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
  • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
  • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
  • C25B11/031—Porous electrodes
• • 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

Definitions

• the subject of the present invention is a cathode element devoid of fibers. asbestos, its preparation process and its use for obtaining solution of alkali metal hydroxide.
• Materials used for the preparation of the cathode element of a cell must meet several specific characteristics. So, they have to have a low electrical resistivity, compatible with operation, at a acceptable energy level, of the electrolyser equipped with such a cathode element. They must also also make it possible to obtain a thin element while by giving the said element a large specific surface area which may exceed several square meters.
• Such cathode elements are generally obtained by depositing, by filtration at through a porous support, a dispersion of the materials used.
• One of the difficulties of this type of process is to be able to control the quantity of product actually retained at the surface of the porous support, the latter having an opening rate or large hole diameters in relation to the size of the materials used.
• the tablecloth must have controlled and reproducible porosity characteristics, homogeneity, in terms of thickness of the sheet and distribution of these constituents, under penalty of obtaining unusable or poorly performing cathode elements.
• cathode element One of the first generations of cathode element consisted in depositing a suspension comprising carbon fibers, asbestos fibers, a fluoropolymer fiber-binding, an electrocatalytic agent and a blowing agent.
• the object of the present invention is to provide a fibrous web composition. free of asbestos, organic and mineral fibers such as those that come to be mentioned.
• the invention relates to a cathode element devoid of asbestos fibers capable of being obtained by depositing by filtration through a porous support, a aqueous suspension comprising electrically conductive fibers, at least one cationic polymer, at least one electrocatalytic agent, at least one porogenic agent and at least one binder chosen from fluoropolymers.
• the present invention makes it possible to obtain a suspension which is possible to filter vertically, that is to say under industrial conditions. This characteristic was not obvious either because the formulation of the suspension according to the invention is devoid of a thickening agent of the xanthan gum type, previously considered essential for achieving this result.
• the cathode element according to the invention is capable of being obtained by deposition by filtration through a porous support of a dispersion comprising electrically conductive fibers, at least one polymer cationic, at least one electrocatalytic agent, at least one pore-forming agent, at the minus a binder.
• this dispersion is aqueous.
• Electrically conductive fibers can be intrinsically fibers conductive or treated so as to make them such.
• fibers are used intrinsically conductive, such as carbon or graphite fibers in particular.
• these fibers are in the form of filaments whose diameter is generally less than 1 mm and more particularly between 10 -3 and 0.1 mm and whose length is greater than 0.5 mm and more especially between 1 and 20 mm.
• the conductive fibers preferably have a distribution of monodispersed length, i.e. a distribution such that the length of at least 80% and advantageously at least 90% of the fibers corresponds to the length average to within ⁇ 10%.
• binder this is chosen from fluorinated polymers.
• fluoropolymers homopolymers or copolymers derived at least in part from olefinic monomers substituted by atoms of fluorine, or substituted by a combination of fluorine atoms and at least one of chlorine, bromine or iodine atoms, per monomer.
• homopolymers or fluorinated copolymers can be consisting of polymers and copolymers derived from tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, bromotrifluoroethylene.
• Such polymers can also comprise up to 75 mol% of units derived from other ethylenically unsaturated monomers containing at least as much fluorine atoms than carbon atoms, such as (di) fluoride vinylidene, vinyl and perfluoroalkyl esters, such as perfluoroalkoxyethylene.
• This fluoropolymer, or binder is more particularly in the form of a aqueous dispersion containing 30 to 80% by weight of dry polymer, the particle size is between 0.1 and 5 ⁇ m and preferably between 0.1 and 1 ⁇ m.
• the fluoropolymer is the polytetrafluoroethylene.
• All types of metals can be used as electrocatalytic agent known in the art to activate the electrolysis reaction.
• a Raney metal such as preferably nickel, or even a precursor of this Raney metal, consisting in fact of an alloy based on said metal associated with another that can be easily eliminated. More particularly, it is an alloy comprising aluminum which can be leached, for example by a basic treatment.
• This guy of electrocatalytic agent has in particular been described in European patent EP 296 076 to which we can refer on this subject.
• electrocatalytic agent particles comprising an oxide of ruthenium, platinum, iridium, palladium, or a mixture of these oxides.
