WO2025099039A1 - Process for the depolymerization of plastic waste material - Google Patents

Abstract

A process for the depolymerizing waste plastic material and producing a pyrolytic oil comprising two agitated vessel depolymerization reactors and an interposed Liquid-Liquid extraction unit is disclosed. The process is endowed with high efficiency and easy operation and can produce a quality pyrolytic product in the form of oil having low content of contaminants.

Description

TITLE PROCESS FOR THE DEPOLYMERIZATION OF PLASTIC WASTE MATERIAL FIELD OF THE INVENTION [0001] The present disclosure relates to the field of depolymerization of plastic waste material into new products, comprising hydrocarbon oil, which have valuable and useful properties. In one aspect, the present disclosure relates to a process for converting plastics to liquid hydrocarbons carried out in at least two sequential depolymerization stage including a purification stage interposed between said depolymerization stages. BACKGROUND OF THE INVENTION [0002] The awareness that waste plastic materials have a negative impact on the environment and, as a consequence on the health of any form of life, is rapidly increasing. [0003] One of the attempts to mitigate the impact is constituted by the recycling of plastic materials coming from domestic and industrial waste which allows a part of these materials to be reintroduced into the production cycle. This would involve further positive results such as lower use of fossil hydrocarbon sources to produce plastic items. [0004] However, various factors indicate that this solution alone would not be sufficient for reaching the sustainability targets. In fact, mechanical recycling of plastic materials produces substances with usually lower quality, is relatively costly and burdensome and not applicable to certain urban waste in which plastic is mixed to various different materials. [0005] As a consequence, a large part of plastic waste is either used as a source of thermal energy in plants such as incinerators, or simply stored in landfills which, as mentioned, contribute to degrade the earth environment by raising the CO₂ emissions and by the release of hazardous chemicals. [0006] In view of the above, numerous attempts have been made in the past to efficiently re- process a feedstock of waste plastics back into a liquid hydrocarbon product that has valuable and useful properties. FE7661-WO-01 [0007] Thermocatalysis is a basic process whereby plastic waste material is converted to hydrocarbon oil (pyrolytic product) by effect of thermal and optionally catalytical degradation in the absence of oxygen. Plastic waste is typically first melted within a stainless steel chamber under an inert purging gas, such as nitrogen. In a first thermal step this chamber heats the molten material to a gaseous state which, in a successive thermocatalytic step, is cracked to form hydrocarbon chains of variable length. [0008] The use of one or more catalytic cracking stages helps in lowering the operative degrading temperature and may also drive the product composition towards the desired target. [0009] However, the plastic waste is typically mixed plastic waste composed of different types of polymers including, for example, not only polyolefins but also PET, polyamides (nylon), PU polymer, PVC etc. In addition, plastic waste typically contains heteroatom- based additives such as stabilizers and plasticizers that have been incorporated to improve the performance of the polymers. Such additives also often comprise nitrogen, halogen and sulfur containing compounds and heavy metals. In view of this complex composition, the unpurified pyrolysis oils from waste plastic chemical recycling contains relatively high amounts of undesired contaminants such as oxygen, nitrogen, sulphur, halogens and metals. [0010] When the process comprises two depolymerization reactor in series, the pyrolysis oil obtained from the condensation of the gaseous fraction generated in the first depolymerization stage, may contain those relatively high amounts of undesired contaminants such as oxygen, nitrogen, sulphur, halogens and metals. These contaminants, if not removed or reduced, may deactivate or poison catalysts used in the further depolymerization stage. Moreover, even if a catalyst is not used in the second depolymerizaion stage, the contaminants may be harmful as well, because halogen-containing compounds can damage the metal parts due to their corrosive action, and nitrogen-containing impurities may also involve formation of explosive NOx when heated. [0011] For the above reasons, a stage of purification for the reduction or complete removal of contaminants is often needed to upgrade the pyrolysis oil allowing its smooth use in the refinery process. [0012] Removal of contaminants via the use of solid adsorbents is the most common technique used in the art for this specific field. FE7661-WO-01 [0013] US 2013/0043160 describes a process for removing sulfur, nitrogen and metals from an oil feedstock such as heavy oil, bitumen, shale oil by treating the feedstock with an alkali metal and a radical trapping substance. [0014] WO 2017/100617 describes the removal of oxygen, sulfur and nitrogen heteroatoms from fluids such as hydrocarbons with different adsorbents. US 6,248,230 describes a method for manufacturing cleaner fuels by removing natural, polar compounds, i.e. sulfur and nitrogen containing compounds by adsorption as an effective pretreatment, upstream of a hydrodesulfurization unit. [0015] However, adsorption methods suffer from the drawbacks that when the adsorbent is saturated, its removal and decontamination is burdensome and does not allow a continuous process. Also, changing the type of adsorbent in a column, to meet the specific requirements based on different type of contaminants of the feedstock, requires interruption of the process in the said column and, as a consequence, of a twin column set-up if a global continuous process is desired. [0016] WO2023/141109, discloses a liquid-liquid extraction process in which acidified water is used to remove contaminants from pyrolytic oil which can then be subject to a steam cracking step. WO2021/105327 discloses a liquid-liquid extraction process in which caustic water is used to remove contaminants from pyrolytic oil which can then be subject to a steam cracking step. [0017] Although the use of water can remove part of the contaminants, its residual amount in the pyrolytic oil, even if low, may generate emulsions when the treated pyrolytic oil is fed to the second polymerization reactor and act as a poison itself for the catalyst. [0018] In light of the foregoing, an object of the present disclosure is to provide for a plastic waste pyrolytic process carried out in two sequential depolymerization stages including a smooth and