Depolymerization process of plastic waste material

Abstract

A process for depolymerizing waste plastic materials and producing pyrolysis oil is disclosed. The process comprises two stirred-vessel depolymerization reactors and an inserted liquid-liquid extraction unit. This process is highly efficient and easy to operate, and can produce high-quality pyrolysis products in the form of oil with low contaminant content.

Description

Technical Field

[0001] This disclosure relates to the field of depolymerizing plastic waste materials into novel products including hydrocarbon oils, which have valuable and useful properties. In one aspect, this disclosure relates to a process for converting plastics into liquid hydrocarbons, the process being carried out in at least two successive depolymerization stages (including a purification stage interspersed between said depolymerization stages). Background Technology

[0002] The awareness that waste plastics have a negative impact on the environment and therefore on the health of all forms of life is rapidly increasing.

[0003] One attempt to mitigate the impact is to recycle plastic materials from household and industrial waste, allowing a portion of these materials to re-enter the production cycle. This would lead to further positive outcomes, such as less use of fossil hydrocarbon sources in the production of plastic products.

[0004] However, various factors indicate that this solution alone is insufficient to achieve sustainability goals. In fact, the mechanical recycling of plastic materials typically produces lower-quality materials, is relatively costly, cumbersome, and unsuitable for municipal waste containing certain plastics mixed with various other materials.

[0005] Therefore, most plastic waste is either used as thermal energy in equipment such as incinerators or simply stored in landfills, which, as mentioned, contribute to the degradation of the Earth's environment by increasing CO2 emissions and releasing harmful chemicals.

[0006] In light of the above, many attempts have been made in the past to efficiently reprocess waste plastic raw materials into liquid hydrocarbon products, which have valuable and useful properties.

[0007] Thermocatalysis is a fundamental process in which plastic waste is converted into hydrocarbon oils (pyrolysis products) through thermal action and, optionally, catalytic degradation in the absence of oxygen. Plastic waste is typically first melted in a stainless steel chamber under an inert purging gas, such as nitrogen. In the first thermal step, the chamber heats the molten material to a gaseous state, where, in a subsequent thermocatalytic step, the gaseous state is cracked to form hydrocarbon chains of varying lengths.

[0008] The use of one or more catalytic cracking stages helps to reduce the operating degradation temperature and can also push the product composition toward the desired target.

[0009] However, plastic waste is typically a mixture of different types of polymers, including not only polyolefins but also PET, polyamide (nylon), PU polymers, PVC, etc. Furthermore, plastic waste often contains heteroatom-based additives, such as stabilizers and plasticizers, incorporated to improve polymer properties. These additives often also include compounds containing nitrogen, halogens, and sulfur, as well as heavy metals. Given this complex composition, unpurified pyrolysis oil from the recycling of waste plastic chemicals contains relatively high levels of undesirable contaminants such as oxygen, nitrogen, sulfur, halogens, and metals.

[0010] When the process includes two depolymerization reactors in series, the pyrolysis oil obtained from the condensation of the gaseous fraction generated in the first depolymerization stage may contain relatively high amounts of undesirable contaminants such as oxygen, nitrogen, sulfur, halogens, and metals. If these contaminants are not removed or reduced, they can deactivate or poison the catalyst used in further depolymerization stages. Furthermore, even if no catalyst is used in the second depolymerization stage, the contaminants can still be harmful, as halogen-containing compounds can damage metal components due to their corrosive effects, and nitrogen-containing impurities may also be involved in the formation of explosive NOx upon heating.

[0011] For the reasons mentioned above, a purification stage is usually required to reduce or completely remove contaminants in order to improve the quality of pyrolysis oil, thereby enabling its smooth use in refining processes.

[0012] Removing pollutants through the use of solid adsorbents is the most commonly used technique in this specific field.

