WO2023275855A2

WO2023275855A2 - Plant and process for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons

Info

Publication number: WO2023275855A2
Application number: PCT/IB2022/060598
Authority: WO
Inventors: Nicola MINZOCCHI
Original assignee: Lifenergy Italia S.R.L.
Priority date: 2021-11-04
Filing date: 2022-11-03
Publication date: 2023-01-05
Also published as: WO2023275855A3; IT202100028121A1

Abstract

The present invention relates to a plant (1) for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons comprising a reactor (10) inside which pyrolysis reactions of polyolefin plastic materials are intended to occur in the presence of a catalyst, with the consequent at least partial depolymerization thereof and the production of relatively low boiling hydrocarbons. The reactor (10) comprises at least one side wall (11), a bottom wall (12) and an upper wall (13) delimiting a reaction chamber (14), inside which the catalyst and polyolefin plastic materials are intended to be arranged. The reactor further comprises heating means (17) associated with at least one of the walls of said reactor and an internal mixer (18). The plant comprises at least one external recirculation chamber (20; 30) of the polyolefin plastic materials mixed with the catalyst contained in the reactor (10), said at least one external recirculation chamber (20; 30) being: arranged outside the reactor; fluidically connected to the reaction chamber of the reactor by means of an upper opening (21; 31) obtained near the upper wall (13) of the reactor and a lower opening (22; 32) obtained near the bottom wall (12) of the reactor; provided with an internal mixer (23; 33) configured to impart, in use, to the polyolefin plastic materials mixed with the catalyst an upward motion through said recirculation chamber (20; 30) from the lower opening (22; 32) to the upper opening (21; 31) so as to generate descending convective motions from the upper opening (21; 31) towards the lower opening (22; 32) in the reaction chamber; and provided with heating means (24; 34).

Description

"PLANT AND PROCESS FOR THE THERMO-CATALYTIC DEPOLYMERIZATION OF POLYOLEFIN PLASTIC MATERIALS FOR THE PRODUCTION OF HYDROCARBONS"

DESCRIPTION Field of application

[0001]The present invention relates to a plant and a process for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons . [0002]Advantageously, the depolymerization plant and process according to the invention are intended in particular to use as Raw Material the industrial polyolefin plastic waste (table UNI 10667/18) intercepted before disposal as waste to convert them into hydrocarbons .

[0003]In particular, the features of the hydrocarbons which may be produced with the plant and the process according to the invention fall within the criteria envisaged by the EN 590 standard. The depolymerization plant and process according to the invention are therefore able to start from a polyolefin Secondary Raw Material "SRM" (as defined by the standard) to obtain a directly marketable diesel oil, without further treatment, after mixing with a similar product of fossil origin in variable percentages depending on the degree of purity of the hydrocarbon obtained by the plant according to the invention.

[0004]Optionally, the depolymerization plant and process according to the invention may be intended to use also plastic waste as Raw Material.

Prior art

[0005]Generally, the known processes of thermo-catalytic depolymerization of plastic materials have a low productivity, in terms of the fraction of plastic material transformed into hydrocarbons.

[0006]The depolymerization process is carried out by heating the plastic material inside a reactor in the presence of catalysts so as to trigger pyrolysis reactions. To maximize the yield of the process it is necessary to ensure a pyrolysis temperature as homogeneous as possible throughout the mass of plastic material inside the reactor. The reactor heating methods therefore play an essential role not only in productivity, but also in the quality of the hydrocarbons produced.

[0007]Patent EP1212387B1 describes a thermo-catalytic depolymerization process of plastic material inside a reactor which is heated externally by a combustion chamber inside which part of the gaseous compounds obtained from depolymerization are burned. The reactor is internally provided with a mixer.

[0008]The international application W02005/087897 also describes a thermo-catalytic depolymerization process of plastic material inside a reactor, which is heated only externally and is provided with a mixer.

[0009]Heating the reactor from the outside inevitably leads to the formation of temperature gradients in the mass of plastic material. Generally, in fact, the mixing action exerted by the mixer is not sufficient to homogenize the mass of plastic material. This negatively affects both the productivity of the process, which is low, and the quality of the hydrocarbons produced, which is very variable and difficult to control.

[0010]This problem has been addressed in the patent EP2242570B1, in which it is proposed to heat the reactor not only externally, but also internally. The reactor is provided with an internal mixer, the blades of which are provided with electrical resistances. In this way, it is also possible to supply heat from inside the reactor, reducing the thermal gradients within the mass of plastic material.

[0011]The solution proposed in EP2242570B1, while allowing a reduction of the thermal gradients inside the reactor, nevertheless has operating limits linked to the fact that due to the strong friction involved, the electrical resistances wear out very quickly. This requires continuous maintenance interventions that negatively affect the operation of the plant and the efficiency of the production process. [0012]There is therefore a strong need to have plants and processes for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons which may guarantee more uniform temperature conditions in the thermo-catalytic depolymerization reactor and at the same time operating stability so as to achieve high productivity.

[0013]To date, however, this need is still unsatisfied. Disclosure of the invention

[0014]Therefore, the main object of the present invention is to eliminate in whole or in part the drawbacks of the aforementioned prior art, by providing a plant for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons, which may guarantee more uniform temperature conditions inside the thermo-catalytic depolymerization reactor.

[0015]A further object of the present invention is to provide a plant for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons which allows greater operating stability so as to achieve high productivity. [0016]A further object of the present invention is to provide a plant for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons which may be fed efficiently with industrial polyolefin plastic waste as raw material without penalizing the operating stability thereof.

[0017]A further object of the present invention is to provide a plant for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons which is operationally reliable and simple to manage.

[0018]A further object of the present invention is to provide a process for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons, which may guarantee more uniform temperature conditions inside the thermo- catalytic depolymerization reactor.

[0019]A further object of the present invention is to provide a process for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons which may be fed efficiently with industrial polyolefin plastic waste as raw material without penalizing the operating stability thereof.

Brief description of the drawings [0020]The technical features of the invention, according to the aforesaid objects, may be clearly seen in the contents of the claims below, and its advantages will become more readily apparent in the detailed description that follows, made with reference to the accompanying drawings, which represent one or more purely exemplifying and non-limiting embodiments thereof, wherein:

[0021]- Fig. 1 shows a simplified diagram of a depolymerization plant according to a preferred embodiment of the invention; [0022]- Fig. 2 shows an enlarged detail of a part of the plant of Fig. 1 relating to a reactor and two external recirculation chambers;

[0023]- Fig. 3 shows an orthogonal sectional view of a reactor of the plant of Fig. 1; [0024]- Fig. 4 shows a perspective view of an internal mixer of the reactor of Fig. 3;

[0025]- Fig. 5 shows an orthogonal sectional view of a first external recirculation chamber of the plant of Fig. 1; [0026]- Fig. 6 shows a perspective view of an internal mixer of the first external recirculation chamber of Fig. 5;

[0027]- Fig. 7 shows an orthogonal sectional view of a concentration chamber of the solid residue of the plant of Fig. 1; [0028]- Fig. 8 shows a perspective view of an internal mixer of the concentration chamber of the solid residue of Fig. 7; and

[0029]- Fig. 9 shows a flow diagram of a pre-treatment section of waste polyolefin materials to be fed to the plant of Fig. 1.

