Method for recycling catalytic ink residues in a plant for producing and / or depositing catalytic ink intended for fuel cells

Abstract

The invention relates to a method in which an effluent comprising catalytic ink residues and water or a hydro-alcoholic mixture of water and alcohol A is produced, which is heated to a temperature point and to a pressure causing the evaporation of water and / or alcohol A and the concentrate is recovered. The latter contains the catalytic particles and the electrolytic polymer substantially in their known relative amounts in the catalytic ink. This concentrate is then used to produce a fresh ink, in particular by adding this concentrate to a production ink.

Description

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

[0002] The present invention relates to a method for recycling 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.

[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 which is an electrolytic polymer or 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, particularly 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 capable of forming an electrode on a fuel cell membrane comprises a dispersion of electrolytic polymer and catalytic particles in a mixture of water and organic solvent, which may comprise at least one volatile alcohol which may have a boiling point of between 75 and 130°C, in particular between 75 and 100°C and / or a high-boiling alcohol, generally 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 electrolyte polymer or electrolytic polymer present in the ink comprises or consists of a perfluorosulfonated acid ionomer or perfluorosulfonic acid (PFSA), 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 ioniomer 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] In addition, unexploited sources of platinum or other catalytic metal loss are located in ink production lines (including tanks, pipes, valves and other devices) and catalytic ink deposition facilities 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 seem insufficient.

[0008] One objective of the invention is thus to propose a method for recovering and easily recycling with high yield the recoverable ingredients of a catalytic ink, in a production and / or deposition installation for catalytic ink intended for fuel cells, and in the catalytic layers of MEAs.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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 the production and / or deposition lines before their cleaning are homogeneous in the sense that they include the non-volatile compounds that are the catalytic particles, the electrolytic polymer, as well as the organic solvent part, generally formed of a low boiling point solvent (referred to as solvent or alcohol B in the following) and a high boiling point solvent (referred to as solvent C 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, having different boiling points, directed the inventors towards the production of a controlled concentrate from the original ink, this concentrate then being directly recyclable for example by incorporation into 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 concentrate, 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.

[0013] In particular, from an effluent containing ink residues, the process for producing a concentrate makes it possible to recover all or almost all of the catalytic particles and the electrolytic polymer. From an effluent containing residues of an ink of known composition, called the original ink, the concentrate is found to contain the catalytic particles and the electrolytic polymer in the same known ratio as the original ink from which the residues originated. This knowledge advantageously makes it possible to very precisely add the concentrate to fresh ink, with, if necessary, a known addition of water and organic solvent (in particular solvent B with a low boiling point), so as not to have any drift in the final composition of the ink.

[0014] On this basis, a process is therefore proposed for recovering and recycling catalytic ink residues in a catalytic ink production and / or deposition facility for fuel cells. It has also been found that it is industrially advantageous to use the concentrate to supplement fresh 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, the electrolytic polymer, possibly a high-boiling solvent, and possibly residual water, and to reuse this mixture by reintegrating it in a perfectly controlled manner from a quantitative point of view, into freshly produced ink. Another advantage is that the production of the concentrate and its recycling can be integrated into a catalytic ink production line, in which the concentrate is integrated in a quantitatively controlled manner.But it is also possible to use the concentrate as a basis for producing fresh ink.

[0015] The subject of the invention is therefore a process for recycling catalytic ink residues (known as original), said residues comprising catalytic particles, an electrolytic polymer, water, optionally an organic solvent, the process comprising

[0016] (a) providing an effluent, said effluent comprising catalytic ink residues and water or a hydro-alcoholic mixture of water and alcohol A, said effluent containing catalytic particles and electrolytic polymer substantially in their relative amounts known in the catalytic ink, (b) heating said effluent to a temperature point and pressure causing the evaporation of water and / or alcohol A in the form of a vapor phase, and the formation of a concentrate containing catalytic particles and electrolytic polymer in said relative amounts,

[0017] (c) the separation between the vapor phase and the concentrate,

[0018] (d) recovering this concentrate containing catalytic particles and electrolytic polymer in, or substantially in, their known relative amounts in the catalytic ink.

[0019] By definition, throughout the application and unless otherwise indicated, relative quantities are understood to mean the weight ratios between the species mentioned. For example, in the case of the 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. The term "substantially" in conjunction with the relative quantities in the concentrate means that there may be a minor and insignificant variation from the relative quantities of the original ink.

[0020] The process of the invention is remarkable in that it produces a controlled concentrate, because it contains the catalytic particles and the ionomer or polymer electrolyte in the known relative quantities, which are those of the original ink, and ready to use for inclusion in a new ink (called fresh ink).

[0021] 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 process may therefore comprise such a dissolution or solution treatment in order to obtain the effluent used in (a).

[0022] 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.

