JPH04297591A - Ion exchange membrane for electrolysis of alkali metal chloride - Google Patents

Abstract

PURPOSE:To prevent reduction of strength of a cation exchange membrane and to prolong its life by depositing a specified amt. of inorg. particle layer on the anode surface of the cation exchange membrane in the area where chlorine gas in an electrolytic bath is apt to remain and then effecting electrolysis. CONSTITUTION:An alkali metal chloride is subjected to electrolysis in an electrolytic cell which is divided into an anode room and cathode room by a cation exchange membrane 3 supported by gaskets 2 provided on the frame of the electrolytic cell. During electrolysis, chlorine gas is apt to remain in the area (A) where the ion exchange membrane 3 is not pressed by the frame 1 of the electroytic cell and also in a zone (B) within about 10mm distance from the area (A). Therefore, the surface of the anode side of the cation exchange membrane 3 corresponding to the area (A) and (B) where chlorine gas is apt to remain is coated with a layer containing 0.2-5mg/cm<2> inorg. particles. This coating layer consists of 5-70wt.% of fluorine-contg. polymer containing ZrO2 of 0.01-0.20mum particle size, etc., and is preferably a porous layer having about >=15% porosity.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cation exchange membrane for electrolyzing alkali metal chlorides and a method for electrolyzing alkali metal chlorides using the same.

0002

BACKGROUND OF THE INVENTION Ion exchange membranes used in the production of alkali metal hydroxides must have high current efficiency, low electrical resistance, and high mechanical strength. In the mainstream filter-press type electrolytic cell, an ion exchange membrane is fastened to an electrolytic cell frame via a gasket, and the ion exchange membrane separates the cell into an anode chamber and a cathode chamber.

When electrolysis of alkali metal chlorides is carried out in such an electrolytic cell, the ion-exchange membrane is placed around the entire periphery of the electrolytic cell frame, that is, the part near the gasket, compared to the central part, which is the normal electrolytic surface. The deterioration in strength is significant, and due to the decrease in strength of this small portion and even breakage, it must be replaced in a short period of time. In addition, damage to the electrolytic cell due to damage to this part,
Problems such as a decline in alkali metal hydroxide productivity are also occurring due to suspension of electrolysis for renewal of electrolyzers and ion exchange membranes.

[0004] The parts where the mechanical strength of the membrane is likely to deteriorate or be damaged correspond to the parts where chlorine gas in the anolyte tends to stay.
The reason may be as follows. In other words, chlorine gas diffuses into the membrane from the anode side of the ion exchange membrane, while alkali metal hydroxide also diffuses into the membrane from the cathode side, where they meet in the membrane and the next Reactions like (
Due to chemical reaction 1), alkali metal chlorides with low solubility are generated and precipitated in the ion exchange membrane, and the nascent oxygen is generated, which destroys the structure of the ion exchange membrane, resulting in the decrease in mechanical strength as described above. It is thought that it will happen.

[0005]

[Chemical formula 1]

[0006] Conventionally, as a method for preventing such local strength reduction of the ion exchange membrane, a method has been proposed in which one or both sides of the ion exchange membrane is coated with a gas-impermeable material in the area where chlorine gas is retained in the electrolytic cell (Japanese Patent Laid-Open Publication No. 52-144399, JP-A-54-71780), a method in which the cathode side is covered with a porous film and the anode side is covered with a gas release layer and a porous layer whose pores are hydrophilic ( JP-A-63-1180
However, bonding these films and porous bodies to different ion exchange membranes requires heating and pressure, which is difficult to work with, and the area around the bonded area changes in size and becomes flat. It is difficult to obtain a membrane, difficult to attach to a large battery tank, and leakage of the electrolyte to the outside of the tank is likely to occur. Further, it has drawbacks such as insufficient bonding force and easy peeling during electrolytic use.

[0007]

[Problems to be Solved by the Invention] The present invention prevents a decrease in the strength of the ion exchange membrane in areas where chlorine gas tends to accumulate in an electrolytic cell, and prevents the life of the membrane itself from being shortened due to the decrease in strength only in specific areas. It is an object of the present invention to provide a novel ion exchange membrane for electrolysis of alkali metal chlorides, which is free from the above.

