JP2002249889A - Operation starting method of electrolysis vessel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively enable the starting of an operation of ion exchange membrane electrolysis vessel having a gas diffusion electrode. SOLUTION: In this operation starting method in ion exchange membrane electrolysis vessel for electrolysis of halogenated alkali metal aqueous solution, the gas diffusion electrode is arranged in a cathode chamber of the ion exchange membrane electrolysis vessel which is divided to an anode chamber and the cathode chamber by cation exchange membrane and a hydrophilic liquid permeation layer is disposed between the cation exchange membrane and the gas diffusion electrode. Therein further, the anode chamber is filled with halogenated alkali metal aqueous solution, at the same time, the hydrophilic liquid permeation layer is filled with alkali metal hydroxide aqueous solution, thereafter, oxygen-containing gas is supplied into a gas chamber and the energizing is started.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for starting operation of an ion exchange membrane electrolytic cell of an aqueous solution of an alkali metal halide such as sodium chloride using a gas diffusion electrode. The present invention relates to a method for starting the operation of an electrolytic cell that can be operated with a battery.

[0002]

BACKGROUND OF THE INVENTION Sodium hydroxide and chlorine, which are important industrial materials, are produced by electrolysis of aqueous sodium chloride solution. In the production by electrolysis, the electric energy required for electrolysis accounts for a large proportion of the basic unit. Therefore, in the current mainstream ion exchange membrane electrolytic cell, the distance between the anode and the cathode is reduced,
The electrolysis voltage can be reduced by a method such as operating the cation exchange membrane and the anode and the cathode substantially in close contact with each other, or employing an electrode formed with an electrode catalyst coating having a small hydrogen overvoltage as the cathode. Have been done.

In an ion-exchange membrane electrolytic cell of an aqueous solution of sodium chloride, a hydrogen generation reaction occurs at the cathode. However, when an oxygen gas diffusion electrode is used in place of the hydrogen generation electrode, no hydrogen is generated at the cathode. Theoretically, it is possible to lower the electrolysis voltage of 1.2 V, which is equivalent to the electrolysis voltage of water.
Since an extremely large reduction of the electrolysis voltage of 9 V can be obtained, the development of an ion exchange membrane electrolytic cell using a gas diffusion electrode as a cathode has been promoted.

In a conventional ion exchange membrane electrolytic cell using a gas diffusion electrode, there has been a problem that the electrolyte leaks to the gas chamber through the gas diffusion electrode. As a method for solving such problems, in a cathode chamber partitioned by an ion exchange membrane, a hydrophilic liquid permeable material is provided on a side facing a counter electrode of a gas diffusion electrode, and an oxygen-containing gas is supplied to the gas chamber. Japanese Patent Application Laid-Open No. H11-12469 discloses that an alkali metal hydroxide generated in an electrolytic cell is taken out to a gas chamber side.
No. 8 proposes this. By using the gas chamber of the gas diffusion electrode for taking out the cathode-generated liquid in this manner, the structure of the electrolytic cell is simplified, which is extremely advantageous in a commercial electrolytic cell.

[0005] The hydrophilic liquid permeable layer disposed on the surface of the gas diffusion electrode must hold an alkaline electrolyte such as an aqueous solution of sodium hydroxide, and must be in a state where sufficient current is supplied during electrolysis. It is. However, after assembling the electrolytic cell, a saline solution or the like is introduced into the anode chamber, and an oxygen-containing gas or an oxygen-containing gas containing water is introduced into the gas chamber of the gas diffusion electrode. The hydrophilic liquid permeable layer provided between the gas diffusion electrodes is not sufficiently impregnated with the aqueous sodium hydroxide solution. For this reason, it is difficult to supply a sufficient current, and if the impregnation is not uniform, a concentrated portion of the current may occur, causing irreparable damage to the cation exchange membrane and the electrode.

