JPS62133095A - Electrolytic cell for aqueous alkali chloride solution - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a cation exchange membrane in an electrolytic cell divided into anode and cathode chambers with the membrane by coating the cathode side surface of the membrane kept in noncontact with an electrolytic soln. at the upper part of the cell with a film impermeable to an aqueous alkali hydroxide soln. CONSTITUTION:An electrolytic cell for an aqueous alkali chloride soln. is divided into anode and cathode chambers with a cation exchange membrane. The membrane comes in contact with alkali hydroxide on the cathode side. The cathode side surface of the membrane kept in noncontact with an electrolytic soln. at the upper part of the cell is coated with a film impermeable to an aqueous alkali hydroxide soln. The film has <=10<6>eq/cm<2>.hr.DELTAN diffusion coefft. to the aqueous alkali hydroxide soln. and is made of the same polymer as the cation exchange membrane containing fluorine.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrolytic cell for an aqueous alkali chloride solution.

[Conventional technology] In recent years, cation exchange II has been used as a barrier.

Diaphragm electrolysis is known in which highly pure -IY alkali and chlorine are produced by electrolyzing an aqueous alkali chloride solution. For this reason, as an electrolytic cell, for example, a so-called filter press type electrolytic cell has been proposed, in which an anode chamber frame and a cathode chamber frame are fastened together to form an anode chamber and a cathode chamber through a cation exchange membrane. There is.

When electrolysis of an aqueous alkali chloride solution is carried out in an electrolytic cell having such a cation exchange membrane as a diaphragm, according to the findings of the present inventors, the cation exchange membrane used is The part facing the electrolyte that does not come in contact with the electrolyte has a large difference in deterioration of mechanical strength, such as tensile strength and tensile elongation, compared to the majority of the electrolyte surface that is in contact with the electrolyte. We have discovered a phenomenon in which the mechanical strength of the portion of the cation exchange membrane that does not come into contact with the electrolyte is greatly degraded, reducing the life span of the cation exchange membrane as a whole.

Conventionally, in order to prevent deterioration of the portion of the cation exchange membrane that does not come into contact with the electrolyte, it is known that, for example, the anode side or both sides of the cation exchange membrane are coated with a gas-impermeable substance such as chlorine gas. Iruga (Japanese Patent Application Laid-Open No. 52-144399)
According to the research conducted by the present inventor, these methods are insufficiently effective, and when the surface of the cation exchange membrane is covered with a dense gas-impermeable material, rU The vague resistance had no choice but to rise to L.

[Problems to be Solved by the Invention] The present invention has discovered a new means that can effectively prevent deterioration in a cation exchange bath that does not come into contact with the electrolytic solution in the upper part of an electrolytic cell, and has developed a novel method using such a means. Na114
The second object of the present invention is to provide an electrolytic cell for an aqueous alkali solution.

[Step F for solving the problems] The present invention provides an electrolytic cell for an aqueous alkali chloride solution in which an anode chamber and a cathode chamber are formed through a cation exchange membrane. An electrolytic cell for an aqueous alkali chloride solution, characterized in that the cathode side surface of the ion exchange membrane is coated with a film impermeable to the aqueous alkali hydroxide solution.

In the present invention, the mechanism by which deterioration of the cation exchanger that is not in contact with the electrolyte is prevented is not necessarily clear, partly because the cause of deterioration is not clear.
It is estimated as follows. In other words, the space above the electrolytic cell that is not filled with electrolyte is filled with chlorine gas generated at the anode, and some of it penetrates into the cation exchanger +1Q that is in contact with it. .

- On the other hand, the first stage of cation exchange in the electrolytic cell is in contact with the 1°Y alkali on the cathode side, and the 1D alkali also penetrates into the ion exchange membrane, resulting in - The Y alkali is 012 + 2M in the membrane with chlorine in L.
OH-” MCI+ MC1O+ H2O(M
- Alkali metal) reaction produces alkali chloride, which has low solubility, and hypochlorous acid, which has strong oxidizing properties, and alkali chloride precipitates as crystals. Therefore, the cation exchange membrane shows a swelling phenomenon and the primary hypochlorite I basin changes from MCl0→MC1+%02.
It is thought that the structure of the ion exchange membrane is destroyed by decomposition due to the reaction and the generation of oxygen in the cation exchange membrane, resulting in the deterioration of the mechanical strength as described above.

