EP0683247A1 - Process for manufacturing stable graphite cathodes for the electrolysis of chlorhydric acid - Google Patents
Process for manufacturing stable graphite cathodes for the electrolysis of chlorhydric acid Download PDFInfo
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- EP0683247A1 EP0683247A1 EP95107029A EP95107029A EP0683247A1 EP 0683247 A1 EP0683247 A1 EP 0683247A1 EP 95107029 A EP95107029 A EP 95107029A EP 95107029 A EP95107029 A EP 95107029A EP 0683247 A1 EP0683247 A1 EP 0683247A1
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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
- C25B1/24—Halogens or compounds thereof
- C25B1/26—Chlorine; Compounds thereof
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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
- C25B11/042—Electrodes formed of a single material
- C25B11/043—Carbon, e.g. diamond or graphene
- C25B11/044—Impregnation of carbon
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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
- C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
- C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
Definitions
- the invention relates to a method for producing stable graphite cathodes and the use of these cathodes in hydrochloric acid electrolysis.
- the catholyte together with hydrogen gas and the anolyte together with chlorine gas at the head of the cell are drawn off into channels provided for this purpose. Then a gas / hydrochloric acid separation and the hydrochloric acid is saturated again with hydrogen chloride gas and returned to the cell.
- noble metals or dissolved noble metals are also discharged from the cell with the electrolyte-gas mixtures and that these are distributed over the entire system.
- a recovery of the noble metals is not described in the literature for the hydrochloric acid electrolysis. It is also not justifiable for economic reasons because the noble metals are evenly distributed in the entire apparatus system downstream of the cells.
- DD-3725 describes spray coatings and vapor deposition of metals on graphite in order to lower the voltage in the cell.
- the very limited durability is attributed to the fact that the adhesion of the metal crystals is too poor and that they break off too easily from the surface of the graphite.
- EP-A 205 631 describes a method for coating graphite bodies which are used as cathodes in electrolysis by soaking the surface of the graphite body with a solution of a platinum metal salt and a further metal salt in alcohol and then heating it to 250 to 600 ° C .
- Ethanol, propanol and butanol are mentioned as preferred alcohols.
- the temperature treatment is carried out in such a way that the graphite body as a whole is heated to the temperatures mentioned. During the heating phase, the alcohol is partially evaporated, so that it is no longer available in the reaction.
- the furnace in which the graphite body is subjected to the temperature treatment An exhaust system must be installed downstream to break down the oxidation products of the alcohol.
- the object was therefore to provide a method for producing electrodes, in particular for hydrochloric acid electrolysis, which makes it possible to produce stable, corrosion-resistant, abrasion-resistant electrodes with a low overvoltage, and which is simple and inexpensive.
- the invention relates to a process for the production of graphite cathodes for electrolytic processes, in particular for HCl electrolysis, a solution of iridium salts or rhodium salts or of mixtures of iridium salts or rhodium salts with salts of the other metals in the pores of the graphite body prior to its use as a cathode from the platinum group consisting of platinum, palladium, osmium and ruthenium in mono- or polyhydric alcohols with 2 to 4 carbon atoms or in mixtures of mono- or polyhydric alcohols with 2 to 4 carbon atoms, then optionally with mono- or polyhydric alcohols with 2 up to 4 carbon atoms or a mixture of mono- or polyhydric alcohols with 2 to 4 carbon atoms, then heated and then cooled, which is characterized in that the soaked graphite body with open gas flames on the surface soaked with the solution in one Depth up to about 1 mm to temperatures between 200 to 450
- a preferred process variant is that solutions of the abovementioned salts or of the abovementioned salt mixtures in 1,2-ethanediol or in glycerol are introduced into the pores of the graphite body and optionally rinsed with 1,2-ethanediol or glycerol.
- the graphite body After heating with the open gas flames and after cooling, the graphite body can be treated again with pure, mono- or polyhydric alcohols with 2 to 4 carbon atoms, then again subjected to the gas flame treatment and then cooled.
- the noble metals or alloys mentioned are preferably present in an amount of 5 to 20 g / projected area of 1 m2.
- the graphite cathodes produced according to the invention are preferably used in the electrolysis of hydrochloric acid in cells with a diaphragm or ion exchange membrane.
- the starting material used on the market are graphite cathodes, which consist of special electrode graphite (graphite for technical electrolytic processes), such as from the company COVA / CONRADTY, Nuremberg graphite of the quality AC or from the company SIGRI, Meitingen graphite of the qualities ES and EH.
- graphite grades usually have an intrinsic porosity (acc. Pore volume) of 12 to 18%, the specific resistance is 7.5 to 12.5 ⁇ ⁇ mm2 / m, and the apparent density (bulk density) is 1.70 up to 1.77 g / cm3.
- Electrode graphite is produced using well-known petrochemical, ceramic and finishing stages, whereby the species-specific porous surface structure is created.
- the graphite cathodes produced according to the invention have high corrosion resistance and an extraordinarily long service life, the voltage reduction remaining over the entire service life.
- the method according to the invention is very energy-efficient and easy to carry out. A downstream exhaust gas treatment system is not required.
- the in-situ coating as well as the galvanic precoating in neutral medium lead to an electrocrystallization of the noble metals on the outer graphite surface, whereby these crystal agglomerates are neither chemically nor physically connected to the graphite, but are only loosely attached and therefore break off easily.
- the noble metal is deposited at preferred locations on the graphite surface, so that there is no desired uniform distribution of the noble metal.
- the spray coating according to the prior art for example with the aid of a plasma torch, leads to a covering of the large pore and column-rich, large graphite surface, so that a low-surface cathode is formed, and the metal layer flakes off very easily.