[0006] In a small laboratory-scale electrolytic cell, it is possible to mount the hydrophilic liquid permeable layer on the electrolytic cell after the hydrophilic liquid permeable layer is uniformly impregnated in advance by immersion treatment or the like. Moreover, in a commercial electrolytic cell in which a large number of unit electrolytic cells are stacked, it is difficult to adopt such a method. For this reason, problems occur with the cation exchange membrane and the gas electrode at the time of initial energization after assembling the electrolytic cell or at the time of starting operation such as re-energizing after stopping energization of some electrolytic cells. It is indispensable to start energization from a small current density and gradually increase the energization current so as not to cause the problem.Especially when starting operation with many electrolytic cells connected in series, consideration should be given to differences in the characteristics of electrolytic cells. And it took a long time for the operation of the electrolytic cell to reach a steady state.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a gas diffusion electrode is disposed in a cathode chamber of an ion exchange membrane electrolytic cell divided into an anode chamber and a cathode chamber by a cation exchange membrane. At the start of operation of an ion-exchange membrane electrolytic cell provided with a hydrophilic liquid permeable layer between the electrodes, the same operation as the operation at the start of operation in a conventional ion-exchange membrane electrolytic cell without complicated operation start operation An object of the present invention is to provide a method for starting operation of an ion-exchange membrane electrolytic cell capable of starting operation.

[0008]

According to the present invention, a gas diffusion electrode is arranged in a cathode chamber of an ion exchange membrane electrolytic cell divided into an anode chamber and a cathode chamber by a cation exchange membrane. In the method for starting operation in an ion exchange membrane electrolytic cell for electrolysis of an alkali metal halide aqueous solution provided with a hydrophilic liquid permeable layer between electrodes, the anode chamber is filled with an alkali metal halide aqueous solution and the hydrophilic liquid permeable layer is filled. Is filled with an aqueous alkali metal hydroxide solution, and then an oxygen-containing gas is supplied to a gas chamber formed on the gas diffusion electrode on the side opposite to the cation exchange membrane to start energization. This is a method for starting operation of the electrolytic cell, wherein the cathode chamber is filled with an aqueous alkali metal hydroxide solution and then extracted. Also, after circulating the aqueous alkali metal hydroxide solution in the cathode chamber, filling the hydrophilic liquid permeable layer with the aqueous alkali metal hydroxide solution, extracting the aqueous alkali metal hydroxide solution from the cathode chamber, and then into the gas chamber. This is a method for starting operation of the electrolytic cell, in which an oxygen-containing gas is supplied to start energization.
The method for starting operation of the electrolytic cell described above, wherein the oxygen-containing gas contains water.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a cation exchange membrane is divided into an anode chamber and a cathode chamber, a gas diffusion electrode is provided in the cathode chamber, and a hydrophilic liquid permeates between the cation exchange membrane and the gas diffusion electrode. In an ion exchange membrane electrolytic cell provided with a layer,
Attention was paid to the fact that it is difficult to conduct electricity at a sufficient current density because the aqueous solution of an alkali metal hydroxide is not sufficiently and uniformly impregnated in the hydrophilic liquid permeable layer at the start of electricity supply.

Then, the hydrophilic liquid permeable layer between the cation exchange membrane and the gas diffusion electrode is impregnated with an alkali metal hydroxide aqueous solution, or the alkali metal hydroxide aqueous solution is supplied to the gas chamber, After being transferred to the hydrophilic liquid permeable layer side and filling the hydrophilic liquid permeable layer, at least one of the methods of extracting the aqueous alkali metal hydroxide solution from the gas chamber is equivalent to a conventional ion exchange membrane electrolytic cell. It has been found that the energization start operation can be performed by the operation start current.

The present invention will be described below with reference to the drawings.
FIG. 1 is a diagram illustrating a method for starting operation of an ion exchange membrane electrolytic cell according to the present invention. The electrolytic cell 1 of the present invention is divided into an anode chamber 3 and a cathode chamber 4 by a cation exchange membrane 2, and a porous anode 5 is arranged on the anode chamber 3 side of the cation exchange membrane 2. 2, a hydrophilic liquid permeable layer 6 is provided on the cathode chamber 4 side, and a cathode 7 composed of a gas diffusion electrode is provided on the side of the hydrophilic liquid permeable layer 6 opposite to the cation exchange membrane 2 side. The cathode 7 has a gas diffusion electrode 8 on a porous cathode support 9. A saline solution whose concentration or the like is adjusted by an anolyte adjusting device 11 is supplied from an anolyte supply port 10 provided at the bottom of the anolyte chamber 3 to the electrolytic cell 1.
From this, chlorine generated by electrolysis and fresh salt water having a reduced concentration are discharged. After the chlorine is separated in the gas-liquid separator 13, the fresh brine is returned to the anolyte controller 11,
After passing through a predetermined process, it is supplied to the anode chamber 3.

