Method for recycling catalyst ink residues in a catalyst ink production and / or deposition plant for fuel cells

Abstract

The invention relates to a method for recycling residues of a catalyst ink comprising catalyst particles, an electrolyte polymer, and water. The method comprises providing an effluent containing the catalyst ink residues, filtering the effluent through a filter membrane, leading to the formation of a retentate containing the catalyst particles contained in the effluent, all or part of the electrolyte polymer, and water, and then, preferably, the diafiltration thereof by adding water. Filtration and diafiltration are preferably tangential and dynamic. The ink residues may originate from the cleaning of a catalyst ink production and / or deposition plant, or from the dissolution of ink layers on the surface of a fuel cell membrane electrode assembly. The invention further relates to a composition for recycling and to a method for producing a new ink incorporating the composition for recycling.

Description

[0001] TITLE: Process for recycling catalytic ink residues in a production and / or depot facility for catalytic ink intended for fuel cells

[0002] The present invention relates to a method for recovering catalytic ink residues, such as those generated in a catalytic ink production facility for fuel cells, in an ink deposition facility or from ink layers on the surface of a membrane or any other support, as well as a method for manufacturing a new catalytic ink.

[0003] In the field of fuel cells, electrochemical cells are formed by membrane-electrode assemblies and bipolar plates. A membrane-electrode assembly is sometimes referred to as an MEA, and generally comprises a base membrane, which may be coated on one or both sides with a catalytic layer comprising a catalyst. The membrane-electrode assembly may also comprise a frame that supports this membrane. The catalyst is typically in the form of catalytic particles, in particular in the form of carbon particles supporting platinum and / or cobalt. The MEA may also comprise one or more GDLs (Gas Diffusion Layers), and a layer of catalytic ink may be present on the surface of the GDLs, as is known per se.

[0004] More generally, the catalyst comprises or consists of a noble metal, several noble metals or an alloy of noble metals. This metal, these metals or this alloy of metals is optionally associated with a carbon support to form the catalytic particle. The noble metal is selected from: platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), gold (Au), osmium (Os), rhodium (Rh), osmium (Os), tungsten (W), lead (Pb), iron (Fe), chromium (Cr), cobalt (Co), nickel (Ni), manganese (Mn), vanadium (V), molybdenum (Mo), gallium (Ga), aluminum (Al) or any other metal having catalytic activity.An alloy of two or more of these metals, selected from platinum (Pt)-palladium (Pd) alloys, platinum (Pt)-ruthenium (Ru) alloys, platinum (Pt)-iridium (Ir) alloys, platinum (Pt)-osmium alloys, platinum (Pt)-M alloys (M being Ti, V, Cr, Mo, W, Mn, Fe, Co, Rh, Ni, Cu, Ag, Au, Zn, Ga and / or Sn) or a combination thereof, but not limited to, may also be associated with a carbon support to form the catalytic particle. The carbon support is preferably a particle comprising carbon, for example taken from: carbon black, activated carbon, carbon powder, acetylene black, ketjen black, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon beads, carbon nanowires, carbon nanohorns, carbon aerogels, carbon crerogels or carbon nanorings, or a mixture of two or more of these elements.Advantageously, the catalyst comprises or consists of a platinum-based catalyst supported on a carbon support (Pt / C). The catalyst may also comprise or consist of, for example, a platinum and cobalt alloy supported on a carbon support (PtCo / C).

[0005] The base membrane is often made of a polymer material that is a perfluorosulfonic acid ionomer or perfluorosulfonic acid (PFSA), preferably a copolymer of tetrafluoroethylene and sulfonyl fluoride vinyl ether such as NAFION™ or Aquivion®, while the catalytic layers comprise catalyst as defined above, in particular in the form of catalytic particles. The deposition of these catalytic layers on the base membrane involves the use of an ink containing water and organic solvents and their evaporation to leave a dry layer. More specifically, an ink suitable for forming an electrode on a fuel cell membrane generally comprises a dispersion of electrolytic ionomer or polymer and catalytic particles in a mixture of water and organic solvent, generally containing a volatile alcohol which may have a boiling point between 75 and 130°C, in particular between 75 and 100°C.Typically, the catalytic ink also includes a high boiling alcohol, typically of the polyhydric alcohol type, e.g., ethylene glycol, propylene glycol, triethylene glycol, butylene glycol, 1,4-butanediol, 2,3-butanediol, and glycerin; polyalkylene glycols, diethylene glycol, dipropylene glycol; and monoalkyl ether derivatives such as monomethyl ethers and monoethyl ethers. The ionomer in the ink includes or consists of a perfluorosulfonated acid or perfluorosulfonic acid (PFSA) ionomer, preferably a copolymer of tetrafluoroethylene and sulfonyl fluoride vinyl ether, such as NAFION™ or Aquivion™.

