EP1061158A2 - Parallel operating of amalgam and membrane electrolytic cells - Google Patents

Parallel operating of amalgam and membrane electrolytic cells Download PDF

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Publication number
EP1061158A2
EP1061158A2 EP00111000A EP00111000A EP1061158A2 EP 1061158 A2 EP1061158 A2 EP 1061158A2 EP 00111000 A EP00111000 A EP 00111000A EP 00111000 A EP00111000 A EP 00111000A EP 1061158 A2 EP1061158 A2 EP 1061158A2
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Prior art keywords
brine
amalgam
station
mercury
membrane
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German (de)
French (fr)
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EP1061158A3 (en
EP1061158B1 (en
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Fritz Dr. Gestermann
Hans-Dieter Pinter
Helmut Ziegler
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Covestro Deutschland 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
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
    • C25B1/36—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in mercury cathode cells
    • C25B1/42—Decomposition of amalgams
    • 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
    • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
    • 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
    • C25B15/02—Process control or regulation
    • 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
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes

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  • the invention relates to a method for the parallel operation of amalgam electrolyzers and membrane electrolysers with a common brine circuit below Use of a mercury-resistant oxygen consumption cathode in the Membrane electrolyser.
  • the oxygen consumption cathode for use in NaCl electrolysis is from the literature basically known.
  • brine is of the usual membrane cell quality used. This brine is mercury-free to protect the cathode activation held.
  • the mercury contamination for chloralkali electrolysis using the amalgam process known NaCl brine is typically from about 10 mg / l to 400 mg / l in normal operation or as a peak value after the system has come to a standstill.
  • Another aspect is the gradual changeover from amalgam electrolysis on membrane processes play an important role: if the energetically less favorable, Mercury-resistant cathode activation should be used during the parallel operation of amalgam and membrane processes, with the aim of being more complete Conversion to the optimal cathode activation, which is sensitive to mercury the entire brine and alkali cycle must be completely changed mercury-free, which causes enormous problems, especially in the Alkaline cycle that mercury can be partially in metallic form.
  • the task is therefore to provide an electrolysis process in which an amalgam electrolysis and a Membrane electrolysis, preferably using an oxygen consumable cathode, can be operated in parallel with the same brine circuit.
  • the procedure is said to Have advantages of known methods with oxygen consumption cathodes.
  • the object is achieved according to the invention through the use of oxygen consumable cathodes solved in a membrane electrolysis process, which against the effects of Mercury are resistant.
  • the task is also accomplished through the use of a Ca / Mg ion exchanger dissolved, the Ca / Mg content even with mercury Brine lowers to ⁇ 20 ppb, which is necessary for the full life of the membranes to ensure.
  • the carbon soot can be omitted from the oxygen depletion cathode so that the electrode matrix consists only of Teflon and silver, whereby the silver takes on the function of the catalyst as well as that of electron conduction and accordingly such a high Ag loading is necessary that the particles separate touch and form conductive bridges with each other.
  • the wire mesh, a fine expanded metal as known from battery technology, as also a felt made of silver, silver-plated nickel or silver-plated alkali-resistant material, e.g. Inconnel steel. It is essential that the silver catalyst is stable behaves towards mercury.
  • sulfate content at ⁇ 5 g / l is achieved by appropriate operation, for example continuous or discontinuous removal of the sulfate by means of precipitation or partial stream precipitation, for example with addition of CaCO 3 , BaCl 2 or BaCO 3 , or in particular in the case of very low-sulfate salts, can be adjusted by discharging a partial stream of the depleted brine.
  • Another possibility is the nanofiltration of the brine or a partial flow of the brine by means of ion-selective membranes in the feed upstream of the membrane electrolyzer, or another separation process, for example using ion exchangers. It is important that only the partial flow to the membrane electrolyzer has to be set to the sulfate ion concentration mentioned, with the side effect that the main flow also gradually adjusts to a lower content in the circuit.
  • the SiO 2 content in the NaCl brine can easily be kept at ⁇ 5 ppm by avoiding free concrete areas in the salt store (brine bunker).
  • Peak mercury levels with a concentration of up to 400 mg Hg / l in the brine are from the oxygen consumption cathode operated behind the membrane in the sodium hydroxide solution survived easily.
  • the usual concentration of 150-200 mg / l mercury at normal peaks and ⁇ 10 mg / l mercury in normal operation is for the operation of the oxygen consumption cathode no barrier.
  • the method according to the invention with an oxygen consumption cathode enables parallel operation of classic amalgam electrolysers and membrane electrolysers with a common brine circuit without additional preparation the brine.
  • the precipitation takes place in a side stream with 100 mg / l NaOH and 200 mg / l Na 2 CO 3 .
  • the sulfate level can only be kept at a level of 10 to 15 g / l via the water quantities to be discharged as thin brine from various rinsing and process processes. This high level is harmless for the amalgam system.
  • this anolyte stream 13 coincides with the anolyte stream of the amalgam electrolysis plant 5.
  • the common anolyte stream 14 is again in the salt dissolving station 1 with salt 12 concentrated.
  • the sulfate content can be controlled via a moderate discharge of brine, this is appropriate in the area of the lowest salt concentration in the overall system Outlet 8 behind the electrolytic cell 4. In favorable cases, particularly good salt quality can this outlet 8 also the level of the otherwise in the hydroxide precipitation 6th keep precipitated ions below the tolerance limit for membrane electrolysis.
  • a membrane electrolysis cell 4 with an oxygen consumption cathode with an area of 100 cm 2 made of soot, Teflon and silver catalyst on silver-plated nickel fabric from NeNora (type ESNS) was operated with mercury-containing NaCl brine.
  • the mercury contamination of the NaCl brine fluctuated between a content of 10 mg / l and 400 mg / l and simulated a level of mercury, such as occurs from an amalgam electrolysis plant 5 during typical normal operation or after plant 5 has come to a peak.
  • the electrolytic cell 4 surprisingly showed a complete mercury tolerance the oxygen consumption cathode over an operating period of at least 360 days.
  • the operating voltage of the electrolytic cell 4 was between 1.92 and 1.97 volts under standard conditions (current density: 3kA / m 2 ; operating temperature: 85 ° C; brine concentration: 210 g / l; NaOH concentration: 32% by weight). Electrolytic cells with an oxygen consumable cathode consistently showed a 30 to 80 mV higher operating voltage in mercury-free operation.
  • a typical amalgam cell brine 9 with an Hg content between 7 and 14 mg / l and a Ca loading of 7 mg / l was passed through a Ca / Mg ion exchanger 3 of the type TP 208 with a brine throughput of 1 or 2 l / h headed by Bayer AG.
  • the bed volume was 100 cm 3 with a column diameter of 3.1 cm.
  • the operating temperature was 65 ° C, the pH of the brine was 9.5.

