EP0241633A1 - Process for the electrolysis of alkali chloride solutions - Google Patents

Process for the electrolysis of alkali chloride solutions Download PDF

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Publication number
EP0241633A1
EP0241633A1 EP87100085A EP87100085A EP0241633A1 EP 0241633 A1 EP0241633 A1 EP 0241633A1 EP 87100085 A EP87100085 A EP 87100085A EP 87100085 A EP87100085 A EP 87100085A EP 0241633 A1 EP0241633 A1 EP 0241633A1
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cathode
space
anode
gas
cell
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German (de)
French (fr)
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EP0241633B1 (en
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August Prof. Dr. Winsel
Rudolf Dr. Staab
Nikolaj Medic
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Hoechst AG
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Hoechst 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
    • C25B1/46—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in diaphragm cells
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
    • C25B11/095—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds at least one of the compounds being organic

Definitions

  • the invention relates to a method for the electrolysis of aqueous alkali metal chloride solutions by the membrane method in an electrolysis cell which is equipped with a porous cathode and in which the cell wall together with that side of the cathode which faces away from the cathode space form a closed space ("gas space"). forms.
  • the membrane cell for the alkali chloride electrolysis usually consists of two electrolysis chambers, each with a gas-generating electrode, which are separated from one another by a cation exchange membrane.
  • perforated materials such as perforated sheets, expanded metal, nets etc. are used as the electrode substrates.
  • the perforated electrode structure is necessary so that the resulting gas can be removed to the back of the electrode as quickly as possible, and thus the electrolyte resistance is not unnecessarily increased by the formation of a gas cushion between the anode and the cathode.
  • the object was therefore to develop a process for the electrolysis of alkali chloride solutions in which the formation of the gas cushion between the cathode and membrane is eliminated as far as possible.
  • this method should be suitable when using porous, foil-like Raney nickel cathodes.
  • the method is characterized in that a higher pressure is set in the cathode compartment than in the gas compartment
  • the gas space has a device (in practice mostly a pipe connection) for removing hydrogen and possibly condensed water.
  • Current densities of at least 500 A / m 2 are preferred, in particular at least 1000 A / m 2 .
  • a reasonable upper limit for the current density used is a maximum of 8000 A / m 2 , better a maximum of 6000 A / m 2, in particular a maximum of 4000 A / m 2.
  • No gas or gas containing oxygen should be introduced into the gas space of the cell according to the method of the invention.
  • Raney nickel electrodes behave particularly favorably, in particular those which consist of a nickel mesh which is covered on at least one side by a compressed mixture of Raney nickel and polytetrafluoroethylene. On the gas side, this Raney nickel electrode can also be covered with a film made of polytetrafluoroethylene. Such electrodes are described in DE-OS 33 42 969, to which express reference is made here.
  • the figure shows schematically a cross section through an electrochemical cell for the electrolysis of aqueous alkali chloride solutions, which is equipped with a porous, film-like cathode.
  • the cell is divided into an anode compartment (1), a cathode compartment (2) and a gas compartment (3).
  • saturated sodium chloride brine is pumped into the anode compartment (1) via a feed line (4).
  • Chloride ions are discharged to elemental chlorine at the anode (5).
  • Dimensionally stable anodes made of expanded titanium mesh or perforated sheets are preferably used, which are equipped with an activation in order to keep the chlorine overvoltage low.
  • the chlorine formed and the depleted brine leave the anode compartment (1) via line (6).
  • the cation exchange membrane (7) Between the anode compartment (1) and the cathode compartment (2) is the cation exchange membrane (7) through which sodium ions migrate into the cathode compartment (2).
  • Water is fed to the cell in the form of deionized water or dilute sodium hydroxide solution via the feed line (9).
  • Alkaline lye is formed in the cathode compartment (2) and leaves the cell via the opening (10).
  • Cathode compartment (2) and gas compartment (3) are separated from each other by the porous, foil-like Raney nickel cathode (8).
  • the gas compartment (3) is provided with an opening (11) through which the hydrogen generated is removed.
  • the porous, foil-like cathode (8) consists of a carrier mesh (13) which is made of nickel, for example, and at the same time serves for power supply and current distribution in the Raney nickel (14) catalyst.
  • the cathode can be provided with a thin, porous polytetrafluoroethylene layer (15) on the side facing the gas space.
  • This PTFE film is gas-permeable, but liquid-impermeable and is therefore used for gas-liquid separation in the cell. she is not absolutely necessary. If the electrolysis is operated without said film, however, an increased amount of condensate in the gas space (3) is to be expected.
  • the pressure is set in a simple manner by providing the line (10) with a throttle valve (12) or extending the line (10) upwards to an overflow in such a way that a defined lye column is formed.
  • the gas space is usually at atmospheric pressure, i.e. operated without pressure.
  • a 40 cm 2 membrane electrolysis cell equipped with an activated titanium anode and a cation exchange membrane from the company DU PONT of the type Nafion (R) NX 90209, was equipped with a Raney nickel electrode without PTFE foil on the gas space side in accordance with DE-OS 3 342 969 (area 40 cm 2 ) operated so that the cathode separated a 3 mm deep cathode space from a 10 mm deep gas space.
  • the operating conditions for the electrolysis were 80 ° C., 3 kA / m 2 , input molecule concentration of 300 g / l, anolyte concentration of 200 g / l and alkali concentration of 33% by weight.
  • the cell voltage was 3.12 V under the specified conditions.
  • the electrolysis was carried out under the same conditions, with the same electrodes and the same cation exchange membrane as in Example 1, but the gas space was flooded with sodium hydroxide solution. Only the pressure difference between the cathode compartment and the gas compartment was left at 25-30 cm WS (overpressure in the cathode compartment). 98% of the gas came from the gas space and 2% from the cathode space. At a current density of 3 kA / m 2 , the cell voltage was 3.15 V.
  • a 450 cm 2 membrane electrolysis cell with an activated titanium anode and a cation exchange membrane of the type Nafion ( R ) NX 90209 was equipped with a Raney nickel cathode with PTFE film on the gas space side in accordance with DE-OS 3 342 696.
  • the cathode was 9 cm wide and 50 cm long.
  • the electrolysis cell was operated horizontally, so that the anode came to lie above and the cathode below the cation exchange membrane.
  • the distance between the cathode and the membrane was about 4 mm.
  • the sodium hydroxide solution flowed longitudinally through the cathode compartment.
  • the brine in the cell was depleted from 300 g / l to about 220 g / l and 33% by weight sodium hydroxide solution was produced.
  • an overpressure in the cathode compartment of 150 cm WS 92% of the hydrogen formed left the cell via the gas compartment; an attack of sodium hydroxide solution in the gas space was not observed.
  • the cell voltage was 3.20 V.
  • the electrolysis was carried out in a 40 cm 2 cell under the same conditions as in Example 1, but there was pressure equalization between the cathode space and gas space. More than 90% of the hydrogen was generated in the cathode compartment and the cell voltage rose rapidly to values above 3.40 V.

