JPH0624713A - Production of sodium percarbonate having excellent water solubility - Google Patents

Abstract

PURPOSE:To obtain sodium percarbonate suitable for bleaching agent, having excellent water solubility, particle strength, etc., by reacting Na2CO3 with H2O2, crystallizing the reaction product from a crystallization mother liquor containing specific two kinds of inorganic compounds and granulating. CONSTITUTION:Sodium carbonate is reacted with hydrogen peroxide to form sodium percarbonate. Formed sodium percarbonate is crystallized from a crystallization mother liquor containing sodium sulfate as a salting-out agent and a water-soluble alkali metal salt of silicic acid as a stabilizer. Then crystallized crystal is granulated by a method such as pushing granulation to give sodium percarbonate having excellent water solubility. In the crystallization, a method wherein preplacing crystallization tank is laid, seed crystal of sodium percarbonate is precipitated in the preplacing crystallization tank, the seed crystal is thrown to a reaction tank, crystal diameter of the precipitated sodium percarbonate is controlled to <=100mu and then the crystal is granulated is preferable.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing sodium percarbonate having excellent water solubility.

[0002]

BACKGROUND OF THE INVENTION Sodium percarbonate is a typical oxygen-based bleaching agent along with sodium perborate, and its bleaching effect is slightly inferior to that of chlorine-based bleaching agents. Since it is mild, it does not damage the fabric even if it is made of synthetic fibers, animal and plant fibers, or dyed fibers, and has no color fading, and there is no danger of sudden chlorine generation. Very useful as a commercial bleach. Due to its excellent physical properties, it has been used very much in recent years, and the quality has also been improved a lot. When this sodium percarbonate is used for the purpose of bleaching, it is common to add it to normal water or warm water and then add the substance to be bleached. In order for sodium percarbonate to exert its bleaching effect, the added sodium percarbonate must first be dissolved in water, and in order to bleach within a limited time such as when bleaching at the same time during washing It is clear that the faster the dissolution rate of soda, the better the bleaching effect. Therefore, sodium percarbonate having excellent solubility is desired,
Conventionally, (A) a method in which an organic acid such as succinic acid is blended and foamed by the reaction between sodium carbonate and the organic acid when poured into water to accelerate the dissolution of sodium percarbonate (Japanese Patent Publication No. 56-2
1797), (B) A method of reducing the secondary particle size to make it easier to dissolve has been studied.

However, in the method of blending the organic acid (A), the effective oxygen content of the sodium percarbonate is relatively lowered by blending the organic acid, and the organic acid may not be preferable depending on the use. . This method is not a method of improving the solubility of sodium percarbonate itself, but a method relating to the application of sodium percarbonate.

Regarding the method of reducing the secondary particle diameter of (B), the effect is small even if the secondary particle diameter is reduced unless the basic solubility of sodium percarbonate is changed. If the value is reduced, problems such as generation of dust and difficulty in handling occur.

[0005]

[Means for Solving the Problems] As a result of various studies in view of the above-mentioned drawbacks, the present inventors have added sodium sulfate as a salting-out agent and an alkali metal silicate salt as a stabilizer during crystallization, and further, A method for producing sodium percarbonate having a remarkably high dissolution rate was found by providing a pre-crystallization tank to control the crystal diameter of the precipitated sodium percarbonate to 100 μm or less and granulating the obtained crystals. Invented.

That is, the present invention is a method for producing sodium percarbonate by crystallization by reacting sodium carbonate with hydrogen peroxide, in which sodium sulfate and a water-soluble alkali metal silicate are added to the crystallization mother liquor, and A method for producing a highly water-soluble sodium percarbonate characterized by granulating the obtained crystals, and in the above invention, particularly in the method for producing sodium percarbonate, a pre-crystallization tank at the time of crystallization Is provided, and seed crystals of sodium percarbonate are precipitated in the pre-crystallization tank, and the size of the crystals of sodium percarbonate to be precipitated is controlled by introducing the seed crystals into the reaction tank. Of sodium percarbonate having excellent water-solubility and sodium sulphate in the crystallization mother liquor in an amount of 2 to 20% by weight. Production of sodium percarbonate having excellent water solubility, wherein the amount added alkali metal salt is sodium silicate or potassium silicate is 0.01 to 1% relative to sodium percarbonate which crystallized as SiO ₂ It provides a method.

