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 noble metal-coated nickel electrodes for use in sodium chloride electrolysis.
• the invention is based on the known use of nickel electrodes as hydrogen-developing electrodes in alkali metal chloride electrolysis and the known improvement methods by coating nickel electrodes with noble metals or noble metal oxides.
• Cathodes for sodium chloride electrolysis, on which hydrogen is developed in an alkaline solution usually consist of iron or nickel. If nickel electrodes are used, they can consist entirely of nickel, or only nickel surfaces are used in which substrates made of other metals are nickel-plated on the surface.
• nickel electrodes can be used with a metal from subgroup VIII, especially 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 be coated.
• platinum metals including Pt, Ru, Rh, Os, Ir, Pd
• the electrode thus produced can e.g. B. in sodium chloride electrolysis as a cathode for water development.
• Many coating variants are known here, since the coating made of metal oxides can be modified in various ways, so that different compositions are formed on the surface of the nickel electrode.
• US-A-5 035 789 e.g. B. a ruthenium oxide-based coating on nickel substrates is used as the cathode.
• the quality of the electrode decreases over time, in the form that the cell voltage increases during sodium chloride electrolysis, so that it may be necessary to re-coat the electrode. This is technically complex since the electrolysers have to be switched off and the electrodes have to be removed from the electrolysis cells.
• EP 1 487 747 A1 a 0.1 to 10% by weight platinum-containing compound is added for sodium chloride electrolysis.
• the solution of the platinum-containing compound is added to the water which forms the catholyte, 0.1 to 2 liters of the aqueous solution of the platinum compound being added per liter of water.
• EP 1 487 747 A1 does not disclose any information about the conditions used in the process for electrodes, electrode areas, current density etc.
• a soluble compound of a metal from the platinum group of the sodium hydroxide solution is added to the catholyte during the operation of sodium chloride electrolysis.
• a salt concentration of 200 g / 1 sodium chloride at 90 ° C and a current density of 2.35 kA / m 2 is added to the catholyte during the operation of sodium chloride electrolysis.
• the cathode is nickel-plated for pretreatment and then nickel-plated in a nickel bath.
• Platinum chlorate for example, was metered into the catholyte as the active compound, which led to a decrease in the cell voltage by 100 mV.
• metal compounds are added in the catholyte during the electrolysis of alkali metal chlorides, which are intended to reduce the hydrogen overvoltage and thus to reduce the cell voltage.
• the examples listed in US-A-4,105,516 in turn describe the dosage and effects resulting from the addition of an iron compound added to the catholyte of a sodium chloride diaphragm laboratory cell.
• the cell has an anode made of expanded titanium, which is coated with ruthenium and titanium oxide.
• the cathode consists of iron in the form of expanded metal.
• the examples show the use of cobalt or iron solution on the iron cathode.
• the disadvantages of iron compounds in the treatment of coated nickel electrodes have already been mentioned above.
• metal ions which have a low hydrogen overvoltage can be added to catholytes in a membrane electrolysis cell of sodium chloride electrolysis in order to coat the cathode.
• the addition takes place during the electrolysis.
• platinum oxide to improve an iron or copper cathode is given as an example.
• the cathode coatings in sodium chloride electrolysis usually consist of platinum metals, platinum metal oxides or mixtures thereof, e.g. a mixture of ruthenium and ruthenium oxide.
• the usable platinum metals include ruthenium, iridium, platinum, palladium and rhodium.
• the cathode coating is not long-term stable, especially not under conditions in which no electrolysis takes place or in the event of interruptions in the electrolysis, e.g. reverse electrical currents can occur. This means that there is more or less damage to the precious metal coating over the operating time of the electrolyzer.
• Impurities e.g. from the brine by diffusion into the lye, e.g. Iron ions, deposit on the cathode or especially on the active centers of the noble metal-containing coating and thereby deactivate it.
• a further method for improving noble metal-coated nickel electrodes has become known from DE 102007003554A1, in which during the operation of the sodium chloride electrolysis at production current density in the range of several kA / m 2 into the sodium hydroxide solution, in which a cathode coated with ruthenium oxide is operated , a hexachloroplatinate or sodium hexachloroplatinate solution is dosed.
• the cell voltage should vary in a voltage range from 0 to 5 volts or 0.5 - 500mV and a frequency of 10-100 Hz with an amplitude of 20-100mV.
• the dosing of the platinum compound in the catholyte takes place in particular in the feed to the cathode chamber a cathode area of 2.7 m 2 with a current density of 1 to 8 kA / m 2 .
