Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
  • C25B1/46—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in diaphragm cells
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/052—Electrodes comprising one or more electrocatalytic coatings on a substrate
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
  • C25B11/057—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material consisting of a single element or compound
  • C25B11/061—Metal or alloy
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
  • C25B11/093—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds at least one noble metal or noble metal oxide and at least one non-noble metal oxide
• • 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
  • C25B15/00—Operating or servicing cells

Definitions

• the invention relates to a method for improving the performance of nickel electrodes, in particular of noble metal-coated nickel electrodes for use in sodium chloride electrolysis.
• the invention proceeds from the known use of nickel electrodes as hydrogen-evolving electrodes in alkali metal chloride electrolysis and the improvement methods known per se by coating nickel electrodes with noble metals or noble metal oxides.
• Cathodes for sodium chloride electrolysis, at which hydrogen is evolved in alkaline solution usually consist of iron or nickel. If nickel electrodes are used, these can consist entirely of nickel or only nickel surfaces in which substrates composed of other metals are nickel plated on the surface are used.
• nickel electrodes can be coated with a metal of transition group VIII, especially the platinum metals (including Pt, Ru, Rh, Os, Ir, Pd), of the Periodic Table of the Elements or an oxide of such a metal or mixtures thereof.
• platinum metals including Pt, Ru, Rh, Os, Ir, Pd
• the electrode produced in this way can, for example, be used in sodium chloride electrolysis as cathode for the evolution of hydrogen.
• many coating variants are known since the coating composed of metal oxides can be modified in various ways so that different compositions are formed on the surface of the nickel electrode.
• U.S. Pat. No. 5,035,789 a coating based on, for example, ruthenium oxide on nickel substrates is used as cathode.
• iron compounds or finely divided iron are added to the catholyte in order to decrease the cell voltage in sodium chloride electrolysis.
• covering the cathodes with iron can have an adverse effect on the electrolysis and increase the cell voltage.
• EP 1 487 747 A1 a compound containing from 0.1 to 10% by weight of platinum is added to the sodium chloride electrolysis.
• the solution of the platinum-containing compound is introduced into the water which forms the catholyte, with from 0.1 to 2 liters of the aqueous solution containing the platinum compound being added per liter of water.
• EP 1 487 747 A1 discloses no information about the conditions, electrodes, electrode areas, current density, etc., used in the process, as is required for industrial implementation, apart from the general reference to the use of the platinum compound during the electrolysis.
• JP 1011988 A a soluble compound of a metal of the platinum group is added to the sodium hydroxide solution in the catholyte during operation of the sodium chloride electrolysis to restore the activity of a deactivated cathode based on a Raney nickel structure having a low hydrogen overvoltage.
• a sodium chloride electrolysis cell is operated with 32% strength by weight sodium hydroxide, a salt concentration of 200 g/l of sodium chloride at 90° C. and a current density of 2.35 kA/m 2 .
• the cathode is electrolessly coated with nickel and subsequently nickel plated in a nickel bath.
• active compound platinum chlorate, for example, was added to the catholyte, which led to a decrease in the cell voltage by 100 mV.
• metal compounds are added to the catholyte during the electrolysis of alkali metal chlorides; these are said to decrease the hydrogen overvoltage and thus reduce the cell voltage.
• the examples set forth in U.S. Pat. No. 4,105,516 again describe the added amounts and effects arising from addition of an iron compound which is added to the catholyte of a laboratory sodium chloride diaphragm cell.
• the cell has an anode which consists of titanium expanded metal coated with ruthenium oxide and titanium oxide.
• the cathode here consists of iron in the form of expanded metal.
• the examples disclose the use of cobalt or iron solution at the iron cathode.
• the disadvantages of iron compounds in the treatment of coated nickel electrode have been indicated above.
• metal ions which have a low hydrogen overvoltage can be added to catholytes of a membrane electrolysis cell for sodium chloride electrolysis in order to coat the cathode.
• the addition is carried out during the electrolysis.