[0007] Usually, the mechanism when the particles obtained by granulating a powder having a fine primary particle diameter are dissolved in water is considered as follows. When the particles are thrown into water, the water penetrates into the gaps between the crystals and dissolves the substances that bind the crystals together. As a result, the granulated particles disperse in water in pieces. Sodium percarbonate particles themselves dispersed in water dissolve in water.

In the case of dissolution by the above mechanism, the factors affecting the solubility are considered to be as follows. (1) Solubility and amount of crystal-to-crystal binding substance (2) Solubility of sodium percarbonate primary particles (3) Size of sodium percarbonate primary particles Dissolved by considering the above items It is considered possible to obtain sodium percarbonate having excellent properties.

The inventors of the present invention have invented a method for producing sodium percarbonate having excellent solubility by solving these items in order and combining them.
The crystal and the substance binding the crystal of (1) correspond to an organic or inorganic binder or a kind of stabilizer usually used at the time of granulation. Organic binders include water-soluble polymeric materials such as sodium polyacrylate, starch, polyethylene glycol. Inorganic binders include aluminum salts such as aluminum phosphate and silicates typified by sodium silicate. Addition of these binders at the time of granulation has the advantage that the strength of the particles is increased and the granulation yield is improved. However, the addition of these binders, although to some extent, clearly inhibits solubility, and it is preferable not to add a binder. However, among these binders, silicates are indispensable as a stabilizer for sodium percarbonate and must be added. As a result of various studies in view of this fact, the present inventors have found that the addition of silicate during crystallization does not affect the solubility. Due to this fact, an attempt was made to add no binder that affects the solubility during granulation.

Next, attention was paid to the solubility of the primary particles of sodium percarbonate (2). Regarding the solubility of the primary particles of sodium percarbonate, it is considered that there is no change in the solubility if the sodium percarbonate is a pure substance, but sodium percarbonate used for bleach usually contains various stabilizers and It was considered that a salting-out agent was added for the purpose of suppressing the amount of sodium percarbonate dissolved in the mother liquor and improving the yield of hydrogen peroxide, and these effects may change the solubility. In particular, we paid attention to salting out agents, which were added in a larger amount than the stabilizers, and conducted various studies on the solubility of primary particles due to the difference in the salting out agents. Usually, salting-out agents used for the production of sodium percarbonate include water-soluble inorganic salts having sodium as a common ion, that is, sodium chloride, sodium sulfate, sodium bicarbonate, etc. It was found that the solubility of primary particles of sodium percarbonate was the fastest when sodium sulfate was used as the internal salting-out agent.

Sodium sulphate is added as a salting-out agent at the time of crystallization and silicate as an indispensable stabilizer is added at the time of crystallization to form a binder or a binder when the obtained crystals are granulated. By adding no possible stabilizer, it has become possible to produce sodium percarbonate having excellent water solubility.

The product obtained by the above method is very excellent in solubility, and it is considered that there is no practical problem in strength, but depending on the application, a product having higher granulated particle strength is desired. Mareta.

As a result of further study on this problem, the present inventors have found that in order to increase the strength of particles granulated without adding a binder at the time of granulation, the primary particle diameter of the crystal to be crystallized I thought that it could be solved by controlling it small. Reducing the primary particle size of the crystals also has the effect of improving the solubility. However, the particle size of the crystals of sodium percarbonate to be crystallized is set to a size suitable for granulation, that is, 100.
It was not possible to reduce the particle size to less than or equal to micron by a commonly used method, that is, control of the slurry concentration, stirring strength, slurry residence time and the like. Therefore, a pre-crystallizing tank described in Japanese Patent Application No. 3-7412 proposed by the present applicant is provided, and a part or the whole amount of the circulating reaction mother liquor and hydrogen peroxide to be added is charged into the pre-crystallizing tank. It was possible to control the average primary particle diameter to 100 μm or less by introducing the precipitated seed crystal into the reaction tank, improve the granulation yield, and increase the particle strength.

As a result of the above, the use of sodium sulfate as a salting-out agent during crystallization, the addition of a silicate as an indispensable stabilizer during crystallization, and the binder which can be a binder or a binder during granulation Sodium percarbonate with excellent water solubility and high grain strength by adding no pre-mixture and controlling the average size of primary particles to be crystallized to 100 μm or less by providing a pre-crystallization tank attached to the crystallization tank. Can be manufactured.