• the dosing rate of the platinum-containing solution based on the platinum content per m 2 of cathode surface is between 0.001 g Pt / (h * m 2 ) and 1 g Pt / (h * m 2 ).
• a disadvantage of the coating method disclosed in DE 102007003554A1 is that if the electrolysis is at a standstill, the positive effect which is initially achieved by the platinum doping described cannot be maintained. Since electrolysers fail or have to be issued for various technical reasons, a new platinum dosage must be carried out after each standstill, which introduces additional complexity into the operating sequence, which is disadvantageous for a production company. Apparently the coating of the electrode with platinum or platinum oxide that can be achieved with this method is not as durable as would be desirable for the production method. In addition, under certain circumstances, platinum is not completely deposited from the platinum solution on the electrode surface and thus rare and expensive precious metal material is lost.
• the object of the invention is to develop a special method for improving nickel electrodes which are coated with platinum metals, platinum metal oxides or mixtures thereof, or for nickel electrodes without a coating for use as cathodes in the electrolysis of sodium chloride, which can be used in the ongoing electrolysis operation , avoids a longer interruption of the electrode operation to restore the cathode activity and produces an improvement in the activity of the nickel electrodes which is not immediately lost when the machine is at a standstill.
• the method should not impair the functioning of the electrolysis plant.
• the invention relates to a method for improving the performance of nickel electrodes which are uncoated or which have a coating based on platinum metals, platinum metal oxides or a mixture of platinum metals and platinum metal oxides, and are used in the sodium chloride electrolysis according to the membrane process in which the electrolysis of sodium chloride, a water-soluble or sodium hydroxide-soluble platinum compound, in particular hexachloroplatinic acid or particularly preferably a sodium platinumate, particularly preferably sodium hexachloroplatinate (Na2PtCle) and / or sodium hexahydroxyplatinate (Na 2 Pt (OH) 6 ) is metered into the catholyte, characterized in that the Addition in electroysis operation at a current density of 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
• Electrode surface here means in particular the entire active electrode surface wetted by the catholyte.
• the electrode area preferably refers to the geometric dimension of the active electrode area wetted by the catholyte.
• the sodium hexachloroplatinate can be metered into the catholyte as an aqueous solution or in alkaline solution, or the hexachloroplatinic acid can be metered directly into the catholyte, in particular the sodium hydroxide solution, in which case a reaction with the alkali to give the sodium chloroplatinate takes place.
• the platinum compound is added according to the invention while the electrolysis is running under a greatly reduced load, ie the current density for the platinum metering is at most 95 A / m 2 set.
• a further preferred embodiment of the addition of platinum consists in that when the platinum compound is added the temperature of the catholyte is 60 to 90 ° C., preferably 75 to 90 ° C.
• the electrode coating is in the form of platinum metals and / or platinum metal oxides on the coated nickel electrodes, the platinum metals / platinum metal oxides being based on one or more metals from the series: ruthenium, iridium, palladium, platinum, rhodium and osmium, in particular preferred on those of the series: ruthenium, iridium and platinum.
• a further preferred embodiment of the new process consists in that, in addition to the above-mentioned soluble platinum compound, other further water-soluble compounds of the noble metals of subgroup 8 of the Periodic Table of the Elements, in particular compounds of palladium, iridium, rhodium, osmium or ruthenium, preferably palladium or Ruthenium can be added to the catholyte. These are used in particular in the form of water-soluble salts or complex acids.
• the noble metal content of the further water-soluble compounds of the noble metals of subgroup 8 is 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 0.01 to 310 mg / L, preferably 0.02 to 250 mg / L, particularly preferably 0.03 to 160 mg / L is.
• the volume flow of the catholyte during the metering is from 0.1 to 10 L / min, preferably from 0.2 to 5 L / min.
• the concentration of platinum metal in the catholyte emerging from the electrolytic cell is monitored continuously or discontinuously in a particularly preferred embodiment of the new method.
• Sodium chloride electrolysis by the membrane process is typically carried out as follows, for example.
• a solution containing sodium chloride is fed to an anode chamber with an anode, a sodium hydroxide solution is fed into a cathode chamber with a cathode.
• the two chambers are separated by an ion exchange membrane.
• Several of these anode and cathode chambers are combined to form an electrolyser.
• the anode chamber leaves a less concentrated solution containing sodium chloride than was supplied.
• the cathode chamber leaves a more concentrated sodium hydroxide solution than was supplied.
• the production current density is, for example, 4 kA / m 2 .
• the geometrically projected cathode area is 2.7m 2 , this corresponds to the membrane area.
• the cathode consists of a nickel expanded metal, which is provided with a special coating (here sometimes also called coating) (manufacturer eg Industrie De Nora) to reduce the hydrogen overvoltage.