easy to handle purification step interposed between two depolymerization stages. SUMMARY OF THE INVENTION [0019] It is therefore an aspect of the present disclosure a process for depolymerizing waste plastic material and producing a pyrolytic product, wherein said process comprises the following steps: (a) feeding a mixture comprising waste plastic materials, into a first depolymerization reactor (2), maintained at a temperature ranging from 280 to 600°C and operated under a pressure ranging from 0.5 to 10 barg in which pyrolysis takes place thereby forming at least a gaseous effluent; FE7661-WO-01 (b) at least partially condensing the gaseous effluent from reactor (2) thereby obtaining a pyrolysis oil stream (A) containing at least one contaminant selected from aromatics, oxygen, nitrogen, sulphur, halogens and metals; (c) direct the pyrolysis oil stream (A) to a Liquid-Liquid extraction unit (LLEU) (6) where a cleaning liquid and pyrolysis oil stream (A) are brought in contact forming an exhausted cleaning liquid stream and an at least partially decontaminated pyrolysis oil stream (B) in which the content of at least one contaminant selected from aromatics, oxygen, nitrogen, sulphur, halogens and metals, in said stream (B), is lower than the content of the same contaminant in the said stream (A), said cleaning liquid being a a non-hydrocarbon liquid polar compound (LPC) selected from eutectic complexes of formula [A][B]x where x ranges from 0.3 to 20, [A] is selected from metal salts, non-metal salts and non-ionic hydrogen bond acceptor (HBA), and [B] is selected from metal salts, hydrated metal salts and non-ionic hydrogen bond donor compounds (NIHBD); (d) feeding the decontaminated pyrolysis oil stream (B) to a second depolymerization reactor (4), where pyrolysis take place in the absence of air or steam at a temperature ranging from 280 to 600°C under a pressure ranging from 0.5 to 10 barg thereby forming a gaseous effluent; and (e) withdrawing the gaseous effluent from said depolymerization reactor (4) and feeding it to a second condensation unit (5) for condensing and recovering a final pyrolytic oil. BRIEF DESCRIPTION OF DRAWINGS [0020] Fig.1 is a schematic view of an example of the thermo-catalytic process plant DETAILED DESCRIPTION OF THE INVENTION [0021] Preferably, the process is carried out in a continuous mode. [0022] Preferably, the a mixture comprising waste plastic materials, in an oxygen-free atmosphere, is fed to the depolymerization reactor via a feeding system comprising at least one screw extruder (1), which is heated to allow the melting of said plastic material. [0023] The feeding system allows charging, preferably in continuous mode, waste plastic materials to be fed, into the reactor (2). Care should be taken for not introducing oxygen containing atmosphere into the system. The barrier to the potentially oxygen-containing atmosphere can be obtained in different ways such as nitrogen blanketing or vacuum system connected to a barrel of the extruder. FE7661-WO-01 [0024] More specifically, the plastic waste mixture, is charged into the feeding system of the depolymerization reactor (2) by means of a hopper, or two or more hoppers in parallel, and the oxygen present in the atmosphere of the plastic waste material is substantially eliminated inside the hopper(s). [0025] The process according to the present disclosure is very flexible and can be fed with a wide range of plastic waste composition as, for example, a heterogeneous mixture of waste plastic materials (called Plasmix in Italy) in which polyolefins are the most abundant component but for which a further sorting step is no longer economical. It is preferred, especially when the pyrolytic product is to be recirculated back to a cracking/refining unit, to depolymerize a plastic waste mixture in which the polyolefin (PE and PP) content is equal to or higher than 70%wt. [0026] The waste plastic material preferably undergoes a pre-treatment stage in which it is melted by heat and possibly mixed with an additive which can be an alkaline material. By the melting pretreatment, a non-uniform mixture of different kinds of waste plastics can be transformed into a mass of uniform plastic composite. Therefore, this pretreatment is also preferable for the case in which the pyrolytic decomposition is performed without additives. [0027] The heating temperature in the pretreatment stage is appropriately set to a temperature in accordance with the kind and content of the plastic contained in the waste plastic material such that pyrolytic decomposition of the plastic material to be treated is inhibited. Such a temperature is, in general, within a range of 100°C to 300°C, and preferably, 150°C to 250°C. At a temperature close to 300°C or more, elimination of HCl from the PVC resin possibly present, takes place. [0028] The HCl forming gas can be either removed via a venting system and successively neutralized or trapped if the waste plastic material is mixed with an alkaline material during the melting/kneading pretreatment. For performing the melting operation, ordinary kneaders, extruders with a screw and the like are applicable. Plastic waste is preferably fed to the depolymerization reactor by means of an extruder. [0029] The extruder melts the plastic scrap, brings it at high temperature (250-350°C) and injects it into the first depolymerization reactor (2). The extruder may receive the plastic scrap cut in small pieces into the feed hopper, convey the stream in the melting section and heat the polymer by combined action of mixing energy and heat supplied by barrel heaters. [0030] Additives can be optionally incorporated in the melt aiming at reducing corrosivity of plastic scrap received or to improve conversion process in the reaction section. FE7661-WO-01 [0031] During the extrusion, one or more degassing steps can be foreseen to remove residual humidity present in the product. [0032] Before being fed to the reactor (2), the melt stream can be filtered by in order to remove solid impurities present in the plastic waste. [0033] Any extrusion systems can be applied, as single screw extruders, twin screw extruders, twin screw extruders with gear pump, or combination of the above. [0034] In step (b) the depolymerization reactor (2) is preferably a continuously stirred tank reactor. Preferably, it is operated at temperature ranging from 300 to 550 and more preferably from 350 to 500°C. [0035] The operative pressure is preferably kept in the range 1.0 to 8.0 barg, more preferably in the range 1.5 to 7.0 barg . [0036] The depolymerization reactor (2) preferably has a cylindrical section, preferably with a rounded bottom. [0037] Preferably, it has a mixer installed in the vertical axis of the reactor, completed with a gear motor which allows the blades of the mixer rotating in order to maintain