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  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
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Abstract

A process is described for electrolyzing aqueous alkali metal chloride solutions in a membrane cell which contains an anode chamber with the anode and a cathode chamber with the cathode, the two chambers being separated from one another by a cation exchanger membrane. The cathode is porous and foil-like. The cathode and cation exchanger membrane form the actual cathode chamber filled with catholyte and the cathode and cell wall form a gas space. Water is fed into the cathode chamber and alkali metal hydroxide solution is withdrawn from it, hydrogen is withdrawn from the cathode chamber and gas space, and aqueous alkali metal chloride solution is fed into the anode chamber and gaseous chlorine, together with depleted alkali metal chloride solution, is withdrawn from it. A direct voltage which is at least the same as the decomposition voltage is applied to the cathode and anode. A higher pressure is established in the cathode chamber than in the gas space.

Description

Gegenstand der Erfindung ist ein Verfahren zur Elektrolyse von wäßrigen Alkalichlorid-Lösungen nach dem MembranVerfahren in einer Elektrolysezelle, die mit einer porösen Kathode ausgerüstet ist und in der die Zellwand zusammen mit dem der dem Kathodenraum abgewandten Seite der Kathode einen abgeschlossenen Raum ("Gasraum") bildet.The invention relates to a method for the electrolysis of aqueous alkali metal chloride solutions by the membrane method in an electrolysis cell which is equipped with a porous cathode and in which the cell wall together with that side of the cathode which faces away from the cathode space form a closed space ("gas space"). forms.

Etwa 50 % der Weltkapazität zur Erzeugung von elementarem Chlor werden in Elektrolysezellen produziert, die nach dem Amalgamverfahren arbeiten. Die theoretische Zersetzungsspannung von Alkalichlorid in der Quecksilberzelle beträgt etwa 3,15 bis 3,20 Volt. Demgegenüber ergibt sich eine theoretische Zersetzungsspannung von etwa 2,20 Volt, wenn man die Alkalichloridelektrolyse in einer Membranzelle mit wasserstofferzeugender Kathode durchführt. Durch die Einführung des Membranverfahrens läßt sich folglich theoretisch die Zellspannung um etwa 1 Volt senken, was in Zeiten steigender Energiekosten von erheblicher wirtschaftlicher Bedeutung ist.Around 50% of the world's capacity for the production of elemental chlorine is produced in electrolysis cells that use the amalgam process. The theoretical decomposition voltage of alkali chloride in the mercury cell is approximately 3.15 to 3.20 volts. In contrast, there is a theoretical decomposition voltage of about 2.20 volts if the alkali metal chloride electrolysis is carried out in a membrane cell with a hydrogen-generating cathode. By introducing the membrane process, the cell voltage can theoretically be reduced by about 1 volt, which is of considerable economic importance in times of increasing energy costs.

