EP0296076B1 - Production of an electroactive material based on conductive fibers and its use in the production of cathode elements - Google Patents

Abstract

An electroactivated material comprising fibres at least part of which is electrically conductive and a binder chosen from fluoropolymers, the said material exhibiting a resistivity lower than 0.4 ohm cm and being characterised in that it comprises at least one electrocatalytic agent uniformly distributed in its bulk, the said agent being chosen from the group consisting of Raney metals and Raney alloys from which most of the easily removable metal(s) and alloys thereof have been removed. <??>The invention also relates to composite materials formed by the combination of at least one electroactivated material and of an elementary cathode consisting of a metal surface, assembled with a diaphragm if appropriate, and a process for the manufacture of the said materials. <??>These materials can be employed especially in a cell for the electrolysis of sodium chloride.

Description

The subject of the present invention is a process for the preparation of an electroactivated 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 preparation of the cathode element comprising said material.

These materials have a low overvoltage with respect to the hydrogen evolution reaction at the cathode and, therefore, allow appreciable energy gains. Other advantages presented by said materials will appear on reading the following.

In European patent application EP-A-0132425, a material has been proposed comprising fibers and a binder, usable in particular for producing the cathode element of an electrolysis cell, said material being characterized in that '' at least part of the free consists of electrically conductive fibers, in that the binder is chosen from fluoropolymers and in that the resistivity of said material is less than 0.4 ohm.cm and preferably less than O, 1 ohm.cm.

The conductive fibers may be carbon fibers and, non-conductive fibers, such as asbestos fibers may be present among the fibers constituting the material in question.

Said material may also contain one or more electrocatalytic agents capable of being in the form of powder with a particle size between 1 and 10 μm (microns). Among the electrocatalytic agents, platinum, palladium, nickel-zinc, nickel-aluminum, titanium-nickel, molybdenum-nickel sulfur-nickel, nickel-phosphorus, cobalt-molybdenum, lanthanum-nickel alloys are contemplated.

In this application, the amount of electrocatalytic agent could represent up to 50% of the weight of the bonded sheet, a content of between 1 and 30% of said weight being recommended.

• le recours à des fibres non conductrices rendues conductrices par métallisation , telles des fibres d'amiante nickelées, ou à des libres de carbone nickelées est non seulement coûteux, ce qui limite le développement à l'échelle industrielle, mais ne saurait remplacer l'agent électrocatalytique sur le strict plan de l'efficacité ; par ailleurs ces fibres peuvent être altérées par les traitements thermiques.
• le recours au dépôt électrochimique d'un alliage Ni,Zn par exemple, sur une nappe précathodique (c'est-à-cire une nappe de fibres, composite et déposée sur une cathode élémentaire, cette nappe remplissant notamment la fonction usuelle d'une cathode) présente le défaut majeur de n'activer la nappe qu'en surface, le coeur n'en étant pas touché, ce qui diminue notablement les avantages escomptés d'une électrode volumique ; en outre l'électroactivateur étant situé à l'interface diaphragme/précathode, la majeure partie du dégagement d'hydrogène se déroule à cette interface et contribue à la désolidarisation de l'ensemble. Au surplus, une telle nappe ne peut que difficilement être couplée à un diaphragme, en raison de la couche métallique formée à sa surface,
• l'incorporation du composé Ni-Al sous forme de poudre dans ce type de matériaux pour réaliser des éléments cathodiques, ne permet pas d'augmenter leurs performances de manière satisfaisante comme le montre la comparaison des valeurs de la tension (aux bornes de l'électrolyseur) d'extrapolation à intensité nulle (ΔU_I->o), respectivement obtenues sans activation et avec activation rappelées dans le dernier tableau de la demande européenne en cause.

However, all of the materials capable of being prepared according to the teaching of this European application, provided that they are electroactivated have at least one of the following drawbacks:

• the use of non-conductive fibers made conductive by metallization, such as nickel-plated asbestos fibers, or nickel-free carbon fibers is not only costly, which limits development on an industrial scale, but cannot replace the agent electrocatalytic in the strict sense of efficiency; moreover, these fibers can be altered by heat treatments.
• recourse to the electrochemical deposition of an Ni, Zn alloy for example, on a precathode layer (that is to say a fiber layer, composite and deposited on an elementary cathode, this layer fulfilling in particular the usual function of a cathode) has the major defect of activating the sheet only at the surface, the heart not being affected, which significantly reduces the expected benefits of a volume electrode; in addition, the electroactivator being located at the diaphragm / precathode interface, most of the hydrogen evolution takes place at this interface and contributes to the separation of the assembly. Furthermore, such a ply can only be difficult to couple with a diaphragm, because of the metal layer formed on its surface,
• the incorporation of the Ni-Al compound in powder form in this type of material for producing cathode elements, does not make it possible to increase their performance satisfactorily as shown by the comparison of the values of the voltage (at the terminals of the electrolyser) extrapolation at zero intensity (ΔU _{I-> o} ), respectively obtained without activation and with activation recalled in the last table of the European application in question.

In this same patent application, a method of manufacturing these materials has also been proposed which consists in preparing a suspension comprising the conductive fibers and the binder, then in remove the liquid medium and dry the sheet obtained. The suspension may also contain non-conductive fibers, blowing agents and / or catalytic agents.

The sheet can be formed by filtration of the suspension through a highly porous material, under programmed vacuum, then dried for 1 to 24 hours at a temperature between 70 and 120 ° C, then bonded by heating to a temperature of 5 to 50 ° C higher than the melting or softening point of the fluoropolymer for a period which can range from 2 to 60 min.

Finally, it has also been proposed in this European application the application of the materials which have just been mentioned in the production of composite materials by association of said materials with an elementary cathode constituted by a metallic surface and the application according to which said association is achieved by filtration of the suspension containing the fibers and the fluoropolymer directly through said elementary cathode, followed by the melting of the binder.

Furthermore, in European patent application No. 86 / 420184.3 it was shown the importance, both in terms of the quality of microporous materials containing electrically conductive fibers such as carbon or graphite fibers, that in terms of the production on an industrial scale of such materials by vacuum filtration of a suspension of fibers and binder, of the monodispersed nature of the lengths of the fibers used.

By monodisperse distribution is meant a distribution of lengths such that the length of at least 80%, and advantageously 90% of the fibers corresponds to the average length of the fibers to within ± 20% and, advantageously to within ± 10%.

According to an advantageous procedure, the average length of the fibers is, at most, equal to the diameter of the perforations of the perforated rigid substrate on which the fibrous sheet is deposited.

It has also been shown in European patent application No. 86 / 420237.9 the importance, both in terms of microporosity and that of the consolidation of microporous materials, of the use of certain derivatives based on silica, as an agent for network formation binder based on latex of a fluoropolymer and more particularly when carbon or graphite fibers are caused to be bonded by a polytetrafluoroethylene latex.

All of the previous work recalled above testifies to the importance of the various improvements made to the basic technique and to the technological difficulties encountered during the development on an industrial scale of a technique whose interest in principle is not not disputed.

An object of the present invention lies in obtaining electroactivated materials, improved in terms of their electrocatalytic performance and whose mechanical properties are maintained, or even improved, in particular by greater cohesion of the assembly.

Another object of the present invention lies in the preparation of electroactivated composite materials with a porous structure, improved both in terms of their electrical and catalytic performance as in that of their mechanical and / or physical properties.

The object of the present invention is therefore to obtain an electro-activated material comprising fibers, at least part of which is electrically conductive, and a binder, chosen from fluorinated polymers, said material having a resistivity less than 0, 4 ohm.cm, and being characterized in that it comprises at least one active electrocatalytic agent uniformly distributed in its mass, said agent being chosen from the group consisting of Raney metals and Raney alloys, the major of which has been eliminated easily removable part (s) of metal (s), and mixtures thereof.

The preferred materials obtained according to the invention are those in which said agent represents from 30 to 70% of the weight of the assembly (fibers + binder + electrocatalytic agent).

