EP0848764A1 - Electrolytic method for the production of sodium and aluminium chloride - Google Patents

Electrolytic method for the production of sodium and aluminium chloride

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Publication number
EP0848764A1
EP0848764A1 EP96930164A EP96930164A EP0848764A1 EP 0848764 A1 EP0848764 A1 EP 0848764A1 EP 96930164 A EP96930164 A EP 96930164A EP 96930164 A EP96930164 A EP 96930164A EP 0848764 A1 EP0848764 A1 EP 0848764A1
Authority
EP
European Patent Office
Prior art keywords
sodium
aluminum
electrolyte
anode
cathode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP96930164A
Other languages
German (de)
French (fr)
Other versions
EP0848764B1 (en
Inventor
Hermann Pütter
Günther Huber
Luise Spiske
Hans Stark
Dieter SCHLÄFER
Gerhard Pforr
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BASF SE
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BASF SE
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Publication of EP0848764A1 publication Critical patent/EP0848764A1/en
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/02—Electrolytic production, recovery or refining of metals by electrolysis of melts of alkali or alkaline earth metals
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/24—Halogens or compounds thereof

Definitions

  • the present invention relates to a new process for the electrochemical production of sodium and aluminum chloride.
  • the invention further relates to an electrolysis cell suitable for carrying out this method and to a method for cleaning this cell.
  • Sodium is an important inorganic basic product that is used, for example, for the production of sodium amide and sodium alcoholates. It is obtained technically after the Downs process by electrolysis of molten table salt. This process has a high energy consumption of over 10 kWh / kg sodium (Büchner et al., Industrial Inorganic Chemistry, 2nd edition, Verlag Chemie, p. 228 f). Furthermore, the method has the serious disadvantage that the electrolysis cells are destroyed by the solidification of the molten salt when it is switched off.
  • Aluminum chloride is mainly used as a catalyst, e.g. in Friedel-Crafts reactions. It is largely manufactured by direct chlorination of molten aluminum. (Büchner et al., Industrial Inorganic Chemistry, 2nd edition, Verlag Chemie, p. 262). A substantial part of the energy that was used in the form of electrical current for the electrolytic production of chlorine and aluminum is released unused.
  • GB-A 2 056 757 describes a process for lowering the melting points of alkali metal tetrachloroaluminates by adding an alkali metal fluoride and using such mixtures as the electrolyte.
  • DE-A 37 18 920 relates to the coupled electrochemical production of an alkali metal and an alkali metal-metal halide compound such as sodium tetrachloroaluminate.
  • the by-product thus formed in addition to the alkali metal is, however, unattractive for production on an industrial scale.
  • the formation of sodium tetrachloroaluminate from sodium chloride and aluminum chloride automatically follows the formation of the aluminum chloride. According to the teaching of Scripture, a concentration of
  • Aluminum chloride can be avoided to damage the sepa- avoid torsion between the anode and cathode space and an increase in cell voltage.
  • the object was to provide a process which allows sodium to be produced more economically than the Downs process.
  • As a by-product a substance that can be used on an industrial scale is to be obtained. Both process products are said to be so pure that further elaborate cleaning steps are not necessary.
  • Another aspect of the task was to find a method which allows the electrolysis process to be carried out several times in the same electrolysis cell. It was also part of the task to find an electrolytic cell suitable for this process. Furthermore, a method for cleaning the electrolysis cell used for the reaction should be found.
  • a process for the electrochemical production of sodium and aluminum chloride which is characterized in that a molten, essentially from an electrolytic cell with aluminum as the anode and sodium as the cathode, which are separated from one another by a sodium ion-conducting solid electrolyte Sodium tetrachloroaluminate existing electrolytes electrolyzed in the anode compartment, thereby evolving aluminum chloride evaporates from the electrolytic cell and withdraws sodium from the cathode compartment.
  • the method according to the invention is operated in an electrolytic cell with an aluminum anode.
  • This is a sacrificial anode, which dissolves during the reaction, so that aluminum must be added in continuous operation.
  • Aluminum can be in the form of plates, but preferably in the form of small pieces of metal that can be filled with large ones
  • the particle size can generally be 0.01 to 10 mm, preferably 0.1 to 2 mm.
  • Commercially available aluminum with a purity of approx. 99.3% or aluminum scrap with a purity of 95% are possible.
  • the anode-side power supply is preferably via aluminum rods, which can be replaced from the outside in continuous operation of the cell without interrupting the process.
  • the cathode consists of sodium, which is liquid at the temperatures required to liquefy the electrolyte. At the beginning of the electrolysis, the sodium is advantageously brought into the cathode compartment in liquid form.
  • the sodium formed in the process according to the invention can be removed in a technically simple manner by an overflow from the cathode compartment.
  • the cathodic power supply can e.g. over aluminum rods.
  • the anode and cathode compartments are separated from each other by a solid electrolyte that conducts sodium ions.
  • Ceramic materials such as NASICON®, the composition of which is specified in EP-A 553 400, are suitable for this purpose. Glasses which conduct sodium ions are also suitable, as are zeolites and feldspar. However, ⁇ "aluminum oxide is preferred.
  • the electrolyte for starting the reaction is preferably produced by melting stoichiometric amounts of sodium chloride and aluminum chloride.
  • the amount of electrolyte does not change during the reaction in continuous operation.
  • aluminum chloride is evaporated from the anode compartment.
  • the anode compartment is therefore above the electrolyte surface with a drain, e.g. in the form of a tube, through which the aluminum chloride can escape.
  • the discharge device is followed by a storage vessel in which the aluminum chloride is desublimated by lowering the temperature compared to the electrolysis cell. This is usually reflected as a wall covering that can be removed by mechanical methods.
  • the reaction temperature is generally at the liquefaction temperature of the electrolyte as the lower limit (approx. 150 ° C.) and 400 ° C., preferably 250 to 350 ° C.