When sodium sulfate is used as a salting-out agent, if the addition amount is small, the salting-out effect is small and the contribution to the solubility is small. On the other hand, if the amount added is too large, it cannot exist as a solution and precipitates as crystals. Therefore, 2 to 20 w%, preferably 5 to 15% in the crystallization mother liquor is preferable.
w% is suitable. As the water-soluble alkali metal silicate added as a stabilizer, there are sodium silicate, potassium silicate, and the like. However, if the addition amount is too large, the solubility is adversely affected, so sodium percarbonate that crystallizes as SiO ₂ 0.01 to 1% by weight gives a preferable result.

Other commonly used stabilizers for improving stability may be added both during crystallization and during granulation. Furthermore, sodium percarbonate is a compound that rapidly generates oxygen when heated, and exerts an auxiliary combustion property to other inevitable substances, but various diluents are used for the purpose of reducing the risk of generating oxygen. For example, sodium bicarbonate, sodium carbonate, sodium sulfate or the like may be added at the time of granulation.

As for the granulation method, extrusion granulation which is usually carried out gives a favorable result, but the granulation method is not limited to this, and any granulation method can be used.

[0018]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 Sodium carbonate 1 as a solution in a reaction tank having a volume of 6.5 L
0.5w%, hydrogen peroxide 1.6w%, sodium sulfate 1
A slurry having a composition of 2.5 w%, 0.03 w% of JIS No. 3 sodium silicate as SiO ₂ , 0.15 w% of EDTA, and 20 w% of sodium percarbonate as a solid content was prepared. 860 g / Hr of 60% hydrogen peroxide, 1100 g / Hr of granular anhydrous sodium carbonate, 1.6 g / Hr of JIS No. 3 sodium silicate as SiO ₂ , EDTA 8
g / Hr, sodium sulfate 62 g / Hr and sodium carbonate 10.5 w%, hydrogen peroxide 1.6 w%, sodium sulfate 12.5 w%, JIS No. 3 sodium silicate as SiO ₂ 0.03 w%, EDTA 0.15 w% The mother liquor having the composition was continuously supplied to the reaction tank at 6000 g / Hr, and the reaction was carried out while maintaining the liquid temperature at 25 ° C. for a residence time of the slurry of 1 hour.

The produced sodium percarbonate slurry was withdrawn from the reaction vessel by overflow and crystallized by a centrifuge, and then the filtrate was circulated in a pre-crystallization vessel for continuous reaction crystallization. At 8 hours after the start of the continuous reaction, the water content of the cake obtained by centrifuging and dehydrating the obtained slurry at 1000 G for 3 minutes was 7.5%.
And the average particle size at that time was 130 microns. The average particle size was measured by using a laser type particle size distribution analyzer with ethanol as a medium.

Next, 0.2% by weight of magnesium sulfate as a stabilizer was added to the obtained sodium percarbonate to adjust the water content to 10%.
After adjusting to -15% and kneading for 15 minutes, it was granulated by a twin-screw extrusion type pelletizer (manufactured by Fuji Paudal Co., Ltd.), and the granulated product was dried by a fluidized bed dryer to obtain a product.

Further, the grain strength (pulverization rate) and the dissolution rate of the obtained product were measured by the following methods. The measurement results are shown in Table 1. * Measurement method of powdering rate: 100 g of the product (16 mesh to 32 mesh) is put into a 60 mesh sieve and 50 by a shaker.
The mixture was shaken at 0 rpm for 1 hour, and the amount of powder generated was measured and defined as the powdering rate. * Dissolution rate measuring method: 1 L of clean water at 0 ° C. was stirred at a speed of 200 rpm, 5 g of the product was added, and the time until complete dissolution was measured.

