EP0384194B1 - Dimensionally stable anodes and their use in the production of alkalidichromates and chromic acid - Google Patents
Dimensionally stable anodes and their use in the production of alkalidichromates and chromic acid Download PDFInfo
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- EP0384194B1 EP0384194B1 EP90102143A EP90102143A EP0384194B1 EP 0384194 B1 EP0384194 B1 EP 0384194B1 EP 90102143 A EP90102143 A EP 90102143A EP 90102143 A EP90102143 A EP 90102143A EP 0384194 B1 EP0384194 B1 EP 0384194B1
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- platinum
- anodes
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- iridium
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- 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
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/14—Alkali metal compounds
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- 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
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/22—Inorganic acids
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- 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
Definitions
- the invention further relates to a process for the preparation of alkali dichromates and chromic acid by electrolysis of alkali monochromate and / or alkali dichromate solutions using the electrodes according to the invention.
- anodes that consist of an electrically conductive valve metal such as titanium, tantalum and niobium and are coated with an electrocatalytically active substance. These anodes are commonly called dimensionally stable (“dimensionally stable”) anodes or referred to as DSA®. Metals from the platinum group and their oxides, as well as lead dioxide and manganese dioxide, are primarily used as electrocatalytically active substances. Such anodes are described for example in BE-A 710 551, DE-B 2 300 422 and US-A 3 711 385.
- This intermediate layer can consist of one or more metal oxides, such as oxides of platinum metals, oxides of titanium, vanadium, niobium, Tantalum and other base metals exist.
- metal oxides such as oxides of platinum metals, oxides of titanium, vanadium, niobium, Tantalum and other base metals exist.
- Such anodes are described for example in DE-A 3 219 003, DE-C 3 330 388, DE-A 3 715 444 and DE-A 3 717 972.
- US-A 3 775 284 discloses anodes which have intermediate layers of precious metals such as platinum and iridium, which are applied by wet electroplating processes.
- the described intermediate layers can slow down the passivation and thus extend the life of the anodes, but these anodes still do not have sufficient durability, especially at temperatures above 60 ° C.
- Typical processes in which oxygen is formed anodically are the electrolytic production of alkali dichromates, chromic acid, perchlorates, chlorates, persulphates and hydrogen peroxide, the electrolytic deposition of metals such as chromium, copper, zinc or noble metals and various electroplating processes or electroplating.
- the object of the invention was to provide dimensionally stable anodes which do not have the disadvantages described.
- the layer thickness of the intermediate layer according to the invention is preferably 1.5 to 30 ⁇ m, layer thicknesses of 1.5 to 5 ⁇ m being particularly preferred. However, layer thicknesses of less than 1.5 ⁇ m and greater than 30 ⁇ m are also possible.
- valve metal of the dimensionally stable anode consists of titanium, tantalum, niobium, zirconium or their alloys, preference being given to titanium for reasons of cost.
- Niobium and tantalum are used in particular when voltages above 10 V are required.
- the electrode coating can consist of all electrocatalytically active substances that are customary in practice. Electrode coatings which consist of one or more oxides of titanium, tantalum, niobium, zirconium and / or one or more oxides of platinum metals are preferred. Such electrode coatings can be produced by means of pyrolytic processes, for example by thermal decomposition of compounds of the metals mentioned. Electrode coatings consisting of a platinum oxide and / or iridium oxide are particularly preferred.
- the dimensionally stable anodes according to the invention are notable for excellent stability when used in electrolytic processes in which oxygen is anodically formed as the main or by-product. Even at temperatures above 6 ° C, the service life of the anodes required for the economical operation of electrolytic processes can be achieved with constant oxygen overvoltages over a long period of time. Of course, the dimensionally stable anodes according to the invention can also advantageously be used at temperatures below 60 ° C.
- Another object of the invention is a process for the production of alkali dichromates and / or chromic acid by electrolysis of alkali monochromate and / or alkali dichromate solutions, which is characterized in that a dimensionally stable anode according to the invention is used.
- alkali dichromates the electrolytic production of dichromates and chromic acid takes place in electrolytic cells, the electrode spaces of which are separated by cation exchange membranes.
- alkali monochromate solutions or suspensions are introduced into the anode compartment of the cell and converted into an alkali dichromate solution by selectively transferring alkali ions through the membrane into the cathode compartment.
- chromic acid alkali dichromate or alkali monochromate solutions are introduced into the anode compartment and into those containing chromic acid Solutions transferred.
- sodium monochromate and / or sodium dichromate are used for these processes.
- an alkaline solution containing alkali ions is obtained in the cathode compartment, which can consist, for example, of an aqueous sodium hydroxide solution or, as described in CA-A 739 447, of an aqueous solution containing sodium carbonate.
- anodes made of lead and lead alloys and dimensionally stable anodes with electrocatalytically active layers made of noble metals or noble metal oxides are suitable as anode materials.
- anodic current densities of 2 to 5 kA / m2 and electrolysis temperatures above 60 ° C these anodes have an insufficient service life for the reasons mentioned above.
