ES2759939B2 - PROCEDURE TO CONVERT PLASTIC WASTE INTO LIQUID PRODUCTS USEFUL IN THE PETROCHEMICAL INDUSTRY - Google Patents

Description

DESCRIPTION

PROCEDURE TO CONVERT PLASTIC WASTE INTO

USEFUL LIQUID PRODUCTS IN THE PETROCHEMICAL INDUSTRY

Field of the invention

The present invention relates generally to the field of waste recycling, and more specifically to a process for obtaining high added value pyrolysis liquids for use as raw material in the petrochemical industry.

Background of the invention

The increasing consumption of plastic materials has caused an increase in the volume of their waste. Its management is a source of growing social concern due to the depletion of landfill space, the loss of potential raw materials and the inevitable environmental contamination. The magnitude of the problem can be roughly estimated from plastic consumption figures, since many of the applications of plastic materials are characterized by having a short useful life (Lopez et al., 2017; Panda et al., 2010).

Since the second half of the 20th century, the production of plastic materials has grown exponentially, as it has driven the development of pioneering innovations that have made it possible to improve the quality of life and well-being of society (Al-Salem et al., 2009 ). Today, they are present in a large number of industrial and consumer products, so it is difficult to imagine daily life without them (Hestin et al., 2015; Lopez et al., 2017; Park et al., 2019; Wang et al., 2015). According to the latest data published by Plastics Europe (Plastics - the Facts 2018), world plastics production went from 1.5 million tons (Tm) in 1950 to 348 Tm in 2017, from which only 64.4 Mt were produced in Europe (18.5%). It is estimated that on the assumption that the current situation continues, world plastics production could triple between now and 2050. During 2017, polyethylene and polypropylene continued to be the most demanded polymers, with the packaging industry being the main user end of this type of polymers (39.7%; 2017) and, therefore, this sector is also responsible for most of the flow of plastic waste generated (62% of the total flow of post-consumer plastic waste in Europe) . This is also due to the fact that packaging plastics have a much shorter life cycle compared to other types of plastic products (Achilias et al., 2007).

According to the latest data published by Plastics Europe (Plastics - the Facts 2018), the European Union generated 27.1 tonnes of plastic waste in 2016. Of this total, 27.3% (7.4 tonnes) were deposited in landfills, 41.6% (11.3 Tm) was recovered energetically and 31.1% (8.4 Tm) was recycled (mainly through mechanical recycling). The landfill rate in Spain (46.4%; 2.3 Tm) is above the European average (27.3%). In a similar way to what happens in Europe, the largest amount of plastic waste collected in Spain in 2016 also corresponded to packaging waste (1.5 Tm), of which 38.2% was destined for the landfill .

In this context therefore arises the need to evolve towards a society much more efficient in the use of resources, promoting prevention, recycling and recovery actions. From the point of view of the efficient use of resources, it is especially important to avoid the disposal of plastic waste in landfills, since it represents an obvious loss of resources. However, as mentioned above, the percentage of deposit of plastic waste in Spanish landfills continues to be high due to the lack of adequate alternatives. In conclusion, plastic waste, due to its composition and origin derived from petroleum and, therefore, from an exhaustible raw material, is a valuable resource. In accordance with European environmental policies, the necessary measures must be promoted to develop treatment methods that allow the obtaining of new products or their conversion into an important source of energy. Progress must be made towards a circular economy, low in carbon and efficient in the use of resources.

