JP2910493B2 - Stabilization method of sodium hypochlorite solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stabilizing a sodium hypochlorite solution by removing impurities which are decomposition-causing substances that make the sodium hypochlorite solution unstable.

[0002]

2. Description of the Related Art Sodium hypochlorite has been used in large quantities for the bleaching of paper, pulp, and fibers, and for the treatment of water for sewage and sewer systems. It is widely used for Sodium hypochlorite is usually shipped from manufacturers in tank lorries or polyethylene containers as an aqueous solution with an effective chlorine concentration of 12% by weight or more for various uses. Those that pass the deadline may cause various troubles. For example, the concentration of the active ingredient is less than the value specified in the container, the plug is blown off due to generation of a decomposition gas in a closed container, and the container is overturned due to swelling of the container.

[0003] Sodium hypochlorite is inherently an unstable compound and is known to decompose gradually. The decomposition reaction is mainly due to the following two reactions. 3NaClO → 2NaCL + NaClO ₃ ‥‥‥‥‥ (A) 2NaClO → 2NaCL + O ₂ ‥‥‥‥‥ (B) The reaction (A) is a self-decomposition reaction which is the reason that sodium hypochlorite is inherently unstable. The reaction rate is affected by sunlight irradiation, component concentration or pH and temperature. Naturally, the higher the concentration or the higher the temperature, the faster the reaction rate, and when exposed to sunlight, the decomposition is also promoted. Therefore, it is common knowledge that the sodium hypochlorite solution is stored in a cool and dark place, and end products for household use have been diluted with an effective chlorine concentration of about 6% by weight.

[0004] The reaction (B) is not a self-decomposition reaction but a decomposition reaction by a catalytic action of impurities mixed in a sodium hypochlorite solution. Iron is the medium substance,
Metal oxides such as nickel, cobalt, and copper are known. In fact, suspended solids containing these metal components are present in the sodium hypochlorite solution during the process, and are caused by the raw material caustic soda. The reduction of available chlorine involves both (A) and (B) decomposition, whereas gas evolution is based solely on the decomposition reaction of (B). Manufacturers of sodium hypochlorite work to incorporate filters and coolers in the manufacturing process and provide light-blocking measures in product tanks and containers to ensure product stability and prevent degradation. Also, in order to efficiently capture and separate heavy metals, sodium silicate is added to generate an insoluble substance (Japanese Patent Publication No. 42-531), or an alkali metal silicate and a water-soluble magnesium salt are added to a sodium hypochlorite solution. Are successively added and the resulting insoluble precipitate is filtered (Japanese Patent Publication No. 53-37835).

[0005]

However, the method of simply adding sodium silicate to generate an insoluble substance does not sufficiently remove impurities, and further, an alkali metal silicate and a water-soluble magnesium salt are added to a sodium hypochlorite solution. The method of filtering the insoluble precipitate formed by successively adding, has problems such as that a precipitate having good filterability cannot be obtained by the operation of adding two kinds of additives. The problem to be solved by the present invention is to remove even trace amounts of the substance causing the decomposition reaction (B). As mentioned above, sodium hypochlorite manufacturers install a filter in the manufacturing process to filter products.

The present inventors have intensively studied the filtration of this sodium hypochlorite solution. As a result, in the sodium hypochlorite solution, a large amount of the metal oxide serving as a medium substance of the decomposition reaction was contained. Since the part was suspended and suspended solids, it should have been removed by filtration. However, it was found that a very small amount of the same kind of metal was still dissolved after filtration. In addition, it has also been discovered that a part of the dissolved impurity dissolved metal is precipitated as time passes, and the metal is present as a new solid content of the decomposition reaction medium. The composition analysis of this solid content revealed that the decomposition reaction medium metal component contained only a small amount, and the main components were alkaline earth metal carbonates and hydroxides. That is, the metal component of the decomposition reaction medium is presumed to be contained in newly generated solid content in the state of being occluded by the carbonates and hydroxides of these alkaline earth metals. It is considered that the reason why the medium effect is exhibited even though the medium metal component is contained only in a trace amount is that the metal component is concentrated near the surface of the solid.

