JPS5935692A - Composite membrane for electrolysis - Google Patents

Abstract

PURPOSE:To provide a titled composite membrane which permits production of alkali hydroxide with a low voltage, is inexpensive and is easy to manufacture, by the constitution wherein rough surface films having liquid permeability and foam desorbability are superposed via a material to be dissolved by electrolysis on an ion exchange membrane. CONSTITUTION:Carbon powder of about <=50mu grain size is dispersed in water by a nonionic surfactant and asbestos fibers of about <=0.1mu diameter and about <=2mm. length are mixed therewith. The mixing ratio of both is controlled adequately at about 2-20 times the carbon powder based on the weight of the asbestos. A dispersed emulsion of a heat resistant and alkali resistant binder of PE, etc., having about <=1mu grain size is added to the liquid mixture, whereby the raw liquid for forming porous layers is prepd. Thin layered Japanese paper 3 which is of about 50mu thickness and is made resistant to water by viscose is held horizontally, and the above-mentioned raw liquid is supplied thereon to form about 50-150mu layer as a material to be dissolved by electolysis. The paper is heated and calcined at about 160-180 deg.C after drying and dehydration, whereby a rough surface film 4 is obtd. Such films 4 are superposed via the paper 3 on a cation exchange membrane 2, whereby a composite membrane 1 is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite membrane for electrolysis that allows alkali hydroxide to be advantageously produced at low pressures.

In ion exchange membrane electrolysis of alkali chloride, especially sodium chloride aqueous solutions, an anode chamber and a cathode chamber are generally separated by a cation exchange membrane, and the anode faces the anode surface of the cation exchange membrane, and the cathode faces the cathode surface. , the anode chamber is filled with a sodium chloride aqueous solution and the cathode chamber is filled with a sodium hydroxide aqueous solution, and the sodium chloride concentration of the anolyte is adjusted to 200 to 220 f/°.
/, electrolysis is performed by supplying salt water and pure water to maintain the sodium hydroxide concentration in the catholyte at 25 to 35% by weight, producing chlorine gas in the anode chamber and sodium hydroxide and hydrogen gas in the cathode chamber. I try to do that.

The progress of water droplet technology in recent years has been remarkable, and effective means for reducing power costs as an energy saving measure, such as optimizing the electrode shape, shortening the distance between electrodes, reducing the hydrogen overvoltage of the cathode, and the unique characteristics of ion exchange membranes, have been developed in recent years. Measures to prevent hydrogen bubbles from adhering to the ion exchange membrane by reducing resistance and roughening the surface have been developed and implemented. It is related.

At the American Electrochemical Society meeting held in October 1977, it was reported that hydrogen gas bubbles generated by electrolysis tend to adhere to the ion exchange membrane surface, and that preventing bubbles from adhering is effective in reducing sliding voltage. Ever since this was published by Mr. Beltsin of DuPont, measures have been proposed to prevent the adhesion of air bubbles by forced circulation of the catholyte, addition of surfactants, etc. Recently, in order to bring the anode and cathode close to the ion exchange membrane and minimize the distance between the electrodes to minimize solution resistance and reduce the electric voltage, at least one of the cathode or anode is made of gold or ion exchange membrane. An electrolytic cell with a structure in which the anode is in close contact with the membrane surface has been proposed, but while it is effective to have the anode in close contact with the membrane surface, on the cathode side, hydrogen gas forms fine bubbles and adheres to the ion exchange membrane, causing damage to the ion exchange membrane. Since the current of
If the cathode is brought close to the membrane, the voltage will actually increase, and if the cathode is brought into close contact with the membrane, current concentration will occur between the electrodes, not only increasing the voltage but also degrading the performance of the ion exchange membrane. This will lead to unfavorable results. In addition, when an anode is placed in close contact with an ion exchange membrane, the coating material becomes brittle due to alkali migrating back from the cathode side, causing a phenomenon in which the anode potential increases and the sliding voltage increases.

