JP3128269B2 - Alkaline chloride aqueous solution electrolyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic cell for alkali chloride electrolysis using an ion exchange membrane method for electrolyzing an aqueous alkali metal chloride solution to produce chlorine and an alkali metal hydroxide.

[0002]

2. Description of the Related Art An ion-exchange membrane electrolytic cell for producing high-purity alkali metal hydroxides with high current efficiency is composed of a cathode chamber with a cathode attached thereto, an anode frame with an anode attached thereto, and a cation exchange membrane. Well-known are a filter press type electrolytic cell which is brought into close contact with a gasket, a box type electrolytic cell in which a cation exchange membrane is processed into a bag shape as a diaphragm, and is attached to an anode chamber or cathode chamber frame. These electrolytic cells are filled with an alkali and an alkali chloride as an electrolytic solution and chlorine and hydrogen as a gas, and leaking to the outside is harmful to the environment and health. Therefore, many devices have been devised in order to reliably seal between the electrolytic cell frames. For example, as a gasket for sealing,
No. 164,088 has a rubber sheet lined with a reinforcing cloth,
It has been proposed to appropriately define the thickness of the rubber layer in contact with the ion exchange membrane and the thickness of the entire rubber layer. Further, Japanese Utility Model Publication No. Sho 62-14130 proposes that a rubber layer provided in contact with an electrolytic cell be provided with a recess. However, in the electrolytic cell, chlorine is always generated, and the electrolytic solution containing a large amount of chlorine and hypochlorite ions, and the portion of the gasket exposed in the anode chamber due to the flowing gas gradually corrode. However, there is a disadvantage that the sealing properties are gradually lowered and fall off.

In order to increase the durability of a gasket against chlorine, sodium hypochlorite, etc.
No. 8287 proposes an electrolytic cell in which a portion of a gasket exposed in an anode chamber is covered with a fluorine resin sheet. Further, Japanese Patent Application Laid-Open No. 3-64490 proposes a gasket using a fluorine resin. Certainly, these gaskets have excellent corrosion resistance and are unlikely to corrode the gasket itself even when used for a long period of time. May cause corrosion of the surface titanium. Such titanium corrosion is likely to occur between the fluorine resin layer of the gasket surface layer and the flange surface of the electrolytic cell frame,
Such corrosion of titanium may impair the smoothness of the flange surface, cause poor sealing, or, in extreme cases, may render the electrolytic cell itself unusable.

[0004]

SUMMARY OF THE INVENTION The present invention improves the corrosion resistance of a conventionally used gasket, and eliminates the need for gasket replacement for a long period of time without causing corrosion of titanium or the like. It is an object of the present invention to provide an electrolytic cell capable of carrying out electrolysis of an aqueous alkali chloride solution.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an electrolytic cell for electrolyzing an aqueous alkali chloride solution using a cation exchange membrane, wherein a gasket disposed between the anode chamber flange surface and the cation exchange membrane has a rubber elasticity. And at least a part of the side in contact with the anion exchange membrane, a part exposed in the electrolytic chamber, and a part of the side in contact with the electrolytic cell frame flange, are covered with a fluorine resin sheet, The present invention also relates to an alkaline chloride aqueous solution electrolytic cell, characterized in that a rubber liner having a thickness of 0.1 mm to 1 mm is provided on a fluorine resin sheet on a side of the gasket in contact with an electrolytic cell frame flange surface.

The present inventors have been improving the gasket used in the alkaline chloride electrolytic cell over a long period of time. The points of the improvement are (a) improvement of sealing performance,
(B) improvement of corrosion resistance to chlorine and hypochlorous acid, (c)
This is to prevent creep and breakage of the gasket and breakage of the ion exchange membrane due to the tightening pressure, and (d) prevent titanium corrosion on the electrolytic tank flange surface.

