Process for the depolymerization of plastic waste material with pyrolytic oil distillation and condensation

Abstract

A thermo-catalytic process for the depolymerizing of waste plastic material is disclosed. The process comprises processing in two depolymerization reactors, a distillation unit and a condensation. The process is endowed with high efficiency and versatility and can produce a pyrolytic product in the form of oil for various end-uses.

Description

TITLEPROCESS FOR THE DEPOLYMERIZATION OF PLASTIC WASTE MATERIAL WITH PYROLYTIC OIL DISTILLATION AND CONDENSATIONFIELD 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, in particular to be used as hydrocarbon feedstock.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 users which allows a part of these plastics to be reintroduced into the production cycle. This would involve positive results such as lower use of fossil hydrocarbon sources to produce plastic items.

[0004] However, various factors indicate that this means alone would not suffice. In fact, mechanical recycling of plastic materials produces substances with 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 reprocess a feedstock of waste plastics back into a liquid hydrocarbon product that has valuable and useful properties particularly as a fuel.

[0007] Thermolysis is a basic process whereby plastic waste material is converted to liquid fuel by thermal degradation (cracking) in the absence of oxygen. Plastic waste is typically first meltedwithin a stainless steel chamber under an inert purging gas, such as nitrogen. This chamber then heats the molten material to a gaseous state that is drawn into a catalytic converter and cracked to form carbon chain of variable length.

[0008] Hot pyrolytic gases of the desired carbon length range are then condensed in one or more condensers to yield a hydrocarbon distillate comprising straight and branched chain aliphatic, cyclic aliphatic and aromatic hydrocarbons. Depending on the composition, the resulting mixture is used in a variety of applications but, in any case, the requirement of product consistency and quality has always to be met. Also in view of the unstable composition of the plastic waste raw material, quality consistency of the recovered oil is difficult to be met.

[0009] The large temperature difference between a condenser and a subsequent depolymerization reactor requires significant energy to be put into the reactor to achieve depolymerisation reaction conditions and makes the overall process more energy intensive.

[0010] In light of the foregoing, an object of the present disclosure is to provide a process that provides high quality depolymerisation products in gaseous and liquid form with lower energy consumption.SUMMARY OF THE INVENTION

[0011] The present disclosure therefore relates to a process for depolymerizing waste plastic material.

[0012] In one aspect of the disclosure, a gaseous effluent from a first depolymerisation reactor is directed to a distillation unit from which a gaseous stream and a liquid stream are generated, which gaseous stream is directed to a condensation unit to yield pyrolytic oil and pyrolytic gas. The liquid stream from the distillation unit is directed to a second depolymerization reactor, the stream having a temperature close to the depolymerization reaction temperature, therefore little additional energy is required for operating the second depolymerization reactor.BRIEF DESCRIPTION OF DRAWINGS

[0013] Fig. 1 is a schematic view of the depolymerization process plant.DETAILED DESCRIPTION OF THE INVENTION

[0014] The process of the present disclosure for depolymerizing waste plastic material and producing a pyrolytic product comprises the following steps:

[0015] (a) feeding a mixture comprising waste plastic materials, in an oxygen-free atmosphere, into a feeding system comprising at least one screw extruder (1), which is heated at melting temperature of said plastic material;

[0016] (b) feeding the molten plastic material coming from the extruder into a first depolymerisation reactor (2), which first depolymerisation reactor (2) is maintained at a temperature ranging from 280 to 600°C and is operated under a pressure ranging from 1 to 10 barg so that depolymerization takes place, thereby forming a gaseous effluent and a liquid effluent;

[0017] (c) directing at least a portion of the liquid effluent produced in the first depolymerization reactor (2) to a char handling section (6), and feeding the gaseous effluent from reactor (2) to a distillation unit (3) from which a gaseous stream and a liquid stream are generated, which distillation unit (3) comprises two or more equilibrium stages and is operated with a distillation column having a bottom temperature ranging from 250 to 420°C;

