JPS63118083A - Electrolytic method using double-layer diaphragm - Google Patents

Abstract

PURPOSE:To obtain the high current efficiency, low resistance, and high mechanical strength of a diaphragm by using a double-layer diaphragm obtained by laminating a hydrophilic cellular body layer and ion-exchange resin layer and closing the cells in the low-current density region as the electrolytic diaphragm. CONSTITUTION:In the electrolytic cell for an aq. soln. wherein an anode chamber and cathode chamber are formed, the double-layer diaphragm obtained by laminating a hydrophilic cellular body layer having 1-1,000 Garley number and an ion-exchange resin layer is used as the electrolytic diaphragm. In this case, the cells in the region of the hydrophilic cellular body layer having the <=1/2 times current density for the mean current density of the diaphragm are closed in the double-layer membrane. The clamped part on the peripheral part of the diaphragm, the part which is not brought into contact with an electrolyte, the curved corner part not opposed to the effective electrolytic surface of the anode of a finger-type electrolytic cell, etc., are appropriately exemplified as the closed-cell region. The Garley number of the cellular body layer is increased to >=10<4> by the cell closing treatment. As a result, a diaphragm having excellent characteristics is obtained, and a high-purity product can be obtained by electrolysis.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electrolytic method using a multilayer diaphragm, and more specifically, high current efficiency, low membrane resistance, and high mechanical strength are required. The present invention relates to a novel electrolysis method for electrolyzing aqueous solutions such as water, alkali chloride, alkali hydroxide, or acid aqueous solutions.

[Prior art] Ion exchange membrane methods have been proposed in recent years for the electrolysis of water, alkali chloride, alkali hydroxide, or acid aqueous solutions, but the ion exchange membranes used in these methods have high current efficiency and low membrane It is essential to have high mechanical strength in terms of handling while having resistance.

Films made of polymers with ion exchange groups have low tear strength, so it is known that reinforcing materials such as rope can be used to improve tear strength. Also, since it blocks the flow of electricity, it has the disadvantage of high resistance.

In order to improve this drawback, an ion exchanger layer with a high water content and low electrical resistance was used, although the current efficiency was not high.
A thick film reinforced with polytetrafluoroethylene woven fabric or polytetrafluoroethylene microfibrils, and a thin film with a low water content and ion exchange layer that exhibits high current efficiency and high electrical resistance. , multilayer ion exchange membranes that are integrally laminated by heating and pressure bonding have been proposed (Japanese Patent Application Laid-Open Nos. 57-3658f1 and 1983-1999).
132089, Japanese Unexamined Patent Publication No. 57-84910, etc.), considerable high performance has been achieved.

However, in such a multilayer ion exchange membrane, if you want to lower the membrane resistance and further save energy, you will have to increase the water content or reduce the membrane thickness. However, there is a limit as it causes a rapid decrease in film strength.

As a method to overcome these problems, Japanese Patent Application Laid-Open No. 61-13347
Supported by a hydrophilic porous material as shown in the publication,
A novel diaphragm is provided which consists of an ion exchanger layer that is as thin as possible. However, with such a hydrophilic porous layer,
When a diaphragm consisting of a thin ion exchanger layer with low resistance is used in electrolytic cells of various types and structures to electrolyze an aqueous alkali chloride solution, the content of alkali metal chloride in the caustic alkali produced in a particular electrolytic cell can be reduced. It was found that this value is high and may increase over time. Furthermore, it has been found that when an EPDM rubber gasket, which is widely used in industrial electrolytic cells, is used as a backing material and the membrane is tightened for electrolysis, the rubber gasket is severely eroded. In addition, when attaching a membrane to an industrial electrolytic cell, in an electrolytic cell where the clamping pressure is low due to the structure of the electrolytic cell, leakage of electrolyte to the outside of the electrolytic cell may occur through the hydrophilic porous layer that is the support of the membrane. It was also acknowledged that there are cases.

It is known that the purity of caustic alkali is lower in finger-type electrolyzers than in filter press-type electrolyzers when the same membrane is used for electrolysis. It has also been found that when electrolysis is carried out in a finger-type electrolytic cell as a diaphragm, the alkali metal chloride content in the produced caustic alkali becomes even higher.

