Method for reusing effluents from a cvi process

Abstract

The invention relates to a method for recycling effluents (10) from a chemical vapour infiltration process, the method comprising at least the following steps: - a step (E1) of separating effluent gases from a chemical vapour infiltration process that makes it possible to separate these effluents into a heavy portion (101) and a light portion (201); - a step (E2) of reforming the heavy portion (201) obtained at the end of the separation step, the reforming step being carried out under thermodynamically favourable conditions for obtaining unsaturated hydrocarbons comprising chains with two carbon atoms; - a step (E3) of hydrogenating the products obtained at the end of the reforming step; then - a step of reintroducing the transformed effluents (104) into an enclosure intended for carrying out a chemical vapour infiltration process (E5).

Description

Process for valorizing effluents from a CVI process Technical Field

[0001] This presentation concerns a chemical vapor phase infiltration process and more specifically a process for recycling the effluents of such a process which reduces the amount of reagents to be introduced. Previous technique

[0002] Carbon / pyrolytic carbon material parts are attracting increasing technological interest due to the good compromise they offer in terms of strength and weight.

[0003] It is known to produce carbon / carbon pyrolytic parts by chemical infiltration or chemical vapor deposition. Such processes use a carbon-rich reactive gas phase, particularly light hydrocarbons, which is brought into contact with porous substrates under conditions such that the gas phase can react with the substrate to form a matrix within the substrate's pores. The choice of gas for the gas phase and the temperature and pressure conditions in the furnace determine the nature of the matrix formed within the composite parts.

[0004] However, such processes generate gaseous effluents to produce a final part. These effluents are generally not recovered in current processes. Recovering these effluents would reduce costs and the environmental footprint of the preparation processes, and therefore of the parts obtained.

[0005] On the other hand, chemical vapor phase infiltration processes used for the manufacture of a carbon / carbon composite material use a reactive gas phase consisting mainly of methane but also a longer alkane, for example ethane, propane or unsaturated species such as propene or acetylene.

[0006] This compound initiates the radical reactions involved in the chemical vapor infiltration process. Furthermore, the longer alkane also acts as an initiator of the radical reaction mechanism required for the production of a carbon / carbon composite material.

[0007] However, while sources of such longer alkanes are numerous, obtaining them in good purity is more complex. Furthermore, supply possibilities are dwindling due to increasing pressures on natural gas supply. This necessitates to manufacturers of carbon / carbon composite materials to find new sources for these initiators of the pyrocarbon deposition reaction. Description of the invention

[0008] The invention aims precisely to address both of these problems simultaneously.

[0009] For this purpose, it concerns a process for recycling effluents from a chemical vapor infiltration process comprising at least the following steps: - a gas separation step from a chemical vapor phase infiltration process allowing these effluents to be separated into a heavy portion and a light portion; - a reforming step of the heavy portion obtained at the end of the separation step, the reforming step being carried out under thermodynamically favorable conditions for obtaining unsaturated hydrocarbons comprising chains with two carbon atoms; - a hydrogenation step of the products obtained at the end of the reforming step; then - a step of reintroducing the transformed effluents into a chamber intended for carrying out a chemical vapor phase infiltration process of the products from the hydrogenation step.

[0010] The described process makes it possible to generate, from the effluents of a process, a reagent of great value for that same process.

[0011] These effluents are usually destined for destruction. The described process thus reduces the ecological footprint of a chemical vapor infiltration process by recycling a portion of the reactive phase that has not been consumed.

[0012] In one embodiment, the effluent gas separation step of a vapor phase infiltration process is preceded by a first step of trapping polycyclic aromatic hydrocarbons.

[0013] The presence of such trapping reduces cleaning needs and increases the lifespan of all the elements used to carry out the steps of the described process.

[0014] Indeed, particularly when they are no longer under the pressure and temperature conditions of a chemical vapor phase infiltration process, polycyclic aromatic hydrocarbons can deposit as solid soot and cause fouling of pipes and enclosures.

[0015] The chemical vapor infiltration process is usually carried out at reduced pressure, and such soot is not problematic in the main containment of a such a process. However, this is not necessarily the case for all the steps of the recycling process described above, and that is why it is preferable to remove polycyclic aromatic hydrocarbons from the gaseous effluents as soon as they leave the furnace.

[0016] In one embodiment, the effluent gas separation step can be carried out by distillation or stripping.

[0017] Preferably, the separation step is carried out by stripping, i.e. by extraction with an inert gas.

