Recycling method for used plastics using a light hydrocarbon solvent

Abstract

A method for purifying a plastic raw material, comprising: a) a dissolution step of bringing the plastic raw material into contact with a dissolution solvent containing a hydrocarbon compound having a boiling point of 15 to 100 °C at a dissolution temperature of 120 to 250 °C and a dissolution pressure of 1.0 to 25.0 MPa to obtain a crude polymer solution; b) a step of purifying the crude polymer solution to obtain a purified polymer solution, comprising: b1) separation of insoluble substances; and / or b2) washing by contact with a concentrated solution; and / or b3) extraction by contact with an extraction solvent; and / or b4) adsorption of impurities; then c) a solvent-polymer separation step using a supercritical separation section operating at 160 to 300 °C and a pressure of 2.7 to 10.0 MPa, followed by at least one solvent recovery section to obtain a purified thermoplastic plastic.

Description

Technical Field

[0001] The present invention relates to a method for treating used plastics to obtain a stream of purified thermoplastic polymers that can be economically upgraded, for example, in the manufacture of new plastic objects. More particularly, the present invention relates to a method for purifying a plastic feedstock, especially one obtained from plastic waste, including a thermoplastic polymer, especially a polyolefin, the method comprising dissolving the thermoplastic polymer in a light hydrocarbon solvent, especially one based on one or more alkanes having a boiling point of -15°C to 100°C, purifying the resulting polymer solution to at least partially remove impurities, especially additives conventionally used in plastic-based materials, and an optimized step of separating the polymer from the solvent to recover the purified thermoplastic polymer, wherein the recovered purified thermoplastic polymer can be reused, thus enabling the economic upgrading of the plastic feedstock.

Background Art

[0002] Plastics obtained from collection and sorting channels can be economically upgraded in various channels.

[0003] By "mechanical" recycling, certain waste can be partially reused directly into new objects or by mixing the mechanically sorted plastic waste stream with the stream of unused polymers. This type of economic upgrading is limited because mechanical sorting can improve the purity of a given type of polymer stream, but generally does not allow for the complete removal of impurities, such as additives, such as fillers, colorants, pigments, and metals, that are at least partially trapped in the polymer matrix.

[0004] "Chemical" recycling generally aims to at least partially reform monomers through a complex series of processes. For example, plastic waste often undergoes a pyrolysis process, and the recovered pyrolysis oil can generally be at least partially converted to, for example, olefins by steam cracking after purification. These olefins can then be polymerized subsequently. This type of sequence may be suitable for feedstocks or sorting center waste that has received little sorting, but it generally requires a large amount of energy consumption, especially for high-temperature treatment.

[0005] Another route for recycling plastic waste consists of at least partially dissolving plastics, especially thermoplastics, and aims to purify them by removing polymers and / or impurities other than the targeted one or more polymers in the feedstock, such as additives, for example, fillers, colorants, pigments, and metals.

[0006] Therefore, several studies have presented various methods for treating plastic waste by dissolution and purification. Patent Document 1 describes a specific method for purifying a polymer feedstock, especially one obtained from plastic waste, by dissolving the polymer in a solvent under specific temperature and pressure conditions and then contacting the resulting polymer solution with a solid.

[0007] Patent Document 2 proposes, among other things, a method of dissolving plastics in a solvent at a dissolution temperature close to the boiling point of the solvent. However, the method of Patent Document 2 does not make it possible to efficiently treat impurities other than polymers.

[0008] Patent Document 3 proposes a treatment method by liquefying thermoplastics in a solvent and then separating out insoluble substances and / or gases. The method of Patent Document 3 does not make it possible to efficiently treat impurities soluble in the solvent.

