JP2015529745A - Method for producing alkali metal - Google Patents

Abstract

A method for producing an alkali metal from a salt of an alkali metal soluble in a solvent, comprising: (a) a first electrolysis cell (1) comprising an anode chamber (3) and a cathode chamber (5) ), In which the anode chamber (3) and the cathode chamber (5) of the first electrolysis cell (1) are separated by an alkali metal cation permeable membrane (7), Here, an alkali metal salt dissolved in a solvent is supplied to the anode chamber (3), a suspension containing sulfur and a second solvent is supplied to the cathode chamber (5), and a second solvent, an alkali is supplied. A mixture comprising a metal cation, a (poly) sulfide anion and a further ionic sulfur compound is removed from the cathode chamber (5), (b) a second solvent, an alkali metal cation, (poly) sulfide anion removed from the cathode chamber And further ionic sulfur A step of concentrating the mixture containing the compound to form an alkali metal (poly) sulfide melt containing almost no solvent; (c) in the second electrolysis cell (71) comprising the anode chamber (73) and the cathode chamber; Performing the second electrolysis at a temperature above the melting temperature of the alkali metal, wherein the anode chamber (73) of the second electrolysis cell and the cathode chamber are separated by an alkali metal cation conductive solid electrolyte. Supplying the alkali metal (poly) sulfide melt of step (b) to the anode chamber (73), removing sulfur from the anode chamber, and removing liquid alkali metal from the cathode chamber.

Description

  The present invention relates to a method for producing an alkali metal from a salt of an alkali metal soluble in a solvent.

  Alkali metals used as important inorganic basic chemicals are in particular lithium, potassium and sodium. For example, lithium is used, for example, in the manufacture of organolithium compounds, as an alloy additive to aluminum or magnesium, and in lithium batteries. Industrially, lithium is produced by melt electrolysis of a eutectic mixture of lithium chloride and potassium chloride at 400-460 ° C. However, this process is energy intensive. Furthermore, the process has a serious disadvantage that only anhydrous lithium chloride can be used. Therefore, lithium chloride that is primarily present as an aqueous solution needs to be post-treated in an energetic manner to an anhydrous solid. Lithium chloride is hygroscopic and requires special costs for drying and handling.

  In carrying out the organolithium reaction, an aqueous lithium salt solution is often produced. Due to the increased consumption of lithium batteries, waste containing lithium is also generated there. This waste may be converted into an aqueous lithium salt solution. Since lithium is very expensive in its salt form, lithium recycling is important.

  Sodium is used, for example, in the production of sodium amide, sodium alkoxide and sodium borohydride. Industrially, sodium is obtained by the Downs method by electrolysis of molten salt. This process has a high energy consumption of over 10 kWh / kg sodium. Furthermore, the method has the serious disadvantage that the electrolysis cell becomes unusable due to the solidification of the salt melt when stopped. Furthermore, sodium metal obtained by the Downs method has a disadvantage that it is mixed with calcium with the process and its residual content is slightly reduced by an additional washing step, but can never be completely removed. .

  Potassium is used, for example, in the production of potassium alkoxides, potassium amides and potassium alloys. Currently, potassium is obtained industrially, in particular by the reaction of potassium chloride and sodium. Here, the sodium potassium alloy NaK is first produced and subsequently fractionated. Potassium vapor is withdrawn constantly from the reaction zone, whereby an excellent yield is achieved by moving the reaction equilibrium to the potassium side. However, this process is operated at a high temperature of about 870 ° C. Furthermore, the resulting potassium contains about 1% sodium as an impurity and therefore needs to be further purified by further rectification. The biggest drawback, however, is that the sodium used is expensive because it must be obtained industrially by the Downs method by electrolysis of molten salt.

  An alternative method for obtaining alkali metals from aqueous solutions is described in WO 01/14616 A1. For this purpose, an aqueous solution of an alkali metal salt is supplied to an electrolysis cell having a cathode chamber and an anode chamber separated from each other by a solid electrolyte. Here, the stationary electrolyte has at least one further ion-conducting layer. The cathode chamber has a fixed cathode center and is filled with molten alkali metal or liquid electrolyte. Alkali metals are generated at the cathode and can rise in the liquid electrolyte and then be extracted. As the liquid electrolyte, the alkali metal salt melt to be obtained is preferably used. The disadvantages of the method are that the electrical resistance is increased and the stability of the combination of the solid electrolyte and the further ion conductive layer is insufficient.

  A further alternative method for producing the alkali metal sodium is described in DE 195332214 A1. Here, the electrolyte substantially containing sodium tetrachloroaluminate is electrolyzed in the anode chamber of the electrolysis cell, where the resulting aluminum chloride evaporates and the sodium passes through a sodium ion conductive solid electrolyte. Extracted from the cathode chamber. The disadvantage of the process is the by-product of aluminum chloride and sodium if the product is not sought to the same extent.

  The object of the present invention is, in particular, to provide a process for the production of alkali metals which does not have the disadvantages known from the prior art, but which can be operated in particular with a relatively low energy requirement and relatively low equipment costs. is there.