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Abstract

The invention relates to a process for the electrolysis of sodium chloride-containing brine with parallel operation of amalgam electrolysis units (5) and membrane electrolysis units (4) with a common brine circuit using a mercury-resistant oxygen consumable cathode in the membrane electrolysis unit (4).

Description

Die Erfindung betrifft ein Verfahren zum parallelen Betrieb von Amalgamelektrolyseuren und Membranelektrolyseuren mit einem gemeinsamen Solekreislauf unter Verwendung einer gegen Quecksilber resistenten Sauerstoffverzehrkathode im Membranelektrolyseur.The invention relates to a method for the parallel operation of amalgam electrolyzers and membrane electrolysers with a common brine circuit below Use of a mercury-resistant oxygen consumption cathode in the Membrane electrolyser.

Aus der Literatur ist die Sauerstoffverzehrkathode für den Einsatz in der NaCl-Elektrolyse grundsätzlich bekannt. Für ihren Betrieb z.B. in druckkompensierter Anordnung, wie in DE 19622744 C1 beschrieben, wird Sole in üblicher Membranzellenqualität eingesetzt. Zum Schutz der Kathodenaktivierung wird diese Sole quecksilberfrei gehalten.The oxygen consumption cathode for use in NaCl electrolysis is from the literature basically known. For their operation e.g. in a pressure-compensated arrangement, As described in DE 19622744 C1, brine is of the usual membrane cell quality used. This brine is mercury-free to protect the cathode activation held.

Die Quecksilber-Verunreinigung der für die Chloralkalielektrolyse nach dem Amalgamverfahren bekannten NaCl-Sole beträgt typischerweise von etwa 10 mg/l bis 400 mg/l im Normalbetrieb bzw. als Spitzenwert nach Stillstand der Anlage.The mercury contamination for chloralkali electrolysis using the amalgam process known NaCl brine is typically from about 10 mg / l to 400 mg / l in normal operation or as a peak value after the system has come to a standstill.

Von gängigen Membranelektrolyseuren ist bekannt, dass Quecksilber, insbesondere in der oben genannten hohen Konzentration, relativ schnell zu einer Passivierung des Kathodencoatings (Kathodenmaterials) durch über die Membran aus dem Anodenraum einwandernde Quecksilber-Ionen führt. Dies zieht einen irreversiblen Spannungsanstieg zum Betrieb des Elektrolyseurs nach sich und erfordert einen höheren Energieeinsatz. Ein Parallelbetrieb von klassischen Amalgamelektrolyseuren und Membranelektrolyseuren mit einem gemeinsamen Solekreislauf verbietet sich deshalb, sieht man von der Alternative ab, eine aufwendige Quecksilber-Abtrennung (Fällung) aus der für die Membranelektrolyseure bestimmten Sole vorzunehmen oder aber einen separaten, quecksilberfreien Solekreislauf aufzubauen. Beide Varianten sind mit hohem Aufwand verbunden. It is known from common membrane electrolysers that mercury, in particular in the above high concentration, relatively quickly to passivate the Cathode coatings (cathode material) through the membrane from the anode compartment immigrant mercury ions. This causes an irreversible increase in voltage to operate the electrolyzer itself and requires a higher one Use of energy. A parallel operation of classic amalgam electrolysers and Membrane electrolysers with a common brine circuit are therefore prohibited apart from the alternative, a complex mercury separation (Precipitation) from the brine intended for the membrane electrolysers or but to build a separate, mercury-free brine circuit. Both types are associated with great effort.

Versuche, quecksilberresistente Kathodenaktivierungen zu entwickeln, haben nicht den erhofften Erfolg gebracht, so dass zur vollen Nutzung der Energieeinsparung auch weiterhin von einer quecksilberfreien Sole ausgegangen werden muss. Dies wird üblicherweise über getrennte Solekreisläufe oder eine Quecksilberfällung mit Na2S durchgeführt. Beide Wege sind aufwendige Verfahren.Attempts to develop mercury-resistant cathode activations have not brought the hoped for success, so that to the full use of energy saving a mercury-free brine must also be assumed. This is usually carried out using separate brine circuits or mercury precipitation Na2S performed. Both ways are complex procedures.

