JPS59200777A - Method for electrolyzing salt - Google Patents

Abstract

PURPOSE:To manufacture sodium hydroxide contg. little sodium chloride with high current efficiency by using an ion exchange membrane formed by introducing carboxylic acid into a film of an alternate multicomponent copolymer consisting of tetrafluoroethylene, alpha,beta,beta-trifluoro-acrylate and alpha-olefin. CONSTITUTION:An alternate multicomponent copolymer consisting of CF2=CF2, one or more kinds of alpha,beta,beta-trifluoroacylate represented by formula I (where n is >=1) and one or more kinds of alpha-olefins represented by formula II (where each of l and m is an integer of 0-11) is prepd. The copolymer is molded into a transparent film by hot pressing or other method, and carboxylic acid groups are introduced into the film to form an ion exchange membrane. This membrane has low electric resistance and high cation permeability as well as high chemical stability at high temp., superior mechanical strength and durability. An electrolytic cell is divided into cathode and anode chambers with the membrane, and brine is fed to the anode chamber and electrolyzed. Sodium hydroxide contg. little sodium chloride can be manufactured with high current efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for electrolyzing salts. To be more specific,
The present invention is a fluorinated monomer consisting of tetrafluoroethylene (hereinafter sometimes abbreviated as "TFE"), α, β, β-trifluoroacrylate (hereinafter sometimes abbreviated as @TFA), and α-olefin. The present invention relates to an electrolytic method characterized in that an ion exchange membrane formed by introducing a carboxylic acid group into an alternating multi-component copolymer of and α-olefin is used as a diaphragm.

Explanation of the prior art 1 In the past, the production of caustic soda and chlorine through salt electrolysis was mainly carried out using the mercury method and the asbestos diaphragm method, but by 1976, approximately 60% of the mercury method had been converted to the diaphragm method. .

However, the quality of the caustic soda produced by the diaphragm method is poor and the cost is high, so the ion exchange membrane method, which has appeared as a new technology, is attracting attention, and the transition to the ion exchange membrane method is currently progressing gradually.

The ion exchange membrane used for salt electrolysis has low electrical resistance and contains ions. 'It must satisfy many conditions, such as having a large selective diaphragm property, high chemical stability such as alkali resistance and rigid chlorine resistance even at high temperatures, and excellent mechanical strength and durability. (No. Hydrocarbon-based membranes that have been used in the past cannot be sold in such situations, and recently fluorocarbon-based membranes have been used as practical membranes.Fluorocarbon A typical example of such membranes is the perfluorosulfonic acid membrane (trade name "Nafion'), which is a fluorine-containing polymer with sulfonic acid groups developed by DuPont in the 1940s.
Or there is a modified membrane thereof. However, since the sulfonic acid group has extremely low hydrophilicity, hydroxide ions tend to move back through the IF from the cathode chamber to the anode chamber, resulting in a low current efficiency. In contrast, recently, various fluorine-containing ion exchange membranes have been developed, such as ion exchange membranes made of fluorine-based polymers having 4QI trout as carboxyl groups. Both membranes are copolymers of tetrafluoroethylene and perfluorovinyl ether, which removes functional groups, and do not contain hydrogen atoms or molecules within the molecule except for functional groups, so they are thermally and chemically stable. It is stable when pressed. Therefore, perfluorocarbon membranes have been used as practical diaphragms for salt electrolysis. However, these exchange membranes have practical disadvantages in that the synthesis of the raw material 7mer is complicated and the membranes are expensive.

An object of the present invention is to provide an ion exchange membrane for salt electrolysis that has low electrical resistance, high cation permselectivity, high chemical stability even at high temperatures, and excellent mechanical strength and durability. .

The present invention relates to tetrafluoroethylene, general formula CF=CF
COCH (where R is an integer from 1 to H) 2 2
One or more types of α, β, represented by n 2yz+1
An alternating multi-component copolymer of a fluorine-containing monomer and an α-olefin consisting of β-trifluoroacrylate and one or more α-olefins represented by the general formula (where ) and the door are independent integers from O to 11. Ion exchange capacity with carboxylic acid group introduced is 05 to 3 m eq/
g-Regarding a salt electrolysis method characterized by using a dry membrane ion exchange membrane as a diaphragm.

Since the present invention relates to an ion exchange membrane used as a diaphragm for salt electrolysis, a method for manufacturing this ion exchange membrane ($77) will be described below, and its physical properties will be explained.