Die Membranzelle für die Alkalichlorid-Elektrolyse besteht üblicherweise aus zwei Elektrolysekammern mit jeweils einer gasentwickelnden Elektrode, die durch eine Kationenaustauschermembran voneinander getrennt sind.The membrane cell for the alkali chloride electrolysis usually consists of two electrolysis chambers, each with a gas-generating electrode, which are separated from one another by a cation exchange membrane.

Als Elektrodensubstrate werden in der Praxis durchbrochene Materialien wie Lochbleche, Streckgitter, Netze etc. verwendet. Die durchbrochene Elektrodenstruktur ist erforderlich, damit entstehendes Gas möglichst rasch zur Elektrodenrückseite abgeführt werden kann, und somit der Elektrolytwiderstand durch Bildung eines Gaspolsters zwischen Anode und Kathode nicht unnötig erhöht wird.In practice, perforated materials such as perforated sheets, expanded metal, nets etc. are used as the electrode substrates. The perforated electrode structure is necessary so that the resulting gas can be removed to the back of the electrode as quickly as possible, and thus the electrolyte resistance is not unnecessarily increased by the formation of a gas cushion between the anode and the cathode.

Wegen der Überspannungen für die Chlor- und Wasserstoffentwicklung verwendet man katalysierte Elektroden. Anodenseitig hat sich Titan als Elektrodensubstrat, welches mit Edelmetalloxiden aktiviert ist, bewährt. Für die kathodische Wasserstoffentwicklung setzt man Normalstahl-, Edelstahl- oder Nickelelektroden ein, die mit Edelmetallen oder Raney-Nickel aktiviert sein können. Insbesondere Raney-Nickel ist, nicht zuletzt aufgrund seiner extrem großen inneren Oberfläche, besonders geeignet, die Wasserstoffabscheidung zu katalysieren. Andererseits ist es jedoch schwierig, Raney-Nickel auf durchbrochene Elektrodenstrukturen wie Lochbleche oder Streckgitter aufzubringen. Raney-Nickelelektroden stehen deshalb bisher nur in Form von beschichteten Platten oder beschichteten Blechen zur Verfügung. Beim Einbau solcher flächigen Elektroden in eine Elektrolysezelle besteht dann aber die Gefahr des "Gasblaseneffektes", d.h. es bildet sich ein Gaspolster zwischen Kathode und Kationenaustauschermembran aus, da der Wasserstoff bevorzugt auf der Elektrodenvorderseite abgeschieden wird. Der Elektrolytwiderstand steigt an, und Zellspannung und Energieaufwand werden unwirtschaftlich hoch.Because of the surge voltages for the chlorine and hydrogen evolution, catalyzed electrodes are used. On the anode side, titanium has proven itself as an electrode substrate which is activated with noble metal oxides. Normal steel, stainless steel or nickel electrodes, which can be activated with precious metals or Raney nickel, are used for the cathodic hydrogen evolution. Raney nickel in particular, not least because of its extremely large inner surface, is particularly suitable for catalyzing hydrogen deposition. On the other hand, however, it is difficult to apply Raney nickel to perforated electrode structures such as perforated sheets or expanded metal. So far, Raney nickel electrodes have only been available in the form of coated plates or coated sheets. When installing such flat electrodes in an electrolytic cell, however, there is then the risk of the "gas bubble effect", i.e. a gas cushion forms between the cathode and the cation exchange membrane, since the hydrogen is preferably deposited on the front side of the electrode. The electrolyte resistance increases, and cell voltage and energy consumption become uneconomically high.

Ein einfaches Verfahren zur Herstellung einer porösen folienartigen Gaselektrode auf Basis von Raney-Nickel wird in der DE-OS 3 342 969 beschrieben. Jedoch tritt auch mit einer solchen Elektrode bei der Alkalichlorid- Elektrolyse der "Gasblaseneffekt, d.h. die Ausbildung eines Gaspolsters zwischen Elektrode und Membran auf.A simple method for producing a porous, foil-like gas electrode based on Raney nickel is described in DE-OS 3 342 969. However, the "gas bubble effect", i.e. the formation of a gas cushion between the electrode and the membrane, also occurs with such an electrode in alkali chloride electrolysis.

