Method of producing graphite electrodes with coating, preferably of noble metals, for electrolytic processes, especially for hydrochloric acid electrolytes. RU patent 2505625.

FIELD: chemistry.

SUBSTANCE: described is a method of producing graphite electrodes with a coating, preferably of noble metals, for electrolytic processes, particularly for hydrochloric acid electrolytes, wherein the surface of a graphite electrode is coated with an aqueous solution of a noble metal compound, followed by heat treatment of the graphite electrode in the presence of reducing gases and/or gases which do not primarily contain oxygen at temperature of 200-450°C.

EFFECT: longer service life of graphite electrodes used when producing chlorine and hydrogen.

5 ex, 11 cl

The invention relates to the electrodes for electrolytic processes, especially the method of production of graphite electrodes coated, preferably from precious metals for electrolytic processes, especially for the electrolysis of hydrochloric acid.

Method of electrolysis hydrochloric acid is described in Ullmanns Encyclopedia of Industrial Chemistry, Chlorine 10.1 Electrolysis of Hydrochloric Acid, 2006, Wiley-VCH Verlag. Cells normally used in the electrolysis of hydrochloric acid, typically consist of graphite electronic plates, connected to the poles and placed in rows next to each other on the principle of . Anode and cathode space, as a rule, separated by a diaphragm or cation exchange membranes. On the anode side usually receive chlorine, and the cathode - hydrogen. In cathode cell space in continuous or intermittent duty type of salt noble metals, such as platinum salts, palladium or rhodium, to reduce the potential of hydrogen and, consequently, the voltage of the cell. While on graphite electrodes is allocated noble metal. A significant disadvantage of this way of work is that precious metal extraction only briefly leads to the desired effect of reducing tension, and require regular updates, including means high consumption of precious metal. Another drawback is according to the European patent application EP 683 247 A1 is that metals can be deposited on the whole equipment following the cells.

In the European patent application EP 683 247 A1 describes a method for graphite electrodes, in the pores of the graphite surface of which there are deposits of precious metals, for example, iridium deposits and/or rhodium. Getting graphite electrodes according to the EP 683 247 A1 exercise, entering in graphite solutions of salts or iridium, rhodium, or a mixture of salts or iridium, rhodium salts other platinum group metals in or polyatomic alcohols with 2 - 4 carbon atoms, or in mixtures of alcohols. Then impregnated graphite products heated open gas flame, influencing them on the moistened with a solution of a surface at a depth of about 1 mm, to a temperature of from 200 to 450 C for 2-10 minutes, the gas flame affects impregnated graphite products vertically downwards only when the flame is all impregnated graphite products.

Using this method are covering of precious metals, which a certain time sustainably in terms of electrolysis hydrochloric acid, and which need not be renewed.

Disadvantages of the method according to the application of the EP 683 247 A1 are still not reaching the optimum electrolysis of excessive voltage electrodes modified in this way, the use of alcoholic solvents, which can form explosive mixtures in air and therefore require special precautions during this way, which includes work with an open flame, and insufficiently precise temperature control for heating due to the considerable temperature difference between the applied gas flame, impregnated graphite surface and the volume of graphite.

Objective of the invention is to offer an improved method of obtaining graphite electrodes for electrolytic processes, not possessing the above-mentioned shortcomings.

The object of the present invention is a method for producing graphite electrodes coated, mainly of precious metal, for electrolytic processes, in particular, for the electrolysis of hydrochloric acid, which differs that the surface of graphite electrode is covered by water solution of compounds of precious metals, remove the solvent, and then graphite electrode is subjected to thermal treatment in the presence of reducing and/or basically do not contain oxygen gas at a temperature of 150 to 650 C.

The finished coating of the electrode contains, in particular, at least 95%of the mass., preferably, at least 99%. metal.

The precious metal compound as the use of at least one connection from the following series: connection iridium, ruthenium, rhodium, platinum, palladium, especially inorganic salts or organic acids or complex compounds by themselves or in any mixture. Preferably use halides, acetates, oxalates, nitrates, or iridium, ruthenium, rhodium, platinum, palladium, in particular, preferably, halides of these metals, especially preferably, chlorides precious metals. Especially it is preferable to use chloride iridium. Chloride iridium can, for example, a formula for IrCl 3 or IrCl 4 , or to be a mixture of both compounds. Because as a solvent use water, these compounds may also contain hydrated water. Also, for example, you can use sour solution halogenide iridium, for example, (IV) acid.