Ein weiterer Aspekt spielt bei schrittweiser Umrüstung von der Amalgamelektrolyse auf Membranverfahren eine wichtige Rolle: wenn die energetisch ungünstigere, quecksilberresistente Kathodenaktivierung während des Parallelbetriebs von Amalgam- und Membranverfahren zum Einsatz kommen sollte, mit dem Ziel, nach vollständiger Umrüstung auf die optimale, aber gegen Quecksilber empfindliche Kathodenaktivierung umzustellen, muss der gesamte Sole- und Laugekreislauf erst vollständig quecksilberfrei gemacht werden, was enorme Probleme bereitet, zumal im Laugekreislauf das Quecksilber teilweise in metallischer Form vorliegen kann.Another aspect is the gradual changeover from amalgam electrolysis on membrane processes play an important role: if the energetically less favorable, Mercury-resistant cathode activation should be used during the parallel operation of amalgam and membrane processes, with the aim of being more complete Conversion to the optimal cathode activation, which is sensitive to mercury the entire brine and alkali cycle must be completely changed mercury-free, which causes enormous problems, especially in the Alkaline cycle that mercury can be partially in metallic form.

Es stellt sich deshalb ausgehend von dem bekannten Stand der Technik die Aufgabe, ein Elektrolyseverfahren bereitzustellen, bei dem eine Amalgamelektrolyse und eine Membranelektrolyse, bevorzugt unter Verwendung einer Sauerstoffverzehrkathode, parallel mit gleichem Solekreislauf betrieben werden können. Das Verfahren soll die Vorteile bekannter Verfahren mit Sauerstoffverzehrkathoden aufweisen.Based on the known prior art, the task is therefore to provide an electrolysis process in which an amalgam electrolysis and a Membrane electrolysis, preferably using an oxygen consumable cathode, can be operated in parallel with the same brine circuit. The procedure is said to Have advantages of known methods with oxygen consumption cathodes.

Die Aufgabe wird erfindungsgemäß durch den Einsatz von Sauerstoffverzehrkathoden in einem Membranelektrolyseverfahren gelöst, die gegen Einwirkungen von Quecksilber resistent sind. Die Aufgabe wird darüber hinaus durch den Einsatz eines Ca/Mg-Ionenaustauschers gelöst, der den Ca/Mg-Gehalt auch bei quecksilberhaltiger Sole auf < 20 ppb senkt, was notwendig ist, um die volle Lebensdauer der Membranen zu gewährleisten.The object is achieved according to the invention through the use of oxygen consumable cathodes solved in a membrane electrolysis process, which against the effects of Mercury are resistant. The task is also accomplished through the use of a Ca / Mg ion exchanger dissolved, the Ca / Mg content even with mercury Brine lowers to <20 ppb, which is necessary for the full life of the membranes to ensure.

Gegenstand der Erfindung ist ein Verfahren zur Elektrolyse Natriumchlorid-haltiger Sole mit einem parallelen Betrieb von Amalgamelektrolyseuren und Membranelektrolyseuren mit einem gemeinsamen Solekreislauf, mit den Schritten:

  • Zuführen der Sole von einer Salzlösestation zu einer Fäll- und Filterstation und grobes Abtrennen von Sulfat-, Calzium- und Magnesiumionen aus der Sole in der Fäll- und Filterstation,
  • Aufteilen der Sole in einen Hauptstrom und einen Teilstrom, Elektrolysieren des Hauptstroms der Sole in einem Amalgamelektrolyseur,
  • Vorbehandeln des Teilstroms der Sole durch Entfernen von freiem Chlor in einer Entchlorungsstation, Ausfällen von insbesondere Al-, Fe- und Mg-Ionen in einer Hydroxidfällungsstation und ggf. Abtrennen von Calzium- und Magnesiumionen aus der Sole,
  • anschließend Elektrolysieren des Teilstroms der Sole in einem Membranelektrolyseur und
  • Zusammenführen der Anolytströme des Membranelektrolyseurs und des Amalgamelektrolyseur in einen gemeinsamen Anolytstrom, wobei ein Membranelektrolyseur mit einer quecksilberresistenten Sauerstoffverzehrkathode verwendet wird.
    • The invention relates to a process for the electrolysis of sodium chloride-containing brine with a parallel operation of amalgam electrolysers and membrane electrolysers with a common brine circuit, comprising the steps:
  • Feeding the brine from a salt dissolving station to a precipitation and filter station and rough separation of sulfate, calcium and magnesium ions from the brine in the precipitation and filter station,
  • Dividing the brine into a main stream and a partial stream, electrolyzing the main stream of the brine in an amalgam electrolyzer,
  • Pretreatment of the partial current of the brine by removing free chlorine in a dechlorination station, precipitation of in particular Al, Fe and Mg ions in a hydroxide precipitation station and, if necessary, separating calcium and magnesium ions from the brine,
  • then electrolyzing the partial current of the brine in a membrane electrolyzer and
  • Merging the anolyte streams of the membrane electrolyzer and the amalgam electrolyzer into a common anolyte stream, wherein a membrane electrolyzer with a mercury-resistant oxygen consumable cathode is used.

