JPS5869702A - Preparation of calcium hypochlorite - Google Patents

Abstract

PURPOSE:To prepare calcium hypochorite in high purity and yield, by adding slaked lime to a part of the liquid obtained by separating sodium chloride from the first-stage chlorination product, adding the resultant concentrated slaked lime slurry to the above separated liquid, and carrying out the second-stage chlorination. CONSTITUTION:An aqueous solution containing calcium hypochlorite and sodium chloride and obtained by the addition of the separated mothor liquor of the second-stage chlorination, is added with sodium hydroxide or sodium hydroxide and slaked lime to effect the first-stage chlorination, and the deposited sodium chloride is separated from the system. A concentrated slaked lime dispersion slurry is prepared by adding and dispersing slaked lime or slaked lime and sodium hydroxide to a part of the above separated liquid, and the slurry is mixed with the remaining part of the above separated liquid to obtain the raw material for the second-stage chlorination. The amount of the slaked lime added to the separated liquid is about equivalent to the sodium hypochlorite in the raw material. The reaction slurry obtained by the second-stage chlorination is centrifuged to obtain calcium hypochlorite crystals.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing calcium hypochlorite, and more specifically, in a rounding two-stage chlorination method for producing calcium hypochlorite, A highly concentrated slaked lime dispersion slurry is prepared by dispersing the slaked lime in the raw material slurry for the second stage chlorination, and the mosquito slurry is combined with the first stage separated liquid to form the raw material slurry for the second stage chlorination. The present invention relates to a method for producing calcium hypochlorite.

Slaked lime is a very important compound that is widely used for neutralization and as a raw material for various synthetic reactions, and in particular is the main raw material for highly bleached powder whose main component is calcium hypochlorite.

In recent years, there have been strong demands when manufacturing Mando Komako to minimize the amount of by-product bleaching liquid and to obtain a high-quality product with little insoluble residue.

In this regard, the inventors have discovered that calcium hypochlorite,
When adding slaked lime to an aqueous solution containing sodium hypochlorite and sodium chloride for chlorination, we believe that it is extremely important to uniformly and highly disperse the added slaked lime, but this cannot be satisfied using conventional techniques. Since there was no such thing available, we continued to conduct intensive research on a method for producing calcium hypochlorite using a two-stage chlorination method, especially on a method for dispersing slaked lime.

As a conventional dispersion method, for example, Japanese Patent Publication No. 43-2514
As shown in the specification of No. 3, there is a method in which slaked lime and water are mixed to form milk of lime, and then added to an aqueous solution containing calcium hypochlorite, sodium hypochlorite, and sodium chloride. In this case, in order to obtain a uniform slurry as milk of lime, it is necessary to use a large amount of water relative to slaked lime. After the chlorination reaction, the water used for preparing the milk of lime dissolves a considerable amount of calcium hypochlorite, which is the main target, and becomes a by-product bleaching solution.

As a result, there is a drawback that the amount of surplus liquid waste is increased per unit production of highly bleached powder.

On the other hand, there is a method in which slaked lime is added in powder form to an aqueous solution containing a high concentration of calcium hypochlorite.

However, this method of adding slaked lime was
As described in No. 3694, added slaked lime and calcium hypochlorite in an aqueous solution form a double salt, and the double salt forms a coarse solid substance that makes it difficult to uniformly disperse slaked lime. The inventors have already published JP-A-55-167103.
In this issue, sodium chloride is converted into an aqueous solution containing calcium hypochlorite, sodium hypochlorite, and sodium chloride in the first stage chlorination reaction, which is one of the manufacturing processes for highly bleached powder, and the second stage chlorination reaction. We have discovered a method for uniformly dispersing slaked lime in the separated liquid after the first stage chlorination reaction of a two-stage chlorination method to obtain calcium hypochlorite through the reaction. This method involves adding and dispersing slaked lime and then mixing the remaining first-stage separated liquid. It is possible to uniformly disperse slaked lime, and the obtained raw material for the second stage is chlorinated to increase the It is possible to obtain high-yield and high-quality calcium hypochlorite, but as a result of intensive study on a method for dispersing slaked lime that is easier to operate and more economical, we found that the hypochlorite of the present invention We have discovered a method for producing calcium acid.