the system in stirred state. The design of the mixer and the power of the motor can vary in respect of the reactor content, volume and shape, however, as a non-limiting example, it is preferred to operate the reactor with a power input ranging from 0.2 to 4 kW/m³, preferably 0.2-2 kW/m³ and more preferably from 0.3 to 1.5 kW/m³. [0038] The heating of the reactor might take place by means of the thermal transfer induced by a flow of molten salt, heated to a temperature ranging from 300°C to 570°C. [0039] The molten salt is preferably molten solar salt preferably constituted by a mixture of sodium nitrate and potassium nitrate, even more preferably in a weight ratio ranging from 2:3 to 3:2. [0040] Preferably, the heat associated to molten salt is transferred to the depolymerization reactor by circulating the molten salt through a jacket which envelops the whole reactor and/or by feed it to an external heat exchanger described below. [0041] In both cases the salt is circulated by means of a circulation pump. [0042] The pyrolysis taking place within the reactor produces molecules having reduced chain length and low boiling point. This continuously running chain breakage mechanism, produces FE7661-WO-01 molecules increasingly smaller part of which, at the operating temperature and pressure, are gaseous. [0043] As a result, the composition within the reactor covers a broad range of hydrocarbons from methane to heavier products, both saturated and olefinic, with linear or highly branched structures. Some aromatic product can be also present as well as fused rings structures. [0044] As a result of the pyrolysis, the content of the reactor (2) can be defined as coexistence of a liquid slurry phase, in which solid especially carbonaceous substances, and inorganic substances, are dispersed in a liquid hydrocarbon mixture, and a gaseous phase. [0045] Preferably, at least a portion of the liquid slurry phase is withdrawn from the reactor, preferably from the bottom of the reactor and constitutes the liquid effluent sent to a char handling section for further treatment. [0046] In a particular and preferred embodiment, part of the liquid slurry withdrawn from the the reactor (2), is recirculated, via a recycling pump (7), back to the reactor top optionally through an external heater (8). As mentioned above, heat to the external heater is preferably provided by the molten salt. This embodiment may provide both increased homogeneity of reactor content and reactor heating. [0047] The gaseous phase of the reactor (2) constitutes the gaseous effluent which is sent to the condensation unit (3) for further treatment. [0048] The gaseous effluent comprises a mixture of light hydrocarbons which may also include some heavy hydrocarbons and char particles entrained. The gaseous effluent is preferably conveyed from the reactor top to a condenser (3) preferably operated at a pressure slightly lower than that of the reactor . [0049] Preferably, the condenser (3) is better designed as a scrubber column in order to suppress the entrained char. The condenser temperature is selected in such a way that the heavy hydrocarbons are condensed and the light hydrocarbons are released as gaseous stream. The gaseous stream (H2 and light hydrocarbons) may be directed to a further condensation unit (5) working at a temperature lower than the condensation unit (3) from which oil is recovered. [0050] The operative temperature of the condensing unit (3) may vary in a wide range also depending on the operative pressure. The temperature, referred to atmospheric pressure, can be from 20°C to 200°C more preferably from 50 to 200°C and especially from 60 to 180°C. The temperature range can be of course different when a higher operating pressure is chosen. FE7661-WO-01 [0051] The hydrocarbon condensate, preferably having more than C7 carbon atoms, constitutes the pyrolysis oil stream (A) containing at least one contaminant selected from aromatics, oxygen, nitrogen, sulphur, halogens and metals which is then transferred, preferably by means of a pump (11), to the LLEU (6). [0052] The LLEU (6) is depicted in Fig.1 as a column but it can be implemented in a variety of alternative technical solutions. Preferably, the LLEU is based on extraction equipment selected from mixed settlers, column contactors and centrifugal extractors. In the simplest configuration, a stirred vessel could be used followed by a separation unit exploiting different densities. Considerations on the most suited equipment are based on several criteria including, but not limited to, volume of liquids, type of liquids (density, viscosity) and residence time. Based on the evaluation of such specific parameters the skilled in the art is able, in each case, to select the most appropriate equipment knowing that they are easily available on the market. [0053] According to one of the preferred ways, the two immiscible liquids are contacted into a mixed settler extractor provided with stirring and temperature regulation and having a bottom with a design which facilitates the draining of the denser liquid. After reaching the desired time, the stirring is stopped and the system is allowed to reach the phase separation condition. At that point, the denser liquid, is drained from the bottom of the recipient, or alternatively, the less dense liquid can be siphoned off from the top of the recipient. The same operation can be repeated multiple times. [0054] Another preferred extraction equipment can be a selected from the group of column contactors in particular from either static tray type or agitated rotary type. [0055] The cleaning liquid used for extracting contaminants from the pyrolysis oil stream (A) is preferably selected from a non-hydrocarbon liquid polar compound (LPC). The cleaning liquid is liquid in the range 10-250°C, more preferably 15-200°C under atmospheric pressure. In particular, it is preferably selected from eutectic complexes of at least two compounds, which exhibit a single melting point which is typically lower than the melting points of each of the individual compounds. [0056] With the term eutectic complexes it is meant a group of complexes of formula [A][B]x where x ranges from 0.5 to 20, [A] is selected from metal salts, non-metal salts and non-ionic hydrogen bond acceptor (NIHBA), and [B] is selected from metal salts, hydrated metal salts and non-ionic hydrogen bond donor compounds (NIHBD). FE7661-WO-01 [0057] When [A] is a metal salt it is preferably selected from compounds of formula MXy where M is a metal or metalloid element belonging to one of the groups 3-15 of the periodic table of elements (Iupac ), preferably Al or Zn, X is a halogen, preferably Cl, and y is the valence of the metal. [0058] When [A] is a non-metal salt, it is preferably selected from those formed by the cations and anions reported below:

FE7661-WO-01 where R₁ to R₄ groups are, independently, selected from C₁-C₂₀ alkyl or arylalkyl and C₆-C₂₀ aryl or alkylaryl groups. [0059] When A is a non-ionic hydrogen bond acceptor (NIHBA) it is preferably selected from lactam compounds, such as caprolactam. Examples of such compounds are disclosed in WO2020/221916 the relevant part of which is herein enclosed by reference. [0060] When [B] is selected from metal salts, it is preferably selected from compounds of formula MXy where M is a metal or metalloid element belonging to one of the groups 3-15 of the periodic table of elements (Iupac ), preferably Al, Zn Sn, Ga, In, Cu, X is a halogen, preferably Cl, and x is the valence of the metal. [0061] It is also possible to select [B] from hydrated metal salts of formula MXy^nH2O, where M, X and y have the same meaning as above and n is from 1 to 10. [0062] When [B] is selected from non-ionic hydrogen bond donor compounds (NIHBD), it is preferably selected from amides, including cyclic amides, carboxylic acids and alcohols. Among them, particularly preferred compounds are those reported below: FE7661-WO-01

[0063] It can be recognized that some compounds can fall both [A] and [B] lists. This is due to the fact that there are many possibilities to form eutectic complexes. However, it is clear that eutectic complexes cannot be formed and does not exist if [A] and [B] are the same. [0064] In a particularly preferred combination, [A] is selected from non-metal salts and [B] is selected from is selected from metal salts, hydrated metal salts and non-ionic hydrogen bond donor compounds (NIHBD). Still more preferred are the eutectic complexes obtained from [A] being selected from a non-metal salt formed by the cations and anions reported below: FE7661-WO-01