    • Die Sauerstoffverzehrkathode hat vorzugsweise folgenden Aufbau:

  • Der metallische Träger zur Verteilung der Elektronen besteht aus Gewebe aus Silberdraht oder versilbertem Nickeldraht oder einer anderen laugefesten Legierung, z.B. Inconel, die zur Vermeidung von schlecht leitenden Oxid- oder Hydroxidschichten ebenfalls versilbert oder anders veredelt sein sollten. Besonders vorteilhaft ist die Verwendung eines tiefstrukturierten Trägers wie z.B. Filz aus feinen Fasern des oben genannten Gewebematerials. Die Katalysatormatrix besteht aus dem bekannten Gemisch aus Teflon zur Einstellung der Hydrophobie und der Porosität für die Gasdiffusion, einem elektrisch leitfähigen Träger, z.B. Vulkanruß oder Acetylenruß, und dem darin fein verteilten Katalysatormaterial selbst, das in Form von katalytisch aktiven Silberpartikeln untergemischt ist. Die Katalysatormatrix ist mit dem Träger versintert oder verpresst. Alternativ kann auch auf die Kohlenstoffanteile (Ruß) verzichtet werden, wenn die Katalysatordichte und/oder der leitfähig gemachte hydrophobe Träger so eingestellt sind, dass die überwiegende Menge der Katalysatorpartikel auch elektrisch kontaktiert werden.
    • The oxygen cathode preferably has the following structure:
  • The metallic carrier for the distribution of the electrons consists of tissue made of silver wire or silver-plated nickel wire or another alkali-resistant alloy, eg Inconel, which should also be silver-plated or otherwise refined to avoid poorly conductive oxide or hydroxide layers. It is particularly advantageous to use a deeply structured carrier, such as felt made of fine fibers of the above-mentioned fabric material. The catalyst matrix consists of the known mixture of Teflon for adjusting the hydrophobicity and porosity for gas diffusion, an electrically conductive carrier, for example volcanic carbon black or acetylene black, and the catalyst material itself which is finely divided therein and which is mixed in in the form of catalytically active silver particles. The catalyst matrix is sintered or pressed with the support. Alternatively, the carbon content (soot) can also be dispensed with if the catalyst density and / or the rendered hydrophobic support are set such that the predominant amount of the catalyst particles are also contacted electrically.

    • Als Alternative kann der Kohlenstoffruß in der Sauerstoffverzehrkathode weggelassen werden, sodass die Elektrodenmatrix nur aus Teflon und Silber besteht, wobei das Silber neben der Katalysatorfunktion auch die der Elektronenleitung übernimmt und entsprechend eine so hohe Ag-Beladung notwendig ist, dass die Teilchen sich berühren und leitfähige Brücken untereinander bilden. Als Träger kann hier sowohl das Drahtgewebe, ein feines Streckmetall, wie aus der Batterietechnik bekannt, als auch ein Filz aus Silber, versilbertem Nickel oder versilbertem laugefestem Material, z.B. Inconnel-Stahl, dienen. Wesentlich ist, dass sich der Silberkatalysator stabil gegenüber Quecksilber verhält.Alternatively, the carbon soot can be omitted from the oxygen depletion cathode so that the electrode matrix consists only of Teflon and silver, whereby the silver takes on the function of the catalyst as well as that of electron conduction and accordingly such a high Ag loading is necessary that the particles separate touch and form conductive bridges with each other. As a carrier, both the wire mesh, a fine expanded metal, as known from battery technology, as also a felt made of silver, silver-plated nickel or silver-plated alkali-resistant material, e.g. Inconnel steel. It is essential that the silver catalyst is stable behaves towards mercury.

    Weitere bevorzugte Voraussetzungen für einen Parallelbetrieb von Amalgam- und Membranelektrolysen mit Sauerstoffverzehrkathoden sind die Einhaltung des Sulfatgehaltes bei <5 g/l, der durch entsprechende Fahrweise, z.B. kontinuierliches oder diskontinuierliches Ausschleusen des Sulfates mittels Fällung oder auch Teilstromfällung, beispielsweise unter Zufügung von CaCO3, BaCl2 oder BaCO3, oder aber auch insbesondere bei sehr sulfatarmen Salzen durch Ausschleusen eines Teilstroms der abgereicherten Sole eingestellt werden kann. Eine weitere Möglichkeit ist die Nanofiltration der Sole oder eines Teilstroms der Sole mittels ionenselektiver Membranen im Zulauf vor dem Membranelektrolyseur, oder aber ein anderes Trennverfahren, z.B. mittels Ionenaustauschern. Wichtig ist, dass nur der Teilstrom zum Membranelektrolyseur auf die genannte Sulfat-Ionenkonzentration eingestellt werden muss, mit dem Nebeneffekt, dass auch der Hauptstrom sich im Kreislauf allmählich auf einen niedrigeren Gehalt einstellt. Further preferred prerequisites for parallel operation of amalgam and membrane electrolysis with oxygen consumable cathodes are compliance with the sulfate content at <5 g / l, which is achieved by appropriate operation, for example continuous or discontinuous removal of the sulfate by means of precipitation or partial stream precipitation, for example with addition of CaCO 3 , BaCl 2 or BaCO 3 , or in particular in the case of very low-sulfate salts, can be adjusted by discharging a partial stream of the depleted brine. Another possibility is the nanofiltration of the brine or a partial flow of the brine by means of ion-selective membranes in the feed upstream of the membrane electrolyzer, or another separation process, for example using ion exchangers. It is important that only the partial flow to the membrane electrolyzer has to be set to the sulfate ion concentration mentioned, with the side effect that the main flow also gradually adjusts to a lower content in the circuit.

    Der SiO2-Gehalt in der NaCl-Sole kann durch Vermeidung freier Betonflächen im Salzvorrat (Solebunker) leicht bei < 5 ppm gehalten werden.The SiO 2 content in the NaCl brine can easily be kept at <5 ppm by avoiding free concrete areas in the salt store (brine bunker).

    Mit der Erfindung ergeben sich unter anderem die folgenden Vorteile:

  • Der Silber-Katalysator in der vorliegenden Matrix aus Ruß und Teflon der vorzugsweise verwendeten Sauerstoffverzehrkathode ist offenkundig völlig unempfindlich gegenüber Quecksilber.
    • The advantages of the invention include the following:
  • The silver catalyst in the present carbon black and Teflon matrix of the oxygen consumable cathode which is preferably used is obviously completely insensitive to mercury.

