IT202300001860A1 - PROCESS FOR PRODUCING PYROLYSIS OIL INCLUDING LIQUID HYDROCARBONS FROM PLASTICS WITH HIGH EXERGETIC EFFICIENCY AND RELATED PLANT - Google Patents

Description

Process for producing a pyrolysis oil comprising liquid hydrocarbons from plastic material with high exergy efficiency, and related plant

Description

The present invention relates to a sustainable process for producing a pyrolysis oil comprising liquid hydrocarbons from plastic material, preferably waste material.

The field of application is the pyrolysis of plastic material to produce a pyrolysis oil comprising hydrocarbons. After further treatment, this pyrolysis oil can be converted into monomers useful for producing polymers, thus closing the cycle.

In the chemical industry and more specifically in polymers, it is increasingly strategic not only to recycle them but also to be able to do so in a sustainable way. In fact, a "closed cycle" recycling process that is "closed" in terms of the material but not the energy required (i.e. it uses fossil fuels or any energy that comes mainly from these sources) is not truly closed, especially considering the remarkably high amount of thermal energy required for the pyrolysis process. Consequently, the resulting carbon footprint can be so large that it endangers the effectiveness of the entire recycling cycle, making the process no longer appropriate.

An integrated solution, such as the new proposal, not only allows the use of "green" energy, but also maximizes its effectiveness. This improvement in efficiency is significant, considering that the low solar irradiation and the high concentration factor required determine a high value of land surface per unit of pyrolysis oil produced.

However, the process that can close the plastics cycle and which, consequently, can be extremely desirable requires significant amounts of thermal energy at high temperatures. For this purpose, the combustion of natural gas and/or electricity is conventionally used, which, in turn, is largely obtained using the combustion of carbonaceous materials (gas, hydrocarbons, coal). Consequently, the carbon footprint of the process is high.

There are known technological solutions that use solar rays as an energy source for gasification processes (therefore very similar to the pyrolysis of plastic materials). Typically, in these processes, solar rays are concentrated directly on an absorber located in the reactor or on its external surface. In other processes (for example, for the pyrolysis of biomass), a heat transfer fluid with molten salts is used, but obviously it must be brought at least to the maximum temperature required for pyrolysis.

Consequently, the use of solar radiation as an energy source may be a known solution, however the solutions illustrated so far have serious limitations, including in particular the fact that heating a fluid to the required temperature by the pyrolysis process (or direct heating of the pyrolysis reactor) requires significantly high temperatures, i.e. requiring a significantly high concentration factor which is associated with a significantly reduced efficiency, the latter being linked, among other factors, to the drastic increase in emissivity of the absorber tubes, so that a large part of the radiant energy is re-emitted into the environment. This implies the use of a significantly high surface area of mirrors for a given fixed production of pyrolysis oil.

Consequently, a pyrolysis process that allows the use of solar energy is desirable, but which limits the amount of radiant surface required for a given production. The solution of the present invention achieves this goal.

Several patent applications illustrate processes of thermal or catalytic pyrolysis of plastic materials. Some of them address the possibility of using solar energy.

U.S. Patent 4,415,339, Department of Energy (DOE), teaches a method of producing substantially hydrocarbon-free product gas (synthesis gas) from a carbonaceous feedstock in a solar reactor, which method includes directing solar energy into the reactor. The solar energy is supplied directly, that is, by means of a window through which solar rays can pass and heat the gasification materials.

US 4,582,590 (National Aeronautics and Space Administration) illustrates a method of shale pyrolysis involving the use of concentrated solar radiation. Solar radiation passes through a “solar window” to a honeycomb ceramic receiver which is subsequently heated to 350 ?C.

WO 2010/103520 illustrates a solar-powered device for converting sludge by pyrolysis, which includes a pyrolysis reactor that can be driven by solar energy. This solar energy is concentrated and redirected to the receiver located inside the pyrolysis reactor by means of focusing mirrors. The reactor is deactivated when a sensor detects that the radiation intensity of sunlight falls below a threshold.

WO 2017/055652 (Department of Energy) describes a solar hybrid power plant comprising a molten salt solar receiver configured to heat the molten salts using solar energy. There is a cold storage tank and a hot salt storage tank, a steam generator, a condenser and a salt-biomass exchanger-reactor to exchange heat between a continuous flow of salts and the biomass.

CN109207179 illustrates a system for producing synthesis gas through concentrated solar molten salt pyrolysis of carbonaceous material. For example, the carbonaceous material can be rice husks, cotton straw residues, corn straw residues, and municipal household waste, and the temperature can be above 800 ?C, for example 1000 ?C.

WO/2020/150244 (Sabic) illustrates the use of renewable energy in olefin synthesis. In the claimed plant, at least one of the furnaces is an electrified furnace, in which at least 90% of the heating is produced without combustion of a fuel.

None of the cited patents illustrate a process for treating plastic materials to produce a pyrolysis oil, using a solar energy source. Furthermore, in many cases, solar energy is used directly, for example by focusing solar radiation directly onto an absorber surface that is located inside the reactor.

Some patent applications illustrate the use of a molten salt as a heat transport medium to produce synthesis gas from biomass (such as municipal household waste, cotton straw and corn, rice husks). Biomasses are chemically quite different from plastics and the product (synthesis gas) is completely different from pyrolysis oils. Consequently, the required operating conditions, such as temperature, are quite different (even above 1000 °C). Typically this process is not capable of performing the task of the present invention: for example, as illustrated in the cited CN109207179, the used molten salts melt at about 400 °C. Generally, it is not safe to use molten salts close to their melting point to avoid a solidification of the salt mixture in the apparatus, which means that it is not possible to use that process for the pyrolysis of plastics, which requires a temperature of 400-520 °C.

Pyrolysis of plastics is a highly desirable process because it allows recycling mixed waste plastics by breaking the polymer chains into small organic molecules that, after appropriate refining processes, can be used in polymer synthesis. Most other recycling processes, such as so-called mechanical recycling (i.e. extruding waste plastic with virgin plastic to produce a blend) require the use of highly pure plastic waste (i.e. comprising only one specific polymer, for example expanded polystyrene or linear low-density polyethylene or polyethylene terephthalate). In fact, different polymers are not compatible with each other and, consequently, blending such a polymer blend with a specific virgin polymer drastically reduces its performance.

Other recycling processes, such as solvent dissolution and precipitation, can be used specifically to dissolve a specific plastic material, so that a nearly pure polymer can be precipitated. However, extremely large amounts of solvent are required, and it is also necessary to remove the plastic that does not dissolve and to purify the solvent from all dissolved and dispersed contaminants (such as short-chain molecules, inorganic additives that are used as fillers, and the like). Furthermore, the process is only available for selected plastics, as it is quite difficult to dissolve polyolefins, for example.

Plastic pyrolysis has the key advantage that it can work effectively with mixed plastic waste, even in the presence of non-plastic waste materials such as paper; furthermore, unlike other techniques, it has the ability to recycle mixed plastic waste in an unlimited manner, i.e. there are unlimited cycles: production of plastic from monomers, use of the plastic, collection of the related waste after use, and production of monomers by pyrolysis of the related waste; then closing the loop. For this reason, this process is often referred to as ?closed loop recycling?.

However, this is a highly endothermic process and, therefore, requires a large amount of heat energy. Furthermore, since the required pyrolysis temperature is quite high (> 500 °C), a large amount of heat (i.e., high exergy) is required. Consequently, only a few energy sources can be used for this purpose. Typically, this energy source is a gas heater (burning natural gas and/or non-condensable gases produced by the pyrolysis process itself) or by direct electrical heating via the Joule effect. Electrical energy has an extremely high exergy content and is not suitable for use with Joule heating. Furthermore, both electrical energy and gas heating contribute significantly to the carbon footprint, since the combustion of hydrocarbons produces large amounts of carbon dioxide (CO2) and, in most countries, electrical energy is produced from gas, oil or carbon combustion. Furthermore, due to the high temperature, it is practically not feasible to use heat pumps to pump heat from lower energy heat sources (such as steam or geothermal energy).

Consequently, there is a high risk that the unlimited recycling capacity of pyrolysis (?closed loop recycling?) is in fact limited by the fact that large quantities of valuable and/or non-environmentally friendly energy sources have to be used.

As previously reported, some patents illustrate the use of direct sunlight, collected and concentrated by focusing mirrors, directly to a receiver located in the reactor chamber to produce synthesis gas. However, sunlight is a discontinuous source and, consequently, synthesis gas production may stop soon after a decrease in sunlight. Since these processes require high temperature and an extended period of time to stabilize, the use of direct sunlight is a serious limitation to their practical implementation.

Consequently, there has long been a need for a process to produce pyrolysis oil from essentially plastic materials that uses a heat source with virtually no impact on CO2 production and that is able to use this energy source efficiently.

SUMMARY OF THE INVENTION

The Applicant has surprisingly discovered a process for producing at least one pyrolysis oil from essentially plastic materials which comprises the steps of:

a) heating a first heat transfer fluid F1 to a temperature T1 between 400 ?C and 520 ?C by means of solar radiation;

b) heating a second heat transfer fluid F2 to a temperature T2 higher than the temperature T1 by means of solar radiation;

c) heating a first pyrolysis reactor R1 by means of the first heated heat transfer fluid F1 which is consequently cooled during the operation;

d) heating a second pyrolysis reactor R2 by means of the second heated heat transfer fluid F2 which is consequently cooled during the operation;

e) feed the first pyrolysis reactor R1 with at least one essentially plastic material M1;

f) maintaining said essentially plastic material M1 in said first pyrolysis reactor for a residence time RT1 which is at least 2 minutes and in any case sufficient to produce a gaseous fluid M2 containing hydrocarbons;

g) feeding said gaseous fluid M2 containing hydrocarbons produced in the first pyrolysis reactor R1 to a second pyrolysis reactor R2;

h) maintaining said fluid in the gaseous state M2 in said second pyrolysis reactor for a residence time RT2 which is at least 10 seconds;

(i) condensing, totally or partially, the gas exiting from said second pyrolysis reactor R2 so as to form at least a liquid comprising hydrocarbons having a standard boiling point of not less than 25 °C.

The process illustrated and claimed in the present invention has the following advantages over processes known in the prior art:

- ready for closed-loop recycling: The illustrated process is capable of producing liquid hydrocarbons which, after further processing (e.g. by cracking and/or refining), can be used to produce polymers. After use, articles made from these polymers can be fed back into the illustrated process. The process can be repeated indefinitely. As a result, plastic materials can be recycled virtually an infinite number of times. - GHG emission-free: The heat required for the pyrolysis process is obtained without direct and/or indirect production of greenhouse gases (such as carbon dioxide, CO2).

- efficient use of molten salt heat transfer fluid: the heat transfer fluid, which is preferably molten salt, is the same for both the solar system and the pyrolysis system, so that the same fluid can flow in both systems. As a result, there is no need for expensive heat exchangers.

- maximized use of solar energy: Solar energy is a valuable source, especially when high temperature heat is required. In fact, in this case a high concentration factor is required, which in turn means that a large area of incoming solar radiation has to be reflected onto a relatively small area of heat. The specific synergic process configuration illustrated in the present application is able to address this very specific problem, since the provided solution is in fact able to reduce the average concentration factor required, as will be shown later.

- ready for mixed plastic and plasmix waste:

Preferably, the process is fed with mixed waste plastic materials, hence, no or little preliminary processing is required and there is no need to feed unique material sources such as essentially pure polyethylene. Even more preferably, the process is fed with residual plastics after the sorting process has already sorted and extracted the unique materials (in particular, polymers that can be reused as such when contamination is low, such as polyethylene terephthalate (PET) and low density polyethylene (LDPE)). Such a feed is sometimes referred to as a “Plasmix” (from “plastic mix”). The essentially plastic material that may be fed to the process may contain minor amounts of non-plastic materials, such as wood, paper, concrete, metals and biomass. Plastics including inorganic fillers and halogens (such as polyvinyl chloride) may also be fed and processed.

- scale-free: the process is free from scale and carbon build-up, blockages, even when the essentially plastic material being fed is rich in high carbon/hydrogen ratio plastics such as polystyrene or oxygen-rich polymers such as polyethylene terephthalate.