FE7661-WO-01 [0065] where R₁ to R₄ groups are, independently, selected from C₁-C₂₀ alkyl or arylalkyl and C₆-C₂₀ aryl or alkylaryl groups; and [B] being selected from the following NIHBD compounds.

[0066] For these eutectic complexes the value of x ranges from 0.3 to 20, preferably from 0.5 to 15, more preferably from 1 to 10 and especially from 1 to 8. FE7661-WO-01 [0067] Specific examples are listed below

Abbreviation Benzyltriphenylphosphonium chloride Triethylene glycol BzTPPCl:TEG (1:8) Tetraphenylphosponium chloride Triethylene glycol TPPC:TEG (1:3) Tetrabutylammonium bromide Triethylene glycol TBABr:TEG (1:3) Methyltriphenylphosponium bromide Triethylene glycol MTPPBr:TEG (1:4) Tetrabutylammonium bromide Levulinic acid TBABr:LA (1:3) Tetrabutylammonium bromide Levulinic acid TBABr:LA (1:2) Methyltriphenylphosponium bromide Levulinic acid MTPPBr:LA (1:4) Tetrabutylammonium bromide Ethylene glycol TBABr:EG (1:2) Tetrabutylphosphonium bromide Ethylene glycol TBPBr:EG (1:2) Tetraethylammonium bromide Levulinic acid TEABr:LA (1:3) Methyltriphenylphosponium bromide Ethylene glycol MTPPBr:EG (1:5) Choline chloride Triethylene glycol ChC:TEG (1:3) Choline chloride Triethylene glycol ChC:TEG (1:2) Choline chloride Tartaric acid ChCl:TA (2:1) Choline chloride 1,4-Butanediol ChCl:1,4-BD (1:4) Tetrabutylammonium chloride Malonic acid TBACl:MalA (1:3) Benzyltrimethylammonium chloride Levulinic acid BzTMACl:LA (1:4) Tetraethylammonium chloride Glycerol TEACl:Gly (1:2) 1-ethyl-3-methylimidazolium chloride Ethylene glycol EmimCl:EG (1:2) Tetramethylammonium chloride Ethylene glycol TMACl:EG (1:3) Choline chloride 1,2-Propanediol ChCl:PD (1:4) L-carnitine Phenol Carn:Phe (1:3) Choline chloride Levulinic acid ChCl:LA (1:3) Choline chloride Diethylene glycol ChCl:DEG (1:2) Choline chloride Diethylene glycol ChCl:DEG (1:3) Choline chloride 1,4-Butanediol ChCl:1,4-BD (1:2) Choline chloride 1,3-Butanediol ChCl:1,3-BD (1:2) FE7661-WO-01 Choline chloride 1,6-Hexanediol ChCl:1,6-HD (1:2) Choline chloride Phenylpropionic acid ChCl:PhPA (1:2) Choline chloride Ethylene glycol ChCl:EG (1:2) Tetramethylammonium chloride Glycerol TMACl:Gly (1:2) Choline chloride Acetic acid ChCl:AcA (1:2) Choline chloride 2,3-Butanediol ChCl:2,3-BD (1:2) Choline chloride Levulinic acid ChCl:LA (1:2) Tetramethylammonium chloride Glycerol TMACl:Gly (1:5) Tetramethylammonium chloride Phenylacetic acid TMACl:PAA (1:2) Choline chloride 1,2-Butanediol ChCl:1,2-BD (1:2) Tetramethylammonium chloride Glycerol TMACl:Gly (1:4) Choline chloride Phenylacetic acid ChCl:PhAA (1:2) Choline chloride Benzoic acid ChCl:BzA (1:2) Choline chloride Glycerol ChCl:Gly (1:4) Choline chloride Urea ChCl:Ur (1:2) Choline chloride Xylitol ChCl:Xy (1:1) Choline chloride Glycerol ChCl:Gly (1:2) Choline chloride Malonic acid ChCl:MalA (1:1) Choline chloride D-sorbitol ChCl:Sorb (1:1) Choline chloride Malic acid ChCl:MA (1:1) Choline chloride Oxalic acid ChCl:OA (1:1) Choline bromide Urea ChBr:Ur (1:2) Choline chloride Citric acid ChCl:CA (1:1) Choline chloride Glycolic acid ChCl:GA (1:3) Chlorocholine chloride Urea ClChCl:Ur (1:2) Choline chloride Thiourea ChCl:Tur (1:2) [0068] The temperature at which the decontamination of the pyrolysis oil stream A is carried out ranges from 20 to 250°C more preferably from 25 to 150°C, especially from 25 to 100°C. [0069] The LLEU may be set-up as to comprise a single extraction step or a plurality of steps with the same or different eutectic complex. As an example, a single step may be carried out with one or more eutectic complexes and when a plurality of steps is carried out each step can be the FE7661-WO-01 same or different from the others and each step can be carried out with one or more eutectic complexes. [0070] Generally speaking, the total mass ratio between pyrolysis oil stream (A) and the non - hydrocarbon liquid polar compound (LPC) is such that, in the whole LLEU, the mass ratio LPC/Pyoil ranges from LPC/Pyoil ranges from 0.01:1 to 100:1. In a particular embodiment, the LPC/Pyoil mass ratio ranges from 1:1 to 100:1 preferably from 2:1 to 80:1 and more preferably from 2:1 to 50:1. In another particular embodiment, the LPC/Pyoil mass ratio ranges from 0.01:1 to 1:1 preferably from 0.02:1 to 0.8:1 and more preferably from 0.02:1 to 0.5:1. [0071] In another preferred