[0006] Processes for recovering platinum from used fuel cells are known, which involves treating the solid residues of the MEA in order to separate the platinum from the other constituents. In particular, in recycling processes from MEA, dissolutions using appropriate solvents on ground MEA lead to the recovery of an effluent containing the catalytic particles and the electrolytic polymer originating from both the catalytic layer and the membrane itself in uncontrollable proportions, requiring the treatments to be carried out until the separation of the catalytic particles from the electrolytic polymer.

[0007] Furthermore, as yet unexploited sources of loss of platinum or other catalytic metal are located in the ink production lines (comprising tanks, pipes, valves and other devices) and the catalytic ink application installations in which residues form over time, as well as in the ink layers in the MEAs. However, it is necessary to be able to propose an economically attractive recycling process, while the quantities of residues and therefore of recoverable compounds may appear insufficient. One objective of the invention is thus to propose a process making it possible to recover and recycle with a high yield the recoverable ingredients of a catalytic ink, in a catalytic ink production and / or deposition installation intended for fuel cells, and in the catalytic layers of the MEAs.

[0008] Another objective of the invention is to provide such a method making it easy to control the reuse of recovered ingredients, when formulating a fresh ink of known qualitative and quantitative composition incorporating a determined proportion of recycled ingredients.

[0009] Another objective of the invention is to provide such a process which does not require harsh and polluting treatments, leading to modifications of the ingredients, and which is economical in terms of energy consumption.

[0010] Yet another objective of the invention is to make possible the complete or substantially complete recycling of all process streams, effluents from ink residues, and effluents from the reprocessing itself.

[0011] These objectives are achieved by designing a process that does not seek to recover in isolation the catalytic particles or the metal catalyst itself (such as platinum or its alloys) which are the most important elements from an economic value point of view. This process takes into account an analysis made by the inventors that the ink residues that form in a production and / or deposition line before its cleaning are relatively homogeneous in the sense that they include the non-volatile compounds that are the catalytic particles and the electrolytic ionomer or polymer (these two terms will be used interchangeably in the following).The analysis of the products present, of their chemical and physical properties, in particular the presence of volatile and non-volatile solvents under the conditions of use of the inks, directed the inventors towards the production of a controlled composition for recycling, derived from the original ink, this composition for recycling then being directly recyclable by incorporation during the formulation of a fresh ink in suitable controlled proportions. An advantage of the invention is that it is possible to know the composition both in qualitative and quantitative terms of the composition for recycling, in particular catalytic particles and electrolytic polymer, and to control the relative quantities of the ingredients used in the formulation of a new ink, called fresh ink.

[0012] On this basis, a process is therefore proposed for recovering and recycling catalytic ink residues in a catalytic ink production facility for fuel cells. It has also been found that it is industrially preferable and advantageous to use the composition for recycling to supplement, in addition to new solid compounds (catalytic particles and ionomer), the quantity of solids required in a fresh ink, rather than wanting to use the composition for recycling as the sole basis for producing an ink. The process makes it possible, in a very advantageous, efficient and economical manner, to recover a recoverable mixture, containing in particular the catalytic particles and the ionomer, and water, and to reuse this mixture by reintegrating it in a perfectly controlled manner from a quantitative point of view, into the production of a fresh ink.Another advantage is that the production of the composition for recycling and its recycling can be integrated into a catalytic ink production line, in which the composition for recycling is integrated in a quantitatively controlled manner.

[0013] The invention therefore relates to a method of recycling catalytic ink residues, the catalytic ink comprising catalytic particles, an electrolytic polymer, water, and optionally an organic solvent, the method comprising a. providing an effluent, said effluent containing the catalytic ink residues and water, this effluent containing catalytic particles and electrolytic polymer of the catalytic ink, b. filtering this effluent on a filtration membrane, which generates the formation of i. a retentate, containing the catalytic particles contained in the effluent, all or part of the quantity of electrolytic polymer contained in the effluent, and water, ii. a permeate containing water, but not containing catalytic particles.

[0014] Preferably, filtration b. is tangential. It proves to be perfectly adapted to the low concentration of solids and the very small size of the particles (generally between 0.5 and 100 pm) to be retained.

[0015] Cross-flow filtration uses porous membranes or porous discs to ensure efficient filtration. Solids buildup on their surface is prevented by an inlet liquid flow circulating parallel to the membrane. This flow can be ensured by means of a pump.

[0016] According to a preferred method, the effluent in a. further contains an alcohol A, and the retentate in i. also contains alcohol A; and this retentate, then called the first retentate, is subjected to a diafiltration c. using water, leading to the production of a second retentate containing the catalytic particles contained in the effluent, all or part of the quantity of electrolytic polymer contained in the effluent, and water, and recovery of this second retentate, while the alcohol A is eliminated in the permeate.

