Process for producing olefins by steam cracking by upgrading a pyrolysis gas

Abstract

A process for producing olefins from a feedstock containing plastic and / or tyres and / or solid recovered fuels, said process comprising the following steps: (a) performing a step of pyrolysis of a feedstock containing plastic and / or tyres and / or solid recovered fuels in a pyrolysis unit so as to recover at least a first gaseous effluent containing a mixture of H2, CO, CO2 and C1 to C6 hydrocarbons, and a first liquid effluent containing C7+ hydrocarbons; (b) compressing and then cooling said first gaseous effluent, and then separating said compressed and cooled first gaseous effluent so as to obtain a second liquid effluent containing predominantly C3+ hydrocarbons and a residual second gaseous effluent concentrated in H2, CO and CO2; (c) introducing said second liquid effluent into a steam cracking unit in the presence of steam.

Description

[0001] PROCESS FOR PRODUCING OLEFINS BY STEAM CRACKING BY USING A PYROLYSIS GAS

[0002] TECHNICAL FIELD

[0003] The present invention relates to the field of recycling plastics and / or tires and / or solid recovered fuels (SRF). The present invention aims to maximize the production of olefins constituting plastic and / or tire polymers and / or SRF through a steam cracking unit by recovering light pyrolysis gases, thus allowing a significant increase in olefin yield and a reduction in environmental impact.

[0004] PRIOR TECHNIQUE

[0005] Plastics from collection and sorting channels or recycled tires or solid recovered fuels (SRF) can undergo a pyrolysis step in order to recover them. Pyrolysis consists of heating with or without a catalyst a charge containing plastic and / or recycled tires and / or SRF in the absence of oxygen, leading to the formation of three main products: a liquid hydrocarbon phase at room temperature also called pyrolysis oil, a light gas phase also called pyrolysis gas and a solid residue also called char according to Anglo-Saxon terminology.

[0006] The liquid hydrocarbon phase, pyrolysis oil, is generally used as a feedstock for a steam cracking unit to (re)create olefins, the latter being constituent monomers of certain polymers. Pyrolysis oils have impurities at levels that are often high and incompatible with steam cracking units or units located downstream of steam cracking units, in particular polymerization processes and selective hydrogenation processes, which often requires purification steps upstream of the steam cracking step, for example by at least one hydrotreatment step.

[0007] As for the light gas phase resulting from pyrolysis, it is generally used (recycled) as fuel to provide the energy necessary for the pyrolysis reaction. Such processes are for example described in WO2005 / 087897, WO20 18 / 000050, US2018 / 0010050, US2018 / 0142164, WO2014 / 006273 or US2015 / 0080624.

[0008] Another way to valorize the light gas phase is to send it, possibly after pretreatment to remove H2S in particular, directly to a steam cracking unit in order to increase the olefin yield. Such processes are for example described in WO2016142808, WO2016142809 or WO2018069794. However, none of the documents describe the removal of CO and CO2 before introduction into the steam cracker.

[0009] Sending this light gas phase to a steam cracking unit, however, comes up against two constraints:

[0010] - the first is that it is often necessary to purify this light gas phase (by desulfurization, dechlorination, denitrogenation) before sending it to a steam cracking unit in order to maintain a stable operation and without substantial modification of the steam cracking unit. If the majority of impurities (chlorine, sulfur, nitrogen, metals, etc.) can be treated upstream of the steam cracking stage by hydrotreatment processes (HDT), the CO and CO2 present in the light gas phase must also be eliminated because, on the one hand, the presence of CO has a negative (inhibitory) impact on the activity of the catalysts used in units located downstream of the steam cracker and, on the other hand, the presence of CO2 can cause the formation of ice crystals in the cold train of the steam cracker.

[0011] - the second is that it is advantageous to preserve the possibility of using at least part of the light gas phase resulting from pyrolysis to provide the energy necessary for the pyrolysis reaction in order to reduce energy dependence as well as the carbon footprint of the production site.

[0012] The present invention makes it possible to meet the two constraints above simultaneously by introducing a step of compression of the light pyrolysis gas phase so as to condense at least the C3+ hydrocarbons and then separate them from the incondensable gases (mainly H2, CO, CO2, C1 and C2). The condensed stream containing the C3+ hydrocarbons is advantageously sent to a purification unit (HDT) so as to meet the specifications required to be used as feedstock for a steam cracking unit. Alternatively, if the condensed stream rich in C3+ hydrocarbons is of satisfactory quality, it can be sent directly, possibly with another hydrocarbon feedstock, to a steam cracking unit.

[0013] As for the light products contained in the incondensable gases, they are advantageously used as fuel to provide the energy necessary to operate, for example, the pyrolysis unit. Within the framework of the invention, the conditions of the compression step can be adjusted according to the energy requirements of the pyrolysis unit in order to produce more or less light incondensable products.

[0014] SUMMARY OF THE INVENTION

[0015] More specifically, the invention relates to a process for producing olefins from a feedstock containing plastic and / or tires and / or solid recovered fuels, said process comprising the following steps:

[0016] (a) a step of pyrolysis of a load containing plastic and / or tires and / or solid recovered fuels is carried out in a pyrolysis unit so as to recover at least a first gaseous effluent containing a mixture of H2, CO, CO2 and hydrocarbons comprising C1 to C6 hydrocarbons and a first liquid effluent containing mainly C7+ hydrocarbons;

[0017] (b) said first gaseous effluent from step a) is compressed and then cooled, then said first compressed and cooled gaseous effluent is separated in a separation unit so as to obtain a second liquid effluent containing mainly C3+ hydrocarbons and a second residual gaseous effluent concentrated in H2, CO and CO2;

[0018] (c) introducing said second liquid effluent into a steam cracking unit in the presence of water vapor so as to produce olefins.

[0019] According to a variant, said first liquid effluent is introduced into said steam cracking unit of step c). According to a variant, in step b) at least a portion of the first liquid effluent is introduced into said separation unit, mixed or not with said first compressed gaseous effluent, then the mixture is separated so as to obtain an intermediate liquid effluent and said second residual gaseous effluent concentrated in H2, CO and CO2, then said intermediate liquid effluent is separated in a second separation unit so as to obtain said second liquid effluent containing mainly C3+ hydrocarbons and a third residual gaseous effluent concentrated in H2, CO and CO2.

[0020] According to one variant, a step of purifying said second liquid effluent from step b) is carried out in a purification unit upstream of the steam cracking unit of step c).

[0021] According to one variant, a step of purifying said first liquid effluent from step a) is carried out in a purification unit upstream of the steam cracking unit of step c).

[0022] According to a variant, step b) is carried out in such a way that during the separation(s) the pressure is between 0.5 and 2.5 MPa relative, preferably between 1.0 and 1.5 MPa relative, and the temperature is between 20 and 55°C, preferably between 30 and 45°C.

[0023] According to one variant, the purification step comprises a step of pretreatment of said second liquid effluent from step b) and / or of said first liquid effluent from step a), said pretreatment step being carried out upstream of step c) and comprises an adsorption step and / or a filtration step and / or a centrifugation step and / or a decantation step and / or an electrostatic separation step and / or a washing step using an aqueous solution and / or a gas stripping step.

[0024] According to a variant, the purification step comprises a hydrotreatment step implemented in a hydrotreatment reaction section, implementing at least one fixed-bed reactor having n catalytic beds, n being an integer greater than or equal to 1, each comprising at least one hydrotreatment catalyst, said hydrotreatment reaction section being fed with said second liquid effluent from step b), optionally pretreated, and / or said first liquid effluent from step a), optionally pretreated, and a gas stream comprising hydrogen, said hydrotreatment reaction section being implemented at an average temperature between 150 and 430°C, a hydrogen partial pressure between 1.0 and 10.0 MPa abs. and an hourly volumetric flow rate between 0.1 and 10.0 h -1 to obtain a second purified liquid effluent and / or a first purified liquid effluent.

[0025] According to one variant, said hydrotreatment catalyst comprises a support chosen from alumina, silica, silica-aluminas, magnesia, clays and their mixtures and a hydro-dehydrogenating function comprising either at least one element from group VIII and at least one element from group VIB, or at least one element from group VIII.

[0026] According to a variant, the hydrotreatment step is followed by a washing / separation step, fed with said second purified liquid effluent, optionally pretreated, and / or said first purified liquid effluent, optionally pretreated, and an aqueous solution to obtain at least one gaseous effluent, one aqueous effluent and said second washed purified liquid effluent and / or said first washed purified liquid effluent.

[0027] According to a variant, said second purified liquid effluent, optionally pretreated and / or washed, and / or said first purified liquid effluent, optionally pretreated and / or washed, is subjected to at least one fractionation step in a fractionation unit to obtain at least one gaseous stream and at least one liquid stream of C3+ hydrocarbons.

[0028] According to one variant, the fractionation unit comprises a depentanizer column from which a liquid stream of C3-C4 hydrocarbons and a liquid stream of C5+ hydrocarbons are withdrawn.

[0029] According to one variant, at least one of the liquid streams from the fractionation stage is at least partly sent to the steam cracking unit of stage c).

[0030] According to one variant, the steam cracking step c) is carried out in at least one pyrolysis furnace at a temperature between 700 and 900°C and at a pressure between 0.05 and 0.3 MPa relative in the presence of water vapor.

[0031] According to a variant, in the steam cracking step c) the residence time of the hydrocarbon compounds is less than or equal to 1.0 seconds and the quantity of water introduced, in the form of water vapor, is between 0.3 and 3.0 kg of water per kg of hydrocarbon compounds at the inlet of the steam cracking step c).

[0032] Alternatively, the feedstock consists of plastic and / or tires and / or recovered solid fuels. In the remainder of the text, "pyrolysis oil" means oil resulting from the pyrolysis of plastics and / or tires and / or CSR, unless otherwise stated.

[0033] In the following text, "pyrolysis gas" means a gas resulting from the pyrolysis of plastics and / or tires and / or CSR, unless otherwise indicated.

[0034] According to the present invention, the expressions "between ... and ..." and "between .... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this were not the case and the limit values ​​were not included in the range described, such precision will be provided by the present invention.