[0013] US 2013 / 0043160 describes a process for removing sulfur, nitrogen, and metals from oil feedstocks such as heavy oil, bitumen, and shale oil by treating the feedstock with alkali metals and free radical capture substances.

[0014] WO 2017 / 100617 describes the removal of oxygen, sulfur, and nitrogen heteroatoms from liquids such as hydrocarbons using different adsorbents. US 6,248,230 describes a method for producing cleaner fuels by adsorption removal of naturally occurring polar compounds (i.e., compounds containing sulfur and nitrogen) via an efficient pretreatment upstream of a hydrodesulfurization unit.

[0015] However, adsorption methods have drawbacks: removal and purification become cumbersome when the adsorbent is saturated, and continuous processing is not permitted. Furthermore, changing the type of adsorbent in the tower to meet specific requirements based on different types of raw material contaminants necessitates interrupting the process in that tower; therefore, if a globally continuous process is desired, the dual-tower system must be interrupted.

[0016] WO2023 / 141109 discloses a liquid-liquid extraction process in which contaminants are removed from pyrolysis oil using acidified water, and the pyrolysis oil can then be subjected to a steam cracking step. WO2021 / 105327 discloses a liquid-liquid extraction process in which contaminants are removed from pyrolysis oil using caustic water, and the pyrolysis oil can then be subjected to a steam cracking step.

[0017] Although the use of water can remove some contaminants, even a low residual amount in the pyrolysis oil can still form an emulsion when the treated pyrolysis oil is fed into the second polymerization reactor, and it itself can poison the catalyst.

[0018] In view of the foregoing, one object of this disclosure is to provide a plastic waste pyrolysis process that is carried out in two successive depolymerization stages (including a smooth and easily handled purification step inserted between the two depolymerization stages). Summary of the Invention

[0019] Therefore, one aspect of this disclosure is a process for depolymerizing waste plastic materials and producing pyrolysis products, wherein the process includes the following steps:

[0020] (a) A mixture containing waste plastic material is fed into a first depolymerization reactor (2), which is operated at a temperature ranging from 280 to 600°C and a pressure ranging from 0.5 to 10 barg, in which pyrolysis occurs to form at least a gaseous effluent;

[0021] (b) The gaseous effluent from reactor (2) is condensed at least partially to obtain a pyrolysis oil stream (A) containing at least one contaminant selected from aromatic compounds, oxygen, nitrogen, sulfur, halogens and metals.

[0022] (c) The pyrolysis oil stream (A) is directed to a liquid-liquid extraction unit (LLEU) (6), in which a cleaning liquid is brought into contact with the pyrolysis oil stream (A) to form a discharged cleaning liquid stream and a pyrolysis oil stream (B) that is at least partially purified, wherein the content of at least one contaminant selected from aromatic compounds, oxygen, nitrogen, sulfur, halogens and metals in the stream (B) is lower than the content of the same contaminant in the stream (A), wherein the cleaning liquid is a nonhydrocarbon liquid polar compound (LPC) selected from a eutectic complex of formula [A][B]x, wherein x ranges from 0.3 to 20, [A] is selected from metal salts, nonmetal salts and nonionic hydrogen bond acceptors (HBA), and [B] is selected from metal salts, hydride metal salts and nonionic hydrogen bond donor compounds (NIHBD);

[0023] (d) The purified pyrolysis oil stream (B) is fed into a second depolymerization reactor (4), in which pyrolysis is carried out in the absence of air or steam at a temperature ranging from 280 to 600°C and a pressure ranging from 0.5 to 10 barg, thereby forming a gaseous effluent; and

[0024] (e) The gaseous effluent is discharged from the depolymerization reactor (4) and fed into the second condensation unit (5) for condensation and recovery of the final pyrolysis oil. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of an example of a thermocatalytic process equipment. Detailed Implementation

[0026] Preferably, the process is carried out in a continuous mode.

