Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C1/00—Electrolytic production, recovery or refining of metals by electrolysis of solutions
  • C25C1/02—Electrolytic production, recovery or refining of metals by electrolysis of solutions of light metals
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to an electrochemical process for obtaining alkali metals from aqueous solution by an electrochemical process, and to an electrolysis cell for carrying out this process.
• the invention further relates to an electrochemical process for recycling alkali metals from aqueous solution.
• alkali metal as used in the context of this invention denotes lithium, sodium and potassium.
• Lithium is an important inorganic basic chemical and is used in a number of applications. It is used for the preparation of organolithium compounds, as an alloy additive to aluminum or magnesium and for lithium batteries.
• lithium is produced by melt flow electrolysis of a eutectic mixture of lithium chloride and potassium chloride at 400 to 460 ° C. (Ulimann's Encyclopedia of Industrial Chemistry, Sixth Edition, 1998 Electronic Release). This process has a high energy consumption (28-32 kWh / kg Li).
• the process has the serious disadvantage that only anhydrous lithium chloride can be used.
• the lithium chloride which is primarily present as an aqueous solution, must therefore be worked up to an anhydrous solid in an energy-intensive process. Since lithium chloride is hygroscopic, drying and handling require a special effort.
• Aqueous lithium salt solutions are often obtained when organolithium reactions are carried out. Due to the increasing consumption of lithium batteries, lithium-containing waste is also generated there. These can also be converted into aqueous lithium solutions. Since lithium is also very expensive in the form of its salts, recycling lithium is interesting.
• a 2 cm salt melt of two alkali metal iodides serves as the electrolyte (preferably Lil and Csl or Lil and KI), while lithium metal is deposited cathodically.
• the current density is between 1 and 4 kA / m 2 without a mass transfer limitation occurring.
• Sodium is an important inorganic basic product that is used, for example, for the production of sodium amide, sodium alcoholates and sodium borohydride. It is obtained technically after the Downs process by electrolysis of molten table salt. This process has a high energy consumption of> 10 kWh / kg sodium (Büchner et al., Industrial Inorganic Chemistry, 2nd edition, Verlag Chemie, pages 228 ff). Furthermore, the method has the serious disadvantage that the electrolysis cells are destroyed by the solidification of the molten salt when switched off. Furthermore, the sodium metal obtained by the Downs process has the disadvantage that, due to the process, it is contaminated with calcium, the residual content of which can only be reduced by subsequent cleaning steps, but can never be completely eliminated.
• Potassium is also an important basic inorganic product that is used, for example, for the production of potassium alcoholates, potassium amides and potassium alloys.
• the disadvantage is that the process works at high temperatures (870 ° C).
• the resulting potassium contains about 1% sodium as an impurity and must therefore be purified by a further rectification.
• the main disadvantage is that the sodium used is expensive. This is because sodium is technically melted after the Downs process by electrolysis Table salt is obtained, whereby an energy expenditure of at least 10 kWh / kg sodium is necessary. This corresponds to about 5.3 kWh / kg of potassium (with 100% yield).
• GB 1,155,927 describes a process in which using a solid sodium ion conductor, such as. B. ß-Al 2 O 3 , with amalgam as the anode and sodium as the cathode can be obtained electrochemically sodium metal from sodium amalgam.
• a solid sodium ion conductor such as. B. ß-Al 2 O 3
• amalgam as the anode
• sodium as the cathode
• the execution of the method described in GB 1,155,927 does not lead to the results described there with regard to sodium conversion, product purity and current density.
• the system described there behaves unstably over the course of a few days if the claimed temperature range is maintained.
• Electrolytic cells that are used in an electrochemical process for producing alkali metal and have a solid ion conductor are often not suitable for long-term operation.
• One reason for this is the mechanical instability of the solid ion conductor, which occurs after a certain operating time.
• the object was therefore to develop a process which does not have the disadvantages described above (high energy consumption, calcium content of sodium, high temperature, etc.). Another task was to provide an electrolytic cell suitable for carrying out these processes. In addition, the object was to find a process which makes it possible to recycle alkali metals from aqueous alkali metal wastes, in particular lithium from aqueous lithium wastes.
• an electrolysis is carried out in an electrolytic cell according to the invention with a solid ion conductor.
• the ion conductor separates the electrolytic cell into two parts.