Ion exchange I+ used as a diaphragm for salt electrolysis in the present invention!
', represents tetrafluoroethylene, general formula % formula % 2 □U2yL+1 (wherein L is an integer of 1 or more) and α, β, β-trifluoroacrylate of one rod or more and the general formula (where m and ! is an independent integer from 0 to 11), an alternating multi-component polymer of a fluorine-containing monomer and an α-olefin consisting of an α-olefin of 1 or higher is hydrolyzed to form TFA with the J4I-position. Produced by converting an ester group to a carboxylic acid group.

The fluorine-containing multi-component copolymer used as the diaphragm in the present invention has a wide range of monomer compositions, including fluorine-containing monomers (TFE),
It is an alternating multi-component copolymer in which an alternating bond structure is formed between TFA) and α-olefin, and the ester groups in the copolymer can be changed by changing the composition ratio of TFE and TFA in the monomer mixture during polymerization. The concentration can be easily controlled, and the properties and moldability can be freely controlled by changing the type of α-olefin or the composition ratio of multiple α-olefins.

Specifically, TFA, which is a raw material for manufacturing the ion exchange membrane used as a diaphragm in the present invention, includes α and β.

Examples include β-ethyl trifluoroacrylate, α, β, β-butyl trifluoroacrylate, and the like. -Pentene, 1-hexene, 1-
Heptene, 1-octyne, 1-nonene, 1-decene, 1
- Undecene, isobutylene, 2-methyl-1-butene, 2-methyl-1- is exemplified by furan, 2-methyl-1-hexene, 2-methyl-1-heptene, 2-methyl-1-octene, etc. .

In producing the ion exchange membrane used as a diaphragm in the present invention, the above-mentioned alternating multicomponent copolymer can be easily hydrolyzed by known or well-known means. That is,
KO the ester group (-GoOCH group) in the raw material copolymer
Reacting with a basic aqueous solution such as H,N(ZOH) produces a compound that converts the raw copolymer into a salt of carboxylic acid, and then reacting with a strong inorganic acid such as HGl to form a carboxylic acid salt. It can also be converted into a pot.Also, in order to promote contact between the basic aqueous solution and the raw material copolymer, an organic solvent that is water-soluble and has an affinity for the raw material copolymer, such as methanol, acetone, or tetrahydrofuran, is added. It's also good to do.

According to the method for producing an ion exchange membrane described above, α-olefin is 50 mol%, TEA is 0 to 50 mol%, and TFE is
A copolymer containing 50 to 0 mol% of 9- An ion exchange membrane with carboxylic acid groups of the dry membrane is produced.

The membrane used in the present invention contains 60 moles of α-olefin, TI
/%, it is characterized by excellent heat resistance and oxidation resistance, and this excellent property is due to the alternating bond structure of the fluorine-containing monomer and α-olefin. , TFE-ethylene alternating copolymers or TFE-propylene alternating copolymers exhibit excellent heat resistance and chemical resistance.

The ion exchange membrane used in the present invention allows ions to pass through easily and with high selectivity in a neutral and alkaline environment due to the concentration gradient and similar voltage gradient.

The ion exchange membrane used in the present invention has an exchange capacity of 0.1 to 6 rneq19-dry membrane as a carboxylic acid group, preferably 0.5 to 9 m eq/9-exchange capacity of dry membrane. Motsu. Ion exchange capacity is 0.5 meq/
g- If it is smaller than the dry film, the electrical resistance will be high. On the other hand, the ion exchange capacity is! If 1IrlLeP/g is larger than the dry membrane, the mechanical strength of the membrane is low, and when used for electrolysis of salt water, the swelling property of 1IrlLeP/g is too thick, resulting in a large amount of salt being mixed into the cathode. The quality of the product produced is reduced. In addition, the electrical resistance of Iψ (ion exchange) is due to the functional factors in the membrane,
(By changing the concentration, it can be set freely in the range of 10 to 7000 Ω・min (25 Mi amount%,
(measured in aqueous caustic soda solution at a temperature of 25°C).

The present inventors used a conventional perfluorocarbon sulfonic acid membrane as the ion exchange membrane described above to perform gas decomposition of a saline solution. The results are shown in Table-1.

Table-1 Cabinet Pickles (1) Caustic soda temperature: 25% by weight.

(2) Salt] There is a large concentration of salt in raw soda.

From these results, the ion exchange membrane used in the present invention has higher current efficiency than conventional perfluorosulfonic acid membranes, lowers the concentration of salt mixed into the produced powder, and is an excellent ion exchange membrane for salt electrolysis. It can be seen that it can be used as

In the present invention, if high dimensional stability and mechanical strength are required for the ion exchange membrane, nets or cloths made of polyethylene, Akron, Teflon, etc. can be used. It is also possible to use a heterogeneous model by gluing together membranes with different numbers or membranes with different functional groups. The thickness of the membrane is generally 0.01 to 1 mm, or 0.05 depending on the specific conductivity, current efficiency, mechanical strength, etc. of the membrane.
It is selected for whitewashing in the range of ~0.5 rnm.