- the electrolytic cells used in the examples consisted of anode compartments made of pure titanium and cathode compartments made of stainless steel. Cation exchange membranes from DuPont with the designation Nafion® 324 were used as membranes. The cathodes were made of stainless steel and the anodes were made of titanium with the electrocatalytically active coatings described in the individual examples. The distance between the electrodes and the membrane was 1.5 mm in all cases.
- Sodium dichromate solutions containing 800 g / l Na2Cr2O7 ⁇ 2 H2O were introduced into the anode compartments. The rate of introduction was chosen so that a molar ratio of sodium ions to chromium (VI) of 0.6 was established in the anolytes leaving the cells.
- the electrolysis temperature was 80 ° C in all cases and the current density was 3 kA / m2 projected front surface of the anodes and cathodes.
- a titanium anode with an iridium layer was used, which was produced according to the so-called baking process as follows: a titanium electrode with a front projected surface measuring 11.4 cm x 6.7 cm, after removal of the oxide layer and etching with oxalic acid, a solution with the following composition was wetted with a hair brush: 0.8 g IrCl4 ⁇ xH2O (51% Ir) 6.2 ml of 1-butanol 0.4 ml 37% hydrochloric acid 3 ml titanium tetrabutyl ester The wetted anode was dried at 250 ° C. for 15 minutes and then annealed in an oven at 450 ° C. for 20 to 30 minutes. This measure was repeated six times, the heat treatment being carried out only after every second step after wetting and drying.
- This anode was used to convert a sodium dichromate solution into a solution containing chromic acid. During the test period of 250 days, a constant cell voltage of 3.8 V was established, which shows that no passivation of the anode occurred and that the electrocatalytically active layer was thus fully functional during the entire test period.
- a dimensionally stable titanium anode was used, the electrocatalytically active layer of which consisted exclusively of a platinum layer electrodeposited from the melt.
- the platinum layer thickness was 2.5 ⁇ m.
- Example 3 shows, however, that the anode of Example 3 has a significantly higher oxygen voltage.
Description
Die Erfindung betrifft formstabile Anoden, bestehend aus
- a) einem elektrisch leitfähigen Ventilmetall
- b) einer leitfähigen Zwischenschicht und
- c) einem Elektrodenüberzug aus einer elektrokatalytisch aktiven Substanz.
- a) an electrically conductive valve metal
- b) a conductive intermediate layer and
- c) an electrode coating made of an electrocatalytically active substance.
Ferner betrifft die Erfindung ein Verfahren zur Herstellung von Alkalidichromaten und Chromsäure durch Elektrolyse von Alkalimonochromat und/oder Alkalidichromatlösungen unter Verwendung der erfindungsgemäßen Elektroden.The invention further relates to a process for the preparation of alkali dichromates and chromic acid by electrolysis of alkali monochromate and / or alkali dichromate solutions using the electrodes according to the invention.
Bei vielen elektrochemischen Prozessen kommen Anoden zum Einsatz, die aus einem elektrisch leitfähigen Ventilmetall wie beispielsweise Titan, Tantal und Niob bestehen und mit einer elektrokatalytisch aktiven Substanz beschichtet sind. Diese Anoden werden allgemein als formstabile ("dimensionsstabil") Anoden bzw. als DSA® bezeichnet. Als elektrokatalytisch aytive Substanzen werden vornehmlich Metalle der Platingruppe und deren Oxide sowie Bleidioxid und Mangandioxid eingesetzt. Solche Anoden sind beispielsweise in der BE-A 710 551, DE-B 2 300 422 und der US-A 3 711 385 beschrieben.Many electrochemical processes use anodes that consist of an electrically conductive valve metal such as titanium, tantalum and niobium and are coated with an electrocatalytically active substance. These anodes are commonly called dimensionally stable ("dimensionally stable") anodes or referred to as DSA®. Metals from the platinum group and their oxides, as well as lead dioxide and manganese dioxide, are primarily used as electrocatalytically active substances. Such anodes are described for example in BE-A 710 551, DE-B 2 300 422 and US-A 3 711 385.
Zur Einsparung des teuren Ventilmetalls wurde gemäß EP-A 5674 vorgeschlagen, Kupfer- oder Eisenanoden mit einer schmelzgalvanisch aufgebrachten Ventilmetallschicht zu versehen und anschließend zu aktivieren, wobei die Aktivierungsschicht ebenfalls schmelzgalvanisch oder naßgalvanisch aufgebracht wird.In order to save the expensive valve metal, it has been proposed according to EP-A 5674 to provide copper or iron anodes with a galvanically applied valve metal layer and then to activate them, the activation layer likewise being applied by galvanic or wet electroplating.
Bei Einsatz dieser Anoden in der Chloralkalielektrolyse werden lange Laufzeiten bei einer niedrigen, über lange Zeit konstant bleibenden Chlorüberspannung erreicht.When using these anodes in chlor-alkali electrolysis, long run times are achieved with a low chlorine overvoltage that remains constant over a long period of time.
