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
  • 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
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/02—Hydrogen or oxygen
  • C25B1/04—Hydrogen or oxygen by electrolysis of water
• • 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
  • C25B15/02—Process control or regulation
  • C25B15/021—Process control or regulation of heating or cooling

Definitions

• the present invention relates to a cathode, usable for the preparation of an alkali metal chlorate by electrolysis of chloride corresponding, and its manufacturing process.
• Industrially sodium chlorate is manufactured in electrolytic cells, each of them comprising several cathodes in mild steel and several titanium anodes coated with ruthenium oxide. They are generally supplied with an electrolytic solution consisting about 100 g / l sodium chloride, about 600 g / l sodium chlorate sodium and sodium dichromate in an amount between 2 and 5 g / l. The latter being used to reduce or even eliminate the reaction of reduction of the hypochlorite ion.
• chromium (VI) is today threatened because the alkali metal chlorate thus prepared requires a purification stage, but above all because it pollutes the environment. Through Therefore, it appears capital for the sake of ecology to find a alternative.
• a cathode whose substrate is a titanium plate, made of zirconium, niobium or an alloy essentially constituted by a association of these metals and on which an oxide layer is applied metallic, essentially consisting of an oxide of one or more 5 metals chosen from ruthenium, rhodium, palladium, osmium, iridium and platinum and optionally an oxide of one or more metals chosen from calcium, magnesium, strontium, barium, zinc, chromium, molybdenum, tungsten, selenium and tellurium, has been disclosed in French patent FR 2,311,108.
• the applicant company has now found a cathode allowing inhibit the hypochlorite ion reduction reaction while retaining good properties with respect to the water reduction reaction.
• This specific cathode comprises a substrate in one element selected from the group consisting of titanium, nickel, tantalum, zirconium, nobium and of their alloys, coated with an intermediate layer of mixed oxide based titanium and ruthenium and an outer layer of metal oxides comprising titanium, zirconium and ruthenium.
• the intermediate layer contains a mixed oxide titanium and ruthenium.
• the outer layer of metal oxides contains titanium, zirconium and ruthenium.
• the outer layer consists essentially of ZrTiO 4 accompanied by RuO 2 and possibly ZrO 2 and / or TiO 2 .
• titanium or nickel or titanium or nickel alloys it is preferred to use, as substrate, titanium or nickel or titanium or nickel alloys. Better still, we prefer use titanium.
• the ruthenium / titanium molar ratio in the intermediate layer is preferably between 0.4 and 2.4.
• the zirconium / titanium molar ratio in the outer layer is generally between 0.25 and 9, preferably between 0.5 and 2.
• Ruthenium in the outer layer represents between 0.1 and 10% molar, preferably between 0.1 and 5 mol% relative to metals entering into the composition of this layer.
• the pretreatment generally consists in subjecting the substrate, i.e. sandblasting followed by acid washing, or pickling using a aqueous solution of oxalic acid, hydrofluoric acid, a mixture hydrofluoric acid and nitric acid, a mixture of acid hydrofluoric acid and glycerol, of a mixture of hydrofluoric acid, acid nitric and glycerol or a mixture of hydrofluoric acid, acid nitric and hydrogen peroxide, followed by one or more washing (s) degassed demineralized water.
• the substrate can be in the form of a solid plate, plate perforated, expanded metal or cathode basket made from metal deployed or perforated.
• Solution A is generally prepared by reacting room temperature and with stirring, essentially a mineral salt or organic titanium and ruthenium with water or in a solvent organic, possibly in the presence of a chelating agent.
• the temperature can be raised slightly above ambient for facilitate the dissolution of salts.
• a mineral or organic salt of titanium and ruthenium with water or in an organic solvent, possibly in the presence of a chelating agent.
• Titanium and ruthenium are preferably present in the solution A in a concentration equivalent to each of 0.5 to 10 mol / l.
• Solution B is generally prepared by reacting, room temperature and with stirring, a mineral or organic salt of titanium, zirconium, ruthenium and possibly other metals with water or in an organic solvent, optionally in the presence of a chelating agent. When the reaction is exothermic, a bath is used ice to cool the reaction medium.
• a mineral or organic salt of titanium, zirconium and ruthenium with water or in a solvent organic, possibly in the presence of a chelating agent is advantageousously, a mineral or organic salt of titanium, zirconium and ruthenium with water or in a solvent organic, possibly in the presence of a chelating agent.
• the preferred titanium and ruthenium salts are chlorides, oxychlorides, nitratres, oxynitrates, sulfates and alkoxides.
• Advantageously ruthenium chlorides, titanium chlorides and titanium oxychlorides are used.
• zirconium salts chlorides, sulfates, zirconyl chlorides, zirconyl nitrates, alkoxides such as butyl zirconate.
• Zirconium and zirconyl chlorides are particularly favorite.
• organic solvent there may be mentioned light alcohols of preferably isopropanol and ethanol, and better still isopropanol and absolute ethanol.