Detailed description

[0030]The plant for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons according to the invention has been indicated as a whole with reference numeral 1 in the accompanying figures.

[0031]Unless otherwise explicitly specified, the following terms in the present text have the meanings given below. [0032]By polyolefin plastic materials it is meant a polymeric material, advantageously also polymeric waste material (or waste), consisting mainly of polyolefins. The expression plastic material consisting mainly of polyolefins means a plastic material whose polyolefin content is at least 80% by weight (with respect to the total weight of the plastic material), preferably at least 95% by weight.

[0033]By relatively low boiling compounds it is meant compounds which are released (i.e. separated) from the plastic materials during the at least partial, advantageously complete, depolymerization of at least part of said plastic materials. Relatively low boiling compounds exhibit boiling temperatures below the boiling temperature of plastic materials. [0034]By substantially incondensable gases it is meant substances whose boiling temperature is lower than 25 °C, advantageously lower than 10 °C, in particular propane and/or butane.

[0035]Advantageously, the depolymerization plant according to the invention is intended to use as raw material the industrial polyolefin plastic waste (table UNI 10667/18) intercepted before their disposal as waste to convert them into hydrocarbons.

[0036]In particular, the features of the hydrocarbons which may be produced with the plant according to the invention fall within the criteria envisaged by the EN 590 standard. The depolymerization plant according to the invention is therefore able to start from a polyolefin Secondary Raw Material "SRM" (as defined by the standard) to obtain a directly marketable diesel oil, without further treatment, after mixing with a similar product of fossil origin in variable percentages depending on the degree of purity of the hydrocarbons obtained by the plant according to the invention. [0037]The plant 1 may however use as polyolefin plastic materials also materials that are not necessarily waste. [0038]Optionally, the depolymerization plant and process according to the invention may be intended to use also plastic waste as Raw Material. [0039]According to a general embodiment of the invention, the thermo-catalytic depolymerization plant 1 comprises a reactor 10 inside which pyrolysis reactions of polyolefin plastic materials are intended to occur in the presence of a catalyst, with the consequent at least partial depolymerization thereof and the production of relatively low boiling hydrocarbons.

[0040]Inside the reactor, in addition to the relatively low boiling hydrocarbons that separate from the mass of plastic materials and catalyst in the form of vapor, a solid residue is formed, consisting of coke and catalyst, which tends to accumulate at the bottom of the reactor. [0041]As illustrated in Figs. 2 and 3, the reactor 10 comprises at least one side wall 11, a bottom wall 12 and an upper wall 13 delimiting a reaction chamber 14, inside which the catalyst and polyolefin plastic materials are intended to be arranged.

[0042]The reactor 10 comprises at least one feed opening 15 through which the polyolefin plastic materials and the catalyst are fed to said reactor 10 and which is obtained near the upper wall 13. [0043]Advantageously, the plant 1 comprises a system 40 for feeding polyolefin plastic materials and catalyst in the reactor 10. Such system 40 will be described in more detail below. [0044]The reactor 10 comprises at least one outlet opening

16 through which the relatively low boiling hydrocarbons (generated by the pyrolysis reactions) leave the reactor and which is obtained near the upper wall 13.

[0045]The plant 1 comprises a system 60 for collecting the relatively low boiling hydrocarbons generated in the reactor 10. Such system 60, which will be described in more detail below, is fluidically connected to the outlet opening 16 of the reactor.

[0046]Advantageously, the reactor 10 comprises at least one extraction opening 19 through which the solid residue of the pyrolysis reactions may be extracted from the reactor 10 and which is obtained near the bottom wall 12. Advantageously, the plant 1 comprises a system 50 for extracting the solid residue, which is fluidically connected to the extraction opening 19 and which will be described in more detail below.

[0047]The reactor 10 further comprises:

[0048]- heating means 17 associated with at least one of the walls of said reactor, preferably the side wall 11; and [0049]- an internal mixer 18.

[0050]Preferably, the heating means 17 consist of electrical resistances. In particular, the heating means 17 consist of electric heating bands mounted outside the reactor 10. The heating then takes place by conduction, that is, the heating band in contact with the outer wall of the reactor heats the external surface of the reactor shell which, by conduction, transfers the heat to the fluid inside it. [0051]Advantageously, the heating means 17 are regulated by a control unit (not shown in the accompanying figures) as a function of the temperature inside the reactor 10, detected by means of a plurality of temperature sensors 170 with which the reactor 10 is advantageously provided. [0052]Advantageously, the possible increase in pressure inside the reaction chamber 14 in use is monitored by pressure indicators and transmitters (not shown in the accompanying figures) connected to the aforementioned control unit. In case of pressure increase beyond a predefined threshold limit, the activation of breather devices (for example rupture discs) fluidically connected to a torch (not shown in the accompanying figures) envisaged for the thermo-oxidation of hydrocarbon vapors expelled from the reactor in overpressure. [0053]Preferably, as illustrated in Figs. 3 and 4, the internal mixer 18 of the reactor 10 is configured to mix the mass of polyolefin plastic materials and catalyst only near the bottom wall 12 of the reactor 10 (preventing this mass from sticking to the bottom) and to facilitate the movement of said mass towards the side wall 11 of the reactor 10. The action of the internal mixer 18 favors the flow of the mass of polyolefin plastic materials and catalyst, as well as of the solid residue being formed towards one or more lower openings 22, 32 obtained in the side wall 11, the function of which will be clarified in the following description.

[0054]More in detail, the reactor mixer is driven by an electric motor/reduction unit 18a (preferably with a constant number of revolutions) by means of a shaft 18b, which is coaxial to the reaction chamber 14 and to the base of which the blades 18c of the mixer are keyed.

[0055]According to the invention, the plant 1 comprises at least one external recirculation chamber 20, 30 of the polyolefin plastic materials mixed with the catalyst contained in the reactor 10.

