Carbon black recovery process by solvolysis of spent elastomers

Abstract

The present invention relates to the field of recovery of carbonaceous materials such as carbon black, particularly so-called "recovered" carbon black (or rCB) obtained through a solvolysis process of spent elastomers. It concerns a process for preparing recovered carbon black via a solvolysis process of spent elastomers with recycling of a hydrocarbon fraction comprising aromatic compounds, followed by a centrifugation step of the solvolysis effluent and conduction drying to obtain the recovered carbon black. [Fig. 1] to be published for the abstract

Description

Title of the invention: Process for recovering carbon black by solvolysis of spent elastomers. Field of the invention

[0001] The present invention relates to the field of recovery of carbon materials of the carbon black type, in particular to so-called "recovered" carbon blacks (or rCB for "recovered carbon black" according to Anglo-Saxon terminology) by a solvolysis process of used elastomers. State of the art

[0002] Elastomers are chemically cross-linked polymers of natural or synthetic rubber. Due to their chemical bonds, they do not melt but begin to decompose at high temperatures. Natural rubber is primarily composed of polyisoprene, a natural polymer found in the rubber tree (Hevea brasiliensis) and guayule. Synthetic rubbers are either general-purpose or specialty rubbers and are created by combining different polymers, monomers, and laminates.Common synthetic rubbers include (but are not limited to) styrene-butadiene copolymer (SBR), polybutadiene (BR), isobutylene-isoprene copolymer (IIR, CIIR, BIIR), ethylene-propylene-diene monomer (EPDM), polychloroprene (CR), acrylonitrile-butadiene copolymer (NBR, HNBR), chlorosulfonated polyethylene (CSM), fluoroelastomer (FKM), polyacrylate rubber (ACM), epichlorohydrin rubber (ECO), and silicone rubber (VMQ).

[0003] These materials are used to manufacture various objects such as tires for light vehicles, heavy goods vehicles, two-wheelers or any type of special equipment, treads in conveyor systems, vehicle door seals, but also objects such as shoe soles or rubber boots.

[0004] At the end of their life, these elastomer-rich objects undergo, to facilitate their material recovery, for example, a granulation treatment to isolate the elastomer-rich parts of the objects in question and to eliminate the majority of the other constituents (such as, for example, the metallic or synthetic fabrics and fibers often incorporated into the elastomers to enhance their properties) and to form granules generally smaller than 25 mm. Granulation generally consists of a series of grinding and separation steps and makes it possible to obtain a resulting material composed of the elastomer and the reinforcing fillers incorporated with the elastomer, such as carbon black or silica, for example.

[0005] Carbon black (or CB, as it is known in English) is used in tire formulations to improve their resistance (in terms of strength and lifespan), to limit tire deformation during use, and to facilitate heat transfer between the tires and the road surface. It is generally obtained by the incomplete combustion of hydrocarbons or vegetable oils, and more than 35 grades are commercially available and used as fillers (primarily in tire compound formulations). Their quality varies according to their intrinsic properties.

[0006] Most carbon blacks are characterized by high elemental carbon contents (> 90% by weight relative to the total weight of the carbon black) and may contain other chemical elements such as hydrogen, oxygen, nitrogen and sulfur which are chemically bonded to the carbon. They generally appear in the form of black powders made up of graphitic (more or less well crystallized) and quasi-spherical (10 to 500 nm) elemental particles, forming aggregates (100 nm to 1000 nm) which can themselves come together in the form of agglomerates (1 pm to 100 pm), the whole of which can then be transformed into granules (0.1 to 1 mm). The size of the elementary particles and the structure of the objects (morphology, size, density / aeration of the aggregates / agglomerates) will largely impact the ability of carbon blacks to disperse in an elastomeric matrix and therefore, ultimately, the reinforcing properties of the latter within this matrix.The specific surface area (SBEt) parameter, determined by nitrogen physisorption, is characteristic of the size of the elementary particles and indicates the surface area of ​​the carbon black potentially interacting with the elastomeric matrix. The structure of a carbon black is characterized by its ability to develop porosity that can be filled by a paraffinic oil, and therefore ultimately by an elastomeric matrix. A structure index, equivalent to an oil adsorption index, is then determined, the associated analytical method being the OAN (Oil Adsorption Number). Each carbon black is then assigned a code of the type NXYZ, where X is a number characteristic of the carbon black's SBEt, and Y and Z are numbers arbitrarily assigned based on the observed structure.In summary, there is a relationship between SBEt and OAN structure index that allows the various carbon blacks to be classified according to their grade and whether they have a reinforcing or non-reinforcing effect. For example, NI 10, N120, and N234 carbon blacks, which are very good reinforcing additives, are characterized by a high specific surface area and structure index. Depending on their intrinsic properties, carbon blacks are used to formulate different rubber compounds, which are themselves used in the various components of a tire.

[0007] During recycling, elastomer-rich materials are generally initially ground to obtain either elastomer granulates still containing some textile and metallic fibers (typically pieces from 1 to 10 cm in size), or granules (generally smaller than 6 mm) free of all fibers. These can then be converted into gaseous, liquid, and solid fractions via thermal decomposition processes. The resulting solid fraction consists mainly of various grades of carbon black mixed with inorganic ash (primarily silica and zinc-based compounds). Furthermore, the thermal decomposition of the elastomer fraction generates various carbon compounds (various decomposition products, possibly recondensed) that can be deposited on the surface of the carbon black.Similarly, depending on the operating conditions of these processes, undecomposed elastomer polymer chains can adsorb onto the surface. For a given conversion process applied to a specific "spent elastomer" feedstock, the recovered carbon black then represents the entire solid fraction consisting of the initial carbon blacks mixed and modified on the surface by various carbon deposits (decomposition products and / or elastomer residues), as well as inorganic ash. The intrinsic properties of recovered carbon black therefore depend on its constituent elements.In particular, the chemical composition of the recovered carbon black, the agglomeration rate of the aggregates and their structure, and consequently the redispersion properties of the recovered carbon black in an elastomer matrix, can be drastically modified compared to those of the initial carbon blacks depending on the composition of the end-of-life tires treated (choice of charge) and the recycling process envisaged.