[0018] (d) directing the gaseous stream from the distillation unit (3) to a condensation unit (5) working at temperature lower than said distillation unit (3), and directing the liquid stream coming from the distillation unit (3), the liquid stream having a temperature of equal to or greater than 200°C, to a second depolymerization reactor (4), which second depolymerization reactor (4) is maintained at a temperature ranging from 280 to 600°C and is operated under a pressure ranging from 1 to 10 barg so that depolymerization takes place, thereby forming a gaseous effluent and a liquid effluent;

[0019] (e) withdrawing the gaseous effluent from said second depolymerization reactor (4) and feeding it to the distillation unit (3), and / or to the condensation unit (5), and recycling at least a portion of the liquid effluent coming from the second depolymerization reactor (4) to the first depolymerization reactor (2): and

[0020] (f) recovering a pyrolytic oily product from the condensation unit (5).

[0021] Preferably, the process is carried out in a continuous mode.

[0022] In stage (a) a charging 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- containingatmosphere can be obtained with a series of expedients such as nitrogen blanketing, vacuum system connected to a barrel of the extruder.

[0023] 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).

[0024] The process according to the present disclosure is very flexible and can be preferably fed with a wide range of plastic waste composition in which polyolefins are the most abundant component. This would improve the yield in high value depolymerization products. 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.

[0025] 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 pre-treatment, a non-uniform mixture of different kinds of waste plastics can be transformed into a mass of uniform plastic composite. Therefore, this pre-treatment is also preferable for the case in which the main pyrolytic decomposition is performed without additives.

[0026] The heating temperature in the pre-treatment 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 HC1 from the PVC resin possibly present, takes place.

[0027] The HC1 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 pre-treatment. 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.

[0028] 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 receives the plastic scrap cut in small pieces into the feed hopper, conveys the stream in the melting section and heats the polymer by combined action of mixing energy and heat supplied by barrel heaters.

[0029] Additives can be optionally incorporated in the melt aiming at reducing corrosivity of plastic scrap or at improving conversion process in the reaction section.

[0030] During the extrusion, one or more degassing steps can be foreseen to remove residual humidity present in the product.

[0031] 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.

[0032] Any extrusion systems can be applied, as single screw extruders, twin screw extruders, twin screw extruders with gear pump, or combination of the above.

[0033] In a preferred embodiment, at least one of the depolymerization reactors (2) and (4) operates in the presence of a depolymerization catalyst. Advantageously, this lowers the required reaction temperature and / or improves the reaction yield.

[0034] The depolymerization reactor (2) and / or the depolymerization reactor (4) can be a continuously stirred tank reactor, preferably both depolymerization reactors (2) and (4) are continuously stirred tank reactors.

[0035] In a preferred embodiment, the depolymerization reactor (2) is an agitated vessel operated at temperature ranging from 300 to 550°C and preferably from 350 to 500°C and under a pressure kept in the range 2.0 to 8 barg, preferably in the range 2.5 to 7 barg. These reaction conditions have been found to result in a more efficient process.

[0036] In an attempt to improve mass fluidity, it constitutes a preferred embodiment premixing, preferably in a dedicated vessel, the molten mass of waste plastics entering the reactor with hydrocarbon oil.

[0037] The depolymerization reactor (2) preferably has a cylindrical section, preferably with a rounded bottom.

[0038] 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 0.2-2 kW / m3more preferably from 0.3 to 1.5 kW / m3.

[0039] In a particular and preferred embodiment, part of the liquid slurry withdrawn from the bottom of the reactor (2) is recirculated, via a recycling pump (7), back to the reactor top optionally through an external heater (8).

[0040] Preferably, the heating of the reactor takes 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 and circulated within the reactor jacket and / or the above mentioned external heater. This allows the transfer and distribution of heat to the reactor without heating the reactor itself by a furnace.

[0041] The feeding circuit (not shown) of the molten salt to the reactor jacket is constructed in such a way to prevent molten salt leakage. The molten salt is 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. The solar salt receives in turns heat from a dedicated furnace that may be either electric or be fed with fuel. In the latter case, part of the recovered oil from the condensation unit (5) may be used to feed the furnace. In the alternative, or in combination, the heat can be generated by combustion of gaseous or liquid hydrocarbons. The use of gaseous hydrocarbons is preferred.

