EP0224790A1 - Process for cleaning of cathodes in the electrolysis of alkalichlorides - Google Patents

Process for cleaning of cathodes in the electrolysis of alkalichlorides Download PDF

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Publication number
EP0224790A1
EP0224790A1 EP19860115954 EP86115954A EP0224790A1 EP 0224790 A1 EP0224790 A1 EP 0224790A1 EP 19860115954 EP19860115954 EP 19860115954 EP 86115954 A EP86115954 A EP 86115954A EP 0224790 A1 EP0224790 A1 EP 0224790A1
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EP
European Patent Office
Prior art keywords
cell
electrolysis
catholyte
cathodes
alkalichlorides
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Application number
EP19860115954
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German (de)
French (fr)
Inventor
Franz-Rudolf Dr. Minz
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Bayer AG
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Bayer AG
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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
    • C25B15/00—Operating or servicing cells

Definitions

  • the present invention relates to a method for removing cathodically deposited metallic contaminants in alkali metal chloride electrolysis.
  • any conductive material that is stable under the electrolysis conditions can be used as the cathode material in alkali metal chloride electrolysis. Since the cell voltage is determined, among other things, by the deposition potential of the protons on the cathode, efforts are made to select a material with the lowest possible H2 overvoltage. Such materials are described in EP-A 129231, EP-A 129374 and DE-A 3322169.
  • the low rate of corrosion of a material considered to be stable is sufficient to poison the catholyte with traces.
  • the gettering effect of the cathode shifts the initially low H2 deposition potential to higher values, i.e. the cell voltage increases over time. This increase in voltage is directed among other things on the type and concentration of impurities; so z.
  • B. a content of 1 ppm Fe in the supplied electrolyte can increase the cell voltage in the course of a few weeks to the level of a pure mild steel cathode.
  • the object of the present invention is to eliminate these disadvantages which arise for optimal operation of an alkali metal chloride electrolysis.
  • the present invention thus relates to a process for removing cathodically deposited metallic impurities in alkali metal chloride electrolysis, characterized in that the electrolytic cell is short-circuited and the electrolyte is discharged.
  • the method according to the invention can be used regardless of the type of electrolysis, i.e. for the case that the electrolysis cell is an undivided cell, in particular an amalgam cell, or also for the case that the electrolysis cell is a divided cell, in particular a diaphragm or membrane cell.
  • the short circuit should be carried out for 10 minutes to 10 hours. Particularly favorable results, also with regard to economic factors, are obtained if the short circuit is carried out for 30 minutes to 5 hours.
  • An advantage of the method according to the invention is that existing installations can be used.
  • a switch for bridging a cell is available according to the state of the art in order to be able to remove the corresponding cell from the circuit when repairing a cell or when replacing the diaphragm or the membranes.
  • the method according to the invention avoids the use of non-electrolyte additives, such as those e.g. in EP-A 132 816 and EP-A 136 794.
  • the contaminants deposited on the cathode dissolve again when the cell is electrically bridged.
  • the advantages of the method according to the invention are also achieved in the case of the membrane or diphragm method. if only the catholyte is removed.
  • the cathode chamber should also be flushed with catholyte.
  • the running catholyte is not returned to the circuit, but is collected separately.
  • the liquor obtained here can be used advantageously for alkalizing the brine before cleaning.
  • the cell was rinsed with 1/3 of the amount of electrolyte usual during operation.
  • the running catholyte had a 10-fold higher iron concentration than the feed.
  • the catholyte thus enriched with detached Fe was collected separately and used for alkaline "brine precipitation".
  • the cell voltage was 200 mV below the switch-off value and rose again to the same extent as before.

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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)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Abstract

The process removes metallic contaminants cathodically deposited in the electrolysis of alkali chlorides.

Description

Die vorliegende Erfindung betrifft ein Verfahren zur Ent­fernung kathodisch abgeschiedener metallischer Verunreini­gungen bei der Alkalichloridelektrolyse.The present invention relates to a method for removing cathodically deposited metallic contaminants in alkali metal chloride electrolysis.

Als Kathodenmaterial bei der Alkalichloridelektrolyse kann jedes unter den Elektrolysebedingungen beständige leitfähige Material verwendet werden. Da die Zellenspannung unter anderem auch vom Abscheidungspotential der Protonen an der Kathode be­stimmt wird, ist man bestrebt, ein Material mit möglichst niedriger H₂-Überspannung auszuwählen. Derartige Materi­alien sind beschrieben in den EP-A 129231, EP-A 129374 und DE-A 3322169.Any conductive material that is stable under the electrolysis conditions can be used as the cathode material in alkali metal chloride electrolysis. Since the cell voltage is determined, among other things, by the deposition potential of the protons on the cathode, efforts are made to select a material with the lowest possible H₂ overvoltage. Such materials are described in EP-A 129231, EP-A 129374 and DE-A 3322169.