The present invention also discloses and claims a system for producing at least one pyrolysis oil from essentially plastic materials which comprises:

A) a first pyrolysis reactor 70 which has at least one inlet into which an essentially plastic material is fed, an outlet into which at least one gaseous effluent is removed, and a jacket and/or coil equipped with at least one inlet and one outlet for molten salts;

B) a second pyrolysis reactor 71 which has at least one inlet into which at least one continuous gaseous flow is fed from the reactor 70, an outlet into which at least one gaseous effluent is removed, and a jacket and/or coil equipped with at least one inlet and one outlet for molten salts;

C) a first tank 63, also called the "cold tank", in which the low-temperature molten salts are collected;

D) a second tank 64, also called the "warm tank", in which the molten salts at medium temperature are collected;

E) a third tank 65, also called the "hot tank", in which the molten salts at high temperature are collected;

F) a first solar collector assembly 61 comprising a first solar receiver, the latter comprising at least one inlet and one outlet for molten salts, wherein said solar collector assembly is capable of delivering concentrated solar radiation to said first solar receiver which, in turn, is configured to heat said molten salts; G) a second solar collector assembly 62 comprising a second solar receiver, the latter comprising at least one inlet and one outlet for molten salts, wherein said solar collector assembly is capable of delivering concentrated solar radiation to said second solar receiver which, in turn, is configured to heat said molten salts;

H) a condenser 72 with at least one inlet for the continuous gaseous flow comprising hydrocarbons and an outlet for the condensed liquid, which is capable of at least partially condensing the continuous gaseous flow comprising hydrocarbons;

wherein said first solar collector 61 is fluidly connected to said first tank 63 at one end of the tube receiver and to said second tank 64 at the other end of the tube receiver; and wherein said second solar collector 62 is fluidly connected to said second tank 64 at one end of the tube receiver and to said third tank 65 at the other end of the tube receiver; wherein said first tank 63 and second tank 64 are fluidly connected to said jacket and/or coil of said first pyrolysis reactor 70; wherein said second tank 64 and third tank 65 are fluidly connected to said jacket and/or coil of said second pyrolysis reactor 71; wherein said condenser 72 is fluidly connected to said second pyrolysis reactor 71, so as to be able to partially condense the pyrolysis vapours produced by said first and second pyrolysis reactors.

DEFINITIONS

In the description of the present invention, unless otherwise indicated, range values (e.g. ranges of pressure, temperature, quantity, etc.) which include the extreme values are to be considered.

In the description of this invention, unless otherwise indicated, percentages are by weight (i.e., mass). The symbol "%" indicates percent, unless otherwise indicated, by weight (mass).

In the description of the present invention, the term "comprising" also includes as a particular limiting case its meaning as "consisting of" and "essentially consisting of".

In the description of the present invention, the term essentially consisting of? means that the composition or formulation (i) necessarily includes the listed ingredients and (ii) is open to non-listed ingredients that do not materially affect the basic properties and novel properties of the composition.

In the description of the present invention, unless otherwise indicated, the act of maintaining a certain parameter (e.g. pressure) within a specified range means that operations are actively performed so that this parameter falls within the range, for example by checking that the measured value falls within the specified range, and/or by adjusting the parameter by means of a feedback regulation system in which a value of this parameter is set within the specified range.

In the description of the present invention, with "essentially plastic material" is indicated a composition of one or more plastics, optionally comprising up to 30% by weight, based on the weight of the essentially plastic material, of non-plastic materials.

In the description of the present invention, "plastic material" means a generic polymeric material that may contain other substances to improve performance and/or reduce costs, as per the IUPAC (Pure Appl.

Chem. Volume 84 n? 2, pages 377-410, 2012).

In the specification of the present invention, ?hydrocarbons having a standard boiling point not lower than 25 ?C? means that such hydrocarbons individually have a standard boiling point, as defined by IUPAC, of at least 25 ?C (i.e., at or above 25 ?C).

In the description of the present invention, the act of condensing, totally or partially, the gas exiting from said second pyrolysis reactor R2 so as to form at least one liquid comprising hydrocarbons having a standard boiling point not lower than 25 °C does not exclude that such liquid may also comprise hydrocarbons having a boiling point below 25 °C, and non-hydrocarbon compounds.

In the description of the present invention, ?pyrolysis vapors? means the gaseous phase which is produced in the pyrolysis of the essentially plastic material, such as the gaseous effluent of the first pyrolysis reactor. The latter contains the pyrolysis product, but also compounds which are in the gaseous state under the pyrolysis pressure and temperature conditions which were already present in the essentially plastic material subjected to pyrolysis or added to or already present in the first pyrolysis reactor (for example, in the inert gas) such as nitrogen, water or low boiling point plasticizers. In the pyrolysis vapors, the hydrocarbon content is typically greater than 50% by weight.

In the description of the present invention, pyrolysis oil means the liquid formed by partial or total condensation of pyrolysis vapors and which comprises hydrocarbons having a standard boiling point not lower than 25 °C. In pyrolysis oil, the hydrocarbon content typically exceeds 50% by weight.

In the description of the present invention, pyrolysis residue (or equivalently char) means the product which is in the liquid, solid or liquid and solid (i.e. semi-solid) state in the first pyrolysis reactor or which is in the liquid and/or solid state under the conditions of temperature, pressure and composition in the pyrolysis.

In the description of the present invention, unless otherwise indicated, by substantially absent oxygen it is meant that the oxygen (including molecular oxygen) in the pyrolysis vapors is less than 2% by weight, preferably less than 0.8% by weight, even more preferably between 20 and 4000 ppm by weight, with respect to the total weight of the composition of said vapors.

In the description of the present invention, "heat transfer fluid" means a solid, liquid, gaseous or multiphase fluid that is used to transfer heat from one system to another, in particular from a heat source to other heat demands (heat demand). Preferably, heat transfer fluids are fluids specifically manufactured for the purpose of transferring heat and which are stable (i.e. do not degrade rapidly) under the process conditions used.

In the description of the present invention, the first heat transfer fluid need not be different in composition from the second heat transfer fluid, however, they preferably have different temperatures.

In the description of the present invention, ?SCA? means the solar collector assembly which generally comprises reflectors (mirrors, such as Fresnel reflectors, or parabolic mirrors in the case of parabolic cylinders), the metal support structure, the one or more receiver tubes and optionally the tracking system which includes the drive, sensors and controls. The length of the receiver tubes does not have to be equal to the length of the reflector, since several receiver tubes can be connected in series to form a longer receiver tube (so that a length greater than 200 m can also be obtained) which, in turn, can receive the sunlight radiation from multiple mirrors/reflectors in series. Furthermore, in order to optimize the weight flow rate of the heat transfer fluid in the receiver tubes, as well as to maximize the solar radiation, it is useful to divide the flow of the heat transfer fluid to be heated into several absorber tubes in parallel. For this reason, in the description of the present invention, the solar collector assembly generally comprises a plurality of reflectors (mirrors, such as Fresnel reflectors, or parabolic mirrors in the case of parabolic cylinders). of mirrors/reflectors and related absorber tubes, preferably combined in series, in parallel and in series-parallel combinations.

In the description of the present invention, "molten salt" or equivalently, "molten salts" means a salt that is solid at standard temperature and pressure but enters the liquid phase due to the elevated temperature. Molten salts may be composed of a single component (for example, only sodium nitrate) or a mixture of salts (for example, a mixture of sodium and potassium nitrate).

In the description of the present invention, by "charged device" is meant any device that is heated by means of the heat transfer fluid. Examples of "charged device" are the first and second pyrolysis reactors, the coker, the preheater.

In the description of the present invention, the terms "fluid cycle", "heat transfer fluid cycle", "hot cycle", and "warm cycle" mean processes by which the heat transfer fluid is recirculated substantially entirely in the process.

By substantially entirely recirculated is meant that the heat transfer fluid is not generated or consumed in the process, so there is no continuous net inflow or outflow; however, where appropriate, the fluid may be spilled or slowly replaced, particularly since most heat transfer fluids are known to degrade over time at elevated temperatures. Preferably, a substantially entirely recirculated fluid has a total inflow or outflow weight flow rate that is less than 1% of the recirculation weight flow rate, even more preferably less than 0.1%.

In the description of the present invention, unless otherwise indicated, a value of a parameter that is mostly equal to a given value X means that the parameter is equal to X or less than X; and a value of a parameter that is at least equal to a given value X means that the parameter is equal to X or greater than X.

In the description of the present invention, unless otherwise indicated, yield in the production of a product means the percentage by weight of that product with respect to the total of the products obtained.

Unless otherwise indicated, in this document "part" and "parts" mean part by weight and parts by weight, respectively. Weight means mass, i.e. kg in YES units.

Unless otherwise indicated, in this document the combination of a single range from one list with another single range that comes from a second list of ranges and relates to a different characteristic shall be considered as illustrated in the application, even in the absence of a clear indicator of such a combination.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an illustrative process diagram of an embodiment of the present invention, featuring three heat transfer fluid tanks and two pyrolysis reactors.

Figure 2 shows an illustrative process diagram of one embodiment of the present invention featuring the addition of a plastic preheater (such as an extruder or screw device).

Figure 3 shows an illustrative process scheme of an embodiment of the present invention, featuring the addition of an additional device (?coking device?) that additionally treats the liquid/solid/semi-solid residue (char) effluent from the reactor.

Figure 4 shows an illustrative process scheme of an embodiment of the present invention, characterized by the presence of both said coking device which additionally treats the liquid/solid/semi-solid residue (char) effluent from the reactor, and the plastic preheater (such as an extruder or screw device).

Figure 5 shows an illustrative process diagram of an embodiment of the present invention, characterized in that the condensation of the pyrolysis gas is carried out in more than one unit, and wherein the first of such units of said pyrolysis gas is cooled by the heat transfer fluid before entering the cold tank, thereby providing a heat recovery unit.

Figure 6 shows an illustrative process diagram of an embodiment of the present invention, characterized in that the heat transfer fluid exiting the warm tank is delivered to the first pyrolysis reactor and the semi-series preheater device by means of a weir device 78 before returning to the cold tank.

Figure 7 shows an illustrative process diagram of an embodiment of the present invention, characterized in that the heat transfer fluid exiting the hot tank is delivered to the coker and the second semi-series pyrolysis reactor by means of a weir device 79 before returning to the cold tank.

Figure 8 shows a process diagram with a dual heat transfer fluid circuit, corresponding to Example 1 (of the invention).

Figure 9 shows a process diagram with a single heat transfer fluid circuit, corresponding to Example 2 (comparative).

Figure 10 shows an illustrative process diagram of an embodiment of the present invention, characterized in that the first heat transfer fluid and the related heat transfer fluid cycle are not in fluidic connection with the second heat transfer fluid and the related heat transfer cycle.

Figure 11 shows an illustrative process diagram of some embodiments of the present invention, characterized in that the location of the additional power sources is shown in three different positions (66A for parallel arrangement, 66B and 66C for series arrangement).

Figure 12 shows an illustrative process diagram of one embodiment of the present invention, featuring the use of three tanks and focusing to show the hot and warm cycles and their distinction.

Figure 13 shows an illustrative process diagram of one embodiment of the present invention, featuring the use of four tanks and two completely independent cycles, focusing on showing the hot and warm cycles and their distinction.

Figure 14 shows an illustrative process diagram of an embodiment of the present invention, featuring three tanks and two fully independent or partially independent cycles.

DETAILED DESCRIPTION OF THE INVENTION

According to one embodiment, the process for producing at least one pyrolysis oil from essentially plastic materials is characterized in that the fluids F1 and F2 are recirculated substantially in their entirety.

A first embodiment of the present invention is shown in Figure 1. The scheme comprises:

- a first pyrolysis reactor 70 (at lower temperature), also referred to as the primary pyrolysis reactor;

- a second pyrolysis reactor 71 (at a higher temperature), also referred to as a secondary pyrolysis reactor;

- a condenser 72 which condenses the effluent of the second pyrolysis reactor 71;

- a separator 73 which separates the gaseous phase (not condensed) from the liquid phase;

- a medium temperature solar collector group 61 (SCA); - a high temperature solar collector group 62 (SCA); - a cold heat transfer fluid tank 63;

- a warm tank of heat transfer fluid 64;

- a hot tank of heat transfer fluid 65;

- heat transfer fluid pumps 66 that deliver the heat transfer fluid to the heating system (solar receivers) and applications (pyrolysis reactors);

- optional bypasses from B1 to B4.

The essentially plastic material 51 is fed to the first pyrolysis reactor 70 which is heated by the medium temperature heat transfer fluid 33 coming from the warm tank 64. The heat transfer fluid coming from the first pyrolysis reactor 70 (consequently, at a lower temperature) is brought to the cold tank 63.

