EP1463847A2 - Electrode for conducting electrolysis in acid media - Google Patents

Electrode for conducting electrolysis in acid media

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Publication number
EP1463847A2
EP1463847A2 EP02805772A EP02805772A EP1463847A2 EP 1463847 A2 EP1463847 A2 EP 1463847A2 EP 02805772 A EP02805772 A EP 02805772A EP 02805772 A EP02805772 A EP 02805772A EP 1463847 A2 EP1463847 A2 EP 1463847A2
Authority
EP
European Patent Office
Prior art keywords
titanium
intermediate layer
electrode
electrode according
electrochemically active
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP02805772A
Other languages
German (de)
French (fr)
Other versions
EP1463847B1 (en
Inventor
Fritz Gestermann
Hans-Dieter Pinter
Gerd Speer
Peter Fabian
Robert Scannel
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Covestro Deutschland AG
De Nora Elettrodi SpA
Original Assignee
Bayer AG
Bayer MaterialScience AG
De Nora Elettrodi SpA
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Publication of EP1463847A2 publication Critical patent/EP1463847A2/en
Application granted granted Critical
Publication of EP1463847B1 publication Critical patent/EP1463847B1/en
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Expired - Lifetime legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/052—Electrodes comprising one or more electrocatalytic coatings on a substrate
    • C25B11/053—Electrodes comprising one or more electrocatalytic coatings on a substrate characterised by multilayer electrocatalytic coatings
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D17/00—Constructional parts, or assemblies thereof, of cells for electrolytic coating
    • C25D17/10—Electrodes, e.g. composition, counter electrode

Definitions

  • the invention relates to stable electrodes for electrolytic processes, in particular for the electrolysis of hydrochloric acid or aqueous solutions of alkali dichromate, a process for their production and their use.
  • hydrochloric acid Aqueous solutions of hydrogen chloride, hereinafter referred to as hydrochloric acid, are a by-product of many processes, particularly those in which organic hydrocarbon compounds are chlorinated with chlorine in an oxidizing manner. It is economically interesting to recover chlorine from these hydrochloric acids, which can then be used for further chlorinations, for example.
  • Chlorine can be recovered, for example, electrolytically in an electrochemical cell which essentially consists of an anode compartment with an anode and a cathode compartment with a cathode, the anode and cathode compartments being separated from one another by an ion exchange membrane.
  • US-A 5 411 641 discloses a process for the production of dry halogen by electrolysis of anhydrous hydrogen chloride in an electrolysis cell in which
  • Anode and cathode have direct contact with a cation exchange membrane.
  • the anode and cathode are based on carbon and are coated with a catalytically active material, for example ruthenium oxide.
  • a method for the electrolysis of an aqueous hydrochloric acid solution is known from US Pat. No. 5,770,035, an anode consisting of a corrosion-resistant substrate and an electrochemically active coating being used.
  • the corrosion-resistant substrate is graphite or titanium, titanium alloys, niobium or tantalum. Standard activation of mixtures of oxides of ruthenium, iridium and titanium is used as the electrochemically active coating.
  • a carbon-based gas diffusion cathode with a coating of a metal from the platinum group or a corresponding oxide is described as the cathode.
  • the long-term stability of the gas diffusion cathode is low, presumably because there is a loss of contact between the carbon-based gas diffusion electrode and the necessary current distribution electrode resting on the gas diffusion cathode.
  • Another reason for a loss of contact is the formation of poorly conductive oxides on the electrodes during electrolysis stoppages.
  • the formation of such oxides can be prevented by coating the current distribution electrode with a mixed metal oxide, which can also be used for the anode coating.
  • the mixed metal oxide adheres poorly to the electrode, so that the long-term stability of the electrode remains unsatisfactory.
  • the electrodes described are produced by directly applying the catalytically active layer to a support and have the disadvantage that the standing times of the electrodes are not satisfactory under the conditions of electrolysis.
  • US Pat. No. 4,392,927 proposes the use of composite electrodes for sodium chloride electrolysis, consisting of an electrically conductive substrate and an electrochemically active cover layer.
  • the electrochemically active top layer is applied to the carrier by thermal spraying of a powder, the powder also containing electrocatalytically active particles in addition to matrix particles.
  • a powder for example, titanium oxide, titanium boride and titanium carbide are suitable as matrix particles, and metals of the platinum group or of the electrocatalytically active particles
  • a method for producing electrodes with improved long-term stability under the conditions of alkali metal chloride electrolysis is known from US Pat. No. 4,140,813.
  • a first coating of titanium suboxide is applied to a metallic carrier, preferably made of titanium or a titanium alloy, by means of flame or plasma spraying.
  • An element of the platinum group or a compound of such an element is then applied as the electrochemically active substance.
  • Such electrodes have an improved service life under the conditions of sodium dichromate electrolysis. They can also be used when the sodium chloride electrolysis is carried out under acidic conditions or when hydrochloric acid is to be electrolyzed. However, especially under the strongly acidic conditions in hydrochloric acid electrolysis or alkali dichromate electrolysis at low pH, the service life is still not sufficient.
  • the invention therefore relates to an electrode, at least comprising an electrically conductive carrier made of a titanium-palladium alloy, titanium, tantalum or compounds or alloys of titanium or tantalum, an electrochemically active one
  • the electrodes according to the invention are characterized by increased stability, since by using a Intermediate layer improves both the adhesive strength to the support and the adhesive strength of the catalytically active layer.
  • the electrodes according to the invention can be used as an anode, as a cathode and also as a cathodic current distributor. They show a very high resistance when used in hydrochloric acid electrolysis or alkahdichromate electrolysis in an acidic medium.
  • these electrodes are also extremely stable in the electrolysis of hydrochloric acid with a concentration of ⁇ 20% by weight HC1 at temperatures up to 70 ° C and high specific current densities of up to 8kA / m 2 .
  • the intermediate layers made of titanium carbide and titanium boride are distinguished by the fact that they are extremely dense. This prevents aggressive media such as hydrochloric acid from attacking the carrier.
  • the adhesion of the electrochemically active layer is significantly improved.
  • the electrochemically active coating can contain, for example, an oxide of an element from the platinum metal group (Ru, Rh, Pd, Os, Ir, Pt).
  • the electrochemically active layer preferably consists of platinum, iridium dioxide or both or a mixed metal oxide which contains iridium dioxide.
  • the loading of the carrier with the intermediate layer is preferably 10-5000 g / m 2 .
  • the intermediate layer consists of more than one layer, i.e. the intermediate layer is multilayered by flame or
  • the intermediate layer is preferably a layer of titanium carbide.
  • the electrodes according to the invention can be produced, for example, by applying an intermediate layer to a carrier by means of flame or plasma spraying and then applying an electrochemically active coating to the intermediate layer, wherein differently when the intermediate layer is applied by flame or plasma spraying, titanium carbide and / or titanium boride powder Grain sizes, ie with a grain size distribution, can be used.
  • a mesh, woven fabric, braid, knitted fabric, fleece or foam made of a titanium-palladium alloy, titanium, tantalum or compounds or alloys of titanium or tantalum serves as the carrier.
  • the titanium carbide and or titanium boride powders used to apply the intermediate layers by flame or plasma spraying preferably have grain sizes of 10 to 200 ⁇ m.
  • particle size is understood to mean the particle diameter as determined, for example, by means of sieve analysis.
  • titanium carbide or titanium boride powder can be obtained using a commercially available plasma
  • a mixture of nitrogen and hydrogen, the volume ratio of nitrogen to hydrogen being between 70/30 and 95, for example / 5 can be used in an amount of, for example, 5 to 20 minutes and nitrogen as the carrier gas
  • the spraying process can be carried out, for example, at a current of 200 to 400 amperes and a voltage of 50 to 90 V.
  • the distance between the plasma torch and the carrier can be, for example, 130 to 200 mm.
  • the electrochemically active coating can be applied in a manner known per se.
