Process for valorizing effluents from a CVI process

Abstract

Process for Valorizing Effluents from a CVI Process The invention relates to a process for recycling effluents (10) from a chemical vapor infiltration process comprising at least the following steps: - a step (E1) for separating the effluent gases from a chemical vapor infiltration process, allowing these effluents to be separated into a heavy portion (101) and a light portion (201); - a step (E2) for reforming 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) for hydrogenating the products obtained at the end of the reforming step; and then - a step for reintroducing the transformed effluents (104) into a vessel intended for carrying out a chemical vapor infiltration process (E5). Figure for the abstract: Fig. 1.

Description

Title of the invention: Process for valorizing effluents from a CVI process. Technical field

[0001] The present exposition relates to a chemical vapor phase infiltration process and more specifically to a process for recycling the effluents of such a process which makes it possible to reduce the quantity of reagents to be introduced. Previous technique

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

[0003] It is known to obtain parts made of carbon / pyrolytic carbon material by chemical infiltration or chemical vapor deposition. Such processes use a carbon-rich reactive gas phase, particularly light hydrocarbons, 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 constituting the gas phase and the temperature and pressure conditions prevailing in the furnace determine the nature of the matrix formed within the composite material 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 as well as 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 gaseous phase comprising mainly methane but also a longer alkane, for example ethane, propane or unsaturated species such as propene or acetylene.

[0006] The latter enables the initiation of the radical reactions involved in the chemical vapor infiltration process. In addition, the longer alkane also plays a role in initiating the radical mechanism of the reactions necessary for the manufacture 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 decreasing due to increasing tensions on the natural gas supply. This requires manufacturers of carbon / carbon composite materials to find new sources for these pyrocarbon deposition reaction initiators. Description of the invention

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

[0009] For this purpose, it relates to a process for recycling the effluents of a chemical vapor infiltration process comprising at least the following steps: - a gas separation step from a chemical vapor 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 intended for destruction. The described process thus allows for a reduction in 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 makes it possible to reduce the need for cleaning and to increase the lifespan of all the elements used to carry out the steps of the process described.

[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 be deposited in the form of solid soot and cause fouling of the ducts 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 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 oven.

[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, the stripping can be carried out with methane or nitrogen as an inert gas.

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

[0020] Alternatively, the stripping step can be carried out under reduced pressure, which also makes it possible to limit the amount of inert gas then 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 “abs bar” 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 of which 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] Starting from effluent gases from a chemical vapor phase infiltration process, the separation step makes it possible to separate a light portion, mainly consisting of dihydrogen and methane, 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.

[0025] The light portion can be reused either as such or after one or more chemical transformation(s).

[0026] 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, in particular because it comprises a mixture of mainly aromatic and predominantly unsaturated species.

[0027] In one embodiment, the heavy phase obtained after the separation step is used as a reagent in a reforming step.

[0028] The reforming step allows the creation of given hydrocarbons, by the application of particular temperature and pressure conditions which thermodynamically favor the desired species.

[0029] In one embodiment, the reforming step can be carried out at a temperature between 1000°C and 1300°C.

[0030] 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.

[0031] These pressure and temperature conditions are optimal for the thermodynamic stability of unsaturated hydrocarbons comprising two-carbon chains, in particular acetylene and ethylene, compared to other carbon species.

[0032] 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.

[0033] In one embodiment, the reforming step can be carried out in the presence of one or more catalysts.

[0034] Such catalysts make it possible to choose precisely which species will be obtained under the pressure and temperature conditions of the reforming step.

[0035] In one embodiment, such a catalyst can be solid carbon.

[0036] Indeed, the presence of solid carbon plays a catalytic role in the reactions chemical processes involved in the reforming stage, and in particular as a support for heterogeneous reactions.

[0037] 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.

[0038] 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 prior art catalysts.

[0039] In one embodiment, the catalyst may be carbon fibers arranged in the form of a sheet or block, arranged so that the gas does not have a preferential path.

[0040] This ensures a controlled flow in the reactor, ensuring a better controlled residence time in the reactor.

[0041] In addition, this allows for a flow close to a piston flow.

[0042] 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.

[0043] If necessary, this makes it possible to increase the quantity of reagents available for the reforming phase and thus to create at the end of the process a greater quantity of products.

[0044] 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.

[0045] 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.

[0046] 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 be used.

[0047] 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.

[0048] For example, at least part of the dihydrogen used for the hydrogenation step can be obtained after separation of 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.

[0049] The process finally includes a step of introduction into an enclosure intended for carrying out a chemical vapor phase infiltration process of the transformed effluents.

[0050] The expression "transformed effluents" is intended to characterize the effluent gases from a chemical vapor-phase infiltration process that have undergone transformation steps such as reforming, hydrogenation and possibly separation.

[0051] In other words, the process and the steps described thus make it possible to provide a part of the reagents necessary for a chemical vapor phase infiltration process using effluents, and it is these effluents that are transformed to make them valuable.