- the method according to the invention made it possible to produce graphite cathodes in which the metals are firmly anchored (sealed) in the pores and columns of the graphite.
- the total heating time is also only 2 to 10 minutes, preferably 4 to 6 minutes, and only carbon dioxide and water vapor are produced as exhaust gas. If you consider the dimensions of technical electrolysers with graphite electrodes of e.g. 1.50x0.35x0.07 m, with a single electrolyzer already being made up of more than 100 electrodes of this type, it can be seen what savings potential there is from the method according to the invention.
- FIG 1 shows an arrangement with which the inventive method can be carried out.
- the impregnated electrode plate made of graphite 1 is provided with longitudinal slots 2 and lies on a table 3.
- Gas burners 4 are arranged above the plate 1 and are supplied with combustible gas (e.g. propane / butane mixture) via lines 5.
- Control and safety devices are accommodated in the housing 6. The gas pressure and the distance of the gas burner from the graphite plate are adjusted so that the gas flames 7 completely cover the graphite surface.
- FIG. 2 shows a section from FIG. 1.
- Burners which are usually used to apply bitumen welding strips in the roofing trade, are advantageously used.
- the graphite plate is placed under the gas burners before the gas burners are ignited.
- hydrochloric acid was electrolyzed.
- 1 shows the cell housing made of polypropylene.
- the cathode 2 and the anode 3 are sealed into the housing with power supply bolts 4.
- Both cell halves are separated by a diaphragm (or a cation exchange membrane) 5.
- the electrolyte can be pumped 7 in both cell halves, varying the throughput.
- Fresh 30% hydrochloric acid 8 is fed to these circuits via pumps 9.
- the gases 10, 11 and the depleted electrolytes 12 leave the cell through the gas / liquid separators 6.
- a current density of 3 kA / m2 was set with a power supply device.
- the resulting cell voltage was tapped with 2 graphite tips, each isolated in the lead in the front edges of the electrodes.
- the cell voltage was 2.10 volts.
- an aqueous metal salt solution containing 0.3 mg Pt and 0.6 mg Pd was metered in, the voltage immediately dropped by approximately 0.4 volts. The voltage remained at this level for about 100 days and then slowly rose again to the original value before the doping.
- Increasing the electrolyte throughputs to 35 l / h led to a faster rise in the voltage after the solution had been metered in to the value before the doping within 1 to 2 days. This resulted in an average voltage of approximately 1.90 volts (start: 2.10 volts; drop to 1.70 V; rise to 2.10 volts).
- the plate was again spread evenly with 1 ml of pure 1,2-ethanediol and the heating described repeated.
- the graphite plate was installed in the electrolysis cell. With electrolyte throughputs of 0.1 to 35 l / h, a cell voltage of 1.55 volts remained constant over several months. During the electrolysis the corrosion rate was 1 ⁇ g Ir / l electrolyte, in the de-energized state 400 ⁇ g Ir / l electrolyte.
- the graphite plate was installed as a cathode in an HCl electrolysis cell with a diaphragm (FIG. 3). With electrolyte throughputs of 0.1 to 35 l / h, a cell voltage of 1.45 volts remained constant over several months. During the electrolysis, the corrosion rate was 1 ⁇ g Pt / l and 2 ⁇ g Ir / l electrolyte, in the de-energized state it was 18,000 ⁇ g Pt / l and 20,000 ⁇ g Ir / l.
- RhCl3 ⁇ H2O content about 0.12 g Rh
- Rh metal was sealed in the pores of the graphite in accordance with Example 2. This plate, used as a cathode, led to a constant cell voltage of 1.67 volts over 10 days.
- Example 5 0.236 g IrCl4 ⁇ H2O were dissolved in 2 ml glycerol and the solution applied evenly to the graphite plate. The heating was carried out in accordance with Example 2. A cell voltage of 1.60 volts was established. The corrosion rate corresponded to that of Example 2.
Abstract
Description
Die Erfindung betrifft ein Verfahren zur Herstellung stabiler Graphitkathoden sowie die Verwendung dieser Kathoden in der Salzsäureelektrolyse.The invention relates to a method for producing stable graphite cathodes and the use of these cathodes in hydrochloric acid electrolysis.
Der Prozeß der technischen Salzsäure-Elektrolyse ist in Ullmanns Encyclopedia of Industrial Chemistry Vol A 6, Seite 459 (1986) beschrieben. Zwischen Elektroden aus Graphit befindet sich in der Elektrolysezelle ein Gewebediaphragma oder eine Kationenaustauschermembran (Minz, Chemie, Anlagen, Verfahren (1992) S. 77). Durch Zugabe bestimmter Salze in den Katholyten, z.B. Salze von Pt, Pd, Cu, Ni, Sb, Ag, Mo, Co kann die Zellenspannung herabgesetzt werden (DE-AS 1 216 852, FR-A 1 208 508, DD 3 725).The process of technical hydrochloric acid electrolysis is described in Ullmann's Encyclopedia of Industrial Chemistry Vol A 6, page 459 (1986). A tissue diaphragm or a cation exchange membrane is located between electrodes made of graphite in the electrolysis cell (Mint, Chemistry, Systems, Process (1992) p. 77). By adding certain salts in the catholyte, e.g. Salts of Pt, Pd, Cu, Ni, Sb, Ag, Mo, Co can reduce the cell voltage (DE-AS 1 216 852, FR-A 1 208 508, DD 3 725).
