JPS62121733A - Detection of pinhole or the like in fluororesin cation exchange membrane for electrolysis of alkali chloride - Google Patents

Abstract

PURPOSE:To detect simply a pinhole or the like in a fluororesin cation exchange membrane for use in electrolysis of an alkali chloride, by applying an anionic surfactant solution to the ion exchange membrane, adjusting the pressure on one side of the membrane to be larger than that on the other side of the membrane and detecting the formation of bubbles. CONSTITUTION:An anionic surfactant solution is applied by, for example, coating or spraying, to a fluororesin cation exchange membrane for use in electrolysis of an alkali chloride (e.g., a cationic membrane comprising a perfluorocarbon polymer). Suitable examples of the anionic surfactants include sodium oleate, ammonium perfluorooctanoate and ammonium perfluorooctanesulfonate. Its concentration is suitably 0.001-5wt%. The pressure on one side of the cation exchange membrane is adjusted to be larger than that on the other side, and pinholes or the like are detected by bubbles resulting from a gas passing through the pinholes or the like present in the membrane.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for detecting pinholes, etc. in a fluorine-containing resin cation exchange membrane used to produce alkali hydroxide by electrolyzing alkali chloride. It is.

[Prior art] When pinholes, cracks, etc. (hereinafter referred to as pinholes, etc.) occur in the fluorine-containing resin cation exchange membrane used for electrolysis of aqueous alkali chloride solutions, current efficiency decreases and caustic alkaline earth metal decreases. This results in severe performance deterioration. Various methods have been proposed for repairing scratches such as pinholes (for example, Japanese Patent Laid-Open Nos. 58-70863 and 58-370).
(See Publication No. 29) No effective method has been known to detect pinholes (especially when pinholes occur in an ion exchange membrane having a bag-like or cylindrical shape) without leaking.

The present inventor applied a surfactant solution to the surface of an ion-exchange membrane, made the pressure on one side of the membrane higher than the pressure on the other side, and caused the gas to pass through pinholes etc. present in the membrane. It has been found that pinholes and the like can be completely and easily detected by utilizing the generated air bubbles, but this method has the following drawbacks.

In other words, depending on the type of fluorine-containing resin cation exchange membrane or the type of surfactant, the surfactant may be adsorbed on the C ion exchange membrane, and the ion exchange membrane may be used to electrolyze alkali chloride. Voltage increases by L, current efficiency decreases, etc.
Performance may deteriorate, and in order to restore performance, the ion exchange membrane may need to be washed with water for a long time or special treatment may be required.

[Problems to be Solved by the Invention] The present invention aims to eliminate the above-mentioned drawbacks of the prior art.

Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes applying an anionic surfactant solution to a fluorine-containing resin cation exchange membrane for alkali chloride electrolysis, The method is characterized in that the air pressure on one side of the membrane is made higher than the air pressure on the other side, and pinholes, etc., are detected by bubbles generated due to gas passing through the pinholes, etc., present in the membrane. This provides a method for detecting pinholes, etc.

Next, the present invention will be explained in more detail.

In the present invention, the anionic surfactant has the general formula R
-X, (here R: preferably an alkyl group of 05 or more, more preferably C1 or more, or if -y o O7/l
/ * /l/ group, X: -(00M, -303M
.

-0S03 M, -0P03 M2, or -PO
A compound represented by 3M2 group, M: alkali metal or NH4) can be preferably used.

As R, an alkyl group having 5 or more carbon atoms and a fluoroalkyl group are suitable, and preferably oleate, perfluorooctanoate, perfluorooctasulfonate, sodium lauryl sulfate, dodecylbenzenesulfonic acid 1 ′! ! etc. can be used particularly preferably.

The concentration of the surfactant solution is preferably 0.001~
5fff amount%, especially 0. Approximately 1 to 1% by weight of O is suitable. If the 7M degree is too low, the foaming properties will not be sufficient, and there is no practical benefit even if the concentration is increased too much.On the contrary, the solution viscosity will be high and the handling properties will be poor.

The fluorine-containing resin cation exchange membrane used in the present invention is not particularly limited, but it is particularly effective in the case of a cathine exchange membrane made of perfluorocarbon polymer and having ion exchange groups such as carboxylic acid, sulfonic acid, phosphoric acid, etc. It is.

These membranes are used in the form of films or molded bags. Particularly preferably, an ion exchange membrane made of a perfluorocarbon polymer having carboxylic acid groups is used,
In particular, in an ion exchange membrane electrolysis system in which asbestos in the diaphragm method is replaced with an ion exchange membrane, the membrane is processed into a bag shape.