It also has for object, the preparation of a composite material formed by the association of an electroactivated material defined above and of an elementary cathode made up of a metallic surface and, the preparation of a material composite formed by the assembly of an electroactivated material, an elementary cathode, both defined above and a diaphragm.

The electro-activated material obtained according to the invention is in the form of a sheet, in the sense given to this term, for example in European application No. 0132425, the thickness of which is generally between 0.1 and 5 mm and advantageously , between 0.5 and 3 mm and whose surface can reach several tens of m², the shape can be very varied.

The material in question comprises fibers of which at least part is electrically conductive; the choice of conductive fibers and their possible association in particular with non-conductive free materials are dictated, in particular, by the electrical and mechanical properties sought for the consolidated sheet as well as by considerations linked to the availability, cost and / or ease of Implementation.

Currently designated by electrically conductive fibers any material in the form of a filament whose diameter is generally less than 1mm and preferably between 10⁻⁵ and 0.1 mm and whose length 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 ohm.cm.

Such fibers may consist entirely of a material that is intrinsically electrically conductive: as examples of such materials, mention may be made of metallic fibers, and in particular those free of iron, ferrous alloys or nickel, the fibers carbon or graphite. 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 the free zirconia (ZrO₂), 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.

It should nevertheless be noted that metal fibers are relatively rare and do not always have the mechanical qualities or chemical, such as corrosion resistance, required for industrial application. Furthermore, their high density makes it difficult to control the homogeneity of a suspension and, consequently, the isotropy of the final material.

Furthermore, the non-conductive fibers, rendered conductive, can be altered by heat treatments and corrosion and therefore prove to have the same defects as the metallic fibers which have just been mentioned.

Among the free conductors, the Applicant recommends the use of free carbon or graphite and more particularly to those having a monodispersed length in the sense indicated at the head of this specification.

Subject to respecting the maximum resistivity values indicated above, the free conductors and, in particular carbon or graphite fibers, can be combined with fibers that do not conduct electricity. These fibers are generally in the form of filaments whose geometric characteristics are similar to those given for conductive fibers but whose resistivity will, by convention, be greater than 0.4 ohm.cm.

The use of non-conductive fibers can satisfy various mechanical and economic constraints fixed for the consolidated sheet and / or facilitate the implementation of their manufacturing process.

By way of illustration of non-conductive fibers within the meaning of the invention, mention will be made in particular of mineral fibers such as asbestos fibers, glass fibers, quartz fibers, zirconia fibers, or organic fibers such as fibers polypropylene or polyethylene, optionally halogenated and in particular fluorinated, polyhalovinylidene fibers and in particular polyvinylidene fluoride or also fibers of fluoropolymers which will be discussed below in connection with the binder of the plies according to the invention.

The Applicant recommends the use of asbestos fibers in particular in combination with carbon or graphite fibers.

In a combination (conductive fibers - non-conductive fibers) the proportion of non-conductive fibers should not exceed 50% by weight and, preferably 30% by weight to ensure in particular a satisfactory consolidation of the entire material.

The binder of the materials in accordance with the present invention consists of a binder chosen from fluorinated polymers. The term “fluoropolymer” means a homopolymer or a copolymer derived at least in part from olefinic monomers which are totally substituted with fluorine atoms or totally substituted with a combination of fluorine atoms and at least one of chlorine atoms , bromine or iodine per monomer.

Examples of 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.

It is naturally possible to use in the invention several fluorinated homo- or copolymers as defined above. It goes without saying that it would not go beyond the scope of the invention to combine with these fluorinated polymers a small amount, for example up to 10 or 15% by weight of polymers whose molecule does not contain fluorine atoms , such as polypropylene.

The fluoropolymer used here as a binder of a set of fibers and of electrocatalytic agent may be present in the material in question in variable quantities within wide limits, taking into account the content of fibers and of electrocatalytic agent, or even the nature of the various constituents of said material.

However, to ensure good consolidation of the assembly, the binder will preferably represent from 20 to 50% by weight in the sub-assembly (Fibers + binder).

The electroactivated material obtained according to the invention also comprises an active electrocatalytic agent uniformly distributed in its mass, said agent being chosen from the group consisting of Raney metals and Raney alloys from which the major part of ( ) easily removable metal (s), and mixtures thereof.

By Raney metal (or of the Raney type) essentially means particular catalytic forms of large surface area of the following metals: nickel, cobalt, iron and copper, optionally doped or stabilized with at least one metal chosen from the group consisting of: chromium, cobalt, titanium, molybdenum, tungsten, vanadium and manganese.

However, without wanting to be limited by its explanations, the Applicant has noted, in the context of its work that this agent, designated above by the term metal of Raney, is likely to be transformed both chemically and physical as a result of the treatments undergone during the preparation of the material and / or during its use.

These particular large-surface catalytic forms are generally obtained, in a manner known per se, from an alloy containing one or more of these catalytically active metals and one or more easily removable metals such as aluminum, silicon, magnesium and zinc; said catalytically active metal being present in the "dissolved" state in the easily removable metal. The starting alloy (or precursor) may also contain minor quantities generally not exceeding 5% by weight of the active metal (s), of one or more stabilizing or doping metals chosen from chromium , cobalt, titanium, molybdenum, tungsten, vanadium and manganese. During the alkaline leaching of such a precursor, most of the easily removable metal (s) is removed. It should be specified here that by the expression "Raney alloys, from which most of the easily removable metal (s) have been eliminated", is meant, within the framework of the present invention, alloys "precursors" which have just been mentioned, but which have been treated with a view to removing most of the easily removable metal (s). These alloys can nevertheless contain, after treatment, up to 20% by weight of these easily removable metals.

• Chemical Technology Review n° 94, "Hydrogenation catalysts"R.J. PETERSON/NOYES DATA Corp. 1977, "Preparation of Nickel Hydrogenation catalyst", pages 3-10.
• R.L. AUGUSTINE "Catalytic Hydrogenation", Marcel Dekker Inc. NY 1965, pages 26-32, et annexes pages 147-149.

The references below are cited to represent general knowledge in the field and in particular with regard to the various preparations:

• Chemical Technology Review No. 94, "Hydrogenation catalysts" RJ PETERSON / NOYES DATA Corp. 1977, "Preparation of Nickel Hydrogenation catalyst", pages 3-10.
• RL AUGUSTINE "Catalytic Hydrogenation", Marcel Dekker Inc. NY 1965, pages 26-32, and appendices pages 147-149.

A first class of electroactivated materials according to the invention, which are preferred, comprise Raney nickel.

A second class of electroactivated materials according to the invention, which are preferred, comprise an alloy of nickel and aluminum optionally doped with titanium. In the precursor alloys, nickel represents from 30 to 60% by weight, the dopant from 0 to 5% by weight, the complement being aluminum, the identified phases are mainly Ni₂Al₃ and NiAl₃; the presence of the NiAl phase must be minimized because it is difficult to attack by alkaline solutions and leads to unsatisfactory electroactivation of the material.

These nickel-containing materials have, on a more or less large scale, depending on their particular constitution, the additional advantage of considerably reducing the chlorate content of the soda produced by electrolysis of a sodium chloride solution when they constitute a precathode layer. of the cathode element of the electrolysis cell.

As already indicated at the beginning of this specification, the electrocatalytic agent advantageously represents from 30 to 70% by weight of the whole (Fibers + binder + electrocatalytic agent) and, preferably at least 35% by weight.

An essential characteristic of said material resides in the homogeneous distribution in its mass of (or) electrocatalytic agent (s); this homogeneous distribution largely contributes to imparting good electrical and electrocatalytic properties to said material.

• le recours à des agents électrocatalytiques ou à leurs précurseurs, se présentant sous forme de poudres de granulométrie appropriée,
• dispersion préalable des divers constituants du matériau en milieu gazeux en lit fluidisé, suivie du dépôt sur une surface,
• dispersion de l'ensemble des constituants en milieu liquide en présence d'agents de contrôle de la viscosité et/ou de la densité du milieu, pour obtenir une dispersion régulière et stable dans le temps et un dépôt homogène par diverses techniques telle la filtration.