• mixture particles comprising in themselves, a mixture oxides, but also particles, based on a metal oxide, mixed with other particles comprising a different oxide.
• mixture particles comprising in themselves, a mixture oxides, but also particles, based on a metal oxide, mixed with other particles comprising a different oxide.
• Said agent can also be in the form of particles made up an electrically conductive support, comprising a coating in the form of oxide ruthenium, platinum, iridium, palladium; these oxides being alone or in mixture in the sense just explained.
• the electrocatalytic agent according to the invention is presented under the form of a coating of a support such as in particular iron, cobalt, nickel, iron of Raney, cobalt of Raney, nickel of Raney, the elements of columns IVA and VA of the periodic table, carbon, graphite.
• a support such as in particular iron, cobalt, nickel, iron of Raney, cobalt of Raney, nickel of Raney, the elements of columns IVA and VA of the periodic table, carbon, graphite.
• the periodic table of the elements to which reference is made is that published in the supplement to the Bulletin de la departments Chimique de France (no.1-1966).
• the aqueous dispersion also comprises at least one pore-forming agent.
• derivatives based on silica are particularly interesting because they do not deconsolidate practically not the electroconductive microporous material and form networks with the fiber-binding polymer, when the latter is used in the form of a latex. Furthermore, these compounds are eliminated by leaching with a base such as sodium hydroxide. for example.
• sica derivatives is meant according to the invention precipitated silicas and combustion or pyrogenic silicas. They more particularly have a BET specific surface area of between 100 m 2 / g and 300 m 2 / g and / or a particle size evaluated with the COULTER® counter between 1 and 50 ⁇ m and, preferably, between 1 and 15 ⁇ m.
• nanoparticulate systems which are thermally destroyed, more particularly during the sintering operation of the cathode element, as the nanolatex or latex sizes less than 100 ⁇ m.
• one of the essential constituents of the dispersion used according to the invention consists of a cationic polymer.
• Suitable cationic polymers two categories can be mentioned of polymers, organic polymers and inorganic polymers, which can be used alone or as a mixture.
• polymers of the first category the polymers of synthesis chosen from epychlorohydrin, polyimines, polyacrylamides, polyacrylamines are polymers likely to enter into the composition of the suspension used in the invention.
• Polymers of natural origin such as especially cationic starches, cationic guars are compounds suitable for the invention.
• inorganic polymers there may be mentioned without intending to be limited the clays, bentonites, aluminum sulfate, poly aluminum chloride.
• the suspension according to the invention comprises at least one polymer of the polyacrylamine type, sold in particular under the name FLOERGER® by the company Floerger, of the type of cationic starches, such as hot-soluble cationic starches (cationic HI-CAT® starches, sold by the company Roquette), as well as the cationic starches soluble in cold, cationic guar ytpe marketed under the MEYPRO® brand by the Meyhall company; these polymers can be present alone or as a mixture.
• FLOERGER® hot-soluble cationic starches
• a nanoparticulate system when used, it is associated with minus a cationic polymer.
• a cationic polymer chosen from epychlorohydrin, polyimines, polyacrylamides or even cationic starches.
• the suspension used in the process according to the invention can comprise additionally additional compounds.
• the suspension comprises, in the case if necessary, a fibrous material.
• the fibrous material is chosen from cellulose-based fibers, cellulose-based fibers to which a positive ionic charge, glass fibers or calcium silicate fibers.
• fibers BECOFLOC® like calcium silicate fibers, PROMAXON® fibers.
• additives can enter into the composition of the suspension. according to the invention.
• the suspension comprises, in addition to the above-mentioned constituent elements, at least a surfactant.
• non-ionic compounds are used more particularly, such as ethoxylated alcohols or fluorocarbon compounds with groups functionalized, generally presenting carbon chains comprising 6 to 20 carbon atoms.
• ethoxylated alcohols chosen from the ethoxylated alkylphenols, such as in particular octoxynols.
• the suspension according to the invention is therefore deposited on a porous support.
• This porous support is generally conductive of electricity. It should be noted that no one would not depart from the scope of the present invention by depositing the suspension on a support not electrically conductive so as to create a fibrous sheet which would be continuation associated with a porous support conducting electricity.
