JP5907501B2 - Method for producing hypochlorite - Google Patents

Description

  The present invention relates to a method for producing hypochlorite (hereinafter also simply referred to as “manufacturing method”), and in particular, to an improvement in a method for producing hypochlorite having a high concentration by electrolysis.

  Hypochlorite typified by sodium hypochlorite is used as a bleaching agent and disinfectant in various fields such as water and sewage treatment and wastewater treatment. Hypochlorite can be produced by reacting chlorine obtained by electrolysis of an alkali metal chloride aqueous solution typified by saline and an alkali metal hydroxide aqueous solution, or by alkali metal chloride. A general method is to produce a hypochlorite directly in an electrolytic cell by electrolyzing an aqueous solution of a physical solution in a non-diaphragm electrolytic cell.

  Among these, in the latter method, the produced hypochlorite is reduced to an alkali metal salt on the cathode, and the produced hypochlorite is anodized to form a chlorate having no oxidizing power. Since it is converted, it is difficult to obtain a high concentration hypochlorite aqueous solution. Therefore, the use of hypochlorite produced by this method is currently limited to biological growth / growth in seawater used in heat exchange water for power plants and axial cooling water for rotating equipment, water and sewage treatment, and wastewater. Processing applications are common.

  On the other hand, the former method is typically a method for producing high-concentration sodium hypochlorite in a salt electrolysis plant, but the salt electrolysis system requires an advanced salt water purification system that removes heavy metal impurities. In order to reuse the saline solution whose concentration has decreased after electrolysis, the equipment is required because a system for decomposing and removing hypochlorous acid and dissolved chlorine contained in the salt water after electrolysis is essential. It will be a big one. In addition, the main purpose of the salt electrolysis plant is not the production of sodium hypochlorite, but the production of caustic soda and chlorine gas, which have many industrial uses, so it produces tens of thousands to hundreds of thousands of tons per year in terms of caustic soda. There are many relatively large plants. On the other hand, since the number of salt electrolysis plants is overwhelmingly small compared with the number of water supply plants that require high-concentration hypochlorite, chlorine or hypochlorous acid required for sterilization of water There is a need to transport and store salt, and there is always a danger of human disasters and environmental destruction due to liquid leakage from storage facilities. In particular, with regard to chlorine gas, major accidents have occurred in various countries due to traffic accidents involving tank trucks used for transportation, and there is an active movement to enact laws prohibiting the transport of chlorine gas in the United States. It has become.

  Under these circumstances, a small alkali metal chloride electrolyzer is installed at a hypochlorite facility such as a water supply station, and on-site manufactures the required amount of hypochlorite when needed. Various methods for producing high-concentration hypochlorite of the type have been proposed. For example, in Patent Document 1, in an ion exchange membrane electrolytic cell partitioned into an anode chamber and a cathode chamber by an ion exchange membrane, the chlorine gas obtained by electrolyzing an alkali metal salt aqueous solution in the anode chamber and the concentration decreased by electrolysis. Among the alkali metal chloride aqueous solutions, the alkali metal chloride aqueous solution is introduced into the cathode chamber to produce an alkali metal hydroxide aqueous solution, which is then introduced into the reaction vessel provided outside the electrolytic cell together with chlorine gas, so It has been proposed to produce chlorates. Patent Documents 2 and 3 do not introduce an alkali metal chloride aqueous solution having a reduced concentration after electrolysis into the cathode chamber, but directly introduce it into the reaction chamber together with the metal alkali hydroxide aqueous solution generated in the cathode chamber. It has been proposed to produce highly concentrated hypochlorite.

  The methods described in Patent Documents 1 to 3 are all essential when producing hypochlorite in an alkali metal chloride electrolysis plant. This achieves the elimination of the chlorous acid removal process, and simplifies the system required for on-site manufacturing equipment. Also, Patent Document 4 discloses an improved technique related to a hypochlorite production apparatus by electrolysis of salt water.