[0018] In one embodiment, stripping can be carried out with methane or nitrogen as an inert gas.

[0019] In particular, in one embodiment, stripping can be carried out at atmospheric pressure.

[0020] Alternatively, the stripping step can be carried out under reduced pressure, which also limits the amount of inert gas used.

[0021] In one embodiment, the effluent gas separation step can be carried out at a pressure between 1.0 mbar abs and 1.2 bar abs, or even between 10 mbar abs and 1.05 bar abs, better between 100 mbar abs and 1.05 bar abs.

[0022] The unit "bar abs" is read as absolute bar and understood to characterize absolute pressure in the usual sense of this term in the field of process engineering, i.e. a pressure scale where 0 is absolute vacuum.

[0023] In one embodiment, the separation step can be carried out at a temperature between 70°C and 140°C, or even between 80°C and 120°C.

[0024] Vapor-phase pyrocarbon chemical infiltration processes utilize mixtures of gaseous hydrocarbons that pass through reactors, undergoing multiple chemical transformations. Chemical equilibrium conditions are not met, often due to insufficient residence times. At the reactor outlet, the gaseous mixture, also called effluent gas or effluent, contains a wide range of hydrocarbon compounds. The gaseous mixture consists primarily of methane and dihydrogen, with a concentration exceeding 70% by volume. The remainder of the mixture comprises hydrocarbons, including alkanes, alkenes, and alkynes with at least two carbon atoms. Aromatic compounds are also present, such as benzene, toluene, ethylbenzene, and / or xylene. The heaviest compounds are polycyclic aromatics. The separation step divides the effluent gases into two parts: a light portion and a heavy portion. The light portion is primarily composed of methane and hydrogen, and also includes hydrocarbons with two or three carbon atoms. The heavy portion comprises the compounds present in the effluent gases that are not found in the light portion, particularly aromatic compounds present in the effluent mixture. In one particular embodiment, the light portion consists mainly of methane, hydrogen, and hydrocarbons with two or three carbon atoms.

[0025] The heavy phase may contain compounds that do not originate from the gaseous effluents. For example, in one particular embodiment, the separation step is carried out using an absorption fluid, and the regeneration of the absorption fluid can be achieved by stripping with natural gas, so that the stripping gas ends up in the heavy portion.

[0026] Starting from effluent gases from a chemical vapor infiltration process, the separation step allows a light portion, mainly consisting of dihydrogen and methane, to be separated from a heavy portion which includes alkanes, alkenes or alkynes comprising at least two carbon atoms, for example four or more carbon atoms, and in particular aromatic compounds, for example benzene, toluene, ethylbenzene and / or xylene.

[0027] The lighter portion can be reused either as is or after one or more chemical transformation(s).

[0028] In one process of the invention, it is the heavy portion of the separation that is proposed to be recovered. This portion is usually considered as waste, particularly since it comprises a mixture of mainly aromatic and predominantly unsaturated species.

[0029] In one embodiment, the heavy phase obtained after the separation step is used as a reagent in a reforming step.

[0030] The reforming stage allows the creation of given hydrocarbons, by applying specific temperature and pressure conditions that thermodynamically favor the desired species.

[0031] In one embodiment, the reforming step can be carried out at a temperature between 1000°C and 1300°C.

[0032] In one embodiment, the reforming step can be carried out at a pressure between 10 mbar abs and 800 mbar abs and preferably between 100 mbar abs and 600 mbar abs.

[0033] These pressure and temperature conditions are optimal for the thermodynamic stability of unsaturated hydrocarbons comprising two-carbon chains, notably acetylene and ethylene, compared to other carbon species.

[0034] In one embodiment, the reforming step can be carried out in the presence of dihydrogen, which limits the polymerization of any aromatic compounds present into polycyclic aromatic compounds.

[0035] In one embodiment, the reforming step can be carried out in the presence of one or more catalysts.

[0036] Such catalysts make it possible to choose precisely which species will be obtained under the pressure and temperature conditions of the reforming stage.

[0037] In one embodiment, such a catalyst can be solid carbon.

[0038] Indeed, the presence of solid carbon plays a catalytic role in the chemical reactions involved in the reforming stage, and in particular as a support for heterogeneous reactions.

[0039] For example, the solid carbon used in the reforming step can be introduced into the reforming chamber in the form of chopped fibers or graphite powder, for example compressed into beads or pellets. In one embodiment, the solid carbon can consist of carbon fiber scraps, for example, carbon fibers from the waste of a weaving process.