embodiment, LPC/Pyoil ranges from 0.05:1 to 3:1, preferably from 0.1:1 to 2:1, more preferably from 0.2:1 to 1:1.. [0072] As already mentioned, the total contact time and are parameters may be suitably determined by the skilled in the art based on the available knowledge. Generally speaking allowing more time for the contact should allow a higher amount of contaminants to be extracted by the LPC. However, the skilled in the art based on the specific conditions will be clearly able to establish a point in time over which prolonging the contact would be inefficient based on productivity criteria. In certain specific embodiments the applicant has obtained satisfying results in terms of pyoil purification operating for total contact times ranging from 0.5 to 10 hours, more specifically from 1 to 6 hours. [0073] The spent LPC and the decontaminated pyrolysis oil stream B obtained as effluents of the LLEU, can be separated a result of their immiscibility and density difference. Generally the spent LPC is the denser phase with the extracted contaminants which can be drained from the bottom of the column, while the decontaminated pyrolysis oil stream B is usually the lighter phase can be drained from the top of the column. [0074] Preferably, a clean LPC at least partially recovered from the spent LPC (by a step of contaminants removal. This can be obtained with various techniques. One of the preferred ways to recover clean LPC would be that of directing the spent LPC to a flash distillation column (14) where the more volatile contaminants will be blown away. Metal residues can also be removed with other techniques available in the art such as membrane separation. [0075] The recovered LPC can then be fed back to the LLEU. [0076] Once separated from the spent LPC the decontaminated pyrolysis oil stream (B) has a lower content for at least one of the contaminants selected from aromatics, oxygen, nitrogen, FE7661-WO-01 sulphur, halogens and metals. Preferably, at least oxygen and nitrogen compounds are present in a reduced amount, more preferably oxygen and nitrogen compounds and aromatics are present in a reduced amount. The extent of removal depends on the conditions used but in general when considering oxygen and nitrogen compounds, their amount with respect to pyrolysis oil stream B is at least 50%wt lower, preferably at least 70%wt lower and more preferably at least 80%wt lower and especially more than 90%wt lower. For some specific contaminants like caprolactam is it possible to reach the complete removal, meaning that it is no more detectable under GC technique. [0077] The decontaminated pyrolysis oil stream (B) is fed to the second depolymerization reactor (4) which is preferably of the same type as the first one and more preferably a continuously stirred tank reactor which works in the absence of air and steam. [0078] Depolymerization takes place in the same range of temperatures but, in order to limit the volatility of the heavy hydrocarbons, it is preferably operated at a pressure higher than the first reactor and in particular in the range from 2 to 10 barg, preferably from 3 to 9 barg and more preferably from 3 to 8 barg. [0079] The depolymerization process of the present disclosure can be carried out in the presence of a depolymerization catalyst. [0080] According to the present disclosure, the catalyst can be selected from those active as depolymerization/cracking catalysts in thermocatalytic processes. In particular, it can be selected from metal oxides, heteropolyacids, mesoporous silica, aluminosilicates catalysts, such as halloysite and kaolinite, and preferably from zeolites. Among them, particularly preferred zeolites are synthetic Y-type zeolite and ZSM-5. Additives can optionally be incorporated in the melt aimed at reducing corrosivity of plastic scrap or improving depolymerization efficiency. A poison- suppressing agent can be used possibly in association with the catalyst. Preferably, it can be selected from the group consisting of Ca(OH)₂, Mg(OH)₂, Ba(OH)₂, Sr(OH)₂, CaO, Al₂O₃, aluminosilicates such as bentonite, and Zr(HPO₄)₂ and mixtures thereof_. Among them, the use of Ca(OH)2, aluminosilicates Zr(HPO4)2 is preferred. [0081] . [0082] In a particularly preferred embodiment, the amount of catalyst feed is not more than 10% preferably not