• Another object of the invention is a process for the production of chlorine, sodium hydroxide solution and hydrogen according to the principle of membrane electrolysis on a production scale using nickel electrodes or coated nickel electrodes as cathode with the steps:
• Supply of the sodium chloride-containing solution discharged from the anode compartment for concentration and purification the concentration and purification in particular includes at least the following steps: destruction of chlorate by-products, dechlorination, concentration increase by adding sodium chloride, purification by precipitation reagents, filtration and ion exchange to remove unwanted cations, then reintroduction of the sodium chloride-containing solution into the anode chamber;
• Dilution of a portion of the sodium hydroxide solution discharged from the cathode compartment with water and reintroduction into the cathode compartment characterized in that 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 when a predetermined average maximum voltage value is reached in electrolysis operation, then the method according to one of claims 1 to 8 is carried out and then the current density is raised to the production current density again and production is continued.
• Production current density here means in particular a current density of at least 1 kA / m 2 .
• the production scale here is in particular the conversion of at least 5 kg / h sodium chloride to chlorine and sodium hydroxide solution per electrolysis cell.
• the maximum voltage value is in particular the maximum electrolysis voltage across the individual cell, which can be regarded as tolerable in terms of the energy efficiency of the electrolysis process.
• This threshold value is typically around 80mV above the best average voltage value after the cell has been started up.
• the mean value of the measured voltages is used as a comparison value for the sake of simplicity.
• the concentration of the sodium chloride-containing solution is at least 150 g / L. In a further preferred embodiment of the new electrolysis process, the NaOH content in the sodium hydroxide solution is at least 25 percent by weight.
• Sodium chloride-containing solution and sodium hydroxide solution are preferably heated to at least 60 ° C. before being introduced.
• the sodium chloride-containing solution is brought to a pH below 6.
• test examples were carried out on technical electrolyzers with 144 elements each (single electrolysis cells), the nickel cathodes of which were provided with a coating based on a mixture of ruthenium / ruthenium oxide from Denora.
• the average voltage for each electrolyzer was calculated from the average of the 144 elements.
• the voltage values at a current density in electrolysis operation of 4.5 kA / m 2 were used to compare the voltages or voltage changes in the electrolysis.
• the measured voltage was converted to the voltage corresponding to the current density of 4.5 kA / m 2 .
• the conversion was carried out using 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 characteristic of an electrolyser is linear. example 1
• a technical electrolyser was operated at an average voltage of 3.27 V and a current density of 4.5 kA / m 2 .
• the current density was reduced from 4.5 kA / m 2 to a current density of 11.8 A / m 2 within 30 min and was kept constant at this value. After 10 minutes, 8 L became one
• the temperature of the sodium hydroxide solution varied in the range from 76 to 90 ° C.
• the volume flow of sodium hydroxide solution during the metering time was 3.6 L / min per element.
• 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 drop is still 140 mV ,
• the mean voltage at 4.5 kA / m 2 was 3.16 V.
• the voltage drop is still 110 mV.
• the mean voltage at 4.5 kA / m 2 was 3.17 V.
• the voltage drop is still 100 mV.
• a technical electrolyser 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 results in a voltage of 3.19 V.
• a technical electrolyser 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 results in a voltage of 3.2 V.
• the current density was reduced from 4.3 kA / m 2 to a current density of 11.8 A / m 2 within 30 min and was kept constant at this value.
• 8 L of a solution of hexachloroplatinate solution (6.25 g Pt / L) were metered into the sodium hydroxide solution at 0.8 L / h within 10 min.
• the current density remained at the constant value of 11.8 A / m 2 and was kept at this value for a further 30 min after the addition.
• the time at which the current density was kept at 11.8 A / m 2 was 40 minutes since the start of the addition.
• the current density was then raised to 3.8 kA / m 2 within 45 minutes.
• the temperature of the sodium hydroxide solution varied in the range from 76 to 90 ° C. 50 g of platinum thus reached the surface of 144 cathodes (surface of a cathode: 2.7 m 2 ). This corresponds to an amount of platinum of 0.13 g / m 2 .
• an average voltage of 3.0 V was determined at a current density of 3.8 kA / m 2 . Converted to a current density of 4.5 kA / m 2, this results in an average voltage of 3.1 V. The voltage reduction is therefore 100 mV. After a total of 8 operating days after metering in and switching off, an average voltage of 3.19 V was measured at a current density of 4.5 kA / m 2 . The voltage drop is therefore only 10 mV and is therefore almost completely eliminated.

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

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