On the other hand, according to the present invention, by coating the cathode side surface of the cation exchange IN that does not come into contact with the electrolyte of the cation exchange membrane with a film impermeable to an aqueous alkali hydroxide solution,
Prevents penetration of PA/Y alkali into ion exchange 1p2
, the reaction L is inhibited, precipitation of ζ↓ alkali does not occur within the film, and as a result, deterioration of mechanical strength is prevented. It should be noted that the speculation described in (1) is for explaining the deterioration mechanism, and is not intended to limit the present invention.

The cation exchange membrane used in the present invention has upper air chemical performance [2, lf'f or ion exchange groups such as sulfonic acid groups, carbonic acid groups, acid amides, esters, alcohol halides, etc.] These derivatives), (consisting of 11
From the viewpoint of corrosion resistance, it is preferably formed from a fluorine-containing polymer. As such a fluorine-containing polymer, it is preferable to use a fluorine-containing conjugate having the following general formula.

(() (-Oh-CXX”) , (0) 4
CF2-OX') where X is fluorine, chlorine, water or -CF3, and x' is Ch(CF2)P
p is 1 to 5, and Y is selected from the following.

-(CF7)Q-A, -0-(CF,)-0A, (
0-OF2-7Fn. A9Q, ttr, n are all 1
~10, and Z and Rr are -F or) the father element fit-
10 perfluoroalkyl groups, A is -5(hH, -COO)I or -502F,
-(, N, -COF, -COOR, and other functional groups that can be converted into these groups by hydrolysis. The ratio of L (a) and (b) in the copolymer is the ion exchange 11I2 ion It is related to the exchange capacity, and its preferable range varies depending on the type of exchange group in the ion exchange membrane, but in the case of sulfonic acid type, the ion exchange capacity (milli equivalent/gram dry resin) is preferably 0.6 to 1. .2, especially 0.7 to 1.2
is preferable, and in the case of a carboxylic acid type, the ion exchange capacity is preferably 0.7 to 2.0. Especially 0.8 to 1.
It is preferable to set it to 8.

A film impermeable to an alkali hydroxide aqueous solution for covering the L leg side of the cation exchange membrane that does not come into contact with the electrolyte is prepared using a diffusion coefficient of an alkali hydroxide aqueous solution (3.5N salt water as an anolyte, a catholyte of As 35 tonxing%N a Ot
(in an electrolytic cell filled with

(measured at 90℃) or 10 'eq/c+s'・hr・ΔN
NF2 preferably 5. OX 10'eq/cm2・h
A value of r-ΔN or less is suitable. ! -The above-mentioned reaction proceeds within the range (in case of -), and the strength of the cation exchange membrane decreases in the long run. The material for the film that covers the cathode side surface of the cation exchange membrane is 1.
Those with alkali resistance are preferred; examples thereof include tetrafluoroethylene polymer, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-perfluoroethylene. Examples include propyl vinyl ether copolymers. In particular, the same type of polymer as that forming the cation exchanger 1 is preferable because it has good bonding properties with the membrane body.

When the bonding property between the cation exchange membrane and the film described in L is good, the four stages of providing the fluorine-containing bead combined film on the cation exchange membrane are 1, for example, 150 to 350°C, (1
It can also be heat fused under the conditions of 5 to 200 kg/cm2, and if the film is the same as the main body of the cation exchange membrane,
It is particularly preferred for the present invention because it has excellent bonding properties with the cation exchange membrane by thermal fusion.

The thickness of the fluorine-containing composite film L provided on the cation exchange membrane is not particularly limited as long as the object of the present invention can be achieved, and for example, the thickness of the ion exchange membrane is 171 to 115, and 20 to 300μ is adopted. . When the film is too thick.

Fluorine-containing polymer films, which are undesirable because they increase film material cost and are difficult to handle, are used for cation exchange, in areas that do not come into contact with the electrolyte, that is, in the normal electrolytic cell. It is preferable to cover as many parts as possible. The part to be coated is not necessarily limited to the part that does not come into contact with the electrolyte, but may also extend partially to the part that comes into contact with the electrolyte, and in the case of a filter press type device, the anode chamber frame and the cathode The tightening of the cation exchange membrane may be partially extended by the chamber frame or the like. Particularly when the film is extended to the L section, the film acts as a backing for the L section, and since the film often has a high electrical resistance, the L section It is also possible to prevent leakage current through the frame.