[0035] In this description, the term "include" is synonymous with (means the same as) "include" and "contain", and is inclusive or open and does not exclude other elements not mentioned. It is understood that the term "include" includes the exclusive and closed term "consist".

[0036] For the purposes of the present invention, the different parameter ranges for a given step such as pressure ranges and temperature ranges may be used alone or in combination. For example, for the purposes of the present invention, a range of preferred pressure values ​​may be combined with a range of preferred temperature values.

[0037] In the following, particular and / or preferred embodiments of the invention may be described. They may be implemented separately or combined with each other, without limitation of combination when technically feasible.

[0038] In the following, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, 81 èmeedition, 2000-2001). For example, group VIII (or VIIIB) according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IIIPAC classification.

[0039] The metal content is measured by X-ray fluorescence. DETAILED DESCRIPTION

[0040] The charge

[0041] Plastic waste is generally a mixture of several polymers. The feedstock used in the process according to the invention may comprise, alone or in a mixture, polyethylene (low and / or high density), polypropylene, polyethylene terephthalate, polyvinyl chloride and polystyrene. In addition, depending on the uses, the plastics may contain, in addition to the polymers, other compounds, such as plasticizers, pigments, dyes or even residues of polymerization catalysts. Plastic waste may also contain, to a minor extent, biomass originating for example from household waste.

[0042] As for tires, they are mainly made of rubber for their elastic property (mixture of elastomers of the crosslinked natural and synthetic rubber type, added with additives of the silica, resin, sulfur, zinc oxide, carbon black, etc. type) and textile and metallic fibers for their reinforcing property.

[0043] Solid recovered fuels (SRF), also known as refuse derived fuel (RDF), or solid recovered fuels (SRF) in English, are solid non-hazardous waste prepared for energy recovery, whether they come from household and similar waste, waste from economic activities or construction and demolition waste. SRF are generally a mixture of any combustible waste such as used tires, food by-products (fats, animal meal, etc.), viscose and wood waste, light fractions from shredders (e.g. from used vehicles, electrical and electronic equipment (WEEE), household and commercial waste, residues from the recycling of various types of waste, including certain municipal waste, plastic waste, textiles, wood among others. SRF generally contains plastic waste.

[0044] The feedstock used in the process according to the invention contains plastic and / or tires and / or CSR. Preferably, the feedstock consists of plastic and / or tires and / or CSR. In the case of a mixture of plastics, tires and / or CSR, this mixture can be carried out in any proportion. Step a) of pyrolysis

[0045] According to step a) of the method according to the invention, a step of pyrolysis of a feedstock containing plastic and / or tires and / or CSR is carried out in a pyrolysis unit so as to recover at least a first gaseous effluent containing a mixture of H2, CO, CO2 and hydrocarbons comprising C1 to C6 hydrocarbons, also called pyrolysis gas, and a first liquid effluent containing mainly C7+ hydrocarbons (i.e. having a C7+ hydrocarbon content greater than or equal to 50% by weight relative to the mass of the liquid effluent), also called pyrolysis oil.

[0046] The pyrolysis step of the load containing plastic and / or tires and / or CSR can be carried out by thermal or catalytic pyrolysis treatment or can be prepared by hydropyrolysis (pyrolysis in the presence of a catalyst and hydrogen).

[0047] The pyrolysis step is generally carried out at a temperature between 250°C and 750°C. The pyrolysis step can be carried out under more or less severe conditions.

[0048] The low severity pyrolysis step is carried out at a temperature of between 250°C and 450°C, preferably between 275°C and 425°C, and particularly preferably between 300°C and 400°C. The low severity pyrolysis step produces pyrolysis oils rich in mono- and di-olefins as well as a significant amount of aromatics, and which may include chlorinated compounds.

[0049] The high severity pyrolysis step is carried out at a temperature between 450°C and 750°C, preferably between 500°C and 700°C, and particularly preferably between 550°C and 650°C. The high severity pyrolysis step produces pyrolysis oils rich in aromatics, which may include chlorinated compounds.

[0050] The pyrolysis unit may include one or more reactors configured to convert the feedstock into gas-phase and liquid-phase products (e.g., simultaneously). The reactor(s) may contain one or more beds of inert materials or pyrolysis catalysts including sand, zeolite, or combinations thereof. Typically, the pyrolysis catalyst is capable of transferring heat to the components undergoing the pyrolysis process in the pyrolysis unit.

[0051] The pyrolysis unit may include one or more pieces of equipment, for example, one or more heated extruders, a heated rotary kiln, heated tank-type reactors, empty heated vessels, closed heated surfaces where the feedstock flows along the wall, vessels surrounded by ovens or furnaces, or other equipment providing a heated surface.

[0052] In one or more embodiments of the pyrolysis unit, a purge gas is used in all or part of the pyrolysis stage(s) to enhance plastics cracking, produce valuable products, provide feed for steam cracking, or combinations thereof. The purge gas may include hydrogen (H2), nitrogen (N2), steam, product gases, or combinations thereof.

[0053] The pyrolysis step makes it possible to produce at least a first gaseous effluent containing a mixture of H2, CO, CO2 and hydrocarbons comprising C1 to C6 hydrocarbons, also called pyrolysis gas, and a first liquid effluent containing mainly C7+ hydrocarbons, also called pyrolysis oil.

[0054] Said first liquid effluent containing predominantly C7+ hydrocarbons is a pyrolysis oil, advantageously in liquid form at room temperature. The pyrolysis oil comprises in particular a mixture of hydrocarbon compounds, in particular paraffins (n- and i-paraffins), olefins (mono- and / or diolefins), naphthenes and aromatics. At least 80% by weight of these hydrocarbon compounds preferably have a boiling point below 700°C, and preferably below 550°C. In particular, depending on the origin of the feedstock treated by the pyrolysis unit, the pyrolysis oil may comprise up to 70% by weight of paraffins, up to 90% by weight of naphthenes, up to 90% by weight of olefins and up to 90% by weight of aromatics, it being understood that the sum of the paraffins, naphthenes, olefins and aromatics is equal to 100% by weight of the hydrocarbon compounds.

[0055] Said first liquid effluent contains predominantly C7+ hydrocarbons, i.e. a C7+ hydrocarbon content greater than or equal to 50% by weight relative to the mass of said first liquid effluent. The pyrolysis oil may comprise diolefins. The diolefin content is commonly determined indirectly as the maleic anhydride index (or MAV). The method is based on the Diels-Alder addition reaction between conjugated diolefins and maleic anhydride. The method for determining the MAV is described in C. Lépez-Garcîa et al., Near Infrared Monitoring of Low Conjugated Diolefins Content in Hydrotreated FCC Gasoline Streams, Oil & Gas Science and Technology - Rev. IFP, Vol. 62 (2007), No. 1, pp. 57-68. MAV is expressed in mg of maleic anhydride reacted with 1 g of sample (mg / g). MAV varies between 5 and 100 mg / g in pyrolysis oils.

[0056] The density of pyrolysis oil, measured at 15°C according to the ASTM D4052 method, is generally between 0.75 g / cm 3 and 0.99 g / cm 3 , preferably between 0.75 g / cm 3 and 0.95 g / cm 3 .

[0057] Pyrolysis oil may include, and most often does include, additionally impurities such as metals, in particular iron, silicon, halogenated compounds, in particular chlorinated compounds. These impurities may be present in the pyrolysis oil at high levels, for example up to 500 ppm by weight or 700 ppm by weight or even 1000 ppm by weight, and even 5000 ppm by weight, of halogenated elements (in particular chlorine but also bromine, fluorine or iodine) provided by halogenated compounds, and generally between 1 and 1000 ppm by weight or between 1 and 700 ppm by weight or between 1 and 500 ppm by weight of halogenated elements. Pyrolysis oil can contain up to 500 ppm by weight or 700 ppm by weight or even 1000 ppm by weight or even 5000 ppm by weight of chlorine element provided by chlorinated compounds, and generally between 1 and 1000 ppm by weight or between 1 and 700 ppm by weight or even between 1 and 500 ppm by weight of chlorine elements.

[0058] The oil may contain up to 200 ppm by weight, or even 1500 ppm by weight of metallic or semi-metallic elements, and generally between 1 and 200 ppm by weight or between 1 and 1500 ppm by weight of metallic or semi-metallic elements. Alkali metals, alkaline earth metals, transition metals, poor metals and metalloids may be considered as contaminants of a metallic nature, called metals or metallic or semi-metallic elements. In particular, metals or metallic or semi-metallic elements include silicon, iron or both of these elements. Pyrolysis oil may contain, in particular, up to 200 ppm by weight or even 1000 ppm by weight of silicon, and generally between 1 and 200 ppm by weight or between 1 and 1000 ppm by weight or even between 1 and 500 ppm by weight of silicon. Pyrolysis oil can contain up to 50 ppm by weight or 100 ppm by weight of iron, and generally between 1 and 50 ppm by weight or between 1 and 100 ppm by weight of iron.Pyrolysis oil may also include phosphorus, sodium, calcium, potassium, and magnesium.

[0059] The pyrolysis oil may also include other impurities such as heteroelements provided in particular by sulfur compounds, oxygenated compounds and / or nitrogenous compounds, at contents generally less than 40,000 ppm by weight of heteroelements and preferably less than 15,500 ppm by weight of heteroelements, and generally between 1 and 40,000 ppm by weight or between 1 and 15,500 ppm by weight of heteroelements.

[0060] The sulfur compounds are generally present in a content of less than 15,000 ppm by weight and preferably less than 10,000 ppm by weight, and generally between 1 and 15,000 ppm by weight or between 1 and 10,000 ppm by weight of sulfur compounds. The oxygen compounds are generally present in a content of less than 15,000 ppm by weight and preferably less than 10,000 ppm by weight, and generally between 1 and 15,000 ppm by weight or between 1 and 10,000 ppm by weight of oxygen compounds. The nitrogen compounds are generally present in a content of less than 10,000 ppm by weight and preferably less than 5,000 ppm by weight, and generally between 1 and 10,000 ppm by weight or between 1 and 5,000 ppm by weight of nitrogen compounds.