[0008]

[Means for Solving the Problems] The present invention uses an electrolytic cell separated into an anode chamber and a cathode chamber by an ion exchange membrane, which corresponds to the part of the electrolytic cell where chlorine gas stays when electrolyzing alkali metal chlorides. This is a cation exchange membrane for alkali metal chloride electrolysis, in which the anode side surface of the ion exchange membrane is coated with inorganic particles of 0.2 mg/cm2 to 5 mg/cm2. The part of the ion exchange membrane that corresponds to the part of the electrolytic cell where chlorine gas tends to stay is the gasket in the case of a filter press type electrolytic cell where the ion exchange membrane is tightened with the electrolytic cell frame via a gasket. The part that is not pressed by the electrolytic cell frame (Figure 1A
) and the periphery, that is, a zone having a width of at least 10 mm from the gasket to the current-carrying part side (the part shown in FIG. 1B). It is not clear why Cl2 gasket stays in such areas, but Cl2 gaskets accumulate due to subtle irregularities due to the difference in level between the gasket and the membrane, or due to gasket deterioration.
It is thought that two gases remain.

[0009] Furthermore, although Cl2 gas remains on all four sides of the gasket, including the top, bottom, left and right sides,
The frequency of Cl2 gas retention increases in the order of the bottom side and the left and right sides. At this point, chlorine gas and alkali metal hydroxide react in the membrane, and the membrane structure is thought to be destroyed by the production and precipitation of alkali chloride and the production of oxygen. A patent application was filed for the following invention. That is, the cathode side surface of the cation exchange membrane, which corresponds to the part where chlorine gas tends to accumulate in the electrolytic cell, is coated with a layer in which the diffusion of alkali metal hydroxide is greater than that of the cathode side surface layer of the cation exchange membrane. This is a film in which the diffusion of alkali metal hydroxide is greater on the cathode side surface than on the cathode side surface layer, and the anode side surface is also coated with inorganic particles. However, when manufacturing such a membrane, for example, when coating the cathode side of the membrane using a spray method that is efficient in terms of membrane performance, extremely strict control is required by masking the areas that are not intended to be coated. The masking portion will be coated with a coating material of about 0.01 mg/cm2. If more than 0.01 mg/cm2 of a highly diffusive coating composition adheres to the current-carrying surface on the cathode side, the current efficiency is determined by the properties of the surface layer of the membrane cathode surface, so the current efficiency decreases. This is a major drawback in terms of performance. Furthermore, although it is not clear why it is possible to prevent a decrease in the strength of the membrane in areas where chlorine gas tends to accumulate, it is possible to increase the diffusion of alkali metal hydroxide by coating the cathode side with a coating with a large diffusion layer. This is because the reaction between chlorine gas and alkali metal hydroxide occurs not inside the membrane but outside the membrane, that is, on the anode side, and the effect of the inorganic particle layer on the anode surface to prevent strength reduction is small, and the reaction occurs on the cathode surface in that area. It was believed that a large layer of coating was necessary to maintain sufficient strength.

Under such circumstances, it is surprisingly possible to prevent the strength of the membrane from decreasing by coating only the anode side of the ion-exchange membrane where chlorine gas tends to accumulate with a layer containing a specific amount of inorganic particles. I discovered something. In the present invention, the coating amount of inorganic particles is 0.2 mg/cm2.
The concentration ranges from 5 mg/cm2 to 5 mg/cm2. From a cost perspective, it is preferable to use as little as possible, but 0.2 mg/cm
If it is less than 2, there is no effect, and in order to prevent a decrease in strength, a coating amount of 0.2 mg/cm2 or more is required. If the coating amount exceeds 5 mg/cm2, there will be a problem that the coating layer will peel off when handling the membrane, and in addition, if the coating amount exceeds 0.05 mg/cm
2 or more, which is not desirable.

