JPS6239093Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention mainly relates to an electrolytic cell for an aqueous alkali metal halide solution, especially an alkali chloride salt aqueous solution. The present invention relates to an apparatus for efficiently obtaining high quality caustic alkali.

A horizontal electrolytic cell is divided into an upper anode chamber and a lower cathode chamber by a horizontally stretched diaphragm. The mercury method electrolyzer, which is the most typical horizontal electrolyzer, has been widely used since it can produce a relatively highly concentrated sodium hydroxide solution. However, because the mercury used in the cathode is an environmental pollutant, it is destined to be discontinued in the near future. However, it is not at all desirable from an economic or industrial policy standpoint to scrap all the mercury electrolyzers and ancillary equipment that have been widely used in the past.
This is an extremely serious problem for this industry as well. Under such circumstances, it is extremely desirable to convert to other safer electrolytic cells without scrapping the mercury method electrolytic cell and its ancillary equipment.

From this perspective, the applicant has conducted extensive research and developed a technology that can advantageously convert a mercury method electrolyzer into a cation exchange membrane method electrolyzer, and has previously filed a patent application (Japanese Patent Application No. 131377-1982). etc).

By the way, mercury method electrolyzers generally have a rectangular shape with the long sides several to several tens of times larger than the short sides, and when this is repurposed into a horizontal cation exchange membrane electrolyzer, the cathode and cation If the catholyte is circulated in parallel to the long sides to prevent cathode gas from adhering to the exchange membrane, the gas/liquid ratio near the outlet will increase, gas bubbles will come together, and the gas and liquid will separate. As a result, vibrations occur around the cathode chamber, which not only damages the membrane but also increases the electrical resistance of the catholyte and causes a current density distribution in the flow direction. Furthermore, if the amount of circulating liquid is increased in order to reduce the gas/liquid ratio near the outlet, the pressure loss inside the cathode chamber will increase, leading to the risk of membrane damage and an increase in the cost of power required for circulation. On the other hand, if a catholyte plate with a flat surface is used and the catholyte is circulated parallel to the short side, the distance between the membrane and the cathode plate must be set to 2 to 5 mm in order to lower the gas/liquid ratio, and the electrolysis voltage must be reduced. raise.

In view of these circumstances, the inventors of the present invention have conducted intensive research and have completed the present invention, which can solve the above-mentioned problems at once.

That is, the present invention consists of an upper anode chamber and a lower cathode chamber partitioned by a cation exchange membrane stretched substantially horizontally, and the cathode chamber has a substantially rectangular shape that is impermeable to gas and liquid. The horizontal electrolytic cell is equipped with a cathode plate, and the surface of the cathode plate has an uneven structure parallel to the short side.

Hereinafter, the present invention will be described based on drawings showing embodiments of the present invention. In the following explanation, sodium chloride, which is the most common representative example of an alkali metal halide, and caustic soda as its electrolytic product are used for convenience, but these are not intended to limit the present invention. Of course, it can also be immediately applied to other inorganic salt aqueous solutions such as potassium chloride, water electrolysis, etc.

Figure 1 is a partially cutaway front view of the electrolytic cell of the present invention.
FIG. 2 is a side sectional view and a schematic diagram showing an example of the catholyte circulation system.

In FIGS. 1 and 2, the electrolytic cell of the present invention is composed of a rectangular anode chamber 1 whose length is larger than its width, preferably several times the length, and a cathode chamber 2 located directly below the rectangular anode chamber 1. The anode chamber 1 and the cathode chamber 2 are partitioned by a cation exchange membrane 3 stretched substantially horizontally. Here, "substantially horizontal" also includes a case where the surface is slightly inclined (for example, a slope of about 2/10 is applied) as necessary.

