Process for the production of olefins by steam cracking of feedstocks from plastic waste

Abstract

The invention relates to a process for the production of olefins by steam cracking, in particular from feedstocks from plastic waste, especially from a composition comprising a plastic liquefaction oil, said composition comprising paraffins, olefins, aromatics and heteroatoms. The process comprises: (a) a step of separating a portion of the paraffins and olefins contained in said composition, comprising at least one step of crystallizing (i) the composition by lowering the temperature by 10°C to 60°C from an initial temperature at which the composition is entirely liquid, and obtaining a mixture comprising a paraffin-enriched solid product depleted of olefins, aromatics and heteroatoms and a paraffin-depleted effluent enriched in olefins, aromatics and heteroatoms, followed by at least one step of separating (ii) said solid product and said effluent, (b) a step of hydrotreating the solid product of step (a) and obtaining a hydrotreated effluent having a reduced olefin content, and optionally a reduced content of heteroatoms and aromatics, (c) a step of steam cracking the hydrotreated effluent and obtaining an effluent containing olefins.

Description

[0001]TITLE: PROCESS FOR PRODUCING OLEFINS BY STEAM CRACKING FEEDSTOCKS FROM PLASTIC WASTE Technical field The present invention relates to a process for producing olefins by steam cracking, in particular from feedstocks from plastic waste. Context of the invention Olefins, and in particular light C2-C5 olefins, such as ethylene, propylene, butadiene, isobutene, n-butene and isoprene, are monomers that can be used to produce a whole range of polymers by appropriate treatments (chlorination, oxidation, polymerization, etc.). These olefins are most often obtained by steam cracking fossil hydrocarbons such as naphtha, gasoline, ethane. With the scarcity of fossil resources and growing environmental constraints, manufacturers are looking for other hydrocarbon feedstocks to produce olefins by steam cracking. Furthermore,The significant quantities of plastic waste produced and the environmental problems they generate have led manufacturers to seek ways to recycle this waste, in particular those allowing the production of new monomers and then polymers and thus closing the life cycle of plastic. This recycling route is a chemical route consisting of liquefying plastic waste, in particular by thermal means (typically by pyrolysis or hydrothermal liquefaction), then reintroducing the effluent produced into a conventional refining circuit. This liquefaction is however energy-intensive and is therefore only considered for treating contaminated plastic waste,cannot be treated in any other way (e.g., by mechanical recycling or depolymerization). The significant amount of impurities present in plastic waste liquefaction oils requires pretreatment before injection into a conventional refining circuit. Thus, pyrolysis or hydrothermal liquefaction of plastic waste is typically followed by purification including hydrotreatment and removal of contaminants using various purification processes such as distillation. There are thus many pretreatment processes focused on the removal of chlorinated compounds. However, other impurities present in plastic liquefaction oil simply prohibit their direct use in other processes such as steam cracking. Indeed,Steam crackers are very sensitive to the presence of olefins or dienes in the feed and to the presence of silicon or organosilicon compounds. In addition, oxygenated compounds present in plastic liquefaction oil can be converted to peroxides and thus promote the formation of polymers and gums. In particular, the presence of olefins and oxygenated compounds can lead to undesirable polymerization during storage, transport from the production site to the place of further processing as well as during purification and further processing. Since purification operations are often carried out at elevated temperatures,an increase in the undesirable polymerization rate can thus be observed. Document WO2021 / 115982 describes a process for the recovery by dewaxing of aliphatic hydrocarbons from a hydrocarbon feedstock comprising aliphatic hydrocarbons and polar compounds containing a heteroatom. This feedstock includes the liquid products resulting from the pyrolysis of plastic waste. The process described consists of mixing the feedstock to be treated with a solvent, cooling the mixture in a temperature range of 5°C to -30°C to obtain wax crystals and separating them in order to produce aliphatic hydrocarbons comprising wax and a dewaxed liquid comprising the solvent, the polar compounds and optionally aromatics. This document provides for steam cracking of the aliphatic hydrocarbons comprising wax directly,without intermediate hydrotreatment. These aliphatic hydrocarbons are defined as non-olefinic (paraffinic) aliphatic compounds and olefinic aliphatic compounds. However, the specifications of current steam cracking units require reduced olefin contents (typically less than 1 ppm) to limit the risks of coking, which are not achieved by the dewaxing treatment described here. Furthermore, the behavior of plastic waste liquefaction oils is difficult to predict due to the complexity of these oils. For example, gas chromatographic analysis of plastic waste pyrolysis oil can only identify 25 to 45% by weight of the compounds containing oxygen and nitrogen. In addition,the composition of these oils varies greatly depending on the nature of the plastic waste being processed. There is therefore a continuing need to develop methods for producing high-value chemicals from plastic waste, regardless of its origin, in particular using existing conventional refining units. Summary of the invention The invention aims to provide a process for producing olefins by steam cracking from a composition comprising a plastic liquefaction oil, said composition comprising paraffins, olefins, aromatics and heteroatoms,the process comprising: (a) a step of separating a portion of the paraffins and olefins