JP6469161B2 - Sodium hypochlorite pentahydrate crystal and method for producing the same - Google Patents

Description

  The present invention relates to sodium hypochlorite pentahydrate crystals and a method for producing the same.

  Sodium hypochlorite (NaClO) is widely used as a disinfectant for water and sewage systems, hot spring facilities, pools, households and the like because of its excellent bleaching effect and bactericidal effect. In addition, sodium hypochlorite is a bleaching agent for paper industry, textile industry, wastewater treatment agent for various industries, or slime damage that occurs in plant cooling circulation water system, wastewater treatment water system of various factories ( It is used in a wide range of applications such as slime cleaning agents that prevent the occurrence of slime due to algae, bacteria, etc., which prevents failures such as a decrease in thermal efficiency and blockage of water pipes. The oxidizing action of sodium hypochlorite is also used in the field of organic synthesis, and sodium hypochlorite is widely used in the production of pharmaceuticals and agricultural chemicals.

Among them, sodium hypochlorite plays an extremely important role as a water purification agent used for disinfecting various bacteria such as Escherichia coli. Moreover, since the water for waterworks is used for drinking water, the quality of chemicals for water purification is strictly controlled according to water supply standards. And by the recommendation of WHO, the chemical standards for water purification are becoming stricter. In recent years, in the water supply standards relating to chemicals for water purification, the concentration standards for bromic acid and chloric acid contained in purified water have been strengthened, and in particular, the concentration of sodium chlorate (NaClO ₃ ) has been severely restricted.

  However, since sodium hypochlorite causes a disproportionation reaction of the following formula 1 at room temperature, the sodium chlorate concentration gradually increases.

  Since this disproportionation reaction is accelerated as the temperature increases, the following method has been established as a water supply technology. Sodium hypochlorite is usually cooled to about 20 ° C. or less by a product storage tank at a factory, a lorry vehicle at the time of transportation, a receiving tank, etc., and stored for a long period of time. As another method, sodium hypochlorite is stored at a reduced decomposition rate due to the disproportionation reaction by reducing the concentration of the aqueous sodium hypochlorite solution.

  For sodium hypochlorite suppliers, storing sodium hypochlorite by these methods means cooling equipment costs and cooling running costs for sodium hypochlorite aqueous solution storage tanks, cooling sodium hypochlorite aqueous solution products. However, it increases the cost of transportation and causes an increase in product cost. In addition, each water department also requires excessive human costs and inspection costs for cooling the disinfectant chemical storage tank, temperature control, sodium chlorate concentration control, etc. It has become.

  On the other hand, monohydrate, 2.5 hydrate, pentahydrate, and hexahydrate are known for sodium hypochlorite crystals. Each hydrate has a melting point of about 80 ° C., about 60 ° C., about 30 ° C., and about 20 ° C., and becomes a low melting point as the hydration progresses. For example, pentahydrate made from high-concentration sodium hydroxide aqueous solution, which is relatively easy to produce, is easy to melt at room temperature, has deliquescence and is easy to be liquefied, and easily decomposes even in an air or nitrogen atmosphere. There is a problem that progresses. If it is stored in crystalline form, the volume can be greatly reduced with respect to the liquid form product, so that there is a merit that cooling cost, transportation cost etc. can be greatly reduced, but for this decomposability, Even if various types of hydrate crystals were produced, it was not possible to adopt a business form in which the crystals themselves were transported or sold.

  Ingenuity to suppress the decomposition of sodium hypochlorite has been tackled in the past. For example, in Patent Document 1, sodium hydroxide (solid) and an aqueous alkali phosphate solution are added to and mixed with a concentrated sodium hypochlorite solution obtained by melting sodium hypochlorite pentahydrate. It is disclosed that crystals mainly composed of sodium chlorite 2.5 hydrate are crystallized.

  Further, in Patent Document 2, when drying a sodium hypochlorite wet crystal containing 2.5 hydrate as a main component, a high-concentration sodium hydroxide aqueous solution is added to the hydrate. A 2.5 hydrate crystal containing sodium hydroxide, obtained by drying at a drying temperature of

  Furthermore, Patent Document 3 discloses a method for producing sodium hypochlorite pentahydrate. The pentahydrate crystals are dissolved in water to form an aqueous solution of about 12% effective chlorine. Supplied to the market.