In der betrieblichen Praxis werden Edelmetallverbindungen der Platingruppe dem Elektrolyten zugesetzt und damit eine Spannungsabsenkung von 300 bis 500 mV erreicht (Winnacker-Küchler, Chemische Technologie I S. 280 (1969)).In operational practice, precious metal compounds from the platinum group are added to the electrolyte and a voltage drop of 300 to 500 mV is achieved (Winnacker-Küchler, Chemische Technologie I p. 280 (1969)).
Derart hervorgerufene Spannungsabsenkungen sind allerding nicht dauerhaft, so daß eine Dosierung von Edelmetallsalzen kontinuierlich oder diskontinuierlich aufrechterhalten werden muß (DE-AS 1 216 852).However, voltage reductions caused in this way are not permanent, so that a metering of precious metal salts must be maintained continuously or discontinuously (DE-AS 1 216 852).
Nach der üblichen Bauweise der Elektrolyseure für Salzsäure wird der Katholyt gemeinsam mit Wasserstoffgas und der Anolyt gemeinsam mit Chlorgas am Kopf der Zelle in dafür angebrachte Kanäle abgezogen. Danach wird eine Gas/Salzsäuretrennung vorgenommen und die Salzsäure wird wieder mit Chlorwasserstoffgas aufgesättigt und in die Zelle zurückgeführt.According to the usual design of the electrolysers for hydrochloric acid, the catholyte together with hydrogen gas and the anolyte together with chlorine gas at the head of the cell are drawn off into channels provided for this purpose. Then a gas / hydrochloric acid separation and the hydrochloric acid is saturated again with hydrogen chloride gas and returned to the cell.
Es wird angenommen, daß mit den Elektrolyt-Gasgemischen auch Edelmetalle oder gelöste Edelmetalle aus der Zelle ausgetragen werden und daß diese sich so auf das gesamte System verteilen. Eine Rückgewinnung der Edelmetalle ist in der Literatur für die Salzsäureelektrolyse nicht beschrieben.. Sie ist auch aus wirtschaftlichen Gründen nicht vertretbar, weil sich die Edelmetalle im gesamten, den Zellen nachgeschalteten Apparatesystem gleichmäßig verteilt ablagern.It is assumed that noble metals or dissolved noble metals are also discharged from the cell with the electrolyte-gas mixtures and that these are distributed over the entire system. A recovery of the noble metals is not described in the literature for the hydrochloric acid electrolysis. It is also not justifiable for economic reasons because the noble metals are evenly distributed in the entire apparatus system downstream of the cells.
In einer Publikation von Gallone und Messner, Electrochemical Technology 3 (1965) 321 bis 326, wird, um den Edelmetallverlust zu vermeiden, eine oberflächliche Behandlung der Graphitelektroden mit einer 80 % Pt / 20 % Ir-Legierung erwähnt, wobei diese Legierung in einer Menge von 12,4 g/m² aufgebracht ("deposited") wird. Diese Maßnahme wird von Gallone und Messner selbst als "small advantage" bezeichnet. Die Methode der Beschichtung selbst ist nicht beschrieben, auch ist nicht angegeben, ob die Beschichtung vor Einbau der Elektroden oder - wie in der Praxis üblich - durch in-situ-Zugabe von Edelmetallsalzen während der Elektrolyse erfolgte.In a publication by Gallone and Messner, Electrochemical Technology 3 (1965) 321 to 326, in order to avoid the loss of precious metal, a superficial treatment of the graphite electrodes with an 80% Pt / 20% Ir alloy is mentioned, this alloy in a quantity of 12.4 g / m² is deposited. This measure is described by Gallone and Messner as a "small advantage". The method of the coating itself is not described, nor is it specified whether the coating was carried out before the electrodes were installed or, as is customary in practice, by in-situ addition of noble metal salts during the electrolysis.
In DD-3725 werden Spritzbeschichtungen und Aufdampfungen von Metallen auf Graphit beschrieben, um die Spannung in der Zelle abzusenken. Die nur sehr begrenzte Haltbarkeit wird darauf zurückgeführt, daß die Haftung der Metallkristalle zu schlecht ist und diese zu leicht von der Oberfläche des Graphits abbrechen.DD-3725 describes spray coatings and vapor deposition of metals on graphite in order to lower the voltage in the cell. The very limited durability is attributed to the fact that the adhesion of the metal crystals is too poor and that they break off too easily from the surface of the graphite.
EP-A 205 631 beschreibt ein Verfahren zur Beschichtung von Graphitkörpern, die als Kathode in der Elektrolyse benutzt werden, indem der Graphitkörper mit einer Lösung eines Platinmetallsalzes und eines weiteren Metallsalzes in Alkohol an der Oberfläche getränkt und anschließend auf 250 bis 600°C erhitzt wird. Als bevorzugte Alkohole werden Ethanol, Propanol und Butanol genannt. Die Temperaturbehandlung erfolgt derart, daß der Graphitkörper insgesamt auf die genannten Temperaturen erhitzt wird. Während der Aufheizphase wird der Alkohol teilweise verdampft, so daß er bei der Reaktion nicht mehr zur Verfügung steht. Dem Ofen, in dem der Graphitkörper der Temperaturbehandlung ausgesetzt wird, muß eine Abgasanlage nachgeschaltet werden, um die Oxidationsprodukte des Alkohols abzubauen.EP-A 205 631 describes a method for coating graphite bodies which are used as cathodes in electrolysis by soaking the surface of the graphite body with a solution of a platinum metal salt and a further metal salt in alcohol and then heating it to 250 to 600 ° C . Ethanol, propanol and butanol are mentioned as preferred alcohols. The temperature treatment is carried out in such a way that the graphite body as a whole is heated to the temperatures mentioned. During the heating phase, the alcohol is partially evaporated, so that it is no longer available in the reaction. The furnace in which the graphite body is subjected to the temperature treatment An exhaust system must be installed downstream to break down the oxidation products of the alcohol.
