JPH01290A - Electrolysis method of aqueous alkali chloride solution - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for electrolyzing an aqueous alkali chloride solution using a cation exchange membrane preferably made of a perfluorocarbon polymer, characterized in that the electrolysis is carried out under a magnetic field. It is something.

[Prior Art] The ion exchange membrane method uses a perfluorocarbon polymer cation exchange membrane (hereinafter referred to as perfluoro cation exchange membrane) as a diaphragm as a method for producing caustic soda and chlorine by electrolyzing sodium chloride.

Compared to the conventional mercury method and asbestos diaphragm method, this method is more advantageous in terms of pollution prevention and energy saving, and has attracted attention in recent years because it can produce high-quality caustic soda with a low sodium chloride content.

Various improvements have been made to such ion exchange membrane methods in order to increase current efficiency. For example, JP-A-5
Publication No. 0-120492 discloses perfluoro ion exchange membranes made by copolymerizing a carboxylic acid type fluoromonomer and a tetrafluoroethylene monomer, and a membrane made by impregnating and polymerizing a carboxylic acid type monomer into a sulfonic acid type fluororesin membrane. Are listed. These are said to have both high current efficiency due to the carboxylic acid group and high electrical conductivity due to the sulfonic acid group.

Further, JP-A-52-36589 describes a blend membrane of a carboxylic acid type perfluorocarbon polymer and a sulfonic acid type perfluorocarbon polymer, and a laminated membrane of a carboxylic acid type membrane and a sulfonic acid type membrane. Furthermore, the surface of the perfluorocarbon polymer having sulfonic acid groups is subjected to reduction treatment and oxidation treatment to chemically change the sulfonic acid groups to carboxylic acid groups, thereby forming a carboxylic acid type thin film layer on the surface of the sulfonic acid film ( Unexamined Japanese Patent Publication No. 52-24175. No. 52-2417
6, 52-24177), etc. are known.

However, when electrolyzing an aqueous alkali chloride solution using these perfluorinated cation exchange membranes, a new means is required to obtain even better current efficiency.

[Problems to be Solved by the Invention] The present invention provides an electrolytic method with higher current efficiency by employing a new means that was previously unknown when electrolyzing an aqueous alkali chloride solution using an ion exchange membrane. The purpose is to provide new services.

[Means for Solving the Problems] Thus, the present invention supplies an aqueous alkali chloride solution to an anode chamber partitioned by a cation exchange membrane, supplies water or a diluted aqueous alkali hydroxide solution to a cathode chamber, and applies a magnetic field. The present invention provides a method for electrolyzing an aqueous alkali chloride solution, which is characterized in that electricity is passed between both electrodes to produce alkali hydroxide in a cathode chamber. .

According to the present invention, in the case of a cation exchange membrane that already has a high current efficiency, an aqueous alkali chloride solution can be electrolyzed with a high current efficiency that has never been obtained, and any cation exchange membrane can be used. Current efficiency can also be improved when electrolyzing an aqueous alkali chloride solution using a membrane.

Further, according to the present invention, the electrolysis efficiency can be increased even in electrolysis using a cation exchange membrane whose current efficiency has decreased due to long-term use or electrolysis conditions, such as temperature changes.

In the method of the present invention, electricity is applied to the anolyte consisting of an aqueous alkali chloride solution present in the anode chamber separated by a cation exchange membrane and the catholyte consisting of an aqueous alkali hydroxide solution present in the cathode chamber, to electrolyze the aqueous alkali chloride solution. When performed, a magnetic field is applied. The magnetic field may be a permanent magnet or an electromagnet.

The applied magnetic field is preferably 45~
The angle is preferably 135°, especially 75 to 105°,
The magnitude of the magnetic field is preferably 80 to 500 Gauss, particularly 100 to 300 Gauss per current density IA/dm.The magnetic field is applied uniformly to both the anolyte, cation exchange membrane and catholyte. It is not necessary to apply it, and according to the findings of the present inventors, it has been found that it is preferable to apply it at a high density to the cation exchange membrane.

Methods for applying a magnetic field include placing the electrolytic cell inside a magnet that generates a magnetic field, placing a magnet of an appropriate shape inside or on the frame, clamping frame, or even the ion exchange membrane that constitutes the electrolytic cell. Appropriate means such as burying are adopted.

The cation exchange membranes used in the present invention are preferably formed from perfluoropolymers, which consist of copolymers of at least two monomers, preferably:
Consists of a copolymer having polymerized units (a) and (b).