Japanese Patent Publication No.49-010919 Japanese Patent Publication No. 49-028354 Patent No. 4211130

  Storage and transportation in an aqueous solution requires equipment such as a lorry vehicle and a storage tank with temperature control, and additional facilities for temperature control are required, resulting in excessive disinfection costs. There was a problem of becoming. In addition, sodium chlorate, which has stricter restrictions on concentration, is produced by gradually decomposing sodium hypochlorite during storage of an aqueous sodium hypochlorite solution. There was a problem that management was required to be strict and the cost for quality control was high. For example, in aqueous solution storage, even if the concentration of the aqueous solution is reduced, the concentration of sodium chlorate increases if stored for more than one month and cannot be used for disinfection. Therefore, it is necessary to pay close attention to the concentration management. There was a problem that it took time and effort. On the other hand, sodium hypochlorite pentahydrate crystals have the problem that decomposition proceeds easily even in an air atmosphere or a nitrogen atmosphere, as described above, and sodium hypochlorite pentahydrate crystals are produced. Therefore, the business form of transporting and selling it could not be adopted.

  An object of the present invention is to provide a sodium hypochlorite pentahydrate crystal in which the content of sodium chlorate, which is considered to be harmful to health, is reduced.

(1)
In the sodium hypochlorite pentahydrate crystal according to the present invention, the content of sodium chlorate is 200 ppm or less.

  This sodium hypochlorite pentahydrate crystal can be suitably used as a water purification agent because the content of sodium chlorate, which is considered to be harmful to health, is reduced.

(2)
In the sodium hypochlorite pentahydrate crystal described in (1), the sodium hydroxide component contained in the surface or inside of the crystal is 0.01 to 0.8% by weight.

  It is necessary to maintain the pH at about 10 in order to prevent decomposition due to acidic components, so it is necessary to add NaOH. However, if too much is added, the water content increases due to deliquescence of NaOH, and decomposition due to disproportionation occurs. Promote. That is, the storage stability is improved by adding an appropriate amount of NaOH.

(3)
In the sodium hypochlorite pentahydrate crystal described in (1) or (2), the water content other than hydrated water contained on the surface or inside is 2.5% by weight or less.

  Dissolution by moisture other than hydration water accelerates the disproportionation reaction and decomposition reaction. That is, storage stability improves by reducing the water content other than hydration water.

(4)
In the sodium hypochlorite pentahydrate crystal according to any one of (1) to (3), the content of sodium chloride contained on the surface or inside is 1.5% by weight or less.

  By containing sodium chloride, side reactions may occur when used as an organic synthesis raw material such as an oxidizing agent. That is, by reducing the content of sodium chloride, it can be applied to a precise organic synthesis reaction.

(5)
The method for producing sodium hypochlorite pentahydrate crystals according to the present invention includes a first step of reacting an aqueous sodium hydroxide solution with chlorine gas to obtain a mother liquor, and a second step of solid-liquid separation of sodium chloride from the mother liquor. A third step of adding seed crystals to the mother liquor set to a cooling start temperature at which sodium hypochlorite pentahydrate and sodium chlorate do not precipitate even if seed crystals are added to the mother liquor, and hypochlorous acid The sodium hypochlorite pentahydrate crystals are precipitated by cooling the mother liquor at a cooling rate of 1 to 20 ° C./hour until the cooling end temperature at which sodium pentahydrate is precipitated and no sodium chloride is precipitated. 4 steps and a fifth step of solid-liquid separating sodium hypochlorite from sodium hypochlorite pentahydrate crystals.

  In the third step, by adding seed crystals at the cooling start temperature at which sodium hypochlorite pentahydrate and sodium chlorate do not precipitate even if seed crystals are added, precipitation of sodium chlorate is prevented, The purity of sodium chlorite pentahydrate can be increased. Further, in the fourth step, sodium hypochlorite pentahydrate is precipitated, and the crystal grows by cooling at a cooling rate of 1 to 20 ° C./hour until the cooling end temperature at which sodium chloride does not precipitate. The crystals are large in size and excellent in dewaterability. That is, in this production method, sodium chlorate, sodium hydroxide, sodium chloride, and water content (excluding hydrated water) can be reduced.

(6)
In the method for producing sodium hypochlorite pentahydrate crystals described in (5), the effective chlorine concentration in the mother liquor in the third step is 20% or more, and the cooling start temperature is 15 to 25 ° C.

  In order to increase the crystallization rate in the subsequent fourth step and increase the yield, the addition of seed crystals is effective. In the concentration of the sodium hypochlorite aqueous solution produced in the third step, the temperature at which sodium hypochlorite pentahydrate and sodium chlorate do not precipitate even when seed crystals are added (cooling start temperature) is 15 to 25. ° C. Moreover, if it is this temperature, malfunctions, such as decomposition | disassembly of sodium hypochlorite pentahydrate by excessive crystallization heat generation | occurrence | production, can be suppressed and surplus sodium chloride byproduct can be suppressed. That is, in this production method, sodium hypochlorite pentahydrate with a low content of sodium chlorate and sodium chloride can be obtained in high yield.