[0017] Preferably, the first retentate i. is diafiltered in the presence of deionized water. Preferably, the diafiltration is tangential. The diafiltration, preferably tangential, removes the alcohol A present, which was used during the cleaning of the installation. It can also lead to the removal of a part of the electrolytic polymer. It produces a second retentate forming the composition for recycling, containing the catalytic particles and electrolytic polymer.

[0018] The method comprises recovering the second retentate forming the composition for recycling.

[0019] Preferably, filtration b. and / or diafiltration c. are tangential and dynamic. This filtration is called dynamic because it is carried out on filtration membranes which are in motion, relative to the effluent or the effluent flow, preferably around an axis (AA) parallel to the filtration direction (see Figure 1).

[0020] In this case, the surface of the filtration membrane or membranes undergoes movements during filtration relative to the effluent to be filtered, preferably movements in the plane of the membrane or membranes, in order to prevent the accumulation of solids on the surface of the membrane or membranes. This induces a flow of liquid parallel to the membrane generated by the movement, in particular the rotation of the membrane disc or discs. Preferably, these membrane discs rotate around one or more hollow shafts, making the filtration surface mobile relative to the liquid, while the filtrate or permeate is evacuated by the hollow shaft.

[0021] During this filtration, a certain proportion, possibly the majority, of the organic solvent part of the original ink is eliminated.

[0022] Tangential filtration b. is followed by tangential diafiltration, which effectively removes unwanted solvents from the formulation by continuously adding water, particularly deionized water, to the filtration device, which gradually replaces these solvents in the retentate. Tangential diafiltration proves effective here in removing alcohol A. Preferably, it is also dynamic, as explained above, which increases its effectiveness.

[0023] Tangential filtration b. can cause part of the electrolytic polymer to pass through the membrane(s). However, surprisingly and advantageously, an equilibrium is reached in which the proportion of electrolytic polymer remaining in the retentate is stable even if the number of diafiltration washes is multiplied. The advantage is then that it is possible, particularly through experience, to know the proportion of electrolytic polymer in the retentate, which facilitates the process of controlled complementation during the formulation of fresh ink.

[0024] In one embodiment, filtration b. and diafiltration c. are carried out in the same tangential filtration device, preferably dynamic for both types of filtration, the method comprising the use of this device for filtration b., then for diafiltration c. by adding diafiltration water. Preferably, tangential filtration is carried out until a retentate concentrated in solids is obtained, then diafiltration is applied in the same device to remove alcohol A. As is known per se, filtration and diafiltration produce a permeate. Preferably, during the course of the filtration, respectively diafiltration, a withdrawal of the permeate resulting from the filtration in c. and / or the permeate resulting from the diafiltration in d. is carried out.

[0025] Filtration and diafiltration can be carried out at a temperature between about 10 and about 80°C, for example at room temperature (about 20 to about 25°C).

[0026] Preferably, filtration b. and / or diafiltration c. are carried out on filtration membranes which are in motion, preferably around an axis AA parallel to the filtration direction. These membranes may be carried by hollow discs, or may form the walls of these hollow discs. These hollow discs further carry a permeate discharge channel arranged in their center.

[0027] In the dynamic tangential filtration preferably used for the two successive filtrations, several discs (at least two) are driven in rotation. According to the simplest embodiment, all the discs are carried and driven by the same drive shaft. The rotation speed of the discs can be identical or it can be different, thanks to suitable means. It is also possible to have two discs or two groups of discs carried and driven by different drive shafts, and possibly, the discs of each group are arranged in a parallel manner and spaced orthogonally to their parallel axes while partially overlapping in their plane. The rotation speed of the discs can be identical or it can be different.All these solutions create a shear effect that helps clean the membrane surfaces and prevents them from becoming clogged, meaning that a decrease in filtration performance due to the accumulation of solids can be largely avoided.

[0028] In a favorable embodiment, rotating membrane discs are used as membranes. This allows for smooth movement with favorable permeate removal.

[0029] A favorable embodiment of the invention is characterized in that at least two hollow membrane discs are provided, each of which rotates around a hollow shaft. The permeate that has passed through the membrane discs is fed into the body of the hollow disc, radially to the axis of rotation, and is conducted outwardly through the hollow shaft. The membrane discs preferably have the same direction of rotation and turbulence is created on the surface of the membranes in the overlapping area of ​​at least two membrane discs. An example of such a device can be found in EP 1 154 840, to which the skilled person may refer and incorporated by reference herein.

[0030] Advantageously, the membranes are provided to have a relative oscillating motion and turbulence is caused on the membrane surface in the overlapping region. Advantageously, the membrane discs rotate in the same direction and turbulence is produced in the region where at least two membrane discs overlap. As a result, an overflow velocity is generated on the membrane surface.

[0031] These different configurations prevent or at least minimize the accumulation of a cover layer and the obstruction of the membranes.

[0032] Alternatively, the membrane discs can be arranged to rotate in opposite directions. With this mode of operation, constant relative speeds can be achieved in the overlap zone.

