-purity sodium hypochlorite aqueous solution, which comprises the step of dissolving crystal 1 and crystal 2 of high-purity sodium hypochlorite pentahydrate obtained in the production method according to any one of claims 1 to 6 in water. The method for producing a high-purity sodium hypochlorite aqueous solution according to claim 7, wherein the high-purity sodium hypochlorite aqueous solution has an effective chlorine concentration of 5 to 20% by mass. A method for producing a high-purity sodium hypochlorite aqueous solution according to claim 7 or 8, wherein the sodium chloride concentration of the high-purity sodium hypochlorite aqueous solution is less than 2% by mass. A method for producing an aqueous solution of sodium hypochlorite having an effective chlorine concentration of 5 to 20% by mass and a sodium chloride concentration of 2 to 20% by mass, which comprises the following steps: introducing chlorine into a sodium hydroxide aqueous solution for chlorination a step of separating the supernatant sodium chloride precipitated in the chlorination step from the reaction liquid to obtain a separation step (1) of the filtrate 1, and cooling the precipitate 1 to precipitate a crystal 1 of high-purity sodium hypochlorite pentahydrate ( 1) separating and recovering the foregoing knot from the reaction liquid passing through the crystallization step (1) Crystal 1 , at the same time obtaining the separation step (2) of the filtrate 2, and crystallization of the crystal 2 of the high-purity sodium hypochlorite pentahydrate in the presence of the seed crystal of sodium hypochlorite pentahydrate to precipitate the crystallization step 2 (2) of the high-purity sodium hypochlorite pentahydrate The reaction liquid of the crystallization step (2) is separated and recovered to recover the crystal 2, and the separation step (3) of the filtrate 3 and the step of diluting the filtrate 3 with water are obtained.