[0056]As illustrated in Figs. 1 and 2 such at least one external recirculation chamber 20, 30 is:

[0057]- arranged outside the reactor;

[0058]- fluidically connected to the reaction chamber 14 of the reactor 10 by means of an upper opening 21, 31 obtained near the upper wall 13 of the reactor and a lower opening 22, 32 obtained near the bottom wall 12 of the reactor;

[0059]- provided with an internal mixer 23, 33 configured to impart, in use, to the polyolefin plastic materials mixed with the catalyst an upward motion through said recirculation chamber 20, 30 from the lower opening 22,

32 to the upper opening 21, 31 so as to generate descending convective motions from the upper opening 21, 31 towards the lower opening 22, 32 in the reaction chamber 14; and

[0060]- provided with heating means 24, 34 which in use are suitable to supply heat to the flow of plastic materials/catalyst which passes through the recirculation chamber 20, 30.

[0061]It has been possible to verify that the aforementioned descending motions induced inside the reactor 10 by the external recirculation and the heat supplied inside said recirculation chamber 20, 30 to the circulating flow reduce the thermal gradients in the mass of polyolefin plastic materials and catalyst inside the reactor, thus favoring temperature uniformity in every point of the reactor.

[0062]The increased uniformity of temperature favors the yield of the pyrolysis process and therefore the productivity of the plant 1.

[0063]The thermo-catalytic depolymerization plant according to the invention may therefore guarantee more uniform temperature conditions inside the thermo- catalytic depolymerization reactor with respect to similar plants of known type. This also results in greater operating stability of the plant 1.

[0064]The uniformity of temperature and the correlated operating stability of the plant also allow the production of relatively low boiling hydrocarbons having a less variable and therefore more controllable quality. [0065]Advantageously, the depolymerization plant 1 may comprise two or more distinct external recirculation chambers, each of which is fluidically connected to the reaction chamber 14 of the reactor 10 through a respective lower opening and a respective upper opening. [0066]The number and dimensions of the external recirculation chambers are related to the dimensions of the reactor 10. As the size of the reactor increases, the number and/or size of the external recirculation chambers increases. Those skilled in the art, having defined the dimensions of the reactor, are able to size the recirculation chambers in order to ensure recirculation phenomena inside the reactor such as to ensure the most uniform temperature conditions inside the reactor itself. [0067]Preferably, the ratio Vr/åVcr between the reactor volume Vr and the sum of the volumes of the external recirculation chambers åVcr may be of between 3.5 and 4.0. Preferably, the reactor is made with a ratio L/D between height L and internal diameter D of between 1.0 and 1.25.

[0068]In accordance with the preferred embodiment of the invention, illustrated in the accompanying figures, the plant 1 comprises two distinct external recirculation chambers of the polyolefin plastic materials mixed with the catalyst contained in the reactor 10. A first recirculation chamber is indicated with reference numeral 20, while a second recirculation chamber is indicated with reference numeral 30. [0069]Preferably, said two distinct external recirculation chambers 20 and 30 are arranged externally to the reactor in diametrically opposite positions. The first external recirculation chamber 20 is connected to the reaction chamber 14 by means of a first upper opening 21 and a first lower opening 22; the second external recirculation chamber 30 is connected to the reaction chamber 14 by means of a second upper opening 31 and a second lower opening 32.

[0070]Advantageously, the mixer 23,33 of each recirculation chamber is driven by an electric motor/reduction group 23a/33a through a shaft 23b/33b, on which the blades 23c/33c of the mixer are keyed. Preferably, the electric motor/reduction unit 23c/33c is variable speed. Operationally, the possibility of varying the revolutions of the mixer allows the efficiency of the pyrolysis reaction to be controlled by actually changing the residence time of the fluid (plastic materials/catalyst) in the reactor. The residence time is inversely proportional to the rotation speed of the mixer of the recirculation chamber.

[0071]Preferably, each recirculation chamber 20, 30 is delimited by a tubular body 200, 300. The internal mixer

23, 33 of each recirculation chamber 20, 30 comprises a plurality of blades which are distributed along the entire longitudinal extension of said tubular body and are rotatable around an axis of rotation coaxial to said tubular body 200, 300. Advantageously, as illustrated in

Fig. 5, the blades are substantially flush with the internal surface of the tubular body. [0072]In accordance with the preferred embodiment of the invention, illustrated in Figs. 5 and 6, the aforementioned plurality of blades comprises:

[0073]- mixing blades 23a configured to impart to the polyolefin plastic materials mixed with the catalyst an upward motion along said tubular body; and [0074]- chipping blades 23b for breaking any solid parts still present in the mass of polyolefin plastic materials and catalyst.

[0075]Preferably, as illustrated in Figs. 5 and 6, the chipping blades 23b are concentrated in a single group and are preceded and followed by one or more of said mixing blades 23a.

[0076]Preferably, the heating means 24, 34 of each recirculation chamber 20, 30 consist of electrical resistances. In particular, the heating means 24, 34 consist of electric heating bands mounted outside the tubular body 200, 300 which forms the shell of each recirculation chamber.

[0077]Advantageously, the heating means 24, 34 are regulated by a control unit (not shown in the accompanying figures) as a function of the temperature inside the recirculation chamber 20, 30 detected by means of a plurality of temperature sensors 240 with which the recirculation chamber 20, 30 is advantageously provided. [0078]Preferably, as illustrated in Fig. 1, the system 40 for feeding polyolefin plastic materials and catalyst into said reactor 10 comprises a screw extruder 41 which is provided with heating means 42 and is suitable to transform a mixture of polyolefin plastic materials and catalyst into a fluid mass to be fed to the reactor 10. [0079]Advantageously, the screw extruder 41 is provided with a degasser (not illustrated in the accompanying figures), to eliminate the traces of light volatile compounds including the water molecules present in the form of humidity.

[0080]Preferably, the catalyst is mixed with the polyolefin plastic materials in the extruder 41. To this end, the extruder 41 comprises a loading hopper 44 which receives the polyolefin plastic materials and the catalyst dosed by means of a dispenser.

[0081]Advantageously, the extruder 41 may be provided at the outlet with a filter for retaining any solid materials possibly present in the plastic materials.

[0082]Operationally, the softening of the plastic materials inside the extruder 41 is monitored by means of a precise control of the temperature, carried out in a plurality of zones along the entire extruder.

[0083]Advantageously, the level of the material inside the reactor 10 is detected by means of a level transmitter connected to the control unit. The regulation loop provided for maintaining the desired level inside the reactor acts on the flow rate of the plastic materials and catalyst loaded into the reactor, varying the speed of the screw of the extruder 41. [0084]Advantageously, the extruder 41 is sized according to the production capacity of the plant 1, as well as the features of the plastic materials treated. Such sizing is in itself within the reach of those skilled in the art. [0085]Preferably, the reactor 10 may be loaded with polyolefin plastic materials and catalyst up to 40-65% of its height, in order to leave a free volume at the top for the evaporation of the relatively low boiling hydrocarbons.