The coating layer is a liquid and gas permeable porous layer having a porosity of 15% or more and made of inorganic particles and a fluorine-containing polymer with a high water content, and/or inorganic particles and a fluorine polymer such as polytetrafluoroethylene. It is. As the inorganic particles, oxides, nitrides, or carbides of zirconium, silicon, and titanium are used. The particle size of these inorganic substances is 0
．． 01 to 0.20 μm, preferably 0.02 to 0.0
It is 8 μm.

The fluorine-containing polymer having a water content is, for example, a fluorine-containing polymer having a sulfonyl fluoride group and/or a carboxylic acid group, and a specific example thereof includes a copolymer shown in Chemical Formula 2.

[0013]

[Case 2]

In the mixture of inorganic particles and fluorine-containing polymer used as the coating layer on the anode surface side, the proportion of the fluorine-containing polymer in the mixture is in the range of 5 to 70 wt%, and the porosity is 15% or more by Hg injection method. It is preferable that In the case of a multi-layered cation exchange membrane, the anode surface of the cation exchange membrane in the present invention is the surface where the water content of the layer existing on the surface layer is high in the part where there is no coating layer, and the cathode surface is the surface where the water content is high. Refers to a small side.

These coating layers are sandwiched between the parts of the electrolytic cell to be installed where chlorine gas tends to accumulate, that is, the gaskets, and are at least 10 mm wide from the part not pressed by the electrolytic cell frame and the gasket toward the current-carrying part. It is sufficient to apply the coating only to the film surface corresponding to the zone within the range. However, for industrial implementation, it is preferable to cover with a width of 20 to 300 mm, taking into consideration misalignment during installation. In addition, from the viewpoint of effective use of the membrane and because it is important to prevent the parts provided with these coating layers from entering current-carrying parts as much as possible, the distance occupied by the coating layers from the edge of the membrane is preferably 300 mm. within, more preferably 15
It is necessary to keep it within 0 mm.

[0016] These coating layers are preferably provided on each of the four sides (top, bottom, left and right), but it is effective and industrially advantageous to provide them only on the top and bottom sides where Cl2 gas is particularly likely to accumulate. By providing these coating layers over the entire surface of the ion exchange membrane, if the anolyte concentration decreases due to trouble during operation,
Membrane performance deteriorates easily. In addition, production costs also increase, so it is necessary to avoid current-carrying surfaces and provide a coating layer only around the surroundings.
It is preferably 40% or less of the total membrane area, more preferably 20% or less.

The cation exchange membrane used as the base membrane of the cation exchange membrane of the present invention is known per se and is clear to those skilled in the art, but it contains sulfonic acid and/or carboxylic acid ion exchange groups. This is an ion exchange resin membrane obtained by hydrolyzing a polymer consisting of a fluorocarbon main chain and having a meltable side chain containing a sulfonyl group and/or a carboxyl group. Next, a general method for producing this fluorinated polymer will be explained in detail, but this is not intended to limit the scope of the present invention.

The fluorinated polymer is a copolymer of at least one monomer selected from the first group described below and at least one monomer selected from the second group and/or the third group. It can be manufactured by The first group of monomers is at least one fluorinated vinyl compound, such as vinyl fluoride, hexafluoropropylene, vinylidene fluoride, perfluoro(alkyl vinyl ether), and tetrafluoroethylene.

The second group of monomers is a vinyl compound having a functional group that can be converted into a carboxylic acid type ion exchange group. That is, a monomer represented by formula (3) is generally used.

[0020]

[Chemical formula 3]

Specific examples of preferred monomers include (Chemical formula 4)
) formula can be mentioned.

[0022]

[C4]

The third group of monomers is a vinyl compound having a functional group that can be exchanged with a sulfonic acid type ion exchange group. This is a vinyl compound that can be represented by the general formula (Formula 5).

[0024]

[C5]

The T group in the above formula may be branched or unbranched (ie, linear) and may have one or more ether bonds. Preferably, the vinyl group is bonded to the T group via an ether bond. That is, monomers of the formula CF2=CFOTCF2-SO2F are preferred. A specific example of a suitable sulfonyl fluoride-containing monomer is shown in (Chemical formula 6).