[Problems to be Solved by the Invention] The present invention solves problems when using a novel cation exchange membrane having a hydrophilic porous layer as a support for electrolysis as a diaphragm. This technology solves the above-mentioned problems caused by low membrane resistance and low membrane resistance, and provides a technology that enables industrial use of high-performance membranes with low energy consumption. The purpose of the present invention is to provide a method for using an electrolytic diaphragm necessary for producing a small amount of highly pure caustic alkali.

[Means for Solving the Problems] The present invention has been made to achieve the above object, and provides a multi-layered structure in which a hydrophilic porous layer of Gurley Number 1-1000 and an ion exchange resin layer are laminated. When using a diaphragm as an electrolytic diaphragm in an aqueous solution electrolytic cell with an anode chamber and a cathode chamber, the hydrophilic porous layer of the multilayer diaphragm in the area where the current density is less than the average current density of the membrane. The present invention provides an electrolysis method using an electrolytic diaphragm characterized in that the pores are closed.

In the present invention, it is preferable that the Gurley number of the porous layer whose pores have been blocked is 104 or more, particularly 105 or more. The liquid flow rate is lowered, and the membrane resistance in the area where the pores are blocked becomes high, which makes it possible to reduce the mutual diffusion of the anolyte and catholyte, resulting in high current efficiency and
We can provide electrolysis that provides high product purity.

Although the present invention is applicable to the electrolysis of any aqueous solution such as alkali chloride, alkali, water, and acid aqueous solution, the electrolysis of aqueous alkali chloride solution will be described in particular, where the influence of interdiffusion of anolyte and catholyte is greatest. , it goes without saying that the invention is not limited to this.

The mechanism for suppressing the leakage of alkali metal chloride into the caustic alkali, the leakage of the electrolyte to the outside of the electrolytic cell, and the erosion of the gasket, which have been pointed out as problems, is estimated to be approximately as follows. Caustic Alka.

It is believed that leakage of alkali metal chloride into the reactor occurs from areas other than the effective electrolytic surface where electrolysis is substantially occurring.

At the electrolytic side end of the tightening area around the membrane, a slight shift in the gasket position during membrane installation may cause a non-current-conducting part of the membrane, and a portion of the membrane that is not in contact with the electrolyte at the top of the electrolytic cell. is a region where substantially no electrolysis occurs. In a finger type electrolytic cell, the anode and cathode face each other, and the straight line distance between the anode and cathode is short, and the corner curved part of the membrane that does not face the effective electrolytic surface of the anode where electrolysis actually occurs,
The part of the membrane that is not in contact with the electrolyte at the top of the electrolytic cell is a slightly energized part or a non-energized part.

Alkali metal chloride diffuses and leaks into the caustic alkali through such a membrane portion, and the amount of the alkali metal chloride is greater as the resistance of the membrane is lower.

Furthermore, the caustic alkali that diffuses to the alkali metal chloride side reacts with chlorine to produce hypochlorous acid, which corrodes the gasket. This phenomenon is also caused by the diffusion of caustic alkali, and becomes more pronounced as the resistance of the membrane decreases. This phenomenon is a phenomenon that inevitably occurs when membrane resistance is reduced in an attempt to reduce electrolytic energy, and research by the present inventors has revealed that it is a new problem when using a diaphragm with low membrane resistance. Became. In addition, leakage of the electrolyte to the outside of the electrolytic cell will occur because the cation exchanger is supported by a wood-based porous material with good liquid flow, so if the electrolyte leaks out of the cell through the pores of this porous material layer, it will occur. Conceivable.

According to the present invention, the pores of the hydrophilic porous layer are blocked by blocking the pores of the porous layer in the above-mentioned low current density region of the cation exchange membrane supported by the hydrophilic porous layer. The resistance of the membrane in the occluded part can be increased.

So through the membrane in that area? ,? This makes it possible to suppress the diffusion of alkali metal chlorides, making it possible to produce high-purity caustic alkali with a low content of alkali metal chlorides in the caustic alkali. Also, erosion of the gasket at the tightened end of the membrane can be prevented. Furthermore, by blocking the pores in the hydrophilic porous layer in the tightening area around the membrane, the liquid flow through the porous layer is eliminated, and in an electrolytic cell with a low structural tightening pressure, the '1 solution is prevented from flowing out of the tank. leakage can be prevented. Note that the discussion in Section E is intended to explain the mixing of alkali metal chlorides into caustic alkali, gasket erosion, and the mechanism of liquid leakage to the outside of the tank.
This is not intended to limit the invention.