On the other hand, in the cathode chamber 4, a space formed by the porous cathode support 9 of the cathode 7 on which the gas diffusion electrode 8 is formed forms a gas chamber 14, and the oxygen-containing gas supply port 1 is formed.
From 5, the oxygen-containing gas is supplied to the oxygen-containing gas preparation device 16 in which the oxygen concentration, the water content, the temperature and the like are humidified to predetermined values. Oxygen is concentrated by any method such as liquefaction separation method, PSA method, and gas concentration membrane method as long as it removes carbon dioxide that causes the formation of sodium carbonate in the gas diffusion electrode or electrolytic cell. Can be used, and those having a higher concentration are preferred because the effect of lowering the electrolysis voltage is increased.

The sodium ions that have passed through the cation exchange membrane 2 by electrolysis generate an aqueous solution of sodium hydroxide in the cathode chamber, and are discharged together with excess oxygen-containing gas from the cathode chamber outlet 17 to the sodium hydroxide storage tank 18. Collected. The water supplied along with oxygen from the oxygen-containing gas supply port 15 is used to properly maintain the concentration of the aqueous sodium hydroxide solution generated in the cathode chamber, but only by the water passing through the cation exchange membrane. It is also possible to carry out electrolysis. At the start of the operation of the ion exchange membrane electrolytic cell of the present invention, a saline solution is supplied into the anode chamber, and at the same time, a sodium hydroxide aqueous solution is supplied from the sodium hydroxide storage tank 18 to the heat exchanger 19 to reach a predetermined temperature. It is introduced into the cathode chamber 4 from the chamber outlet 17.

The aqueous sodium hydroxide solution introduced into the cathode chamber 4 is transferred from the upper and lower portions of the gas diffusion electrode 8 to the hydrophilic liquid permeable layer 6 from the gas chamber side formed by the porous cathode support 9. You. The aqueous sodium hydroxide solution may be allowed to stand for a predetermined period of time after filling the cathode chamber, and may be extracted from the cathode chamber outlet 17 after sufficiently impregnating the hydrophilic liquid permeable layer 6. The sodium aqueous solution may be discharged from the oxygen-containing gas supply port 15, supplied to the heat exchanger 19, adjusted to a predetermined temperature, circulated in the cathode chamber, and then extracted from the gas chamber.

In the above description, at the start of operation, an aqueous sodium hydroxide solution is introduced from the cathode chamber outlet to penetrate from above and below the hydrophilic liquid permeable layer, and from the gas chamber to above and below the hydrophilic liquid permeable layer. The method of transferring the sodium aqueous solution and filling the hydrophilic liquid permeable layer was described.However, a supply means of the sodium hydroxide aqueous solution was provided between the gas diffusion electrode and the cation exchange membrane, and the space between the cation exchange membrane and the gas diffusion electrode was provided. It may fill the hydrophilic liquid permeable layer located. Also, the method of supplying the aqueous sodium hydroxide solution from the gas chamber side can be used without modifying the conventional ion-exchange membrane electrolytic cell having the gas diffusion electrode because it is only necessary to provide a supply means of the aqueous sodium hydroxide solution. be able to.

After the hydrophilic liquid permeable layer is filled with the aqueous sodium hydroxide solution at the start of the operation, if the aqueous sodium hydroxide solution does not exist in the gas chamber or the amount does not hinder the energization, water is added. The oxygen-containing gas may be supplied without passing through the step of extracting the aqueous sodium oxide solution to supply electricity to the electrolytic cell. Further, the concentration of the aqueous sodium hydroxide solution supplied to the cathode chamber at the start of the operation is preferably from 28% by weight to 35% by weight, more preferably from 30% by weight to 33% by weight. The temperature is between 75 ° C and 9
The temperature is preferably set to 0 ° C.

The rate at which the aqueous sodium hydroxide solution is introduced into the cathode chamber varies depending on the size of the electrolytic cell. However, excessive expansion and contraction of the cation exchange membrane is suppressed so that pinholes do not occur. 10 minutes to 60 minutes,
Preferably, it is desirable to satisfy the condition in 30 minutes to 60 minutes. Also, the speed at which the aqueous sodium hydroxide solution is withdrawn is preferably 10 minutes to 60 minutes, preferably 30 minutes to 60 minutes, as in the supply.

