JPS5935689A - Electrolytic cell by ion exchange membrane - Google Patents

Abstract

PURPOSE:To provide a titled electrolytic cell which protects inexpensively a cation exchange membrane with a simple technique and can operate on a low voltage, by the constitution wherein a cathode or/and anode are adhered tightly to the cation exchange membrane via rough surface films having liquid permeability and foam desorbability. CONSTITUTION:Rough surface films 14 having liquid permeability and foam desorbability are integrally superposed with a material 13 which is dissolved by electrolysis on both surfaces of a cation exchange membrane 12 to form a composite membrane 11, and a cathode 1 and an anode 19 placed oppositely to the films 14 are adhered tightly to the films 14 in an electrolytic cell by a vertical ion exchange membrane method for electrolysis of an aq. alkali chloride soln. which produces alkali hydroxide. The cathode 1 is formed by plating Rh, etc. on a base material of iron or the like which is made porous. The anode 19 is formed by plating Pt or the like on a base material of Ti, or the like which is made porous, and both electrodes are mounted to the top part of a conductive bar 6 of copper or the like. The rough surface films 14 of the composite membrane 11 are obtd. by supplying a raw material liquid contg. carbon powder, asbestos fibers and a binder onto soluble Japanese paper to form a porous layer and calcining the same after filtering, drying and dehydrating.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved ion-exchange removal electrolytic cell, and particularly to a vertical ion-exchange removal electrolytic cell for aqueous alkali chloride solution electrolysis, which allows alkali hydroxide to be advantageously produced at low voltage.

In membrane electrolysis where ions of alkali chloride, especially sodium chloride aqueous solution, are exchanged, an anode chamber and a cathode chamber are generally separated by a cation exchange membrane, and the anode faces the anode side of the cation exchange membrane, and the cathode faces the cathode side. Fill the anode chamber with a sodium chloride aqueous solution and the cathode chamber with an IJium aqueous solution to bring the sodium chloride concentration of the anolyte to 200 to 220f.
/e, the catholyte is hydroxylated) The IJ concentration is 25 to 6.
Salt water and pure water are supplied and electrolyzed so as to maintain the temperature at 51 cm, so that chlorine gas is produced in the anode chamber, and sodium hydroxide and hydrogen gas are produced in the cathode chamber.

The technology of this method has made remarkable progress in recent years, 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 using ion exchange membranes, have been developed. Measures to prevent hydrogen bubbles from adhering to the ion exchange membrane by reducing the specific resistance and roughening the surface have been developed and implemented. This is related to.

At the American Electrochemical Society meeting held in October 1977, it was reported that hydrogen gas bubbles produced by 1JiLM tend to adhere to the ion exchange membrane surface, and that preventing the bubbles from adhering is effective in reducing the sliding voltage. Since something was published by Mr. Beltwin of DuPont, forced circulation of the catholyte,
Measures have been proposed to prevent the adhesion of air bubbles, such as by adding a surfactant. Recently, in order to bring the anode and cathode closer to the ion exchange membrane and to minimize the distance between the electrodes to minimize solution resistance and reduce electrolysis voltage, at least one of the cathode or anode has been brought into close contact with the surface of the ion exchange membrane. However, while it is effective to have the anode in close contact with the membrane surface, on the cathode side, hydrogen gas becomes fine bubbles and adheres to the ion exchange membrane, causing the current to flow to that part. is shielded, so if the cathode is brought close to the membrane, it will actually cause an increase in voltage, and if the cathode is brought into close contact with the membrane, current concentration will occur between the electrodes, and the voltage will not only increase by -1- , which will have the disadvantageous effect of deteriorating the performance of the ion exchange membrane. or,
When an anode is placed in close contact with an ion exchange membrane, the coating material becomes brittle due to the 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 hairs 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 powder/particles such as metal oxides and metal nitrides that does not function as an electrode 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 film between the cathode and the ion exchange membrane with the purpose of preventing hydrogen bubbles from adhering to the ion exchange membrane is removable and flexible. A structure that is stacked on a porous wire mesh with a low hydrogen overvoltage and closely adhered to an ion exchange membrane (Japanese Patent Application Laid-Open No. 56-58486
) has been proposed.