[0042] In particular, during functioning, the salt is pushed into the jacket / and or heat exchanger, from a circulation pump. A series of fins guarantees a homogeneous distribution of the flow of molten salts and maximization of the thermal exchange coefficient.

[0043] The depolymerization process taking place within the reactor produces molecules having reduced chain length and low boiling point. This continuously running chain breakage mechanism, particularly close to the reactor walls, produces molecules increasingly smaller part of which, at the operating temperature and pressure, are gaseous.

[0044] 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.

[0045] Those that are still liquid at the operative conditions, contribute to lower the liquid mass viscosity. As a result of the depolymerization process and of the composition of the feed, 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.

[0046] At least a portion of the liquid slurry phase is withdrawn from the bottom of the reactor and constitutes the liquid effluent sent to the char handling section (6) which is not shown in Fig.1.

[0047] From the operative point of view, the withdrawal of the slurry phase from the bottom of the reactor is preferably triggered by density sensors detecting the density of the liquid slurry reaching a predetermined value.

[0048] As already mentioned, in a particular and preferred embodiment, part of the liquid slurry withdrawn from the bottom of the reactor (2) is recirculated, via a recycling pump (7), back to the reactor top optionally through an external heater (8).

[0049] According to a preferred embodiment, the liquid slurry portion recirculated to the reactor is withdrawn from a point of the reactor different from the point of the withdrawal of the liquid slurry portion sent to the char handling,

[0050] According to another preferred embodiment, both the liquid slurry portion recirculated to the reactor and the liquid slurry portion sent to the char handling are withdrawn from the same point and then successively split.

[0051] The split between the portion of liquid slurry directed to char handling and the portion recirculated to the reactor can take place either before or after the recycling pump (7). In this latter embodiment, the liquid slurry is first fed to a dedicated vessel equipped with a lower and upper exit point. The liquid portion directed to char handling (6) is withdrawn in a concentrated form the lower exit point while the liquid portion to be recycled to the reactor (2) is withdrawn from the upper exit point.

[0052] The gaseous phase of the reactor (2) constitutes the gaseous effluent which is sent to the distillation unit (3) for further treatment.

[0053] 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 the distillation unit (3).

[0054] The distillation unit (3) is preferably designed in a way to combine a scrubber zone and a distillation zone which are preferably located in the same column.

[0055] In a preferred design, the lower portion of the column is the scrubber zone where a liquid stream, preferably recirculated from the bottom of said column, flows downward in countercurrent with the gaseous effluent, coming from reactor (2) and preferably (4), which is fed to the lower part of the column and is directed upward.

[0056] The distillation zone is preferably located in the upper portion of the column where a thermal gradient is established between the cold liquid stream coming from condensation unit (5) and the hot gaseous effluent coming up from the scrubber zone.

[0057] In a preferred embodiment, the distillation is based on the use of packing material, so is a packed distillation column.

[0058] Preferably, the distillation unit (3) is endowed with three or more equilibrium stages, preferably four or more equilibrium stages, especially from 5 to 20 equilibrium stages. The increased number of equilibrium stages improves the separation of components by their respective boiling points.

[0059] In a preferred embodiment, the liquid stream, collected at the bottom of the distillation unit (3) and sent to the second depolymerization reactor (4), has a temperature, measured at the bottom of the distillation unit (3), of more than 250°C, preferably more than 300°C, more preferably from 330°C to 450°C, especially ranging from 350 to 400°C. This temperature is close to the reaction temperature in the second depolymerization reactor (4) which allows to save energy in the process.

[0060] While the characteristics of the oil collected at the bottom of the distillation unit (3) may vary in dependence of the specific feedstock and depolymerization conditions, in a specific and preferred embodiment, the average molecular weight (Mw) of the liquid stream from the distillation unit (3) is greater than 220 g / mol, preferably is greater than 250 g / mol, more preferably greater than 280 g / mol and especially is greater than 300 g / mol. This would advantageously allow subjecting to a further depolymerization stage mainly molecules of high molecular weight.