  • Oxides is implemented. This procedure is advantageously repeated several times.
  • the electrodes according to the invention can be used, for example, as gas-developing electrodes.
  • the electrodes in an electrochemical cell it is preferred to use the electrodes in an electrochemical cell to produce chlorine from aqueous hydrochloric acid solutions or chromic acid from a sodium dichromate / chromic acid solution with evolution of oxygen.
  • the electrochemical cell used can contain, for example, an anode compartment with an anode and a cathode compartment with a gas diffusion electrode and current collector, the anode compartment and cathode compartment being separated from one another by a cation exchange membrane and an electrode according to the invention being used as anode, cathode and / or current collector.
  • An oxygen-containing gas for example pure oxygen, a mixture of oxygen and inert gases, in particular nitrogen, or air, preferably oxygen or an oxygen-rich gas, can be introduced into the cathode compartment.
  • the oxygen-containing gas is advantageously fed in such an amount that oxygen is present in a stoichiometric amount based on the amount theoretically required according to equation 1.
  • the aqueous solution of the hydrogen chloride is generally introduced into the anode chamber.
  • the temperature of the supplied aqueous solution of hydrogen chloride is preferably 30 to 90 ° C, particularly preferably 50 to 70 ° C.
  • aqueous solutions of hydrogen chloride with a hydrogen chloride concentration of ⁇ 20% by weight can be used.
  • the hydrochloric acid electrolysis is preferably carried out at a pressure in the anode compartment greater than 1 bar absolute, particularly preferably 1.05 to 1.4 bar.
  • the electrodes according to the invention can also advantageously be used in an electrochemical cell for producing chromic acid from an aqueous alkali dichromate solution, in particular from an aqueous sodium dichromate solution.
  • the use is particularly advantageous when the electrolysis of the aqueous sodium dichromate solution takes place under acidic conditions, because in this case conventional electrodes rapidly lose activity.
  • Electrodes in an electrochemical cell for producing chlorine from aqueous hydrochloric acid solutions as an electrical current distributor in a gas diffusion electrode for reducing oxygen.
  • an expanded metal made of a standard titanium-palladium alloy (titanium grade 11) was roughened to a roughness depth of 30 to 40 ⁇ m by blasting with steel gravel. The expanded metal was then coated with a 20% by weight
  • a layer of titanium carbide was applied to the pretreated expanded metal by means of a plasma coating system of the plasma technology type. This was done
  • Plasma powder from H.C. Starck, type AMPERIT 570.3 is used.
  • the grain size distribution was determined according to Microtrac to - 5.6 ⁇ m and by means of sieve analysis according to Rotap to + 45.
  • Helium was used as the plasma gas at a flow rate of 1.3 l / min.
  • TiCl 3 and RuCl 3 (molar ratio 1: 1) dissolved in dilute hydrochloric acid (approx. 2n HC1) and applied to the expanded metal using a brush.
  • the coated expanded metal was then heated to 500 ° C in air. This process was repeated several times, preferably 4 to 12 times.
  • the coated expanded metal was used as an anode and / or cathode network, which served as a current feed for an oxygen consumable cathode, ie as a current distributor.
  • an expanded metal made of a standard titanium-palladium alloy (titanium grade 11) was roughened to a roughness depth of 30 to 40 ⁇ m by blasting with steel gravel. The expanded metal was then pickled with a 20% by weight hydrochloric acid for about 10 minutes. This also removed the remnants of the abrasive.
  • the coated expanded metal was used as an anode and / or cathode network, which served as the power supply for an oxygen consumable cathode.
  • An aqueous hydrochloric acid solution (15-30% by weight) was pumped from a storage vessel by means of a pump into an anolyte circuit and from there by means of a further pump via a heat exchanger into the anode compartment of an electrochemical cell.
  • a portion of the depleted hydrochloric acid solution was passed through a line into a columnar vessel, together with the chlorine gas developed at the anode which gas / liquid separation took place.
  • a certain pressure was set in the electrochemical cell and in the anolyte via a line which was immersed in the liquid of the columnar vessel.
  • the cation exchange membrane was pressed onto the oxygen consumption cathode, which in turn rested on the power distributor.
  • Oxygen was fed via a line into a vessel which was filled with water and was used to moisten the oxygen.
  • the moistened oxygen was fed to the cathode compartment, was reduced at the oxygen consumption cathode and reacted to water with the protons that had migrated over the cation exchange membrane. Residual oxygen was removed together with the condensate formed in a condensate separator. The excess oxygen and the condensate were removed from the electrochemical cell.
  • the anode test was carried out as follows:
  • An aqueous approximately 30% by weight hydrochloric acid solution was metered into a hydrochloric acid circuit in such a way that the acid concentration in the anolyte circuit and in the cell was approximately 12-15% by weight HC1.
  • the temperature of the anolyte solution was set at 60-70 ° C.
  • the electrolysis was operated at a current density of 5 kA / m 2 .
  • Cation exchange membrane a membrane based on a polymer of the Perfluorsulfonat- DuPont (Nafion ® 324) was used. An oxygen-consuming cathode from E-TEK based on carbon with a platinum catalyst was used.
  • the complete cell housing was made of PTFE (polytetrafluoroethylene) or PVDF (polyvinylidene fluoride).
  • the anode and the current distributor were examined at regular intervals and the degree of destruction was determined. The determination was made qualitatively by examining the anode and the current distributor under the light microscope. The degree of destruction was quantified by
  • Example 1 showed extremely high stability under the conditions mentioned above.
  • the anode potential was still unchanged after a running time of 408 days. changed.
  • the comparison test with an anode manufactured according to Example 2 had to be stopped after 280 days due to destruction of the anode coating.
  • the degree of destruction of the current distributor used was also significantly lower when using an electrode according to the invention according to Example 1 than when using an electrode according to Example 2.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrodes For Compound Or Non-Metal Manufacture (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Abstract

Electrode at least comprising an electroconductive support of a titanium-palladium alloy, titanium, tantalum or compounds or alloys of titanium or of tantalum, an electrochemically active coating and an interlayer between the support and the electrochemically active coating, wherein the interlayer consists of titanium carbide and/or titanium boride and is applied to the support by flame or plasma spraying. Process for producing these electrodes and their use in an electrochemical cell for producing chlorine or chromic acid.

Description

Elektrode für die Elektrolyse in sauren MedienElectrode for electrolysis in acid media
Die Erfindung betrifft stabile Elektroden für elektrolytische Prozesse, insbesondere für die Elektrolyse von Salzsäure oder wässriger Lösungen von Alkalidichromat, ein Verfahren zu deren Herstellung und deren Verwendung.The invention relates to stable electrodes for electrolytic processes, in particular for the electrolysis of hydrochloric acid or aqueous solutions of alkali dichromate, a process for their production and their use.
Wässrige Lösungen von Chlorwasserstoff, nachfolgend Salzsäure genannt, fallen als Nebenprodukt bei vielen Prozessen an, insbesondere bei solchen, bei denen organische Kohlenwasserstoff-Verbindungen mit Chlor oxidierend chloriert werden. Wirtschaftlich interessant ist die Wiedergewinnung von Chlor aus diesen Salzsäuren, das dann beispielsweise für weitere Chlorierungen eingesetzt werden kann.Aqueous solutions of hydrogen chloride, hereinafter referred to as hydrochloric acid, are a by-product of many processes, particularly those in which organic hydrocarbon compounds are chlorinated with chlorine in an oxidizing manner. It is economically interesting to recover chlorine from these hydrochloric acids, which can then be used for further chlorinations, for example.
Die Wiedergewinnung von Chlor kann beispielsweise elektrolytisch in einer elektrochemischen Zelle erfolgen, die im Wesentlichen aus einem Anodenraum mit Anode und einem Kathodenraum mit Kathode besteht, wobei Anoden- und Kathodenraum durch eine Ionenaustauschermembran voneinander getrennt sind.Chlorine can be recovered, for example, electrolytically in an electrochemical cell which essentially consists of an anode compartment with an anode and a cathode compartment with a cathode, the anode and cathode compartments being separated from one another by an ion exchange membrane.