[0086]More in detail, a possible way of regulating the filling level of the reaction chamber 14 provides for the extruder 41 to feed the set point flow rate between the zero level value and 50% of the maximum achievable level. Once a level equal to 50% of the maximum achievable level has been reached, the extruder 41 slows down the rotation speed of the screw in order to scale the supplied flow rate proportionally to the set point value to zero until the maximum level is reached.

[0087]Preferably, as illustrated in Fig. 1, the feeding system 40 is fluidically connected to the reactor 10 indirectly through a first external recirculation chamber 20. In this case, the feed opening 15 of the reactor 10 coincides with the upper opening 21 to which said first recirculation chamber 20 is connected. In turn, the first recirculation chamber 20 is provided with an inlet opening 25 at which it is fluidically connected to the feeding system 40. In particular, the screw extruder 41 is fluidically connected at the outlet to the first recirculation chamber 20 at said inlet opening 25.

[0088]Preferably, the inlet opening 25 is arranged between the upper opening 21 and the lower opening 22 of the first recirculation chamber 20, even more preferably in proximity to said lower opening 22.

[0089]Preferably, as illustrated in Fig. 1, the system 50 for extracting the solid residue is fluidically connected to the reactor 10 indirectly through a second external recirculation chamber 30. In this case, the extraction opening 19 of the reactor 10 coincides with the lower opening 32 to which the second recirculation chamber 30 is connected. In turn, the second recirculation chamber 30 is provided with a discharge opening 35 at which the second chamber 50 is connected to the extraction system 50.

[0090]More in detail, from an operational point of view, the flow through the upper opening 31 is regulated by a first valve 36, while the flow through the discharge opening 35 is regulated by a second valve 37. The first valve 36 and the second valve 37 may be piloted in a coordinated manner so that the flow through the upper opening 31 is alternative to the flow through the discharge opening 35. In use when the flow through the upper opening 31 is prevented, the mixer 33 of said second recirculation chamber gives the solid residue accumulated at the bottom of the reactor 10 an upward motion through the second recirculation chamber 30 from the lower opening 32 towards the discharge opening 35.

[0091]Advantageously, as illustrated in Figs. 1 and 2, the plant 1 may comprise a pump 38, preferably with gears, which is installed in a connection duct between the lower opening 32 of the reactor 10 and the second recirculation chamber 30 and is suitable to generate a flow towards said second recirculation chamber 30.

[0092]According to the preferred embodiment of the invention, illustrated in the accompanying figures, the extraction system 50 of the solid residue comprises a solid residue concentration chamber 51 which:

[0093]- is fluidically connected at the inlet to the discharge opening 35 of the second recirculation chamber 30;

[0094]- is provided with an internal mixer 52 and heating means 53;

[0095]- is fluidically connected to the outlet of the relatively low boiling hydrocarbon collection system 60 so that any amount of relatively low boiling hydrocarbons released by evaporation from the solid residue can be collected; and [0096]- is provided with an opening 54 for the expulsion of the concentrated solid residue.

[0097]Operationally, the concentration chamber 51 concentrates the solid residue (pyrolysis coke and catalyst), mixing the solid residue and operating at the reaction temperature so as to favor the evaporation of the liquid fraction still present which joins the main vapor flow.

[0098]By virtue of the action of the concentration chamber 51 it is possible to extract from the solid residue substantially all the residual amount of relatively low boiling hydrocarbons still present, on the one hand by evaporating the amounts already present and on the other by completing the pyrolysis reactions. [0099]Preferably, as illustrated in the accompanying figures, the concentration chamber 51 is delimited by a hopper 500 having a cylindrical upper part and a frusto- conical lower part.

[00100] Preferably, as illustrated in Figs. 7 and 8, the internal mixer 52 of the concentration chamber 51 of the solid residue comprises:

[00101] - a plurality of mixing augers 52a, which substantially engage the entire volume of the chamber 51, and [00102] a plurality of scraper blades 52b which are configured to scrape at least the bottom of said chamber 51, preferably the walls of the frusto-conical portion of the hopper 500.

[00103] Advantageously, the mixer 52 is configured to perform two different operating functions: the first is mixing the solid residue during the concentration step, the second is simultaneously facilitating the unloading and cleaning of the lower, frusto-conical part of the shell of the concentration chamber 51. [00104] More in detail, the mixer 52 of the concentration chamber 51 is driven by an electric motor/reduction unit 52c (preferably with a constant number of revolutions) by means of a shaft 52d, which is coaxial to the concentration chamber 51 and to which the mixing augers and scraper blades are keyed.

[00105] Preferably, the heating means 53 of the concentration chamber 51 consist of electrical resistances. In particular, the heating means 53 consist of electric heating bands mounted on the outside of the frusto-conical hopper 500 which forms the shell of the concentration chamber 51.

[00106] Advantageously, the heating means 53 are regulated by a control unit (not shown in the accompanying figures) as a function of the temperature inside the concentration chamber 51 detected by means of a plurality of temperature sensors 530 with which the concentration chamber 51 is advantageously provided.

[00107] Advantageously, the concentrated solid residue is discharged from the concentration chamber 51 through the expulsion opening 54. In particular, as illustrated in Fig. 1, once discharged, the concentrated solid residue is collected by a conveyor belt 55 immersed in a water bath, in such a way as to cool the residue to room temperature before collecting it in disposal containers. [00108] Preferably, as illustrated in Fig. 1, the relatively low boiling hydrocarbon collection system 60 comprises:

[00109] - a two-phase separator 61, in which, in use, the relatively low boiling hydrocarbons generated in the plant 1 in the vapor state form a liquid/vapor mixture;

[00110] - at least one condenser 62, connected to the two-phase separator 61 to receive the vapor phase of the liquid/vapor mixture and condense it so as to separate the fraction of non-condensable gases from the condensable fraction;

[00111] - at least one condensable hydrocarbon collection tank 63, which is connected to said two-phase separator 61 and to said at least one condenser 62 to collect the condensable fraction of the relatively low boiling hydrocarbons generated in said plant 1; and [00112] - a system 70 for extracting non-condensable gases which is connected to said at least one condenser 62 to extract the non-condensable fraction of the relatively low boiling hydrocarbons generated in the plant 1.

[00113] In particular, the system 70 for extracting non-condensable gases may comprise an ejector and a thermo-oxidation torch (not shown in the accompanying figures). As an alternative to torch combustion, the non- condensable gases may be fed to an endothermic engine combined with an alternator unit for the production of electricity (usable in the same plant 1). Advantageously, the heat of the combustion fumes of the internal combustion engine may be recovered in a heat exchanger (for example with tube bundle), for example for the production of hot air usable to preheat the polyolefin plastic materials.