This homogeneous distribution can be ensured by various techniques, including:

• the use of electrocatalytic agents or their precursors, in the form of granulometry powders appropriate,
• prior dispersion of the various constituents of the material in a gaseous medium in a fluidized bed, followed by deposition on a surface,
• dispersion of all the constituents in a liquid medium in the presence of agents for controlling the viscosity and / or the density of the medium, in order to obtain a regular and stable dispersion over time and a uniform deposit by various techniques such as filtration.

The materials obtained according to the present invention have been defined by their essential constituents, that is to say the fibers, the binder and the electrocatalytic agent. It goes without saying that these materials can at one or the other moment of their development or, to more particularly satisfy additional requirements linked in particular to their final destination, contain various other additives, present simultaneously or, which can succeed one another in the various stages of development of said materials.

Thus the materials according to the present invention can also contain hydrophilic agents.

The use of such agents is 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 examples of such agents, mention may be made of surfactants or surfactants, such as sodium dioctylsulfosuccinate, etc. or inorganic compounds such as asbestos in powder or short fibers, zirconia, cerium dioxide, potassium titanate, hydrated oxides and especially alumina.

The amount of hydrophilic agent which may be present in the sheets 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 layers) and the nature of the hydrophilic agent. On 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 materials can also contain pore-forming agents, the role of which is to regulate their porosity, porosity which in the hypothesis 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 material, 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. By way of illustration of the pore-forming agents, mention will be made of the mineral salts which can then be removed by leaching and the salts which can be removed by chemical or thermal decomposition to which preference is given.

These various products can in particular be chosen from alkaline or alkaline-earth salts, such as the sulphate halides, sulfinates, bisulphites, phosphates, carbonates, bicarbonates. Mention may also be made of amphoteric alumina, and especially silica, which can be eliminated in an alkaline medium.

It goes without saying that the quantity and the particle size of the blowing agents - when such agents are used - is closely linked to the application for which the materials are intended. Simply as an order of magnitude, it will be specified that the particle size of the blowing agents most often varies between 1 and 50 μm, and that the quantity is chosen as a function of the desired porosity, this porosity possibly reaching up to 90%, or more (according to ASTM D 276-72)

Another object of the present invention is to obtain a composite material formed by the association of at least one electroactivated material previously defined and of an elementary cathode constituted by a metal surface. By elementary cathode is meant the metallic structure generally 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 can consist of one or an assembly of flat surfaces or, in the case of electrolysis cells of the "thermowell" type, be in the form of a cylinder whose directrix is a more or less complex surface, generally substantially rectangular with rounded corners.

The association of such a material and of an elementary cathode can be carried out by various techniques which will appear on reading the following.

The composite material resulting from said association in fact constitutes the cathode itself of an electrolysis cell, this application to the production of cathode element of electrolysis cell constituting the privileged but not exclusive field of electroactivated materials according to the invention. In the hypothesis of such an application, it is possible, according to a practice now common, to use in the cell 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 in accordance with the invention.

Notwithstanding the voltage gain already observable by the present of conductive fibers, an additional voltage gain is obtained by the presence within the material of particular electrocatalytic agents and distributed homogeneously in the mass of said material.

The composite material, resulting from the association of an electroactivated material and an elementary cathode, which has just been described can also be associated with a diaphragm.

This diaphragm, which can 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 electroactivated material or on the composite electroactivated material / elementary cathode. This direct manufacture is particularly easy when the diaphragm is produced by filtration of a suspension. These techniques for manufacturing porous and microporous membranes or diaphragms are described for example in French patents n ° 2. 229.739, 2.280.435 or 2.280.609 and French patent applications n ° 81.9688 and 85.14327 the content of these patents and patent application being incorporated here by reference.

The composite materials, constituted by an assembly comprising, from one face to the other, the elementary cathode, the electroactivated material bound by the fluoropolymer and the porous or microporous membrane or diaphragm constitute coherent assemblies, benefiting from all the own advantages to the electro-activated material and to the electro-activated material / elementary cathode composite, to which is added the considerable advantage represented by the elimination of the traditional diaphragm / cathode interface and of its harmful effects, namely a parasitic ohmic drop in the gas emulsion- liquid close to the cathode substrate.

As indicated above, the electroactivated materials according to the present invention can be prepared according to various known techniques, (implementation of a fluidized bed, followed by deposition on a surface and consolidation; preparation of a sheet by way stationery followed by its consolidation ...) some of them must nevertheless be adapted and this without great difficulty for a man of the art.

However, the Applicant recommends an embodiment by the wet method, a process which also constitutes an object of the present invention. This type of process is more particularly suitable for the preparation of a material to be consolidated on a cathode of complex geometry used in industry.

• (a) préparation en milieu aqueux d'une dispersion comprenant des fibres dont une partie au moins est conductrice de l'électricité, un liant choisi parmi les polymères fluorés, choisis parmi un homopolymère ou un copolymère dérivé(s) au moins en partie de monomères oléfiniques totalement substitués avec des atomes de fluor et l'un au moins des atomes de chlore, de brome ou d'iode par monomère, au moins un agent électrocatalytique, choisi dans le groupe des métaux de Raney,
• (b) dépôt d'une nappe par filtration sous vide programmé de ladite suspension à travers un matériau de porosité élevée,
• (c) élimination du milieu liquide et séchage de la nappe ainsi formée,
• (d) frittage de ladite nappe,
• (e) lessivage de la nappe au moyen d'une solution qui n'attaque pas la partie électrocatalytique dudit précurseur.

Thus, the method according to the invention for manufacturing an electro-activated material comprises the following steps:

• (a) preparation in an aqueous medium of a dispersion comprising fibers of which at least part is electrically conductive, a binder chosen from fluorinated polymers, chosen from a homopolymer or a copolymer derived from at least part of olefinic monomers fully substituted with fluorine atoms and at least one of chlorine, bromine or iodine atoms per monomer, at least one electrocatalytic agent, chosen from the group of Raney metals,
• (b) deposition of a sheet by programmed vacuum filtration of said suspension through a material of high porosity,
• (c) elimination of the liquid medium and drying of the sheet thus formed,
• (d) sintering of said sheet,
• (E) leaching of the sheet by means of a solution which does not attack the electrocatalytic part of said precursor.

According to a first variant, the electrocatalytic agent, chosen from the group of Raney metals, is used in the form of a precursor of said agent, such as Raney alloys, comprising one or more easily removable metals. According to this variant, the suspension prepared in step (a) further comprises at least silica as a blowing agent.

According to a second variant, the electrocatalytic agent is chosen from the group of Raney metals.

Advantageously, a small quantity of a thickening agent is incorporated into the aqueous medium, chosen for example from natural or synthetic polysaccharides.

Of course, the dispersion will contain all the essential constituents of the sheet, the electrocatalytic agent possibly being present in the dispersion in the form of a precursor alloy in the sense indicated above and, if appropriate, various additives such as non-conductive fibers. , hydrophilic agents, pore-forming agents and dispersing agents or surface-active agents, in particular anionic sulfonic surfactants, commonly used in practice.

The electrocatalytic agent or its precursor will be introduced in the form of a powder with a particle size generally less than 500 μm. Commercial products are generally found in the form of such a powder in a liquid, generally aqueous, medium. These products can be added as is to the dispersion used to form said sheet.

In the event that products with a much coarser particle size are used, it will be necessary to grind them beforehand.

The fluoropolymer is generally in the form of dry powder or of fibers or of aqueous dispersion (latex) the dry extract of which represents from 30 to 70%.

As is well known to specialists, the suspension in question is generally highly diluted, the dry matter content (fibers, polymer, electrocatalytic agent and additives) represents of the order of 1 to 5% of the weight of the whole for facilitate handling on an industrial scale.

The sheet is then formed, by filtration under programmed vacuum, of the suspension through a material of high porosity such as metallic grids for example, of iron, or fabrics, for example asbestos, of which the mesh vacuum (or the perforations ) can be between 20 µm and 5 mm. The vacuum program can be continuous and / or stepwise, from atmospheric pressure to final depression (1.5.10⁻³ to 4.10⁻⁴ Pa).