An anionic surfactant solution (hereinafter simply referred to as "solution") is applied to the surface of the fluororesin cation exchange membrane by coating, spraying, or the like. Alternatively, the "solution" can also be applied by immersing the ion exchange membrane in the "solution".

Next, the air pressure on one surface of the ion exchange membrane is made greater than the air pressure on the other surface.

Specifically, when the ion exchange membrane is bag-shaped, air is blown into the bag to increase the pressure to atmospheric pressure. Alternatively, the ion exchange membrane is airtightly engaged with the top surface of the box with the top open (with the side to which the "solution" has been applied facing upward) to increase the pressure inside the box. The pressure difference is 1-1
000100O, preferably 10 to 1100 mm1 (approximately 10 to 1100 mm1). Due to the bubbles generated due to the gas passing through the pinhole etc., the pinhole can be visually detected without leakage and easily.

[Effect 1 It seems that anionic surfactants are hardly or not adsorbed at all on fluorine-containing resin cation exchange membranes for alkali chloride electrolysis, or even if they are adsorbed, they do not affect the performance of the ion exchange membranes. . This tendency is particularly remarkable in the case of cation exchange membranes made of perfluorocarbon polymers.

[Example] Example I CF2 = CF2 and CF2 = CFO(CF2
Two types of hGOOclb copolymers with ion exchange capacities (AR) of 1.2 meq/g and 1.8 meq/g were made into films with a thickness of 50 JL and 200 JL, respectively.
These two films were laminated to obtain a cation exchange membrane.

After this membrane was hydrolyzed, it was placed in a battery tank with the AR1,2 meq/g side as the cathode side, and salt electrolysis was performed. Since the current efficiency decreased from the initial 96% to 85%, it was dismantled and a pinhole inspection was performed.

The membrane was airtightly assembled in a box-shaped frame, and pressurized gas of 50 Hg was introduced from one side, and 0% of sodium oleate was introduced to the other side.
．． When a 1% aqueous solution was applied, bubbles were generated and pinholes were detected. After repairing this pinhole by covering it with an ion exchange membrane film and bonding it under heat, a pinhole inspection was conducted again in the same manner, but no pinholes were detected. When this membrane was used again for salt electrolysis, the current efficiency was 9.
6% and the sliding voltage is 3. It showed a normal value of Ov.

Comparative Example 1 The same procedure as in Example 1 was carried out except that polyoxyethylene nonylphenyl ether, which is a nonionic surfactant, was used as the surfactant.The membrane performance after pinhole repair was 88% in current efficiency. , the sliding voltage was 3.3■.

Example 2 The same procedure as in Example 1 was performed except that ammonium per-2-fluorooctanoate was used as the surfactant.
After pinhole repair, the membrane part had a current efficiency of 96% and a sliding voltage of 3. It was OV.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the cationic surfactant n-octadecylamine hydrochloride was used as the surfactant. The film performance after pinhole repair was 8 in current efficiency.
The sliding voltage was as low as 0% and as high as 3.5V.

Example 3 The same procedure as in Example 1 was carried out except that ammonium perfluorooctane sulfonate was used as the surfactant. After repairing the pinholes, the membrane source had a current efficiency of 96% and a sliding voltage of 3. It was OV.

[Effects of the Invention] When using the method of the present invention, pinholes and the like can be detected easily and without leakage, and there is no need to wash the ion exchange membrane with water or perform post-treatment after pinhole detection.

Claims (4)

[Claims] (1) Apply an anionic surfactant solution to a fluorine-containing resin cation exchange membrane for alkali chloride electrolysis, make the pressure on one side of the membrane greater than the pressure on the other side, and remove the pins present in the membrane. A method for detecting pinholes, etc., characterized in that the pinholes, etc. are detected by bubbles generated due to gas passing through the holes, etc. (2) The method for detecting pinholes and the like according to claim 1, wherein the anionic surfactant is a compound represented by the general formula R-X. R: C_5 or more alkyl group or fluoroalkyl group X: -COOM, -SO_3M, -OSO_3M, -P
O_3M_2, or OPO_3M_2 M: Alkali metal or NH_4 (3) The concentration of anionic surfactant solution is 0.001~
The method for detecting pinholes, etc. according to claim 2 or 3, characterized in that the amount is 5% by weight. (4) The method for detecting pinholes and the like according to claims 1 to 3, wherein the fluorine-containing resin cation exchange membrane is a cation membrane made of perfluorocarbon polymer.