These methods are excellent in principle if they can prevent bubbles from adhering to the film surface and reduce the sliding voltage.

However, in the first method, the ion exchange membrane whose surface is roughened by sandpapering, for example, does not allow hydrogen bubbles to adhere to it and makes it possible to reduce the voltage, but it does not damage the ion exchange membrane. However, the disadvantage is that the durability of the membrane is impaired and the life of the membrane is shortened. In addition, the second method requires advanced technology and expensive mechanical equipment to heat and press the porous layer to a uniform thickness over the entire wide membrane surface of the existing ion exchange membrane, resulting in lower processing costs and lower voltage. Not only does this consume most of the benefits obtained by using the ion conversion membrane, it also impairs the physical properties of the ion conversion membrane and may shorten its lifespan. Porous materials tend to peel off due to changes in dimensions and thickness due to shrinkage, expansion, etc. due to various conditions, and they have the disadvantage that strict care is required when handling them.

In addition, a method has been proposed in which a porous layer is formed using Teflon particles on a metal oxide adhesive for the purpose of preventing peeling (Japanese Patent Application Laid-open No. 57-60081).
Since the holding process requires advanced processing technology, the cost is high, so it is still difficult to say that it is economically advantageous. Furthermore, regarding the third method, films in the form of hydrophilically treated polyflon seals, Teflon woven fabrics, etc., as disclosed in JP-A-57-60081, have substantially the same membrane resistance. Because the hydrogen bubbles are large and the release properties of the hydrogen bubbles are not sufficient, and because 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, and contact resistance It is not easy to reduce the cell voltage due to voltage loss, and in order to effectively reduce the cell voltage, a high degree of precision is required in starting up the electrolytic cell.

Based on the above considerations, the present inventors have conducted various studies in pursuit of methods that can be applied on a practical scale using inexpensive materials and simple techniques. Graphite powder, asbestos fiber,
A rough membrane obtained by a relatively simple and easy method of uniformly forming a thin layer of a compound such as a polymeric binder using a papermaking method and then drying and baking is layered on an ion exchange membrane and moistened. This composite membrane has good adhesion when pressure-adhered to the electrode surface, good gas bubble release properties, and stability under electrolytic conditions. It has been discovered that electrolysis can reduce the sliding voltage.

That is, the present invention forms a composite membrane by integrally superimposing a rough membrane having liquid permeability and bubble releasability on the cathode and/or anode side of a cation exchange membrane via a substance dissolved by electrolysis. This is an ion-exchange dehydration electrolytic cell in which the rough-surfaced membrane is brought into close contact with opposing electrodes, and will be specifically described below with reference to the accompanying drawings.

FIG. 1 is a longitudinal cross-sectional view showing an example of an ion-exchange removal electrolytic cell according to the present invention, and FIG. 2 is an enlarged cross-sectional view of the main parts.

1 is a plurality of porous and hollow tubular cathodes made of conductive metal such as iron, stainless steel, or nickel; the cough cathode 1 extends from one inner side wall of the electrolytic cell body to the opposite inner side wall; The electrolytic cell body is integrated into one. 2 is
A bottom plate of an electrolytic cell formed by laminating a corrosion-resistant sheet 4 made of fluororesin or the like on a power supply plate 3, and two adjacent cathodes 1 on the bottom plate 2.
．． A plurality of circular holes 5 through which conductive rods, which will be described later, can pass through are bored at intermediate positions of the holes 1. Reference numeral 6 denotes a cylindrical conductive rod made of copper or the like with a screw 7 carved in the lower part and a protrusion 8 horizontally formed slightly above the screw 7, and the outer peripheral surface of the conductive rod 6 above the protrusion 8. is coated with a coating layer 9 made of titanium, titanium alloy, or the like.