  • the electrical potential is generally 2 to 5 V, the cathodic current density 1 to 10 kA / m 2 .
  • the electrolyte can be pumped around during the reaction. This can be done by a pump, but blowing in an inert gas such as argon is preferred. This gas feed supports the evaporation of the aluminum chloride from the anode compartment.
  • the externally heatable cell is constructed analogously to a tube bundle circulation evaporator (see FIG. 1), i.e. a cylinder, closed at the top, made of ⁇ "aluminum oxide 1, which is filled with sodium 2, contains an overflow 3, and is connected to a voltage source as a cathode via an aluminum rod 4, projects into the anode chamber 5, which has solid aluminum parts and The anode is connected to a voltage source via an aluminum rod 6.
  • a circulation tube 7 into which inert gas is blown serves to circulate the electrolyte.
  • Aluminum chloride is discharged through the discharge line 8.
  • the devices for dosing sodium chloride and preferably aluminum powder are advantageously arranged so that the solids are directly in de n electrolytes fall, i.e. they are preferably arranged directly above the anode space.
  • the starting compounds aluminum and sodium chloride introduce foreign substances such as iron, silicon and potassium into the electrolytic cell, which can concentrate in the electrolyte. These can be reduced by partial streams of the electrolyte, about 1 to 10% by weight, based on the total amount of electrolyte, being electrolyzed in the side stream.
  • Anodic electrolysis on graphite electrodes reduces the oxide content of the melt. Iron and any other heavy metals present in the liquid electrolyte can be deposited on iron cathodes.
  • the problematic handling of the solidified electrolyte melt with residues of metallic sodium can be omitted if the melt is gassed with SO 2 during cooling.
  • the melt remains dough between 150 and approx. 70 ° C. with the absorption of SO 2 , and it becomes liquid at lower temperatures. This means that it can be easily removed from the cell, which greatly simplifies repairs.
  • the liquid, SO 2 -containing melt can be filtered, which is particularly advantageous for the removal of potassium compounds. Then the liquid S0 2 -containing melt can be in the Electrolysis cell are filled back, where the SO 2 can be driven off with heating to approx. 165 ° C. in the presence of an excess of sodium chloride.
  • the solid electrolyte By periodically reversing the polarity of the cell, the solid electrolyte can be cleaned of cationic impurities such as potassium ions.
  • the electrochemical process according to the invention for the coupling production of sodium and aluminum chloride requires only approx. 50% of the amount of energy which is required for the production of sodium by the Downs process.
  • the operating temperatures are significantly lower than those of the mentioned method (approx. 650 ° C), which considerably simplifies the selection and processing of the reaction cells. Parking the electrolysis cells is possible without damage.
  • the products obtained according to the invention are highly pure.
  • aluminum chloride is colorless, which makes it particularly attractive for applications in which the color of the end product is an essential feature.
  • the sodium yield is practically quantitative, the yield of aluminum chloride is well over 90%.
  • the process can also be used for the production of sodium and other metal halides which are volatile under the reaction conditions, for example SiCl 4 , GeCl 4 , TiCl 4 .
  • the anode and electrolytes must each have the corresponding metal.
  • the electrolysis cell according to FIG. 1 used to carry out the method consisted of a standing tube (with an inner diameter of 50 mm and a length of 400 mm) made of borosilicate glass, in which the anode current supply in the form of a hollow cylinder made of aluminum was tightly clamped was.
  • the sodium ion-conducting solid electrolyte made of ⁇ "aluminum oxide (25 mm outer diameter, 210 mm long) was flanged together with the cathode current supply at the lower end.
  • the upper part of the tube was provided with connecting pieces which were used for filling with electrolyte, aluminum and Sodium chloride and were used to discharge the AlCl 3 vapors.
  • the cell was heated with hot air.
  • the anode was introduced in the form of a bed of aluminum shredder.
  • the cathode was used liquid sodium which was presented at the start of the reaction.
  • the sodium formed in the reaction drained down in free overflow.
  • the AlCl 3 vapors were precipitated in an air-cooled de-sublimator.
  • the external circulation with inert gas supply was used to circulate the melt.
  • the electrolysis cell was heated to 280 ° C. In the melting vessel, 85 g of sodium were melted at 150 ° C. and added to the cathode compartment until it was filled to the overflow. 485 g of A1C1 3 and 215 g of NaCl were initially introduced as solids and stirred under argon. After heating to 165 ° C., the mixture formed a homogeneous liquid phase which was filled into the anode compartment. 150 g of aluminum with a grain size of 0.4 to 1.5 mm were introduced into the anode compartment. The liquid electrolyte was kept in circulation by means of argon gas at the bottom of the circulation line. A current of 30 A was impressed, the cell voltage was determined to be 3.5 V.
  • the current density was 2200 A / m 2 with a surface area of 137 cm 2 (at 30 A). 15 minutes after switching on the power, the rise of AlCl 3 vapors was observed for the first time, which was reflected in the de-sublimator. At intervals of 15 minutes, 16.4 g of NaCl were metered in as a solid. The AlCl 3 development came to a standstill for a few minutes immediately after the NaCl addition, and a reduction in the cell voltage was observed at the same time. The cell voltage varied between 3.5 and 3.8 V in the interval of NaCl dosing. In the interval of 30 minutes, the electrolysis current was reversed for 90 seconds each. The liquid sodium ran out in drops at regular intervals and solidified into small balls in a template filled with paraffin oil. The electrolyte assumed a dark brown color after start-up.

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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)
  • Inorganic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Secondary Cells (AREA)

Abstract

Proposed is an electrolytic method for the production of sodium and aluminium chloride in an electrolytic cell with an aluminium anode and a sodium cathode separated from each other by a sodium-ion-conducting solid electrolyte. In the anode region, molten electrolyte containing essentially sodium tetrachloroaluminate is electrolysed, the aluminium chloride produced being evaporated out of the cell and the sodium produced being tapped off from the cathode region.

