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
• • 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
  • C25B11/095—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 of the compounds being organic
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T442/00—Fabric [woven, knitted, or nonwoven textile or cloth, etc.]
  • Y10T442/60—Nonwoven fabric [i.e., nonwoven strand or fiber material]
  • Y10T442/69—Autogenously bonded nonwoven fabric
  • Y10T442/692—Containing at least two chemically different strand or fiber materials

Definitions

• the subject of the present invention is a material which can be used in particular for the production of the cathode element of an electrolysis cell, and in particular of an electrolysis cell of aqueous solutions of alkali halides. It also relates to the cathode element comprising said material. The invention also applies to the process for manufacturing said materials and said cathode elements.
• the material to which the invention relates in the first place consists of a sheet comprising fibers and a binder, this sheet being characterized in that at least part of the fibers consists of electrically conductive fibers, in that the binder is chosen from fluoropolymers and in that the resistivity is less than 0.4 Q.cm and preferably less than 0.1 ⁇ .cm.
• tablette designates a three-dimensional assembly whose thickness is substantially less than the smallest of the other dimensions, said assembly possibly or not having two parallel surfaces.
• These plies generally have substantially flat and rectilinear surfaces but can also have the most diverse shapes, said shape being able in particular to be determined by the shape of the material with which the ply may be associated, as will be specified below.
• the thickness of this sheet can be between 0.1 and 5 mm, one of the large dimensions, which can substantially correspond to the height of the cathode element, which can reach 1 m, or even more, the other large dimension, which can correspond substantially to the perimeter of said element up to several tens of meters. It should be recalled that these values are indicated at present for the sole purpose of giving an order of magnitude of sheets in accordance with the invention, but it is obvious that such indications cannot in any way limit the field concerned by the present invention to sheets of precise dimensions.
• one of the constituents of the sheets according to the invention consists of fibers, at least part of which are electrically conductive fibers.
• the choice of conductive fibers and their possible association with non-conductive fibers proceed from various criteria and in particular from compliance with the value chosen for the electrical resistance of the final sheet, taking into account the presence of the polyfluoroolefin binder.
• electrically conductive fibers will denote any material in the form of a filament the diameter of which is generally less than 1 mm and preferably between 10 and 0.1 mm and the length of which is greater than 0.5 mm and preferably between 1 and 20 mm, said material having a resistivity equal to or less than 0.4 ⁇ Lcm.
• Such fibers may consist entirely of a material that is intrinsically conductive of electricity; as examples of such materials, mention may be made of metallic fibers, and in particular iron fibers, ferrous alloys or nickel or carbon fibers. It is also possible to use fibers originating from material which is not electrically conductive but which are made conductive by a treatment: mention may be made, for example, of asbestos fibers, made conductive by chemical or electrochemical deposition of a metal such as nickel , or zirconia fibers (Zr 02), made conductive by nickel plating. In the case of fibers made conductive by treatment, this will be carried out under conditions such that the resulting fiber has the resistivity mentioned above.
• the two types of fibers can be combined in the plies according to the invention, namely the intrinsically conductive fibers and the fibers made conductive, as explained above.
• the invention includes the use of intrinsically conductive fibers, that is to say fibers having the maximum resistivity value mentioned above, these fibers having themselves undergone a treatment such as for example nickel plating to increase their conductivity.
• the conductive fibers can be associated with non-electrically conductive fibers, this expression designating, by hypothesis, any filament whose resistivity is greater than 0.4 Q. cm .
• these fibers have a diameter less than 1 mm and preferably between 10 and 0.1 mm and a length greater than 0.5 mm and more generally between 1 and 20 mm.
• non-conductive fibers can meet various requirements and in particular can be justified by the mechanical properties desired for the sheet of fibers.
• non-conductive fibers within the meaning of the invention, particular mention will be made of mineral fibers such as asbestos fibers, glass fibers, quartz fibers, zirconia fibers, or organic fibers such as fibers of polypropylene or polyethylene, optionally halogenated and in particular fluorinated, polyhalovinylidene fibers and in particular polyvinylidene fluoride or also fibers of fluorinated polymers which will be discussed below with regard to the binder of the plies according to the invention.
• the sheet of fibers is intended for application as a cathode element of a sodium chloride electrolysis cell.
• non-conductive fibers and in particular asbestos fibers with conductive fibers, which can advantageously be constituted by carbon fibers.