• platinum oxide for improving an iron or copper cathode is indicated by way of example.
• the cathode coatings in sodium chloride electrolysis usually consist of platinum metals, platinum metal oxides or mixtures thereof, e.g. a ruthenium/ruthenium oxide mixture.
• the usable platinum metals include ruthenium, iridium, platinum, palladium and rhodium.
• the cathode coating is not stable in the long term, especially not under conditions at which no electrolysis takes place or during interruptions to the electrolysis during which electric reverse currents, for example, can occur. Thus, more or less severe damage to the noble metal coating occurs over the time of operation of the electrolyzer.
• impurities which, for example, get from the brine into the alkali by diffusion, e.g. iron ions, can deposit on the cathode or especially on the active sites of the noble metal-containing coating and thereby deactivate the latter.
• Still a further method for improving noble metal-coated nickel electrodes has become known from DE 102007003554A1, in which a hexachloroplatinate solution or sodium hexachloroplatinate solution is metered into the sodium hydroxide solution in which a cathode coated with ruthenium oxide is operated during operation of the sodium chloride electrolysis at a production current density in the region of several kA/m 2 .
• a variation of the cell voltage in a voltage range from 0 to 5 volt or 0.5-500 mV and a frequency of 10-100 Hz with an amplitude of 20-100 mV is said to be carried out.
• the introduction of the platinum compound into the catholyte is carried out, in particular, into the feed stream to the cathode chamber at a cathode area of 2.7 m 2 and a current density of from 1 to 8 kA/m 2 .
• the metering rate of the platinum-containing solution based on the platinum content per m 2 of cathode area is in the range from 0.001 g of Pt/(h*m 2 ) to 1 g of Pt/(h*m 2 ).
• a disadvantage of the coating method disclosed in DE 102007003554A1 is that the positive effect which is initially achieved by the platinum doping described cannot be maintained during a stoppage of the electrolysis. Since electrolyzers go down or have to be switched off for various technical reasons, a renewed introduction of platinum has to be carried out after each downtime, as a result of which additional complexity is introduced into the operating procedure, representing a disadvantage for production operation.
• the coating of the electrode with platinum or platinum oxide which can be achieved by this method is obviously not as stable as would be desirable for the production process. In addition, platinum may sometimes not be deposited completely from the platinum solution onto the electrode surface and rare and costly noble metal material is thus lost.
• the method should not impair the function of the operating plant for the electrolysis.
• the invention provides a method for improving the performance of nickel electrodes which are uncoated or have a coating based on platinum metals, platinum metal oxides or a mixture of platinum metals and platinum metal oxides and are used in sodium chloride electrolysis by the membrane process, where a platinum compound which is water-soluble or soluble in sodium hydroxide solution, in particular hexachloroplatinic acid or particularly preferably a sodium platinate, particularly preferably sodium hexachloroplatinate (Na 2 PtCl 6 ) and/or sodium hexahydroxyplatinate (Na 2 Pt(OH) 6 ), is metered into the catholyte in the electrolysis of sodium chloride, characterized in that the addition is carried out during electrolysis operation at a current density of from 0.2 A/m 2 to 95 A/m 2 , preferably from 0.5 A/m 2 to 70 A/m 2 , particularly preferably from 1 A/m 2 to 50 A/m 2 , at a temperature of the catholyte in the range from
• an amount of platinum per m 2 of electrode area of from 0.3 g/m 2 to 10 g/m 2 , preferably from 0.35 g/m 2 to 8 g/m 2 , particularly preferably from 0.4 g/m 2 to 5 g/m, with the decreased current density being maintained from the commencement of the metered addition for a total of from 2 to 360 minutes, preferably from 20 minutes to 300 minutes, particularly preferably from 30 minutes to 200 minutes.
• the amount of platinum refers to the content of platinum metal in the platinum compound introduced.
• Electrode area here means, in particular, the total active electrode area wetted by the catholyte.
• the electrode area preferably refers to the geometric dimensions of the active electrode area wetted by the catholyte.