Description

Verfahren zur elektrochemischen Herstellung von Natrium und AluminiumchloridProcess for the electrochemical production of sodium and aluminum chloride
Beschreibungdescription
Die vorliegende Erfindung betrifft ein neues Verfahren zur elek¬ trochemischen Herstellung von Natrium und Aluminiumchlorid.The present invention relates to a new process for the electrochemical production of sodium and aluminum chloride.
Weiterhin betrifft die Erfindung eine zur Ausübung dieses Verfah¬ rens geeignete Elektrolysezelle sowie ein Verfahren zur Reinigung dieser Zelle.The invention further relates to an electrolysis cell suitable for carrying out this method and to a method for cleaning this cell.
Natrium ist eine wichtiges anorganisches Grundprodukt, das bei- spielsweise für die Herstellung von Natriumamid und Natriumal- koholaten verwendet wird. Es wird technisch nach dem Downs-Prozeß durch Elektrolyse von geschmolzenem Kochsalz gewonnen. Dieser Prozeß weist einen hohen Energieverbrauch von über 10 kWh/kg Natrium auf (Büchner et al., Industrielle Anorganische Chemie, 2. Auflage, Verlag Chemie, S. 228 f) . Weiterhin hat das Verfahren den gravierenden Nachteil, daß die Elektrolysezellen beim Abstel¬ len durch das Erstarren der Salzschmelze zerstört werden.Sodium is an important inorganic basic product that is used, for example, for the production of sodium amide and sodium alcoholates. It is obtained technically after the Downs process by electrolysis of molten table salt. This process has a high energy consumption of over 10 kWh / kg sodium (Büchner et al., Industrial Inorganic Chemistry, 2nd edition, Verlag Chemie, p. 228 f). Furthermore, the method has the serious disadvantage that the electrolysis cells are destroyed by the solidification of the molten salt when it is switched off.
Aluminiumchlorid wird überwiegend als Katalysator, z.B. in Friedel-Crafts-Reaktionen, eingesetzt. Die Herstellung erfolgt in großem Maße durch Direktchlorierung von geschmolzenem Aluminium. (Büchner et al., Industrielle Anorganische Chemie, 2. Auflage, Verlag Chemie, S. 262) . Dabei wird ein wesentlicher Teil der Energie, die in Form elektrischen Stroms für eine elektrolytische Herstellung von Chlor und Aluminium aufgewendet wurde, ungenutzt frei.Aluminum chloride is mainly used as a catalyst, e.g. in Friedel-Crafts reactions. It is largely manufactured by direct chlorination of molten aluminum. (Büchner et al., Industrial Inorganic Chemistry, 2nd edition, Verlag Chemie, p. 262). A substantial part of the energy that was used in the form of electrical current for the electrolytic production of chlorine and aluminum is released unused.
Die GB-A 2 056 757 beschreibt ein Verfahren zur Erniedrigung der Schmelzpunkte von Alkalimetalltetrachloroaluminaten durch Zugabe eines Alkalimetallfluorids und die Verwendung solcher Gemische als Elektrolyt.GB-A 2 056 757 describes a process for lowering the melting points of alkali metal tetrachloroaluminates by adding an alkali metal fluoride and using such mixtures as the electrolyte.
Die DE-A 37 18 920 betrifft die gekoppelte elektrochemische Her¬ stellung eines Alkalimetalls und einer Alkalimetall-Metallhaloge- nidverbindung wie Natriumtetrachloroaluminat. Das so neben dem Alkalimetall gebildete Koppelprodukt ist jedoch für eine Produk¬ tion im technischen Maßstab unattraktiv. Die Bildung von Natrium¬ tetrachloroaluminat aus Natriumchlorid und Aluminiumchlorid schließt sich automatisch an die Bildung des Aluminiumchlorids an. Nach der Lehre der Schrift soll eine Konzentration vonDE-A 37 18 920 relates to the coupled electrochemical production of an alkali metal and an alkali metal-metal halide compound such as sodium tetrachloroaluminate. The by-product thus formed in addition to the alkali metal is, however, unattractive for production on an industrial scale. The formation of sodium tetrachloroaluminate from sodium chloride and aluminum chloride automatically follows the formation of the aluminum chloride. According to the teaching of Scripture, a concentration of
Aluminiumchlorid vermieden werden, um eine Schädigung des Separa- tors zwischen Anoden- und Kathodenraum und ein Ansteigen der Zellspannung zu vermeiden.Aluminum chloride can be avoided to damage the sepa- avoid torsion between the anode and cathode space and an increase in cell voltage.
Es bestand die Aufgabe, ein Verfahren bereitzustellen, das eine energetisch günstigere Herstellung von Natrium erlaubt als das Downs-Verfahren. Als Koppelprodukt soll dabei ein im technischen Maßstab einsetzbarer Stoff anfallen. Beide Verfahrensprodukte sollen in so hoher Reinheit anfallen, daß weitere aufwendige Reinigungsschritte nicht nötig sind. Ein weiterer Aspekt der Auf- gäbe bestand darin, ein Verfahren zu finden, das es erlaubt, den Elektrolyseprozeß in der gleichen Elektrolysezelle mehrfach durchführen zu können. Außerdem war es Teil der Aufgabe, eine für dieses Verfahren geeignete Elektrolysezelle zu finden. Weiterhin sollte ein Verfahren zur Reinigung der für die Reaktion benutzten Elektrolysezelle gefunden werden.The object was to provide a process which allows sodium to be produced more economically than the Downs process. As a by-product, a substance that can be used on an industrial scale is to be obtained. Both process products are said to be so pure that further elaborate cleaning steps are not necessary. Another aspect of the task was to find a method which allows the electrolysis process to be carried out several times in the same electrolysis cell. It was also part of the task to find an electrolytic cell suitable for this process. Furthermore, a method for cleaning the electrolysis cell used for the reaction should be found.