• the asbestos fibers and more generally the non-conductive fibers can represent up to 90% and preferably 20 to 70% of the weight of the conductive fiber / non-conductive fiber assembly.
• the binder of the plies according to the invention consists of a fluoropolymer.
• fluoropolymer currently designates a homopolymer or a copolymer derived at least in part from olefinic monomers fully substituted with fluorine atoms, or totally substituted with a combination of fluorine atoms and at least one of chlorine, bromine or iodine atoms per monomer.
• fluorinated homo- or copolymers can be constituted by polymers and copolymers derived from tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, bromotrifluoroethylene.
• Such fluorinated polymers can also contain up to 75 mole percent of units derived from other ethylenically unsaturated monomers containing at least as many fluorine atoms as carbon atoms, such as for example vinylidene (di) fluoride, vinyl and perfluoroalkyl esters, such as perfluoroalkoxyethylene.
• units derived from other ethylenically unsaturated monomers containing at least as many fluorine atoms as carbon atoms such as for example vinylidene (di) fluoride, vinyl and perfluoroalkyl esters, such as perfluoroalkoxyethylene.
• the fluoropolymer is currently used as a binder of fibers defined above.
• the different modes of implementation of said binder will be explained below. It will simply be indicated here that, in the sheets according to the invention, the fluoropolymer can represent up to 60% of the total weight of the sheet, that is to say fibers (conductive fibers, possibly associated with non-conductive fibers ) + binder, this rate being more generally between 5 and 50%.
• the layers according to the invention have been defined above by their essential constituents, namely the fibers and the binder. Depending on the different applications for which these layers will be intended, they may, at one or the other moment of their existence, contain other materials or additives. These materials or additives are listed below, it being specified that the additives can be present simultaneously or, on the contrary, succeed one another within the sheet, in the case of treatments carried out on said sheet.
• such materials may in particular be constituted by powders, whether they are conductive powders such as graphite, nickel, iron or magnetite powders or non-conductive powders, the concept of powder designating a product whose particle size is less than 50 ⁇ m and the conductivity being appreciated as in the case of fibers.
• conductive powders such as graphite, nickel, iron or magnetite powders or non-conductive powders
• non-conductive powders which may consist for example of asbestos powders or hydrated oxide can contribute with the binder to obtain the cohesion of the sheet of fibers.
• the quantity of powdered additive can reach 30% of the weight of the conductive fibers + fluoropolymer assembly.
• the sheets may also contain one or more electrocatalytic agents.
• electrocatalytic agents which can be in the form of powder, the particle size of which can vary for example between 1 and 100 mm, makes it possible to combine the advantages linked to the use of an elementary cathode directly comprising a deposit of electrocatalytic agent. (voltage gain of the order of 150 mV in the case of sodium chloride electrolysis) and the advantages linked to the use of fiber layers in terms of current distribution, diaphragm support, etc.
• platinum group metals and in particular platinum itself and palladium, nickel-zinc, nickel-aluminum, titanium-nickel, molybdenum- and alloys and couples. nickel, sulfur-nickel, nickel-phosphorus, cobalt-molybdenum, lanthanum-nickel.
• the quantity of electrocatalytic agent in whatever form it may appear, may represent up to 50% of the weight of the bound sheet and more generally from 1 to 30% of this weight, depending on the nature of the catalyst.
• the sheets can also contain hydrophilic agents.
• hydrophilic agents are particularly recommended when the web is used in an aqueous medium, for example in a process for the electrolysis of aqueous solutions of sodium chloride.
• the hydrophilic agent contributes to improving the wettability of the sheet of fibers by somewhat counterbalancing the highly hydrophobic nature of the fluoropolymers.
• Hydrophilic agents can be chosen from various families of products. It can generally be liquid or pulverulent products, of organic or inorganic nature. As illustrative examples of such agents, mention may be made of surfactants or surfactants, such as sodium dioctylsulfosuccinate, etc. or inorganic compounds such as asbestos powder or short fibers, zirconia, carbon dioxide cerium, potassium titanate, hydrated oxides and in particular alumina.
• surfactants or surfactants such as sodium dioctylsulfosuccinate, etc. or inorganic compounds such as asbestos powder or short fibers, zirconia, carbon dioxide cerium, potassium titanate, hydrated oxides and in particular alumina.