contained in said composition comprising at least one step of crystallization (i) of said composition by lowering the temperature from 10°C to 60°C from an initial temperature at which said composition is entirely liquid and obtaining a mixture comprising a solid product enriched in paraffins and depleted in olefins, aromatics and heteroatoms, and an effluent depleted in paraffins and enriched in olefins, aromatics and heteroatoms, followed by at least one step of separation (ii) of said solid product and said effluent, (b) a step of hydrotreatment of the solid product of step (a) and obtaining a hydrotreated effluent having a reduced content of olefins, and optionally a reduced content of heteroatoms and aromatics,(c) a step of steam cracking the hydrotreated effluent and obtaining an effluent containing olefins. This particular sequence of steps makes it possible to treat in a steam cracker an effluent resulting from a composition comprising a plastic liquefaction oil but having olefin, aromatic and heteroatom contents in accordance with those required at the inlet of a steam cracking process, regardless of the contaminant content of the composition. The process according to the invention makes it possible in particular to produce olefins from compositions containing C5-C150 hydrocarbons, most often C5-C100. In particular,the separation step (a) can be carried out to separate the paraffins from the olefins present in compositions containing hydrocarbons without limitation as to the number of carbon atoms constituting them. The composition treated by the process according to the invention can comprise at least 2% by mass of plastic liquefaction oil(s). The remainder may then be composed of at most 98% by mass of a diluent or solvent such as a hydrocarbon and / or one or more components such as: a biomass liquefaction oil such as Panicum virgatum, a tall oil, a used cooking oil, an animal fat, a vegetable oil such as rapeseed oil, canola oil, castor oil, palm oil, soybean oil, an oil extracted from an algae, an oil extracted from a fermentation of oleaginous microorganisms such as oleaginous yeasts, a biomass liquefaction oil such as a lignocellulosic biomass such as a wood liquefaction oil,of paper and / or cardboard, an oil obtained by pyrolysis of crushed used furniture, an elastomer liquefaction oil, for example optionally vulcanized latex or tires, as well as mixtures thereof. In one embodiment, the composition may comprise at least 5% by mass, at least 10% by mass, at least 25% by mass, at least 50% by mass, at least 75% by mass, at least 90% by mass or 100% by mass of plastic liquefaction oil(s). The mass content of plastic liquefaction oil(s) in the composition may be within any range defined by two of the limits previously set. The heteroatoms contained in the composition treated in the present invention may be oxygen, nitrogen, sulfur, silicon, a metal and / or a halogen, in particular chlorine. The solid product from step (a) may contain from 45% m / m to 90% m / m of paraffins, preferably from 50% m / m to 90% m / m of paraffins, from 10 to 50% m / m of olefins,preferably from 10 to 40% m / m of olefins, from 0 to 2% m / m of aromatics, from 2 to 15% m / m of naphthenes, and optionally at most 2% m / m of heteroatoms. In particular, step (a) can make it possible to eliminate at least 80% m / m of chlorine and / or at least 85% m / m of nitrogen and / or at least 50% m / m of sulfur and / or at least 60% m / m of silicon relative to the respective quantities of chlorine, nitrogen, sodium and silicon initially present in the composition entering into the process according to the invention. The hydrotreated effluent produced in step (b) can contain from 0 to 2% m / m of olefins, preferably from 0 to 1% m / m. The total heteroatom content can be from 0 to 1% m / m. Thus, the effluent produced in step (b) may contain 70%m / m or more of paraffins, preferably 80%m / m or more of paraffins, more preferably 90%m / m or more of paraffins, in particular 97%m / m or more of paraffins, preferably 98%m / m or more of paraffins. The effluent from step (b) may advantageously contain C10+ paraffins,for example C10-C100 paraffins, most often C10-C80. Advantageously, the hydrotreated effluent produced in step (b) may also contain: - at most 100 ppm of oxygen (measured according to the ASTM D5622 / D2504 standard), - at most 20 ppm of nitrogen (measured according to the ASTM D4629 standard), - at most 500 ppm of sulfur (measured according to the ISO 20846 standard), - at most 120 ppm of chlorine (measured according to the ASTM D7359-18 standard), - optionally at most 15 ppm of silicon (measured by XRF). In one embodiment, during the separation step (a), said composition may be mixed with at least one solvent prior to the at least one crystallization step (i). It will then be possible to advantageously provide a separation step (iii) of the at least one solvent from the effluent resulting from the separation step (ii) and the return of the at least one solvent separated to step (i). The solvent may advantageously be an organic solvent, for example chosen from an aliphatic hydrocarbon,an aromatic hydrocarbon, a ketone, an alcohol or mixtures thereof, preferably a ketone or an alcohol. Examples of solvents that can be used include acetone, methyl ethyl ketone, isopropanol. In particular, a solvent or a mixture of solvents may be chosen which does not crystallize at the crystallization temperature of the paraffins to be separated, preferably a solvent or a mixture of solvents in the liquid state and miscible with the composition at the temperatures for carrying out step (a) of the process of the present invention and in particular of the at least one crystallization step (i). A person skilled in the art will be able to determine the most appropriate solvent or mixture of solvents based on the temperatures used during step (a) by tests and / or simulations. In particular, when the feedstock to be treated is solid and / or very viscous,it may be necessary to heat the feedstock to reach the initial temperature before lowering the temperature from 