(A") (CF, -CXX') (B) (CF, -CX Arrow -A Here, x, x' are -F, -C1, -H or -CF3
te, A is -soaM, or -COOM (M represents hydrogen, an alkali heavy metal or a group converted into these groups by hydrolysis), Y is selected from the following, where z, z ' represents -F or a perfluoroalkyl group having 1 to 10 carbon atoms, and x and y represent integers of 1 to 10.

-(CF, )-,, -0-(CF, arrow 3. (0-
CF, -CF arrow,.

ZZ'' The composition ratio (molar ratio) of (a) and (b) forming the above polymer is such that the fluorine-containing polymer preferably has an ion exchange capacity of 0.5 to 2.0 meq/g. Dry resin is selected, especially between 0.8 and 1.9 meq/g dry resin.

The above-mentioned fluorine-containing polymer is preferably a perfluoropolymer, and preferable examples thereof include CF, CF2 and CF2CFOCjaCF (CFs) OCF*CF
-Copolymer with 3O□F, CF, ・CF, and CF, ・C
FO(CF,) x~, copolymer with SO□, CF*
=CF- and CF, CFOfcF, ) , -, C00C
11゜Which copolymer, CF2=CF2 and CF 1c)
QC) zcF (C) alo (CF,), ~,
A copolymer with CODCII, 1 is exemplified.

The cation exchange membrane used in the present invention has a total thickness of 100 to 400 microns, preferably 100 to 300 microns. If necessary, it can be reinforced by the presence of a cloth, a woven fabric such as a net, a nonwoven fabric, a metal mesh, a porous body, etc., preferably made of polytetrafluoroethylene. Also, JP-A-5
No. 3-149881, No. 54-] No. 283, No. 54-
Copolymerization of a small amount of polytetrafluoroethylene fibrillated fibers described in JP-A-56-79110, etc. It may be reinforced by blending fibrillated fibers of polytetrafluoroethylene modified by polytetrafluoroethylene, or reinforcing by blending a low molecular weight substance thereof. Furthermore, the surface of the ion exchange membrane of the present invention can be roughened or a porous thin layer made of metal oxide particles can be formed on the surface.

When electrolyzing an aqueous alkali chloride solution using the cation exchange membrane of the present invention, the electrolytic cell may be of a monopolar type or a bipolar type.

When disposing electrodes, the electrodes may be disposed in contact with the cation exchange membrane of the present invention, or may be disposed at appropriate intervals. Rather than firmly pressing the electrode against the cation exchange membrane, the electrode should be pressed onto the surface of the cation exchange membrane, e.g.
The material constituting the electrolytic cell is preferably one that is resistant to aqueous alkali chloride and chlorine in the case of the anode chamber, for example in the case of electrolysis of an aqueous alkali chloride solution. Certain materials are used, such as valve metal, titanium, and in the case of the cathode chamber, iron, stainless steel or nickel, which are resistant to alkali hydroxides and hydrogen.

Known conditions can be employed as process conditions for electrolyzing an aqueous alkali chloride solution using the cation exchange membrane of the present invention. For example, preferably 100 to 350 for the anode chamber.
g/I aqueous alkali chloride solution, water or diluted alkali hydroxide is supplied to the cathode chamber, preferably 2 g/I.
In order to produce an aqueous alkali hydroxide solution of 0 to 45% by weight, particularly 25 to 40% by weight, preferably 80°C to 120°C,
Electrolysis is carried out at a current density of 10 to 100A/dm. In such a case, heavy metal ions such as calcium and magnesium in the aqueous alkali chloride solution cause deterioration of the ion exchange membrane, so it is preferable to minimize them as much as possible. Further, an acid such as hydrochloric acid can be added to the aqueous alkali chloride solution in order to prevent the generation of oxygen at the anode as much as possible.

[Function] In the electrolysis of the aqueous alkali chloride solution of the present invention, the effect of the magnetic field that improves the current efficiency is not necessarily clear, but it is thought to be approximately as follows. The selective permeation of Na'' ions through perfluoro ion exchange membranes is controlled by the size and water content of channels connecting ion clusters formed in the membrane.
Those that move while repeatedly bonding and dissociating with exchange groups,
It is thought that some substances move in the free water in the membrane, regardless of the exchange groups in the membrane ("Soda and Chlorine" 19B).
6.10. p413).

Factors that reduce the current efficiency include so-called ion pair formation, in which Na'' ions are bound to exchange groups. When a magnetic field is applied to such a membrane, a force other than the electric field is applied to the Na'' ions, which has the effect of reducing the binding caused by the exchange group, making it easier for Na+ ions to permeate, thereby increasing the current efficiency. is expected to increase.