Es bestand daher die Aufgabe, ein Verfahren zur Elektrolyse von Alkalichloridlösungen zu entwickeln, bei dem die Ausbildung des Gaspolsters zwischen Kathode und Membran möglichst ausgeschaltet wird. Inbesondere sollte dieses Verfahren geeignet sein bei Einsatz von porösen folienartigen Raney-Nickel-Kathoden.The object was therefore to develop a process for the electrolysis of alkali chloride solutions in which the formation of the gas cushion between the cathode and membrane is eliminated as far as possible. In particular, this method should be suitable when using porous, foil-like Raney nickel cathodes.

Es wurde nun ein Verfahren zum Elektrolysieren von wäßrigen Alkalichlorid-Lösungen in einer Membranzelle gefunden, die einen Anodenraum mit Anode und einen Kathodenraum mit Kathode enthält, beide Räume durch eine Kationenaustauscher- Membran voneinander getrennt sind, wobei die Kathode porös und folienartig ist, Kathode und Kationenaustauscher- Membran den eigentlichen mit Katholyt gefüllten Kathodenraum bilden, Kathode und Zellenwand einen Gasraum bilden, man in den Kathodenraum Wasser einspeist und aus ihm Alkalihydroxyd-Lösung abzieht, aus Kathodenraum und Gasraum Wasserstoff abzieht, in den Anodenraum wäßrige Alkalichlorid-Lösung einspeist und aus ihm gasförmiges Chlor zusammen mit verarmter Alkalichlorid-Lösung abzieht und man an Kathode und Anode eine Gleichspannung anlegt, die . mindestens gleich der Zersetzungspannung ist. Das Verfahren ist dadurch gekennzeichnet, daß im Kathodenraum ein höherer Druck eingestellt wird, als im Gasraum.A method has now been found for the electrolysis of aqueous alkali metal chloride solutions in a membrane cell which contains an anode space with an anode and a cathode space with a cathode, both spaces being separated from one another by a cation exchange membrane, the cathode being porous and film-like, cathode and Cation exchanger membrane form the actual cathode space filled with catholyte, cathode and cell wall form a gas space, water is fed into the cathode space and alkali hydroxide solution is withdrawn from it, hydrogen is withdrawn from the cathode space and gas space, aqueous alkali chloride solution is fed into the anode space and from it withdrawing gaseous chlorine together with depleted alkali chloride solution and applying a direct voltage to the cathode and anode, which. is at least equal to the decomposition voltage. The method is characterized in that a higher pressure is set in the cathode compartment than in the gas compartment.

Aus der DE-OS 3 332 566 ist bereits ein elektrolytisches Verfahren zur Herstellung von Natronlauge unter Verwendung einer Kathionenaustauscher-Membran und einer folienförmigen Kathode bekannt. Dabei wird jedoch die Kathode als Sauerstoffdiffusionskathode betrieben, so daß kein Wasserstoff gewonnen wird.From DE-OS 3 332 566 an electrolytic process for the production of sodium hydroxide solution using a cathode exchange membrane and a film-shaped cathode is already known. However, the cathode is operated as an oxygen diffusion cathode so that no hydrogen is obtained.

Es ist ein Vorteil des erfindungsgemäßen Verfahrens, daß der überwiegende Teil des bei der Elektrolyse erzeugten Wasserstoffs durch die Kathode zu deren Rückseite transportiert wird, und dort in einfacher Weise entsorgt werden kann. Daher erfolgt die Trennung des Wasserstoffs von der produzierten Lauge bereits in der Elektrolysezelle.It is an advantage of the method according to the invention that the major part of the hydrogen generated in the electrolysis is transported through the cathode to the rear and can be disposed of there in a simple manner. For this reason, the hydrogen is separated from the lye produced in the electrolysis cell.

Auf diese Weise wird der "Gasblaseneffekt" erheblich reduziert und die Elektrolyse kann mit niedriger Zellspannung durchgeführt werden. Der Gasraum weist eine Einrichtung (in der Praxis meist ein Rohranschluß)zum Abführen von Wasserstoff und eventuell kondensiertem Wasser auf.In this way the "gas bubble effect" is considerably reduced and the electrolysis can be carried out with a low cell voltage. The gas space has a device (in practice mostly a pipe connection) for removing hydrogen and possibly condensed water.

Je höher die Stromdichte des erfindunggemäßen Verfahrens an der Kathode ist, umso höher ist die Tendenz zur Entwicklung eines Gaspolsters. Bevorzugt sind Stromdichten von mindestens 500 A/m2 insbesondere mindestens 1000 A/m2. Eine sinnvolle Obergrenze für die verwendete Stromdichte liegt bei maximal 8000 A/m2, besser maximal 6000 A/m2 insbesondere maximal 4000 A/m2. In den Gasraum der Zelle soll nach dem erfindungsgemäßen Verfahren kein Sauerstoff oder Sauerstoff enthaltendes Gas eingeführt werden.The higher the current density of the method according to the invention at the cathode, the higher the tendency to develop a gas cushion. Current densities of at least 500 A / m 2 are preferred, in particular at least 1000 A / m 2 . A reasonable upper limit for the current density used is a maximum of 8000 A / m 2 , better a maximum of 6000 A / m 2, in particular a maximum of 4000 A / m 2. No gas or gas containing oxygen should be introduced into the gas space of the cell according to the method of the invention.