The problem is solved by a method for producing an alkali metal from a solvent-soluble alkali metal salt comprising the following steps:
(A) A step of performing first electrolysis in a first electrolysis cell including an anode chamber and a cathode chamber, wherein the anode chamber and the cathode chamber of the first electrolysis cell are separated by an alkali metal cation permeable membrane. Here, an alkali metal salt dissolved in a solvent is supplied to the anode chamber, a suspension containing sulfur and a second solvent is supplied to the cathode chamber, and a second solvent, an alkali metal is supplied. A mixture comprising a cation, a (poly) sulfide anion and an anion of an oxygen sulfur compound is removed from the cathode chamber;
(B) Concentrating a mixture containing the second solvent, an alkali metal cation, a (poly) sulfide anion and an anion of oxygen-sulfur compound, which is taken out from the cathode chamber, to obtain an alkali metal (poly) sulfide melt containing almost no solvent. The process of
(C) In a second electrolysis cell including an anode chamber and a cathode chamber, a step of performing second electrolysis at a temperature above the melting temperature of the alkali metal, wherein the anode chamber and the cathode chamber of the second electrolysis cell Is separated by an alkali metal cation conductive solid electrolyte, and the alkali metal (poly) sulfide melt of step (b) is fed to the anode chamber from which sulfur and unreacted alkali metal ( The poly) sulfide melt is removed and the liquid alkali metal is removed from the cathode chamber.

  The process according to the invention is suitable for the production of substantially pure alkali metals, in particular for the production of sodium, potassium and lithium, particularly preferably for the production of sodium.

  Substantially pure means within the scope of the invention that the proportion of impurities due to impure metals in the alkali metal is at most 30 ppm.

(Poly) sulfide anion is understood within the scope of the present invention to be an anion of the general formula S _x ²⁻ , where x is any integer from 1 to 6.

［式中、Ｍｅはアルカリ金属、例えば、ナトリウム、カリウムまたはリチウムを表し、ｘは、１〜６の任意の整数である］のあらゆる化合物であると理解される。 The alkali metal (poly) sulfide within the scope of the present invention is the following general formula:

It is understood that any compound of [wherein Me represents an alkali metal such as sodium, potassium or lithium and x is any integer from 1 to 6].

  Alkali metal (poly) sulfide melts that contain little solvent are, within the scope of the present invention, that the alkali metal (poly) sulfide melt has up to 5% by weight of solvent, preferably up to 3% by weight of solvent, in particular solvent. Is contained in a maximum of 1.5 mass%.

  In order to produce the alkali metal, in the first step (a), first electrolysis is performed in a first electrolysis cell including an anode chamber and a cathode chamber. An alkali metal salt dissolved in a solvent is supplied to the anode chamber of the electrolytic cell. As the salt supplied to the anode chamber of the first electrolysis cell, an alkali metal halide is particularly suitable. Particular preference is given to using alkali metal chlorides. The solvent is, for example, water or an organic solvent such as an alcohol. The solvent is preferably water. When the method is used for the production of sodium, in particular an aqueous sodium chloride solution is supplied to the anode chamber of the first electrolysis cell.

  When an alkali metal salt aqueous solution, such as a sodium chloride aqueous solution or a potassium chloride aqueous solution, is used, it is preferable to use a solution that is common in chlor-alkali electrolysis. This alkali metal chloride solution is generally refined to remove non-alkali metal ions before being added to the anode chamber of the first electrolysis cell.

  When the method is used for the production of sodium and a sodium chloride solution is supplied as the solution supplied to the anode chamber, this solution has a maximum of 500 ppm relative to the total mass of sodium and potassium contained in the solution. It preferably contains potassium.

  When the method is used for the production of potassium, it is likewise preferred to use a potassium chloride aqueous solution which is likewise purified as known from chlor-alkali electrolysis and does not contain non-alkali metal ions. Here, the solution preferably contains a maximum of 0.1% by mass of sodium with respect to the total mass of potassium and sodium in the solution.

  The alkali metal salt solution supplied to the anode chamber of the first electrolysis cell is preferably almost saturated, for example, sodium chloride is preferably 5-27% by mass, especially 15-25% by mass, for example, chloride. Contains 23% by weight of sodium.

  A second solvent and sulfur powder are supplied as a suspension to the cathode chamber of the electrolysis cell. The solution supplied to the cathode chamber further contains a conductivity salt such as an alkali metal hydroxide or particularly preferably an alkali metal (poly) sulfide in order to increase the conductivity of the solution. preferable. Here, it is preferable that the alkali metal of the alkali metal hydroxide or alkali metal (poly) sulfide is the same alkali metal as the alkali metal to be obtained. The solution supplied to the cathode chamber preferably contains 50 to 95% by mass of solvent and 2 to 25% by mass of elemental sulfur. Further, it preferably contains 2 to 5% by mass of an alkali metal hydroxide and 0 to 48% by mass of an ionic alkali metal sulfur compound. It is particularly preferred that the solution is circulated through the cathode chamber in a continuous operation. Since the second solvent and the sulfur powder are continuously supplied to the circulated solution, the circulated solution contains an ionic sulfur compound having a concentration of 25 to 50% by mass. This is achieved by adding a suspension of 50 to 82% by weight of water and 18 to 50% by weight of sulfur powder to the circulated solution. The second solvent may be an organic solvent such as alcohol or water. The second solvent is preferably water.

  The anode chamber and cathode chamber of the first electrolysis cell are separated by a membrane that transmits alkali metal cations but does not transmit anions. As the alkali metal cation permeable membrane, any cation selective membrane that transmits an alkali metal cation is suitable. A suitable cation permeable membrane is, for example, the commercially available Nafion® membrane. Such membranes usually have a basic skeleton of polytetrafluoroethylene having immobilized anions, generally sulfonic acid groups and / or carboxylic acid groups.

