CS216587B1 - Electrode for electrochemical procedures - Google Patents

Abstract

The invention relates to the field of electrochemistry and, in a narrow sense, to electrodes for electrochemical processes. According to the invention, the electrode is made as an electrically conductive carrier of a passivating metal, such as aluminum, titanium, tantalum, zirconium, niobium, bismuth, tungsten and alloys of these metals, on which is deposited an active material of the following mass composition: 10 to 90% silicon dioxide, 5 to 45% platinum group metal oxides and 5 to 45% oxides of the above-mentioned passivating metals. The electrodes can be used as anodes in the production of chlorine and sodium hydroxide as well as in the implementation of electrolytic processes for the production of chlorates and hypochlorites.

Description

1 216587

The invention also relates to electrodes which are used in carrying out electrochemical processes which include an electrically conductive active substance support of metal oxides and silicon oxide deposited on a support, the electrode being intended to be used as an anode in carrying out the electrolysis of alkali metal chloride solutions at the production of chlorine and sodium hydroxide in mercury cathode cells and filter diaphragm cells, as well as in the performance of electrolytic processes for hypochlorite, hypochlorite, electro-organic synthesis, wastewater electrochemical purification, or regeneration of chlorine-containing hydroxide solutions. Until recently, in a wide variety of electrochemical products, a wide scale anode was used. These graphite anodes have a number of advantages, namely that they use non-scarce material to produce them; moreover, these anodes are not short-circuit-sensitive. At the same time, graphite anodes have a higher chlorine depletion potential and thus higher voltages in the electrolytic cell, I will wear anode material wear, which requires frequent repairs to replace anode sets; The graphite anodes have considerable dimensions and weight, which leads to an unjustified increase in the size of the electrolysers and thus of the operating areas of the electrolysis compartment. At present, electrodes and an electrically conductive carrier and active mass applied to the support are widely used. The electrically conductive carrier is made of metal that is passivated by the polarization polarization. Such metals include, for example, titanium, tantalum, zirconium, niobium, aluminum, bismuth, tungsten, and alloys of these metals. The conductive carrier may have any form of conduit, for example in the form of a flat plate with or without punching, may have rods, nets, grids, ceramic bodies, and the like.

The active substance comprises oxides or mixtures of oxides of the platinum group, for example ruthenium, iridium, and oxides of passivating metals such as titanium, tantalum, zirconium, aluminum, niobium, bismuth, tungsten and alloys thereof. The active mass is applied in the form of a thin layer having a thickness of 3 to 10 µm. Metal oxide anodes are characterized by improved electrochemical parameters, lower chlorine depletion potential, unchanged dimensions and weight during continuous operation, higher active mass stability, longer, multi-year service life of two interchangeable anode sets, compared to graphite anodic.

Industrial applications have widespread anodes of metal oxides whose active mass contains 46% by weight of ruthenium oxide RuOg and 54% by weight of titanium dioxide TiOg (see USSR Certificate 369 923). The active mass consumption in the conditions of electrolytic production of chlorine under stable operating conditions at a current density of 0.2 to 0.4 A / cm is 2.6 x 10 g / cm. The principle of the radiochemical procedure in the analysis consists in subjecting the sample with active mass to a neutron irradiation (1.2-3.10 p neutrons / cm) for 200-400 hours, followed by solution in the solution. the sludge and in the gas phase of electrolysis, determine the mass of radioactive ruthenium isotopes.

A variable polarity and amalgamation method was used to determine the stability of the active mass, which was widely used as a very fast method for evaluating the quality of the active coating, namely amalgamma stability, adhesion on an electrically conductive carrier, resistance to high-voltage polarization and short-circuits. 216587 2

The principle of variable polarity and amalgamation is based on the following procedure. Samples are filled with a current density of 1 A / µm, alternatively exposed to 60 ° C in a solution of sodium chloride 3θ0 / g for 40 minutes (2 minutes anode polarization, 2 minutes cathode polarization) anode and cathode polarity. This means that the test cycle lasts 40 minutes. Then it is anodized to sodium 0.2% amalgam sodium for 3 seconds. %. After these tests, the anode is rinsed with distilled water, dried and the weight loss determined. The results obtained by measuring the active mass consumption of the anode determined by the alternating polarity and amalgamation method are shown in Table 1.