[0033] In one method, the retentate is discharged under overpressure. Filtration is improved by applying overpressure to the retentate side of the membrane.

[0034] The term “effluent” means a reprocessing fluid containing residues of industrial origin, in this case catalytic ink residues. The effluent in a. may be the result of dissolving residues from an ink production facility, and / or from an ink deposition or application facility, or from dissolving ink from catalytic layers present on a base membrane, a GDL or an MEA. The method may therefore comprise such a dissolution or solution treatment in order to obtain the effluent used in a.

[0035] According to one aspect, in a. the method comprises cleaning a catalytic ink production and / or deposition installation using water or a hydroalcoholic mixture formed of water and an alcohol A, and recovering an effluent containing the ink residues, or having such an effluent previously produced during such installation cleaning.

[0036] According to a preferred embodiment, the effluent in a. contains a hydro-alcoholic mixture and this comprises an alcohol A. Alcohol A may in particular comprise ethanol, methanol, propan-1-ol, and / or propan-2-ol. Ethanol is preferred.

[0037] The hydro-alcoholic cleaning mixture comprises in particular from approximately 10 to approximately 90% of alcohol A by weight, preferably from approximately 30 to approximately 70% of alcohol A by weight, typically from approximately 50% of alcohol A by weight, defined relative to the total weight of water + alcohol of said mixture.

[0038] The volume of hydro-alcoholic mixture must be sufficient to clean the entire installation and remove substantially all ink residue. That being said, the exact volume is not a fundamental parameter. However, it is preferable not to use a significant excess volume, so as not to dilute the effluent too much and consume more energy during filtration.

[0039] According to another aspect, in a. the dissolution of an ink layer present on a base membrane, a GDL, or an MEA is carried out using one or more solvents suitable for dissolving dry ink, and the recovery of an effluent containing the ink residues, or the fact of having such an effluent previously produced during such dissolution.

[0040] According to a preferred embodiment, the invention relates to the method for producing a composition "for recycling", from the residues of so-called original catalytic ink present in a production and / or deposition installation of original catalytic ink intended for fuel cells, the original catalytic ink comprising catalytic particles, an electrolytic polymer, water, optionally an organic solvent, in known relative quantities, the method comprising: a.cleaning the installation using a hydro-alcoholic mixture formed of water and an alcohol A, and recovering a hydro-alcoholic effluent containing the original catalytic ink residues; or having such a hydro-alcoholic effluent previously produced during such installation cleaning; this hydro-alcoholic effluent containing catalytic particles and electrolytic polymer substantially in their relative quantities known in the original catalytic ink, b. tangential filtration, preferably dynamic, of this hydro-alcoholic effluent on a filtration membrane, which generates the formation i. of a first retentate, containing the catalytic particles contained in the hydro-alcoholic effluent, all or part of the quantity of electrolytic polymer contained in the hydro-alcoholic effluent, and the hydro-alcoholic mixture formed of water and alcohol A, ii.of a permeate containing a hydro-alcoholic mixture formed of water and alcohol A, but not containing catalytic particles, which may optionally contain electrolytic polymer, c. a tangential diafiltration, preferably dynamic, of the first retentate using water, in particular deionized water, this diafiltration eliminating alcohol A and part of the electrolytic polymer, and producing a second retentate forming a composition for recycling, containing the catalytic particles and electrolytic polymer, d. recovery of this composition for recycling.

[0041] According to another aspect, in a. the dissolution of an ink layer present on a base membrane, a GDL, or an MEA is carried out using one or more solvents suitable for dissolving dry ink, and the recovery of an effluent containing the ink residues, or the fact of having such an effluent previously produced during such dissolution.

[0042] The duration of diafiltration allows all of the alcohol A to be eliminated. This duration can range from a few minutes to several hours depending on the volume of alcohol, for example ethanol, to be eliminated.

[0043] The process is adjusted to produce a composition for recycling (the retentate after diafiltration), which is itself another object of the invention.

[0044] According to one embodiment of the invention, this composition has a liquid content of between approximately 60% and approximately 99% by mass, in particular between approximately 85% and approximately 95% by mass, typically approximately 90% by mass. The liquid part of the retentate is understood to contain water. The solid part is understood to be composed of the catalytic particles and the ionomer. This proportion of liquid has the double advantage of making the composition for recycling a composition which can be easily pumped, sucked up and made to flow.

[0045] According to one embodiment of the invention, the composition for recycling has a catalytic particle / ionomer or electrolytic polymer weight ratio of between approximately 70% / 30% and approximately 90% / 10%, typically approximately 75% / approximately 25%.

[0046] According to one embodiment of the invention, the composition for recycling has a viscosity less than or equal to about 4000 mPa.s at 25°C, measured by a Brookfield viscometer. The viscosity of the composition for recycling typically varies from about 20 mPa.s to about 4000 mPa.s at 25°C, measured by a Brookfield viscometer.

