KR850000707B1 - Electrolytic process for the preparation of sodium chlorate - Google Patents

Abstract

Sodium chlorate is prepared with increased Faraday yield using electrolysis in a tank equipped with metal electrodes coated with electrochemical activating agents, such as platinum-iridium or ruthenium oxide, in the presence of hydrochloric acid for pH control Phosphoric acid, in the required amount per 1 ton NaClO3 is 0.85-1.7 kg, is added into the electrolyte to increase the Faraday yield due to reduction of oxygen-gas generation.

Description

Sodium chlorate manufacturing method of improving Faraday water

The present invention relates to advances in the production of sodium chlorate by electrolytic method, and more specifically, electrolytic sodium chlorate using an electrolytic cell composed of a titanium positive electrode on which an electrochemically active substance such as platinum-iridium or ruthenium oxide is deposited. It is related with the method of improving the FARADAY yield at the time of manufacture.

In the electrolytic preparation of sodium chlorate, an aqueous solution of sodium chloride is prepared by electrolysis.

And the reaction in the electrode is as follows.

At the anode -ion produces chlorine by the reaction

Chlorine produced at the anode reacts with water as follows:

The resulting hypochlorite is converted to chloric acid as shown in the following reaction formula.

_{^{2HClO + ClO - → ClO 3 _}} + 2H + + 2Cl _ ... … … … (5)

In the same step, the ions of hypochlorite are electrochemically produced as shown in the following scheme.

O₂+

…………(6) _{^{6ClO _ + 3H 2 O → 2ClO}} - + 4Cl _ + 6H + +

O ₂ +

… … … … (6)

In this case [refers to (6)], oxygen is inevitably generated during the electrolysis process, and this oxygen generation is the most important cause of decreasing the Faraday yield.

At the cathode, -electricity produces hydrogen as follows:

→ 3H₂…………(7)6H ⁺ +

→ 3H ₂ ... … … … (7)

And hypochlorite generated in the electrolytic cell can be reduced by this hydrogen as follows.

_{^{ClO _ + H 2 → Cl -}} + H 2 O ... … … … (8)

The secondary reaction of (8) also causes a decrease in the Faraday yield, but this secondary reaction is generally prevented by adding and dissolving sodium dichromate in an amount of 2-10 g / l in the electrolyte to cause a reverse reaction.

Another cause of the decrease in Faraday yield is that chlorine produced at the anode is not absorbed into the electrolyte and is released from the electrolytic cell as gaseous chlorine, as shown in the following equation:

There is a slight vapor pressure of chlorine on the upper side of the electrolyte, so it is certain that a small amount of chlorine is released from all surface portions of the electrolyte.

Reaction formula (5) mentioned above is the most important reaction for the production of chlorate, and this reaction is promoted by pH 6 to 6.5, and the optimum value of pH is determined by the operating temperature. In order to maintain the most suitable pH, it is known to add an acid solution, which is generally hydrochloric acid, to the electrolyte solution, thereby reducing the loss of chlorine.

The addition method of hydrochloric acid solution is added as in the known addition method, for example

-To the solution supplied to the electrolytic bath,-directly into the electrolytic bath,-or to the two methods described above, and generally the pH conditions are to be carried out automatically.

General operating conditions are illustrated as follows.

Electrolyte and Electrolytic Conditions:

NaClO ₃ (g / L): 0 ~ 700 Operating Temperature: 55 ~ 85 ℃

NaCl (g / L): 320 to 120 pH during operation: 6 to 6.5

Sodium dichromate (g / L): 2 to 10

The above pH is obtained by maintaining 25 to 40 kg of hydrochloric acid at a concentration of 33% for the production of one ton of sodium chlorate.

Current density A / ㎡: 1,500-6,000

The composition of the anode is a titanium anode on which RuO ₂ or Pt / Ir is deposited, and the composition of gas generated in the cathode is as follows.

H ₂ 96% O ₂ 3.5%

Cl ₂ 0.2 to 0.5%

Faraday yields are generally slightly higher than 92%. The addition of sodium chlorate to the raw material liquid for electrolysis is to improve the economics of electrolysis, which is known.

Various studies have been conducted to improve the Faraday yield. To this end, it has been reported to use several different solutions, all of which are merely to measure the adhesion of the positive electrode, such as, for example, French Patent No. 2,187,416.

The inventors have completed the method of improving the Faraday yield of 1 to 3% over that of the conventional one by directly controlling the electrolyte solution.

The method of the present invention is a method of adding 0.85 to 1.7 kg of phosphoric acid (H ₃ PO ₄ ) to 1 ton of sodium chlorate to be added to hydrochloric acid used to maintain optimal pH. This corresponds to 1-2 kg of phosphoric acid with a concentration of 85% relative to 1 ton of NaClO ₃ produced, so that it corresponds to 0.85-1.7 kg with H ₃ PO ₄ .