• the porous support is more particularly constituted by fabrics or grids whose mesh void, perforations or porosity can be between 20 ⁇ m and 5 mm.
• the porous support may have one or more flat surfaces or cylindrical, commonly called “thimble", having an open surface.
• the porous conductive support consists in particular of iron, nickel, or still of any material treated so as to make it even less sensitive to corrosivity of the medium, such as iron on which a deposit of nickel.
• the fibrous sheet deposited on the porous support conducting electricity is associated with a microporous diaphragm.
• a first embodiment consists in depositing the diaphragm on the sheet fibrous. This type of process is known to those skilled in the art and has in particular been the subject of of the following patents:
• the diaphragm is not deposited on the fibrous web but is arranged separately so as to separate the anode and cathode compartments.
• Such diaphragms are commercially available and are especially based on ceramic type fibers, or Teflon.
• the cathode comprising the sheet fibrous deposited on a support conducting electricity, is associated with a membrane.
• membranes suitable for the process according to the invention perfluorosulfonic membranes, of the Nafion type (sold by the DU PONT company), or perfluorinated membranes comprising carboxylic functional groups (series 890 or Fx-50, marketed by the ASAHI GLASS). It is also possible to use bilayer membranes, comprising sulfonic groups on one side and groups on the other carboxylic.
• the content of conductive fibers is determined so that the resistivity overall of the final fibrous web is less than or equal to 0.4 ⁇ .cm.
• the suspension more particularly comprises 20 to 100 parts by weight of fibers conductive.
• the fiber content conductive is between 50 and 90 parts by weight.
• binder its content is between 10 to 60 parts by weight dry.
• the amount of catalytic agent can vary within wide limits.
• the content of this compound in the aqueous suspension is between 20 and 200 parts by weight. More specifically, the content is understood between 60 and 120 parts by weight.
• the amount of blowing agent used in the composition of the dispersion varies it too in a wide area.
• this content is generally between 30 and 200 parts. More particularly, the amount of blowing agent entering into the composition of the suspension is between 30 and 100 parts in weight.
• the amount in this type of compound is more particularly between 10 and 200 parts by weight.
• the quantity of blowing agents corresponding to a mixture of agents chemically and thermally eliminable is more particularly between 30 and 200 parts by weight.
• the aqueous suspension according to the invention also comprises at least one cationic polymer.
• the content of this polymer in the suspension is such that the measurement of the turbidity of the supernatant liquid after settling of the suspension is greater than or equal to 50, and preferably greater than or equal to 75. It should be noted that the same measurement made with pure water gives a value of 100.
• the measurement of turbidity is carried out by transmission at 630 nm on a Methrom type turbidimeter 662 Photometer®.
• Another criterion concerning the choice of the polymer content cationic depends on the viscosity imparted to the suspension. This preferably be such that it does not cause undue difficulty in filtering the suspension.
• the content varies between 10 and 80 parts by dry weight.
• the cationic polymer content varies between 20 and 40 parts by dry weight.
• the content of fibrous material, other than cellulose fibers, loaded or not positively, is governed by the same conditions as the aforementioned conductive fibers. Thus, their content is such that the overall resistivity of the final fibrous web is less than or equal to 0.4 ⁇ .cm.
• the suspension comprises fibers based on cellulose, charged or not positively charged, as a fibrous material
• their content is at most 60 parts by dry weight.
• the content of cellulose fibers is between 10 and 40 parts by weight.
• the amount of surfactant used in the composition of the suspension varies in generally from 0.5 to 5 parts by weight, although quantities outside of this range are quite possible.
• the suspension is left to stand for at least one hour. aqueous thus prepared.
• a next step [b] the suspension obtained above is deposited on a porous support, which, preferably, conducts electricity.
• the sheet is deposited on the porous support by programmed vacuum filtration. This is carried out in a manner known per se and can be carried out continuously or in stages, at a final depression of 1.5 .10 3 to 5.10 4 Pa.
• the filtration of the suspension obtained can be performed vertically, which is a particularly advantageous advantage for industrial scale operation. Obviously, a deposit of the suspension by horizontal filtration is entirely possible.
• the tablecloth is deposited, it is wrung out by maintaining the vacuum for a few moments and then optionally air-dried at a temperature between room temperature and 150 ° C.
