JP2001049478A - Electrolysis method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolysis method which is an oxygen cathode salt electrolysis method of a two chamber type and enables the additional lowering of light voltage consumption. SOLUTION: This electrolysis method consists in obtaining chlorine and an aqueous caustic soda solution by introducing brine into an anode chamber of a vertical type electrolytic cell, which is isolated to the anode chamber 5 and a cathode chamber by a cation exchange membrane 4, is disposed with anodes and cathodes in proximity to the cation exchange membrane respectively from both sides in the respective chambers and in which the cathode is a liquid permeation type gas diffusion electrode 5, and introducing oxygen-containing gas and water into the cathode chamber. In the method described above, the entire amount of the oxygen-containing gas and the water is introduced from the side into the upper part of the cathode chamber from plural introducing ports disposed in a horizontal direction from the introducing section 29 disposed laterally in the uppermost part of the cathode chamber. The excess gaseous oxygen and the formed aqueous caustic soda solution are withdrawn sideways from the lower part of the cathode chamber through the plural discharge ports disposed in a horizontal direction then to a discharge port 30 disposed laterally in the lowermost part of the cathode chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolysis method using a gas diffusion cathode, and more particularly, to an electrolysis method for a saline solution in a two-chamber electrolytic cell.

[0002]

2. Description of the Related Art Caustic soda, chlorine, and the like, which are basic materials in industry, are produced by electrolysis of saline, but use a large amount of electric power. For this reason, in the past, vigorous energy saving efforts were made in the saline electrolysis method, and significant energy saving was achieved. For the future, an oxygen-cathode salt electrolysis method, which can be expected to further save energy, is being studied. In this method, from salt, oxygen and water,
An aqueous caustic soda solution and chlorine gas can be obtained. The oxygen-cathode salt electrolyzer has usually adopted a three-chamber method. The three-chamber method is divided into an anode chamber, a catholyte chamber, and a gas chamber by a cation exchange membrane and a liquid-impermeable gas diffusion cathode.

On the other hand, a two-chamber method using a liquid-permeable gas diffusion electrode is also being studied. In the two-chamber method, the electrolytic cell is divided into two chambers, an anode chamber and a cathode chamber, by a cation exchange membrane, and a gas diffusion cathode is arranged in the cathode chamber. A high water content spacer is arranged between the cation exchange membrane and the gas diffusion electrode,
The electrolysis can be continued by holding the caustic soda aqueous solution. An oxygen-containing gas is supplied to the back of the gas diffusion cathode. Oxygen gas diffuses through the gas diffusion cathode, which has excellent gas permeability, and produces caustic soda at the reaction point. The generated aqueous caustic soda solution falls in the spacer, is drawn out to the back of the electrode through the hole, and is discharged out of the electrolytic cell together with the excess oxygen-containing gas.

[0004]

According to the study of the present inventor, it has been found at the research stage that the two-chamber oxygen cathode salt electrolysis method is also operated at a power consumption comparable to that of the three-chamber method. . The two-chamber type essentially has a smaller distance between the poles as compared with the three-chamber method, and is basically a factor of low voltage consumption. However, since the liquid side and the gas side are not clearly distinguished, there is a disadvantageous factor in terms of mass transfer as compared with the three-chamber method, and this is a cause that the consumption voltage cannot be reduced. Therefore, more excellent voltage reducing means is required. In addition, in the case of the two-chamber type, since there is no sufficient gap between the ion exchange membrane and the gas diffusion electrode and only the spacer is provided, the aqueous solution of caustic soda having a predetermined concentration cannot be flowed. It is designed to supply moisture. In that case, moisture is supplied to the gas chamber together with the oxygen-containing gas, and in some cases, the moisture is supplied in the form of water vapor.

