SU1411353A1 - Method of producing alkali - Google Patents

Abstract

The invention relates to the electrolytic production of alkalis and makes it possible to reduce the cost of the process by eliminating the use of scarce materials. In this method, the alkali is obtained by electrolysis of an alkali metal carbonate solution in a cell with two asbestos-based filtering diaphragms located between the anode and the cathode. A solution of -98, chi and itineosis and an alkali metal carbonate dienvor are fed into the interdiafragment space and it is filtered through the diaphragm nearest to the anode and through the cathode diaphragm to the cathode. The depleted anolyte in the form of a mixed solution of basic and acid carbonate salts of an alkali metal is removed from the anode space. Electrolytic alkali is removed from the cathode space — a mixed solution of alkali and alkali metal carbonate. Oxygen is released at the anode; anode gas contains oxygen and carbon dioxide. Hydrogen is released at the cathode. The process is conducted in such a way that the concentration of the obtained alkali is maintained within 0.9-2.5 g-eq / l, and the anolyte contains a total of 2.2-4.0 g-eq / l Ma2CO3 + NaHCOs or 1.4 -8.0 g-eq / l К2СОз + КНСОз. 1 3. p. F-crystals, 2 tables. € (L

Description

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This invention relates to the electrolytic production of alkalis by the electrolysis of carbonate properties of alkali metals.

The purpose of the invention is to make the process cheaper by eliminating the use of deficient materials.

Example 1. Sodium carbonate solution is electrolyzed by a known method at a current density of 0.2 kA / cm, 90 ° C in a 10 A electrolyzer with a titanium case, a steel mesh cathode with a cation-exchange membrane, a steel cathode. platinum anode.

A solution of soda with a content of 4.0 g-eq / l Na2CO3 is supplied to the anode space, and a depleted anolyte with a content of 3.9 g-eq / l Na2CO3 + 0.1 g-eq / l NaHCO is fed into the cathode space. water in an amount of 20 g / h; and an alkali solution with a content of 5 g-eq / l NaOH is removed. The alkali current output is 86%, the voltage on the electrolyzer is 4.0 V.

Example 2. A 10 A electrolysis was carried out with a 10 A electrolyzer with a titanium JCOM, a steel mesh cathode and an asbestos diaphragm mounted on it and a guitar / platinum anode. A solution with a content of i, 0 g-eq / l of Ma2CO3, which is filtered by a jepe3 diaphragm to the cathode, is fed into the anode space, and the catholyte is removed from the cathode space. Electrolysis

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conducted at a current density of 0.1 A / cm and 90 ° C. Catholyte contains 4.0 g-eq / l NagCOa, there is no alkali in it, and the alkali output on current is zero.

Example 3. Alkali is obtained in a 10 A laboratory electrolyzer with a titanium case, a steel mesh cathode with an asbestos diaphragm pumped onto it and a diaphragm located between the anode and cathode diaphragm, from three sheets of asbestos paper and a titanium-platinum anode. The electrolyzer is fed with a solution containing 4.0 g-eq / l of sodium carbonate, which is fed into the interdiafragment space of the electrolyzer.

The electrolysis is carried out at 90 ° C and a current density of 0.1 A / cm. A depleted anolyte with a content of 2.26 g-eq / l of Ma2CO3 + 0.44 g-eq / l of NaHCOa is removed from the anode space, a solution of electrolytic alkali with a content of 2.5 g-eq / l of NaOH-) is removed from the cathode space -1.9 g-eq / l Na2CO3 and hydrogen. Anode gas contains 78% O2 + 13% CO2. Alkali current output is 90%, voltage 4.1 V.

Example 4. Alkali production is carried out in the same electrolyzer as in example 3. The operation mode of the electrolyzer and its performance are given in Table. 1 (feed solution - 4.0 g-eq / l Na2CO3, 90 ° С, 0.1 A / cm).

Table 1

Example 5. Caustic alkali is obtained in the same electrolyzer as in example 3, when feeding it with a solution of potassium carbonate containing

8 g-eq / l K2COz. The operating conditions and 55 indicators of his work are given in Table. 2 (feed solution - 8 g-eq / l K2COz, 90 ° C, 0.1 A / cm).

Examples 4 and 5 show that with a total concentration of carbonate and bicarbonate in the anolyte below 2.2 g-eq / l for the process of producing sodium alkali and 1.4 g-eq / l for producing potassium alkali, the voltage increase on the electrolyzer in connection with a decrease in the electrical conductivity of the anolyte and an anodic potential increase.

The upper limit on the concentration of carbonate and bicarbonate is limited by the solubility, respectively, of 4.0 g-eq / l Na2CO3 and 8.0 g-eq / l K2CO3.

When the alkali concentration is below 0.9 g eq / l, the voltage on the electrolyzer increases due to a decrease in electrical conductivity of the catholyte impregnating the cathode diaphragm and an increase in the voltage drop in the diaphragm. When the concentration of alkali is higher than 2.5 g-eq / l, the output of alkali in current decreases due to increased migration of hydroxyl ions from the cathode space.

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towards the anode with loss of alkali for this reason.

Claims (2)

Invention Formula A method for producing alkali by electrolysis of an alkali metal carbonate solution in an electrolyzer with separated electrode spaces, characterized in that, in order to save the process by eliminating the use of scarce materials, the process is carried out in an electrolyzer with two filtering diaphragms when feeding carbonate solution into the interdiaphragmatic space, while maintaining concentration alkali in catholyte 0.9-2.5 g-eq / l and the total content of carbonate and bicarbonate in the anolyte 2.2-4.0 g-eq / l during the electrolysis of sodium carbonate or 1.4-8, 0 g-eq / l in the electrolysis of potassium carbonate. 2. A method according to claim 1, characterized in that an asbestos-based diaphragm is used.