The tablecloth thus formed, can be dried in itself known, and if necessary consolidated by heating per se known at a temperature above the melting or softening point of the fluoropolymer.

In the event that only the production of the sheet thus formed is targeted, this consolidation must be carried out and, in the event that a precursor alloy in the sense given in this specification, has been used in the preparation of said sheet, consolidation will be followed by the elimination of the metal (or metals) which can be easily eliminated by leaching out of the sheet by means of a solution which does not attack the electroactive part of the alloy. Thus, for example, the elimination of most of the aluminum contained in a nickel-based precursor alloy can advantageously be carried out by treatment at a temperature between 60 and 100 ° C. for approximately 30 min to 6 h at using an aqueous sodium hydroxide solution whose concentration will be between 100 and 180 g / l.

Insofar as the association of the sheet formed by filtration as indicated above and of a diaphragm is targeted, the Applicant recommends carrying out said association by filtration on the possibly consolidated sheet of a suspension of the constituents necessary for the manufacture diaphragm in a suitable liquid medium, followed by consolidation of the diaphragm or the assembly.

• (a) préparation en milieu aqueux d'une dispersion comprenant des fibres dont une partie au moins est conductrice de l'électricité, un liant choisi parmi les polymères fluorés, choisis parmi un homopolymère ou un copolymère dérivé(s) au moins en partie de monomères oléfiniques totalement substitués avec des atomes de fluor et l'un au moins des atomes de chlore, de brome ou d'iode par monomère (dans la suite on n'utilisera la dénomination : polymères fluorés), au moins un agent électrocatalytique, choisi dans le groupe des métaux de Raney, sous la forme d'un précurseur dudit agent, comme les alliages de Raney, comprenant un ou plusieurs métaux facilement éliminables (par la suite désigné par les termes : précurseur), et au moins la silice en tant qu'agent porogène,
• (b) dépôt d'une nappe par filtration sous vide programmé de ladite suspension à travers une cathode élémentaire constituée d'une surface métallique présentant un vide de maille ou des perforations compris entre 20 µm et 5 mm,
• (c) élimination du milieu liquide et séchage de la nappe ainsi formée,
• (d) frittage de ladite nappe, à une température supérieure ou égale au point de fusion ou de ramollissement du polymère fluoré,
• (e) lessivage de la nappe au moyen d'une solution qui n'attaque pas la partie électrocatalytique dudit précurseur,
• (f) filtration, sur la nappe ainsi obtenue, d'une dispersion aqueuse comprenant au moins des fibres, un liant,
• (g) élimination du milieu liquide et séchage du diaphragme ainsi formé,
• (h) frittage dudit diaphragme, à une température supérieure ou égale au point de fusion ou de ramollissement du polymère fluoré.

Thus, according to a first embodiment, the following steps are carried out:

• (a) preparation in an aqueous medium of a dispersion comprising fibers of which at least part is electrically conductive, a binder chosen from fluorinated polymers, chosen from a homopolymer or a copolymer derived from at least part of olefinic monomers totally substituted with fluorine atoms and at least one of chlorine, bromine or iodine atoms per monomer (in the following we will not use the name: fluorinated polymers), at least one electrocatalytic agent, chosen in the group of Raney metals, in the form of a precursor of said agent, such as Raney alloys, comprising one or more easily removable metals (hereinafter called the precursor), and at least silica as that blowing agent,
• (b) deposition of a sheet by programmed vacuum filtration of said suspension through an elementary cathode constituted by a metal surface having a mesh vacuum or perforations of between 20 μm and 5 mm,
• (c) elimination of the liquid medium and drying of the sheet thus formed,
• (d) sintering of said sheet, at a temperature greater than or equal to the melting or softening point of the fluoropolymer,
• (e) leaching of the sheet by means of a solution which does not attack the electrocatalytic part of said precursor,
• (f) filtration, on the sheet thus obtained, of an aqueous dispersion comprising at least fibers, a binder,
• (g) elimination of the liquid medium and drying of the diaphragm thus formed,
• (h) sintering said diaphragm, at a temperature greater than or equal to the melting or softening point of the fluoropolymer.

• (a) préparation en milieu aqueux d'une dispersion comprenant au moins des fibres dont une partie au moins est conductrice de l'électricité, un liant choisi parmi les polymères fluorés, au moins un agent électrocatalytique, choisi dans le groupe des métaux de Raney, sous la forme d'un précurseur dudit agent, et au moins la silice en tant qu'agent porogène,
• (b) dépôt d'une nappe par filtration sous vide programmé de ladite suspension à travers une cathode élémentaire telle que définie ci avant,
• (c) élimination du milieu liquide et séchage de la nappe ainsi formée,
• (d) éventuellement, frittage de ladite nappe, à une température supérieure ou égale au point de fusion ou de ramollissement du polymère fluoré,
• (e) filtration, sur la nappe ainsi obtenue, d'une dispersion aqueuse comprenant au moins des fibres, un liant,
• (f) élimination du milieu liquide et séchage du diaphragme ainsi formé,
• (g) frittage dudit diaphragme, à une température supérieure ou égale au point de fusion ou de ramollissement du polymère fluoré,
• (h) lessivage au moyen d'une solution qui n'attaque pas la partie électrocatalytique dudit précurseur, réalisé en maintenant la face où la cathode élémentaire est apparente, en dépression par rapport à la face du diaphragme.

According to a second embodiment of the invention, the following steps are carried out:

• (a) preparation in an aqueous medium of a dispersion comprising at least fibers, at least part of which is electrically conductive, a binder chosen from fluorinated polymers, at least one electrocatalytic agent, chosen from the group of Raney metals , in the form of a precursor of said agent, and at least silica as a pore-forming agent,
• (b) deposition of a sheet by programmed vacuum filtration of said suspension through an elementary cathode as defined above,
• (c) elimination of the liquid medium and drying of the sheet thus formed,
• (d) optionally, sintering of said sheet, at a temperature greater than or equal to the melting or softening point of the fluoropolymer,
• (e) filtration, on the sheet thus obtained, of an aqueous dispersion comprising at least fibers, a binder,
• (f) elimination of the liquid medium and drying of the diaphragm thus formed,
• (g) sintering said diaphragm, at a temperature greater than or equal to the melting or softening point of the fluoropolymer,
• (h) leaching by means of a solution which does not attack the electrocatalytic part of said precursor, produced by maintaining the face where the elementary cathode is visible, in depression relative to the face of the diaphragm.

• (a) préparation en milieu aqueux d'une dispersion comprenant au moins des fibres dont une partie au moins est conductrice de l'électricité, un liant choisi parmi les polymères fluorés, au moins un agent électrocatalytique choisi dans le groupe des métaux de Raney, sous la forme d'un précurseur dudit agent ou du métal de Raney,
• (b) dépôt d'une nappe par filtration sous vide programmé de ladite suspension à travers une cathode élémentaire telle que définie précédemment,
• (c) élimination du milieu liquide et séchage de la nappe ainsi formée,
• (d) éventuellement, frittage de ladite nappe, à une température supérieure ou égale au point de fusion ou de ramollissement du polymère fluoré, et, dans le cas où l'agent électrocatalytique est utilisé sous la forme d'un précurseur, lessivage au moyen d'une solution qui n'attaque pas la partie électrocatalytique dudit précurseur,
• (e) filtration, sur la nappe ainsi obtenue, d'une dispersion aqueuse comprenant au moins des fibres, un liant,
• (f) élimination du milieu liquide et séchage du diaphragme ainsi formé,
• (g) frittage dudit diaphragme, à une température supérieure ou égale au point de fusion ou de ramollissement du polymère fluoré.