[0027] Preferably, the mixture containing waste plastic material is fed into the depolymerization reactor in oxygen-free gas via a feeding system comprising at least one screw extruder (1), which is heated to allow the plastic material to melt.

[0028] The feeding system allows waste plastic material to be fed into the reactor (2) preferably in a continuous mode. Care should be taken not to introduce oxygen-containing gases into the system. Barriers to potential oxygen-containing gases can be achieved in various ways, such as nitrogen covering or a vacuum system connected to the extruder barrel.

[0029] More specifically, the plastic waste mixture is fed into the feeding system of the depolymerization reactor (2) through a hopper or two or more parallel hoppers, and the oxygen present in the gaseous plastic waste material is substantially eliminated inside the hopper.

[0030] The process according to the invention is highly flexible and can feed a wide range of plastic waste compositions, for example, as heterogeneous mixtures of waste plastic materials (called Plasmix in Italy) in which polyolefins are the most abundant component, but for which further sorting steps are no longer economical. In particular, when pyrolysis products are recycled back to the cracking / refining unit, it is preferable to depolymerize plastic waste mixtures in which the polyolefin (PE and PP) content is equal to or greater than 70% by weight.

[0031] Waste plastic materials preferably undergo a pretreatment stage, in which they are heated and melted and, where possible, mixed with additives, which may be alkaline materials. This melt pretreatment transforms heterogeneous mixtures of different types of waste plastics into a large quantity of homogeneous plastic composite materials. Therefore, this pretreatment is also preferred for pyrolysis without additives.

[0032] The heating temperature in the pretreatment stage is appropriately set according to the type and content of plastics contained in the waste plastic material, thereby inhibiting the pyrolysis of the plastic material to be treated. Such temperatures are typically in the range of 100°C-300°C, preferably 150°C-250°C. At temperatures approaching 300°C or higher, HCl is eliminated from any PVC resin that may be present.

[0033] If waste plastic materials are mixed with alkaline materials during the melting / kneading pretreatment process, the resulting HCl gas can be removed and continuously neutralized or captured via the exhaust system. For the melting operation, a conventional kneader, an extruder with a screw, or similar equipment can be used. The plastic waste is preferably fed into the depolymerization reactor via an extruder.

[0034] The extruder melts the plastic waste to a high temperature (250-350°C) and injects it into the first depolymerization reactor (2). The extruder can receive the plastic waste cut into small pieces into the feed hopper, transport the flow in the molten section, and heat the polymer through a combination of mixed energy and heat provided by the barrel heater.

[0035] Additives can be selectively incorporated into the melt to reduce the corrosivity of the received plastic waste or to improve the conversion process in the reaction section.

[0036] During the extrusion process, one or more degassing steps can be anticipated to remove residual moisture present in the product.

[0037] Before being fed into reactor (2), the melt stream can be filtered to remove solid impurities present in the plastic waste.

[0038] Any extrusion system can be used, such as a single-screw extruder, a twin-screw extruder, a twin-screw extruder with a gear pump, or a combination thereof.

[0039] In step (b), the depolymerization reactor (2) is preferably a continuous stirred tank reactor. Preferably, it is operated at a temperature in the range of 300 to 550°C, and more preferably 350 to 500°C.

[0040] The operating pressure is preferably maintained in the range of 1.0 to 8.0 barg, more preferably in the range of 1.5 to 7.0 barg.

[0041] The depolymerization reactor (2) preferably has a cylindrical portion and preferably has a circular bottom.

[0042] Preferably, it has a mixer mounted on the vertical axis of the reactor, which is operated by a geared motor that allows the mixer blades to rotate to keep the system in a stirred state. The design of the mixer and the power of the motor can vary in terms of the reactor contents, volume, and shape; however, as a non-limiting example, a range of 0.2 to 4 kW / m³ is preferred. 3 Preferably 0.2 to 2 kW / m 3 And more preferably 0.3 to 1.5 kW / m 3 The power input operates the reactor.