  As the anode, for example, an anode known from chlor-alkali electrolysis is used. With regard to electrode design, generally, for example, a perforated material finished in the form of a mesh, a laminar, an oval profile, a V-shaped column or a circular column may be used. Said anode is generally preferably a dimensionally stable anode formed from coated titanium, where a mixed metal oxide of titanium, tantalum and / or platinum metals, eg iridium, ruthenium, platinum and rhodium Is used for coating. The choice of platinum metal and the proportion of metal are adjusted so that the chlorine deposition overvoltage is as low as possible and the oxygen overvoltage is as high as possible. For example, the chlorine overvoltage is 0.1 to 0.4 Volt, and the oxygen overvoltage is 0.6 to 0.9 Volt. In principle, graphite is also suitable as the material of the anode, however, graphite is generally not dimensionally stable under the operating conditions, so that the anode produced from it is in the cell during operation. In the case of titanium that has been readjusted and periodically replaced with mixed oxide passivated, the coating only needs to be replaced after 2-4 years of continuous operation.

  As the cathode, a cathode known from chlor-alkali electrolysis may be used. For example, a special steel cathode or a nickel electrode. In a preferred embodiment, graphite felt is further introduced into the electrode gap between the special steel cathode and the membrane.

  The first electrolysis is preferably carried out continuously, wherein the anode chamber is continuously supplied with an alkali metal salt dissolved in a solvent, and the cathode chamber has a sulfur suspension. The (poly) sulfide sulfur mixture and the second solvent returned from the liquid or the second electrolysis are continuously fed. Since an electric current is applied in the electrolysis, the alkali metal cation moves from the anode side to the cathode side through the cation selective membrane. Chlorine is produced at the anode, and this chlorine is removed from the anode chamber. Further, a solution containing an alkali metal salt is taken out from the anode chamber. This removed alkali metal salt solution is, in one embodiment, dechlorinated, concentrated to a feed concentration, washed and returned to the anode chamber. In order to concentrate, for example, it is possible to introduce the alkali metal salt directly into a solution of the alkali metal salt.

  In the cathode chamber, a mixture of an alkali metal (poly) sulfide and an ionic sulfur compound such as sulfite or thiosulfate is formed, thereby obtaining a solution containing an alkali metal cation and an ionic sulfur compound. . Further, the solution further comprises unreacted undissolved elemental sulfur for the time being. The solution is preferably removed from the cathode chamber and circulated to concentrate the products, ie alkali metal cations and ionic sulfur compounds. The partial stream is taken from the mixture comprising the second solvent, alkali metal cation, (poly) sulfide anion and ionic sulfur compound leaving the cathode chamber and concentrated in step (b).

The electrolysis in step (a) is preferably carried out at a temperature in the range of 25-120 ° C, preferably in the range of 50-90 ° C, in particular in the range of 75-85 ° C. A suitable current density is in the range of 400 to 4000 A / m ² and a suitable voltage is in the range of 2.5 to 6 Volt.

  In the electrolysis, sulfur is preferably reduced as compared to the hydrolysis of the cathode to hydrogen and hydroxide anions, so that the mixture leaving the cathode chamber is substantially free of alkali metal cations and (poly) sulfide anions. Which form alkali metal (poly) sulfides in the concentration and removal of the solvent.

  The mixture leaving the cathode chamber and containing the second solvent, alkali metal cation and (poly) sulfide anion and further ionic sulfur compound is concentrated by removing the second solvent in step (b). Here, the concentration of the second solvent, the alkali metal cation and the (poly) sulfide anion and the further ionic sulfur compound taken out from the cathode chamber is preferably carried out in an evaporator.

  The evaporator may be operated continuously or discontinuously. Here, any evaporator known to a person skilled in the art for carrying out the concentration in step (b) is suitable. In the case of continuous evaporation, for example, a natural circulation circulation evaporator, a forced circulation circulation evaporator, a falling liquid film evaporator, or a thin film evaporator is suitable. In the case of discontinuous concentration by evaporation, a stirred tank is particularly suitable. It is preferred to use an evaporator with a condenser, whether continuous or discontinuous.

  The mixture comprising alkali metal cations, (poly) sulfide anions and further ionic sulfur compounds and a second solvent supplied to the evaporator may be pre-warmed before being added to the evaporator. To that end, any arbitrary device for warming a liquid mass stream may be used. A heat exchanger is preferably utilized. Warming may be performed by a heat transfer medium or electrically. Suitable heat transfer media are, for example, heat transfer oil, steam or any other heat transfer medium known to those skilled in the art.

  Concentration by evaporation of alkali metal cations and (poly) sulfide anions is preferably carried out at temperatures in the range from 80 to 400 ° C., in particular in the range from 120 to 350 ° C., particularly preferably in the range from 150 to 300 ° C. Is done. The vapor pressure of the evaporation is preferably in the range of 0.1 to 2 bar (absolute pressure), more preferably in the range of 0.2 to 1 bar (absolute pressure), in particular in the range of 0.5 to 1 bar (absolute pressure). .

  The evaporator used may be heated by steam up to 200 ° C., for example. To that end, on the one hand, it is possible to pass the steam through the pipes in the corresponding heat exchangers or use a device with a double jacket. Similarly, heating by piping through the apparatus and heating by a double jacket are possible. In addition to steam, any other heat medium may be used, for example heat medium oil or salt melt. Furthermore, the heat required for evaporation can be supplied by electric heating or direct combustion.

  The evaporation may be performed in one stage or in multiple stages. In multi-stage evaporation it is further advantageous if the steam return is intended in countercurrent with or without compressing the steam. Here, it is preferable that the multi-stage evaporation is carried out directly. When evaporating directly, the same or different evaporator types may be used in the individual stages of the evaporator cascade.

  In the evaporation of step (b), a top stream containing a second solvent and optionally hydrogen sulfide is generated.