The gas diffusion electrode used as the cathode in the present invention is made of a material such as a wire mesh, expanded metal, powder sintered body, metal fiber sintered body, foamed body made of a corrosion resistant material such as stainless steel, nickel and silver. And a cathode support. A gas diffusion electrode containing an electrocatalyst is formed on such a cathode support. As the electrocatalyst, metals such as platinum, palladium, ruthenium, iridium and silver or oxides thereof can be used. These electrode catalysts can be formed by a method such as kneading and applying a hydrophobic material such as fluorinated graphite or fluororesin, or a fluororesin binder.

In the present invention, the gas chamber formed in the cathode chamber may be of any type as long as it forms a space capable of uniformly supplying an oxygen-containing gas to the gas diffusion electrode. In order to supply a current to the gas diffusion electrode through the gas chamber, a conductive mesh, a porous body, a foam, or the like which does not hinder the gas flow may be provided. By arranging a conductive network, a porous body, or the like in the gas chamber, it is possible to improve the adhesion of the ion exchange membrane, the hydrophilic liquid permeable layer, and the laminate of the gas diffusion electrodes.
In particular, when a material having flexibility is used, uniformity of close contact of the stacked body can be improved. Materials that can be used for these purposes include nickel, silver, and materials such as copper coated with these metals.

For the hydrophilic liquid permeable layer, a porous hydrophilic material made of metal, carbon fiber, synthetic resin or the like having corrosion resistance can be used. Preferably, carbon fibers, ceramics such as zirconium oxide and silicon carbide, hydrophilic fluororesins, and the like can be used, and those having a structure such as a woven fabric, a nonwoven fabric, or a net can be used. Also, 0.1
It is preferable to form a sheet of about 10 mm to 10 mm,
It is preferable that the material is elastic and deforms when pressure non-uniformity occurs, thereby reducing the pressure non-uniformity.

[0021]

The present invention will be described below with reference to examples and comparative examples. Example 1 An electrolytic cell having an electrolysis surface having a width of 100 mm and a height of 600 mm was partitioned into an anode chamber and a cathode chamber by a cation exchange membrane (Flemion 8934 manufactured by Asahi Glass Co., Ltd.), and the anode chamber was coated with an electrode catalyst made of a platinum group metal oxide. Was provided on a titanium expanded metal substrate, and an insoluble electrode (Permelec electrode) was provided.
mm carbon fiber woven fabric (Zoltek Corp. Pa)
next30 Low Oxidation Nitted Carbon Fabrics P
W03). Further, a nickel foam having a thickness of 1 mm (manufactured by Nippon Heavy Chemical Industry Co., Ltd.) was subjected to silver plating with a thickness of 10 μm to prepare a cathode support, and a polytetrafluoroethylene aqueous suspension was prepared on the surface of the cathode support. Solution (30J, manufactured by DuPont-Mitsui Fluorochemicals Co., Ltd.) and fine powder of silver (500A, manufactured by Vacuum Metallurgy Co., Ltd.) are mixed and dispersed at a ratio of 1: 1 (volume ratio), and an aqueous suspension is applied at a coating amount of 500 g per square meter. Apply and apply 35 in an electric furnace with nitrogen atmosphere.
After firing at 0 ° C for 50 minutes,
A liquid-permeable gas diffusion electrode having a width of 100 mm, a height of 600 mm, and a thickness of 0.5 mm was manufactured and placed in contact with the carbon fiber fabric. The inner volume of the gas diffusion electrode in the cathode chamber on which the gas diffusion electrode was formed on the side opposite to the cation exchange membrane was 240 ml.

An aqueous solution of sodium chloride having a concentration of 300 g / l is supplied to the anode compartment, and a temperature of 78 ° C. and a concentration of 31.8% by weight are supplied to the cathode compartment from a cathode compartment outlet provided below the cathode compartment.
Sodium hydroxide solution over 32 minutes
After holding for 0 minutes, it was withdrawn from the catholyte outlet over 30 minutes. Next, a gas consisting of 93.5% by volume of oxygen, the balance of nitrogen and an inert gas, and water at 97 ° C. were mixed to prepare an oxygen-containing gas having a water content of 76% by volume, and the oxygen provided at the top of the cathode chamber was prepared. While supplying from the containing gas supply port, energization was started at a current density of 1.5 kA / m ^{2, and} an aqueous sodium hydroxide solution was taken out from the cathode chamber discharge port.
At this time, the electrolytic cell voltage was 1.82 V, and the temperature in the electrolytic cell was 88 ° C. Current density of 3 per minute
Raise at a rate of 3.3 A / m ² , and after 45 minutes 3
The steady-state current density of kA / m ² was reached. The electrolytic cell voltage at this time was 2.12V.