A third embodiment of the invention consists in carrying out the following steps:

• (a) preparation in an aqueous medium of a dispersion comprising at least fibers of which at least part is electrically conductive, a binder chosen from fluorinated polymers, at least one electrocatalytic agent chosen from the group of Raney metals, in the form of a precursor of said agent or of Raney metal,
• (b) deposition of a sheet by programmed vacuum filtration of said suspension through an elementary cathode as defined above,
• (c) elimination of the liquid medium and drying of the sheet thus formed,
• (d) optionally, sintering of said sheet, at a temperature greater than or equal to the melting or softening point of the fluoropolymer, and, in the case where the electrocatalytic agent is used in the form of a precursor, leaching by means of a solution which does not attack the electrocatalytic part of said precursor,
• (e) filtration, on the sheet thus obtained, of an aqueous dispersion comprising at least fibers, a binder,
• (f) elimination of the liquid medium and drying of the diaphragm thus formed,
• (g) sintering said diaphragm, at a temperature greater than or equal to the melting or softening point of the fluoropolymer.

When the binder of the diaphragm is of the same nature as the binder of the sheet, the intermediate consolidation of the sheet can become superfluous, the consolidation can then be carried out on the whole.

This consolidation can then be followed by an appropriate treatment to eliminate the porogen contained in the deposited diaphragm: when the sheet contains a Raney metal such as Raney nickel and when the deposited diaphragm contains silica, consolidation is carried out on the The assembly and the treatment with an aqueous sodium hydroxide solution described above is carried out on the consolidated assembly with a view to eliminating the silica contained in the diaphragm. When the sheet contains a precursor alloy in the sense given above, such as a nickel and aluminum alloy and, when the deposited diaphragm contains silica, consolidation can be carried out separately for the sheet and if necessary, followed by solution treatment aqueous sodium hydroxide to remove aluminum; the diaphragm will then be deposited then consolidated and treated in order to eliminate the silica; consolidation can advantageously be carried out on the whole then, followed by a single treatment with the aqueous sodium hydroxide solution to remove both the aluminum from the sheet and the silica from the diaphragm.

When the binder of the diaphragm is of a distinct nature from that of the tablecloth, it is necessary to consolidate each member of the association separately and to proceed, if necessary, to the elimination of the metal (or metals) which can easily be eliminated. , after consolidation of the sheet whether or not the diaphragm is previously deposited.

It should be noted that a sheet obtained by filtration and consolidated as indicated above and which contains a precursor alloy such as a nickel and aluminum alloy can advantageously be associated with a diaphragm by filtration of a suspension of the constituents of the diaphragm. the binder of which is dispersible in the liquid medium capable of eliminating, for example, aluminum, without attacking the nickel in the present case, the operation of depositing the diaphragm allowing it alone to eliminate the major part of the aluminum contained in the consolidated sheet.

Such is, for example, the possibility offered by the deposition of a diaphragm whose essential constituents (asbestos fibers, polychlorotetrafluoroethylene powder) are dispersible in an aqueous solution of sodium hydroxide containing, if appropriate, sodium chloride.

• (a) préparation en milieu aqueux d'une dispersion comprenant au moins des fibres dont une partie au moins est conductrice de l'électricité, un liant choisi parmi les polymères fluorés, au moins un agent électrocatalytique, choisi dans le groupe des métaux de Raney, sous la forme d'un précurseur dudit agent, et au moins la silice en tant qu'agent porogène,
• (b) dépôt d'une nappe par filtration sous vide programmé de ladite suspension à travers une cathode élémentaire telle que définie précédemment,
• (c) élimination du milieu liquide et séchage de la nappe ainsi formée,
• (d) éventuellement frittage de ladite nappe, à une température supérieure ou égale au point de fusion ou de ramollissement du polymère fluoré,
• (e) filtration, sur la nappe ainsi obtenue, d'une dispersion dans une solution aqueuse d'hydroxyde de sodium, comprenant au moins des fibres, un liant, choisi parmi les polymères fluorés dispersibles dans une telle solution,
• (f) élimination du milieu liquide et séchage du diaphragme ainsi formé,
• (g) frittage dudit diaphragme, à une température supérieure ou égale au point de fusion ou de ramollissement du polymère fluoré.

Thus, according to a first variant of this particular embodiment, the following steps are carried out:

• (a) preparation in an aqueous medium of a dispersion comprising at least fibers, at least part of which is electrically conductive, a binder chosen from fluorinated polymers, at least one electrocatalytic agent, chosen from the group of Raney metals , in the form of a precursor of said agent, and at least silica as a pore-forming agent,
• (b) deposition of a sheet by programmed vacuum filtration of said suspension through an elementary cathode as defined above,
• (c) elimination of the liquid medium and drying of the sheet thus formed,
• (d) optionally sintering said sheet, at a temperature greater than or equal to the melting or softening point of the fluoropolymer,
• (e) filtration, over the sheet thus obtained, of a dispersion in an aqueous sodium hydroxide solution, comprising at least fibers, a binder, chosen from fluoropolymers dispersible in such a solution,
• (f) elimination of the liquid medium and drying of the diaphragm thus formed,
• (g) sintering said diaphragm, at a temperature greater than or equal to the melting or softening point of the fluoropolymer.

• (a) préparation en milieu aqueux d'une dispersion comprenant au moins des fibres dont une partie au moins est conductrice de l'électricité, un liant choisi parmi les polymères fluorés, au moins un agent électrocatalytique choisi dans le groupe des métaux de Raney,
• (b) dépôt d'une nappe par filtration sous vide programmé de ladite suspension à travers une cathode élémentaire telle que définie précédemment
• (c) élimination du milieu liquide et séchage de la nappe ainsi formée,
• (d) éventuellement, frittage de ladite nappe, à une température supérieure ou égale au point de fusion ou de ramollissement du polymère fluoré,
• (e) filtration, sur la nappe ainsi obtenue, d'une dispersion dans une solution aqueuse d'hydroxyde de sodium, comprenant au moins des fibres, un liant, choisi parmi les polymères fluorés dispersibles dans une telle solution,
• (f) élimination du milieu liquide et séchage du diaphragme ainsi formé,
• (g) frittage dudit diaphragme, à une température supérieure ou égale au point de fusion ou de ramollissement du polymère fluoré.

A second variant of this particular embodiment of the invention comprises the following steps:

• (a) preparation in an aqueous medium of a dispersion comprising at least fibers of which at least part is electrically conductive, a binder chosen from fluorinated polymers, at least one electrocatalytic agent chosen from the group of Raney metals,
• (b) deposition of a sheet by programmed vacuum filtration of said suspension through an elementary cathode as defined above
• (c) elimination of the liquid medium and drying of the sheet thus formed,
• (d) optionally, sintering of said sheet, at a temperature greater than or equal to the melting or softening point of the fluoropolymer,
• (e) filtration, over the sheet thus obtained, of a dispersion in an aqueous sodium hydroxide solution, comprising at least fibers, a binder, chosen from fluoropolymers dispersible in such a solution,
• (f) elimination of the liquid medium and drying of the diaphragm thus formed,
• (g) sintering said diaphragm, at a temperature greater than or equal to the melting or softening point of the fluoropolymer.

The following examples illustrate the present invention.

EXAMPLES Preparation A : Preparation of materials, possibly electro-activated, used as precathode layers.

• 932 g d'eau adoucie,
• 4 g de fibres d'amiante chrysotile dont la longueur moyenne est de 1 à 5 mm et dont le diamètre est de 20 nm (200 Angström) environ,
• 0,13g de dioctylsulfosuccinate de sodium.

A suspension is prepared from:

• 932 g of softened water,
• 4 g of chrysotile asbestos fibers with an average length of 1 to 5 mm and a diameter of around 20 nm (200 Angstroms),
• 0.13 g of sodium dioctylsulfosuccinate.

• 4,7g de polytétrafluoroéthylène sous forme de latex à 60 % en poids d'extrait sec,
• 13,4g de silice précipitée sous forme de particules de granulomètrie moyenne de 3 µm et dont la surface B.E.T. est de 250 m².g⁻¹,
• 9,4g de fibres de graphite dont le diamètre est d'environ 10 µm et dont la longueur moyenne est de 1,5 mm.