[0047] The composition can combine two or three of these characteristics.

[0048] Thus, the invention also relates to this composition for recycling, and also to a composition capable of being obtained by implementing the method described above.

[0049] By definition, throughout the application and unless otherwise indicated, "relative quantities" means the weight ratios between the species mentioned. For example, in the case of catalytic particles and the electrolytic polymer, "their relative quantities" are the proportion by weight of the catalytic particles to the weight of the electrolytic polymer in the product containing them.

[0050] The invention also relates to a method for recycling the original catalytic ink residues, starting from the composition for recycling, or beginning with the production of this composition for recycling.

[0051] The term "original catalytic ink" here refers to the ink that was produced or deposited with the installation targeted by the cleaning, or the ink forming the layer on the surface of a base membrane or a GDL, and from which the effluents originate. The term "fresh ink" here refers to a newly produced catalytic ink. The original catalytic ink comprises catalytic particles, an electrolytic or ionomer polymer, water, possibly an organic solvent, in known relative quantities.

[0052] The recycling process includes in particular starting from a composition for recycling, resulting from the implementation of the process described here, applied to the production of a composition for recycling containing catalytic particles and ionomer from the original catalytic ink residues. The recycling process can also be defined as integrating all or part of the steps, typically all the steps of the preceding process, leading to the production of a composition for recycling.

[0053] The recycling process includes mixing a determined quantity of the composition for recycling with ingredients to formulate a new catalytic ink (fresh ink).

[0054] The ingredients in question are all the constituent ingredients of the ink to be produced, in particular: electrolytic polymer, catalytic particles, water, organic solvent part, generally formed from a low boiling point solvent (called solvent or alcohol B) and / or a high boiling point solvent (called solvent C).

[0055] In a preferred embodiment, the fresh ink or new ink produced and the original catalytic ink are of the same composition. In this case, the formulation of the new ink comprises the mixing of a determined quantity of composition for recycling and suitable quantities of the ingredients for formulating the new ink. The quantities of products lost during the process, notably combining filtration and diafiltration, can be adjusted so that the supplemented ink (composition for recycling + added products) retains or reaches the qualitative and quantitative composition of the fresh ink. For this, the water content of the composition for recycling can be measured, making it possible to determine the final composition of the composition for recycling, mainly catalytic particles, ionomer and water. The ratios of catalytic particles and water are in principle unchanged, and the proportion of water in the composition has thus been determined.

[0056] The method comprises in particular (i) taking a mass M of composition for recycling, (2i) measuring or having measured the water content of this composition for recycling, (3i) calculating the mass of solids = catalytic particles + electrolytic polymer and (4i) possibly determining the content of each of these solids by referring to their respective contents in the original ink.

[0057] The measurement of water content can be carried out on a sample using methods known to those skilled in the art. This measurement can in particular be carried out using the Karl-Fisher method.

[0058] Preferably, a determined amount of water can be added depending on the mass of new ink to be produced and the water content of the portion of recycling composition incorporated, in order to obtain the water / solids ratio of the target ink produced. The respective amounts of solvents or alcohols B and C to be added are further determined, depending on the mass of solids introduced.

[0059] In one embodiment, the mass proportions of the different ingredients in the inks according to the invention (original ink and / or new ink) may be, relative to the total mass of the ink resulting from this mixture: from approximately 55 to approximately 70% water, from approximately 4 to approximately 20% solvent or alcohol B, from approximately 4 to approximately 20% organic solvent C, from approximately 2 to approximately 8% ionomer, and from approximately 5 to approximately 7% supported catalyst. According to a preferred method, the following mass proportions are retained, relative to the total mass of the ink resulting from this mixture: from approximately 61 to approximately 69% of water, from approximately 8 to approximately 18% of polyalkylene glycol (solvent C), from approximately 8 to approximately 18% of alcohol B, from approximately 3 to approximately 6% of ionomer, and from approximately 5 to approximately 7% of supported catalyst.Typically, it is a mixture of: about 62 to about 66% water, about 12 to about 14% polyalkylene glycol (solvent C), about 12 to about 14% alcohol B, about 3 to about 4% ionomer, and about 5.5 to about 6.5% supported catalyst.

[0060] Preferably, the recycling composition used is from one facility cleaning, or is a pool of recycling compositions from two or more facility cleanings.

[0061] According to one feature, the catalytic ink that has been produced in the ink production facility, and therefore the catalytic ink residues reprocessed here, further contain a volatile solvent B, preferably an alcohol, having in particular a boiling point of between 75 and 130°C, in particular between 75 and 100°C at atmospheric pressure, this solvent being in a known relative quantity. This solvent being completely eliminated during the preparation of the composition for recycling, the quantity of solvent B to be added during the formulation of the new catalytic ink is easily accessible. After step (d), the water content in the composition for recycling can be measured, making it possible to determine the quantity of water required to be added.Thus, the relative amounts of catalytic particles, ionomer, and water in the recycling composition are easily determined, as well as the relative amounts of catalytic particles, ionomer, solvent B, and water to formulate a catalytic ink of the desired composition.