[0061] The contents of sulfur, oxygenated and / or nitrogen compounds often depend on the origin of the treated feedstock. Thus, tire pyrolysis oils generally contain more heteroelements than plastic pyrolysis oils, particularly sulfur compounds.

[0062] Pyrolysis oil may also include other impurities such as heavy metals such as mercury, arsenic, zinc and lead, for example up to 100 ppb by weight or 200 ppb by weight of mercury or arsenic, and generally between 1 and 200 ppb by weight or between 1 and 100 ppb by weight of heavy metals. As for said first gaseous effluent from pyrolysis, also called pyrolysis gas, it contains a mixture of H2, CO, CO2 and hydrocarbons including C1 to C6 hydrocarbons. It may also contain halogens (particularly in the form of chlorinated compounds), water, sulfur and nitrogen.

[0063] Said first gaseous effluent generally contains hydrocarbons comprising C1 to C6 hydrocarbons at a content of at least 20% by volume, preferably at least 30% by volume and particularly preferably at least 40% by volume relative to the total volume of said first gaseous effluent.

[0064] Said first gaseous effluent generally contains CO and CO2 at a content of at least 1% by volume, generally at least 2% by volume and often at least 3% by volume relative to the total volume of said first gaseous effluent.

[0065] Said first gaseous effluent from pyrolysis may contain halogens, in particular chlorine, depending on the nature of the pyrolyzed feedstock. Said first gaseous effluent from pyrolysis generally contains halogens, and in particular chlorine at a content greater than 25 ppm by weight, generally greater than 50 ppm by weight, and often greater than 70 ppm by weight relative to the total weight of said first gaseous effluent.

[0066] Step b) compression, cooling and separation of the pyrolysis gas

[0067] The treatment of said first gaseous effluent according to the invention during step b) is carried out in such a way as to condense the C3+ hydrocarbons contained in the first gaseous effluent in a liquid phase (also called condensate), while the compounds H2, CO, CO2, and the light hydrocarbons C1 to C2 are separated in a non-condensable gaseous flow.

[0068] It is in fact the condensation of C3+ hydrocarbons in the pyrolysis gas which makes it possible to increase the olefin yield during the steam cracking stage, while at the same time limiting in particular the presence of CO and CO2 in the condensate in order to limit the deactivation of the catalysts in the purification stages when they are present but also that of the catalysts which are possibly used in the units downstream of the steam cracker for the treatment ("polishing" according to the Anglo-Saxon terminology) of the products formed by the steam cracker. This stage b) thus makes it possible to selectively extract the valuable compounds (C3+ hydrocarbons, in particular C3 to C6) for the steam cracker.

[0069] The remaining gas stream is non-condensable and can be used to provide the energy needed to operate the pyrolysis stage.

[0070] Thus, during step b) of the process according to the invention, said first gaseous effluent from step a) is compressed and then cooled, then said first compressed and cooled gaseous effluent is separated in a separation unit so as to obtain a second liquid effluent containing mainly C3+ hydrocarbons, in particular C3 to C6, and a second residual gaseous effluent concentrated in H2, CO and CO2.

[0071] Step b) is carried out in such a way that during separation the relative pressure is between 0.5 and 2.5 MPa relative (5 and 25 bars relative or barg according to English terminology) and the temperature is between 20 and 55°C. Preferably the pressure is between 1.0 and 1.5 MPa relative, and the temperature is between 30 and 45°C, or even between 35 and 40°C.

[0072] The compression of said first gaseous effluent is generally carried out in at least one compressor. The cooling of said first gaseous effluent is generally carried out by a heat exchanger.

[0073] The separation can advantageously be implemented by any method known to those skilled in the art such as, for example, the combination of one or more separator(s) (balloon(s)), and / or one or more stripping column(s), this or these separator(s) (balloon(s)) and / or columns optionally being able to be supplied with a stripping gas, for example a hydrogen-rich gas stream. Preferably, the separation is carried out in a separator ball.

[0074] Step b) makes it possible to obtain a second liquid effluent containing mainly C3+ hydrocarbons and a second residual gaseous effluent containing H2, CO, CO2, and light hydrocarbons C1 to C2. A second liquid effluent containing “mainly C3+ hydrocarbons” means a liquid effluent having a C3+ hydrocarbon content greater than or equal to 50% by weight relative to the weight of said second liquid effluent.

[0075] Said second liquid effluent containing mainly C3+-C6 hydrocarbons is low in CO and CO2. The term “low in CO and CO2” means a CO and CO2 content of less than or equal to 5000 ppm, preferably less than or equal to 3000 ppm by weight relative to the weight of said second liquid effluent.

[0076] Indeed, following the sequence of compression, cooling and separation of step b), the CO and CO2 (and the H2) are concentrated in said second residual gaseous effluent. This makes it possible to recover said second liquid effluent having an acceptable CO and CO2 content to be sent to step c) of steam cracking or to a purification step upstream of step c) of steam cracking.

[0077] According to another embodiment, at least a portion of the first liquid effluent from pyrolysis step a) may be introduced into said separation unit, whether or not mixed with said first compressed gaseous effluent. More particularly, the method according to the invention may comprise a step b) in which at least a portion of the first liquid effluent is introduced into said separation unit, whether or not mixed with said first compressed gaseous effluent, then the mixture is separated so as to obtain an intermediate liquid effluent and said second residual gaseous effluent concentrated in H2, CO and CO2, then said intermediate liquid effluent is separated in a second separation unit so as to obtain said second liquid effluent containing mainly C3+ hydrocarbons and a third residual gaseous effluent concentrated in H2, CO and CO2.

[0078] This embodiment allows for further extraction of organic components from the first gaseous effluent into the liquid phase resulting from the separation. The recovered components include C3 hydrocarbons (e.g., propane, propylene) and hydrocarbons with higher boiling points, but may also include C2 hydrocarbons (e.g., ethylene, ethane) as valuable petrochemical feedstocks. In addition, this embodiment aims to maximize the recovery of organic chlorinated compounds and other impurities to clean the first gaseous effluent and concentrate the impurities in the liquid phase to be further purified in a purification step.Contacting the first gaseous effluent with the first liquid effluent at elevated pressure lowers the partial pressure of the vapor in the separation liquid, thus entraining the heavier organic components of the vapor phase of the first gaseous effluent into the liquid phase, creating a "sponge" effect. There are several options for sending all or part of the first liquid effluent to the separation:

[0079] • the first liquid effluent from step a) is sent directly to the separation unit

[0080] • the first liquid effluent from step a) is mixed with the first compressed gaseous effluent upstream or downstream of its cooling and the mixture is sent to the separation unit.

[0081] In this embodiment, the separation of the mixture can advantageously be implemented by any method known to those skilled in the art such as for example a separator flask or an absorbent column in which the first liquid effluent is introduced at the top and the first gaseous effluent is introduced at the bottom.

[0082] The gaseous phase resulting from the separation of the mixture, the second residual gaseous effluent, has a lower impurity content than the first gaseous effluent, thus allowing easier use as fuel either for the pyrolysis unit or an external application, or as a feedstock for the steam cracker.

[0083] The liquid recovered from the separation of the mixture, the intermediate liquid effluent, is then treated in a second separation unit to produce said second liquid effluent and a third residual gaseous effluent. This separation step further allows the removal of light components such as H2, CO and / or COa from the intermediate liquid effluent, generally at a content of at most 1000 ppm, often less than 100 ppm, but preferably less than 10 ppm by weight of light components. The removal of these components prevents them from entering either the steam cracking unit or the purification unit.

[0084] The separation of the intermediate liquid effluent can advantageously be carried out by any method known to those skilled in the art such as, for example, by distillation (for example, by a tray distillation column or a packed distillation column), the combination of one or more separating flask(s), a pervaporation membrane, or any combination thereof.

[0085] The separation of the intermediate liquid effluent can be carried out in the same pressure and temperature ranges as the separation of the mixture. The pressure and temperature conditions can be the same or different. When using a distillation column as the second separation unit, the separation temperature can be between 80 and 150°C at the bottom of the column and the pressure can be between 1 and 1.5 MPa.

[0086] Said third residual gaseous effluent is concentrated with the light components which may include CO, CO2, methane, but also includes certain light hydrocarbon components, in particular ethylene and heavier hydrocarbon compounds. Said third residual gaseous effluent may be recycled and mixed with the first gaseous effluent upstream of its compression or cooling so that a portion of the light hydrocarbon components may be recovered in the liquid phase of the separation of the mixture.

[0087] Optionally, said third residual gaseous effluent may also be mixed with the second residual gaseous effluent or the fuel of the pyrolysis unit to use its energy value as fuel either for the pyrolysis unit or for an external application.

[0088] Step c) of steam cracking

[0089] According to step c) of the process according to the invention, said second liquid effluent (condensate) is introduced into a steam cracking unit in the presence of water vapor so as to obtain olefins.

[0090] Advantageously, said first liquid effluent containing mainly C7+ hydrocarbons (pyrolysis oil) is also introduced into said steam cracking unit of step c), mixed or not with said second liquid effluent (condensate).

[0091] Said second liquid effluent (condensate) may represent between 0.5 and 10% by weight relative to the total weight of the feedstock mixture introduced into the steam cracking step. Said steam cracking step c) is advantageously carried out in at least one pyrolysis furnace at a temperature of between 700 and 900°C, preferably between 750 and 850°C, and at a pressure of between 0.05 and 0.3 MPa relative in the presence of water vapor. The residence time of the hydrocarbon compounds is generally less than or equal to 1.0 seconds (denoted s), preferably between 0.1 and 0.5 s. Advantageously, water vapor is introduced upstream of steam cracking step c). The quantity of water introduced, in the form of water vapor, is advantageously between 0.3 and 3.0 kg of water per kg of hydrocarbon compounds entering the steam cracking stage.

