CS215039B2 - Method of electrolytic production of the sodium chlorate, facilitating the ammelioration of the produce according to faraday - Google Patents

Description

The invention relates to an improvement in the electrolytic production of sodium chlorate, in particular to a Faraday yield improving agent when using electrolytic cells equipped with titanium anodes coated with an electroactive layer, for example platiniridium or ruthenium dioxide.

The electrolytic production of sodium chlorate is mainly carried out by electrolysis of the sodium chloride solution.

Reactions taking place on electrodes can be described by the following schemes:

a) chlorine evolution occurs according to reaction (1) β СГ ------ 3 C12 + 6e ~ (1), chlorine formed on the anode reacts with water according to reaction scheme (2), (3), (4),

Cl., * 3 4,0 3 И + ЗСГ + 3 НСЮ (2) not 3H ** 3 ею (3) and the hypochlorite formed is converted to chlorate according to equation (5)

HC1O 4- С1СГ - 0103 '+ 2 H ⁺ + 2 СГ (5).

Simultaneously electrochemical formation of chlorate from hypochlorite ions occurs according to equation (6)

H ₂ O 3 OH - t 3 H ⁺ W

C1O- + 3 H2O - 2 CIO5- + + 4 СГ + 6 H + + O2 + 6 e- (6).

This reaction releases oxygen produced by electrolysis; this release is a major cause of the Faraday yield reduction.

b] Hydrogen evolution occurs at the cathode according to the reaction (7)

H + + 6 e ~ -3 H2 (7).

The hypochlorite produced in the cell can be reduced by the released hydrogen according to equation (8)

C10-4H2-Cl- + HaO (8).

This parasitic reaction (8), which is another cause of the Faraday yield reduction, is usually suppressed by the addition of 2 to 10 g / liter of sodium dichromate added to the electrolyte.

Another reason for the reduction in Faraday yield is that the chlorine that is released on the anode can escape directly from the electrolyzer without being absorbed as shown by the equilibrium in the reactions

ClO-f HCtO

HCCO + H ⁺ t 11 - -: ^ = ± Cl ^ -t- H _Z O There is a certain chlorine gas voltage above the solution and can therefore escape from the entire surface of the liquid.

Reaction (5) is most important for the formation of chlorate and is supported by a pH of between 6 and 6.5, the optimum value depending on the temperature at which the reaction is carried out. In order to maintain this optimum value, an acid solution, typically hydrochloric acid, is therefore added to the electrolyte, which also makes it possible to compensate for any possible loss of chlorine.

According to the prior art, this addition is carried out either - into the solution to be fed - as injection into the electrolyzer, - or directly into the electrolyzer, - or both, and is usually automated by pH regulation.

Under normal operating conditions NaC103 g / liter 0 to700

NaCl g / liter 320 to 120 sodium dichromate g / liter 2 to 10 operating temperature 55 to 85 ° C pH value 6 to 6.5, achieved by addition of 25 to 40 kg of 33o / o HCl based on 1 ton of produced sodium chlorate current density A / m2 1500 to 6000 anode The titanium carrier, coated with platiniridium or ruthenium dioxide, has the following evolving gases:

H2 66%

O2 3.5%

Ch 0.2 to 5% and Faraday yield greater than 92%.

Attempts have been made to improve this yield. Various solutions have been proposed, all of which consisted in improving the anode coatings as described in French Patent No. 2 187 416.

A method has now been developed which makes it possible to achieve an increase in Faraday yield of 1 to 3 percent by direct action on the electrolyte.

The process according to the invention is therefore characterized in that phosphoric acid in an amount of 1 to 2 kg of 85% phosphoric acid, based on 1 ton of sodium chlorate produced, is added to the hydrochloric acid used to maintain the optimum pH.

The increase in yield depends on the electrolyte yield, the electrolysis technology and the operating conditions used.

The following examples illustrate the invention without limiting its scope.

Example 1

1. Electrolysis is carried out according to a conventional procedure in an industrial electrolyser -35-000- A equipped with titanium anodes coated with ruthenium dioxide. A solution of the composition is fed to the electrolyzer

NaCl g / liter 210 NaClOs g / liter 325 dvojchroman g / liter 7 NaClO g / liter 0.3 Ca + Mg mg / liter 35 Fe, CO, Ni mg / liter 2 at 120 l / h. Continuously into the electrolyzer brings 550 ml - 33% hydrochloric acid. Electrolyser works with density current 2000 Am ² at temperature 70 ° C. The pH is 6.3. Composition of the solution leaving the electrolyte zeru, is this: NaCl g / liter 110 NaClOs g / liter 520 dvojchroman g / liter 7 NaClO g / liter 1.5 Ca 4- Mg mg / liter 15 Dec Fe, CO, Ni mg / liter 2

The gases produced by electrolysis have the following composition:

H2 96.7%

O2 2.9%

C12 0,4%

Faraday yield 92.7%.

2. According to the method according to the invention, it is added to the same operating conditions

Example 2 hydrochloric acid continuous addition of 220 ml of 10% phosphoric acid produced by a thermal process. The composition of the resulting gases is

H2

C12 and Faraday yield 94.5%. The process according to the invention thus achieves an improvement in yield of 1.8%.

A process for the electrolytic production of sodium chlorate to improve Faraday yield on metal anodes coated with a platinum-di-rhodium or ruthenium dioxide layer, characterized in that the

Claims (2)

The hydrochloric acid used to maintain the optimum pH value adds 1 to 2 kg of 85% acid per tonne of sodium chlorate produced. 97.6% 2% 0.4% Under the same electrolysis operating conditions as in Example 1, 10% wet phosphoric acid is added such that its content in 1 liter of electrolyte is 0.15 g of acid. The amount of oxygen in the resulting gases is lower by 0.3%, which increases the Faraday yield from 92.72% to 93.32%.