    • Die Menge des durch die Membran aus dem Anodenraum in den Kathodenraum einwandernden Quecksilbers ist unter Umständen beträchtlich und kann an makroskopischen Amalgam-Ablagerungen am Zellenboden erkannt werden. Eine Störung der Sauerstoffverzehrkathode wird dabei nicht beobachtet.The amount of immigrating through the membrane from the anode compartment into the cathode compartment Mercury can be considerable and can be macroscopic Amalgam deposits can be recognized on the cell bottom. A disturbance of the Oxygen consumption cathode is not observed.

    Quecksilber-Spitzenbelastungen mit einer Konzentration von bis zu 400 mg Hg/l in der Sole werden von der hinter der Membran in der Natronlauge betriebenen Sauerstoffverzehrkathode problemlos überstanden.Peak mercury levels with a concentration of up to 400 mg Hg / l in the brine are from the oxygen consumption cathode operated behind the membrane in the sodium hydroxide solution survived easily.

    Die übliche Konzentration von 150 - 200 mg/l Quecksilber bei normalen Spitzen sowie <10 mg/l Quecksilber im Normalbetrieb ist für den Betrieb der Sauerstoffverzehrkathode kein Hindernis.The usual concentration of 150-200 mg / l mercury at normal peaks and <10 mg / l mercury in normal operation is for the operation of the oxygen consumption cathode no barrier.

    Versuche haben ergeben, dass bei dem erfindungsgemäßen Verfahren Betriebsspannungen für die Elektrolysezelle angewendet werden können, die unter denen eines quecksilberfreien Betriebs liegen. Die Differenz beträgt typischerweise 30 bis 80 mV. Die Erniedrigung der Betriebsspannung bleibt unerwarteterweise über einen langen Betriebszeitraum (1 Jahr) stabil.Tests have shown that with the method according to the invention operating voltages can be used for the electrolytic cell, among which one mercury-free operation. The difference is typically 30 to 80 mV. The lowering of the operating voltage unexpectedly remains above one long operating period (1 year) stable.

    Das erfindungsgemäße Verfahren mit Sauerstoffverzehrkathode ermöglicht den parallelen Betrieb von klassischen Amalgamelektrolyseuren und Membranelektrolyseuren mit einem gemeinsamen Solekreislauf ohne weitere zusätzliche Aufbereitung der Sole.The method according to the invention with an oxygen consumption cathode enables parallel operation of classic amalgam electrolysers and membrane electrolysers with a common brine circuit without additional preparation the brine.

    Der Parallelbetrieb von Amalgamelektrolyseuren und Membranelektrolyseuren mit einem gemeinsamen Solekreislauf spielt bei der Umstellung von der Amalgamelektrolyse auf die Membranelektrolyse eine besondere Rolle.The parallel operation of amalgam electrolysers and membrane electrolysers with A common brine cycle plays in the changeover from amalgam electrolysis plays a special role in membrane electrolysis.

    Im folgenden wird das erfindungsgemäße Verfahren anhand von Figur 1 beispielhaft näher erläutert.

  • Figur 1 zeigt das Schema eines Parallelbetriebs einer Membranelektrolyse mit Sauerstoffverzehrkathoden und einer Amalgamelektrolyse.
    • The method according to the invention is explained in more detail below with reference to FIG. 1.
  • Figure 1 shows the scheme of a parallel operation of a membrane electrolysis with oxygen consuming cathodes and an amalgam electrolysis.

    • BeispieleExamples Beispiel 1example 1 Gesamtverfahren:Overall process:

    Die in der Salzlösestation 1 auf eine Betriebskonzentration von 300 bis 320 g/l aufgestärkte Sole 9 aus NaCl 12 durchläuft die gemeinsame Fäll- und Filterstation 2, in der je nach Salzherkunft Sulfat, Calzium, Magnesium abgetrennt werden unter Belassung einer für Amalgamelektrolysen zulässigen Restverunreinigung:

    Fe
    ∼ 0,12 mg/l
    Al
    ∼ 0,25 mg/l
    Ca
    ∼ 4,5 mg/l
    Mg
    ∼ 0,15 mg/l
    SO4 2-
    ∼7-10 g/l
    The brine 9 made of NaCl 12, which has been strengthened in the salt dissolving station 1 to an operating concentration of 300 to 320 g / l, passes through the common precipitation and filter station 2, in which, depending on the origin of the salt, sulfate, calcium, magnesium are separated off, leaving a residual contamination permissible for amalgam electrolysis:
    Fe
    ∼ 0.12 mg / l
    Al
    ∼ 0.25 mg / l
    Approx
    ∼ 4.5 mg / l
    Mg
    ∼ 0.15 mg / l
    SO 4 2-
    ∼7-10 g / l

    Die Fällung erfolgt im Nebenstrom mit 100 mg/l NaOH und 200 mg/l Na2CO3. Dabei fallen Ca, Mg, Fe sowie nur zu einem Teil Si und Al aus, die zusammen abgefiltert werden. Der Sulfatpegel kann lediglich über die als Dünnsole auszuschleusenden Wassermengen aus diversen Spül- und Prozessvorgängen auf einem Pegel von 10 bis 15 g/l gehalten werden. Dieser hohe Pegel ist für die Amalgamanlage unbedenklich.The precipitation takes place in a side stream with 100 mg / l NaOH and 200 mg / l Na 2 CO 3 . Ca, Mg, Fe and only some of the Si and Al precipitate out, which are filtered out together. The sulfate level can only be kept at a level of 10 to 15 g / l via the water quantities to be discharged as thin brine from various rinsing and process processes. This high level is harmless for the amalgam system.