[0023] According to a preferred embodiment, the effluent in (a) contains a hydroalcoholic mixture and this comprises an alcohol A having a boiling point lower than that of water. Heating may be carried out in (b) to evaporate this alcohol A. It is preferable to use an alcohol A having a boiling point lower than that of water. In the hydroalcoholic mixture for cleaning the production and / or depot installation, and therefore the effluent in (a), the alcohol A may in particular comprise or consist of ethanol, methanol and propanol.

[0024] The hydro-alcoholic cleaning mixture comprises in particular from approximately 10 to approximately 90% of alcohol A by weight, preferably from approximately 40 to approximately 60% 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.

[0025] Preferably alcohol A is ethanol.

[0026] Cleaning the installation causes the ink residues to be carried away and dissolved. An aqueous or hydro-alcoholic effluent containing the ink residues is therefore recovered in (a). Alternatively, such an effluent previously produced during such installation cleaning is used in (a).

[0027] 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.

[0028] In these various aspects, the effluent contains catalytic particles and electrolytic polymer substantially or precisely in their relative quantities known in the catalytic ink (this effluent being a dilution or dissolution of the catalytic ink, i.e. containing as many catalytic particles and electrolytic polymer as the original catalytic ink).

[0029] In (b), in the case of a hydro-alcoholic mixture comprising an alcohol A having a boiling point lower than that of water, the heating of the effluent in (b) is preferably carried out at a temperature point and at a pressure causing the evaporation of the alcohol A only, or of the alcohol A and water, in the form of a vapor phase, and the formation of a concentrate containing catalytic particles and electrolytic polymer in said relative quantities.

[0030] Here, the term "original catalytic ink" 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. Here, the term "fresh ink" refers to a newly produced catalytic ink.

[0031] In one aspect, the method further comprises in (e) or in an additional step (e) using the concentrate to form a fresh ink or to supplement a fresh ink. In one embodiment, the method further comprises in (e) adding the concentrate (d) to a fresh ink.

[0032] The proportion of concentrate in the ink resulting from the mixture of concentrate and fresh ink may vary in certain proportions. According to one method, the proportion by mass of solid of the concentrate may be in particular from about 1 to about 30% by mass, preferably from about 1 to about 10% by mass, typically of the order of about 5% by mass, relative to the mass of solid of the ink resulting from the mixture of concentrate and fresh ink.

[0033] In this method, to a fresh ink having determined relative quantities of catalytic particles, electrolytic polymer and water, quantities of concentrate and optionally water are added calculated to reproduce the determined relative quantities of the fresh ink.

[0034] In a preferred embodiment, the fresh ink and the original catalytic ink are of the same composition. The concentrate is incorporated into fresh ink of the same composition as the original ink. The quantities of products vaporized during heating can be adjusted so that the supplemented ink (fresh ink + concentrate + added products) retains the qualitative and quantitative composition of the fresh ink. The concentrate containing catalytic particles and electrolytic polymer is then incorporated into the fresh ink in known relative quantities, identical to those of the fresh ink.

[0035] For non-vaporizable and non-vaporized elements, namely in particular the catalyst particles and the electrolytic polymer, the percentage by weight of these elements is proportional to the initial values ​​of the original ink. The composition of the solid (electrolytic polymer and catalyst particles) is constant or substantially constant throughout the process. This is valid for any compound of the original ink that is not vaporized during the implementation of the process. This is generally the case for high-boiling solvents (solvent or alcohol C) commonly used in catalytic inks. The concentrate containing catalytic particles, electrolytic polymer and high-boiling solvent is then incorporated into the fresh ink in known relative quantities, identical to those of the fresh ink.

[0036] Furthermore, the water content of the concentrate can be measured as the first part of step (e), or in an additional step occurring before step (e) then reduced to the actual mixture. This makes it possible to determine the addition of water necessary to recover the relative quantities of the catalytic particles, the electrolytic polymer, and the water of the original catalytic ink or the fresh ink. The concentrate, possibly water, and fresh ink can then be mixed. Measuring the water content of the concentrate generally makes it possible to determine the concentration of solids in the concentrate, which can be compared to that of the fresh ink and therefore of the target ink. This measurement 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.This also makes it possible to know the mass proportion of solids in the concentrate and therefore to determine the quantity of concentrate to add to fresh ink to respect the mass proportions of solids during mixing, mentioned above.

[0037] In one modality, the measurement of the content of one of the solid elements (electrolytic polymer or catalytic particles) can also be carried out. These measurements are carried out as the first part of step (e), or in an additional step occurring before step (e) reduced to the mixture itself.

[0038] In another modality, a parameter related to the solids content in the concentrate is measured as the first part of step (e), or in an additional step occurring before step (e) reduced to the actual mixture.

[0039] For example, the viscosity of the concentrate, the optical density (OD), or the absorbance can be measured. Knowing the water content, the solids content can be deduced. Knowing the relative quantities of solid particles / electrolytic polymer (possibly solvent C) in the original ink, and the fact that these are retained in the concentrate, their concentration in the concentrate can be deduced. In this way, the quantities of water and other additives (particularly solvent B) that must be added during mixing in step (e) can be deduced.