Japanese Patent Laid-Open No. 5-179475 (Japanese Patent No. 3283552, claims, etc.) Japanese Patent Laid-Open No. 10-121280 (Patent No. 3729432, claims, etc.) JP 2000-265289 A (Patent No. 3,818,619, claims, etc.) Japanese Patent Laid-Open No. 07-252683 (Patent No. 3334996, claims)

According to the techniques described in Patent Documents 1 to 3, it is possible to produce a high concentration of hypochlorite, but there are still problems to be solved. For example, in the method for producing a high-concentration hypochlorite described in Patent Document 1, an alkali metal chloride that has been electrolyzed is introduced into the cathode chamber by introducing an alkali metal chloride aqueous solution that has been electrolyzed in the anode chamber to a reduced concentration. Since the metal chloride aqueous solution contains dissolved chlorine and hypochlorous acid, these react with the metal alkali hydroxide generated together with hydrogen in the cathode chamber, and the target product hypochlorite is obtained. (See the following reaction formulas (1) and (2)). However, in this case, the generated hypochlorite may be reduced to an alkali metal chloride on the cathode (see the following reaction formula (3)).
Cl ₂ + 2OH ⁻ → ClO ⁻ + Cl ⁻ + H ₂ O (1)
HClO + OH ⁻ → ClO ⁻ + H ₂ O (2)
ClO ⁻ + H ₂ O + 2e → Cl ⁻ + 2OH ⁻ (3)

  Since the standard electrode potential of the reaction of the above reaction formula (3) is +0.89 V, which is more precious than the standard electrode potential of hydrogen generation (0 V), the reaction of the above reaction formula (3) is the hydrogen generation reaction. There is a risk of proceeding with priority over. As for the cathodic reduction of hypochlorite ions, as described in detail in Patent Document 4, the applicant has decomposed hypochlorite, which is the target production substance, by reduction during electrolysis. As a result, this results in a decrease in manufacturing efficiency and an increase in cost.

  On the other hand, in the methods shown in Patent Documents 2 and 3, since the hypochlorite formation reaction proceeds outside the anode chamber and the cathode chamber of the electrolytic cell, a part of the hypochlorite is formed in the cathode chamber. The problem of being reduced can be avoided. However, these technologies do not have a mechanism for adjusting the concentration of the alkali metal hydroxide generated in the cathode chamber in the portion reaching the reaction vessel from the cathode chamber, so if the generated caustic alkali concentration is high, Due to the mutual solubility relationship between hypochlorite produced in the tank and alkali metal chloride generated by the side reaction, the alkali metal chloride may precipitate as crystals in the reaction tank. This indicates that alkali metal chloride precipitates and accumulates in the reaction tank, and is a cause of hindering stable operation of the production apparatus, which is not preferable.

  In order to avoid the above problem, it is necessary to reduce the concentration of the alkali metal hydroxide aqueous solution in the cathode chamber. In this case, the concentration of hypochlorite, which is the target production substance, is also reduced. End up. Therefore, for example, a commercially available sodium hypochlorite aqueous solution having an effective chlorine concentration exceeding 12% by mass cannot be stably produced. As a result, even an on-site production facility is hypochlorous acid. A large capacity of the acid storage tank is unavoidable, and the equipment cannot be made compact.

  Accordingly, an object of the present invention is to solve the above-mentioned problems and to produce a high concentration hypochlorite stably and efficiently at an on-site production facility at a low cost. Another object of the present invention is to provide a method for producing hypochlorite that can contribute to downsizing.

  As a result of intensive investigations to solve the above problems, the present inventors have obtained hypochlorite by reaction of an anolyte, chlorine gas and an aqueous alkali metal hydroxide solution in a reaction tank provided separately from the electrolytic cell. In the production, the alkali metal in the reaction vessel is added by adding water to the anolyte or alkali metal hydroxide aqueous solution before being introduced into the reaction vessel, or to the mixture after being introduced into the reaction vessel. The inventors have found that the precipitation of chloride can be prevented, and have completed the present invention.