The pyrolysis gases evolved in reactor 70 are delivered to the second pyrolysis reactor 71, which is at a higher temperature than the first pyrolysis reactor 70, while the solid or semi-solid residue (such as char) is recovered in 53.

In some embodiments, a portion of the liquid contained in the reactor 70 can also be recovered from 53.

In the second pyrolysis reactor 71, the pyrolysis gas from the first reactor 70 is further heated to a higher temperature by means of the heat transfer fluid 37 from the hot tank 65. As a result, in the second reactor 71 the gases are further pyrolyzed. The effluent from the second reactor 71 is cooled and condensed by means of the condenser 72. The gases which are not condensed are recovered in 55. The condensate forms the pyrolysis oil which is collected in the tank 73 and recovered in 56. The tank 73 can be integrated into the condenser 72. The heat transfer fluid exiting the second pyrolysis reactor is led to the warm tank 64.

Optional B1 to B4 bypasses are useful for recharging tanks, without having to pass through the heating system and applications (for maintenance and/or to decouple the flow from the thermal demand).

The medium temperature solar collector group (SCA) 61 heats the heat transfer fluid 31 from the cold tank 63, while the high temperature solar collector group 62 heats the heat transfer fluid 35 from the warm tank 64. From the medium temperature solar collector group 61 the heat transfer fluid is carried to the warm tank 64, while from the high temperature solar collector group 62 the heat transfer fluid is carried to the hot tank 65.

According to a preferred embodiment, the heat transfer fluid in a cycle is heated by at least one solar collector assembly and is cooled, releasing its heat, in at least one pyrolysis reactor before returning to the solar collector assembly (possibly passing through a heat transfer fluid tank).

According to a preferred embodiment, in the process for producing at least one pyrolysis oil from essentially plastic materials, fluids F1 and F2 are recirculated substantially in their entirety.

Preferably, the process of the present invention is a double-loop process (or alternatively ?two-loop process?).

This means that there are two substantially independent thermal cycles: in the so-called "warm temperature thermal cycle" (or more synthetically "warm cycle"), the heat transfer fluid F1 is heated from a low temperature to a "warm" temperature by means of a first solar collector group (at a lower temperature). This fluid is used in the first pyrolysis reactor and optionally in other devices as conceived in the illustration of the present invention.

In the so-called ?hot temperature thermal cycle? (?hot cycle?), the heat transfer fluid F2 is heated from a ?warm? temperature to a ?hot? temperature by means of a second solar collector assembly. This fluid is used in the second pyrolysis reactor and optionally in other devices as conceived in the illustration of the present invention.

According to a preferred embodiment, the recirculation of the fluid F1 forms a first heat transfer fluid cycle (?warm cycle?) and the recirculation of the fluid F2 forms a second heat transfer fluid cycle (?hot cycle?).

In the double-loop process, it is possible that the molten salt fluids of the two cycles mix at some point (typically in the warm tank). However, the essential feature that distinguishes the double-loop process from the single-loop process is that the heat transfer fluid is at least partially extracted from at least two points of the one or more solar collector groups (F1, F2) at different temperatures (T1, T2) and used at least partly separately to heat the pyrolysis devices (such as reactors) at different temperatures.

By ?used at least partly separately? it is meant that there are at least two distinct circuits (?hot cycle?, ?warm cycle?) in which the heat transfer fluid flows and in which the charged devices (such as pyrolysis reactors) are fluidically connected.

According to one embodiment, said first heat transfer fluid F1 and said second heat transfer fluid F2 have the same composition but at a different temperature. According to one embodiment, at a certain point the fluids F1 and F2 may mix, preferably when they have substantially the same temperature.

According to one embodiment, said first heat transfer fluid F1 and said second heat transfer fluid F2 have the same composition, but at different operating temperatures (T1 and T2), and mix at a single point, preferably in a tank (such as the ?warm tank?).

A simplified view of this embodiment is shown in Figure 12, which is provided to clearly show the flow of the heat transfer fluid in each cycle. In Figure 12, it is observed that in the “warm” tank 64 the two cycles mix together, however, the two cycles are kept substantially distinct since there is only a single point of contact. In Figure 12, the dotted box has been placed around the coker 76 and preheater 74 to show that they are optional. The dotted lines in the tanks show the direction of flow within the tank.

Cold, hot and warm tanks may optionally include some mixing features, such as an internal recirculation pump or an agitator, such as an anchor agitator, turbine agitator or inclined-vane impeller. Such mixing means improve the homogenization of the tank temperature and, in particular, can be particularly useful at start-up.

However, even without such mixing feature, the flow of the heat transfer fluid from the inlets to the outlets and the natural convection contribute to a certain degree of internal recirculation and mixing in the tanks. Consequently, the said dotted lines, especially in the warm tank, are symbolic representations of the directions of flow of the heat transfer fluid inside the tanks, but should not be conceived as the only flows that can occur inside the tanks.

Accordingly, referring to the process steps of the present invention already illustrated, an object of the present invention is a process for producing at least one pyrolysis oil from essentially plastic materials, wherein the first cycle comprises said step a) and said step c) and the second cycle comprises said step b) and d).

According to another embodiment, the process for producing at least one pyrolysis oil from essentially plastic materials additionally comprises the steps of:

j) store the first heat transfer fluid F1 from phase c) in a tank (?cold tank?) before using it in phase a);

k) store the second heat transfer fluid F2 heated in phase b) in a tank (?hot tank?) before using it in phase d).

According to another embodiment, in the process for producing at least one pyrolysis oil from essentially plastic materials, the heat transfer fluid F1 has the same composition as the heat transfer fluid F2.

When fluids F1 and F2 have the same composition, according to another embodiment, the process of the present invention for producing at least one pyrolysis oil from essentially plastic materials additionally comprises the steps of:

l) store the first heat transfer fluid F1 heated in phase a) before its use in phase c) and the second heat transfer fluid F2 cooled in phase d) before its use in phase b) in a tank (?warm tank?).

Another embodiment of the present invention, having ?separate cycles?, is shown in Figure 10. The scheme includes the same devices as in Figure 1, except that the warm tank 64 is divided into two separate tanks 64A and 64B:

- The first ?warm? tank (?warm tank A?, 64A) collects the heat transfer fluid coming from the first solar collector group 61.

- The first “warm” tank 64A supplies the heat transfer fluid to the pyrolysis devices requiring lower temperatures, such as the first pyrolysis reactor 70 and optionally the preheater or organic heat transfer fluid heat exchangers.

- The second ?warm? tank (?warm tank B?, 64B) collects the heat transfer fluid from devices requiring higher temperatures, such as the second pyrolysis reactor or the coking device. - The second ?warm? tank 64B delivers the heat transfer fluid to the second solar collector group 62.

A simplified view of the same embodiment is shown in Figure 13, which is provided to clearly show the flow of the heat transfer fluid in each cycle.

Accordingly, one embodiment of the present invention is a process for producing at least one pyrolysis oil from essentially plastic materials, which additionally comprises the steps of:

m) store the first heat transfer fluid F1 heated in phase a) before its use in phase c) in a tank (?warm tank A?);

n) store the second heat transfer fluid F2 cooled in phase d) before its use in phase b) in a tank (?warm tank B?).

According to the said embodiment with separate cycles, the closed heat transfer fluid cycles can be completely separated, as a result, it is possible to use different fluids for the hot cycle and the warm cycle. For example, it is possible to use molten salts having a lower melting point for such a cycle. Generally, it is advantageous to use molten salts with a low melting point as this means that it is possible to safely operate the system at lower temperatures (generally, it is advisable to operate the system in such a way that at the coldest point the molten salts have a temperature at least 50 °C above their melting point), as restarting after prolonged shutdowns takes less time.

However, typically molten salts having a lower melting point also have a lower thermal stability, such that they cannot be used for the hot cycle which requires a significantly high temperature.

According to this embodiment, it is therefore advantageous to use a heat transfer fluid for the warm cycle that is different from the heat transfer fluid of the hot cycle. According to this embodiment, preferably, the heat transfer fluid of the warm cycle has a lower melting point than the heat transfer fluid of the hot cycle, more preferably the heat transfer fluid of the warm cycle has a melting point that is at most 180 °C, even more preferably at most 150 °C.

For example, it is possible to use as a heat transfer fluid the so-called Hitec molten salts (7% sodium nitrate by weight, 53% potassium nitrate by weight, 40% sodium nitrite by weight) or ternary mixtures of lithium nitrate, sodium nitrate and potassium nitrate, for example the eutectoid mixture having a composition of 25.9% lithium nitrate by weight, 20.6% sodium nitrate by weight and 54.1% potassium nitrate by weight.

For example, it is possible to use the quaternary mixture of sodium nitrate, potassium nitrate, lithium nitrate and calcium nitrate, for example the mixture composed of 9.5 mol% sodium nitrate, 52.8 mol% potassium nitrate, 27.6 mol% lithium nitrate and 10.1 mol% calcium nitrate, having a melting point of only 98.3 ?C.

Another embodiment of the present invention, having “separate cycles,” is shown in Figure 14. In this embodiment, the warm tank 64 is divided into two tanks 64A and 64B, as in the embodiment of Figure 13, however, the two tanks 64A and 64B are located within the same container (such as a tank) and are separated by a weir 64C. In this way, it is possible to reduce the number of units to be built, thereby reducing installation costs. Furthermore, the weir 64C allows a heat transfer fluid to overflow into the other tank in the event the level becomes too high.

Optionally, the weir 64C includes at least one opening 64D, preferably in the bottom part of the weir, which allows the levels of the two tanks 64A and 64B to be equilibrated. When at least one opening is present, the separation of the fluids in the two tanks 64A and 64B is not complete. Consequently, when the opening is large, the scheme in Figure 14 corresponds to the scheme in Figure 12, since the contact surface in which the fluids of the two tanks are in contact is large. Conversely, when the opening is small, the scheme in Figure 14 corresponds to the scheme in Figure 13, since the contact surface is minimal or even zero.

Accordingly, one embodiment of the present invention is the process for producing at least one pyrolysis oil from essentially plastic material which additionally comprises steps m) and n) characterized in that said warm tank A and warm tank B are comprised in the same container and are preferably separated by a weir. According to another embodiment, in said process said weir comprises at least one opening which allows fluid in said warm tank A to flow into said warm tank B and vice versa.

Preferably, the essentially plastic material comprises compositions of different plastics. Even more preferably, said compositions of different plastics comprise at least polymers with a high H/C ratio, such as for example polyethylene, polypropylene, polyamides, polymethyl methacrylate, and polymers with a low H/C ratio, such as polystyrene, polycarbonate, polyethylene terephthalate.

Alternatively or in combination, said different plastic compositions include high carbon index polymers, such as polyethylene (including LDPE, LLDPE, HDPE), polypropylene, polystyrene, elastomers and low carbon index polymers, such as polyamides, polymethyl methacrylate, polyethylene terephthalate, polyvinyl chloride and cellulose.

Preferably, said essentially plastic material is characterised by an H/C ratio (H/C index) equal to at least 70, preferably between 80 and 98, more preferably between 85 and 96.

Preferably, said essentially plastic material is characterised by a carbon index of at least 55, preferably between 65 and 95, more preferably between 75 and 90.

The H/C index is proportional to the ratio of the total mass of hydrogen atoms to the total mass of carbon atoms present in the essentially plastic material and is calculated using the following formula:

The carbon index is proportional to the ratio of the total mass of carbon atoms to the total mass of all atoms present in the essentially plastic material and is calculated using the following formula:

where ?weight of ALL atoms? corresponds to the weight of the essentially plastic material.

Preferably, said essentially plastic material contains at least one non-plastic material in an amount ranging from 0.01% to 10% by weight with respect to the weight of the essentially plastic material, more preferably in an amount ranging from 0.05% to 7.5%, also more preferably in an amount ranging from 0.2% to 5%. Said non-plastic material preferably comprises at least one of the following materials: paper, cardboard, wood, compost (as defined by IUPAC in “Terminology for biorelated polymers and applications (IUPAC Recommendations 2012)”, Pure Appl. Chem., Volume 84, No. 2, pages 377-410, 2012, DOI 10.1351/PAC-REC-10-12-04), metallic materials such as aluminum and iron, and/or inert materials.

Optionally, said essentially plastic material contains inorganic fillers such as, for example, silica, titanium oxide, talc, coke, graphite, carbon black, calcium carbonate.