[0005] Oxygen-containing gas and moisture are usually supplied from the upper part of the gas chamber through an inlet pipe because the thickness of the gas chamber is thin. However, even if the moisture is supplied in a heated water state, Even when supplied in the form of steam, along with the oxygen-containing gas,
In addition, since the gas enters vertically, it is influenced by the gas flow or the gravity, so that it is inevitable that the gas chamber (cathode chamber) is unevenly distributed, and the caustic soda aqueous solution is unevenly distributed in the gas chamber (cathode chamber). There are problems such as uneven density. In some cases, it may adversely affect the wetting of the gas diffusion electrode on the gas supply layer side. It is an object of the present invention to provide a two-chamber type oxygen cathode electrolysis method which can further reduce the consumption voltage and which does not cause the above-mentioned problems.

[0006]

The present invention has solved the above-mentioned problems by the following means. (1) The cation exchange membrane is separated into an anode chamber and a cathode chamber. In each chamber, the anode and the cathode face the cation exchange membrane from both sides, respectively, and the cathode is a liquid-permeable gas diffusion electrode. In the electrolysis method where salt water is introduced into the anode compartment of the electrolytic cell and oxygen-containing gas and moisture are introduced into the cathode compartment to obtain chlorine and caustic soda aqueous solution, the entire amount of oxygen-containing gas and moisture is provided at the uppermost side of the cathode compartment. From the inlet into the upper part of the cathode chamber from the plurality of inlets provided horizontally, and from the lower part of the cathode chamber to the outlet provided at the bottom of the cathode chamber from the plurality of outlets provided horizontally. An electrolytic method characterized in that an excess gas and an aqueous solution of generated caustic soda are extracted to a side portion. (2) The electrolysis method according to (1), wherein the water introduced into the upper part of the cathode chamber is heated water. (3) The electrolysis method according to (2), wherein the temperature of the heated water is 70 to 100 ° C. (4) The amount of water introduced into the upper part of the cathode compartment is insufficient for electroosmotic water supplied from the anode compartment through the ion exchange membrane to form an aqueous caustic soda solution in the cathode compartment. The electrolysis method according to (1).

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings. FIG. 1 is a conceptual diagram of an example of an electrolysis apparatus that is preferably used in practicing the present invention using a two-chamber electrolytic cell. Arrows indicate the direction of movement of the substance during operation. A two-chamber electrolytic cell 1 is provided, and an anode chamber outlet 2 thereof communicates with a gas-liquid inlet of a gas-liquid separator 11. The gas-liquid separator 11 has a chlorine gas outlet 12 and a gas-liquid separator 11.
Of the heat exchanger 14 through the fresh salt water recovery port 13
To the secondary pipe inside. This secondary tube of the heat exchanger 14 is connected to the anode chamber inlet 3 of the electrolytic cell 1 via a purified saturated saline inlet 15 on the way.

[0008] In the electrolytic cell 1, an ion exchange membrane 4 is vertically stretched inside, and partitions the inside into an anode chamber 5 and a cathode chamber 6. The anode chamber 5 is provided with an anode 7 in contact with the surface of the ion exchange membrane 4, and the cathode chamber 6 is provided with a gas diffusion cathode 8 with a spacer (shown in FIG. 2) between the ion exchange membrane 4 and the ion exchange membrane 4.
Is installed, and the anode 7 and the gas diffusion cathode 8 are connected to the cation exchange membrane 4.
And confront each other from both sides. On the opposite side of the surface on which the spacers are provided, that is, on the back surface of the gas diffusion cathode 8, a gas-permeable porous filler (not shown) is arranged as a gas chamber in contact therewith. The cathode chamber 6 is provided with a cathode chamber inlet 9 through which oxygen and moisture flow, and a cathode chamber outlet 10 through which generated caustic soda and excess oxygen flow. Cathode room 6
The gas diffusion cathode 8 inside has a gas chamber as described later. A heat medium (or refrigerant) inlet 16 and a heat medium (or refrigerant) outlet 17 are provided on the primary side of the heat exchanger 14.