  The bottom stream obtained from the evaporation also contains sulfur, alkali metal (poly) sulfide and further ionic sulfur compounds, and trace amounts of a second solvent and optionally sodium thiosulfate and sodium hydroxide. The evaporation concentrate residue in the production of sodium preferably contains 65 to 75% by weight of sulfur, 20 to 25% by weight of sodium and 4 to 10% by weight of oxygen for elemental analysis, for example 69% by weight of sulfur, sodium It has a content of 23% by weight and oxygen 8% by weight.

  In the case of potassium production, the evaporation concentrate residue contains, for example, 60-70% by weight of sulfur, 25-37% by weight of potassium, and 4-10% by weight of oxygen with respect to elemental analysis.

  After concentrating the mixture comprising the second solvent, the alkali metal cation, the further ionic sulfur compound and the (poly) sulfide anion by evaporation in step (b), the resulting concentrated mixture resulting from the evaporation as a bottoms stream is: In a preferred embodiment, the ionic sulfur oxygen compound contained therein may be purified before carrying out the second electrolysis in step (c).

  For purification, the bottom stream of step (b) is preferably contacted with a gas stream containing hydrogen sulfide. Here, the hydrogen sulfide used for the purification is preferably industrially pure hydrogen sulfide. In addition to the hydrogen sulfide, the supplied gas stream may contain an inert gas in the case of the method. The inert gas that may be included in the case of the method is, for example, nitrogen, hydrogen or a noble gas, in particular nitrogen.

  In the purification, for example, an alkali metal hydroxide still contained in the tower bottom stream reacts with hydrogen sulfide to become an alkali metal (poly) sulfide and water. At the same time, the second solvent still contained or the water produced in the reaction is removed from the mixture, resulting in an alkali metal (poly) sulfide that is substantially free of impurities.

  Preferably, the concentrated mixture of (b) and the gas stream containing hydrogen sulfide are counter-flowed and purified. Here, it is particularly preferred that a column is used, wherein the concentrated mixture of step (b) is fed at the top of the column and the gas stream comprising hydrogen sulfide is fed to the side feed section. Is supplied through. The hydrogen sulfide rises in the tower and the concentrated mixture of step (b) flows downward in the tower.

  The tower used is preferably a tower having an internal structure. Suitable internal structures are, for example, floors, irregular packings or structural packings.

  The apparatus in which the purification is carried out, for example the column, is dimensioned such that the residence time of the concentrated mixture of step (b) is at least 10 seconds to 30 minutes, preferably at least 2 minutes. Is preferred.

  In a preferred embodiment, the column in which the purification is carried out is further heated below the side feed for the gas stream containing hydrogen sulfide. Here, the heating may be performed, for example, by a double jacket or by a tube introduced into the tower through which the heat medium flows. Alternatively, heating by electricity is also conceivable. As the heat medium, for example, steam, heat medium oil or salt melt is also suitable.

  By the further heating, the hydrogen sulfide salt generated in the mixture is decomposed into hydrogen sulfide and alkali metal (poly) sulfide. For this purpose, the temperature in the range of 320 to 400 ° C., preferably in the range of 340 to 350 ° C., is adjusted by further heating in the tower.

  At the bottom of the apparatus for carrying out the purification, a mixture containing substantially alkali metal (poly) sulfide is obtained. Furthermore, further impurities may be included up to 0.5% by weight, preferably up to 0.1% by weight. Such impurities include in particular alkali metal hydroxides.

  A gas stream comprising a second solvent and hydrogen sulfide is obtained at the top of the apparatus for further purification. A gas stream comprising the second solvent and hydrogen sulfide, which is withdrawn from the apparatus for purification, in particular from the column, at the top of the column, is introduced into a condenser. In this condenser, the second solvent is condensed and removed from the stream containing the second solvent and hydrogen sulfide. Here, the condensed second solvent is generally still mixed with hydrogen sulfide, and is preferably supplied to the cathode chamber of the first electrolysis. The gaseous, substantially solvent-free hydrogen sulfide is returned to the column.

  If multistage, direct evaporation is used in step (b), further purification can be achieved with almost complete removal of the second solvent in one of several evaporation stages, preferably in the last evaporation stage. It is possible to do so.

  After the mixture comprising the second solvent, alkali metal cation and (poly) sulfide anion is concentrated in step (b) or further purified, the resulting stream containing alkali metal (poly) sulfide is: Supplied to the second electrolysis.

  The second electrolysis is preferably carried out in a second electrolysis cell formed from an anode chamber and a cathode chamber separated by an alkali metal cation conductive solid electrolyte. As an electrolytic cell for the second electrolysis, in particular, an electrolytic cell whose structure corresponds to the structure of an electrolytic cell that may be used in a sodium-sulfur battery is suitable.

  The solid electrolyte is preferably an alkali metal cation conductive ceramic, in particular β-aluminum oxide, β ″ -aluminum oxide or β / β ″ -aluminum oxide. Here, each alkali metal cation of the alkali metal to be produced is bonded to the ceramic.

  In addition to alkali metal-β-aluminum oxide, alkali metal-β ″ -aluminum oxide or alkali metal-β / β ″ -aluminum oxide, corresponding alkali metal analogues of NASICON® ceramics are also suitable. . The alkali metals used are each alkali metals obtained by the process according to the invention.

If the alkali metal to be produced is lithium, then LISICON and particularly preferably Li ion conductors with a garnet structure, for example Li ₅ La ₃ Ta ₂ O ₁₂ or Li ₇ La ₃ Zr ₂ O ₁₂ are also suitable. is there.