Example 2 Sodium carbonate 1 as a solution was placed in a reaction vessel having a volume of 6.5 L.
0.5w%, hydrogen peroxide 1.6w%, sodium sulfate 1
A slurry having a composition of 2.5 w%, 0.03 w% of JIS No. 3 sodium silicate as SiO ₂ , 0.15 w% of EDTA, and 20 w% of sodium percarbonate as a solid content was prepared. Then, in the pre-crystallization tank, sodium carbonate 10.5% by weight,
Hydrogen peroxide 1.6w%, sodium sulfate 12.5w%,
JIS3 sodium silicate as SiO ₂ 0.03w
%, 600 ml of mother liquor having a composition of EDTA 0.15 w%
Supplied at 0 g / Hr and 880 with 60% hydrogen peroxide
It was supplied at g / Hr to precipitate fine crystals of sodium percarbonate. A mixed slurry of these fine crystals (seed crystals), hydrogen peroxide, and mother liquor and granular anhydrous sodium carbonate 1100 g / Hr, JI
S3 No. sodium silicate as SiO ₂ 1.6g / H
r, EDTA 8g / Hr, sodium sulfate 62g / Hr
Was continuously supplied to the reaction tank, and the reaction was performed while maintaining the liquid temperature at 25 ° C. for a residence time of the slurry of 1 hour.

The produced sodium percarbonate slurry was withdrawn from the reaction vessel by overflow and crystallized by a centrifuge, and the filtrate was circulated in a pre-crystallization vessel for continuous reaction crystallization. A seed crystal was generated under the conditions that the mother liquor staying time in the pre-crystallization tank was 1 minute and the stirring speed was 200 rpm. When 8 hours had elapsed after the start of the continuous reaction, the water content of the cake obtained by centrifuging and dehydrating the obtained slurry at 1000 G for 3 minutes was 14.
It was 0%, and the average particle size at that time was 28 microns.

Next, 0.2% by weight of magnesium sulfate as a stabilizer was added to the obtained sodium percarbonate to adjust the water content to 10%.
After adjusting to -15% and kneading for 15 minutes, it was granulated by a twin-screw extrusion type pelletizer (manufactured by Fuji Paudal Co., Ltd.), and the granulated product was dried by a fluidized bed dryer to obtain a product. The obtained product had sufficient strength as a bleaching agent. The grain strength (pulverization rate) and dissolution rate of the obtained product were measured, and the results are shown in Table 1.

Example 3 Using the sodium percarbonate cake prepared in Example 2, the same conditions as in Example 2 were used except that 20.0 w% of sodium bicarbonate was further added as a diluent during the granulation operation. It was carried out. The grain strength (pulverization rate) and dissolution rate of the obtained product were measured, and the results are shown in Table 1.

Example 4 Using the sodium percarbonate cake prepared in Example 2, sodium carbonate 1 was further used as a diluent when granulating.
It carried out on the same conditions as Example 2 except having added 8.0 w%. The grain strength (pulverization rate) and dissolution rate of the obtained product were measured, and the results are shown in Table 1.

Example 5 Using the sodium percarbonate cake prepared in Example 2, sodium carbonate 1 was further added as a diluent when granulating.
It was carried out under the same conditions as in Example 2 except that 8.0 w% and sodium tripolyphosphate 0.05 w% were added as a stabilizer. The grain strength (pulverization rate) and dissolution rate of the obtained product were measured, and the results are shown in Table 1.

Comparative Example 1 Sodium carbonate 10.5 as a solution in a 6.5 L reaction tank
w%, hydrogen peroxide 1.6w%, sodium sulfate 12.5
A slurry having a composition of w%, EDTA 0.15w% and sodium percarbonate 20w% as a solid content was prepared. Then, in the pre-crystallization tank, 10.5 w% sodium carbonate, 1.6 w% hydrogen peroxide, 12.5 w% sodium sulfate, EDTA
A mother liquor having a composition of 0.15 w% was supplied at 6000 g / Hr, and 60% hydrogen peroxide was supplied at 880 g / Hr to precipitate fine crystals of sodium percarbonate. A mixed slurry of the microcrystals (seed crystals), hydrogen peroxide, and mother liquor and granular anhydrous sodium carbonate 1100 g / Hr, EDTA 8 g / H
r and 62 g / Hr of sodium sulfate were continuously supplied to the reaction tank, and the reaction was carried out while maintaining the liquid temperature at 25 ° C. for a residence time of the slurry of 1 hour.

