KR100414015B1 - An electrolytic cell for producing Sodium Hypochloride - Google Patents

Abstract

The present invention provides an electrolytic device having an electrode capable of electrolyzing brine to obtain sodium hypochlorite, wherein the anode is made of a cylindrical tin (Sn) -based compound as the anode, and the Hastelloy metal is used as the cathode. The present invention provides a sodium hypochlorite generating electrolyzer, which is characterized by alternating positive and negative electrodes, which is excellent in durability of the electrode, consumes little electrolytic current, and can significantly reduce the frequency of cleaning of the electrode.

Description

An electrolytic cell for producing Sodium Hypochloride

The present invention relates to a sodium hypochlorite generating electrolyzer, and more particularly, in an electrolytic cell equipped with an electrode, a network-like tin (Sn) -based compound is used as an anode, and a hastelloy metal is used as a cathode. The present invention relates to a sodium hypochlorite generating electrolyzer, which is characterized by alternating cathodes and anodes in a cylindrical electrolytic cell, which is excellent in durability of the electrode, has low electrolytic current consumption, and can significantly reduce the frequency of cleaning of the electrode. .

Sodium hypochlorite (NaOCl), as is widely known, is used for water purification plants, sterilizers for sewage treatment plants, cooling water boilers for general chemical plants, desalination process water, cooling water treatment for power plants, drinking water treatment, plants and vegetables, meat processing, It is a colorless, clear liquid with a strong chlorine odor that is used as laundry and papermaking and household bleach outside of pool.

In general, a well-known method for generating sodium hypochlorite is to electrolyze salt to obtain a first-class sodium hypochlorite, and a schematic generation process diagram thereof may be shown in FIG. 1.

According to FIG. 1, the injected water and salt are dissociated into sodium ions (Na ⁺ ) and chlorine ions (Chloride, Cl ⁻ ) so that the chlorine ions are oxidized to chlorine at the anode as follows.

_{^{Cl - → 1/2 Cl 2}} + e -

Sodium ions are reduced at the cathode as follows,

Na ^{+ +} e ^- → Na

The sodium obtained is reacted with water to form sodium hydroxide (caustic soda) and hydrogen

Na + H ₂ O → NaOH + 1 / 2H ₂

Chlorine produced at the positive electrode and sodium hydroxide produced at the negative electrode react to obtain sodium hypochlorite having an electrolytic range of about 0.2% to 0.8%.

NaOH + Cl ₂ → NaOH + HCl

However, the electrolytic device that produces sodium hypochlorite by electrolysis of brine as described above has the disadvantage of low durability of the electrolytic device due to the continuous oxidation and reduction reactions at both electrodes. Configuration of Electrode with Low Electrolytic Power Consumption Second, there is no need for local overheating in the system, uniform electrolyte concentration distribution in the electrolytic cell, and third, an electrolytic cell having excellent resistance to the hardness of the brine is required.

The first electrode durability improvement technology of the prior art for solving the conventional problems provides a method for plating the electrode for sodium hypochlorite generation according to the Korean Patent Application Publication No. 2000-40399, the base material titanium (TI) is a method of heat treatment at 400 to 600 ° C. for 1 hour by varying the composition ratio of platinum (Pt), ruthenium (Ru), and iridium (Ir) composition by brushing method on the surface, but the electrode is expensive In addition, there is a problem that the durability of the electrode containing ruthenium is shortened in the brine is short.

Another prior art for an electrode for an electrolysis device is International Publication No. WO7900709 A1, which discloses an electrode for water electrolysis comprising a nickel-molybdenum, nickel, tungsten, and cobalt-molybdenum oxide catalyst. It is proposed to use an electrode, but a metal such as nickel has a problem that the life of the electrode is rapidly shortened due to excellent reactivity with chlorine.

International Application Publication No. WO9117287 attempts to increase electrolysis efficiency by dispersing electrodes in electrolyte by providing a porous electrode electrolysis method and apparatus to achieve homogenization of electrolyte concentration in an electrolytic cell, but unnecessarily increases the size of the electrolytic cell. There was this.