In elektrolytischen Verfahren, bei denen an der Anode Sauerstoff als Haupt- oder Nebenprodukt gebildet wird, steigt die Spannung infolge einer Passivierung der Anode mit der Zeit an und die Laufzeiten sind wesentlich kürzer. Ursache dieser Passivierung, die letztendlich zum Ausfall der Anode führt, ist eine Korrosion des Ventilmetalls durch Permeation von Sauerstoff durch die elektrokatalytisch aktive Schicht, wobei die Passivierung insbesondere bei Temperaturen oberhalb 60°C sehr rasch erfolgt.In electrolytic processes in which oxygen is formed as the main or by-product at the anode, the voltage increases over time as a result of passivation of the anode and the running times are considerably shorter. The cause of this passivation, which ultimately leads to the failure of the anode, is corrosion of the valve metal by permeation of oxygen through the electrocatalytically active layer, the passivation taking place very quickly, especially at temperatures above 60 ° C.
Zur Verbesserung der Haltbarkeit von sauerstoffentwickelnden formstabilen Anoden wurde vorgeschlagen, zwischen Ventilmetall und elektrokatalytisch aktiver Schicht eine leitfähige Zwischenschicht aufzubringen, die eine Permeation von Sauerstoff zum Ventilmetall unterdrücken soll. Diese Zwischenschicht kann aus einem oder mehreren Metalloxiden, wie beispielsweise Oxiden der Platinmetalle, Oxiden von Titan, Vanadium, Niob, Tantal und anderen Nichtedelmetallen bestehen. Solche Anoden sind beispielsweise in der DE-A 3 219 003, DE-C 3 330 388, DE-A 3 715 444 und DE-A 3 717 972 beschrieben. US-A 3 775 284 offenbart Anoden, die Zwischenschichten aus Edelmetallen wie Platin und Iridium aufweisen, die durch naßgalvanische Verfahren aufgebracht werden.In order to improve the durability of oxygen-generating, dimensionally stable anodes, it has been proposed to apply a conductive intermediate layer between the valve metal and the electrocatalytically active layer, which is to suppress permeation of oxygen to the valve metal. This intermediate layer can consist of one or more metal oxides, such as oxides of platinum metals, oxides of titanium, vanadium, niobium, Tantalum and other base metals exist. Such anodes are described for example in DE-A 3 219 003, DE-C 3 330 388, DE-A 3 715 444 and DE-A 3 717 972. US-A 3 775 284 discloses anodes which have intermediate layers of precious metals such as platinum and iridium, which are applied by wet electroplating processes.
Die beschriebenen Zwischenschichten können zwar die Passivierung verlangsamen und damit die Lebensdauer der Anoden verlängern, jedoch weisen diese Anoden insbesondere bei Temperaturen über 60°C immer noch nicht ausreichende Haltbarkeiten auf.The described intermediate layers can slow down the passivation and thus extend the life of the anodes, but these anodes still do not have sufficient durability, especially at temperatures above 60 ° C.
Typische Verfahren, bei denen anodisch Sauerstoff gebildet wird, sind die elektrolytische Herstellung von Alkalidichromaten, Chromsäure, Perchloraten, Chloraten, Persulfaten und Wasserstoffperoxid, die elektrolytische Abscheidung von Metallen wie Chrom, Kupfer, Zink oder Edelmetalle und verschiedene Galvanisierverfahren bzw. Elektroplattieren.Typical processes in which oxygen is formed anodically are the electrolytic production of alkali dichromates, chromic acid, perchlorates, chlorates, persulphates and hydrogen peroxide, the electrolytic deposition of metals such as chromium, copper, zinc or noble metals and various electroplating processes or electroplating.
Aufgrund der für ein wirtschaftliches Betreiben der Elektrolyten in vielen Fällen unzureichende Haltbarkeit der formstabilen Anoden, kommen auch heute noch massive Edelmetall-Anoden zum Einsatz, deren Verwendung sehr kostenintensiv ist bzw. es kommen Schwermetall-Anoden wie Bleianoden zum Einsatz, die zu Verunreinigungen der Elektrolyten und den damit verbundenen Folgeproblemen führen.Due to the inadequate durability of the dimensionally stable anodes for economical operation of the electrolytes in many cases, massive precious metal anodes are still used today, the use of which is very cost-intensive or heavy metal anodes such as lead anodes are used which contaminate the electrolytes and lead to the related problems.
Die Aufgabe der Erfindung bestand darin, formstabile Anoden zur Verfügung zu stellen, die die beschriebenen Nachteile nicht aufweisen.The object of the invention was to provide dimensionally stable anodes which do not have the disadvantages described.
Es wurde nun gefunden, daß Anoden mit einer Zwischenschicht aus Edelmetallen, die durch elektrolytische Abscheidung aus edelmetallsalzhaltigen Schmelzen erzeugt wurden, hervorragend zur anodischen Sauerstoffentwicklung geeignet sind und lange Standzeiten aufweisen.It has now been found that anodes with an intermediate layer of noble metals, which were produced by electrolytic deposition from melts containing noble metals, are outstandingly suitable for anodic oxygen evolution and have a long service life.