Aufgabe war es daher, ein Verfahren zur Herstellung von Elektroden, insbesondere für die Salzsäureelektrolyse zur Verfügung zu stellen, das es gestattet, stabile, korrosionsfeste, abriebfeste Elektroden mit einer geringen Überspannung herzustellen, und das einfach und kostengünstig ist.The object was therefore to provide a method for producing electrodes, in particular for hydrochloric acid electrolysis, which makes it possible to produce stable, corrosion-resistant, abrasion-resistant electrodes with a low overvoltage, and which is simple and inexpensive.
Diese Aufgabe konnte durch das erfindungsgemäße Verfahren gelöst werden.This problem could be solved by the method according to the invention.
Gegenstand der Erfindung ist ein Verfahren zur Herstellung von Graphitkathoden für elektrolytische Prozesse, insbesondere für die HCl-Elektrolyse, wobei in die Poren des Graphitkörpers vor dessen Einsatz als Kathode eine Lösung von Iridiumsalzen oder Rhodiumsalzen oder von Gemischen aus Iridiumsalzen oder Rhodiumsalzen mit Salzen der übrigen Metalle aus der Platingruppe bestehend aus Platin, Palladium, Osmium und Ruthenium in ein- oder mehrwertigen Alkoholen mit 2 bis 4 Kohlenstoffatomen oder in Gemischen aus ein- oder mehrwertigen Alkoholen mit 2 bis 4 Kohlenstoffatomen eingebracht wird, anschließend gegebenenfalls mit ein- oder mehrwertigen Alkoholen mit 2 bis 4 Kohlenstoffatomen oder einem Gemisch aus ein- oder mehrwertigen Alkoholen mit 2 bis 4 Kohlenstoffatomen gespült wird, dann erhitzt wird und anschließend abgekühlt wird, welches dadurch gekennzeichnet ist, daß der getränkte Graphitkörper mit offenen Gasflammen an der mit der Lösung getränkten Oberfläche in einer Tiefe bis zu etwa 1 mm auf Temperaturen zwischen 200 bis 450°C innerhalb von 2 bis 10 Minuten, vorzugsweise 4 bis 6 Minuten, erhitzt wird, wobei die Gasflammen erst dann von oben senkrecht nach unten auf den getränkten Graphitkörper einwirken, wenn der gesamte getränkte Graphitkörper sich unterhalb der Gasflammen befindet.The invention relates to a process for the production of graphite cathodes for electrolytic processes, in particular for HCl electrolysis, a solution of iridium salts or rhodium salts or of mixtures of iridium salts or rhodium salts with salts of the other metals in the pores of the graphite body prior to its use as a cathode from the platinum group consisting of platinum, palladium, osmium and ruthenium in mono- or polyhydric alcohols with 2 to 4 carbon atoms or in mixtures of mono- or polyhydric alcohols with 2 to 4 carbon atoms, then optionally with mono- or polyhydric alcohols with 2 up to 4 carbon atoms or a mixture of mono- or polyhydric alcohols with 2 to 4 carbon atoms, then heated and then cooled, which is characterized in that the soaked graphite body with open gas flames on the surface soaked with the solution in one Depth up to about 1 mm to temperatures between 200 to 450 ° C within 2 to 10 minutes, preferably 4 to 6 minutes, the gas flames only act vertically downwards on the impregnated graphite body when the entire impregnated Graphite body is located below the gas flames.
Eine bevorzugte Verfahrensvariante ist, daß in die Poren des Graphitkörpers Lösungen der oben genannten Salze oder der oben genannten Salzgemische in 1,2-Ethandiol oder in Glyzerin eingebracht werden und gegebenenfalls mit 1,2-Ethandiol oder Glyzerin gespült wird.A preferred process variant is that solutions of the abovementioned salts or of the abovementioned salt mixtures in 1,2-ethanediol or in glycerol are introduced into the pores of the graphite body and optionally rinsed with 1,2-ethanediol or glycerol.
Nach dem Erhitzen mit den offenen Gasflammen und nach der Abkühlung kann der Graphitkörper erneut mit reinen, ein- oder mehrwertigen Alkoholen mit 2 bis 4 Kohlenstoffatomen behandelt werden, danach erneut der Gasflammenbehandlung ausgesetzt werden und dann abgekühlt werden.After heating with the open gas flames and after cooling, the graphite body can be treated again with pure, mono- or polyhydric alcohols with 2 to 4 carbon atoms, then again subjected to the gas flame treatment and then cooled.
Die genannten Edelmetalle bzw. Legierungen liegen bevorzugt in einer Menge von 5 bis 20 g/projezierte Fläche von 1 m² vor.The noble metals or alloys mentioned are preferably present in an amount of 5 to 20 g / projected area of 1 m².
Bevorzugt werden die erfindungsgemäß hergestellten Graphitkathoden bei der Elektrolyse von Salzsäure in Zellen mit Diaphragma oder Ionenaustauschermembran verwendet.The graphite cathodes produced according to the invention are preferably used in the electrolysis of hydrochloric acid in cells with a diaphragm or ion exchange membrane.