Demgemäß wurde ein Verfahren zur elektrochemischen Herstellung von Natrium und Aluminiumchlorid gefunden, das dadurch gekenn¬ zeichnet ist, daß man in einer Elektrolysezelle mit Aluminium als Anode und Natrium als Kathode, die durch einen Natriumionen leitenden Festelektrolyten voneinander getrennt sind, einen schmelzflüssigen, im wesentlichen aus Natriumtetrachloroaluminat bestehenden Elektrolyten im Anodenraum elektrolysiert, dabei ent¬ stehendes Aluminiumchlorid aus der Elektrolysezelle abdampft und Natrium aus dem Kathodenraum abzieht.Accordingly, a process for the electrochemical production of sodium and aluminum chloride has been found, which is characterized in that a molten, essentially from an electrolytic cell with aluminum as the anode and sodium as the cathode, which are separated from one another by a sodium ion-conducting solid electrolyte Sodium tetrachloroaluminate existing electrolytes electrolyzed in the anode compartment, thereby evolving aluminum chloride evaporates from the electrolytic cell and withdraws sodium from the cathode compartment.
Außerdem wurde eine unten näher beschriebene Elektrolysezelle gefunden, in der das erfindungsgemäße Verfahren betrieben werden kann.In addition, an electrolysis cell was described in more detail below, in which the method according to the invention can be operated.
Weiterhin wurde ein Verfahren zur Reinigung einer für das be¬ schriebene Verfahren geeigneten Elektrolysezelle durch Begasen des Elektrolyten mit S02 gefunden.Furthermore, a method for cleaning an electrolytic cell suitable for the described method by gassing the electrolyte with SO 2 was found.
Das erfindungsgemäße Verfahren wird in einer Elektrolysezelle mit einer Aluminiumanode betrieben. Hierbei handelt es sich um eine Opferanode, die sich während der Reaktion auflöst, so daß im kontinuierlichen Betrieb Aluminium zugesetzt werden muß. Aluminium kann in Form von Platten, bevorzugt aber in Form von kleinen Metallstücken, die sich beim Einfüllen mit großenThe method according to the invention is operated in an electrolytic cell with an aluminum anode. This is a sacrificial anode, which dissolves during the reaction, so that aluminum must be added in continuous operation. Aluminum can be in the form of plates, but preferably in the form of small pieces of metal that can be filled with large ones
Zwischenräumen zwischen den einzelnen Stücken anordnen wie Späne, Grieß oder Schredderteile. Die Partikelgröße kann im allgemeinen 0,01 bis 10 mm betragen, bevorzugt 0,1 bis 2 mm. Es kommt han¬ delsübliches Aluminium mit einer Reinheit von ca. 99,3 % oder Aluminiumschrott mit einer Reinheit von 95 % in Betracht. Die anodenseitige Stromzufuhr erfolgt bevorzugt über Aluminiumstäbe, die im kontinuierlichen Betrieb der Zelle von außen ohne Unter¬ brechung des Verfahrens ersetzt werden können.Arrange gaps between the individual pieces such as chips, semolina or shredder parts. The particle size can generally be 0.01 to 10 mm, preferably 0.1 to 2 mm. Commercially available aluminum with a purity of approx. 99.3% or aluminum scrap with a purity of 95% are possible. The anode-side power supply is preferably via aluminum rods, which can be replaced from the outside in continuous operation of the cell without interrupting the process.
Die Kathode besteht aus Natrium, das bei den Temperaturen, die zur Verflüssigung des Elektrolyten erforderlich sind, flüssig vorliegt. Zu Beginn der Elektrolyse wird das Natrium vorteilhaft flüssig in den Kathodenraum gebracht. In technisch einfacher Weise kann das im erfindungsgemäßen Verfahren gebildete Natrium durch einen Überlauf aus dem Kathodenraum abgetrennt werden. Die kathodische Stromversorgung kann z.B. über Aluminiumstäbe erfol¬ gen.The cathode consists of sodium, which is liquid at the temperatures required to liquefy the electrolyte. At the beginning of the electrolysis, the sodium is advantageously brought into the cathode compartment in liquid form. The sodium formed in the process according to the invention can be removed in a technically simple manner by an overflow from the cathode compartment. The cathodic power supply can e.g. over aluminum rods.
Der Anoden- und der Kathodenraum sind durch einen Natriumionen leitenden Festelektrolyten voneinander getrennt. Für diesen Zweck kommen keramische Materialien wie NASICON® in Betracht, deren Zusammensetzung in der EP-A 553 400 angegeben ist. Auch Natrium¬ ionen leitende Gläser sind geeignet sowie Zeolithe und Feldspate. Bevorzugt ist jedoch ß" -Aluminiumoxid.The anode and cathode compartments are separated from each other by a solid electrolyte that conducts sodium ions. Ceramic materials such as NASICON®, the composition of which is specified in EP-A 553 400, are suitable for this purpose. Glasses which conduct sodium ions are also suitable, as are zeolites and feldspar. However, β "aluminum oxide is preferred.