[0040] If the concentrate contains a lower water content than the fresh ink compared to the solid contained in the concentrate, water must be added. Once the concentration difference between the concentrate and the fresh ink is known, the amount of water necessary to balance the concentrations is added.

[0041] If the concentrate contains a water content substantially equal to that of the fresh ink in relation to the solid contained in the concentrate, addition of water is not necessary.

[0042] Alternatively, if the concentrate contains a water content greater than that of the fresh ink relative to the solid contained in the concentrate, step (e) does not add additional water. In this case, according to one method, the quantities of solids (electrolytic polymer and catalyst particles, possibly solvent C) can be added to achieve the desired concentrations for the supplemented ink. In one embodiment, the viscosity, optical density (OD), or absorbance of the concentrate is measured at regular intervals or continuously and serves as a stopping point for heating (b) and therefore for evaporation. In this case, the water composition of the concentrate is controlled. In a preferred embodiment, the heating and evaporation are stopped when a solids concentration value corresponding substantially or precisely to that of the fresh ink has been reached.We then proceed to mix fresh ink, concentrate, and volatile ingredients such as solvent B.

[0043] The mass proportions of the different ingredients in the ink according to the invention may be, relative to the total mass of the ink resulting from this mixture: from approximately 55 to approximately 70% of water, from approximately 4 to approximately 20% of solvent or alcohol B with a low boiling point, from approximately 4 to approximately 20% of organic solvent C or alcohol with a high boiling point, from approximately 2 to approximately 8% of electrolytic polymer, and from approximately 5 to approximately 7% of 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 electrolytic polymer, 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% electrolyte polymer, and about 5.5 to about 6.5% supported catalyst.

[0044] In addition to water, some or all of the solvent or alcohol B may have been vaporized during step (b).

[0045] In a preferred embodiment, step (b) is carried out in such a way as to evaporate all or almost all of the solvent or alcohol B. This avoids having to measure a significant residual content in the concentrate. This therefore makes it possible to add to step (e) a quantity of this same solvent or alcohol B calculated so that the supplemented ink has the qualitative and quantitative composition of the fresh ink. The management of any necessary adjustment of the concentration of solids in the concentrate will therefore be combined with the addition of the alcohol or solvent B.

[0046] Thus, according to one characteristic, the catalytic ink which has been produced in the ink production and / or deposition installation, and therefore the catalytic ink residues, 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. In this case, the quantity of this solvent B removed in step (b) is taken into account, in order to add this solvent B during mixing in step (e) and compensate for this loss due to evaporation, which makes it possible to maintain the relative quantities. In other words, an addition of solvent B is made during mixing so that the ink composition produced has the same relative quantities of ingredients as the fresh ink.

[0047] As stated, step (b) can advantageously be carried out to evaporate all of this solvent B (case 1).

[0048] If this is not the case (case 2), then the water content and solvent B of the concentrate can be measured at the mixing stage, making it possible to determine the quantity of water needed to be added, and the quantity of solvent B to be added, to recover the relative quantities of catalytic particles, electrolytic polymer, and water from the catalytic ink, then the concentrate, possibly water, solvent B, and fresh ink having the same relative quantities of catalytic particles, electrolytic polymer, solvent B, and water can be mixed.

[0049] According to one characteristic, for case 2, the heating in step (b) can advantageously be carried out at a temperature higher than the evaporation temperature of the hydro-alcoholic mixture but lower than the boiling temperature of the volatile alcohol B taken alone, under the pressure conditions applied.

[0050] According to a characteristic, for case 1, the heating in step (b) can be carried out at a temperature higher than the evaporation temperature of the hydro-alcoholic mixture and that of the volatile alcohol B taken alone, under the applied pressure conditions. In this case, all of the alcohol B is vaporized.

[0051] Step (b) is preferably carried out at a pressure lower than atmospheric pressure, preferably at a pressure of between approximately 10 mbar and approximately 500 mbar, preferably between approximately 10 mbar and approximately 250 mbar and / or at a temperature of between approximately 40 and approximately 120°C, preferably between approximately 50 and approximately 85°C. Advantageously, the use of a low pressure makes it possible to reduce the temperature allowing the volatile species to evaporate and therefore to limit the energy consumption linked to heating. The temperature and pressure conditions can be chosen in these ranges depending on the solvent or alcohol B, and depending on the case 1 or 2 retained.