The anode chamber 1 includes a lid 4, an anode chamber side wall 5 extending to surround the anode, which is composed of an anode conductive rod 6, an anode conductive rod cover 9, an anode plate 12, etc., and an upper surface of the cation exchange membrane 3. The anode conductive rods 6 are suspended by an anode suspension device 7 erected on the lid 4, and the anode conductive rods 6 are electrically connected to each other by an anode bus bar 8. The lid body 4 has a hole 10 through which the anode conductive rod cover 9 is inserted, and the hole 10 is hermetically sealed by a sheet 11. An anode plate 12 is attached to the lower end of the anode conductive rod 6, and since the anode plate 12 is connected to the anode suspension device 7, it can be adjusted up and down by operating the anode suspension device 7, and the anode can be adjusted up and down by operating the anode suspension device 7. It can be placed in contact with the ion exchange membrane 3. Of course, the anode is not limited to being suspended from an anode suspension device provided upright on the lid, and may be suspended or supported by other methods. Furthermore, the anode chamber has at least one anolyte inlet 13, which can be provided on the lid 4 or on the side wall 5 of the anode chamber. On the other hand, at least one anolyte outlet 14 is provided, and these can be provided on the side wall 5. Further, an anode gas (chlorine gas) outlet 15 is provided at an appropriate location on the lid 4 or the side wall 5. Of course, both the anode gas and the anolyte may be extracted as a mixed phase liquid, the gas and liquid may be separated outside the anode chamber, and only the anolyte may be circulated as necessary. In this case, the anode gas outlet 13 is not necessary.

As the lid body 4, anode chamber side wall 5, anode conductive rod cover 9, and sheet 11 constituting the above-mentioned anode chamber 1, the lid body, anode chamber side wall, etc. constituting the mercury method electrolytic cell may be used. In addition, any material that can withstand chlorine can be suitably used without any particular restrictions. For example, chlorine-resistant metals such as titanium and titanium alloys, fluorine-based polymers, hard rubber, etc. can be used. Furthermore, iron lined with the above-mentioned metals, fluorine-based polymers, hard rubber, etc. can also be used.

Although a graphite anode can be used as the anode plate 12 for carrying out the anode reaction, an insoluble anode made of a metal such as titanium or tantalum coated with, for example, a platinum group metal, an oxidized platinum group metal, or a mixture thereof is preferable. . Of course, it is economical to use the same size and shape of the anode plate used in the mercury electrolyzer.

Next, the cathode chamber 2 is formed between the lower surface of the cation exchange membrane 3 and the cathode plate 1 which is impermeable to gas and liquid and has an uneven surface structure.
6, and a cathode chamber side wall 17 standing upright along the edge of the cathode plate so as to surround the cathode plate. The cathode chamber side wall 17 can be made of something like a rigid frame edge, or it can be made of something like a packing-like elastic material such as elastic rubber or plastic.

In addition to the above-mentioned materials, the material for forming the cathode chamber side wall 17 is not particularly limited as long as it can withstand caustic alkali such as caustic soda, and iron, stainless steel, nickel, nickel alloy, etc. can be used. Furthermore, a material obtained by lining an alkali-resistant material on an iron base material can also be suitably used. Furthermore, materials such as rubber, plastic, etc. can also be used. Examples of such materials include rubber-based materials such as natural rubber, butyl rubber, and ethylene propylene rubber (EPR); Examples include base polymer materials, polyvinyl chloride, and reinforced plastics (FRP).

The cathode plate 16 used in the present invention is made of a conductive material such as iron or nickel. Of course, it is a desirable embodiment to subject these surfaces to hydrogen overvoltage reduction treatment. For example, the hydrogen overvoltage reduction process is performed by Nickel,
cobalt, chromium, molybdenum, tungsten,
This is done by flame or plasma spraying or plating of platinum group metals, silver, alloys thereof, and mixtures thereof.

The cathode plate 16 of the present invention has a surface having an uneven structure parallel to the short side. The uneven structure can be obtained by, for example, cutting out parallel grooves in a flat plate, attaching a thin rod-shaped body such as a round bar or a square bar to the flat plate by welding, or by integrally protruding it. Furthermore, the cathode plate itself can be made using a corrugated plate. There is no particular restriction on the shape of the uneven structure;
Rectangular waveforms, trapezoidal waveforms, sinusoidal waveforms, circular shapes, cycloidal shapes, etc. can be used alone or in combination. Furthermore, the unevenness does not necessarily have to be continuous in the direction of flow of the catholyte, and may be cut in the middle. Furthermore, another metal plate having a corrugated or uneven structure can be laminated on the bottom plate. There are no special restrictions on the uneven structure, but the height is about 0.5 mm to about 10 mm, and the width is about 3 mm.
A convex-concave structure having convex portions of about 3 cm strips arranged at intervals of about 3 mm to about 20 cm is suitable.

