JP2014015649A - Production method of caustic soda - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of caustic soda that is not affected with demand and supply of caustic soda and chlorine because there is not byproduct of chlorine.SOLUTION: In a method in which a sodium salt aqueous solution is subjected to electrolysis by an ion exchange membrane method to produce caustic soda, a hydrogen gas diffusion electrode is used in a positive electrode, caustic soda is generated in a negative electrode chamber, an acid is generated in a positive electrode chamber, the acid is reacted with soda ash and/or sodium bicarbonate to generate a sodium salt to be used in electrolysis.

Description

  The present invention relates to a method for producing caustic soda by electrolyzing an aqueous sodium salt solution by an ion exchange membrane method, and does not co-produce chlorine and hydrogen, and does not affect the demand for their gas components, particularly chlorine. The present invention relates to a method for selectively manufacturing the above.

  Conventionally, a manufacturing method of caustic soda that electrolyzes saline by ion exchange membrane method has been widely used industrially, and improvement of anode, cathode, and ion exchange membrane has advanced energy saving by high current efficiency and low voltage. It is out.

  On the other hand, in the conventional electrolysis method, since chlorine and hydrogen are produced together with caustic soda, there is a problem that production of caustic soda is restricted particularly by fluctuations in demand for chlorine.

  As a method for producing caustic soda that does not generate chlorine, for example, a method of electrolyzing a sodium sulfate aqueous solution instead of saline is known (for example, see Patent Document 1). By using an aqueous solution of sodium nitrate, chlorine is not generated, but sulfuric acid is by-produced in the anode chamber, the pH of the anode chamber is lowered, and caustic soda cannot be generated, or current efficiency is lowered. In addition, sodium sulfate is more expensive than salt, and there is a problem that high concentration electrolysis cannot be performed due to low solubility.

Japanese Patent No. 3196382

  The present invention provides a method for producing only caustic soda without electrolyzing chlorine or a chlorine-containing compound when an aqueous sodium salt solution is electrolyzed by an ion exchange membrane method.

  As a result of intensive studies on a method for producing caustic soda that electrolyzes saline by an ion exchange membrane method, the present inventors have produced a caustic soda in the cathode chamber using a hydrogen gas diffusion electrode as the anode, and an acid in the anode chamber. And the acid is reacted with soda ash and / or sodium bicarbonate to regenerate the sodium salt, which is further electrolyzed to find that caustic soda can be produced without chlorine by-products, thereby completing the present invention. It came to.

  Hereinafter, the manufacturing method of the caustic soda of this invention is demonstrated.

  The electrolysis of the present invention uses a hydrogen gas diffusion electrode as an anode in a method for producing caustic soda that electrolyzes saline by an ion exchange membrane method.

  In the conventional electrolysis method, electrodes such as metal and / or metal oxide are used. However, when saline is used as a raw material, chlorine gas and hydrogen gas are generated. On the other hand, in the method of the present invention, chlorine gas is not generated and energy consumption can be reduced by using a hydrogen gas diffusion electrode.

  On the other hand, in the cathode chamber, caustic soda is generated in the same manner as in normal electrolysis, and hydrogen is generated from the electrodes. The generated hydrogen can be used as hydrogen (or a part thereof) supplied to the hydrogen gas diffusion electrode.

  Acid is generated in the anode chamber, which reacts with soda ash and / or sodium bicarbonate to regenerate the sodium salt. The regenerated sodium salt is further recycled for electrolysis.

  In the method of the present invention, carbon dioxide gas is generated in the reaction between the acid generated in the anode chamber and soda ash and / or sodium bicarbonate, but the carbon dioxide gas generated by the method of the present invention is extremely high in purity and concentration. It has high value as an industrial raw material.

  In the method of the present invention, the reaction between the generated acid and soda ash and / or sodium bicarbonate may be carried out in a separate reaction chamber. However, by introducing soda ash and / or sodium bicarbonate into the anode chamber, A more compact reactor design is possible by reacting simultaneously with generation.

  In the method of the present invention, by introducing soda ash and / or sodium bicarbonate into the anode chamber, when the reaction is carried out simultaneously with the generation of acid by electrolysis, scaling in the electrolytic cell and the suppression of troubles in the electrolysis reaction, In order to promote the progress of the reaction and the degassing of carbon dioxide, it is preferable to warm and stir.