[0009] The present invention aims to overcome these drawbacks and to be involved in the recycling of plastics. More specifically, the present invention processes plastic feedstock, especially that obtained from plastic waste, to efficiently remove impurities it contains, especially at least partially additives it contains and which have conventionally been added to plastics, and to propose an effective, simple and economically feasible method for at least partially eliminating them, so as to be able to economically upgrade said plastic feedstock, more specifically plastic waste. The present invention actually aims to efficiently separate impurities from the thermoplastics contained in used plastics, especially polyolefins, and to recover purified thermoplastic polymers, especially polyolefins, so that they can be used, for example, as a polymer base in the manufacture of new plastic objects, especially instead of virgin resin.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Means for Solving the Problems

[0011] (Summary of the Invention) The present invention relates to a method for purifying plastic feedstock, said method comprising the following steps: a) Dissolution step; placing the plastic feedstock in contact with a dissolution solvent; the dissolution solvent contains at least one hydrocarbon-based compound and has a boiling point of -15 to 100 °C; the dissolution temperature at that time is 120 °C to 250 °C, and the dissolution pressure is 1.0 to 25.0 MPa (absolute); obtaining at least one crude polymer solution; b) Step of purifying the crude polymer solution; obtaining a purified polymer solution; including the following sub-steps: b1) Sub-step of separating out insoluble matter; and / or b2) Sub-step of washing by contact with a concentrated solution; and / or b3) Sub-step of extraction by contact with an extraction solvent; and / or b4) Sub-step of adsorbing impurities by contact with an adsorbent; then c) Solvent-polymer separation step; using at least one supercritical separation section operated at a temperature of 160 to 300 °C and a pressure of 2.7 to 10.0 MPa (absolute) (P supercritical), followed by at least one solvent recovery section; obtaining at least one purified thermoplastic polymer fraction.

[0012] The advantage of the method according to the invention lies in proposing a method for efficiently processing a feedstock containing plastics, plastic waste, in particular plastic waste obtained from collection and sorting channels, recovering the thermoplastic polymers it contains, in particular polyolefins, so that they can be recycled for any type of use. By the method according to the invention, it becomes possible to obtain a stream of purified thermoplastic plastic, which advantageously contains impurities, in particular additives and solvents, in particular dissolving solvents, the content of which is negligible or at least sufficiently low and can be introduced into any type of plastic formulation instead of virgin resin. For example, the stream of purified thermoplastic plastic obtained at the end of the method according to the invention, in particular the stream of purified polyolefin, advantageously contains less than 5% by weight of impurities, very advantageously less than 1% by weight of impurities, and very advantageously less than 5% by weight of solvent (in particular dissolving solvent), preferably less than 1% by weight of solvent, preferably less than 0.1% by weight of solvent.

[0013] By the method according to the invention, therefore, a simple scheme corresponding to a series of operations is proposed, which makes it possible to remove at least part of the impurities, in particular at least part of the additives, from the plastic waste and to recover a purified thermoplastic polymer, advantageously containing little or no solvent, and to economically upgrade the plastic waste by recycling said purified thermoplastic plastic. Advantageously, depending on the conditions used in the process of the method, the additives present in the plastic feedstock may be soluble or insoluble in the solvent used throughout the method according to the invention, enabling efficient purification and separation of the polymer.

[0014] Furthermore, by the method according to the invention, a series of operations is proposed which is carried out under optimal operating conditions, in particular with respect to temperature and pressure, but under reasonable operating conditions, in order to efficiently separate impurities and solvents from the thermoplastic polymer, and therefore to limit the energy consumption of the method, as a result making said method economically advantageous.

[0015] The present invention also has the advantage of participating in the recycling of plastics and the conservation of fossil resources by enabling the economic upgrading of plastic waste. Specifically, it enables the purification of plastic waste for the purpose of obtaining a purified thermoplastic polymer fraction, in particular purified polyolefin, with a reduced impurity content. These are, in particular, decolorized and deodorized thermoplastic plastic fractions, which may be reused to form new plastic objects. The resulting purified thermoplastic plastic fraction may therefore be used directly in formulations, as a mixture with additives such as colorants, pigments or other polymers, instead of or as a mixture with virgin resin, for the purpose of obtaining plastic products having aesthetic, mechanical or rheological processing properties that promote their reuse and their economic upgrading.