Besonders günstig verhalten sich beim erfindungsgemäßen Verfahren als Kathode Raney-Nickel-Elektroden, insbesondere solche die aus einem Nickelnetz bestehen, das mindestens auf einer Seite von einem komprimierten Gemisch aus Raney-Nickel und Polytetrafluoräthylen bedeckt ist. Gasseitig kann diese Raney-Nickel-Elektrode noch mit einer Folie aus Polytetrafluoräthylen überzogen sein. Solche Elektroden sind beschrieben inder DE-OS 33 42 969 auf die hier ausdrücklich Bezug genommen wird.In the process according to the invention, Raney nickel electrodes behave particularly favorably, in particular those which consist of a nickel mesh which is covered on at least one side by a compressed mixture of Raney nickel and polytetrafluoroethylene. On the gas side, this Raney nickel electrode can also be covered with a film made of polytetrafluoroethylene. Such electrodes are described in DE-OS 33 42 969, to which express reference is made here.

Der Druckunterschied zwischen Katholytraum und Gasraum beträgt ca. 10 mbar bis 0,5 bar, insbesondere 20 mbar bis 0,2 bar (1 mbar = 1 hPa).The pressure difference between the catholyte space and the gas space is approximately 10 mbar to 0.5 bar, in particular 20 mbar to 0.2 bar (1 mbar = 1 hPa).

Da sich in einer vertikalen Zelle ein Laugedruckgradient aufbaut, ist es günstig das Verfahren in einer Zelle zu betreiben, bei der Kathode, Anode und Membran horizontal angeordnet sind, so daß die vom Anolyt bedeckte Anode oberhalb der Membran und die vom Katholyt bedeckte Kathode unterhalb der Kationenaustauschermembran zu liegen kommt und der Gasraum unterhalb der porösen folienartigen Kathode angeordnet ist. Bei dieser Ausgestaltung herrscht an jeder Stelle der Kathode der gleiche Druck. Damit wird verhindert, daß an Stellen mit höheren Laugedrücken Lauge durch die kathode in den "Gasraum" übertritt.Since a lye pressure gradient builds up in a vertical cell, it is advantageous to operate the method in a cell in which the cathode, anode and membrane are arranged horizontally, so that the anode covered by the anolyte above the membrane and the cathode covered by the cathode below Cation exchange membrane comes to rest and the gas space is arranged below the porous film-like cathode. With this configuration, the same pressure prevails at every point on the cathode. This prevents alkali from passing through the cathode into the "gas space" at locations with higher alkali pressures.

Die Figur zeigt schematisch einen Querschnitt durch eine elektrochemische Zelle zur Elektrolyse wäßriger Alkalichloridlösungen, die mit einer porösen, folienartigen Kathode ausgerüstet ist. Die Zelle ist in einen Anodenraum (1), einen Kathodenraum (2) und einen Gasraum (3) unterteilt. Über eine Zuleitung (4) wird beispielsweise gesättigte Natriumchlorid-Sole in den Anodenraum (1) gepumpt. An der Anode (5) werden Chloridionen zu elementarem Chlor entladen. Vorzugsweise werden dimensionsstabile Anoden aus Titan-Streckgittern oder -Lochblechen eingesetzt, die mit einer Aktivierung ausgestattet sind, um die Chlorüberspannung gering zu halten. Über Leitung (6) verlassen das gebildete Chlor und die verarmte Sole den Anodenraum (1). Zwischen Anodenraum (1) und dem Kathodenraum (2) befindet sich die Kationenaustauscher-Membran (7) durch die Natriumionen in den Kathodenraum (2) wandern.The figure shows schematically a cross section through an electrochemical cell for the electrolysis of aqueous alkali chloride solutions, which is equipped with a porous, film-like cathode. The cell is divided into an anode compartment (1), a cathode compartment (2) and a gas compartment (3). For example, saturated sodium chloride brine is pumped into the anode compartment (1) via a feed line (4). Chloride ions are discharged to elemental chlorine at the anode (5). Dimensionally stable anodes made of expanded titanium mesh or perforated sheets are preferably used, which are equipped with an activation in order to keep the chlorine overvoltage low. The chlorine formed and the depleted brine leave the anode compartment (1) via line (6). Between the anode compartment (1) and the cathode compartment (2) is the cation exchange membrane (7) through which sodium ions migrate into the cathode compartment (2).