After rotary stirring for 30 min, the following is added:

• 4.7 g of polytetrafluoroethylene in the form of latex at 60% by weight of dry extract,
• 13.4 g of silica precipitated in the form of particles with an average particle size of 3 μm and whose BET surface is 250 m².g m²¹,
• 9.4g of graphite fibers whose diameter is approximately 10 µm and whose average length is 1.5 mm.

After rotary agitation of 30 mm, the electroactivating agent, or if necessary one of its precursors, the nature and quantity of which will be specified in the examples and the attached table, is added.

The whole is then agitated and then, by filtration, 110 g of the mixture thus obtained are deposited on a cathode element of 1 dm² consisting of a braided and laminated iron grid whose opening is 2 mm and the diameter of the wires is 2 mm.

• 1000 Pa. min⁻¹ pendant 10 mn,
• 5000 Pa. min⁻¹ pour atteindre une dépression finale de 25 000 Pa.

The filtration is carried out under vacuum programmed as follows:

• 1000 Pa. Min⁻¹ for 10 min,
• 5000 Pa. Min⁻¹ to reach a final depression of 25,000 Pa.

The whole is then dried for 12 h at 100 ° C. and then, if necessary, consolidated by melting the fluoropolymer at 350 ° C. for 7 min. (This separate prior consolidation is not necessary in the event that the precathode element is associated with a diaphragm whose binder is the same as that of the sheet.)

Preparation B : Preparation of an aqueous dispersion of fibers for the production of a microporous diaphragm and production of a composite material comprising a precathode sheet and such a diaphragm

• 953g d'eau adoucie,
• 14,5g de fibres d'amiante chrysotile de diamètre 20 nm (200 Å) et de moins d'1 mm de longueur,
• 14,5g de fibres d'amiante chrysotile de diamètre 20 nm (200 Å) et de longueur moyenne comprise entre 1 et 5 mm .
• 0,29g de dioctylsulfosuccinate de sodium.

A suspension is prepared from:

• 953g of softened water,
• 14.5 g of chrysotile asbestos fibers with a diameter of 20 nm (200 Å) and less than 1 mm in length,
• 14.5 g of chrysotile asbestos fibers with a diameter of 20 nm (200 Å) and an average length of between 1 and 5 mm.
• 0.29 g of sodium dioctylsulfosuccinate.

• 5,8g de polytétrafluoroéthylène sous forme d'un latex à 60 % en poids d'extrait sec,
• 7,25g de silice précipité sous forme de particules de granulométrie moyenne de 3 µm et dont la surface B.E.T. est de 250 m². g⁻¹.

After rotary stirring for 30 min, we add:

• 5.8 g of polytetrafluoroethylene in the form of a latex at 60% by weight of dry extract,
• 7.25 g of silica precipitated in the form of particles with an average particle size of 3 µm and whose BET surface is 250 m². g⁻¹.

The whole is then agitated for 30 min, then after a rest of 48 h, the suspension is again agitated and 350 g of this mixture are filtered on 1 dm² of dried but unconsolidated pre-cathodic sheet or on 1 dm² of canvas. asbestos. Filtration is carried out under vacuum programmed from 5000 Pa. Mn⁻¹ to reach 80,000 Pa.

The composite thus obtained is dried for 12 h at 100 ° C and consolidated by melting the fluoropolymer at 350 ° C for 7 min.

Preparation C : Preparation of an aqueous dispersion of asbestos fibers for the production of a diaphragm and production of a composite material formed from a precathode layer and a diaphragm

• 978g d'une solution aqueuse renfermant 140 g.l⁻¹ de soude et 160 g.l⁻¹ de chlorure de sodium,
• 20g de fibres d'amiante chrysotile de diamètre 200 Å et de 1 à 5 mm de longueur moyenne,
• O,11g d'isooctylphénoxypolyéthoxyéthanol,
• 1,6g de polychlorotrifluoroéthylène sous forme de poudre de granulométrie moyenne de 50 µm (PCTFE).

A suspension is prepared from:

• 978g of an aqueous solution containing 140 gl⁻¹ of soda and 160 gl⁻¹ of sodium chloride,
• 20g of chrysotile asbestos fibers 200 Å in diameter and 1 to 5 mm in average length,
• 0.11 g of isooctylphenoxypolyethoxyethanol,
• 1.6 g of polychlorotrifluoroethylene in the form of a powder with an average particle size of 50 μm (PCTFE).

The mixture is stirred by injecting air for 30 min. 500g of this suspension are filtered through 1 dm² of pre-consolidated tablecloth.

The composite obtained is dried at 100 ° C for 12 h and the consolidation of the diaphragm is carried out by melting the polymer (PCTFE) at 260 ° C for 30 min.

Example 1 : Production of a composite material comprising a precathode sheet electroactivated by Raney nickel and a microporous diaphragm.

According to procedure A, described above, a precathode layer is prepared containing 3.5 g of nickel and aluminum alloy (Raney alloy 20 sold by the company PROCATALYSE, containing 50 parts by weight of nickel for 50 parts by weight of aluminum), said alloy having been added to the suspension in the form of a powder with an average particle size of 20 μm.

The sheet thus prepared and consolidated is then treated for 4 h at 80 ° C. with an aqueous solution containing 140 g.l⁻¹ of sodium hydroxide, operation carried out with the aim of eliminating the aluminum.

This sheet is then rinsed carefully with softened water and covered with a microporous diaphragm prepared separately according to procedure B, by filtration on 1 dm² of asbestos cloth.

Most of the silica is removed therefrom by alkaline attack under the conditions described above for treating the sheet.

Control test a : Production of a composite material not in accordance with the present invention.

Example 1 is reproduced above, omitting the treatment of the consolidated sheet with the aqueous sodium hydroxide solution and covering it with a microporous diaphragm similar to the previous one, except that the elimination of silica by alkaline treatment, is carried out before the deposition of said diaphragm on the precathode element.

Control test b :

A precathode layer without an electroactivator is prepared according to (A) and then covered with an asbestos / PCTFE diaphragm obtained according to (C).

Control test c : (Absence of precathode element)

A braided and rolled steel grid is covered with an asbestos / PCTFE diaphragm by preparing a suspension in which 50% of the chrysotile asbestos fibers of length 1 to 5 mm have been replaced by fibers of length between 5 and 20 mm. (This device is representative of current practices in the chlorine industry).

Example 2 :

Production of a composite material comprising a precathode layer, said layer containing a Raney alloy based on nickel and aluminum, and a diaphragm based on asbestos fibers and PCTFE, eliminating most of the aluminum being performed during deposition of the diaphragm.

According to procedure A, described above, a precathode layer is prepared containing 3.5 g of nickel and aluminum alloy (Raney alloy 20 sold by the company PROCATALYSE, containing 50 parts by weight of nickel for 50 parts by weight of aluminum), said alloy having been added to the suspension in the form of a powder with an average particle size of 20 μm.

The tablecloth thus prepared is consolidated. 500 g of the suspension prepared according to procedure C, above, are then filtered on 1 dm² of this sheet. The composite is then dried and the diaphragm is consolidated as indicated in preparation C.

Example 3 :

Example 2 is reproduced above, by modifying the deposition mode of the diaphragm by the fact that it is operated under a controlled vacuum program of 1000 Pa. Min⁻¹ to reach a final vacuum of 80,000 Pa .

Example 4 :

Production of a composite material comprising a precathode sheet electroactivated by Raney nickel and a diaphragm based on asbestos fibers and PCTFE.

A precathode layer containing 2 g of Raney nickel in the form of a 10 μm powder (Ni 20 marketed by PROCATALYSE, in the form of a powder stored in water) was prepared according to the procedure (A) and consolidated.

It is covered with an asbestos / PTCFE diaphragm like the one prepared in C.

Example 5 :

Production of a composite material comprising a precathode layer, said layer containing a Raney alloy based on nickel and aluminum, and a diaphragm based on asbestos and PTFE free, the sintering and consolidation of the assembly being carried out in one operation, the removal of the aluminum from the sheet and the silica from the diaphragm being carried out in an alkaline etching operation.