Gegenstand der Erfindung ist die Verwendung formstabiler Anoden, bestehend aus
- a) einem elektrisch leitfähigen Ventilmetall
- b) einer durch galvanische Abscheidung aus edelmetallsalzhaltigen Schmelzen auf das Ventilmetall aufgebrachten Zwischenschicht aus Platin und/oder Iridium, und/oder einer Platin-Iridium-Legierung, und
- c) einer pyrolytisch erzeugten Überzugsschicht aus einer elektrokatalytisch aktiven Substanz
- a) an electrically conductive valve metal
- b) an intermediate layer of platinum and / or iridium, and / or a platinum-iridium alloy, applied to the valve metal by electroplating from precious metal salt-containing melts, and
- c) a pyrolytically produced coating layer made of an electrocatalytically active substance
Die Erzeugung solcher Edelmetallschichten auf Ventilmetallen durch galvanische Abscheidung aus edelmetallsalzhaltigen Schmelzen ist beispielsweise in "G. Dick, Galvanotechnik 79 (1988), Nr. 12, S. 4066-4071" beschrieben.The generation of such noble metal layers on valve metals by galvanic deposition from melts containing noble metal salts is described, for example, in "G. Dick, Galvanotechnik 79 (1988), No. 12, pp. 4066-4071".
Die Schichtdicke der erfindungsgemäßen Zwischenschicht beträgt vorzugsweise 1,5 bis 30 µm, wobei Schichtdicken von 1,5 bis 5 µm besonders bevorzugt sind. Es sind aber auch Schichtdicken von kleiner 1,5 µm und größer 30 µm möglich.The layer thickness of the intermediate layer according to the invention is preferably 1.5 to 30 μm, layer thicknesses of 1.5 to 5 μm being particularly preferred. However, layer thicknesses of less than 1.5 µm and greater than 30 µm are also possible.
Es ist vorteilhaft, wenn das Ventilmetall der formstabilen Anode aus Titan, Tantal, Niob, Zirkonium oder deren Legierungen besteht, wobei aus Kostengründen dem Titan der Vorzug gegeben wird. Niob und Tantal kommen insbesondere dann zum Einsatz, wenn Spannungen über 10 V erforderlich sind.It is advantageous if the valve metal of the dimensionally stable anode consists of titanium, tantalum, niobium, zirconium or their alloys, preference being given to titanium for reasons of cost. Niobium and tantalum are used in particular when voltages above 10 V are required.
Der Elektrodenüberzug kann prinzipiell aus allen in der Praxis üblichen elektrokatalytisch aktiven Substanzen bestehen. Bevorzugt sind Elektrodenüberzüge, die aus einem oder mehreren Oxiden von Titan, Tantal, Niob, Zirkonium und/oder einer oder mehreren Oxiden der Platinmetalle bestehen. Solche Elektrodenüberzüge können mittels pyrolytischen Verfahren, beispielsweise durch thermische Zersetzung von Verbindungen der genannten Metalle erzeugt werden. Besonders bevorzugt sind Elektrodenüberzüge, die aus einem Platinoxid und/oder Iridiumoxid bestehen.In principle, the electrode coating can consist of all electrocatalytically active substances that are customary in practice. Electrode coatings which consist of one or more oxides of titanium, tantalum, niobium, zirconium and / or one or more oxides of platinum metals are preferred. Such electrode coatings can be produced by means of pyrolytic processes, for example by thermal decomposition of compounds of the metals mentioned. Electrode coatings consisting of a platinum oxide and / or iridium oxide are particularly preferred.
Die erfindungsgemäßen formstabilen Anoden zeichnen sich durch eine hervorragende Beständigkeit beim Einsatz in elektrolytischen Verfahren aus, bei denen anodisch Sauerstoff als Haupt- oder Nebenprodukt gebildet wird. Sogar bei Temperaturen über 6°C werden die für ein wirtschaftliches Betreiben von elektrolytischen Verfahren erforderlichen Standzeiten der Anoden bei langer Zeit konstant bleibenden Sauerstoffüberspannungen erreicht. Selbstverständlich können die erfindungsgemäßen formstabilen Anoden mit Vorteil ebenso bei Temperaturen unterhalb 60°C eingesetzt werden.The dimensionally stable anodes according to the invention are notable for excellent stability when used in electrolytic processes in which oxygen is anodically formed as the main or by-product. Even at temperatures above 6 ° C, the service life of the anodes required for the economical operation of electrolytic processes can be achieved with constant oxygen overvoltages over a long period of time. Of course, the dimensionally stable anodes according to the invention can also advantageously be used at temperatures below 60 ° C.
Ein weiterer Gegenstand der Erfindung ist ein Verfahren zur Herstellung von Alkalidichromaten und/oder Chromsäure durch Elektrolyse von Alkalimonochromat- und/oder Alkalidichromatlösungen, welches dadurch gekennzeichnet ist, daß eine erfindungsgemäße formstabile Anoden eingesetzt wird.Another object of the invention is a process for the production of alkali dichromates and / or chromic acid by electrolysis of alkali monochromate and / or alkali dichromate solutions, which is characterized in that a dimensionally stable anode according to the invention is used.