[Example] Example I Tetrafluoroethylene and cF! -, cFo (CF,
), C00CIL was polymerized and the ion exchange capacity was 1.
A copolymer having a concentration of 30 meq/g was obtained. This copolymer was extrusion molded to obtain a film with a thickness of 200 μm. The membrane is 2
Hydrolysis was carried out with a 5% caustic soda aqueous solution at 70° C. for 16 hours to obtain a sodium type ion exchange membrane.

The thus obtained film was used as an anode in which a punched titanium metal was coated with a solid solution of ruthenium oxide, iridium oxide, and titanium oxide.
Set in an electrolytic cell using a cathode electrodeposited with aluminum (0%, aluminum 45%) with a spacing of 2 mm, the sodium chloride concentration in the anode chamber was adjusted while supplying a 300 g/l sodium chloride aqueous solution to the anode chamber and water to the cathode chamber. While maintaining the concentration of caustic soda at 200 g/I and the concentration of caustic soda in the cathode chamber at 35% by weight, at 90°C and 30%
Electrolysis was carried out under the conditions of "A/di". After 5 days of electrolysis, the current efficiency was 95%. After that, when a magnetic field of 8000 Gauss was applied perpendicular to the current direction, the current efficiency was 0.5%. The rate rose to 95.5%.

Example 2 Using the same membrane and electrolytic cell as in Example 1, at 60°C and 25A/
Electrolysis was carried out under the conditions of ``dm''. After 5 days of electrolysis, the current efficiency was 94%. After that, when a magnetic field of 10,000 Gauss was applied perpendicular to the current direction, the current efficiency was 0.8%. The current efficiency increased to 94.8%.When the magnetic field was further increased to 12,000 Gauss, the current efficiency further decreased to 0.
It rose 5% to 95.3%.

Example 3 Tetrafluoroethylene and CF, CFO (CFi)
acOOC1+ is polymerized, and the ion exchange capacity is 1.2.
A copolymer with a concentration of 0 meq/g was obtained. This copolymer was extrusion molded to obtain a film with a thickness of about 100 μm. The membrane is 2
Hydrolysis was carried out with a 5% by weight aqueous sodium hydroxide solution at 70° C. for 16 hours to obtain a sodium type ion exchange membrane.

The membrane thus obtained was used in the same electrode, electrolytic cell, and
Electrolysis was performed using an electrolytic solution and an electromagnet. 90℃, 30
When electrolysis was carried out for 5 days under the condition of "A/dm", the current efficiency was 96%.Furthermore, the conditions were changed to 60℃ and 30A.
/dm'' for 3 days, the current efficiency was 9.
It became 1%. When electrolysis was carried out again at 90°C and 30 A/dm'' for 3 days, the current efficiency was 93%.After that, when a magnetic field of 8000 Gauss was applied perpendicular to the current direction, the current efficiency increased by 1.5% to 94. The current efficiency was 92.5% when the temperature was lowered to 60°C and electrolysis was carried out for 3 days while applying a magnetic field in the same direction and strength.
Met.

[Effects of the Invention] By electrolyzing the aqueous alkali chloride solution of the perfluoro ion exchange membrane under a magnetic field, the current response rate is improved, which is effective in reducing the cost of electrolysis. Furthermore, conventional electrolysis at relatively low temperatures resulted in a decrease in current efficiency, and due to the electrolytic current, only suppressed electrolysis could be performed, but by adopting the method of the invention, it becomes possible to use electric power efficiently.

In addition, it has the effect that even if the performance has deteriorated due to long-term use, some functions can be recovered by nature.

Claims (5)

[Claims] (1) Supply an aqueous alkali chloride solution to the anode chamber divided by a cation exchange membrane, supply water or a dilute aqueous alkali hydroxide solution to the anode chamber, apply electricity between both electrodes under the application of a magnetic field, and add water to the cathode chamber. A method for electrolyzing an aqueous alkali chloride solution, characterized by producing an alkali oxide. (2) The strength of the magnetic field is 8 per current density 1A/dm^2.
The method according to claim (1) or (2), which is 0 Gauss or more. (3) The method according to claim (1) or (2), wherein the magnetic field is applied at an angle of 45° to 135° with respect to the current direction. (4) The concentration of aqueous alkali chloride solution is 100 to 300 g/
l, and the concentration of the aqueous alkali hydroxide solution is 20 to 45
Claims (1), (2) or (3) which are weight %
the method of. (5) Claims (1), (2), (3) or (4) in which the cation exchange membrane is made of a perfluorocarbon polymer and has at least a carboxylic acid group as an ion exchange membrane.
)the method of.