• One part contains the liquid alkali metal, which is connected as the cathode.
• an aqueous salt solution of this alkali metal which is in contact with an anode.
• Any commercially available anode materials can be used as the anode
• alkali metal ion conductors are not stable against water and / or against alkali metal ions, so that the alkali metal ion conductor is destroyed after a short time during the experiment. This destruction can either lead to mechanical failure of the ion conductor or loss of conductivity of the ion conductor. It is therefore a further object of the invention to keep the ion conductor stable over longer service lives.
• the service life of the ion conductor can be greatly increased by applying an ion-conducting protective layer on the corresponding side of the ion conductor.
• the present invention also relates to an electrolytic cell comprising an anode compartment which comprises an aqueous solution of at least one alkali metal salt, a cathode compartment and a solid electrolyte, by which the anode compartment and the cathode compartment are separated from one another, which is characterized in that the part of the surface of the Solid electrolyte which has at least one further ion-conducting layer with the anode compartment and / or the part of the surface of the solid electrolyte which is in contact with the cathode compartment.
• the present invention also relates to a method for producing an alkali metal from an aqueous solution comprising at least one salt of this alkali metal using this electrolysis cell.
• aqueous alkali metal salt solution in the anode compartment, and all suitable alkali metal salt solutions can be used.
• mixtures with water-miscible organic solvents can also be used as long as the organic solvents are stable under the reaction conditions.
• solvents are alcohols, such as. As methanol and ethanol, and carbonates, such as. B. propylene or ethylene carbonate.
• the process according to the invention is generally carried out in such a way that the aqueous alkaline metal salt solution is in motion in the anode compartment and the anode is immersed in the aqueous solution.
• the movement of the solution can be brought about by any means, with stirring with a stirring device or pumping over being preferred.
• Any commercially available anode material can be used as the anode, which is immersed in the aqueous solution.
• Suitable anode materials are, for example, noble metals such as platinum or metal oxides on titanium or mixed oxides of the RuOxTiOx type, as well as graphite, carbon electrodes and lead dioxides.
• the anode and cathode compartments of the electrolysis cell according to the invention are separated from one another by a helium-tight alkali metal ion-conducting solid electrolyte.
• the ionic conductors preferably meet the following conditions:
• the ion conductors show good alkali metal ion conductivity at the reaction temperature ( ⁇ > 0.005 S / cm).
• the ion conductors have a negligibly low electron conductivity.
• Ceramic materials such as NASICON (Na + super ionic conductor) come into consideration in sodium production, the composition of which is described in detail in EP-A 0 559 400 and in “A. D. Robertson, AR West, AG Ritchie, Solid State Ionics, 1997, 104, pages 1-11 and literature cited therein, in particular page 3, left column ".
• Sodium ion-conducting glasses as well as zeolites and feldspar are also suitable.
• Preferred Sodium ß "alumina, sodium ß alumina or sodium ß / ß" alumina is used.
• a large number of materials can also be used in the production of potassium. Both the use of ceramics and the use of glasses are possible.
• the following materials can be considered: KBiO 3 (TN Nguyen et al., Chem. Mater., 1993, 5, pages 1273-1276), gallium oxide-titanium dioxide-potassium oxide systems (pages Yoshikado et al., Solid State Ionics, 1992 , 53-56, pages 754-762), Alumim ' umoxid-titanium dioxide-potassium oxide systems and KASICON (K + super ionic conductor), the composition of which is described in detail in “M. Lejeune et al., J. Non-Cryst.
• Potassium- ⁇ " aluminum oxide, potassium- ⁇ -aluminum oxide or potassium- ⁇ / ⁇ "aluminum oxide are preferably used, starting from sodium ⁇ " aluminum oxide, sodium -ß-alumina or sodium-ß / ß "- alumina can be produced by cation exchange.
• a large number of materials can also be used in the production of lithium. Ceramic materials or glasses are particularly suitable.
• the following solid electrolytes are particularly suitable for the production of lithium by the process according to the invention:
• Li-ß "-Al 2 O 3 or Li-ß-Al 2 O 3 their production from Na-ß" -Al 2 O 3 or from Na-ß-Al 2 O 3 by replacing the sodium ions with lithium ions is possible (O. Schaf, T.