[0040] The particular choice of solid carbon as a catalyst for the reaction also allows excellent resistance of the catalyst to the phenomenon of carbon fouling (known as "coking") observed for other catalysts of the prior art.

[0041] In one embodiment, the catalyst can be carbon fibers arranged in the form of a sheet or block, arranged so that the gas has no preferential path.

[0042] This ensures controlled flow in the reactor, resulting in a better controlled residence time in the reactor.

[0043] Furthermore, this allows for a flow close to that of a piston flow.

[0044] In one embodiment, prior to the reforming step, natural gas and / or a portion of the light phase may be added to the heavy phase of the separation undergoing the reforming step.

[0045] If necessary, this allows increasing the quantity of reagents available for the reforming phase and thus creating a larger quantity of products at the end of the process.

[0046] This can be particularly useful at the beginning of the process, when gaseous effluents are not yet present in sufficient quantity to obtain enough of the compounds reintroduced in the chemical vapor phase infiltration step.

[0047] After the reforming step, the process may include a hydrogenation step of the reforming products to convert unsaturated hydrocarbons into alkanes. This catalytic hydrogenation transforms the alkenes and alkynes formed at the end of the reforming step into alkanes without altering the length of their carbon chains.

[0048] Catalytic hydrogenation then makes it possible to transform dihydrogen and unsaturated species which would not allow the formation of a pyrolytic carbon deposit into linear alkanes which can then be used.

[0049] In one embodiment, at least part of the dihydrogen used for the hydrogenation step is derived from the effluent gases of a chemical vapor phase infiltration process.

[0050] For example, at least some of the dihydrogen used for the hydrogenation step can be obtained after separating the gases from the light portion of the earlier separation step, provided that the remainder of the light portion has not undergone chemical transformations consuming all of the dihydrogen it contained.

[0051] The process finally includes a step of introduction into a chamber intended for carrying out a chemical vapor phase infiltration process of the transformed effluents.

[0052] The expression "transformed effluents" is intended to characterize the effluent gases from a chemical vapor infiltration process that have undergone transformation steps such as reforming, hydrogenation and possibly separation.

[0053] In other words, the process and steps described thus make it possible to provide a portion of the reagents needed for a chemical vapor infiltration process using effluents, and it is these effluents that are transformed for valorization.

[0054] The reagents provided do not replace the large quantities of methane needed, but they can replace the longer alkanes introduced together with methane in a chemical vapor phase infiltration process, which allow the radical mechanisms enabling the pyrolysis of methane to be initiated.

[0055] These longer alkanes, introduced in a smaller proportion, ensure an acceleration of the infiltration kinetics of the gaseous reactive phase, and are used in the process as initiators of radical mechanisms.

[0056] They are currently less commercially available than methane or natural gas, and having such a process makes it possible to avoid the risk of supplying these alkanes, which are nevertheless essential for the processes.

[0057] In one embodiment, the process may further include a separation step after the hydrogenation step and before the reintroduction of the transformed effluents into a chamber intended for carrying out a chemical vapor phase infiltration process.

[0058] Such a separation step can in particular allow the selective removal of dihydrogen which may not have reacted during the hydrogenation step of the stream reintroduced into the chemical vapor phase infiltration process.

[0059] Such a separation step ensures that the reintroduced stream is even richer in hydrocarbons and comprises less than 5.0% by volume, or even less than 1.0% by volume of dihydrogen or does not contain any dihydrogen.

[0060] In one embodiment, such a separation step can be carried out by membrane separation.

[0061] For example, the gas stream intended for the separation step may include a compression step, for example to a pressure between 4 bar abs and 9 bar abs, then exposure of said gas stream to a membrane permeable to short-chain carbon alkanes, and then to a membrane permeable only to dihydrogen.

[0062] This allows the separation of the dihydrogen, which passes through the membrane and constitutes the permeate of the separation step, from the rest of the gas stream. The remaining gas stream is the retentate of the membrane separation step and is intended to be reintroduced into the chamber for the vapor-phase infiltration process.

[0063] Such membrane separation is particularly preferred in the process described here because it allows excellent separation of dihydrogen from the gas stream. intended to be reintroduced into a chamber intended for the implementation of a chemical vapor phase infiltration process.