Aqueous solution of compounds of precious metals may additionally contain surfactants, other salts or, in particular, mineral acids, and also suitable for mixing with water, organic solvents, in particular, alcohol or ketones.

The number of compounds of precious metals define so that the formed coating contain from 5 to 40 g/m 2 , preferably, from 7.5 to 20 g/m 2 precious metals per square graphite electrodes, i.e. on the surface formed by the external dimensions (by lengths of the edges).

In a preferred embodiment, the method according to the invention processing is carried out in restoring and/or mostly not containing oxygen gas atmosphere at a temperature of 200 to 450 C, particularly preferably at a temperature of 250 to 350 degrees C.

In particular, the treatment is carried out in a furnace or a heating Cabinet, and gases around the covered surface of the electrodes. For this in the oven or the heating Cabinet has, for example, opening for the entry of gas and outlet for gas, and from the outside air wardrobe hermetically . case, for example, incomplete gas-tightness can it work with a slight overpressure in the inner space in comparison with the environment, to prevent penetration of air. In particular, the work at the residual concentration of air no more than 25%about., preferably, a maximum of 5%about., especially preferably not more than 2%. The proportion of oxygen in gas for heat treatment is, in particular, not more than 5%about., preferably not more than 3%about., especially preferably not more than 1%vol.

It is advisable to use the gas atmosphere consisted of inert gas, in particular, nitrogen or noble gas, preferably, helium, argon, neon, krypton, radon or xenon, or carbon dioxide or a mixture of one of the inert gases, hydrogen, or pure hydrogen. The share of hydrogen can, therefore, be in the range of 0%about. (pure inert gas) to 100 percent. (pure hydrogen), but preferably use hydrogen concentration, lying in the range from 1 to 5.5%vol. As an inert gas especially preferable to use nitrogen. Suitable mixture of hydrogen and nitrogen are presented on the market under the trading name Formiergas.

The duration of the processing in a reducing and/or mostly free from oxygen gas atmosphere preferably from 1 to 5 hours, especially preferably, from 2 to 3 hours.

In a preferred embodiment, the invention of the microwave after loading of one or more of graphite electrodes close the first and rinsed thoroughly described the gas atmosphere at room temperature until the residual concentration of air is below 25%about., preferably, 5%about., especially preferably, 1%vol. Then, microwave, continuing its purging, heated up to the temperature and leave it at this temperature, the time duration of processing, continuing purging. Then, continuing to blow down the volume of blast furnace gas, its cool, and when the temperature drops below 100 C, preferably below 50 C, extract the contents of the furnace.

Graphite electrodes covered by the method according to the invention, perfectly suited to produce chlorine and hydrogen via electrolysis of hydrochloric acid.

Therefore, another object of the invention is the use of graphite electrodes covered with precious metal, which receive method according to the invention, as electrodes (cathode and/or anode) in obtaining chlorine and hydrogen via electrolysis of hydrochloric acid.

HCl concentration in the electrolysis of hydrochloric acid with the use of covered according to the invention of graphite electrodes can be from 5 to 36%of the mass. As a rule, use acid in concentration 10-30%of the mass. Preferably, the HCl concentration in the range from 15 to 25%of the mass.

Electrolysis hydrochloric acid hydrochloric acid with the use of covered according to the invention of graphite electrodes is usually carried out at a temperature from 30 to 100 C, preferably 50 to 100 C, particularly preferably, from 70 up to 90 degrees C.

To obtain graphite electrodes coated according to the invention preferably use an electrode graphite graphite for technical electrolytic processes, such as the type of graphite production company Graphite COVA GmbH, Rothenbach with the quality of the AH or graphite, published by SGL Carbon GmbH, Meitingen, quality HL, ML or AL. Similar, particularly suitable grades of graphite usually have their own porosity (accumulated volume of ERP) from 12 to 23%, the resistivity is from 5.0 to 12.5 µohm, apparent density (bulk density), to 1.80 1.60 g/cm 3 , and the ash content is not more than 0.1%.

To improve the diversion produced during the electrolysis gases (anode: chlorine, cathode: hydrogen) surface of graphite electrodes can be structured, for example, by drawing on a surface of graphite electrodes cuts in width from 1 to 3 mm, located at a distance of 3 to 7 mm, depth from 10 to 30 mm In the case of graphite electrodes with a structured surface of the new way of covering is especially expedient in view of the high uniformity of the coating.

Diaphragm, preferably used for the separation of anodic and cathodic space in electrolysis, preferably consist of PVC fabric, blended fabric, PVC PVDF (polyvinylidene fluoride) or from a fabric made of PVDF.

