CZ278744B6 - Process of electrochemical production of ferrates(vi) - Google Patents

Abstract

Anodic oxidation of iron in alkaline solutions, based on the superimposing of alternating components of electric current with an amplitude of current density in a range of 2.1 to 2.5 times the current density of the direct components of the electric current with a frequency of 1 to 30 Hz to direct current. The alternating component prevents gradual passivation of the anode during electrolysis.

Description

Method of electrochemical production of ferrates

Technical field

The invention relates to a process for the electrochemical production of ferrates by the electrochemical oxidation of an iron anode.

BACKGROUND OF THE INVENTION

Iron (VI) compounds are promising substances which can replace, for example, permanganates in various areas of the chemical industry.

The most preferred methods for producing ferrates include the electrochemical oxidation of iron and cast iron in alkali hydroxide solutions. Usually a direct current of suitable anodic current density is used for this purpose. A disadvantage appears to be the fact that the anode surface is passivated during electrolysis and the current yields in this case decrease significantly with time. The integral current yield is of course very low.

As found by G. Grube and H. Gmelin (Zeitschrift fur Electrochemistry 7, 153 (1920)), the passivation of the anode surface can be slowed and the current yield can be greatly increased by using an AC component with a suitable ratio of the AC current amplitude to DC current density. . This prevents the current yields from decreasing with time. However, the optimum ratio varied with the electrolyte temperature, for example at 30 ° C was 2.5 and at 35 ° C the ratio was 1.5, making it considerably more difficult to use this method to prevent anode passivation during ferrate production. The frequency effect was not considered important and was therefore not monitored. All experiments were carried out at a constant frequency of the superposed alternating current component of 50 Hz. In the current applications, due to the current requirements for iron oxidation from the metal state to the sixth oxidation stage, there was a considerable loss of electric charge or current, respectively.

SUMMARY OF THE INVENTION

These drawbacks are overcome by the method of electrochemical production of ferrates according to the invention using alternating current components superimposed on a direct current component. It is an object of the invention that the frequency of the AC superposed component of the electric current is in the range of 1.0 to 30.0 Hz at a ratio of the amplitude of the AC current density to the DC current density in the range of 2.1 to 2.5.

The advantage of the method of electrochemical production of ferrates pc according to the invention is that when the device operates in this mode, the optimum frequency of the AC component is not temperature dependent, therefore the device does not need to be thermostatized and the power source can also be designed for one AC current to the current density of the DC component and one frequency of the AC component, thereby reducing the investment cost of the technology and its energy consumption.

-1GB 278744 B6

DETAILED DESCRIPTION OF THE INVENTION

Example 1

A 14 mol / dm ³ sodium hydroxide solution was poured into a cathode-iron anode electrolyser with an unfilled polyvinyl chloride diaphragm.

The anode was cathodically activated for 30 minutes at a DC current density of 20 mA / cm ² . Then the actual electrolysis was started. At an electrolyte temperature of 20 ° C, an anodic current density having a DC component of 16.7 mA / cm ² and an AC component amplitude of 35 mA / cm ^{2 was used} . The ratio of the amplitude of the AC current density to the DC current density was 2.1 at an AC frequency of 1 Hz. After 180 minutes of electrolysis, the anolyte was drained from the electrolyzer and the sodium ferrate content was determined by titration to 192 mg, corresponding to a current yield of 20.2%.

Example 2

The procedure was the same as in Example 1. except that the AC current amplitude was 41.75 mA / cm ^2, and the AC current to DC current density was in this case 2.5. Under these conditions, a current yield of 23.5% was achieved.

Example 3

The procedure was the same as in Example 1, with the difference in the frequency of the superimposed alternating component which in this case was 30 Hz. Under these conditions a current yield of 22.6% was achieved.

Example 4

The procedure was the same as in Example 1. with the difference in the frequency of the superimposed AC component, which in this case was 30 Hz, and in the amplitude of the AC current density, which was 41.75 mA / cm ² . The ratio of the amplitude of the AC current density to the DC current density was 2.5. Under these conditions, the current yield was 25.1%.

Example 5

The procedure was identical to that of Example 1, with the difference in the frequency of the AC component, which in this case was 5 Hz, and the amplitude of the AC current density of the electric component.

The current was 38.4 mA / cm ² . The ratio of the amplitude of the AC current density to the DC current density was 2.3. Under these conditions a current yield of 32.1% was achieved.

Industrial applicability

The process of electrochemical production of ferrates according to the invention can be used for the production of substances used for disinfection and chemical treatment of drinking and service water or for the realization of some types of chemical syntheses as oxidizing and condensing agent in all areas of chemical and pharmaceutical industry.

PATENT CLAIMS

Claims (1)

A method for the electrochemical production of ferrates using an AC component superposed on a DC component, characterized in that the frequency of the AC superposed component is between 1.0 Hz and 30.0 Hz, wherein the amplitude ratio of the AC current density is The electrical current to the current density of the direct current component is in the range of 2.1 to 2.5.