[0092] The steam cracking stage can be carried out in several pyrolysis furnaces in parallel in order to adapt the operating conditions to the different streams feeding the steam cracking stage, and also to manage the decoking times of the tubes. A furnace comprises one or more tubes arranged in parallel. A furnace can also refer to a group of furnaces operating in parallel. For example, one furnace can be dedicated to cracking the middle distillate cut.

[0093] The effluents from the various steam cracking furnaces are generally recombined before separation in order to constitute an effluent. It is understood that the steam cracking stage includes the steam cracking furnaces but also the sub-stages associated with steam cracking well known to those skilled in the art. These sub-stages may include in particular heat exchangers, columns and catalytic reactors and recycling to the furnaces. A column generally makes it possible to fractionate the effluent in order to recover at least a light fraction comprising hydrogen and compounds having 2 to 5 carbon atoms, and a fraction comprising pyrolysis gasoline, and possibly a heavier fraction. Columns make it possible to separate the different constituents of the light fractionation fraction in order to recover at least an ethylene-rich cut (C2 cut) and a propylene-rich cut (C3 cut) and possibly a butene-rich cut (C4 cut).Catalytic reactors are used in particular to carry out hydrogenations of C2, C3 and even C4 cuts and pyrolysis gasoline. Saturated compounds, in particular saturated compounds having 2 to 4 carbon atoms, are advantageously recycled to the steam cracking furnaces so as to increase the overall olefin yields. This steam cracking step c) makes it possible to obtain at least one effluent containing olefins comprising 2, 3 and / or 4 carbon atoms (i.e. C2, C3 and / or C4 olefins), at satisfactory contents, in particular greater than or equal to 30% by weight of total olefins comprising 2, 3 and 4 carbon atoms relative to the weight of the steam cracking effluent in question. Said C2, C3 and C4 olefins can then be advantageously used as polyolefin monomers.

[0094] According to one embodiment, and when said second liquid effluent (condensate) and / or said first liquid effluent (pyrolysis oil) does not meet the specifications (in particular in chlorine) at the inlet of the steam cracking unit, these specifications can be achieved by dilution at the inlet of the steam cracking unit with a feedstock containing no or very little chlorine, for example a petroleum feedstock. The petroleum feedstock is preferably chosen from naphtha, kerosene, diesel, or mixtures of such feedstocks.

[0095] According to another embodiment, said second liquid effluent (condensate) and / or said first liquid effluent (pyrolysis oil) not meeting the specifications (in particular in chlorine) at the inlet of the steam cracking unit may undergo at least one purification step before being introduced into the steam cracking step c).

[0096] Purification step(s) upstream of the steam cracking step (optional)

[0097] Said second liquid effluent from step b) (condensate) may contain impurity levels that are too high compared to the specifications of the steam cracking unit. These impurities are in particular halogenated compounds, in particular chlorine-based compounds, but also diolefins, olefins, metals, in particular iron, silicon, or heteroelements such as sulfur, oxygen and nitrogen.

[0098] Steam cracking units require very high feed purities, including low chlorine, diolefin, olefin, metal and sulfur contents. The specification for the chlorine content at the inlet of a steam cracking unit is typically 3 ppm by weight maximum, preferably 1 ppm by weight maximum. Said second liquid effluent from step b) (condensate) can thus undergo at least one purification step in a purification unit upstream of the steam cracking unit in order to achieve the specifications required for steam cracking step c).

[0099] The same applies to said first liquid effluent containing mainly C7+ hydrocarbons from step a) (pyrolysis oil) which may include in particular halogenated compounds, in particular chlorine-based compounds, but also diolefins, olefins, metals, in particular iron, silicon, or even heteroelements such as sulphur, oxygen and nitrogen, and insolubles.

[0100] Said first liquid effluent from step a) (pyrolysis oil) can thus also undergo at least one purification step in a purification unit upstream of the steam cracking unit in order to achieve the specifications required for the steam cracking step c).

[0101] The purification step may comprise a hydrotreatment step, possibly preceded by a pretreatment and / or possibly followed by a washing / separation step.

[0102] According to one variant, only said second liquid effluent undergoes at least one purification step in a purification unit upstream of the steam cracking unit c).

[0103] According to another variant, only said first liquid effluent undergoes at least one purification step in a purification unit upstream of the steam cracking unit c).

[0104] According to yet another preferred variant, said second liquid effluent and said first liquid effluent undergo at least one purification step in a purification unit upstream of the steam cracking unit, preferably in the same purification unit. Thus, said second liquid effluent (condensate) can be sent, mixed or not, with said first liquid effluent (pyrolysis oil) to a hydrotreatment step, followed by a washing / separation step.

[0105] According to yet another variant, said second liquid effluent and said first liquid effluent may undergo several purification stages, some alone and others in common. Thus, said first liquid effluent (pyrolysis oil) may, for example, undergo pretreatment, then be sent with said second liquid effluent (condensate) to a hydrotreatment stage, followed by a washing / separation stage, or even directly to the steam cracking stage c).

[0106] Pre-treatment (optional)

[0107] One way to eliminate the impurities contained in said second effluent and / or in said first liquid effluent is to carry out a pretreatment, generally carried out after the pyrolysis step, and upstream of a hydrotreatment step if it is present.

[0108] Alternatively, this optional pretreatment step can reduce the amount of contaminants and solid particles. This optional pretreatment step can notably eliminate sediments that may form due to the unstable nature of pyrolysis oils and / or a compatibility problem between two different feedstocks.

[0109] Said optional pretreatment step may be implemented by any method known to those skilled in the art for reducing the quantity of contaminants. It may in particular comprise an adsorption step and / or a filtration step and / or a centrifugation step and / or a decantation step and / or an electrostatic separation step and / or a washing step using an aqueous solution and / or a gas stripping step.

[0110] The optional pretreatment step is advantageously carried out at a temperature between 20 and 400°C, preferably between 40 and 350°C, and at a pressure between 0.15 and 10.0 MPa abs, preferably between 0.2 and 7.0 MPa abs.

[0111] According to one variant, said optional pretreatment step is implemented in an adsorption section operated in the presence of at least one adsorbent. The adsorbent may be chosen from a zeolite, activated carbon, a clay, a silica or an alumina. Advantageously, said adsorbent comprises less than 1% by weight of metallic elements, preferably is free of metallic elements. By metallic elements of the adsorbent, it is meant the elements of groups 6 to 10 of the periodic table of elements (new IUPAC classification). According to another variant, said optional pretreatment step is implemented in a washing section with an aqueous solution, for example water or an acidic or basic solution.This washing section may include equipment for bringing the pyrolysis oil and / or the condensate into contact with the aqueous solution and for separating the phases so as to obtain the pretreated feedstock on the one hand and the aqueous solution comprising impurities on the other hand. Among this equipment, there may be for example a stirred reactor, a decanter, a mixer-decanter and / or a co- or counter-current washing column.

[0112] According to another variant, said optional pretreatment step is implemented by filtration. The filtration step makes it possible to remove inorganic solids, sediments and / or fines contained in the pyrolysis oil and / or the condensate, in particular metals, metal oxides and metal chlorides. A filter is generally used whose pore size (for example the diameter or equivalent diameter) is less than 25 μm, preferably less than or equal to 10 μm, even more preferably less than or equal to 5 μm. It is also possible to use a series of filters with different pore sizes, in particular a series of filters having decreasing pore sizes in the direction of flow of the feed. These filter media are well known for industrial uses. Cartridge filters, self-cleaning filters, for example, are suitable.

[0113] According to another variant, said optional pretreatment step is implemented by centrifugation, by decantation or by electrostatic separation.

[0114] In another embodiment, said optional pretreatment step is implemented by gas stripping, thereby reducing the oxygen content in the feedstock. Gas stripping may remove oxygen (O2) that may be dissolved in the pyrolysis oil and / or condensate thereby reducing the likelihood of free radical formation leading to polymerization in downstream steps. The process typically involves contacting the pyrolysis oil and / or condensate with a stripping gas (e.g. H2, N2 or a mixture thereof), thereby transferring at least some of the dissolved oxygen from the feedstock to the stripping gas, followed by separation of the stripping gas from the pyrolysis oil and / or condensate. Any dissolved H2 remaining in the pyrolysis oil and / or condensate after the gas stripping step is not a concern, given the hydrotreatment step typically performed downstream.

[0115] Said optional pre-treatment step generally comprises one or more, preferably several treatments described above.

[0116] Said optional pretreatment step thus makes it possible to obtain said second pretreated effluent and / or said first pretreated liquid effluent which can then feed the hydrotreatment step or be sent to the steam cracking step c), possibly after having carried out a fractionation step.

[0117] Hydrotreatment step (optional)

[0118] Another way to remove the impurities contained in said second liquid effluent and / or in said first liquid effluent is to carry out a hydrotreatment step in the presence of a catalyst.

[0119] Thus, the purification step may comprise a hydrotreatment step implemented in a hydrotreatment reaction section, implementing at least one fixed-bed reactor having n catalytic beds, n being an integer greater than or equal to 1, each comprising at least one hydrotreatment catalyst, said hydrotreatment reaction section being fed with said second liquid effluent from step b), optionally pretreated, and / or said first liquid effluent from step a), optionally pretreated, and a gas stream comprising hydrogen, said hydrotreatment reaction section being implemented at an average temperature between 150 and 430°C, a hydrogen partial pressure between 1.0 and 10.0 MPa abs. and an hourly volumetric flow rate between 0.1 and 10.0 h -1 to obtain a second purified liquid effluent and / or a first purified liquid effluent.

[0120] Advantageously, the hydrotreatment step uses hydrotreatment reactions well known to those skilled in the art, and more particularly hydrotreatment reactions such as hydrodemetallation, hydrogenation of aromatics, hydrodesulfurization and hydrodenitrogenation as well as the hydrogenation of olefins (mono- and di-olefins) and halogenated compounds (in particular chlorinated ones).

