JPH02301584A - Electrolytic cell of alkali chloride - Google Patents

Abstract

PURPOSE:To electrolyze alkali chloride at high current efficiency and low voltage by utilizing an ion exchange membrane having surface roughness of specified value for the cathodic face thereof and comparting between an anode and a cathode by the ion exchange membrane wherein uneven work for specifying depth and a pitch has been applied. CONSTITUTION:An ion exchange membrane having <=0.005mm surface roughness is utilized for the cathodic surface thereof. Furthermore the interval between an anode and a cathode is comparted by the ion exchange membrane wherein uneven work having >=0.01mm depth has been applied at a pitch of 0.1-1mm or below. The ion exchange membrane having fine surface roughness of >=0.005mm preferably <=0.002mm depth is utilized for the anodic surface thereof. Furthermore as the uneven shape of the anodic surface of the ion exchange membrane, >=0.01mm preferably >=0.025mm depth is favorable in the effect for preventing sticking of gas. The uneven pitch having >=0.1mm especially >=0.25mm is preferable to stabilize current efficiency. The power cost occupied in the production of caustic soda is drastically reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an alkaline chloride electrolytic cell, and more particularly to an alkaline chloride electrolytic cell that has a low sliding voltage (and high current efficiency).

[Conventional technology].

Conventionally, alkaline chloride electrolyzers using ion exchange membranes have been known to have relatively high sliding voltages due to gases generated during electrolysis adhering to the membrane surface. In order to prevent this phenomenon, it has been found that a low sliding voltage can be obtained by coating the membrane surface with a hydrophilic inert inorganic substance that prevents gas adhesion to the membrane to form a porous layer. For example, JP-A-56-720
This is disclosed in Publication No. 22 and Japanese Patent Application Laid-Open No. 57-39185.

On the other hand, as stated in Japanese Patent Publication No. 60-45711, it is effective to make the cathode surface of an ion exchange membrane have a surface roughness of 0.4 to 1.3 microns in order to obtain high current efficiency. be.

[Problem to be solved by the invention].

JP-A-56-72022, JP-A-57-3918
Although the conventional technology shown in Publication No. 5 and others is highly effective as a method for facilitating gas desorption and reducing the sliding voltage, it has the following problems due to its method of adhering to the film surface. had.

(1) When an inorganic substance is embedded in the film surface by heating and pressurizing it, surface roughness due to the inorganic substance increases, which tends to reduce current efficiency. Conventionally, this problem has been dealt with by reducing the size of the particles and by not increasing the degree of embedding more than necessary, so as not to reduce the current efficiency. However, compared to the current efficiency of a membrane with a surface roughness of 2 microns or less without embedding an inorganic porous layer,
~2% lower (there was a tendency to become lower).

(2) There is a method of applying a mixture of a glue and an inorganic substance that will stick to the membrane onto the membrane surface by, for example, spraying the mixture and then heat-treating the mixture. In this case, increase in surface roughness due to embedding of inorganic substances can be prevented, and high current efficiency can be achieved. However, since there is no membrane material that has sufficient bonding strength with the membrane material, inorganic particles fall off over time within the electrolytic cell, and there is a corresponding increase in the sliding voltage over time.

The present invention aims to provide an alkaline chloride electrolytic cell that achieves both low sliding voltage and high current efficiency, which have been difficult to achieve with conventional techniques, and also achieves stabilization of the above characteristics over time. It is something.

[Means for Solving the Problems] The present invention has been made to achieve the above-mentioned object, and gas adhesion to the membrane surface is not only due to the hydrophilicity and hydrophobicity of the surface, but also due to the shape. This was devised based on the experimental fact that there are differences depending on factors, especially the shape of the unevenness.

That is, on the cathode surface of the ion exchange membrane having a surface roughness of 0.005 mm or less, the anode is partitioned by an ion exchange membrane which is further textured with a depth of 0.01 mm or more at a pitch of 0.1 mm to 1 mm or less. The present invention provides an alkali chloride electrolytic cell characterized by the following characteristics.

The ion exchange membrane used in the present invention has a depth of at least 0.005 mm or less on the anode surface, preferably 0.002 mm.
A material having a surface roughness of the following fine irregularities is used.

Further, in the present invention, relatively large irregularities are formed on the anode surface of the ion exchange membrane. The uneven shape used in the present invention preferably has a depth of 0.01 mm or more, preferably 0.025 mm or more from the viewpoint of preventing gas adhesion. The pitch of the concavities and convexities (distance from one concavity to the next) is 1.
A thickness of 0.1 mm or more, particularly 0.25 mm or more is preferable from the viewpoint of stable current efficiency. On the other hand, from the viewpoint of preventing gas adhesion, the thickness is preferably 1 mm or less.

The large uneven shape may be continuous or independent. Note that the depth of the uneven shape described above represents the difference between the average height of the image area and the average height of the open area.