[0007]

According to the present invention, there is provided a hypochlorite solution comprising adding sodium aluminate and sodium silicate to a sodium hypochlorite solution to form an insoluble precipitate, which is filtered. This is a method for stabilizing a sodium acid solution. Sodium aluminate to be used in the present invention is the molecular formula Na ₂ O. White powder or _{Na 2 O / AL 2 O 3} = 0.8~2.6 but is intended to be subjected with a solution (molar ratio) that of the solution is easy to handle represented by AL ₂ O ₃ . Sodium silicate has the molecular formula Na ₂ O. m
Indicated by SiO ₂ · nH ₂ O, SiO ₂ / Na ₂ O = 0.45
-3.3 (molar ratio) or a colorless powder (3.3 molar ratio), which is also a solution and is easy to handle. In the present invention, it does not matter whether sodium aluminate or sodium silicate is added to the sodium hypochlorite solution first, and it is not important to add the other one after adding one of them and then add the other simultaneously. Alternatively, a method of mixing a sodium hypochlorite solution to which one is added and a sodium hypochlorite solution to which the other is added may be used. Ratio _{SiO 2 / AL 2 O 3 =} 1~ added
10 is good. A ratio outside this range may have some effect but is not efficient. Add The amount is 5~2000ppm effective as SiO _2, preferably 5 to
1500 ppm is good. If it is less than 5 ppm, the effect is insufficient, and if it exceeds 2,000 ppm, not only is it uneconomical, but also the load of subsequent filtration increases, which is not an appropriate measure.

In the present invention, sodium aluminate and sodium silicate react in a sodium hypochlorite solution to form a precipitate of aluminum silicate. This aluminum silicate has a feature that it is formed in a very porous form and that the subsequent filtration can be performed very smoothly, and furthermore, it strongly adsorbs the above-mentioned impure dissolved metal component dissolved in the sodium hypochlorite solution. Due to the nature, even if the formed precipitate is separated by filtration, even trace amounts of the metal of the decomposition reaction medium are no longer present in the sodium hypochlorite solution. It should also be noted that even if the precipitate of aluminum silicate formed is not completely removed from the sodium hypochlorite solution by filtration and remains in the solution, it has the ability to decompose sodium hypochlorite. It is changing to something that does not. Therefore, even if the filtration is incomplete due to an operation error, it does not adversely affect the stability. In carrying out the present invention, it may be applied to a sodium hypochlorite solution immediately after production, or may be applied after filtration by a conventional method. Filtration accuracy is about the same as normal microfiltration, and simple filtration that can remove particles of 2 microns can be expected to have a considerable effect in terms of safety.
If it can remove particles of 0.1 micron, it can be said that quality is satisfactory. An important point in carrying out the present invention is to sufficiently agitate the sodium hypochlorite solution at the stage of producing aluminum silicate. Local reactions do not have the expected effect.

[0009]

Although the form of the precipitate of sodium silicate formed in the present invention is not always clear, according to the result of the composition analysis of the precipitate actually formed in the sodium hypochlorite solution, it was found that other than Si and AL, F in question
It is considered that a large amount of cationic substances such as Na, Ca, and Mg are contained in addition to e and Ni, so that a compound having a very high adsorptivity is generated. However, the same effect can be obtained by reacting sodium aluminate and sodium silicate in a dilute sodium hydroxide solution in advance to form this precipitate, and adding this to the sodium hypochlorite solution. It seems that there is an effect that produces a special effect on the precipitate formed by the reaction.

[0010]

Next, the present invention will be described with reference to Examples and Comparative Examples. In the examples,% indicates weight% unless otherwise specified. Example 1 A low-sodium sodium hypochlorite solution having an effective chlorine concentration of 13.55% manufactured from 48.5% caustic soda manufactured by an ion exchange membrane electrolysis method and concentrated using a concentrator (the following example) The same solution was used in the comparative example) 2.5
Sodium aluminate per kilogram (molar ratio: N
a ₂ O / AL ₂ O ₃ = 1.42, AL ₂ O ₃ : 22%, the same solution was used in the following Examples and Comparative Examples), 75 mg was added, and the mixture was stirred for 10 minutes. (Molar ratio: SiO ₂ / Na ₂ O = 3.3, SiO
(29: 29%, the same solution was used in the following Examples and Comparative Examples) was added over 1 minute while stirring the sodium hypochlorite solution. A white precipitate formed. This was filtered through a glass fiber filter (GF-100 manufactured by Advantech; filtration pore size: 1 micron) to obtain a turbidity-free sodium hypochlorite solution.