[0052] The reagents provided do not replace the large quantity of methane required but allow the replacement of the longer alkanes introduced together with methane in a chemical vapor phase infiltration process, and which allow the radical mechanisms enabling the pyrolysis of methane to be initiated.

[0053] 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.

[0054] They are currently less commercially available than methane or natural gas and having such a process makes it possible to avoid the risk of supply of these alkanes which are nevertheless essential for the processes.

[0055] 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.

[0056] 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.

[0057] 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 comprise any dihydrogen.

[0058] In one embodiment, such a separation step can be carried out by membrane separation.

[0059] 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, then to a membrane permeable only to dihydrogen.

[0060] This allows the separation of dihydrogen, which passes through the membrane and constitutes the permeate of the separation step, from the remainder of the gas stream. The remainder of the gas stream is the retentate of the membrane separation step and is intended to be reintroduced into the chamber for carrying out a vapor-phase infiltration process.

[0061] Such membrane separation is particularly preferred in the context of the process described here because it allows excellent separation of dihydrogen from the gas stream intended to be reintroduced into a chamber intended for carrying out a chemical vapor phase infiltration process.

[0062] 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

[0063] [Fig.1] Fig.1 is a schematic representation of a process in one embodiment of the invention. Description of the implementation methods

[0064] The invention is now described by means of figures, which are present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0065] For the sake of simplicity, [Fig. 1] represents a more complex embodiment than the one claimed, describing numerous optional steps. For clarity, the optional steps are shown as dashed lines.

[0066] Fig. 1 represents first of all a chemical vapor phase infiltration step E5.

[0067] In a conventional manner, this step E5 is carried out in a densification oven and allows, for example, the deposition of pyrocarbon on fibrous preforms comprising carbon.

[0068] It can be achieved by introducing into a chamber comprising said fibrous preforms, a gaseous feed stream 1000 comprising between 75% and 95% by volume of methane and other longer linear alkanes, for example ethane or propane.

[0069] These longer alkanes play a role in accelerating the kinetics of pyrocarbon deposition during the chemical vapor phase infiltration process.

[0070] After step E5, a gaseous phase 10 emerges from the enclosure in which step E5 was carried out.

[0071] This gaseous phase 10 includes in particular dihydrogen, formed after part of the carbon from the reactive phase 1000 has been deposited in the form of pyrocarbon.

[0072] The gaseous phase 10 further comprises linear alkanes composing the initial reactive phase 1000 which have not reacted.

[0073] 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 enclosure of the chemical infiltration in vapor phase.

[0074] The process may optionally include a phase E10 for trapping polycyclic aromatic hydrocarbons.

[0075] Indeed, it may be desirable to get rid of these species upstream of any further process step, because polycyclic aromatic hydrocarbons can form soot which increases the need for cleaning pipes.

[0076] It is therefore preferable to carry out a step E10 of trapping polycyclic aromatic hydrocarbons as soon as the end of step E5.

[0077] This step can for example be carried out in an oil trap sometimes called an oil gas scrubber.

[0078] 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.

[0079] Such a separation step El must allow the gaseous phase to be separated into a heavy portion 101 and a light portion 201.

[0080] Such a separation step can be a stripping step or a distillation step.

[0081] In a preferred embodiment, step El is a stripping step.

[0082] For example, such a step El 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 an inert gas for stripping.

[0083] 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.

[0084] In a described process, the heavy portion 101 undergoes a reforming step E2.

[0085] Such a reforming step is carried out in a pressure and environment temperature at which compounds with two carbon atoms are thermodynamically most stable.

[0086] The stability of gaseous species during a reforming step can be determined by a thermochemical calculation performed with reference data. For example, data from NIST (National Institute of Science and Technology), JANAF tables, and a thermochemical calculation tool such as NASA's "Chemical Equilibrium Application" can be used to establish these curves.

[0087] By way of example, reference curves are described in the reference: A. Holmen et al. Fuel processing technology 42 (1995) 249-267.

[0088] 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 favoured.

[0089] Thus, the inventors propose a reforming step E2 in which ethylene and acetylene are thermodynamically the most stable.

[0090] In one embodiment, the pressure of the reforming step E2 can be between 10 mbar abs and 800 mbar abs.

[0091] In one embodiment, the temperature of step E2 can be between 1000°C and 1300°C.

[0092] In one embodiment, step E2 is further carried out by placing phase 101 in the presence of solid carbon.

[0093] The inventors have indeed observed that solid carbon has a catalytic action on the complex reactions involved in the E2 reforming step.

[0094] 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.

[0095] The inventors have indeed determined that under these conditions step E2 allowed the reforming of the hydrocarbons composing phase 101 into ethylene and acetylene.

[0096] In one embodiment, if necessary, dihydrogen can be added to phase 101 before it undergoes step E2.

[0097] This dihydrogen can shift thermodynamic equilibria towards the production of ethylene and acetylene, or provide the dihydrogen necessary for chemical reforming reactions.

[0098] 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.

[0099] In one embodiment, this step can then undergo a hydrogenation step E3 allowing both ethylene and acetylene to be transformed into ethane.