  In the second electrolysis cell, the alkali metal (poly) sulfide melt obtained by concentration in step (b) or the alkali metal (poly) sulfide from the further purification is electrochemically separated into alkali metal and sulfur. Is done. This electrolysis is carried out at a temperature at which the alkali metal to be produced is present in a molten state. The electrolysis is preferably carried out at a temperature in the range of 290 to 330 ° C., in particular 310 to 320 ° C. and atmospheric pressure.

  On the anode side of the electrolysis cell is a special steel stabilized with molybdenum, for example an electrode made of special steel, material number 1.4571, which may be chromed, or, for example, steel with material number 1.7218. A chromium steel electrode is preferably used. The cathode is preferably an alkali metal electrode. Here, the obtained alkali metal is also used as an electrode.

  In order to operate the second electrolysis, the alkali metal (poly) sulfide is supplied in liquid form to the anode chamber. This alkali metal (poly) sulfide is decomposed into an alkali metal cation and a (poly) sulfide anion. The alkali metal cation is passed through the solid electrolyte and thus reaches the cathode chamber. In this cathode chamber, the alkali metal cations receive electrons and thus form the molten liquid alkali metal. In the anode chamber, since the (poly) sulfide anion passes electrons through the anode, reduced (poly) sulfide is generated first, and finally sulfur is generated. Due to the electrolysis temperature, sulfur is present in liquid form and can be removed from the anode chamber. Usually, sulfur is removed from the upper portion of the anode chamber because sulfur is less dense than alkali metal (poly) sulfides. Therefore, sulfur increases.

  In a particularly preferred embodiment, the sulfur obtained in the second electrolysis and the unreacted ionic sulfur compound are returned to the first electrolysis. For this purpose, sulfur is preferably sprayed together with unreacted ionic sulfur compounds in the form of a melt onto the suspension introduced into the cathode compartment of the first electrolysis. Here, the melt is solidified to produce finely dispersed sulfur particles in the second solvent.

  Embodiments of the invention are illustrated in the drawings and are described in detail in the following description.

  In FIG. 1, the first electrolysis is shown as a process flow diagram.

  The first electrolysis cell 1 includes an anode chamber 3 and a cathode chamber 5 which are separated from each other by a membrane 7. In the anode chamber 3 there is an anode 9 which is preferably made of coated titanium, wherein the coating is made of titanium, tantalum and / or platinum metals, for example iridium, ruthenium, platinum and rhodium metals. It is formed from a mixed oxide. The cathode chamber 5 houses a cathode 11 which is preferably made of special steel.

  An alkali metal salt solution is supplied from the first receiver 15 to the anode chamber 3 via the first supply 13. The alkali metal salt solution contained in the first receiver 15 is preferably an alkali metal halide aqueous solution, for example, an alkali metal chloride aqueous solution. The alkali metal halide is particularly preferably sodium chloride.

  Here, the alkali metal salt is preferably dissolved in water as a solvent. However, it is also possible to dissolve this alkali metal salt in a suitable organic solvent, for example an alcohol.

  For this purpose, the alkali metal salt is supplied to the first receiver 15 via the alkali metal salt conduit 17 and the solvent, in particular water, via the solvent conduit 19.

  By applying an external voltage, the circuit is closed and chlorine is produced at the anode 9, which is removed from the anode chamber 3 together with the circulated alkali metal salt solution.

  In the degassing device 21, chlorine is removed from the stream taken out from the anode chamber and the remaining stream is returned to the first receiver 15. Chlorine is removed from this process via a chlorine removal conduit 23.

  In the electrolytic cell 1, alkali metal cations enter the cathode chamber 5 through the cation selective membrane 7. A suspension containing elemental sulfur and a second solvent, such as an organic solvent or water, preferably water, flows into the cathode chamber via a second supply 25.

  For this purpose, elemental sulfur is introduced via the sulfur conduit 27 and a second solvent is introduced via the solvent conduit 29 into the second receiver 31 where they are mixed. A mixture containing the second solvent and sulfur is introduced from the second receiver 31 into the cathode chamber 5 of the first electrolysis via the second supply 25. In order to increase the conductivity of the mixture containing the second solvent and sulfur in the second receiver 31, a smaller amount of alkali metal hydroxide may be added to the mixture.

  Instead of the first receptor 15 in which the solvent and the alkali metal salt are mixed and the second receptor 31 in which the elemental sulfur and the second solvent are mixed, any other alternative known to those skilled in the art. It is also possible to use a device. Therefore, for example, it is possible to spray sulfur as a melt on the second solvent and then supply it to the cathode chamber 5. Furthermore, for example, the alkali metal salt can be directly metered into a pipe through which the solvent passes.

  A mixture containing the second solvent, the alkali metal cation and the (poly) sulfide anion is taken out from the cathode chamber 5 through the cathode outflow portion 33. Furthermore, the mixture taken out via the cathode outflow portion 33 may contain an alkali metal hydroxide. The alkali metal cation and (poly) sulfide anion contained in the mixture usually form an alkali metal (poly) sulfide.

  In one embodiment, the mixture withdrawn via the cathode outlet 33 is circulated to enrich sulfur and the second solvent. For this purpose, for example, the mixture taken out via the cathode outflow part 33 can first be returned to the second receiver 31.

  When the mixture taken out through the cathode outflow part 33 is not circulated, the mixture containing the second solvent, the alkali metal cation and the (poly) sulfide anion taken out through the cathode outflow part 33 is supplied to the concentration step. When the mixture taken out via the cathode outlet 33 is circulated, a partial stream is taken out and supplied to the concentration step. FIG. 2 exemplarily shows a concentration process by evaporation as a flow diagram.