10 to 60°C: a solvent or mixture of solvents will then be chosen which remains liquid at these temperatures. The volume ratio of said composition to the solvent may be from 10 / 90v / v to 90 / 10v / v, or from 20 / 80v / v to 80 / 20 v / v, preferably from 40 / 60v / v to 60 / 40v / v or from 45 / 55v / v to 55 / 45v / v, for example 50 / 50 v / v, or in any interval defined by two of these ratios. The separation step (a) may be carried out in a single step or in two steps to improve the separation and recovery of the paraffins. The separation step (a) can then comprise: (i-1) a first crystallization step by lowering the temperature of said composition from 10°C to 60°C from a first initial temperature at which said composition is entirely liquid and obtaining a first mixture comprising a first solid product enriched in paraffins and depleted in olefins,in aromatics and heteroatoms, and a first effluent depleted in paraffins and enriched in olefins, aromatics and heteroatoms, (ii-1) a first step of separating said first solid product and said first effluent, (i-2) a second step of crystallization by lowering the temperature of said first effluent from 10°C to 60°C from a second initial temperature at which said first effluent is entirely liquid and obtaining a second mixture comprising a second solid product enriched in paraffins and depleted in olefins, aromatics and heteroatoms, and a second effluent depleted in paraffins and enriched in olefins, aromatics and heteroatoms, (ii-2) a second step of separating said second solid product and said second effluent, and the first solid product and the second solid product are subjected to step (b) of hydrotreatment. When a solvent or a mixture of solvents is added to the composition,it is then added before the first crystallization step (i-1). Preferably, no solvent is added before the second crystallization step (i-2). Crystallization step (i) or each of crystallization steps (i-1) and (i-2) is carried out from an initial temperature at which the composition (alone or in a mixture with a solvent), or the first effluent, is entirely liquid, to a final temperature, 10 to 60°C lower than the initial temperature. The initial temperature of step (i) or of each of steps (i-1) and (i-2), can be easily determined by a person skilled in the art by standard measuring methods. The initial temperature is typically higher (for example by 5 to 10°C) than the crystallization temperature of the paraffins to be separated from the composition. This crystallization temperature can be determined by differential scanning calorimetry measurements (P.Claudy et al,Diesel fuels: determination of onset crystallization temperature, pour point and filter plugging point by differential scanning calorimetry. Correlation with standard test methods. Fuel, 1986, vol 65, pp 861-4). Step (a) can advantageously be carried out under conditions suitable for separating C10+ paraffins, for example C10-C100 paraffins, most often C10-C80. These conditions include the final temperature of step (i) or of each of the steps (i-1) and (i-2) mentioned above, typically lower than the melting temperature of the paraffins of interest, and optionally the cooling rate and / or the quantity of solvent used. The conditions for separating the paraffins of interest can be easily determined by a person skilled in the art by tests and / or simulations. In separation step (a), separation step (ii), (ii-1) or (ii-2) may be carried out by at least one step chosen from filtration,decantation, centrifugation. This separation step (ii), (ii-1) or (ii-2) is typically carried out at a temperature lower than or equal to the final temperature of step (i), (i-1) or (i-2) in order to recover the solid product. In one embodiment, the solid product from step (a), before being hydrotreated in step (b), may be washed, in one or more times, typically three times, with at least one solvent, preferably at a temperature lower than or equal to the final temperature. This solvent is as defined above. When at least one solvent is used during the crystallization step (i), (i-1) or (i-2), the same solvent or mixture of solvents may advantageously be used for this washing step. This washing step may advantageously be followed by a drying or evaporation step of the washed solid product, making it possible to remove the residual solvent(s) before hydrotreatment (b). In the hydrotreatment of step (b),98%m / m or more of the olefins can be hydrogenated, in particular by choosing suitable operating conditions. The effluent from step (b) can advantageously contain 70%m / m or more of C10+ paraffins, for example C10-C100 paraffins, most often C10-C80, preferably 80%m / m or more of these paraffins, more preferably 90%m / m or more of these paraffins, in particular 97%m / m or more of these paraffins, preferably 98%m / m or more of these paraffins. The hydrotreatment of step (b) can be carried out in a single stage or in two stages. When carried out in a single step, the solid product(s) from step (a) are hydrogenated at a temperature of 200 to 450°C, preferably 200 to 340°C in the presence of hydrogen at an absolute pressure of 20 to 140 bars, preferably 30 to 100 bars and in the presence of a hydrotreatment catalyst,for example a hydrogenation catalyst comprising NiMo (0.1-60% by mass) and / or CoMo (0.1-60% by mass). Alternatively, the hydrotreatment of step (b) can be carried out in a first step (b-1) in which the solid product(s) from step (a) are hydrogenated at a temperature of 80 to 250°C, preferably 130 to 190°C in the presence of hydrogen at an absolute pressure of 5 to 60 bars, preferably 20 to 30 bars and in the presence of a first hydrotreatment catalyst, for example a hydrogenation catalyst comprising Pd (0.1-10% by weight) and / or Ni (0.1-60% by weight) and / or NiMo (0.1-60% by weight), and in a second step (b-2) in which the effluent from step (b-1) is hydrogenated at a temperature of 200 to 450°C, preferably 200 to 34 ... second hydrotreatment catalyst, for example a hydrogenation catalyst comprising Pd (0.1-10% by weight) and / or Ni (0.1-60% by weight) and / or