[0008] Among the possible thermal decomposition conversion processes for treating end-of-life elastomers, particularly tires, pyrolysis processes are very frequently encountered (J. Yu et al., Frontiers of Environmental Science & Engineering, 2020, 14, 2, 7982; SQ Li et al., Ind. Eng. Chem. Res. 2004, 43, 5133; EP2661475). They usually consist of exposing the elastomers to temperatures between 350°C and 800°C in the absence of oxygen, or in the presence of a very small amount of oxygen or air intended to provide, through very partial combustion, the energy necessary for the pyrolysis process. This last step takes place at the atmospheric pressure of the gas(s) in question or sometimes under vacuum, in order to minimize the secondary post-degradation reactions of the tire rubbers which frequently lead to the formation of residual carbon deposits on the surface of the final recovered carbon black already mentioned.The yields of these processes in recovered carbon black are very variable (between approximately 25 and 60%) and the same is true for the intrinsic properties of the latter (for example, the rate of . Residual inorganic ash can vary from 8 to 41% by weight. In contrast, the recovered carbon blacks obtained post-pyrolysis (also frequently called "pCB") are all characterized by the significant presence of carbon deposits on the surface of the initial carbon blacks. These are characterized in particular using the X-ray Photoelectron Spectroscopy (XPS) surface analysis technique, also known as ESCA ("Electron Spectroscopy for Chemical Analysis" in English). Firstly, this surface analysis makes it possible to define the elemental chemical composition of a material and thus determine the present contents of C, O, N, S, Si, Al, Zn, etc. Secondly, the precise analysis of the spectrum associated with the carbon element (Cls spectrum) provides information on the chemical environment of the carbon atoms constituting the recovered carbon black (Ludovic Moulin's thesis: Valorization of recovered carbon black, process-product relationship).Process Engineering. Ecole des Mines d'Albi-Carmaux, 2018). It notably allows us to distinguish the carbon associated with the initial carbon blacks (Co peak corresponding to a bond energy of approximately 284.2 / 284.8 eV, characteristic of CC / CH bonds of a graphitic structure) from that relating to carbon compounds likely to be deposited on the surface (Ci peak corresponding to a bond energy of approximately 284.8 / 285.6 eV, characteristic of CC / CH bonds of aliphatic structures or small aromatic compounds, associated here with the carbon deposits formed during pyrolysis processes). Thus, the pCBs exhibit carbon deposit contents, evaluated as % of area by XPS, ranging from 5% to 40% (calculation based on the total area of ​​the Co and Ci peaks previously described and the C2, C3, C4 and C5 peaks respectively attributed to CO, C=O, COOH bonds and jt-jt* transitions).These carbon deposits are largely responsible for the agglomeration phenomena that bind the various structures of the recovered carbon blacks at different scales: the solid exiting the reactor is often present in the form of blocks several millimeters / centimeters in size, which must then be finely ground in order to be reused (notably as an additive for the formulation of new rubbers), which requires significant energy expenditure. It should be noted that these carbon deposits appear to be strongly linked to the surface area of ​​the initial carbon blacks, since even post-thermal treatments at higher temperatures than the pyrolysis process itself are insufficient to eliminate them (reduction from 40% to 20% of the peak area Ci for a post-pyrolysis thermal treatment at 600°C: H. Darmstadt et al., Carbon, 1995, 33, 10, 1449).

[0009] To limit the formation of carbon deposits on the recovered carbon black, it is possible to lower the partial pressure of hydrocarbons by injecting steam during the cracking reactions (steam-thermolysis processes). Unfortunately, the high temperature conditions generally applied (often exceeding At temperatures of 500°C, these processes still lead to the formation of carbon deposits, albeit in limited proportions (5 to 6% of the peak area in Ci). Furthermore, these gas-solid processes present other drawbacks. They generally induce high production levels of non-condensable gases (under atmospheric conditions), often between 10% and 25% by weight relative to the amount of spent elastomer entering the reactor. This comes at the expense of the quantity of potentially recoverable and easily usable liquid products. Indeed, these liquid fractions can be used to produce new hydrocarbon fractions (naphtha, gasoline, kerosene, diesel fuel, vacuum distillate, residues), which are used in refineries to produce fuels or in petrochemicals to produce bases used subsequently in the manufacture of plastics.

[0010] Another interesting alternative method for limiting the presence of these carbon deposits on recovered carbon black consists of contacting the elastomer fillers with a liquid under suitable operating conditions (particularly temperature) and dissolving and converting the elastomers in a homogeneous liquid phase in which the elastomer filler would be agitated and would gradually disappear. US patents 3,978,199 and 3,704,108 disclose processes for converting spent elastomers comprising a step of dissolving the solid spent elastomer-based filler in the presence of a solvent corresponding to a recycle stream of the heavy liquid fraction of the filtrate obtained after distillation, comprising aromatic-rich compounds (preferably mono-aromatic).Unfortunately, the conditions for implementing such processes, and more specifically the choice of a heavy liquid fraction as a solvent, are not favorable to preventing the formation of carbon deposits contained in the final recovered carbon black.

[0011] French patent FR2009912 discloses a process for converting elastomers from used tires to obtain a so-called "recycled" carbon black (recovered carbon black) with a very low content of carbon residues (decomposition products of tire rubber and / or elastomer residues), thereby also limiting the agglomeration phenomena of the various structures of the recovered carbon black commonly encountered in processes described in the literature. The process consists of recycling a load of used tires at a temperature of 400°C or lower and a pressure of less than 1.5 MPa, by contacting said load with a solvent consisting of at least one hydrocarbon fraction comprising a high content of aromatic compounds, a low content of C40+ compounds (vacuum residues), and a moderate content of C5-C10 hydrocarbon compounds (gasoline). This solvent may be produced by the process itself (recycled).The operating conditions, the composition of the hydrocarbon cut and the mass ratio. The defined solvent / solid feedstock ratio maximizes the production of recovered carbon black through improved dissolution / decomposition of the solid feedstock while minimizing the presence of carbon residues in the final recovered carbon black. The carbon black recovery step in the solvolysis effluent (recovered carbon black) is performed by frontal filtration, solvent washing, and drying. The washing solvent for the filtered cake is chosen from toluene or xylene to lower the viscosity of the medium and facilitate frontal filtration and drying. Solvent regeneration steps by distillation are then necessary to purify and recycle the solvent within the process, which requires significant energy consumption.

[0012] It turns out that frontal filtration of a mixture of hydrocarbon liquid and solid carbon black particles is not a suitable separation technology for the recycling process of spent elastomers when the carbon black particles are very fine, i.e., between 1 µm and 30 µm, which results in the formation of a paste rather than a cake on the filter medium. The filtration flow rate is then prohibitive for industrial implementation.

[0013] In patent FR2387763, an alternative consists of separating the carbon black from the solvent by pure heat treatment without prior liquid / solid separation (evaporation and / or Soxhlet extraction). All the solvent is thus evaporated and the carbon black dried, which requires a significant energy expenditure.

[0014] US patent 3890141 discloses a process for converting solid waste from used tires into thermal energy while recovering metal oxides such as zinc oxide and titanium oxide. The densest carbon black particles contained in the used elastomers can optionally be recovered upstream of the combustion step by sedimentation and / or centrifugation. No operating conditions are specified in the patent.

[0015] US patent 6525105 discloses a process for liquefying gum, vulcanized or unvulcanized, at ambient temperature and pressure in an organic solvent containing peroxide. The carbon black can be recovered by a centrifugation, membrane separation, or sedimentation step, but no operating conditions are given in the patent.

[0016] The recovery of carbon black contained in the solvolysis slurry therefore appears critical from an operability and cost point of view.

[0017] The Applicant has developed a new solvolysis process for converting spent elastomers to overcome these drawbacks in order to recover carbon black. This process combines a solvolysis reaction step with optimized liquid / solid separation and carbon black drying steps to recover high-quality carbon black, with improved operability and efficiency. Controlled energy cost. The process consists of recycling an elastomer feedstock by contacting it with a solvent composed of at least one hydrocarbon fraction containing a high content of aromatic compounds, a low content of C40+ compounds (vacuum residues), and a moderate content of C5-C10 hydrocarbon compounds (gasoline). The solvent may be produced from the process itself (recycled). The operating conditions, the composition of the hydrocarbon fraction, and the solvent / solid feedstock mass ratio, as defined, allow for:

[0018] - minimize gas production and therefore maximize the oils of interest;

[0019] - to generate higher quality oils by limiting their aromatic content total and within the aromatics by significantly limiting the proportion of heavy aromatics;

[0020] - to maximize the production of recovered carbon black via a better dissolution / decomposition of the solid charge while limiting the presence of carbonaceous residues in the final recovered carbon black.