  A substance stream containing the second solvent, the alkali metal cation and the (poly) sulfide anion extracted as the cathode outlet 33 is supplied to the evaporator 41. The evaporator 41 is, for example, a natural circulation type evaporator as shown in FIG. Alternatively, it is also possible to use a forced circulation circulating evaporator, a falling liquid film evaporator or a thin film evaporator. Any optional other evaporator known to those skilled in the art may be used. When evaporation is performed discontinuously, for example, a stirred tank may be used instead of the natural circulation circulating evaporator shown here.

  The evaporator 41 is preferably provided with a liquid separator 43.

  When using a circulation evaporator, the liquid reaches the evaporator device 47 via the circulation conduit 45. The evaporator device 47 may be formed, for example, in the form of a tube bundle heat medium. Here, a heat medium such as steam, heat transfer oil or salt melt flows through the tubes of the tube bundle. Additionally or alternatively, the evaporator device 47 may have a double jacket for heating. Further, instead of the heating device, it is possible to electrically heat with a temperature control medium or to heat by a direct heating method. In the uppermost part of the evaporator device 47, an upper stream containing a gaseous second solvent, a liquid second solvent, an alkali metal cation and a (poly) sulfide anion is taken out and supplied to the liquid separator 43. In the liquid separator 43, the gaseous second solvent is separated and removed from the process via a solvent removal conduit 49. The mixture comprising the second solvent, alkali metal cation and (poly) sulfide anion is circulated until a desired concentration of residual solvent is obtained. As soon as a steady state is reached, the mixture comprising the second solvent, the alkali metal cation and the (poly) sulfide anion is fed uniformly through the cathode outlet 33 flowing out to the circulation conduit 45 before the mixture is fed. In addition, a mixture containing the concentrated second solvent and alkali metal (poly) sulfide is taken out from the circulation conduit via the takeout pipe 51.

  In a preferred embodiment, the mixture removed through the extraction line 51 is further purified. This purification is shown schematically in FIG. 3 using a flow diagram.

  The concentrated alkali metal (poly) sulfide melt is optionally fed to a preheater 53 where it is heated. Here, the preheating may be performed, for example, electrically, by a heat medium, for example, steam, heat transfer oil or salt melt. The prewarmed alkali metal (poly) sulfide melt is then preferably fed to the upper region of the column 55. Column 55 generally includes internal structures, such as floors, irregular packings or structured packings or non-structural packings.

  In the lower range, hydrogen sulfide is added to the tower 55 through the side supply 57. This hydrogen sulfide may additionally be mixed with an inert gas, for example nitrogen. Within the column 55, it is preferred that the hydrogen sulfide and the alkali metal (poly) sulfide melt be countercurrently and mixed vigorously. Thereby, the alkali metal hydroxide optionally still contained in the alkali metal (poly) sulfide melt is converted into alkali metal (poly) sulfide and water.

  From the tower 55, a tower top stream 59 containing water and hydrogen sulfide is taken out at the tower top. The top stream 59 is introduced into the condenser 61 where water is condensed. Further, the hydrogen sulfide existing as a gas is returned to the tower 55 via the circulation conduit 63. Water that still contains hydrogen sulfide residues is withdrawn from the condenser 61 (if water is used as the second solvent) and returned to the first electrolysis cathode chamber via a withdrawal conduit 65. Is done.

  At the bottom of the column 55, a substance stream 67 containing alkali metal (poly) sulfide substantially free of solvent is taken off.

  The alkali metal (poly) sulfide melt obtained by the evaporation or the substance stream 67 containing the alkali metal (poly) sulfide obtained in the implementation of the purification shown in FIG. 3 is supplied to the second electrolysis. This is exemplarily shown in FIG.

  The second electrolysis may be performed in multiple stages. For this purpose, a plurality of electrolysis cells 71 are connected in parallel.

  The electrolysis cell 71 has an anode chamber 73 into which a plurality of electrode devices 75 are introduced in the embodiments described in the present application. The electrode device 75 includes one cylindrical body made of a solid electrolyte, and divides the cathode chamber and the anode chamber 73 existing in the solid electrolyte. Via conduit 79, the alkali metal (poly) sulfide melt from the evaporative concentration step shown in FIG. 2 or, if further purification is carried out, the alkali metal (poly) sulfide from the purification shown in FIG. , And supplied to the anode chamber 73 of each of the electrolytic cells.

  In the operation of the electrolytic cell 71, the alkali metal polysulfide is decomposed into alkali metal and sulfur by electrolysis. Therefore, the alkali metal cation reaches the cathode chamber where the alkali metal is formed through the alkali metal cation conductive solid electrolyte. This alkali metal is removed from the cathode chamber and discharged via the product conduit 77. Meanwhile, sulfur is formed from polysulfide at the anode. Here, the electrolysis is operated at a temperature at which the alkali metal is present in liquid form.

  Therefore, it is preferable that a special steel electrode is accommodated in the anode chamber. The generated sulfur rises because it has a lower density than the alkali metal polysulfide. The sulfur may then be removed via the sulfur removal conduit 81 in the upper part of the anode chamber 73. The sulfur taken out via the sulfur take-out conduit 81 is preferably returned to the first electrolysis shown in FIG. For this purpose, the sulfur is introduced into the second receiver 31 via, for example, a sulfur conduit 27. Alternatively, as described above, the second electrolysis sulfur taken out as a sulfur melt can be sprayed onto the second solvent and then supplied to the first electrolysis cell 1.

  The entire process without additional purification shown in FIG. 3 is exemplarily shown in FIG.