That is, the present invention performs M1 stage chlorination by adding caustic soda or caustic soda and slaked lime to an aqueous solution containing calcium hypochlorite and sodium chloride, and separating the precipitated sodium chloride. Add slaked lime or slaked lime and caustic soda to the liquid to make a raw material slurry for second stage chlorination, and prepare for second stage chlorination.
A part of the raw material slurry for second-stage chlorination is extracted, and slaked lime to be supplied to second-stage chlorination is added and dispersed therein to prepare a high-concentration slaked lime-dispersed slurry. 6. A method for producing calcium hypochlorite, which is characterized in that it is combined with a first-stage separated liquid to form a raw material slurry for second-stage chlorination.

The second part used for dispersing slaked lime in the present invention
The raw material for stage chlorination is a slurry containing calcium hypochlorite, sodium hypochlorite, sodium chloride, and slaked lime, in which the slaked lime forms a double salt with calcium hypochlorite and is precipitated. The preferred concentration of each component in this second stage chlorination raw material is calcium hypochlorite 5 to 1
0 weight t, sodium hypochlorite 3-7% by weight, sodium chloride 14-19% by weight, and slaked lime 3-7% by weight, and calcium hypochlorite and slaked lime form a double salt and precipitate. ing.

By stirring and mixing slaked lime into a slurry with such a composition using a conventional method, it is possible to prepare a highly concentrated slaked lime dispersion slurry containing no coarse solids and in which slaked lime is uniformly dispersed, very easily and efficiently. be.

The slaked lime concentration in the slaked lime slurry obtained by the method of the invention can be up to 40% by weight.

If the slaked lime concentration is higher than this, the viscosity increases over time during stirring, making handling difficult and making it impossible to process quantitatively.

The slaked lime used in the method of the present invention can be used either as a reagent or for industrial use. However, it goes without saying that slaked lime containing impurities that adversely affect the stability of the resulting calcium hypochlorite should not be used.

Father, slaked lime can be added all at once to the raw material for second-stage chlorination.

In the present invention, the temperature during dispersion of slaked lime is 50°C or lower, since the slurry with a higher concentration of slaked lime in which the raw materials for second-stage chlorination and slaked lime used are uniformly dispersed will decompose.
is preferred.

In addition, the increase in viscosity over time is affected by temperature, and the rate of increase in viscosity accelerates at high temperatures. Calcium hypochlorite is obtained by combining and mixing with the separated liquid obtained by separation and subjecting it to solid-liquid separation operation of the raw material for second stage chlorination.

Next, one embodiment of the present invention will be described using FIG. 1.

Caustic soda or caustic soda and slaked lime 7 are added to the second stage chlorination separation mother liquor 12, and the mixture is supplied to the first stage raw material tank 1. After the first stage chlorination, this is transferred to step 2, where chlorine 8 is introduced to perform the first stage chlorination.

After chlorination, the slurry is transferred to the first stage separator 3 to separate sodium chloride 9. Adding slaked lime or slaked lime and caustic soda IO to the slurry containing calcium hypochlorite, sodium hypochlorite, sodium chloride, and slaked lime in the second stage raw material tank 4 to obtain a slurry in which slaked lime is uniformly dispersed; This is added to the first stage separated liquid.

In this case, it is desirable that the mixing ratio of the slurry in which slaked lime is uniformly dispersed and the first-stage separated liquid be such that the slaked lime and sodium hypochlorite in the slurry after mixing are approximately equivalent. Subsequently, the slurry in the M2 raw material tank is transferred to 5 after the first stage chlorination, and chlorine 11 is introduced to perform the second stage chlorination. The slurry after the second stage chlorination is transferred to the second stage separator 6.
After centrifugation, calcium hypochlorite crystals (highly bleached powder) 13 are obtained.