Alternatively, you can also use the membrane of acids (e.g., membrane production of DuPont company, Nafion type® 430).

Hydrochloric acid, preferably used in electrolysis with graphite electrodes with coating according to the invention, formed, for example, in the synthesis of organic compounds, for example, polyisocyanates. It appeared advisable before entering the electrolytic cells release hydrochloric acid from pollution, in particular, organic pollutants. For this hydrochloric acid is treated with activated carbon. As an alternative treatment is possible ozone or extractants. Inorganic dirt can be removed with the help of ion-exchange method.

Below is a detailed explanation of the invention on the basis of examples.

Example 1 (control sample)

In an electrolytic cell diaphragm is PVC with two do not have coverage graphite electrodes (COVA type AH-20), in each case with an area of 100 mm x 100 mm, 60 mm thick, and fourteen of the tabs width of 5 mm, structured 13 cuts width OK. 2 mm 19 mm and a depth of spent hydrochloric acid electrolysis. Turnover of hydrochloric acid in both electrode spaces in the circulation loop with pumping amounted to 6 l/h The distance between the surfaces of vertically arranged cathode and anode was 5 mm, moreover, the slots were arranged vertically. Enclosure panel consisted of plastic that is resistant to acid and chlorine. The cathode and the anode were fixed in the body cells with seal, using current screws. Half of the cells were separated by a diaphragm made of PVC. Pumping electrolyte may be implemented in both halves of the cell, varying turnover from 2 l/h up to 10 l/h In these circuits by dosing pumps have introduced a fresh 30%hydrochloric acid so that the electrolyte cells established the concentration of hydrochloric acid OK. 20%of the mass. Gaseous products and depleted electrolytes leave the cell via the isolating liquid and gas. Using a power source installed a current of 50 A and, consequently, the current density of 5 kA/m 2 . Installed capacity of the cell filmed two graphite tips, in each case, isolated in supply, with the front edges of the electrodes.

After the installation of a period of 5 days the potential of the cell was 1,97 V at a temperature of 75C

Then the aperture from PVC replaced nor an ion-exchange membrane type Nafion® 430 production by DuPont. After the installation of the period of 7 days the potential of the cell was 1,99 volts at 81°C.

Example 2 (control sample)

0,286 g iridium (IV) chloride hydrate (IrCl 4 H 2 O, content Ir 52,23%mass.) dissolved in 1,245 ml 1,2-ethanediol. All this solution is uniformly dealt a tassel on 14 surfaces projections (each 5 mm x 100 mm) graphite electrode of the same structure and size, as in example 1. The quantity of the applied iridium amounted to 15.0 g/m 2 based on the geometric size of the graphite electrode (100 mm x 100 mm). After about 15 minutes towards the treated solution (later - the cathode side, electrolysis), heated in the flame of a propane-butane gas burner for 5 minutes, and after this was achieved to a temperature of 450 C, and moreover plate placed under the burner even before the inclusion of the latter. After cooling down to a temperature below 90 degrees Celsius surface protrusions graphite electrode evenly coated 1,245 ml 1,2-ethanediol (without the addition of metal) and immediately afterwards (without a break) repeated heating. Graphite plate built as cathode described in example 1 electrolyte fuel cell. If the turnover of the electrolyte, 6 l/h and an aperture of PVC established invariable during 8 days potential 1.77 V at a current density of 5 kA/m 2 and temperature 75C, C.

Example 3 (according to the invention)

0,289 g iridium (IV) chloride hydrate (IrCl 4 H 2 O, content Ir 52,23%mass.) dissolved in 1,512 g deionized water. All this solution is uniformly dealt a tassel on 14 surfaces projections (each 5 mm x 100 mm) graphite electrode of the same structure and size, as in example 1, having received downloading iridium 15.0 g/m 2 based on the geometric size of the graphite electrode (100 mm x 100 mm). Then coated thus electrode unit is directly handled in a vertically standing of tubular furnaces, with internal diameter of 15 cm and interior volume OK. 5 l with the first electrode unit purged at room temperature gas mixture consisting of 5%about. hydrogen and 95%about. nitrogen with volumetric gas flow 50 l/h for 30 minutes. Then with the speed of a microwave OK. 10 C/min was heated to 250 C, and treated electrode unit in the same stream gas for 3 hours. After that, the furnace turned off and cooled electrode unit at a constant gas flow. For about 3 hours oven temperature dropped below 100 C, and the current gas was withdrawn and closed microwave during the night cooled down to a temperature below 50 C, and only then it was opened for extraction electrode.