Über die Zuleitung (9) wird Wasser der Zelle in Form von entionisiertem Wasser oder verdünnter Natronlauge zugeführt. Im Kathodenraum (2) wird Alkalilauge gebildet, die die Zelle über die Öffnung (10) verläßt. Kathodenraum (2) und Gasraum (3) werden durch die poröse, folienartige Raney-Nickel-Kathode (8) voneinander getrennt, Der Gasraum (3) ist mit einer Öffnung (11) versehen, über die der erzeugte Wasserstoff entfernt wird.Water is fed to the cell in the form of deionized water or dilute sodium hydroxide solution via the feed line (9). Alkaline lye is formed in the cathode compartment (2) and leaves the cell via the opening (10). Cathode compartment (2) and gas compartment (3) are separated from each other by the porous, foil-like Raney nickel cathode (8). The gas compartment (3) is provided with an opening (11) through which the hydrogen generated is removed.

Wie in der Figur zu erkennen ist, besteht die poröse, folienartige Kathode (8) aus einem Trägernetz (13), das z.B. aus Nickel gefertigt ist und gleichzeitig für Stromversorgung und Stromverteilung im Katalysator aus Raney-Nickel (14) dient. Auf der dem Gasraum zugewandten Seite kann die Kathode mit einer dünnen, porösen Polytetrafluorethylenschicht (15) versehen sein. Diese PTFE-Folie ist gasdurchlässig, jedoch flüssigkeitsundurchlässig und dient somit zur Gas-Flüssigkeitstrennung in der Zelle. Sie ist nicht zwingend erforderlich. Falls die Elektrolyse ohne besagte Folie betrieben wird, ist jedoch mit einem erhöhten Kondensatanfall im Gasraum (3) zu rechnen.As can be seen in the figure, the porous, foil-like cathode (8) consists of a carrier mesh (13) which is made of nickel, for example, and at the same time serves for power supply and current distribution in the Raney nickel (14) catalyst. The cathode can be provided with a thin, porous polytetrafluoroethylene layer (15) on the side facing the gas space. This PTFE film is gas-permeable, but liquid-impermeable and is therefore used for gas-liquid separation in the cell. she is not absolutely necessary. If the electrolysis is operated without said film, however, an increased amount of condensate in the gas space (3) is to be expected.

Die Druckdifferenz zwischen Kathodenraum (2) und Gasraum beträgt 10 - 5000 cm Wassersäule (cm WS) insbesondere 20 - 200 cm WS (1 cm WS = 0,98 hPa). In der Praxis erfolgt die Druckeinstellung in einfacher Weise dadurch, daß man die Leitung (10) mit einem Drosselventil (12) versieht oder die Leitung (10) nach oben zu einem Überlauf hin verlängert, daß sich eine definierte Laugesäule ausbildet. Der Gasraum wird üblicherweise mit Atmosphärendruck, d.h. überdrucklos betrieben.The pressure difference between the cathode compartment (2) and the gas compartment is 10 - 5000 cm water column (cm WS), in particular 20 - 200 cm WS (1 cm WS = 0.98 hPa). In practice, the pressure is set in a simple manner by providing the line (10) with a throttle valve (12) or extending the line (10) upwards to an overflow in such a way that a defined lye column is formed. The gas space is usually at atmospheric pressure, i.e. operated without pressure.

Unter den beschriebenen Bedingungen entweichen mehr als 90 % des entstehenden Wasserstoffs über den Gasraum.Under the conditions described, more than 90% of the hydrogen produced escapes through the gas space.

Die Erfindung wird im folgenden anhand der Figur und der Beispiele näher erläutert.The invention is explained in more detail below with reference to the figure and the examples.

Beispiel 1example 1

Eine 40 cm2-Membranelektrolysezelle, ausgerüstet mit einer aktivierten Titananode und einer Kationenaustauscher- membran der Firma DU PONT vom Typ Nafion (R )NX 90209, wurde mit einer Raney-Nickel-Elektrode ohne PTFE-Folie auf der Gasraumseite gemäß DE-OS 3 342 969 (Fläche 40cm2) so betrieben, daß die Kathode einen 3 mm tiefen Kathodenraum von einem 10 mm tiefen Gasraum trennte. Die Betriebsbedingungen der Elektrolyse waren 80°C, 3 kA/m2, Eingangssolekonzentration von 300 g/l, Anolytkonzentration von 200 g/l und Laugekonzentration von 33 Gew.-%. Der Überdruck des Katholyts betrug 25-30 mbar (= 25-30 hPa), der des Gasraumes 0 mbar, bezogen auf Atmosphäre. Unter diesen Bedingungen kamen 99 % des produzierten Wasserstoffs aus dem Gasraum und lediglich 1 % aus dem Kathodenraum. Die Zellspannung betrug bei den angegebenen Bedingungen 3,12 V.A 40 cm 2 membrane electrolysis cell, equipped with an activated titanium anode and a cation exchange membrane from the company DU PONT of the type Nafion (R) NX 90209, was equipped with a Raney nickel electrode without PTFE foil on the gas space side in accordance with DE-OS 3 342 969 (area 40 cm 2 ) operated so that the cathode separated a 3 mm deep cathode space from a 10 mm deep gas space. The operating conditions for the electrolysis were 80 ° C., 3 kA / m 2 , input molecule concentration of 300 g / l, anolyte concentration of 200 g / l and alkali concentration of 33% by weight. The overpressure of the catholyte was 25-30 mbar (= 25-30 hPa), that of the gas space 0 mbar, based on the atmosphere. Under these conditions, 99% of the hydrogen produced came from the gas space and only 1% from the cathode space. The cell voltage was 3.12 V under the specified conditions.