• the amount of hydrophilic agent that can be present in the sheets according to the invention obviously depends on the use intended for this sheet, on the amount of hydrophobic product (essentially the fluorinated binder but also certain fibers contained in these sheets) and on the nature of the hydrophilic agent. As an order of magnitude, it can be indicated that the quantity of hydrophilic agent can reach 10% of the weight of the fluorinated binder and more specifically from 0.1 to 5% of the weight of said binder.
• the sheets may also contain pore-forming agents, the role of which is to regulate the porosity of the sheet, porosity which, in the event of an application in electrolysis, influences the flow of liquids and the evacuation of gases. It should be understood that, when such pore-forming agents are used, the final layer, the porosity of which, under the effect of decomposition or elimination of these agents, has been adjusted or modified, will in principle no longer contain such agents.
• pore-forming agents the role of which is to regulate the porosity of the sheet, porosity which, in the event of an application in electrolysis, influences the flow of liquids and the evacuation of gases.
• alkaline or alkaline-earth salts such as halides, sulfates, sulfites, bisulfites, phosphates, carbonates, bicarbonates. Mention may also be made of amphoteric alumina or silica which can be eliminated in an alkaline medium.
• the quantity and the particle size of the blowing agents - when such agents are used - is closely linked to the application for which the sheets are intended. Simply as an order of magnitude, it will be specified that the particle size of the blowing agents generally varies between 5 and 50 ⁇ m, and that the quantity is chosen according to the desired porosity, this porosity being able to reach up to 90% or even more (according to standard ASTM D 276-72).
• each of the layers defined above by its essential constituents and by its additives. constitutes in itself a new product, directly targeted by the present invention.
• the present invention also relates to a method of manufacturing the plies defined above. It should be understood that the process which will be described below constitutes an embodiment of the sheets, an embodiment by the wet method as will appear on reading the following, but that this description does not in any way constitute a limitation of the field of the invention and that any process making it possible to obtain the plies claimed, whether it be a wet method or a dry process, is part of the field of said invention.
• the suspension comprises, as indicated above, on the one hand the electrically conductive fibers and on the other hand the binder consisting of a fluoropolymer, these constituents being dispersed in a liquid medium.
• this medium can be of very diverse natures, an aqueous medium or an electrolytic medium is generally used.
• the medium may contain, in addition to water, caustic soda, for example at a rate of 5 to 20% and sodium chloride, for example at a rate of 5 to 20%. It goes without saying that this indication is valid for an electrolytic medium corresponding to the electrolysis of sodium chloride but that it is possible, mutatis mutandis, to use any other electrolytic medium.
• aqueous or electrolytic medium a small amount - for example 0.1 to 5% relative to the weight of the solid materials to be dispersed - of dispersing agents or surfactants such as, for example, sodium dioctylsulfosuccinate and, more generally, anionic sulfonic surfactants, such as sulfonates, sulfosuccinates, C G to C 24 ' alkyl sulfosuccinamates
• the final sheet must contain other additives and in particular those listed above such as non-conductive fibers, conductive or non-conductive powders, hydrophilic agents, pore-forming agents, catalytic agents, these can generally be incorporated as soon as the initial suspension is prepared. It can however be specified that, apart from the case of additional fibers which, in principle, must be dispersed among the conductive fibers, the other additives can also be introduced into the sheet, for example by filtration through said sheet of a suspension containing such agents.
• the fluoropolymer is generally in the form of a dry powder or of fibers or of an aqueous dispersion (latex) generally containing 30 to 70% of dry polymer.
• the largest dimension of the particles or fibers of fluoropolymer is less than 50 ⁇ m, the particle size usually being between 0.1 and 10 mm in the case of powdered polymer.
• suspension defined above by its essential constituents and by its optional additives is generally highly diluted in the sense that the ratio: suspension medium / dry matter (fibers, polymer, additives) is of the order of 30 to 100 : 1. These indications correspond to a suspension which can be used industrially, but one could obviously use a much higher ratio.
• a thickening agent chosen, for example, from natural or synthetic polysaccharides, can be added to the suspension if necessary.
• the various constituents can be directly introduced into the medium, in particular the aqueous, optionally electrolytic medium.
• a dispersion of the fibrous materials is first carried out, with the addition of a dispersing agent, in a fraction, for example 1/5 to 1/2 of the final amount of dispersion medium, then the fluoropolymer is incorporated into this dispersion, the suspension then being diluted and homogenized.
• the next phase of the process according to the invention consists in forming the sheet comprising the fibers, the fluorinated binder and possibly the other additives.