(7)
In the method for producing sodium hypochlorite pentahydrate crystals described in (6), the cooling end temperature is 0 to 12 ° C.

  Precipitation of sodium chloride can be suppressed by setting the cooling end temperature in the fourth step to 0 to 12 ° C. That is, in this production method, sodium hypochlorite pentahydrate having a low sodium chloride content can be obtained.

  INDUSTRIAL APPLICABILITY According to the present invention, sodium hypochlorite pentahydrate crystals having a very low content of sodium chlorate and sodium chloride can be produced over a long period of 3 months or more. Sodium hypochlorite pentahydrate By selling and transporting crystals, significant energy savings can be achieved compared to conventional aqueous solution sales.

  In addition, when the stored crystals are dissolved in water and used as a sodium hypochlorite aqueous solution for water purification, the content of sodium chlorate decomposed and by-produced during storage and transportation is greatly reduced. Can be reduced. Furthermore, since it is in a crystalline form, it can be easily transported, and a disinfectant can be easily provided at places of use around the world such as a simple waterworks where it is difficult to transport an aqueous solution.

The manufacturing process flow of the sodium hypochlorite pentahydrate crystal | crystallization based on this invention is shown as schematic.

  The sodium hypochlorite pentahydrate crystal of the present invention has a sodium chlorate content of 200 ppm or less, preferably 190 ppm or less, more preferably 180 ppm or less, from the viewpoint of health hazard. In addition, the content of sodium hydroxide on the surface or inside of the sodium hypochlorite pentahydrate crystal is preferably 0.01 to 0.8% by weight, and 0.02 to 0.0. 3 weight% is more preferable and 0.03 to 0.1 weight% is further more preferable.

  The content of sodium chloride is preferably 1.8% by weight or less, more preferably 1.7% by weight or less, and further preferably 1.5% by weight or less from the viewpoint of suppressing side reactions at the time of use in an organic synthesis reaction. preferable.

  The water content other than the hydrated water contained on the surface or inside of the sodium hypochlorite pentahydrate crystal is preferably 2.5% by weight or less. Storage of sodium hypochlorite pentahydrate crystal From the viewpoint of improving stability, the content is more preferably 2.4% by weight or less, and further preferably 2.3% by weight or less.

  Sodium hypochlorite pentahydrate crystals reduce the water content and reduce the contents of impurities sodium chlorate and sodium chloride to increase the purity of the crystals, thereby reducing sodium hypochlorite. Decomposition of pentahydrate crystals can be further suppressed. However, what is contained in the sodium hypochlorite pentahydrate crystal | crystallization of this invention is not limited to sodium chlorate, sodium hydroxide, and sodium chloride, A thing other than these may be contained. In addition, although it may contain sodium bromate, it is preferable not to contain sodium bromate. Sodium hypochlorite pentahydrate crystals that do not contain sodium bromate are produced, for example, using chlorine gas obtained by the production method described in Japanese Patent No. 4308810.

  As shown in FIG. 1, the method for producing sodium hypochlorite pentahydrate crystals of the present invention comprises a reaction step (first step), an NaCl separation step (second step), and a seed crystal addition step (first step). 3 steps), a crystallization step (fourth step), and a solid-liquid separation step (fifth step). However, it is not limited to the 1st-5th process, You may enter processes other than these. For example, a step of drying crystals of sodium hypochlorite pentahydrate may be included after the fifth step. Hereinafter, each step will be described in detail.

Reaction step (first step)
In the reaction step, an aqueous sodium hydroxide solution is reacted with chlorine gas to obtain an aqueous sodium hypochlorite solution. In the present invention, it is preferable to use a 32 to 38% aqueous sodium hydroxide solution in the reaction step of chlorination reaction. Within this range, the production rate of sodium hypochlorite by the chlorination reaction represented by the following formula 2 can be maintained high, and the production of sodium chlorate based on the disproportionation reaction can be controlled very little. A sodium hypochlorite aqueous solution with a low content can be produced.

  This aqueous sodium hydroxide solution used in the reaction process should be used as a raw material with limited contact with the atmosphere as much as possible in order to suppress the formation of sodium bicarbonate that promotes the decomposition of sodium hypochlorite pentahydrate crystals. The chlorination reaction is more preferably carried out in a system that does not come into contact with the atmosphere.

  In the present invention, the reaction temperature in the reaction step is not particularly limited, but is preferably 22 to 26 ° C. Within this range, the chlorination reaction proceeds smoothly, and the production of sodium chlorate accompanying the disproportionation reaction can be greatly suppressed.