    Die Sole 9 wird im Hauptstrom 10 in die vorhandene Amalgamelektrolyse 5 eingespeist. Im Teilstrom 11 zur Membranelektrolyse mit Sauerstoffverzehrkathode 4 wird zunächst in der Entchlorungsstation 7 das freie Chlor vernichtet und anschließend in einer Hydroxidfällungsstation 6 insbesondere der Gehalt an Al, Fe und Mg auf das für Membranzellen notwendige Maß abgesenkt. Im Ca/Mg-Ionenaustauscher 3 schließlich wird die immer notwendige abschließende Feinreinigung der Sole durch Abtrennung der störenden Ca-/Mg-Verunreinigungen durchgeführt. Es werden eingestellt:

  • Al <100 ppb
  • Fe <200 ppb
  • Ca + Mg <20 ppb
    • The brine 9 is fed into the existing amalgam electrolysis 5 in the main stream 10. In the partial stream 11 for membrane electrolysis with oxygen consumable cathode 4, the free chlorine is first destroyed in the dechlorination station 7 and then in a hydroxide precipitation station 6 in particular the content of Al, Fe and Mg is reduced to the level necessary for membrane cells. Finally, in the Ca / Mg ion exchanger 3, the final fine cleaning of the brine, which is always necessary, is carried out by removing the troublesome Ca / Mg impurities. The following are set:
  • Al <100 ppb
  • Fe <200 ppb
  • Ca + Mg <20 ppb

    • Nach Verlassen der Membranelektrolyse 4 mit Sauerstoffverzehrkathode vereinigt sich dieser Anolytstrom 13 mit dem Anolytstrom der Amalgamelektrolyseanlage 5. Der gemeinsame Anolytstrom 14 wird in der Salzlösestation 1 wieder mit Salz 12 aufkonzentriert.After leaving the membrane electrolysis 4 combined with oxygen cathode this anolyte stream 13 coincides with the anolyte stream of the amalgam electrolysis plant 5. The common anolyte stream 14 is again in the salt dissolving station 1 with salt 12 concentrated.

    Kann der Sulfatgehalt über eine moderate Ausschleusung von Sole gesteuert werden, bietet sich diese im Bereich niedrigster Salzkonzentration im Gesamtsystem am Auslass 8 hinter der Elektrolysezelle 4 an. In günstigen Fällen besonders guter Salzqualität kann dieser Auslass 8 auch den Pegel der ansonsten in der Hydroxidfällung 6 auszufällenden Ionen unter der Toleranzgrenze für die Membranelektrolyse halten.If the sulfate content can be controlled via a moderate discharge of brine, this is appropriate in the area of the lowest salt concentration in the overall system Outlet 8 behind the electrolytic cell 4. In favorable cases, particularly good salt quality can this outlet 8 also the level of the otherwise in the hydroxide precipitation 6th keep precipitated ions below the tolerance limit for membrane electrolysis.

    Betrieb einer Hg-resistenten Elektrode:

  • Es wurde eine für das Gesamtverfahren geeignete Elektrode unter Laborbedingungen getestet.
    • Operation of a mercury-resistant electrode:
  • An electrode suitable for the overall process was tested under laboratory conditions.

    • Eine Membranelektrolysezelle 4 mit einer Sauerstoffverzehrkathode von 100 cm2 Fläche aus Ruß, Teflon und Silberkatalysator auf versilbertem Nickelgewebe der Fa. NeNora (Typ ESNS) wurde mit quecksilberhaltiger NaCl-Sole betrieben. Die Quecksilber-Verunreinigung der NaCl-Sole schwankte zwischen einem Gehalt von 10 mg/l und 400 mg/l und simulierte einen Quecksilber-Pegel, wie er aus einer Amalgamelektrolyseanlage 5 bei typischem Normalbetrieb oder nach Stillstand der Anlage 5 als Spitzenwert auftritt. A membrane electrolysis cell 4 with an oxygen consumption cathode with an area of 100 cm 2 made of soot, Teflon and silver catalyst on silver-plated nickel fabric from NeNora (type ESNS) was operated with mercury-containing NaCl brine. The mercury contamination of the NaCl brine fluctuated between a content of 10 mg / l and 400 mg / l and simulated a level of mercury, such as occurs from an amalgam electrolysis plant 5 during typical normal operation or after plant 5 has come to a peak.

    Die Elektrolysezelle 4 zeigte überraschenderweise eine vollständige Quecksilber-Toleranz der Sauerstoffverzehrkathode über einen Betriebszeitraum von wenigstens 360 Tagen.The electrolytic cell 4 surprisingly showed a complete mercury tolerance the oxygen consumption cathode over an operating period of at least 360 days.

    Die Betriebsspannung der Elektrolysezelle 4 lag unter Normbedingungen (Stromdichte: 3kA/m2; Betriebstemperatur: 85°C; Solekonzentration: 210 g/l; NaOH--Konzentration: 32 Gew.-%) zwischen 1,92 und 1,97 Volt. Elektrolysezellen mit Sauerstoffverzehrkathode zeigten im quecksilberfreien Betrieb durchweg eine um 30 bis 80 mV höhere Betriebsspannung.The operating voltage of the electrolytic cell 4 was between 1.92 and 1.97 volts under standard conditions (current density: 3kA / m 2 ; operating temperature: 85 ° C; brine concentration: 210 g / l; NaOH concentration: 32% by weight). Electrolytic cells with an oxygen consumable cathode consistently showed a 30 to 80 mV higher operating voltage in mercury-free operation.