[0026]

[C6]

In copolymerization, the type and proportion of monomers selected from the three groups mentioned above are determined depending on the type and amount of functional groups desired in the fluorinated polymer. for example,
When a polymer containing only carboxylic acid ester functional groups is required, at least one monomer from the first group and the second group may be selected and copolymerized. The mixing ratio of each monomer is determined by the amount of functional groups required per unit polymer. When increasing the amount of functional groups, the proportion of monomers selected from the second and third groups may be increased. Generally, the amount of total functional groups added to the exchange group is between 0.5 and 2.
0 meq/g, preferably 0.6-1.5 meq/g
It is used within the range of ion exchange capacity of 1.5 g.

As is clearly known to those skilled in the art, in order to obtain a cation exchange membrane with good power consumption performance, it is preferable to use a cation exchange membrane with a multilayer structure. During operation, high performance can be achieved by placing a layer with a low water content on the cathode side at the alkali hydroxide concentration (cathode solution concentration) produced in order to place the layer with high barrier properties on the cathode side. I can demonstrate it.

In fluorine-based ion-exchange resins, when the functional groups are the same, the water content increases as the exchange capacity increases, and when comparing the same exchange capacity, the longer the side chain structure, the stronger the functional group is. It is known that the water content is high, and cation exchange membranes are designed with these factors in mind. The reinforced woven fabric used in the present invention includes a reinforced yarn that is a monofilament yarn or a multifilament yarn of a fluorinated polymer;
It is a woven fabric consisting essentially of warp and weft yarns, optionally using sacrificial yarns that are hydrocarbon monofilament yarns or multifilament yarns.

The membrane of the present invention is preferably composed of the above-described fluorinated polymer film and reinforced woven fabric. In addition, as a method for coating inorganic materials on the anode side of a cation exchange membrane, inorganic particles are added to a suspension of a fluorine-containing polymer such as polytetrafluoroethylene, uniformly dispersed, and then screen printing is performed. Inorganic particles are applied by heating and dissolving a fluoropolymer with a high water content in an aqueous solution containing 20 wt% or more of an alcoholic solvent to a concentration of 1 to 20 wt%. There is a method in which the composition is added, uniformly dispersed using a ball mill, etc., and applied by a spray method, a roll method, etc., but the present invention is not limited thereto.

In order to obtain a membrane for producing alkali hydroxide, a polymer having meltable side chains (ion exchange group precursor membrane) is hydrolyzed using an acid or base to remove all functionalities. It is necessary to convert the group into an ionizable functional group, but when applying the coating layer, it can be carried out on the membrane after hydrolysis treatment, but it can be carried out on the membrane after hydrolysis treatment, but it is not necessary to convert It is industrially advantageous.

Known conditions can be applied to electrolyze the alkali metal chloride of the present invention. For example, the concentration of the alkali metal chloride aqueous solution in the anode chamber is maintained at 2.5 to 5N, the concentration of the alkali metal hydroxide in the cathode chamber is maintained at 20 to 50%, the temperature is 50 to 100℃, and the current density is 10 to 60A/dm2.
It is driven by.

[0033]

[Examples] Examples of the present invention are shown below, but the present invention is not limited thereto.

[0034]

[Example 1, 2, 3] CF2 = CF2 and CF2
=CFOCF2 CF(CF3)O(CF2)2
Equivalent weight obtained by copolymerization with COOCH3: 110
Polymer A of No. 0 was extrusion molded into a film with a thickness of 25 μm. On the other hand, CF2 = CF2 and CF2 = CFOC
F2 CF and (CF3 )O(CF2 )3 SO2
Polymer B having an equivalent weight of 1050 obtained by copolymerization with F was extrusion molded into a 100 μm film. Further, the film A, the film B, and a 50-mesh plain woven fabric made of 100-denier PTFE yarn as a reinforcing agent were layered in the above order, and then heated and molded to produce a laminated film.