Besonders bevorzugt wird bei der Verwendung der erfindungsgemäß hergestellten Graphitkathoden in der Elektrolyse von Salzsäure beim Stillstand der Elektrolyse in den Zellen ein Mindeststrom von 0,1 bis 1,5 mA/cm², vorzugsweise von 0,5 bis 0,75 mA/cm², aufrecht erhalten.When using the graphite cathodes produced according to the invention in the electrolysis of hydrochloric acid when the electrolysis in the cells is at a standstill, a minimum current of 0.1 to 1.5 mA /
Als Ausgangsmaterial werden auf dem Markt erhältliche Graphitkathoden, die aus speziellem Elektrodengraphit (graphite for technical elektrolytic processes) bestehen, verwendet, wie z.B. von der Firma COVA/CONRADTY, Nürnberg Graphit der Qualität AC oder von der Firma SIGRI, Meitingen Graphit der Qualitäten ES und EH. Derartige Graphitsorten weisen üblicherweise eine arteigene Porosität (acc. pore volume) von 12 bis 18 % auf, der spezifische Widerstand liegt bei 7,5 bis 12,5 Ω·mm²/m, und die scheinbare Dichte (bulk density) beträgt 1,70 bis 1,77 g/cm³. Der Elektrodengraphit wird über allgemein bekannte petrochemische, keramische und Veredlungsstufen hergestellt, wobei die artspezifische poröse Oberflächenstruktur entsteht.The starting material used on the market are graphite cathodes, which consist of special electrode graphite (graphite for technical electrolytic processes), such as from the company COVA / CONRADTY, Nuremberg graphite of the quality AC or from the company SIGRI, Meitingen graphite of the qualities ES and EH. Such graphite grades usually have an intrinsic porosity (acc. Pore volume) of 12 to 18%, the specific resistance is 7.5 to 12.5 Ω · mm² / m, and the apparent density (bulk density) is 1.70 up to 1.77 g / cm³. Electrode graphite is produced using well-known petrochemical, ceramic and finishing stages, whereby the species-specific porous surface structure is created.
Gegenüber dem Stand der Technik weisen die erfindungsgemäß hergestellten Graphitkathoden eine hohe Korrosionsfestigkeit auf sowie eine außergewöhnlich hohe Lebensdauer, wobei die Spannungserniedrigung über die gesamte Lebensdauer bestehen bleibt. Außerdem ist das erfindungsgemäße Verfahren sehr energiegünstig und einfach durchzuführen. Eine nachgeschaltete Abgasaufbereitungsanlage ist nicht erforderlich.Compared to the prior art, the graphite cathodes produced according to the invention have high corrosion resistance and an extraordinarily long service life, the voltage reduction remaining over the entire service life. In addition, the method according to the invention is very energy-efficient and easy to carry out. A downstream exhaust gas treatment system is not required.
Die in-situ-Beschichtung wie auch die galvanische Vorbeschichtung in neutralem Medium nach dem Stand der Technik führen zu einer Elektrokristallisation der Edelmetalle auf der äußeren Graphitoberfläche, wobei diese Kristallagglomerate weder chemisch noch physikalisch mit dem Graphit verbunden sind, sondern nur locker angelagert sind und daher leicht abbrechen. Zudem erfolgt bei der in-situ-Beschichtung die Edelmetallabscheidung an bevorzugten Stellen der Graphitoberfläche, so daß es nicht zu einer gewünschten gleichmäßigen Verteilung des Edelmetalls kommt. Die Spritzbeschichtung nach dem Stand der Technik, beispielsweise mit Hilfe eines Plasmabrenners, führt zu einer Abdeckung der poren- und spaltenreichen, großen Graphitoberfläche, sodaß eine oberflächenarme Kathode entsteht, und die Metallschicht platzt sehr leicht ab.The in-situ coating as well as the galvanic precoating in neutral medium according to the prior art lead to an electrocrystallization of the noble metals on the outer graphite surface, whereby these crystal agglomerates are neither chemically nor physically connected to the graphite, but are only loosely attached and therefore break off easily. In addition, in the case of in-situ coating, the noble metal is deposited at preferred locations on the graphite surface, so that there is no desired uniform distribution of the noble metal. The spray coating according to the prior art, for example with the aid of a plasma torch, leads to a covering of the large pore and column-rich, large graphite surface, so that a low-surface cathode is formed, and the metal layer flakes off very easily.
Anstelle der oberflächlichen Metallabscheidung auf Graphitkörpern gelang es mit dem erfindungsgemäßen Verfahren, Graphitkathoden herzustellen, in denen die Metalle in den Poren und Spalten des Graphits fest verankert (verplombt) vorliegen.Instead of the superficial metal deposition on graphite bodies, the method according to the invention made it possible to produce graphite cathodes in which the metals are firmly anchored (sealed) in the pores and columns of the graphite.
Die gesamte Erhitzungsdauer beträgt zudem nur 2 bis 10 Minuten, vorzugsweise 4 bis 6 Minuten, und als Abgas entstehen lediglich Kohlendioxid und Wasserdampf. Betrachtet man die Dimensionen technischer Elektrolyseure mit Graphitelektroden von z.B. 1,50x0,35x0,07 m, wobei ein einzelner Elektrolyseur bereits aus über 100 derartiger Elektroden aufgebaut ist, so wird ersichtlich, welches Einsparungspotential durch das erfindungsgemäße Verfahren gegeben ist.The total heating time is also only 2 to 10 minutes, preferably 4 to 6 minutes, and only carbon dioxide and water vapor are produced as exhaust gas. If you consider the dimensions of technical electrolysers with graphite electrodes of e.g. 1.50x0.35x0.07 m, with a single electrolyzer already being made up of more than 100 electrodes of this type, it can be seen what savings potential there is from the method according to the invention.