    Nach einer betriebsbedingten zwischenzeitlichen Abschaltung der Elektrolysezelle 4, bei der ursprünglich nicht mit einem Wiederbetrieb der Sauerstoffverzehrkathode gerechnet worden war, da sich Verstopfungen durch Amalgam in den kleinen (2 mm) Auslaufkanälen der Zelle gebildet hatten, konnte die Sauerstoffverzehrkathode der Elektrolysezelle 4 dennoch wieder in Betrieb genommen werden. Nach der Reinigung der Sauerstoffverzehrkathode wurde die Elektrolysezelle 4 mit derselben Kathode versuchsweise gestartet. Überraschenderweise arbeitete die Kathode erneut mit derselben niedrigen Betriebsspannung (1,92V) wie vor der Verstopfung des Auslaufs, bei der u.a. auch Natronlauge durch die Sauerstoffverzehrkathode in den Gasraum der Zelle 4 gedrückt worden war. Die Zelle 4 konnte nach der Störung noch über wenigstens 130 Tage problemlos weiterbetrieben werden.After an operational shutdown of the electrolytic cell 4, where the oxygen consumption cathode was not originally expected to operate again due to amalgam blockages in the small (2 mm) Had formed the cell's outlet channels, the oxygen consumption cathode could Electrolysis cell 4 can still be put into operation. After cleaning the electrolytic cell 4 became the oxygen consumable cathode with the same Trial started cathode. Surprisingly, the cathode worked again with the same low operating voltage (1.92V) as before the plugging of the Outlet, at which also sodium hydroxide solution through the oxygen consumption cathode in the Gas space of cell 4 had been pressed. Cell 4 failed after the disturbance can be operated without problems for at least 130 days.

    Das Beispiel zeigt, dass unter Verwendung der beschriebenen Elektrode das Gesamtverfahren problemlos ermöglicht wird, ohne dass man Störungen durch den Quecksilbergehalt der Sole 9, 11 erwarten muss.The example shows that using the described electrode the whole process is made possible without problems by the mercury content the brine 9, 11 must expect.

    Beispiel 2Example 2

    Eine typische Amalgamzellensole 9 mit einem Hg-Gehalt zwischen 7 und 14 mg/l und einer Ca-Beladung von 7 mg/l wurde mit einem Soledurchsatz von 1 bzw. 2 l/h durch einen Ca/Mg-Ionenaustauscher 3 des Typs TP 208 der Bayer AG geleitet. Das Bettvolumen betrug 100 cm3 bei einem Säulendurchmesser von 3,1 cm. Die Betriebstemperatur betrug 65°C, der pH-Wert der Sole lag bei 9,5.A typical amalgam cell brine 9 with an Hg content between 7 and 14 mg / l and a Ca loading of 7 mg / l was passed through a Ca / Mg ion exchanger 3 of the type TP 208 with a brine throughput of 1 or 2 l / h headed by Bayer AG. The bed volume was 100 cm 3 with a column diameter of 3.1 cm. The operating temperature was 65 ° C, the pH of the brine was 9.5.

    Der Effekt der Ca-Abtrennung unter Hg-Belastung wurde in zwei Testläufen untersucht: Bei einem Durchsatz von 2 l/h, d.h. 20 Bettvolumina pro Stunde, konnte der Ca/Mg-Pegel über eine Durchflussmenge von insgesamt 800 Bettvolumina unterhalb der spezifizierten Grenze von 20 ppb gehalten werden. Danach wurde der Ionenaustauscher gemäß Anwendervorschrift regeneriert. Insgesamt wurden 15 Belade- und Regenerierzyklen gefahren. Es zeigte sich, dass die aus quecksilberfreiem Betrieb bekannte Beladekapazität von 7 bis 9 g/l Ca + Mg pro Liter Ionenaustauscher zu 60 % im stabilen Dauerbetrieb erreicht werden konnte.The effect of Ca separation under Hg exposure was examined in two test runs: With a throughput of 2 l / h, i.e. 20 bed volumes per hour, the Ca / Mg level over a total flow of 800 bed volumes below the specified limit of 20 ppb. After that, the ion exchanger Regenerated according to user instructions. A total of 15 loading and Regeneration cycles driven. It turned out that the one known from mercury-free operation Loading capacity of 7 to 9 g / l Ca + Mg per liter of ion exchanger at 60% could be achieved in stable continuous operation.

    Bei Halbierung des Soledurchsatzes auf 1 l/h, d.h. 10 Bettvolumina pro Stunde, konnte die volle Beladekapazität von 7 bis 9 g/l Ca + Mg pro Liter Ionenaustauscher erzielt werden, so dass erst nach 1200 Bettvolumina Soledurchfluss der Ca/Mg-Grenzwert überschritten wurde und der Ionenaustauscher regeneriert werden musste. Dieser Zustand war über drei weitere Beladezyklen mit derselben Ionenaustauscherfüllung stabil.If the brine throughput is halved to 1 l / h, i.e. 10 bed volumes per hour, could the full loading capacity of 7 to 9 g / l Ca + Mg per liter of ion exchanger can be achieved so that the Ca / Mg limit value is reached only after 1200 bed volumes of brine flow was exceeded and the ion exchanger had to be regenerated. This state was over three more loading cycles with the same ion exchange filling stable.