[0007] With the recent improvement in performance of ion exchange membranes and prolonged life, particularly demanded are improvements in the durability of gaskets and prevention of titanium corrosion. In general, titanium is well known as a corrosion-resistant material.
Excellent corrosion resistance in wet chlorine atmosphere. However, corrosion called crevice corrosion may progress in a seal portion such as a flange surface. As a countermeasure, corrosion is prevented by using an alloy of titanium and palladium. However, titanium containing palladium is expensive, and particularly in an apparatus using a large amount of titanium, such as an alkaline chloride electrolytic cell, the cost is too high to be practical. Therefore, an oxide film is formed by firing the flange surface, or a noble metal or a noble metal oxide is coated. However, such a method is not perfect, and may cause corrosion depending on the usage over a long period of time.

In order to solve this problem and perform stable electrolysis for a long period of time, the present inventors have proposed a gasket made of a fluorine resin molded product and a gasket made of a composite material of a fluorine resin and a non-fluoro rubber. We have repeated various studies. As a result, even if the fluororesin and the composite material with the fluororesin have excellent corrosion resistance and sealability, if they are used for long-term electrolysis, titanium corrosion will occur on the contact surface between the electrolytic tank frame flange surface and the fluororesin. It was found to be prone. On the other hand, it has been found that a rubber gasket is inferior in durability against corrosion deterioration, but is less susceptible to titanium corrosion than fluorine resin.

Although it is not clear why the fluororesin tends to cause corrosion of titanium for any reason, the resin is poor in elasticity as compared with rubber and cannot completely fill the fine irregularities on the titanium surface. This is considered to be related to the fact that the gas and liquid permeability of the resin is different from that of the rubber. Therefore, as a result of diligent studies to develop an ideal gasket that makes use of the advantages of both, the portion of the gasket exposed inside the electrolytic chamber is wrapped with a fluoro resin sheet, which comes into contact with the electrolytic cell flange portion of the fluoro resin portion. By lining the rubber with a minimum thickness that does not cause titanium corrosion in the part, we found that gasket corrosion deterioration did not occur even with long-term electrolysis and titanium corrosion did not occur, and completed the present invention It was made. Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. 1, 2, and 3
4 is a cross-sectional view showing some examples of a gasket to be mounted on an electrolytic cell frame flange portion of the present invention. FIG. 4 is an electrolytic cell showing one embodiment of the present invention for a filter press type ion exchange membrane electrolytic cell. It is sectional drawing of a frame flange part. The numbers in the figure correspond to each other, and the same numbers indicate the same things. As shown in FIGS. 1 to 3, the gasket covers a portion of the rubber sheet 1 having elasticity, which is exposed to the electrolytic solution and gas in the electrolytic chamber, with the fluororesin sheet 2. The fluoro resin sheet 2 on the side to be in contact with is covered with a backing rubber 3.

The rubber sheet may be made of natural rubber, isoprene rubber, styrene / butadiene rubber, butyl rubber, butadiene rubber, ethylene / propylene rubber, acrylonitrile / butadiene rubber, chloroprene rubber, chlorosulfonated polyethylene rubber, urethane rubber, and many others. Sulfurized rubber,
Examples include silicone rubber, acrylic rubber, epichlorohydrin rubber, ethylene / acryl rubber, and fluorine rubber. Among them, ethylene / propylene rubber is preferred in terms of cost and durability.

The shape of the rubber sheet may be variously modified in order to increase the sealing property. For example, the rubber sheet may have a smooth cross section as shown in FIG. 1 or may be in contact with the electrolytic cell flange as shown in FIG. As the side, for example, one having a trapezoidal unevenness, one having an unevenness on the side in contact with the electrolytic cell frame flange as shown in FIG. 3, and the other side in contact with the ion exchange membrane can be applied. The height of the unevenness is 0.1 mm to 2 mm, preferably 0.1 mm.
It is 2 mm to 1 mm. Although the thickness of the rubber sheet varies depending on the structure of the electrolytic cell frame used, a sufficient sealing property is determined empirically within a range where the distance between the electrodes is not so large. It is within 5 mm to 5 mm. The width of the rubber sheet is 15mm from the sealing surface
~ 50 mm is preferred. As the rubber sheet, a sheet having a reinforcing cloth as a core material to prevent creep or excessive elongation due to the tightening pressure at the electrolytic cell frame flange may be used.