Gemäß US-A 3 305 463 und CA-A 739 447 erfolgt die elektrolytische Herstellung von Dichromaten und Chromsäure in Elektrolysezellen, deren Elektrodenräume durch Kationenaustauschermembranen getrennt sind. Bei der Erzeugung von Alkalidichromaten werden Alkalimonochromatlösungen oder -suspensionen in den Anodenraum der Zelle eingeleitet und in eine Alkalidichromatlösung umgewandelt, indem Alkaliionen selektiv durch die Membran in den Kathodenraum überführt werden. Zur Herstellung von Chromsäure werden Alkalidichromat- oder Alkalimonochromatlösungen in den Anodenraum eingeleitet und in Chromsäure-haltige Lösungen überführt. In der Regel kommen für diese Prozesse Natriummonochromat und/oder Natriumdichromat zum Einsatz. Im Kathodenraum wird bei beiden Prozessen eine alkalische Alkalionen-haltige Lösung erhalten, die beispielsweise aus einer wäßrigen Natriumhydroxidlösunge oder, wie in der CA-A 739 447 beschrieben, aus einer wäßrigen Natriumcarbonat-haltigen Lösung bestehen kann.According to US Pat. No. 3,305,463 and CA-A 739 447, the electrolytic production of dichromates and chromic acid takes place in electrolytic cells, the electrode spaces of which are separated by cation exchange membranes. In the production of alkali dichromates, alkali monochromate solutions or suspensions are introduced into the anode compartment of the cell and converted into an alkali dichromate solution by selectively transferring alkali ions through the membrane into the cathode compartment. To produce chromic acid, alkali dichromate or alkali monochromate solutions are introduced into the anode compartment and into those containing chromic acid Solutions transferred. As a rule, sodium monochromate and / or sodium dichromate are used for these processes. In both processes, an alkaline solution containing alkali ions is obtained in the cathode compartment, which can consist, for example, of an aqueous sodium hydroxide solution or, as described in CA-A 739 447, of an aqueous solution containing sodium carbonate.
Als Anodenmaterialien sind nach der DE-A 3 020 260 Anoden aus Blei und Bleilegierungen und formstabile Anoden mit elektrokatalytisch aktiven Schichten aus Edelmetallen oder Edelmetalloxiden geeignet. Bei anodischen Stromdichten von 2 bis 5 kA/m² und Elektrolysetemperaturen oberhalb 60°C weisen diese Anoden aus den oben genannten Gründen jedoch nur unzureichende Standzeiten auf.According to DE-A 3 020 260, anodes made of lead and lead alloys and dimensionally stable anodes with electrocatalytically active layers made of noble metals or noble metal oxides are suitable as anode materials. However, with anodic current densities of 2 to 5 kA / m² and electrolysis temperatures above 60 ° C, these anodes have an insufficient service life for the reasons mentioned above.
Bei Einsatz der erfindungsgemäßen Anoden werden dagegen lange Standzeiten bei gleichbleibender Zellspannung erreicht.By contrast, when using the anodes according to the invention, long service lives are achieved with constant cell voltage.
Vorzugsweise werden solche formstabile Anoden eingesetzt, die aus
- a) Titan,
- b) einer galvanisch aus der Schmelze aufgebrachten Zwischenschicht aus Platin und/oder Iridium und/oder einer Platin-Iridium-Legierung und
- c) einem Elektrodenüberzug aus einem Platin- und/oder Iridiumoxid
- a) titanium,
- b) an intermediate layer of platinum and / or iridium and / or a platinum-iridium alloy applied galvanically from the melt and
- c) an electrode coating made of a platinum and / or iridium oxide
Die Erfindung wird anhand der folgenden Beispiele näher erläutert:The invention is illustrated by the following examples:
Die in den Beispielen verwendeten Elektrolysezellen bestanden aus Anodenräumen aus Rein-Titan und Kathodenräumen aus Edelstahl. Als Membranen wurden Kationenaustauschermembranen der Firma DuPont mit der Bezeichnung Nafion® 324 verwendet. Die Kathoden bestanden aus Edelstahl und die Anoden aus Titan mit den in den einzelnen Beispielen beschriebenen elktrokatalytisch aktiven Beschichtungen. Der Abstand der Elektroden zur Membran betrug in allen Fällen 1,5 mm. In die Anodenräume wurden Natriumdichromatlösungen mit 800 g/l Na₂Cr₂O₇ · 2 H₂O eingeleitet. Die Geschwindigkeit des Einleitens wurde so gewählt, daß sich in den die Zellen verlassenden Anolyten ein molares Verhältnis von Natriumionen zu Chrom(VI) von 0,6 einstellte. Den Kathodenräumen wurde Wasser mit einer solchen Geschwindigkeit zugeführt, so daß 20 %ige Natronlauge die Zellen verließ. Die Elektrolysetemperatur betrug in allen Fällen 80°C und die Stromdichte betrug 3 kA/m² projizierte vordere Fläche der Anoden und Kathoden.The electrolytic cells used in the examples consisted of anode compartments made of pure titanium and cathode compartments made of stainless steel. Cation exchange membranes from DuPont with the designation Nafion® 324 were used as membranes. The cathodes were made of stainless steel and the anodes were made of titanium with the electrocatalytically active coatings described in the individual examples. The distance between the electrodes and the membrane was 1.5 mm in all cases. Sodium dichromate solutions containing 800 g / l Na₂Cr₂O₇ · 2 H₂O were introduced into the anode compartments. The rate of introduction was chosen so that a molar ratio of sodium ions to chromium (VI) of 0.6 was established in the anolytes leaving the cells. Water was supplied to the cathode compartments at such a rate that 20% sodium hydroxide solution left the cells. The electrolysis temperature was 80 ° C in all cases and the current density was 3 kA / m² projected front surface of the anodes and cathodes.