• the sheet is then sintered by heating to a temperature greater than or equal to the melting point of the fluoropolymer.
• a temperature greater than or equal to the melting point of the fluoropolymer is in general thermally degraded. This is particularly the case when the blowing agent is made up at least in part by the nanoparticulate system mentioned before.
• blowing agent is constituted at least in part by agents such as the silica derivatives
• a step of removing the blowing agent is then carried out, in particular by means of an aqueous solution of alkali metal hydroxide.
• this pore-forming agent can be done not only "in situ", that is to say during the first moments of cathode use, but also before use of electroconductive microporous material. This last possibility presents the advantage of minimizing pollution of the electrolytic medium.
• the cathode used in the method according to the invention comprises an associated diaphragm
• steps [a] to [d] are carried out as indicated above.
• the filing of the suspension comprising the constituent elements of the fibrous sheet of the diaphragm as described in particular in the patents EP 412 917 and EP 642 602 can be produced either on the sintered fibrous web or not, on which one will have carried out or not a treatment of elimination of the blowing agent or no.
• a sintering step is carried out at a temperature greater than or equal to the melting or softening temperature of the binder present in the fibrous web of the diaphragm, before eliminating the blowing agent by a treatment carried out before the use of the cathode or when using it.
• the suspension obtained is filtered, after having stirred it, under vacuum, on a braided iron mesh and rolled steel type "Gantois" whose opening is 2 mm and whose wire diameter is 1 mm, the deposition area being 1.21 dm 2 .
• the depression is therefore established and increases by 50.10 2 Pa per minute to reach a depression indicated in the table below. This maximum depression is maintained for approximately 15 minutes.
• the whole is then dried, then consolidated by melting the fluoropolymer at 350 ° C.
• the silica is eliminated "in situ" in the electrolyser by dissolution in an alkaline medium especially during the first hours of electrolysis.
• Test 1 was carried out one hour after the preparation of the aqueous suspension.
• Tests 2 and 3 were carried out respectively 5 and 4 days after the preparation of suspension.
• Tests 1 and 2 show that the storage of the suspension has little influence on the filtration conditions thereof and rather goes in the direction of improving the vacuum final for the same weight deposited. The feasibility of the operation is increased.

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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)
• Catalysts (AREA)
• Chemical Or Physical Treatment Of Fibers (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)
• Paper (AREA)

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• 1995
  • 1995-12-29 FR FR9515712A patent/FR2743090B1/fr not_active Expired - Fee Related
• 1996
  • 1996-12-27 PL PL96327570A patent/PL327570A1/xx unknown
  • 1996-12-27 CA CA002241230A patent/CA2241230C/fr not_active Expired - Fee Related
  • 1996-12-27 DE DE69603092T patent/DE69603092T2/de not_active Expired - Fee Related
  • 1996-12-27 US US09/101,010 patent/US6099704A/en not_active Expired - Fee Related
  • 1996-12-27 WO PCT/FR1996/002091 patent/WO1997024474A1/fr not_active Application Discontinuation
  • 1996-12-27 EA EA199800613A patent/EA000808B1/ru not_active IP Right Cessation
  • 1996-12-27 UA UA98063370A patent/UA47449C2/uk unknown
  • 1996-12-27 EP EP96944091A patent/EP0870077B1/fr not_active Expired - Lifetime
  • 1996-12-27 AU AU13810/97A patent/AU1381097A/en not_active Abandoned
  • 1996-12-27 CN CNB961998032A patent/CN1163636C/zh not_active Expired - Fee Related
  • 1996-12-27 BR BR9612313-3A patent/BR9612313A/pt not_active IP Right Cessation
  • 1996-12-27 JP JP9524075A patent/JP2000502753A/ja active Pending
  • 1996-12-27 MX MXPA98005187A patent/MXPA98005187A/es not_active Application Discontinuation
  • 1996-12-27 KR KR1019980705039A patent/KR19990076911A/ko not_active Application Discontinuation
• 1998
  • 1998-06-19 BG BG102564A patent/BG62785B1/bg unknown
  • 1998-06-26 NO NO983011A patent/NO983011L/no not_active Application Discontinuation

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