As the material of the fluorine resin sheet, a material having excellent chemical resistance and chlorine resistance such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride and the like can be used. The thickness of the fluorine resin sheet may be any range as long as the elasticity of the base rubber sheet is not lost.
Those having a thickness of 1 mm or less, preferably 0.5 mm or less are easy to use. The rubber sheet is preferably covered with a fluororesin sheet not only on the part that is directly exposed to the electrolyte or gas, but also on the part where the electrolyte or gas may penetrate. It is preferable to cover both the front and back with a width of 5 mm to 20 mm in the outward direction from the part to be formed.

When the thickness of the backing rubber 3 is 1 mm or more, the portion exposed to the electrolytic solution increases, and the corrosion of the rubber progresses to deteriorate the sealing property, and the corrosion of titanium on the flange surface of the electrolytic cell occurs. May be undesirable. Also, even if it is too thin, the corrosion of titanium, which is the effect of backing the rubber, cannot be prevented, so the range is preferably 0.1 mm to 1 mm, more preferably 0.1 mm to 0.5 mm.
mm. In this range, the portion exposed to the electrolytic solution and chlorine gas is small, so that the penetration of the electrolytic solution and the like becomes small, and the corrosion of the backing rubber hardly progresses. In addition, the progress of corrosion due to the falling off of the relatively stable chlorinated layer formed in the portion exposed in the electrolytic cell is desirably suppressed. The backing rubber is preferably made of the same material as the rubber sheet as the base material, since it can be integrally formed in processing. However, another rubber material may be bonded with an adhesive or the like.

In the electrolytic cell of the present invention, the gasket is mounted, for example, as shown in FIG. In FIG. 4, the anode-side gasket 7 is mounted on the flange portion of the anode-side electrolytic cell frame, and the cathode-side gasket 8 without using a fluorine resin sheet is mounted on the flange portion of the cathode-side electrolytic cell frame. Tightening. The anode-side gasket 7 may be mounted so as to protrude into the electrolytic cell, or may be mounted so as not to protrude. If it is mounted so as to protrude, the backing rubber exposed in the electrolytic cell may be corroded and fall off, but near the boundary between the lower part of the anode-side electrolytic cell frame flange 5 and the anode chamber 13, For the reasons described above, the progress of the gasket corrosion is stopped, so that the gasket life is not affected.

As described above, the present invention is an electrolytic cell using a gasket which is extremely durable and has a long service life which does not cause corrosion of titanium on the electrolytic tank frame flange surface. Stable electrolysis can be performed without the need to stop for a long time without worrying that the exchange membrane will be damaged. Next, examples of the present invention will be described, but the present invention is not limited to these examples.

[0016]

Example 1 In an electrolytic cell having an energization area of 270 dm ² ,
The gasket shown in FIG. 2 is referred to as an anode gasket 7, a gasket having the same shape but without a fluorine resin sheet as a cathode gasket 8, and a cation exchange membrane 6 as ACIPLEX (registered trademark) F- made by Asahi Kasei Corporation. 4100 was used to construct the electrolytic cell shown in FIG. The anode side gasket 7
Ethylene / propylene rubber sheet with hardness Hs 70 degrees,
A gasket inner peripheral portion is covered with a sheet made of polytetrafluoroethylene having a thickness of 0.03 mm so as to wrap the inner peripheral portion of the gasket with a width of 15 mm from the side in contact with the flange surface of the electrolytic cell to the side in contact with the ion-exchange membrane. Was backed with a thickness of 0.3 mm. Also, in order to enhance the sealing property, 2 m is set on the side in contact with the electrolytic tank frame flange surface.
0.5mm at the top, 1.5mm at the bottom, 0.8 height at m intervals
mm trapezoidal irregularities were provided, and the side in contact with the ion exchange membrane was formed into a smooth shape. The size of the gasket is 1162 mm in inner size, 2362 mm in width, 1222 mm in outer size,
The width was 2422 mm, the gasket width was 30 mm, and the average thickness was 2.0 mm. The cathode-side gasket 8 had exactly the same shape and the same size as the anode-side gasket except that the fluorine resin sheet was not used.