[0021] The liquid / solid separation of the suspension (slurry, according to Anglo-Saxon terminology) obtained downstream of the solvolysis reactor is then carried out by at least one centrifugation step to remove as much liquid as possible by a low-energy physical method, followed by a drying step to remove the residual liquid by a moderate thermal method. This sequence eliminates the need for percolation of the liquid through a compact cake and the energy-intensive washing step. Furthermore, optimizing the formulation of the internal solvent, which consists of a fraction of light oil and heavy oil, significantly reduces the temperature required during the drying step. Objects of the invention

[0022] The present invention relates to a process for converting used elastomers by solvolysis to obtain recovered carbon black, said process comprising at least the following steps:

[0023] a) a solid charge of spent elastomers is sent into a reaction zone in the presence of a liquid solvent comprising aromatic compounds to dissolve at least part of said solid charge and thermally decompose said at least partially dissolved solid charge at a temperature below 400°C and at a pressure below 1.5 MPa in order to obtain a first gaseous effluent and a first liquid effluent comprising carbon black, the mass ratio between the liquid solvent and the solid charge being greater than 3 weight / weight;

[0024] b) the first liquid effluent obtained in step a) is sent into a centrifugation zone at a centrifugal force of between 1000 G and 16000 G for a period of between 30 seconds and 30 minutes in order to obtain a centrifuged carbon black cake and a second liquid effluent;

[0025] c) at least part of said first gaseous effluent obtained at the end of step a), at least part of a second gaseous effluent obtained at the end of step e), and at least part of the second liquid effluent obtained at the end of step b) are sent to a fractionation zone to obtain at least one light hydrocarbon cut having a final boiling point between 250°C and 325°C and at least one hydrocarbon cut comprising an aromatic compound content exceeding 30% by weight relative to the total weight of said hydrocarbon cut, and further comprising:

[0026] - a C5-C10 hydrocarbon compound content of less than 20% by weight per ratio to the total weight of the hydrocarbon cutting; and

[0027] - a C40+ hydrocarbon compound content of less than 5% by weight relative to to the total weight of said hydrocarbon cutting;

[0028] d) at least a portion of said light hydrocarbon cut and at least a portion of said hydrocarbon cut obtained at the end of step c) are sent into the reaction zone as liquid solvent of step a), characterized in that the mass ratio between said hydrocarbon cut and the liquid solvent is between 0.2 and 0.95 weight / weight;

[0029] e) the centrifuged carbon black cake obtained at the end of step b) is dried in a conduction drying zone at a temperature between 150°C and 350°C, a vacuum pressure between 0.0001 MPa and 0.01 MPa absolute, under agitation between 2 rpm and 150 rpm for a period between 1 hour and 8 hours to obtain the recovered carbon black and said second gaseous effluent.

[0030] Advantageously, the mass ratio between said hydrocarbon cut and the liquid solvent is between 0.4 and 0.9 weight / weight.

[0031] Advantageously, the centrifugation force of step b) is between 2000 G and 8000 G.

[0032] Advantageously, the centrifugation time of step b) is between 1 minute and 20 minutes.

[0033] Advantageously, the volatile organic compound content in the recovered carbon black obtained at the end of step e), measured by thermogravimetric analysis known as TGA, is less than 10% by weight of volatile organic compounds in said recovered carbon black.

[0034] Advantageously, the second liquid effluent obtained at the end of step b) consists of at least 40% by weight of the first liquid effluent.

[0035] Advantageously, the agitation speed in the conduction drying zone of step e) is between 5 revolutions / min and 100 revolutions / min.

[0036] Preferably, the agitation speed in the conduction drying zone of step e) is between 10 rpm and 80 rpm.

[0037] Advantageously, step e) of drying is carried out at a pressure under absolute vacuum of between 0.0002 MPa and 0.005 MPa.

[0038] Advantageously, step e) of drying is carried out at a temperature between 200°C and 320°C.

[0039] Advantageously, the duration of step e) of drying is between 2 hours and 7 hours.

[0040] Preferably, the duration of step e) of drying is between 3 hours and 6 hours.

[0041] Advantageously, step a) comprises the following substeps:

[0042] al) said solid charge and said liquid solvent are sent into a first stirred reactor to dissolve said solid charge at least in part;

[0043] a2) said solid charge obtained at the end of is sent at least partially dissolved step a1) in a second stirred reactor to thermally decompose said solid feed at a temperature less than or equal to 400°C and obtain a liquid effluent containing suspended carbon black particles.

[0044] Advantageously, the aromatic compound content of the hydrocarbon cut is greater than 40% by weight relative to the total weight of said cut.

[0045] Advantageously, the solid charge (100) is based on used tires. List of figures

[0046] [Fig-1] Fig. 1 is a schematic representation of an embodiment obtaining carbon black according to the invention. Detailed description of the invention

[0047] 1. Definitions

[0048] By hydrocarbon Cn cut, we mean a cut comprising hydrocarbons with n carbon atoms.

[0049] By Cn+ cut, we mean a cut comprising hydrocarbons with at least n carbon atoms.

[0050] The specific surface area BET is measured by nitrogen physisorption according to ASTM D3663-03 as described in Rouquerol F.; Rouquerol J.; Singh K. “Adsorption by Powders & Porous Solids: Principle, methodology and applications”, Academy Press, 1999.

[0051] The CHNS-O elemental analyzer, manufactured according to ASTM D5291, is a method well known to those skilled in the art, allowing the rapid determination of the content of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) in organic matter and other types of materials, based on the total combustion of the analytical sample at 1000°C under oxygen.

[0052] The carbon residue content is evaluated by the X-Ray Photoelectron Spectroscopy (XPS) surface analysis technique, well known to those skilled in the art, and, in particular, by the precise analysis of the spectrum associated with the carbon element (Cls spectrum) which provides information on the chemical environment of the C atoms constituting the recovered carbon black. Indeed, the content of said carbon residues is determined by the % area of ​​peak Ci corresponding to a bond energy of approximately 284.8 / 285.6 eV, characteristic of CC / CH bonds of aliphatic structures or small aromatic compounds, associated with said residues and calculated in relation to the total area of ​​peaks Co to C5 (Co being the peak associated with CC / CH bonds of a graphitic structure and C2, C3, C4 and C5 the peaks respectively attributed to CO, C=O, COOH bonds and jt-jt* transitions).The method for measuring the carbon residue content is described in detail in the publication by Darmstadt H., Roy C., Kaliaguine S., “Characterization of pyrolytic carbon blacks from commercial tire pyrolysis plants Carbon” (1995), Carbon, Volume 33, No. 10, pp. 1449-1455, but also in the publication by Sahouli, Bendida; Blacher, Silvia; Brouers, François; Darmstadt, Hans; Roy, Christian; Kaliaguine, Serge: “Surface morphology and chemistry of commercial carbon black and carbon black from vacuum pyrolysis of used tyres” (1996), Fuel, Vol. 75, No. 10, pp. 1244-1250, or in the thesis by Ludovic Moulin: Valorisation du noir de carbone retrouvée, relation processus-produit. Génie des processus. Ecole des Mines d'Albi-Carmaux, 2018.