In diesem Beispiel wurde eine Titananode mit einer Iridium-Schicht eingesetzt, die nach dem sogenannten Einbrennverfahren wie folgt hergestellt wurde: Eine Titanelektrode mit einer vorderen projizierten Fläche von 11,4 cm x 6,7 cm wurde nach Entfernung der Oxidschicht und Ätzen mit Oxalsäure mit einer Lösung folgender Zusammensetzung mit einem Haarpinsel benetzt:
0,8 g IrCl₄ · xH₂O (51 % Ir)
6,2 ml 1-Butanol
0,4 ml 37 %ige Salzsäure
3 ml Titansäuretetrabutylester
Die benetzte Anode wurde 15 Minuten bei 250°C getrocknet und anschließend in einem Ofen bei 450°C 20 bis 30 Minuten getempert. Diese Maßnahme wurde sechsmal wiederholt, wobei die Temperung nur nach jedem zweiten Schritt nach erfolgter Benetzung und Trocknung durchgeführt wurde.In this example, a titanium anode with an iridium layer was used, which was produced according to the so-called baking process as follows: a titanium electrode with a front projected surface measuring 11.4 cm x 6.7 cm, after removal of the oxide layer and etching with oxalic acid, a solution with the following composition was wetted with a hair brush:
0.8 g IrCl₄ · xH₂O (51% Ir)
6.2 ml of 1-butanol
0.4 ml 37% hydrochloric acid
3 ml titanium tetrabutyl ester
The wetted anode was dried at 250 ° C. for 15 minutes and then annealed in an oven at 450 ° C. for 20 to 30 minutes. This measure was repeated six times, the heat treatment being carried out only after every second step after wetting and drying.
Auf der Titanelektrode wurde dabei ein Elektrodenüberzug erzeugt, der ca. 200 mg Iridium enthielt. Mit Hilfe dieser Anode wurde eine Natriumdichromatlösung in eine chromsäurehaltige Lösung umgewandelt. Während des Versuchs stieg die Zellspannung von anfänglich 4,4 V innerhalb von 32 Tagen allmählich auf 8,1 V an. Ursache dieses Spannungsanstiges war eine nahezu vollständige Zerstörung der elektrokatalytisch aktiven Platinschicht der Titananode.An electrode coating containing approximately 200 mg of iridium was produced on the titanium electrode. With the help of this anode, a sodium dichromate solution was converted into a solution containing chromic acid. During the experiment, the cell voltage gradually increased from initially 4.4 V to 8.1 V within 32 days. The cause of this voltage increase was an almost complete destruction of the electrocatalytically active platinum layer of the titanium anode.
In diesem Beispiel wurde ein erfindungsgemäße formstabile Anode eingesetzt, die wie folgt hergestellt wurde.In this example, a dimensionally stable anode according to the invention was used, which was produced as follows.
Eine durch galvanische Abscheidung aus einer platinhaltigen Schmelze mit Platin beschichteten Titanelektrode mit einer vorderen projizierten Fläche von 11,4 cm x 6,7 cm und einer Platinschichtdicke von 2,5 µm wurde mit einer Lösung folgender Zusammensetzung mit einem Haarpinsel benetzt:
0,8 g IrCl₄ · xH₂O (51 % Ir)
6,2 ml 1-Butanol
0,4 ml 37 %ige Salzsäure
Die benetzte Anode wurde 15 Minuten bei 250°C getrocknet und anschließend in einem Ofen bei 450°C 20 bis 30 Minuten getempert. Diese Maßnahme wurde sechsmal wiederholt, wobei die Temperung nur nach jedem zweiten Schritt nach erfolgter Benetzung und Trocknung durchgeführt wurde. Auf der Platinzwischenschicht der Titanelektrode wurde dabei ein Elektrodenüberzug erzeugt, der ca. 200 mg Iridium enthielt.A titanium electrode with a front projected area of 11.4 cm × 6.7 cm and a platinum layer thickness of 2.5 μm, which was coated with platinum by a galvanic deposition from a platinum-containing melt, was wetted with a solution of the following composition using a hair brush:
0.8 g IrCl₄ · xH₂O (51% Ir)
6.2 ml of 1-butanol
0.4 ml 37% hydrochloric acid
The wetted anode was dried at 250 ° C. for 15 minutes and then annealed in an oven at 450 ° C. for 20 to 30 minutes. This measure was repeated six times, the heat treatment being carried out only after every second step after wetting and drying. An electrode coating which contained approximately 200 mg of iridium was produced on the platinum intermediate layer of the titanium electrode.
Mit dieser Anode wurde eine Natriumdichromatlösung in eine chromsäurehaltige Lösung umgewandelt. Während der Versuchsdauer von 250 Tagen stellte sich eine konstant bleibende Zellspannung von 3,8 V ein, was zeigt, daß keine Passivierung der Anode eingetreten ist und somit die elektrokatalytisch aktive Schicht während der gesamten Versuchszeit voll funktionsfähig war.This anode was used to convert a sodium dichromate solution into a solution containing chromic acid. During the test period of 250 days, a constant cell voltage of 3.8 V was established, which shows that no passivation of the anode occurred and that the electrocatalytically active layer was thus fully functional during the entire test period.