Optionally, said essentially plastic material contains brominated and chlorinated additives used to make the plastic material flame retardant or in any case to confer flame retardant properties. Examples of such additives are hexabromocyclododecane, decabromodiphenyloxide, polybrominated diphenyl ethers and brominated polymers such as brominated styrene-butadiene copolymers or brominated polystyrene.

Optionally, said essentially plastic material contains non-halogenated additives used to make the plastic material flame retardant or in any case to confer flame retardant properties, such as phosphorus and nitrogen compounds.

Preferably, said essentially plastic material is recycled material, such as waste material or secondary raw material.

Preferably, said essentially plastic material also contains halogens (typically, from polyvinyl chloride) in an amount ranging from 0.01% to 10% by weight of halogens based on the weight of the essentially plastic material.

Preferably, said essentially plastic material is obtained from a plastic material sorting process. Even more preferably, said essentially plastic material is the residual material of essentially plastic material, i.e. the fraction of essentially plastic material that remains after recovering some plastics or after selectively extracting some plastics from the essentially plastic material fed to the sorting process. Selective extraction consists in the essentially monomaterial extraction (i.e. of a monoplastic) of certain plastics. Typically, in a sorting (sorting) process it is possible to extract continuous streams of substantially pure plastic (i.e., a monoplastic) of the components polyethylene, polypropylene and polyethylene terephthalate. In this preferred sorting, therefore, the residual material of essentially plastic material is the material that remains after the extraction of said substantially pure plastics. This fraction is known in Italy with the term "Plas Mix" or "Plasmix", defined as "the set of heterogeneous plastics included in post-consumer packaging and not recovered as single polymers" (Article 1 of the draft law of the Chamber of Deputies n? 4502 of 18/05/2017).

According to another embodiment of the present invention, shown in Figure 2, the essentially plastic material is preheated before being fed to the first pyrolysis reactor 70 in a preheating device 74. Advantageously, according to this embodiment, the heat transfer fluid 33 is fed from the warm reservoir to the heating jacket of the first pyrolysis reactor 70. The heat transfer fluid exiting the pyrolysis reactor jacket is sent to the jacket of said preheating device 74. The heat transfer fluid exiting the preheating device 34 returns to the cold reservoir.

In accordance with another embodiment of the present invention, shown in Figure 3, solid, semi-solid, or liquid material from the first pyrolysis reactor 70 is delivered to the coking treater 76. A separator 77 (which may be integrated into the coking device) allows the gaseous phase 53E to be recycled back into the process (e.g., into the first pyrolysis reactor as shown in Figure 3), while the non-gaseous phase is collected in stream 53D.

The char feeder 75 may be a pumping device that moves solid, semisolid, or liquid material from the first pyrolysis reactor to said coker while allowing for a physical separation between the two devices. An example of such a device is a gear pump. Alternatively, the char feeder 75 may be a valve, such as a rotary valve, gate valve, or butterfly valve.

Advantageously, according to this embodiment, the heat transfer fluid from the hot tank 37 is supplied first to said coker 76 and, subsequently, at 53B to the second pyrolysis reactor 71 before returning to the warm tank 38. Advantageously, said char feeder 75 may be heated by the heat transfer fluid 34A exiting the heating jacket of the first pyrolysis reactor 70, before returning to the cold tank.

According to another embodiment of the present invention, shown in Figure 4, both embodiments shown in Figure 2 and Figure 3 are combined together. Accordingly, the essentially plastic material is preheated in said preheater 74 and the solid, semi-solid or liquid material from the first pyrolysis reactor 70 is delivered by means of the char feeder 75 to the coker 76. Advantageously, the heating of such devices is carried out by means of the heat transfer fluid from the hot and warm tanks, as described earlier in the explanation of the embodiments of Figures 2 and 3.

In the coker 76, said material is heated at a temperature of 500 °C to 1200 °C, preferably 600 °C to 1000 °C, more preferably 700 °C to 900 °C, for a time of at least 5 minutes, preferably 15 to 180 minutes, more preferably 30 to 120 minutes. As a result of such heat treatment, the char is purified, in particular the more volatile components are separated and collected in the gas phase and the char is further pyrolyzed, producing a solid product that has a lower H/C ratio and a higher carbon index and with a better health, safety and environmental (HSE) profile.

Any device capable of performing this operation is suitable as a coking device. Preferably, such a coking device is a device comprising a rotating screw. More preferably, such a rotating screw is horizontal or has an inclination of up to 30° from the horizontal axis.

The coking device can be heated by means of a heat transfer fluid and, optionally, also by means of a gas heater, by means of electrical resistance (Joule effect) or combinations thereof. In the case of using the heat transfer fluid, it is preferred to use the heat transfer fluid coming from the hot tank.

Accordingly, according to one embodiment of the present invention, the process for producing at least one pyrolysis oil from essentially plastic materials additionally comprises the steps of:

o) heating the liquid, solid or semi-solid residue of the pyrolysis of phase f) (the char) by means of the second heated heat transfer fluid F2 and optionally also by means of a gas heater, by means of resistance (Joule effect) or combinations thereof.

Preferably, in step (o), said char is heated to a temperature of 500 ?C to 1200 ?C, preferably 600 ?C to 1000 ?C, more preferably 700 ?C to 900 ?C, for a time of at least 5 minutes, preferably 15 to 180 minutes, more preferably 30 to 120 minutes.

According to another embodiment of the present invention, shown in Figure 5, the condensation of the pyrolysis gas exiting the second pyrolysis reactor is divided into more than one unit 72A, 72B. In more detail, the pyrolysis gas 54 exiting the second pyrolysis reactor 71 passes through a first ?high temperature? condenser 72A and a first separator 73A, which separates the condensed liquid 56A from the uncondensed vapors 55A. Said uncondensed vapors 55A then pass through a second ?low temperature? condenser 72B and a second separator 73B, which separates the condensed liquid 56B from the uncondensed vapors 55.

Advantageously, according to this embodiment, the cooling of the first condenser 72A is carried out by means of the heat transfer fluid 33E already used to heat the first pyrolysis reactor 70, before entering the cold tank 63. In this way, there is a heat recovery that allows to reduce the overall thermal demand for condensing the pyrolysis oil and, at the same time, by heating the heat transfer fluid, to reduce the thermal demand of the solar collector group 61.

In one embodiment, heating of the first pyrolysis reactor 70, the char feeder 75 and the preheater 74 in the same temperature range can be accomplished using heat transfer fluid 33 from the warm tank 64.

All other various auxiliary devices and the parts connecting these devices (for example, connecting pipes) can be heated with the same heat transfer fluid.

Preferably, the distribution of the heat transfer fluid to such devices can be carried out in series, in parallel or in semi-series.

When in series, preferably, the heat transfer fluid from the warm tank 64 is fed first to the pyrolysis reactor and then to other devices, such as the preheater 74 or the char feeder 75. Most preferably, the order is: first pyrolysis reactor 70, then (if present) the preheater 74 and then (if present) the char feeder 75. According to a further embodiment, if the condensation is divided into two or more phases and the cooling fluid in the first condenser is the heat transfer fluid, as shown in Figure 5, such series also includes said first condenser and, preferably, in said order the last element is said first condenser. Accordingly, more preferably, the order is: first pyrolysis reactor 70, then (if present) the preheater 74 and then (if present) the char feeder 75. preferably, the order is: first pyrolysis reactor 70, then (if present) the preheater 74, then (if present) the char power supply device 75 and lastly (if present) the first capacitor 72A.

Semi-series configurations are combinations of series and parallel configurations that allow the advantages of both series and parallel operation to be achieved.

An embodiment of a semi-series configuration is shown in Figure 6 and Figure 7.

Figure 6 shows a weir device 78 that receives heat transfer fluid from warm tank 64 and delivers that fluid to the first pyrolysis reactor 70 and preheater 74, finally releasing that fluid to the cold tank 63. In this embodiment, the weir device includes a first chamber, into which oil from said warm tank is fed. In this first chamber is located a first pump 66B that delivers heat transfer fluid to the first pyrolysis reactor 70. Heat transfer fluid exiting the first pyrolysis reactor enters the same chamber. A weir, which may be for example a Bazin weir, ensures that there is sufficient head (net positive suction head) to avoid cavitation during pumping of heat transfer fluid to the first pyrolysis reactor 70, as well as carryover of the gas phase. This weir also forms the containment wall of said first chamber, so that the fluid is recirculated within the chamber. This ensures uniformity in the fluid temperature within the chamber, as well as high resilience to instabilities in the flow rate of the fluid entering from the warm tank.

The excess heat transfer fluid overflows the overflow, thereby entering the next chamber. Similar to the first chamber, the next chamber includes another pump 66B that delivers heat transfer fluid to the preheater 74 and collects its return. Similarly, another overflow ensures that the pump 66B that delivers fluid to the preheater has enough NPSH and that no gas is carried over. Finally, the last chamber includes another pump to deliver heat transfer fluid to the cold tank 63. The starting and stopping of this pump may be managed automatically by means of a level switch, such that the pump will only start when the level in the last chamber is above a certain height.

Unlike the series configuration, the weir device 78 allows for different flow rates of heat transfer fluid to be delivered to each device. Unlike the parallel configuration, where all devices share the same source (the warm tank), the weir device allows for a higher temperature heat transfer fluid to be delivered to the device that requires a higher temperature and higher relevance (i.e., in order to have a constant temperature on the heat transfer fluid relative to the temperature of subsequent chambers).

As a result, the weir device allows for greater flexibility and effectiveness when compared to standard parallel and series configurations.

In another embodiment, such a device may be located within the warm tank itself, such that the pump that delivers the heat transfer fluid to the weir device is no longer required. In another embodiment, the warm, cold, and hot tanks may be located in the solar field, while the pyrolysis system may be located some distance from the solar field. In such cases, a buffer tank is required to prevent any problem in the heat transfer fluid delivery from causing a failure in the pyrolysis process.

In these cases, weir devices can also act as a buffer tank.

It is well known that there are many other different customizations of the weir device, for example allowing multiple chambers to handle multiple devices to be heated by the heat transfer fluid.

Advantageously, all devices receiving the heat transfer fluid are placed at different height levels so that the minimum number of heat transfer pumps is required.

More precisely, according to this embodiment, the first device that receives the heat transfer fluid from the pumps 66 is placed at the maximum height level and the devices that receive the heat transfer fluid exiting from the first device are placed at a lower height level, so that the fluid can flow into the device by gravitational force. By doing this, there is no need for additional pumps.

This is advantageous because any moving part on the high temperature fluid, which may also show a high melting temperature, is particularly delicate and may require specific measures for proper start-up and maintenance in case of failure. Furthermore, in this way, the pressure of the heat transfer fluid in such devices can be atmospheric, simplifying the design and reducing the cost of the devices. Last but not least, as it is not under pressure, an accidental rupture of the thermal jacket is safer since the spillage from the rupture is reduced.

According to a preferred embodiment, all heat transfer fluid tanks are located at the bottom level.

The preheater 74 may be any device in which the essentially plastic material can be heated and, preferably, partially or totally melted.

Examples of such devices are single-screw extruders, twin-screw extruders or more generally screw devices that are capable of dispensing a plastic material and that have a jacket or equivalent means in which the heat transfer fluid can flow.

Optionally, the heat transfer fluid also flows inside the screw, thus improving the effectiveness of the device.

Preferably, such a device is capable of being nearly gas-tight, such that gases in the first pyrolysis reactor 70 do not escape from the pyrolysis reactor 70. One means of achieving this is to use the same molten plastics that flow between the screws and cylinders as a means of achieving gas-tightness.

Said preheating apparatus may be equipped with a degassing device for the evacuation of water vapor and any other gas produced, such as in particular hydrogen chloride (HCl). For this purpose, it may be advantageous to feed said preheating apparatus, in addition to said essentially plastic material, also with additives capable of promoting the evolution of hydrochloric acid or to salify it. These additives are preferably composed of elements of group IA and IIA. Even more preferably, they are the oxides, hydroxides, carbonates, silicates and aluminosilicates of group IA and IIA. Even more preferably, they are calcium oxide, calcium hydroxide, calcium carbonate, sodium oxide, sodium hydroxide, sodium carbonate, potassium oxide, potassium hydroxide, potassium carbonate, sodium aluminosilicate.