In order to prevent this phenomenon and reduce the sliding voltage, we applied the principle in nature in which the villi on the leaves of plants repel water droplets and turn them into water beads. A method of roughening the surface by heat pressing, polishing, dry blasting, etching, glow discharge, etc.
0786.57-39187 etc.), secondly, a gas and liquid permeable porous layer made of inorganic powders and particles such as metal oxides and metal nitrides that do not act as electrodes is placed on the surface of the ion exchange membrane. A method of forming by heating and pressing together with a binder such as a Teflon binder (Japanese Unexamined Patent Publication No. 56-75583
．． 56-112487, etc.), and thirdly, a porous filtration film between the cathode and the ion exchange membrane, which is designed to prevent hydrogen bubbles from adhering to the ion exchange membrane, is removable. A structure that is layered on a flexible porous wire mesh with low hydrogen overvoltage and adhered to the ion exchange membrane (Japanese Patent Laid-Open No. 56-38
486) has been proposed.

These methods are excellent in principle because they prevent air bubbles from adhering to the film surface and enable a reduction in sliding voltage. However, in the first method, for example, polishing the ion exchange membrane with sandpaper or the like to make it rough makes it difficult for hydrogen bubbles to adhere to it and makes it possible to reduce the voltage, but it results in damage to the ion exchange membrane. However, the second method has the disadvantage of impairing the durability of the membrane and significantly shortening its lifespan.
(In order to eliminate the need for advanced technology and expensive mechanical equipment to heat and press the porous layer to a uniform thickness over the entire wide membrane surface of existing ion exchange membranes, the cost is reduced by reducing the voltage.)
Not only does it consume most of the benefits that can be obtained12, but it also impairs the physical properties of the ion exchange membrane and shortens its lifespan.
Porous materials tend to peel off due to changes in size and thickness due to contraction, expansion, etc. due to various conditions inside the electrolytic cell, and there are disadvantages in that strict pouring is required for handling.

In addition to this, a method has been proposed in which a porous layer is formed using Teflon particles instead of metal oxides for the purpose of preventing peeling (Japanese Patent Application Laid-Open No. 1983-60081), but this requires special and advanced processing technology. Therefore, the cost is high, and it is still difficult to find it economically advantageous. Furthermore, the third
Regarding the method of JP-A No. 57-40081, films in the form of hydrophilically treated polyflon seals, Teflon woven fabrics, etc. have a substantially high membrane resistance and In addition, the ability of hydrogen bubbles to separate is insufficient, and since the electrical connection between the flexible low hydrogen overvoltage wire mesh and the rigid cathode plate is made by crimping, uniform crimping is difficult on a practical scale, resulting in voltage loss due to contact resistance. Therefore, it is not possible to easily reduce the cell voltage, and in order to obtain an effective cell voltage reduction, a high degree of precision is required in assembling the electrolytic cell.

Based on the above considerations, the present inventors have conducted various studies in pursuit of means that can be applied on a practical scale using inexpensive materials and simple techniques. As a result, for example, the inventors have found that water resistance can be imparted through viscose processing. Graphite powder, asbestos fiber,
After uniformly forming a thin layer of a compound such as a polymeric binder using a papermaking method, a rough membrane obtained by a relatively simple and easy method of drying and baking is applied to an ion exchange membrane and wetted. This composite membrane has good adhesion when pressure-adhered to the electrode surface, gas bubble release properties, and stability under electrolytic conditions. It has been found that electrolyzing the voltage jF can be reduced.

That is, the present invention provides an electrolytic composite in which a rough membrane having liquid permeability and bubble separation property is integrally laminated on the cathode and/or anode side of a cation exchange membrane via a substance that is dissolved by electrolysis. It is a membrane, and will be explained below based on the attached drawings.

FIG. 1 is a sectional view showing an example of a composite membrane for electrolysis according to the present invention.

1, at least the anode and cathode portions are formed of a cation exchange membrane 2, and both surfaces thereof have liquid permeability and bubble separation properties formed by a method described later through a substance 3 that is dissolved by electrolysis. It is a composite membrane formed by overlapping 111-sided membranes 4, and the substance 5 that dissolves by electrolysis is
For example, it is best to use Japanese paper that is made to a thickness of about 50μ and has water-repellent properties, or woven silk.
The rough surface film 4 is preferably formed by laminating a mixture of graphite powder, titanium oxide powder, asbestos, and the like.