The precathode layer containing 3.5 g of the above-mentioned alloy is prepared according to procedure A; after drying, it is covered with a diaphragm as described in B. The assembly is consolidated and then subjected to an alkaline attack with an aqueous solution of sodium hydroxide at 140 g.l⁻¹ at 60 ° C for 4 h. The face, where the steel grid is visible, is kept in depression (between 400 and 20,000 Pa) relative to the face of the diaphragm. The operation is carried out on 1 dm² of composite.

During the operation, the permeability increases regularly.

Examples 6 to 8 :

Production of composite materials comprising a precathode layer electroactivated with Raney nickel and an Asbestos / PTFE diaphragm

For each example, a sheet is prepared containing pyrophoric Raney nickel in the form of a 10 μm powder (Ni 20 from Procatalysis) according to procedure A, then it is covered with a diaphragm such as that described in B. the whole and the silica is eliminated by alkaline attack.

Examples 9 to 11 :

These examples are respectively analogous to Examples 6 to 8 above, except that we use extinct Raney nickel, in the form of a 50 μm powder (NiPS2 from DODUCO marketed by PROCATALYSE).

Examples 12 to 14 :

These examples are analogous respectively to Examples 6 to 8 above, except that Raney nickel doped with titanium was used, this agent being prepared from an alloy of nickel, aluminum and titanium by etching. alkaline, as described in J. of the Electrochemical Society "Electrochemical Science and Technology" Vol 124 No. 1, p.1 - (1977). This alloy contains 5% by weight of titanium and equiponderal amounts of aluminum and nickel. After grinding, the aluminum is removed and then it is used in the manufacture of sheets according to procedure A.

• Anode en titane déployé, laminé, revêtu de TiO₂-RuO₂.
• Elément cathodique en acier doux tressé et laminé ; fils de 2 mm, maille de 2 mm ou ledit élément recouvert de la nappe.
• Distance anode-élément cathodique : 6 mm.
• Surface active de l'électrolyseur : O,5 dm².
• Cellule assemblée selon le type filtre-presse.
• Densité de courant : 25 A dm⁻².
• Température : 85°C.
• Fonctionnement à chlorure anodique constant : 4,8 mole.l⁻¹.
• Titre de la soude électrolytique : 180 g.l⁻¹.

The performance of the various composite materials, the manufacture of which has just been described, was then evaluated in an electrolysis cell which has the following characteristics and the operating conditions of which are indicated below:

• Anode in rolled titanium, laminated, coated with TiO₂-RuO₂.
• Cathode element in braided and rolled mild steel; 2 mm son, 2 mm mesh or said element covered with the web.
• Distance anode-cathode element: 6 mm.
• Active surface area of the chlorinator: 0.5 dm².
• Cell assembled according to the filter press type.
• Current density: 25 A dm⁻².
• Temperature: 85 ° C.
• Constant anodic chloride operation: 4.8 mole.l⁻¹.
• Title of electrolytic soda: 180 gl⁻¹.

• ΔU_i->o : tension d'extrapolation à intensité nulle (par tracé de la courbe $\text{ΔU = f(I)}$
  
  ).
• ΔU₂₅ : tension aux bornes de l'électrolyseur à 25 A dm⁻².
• RF : rendement Faraday.
• CE : consommation énergétique du système en kilowattheure par tonne de chlore produit.
• (ClO $\genfrac{}{}{0ex}{}{\text{-}}{\text{3}}$
  
  )_a : concentration en ClO $\genfrac{}{}{0ex}{}{\text{-}}{\text{3}}$
  
  dans l'anolyte (mole. 1⁻¹).
• (ClO $\genfrac{}{}{0ex}{}{\text{-}}{\text{3}}$
  
  )_c : concentration en ClO $\genfrac{}{}{0ex}{}{\text{-}}{\text{3}}$
  
  dans la soude électrolytique.
• T.R.(%) : taux de réduction des chlorates, anodiques, soit le rapport
  
• M : Masse déposée en g.dm⁻².

The specific conditions and the results obtained are collated in table (I) below in which the following conventions are used:

• ΔU _{i-> o} : extrapolation voltage at zero intensity (by drawing the curve $\text{ΔU = f (I)}$
  
  ).
• ΔU₂₅: voltage across the electrolyser at 25 A dm⁻².
• RF: Faraday yield.
• EC: energy consumption of the system in kilowatt hours per tonne of chlorine produced.
• (ClO $\genfrac{}{}{0ex}{}{\text{-}}{\text{3}}$
  
  ) _a : ClO concentration $\genfrac{}{}{0ex}{}{\text{-}}{\text{3}}$
  
  in the anolyte (mole. 1⁻¹).
• (ClO $\genfrac{}{}{0ex}{}{\text{-}}{\text{3}}$
  
  ) _c : ClO concentration $\genfrac{}{}{0ex}{}{\text{-}}{\text{3}}$
  
  in electrolytic soda.
• TR (%): reduction rate of chlorates, anodic, i.e. the ratio
  
• M: Mass deposited in g.dm⁻².

By nature of the agent used in the preparation of the sheet, is meant the Raney metal or the precursor alloy put in the suspension and by the precise quantity, that put in the suspension during the preparation according to (A) .

By nature of the diaphragm is meant the type of preparation B or C thereof.

The results appearing in the annexed table (I) show that at identical sodium hydroxide concentration and for an equivalent deposited diaphragm weight, the Faraday yields do not present any significant differences.

They also show that the composite material resulting from the association by direct deposition of a diaphragm on an electroactivated precathode sheet according to the invention, offers improved performance in the field of electrolysis and in particular lower energy consumption and a reduction in the chlorate content.

Extrapolation voltages at zero intensity highlight in particular the importance of eliminating aluminum when a precursor alloy is used.

In addition, the performances indicated are maintained after 3000 hours of operation.

Examples 15 and 16, control test d :

The performance of the composite materials, the preparation of which was described in Examples 5 and 7 and in the control test b above, was evaluated in an electrolysis cell similar to that previously described, except that the anode is made up of expanded titanium, laminated and coated with a 0.7 μm thick layer composed of 75% by weight of platinum and 25% by weight of iridium.

The conditions for electrolysis are, moreover, unchanged. The results obtained are collated in Table (II) below.

Claims (12)

1. Process for the manufacture of an electroactivated material including at least one active electrocatalytic agent uniformly distributed in its bulk and exhibiting a resistivity lower than 0.4 Ω cm, including the following stages:

   (a) preparation in an aqueous medium of a dispersion including fibres at least a proportion of which is a conductor of electricity, a binder chosen from fluoropolymers which are chosen from a homopolymer or a copolymer derived at least partially from olefinic monomers totally substituted with fluorine atoms and at least one of the atoms of chlorine, bromine or iodine per monomer, at least one electrocatalytic agent chosen from the group of Raney metals, in the form of a precursor of the said agent, like Raney alloys, including one or a number of easily removable metals, and at least silica as pore-forming agent,

   (b) deposition of a sheet by programmed vacuum filtration of the said suspension through a material of high porosity,

   (c) removal of the liquid medium and drying of the sheet thus formed,

   (d) sintering of the said sheet,

   (e) leaching of the sheet by means of a solution which does not attack the electrocatalytic part of the said precursor.
2. Process for the manufacture of a composite material based on an electroactivated material including at least one active electrocatalytic agent uniformly distributed in its bulk and exhibiting a resistivity lower than 0.4 Ω cm, including the following stages:

   (a) preparation in an aqueous medium of a dispersion including fibres at least a proportion of which is a conductor of electricity, a binder chosen from fluoropolymers which are chosen from a homopolymer or a copolymer derived at least partially from olefinic monomers totally substituted with fluorine atoms and at least one of the atoms of chlorine, bromine or iodine per monomer, at least one electrocatalytic agent chosen from the group of the Raney metals, in the form of a precursor of the said agent, like the Raney alloys, including one or a number of easily removable metals and at least silica as pore-forming agent,

   (b) deposition of a sheet by a programmed vacuum filtration of the said suspension through an elementary cathode consisting of a metal surface which has a mesh gap or perforations of between 20 µm and 5 mm,