NiMo (0.1-60% by weight), and in a second step (b-2) in which the effluent from step (b-1) is hydrogenated at a temperature of 200 to 450°C, preferably 200 to 340°C in the presence of hydrogen at an absolute pressure of 5 to 60 bars, preferably from 20 to 140 bars, preferably from 30 to 100 bars and in the presence of a second hydrotreatment catalyst,for example a hydrogenation catalyst comprising NiMo (0.1-60% by weight) and / or CoMo (0.1-60% by weight). The first step can then allow the hydrogenation of dienes initially present in the composition and which have been crystallized with the paraffins in the solid product(s). Prior to steam cracking step (c), the hydrotreated effluent from step (b) can be subjected to a cracking reaction in order to reduce the length of the carbon chains of the paraffins present in the hydrotreated effluent. Typically, this cracking reaction is a hydrocracking reaction carried out at a temperature of 250 to 480°C, a hydrogen partial pressure of 1.5 to 25 MPa abs. and an hourly volumetric flow rate of 0.1 to 10 h, -1. Steam cracking step (c) consists of thermally cracking in one or more reactors a mixture of the hydrotreated effluent and water vapor at high temperatures of the order of 650 to 1000°C, preferably 700 to 900°C, typically 750 to 850°C, under low pressures (1 to 3 bars). The cracking reaction is carried out in the absence of oxygen. The reaction time is usually very short, of the order of milliseconds. These conditions make it possible to break the carbon-carbon bonds and produce unsaturated hydrocarbons with molecules smaller than the feedstock introduced into the reactor(s). The effluents leaving the reactor(s) are then rapidly cooled to temperatures of 400 to 550°C in order to limit side reactions such as the polymerization of olefins, dienes and acetylenes.The cooled effluents are finally fractionated to recover the light C2-C5 olefins, such as ethylene, propylene, butadiene, isobutene, n-butene and isoprene. The invention also relates to a process for the recovery of plastic waste comprising the following steps: (A) a step of liquefying waste containing plastics and obtaining a hydrocarbon product comprising a gaseous phase, a liquid phase and a solid phase, (B) a step of separating the liquid phase from said product, said liquid phase forming a plastic liquefaction oil, (C) a step of treating at least part of the liquid phase by a process for producing olefins according to the invention.The liquefaction step (A) may comprise a pyrolysis step, typically carried out at a temperature of 300 to 1000°C or 400 to 700°C, this pyrolysis being for example a fast pyrolysis or a flash pyrolysis or a catalytic pyrolysis or a hydropyrolysis. Alternatively or in combination, the liquefaction step (A) may comprise a hydrothermal liquefaction step, typically carried out at a temperature of 250 to 500°C and at pressures of 10 to 25-40 MPa. The waste treated in step (A) may be plastic waste possibly mixed with biomass, as previously described. The separation step (B) makes it possible to eliminate the gaseous phase, essentially the C1-C4 hydrocarbons and the solid phase (typically char) to recover only the liquid organic phase forming a liquefaction oil.This plastic liquefaction oil typically comprises 30 to 55% by mass of paraffins, 10 to 50% m / m of olefins, 5 to 12% m / m of aromatics. These contents can be determined by gas chromatography. In particular, a plastic liquefaction oil can comprise a Bromine index of 20 to 60 g Br / 100g and / or a maleic anhydride index (UOP326-82) of 1 to 20 mg maleic anhydride / 1g. A plastic liquefaction oil may include, but is not limited to, one or more of the following heteroatom contents: 0 to 8% w / w oxygen (measured according to ASTM D5622), 1 to 13000 ppm nitrogen (measured according to ASTM D4629), 2 to 10000 ppm sulfur (measured according to ISO 20846), 1 to 10000 ppm metals (measured by ICP), 50 to 6000 ppm chlorine (measured according to ASTM D7359-18), 0 to 200 ppm bromine (measured according to ASTM D7359-18), 1 to 40 ppm fluorine (measured according to ASTM D7359-18), 1 to 2000 ppm silicon (measured by XRF).A liquefaction oil may in particular comprise one or more of the following heteroatom contents: from 0 to 8% m / m of oxygen, from 250 to 3800 ppm of nitrogen, from 35 to 850 ppm of sulfur, from 34 to 900 ppm of metals, from 50 to 6000 ppm of chlorine, from 0 to 10 ppm of bromine, from 1.5 to 10 ppm of fluorine. This liquid phase may then be subjected, in part (in particular a fraction thereof) or in its entirety, to the olefin production process of the invention, alone or in a mixture with other components as previously described to produce the olefins of interest by steam cracking. In particular, a fraction of this liquid phase, corresponding for example to a naphtha or diesel cut, may be subjected to the olefin production process according to the invention, alone or in a mixture with other components as previously described.Advantageously, the composition treated in the present invention may have at least 50% m / m of paraffins and olefins, in particular C5-C150 paraffins and olefins, most often C5-C100, preferably at least 55% m / m, 60% m / m or 65% m / m of paraffins and olefins, and / or at most 95% m / m, 90% m / m, 85% m / m or 80% m / m of paraffins and olefins. The content of paraffins and olefins, in particular C5-C150 paraffins and olefins, most often C5-C100, of the treated composition may be included in any range defined by two of these limits. Definitions The terms “comprising” and “comprises” as used herein are synonymous with “including,” “includes,” or “contains,” “containing,” and are inclusive or unbounded and do not exclude additional features, elements, or method steps not specified.The expressions % by weight and % by mass have an equivalent meaning and refer to the proportion of the mass of a product relative to 100g of a composition comprising it. The expression "plastic liquefaction oil" or "oil resulting from the liquefaction of plastic" or "plastic waste liquefaction oil" or "liquefaction oil resulting from the