The main constituents of post-consumer plastic waste are polyolefins: high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP) and linear low-density polyethylene (LLDPE). These four polymers represent 67% of the total plastics present in municipal solid waste (MSW). Other plastics in MSW are polystyrene (PS, 13.3%), poly (vinyl chloride) (PVC, 10.3%) and polyethylene terephthalate (PET, 5.3%). Currently, the main recycling route to recover the intrinsic value of these polymers is mechanical recycling (Ellen MacArthur Foundation, 2016; European Parliamentary Research Service Blog, 2017; Ragaert et al., 2017), which consists of washing, crushing and melting plastic waste to re-generate recovered plastic pellets, which are later transformed into new recycled plastic objects by molding or injection. Despite being the main recycling route, there are technical and economic barriers to the application of mechanical recycling (Dahlbo et al., 2018). Plastic pellets Recovered must meet the safety requirements for health and the environment according to the application to which it is intended. Due to the low compatibility of different types of plastics, the properties of mechanically recycled plastics are often inferior to those of virgin polymers. In addition, mechanical recycling is only applicable to thermoplastic materials (PE, PP, etc.) and requires carrying out the separation of the different types of plastics to obtain a high purity plastic waste, that is, it is not contaminated with other fractions of plastics or other materials in order to guarantee the quality of the final product. On many occasions this degree of separation is not technically possible due to the composition of the plastic waste stream, color or associated contamination. On the other hand, it is important to note that mechanical recycling cannot be carried out indefinitely, since after successive stages of heating and molding the plastic, it progressively loses its properties. From an economic point of view, mechanical recycling is not always economically viable, since the cost of the recycling process is not covered by the profits obtained from the sale of recycled plastic. In general, the average cost of mechanical recycling is around € 450-800 per ton of plastic processed. During pretreatment and sorting operations, there is usually a 35% waste of material. The yield from mechanical recycling of the remaining material is approximately 75%. Therefore, taking into account all the above, for each ton of plastic waste processed, less than 500 kg of recycled plastic will be obtained. The market price of recycled plastics varies around € 650-1000 per ton, a value that, taking into account the performance of the process, it is transformed into € 350-500 per ton of processed plastic waste (Hestin et al., 2015). Therefore, in many cases the costs of mechanical recycling are greater than the benefits obtained from the sale of recycled plastic.

In addition, the lack of a clear framework to apply the end-of-waste condition is also a barrier to the commercialization of recycled plastic materials. Taking into account the barriers of mechanical recycling, currently only two types of polymers from MSW are mechanically recycled: HDPE and PET. The mechanical recycling of other types of plastic waste is not economically viable due to the lack of quantity (constant production) and / or quality (homogeneity), making it necessary to consider other sustainable management alternatives. This is especially important in the case of film plastic (mainly low-density polyethylene), since it is the most abundant polymer in post-consumer plastic waste (Dahlbo et al., 2018; Diaz-Silvarrey and Phan, 2016; Horodytska et al., 2018; Kunwar et al., 2016).

The main alternative to mechanical recycling is chemical recycling, a more complex and costly process that allows treating highly degraded or heterogeneous plastics. The objective of chemical or tertiary recycling is the transformation of plastic waste into hydrocarbon chains that can be used as raw materials for the petrochemical industry or as fuels. The methods can be chemical or thermochemical, depending on the type of polymer, and can be classified into five large groups: chemical depolymerization or solvolysis (hydrolysis, alcoholysis, glycolysis, aminolysis, etc.), gasification with oxygen / water vapor mixtures for the obtaining synthesis gas (CO + H ² ) that can be used as a petrochemical raw material or for energy production, thermal cracking, catalytic cracking and hydrocracking.

Of the aforementioned processes, the thermal cracking process (also called pyrolysis) is emerging as one of the most promising alternatives for the treatment of plastic waste (mainly LDPE) (Czajcynska et al., 2017; Diaz-Silvarrey and Phan, 2016 ; Khoo, 2019; Lopez et al., 2017, Sharuddin et al., 2016; Singh et al., 2019; Sriningsih et al., 2014; Syamsiro et al., 2014; Park, 2019). To obtain high-quality pyrolysis liquids, which can be used as automotive fuels and / or as raw material to obtain new products, catalysts have been used to reduce the operating temperature and residence time. , improving the quality of the liquid product obtained (Santos et al., 2018). However, direct catalytic cracking processes also have important limitations, such as the difficulty of recovering the catalyst after use, which increases operating costs (Santos et al., 2018), or the high olefin content of the products obtained (Escola et al., 2011). In addition, the direct contact of the catalyst with plastic waste causes its rapid deactivation by coke deposition and poisoning due to the presence of elements, such as chlorine, sulfur, nitrogen and metals contained in some of the additives used to improve the properties of the polymers (Escola et al., 2011; López et al., 2011).

As an alternative to the direct catalytic cracking process, some authors have proposed carrying out a two-stage process (Artetxe et al., 2012; Escola et al., 2014; Park et al., 2019; Syamsiro et al., 2014), a first stage of thermal cracking, followed by a second stage of catalytic improvement of the quality of the pyrolysis liquids. This two-stage process allows solving the problem of rapid deactivation of the catalyst discussed above, however, it increases the complexity and operational costs of the process.

Document ES2706283T3 refers to a process for the conversion of plastic material into diesel fuel. Heterogeneous plastics are used as raw material to carry out their pyrolysis and subsequently the gases obtained are transferred to a catalytic converter medium to alter their molecular structure.