[0035] Also, CF2 = CF2 and CF2 = C
FOCF2 CF(CF3)O(CF2)3SO
200 g of a polymer with an equivalent weight of 1000 obtained by copolymerization with F was hydrolyzed into an acid form, and ethanol 4
A mixture of 500 g/4500 g of water was obtained. Next, the laminated film created by heat molding is hydrolyzed to obtain a cation exchange membrane, and the periphery of the surface of the layer facing the anode side of this ion exchange membrane (layer after hydrolysis of B film: B layer), Apply the coating composition to the area near the gasket using a spray method.
When dried, the amount of inorganic particles is 0.2 mg per 1 cm2.
, 0.5 mg, and 1 mg of ion exchange membranes were obtained. Note that the amount of the adhering composition adhering to the anode surface other than the part concerned was 0.05 mg/cm2 or less.

[0036] The size of the membrane is 1270 mm x 2455 mm.
, and the coating layer was applied around the periphery with a width of 125 mm, so
The size of the non-coated surface was 1020 x 2205 mm. This ion exchange membrane was assembled into a filter press type electrolytic cell with a conductive surface of 1154 mm x 2354 mm so that the surface with the coating layer on the B layer side became the cathode surface, and the sodium chloride concentration in the anode chamber was adjusted to 3. 5N, while maintaining the sodium hydroxide concentration in the cathode chamber at 35%, at a temperature of 90°C and a current density of 40A/d.
Electrolysis was carried out at m2 for 180 days.

When the electrolysis was stopped and the cross section of the membrane near the gasket at the top of the container was observed, it was found that there was almost no precipitation of sodium chloride crystals and there was only slight destruction of the membrane structure. Table 1 shows the mechanical strength measurement results of similar parts and the average current efficiency for 180 days.

[0038]

[Comparative Example 1] Around the surface of B in Example-1,
The same ion exchange membrane as in Example 1 was subjected to electrolysis in the same manner as in Example 1 except that the coating layer was not provided in the area near the gasket. After stopping the electrolysis, the cross section of the membrane near the gasket at the top of the container was observed, and as a result, precipitation of sodium chloride crystals was observed. After washing with water to remove the sodium chloride, it was found to be hollow, indicating that the membrane structure had been destroyed.

Mechanical strength measurement results of similar parts and 180
The daily average current efficiency is shown in Table 1.

[0040]

[Comparative Examples 2 and 3] The same ion exchange membrane as in Example 1 was used in Example 1, except that the amount of inorganic particles coated was 0.05 mg/cm2 and 0.1 mg/cm2.
Electrolysis similar to 1 was performed. After stopping the electrolysis, the cross section of the membrane near the gasket at the top of the container was observed, and as a result, precipitation of sodium chloride crystals was observed. After washing with water to remove the sodium chloride, it was found to be hollow, indicating that the membrane structure had been destroyed.

Mechanical strength measurement results of similar parts and 180
The daily average current efficiency is shown in Table 1.

[0042]

[Comparative Example 4] An ion exchange membrane was prepared in the same manner as in Example 1 except that the amount of inorganic particles coated was 5 mg/cm2, but the coating layer peeled off when the membrane was handled before installation.

[0043]

[Example 4] CF2 = CF2 and CF2 = CFOC
F2 CF(CF3)O(CF2)2COOCH3
Polymer A with an equivalent weight of 1100 obtained by copolymerization with CF2 = CF2 and CF2 = CFOCF2 CF
Polymer B with an equivalent weight of 1030 obtained by copolymerization with (CF3)O(CF2)2SO2F was coextruded, and the thickness of polymer A was 25μ and the thickness of polymer B was 75μ.
, a film C having a total thickness of 100 μm was produced. Furthermore, Polymer B was extrusion molded to produce a 40μ film D. An 18 mesh plain woven fabric made of 200 denier PTFE yarn was added as a reinforcing agent between Film C and Film D to produce a laminated film. However, the side of film C that comes into contact with the plain woven fabric is the polymer B side. 200 g of the acid form obtained by hydrolyzing Polymer B was dissolved in a mixture of 4,500 g of ethanol/4,500 g of water, and 800 g of zirconium oxide was decomposed in this to obtain a coating composition.