In diesem Beispiel wurde eine formstabile Titananode eingesetzt, deren elektrokatalytisch aktive Schicht ausschließlich aus einer galvanisch aus der Schmelze abgeschiedene Platinschicht bestand. Die Platinschichtdicke betrug 2,5 µm.In this example, a dimensionally stable titanium anode was used, the electrocatalytically active layer of which consisted exclusively of a platinum layer electrodeposited from the melt. The platinum layer thickness was 2.5 µm.
Mit dieser Anode wurde wie im Beispiel 1 und 2 eine Natriumdichromatlösung unter identischen Bedingungen in eine chromsäurehaltige Lösung umgewandelt.With this anode, as in Examples 1 and 2, a sodium dichromate solution was converted into a solution containing chromic acid under identical conditions.
Während der Versuchsdauer von 361 Tagen stellte sich eine konstant bleibende Zellspannung von 4,8 V ein. Es ist somit keine Passivierung der Anode eingetreten. Der Vergleich zu Beispiel 2 zeigt jedoch, daß die Anode des Beispiels 3 eine deutlich höhere Sauerstoffspannung hat.During the test period of 361 days, the cell voltage remained constant at 4.8 V. No passivation of the anode has thus occurred. The comparison to Example 2 shows, however, that the anode of Example 3 has a significantly higher oxygen voltage.
Claims (5)
- The use of dimensionally stable anodes consisting ofa) an electrically conductive valve metal,b) an interlayer of platinum and/or iridium and/or a platinum/iridium alloy applied to the valve metal by electrodeposition from melts containing noble metal salts andc) a pyrolytic coating of an electrolytically active substancein electrolytic processes where oxygen is formed as the main or secondary product at the anode.
- The use claimed in claim 1, characterized in that the electrolytic process is the electrolysis of alkali metal chromates or alkali metal dichromates for the production of chromic acid.
- A process as claimed in claim 1 or 2, characterized in that the coating c) consistins of one or more oxides of the platinum metals.
- The use claimed in claim 3, characterized in that the coating consists of platinum oxide and/or iridium oxide.
- The use claimed in any of claims 1 to 4, characterized in that the interlayer b) has a thickness of 1.5 to 30 µm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3905082 | 1989-02-18 | ||
| DE3905082A DE3905082A1 (en) | 1989-02-18 | 1989-02-18 | STABLE ANODES AND THEIR USE IN THE PRODUCTION OF ALKALIDICHROMATES AND CHROME ACID |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| EP0384194A2 EP0384194A2 (en) | 1990-08-29 |
| EP0384194A3 EP0384194A3 (en) | 1991-06-05 |
| EP0384194B1 true EP0384194B1 (en) | 1994-03-09 |
Family
ID=6374469
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP90102143A Revoked EP0384194B1 (en) | 1989-02-18 | 1990-02-03 | Dimensionally stable anodes and their use in the production of alkalidichromates and chromic acid |
Country Status (14)
| Country | Link |
|---|---|
| US (1) | US5128000A (en) |
| EP (1) | EP0384194B1 (en) |
| JP (1) | JP2641584B2 (en) |
| KR (1) | KR960016418B1 (en) |
| AR (1) | AR246311A1 (en) |
| BR (1) | BR9000721A (en) |
| CA (1) | CA2010221A1 (en) |
| DD (1) | DD298437A5 (en) |
| DE (2) | DE3905082A1 (en) |
| ES (1) | ES2050287T3 (en) |
| MX (1) | MX173097B (en) |
| RU (1) | RU1838450C (en) |
| TR (1) | TR26579A (en) |
| ZA (1) | ZA901196B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7556722B2 (en) | 1996-11-22 | 2009-07-07 | Metzger Hubert F | Electroplating apparatus |
| US8298395B2 (en) | 1999-06-30 | 2012-10-30 | Chema Technology, Inc. | Electroplating apparatus |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1997028293A1 (en) * | 1996-02-01 | 1997-08-07 | Motorola Inc. | Composite multilayer electrodes for electrochemical cells |
| FR2748495B1 (en) * | 1996-05-13 | 1998-07-17 | Electricite De France | IMPROVED LONGEVITY ANODE AND MANUFACTURING METHOD THEREOF |
| US6217729B1 (en) | 1999-04-08 | 2001-04-17 | United States Filter Corporation | Anode formulation and methods of manufacture |
| DE10029837B4 (en) * | 2000-06-16 | 2005-02-17 | Degussa Galvanotechnik Gmbh | Process for the production of unilaterally platinated plates and expanded metal gratings of refractory metals |