[00114] Preferably, the reactor 10 with the relative external recirculation chambers 20 and 30, and, if provided, the concentration chamber 51 of the solid residue, operate at a pressure slightly higher than the atmospheric one to avoid air entry into the plant 1. For this purpose, these parts of the plant 1 are buffered with nitrogen. [00115] Advantageously, as already mentioned, the depolymerization plant 1 according to the invention is intended to be fed with polyolefin plastic materials consisting of waste polyolefin materials. In this case, as illustrated in Fig. 9, the system 40 for feeding polyolefin plastic materials and catalyst into the reactor 10 preferably comprises a section 400 for the pre-treatment of said waste polyolefin materials.

[00116] In turn, the section 400 for the pre-treatment of waste polyolefin materials comprises: [00117] - a first pre-treatment line 410 intended for treating waste polyolefin materials having structural rigidity; and

[00118] - a second pre-treatment line 420 intended to treat waste polyolefin materials without structural rigidity.

[00119] In particular, waste polyolefin materials having structural rigidity may consist of sprues, purging residues from manufacturing machines, extruded and blown objects, rigid finished objects. [00120] Waste polyolefin materials without structural rigidity may consist of waste from extruded and laminated sheet products (waste reels of film for packaging, stretch film, film for raffia bags, for shoppers, for adhesive tapes, top of covers, reel trims, etc.). It is a material that, once pre-cut, is characterized by flexibility and in some cases by impalpability.

[00121] Preferably, as illustrated in Fig. 9, the first pre-treatment line 410 comprises a shredding device 411 suitable to shred the waste polyolefin materials to reduce them to a material having a predefined homogeneous size, which may be introduced directly into the extruder through the forced feeding hopper. For example, this size may have the appearance of "shapeless squares" with maximum dimensions of 14 x 14 mm with thicknesses on the order of a few millimeters, compatible with the loading mouth of the extruder screw.

[00122] Advantageously, the first pre-treatment line

410 may also comprise a sieving device 412 downstream of said shredding device 411. [00123] Alternatively, the pre-treatment section 400 may be devoid of the first pre-treatment line 410 if the waste polyolefin materials having structural rigidity are fed from the outside already pre-shredded, in the predefined size, for example inside big bags which will be emptied in a special pre-treatment department; subsequently, through a screw conveyor, the material will be sent to a rigid material silo.

[00124] Preferably, as illustrated in Fig. 9, the second pre-treatment line 420 comprises means for agglomerating the waste polyolefin materials without structural rigidity. In particular, the aforesaid agglomeration means may consist of a densifier device for low-melting plastics 421 suitable to transform the waste polyolefin materials without structural rigidity into a higher density material having a predefined homogeneous size.

[00125] Operationally, the agglomeration and volume reduction treatment allows a compaction that gives the plastic material the consistency necessary for subsequent transport to the extruder hopper.

[00126] Preferably, the waste polyolefin materials without structural rigidity will be delivered by the supplier in lengths with maximum dimensions consistent with the provisions of the UNI 10667-2018 table; therefore for at least 80% of the amount supplied, these materials will be in the form of lengths of less than or equal to 100 x 100 mm; preferably, delivery will take place via big bags which will be emptied into the loading hopper of a weighing belt feeding the densifier. Once densified, the material is sent to a silos dedicated to the densified material by means of an auger.

[00127] Advantageously, the aforementioned section 400 for the pre-treatment of said waste polyolefin materials comprises a collection silo 430 into which the first 410 and the second 420 pre-treatment lines converge. The collection silos 430 is provided with an internal mixer 431 for mixing the polyolefin materials coming from said two pre-treatment lines and obtaining a homogeneous mixture of these two materials. [00128] In turn, the collection silo 430 is connected to the aforesaid screw extruder 41 to feed it with the homogeneous mixture of polyolefin materials from said two pre-treatment lines.

[00129] Advantageously, the system 40 for feeding polyolefin plastic materials and catalyst into the reactor 10 comprises a dispenser (not shown in the accompanying figures) suitable to feed said screw extruder 41 with catalyst.

[00130] By virtue of the pre-treatment section 400 it is therefore possible to obtain a homogeneous material from waste polyolefin materials which may be efficiently fed to the extruder and therefore to the reactor. In particular, all the drawbacks related to the feeding of non-homogeneous material are avoided. [00131] In this sense, the pre-treatment of polyolefin waste materials without structural rigidity is particularly important. The pre-treatment reduces the size of the plastic fragments and re-aggregates them in the form of pieces with higher density and predefined dimensions. In this way, a more uniform feeding and a consequent better rationality of the plants will be obtained, as well as a higher production of extrusion as the material will be compacted and homogenized so as to make it similar to a mono-product with other advantages also in terms of adjustment of the parameters of the subsequent sections of the plant 1. In particular, the substantial decrease in the volume of the introduced material allows further advantages also in terms of reduction of the storage spaces of the treated plastic material and simplification of its transport.

[00132] By virtue of the pre-treatment section 400, the plant 1 for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons according to the invention may therefore be fed efficiently with industrial polyolefin plastic waste as raw material without penalizing the operating stability thereof.

[00133] The operating stability, in combination with homogeneous temperature conditions inside the reactor (which ensure high-yield and stable pyrolysis reactions), allows the production of hydrocarbons having a non^¬ variable and controllable quality, these are important features (together with the type of fed plastic material) to allow the production of high quality diesel oil. EXAMPLE [00134] A plant for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons has been built in accordance with the provisions of the invention. [00135] In particular, the plant is provided with a reactor and two distinct external recirculation chambers. [00136] The reactor has the following dimensions: internal diameter 1188 mm; height 1334 mm. The reactor mixer is driven by an electric motor/reduction unit with a power of 5.5 kW, with a rotation speed of 25 RPM.

[00137] Each external mixing chamber has the following dimensions: internal diameter 400 mm; height 1480 mm. The mixer of each external recirculation chamber is driven by an 11 kW electric motor/reduction unit operated by a "Variable Speed Drive" VSD in order to change the rotation speed from 200 RPM to 700 RPM.