[0061] In a further preferred embodiment, a pump (9) recycles the liquid that collects in the bottom of the column to the top of the scrubber section of the column. The recycled liquid is cooled in a dedicated heat exchanger (10) before injection into the column top as reflux.

[0062] The gaseous stream (H2 and light hydrocarbons) coming from the distillation unit (3) is conveyed to the condensation unit (5) from which oil is recovered.

[0063] As mentioned, at least part of the liquid condensate of the distillation unit (3) is transferred by means of a pump (11) to the second depolymerization reactor (4).

[0064] Preferably, the second depolymerization reactor (4) is operated at a temperature ranging from 280 to 600°C and 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. Thiscomplements the reaction conditions of the first depolymerization reactor (2), improving the overall output of the process.

[0065] In a preferred embodiment form, set-up and operation conditions of the second reactor are the same as those of the first reactor.

[0066] The gaseous effluent produced in reactor (4) is preferably sent to distillation column (3) more preferably combined with the gaseous effluent coming from reactor (2).

[0067] In an alternative embodiment, the gaseous effluent is sent to condensation unit (5).

[0068] The liquid effluent coming from reactor (4) is preferably a highly concentrated hydrocarbon slurry. It is discharged from the second reactor and 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).

[0069] 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).

[0070] Since the reactor (4) is fed with the condensed effluents coming from the reactor (2), it contains less impurities and produces less char. Preferably, fresh catalyst is fed to reactor (4).

[0071] According to the present disclosure, the catalyst can be selected from those active as depolymerization / cracking catalysts in thermo-catalytic processes. In particular, it can be selected from aluminosilicates catalysts and preferably from zeolites. Among them, particularly preferred zeolites are synthetic Y-type zeolite and ZSM-5.

[0072] 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.

[0073] In a preferred embodiment, the catalyst is injected as powder dispersed into a hydrocarbon oil, preferably the liquid pyrolytic product (oil) obtained from distillation unit (3) and / or condensation unit (5). In a preferred embodiment, the pyrolytic oil dispersing the catalyst is preferably withdrawn from the condensation unit (5).

[0074] Preferably, the catalyst slurry is prepared in a pot, continuously stirred vessel where the catalyst is poured from a dedicated silo.

[0075] 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.

[0076] The gaseous effluent coming from the distillation unit (3) is conveyed to the condensation unit (5) for the recovering of the pyrolytic product in form of an oil.

[0077] Preferably, the condensation unit (5) is operated at a temperature ranging from 35 to 100°C, more preferably from 40 to 80°C.

[0078] The pressure value for condensation unit (5) should preferably be lower than that of distillation unit (3) so as to allow incondensable gases from unit (3) to enter unit (5) without further pressurization.

[0079] Preferably, the lower portion of the condensation unit (5) is designed as scrubber column in order to suppress the entrained solid particles. Also in this case, part of the liquid stream for the scrubbing action is preferably recirculated from the bottom of said column.

[0080] In a preferred setup of the condensation unit (5), a dephlegmator (partial condenser) is installed on top of the column and works at a temperature lower than that inside the column. The condensate flows down as reflux for the scrubber by virtue of gravity.

[0081] The dephlegmator can be installed either as a separate piece of equipment or integrated inside the column.

[0082] As previously mentioned, the pyrolytic product in form of oil recovered from the condensation unit (5) is the final product of the depolymerization process of the present disclosure.

[0083] In a preferred embodiment, part of the oil recovered from the condensation unit (5) is fed to the top of the condensation unit (3). The cold oil stream coming from the condensation unit (5) can therefore be used to cool and partially condense the hot vapour coming from one or more of the pyrolytic reactors.

[0084] The set-up of the present disclosure allows to produce a final pyrolytic oil of high quality and in some cases also improved over the pyrolytic product obtained in the absence of the distillation unit (3). The quality improvement can be seen through the values of different parameters such as final boiling point, composition fractionation and distribution, low amount of high molecular weight and high boiling point fractions.