FIG. 3 shows an example in which a corrugated metal plate 24 is welded onto the flat cathode plate 16, and FIG. 4 shows an example in which round bars 25 are arranged in parallel on the flat cathode plate 16. .

The cathode plate of the present invention is extremely economical if the bottom plate of a mercury electrolyzer is used. In this case as well, the uneven structure can be obtained by processing similar to the above. Fifth
The figure shows a groove structure in which a metal plate 26 having an uneven structure is previously superimposed on the surface of a bottom plate 27 of a mercury method electrolyzer.
With such a structure, it is convenient because it is only necessary to perform pre-warping, low hydrogen overvoltage treatment, etc., and set it on the bottom plate at the site. It goes without saying that the bottom plate 27 of the mercury method electrolyzer can be used as the cathode plate 16 in FIGS. 3 and 4 as well.

When performing electrolysis using the electrolytic cell of the present invention, it is a preferred embodiment that the tip of the convex part of the convex-concave structure is adjacent to or in contact with the cation exchange membrane. With such a configuration, not only can vibration of the membrane be suppressed, but also the distance between the poles can be made uniform.

FIG. 6 shows an example in which the cathode structure shown in FIG. 4 is provided, and the catholyte inlet 19 and multiphase liquid outlet 20 are arranged so as to be introduced or discharged in a direction substantially perpendicular to the horizontal plane of the cathode plate. shows.

Examples of cation exchange membranes suitable for the present invention include membranes made of perfluorocarbon polymers having cation exchange membranes. Membranes made of perfluorocarbon polymers with sulfonic acid groups as exchange groups are manufactured by E.I.
It is commercially available under the trade name "Nafion" from Pont de Nemours & Company. Furthermore, it is known that cation exchange membranes use a reinforcing backing material to increase membrane strength, and the cation exchange membranes have a smooth surface and an uneven surface. In such a case, it is advantageous to use a cation exchange membrane having at least a smooth cathode surface, since a low voltage can be obtained at a low linear velocity.

FIG. 7 is a schematic diagram showing an example of the electrolyte circulation system of the electrolytic cell of the present invention. Explaining based on FIG. 7, salt water is supplied to the anode chamber 1 through the anolyte inlet 13, and chlorine gas generated by electrolysis is taken out along with the fresh salt water through the anode mixed phase liquid outlet 28. After the fresh salt water is separated into gas and liquid in the fresh salt water receiving tank 29, part of the fresh salt water is circulated to equalize the salt water concentration and pH within the electrolytic cell. Further, gas-liquid separation of fresh salt water and chlorine gas can also be performed in a conduit between the mixed phase liquid outlet and the fresh salt water receiving tank. Although not shown in the figure, an anolyte dispersion tube connected to the anolyte inlet 13 and extending over almost the entire length inside the anode chamber is provided, and the anolyte is introduced into the anode chamber through holes made in the dispersion tube as appropriate. The anolyte in the anode chamber can also be made uniform by supplying the anolyte in a distributed manner.

The catholyte is supplied from the catholyte inlet 19, becomes a multiphase flow with hydrogen gas generated in the cathode chamber 2, and is taken out from the multiphase liquid outlet 20, and the hydrogen gas and catholyte are separated by the separator 21. . The substantially gas-free catholyte from which the gas has been separated is circulated into the cathode chamber 2 through the catholyte inlet 19 by a pump 22 . The separator 21 and the pump 22 may be provided one for a plurality of electrolytic cells, or may be provided for each electrolytic cell.

Current is supplied from the anode busbar 8 and the cathode chamber 2
passes through the cathode plate 16 and is taken out from the cathode busbar 18.