The conductive rod 6 is inserted into the circular hole 5 from above so that the lower surface of the protrusion 8 comes into contact with the bottom plate 2, and the nut 1 is attached to the screw 7.
0 are screwed together and fixed vertically to the bottom plate 2. 11
is a bag-shaped composite membrane with a through hole having the same diameter as the protrusion 8 in its lower part and an opening at the top, and is fitted onto the outer edge of the protrusion 8. This composite membrane 11 has at least the portion facing the anode and cathode formed of a cation exchange membrane 12, and has liquid permeability and air bubbles formed by a method described later through a substance 13 that is dissolved by electrolysis on both surfaces. The rough surface film 14 having releasability is separated into a car. Examples of substances that can be dissolved by electrolysis include paper No. 11 made into paper of about 50μ and coated with water resistance. It is preferable to use woven silk, etc., and the rough surface membrane 14 is preferably formed by laminating a mixture of graphite powder, titanium oxide powder, asbestos, etc. 15 and 16 are a pair of sealing materials that sandwich the vicinity of the outer edge of the protrusion 8 of the composite membrane 11;
For 5, it is desirable to use fluorine thread resin that has durability against chlorine generated in the anode chamber, and for the sealing material 1 on the F side.
6 is economically preferable to be made of ordinary Goto.

17 is a flange fixed by welding to the upper surface of the protrusion 8 and the outer periphery of the coating layer 90F, and 18 is fixed between the upper sealing material 15 and the flange 170 in order to protect the W gold film 11. A protector made of fluororesin. Reference numeral 19 denotes a net-like expandable anode connected to the upper part of the conductive rod 6. This anode 19 and the cathode 1 are in close contact with the screen of the composite membrane 11, and the distance between the electrodes is substantially equal to the composite membrane 1.
The thickness is equal to 1.

In this example, the anode and cathode were brought into close contact with the composite membrane, but the present invention is not limited to this. A rough membrane was formed only on one side of the cation exchange membrane, and only that side was used as an electrode. They may be brought into close contact. Furthermore, the structure of the electrolytic cell is not limited to the above example, and may be a filter press type electrolytic cell. In the above example, the Japanese paper etc. present in the rough surface film are dissolved and disappear 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 a protruding surface on the leaf surface of a plant and a magnetically attracted composite surface that holds space. In the present invention, carbon powder, titanium oxide powder, etc. can be used as the former, and asbestos fiber, carbon fiber, etc. can be used as the latter. The formation of a rough surface film will be explained.

As carbon powder, graphite powder with a particle size of 50p or less, activated carbon,
Using peat, etc., asbestos is made by milling white asbestos with a fiber diameter of 011p or less and thoroughly opening it to a length of 2Ilf.
10 to 5 sifted to below fI+ before use
0qb of hydroxide) is boiled in a lium aqueous solution to elute the dissolved components, and then hydroxylated) Separated by sedimentation from an IJ ium aqueous solution and washed with pure water, leaving the fibers suspended in water with a pH of 8 to 10. I'll leave it as that.

To this, 2 to 20 times the asbestos weight of the graphite powder is stirred in advance with a nonionic surfactant to sufficiently disperse it in water, and then mixed with the asbestos fiber and gently stirred. Graphite powder is absorbed into the tangles of floating asbestos fibers and is evenly mixed and dispersed. The content of graphite powder and asbestos fibers is desirably 1 to 10 f/100 fHxO, and strong stirring or long-time stirring must be avoided since the mixture of fibers and graphite powder will be granulated into lumps.

A dispersion emulsion of a heat-resistant and alkali-resistant binder such as polyethylene or polytetrafluoroethylene with a particle size of 1 p or less is added to the thus obtained mixed liquid at a temperature of 15°C or less, and the minimum stirring necessary for uniform mixing is carried out. A raw material solution for forming a rough porous layer is obtained.