Document US2018010050A1 refers to a method to recover hydrocarbons from plastic waste, in particular waste rich in polyolefins, by means of thermolytic cracking that comprises melting the plastic waste in two heating devices, in which a recirculation stream derived from the reactor of Cracked and purified in a separator system is mixed with the molten plastic residue from the heating device. The mixed plastic stream is further heated in the second heating device, and from there it is guided into the cracking reactor, in which the plastic materials are cracked, and by means of subsequent distillation they are separated into components of low boiling point and diesel.

Therefore, there is still a need in the art for an alternative procedure that makes it possible to convert plastic waste (mainly LDPE), which is currently mainly landfilled, into high-quality, value-added pyrolysis liquids that can be used as material. premium for industry petrochemical plant for the production of new plastics or other products (solvents, extractants, hydrocarbons, etc.), without using any type of catalyst. It is further desirable that the process has improved performance and reduced cost compared to alternative processes known in the state of the art.

Summary of the invention

To solve the above technical problem, the present invention discloses a method for converting plastic waste into liquid products useful in the petrochemical industry, which comprises obtaining a pyrolysis liquid by means of the steps of:

a) carry out the fusion and homogenization of raw material of plastic waste continuously; b) carrying out the thermal cracking of the molten raw material from stage a) in a thermal cracking reactor; Y

c) subjecting volatile products from stage b) to rapid cooling;

whereby an outlet flow formed by pyrolysis liquid useful in the petrochemical industry as well as permanent gases of high calorific value is obtained at the exit of step c).

A detailed description of some preferred embodiments of the process according to the present invention is provided below. However, such detailed description is not intended to limit in any way the scope of protection sought by the present invention, defined solely by the appended claims and technical equivalents thereof.

Detailed Description of the Preferred Embodiments According to a preferred embodiment, the present invention relates to a catalyst-free, continuous pyrolysis process for converting plastic waste, preferably low-density polyethylene film and polypropylene, into high-value-added liquid products useful for used as raw material in the petrochemical industry to obtain new products, preferably new plastics.

The procedure comprises obtaining a pyrolysis liquid through the steps of:

a) carry out the fusion and homogenization of raw material of plastic waste continuously; b) carrying out the thermal cracking of the molten raw material from stage a) in a thermal cracking reactor; Y

c) subjecting volatile products from stage b) to rapid cooling;

whereby an outlet flow formed by pyrolysis liquid useful in the petrochemical industry as well as permanent gases of high calorific value is obtained at the exit of step c).

Furthermore, according to the preferred embodiment of the present invention, the process comprises a previous stage of conditioning the plastic waste raw material, before stage a), to eliminate unwanted compounds and homogenize the raw material.

The previous stage of conditioning of the plastic waste raw material (preferably plastic film bales from municipal solid waste treatment plants) is a key point to improve the efficiency and operational stability of the process and obtain high quality pyrolysis liquids and composition constant, factors necessary to guarantee a final market for the product. According to a preferred embodiment of the present invention, the pre-conditioning step comprises a selected step of optical separation, grinding, screening, magnetic and / or Foucault separation, centrifugation, density separation, agglomeration and any combination thereof. In this way, unwanted compounds, such as organic fraction, paper, cardboard, metal, glass, etc., are removed from the raw material.

The pre-conditioning step according to the preferred embodiment also comprises agglomeration or densification of the raw material to a density of 200-450 kg / m3.

The conditioned product obtained after the previous conditioning stage, and which will serve as raw material for stage a) as described in more detail hereinafter, is an agglomerate containing more than 90% by weight of polyethylene of low density, a size between 10 and 30 mm and a maximum moisture content of 15% by weight. The remainder of the material may comprise high-density polyethylene and polypropylene (the sum of both polymers being less than 10% by weight), less than 5% by weight of polystyrene and less than 2% by weight of other plastics, such as poly ( ethylene terephthalate) and poly (vinyl chloride).

Furthermore, the conditioned product preferably comprises a lower calorific value (PCI) greater than 9500 kcal / kg, a carbon content greater than 80% by weight and a hydrogen content greater than 13% by weight.

After conditioning in the previous stage described above, the raw material of plastic waste (in this case the conditioned product) is subjected to the conversion procedure itself according to the present invention. As mentioned above, said procedure comprises three stages.

