GB2075060A

GB2075060A - Electrode for Electrochemical Processes and Process for Producing Same

Info

Publication number: GB2075060A
Application number: GB8013329A
Authority: GB
Original assignee: Sklyariv A T
Current assignee: Sklyariv A T
Priority date: 1980-04-23
Filing date: 1980-04-23
Publication date: 1981-11-11
Also published as: GB2075060B

Abstract

The electrode comprises a graphite base having, in its pores, metals or compounds of metals possessing electrocatalytical properties and being in an electric contact with graphite; and electrochemically inert organic compound insoluble in the electrolyte and having its dropping point and/or the temperature of transition to the gas state exceeding the electrode temperature during electrolysis. The electrode is produced by introducing into the graphite base pores firstly the electrocatalytic material and then the organic compound. The electrodes are used in the electrochemical production of chlorine, chlorates, hyperchlorite, possessing long service life and capable of operating at commercial current density values.

Description

SPECIFICATION Electrode for Electrochemical Processes and Process for Producing Same The present invention relates to electrochemical processes and, more specifically, to an electrode therefor.

At the present time, in the manufacture of chlorine in electrochemical processes with a solid and liquid cathode, as well as in the production of chlorates, hypochlorite and other products use is made of graphite anodes which, however, have a disadvantage residing in a short service life and the formation of a considerable amount of slime during the electrolysis.

During the recent decade an ever growing application is enjoyed by electrodes comprising a metal base with deposited thereonto a thin coating of a compound possessing electrocatalytic properties.

Thus, known in the art are electrodes comprising a current-conducting substrate of titanium, niobium, tantalum, zirconium and a coating deposited thereonto and resistant against the electrolyte and the electrolysis products; said coating consists of a mixture of one or more oxides of film-forming metals such as aluminium, tantalum, titanium, zirconium, niobium, bismuth and tungsten with one or more metals such as palladium, platinum, rhodium, iridium, ruthenium, osmium, gold, silver, iron, nickel, chromium, lead, copper, manganese, oxides of these metals, nitrides, carbides, sulphides thereof and their mixtures as well (cf. USSR Inventor's Certificate No. 369923).

These electrodes have substantial advantages over the prior art graphite electrodes. The principal advantages of the metal-oxide electrodes over graphite ones reside in the following: 1. a considerably longer service life of electrodes; 2. stable dimensions of electrodes excluding the voltage increase with time during electrolysis in processes with a solid cathode and avoiding the need in adjusting the electrode position to maintain a constant voltage in electrolyzers with a mercury cathode; 3. The absence of slime contaminating the membrane.

However, despite the above-mentioned advantages, a wide application of metal-oxide anodes is restricted first of all by a high production cost thereof as compared to that of graphite electrodes.

An essential disadvantage of metal-oxide anodes resides also in a high sensitivity thereof to shortings which restricts a broad application thereof in electrolyzers with a mercury cathode.

For this reason, numerous attempts have been taken to develop graphite electrodes possessing improved operation characteristics.

Known in the art are graphite electrodes impregnated with different electrochemically inert organic substances such as products of polymerization of oils (cf. Canadian Patent No. 602,053), polyester resin (Czechoslovakian Patent No 95,463), allyl resins (Japanese Patent No. 48-15149, Cl.

13/7 Do 31), products of polymerization of tall stand oil (cf. USSR Inventor's Certificate No.167832).

In practicing of graphite electrodes impregnated with electrochemically inert organic substances as anodes for chlorine electrolyzers the anode stability is increased by not more than 1.5 times as compared to anodes from a non-impregnated graphite.

A disadvantage of these anodes is in limited allowable operating current densities (for example, not more than 1.5 kA/m2 in the production of chlorine with a solid cathode and not more than 8-9 kA/m2 in the production of chlorine by processes with a mercury cathode). At higher current densities an accelerated destruction of the anode is possible due to a surpassed critical swelling potential. The reason for limitation of a working current density of such electrodes resides in a higher potential of the anode after impregnation thereof with an inert organic substance. For the electrode impregnated so that all its pores are totally closed (which is most advantagous from the standpoint of lowering the inside wear), the permissible current density is substantially lower than the one employed in modern electrolyzers.

Also known in the art are graphite based electrodes, wherein the porous graphite base contains, either on the surface or in pores thereof, metals or metal compound possessing electrocatalytical properties. Thus, known is an electrode comprising a current-conducting base of graphite with a coating consisting of a mixture of one or more oxides of the following film-forming metals: aluminium, titanium, tantalum, zirconium, niobium, bismuth and tungsten with one or more of the following metals: palladium, platinum, rhodium, iridium, ruthenium, osmium, gold, silver, iron, nickel, chromium, lead, copper, manganese; oxides of these metals, their nitrides, carbides, sulphides, as well as mixtures thereof (cf. USSR Inventor's Certificate No. 369923).

Known are also electrodes with an electroconducting (including graphite) base coated with oxides of metals of the platinum group added with oxides of non-noble metals such as tin (cf. FRG Application No. 2,710,802), P-manganese dioxide (cf. FRG Application No. 2,636,447), cobalt oxides of the general formula Co304 (cf. USSR Inventor's Certificate No. 492301).

These electrodes are considerably cheaper than those having a metal base and their wear during the initial operation period (generally about one month) is substantially lower than wear of a graphite anode impregnated with an electrochemically inert organic compound. However, with lapse of time, the process becomes occurring substantially totally on the graphite due to a broken contact "electrocatalytic compound-graphite" and the anode is subjected to wear in much the same manner as a non-treated graphite anode. This disadvantage of graphite anodes containing electrocatalytic compounds is responsible for the fact that said anodes have not obtained any practical application.

It is an object of the present invention to provide such a graphite electrode which would possess a long service life and could operate at commercial current density values.

This object is accomplished by that an electrode consisting of a porous graphite base having metals or metal oxides possessing electrocatalytic properties and being in contact with graphite in its pores, in accordance with the present invention contains an electrochemically inert organic compound insoluble in the electrolyte in at least a portion of pores of the graphite base, said organic compound having its dropping point and/or the temperature of transition to the gas state above the electrode temperature during the electrolysis.