Die Herstellung von Chromsäure durch Elektrolyse von Natriumdichromat-Lösungen ist ebenfalls in elektrochemischen Zellen des genannten prinzipiellen Aufbaus möglich.The production of chromic acid by electrolysis of sodium dichromate solutions is also possible in electrochemical cells of the basic structure mentioned.
Für elektrolytische Prozesse, insbesondere für die Elektrolyse von Salzsäure oder wässriger Lösungen von Natriumdichromat, sind eine Vielzahl von Elektroden beschrieben.A large number of electrodes have been described for electrolytic processes, in particular for the electrolysis of hydrochloric acid or aqueous solutions of sodium dichromate.
DE 29 08 269 AI beschreibt bipolare Elektroden auf Kohlenstoff-Basis, die jedoch unter den Elektrolysebedüigungen nur eine begrenzte Lebensdauer aufweisen. Auch aus DE 44 17 744 CI sind Elektroden auf Kohlenstoff-Basis bekannt, wobei eine Aktivierung der Kathodenseite durch Aufbringen von Edelmetallverbindungen er- folgt. Zur Herstellung dieser Elektroden wird ein Graphitkörper mit einer Lösung der Edelmetallverbindung getränkt und anschließend mit offener Gasflamme auf 200 bis 450°C erhitzt.DE 29 08 269 AI describes bipolar electrodes based on carbon, which, however, have only a limited service life under electrolysis requirements. Electrons on a carbon basis are also known from DE 44 17 744 CI, the cathode side being activated by applying precious metal compounds. To produce these electrodes, a graphite body with a solution of Precious metal compound soaked and then heated to 200 to 450 ° C with an open gas flame.
US-A 5 411 641 offenbart ein Verfahren zur Herstellung von trockenem Halogen durch Elektrolyse von wasserfreiem Chlorwasserstoff in einer Elektrolysezelle, in derUS-A 5 411 641 discloses a process for the production of dry halogen by electrolysis of anhydrous hydrogen chloride in an electrolysis cell in which
Anode und Kathode direkten Kontakt zu einer Kationenaustauschermembran aufweisen. Anode und Kathode basieren auf Kohlenstoff und sind mit einem katalytisch aktiven Material, beispielsweise Rutheniumoxid beschichtet.Anode and cathode have direct contact with a cation exchange membrane. The anode and cathode are based on carbon and are coated with a catalytically active material, for example ruthenium oxide.
Aus US-A 5 770 035 ist ein Verfahren zur Elektrolyse einer wässrigen Salzsäurelösung bekannt, wobei eine Anode aus einem korrosionsbeständigen Substrat und einer elektrochemisch aktiven Beschichtung zum Einsatz kommt. Bei dem korrosionsbeständigen Substrat handelt es sich um Graphit oder aber um Titan, Titanlegierungen, Niob oder Tantal. Als elektrochemisch aktive Beschichtung wird eine Standardakti- vierung aus Mischungen von Oxiden von Ruthenium, Iridium und Titan eingesetzt.A method for the electrolysis of an aqueous hydrochloric acid solution is known from US Pat. No. 5,770,035, an anode consisting of a corrosion-resistant substrate and an electrochemically active coating being used. The corrosion-resistant substrate is graphite or titanium, titanium alloys, niobium or tantalum. Standard activation of mixtures of oxides of ruthenium, iridium and titanium is used as the electrochemically active coating.
Als Kathode wird eine Gasdiffusionskathode auf Kohlenstoff-Basis mit einer Beschichtung aus einem Metall der Platingruppe oder einem entsprechenden Oxid beschrieben. Die Langzeitstabilität der Gasdiffusionskathode ist gering, vermutlich weil es zu einem Kontaktverlust zwischen der auf Kohlenstoff basierenden Gasdiffusions- elektrode und der notwendigen, auf der Gasdiffusionskathode aufliegenden Stromverteilungselektrode kommt. Ein weiterer Grund für einen Kontaktverlust ist die Bildung von elektrisch schlecht leitenden Oxiden auf den Elektroden während Stillständen der Elektrolyse. Die Bildung solcher Oxide kann durch eine Beschichtung der Stromverteilerelektrode mit einem Metallmischoxid, welches auch für die Ano- denbeschichtung verwendet werden kann, verhindert werden. Das Metallmischoxid haftet jedoch schlecht auf der Elektrode, so dass die Langzeitstabilität der Elektrode nach wie vor unbefriedigend bleibt.A carbon-based gas diffusion cathode with a coating of a metal from the platinum group or a corresponding oxide is described as the cathode. The long-term stability of the gas diffusion cathode is low, presumably because there is a loss of contact between the carbon-based gas diffusion electrode and the necessary current distribution electrode resting on the gas diffusion cathode. Another reason for a loss of contact is the formation of poorly conductive oxides on the electrodes during electrolysis stoppages. The formation of such oxides can be prevented by coating the current distribution electrode with a mixed metal oxide, which can also be used for the anode coating. However, the mixed metal oxide adheres poorly to the electrode, so that the long-term stability of the electrode remains unsatisfactory.
Die beschriebenen Elektroden werden durch direktes Aufbringen der katalytisch ak- tiven Schicht auf einen Träger hergestellt und haben den Nachteil, dass die Stand- zeiten der Elektroden unter den Bedingungen der Elektrolyse nicht zufriedenstellend sind.The electrodes described are produced by directly applying the catalytically active layer to a support and have the disadvantage that the standing times of the electrodes are not satisfactory under the conditions of electrolysis.
Die Anwendung von Elektroden mit aufgerauten Oberflächen zur Verbesserung der Lebensdauer dieser Elektroden, speziell durch raue, plasmagespritzte metallischeThe use of electrodes with roughened surfaces to improve the service life of these electrodes, especially through rough, plasma-sprayed metallic
Beschichtungen, ist in EP 493 326 A2 beschrieben. Kernpunkt ist die Erzeugung sehr rauer Oberflächen.Coatings is described in EP 493 326 A2. The key point is the creation of very rough surfaces.
US-A 4 392 927 schlägt für die Natriumchlorid-Elektrolyse die Verwendung von Verbundelektroden, bestehend aus einem elektrisch leitfähigen Substrat und einer elektrochemisch aktiven Deckschicht vor. Die elektrochemisch aktive Deckschicht wird durch thermisches Spritzen eines Pulvers auf den Träger aufgebracht, wobei das Pulver neben Matrixpartikeln auch elektrokatalytisch aktive Partikel enthält. Als Matrixpartikel kommen beispielsweise Titanoxid, Titanborid und Titancarbid in Frage, als elektrokatalytisch aktive Partikel Metalle der Platingruppe oder derUS Pat. No. 4,392,927 proposes the use of composite electrodes for sodium chloride electrolysis, consisting of an electrically conductive substrate and an electrochemically active cover layer. The electrochemically active top layer is applied to the carrier by thermal spraying of a powder, the powder also containing electrocatalytically active particles in addition to matrix particles. For example, titanium oxide, titanium boride and titanium carbide are suitable as matrix particles, and metals of the platinum group or of the electrocatalytically active particles
Eisengruppe oder Oxide dieser Metalle.Iron group or oxides of these metals.