In the first stage (stage a) the melting and homogenization of the plastic waste raw material is carried out continuously, by means of an extruder that introduces the raw material in a cyclical way in alternating sequence in two transfer chambers previously inerted (preferably with nitrogen) , provided with means of agitation, in order to obtain a continuous process. Thus, stage a) is preferably divided into the following substages:

- firstly, fill a first transfer chamber;

- when said first transfer chamber is full, stop filling the first transfer chamber and start filling a second transfer chamber;

- simultaneously with the filling of the second transfer chamber, heat the raw material in the first transfer chamber and pressurize with nitrogen; - after reaching the appropriate temperature and pressure, feeding the molten raw material to the cracking reactor of step b); Y

- Cyclically repeat the previous stages, alternating filling, heating and pressurization of the first and second transfer chambers.

Preferably, during stage a) the raw material is heated in the transfer chambers until reaching a temperature of between 270-310 ° C, with the aim of reducing the viscosity of the material, and is pressurized with nitrogen until reaching a pressure value of between 1 5 barg above the operating pressure of the thermal cracking reactor of stage b), described later.

Once the working conditions of the first transfer chamber have been reached, the molten raw material is fed from this transfer chamber to stage b) of pressure gradient thermal cracking. During the conditioning time of the raw material from the first transfer chamber and feed to the thermal cracking reactor, the second transfer chamber is filled and the process begins again.

The use of the double transfer chamber system makes it possible to homogenize and stabilize the operation, since having a double chamber can cushion possible failures or changes in the conditions of the material that is fed from the extruder. In addition, this system allows the use of a pressure gradient to transfer the molten polymer, dispensing with mechanical elements such as endless screws, etc.

According to one embodiment of the invention, the chambers consist of cylindrical tanks made of steel with a klopper bottom and the heating system of these tanks can be carried out by means of hot gases from the burner (used for the energy use of the gas generated during the thermal cracking process ) or by means of a thermal oil jacket.

In the second stage (stage b) the thermal cracking of the molten raw material from stage a) is carried out in a thermal cracking reactor. Thermal cracking is preferably carried out under temperature conditions of between 375-525 ° C, at a pressure of between 1-20 barg and with a residence time of between 0.5 and 5 h (defined as the amount of material in the inside of the reactor in kg divided by the feed rate in kg-h-1).

More preferably, the thermal cracking conditions are a temperature between 400-450 ° C, a pressure between 1-10 barg and a residence time of between 0.5-2 h.

To carry out the process according to the preferred embodiment of the present invention, the reactor of the thermal cracking stage is a continuous stirred tank reactor (called complete mixing reactor). Cracking is exclusively thermal, in the absence of any catalyst, so that the risk associated with its deactivation is avoided (by deposition of coke and poisoning due to the presence of elements, such as chlorine, sulfur, nitrogen and metals contained in some of the additives used to improve the properties of polymers), consumption, recovery and management as a waste thereof. This further enables the costs associated with the process of the present invention to be reduced.

According to the preferred embodiment of the present invention, the use of any inert carrier gas is not necessary to carry out the thermal cracking step. The pressure that is achieved in the reactor autogenously, with the gases themselves formed during the degradation of the polymeric material, is sufficient to drive the volatile products produced to the next stage c) of the process.

To carry out the process of the present invention by means of a continuous process, the process also comprises continuously extracting a solid generated during the thermal cracking of step b). This extraction can be carried out by mechanical devices, such as for example a centrifuge or a hot filtration system. The cracked liquid polymer, free of solids, is recirculated back to the thermal cracking reactor of stage b), keeping its fill level constant at all times.

According to one embodiment of the invention, the solid extraction system is specifically designed for a pressure reactor, allowing the solid to be separated from the liquid phase and returning the solid-free product to the reactor, keeping the level constant. This system consists of a heat exchanger, a buffer tank, a safety filter, an automatic filter with a 1-40 micron mesh, a pumping system to the reactor, a second heat exchanger and an auxiliary cleaning and maintenance system.

In the third stage of the process (stage c), the rapid cooling of volatile products from stage b) of thermal cracking is carried out. Rapid cooling is carried out, for example, by using shell and tube exchangers (using as a cooling agent a mixture of water and monoethylene glycol at 30% by volume) or by direct cooling or "quenching" using the pyrolysis liquids generated. in the process itself. As a result of the cooling of step c), an outlet flow is obtained at a temperature lower than 80 ° C, more preferably lower than 50 ° C, formed by pyrolysis liquids and permanent gases. The pyrolysis liquids are collected in a tank equipped with a mechanical stirring system, in which they are stored in an inert atmosphere and at a temperature above the cloud point to prevent the paraffins from freezing.