[0064] In one embodiment, the dihydrogen isolated by the separation step can be reused for the hydrogenation step. Alternatively, the dihydrogen can be used for other purposes independent of the process described, for example, methanation processes. Brief description of the drawings

[0065] [Fig. 1] Figure 1 is a schematic representation of a process in one embodiment of the invention. Description of the implementation methods

[0066] The invention is now described by means of figures, which are provided for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0067] For the sake of simplicity, Figure 1 represents a more complex embodiment than the one claimed, describing numerous optional steps. For clarity, the optional steps are shown as dashed lines.

[0068] Figure 1 first represents a chemical vapor phase infiltration step E5.

[0069] Typically, this E5 step is carried out in a densification oven and allows, for example, the deposition of pyrocarbon onto fibrous preforms containing carbon.

[0070] It can be achieved by introducing into a chamber comprising the said fibrous preforms, a gaseous feed stream comprising between 75% and 95% by volume of methane and other longer linear alkanes, for example ethane or propane.

[0071] These longer alkanes play a role in accelerating the kinetics of pyrocarbon deposition during the chemical vapor phase infiltration process.

[0072] After step E5, a gaseous phase 10 emerges from the enclosure in which step E5 was carried out.

[0073] This gaseous phase 10 includes, in particular, dihydrogen, formed after some of the carbon from the reactive phase 1000 has been deposited in the form of pyrocarbon.

[0074] The gaseous phase 10 further includes linear alkanes composing the initial reactive phase 1000 which have not reacted.

[0075] The gaseous phase 10 finally includes heavier species, for example polycyclic aromatic hydrocarbons, aromatic components including benzene and toluene, formed by parasitic reactions of the reactive phase with itself which may have taken place within the chemical vapor phase infiltration enclosure.

[0076] The process may optionally include an E10 phase for trapping polycyclic aromatic hydrocarbons.

[0077] Indeed, it may be desirable to get rid of these species upstream of any subsequent process step, as polycyclic aromatic hydrocarbons can form soot which increases the need for pipe cleaning.

[0078] It is therefore preferable to carry out an E10 step for trapping polycyclic aromatic hydrocarbons as soon as the E5 step is completed.

[0079] This step can, for example, be carried out in an oil trap, sometimes called an oil gas scrubber.

[0080] After such a step, the gaseous phase 11 comprising the effluent gases from a chemical vapor-phase infiltration step E5 from which step E10 has possibly removed polycyclic aromatic hydrocarbons is used in a separation step El.

[0081] Such a separation step El should allow the gaseous phase to be separated into a heavy portion 101 and a light portion 201.

[0082] Such a separation step can be a stripping step or a distillation step.

[0083] In a preferred embodiment, step El is a stripping step.

[0084] For example, such an El step can be carried out at a temperature between 70 °C and 140 °C at a pressure between 1 mbar abs and 1.2 bar abs with methane as the inert gas for stripping.

[0085] It has been established by the inventors that these parameters allow excellent separation of the heavy 101 and light 201 portions of the effluent gases 11.

[0086] In a described process, the heavy portion 101 undergoes a reforming step E2.

[0087] Such a reforming step is carried out in a pressure and temperature environment where two-carbon-atom compounds are thermodynamically most stable.

[0088] The stability of gaseous species during a reforming step can be determined by a thermochemical calculation performed using reference data. For example, data from the NIST (National Institute of Science and Technology), the JANAF tables, and a thermochemical calculation tool such as NASA's "Chemical Equilibrium Application" can be used to establish these curves.

[0089] As an example, reference curves are described in the reference: A. Holmen et al. Fuel processing technology 42 (1995) 249-267.

[0090] More specifically, the curve proposes to establish, as a function of temperature, pressure and the variation of standard free enthalpy of a reaction, which species will be thermodynamically favored.

[0091] Thus, the inventors propose a reforming step E2 in which ethylene and acetylene are thermodynamically the most stable.

[0092] In one embodiment, the pressure of the reforming step E2 can be between 10 mbar abs and 800 mbar abs.

[0093] In one embodiment, the temperature of step E2 can be between 1000°C and 1300°C.

[0094] In one embodiment, step E2 is further carried out by placing phase 101 in the presence of solid carbon.

[0095] The inventors have indeed observed that solid carbon has a catalytic effect on the complex reactions involved in the E2 reforming step.

[0096] In one embodiment, the residence time of the gaseous phase species 101 in the reactor used for the reforming step E2 can be between 0.1 s and 2.0 s.

[0097] The inventors determined that under these conditions, step E2 allowed the reforming of the hydrocarbons composing phase 101 into ethylene and acetylene.