The present invention is suitable for a two-chamber oxygen cathode salt electrolysis method. In the three-chamber method, it is hindered by an ion-exchange membrane and a liquid-impermeable gas diffusion cathode, and is divided into an anode chamber, a catholyte chamber, and a gas chamber, and the catholyte cannot freely enter and leave each other. In addition, strict sealing may be applied to prevent free access. Since a liquid-permeable gas diffusion cathode is used in the two-chamber method, the catholyte can also enter the gas chamber by means of permeation or sneaking. In order to carry out efficient electrolysis in the two-chamber method, the catholyte must be filled between the ion exchange membrane 4 and the gas diffusion cathode 8. Simply contacting the ion exchange membrane 4 and the gas diffusion cathode 8 cannot maintain a sufficient liquid. In addition, when the ion exchange membrane 4 and the gas diffusion cathode 8 are brought into close contact with each other, there is caused a trouble that Ni components and the like constituting the gas diffusion cathode 8 are accumulated in the ion exchange membrane 4. Therefore, it is necessary to insert a porous material having excellent liquid retention properties as a spacer between the ion exchange membrane 4 and the gas diffusion cathode 8. Cloths, felts and the like made of carbon fibers are particularly suitable materials for such spacers.

An oxygen gas is supplied to the back of the gas diffusion cathode 8. Since the oxygen gas needs to be introduced into the gas diffusion cathode 8 as effectively as possible, the thickness of the gas chamber is made as small as possible. Turbulence. It is also necessary to supply electricity to the gas diffusion cathode 8. The gas chamber filling uses a conductive material, and this filling is also used as a current collector. For example, wire mesh, expanded metal, sponge metal, and the like are used. The material must be a material that can withstand oxygen and high-temperature alkali. A Ni material or a Ni material plated with Ag to enhance corrosion resistance is preferable. Further, the film, the spacer, and the gas diffusion cathode are required to maintain a state in which they are in close contact with each other, and for that purpose, it is desirable that the film, the spacer, and the gas diffusion cathode have overall elasticity. In that sense, the gas chamber filling is preferably a wire mesh, expanded metal, sponge metal or the like.

As raw materials for the cathodic reaction, oxygen and moisture are required. Most of the water is supplied from the anode chamber through the ion exchange membrane as electroosmotic water, but the current ion exchange membrane alone is insufficient for water. The shortage of water
It is necessary to supply the gas to the gas diffusion cathode via the gas chamber. Electroosmotic water is about 4 moles per mole of Na ion. If it is desired to obtain a 32% aqueous solution of caustic soda, it is necessary to supply more than 1.2 mol of water per mol of NaOH, taking into account 0.5 mol consumed in the cathode chamber 6. As the supplied water, steam, spray water, or liquid water can be used. In the present invention, the replenished water is collectively introduced into the uppermost portion of the gas chamber together with the oxygen-containing gas from the side, and is caused to flow down from the upper end of the gas diffusion cathode 8.
That is, the entire amount of the oxygen-containing gas and the water is introduced laterally into the upper part of the cathode chamber from a plurality of introduction ports provided in the horizontal direction from the introduction part provided on the uppermost side of the cathode chamber. Thereby, moisture can be uniformly supplied from the upper part in the gas chamber.

A large amount of the introduced water is consumed in the electrolytic reaction performed on the entire surface of the gas diffusion cathode 8, and is used for diluting the aqueous solution of caustic soda. The caustic soda produced at the top of the cathode compartment 6 becomes very diluted due to the presence of a large excess of moisture. The concentration of caustic soda gradually increases as it moves to the lower part, and a predetermined concentration,
For example, it is about 32%. The aqueous solution of caustic soda generated on the entire surface of the gas diffusion cathode 8 falls in the spacer,
Alternatively, the gas passes through holes, cuts, and surrounding spaces in the gas diffusion cathode 8. Further, the gas is moved to the gas chamber in which a porous filler (not shown) is disposed on the back surface in the gas diffusion cathode 8 and is discharged from the cathode chamber outlet 10 together with excess gas to the outside. In the present invention, it is important to introduce the entire amount of water into the upper portion of the cathode chamber in a lump and from the side. By uniformly introducing water into each part of the gas electrode from above, the concentration of the generated caustic soda in each part becomes relatively uniform, and it becomes difficult to form a large concentration gradient with caustic soda.