Using this electrolytic cell, 40 A / dm ² , an electrolysis temperature of 90 ° C., a catholyte soda concentration of 30 to 33 w%,
Anolyte salt concentration 195 to 210 g / l, internal pressure of electrolytic cell 1.
After operating at 0 kg / cm ² G for 360 days, the electrolysis was stopped, and the cation exchange membrane, gasket, and anode-side electrolytic cell frame flange were inspected. During this time, there was no leakage of the electrolytic solution or gas from the electrolytic cell frame, and there was no increase in electrolytic voltage and no decrease in current efficiency. For the anode side gasket,
The exposed portion of the backing rubber inside the electrolytic bath turned slightly white and the irregularities of the backing rubber that was in contact with the flange of the electrolytic cell frame were crushed, and the gasket width and thickness in other places due to corrosion No decrease was seen. Even if the gasket was operated without removing the gasket, it could be used for at least 4 to 5 years without any problem.

The cation exchange membrane had no apparent change from the initial stage, and had no damage such as pinholes or tears. There was no corrosion of titanium in the flange portion of the anode-side electrolytic cell frame, as in the initial stage, and no discoloration was observed.

[0019]

[Comparative Example 1] An electrolytic cell exactly the same as that in Example 1 was assembled except that a gasket whose inner peripheral portion was not covered with a fluorine resin sheet was used as the anode-side gasket, and electrolysis was performed for 360 days under the same electrolytic conditions. Thereafter, the cation exchange membrane, the gasket, and the anode-side electrolytic cell frame flange were similarly inspected. During the electrolysis, there was no leakage of the electrolytic solution or gas from the electrolytic cell frame, and there was no increase in the electrolytic voltage and no decrease in the current efficiency.

With respect to the anode side gasket, 2 mm to 1 mm from the portion exposed in the rubber electrolytic tank to the outside.
With a width of 0 mm, the gasket discolored white over the entire inner circumference, and in some places, this white chlorinated product fell off, and the gasket width was reduced by 2 mm to 4 mm. Also, the irregularities of the backing rubber in contact with the flange portion of the electrolytic cell frame were crushed. If the gasket had been used as it was, it was in a state where leakage to the outside of the electrolytic cell, breakage of the cation exchange membrane, and the like were expected at least within one to two years.

The cation exchange membrane did not suffer any damage such as pinholes or tears, but there were some parts of the gasket that had fallen off from corrosion and were discolored whiter than the surroundings. No clear corrosion of titanium was observed at the anode-side electrolytic cell frame flange, but a pale black discoloration was observed at the portion where the gasket had fallen off due to corrosion.

[0022]

Comparative Example 2 An electrolytic cell was assembled in the same manner as in Example 1 except that a gasket made of polytetrafluoroethylene resin and having exactly the same shape as the anode-side gasket of Example 1 was used as the anode-side gasket. After 360 days of electrolysis under electrolysis conditions, the cation exchange membrane, gasket, and anode-side electrolytic cell frame flange were inspected. During the electrolysis, there was no leakage of the electrolytic solution or gas from the electrolytic cell frame, and there was no increase in the electrolytic voltage and no decrease in the current efficiency. Regarding the anode-side gasket, there was no corrosion or dimensional change because only the unevenness of the portion in contact with the electrolytic cell frame flange was crushed.