[00138] The reactor is provided with a plurality of temperature sensors suitable to detect the temperature trend inside the reaction chamber. [00139] The plant was put into operation; in steady state conditions, i.e. once the pyrolysis temperature was reached, the temperature trend inside the reactor was evaluated. The average thermal gradient detected inside the reactor in the mass of polyolefin plastic materials and catalyst, between the top and the base of such mass was about 5 °C. These are very homogeneous temperature conditions when compared with similar systems of known type. [00140] The present invention relates to a process for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons. [00141] The process according to the invention is carried out in a plant for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons, in particular as the one object of the present invention and in particular as described above. For this reason, the process is described below using the same numerical references used to describe the depolymerization plant 1. For the description of the depolymerization plant in which the process according to the invention is carried out, reference is made to the previously made description of the plant 1. In addition, the advantages obtainable by the process according to the invention are the same as those described in conjunction with the plant 1. For simplicity of disclosure, the advantages of the process according to the invention will not be described again either. [00142] According to a general embodiment of the invention, the process for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons is carried out in a plant 1 for the thermo-catalytic depolymerization of polyolefin plastic materials according to the invention and comprises the following operational steps:

[00143] - a) feeding polyolefin plastic materials and a catalyst into the reactor 10 through the feed opening 15; [00144] - b) heating the mass of polyolefin plastic materials and catalyst at a temperature between 380°C and 450°C by the heating means 17 of the reactor 10 to trigger, in the presence of the catalyst, pyrolysis reactions of the polyolefin plastic materials with at least partial depolymerization thereof and production of relatively low boiling hydrocarbon leaving the reactor 10 in vapor phase through the outlet opening 16; and [00145] - c) recirculating - during said b) heating step - a part of the mass of polyolefin plastic materials and catalyst contained in the reactor through at least one external recirculation chamber 20, 30, simultaneously heating said recirculated part to a temperature between 380 °C and 450 °C through the heating means 24, 34 of said recirculation chamber 20, 30, so as to generate descending motions in the mass of polyolefin plastic materials and catalyst inside the reactor. [00146] The aforementioned descending motions inside the reactor 10 and the heat fed inside said recirculation chamber 20, 30 reduce the thermal gradients in the mass of polyolefin plastic materials and catalyst. [00147] The catalyst is selected so as to favor the depolymerization reaction of the polyolefin plastic materials. Non-limiting examples of catalysts which may be used for this purpose are described in US4584421, the content of which is referred to in its entirety for the sake of completeness of description. Preferably, the catalyst consists of natural zeolite.

[00148] Preferably, in said feeding step a) the polyolefin plastic materials are fed to the reactor 10 in a fluid state, after having passed through the heated extruder 41, which by mechanical compression action and heating action causes the softening of the polyolefin plastic materials.

[00149] Preferably, the catalyst is fed into the reactor 10 together with the plastic materials, premixed therewith in the extruder 41.

[00150] [00150] Preferably, the aforesaid feeding step a) is performed by means of a first external recirculation chamber 20 which acts as a fluidic connection between the extruder 41 and the reactor 10. [00151] Preferably, the polyolefin plastic materials fed to the reactor consist of waste polyolefin materials, which even more preferably consist of 95% by weight of polyolefins.

[00152] Preferably, the waste polyolefin materials consist of one or more polymers selected from the group consisting of polyethylene, polypropylene, polybutadiene and polystyrene.

[00153] Advantageously, the thermo-catalytic depolymerization process comprises a step d) of pre- treating said waste polyolefin materials separately, separating them into two types:

[00154] - waste polyolefin materials having structural rigidity; and

[00155] - waste polyolefin materials without structural rigidity.

[00156] Advantageously, in the aforesaid pre-treatment step d) the waste polyolefin materials having structural rigidity are shredded to reduce them to a material having a predefined homogeneous size. [00157] Advantageously, in the aforesaid pre-treatment step d) the waste polyolefin materials without structural rigidity are agglomerated and densified so as to obtain higher density material having a predefined homogeneous size. [00158] Preferably, the waste polyolefin materials without structural rigidity are agglomerated and densified so as to obtain higher density material having a predefined homogeneous size, by means of a continuous densification treatment for low-melting plastics comprising:

[00159] - a plasticization of the material by friction with rotating blades so as to raise the temperature of the material itself and make it homogeneous and with a higher density; [00160] - a solidification of the homogeneous material, preferably by means of cooling with water jets; and [00161] - a shredding of the homogeneous solidified material by means of said rotating blades to reduce it to a predefined size, preferably in irregular spherical-like form, preferably having dimensions of about 2 mm in diameter.

[00162] Advantageously, after the pre-treatment step d), the aforesaid two types of waste polyolefin materials are mixed together and fed to the extruder 41 to be then sent to the reactor 10.

[00163] Preferably, the depolymerization process further comprises:

[00164] - a step e) of extracting the solid residue of the pyrolysis reactions from the reactor 10 through the extraction opening 19, preferably said step e) being carried out in discontinuous manner; and

[00165] - a step f) of concentrating said solid residue extracted from said reactor 10, wherein inside the concentration chamber 51 the solid residue is mixed at a temperature between 250 °C and 450 °C, evaporating the relatively low boiling hydrocarbon liquid fraction still present.

[00166] The concentrated solid residue is discharged from the bottom of said concentration chamber 51, while the relatively low boiling hydrocarbons are extracted from the top of said chamber 51 and collected together with the hydrocarbons leaving the reactor 10.

[00167] Preferably, the aforesaid step e) of extracting the solid residue is performed by means of a second external recirculation chamber 30 fluidically connected to the concentration chamber 51 temporarily.

[00168] Preferably, the depolymerization process further comprises a step g) of condensing the relatively low boiling hydrocarbons which in the vapor phase leave the reactor 10 and possibly the solid residue concentration chamber 51, separating the condensable fraction from the non-condensable fraction.

[00169] The invention allows numerous advantages to be obtained, which have already been described in part. [00170] The plant 1 for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons according to the invention allows more uniform temperature conditions to be obtained inside the thermo-catalytic depolymerization reactor. [00171] The plant 1 for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons according to the invention is capable of ensuring greater operating stability so as to achieve higher productivity. [00172] The plant 1 for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons according to the invention may be fed efficiently with industrial polyolefin plastic waste as raw material without penalizing the operating stability thereof.

[00173] The operating stability, in combination with homogeneous temperature conditions inside the reactor (which ensure high-yield and stable pyrolysis reactions), allows the production of hydrocarbons having a non- variable and controllable quality, these are important features (together with the type of fed plastic material) to allow the production of high quality diesel oil.

[00174] The plant 1 for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons according to the invention is operationally reliable and simple to manage.

[00175] The process for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons according to the invention allows the thermo-catalytic depolymerization of polyolefin plastic materials to be carried out under more uniform temperature conditions.

[00176] Finally, the process for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons according to the invention may be fed efficiently with industrial polyolefin plastic waste as raw material without penalizing the operating stability thereof.

[00177] The invention thus conceived therefore achieves its intended objectives.

[00178] Obviously, in practice it may also assume different forms and configurations from the one illustrated above, without thereby departing from the present scope of protection. [00179] Furthermore, all details may be replaced with technically equivalent elements, and the dimensions, shapes, and materials used may be any according to the needs.