[0085] In one specific embodiment, the average Mw of the pyrolytic product in form of oil recovered from the condensation unit (5) is equal to or smaller than 165 g / mol, preferably is smaller than 163g / mol, more preferably is smaller than 161g / mol, and especially is smaller than 160g / mol.

[0086] In an alternative preferred embodiment, the pyrolytic product in form of oil recovered from the condensation unit (5) has the following composition (GC determined): about 10-15% wt% of a fraction having retention time equal or less then n-heptane; about 70-75wt% of a fraction with retention time comprised by n-heptane and n- dodecane, and about 12-20 wt% of product having a retention time higher than that of n-dodecane and lower than that of n-octacosane.

[0087] It is preferred that, the pyrolytic product in form of oil recovered from the second condensation unit is used as hydrocarbon feedstock in cracking plants.EXAMPLES

[0088] The following experiments are based on thermodynamic simulation of a depolymerization process carried out in an apparatus consisting of two reactors connected in series. Each setup comprises two pyrolytic reactors and two pyrolytic oil scrubbers, the scrubbers being either two condensation units (comparative) or a distillation and a condensation unit.

[0089] The 1st pyrolytic oil scrubber (distillation unit) receives the vapour vented from the 1st pyrolytic reactor and can also receive the vapour vented from the 2nd pyrolytic reactor (Ex. 2). Here the hot vapour is cleaned by the eventual solid particles thanks to pump recycle to the tower, is cooled and partially condensed by means of a cold stream coming from the bottom of the 2nd pyrolytic oil scrubber (condensation unit).

[0090] The cold stream coming from the bottom of the 2nd pyrolytic oil scrubber is fed at the top of the distillation tower and its flowrate is fixed by the desired quality of the final pyrolytic oil.

[0091] The section is operated at about.1.5 barg.

[0092] The lighter fraction from the top of the column is delivered to the 2nd pyrolytic oil scrubber (condensation unit).

[0093] The heavier fraction from the column bottom is fed to the 2nd pyrolytic reactor to be further cracked by means of the 1st stage pyrolytic oil pumps.

[0094] The 2nd pyrolytic oil scrubber receives the vapour vented from the 1st pyrolytic oil scrubber and could receive the vapour vented from the 2nd pyrolytic reactor; here part of the vapour is condensed by the top condenser, exercised with jacket water.

[0095] The condensation temperature is about 50°C to maximize the pyrolytic oil production.The section is operated at about.1 barg.Reference case:

[0096] Vapour from top of 1streactor is fed to the condensation unit.Example 1

[0097] Vapour from top of 1streactor is fed to the distillation unit.Example 2:

[0098] Vapour from top of 1stand 2ndreactor is fed to the distillation unit.(*) The duty saving is calculated considering the delta of the total duty in the specific example respect to the total duty of the reference case divided by the total duty of the reference case and multiplied by 100.

[0099] The optimized amount of the reflux stream from condensation unit to distillation unit, was selected in order to guarantee a good balance between duty savings and quality of the final pyrolytic oil.

[0100] With respect to reference case, Example 1 shows improved yields in pyrolytic oil and both reactor and condensation duty savings. In Example 2 both the vapour from the top of the first reactor and the vapour from the top of the second reactor were sent to the distillation column. In addition to a slight improved yield, further duty savings were obtained in comparison with Example 1. In addition, both examples (1 and 2) show a lighter final pyrolytic oil (the lower is the Mw, the lighter is the pyrolytic oil) with respect to the reference case.