The cation exchange membrane had no apparent change from the initial stage, and had no damage such as pinholes or tears.
On the anode-side electrolytic cell frame flange portion, a width of 5 mm to 10 mm and a length of 10 mm to 50 m from the inner side of the electrolytic cell to the outside.
Many small holes of 1 mm or less were formed on the titanium surface of the electrolytic cell frame flange at seven locations in the range of m, and local swelling of titanium occurred. Even if this electrolytic cell frame is used as it is, it is determined that after the electrolytic use within one year thereafter, the leakage of titanium to the outside of the electrolytic cell and the corrosion of titanium will progress to a state where the electrolytic cell cannot be repaired. Condition.

[0024]

Comparative Example 3 The anode side gasket was the same as FIG. 2 except that no rubber lining was provided on the side in contact with the electrolytic cell frame flange, and the gasket inner peripheral portion exposed in the electrolytic cell with a fluorine resin sheet was used. Using a gasket covered in
An electrolytic cell exactly the same as that in Example 1 was assembled, and electrolysis was performed for 360 days under the same electrolytic conditions.
The gasket and the electrolytic cell frame flange on the anode side were inspected. During the electrolysis, there was no leakage of the electrolytic solution or gas from the electrolytic cell frame, and there was no increase in the electrolytic voltage and no decrease in the current efficiency. The gasket was not corroded almost as in the initial stage, except that the irregularities in the portion in contact with the electrolytic cell frame flange were crushed.

The cation exchange membrane did not change in appearance at all, and there was no damage such as pinholes or tears. The anode-side electrolytic cell frame flange has a width of 3 mm to 10 mm and a length of 5 mm to 20 mm from the inner side of the electrolytic cell to the outside.
Many small holes of 1 mm or less were formed on the titanium surface of the anode-side electrolytic cell frame flange portion, or local swelling of titanium occurred in five places in the range of mm. Even if this electrolytic cell frame is used as it is, it is determined that, after one to two years of electrolytic use, the leakage of the electrolytic cell to the outside or the corrosion of titanium proceeds to a state where the electrolytic cell cannot be repaired. Condition.

[0026]

As is clear from the above description, the electrolytic cell according to the present invention is excellent in corrosion resistance as a gasket because it is covered with a fluorine resin sheet around the portion exposed as an anode gasket in the electrolytic cell. The cation exchange membrane is not damaged, and the side in contact with the anode-side electrolytic cell frame flange is lined with rubber of an appropriate thickness. ,
Electrolysis can be performed stably without leakage or stoppage of the electrolytic solution or gas outside the electrolytic cell, so that the cost of downtime and replacement of gaskets and cation exchange membranes can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a gasket having no unevenness on a surface according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a gasket having unevenness in a portion in contact with an electrolytic cell frame flange surface according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a gasket according to an embodiment of the present invention, in which a portion in contact with a flange surface of an electrolytic cell frame and a surface in contact with a cation exchange membrane have irregularities.

FIG. 4 is a cross-sectional view showing one embodiment of the electrolytic cell of the present invention in which a gasket is attached to an electrolytic cell frame flange.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rubber sheet 2 Fluoro resin sheet 3 Backing rubber 4 Gasket unevenness 5 Anode-side electrolytic cell frame flange 6 Cation exchange membrane 7 Anode-side gasket 8 Cathode-side gasket 9 Cathode-side electrolytic cell frame flange 10 Anode 11 Cathode 12 Anode chamber 13 Cathode chamber

Claims (1)

(57) [Claims] 1. An electrolytic cell for electrolyzing an aqueous alkali chloride solution using a cation exchange membrane, wherein a gasket disposed between the anode chamber flange surface and the cation exchange membrane has rubber elasticity, A part of the side in contact with the anion exchange membrane, a part exposed in the electrolytic chamber, and a part of the side in contact with the flange of the electrolytic cell frame are covered with a fluorine resin sheet, and the electrolytic cell frame of the gasket the fluorine-based resin sheet on the side in contact with the flange surface, 0.1 thickness
An alkaline chloride aqueous solution electrolysis tank characterized by being lined with rubber of 1 mm to 1 mm .