  In the method of the present invention, the anode chamber is preferably electrolyzed at 2 ≦ pH ≦ 6. In the region where the pH is less than 2, hydrogen ions on the liquid phase side of the anode chamber have a high concentration and move to the cathode chamber side through the cation exchange membrane, so that the current efficiency of caustic soda generation decreases. Further, in the region where the pH exceeds 6, the neutralization reaction is slow, and soda ash and / or sodium bicarbonate and generated carbon dioxide are likely to remain in the solution. The pH of the anode chamber is particularly preferably adjusted to 3-4.

  In addition to the gas generating electrode, a gas diffusion electrode that introduces oxygen can be used as the cathode. A cation exchange membrane is used as the ion exchange membrane. The material of the electrode and the cation exchange membrane are not particularly limited, but those used for the production of caustic soda by conventional electrolysis can be used.

  According to the method of the present invention, in the production of caustic soda by the ion exchange membrane electrolysis method, it is possible to produce caustic soda without generating chlorine and hydrogen as a by-product and not being affected by the supply and demand of gas, and to reduce energy consumption in the electrolysis method. be able to.

An overview of the electrolytic cell and external neutralization process is shown. An outline of the electrolytic cell and the neutralization process in the cell is shown.

  Next, although this invention is demonstrated with a specific Example, this invention is not limited to these Examples.

Example 1
A two-chamber electrolytic cell equipped with a porous chamber electrode carrying platinum as an anode and a nickel electrode as a cathode and separated into an anode chamber and a cathode chamber by a cation exchange membrane (Naupion membrane manufactured by Deyupon) was used. 300 g / L saline was supplied to the anode chamber liquid phase side, and the flow rate was adjusted so that the pH of the discharged brine was 3. Hydrogen gas was supplied to the anode chamber gas phase side at a rate of 1 L / min. Electrolysis was performed at an electrolytic current density of 3 kA / m ² while supplying pure water to the cathode chamber so that the caustic concentration was 30 wt%. The electrolytic voltage at this time was 2.4 V, and the current efficiency of caustic soda generation was 93%.

  Soda ash was added to the mixed aqueous solution of hydrochloric acid and saline discharged from the anode chamber to neutralize the hydrochloric acid and adjust the saline concentration to 300 g / L, which was reused for electrolysis. Carbon dioxide generated when soda ash was added was recovered as a high-purity product.

Example 2
Electrolysis was carried out under the same conditions as in Example 1 except that 250 g / L of an aqueous sodium silicate solution was supplied to the anode chamber liquid phase side. The electrolytic voltage at this time was 2.6 V, and the current efficiency of caustic soda generation was 90%.

  Soda ash was added to the mixed aqueous solution of sulfuric acid and mirabilite discharged from the anode chamber to neutralize the sulfuric acid, and the concentration of mirabilite water was adjusted to 250 g / L, which was reused for electrolysis. Carbon dioxide generated when soda ash was added was recovered as a high-purity product.

Example 3
Using the same electrolytic cell as in Example 1, 200 g / L of saline was applied to the anode chamber liquid phase side. Electrolysis was carried out under the same conditions as in Example 1 while supplying a soda ash solution so that the pH of the saline solution in the anode chamber was 6. The electrolytic voltage at this time was 2.7 V, and the current efficiency of caustic soda generation was 95%.

  Carbon dioxide generated from the anode chamber liquid side was recovered as a high-purity product.

Comparative Example 1
The experiment was performed under the same conditions as in Example 1 except that the pH of the discharged salt water was 1. The electrolytic voltage at this time was 2.3 V, and the current efficiency of the caustic soda purification was 75%.

  The present invention can be used to produce caustic soda that does not produce chlorine as a by-product.

Claims (6)

In a method for producing caustic soda by electrolyzing a sodium salt aqueous solution by an ion exchange membrane method, a hydrogen gas diffusion electrode is used as an anode, caustic soda is produced in a cathode chamber, an acid is produced in an anode chamber, and the acid is produced as soda ash. A method for producing caustic soda characterized by reacting with sodium bicarbonate and / or sodium bicarbonate to produce sodium salt, which is used for electrolysis. The method for producing caustic soda according to claim 1, wherein the reaction between the soda ash and / or sodium bicarbonate and the acid generated in the anode chamber is carried out in the anode chamber. 3. The method for producing caustic soda according to claim 1, wherein the electrolytic solution in the anode chamber is electrolyzed at 2 ≦ pH ≦ 6. The method for producing caustic soda according to any one of claims 1 to 3, wherein the sodium salt is sodium chloride. The method for producing caustic soda according to any one of claims 1 to 3, wherein the sodium salt is sodium sulfate or sodium nitrate. The method for producing caustic soda according to any one of claims 1 to 5, wherein the cathode is an oxygen gas diffusion electrode.

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