It is quite obvious that substances which are solid at the above-specified temperature do satisfy this requirement.

As the electrochemically inert organic compound the electrode contains compounds selected from the group consisting of carbochain polymers, heterochain polymers, naturally-occurring gums and synthetic resins, bitumens, pitches, products of polymerization of oils and stand oils, as well as mixtures of said compounds.

Among the group of the carbochain polymers as the inert organic compound according to the present invention the electrode may contain, in particular, polystyrene, polyethylene, polymethyl methacrylate, polyvinylchloride.

Among the group of heterochain polymers the electrode may contain polyesteracrylate.

Out of the group of naturally-occurring gums and synthetic resins the electrode may contain rosin, phenol-formaldehyde, furan and polyester resins.

Out of the group of bitumens the electrode may contain oxidized petroleum bitumen.

Out of the group of pitches use may be made in the electrode of coal-tar pitch.

Out of the group of products of polymerization of oils and stand oils the electrode may contain a product of copolymerization of tall oil and lin-seed oil and a product of polymerization of tall stand oil.

The above-mentioned.list of compounds does not limit the scope of all possible particular compounds which can be used as an inert impregnation agent for the electrode according to the present invention.

These compounds may be contained in the electrode composition both individually and in all possible combinations thereof.

As the metals or compounds of metals possessing electrocatalytic properties, the electrode may contain substantially any metals, simple and mixed oxides of metals, as well as mixtures of oxides and metals, mixtures of different oxides with each other and mixtures of oxides with other compounds of metals possessing an overtension of the basic electrode reaction which is below or at least equal to the overtension of this reaction on graphite and breaking at the rate which is not faster than that of graphite under the electrolysis conditions.

As said electrocatalytic compounds the electrode may contain such metals as platinum, palladium, iridium, ruthenium, mixtures thereof, alloys and oxides, as well as oxides of gold, silver, iron, cobalt, nickel, chromium, copper, lead, manganese both separately or in various combinations thereof, as well as in a mixture with oxides of film-forming metals such as titanium, tantalum, zirconium, aluminium, bismuth, tungsten, nionium, with compounds of tin, vanadium, molybdenum, silicon, carbon, phosphorus, boron and sulphur.

A high stability of the electrode according to the present invention is explained by that the electrochemically inert organic compound not only protects the surface of inner pores of the electrode from any electrochemical or chemical destruction, but also ensures a durable and reliable contact of the electrocatalytic compound with graphite.

At the same time, the presence in pores and at the surface of graphite of said electrocatalytic compound having a lower, as compared to that of graphite, overvoltage of the basic electrode reaction, as well as the presence of said inert organic compound makes it possible to substantially reduce the value of the true surface area of the electrode which is in contact with the electrolyte. Therefore, use may be made of an electrode containing a higher amount of an inert organic compound than the prior art electrode, without surpassing the critical swelling potential.

The process for the manufacture of the electrode for electrochemical processes according to the present invention comprises introduction, into at least a portion of pores of the graphite base, of at least one metal and/or a compound of a metal possessing electrocatalytic properties, followed by introduction, into at least a portion of pores of said graphite base, of an electrochemically inert organic compound which has its dropping point and/or the temperature of the transition to the gas state above the electrode temperature during the electrolysis.

The introduction of said organic compound may be effected by any conventional method, but the most preferred method is impregnation which is the simpliest and most accessible technique.

To carry out the impregnation, use is made of solutions of the organic compound with which the graphite base should be impregnated, followed by the removal of the solvent; in another embodiment, the graphite base is impregnated with a melt of said organic compound, followed by cooiing to the dropping temperature of this compound.

The organic compound meeting the above-specified requirements may be prepared directly inside the pores of the graphite base by way of impregnation thereof with a liquid monomer such as styrene or with a liquid oligomer, followed by polymerization or polycondensation.

For the impregnation of the graphite base use may be made of solutions of polystyrene, polyvinylchloride, polymethylmethacrylate, polyethylene or melts of oxidized petroleum bitumen, coaltar pitch, rosin or other suitable compounds.

As the graphite use is made of porous graphite, wherefrom a base (or block) of any desired size is cut out. This base is set under vacuum and impregnated first with solution of the above-indicated compounds of metals, followed by drying and heat-treatment, whereafter impregnation is effected using a solution or a melt of said organic compound.

Metals or metal compounds possessing electrocatalytic properties may be introduced into pores of the graphite base by, for example, impregnation thereof with solutions of metal compounds, followed by drying and heat-treatment, deposition of metals or compounds thereof from the gas phase, impregnation with molten metals or by any other conventional techniques.

Depending on the conditions of electrolysis, properties of the electrocatalytic compound and the quality of graphite, the electrode may be produced either with a substantially total closing of pores with the inert compound (impregnation from a melt, impregnation with a liquid monomer with a subsequent block-polymerization thereof inside the electrode pores), or with only a partial filling of pores (impregnation with solutions in volatile solvents).

The practical application of the electrode according to the present invention provides the following technical effects.

The use of the electrode in electrochemical processes instead of conventional graphite anodes makes it possible to prolong, by several times, the service life of anodes and reduce the electric power consumption rate without, however, resorting to re-arrangement of the existing electrolyzers; it also makes possible to avoid the use of expensive and hardly available metals as the base, e.g. titanium.

The electrode according to the present invention is resistant to shortings in substantially much the same manner as a conventional graphite electrode which constitutes an advantage over metallic electrodes wherein their active coating is dissolved upon shortings and the metal base is damaged.

This enables operation of electrolyzers without using systems of protection from shortings and apply less severe requirements to the electrolyte and mercury purity as compared to electrolyzers provided with anodes having a metal base. These advantages of the electrode according to the present invention would not be obtained unless the required sequence of introduction of an electrocatalytic compound and an electrochemically inert organic compound into pores of the graphite base is strictly obeyed.