[0043] The reactor can be heated to a temperature range of 300°C to 570°C by heat transfer caused by the molten salt flow.

[0044] The molten salt is preferably molten solar salt, which is preferably composed of a mixture of sodium nitrate and potassium nitrate, and even more preferably in a weight ratio ranging from 2:3 to 3:2.

[0045] Preferably, the heat associated with the molten salt is transferred to the depolymerization reactor by circulating the molten salt through a jacket surrounding the entire reactor and / or by feeding it into an external heat exchanger described below.

[0046] In both cases, the salt is circulated using a circulation pump.

[0047] The pyrolysis occurring within the reactor produces molecules with reduced chain lengths and low boiling points. This continuously operating chain-breaking mechanism generates increasingly smaller, gaseous molecules at operating temperatures and pressures.

[0048] As a result, the compositions within the reactor encompass a wide range of hydrocarbons, from methane to heavier products, saturated and olefinic hydrocarbons, with straight-chain or highly branched structures. Some aromatic products and fused-ring structures may also be present.

[0049] As a result of pyrolysis, the contents of reactor (2) can be defined as the coexistence of a liquid slurry phase (in which solids, especially carbonaceous and inorganic substances, are dispersed in a liquid hydrocarbon mixture) and a gas phase.

[0050] Preferably, at least a portion of the liquid slurry phase is discharged from the reactor, preferably from the bottom of the reactor, and constitutes a liquid effluent sent to the carbon treatment section for further processing.

[0051] In a particular and preferred embodiment, a portion of the liquid slurry discharged from reactor (2) is optionally recirculated back to the top of the reactor via a recirculation pump (7) and an external heater (8). As described above, heat is preferably supplied to the external heater via molten salt. This embodiment can provide increased uniformity of reactor contents and reactor heating.

[0052] The gas phase of reactor (2) constitutes a gaseous effluent, which is sent to the condensation unit (3) for further processing.

[0053] The gaseous effluent comprises a mixture of light hydrocarbons, which may also contain some heavy hydrocarbons and entrained carbon particles. The gaseous effluent is preferably fed from the top of the reactor to a condenser (3), which is preferably operated at a pressure slightly below the reactor pressure.

[0054] Preferably, the condenser (3) is better designed as a scrubbing tower to contain entrained carbon. The condenser temperature is selected in such a way that heavy hydrocarbons are condensed and light hydrocarbons are released as a gaseous stream. The gaseous stream (H2 and light hydrocarbons) can be directed to another condenser (5) operating at a lower temperature than the condenser (3) from which the oil is recovered.

[0055] The operating temperature of the condenser unit (3) can also vary over a wide range depending on the operating pressure. The temperature, i.e., atmospheric pressure, can be 20°C to 200°C, more preferably 50°C to 200°C, and especially 60°C to 180°C. When a higher operating pressure is selected, the temperature range can of course be different.

[0056] Hydrocarbon condensate (preferably having more than C7 carbon atoms) constitutes a pyrolysis oil stream (A) containing at least one contaminant selected from aromatic compounds, oxygen, nitrogen, sulfur, halogens and metals, which is then preferably transferred to the LLEU (6) via a pump (11).

[0057] LLEU(6) in Figure 1 The liquid is depicted as a tower, but it can be implemented using a variety of alternative techniques. Preferably, the LLEU is based on an extraction device selected from mixing and clarifying tanks, tower contactors, and centrifugal extractors. In the simplest configuration, a stirred vessel can be used, followed by separation units of varying densities. Considerations for the most suitable device are based on several criteria, including but not limited to the volume of the liquid, the type of liquid (density, viscosity), and residence time. Based on the evaluation of such specific parameters, those skilled in the art can select the most appropriate device in each case, while knowing that such devices are readily available on the market.