[0053] Thermogravimetric analysis is a widely used and well-known technique for those skilled in the art, for measuring the moisture content, volatile organic compound (VOC) content, and ash content of recovered carbon black. The protocol used is derived from ISO 9924-2, a standard primarily used for vulcanized and non-vulcanized mixtures. An initial temperature increase from 25°C to 600°C under nitrogen allows for the measurement of water content (mass loss in % between 25°C and 150°C) and the content of volatile organic compounds and / or pyrolyzable phase (mass loss between 150°C and 600°C). Following this first step, the sample is then cooled under nitrogen to 400°C. A second temperature increase, under air, between 400°C and 950°C allows the carbon to be burned and the quantity of carbon to be measured (carbon black recovered and any carbon residues).The final mass measured at the end of the protocol allows the mineral content to be determined. This analytical method is described in detail in the publication by Noms, C.; Haie, Mike; . Bennett, M. (2014) “Pyrolytic carbon: Factors controlling in-rubberperformance”, Plastics, Rubber and Composites, vol. 43, p. 245-256.

[0054] If specified, pressure is defined as absolute pressure and expressed in MPa.

[0055] The number of Gs is defined by the ratio between the acceleration considered and the acceleration due to Earth's gravity (9.81 m / s2).

[0056] The average size of carbon black particles in the liquid effluent is measured by laser particle size analysis (Mastersizer 3000).

[0057] 2. Description

[0058] The present invention relates to a process for converting spent elastomers by solvolysis to obtain recovered carbon black (520), said process comprising at least the following steps:

[0059] a) a solid charge (100) based on used elastomers is sent into a reaction zone (80) in the presence of a liquid solvent (760) comprising aromatic compounds to dissolve at least part of said solid charge and thermally decompose said at least partially dissolved solid charge at a temperature below 400°C and at a pressure below 1.5 MPa in order to obtain a first gaseous effluent (310) and a first liquid effluent (320) comprising carbon black, the mass ratio between the liquid solvent (760) and the solid charge (100) being greater than 3 weight / weight;

[0060] b) the first liquid effluent (320) obtained in step a) is sent into a centrifugation zone (40) at a centrifugal force between 1000 G and 16000 G for a period between 30 seconds and 30 minutes in order to obtain a centrifuged carbon black cake (420) and a second liquid effluent (410);

[0061] c) at least part of said first gaseous effluent (310) obtained at the end of step a), at least part of a second gaseous effluent (510) obtained at the end of step e) and at least part of the second liquid effluent (410) obtained at the end of step b) are sent to a fractionation zone (70) to obtain at least one light hydrocarbon cut (720) having a final boiling point between 250°C and 325°C and at least one hydrocarbon cut (730) comprising an aromatic compound content exceeding 30% by weight relative to the total weight of said hydrocarbon cut (730), and further comprising:

[0062] - a C5-C10 hydrocarbon compound content of less than 20% by weight per ratio to the total weight of the hydrocarbon cutting; and

[0063] - a C40+ hydrocarbon compound content of less than 5% by weight relative to to the total weight of said hydrocarbon cutting;

[0064] d) at least a portion of said light hydrocarbon cut (720) and at least a portion of said hydrocarbon cut (730) obtained at the end of step c) are sent into the reaction zone (80) as liquid solvent (760) of step a), characterized in that the mass ratio between said hydrocarbon cut (730) and liquid solvent (760) is between 0.2 and 0.95 weight / weight;

[0065] e) the centrifuged carbon black cake (420) obtained at the end of step b) is dried in a conduction drying zone (50) at a temperature between 150°C and 350°C, a vacuum pressure between 0.0001 MPa and 0.01 MPa absolute, under agitation between 2 rpm and 150 rpm for a period between 1 hour and 8 hours to obtain the recovered carbon black (520) and said second gaseous effluent (510). The charge

[0066] The solid filler (100) used in the context of the present invention is advantageously based on used elastomers that can come from any source, from tires of light vehicles (LV) or heavy goods vehicles (HGV), two-wheelers or any type of special equipment, vehicle door seals, but also from objects such as shoe soles or rubber boots. Preferably, the solid filler (100) is based on used tires and / or vehicle door seals, and more preferably on used tires.

[0067] Said solid filler can advantageously be in the form of elastomer granules, i.e. in the form of particles of sizes less than 25 mm containing more than 80% elastomers and reinforcing filler (carbon black, silica, etc.), from the treatment of end-of-life waste containing large quantities of elastomers.

[0068] Thus, according to a preferred embodiment of the invention, the solid feed (100) is sent to a pretreatment unit (10) in order to remove textile fibers and metal wires (110) from the solid feed (100). Such a pretreatment unit is well known to those skilled in the art and can consist of crushers of different types (i.e., a rotary shear, a shredder, a granulator, a refiner), a magnetic separator, or even a vibrating screen or a separation table. Step a)

[0069] According to step a) of the conversion process, the gum contained in the solid feedstock (100) is dissolved upon contact with the liquid solvent (760) and then thermally decomposed. The origin and composition of the liquid solvent (760) will be described in detail below. Step a) is preferably carried out at a temperature below 400°C, preferably between 365°C and 395°C, and even more preferably between 380°C and 395°C, and at a pressure below 1.5 MPa absolute, preferably between 0.2 MPa and 1.2 MPa absolute. At the end of step a), at least one gaseous effluent (310) and the first liquid effluent (320) are obtained. including carbon black and possibly solid material residues (210) contained in used elastomers, particularly in used tires, such as metal wires or textile fibers, which are released and separated from the liquid effluent (320) obtained at the end of this step. The mass ratio between the liquid solvent (760) and the solid feed (100) is greater than 3 wt / w, preferably between 3 wt / w and 10 wt / w, more preferably between 4 wt / w and 7 wt / w.

[0070] Advantageously, the residence time in the reaction zone (80) is between 0.5 hours and 4 hours.

[0071] According to one or more embodiments, step a) comprises the following substeps:

[0072] a) said solid charge and said liquid solvent are sent into a first stirred reactor to dissolve at least part of said solid charge; with a residence time between 30 minutes and 2 hours, at a temperature less than or equal to 300°C;

[0073] a2) the liquid effluent obtained at the end of step a1) is sent to a second agitated reactor to thermally decompose at a temperature less than or equal to 400°C (residence time between 30 minutes and 2 hours) said solid feed and obtain a liquid effluent containing suspended carbon black particles. Step b)

[0074] The first liquid effluent (320) containing carbon black is then sent to a centrifugation zone (40) to recover a centrifuged carbon black cake (420) and a second liquid effluent (410). This step is advantageously carried out at a temperature between 5°C and 350°C, preferably between 50°C and 300°C. According to a particular embodiment of the invention, a heat exchanger (not shown in [Fig. 1]) allows the temperature of the first liquid effluent (320) to be lowered between the reaction zone (80) and the centrifugation zone (40).

[0075] The centrifugal force is between 1000 G and 16000 G, preferably between 2000 G and 8000 G, preferably between 3000 G and 6000 G. A person skilled in the art can use any type of centrifuge technology, in particular a plate centrifuge or a decanter centrifuge.

[0076] The centrifugation time is between 30 seconds and 30 minutes, preferably between 1 minute and 20 minutes, and more preferably between 2 minutes and 10 minutes.