Any known configuration can be adopted for the parts other than the footrest to configure the electrolytic cell of the present invention. That is, the type of electrolytic cell may be either a filter press type or a finger type, and may be either a polar cell or a bipolar cell. As the anode, a dimensionally stable electrode in which a graphite or titanium base material is coated with a platinum group metal or an oxide of a platinum group metal can be used, and as a cathode, iron or stainless steel can also be used.

Examples of the present invention will be shown below, but it goes without saying that the present invention is not limited to these Examples.

[Effects of the Invention] As described in (2) below, the present invention provides a perfluorocarbon suitable for alkali chloride electrolysis, in which the cathode surface of the cation exchange IIA facing the gas phase is coated with a low-diffusion film. System ion exchange +? This prevents salt precipitation in the membrane in the gas phase of the battery over a long period of time.
As a result, a decrease in the mechanical strength of the membrane can be suppressed, and long-term electrolysis operation becomes possible. Additionally, the effect of slightly reducing the alkali chloride content in the alkali hydroxide was also observed.

[Example] Example 1 CF2 = CF2 and CF2 = CFO (C:
By catalytically polymerizing F2hCOOCH:+ and changing the polymerization pressure and temperature, the ion exchange capacity was 1.40.
Copolymer A with milliequivalents of 7 g dry resin, and 1.25
A copolymer B having a milliequivalent weight of 7 g dry resin was obtained. Copolymer A
was extrusion molded to obtain a film A-1 having a thickness of 250μ. Similarly, copolymer B was extruded to form a 20μ film B-
I got 1.

Next, stack A-1 and B-1 and roll them 2 using a hot roll.
Lamination was carried out at 00°C to obtain composite jlI2. Furthermore, B-1
On the surface of the 16th part of the side, Na0 prepared in the same manner as described above.
)l diffusion coefficient is 4X IQ 'eq/ctalhr-Δ
Ion exchange membrane II10, which is N, 84 mm = + state/g
A film of dried resin (polymer) having a thickness of 50 μm was adhered at 250° C. by hot pressing to obtain a cation exchange membrane having a film impermeable to a 1° Y-type aqueous solution in the northern part.

10 parts of zirconium oxide powder with a particle size of 5 μm, methylcellulose (viscosity of 2% aqueous solution: 1500 centivoise)
A paste was obtained by kneading a mixture containing 0.4 parts of water, 19 parts of water, 2 parts of cyclohexanol, and 1 part of cyclohexanone. The paste was mixed with mesh a200. Using a 75μ thick Tetron screen, a printing plate with a 30μ thick screen mask underneath, and a polyurethane squeegee, screen printing was performed on the A-1 side of the cation exchange II2 created by laminating the above. , I was young.

Furthermore, β silicon carbide particles having an average particle size of 0.3 μm were similarly attached to the other surface of the obtained cation exchange membrane having a porous layer. After that, knitting is done at 40℃ and pressure is 30k.
g/cm2 by pressing the particles and layers on both sides onto the cation exchange membrane surface.

On the anode and cathode sides of the membrane, zirconium particles and silicon carbide particles were added per 1 cm of membrane surface, respectively.
A cation exchange n9 with 0 parts and 0.7+sg$l was prepared. The 1 model was planted in 25 layers with an aqueous soda solution for 7 days.
Hydrolysis was carried out at 0° C. for 50 hours to convert the ion exchange group from 1,000 CH3 to -COONa to obtain a cation exchange membrane having a film impermeable to an aqueous soda solution on one side.

Thus, titanium punched metal (hl!2I1m,
Anode coated with ruthenium oxide, iridium oxide, and titanium oxide (g diameter 5 mm), SO5304 punched metal (minor axis 2 mm, major axis 5 mm) with ruthenium nickel (ruthenium 5%, nickel 50%, aluminum 45%) Using an electrolytic cell equipped with a cathode and a gas phase section installed in the northern part of the electrolytic chamber, a surface having an impermeable film of an aqueous soda solution on the northern part of the cation exchange membrane between the two electrodes is used. was installed so that the film was directed toward the cathode and the film hit the gas phase. Next, 300g was placed in the anode chamber.
While supplying water to the cathode chamber, the IQ sodium chloride aqueous solution was adjusted to a sodium chloride concentration of 200 g/+2 in the anode chamber.
In addition, the current density was 30 A/d+++2 while maintaining the concentration of heliophilic soda in the cathode chamber at 35 ton percent.