[0058] In a preferred manner, two immiscible liquids are brought into contact in a mixing and clarifying extractor equipped with agitation and temperature control, and designed at the bottom to facilitate the discharge of the denser liquid. After a desired time has elapsed, agitation is stopped, allowing the system to reach phase separation conditions. At this point, the denser liquid is discharged from the bottom of the receiver, or alternatively, the less dense liquid can be siphoned from the top of the receiver. This same operation can be repeated multiple times.

[0059] Another preferred extraction device may be selected from the group of tower contactors, particularly from the static tray type or the stirring and rotating type.

[0060] The cleaning fluid used to extract contaminants from the pyrolysis oil stream (A) is preferably selected from non-hydrocarbon liquid polar compounds (LPCs). The cleaning fluid is liquid at atmospheric pressure in the range of 10-250°C, more preferably 15-200°C. In particular, it is preferably selected from a eutectic complex of at least two compounds, which exhibits a single melting point that is generally lower than the melting point of each of the individual compounds.

[0061] The term eutectic complex refers to a complex of the formula [A][B]x, wherein x ranges from 0.5 to 20, [A] is selected from metal salts, nonmetal salts and nonionic hydrogen bond acceptors (NIHBA), and [B] is selected from metal salts, hydrated metal salts and nonionic hydrogen bond donor compounds (NIHBD).

[0062] When [A] is a metal salt, it is preferably selected from compounds of the formula MXy, where M is a metal or metalloid element belonging to Groups 3-15 of the periodic table (Iupac), preferably Al or Zn, X is a halogen, preferably Cl, and y is the valence of the metal.

[0063] When [A] is a nonmetallic salt, it is preferably selected from nonmetallic salts formed by cations and anions as reported below:

[0064]

[0065] The R1 to R4 groups are independently selected from C1-C1. 20 Alkyl or arylalkyl and C6-C 20 Aryl or alkylaryl groups.

[0066] When A is a nonionic 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 portions of which are incorporated herein by reference.

[0067] When [B] is selected from metal salts, it is preferably selected from compounds of the formula MXy, where M is a metal or metalloid element belonging to Groups 3-15 of the periodic table (Iupac), preferably Al, Zn, Sn, Ga, In, Cu, X is a halogen, preferably Cl, and x is the valence of the metal.

[0068] Alternatively, hydrated metal salts of the formula MXy·nH2O can be selected [B], where M, X, and y have the same meaning as above, and n is 1 to 10.

[0069] When [B] is selected from nonionic hydrogen bond donor compounds (NIHBD), it is preferably selected from amides, carboxylic acids, and alcohols, including cyclic amides. Particularly preferred compounds are those reported below:

[0070]

[0071] It can be recognized that some compounds can belong to both lists [A] and [B]. This is due to the fact that there are many possibilities for forming eutectic complexes. However, it is clear that if [A] and [B] are the same, then eutectic complexes cannot be formed, nor do they exist.

[0072] In particularly preferred combinations, [A] is selected from nonmetallic salts, and [B] is selected from metallic salts, hydrated metallic salts, and nonionic hydrogen bond donor compounds (NIHBD). More preferably, the eutectic complex obtained from [A] is selected from nonmetallic salts formed by cations and anions, as reported below:

[0073]

[0074] The R1 to R4 groups are independently selected from C1-C1. 20 Alkyl or arylalkyl and C6-C 20 Aryl or alkylaryl groups; and [B] is selected from the following NIHBD compounds.

[0075]

[0076] For these eutectic compounds, 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.

[0077] Specific examples are listed below:

[0078]

[0079]

[0080]

[0081] The temperature range for purifying pyrolysis oil stream A is 20 to 250°C, more preferably 25 to 150°C, and especially 25 to 100°C.

[0082] LLEU can be configured to include a single extraction step or multiple steps using the same or different eutectic compounds. For example, a single step can be performed using one or more eutectic compounds, and when multiple steps are performed, each step can be the same as or different from the other steps, and each step can be performed using one or more eutectic compounds.