Figur 1 zeigt eine Anordnung, mit der das erfindungsgemäße Verfahren durchgeführt werden kann. Die getränkte Elektrodenplatte aus Graphit 1 ist mit Längsschlitzen 2 versehen und liegt auf einem Tisch 3 auf. Über der Platte 1 sind Gasbrenner 4 angeordnet, die über Leitungen 5 mit brennbarem Gas (z.B. Propan/Butan-Gemisch) versorgt werden. Im Gehäuse 6 sind Regel- und Sicherheitseinrichtungen untergebracht. Der Gasdruck und der Abstand des Gasbrenner von der Graphitplatte werden so eingestellt, daß die Gasflammen 7 die Graphitoberfläche vollständig abdecken.Figure 1 shows an arrangement with which the inventive method can be carried out. The impregnated electrode plate made of graphite 1 is provided with
Die Figur 2 zeigt einen Ausschnitt aus der Fig. 1.FIG. 2 shows a section from FIG. 1.
Vorteilhaft werden Brenner eingesetzt, die üblicherweise zum Aufbringen von Bitumen-Schweißbahnen im Dachdeckerhandwerk verwendet werden.Burners, which are usually used to apply bitumen welding strips in the roofing trade, are advantageously used.
Die Graphitplatte wird unter die Gasbrenner gelegt, bevor die Gasbrenner gezündet werden.The graphite plate is placed under the gas burners before the gas burners are ignited.
Die Erfindung soll anhand des nachfolgenden Beipiels näher erläutert werden.The invention will be explained in more detail with the aid of the following example.
In einer Elektrolysezelle mit Diaphragma nach Fig. 3 mit unbeschichteten Graphitelektroden mit den Maßen (110 x 73) mm² und einem internen Umpump von 0,1 l/h in beiden Elektrodenräumen wurde Salzsäure elektrolysiert. 1 stellt das Zellengehäuse aus Polypropylen dar. Die Kathode 2 und die Anode 3 sind mit Stromzuführungsbolzen 4 in das Gehäuse eingedichtet. Beide Zellenhälften sind durch ein Diaphragma (bzw. eine Kationenaustauschermembran) 5 getrennt. Der Elektrolyt kann in beiden Zellenhälften unter Variation des Durchsatzes umgepumpt 7 werden. Diesen Kreisläufen wird frische 30 %ige Salzsäure 8 über Pumpen 9 zugeführt. Durch die Gas/Flüssigkeitsabscheider 6 verlassen die Gase 10, 11 und die verarmten Elektrolyte 12 die Zelle. Mit einem Stromversorgungsgerät wurde eine Stromdichte von 3 kA/m² eingestellt. Die sich einstellende Zellenspannung wurde mit 2 Graphitspitzen, in der Zuführung jeweils isoliert in den Vorderkanten der Elektroden abgegriffen.In an electrolysis cell with a diaphragm according to FIG. 3 with uncoated graphite electrodes with the dimensions (110 x 73) mm² and an internal pumping of 0.1 l / h in both electrode spaces, hydrochloric acid was electrolyzed. 1 shows the cell housing made of polypropylene. The
Nach einer Einfahrperiode von 5 Tagen betrug die Zellenspannung 2,10 Volt. Durch Zudosierung einer wäßrigen Metallsalzlösung mit einem Gehalt von 0,3 mg Pt und 0,6 mg Pd fiel die Spannung sofort um ca. 0,4 Volt ab. Auf diesem Niveau verblieb die Spannung über etwa 100 Tage und stieg dann wieder langsam auf den ursprünglichen Wert vor der Dotierung an. Die Vergrößerung der Elektrolytdurchsätze auf 35 l/h führte zu einem schnelleren Wiederanstieg der Spannung nach der Zudosierung der Lösung auf den Wert vor der Dotierung innerhalb von 1 bis 2 Tagen. Dadurch ergab sich eine mittlere Spannung von ca. 1,90 Volt (Start: 2,10 Volt; Abfall auf 1,70 V; Wiederanstieg auf 2,10 Volt).After a running-in period of 5 days, the cell voltage was 2.10 volts. When an aqueous metal salt solution containing 0.3 mg Pt and 0.6 mg Pd was metered in, the voltage immediately dropped by approximately 0.4 volts. The voltage remained at this level for about 100 days and then slowly rose again to the original value before the doping. Increasing the electrolyte throughputs to 35 l / h led to a faster rise in the voltage after the solution had been metered in to the value before the doping within 1 to 2 days. This resulted in an average voltage of approximately 1.90 volts (start: 2.10 volts; drop to 1.70 V; rise to 2.10 volts).