more than 5% and especially not more than 2% wt with respect to the plastic waste feed. FE7661-WO-01 [0083] In a preferred embodiment, the catalyst is injected into the second reactor as powder dispersed into a hydrocarbon oil preferably the liquid pyrolytic product (oil) obtained from condensation units (3) or (5), preferably from condensation unit (3). [0084] Preferably, the catalyst slurry is prepared in a pot, continuously stirred vessel where the catalyst is poured from a dedicated silo in order to keep constant the concentration of the catalyst in the slurry. [0085] The pyrolytic oil dispersing the catalyst is preferably withdrawn from the condensation unit (3) in order to keep constant the slurry level in the pot. Once ready the catalyst slurry can be injected, preferably into the second reactor, preferably by means of a progressive cavity pump in order to keep its level constant. In the preferred embodiment of Fig.1, fresh catalyst is fed to reactor (4) through conduit (15). [0086] The liquid effluent coming from reactor (4) is preferably a highly concentrated hydrocarbon slurry which preferably contains the depolymerization catalyst. It is discharged from the second reactor and in a preferred embodiment is sent back to the first reactor via the conduit (16). The same density control in reactor (4) for the withdrawal of the slurry is preferably operated also for reactor (2). [0087] The slurry density can be controlled via available methods such as γ-ray measurement or Coriolis densimeter. When the operative pressure of the first reactor is lower than the second one, the light hydrocarbons of the slurry entering the first reactor are expected to vaporize and be extracted with the gaseous effluent produced in reactor (2). [0088] Preferably, the amount of slurry recycled to the first reactor ranges from 5 to 40% in volume more preferably from 10 to 30% in volume of the second reactor content. [0089] Also in reactor (4) it constitutes a preferred embodiment that part of the liquid slurry withdrawn from the bottom of the reactor (4) is recirculated, with a recycling pump (12), back to the reactor top through an external heater (13). [0090] The gaseous effluent produced from reactor (4) is conveyed to the condensation unit (5) for the recovering the final pyrolytic product in form of an oil. [0091] In this respect, it will be apparent to the skilled in the art that the second depolymerization stage is not to be considered as a cracking or steam cracking section generating a range of final hydrocarbon fractionated products. This would be clear from the fact that the second depolymerization stage according to the present disclosure produces a final pyrolityc oil FE7661-WO-01 and from the way the second it is operated (no air, no steam, continuously stirred reactor). It is the final pyrolytic oil obtained after the second depolymerization stage that may be directed as a feedstock to the cracking unit. [0092] The condensation unit (5) has preferably a similar configuration to condensation unit (3). [0093] Preferably, the operative conditions of the condensation unit (5) are selected in a way that it has a lower operating temperature and pressure with respect to condensation unit (3). [0094] In particular, the temperature may range from 20 to 80°C and preferably from 30 to 70°C. The pressure value should preferably be lower than that of condensation unit (3) so as to allow incondensable gases from unit (3) to enter unit (5) without further pressurization. The pyrolytic oil recovered from the condensation unit (5) is generally lighter than that recovered from the first condensation unit and may be directed to further processing or uses. [0095] Although not strictly necessary, the pyrolytic oil recovered from the condensation unit (5) can be subject to a further decontamination step. While any decontamination process can be used, it is preferred that the same decontamination process applied to pyrolysis oil stream (A) is also used for the pyrolytic oil recovered from the last condensation unit. [0096] As already mentioned, the preferred use of the main product of the pyrolytic process of the disclosure is as hydrocarbon feedstock partially replacing oil feedstock in cracking plants. However, other uses, such as fuel, are also contemplated. FE7661-WO-01