[0083] Generally, the total mass ratio between the pyrolysis oil stream (A) and the non-hydrocarbon liquid polar compound (LPC) results in an LPC / pyrolysis oil mass ratio ranging from 0.01:1 to 100:1 throughout the LLEU. In specific embodiments, the LPC / pyrolysis oil 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 / pyrolysis oil 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.

[0084] In another preferred embodiment, the LPC / pyrolysis oil ratio ranges from 0.05:1 to 3:1, preferably from 0.1:1 to 2:1, and more preferably from 0.2:1 to 1:1.

[0085] As already mentioned, the total contact time and parameters can be appropriately determined by those skilled in the art based on available knowledge. Generally, allowing more contact time will allow for the extraction of higher amounts of contaminants by LPC. However, those skilled in the art will be able to clearly establish, based on specific conditions, a time point after which, based on production capacity standards, extending the contact would be inefficient. In certain specific embodiments, the applicant has achieved satisfactory results in the purification of pyrolysis oil with total contact times ranging from 0.5 to 10 hours, more specifically 1 to 6 hours.

[0086] Used LPC and purified pyrolysis oil stream B, obtained as LLEU effluents, can be separated due to their immiscibility and density difference. Typically, used LPC is the denser phase with extracted contaminants that can be discharged from the bottom of the column, while purified pyrolysis oil stream B is typically the lighter phase that can be discharged from the top of the column.

[0087] Preferably, the clean LPC is at least partially recovered from the used LPC through a contaminant removal step. This can be achieved using various techniques. A preferred method for recovering clean LPC would be to direct the used LPC to a flash distillation column (14), in which more volatile contaminants are blown away. Metal residues can also be removed using other techniques available in the art, such as membrane separation.

[0088] The recovered LPC can then be fed back into the LLEU.

[0089] Once separated from the used LPC, the purified pyrolysis oil stream (B) has a lower content of at least one contaminant selected from aromatic compounds, oxygen, nitrogen, sulfur, halogens, and metals. Preferably, at least oxygen and nitrogen compounds are present in reduced amounts, more preferably oxygen and nitrogen compounds and aromatic compounds are present in reduced amounts. The degree of removal depends on the conditions used, but generally, when considering oxygen and nitrogen compounds, their amount relative to the pyrolysis oil stream B is reduced by at least 50% by weight, preferably by at least 70% by weight, and more preferably by at least 80% by weight, and especially by more than 90% by weight. For some specific contaminants (such as caprolactam), complete removal can be achieved, meaning that they are no longer detectable under GC technology.

[0090] The purified pyrolysis oil stream (B) is fed into a second depolymerization reactor (4), which is preferably of the same type as the first depolymerization reactor, and more preferably a continuous stirred tank reactor that operates in the absence of air and steam.

[0091] Depolymerization is carried out within the same temperature range, but in order to limit the volatility of heavy hydrocarbons, it is preferably operated at a pressure higher than that of the first reactor, and particularly at a pressure in the range of 2 to 10 barg, preferably 3 to 9 barg, and more preferably 3 to 8 barg.

[0092] The depolymerization process disclosed herein can be carried out in the presence of a depolymerization catalyst.

[0093] According to this disclosure, the catalyst can be selected from catalysts that are active as depolymerization / cracking catalysts in thermocatalytic processes. In particular, it can be selected from metal oxides, heteropoly acids, mesoporous silica, aluminosilicate catalysts, such as hydrous kaolinite and kaolinite, and preferably from zeolites. Particularly preferred zeolites are synthetic Y-type zeolites and ZSM-5. Additives can optionally be incorporated into the melt to reduce the corrosivity of plastic waste or improve depolymerization efficiency. Poison inhibitors can be used in combination with the catalyst. Preferably, they 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, aluminosilicate, and Zr(HPO4)2 is preferred.