Beispiel 2Example 2

Die Elektrolyse wurde unter den gleichen Bedingungen, mit den gleichen Elektroden und der gleichen Kationenaustauschermembran wie in Beispiel 1 durchgeführt, jedoch wurde der Gasraum mit Natronlauge geflutet. Lediglich die Druckdifferenz zwischen Kathodenraum und Gasraum wurde bei 25-30 cm WS (Überdruck im Kathodenraum) belassen. 98 % des Gases kamen aus dem Gasraum und 2 % aus dem Kathodenraum. Bei einer Stromdichte von 3 kA/m2 betrug die Zellspannung 3,15 V.The electrolysis was carried out under the same conditions, with the same electrodes and the same cation exchange membrane as in Example 1, but the gas space was flooded with sodium hydroxide solution. Only the pressure difference between the cathode compartment and the gas compartment was left at 25-30 cm WS (overpressure in the cathode compartment). 98% of the gas came from the gas space and 2% from the cathode space. At a current density of 3 kA / m 2 , the cell voltage was 3.15 V.

Beispiel 3Example 3

Eine 450 cm2-Membranelektrolysezelle mit einer aktivierten Titananode und einer Kationenaustauschermembran vom Typ Nafion (R)NX 90209 wurde mit einer Raney-Nickel-Kathode mit PTFE-Folie auf der Gasraumseite gemäß DE-OS 3 342 696 ausgerüstet. Die Kathode hatte eine Breite von 9 cm und eine Länge von 50 cm. Die Elektrolysezelle wurde horizontal betrieben, so daß die Anode oberhalb und die Kathode unterhalb der Kationenaustauschermembran zu liegen kam. Der Abstand der Kathode von der Membran betrug dabei etwa 4mm. Im Kathodenraum befand sich als Abstandshalter eingrobmaschiges Polypropylennetz. Der Kathodenraum wurde in Längsrichtung von der Natronlauge durchströmt. Bei einer Betriebstemperatur von 80°C und einer Stromdichte von 3 kA/m2 wurde die Sole in der Zelle von 300 g/l auf etwa 220 g/l abgereichert und 33 Gew.-%ige Natronlauge produziert. Bei einem Überdruck im Kathodenraum von 150 cm WS verließen 92 % des gebildeten Wasserstoffs über den Gasraum die Zelle; ein Anfall von Natronlauge im Gasraum wurde nicht beobachtet. Unter den angegebenen Bedingungen betrug die Zellspannung 3,20 V.A 450 cm 2 membrane electrolysis cell with an activated titanium anode and a cation exchange membrane of the type Nafion ( R ) NX 90209 was equipped with a Raney nickel cathode with PTFE film on the gas space side in accordance with DE-OS 3 342 696. The cathode was 9 cm wide and 50 cm long. The electrolysis cell was operated horizontally, so that the anode came to lie above and the cathode below the cation exchange membrane. The distance between the cathode and the membrane was about 4 mm. In the cathode compartment there was a single-mesh polypropylene mesh as a spacer. The sodium hydroxide solution flowed longitudinally through the cathode compartment. At an operating temperature of 80 ° C and a current density of 3 kA / m 2 , the brine in the cell was depleted from 300 g / l to about 220 g / l and 33% by weight sodium hydroxide solution was produced. With an overpressure in the cathode compartment of 150 cm WS, 92% of the hydrogen formed left the cell via the gas compartment; an attack of sodium hydroxide solution in the gas space was not observed. Under the specified conditions, the cell voltage was 3.20 V.

VergleichsbeispielComparative example

Die Elektrolyse wurde in einer 40 cm2-Zelle unter den gleichen Bedingungen wieim Beispiel 1 durchgeführt, jedoch herrschte Druckausgleich zwischen Kathodenraum und Gasraum. Mehr als 90 % des Wasserstoffs entstanden im Kathodenraum, und die Zellspannung stieg rasch auf Werte über 3,40 V an.The electrolysis was carried out in a 40 cm 2 cell under the same conditions as in Example 1, but there was pressure equalization between the cathode space and gas space. More than 90% of the hydrogen was generated in the cathode compartment and the cell voltage rose rapidly to values above 3.40 V.