Diesen Kathode ist jedoch gemeinsam, daß neben Wasser­stoff auch in bezug auf das Kathodenmaterial unedlere Me­talle, die spurenweise im Elektrolyten vorhanden sind, ab­geschieden werden. Diese Spuren lassen sich häufig nicht vermeiden, wenn z.B. aus Gründen der Wärmebilanz der Katholyt im Kreislauf geführt und über einen Wärmetauscher geleitet werden muß.What is common to these cathodes, however, is that, in addition to hydrogen, less noble metals, which are present in traces in the electrolyte, are deposited with respect to the cathode material. These traces can often not be avoided if, for example, for reasons of heat balance, the catholyte has to be circulated and passed through a heat exchanger.

Die geringe Korrosionsrate eines als beständig geltenden Materials reicht aus, den Katholyten mit Spuren zu ver­giften. Durch den Getterungseffekt der Kathode wird das anfangs niedrige H₂-Abscheidungspotential zu höheren Wer­ten verschoben, d.h. die Zellenspannung steigt im Laufe der Zeit an. Dieser Spannungsanstieg richtet sich u.a. nach Art und Konzentration der Verunreinigungen; so kann z. B. ein Gehalt von 1 ppm Fe im zugespeisten Elektro­lyten die Zellenspannung im Laufe von einigen Wochen bis auf das Niveau einer reinen Weichstahlkathode ansteigen lassen.The low rate of corrosion of a material considered to be stable is sufficient to poison the catholyte with traces. The gettering effect of the cathode shifts the initially low H₂ deposition potential to higher values, i.e. the cell voltage increases over time. This increase in voltage is directed among other things on the type and concentration of impurities; so z. B. a content of 1 ppm Fe in the supplied electrolyte can increase the cell voltage in the course of a few weeks to the level of a pure mild steel cathode.

Es wäre denkbar, die Verunreinigung aus dem Katholytstrom in einer vorgeschalteten Zelle kathodisch abzuscheiden. Bei der Vielzahl von Zellen, die normalerweise in einer Produktionsanlage vorhanden sind, wäre jedoch der zu rei­nigende Volumenstrom in der Regel zu groß.It would be conceivable to cathodically separate the contamination from the catholyte stream in an upstream cell. Given the large number of cells that are normally present in a production plant, the volume flow to be cleaned would normally be too large.

Die Aufgabe der vorliegenden Erfindung besteht darin, die­se für eine optimale Betriebsweise einer Alkalichlorid­elektrolyse entstehenden Nachteile zu beseitigen.The object of the present invention is to eliminate these disadvantages which arise for optimal operation of an alkali metal chloride electrolysis.

Überraschenderweise wurde gefunden, daß dies dadurch gelingt, indem die elektrolytgefüllte Kammer kurzge­schlossen wird.Surprisingly, it was found that this can be achieved by short-circuiting the electrolyte-filled chamber.

Gegenstand der vorliegenden Erfindung ist somit ein Ver­fahren zur Entfernung kathodisch abgeschiedener metal­lischer Verunreinigungen bei der Alkalichloridelektrolyse, dadurch gekennzeichnet, daß die Elektrolysezelle kurzge­schlossen und der Elektrolyt ausgeschleust wird.The present invention thus relates to a process for removing cathodically deposited metallic impurities in alkali metal chloride electrolysis, characterized in that the electrolytic cell is short-circuited and the electrolyte is discharged.

Das erfindungsgemäße Verfahren ist anwendbar unabhängig vom Typ der Elektrolyse, also für den Fall, daß die Elektrolysezelle eine ungeteilte Zelle, insbesondere eine Amalgamzelle ist, oder auch für den Fall, daß die Elektro­lysezelle eine geteilte Zelle, insbesondere eine Dia­phragma- oder Membranzelle, ist.The method according to the invention can be used regardless of the type of electrolysis, i.e. for the case that the electrolysis cell is an undivided cell, in particular an amalgam cell, or also for the case that the electrolysis cell is a divided cell, in particular a diaphragm or membrane cell.

Je nach Art der Elektrolyse, des Kathodenmaterials oder der Verunreinigungen sollte der Kurzschluß für 10 Minuten bis 10 Stunden durchgeführt werden. Besonders günstige Ergebnisse auch im Hinblick auf wirtschaftliche Faktoren werden erhalten, wenn der Kurzschluß für 30 Minuten bis 5 Stunden durchgeführt wird.Depending on the type of electrolysis, the cathode material or the impurities, the short circuit should be carried out for 10 minutes to 10 hours. Particularly favorable results, also with regard to economic factors, are obtained if the short circuit is carried out for 30 minutes to 5 hours.