Aus US-A 4 140 813 ist ein Verfahren zur Herstellung von Elektroden mit verbesserter Langzeitstabilität unter den Bedingungen der Alkalichlorid-Elektrolyse be- kannt. Auf einen metallischen Träger, vorzugsweise aus Titan oder einer Titanlegierung wird mittels Flamm- oder Plasmaspritzen eine erste Beschichtung aus Titansuboxid aufgebracht. Anschließend wird als elektrochemisch aktive Substanz ein Element der Platingruppe oder eine Verbindung eines solchen Elements aufgebracht. Solche Elektroden weisen eine verbesserte Lebensdauer unter den Bedingungen der Natriumdichromat-Elektrolyse auf. Sie können auch dann eingesetzt werden, wenn die Natriumchlorid-Elektrolyse unter sauren Bedingungen durchgeführt wird oder wenn Salzsäure elektrolysiert werden soll. Insbesondere unter den stark sauren Bedingungen bei der Salzsäure-Elektrolyse oder der Alkalidichromat-Elektrolyse bei niedrigem pH ist jedoch auch hier die Lebensdauer noch nicht ausreichend. Bei der Untersuchung von Anoden mit herkömmlichen Anodenbeschichtungen zeigte sich, dass es schon nach vergleichsweise geringer Einsatzdauer zu einem Abplatzen der aktiven Schicht vom Träger kommt. Als Ursache kommt einerseits eine grundsätzliche schlechte Haftung zwischen Träger und aktiver Schicht, andererseits eine Korrosion zwischen der aktiven Schicht und dem metallischen Träger in Frage, wobei die Korrosion die Haftung verschlechtert, was letztlich zur Zerstörung der Anodenbeschichtung führt.A method for producing electrodes with improved long-term stability under the conditions of alkali metal chloride electrolysis is known from US Pat. No. 4,140,813. A first coating of titanium suboxide is applied to a metallic carrier, preferably made of titanium or a titanium alloy, by means of flame or plasma spraying. An element of the platinum group or a compound of such an element is then applied as the electrochemically active substance. Such electrodes have an improved service life under the conditions of sodium dichromate electrolysis. They can also be used when the sodium chloride electrolysis is carried out under acidic conditions or when hydrochloric acid is to be electrolyzed. However, especially under the strongly acidic conditions in hydrochloric acid electrolysis or alkali dichromate electrolysis at low pH, the service life is still not sufficient. Examination of anodes with conventional anode coatings showed that the active layer flakes off the support after a comparatively short period of use. The cause is, on the one hand, a fundamentally poor adhesion between the support and the active layer, and, on the other hand, corrosion between the active layer and the metallic support, the corrosion impairing the adhesion, which ultimately leads to the destruction of the anode coating.
Aufgabe der Erfindung ist es daher, Elektroden mit einer verbesserten Lebensdauer unter den Bedingungen der Elektrolyse, insbesondere unter den stark sauren Bedingungen bei der Salzsäure-Elektrolyse oder einer Durchführung der Alkalidichromat- Elektrolyse in saurem Medium zu entwickeln.It is therefore an object of the invention to develop electrodes with an improved service life under the conditions of the electrolysis, in particular under the strongly acidic conditions in the hydrochloric acid electrolysis or when the alkali metal dichromate electrolysis is carried out in an acidic medium.
Überraschenderweise wurde nun gefunden, dass diese Aufgabe gelöst werden kann, wenn Elektroden vor Aufbringung der katalytisch aktiven Schicht mit einer speziellen Zwischenschicht versehen werden.Surprisingly, it has now been found that this object can be achieved if electrodes are provided with a special intermediate layer before the catalytically active layer is applied.
Gegenstand der Erfindung ist daher eine Elektrode, wenigstens enthaltend einen elektrisch leitfähigen Träger aus einer Titan-Palladium-Legierung, Titan, Tantal oder Verbindungen oder Legierungen des Titans oder Tantals, eine elektrochemisch aktiveThe invention therefore relates to an electrode, at least comprising an electrically conductive carrier made of a titanium-palladium alloy, titanium, tantalum or compounds or alloys of titanium or tantalum, an electrochemically active one
Beschichtung und eine Zwischenschicht zwischen Träger und elektrochemisch aktiver Beschichtung, wobei die Zwischenschicht aus Titancarbid und/oder Titanborid besteht und durch Flamm- oder Plasmaspritzen auf den Träger aufgebracht ist.Coating and an intermediate layer between the carrier and the electrochemically active coating, the intermediate layer consisting of titanium carbide and / or titanium boride and being applied to the carrier by flame or plasma spraying.
Im Vergleich zu den in US-A 4 392 927 für die Natriumchlorid-Elektrolyse beschriebenen Verbundelektroden, die nur eine elektrochemisch aktive Deckschicht enthalten, die neben Matrixpartikeln auch elektrokatalytisch aktive Partikel umfasst, zeichnen sich die erfindungsgemäßen Elektroden durch erhöhte Stabilität aus, da durch Einsatz einer Zwischenschicht sowohl die Haftfestigkeit zum Träger, als auch die Haftfestigkeit der katalytisch aktiven Schicht verbessert wird. Die erfmdungsgemäßen Elektroden sind als Anode, als Kathode und auch als kathodischer Stromverteiler verwendbar. Sie zeigen eine sehr hohe Beständigkeit beim Einsatz in der Salzsäureelektrolyse bzw. der Alkahdichromat-Elektrolyse in saurem Medium. Beispielsweise sind diese Elektroden auch bei der Elektrolyse von Salzsäure mit einer Konzentration von < 20 Gew.-% HC1 bei Temperaturen bis zu 70°C und hohen spezifischen Stromdichten von bis zu 8kA/m2 äußerst stabil. Im Vergleich zu Zwischenschichten aus Titanoxid oder Titansuboxid zeichnen sich die Zwischenschichten aus Titancarbid und Titanborid dadurch aus, dass sie äußerst dicht sind. Dadurch wird ein Angriff von aggressiven Medien, etwa Salzsäure am Träger verhindert. Zudem wird die Haftung der elektrochemisch aktiven Schicht deutlich verbessert.In comparison to the composite electrodes described for the sodium chloride electrolysis in US Pat. No. 4,392,927, which only contain an electrochemically active cover layer which, in addition to matrix particles, also comprises electrocatalytically active particles, the electrodes according to the invention are characterized by increased stability, since by using a Intermediate layer improves both the adhesive strength to the support and the adhesive strength of the catalytically active layer. The electrodes according to the invention can be used as an anode, as a cathode and also as a cathodic current distributor. They show a very high resistance when used in hydrochloric acid electrolysis or alkahdichromate electrolysis in an acidic medium. For example, these electrodes are also extremely stable in the electrolysis of hydrochloric acid with a concentration of <20% by weight HC1 at temperatures up to 70 ° C and high specific current densities of up to 8kA / m 2 . Compared to intermediate layers made of titanium oxide or titanium suboxide, the intermediate layers made of titanium carbide and titanium boride are distinguished by the fact that they are extremely dense. This prevents aggressive media such as hydrochloric acid from attacking the carrier. In addition, the adhesion of the electrochemically active layer is significantly improved.
Die elektrochemisch aktive Beschichtung kann beispielsweise ein Oxid eines Ele- ents der Platinmetall-Gruppe (Ru, Rh, Pd, Os, Ir, Pt) enthalten.The electrochemically active coating can contain, for example, an oxide of an element from the platinum metal group (Ru, Rh, Pd, Os, Ir, Pt).
Vorzugsweise besteht für die Alkalidichromat-Elektrolyse die elektrochemisch aktive Schicht aus Platin, Iridiumdioxid oder beidem oder einem Mischmetalloxid, welches Iridiumdioxid enthält.For the alkali dichromate electrolysis, the electrochemically active layer preferably consists of platinum, iridium dioxide or both or a mixed metal oxide which contains iridium dioxide.
Die Beladung des Trägers mit der Zwischenschicht beträgt bevorzugt von 10-5000 g/m2.The loading of the carrier with the intermediate layer is preferably 10-5000 g / m 2 .
In einer besonderen Ausfuhrungsform besteht die Zwischenschicht aus mehr als einer Schicht, d.h. die Zwischenschicht ist mehrschichtig durch Flamm- oderIn a special embodiment, the intermediate layer consists of more than one layer, i.e. the intermediate layer is multilayered by flame or
Plasmaspritzen aufgebracht.Plasma spraying applied.