The above-specified sequence-of operations is mandatory in practicing the process according to the present invention: in the case of an inverted sequence of operations, i.e. upon introduction first of an electrochemically inert compound, provided that it fills the total volume of open pores of the graphite base, the introduction of an electrocatalytic compound becomes impossible.If the graphite base is impregnated with the organic compound only partially, then upon a subsequent introduction of the electrolytical compound its electrical contact with the graphite base is hindered and not protected from the detrimental effect of the electrolyte and the electrolysis products; In this case the rate of destruction of the electrode does not substantially differ from the rate of destruction of the untreated graphite base which is further proven by one of the illustrative examples given hereinbelow.

Therefore, as it follows from the foregoing, the sequence of operations in the process according to the present invention is not at all obvious in view of the prior art.

For a better understanding of the present invention, some specific examples illustrating the electrode according to the present invention in comparison with the prior art electrode are given hereinbelow.

Example 1 A graphite electrode according to the present invention with the dimensions of 50x50x100 mm has a graphite base with a porosity of 20%. The electrode is manufactured in the following manner.

From a plate of electrode graphite a block (base) is cut out with the dimensions of 50x50x 100 mm.

The graphite block is set under vacuum and then impregnated with an aqueous solution of Co(NO3)2 having concentration of 125 g/l, whereafter it is dried by gradually elevating temperature to 1 400C and calcined for 10 minutes at 3000C. After calcination the graphite block is set under vacuum and then impregnated with a solution of polystyrene in styrene with the concentration of 90 g/l under the pressure of 10 atm.g, dried for 3 hours while gradually elevating temperature from 80 to 1600 C, whereafter the impregnation with the solution of polystyrene and drying is repeated for one more time.

The thus-manufactured electrode contains 0.5% of Co304 and 1.5% of polystyrene (polystyrene is a solid compound at a temperature of up to 900 C). The electrode is tested as an anode in a laboratorytype electrolyzer in electrolysis of a solution of NaCI with a concentration of 280-300 g/l at a temperature within the range of from 80 to 850C and a pH=2.5-3; the current passed through the anode is 125 A (the current density is 5 kA/cm2). The electrode temperature during electolysis here in the Examples hereinbelow exceeds the electrolyte temperature by not more than 50C.

The electrode weight loss (wear) for the first 10 days of the tests is 1 5.3 g, for the second 1 0 days-34.4 g and over the third 10 days-38.9 g which corresponds to the wear rate of 0.0005 g/A. her,0.00115 g/A. hr and 0.001295 g/A. hr respectively.

For the purpose of comparison there have been carried out tests of the prior art graphite electrodes containing Co304 or impregnated with polystyrene, as well as of an electrode from graphite not subjected to a special treatment.

A graphite electrode having the same dimensions as the one described hereinabove with a base made of the same graphite and containing 0.5% of Co304 in its pores has been subjected to tests under the conditions described hereinabove. The introduction of Co304 is effected in a manner similar to the above-described. Weight decrease of the electrode over the first 10 days of the tests is 18.7 g, over the second 10 days-53.5 g, over the third 10 days-74.6 g.

A graphite electrode having the same dimensions and the base of the same graphite containing 1.5% of polystyrene in its pores is tested under the above-described conditions. The introduction of polystyrene is effected following the above-described procedure. The content of polystyrene of 1.5% has been selected because it provides the maximum wear decrease for a given type of graphite under the conditions of tests for the case of impregnation with polystyrene only. The weight decrease of the electrode over the first 10 days of the tests was 31.3 g, over the second 10 days 49.2 g, over the third 10 days-54.8 g.

A graphite electrode of the same dimensions as the above-described, made of the same graphite and subjected to no special treatment (i.e. identic to the base of the above-described electrodes) is tested under the above-mentioned conditions. The electrode weight decrease over the first 10 days of the tests is 55.2 g, over the second 10 days-75.0 g, over the third 10 days82.1 g.

Example 2 A graphite electrode according to the present invention having the same dimensions as in Example 1 hereinbefore incorporates a graphite base with the porosity of 20%. Co304 is introduced into the graphite block following the procedure described in Example 1, whereafter the block is impregnated with styrene. The impregnation is also conducted following the procedure of the foregoing Example 1. After the impregnation with styrene the block is gradually heated to polymerize styrene by elevating temperature from 100 to 1 400C within the period of 35 hours The thusmanufactured electrode contains 0.5% of Co304 and 9% of polystyrene (polystyrene and Co304 occupy substantially all volume of open pores of the graphite. The electrode is tested under the conditions described in Example 1.The electrode weight decrease within the first 10 days of the tests was 17.2 g, over the second 10 days it was 21.4 g, over the third 10 days21.6 g.

For the purpose of comparison, an electrode produced by the prior art process is subjected to similar tests. To this end, a graphite electrode of the same dimensions as described hereinabove, with the base made of the same graphite and containing 9% of polystyrene in its pores is tested under the conditions of Example 1. The introduction of styrene and polymerization thereof are effected as described in the foregoing Example 2. After the first 10 days of tests the electrode was completely broken.

Example 3 A graphite electrode according to the present invention having the same dimensions as in Example 1 hereinbefore has a graphite base with the porosity of 20%. Co3O4 is introduced into the graphite block as in Example 1, then the graphite block is set under vacuum and impregnated with a molten oxidized petroleum bitumen (OPB) heated to a temperature of from 220 to 2300C under the pressure of 10 atm.g; dropping point of the OPB is 1 350C. (Here and afterwards the dropping point is determined by the Ubbelohde method, see Polymeric Encyclopaedia, Moscow, Sovetskaja Encyclopedia Publishing House, 1974 vol. I, page 934). The thus-manufactured electrode contains 0.5% of Co304 and 9% of OPB (OPB and Co304 occupy almost all volume of open pores of the graphite).The electrode is then tested under the conditions described in Example 1. The electrode weight loss for the first 10 days of the tests is 19.3 g, over the second 10 days2 1.6 g, over the third 10 days-21.7 g.

For the purpose of comparison, an electrode produced by the prior art process is subjected to similar tests. To this end, a graphite electrode with the same dimensions as those described hereinabove and the same graphite base containing of Example 1. The introduction of OPB is effected as described in the foregoing Example 3. For the first 10 days of the tests the electrode was totally broken.