Der Elektrolyt zum Starten der Reaktion wird vorzugsweise durch Aufschmelzen stöchiometrischer Mengen Natriumchlorid und Aluminiumchlorid hergestellt. Während der Reaktion verändert sich die Elektrolytmenge im kontinuierlichen Betrieb nicht. Während der Reaktion wird Aluminiumchlorid aus dem Anodenraum abgedampft. Der Anodenraum ist daher oberhalb der Elektrolytoberfläche mit einer Ableitung, z.B. in Form eines Rohrs, verbunden, durch die das Aluminiumchlorid entweichen kann. Vorteilhaft schließt sich an die Ableitungsvorrichtung ein Vorratsgefäß an, in dem durch Absenkung der Temperatur gegenüber der Elektrolysezelle die Desublimation des Aluminiumchlorids erfolgt. Dies schlägt sich in der Regel als Wandbelag ab, der durch mechanische Methoden ent¬ fernt werden kann.The electrolyte for starting the reaction is preferably produced by melting stoichiometric amounts of sodium chloride and aluminum chloride. The amount of electrolyte does not change during the reaction in continuous operation. During the reaction, aluminum chloride is evaporated from the anode compartment. The anode compartment is therefore above the electrolyte surface with a drain, e.g. in the form of a tube, through which the aluminum chloride can escape. Advantageously, the discharge device is followed by a storage vessel in which the aluminum chloride is desublimated by lowering the temperature compared to the electrolysis cell. This is usually reflected as a wall covering that can be removed by mechanical methods.
Für einen kontinuierlichen Betrieb der Elektrolyse müssen Aluminium als Opferanode sowie Natriumchlorid nach Maßgabe des ausgetragenen Natriums bzw. Aluminiumchlorids nachdosiert werden. Natriumchlorid wird bevorzugt als Siedesalz mit einer Reinheit von 99,9 % als Feststoff in den Anodenraum dosiert. Die Reak¬ tionstemperatur liegt im allgemeinen bei der Verflüssigungstempe- ratur des Elektrolyten als üntergrenze (ca. 150°C) und 400°C, be¬ vorzugt 250 bis 350°C. Das elektrische Potential liegt im allge¬ meinen bei 2 bis 5 V, die kathodische Stromdichte bei 1 bis 10 kA/m2. Während der Reaktion kann der Elektrolyt umgepumpt werden. Dies kann durch eine Pumpe erfolgen, bevorzugt ist aber das Einblasen eines Inertgases wie Argon. Diese Gaseinspeisung unterstützt das Abdampfen des Aluminiumchlorids aus dem Anodenraum.For continuous operation of the electrolysis, aluminum as the sacrificial anode and sodium chloride must be replenished in accordance with the sodium or aluminum chloride discharged. Sodium chloride is preferably dosed as evaporated salt with a purity of 99.9% as a solid in the anode compartment. The reaction temperature is generally at the liquefaction temperature of the electrolyte as the lower limit (approx. 150 ° C.) and 400 ° C., preferably 250 to 350 ° C. The electrical potential is generally 2 to 5 V, the cathodic current density 1 to 10 kA / m 2 . The electrolyte can be pumped around during the reaction. This can be done by a pump, but blowing in an inert gas such as argon is preferred. This gas feed supports the evaporation of the aluminum chloride from the anode compartment.
In einer bevorzugten Ausführungsform der Elektrolysezelle wird die von außen beheizbare Zelle analog zu einem Rohrbündelumlauf- Verdampfer aufgebaut (s. Figur 1), d.h. ein oben geschlossener Zylinder aus ß"-Aluminiumoxid 1, der mit Natrium 2 gefüllt ist, einen Überlauf 3 enthält, und über einen Aluminiumstab 4 an eine Spannungsquelle als Kathode geschaltet wird, ragt in den Anoden¬ raum 5 hinein, der mit festen Aluminiumteilen sowie einem flüssi¬ gen, im wesentlichen Natriumtetrachloroaluminat enthaltenden Elektrolyten versehen ist. Über einen Aluminiumstab 6 wird die Anode an eine Spannungsquelle angeschlossen. Ein Umlaufröhr 7, in das Inertgas geblasen wird, dient zur Umwälzung des Elektrolyten. Durch die Ableitung 8 wird Aluminiumchlorid ausgetragen. Für eine technische Produktion können mehrere dieser Zellen parallel ge¬ schaltet werden bzw. ein großer Anodenraum mit mehreren Kathoden versehen werden, wobei die Kathode sowohl von oben wie auch von unten in den Anodenraum ragen kann. Die Vorrichtungen zur Dosie¬ rung von Natriumchlorid und bevorzugt Aluminiumgrieß sind vor¬ teilhaft so angeordnet, daß die Feststoffe direkt in den Elektro¬ lyten fallen, d.h. vorzugsweise sind sie direkt über dem Anoden- räum angeordnet.In a preferred embodiment of the electrolysis cell, the externally heatable cell is constructed analogously to a tube bundle circulation evaporator (see FIG. 1), i.e. a cylinder, closed at the top, made of β "aluminum oxide 1, which is filled with sodium 2, contains an overflow 3, and is connected to a voltage source as a cathode via an aluminum rod 4, projects into the anode chamber 5, which has solid aluminum parts and The anode is connected to a voltage source via an aluminum rod 6. A circulation tube 7 into which inert gas is blown serves to circulate the electrolyte. Aluminum chloride is discharged through the discharge line 8. For In a technical production, several of these cells can be connected in parallel, or a large anode compartment can be provided with several cathodes, the cathode being able to protrude into the anode compartment both from above and from below The devices for dosing sodium chloride and preferably aluminum powder are advantageously arranged so that the solids are directly in de n electrolytes fall, i.e. they are preferably arranged directly above the anode space.
Durch die Ausgangsverbindungen Aluminium und Natriumchlorid werden Fremdstoffe wie Eisen, Silizium und Kalium in die Elektro¬ lysezelle eingebracht, die sich im Elektrolyten aufkonzentrieren können. Diese können dadurch abgebaut werden, daß Teilströme des Elektrolyten, etwa 1 bis 10 Gew.-%, bezogen auf die Gesamtelek¬ trolytmenge, im Seitenstrom elektrolysiert werden. So reduziert eine anodische Elektrolyse an Graphitelektroden den Oxidgehalt der Schmelze. An Eisenkathoden können Eisen sowie gegebenenfalls weitere im flüssigen Elektrolyten vorhandene Schwermetalle abge¬ schieden werden.The starting compounds aluminum and sodium chloride introduce foreign substances such as iron, silicon and potassium into the electrolytic cell, which can concentrate in the electrolyte. These can be reduced by partial streams of the electrolyte, about 1 to 10% by weight, based on the total amount of electrolyte, being electrolyzed in the side stream. Anodic electrolysis on graphite electrodes reduces the oxide content of the melt. Iron and any other heavy metals present in the liquid electrolyte can be deposited on iron cathodes.