Vorzugsweise handelt es sich bei der Zwischenschicht um eine Schicht aus Titancarbid. Die erfmdungsgemäßen Elektroden lassen sich beispielsweise durch Aufbringen einer Zwischenschicht mittels Flamm- oder Plasmaspritzen auf einen Träger und anschließendes Aufbringen einer elektrochemisch aktiven Beschichtung auf die Zwischenschicht herstellen, wobei beim Aufbringen der Zwischenschicht durch Flamm- oder Plasmaspritzen, Titancarbid- und/oder Titanborid-Pulver unterschiedlicher Korngrößen, d.h. mit einer Korngrößenverteilung, verwendet werden.The intermediate layer is preferably a layer of titanium carbide. The electrodes according to the invention can be produced, for example, by applying an intermediate layer to a carrier by means of flame or plasma spraying and then applying an electrochemically active coating to the intermediate layer, wherein differently when the intermediate layer is applied by flame or plasma spraying, titanium carbide and / or titanium boride powder Grain sizes, ie with a grain size distribution, can be used.
Als Träger dient dabei ein Netz, Gewebe, Geflecht, Gewirke, Vlies oder Schaum aus einer Titan-Palladium-Legierung, Titan, Tantal oder Verbindungen oder Legierungen des Titans oder Tantals.A mesh, woven fabric, braid, knitted fabric, fleece or foam made of a titanium-palladium alloy, titanium, tantalum or compounds or alloys of titanium or tantalum serves as the carrier.
Die eingesetzten Titancarbid- und oder Titanborid-Pulver zum Aufbringen der Zwischenschichten durch Flamm- oder Plasmaspritzen weisen vorzugsweise Korngrößen von 10 bis 200 μm auf.The titanium carbide and or titanium boride powders used to apply the intermediate layers by flame or plasma spraying preferably have grain sizes of 10 to 200 μm.
Unter Korngröße wird im Sinne dieser Anmeldung der Partikeldurchmesser verstanden, wie er beispielsweise mittels Siebanalyse bestimmt wird.For the purposes of this application, particle size is understood to mean the particle diameter as determined, for example, by means of sieve analysis.
Das Flamm- oder Plasmaspritzen erfolgt in üblicher Weise. Beispielsweise kann Titancarbid- oder Titanborid-Pulver mittels eines kommerziell verfügbaren Plasma-Flame or plasma spraying is carried out in the usual way. For example, titanium carbide or titanium boride powder can be obtained using a commercially available plasma
Brenners auf den Träger aufgebracht werden. Einzelheiten zur Plasmaspritztechnik können beispielsweise der Broschüre „Plasmaspritztechnik, Grundlagen und Anwendungen, 1975" der Firma Plasma-Technik AG entnommen werden. Als Plasmagas kann beispielsweise ein Gemisch von Stickstoff und Wasserstoff, wobei das Volumenverhältnis von Stickstoff zu Wasserstoff beispielsweise zwischen 70/30 und 95/5 liegen kann, in einer Menge von beispielsweise 5 bis 20 17min und als Trägergas Stickstoff eingesetzt werden. Der Spritzvorgang kann beispielsweise bei einem Strom von 200 bis 400 Ampere und einer Spannung von 50 bis 90 Volt durchgeführt werden. Der Abstand zwischen Plasmabrenner und Träger kann beispielsweise 130 bis 200 mm betragen. Das Aufbringen der elektrochemisch aktiven Beschichtung kann in an sich bekannter Weise erfolgen. Beispielsweise kann so vorgegangen werden, dass eine Lösung oder Dispersion einer Verbindung eines Elements der Platinmetall-Gruppe (Ru, Rh, Pd, Os, Ir, Pt) und gegebenenfalls einer Verbindung des Titans auf die Zwischenschicht aufgebracht und durch anschließende thermische Behandlung zu den entsprechendenBrenner are applied to the carrier. Details on plasma spraying technology can be found, for example, in the brochure "Plasma Spraying Technology, Fundamentals and Applications, 1975" from the company Plasma-Technik AG. For example, a mixture of nitrogen and hydrogen, the volume ratio of nitrogen to hydrogen being between 70/30 and 95, for example / 5 can be used in an amount of, for example, 5 to 20 minutes and nitrogen as the carrier gas The spraying process can be carried out, for example, at a current of 200 to 400 amperes and a voltage of 50 to 90 V. The distance between the plasma torch and the carrier can be, for example, 130 to 200 mm. The electrochemically active coating can be applied in a manner known per se. For example, one can proceed in such a way that a solution or dispersion of a compound of an element of the platinum metal group (Ru, Rh, Pd, Os, Ir, Pt) and optionally a compound of titanium are applied to the intermediate layer and then to the corresponding ones by subsequent thermal treatment
Oxiden umgesetzt wird. Vorteilhafterweise wird dieses Vorgehen mehrmals wiederholt.Oxides is implemented. This procedure is advantageously repeated several times.
Die erfindungsgemäßen Elektroden können beispielsweise als gasentwickelnde Elektroden eingesetzt werden.The electrodes according to the invention can be used, for example, as gas-developing electrodes.
Bevorzugt ist die Verwendung der Elektroden in einer elektrochemischen Zelle zur Herstellung von Chlor aus wässrigen Salzsäurelösungen oder von Chromsäure aus einer Natriumdichromat/Chromsäure-Lösung unter Sauerstoffentwicklung.It is preferred to use the electrodes in an electrochemical cell to produce chlorine from aqueous hydrochloric acid solutions or chromic acid from a sodium dichromate / chromic acid solution with evolution of oxygen.
Die eingesetzte elektrochemische Zelle kann dabei beispielsweise einen Anodenraum mit Anode und einen Kathodenraum mit Gasdiffusionselektrode und Stromkollektor enthalten, wobei Anodenraum und Kathodenraum durch eine Kationenaustauschermembran voneinander getrennt sind und als Anode, Kathode und/oder Stromkollek- tor eine erfindungsgemäße Elektrode eingesetzt wird.The electrochemical cell used can contain, for example, an anode compartment with an anode and a cathode compartment with a gas diffusion electrode and current collector, the anode compartment and cathode compartment being separated from one another by a cation exchange membrane and an electrode according to the invention being used as anode, cathode and / or current collector.
In den Kathodenraum kann ein sauerstoffhaltiges Gas, beispielsweise reiner Sauerstoff, ein Gemisch aus Sauerstoff und inerten Gasen, insbesondere Stickstoff, oder Luft eingeleitet werden, vorzugsweise Sauerstoff oder ein sauerstoffreiches Gas.An oxygen-containing gas, for example pure oxygen, a mixture of oxygen and inert gases, in particular nitrogen, or air, preferably oxygen or an oxygen-rich gas, can be introduced into the cathode compartment.
Das sauerstoffhaltige Gas wird dabei vorteilhaft in einer solchen Menge zugeführt, dass Sauerstoff bezogen auf die gemäß Gleichung 1 theoretisch benötigte Menge überstöchiometrisch vorliegt. Anodenreaktion: 4 HC1 → 2 Cl2 + 4 H+ + 4 e" Kathodenreaktion: O2 + 4 H+ + 4 e" → 2 H2OThe oxygen-containing gas is advantageously fed in such an amount that oxygen is present in a stoichiometric amount based on the amount theoretically required according to equation 1. Anode reaction: 4 HC1 → 2 Cl 2 + 4 H + + 4 e " Cathode reaction: O 2 + 4 H + + 4 e " → 2 H 2 O
Gesamtreaktion: 4 HC1 + O2 → 2 Cl2 + 2 H2O (1)Overall reaction: 4 HC1 + O 2 → 2 Cl 2 + 2 H 2 O (1)
Bei der Verwendung der Elektroden in einer elektrochemischen Zelle zur Herstellung von Chlor aus wässrigen Salzsäurelösungen wird die wässrige Lösung des Chlorwasserstoffs in der Regel in die Anodenkammer eingeleitet. Die Temperatur der zugeführten wässrigen Lösung von Chlorwasserstoff beträgt vorzugsweise 30 bis 90°C, insbesondere bevorzugt 50 bis 70°C.When the electrodes are used in an electrochemical cell for producing chlorine from aqueous hydrochloric acid solutions, the aqueous solution of the hydrogen chloride is generally introduced into the anode chamber. The temperature of the supplied aqueous solution of hydrogen chloride is preferably 30 to 90 ° C, particularly preferably 50 to 70 ° C.
