Method for purifying an aromatic hydrocarbon oil and plant for recycling same

Abstract

The invention relates to a method for the continuous purification of an aromatic hydrocarbon oil used for scrubbing gaseous effluents generated in a pyrolysis furnace, such as a chemical vapour infiltration furnace, for example. The method comprises a step of mixing the aromatic hydrocarbon oil with a solvent in a continuous countercurrent contactor, the solvent being in an amount sufficient to collect a light phase rich in oil and a heavy phase rich in contaminants, a step of distilling the solvent contained in the light phase in order to regenerate it in the contactor, and a step of extracting the solvent contained in the heavy phase in order to inject it into the distillation device. This method makes it possible to purify an aromatic hydrocarbon oil continuously in a plant which consumes little energy and which minimises the amounts of make-up solvent.

Description

Process for purifying an aromatic hydrocarbon oil and installation for its recycling Technical Field

[0001] The invention relates to the field of treatment of effluent gases from chemical processes of vapor phase synthesis of pyrocarbon.

[0002] More specifically, the invention relates to a process for the treatment of an aromatic capture oil used to remove reaction by-products from chemical vapor deposition processes or from chemical vapor infiltration processes of pyrocarbon.

[0003] The invention also relates to an installation for implementing this process. Previous technique

[0004] Chemical processes for depositing or infiltrating carbon in the vapor phase involve placing a substrate in a furnace supplied with a reactive gas containing methane and propane which, under the effect of pressure and temperature, decompose into carbon in contact with the substrate, into dihydrogen and various unsaturated by-products.

[0005] The fraction of reactive gas that has not reacted, as well as the reaction by-products, form a gaseous effluent, the temperature of which at the outlet of the furnace remains very high, so that the by-products are themselves reactive and condense and polymerize in cascade to lead to polycyclic aromatic hydrocarbons (PAHs).

[0006] As the exhaust gas cools downstream of the furnace, polycyclic aromatic compounds condense on the surface of the pumping equipment and piping. Therefore, the gas is scrubbed with oil at the furnace outlet to remove these pollutants. This process is carried out by immersing the exhaust gas in a gas scrubber containing a capture oil, which adsorbs and condenses the majority of the pollutants. Aromatic hydrocarbon oils have proven effective in maintaining the proper functioning of the equipment downstream of the furnace, particularly the pumps. However, the capture oil gradually loses its physical properties, notably through an increase in viscosity, as it becomes contaminated. Eventually, it must be removed and replaced. Treated as hazardous waste, it is generally used as fuel in cement plants.

[0007] Various processes exist for treating aromatic oils contaminated by PAHs.

[0008] The most classic method involves treating the oil by filtering it through a bed of adsorbent, based on zeolites for example.

[0009] Vacuum distillation is also a widely used process for removing pollutants from used oils. Through low-pressure operation, it is possible to separate the pollutants in the oil by leveraging their differences in volatility. While this process is known for its separation efficiency, it has the drawback of being energy-intensive and requiring frequent maintenance.

[0010] The need therefore remains to develop a treatment process for used aromatic hydrocarbon oil that can be industrialized in a low-energy installation. Ideally, a treatment process would reduce the maintenance frequency of industrial chemical vapor-phase carbon infiltration units, which are found particularly at carbon-carbon composite production sites. A particularly efficient treatment process should allow for the continuous recycling of the contaminated aromatic oil and its reuse during the scrubbing of emitted gaseous effluents. Description of the invention

[0011] The present invention precisely addresses this need by proposing a process for purifying an aromatic hydrocarbon oil used for treating gaseous effluents from pyrocarbon synthesis, said process comprising: - a vertical counter-current DC power supply, by a charge of a polluted aromatic hydrocarbon oil, in the upper part, and a power supply of said contactor by a charge of solvent, in the lower part, - the collection of a light phase at the top of the contactor, followed by the introduction of the light phase into a distillation device to separate a solvent fraction and a purified aromatic oil, followed by the recycling of the solvent fraction into the contactor, and - the collection of a heavy phase at the bottom of the contactor, followed by the treatment of the heavy phase in a finishing unit to separate a solvent fraction and polycyclic aromatic compounds, said treatment being followed by the recycling of the solvent fraction into the distillation device.

[0012] The high purification rate of aromatic hydrocarbon oil achieved by the process of the invention allows the aromatic hydrocarbon oil to regain its properties, enabling it to be recycled for the treatment of gaseous effluents. Furthermore, the energy consumption associated with regenerating the solvent used in this purification process is minimized. These two aspects contribute to reducing the installation's carbon footprint.

