JPH01234585A - Method and device for electrolysis using gas diffusion electrode - Google Patents

Abstract

PURPOSE:To prevent the generation of a harmful gas from an electrolytic cell and to lower the electrolytic voltage by using a gas diffusion electrode as the anode and cathode of a diaphragm electrolytic cell, and connecting the gas chambers of the anode and cathode to chemically combine the gases generated from both electrodes. CONSTITUTION:A gas diffusion electrode is used as the anode 3 and cathode 4 of the electrolytic cell 50 of an aq. NaCl soln., and the gas chambers 5 and 5 are respectively provided behind the electrodes, and connected by a pipe 16. The inside of the cell 50 is separated by cation-exchange membranes 1 and an anion-exchange membrane 2, aq. NaCl 12 is supplied to the anode chamber 6 and a desalting chamber 8, and gaseous Cl is introduced into the gas chambers 5 and 5 and a connecting pipe 16. A current is applied to the anode 3 and cathode 4 of the cell 50, and the Cl<-> ion in the anode chamber 6 is oxidized to Cl by the anode 3, discharged into the gas chamber 5, introduced into gas chamber 5 of the cathode chamber 4 through the connecting pipe 16, and reduced to Cl<-> by the cathode 4. The Cl<-> ion chemically combines with the Na<+> ion permeated through the cation-exchange membrane 1 to form NaCl. The cathode chamber 7 acts as a concentration chamber, hence gaseous Cl and H2 are not generated, the electrolytic voltage is lowered, and the consumption of electric power is reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to methods and apparatus for electrolytic processes.

[Prior Art] Conventionally, there is an ion exchange membrane process in which electrolysis is performed using an ion exchange membrane as a diaphragm. For example, electrodialysis, in which anion exchange membranes and cation exchange membranes are arranged alternately between the anode and cathode and the saline is concentrated by applying electricity, or an anion exchange membrane is used to separate the anolyte and catholyte. There is an electrolytic process that recovers sulfuric acid, etc. from the waste acid used as the catholyte to the anolyte.

[Problems to be Solved by the Invention] Incidentally, these electrolytic processes involve the generation of force from the electrodes for conducting electricity. For example, when saline is electrodialyzed to produce concentrated irrigation, chlorine is generated at the anode and hydrogen is generated at the cathode. In the case of sulfuric acid, oxygen is generated at the anode and hydrogen is generated at the cathode during acid recovery using the electrolytic method. When the generated chlorine is released into the atmosphere, it is highly toxic, corrosive, difficult to dispose of, and highly dangerous. However, the generated oxygen and hydrogen are normally released into the atmosphere and have no utility value. Furthermore, hydrogen is also at risk of explosion.

An electrolytic voltage of several volts is required to generate chlorine or oxygen and hydrogen, and if this generated gas is not used, energy is wasted, which also causes high operating costs for the electrolytic process. ing.

[Purpose of the Invention] The purpose of the present invention is to eliminate unnecessary gases from being released outside the electrolytic cell in an electrolytic process using an ion exchange membrane, etc., to achieve non-pollution, energy saving, high efficiency, miniaturization of the device, and ease of work. The purpose is to provide a good electrolysis method and device.

[Means for solving the problem] In an electrolysis device having an ion exchange membrane, gas diffusion electrodes are arranged at the cathode and anode, and the gas generated at one electrode is oxidized or reduced and consumed at the other electrode. did. Furthermore, in an electrolytic device that does not involve gas generation at the cathode, the anode is used as a gas diffusion electrode, and hydrogen is supplied to the anode.

[Function] Since the electrolyzer having an ion exchange membrane is configured as described above, when the gas diffusion electrode is accompanied by gas generation, for example,
When using a cathode that generates hydrogen, bubbles are generated in the electrolyte with a normal plate electrode, but with a gas diffusion electrode, gas can be taken out from the back of the electrode without being generated as bubbles on the electrolyte side. By oxidizing and consuming this hydrogen at the other anode consisting of a gas diffusion electrode, the generated gas is treated within the electrolytic cell and does not exit the system. As a result, hydrogen ions in the cathode chamber moved to the anode chamber.

In addition, when using an anode that generates chlorine, chlorine bubbles are generated in the electrolyte with a normal plate electrode, but with a gas diffusion electrode, the chlorine can be extracted from the back of the electrode, and this chlorine is reduced at the other cathode, which is a gas diffusion electrode. By consuming the chlorine gas, it is processed in the electrolytic cell and no longer leaves the system. As a result, chlorine ions in the anode chamber moved to the cathode chamber. If a gas diffusion electrode having a reaction layer according to the present invention is used, hydrogen ions and chloride ions can be easily moved because it is in the form of a membrane.