Es können insbesondere wässrige Lösungen von Chlorwasserstoff mit einer Chlorwasserstoffkonzentration von < 20 Gew.-% eingesetzt werden.In particular, aqueous solutions of hydrogen chloride with a hydrogen chloride concentration of <20% by weight can be used.
Die Salzsäure-Elektrolyse wird vorzugsweise bei einem Druck im Anodenraum größer als 1 bar absolut durchgeführt, besonders bevorzugt 1,05 bis 1,4 bar.The hydrochloric acid electrolysis is preferably carried out at a pressure in the anode compartment greater than 1 bar absolute, particularly preferably 1.05 to 1.4 bar.
Die erfindungsgemäßen Elektroden lassen sich aber auch vorteilhaft in einer elektrochemischen Zelle zur Herstellung von Chromsäure aus einer wässrigen Alkalidichromat-Lösung, insbesondere aus einer wässrigen Natriumdichromatlösung einsetzen. Besonders vorteilhaft ist die Verwendung dann, wenn die Elektrolyse der wässrigen Natriumdichromatlösung unter sauren Bedingungen erfolgt, weil in diesem Fall herkömmliche Elektroden rasch an Aktivität verlieren.However, the electrodes according to the invention can also advantageously be used in an electrochemical cell for producing chromic acid from an aqueous alkali dichromate solution, in particular from an aqueous sodium dichromate solution. The use is particularly advantageous when the electrolysis of the aqueous sodium dichromate solution takes place under acidic conditions, because in this case conventional electrodes rapidly lose activity.
Es ist auch denkbar, die Elektroden in einer elektrochemischen Zelle zur Herstellung von Chlor aus wässrigen Salzsäurelösungen als elektrischer Stromverteiler einer Gas- diffusionselektrode zur Reduktion von Sauerstoff einzusetzen.It is also conceivable to use the electrodes in an electrochemical cell for producing chlorine from aqueous hydrochloric acid solutions as an electrical current distributor in a gas diffusion electrode for reducing oxygen.
In den folgenden Beispielen wird das erfindungsgemäße Verfahren weiter erläutert, wobei die Beispiele nicht als Einschränkung des allgemeinen Erfindungsgedankens zu verstehen sind. Beispiel 1The process according to the invention is further explained in the following examples, the examples not being to be understood as restricting the general inventive concept. example 1
Die Oberfläche eines Streckmetalls aus einer Standard Titan-Palladium-Legierung (Titan Grade 11) wurde mittels Strahlen mit Stahlkies auf einer Rautiefe von 30 bis 40 μm aufgeraut. Anschließend wurde das Streckmetall mit einer 20 Gew.%The surface of an expanded metal made of a standard titanium-palladium alloy (titanium grade 11) was roughened to a roughness depth of 30 to 40 μm by blasting with steel gravel. The expanded metal was then coated with a 20% by weight
Salzsäure ca. 10 Minuten gebeizt. Damit konnten auch die Reste des Strahlmittels entfernt werden.Hydrochloric acid pickled for about 10 minutes. This also removed the remnants of the abrasive.
Auf das vorbehandelte Streckmetall wurde mittels einer Plasmabeschichtungsanlage vom Typ Plasmatechnik eine Schicht Titancarbid aufgebracht. Dazu wurdeA layer of titanium carbide was applied to the pretreated expanded metal by means of a plasma coating system of the plasma technology type. This was done
Plasmapulver der Firma H.C. Starck, Typ AMPERIT 570.3, verwendet. Die Korngrößenverteilung wurde nach.Microtrac zu - 5,6 μm und mittels Siebanalyse nach Rotap zu + 45 bestimmt.Plasma powder from H.C. Starck, type AMPERIT 570.3, is used. The grain size distribution was determined according to Microtrac to - 5.6 μm and by means of sieve analysis according to Rotap to + 45.
Als Plasmagas wurde Helium mit einer Durchflussmenge von 1,3 1/Min. undHelium was used as the plasma gas at a flow rate of 1.3 l / min. and
Stickstoff mit einer Durchflussmenge von 2,5 1/Min. verwendet. Als Trägergas für den Transport des Plasmapulvers zum Brenner wurde Stickstoff mit 6,5 1/Min. verwendet. Die Brennerleistung betrug 560 A bei 62 V. Der Plasmabrenner wurde in der schallgeschützten Anlage von einem oszillierenden Hubgerüst bewegt. Die Hubgeschwindigkeit betrug 12 m Min. Die horizontale Schrittlänge betrug 10 mm pro Doppelhub. Der Brennerabstand betrug ca. 150 mm bei einem Winkel von 90°. Die Titancarbidschicht wies ein Flächengewicht von 50 bis 80 g/m2 auf.Nitrogen with a flow rate of 2.5 l / min. used. Nitrogen was used as the carrier gas for the transport of the plasma powder to the burner at 6.5 l / min. used. The burner output was 560 A at 62 V. The plasma torch was moved in the soundproof system by an oscillating mast. The lifting speed was 12 m min. The horizontal stride length was 10 mm per double stroke. The burner distance was approx. 150 mm at an angle of 90 °. The titanium carbide layer had a basis weight of 50 to 80 g / m 2 .
Anschließend wurde auf das mit der Zwischenschicht versehene Streckmetall eine elektrochemisch aktive Schicht aus RuO und TiO2 aufgebracht. Dazu wurde eineAn electrochemically active layer of RuO and TiO 2 was then applied to the expanded metal provided with the intermediate layer. In addition, a
Mischung aus TiCl3 und RuCl3 (Molverhältnis 1 : 1) in verdünnter Salzsäure (ca. 2n HC1) gelöst und mittels eines Pinsels auf das Streckmetall aufgebracht. Das beschichtete Streckmetall wurde anschließend in Luft auf 500°C erhitzt. Dieser Vorgang wurde mehrmals, vorzugsweise 4 bis 12 mal, wiederholt. Das beschichtete Streckmetall wurde als Anode und/oder Kathodennetz, welches als Sttomzuführung einer Sauerstoffverzehrkathode diente, d.h. als Stromverteiler eingesetzt.Mixture of TiCl 3 and RuCl 3 (molar ratio 1: 1) dissolved in dilute hydrochloric acid (approx. 2n HC1) and applied to the expanded metal using a brush. The coated expanded metal was then heated to 500 ° C in air. This process was repeated several times, preferably 4 to 12 times. The coated expanded metal was used as an anode and / or cathode network, which served as a current feed for an oxygen consumable cathode, ie as a current distributor.
Beispiel 2 (Vergleichsbeispiel)Example 2 (comparative example)
Die Oberfläche eines Streckmetalls aus einer Standard Titan-Palladium-Legierung (Titan Grade 11) wurde mittels Strahlen mit Stahlkies auf einer Rautiefe von 30 bis 40 μm aufgeraut. Anschließend wurde das Streckmetall mit einer 20 Gew.-% Salzsäure ca. 10 Minuten gebeizt. Damit konnten auch die Reste des Strahlmittels entfernt werden.The surface of an expanded metal made of a standard titanium-palladium alloy (titanium grade 11) was roughened to a roughness depth of 30 to 40 μm by blasting with steel gravel. The expanded metal was then pickled with a 20% by weight hydrochloric acid for about 10 minutes. This also removed the remnants of the abrasive.
Auf das vorbehandelte Streckmetall wurde eine elektrochemisch aktive Schicht aus RuO2 und TiO2 aufgebracht. Das Aufbringen erfolgte wie in Beispiel 1 beschrieben.An electrochemically active layer of RuO 2 and TiO 2 was applied to the pretreated expanded metal. The application was carried out as described in Example 1.