liquefaction of waste containing plastics" refers to the liquid products obtained at the end of pyrolysis or hydrothermal liquefaction of thermoplastic, thermosetting or elastomeric polymers, alone or in a mixture and generally in the form of waste, optionally in a mixture with at least one other waste such as biomass, for example chosen from lignocellulosic biomass, paper and cardboard.The pyrolysis process should be understood as a thermal cracking process, carried out in the presence or absence of a catalyst (for example, fast pyrolysis, catalytic or not, etc.). The hydrothermal liquefaction process (or HTL for "Hydrothermal Liquefaction" in English) is a thermochemical conversion process using water as a solvent, reagent and catalyst for the degradation reactions of plastics or biomass, the water typically being in a subcritical or supercritical state. The plastic can be of any type, including any type of new or used plastic, included in household (post-consumer) or industrial waste. By plastics, we mean materials made of polymers and optionally auxiliary components such as plasticizers, fillers, colorants, catalysts, flame retardants, stabilizers, etc.For example, these polymers can be halogenated polyethylene (Cl, F) or not, polypropylene, polystyrene, polybutadiene, polyisoprene, poly(ethylene terephthalate) (PET), acrylonitrile-butadiene-styrene (ABS), polybutylene, poly(butylene terephthalate) (PBT), polyvinyl chloride (PVC), polyvinylidene chloride, a polyester, a polyamide, a polycarbonate, a polyether, an epoxy polymer, a polyacetal, a polyimide, a polyesteramide, silicone etc. In general, any polymer or polymer mixture capable of producing paraffins by liquefaction can be used. These plastic liquefaction oils contain paraffins, i-paraffins (iso-paraffins), dienes, alkynes, olefins, naphthenes and aromatics.Plastic liquefaction oils also contain heteroatom-containing impurities, such as chlorinated, oxygenated, and / or silylated organic compounds, metals, salts, phosphorus, sulfur, and nitrogen compounds. The composition of plastic liquefaction oil depends on the nature of the liquefied plastic and is primarily (especially more than 80% m / m, most often more than 90% m / m) composed of hydrocarbons with 1 to 150 carbon atoms and impurities. Biomass can be defined as an organic plant or animal product.Biomass thus includes (i) biomass produced by surplus agricultural land, not used for human or animal food: dedicated crops, called energy crops; (ii) biomass produced by deforestation (forest maintenance) or the clearing of agricultural land; (iii) agricultural residues from cereal crops, vines, orchards, olive trees, fruits and vegetables, agri-food residues, etc.; (iv) forest residues from forestry and wood processing; (v) agricultural residues from livestock farming (manure, slurry, bedding, droppings, etc.); (vi) household organic waste (paper, cardboard, green waste, etc.); (vii) ordinary industrial organic waste (paper, cardboard, wood, putrescible waste, etc.).The liquefaction oil treated by the invention may originate from the liquefaction of waste containing at least 1% m / m, optionally from 1 to 50% m / m, from 2 to 30% m / m or in a range defined by any two of these limits, of one or more of the aforementioned biomasses, residues and organic wastes, and the remainder consisting of plastic waste. The term "MAV" (acronym for "Maleic Anhydric Value") refers to the UOP326-82 method which is expressed in mg of maleic anhydride which react with 1 g of sample to be measured. The term "Bromine Index" is the number of milligrams of bromine which react with 100 g of sample and can be measured according to the ASTM D1159-07 (2017) method. The concentration of metals in hydrocarbon matrices can be determined by any known method. Acceptable methods include X-ray fluorescence (XRF) and inductively coupled plasma atomic emission spectrometry (ICP-AES).Analytical scientists know how to identify the most suitable method for measuring each metal and heteroelement depending on the hydrocarbon matrix in question. The content of paraffins, olefins, naphthenes and aromatic hydrocarbons can be determined by multidimensional gas chromatography, for example according to the method described in Duhamel, Journal of Chromatography A, 1387 (2015) 95–103, Comparison of cryogenic and differential flow modulator. The oxygen content can be measured according to the standard: ASTM D5622-17 / D2504-88 (2015). The nitrogen content can be measured according to the standard: ASTM D4629-17. The sulfur content can be measured according to the standard ISO 20846:2011. The halogen content, including chlorine, bromine, fluorine, can be measured according to the standard: ASTM D7359-18. Silicon content can be measured by XRF.The particular features, structures, properties, embodiments of the invention may be freely combined into one or more embodiments not specifically described herein, as may be apparent to those skilled in the art of plastic liquefaction oil processing using their general knowledge. By "hydroprocessing catalyst" is meant a catalyst promoting the incorporation of hydrogen into the products. This type of catalyst is typically a metal catalyst comprising one or more metals from groups 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 and 14 of the periodic table. Description of the Invention Figure 1 represents the GC-MS spectra of the products of Example 4. Examples The embodiments of the present invention are illustrated by the following non-limiting examples. crystallization in acetone or in a A plastic pyrolysis oil HPP1 was mixed at room temperature (i.e. approximately 10°C above the crystallization temperature of the paraffins to be separated) (T° = 25°C, P = 1 atm) with a crystallization solvent (acetone or a 50 / 50 (v / v) mixture of acetone and isopropanol) to produce a clear, homogeneous solution. The temperature of the mixture was then lowered from this initial temperature of 25°C to a final temperature of -20°C (i.e. a temperature delta of 45°C). The formation of a solid product (called cake) was observed. The cake was separated