[0121] Said hydrotreatment reaction section is advantageously carried out at a medium temperature (or WABT as defined below) of hydrotreatment between 150 and 430°C, preferably between 280 and 380°C, at a partial pressure of hydrogen between 1.0 and 10.0 MPa abs. and at an hourly volumetric velocity (WH) between 0.1 and 10.0 h' 1 , preferably between 0.1 and 5.0 h' 1 , preferably between 0.2 and 2.0 h -1 , preferably between 0.2 and 1 h' 1The hydrogen coverage is advantageously between 50 and 1000 Nm 3 of hydrogen per m 3 of charge which feeds the hydrotreatment stage, and preferably between 50 and 500 Nm 3 of hydrogen per m 3 load, preferably between 100 and 300 Nm 3 of hydrogen per m 3 dump.

[0122] The "average temperature" of a reaction section corresponds to the Weight Average Bed Temperature (WABT) according to the established Anglo-Saxon term, well known to those skilled in the art. The average temperature is advantageously determined according to the catalytic systems, equipment, and their configuration used. The average temperature (or WABT) is calculated as follows:

[0123] WABT = (TæjHfi. + Tg^^ with Tentry: the temperature of the effluent at the inlet of the reaction section and Toutlet: the temperature of the effluent at the outlet of the reaction section.

[0124] The hourly volume flow rate (WH) is defined here as the ratio between the hourly volume flow rate of the feedstock, possibly pretreated, by the volume of catalyst(s).

[0125] The hydrogen coverage is defined as the ratio of the volume flow rate of hydrogen taken under normal temperature and pressure conditions to the volume flow rate of charge, possibly pretreated, without taking into account a possible recycled fraction, at 15°C (in normal m 3 , noted Nm 3 , of H2 per m 3 dump).

[0126] Preferably, the method according to the invention comprises a hydrotreatment step implemented in a hydrotreatment reaction section, implementing at least one fixed-bed reactor having n catalytic beds, n being an integer greater than or equal to 1, preferably between one and ten, preferably between two and five, each comprising at least one hydrotreatment catalyst. Said hydrotreatment reaction section is fed at least by said second liquid effluent from step b) and / or said first liquid effluent from step a), and a gaseous stream comprising hydrogen, advantageously at the first catalytic bed of the first reactor in operation. An injection of at least a portion of the feedstock and / or at least a portion of hydrogen between the different catalytic beds is also possible.

[0127] The hydrotreatment reaction section using at least one fixed bed reactor can operate with a descending or ascending flow of gas and liquid.

[0128] The gas stream comprising hydrogen, which feeds the hydrotreatment reaction section, may consist of hydrogen makeup and / or recycled hydrogen. The gas stream comprising hydrogen may come from a fossil source or a renewable source, for example from the gasification of plastic waste or produced by electrolysis.

[0129] Preferably, an additional gas stream comprising hydrogen is advantageously introduced at the inlet of each reactor, in particular operating in series, and / or at the inlet of each catalytic bed from the second catalytic bed of the reaction section. These additional gas streams are also called cooling streams. They make it possible to control the temperature in the reactor in which the reactions carried out are generally very exothermic.

[0130] Preferably, the hydrotreatment step may use, upstream of the hydrotreatment catalyst(s), at least one guard bed containing adsorbents of the alumina, silica, silica-alumina, zeolite and / or activated carbon type, possibly containing metals from group VIB and / or VIII. It is also possible to use a series of guard beds with particles of different diameters, in particular a series of guard beds having decreasing diameters in the direction of circulation of the feedstock (also called “grading” according to English terminology).

[0131] Advantageously, said hydrotreatment catalyst comprises a support, preferably mineral, and a hydro-dehydrogenating function. According to one variant, the hydro-dehydrogenating function comprises in particular at least one element from group VIII, preferably chosen from nickel and cobalt, and at least one element from group VIB, preferably chosen from molybdenum and tungsten. According to this variant, the total content expressed as oxides of the metal elements from groups VIB and VIII is preferably between 1% and 40% by weight, preferably from 5% to 30% by weight relative to the total weight of the catalyst. When the metal is cobalt or nickel, the metal content is expressed as CoO and NiO respectively. When the metal is molybdenum or tungsten, the metal content is expressed as MoChet WO3 respectively.The weight ratio expressed in metal oxide between the metal (or metals) of group VIB relative to the metal (or metals) of group VIII is preferably between 1 and 20, and preferably between 2 and 10.

[0132] According to this variant, the reaction section of said hydrotreatment step comprises for example a hydrotreatment catalyst comprising between 0.5% and 12% by weight of nickel, preferably between 0.9% and 10% by weight of nickel (expressed as nickel oxide NiO relative to the weight of said catalyst), and between 1% and 30% by weight of molybdenum, preferably between 3% and 20% by weight of molybdenum (expressed as molybdenum oxide MoOs relative to the weight of said catalyst) on a preferably mineral support, preferably on an alumina support.

[0133] According to another variant, the hydro-dehydrogenating function comprises, and is preferably made up of, at least one element from group VIII, preferably nickel. According to this variant, the content of nickel oxides is preferably between 1 and 50% by weight, preferably between 10% and 30% by weight relative to the weight of said catalyst. This type of catalyst is preferably used in its reduced form, on a preferably mineral support, preferably on an alumina support.

[0134] According to another aspect of the invention, the hydrotreatment catalyst as described above further comprises one or more organic compounds containing oxygen and / or nitrogen and / or sulfur. Such a catalyst is often referred to as an "additive catalyst". Generally, the organic compound is chosen from a compound comprising one or more chemical functions chosen from a carboxylic function, alcohol, thiol, thioether, sulfone, sulfoxide, ether, aldehyde, ketone, ester, carbonate, amine, nitrile, imide, oxime, urea and amide or compounds including a furan cycle or sugars.

[0135] The support of said hydrotreatment catalyst is preferably chosen from alumina, silica, silica-aluminas, magnesia, clays and mixtures thereof. Said support may contain doping compounds, in particular oxides chosen from boron oxide, in particular boron trioxide, zirconia, ceria, titanium oxide, phosphoric anhydride and a mixture of these oxides. Preferably, said hydrotreatment catalyst comprises an alumina support, optionally doped with phosphorus and optionally boron. When phosphoric anhydride P2O5 is present, its concentration is less than 10% by weight relative to the weight of the alumina and advantageously at least 0.001% by weight relative to the total weight of the alumina. When boron trioxide B2O3 is present, its concentration is less than 10% by weight relative to the weight of the alumina and advantageously at least 0.001% relative to the total weight of the alumina.The alumina used can be, for example, a y (gamma) or q (eta) alumina.

[0136] Said hydrotreatment catalyst is for example in the form of extrudates or in the form of beads.

[0137] The preparation of the catalyst for the hydrotreatment step is known and generally includes a step of impregnation of the metals of group VIII and group VIB when present, and possibly phosphorus and / or boron on the support, followed by drying, then possibly calcination. The catalyst can also be a catalyst used in its reduced form, thus involving a reduction step in its preparation.

[0138] Before their use in a process step, the catalysts are generally subjected to sulfurization in order to form the active species. Depending on the content of sulfur compounds in the initial feed to be treated, a stream containing a sulfurizing agent can be injected upstream of the optional pretreatment step or the hydrotreatment step, preferably upstream of the hydrotreatment step in order to ensure a sufficient quantity of sulfur to form the active species of the catalyst (in sulfide form). This activation or sulfurization step is carried out by methods well known to those skilled in the art, and advantageously under a sulfide-reducing atmosphere in the presence of hydrogen and hydrogen sulfide.The sulfurizing agents are preferably H2S gas, elemental sulfur, CS2, mercaptans, sulfides and / or polysulfides, hydrocarbon fractions with a boiling point below 400°C containing sulfur compounds or any other compound containing sulfur used for the activation of hydrocarbon feedstocks in order to sulfurize the catalyst. Said sulfur-containing compounds are advantageously chosen from alkyl disulfides such as, for example, dimethyl disulfide (DMDS), alkyl sulfides, such as, for example, dimethyl sulfide, thiols such as, for example, n-butyl mercaptan (or 1-butanethiol) and polysulfide compounds of the tert-onylpolysulfide type. The catalyst may also be sulfurized by the sulfur contained in the feedstock to be desulfurized. Preferably, the catalyst is sulfurized in situ in the presence of a sulfurizing agent and a hydrocarbon feedstock.Most preferably, the catalyst is sulfurized in situ in the presence of the dimethyl disulfide additive charge. The sulfurizing agent can be injected continuously.

[0139] According to a variant, the second hydrotreated liquid effluent and / or the first liquid effluent may be supplemented with a conventional petroleum feedstock or a feedstock resulting from the conversion of biomass which is then co-treated in the pretreatment and / or the hydrotreatment step.

[0140] The conventional petroleum feedstock can advantageously be a cut or a mixture of cuts of the naphtha or diesel type.

[0141] The feedstock resulting from the conversion of biomass may advantageously be chosen from vegetable oils, algae or algal oils, fish oils, used edible oils, and fats of vegetable or animal origin; or mixtures of such feedstocks. Said vegetable oils may advantageously be crude or refined, totally or partially, and derived from plants chosen from rapeseed, sunflower, soybean, palm, olive, coconut, copra, castor oil, cottonseed, peanut, linseed and crambe oils and all oils derived for example from sunflower or rapeseed by genetic modification or hybridization, this list not being exhaustive. Said animal fats are advantageously chosen from lard and fats composed of residues from the food industry or from the catering industries.Frying oils, various animal oils such as fish oils, tallow, lard can also be used. The feedstock resulting from biomass conversion can also advantageously be chosen from fatty acid methyl esters of vegetable and / or animal origin or fatty acid methyl esters from used edible vegetable oils.

[0142] The feedstock from biomass conversion may also be selected from feedstocks from thermal or catalytic biomass conversion processes, such as oils that are produced from biomass, particularly lignocellulosic biomass, with various liquefaction methods, such as hydrothermal liquefaction or pyrolysis. The term "biomass" refers to material derived from recently living organisms, which includes plants, animals, and their by-products. The term "lignocellulosic biomass" refers to biomass derived from plants or their by-products. Lignocellulosic biomass is composed of carbohydrate polymers (cellulose, hemicellulose) and an aromatic polymer (lignin).

[0143] The feedstock from biomass conversion can also advantageously be chosen from feedstocks from the paper industry.