[0052] In this step (b), for a given pressure, the heating is preferably carried out at a temperature higher than the evaporation temperature of the hydroalcoholic mixture. In the case where the azeotropy point is reached, it is possible but not essential for this temperature to be lower than the boiling point of the volatile alcohol A taken alone. Step (b) can have a determined duration to obtain a concentrate more or less concentrated in solid matter, which can range from viscous liquid to a paste, a solid, or a powder. According to one embodiment of the invention, the process produces a concentrate comprising catalytic particles and an electrolytic polymer, and water representing from 0 to 40, preferably from 1 to 40, typically from 5 to 25% or even from 5 to 15%, by weight relative to the concentrate.The conditions of the heating step that allow this result to be achieved, namely temperature, pressure, volatile alcohol A content, choice of this alcohol and also the heating time and the evacuation of the vapors formed, are parameters to be taken into account. It should be noted that a fresh ink typically has a water content ranging from 50 to 85% by weight of water relative to the total weight of the fresh ink. A dried ink typically has a water content ranging from 0 to 3% by weight relative to the total weight of the dried ink.

[0053] The temperature and pressure conditions, and the duration of heating under these temperature and pressure conditions, are chosen so that substantially all of the alcohol A is evaporated. In one aspect of the invention, all or part of the water present is also evaporated. The pressure and temperature conditions are controllable by a person skilled in the art to be just sufficient and effective to evaporate substantially all of the alcohol A and part of the other volatile species under the conditions chosen, including taking into account azeotropic behavior of the mixture of alcohol A, water, and optionally alcohol B. These conditions make it possible to control with sufficient precision the final concentration of solid matter in the concentrate, relative to the residual liquid phase (not evaporated) formed of water, solvent C, and optionally alcohol B.

[0054] The catalytic ink residues in fact generally contain a solvent C, preferably a polyhydric alcohol, which is not evaporated under the heating conditions in (b), and this solvent C is found in the concentrate in the known relative quantities with the catalytic particles and the electrolytic polymer of the original ink.

[0055] Solvent C is generally a solvent 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. Consequently, the concentrate according to the invention contains this or these compounds initially present in the catalytic ink residues.

[0056] 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, in order to limit energy expenditure during the heating stage, and during the possible recycling of effluents.

[0057] According to one method, in (e), (i) a known quantity of concentrate is mixed, (2i) a known quantity of fresh catalytic ink of composition substantially identical to the initial composition of the ink having generated said residues, and (3i) a known quantity of volatile solvent B and water, whereby a final catalytic ink is obtained containing a known proportion of recycled ink, the quantities of (i) 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 whose residues have just been recycled into this final ink. The quantities of (i) and (3i) are such that they reconstitute a reconstituted ink substantially of the same composition as the fresh catalytic ink.

[0058] According to one method, in particular if there is an excess of water in the concentrate compared to the fresh ink or the final ink targeted, it is possible to add ink compounds other than water (e.g. electrolytic polymer, catalytic particles, alcohol B and solvent C) in relative quantities which are similar between the concentrate and the fresh ink.

[0059] When heating (b), it is preferable that at least the surface of the effluent is subjected to the action of a stirring or agitation device, or to jets of air or liquid, and the like. This makes it possible, in particular, to reduce or prevent phenomena of projection of material linked to the formation of steam in the area close to the surface of the effluent, and to promote evaporation.

[0060] According to one embodiment, the method comprises in (e), the formation of a fresh ink from the concentrate, comprising the addition to the concentrate of appropriate quantities of water and alcohol B, and optionally other ingredients such as solvent C.

[0061] In one embodiment, a shut down ink production line is cleaned, the concentrate is recovered, the concentrate is stored, the ink production line is restarted, and a controlled addition of the concentrate, volatile alcohol B and water is carried out in a production step of the ink produced by the restarted production line.

[0062] In another embodiment, a shut-down ink production line is cleaned, the concentrate is recovered, and the concentrate is used to make a controlled addition of the concentrate, volatile alcohol B, and water to the ink produced by a second production line.

[0063] In both cases, the concentrates from 2 or more cleanings can be stored and all or part of these successive concentrates or a mixture or pool of them can be incorporated into fresh ink production.

[0064] Depending on the solids concentration of the concentrate, a mixture with a low-boiling alcohol and / or water may be required to thin the concentrate before mixing it with the fresh ink. Adjustments to the quantities of water and this solvent can also be made at this stage.

[0065] Advantageously, evaporation or separation between distillate and concentrate or fractional distillation can be carried out to recover water, alcohol B, and solvent or alcohol C. These recovered products can be reused in the recycling process, in the hydro-alcoholic cleaning composition for water and alcohol B, or as an adjustment ingredient for alcohol A and water.

[0066] The concentrate is more or less concentrated in solid matter, ranging from a more or less fluid liquid, to a viscous liquid, to a paste, to a solid, or to a powder.

[0067] The concentrate therefore differs more or less from a catalytic ink in terms of its solids content and / or its solvent content, e.g. water. With its reduced volume, or even pasty, solid or powdery consistency, this concentrate can be easily stored, handled, packaged, shipped, etc.

[0068] Thus, the invention also relates to a concentrate of pasty, solid or powder consistency.