This is placed on a screen flatly placed with Japanese paper made to a thickness of about 50μ and made water-resistant by viscose processing, to a thickness of 20μ to 200μ, preferably 50μ to 150μ.
The material is supplied so as to have a rough surface porous layer, and after being dried and dehydrated, it is heated and fired at 160 to 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, the porous rough membrane thus obtained is
It is used by being superimposed on the cathode surface and/or the anode surface of the ion exchange membrane in an ion exchange membrane electrolytic cell, and inserted and brought into close contact between the expanded band anode and/or expanded band cathode made of porous electrode material and the ion exchange membrane. Alternatively, it is used by being inserted between the anode and cathode of a filter press type electrolytic cell.

The ion exchange membrane used in the present invention is a perfluorocarbon-based membrane having a carboxylic acid group, a sulfonic acid group, or a sulfonamide group, etc., and has been subjected to a special surface treatment commonly used in alkaline electrolysis. Any of the following membranes can be applied. As an anode, a so-called dimensionally stable electrode (I) is formed by coating the surface of a porous substrate such as expanded metal or punched metal mesh made of titanium with platinum group metal or its oxide.
), but the cathode and 1.7 are porous substrates made of materials such as iron, nickel, and stainless steel, similar to the IJ4 electrodes, or special metal hollows such as Rh and On, or nickel and nickel oxide on their surfaces. Hydrogen overvoltage is lowered by 1 level by applying treatments such as thermal spray coating.

The fluctuation range of the electrolytic force and pressure Q of the electrolytic cell assembled in this way is extremely small and stable at 0 to 3 mV, and the gap between the cathode and the ion exchange membrane, which was a common phenomenon in the past, has been reduced to 2. The voltage increase that appears when the voltage is lower than 100 nm disappears, the solution resistance decreases due to the shortening of the electrode distance, and the ion exchange membrane shielding effect of gas bubbles is eliminated, making it possible to obtain a significant pressure reduction and to directly Do not heat or press inorganic or organic powder onto the ion-exchange membrane surface, or use sandpaper, sandblasting, etc. to damage the membrane surface, which may affect the inherent properties of the membrane, especially the lifespan of expensive membranes. It has the feature that it does not cause any damage and can form a rough surface film at low cost due to the ease of raw materials and processing.

Therefore, 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,
There is a concern that the presence of a rough membrane may result in a decrease in current efficiency, and in fact, when the rough membrane is formed and the adhesion between the ion exchange membrane and the ion exchange membrane is inappropriate, the current efficiency for alkali hydroxide generation is reduced. However, these phenomena can be minimized by appropriately selecting the thickness, porosity, air permeability, and hydrophilicity of the roughened membrane.

In addition, in the so-called zero-gap method in which the electrode is closely attached to the ion exchange membrane, the surface is usually flattened or a flexible mesh without edges is used to prevent the membrane from being damaged by the edges or protrusions of the electrode. However, in the present invention, since the porous rough membrane serves to protect the ion exchange membrane surface, these considerations are not necessarily taken into account. There's no need. In addition, the surface of the low hydrogen overvoltage cathode activated by means such as nickel spraying has minute protrusions that create pinholes when pressed against the ion exchange membrane, making it difficult to utilize the positive characteristics for low hydrogen overgamma to zero gap. However, the porous membrane of the present invention has the feature that it enables a zero gap without damaging the ion exchange membrane and can maintain a lower electrolytic voltage.

In the electrolytic cell of the present invention, the roughened membrane can be inserted on the cathode side or on both sides of the cathode and anode, but it is particularly effective on the cathode side.

As detailed above, the present invention forms a composite membrane by integrally superimposing a rough membrane having liquid permeability and bubble releasability on the cathode and/or anode side of a cation exchange membrane. The membrane is brought into close contact with the electrodes of the ion-exchange dehydration electrolyzer, and hydrogen generated during electrolysis does not adhere to the membrane surface, eliminating the shielding effect of air bubbles and preventing voltage increases due to air bubbles. Furthermore, since the cation exchange membrane itself is not damaged, the life of the membrane will not be shortened.

