JPH09268002A - Method for generating chlorine dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To safely obtain an aqueous solution of chlorine dioxide at a low cost without generating harmful chlorine-based organic compounds by mixing an aqueous solution of hydrogen peroxide acidified with a mineral acid and an aqueous solution of a chlorous acid salt at a ratio to get a specific pH. SOLUTION: An aqueous solution of a chlorous acid salt is mixed with an aqueous solution of hydrogen peroxide acidified with a mineral acid added in an amount to get a pH of 4-8, preferably 5.5-7.0 at the end of reaction.

Description

Detailed Description of the Invention

[0001]

The present invention relates to chlorine and hypochlorite used for water and sewerage treatment for the purpose of disinfection, sterilization, deodorization, decolorization, etc., factory wastewater treatment, pool water treatment, food processing plants, etc. Alternatively, it relates to a method of generating chlorine dioxide as an alternative to an oxidizing agent such as ozone.

[0002]

2. Description of the Related Art Chlorine dioxide is obtained on-site by a method using chlorate as a reducing agent from sulfurous acid gas, salt or hydrochloric acid in a pulp mill where a large amount of it is used as an oxidizing agent for pulp. . On the other hand, water and sewage treatment for the purpose of disinfection, sterilization, deodorization, decolorization, etc., factory wastewater treatment,
Chlorine dioxide for pool water treatment, food processing plants, etc., which is an alternative market for oxidants such as chlorine, hypochlorite or ozone, uses chlorine or hydrochloric acid or hypochlorite as an oxidant from chlorite. It is obtained on-site by the method. As mentioned above, chlorine dioxide is a relatively unstable gas, so it cannot be stored or transported unless it is used in a very small amount such as for household use, and it is necessary to generate it onsite at the stage of use. There is.

Even in this case, the aqueous solution is stable, but if the gas concentration in the air exceeds 10%, there is a risk of explosion if there is an ignition source. Therefore, the gas is generated and stored at a concentration of 2% or less for storage. It is important to ventilate the inside of the equipment to 0.4% or less so as to prevent the accumulation of gas, and in some countries, such as Germany, compliance with these concentrations is legally required. Generally, an accurate metering pump is used to control these concentrations, but as in Japanese Patent Publication No. 3-62641, the generated chlorine dioxide is sucked by an ejector,
A method has also been devised to secure safety by diluting with process water immediately after occurrence.

[0004]

As a method for obtaining chlorine dioxide by oxidation of chlorite, the following methods have been conventionally used and are represented by chemical formulas: (1) Aurin method (USP 4,013,761) 2NaClO ₂ + NaClO + 2HCl → 2ClO ₂ +
3NaCl + H ₂ O (2) Prominent method (Germany Prominent GmbH) 5NaClO ₂ + 4HCl → 4ClO ₂ + 5NaCl
+ 2H ₂ O (3) Rio Linda method (USP 4,590,057; US
P4,247,531) 2NaClO ₂ + Cl ₂ → 2ClO ₂ + 2NaCl (2NaClO ₂ + NaClO + 2HCl → 2ClO ₂
+ 3NaCl + H ₂ O) (NaClO + 2HCl → Cl ₂ + NaCl + H ₂ O) and the like. When chlorine or hypochlorite is used as an oxidant for chlorite, chlorine causes leakage of toxic gas during transportation and storage, and hypochlorite causes a problem such as reduction in effective reaction rate due to self-decomposition. Occurs, and the reaction rate when hydrochloric acid is used is remarkably low as compared with other methods.