The preheating temperature may be between 120 °C and 430 °C, preferably between 150 °C and 320 °C, more preferably between 180 °C and 220 °C. The residence time in said preheating apparatus is preferably less than 20 minutes, more preferably less than 4 minutes, in particular less than one minute.

Accordingly, one embodiment of the present invention is a process for producing at least one pyrolysis oil from essentially plastic materials, which additionally comprises the step of:

p) heat the essentially plastic material before phase e) by means of the first heated heat transfer fluid (F1).

According to this embodiment, preferably in phase p), the essentially plastic material is brought to a temperature between 120 °C and 430 °C, more preferably between 150 °C and 320 °C, even more preferably between 180 °C and 220 °C, and wherein the average residence time of phase p) is preferably less than 20 minutes, even more preferably less than 4 minutes, in particular less than one minute.

The first pyrolysis reactor 70 can be any reactor that is capable of receiving an essentially plastic feedstock and bringing it to pyrolysis conditions (temperature and pressure).

The first pyrolysis reactor for the pyrolysis of essentially plastic material can be operated in batch mode, continuous mode and semi-continuous mode. In the last mode, the essentially plastic material is continuously loaded, the generated vapours are continuously extracted, but any solid residue is kept inside the pyrolysis reactor.

When the amount of solid residue inside the reactor increases above a certain threshold, or at predefined time intervals, for example with a frequency ranging from 2 to 10 days, the solid material contained in the reactor is removed.

Preferably, the reactor is operated in continuous or semi-continuous mode, more preferably in semi-continuous mode.

The pyrolysis process of the present invention is not limited by any particular type of reactor.

In particular, horizontal or vertical reactors, stirred or unstirred, oven reactors or screw reactors can be used. Fluidized bed reactors are not preferred.

Among the stirred reactors, continuously stirred reactors (CSTR) and multizone reactors can be used. Plug flow reactors (PFR) can also be used, preferably stirred to facilitate heat transfer.

Among the continuously stirred reactors (CSTRs) it is possible to use completely packed reactors (which means that there is essentially no gas phase on the molten treated plastic and reaction products such as char) and reactors with a separation of the gas phase from the phase that includes the liquid and other possible phases, such as the solid char produced, i.e. reactors in which there is a free surface.

Preferably, the reactor is a stirred reactor with a free surface.

The residence time of the essentially plastic material (M1) in said first pyrolysis reactor is at least 2 minutes and in any case sufficient to produce a fluid in the gaseous state (M2) containing hydrocarbons. This means that in any case the residence time must be sufficient to produce a fluid in the gaseous state and that this time may be greater than 2 minutes. This time may be different depending on the composition of the essentially plastic material fed to the reactor, however, if no gas is produced, the person skilled in the art has no difficulty in increasing the residence time so as to satisfy this condition.

The temperature of the material in pyrolysis reactors can be measured by any method known in the art. For example, the following devices can be used: thermocouples with a membrane face aligned with the inner surface of the reactor, to reduce fouling; or thermometric thermocouples for more precise measurement inside the reactor; or thermocouples measuring the metal temperature near the polymer-wetted surface of the reactor; or non-contact measurement systems, for example infrared devices. Multiple systems can be used simultaneously for improved reliability.

The temperature can be regulated by acting on the thermal energy introduced into the reactor. The thermal energy is obtained by the flow of said heat transfer fluid in the reactor.

The parts in contact with this heat transfer fluid are separated from the parts in contact with the process fluids (inlet for plastic, liquefied plastics, char, gas produced by pyrolysis, etc.).

Preferably, the heat transfer fluid flows in a jacket. Optionally, the heat transfer fluid also flows inside the stirrer, so that the stirrer is also heated.

Preferably, the heat transfer fluids F1 and/or F2 are molten salts.

For the present invention, any molten salt may be used. According to one embodiment, the molten salts are a molten salt of a group IA and IIA of the periodic table, preferably sodium nitrate, sodium nitrite, potassium nitrite, potassium nitrate, lithium nitrate, calcium nitrate or mixtures thereof.

According to one embodiment, the molten salts that may be used are nitrate/nitrite mixtures, in particular mixtures of potassium nitrate and sodium nitrate, optionally with the addition of sodium nitrite and calcium nitrate.

According to one embodiment, such nitrate/nitrite mixture is the eutectic mixture of 53 wt.% potassium nitrate, 40 wt.% sodium nitrite, and 7 wt.% sodium nitrate; alternatively, according to another embodiment, such K/Na nitrate/nitrite mixtures are the eutectic mixture of 45.5 wt.% potassium nitrate and 54.5 wt.% sodium nitrite.

According to one embodiment, this nitrate/nitrite mixture is the so-called "solar salt", characterized by 60% by weight of sodium nitrate and 40% by weight of potassium nitrate.

According to one embodiment, this nitrate/nitrite mixture is the so-called "Hitec XL", characterized by 7% by weight of sodium nitrate, 45% by weight of potassium nitrate and 48% by weight of calcium nitrate.

In one embodiment, the nitrate/nitrite mixture is 100% by weight lithium nitrate.

In one embodiment, the nitrate/nitrite mixture is 25 wt% lithium nitrate, 25 wt% sodium nitrate, and 50 wt% potassium nitrate.

In one embodiment, the molten salts are a mixture of chlorides, such as sodium chloride, and mixtures of sodium and potassium chlorides, optionally with magnesium chloride.

According to a further embodiment, the heat transfer fluid is a molten salt comprising metal fluorides of Groups IA and IIA, preferably lithium, sodium, potassium and calcium fluoride. Even more preferably, the heat transfer fluid is constituted by a molten salt comprising sodium nitrite, sodium nitrate and potassium nitrate. Even more preferably, the heat transfer fluid is constituted by a molten salt comprising sodium nitrate and potassium nitrate.

Preferably, the heat transfer fluid has a low melting temperature. More preferably, said melting temperature is at most 340 °C, even more preferably at most 270 °C, even more preferably at most 240 °C.

Preferably, this heat transfer fluid has a high decomposition temperature. More preferably, said decomposition temperature is at least 400 °C, even more preferably at least 450 °C, even more preferably at least 490 °C, most preferably at least 540 °C.

According to one embodiment, the melting temperature of the heat transfer fluid is at least 60 °C, preferably greater than 80 °C, more preferably greater than 105 °C.

Preferably, this heat transfer fluid has a low chloride content. Preferably, the chloride content is less than 1000 ppm by weight. More preferably, the chloride content is less than 100 ppm by weight.

In one embodiment, any component of the process, such as the reactor, coker, preheater, valves, etc., that is designed to contain the molten salts is gravity drainable. For example, the tanks (hot, cold, warm) may be located at the lowest point, such that in the event of a failure (such as failure of molten salt pumps 66 or sudden interruption of electrical power source) the heat transfer fluid drains into the tanks by gravity. In another embodiment, any component comprising molten salts that is characterized by the presence of movable parts (such as valves) or large length/width ratios (e.g. pipes) has an electrical heat trace that can be activated prior to starting the system, so as to melt the heat transfer medium.

The solar collector assembly (SCA) may be of any type. In one embodiment, the solar collector is a “single focal point,” meaning that the sun’s rays are reflected into a focal zone that is essentially limited in size. Examples of a “single focal point” are the parabolic dish and the power tower. In another embodiment, the solar collector is a “line focal,” meaning that the sun’s rays are reflected into a focal zone that is essentially a line. Examples of such solar collectors are the parabolic trough and the linear Fresnel. There are several specific types of parabolic trough and linear Fresnel, such as the “compact linear Fresnel reflector” (CLFR) or the “enclosed collector system,” which may also be used in the present invention.

Preferably, the solar collector is a parabolic collector or a linear Fresnel, in the latter case in particular the compact linear Fresnel.

Accordingly, according to an embodiment of the process of the present invention, the heating of phase a) and b) is carried out by means of at least one solar collector group comprising a parabolic collector, a linear Fresnel or a combination thereof. According to a preferred embodiment of the process of the present invention, the heating of phase a) and b) is carried out by means of at least one solar collector group consisting of a parabolic collector, a linear Fresnel or a combination thereof.

The solar rays that are collected by such collectors are reflected onto so-called solar receivers. In one embodiment, such solar receivers consist of a heat exchanger in which the heat transfer fluid is heated. Typically, in such receivers the fluid flows in tubes that are heated by the solar rays.

In another embodiment, such solar receivers consist of a tube into which the solar rays are directed. The tube, typically a metal tube, is called an “absorber”. The tube is coated with a selective coating that maximizes the absorption of sunlight, while minimizing heat losses through infrared emission. A glass tube that encloses said absorber tube is transparent, so that sunlight can pass through it. A high vacuum is produced between the two tubes, so as to limit heat losses by convection. Sometimes, a degassing nozzle and/or a getter is added, so that this vacuum can be maintained over time.

The solar receiver ends with bellows to achieve differential thermal expansion of glass and metal materials.

Solar collectors and their receivers can be assembled in parallel, in series or in a combination of parallel and series configurations. The combination of parallel and series configurations is preferred.

In some cases, especially for linear Fresnel (and compact linear Fresnel), a single receiver can receive the concentrated solar radiation from several reflectors.

The concentration factor (sometimes also called the ?concentration ratio?) is the ratio of the radiant energy density at the receiver divided by the radiant energy density of the sun without any concentration, hence, it is the factor by which the incident energy flux is optically increased on the receiving surface. The concentration factor according to the present invention is from 8 to 1000, more preferably from 10 to 100, still more preferably from 15 to 80.

In one embodiment of the present invention, the concentration factor of the solar collector assembly 62 that heats the hot tank 65 is higher than the concentration factor of the solar collector assembly 61 that heats the warm tank 64.

Accordingly, according to one embodiment of the process of the present invention, the concentration factor of the at least one solar collector group of step b) is higher than the concentration factor of the at least one solar collector group of step a).

The hot, warm and cold tank can be any container that can be filled with a heat transfer fluid, such as a vertical or horizontal tank. Advantageously, these containers are thermally insulated to limit heat loss.

According to one embodiment, the heat transfer fluid pump 66 is located inside the tank.

In one embodiment, the level of heat transfer fluid in the tank is monitored so as to limit the pyrolysis efficiency when the level of heat transfer fluid in the hot or warm tank becomes too low.

According to one embodiment of the present invention, there is also an additional heat transfer fluid tank, so as to supply heat transfer fluid at more than two temperatures to the pyrolysis devices.

According to one embodiment, such a first pyrolysis reactor is a vertical container, preferably with an essentially cylindrical shape.

Preferably, the top and bottom ends of the first pyrolysis reactor are conical, ellipsoidal or semi-ellipsoidal. In this way, better recirculation is achieved and less fouling is observed. In fact, fouling is critical in pyrolysis reactors.

Preferably, the first pyrolysis reactor 70 has at least one agitator. This agitator should be of adequate size to ensure that at least the entire reactor volume filled with liquid and solid phase is continuously or semi-continuously agitated (e.g., not necessarily the gas phase). Preferably, the agitator should also be capable of periodically moving material close to the reactor wall, in order to clean the surface and reduce fouling.

An example of such agitators are anchor or belt agitators or, in some cases, turbine agitators.

The speed of such agitators is typically 1 to 300 rpm, preferably 5 to 120 rpm.

In some embodiments, it is possible to use more than one stirrer. In this case, advantageously, the stirrers have different stirrer speeds. A simple way to accomplish this task is to leave one stirrer free to rotate, so that it is dragged by the fluid at a rotational speed that is below the actively moving stirrer, but above zero.

By ?condenser? we mean any apparatus which receives a fluid in the gaseous state and is capable of removing sufficient heat from that fluid, so as to generate at least a portion of the fluid in the liquid state.

Examples of this equipment are condensers comprising coils inside which a heat transfer fluid flows, capable of removing heat from the gaseous fluid being processed.

Other ways to remove heat can be used, for example, alternatively or in combination, the condenser can be equipped with a jacket in which said heat transfer fluid flows in order to remove heat.

Advantageously, submerged condensers can also be used, in which the condenser is partially submerged in the liquid phase produced and whose condensation power is regulated by varying the height of said liquid phase, since only the coil that is not submerged is able to absorb heat from the vapor to be condensed. Consequently, this allows effective regulation of the condenser power.