[0069] The invention relates in particular to a concentrate comprising catalytic particles and an electrolytic polymer, and water representing from 0 to approximately 40%, in particular from approximately 1 to approximately 40%, preferably from approximately 5 to approximately 25% or even from 5 to 15% by weight relative to the concentrate.

[0070] It also relates to a concentrate obtained or capable of being obtained by implementing the process described above.

[0071] The invention also relates to the use of such a concentrate to supplement a fresh ink or to serve as a base for the formulation of a fresh ink.

[0072] The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of embodiments of catalytic inks and their application to a base membrane for a fuel cell, given solely by way of example and referring to the figures.

[0073] [Fig 1] Figure 1 is a graph showing the Karl-Fisher monitoring of the water content of the concentrate as a function of evaporation time.

[0074] [Fig 2] Figure 2 is a graph showing the polarization curve corresponding to the membrane electrode assembly whose cathode comes from a partially (20%) recycled ink (example 1) compared to that obtained with a membrane comprising a reference cathode. Surface current density i (A / cm 2 ) on the abscissa, Ewe voltage (V) on the ordinate.

[0075] [Fig 3] Figure 3 is a graph showing the polarization curves corresponding to the membrane electrode assembly whose cathode comes from partially (5, 10, 20%) recycled ink (examples 2, 3 and 4) compared to that obtained with a membrane comprising a reference cathode. Surface current density i (A / cm 2 ) on the abscissa, Ewe voltage (V) on the ordinate.

[0076] Example 1: Catalytic ink containing 20% ​​recycled solids with a first formulation

[0077] Step 1: Effluent concentration process

[0078] The catalytic effluents to be treated in this example are artificially created by diluting a freshly formulated ink containing a Pt / C (high surface area carbon / high platinum) catalyst, an electrolyte polymer (sold under the brand name Nation®), 1-propanol, water, and ethylene glycol in a water / ethanol solution that simulates the role of a wash solution. The dilution ratio is 1:20.

[0079] 350 mL of this catalytic effluent (ink residues + water / ethanol mixture) are introduced into the 2L evaporation flask of a rotary evaporator. The flask thus filled is placed in a water bath at 60°C and subjected to a rotation of 50 rpm. The entire assembly is connected to a pump allowing vacuum to be drawn and the pressure inside the assembly to be controlled. The solvents have the following boiling points: ethanol: 78°C; 1-propanol: 97.1°C; water: 100°C; ethylene glycol: 197.6°C. The evaporation process begins at a pressure of 200 mbar and is gradually lowered in stages to avoid bubbling phenomena linked to the increasing concentration of electrolytic polymer.At the end of evaporation, a plateau of 30 mbar is reached and the vacuum is cut when the viscosity of the fluid no longer changes (which is evaluated in the examples by observing the evolution of the appearance of the concentrate and stopping when it no longer changes with the naked eye, and appears as a more or less dry paste). The final water content of the concentrate can then be measured by the Karl-Fischer method: here it is 15% by mass. The monitoring of the evaporation was also carried out by Karl-Fischer and is available in figure 1. The graph here represents the evolution of the water content in the evaporation flask as a function of time. Evaporation begins under vacuum at 180 mbar, then the pressure is gradually lowered by carrying out stages to reach a final plateau of 30 mbar. During the first twenty minutes, the alcohols with low boiling temperatures evaporate.Indeed, the water has not yet evaporated and the mixture becomes depleted in alcohol, thus the water content increases. Then the water content reaches a plateau indicating that the composition of the mixture is no longer changing. There are therefore no more low-boiling alcohols to evaporate: they have been eliminated. In a third step, the water content decreases: the water evaporates. Evaporation is continued until a concentrated mixture with a water content of approximately 15% is obtained. The concentration step is then considered complete because there is no more ethanol in the concentrate and the concentrate is sufficiently concentrated to proceed with reformulation.

[0080] Step 2. Formulation of a partially recycled ink

[0081] To make 20 grams of 20% partially recycled ink, 1.086 grams of concentrate are added to a 100 milliliter beaker, along with 2.364 grams of deionized water and 0.522 grams of 1-propanol (Fisher, purity greater than 99%). 16.028 grams of fresh ink, identical in composition to that used for dilution, are added to the beaker. The resulting solution is then magnetically stirred and mixed using a rotor-stator mixer.

[0082] Step 3. Characterization of partially recycled ink

[0083] 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 0.1 and 500 s -1 (per second) and at a temperature of 20°C. The ink has a shear-thinning behavior and has a viscosity of 0.7 pascals per second for a shear rate of 1 s -1, measured at a temperature of 20°C.

[0084] Step 4. Depositing the ink

[0085] The ink is deposited onto a PFSA (perfluorosulfonic acid) proton exchange membrane using a bar coater. The desired amount of platinum is between 0.8 and 1.2 milligrams of platinum per square centimeter of membrane. To evaporate the solvent, the ink-coated membrane is heated for several minutes.