  When sodium is produced by the process according to the invention, sodium chloride is preferably fed via the alkali metal salt conduit 17 and preferably via the solvent conduit 19, said sodium chloride being dissolved in water and It is introduced into the electrolysis cell via a supply 13. In the first electrolysis cell 1, sodium chloride is separated into sodium ions and chlorine. Chlorine is withdrawn from the anode chamber of the first electrolysis cell 1 together with the circulated sodium chloride solution. The chlorine is separated and removed from the process through a chlorine removal conduit 23. The remaining sodium chloride solution is concentrated by adding additional sodium chloride and returned to the anode chamber of the first electrolysis cell 1.

  The sodium ions penetrate the cation permeable membrane 7 and reach the cathode chamber 5. Here, a mixture containing a solvent, preferably water and sulfur, flows through the cathode chamber 5. Since sulfur is preferably reduced compared to hydrogen, sodium (poly) sulfide is formed in the cathode chamber, where sodium (poly) sulfide is separated into sodium cation and (poly) sulfide anion. The A solution containing sodium (poly) sulfide is supplied to the evaporator 41 from the cathode chamber. In the evaporator 41, sodium (poly) sulfide is concentrated by evaporation of water. The concentrated sodium (poly) sulfide is then passed through the second electrolysis cell 71, where the sodium (poly) sulfide is decomposed into sodium and sulfur by electrolysis. Sodium ions permeate the sodium ion conductive solid electrolyte and reach the cathode chamber, from which the generated sodium is taken out as a molten liquid. Sulfur is extracted from the anode chamber and returned to the first electrolysis.

First electrolysis process flow chart Concentration process flow chart Additional purification process flow diagram Second electrolysis process flow chart Process flow diagram of the entire method The figure which shows the electrolytic cell for experiment for execution of the second electrolysis

Example:
First electrolysis stage:
Electrolysis of the saline solution was performed in the electrolytic cell shown in FIG. The electrolysis cell was divided into an anode chamber and a cathode chamber using a cation exchange membrane (Nafion® 324). As the anode, a titanium anode coated with a Ru / Ir-titanium mixed oxide was used in the form of expanded metal. The cathode was a special steel expanded metal with material number 1.4571.

  Electrolysis was carried out discontinuously with increasing sodium chloride stepwise. The anolyte was circulated and pumped from the first receiver 15 through the anode chamber 3 of the electrolysis cell using a laboratory circulation pump. At the beginning, 1566 g of 23% aqueous sodium chloride solution was charged as the anolyte.

  The catholyte was circulated and pumped from the second receiver 31 through the cathode chamber 5 of the electrolysis cell using an experimental circulation pump. At the beginning, 1700 g of a 2.5% aqueous sodium tetrasulfide solution was charged as the catholyte. To this solution, 80 g of sulfur powder was added.

The electrolysis was performed at a temperature in the range of 75 ° C. to 80 ° C., a current density i of 2000 A / m ² , and a cell voltage in the range of 3.5 to 5 Volt.

  The electrolysis was performed batchwise in 4 stages of 40 Ah each, resulting in a total conversion of 160 Ah. After the 40 Ah first electrolysis stage, 85 g of sodium chloride was added to the anolyte and 80 g of sulfur to the catholyte. This was performed a total of 3 times, resulting in a total addition of 320 g sulfur and 255 g sodium chloride.

  During the electrolysis, the anode side was washed with nitrogen. The anode side exhaust gas passed through two front and rear cleaning devices operated with 10% aqueous NaOH.

  Similarly, the cathode side was also washed with nitrogen. The cathode side exhaust gas was passed through a gas analyzer that measures the hydrogen content. The solution was drained after electrolysis and analyzed for elements.

  175 g of chloride was detected in both of the cleaning apparatuses for the anode exhaust gas.

concentrated:
The cathode discharge was evaporated and concentrated at elevated temperatures while stirring discontinuously in an electrically heated distillation flask. The boiling temperature rose from 102 ° C to 200 ° C during this concentration. The evaporative concentration system was limited to 200 ° C. The contents in the distillation flask were in a liquid state over the course of concentration. Distillation was stopped when the distillate no longer overflowed.

  1684 g of vapor condensate was obtained. The flask contents were then cooled to room temperature where the contents solidified. The solidified sodium (poly) sulfide melt was crushed in a glove box inactivated with nitrogen to obtain sodium (poly) sulfide powder. A partial amount of the sodium (poly) sulfide powder was quantitatively analyzed with respect to elements.

Second electrolysis stage:
The electrolysis of the sodium (poly) sulfide melt was carried out in an experimental apparatus having a chamber in a steel vessel 100, which is heated by an electric heating apparatus 101, as shown in FIG. The electrolysis cell 90 is a U-shaped tube made of borosilicate glass, where both electrodes are placed in an electrolysis leg 91 together with a ceramic membrane, while the second leg 92 is nothing. It was in the state of not being attached (ohne Einbau). The membrane 93 was a sodium ion conductive β ″ -Al ₂ O ₃ ceramic. Membrane 93 was in the form of a tube closed on one side, where sodium 94 was placed inside the tube and sodium (poly) sulfide melt was placed outside the tube. The effective surface area of the tubular membrane 93 was 14 cm ² . A graphite felt of the type GFD5EA (manufacturer SGL) is used as the anode 96, and this graphite felt is brought into electrical contact with the positive side of the power supply device through four contact plates 97 made of chrome-plated steel of material number 1.4404. It was. As the cathode, molten sodium 94 functioned in electrical contact with the negative side of the power supply device through a special steel rod 98 functioned. Both electrode chambers were deactivated with nitrogen.