• the sodium hexachloroplatinate can, as desired, either be introduced as aqueous solution or in alkaline solution into the catholyte or the hexachloroplatinic acid is introduced directly into the catholyte, in particular the sodium hydroxide solution, with a reaction with the alkali to form sodium chloroplatinate then occurring.
• the addition of the platinum compound is, according to the invention, carried out during ongoing electrolysis under a greatly reduced load, i.e. the current density is set to not more than 95 A/m 2 for the introduction of platinum.
• the temperature of the catholyte is from 60 to 90° C., preferably from 75 to 90° C., during addition of the platinum compound.
• the electrode coating is present in the form of platinum metals and/or platinum metal oxides on the coated nickel electrodes, where the platinum metals/platinum metal oxides are based on one or more metals of the group consisting of: ruthenium, iridium, palladium, platinum, rhodium and osmium, particularly preferably on those of the group consisting of: ruthenium, iridium and platinum.
• these are used in the form of water-soluble salts or complex acids.
• the proportion of noble metal of the further water-soluble compounds of the noble metals of transition group 8 is from 1 to 50% by weight, based on the platinum metal of the soluble platinum compound.
• a preferred variant of the new method is characterized in that the proportion of platinum in the platinum compound in the catholyte after the addition is from 0.01 to 310 mg/l, preferably from 0.02 to 250 mg/l, particularly preferably from 0.03 to 160 mg/l.
• the volume flow of the catholyte during the addition is from 0.1 to 10 l/min, preferably from 0.2 to 5 l/min
• the concentration of platinum metal in the catholyte exiting from the electrolysis cell is continuously or discontinuously monitored in a particularly preferred embodiment of the new method.
• the sodium chloride electrolysis by the membrane process is typically carried out, by way of example, as follows.
• a solution containing sodium chloride is fed into an anode chamber having an anode, while a sodium hydroxide solution is fed into a cathode chamber having a cathode.
• the two chambers are separated by an ion-exchange membrane.
• a plurality of these anode and cathode chambers are assembled to form an electrolyzer.
• a sodium chloride-containing solution having a lower concentration than that fed to the anode chamber leaves the anode chamber.
• Hydrogen and a sodium hydroxide solution having a higher concentration than that fed into the cathode chamber leave the cathode chamber.
• the production current density is, for example.
• the geometrically projected cathode area is 2.7 m 2 , which corresponds to the membrane area.
• the cathode consists of a nickel expanded metal provided with a specific coating (here also variously described simply as coating) (manufacturer: for example Industrie De Nora) in order to decrease the hydrogen overvoltage.
• the invention further provides a process for producing chlorine, sodium hydroxide and hydrogen according to the principle of membrane electrolysis on a production scale using nickel electrodes or coated nickel electrodes as cathode, comprising the steps:
• the current density is reduced to a value of less than 100 A/m 2 but at least 0.2 A/m 2 in order to lower the electrolysis voltage on attainment of a prescribed average maximum voltage value during electrolysis operation, the method as claimed in any of claims 1 to 8 is then carried out and the current density is subsequently increased again to the production current density and production is continued.
• production current density is, in particular, a current density of at least 1 kA/m 2 .
• production scale is, in particular, the conversion of at least 5 kg/h of sodium chloride into chlorine and sodium hydroxide per electrolysis cell.
• the maximum voltage value is in the case of individual cells the maximum electrolysis voltage across the individual cell which is considered to be tolerable in respect of energy efficiency of the electrolysis process.
• This threshold value is typically about 80 mV above the best average voltage value after start-up of the cell.
• the average of the measured voltages is used as comparative value in the interests of simplicity.
• the concentration of the solution containing sodium chloride is at least 150 g/l.
• the content of NaOH in the sodium hydroxide solution is at least 25% by weight.
• Sodium chloride-containing solution and sodium hydroxide solution are preferably heated to at least 60° C. before introduction.
• the sodium chloride-containing solution is brought to a pH below 6.
• the average voltage for each electrolyzer was calculated from the average of the 144 elements.