Beim Abstellen der Elektrolyse kann die problematische Handhabung der erstarrten Elektrolytschmelze mit Resten metallischen Natriums entfallen, wenn man während des Abkühlens die Schmelze mit S02 begast. Die Schmelze bleibt unter Aufnahme von S02 zwischen 150 und ca. 70°C teigig, und sie wird bei tieferen Tempe¬ raturen flüssig. Somit kann sie problemlos aus der Zelle abgelas¬ sen werden, was eine starke Vereinfachung im Reparaturfall dar- stellt. Die flüssige, S02-haltige Schmelze kann filtriert werden, was insbesondere zur Abtrennung von Kaliumverbindungen vorteil¬ haft ist. Danach kann die flüssige S02-haltige Schmelze in die Elektrolysezelle zurückgefüllt werden, wo unter Erhitzen auf ca. 165°C in Gegenwart eines Natriumchloridüberschusses das S02 ausgetrieben werden kann.When the electrolysis is switched off, the problematic handling of the solidified electrolyte melt with residues of metallic sodium can be omitted if the melt is gassed with SO 2 during cooling. The melt remains dough between 150 and approx. 70 ° C. with the absorption of SO 2 , and it becomes liquid at lower temperatures. This means that it can be easily removed from the cell, which greatly simplifies repairs. The liquid, SO 2 -containing melt can be filtered, which is particularly advantageous for the removal of potassium compounds. Then the liquid S0 2 -containing melt can be in the Electrolysis cell are filled back, where the SO 2 can be driven off with heating to approx. 165 ° C. in the presence of an excess of sodium chloride.
Durch periodisches Umpolen der Zelle kann man den Festelektroly¬ ten von kationischen Verunreinigungen wie Kaliumionen reinigen.By periodically reversing the polarity of the cell, the solid electrolyte can be cleaned of cationic impurities such as potassium ions.
Das erfindungsgemäße elektrochemische Verfahren zur Koppelproduk¬ tion von Natrium und Aluminiumchlorid benötigt nur ca. 50 % der Energiemenge, die zur Natriumherstellung nach dem Downs-Prozeß erforderlich ist. Die Betriebstemperaturen liegen deutlich unter denen des genannten Verfahrens (ca. 650°C) , was die Auswahl und Verarbeitung der Reaktionszellen beträchtlich vereinfacht. Das Abstellen der Elektrolysezellen ist ohne Schaden möglich.The electrochemical process according to the invention for the coupling production of sodium and aluminum chloride requires only approx. 50% of the amount of energy which is required for the production of sodium by the Downs process. The operating temperatures are significantly lower than those of the mentioned method (approx. 650 ° C), which considerably simplifies the selection and processing of the reaction cells. Parking the electrolysis cells is possible without damage.
Die erfindungsgemäß erhaltenen Produkte sind hochrein. Aluminium- chlorid fällt im Gegensatz zu den meisten handelsüblichen Produk¬ ten farblos an, was es für Anwendungen besonders attraktiv macht, in der die Farbe des Endprodukts ein wesentliches Merkmal ist. Bei einer Stromausbeute von über 90 % ist die Natriumausbeute praktisch quantitativ, die Ausbeute an Aluminiumchlorid liegt deutlich über 90 %.The products obtained according to the invention are highly pure. In contrast to most commercially available products, aluminum chloride is colorless, which makes it particularly attractive for applications in which the color of the end product is an essential feature. With a current yield of over 90%, the sodium yield is practically quantitative, the yield of aluminum chloride is well over 90%.
Eine Schädigung des Festelektrolyten konnte auch nach Langzeit- tests nicht festgestellt werden.Damage to the solid electrolyte was not found even after long-term tests.
Das Verfahren läßt sich prinzipiell auch für die Herstellung von Natrium und anderen Metallhalogeniden anwenden, die unter den Reaktionsbedingungen flüchtig sind, z.B. SiCl4, GeCl4, TiCl4. Anode und Elektrolyte müssen dazu jeweils das entsprechende Metall aufweisen.In principle, the process can also be used for the production of sodium and other metal halides which are volatile under the reaction conditions, for example SiCl 4 , GeCl 4 , TiCl 4 . For this purpose, the anode and electrolytes must each have the corresponding metal.
Beispiel 1example 1
Apparatur:Apparatus:
Die zur Durchführung des Verfahrens eingesetzte Elektrolysezelle nach Figur 1 bestand aus einem stehenden Rohr (mit einem Innen¬ durchmesser von 50 mm und einer Länge von 400 mm) aus Borosili- katglas, in welches die Anodenstromzuführung in Form eines Hohl- Zylinders aus Aluminium dicht eingespannt war. Der Natriumionen leitende Festelektrolyt aus ß"-Aluminiumoxid (25 mm Außendurch¬ messer, 210 mm Lange) war am unteren Ende zusammen mit der Katho¬ denstromzuführung eingeflanscht. Der obere Teil des Rohres war mit Stutzen versehen, die zum Befüllen mit Elektrolyt, Aluminium und Natriumchlorid und zur Ableitung der AlCl3-Dämpfe dienten. Die Zelle wurde mit Heißluft beheizt. Die Anode wurde in Form einer Schüttung von Aluminiumschredder eingebracht. Als Kathode diente flüssiges Natrium, das zum Start der Reaktion vorgelegt wurde. Das bei der Reaktion gebildete Natrium lief in freiem Überlauf nach unten ab. Die AlCl3-Dämpfe wurden in einem luftgekühlten De- sublimator niedergeschlagen. Zur Umwälzung der Schmelze diente der außen angebrachte Umlauf mit Inertgaszuführung.The electrolysis cell according to FIG. 1 used to carry out the method consisted of a standing tube (with an inner diameter of 50 mm and a length of 400 mm) made of borosilicate glass, in which the anode current supply in the form of a hollow cylinder made of aluminum was tightly clamped was. The sodium ion-conducting solid electrolyte made of β "aluminum oxide (25 mm outer diameter, 210 mm long) was flanged together with the cathode current supply at the lower end. The upper part of the tube was provided with connecting pieces which were used for filling with electrolyte, aluminum and Sodium chloride and were used to discharge the AlCl 3 vapors. The cell was heated with hot air. The anode was introduced in the form of a bed of aluminum shredder. The cathode was used liquid sodium which was presented at the start of the reaction. The sodium formed in the reaction drained down in free overflow. The AlCl 3 vapors were precipitated in an air-cooled de-sublimator. The external circulation with inert gas supply was used to circulate the melt.