[0013] A second object of the invention relates to an installation for implementing a process according to the preceding description. The installation is useful for the continuous purification of a washing oil from pyrolysis effluents.

[0014] In one particular embodiment, the installation comprises a counter-current continuous contactor, a finishing unit equipped with a vacuum pumping device, and a distillation unit located downstream of the finishing unit. The installation is advantageously designed to reduce the energy consumption of solvent regeneration and minimize the amount of makeup solvent required.

[0015] Finally, according to a particular application of the process and installation described above, the invention relates to a process for manufacturing composite parts comprising chemical infiltration in the gas phase to densify a carbon fiber preform with a pyrocarbon matrix in a reactor, and the capture of reaction by-products contained in the gaseous effluent in an oil trap. The oil, now laden with pollutants, is then treated according to a continuous purification process described previously. This process may advantageously include a step of recycling the purified aromatic hydrocarbon oil back into the oil trap.

[0016] The Applicant acts, at all stages of aircraft design and development, on parameters that enable the production of more environmentally friendly components and products, the integration and use of which in civil aviation minimize environmental consequences. Consequently, the Applicant continuously works to reduce its negative climate impact by employing methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions and consume less energy, in order to reduce the environmental footprint of its activities. Brief description of the drawings

[0017] A particular embodiment of the invention is illustrated in Figure 1, which should not be interpreted as limiting the latter.

[0018] Figure 1 is a schematic representation of an installation and a process according to the invention. It includes the supply of a counter-current continuous contactor 100 with a solvent and a capture oil loaded with pollutants, a unit definition 200 of a heavy phase recovered at the bottom of the contactor, and a distillation device 300 of a light phase recovered at the top of the contactor. Description of the implementation methods

[0019] According to a first object of the invention illustrated by Figure 1, the process for the continuous purification of an aromatic hydrocarbon oil used for scrubbing gaseous effluents produced by pyrolysis, said process comprising: - a supply at the upper part of a vertical counter-current continuous contactor 100 by a charge of polluted aromatic hydrocarbon oil 120, and a supply at the lower part of said contactor 100 by a charge of solvent 110, - the collection of a light liquid phase 140 at the head of the contactor, and the introduction of said light phase 140 into a distillation device 300 to separate a solvent fraction 310 and a purified aromatic oil 320, followed by the recycling, in the contactor 100, of the solvent fraction 310, and - the collection of a heavy phase 130 at the bottom of the contactor 100, followed by treatment of the heavy phase 130 in a finishing unit 200 to separate a solvent fraction 210 and pollutants 220, said treatment being followed by recycling of the solvent fraction 210 in the distillation device 300.

[0020] The treatment of the heavy phase 130 advantageously consists of placing said heavy phase 130 under vacuum to regenerate the solvent fraction 310 in gaseous form.

[0021] Furthermore, the quantity of solvent injected into the charge 110 is preferably sufficient to ensure that the heavy phase 130 has the appropriate fluidity. This characteristic offers two advantages: the collection of the heavy phase can be carried out continuously and by pumping.

[0022] The process of the invention advantageously enables the continuous treatment of aromatic hydrocarbon oil laden with pollutants using a solvent. The aromatic hydrocarbon oil is preferably solubilized by the solvent and recovered by distillation, while the heavy phase containing the pollutants and residual solvent undergoes a finishing treatment by vacuum sealing. The generated residual solvent vapors can be recycled and used in the distillation process.

[0023] The purification rate of the aromatic hydrocarbon oil achieved by the purification process is sufficient to restore the treated aromatic hydrocarbon oil, which is directly produced by the process described above, to its original functionality and allow it to be recycled in another on-site unit or in another off-site facility. Furthermore, the energy cost of regenerating the solvent used for purification is minimized. These two aspects contribute to reducing the facility's carbon footprint.

[0024] An "aromatic hydrocarbon oil" within the meaning of the invention is a liquid compound at room temperature consisting of carbon and hydrogen, whose molecular structure includes at least one benzene ring. The aromatic hydrocarbon oil is, of course, non-polycyclic. An example is 2,3-dibenzyltoluene.

[0025] The term "capture oil" refers to an oil used in a gas scrubber located in a pyrolytic carbon synthesis plant. Capture oil is capable of condensing, or even solubilizing, the reaction byproducts of a vapor-phase chemical process, the process of which involves the deposition or infiltration of pyrocarbon. Capture oil is generally suitable for the removal of gaseous byproducts generated by pyrolysis.