Manufactured thus graphite electrode built as cathode described in example 1 electrolyte fuel cell. If the turnover of the electrolyte, 6 l/h and an aperture of PVC on the fifth working day of the established capacity of the cell, equal 1,59 V at a current density of 5 kA/m 2 and temperature 75C, C. The experiment continued, holding off and varying the current density and the temperature of the duration of 150 days, and quality reduction is not observed.

Example 4 (according to the invention)

0,289 g iridium (IV) chloride hydrate (IrCl 4 H 2 O, content Ir 52,23%mass.) dissolved in 1,525 g deionized water and, as in example 3, inflicted on the surface protrusions graphite electrode. Subsequent processing in furnaces also conducted, as described in example 3, with the sole difference that the furnace was heated to a temperature of 450 C, and the processing time at this temperature was 2 hours.

Manufactured thus graphite electrode built as cathode described in example 1 electrolyte fuel cell. If the turnover of the electrolyte, 6 l/h and an aperture of PVC on the eighth day of the established capacity of the cell, equal 1,73 V at a current density of 5 kA/m 2 and a temperature of 74 deg C. the Experiment continued, holding off and varying the temperature of up to a duration of 45 days, a quality reduction is not observed.

Example 5 (according to the invention)

0,190 g ruthenium (III) chloride hydrate (RuCl 3 *H 2 O, contents EN 40,07%mass.) and 0,143 g iridium (IV) chloride hydrate (IrCl 4 H 2 O, content Ir 52,23%mass.) dissolved in 1,504 g deionized water. All this solution is uniformly dealt a tassel on 14 surfaces projections (each 5 mm x 100 mm) graphite electrode of the same structure and size, as in example 1, having received the download ruthenium 7.6 g/m 2 and iridium 7.5 g/m 2 based on the geometric size of the graphite electrode (100 mm x 100 mm).

Processing in furnaces was conducted similarly to example 3.

Manufactured thus graphite electrode built as cathode described in example 1 electrolyte fuel cell. If the turnover of the electrolyte, 6 l/h and the use of ion-exchange membrane Nafion® 430 at the fifth working day of the established capacity of the cell, equal 1,66 V at a current density of 5 kA/m 2 and a temperature of 67 C.

1. Method of obtaining of graphite electrodes coated mainly of precious metal for electrolytic processes, especially for the electrolysis of hydrochloric acid, which includes deposition on the surface of graphite electrode solution compounds of precious metals, the solvent and thermal processing of the received graphite electrode, wherein the temperature processing is carried out in the presence of reducing and/or basically do not contain oxygen gases at temperatures of 200 to 450 C, with the solvent used water.

2. The method according to claim 1, characterized in that in a precious metal compound as the use of at least one connection from the following series: connection iridium, ruthenium, rhodium, platinum, palladium, especially the salt of inorganic or organic acids or compound alone or in any combination.

3. The method according to claim 1, characterized in that in a precious metal compound as the use halide, acetate, oxalate, nitrate or iridium, ruthenium, rhodium, platinum, palladium, preferably halide these precious metals.

4. The method of claim 3, wherein the precious metal compound as the use chloride iridium, ruthenium, rhodium, platinum, palladium, preferably chloride iridium, particularly preferably IrCl 3 , or IrCl 4 , or a mixture of IrCl 3 and IrCl 4 .

5. Method 1, characterized in that the formed coating contains from 5 to 40 g/m 2 , preferably from 7.5 to 20 g/m 2 precious metals per area of graphite electrodes.

6. The method according to claim 1, characterized in that the heat treatment of electrodes is carried out in the presence of reducing and/or basically do not contain oxygen gas at a temperature of 250 to 350 degrees C.

7. The method according to claim 1, characterized in that the gases are a mixture of chemically inert gas, in particular nitrogen or noble gas, hydrogen.

8. The method according to claim 7, wherein the hydrogen content in the gas mixture in the range from 1 to 5.5%vol.

9. Way to one of claims 1 to 8, wherein the duration of heat treatment in a reducing and/or mostly free from oxygen gas atmosphere is from 1 to 5 hours, preferably from 2 to 3 hours

10. Way to one of claims 1 to 8, characterized in that the proportion of oxygen in gas for heat treatment is not more than 5% preferably not more than 3% especially preferably not exceeding 1%.

11. The method of claim 9, wherein the proportion of oxygen in gas for heat treatment is not more than 5% preferably not more than 3% especially preferably not exceeding 1%.