Comparative Example 1 A low-sodium sodium hypochlorite solution was filtered through a glass fiber filter to obtain a cloudless sodium hypochlorite solution.

Comparative Example 2 100 mg of sodium aluminate was added to 2.5 kg of a low salt sodium hypochlorite solution, and
After stirring for minutes, the mixture was filtered through a glass fiber filter to obtain a cloudless sodium hypochlorite solution.

Comparative Example 3 100 mg of No. 3 sodium silicate was added to 2.5 kg of a low salt sodium hypochlorite solution, and
After stirring for minutes, the mixture was filtered through a glass fiber filter to obtain a cloudless sodium hypochlorite solution.

Comparative Example 4 500 mg of a 10% magnesium chloride solution was added to 2.5 kg of a low-sodium sodium hypochlorite solution, and the mixture was stirred for 10 minutes. The resulting white precipitate was filtered through a glass fiber filter. A turbid sodium hypochlorite solution was obtained.

Comparative Example 5 100 mg of No. 3 sodium silicate was added to 2.5 kg of a low-sodium sodium hypochlorite solution, and the mixture was stirred for 10 minutes.
Milligrams were added over 1 minute while stirring the sodium hypochlorite solution. The resulting white precipitate was filtered through a glass fiber filter to obtain a cloudless sodium hypochlorite solution.

Comparative Example 6 No treatment was applied to the low salt sodium hypochlorite solution. In addition to having a slightly reddish color tone, the presence of very fine suspended solids that did not easily settle was confirmed.

Examples 2 to 8 In addition, the amounts and the ratios (molar ratios) of sodium aluminate and sodium silicate No. 3 to the sodium hypochlorite solution were adjusted as shown in Table 1 and adjusted. Filtration was performed as in 1.

[0018]

[Table 1]

The various sodium hypochlorite solutions prepared as described above were subjected to an effective chlorine concentration of 6 using ion-exchanged water.
%, The mixture was put into a 1 L gas generation rate measuring bottle, immersed in a 50 ° C. constant temperature bath, and the generated gas was collected in a cylinder with a scale above the measuring bottle under atmospheric pressure and pressure equalization, and the change with time was measured. The results are shown in FIG. 1 and FIG.

As shown in FIG. 1 and FIG. 2, each of the examples has a small amount of oxygen generated after 24 hours, while each of the comparative examples has a small amount of generated oxygen even after 12 hours. It turns out that there are many.

When the separately stored sodium hypochlorite solution was observed 10 days later, no change was observed in Examples 1 to 8, whereas a slight amount was observed in Comparative Examples 1 to 6. However, it was confirmed that suspended solids were newly formed.

[0022]

According to the method of the present invention, the decomposition reaction of the sodium hypochlorite solution accompanying the generation of oxygen gas can be remarkably suppressed and stabilized. Further, the precipitate formed by the method of the present invention is porous and strongly adsorbs impurities and can be easily filtered.

[Brief description of the drawings]

FIG. 1 is a graph showing the change over time in the amount of generated oxygen gas in Example 1 and Comparative Examples.

FIG. 2 is a graph showing the change over time in the amount of generated oxygen gas in Examples 2 to 8.

Claims (2)

(57) [Claims] 1. A method for stabilizing a sodium hypochlorite solution, comprising adding sodium aluminate and sodium silicate to a sodium hypochlorite solution to form an insoluble precipitate and filtering the precipitate. 2. The hypochlorous acid according to claim 1, wherein the sodium silicate and the sodium aluminate are added in such a manner that the molar ratio thereof is substantially SiO ₂ / AL ₂ O ₃ = 1 to 10. Method of stabilizing sodium solution.