Das beschichtete Streckmetall wurde als Anode und/oder Kathodennetz, welches als Stromzuführung einer Sauerstoffverzehrkathode diente, eingesetzt.The coated expanded metal was used as an anode and / or cathode network, which served as the power supply for an oxygen consumable cathode.
Beispiel 3 (Elektrodentest)Example 3 (electrode test)
In eine elektrochemische Zelle enthaltend einen Anodenraum mit Anode, eine Kationenaustauschermembran und einen Kathodenraum mit Sauerstoffverzehrkathode und Stromkollektor wurden mit der notwendigen Peripherie als Anode und als Stromkollektor die in den Beispielen 1 bzw. 2 beschriebenen Elektroden mit aktiven Oberflä- chen von j eweils 100 cm2 eingebaut und getestet.In an electrochemical cell containing an anode compartment with anode, a cation exchange membrane and a cathode compartment with oxygen-consuming cathode and current collector, the electrodes described in Examples 1 and 2 with active surfaces of 100 cm 2 each were used with the necessary periphery as an anode and as a current collector installed and tested.
Aus einem Vorratsgefäß wurde eine wässrige Salzsäurelösung (15-30 Gew.-%) mittels einer Pumpe in einen Anolytkreislauf und von dort aus mittels einer weiteren Pumpe über einen Wärmetauscher in den Anodenraum einer elektrochemischen Zelle gepumpt. Ein Teil der abgereicherten Salzsäurelösung wurde zusammen mit dem an der Anode entwickelten Chlorgas über eine Leitung in ein säulenförmiges Gefäß, in dem eine Gas/Flüssigkeitstrennung erfolgte, abgeführt. Über eine Leitung, die in die Flüssigkeit des säulenförmigen Gefäßes eingetaucht war, wurde ein bestimmter Druck in der elektrochemischen Zelle und im Anolyten eingestellt. Dadurch wurde die Kationenaustauschermembran auf die Sauerstoffverzehrkathode gepresst, die ihrerseits auf dem Stromverteiler auflag.An aqueous hydrochloric acid solution (15-30% by weight) was pumped from a storage vessel by means of a pump into an anolyte circuit and from there by means of a further pump via a heat exchanger into the anode compartment of an electrochemical cell. A portion of the depleted hydrochloric acid solution was passed through a line into a columnar vessel, together with the chlorine gas developed at the anode which gas / liquid separation took place. A certain pressure was set in the electrochemical cell and in the anolyte via a line which was immersed in the liquid of the columnar vessel. As a result, the cation exchange membrane was pressed onto the oxygen consumption cathode, which in turn rested on the power distributor.
Sauerstoff wurde über eine Leitung in ein Gefäß, welches mit Wasser gefüllt war und zur Anfeuchtung des Sauerstoffes diente, geleitet. Der angefeuchtete Sauerstoff wurde dem Kathodenraum zugeführt, wurde an der Sauerstoffverzehrkathode redu- ziert und reagierte mit den über die Kationenaustauschermembran gewanderten Protonen zu Wasser. Restsauerstoff wurde zusammen mit dem gebildeten Kondensat in einen Kondensatabscheider abgeführt. Der überschüssige Sauerstoff und das Kondensat wurden aus der elektrochemischen Zelle entfernt.Oxygen was fed via a line into a vessel which was filled with water and was used to moisten the oxygen. The moistened oxygen was fed to the cathode compartment, was reduced at the oxygen consumption cathode and reacted to water with the protons that had migrated over the cation exchange membrane. Residual oxygen was removed together with the condensate formed in a condensate separator. The excess oxygen and the condensate were removed from the electrochemical cell.
Der Test der Anode wurde wie folgt durchgeführt:The anode test was carried out as follows:
Eine wässrige ca. 30 gew.-%ige Salzsäurelösung wurde so in einen Salzsäurekreislauf eindosiert, dass die Säurekonzentration im Anolytkreislauf und in der Zelle ca. 12- 15 Gew.-% HC1 betrug. Die Temperatur der Anolytlösung wurde auf 60-70°C eingestellt. Die Elektrolyse wurde mit einer Stromdichte von 5 kA/m2 betrieben. AlsAn aqueous approximately 30% by weight hydrochloric acid solution was metered into a hydrochloric acid circuit in such a way that the acid concentration in the anolyte circuit and in the cell was approximately 12-15% by weight HC1. The temperature of the anolyte solution was set at 60-70 ° C. The electrolysis was operated at a current density of 5 kA / m 2 . As
Kationenaustauschermembran wurde eine Membran auf Basis eines Perfluorsulfonat- polymers der Firma DuPont (Typ Nafion® 324) verwendet. Es wurde eine Sauerstoffverzehrkathode der Firma E-TEK auf Kohlenstoffbasis mit Platinkatalysator eingesetzt. Das komplette Zellengehäuse war aus PTFE (Polytetrafluorethylen) bzw. PVDF (Polyvinylidenfluorid) gefertigt.Cation exchange membrane, a membrane based on a polymer of the Perfluorsulfonat- DuPont (Nafion ® 324) was used. An oxygen-consuming cathode from E-TEK based on carbon with a platinum catalyst was used. The complete cell housing was made of PTFE (polytetrafluoroethylene) or PVDF (polyvinylidene fluoride).
Während der Laufzeit der Elektrolyse wurden in regelmäßigen Abständen die Anode und der Stromverteiler untersucht und der Grad der Zerstörung ermittelt. Die Ermittlung erfolgte qualitativ durch Untersuchung der Anode und des Stromverteilers unter dem Lichtmikroskop. Quantitativ wurde der Grad der Zerstörung durchDuring the running time of the electrolysis, the anode and the current distributor were examined at regular intervals and the degree of destruction was determined. The determination was made qualitatively by examining the anode and the current distributor under the light microscope. The degree of destruction was quantified by
Schichtdicken-Messungen mittels Röntgenfluoreszenzmessung bestimmt. Die Er- gebnisse der Untersuchungen sind in Tabelle I (Anode) und Tabelle II (Stromverteiler) zusammengefasst. Der Grad der Zerstörung ist in % angegeben, wobei darunter der Anteil an aktiver Beschichtung zu verstehen ist, der im Vergleich zur ursprünglich vorhandenen Schichtdicke aktiver Beschichtung abgetragen worden ist.Layer thickness measurements determined by means of X-ray fluorescence measurement. Which he- Results of the tests are summarized in Table I (anode) and Table II (current distributor). The degree of destruction is given in%, which means the proportion of active coating which has been removed in comparison to the layer of active coating originally present.
Tabelle I: Zustand der Anodenbeschichtungen:Table I: Condition of the anode coatings:
keine Bestimmung erfolgtno determination made
Tabelle II: Zustand der Beschichtung der Kathoden-Stromverteiler:Table II: Condition of the coating of the cathode current distributors:
Überraschenderweise haben die Untersuchungen ergeben, dass die in Beispiel 1 gefertigte Anode eine extrem hohe Stabilität unter den oben genannten Bedingungen zeigte. Das Anodenpotential war nach einer Laufzeit von 408 Tagen noch unverän- dert. Der Vergleichstest mit einer nach Beispiel 2 gefertigten Anode musste wegen Zerstörung der Anodenbeschichtung nach einer Laufzeit von 280 Tagen abgebrochen werden.Surprisingly, the investigations have shown that the anode produced in Example 1 showed extremely high stability under the conditions mentioned above. The anode potential was still unchanged after a running time of 408 days. changed. The comparison test with an anode manufactured according to Example 2 had to be stopped after 280 days due to destruction of the anode coating.
Auch der Grad der Zerstörung des eingesetzten Stromverteilers war bei Verwendung einer erfmdungsgemäßen Elektrode gemäß Beispiel 1 deutlich niedriger, als bei Verwendung einer Elektrode nach Beispiel 2. The degree of destruction of the current distributor used was also significantly lower when using an electrode according to the invention according to Example 1 than when using an electrode according to Example 2.