The amount of water introduced into the upper part of the cathode chamber 6 from the cathode chamber inlet 9 is determined by the concentration of the caustic soda to be obtained. The water to be introduced may be a gas, but is preferably a liquid. In the case of a liquid, it is desirable to introduce it at a temperature close to the operating temperature of the electrolytic cell. That is, 70 to 100 ° C. is desirable. If the temperature is lower than this, the upper part of the cathode chamber is cooled, and the current hardly flows. Although steam may be used, the temperature tends to rise above a predetermined temperature. The gas diffusion cathode needs to have a structure in which moisture and gas components can move on the front and back of the electrode. A structure in which the gas diffusion cathode itself can partially permeate the liquid,
For example, an electrode using an Ag-plated sponge-like metal for the skeleton may be used, or even if the electrode itself is liquid-impermeable, the liquid can be substantially circulated by means such as making a hole or making a cut. What is necessary is just to be the structure which can be performed.

The electrolysis works well in the temperature range from 80 ° C. to 90 ° C. If it is lower than this, the cell voltage rises abnormally, causing deterioration of the power consumption unit. On the other hand, when the temperature exceeds 90 ° C., deterioration of the ion exchange membrane and the gas diffusion cathode is accelerated. If the temperature is not artificially controlled, the temperature of the electrolytic cell 1 is usually kept at a certain temperature due to heat generation and heat radiation accompanying the electrolytic reaction, but the temperature varies greatly depending on the load, the temperature, and the elapsed time. There is. In the case of the two-chamber method, as understood from the above description, it is extremely difficult to circulate the caustic soda solution externally, and the temperature of the electrolytic cell is adjusted by circulating the anolyte to the external heat exchanger 14 and exchanging heat. I do.

The reason why a low voltage is obtained by the present invention is considered as follows. Although 30% or more of caustic soda can be obtained from the cathode chamber outlet 10, the average concentration of caustic soda in the cathode chamber 6 is lower than this, and the upper part of the electrolytic cell 1 is thinner. The electric conductivity of the ion exchange membrane 4 increases as the concentration of caustic soda decreases, and the voltage decreases if the current is constant. Also, in the cathodic reaction, the lower the concentration of caustic soda, the easier the supply of water and the more easily the generated caustic soda is separated from the reaction point in the electrode, the more the reaction proceeds, the overvoltage decreases, and the voltage decreases. Since the voltage between the electrodes in the electrolytic cell 1 is constant,
The current density is higher at the top. It is possible to operate at a voltage lower than expected from the caustic soda concentration thus obtained. As understood from this description, the higher the electrolytic cell 1 is, the lower the concentration of the upper caustic soda is. Therefore, the voltage lowering effect is more remarkable in the electrolytic cell having a longer drop distance of the supplied water, that is, a higher electrolytic cell. In the present invention, the entire amount of moisture is introduced together with the oxygen-containing gas from the side into the upper portion of the cathode chamber,
Since the gas is dropped along the entire surface of the gas diffusion cathode, the electrolytic reaction is performed by efficiently using the entire surface of the gas diffusion cathode. As a result, the reaction can be covered economically with low consumption voltage.

[0016]

The present invention will be described below in detail with reference to examples. However, the present invention is not limited to these examples.