Furthermore, the composite membrane does not require sophisticated technology and can be manufactured at low cost. Moreover, since the rough surface membrane protects the expensive cation exchange membrane, it is possible to eliminate the need for a protector between the composite membrane and the electrode to prevent damage to the cation exchange membrane. .

Example 1 1f of Canadian standard 6 class 6D chrysotile asbestos fibers was hydroxylated at a concentration of 1.0%) +7um aqueous solution 100ml
After heating at 90°C for 1 hour, the mixture was allowed to cool and settle to separate the supernatant caustic solution. Subsequently, add 2 ml of pure water to make the asbestos fibers that have been sufficiently opened into a floating suspension state, separate a small amount of sedimented components by decantation, let it settle and remove the supernatant, and then repeat the same operation. 100 m of asbestos-containing water with a pH of 9 and containing 0.94 F of floating single fibers was prepared.

Next, 100m7 of pure water containing 3f of graphite powder with a particle size of 30p or less and a trace amount of nonionic surfactant added! and stirred to disperse in water. Next, the asbestos dispersion water was added and stirred to prepare a dispersion of graphite and asbestos, and then 60% by weight R% of tetrafluoroethylene resin with an average particle size of 0.2 to 0.41 t was added.
Disverge air containing 3mal f added and mixed,
Approximately 200 ml of porous layer forming raw material solution was prepared.

On the other hand, on one screen of a pigeon plow box for paper making, which has a paper making screen measuring 10 rrn in length and 25 rrn in width, a sheet of paper with a thickness of about 50 mm cut to the flange size of the outer periphery of the screen was used.
After setting the C1 suki-tub with a thin layer of washi paper made with J's viscose processing to give it ice-shaving properties and fixing the washi paper on the screen, pure water was poured up to 5 m above the screen. A layer-forming stock solution was injected, stirred in the manner of papermaking to uniformly disperse it, and then drained to form a composite porosity, Iv4, consisting of graphite particles and asbestos fibers on the Japanese paper.

The film was then air-dried, peeled off from the screen, transferred to an electric furnace, and fired at 160° C. for 50 minutes to complete a rough surface film. The average thickness of the porous layer on Japanese paper is 126±
The porosity was 15μ and the porosity was 72μ.

An electrolytic test was carried out by attaching the thus obtained rough surface to an ion exchange removal vertical electrolytic cell with an electrolysis area of 2.5 dm.The ion exchange membrane was Dapon's Nafion 901, and the anode was Titanium Exband Metal 6 long diameter x 3.5 t short diameter
A DSE electrode whose surface is coated with ruthenium oxide and iridium (ar+) is used, and the cathode is an active electrode sprayed on 5US310S extended metal (length: 6mm x width: 15vns), and between the cathode and the ion exchange membrane. After inserting the rough surface membrane, the anode, which can be expanded by a spring, is brought into contact with pressure at about 0.15 Kf/cd, and the distance between the electrodes is set to about 1.
1.5 m, the anode chamber salt concentration was 20Of/V, the cathode chamber sodium hydroxide concentration was 32% by weight, and the temperature was 90%.
When electrolysis was performed while maintaining the temperature at ℃, the voltage between electrodes was as follows.

Current density (A/dm”) Electrode voltage (V) 20
2.94 30 516 In addition, the increase in instantaneous variation in sliding voltage that normally appears when the gap between electrodes is about 2 mm or less was eliminated, and an extremely stable voltage with a variation range of 0 to 5 mV was exhibited.

After the start of electrolysis, it was operated at 30 A/dm' for 30 days, during which the voltage remained almost constant at 1, and the current efficiency during that period was 93.8. '% M, The operation was stopped after 30 days and restarted after being left for 2 days, but the voltage immediately returned to the voltage before the stop.