  In order to produce sodium hypochlorite pentahydrate crystals with a very low sodium chlorate content, it is important to suppress the disproportionation reaction and to suppress the perchlorination reaction. It is important to balance.

NaCl separation step (second step)
In the NaCl separation step, sodium chloride is solid-liquid separated from the sodium hypochlorite aqueous solution to obtain a crystallization mother liquor. Specifically, the sodium hypochlorite aqueous solution produced by chlorination contains a large amount of by-produced sodium chloride crystals. Therefore, in the NaCl separation step, although not particularly limited, for example, solid-liquid separation is performed by a centrifuge.

  This sodium hypochlorite aqueous solution may contain 0 to about 0.3% or less of sodium hydroxide used as a raw material, but the crystallized sodium hypochlorite pentahydrate crystals are decomposed. It is not enough to suppress this. Therefore, in this step, the concentration of sodium hydroxide in the sodium hypochlorite aqueous solution (mother liquor) is set to 2.0 to 5.0% by adding the sodium hydroxide aqueous solution to the sodium hypochlorite aqueous solution. Is preferred. By adjusting the concentration of sodium hydroxide in the mother liquor within this range, sodium hydroxide can be efficiently distributed in the vicinity of the surface of the sodium hypochlorite pentahydrate crystal after crystallization, and sodium hypochlorite Decomposition of pentahydrate crystals can be suppressed for a long time.

  The aqueous sodium hydroxide solution used here is preferably an aqueous solution having a sodium hydroxide concentration of 45% or more. That is, maintaining the pH of the reaction system lowered by the chlorination reaction at a high pH (10 or more) is effective in suppressing the decomposition of crystals.

  When sodium hydroxide is present in the vicinity of the surface of sodium hypochlorite pentahydrate crystal, it is washed with an aqueous sodium hydroxide solution in the solid-liquid separation step (fifth step) after crystallization, or A method such as blending and adding sodium hydroxide solid powder to sodium chlorate pentahydrate crystals is assumed. However, cleaning with a high-concentration sodium hydroxide aqueous solution may cause equipment problems. In addition, there arises a problem that the yield is reduced by washing with a low concentration sodium hydroxide aqueous solution. In the method of adding and adding the sodium hydroxide solid powder, the heat of fusion of the sodium hydroxide crystal is generated, and the heat causes decomposition of sodium hypochlorite pentahydrate. Therefore, by adding the above sodium hydroxide aqueous solution to the sodium hypochlorite aqueous solution, the concentration of sodium hydroxide in the sodium hypochlorite aqueous solution (mother liquid) used for crystallization is 2.0 to 5.0%. Is the most preferred method.

Seed crystal addition step (third step)
In the present invention, the pretreatment (second step) sodium hypochlorite aqueous solution (mother liquor) is introduced into the crystallizer for crystallization. The effective chlorine concentration in the mother liquor is preferably 20% or more, more preferably 23% or more, and even more preferably 26%, from the viewpoint of crystallization efficiency.

  A small amount of seed crystals can be used for the purpose of increasing the crystallization speed. As a condition for introducing the seed crystal, it is preferable to add the seed crystal to the mother liquid set to a cooling start temperature at which sodium hypochlorite pentahydrate and sodium chlorate do not precipitate even if the seed crystal is added to the mother liquid. . Specifically, it is preferable to introduce seed crystals when the cooling start temperature (the temperature of the mother liquor) is 15 to 25 ° C. At this temperature, sodium hypochlorite pentahydrate and sodium chlorate do not precipitate even when seed crystals are added to the sodium hypochlorite aqueous solution, and hypochlorite is generated due to excessive crystallization heat generation. Decomposition of sodium acid pentahydrate can be suppressed, and excessive sodium chloride by-product can be suppressed. Considering that the seed crystal dissolves before crystallization, the cooling start temperature for adding the seed crystal is more preferably 16 to 23 ° C, and further preferably 17 to 20 ° C.

Crystallization process (4th process)
In the present invention, crystallization is not performed at a constant temperature, but is performed while cooling at a constant cooling rate.

  The cooling rate is preferably 1 to 20 ° C./hour. Within this range, not only the eutectic of sodium chlorate and sodium chloride can be prevented, but also the crystal scale adhering to the crystallizer wall can be prevented. Increased stirring power due to the formation of fine crystals and liquid removal during solid-liquid separation. It can prevent the deterioration of sex. In addition, the mother liquor can be cooled at a speed that does not affect the productivity. In order to achieve the optimum balance, the cooling rate is more preferably 2 to 15 ° C / hour, and further preferably 3 to 10 ° C / hour.