| JP4615847B2 (en) * | 2003-11-25 | 2011-01-19 | 株式会社フルヤ金属 | Corrosion resistant material and method for producing the same |
| JP2008156684A (en) * | 2006-12-22 | 2008-07-10 | Tanaka Kikinzoku Kogyo Kk | Anode electrode for hydrochloric acid electrolysis |
| US7713401B2 (en) * | 2007-08-08 | 2010-05-11 | Battelle Energy Alliance, Llc | Methods for performing electrochemical nitration reactions |
| TWI432607B (en) * | 2008-07-03 | 2014-04-01 | Asahi Kasei Chemicals Corp | Hydrogen generation cathode and its manufacturing method |
| US20110052896A1 (en) * | 2009-08-27 | 2011-03-03 | Shrisudersan Jayaraman | Zinc Oxide and Cobalt Oxide Nanostructures and Methods of Making Thereof |
| US20110086238A1 (en) * | 2009-10-09 | 2011-04-14 | Shrisudersan Jayaraman | Niobium Nanostructures And Methods Of Making Thereof |
| CN104593818B (en) * | 2014-12-24 | 2017-04-26 | 中南大学 | Titanium-based composite anode as well as preparation method and application thereof |
| CN113355705B (en) * | 2021-06-02 | 2022-05-03 | 建滔（连州）铜箔有限公司 | Titanium anode plate for electrolytic copper foil and back treatment process |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3454478A (en) * | 1965-06-28 | 1969-07-08 | Ppg Industries Inc | Electrolytically reducing halide impurity content of alkali metal dichromate solutions |
| US3663414A (en) * | 1969-06-27 | 1972-05-16 | Ppg Industries Inc | Electrode coating |
| DE2113676C2 (en) * | 1971-03-20 | 1985-09-12 | Conradty GmbH & Co Metallelektroden KG, 8505 Röthenbach | Electrode for electrochemical processes |
| JPS5119429A (en) * | 1974-08-09 | 1976-02-16 | Oki Electric Ind Co Ltd | FUSETSUKYOKUSHIKI BETSUHOSHIKI |
| JPS5325838A (en) * | 1976-08-23 | 1978-03-10 | Matsushita Electric Ind Co Ltd | Storage battery electrode plate |
| FR2426095A1 (en) * | 1978-05-19 | 1979-12-14 | Anger Roger | ANODIC ELECTRODE STABLE IN DIMENSIONS AND MANUFACTURING PROCESS |
| US4157943A (en) * | 1978-07-14 | 1979-06-12 | The International Nickel Company, Inc. | Composite electrode for electrolytic processes |
| JPS565986A (en) * | 1979-05-29 | 1981-01-22 | Diamond Shamrock Corp | Cromic acid production by using three chambered electrolysis tank |
| JPS5940914A (en) * | 1982-08-31 | 1984-03-06 | Mazda Motor Corp | Vehicle attitude control device |
-
1989
- 1989-02-18 DE DE3905082A patent/DE3905082A1/en not_active Withdrawn
-
1990
- 1990-01-29 MX MX019298A patent/MX173097B/en unknown
- 1990-02-03 EP EP90102143A patent/EP0384194B1/en not_active Revoked
- 1990-02-03 DE DE90102143T patent/DE59004842D1/en not_active Revoked
- 1990-02-03 ES ES90102143T patent/ES2050287T3/en not_active Expired - Lifetime
- 1990-02-14 JP JP2031655A patent/JP2641584B2/en not_active Expired - Lifetime
- 1990-02-16 ZA ZA901196A patent/ZA901196B/en unknown
- 1990-02-16 DD DD90337917A patent/DD298437A5/en unknown
- 1990-02-16 RU SU904743064A patent/RU1838450C/en active
- 1990-02-16 BR BR909000721A patent/BR9000721A/en not_active Application Discontinuation
- 1990-02-16 CA CA002010221A patent/CA2010221A1/en not_active Abandoned
- 1990-02-16 KR KR1019900001875A patent/KR960016418B1/en not_active IP Right Cessation
- 1990-02-16 AR AR90316181A patent/AR246311A1/en active
- 1990-03-13 TR TR90/0185A patent/TR26579A/en unknown
-
1991
- 1991-04-01 US US07/680,602 patent/US5128000A/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7556722B2 (en) | 1996-11-22 | 2009-07-07 | Metzger Hubert F | Electroplating apparatus |
| US7914658B2 (en) | 1996-11-22 | 2011-03-29 | Chema Technology, Inc. | Electroplating apparatus |
| US8298395B2 (en) | 1999-06-30 | 2012-10-30 | Chema Technology, Inc. | Electroplating apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| DE59004842D1 (en) | 1994-04-14 |
| EP0384194A3 (en) | 1991-06-05 |
| KR900013109A (en) | 1990-09-03 |
| DE3905082A1 (en) | 1990-08-23 |
| MX173097B (en) | 1994-02-01 |
| EP0384194A2 (en) | 1990-08-29 |
| CA2010221A1 (en) | 1990-08-18 |
| US5128000A (en) | 1992-07-07 |
| TR26579A (en) | 1995-03-15 |
| RU1838450C (en) | 1993-08-30 |
| ES2050287T3 (en) | 1994-05-16 |
| AR246311A1 (en) | 1994-07-29 |
| JPH02247392A (en) | 1990-10-03 |
| KR960016418B1 (en) | 1996-12-11 |
| BR9000721A (en) | 1991-01-22 |
| ZA901196B (en) | 1990-11-28 |
| JP2641584B2 (en) | 1997-08-13 |
| DD298437A5 (en) | 1992-02-20 |
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