The rate of improvement in Faraday yield by the present method is slightly different depending on the conditions of the electrolyte and the electrolytic cell and its operating conditions. As for the improvement of the Faraday yield, the present invention has not been achieved on the basis of some theoretical basis from the beginning, so it is impossible to explain it theoretically. However, it is observed that the amount of oxygen generated in the electrolytic cell is 2.9% of the conventional one, whereas in the present invention, the amount of oxygen generated is reduced to 2.0%, and this reduction of oxygen generation is interpreted to improve the Faraday yield. will be.

In more detail, in general, in preparing sodium chlorate by the electrolytic method, the Faraday yield (R%) is calculated by the following formula, and the general formula is R% = 100% -oxygen generation% × 2-chlorine generation% x 1-1.1. On the other hand, in the conventional method, since the oxygen generation amount is 2.9% and the chlorine generation amount is 0.4%, R% = 100% -2.9% × 2-0.4% × 1-1.1% = 92.7, as in the case of the present invention. The addition of 0.85 to 1.7 kg of phosphoric acid per tonne of sodium chlorate produced to the known hydrochloric acid added for pH adjustment reduced oxygen production to 2.0%, that is, 0.9% reduction of oxygen production compared to the conventional method, This is interpreted as a cause of improvement in Faraday yield. Therefore, in the case of the present invention: R% = 100-2.9% × 2-0.4% -1.1% = 94.5% bar, the reduction of 0.9% oxygen generation during the electrolysis process by the addition of phosphoric acid as described above Faraday It would be reasonable to interpret this as the cause of the yield improvement.

The following examples are illustrated by way of example and not by the invention only.

Example 1

1) 1) of Example 1 is a comparative example and relates to a known method. An industrial electrolytic cell using 35,000 A as an operating current was installed in accordance with a known method by installing a titanium anode on which ruthenium dioxide was deposited. In view of the economics of electrolysis, the electrolyte solution charged into this electrolytic cell is obtained by separating only part of the sodium chlorate produced in the continuous electrolysis and charging the electrolyte solution containing the remainder of sodium chlorate in accordance with the known.

NaCl (g / L): 210 Ca and Mg (mg / L): 35

NaClO ₃ (g / L): 325 Fe, CO, Ni (mg / L): 2

Dichromate (g / ℓ): 7 Flow rate ratio of filling of electrolyte solution (ℓ / h): 120

NaClO (g / L): 0.3

550 mL of hydrochloric acid of 33% HCl is added continuously to the electrolytic cell. The electrolyzer operates at a current density of 2,000 A / m 2 at 70 ° C. and has a pH of 6.3.

The composition of the liquid emitted from this electrolytic cell is as follows.

NaCl (g / ℓ): 110 NaClO (g / ℓ): 1.5

NaClO ₃ (g / l): 520 Ca and Mg (mg / l): 15

Dichromate (g / ℓ): 7 Fe, CO, Ni (mg / ℓ): 2

The composition of gases generated during electrolysis is as follows:

H ₂ 96.7% O ₂ 2.9%

Cl ₂ 0.4%

And the number of Faraday R% is 92.7% as described above.

2) 2) of this Example 1 relates to the present invention.

All the operating conditions are carried out in accordance with the above 1), except that 220ml / h of 10% phosphoric acid, prepared by heat treatment, is added to hydrochloric acid of a known method for pH adjustment in a continuous flow and electrolytically. Perform. The feed of 220 ml / h of phosphoric acid with the above-mentioned concentration of 10% is calculated as 0.98 kg for 1 ton of sodium chlorate produced.

The composition of the gas generated is as follows.

H ₂ 97.6% O ₂ 2%

Cl ₂ 0.4%

Faraday yield was 94.5% and is consistent with the calculated value of Faraday yield (R%). Therefore, the Faraday yield is increased by 1.8% by the method of the present invention 2) from the above 1).

Example 2

In the electrolysis by the method of Example 1 described above, it is operated with the concentration of 10% phosphoric acid prepared by the wet method being added so that 0.15 g of phosphoric acid is contained in 1 liter of the electrolyte. The amount of phosphoric acid used above corresponds to the addition of 0.77 kg of H ₃ PO ₄ to 1 tonne of NaClO ₃ produced.

Oxygen in the exhaust gas was reduced by 0.3%, which is why the conventional Faraday yield was 92.72%, which is increased to 93.32% in the case of the present invention described in this example. This 93.32% is less than 2) of Example 1, but increased from 1) of Example 1.

Claims (1)

In the production of sodium chlorate by electrolytic method using an electrolytic cell with a metal anode with platinum-iridium or ruthenium oxide and adding hydrochloric acid to the electrolytic solution for pH adjustment, the amount of sodium chlorate produced per tonne of sodium chlorate (H ₃ PO ₄ ) Sodium chlorate production method characterized by improving the Faraday yield by adding 0.85 to 1.7kg to the above-mentioned known electrolytic liquid and electrolytically.