by filtration, washed with the crystallization solvent, then dried and analyzed. Table 1 lists the compositions of the pyrolysis oil and the cakes from the two filtrations. It is found that the recovered solid product contains mainly paraffins, with a significant quantity of olefins and a very small quantity of aromatics.In addition, a reduction of more than 80% m / m of Cl, more than 85% m / m of nitrogen, more than 50% m / m of sulfur and more than 60% m / m of Si initially present in HPP1 could be determined. Table 1 HPP1 Gât 1 Gât 2. (*): includes linear and branched olefins, linear and branched diolefins, saturated naphthenes. Example 2: separation of paraffins by crystallization in acetone or in an acetone-isopropanol mixture A plastic pyrolysis oil HPP1' was subjected to the same treatment as that described in Example 1 and a cake (denoted cake 1') was recovered. Tables 2 and 3 give the compositions of the HPP1' oil and cake 1' respectively. The HPP1' oil and cake 1' were analyzed by GCxGC-FID using a two-dimensional GCxGC chromatograph equipped with a non-polar capillary column in the first dimension (1D) and a capillary column of intermediate polarity in the second dimension (2D). Detection is carried out by a flame ionization detector (FID). A first separation on the 1D column allows the compounds to be separated according to their boiling points.They are periodically trapped in the modulation loop and injected into a second column that separates the compounds according to their polarities. The resulting chromatogram is demodulated as a two-dimensional retention plane and processed using dedicated software (e.g., GC Image). Compound quantification is performed by normalizing the compounds detected by the FID to 100%. In Tables 2 and 3, the n-olefin contents include both n-olefin and n-diolefin contents. Table 2. Unidentified unknowns 0.50 1.99 Other molecules 000 000 Table 3 HPP1' Cake 1' npnnnnnnnnnnnnnnnnnn nnnnn C30 0.00 C30 0.00 nC30 0.01 C30 0.00 nC31 0.00 C30+ 0.00 nC31 0.00 C30+ 0.00 T Example 3: Separation of paraffins by crystallization in acetone or in an acetone-isopropanol mixture. Four tests were carried out on another HPP2 plastic pyrolysis oil using acetone and an 80 / 20v / v acetone / isopropanol mixture as crystallization solvents. The HPP2 plastic pyrolysis oil was mixed at room temperature (T° = 25°C, P= 1atm) with the crystallization solvent (acetone or an 80 / 20 (v / v) mixture of acetone and isopropanol) and then the temperature of the mixture was lowered from this initial temperature of 25°C to a final temperature of 5°C and 0°C for tests 1 and 2 and -10°C for tests 3 and 4. The formation of a solid product (called cake) is observed. The cake was separated by filtration, washed with the crystallization solvent, then dried and analyzed. The test conditions are listed in Table 4.The analyses of the recovered solids (cakes) for tests 1 to 4 as well as the analyses of the plastic pyrolysis oil are collected in Table 5. Table 4 -. yield (%m) ,5 8, 8,8 ,7 Table 5 HPP2 Cake trial 3 Cake trial 4 Tables 6 and 7 give the compositions of HPP2 oil and test 3 cake, respectively. In these tables, the n-olefin contents include the n-olefin and n-diolefin contents. HPP2 oil and test 3 cake were analyzed by GCxGC-FID using the same procedure as described for the analyses in Example 2. Table 6 TOTAL 100.00 100.00 Table 7 HPP2 Cake test 3 npnnnnnnnnnnnnnnnnn nnnnnn T , , , , Example 4: Separation of paraffins by crystallization in acetone A diesel cut of plastic pyrolysis oil was dewaxed by crystallization. This diesel cut, denoted "diesel ex HPP", consists of C10-C30 hydrocarbons and contains 49.55% m / m of paraffins and 41.30% m / m of olefins. The diesel cut was mixed at room temperature (i.e. approximately 10°C above the crystallization temperature of the paraffins to be separated) (T° = 25°C, P = 1 atm) with acetone (volume ratio diesel ex HPP / acetone of 50:50) to produce a clear homogeneous solution. Then the temperature of the mixture was lowered from this initial temperature of 25°C to a final temperature of -20°C. The formation of a solid product (called cake) is observed. The cake containing the crystallized paraffins was separated by filtration, washed with acetone, then dried and analyzed.The paraffins contained in the cake were extracted by dissolving in n-heptane heated to 90°C and then evaporating the n-heptane under a nitrogen stream. The dewaxed oil (called filtrate) separated from the cake was recovered. The acetone contained in the filtrate was evaporated using a rotary evaporator at 70°C under vacuum at a rotation speed of 60 rpm, then the vacuum was cut to send a nitrogen stream into the flask in order to have total evaporation of the acetone. The compositions of the extracted paraffins and the filtrate were analyzed as described with reference to Example 2. The results are summarized in Table 8. The heteroatom contents of the ex HPP diesel, the extracted paraffins and the filtrate are summarized in Table 9. Table 8. Mono aromatics 11.27 0.10 Di aromatics 151,000 Table 9 The ex HPP diesel cut, extracted paraffins and dewaxed oil were analyzed by GC-MS under the following conditions: Sample preparation: • All samples were diluted in CS2 and analyzed by GCMS under the same conditions. • Approximately 0.1 g of product in 6 g of CS2 Analytical conditions Injection on a GC-MS (GC-QTOF from Agilent) under the same conditions (slow programming to spread the detected molecules): Injector Split mode: 250°C – split ratio 100 – injected volume 1 µL Column flow rate (He): 1 mL / min Oven: 35 °C for 10 min, then 4 °C / min up to 325 °C for 10 min Apolar column: Thermo TG-5HT brand 30 m * 0.25 mm * 0.25 µm Source temperature: 200 °C Quad temperature: 150 °C Electron impact source at 70eV. The GC-MS analysis spectra obtained are gathered in figure 1.In the ex-HPP diesel spectrum, if we take nC15 for example, the peak with high intensity is paraffin, the neighboring peak with lower intensity is the corresponding linear olefin. In this example, the ex-HPP diesel cut contains linear paraffins and linear olefins