Table I

Number of test cycles 1-3 4-6 7-9 10-12 13-15 16-18 Consumption of active mass in three consecutive - 0,595 0,610 0,140 0,180 0,190 0,1702 test cycles (mg / cm) Results of radiochemical tests and the test results shown in Table I show that the anodes which are widely used in the world of electrolysis practice are characterized by insufficient stability of the active mass, insufficient resistance to amalgamation in mercury cathode electrolysis conditions, and the consumption of precious metallomer in the production of anode coating high. When carrying out the electrolysis to produce chlorine using a mercury cathode, the anode lifetime is not more than 1 to 2 years, while in electrolysis conditions and diaphragm mode, the anode lifetime is 4 to 5 years.

An electrode is known in which an electrically conductive titanium carrier nsx-3 is used to increase the resistance of the platinum oxide metal electrode as well as a considerable amount of silicon dioxide. % of RuO2 and 58 wt. % SiO 2. The consumption of the active mass of said electrode, which has been determined by the method of variable polarity and amalgamation, is in the course of 3 test cycles 0.99 to 1.20 mg / cm (French Patent No. 2,040,116 or U.S. Pat. No. 3,846,273) .

Electrodes are known in which silica, together with titanium dioxide or another passivating metal oxide, is introduced into the active mass, and the active mass contains more than 50 wt. % of the platinum group metal oxides (see U.S. Pat. No. 1,168,558). % ruthenium oxide RuOg and 37.5 wt. % SiO 2 and 9.2 wt. % titanium dioxide TiO 2, as determined by the variable polarity and amalgamation method, is 0.75mg / cm during 3 test cycles. A significant disadvantage of all these electrodes is the considerable consumption of precious metal. Leading even large amounts of silica together with the platinum dioxide metal of the platinum group does not guarantee an increase in the strength of the active mass. Furthermore, an electrode is known which is supported on a support made of passivating metals with a mass of more than 5% by weight of the metal-passivating oxides, such as the oxides of the platinum group and the silica additive (see British Patent Specification No. 1,163,553). ). With such an electrode, the active mass of which contains 34.8 wt. % ruthenium trioxide RuOg, 61.6 wt.% titanium dioxide TiOg and 3.6 wt. % SiO 2, the active mass consumption, as determined by the variable polarity and amalgamation method, is 0.7 mg / cm 3 over 3 cycles. That is, such an electrode is, with respect to the 216587 stability of the active mass, practically close to the aforementioned known electrode, the advantage of which is the train is that less metal is required to make it. It is an object of the present invention to reduce the metal consumption of the platinum group required to produce the electrode without impairing the electrode electrochemical parameters and shortening its life. SUMMARY OF THE INVENTION It is an object of the present invention to provide such active mass compositions for an electrode that can reduce the metal consumption of the platinum group.

Thus, according to the invention, there is provided an electrode for conducting electrochemical processes comprising an electrically conductive carrier of a passivating metal such as aluminum, titanium, tantalum, zirconium, niobium, bismuth, tungsten and alloys thereof, with active mass, supported on a support, silicon oxide. , the oxides of the passivating metals and the metal oxides of the platinum group, with said weight ratio of 10 to 90% of the silica, 5 to 45% of the oxides of the platinum group and 5 to 45% of the oxides of the passivating metals.

The recommended mass of oxides of the platinum group guarantees a high electrochemical activity of the electrode, which up to 5U wt. % and does not increase substantially, but it leads to an increase in the active mass losses during the electrolysis process, i. to reduce electrode stability.

The introduction of metal-passivating oxides, such as the introduction of titanium oxide, has a beneficial effect on the electrode stability compared to the active-mass electrode, which consists solely of the oxides of the platinum group and of the silica.

It has been found that with a silica content above 10 wt. % as well as for the passivating metal, for example titanium dioxide, below 50 wt. % and the metal oxide content of the platinum group, for example ruthenium oxide, below 50% by weight increases the stability of the active electrode mass. Increase of silica content above 90 wt. % leads to a significant reduction in electrode electrochemical activity.

One embodiment of the invention is represented by electrodes in which the active masses can contain individual components in this weight ratio (in weight%) and silicon dioxide in the metals of the platinum group, passivating metals or the silicon oxide of the metals of the platinum group, passivating metals 10 to 7520 to 45 5 to 45 10 to 3035 to 4535 to 45

The electrode according to the invention makes it possible to reduce the consumption of the active mass which contains the oxide group of the platinum by about 20 to 25%. With their electrocatalytic properties, the electrodes of the invention are similar to known electrodes. The evaluation of electrocatalytic activity was performed according to the anode potential compared to the normal hydrogen reference electrode under chlorine electrolysis conditions. The electrodes of the invention exhibit a potential in the anode polarization range of 1.32 to 1.35 volts at a current density of 0.2 .mu.m / cm @ 2, at a temperature of 90 DEG C. in a solution containing 300 g / l of sodium chloride. comparison to a normal hydrogen reference electrode. 216587 4 Exemplary embodiments of the invention are illustrated by the following examples. Example 1