Alternatively, the condenser may be a distillation column. In this case, the condensed fluid originates in the column condenser and the condensed liquid flows back by gravity or pumping into the column, condensing the vapors within it. In this way, a better fractionation of the incoming vapors is also achieved, that is, a better separation is achieved between higher boiling components that are condensed and lower boiling components, which remain in the vapor phase, since at each stage there is an enrichment of the liquid phase with heavy substances and an enrichment of the gas phase with light substances. In addition, the vapor scrubbing performed by the column allows any solid particulates present in the incoming vapors to be separated and reunited in the liquid phase.

The pyrolysis vapor condenser can be a single capacitor or multiple capacitors in series or parallel. Preferably, when more than one capacitor is used, two to four capacitors in series are used, even more preferably three capacitors in series are used.

When the capacitors are in series, each capacitor receives the uncondensed gas that has left the previous capacitor, while the first capacitor receives the pyrolysis vapors.

In this preferred mode, the condenser receiving the pyrolysis vapors (the first condenser) operates at a higher temperature than the second condenser receiving the uncondensed vapors from the first condenser. If there are more than one condenser, the next one (for example the third one) receives the uncondensed vapors from the previous one and operates at a lower temperature.

According to a preferred method, part of the liquid fluid condensed in at least one condenser is recycled into the first pyrolysis reactor. Preferably, the fluid recycled into the reactor is taken from the first condenser.

According to one embodiment, when more than one condenser is used, heat is removed from the first condenser by means of the heat transfer fluid already described in Figure 5 (condenser 72A).

The fluid comprising hydrocarbons which, after passing through said at least one condenser have not been condensed, hereinafter referred to as residual gas, advantageously contains at least 40% by weight of light hydrocarbons (C1-C5) and can advantageously be used as a fuel gas. A portion of this gas can be burned to supply additional heat energy which can be useful for the pyrolysis process and related devices, in particular those requiring a higher temperature such as the second pyrolysis reactor and the coker. For this purpose, for example, a gas heater can be used, which gas heater regulates the temperature of the heat transfer fluid circulating in the reactor jacket. Alternatively or in combination, this residual gas can advantageously be used to supply refinery plants, such as for example a cracking plant.

According to the invention, the fluid which is in the liquid state after condensation in said at least one capacitor is quantitatively at least 10% by mass, preferably between 20% and 92%, even more preferably between 30% and 85%, even more preferably between 40% and 75%, with respect to the mass of the essentially plastic material fed. If several capacitors are used, this quantity is calculated by adding the quantity of mass of liquid produced by each capacitor.

According to the invention, at least one fluid is formed after condensation in said at least one condenser, which fluid is in the liquid state and comprises hydrocarbons having a standard boiling point of not less than 25 °C, preferably not less than 40 °C, more preferably between 80 °C and 220 °C.

Preferably, at least the first pyrolysis reactor is operated at a pressure that is atmospheric or supra-atmospheric (i.e., greater than atmospheric pressure). In one embodiment, the pressure is between 1.1 and 20 bara, more preferably between 2 and 10 bara, and also most preferably between 2.2 and 6 bara.

Preferably, the temperature to which the essentially plastic material is brought in said first pyrolysis reactor is from 330 °C to 580 °C, preferably from 340 to 540 °C, more preferably from 360 to 500 °C, still more preferably from 380 to 480 °C, also most preferably from 410 to 450 °C. Any technique known in the art can be used to maintain the pressure in the first pyrolysis reactor at a defined value, wherein the maintained pressure can have different values as a function of the pyrolysis temperature. According to a first method, the pressure can be maintained at a defined value by regulating the heat extracted from the condenser located downstream of the reactor and in fluidic connection with it. In this manner, an increase in the heat removed from the condenser results in increased condensation of vapor. This condensation, which brings the evaporated material from the gaseous state to the liquid state, having a significantly higher density, causes a reduction in pressure.

Alternatively, the pressure can be controlled by introducing a gas, such as nitrogen, argon, or water vapor, and regulating the flow of that gas by means of a valve. In one embodiment, that gas is introduced into the first pyrolysis reactor and also serves as an inert gas (i.e., a gas that does not directly participate in the pyrolysis reactions and that can displace oxygen present in the reactor when it is opened to the atmosphere, for example during maintenance or before start-up).

According to a preferred embodiment, the pressure can be controlled by regulating the flow of the continuous gas stream that is not condensed (in case more than one condenser is used in series, the continuous gas stream of the last condenser).

According to one embodiment, the pyrolysis of the essentially plastic material of the present invention is carried out in the substantial absence of oxygen, with the meaning of ?substantial absence of oxygen? defined above.

Accordingly, according to this embodiment, the process for producing at least one pyrolysis oil from essentially plastic materials is also characterized in that step f) and step h) are carried out in the substantial absence of oxygen.

The heat supply to the first pyrolysis reactor and the second pyrolysis reactor can be regulated by controlling the flow rate of the heat transfer fluid or its temperature or both.

Advantageously, the pyrolysis process of the present invention produces a product particularly useful for use as a jet fuel or as virgin naphtha, particularly suitable for steam cracking to produce monomers of industrial interest or suitable for the synthesis of polymers.

Preferably, the second pyrolysis reactor is operated at a temperature that is higher than the temperature of the first pyrolysis reactor. More preferably, the temperature difference between the second pyrolysis reactor and the first pyrolysis reactor is at least 10? C, even more preferably between 30? C and 300? C, even more preferably between 60? C and 250? C.

According to another embodiment, the second pyrolysis reactor is always operated at a temperature that is at least 10 °C higher than the temperature of the first pyrolysis reactor, with the additional condition that this temperature is between 400 °C and 650 °C, preferably between 440 °C and 550 °C, more preferably between 460 °C and 530 °C; meaning that when the minimum temperature of these ranges is lower than the temperature of the first pyrolysis reactor plus 10 °C, the latter (T first pyrolysis reactor 10 °C) shall be considered the lower range.

Accordingly, included in the invention is a process for producing at least one pyrolysis oil from essentially plastic material, wherein the gaseous effluent of the first pyrolysis reactor, prior to condensation, is taken to a second pyrolysis reactor, wherein the continuous gaseous stream is heated to a temperature that is at least 10 °C higher than the temperature of the essentially plastic material in the first pyrolysis reactor.

Accordingly, according to one embodiment of the present invention, a process is provided for producing at least one pyrolysis oil from essentially plastic materials, wherein the temperature difference between the temperature T2 of step b) and the temperature T1 of step a) is at least 10 °C, even more preferably between 30 °C and 300 °C, even more preferably between 60 °C and 250 °C.

The residence time of the pyrolysis vapours in said second pyrolysis reactor, calculated by dividing the volume occupied by the vapours in the reactor by the volumetric flow rate, is at least 10 seconds, preferably between 30 seconds and 6 minutes, even more preferably between 1 and 4 minutes.

Preferably, the second pyrolysis reactor is catalytic. More preferably, said gaseous effluent is in relative motion with respect to said solid catalyst in contact with said gaseous effluent, and said relative motion is at a velocity of at least 0.5 m/s, more preferably 2 to 50 m/s.

All pyrolysis catalysts known in the art can be used, including in particular zeolites.

The second pyrolysis reactor may be operated at the same pressure as the first pyrolysis reactor 70 or at a lower pressure, preferably the second pyrolysis reactor is operated at a pressure between atmospheric pressure and the pressure of the first pyrolysis reactor. Even more preferably, it is operated at a pressure between the pressure of the first pyrolysis reactor and the same pressure decreased by 10000 Pa.

Advantageously, the first pyrolysis reactor can be more than one unit, as can the second pyrolysis reactor. This makes it possible to easily scale up the process.

In addition, when the liquid/solid/semi-solid residue (char) from the first reactor accumulates in a unit, it is possible to stop that unit, discharge the char, clean the unit, and restart it. If the production plant of each first pyrolysis reactor is set in a scheduled manner, it is possible to set individual units to stop for maintenance regularly and one at a time, thus keeping the entire pyrolysis stable over time.

Advantageously, the second pyrolysis reactors can be fed by the outgoing pyrolysis vapors from more than one first pyrolysis reactor unit. Preferably, the gaseous vapors from 2 to 20 first pyrolysis reactor units are fed to a single second pyrolysis reactor, even more preferably from 3 to 8 units.

Similarly, char produced from more than one first pyrolysis reactor unit is fed to a single char treatment device (such as a ?coker?).

To support the pyrolysis process while the radiation power of sunlight is too low to provide the required heat, for example after sunset or in cloudy or rainy conditions, the heat transfer fluid stored in the hot and warm tank can be used. Typically, the temperature of the tanks is not changed in order to ensure stable pyrolysis and not to influence the quality of the pyrolysis oil that is obtained.

Conversely, it is possible to stop or reduce the flow rate of the heat transfer fluid in the charging section (the solar collector groups), while at the same time keeping the flow rate of the heat transfer fluids from the hot and warm tanks unchanged (or slightly reducing it). In this way, the level of the heat transfer fluid in the hot tank decreases, possibly also the level of the warm tank decreases (depending on the relative ratio of the flow rates by weight), while the level of the cold tank increases.

The larger the volume of the tanks, the longer the period of time during which the process can be operated on such additional "discharge" power sources. Especially in these cases, the tank size can be very large, consequently, it may be advisable to divide the tanks into several units which, for example, can be operated in parallel.

Furthermore, it is possible to increase the energy storage and, consequently, the hours of operation in complete discharge, by allowing the heat transfer fluid to exchange thermal energy with solid materials that can withstand the temperature of the heat transfer fluid, such as, for example, concrete, sand, stones, etc. A simple means of realizing this embodiment is to place large masses of such materials in the tank or on its walls or on its base.

The additional power source is an energy source other than concentrated solar power (CSP) that can be used, for example, for emergency shutdowns or to start up the plant. Alternatively or in combination, such additional power sources can be used, for example, to stabilize the pyrolysis production or to supercharge it. Such sources can be, for example, a so-called renewable source (such as wind, solar PV, tidal, nuclear, hydro, biomass) or fossil fuel (coal, oil, shale, natural gas).

Preferred sources of such additional power sources are photovoltaics, biomass, nuclear and natural gas, with natural gas being particularly preferred.

In the case of natural gas, particular preference is given to gas heaters. Even more preferably, the gas that is burned in the gas heater comprises the residual gas from the pyrolysis process (which, as already described, is the pyrolysis gas that is not condensed, e.g. continuous flow 55 in Figure 11).

This additional power source can be placed in series or in parallel with the heat transfer fluid to be heated.

Figure 11 shows some embodiments of the present invention, including such additional power source in parallel 68A or in series 68B and 68C.

Parallel configuration means that the power source, in parallel with the solar collector assembly, pulls part of the heat transfer fluid from a colder tank (the cold or warm one), heats the fluid to the target temperature (usually the temperature of the destination tank) and delivers the heat transfer fluid to said destination tank. The destination tank is the warm tank 64 or the hot tank 65, in case the fluid is pulled from the cold tank 63, and the hot tank 65, in case the fluid is pulled from the warm tank 64.

In the series configuration, the input of this additional power source is the output of the solar collector assembly and its output is the input of the receiving heat transfer fluid tank. Referring to Figure 11, one embodiment of this solution is as follows: heat transfer fluid from the warm tank 64 is sent to the hot solar collector assembly 62, then to the additional power source 68B, then to the hot tank 65.

Alternatively, still in the series configuration, the input of this additional power source is the hot tank outlet and the output is the hot tank exhaust loop (the loop feeding the second pyrolysis reactor and optionally the coker). This is the most preferred option.

Referring to Figure 11, one embodiment of this solution is as follows: the heat transfer fluid from the hot reservoir 65 is sent to the additional feed source 68C, upon request (second pyrolysis reactor 71).

Preferably, when such an additional power source is present, its power is between 3% and 40%, more preferably between 6% and 20%, even more preferably between 8% and 15% of the power supplied by the hot and warm solar collector groups.

Examples

The present Examples report the simulation of a process using the invention process operated by a double heat transfer fluid (double cycle) compared to the conventional process operated by a single fluid (single cycle). For the sake of clarity, they are prophetic Examples and, consequently, the present indicative is used.

Example 1 (according to the invention)

Solar pyrolysis process driven by two fluids (dual heat transfer fluid cycles) of the same composition.

The process corresponding to this Example is given in Figure 8.

The heat transfer fluid is the solar mixture of molten salts (?solar salt?) having 60% by weight of sodium nitrate and 40% by weight of potassium nitrate.