in C10-C30. The extracted paraffins are mainly in nC15-nC30, with a small proportion of linear olefins. On the other hand, the filtrate contains mainly lighter fractions in C10-C19, with a higher proportion of olefins compared to the extracted paraffins. Example 5: Hydrotreatment and steam cracking of the solid product of Examples 1, 2, 3 or 4 One of the solids from the tests of Examples 1 to 4 can be hydrotreated according to the following procedure: The solid can be introduced into a first optional hydrotreatment section (HDT1), essentially to hydrogenate the diolefins, and which is operated in the liquid phase.This step may include a plurality of reactors in series and / or parallel if guard reactors are used upstream or downstream of the first hydrogenation reactor. These guard reactors can reduce the concentration of certain undesirable chemical species and / or elements such as chlorine, silicon and metals. Particularly undesirable metals include Si, Na, Ca, Mg, Fe and Hg. A second hydrotreating section (HDT2) is dedicated to the hydrogenation of olefins and demetallation (HDM), desulfurization (HDS), denitrogenation (HDN) and deoxygenation (HDO). HDT2 is operated in the gas phase. This section consists of one or more reactors operated in series, lead-lag or in parallel. Since the hydrotreating reactions in sections HDT1 and HDT2 are exothermic, a cold hydrogen quench can be used to moderate the temperature increase and control the reaction.Isolated, lead-lag, series and / or parallel guard reactors can be considered depending on the nature and quantity of the contaminant in the stream to be treated. In the event that the treatments of examples 1, 2, 3 or 4 do not provide sufficient impurity reduction, guard reactors to remove chlorine and silicon can be operated in the gas phase. Silicon can also be trapped on the upper bed of a reactor in section HDT2 or separately, upstream or downstream by treating the hot gases leaving section HDT2. Chlorine and mercury can be separated by guard reactors in the liquid or gas phase. There may be intermediate quenches between the beds or between reactors HDT1 and HDT2 or no quenching. In the latter case, recycling of part of the stream leaving HDT1 or HDT2 must be carried out to control the temperature.Strict temperature control in HDT1 must be conducted when this step is implemented, in order to avoid reactor plugging and degradation of catalytic hydrogenation conditions. The operating pressure in each of the HDT1 and HDT2 hydrotreatments is 5-140 bar, preferably 20-30 bar for HDT1 and 20-140 bar, preferably 30-100 bar for HDT2, typically 30-40 bar for HDT2. Typical temperature range at the inlet of HDT1 at the start of run (SOR): 150-200°C. The catalyst for HDT 1 usually comprises Pd (0.1-10% by weight) and / or Ni (0.1-60% by weight) and / or NiMo (0.1-60% by weight). Typical temperature range at the inlet of HDT2 at the start of the cycle (SOR: start of run): 200-340°C. Typical temperature range at the outlet of HDT2 (SOR): 300-380°C, up to 450°C.The catalyst for HDT 2 usually comprises a NiMo (any type of commercial catalyst for refining or petrochemical applications), potentially a CoMo in the very last beds at the bottom of the reactor (any type of commercial catalyst for refining or petrochemical applications). The top bed of HDT2 should preferably be operated with a NiMo having hydrogenating capacity as well as silicon trapping capacity. Such a top bed can be considered as an adsorbent as well as a metal trap having also HDN activity and hydrogenating capacity. An example of an acceptable top bed for this function includes commercially available NiMo catalyst adsorbents such as ACT971, ACT981 from Axens or equivalents from Haldor Topsoe, Axens, Criterion, etc.It is possible to have two separate beds in an HDT2 reactor, with quenching between the two beds or between the two reactors, if the two beds are in two separate reactors, or no quenching at all. Ideally, the intermediate quench is carried out using cold HDT2 effluent or by supplying cold hydrogen, i.e. at a temperature generally ranging from 15 to 30°C, in order to control the HDT2 exotherm. Dilution by recycling the hydrocarbon stream to the upper HDT2 bed is not recommended due to the increased risk of bed fouling. The feedstock arriving at the HDT2 catalyst should be completely vaporized at all times, including in variable regimes such as during start-ups. Sending liquid hydrocarbons to the upper bed of an HDT2 reactor can generate fouling and an increase in the pressure difference between the inlet and outlet of said HDT2 reactor and lead to premature shutdown.Depending on the metals possibly present in the solid to be hydrotreated, a hydrodemetallization catalyst, for example a commercial one, may be added to the upper bed of the HDT2 section in order to protect the lower catalytic beds from deactivation. The hydrotreated effluent leaving the HDT2 section may be used as is or fractionated according to distillation temperature ranges, to feed a steam cracker, optionally after undergoing cracking in an FCC, a hydrocracker, or a catalytic reformer, preferably a hydrocracker. This hydrocracking comprises for example contacting the hydrotreated effluent with a hydrotreatment catalyst, in particular a hydrocracking catalyst, in the presence of H2 to produce an effluent meeting the specifications of a steam cracker in terms of final boiling point (<370°C), chlorine content (<5 ppm by mass) and olefins (<1% m).This hydrocracking can be carried out at a temperature of 250 to 480°C, a hydrogen partial pressure of 1.5 to 25 MPa abs., and an hourly volumetric flow rate of 0.1 to 10 h. -1 A usable hydrocracking catalyst comprises, for example, a support chosen from halogenated aluminas, combinations of boron and aluminum oxides, amorphous silica-aluminas and zeolites and a hydro-dehydrogenating function comprising at least one metal from group VIB chosen from chromium, molybdenum and tungsten, alone or as a mixture, and / or at least one metal from group VIII chosen from iron, cobalt, nickel, ruthenium, rhodium, palladium and platinum.