In electrolyzers that do not involve gas generation from the cathode, hydrogen is supplied to the anode gas diffusion electrode and oxidized, so chlorine or oxygen gas is not generated. As a result, chlorine, which is highly toxic, corrosive, difficult to dispose of, and highly dangerous, is no longer generated. As a result, corrosion of the device was reduced and the life of the electrodes was extended because they were exposed to an oxidizing atmosphere. Additionally, oxygen and hydrogen are no longer released into the atmosphere and there is no danger of explosion. Since no bubbles are released into the electrolyte, the bubble effect is eliminated, reducing overvoltage and reducing the distance between electrodes, making it possible to lower overvoltage. The reduced distance between poles makes the device more compact. As a result of the reduction in the voltage required for the generation of chlorine or oxygen, the bath voltage was reduced by 2 to 3 μm, and power consumption was reduced accordingly. This eliminates the need for voltage to generate chlorine or oxygen and hydrogen, resulting in an energy-saving electrolyzer.

[Example 1] In a conventional electrodialysis apparatus which is widely known as an example of the coin ion exchange membrane electrolysis process, as shown in FIG.
When the Na and C ions are supplied and electrolyzed, they pass through the anion and cation exchange membranes 2.1, respectively, and are concentrated in the concentration chamber 9.
Hydrogen is generated at the cathode 4 and chlorine is generated at the anode 3, and hydrogen 15 is discharged from the cathode chamber 7 and chlorine 17 is discharged from the anode chamber 6. At this time, a force sorter is generated in the cathode chamber. Chlorine and Na
This process is unsuitable if OH is not required.

The electrolytic device to which the present invention is applied is explained with reference to FIG. 2. 50 is 120 mm long, 120 mm wide, and 70 mm deep.
electrolytic cell, l is a cation exchange membrane, 2 is an anion exchange membrane,
The anodes and cathodes 3 and 4 are composed of 120 mm square gas diffusion electrodes, and the air chambers of the anode and cathode are connected by a connecting tube 16.

Next, an electrolysis method for the electrodialysis apparatus of the present invention using the electrolysis apparatus having the above-mentioned configuration will be explained. Na in the anode chamber 6 and demineralization chamber 8
Cl water is supplied. The air chamber and connecting tube are filled with chlorine gas in advance, and when the electrode is energized, the anode chamber 60C1- ions are oxidized to chlorine at the anode 3 and released as chlorine gas into the air chamber 5, passing through the connecting tube 16 to the cathode air chamber 5. They move and become CI- ions again at the cathode. This C1- ion and the Na'' ion that has passed through the cation exchange membrane become NaCl.
In this way, in this method, the cathode chamber 7 also functioned as a concentration chamber, and no chlorine or hydrogen was generated. In the apparatus of the present invention, since chlorine generation and chlorine reduction are performed, the sliding voltage required for the reaction was significantly lowered to 1.2V. In this embodiment, the anode air chamber and the cathode air chamber of a single electrolytic cell were connected, but it goes without saying that the anode air chamber and the cathode air chamber of a plurality of electrolytic cells may be connected.

[Example 2] Fig. 3 shows the configuration of an electrolytic cell applied to the separation of NaCl water into hydrochloric acid and sodium chloride.

Put NaCl water in the demineralization chamber 8, dilute hydrochloric acid in the anode chamber 6, and dilute NaOH water in the cathode chamber 7, and fill the air chamber 5 connecting tube 16 between the cathode and anode with hydrogen. When electricity is applied, hydrogen is generated at the cathode. It passes through the air chamber of the cathode and the connecting tube 16, and is supplied from the air chamber of the anode to the gas diffusion electrode of the anode, where it is oxidized and attached again. In the cathode chamber, C1 that has passed through the ion-anion exchange membrane
- Hydrochloric acid is produced with ions. In the anode chamber, Na'' ions that have passed through the cation exchange membrane are combined with OH- ions generated by hydrogen generation at the cathode to generate NaOH.

Hydrochloric acid and hydrochloric soda could be produced without generating chlorine gas.

It is similarly applicable to the separation of other salts into acids/alkali. The amount of salt waste discharged from various industries is enormous. Separating salt waste into acid and alkali and reusing it has environmental and economic value.

[Example 3 A case in which this method is applied to acid recovery by co-electrolysis method is shown in FIG. 4. A fluorine-based cation exchange membrane 2 with excellent acid resistance and two gas diffusion electrodes 3.4 are used, and connecting tubes 16 are attached above and below.The upper connecting tube is a drying tube filled with silica gel, and the lower connecting tube is a drying tube filled with silica gel. A circulation pump 21 is added to circulate the hydrogen while drying it. Additionally, hydrogen that leaked from the hydrogen replenishment device was refilled. When one drop of sulfuric acid was added as a waste acid to the catholyte 7 and electrolyzed, 40% concentration of sulfuric acid could be recovered in the anolyte 6 with a current efficiency of about 50%. Hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, phosphoric acid,
It is possible to recover acids such as chromic acid.