Ein Vorteil des erfindungsgemäßen Verfahrens liegt darin, daß auf vorhandene Installationen zurückgegriffen werden kann. Ein Schalter zum Überbrücken einer Zelle ist nach dem Stand der Technik vorhanden, um bei Reparaturarbeiten an einer Zelle oder beim Erneuern des Diaphragmas bzw. der Membranen die entsprechende Zelle aus dem Stromkreis ausbinden zu können. Weiterhin vermeidet das erfindungsgemäße Verfahren die Verwendung von elektrolytfremden Zusätzen, wie sie z.B. in den EP-­A 132 816 und EP-A 136 794 beschrieben werden.An advantage of the method according to the invention is that existing installations can be used. A switch for bridging a cell is available according to the state of the art in order to be able to remove the corresponding cell from the circuit when repairing a cell or when replacing the diaphragm or the membranes. Furthermore, the method according to the invention avoids the use of non-electrolyte additives, such as those e.g. in EP-A 132 816 and EP-A 136 794.

Die auf der Kathode abgeschiedenen Verunreinigungen gehen wieder in Lösung, wenn die Zelle elektrisch überbrückt wird.The contaminants deposited on the cathode dissolve again when the cell is electrically bridged.

Die Vorteile des erfindungsgemäßen Verfahrens werden im Falle des Membran- oder Diphragmaverfahrens auch erreicht, wenn nur der Katholyt ausgeschleust wird. Weiterhin sollte die Kathodenkammer mit Katholyt gespült werden. Der ab­laufende Katholyt wird nicht in den Kreislauf zurückge­leitet, sondern getrennt aufgefangen. Die hier anfallende Lauge kann vorteilhaft zur Alkalisierung der Sole vor der Reinigung eingesetzt werden.The advantages of the method according to the invention are also achieved in the case of the membrane or diphragm method. if only the catholyte is removed. The cathode chamber should also be flushed with catholyte. The running catholyte is not returned to the circuit, but is collected separately. The liquor obtained here can be used advantageously for alkalizing the brine before cleaning.

Die Erfindung wird im nachfolgenden Beispiel erläutert, ohne daß hierin eine Einschränkung zu sehen ist.The invention is illustrated in the example below, without any restriction being seen here.

Beispielexample

Durch eine handelsübliche Membranzelle zur Elektrolyse von NaCl wurd bei einer spezifischen Belastung von 3 KA/m² je 1 m³ Anolyt und Katholyt geleitet. Der Katholytstrom wurde über einen Sammelbehälter und einen Wärmetauscher aus Incolloy im Kreislauf geführt. Eine der Prokuktion an NaOH entsprechende Menge Wasser wurde dem Katholyt-Kreis­lauf zugespeist und die resultierende Menge NaOH-Lösung wurde abgezogen. Die Zelle enthielt mit Edelmetall beschichtete Nickelkathoden. Die Zellenspannung stieg im Laufe von 3 Monaten um 250 mV an. Eine Analyse ergab im Katholytzulauf eine Konzentration von ca. 0,1 ppm Fe, im Ablauf von <0,06 ppm. Nach drei Monaten wurde die Zelle elektrisch überbrückt. 3 Stunden lang wurde die Zelle mit 1/3 der während des Betriebs üblichen Elektrolytmenge gespült. Der ablaufende Katholyt wies eine um den Faktor 10 höhere Eisen-Konzentration auf als der Zulauf. Der so mit abgelöstem Fe angereicherte Katholyt wurde getrennt aufgefangen und zur alkalischen "Solefällung" verwendet. Nach dem Wiedereinschalten lag die Zellenspannung um 200 mV unter dem Ausschaltwert und stieg in demselben Maß wie vorher wieder an.1 m³ of anolyte and catholyte were passed through a commercially available membrane cell for the electrolysis of NaCl at a specific load of 3 KA / m². The catholyte stream was circulated through a collection container and a Incolloy heat exchanger. An amount of water corresponding to the production of NaOH was fed to the catholyte circuit and the resulting amount of NaOH solution was drawn off. The cell contained nickel cathodes coated with precious metal. The cell voltage rose by 250 mV in the course of 3 months. An analysis showed a concentration of approx. 0.1 ppm Fe in the catholyte inlet and <0.06 ppm in the outlet. After three months, the cell was bridged electrically. For 3 hours, the cell was rinsed with 1/3 of the amount of electrolyte usual during operation. The running catholyte had a 10-fold higher iron concentration than the feed. The catholyte thus enriched with detached Fe was collected separately and used for alkaline "brine precipitation". After switching on again, the cell voltage was 200 mV below the switch-off value and rose again to the same extent as before.