Solar collectors and receivers 61,62 consist of Luz-type parabolic trough collectors (PTC) (SEGS) LS-2 with solar receivers with an external diameter of 70 mm evacuation tube. This model has a width W of 5.0 m and a length L of 7.8 m. The detailed characteristics and characterization of this parabolic trough collector are given in ?SEGS LS2 solar collector-test results?. 958 Report of Sandia National Laboratories, SAN94-1884, 1994, and are given more concisely in Tables 1 and 2 of Bellos, Evangelos & Tzivanidis, Christos ?A detailed exergetic analysis of parabolic trough collectors?, Energy Conversion and Management, (149) 275-292, 2017 doi: 10.1016/j.enconman.2017.07.035. This document, which will be referred to as the Bellos document below, is also used for detailed energy and exergy balance.

A code reproducing the model developed in the Bellos paper was prepared and tested for validation of the Sandia National Laboratory test case 4 (Table 4 on page 11 of the Bellos paper). The results closely matched those shown in Tables 4 and 5 of the Bellos paper for this test case, which in turn was found to be very close to the experimental values.

The flow rate of molten salts in the solar collector group 62 is 24.2 kg/s. The receivers of the solar collector group are arranged in 20 parallel lines, each receiving 24.2/20 = approximately 1.21 kg/s of solar salts. Each line comprises 19 receivers. This is the number of receivers (each 7.8 m long) required to raise the temperature from 485 °C to 565 °C. The calculation is made as follows: the ambient conditions (ambient temperature, sky temperature, sun temperature, incidence angle) are as per Table 3 of the Bellos paper, except that the specific air humidity (humidity ratio) has been taken to be 0.01 (i.e., 10 g of water per kg of air). Furthermore, the direct solar irradiance (Gb) is 0.01 (i.e., 10 g of water per kg of air). selected at 650 W/m<2>, since the values of about 900 W/m<2 >reported in Table 4 of the Bellos paper are quite high and available only in selected regions of the earth and for a limited period of time. The PTC module characteristics and optical properties are as per Table 1 and 2 of the Bellos paper. The equations that are used are those described in the Bellos paper.

The physical properties of the ?solar salt? heat transfer fluid are calculated with the following expressions, taken from ?Solar Salt ? thermal Property Analysis?, Scientific Report DLR-FB-2021-19 31.08.2021, Deutsches Zentrum f?r Luftund Raumfahrt:

The heat capacity is considered independent of temperature since there are large inconsistencies in the measurement of this parameter, therefore it was decided to use a constant value.

To perform the calculations, Bellos used the software "Engineering Equation Solver", however it turned out that they can be easily solved with an algorithm in any programming or writing language, since the most difficult equation to solve is a fourth degree equation (fourth degree polynomial) to calculate the temperature at the roof (Tc, in Kelvin), which has only two real roots, of which only one is positive (so only this root is significant and must be selected), plus two iterative calculations (on outlet temperature and Tc), which in any case converge very quickly and without the presence of alternative solutions.

The simulation is performed for each solar receiver, starting with the first one receiving molten salt from the cold tank. The calculated molten salt temperature at the outlet of the first receiver is set to be the molten salt inlet temperature at the inlet of the second receiver. Therefore, the molten salt temperature at the outlet of the second receiver can be calculated, which becomes the molten salt inlet temperature at the third receiver, and so on. In this way, the number of receivers required to reach the target molten salt temperature can be calculated (in this case, 19 receivers per line to reach 565 °C).

The total energy and exergy flux are calculated by adding the contributions of each receiver.

The solar group 62 receives solar salt from the warm tank 64, heats the solar salt to the target temperature, then sends the hot solar salt to the hot tank 65. From the hot tank, the solar salt is sent to the units requiring the highest operating temperature: the coker 76 and the secondary pyrolysis reactor 71.

The molten salts are fed directly to the coker, i.e. without a weir. The weir can allow for fine control of temperature and high flow rate (not required in the coker), but at the expense of a reduced flow rate, while the coker benefits from a high temperature of molten salts in the jacket.

The molten salt supply to both the first pyrolysis reactor 70 and the second pyrolysis reactor 71 is accomplished by means of the weirs 78, 79. These weirs have two chambers. The first receives the hot molten salts and delivers them to the pyrolysis reactor jacket (e.g., by means of a submersible pump). Unlike the weirs shown in Figure 6 and Figure 7, the return of these molten salts from the reactor is sent to the second chamber. The flow rate of molten salts that is circulated in the pyrolysis reactors is significantly greater than the flow rate of hot molten salts delivered from the reservoir. This high flow rate is desirable because it reduces the temperature difference within the pyrolysis reactors as well as maximizes heat transfer. As a result, some of the molten salts in the second chamber overflows the weir between the first and second chambers and falls into the first chamber. This ensures that the pump in the first chamber is able to deliver the required flow rate, while maximizing the temperature of the solar salts delivered to the pyrolysis reactors.

The molten salts from the coker are delivered to the weir 79 which feeds the molten salts to the second pyrolysis reactor 71. The molten salts exiting the weir 79 are sent to the warm tank 64, thus closing the ?hot cycle? of the heat transfer fluid.

The solar receiver 61 receives the solar salt from the cold tank 63, heats the solar salt to the target temperature (485 °C in this case), then sends the warm solar salt to the warm tank 64. The solar receiver 61 is made of 75 parallel lines, each comprising 8 receiver tubes in series (each receiver tube always having a length of 7.8 m). In this way, the flow rate of each line is 91.6/75=1.22 kg/s, therefore very similar to the flow rate of the hot receiver 62.

Ensuring a sufficiently high flow rate in the receiver tubes is required for safe operation of the solar collector assembly, in particular to reduce the temperature difference between the part of the tube exposed to different intensities of sunlight irradiation and related bending of the tubes.

From the warm tank the solar salt is sent to the first pyrolysis reactor 70 by means of the overflow device 78.

Part of the solar salt exiting the first pyrolysis reactor is sent to the hot oil exchanger 81. The hot oil exchanger is a heat exchanger that heats an organic heat transfer fluid (Eastman's Marlotherm SH), renamed 'oil', to about 320 ?C by means of 'low' temperature molten salts coming from the first pyrolysis reactor.

The use of an organic heat transfer fluid for low temperature operation is advantageous because it has a low melting point, thus eliminating the risk of solid salts freezing in areas where circulation is poor or thermal insulation is insufficient. Furthermore, heat tracing is not required for oil-lined lines. Since the demand is much lower than the demand of the first pyrolysis reactor, only a portion of the molten salts exiting the first pyrolysis reactor is diverted to the hot oil exchanger.

The solar salt exiting the first pyrolysis reactor is collected in the cold molten salt tank 63, closing the “warm cycle” of molten salts.

The heat losses in the solar receiver 62 are calculated in the above-mentioned Bellos model. The heat losses in the so-called collectors and connecting pipes of the solar collector group are neglected since they are considered negligible compared to the heat losses in the receivers.

The heat losses in the molten salt circuit, comprising the coker and the second pyrolysis reactor and related connecting pipes, are concentrated in a concentrated heat loss 83, called ?enthalpy loss 2?. The heat losses in the molten salt comprising the first pyrolysis reactor, the hot oil exchanger and related connecting pipes are concentrated in a second concentrated heat loss 82, called ?enthalpy loss 1?.

The exergy balance is made considering as control volume the internal walls in which the molten salts circulate, with the exception of the solar collector group (SCA) where the calculation is performed following the above-mentioned Bellos model and equations. Consequently, only for the SCA (i.e. for the exergy input) the boundary is on the incoming radiation from the sun.

Since there are no flows of matter across the chosen boundaries, the only continuous flows of exergy are:

- the incoming solar radiation exergy (sign ?+?)

- the outgoing exergy associated with the heat flow at:

or pyrolysis reactors, coking device, hot oil exchanger

o Concentrated heat losses in “enthalpy loss” devices.

It can be assumed that the temperature at the boundaries changes linearly with the heat flux. This assumption is even more realistic considering that the temperature change along the heat flux boundary is small compared to its absolute value (in Kelvin). Consequently, the exergy flux at such boundaries can be calculated with the <following equation> <:>

in which:

- T1 and T2 are the temperature at the beginning and end of the heat exchange boundary in Kelvin.

- T0 ? the reference temperature (in this case, 298 K)

- ?Q ? the heat flow

- ?? ? the exergy flow.

T1 and T2 correspond to the inlet and outlet temperatures, except when a weir device is used. In this case, the recirculation pump inside the weir device reduces the temperature difference between the inlet and outlet of the recirculated molten salt flow (in the limit of infinite flow, T1 is equal to T2).

The following table shows the detailed calculations, as well as the calculation of the total heat and exergy flux obtained by adding all the individual contributions.

It can be observed that the enthalpy balance (?heat flow?) is zero (indicating that all the net energy received by the solar collector groups is delivered to the demands or lost in said concentrated ?enthalpy loss?) while the sum of all exergy contributions is positive.

This exergy imbalance represents exergy losses (associated with heat losses), only for SCA, plus exergy destruction (associated with irreversible loss of thermal quality, i.e. during mixing of two fluids at different temperatures: the enthalpy before and after mixing is the same, but on the contrary exergy is lost).

This Example is applied to the pyrolysis of mixed plastic waste as follows:

- The essentially plastic material (mixed plastic waste) is fed to a screw heater whose jacket

? heated by the organic heat transfer fluid (Marlotherm SH) which has been heated by means of the hot oil exchanger, bringing its temperature to approximately 290 ?C.

- The essentially plastic material heated by the extruder is fed to the first pyrolysis reactor, heated by molten salts at a "warm" temperature, where it is pyrolyzed, forming a gaseous phase and a semi-solid phase (char). The reactor is a substantially vertical cylinder with an anchor stirrer.

- The gaseous effluent from the first pyrolysis reactor is fed to a second pyrolysis reactor. This reactor is essentially a tubular heat exchanger, which can optionally be filled with a catalyst, in which the pyrolysis vapors are heated and further pyrolyzed into smaller molecules.

- The gaseous effluent of the second pyrolysis reactor is fed to a condensation section, in which at least a continuous flow of liquid is obtained, which is quantitatively greater than 10% by weight of the initial weight of the fed plastic material, and which includes hydrocarbons for a large fraction.

- The char obtained in the first pyrolysis reactor is sent to a coker heated by hot molten salts, in order to produce a solid material with a better HSE (health, safety, environment) profile and useful not only as an energy source, but also as a filler. The gases evolved in this treatment are brought to the condensation section, thus increasing the pyrolysis yield.

Comparative example 2

Solar pyrolysis process driven by a single fluid (single heat transfer fluid cycle).

The process corresponding to this Example is given in Figure 9.

The heat transfer fluid is the same solar molten salt mixture (?solar salt?) as in Example 1 and the same physical property correlations have been used.

The solar collector group 62 is of the same type as in Example 1.

The code used to calculate the performance of the solar receivers is the same code used in Example 1 and with the same values of the geometric, optical, physical constants and ambient conditions.

The molten salt efficiencies were the same as in Example 1, both in terms of heat flux power (in Watts) and molten salt inlet and outlet temperatures.

Under these constraints, the required mass flow rate of molten salts through the solar receiver 63 is 42.6 kg/s. The inlet temperature of the solar salts is 418 ?C and the outlet temperature is 565 ?C.

The hot receiver 64 receives the solar salt exiting from SCA 62. The hot solar salt from the hot reservoir is fed, in parallel, to the units requiring the highest operating temperature (e.g., the coker 76 and the secondary pyrolysis reactor 71), and to the first pyrolysis reactor 70. In fact, the first pyrolysis reactor requires a higher heat flux at a lower temperature. Therefore, the setup shown in Figure 9 and in more detail herein is specifically designed to maximize the efficiency in this configuration: the solar salt, after passing through the coker and the second pyrolysis reactor, is still sufficiently high in temperature to heat the first pyrolysis reactor, but its quantity is insufficient for the (large) heat required to be fed. Consequently, an additional continuous flow of solar salt is fed directly from the hot reservoir to the first reactor.

Heating of both the first pyrolysis reactor 70 and the second pyrolysis reactor 71 is carried out by means of the weir devices 78, 79. These weir devices were the same as those used in Example 1.

Part of the solar salt exiting the first pyrolysis reactor is sent to the hot oil exchanger 81. The hot oil exchanger is a heat exchanger that heats the organic heat transfer fluid by means of ?low? temperature molten salts coming from the first pyrolysis reactor, in the same way as in Example 1.

Since the demand is much lower than the demand of the first pyrolysis reactor, only a portion of the molten salts exiting the first pyrolysis reactor is diverted to the hot oil exchanger.