FIG. 2 is a longitudinal sectional view showing the composite membrane installed in an electrolytic cell for alkali chloride electrolysis.

Reference numeral 5 denotes a plurality of porous and hollow tubular cathodes made of conductive metal such as iron, stainless steel, or nickel. and the electrolytic cell body are integrated. 6 is
The bottom plate of an electrolytic cell is made by laminating a corrosion-resistant sheet 8 made of fluorine resin or the like on one of the power supply plates 7, and a conductive rod (described later) can pass through the bottom plate 6 at an intermediate position between two adjacent cathodes 5.5. A plurality of circular holes 9 are bored. 10 is a cylindrical conductive rod made of copper or the like, with a screw 11 carved in the lower part and a protrusion 12 horizontally formed slightly above the screw 11; One outer peripheral surface is coated with butane, titanium alloy, etc. ;413 is coated.

The conductive rod 10 is inserted into the circular hole 9 from above so that the lower surface of the protrusion 12 contacts the bottom plate 6, and is fixed vertically to the bottom plate 6 by screwing the nut 14 into the screw 11. . Reference numeral 15 denotes a molded body in which the composite membrane 1 is molded into a bag shape that opens at the top, and a through hole having the same diameter as the cutout 13 protrusion 12 is bored in the lower part, and the molded body 15 includes: It is joined to the outer edge of the protrusion 1-2. 16 and 17 are a pair of sealing materials that sandwich the vicinity of the outer edge of the protrusion 12 of the molded body 15, and the sealing material 16fJ on the - side is made of fluororesin that has durability against chlorine generated in the anode chamber. is desired (7ku,
It is economical to make the lower sealing material 17 made of ordinary rubber. 18tJ is a flange fixed by welding to the upper surface of the protrusion 12 and the lower outer periphery of the covered layer 13, and 19 is fixed between the upper seal 1A and the flange 18 in order to protect the molded body 15. This is a glob lid made of fluororesin. 20 is the conductive rod 1
This anode 20 and the cathode 5 are in close contact with both surfaces of the molded body 15, and the distance W1 between the electrodes is substantially equal to the thickness of the molded body 15. ing.

In this example, the anode and cathode are brought into close contact with the composite membrane, but the present invention is not limited thereto. Alternatively, only the electrode may be brought into close contact with the electrode. Also,
'The structure of the electrolytic cell is not limited to the above example, and may be a filter press type electrolytic cell. It should be noted that the Japanese paper and the like present in the rough surface film when raised and lowered in the negative direction are dissolved and disappeared by electrolysis.

Next, a method for forming a rough surface film in the present invention will be explained. In order to form a surface that is repellent to air bubbles, it is effective to use a material that corresponds to the protruding surfaces on the leaf surfaces of plants and the magnetic needle-like composite surfaces that hold spaces. In the present invention, carbon powder, titanium oxide powder, etc. can be used as equivalent to the former, and asbestos fiber, calf+in fiber, etc. can be used as complementary to the latter. As an example, the rough surface film shape will be explained.

As carbon powder, use graphite powder, activated carbon, peat charcoal, etc. with a particle size of 5071 or less.
White asbestos with p or less is thoroughly opened by milling, and the length is 2.
Before use, sieve to 10 to 30%
After boiling in an aqueous IJ solution to elute the dissolved components, the fibers are separated by sedimentation from an aqueous sodium hydroxide solution (17) and washed with pure water to suspend the fibers in water with a pH of 8 to 10. Put C.

To this, mix 2 to 20 times the amount of asbestos-type can of 112 graphite powder, which was previously stirred with a nonionic surfactant and sufficiently dispersed in water, with the asbestos fibers, and gently stir. As a result, graphite powder is adsorbed into the tangles of loose asbestos fibers and is uniformly mixed and dispersed. The content I of graphite powder and asbestos fiber is 1 to 1°f/100f 112
A value of 0 is desirable, and strong stirring or long-time stirring must be avoided since it will granulate the mixture of fibers and graphite powder into lumps.