Similarly, by using a fluorine-based cation exchange membrane with excellent acid resistance and two gas diffusion electrodes, and by adding waste alkali to the catholyte and electrolyzing it, a high concentration of alkali can be recovered into the catholyte with high current efficiency.

[Example 4] Fig. 5 shows a case where the present invention is applied to precious metal processing. An electrolytic cell is constituted by an anode 3 consisting of a gas diffusion electrode, an anion exchange membrane 2, and a platinum plate 24. The anolyte 6 contains a dilute salt M25, and the catholyte contains a dilute salt M25.
Hydrochloric acid solution 26 containing ppm of platinum ions was electrolyzed by supplying hydrogen gas from the supply port. As a result, I,5
When electrolyzed at mA/dm2 for 25 hours, Pt was 97%
The current efficiency was 40%. Furthermore, no chlorine was generated at the cathode, and the concentration of hydrochloric acid increased.

In the above example, the cathode and anode gas diffusion electrodes were separated at both ends of the electrolytic cell, but they may be arranged symmetrically with the reaction layers of the gas diffusion electrodes facing outward as shown in FIG. Furthermore, as shown in FIG. 7, it may be integrally joined on both sides with the gas diffusion layer at the center.

This electrode is made by forming a sheet of a mixture of acetylene black and polytetrafluoroethylene disversion as hydrophobic carbon particles together with solvent naphtha on a roll machine. It is obtained by stacking two sheets of the mixture together with solvent naphtha on both sides to a thickness of about 1 mm, heat-treating at 280°C for 2 hours, hot-pressing at 380°C at 600kg/cn+2, and supporting platinum on the reaction layer. .

These electrodes can be used as ion exchange membranes for chloride ions and hydrogen ions.

In addition to the above embodiments, polyvalent metal ions that take multiple oxidation states, such as noble metal ions, are required to exist at a certain valence in applications such as catalysts. The present invention can also be applied to such a valence exchange control method, =10-, and an electrolytic ion replacement method.

[Effects of the Invention] As can be seen from the above explanation, according to the present invention, when the gas diffusion electrode is used as one electrode in an electrolysis device such as an ion exchange membrane process, the generated gas is not generated as bubbles on the electrolytic solution side but from the back of the electrode. It can be taken out. This gas is introduced into the other electrode, which is a gas diffusion electrode, and is consumed to move ions from one electrode chamber to the other. That is, it can be used in place of an ion exchange membrane. As a result, chlorine gas, oxygen gas, etc. were no longer generated from the anode, and hydrogen gas was no longer generated from the cathode. In electrolyzers that do not involve gas generation from the cathode, hydrogen is supplied to the anode gas diffusion electrode and oxidized, so chlorine or oxygen gas is not generated. As a result, chlorine, which is highly toxic, corrosive, difficult to dispose of, and highly dangerous, is no longer generated. Additionally, oxygen and hydrogen are no longer released into the atmosphere and there is no danger of explosion. This eliminates the need for voltage to generate chlorine or oxygen and hydrogen, resulting in an energy-saving electrolyzer. Since no bubbles are released into the electrolyte, the bubble effect is eliminated, reducing overvoltage and reducing the distance between electrodes, making it possible to lower overvoltage. It can be a low-pollution, energy-saving, and compact electrolyzer.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional electrolytic dialysis apparatus. FIG. 2 is a configuration diagram in which the present invention is applied to an electrolytic dialysis device. FIG. 3 is a diagram illustrating the configuration of a salt acid/alkali separation device. FIG. 4 is a diagram showing the configuration of a sulfuric acid concentrator. FIG. 5 shows a configuration of a platinum recovery device. Figure 6 is a diagram of two gas diffusion electrodes put together. FIG. 7 is a diagram showing an electrode in which reaction layers are bonded to both sides of a gas diffusion layer.

Claims (5)

[Claims] (1) In the electrolytic process, the cathode and anode consist of a gas diffusion electrode, and the gas generated by the electrode reaction at one electrode is consumed by the electrode reaction at the other electrode, and ions are transferred from one electrode chamber to the other electrode chamber. An electrolytic method characterized by moving. (2) An electrolytic device characterized in that the air chambers of the cathode and anode gas diffusion electrodes are hermetically connected to each other in the electrolytic process, so that gas generated at one electrode is guided to the other electrode. (3) A membrane made of hydrophilic carbon particles, a catalyst, hydrophobic carbon particles, and a fluororesin is bonded to both sides of a gas diffusion membrane made of hydrophobic carbon particles and a fluororesin such as polytetrafluoroethylene. An electrode for an electrolytic device according to claim 2, characterized in that: (4) An electrolytic method characterized in that hydrogen is supplied to the anode in an electrolyzer comprising an ion exchange membrane and a gas diffusion electrode as the anode so that oxidation products are not produced. (5) An electrolytic device comprising an ion exchange membrane, an anode, and a gas diffusion electrode, characterized in that the electrolytic device has a hydrogen supply port and a hydrogen discharge port.