Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C5/00—Electrolytic production, recovery or refining of metal powders or porous metal masses
  • C25C5/02—Electrolytic production, recovery or refining of metal powders or porous metal masses from solutions
• • 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
  • C25C1/16—Electrolytic production, recovery or refining of metals by electrolysis of solutions of zinc, cadmium or mercury

Definitions

• the invention relates to a process for preparing reactive zinc by electrochemical reduction, wherein iron or steel is used as cathode material.
• transmetalation is the reaction of a metal organyl with a usually inorganic metal salt, resulting in the organyl part being transferred from one metal to the other.
• Li and Mg organyls can also be used to generate the various corresponding zinc organyls.
• a great disadvantage of this process is that it is usually only possible to prepare unfunctionalized metal organyls since many functional groups are not compatible with Li and Mg organyls.
• Functional groups such as nitriles, carboxylic esters, ketones or tertiary amides are attacked by addition of Li and Mg organyls and are thus no longer available for further reactions.
• Other functions such as acetylides, secondary amides or nitro compounds which comprise moderately acidic protons can be deprotonated by strong metal organyls, as a result of which these, too, are no longer available for further reactions.
• Zinc is chemically activated in classical processes by means of LiCI, iodide, dibromoethane or TMSCI as auxiliaries. All these reagents serve to overcome the passivating ZnO layer. The disadvantage of these reactions is that the chemical auxiliaries have to be added in substoichiometric or stoichiometric amounts and must not interfere in subsequent reactions of the zinc organyls. The use of these zinc organyls is therefore limited.
• Rieke® zinc is a reactive zinc-comprising reagent which is obtained by chemical reduction of ZnCl 2 by means of lithium metal in the presence of naphthalene.
• This material has a very high reactivity compared to chemically activated zinc. This reactivity results from generation of the zinc under oxygen- and water-free conditions, as a result of which the formation of a passivating oxide layer is avoided.
• a disadvantage of this reaction is that lithium has to be used in stoichiometric amounts, so that high raw material costs are incurred and it is also necessary to accept an increased outlay for safety measures for handling the reactive alkali metal.
• WO-A 01/02625 describes the transition metal-catalyzed electrochemical reduction.
• a zinc anode is dissolved anodically to generate Zn 2+ in solution.
• the transition metal is reduced at the cathode, and is then inserted into the C-halogen bond and transfers the organic radical to the Zn 2+ .
• Transition metals which can be used are Ni, Co and Fe. A disadvantage of this method is the presence of the transition metal in the future product.
• the zinc organyl produced is inherently contaminated with the transition metal which can then also be present in the products of downstream stages.
• contamination by transition metals has to be avoided and zinc organyls from the above-described method are therefore not suitable for this purpose.
• the process of the invention is advantageous when N,N-dimethylformamide is used as electrolyte.
• the process of the invention is advantageous when tetrabutylammonium tetrafluoroborate is used as electrolyte salt.
• the electrolyte further comprises a redox mediator selected from the group consisting of naphthalene, N,N-dimethyl-1-naphthalene and further 1-substituted naphthalenes and also phenanthrene, anthracene, 4,4′-bipyridyl, and 4,4′-di-tert-butylbiphenyl.
• a redox mediator selected from the group consisting of naphthalene, N,N-dimethyl-1-naphthalene and further 1-substituted naphthalenes and also phenanthrene, anthracene, 4,4′-bipyridyl, and 4,4′-di-tert-butylbiphenyl.
• the process of the invention is advantageous when the temperature at which the electrochemical reduction is carried out is in the range from 35 to 45° C.
• the process of the invention is advantageous when a current density of from 1 to 4 A/dm 2 is set.
• the process of the invention is advantageous when an undivided electrolysis cell is used.
• the process of the invention is advantageous when an iron or steel tube is used as cathode and the zinc anode is arranged concentrically within the cathode.
• the process of the invention is advantageous when it is carried out batchwise.
• the process of the invention is advantageous when it is carried out continuously.
• the activated zinc is produced by electrochemical reduction of zinc ions provided by dissolution of the zinc anode in an electrolysis cell.