Example 4 A graphite electrode according to the present invention having the same dimensions as in Example 1 incorporates a 3graphite base of the porosity of 20%. The graphite block is impregnated with an aqueous solution of RuC13 and TiCI3 of the concentration of 65 g/l as calculated for Ru02 and 79.5 g/l as claculated forTiO2 and then dried. The impregnation and drying are conducted in a manner similar to that in the impregnation with the solution of Co(NO3)2 in Example 1. After drying the graphite block is set under vacuum and impregnated under the pressure of 20 atm.g with a mixture of the following composition (parts by weight): an unsaturated polyester resin of the maleinate type modified with rosin 50, styrene 47, isopropylbenzoyl hydroperoxide 3.To cure the resin, the block is gradually heated to 1 000C and maintained for 5 hours at this temperature.

The thus-produced electrode contains 1.3% of the mixture of ruthenium oxide and titanium oxide and 10% of polyester resin (which is a solid substance at the temperature of electrolysis). The resin and the oxide occupy substantially total volume of open pores of graphite. The electrode is tested under the conditions described in the foregoing Example 1. The electrode weight decrease for the first 10 days of the tests is 1 8.3 g, for the second ten days-23.2 g, for the third 10 days-25.4 g.

Example 5 A graphite electrode according to the present invention having the same dimensions as in Example 1 hereinbefore has a graphite base with the porosity of 20%. The graphite block is impregnated with an aqueous solution of H2PtCl6 with the concentration of 55 g/l as claculated for the metal. The impregnation is effected in much the same manner as the impregnation with an aqueous solution of Co(N03)2 in Example 1. The impregnated block is dried for two hours at the temperature of 1 000C and then calcined in the atmosphere of argon for 1 hour at the temperature of 5500C.

After the introduction of platinum the graphite block is set under vacuum and impregnated, at the temperature of 1 300C under the pressure of 10 atm.g with rosin having the dropping point of 700C.

The thus-produced electrode contains 0.5% of platinum and 9% of rosin. The electrode is tested as an anode of a cathodic protection unit in water containing 35 mg/l of Cl- and 40 mg/l of S042--at the anodic current density of 250 A/m2 and at a temperature of from 1 6 to 21 OC. The rate of wear of the electrode is equal to 0.048 g/A. hr.

Example 6 A graphite electrode of the same dimensions as the one described above is manufactured from the same graphite and subjected to no special treatment. This electrode is tested under the conditions described hereinabove in this Example. The rate of wear of the electrode is 0.128 g/A . hr.

A graphite electrode according to the present invention with the dimensions of 40x40x 12 mm has a graphite base with the porosity of 27%. The electrode is produced in the following manner. From a plate of electrode-grade graphite a block with the dimensions of 40x40x 1 2 mm is cut out. The introduction of Co304 is effected as in Example 1, though the concentration of the solution of Co(N03)2 is 500 g/l; after the first calcination of the block the operations of impregnation and calcination are repeated once more.

After the second calcination, the graphite block is set under vacuum and impregnated with a solution of tall stand oil in CCI4 containing 1 5% by volume of the tall drying oil and a lead-manganese siccative in the amount of 0.45% as for pyrolusite and 0.9% of lead oxide by weight of the drying oil; then the block is dried under vacuum for 3 hours at room temperature, 3 hours with a gradual elevation of temperature from room temperature to 900C and to a constant weight at 900C without vacuum.

The thus-manufactured electrode contains 8% of Co304 and 3% of the product of polymerization of tall stand oil (decomposes with the formation of gaseous products above 2600C). The electrode is tested under the conditions of production of sodium chlorate in an electrolyte containing 130 g/l of NaCI, 450 g/l of NaClO3 and 2 g/l of Na2CrO4 at a pH=6.6 to 7.6, temperature of 400C and current of 5.1 A. The electrode weight decrease for the first 10 days of the tests was 0.9 g, for the second 10 days--1.2 g, for the third 10 days-1 .3 g.

For the purpose of comparison, there are tested under the same conditions the prior art electrodes, as well as an electrode of graphite subjected to no special treatment and a graphite electrode produced by the process with a reversed sequence of operations.

A graphite electrode having the same dimensions as the one described hereinabove and the same graphite base containing 8% of Co304 in its pores is tested under the above-mentioned test conditions.

The introduction of Co304 is effected as in Example 6. The electrode weight loss for the first 10 days of the test is 1.5 g, for the second 10 days-2.7 g, for the third 10 days-4.6 g.

A graphite electrode having the same dimensions as the above-described with the same graphite base containing in its pores 3% of a product of polymerization of tall stand oil is tested under the above-described conditions. The impregnation with the solution of tall stand oil and the heat-treatment is conducted as described hereinbefore. The electrode weight loss for the first 10 days of the tests is 1.1 g, for the second 10 days1.9 g, for the third 10 days-2.4 g.

A graphite electrode of the same dimensions as described above, with the same graphite base non-subjected to any special treatment is tested under the conditions mentioned above. The electrode weight loss for the first 10 days of tests is 2.4 g, for the second 10 days-2.8 g, for the third 10 days4.6 g.

Into a graphite base of the dimensions described hereinbefore produced from the same graphite there is introduced a product of polymerization of tall stand oil as described in Example 6, whereafter Co304 is added following the procedure of the foregoing Example 6.

The thus-made electrode is tested under the conditions similar to those employed hereinbefore.

The electrode weight loss for the first 10 days of tests is 2.2 g, for the second 10 days-2.75 g, and for the third 10 days 4.6 g.

Example 7 A graphite electrode according to the present invention with the same dimensions as those in Example 6 has a graphite base with porosity of 27%. Co304 is introduced into the graphite block as in Example 6, whereafter the graphite block is set under vacuum and impregnated with a mixture having the following composition (parts by volume): tall oil 10.5, lin-seed oil 4.5, CCI4 85, which is added with a lead-manganese siccative in the amount of 0.5% for pyrolisite and 1.0% for lead oxide by weight of the tall oil. Thereafter, the block is dried in much the same manner as after drying with a solution of tall drying oil (Example 6).The thus-manufactured electrode contains 8% of Co3O4 and 3% of the product of copolymerization of tall oil and lin-seed oil) decomposes with the formation of gaseous products above 2600 C). The electrode is tested under the conditions described in Example 6 hereinbefore.