• the voltage values having a current density in electrolysis operation of 4.5 kA/m 2 were employed for comparison of the voltages or voltage changes in the electrolysis.
• the measured voltage was converted by calculation to the voltage corresponding to the current density of 4.5 kA/m 2 .
• the conversion was carried out by means of a linear regression of the current-voltage data in the range from 3 to 5 kA/m 2 . In this current range, the current-voltage characteristics of an electrolyzer are linear.
• An industrial electrolyzer was operated at an average voltage of 3.27 V and a current density of 4.5 kA/m 2 .
• the current density was decreased from 4.5 kA/m 2 to a current density of 11.8 A/m 2 over a period of 30 minutes and kept constant at this value.
• 8 l of a solution of hexachloroplatinate 25 g of Pt/l
• the proportion of platinum of the platinum compound in the sodium hydroxide solution increased to 16 mg/l here.
• the current density remained at the constant value of 11.8 A/m 2 and after the addition was complete was kept at this value for a further 30 minutes.
• the time for which the current density was kept at 11.8 A/m 2 from the commencement of the addition was 40 minutes.
• the current density was then increased again to 4.5 kA/m 2 over a period of 45 minutes.
• the temperature of the sodium hydroxide solution varied in the range from 76 to 90° C. over the total procedure.
• the volume flow of sodium hydroxide solution during the addition time was 3.6 l/min per element.
• the average voltage at 4.5 kA/m 2 dropped from the initial value of 3.27 V to 3.10 V after the addition. This corresponds to a voltage decrease of 170 mV.
• the average voltage at 4.1 kA/m 2 was 3.07 V. Converted to a current density of 4.5 kA/m 2 , this corresponds to an average voltage of 3.13 V. The voltage decrease is 140 mV.
• the average voltage at 4.5 kA/m 2 was 3.16 V.
• the voltage decrease is 110 mV.
• the average voltage at 4.5 kA/m 2 was 3.17 V.
• the voltage decrease is 100 mV.
• An industrial electrolyzer was operated at an average voltage of 3.15 V and a current density of 4.2 kA/m 2 . Converted to a current density of 4.5 kA/m 2 , this corresponds to a voltage of 3.19 V.
• An industrial electrolyzer was operated at an average voltage of 3.17 V and a current density of 4.3 kA/m 2 . Converted to a current density of 4.5 kA/m 2 , this corresponds to a voltage of 3.2 V.
• the current density was decreased from 4.3 kA/m 2 to a current density of 11.8 A/m 2 over a period of 30 minutes and kept constant at this value.
• 8 l of a solution of hexachloroplatinate (6.25 g of Pt/l) were metered at 0.8 l/h into the sodium hydroxide solution over a period of 10 minutes.
• the current density here remained at the constant value of 11.8 A/m2 and after the addition was complete was kept at this value for a further 30 minutes.
• the time for which the current density was kept at 11.8 A/m 2 from the beginning of the addition was 40 minutes.
• the current density was then increased to 3.8 kA/m 2 over a period of 45 minutes.
• the temperature of the sodium hydroxide solution over the total procedure varied in the range from 76 to 90° C.

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• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)

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• 2018
  • 2018-07-20 PT PT181846940T patent/PT3597791T/pt unknown
  • 2018-07-20 HU HUE18184694A patent/HUE057761T2/hu unknown
  • 2018-07-20 EP EP18184694.0A patent/EP3597791B1/de active Active
• 2019
  • 2019-07-12 JP JP2021502744A patent/JP2021530619A/ja active Pending
  • 2019-07-12 KR KR1020217004643A patent/KR20210032469A/ko not_active Application Discontinuation
  • 2019-07-12 WO PCT/EP2019/068789 patent/WO2020016122A1/de unknown
  • 2019-07-12 CN CN201980048650.4A patent/CN112513334B/zh active Active
  • 2019-07-12 US US17/261,864 patent/US20210292922A1/en active Pending
  • 2019-07-12 EP EP19741999.7A patent/EP3824118A1/de not_active Withdrawn

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