Claims

CLAIMS What is claimed is: 1. A process for depolymerizing waste plastic material and producing a pyrolytic product, wherein said process comprises the following steps: (a) feeding a mixture comprising waste plastic materials, into a first depolymerization reactor (2), maintained at a temperature ranging from 280 to 600°C and operated under a pressure ranging from 0.5 to 10 barg in which pyrolysis takes place thereby forming at least a gaseous effluent; (b) at least partially condensing the gaseous effluent from reactor (2) thereby obtaining a pyrolysis oil stream (A) containing at least one contaminant selected from aromatics, oxygen, nitrogen, sulphur, halogens and metals; (c) direct the pyrolysis oil stream (A) to a Liquid-Liquid extraction unit (LLEU) (6) where a cleaning liquid and pyrolysis oil stream (A) are brought in contact forming an exhausted cleaning liquid stream and an at least partially decontaminated pyrolysis oil stream (B) in which the content of at least one contaminant selected from aromatics, oxygen, nitrogen, sulphur, halogens and metals, in said stream (B), is lower than the content of the same contaminant in the said stream (A), said cleaning liquid being a a non-hydrocarbon liquid polar compound (LPC) selected from eutectic complexes of formula [A][B]x where x ranges from 0.3 to 20, [A] is selected from metal salts, non-metal salts and non-ionic hydrogen bond acceptor (HBA), and [B] is selected from metal salts, hydrated metal salts and non-ionic hydrogen bond donor compounds (NIHBD); (d) feeding the decontaminated pyrolysis oil stream (B) to a second depolymerization reactor (4), where pyrolysis take place in the absence of air or steam at a temperature ranging from 280 to 600°C under a pressure ranging from 0.5 to 10 barg thereby forming a gaseous effluent; and (e) withdrawing the gaseous effluent from said depolymerization reactor (4) and feeding it to a second condensation unit (5) for condensing and recovering a final pyrolytic oil.

2. The process according to any of the preceding claims in which the first and the second depolymerization reactors are continuously stirred tank reactors. FE7661-WO-01

3. The process according to claim 1 or 2 in which [A] is a non-metal salt selected from those formed by the following cations and anions

where R1 to R4 groups are, independently, selected from C1-C20 alkyl or arylalkyl and C6-C20 aryl or alkylaryl groups.

4. The process according to any of the preceding claims in which [B] is selected from non-ionic hydrogen bond donor compounds (NIHBD), chosen from amides, including cyclic amides, carboxylic acids and alcohols. FE7661-WO-01

5. The process according to claim 4 in which [B] is selected from the following compounds:

6. The process according to any of the preceding claims in which the eutectic complexes are formed by [A] being selected from a non-metal salt according to claim 3 and [B] from NIHBD compounds according to claim 5. 7. The process according to any of the preceding claims in which in the eutectic complexes the value of x ranges from 0.5 to 15, more preferably from 1 to 10 and especially from 1 to 8. 8. The process according to any of the preceding claims in which step (c) is carried out at a temperature ranging from 20 to 250°C more preferably from 25 to 150°C, especially from 25 to 100°C. 9. The process according to any of claims the preceding claims in which total mass ratio between pyrolysis oil stream A and the non -hydrocarbon liquid polar compound (LPC) is FE7661-WO-01 such that, in the whole LLEU, the mass ratio LPC/Pyoil ranges from 0.01:1 to 100:1, preferably from 1:1 to 100:1 preferably from 2:1 to 80:1 and more preferably from 2:1 to 50:1. 10. The process according to any of the preceding claims in which the LPC/Pyoil mass ratio ranges from 0.01:1 to 1:1 preferably from 0.02:1 to 0.8:1 and more preferably from 0.02:1 to 0.5:1. 11. The process according to any of the preceding claims in which the LLEU is based on extraction equipment selected from mixed settlers, column contactors and centrifugal extractors. 12. The process according to claim 11 in which the LLEU is equipped with one or more mixed settler extractor connected in series. 13. The process according to claim 11 in which the LLEU is equipped with one or more column contactors in particular of static tray type or agitated rotary type. 14. The process according to any of the preceding claims in which , a clean LPC at least partially recovered from the spent LPC by a step of contaminants removal. 15. The process according to any of the preceding claims in which oxygen and nitrogen compounds are present in the pyrolysis oil stream B in an amount at least 50%wt lower, preferably at least 70%wt lower and more preferably at least 80%wt lower and especially more than 90%wt lower than the corresponding amount in pyrolysis oil stream A. FE7661-WO-01