The electrode weight loss for the first 10 days of the tests is 0.7 g, for the second 10 days .3 g, for the third 10 days .5 g.

Example 8 A graphite electrode according to the present invention with the dimensions as in Example 1 has the graphite base with the porosity of 20%. The graphite block is impregnated with an aqueous solution containing 17.5 g/l of RuCI3 and 30 g/l of Fe(OH)3 prepared by precipitation from a solution of FeCI3 by ammonia. The impregnation is conducted as in the case of impregnation with a solution of Co(NO3)2 in Example 1, whereafter the graphite block is dried for one hour at the temperature of 1 000C, then the temperature is elevated uniformly to 4500C over one hour and the block is maintained at this temperature for one hour.

The thus-treated block is impregnated with an oligoesteracrylate based on phthalic anhydride, triethylene glycol and methacrylic acid containing 2% of benzoyl peroxide. The impregnation is conducted in much the same manner as the impregnation with styrene in Example 2. To form a polyesteracrylate, the block is maintained for three hours at the temperature of 800C and for three hours at 1 000C. The thus-produced electrode contains 0.3% of a mixture of oxides of ruthenium and iron and 10.5% of a polyesteracrylate (which is a solid product at the electrode temperature during electrolysis). The electrode is tested under the conditions described in Example 1. The weight loss of the electrode for the first 10 days of tests was 20.2 g.

Example 9 A graphite electrode according to the present invention with the same dimensions as in Example 1 has a graphite base with the porosity of 20%. The graphite block is successively impregnated first with an aqueous solution of Mn(NO3)2 of the concentration of 52 g/l, followed by drying for 1 hour at 1 000C and calcination for 10 minutes at 1 900C, and then impregnated with an aqueous solution of Co(N03)2 with the concentration of 65 g/l, followed by drying and calcination. The impregnation with aqueous solutions, as well as drying and calcination after impregnation with the solution of Co(N03)2 are conducted following the procedure described in Example 1.

The thus-treated block is set under vacuum and dipped into a molten resol-type phenolformaldehyde resin heated to the temperature of 800 C, whereafter over the molten resin there is created the pressure of argon of 10 atm.g and impregnation is carried out under these conditions of temperature and pressure for two hours. Then the graphite block is extracted from the resin, the excessive resin is removed from its surface and then the block is subjected to a heat treatment to cure the resin while gradually elevating temperature from 80 to 1 300C at the rate of 30C/hr.

The thus-produced electrode contains 0.5% of a mixture of MnO2 and Co305 in the ratio of 1:1 and 7% of the phenol-formaldehyde resin (which is a solid product at the electrode temperature during electrolysis). The electrode is tested under the conditions described in Example 1. The electrode weight loss for the first 10 days of tests is 1 8.5 g, for the second ten days-20.2 g, for the third ten days-20.6 g.

Example 10 A graphite electrode according to the present invention with the same dimensions as in Example 1 has a graphite base with the porosity of 20%. The graphite block is impregnated with a solution of RuCI3 of the concentration of 35 g/l with subsequent heat-treatment. The impregnation and heattreatment are effected in much the same manner as in the case of introduction of a mixture of oxides of ruthenium and iron (Example 8). Then the graphite block is immersed into a boiling solution of polyethylene in CCl4 with the concentration of 110 g/l and heated at reflux for 4 hours, whereafter impregnation with this polyethylene solution is effected under the pressure of 10 atm.g at the temperature of 750C for 4 hours. After the impregnation the graphite block is dried for 1 hour at 700C, one hour at 1000C and 1 hour at 2000C. The thus-produced electrode contains 0.2% of RuO2 and 1% of polyethylene (which is a solid product at the electrode temperature during electrolysis). The electrode is tested as an anode in a laboratory electrolyzer to produce sodium hypochlorite. The electrolyte contains 90 g/l of NaCI and 10 g/l of NaCIO; the electrolysis is conducted at the temperature of 25"C, and the current density of 2 kA/m2. The electrode weight decrease for 10 days of tests is 63 g.

For the purpose of comparison, an electrode of the same dimensions and made of the same graphite subjected to no special treatment is tested under the same conditions. The electrode weight decrease for 1 0 days of tests is 1 50 g.

Example 11 A graphite electrode according to the present invention with the same dimensions as in Example 1 has a graphite base with the porosity of 20%. Into the graphite block Ru02 is introduced following the procedure of Example 10, whereafter the block is set under vacuum and impregnated with a mixture of mono- and difurfurylidenacetone in the ratio of 3:2 containing 5% of para-toluenesulphochloride.

The impregnated block is heated for one hour from room temperature to 800 C, then from 80 to 150"C at the rate of 1 00C/hr and maintained for three hours at 1 500C.

The thus-produced electrode contains 0.2% of Ru02 and 8.5% of furan resin (solid product at the electrode temperature during electrolysis). The electrode is tested under the conditions described in Example 5 hereinbefore. The rate of wear of the electrode is 0.056 g/A. hr.

Example 12 A graphite electrode according to the present invention with the same dimensions as in Example 1 has a graphite base with the porosity of 20%. Into the graphite block platinum is introduced following the procedure described in Example 5. Thereafter, the block is impregnated with a 2% solution of polyvinylchloride in cyclohexanone (the impregnation procedure is effected as in the case of impregnation with a solution of polystyrene in Example 1) and dried for three hours at the temperature of 90"C. The operations of drying and impregnation are repeated while increasing, each time, the drying duration by 1 hour until a weight gain of 2% (by weight of the graphite base) is obtained.

The thus-produced electrode contains 0.5% of platinum and 2% of polyvinylchloride (polyvinyl chloride is decomposed with the formation of gaseous products at a temperature of above 900 C). The electrode is tested under the conditions described in the foregoing Example 1. The electrode weight loss for the first 10 days of tests is 1 6.7 g, for the second 10 days31.3 g, for the third 10 days 33.2 g.