[0062] High boiling point solvent C, or high boiling point alcohol, is notably of the type usually used in catalytic inks. These are generally solvents of the polyhydric alcohol type, e.g. ethylene glycol, propylene glycol, triethylene glycol, butylene glycol, 1,4-butanediol, 2,3-butanediol and / or glycerin; polyalkylene glycols, diethylene glycol, and / or dipropylene glycol; and monoalkyl ether derivatives such as monomethyl ethers and / or monoethyl ethers. This solvent C is also not normally found in the composition for recycling.

[0063] According to one method, (i) a mass M of composition for recycling, (2i) a determined quantity of water and (3i) a determined quantity of catalytic particles, ionomer, solvent system (in particular solvent B or solvent B and C) are mixed. A final catalytic ink is obtained containing a known proportion of recycled ink, the quantities of (i), (2i) and (3i) being chosen so that this final catalytic ink has the desired concentrations for each of its ingredients. This final ink can thus have a composition similar to the original ink produced previously and whose residues have just been recycled into this final ink.

[0064] According to one method, in particular if there is an excess of water in the composition for recycling compared to the fresh ink or the final ink in question, it is possible to add ink compounds other than water (e.g. ionomer, catalytic particles, alcohol B and solvent C) in relative quantities which are similar in the composition for recycling and the fresh ink.

[0065] By definition, throughout the application and unless otherwise indicated, relative quantities are understood to mean the mass ratios between the species considered, which does not include water. For illustration purposes, in the preceding paragraph, the relative quantities are those of the ionomer ingredients, catalytic particles, alcohol B and solvent C, relative to each other.

[0066] In the invention, the proportion of composition for recycling in the new ink can vary in certain proportions. According to one method, the proportion by mass of solid of the composition for recycling can be in particular from approximately 1 to approximately 40% by mass, preferably from approximately 1 to approximately 20% by mass, typically of the order of approximately 5% by mass, relative to the mass of solid of the ink resulting from the mixture of composition for recycling and fresh ink.

[0067] In a variant, the composition for recycling is used to complement a new ink whose composition is not identical to the original ink. In particular, the difference may be found in the respective quantities of all or part of the ingredients, and / or in the solvent system, catalytic particles and / or ionomer being of the same nature, etc.

[0068] In one embodiment, a shut-down ink production line is cleaned, the composition for recycling is produced and recovered, this composition is stored for recycling, the ink production line is restarted, and a controlled addition of composition for recycling, water, ionomer, solvent or volatile alcohol B, possibly catalytic particles, and / or solvent C is carried out in a production step of the ink produced by the restarted production line. When producing a new ink on an industrial scale, generally, it will be necessary to add all the compounds used in the composition of this new ink, since the composition for recycling does not provide the necessary quantities.

[0069] In another embodiment, a shut-down ink production line is cleaned, the composition for recycling is recovered, and the composition is used to carry out its controlled addition in a second production line. A controlled addition of composition for recycling, ionomer, solvent or volatile alcohol B, water, possibly catalytic particles, and / or solvent C, is carried out in a production step of the ink produced by this other production line. When producing a new ink on an industrial scale, it will generally be necessary to add all the compounds used in the composition of this new ink, since the composition for recycling does not allow the necessary quantities to be provided.

[0070] In both cases, the recycling compositions from 2 or more cleanings can be stored and all or part of these successive recycling compositions or a mixture or pool of them can be incorporated into a fresh ink production.

[0071] In one embodiment, the partially recycled target fresh ink (i.e., incorporating a portion of composition for recycling) has the same mass content of catalytic particles, electrolyte polymer, water, solvent B, and optionally high boiling solvent C as the original catalytic ink.

[0072] In another embodiment, the partially recycled target fresh ink has a mass content of at least one of its components taken from catalytic particles, electrolytic polymer, water, solvent B, high boiling solvent C, which is different from the composition of the original catalytic ink.

[0073] The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0074] [Fig 1] Figure 1 is a schematic representation of a tangential flow filtration device, usable for filtration and diafiltration.

[0075] [Fig 2] Figure 2 is a graph showing the evolution of the ethanol content at the filtration outlet as a function of the volume of water injected during diafiltration.

[0076] [Fig 3] Figure 3 shows the polarization curve, voltage versus current density, between the reference (fresh ink only) and a partially recycled ink at 20%.