Thereafter, the electrolysis voltage shows a tendency to decrease,
It became almost stable three hours after the start of operation. The electrolytic cell voltage at this time was 2.04V. FIG. 2 shows changes in the electrolytic cell voltage from the start of energization. After reaching the steady-state operating current, the concentration of the fresh salt water discharged from the anode chamber is 210 g / liter, and the concentration of the generated sodium hydroxide aqueous solution is 32.8.
% By weight.

Comparative Example 1 Electrolysis was carried out in the same manner as in Example 1 except that the aqueous solution of sodium hydroxide was not filled in the cathode chamber at the start of the operation of the electrolytic cell. The electrolytic cell voltage immediately exceeded 2.7 V. The energization was stopped because it was not preferable for the components of the electrolytic cell.

Comparative Example 2 At the start of energization, the cathode chamber was not filled with an aqueous solution of sodium hydroxide, and the current density was 0.16, which was 1/18 of the steady operating current.
A current of 7 kA / m ² was supplied. The electrolytic cell voltage temporarily exceeded 2.2 V, but gradually decreased to less than 2 V. Five minutes later, the current continued to increase at a rate of 16.5 A / m ² per minute, and reached a steady operating current density after 95 minutes. The electrolytic cell voltage at this time was 2.39 V
Met. The electrolysis voltage after a lapse of 3 hours from the start of operation was 2.34 V. FIG. 2 shows the transition of the electrolysis voltage. The anolyte concentration after reaching the steady operating current is 212 g
/ Liter, the concentration of the generated sodium hydroxide aqueous solution is 3
It was 3.1% by weight. Seven hours after the start of operation, the electrolysis voltage dropped to 2.05 V and stabilized.

[0026]

In the electrolytic cell using the gas diffusion electrode,
The energizing current at the start of the operation of the electrolytic cell can be approximately half the energizing current density in the steady state, and the operation of the electrolytic cell can be performed at an early stage with the energizing current density in the steady state.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for starting operation of an ion exchange membrane electrolytic cell of the present invention.

FIG. 2 is a diagram for explaining changes in electrolytic cell voltage in Examples of the present invention and Comparative Examples.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electrolysis tank, 2 ... Cation exchange membrane, 3 ... Anode compartment, 4 ... Cathode compartment, 5 ... Anode, 6 ... Hydrophilic liquid permeable layer, 7 ... Cathode, 8 ...
Gas diffusion electrode, 9: cathode support, 10: anolyte supply port,
Reference numeral 11: anolyte adjusting device, 12: anolyte outlet, 13: gas-liquid separator, 14: gas chamber, 15: oxygen-containing gas supply port, 16: oxygen-containing gas preparation device, 17: cathode chamber outlet, 18 ... Sodium hydroxide storage tank, 19 ... Heat exchanger

Claims (4)

[Claims] 1. A gas diffusion electrode is disposed in a cathode chamber of an ion exchange membrane electrolytic cell partitioned into an anode chamber and a cathode chamber by a cation exchange membrane, and a hydrophilic liquid permeates between the cation exchange membrane and the gas diffusion electrode. In the method for starting operation in an ion exchange membrane electrolytic cell for electrolysis of an aqueous alkali metal halide solution provided with a layer, the anode chamber is filled with an aqueous alkali metal halide solution and the hydrophilic liquid permeable layer is coated with an aqueous alkali metal hydroxide solution. A method for starting operation of an electrolytic cell, characterized in that after filling, an oxygen-containing gas is supplied to a gas chamber formed on a side of the gas diffusion electrode opposite to the cation exchange membrane to start energization. 2. The method for starting operation of an electrolytic cell according to claim 1, wherein the cathode chamber is filled with an aqueous alkali metal hydroxide solution and then withdrawn. 3. After circulating an aqueous alkali metal hydroxide solution in the cathode chamber, filling the hydrophilic liquid permeable layer with the aqueous alkali metal hydroxide solution, extracting the aqueous alkali metal hydroxide solution from the cathode chamber, The method for starting operation of an electrolytic cell according to claim 1, wherein the energization is started by supplying an oxygen-containing gas to the gas chamber. 4. The method according to claim 1, wherein the oxygen-containing gas contains water.