• lithium- ⁇ "aluminum oxide, lithium- ⁇ -aluminum oxide and lithium- ⁇ / ⁇ " aluminum oxide each starting from sodium- ⁇ "aluminum oxide, sodium- ⁇ -aluminum oxide or sodium- ⁇ / ⁇ " - Alumina can be produced by cation exchange.
• Lithium analogs of NASICON ceramics are also preferred.
• the present invention also relates to an electrolysis cell as described above, which is characterized in that
• the at least one alkali metal salt is a lithium salt or a mixture of two or more thereof and the solid electrolyte is selected from the group consisting of LitWum- ⁇ -aluminum oxide, lithium- ⁇ "aluminum oxide, lithium- ⁇ / ⁇ " - Alumina and lithium analogs from NASICON ceramics, or that
• the at least one alkali metal salt is a sodium salt or a mixture of two or more thereof and the solid electrolyte is selected from the group consisting of Sodium ß-aluminum oxide, sodium ß '' - aluminum oxide, sodium ß / ß "-
• the at least one alkali metal salt is a potassium salt or a mixture of two or more thereof and the solid electrolyte is selected from the group consisting of potassium- ⁇ -aluminum oxide, potassium- ⁇ "aluminum oxide, Potassium ß / ß '' - Almnini ⁇ ra ⁇ oxid and potassium analogues from NASICON ceramics.
• the solid electrolyte expediently has the form of a thin-walled but nevertheless pressure-resistant tube which is closed on one side (EP-B 0 424 673) and on the open end of which an electrically insulating ring is applied by means of a helium-tight, likewise electrically insulating glass solder connection (GB 2 207 545, EP- B 0 482 785).
• the wall thickness of the solid electrolyte which conducts alkali metal ions is generally in the range from 0.3 to 5 mm, preferably in the range from 1 to 3 mm and particularly preferably in the range from 1 to 2 mm.
• cross-sectional shape of the tube closed on one side is circular in the preferred embodiment.
• cross-sectional shapes with an enlarged surface are also conceivable, which can be derived, for example, from a combination of several circular surfaces.
• solid electrolytes are generally used, which have a leak rate of less than 10 " (mbar • l) / s in a helium leak test, ie are helium-tight within the detection limit.
• the strict requirements with regard to tightness are imperative Necessary since oxygen and / or air humidity must be kept away from the alkali metal in any case, and it is also necessary to separate the alkali metal and aqueous solution from one another, since otherwise safe operation of the electrolytic cell or safe implementation of the method according to the invention due to the strong exothermic reaction between water and moisture on the one hand and alkali metal on the other hand cannot be guaranteed.
• reaction conditions includes both the physical conditions, such as electrolysis voltage, Temperature or pressure, as well as the chemical conditions, such as the pH of the reaction or composition of the anolyte or the catholyte.
• the present invention relates to an electrolysis cell as described above, which is characterized in that the at least one ion-conducting layer, which has the surface of the solid electrolyte in contact with the anode compartment, a polymer electrolyte (for lithium: e.g. BL Kavan et al, Chem Rev., 1997, 97 pages from 3061 to 3082 and references cited therein; for sodium.. for example NAFION ® (a trademark of DuPont; this refers to ion-exchange membranes of a tetrafluoroethylene Perfluorvinylethercopolymer with.
• a polymer electrolyte for lithium: e.g. BL Kavan et al, Chem Rev., 1997, 97 pages from 3061 to 3082 and references cited therein; for sodium.. for example NAFION ® (a trademark of DuPont; this refers to ion-exchange membranes of a tetrafluoroethylene Perfluorviny
• Carboxylic acid groups as described in "Ulimanns Enzyklopadie, 1999, Wiley-VCH"), a ceramic electrolyte (perovskite structures for Li, Na, K; LISICON or lithium analogs from NASICON ceramics for Li; NASICON for Na; KASICON for K) a compound which intercalates the alkali metal ions of the at least one alkali metal salt of the aqueous solution of the anode compartment, or is a mixture of two or more of them.
• a ceramic electrolyte perovskite structures for Li, Na, K; LISICON or lithium analogs from NASICON ceramics for Li; NASICON for Na; KASICON for K
• a compound which intercalates the alkali metal ions of the at least one alkali metal salt of the aqueous solution of the anode compartment or is a mixture of two or more of them.