That is, in the method for producing hypochlorite of the present invention, an alkaline metal chloride aqueous solution is supplied to the anode chamber of an electrolytic cell partitioned into an anode chamber and a cathode chamber by an ion exchange membrane, and the cathode chamber is supplied to the cathode chamber. Electrolysis is performed by supplying pure water, the anolyte and generated chlorine gas in the anode chamber after electrolysis, and the generated alkali metal hydroxide aqueous solution in the cathode chamber are introduced into the reaction tank, and the reaction tank A process for producing hypochlorite by reaction of an anolyte, chlorine gas and an aqueous alkali metal hydroxide solution,
As the ion exchange membrane, an ion exchange membrane that is a two-layer membrane including a carboxylic acid layer is used, and the anolyte in the supply path for introducing the anolyte in the anode chamber into the reaction vessel, or Water is added to the mixture of the anolyte, chlorine gas, and alkali metal hydroxide aqueous solution introduced into the reaction vessel.

  In the present invention, water is preferably added to the mixture of the anolyte, chlorine gas, and alkali metal hydroxide aqueous solution introduced into the reaction vessel. According to the present invention, hypochlorite having an effective chlorine concentration of 5% by mass or more can be produced.

  According to the present invention, the above-described configuration enables high-concentration hypochlorite to be produced stably and efficiently at an on-site production facility at a low cost. It became possible to realize a hypochlorite production method that could contribute to compactness.

It is an apparatus block diagram which shows an example of the manufacturing apparatus of the hypochlorite used for this invention. It is a graph which shows the relationship between the current efficiency at the time of using a sulfonic acid type ion exchange membrane in salt electrolysis, and the caustic soda density | concentration obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.
In FIG. 1, the apparatus block diagram of an example of the manufacturing apparatus of the hypochlorite used for this invention is shown. In the present invention, an alkali metal chloride aqueous solution 4 is supplied to the anode chamber 2 and pure water 5 is supplied to the cathode chamber 3 of the electrolytic cell 10 partitioned by the ion exchange membrane 1 into the anode chamber 2 and the cathode chamber 3. Electrolysis is then performed. Thereafter, the anolyte 6 and the generated chlorine (Cl ₂ ) gas 7 in the anode chamber 2 after electrolysis and the generated alkali metal hydroxide aqueous solution 8 in the cathode chamber 3 are introduced into the reaction tank 18, Hypochlorite is produced by the reaction of the anolyte 6, chlorine gas 7 and aqueous alkali metal hydroxide solution 8 in 18. Here, the anolyte 6 is a salt solution, a potassium chloride aqueous solution, or the like (alkali metal chloride aqueous solution) whose concentration has decreased to, for example, less than 100 g / liter after electrolysis. Reference numeral 9 denotes hydrogen (H ₂ ) gas discharged from the cathode chamber 3.

  In the present invention, the anolyte 6 or alkali metal hydroxide aqueous solution 8 before being introduced into the reaction vessel 18, or the anolyte 6, chlorine gas 7 and alkali metal hydroxide aqueous solution after being introduced into the reaction vessel 18. The point that water 11 is added to the mixture of 8 is important. By adding water 11 to the anolyte 6 or the alkali metal hydroxide aqueous solution 8 before the introduction of the reaction vessel, or the mixture after the introduction of the reaction vessel, hypochlorite in the reaction vessel. It became possible to stably produce a high concentration hypochlorite aqueous solution 12 while preventing the alkali metal chloride by-produced during the formation from being crystallized and precipitated. Therefore, according to the present invention, a high concentration hypochlorite can be manufactured stably and efficiently at a low cost in an on-site compact manufacturing facility. In addition, in the present invention, equipment for re-saturating the alkali metal chloride solution, which is an anolyte diluted after electrolysis, is also unnecessary, so that the apparatus can be made compact so that hypochlorite is consumed in the hypochlorite consumption place. The chlorate can be easily produced.

  In the present invention, preferably, water is added to a mixture of an alkali metal hydroxide aqueous solution before being introduced into the reaction vessel 18 or an anolyte introduced into the reaction vessel 18. This is for preventing the precipitation of salt in the reaction vessel.

  In the present invention, the amount of water added can be appropriately set within a range in which an alkali metal chloride is not precipitated and a hypochlorite having an effective chlorine concentration of 5% by mass or more can be obtained. Is not to be done. If the amount of water added is too small, the effect of preventing precipitation of alkali metal chloride may not be sufficiently obtained. From the standpoint of preventing the precipitation of alkali metal chlorides, there is no upper limit for the amount of water added. However, if the amount of water added is too large, the concentration of hypochlorite produced in the reaction vessel is diluted. End up. More specifically, the appropriate amount of water added is the electrolytic cell operating current density, current efficiency, operating temperature, electrolyzed anolyte concentration, caustic alkali concentration, alkali metal hydroxide generation current efficiency, ion exchange It varies based on various factors such as the amount of osmotic water in the membrane. Therefore, although it is difficult to generalize, for example, within the operating conditions in Example 1 to be described later, as a range in which the generated sodium hypochlorite concentration can maintain 12% by mass or more, 1.8 to 2 .1 liter / KAh is an appropriate range. In the present invention, the water 11 can be added from the water supply source 13 to the anolyte supply path or the like, and pure water is particularly suitable.

The production method of the present invention is characterized in that a hypochlorite with a high concentration which has not been obtained conventionally can be obtained. Examples of the hypochlorite obtained in the present invention include sodium hypochlorite and potassium hypochlorite. Here, by the production method of the present invention, a highly concentrated hypochlorite salt solution such as a commercially available sodium hypochlorite aqueous solution having an effective chlorine concentration exceeding 5% by mass can be stably and on-site production equipment. In order to manufacture efficiently, it is necessary to satisfy the following requirements.
(I) To maintain a high concentration of hypochlorite to be produced, an alkali metal hydroxide aqueous solution having a concentration as high as possible is produced in the cathode chamber.
(Ii) The alkali metal chloride concentration in the anolyte after electrolysis should be made as small as possible in order to reduce the basic unit of alkali metal chloride in the hypochlorite to be produced.

  In order to satisfy the above conditions i) and ii), it is necessary to produce a high-concentration alkali metal hydroxide aqueous solution in the cathode chamber of the electrolytic cell. However, when a cation exchange membrane having a sulfonic acid ion exchange group as used in Examples of Patent Documents 2 and 3 is used, as shown in FIG. Even if it is a dense region of 190 to 220 g / liter, in order to achieve a high current efficiency of 90% or more, it is necessary to maintain a low concentration of 10% by mass or less as a sodium hydroxide concentration. It is impossible to achieve such high concentrations as commercially available sodium hypochlorite aqueous solutions. On the contrary, for example, in order to achieve a sodium hydroxide concentration of 30% by mass or more, the sodium hydroxide production current efficiency becomes 60% or less, and the anolyte concentration is reduced in order to reduce the basic unit of alkali metal chloride. If it is lowered to 100 g / liter or less, a further decrease in generated current efficiency is expected, so that it is not practical from the viewpoint of power cost.

  From this point, in the present invention, as the ion exchange membrane 1 in the electrolytic cell 10, it is necessary to use an ion exchange membrane for producing high-concentration caustic alkali for electrolysis of sodium chloride or potassium chloride. Thereby, since current efficiency and the high concentration of the obtained hypochlorite can be made compatible, the effective chlorine concentration of a commercial item level is 5 mass% or more, for example, 5-12 mass% hypochlorite. It is possible to manufacture stably, more efficiently, and at low cost with an on-site manufacturing facility. Specific examples of the ion exchange membrane for generating high concentration caustic alkali include a bilayer membrane including a carboxylic acid layer such as a sulfonic acid-carboxylic acid bilayer membrane.