An electrode is produced which comprises an electrically conductive titanium plate of 20 x 30 x 2 with an active mass deposited on a carrier which contains 10 wt. % silicon dioxide, 45 wt. % ruthenium oxide and 45 wt. % titanium dioxide. The electrodase produces a titanium plate tartrate over a period of 10 minutes at 60 ° C in 5% sodium hydroxide solution, then sealed for 10 minutes at 100 ° C in 20% by weight. % hydrochloric acid solution. A solution containing 103 ml of n-propyl alcohol, 1.64 ml of titanium tetrachloride, 0.55 ml of silicon tetrachloride and 3.2 ml of ruthenium chloride solution with a ruthenium concentration of 15.2 wt. %. This solution is applied to the prepared surface of the titanium plate and subjected to heat treatment at a temperature in the range of 370 to 470 ° C. This workflow is repeated several times. The total ruthenium content is 3.5 g per m of electrode surface.

The electrode is then tested by the variable polarity and amalgamation method.

Changes in active mass loss, as determined by the variable polarity and amalgamation method, are shown in Table II.

Table II

Test cycles 1-3 4-6_7-9_10-12 Active mass loss during 3 test cycles, 0.48 0.22 0.05 0.06 mg / cmz

This electrode is also subjected to a solution containing 300 g / l sodium chloride, at a temperature of 90 ° C and an anode current density of 0.2 A / cm 2. The anode potential is 1.32 V compared to a normal conductive electrode.

The known electrode, whose active substance contains 46% by weight. % ruthenium oxide and 54 wt. titanium dioxide, is tested by the variable polarity and amalgamation method. The results of the tests are shown in Table I. As already mentioned, the known electrode reduces the active mass, which is determined by radiochemical method under the electrolysis conditions to produce chlorine under stable operating conditions at a current density in the range of 0.2 to 0.4 A /. cm, 2.6 x 10g / cm .h. Example 2

An electrode is made similar to Example 1; the active substance contains 3% by weight of the active substance. % silica, 35 wt. % ruthenium oxide and 35 wt. % titanium dioxide. To apply the active mass, a solution is prepared containing 6 ml of n-propyl alcohol, 1.44 ml of titanium tetrachloride, 1.72 ml of silicon tetrachloride and 2.52 ml of ruthenium chloride solution. This solution is applied to the prepared surface of the wafer plate and subjected to heat treatment as in Example 1.

The electrode is subjected to a variable polarity and amalgamation test. The resulting decrease in active mass, determined by the variable polarity and amalgamation method, is shown in Table III.

Number of test cycles 1-3 4-6 7-9 10-12 13-15 16-18 49-21 22-24 cycles, in mg / om * 0,098 0,100 0,073 0,086 5 216587

The electrode aa is subjected to the chlorine electrolysis test described in Example 1 to determine the loss of ruthenium from the active mass by the radiochemical method to anode current density in the range of 0.2 to 0.4 and / or 2. The ruthenium loss was 2.2.10-8g / cm.h. The potential was 1.33 V. Compared to a normal hydrogen electrode. Example 3 i

The electrode is produced in the same way as in the example lj the active mass contains 3? wt. % silica, 20 wt. % ruthenium oxide and 45 wt. % titanium dioxide. A solution containing 65.5 ml of n-propyl alcohol, 1.28 ml of titanium tetrachloride, 1.39 ml of silicon tetrachloride and 1 ml of ruthenium chloride solution is prepared for non-deposition. The solution is applied to the treated titanium plate surface and subjected to heat treatment as in Example 1. The electrode is tested by the variable polarity and amalgamma method. The weight loss of the active tip during the three test cycles is 0.50 mg / em. The potential under the conditions of electrolysis for chlorine production, as shown in Example 1, is 1.33 V compared to the normal hydrogen electrode. Example 4

An electrode is produced similarly to Example 1; the active substance contains 75 wt. % silica, 20 wt. % ruthenium oxide and 5 wt. % of titanium dioxide. To apply the active mass, a solution is prepared which contains 49.5 ml of n-propyl alcohol, 0.1 ml of titanium tetrachloride, 2.08 ml of horseradish chloride and 0.7 ml of ruthenium chloride solution.