• the present invention relates to an electrolysis cell, as described above, which is characterized in that the at least one ion-conducting layer, which has the surface of the solid electrolyte in contact with the cathode compartment, an alkali metal salt, the alkali metal being equal to that of the Alkali metal salt of the aqueous solution of the anode compartment is a compound that intercalates the alkali metal ions of the at least one alkali metal salt of the aqueous solution of the anode compartment, or a mixture of two or more thereof.
• the present invention relates to an electrolysis cell as described above, which is characterized in that (a) the at least one alkali metal salt of the aqueous solution of the anode compartment is a lithium salt or a mixture of two or more thereof, and
• the alkali metal salt which has the surface of the solid electrolyte in contact with the cathode compartment is selected from the group consisting of LiOH, LiNH 2 , LiCl, LiBr, Lil, LiOR and a mixture of two or more thereof,
• the compound that intercalates lithium ions e.g. B. graphite, C 6 Li, LiCoO 2 ,
• the at least one alkali metal salt of the aqueous solution of the anode compartment is a sodium salt or a mixture of two or more thereof and
• the alkali metal salt which has the surface of the solid electrolyte which is in contact with the cathode compartment is selected from the group consisting of NaOH, NaNH 2 , NaCl, NaBr, NaI, NaOR and one
• the at least one alkali metal salt of the aqueous solution of the anode compartment is a potassium salt or a mixture of two or more thereof and
• the alkali metal salt which has the surface of the solid electrolyte in contact with the cathode compartment, is selected from the group consisting of KOH, KNH, KC1, KBr, KI, KOR and a mixture of two or more thereof
• the compound that intercalates potassium ions is graphite, CgK or a mixture thereof, the radical R being a straight-chain or branched-chain alkyl radical having 1 to 5 carbon atoms.
• alkali metal salts MOH, MNH 2 , MCI, MBr, MI, MOR, where M stands for Li, Na or K, can be applied to the solid electrolyte in the process according to the invention by all conceivable and suitable processes according to the prior art.
• these salts are applied to the solid electrolyte in the form of a melt, an aqueous solution or an alcoholic solution.
• the present invention also relates to a method as described above, which is characterized in that the part of the surface of the solid electrolyte which is in contact with the cathode compartment is conditioned, the at least one alkali metal salt LiOH, LiNH 2 used for conditioning LiCl, LiBr, Lil, LiOR or a mixture of two or more thereof or NaOH, NaNH 2 , NaCl, NaBr, NaI, NaOR or a mixture of two or more thereof or KOH, KNH 2 , KC1, KBr, KI, KOR or a mixture of two or more thereof is used as a molten salt and / or aqueous solution and / or alcoholic solution.
• the at least one alkali metal salt LiOH, LiNH 2 used for conditioning LiCl, LiBr, Lil, LiOR or a mixture of two or more thereof or NaOH, NaNH 2 , NaCl, NaBr, NaI, NaOR or a mixture of two or more thereof or KOH, KNH 2
• the at least one chemical compound or the mixture comprising two or more of them may be the same or different in the individual conditioning steps.
• both surfaces have at least one of the ion-conducting layers mentioned. If the term "two" surfaces is used in the context of the present application, it does not mean “two” surfaces within the meaning of the number 2, but rather two types of surfaces which differ in which compartment of the electrolytic cell they are in contact with.
• two surfaces thus includes, for example, a type of cell according to the invention in which, for example, two surface sections of the solid electrolyte are in contact with, for example, the anode compartment and one surface section of the solid electrolyte is in contact with the cathode compartment.
• the cathode consists of different materials.
• the cathode consists of the alkali metal which is to be produced by the process according to the invention.
• the reaction temperature is chosen as high as possible in the process according to the invention, the temperature limit in the anode compartment being determined by the boiling temperatures of the aqueous solution of the alkali metal salt used at the selected pressure. Temperatures that are as high as possible are also selected in the cathode compartment. The reaction pressure and temperature are chosen so that the alkali metal used as the cathode in the preferred embodiment is in liquid form.