In the present invention, the treatment for clogging the pores of the lignified porous material layer can be carried out at any stage during or after the lamination of the porous material layer and the ion exchange resin layer, before or after the hydrolysis of the ion exchange layer. However, when using compaction of the porous material layer, 50 kg/kg of the area to be occluded is used.
This is done by applying a pressure north of cm2, particularly a pressure of 100 kg/c12 or more, using a press or the like. If necessary, heating can also be used, for example, 50 to 35
Heat consolidation can also be carried out under conditions of 0°C, preferably 100 to 250°C.

When applying grease or dispersion to block the holes,
Greases or dispersions of fluorine-based polymers that are resistant to chlorine and preferably resistant to alkali are desirable; examples of these include silicone greases, polytetrafluoroethylene, polychlorotrifluoroethylene, and polyhexafluoropropylene oxide. Greases and dispersions, dispersions and solutions of tetrafluoroethylene copolymers containing carboxylic acid or sulfonic groups are used.

The pore blocking treatment of the hydrophilic porous layer performed by any of the above methods is carried out in as many areas as possible where the current density is less than or equal to the average current density of the membrane, and more efficiently, less than or equal to the average current density of the membrane. However, it is not necessarily limited to the above-mentioned region of current density, but may partially extend to the normal electrolytic surface depending on the case.

The cation exchange layer of the cation exchange membrane having a hydrophilic porous layer as a support used in the present invention has the following characteristics in terms of electrochemical performance:
Preferably, the ion exchange group consists of a sulfonic acid group, a carboxylic acid group, or a derivative group such as an acid amide, ester, or acid halide, and is preferably formed from a fluorine-containing polymer from the viewpoint of corrosion resistance. The thickness of the ion exchanger layer is 1 to 450 mm, preferably 10 to 150 mm, and the ion exchange capacity is preferably 0.5 to 2.0 mm. Omeq/g dry resin,
In particular, a dry resin of 0.8 to 1.8+seq/g is selected. The porous layer has a Gurley number of 1-1000 and a pore diameter of 0.
It is preferable that the porosity is 30 to 95%, and the thickness is preferably 30 to 450 from the viewpoint of low membrane resistance and mechanical strength. It is preferable that the Gurley number is 3 to 300, the pore size is 0.1 to 8, and the porosity is 5.
A stretched porous PTFE body having a thickness of 0 to 80% and a thickness of 60 to 300 g is preferable.

There are no particular restrictions on the method of laminating and supporting the cation exchanger layer with the porous layer, but it is preferable to stack the ion exchanger membrane and the porous layer, and to heat the layer at a temperature higher than the conversion temperature of the ion exchanger, preferably. is 100 to 250 above the melting temperature
There is a method of heating and fusing the polymer forming the ion exchanger at a temperature of Methods such as steaming or heating above the conversion temperature of the polymer to form a film can be used.

The layered support of the ion exchanger layer by the porous layer can support the surface of the ion exchanger layer on the cathode side or the anode side, or furthermore, on both the anode and cathode membrane surfaces. Furthermore, in order to further improve the strength of the membrane, if necessary, a woven fabric made of a fluorine-containing polymer such as polytetrafluoroethylene can be inserted into the membrane as a reinforcing material. In this case, the fabric is inserted between the ion exchanger layer and the porous layer or into the porous layer.