Claims

1. Plant (1) for the thermo-catalytic depolymerization of polyolefin plastic materials for the production of hydrocarbons comprising a reactor (10) inside which pyrolysis reactions of polyolefin plastic materials are intended to occur in the presence of a catalyst, with the consequent at least partial depolymerization thereof and the production of relatively low boiling hydrocarbons, wherein said reactor (10) comprises: - at least one side wall (11), a bottom wall (12) and an upper wall (13) delimiting a reaction chamber (14), inside which the catalyst and polyolefin plastic materials are intended to be arranged; at least one feed opening (15) through which the polyolefin plastic materials and the catalyst are fed to said reactor (10) and which is obtained near the upper wall (13); at least one outlet opening (16) through which the relatively low boiling hydrocarbons leave the reactor and which is obtained near the upper wall (13);

- heating means (17) associated with at least one of the walls of said reactor, preferably the side wall (11); and

- an internal mixer (18); wherein said plant (1) comprises a system (60) for collecting the relatively low boiling hydrocarbons generated in said reactor which is fluidically connected to the outlet opening (16) of said reactor (10), characterized in that it comprises at least one external recirculation chamber (20; 30) of the polyolefin plastic materials mixed with the catalyst contained in the reactor (10), said at least one external recirculation chamber (20; 30) being:

- arranged outside the reactor;

- fluidically connected to the reaction chamber of the reactor by means of an upper opening (21; 31) obtained near the upper wall (13) of the reactor and a lower opening (22; 32) obtained near the bottom wall (12) of the reactor;

- provided with an internal mixer (23; 33) configured to impart, in use, to the polyolefin plastic materials mixed with the catalyst an upward motion through said recirculation chamber (20; 30) from the lower opening

(22; 32) to the upper opening (21; 31) so as to generate descending convective motions from the upper opening (21; 31) towards the lower opening (22; 32) in the reaction chamber; and

- provided with heating means (24; 34).

2 . Depolymerization plant (1) according to claim 1, comprising at least two separate external recirculation chambers (20; 30) of the polyolefin plastic materials mixed with the catalyst contained in the reactor (10), said at least two separate external recirculation chambers (20; 30) being arranged outside the reactor in diametrically opposite positions from each other and being fluidically connected to the reaction chamber (14) by means of separate upper openings (21; 31) and lower openings (22; 32).

3. Depolymerization plant (1) according to claim 1 or 2, wherein the internal mixer (18) of said reactor (10) is configured to mix the mass of polyolefin plastic materials and catalyst near the bottom wall (12) of the reactor (10) and to facilitate the movement of said mass towards the side wall (11) of the reactor (10).

4 . Depolymerization plant (1) according to claim 1, 2 or 3, wherein each recirculation chamber (20; 30) is delimited by a tubular body and wherein the internal mixer (23; 33) of each recirculation chamber (20; 30) comprises a plurality of blades which are distributed along the entire longitudinal extension of said tubular body and are rotatable around a rotation axis coaxial to said tubular body, and wherein preferably said plurality of blades comprises: mixing blades (23a) configured to impart to the polyolefin plastic materials mixed with the catalyst an upward motion along said tubular body; and chipping blades (23b) for breaking any solid parts present in the mass of polyolefin plastic materials and catalyst.

5 . Depolymerization plant (1) according to one or more of the preceding claims, comprising a system (40) for feeding polyolefin plastic materials and catalyst into said reactor (10), wherein said feeding system (40) comprises a screw extruder (41) which is provided with heating means (42) and is suitable to transform a mixture of polyolefin plastic materials and catalyst into a fluid mass to be fed to the reactor (10), preferably said screw extruder (41) being provided with a degasser (43).

6. Depolymerization plant (1) according to claim 5, wherein said feeding system (40) is fluidically connected to said reactor (10) indirectly through a first external recirculation chamber (20), said feed opening (15) of the reactor (10) coinciding with the upper opening (21) to which said first recirculation chamber (20) is connected, and wherein said first recirculation chamber (20) is provided with an inlet opening (25) for fluid connection with said feeding system (40), said screw extruder (41) being fluidically connected at the outlet to said first recirculation chamber (20) at said inlet opening (25).

7 . Depolymerization plant (1) according to any one of the preceding claims, wherein said reactor (10) comprises at least one extraction opening (19) through which the solid residue of the pyrolysis reactions is extracted from the reactor (10) and which is obtained near the bottom wall (12), and wherein said plant (1) comprises a system (50) for extracting the solid residue which is fluidically connected to said extraction opening (19).

8. Depolymerization plant (1) according to claim 7, wherein said extraction system (50) is fluidically connected to said reactor (10) indirectly through a second chamber (30) of external recirculation (20; 30), said extraction opening (19) of the reactor (10) coinciding with the lower opening (32) to which said second recirculation chamber (30) is connected, and wherein said second recirculation chamber (30) is provided with a discharge opening (35) at which the second chamber (50) is connected to the extraction system (50), the flow through said upper opening (31) being regulated by a first valve (36), while the flow through said discharge opening (35) being regulated by a second valve (37), said first valve (36) and said second valve (37) being drivable in a coordinated manner so that the flow through said upper opening (31) is alternative to the flow through said discharge opening (35), in use when the flow through said upper opening (31) is prevented, the mixer (33) of said second recirculation chamber imparting an upward movement to the solid residue accumulated on the bottom of the reactor (10) through said second recirculation chamber (30) from the lower opening (32) towards the discharge opening (35). 9. Depolymerization plant (1) according to claim 8, comprising a pump (38), preferably with gears, which is installed in a connection duct between the lower opening (32) of the reactor (10) and the second recirculation chamber (30) and is suitable to generate a flow towards said second recirculation chamber (30).

10 . Depolymerization plant (1) according to claim 7, 8 or 9, wherein said extraction system (50) of the solid residue comprises a concentration chamber (51) of the solid residue which: - is fluidically connected at the inlet to the discharge opening (35) of the second recirculation chamber (30);

- is provided with an internal mixer (52) and heating means (53); is fluidically connected to the outlet of the relatively low boiling hydrocarbon collection system (60) so that any amount of relatively low boiling hydrocarbons released by evaporation from the solid residue can be collected; and is provided with an opening (54) for the expulsion of the concentrated solid residue.

11 . Depolymerization plant (1) according to claim 10, wherein the internal mixer (52) of said concentration chamber (51) of the solid residue comprises a plurality of mixing augers (52a), which substantially engage the entire volume of the chamber (51), and a plurality of scraper blades (52b) which are configured to scrape at least the bottom of said chamber (51).