[0044] In the laminated film, the side on which polymer A is present in the surface layer is referred to as side A, and the side on which polymer B is present on the surface layer is referred to as side B. Apply 1 cm2 of coating composition to the B side of the laminated film in the area near the upper and lower gaskets when it is assembled into a battery case.
0.3mg per unit (0.24mg/c as inorganic particles)
m2) by spraying, and after drying,
An ion exchange membrane was obtained by hydrolysis. The size of the membrane is 127
The size of the non-painted surface was 1020 mm x 2455 mm because the coating layer was applied to both the cathode side and the anode side with a width of 125 mm on the top and bottom. Although we tried to prevent the uncoated surface from being coated by masking, the amount of coating that adhered to the uncoated anode surface was 0.0 on average.
It was 2 mg/cm2.

[0045] This ion exchange membrane was assembled into a filter press type electrolytic cell similar to that in Example 1 so that the A side was on the cathode side, and the sodium chloride concentration in the anode chamber was adjusted to 200 g/l.
While maintaining the sodium hydroxide concentration in the cathode chamber at 33%, the temperature is 85 to 90°C, and the current density is 15 A/dm2 to 40 A/d.
Electrolysis was carried out at m2 for 180 days. After stopping the electrolysis and observing the cross section of the membrane near the gasket at the top of the cell, we found that only a small amount of sodium chloride crystals had been deposited and there was almost no destruction of the membrane structure.

Mechanical strength measurement results of similar parts and 18
Table 2 shows the average current efficiency for 0 days.

[0047]

[Comparative Examples 5 and 6] Peripheral areas of side A and both sides of side A and side B,
Apply 1cm2 of coating composition to the area near the gasket.
Electrolysis was carried out in the same manner as in Example 4 using the same ion exchange membrane as in Example 4, except that the ion exchange membrane was applied in an amount of 0.3 mg per sample. The average amount of deposits on the non-coated side of A side is 0.02 mg/
It was cm2. Table 2 shows the mechanical strength of the removed membrane near the gasket at the top of the battery case and the average current efficiency for 180 days.
Shown below.

[0048]

[Comparative Example 7] Electrolysis was performed in the same manner as in Example 4 using the same ion exchange membrane as in Example 4 except that the coating layer was not provided in the peripheral area and the area near the gasket. Table 2 shows the mechanical strength of the membrane taken out near the gasket at the top of the battery case and the average current efficiency for 180 days.

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Effects of the Invention] The present invention prevents the local mechanical strength of the ion exchange membrane from decreasing by coating the layer facing the anode side of the ion exchange membrane, which is the part of the electrolytic cell where chlorine gas tends to accumulate, with an inorganic particle layer. This has the effect of extending the life of the ion exchange membrane and enabling stable long-term operation.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an ion exchange membrane in a filter press type electrolytic cell that is fastened to an electrolytic cell frame via a gasket, showing an embodiment of the present invention. In the figure, there are 1 electrolytic cell frame, 2 gaskets, and 3 cation exchange membranes. Part A is sandwiched between the gaskets and is not pressed by the electrolytic cell frame. The part B is the peripheral part, that is, at least 1 width from the gasket to the current-carrying part side.
This is a zone within 0 mm.

FIG. 2 shows the relationship between the tensile elongation of portions A and B after 180 days of energization and the amount of coating on the anode surface for Examples 1 to 3 and Comparative Examples 1 to 3.

Claims (2)

[Claims] Claim 1: In an electrolytic cell separated into an anode chamber and a cathode chamber by a cation exchange membrane, the anode of the cation exchange membrane corresponds to a portion of the electrolytic cell where chlorine gas tends to remain when electrolyzing alkali metal chlorides. On the side surface, 0.2 to 5 mg/
A cation exchange membrane for alkali metal chloride electrolysis, which is coated with a layer containing inorganic particles of cm2 or less. 2. An alkali metal chloride electrolysis method using the membrane according to claim 1.