  The stirring during the crystallization is preferably performed at a stirring blade tip speed of 0.2 to 3 m / sec. By selecting this range, it is possible to prevent crystal scales adhering to the crystallizer wall surface, and to prevent an increase in stirring power due to the formation of fine crystals and deterioration of the liquid removal during solid-liquid separation. Further, by selecting this range, a sufficient cooling rate can be ensured, and productivity can be ensured. In order to achieve the optimum balance, the tip speed of the stirring blade is particularly preferably 0.3 to 2 m / sec.

  The temperature finally reached in the crystallization step (cooling end temperature) is preferably a temperature at which sodium hypochlorite pentahydrate precipitates and sodium chloride does not precipitate. Specifically, the temperature finally reached in this step (cooling end temperature) is preferably 0 to 12 ° C. If it is this temperature, moderate slurry viscosity can be maintained and the solid-liquid separation (5th process) of the following process will become easy. If the temperature reached is low, the by-product of sodium chloride crystals increases and the energy required for cooling becomes excessive. On the other hand, when the cooling end temperature is high, the production of sodium hypochlorite pentahydrate crystals is insufficient and the production efficiency is lowered. From this balance, the cooling end temperature is more preferably 2 to 10 ° C, and further preferably 3 to 7 ° C.

Solid-liquid separation process (5th process)
In the present invention, the slurry containing sodium hypochlorite pentahydrate crystals obtained in the crystallization step is subjected to the following step from sodium hypochlorite pentahydrate crystals using a solid-liquid separator such as a centrifuge. Sodium chlorite is separated into solid and liquid to obtain sodium hypochlorite pentahydrate crystals.

  In the solid-liquid separation process, if excessive centrifugal force is applied or the filtration time is excessively long, the temperature of the sodium hypochlorite pentahydrate crystal rises during solid-liquid separation, and melts and decomposes. Concerns increase. Therefore, the centrifugal force range of the centrifuge is preferably 200G to 400G, more preferably 270G to 350G, and further preferably 250G to 300G from the viewpoint of suppressing the temperature rise of the sodium hypochlorite pentahydrate crystal. . The filtration time is preferably 1 to 15 minutes, more preferably 2 to 10 minutes, and further preferably 3 to 8 minutes.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. In the following examples and comparative examples,% is based on weight unless otherwise specified.

  The physical properties of sodium hypochlorite pentahydrate crystals, the effective chlorine concentration, and the concentrations of sodium hydroxide, sodium chlorate and sodium chloride contained were quantified by the following method.

(Sample 1 adjustment)
The sodium hypochlorite pentahydrate crystal to be measured was accurately weighed in a conical beaker and dissolved in Yg water to prepare a sodium hypochlorite aqueous solution, which was designated as sample 1.

(Sample 2 adjustment)
Sample 1 was accurately weighed into a 250 mL volumetric flask with a 10 mL hole pipette, pure water was added up to the marked line, and the mixture was shaken well to obtain Sample 2.

(Sample 3 adjustment)
20-30 mL of pure water is put in a 100 mL volumetric flask in advance, and 2 mL of sample 1 is accurately collected with a micropipette. 10 mL of 3% aqueous hydrogen peroxide solution was added, and the mixture was thoroughly shaken to decompose all sodium hypochlorite, and then pure water was added up to the marked line.

(specific gravity)
Sample 1 was accurately placed in a conical beaker with a 25 mL hole pipette, the weight Zg was measured, and the specific gravity (hereinafter, also referred to as “SG”) of the sodium hypochlorite aqueous solution was determined using Equation 3 shown below.

(Effective chlorine concentration)
10 mL of sample 2 was put in a beaker, and then 25 mL each of 10% potassium iodide aqueous solution and 10% acetic acid aqueous solution were added, and titrated with 1 / 10N sodium thiosulfate aqueous solution. When the color of the liquid changed from brown to light yellow, about 3 drops of an aqueous starch solution were added, and titration was again performed with a 1 / 10N aqueous sodium thiosulfate solution until the color of the liquid changed from brown to colorless. At this time, the amount of the required 1 / 10N sodium thiosulfate aqueous solution was set to AmL, and it was combined with the specific gravity obtained in the previous measurement, and was substituted into the following formula 4 to obtain the sodium hypochlorite pentahydrate crystal in the crystal. The effective chlorine concentration was determined.

(Sodium hydroxide and sodium carbonate concentration)
25 mL of Sample 1 was accurately placed in a beaker, and a 3% aqueous hydrogen peroxide solution was gradually added, and the addition of the 3% aqueous hydrogen peroxide solution was stopped when oxygen gas production was stopped by the reaction. After thoroughly shaking, 1 or 2 drops of phenolphthalein solution was added and titrated with a 1 / 10N aqueous sulfuric acid solution until the red color disappeared. At this time, the amount of the required 1 / 10N sulfuric acid aqueous solution was set to BmL.