[0144] After the hydrotreatment step, a second purified liquid effluent and / or a first purified liquid effluent are obtained.

[0145] Washing / separation step

[0146] According to a variant, the hydrotreatment step may be followed by a washing / separation step, fed with said second purified liquid effluent, optionally pretreated, and / or said first purified liquid effluent, optionally pretreated, and an aqueous solution to obtain at least one gaseous effluent, one aqueous effluent and said second washed purified liquid effluent and / or said first washed purified liquid effluent.

[0147] This washing / separation step makes it possible in particular to eliminate the ammonium chloride salts, which are formed by reaction between the chloride ions, released by the hydrogenation of the chlorinated compounds in HCl form, in particular during the hydrotreatment step and then dissolution in water, and the ammonium ions, generated by the hydrogenation of the nitrogen compounds in the form of NH3 during the hydrotreatment step and / or supplied by injection of an amine and then dissolution in water, and thus to limit the risks of blockage, in particular in the transfer lines and / or in the sections of the process of the invention and / or the transfer lines to the steam cracker, due to the precipitation of the ammonium chloride salts. This step also makes it possible to eliminate the hydrochloric acid formed by the reaction of the hydrogen ions and the halide ions released by the hydrogenation of the halogenated compounds during the hydrotreatment step which dissolve in the aqueous solution.When H2S is present in the hydrotreated effluent from the hydrotreatment stage, the washing / separation stage also allows the removal of ammonium sulfide salts ((NH4)2S) which are formed by reaction between the H2S from the hydrodesulfurization of sulfur compounds and the NH3 by dissolving them in the aqueous solution.

[0148] The washing / separation step is advantageously carried out at a temperature between 50 and 450°C, preferably between 100 and 440°C, preferably between 200 and 420°C. It is important to operate in this temperature range (and therefore not to cool the hydrotreatment effluent too much) to avoid the risk of blockage in the lines due to the precipitation of ammonium chloride salts. Advantageously, the washing / separation step is carried out at a pressure close to that used in the hydrotreatment step, preferably between 1.0 and 10.0 MPa abs, so as to facilitate the recycling of hydrogen.

[0149] The aqueous solution can be water. It can also be a basic aqueous solution (by adding NaOH for example). Using a basic solution helps neutralize hydrogen halides and any dissolved salts.

[0150] The washing / separation step can advantageously be carried out in common or separate washing and separation equipment, this equipment being well known (separator tanks which can operate at different pressures and temperatures, pumps, heat exchangers, washing columns, etc.).

[0151] Advantageously, the washing / separation step comprises an injection of an aqueous solution, preferably an injection of water, into the hydrotreated effluent, upstream of the washing / separation section, so as to dissolve at least in part and preferably all of the hydrogen halides (HCl in particular) and any salts present.

[0152] In a possible embodiment of the invention, the washing / separation step comprises the injection of an aqueous solution into the hydrotreated effluent, followed by the washing / separation section advantageously comprising a separation phase making it possible to obtain at least one aqueous effluent loaded with hydrogen halides (HCl in particular) and any dissolved salts, a washed hydrotreated effluent and a partially washed gaseous effluent. Said aqueous effluent and the washed hydrotreated effluent can then be separated in a settling tank in order to obtain said washed hydrotreated effluent and said aqueous effluent.Said partially washed gaseous effluent may in parallel be introduced into a washing column where it circulates countercurrently to an aqueous stream, preferably of the same nature as the aqueous solution injected into the hydrotreated effluent, which makes it possible to eliminate at least in part, preferably in full, the hydrochloric acid contained in the partially washed gaseous effluent and thus to obtain said gaseous effluent, preferably essentially comprising hydrogen, and an acidic aqueous stream. Said aqueous effluent from the settling tank may optionally be mixed with said acidic aqueous stream, and be used, optionally in a mixture with said acidic aqueous stream in a water recycling circuit to supply the washing / separation step with said aqueous solution upstream of the washing / separation section and / or with said aqueous stream in the washing column.Said water recycling circuit may include a water top-up and / or a basic solution and / or a purge to remove impurities.

[0153] According to one embodiment, and depending on the content of chlorinated compounds in said second liquid effluent and / or the first liquid effluent, a stream containing a nitrogen compound such as ammonia or an amine, for example monoethanolamine, diethanolamine and / or monodiethanolamine, may be injected upstream of the hydrotreatment step in order to ensure a sufficient quantity of ammonium ions to combine the chloride ions formed during the hydrotreatment step in the form of ammonium chloride salts, thus making it possible to limit the formation of hydrochloric acid and thus to limit corrosion downstream of the separation section. Said gaseous effluent obtained at the end of the washing / separation step advantageously comprises hydrogen, preferably comprises at least 60% by volume, preferably at least 70% by volume, of hydrogen.Said gaseous effluent obtained at the end of the washing / separation step contains very little chlorine, generally at a content of less than 3 ppm by weight of chlorine, which allows it to be sent to a refining unit requiring hydrogen. According to one embodiment, said gaseous effluent can at least partly be recycled to the hydrotreatment step, the recycling system being able to comprise a purification section (for example adsorption of heavy metals such as mercury).

[0154] The aqueous effluent obtained from the washing / separation step advantageously comprises ammonium salts and / or hydrochloric acid.

[0155] A portion of said second washed purified liquid effluent and / or said first washed purified liquid effluent may be recycled upstream of the hydrotreatment step, which makes it possible, on the one hand, to dilute the impurities and, on the other hand, to control the temperature in the hydrotreatment step in which the reactions involved may be highly exothermic. Diluting the impurities makes it possible to limit undesirable reactions such as the polymerization of diolefins (gum formation) and / or the formation of coke.

[0156] According to another preferred embodiment, said second washed purified liquid effluent and / or said first washed purified liquid effluent is / are sent in part and preferably in full, directly to the inlet of a steam cracking unit.

[0157] Splitting step (optional)

[0158] According to one embodiment, said second purified liquid effluent, optionally pretreated and / or washed, and / or said first purified liquid effluent, optionally pretreated and / or washed, is subjected to at least one fractionation step in a fractionation unit upstream of the steam cracking step to obtain at least one gas stream and at least one liquid stream of C3+ hydrocarbons, for example a naphtha cut and at least one middle distillate cut.

[0159] The term "naphtha cut" means a hydrocarbon cut comprising compounds having a boiling point generally less than or equal to 175°C, in particular between 80 and 175°C. The term "middle distillate cut" means a hydrocarbon cut comprising compounds having a boiling point generally greater than 175°C. The heavy cut may include middle distillates such as a diesel cut and / or a kerosene cut. It may also include heavier compounds.

[0160] Depending on the destination or use of the cuts from the fractionation step, the skilled person will adjust the cut points in the stripping and / or distillation operations. For example, it may be necessary to adjust the end point of the naphtha cut to 150, 175 or 200°C, or even 250°C.

[0161] The fractionation stage makes it possible in particular to eliminate gases dissolved in the liquid hydrocarbon effluent, such as for example ammonia, hydrogen sulfide and light hydrocarbons C1 to C2.

[0162] The fractionation step is advantageously carried out at a pressure less than or equal to 1.0 MPa abs., preferably between 0.1 and 1.0 MPa abs.

[0163] According to one embodiment, the fractionation step can be carried out in a section advantageously comprising at least one stripping column equipped with a reflux circuit comprising a reflux drum. Said second purified liquid effluent, optionally pretreated and / or washed, and / or said first purified liquid effluent, optionally pretreated and / or washed, can be optionally reheated before entering the stripping column. Thus, the lightest compounds are entrained at the top of the column and into the reflux circuit comprising a reflux drum in which a gas / liquid separation takes place. The gaseous phase which comprises the light hydrocarbons C1 to C2, is withdrawn from the reflux drum, in a gas stream. The naphtha cut is advantageously withdrawn from the reflux drum, in a liquid stream. The middle distillate cut is advantageously withdrawn at the bottom of the stripping column.

[0164] According to another embodiment, the fractionation step can be carried out in a section comprising one or more separator tank(s). Advantageously, at least one so-called low-pressure, low-temperature separator tank will be used in order to eliminate the gases dissolved in said second purified liquid effluent, optionally pretreated and / or washed, and / or said first purified liquid effluent, optionally pretreated and / or washed. According to other embodiments, the fractionation step can implement a stripping column followed by a distillation column or only a distillation column.

[0165] According to yet another embodiment, the fractionation step can be carried out in a depentanizer column from which, in addition to the gas stream, a C3-C4 liquid stream and a C5+ liquid stream are withdrawn.

[0166] At least one of the liquid streams obtained by the fractionation stage (naphtha cut, middle distillate cut, C3-C4 liquid stream or C5+ liquid stream) can be sent, in whole or in part, to the steam cracking stage, at the end of which olefins can be (re)formed to participate in the formation of polymers.

[0167] According to another variant, a portion of the C3-C4 liquid stream can be sent to the steam cracking stage, while another portion can be used as a fuel gas to provide a portion of the energy required for the operation of, for example, the pyrolysis unit. Separating a C3-C4 liquid stream that can be sent to the steam cracker or to the pyrolysis unit thus makes it possible to adjust the energy requirements of the pyrolysis unit.

[0168] The gas or liquid fraction(s) resulting from the fractionation stage may be subject to additional purification(s), for example washing with amines, water or soda.

[0169] Alternatively, a portion of at least one of the liquid streams obtained by the fractionation step is optionally recycled in at least one of the steps of the process (for example pretreatment or hydrotreatment) and / or sent to a fuel storage unit, for example a naphtha storage unit, a middle distillate storage unit, from conventional petroleum feedstocks.

[0170] Advantageously, the purification step(s) allows the hydrogenation of at least 80%, and preferably of all of the olefins (mono- and diolefins), but also the conversion at least in part of other impurities present in the feedstock, such as aromatic compounds, metallic compounds, sulfur compounds, nitrogen compounds, halogenated compounds (in particular chlorinated compounds), oxygenated compounds. Preferably, the nitrogen content at the outlet of the purification step is less than 10 ppm by weight.