The solar salt exiting the first pyrolysis reactor is collected in the cold molten salt tank 63, closing the (single) molten salt cycle.

As in Example 1, the heat losses in the molten salt circuit, comprising the coker and the second pyrolysis reactor and related connecting pipes, are concentrated in a concentrated heat loss 83, referred to as "enthalpy loss 2". The heat losses in the molten salt comprising the first pyrolysis reactor, the hot oil exchanger and related connecting pipes are concentrated in a second concentrated heat loss 82, referred to as "enthalpy loss 1".

The exergy balance is also performed in the same way.

<5 >The following table shows the detailed calculations, as well as the calculation of the total heat and exergy flux obtained by adding all the individual contributions.

It is possible to observe that the enthalpy balance (?heat flux?) is zero (as in Example 1) while the sum of all exergy contributions is positive.

Comparison of Example 1 with Comparative Example 2 The following table shows the operating characteristics of Example 1 in comparison to Comparative Example 2:

In both cases, all demands are the same, both in terms of heat flux and exergy flux. The latter is the same, despite the different inlet temperature in the weir, since the internal circulation pump guarantees the same temperature difference (T1 and T2 are the same in both Example 1 and Comparative Example 2).

Consequently, it can be stated that both Example 1 and Comparative Example 2 deliver the same efficiencies at the same temperatures to the loads, hence the pyrolysis process does not show any differences. However, the exergy balance is different: in fact, Example 1 has 14918 kW of imbalance, while Comparative Example 2 has 16570 kW, which is about 11% more.

This means that Comparative Example 2 is less efficient, since it requires the same amount of energy but at a higher quality level (more energy at high temperature).

The reason is that if two continuous flows at different temperatures are mixed, energy is conserved but exergy is not. In fact, in such an operation the continuous flow at high temperature (therefore, at higher quality) is irreversibly destroyed.

Finally, the improved process efficiency of Example 1 results in lower land and plant installation requirements and operating costs, as shown in the following table:

By splitting the solar salt loader (the SCA solar collector assembly) into two separate units, it is possible to generate a continuous flow of molten salt ?hot energy?, at a high temperature but not in large quantities, plus a continuous flow of molten salt ?warm energy?, at a lower temperature but in greater quantities. Solar collectors are more efficient when used to heat low-temperature heat transfer fluids because heat losses are lower, in particular because the evacuated tube allows for a dramatic reduction in thermal conductivity, but does not limit radiant emissions, which increases with the 4th power of the temperature, without even considering that the emissivity of the cermet material applied to the receiver tubes (to limit emissivity) also increases significantly above 500 ?C.

The pyrolysis process of mixed plastic waste to produce a pyrolysis condensate comprising hydrocarbons requires a first pyrolysis reactor (plus optionally a preheater) at relatively low temperature but high efficiency and, in addition, a second pyrolysis reactor (plus optionally a coker) at higher temperature but lower efficiency. Consequently, it is possible to match the higher temperature and lower quantity continuous flow of molten salt to the second pyrolysis reactor and the lower temperature and higher quantity continuous flow of molten salt to the first pyrolysis reactor, thereby optimising efficiency.

Accordingly, the total number of solar receivers in the Example using the double molten salt circuit, according to the present invention, is 980. In contrast, the number of solar receivers for the same requirements, but using a single molten salt circuit is 1050, which is approximately 7% more. This not only implies higher installation and operating costs, but also (obviously) a larger occupied area.

Claims (22)

1. Process for producing at least one pyrolysis oil from essentially plastic materials comprising the steps of: a) heating a first heat transfer fluid (F1) to a temperature (T1) between 400 ?C and 520 ?C by means of solar radiation; b) heating a second heat transfer fluid (F2) to a temperature (T2) higher than the temperature (T1) by means of solar radiation; c) heating a first pyrolysis reactor (R1) by means of the first heated heat transfer fluid (F1); d) heating a second pyrolysis reactor (R2) by means of the second heated heat transfer fluid (F2); e) feeding the first pyrolysis reactor (R1) with at least one essentially plastic material (M1); f) maintaining said essentially plastic material (M1) in said first pyrolysis reactor for a residence time which is at least 2 minutes and in any case sufficient to produce a fluid in the gaseous state (M2) which contains hydrocarbons; (g) feeding said gaseous fluid (M2), which contains hydrocarbons produced in the first pyrolysis reactor (R1), to a second pyrolysis reactor (R2); (h) maintaining said gaseous fluid (M2) in said second pyrolysis reactor (R2) for a residence time of at least 10 seconds; (i) condensing, totally or partially, the gas exiting from said second pyrolysis reactor (R2) so as to form at least a liquid comprising hydrocarbons having a standard boiling point of not less than 25 °C. 2. Process for producing at least one pyrolysis oil from essentially plastic materials according to claim 1, wherein said first and second heat transfer fluid (F1, F2) are recirculated substantially in their entirety. 3. A process for producing at least one pyrolysis oil from essentially plastic materials according to claim 2, wherein the recirculation of the first heat transfer fluid (F1) forms a first heat transfer fluid cycle (?warm cycle?) and the recirculation of the second heat transfer fluid (F2) forms a second heat transfer fluid cycle (?hot cycle?). 4. A process for producing at least one pyrolysis oil from essentially plastic materials according to claim 3, wherein the first heat transfer fluid cycle comprises said step a) and said step c) and the second heat transfer fluid cycle comprises said step b) and said step d). 5. A process for producing at least one pyrolysis oil from essentially plastic materials according to any of claims 1 to 4, additionally comprising the steps of: j) store the first heat transfer fluid (F1) from phase c) in a tank (?cold tank?) before using it in phase a); k) store the second heat transfer fluid (F2) heated in phase b) in a tank (?hot tank?) before using it in phase d). 6. Process for producing at least one pyrolysis oil from essentially plastic materials according to any of claims 1 to 5, wherein the first heat transfer fluid (F1) has the same composition as the second heat transfer fluid (F2). 7. A process for producing at least one pyrolysis oil from essentially plastic materials according to claim 6, which additionally comprises the steps of: l) store the first heat transfer fluid (F1) heated in phase a) before its use in phase c) and the second heat transfer fluid (F2) cooled in phase d) before its use in phase b) in a tank (?warm tank?). 8. A process for producing at least one pyrolysis oil from essentially plastic materials according to any of claims 1 to 6, additionally comprising the steps of: m) store the first heat transfer fluid (F1) heated in phase a) before its use in phase c) in a tank (?warm tank A?); n) store the second heat transfer fluid (F2) cooled in phase d) before its use in phase b) in a tank (?warm tank B?). 9. A process for producing at least one pyrolysis oil from essentially plastic materials according to any of claims 1 to 8, additionally comprising the steps of: p) heat the essentially plastic material before phase e) by means of the first heated heat transfer fluid (F1). 10. A process for producing at least one pyrolysis oil from essentially plastic materials according to any of claims 1 to 9, additionally comprising the steps of: o) heating the liquid, solid or semi-solid residue of the pyrolysis of phase f) (the char) by means of the second heated heat transfer fluid (F2) and, optionally, also by means of a gas heater by means of electric resistance (Joule effect) and combinations thereof. 11. Process according to claim 9, wherein in step p) the essentially plastic material is brought to a temperature between 120 ?C and 430 ?C, preferably between 150 ?C and 320 ?C, even more preferably between 180 ?C and 220 ?C, and wherein the average residence time of step p) is preferably less than 20 minutes, more preferably less than 4 minutes, in particular less than one minute. 12. A process according to claim 10, wherein in step o) said char is heated to a temperature of from 500 ?C to 1200 ?C, preferably from 600 ?C to 1000 ?C, more preferably from 700 ?C to 900 ?C, for a time of at least 5 minutes, preferably between 15 and 180 minutes, more preferably between 30 and 120 minutes. 13. A process according to any of claims 1 to 12, wherein the first and second heat transfer fluids (F1, F2) are molten salts, preferably with a melting temperature of at most 340 °C, more preferably at most 270 °C, even more preferably at most 240 °C. 14. Process according to claim 13, wherein said molten salts are a molten salt of group IA and IIA of the periodic table, preferably sodium nitrate, sodium nitrite, potassium nitrite, potassium nitrate, lithium nitrate, calcium nitrate or mixtures thereof. 15. A process according to claim 13, wherein said molten salts are nitrate/nitrite mixtures, in particular mixtures of potassium nitrate and sodium nitrate, preferably the ?solar salt?, optionally with the addition of sodium nitrite and calcium nitrate. 16. Process according to claim 8, wherein the first heat transfer fluid (F1) has a different composition than the second heat transfer fluid (F2). 17. A process according to claim 16, wherein the first heat transfer fluid (F1) has a lower melting point than the second heat transfer fluid (F2) and, preferably, the first heat transfer fluid (F1) has a melting point that is at most 180 °C, even more preferably at most 150 °C. 18. Process according to any of claims 1 to 17, wherein the temperature difference between the temperature T2 of step b) and the temperature T1 of step a) is at least 10 °C, even more preferably between 30 °C and 300 °C, even more preferably between 60 °C and 250 °C. 19. Process according to any of claims 1 to 18, wherein the heating of step a) and b) is carried out by means of at least one solar collector assembly comprising a parabolic collector, a linear Fresnel or a combination thereof. 20. Process according to claim 19, wherein the concentration factor of the at least one solar collector group of step b) is higher than the concentration factor of the at least one solar collector group of step a). 21. A process according to any one of claims 1 to 20, wherein the temperature to which the essentially plastic material is brought in said first pyrolysis reactor (70) is from 330 °C to 580 °C, preferably from 340 to 540 °C, more preferably from 360 to 500 °C, still more preferably from 380 to 480 °C, also more preferably from 410 to 450 °C, and wherein the temperature difference between the second pyrolysis reactor (71) and the first pyrolysis reactor (70) is at least 10 °C, preferably between 30 °C and 300 °C, more preferably between 60 °C and 250 °C, with the additional condition that such temperature is between 400 ?C and 650 ?C, preferably between 440 ?C and 550 ?C, more preferably between 460 ?C and 530 ?C. 22. Plant for producing at least one pyrolysis oil from essentially plastic materials, comprising: A) a first pyrolysis reactor (70) which has at least one inlet into which an essentially plastic material is fed, an outlet into which at least one gaseous effluent is removed and a jacket and/or coil equipped with at least one inlet and one outlet for molten salts; B) a second pyrolysis reactor (71) which has at least one inlet into which at least one continuous gaseous flow is fed from the first pyrolysis reactor (70), an outlet into which at least one gaseous effluent is removed, and a jacket and/or coil equipped with at least one inlet and one outlet for molten salts; C) a first tank (63, ?cold tank?) in which the low-temperature molten salts are collected; D) a second tank (64, ?warm tank?) in which the molten salts at medium temperature are collected; E) a third tank (65, ?hot tank?) in which the molten salts at high temperature are collected; F) a first solar collector assembly (61) comprising a first solar receiver, preferably consisting of a tube receiver, the first solar receiver comprising at least one inlet and one outlet for molten salts, wherein said solar collector assembly is capable of delivering concentrated solar radiation to said first solar receiver which, in turn, is configured to heat said molten salts; G) a second solar collector assembly (62) comprising a second solar receiver, preferably consisting of a tube receiver, the second solar receiver comprising at least one inlet and one outlet for molten salts, wherein said solar collector assembly is capable of delivering concentrated solar radiation to said second solar receiver which, in turn, is configured to heat said molten salts; H) a condenser (72) with at least one inlet for the continuous gaseous flow comprising hydrocarbons and an outlet for the condensed liquid, which is capable of at least partially condensing the continuous gaseous flow comprising hydrocarbons; wherein said first solar collector (61) is fluidly connected to said first tank (63) at one end of the first solar receiver and to said second tank (64) at the other end of said first solar receiver; and wherein said second solar collector (62) is fluidly connected to said second tank (64) at one end of the second solar receiver and to said third tank (65) at the other end of said second solar receiver; wherein said first tank (63) and second tank (64) are fluidly connected to said jacket and/or coil of said first pyrolysis reactor (70); wherein said second tank (64) and third tank (65) are fluidly connected to said jacket and/or coil of said second pyrolysis reactor (71); wherein said condenser (72) is fluidically connected to said second pyrolysis reactor (71), so as to be able to partially condense the pyrolysis vapours produced by said first and second pyrolysis reactors.