[0094] In a particularly preferred embodiment, the amount of catalyst feed is no more than 10% by weight, preferably no more than 5% by weight, and especially no more than 2% by weight relative to the plastic waste feed.

[0095] In a preferred embodiment, the catalyst is injected into the second reactor as a powder dispersed in hydrocarbon oil, preferably from the condensation unit (3) or (5), and more preferably from the liquid pyrolysis product (oil) obtained from the condensation unit (3).

[0096] Preferably, the catalyst slurry is prepared in a continuous stirred tank, wherein the catalyst is poured from a dedicated silo to maintain a constant concentration of the catalyst in the slurry.

[0097] The pyrolysis oil from the dispersed catalyst is preferably discharged from the condenser unit (3) to maintain a constant slurry level in the tank. Once ready, the catalyst slurry can be injected, preferably into the second reactor, preferably by a screw pump to maintain its constant level. Figure 1 In a preferred embodiment, fresh catalyst is fed into reactor (4) through conduit (15).

[0098] The liquid effluent from reactor (4) is preferably a highly concentrated hydrocarbon slurry, which preferably contains a depolymerization catalyst. It is discharged from the second reactor and, in a preferred embodiment, returned to the first reactor via conduit (16). The same density control used in reactor (4) for discharging the slurry is also preferably applied to reactor (2).

[0099] The slurry density can be controlled by available methods such as gamma-ray measurement or Coriolis density meter. When the operating pressure of the first reactor is lower than that of the second reactor, it is expected that the light hydrocarbons in the slurry entering the first reactor will evaporate and be extracted together with the gaseous effluent generated in reactor (2).

[0100] Preferably, the amount of slurry recycled to the first reactor is 5-40% of the contents of the second reactor, more preferably 10-30% of the contents.

[0101] Also in reactor (4), which is configured in a preferred embodiment, a portion of the liquid slurry discharged from the bottom of reactor (4) is recirculated back to the top of reactor by a recirculation pump (12) through an external heater (13).

[0102] The gaseous effluent generated from the reactor (4) is transported to the condensation unit (5) for the recovery of the final pyrolysis products in the form of oil.

[0103] In this regard, it will be apparent to those skilled in the art that the second depolymerization stage should not be considered as a cracking or steam cracking section that produces a series of final hydrocarbon fractionation products. This will be clear from the fact that the second depolymerization stage according to this disclosure produces the final pyrolysis oil and from its second mode of operation (airless, steamless, continuously stirred reactor). It is precisely after the second depolymerization stage that the final pyrolysis oil can be directed as feedstock to the cracking unit.

[0104] The condensing unit (5) preferably has a similar configuration to the condensing unit (3).

[0105] Preferably, the operating conditions of the condensing unit (5) are selected in such a way that they have a lower operating temperature and pressure than those of the condensing unit (3).

[0106] Specifically, the temperature can be 20-80°C, preferably 30-70°C. The pressure value should preferably be lower than that of the condensation unit (3) so that non-condensable gases from the unit (3) can enter the unit (5) without further pressurization. The pyrolysis oil recovered from the condensation unit (5) is generally lighter than the pyrolysis oil recovered from the first condensation unit and can be directed for further processing or use.

[0107] Although not absolutely necessary, the pyrolysis oil recovered from the condensation unit (5) can be subjected to further purification steps. While any purification process can be used, it is preferred that the same purification process applied to the pyrolysis oil stream (A) be applied to the pyrolysis oil recovered from the final condensation unit.

[0108] As already mentioned, the preferred use of the main product of the pyrolysis process disclosed herein is as a hydrocarbon feedstock to partially replace the oil feedstock in cracking equipment. However, other uses, such as fuel, are also possible.