International Application Publication No. WO9916934 A1 provides an apparatus for electrolyzing brine in multiple stages, but has a disadvantage in that an electrolyzer is enlarged and complicated in a stem for generating low concentrations of sodium salt and low concentrations of sodium hypochlorite.

International Application Publication No. WO 9809917 A1 provides an electrolytic cell system having round and rod-shaped electrodes on a central axis, where electrolyte distribution is better than that of a cube or cuboid electrolytic cell system, but the unit volume per round and rod-shaped electrode array is appropriate. The electrode area has a disadvantage that the electrolytic cell is relatively large.

Prior art for improving the resistance to the hardness of the brine is disclosed in Korean Patent Application Publication No. 1998-19227, in order to disinfect the water in the water purification plant, salt is supplied into the salt storage tank and water is supplied to the water softener. Sodium hypochlorite is produced in the digestion tank and supplied to the water purification plant to provide a water treatment disinfection system for water purification plant. Korean Patent Application Publication No. 1996-7463 discloses a solution for swimming pools, hot springs and public baths. An apparatus for purifying bath water is provided, and an anode and a cathode plate are disposed to face each other, and an electrolytic passage is formed by electrolyzing with a saline solution flowing therebetween to make sterilized water containing active oxygen, and the sterilized water is added to the circulation arc and stirred. Decomposition and active acid by contacting the device with byproducts of the electrolytic reaction hypochlorous acid and sodium hypochlorite Would relates to a catalyst for generating, they could not solve the problems that the magnesium and calcium in hard varnish present in the salt deposited by the electrode.

In addition, International Application Publication No. WO9816477 A1 provides a method of removing the scale attached to the electrode by periodically switching the polarity of the electrode by using a bipolar electrode, which is already used in a small electrolytic system industrially. The technique could not solve the problem of repeated durability changes, which drastically reduced the durability of the electrode.

The conventional techniques described above not only employ expensive electrodes having a short lifespan, but also have a low current efficiency due to uneven distribution of electrolytes in the electrolytic cell, and do not efficiently remove the hardness present in the brine and water. There is a problem in that durability and efficiency are low, expensive equipment costs and operating costs are required.

The present invention has been made to solve the above conventional problems, in the electrolytic apparatus which can obtain sodium hypochlorite by electrolysis of brine, the material of the anode and cathode are tin series and Hastelloy metal, respectively The present invention provides a sodium hypochlorite generating electrolytic apparatus which can be configured in a mesh shape and alternately arranged in a cylindrical electrolytic cell, thereby improving the durability of the electrolytic cell, reducing the electrolytic power consumption, and making the concentration of the electrolyte in the electrolytic cell uniform.

1 is a process chart of generation of conventional sodium hypochlorite using saline,

2 is a schematic diagram of a brine electrolysis tank according to the present invention,

3 is a view showing the movement direction of the electrode arrangement and the electrolyte according to the present invention,

4 is a process chart for generating sodium hypochlorite according to the present invention.

The present invention provides an electrolytic cell equipped with an electrode for producing sodium hypochlorite by electrolysis of brine, wherein the cathode and the positive electrode are formed in a cylindrical electrolytic cell using a networked tin (Sn) -based compound as an anode and a Hastelloy metal as a cathode. It is an object of the present invention to provide a sodium hypochlorite generating electrolyzer, which is characterized by alternating arrangements, excellent durability of the electrode, low electrolytic current consumption, and remarkably reducing the frequency of cleaning of the electrode.

In the electrolytic apparatus for producing sodium hypochlorite by electrolysis of brine, the electrolytic power consumption depends on the chlorine generation efficiency, which is determined by the catalytic performance of the electrode. In general, the material of the electrode is a DSA coated with ruthenium oxide on titanium metal or Pt / Ir coated on titanium metal. These coating electrodes have a lifespan of several years and a very low power consumption, but are disadvantageous. Therefore, the present invention is characterized by using a tin (Sn) -based compound having a relatively low price and excellent chlorine generation efficiency as a positive electrode to compensate for this disadvantage.