[0077] Centrifugation under the conditions of the invention allows for good liquid / solid separation efficiency.

[0078] The second liquid effluent (410) is preferably made up of more than 40% by weight of the first liquid effluent (320), more preferably more than 60% by weight of the first liquid effluent (320).

[0079] The second liquid effluent (410) is then sent to the fractionation column (70).

[0080] Step b'): (optional) additional centrifugation step

[0081] In order to lower the volatile organic compound content of the recovered carbon black (520), either because the required target content decreases or because the vacuum drying tool cannot reach a sufficiently high temperature or low pressure, a second centrifugation step is optionally considered to dilute the concentration of the heaviest hydrocarbons resulting from the feed conversion (100) and those most difficult to remove during the drying step (50). The centrifuged carbon black cake (420) from the first centrifugation step b) will be repelled in solvent (720), (730) or (760) in a stirred tank, and centrifuged again to reduce the concentration of the heaviest hydrocarbons in the second-centrifuged carbon black (the centrifuged liquid containing some of the heaviest hydrocarbons). Step c)

[0082] At least part of said first gaseous effluent (310) obtained at the end of step a), at least part of a second gaseous effluent (510) obtained at the end of step e), and at least part of the second liquid effluent (410) obtained at the end of step b) are sent to a fractionation zone (70) to obtain at least one light hydrocarbon cut (720) having a final boiling point between 250°C and 325°C and at least one hydrocarbon cut (730) comprising an aromatic compound content exceeding 30% by weight relative to the total weight of said hydrocarbon cut (730), and further comprising:

[0083] - a C5-C10 hydrocarbon compound content of less than 20% by weight per ratio to the total weight of the hydrocarbon cutting; and

[0084] - a C40+ hydrocarbon compound content of less than 5% by weight relative to to the total weight of said hydrocarbon cutting;

[0085] Advantageously, the hydrocarbon cut (730) also comprises a content of C10-C20 hydrocarbon compounds of between 20% by weight and 65% by weight relative to the total weight of the hydrocarbon cut, preferably between 30% by weight and 65% by weight, and even more preferably between 45% by weight and 65% by weight.

[0086] Advantageously, the hydrocarbon cut (730) also comprises a content of C20-C40 hydrocarbon compounds of between 30% by weight and 80% by weight relative to the total weight of the hydrocarbon fraction, preferably between 30% by weight and 70% by weight, and even more preferably between 30% and 55% by weight.

[0087] Advantageously, the hydrocarbon fraction (730) also comprises a content of C20-C40 hydrocarbon compounds between 30% by weight and 80% by weight relative to the total weight of the hydrocarbon fraction, preferably between 30% by weight and 70% by weight, and even more preferably between 30% and 55% by weight.

[0088] Advantageously, the hydrocarbon fraction (730) has an initial boiling point between 50°C and 325°C, preferably between 50°C and 250°C, and a final boiling point between 350°C and 520°C, preferably between 350°C and 450°C.

[0089] Advantageously, the light cut (720) comprises at least a content of hydrocarbon compounds in CIO- greater than 60% by weight relative to the total weight of the light cut (720).

[0090] Advantageously, the fractionation zone (70) also allows the obtaining of non-condensable gases (710), and a heavy cut (740), whose initial boiling temperature is preferably between 350°C and 450°C.

[0091] Advantageously, the heavy cut (740) comprises a content of C40+ hydrocarbon compounds greater than 60% by weight relative to the total weight of the heavy cut (740). Step d)

[0092] According to the invention, at least part of a fraction of the light hydrocarbon cut (720) and at least part of the hydrocarbon cut fraction (730) are sent to the reaction zone (80) of step a) as a liquid solvent (760), the other parts (750) and (770) being advantageously sent outside the process according to the invention as a valuable product. The mass ratio between the liquid solvent (760) and the flow rate of the solid feed (100) injected into the reaction zone (80) is greater than or equal to 3 wt / wt, preferably between 3 wt / wt and 10 wt / wt, more preferably between 4 wt / wt and 7 wt / wt.Indeed, one of the characteristics of the liquid solvent (760) is that it contains an aromatics content exceeding 30% by weight relative to the total weight of said liquid solvent (760), enabling it to efficiently dissolve the solid feed (100) and effectively reduce the viscosity of the reaction medium in the reaction zone (80). Another advantage of the process according to the invention is that the use of such a solvent allows it to remain in liquid form while limiting the pressure in the reactors to a level below 1.5 MPa. Fine-tuning the composition of the liquid solvent (760), the ratio of liquid solvent (760) to solid feed (100), and the reactor pressure also allows for targeting a specific carbon black concentration. in the reactor outlet effluent allowing for proper management of this flow as well as suitable conditions for the separation of carbon black.

[0093] Indeed, the proportion of said hydrocarbon cut (730) to constitute the liquid solvent (760) is also adjusted so as to optimize the steps downstream of the reaction zone (80), namely:

[0094] - a solids content at the inlet of the centrifuge advantageously between 5 and 20% dry solid weight, optimal operating range for this stage;

[0095] - the desired temperature at the drying stage downstream of centrifugation. It was It was discovered that the quantity of the hydrocarbon fraction (730) has a significant impact on the drying temperature required to achieve low residual moisture in the recovered carbon black. Indeed, the centrifuged carbon black cake (420) contains interstitial fluid that must be removed by evaporation during the drying step (e). This interstitial fluid to be evaporated consists of the hydrocarbon fraction (730) as well as the heavy fraction (740) resulting from the conversion of the solid feedstock (100). The stream of the light hydrocarbon fraction (720) present in the liquid solvent (760) is vaporized in the reaction zone (80).Since the drying process aims to remove all of the hydrocarbon fraction (730) and a large portion of the heavy fraction (740), the greater the quantity of hydrocarbon fraction (730) relative to the heavy fraction (740), the lower the drying temperature. This is due to the reduction in partial pressures, which facilitates the evaporation of the heavy fraction (740), thus limiting the vacuum drying temperature (<350°C). Limiting the drying temperature is crucial for operability and metallurgical reasons.

[0096] The formulation of the liquid solvent (760) results from a fine optimization to ensure the right conditions of dissolution and reaction, guaranteeing the maximization of valuable products, and the right operating conditions of the centrifugation and drying steps.

[0097] The mass ratio between said hydrocarbon cut (730) and the liquid solvent (760) is between 0.2 and 0.95 weight / weight, preferably between 0.4 and 0.9 weight / weight, and preferably between 0.5 and 0.8 weight / weight.

[0098] During the start-up of the installation, in the absence of production of a stabilized intermediate cut, i.e., the hydrocarbon cut (730), it is possible to temporarily use an imported solvent which will preferably consist of an aromatic molecule content exceeding 40% by weight relative to the total weight of the cut. This cut may therefore consist, for example, of conversion effluents from the FCC (Fluid Catalytic Cracking) process, middle distillate (LCO or "light cycle oil" according to Anglo-Saxon terminology), or of heavy distillate (HCO or "heavy cycle oil" according to Anglo-Saxon terminology) for example. Step e)

[0099] The centrifuged carbon black cake (420) obtained at the end of step b) is sent to a conduction drying zone (50) to obtain the recovered carbon black (520) and said second gaseous effluent (510).