[0026] For the purposes of this description, "pollutants" are defined as non-recoverable hydrocarbons generated by pyrolysis, for example, by the decomposition of organic matter or by the synthesis of pyrocarbon. They consist primarily of polycyclic hydrocarbon compounds. Under certain pyrolysis operating conditions, these organic compounds comprise one or more heteroatoms, such as oxygen, nitrogen, or sulfur, and their molecular mass can reach several thousand grams per mole.

[0027] As illustrated in Figure 1, the solvent charge 110 can be from a downstream solvent stream which has been pressurized and heated before entering the contactor 100.

[0028] In the embodiment shown, the contaminated aromatic oil capture zone 120 is located in the upper part of the countercurrent continuous contactor 100, and the solvent capture zone 110 is located in the lower part of the contactor. This configuration exploits the density difference between the oil and the solvent, as well as the difference in solubility of the oil and the pollutants in the solvent.

[0029] The feed method for the counter-current continuous contactor is chosen so that the denser fluid, the aromatic oil laden with pollutants, is fed into the top of the contactor, and the less dense fluid, the solvent, is introduced from the bottom. Under the influence of gravity, the two fluids mix to form two phases: a lighter phase (140) and a heavier phase (130), which are collected at the contactor outlet.

[0030] A skilled technician will be able to choose the contactor configuration based on their general knowledge. This may include, for example, perforated plates or loose packing.

[0031] The pressure maintained in the contactor is preferably close to atmospheric pressure. The temperature inside the contactor will be selected by a person skilled in the art based on the boiling and freezing points of the solvent. In an advantageous implementation, the temperature is set within a range of 10°C to 40°C.

[0032] The heavy phase 130 contains essentially polycyclic aromatic hydrocarbons that have been separated from the polluted aromatic oil, while the light phase contains essentially aromatic oil.

[0033] In the embodiment shown, the light phase stream 140 is sent to a distillation unit 300 to regenerate the solvent. This yields a solvent stream 310 and the purified aromatic oil 320 at the outlet of the distillation unit. Distillation separates the purified aromatic oil from the solvent fraction carried over from the contactor 100 and regenerates it.

[0034] According to a first, particularly advantageous variant, not shown in Figure 1, the purified aromatic oil 320 is recycled in an on-site unit. In one case, the contaminated aromatic hydrocarbon oil feed 120 comes from a tar trap located downstream of a pyrolysis furnace in a pyrocarbon synthesis unit, and the purified aromatic oil 320 stream is recycled to continuously supply the tar trap. An example of a pyrocarbon production facility includes a chemical vapor infiltration furnace for manufacturing carbon / carbon composite parts by densifying a porous substrate.

[0035] In a second variant, the purified aromatic oil 320 can be stored for later use off-site.

[0036] The separation of pollutants and aromatic hydrocarbon oil can be optimized by modulating the chemical nature and the charge flow rate of the solvent used.

[0037] Preferably, a solvent is chosen whose affinity for the aromatic hydrocarbon oil is greater than its affinity for the pollutants. In one scenario, the solvent has little affinity for the pollutants, while still fulfilling its function as a solvent. In a second scenario, the solvent has no affinity for the pollutants: it can be considered a non-solvent of the pollutants, which then precipitate at the bottom of the contactor. A person skilled in the art will be able to choose the solvent whose solubility parameters are best suited to the chemical nature of the aromatic oil and the characteristics of the pollutant fraction captured by this oil.

[0038] In this embodiment, the mixing step parameters in the contactor 100 are advantageously chosen so that the pollutants are carried along with residual solvent. It is preferred that the heavy phase 130, rich in pollutants at the outlet of the contactor 100, contain a sufficient solvent fraction to remain fluid. This configuration contrasts with prior art practice, whereby the pollutants precipitate at the bottom of the contactor and are periodically collected in solid form. The process of the invention advantageously allows for the design of an aromatic hydrocarbon oil purification system that operates continuously.

[0039] The relative flow rate of the solvent feed 110 and the contaminated aromatic hydrocarbon oil feed 120 is advantageously adjusted according to the nature of the pollutants and the oil. This relative value can be optimized to ensure sufficient fluidity of the heavy phase for processing in the finishing unit 200, thus enabling continuous operation of the plant.