• Titanium and zirconium are generally present in solution B in a concentration equivalent to each of 0.5 to 5 mol / l.
• concentration of rutheniurn in solution B is generally between 10 -3 and 10 -1 mole / l, preferably between 10 -3 and 5.10 -2 mole / l.
• Solution A can be deposited on the pretreated substrate using different techniques such as sol-gel, electrochemical deposition, galvanic plating, spraying or coating.
• the pretreated substrate is coated with solution A, by example using a brush.
• the substrate thus coated is then dried at air and / or in an oven at a temperature below 150 ° C. After the drying, the substrate is calcined in air at a temperature between 300 and 600 ° C and preferably between 450 and 550 ° C during a duration ranging from 10 minutes to 2 hours.
• step (c) of the method according to the present invention it is possible to use the same deposit techniques and the same conditions drying and calcination procedures as step (b) except that the deposit is performed with solution B.
• CVD chemical vapor deposition
• PVD physical vapor deposition
• plasma projection also suitable for coating the pretreated substrate with middle layer and an outer layer.
• step (b) of the process can repeat several times.
• step (c) of the process can repeat several times.
• the thickness of the intermediate layer generally represents between 2 and 60 g / m 2 of substrate and preferably between 20 and 35 g / m 2 .
• the concentration of solution A is judiciously chosen to so that this preferred thickness can be obtained by repeating step (b) in a reasonable number of times and preferably between 1 and 4 time.
• the thickness of the outer layer represents between 5 and 70 g / m 2 of the substrate and preferably between 25 and 50 g / m 2 .
• solution B is prepared so that its concentration makes it possible to obtain an outer layer thickness in the preferred range by repeating step (c) in less than 10 times and preferably between 2 and 5 times.
• the specific cathode can be used in the preparation of an alkali metal chlorate by electrolysis corresponding chloride.
• the specific cathode according to the invention is suitable especially in the preparation of sodium chlorate.
• the ruthenium / titanium molar ratio in this layer is advantageously between 0.4 and 2.4.
• a solution A is prepared, containing ruthenium and titanium in an equimolar amount, by mixing at room temperature with stirring 2.45 g of RuCl 3 , of purity greater than 98%, 3.64 cm 3 of TiOCl 2 , 2HCl at 127 g / l in Ti and 2.5 cm 3 of absolute isopropanol.
• the end of one of the faces of the plate is then coated pretreated, representing an area of dimension 2 cm x 5 cm, with the solution A using a brush, then it is left for 30 minutes at ambient temperature.
• the coated plate is then dried for 30 minutes in an oven at 120 ° C, then calcined in an oven under air at 500 ° C for 30 minutes.
• Solution B A zirconium precursor, ruthenium and titanium with absolute ethanol or water.
• Solution B is cooled using an ice bath and is kept under stirring until use.
• the coated plate in (a) is then coated with solution B to using a paintbrush.
• the coated plate is then dried for 30 minutes in an oven at 120 ° C, then calcined in an oven under air at 500 ° C for 30 minutes.
• the electrolytic solution (i) allows us to characterize the electrode by the value of the cathodic potential, E cath , for a given current density.
• the current-voltage curve obtained with the electrolytic solution (ii) has a current plateau between - 0.8 and -1.2 V / DHW.
• the value corresponding to this level is the limiting current for reduction of hypochlorite ions, i red .
• the current-voltage curve recorded during the evaluation of cathodes with the electrolytic solution (iii) gives us the limit current reduction of hypochlorite ions in the presence of sodium dichromate, ired (Cr), by measuring the residual current between -0.8 and -1.2 V / DHW.
• Solution B is prepared by mixing, with stirring, in a container, cooled using an ice bath, 5.83 g of ZrCl 4 , 0.01 g of RuCl 3 , 2.74 cm 3 of TiCl 4 and 10 cm 3 of absolute ethanol.
• the plate coated with the intermediate layer is then coated with the solution B thus prepared, then it is dried and calcined in air as indicated in the general procedure. These operations are repeated 4 times and at the end of the last calcination, the mass of the outer layer is 30 g / m 2 of the plate.
• the cathode thus prepared was evaluated using the solutions previously described.
• This table also gives the value of the cathodic potential for a current density of 2KA / m 2 and the value of the limiting current for the different cathodes prepared according to the general procedure but with an external layer composition, different from that used in the example 1.
• a mild steel cathode (example 8) and a titanium plate coated with the intermediate layer according to (I - a) (example 9) were evaluated under the same conditions as the cathodes prepared according to the invention.
• the cathodic potential was determined by presence of the dichromate.
• the plateau of the current-voltage curve observed with the electrolytic solution (ii), using the cathodes prepared according to the invention, is greatly attenuated or even nonexistent.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Automation & Control Theory (AREA)
• Inorganic Chemistry (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Catalysts (AREA)
• Manufacture And Refinement Of Metals (AREA)