• the alkali metal is preferably introduced into the anode compartment in the form of a solid reservoir. At the start of the electrolysis, the alkali metal is then melted. However, the alkali metal can also be introduced into the cathode compartment in liquid form at the start of the electrolysis. Accordingly, the present invention also relates to an electrolysis cell as described above, which is characterized in that
• the at least one alkali metal salt of the aqueous solution of the anode compartment is a lithium salt or a mixture of two or more thereof and the cathode consists of lithium, or
• the at least one alkali metal salt of the aqueous solution of the anode compartment is a sodium salt or a mixture of two or more thereof and the cathode consists of sodium, or
• the at least one alkali metal salt of the aqueous solution of the anode compartment is a potassium salt or a mixture of two or more thereof and the cathode consists of potassium.
• the cathode compartment comprises at least one cathode which is separated from the solid electrolyte by a liquid electrolyte.
• cathode material in the cell according to the invention.
• suitable materials can serve as cathode material in the cell according to the invention.
• this include steel, pure nickel with, for example, the DIN material number 2.4066 or electrode graphite.
• the cathode is made of steel.
• the present invention also relates to an electrolysis cell as described above, which is characterized in that the cathode is a steel cathode and is separated from the solid electrolyte by a liquid electrolyte.
• Suitable steels include stainless steel, austenitic steel or unalloyed steel.
• the preferred austenitic steels include the steels with the DIN material numbers 1.4541 or 1.4571, and the preferred non-alloy steels are the steels with the DIN material numbers 1.0305 or 1.0346.
• unalloyed steels are used.
• the cathode is designed as a rod which is built into the solid electrolyte designed as a tube.
• the rod is preferably installed in such a way that a gap with a gap width in the range from 1 to 6 mm is formed between the solid electrolyte and the rod.
• the cathode can of course also have all other suitable geometries in the cell according to the invention. For example, it can be designed as a tube, as a wire mesh or as an expanded metal.
• the alkali metal is formed on the solid cathode in the process according to the invention. This rises in the liquid electrolyte at the cathode designed as a rod in accordance with the preferred embodiment and can be removed as a pure metallic phase.
• the liquid electrolyte is expediently chosen so that it is stable with respect to alkali metal.
• a liquid electrolyte is preferably used which is not consumed in the electrolysis reaction.
• an electrolyte melt is used as the liquid electrolyte.
• the present invention therefore relates to an electrolysis cell as described above, which is characterized in that the liquid electrolyte is an electrolyte melt.
• a LiOH melt is preferably used in the production of lithium, in the production of sodium NaOH melts, NaNH melts or mixtures thereof, in the production of potassium KOH melts, KNH 2 melts or mixtures thereof.
• the present invention relates to an electrolytic cell as described above, which is characterized in that
• the at least one alkali metal salt of the aqueous solution of the anode compartment is a lithium salt or a mixture of two or more thereof and the electrolyte melt is a LiOH melt
• the at least one alkali metal salt of the aqueous solution of the anode compartment is a sodium salt or a Is a mixture of two or more thereof and the electrolyte melt is selected from the group consisting of a NaOH melt, a NaNH 2 melt and a mixture thereof, or that (c) the at least one alkali metal salt of the aqueous solution of the anode compartment is a potassium salt or a Is a mixture of two or more of them and the
• EleküOlytschmelze is selected from the group consisting of a KOH melt, a KNH 2 melt and a mixture thereof. In a particularly preferred embodiment, these melts or their mixtures are used in anhydrous form. In a further particularly preferred embodiment, mixtures and particularly preferably anhydrous mixtures are used as the electrolyte melts. Among them, eutectic mixtures are preferred.
• additives which lower the melting point include additives which lower the melting point.
• all additives which lower the melting point and which do not interfere with the use of the electrolytic cell and the method according to the invention are suitable.
• the present invention also relates to an electrochemical process as described above, which is characterized in that the aqueous solution of the at least one alkali metal salt is obtained from alkali metal wastes.
• a significant amount of lithium halides is obtained in the form of aqueous solutions.
• Aqueous solutions of various lithium salts such as, for example, lithium halides, lithium sulfate, lithium sulfonates or lithium salts of organic acids, can also be recovered from lithium ion batteries, for example dissolved out.
• Another possibility for the recovery of such lithium salt solutions is the acid digestion of the electrolytes and electrodes used in batteries with, for example, hydrochloric acid or sulfuric acid.
• the lithium waste is z. B. converted into an aqueous lithium chloride solution by means of hydrochloric acid.

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