The thus obtained mixture was heated to a particle size of 1 p at a temperature below 15°C.
The following dispersion emulsion of a heat-resistant and alkali-resistant binder such as polyethylene or polytetrafluoroethylene is added, and stirring is performed to the minimum necessary for uniform mixing to obtain a raw material solution for forming a rough porous layer. This is placed on a screen on which washi paper made to a thickness of about 50p and made water-resistant by viscose processing is placed flat, and the thickness is 20p to 200/J, preferably 50p.
The material is supplied so as to have a p-to-150 μm, p-watered to form a rough-surfaced porous layer, dried and dehydrated, and then heated and fired at 160-180°C.

The rough surface membrane thus obtained has sufficient flexibility, the Japanese paper and the rough surface porous layer formed thereon do not peel off easily, and furthermore, it has appropriate gas and liquid permeability and hydrophilicity. ing.

In the present invention, this porous rough membrane is superimposed on the cathode surface and/or anode surface of the ion exchange membrane in an ion exchange membrane electrolytic cell, and the expanded band anode and/or expanded band cathode made of the porous electrode material and the ion It is used by being inserted in close contact with an exchange membrane, or it is used by being inserted between an anode and a cathode of a filter press type electrolytic cell. The ion exchange membrane used in the present invention includes carboxylic acid groups,
Any perfluorocarbon-based membrane having a sulfonic acid group or sulfonamide group, which is generally used in ion-exchange removal alkaline electrolysis, and which has not undergone any special surface treatment can be used. As an anode, a so-called dimensionally stable electrode (DSE) is used, which is made by coating the surface of a porous base material made of titanium such as expanded metal, punched metal, or menoshiko with platinum group metal or its oxide. As a cathode, a porous material similar to the anode made of materials such as iron, nickel, and stainless steel, or a porous material made of materials such as iron, nickel, stainless steel, etc.
The hydrogen overvoltage is reduced by special plating such as hXCo, or by thermal spray coating with nickel or nickel oxide.

The electrolytic voltage of the electrolytic cell assembled in this way is extremely small and stable, with a fluctuation range of 0 to 3 mV. , 7t below? The voltage increase appearing at X disappears, the solution resistance decreases due to the shortening of the electrode gap, and the ion exchange Jf% film aging effect of gas bubbles is eliminated, resulting in a significant reduction in JE. In addition, heat-pressing furnace trowel or organic powder directly onto the ion-exchange membrane surface, or using lindoper, lintoplast, etc., to damage the membrane surface; In particular, it has the characteristic that a rough surface film can be formed at low cost because of the ease of raw materials and processing without causing any trouble that would affect the life of an expensive film.

Therefore, there is concern that the concentration gradient between the ion exchange membrane surface and the electrolyte in the cathode compartment or anode compartment or in the alkali hydroxide or alkaline salt aqueous solution becomes large due to the presence of the rough membrane, resulting in a decrease in current efficiency. In fact, when the formation of a rough membrane and the degree of adhesion between it and the ion exchange membrane are inadequate, a phenomenon occurs that reduces the current efficiency of alkali hydroxide production.
By appropriately selecting the thickness, porosity, air permeability, and hydrophilicity of the roughened membrane, these phenomena can be suppressed to an extremely small level.

In addition, in the so-called zero-gap method in which the electrode is closely attached to the ion exchange membrane, in order to prevent the membrane from being damaged by the edges or protrusions of the electrode, the surface is usually processed with 7-Rats or a flexible mesh without edges is used. is generally used by bonding it to a rigid filler, but in the present invention, since the porous rough membrane plays the role of protecting the ion exchange membrane surface, it is not necessary to take these considerations into consideration. There isn't. or,
The surface of the low hydrogen overvoltage cathode activated by means such as nickel spraying has minute protrusions that create hinholes when pressed against the ion exchange membrane, so the surface of the low hydrogen overvoltage cathode has a low hydrogen overvoltage IJ:
Taking advantage of the characteristic zero gap, the composite membrane of the present invention has the feature of enabling a zero gap without damaging the ion exchange membrane and being able to maintain a lower electrolytic voltage.