Example 1 A filter press type monopolar electrolytic cell equipped with a gas diffusion cathode having an effective area of 10 cm in width and 60 cm in height was used. Rated current density is 3kA /
At m ² , the current is 180A. The gas diffusion cathode 8 has A
A liquid-permeable electrode prepared by hot pressing with Ag fine particles and PTFE particles was used using g-plated sponge Ni as a base material. As shown in FIG. 2, the anode 7 and the ion-exchange membrane (Aciplex 4203, manufactured by Asahi Kasei Corporation) 4 are in close contact with each other, and between the ion-exchange membrane 4 and the gas diffusion cathode 8, a carbon fiber having a thickness of 0.28 mm is provided. Paper (carbon paper SH-28Z, manufactured by Nippon Carbon Co., Ltd.) was inserted as the spacer 26.

On the back surface of the gas diffusion cathode 8, a gas chamber back plate 21 is provided.
A gas chamber 28 is formed between the gas diffusion cathode 8 side and a silver-plated corrugated mesh 25 having a thickness of 1 mm, a silver-plated thickness of 6 mm (before setting), and 20 ppi (from the gas diffusion cathode 8 side). The sponge nickel plate 24 (with an average of 20 holes per inch) was inserted. This sponge plate can transmit gas in three-dimensional directions. Tighten the whole with an end plate (not shown)
The anode 7, the ion exchange membrane 4, the carbon fiber spacer 26, the gas diffusion cathode 8, the corrugated mesh 25, the sponge nickel plate 24, and the gas chamber back plate 21 were adhered to each other. At this time, the sponge nickel plate 24 in the gas chamber 28 has a thickness of 4 mm.
Compressed up to.

In the anode chamber 5, 4 purified saturated saline solutions at 60 ° C.
2 ml / min was supplied. 0.75 Nl / mi of oxygen is supplied from the oxygen / water supply passage 29 provided above the cathode side frame 20 to the upper part of the gas chamber 28 from the oxygen / water inlet 22.
n and 2.45 g / min of water heated to 90 ° C. were introduced. In the oxygen / water inlet 22, five holes each having a diameter of 2 mm and opening in the horizontal direction are arranged at intervals of 15 mm in the horizontal direction. A surplus oxygen / caustic soda discharge passage 30 is provided at a lower portion of the cathode side frame, and a surplus oxygen / caustic soda outlet 23 is provided in the discharge passage 30. The surplus oxygen / caustic soda outlet 23 has a diameter of 6 mm that opens in the horizontal direction. Five holes are arranged horizontally at an interval of 15 mm.

Electrolysis was performed at a current density of 3 kA / m ² while controlling the temperature of the anolyte to 87 ° C. The terminal voltage was 2.00V. At that time, the obtained caustic soda had a concentration of 33.0% and a current efficiency of 97%. The upper, middle, and lower current distributions are each 37.3.
% (Current density 3.36 kA / m ² ), 33.7% (current density 3.04 kA / m ² ), 28.9% (current density 2.
60 kA / m ² ). 20 downward from the top of the electrode
The resulting caustic soda solution at the points of cm and 40 cm was sampled and the concentration was measured.
%Met.

[Comparative Example 1] The height of the electrolytic cell was 10 cm.
An electrolytic cell was constructed in the same manner as in the example except that
3kA / m^TwoAnd an electric current of 30 A. The voltage is 2.1
5V, concentration of generated caustic soda is 33.0%, its current effect
The rate was 96%. Comparative Example 2 An electrolytic cell similar to that of Example 1 was constructed. oxygen
Was introduced all at once from the top. However, water is divided into three
And introduced at 0cm, 20cm and 40cm from the top
did. The voltage was 2.13 V, and the concentration of caustic soda was 3
3.0%, its current efficiency is 96%, current distribution is upper, middle
34.0% (current density 3.06 kA /
m ^Two), 33.3% (current density 3.00 kA / m)^Two),
32.7% (current density 2.95 kA / m^Two)Met.
The obtained caustic soda concentrations are upper, middle and lower, respectively.
Were 32.0, 32.5 and 33.0%.