• Any electrolysis cell known to those skilled in the art e.g. a divided or undivided flow cell, capillary gap cell or plate gap cell, is suitable for this purpose. Preference is given to the undivided flow cell.
• the electrolysis cell is equipped with a zinc anode and an iron or steel cathode.
• a zinc anode and an iron or steel cathode.
• the zinc anode itself can likewise have any shape known to those skilled in the art, e.g. rod-like, as metal sheet, as cone or as loose electrode.
• the zinc anode is particularly preferably in the form of a rod, cylinder or cone.
• any arrangement of the anode relative to the cathode which is known to those skilled in art is possible for carrying out the process of the invention, e.g. arrangement opposite one another, parallel arrangement or a concentric arrangement in which the anode is positioned concentrically within the cathode. Preference is given to the zinc anode being arranged concentrically within the cathode.
• the electrolysis cell is filled with an electrolyte.
• the electrolyte is selected from the group consisting of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-pyrrolidone and other tertiary amides. Preference is given to N,N-dimethylformamide and N,N-dimethylacetamide. The use of N,N-dimethylformamide is particularly preferred.
• the electrolyte further comprises an electrolyte salt selected from the group consisting of quaternary ammonium salts, organic metal salts and inorganic metal salts.
• an electrolyte salt selected from the group consisting of quaternary ammonium salts, organic metal salts and inorganic metal salts.
• Preference is given to tetrabutylammonium tetrafluoroborate, sodium methylsulfonate and zinc chloride. Very particular preference is given to tetrabutylammonium tetrafluoroborate.
• the electrolyte comprises a redox mediator.
• a redox mediator is preferably selected from the group consisting of naphthalene, N,N-dimethyl-1-naphthalene and further 1-substituted naphthalenes and also phenanthrene, anthracene, 4,4′-bipyridyl and 4,4′-di-tert-butylbiphenyl. Particular preference is given to naphthalene.
• the electrolyte is heated to temperatures in the range from 20 to 60° C., preferably in the range from 30 to 50° C., very particularly preferably in the range from 35 to 45° C.
• the temperature is regulated via a heat exchanger integrated into the electrolyte circuit.
• a current density in the range from 1 to 4 A/dm 2 is applied at the anode and cathode.
• the current density is preferably in the range from 1.5 to 3 A/dm 2 , particularly preferably in the range from 1.5 to 2.5 A/dm 2 .
• the electrolysis is stopped when the solids content of reactive zinc in the electrolyte has attained a theoretical content of 2-20% by weight, particularly preferably in the range from 2 to 10% by weight.
• the process of the invention can be operated batchwise or continuously.
• the electrolyte is discharged from the cell at a content of reactive zinc in the range from 2 to 20% by weight, preferably in the range from 2 to 10% by weight.
• an equal amount of fresh electrolyte is introduced. This is continued until the zinc anode has to be replaced because of virtually complete dissolution.
• the electrolyte When a tubular cathode surrounding the anode is used in the process of the invention, it is advantageous for the electrolyte to be circuited by pumping during the electrolysis. Preference is given to a pump circulation rate of from 100 to 600 l/h, particularly preferably from 300 to 600 l/h.
• 12.8 A are applied to the electrolysis cell for 8.4 h, with the voltage initially increasing from 6.5 V to 9.9 V and dropping to 1.2 V over the further course of the electrolysis. A dark suspension of finely divided zinc is obtained. Elemental analysis of the electrolyte gives a zinc (0) concentration of 4.1%, corresponding to a current yield of 82%.

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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)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Electrolytic Production Of Metals (AREA)

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• 2010
  • 2010-04-07 JP JP2012506432A patent/JP2012524171A/ja not_active Withdrawn
  • 2010-04-07 US US13/265,412 patent/US20120031771A1/en not_active Abandoned
  • 2010-04-07 EP EP10715180A patent/EP2421999A1/de not_active Withdrawn
  • 2010-04-07 CN CN2010800174592A patent/CN102405309A/zh active Pending
  • 2010-04-07 KR KR1020117027461A patent/KR20110137832A/ko not_active Application Discontinuation
  • 2010-04-07 WO PCT/EP2010/054559 patent/WO2010121899A1/de active Application Filing
  • 2010-04-07 CA CA2758760A patent/CA2758760A1/en not_active Abandoned

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