Hydrophilicity can be imparted to the porous layer before or after laminating the porous layer and the ion exchanger layer into the a-layer. Various methods can be employed to impart hydrophilicity to the porous layer. For example, when forming a porous body layer, an inorganic lignophilizing agent can be blended to make the material forming the porous body hydrophilic. As an inorganic wood-loving agent,
Oxides, hydroxides, nitrides, carbides such as titanium, zirconium, niobium, tantalum, vanadium, manganese, molybdenum, tin, as well as silicon carbide, barium titanate, barium sulfate, etc., particles with an average particle size of 5 μm or less is added in an amount of 50 to 1000% by weight based on the fluorine-containing polymer, a pore-forming agent is added thereto, mixed, formed into a membrane, and then the pore-forming agent is extracted. Another method is to impregnate and polymerize a hydrophilic monomer to an extent that does not excessively reduce the porosity of the porous layer, or to fill or apply a hydrophilic polymer in the form of a solution and dry or bake it. Examples include a method in which the fluorine-containing porous body itself is formed from a 1ffi polymer having a parent wood group. As the hydrophilic monomer and polymer, a fluorine-containing polymer having a carboxylic acid group, a sulfonic acid group, and/or a phosphoric acid group is used. In this way, these monomers having hydrophilic properties are impregnated into a porous body and polymerized, or a solution of 0.5 to 50% by weight of the polymer (
For example, Japanese Patent Publication No. 48-13333 and Japanese Patent Publication No. 55-1
49338, etc.) is applied to the porous body. These hydrophilic fluorine-containing polymers are preferably attached to the porous body in an amount of 1 to 300% by weight, particularly 2 to 100% by weight.

Next, the present invention will be explained with reference to examples.1 The present invention includes various embodiments within its scope.0 For example, the ion exchange membrane used in the present invention may have a If necessary, a porous material containing gas- and liquid-permeable electrode active particles (Japanese Patent Laid-Open No. 58-755
83 and JP-A No. 57-39185) or a porous layer containing gas- and liquid-permeable electrode active particles (JP-A-54-112398) to reduce the sliding voltage under electrolysis. can be significantly improved.

[Effects of the Invention] As described above, the present invention improves the efficiency of the porous layer of a multilayer diaphragm in which a hydrophilic porous layer and an ion exchange resin layer are laminated in a region where the current density is lower than the average current density of the membrane. By blocking the pores, the new high-strength, low-resistance multi-layer diaphragm can be used for electrolysis, producing high-purity products over a long period of time, and also preventing liquid leakage to the outside of the tank. In addition, the effect of reducing erosion of gaskets made of EPDM or the like, which occurs when a low resistance film is used, is also recognized.

[Examples] Example 1 A mixture of fine powder of polytetrafluoroethylene (hereinafter referred to as PTFE) and white kerosene as a liquid lubricant was formed into a film. After removing the white kerosene and stretching it to one side,
Gurley number 7 with porous structure stabilized by heat treatment, pore diameter 5gm, porosity 80%, film thickness 110p
-rm PTFE porous body was obtained.

As an ion exchanger layer, C2F4 and CF2 = CFO
(CF2)3 Composed of copolymer with COOCH3 Ion exchange capacity 1.25 meq/g dry resin 40
AL thickness membrane (first film) and ion exchange capacity 1.4
4 maq/g dry resin of the above copolymer 20 thick film (
A laminate with a second film) was obtained.

Next, apply PTFE to the second film surface of the ion exchanger.
Porous materials are layered and laminated by heating and compression to a thickness of 170 mm.
A multilayer diaphragm of Ii was obtained.

On the other hand, C2FA and CF2=GFO(CF2-CF)0(C
After converting the copolymer of CF3 ion exchange capacity 1 Lseq/g dry resin with F2hSO2F to the acid form, the following two solutions were prepared.

・Solution 1.15% by weight Ethanol solution of 3% acid type copolymer with 5ruZ r02 particles dispersed ・Solution 2.15% by weight zirconyl chloride, 2% by weight acid type copolymer in water ・Ethanol・Isopropyl alcohol solution The solution 1 thus obtained was added to the above multilayer diaphragm.

The porous layer is impregnated with solution 2, which is spray-coated on both sides, dried and heated to adhere 1 mg/cm2 of Z r02 fine particles, and then dried to coat the inside of the porous layer with zirconyl chloride and acid. A multilayer diaphragm coated with a mixture with type copolymer was obtained.