As a result of thermal cracking under the ideal conditions, high quality pyrolysis liquids are obtained, formed by a mixture of hydrocarbons with a low bromine number of between 20-35 g Br2 / 100 g sample, which indicates that the olefin concentration is low and the impact on oxidation stability is positive, as well as a low content of heteroatoms (N, S, O, Cl, Br) and metals, which is particularly positive for use in downstream catalytic processes in the petrochemical industry.

As a result of thermal cracking, in addition to the pyrolysis liquids, permanent gases formed by H ² and C ¹ -C ⁶ hydrocarbons (mainly gas rich in C4 compounds) are obtained, with a high calorific value, similar to that of commercial butane.

According to a preferred embodiment of the present invention, the permanent gases are taken to a burner used to cover the energy requirements of the process itself. Due to the quantity and quality of the gas generated during thermal cracking, the procedure is self-sufficient from an energy point of view and may even become surplus, in which case, the excess gas not used to meet the energy requirements of the procedure will be to a reciprocating internal combustion engine for electricity production.

A practical example of the implementation of the process according to the present invention is described below, provided solely by way of illustrative example and in no way limiting the process according to the present invention.

EXAMPLE 1

In this example, the process of the invention was carried out in a pilot plant comprising a continuous stainless steel reactor of 250 l capacity heated by electrical resistances and equipped with mechanical stirring. As raw material, low-density polyethylene was used in pellet format prepared according to the procedure described in this document from bales of white plastic film from the all-one line of the urban solid waste (MSW) treatment plant in Zaragoza (recovered by manual sorting in the bulky cabin). 500 kg of raw material were melted in an inert atmosphere and heated to 275 ° C. The fusion chamber was pressurized with nitrogen and the material was transferred to the pressure gradient thermal cracking reactor at a rate of 40kg / h, keeping the reactor fill level constant throughout the process. Cracking was carried out at about 420 ° C and at an autogenous pressure of 6 bar, with stirring at 50 rpm, at steady state for several hours. The liquid product resulting from thermal cracking is a mixture of hydrocarbons with a low olefin content (bromine number: 31 g / 100 g of sample) and contaminants (see table 1). The water content is less than 130 ppm and the aromatics content is approximately 32% by weight.

Table 1. Contaminants in pyrolysis liquids obtained by thermal cracking according to example 1.

The thermal cracking gas obtained according to the embodiment of Example 1 is mainly made up of cis-2-butene (approximately 30% by volume) and has a calorific value similar to that of commercial butane (11,000 kcal / kg). The density of the gas is approximately 1.8 kg / Nm3 and the average molecular weight is approximately 41 g / mol.

Thus, the process according to the present invention provides several advantages over the alternatives known from the prior art. A main advantage is the possibility of carrying out the pyrolysis process without the need for an auxiliary nitrogen gas entrainment and without the need for an external source of energy. The pressure that is achieved in the autogenous cracking reactor, with the gases that are generated when supplying heat, is sufficient to drive the gaseous product up to cooling stage c) (in the case of the condensable part) or to a burner or internal combustion engine in the case of permanent gases. In the rest of the prior art pyrolysis procedures, which are carried out at atmospheric pressure or under vacuum in the main reactor, this entrainment is achieved with nitrogen, which means greater expense and also reduces the calorific value of the gas, making it difficult to use as fuel . In the case of the proposed procedure, this gas has a calorific value similar to that of commercial butane, which, added to the fact that it is generated in a significant amount (8 - 15% by weight of the feed), makes the process self-sufficient from the energy point of view and can even become surplus, in which case the excess gas will be burned in an alternative internal combustion engine to produce electricity.

Another advantage offered by the process of the present invention is that it does not need a catalyst for its operation, thereby avoiding the risk of its deactivation, consumption and management as a waste thereof. Furthermore, the process conditions are conducive to obtaining high added value pyrolysis liquids with a low bromine number, which indicates that the olefin concentration is low and the impact on oxidation stability is positive.

Another advantage of the process according to the present invention is a very low content of heteroatoms (N, S, O, Cl, Br) and metals of the product obtained, which is particularly positive for its use in subsequent catalytic processes of the petrochemical industry. This is due to the combination of two factors, the previous conditioning stage carried out to ensure that the feed material meets the requirements of the procedure and the way in which thermal cracking is carried out, with which it is achieved that many of the unwanted substances that have not been eliminated in the previous conditioning stage remain retained in the solid.