[0086] Example 2: Catalytic ink with 20% recycled solids with a second formulation

[0087] Step 1: Effluent concentration process The catalytic effluents recovered and to be treated come from the washing of an ink production tank containing a Pt / C catalyst (high surface area carbon / medium platinum content), an electrolytic polymer (sold under the brand name Aquivion®), propanol, water and ethylene glycol.

[0088] 350 mL of this catalytic effluent (ink residues + water / ethanol mixture) are introduced into the 2L evaporation flask of a rotary evaporator. The flask thus filled is placed in a water bath at 60°C and subjected to a rotation of 50 rpm. The entire assembly is connected to a pump allowing vacuum to be drawn and the pressure inside the assembly to be controlled. The solvents have the following boiling points: ethanol: 78°C; 1-propanol: 97.1°C; water: 100°C; ethylene glycol: 197.6°C. The evaporation process begins at a pressure of 180 mbar and is gradually lowered in stages to avoid bubbling phenomena linked to the increasing concentration of electrolytic polymer. At the end of evaporation, a plateau of 30 mbar is reached and the vacuum is broken when the viscosity of the fluid no longer changes. The final water content of the concentrate can then be measured by the Karl-Fischer method: here it is 7% by mass.

[0089] Step 2. Formulation of a partially recycled ink

[0090] To produce 30 grams of 20% partially recycled ink, 1.538 grams of concentrate are added to a 100 milliliter beaker, along with 3.774 grams of deionized water and 0.808 grams of 1-propanol (Fisher, purity greater than 99%). 23.887 grams of fresh ink, identical in composition to that produced in the batch from which the ink residues originated, are added to the beaker. The resulting solution is then magnetically stirred and mixed using a rotor-stator mixer.

[0091] Step 3. Characterization of partially recycled ink

[0092] 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 0.1 and 500 s -1(per second) and at a temperature of 20°C. The ink has a shear-thinning behavior and has a viscosity of 0.1 pascal second for a shear rate of 1 s -1 , measured at a temperature of 20°C.

[0093] Step 4. Depositing the ink

[0094] The ink is deposited onto a membrane (standard PFSA membrane for PEMFC MEAs - Proton Exchange Membrane Fuel Cells or proton exchange membrane batteries) using a bar coater. The desired amount of platinum is between 0.3 and 0.5 milligrams of platinum per square centimeter of membrane. The ink-coated membrane is heated to evaporate the solvent. containing 10% solids Step 1: Effluent concentration process

[0095] The catalytic effluents recovered and to be treated come from the washing of an ink production tank containing a Pt / C catalyst (high surface area carbon / medium platinum content), an electrolytic polymer (sold under the brand name Aquivion®), propanol, water and ethylene glycol.

[0096] 350 mL of this catalytic effluent (ink residues + water / ethanol mixture) are introduced into the 2L evaporation flask of a rotary evaporator. The flask thus filled is placed in a water bath at 60°C and subjected to a rotation of 50 rpm. The entire assembly is connected to a pump allowing vacuum to be drawn and the pressure inside the assembly to be controlled. The solvents have the following boiling points: ethanol: 78°C; 1-propanol: 97.1°C; water: 100°C; ethylene glycol: 197.6°C. The evaporation process begins at a pressure of 180 mbar and is gradually lowered in stages to avoid bubbling phenomena linked to the increasing concentration of electrolytic polymer. At the end of evaporation, a plateau of 30 mbar is reached and the vacuum is broken when the viscosity of the fluid no longer changes. The final water content of the concentrate can then be measured by the Karl-Fischer method: here it is 7% by mass.

[0097] Step 2. Formulation of a partially recycled ink

[0098] To produce 30 grams of 10% partially recycled ink, 0.746 grams of concentrate are added to a 100 milliliter beaker, along with 1.835 grams of deionized water and 0.396 grams of 1-propanol (Fisher, purity greater than 99%). 27.016 grams of fresh ink initially produced in the batch from which the effluents originate are added to the beaker. The resulting solution is then magnetically stirred and mixed using a rotor-stator mixer.

[0099] Step 3. Characterization of partially recycled ink

[0100] 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 0.1 and 500 s -1and at a temperature of 20°C. The ink has a shear-thinning behavior and has a viscosity of 0.21 pascal seconds for a shear rate of 1 s -1 , measured at a temperature of 20°C.

[0101] Step 4. Depositing the ink

[0102] 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. The ink-coated membrane is heated to evaporate the solvent. containing 5% solids Step 1: Effluent concentration process

[0103] The catalytic effluents recovered and to be treated come from the washing of an ink production tank containing a Pt / C catalyst (high surface area carbon / medium platinum content), an electrolytic polymer (sold under the brand name Aquivion®), propanol, water and ethylene glycol.