[0077] Referring to Figure 1, the filtration device comprises a cylindrical tank 1 provided with an inlet 2 and an outlet 3. It further comprises a motor 4 provided with a shaft 5 driven in rotation about an axis AA by the motor. This shaft 5 carries ceramic filtration discs 6, three in number in the figure, but a different number can be used. Each of these discs is coaxial with the shaft 5 and secured to it. The discs comprise two walls 6a and 6b delimiting an interior volume 7. The shaft 5 comprises a conduit 8 functionally connected to the interior volumes 7 of the discs, and having an outlet shown as 9.

[0078] Arrow 10 represents an arbitrary direction of rotation of shaft 5 and discs 6. Points 11 represent solid particles, and arrows 12 represent the flow of liquid passing through walls 6a and 6b.

[0079] The device is first used for tangential filtration during which the hydro-alcoholic effluent enters at 2, and is subjected to the filtration process leading to a concentration of solid particles, water and alcohol being progressively eliminated through the discs and drawn off at 9.

[0080] The device is then used for diafiltration when the retentate is sufficiently concentrated. The concentration is considered sufficient when the engine torque has exceeded a certain value or when the filtration flow is lower than a target value. The retentate from the filtration is present in tank 1. Deionized water is then introduced through line 2. The mixture of water and retentate is subjected to the diafiltration process, which does not lead to a concentration of solids since no material is added at the inlet. The diafiltration step leads to a reduction in the alcohol content until total elimination, the alcohols being gradually replaced by water in the retentate, eliminated through the discs and then withdrawn at 9. The retentate or recycle concentrated in solids and without alcohol is then withdrawn at 3.

[0081] Example 1: Catalytic ink with 20% recycled solids

[0082] Step 1: Effluent concentration process by dynamic tangential filtration

[0083] The catalytic effluents recovered and to be treated come from washing with a water / ethanol mixture an ink production tank containing a Pt / C catalyst (high surface area carbon / medium platinum content), an ionomer (sold under the brand name Aquivion®), propanol, water and ethylene glycol.

[0084] 30 liters of this catalytic effluent (ink residues + water / ethanol mixture) are introduced into a feed tank connected to the dynamic tangential filtration (DGF) device. The solution to be filtered will then be continuously conveyed to the filtration chamber in the cylindrical tank 1 through inlet 2 and completely fill it using a compressed air system (not shown) to push the fluid. This chamber remains completely filled throughout the process. The machine used has a filtration chamber volume of 0.375 liters and the filtration membranes 6 used are ceramic. Once the feed is started, the permeate is filtered and collected through outlet 9 in a container external to the DGF system while the concentration of the retentate increases in the filtration chamber. Filtration is stopped when all of the inlet effluent has been filtered: the solid content of the retentate is then 15%.

[0085] Step 2: Removal of unwanted solvents in the formulation by diafiltration

[0086] The diafiltration stage can then begin. Deionized water is continuously injected into the filtration chamber through inlet 2 to gradually replace the ethanol that is released into the permeate. The water supply, and therefore the diafiltration stage, is stopped when the ethanol content in the permeate is below 0.5% (Figure 1). The 0.375 liters of retentate are then collected in a container through outlet 3 or through a tap on the filtration chamber.

[0087] The retentate thus collected has a solids content of 15% and is considered to be composed only of water, catalyst and ionomer. A thermogravimetric analysis makes it possible to know the exact composition of the retentate in order to proceed with the formulation of the new recycled ink. These contents will be those taken into account for the formulation of the recycled ink from the retentate.

[0088] Step 3. Formulation of a partially recycled ink

[0089] Thirty grams of 20% partially recycled ink will be formulated. The formulation includes the preparation of key solutions that will then be mixed to form the final ink: the catalyst dispersion and the ionomer dilution.

[0090] Ionomer Dilution: 3.30 grams of ionomer (sold under the brand name Aquivion®) are added to a 150 milliliter bottle, along with 4.775 grams of deionized water, 1.67 grams of 1-propanol (Fisher, greater than 99% purity), and 2.23 grams of ethylene glycol (Sigma). This ionomer dilution is stirred with a magnetic stirrer.

[0091] Catalyst Dispersion: In a 100 milliliter beaker, 4.39 grams of retentate are mixed with 10.68 grams of deionized water under magnetic stirring at room temperature. 1.99 grams of fresh catalyst, identical to that present in the retentate, are added to this mixture while still stirring. With vigorous stirring, 3.32 grams of 1-propanol (Fisher, purity greater than 99%) and 4.43 grams of ethylene glycol are then introduced into the beaker. This dispersion containing the catalyst is stirred by a dissolver.

[0092] Ink Preparation: 11.05 grams of the ionomer dilution and 18.95 grams of the catalyst dispersion are mixed in a 50 milliliter beaker by a rotor-stator mixer.

[0093] Step 4. Characterization of partially recycled ink

[0094] The ink is characterized by rheology to check whether it is suitable for the deposition process. The rheological measurement consists of a viscosity measurement, at a shear rate between 0.01 and 1000 s -1 (per second) and at a temperature of 20°C. The ink has a shear-thinning behavior and has a viscosity of 0.15 pascals per second for a shear rate of 1 s -1 (per second), measured at a temperature of 20°C.