Vor Inbetriebnahme wurde die Elektrolysezelle auf 280°C aufge¬ heizt. In dem Aufschmelzgefäß wurden 85 g Natrium bei 150°C ge¬ schmolzen und in den Kathodenraum gegeben, bis dieser bis zum Überlauf gefüllt war. 485 g A1C13 und 215 g NaCl wurden als Fest¬ stoff vorgelegt und unter Argon verrührt. Das Gemisch bildete nach dem Aufheizen auf 165°C eine homogene flüssige Phase, die in den Anodenraum gefüllt wurde. In den Anodenraum wurden 150 g Aluminium als Grieß mit einer Körnung von 0,4 bis 1,5 mm einge- tragen. Der flüssige Elektrolyt wurde mittels Argoneingasung am Boden der Umlaufleitung in Umlauf gehalten. Es wurde ein Strom von 30 A aufgeprägt, die Zellspannung wurde mit 3,5 V bestimmt. Die auf den Innendurchmesser des Festelektrolyten bezogene Strom¬ dichte betrug bei einer Oberfläche von 137 cm2 (bei 30 A) 2200 A/m2. 15 Minuten nach Einschalten des Stroms wurde erstmalig das Aufsteigen von AlCl3-Dämpfen beobachtet, welche sich im De- sublimator niederschlugen. In Intervallen von 15 Minuten wurden jeweils 16,4 g NaCl als Feststoff nachdosiert. Die AlCl3-Entwick- lung kam direkt nach der NaCl-Zugabe für wenige Minuten zum Er- liegen, gleichzeitig wurde eine Verminderung der Zellspannung be¬ obachtet. Die Zellspannung variierte im Intervall der NaCl-Dosie- rung zwischen 3,5 auf 3,8 V. Im Intervall von 30 Minuten wurde der Elektrolysestrom für jeweils 90 Sekunden umgepolt. Das flüssige Natrium lief in regelmäßigen Zeitabständen tropfenweise ab und erstarrte in einer mit Paraffinöl gefüllten Vorlage zu kleinen Kugeln. Der Elektrolyt nahm nach Inbetriebnahme eine dunkelbraune Färbung an.Before starting up, the electrolysis cell was heated to 280 ° C. In the melting vessel, 85 g of sodium were melted at 150 ° C. and added to the cathode compartment until it was filled to the overflow. 485 g of A1C1 3 and 215 g of NaCl were initially introduced as solids and stirred under argon. After heating to 165 ° C., the mixture formed a homogeneous liquid phase which was filled into the anode compartment. 150 g of aluminum with a grain size of 0.4 to 1.5 mm were introduced into the anode compartment. The liquid electrolyte was kept in circulation by means of argon gas at the bottom of the circulation line. A current of 30 A was impressed, the cell voltage was determined to be 3.5 V. The current density, based on the inner diameter of the solid electrolyte, was 2200 A / m 2 with a surface area of 137 cm 2 (at 30 A). 15 minutes after switching on the power, the rise of AlCl 3 vapors was observed for the first time, which was reflected in the de-sublimator. At intervals of 15 minutes, 16.4 g of NaCl were metered in as a solid. The AlCl 3 development came to a standstill for a few minutes immediately after the NaCl addition, and a reduction in the cell voltage was observed at the same time. The cell voltage varied between 3.5 and 3.8 V in the interval of NaCl dosing. In the interval of 30 minutes, the electrolysis current was reversed for 90 seconds each. The liquid sodium ran out in drops at regular intervals and solidified into small balls in a template filled with paraffin oil. The electrolyte assumed a dark brown color after start-up.