[0104] 350 mL of this catalytic effluent (ink residues + water / ethanol mixture) are introduced into the 2L evaporation flask of a rotary evaporator. The flask thus filled is placed in a water bath at 60°C and subjected to a rotation of 50 rpm. The entire assembly is connected to a pump allowing vacuum to be drawn and the pressure inside the assembly to be controlled. The solvents have the following boiling points: ethanol: 78°C; 1-propanol: 97.1°C; water: 100°C; ethylene glycol: 197.6°C. The evaporation process begins at a pressure of 180 mbar and is gradually lowered in stages to avoid bubbling phenomena linked to the increasing concentration of electrolytic polymer. At the end of evaporation, a plateau of 30 mbar is reached and the vacuum is broken when the viscosity of the fluid no longer seems to change. The final water content of the concentrate can then be measured by the Karl-Fischer method: here it is 7% by mass.

[0105] Step 2. Formulation of a partially recycled ink

[0106] To produce 30 grams of 5% partially recycled ink, 0.384 grams of concentrate are added to a 100 milliliter beaker, along with 0.964 grams of deionized water and 0.196 grams of 1-propanol (Fisher, purity greater than 99%). 28.459 grams of fresh ink initially produced in the batch from which the effluents originate are added to the beaker. The resulting solution is then magnetically stirred and mixed using a rotor-stator mixer.

[0107] Step 3. Characterization of partially recycled ink

[0108] 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 0.1 and 500 s -1and at a temperature of 20°C. The ink has a shear-thinning behavior and has a viscosity of 0.17 pascal seconds for a shear rate of 1 s -1 , measured at a temperature of 20°C.

[0109] Step 4. Depositing the ink

[0110] 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. The ink-coated membrane is heated to evaporate the solvent. necessary for reformulation The formulations cited in the previous examples are based on precise knowledge of the composition of the concentrate. Knowing this composition is necessary to control the addition of ingredients to formulate an ink of known qualitative and quantitative composition incorporating a determined proportion of recycled ingredients. The composition of the concentrate is known thanks to various hypotheses which will be specified in the following paragraph and thanks to the analysis of the water content in this concentrate.

[0111] - First, the ink waste remaining at the bottom of the reactor after the production of a batch of ink retains the same composition as the ink from which it originated. Therefore, cleaning the reactor can be considered as a "diluting of the ink" in the wash water. The weight percentage of the different compounds (except ethanol and water) in the effluent is then proportional to the initial values ​​of the weight percentage. The composition of the solid (electrolytic polymer / Pt / C ratio) can thus be considered constant throughout the process.

[0112] - No loss of non-evaporable compounds introduced into the reactor / flask during the evaporation process. Therefore, the initial mass of Pt / C, electrolytic polymer and high-boiling solvent in the effluent introduced into the reactor is equal to the final mass obtained at the end of the process in the reactor / flask.

[0113] During evaporation, all of the solvent C added to the evaporation flask / reactor is considered to remain present. Solvent B is considered to be completely evaporated.

[0114] Finally, the water content is measured by Karl-Fischer assay.

[0115] Thanks to this and the known contents, it is possible to establish a proportional link between the content of one of the components of the concentrate and the content of this same component initially in the ink produced in the batch.

[0116] For Y a component of the concentrate, namely the electrolytic polymer, the catalyst or the solvent C, the relationship is of the form: wt%(Y') recyclat= wt%(Y) ink * where wt% is the mass fraction and A is a constant depending on the water content in the ink produced in the batch, the water content in the concentrate and the propanol (or other volatile alcohol C) content initially in the ink produced in the batch.

[0117] Results: In example 1, the ink deposition was made on a membrane with a surface area of ​​36 cm 2and drying did not raise any flammability issues. The appearance of the ink layers was observed with the naked eye; the surface appearance was homogeneous with little or no cracking. The polarization curve corresponding to the membrane-electrode assembly whose cathode comes from a partially recycled ink is confused with that corresponding to the MEA (membrane-electrode assembly) with a reference cathode (Figure 2). Both MEAs were assembled with the same GDLs (Gas Diffusion Layers), the same proton exchange membrane and the same anode to facilitate comparison. The active surface area of ​​these MEAs is equal to 25 cm 2 .

[0118] The performance of two MEAs was compared. These two MEAs are identical in every way except for the cathodic catalytic layer. The reference MEA was made with fresh cathodic ink while the recycled MEA was made with 20% recycled cathodic ink. The polarization curves of these two MEAs are displayed above and are superimposed. It is then possible to state that the use of recycled ink made with the high platinum catalyst and with Nation® allows to obtain the same electrochemical performances as an MEA using a fresh reference ink of identical composition.

[0119] In examples 2, 3 and 4, the ink deposition was made on a membrane with a surface area of ​​36 cm 2and drying did not raise any flammability issues. The appearance of the ink layers was observed with the naked eye, the surface appearance was homogeneous with little or no cracking. The active surface area of ​​these MEAs is equal to 25 cm 2 The electrochemical performances were found to be satisfactory and in line with what is expected for an MEA whose membrane has been coated with a standard fresh ink: > 0.6 V at 1 A / cm 2 (figure 3).