[0171] Preferably, the sulfur content at the outlet of the purification stage is less than 10 ppm by weight.

[0172] Preferably, the oxygen content at the outlet of the purification stage is less than 10 ppm by weight.

[0173] Preferably, the metal content at the outlet of the purification step is less than 10 ppm by weight, and preferably less than 2 ppm by weight, and the silicon content is less than 5 ppm by weight.

[0174] Preferably, the halogen content (in particular chlorine) at the outlet of the purification stage is less than 3 ppm by weight.

[0175] The contents are given in relative weight concentrations, percentage (%) by weight, part(s) per million (ppm) by weight or part(s) per billion (ppb) by weight, relative to the total weight of the stream considered.

[0176] Hydrocracking stage (optional)

[0177] According to a variant, the process of the invention may comprise a hydrocracking step carried out either directly after the hydrotreatment step or after the fractionation step on the middle distillate cut. Compounds having a boiling point above 175°C contain, compared to lighter compounds, more naphthenic, naphtheno-aromatic and aromatic compounds, thus leading to a higher C / H ratio. This high ratio is a cause of coking in the steam cracker, thus requiring steam cracking furnaces dedicated to this cut. When it is desired to minimize the yield of these heavy compounds (middle distillate cut) and maximize the yield of light compounds (naphtha cut), these compounds can be transformed at least in part into light compounds by hydrocracking, a cut generally favored for a steam cracking unit.

[0178] Thus, the process of the invention may comprise a hydrocracking step implemented in a hydrocracking reaction section, implementing at least one fixed-bed reactor having n catalytic beds, n being an integer greater than or equal to 1, each comprising at least one hydrocracking catalyst, said hydrocracking reaction section being fed by said hydrotreated effluent and / or by the middle distillate cut resulting from the fractionation step and a gas stream comprising hydrogen, said hydrocracking reaction section being implemented at an average temperature between 250 and 450°C, a partial pressure of hydrogen between 1.5 and 20.0 MPa abs. and an hourly volumetric velocity between 0.1 and 10.0 h -1 , to obtain a hydrocracked effluent which is sent to the fractionation stage, then preferably to the steam cracking stage c).

[0179] Thus, said hydrocracking reaction section is advantageously carried out at an average temperature between 250 and 480°C, preferably between 320 and 450°C, at a hydrogen partial pressure between 1.5 and 20.0 MPa abs., preferably between 2 and 18.0 MPa abs., and at an hourly volumetric flow rate (WH) between 0.1 and 10.0 h -1 , preferably between 0.1 and 5.0 h' 1 , preferably between 0.2 and 4 h' 1 The hydrogen coverage in the hydrocracking stage is advantageously between 80 and 2000 Nm 3 of hydrogen per m 3 of charge which feeds the hydrocracking stage, and preferably between 200 and 1800 Nm 3 of hydrogen per m 3 feedstock that feeds the hydrocracking stage. The definitions of average temperature (WABT), WH and hydrogen coverage correspond to those described above.

[0180] The hydrotreatment step and the hydrocracking step can advantageously be carried out in the same reactor or in different reactors. In the case where they are carried out in the same reactor, the reactor comprises several catalytic beds, the first catalytic beds comprising the hydrotreatment catalyst(s) and the following catalytic beds comprising the hydrocracking catalyst(s).

[0181] The hydrocracking step can be carried out in one or two stages. When it is carried out in two stages, a separation of the effluent from the first hydrocracking stage is carried out to obtain a heavy cut (unreacted middle distillate cut), which is introduced into the second hydrocracking stage comprising a second dedicated hydrocracking reaction section, different from the first hydrocracking reaction section. This configuration is particularly suitable when it is desired to produce only a naphtha cut. The preferred operating conditions and catalysts used in the second hydrocracking stage are those described for the first hydrocracking stage. The operating conditions and catalysts used in the two hydrocracking stages may be identical or different.

[0182] The hydrocracking catalyst(s) used in the hydrocracking step(s) are conventional hydrocracking catalysts known to those skilled in the art, of the bifunctional type combining an acid function with a hydro-dehydrogenating function and optionally at least one binding matrix. The acid function is provided by supports with a large surface area (150 to 800 m 2 / g generally) with surface acidity, such as halogenated aluminas (chlorinated or fluorinated in particular), combinations of boron and aluminum oxides, amorphous silica-aluminas and zeolites. The hydro-dehydrogenating function is provided by at least one metal from group VIB of the periodic table and / or at least one metal from group VIII. Hydro-dehydrogenating functions of the NiMo, NiMoW, NiW type are preferred.

[0183] LIST OF FIGURES

[0184] The mention of the elements referenced in Figures 1 to 3 allows a better understanding of the invention, without it being limited to the particular embodiments illustrated in Figures 1 to 3. The different embodiments presented can be used alone or in combination with each other, without limitation of combination.

[0185] Figure 1 shows a schematic diagram of a general embodiment of the method of the present invention.

[0186] A charge containing plastics and / or tires and / or CSR (1) is pyrolyzed in a thermal or catalytic pyrolysis unit (U1) leading to the production of at least a first gaseous effluent (2) (pyrolysis gas) containing a mixture of H2, CO, CO2 and hydrocarbons comprising C1 to C6 hydrocarbons and a first liquid effluent containing mainly C7+ hydrocarbons (3) (pyrolysis oil).

[0187] Said first gaseous effluent (2) containing a mixture of H2, CO, CO2 and hydrocarbons comprising C1 to C6 hydrocarbons is then compressed (K1) then cooled (E1) in order to allow the recovery in a separator tank (D1) of a second liquid effluent (4) (condensate) containing mainly C3 to C6 hydrocarbons and little CO and CO2, and of a second residual gaseous effluent (8) concentrated in H2, CO and CO2 (incondensable gas flow).

[0188] As shown in Figure 1, a solid stream (10) which contains coal (char) is also withdrawn from the pyrolysis unit. Said second liquid effluent (4) containing mainly C3 to C6 hydrocarbons is advantageously sent to a purification unit (U2) implemented to purify said second liquid effluent (4) in order to achieve the specifications of a feedstock which can be treated in the steam cracking unit (U3). When the purification unit is a hydrogen hydrotreatment unit (5) is injected.

[0189] Said first liquid effluent containing mainly C7+ hydrocarbons (3) is advantageously also introduced into the purification unit (U2).

[0190] The hydrotreatment unit can be followed by a washing / separation unit, in particular to eliminate chlorine (in the form of HCl and salts) (not shown).

[0191] Said second gaseous effluent (8) from the separator tank (D1), rich in H2, CO and CO2, can be sent in whole or in part to the pyrolysis unit in order to provide the energy necessary for the process or be exported and used as fuel (9) in another installation.

[0192] Downstream of the hydrotreatment section or the chlorine removal section, a separation unit (not shown in Figure 1) may be present and configured to separate the so-called incondensable compounds (H2, CO, CO2, H2S) and recover a stream of C3+ hydrocarbons. According to a preferred embodiment, the separation unit is a stabilization unit (depentanizer) from which a liquid stream of hydrocarbons rich in C5+ compounds (7) is withdrawn at the bottom of the column and at the top of the column after condensation of the head gas, an incondensable gas stream and a cut containing C3-C4 hydrocarbons (6).

[0193] As shown in Figure 1, all or part of the hydrocarbon stream (6), possibly after a purification step (for example washing with amines, water or soda), is sent to the steam cracking unit (U3). As shown in the figure, the hydrocarbon stream (6) can be separated into two parts, one part is used as fuel gas to provide a portion of the energy necessary for the operation of the pyrolysis unit (U1) and the other part is sent to the steam cracking unit (U3) producing a mixture of C3-C4 olefins (eg propylene, butylene, butadiene).

[0194] According to the preferred embodiment of Figure 1, there is a pooling of the steam cracking unit (U3) which is configured to treat in mixture the C5+ hydrocarbon stream (7) and the hydrocarbon stream (6) containing C3-C4 hydrocarbons.

[0195] Figure 2 represents the diagram of another particular embodiment of the process of the present invention which is based on the diagram of Figure 1 and in which said second liquid effluent (4) (condensate) from the separator tank (D1) is sent optionally after a chlorine removal step, into the steam cracking unit (U3) without having undergone treatment in the purification unit U2. This mode of operation is applicable in particular for treating the condensate in coprocessing with another feed whose specifications are compatible with those of a steam cracker feed.

[0196] Figure 3 represents the diagram of another particular embodiment of the method of the present invention which is based on the diagram of Figure 1 and in which at least part of the first liquid effluent (11) is introduced into a separation unit (D1), for example an absorbent column or a separator drum.

[0197] The first liquid effluent (11) can also be mixed with the first compressed gaseous effluent (2) upstream or downstream of its cooling and the mixture is sent to the separation unit (D1) (dotted arrows).

[0198] The separation unit (D1) makes it possible to obtain an intermediate liquid effluent (11') and the second residual gaseous effluent (8) concentrated in H2, CO and CO2 which is recycled in the pyrolysis unit (U1) in order to provide the energy necessary for the process.

[0199] The intermediate liquid effluent (11'), enriched in light hydrocarbon compounds (in particular C2) by the "sponge" effect, is introduced into the second separation unit (D2) so as to obtain said second liquid effluent (4) containing mainly C3+ hydrocarbons (and part of the C2) and a third residual gaseous effluent (12) concentrated in H2, CO and CO2.

[0200] Said third residual gaseous effluent (12) is concentrated with the light components which may include CO, CO2, methane, but also includes certain light hydrocarbon components, in particular ethylene and heavier hydrocarbon compounds. Said third residual gaseous effluent (12) is preferably recycled and mixed with the first gaseous effluent (2) upstream of its compression or its cooling so that a part of the light hydrocarbon components can be recovered in the liquid phase of the separation unit (D1).

[0201] Only the main steps, with the main flows, are shown in the figures, in order to allow a better understanding of the invention. It is understood that all the equipment necessary for operation is present (tanks, pumps, exchangers, ovens, columns, etc.), even if not shown.

[0202] EXAMPLES

[0203] Example 1

[0204] The example is based on the embodiment illustrated in Figure 1.