The produced sodium percarbonate slurry was withdrawn from the reaction vessel by overflow, crystallized by a centrifuge, and the filtrate was circulated in a pre-crystallization vessel for continuous reaction crystallization. A seed crystal was generated under the conditions that the mother liquor staying time in the pre-crystallization tank was 1 minute and the stirring speed was 200 rpm. At 8 hours after the start of the continuous reaction, the water content of the cake obtained by centrifuging and dehydrating the obtained slurry for 3 minutes at 1000 G was 13.8%, and the average particle size at that time was 30 microns. It was

Next, 0.2 w% of magnesium sulfate and JIS No. 3 silicic acid were added to the obtained sodium percarbonate as a stabilizer.
0.1 w% as O ₂ was added, and the water content was 10 to 15%.
And kneading for 15 minutes, and then granulated by a twin-screw extrusion type pelletizer (manufactured by Fuji Paudal Co., Ltd.), and the granulated product was dried by a fluidized bed dryer to obtain a product. The grain strength (pulverization rate) and dissolution rate of the obtained product were measured, and the results are shown in Table 1.

Comparative Example 2 5.1 w of sodium carbonate as a solution in a 6.5 L reaction tank
%, Hydrogen peroxide 1.0 w%, salt 16 w%, JIS No. 3 sodium silicate as SiO ₂ 0.03 w%, EDT
A slurry having a composition of 0.15 w% A and 20 w% sodium percarbonate as a solid content was prepared. Then, a mother liquor having a composition of 5.1 w% sodium carbonate, 1.0 w% hydrogen peroxide, 16 w% hydrogen chloride, 0.03 w% JIS No. 3 sodium silicate as SiO ₂ and 0.15 w% EDTA was placed in the pre-crystallization tank. It was supplied at 6000 g / Hr, and 60% hydrogen peroxide was supplied at 880 g / Hr to precipitate fine crystals of sodium percarbonate. A mixed slurry of the microcrystals (seed crystals), hydrogen peroxide, and mother liquor and granular anhydrous sodium carbonate 1100 g /
Hr, JIS No. 3 sodium silicate as SiO ₂ .
6 g / Hr, EDTA 8 g / Hr, and sodium chloride 70 g / Hr were continuously supplied to the reaction tank, and the reaction was performed while maintaining the liquid temperature at 25 ° C. for a residence time of the slurry of 1 hour.

The produced sodium percarbonate slurry was withdrawn from the reaction tank by overflow and crystallized by a centrifuge, and the filtrate was circulated in a pre-crystallization tank for continuous reaction crystallization. A seed crystal was generated under the conditions that the mother liquor staying time in the pre-crystallization tank was 1 minute and the stirring speed was 200 rpm. At 8 hours after the start of the continuous reaction, the water content of the cake obtained by centrifuging and dehydrating the obtained slurry at 1000 G for 3 minutes was 13.8%, and the average particle size at that time was 31 microns. It was

Then, sodium percarbonate obtained by the same method as in Example 1 was granulated, and the grain strength (pulverization rate) and dissolution rate of the product were measured.

[0034]

[Table 1]

[0035]

Industrial Applicability According to the present invention, it is possible to produce sodium percarbonate having a high grain strength and a very high dissolution rate and excellent water solubility.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Moto Naoyama, Inoue Yamaguchi Prefecture, Ube City 5253 Oki Ube Central Glass Co., Ltd. Ube Laboratory

Claims (4)

[Claims] 1. A method for producing sodium percarbonate by crystallization by reacting sodium carbonate with hydrogen peroxide, which is obtained by adding sodium sulfate and a water-soluble alkali metal silicate to a crystallization mother liquor. A method for producing sodium percarbonate having excellent water solubility, which comprises granulating crystals. 2. In the method for producing sodium percarbonate, a pre-crystallization crystallization tank is provided for crystallization, seed crystals of sodium percarbonate are precipitated in the pre-crystallization crystallization tank, and the seed crystals are reacted. The method for producing a highly water-soluble sodium percarbonate according to claim 1, wherein the size of crystals of the sodium percarbonate precipitated by controlling the precipitation into the tank is controlled. 3. The crystallizing mother liquor contains 2 to 3 of the sodium sulfate.
Claim 1 characterized in that 20w% is present.
A method for producing sodium percarbonate having excellent water solubility as described in the above item. 4. The water-soluble alkali metal silicate is sodium silicate or potassium silicate, and the added amount is SiO 2.
0.01-1w for sodium percarbonate that crystallizes as ₂
%, The method for producing sodium percarbonate having excellent water solubility according to claim 1.