Betriebszeit: 5 h Betriebstemperatur: 280°COperating time: 5 h operating temperature: 280 ° C
Eingesetzte Ladung: 150 AhCharge used: 150 Ah
Eingesetzte Stoffe (Summe): 150 g AI; 262 g NaCl (ohne Erstfüllung der Zelle) Versuchsergebnis: Erhaltene Produkte (Summe) 250 g A1C13 in einer Reinheit von 99,2 % 120 g Na in einer Reinheit von 99,1 %Substances used (total): 150 g AI; 262 g NaCl (without first filling the cell) Test result: Products obtained (total) 250 g A1C1 3 in a purity of 99.2% 120 g Na in a purity of 99.1%
Stromausbeute für Na: 92,4 % Stromausbeute für A1C13: 99,7 % Energieeinsatz für 1 kg Na: 4600 Wh/kg Current yield for Na: 92.4% Current yield for A1C1 3 : 99.7% energy consumption for 1 kg Na: 4600 Wh / kg

Claims

Patentansprüche claims
1. Verfahren zur elektrochemischen Herstellung von Natrium und Aluminiumchlorid, dadurch gekennzeichnet, daß man in einer1. A process for the electrochemical production of sodium and aluminum chloride, characterized in that in a
Elektrolysezelle mit Aluminium als Anode und Natrium als Ka¬ thode, die durch einen Natriumionen leitenden Festelektroly¬ ten voneinander getrennt sind, einen schmelzflüssigen, im we¬ sentlichen Natriumtetrachloroaluminat enthaltenden Elektroly- ten im Anodenraum elektrolysiert, dabei entstehendesElectrolysis cell with aluminum as the anode and sodium as the cathode, which are separated from one another by a solid electrolyte which conducts sodium ions, electrolyzes a molten electrolyte in the anode compartment which essentially contains sodium tetrachloroaluminate, resulting in the process
Aluminiumchlorid aus der Elektrolysezelle abdampft und Natrium aus dem Kathodenraum abzieht.Aluminum chloride evaporates from the electrolysis cell and sodium is withdrawn from the cathode compartment.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man die Elektrolyse bei 250 bis 350°C vornimmt.2. The method according to claim 1, characterized in that one carries out the electrolysis at 250 to 350 ° C.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß man ß" -Aluminiumoxid als Natriumionen leitenden Festelektro¬ lyten verwendet.3. The method according to claim 1 or 2, characterized in that ß "aluminum oxide is used as the sodium ion-conducting Festelektro¬ lyte.
4. Verfahren nach den Ansprüchen 1 bis 3, dadurch gekennzeich¬ net, daß man den flüssigen Elektrolyten durch Einblasen eines Inertgases in den Anodenraum umpumpt.4. The method according to claims 1 to 3, characterized gekennzeich¬ net that the liquid electrolyte is pumped by blowing an inert gas into the anode compartment.
5. Verfahren nach den Ansprüchen 1 bis 4, dadurch gekennzeich¬ net, daß man das Verfahren durch Zugabe von Aluminium und Na¬ triumchlorid entsprechend dem Austrag an Natrium und Aluminiumchlorid kontinuierlich betreibt.5. The method according to claims 1 to 4, characterized gekennzeich¬ net that the method is operated continuously by adding aluminum and sodium chloride according to the discharge of sodium and aluminum chloride.
6. Verfahren nach den Ansprüchen 1 bis 5, dadurch gekennzeich¬ net, daß man den Kathodenraum zylinderförmig ausbildet und aus diesem durch einen Überlauf Natrium entsprechend der wäh¬ rend der Elektrolyse gebildeten Menge abzieht.6. The method according to claims 1 to 5, characterized gekennzeich¬ net that the cathode space is cylindrical and deduced from this by an overflow of sodium corresponding to the amount formed during the electrolysis.
7. Verfahren nach den Ansprüchen 1 bis 6, dadurch gekennzeich¬ net, daß Eisenverunreinigungen im Elektrolyten durch kathodi¬ sche Abscheidung aus einem Seitenstrom des flüssigen Elektro¬ lyten an Eisenelektroden aus diesem entfernt werden. 7. The method according to claims 1 to 6, characterized gekennzeich¬ net that iron impurities in the electrolyte are removed by cathodic separation from a side stream of liquid electrolytes on iron electrodes from this.
8. Verfahren zur Reinigung einer Elektrolysezelle mit Aluminium als Anode und Natrium als Kathode, die durch einen Natrium¬ ionen leitenden Festelektrolyten voneinander getrennt sind, sowie einem im wesentlichen aus Natriumtetrachloroaluminat bestehenden Elektrolyten im Anodenraum, dadurch gekennzeich¬ net, daß man den flüssigen Elektrolyten im Anodenraum mit S02 begast und die so erhaltene Flüssigkeit aus dem Anodenraum abläßt.8. A method for cleaning an electrolytic cell with aluminum as the anode and sodium as the cathode, which are separated from one another by a solid electrolyte which conducts sodium ions, and an electrolyte essentially consisting of sodium tetrachloroaluminate in the anode compartment, characterized in that the liquid electrolyte in the Gassed anode compartment with S0 2 and drains the liquid thus obtained from the anode compartment.
9. Elektrolysezelle zur Ausübung eines Verfahrens gemäß An¬ spruch 1, die eine Aluminiumanode, eine Natriumkathode, einen Natriumionen leitenden Festelektrolyten zur Trennung des Anodenraums und des Kathodenraums, einen flüssigen, im we¬ sentlichen Natriumtetrachloroaluminat enthaltenden Elektroly- ten und eine Vorrichtung zur Ableitung von während der Elek¬ trolyse freigesetztem Aluminiumchlorid aufweist.9. Electrolysis cell for carrying out a method according to claim 1, comprising an aluminum anode, a sodium cathode, a solid electrolyte which conducts sodium ions to separate the anode compartment and the cathode compartment, a liquid electrolyte containing essentially sodium tetrachloroaluminate and a device for discharging has released aluminum chloride during the electrolysis.
10. Elektrolysezelle nach Anspruch 9, die eine Vorrichtung zur Dosierung von Natriumchlorid und Aluminiumgrieß in den Elek- trolyten aufweist. 10. Electrolysis cell according to claim 9, which has a device for metering sodium chloride and aluminum powder in the electrolyte.
EP96930164A 1995-09-08 1996-09-04 Electrolytic method for the production of sodium and aluminium chloride Expired - Lifetime EP0848764B1 (en)

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DE19533214 1995-09-08
PCT/EP1996/003892 WO1997009467A1 (en) 1995-09-08 1996-09-04 Electrolytic method for the production of sodium and aluminium chloride

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CN104254494B (en) 2012-01-04 2016-11-16 克基·霍尔穆斯吉·阿加尔达 A kind of technique producing aluminum from bauxite or its residue
EP2870277B1 (en) * 2012-07-03 2021-04-14 Enlighten Innovations Inc. Apparatus and method of producing metal in a nasicon electrolytic cell
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