In addition, in the composite membrane of the present invention, it is possible to insert the rough surface membrane on the cathode side or on both sides of the cathode and the anode, but ll'!i-
The cathode (1111) is effective for the cathode (1111).As described in detail L7, the present invention integrates a rough membrane having liquid permeability and bubble separation property on the cathode and/or anode side of the cation exchange membrane. A composite membrane is formed in conjunction with 7, and since hydrogen generated by electrolysis does not adhere to the membrane surface, the shielding effect caused by bubbles is eliminated, and a voltage increase due to bubbles does not occur. Since the exchange membrane itself is not damaged, the life of the membrane will not be shortened.Furthermore, the composite membrane can be manufactured at low cost without using advanced technology. Since the expensive cation exchange membrane is protected, it is also possible to avoid interposing a protector gold between the composite membrane and the electrode to prevent the cation exchange membrane from being damaged.

Example 1 1f of chrysotile asbestos fibers of Canadian standard 6 class 6D were immersed in 100 ml of IJum aqueous solution (hydroxidized at a concentration of 10%), heated at 90°C for 1 hour, allowed to cool and settle, and a supernatant caustic solution was separated. . Subsequently, pure water 21 is added to make the fully opened asbestos fibers into a floating suspension state, a small amount of sedimented components are separated by decantation, and the supernatant is removed by sedimentation. Prepare 100ml of asbestos-containing water with a pH of 9 containing single fibers of 0.94F, then add 3f of graphite powder with a particle size of 30μ or less to 100tnl of pure water to which a trace amount of nonionic surfactant has been added]1, stir, and add to the water. Dispersed. Next, asbestos dispersion water was added and stirred to prepare a dispersion of graphite and asbestos, and then a dispersion containing 60 grams of 1 μL plastic tyrene resin with an average particle size of 0.2 to 0.4 p was prepared. 3 ml was added and mixed to prepare about 200 ml of porous layer forming stock solution.

On the other hand, on the screen of Air Suki Oke I, which has a papermaking screen with a length of 10an and a width of 25α, a viscose coating with a thickness of about 50p cut to the flange size around the screen's outer periphery was applied to make it water resistant. Spread a thin layer of Japanese paper, set the Air Suki Oke I, and after fixing the Japanese paper on the screen, pour pure water 5 cm above the screen! ! Brewed with

The above porous layer forming stock solution was injected into this, stirred according to papermaking procedures to uniformly disperse it, and then drained to form a composite porous layer consisting of graphite particles and asbestos fibers on Japanese paper-L. I let it happen.

Next, after drying by air drying, the screen was peeled off, transferred to an electric furnace, and heated and baked at 160°C for 60 minutes to obtain 111
Completed the membrane. The average thickness of the porous layer on Japanese paper is 1
26±15μ, porosity was 72%.

The surface film obtained in this way is 2.5 dm in layer area.
An electrolytic test was carried out by installing it in a vertical fermentation tank using an ion-exchange membrane method. The ion exchange membrane is Denipon's Nafion 901, and the anode is titanium extracted band metal (length: 6 ttm).
A DSE electrode whose surface is coated with ruthenium oxide and iridium is used as the cathode, and an active electrode sprayed on 5U8310B@exband metal (major axis 6n-++x minor axis 55 mm) is used as the cathode. A rough membrane was inserted between the ion exchange membranes, and the anode, which was expandable by a spring, was brought into contact with pressure at about 0.15 Kf/Clft to adjust the distance between the electrodes to about 0.5 wm, and the anode chamber was filled with saline. Concentration to 200
At f/13, the sodium hydroxide concentration in the cathode chamber was adjusted to 32
When electrolysis was carried out at a temperature of 90° C., the interelectrode voltage was as follows.

Current density (A/dm”) Electrode voltage (V') 20
2.94 30 3.16 Moreover, the increase in instantaneous variation in the cell voltage that normally appears when the electrode spacing is about 2 m or less was eliminated, and an extremely stable voltage with a variation range of 0 to 3 mV was exhibited.