Example 13 A graphite electrode according to the present invention with the same dimensions as in Example 6 hereinbefore has a graphite base with the porosity of 20%. The graphite block is set under vacuum and impregnated with an aqueous solution of Na2SiO3 with the concentration of 20 g/l, dried for one hour at the temperature of 1000C and for one hour at 1 500C, boiled for two hours in a concentrated hydrochloric acid, for 2 hours in water and dried for one hour at 1 500C, whereafter Ru02 is introduced into the graphite block as described in Example 10.

Afterwards, the graphite block is set under vacuum and impregnated with a solution of polymethylmethacrylate in cyclohexanone with the concentration of 20 g/l under the pressure of 20, atm.g and then the block is dried for two hours at the temperature of 1 500C and for one hour at 1 700 C. The impregnation with the solution of polymethylmethacrylate and drying are repeated until a weight gain of 1.2% is obtained.

The thus-produced electrode contains 0.1% of SiO2, 0.2% of RuO2 and 1.2% of polymethylmethacrylate. The electrode is tested under the conditions described in Example 6.

The electrode weight loss after the first 10 days of tests is 1.0 g, for the second ten days1.5 g, for the third days1.7 g.

Example 14 A graphite electrode according to the present invention with the same dimensions as in Example 1 has a graphite base with the porosity of 20%. The graphite block is impregnated with an aqueous solution containing 41.5 g/l of Co(NO3)2 and 97.2 g/l Al(NO3)3; the impregnation is carried out following the procedure of impregnation with the solution of Co(NO3)2 in Example 1. The impregnated block is gradually heated to the temperature of 1 200C, maintained for one hour at 1200 C, then progressively heated to 4500C and maintained at this temperature for 2 hours. Then 0.2% of Ru02 is introduced into the graphite base following the procedure of Example 10.The thus-treated graphite block is set under vacuum and then impregnated with a coal-tar pitch (the dropping point thereof is 950C) heated to 2200C under the pressure of 10 atm.g.

The thus-produced electrode contains 0.5% of a mixture of oxides of aluminium and cobalt,0.2% of RuO2 and 11.5% of coal-tar pitch. The electrode is tested under the conditions described in Example 1 hereinbefore. The electrode weight loss for 10 days of tests is 22.5 g.

Example 15 A graphite electrode according to the present invention with the same dimensions as in Example 6 has a graphite base with the porosity of 27%. Into the graphite base there are introduced 2.4% of a mixed oxide of ruthenium and titanium by means of impi cgnation with an aqueous solution of RuCI3 and TiCI3, followed by drying and calcination as described in Example 4. Then into the base there is introduced 1% of a mixture of paraffin with the dropping point of 550C and polyethylene in the ratio of 1:1 by means of impregnation with a solution of 55 g/l of polyethylene and 55 g/l of paraffin in CCl4: the impregnation and drying operations are conducted as in the case of introduction of polyethylene in Example 10.

The thus-produced electrode contains 2.4% a mixed oxide of ruthenium and titanium and 1% of a mixture of paraffin and polyethylene (the mixture is a solid product at the electrode temperature during electrolysis). The electrode is tested under the conditions described in Example 10. The electrode weight loss after 10 days of tests is 54.2 g.

Example 16 A graphite electrode according to the present invention with the same dimensions as in Example 1 has a graphite base with the porosity of 20%. Into the graphite block there is introduced Co304 as in Example 1 and then the block is impregnated with a solution of polystyrene (80 g/l) and polymethylmethacrylate (10 g/l) in styrene stabilized with hydroquinone; the impregnation and the subsequent drying are effected just as in the case of impregnation with a solution of polystyrene in styrene in Example 1. The operations of impregnation and drying are repeated twice.

The thus-produced electrode contains 0.5% of C0304 and 1.5% of a mixture of polystyrene with polymethylmethacrylate (the mixture is a solid product at the electrode temperature during electrolysis). The electrode is tested under the conditions described in Example 1.

The weight loss of the electrode for the first 10 days of the experiment is 16.6 g, for the second ten days-34.7 g, for the third 10 days-37.3 g.

For a better understanding of the present invention, the results of tests of the electrodes in electrolysis of NaCI with a concentration of 280-300 g/l at a temperature of 80-850C (i.e. the conditions of the production of chlorine and caustic soda and under the conditions of the production of sodium chlorate are shown in Table 1 and 2 respectively.

The above-given Examples show that the electrode according to the present invention features considerable advantages over the prior art graphite electrodes; the effect of diminution of the rate of wear of the electrode is not an adding-up effect Thus, for the prior art electrodes of Example 1 a mean wear rate over the period of from 20 to 30 days after the beginning of the experiment (the period during which the rate of wear is close to a stationary one) is respectively 90.9% and 66.7% of the mean rate of wear of the untreated graphite electrode within the same period.The combination of an electrocatalytic compound and an inert organic compound in pores of the electrode would allow a suggestion that the wear rate be equal to 60.6% of the rate of wear of the untreated electrode, whereas it was actually equal to only 47.4%, i.e. it turned to be by almost 1.3 times smaller which was quite unexpected. However, still more unexpected is the diminution, by several times, of the stationary rate of wear of the electrode upon combination of known impregnation agents in such amounts that when taken separately each of them either provides an insignificant positive effect or even results in a more rapid wear. Thus, the introduction of 0.5% of Cho304 (Example 1) lowers the stationary rate of wear by 1.1 time; the introduction of 9% of polystyrene (Example 2) or 9% of OPB (Example 3) results in a drastic increase of the wear rate to a critical value; nevertheless, the stationary rate of wear of the electrode containing 0.5% of Co3O4 and 9% of polystyrene (Example 2) or 0.5% of Co304 and 9% of OPB (Example 3) turned to be by 3.5 times smaller than that in the case of the untreated electrode.