In the method of the present invention, it is not clear why slaked lime can be dispersed uniformly, but it is possible to add slaked lime to the entire amount of the first stage separated liquid, or contrary to the method of the present invention, it is possible to disperse slaked lime evenly. If slaked lime is added after the first stage separated liquid is added to the slaked lime, coarse solids will be generated. A basic salt is generated, and this double salt has poor solubility in water and prevents the slaked lime contained inside from dispersing.
Precipitated as coarse solids [7] This is thought to be due to the fact that the slaked lime slurry could not be uniformly dispersed.

However, as in the present invention, if slaked lime is added and dispersed in the raw material for the second stage in advance, the slaked lime will be highly uniformly dispersed, and even if the first stage separated liquid is added to this slurry, the next step in the first stage separated liquid will be This is presumed to be due to the fact that even if calcium chlorite reacts with slaked lime, which is already uniformly and highly dispersed, it will only form a fine double salt and cannot form a coarse solid substance.

In addition, the double salt of calcium hypochlorite and slaked lime is not a completely combined compound, but maintains an equilibrium state with water, so the amount of calcium hypochlorite in the liquid phase of the raw material slurry for the second stage is This is presumably due to the fact that the concentration is lower than the concentration of calcium hypochlorite in the first-stage separated liquid.

According to the present invention, the slurry in which the slaked lime obtained in the slaked lime dispersion step is uniformly dispersed does not contain any coarse solid matter, is easy to handle, and the first stage separated liquid is continuously added. As a result, it is not necessary to hold the first-stage separated liquid for a long time, and therefore, it is possible to prevent the first-stage separated liquid from decomposing. Furthermore, there is no damage to the pump or the like due to coarse solids, and it is possible to supply the solids quantitatively. or,
In the second-stage chlorinated raw material in the method of the present invention, slaked lime is evenly dispersed, so the absorption rate of chlorine per unit time of unit slurry can be increased during chlorination, and the yield is high. It is possible to increase the reaction rate of slaked lime to a high level. Furthermore, the slurry after the chlorination reaction has good filterability, and it is possible to obtain high quality calcium hypochlorite with little insoluble residue.

Furthermore, it is significant in that it does not require any new water for dispersing the slaked lime that has been used in the past, and it meets the recent demand for reducing by-product bleaching liquid.

EXAMPLES The present invention will be explained in more detail with reference to Examples and Comparative Examples below.

Example 1 6,000 parts of the second stage separated liquid containing 9.8% by weight of calcium hypochlorite (hereinafter simply abbreviated as "CH") and 20.0% of sodium chloride was heated to 48% while stirring and maintaining the temperature at 20°C. .0%
685 parts of a caustic soda aqueous solution was added, followed by 42 parts of 97% slaked lime.

Chlorine was supplied to this slurry at a rate of 324 parts per 7 hours at 20°C to chlorinate the slurry until the alkali reaction rate was 98.5%, and the effective chlorine was 12.8 parts.
705.0 parts of reaction slurry of No. 1 was obtained. As a result, the first
The step chlorination reaction yield was 98.6 excellent. This slurry was immediately centrifuged to obtain crystal 315s. The crystals had a composition of 91.5% sodium chloride and 1.1% available chlorine. In addition, the first stage separated liquid 6, 7 from which the crystals were separated
The available chlorine of 30 parts was 13.4%.

It has a composition of 9.1% calcium hypochlorite, 4.0% sodium hypochlorite, 16.8% sodium chloride, and slaked lime, and the slaked lime contains calcium hypochlorite and fine double salts. 280 parts of slaked lime was added to 1,400 parts of the formed and uniformly dispersed raw material for second stage chlorination at 20°C with stirring to obtain a slurry containing 20% slaked lime. 6,730 parts of the first-stage separated liquid was added to this slurry at 20° C. with stirring to obtain a raw material for second-stage chlorination. 1,000 parts of this second-stage chlorination raw material was sieved using a 48-mesh Z-yu standard sieve, but no coarse solids were observed on the sieve. In addition, chlorine was supplied to 1,000 parts of the obtained raw material for second stage chlorination at a supply rate of 20 parts/hour at 20°C, and chlorination was carried out to an alkali reaction rate of 99%, resulting in effective chlorine of 16 1,030 parts of slurry having . As a result, the yield of the second stage chlorination reaction was almost quantitative. The resulting reaction slurry was centrifuged to remove 56% of available chlorine. (1. 140 parts of crystals with a composition of 33.31% moisture were obtained. The crystals were dried to produce a highly bleached powder containing 75% available chlorine and 4% moisture.
I got 6 copies. The second-stage separated liquid from which the crystals were separated had a composition of 9.8% calcium hypochlorite and 20% sodium chloride.