  Subsequently, 2 drops of methyl orange solution were added and titrated with a 1 / 10N aqueous sulfuric acid solution until a light red color was obtained. At this time, the amount of the required 1 / 10N sulfuric acid aqueous solution was CmL, and the values of B and C were substituted into the following formulas 5 and 6 together with SG obtained in the previous measurement, thereby sodium hypochlorite. The concentration of sodium hydroxide and sodium carbonate in the pentahydrate crystal was determined.

(Sodium chloride concentration)
Place exactly 10 mL of sample 2 in a beaker, add 5 mL of 3% aqueous hydrogen peroxide solution, shake well, add 1 or 2 drops of phenolphthalein solution, and titrate until the red color disappears with 1/10 N aqueous sulfuric acid solution. . Subsequently, 3 drops of potassium chromate indicator were added and titrated with a 1 / 10N aqueous silver nitrate solution until yellow to brown. At this time, the amount of the required 1 / 10N silver nitrate aqueous solution was set to DmL, and was combined with the specific gravity and effective chlorine concentration obtained previously and substituted into the following formula 7 to obtain chloride in the sodium hypochlorite pentahydrate crystal. The concentration of sodium was determined.

(Sodium chlorate concentration)
About 20 mL of sample 3 is passed through a chloride ion removal filter (Thermo SCIENTIFIC, OnGuard2 Ag), further passed through a metal ion removal filter (Thermo SCIENTIFIC, OnGuard2 H), and finally a membrane filter (Nihon Millipore IC MILLEX- LG) was used to remove chlorides, metal ions and insolubles, and then analyzed using ion chromatography. The analytical instrument used was ICS-1000 Ion Chromatography System manufactured by Nippon Dionex Co., Ltd., and the analysis conditions were separation column: IonPac AS9-HC, guard column: IonPac AG9-HC, suppressor: ASRS; recycle mode, current value 45 mA, detector: electric conductivity detector, eluent: 8 mmol / L Na ₂ CO ₃ , 1 mmol / L NaOH, flow rate: 1 mL / min, sample introduction amount: 25 μL. The concentration of sodium chlorate was determined from the peak area ratio of the obtained chromatograph by a calibration curve method.

(Moisture content)
The concentration of sodium hypochlorite pentahydrate is converted from the previously obtained effective chlorine concentration using the following formula 8, and the obtained sodium hypochlorite pentahydrate concentration and the previously determined hydroxylation By substituting the concentrations of sodium, sodium chloride and sodium chlorate into the following formula 9, the water content excluding hydration water was calculated.

(Crystal yield)
As shown in the following formula 10, the obtained sodium hypochlorite pentahydrate was expressed as a weight percent based on the weight of sodium hypochlorite contained in the used aqueous sodium hypochlorite solution.

(Chlorine yield)
As shown in the following formula 11, the effective chlorine amount of the obtained sodium hypochlorite pentahydrate was converted and expressed based on the effective chlorine amount contained in the used sodium hypochlorite aqueous solution.

Example 1
The seed crystal was obtained at the stage when it reached 17 ° C. (cooling start temperature) while gradually cooling the sodium hypochlorite aqueous solution shown in Table 1 obtained by chlorination of sodium hydroxide in the first step and shown in Table 1. (Step 3), and cooled to reach 6 ° C. (cooling end temperature) over 120 minutes (Step 4) to obtain sodium hypochlorite pentahydrate crystals (Step 5). Process). Table 2 shows the physical properties of the obtained sodium hypochlorite pentahydrate.

  Using the obtained sodium hypochlorite pentahydrate, a stability test was conducted. Sodium hypochlorite pentahydrate was placed in a laminzip AL-12 manufactured by Seinichi Co., Ltd. having a triple structure of polyethylene terephthalate (PET) / aluminum (AL) / polyethylene (PE), and the air inside was extruded and sealed. Thereafter, it was stored at 22 ° C. in a cool incubator CN-25C manufactured by Mitsubishi Electric Engineering Co., Ltd. The results are shown in Table 3.

(Comparative Example 1)
The sodium hypochlorite aqueous solution shown in Table 1 obtained by chlorination of sodium hydroxide in the first step and shown in Table 1 was cooled to 13 ° C., and seed crystals were added when it reached (third step) ), Maintaining the temperature for 120 minutes (fourth step) to obtain crystals of sodium hypochlorite pentahydrate (fifth step). Table 2 shows the physical properties of the obtained sodium hypochlorite pentahydrate.

  Moreover, the stability test was done on the conditions similar to Example 1 using the obtained sodium hypochlorite pentahydrate. The results are shown in Table 3.

(Comparative Example 2)
A seed crystal was added when the sodium hypochlorite aqueous solution shown in Table 1 obtained by chlorination of sodium hydroxide in the first step and shown in Table 1 reached 6 ° C. while gradually cooling (third step). Step), the temperature was maintained for 120 minutes (fourth step) to obtain crystals of sodium hypochlorite pentahydrate (fifth step). Table 2 shows the physical properties of the obtained sodium hypochlorite pentahydrate.

  Moreover, the stability test was done on the conditions similar to Example 1 using the obtained sodium hypochlorite pentahydrate. The results are shown in Table 3.

(Comparative Example 3)
The sodium hypochlorite aqueous solution shown in Table 1 obtained by chlorination of sodium hydroxide in the first step and shown in Table 1 was gradually cooled to −4 ° C., and seed crystals were introduced when it reached (first step) 3 steps), the temperature was maintained for 120 minutes (4th step), and crystals of sodium hypochlorite pentahydrate were obtained (5th step). Table 2 shows the physical properties of the obtained sodium hypochlorite pentahydrate.

  Moreover, the stability test was done on the conditions similar to Example 1 using the obtained sodium hypochlorite pentahydrate. The results are shown in Table 3.

  There was no significant difference in the composition of the sodium hypochlorite aqueous solution used for crystallization in Example 1 and Comparative Examples 1 to 3.

  The sodium hypochlorite pentahydrate crystal according to Example 1 has a concentration of sodium chlorate, a concentration of sodium chloride, and a water content other than hydrated water as compared with sodium hypochlorite according to Comparative Examples 1 to 3. Was low. Further, the crystal size was large in both the long axis direction and the short axis direction as compared with Comparative Examples 1 to 3. From this, it was possible to obtain sodium hypochlorite pentahydrate crystals with high purity by preparing the production method of Example 1.

  In Comparative Example 1, since the crystallization temperature is constant at 13 ° C., the crystal growth is small, and it is considered to be a crystal of sodium hypochlorite pentahydrate having low purity due to eutectic crystal with sodium chlorate. It was. Further, the minor axis direction was small, the efficiency in the fifth step was poor, the values of sodium chloride, sodium chlorate and water content were large, and the stability did not reach Example 1.

  In Comparative Example 2, since the crystallization temperature is constant at 6 ° C., there is little crystal growth and it is considered to be a crystal of sodium hypochlorite pentahydrate having low purity due to eutectic with sodium chlorate. It was. Further, both the long axis direction and the short axis direction were small, the efficiency in the fifth step was poor, the values of sodium chloride, sodium chlorate and water content were large, and the stability did not reach that of Example 1.

  In Comparative Example 3, since the crystallization temperature is constant at −4 ° C., there is no crystal growth, and it is a crystal of sodium hypochlorite pentahydrate having low purity due to eutectic with sodium chlorate. it was thought. Further, both the long axis direction and the short axis direction were small, the efficiency in the fifth step was poor, the values of sodium chloride, sodium chlorate and water content were large, and the stability did not reach that of Example 1.

  The sodium hypochlorite pentahydrate of Example 1 clearly shows sodium chloride and chloric acid when compared with the sodium hypochlorite pentahydrate of Comparative Examples 1 to 3 under the condition that the crystallization temperature is constant. Low sodium content, low water content (excluding hydrated water), slow decrease in effective chlorine concentration, and stability. The reason for this is that the crystal growth rate is slowed by gradually lowering the temperature at the time of crystallization, and the high purity sodium hypochlorite pentahydrate crystal is observed in both the major axis direction and the minor axis direction. This is probably due to the fact that it could be obtained in a large size. For this reason, it is considered that the efficiency of separation in the fifth step of performing solid-liquid separation has been improved.

  Since Example 1 had the highest effective chlorine concentration after 14 days and the moisture content was low, the purity was higher than that of Comparative Examples 1 to 3, and the low moisture content is considered to contribute to the stability. .

(Example 2)
Example 1 After adding a sodium hydroxide aqueous solution to the sodium hypochlorite aqueous solution obtained by chlorination of sodium hydroxide in the first step (second step) and adjusting the concentration shown in Table 4 (1.2%), Examples Crystallization was carried out under the same conditions as in No. 1 to obtain sodium hypochlorite pentahydrate crystals.

  As shown in Table 5, the sodium hypochlorite pentahydrate crystals obtained did not contain sodium hydroxide.