Claims

CLAIMS 1. A process for producing olefins by steam cracking from a composition comprising a plastic liquefaction oil, said composition comprising paraffins, olefins, aromatics, and heteroatoms, the process comprising: (a) a step of separating a portion of the paraffins and olefins contained in said composition comprising at least one step of crystallizing (i) said composition by lowering the temperature from 10°C to 60°C from an initial temperature at which said composition is entirely liquid and obtaining a mixture comprising a solid product enriched in paraffins and depleted in olefins, aromatics, and heteroatoms, and an effluent depleted in paraffins and enriched in olefins, aromatics, and heteroatoms, followed by at least one step of separating (ii) said solid product and said effluent,(b) a hydrotreating step of the solid product from step (a) and obtaining a hydrotreated effluent having a reduced olefin content, and optionally a reduced heteroatom and aromatic content, (c) a steam cracking step of the hydrotreated effluent and obtaining an effluent containing olefins.

2. A process according to claim 1, characterized in that, during the separation step (a), said composition is mixed with at least one solvent prior to at least one crystallization step (i), the at least one solvent being in liquid form and miscible with the composition at the temperatures at which step (a) is carried out.

3. A process according to claim 2, further comprising a separation step (iii) of the at least one solvent from the effluent from the separation step (ii) and returning the separated at least one solvent to step (i).

4. Method according to claim 2 or 3,characterized in that at least one solvent is an organic solvent.

5. A method according to claim 4, characterized in that the organic solvent is selected from an aliphatic hydrocarbon, an aromatic hydrocarbon, a ketone, an alcohol, or mixtures thereof.

6. A process according to claim 5, characterized in that the organic solvent is selected from a ketone and an alcohol.

7. A process according to any one of claims 2 to 6, characterized in that the volume ratio of said composition to the solvent is 10 / 90 v / v to 90 / 10 v / v, preferably 20 / 80 v / v to 80 / 20 v / v, more preferably 40 / 60 v / v to 60 / 40 v / v or 45 / 55 v / v to 55 / 45 v / v.

8. A process according to any one of claims 1 to 7, characterized in that: the separation step (a) comprises: (i-1) a first crystallization step by lowering the temperature of said composition from 10°C to 60°C from a first initial temperature at which said composition is entirely liquid and obtaining a first mixture comprising a first solid product enriched in paraffins and depleted in olefins, aromatics and heteroatoms, and a first effluent depleted in paraffins and enriched in olefins, aromatics and heteroatoms,(ii-1) a first step of separating said first solid product and said first effluent, (i-2) a second crystallization step by lowering the temperature of said first effluent from 10°C to 60°C from a second initial temperature at which said first effluent is entirely liquid and obtaining a second mixture comprising a second solid product enriched in paraffins and depleted in olefins, aromatics, and heteroatoms, and a second effluent depleted in paraffins and enriched in olefins, aromatics, and heteroatoms, (ii-2) a second step of separating said second solid product and said second effluent, and the first solid product and the second solid product are subjected to step (b) of hydrotreating.

9. A process according to any one of claims 1 to 8, characterized in that the separation step (ii), (ii-1), or (ii-2) is carried out by at least one step selected from filtration, decantation,centrifugation.

10. A process according to any one of claims 1 to 9, characterized in that the hydrotreatment of step (b) is carried out in a single step in, in which the solid product(s) from step (a) are hydrogenated at a temperature of 200 to 450°C, preferably 200 to 340°C in the presence of hydrogen at an absolute pressure of 20 to 140 bar, preferably 30 to 100 bar and in the presence of a hydrotreating catalyst. 11.A process according to any one of claims 1 to 9, characterized in that the hydrotreating of step (b) is carried out in a first step (b-1) in which the solid product(s) from step (a) are hydrogenated at a temperature of 80 to 250°C, preferably 130 to 190°C in the presence of hydrogen at an absolute pressure of 5 to 60 bar, preferably 20 to 30 bar and in the presence of a first hydrotreating catalyst, and in a second step (b-2) in which the effluent from step (b-1) is hydrogenated at a temperature of 200 to 450°C, preferably 200 to 340°C in the presence of hydrogen at an absolute pressure of 20 to 140 bar, preferably 30 to 100 bar and in the presence of a second hydrotreating catalyst.

12. A process according to any one of claims 1 to 11, characterized in that, prior to step (c) of steam cracking, the hydrotreated effluent from step (b) is subjected to a cracking reaction. 13.A process for the recovery of plastic waste comprising the following steps: (A) a step of liquefying waste containing plastics and obtaining a hydrocarbon product comprising a gaseous phase, a liquid phase and a solid phase, (B) a step of separating the liquid phase of said product, said liquid phase forming a plastic liquefaction oil, (C) a step of treating at least a portion of the liquid phase by an olefin production process according to any one of claims 1 to 12.

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