Table 1 Results of tests of electrodes with a graphite base with the porosity of 20% under the conditions of electrolysis of solutions of NaCI of a concentration 280-300 g/l at 8-85 C Wear of anode (g) Over the Test Period Days Example Electrocatalytic Inert Organic No.Additive Compound 0-10 10-20 2030 1 2 3 4 5 6 1* -- -- 55.2 75.0 82.1 1 * 0.5% of Co304 - 18.7 53.5 74.6 1* - 1.5% of polystyrene 31.3 49.2 54.8 1 0.5% of Co304 1.5 v6 of polystyrene 15.3 34.4 38.9 2* 9% of polystyrene Total - breakdown 2 0.5%ofCo3O4 9% of polystyrene 17.2 21.4 21.6 3* 9% of oxidized pet- Total - - roleum bitumen breakdown 3 0.5% of Co304 9% of oxidized pet- 19.3 21.6 21.7 roleum bitumen 4 1.3% (TiO2+Ru02) 10% of polyester resin 18.3 23.2 25.4 8 0.3% (Fe304+RuO2) 10.5% of polyesteracry- 20.2 - late 9 0.5% (MnO2+Co304) 7% of phenol-formal- 18.5 20.2 20.6 dehyde resin 12 0.5% of Pt 2% of polyvinylchloride 16.7 31.3 33.2 14 0.5% (Al203+Co304) 11% of coal-tar pitch 22.5 - - +0.2% Ru02 16 0.5% C 304 1.5% of a mixture of 16.6 34.7 37.3 polystyrene with poly methylmethacrylate Table 2 Results of tests of electrodes with a graphite base having porosity of 27% under the conditions of preparation of sodium chlorate Wear of anode (g) Over the Test Period (days) Example Electrocatalytic Inert Organic No. Additive Compound 0-10 10-20 20--30 6* 2.4 2.8 4.6 6* 8% of Co304 - 1.5 2.7 4.6 6* - 3% of a product of 1.1 1.9 2.4 polymerization of tall drying oil 6 8%ofCo3O4 3% of a product of 0.9 1.2 1.3 polymerization of tail stand oil 7 8% of Co304 3% of a product of 0.7 1.3 1.5 copolymerization of tail oil and lin seed oil 13 0.1 % SiO2,0.2% RuO 1.2% of polymethyl- 1.0 1.5 1.7 methacrylate

Claims

1. An electrode for electrochemical processes consisting of a porous graphite base containing in at least a portion of pore of said base metals or metal compounds possessing electrocatalytical properties and being in an electric contact with graphite and an electrochemically inert organic compound insoluble in the electrolyte and having the dropping point and/or the point of transition to the gas state above the electrode temperature during the electrolysis.

2. An electrode for electrochemical processes according to Claim 1 ,wherein as the electrochemically inert organic compound insoluble in the electrolyte use is made of a substance selected from the group consisting of carbochain polymers, heterochain polymers, naturally-occurring and synthetic resins, bitumens, pitches, products of polymerization of oils and stand oils, and a mixture of said compounds.

3. An electrode for electrochemical processes according to Claim 1 wherein as the electrochemicaliy inert organic compound insoluble in the electrolyte polystyrene is used.

4. An electrode for electrochemical processes according to Claim 1, wherein as the electrochemically inert organic compound insoluble in the electrolyte polyethylene is used.

5. An electrode for electrochemical processes according to Claim 1, wherein as the electrochemically inert organic compound insoluble in the electrolyte polymethylmethacrylate is used.

6. An electrode for electrochemical processes according to Claim 1, wherein as the electrochemically inert organic compound insoluble in the electrolyte use is made of polyvinylchloride.

7. An electrode for electrochemical processes according to Claim 1, wherein as the electrochemically inert organic compound insoluble in the electrolyte use is made of polyesteracrylate.

8. An electrode for electrochemical processes according to Claim 1, wherein as the electrochemically inert organic compound insoluble in the electrolyte resin is used.

9. An electrode for electrochemical processes according to Claim 1, wherein as the electrochemically inert organic compound insoluble in the electrolyte it a phenol-formaldehyde resin is used.

10. An electrode for electrochemical processes according to Claim 1, wherein as the electrochemically inert organic compound insoluble in the electrolyte a furan resin is used.

11. An electrode for electrochemical processes according to Claim 1 , wherein as the electrochemically inert organic compound insoluble in the electrolyte use is made of a polyester resin.

1 2. An electrode for electrochemical processes according to Claim 1 , wherein as the electrochemically inert organic compound insoluble in the electrolyte oxidized petroleum bitumen is used.

13. An electrode for electrochemical processes according to Claim 1, wherein as the electrochemically inert organic compound insoluble in the electrolyte a product of copolymerization of tall oil and lin-seed oil is used.

14. An electrode for electrochemical processes according to Claim 1 , wherein as the electrochemically inert organic compound insoluble in the electrolyte use is made of a product of polymerization of tall stand oil.

1 5. An electrode for electrochemical processes according to Claim 1, wherein as the electrochemically inert organic compound insoluble in the electrolyte coal-tar pitch is used.

1 6. An electrode for electrochemical processes according to Claim 1, wherein as the electrochemically inert organic compound insoluble in the electrolyte a mixture of ethylene and paraffin is used.

1 7. An electrode for electrochemical processes according to Claim 1, wherein as the electrochemically inert organic compound insoluble in the electrolyte a mixture of polystyrene and polymethylmethacrylate is used.

18. A process for producing an electrode for electrochemical processes comprising introduction, into at least a portion of pores of the graphite base, of at least one metal or a compound of a metal possessing electrocatalytic properties with an overtension of the basic electrode reaction on said metal or metal compound being below or at least equal to the overtension of this reaction on graphite and with the rate of breaking of said metal or metal compounds being not faster than graphite under electrolysis condition, followed by introduction, into at least a portion of said graphite base pores, of an electrochemically inert organic compound insoluble in the electrolyte and having the temperature of transition to the gas state above the electrode.

18. A process for producing an electrode for electrochemical processes comprising introduction, into at least a portion of pores of the graphite base, of at least one metal or a compound of a metal possessing electrocatalytic properties, followed by introduction, into at least a portion of said graphite base pores, of an electrochemically inert organic compound insoluble in the electrolyte and having the temperature of transition to the gas state above the electrode temperature during electrolysis.