Applications Claiming Priority (3)

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• 1998
  • 1998-03-02 FR FR9802485A patent/FR2775486B1/fr not_active Expired - Fee Related
• 1999
  • 1999-02-11 MX MXPA00008615A patent/MXPA00008615A/es not_active IP Right Cessation
  • 1999-02-11 US US09/623,620 patent/US6352625B1/en not_active Expired - Lifetime
  • 1999-02-11 WO PCT/FR1999/000304 patent/WO1999045175A1/fr active IP Right Grant
  • 1999-02-11 NZ NZ506471A patent/NZ506471A/xx unknown
  • 1999-02-11 PL PL99342190A patent/PL193623B1/pl unknown
  • 1999-02-11 ES ES99903733T patent/ES2163931T3/es not_active Expired - Lifetime
  • 1999-02-11 BR BRPI9908390-6A patent/BR9908390B1/pt not_active IP Right Cessation
  • 1999-02-11 DE DE69900266T patent/DE69900266D1/de not_active Expired - Lifetime
  • 1999-02-11 EA EA200000889A patent/EA002200B1/ru not_active IP Right Cessation
  • 1999-02-11 EP EP99903733A patent/EP1060296B1/fr not_active Expired - Lifetime
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  • 1999-02-11 JP JP2000534702A patent/JP4279457B2/ja not_active Expired - Fee Related
  • 1999-02-11 TR TR2000/02508T patent/TR200002508T2/xx unknown
  • 1999-02-11 CA CA002322690A patent/CA2322690C/fr not_active Expired - Fee Related
  • 1999-02-11 CN CNB998030562A patent/CN1147623C/zh not_active Expired - Fee Related
  • 1999-02-11 KR KR1020007009667A patent/KR100577034B1/ko not_active IP Right Cessation
  • 1999-02-11 AT AT99903733T patent/ATE205264T1/de not_active IP Right Cessation
  • 1999-02-11 AU AU24288/99A patent/AU741267B2/en not_active Ceased
  • 1999-02-11 IL IL13716799A patent/IL137167A/xx active IP Right Grant
  • 1999-02-11 ID IDW20001681A patent/ID27559A/id unknown
  • 1999-03-01 ZA ZA9901628A patent/ZA991628B/xx unknown
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• 2000
  • 2000-08-31 NO NO20004332A patent/NO322407B1/no unknown

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