[0100] Drying is carried out under vacuum, which allows the heating temperature to be lowered. The drying pressure is between 0.0001 MPa and 0.01 MPa, preferably between 0.0002 MPa and 0.005 MPa, more preferably between 0.0002 MPa and 0.001 MPa.

[0101] The drying temperature is between 150°C and 350°C, preferably between 200°C and 320°C, more preferably between 220°C and 300°C.

[0102] At the end of the drying step e), the content of volatile organic compounds in the recovered carbon black (520) measured by thermogravimetric analysis known as TGA, is less than 10% by weight, preferably less than 5% by weight, and preferably less than 3% by weight relative to the total mass of recovered carbon black (520).

[0103] The residence time of the centrifuged carbon black cake is adapted to achieve this target volatile organic compound content. The drying time is between 1 and 8 hours, preferably between 2 and 7 hours, more preferably between 3 and 6 hours.

[0104] Drying is carried out by conduction. In conductive drying, heat is transferred to the centrifuged carbon black cake by contact with a wall heated by a fluid. Indeed, given the fineness of the particles, convective drying carries too many particles into the gas stream. Conduction drying, on the other hand, allows for good particle recovery efficiency. To characterize this recovery of solid particles, the diameter d97 is generally defined as the particle diameter below which 97% of the particles by volume are found. After drying, the diameter d97 is less than 60 pm, preferably less than 20 pm, and even more preferably less than 10 pm.

[0105] According to the invention, the centrifuged carbon black cake is agitated during conduction drying in order to renew the solid in contact with the heated wall.

[0106] The rotation speed of the agitator is between 2 revolutions / min and 150 revolutions / min, preferably between 5 revolutions / min and 100 revolutions / min, more preferably between 10 revolutions / min and 80 revolutions / min.

[0107] A person skilled in the art will choose the conductive dryer technology suitable for carbon black. Examples include, but are not limited to, externally heated rotating tube dryers, paddle dryers, and cylinder dryers.

[0108] In order to be able to be incorporated into an elastomer matrix for recycled elastomers, the recovered carbon black (520) can optionally be sent to a crusher in particular a jet crusher (not shown in [Fig.1]).

[0109] The second gaseous effluent (510) from the drying step is sent to the fractionation zone (70).

[0110] Step e'): (optional) additional drying step.

[0111] If the target volatile organic compound (VOC) content in the recovered carbon black (520) is not achieved, the carbon black can undergo a further drying step (e'). This final drying can be carried out using various dryer technologies, including a fluidized bed dryer at atmospheric pressure where the solid particles are kept in suspension at high temperature. Unlike the first dryer in step e), which is fed with a more or less compact cake of wet solid, the second dryer is fed with dry-looking carbon black powder that can be easily suspended. Reclaimed carbon black

[0112] The recovered carbon black (520) at the end of steps a) to e), consists of carbon black (CB), inorganic ash, and carbon residues from the decomposition of tire rubbers and / or elastomeric residues associated with said tire rubbers, characterized in that said carbon residue content, determined with respect to the percentage area of ​​peak Ci measured by X-ray photoelectron spectroscopy, is less than or equal to 1% of said area of ​​peak Ci, preferably between 0.001% area and 0.08% area, more preferably between 0.001% area and 0.07% area, and even more preferably between 0.001% area and 0.05% area, said percentage area of ​​peak Ci being calculated with respect to the total area of ​​peaks Co to C5.

[0113] More particularly, the recovered carbon black (520) comprises between 50% by weight and 98% by weight of carbon element relative to the total weight of said recovered carbon black, preferably between 60% by weight and 90% by weight, and even more preferably between 65% by weight and 85% by weight.

[0114] More particularly, the recovered carbon black (520) comprises between 0.2% by weight and 4% by weight of oxygen element relative to the total weight of the recovered carbon black, preferably between 0.4% by weight and 3% by weight, and even more preferably between 0.8% by weight and 2.7% by weight.

[0115] More particularly, the recovered carbon black (520) comprises between 0.2 wt% and 3 wt% of hydrogen element relative to the total weight of the recovered carbon black, preferably between 0.4 wt% and 2.5 wt%, and even more preferably between 0.5 wt% and 1.5 wt%.

[0116] More particularly, the recovered carbon black (520) comprises between 0.05 wt% and 1 wt% of nitrogen element relative to the total weight of the recovered carbon black, preferably between 0.1 wt% and 0.7 wt%, and even more preferably between 0.15 wt% and 0.4 wt%.

[0117] More particularly, the recovered carbon black (520) comprises between 0.5 wt% and 6 wt% of sulfur element per wt% of the total recovered carbon black, preferably between 1.5 wt% and 5 wt%, and even more preferably between 2 wt% and 3.5 wt%.

[0118] Carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) content was measured by CHNS-O elemental analysis.

[0119] The recovered carbon black (520) obtained at the end of steps a) to e) also comprises inorganic ash. The inorganic ash consists of at least the atomic element Si, predominantly present in its oxidized form SiO2 (silica), and at least the element zinc, predominantly present in its oxidized form ZnO (zinc oxide) and / or its sulfide form ZnS (zinc sulfide), preferably in its sulfide form ZnS. The application of a specific heat treatment (of at least 950°C in air, by TGA analysis) makes it possible to quantify the content of inorganic ash present in the recovered carbon black according to the invention. Thus, the inorganic ash content is advantageously between 4% by weight and 50% by weight relative to the total weight of the recovered carbon black, preferably between 8% by weight and 40% by weight, and even more preferably between 10% by weight and 30% by weight.

[0120] Advantageously, the recovered carbon black (520) according to the invention comprises a specific surface area, determined by nitrogen physisorption, of between 30 m2 / g and 150 m2 / g, preferably between 50 m2 / g and 90 m2 / g and even more preferably between 50 m2 / g and 75 m2 / g.

[0121] Advantageously, the structure index, determined by the analytical method O AN in accordance with ASTM D2414, is between 55 m3 / kg and 110.105 m3 / kg, preferably between 55 m3 / kg and 90.105 m3 / kg. Examples

[0122] The method used to illustrate the invention conforms to that described in [Fig. 1].

[0123] In these examples, the charge of used elastomers consists of 100% used tires.

[0124] Used tire granules (solid charge (100)), produced by granulators using crushers, are used. These granules come from heavy-duty tires, and the resulting granules have a size of approximately 2 millimeters. The tire granules (100) originate from a pretreatment unit (10) and are free of textile fibers. and metallic. The aggregates (100) are then continuously fed into a dissolution and conversion reactor (80) where they are mixed with the liquid solvent from the hydrocarbon fraction (730) recycled from the fractionation zone (70). A portion of the hydrocarbon fractions (720) and (730), whose compositions are shown in Table 1 below, serves as the liquid solvent (760) below. The mass ratio of solvent (760) to aggregate (100) is 5 wt / wt. In the reactor (80), the temperature is maintained at 385°C, which allows the aggregates (100) to dissolve. The residence time in the reactor (80) is 2 hours. The pressure in the dissolution reactor is 0.9 MPa. At the outlet of the reactor (30), a first liquid effluent (320) and a gaseous effluent (310) are recovered, the latter being sent entirely to the fractionation zone (70).

[0125] The composition of hydrocarbon cuts (720), (730) are given in Table 1 below.