[0005]

In the present invention, an aqueous solution of chlorite is mixed with an aqueous solution of mineral acid-acidic hydrogen peroxide,
The amount of mineral acid to be added is adjusted so that the final pH of the reaction is 4 to 8, preferably 5.5 to 7.0, to obtain an aqueous solution of chlorine dioxide. As an example, it is utilized that by adding a theoretical amount of a mineral acid, H ⁺ becomes excessive due to a side reaction and the reaction is slightly completed on the acidic side and falls within this range. (4) The reaction chemical formula for this method is 2NaClO ₂ + H ₂ O ₂ + H ₂ SO ₄ → 2ClO ₂ +
It is represented by Na ₂ SO ₄ + 2H ₂ O. When alkaline, chlorite and hydrogen peroxide have almost the same oxidation potential, so that the reaction does not proceed even if they coexist. Further, chlorite is stable in alkaline, but when acidic, the following decomposition starts at around pH 6 and about 50% is decomposed in 2 hours at pH 2. These side reactions are represented by reaction formulas (5) Side reaction 1 3ClO ₂ ⁻ → 2ClO ₃ ⁻ + Cl ⁻ (6) Side reaction 2 ClO ₂ ⁻ → Cl ⁻ +2 (O) Then, these side reactions proceed and autolysis occurs. In the present invention, hydrogen peroxide is added to proceed the reaction of (4) and adjust the pH to near neutral to stabilize the reaction product and suppress decomposition.

[0006]

In the present invention, the hydrogen peroxide used is 35
% Stabilized aqueous solution is generally readily available, it is also easy to acidify the mineral acid (generally sulfuric acid) beforehand, and mixing with aqueous chlorite solution is also traditionally used. Since a so-called line mixer that uses a certain metering pump is sufficient, both the equipment cost and the consumables cost are low, and the desired product can be obtained safely onsite.

[0007]

EXAMPLE 1 980 g of diluted 1% aqueous sulfuric acid solution and 51.4 g of diluted 3.5% aqueous hydrogen peroxide were mixed to obtain an aqueous solution, which was also diluted with 2.5% chlorous acid. 720 g of an aqueous solution of soda is injected with stirring, and the reaction is carried out at room temperature. Each drug added was in a reaction equivalent amount, the reaction was performed promptly, and the end point of the infusion is regarded as the end point of the reaction. The obtained aqueous solution had a pH of 7.0 and had an equivalent amount of 0.7 by measurement using a conventional chlorine dioxide measuring electrode.
Generation of a 6% chlorine dioxide aqueous solution was confirmed.

Example 2 98 g / min of diluted 10% aqueous sulfuric acid solution and 51.4 g / min of diluted 3.5% hydrogen peroxide solution were mixed with 3,000 ml / min of process water to obtain process water. 180g of a 10% aqueous solution of sodium chlorite diluted
Injection of 0.43% chlorine dioxide product stream 3,33
0 ml / min was obtained.

[0008]

EFFECTS OF THE INVENTION Unlike chlorine, chlorine dioxide sterilizes, bleaches, decomposes harmful substances and deodorizes due to the oxidizing action of oxygen, does not generate harmful chlorinated organic compounds such as trihalomethane, and is second only to ozone in strength. It is an oxidant having the oxidizing power of. Although its effectiveness has been pointed out in the past, its practical application was delayed in Japan in terms of water supply and sewage treatment, wastewater treatment, etc., because the simple chlorine dioxide generator on site was not in practical use. It is expected that the invention makes it possible to produce chlorine dioxide water safely and at low cost, and further promotes the spread in these fields.

[Brief description of drawings]

FIG. 1 shows a block diagram of an on-site chlorine dioxide generator during practical use. Pre-diluted sulfuric acid and hydrogen peroxide solution are injected into the process water with a metering pump to obtain the process water of sulfuric acid hydrogen peroxide solution, and then the sodium chlorite aqueous solution diluted with this process water is injected with the metering pump. A chlorine dioxide water product stream of the desired concentration is obtained.

Claims (1)

[Claims] 1. A mineral acid-acidic hydrogen peroxide aqueous solution is mixed with a chlorite aqueous solution to obtain a reaction end pH of 4 to 8, preferably pH.
A method of obtaining an aqueous solution of chlorine dioxide by adjusting the amount of mineral acid to be added so as to be 5.5 to 7.0.