In the anode chamber 1, the formula A reaction occurs, and the sodium ions in the anode chamber 1 pass through the cation exchange membrane 3 and reach the cathode chamber 2.
On the other hand, in cathode chamber 2, the formula is A reaction occurs, producing hydrogen gas, and
Caustic soda is generated by receiving sodium ions that have migrated from the anode chamber 1 through the cation exchange membrane 3.

The catholyte that is supplied into the cathode chamber and flows through it is carried to the outside of the cathode chamber together with hydrogen gas and generated caustic soda. After the hydrogen gas is separated by the separator 21, the catholyte is returned to the catholyte inlet 19. It is advantageous to use a circulating fluid in which at least a portion of the sodium hydroxide is refluxed, since the concentration of caustic soda can be increased as appropriate, and the concentration can also be adjusted by diluting it with water midway through.

An example of the electrolytic method in which both the catholyte and the anolyte are circulated has been described above, but when only the catholyte is circulated, electrolysis can be carried out using a circulation system as shown in FIG. 2.

As mentioned above, according to the present invention, the gas/liquid ratio at the cathode chamber outlet can be made small, so that gas bubbles do not meet and a smooth liquid flow can be obtained. Furthermore, since the film can be brought into close contact with the tip of the convex part of the uneven structure, the distance between the poles can be easily and uniformly controlled, and the distance between the poles can be made substantially the same as the film thickness. Furthermore, when using a metal plate with an uneven structure, the metal plate with an uneven structure can be removed and subjected to mechanical processing or hydrogen overvoltage reduction treatment.
It is convenient to handle and increases work efficiency.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway front view showing an embodiment of the electrolytic cell of the present invention, Fig. 2 is a side sectional view of the same and a schematic diagram showing an example of a catholyte circulation system, and Figs. 3 to 5 are respectively the electrolytic cell of the present invention. 6 is a side sectional view showing another embodiment of the electrolytic cell of the present invention equipped with the cathode structure shown in FIG. 4, and FIG. 7 is a sectional view showing an embodiment of the cathode structure used in FIG. 2 is a schematic diagram showing an example of a circulation system for both electrolytes. 1... Anode chamber, 2... Cathode chamber, 3... Cation exchange membrane, 4... Lid, 5... Anode chamber side wall, 6...
Anode conductive rod, 7... Anode suspension device, 8... Anode bus bar, 9... Anode conductive rod cover, 10... Hole,
11... sheet, 12... anode plate, 13... anolyte inlet, 14... anolyte outlet, 15... anode gas outlet, 16... cathode plate, 17... cathode chamber side wall, 18... ... Cathode bus bar, 19 ... Cathode liquid inlet, 20 ... Cathode mixed phase liquid outlet, 21 ... Separator, 22 ... Pump, 23 ... Packing, 24
... Corrugated metal plate, 25 ... Round bar, 26 ... Metal plate with uneven structure, 27 ... Bottom plate, 28 ... Anode mixed phase liquid outlet, 29 ... Fresh salt water receiving tank.

Claims (1)

[Claims for Utility Model Registration] 1. Consisting of an upper anode chamber and a lower cathode chamber separated by a cation exchange membrane stretched substantially horizontally, the cathode chamber being impermeable to gas and liquid. 1. A horizontal electrolytic cell comprising a substantially rectangular cathode plate, the surface of the cathode plate having an uneven structure parallel to its short sides. 2. The electrolytic cell according to claim 1, wherein the uneven structure of the cathode plate is obtained by drilling the surface of a flat plate. 3. The electrolytic cell according to claim 1, wherein the cathode plate has a convex-concave structure in which rod-shaped bodies are fixed in parallel on a flat plate. 4 Utility model registration claim No. 1 in which the uneven structure of the cathode plate is obtained by laminating metal plates with an uneven structure on a flat plate
Electrolytic cell described in section. 5. The electrolytic cell according to any one of claims 1 to 4, wherein the tips of the convex portions of the uneven structure are in contact with the cation exchange membrane. 6. The electrolytic cell according to claim 1, wherein the cathode chamber side of the cation exchange membrane has a smooth surface. 7. The electrolytic cell according to claim 1, which is converted from a mercury method electrolytic cell.