The thus obtained multilayer diaphragm was hydrolyzed with a 25% caustic soda aqueous solution, and then a 2-inch thick EPDM rubber gasket was used as the backing material, and a titanium punched metal (minor diameter 2 mm, diameter 5+ am) was used. ) coated with ruthenium oxide, iridium oxide, and titanium oxide, and 5US30
An electrolytic surface equipped with a cathode made by electrodepositing Raney nickel (5% ruthenium, 50% nickel, 45% aluminum) containing ruthenium on punched metal made of No. 4 (minor axis 2III, major axis 5 mm), T & 10 cm x 15 cm filter press (1 j In the electrolytic cell, the pore layer in the area from the gasket tightening part and the tightening part of the multilayer diaphragm to the electrolytic surface side end of cathode gas get-1 to the electrolytic surface side is heated at a pressure of 200 kg/cm2 and a temperature of 50°. The sodium chloride concentration in the cathode chamber was adjusted to 200 g /
fL, and electrolysis was carried out under conditions of a current density of 30 A/ds and 2.90° C. while maintaining the caustic soda concentration in the cathode chamber at 35% by weight. In addition, the tightening was set to 10 kg/cm2.

During the 200 days of operation, the sodium chloride content in the caustic soda was low and no increase over time was observed. Furthermore, no liquid leakage outside the tank was observed, and when the electrolytic cell was opened and observed, no erosion of the gasket was observed.

The Gurley number of the porous layer with the above pores blocked is
When the porous layer was peeled off from a multilayer diaphragm that had been subjected to the same treatment as an equivalent multilayer diaphragm and measured, it was found to be 2X105. Table 1 shows the performance at the initial stage of electrolysis and the performance after 200 days of electrolysis.

Table 1 Comparative Example 1-1 In Example 1, from the gasket tightening part of the multilayer diaphragm and from the tightening part to the electrolytic surface side end of the cathode gasket 5II! Electrolysis was carried out for 60 days using the same membrane, container, and operating conditions as in Example 1, except that the pores in the porous layer in the region up to the electrolysis surface were not blocked. The sodium chloride content in caustic soda was high and increased significantly over time. Furthermore, liquid leakage and severe gasket erosion were observed. Table 2 shows the performance at the initial stage of electrolysis and the performance after 60 days of electrolysis.

Table 2 Comparative Example 1-'2 C2Fa and CF2=CFO(CF2)3 COOCH
Ion exchange capacity i1.25meq consisting of a copolymer with 3
40 pot thick film made of /g dry smoke resin (first film)
A laminated film of the above copolymer 20 thickness film (second film) having an ion exchange capacity μm and 44 meQ/g dry resin was obtained. Solution 1 used in Example 1 was spray-coated on both sides of this laminated film, dried and heated, and ZrO2'$IL
Particles were deposited at 11g/C112. The thus obtained laminated film was hydrolyzed with a 25% by weight aqueous solution of caustic soda, and then heated at 200 °C under the same battery container and operating conditions as in Example 1.
Electrolysis was performed for days.

After disassembling the electrolytic cell and observing it, severe erosion of the gasket was observed. The electrolytic performance is shown in Table 3.

Table 3 Example 2 In Example 1, the chlorine gas-anodic interface of the electrolytic cell was
The gasket tightening part and tightening of the multilayer diaphragm in Example 1 were performed using the same battery case and operating conditions as in Example 1, except that the gas phase part was provided in an area with a width of approximately 4C11 from the upper edge of the backing. Hexafluoropropylene oxide is applied to the area from the electrolytic surface side end of the cathode gas get to the electrolytic surface side of layer 5 and the pores of the porous layer of the multilayer diaphragm corresponding to the gas phase section provided in the anode chamber of the electrolytic cell. General formula F(C(CF3)-C:Fz-0-)n-CF consisting of an oligomer of
(CF3)-0F:+ (average n=100) was applied, and the same membrane as in Example 1 was used, except that the pores of the porous layer were blocked, and electrolysis was carried out for 200 days. The sodium chloride content in the caustic soda was low, and no liquid leakage outside the tank or erosion of the gasket was observed.

The Gurley number of the porous layer with the above pores blocked is
When the porous body was peeled off and measured from a multilayer diaphragm that had been subjected to a similar occluding treatment to an equivalent multilayer diaphragm, it was 106 or more. Table 4 shows the electrolytic performance.

Comparative Example 2 In Example 2, the membrane was the same as Example 2 except that the multilayer diaphragm was not subjected to the treatment to block the pores of the porous layer;
Electrolysis was carried out for 60 days under operating conditions.