The salt water electrolyzer used in the present invention may have a structure in which the electrode and the diaphragm are in close contact with each other, or may be in a structure in which they are separated from each other.

Further, the electrode material is selected from those having high catalytic ability for electrolytic reactions and high stability for products. In other words, the cathode is usually made of iron plated with nickel or a nickel compound, and the anode is preferably made of iron plated with nickel or a nickel compound.
+f! Preferred is a titanium mesh or rod plate coated with a noble metal oxide such as ruthenium tetrachloride.

The temperature at which the salt solution is carried out according to the present invention can range from room temperature to below the boiling point of the solution in the bipolar chamber, but is preferably in the range of 70-90'C.

Below, the configuration and effects of the present invention will be explained in detail through the ``-AI'' section.

Example After purging a stainless steel 1 autoclave containing 5 liters of lees with nitrogen, Freon R-113 and 50 ml of methyl trifluoroacrylate were added, followed by 266 g of tetrafluoroethylene and 78.19 ml of ethylene and thoroughly stirred. This is applied to cobalt-60 gamma rays at a dose rate of 8
．． , irradiated with OX i 03rrtd/hr for 6 hours and 1
00.8 g of a white powdery copolymer was obtained. This co-M(
The combined product was molded into a hot breath mold at 00° C. to produce a transparent film of about 300 μm. This specimen was soaked in a 20% NaOH methanol water bath for 7 nights and hydrolyzed at reflux temperature for one week. The functional group concentration of the ion exchange membrane thus obtained was 1.18 meqη-dry membrane.

Four electrolytic cells were assembled in which a cathode chamber and an anode chamber were separated by an ion exchange membrane with an effective membrane area of 16 cnL. Platinum-plated titanium mesh as anode, perforated SUS as cathode
I used a board.

25% NcL with calcium concentration adjusted to 1 ppm or less
Aqueous solutions C and d are poured into each electrolytic cell from each cathode chamber entrance.
A salt electrolysis test was carried out by supplying pure water to the anode chamber at a rate of 10.7 ml/hr while supplying pure water at a rate of 39 rnl/Ay. The results obtained from this test are shown below.
Shown in 2.

(1) Concentration of common salt mixed in caustic soda Example 2 The same method as in Example 1 was used to reduce the concentration of salt to 1.
An ion exchange membrane of 67 meq/9-dry membrane was manufactured. This ion exchange membrane was attached to the same six electrolytic cells as used in Example 1.

A 25% NaO,L aqueous solution with a calcium concentration of 1 ppm or less was poured 169 m from each negative rod chamber of each electrolytic cell.
While supplying water at a rate of A/hr, pure water was supplied to the positive chamber at a rate of 28.7 ml/hr, and a salt electrolysis test was conducted for 11 times. Table 6 shows the results obtained from this test.
Shown below.

EXAMPLE An ion exchanger 11U manufactured in the same manner as in Example 1 was attached to the same electrolytic cell as used in Example 1.

Add 92.8 ml of 25% KCl aqueous solution to a dark room.
Meanwhile, pure water was supplied to the anode chamber at a rate of 7.2 hr.
The current was supplied at a rate of rnl/hr and at a current density of 20 m/dm. The temperatures of the anode chamber and the cathode chamber during steady state were 45°C and 47°C, respectively. As a result, 61
．． 9% KOH was obtained with a current efficiency of 81.0%. At this time, the amount of KCl mixed into KOH (!:: is 10 pp
m or less.

(4 other people)

Claims (1)

[Claims] 1. Tetrafluoroethylene, general formula CF = CFC
OCH (where ru is an integer greater than or equal to 1) 2 2 n
one or more α, β, β-) IJ fluoroacrylate and one or more α-olefins represented by the general formula (where ! and m are independent integers from 0 to 11); A method for electrolyzing salts, which comprises dividing an electrolytic cell into an anode chamber and a cathode chamber using an ion exchange membrane made by introducing a carboxylic acid group into an alternating multi-component copolymer consisting of the above, and carrying out electrolysis while supplying salt water to the anode chamber. 2. The exchange capacity of the carboxylic acid group of the ion exchange membrane is 0.5
〜lorneq/(9-Claim 1 which is a dry membrane
The method described in section.