Eine kurzfristig aufgetretene höhere Fe-Zulaufkonzentra­tion bewirkte sofort einen entsprechenden sprunghaften An­stieg der Zellenspannung, der durch die oben beschriebene Maßnahme wieder vollständig rückgängig gemacht werden konnte.A briefly occurring higher Fe inflow concentration immediately caused a corresponding jump in the cell voltage, which could be completely reversed by the measure described above.

Claims (7)

1. Verfahren zur Entfernung kathodisch abgeschiedener metallischer Verunreinigungen bei der Alkalichlorid­elektrolyse, dadurch gekennzeichnet, daß die Elektro­lysezelle kurzgeschlossen und der Elektrolyt ausge­schleust wird.1. A process for removing cathodically deposited metallic contaminants in alkali chloride electrolysis, characterized in that the electrolytic cell is short-circuited and the electrolyte is discharged. 2. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, daß die Elektrolysezelle eine ungeteilte Zelle, ins­besondere eine Amalgamzelle, ist.2. The method according to claim 1, characterized in that the electrolytic cell is an undivided cell, in particular an amalgam cell. 3. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, daß die Elektrolysezelle eine geteilte Zelle, insbe­sondere eine Diaphragma- oder Membranzelle, ist.3. The method according to claim 1, characterized in that the electrolytic cell is a divided cell, in particular a diaphragm or membrane cell. 4. Verfahren gemäß einem oder mehrerer der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß der Kurzschluß für 10 min bis 10 Stunden durchgeführt wird.4. The method according to one or more of claims 1 to 3, characterized in that the short circuit is carried out for 10 min to 10 hours. 5. Verfahren gemäß einem oder mehrerer der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß der Kurzschluß für 30 min bis 5 Stunden durchgeführt wird.5. The method according to one or more of claims 1 to 4, characterized in that the short circuit is carried out for 30 min to 5 hours. 6. Verfahren gemäß einem oder mehrerer der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß nur der Katholyt ausgeschleust wird.6. The method according to one or more of claims 1 to 5, characterized in that only the catholyte is removed. 7. Verfahren gemäß Anspruch 6, dadurch gekennzeichnet, daß der Katholyt wieder eingesetzt wird zur Alkali­sierung des Anolyten.7. The method according to claim 6, characterized in that the catholyte is used again for alkalizing the anolyte.
EP19860115954 1985-11-29 1986-11-18 Process for cleaning of cathodes in the electrolysis of alkalichlorides Withdrawn EP0224790A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19853542234 DE3542234A1 (en) 1985-11-29 1985-11-29 METHOD FOR CLEANING CATHODES IN ALKALICHLORIDE ELECTROLYSIS
DE3542234 1985-11-29

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EP0224790A1 true EP0224790A1 (en) 1987-06-10

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EP19860115954 Withdrawn EP0224790A1 (en) 1985-11-29 1986-11-18 Process for cleaning of cathodes in the electrolysis of alkalichlorides

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EP (1) EP0224790A1 (en)
JP (1) JPS62133096A (en)
DE (1) DE3542234A1 (en)
FI (1) FI864842A (en)
NO (1) NO864508D0 (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2020480A1 (en) * 1970-04-27 1971-11-11 Basf Ag Process for the electrolysis of alkali chlorides
US4174269A (en) * 1978-06-21 1979-11-13 Ppg Industries, Inc. Method of treating electrodes
EP0132816A1 (en) * 1983-07-26 1985-02-13 Kanegafuchi Kagaku Kogyo Kabushiki Kaisha A method for preventing degradation in activity of a low hydrogen overvoltage cathode
EP0136794A2 (en) * 1983-08-22 1985-04-10 Imperial Chemical Industries Plc Treatment of cathodes for use in electrolytic cell

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2020480A1 (en) * 1970-04-27 1971-11-11 Basf Ag Process for the electrolysis of alkali chlorides
US4174269A (en) * 1978-06-21 1979-11-13 Ppg Industries, Inc. Method of treating electrodes
EP0132816A1 (en) * 1983-07-26 1985-02-13 Kanegafuchi Kagaku Kogyo Kabushiki Kaisha A method for preventing degradation in activity of a low hydrogen overvoltage cathode
EP0136794A2 (en) * 1983-08-22 1985-04-10 Imperial Chemical Industries Plc Treatment of cathodes for use in electrolytic cell

Also Published As

Publication number Publication date
FI864842A0 (en) 1986-11-27
DE3542234A1 (en) 1987-06-04
FI864842A (en) 1987-05-30
JPS62133096A (en) 1987-06-16
NO864508D0 (en) 1986-11-12

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