It is preferable to provide a gas and liquid permeable porous layer with no electrode activity on the anode surface of the ion exchange membrane used in the present invention. Another method is to apply unevenness to the surface to prevent gas adhesion in the same way as the cathode surface. Furthermore, there is also a method in which the porous layer is transferred onto the membrane surface by coating or pressure heating, and then further roughening is performed. Any of the above treatments may be applied to the anode surface.

Regarding the method of uneven processing on the anode side, please refer to Japanese Patent Application Laid-Open No. 60-39.
184 are preferably used. On the other hand, methods for processing unevenness on the cathode surface include, for example, transfer by pressurizing a mesh-like cloth, non-woven fabric, etc., and a solid surface with an uneven surface that is the opposite of the uneven surface transferred to the membrane surface. Although it is possible to transfer the image to a solid surface, and it can be applied in practice, transfer of a mesh-like cloth or transfer of an uneven shape machined by engraving or the like onto a solid surface are preferable in view of the uniformity of the shape. The transfer method involves placing the ion exchange membrane and cloth at the same time in a flat press or roll press (rolling machine) and applying pressure. There is also a method of applying pressure by installing a roll or a flat plate having an uneven shape on one side of a press machine. In either case, it is common to heat the resin so that it flows and is easily transferred, usually at a temperature of 80 to 220
Set to ℃. Below 80°C, excessive pressure is required, and above 220°C, it becomes difficult to release the transferred cloth or solid surface, and more preferably between 100°C and 180°C.
It is ℃.

The pressing force is carried out within the range of 3 to 200 kg/cm2 depending on the temperature conditions, but is not limited thereto.

The type of ion exchange membrane used in the present invention is one made of a fluorocarbon polymer having a sulfonic acid group or a carboxylic acid group, and may be a single layer or a multilayer membrane of these polymers. Further, it may be laminated with cloth or porous polymer (for example, PTFE) as reinforcement.

When the ion exchange membrane thus obtained is used to construct the alkaline chloride electrolytic cell of the present invention, the ion exchange membrane is placed between the anode and the cathode. Each species and the ion exchange membrane may be arranged at intervals or may be arranged in contact with each other.

These constructions of the alkaline chloride electrolyzer are carried out according to known methods.

[Function] In the present invention, the mechanism by which the unevenness prevents gas adhesion is not necessarily clear, but the size of the gas generated in the electrolytic cell and the adhesion of that gas to the membrane surface are determined by the depth and pitch of the unevenness. The bubbles become thicker than the pitch of the unevenness (as the bubbles become thicker than the pitch of the unevenness), or as the attached gas grows.
This is thought to be due to the fact that the bubbles become supported in a dotted manner, making them more likely to separate from the membrane surface.

[Example Example 1 Tetrafluoroethylene and CFz=CFO(CF-)3cOOcH1 were copolymerized in a trichlorotrifluoroethane solvent using azobisisobutyronitrile as a catalyst to obtain an ion exchange capacity of 1.25 mm, respectively. A copolymer with equivalent weight/g dry resin and an ion exchange capacity of 1.45 milliequivalents was prepared.

The 20 micron thick film with an ion exchange capacity of 1.25 milliequivalents and the 170 μm thick film with an ion exchange capacity of 1.45 milliequivalents are laminated using a pressure roll type laminating press having a metal roll and a rubber roll. A laminated film was obtained.

On the other hand, a mixture containing 10 parts of zirconium oxide powder with a particle size of 1U, 0.4 parts of methylcellulose (2% aqueous solution having a viscosity of 2000 cps), 19 parts of water, and 1 part of cyclohexanone was kneaded to obtain a base. Ta. The ion exchange capacity of the laminated membrane was 1.45 mm by applying the paste using a Tetron screen with a mesh number of 200 and a thickness of 75 microns, a printing plate with a screen mask of 30 microns thick underneath, and a polyurethane squeegee. The equivalent side was screen printed. The adhesive layer obtained on the membrane surface was dried in air. The particle layer was pressed onto the ion exchange membrane using the same press as described above. On the membrane surface thus obtained, 1.0 mg of zirconium oxide was deposited per 1 cm 2 of the membrane surface, forming a porous layer with a thickness of 10 μm. The surface side of the ion exchange membrane thus obtained having an ion exchange capacity of 1.25 milliequivalents was made uneven by the following method. A filament made of saturated polyester resin (trade name Tetron) has a denier of 22De (De;
Indicates the weight of filament per 9km)X 90Me
(Me; mesh indicates the number of filaments per inch (2.54 cm)) A cloth meshed at right angles to the ion exchange membrane with an ion exchange capacity of 1.25 meq. Place it on top of it, heat and pressurize it,
The texture was transferred to the membrane surface. Asperities as shown in FIG. 1 were formed on the cathode surface of the ion exchange membrane thus obtained.