• This sheet can be formed by filtration of the suspension through a highly porous material, such as a metal grid, for example of iron or bronze, whose mesh void can be between 20 ⁇ m and 5 mm.
• this filtration is advantageously carried out under vacuum, generally following a program ranging, continuously or in stages, from atmospheric pressure to final depression (1.5 ⁇ 10 3 3 to 4.10 4 Pa).
• the sheet resulting from this filtration can be dried, for example at a temperature between 70 and 120 ° C. for a period which can range from 1 to 24 hours.
• the final formation of the web possibly after the drying mentioned above, comprises heating to a temperature above the melting or softening point of the fluoropolymer, for example from 5 to 50 ° C above this point, and for a period of time. duration which can range, depending on the polymer and the temperature chosen, from 2 min to 60 min and, more precisely, from 5 to 40 min.
• the sheet thus formed, and constituted by a set of conductive fibers linked by a fluoropolymer constitutes, as has been specified, the primary object of the present invention.
• the invention also relates, and very particularly the aforementioned plies activated by an electrocatalytic agent.
• electrocatalytic agents have been mentioned previously which can be incorporated and dispersed in said sheet. According to an embodiment of electrocatalytic agents, and as far as the nature of the latter allows, these agents can be deposited on the sheet formed by electrochemical deposition. This technique is particularly interesting when one wishes to use as an agent electrocatalytic nickel, which is deposited in the form of a nickel-zinc alloy and then leached in an alkaline medium in order to remove the zinc and obtain large surface nickel.
• the fiber sheet is deposited on a cathode, the anode is made of nickel and the electrocatalytic bath comprises halides of nickel and zinc.
• the nickel / zinc couple is deposited on the electrically conductive fibers, the zinc being eliminated as has just been specified.
• an electrocatalytic agent can be incorporated directly into the suspension in the form of a powder or filtered through the fiber web, before or after melting of the binder, a suspension of electrocatalytic agent in any liquid vehicle, most often water, possibly supplemented with surfactant in order to maintain the dispersion of the powders, for example in the case of the reduction of precious metal salts by borohydride sodium.
• Another object of the invention consists of a composite material comprising the sheet itself comprising the fibers and the fluoropolymer defined above and an elementary cathode.
• the expression elementary cathode currently designates the metal part, generally made of iron or nickel, essentially constituted by a mesh or a piece of perforated metal and playing the role of cathode in an electrolysis cell.
• This elementary cathode may consist of one or an assembly of flat surfaces or, in the case of electrolysis cells of the "thimble" type, may be in the form of a cylinder whose director is a more or less complex surface. , generally substantially rectangular with rounded corners.
• the assembly of the sheet of fibers linked by the fluoropolymer with the elementary cathode can be done by various methods. According to a first way of proceeding, the suspension is directly filtered through the elementary cathode and then brings the elementary cathode / fiber sheet assembly to a temperature allowing the fluoropolymer binder to melt, as indicated above. According to another variant, the suspension is filtered separately and a sheet of fibers is formed and the binder is melted, this only operation being carried out after application of the sheet on the elementary cathode.
• the choice between the different techniques can be linked to the nature of the elementary cathode (grid, perforated metal, expanded metal) and to the desired degree of penetration of the sheet of fibers into the mesh voids or perforations of the elementary cathode.
• the composite material comprising the elementary cathode and the sheet of fibers, as described above constitutes in fact the cathode itself of an electrolysis cell, this application to the production of cathode element of electrolysis cell constituting the privileged but not exclusive area of materials according to the invention.
• a membrane or a diaphragm between the anode and cathode compartments In the case of a membrane, which can be chosen from the many electrolysis membranes described in the literature, the composite element according to the invention constitutes an excellent mechanical support and ensures a remarkable distribution of the current. This distribution of the current is naturally linked to the particular structure of the composite elements according to the invention.
• the multiplicity of current conductors ensures a maximum voltage gain due to the large active area, which gain can be increased when electrocatalytic elements have been, in one or the other form previously disclosed. , dispersed within the fiber sheet.
• the composite material can also be associated with a diaphragm.
• This diaphragm which can also be chosen from the many diaphragms for electrolysis now known, can be manufactured separately. It can also, and this constitutes an advantageous method, be manufactured directly on the fiber web or on the composite fiber web / elementary cathode. This direct manufacture is particularly easy when the diaphragm is produced by filtration of a suspension.