[0100] For example, the hydrogenation step E3 can be carried out at a temperature between 80°C and 130°C.

[0101] In one embodiment, the hydrogenation step E3 can be carried out at a temperature between 100°C and 110°C.

[0102] In one embodiment, step E3 may include a catalyst selected from palladium or nickel catalysts. By way of example, the catalyst available under the trade name LD465 from AXENS may be used.

[0103] In an optional embodiment, and therefore represented in dotted lines on [Fig.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.

[0104] In particular, this dihydrogen 203 can be recovered in the light portion 201 separated during the earlier separation step El described above.

[0105] In one embodiment, dihydrogen 203 can be recovered directly after a step E12 of separation of the different compounds of the light portion 201.

[0106] The steps that the light portion 201 may undergo will be described below.

[0107] The hydrogenation step E3 which the products 102 obtained at the end of the reforming step E2 undergoes makes it possible to obtain a stream 103 mainly composed of ethane, or even made up of ethane.

[0108] 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.

[0109] In one embodiment, this separation step E4 can be carried out via the use of membranes.

[0110] For example, step E4 of separation of gas 103 from hydrogenation step E3 can be carried out by cryogenic separation.

[0111] In one embodiment, the separation step E4 may include a separation step by exposing the stream 103 to a dihydrogen-selective membrane.

[0112] In one embodiment, the separation step comprises only the separation step by exposing the stream to a dihydrogen-selective membrane.

[0113] Alternatively, the E4 separation step includes a separation step by exposure of the stream to a dihydrogen-selective membrane, followed by a cryogenic step.

[0114] It is thus possible to recover the dihydrogen possibly present in the stream 103, and, for example, reinject it into the hydrogenation step E3.

[0115] 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.

[0116] This separation step provides an ethane stream 104 and a hydrogen-rich stream 105, which is shown returning to step E2 or E3, although this is not necessary. Indeed, other methods of valorization can be considered for the hydrogen stream 105, for example, methanation.

[0117] Alternatively, the excess dihydrogen 106 stream at step E4 can be used for other purposes.

[0118] In the described process, the ethane stream 104 is used as a reagent in a chemical vapor phase infiltration process E5.

[0119] Preferably, this chemical vapor phase infiltration process is carried out in the same enclosure from which the effluents 10 originate.

[0120] It is understood from the preceding statement that the process as a whole makes it possible to recover a portion of the effluents 10 of a chemical process in the vapor phase.

[0121] This makes it possible to reduce the supply requirements 1000 of said chemical vapor phase infiltration process accordingly.

[0122] This results in a significant economic gain as well as a reduction in the carbon footprint of the process, since the use of the carbon elements required for the cycle is thus optimized compared to processes not having the steps E1, E2 and E3.

[0123] In addition, the proposed process makes it possible to no longer be dependent on the sources of supply of ethane or propane usually added to methane for chemical vapor phase infiltration processes.

[0124] 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.

[0125] 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.

[0126] In particular, the 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.

[0127] This results in a more industrially robust process which requires only methane as the main reactant 1000, with ethane being generated by the recycling of effluents.

[0128] In one embodiment of the process, the ethane generated by the recycling of the 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.

[0129] 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-phase infiltration process described herein.

[0130] The steps possibly applied to the light portion 201 obtained after the separation step El will now be described.

[0131] It should be borne in mind that these operations are optional and allow for even better use of the effluents 10.

[0132] In one embodiment, the light portion can first undergo a first Eli hydrogenation step.

[0133] For example, this step can be carried out under the conditions described above for the hydrogenation step E3.

[0134] 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.

[0135] Thus, even if a portion of light hydrocarbons other than methane, in particular acetylene, and ethylene or propene or three-atom alkyl carbon would have remained in the light portion 201 of the El separation step, these compounds will be in linear alkane form in the 202 stream.

[0136] The flow 202, or if the Eli step is not present, the flow 201, can be exposed to a separation step El2.

[0137] Preferably, the separation step E12 is a membrane separation step, and to increase its efficiency, the flow 202, or where appropriate 201, can be compressed initially.

[0138] The E12 separation step allows the dihydrogen 203 present in the light portion 201 to be separated.

[0139] For example, the separation step E12 may include exposing the stream 202, or 201, to a dihydrogen-selective membrane, for example chosen from those described for step E4.

[0140] In one embodiment, which is that described in [Fig. 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 processes other than that described here.

[0141] 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.

[0142] In one embodiment, the E5 chemical vapor phase infiltration step can be a densification process of preforms comprising carbon fibers.

[0143] 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 the effluents (10) of a chemical vapor infiltration process comprising at least the following steps: - a step (E1) of separating the effluent gases from a chemical vapor infiltration process allowing these effluents to be separated 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 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 a vessel intended for carrying out a chemical vapor infiltration process (E5).

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 processed effluents into a

9.

10. enclosure intended for carrying out a process (E5) of chemical infiltration in the vapor phase. A method according to claim 8, wherein the separation step (E4) is carried out by membrane separation. 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-phase infiltration process (10).

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