[0095] Step 5. Depositing the ink

[0096] The ink is deposited onto a membrane (standard PFSA membrane for PEMFC MEAs) using a bar coater. The desired amount of platinum is between 0.3 and 0.5 milligrams of platinum per square centimeter of membrane. To evaporate the solvent, the ink-coated membrane is heated for several minutes.

[0097] The ink deposition was made on a membrane with a surface area of ​​64 cm 2 The appearance of the ink layers was observed with the naked eye, the surface appearance was homogeneous with little or no cracking. The electrochemical performances were found to be satisfactory and in line with what is expected for an MEA whose membrane has been coated with standard fresh ink: > 0.6 V at 1 A / cm 2 (figure 3).

[0098] As shown in Figure 2, the deionized water fed into the retentate chamber effectively reduces the ethanol content in the retentate. After a certain washing volume, the ethanol content drops below 0.5% and diafiltration can therefore be stopped.

[0099] The performances of two MEAs were compared (Figure 3). These two MEAs are identical in every respect except for the cathodic catalytic layer. The reference MEA was made with a fresh cathodic ink while the recycled MEA was made with a 20% recycled cathodic ink. The polarization curves of these two MEAs are displayed above and are superimposed. It is then possible to affirm that the use of partially recycled ink formulated using the process of the invention makes it possible to obtain the same electrochemical performances as an ink without recycled compounds.

Claims

CLAIMS 1. A method for recycling catalytic ink residues, the catalytic ink comprising catalytic particles, an electrolytic polymer, water, optionally an organic solvent, the method comprising a. providing an effluent, said effluent containing the catalytic ink residues, said effluent containing catalytic particles and electrolytic polymer of the catalytic ink, b. filtering said effluent on a filtration membrane, which generates the formation of i. a retentate, containing the catalytic particles contained in the effluent, all or part of the quantity of electrolytic polymer contained in the effluent, and water, ii. a permeate containing water, but not containing catalytic particles.

2. Method according to claim 1, in which the filtration b. is tangential.

3. A method according to claim 1 or 2, further comprising diafiltration c. of the retentate i. using water, obtaining a second retentate, containing the catalytic particles contained in the effluent, all or part of the quantity of electrolytic polymer contained in the effluent, and water, and recovery of this second retentate.

4. Method according to claim 3, in which the diafiltration c. is tangential.

5. Method according to claim 3 or 4, in which filtration b. and diafiltration c. are dynamic tangential filtrations, carried out on filtration membranes which are in motion, preferably around an axis (AA) parallel to the filtration direction.

6. Method according to claim 5, in which the filtration b. and the diafiltration c. are carried out in the same dynamic tangential filtration device, the method comprising the use of this device for the filtration b., then for the diafiltration c. by adding diafiltration water.

7. Method according to any one of claims 1 to 6, in which a withdrawal of the permeate from the filtration in b. and / or the permeate from the diafiltration in c. is carried out during the course of the filtration, respectively diafiltration.

8. Method according to any one of claims 1 to 7, the method comprising cleaning a catalytic ink production and / or deposition installation, using water or a hydro-alcoholic mixture comprising water and an alcohol A, obtaining the effluent a.

9. Method according to claim 8, in which the cleaning of the installation is carried out by means of a hydro-alcoholic mixture comprising water and an alcohol A, producing a hydro-alcoholic effluent containing the original catalytic ink residues, water and alcohol A; or the fact of having such an effluent available.

10. The method of claim 9, wherein alcohol A comprises ethanol, methanol, propan-1-ol or propan-2-ol.

11. Composition for recycling comprising catalytic particles, an electrolytic polymer, water, optionally an organic solvent, and having a viscosity less than or equal to 4000 mPa.s at 25°C measured using a Brookfield viscometer, a liquid content of between 60% and 99% by mass, and a weight ratio of catalytic particles and electrolytic polymer of between 70% / 30% and 90% / 10%.

12. Process for producing a catalytic ink, in particular intended for fuel cells, comprising catalytic particles, an electrolytic polymer, water, optionally an organic solvent, process in which a determined quantity of a composition for recycling obtained by implementing the process according to any one of claims 1 to 10, or of the composition according to claim 11, and ingredients for formulating a new catalytic ink are mixed.

13. Method according to claim 12, in which the proportion by mass of solid of the composition for recycling may be in particular from 1 to 40% by mass, preferably from 1 to 20% by mass, typically 5% by mass, relative to the mass of solid of the new ink.

14. Method according to claims 12 or 13, in which (i) a mass M of composition for recycling, (2i) a determined quantity of water and (3i) a determined quantity of catalytic particles, ionomer, and solvent are mixed.

Images