• Composite materials made up of a compre nant, from one face to the other, the elementary cathode, the sheet of fibers linked by the fluoropolymer and the porous or microporous membrane or diaphragm also constitute an object of the invention.
• Such composite materials constitute coherent assemblies, benefiting from all the advantages specific to the fiber sheet and to the fiber sheet / elementary cathode composite, to which is added the considerable advantage represented by the elimination of the traditional diaphragm / cathode interface. and its harmful effects, namely a parasitic ohmic drop in the gas-liquid emulsion close to the cathode substrate.
• Type II alkaline route
• the procedure is as for the aqueous route but replaces the softened water with the same amount of electrolytic soda (150 g / 1 of NaCl and 150 g / 1 of NaOH).
• electrolytic soda 150 g / 1 of NaCl and 150 g / 1 of NaOH.
• PCTFE polychlorotrifluoroethylene
• the suspension is stirred by air for 30 min (air circulation at a flow rate of 10 m 3 / h).
• suspensions I or II are filtered through a bronze grid opening 40 mm while respecting the following vacuum program: 1 min of decantation then successive stages for 1 min at increasing voids (from 100 to 100 Pa).
• the sheet obtained after filtration is detached from the grid and brought to an oven at 350 ° C for 10 min when the polymer is PTFE or at 260 ° C for 30 min when the polymer is PCTFE.
• the composite material resulting from this filtration and from the fusion of the fluoropolymer (12 hours at 100 ° then 10 min at 350 °) is used as a cathode in a sodium chloride electrolysis cell (operation at 25 A / dm 2 to 85 ° C - soda outlet: 120 to 140 g / 1).
• the excess thickness of the sheet of fibers linked by the fluoropolymer relative to the surface of the elementary cathode varies from 0.1 to 1 mm, depending on the amount of suspension filtered.
• the cathode elements were activated by electrochemical deposition (examples 10 and 11), by nickel plating of fibers (examples 12 and 13), and by addition of electrocatalytic element in powder form (examples 14 to 28), the general technique for manufacturing the composite (elementary cathode + sheet of fibers) being that of Examples 4 to 9.
• the electrolysis is carried out in an agitated medium, at 20 ° under a current density of 10 A / dm 2 .
• the operation lasts 30 min.
• this operation during which a nickel-zinc alloy is deposited on the conductive fibers of the cathode element, this element is immersed for 2 hours in electrolytic soda (concentration 150 g / 1) at 80 ° C. At the end of this operation, the zinc was removed and the quantity of nickel deposited represents approximately 30% of the weight of the sheet of fibers.
• Example 4 was repeated using either nickel-plated carbon fibers (63) and asbestos fibers (37), or only nickel-plated asbestos fibers.
• the third activation technique involves the addition of powdered electrocatalytic element.
• the cathode elements are wrung, dried (100 °, 12 h) and brought to 350 ° for 10 min.
• the amount of activator is expressed by weight of platinum or palladium (metal) deposited per dm 2 of surface of the cathode element.
• Powder activators whose particle size is equal to or less than 50 ⁇ m are incorporated directly into the suspension.
• the cathode element used is made from an elementary braided and rolled iron cathode and a type I suspension, containing a PTFE latex, asbestos fibers (A) and a carbon fiber / fiber ratio. asbestos 63/37. This item may be activated.
• the diaphragm is deposited on this element by suction under programmed vacuum of a suspension comprising:
• the programmed vacuum deposition is carried out as follows:
• the cathode element / diaphragm assembly is wrung and placed at 100 ° for 12 hours and then at 350 ° for 10 minutes.
• the porogen is eliminated by alkaline attack before mounting in the electrolyser.
• the electrolysis conditions are those of the previous examples; however the inter-electrode distance is reduced to 6 mm.

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• 1984
  • 1984-06-20 ES ES533583A patent/ES533583A0/es active Granted
  • 1984-06-20 EP EP84401271A patent/EP0132425A1/de not_active Withdrawn
  • 1984-06-20 DE DE3486268T patent/DE3486268T2/de not_active Expired - Lifetime
  • 1984-06-21 CA CA000457162A patent/CA1236048A/fr not_active Expired
  • 1984-06-21 JP JP59126590A patent/JPS6075593A/ja active Granted
• 1986
  • 1986-09-12 US US06/906,435 patent/US4743349A/en not_active Ceased

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