  Using the obtained sodium hypochlorite pentahydrate, a stability test was performed under the same conditions as in Example 1 except that the storage temperature was 15 ° C. The results are shown in Table 5.

(Example 3)
Example 1 After adding a sodium hydroxide aqueous solution to the sodium hypochlorite aqueous solution obtained by chlorination of sodium hydroxide in the first step (second step) and adjusting the concentration (2.0%) shown in Table 4 to Examples Crystallization was carried out under the same conditions as in No. 1 to obtain sodium hypochlorite pentahydrate crystals.

  As shown in Table 5, the sodium hypochlorite pentahydrate crystals obtained contained 0.04% sodium hydroxide.

  Using the obtained sodium hypochlorite pentahydrate, a stability test was performed under the same conditions as in Example 1 except that the storage temperature was 15 ° C. The results are shown in Table 5.

Example 4
Example 1 After adding a sodium hydroxide aqueous solution to the sodium hypochlorite aqueous solution obtained by chlorination of sodium hydroxide in the first step (second step) and adjusting the concentration (2.5%) shown in Table 4 to Examples Crystallization was carried out under the same conditions as in No. 1 to obtain sodium hypochlorite pentahydrate crystals.

  As shown in Table 5, the sodium hypochlorite pentahydrate crystals obtained contained 0.11% sodium hydroxide.

  Using the obtained sodium hypochlorite pentahydrate, a stability test was performed under the same conditions as in Example 1 except that the storage temperature was 15 ° C. The results are shown in Table 5.

(Example 5)
Example 1 After adding a sodium hydroxide aqueous solution to the sodium hypochlorite aqueous solution obtained by chlorination of sodium hydroxide in the first step (second step) and adjusting the concentration shown in Table 4 (4.1%), Examples Crystallization was carried out under the same conditions as in No. 1 to obtain sodium hypochlorite pentahydrate crystals.

  As shown in Table 5, the sodium hypochlorite pentahydrate crystals obtained contained 0.24% sodium hydroxide.

  Using the obtained sodium hypochlorite pentahydrate, a stability test was performed under the same conditions as in Example 1 except that the storage temperature was 15 ° C. The results are shown in Table 5.

(Example 6)
Example 1 After adding sodium hydroxide aqueous solution to the sodium hypochlorite aqueous solution obtained by chlorination of sodium hydroxide in the first step (second step) and adjusting the concentration shown in Table 4 (4.9%), Example Crystallization was carried out under the same conditions as in No. 1 to obtain sodium hypochlorite pentahydrate crystals.

  As shown in Table 5, sodium hypochlorite pentahydrate crystals obtained contained 0.32% sodium hydroxide.

  Using the obtained sodium hypochlorite pentahydrate, a stability test was performed under the same conditions as in Example 1 except that the storage temperature was 15 ° C. The results are shown in Table 5.

(Example 7)
Example 1 After adding a sodium hydroxide aqueous solution to the sodium hypochlorite aqueous solution obtained by chlorination of sodium hydroxide in the first step (second step) and adjusting the concentration shown in Table 4 (8.7%), Examples Crystallization was carried out under the same conditions as in No. 1 to obtain sodium hypochlorite pentahydrate crystals.

  As shown in Table 5, the sodium hypochlorite pentahydrate crystals obtained contained 0.85% sodium hydroxide.

  Using the obtained sodium hypochlorite pentahydrate, a stability test was performed under the same conditions as in Example 1 except that the storage temperature was 15 ° C. The results are shown in Table 5.

  Example 3 gave the best results in a 90 day (3 month) stability test. From the comparison of Example 2 and Example 3, it was considered that the presence of sodium hydroxide was essential for the stability of sodium hypochlorite pentahydrate crystals. Even if there was much sodium oxide, the effect was small and it was thought that there was an optimal point.

Claims (3)

  The concentration of sodium hydroxide contained in the surface or inside of the sodium hypochlorite pentahydrate crystal is 0.01 to 0.8% by weight, and the surface of the sodium hypochlorite pentahydrate crystal or Sodium hypochlorite pentahydrate crystals having a moisture content other than hydrated water contained therein is 2.5% by weight or less. The sodium hypochlorite pentahydrate crystal according to claim 1, which is transported and sold in a crystal form.   A sodium hypochlorite aqueous solution adjusted to an effective chlorine concentration of 20% or more and a sodium hydroxide concentration of 2.0 to 5.0% from a cooling start temperature of 15 to 25 ° C. to a cooling end temperature of 0 to 12 ° C. A method for producing sodium hypochlorite pentahydrate crystals, wherein crystallization is performed while cooling at a cooling rate of 1 to 10 ° C / hour.

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