In the Sn-based anode used in the present invention, SnCl ₄ and RuCl ₄ are dissolved in hydrochloric acid and isopropyl alcohol, and then the electrode to be coated is dipped and dried to sinter in a 500 to 1000 ° C. sintering furnace once. It can manufacture by repeating above.

Carbon, titanium, Hastelloy, and nickel compounds may be used as the material of the anode used in the present invention, and most preferably, Hastelloy having low durability and low hydrogen generation potential is used.

Since the electrode system according to the present invention has high power efficiency and very low power consumption, it is possible to obtain 0.8% sodium hypochlorite with a small amount of salt and power.

Copper, bronze, stainless steel or other metals may not be used as the electrolytic cell. It is preferable to use non-ferrous metals such as titanium and hastelloy, or polypropylene and acrylic polymers, and in consideration of economic aspects, polymer materials are most preferred.

In addition, the gas generated by the electrode reaction rises as the bubbles increase along the electrode surface, which hinders the flow of current, the resistance increases due to the bubbles, and when the resistance increases, the local temperature rises due to Joule heat. Since the sodium hypochlorite produced is decomposed, a consideration in the apparatus for generating sodium hypochlorite is a uniform distribution of the electrolyte.

In the present invention, in order to achieve a uniform distribution of the electrolyte, the electrode structure is characterized by a mesh (mesh). That is, it is preferable to circulate the generated bubbles to the rear of the electrode surface, in the present invention, in order to solve this problem, instead of configuring the electrode as a flat plate using a mesh-shaped electrode.

Furthermore, in the present invention, the inside of the electrolytic cell for generating sodium hypochlorite to eliminate the local dead space generated when the fluid moves a cube or a cube in a cylindrical shape as shown in Figure 2, the electrode is shown in FIG. As can be seen, by alternately arranging the anode and cathode electrodes in the shape of a mesh, it is possible to have a maximum cross-sectional area in a given space, thereby achieving maximum production in the same volume.

In order to solve the shortening of the life of the electrode due to the generation of hardness electrolyte present in the water and salt, which is another problem in the apparatus for generating sodium hypochlorite by electrolysis of the brine, the conventional periodic electrode and electrolytic cell cleaning, A method of changing the polarity of the electrode or pretreatment may be used. However, the method of changing the polarity of the electrode may shorten the life of the electrode. Therefore, it is preferable to combine the pickling method with the pretreatment method to remove the precipitate.

Hereinafter, the present invention will be described in detail with reference to the drawings.

Figure 4 is a process for generating sodium hypochlorite according to the present invention first treated with water softener to remove hardness and then branched into two streams A and B. The branched stream melts the salt stored in the saturation tank (1) to make 30% saturated brine, and adds alkaline solution to this stream A to adjust the pH to 10 in the pH adjustment tank (2) to make the hardness calcium and magnesium The hydroxide is precipitated and removed using an automatic bag filter (3). Stream A and stream B from which hardness is removed are mixed in the mixing tank 5, and the concentration of the brine is 3% and supplied to the electrolytic cell 6 through the flowmeter. The direct current through the transformer and rectifier (4) equipment is supplied to the electrolyzer (6). In the electrolyzer (6), sodium hypochlorite is generated by the electrochemical reaction of brine, and the generated sodium hypochlorite is stored in the reservoir (7). And by-product hydrogen is discharged into the atmosphere by a high efficiency fan. Reference numeral 6 in the figure is to perform the process of periodically cleaning the electrolytic cell with a hydrochloric acid supply system.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention should not be construed as being limited by the following Examples, but the scope of the present invention is within the scope of the claims. It is obvious that it can be transformed by a person with knowledge of.