0,236 g IrCl₄·H₂O (Gehalt ca. 50,9 % Ir) wurden in 1,0 ml 1,2-Ethandiol gelöst. Mit dem Pinsel wurde diese Lösung auf eine Graphitplatte mit Rillen (Fig. 1) und mit den äußeren Maßen (110 x 73) mm² gleichmäßig aufgetragen. Nach einer Zeit von etwa 5 Minuten (Zeit zum Eindringen der Lösung in die Poren des Graphits) wurde die mit der Lösung getränkte Seite (spätere Kathodenseite in der Elektrolyse) mit einer die gesamte Oberfläche überdeckenden Flamme etwa 6 Minuten lang erhitzt, wobei die Starttempertur von 180°C innerhalb von wenigen Sekunden erreicht wurde und eine Temperatur von 450°C nach 6 Minuten erreicht war und wobei die Platte bereits vor Zünden der Flamme unterhalb des Brenners angeordnet worden war. Nach Erkalten wurde die Platte erneut mit 1 ml reinem 1,2-Ethandiol gleichmäßig eingestrichen und die beschriebene Erhitzung wiederholt. Die Graphitplatte wurde in die Elektrolysezelle eingebaut. Bei Elektrolytdurchsätzen von 0,1 bis 35 l/h stellte sich eine über mehrere Monate gleichbleibende Zellenspannung von 1,55 Volt ein. Während der Elektrolyse lag die Korrosionsrate bei 1 µg Ir/l Elektrolyt, im stromlosen Zustand bei 400 µg Ir/l Elektrolyt.0.236 g IrCl₄ · H₂O (content about 50.9% Ir) were dissolved in 1.0 ml of 1,2-ethanediol. With the brush, this solution was applied evenly to a graphite plate with grooves (Fig. 1) and with the external dimensions (110 x 73) mm². After a time of about 5 minutes (time for the solution to penetrate into the pores of the graphite), the side soaked with the solution (later cathode side in the Electrolysis) with a flame covering the entire surface for about 6 minutes, the starting temperature of 180 ° C. being reached within a few seconds and a temperature of 450 ° C. being reached after 6 minutes, and the plate even before the flame was ignited below the burner had been ordered. After cooling, the plate was again spread evenly with 1 ml of pure 1,2-ethanediol and the heating described repeated. The graphite plate was installed in the electrolysis cell. With electrolyte throughputs of 0.1 to 35 l / h, a cell voltage of 1.55 volts remained constant over several months. During the electrolysis the corrosion rate was 1 µg Ir / l electrolyte, in the de-energized state 400 µg Ir / l electrolyte.
0,118 g IrCl₄·H₂O und 0,150 g H₂PtCl₆·6H₂O wurden in 1,0 ml 1,2-Ethandiol gelöst, und diese Lösung wurde auf eine Graphitplatte (110x73) mm² gleichmäßig aufgetragen. Die weitere Behandlung entsprach der des Beispiels 2.0.118 g of IrCl₄ · H₂O and 0.150 g of H₂PtCl₆ · 6H₂O were dissolved in 1.0 ml of 1,2-ethanediol, and this solution was applied to a graphite plate (110x73) mm² evenly. The further treatment corresponded to that of Example 2.
Die Graphitplatte wurde als Kathode in eine HCl-Elektrolysezelle mit Diaphragma (Fig. 3) eingebaut. Bei Elektrolytdurchsätzen von 0,1 bis 35 l/h stellte sich eine über mehrere Monate gleichbleibende Zellenspannung von 1,45 Volt ein. Während der Elektrolyse lag die Korrosionsrate bei 1 µg Pt/l und 2 µg Ir/l Elektrolyt, im stromlosen Zustand bei 18.000 µg Pt/l und 20.000 µg Ir/l.The graphite plate was installed as a cathode in an HCl electrolysis cell with a diaphragm (FIG. 3). With electrolyte throughputs of 0.1 to 35 l / h, a cell voltage of 1.45 volts remained constant over several months. During the electrolysis, the corrosion rate was 1 µg Pt / l and 2 µg Ir / l electrolyte, in the de-energized state it was 18,000 µg Pt / l and 20,000 µg Ir / l.
0,31 g RhCl₃·H₂O (Gehalt ca. 0,12 g Rh) wurden in 1,0 ml 1,2-Ethandiol gelöst. Nach Pinselauftrag auf eine Graphitplatte erfolgte die Plombierung von Rh-Metall in den Poren des Graphits entsprechend Beispiel 2. Diese Platte als Kathode eingesetzt führte über 10 Tage zu einer gleichbleibenden Zellenspannung von 1,67 Volt.0.31 g RhCl₃ · H₂O (content about 0.12 g Rh) were dissolved in 1.0 ml 1,2-ethanediol. After brush application to a graphite plate, Rh metal was sealed in the pores of the graphite in accordance with Example 2. This plate, used as a cathode, led to a constant cell voltage of 1.67 volts over 10 days.