Claims

Patentansprüche claims
1. Elektrode wenigstens enthaltend einen elektrisch leitfähigen Träger aus einer Titan-Palladium-Legierung, Titan, Tantal oder Verbindungen oder Legierungen des Titans oder Tantals, eine elektrochemisch aktive Beschichtung und eine Zwischenschicht zwischen Träger und elektrochemisch aktiver Beschichtung, dadurch gekennzeichnet, dass die Zwischenschicht aus Titancarbid und/oder Titanborid besteht und durch Flamm- oder Plasmaspritzen auf den Träger aufgebracht ist.1. Electrode at least containing an electrically conductive carrier made of a titanium-palladium alloy, titanium, tantalum or compounds or alloys of titanium or tantalum, an electrochemically active coating and an intermediate layer between the carrier and the electrochemically active coating, characterized in that the intermediate layer consists of Titanium carbide and / or titanium boride and is applied to the carrier by flame or plasma spraying.
2. Elektrode nach Anspruch 1 dadurch gekennzeichnet, dass die elektrochemisch aktive Beschichtung ein Oxid eines Elements der Platinmetall-Gruppe enthält.2. Electrode according to claim 1, characterized in that the electrochemically active coating contains an oxide of an element of the platinum metal group.
3. Elektrode nach Anspruch 2, dadurch gekennzeichnet, dass die elektroche- misch aktive Schicht aus Rutheniumdioxid oder einem Metallmischoxid, welches Rutheniumdioxid enthält, oder aus Iridiumoxid oder einem Metallmischoxid, welches Iridiumoxid enthält, besteht.3. Electrode according to claim 2, characterized in that the electrochemically active layer consists of ruthenium dioxide or a mixed metal oxide which contains ruthenium dioxide, or of iridium oxide or a mixed metal oxide which contains iridium oxide.
4. Elektrode nach wenigstens einem der Ansprüche 1 bis 3, dadurch gekenn- zeichnet, dass der Träger eine Beladung mit Zwischenschicht von 10-5000 g/m2 aufweist.4. Electrode according to at least one of claims 1 to 3, characterized in that the carrier has a load with an intermediate layer of 10-5000 g / m 2 .
5. Elektrode nach wenigstens einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, dass die Zwischenschicht mehrschichtig aufgetragen ist.5. Electrode according to at least one of claims 1 to 4, characterized in that the intermediate layer is applied in multiple layers.
6. Verfahren zur Herstellung einer Elektrode gemäß einem der Ansprüche 1 bis 5 durch Aufbringen einer Zwischenschicht auf einen Träger und anschließendes Aufbringen einer elektrochemisch aktiven Beschichtung auf die Zwischenschicht, dadurch gekennzeichnet, dass beim Aufbringen der Zwischenschicht durch Flamm- oder Plasmaspritzen, Titancarbid- und/oder6. A method for producing an electrode according to one of claims 1 to 5 by applying an intermediate layer on a support and then applying an electrochemically active coating on the intermediate layer, characterized in that when the intermediate layer is applied by flame or plasma spraying, titanium carbide and / or
Titanborid-Pulver unterschiedlicher Korngrößen verwendet werden. Titanium boride powder of different grain sizes can be used.
7. Verfahren nach Anspruch 6, dadurch gekennzeichnet, dass die eingesetzten Pulver Korngrößen von 10 bis 200 μm aufweisen.7. The method according to claim 6, characterized in that the powders used have grain sizes of 10 to 200 microns.
8. Verwendung einer Elektrode gemäß einem der Ansprüche 1 bis 5 als gasentwickelnde Elektrode.8. Use of an electrode according to one of claims 1 to 5 as a gas-developing electrode.
9. Verwendung einer Elektrode gemäß einem der Ansprüche 1 bis 5 in einer elektrochemischen Zelle zur Herstellung von Chlor aus wässrigen Salzsäure- lösungen oder zur Herstellung von Chromsäure aus wässrigen9. Use of an electrode according to one of claims 1 to 5 in an electrochemical cell for the production of chlorine from aqueous hydrochloric acid solutions or for the production of chromic acid from aqueous
Alkalidichromatlösungen.Alkali metal dichromate.
10. Verwendung einer Elektrode gemäß eines der Ansprüche 1 bis 5 in einer elektrochemischen Zelle zur Herstellung von Chlor aus wässrigen Salzsäure- lösungen als elektrischer Stromyerteiler einer Gasdiffusionselektrode zur Reduktion von Sauerstoff. 10. Use of an electrode according to one of claims 1 to 5 in an electrochemical cell for the production of chlorine from aqueous hydrochloric acid solutions as an electrical current divider of a gas diffusion electrode for reducing oxygen.
EP02805772A 2002-01-03 2002-12-23 Electrode for conducting electrolysis in acid media Expired - Lifetime EP1463847B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE10200072 2002-01-03
DE10200072A DE10200072A1 (en) 2002-01-03 2002-01-03 Electrodes for electrolysis in acid media
PCT/EP2002/014713 WO2003056065A2 (en) 2002-01-03 2002-12-23 Electrode for conducting electrolysis in acid media

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EP1463847A2 true EP1463847A2 (en) 2004-10-06
EP1463847B1 EP1463847B1 (en) 2005-12-28

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CN (1) CN100415937C (en)
AT (1) ATE314506T1 (en)
AU (1) AU2002367189A1 (en)
DE (2) DE10200072A1 (en)
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DE102006023261A1 (en) 2006-05-18 2007-11-22 Bayer Materialscience Ag Process for the production of chlorine from hydrogen chloride and oxygen
ITMI20061974A1 (en) * 2006-10-16 2008-04-17 Industrie De Nora Spa ANODE FOR ELECTROLYSIS
JP2008156684A (en) * 2006-12-22 2008-07-10 Tanaka Kikinzoku Kogyo Kk Anode electrode for hydrochloric acid electrolysis
CN101280453B (en) * 2008-01-31 2010-06-09 顿力集团有限公司 Preparation of anode with trivalent chromium chrome plating coating
ES2643234T3 (en) 2010-03-30 2017-11-21 Covestro Deutschland Ag Procedure for the preparation of diaryl carbonates and polycarbonates
US9175135B2 (en) 2010-03-30 2015-11-03 Bayer Materialscience Ag Process for preparing diaryl carbonates and polycarbonates
CN101967654B (en) * 2010-10-11 2012-06-27 福州大学 Ruthenium oxide electrode material by adopting carburization and modification of titanium base material and preparation method thereof
DE102010043085A1 (en) * 2010-10-28 2012-05-03 Bayer Materialscience Aktiengesellschaft Electrode for electrolytic chlorine production
ITMI20120158A1 (en) * 2012-02-07 2013-08-08 Industrie De Nora Spa ELECTRODE FOR ELECTROCHEMICAL FILLING OF THE CHEMICAL APPLICATION OF OXYGEN IN INDUSTRIAL WASTE
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CN104021947B (en) * 2014-06-20 2017-04-12 贵州中航聚电科技有限公司 Method for preparing ruthenium oxide electrode for hybrid super capacitor
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CN1612949A (en) 2005-05-04
US20030136669A1 (en) 2003-07-24
EP1463847B1 (en) 2005-12-28
KR20050005405A (en) 2005-01-13
KR101081243B1 (en) 2011-11-08
DE10200072A1 (en) 2003-07-31
ES2255639T3 (en) 2006-07-01
WO2003056065A2 (en) 2003-07-10
ATE314506T1 (en) 2006-01-15
CN100415937C (en) 2008-09-03
WO2003056065A3 (en) 2004-03-11
JP4354821B2 (en) 2009-10-28
US7211177B2 (en) 2007-05-01
AU2002367189A1 (en) 2003-07-15
JP2005513276A (en) 2005-05-12

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