[0126] [Tables 1] Hydrocarbon cut (720) Hydrocarbon cut (730) Gas % wt 0.4 <0.1 Gasoline (C5-205°C) % wt 17.7 4.8 Diesel (205-370°C) % wt 79.3 88.2 VGO (370-520°C) % wt 2.6 7.0 RSV (520°C+) % wt <0.1 <0.1

[0127] The dry solids content in the first liquid effluent (320) is 10% by weight relative to the total weight of the liquid effluent (320). The average size of the carbon black particles in the first liquid effluent (320), measured by Mastersize 3000 laser particle size analysis in liquid-phase ultrasonics, is between 0.5 µm and 30 µm.

[0128] In the following examples 1 to 6, laboratory tests were carried out on the liquid / solid separation of said first liquid effluent (320) and then on the drying of the carbon black obtained after liquid / solid separation. The fraction (760) is obtained after mixing a portion of fractions (720) and (730), with a mass ratio (730) / (760) of 0.7.

[0129] In example 7, the cut (760) is obtained after mixing a part of the cuts (720) and (730), with a mass ratio (730) / (760) of 0.3. Hydrocarbon fraction (760) - obtained for a mass ratio (730) / (760) of 0.7 Hydrocarbon fraction (760) - obtained for a mass ratio (730) / (760) of 0.3 Gas % wt 0.1 0.3 Gasoline (C5-205°C) % wt. 8.6 13.8 Diesel (205-370°C) % wt. 85.6 81.9 VGO (370-520°C) % wt. 5.7 4.0 RSV (520°C+) % wt. <0.1 <0.1

[0130] Example 1: no liquid / solid separation of the liquid effluent (320), mass ratio (730) / (760) of 0.7, conductive drying (not in accordance with the invention)

[0131] Without a prior liquid / solid separation step, a portion of the liquid effluent (320), composed of 10% dry solid and 90% liquid to be evaporated, is directly dried by conduction in a double-jacketed stirred tank at a stirring speed of 33 rpm at 260°C under a vacuum of 0.0005 MPa. To achieve a volatile organic compound (VOC) content in the recovered carbon black (520), measured by thermogravimetric analysis (TGA), of less than 2% by weight of VOCs in the recovered carbon black (520), the drying time required is 9 hours.

[0132] Example 2: Liquid / solid separation of liquid effluent (320) by frontal filtration, mass ratio (730) / (760) of 0.7 (not in accordance with the invention)

[0133] In Example 2, frontal filtration tests were carried out with filter cloths on a portion of the first liquid effluent (320) recovered from the solvolysis outlet. The surface area of ​​the filter cloth is 56 cm². Different cloths (PEEK (polyetheretherketone) cloth and Porostar® metal cloth) and different filtration pressures up to 0.5 MPa were tested. For all the frontal filtration tests, either the filtrate flow rate was almost zero or clearly too low to extrapolate to an industrial scale (the cloth being clogged by the solid), or all the carbon black passed through the overly open cloth, and liquid / solid separation did not occur.

[0134] The samples have not been dried.

[0135] Example 3: Liquid / solid separation of the liquid effluent (320) by centrifugation at 500G, mass ratio (730) / (760) of 0.7 (not in accordance with the invention)

[0136] A portion of the liquid effluent (320) is centrifuged at 500G in a Sorvall 6 RC Plus laboratory centrifuge (rotor F14S-6*250Y) at 20 °C for 5 min. After centrifugation, a second liquid effluent (410) and a centrifuged carbon black cake (420) are obtained.

[0137] The liquid / solid separation is not satisfactory, the liquid (410) is not free of solid, which represents a non-negligible loss of carbon black.

[0138] The cake has not been dried.

[0139] Example 4: Liquid / solid separation of the liquid effluent (320) by centrifugation at 2000G, mass ratio (730) / (760) of 0.7, conductive drying (according to the invention)

[0140] A portion of the liquid effluent (320) is centrifuged at 2000G in a Sorvall 6 RC Plus laboratory centrifuge (rotor F14S-6*250Y) at 20°C for 5 min. After centrifugation, a second liquid effluent (410) and a centrifuged carbon black cake (420) are obtained. 62% by weight of the total liquid of the effluent (320) is removed by centrifugation.

[0141] The centrifuged carbon black cake (420) of Example 4 consists of 23% by weight of dry solid and 77% by weight of liquid to be evaporated. This cake is then dried by conduction in a double-jacketed stirred tank with a stirring speed of 33 rpm at 260°C under a vacuum of 0.0005 MPa.

[0142] To achieve a VOC content in the recovered carbon black (520) measured by thermogravimetric analysis known as TGA of less than 2% weight of VOC in the recovered carbon black (520), the drying time required is 6 hours.

[0143] Example 5: Liquid / solid separation of the liquid effluent (320) by centrifugation at 7500G, mass ratio (730) / (760) of 0.7, conductive drying (according to the invention)

[0144] A portion of the liquid effluent (320) is centrifuged at 7500 G in a Sorvall 6 RC Plus laboratory centrifuge (rotor F14S-6*250Y) at 20 °C for 5 min. After centrifugation, a second liquid effluent (410) and a centrifuged carbon black cake (420) are obtained. 72% wt. of the total liquid of the effluent (320) is removed by centrifugation. The quality of the liquid / solid separation is therefore significantly improved compared to Examples 2 and 3.

[0145] The centrifuged carbon black cake (420) of Example 5 consists of 28% by weight of dry solid and 72% by weight of liquid to be evaporated. This cake is then dried by conduction in a double-jacketed stirred tank at a stirring speed of 33 rpm at 260°C under a vacuum of 0.0005 MPa. To achieve a VOC content in the recovered carbon black (520), measured by thermogravimetric analysis (TGA), of less than 2% by weight of VOCs in the recovered carbon black (520), the drying time required is 5 hours.

[0146] Example 6: Liquid / solid separation of the liquid effluent (320) by centrifugation at 7500G, mass ratio (730) / (760) of 0.7, convective drying (not in accordance with the invention)

[0147] A portion of the liquid effluent (320) is centrifuged at 7500G in a Sorvall 6 RC Plus laboratory centrifuge (rotor F14S-6*250Y) at 20 °C for 5 min. After centrifugation, a second liquid effluent (410) and a centrifuged carbon black cake (420) are obtained (similar to Example 5).

[0148] The centrifuged carbon black cake (420) of Example 6 is composed of 28% by weight of dry solid and 72% by weight of liquid to be evaporated. This cake is then dried by convection in a vacuum vessel (0.0005 MPa absolute) that is not agitated and is not heated by the walls: only nitrogen heated to 260°C (10 NLN2 / h / g dry solid) is used. Injected at the bottom of the tank, the gas facilitates drying. Without mechanical agitation of the wet solid, agglomerates form, with dry crusts around them, leaving the core moist. To make the mixture more homogeneous and improve drying, a higher gas flow rate would be necessary. Since the heat supplied by the gas is significantly less than the heat that can be supplied by conduction (wall heating), an excessively high gas flow rate would be required to improve drying, generating excessive entrainment that is difficult to manage on an industrial scale. Nine hours of drying is insufficient to achieve the target VOC content of 2% by weight in the recovered carbon black (520) (non-homogeneous mixture). This scenario is therefore not considered.