Comparative example 1 Implementation? First stage separated liquid 2.0 having the same composition as lJ 1
00 parts, 82 parts of slaked lime was added at once at 20°C with stirring. When 1,000 parts of the obtained slurry was sieved using a 48 mesh ta semi-sieve, 65 parts of coarse solids remained on the sieve.

Further, when 1.000 parts of the obtained slurry was chlorinated by supplying chlorine at a supply rate of 20 parts/hour under stirring at 20°C, the reaction rate was 92 cm, the reaction yield was 911 parts, and the reaction rate was 96 cm. The reaction yield was 84%. The composition of crystals obtained by centrifuging the reaction slurry was 40% available chlorine and 42% water.

Comparative Example 2 4,000 parts of stage separation liquid was added under stirring at 20°C, and 165 parts of slaked lime was added thereto under stirring at 20°C. 1,000 parts of the obtained slurry was passed through a 48-mesh sieve, leaving 60 parts of coarse crystals on the sieve.

In addition, chlorine was supplied to 1,000 parts of the obtained slug IJ- at a rate of 20 parts/hour while stirring at 20° C. As a result, the alkali reaction rate was 96% and the reaction yield was 90 seconds. In addition, the composition of the crystals obtained by centrifuging the reaction slurry is
The effective chlorine content was 45-1 and the moisture content was 38%.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the manufacturing process of calcium hypochlorite using the method of the present invention.01...First stage raw material tank 2...First stage chlorinator 3...m1 Stage separator 4...Second stage raw material tank 5...Second stage chlorinator 6...Second stage separator 10...Slaked lime or slaked lime and caustic powder 13...Calcium hypochlorite Patent applicant Toagosei Kagaku Kogyo Co., Ltd. Mei 11 Procedural Amendment December 1980 2LP, Japan Patent Office Commissioner Shima 1) Haruki Tono1, Indication of the case 1982 Patent Application No. 1679082, Title of the invention Manufacturing method for calcium hypochlorite 3, relationship with the case of the person making the amendment Patent applicant address: 1-14-1-4 Nishi-Shinbashi, Minato-ku, Tokyo, subject of amendment 1'C, 4, 2, 7-"-/' 5. Contents of the amendment (1) On page 7, line 13 of the specification, the phrase "slaked lime slurry" is corrected to read "high-concentration slaked lime dispersion slurry 1." (2) In the fifth line from the bottom of page 7 of the specification, the phrase "obtained chlorinated liquid" is amended to read "obtained chlorinated slurry." (3) On page 7, line 11 of the specification, it says: [Add this to the first stage separated liquid 0] [Add the first stage separated liquid to this. Correct it to 1.

Claims (1)

[Claims] 1. Perform the first stage chlorination by adding caustic soda or caustic soda and slaked lime to an aqueous solution containing calcium hypochlorite and sodium chloride, separate the precipitated sodium chloride, and add the resulting first stage separated liquid. Slaked lime or slaked lime and caustic soda are added to form a raw material slurry for second-stage chlorination, and when performing second-stage chlorination, a part of the raw material slurry for second-stage chlorination is extracted and added to the second-stage chlorination raw material slurry. Add and disperse slaked lime to be supplied for chlorination to prepare a high concentration slaked lime dispersed slurry, and combine the high concentration slaked lime dispersed slurry with the first stage separated liquid to obtain a raw material slurry for second stage chlorination. A method for producing calcium hypochlorite, characterized by: