JPH0114830B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides an on-site alkaline chloride electrolytic tank that is installed near a water treatment facility to generate an alkaline hypochlorite solution and directly supply it to treated water. This invention relates to a method for producing water treatment chemicals in a method.

(Prior art) Conventionally, chlorine treatment has been used to sterilize water in both water and sewerage systems, but the chlorine source is liquid chlorine, which is liquefied at high pressure and filled into a cylinder, or Sodium chlorite is used. Handling of such high-pressure cylinders requires skilled professionals, as the cylinders themselves are quite heavy and contain highly pressurized toxic substances. Furthermore, when using a sodium hypochlorite solution, the chemical is transported from a manufacturing factory as an aqueous solution of a certain concentration, and it requires a lot of effort and additional equipment to adjust the concentration and amount to be added to the area where it will be used. Furthermore, the concentration of sodium hypochlorite products is usually around 12%, and transporting such an aqueous solution requires transporting a large amount of water, which is also uneconomical.

Therefore, recently, a small diaphragm-type alkaline chloride electrolyzer is installed at the place of use, and saturated brine is made from salt and water.This is electrolyzed to obtain chlorine from the anode chamber and a caustic soda solution from the cathode chamber, and a separate reaction chamber is installed. A method of reacting these in a chamber to obtain a sodium hypochlorite solution is being used. According to this method, not only can the production amount be adjusted by adjusting the amount of electricity, but also the cost of transporting large amounts of water can be reduced.

This type of small diaphragm electrolytic cell is equipped with a synthetic resin diaphragm to prevent a decrease in current efficiency caused by non-diaphragm electrolytic cells, and a communication tube is provided between the anode chamber and the cathode chamber to transfer the anolyte to the catholyte ( The most common method is to mix chlorine gas (caustic alkaline solution) and add the chlorine gas generated in the anode chamber in a separate chamber attached to the electrolytic cell to produce an alkaline hypochlorite solution, which is used as is as a water treatment agent. There is (Special Publication No. 57-53436,
57-94579).

However, in this type of electrolytic cell, the effective chlorine concentration in the alkaline hypochlorite solution produced is 1% by weight.
Good current efficiency can be maintained in the following cases, but
If an attempt is made to increase the decomposition rate of salt water by increasing the effective chlorine concentration to 3 to 4% by weight, there is a drawback that the current efficiency is drastically reduced. In addition, a method that uses a cation exchange membrane as a diaphragm to increase the concentration of caustic alkali in the catholyte and reacts it with chlorine gas to produce an alkaline hypochlorite solution recycles the anolyte after electrolysis into alkali chloride. Since the electrolysis equipment is saturated and circulated through the electrolytic tank, the size of the electrolysis equipment becomes large and the work process becomes complicated, so there are many problems when installing it adjacent to a water treatment facility. Furthermore, although the method of using an asbestos diaphragm as a diaphragm has the advantage of not circulating the anolyte, it has the drawbacks of lower overall current efficiency and a shorter service life of the asbestos diaphragm than the cation exchange membrane method.

(Object of the invention) In view of the above problems, the present invention produces an alkaline hypochlorite solution having an effective chlorine concentration of 2 to 6% by weight as a water treatment agent without providing an anolyte circulation step and with good current efficiency. The purpose is to

(Structure of the Invention) The present invention uses an electrolytic cell in which a cation exchange membrane is provided between the anode and cathodes, and an alkali chloride,
Decomposition rate of alkali chloride while adding water to the cathode chamber
Electrolysis is performed at 50 to 70%, and the anolyte, catholyte, and chlorine gas discharged from the electrolytic tank are mixed to produce an alkaline hypochlorite solution with an effective chlorine concentration of 2 to 6% by weight. This is a unique method for producing water treatment chemicals.

An example of the present invention will be explained with reference to the drawings.
is partitioned by a cation exchange membrane 2, forming an anode chamber 5 into which an anode 3 is inserted and a cathode chamber 6 into which a cathode 4 is inserted. The alkaline chloride solution is introduced into the lower part of the anode chamber 5 from a conduit 7 through a chlorine gas separator 8 . Water for injection is sent from conduit 9 to hydrogen gas separator 10
It is introduced into the lower part of the cathode chamber 6 through the. After electrolysis, the anolyte is circulated to the chlorine gas separator 8 due to the gas lift effect of the generated chlorine gas.
Guided by 3. The caustic alkaline solution (catholyte) generated in the cathode chamber 6 is circulated to the hydrogen gas separator 10 by the gas lift effect of the generated hydrogen gas, the separated hydrogen gas is discharged from the conduit 11, and the catholyte is sent to the reaction tank through the conduit 14. Guided by 13. In the reaction tank 13, the chlorine gas, the anolyte, and the catholyte react to produce an alkaline hypochlorite solution of a predetermined concentration, which is discharged from the pipe 15 as a water treatment agent.

In the method of the present invention, the alkali chloride decomposition rate is 50%
Below 70%, the utilization rate of alkali chloride is poor.
Exceeding this is undesirable because the electrolytic voltage increases. In addition, in order to maintain the effective chlorine concentration of the alkaline hypochlorite solution produced as described above at 2 to 6% by weight, preferably 3 to 5% by weight, the caustic alkali concentration of the catholyte must be 2 to 6% by weight. , preferably 3 to 5% by weight. The current efficiency in this case is 85~
Shows a high value of about 95%. When the caustic alkali concentration is lower than this, the electrolysis voltage increases, and when the caustic alkaline concentration is higher than this, the current efficiency decreases.

The material of the anode used in the present invention may be any material used in ordinary electrolytic cells, such as titanium or the like coated with platinum group metal or its oxide.

Example A sodium hypochlorite solution was continuously produced using the apparatus shown in the drawings. The electrolytic cell was a filter press type made of titanium and stainless steel, the reaction tank was made of titanium and PVC and had a capacity of about 20, and Nafion 315 (trade name, manufactured by DuPont) was used as the cation exchange membrane. In addition, the anode is made of mesh-shaped platinum-metsuki titanium (350 x 500 mm effective area 17.5 dm ² )
The cathode is made of SUS316.

Electrolysis conditions Electrolysis current 350A Anode current density 20A/dm ² Salt concentration supplied to the anode chamber 280-300g/〃 Flow rate 3-3.8/hr Salt decomposition rate 57-68% Amount of water injected into the cathode chamber 8.0-20/hr Cathode Caustic soda concentration in chamber 3-4% by weight Electrolysis voltage 4.5-5.0V Current efficiency 85-95% Electrolysis time 10,000 hours Sodium hypochlorite solution Production volume 11-23.8/hr (Available chlorine concentration 3-5% by weight) (Invention (Effects) The effects of the method of the present invention are as follows.

(1) The electrolysis method of the present invention uses an ion-exchange membrane electrolytic cell for producing a normal chlorine-caustic solution, and the concentration of caustic alkali in the cathode chamber is much higher than the case described above (approximately 20% by weight). Since the concentration is as low as about 5% by weight, good current efficiency can be maintained without considering the back migration phenomenon of the catholyte to the anode chamber, which tends to occur when the concentration is high.

(2) In the method of the present invention, the caustic alkaline solution produced with good electrolysis efficiency as described above is mixed with the anolyte and used as a water treatment agent, so the electrolysis is carried out in the same manner as in ordinary ion exchange membrane electrolysis. There is no need for a subsequent step of re-saturating the anolyte containing chlorine, which simplifies the process and is effective in preventing environmental pollution.

(3) In electrolysis methods that use an asbestos diaphragm as a diaphragm, the liquid moves from the anode chamber to the cathode chamber through the diaphragm, so it is necessary to pressurize the diaphragm with the anolyte at all times during electrolysis. The flow rate of the liquid is limited, but since a liquid-impermeable cation exchange membrane is used in the present invention, the flow rate can be changed arbitrarily depending on the production amount of alkali hypochlorite, which is used as a water treatment agent. .
In addition, the cation exchange membrane used has a lifespan three times that of asbestos diaphragms, and especially since water treatment facilities of this kind are often installed in areas with poor transportation and are operated automatically (unmanned operation), It has the advantage of greatly extending the replacement period.

[Brief explanation of drawings]

The drawing is a flow sheet illustrating the method of the invention. 1... Electrolytic cell, 2... Cation exchange membrane, 3... Anode,
4... Cathode, 7... Supply alkaline chloride solution conduit, 8...
Chlorine gas separator, 9... Water conduit for injection, 10... Hydrogen gas separator, 11... Chlorine gas conduit, 12... Anolyte conduit, 13... Reaction tank, 14... Catholyte liquid conduit.

Claims (1)

[Claims] 1 Using an electrolytic cell equipped with a cation conversion membrane between the anode and cathode, conduct electrolysis at a decomposition rate of alkali chloride of 50 to 70% while adding an alkali chloride solution to the anode chamber and water to the cathode chamber. A method for producing a water treatment agent, which comprises mixing an anolyte, a catholyte, and chlorine gas discharged from a tank to produce an alkaline hypochlorite solution having an effective chlorine concentration of 2 to 6% by weight.