  The electrolysis was performed discontinuously. Before the start of electrolysis, 40 g of sodium (poly) sulfide powder obtained by concentration in the glove box was filled in a leg 92 to which no U-shaped tube was attached. Next, the filling opening 99 was closed. Thereafter, the electrolyzer was heated from room temperature to 300 ° C. for 10 hours. Here, the sodium (poly) sulfide powder was melted. By applying a slight overpressure to the unattached leg, the melt moved to the electrolysis zone.

  The electrolysis was performed at a temperature in the range of 290 ° C. to 310 ° C., a current of 1.4 A, and a cell voltage in the range of 2.5 to 3 Volt over an electrolysis time of 7 hours.

  After electrolysis, 8 g of sodium metal was discharged.

1 First Electrolytic Cell 3 Anode Chamber 5 Cathode Chamber 7 Membrane 9 Anode 11 Cathode 13 First Supply 15 First Receptor 17 Alkali Metal Salt Conduit 19 Solvent Conduit 21 Deaerator 23 Chlorine Extraction Conduit 25 Second Supply 27 Sulfur Conduit 29 Solvent conduit 31 Second receiver 33 Cathode outflow portion 41 Evaporator 43 Liquid separator 45 Circulating conduit 47 Evaporator device 49 Solvent extraction conduit 51 Extraction conduit 53 Preheater 55 Tower 57 Side supply portion 59 Overhead flow 61 Condenser 63 Circulation conduit 65 Extraction conduit 67 Material flow substantially containing alkali metal (poly) sulfide 71 Second electrolysis cell 73 Anode chamber 75 Electrode device 77 Product conduit 79 Conduit 81 Sulfur extraction conduit 90 Electrolysis cell 91 Electrolysis leg 92 Nothing Unattached legs 93 Membrane 94 Sodium 95 Sodium (poly) sulfide Melt 96 Anode 97 Contact plate 98 Special steel rod 99 Filling opening 100 Steel container 101 Electric heating device

Claims (14)

A method for producing an alkali metal from a salt of an alkali metal soluble in a solvent, comprising the following steps:
(A) performing a first electrolysis in a first electrolysis cell (1) including an anode chamber (3) and a cathode chamber (5), wherein the anode chamber (3) of the first electrolysis cell (1) The cathode chamber (5) is separated by an alkali metal cation permeable membrane (7). Here, an alkali metal salt dissolved in a solvent is supplied to the anode chamber (3), and the cathode chamber ( 5) is supplied with a suspension containing sulfur and a second solvent, and a mixture containing the second solvent, alkali metal cation, (poly) sulfide anion and further ionic sulfur compound is removed from the cathode chamber (5).
(B) Concentrating the mixture containing the second solvent, alkali metal cation, (poly) sulfide anion, and further ionic sulfur compound, taken out from the cathode chamber, to thereby obtain an alkali metal (poly) sulfide melt containing almost no solvent. The process of
(C) In the second electrolysis cell (71) including the anode chamber (73) and the cathode chamber, performing the second electrolysis at a temperature exceeding the melting temperature of the alkali metal, wherein the anode of the second electrolysis cell The chamber (73) and the cathode chamber are separated by an alkali metal cation conductive solid electrolyte, and the alkali metal (poly) sulfide melt of step (b) is supplied to the anode chamber (73), Taking out sulfur from the anode chamber and taking out a liquid alkali metal from the cathode chamber,
Including said method.   Alkali metal cations and (poly) sulfide anions in a mixture comprising the second solvent, alkali metal cations, (poly) sulfide anions and further ionic sulfur compounds, taken from the cathode chamber (5) of the first electrolysis cell (1) The process according to claim 1, characterized in that the concentration of is carried out in an evaporator (41).   3. Process according to claim 1 or 2, characterized in that the evaporation is carried out at a temperature in the range from 80 to 400 [deg.] C. and a vapor pressure in the range from 0.1 to 2 bar (absolute pressure).   The method according to any one of claims 1 to 3, characterized in that the concentrated mixture obtained in step (b) is purified prior to performing the second electrolysis.   The process according to claim 4, characterized in that the concentrated mixture of step (b) is purified by contacting with a gas stream comprising hydrogen sulfide.   6. A method according to claim 5, characterized in that the concentrated mixture of step (b) and the gaseous stream comprising hydrogen sulfide are countercurrentd.   The purification is carried out in a column (55), wherein the concentrated mixture of step (b) is fed at the top of the column and the gaseous stream containing hydrogen sulfide is passed through a side feed (57). 7. A method according to any one of claims 4 to 6, characterized in that it is supplied.   The method according to claim 7, characterized in that the column (55) is heated below the side supply (57) for the gas stream comprising hydrogen sulfide.   The alkali metal ion conductive solid electrolyte of the second electrolysis cell (71) is formed from alkali metal-β-aluminum oxide, alkali metal-β ″ -aluminum oxide or alkali metal-β / β ″ -aluminum oxide. 9. The method according to any one of claims 1 to 8, characterized in that:   The sulfur taken out from the anode chamber (73) of the second electrolysis cell (71) is returned to the first electrolysis of the step (a), according to any one of claims 1 to 9. the method of.   The method according to any one of claims 1 to 10, characterized in that the alkali metal is sodium, potassium or lithium.   12. The method according to claim 1, wherein the alkali metal salt is an alkali metal halide.   13. The method according to any one of claims 1 to 12, characterized in that the alkali metal salt is sodium chloride.   14. The method according to claim 1, wherein the solvent in which the alkali metal salt is dissolved and / or the second solvent is water.

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