    Claims (7)

    Verfahren zur Elektrolyse Natriumchlorid-haltiger Sole mit einem parallelen Betrieb von Amalgamelektrolyseuren 5 und Membranelektrolyseuren 4 mit Sauerstoffverzehrkathode mit einem gemeinsamen Solekreislauf, mit den Schritten: Zuführen der Sole 9 von einer Salzlösestation 1 zu einer Fäll- und Filterstation 2 und grobes Abtrennen von Sulfat-, Calzium- und Magnesiumionen aus der Sole 9 in der Fäll- und Filterstation 2, Aufteilen der Sole in einen Hauptstrom 10 und einen Teilstrom 11, Elektrolysieren des Hauptstroms 10 der Sole in einem Amalgamelektrolyseur 5, Vorbehandeln des Teilstroms 11 der Sole durch Entfernen von freiem Chlor in einer Entchlorungsstation 7, Ausfällen von insbesondere Al-, Fe- und Mg-Ionen in einer Hydroxidfällungsstation 6 und ggf. Abtrennen von Calzium-und Magnesiumionen aus der Sole 11 in der Station 3, insbesondere einem Ionenaustauscher, anschließend Elektrolysieren des Teilstroms 11 der Sole in einem Membranelektrolyseur 4 und Zusammenführen der Anolytströme des Membranelektrolyseurs 4 und des Amalgamelektrolyseur 5 in einen gemeinsamen Anolytstrom 14, wobei ein Membranelektrolyseur 4 mit einer quecksilberresistenten Sauerstoffverzehrkathode verwendet wird. Process for the electrolysis of sodium chloride-containing brine with a parallel operation of amalgam electrolyzers 5 and membrane electrolysers 4 with an oxygen consumable cathode with a common brine circuit, with the steps: Supplying the brine 9 from a salt dissolving station 1 to a precipitation and filter station 2 and roughly separating sulfate, calcium and magnesium ions from the brine 9 in the precipitation and filter station 2, Dividing the brine into a main stream 10 and a sub-stream 11, electrolyzing the main stream 10 of the brine in an amalgam electrolyzer 5, Pretreatment of the partial flow 11 of the brine by removing free chlorine in a dechlorination station 7, precipitation of in particular Al, Fe and Mg ions in a hydroxide precipitation station 6 and, if appropriate, removal of calcium and magnesium ions from the brine 11 in station 3, especially an ion exchanger, then electrolysing the substream 11 of the brine in a membrane electrolyzer 4 and Merging the anolyte streams of the membrane electrolyzer 4 and the amalgam electrolyzer 5 into a common anolyte stream 14, a membrane electrolyzer 4 with a mercury-resistant oxygen consumption cathode being used. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass eine Sauerstoffverzehrkathode bestehend wenigstens aus einem elektrisch leitenden metallischen, laugefesten Träger, bevorzugt einem Gewebe, Streckmetall oder Filz aus Silberdraht oder versilbertem Nickel- oder Inconel-Draht und einer mit dem Träger versinterten oder verpressten Katalysatormatrix aus Teflon, elektrisch leitfähigem Matrixmaterial, bevorzugt Ruß, und Katalysatormaterial, bevorzugt katalytisch aktiven Silberpartikeln oder anderen quecksilberverträglichen Katalysatorpartikeln, verwendet wird.A method according to claim 1, characterized in that an oxygen consumption cathode consisting of at least one electrically conductive metallic alkali-resistant carrier, preferably a fabric, expanded metal or felt made of silver wire or silver-plated nickel or Inconel wire and one with sintered or pressed catalyst matrix made of Teflon, electrically conductive matrix material, preferably carbon black, and catalyst material, preferably catalytically active silver particles or other mercury-compatible Catalyst particles is used. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass der Gehalt an Sulfationen in der Fäll- und Filterstation 2, insbesondere durch Fällung mit CaCO3, BaCl2 oder BaCO3 oder durch Nanoflitration auf <5 g/l eingestellt wird.Method according to claim 1 or 2, characterized in that the content of sulfate ions in the precipitation and filter station 2 is adjusted to <5 g / l, in particular by precipitation with CaCO 3 , BaCl 2 or BaCO 3 or by nanoflitration. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass vor dem Elektrolysieren des Teilstroms 11 der Sole im Membranelektrolyseur 4 Calzium- und Magnesiumionen aus der Sole 11 in einem Ca/Mg-Ionenaustauscher 3 bis zu einem Gehalt von <20 ppb abgetrennt werden.Method according to one of claims 1 to 3, characterized in that before the electrolysis of the substream 11 of the brine in the membrane electrolyzer 4 calcium and magnesium ions from brine 11 in a Ca / Mg ion exchanger 3 are separated to a content of <20 ppb. Verfahren nach Anspruch 4, dadurch gekennzeichnet, dass der Ca/Mg-Ionenaustauscher 3 ein quecksilberresistenter Ionenaustauscher ist.A method according to claim 4, characterized in that the Ca / Mg ion exchanger 3 is a mercury-resistant ion exchanger. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass der gemeinsame Anolytstrom 14 von Amalgamelektrolyseur 5 und Membranelektrolyseur 4 in die Salzlösestation 1 zurückgeführt wird.Method according to one of claims 1 to 5, characterized in that the common anolyte stream 14 from amalgam electrolyzer 5 and membrane electrolyzer 4 is returned to the salt dissolving station 1. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, dass der SiO2-Gehalt der Sole vor der Elektrolyse auf <5 ppm gehalten wird.Method according to one of claims 1 to 6, characterized in that the SiO 2 content of the brine is kept at <5 ppm before the electrolysis.
    EP00111000A 1999-06-12 2000-05-30 Parallel operating of amalgam and membrane electrolytic cells Expired - Lifetime EP1061158B1 (en)

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