This solution is applied to the treated titanium plate surface and subjected to heat treatment as in Example 1. The electrode is tested by the variable polarity and amalgamma method. The loss of active matter is 0.41 mg / cm during three test cycles. Under the conditions of electrolysis, the potential is to produce chlorine as described in Example 1, 1.35 V compared to a normal hydrogen electrode.

An electrode is made similar to Example 1; the active substance contains 50 wt. % silica, 45 wt. % ruthenium oxide and 5 wt. % of titanium dioxide. To apply the active mass, a solution is prepared containing 54.0 ml of n-propanol, 0.1 ml of titanium tetrachloride, 1.38 ml of silicon tetrachloride and 1.5 ml of ruthenium chloride solution.

This solution is applied to the treated titanium plate surface and subjected to heat treatment as in Example 1. The electrode is tested by the variable polarity and amalgamma method. The loss of active matter is 0.33 mg / cm during 3 test cycles. The potential in chlorine electrolysis conditions described in Example 1 is 1.33 V compared to a normal hydrogen electrode.

An electrode is produced similarly to that of Example 1 (the active mass contains 45.8 wt. % silica, 33.6 wt. % ruthenium oxide and 20.4 wt. % titanium dioxide. To apply the active mass, a solution is prepared containing 34 ml of n-propyl alcohol, 1.08 ml of silicon tetrachloride, 0.345 ml of titanium tetrachloride and 1 ml of ruthenium chloride solution.

The solution is applied to the treated titanium plate surface and subjected to heat treatment as in Example 1. The electrode is tested by the variable polarity and amalgamma method. The resulting decrease in active mass, as determined by the variable polarity and amalgamate method, is shown in Table IV.

Claims (3)

216587 6 Table I * »Number of test cycles 1-3_4-6_7-9 Active mass consumption during three consecutive 0.46 0.28 0.07 * 2 test cycles in mg / cm Potential makes electrolysis conditions to produce chlorine as described in Example 1, 1.33 V in comparison with a normal hydrogen electrode. Example 7 An electrode is produced similarly to Example 1; the active mass contains 19.0 wt. % silica, 42.2 wt. % ruthenium oxide and 38.6 wt. % zirconium oxide. To apply the active mass, a solution is prepared which contains 40 ml of n-propanol, 0.830 g of zirconium chloride, 0.42 ml of silicon tetrachloride and 1.05 ml of ruthenium chloride solution. This solution is applied to the treated surface of the titanium plate and subjected to heat treatment as in Example 1. The electrode is tested by the variable polarity and amalgamation method. The loss of active matter during the three test cycles is 0.44 mg / cm. The potential in chlorine electrolysis conditions described in Example 1 is 1.32 V compared to a normal hydrogen electrode. Example 8 An electrode is produced similarly to Example 1; the active substance contains 10 wt. % silica, 45 wt. % iridium oxide and 45 wt. % of titanium oxide To prepare the active mass, a solution is prepared which contains 4 ml of n-oropylalcohol, 0.42 ml of silicon tetrachloride, 1.05 ml of iridium chloride solution and 0.4 ml of titanium tetrachloride. and subjected to heat treatment as in Example 1. The electrode is tested by the variable polarity and amalgamation method. The loss of active substance is 0.5 mg / cm during three test cycles, the potential in chlorine electrolysis conditions described in Example 1, 1.34 V compared to a normal hydrogen electrode. As is evident from the exemplary embodiment, the electrodes according to the invention are characterized by about 20-25% lower loss of active mass and scarce precious metal compared to the large-scale anodes used in the world for the active substance electrolysis of chlorine. consisting of ruthenium oxide and titanium dioxide. OBJECT OF THE INVENTION An electrochemical process electrode comprising an electrically conductive carrier of a passivating metal, such as aluminum, titanium, tantalum, zirconium, niobium, bismuth, tungsten and alloys of titanium, and an active mass supported on a carrier consisting of silica, oxides of passivating metals and metal oxides of the platinum group, characterized in that the active mass has a composition by weight of 10 to 90% silicon dioxide, 5 to 45% of oxides of platinum and 5 to 45% of oxides of passivating metals. 2. The electrode according to claim 1, wherein the active material deposited on the electrode has a weight composition of 10 to 75% silicon dioxide, 20 to 45% metal oxides, and 5 to 45% oxides of passivating metals. 3. The electrode according to claim 1, wherein the active material deposited on the electrode has a weight composition of 10 to 30% silicon dioxide, 35 to 45% metal oxides, and 35 to 45% oxides of passivating metals.