Claims (7)

1. Verfahren zum Elektrolysieren von wäßrigen Alkalichlorid- Lösungen in einer Membranzelle, die einen Anodenraum mit Anode und einen Kathodenraum mit Kathode enthält, wobei beide Räume durch eine Kationenaustauscher-Membran voneinander getrennt sind, die Kathode porös und folienartig ist, Kathode und Kationenaustauschermembran den eigentlichen mit Katholyt gefüllten Kathodenraum bilden, Kathode und Zellenwand einen Gasraum bilden, man in den Kathodenraum Wasser einspeist und aus ihm Alkalihydroxyd-Lösung abzieht, aus Kathodenraum und Gasraum Wasserstoff abzieht, in den Anodenraum wäßrige Alkalichlorid-Lösung einspeist und aus ihm gasförmiges Chlor zusammen mit verarmter Alkalichlorid-Lösung abzieht, und man an Kathode und Anode eine Gleichspannung anlegt, die mindestens gleich der Zersetzungsspannung ist, dadurch gekennzeichnet, daß im Kathodenraum ein höherer Druck eingestellt wird, als im Gasraum.1. Process for the electrolysis of aqueous alkali chloride solutions in a membrane cell which contains an anode space with an anode and a cathode space with a cathode, both spaces being separated from one another by a cation exchange membrane, the cathode being porous and film-like, the cathode and cation exchange membrane being the actual one Form cathode space filled with catholyte, form cathode and cell wall a gas space, water is fed into the cathode space and alkali hydroxide solution is withdrawn from it, hydrogen is withdrawn from the cathode space and gas space, aqueous alkali chloride solution is fed into the anode space and gaseous chlorine from it together with depleted chlorine Alkaline chloride solution is drawn off, and a DC voltage which is at least equal to the decomposition voltage is applied to the cathode and anode, characterized in that a higher pressure is set in the cathode compartment than in the gas compartment. 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der Kathode kein Sauerstoff zugeführt wird.2. The method according to claim 1, characterized in that no oxygen is supplied to the cathode. 3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die poröse, folienartige Kathode eine Raney-Nickel-Elektrode ist, die besteht aus einem Nickelnetz, das mindestens auf einer Seite von einem komprimierten Gemisch aus Raney-Nickel und Polytetrafluoräthylen bedeckt ist.3. The method according to claim 1, characterized in that the porous, film-like cathode is a Raney nickel electrode, which consists of a nickel network, which is covered on at least one side by a compressed mixture of Raney nickel and polytetrafluoroethylene. 4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, daß die Raney-Nickel-Elektrode auf der Seite des Gasraums mit einer Folie aus Polytetrafluoräthylen überzogen ist.4. The method according to claim 3, characterized in that the Raney nickel electrode is coated on the side of the gas space with a film made of polytetrafluoroethylene. 5. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der Druck im Katholytraum um 10 mbar bis 0,5 bar, insbesondere um 20 mbar bis 0,2 bar, höher ist als im Gasraum.5. The method according to claim 1, characterized in that the pressure in the catholyte space by 10 mbar to 0.5 bar, in particular by 20 mbar to 0.2 bar, is higher than in the gas space. 6. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Elektrolysezelle horizontal betrieben wird, so daß die vom Anolyt bedeckte Anode oberhalb der Membran, die vom Katholyt bedeckte Kathode unterhalb der Kationenaustauschermembran und der Gasraum unterhalb der porösen, folienartigen Kathode zu liegen kommen.6. The method according to claim 1, characterized in that the electrolytic cell is operated horizontally, so that the anode covered by the anolyte above the membrane, the cathode covered by the catholyte below the cation exchange membrane and the gas space come to lie below the porous, film-like cathode. 7. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Zelle mit einer Stromdichte von mindestens 500 A/m2 (bezogen auf die Kathodenfläche) betrieben wird.7. The method according to claim 1, characterized in that the cell is operated with a current density of at least 500 A / m 2 (based on the cathode surface).
EP87100085A 1986-01-14 1987-01-07 Process for the electrolysis of alkali chloride solutions Expired - Lifetime EP0241633B1 (en)

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DE19863600759 DE3600759A1 (en) 1986-01-14 1986-01-14 METHOD FOR THE ELECTROLYSIS OF ALKALICHLORIDE SOLUTIONS
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DE3600759A1 (en) 1987-07-16
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ATE54343T1 (en) 1990-07-15
CA1314836C (en) 1993-03-23
DE3763506D1 (en) 1990-08-09

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