[0205] A load of plastic waste from a sorting line is thermally pyrolyzed at a temperature of 470°C in the absence of oxygen in unit U1. Said first liquid effluent (C7+) of the pyrolyzate (3) resulting from the pyrolysis reaction is sent to a purification unit (U2) in order to saturate the olefins and diolefins and remove the unwanted impurities in the steam cracking unit (U3), namely silicon, nitrogen, sulfur, chlorine, and metals (Si, P, K, Na, Hg, As, etc.). Said first gaseous effluent (2) rich in CO / CO2 withdrawn from the pyrolysis unit U1 is then compressed then cooled and sent into a separator tank operating at a pressure of 1.1 MPa relative (11 barg) and at a temperature of 40°C, thus making it possible to separate a second liquid effluent (4) rich in hydrocarbons (C3+) and depleted in CO / CO2 from a second gaseous effluent rich in H2, CO and CO2 (8) which is used to provide the energy necessary for the pyrolysis reaction (U1).Said second liquid effluent (4) (condensate) from tank D1, the CO and CO2 content of which is acceptable, is sent to unit U2 in order to reduce the impurity content of Si, N, metals and in particular chlorine, which remains too high compared to the specification of the steam cracking unit (U3). Stream 4 is then treated in a mixture with the pyrolysate (3) in the purification unit (U2) to achieve the specifications required at the inlet of the steam cracker (U3).

[0206] Table 1 shows the pressure, temperature and flow rate of streams 2, 4 and 8. In the example below (Table 2), said first liquid effluent (3) represents 70% by weight of the plastic feedstock introduced into the pyrolysis unit (U1), while said second liquid effluent (4) represents 8% by weight of the plastic feedstock introduced into the pyrolysis unit (U1). Thus, by recombining the two streams (3) and (4) the material yield increases from 70% to 78%, an increase of approximately 11%. This increase in yield remains identical at the outlet of the purification unit (U2) and therefore at the inlet of the steam cracking unit (U3) provided that all the hydrocarbon streams produced by the purification unit (U2) are sent to the steam cracking unit (U3).This means that if the purification step carried out in the purification unit U2 is followed by a stabilisation step (elimination of non-condensable gases), all of the liquid effluents containing hydrocarbons from the stabilisation step are sent to the steam cracking unit (U3), which increases the olefin yield.

[0207] Table 1

[0208] Table 2 Example 2

[0209] Example 2 is based on the embodiment illustrated in Figure 3.

[0210] Example 2 is carried out under the same pyrolysis conditions and with the same plastic load as Example 1.

[0211] In this example, the entirety of said first liquid effluent (C7+) (11) recovered from the pyrolysis unit (U1) is sent with the first gaseous effluent (2) compressed then cooled to the head of an absorbent column (D1) operating at 12 barg and 40°C.

[0212] Before contacting, the first gaseous effluent (2) is compressed and cooled as in example 1 then introduced at the bottom of the absorbent column (D1).

[0213] From the absorption column (D1) an intermediate liquid effluent (11') rich in hydrocarbons (C3+) and depleted in CO / CO2 is recovered from a second residual gaseous effluent rich in H2, CO and CO2 (8) which is used to provide the energy necessary for the pyrolysis reaction (U1). Said intermediate liquid effluent (11') is sent to a separation unit (D2) which is a distillation column.

[0214] From the separation unit (D2) a third residual gaseous effluent (12) is recovered, which is entirely recycled to the compressor (K1) and a second liquid effluent (4) which is introduced into the purification unit (U2). The stream (4) is then treated in a mixture with the pyrolysate (3) in the purification unit (U2) to achieve the specifications required at the inlet of the steam cracker (U3).

[0215] Table 3 indicates the operating conditions under which the contacting / mixing in the separation unit (D1) is carried out between the first liquid effluent (11), representing 70% by weight of the streams recovered from unit U1, with the first gaseous effluent (2), representing 20% ​​by weight of the streams collected from unit U1. This table also indicates the composition of streams (2), (11), (4), (8) and (12) as well as their impurity content (chloromethane).

[0216] Table 4 shows the flow rate of streams (1), (4) and (8). Table 3

[0217] As shown in Tables 3 and 4, the stream (4) recovered from the separation unit (D2) represents approximately 87% by weight of the feedstock treated in unit U1. The stream (4) has a low CO+CO2 content (less than 50 ppm) and substantially few light C1 hydrocarbons, but includes a portion of the recoverable C2 hydrocarbons. This therefore improves the olefin production yield when the stream (4) is treated in the purification unit (U2) and the effluent is steam cracked in unit U3.

[0218] The second gaseous effluent (8) with a flow rate reduced to 2.4% has a reduced content of organic chlorides, such as chloromethane, from 50 ppm initially down to 5 ppm. The stream (8) is therefore lower in quantity and has a lower impurity content, which allows easier recovery, for example as a fuel gas.

Claims

CLAIMS 1. A process for producing olefins from a feedstock containing plastic and / or tires and / or solid recovered fuels, said process comprising the following steps: (a) a step of pyrolysis of a load containing plastic and / or tires and / or solid recovered fuels is carried out in a pyrolysis unit so as to recover at least a first gaseous effluent (2) containing a mixture of H2, CO, CO2 and hydrocarbons comprising C1 to C6 hydrocarbons and a first liquid effluent (3) containing mainly C7+ hydrocarbons; (b) said first gaseous effluent (2) from step a) is compressed and then cooled, then said first compressed and cooled gaseous effluent is separated in a separation unit so as to obtain a second liquid effluent (4) containing mainly C3+ hydrocarbons and a second residual gaseous effluent (8) concentrated in H2, CO and CO2; (c) introducing said second liquid effluent (4) into a steam cracking unit in the presence of water vapor so as to produce olefins.

2. Process according to the preceding claim in which said first liquid effluent (3) is introduced into said steam cracking unit of step c).

3. Method according to one of the preceding claims, in which in step b) at least a portion of the first liquid effluent (11) is introduced into said separation unit, mixed or not with said first compressed gaseous effluent (2), then the mixture is separated so as to obtain an intermediate liquid effluent (11') and said second residual gaseous effluent (8) concentrated in H2, CO and CO2, then said intermediate liquid effluent (11') is separated in a second separation unit so as to obtain said second liquid effluent (4) containing mainly C3+ hydrocarbons and a third residual gaseous effluent (12) concentrated in H2, CO and CO2.

4. Method according to one of the preceding claims, in which a step of purifying said second liquid effluent (4) from step b) is carried out in a purification unit upstream of the steam cracking unit of step c).

5. Method according to one of the preceding claims, in which a step of purifying said first liquid effluent (3) from step a) is carried out in a purification unit upstream of the steam cracking unit of step c).

6. Method according to one of the preceding claims in which step b) is carried out in such a way that during the separation(s) the pressure is between 0.5 and 2.5 MPa relative, preferably between 1.0 and 1.5 MPa relative, and the temperature is between 20 and 55°C, preferably between 30 and 45°C.

7. Method according to one of claims 4 to 6 in which the purification step comprises a step of pretreatment of said second liquid effluent (4) from step b) and / or of said first liquid effluent (3) from step a), said pretreatment step being carried out upstream of step c) and comprises an adsorption step and / or a filtration step and / or a centrifugation step and / or a decantation step and / or an electrostatic separation step and / or a step of washing using an aqueous solution and / or a gas stripping step.

8. Method according to one of claims 4 to 7 wherein the purification step comprises a hydrotreatment step carried out in a hydrotreatment reaction section, using at least one fixed bed reactor having n catalytic beds, n being an integer greater than or equal to 1, each comprising at least one hydrotreatment catalyst, said hydrotreatment reaction section being fed with said second liquid effluent from step b), optionally pretreated, and / or said first liquid effluent from step a), optionally pretreated, and a gas stream comprising hydrogen, said hydrotreatment reaction section being carried out at an average temperature between 150 and 430°C, a hydrogen partial pressure between 1.0 and 10.0 MPa abs. and an hourly volumetric flow rate between 0.1 and 10.0 h' 1 to obtain a second purified liquid effluent and / or a first purified liquid effluent.

9. Method according to the preceding claim, in which said hydrotreatment catalyst comprises a support chosen from alumina, silica, silica-aluminas, magnesia, clays and their mixtures and a hydro- function. dehydrogenating agent comprising either at least one element from group VIII and at least one element from group VIB, or at least one element from group VIII.

10. Method according to one of claims 8 to 9 in which the hydrotreatment step is followed by a washing / separation step, fed with said second purified liquid effluent, optionally pretreated, and / or said first purified liquid effluent, optionally pretreated, and an aqueous solution to obtain at least one gaseous effluent, one aqueous effluent and said second washed purified liquid effluent and / or said first washed purified liquid effluent.

11. Method according to one of claims 4 to 10 in which said second purified liquid effluent, optionally pretreated and / or washed, and / or said first purified liquid effluent, optionally pretreated and / or washed, is subjected to at least one fractionation step in a fractionation unit to obtain at least one gaseous stream and at least one liquid stream of C3+ hydrocarbons.

12. Method according to the preceding claim in which the separation unit comprises a depentanizer column from which a liquid stream of C3-C4 hydrocarbons and a liquid stream of C5+ hydrocarbons are withdrawn.

13. Process according to claims 11 and 12 in which at least one of the liquid streams from the fractionation step is at least partly sent to the steam cracking unit of step c).

14. Process according to one of the preceding claims in which the steam cracking step c) is carried out in at least one pyrolysis furnace at a temperature between 700 and 900°C and at a pressure between 0.05 and 0.3 MPa relative in the presence of water vapor.

15. Process according to one of the preceding claims, in which in the steam cracking step c) the residence time of the hydrocarbon compounds is less than or equal to 1.0 seconds and the quantity of water introduced, in the form of water vapor, is between 0.3 and 3.0 kg of water per kg of hydrocarbon compounds at the inlet of the steam cracking step c).

16. Method according to one of the preceding claims, in which the load consists of plastic and / or tires and / or solid recovered fuels.

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