[0120] The performances of four MEAs were compared. These MEAs are identical in all respects except for the cathodic catalytic layer. The reference MEA was made with a fresh cathodic ink while the recycled MEAs were made with a cathodic ink including 5, 10 or 20% recycled solids. The polarization curves of these MEAs are displayed above and are all superimposed except for the MEA made with a 5% recycled ink which shows better performances. These superior performances are due to parameters independent of the influence of the catalytic layer. On the other hand, it is possible to affirm that the use of recycled ink made with the medium platinum catalyst and with Aquivion® allows to obtain the same electrochemical performances as an MEA using a fresh reference ink of identical composition. Conclusions:

[0121] It was possible to implement and propose an efficient and reproducible evaporation process. The reformulated inks by integrating the concentrates after the evaporation procedure are similar in appearance to the reference inks. The reformulated inks have similar physicochemical properties to the references and can be applied to a base membrane or GDL by the same methods as the references. The catalytic ink layers are obtained, and satisfactory electrochemical properties, similar to the references, are obtained.

Claims

CLAIMS 1. A method for recycling catalytic ink residues, said residues comprising catalytic particles, an electrolytic polymer, water, optionally an organic solvent, in known relative quantities, the method comprising (a) providing an effluent, said effluent comprising catalytic ink residues and water or a hydro-alcoholic mixture of water and alcohol A, said effluent containing catalytic particles and electrolytic polymer substantially in their relative quantities known in the catalytic ink, (b) heating this effluent to a temperature point and pressure causing the evaporation of water and / or alcohol A in the form of a vapour phase, and the formation of a concentrate containing catalytic particles and electrolytic polymer in said relative quantities, (c) the separation between the vapor phase and the concentrate, (d) recovering this concentrate containing catalytic particles and polymer in their known relative quantities in the catalytic ink.

2. Method according to claim 1, characterized in that, in (a), the method comprises cleaning a catalytic ink production and / or deposition installation, using water or a hydro-alcoholic 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.

3. Method according to claim 1 or 2, characterized in that the effluent in (a) contains a hydro-alcoholic mixture and this comprises an alcohol A having a boiling temperature lower than that of water, and heating is carried out in (b) to evaporate this alcohol A.

4. Method according to the preceding claim, in which the alcohol A is ethanol.

5. Method according to any one of the preceding claims, in which the hydro-alcoholic mixture in (a) comprises from 10 to 90% of alcohol A by weight, preferably from 40 to 60% of alcohol A by weight, defined relative to the total weight of water + alcohol.

6. Method according to any one of the preceding claims, further comprising, in (e), adding the concentrate (d) to a fresh ink, in particular at a proportion by mass of solid of concentrate of 1 to 30%, preferably of 1 to 10%, relative to the mass of solid of the fresh ink.

7. Method according to claim 6, characterized in that, in (e), to a fresh ink having determined relative quantities of catalytic particles, electrolytic polymer and water, quantities of concentrate and optionally water are added, calculated to reproduce the determined relative quantities of the fresh ink.

8. Method according to claim 6 or 7, in which in (e), the water content of the concentrate is first measured, making it possible to determine the addition of water necessary to recover the relative quantities of the catalytic particles, the electrolytic polymer, and the water of the fresh ink, then the concentrate, optionally water, and fresh ink having the same relative quantities of catalytic particles and electrolytic polymer as the concentrate are mixed.

9. Method according to any one of the preceding claims, in which the catalytic ink residues further contain a volatile solvent B, preferably an alcohol, having a boiling point between 75 and 130°C at atmospheric pressure, in a known relative quantity, and the heating in (b) is carried out at a temperature above the evaporation temperature of the hydro-alcoholic mixture but below the boiling point of the volatile alcohol B taken alone, under the pressure conditions applied.

10. Method according to any one of claims 6 to 9, in which the catalytic ink residues further contain a volatile solvent B, preferably an alcohol, having a boiling point of between 75 and 130°C at atmospheric pressure, in a known relative quantity, and the quantity of this solvent B removed in (b) is taken into account, to carry out an addition of this solvent B in (e) and compensate for this loss due to evaporation.

11. A method according to any one of the preceding claims, wherein the catalytic ink residues further contain a solvent C, preferably a polyhydric alcohol, which is not evaporated under the heating conditions in (b), and this solvent C is found in the concentrate in the known relative amounts with the catalytic particles and the electrolytic polymer.

12. A method according to any preceding claim, further comprising, in (e), forming a fresh ink, comprising adding to the concentrate appropriate amounts of water and alcohol B.

13. Catalytic ink concentrate comprising catalytic particles and an electrolytic polymer, and water representing from 0 to 40, preferably from 1 to 40, typically from 5 to 25% by weight relative to the concentrate.

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