According to magnified observation using an electron microscope, continuous grooves with a depth of 20 to 50 microns and a pitch of 250 to 320 microns were formed. Further, along these uneven surfaces, the depth of finer unevenness was 2 microns or less.

The ion exchange membrane was immersed in a 125% by weight aqueous sodium hydroxide solution at 70° C. for 16 hours to hydrolyze the exchange groups and convert them into sodium ion type. Titanium punched metal (minor diameter 4
mm, major axis 8 + nm), an anode with low chlorine overvoltage coated with a solid solution of RuO□, iridium oxide, and titanium oxide, and a 52% by weight punched metal made of SO3304 (minor axis 4 mm, major axis 8 mm) on the cathode side. The cathode, which has been etched in a caustic soda aqueous solution at 150°C for 52 hours to have a low hydrogen overvoltage, is brought into pressure contact with an ion exchange membrane. Electrolysis was carried out at 90°C and 30 A/dm2 while supplying the sodium chloride concentration in the anode chamber at 3.5N and the caustic soda concentration at the cathode side at 35% by weight.As a result, the current Efficiency is 97.0%,
The voltage was 2.95V.

[Comparative Example 1] The same ion exchange membrane as in Example 1 was used, except that the surface on the side with an ion exchange capacity of 1.25 meq. , the current efficiency is 97.5%, and the voltage is 3.10 to 3.25V.
Met.

[Comparative Example 2] In Example 1, a porous layer of α-silicon carbide particles (average particle size 0.3 microns) was formed on the cathode side using the same method as the method for forming the porous layer of zirconium oxide on the anode side. When electrolysis was performed using the same ion exchange membrane and the same electrolytic cell, the current efficiency was 95.5% and the voltage was 2.
It was 95V. As shown in Figure 2, the surface of this membrane on the cathode side has dense irregularities of 3 to 6 microns with an ion exchange capacity of 1 to 2.
It was formed on the membrane surface of 5 milliequivalents.

[Example 2] In Example 1, the device used to process the unevenness on the cathode side was a metal machine having independent trapezoidal depressions alternated at 45° and having a center-to-center pitch of 212 microns. It consists of a roll with a diameter of 150 mm and a rubber roll with a rubber hardness of 80 °C and a lining thickness of 10 mm. After heating to a surface temperature of 150 °C and 60 °C, respectively, the ion exchange capacity of the ion exchange membrane is 1.25 mm. When the same ion exchange membrane was used, except that the equivalent surface was textured toward the metal roll side, and electrolysis was performed in the same electrolytic cell, the current efficiency was 97.0%, and the voltage was 2.92V. Met.

On the cathode side surface of this film, independent irregularities with a maximum height difference of 30 to 40 microns and a pitch of 200 to 230 microns are formed as shown in Figure 3, and the irregularities along the finer surface are 1.3 microns. It was below.

[Effects of the Invention] The present invention exhibits stable performance over a long period of time with high current efficiency and low voltage, and can significantly reduce the electricity cost for producing caustic soda.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the ion exchange membrane obtained in Example 1, where 1 is a single layer of polymer with an ion exchange capacity of 1.25 meq/g, and 2 is a polymer layer with an ion exchange capacity of 1.44 meq/g. 3 represents a layer of zirconium oxide particles applied to the membrane surface by screen printing. FIG. 2 is a schematic cross-sectional view of the ion exchange membrane obtained in Comparative Example 2, and 4 in the figure represents a particle layer of carbide carbide applied to the membrane surface by screen printing. FIG. 3 is a schematic cross-sectional view of the ion exchange membrane obtained in Example 2.

Claims (1)

[Claims] (1) A depth of 0.0 mm on the cathode surface with a surface roughness of 0.005 mm or less.
Concave and convex machining of 0.1mm or more with a pitch of 0.1mm or more and 1mm
An alkali chloride electrolytic cell characterized in that an anode and a cathode are separated by an ion exchange membrane as described below. (2) The electrolytic cell according to claim (1), which has a continuous uneven pattern. (3) The electrolytic cell according to claim (1), in which the uneven processing has an independent shape. (4) Claim (1) comprising a gas and liquid permeable porous layer with no electrode activity on the anode side of the ion exchange membrane;
(2) or (3) electrolytic cell. (5) 0.001 to 0.1 m on the anode side of the ion exchange membrane
The electrolytic cell according to claim (1), (2), (3) or (4), wherein the electrolytic cell is textured with a depth of m. (6) Claims (1) to (5) in which the unevenness on the cathode side is formed by transfer of a mesh-like cloth, a roll or flat solid surface having an inverted surface of the uneven shape, or a nonwoven fabric.
) any electrolytic cell. (7) The electrolytic cell according to any of claims (1) to (6), wherein the ion exchange membrane comprises a single or multilayer fluorocarbon polymer layer having a sulfonic acid group or a carboxylic acid group.