   (c) removal of the liquid medium and drying of the sheet thus formed,

   (d) sintering of the said sheet at a temperature higher than or equal to the melting or softening point of the fluoropolymer,

   (e) leaching of the sheet by means of a solution which does not attack the electrocatalytic part of the said precursor,

   (f) filtration, on the sheet thus obtained, of an aqueous dispersion including at least fibres, a binder,

   (g) removal of the liquid medium and drying of the diaphragm thus formed,

   (h) sintering of the said diaphragm at a temperature higher than or equal to the melting or softening point of the fluoropolymer.
3. Process for the manufacture of a composite material based on an electroactivated material including at least one active electrocatalytic agent uniformly distributed in its bulk and exhibiting a resistivity lower than 0.4 Ω cm, including the following stages:

   (a) preparation in an aqueous medium of a dispersion including at least fibres at least a proportion of which is a conductor of electricity, a binder chosen from fluoropolymers which are chosen from a homopolymer or a copolymer derived at least partially from olefinic monomers totally substituted with fluorine atoms and at least one of the atoms of chlorine, bromine or iodine per monomer, at least one electrocatalytic agent chosen from the group of the Raney metals, in the form of a precursor of the said agent, like the Raney alloys, including one or a number of easily removable metals and at least silica as pore-forming agent,

   (b) deposition of a sheet by a programmed vacuum filtration of the said suspension through an elementary cathode consisting of a metal surface which has a mesh gap or perforations of between 20 µm and 5 mm,

   (c) removal of the liquid medium and drying of the sheet thus formed,

   (d) optionally, sintering of the said sheet at a temperature higher than or equal to the melting or softening point of the fluoropolymer,

   (e) filtration, on the sheet thus obtained, of an aqueous dispersion including at least fibres, a binder,

   (f) removal of the liquid medium and drying of the diaphragm thus formed,

   (g) sintering of the said diaphragm at a temperature higher than or equal to the melting or softening point of the fluoropolymer,

   (h) leaching by means of a solution which does not attack the electrocatalytic part of the said precursor, carried out while maintaining the face where the elementary cathode is apparent, at reduced pressure relative to the face of the diaphragm.
4. Process for the manufacture of a composite material based on an electroactivated material including at least one active electrocatalytic agent uniformly distributed in its bulk and exhibiting a resistivity lower than 0.4 Ω cm, including the following stages:

   (a) preparation in an aqueous medium of a dispersion including at least fibres at least a proportion of which is a conductor of electricity, a binder chosen from fluoropolymers which are chosen from a homopolymer or a copolymer derived at least partially from olefinic monomers totally substituted with fluorine atoms and at least one of the atoms of chlorine, bromine or iodine per monomer, at least one electrocatalytic agent chosen from the group of the Raney metals, in the form of a precursor of the said agent, like Raney alloys (including one or a number of easily removable metals) and at least silica as pore-forming agent,

   (b) deposition of a sheet by programmed vacuum filtration of the said suspension through an elementary cathode consisting of a metal surface exhibiting a mesh gap or perforations of between 20 µm and 5 mm,

   (c) removal of the liquid medium and drying of the sheet thus formed,

   (d) optionally sintering of the said sheet at a temperature higher than or equal to the melting or softening point of the fluoropolymer,

   (e) filtration, on the sheet thus obtained, of a dispersion in an aqueous solution of sodium hydroxide, including at least fibres; a binder chosen from the fluoropolymers which are dispersible in such a solution,

   (f) removal of the liquid medium and drying of the diaphragm thus formed,

   (g) sintering of the said diaphragm at a temperature higher than or equal to the melting or softening point of the fluoropolymer.
5. Process according to one of the preceding claims, characterized in that the leaching stages are performed by means of an aqueous solution of sodium hydroxide.
6. Process for the manufacture of an electroactivated material including at least one active electrocatalytic agent uniformly distributed in its bulk and exhibiting a resistivity lower than 0.4 Ω cm, including the following stages:

   (a) preparation in an aqueous medium of a dispersion including fibres at least a proportion of which is a conductor of electricity, a binder chosen from the fluoropolymers which are chosen from a homopolymer or a copolymer derived at least partially from olefinic monomers totally substituted with fluorine atoms and at least one of the atoms of chlorine, bromine or iodine per monomer, at least one electrocatalytic agent chosen from the group of the Raney metals,

   (b) deposition of a sheet by programmed vacuum filtration of the said suspension through a material of high porosity,

   (c) removal of the liquid medium and drying of the sheet thus formed,

   (d) sintering of the said sheet at a temperature higher than or equal to the melting or softening point of the fluoropolymer.
7. Process for the manufacture of a composite material based on an electroactivated material including at least one active electrocatalytic agent uniformly distributed in its bulk and exhibiting a resistivity lower than 0.4 Ω cm, including the following stages:

   (a) preparation in an aqueous medium of a dispersion including at least fibres at least a proportion of which is a conductor of electricity, a binder chosen from the fluoropolymers which are chosen from a homopolymer or a copolymer derived at least partially from olefinic monomers totally substituted with fluorine atoms, and at least one of the atoms of chlorine, bromine or iodine per monomer, at least one electrocatalytic agent chosen from the group of the Raney metals, in the form of a precursor of the said agent, like Raney alloys, including one or a number of easily removable metals, or Raney metal,

   (b) deposition of a sheet by programmed vacuum filtration of the said suspension through an elementary cathode consisting of a metal surface exhibiting a mesh gap or perforations of between 20 µm and 5 mm,

   (c) removal of the liquid medium and drying of the sheet thus formed,

   (d) optionally, sintering of the said sheet at a temperature higher than or equal to the melting or softening point of the fluoropolymer and, in the case where the electrocatalytic agent is employed in the form of a precursor, leaching by means of a solution which does not attack the electrocatalytic part of the said precursor,

   (e) filtration, on the sheet thus obtained, of an aqueous dispersion including at least fibres, a binder,

   (f) removal of the liquid medium and drying of the diaphragm thus formed,

   (g) sintering of the said diaphragm at a temperature higher than or equal to the melting or softening point of the fluoropolymer.
8. Process for the manufacture of a composite material based on an electroactivated material including at least one active electrocatalytic agent uniformly distributed in its bulk and exhibiting a resistivity lower than 0.4 Ω cm, including the following stages:

   (a) preparation in an aqueous medium of a dispersion including at least fibres at least a proportion of which is a conductor of electricity, a binder chosen from the fluoropolymers which are chosen from a homopolymer or a copolymer derived at least partially from olefinic monomers totally substituted with fluorine atoms, and at least one of the atoms of chlorine, bromine or iodine per monomer, at least one electrocatalytic agent chosen from the group of the Raney metals,

   (b) deposition of a sheet by programmed vacuum filtration of the said suspension through an elementary cathode consisting of a metal surface exhibiting a mesh gap or perforations of between 20 µm and 5 mm,

   (c) removal of the liquid medium and drying of the sheet thus formed,

   (d) optionally, sintering of the said sheet at a temperature higher than or equal to the melting or softening point of the fluoropolymer,

   (e) filtration, on the sheet thus obtained, of a dispersion in an aqueous solution of sodium hydroxide, including at least fibres, a binder chosen from fluoropolymers which are dispersible in such a solution,

   (f) removal of the liquid medium and drying of the diaphragm thus formed,

   (g) sintering of the said diaphragm at a temperature higher than or equal to the melting or softening point of the fluoropolymer.
9. Process according to any one of Claims 3, 4, 7 or 8, characterized in that a sintering stage (d) is performed in the case in which the binders of the dispersions of stages (a) and (e) are different.
10. Process according to any one of the preceding claims, characterized in that fibres are employed which are a conductor of electricity and are chosen from carbon or graphite fibres, preferably monodisperse in their length.
11. Process according to any one of Claims 2 to 4 and 7 to 10, characterized in that asbestos fibres are employed essentially in the dispersion of stage (e).
12. Process according to either of Claims 2 and 7, characterized in that a stage of removal of the pore-former is performed, if the dispersion of stage (e) includes it, by alkaline treatment.