Bei 2 Zellen mit je einer Kathode gemäß Beispiel 2 und 3 wurde bei Außerbetriebssetzung ein Reststrom von 0,63 mA/cm² Kathodenoberfläche, entsprechend einer Restspannung von 1,1 bis 1,2 Volt belassen. Die Korrosionsrate in der Zelle mit der Ir-beschichteten Kathode betrug 2 µg Ir/l, in der mit der Pt-beschichteten Kathode 6 µg Ir/l und 3 µg Pt/l.In the case of 2 cells, each with a cathode according to Examples 2 and 3, a residual current of 0.63 mA /
Claims (6)
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4417744A DE4417744C1 (en) | 1994-05-20 | 1994-05-20 | Process for the production of stable graphite cathodes for hydrochloric acid electrolysis and their use |
| DE4417744 | 1994-05-20 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0683247A1 true EP0683247A1 (en) | 1995-11-22 |
| EP0683247B1 EP0683247B1 (en) | 1997-08-13 |
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ID=6518610
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP95107029A Expired - Lifetime EP0683247B1 (en) | 1994-05-20 | 1995-05-09 | Process for manufacturing stable graphite cathodes for the electrolysis of chlorhydric acid |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5575985A (en) |
| EP (1) | EP0683247B1 (en) |
| CN (1) | CN1052038C (en) |
| DE (2) | DE4417744C1 (en) |
| ZA (1) | ZA954106B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2037005A2 (en) | 2007-09-15 | 2009-03-18 | Bayer MaterialScience AG | Method for manufacturing graphite electrodes for electrolytic processes |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TW520575B (en) * | 2000-04-21 | 2003-02-11 | Sony Corp | Positive electrode material and nickel-zinc battery |
| JP4723829B2 (en) * | 2004-08-13 | 2011-07-13 | 独立行政法人科学技術振興機構 | Method for producing noble metal-supported carbon nanohorn |
| DE102005032663A1 (en) * | 2005-07-13 | 2007-01-18 | Bayer Materialscience Ag | Process for the preparation of isocyanates |
| DE102006023261A1 (en) * | 2006-05-18 | 2007-11-22 | Bayer Materialscience Ag | Process for the production of chlorine from hydrogen chloride and oxygen |
| US20110027603A1 (en) * | 2008-12-03 | 2011-02-03 | Applied Nanotech, Inc. | Enhancing Thermal Properties of Carbon Aluminum Composites |
| US20110147647A1 (en) * | 2009-06-05 | 2011-06-23 | Applied Nanotech, Inc. | Carbon-containing matrix with additive that is not a metal |
| US20100310447A1 (en) * | 2009-06-05 | 2010-12-09 | Applied Nanotech, Inc. | Carbon-containing matrix with functionalized pores |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2140599A1 (en) * | 1971-06-10 | 1973-01-19 | Johnson Matthey Co Ltd | |
| EP0021456A1 (en) * | 1979-06-29 | 1981-01-07 | BBC Aktiengesellschaft Brown, Boveri & Cie. | Electrode for the electrolysis of water |
| EP0040897A1 (en) * | 1980-05-23 | 1981-12-02 | Westinghouse Electric Corporation | Process for electrode fabrication having a uniformly distributed catalyst layer upon a porous substrate |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3725C (en) * | M. NEUERBURG in Köln a. Rh | Rake chain for delivery to setting machines | ||
| US2837412A (en) * | 1956-12-18 | 1958-06-03 | George A Bennett | Preparation of impervious graphite by liquid phase impregnation |
| GB834640A (en) * | 1957-06-17 | 1960-05-11 | L Von Roll Ag | Improvements in or relating to electrolytic processes |
| US3242065A (en) * | 1960-12-21 | 1966-03-22 | Oronzio De Nora Impianti | Cell for electrolysis of hydrochloric acid |
| US3375132A (en) * | 1964-03-03 | 1968-03-26 | Union Carbide Corp | Process for impregnating a carbon electrolytic anode and article |
| DE1216852B (en) * | 1964-06-16 | 1966-05-18 | Hoechst Ag | Process for the electrolysis of aqueous hydrochloric acid in diaphragm cells |
| US3632444A (en) * | 1968-12-31 | 1972-01-04 | Hooker Chemical Corp | Graphite anode treatment |
| DE2042225C3 (en) * | 1970-01-22 | 1975-02-27 | Centro Sperimentale Metallurgico S.P.A., Rom | Impregnation solution to improve the oxidation resistance of carbon-containing bodies |
| US3847862A (en) * | 1970-08-10 | 1974-11-12 | Marathon Oil Co | Rubber compositions containing finely divided carbon treated with methanol |
| JPS6033287A (en) * | 1983-07-29 | 1985-02-20 | Toshiba Corp | Preparation of single crystal semiconductor |
| DE3516523A1 (en) * | 1985-05-08 | 1986-11-13 | Sigri GmbH, 8901 Meitingen | ANODE FOR ELECTROCHEMICAL PROCESSES |
-
1994
- 1994-05-20 DE DE4417744A patent/DE4417744C1/en not_active Expired - Fee Related
-
1995
- 1995-05-09 EP EP95107029A patent/EP0683247B1/en not_active Expired - Lifetime
- 1995-05-09 DE DE59500497T patent/DE59500497D1/en not_active Expired - Fee Related
- 1995-05-12 US US08/440,031 patent/US5575985A/en not_active Expired - Fee Related
- 1995-05-19 CN CN95105491A patent/CN1052038C/en not_active Expired - Fee Related
- 1995-05-19 ZA ZA954106A patent/ZA954106B/en unknown
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2140599A1 (en) * | 1971-06-10 | 1973-01-19 | Johnson Matthey Co Ltd | |
| EP0021456A1 (en) * | 1979-06-29 | 1981-01-07 | BBC Aktiengesellschaft Brown, Boveri & Cie. | Electrode for the electrolysis of water |
| EP0040897A1 (en) * | 1980-05-23 | 1981-12-02 | Westinghouse Electric Corporation | Process for electrode fabrication having a uniformly distributed catalyst layer upon a porous substrate |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2037005A2 (en) | 2007-09-15 | 2009-03-18 | Bayer MaterialScience AG | Method for manufacturing graphite electrodes for electrolytic processes |
| DE102007044171A1 (en) | 2007-09-15 | 2009-03-19 | Bayer Materialscience Ag | Process for the production of graphite electrodes for electrolytic processes |
| RU2505625C2 (en) * | 2007-09-15 | 2014-01-27 | Байер Матириальсайенс Аг | Method of producing graphite electrodes with coating, preferably of noble metals, for electrolytic processes, especially for hydrochloric acid electrolytes |
Also Published As
| Publication number | Publication date |
|---|---|
| CN1052038C (en) | 2000-05-03 |
| ZA954106B (en) | 1996-01-19 |
| CN1118020A (en) | 1996-03-06 |
| US5575985A (en) | 1996-11-19 |
| DE4417744C1 (en) | 1995-11-23 |
| EP0683247B1 (en) | 1997-08-13 |
| DE59500497D1 (en) | 1997-09-18 |
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