  The production method of the present invention is appropriately carried out according to a conventional method except for adding water to the anolyte or alkali metal hydroxide aqueous solution before the introduction of the reaction vessel or the mixture after the introduction of the reaction vessel. There is no particular limitation. For example, in the manufacturing apparatus used in the present invention, the anode chamber 2 of the electrolytic cell 10 partitioned by the ion exchange membrane 1 is formed with a coating of an electrode catalyst material containing a platinum group metal oxide on a metal substrate such as titanium. An anode 14 is provided. The cathode chamber 3 is provided with a cathode 15 made of nickel, stainless steel, or titanium, or formed by covering these metals with a cathode active material coating that reduces hydrogen overvoltage.

  The alkali metal chloride aqueous solution 4 and the pure water 5 can be supplied to the electrolytic cell 10 while controlling the concentration and flow rate according to the target amount of hypochlorite produced. The generated alkali metal hydroxide aqueous solution 8 and hydrogen gas 9 are taken out from the upper part of the cathode chamber 3, and among these, the alkali metal hydroxide aqueous solution 8 is supplied to the reaction vessel 18, and the hydrogen gas 9 is discharged to the outside. The Further, from the upper part of the anode chamber 2, the anolyte 6 made of an alkali metal chloride aqueous solution whose concentration is reduced by electrolysis and the chlorine gas 7 are taken out and supplied to the reaction tank 18.

  In the reaction tank 18, chlorine and the alkali metal hydroxide react to produce a hypochlorite aqueous solution 12. Here, the hypochlorite aqueous solution 12 taken out from the reaction vessel 18 is taken out as a product, supplied to the cooling device 17 by the pump 16, cooled, and then circulated through the reaction vessel 18, so that the temperature of the electrolytic vessel is increased. While preventing a raise, decomposition | disassembly of the produced | generated hypochlorite can be prevented.

For example, in the case of producing sodium hypochlorite using sodium chloride as the alkali metal hydroxide, in the electrolytic cell 10, the following general reaction formula:
_{2NaCl + 2H 2 O → 2NaOH +} Cl 2 + H 2
The total amount of sodium hydroxide and chlorine produced by electrolysis according to
2NaOH + Cl ₂ → NaClO + NaCl + H ₂ O
To produce sodium hypochlorite and equimolar sodium chloride. On the other hand, the salt water supplied to the reaction tank 18 in the present invention contains, for example, 90.1 g / liter of sodium chloride in Example 1, so that the following aqueous sodium hypochlorite solution is Both salt produced by the chlorite formation reaction and salt contained in the salt water are included.

  Therefore, in this case, when the obtained sodium hypochlorite is used for an application in which the concentration of sodium chloride becomes a problem, the amount of salt water supplied to the anode chamber is decreased and the decomposition rate of sodium chloride is increased. It is conceivable to reduce the salt content in the anode chamber. In the present invention, the salt decomposition rate in the anode chamber is increased as much as possible, and the electrolyzed anolyte having a sufficiently reduced salt concentration is mixed with the entire amount of the catholyte, so that the sodium hypochlorite is cooled while being centrifuged. Or sodium hypochlorite with a low salt contamination rate can be produced without using conventional methods such as mixing only the generated chlorine without mixing the electrolyzed salt water with the catholyte. Equipment can be omitted, and the apparatus can be made compact.

Hereinafter, the present invention will be described more specifically with reference to examples.
[Example 1]
In the apparatus having the configuration shown in FIG. 1, sodium hypochlorite was produced. The electrolytic area of the electrolytic cell was 100 cm ² , and the flowing current was 40A. As the ion exchange membrane for partitioning the anode chamber and the cathode chamber, Nafion (registered trademark) N2030 manufactured by DuPont Co., Ltd., which is widely used for salt electrolysis, was used.

  The operation was started at a temperature of 80 ° C. with saturated saline in the anode chamber and 30% by mass aqueous caustic soda solution in the cathode chamber. After 1 week of stable operation, the salt concentration of the electrolyzed anolyte is 90.1 g / liter, the generated caustic soda concentration is 31.9% by mass, and the generated current efficiency of caustic soda is 97.1%. Chlorine gas, electrolyzed anolyte and generated caustic soda are introduced into a reaction vessel arranged outside the electrolytic cell, and pure water is supplied to the reaction vessel at a rate of 0.08 liter / hr, and hypochlorous acid is added. Soda was manufactured.