The sodium chloride content in the seams was high, and leakage occurred. Furthermore, as a result of disassembling and observing the electrolytic cell, severe erosion of the gasket was observed. Table 4 shows the electrolytic performance.

Table 4 Example 3 An electrolytic cell similar to Example 1 was used, except that the anode and cathode corresponding to the electrolytic part of the electrolytic cell were removed by 5 cm from the upper edge of the membrane backing, and a non-current-carrying part was provided.
In Example 1, the gasket tightening part of the multilayer diaphragm and the area from the fastening part to the electrolytic surface side end of the cathode gasket to the 5II11 electrolytic surface side and the porous pores of the multilayer diaphragm corresponding to the non-current-carrying part provided in the electrolytic cell The same membrane as in Example 1 was used as the diaphragm, except that the pores in the body layer were coated with 7Fung grease (9401) manufactured by Chias Co., Ltd. and the pores were closed, and the current density was set to 20 ASD/di2. temperature to 80
Electrolysis was carried out for 200 days under the same operating conditions as in Example 1 except that the temperature was changed to .degree.

The sodium chloride content in the caustic soda was low, and no liquid leakage or gasket erosion outside the tank was observed.

The Gurley number of the porous layer with the above pores blocked is
When the porous layer was peeled off and measured from a multilayer diaphragm that had been subjected to a similar blocking treatment, it was found to be 106 or more. The electrolytic performance is shown in Table 5.

Comparative Example 3 In Example 3, electrolysis was carried out for 50 days using the same membrane, electrolytic cell, and operating conditions as in Example 3, except that the multilayer diaphragm was not subjected to a treatment to block the pores of the porous layer.

The sodium chloride content in LY soda is significantly high;
Liquid leakage outside the tank was also observed. The electrolytic performance is shown in Table 5.

Table 5

Claims (10)

[Claims] (1) A multilayer diaphragm in which a hydrophilic porous material layer with a Gurley number of 1 to 1000 and an ion exchange resin layer are laminated is used as an electrolysis diaphragm in an aqueous solution electrolytic cell that forms an anode chamber and a cathode chamber. An electrolytic method using a multilayer diaphragm, characterized in that the pores of the hydrophilic porous layer of the multilayer diaphragm in a region where the current density is 1/2 or less of the average current density of the membrane are blocked. . (2) The electrolytic method according to claim 1, wherein the area where the pores of the hydrophilic porous layer of the multilayer diaphragm are to be blocked is a tightening area at the periphery of the membrane. (3) The electrolytic method according to claim 1, wherein the blocking treatment area of the multilayer diaphragm is a portion of the diaphragm that does not come into contact with the electrolyte at the upper part of the electrolytic cell. (4) The electrolytic method according to claim 1, wherein the closed region of the multilayer diaphragm is a curved corner portion of the membrane that does not face the effective electrolytic surface of the anode in the finger-type electrolytic cell. (5) Claims 1 to 3, wherein the Gurley number of the porous layer is 10^4 or more due to the pore blocking treatment of the porous layer.
The electrolytic method described in Section 4. (6) The electrolytic method according to any one of claims 1 to 5, wherein the pore blocking treatment is performed by consolidating the porous layer by pressure or pressure and heating. (7) Claims 1 to 5, wherein the blocking treatment is performed by coating and blocking the pores of the porous layer with a chlorine-resistant and preferably alkali-resistant grease or a fluorine-based polymer dispersion. The electrolysis method described in section. (8) The multilayer diaphragm has a pore diameter of 0.01 to 30 μm and a membrane thickness of 30 μm.
~450μ, the surface is a gas release layer, the inside of the pores are hydrophilic, and the ion exchange capacity is 0.5~
The electrolytic method according to any one of claims 1 to 7, which is a multilayer diaphragm comprising a cation exchanger layer having a resin content of 2.0 meq/g and being thinner than the porous layer. (9) The electrolysis method according to any one of claims 1 to 8, wherein the cation exchanger layer is made of a fluorine-containing polymer having sulfonic acid or carboxylic acid as an ion exchange group. (10) The electrolysis method according to any one of claims 1 to 9, wherein the aqueous solution is an aqueous alkali chloride solution.