Electrolysis was performed under conditions of 90°C.

120 The blind electrolysis was stopped, the cation exchange membrane was taken out from the electrolytic cell, and as a result of observation, it was confirmed that the membrane surface corresponding to the gas phase in the northern part of the electrolytic chamber was hardly electrolyzed.

Table 1 shows the performance at the initial stage of electrolysis and the performance of the non-electrolytic surface of the electrolytic chamber 1 after 120 El electrolysis.

Table 1 Comparative Example 1 Porous layers were attached to both the anode side and the cathode side in the same manner as in Example 1, except that the impermeable film of the temporal sorter aqueous solution was not attached to the single-sided part. Ion exchange table% 1.40meq/g dry resin, thickness 250μ and ion exchange table 11.25meq/g dry resin, thickness 20
A cation exchange membrane consisting of μ was obtained. The cation exchange membrane was coated with 25 weight percent of 7. ? 70℃ with aqueous soda solution,
Hydrolysis was carried out for 16 hours, and the mixture was placed in the same electrolytic cell as in Example 1, and electrolysis was carried out under the same conditions. Table 2 shows the performance at the initial stage of electrolysis and the performance of the non-electrolytic surface at the top of the electrolysis chamber after 120 days of electrolysis.

Table-2 Example 2 CF2=CF7 and Oh=CFO(CF7
By catalytically polymerizing hcOOcH3 and changing the combined power and temperature, the ion exchange capacity: 1:j, 80 mm
/g of dry resin) (Polymer A, 1.20 mm'￥
A copolymer B of 1 state/g dry resin was obtained. After that, copolymers A and B were each extruded to obtain a film A-1 with a thickness of 200μ and a film B-2 with a thickness of 30μ.Next, A-1 and B-1 were knitted together, 20 using a hot roll
Lamination was carried out at 0°C to obtain a composite membrane.

Furthermore, on the surface of part E on the B-1 side, the NaOH diffusion coefficient created by the open force method as described above is 1.5X 1fL'eq/c.
A 100 μ thick film of copolymer of dry resin with m'・hr・ΔN of ion exchange capacity 7110.80 mm/g was adhered at 250°C using a dry press, and Y-based soda was added to one side of the film. A cation exchange model 1 with an aqueous solution impermeable film was obtained.

The cation exchange membrane was hydrolyzed at 90° C. for 30 hours with a 25% 1.1” sodium aqueous solution to obtain Example 1.
Electrolysis was carried out under the same conditions using the same electrolytic cell.

Electrolysis was carried out for 281 hours, and when the cation exchanger 1 model was taken out from the electrolytic cell and inspected, no abnormality was found. on the other hand,
A similar electrolytic test was conducted for 28 days on a cation exchange membrane with the same structure that did not have an impermeable film for the 7-Y sodium aqueous solution in the h part, and when the cation exchange 11Q was inspected, it was found that salt precipitation was occurring within the membrane. Deterioration was progressing.

・-77T';

Claims (4)

[Claims] (1) In an electrolytic cell containing an alkali chloride aqueous solution that forms an anode chamber and a cathode chamber via a cation exchange membrane, the cathode surface of the cation exchange membrane that does not come into contact with the electrolyte at the top of the electrolytic chamber is covered with an alkali hydroxide aqueous solution. An electrolytic cell for an aqueous alkali chloride solution, characterized in that it is covered with an impermeable film. (2) The electrolytic cell according to claim 1, wherein the impermeable film for an aqueous alkali hydroxide solution has a diffusion coefficient of not more than 10^6 eq/cm^2·hr·ΔN. (3) The electrolytic cell according to claim 1, wherein the film impermeable to the aqueous alkali hydroxide solution is made of the same type of fluoropolymer as that forming the cation exchange membrane. (4) The electrolytic cell according to claim 1, wherein the cation exchange membrane is made of a fluorine-containing polymer having sulfonic acid or carboxylic acid as an ion exchange group.