12 . Depolymerization plant (1) according to any one of the preceding claims, wherein said relatively low boiling hydrocarbons collection system (60) comprises: a two-phase separator (61), in which, in use, the relatively low boiling hydrocarbons generated in the plant (1) in the vapour state form a liquid/vapour mixture; - at least one condenser (62), connected to the two-phase separator (61) to receive the vapour phase of the liquid/vapour mixture and condense it so as to separate the fraction of non-condensable gases from the condensable fraction; - at least one condensable hydrocarbon collection tank

(63), which is connected to said two-phase separator (61) and to said at least one condenser (62) to collect the condensable fraction of the relatively low boiling hydrocarbons generated in said plant (1); and a system (70) for extracting non-condensable gases which is connected to said at least one condenser (62) to extract the non-condensable fraction of the relatively low boiling hydrocarbons generated in said plant (1).

13. Depolymerization plant (1) according to any one of the preceding claims, wherein said plant (1) is intended to be fed with polyolefin plastic materials consisting of waste polyolefin materials and wherein said system (40) for feeding polyolefin plastic materials and catalyst into said reactor (10) comprises a pre-treatment section (400) of said waste polyolefin materials which in turn comprises:

- a first pre-treatment line (410) intended for treating waste polyolefin materials having structural rigidity; and - a second pre-treatment line (420) intended to treat waste polyolefin materials without structural rigidity.

14. Depolymerization plant (1) according to claim 13, wherein said first pre-treatment line (410) comprises a shredding device (411) suitable to shred the waste polyolefin materials to reduce them to a material having a predefined homogeneous size, preferably said first pre treatment line (410) also comprising a sieving device (412) downstream of said shredding device (411).

15. Depolymerization plant (1) according to claim 13 or 14, wherein said second pre-treatment line (420) comprises means for agglomerating the waste polyolefin materials without structural rigidity, preferably said agglomeration means consisting of a densifier device for low-melting plastics (421) suitable to transform the waste polyolefin materials without structural rigidity into a higher density material having a predefined homogeneous size.

16. Depolymerization plant (1) according to claims 13, 14 or 15, wherein said pre-treatment section (400) of said waste polyolefin materials comprises a collection silo (430) into which the first (410) and the second (420) pre-treatment lines converge and wherein the collection silo (430) is provided with an internal mixer (431) for mixing the polyolefin materials coming from said two pre-treatment lines and obtaining a homogeneous mixture of said two materials.

17. Depolymerization plant (1) according to claims 5 and

16, wherein the collection silo (430) is connected to said screw extruder (41) to feed it with said homogeneous mixture of polyolefin materials from said two pre treatment lines.

18. Depolymerization plant (1) according to claim 17, wherein said system (40) for feeding polyolefin plastic materials and catalyst into said reactor (10) comprises a dispenser suitable to feed said screw extruder (41) with catalyst.

19. Thermo-catalytic depolymerization process of polyolefin plastic materials for the production of hydrocarbons characterized in that it is conducted in a thermo-catalytic depolymerization plant (1) of polyolefin plastic materials according to any one of the preceding claims, said process comprising the following operating steps:

- a) feeding polyolefin plastic materials and a catalyst into the reactor (10) through the feed opening (15);

- b) heating the mass of polyolefin plastic materials and catalyst at a temperature between 380°C and 450°C by the heating means (17) of the reactor (10) to trigger, in the presence of the catalyst, pyrolysis reactions of the polyolefin plastic materials with at least partial depolymerization thereof and production of relatively low boiling hydrocarbon leaving the reactor (10) in vapour phase through the outlet opening (16); and

- c) recirculating - during said b) heating step - a part of the mass of polyolefin plastic materials and catalyst contained in the reactor through at least one external recirculation chamber (20; 30), simultaneously heating said recirculated part to a temperature between 380°C and 450°C through the heating means (24; 34) of said recirculation chamber (20; 30), so as to generate descending motions in the mass of polyolefin plastic materials and catalyst inside the reactor, wherein said descending motions inside the reactor (10) and the heat supplied inside said recirculation chamber (20; 30) reduce the thermal gradients in the mass of polyolefin plastic materials and catalyst.

20. Method according to claim 19, wherein in said feeding step a) the polyolefin plastic materials are fed to the reactor (10) in a fluid state, after having passed through the heated extruder (41), which by mechanical compression action and heating action causes the softening of the polyolefin plastic materials, and wherein preferably said catalyst is fed into said reactor together with said plastic materials, premixed therewith in said extruder (41).

21. Process according to claim 19 or 20, wherein the feeding step a) is performed by means of a first external recirculation chamber (20) which acts as a fluidic connection between the extruder (41) and the reactor (10).

22. Process according to claim 19, 20 or 21, wherein the polyolefin plastic materials fed to said reactor consist of waste polyolefin materials, preferably consisting of 95 % by weight of polyolefins, and wherein said process comprises a step d) of pre-treating said waste polyolefin materials separately, separating them into two types:

- waste polyolefin materials having structural rigidity; and

- waste polyolefin materials without structural rigidity. 23. Process according to claim 22, wherein in said pre treatment step d) the waste polyolefin materials having structural rigidity are shredded to reduce them to a material having a predefined homogeneous size.

24 . Process according to claim 22 or 23, wherein in said pre-treatment step d) the waste polyolefin materials without structural rigidity are agglomerated and densified so as to obtain higher density material having a predefined homogeneous size, preferably by means of a continuous densification treatment for low-melting plastics comprising: a plasticization of the material by friction with rotating blades so as to raise the temperature of the material itself and make it homogeneous and with a higher density; - a solidification of the homogeneous material, preferably by means of cooling with water jets; and

- a shredding of the homogeneous solidified material by means of said rotating blades to reduce it to a predefined size, preferably in irregular spherical-like form, preferably having dimensions of about 2 mm in diameter.

25. Process according to claim 22, 23 or 24, wherein said two types of waste polyolefin materials, after the pre-treatment step d), are mixed together and fed to the extruder (41) and then sent to the reactor (10).

26. Process according to any one of claims 19 to 25, comprising: a step e) of extracting the solid residue of the pyrolysis reactions from the reactor (10) through the extraction opening (19), preferably said step e) being carried out in discontinuous manner; and

- a step f) of concentrating said solid residue extracted from said reactor (10), wherein inside the concentration chamber (51) the solid residue is mixed at a temperature between 250°C and 450°C, evaporating the relatively low boiling hydrocarbon liquid fraction still present, wherein the concentrated solid residue is discharged from the bottom of said concentration chamber (51), while the relatively low boiling hydrocarbons are extracted from the top of said chamber (51) and collected together with the hydrocarbons leaving the reactor (10).

27. Process according to claim 26, wherein said step e) of extracting the solid residue is performed by means of a second external recirculation chamber (30) fluidically connected to the concentration chamber (51) temporarily.

28 . Process according to any one of claims 19 to 27, comprising a step g) of condensing the relatively low boiling hydrocarbons which in the vapour phase leave the reactor (10) and possibly the solid residue concentration chamber (51), separating the condensable fraction from the non-condensable fraction.