Although the present invention has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that modifications and variations may be applied to said embodiments without thereby departing from the scope of protection conferred by the following claims.

Claims (18)

Procedure to convert plastic waste into liquid products useful in the petrochemical industry, the procedure comprising obtaining a pyrolysis liquid through the following steps: a) carry out the fusion and homogenization of raw material of plastic waste continuously; b) carry out the thermal cracking of the molten raw material from stage a) in a thermal cracking reactor, keeping its filling level constant at all times; Y c) subjecting volatile products from stage b) to rapid cooling; whereby an outlet flow formed by pyrolysis liquid useful in the petrochemical industry as well as permanent gases of high calorific value is obtained at the exit of step c); where stage a) comprises introducing raw material in a cyclical manner in alternating sequence in two transfer chambers, comprising: - firstly, fill a first transfer chamber; - when said first transfer chamber is full, stop filling the first transfer chamber and start filling a second transfer chamber; - simultaneously with the filling of the second transfer chamber, heat the raw material in the first transfer chamber and pressurize with nitrogen; - after reaching the appropriate temperature and pressure, feeding the molten raw material to the cracking reactor of step b); Y - repeating the previous stages in a cyclical manner, alternating the filling, heating and pressurization of the first and second transfer chambers; where the raw material is pressurized to 1-5 barg above the operating pressure of the thermal cracking reactor of stage b) and the molten raw material is fed from the transfer chamber to stage b) of pressure gradient thermal cracking; where stage b) of thermal cracking is carried out at a temperature of 375-525 ° C and at a pressure of 1-20 barg; where the procedure comprises a previous stage of conditioning the plastic waste raw material, before stage a), to eliminate unwanted compounds and homogenize the raw material, said previous stage comprises a selected stage of optical separation, crushing, screening, magnetic and / or Foucault separation, centrifugation, densimetric separation, agglomeration and any combination thereof and said previous step comprises densifying the raw material to a density of 200-450 kg / m3, After the previous conditioning stage, a conditioned product is obtained that will serve as raw material for stage a), said conditioned product is an agglomerate with more than 90% by weight of low-density polyethylene, with a size between 10 and 30 mm and a maximum moisture content of 15% by weight and said conditioned product comprises less than 10% by weight in total of high-density polyethylene and polypropylene, less than 5% by weight of polystyrene and less than 2% by weight of other plastics . Method according to claim 1, characterized Because the raw material is heated up to 270-310 ° C. Method according to any of claims 1 and 2, characterized in that the transfer chambers are previously inert. Process according to claim 3, characterized in that the transfer chambers are previously inerted with nitrogen. Process according to any of claims 1 to 4, characterized in that the transfer chambers comprise stirring means. Process according to any of the preceding claims, characterized in that step b) of thermal cracking is carried out with a residence time of between 0.5 and 5 h. Process according to claim 6, characterized in that step b) of thermal cracking is carried out at a temperature of 400-450 ° C, at a pressure of 1 10 barg and with a residence time of between 0.5 and 2 h. Process according to any of the preceding claims, characterized in that step b) of thermal cracking is carried out without a catalyst. Process according to any of the preceding claims, characterized in that it also comprises continuously extracting a solid generated during step b) of thermal cracking. Process according to claim 9, characterized in that the continuous extraction is carried out by means of a hot filtration system Process according to claim 10, characterized in that it further comprises recirculating a liquid from thermal cracking, free of solids, back to stage b) of thermal cracking. 12. Process according to any of the preceding claims, characterized in that the outlet flow temperature of step c) is less than 80 ° C. 13. Process according to claim 12, characterized in that the temperature of the outlet flow from step c) is less than 50 ° C. 14. Process according to any of the preceding claims, characterized in that the pyrolysis liquid of the outflow is composed of a mixture of hydrocarbons with a low bromine number between 25-35 g Br2 / 100 g of sample, as well as a low heteroatom and metal content. 15. Process according to any of the preceding claims, characterized in that the permanent gases in the outflow are made up of H2 and Ci-C6 hydrocarbons of high calorific value. 16. Process according to any of the preceding claims, characterized in that the permanent gases from the outlet flow are taken to a burner to cover the energy requirements of the process itself. 17. Process according to claim 1, characterized in that the conditioned product further comprises a lower calorific value greater than 9500 kcal / kg, a carbon content greater than 80% by weight and a hydrogen content greater than 13% by weight. 18. Process according to any of the preceding claims, characterized in that the plastic waste raw material comprises low-density polyethylene and polypropylene film.