Claims

CLAIMSWhat 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, in an oxygen-free atmosphere, into a feeding system comprising at least one screw extruder (1), which is heated at melting temperature of said plastic material;(b) feeding the molten plastic material coming from the extruder into a first depolymerization reactor (2), which first depolymerization reactor (2) is maintained at a temperature ranging from 280 to 600°C and is operated under a pressure ranging from 1 to 10 barg so that depolymerization takes place, thereby forming a gaseous effluent and a liquid effluent;(c) directing at least a portion of the liquid effluent produced in the first depolymerization reactor (2) to a char handling section (6), and feeding the gaseous effluent from reactor (2) to a distillation unit (3) from which a gaseous stream and a liquid stream are generated, which distillation unit (3) comprises two or more equilibrium stages and is operated with a distillation column having a bottom temperature ranging from 250 to 420 C;(d) directing the gaseous stream from the distillation unit (3) to a condensation unit (5) working at temperature lower than said distillation unit (3), and directing the liquid stream coming from the distillation unit (3), the liquid stream having a temperature of equal to or greater than 200°C, to a second depolymerization reactor (4), which second depolymerization reactor (4) is maintained at a temperature ranging from 280 to 600°C and is operated under a pressure ranging from 1 to 10 barg so that depolymerization takes place, thereby forming a gaseous effluent and a liquid effluent;(e) withdrawing the gaseous effluent from said second depolymerization reactor (4) and feeding it to the distillation unit (3) and / or to the condensation unit (5) and recycling at least a portion of the liquid effluent coming from the second depolymerization reactor (4) to the first depolymerization reactor (2); and(f) recovering a pyrolytic product from the condensation unit (5).

2. The process according to claim 1 in which the distillation unit (3) comprises three or more equilibrium stages, preferably five or more equilibrium stages, especially 10 equilibrium stages.

3. The process according to any of the preceding claims 1 or 2 in which the liquid stream, collected at the bottom of the distillation unit (3), and sent to the second depolymerization reactor (4), has a temperature, measured at the bottom of the distillation unit (3), of more than 250°C, preferably more than 300 C, more preferably 330°C to 450°C, especially ranging from 350 to 400°C.

4. The process according to one or more of the preceding claims in which the distillation unit (3) is designed in a way to combine a scrubber zone and a distillation zone which are located in the same column.

5. The process according to any of the preceding claims in which part of the oil recovered from the condensation unit (5) is fed to the top of the distillation unit (3).

6. The process according to claim 4 and 5 in which the lower portion of the column is the scrubber zone where a liquid stream, flows downward in counter-current with the gaseous effluent, coming from reactors (2) and (4), and the upper portion of the column comprises the distillation zone where a thermal gradient is established between the cold liquid stream coming from condensation unit (5) and the hot gaseous effluent coming up from the scrubber zone.

7. The process according to any of the preceding claims in which the condensation unit (5) is operated at a temperature ranging from 35 to 100°C.

8. The process according to any of the preceding claims in which plastic waste is a mixture of waste materials in which polyolefins are the most abundant component.

9. The process according to any of the preceding claims in which at least one of the depolymerization reactors (2) and (4) operates in the presence of a depolymerization catalyst.

10. The process according to any of the preceding claims in which the depolymerization reactor (2) and / or the depolymerization reactor (4) is a continuously stirred tank reactor.

11. The process according to any of the preceding claims in which the depolymerization reactors (2) and (4) are agitated vessels operated at temperature ranging from 300 to 550°C and more preferably from 350 to 500°C and under a pressure kept in the range 2.0 to 8 barg, more preferably in the range 2.5 to 7 barg.

12. The process according to any of the preceding claims in which the gaseous effluent produced in reactor (4) is sent to distillation column (3) more preferably combined with the gaseous effluent coming from reactor (2).

13. The process according to any of the preceding claims in which part of the liquid slurry withdrawn from the bottom of the reactor (2) and (4) is recirculated, via a recycling pump (7), back to the reactors optionally through an external heater (8).

14. The process according to any of the preceding claims in which the heating of the reactor takes 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 and circulated within reactor jacket and / or the external heater .

15. The process according to any of the preceding claims in which the average Mw of the pyrolytic product in form of oil recovered from the condensation unit (5) is equal to or smaller than 165 g / mol, preferably is smaller than 163 g / mol, more preferably is smaller 161 g / mol, and especially is smaller than 160 g / mol.

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