[0098] In one embodiment, if necessary, dihydrogen may be added to phase 101 before it undergoes step E2.

[0099] This dihydrogen can shift thermodynamic equilibria towards the production of ethylene and acetylene, or provide the dihydrogen needed for chemical reforming reactions.

[0100] In one embodiment, step E2 therefore allows the transformation of the hydrocarbons of phase 101 into a phase 102 which is also gaseous but comprising very mainly, or even being made up of, ethylene and acetylene.

[0101] In one embodiment, this step can then undergo a hydrogenation step E3 allowing both ethylene and acetylene to be transformed into ethane.

[0102] For example, the E3 hydrogenation step can be carried out at a temperature between 80°C and 130°C.

[0103] In one embodiment, the hydrogenation step E3 can be carried out at a temperature between 100°C and 110°C.

[0104] In one embodiment, step E3 may include a catalyst selected from palladium or nickel catalysts. For example, the catalyst available under the commercial reference LD465 from AXENS may be used.

[0105] In an optional embodiment, and therefore represented by dotted lines in Figure 1, at least part, or even all, of the dihydrogen required for the hydrogenation step E3 can be supplied by dihydrogen 203 extracted from the effluents of a vapor phase infiltration process 10.

[0106] In particular, this dihydrogen 203 can be recovered in the light portion 201 separated during the earlier El separation step described above.

[0107] In one embodiment, dihydrogen 203 can be recovered directly after a step E12 of separation of the different compounds of the light portion 201.

[0108] The steps that the light section 201 may undergo will be described below.

[0109] The hydrogenation step E3 which the products 102 obtained at the end of the reforming step E2 make it possible to obtain a stream 103 mainly composed of ethane, or even made up of ethane.

[0110] In one embodiment, this stream 103 can undergo an optional separation step to separate the dihydrogen introduced for the hydrogenation step E3 and which would not have reacted. [YES] In one embodiment, this separation step E4 can be carried out via the use of membranes.

[0112] For example, step E4 of separation of gas 103 from hydrogenation step E3 can be carried out by cryogenic separation.

[0113] In one embodiment, the separation step E4 may include a separation step by exposing the stream 103 to a dihydrogen-selective membrane.

[0114] In one embodiment, the separation step only includes the separation step by exposing the stream to a dihydrogen-selective membrane.

[0115] Alternatively, the E4 separation step includes a separation step by exposing the stream to a dihydrogen-selective membrane, followed by a cryogenic step.

[0116] This allows us to recover any dihydrogen present in stream 103, and, for example, reinject it into hydrogenation step E3.

[0117] For example, such a dihydrogen-selective membrane can be chosen from cellular polymer-based membranes, such as cellulose membranes or modified cellulose acetate membranes, polyimide membranes, polytetrafluoroethylene membranes.

[0118] This separation step yields a stream of ethane 104 and a stream rich in dihydrogen 105, which is shown returning to step E2 or E3, although this is not necessary. Indeed, other valorization methods can be considered for the dihydrogen 105 stream, for example, methanation.

[0119] Alternatively, the excess dihydrogen 106 stream at stage E4 can be used for other purposes.

[0120] In the process described, the 104 ethane stream is used as a reagent in a chemical vapor phase infiltration process E5.

[0121] Preferably, this chemical vapor infiltration process is carried out in the same enclosure from which the effluents originate 10.

[0122] It is understood from the preceding explanation that the process as a whole allows for the recovery of a portion of the effluents 10 of a chemical process in the vapor phase.

[0123] This reduces the need for 1000 feedstock for the said chemical vapor infiltration process.

[0124] This results in a significant economic gain as well as a reduction in the carbon footprint of the process, since the use of carbon elements required for the cycle is thus optimized compared to processes not having the E1, E2 and E3 steps.

[0125] In addition, the proposed process makes it possible to no longer be dependent on the supply sources of ethane or propane usually added to methane for chemical vapor phase infiltration processes.

[0126] Indeed, the process proposes to provide a longer linear alkane from the recycling of carbonaceous species present in the gaseous effluents of the chemical infiltration process in the vapor phase.

[0127] In addition, it allows, if necessary, the addition of methane directly to the E2 reforming step to increase the available quantity of linear alkane longer than methane, without having to resort to a Fischer-Tropsch process which presents additional constraints.

[0128] In particular, hydrocarbons produced by a Fischer-Tropsch process are longer than those obtained by a process described here, the Fischer-Tropsch process leads to the presence of water which must be removed, or the Fischer-Tropsch process includes catalytic operations sensitive to deactivation or fouling of the catalyst.