[0149] Only Examples 4 and 5, which combine liquid / solid separation by centrifugation under the conditions of the invention with conductive drying under the same conditions, allow for the recovery of dried carbon black with good recovery efficiency under low-energy conditions. Example 1, which does not use liquid / solid separation upstream of the drying step, allows for the production of dried carbon black, but under very energy-intensive conditions, requiring more than 9 hours of drying. Example 2, which uses frontal filtration, did not allow for the recovery of a carbon black cake; therefore, drying was not possible. Example 3, which uses centrifugation but with a G number not in accordance with the invention, did not allow for the proper separation of the carbon black particles in the suspension. Consequently, drying was not achieved.Example 6, using convective drying, did not allow the cake to dry homogeneously even after a long drying time at a gas flow rate that prevented particle entrainment.

[0150] Example 7: Liquid / solid separation of the liquid effluent (320) by centrifugation at 7500G, mass ratio (730) / (760) of 0.3, conductive drying (according to the invention)

[0151] In example 7, the cut (760) is obtained after mixing a part of the cuts (720) and (730), with a mass ratio (730) / (760) of 0.3 (same conditions as in example 5 except the mass ratio (730) / (760)).

[0152] The centrifuged carbon black cake (420) of Example 7 is composed of 28% by weight of dry solid and 72% by weight of liquid to be evaporated. This cake is then dried by conduction in a double-jacketed stirred tank with a stirring speed of 33 rpm under a vacuum of 0.0005 MPa.

[0153] To achieve a VOC content in the recovered carbon black (520) measured by thermogravimetric analysis known as TGA of less than 2% by weight of VOC in the recovered carbon black (520), the drying time required is 5 hours but the drying temperature required is 315°C (instead of 260°C as in example 5).

[0154] The main liquid / solid separation and drying results are summarized in Table 2.

[0155] [Tables2] Example Ratio (730) / (760) Liquid / Solid Separation Drying Conditions to Obtain Carbon Black with a Residual Moisture of 2% 1 (not compliant) 0.7 Non-Conductive Drying, at 260°C, 33 rpm, 0.0005 MPa, 9 hours 2 (not compliant) 0.7 Frontal Filtration (excessive solid loss or filtration impossible) Undried Solid 3 (not compliant) 0.7 Centrifugation under 500 G (excessive solid loss) Undried Solid 4 (compliant) 0.7 Centrifugation under 2000 G Conductive Drying, at 260°C, 33 rpm, 0.0005 MPa, 9 hours 5 (compliant) 0.7 Centrifugation under 7500 G Conductive Drying, at 260°C, 33 rpm, 0.0005 MPa, 5 hours 6 (non-compliant) 0.7 Centrifugation under 7500G Convective drying 10 NLN2 / h / g dry solid, at 260°C, 0.0005 MPa, >9 hours non-homogeneous solid 7 (compliant) 0.3 Centrifugation under 7500G Conductive drying, at 315°C, 33 rpm, 0.0005 MPa, 5 hours

Claims

1. Demands A process for converting spent elastomers by solvolysis to obtain recovered carbon black (520), said process comprising at least the following steps: a) a solid charge (100) of spent elastomers is sent into a reaction zone (80) in the presence of a liquid solvent (760) comprising aromatic compounds to dissolve at least part of said solid charge and thermally decompose said at least partially dissolved solid charge at a temperature below 400°C and at a pressure below 1.5 MPa in order to obtain a first gaseous effluent (310) and a first liquid effluent (320) comprising carbon black, the mass ratio between the liquid solvent (760) and the solid charge (100) being greater than 3 weight / weight; b) the first liquid effluent (320) obtained in step a) is sent into a centrifugation zone (40) at a centrifugal force between 1000 G and 16000 G for a period between 30 seconds and 30 minutes in order to obtain a centrifuged carbon black cake (420) and a second liquid effluent (410); (c) at least part of said first gaseous effluent (310) obtained at the end of step (a), at least part of a second gaseous effluent (510) obtained at the end of step (e), and at least part of the second liquid effluent (410) obtained at the end of step (b) are sent to a fractionation zone (70) to obtain at least one light hydrocarbon cut (720) having a final boiling point between 250°C and 325°C and at least one hydrocarbon cut (730) comprising an aromatic compound content exceeding 30% by weight relative to the total weight of said hydrocarbon cut (730), and further comprising: - a content of C5-C10 hydrocarbon compounds of less than 20% by weight in relation to the total weight of the hydrocarbon cut; and - a content of C40+ hydrocarbon compounds of less than 5% by weight in relation to the total weight of said hydrocarbon cut; d) at least a portion of said light hydrocarbon cut (720) and at least a portion of said hydrocarbon cut (730) obtained at the end of step c) are sent into the reaction zone (80) as liquid solvent (760) of step a), characterized in that the mass ratio between said hydrocarbon cut (730) and liquid solvent (760) being between 0.2 and 0.95 weight / weight; e) the centrifuged carbon black cake (420) obtained at the end of step b) is dried in a conduction drying zone (50) at a temperature between 150°C and 350°C, a vacuum pressure between 0.0001 MPa and 0.01 MPa absolute, under agitation between 2 rpm and 150 rpm for a period between 1 hour and 8 hours to obtain the recovered carbon black (520) and said second gaseous effluent (510).

2. A method according to claim 1, wherein the mass ratio between said hydrocarbon cut (730) and the liquid solvent (760) is between 0.4 and 0.9 weight / weight.

3. A method according to any one of claims 1 or 2, wherein the centrifugal force of step b) is between 2000 G and 8000 G.

4. A method according to any one of the preceding claims, wherein the centrifugation time of step b) is between 1 minute and 20 minutes.

5. A process according to any one of the preceding claims, wherein the volatile organic compound content in the recovered carbon black (520) obtained at the end of step e), measured by thermogravimetric analysis known as TGA, is less than 10% by weight of volatile organic compounds in said recovered carbon black (520).

6. A process according to any one of the preceding claims, wherein the second liquid effluent (410) obtained at the end of step b) consists of at least 40% by weight of the first liquid effluent (320).

7. A method according to any one of the preceding claims, wherein the agitation speed in the conduction drying zone of step e) is between 5 rpm and 100 rpm.

8. A method according to any one of the preceding claims, wherein the agitation speed in the conduction drying zone of step e) is between 10 rpm and 80 rpm.

9. A method according to any one of the preceding claims, wherein the drying step e) is carried out at an absolute vacuum pressure between 0.0002 MPa and 0.005 MPa.

10. A method according to any one of the preceding claims, wherein the drying step e) is carried out at a temperature between 200°C and 320°C.

11. A method according to any one of the preceding claims, wherein the duration of step e) of drying is between 2 hours and 7 hours.

12. A method according to any one of the preceding claims, wherein the duration of step e) of drying is between 3 hours and 6 hours.

13. A process according to any one of the preceding claims, wherein step a) comprises the following substeps: a1) said solid feed (100) and said liquid solvent (760) are sent into a first stirred reactor (20) to dissolve at least part of said solid feed (100); a2) said at least partially dissolved solid feed obtained at the end of step a1) is sent into a second stirred reactor (30) to thermally decompose said solid feed at a temperature less than or equal to 400°C and obtain a liquid effluent containing suspended carbon black particles.

14. A process according to any one of the preceding claims, wherein the aromatic compound content of the hydrocarbon cut (730) is greater than 40% by weight relative to the total weight of said cut.

15. A method according to any one of the preceding claims, wherein the solid charge (100) is based on used tires.

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