[0040] The commercial reference oil Jarytherm® DBT is an example of an aromatic hydrocarbon oil used for capturing gaseous pollutants produced during the gaseous densification of carbon / carbon materials. For this particular oil, the ratio between the mass flow rate of the solvent feed 110 and the mass flow rate of the polluted oil feed 120 is preferably greater than 5:1, preferably even greater than 10:1, and preferably even greater than 15:1.

[0041] The solvent may be a linear or C5-C8 branched alkane. Alternatively, the solvent is non-toxic and preferably chosen from linear or C2-C6 branched aliphatic alcohols.

[0042] The light phase 140, consisting mainly of aromatic hydrocarbon oil and solvent, is collected at the head of the contactor 100 and conveyed to the distillation unit 300. Distillation can be carried out at atmospheric pressure or under vacuum.

[0043] The finishing treatment of the heavy phase 130 is carried out in the finishing unit 200, which includes a means for collecting the heavy phase 130 at the bottom of the contactor 100. In an advantageous embodiment, the finishing unit also includes a device for vacuum pumping the collected heavy phase 130 to extract the residual solvent, which can feed the distillation device 300. In an advantageous embodiment, the solvent fraction 210 is isolated by vacuum evaporation of the heavy phase 130.

[0044] A second object of the invention relates to an installation for implementing a process according to the preceding description. The installation is useful for the continuous purification of a washing oil from pyrolysis effluents.

[0045] In one particular embodiment, the installation comprises a counter-current continuous contactor, a finishing unit equipped with a vacuum pumping device, and a distillation unit located downstream of the finishing unit. The installation is advantageously designed to reduce the energy consumption of solvent regeneration and minimize the amount of makeup solvent required.

[0046] In more detail, the continuous counter-current contactor includes a solvent loading zone in the lower part, an oil loading zone to be purified in the upper part, a light liquid phase collection zone at the top, and a heavy liquid phase collection zone at the bottom.

[0047] The distillation unit is configured to regenerate the solvent contained in the light liquid phase, while the finishing unit is configured to regenerate the solvent contained in the heavy phase.

[0048] The distillation apparatus comprises a light liquid phase feed zone and a solvent collection zone at the top. The regenerated solvent can advantageously be conveyed to the contactor via a conduit. The distillation apparatus is preferably an atmospheric distillation apparatus, meaning that the pressure within the apparatus is equal to atmospheric pressure. The advantage of such an apparatus lies in its lower energy consumption relative to the large quantities of solvent carried along in the light phase stream, compared to pressurized distillation apparatuses used in the prior art. The distillation apparatus can be a distillation column familiar to those skilled in the art, who can configure it based on their general knowledge according to the boiling point of the solvent.

[0049] As for the finishing unit, it is configured to regenerate the solvent contained in the heavy phase and, for this purpose, includes a heavy phase collection zone and a vacuum pumping device for the liquid heavy phase, configured to regenerate the solvent it contains. The solvent collected at the outlet of the vacuum pumping device can advantageously supply the atmospheric distillation unit, such a configuration contributing to a reduction in the power required for the operation of the atmospheric distillation unit.

[0050] The particular configuration of the three-part installation, combining a continuous counter-current contactor for mixing the polluted organic oil with a solvent, a unit for finishing the heavy phase at the bottom outlet of the contactor by evaporating the solvent under vacuum, and a device for distilling the light phase at the top outlet of the contactor, offers several advantages.

[0051] In one particular embodiment, the installation can be configured to continuously recycle the purified organic oil in a related installation, for example, in an oil trap of a production unit using chemical infiltration of hydrocarbons in the vapor phase. The purification process of the invention and the associated installation make it possible to avoid the disposal and destruction of quenching oils generally practiced in this type of production unit. The invention significantly reduces the costs associated with oil use by recycling it, and also reduces the environmental footprint currently generated by its destruction.

[0052] The installation of the invention can be implemented in any industrial unit comprising a pyrolysis furnace and allows for a reduction in the unit's energy consumption and carbon footprint. According to one example, the industrial unit is a production unit for pyrocarbon parts using chemical vapor deposition (CVD) or chemical vapor infiltration (CVI). Such a unit typically includes a gas-phase chemical reaction furnace for a reactive hydrocarbon and a device for quenching the effluent gas with an aromatic hydrocarbon oil.

[0053] The installation dedicated to the purification of an aromatic hydrocarbon oil can therefore be advantageously integrated into a pyrocarbon parts production unit as a module for purifying the oil for capturing gaseous pollutants.