Claims

1. A process for depolymerizing waste plastic materials and producing pyrolysis products, wherein the process includes the following steps: (a) A mixture containing waste plastic material is fed into a first depolymerization reactor (2), which is operated at a temperature ranging from 280 to 600°C and a pressure ranging from 0.5 to 10 barg, where pyrolysis occurs to form at least a gaseous effluent; (b) The gaseous effluent from reactor (2) is condensed at least partially to obtain a pyrolysis oil stream (A) containing at least one contaminant selected from aromatic compounds, oxygen, nitrogen, sulfur, halogens and metals. (c) The pyrolysis oil stream (A) is directed to a liquid-liquid extraction unit (LLEU) (6), in which a cleaning liquid is brought into contact with the pyrolysis oil stream (A) to form a discharged cleaning liquid stream and a pyrolysis oil stream (B) that is at least partially purified, wherein the content of at least one contaminant selected from aromatic compounds, oxygen, nitrogen, sulfur, halogens and metals in the stream (B) is lower than the content of the same contaminant in the stream (A), wherein the cleaning liquid is a nonhydrocarbon liquid polar compound (LPC) selected from a eutectic complex of formula [A][B]x, wherein x ranges from 0.3 to 20, [A] is selected from metal salts, nonmetal salts and nonionic hydrogen bond acceptors (HBA), and [B] is selected from metal salts, hydride metal salts and nonionic hydrogen bond donor compounds (NIHBD); (d) The purified pyrolysis oil stream (B) is fed into a second depolymerization reactor (4), in which pyrolysis is carried out in the absence of air or steam at a temperature ranging from 280 to 600°C and a pressure ranging from 0.5 to 10 barg to form a gaseous effluent. as well as (e) The gaseous effluent is discharged from the depolymerization reactor (4) and fed into the second condensation unit (5) for condensation and recovery of the final pyrolysis oil.

2. The process according to any one of the preceding claims, wherein the first depolymerization reactor and the second depolymerization reactor are continuous stirred tank reactors.

3. The process according to claim 1 or 2, wherein [A] is a non-metallic salt selected from non-metallic salts formed from the following cations and anions: The R1 to R4 groups are independently selected from C1-C 20 Alkyl or arylalkyl and C6-C 20 Aryl or alkylaryl groups.

4. The process according to any one of the preceding claims, wherein [B] is selected from nonionic hydrogen bond donor compounds (NIHBD), said nonionic hydrogen bond donor compounds (NIHBD) are selected from amides, carboxylic acids and alcohols including cyclic amides.

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

6. The process according to any one of the preceding claims, wherein the eutectic composite is formed from [A] selected from the nonmetallic salts according to claim 3 and [B] selected from the NIHBD compounds according to claim 5.

7. The process according to any one of the preceding claims, wherein in the eutectic composite, 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 one of the preceding claims, wherein step (c) is carried out at a temperature ranging from 20 to 250°C, more preferably from 25 to 150°C, and especially from 25 to 100°C.

9. The process according to any one of the preceding claims, wherein the total mass ratio between the pyrolysis oil stream A and the non-hydrocarbon liquid polar compound (LPC) is such that, throughout the LLEU, the mass ratio LPC / pyrolysis oil 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 one of the preceding claims, wherein the LPC / pyrolysis oil 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 one of the preceding claims, wherein the LLEU is based on an extraction apparatus selected from a mixing clarifier, a tower contactor, and a centrifugal extractor.

12. The process of claim 11, wherein the LLEU is equipped with one or more mixing clarifier extractors connected in series.

13. The process of claim 11, wherein the LLEU is equipped with one or more tower contactors, particularly one or more tower contactors of the static tray type or the stirring-rotation type.

14. The process according to any one of the preceding claims, wherein the cleaned LPC is at least partially recovered from the used LPC through a contaminant removal step.

15. The process according to any one of the preceding claims, wherein the pyrolysis oil stream B contains at least 50% by weight, preferably at least 70% by weight, and more preferably at least 80% by weight, and especially more than 90% by weight, oxygen and nitrogen compounds in amounts at least 50% by weight less than the corresponding amount in the pyrolysis oil stream A.

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