[0129] This results in a more industrially robust process which requires only methane as the main reactant 1000, with ethane being generated by recycling effluents. In one embodiment of the process, the ethane generated by the recycling of effluents can represent by volume a proportion of between 5.0% and 40% or even between 5.0% and 20% of the volume of reagents introduced.

[0131] Indeed, these concentrations are sufficient to ensure the desired role of ethane as a precursor to the radical mechanisms. Furthermore, such quantities are consistent with those actually obtained by recycling the effluents from a chemical vapor infiltration process described herein.

[0132] The steps possibly applied to the light portion 201 obtained after the El separation step will now be described.

[0133] It should be borne in mind that these operations are optional and allow for even better use of effluents 10.

[0134] In one embodiment, the light portion may first undergo a first Eli hydrogenation step.

[0135] For example, this step can be carried out under the conditions described above for the E3 hydrogenation step.

[0136] Such a step ensures that the compounds of the light phase 201 are composed solely of light alkanes at the end of the Eli step.

[0137] Thus, even if a portion of light hydrocarbons other than methane, notably acetylene, and ethylene or propene or three-carbon alkyl, had remained in the light portion 201 of the El separation step, these compounds will be in linear alkane form in the 202 stream.

[0138] Flow 202, or if the Eli step is not present, flow 201, can be exposed to a separation step E12.

[0139] Preferably, the E12 separation step is a membrane separation step, and to increase its efficiency, the 202 flow, or where appropriate 201, can be compressed initially.

[0140] The E12 separation step allows the separation of dihydrogen 203 present in the light portion 201.

[0141] For example, the E12 separation step may include exposing the 202, or 201, stream to a dihydrogen-selective membrane, for example chosen from those described for the E4 step.

[0142] In one embodiment, which is that described in Figure 1, the dihydrogen 203 can be used directly in another step of the process, for example for the hydrogenation step E3. Alternatively, the dihydrogen can join an excess dihydrogen stream 106, usable in other processes than the one described here.

[0143] In one embodiment, the separation step may include exposing the stream 202, or 201, to a membrane selective for short-chain alkanes, for example less than or equal to 3 carbon atoms.

[0144] In one embodiment, the chemical vapor phase infiltration step E5 can be a densification process of preforms comprising carbon fibers.

[0145] In other words, step E5 makes it possible to obtain carbon / carbon composite materials, for example brake discs.

Claims

Demands

1. A process for recycling effluents (10) from a chemical vapor-phase infiltration process comprising at least the following steps: - a step (El) of separating effluent gases from a chemical vapor phase infiltration process allowing these effluents to be separated into a heavy portion (101) and a light portion (201); - a reforming step (E2) of the heavy portion (201) obtained at the end of the separation step, the reforming step being carried out under thermodynamically favorable conditions for obtaining unsaturated hydrocarbons comprising chains with two carbon atoms; - a step (E3) of hydrogenating the products obtained at the end of the reforming step; then - a step of reintroducing the transformed effluents (104) into an enclosure intended for carrying out a process (E5) of chemical infiltration in the vapor phase.

2. Recycling process according to claim 1, wherein the separation step (El) is a stripping step.

3. Recycling process according to claim 1 or 2, wherein the separation step (El) is carried out at a pressure between 1.0 mbar abs and 1.2 bars abs.

4. Recycling process according to any one of claims 1 to 3, wherein the separation step (El) is carried out at a temperature between 70 °C and 140 °C.

5. Recycling process according to any one of claims 1 to 4, wherein the reforming step (E2) is carried out at a pressure between 10 mbar abs and 800 mbar abs.

6. Recycling process according to any one of claims 1 to 5, wherein the reforming step (E2) is carried out at a temperature between 1000°C and 1300°C.

7. Recycling process according to any one of claims 1 to 6, wherein the reforming step (E2) is carried out in the presence of solid carbon.

8. A process according to any one of claims 1 to 7, further comprising a separation step (E4) after the hydrogenation step (E3) and before the reintroduction of the transformed effluents into an enclosure intended for the implementation of a process (E5) of chemical infiltration in the vapor phase.

9. A process according to claim 8, wherein the separation step (E4) is carried out by membrane separation.

10. A process according to any one of claims 1 to 9, wherein at least a portion of the dihydrogen used for the hydrogenation step (E3) is derived from the effluent gases of a chemical vapor infiltration process (10).

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