[0054] Design an installation including a means of recovering the fraction of the solvent charge carried into the heavy phase, but also a means of recovering the fraction of the solvent charge carried into the light phase, which make it possible to limit the amount of solvent needed to ensure the balance of the phases in the contactor, and consequently the overall amount of solvent needed for the proper functioning of the capture oil purification installation.

[0055] Thus, the installation makes it possible to maintain a constant quantity of solvent in the contactor, while limiting both the supply of additional solvent and the energy required for its regeneration, so that the overall energy consumption required for the proper functioning of the installation as a whole is considerably reduced.

[0056] The aromatic hydrocarbon oil purification process according to the invention has application in any field associated with a pyrolytic process.

[0057] This may involve the manufacture of composite material parts such as carbon-carbon brake discs densified by chemical vapor phase infiltration of pyrocarbon into a fibrous carbon fiber preform.

[0058] A third object of the invention therefore relates to a process for manufacturing composite parts comprising a step (A) of chemical infiltration in the gas phase to densify a carbon fiber preform with a pyrocarbon matrix, and a step (B) of capturing pollutants by an aromatic hydrocarbon oil, a step (C) of continuously purifying the aromatic hydrocarbon oil loaded with pollutants during the step (B), the purification being carried out by means of a process according to one of claims 1 to 4, and a step (D) of recycling the aromatic hydrocarbon oil purified in the step (C) into the capture step (B).

[0059] The process scheme of the invention can also be implemented in biomass transformation processes by pyrolysis.

Claims

Demands

1. A process for the continuous purification of an aromatic hydrocarbon oil used for scrubbing gaseous effluents produced by pyrolysis, said process comprising: - a supply at the upper part of a vertical counter-current continuous contactor (100) by a charge of polluted aromatic hydrocarbon oil (120), and a supply at the lower part of said contactor (100) by a charge of solvent (110), - the collection of a light liquid phase (140) at the head of the contactor, and the introduction of said light phase (140) into a distillation device (300) to separate a solvent fraction (310) and a purified aromatic oil (320), followed by the recycling, in the contactor (100), of the solvent fraction (310), and - the collection of a heavy phase (130) at the bottom of the contactor (100), followed by treatment of the heavy phase (130) in a finishing unit (200) to separate a solvent fraction (210) and pollutants (220), said treatment being followed by recycling of the solvent fraction (210) in the distillation device (300).

2. Continuous purification process of an aromatic hydrocarbon oil according to claim 1, characterized in that the solvent fraction (210) is isolated by vacuum evaporation of the heavy phase (130).

3. Continuous purification process of an aromatic hydrocarbon oil according to claim 1 or 2, characterized in that the distillation of the light phase (140) in the distillation device (300) is carried out at atmospheric pressure.

4. Installation for the continuous purification of an aromatic hydrocarbon oil used for scrubbing gaseous effluents produced by pyrolysis, said installation comprising a continuous counter-current contactor (100), a finishing unit (200) and a distillation device (300), - said counter-current continuous contactor (100) comprising a solvent loading zone (110) in the lower part, a polluted aromatic capture oil loading zone (120) in the upper part, a light liquid phase collection zone (140) at the top, and a heavy phase collection zone (130) at the bottom, - the distillation apparatus (300) being a light liquid phase distillation apparatus (140), preferably an atmospheric distillation apparatus, and - the finishing unit (200) comprising a device for evaporating a fraction of solvent contained in the heavy phase (130).

5. Installation for the continuous purification of an aromatic hydrocarbon oil according to claim 4, characterized in that it comprises a conduit for conveying the solvent vapors collected at the head of the distillation device (300), said conduit being connected to the contactor (100).

6. Installation for the continuous purification of an aromatic hydrocarbon oil according to claim 4 or 5, characterized in that it comprises a conduit for conveying the solvent vapors collected at the outlet of the finishing unit (200), said conduit being connected to the distillation device (300).

7. Installation for the continuous purification of an aromatic hydrocarbon oil according to any one of claims 4 to 6, characterized in that the device for the evaporation of a solvent fraction contained in the heavy phase (130) is a vacuum pump.

8. A method for manufacturing carbon-carbon composite parts, said method comprising a step (A) of chemical infiltration in the gas phase to densify a carbon fiber preform with a pyrocarbon matrix, and a step (B) of capturing pollutants with an aromatic hydrocarbon oil, a step (C) of continuously purifying the aromatic hydrocarbon oil loaded with pollutants during step (B), the purification being carried out by means of a process according to any one of claims 1 to 4, and a step (D) of recycling the aromatic hydrocarbon oil purified in step (C) into the capture step (B).

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