(Example 1)

1. Composition of Electrolyzer System

end. Anode; electrode made by pyrolyzing Sn-Ru oxide on titanium metal

I. cathode; Hastelloy metal

All. Electrolytic cell; Cylindrical polypropylene

la. Electrode structure; Mesh electrode

hemp. Temperature; 30 ℃

bar. Electrolyte concentration; 3 wt% brine

four. Interelectrode distance; 2 mm

2. Operation

end. The influent is treated with soft water and stream A flows into the saturation tank (1) to dissolve the stored salt to produce 30% saturated brine.

I. In the pH adjusting tank (2), an alkaline solution was added to stream A to adjust the pH to 10 to precipitate hardness calcium and magnesium hydroxide, which was removed using an automatic bag filter (3) having a Gore-Tex filter, and then the hardness concentration of stream A. Reduce from 5 ppm to 1 ppm or less.

All. In the mixing tank 5, stream A and stream B are mixed, and the concentration of the brine is adjusted to 3% and supplied to the electrolytic cell 6 via a flowmeter.

la. The direct current through the transformer and rectifier equipment (4) is supplied into the electrolytic cell, and the electrolytic cell electrolyzes the brine to generate sodium hypochlorite, and then stores the sodium hypochlorite generated in the sodium hypochlorite storage tank (7).

(Comparative Example 1)

Except for using an electrode made of RuO ₂ and TiO ₂ oxide, the anode material has the same electrolytic cell system and operating conditions as in Example 1.

(Comparative Example 2)

The material of the anode was the same as that of Example 1 except for using an electrode plated with platinum (Pt).

(Comparative Example 3)

The same as in Example 1 except that the electrolytic cell was a cuboid in the system configuration.

(Comparative Example 4)

It is the same as Example 1 except the electrode shape was produced in plate shape.

(Comparative Example 5)

It is the same as Example 1 except the hardness removal process of brine is not installed in the operation process.

Table 1 shows the electricity consumption, durability and washing frequency of the electrolytic cells in Example 1 and Comparative Examples 1 to 5.

Electricity consumption (kWh / kg Cl ₂ ) Durability (hr) Frequency of cleaning (once a day) Example 1 4 25 20 days Comparative Example 1 18 10 15th Comparative Example 2 12 8 15th Comparative Example 3 7.5 20 19th Comparative Example 4 5.5 20 20 days Comparative Example 5 4.5 24 7 days

* Method of Analysis

end. Current efficiency and cleaning frequency measurement

Iii. Power consumption and current efficiency were measured by measuring the voltage and current for one week.

Iii. Sodium hypochlorite concentration was measured once daily.

Iii. The time at which the voltage rises rapidly was measured.

I. The current density was 10 kA / m 2 per electrode area to change the polarity of the electrode once every hour to accelerate the life of the electrode.

In the electrolytic apparatus which generates sodium hypochlorite by electrolyzing about 3% of low concentration of brine, the electrode of the present invention is alternately arranged in the electrolytic cell by damaging the electrode by oxidation and reduction of the brine. In addition to improving durability of the electrode, the concentration distribution of the electrolyte in the electrolytic cell is uniform, and sodium hypochlorite of 0.8% can be manufactured with low power consumption.

Claims (5)

delete delete delete Branching the influent treated with the water softener into one or more streams; Injecting one branched stream into the saturation tank 1 to dissolve the stored salt to produce saturated brine; Adding an alkaline solution to one stream to adjust pH in a pH adjusting tank (2) to precipitate hardness calcium and magnesium hydroxide and to remove it using an automatic bag filter (3); Mixing one stream having another hardness and another stream in the mixing tank 5 to supply 3% of the brine to the electrolytic cell 6; A method of obtaining sodium hypochlorite, comprising the step of electrolyzing a brine by supplying a direct current to a cylindrical electrolytic cell 6 in which a cathode is made of tin compound and the anode is a Hastelloy metal. . The method for obtaining sodium hypochlorite according to claim 4, wherein the pH of the adjusting tank (2) is 10.