1 9. A process for producing an electrode for electrochemical processes according to Claim 18, wherein said introduction of a metal and/or a compound of a metal is effected by means of impregnation of the graphite base with a solution of at least one compound of a metal, followed by a heat-treatment.

20. A process for producing an electrode for electrochemical processes according to Claim 19, wherein said impregnation is effected by means of a metal salt.

21. A process for producing an electrode for electrochemical processes according to Claim 18, wherein said introduction of the organic compound is effected by means of impregnation of the graphite base with a solution of said organic compound, followed by drying to remove the solvents.

22. A process for producing an electrode for electrochemical processes according to Claim 21, wherein said impregnation of the graphite base is effected by means of a solution of polystyrene in styrene.

23. A process for producing an electrode for electrochemical processes according to Claim 21, wherein said impregnation of the graphite base is effected by means of a solution of polyvinylchloride in cyclohexanone.

24. A process for producing an electrode for electrochemical processes according to Claim 21, wherein the impregnation of the graphite base is effected by means of a solution of polymethylmethacrylate in cyclohexanone.

25. A process for producing an electrode for electrochemical processes according to Claim 21, wherein the impregnation of the graphite base is effected by means of a solution of polyethylene and paraffine in carbon tetrachloride.

26. A process for producing an electrode for electrochemical processes according to Claim 21, wherein the impregnation of the graphite base is effected by means of a solution of polystyrene and polymethylmethacrylate in styrene.

27. A process for producing an electrode for electrochemical processes according to Claim 21, wherein said impregnation of the graphite base is effected by means of a solution of polyethylene in carbon tetrachloride.

28. A process for producing an electrode for electrochemical processes according to Claim 18, wherein the introduction of said organic compound is effected by means of impregnation of said graphite base with a melt of said organic compound, followed by cooling to a temperature below the dropping point of this compound.

29. A process for producing an electrode for electrochemical processes according to Claim 28, wherein said impregnation is effected by means of a molten oxidized petroleum bitumen.

30. A process for producing an electrode for electrochemical processes according to Claim 28, wherein said impregnation is effected by means of a molten resin.

31. A process for producing an electrode for electrochemical processes according to Claim 28, wherein said impregnation is effected by means of a molten coal-tar pitch.

32. A process for producing an electrode for electrochemical processes according to Claim 18, wherein the introduction of said organic compound is effected by means of impregnation of said graphite base with a liquid monomer, followed by polymerization to form said electrochemically inert organic compound insoluble in the electrolyte and having its dropping point and/or the temperature of transition to the gas state above the electrode temperature during electrolysis.

33. A process for producing an electrode for electrochemical processes according to Claim 32, wherein said impregnation of the graphite base is effected by means of styrene, followed by thermal polymerization.

34. A process for producing an electrode for electrochemical processes according to Claim 32, wherein said impregnation of the graphite base is effected by means of a solution of tall oil and lin-seed oil in carbon tetrachloride containing a siccative, followed by drying to remove the solvent and copolymerize said oils by heat treatment.

35. A process for producing an electrode for electrochemical processes according to Claim 18, wherein the introduction of said organic compound is effected by means of impregnation of the graphite base with a liquid monomer, followed by polycondensation thereof to form said organic electrochemically inert compound insoluble in the electrolyte and having its dropping point and/or the temperature of transition to the gas state above the electrode temperature during electrolysis.

36. A process for producing an electrode for electrochemical processes according to Claim 35, wherein said impregnation of the graphite base is effected by means of a mixture of monofurfurylideneacetone and difurfurylideneacetone containing p-toluenesulphochloride, followed by polycondensation to form a furan resin.

37. A process for producing an electrode for electrochemical processes according to Claim 18, wherein said introduction of the organic compound is effected by means of impregnation of the graphite base with an oligomer in the liquid state, followed by polymerization thereof to form said electrochemically inert organic compound insoluble in the electrolyte and having its dropping point and/or the temperature of transition to the gas state above the electrode temperature during electrolysis.

38. A process for producing an electrode for electrochemical processes according to Claim 37, wherein said impregnation of the graphite base is effected by means of an oligoesteracrylate containing a polymerization catalyst, followed by polymerization by a heat-treatment.

39. A process for producing an electrode for electrochemical processes according to Claim 37; wherein said impregnation of the graphite base is effected by means of an unsaturated polyester resin containing a polymerization catalyst, followed by polymerization thereof.

40. A process for producing an electrode for electrochemical processes according to Claim 37, wherein said impregnation of the graphite base is effected by means of a solution of tall stand oil in carbon tetrachloride containing a siccative, followed by the removal of the solvent and thermal polymerization.

41. A process for producing an electrode for electrochemical processes according to Claim 18, wherein said introduction of the organic compound is effected by means of impregnation of the graphite base with an oligomer in the liquid state, followed by its polycondensation to form said electrochemically inert organic compound insoluble in the electrolyte and having its dropping point and/or the temperature of transition to the gas state above the electrode temperature during electrolysis.

42. A process for producing an electrode for electrochemical processes according to Claim 40, wherein said impregnation of the graphite base is effected by means of a molten resol phenolformaldehyde resin, followed by polycondensation upon a heat-treatment to obtain resite.

43. A process for producing an electrode for electrochemical processess according to the foregoing claims, substantially as described in the Specification and Examples given hereinbefore.

New Claims or Amendments to Claims filed on 17th July 1981.

New or Amended Claims:

1. An electrode for electrochemical processes consisting of a porous graphite base containing in at least a portion of pore of said base, metals or metal compounds possessing electrocatalytical properties with an overtension of the basic electrode reaction on said metal or metal compounds being below or at least equal to the overtension of this reaction on graphite, and with the rate of breaking of solid metal or metal compound being not faster than graphite under electolysis conditions and being in an electric contact with graphite and an electrochemically inert organic compound insoluble in the electrolyte and having the dropping point and/or the point of transition to the gas state above the electrode temperature during the electrolysis.