[0022]

According to the present invention, all the water to be added to the gas chamber is collectively introduced into the upper portion of the cathode chamber together with the oxygen-containing gas from the side, and the generated caustic soda is extracted from the lower outlet. For electrolysis. If the temperature of the water is set to 80 to 90 ° C., the cell voltage can be lowered. If the amount of supplied water is insufficient for electroosmotic water entering from the ion-exchange membrane, a caustic soda aqueous solution having a high concentration of about 30% can be obtained at a low electrolytic voltage.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an example of an electrolysis apparatus using a two-chamber electrolytic cell according to the present invention.

FIG. 2 shows a longitudinal sectional view of a two-chamber electrolytic cell according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 2-chamber electrolytic cell 2 Anode chamber outlet 3 Anode chamber inlet 4 Ion exchange membrane 5 Anode chamber 6 Cathode chamber 7 Anode 8 Gas diffusion cathode 9 Cathode chamber inlet 10 Cathode chamber outlet 11 Gas-liquid separator 12 Chlorine gas Outlet 13 Fresh salt water recovery port 14 Heat exchanger 15 Salt water inlet 16 Heat medium (or refrigerant) inlet 17 Heat medium (or refrigerant) outlet 20 Cathode side frame 21 Gas chamber back plate 22 Oxygen / moisture inlet 23 Excess oxygen・ Caustic soda outlet 24 Sponge Ni plate 25 Corrugated mesh 26 Carbon fiber spacer 27 Gasket 28 Gas chamber 29 Introductory passage 30 Discharge passage

 ──────────────────────────────────────────────────続 き Continued on the front page (71) Applicant 390014579 Permelec Electrode Co., Ltd. 2023-1520 Endo, Fujisawa-shi, Kanagawa (72) Inventor Koji Saiki 4-6-1-815 Hojo-cho, Toyonaka-shi, Osaka (72) Invention Applicant Akihiro Sakata 1-14-1 Nishi-Shimbashi, Minato-ku, Tokyo, Japan Inside Toagosei Co., Ltd. (72) Inventor Hiroaki Aikawa 3-5-2 Kasumigaseki, Chiyoda-ku, Tokyo Mitsui Chemicals, Inc. (72) Inventor Shuji Nakamatsu 2023-15 Endo, Fujisawa-shi, Kanagawa Prefecture F-term (per reference) 4K011 AA12 AA22 AA68 CA04 DA03 4K021 AA03 AB01 BA02 BA03 BB01 BB05 BC01 CA08 CA09 CA12 DB01 DB04 DB05 DB16 DB31 DB49 DB53

Claims (4)

[Claims] 1. A cation exchange membrane is separated into an anode chamber and a cathode chamber. In each chamber, an anode and a cathode are opposed to the cation exchange membrane from both sides, respectively, and the cathode is a liquid-permeable gas diffusion electrode. In the electrolysis method in which salt water is introduced into the anode compartment of a vertical electrolytic cell and oxygen-containing gas and moisture are introduced into the cathode compartment to obtain an aqueous solution of chlorine and caustic soda, the total amount of oxygen-containing gas and moisture is transferred to the uppermost side of the cathode compartment. Introduced from the side introduced into the upper part of the cathode chamber from a plurality of introduction ports provided in the horizontal direction from the introduction part provided in
An electrolysis method characterized in that surplus oxygen gas and an aqueous solution of generated caustic soda are laterally extracted from a plurality of outlets provided in a horizontal direction from a lower portion of a cathode chamber to an outlet provided on a lower side of the cathode chamber. 2. The electrolysis method according to claim 1, wherein the water introduced into the upper part of the cathode chamber is heated water. 3. The electrolysis method according to claim 2, wherein the temperature of the heated water is 70 to 100 ° C. 4. The amount of water introduced into the upper part of the cathode chamber is insufficient for electroosmotic water supplied from the anode chamber through the ion exchange membrane to form an aqueous caustic soda solution in the cathode chamber. The electrolysis method according to claim 1.