After the start of electrolysis, it was operated at 5 OA/dm' for 30 days, during which the voltage remained almost constant, and the current efficiency during that period was 96.8 cm. Electricity WFWzO stops operation,
After leaving it for two days, it was restarted, but the voltage was immediately restored to the voltage before the shutdown.

f1 operation 1 [] After Fl, the tank was stopped and the tank was opened.The condition of the C111 surface membrane and the ion exchange membrane was observed.The appearance of the rough surface membrane was clearly adhered to the ion exchange membrane (7), and no abnormalities such as peeling were observed. When the rough membrane that could not be removed was artificially exposed to q-1 using ion exchange IA, the Japanese paper dissolved and disappeared.
The surface of the ion exchange membrane (usually young) had no stains such as stains, and remained in almost the same clean condition as before use.

Example 2 Chrysotile asbestos fiber of NoJNada standard 7 class 7F 0.
81? was heated with sodium hydroxide in the same manner as in Example 1,
Rinse with water (1) and add 2V of activated carbon powder with a particle size of 20p or less prepared in advance to 100mg of asbestos-containing water with a pH of 8.8.
The porous layer stock solution obtained by mixing the dispersion liquid dispersed in water of m/m/m and adding 5 ml of 60% by weight PTFFJ disverge reagent to this was prepared using the same method as in Example 1 to prepare a porous layer with a paper area of υ. 10I: For rn
Baked for 0 minutes. Divide the obtained rough surface membrane into two to make an electrolytic area of 1
An active cathode coated with Rh on nickel extract band metal with 2 wI!! in major axis x 1 fin in minor axis was superimposed on the anode and cathode sides of the ion exchange membrane of the electrolytic cell of ``DM''. It is placed on a two-layer electrode made by welding expanded nickel metal, and faces the anode, which has the same two-layer shape as the cathode and has an expandable spring structure made by coating titanium with PT and Ir. , about 0.I
When the electrodes were crimped with Kp/+7 and electrolyzed with the actual interpole distance set to 0.6, the following results were obtained.

Current density (A/dm') Electrode voltage (V) 20
2.92 30 3, 13 It was operated for 10 days at a current density of 30 A/dm", a sodium hydroxide concentration of 30 wt%, and a temperature of 90°C, but the voltage remained stable with extremely small instantaneous fluctuations, and the current efficiency during this period was It was 96.8%.

Comparative Example 1 The distance between the ion exchange membrane and the anode was Ow without inserting the rough membrane.
When an electrolytic cell was assembled and operated for 10 days under the same conditions as in Example 1 except that the distance between the ion exchange membrane and the cathode was set to 7 &: 2 m, the following results were obtained.

Current density (A/dm'') Voltage between electrodes (V) 20
3.0130
3.24 The instantaneous voltage fluctuation range was ±14 mV, and the current efficiency during this period was 94.4 cm.

Comparative Example 2 Without inserting the rough membrane, the distance between the ion exchange membrane and the anode was set to 01,
An electrolytic cell was assembled under the same conditions as in Example 2 except that the distance between the ion exchange membrane and the cathode was 2 tm, and when it was operated for 15 days, the following results were obtained.

Current density (A/dm') Voltage between electrodes (V)2 [
] Ro, 0030 3.22
The instantaneous voltage fluctuation range was ±18 mV, and the current efficiency was 94.2 cm.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a composite membrane for electrolysis according to the present invention, and FIG. 2 is a longitudinal sectional view showing the composite membrane installed in an electrolytic cell for alkali chloride electrolysis. 1... Composite membrane 2... Cation exchange membrane 3... Soluble substance 4... Rough surface membrane 5... Cathode 15... ...Molded body 20...Anode

Claims (3)

[Claims] (1) On the cathode and/or anode side of the cation exchange membrane,
[Composite membrane for MY] characterized by integrally laminating rough membranes having liquid permeability and bubble releasability via a substance that dissolves by electrolysis. (2) 7! , special #Tii? in which the substance dissolved by the solution is thin Japanese paper? +# The electrolytic composite membrane according to the desired range (1). (3) The composite membrane for electrolysis according to claim (1) or (2), wherein the rough surface membrane comprises carbon powder, asbestos fibers, and a binder.