After restarting operation for 10 days, the tank was stopped and the tank was opened at °C.The conditions of the rough membrane and ion exchange membrane were inspected.The rough membrane appeared to be clean and adhered to the ion exchange membrane, and no abnormalities such as peeling were observed. I couldn't. When the rough surface membrane was artificially peeled off from the ion exchange membrane, the Japanese paper had dissolved and disappeared, and the ion exchange membrane surface was free from any stains such as spots that are normally seen, and remained almost as clean as before use. Drooping Example 2 Canadian Standard 7 Class 7F Tallinn Tile Asbestos Fiber 0.8
2 was hydroxylated in the same manner as in Example 1) 100ml of activated carbon powder with a particle size of 20μ or less prepared in advance was added to 100ml of asbestos-containing water (pH &8) obtained by IJ Uno heat treatment and washing with water.
Mix the dispersion in 1 m of water, add 60 m
A porous layer stock solution obtained by adding 5 ml of iI% PTFE disverging solution was added with viscose using a plow to make a paper making area of 10 cm x 25 ryen in the same manner as in Example 1. Pass it evenly on 50μ Japanese paper, layer activated carbon and asbestos, and dry it to 160μm.
It was baked at ℃ for 50 minutes. The obtained rough membrane was divided into two halves and placed on the anode and cathode sides of an ion exchange membrane in an electrolytic cell with an electrolysis area of 1 dm' to form an active cathode made of nickel extract band metal with a major axis of 2 m xai 1 was coated with Rh. is placed on a two-layer electrode made by welding a nickel material expanded metal with a length of 12 mm and a short diameter of 81 Wl, and can be expanded by coating the titanium material with PT and R in the same two-layer shape as the cathode. The electrode was placed facing an anode having a spring structure, and was crimped at about 0.1 Kq/d, and electrolysis was conducted with the effective distance between the electrodes being 0.6 mm. The following results were obtained.

Current density (A/dm”) Electrode voltage (V) 20
2.9230
3.13 Current density 30A/dm'',
1. Operation for 10 days at a sodium hydroxide concentration of 6°wt and a temperature of 90°C. However, the voltage remained stable with extremely small instantaneous fluctuations, and the current efficiency between the temples was 93.8.

Comparative Example 1 An electrolytic cell was assembled and operated for 10 days under the same conditions as in Example 1, except that no rough membrane was inserted and the distance between the ion exchange membrane and the anode was set to 0 and the distance between the ion exchange membrane and the cathode was set to 2. , the following results were obtained.

Current density (A/dm') Electrode voltage (V) 20
3.0130
3.24 The instantaneous voltage fluctuation range is ±14 mV, and the current efficiency during this period is 94.4%.
Met.

Comparative Example 2 Without inserting the rough membrane, the distance between the ion exchange membrane and the anode was set to 0.
Example 2 except that the distance between the ion exchange membrane and the cathode was 2 feet.
When an electrolytic cell was assembled under the same conditions as above and operated for 15 days, the following results were obtained.

Current density (A/dm') Voltage between poles (V)2 〇
5005 〇
522 The instantaneous fluctuation range of voltage is ±18
The mVX current efficiency was 94.2chi.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing an example of an ion-exchange removal electrolytic cell according to the present invention, and FIG. 2 is an enlarged cross-sectional view of the main parts. 1... Cathode 11... Composite membrane 12... Cation exchange membrane 13... Soluble membrane 14... Rough surface membrane 19. ·····anode

Claims (3)

[Claims] (1) On the cathode and/or anode side of the cation exchange membrane,
A composite membrane is formed by integrally overlapping rough membranes having liquid permeability and bubble separation properties through a substance that dissolves by electrolysis, and the rough membrane is brought into close contact with an opposing electrode. Ion exchange membrane method decomposition tank. (2) The ion exchange dehydration electrolytic cell according to claim (1), wherein the substance to be dissolved by electrolysis is thin Japanese paper. (3) The ion-exchange membrane method decomposition tank according to claim (1) or (2), wherein the rough surface membrane is composed of carbon powder, asbestos fibers, and a binder.