  When the operation was stopped 2 hours after the start of the production of sodium hypochlorite and the aqueous sodium hypochlorite solution in the reaction vessel was confirmed after cooling, no precipitation due to crystallization of sodium chloride was observed. When the concentration analysis of this produced sodium hypochlorite was conducted, the effective chlorine concentration was 12.1% by mass.

[Comparative Example 1]
Except that pure water was not supplied to the reaction tank, electrolysis was performed in the same electrolytic tank and electrolytic conditions as in Example 1 to produce sodium hypochlorite. The salt concentration of the electrolyzed anolyte in the electrolytic cell before the start of sodium hypochlorite production was 93 g / liter, the generated caustic soda concentration was 31.5% by mass, and the generated current efficiency of caustic soda was 96.5%. The produced chlorine gas, electrolyzed anolyte and produced caustic soda were introduced into a reaction vessel outside the electrolytic cell to produce sodium hypochlorite.

  When the operation of the electrolytic cell was stopped after 2 hours and the inside of the reaction vessel was confirmed, salt crystals were precipitated at the bottom of the reaction vessel. Precipitated salt was collected by filtration, and the weight was measured after drying, and it was about 2 g. Moreover, when the density | concentration of the sodium hypochlorite which is a filtrate was measured, it was 15.2 mass% in effective chlorine density | concentration.

[Comparative Example 2]
The operation was carried out in the same electrolytic cell and electrolysis conditions as in Example 1 except that the ion exchange membrane separating the anode chamber and the cathode chamber was changed to Nafion (registered trademark) N324 manufactured by DuPont. The salt concentration of the electrolyzed anolyte after one week when the operation is stable is 95 g / liter, the concentration of the produced caustic soda is 28.5% by mass, the production current efficiency of the caustic soda is 51%, and high concentration sodium hypochlorite is used. Although it was able to be manufactured, it was confirmed that it was insufficient in terms of economy as compared with Example 1.

DESCRIPTION OF SYMBOLS 1 Ion exchange membrane 2 Anode chamber 3 Cathode chamber 4 Alkali metal chloride aqueous solution 5 Pure water 6 Anolyte 7 Generated chlorine gas 8 Alkali metal hydroxide aqueous solution 9 Hydrogen gas 10 Electrolysis tank 11 Water 12 Hypochlorite aqueous solution 13 Water Supply source 14 Anode 15 Cathode 16 Pump 17 Cooling device 18 Reaction tank

Claims (3)

In an electrolytic cell partitioned into an anode chamber and a cathode chamber by an ion exchange membrane, an alkali metal chloride aqueous solution is supplied to the anode chamber, pure water is supplied to the cathode chamber, and electrolysis is performed. The anolyte in the anode chamber and the generated chlorine gas, and the generated alkali metal hydroxide aqueous solution in the cathode chamber are introduced into a reaction vessel, and the anolyte, chlorine gas and alkali metal hydroxide aqueous solution in the reaction vessel are introduced. A method for producing hypochlorite by the reaction of
Wherein as an ion-exchange membrane, with an ion-exchange membrane is a bilayer membrane comprising a carboxylic acid layer, the anolyte supply path for introducing the anolyte of the anode chamber to the reactor, or, the A method for producing hypochlorite, comprising adding water to a mixture of an anolyte, chlorine gas and an aqueous alkali metal hydroxide solution introduced into a reaction vessel.   The manufacturing method of Claim 1 which manufactures hypochlorite whose effective chlorine concentration is 5 mass% or more. The manufacturing method of Claim 1 or 2 which adds water with respect to the mixture of the anolyte introduce | transduced into the said reaction tank, chlorine gas, and alkali metal hydroxide aqueous solution.

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