[0016] According to the present invention, it is also possible to efficiently and advantageously separate the target thermoplastic polymer from the solvent used (in particular the dissolving solvent), at a lower cost, while at the same time limiting the thermal degradation of the target thermoplastic polymer. Therefore, the solvent used, in particular the dissolving solvent, for treating the plastic feedstock can be at least partially recovered and recycled into one of the steps of the process, thus avoiding excessive solvent consumption and providing ecological and economic advantages to the process.

[0017] Therefore, the present invention aims to purify plastic feedstock, in particular plastic waste, to obtain purified thermoplastic polymers, more specifically purified polyolefins, so that they can be used in any application, in particular instead of virgin resin.

[0018] More specifically, the present invention proposes a method for obtaining a stream of purified poly thermoplastic polymer, which includes a dissolution step, followed by at least one purification step, and then an optimized solvent / polymer separation.

Embodiments for Carrying Out the Invention

[0019] (Description of Embodiments) According to the present invention, the expressions "comprised between... and...", "comprised between A and B", "between A and B" and "between A and B" are synonymous and mean that the two limit values (A, B) of the interval are included in the described range of values. In cases where this is not so and the two limit values are not included in the described range, such clarification will be provided by the present invention.

[0020] For the purposes of the present invention, various ranges of parameters for a given process, such as pressure ranges and temperature ranges, may be used alone or in combination. For example, for the purposes of the present invention, a range of suitable pressure values can be combined with a range of more suitable temperature values.

[0021] In the following text, certain embodiments of the present invention may be described. They may be implemented together, separately or in combination without restriction where technically feasible.

[0022] According to the present invention, the pressure is absolute pressure and is given in MPa (absolute) (MPa absolute) (or absolute MPa (MPa abs)).

[0023] The terms "upstream" and "downstream" should be understood in accordance with the general flow of one or more fluids or one or more flows under consideration in the present method.

[0024] In the present specification, the terms "thermoplastic polymer" and "thermoplastic plastic" are used interchangeably.

[0025] The term "additive" is a term conventionally used in the field of polymers, particularly in the field of polymer formulations. Additives introduced into a polymer formulation can be, for example, plasticizers, fillers (organic or inorganic solid compounds used to modify the physical, thermal, mechanical and / or electrical properties of the polymer material or to reduce its cost), reinforcing agents, colorants, pigments, curing agents, flame retardants, combustion retardants, stabilizers, antioxidants, UV absorbers, antistatic agents, etc.

[0026] The additives correspond to at least a part of the impurities in the plastic feedstock to be processed and can be at least partially removed by the method according to the invention. Other types of impurities can be use-related impurities, for example, metal impurities, paper / cardboard, biomass, polymers other than one or more targeted polyethylenes, etc.

[0027] Therefore, according to the invention, the additives containing impurities that can be at least partially removed by the method according to the invention are those conventionally used in polymer formulations, generally derived from the life cycle of plastic objects and materials and / or from the circuits of waste collection and sorting. The said impurities can be metallic, organic or mineral type impurities: they can be packaging residues, food residues or compostable residues (biomass). These use-related impurities can include glass, wood, cardboard, paper, aluminum, iron, metal, tires, rubber, silicone, rigid polymers, thermoplastic polymers, thermosetting polymers, household, chemical or cosmetic products, used oil and water.

[0028] According to the present invention, the polymer solution is a solution comprising a dissolution solvent and at least a targeted thermoplastic polymer, in particular a targeted polyolefin, which are dissolved in the dissolution solvent, i.e., in particular, solvated and dispersed, and the dissolved thermoplastic polymer is present from the beginning in the feedstock. The polymer solution may contain soluble impurities (dissolved in the dissolution solvent) and / or insoluble impurities (suspended in the polymer solution). Depending on the steps of the method according to the accepted present invention, the polymer solution may thus contain impurities in the form of insoluble particles, which are preferably suspended in the polymer solution, and may also contain soluble impurities, which are dissolved in the dissolution solvent and / or, in some cases, may contain another liquid phase that does not mix with the polymer solution.

[0029] The critical temperature and critical pressure of the solvent, in particular the dissolution solvent, are specific to the solvent and depend on the chemical nature of the solvent under consideration. For a pure substance, the critical temperature and critical pressure of the pure substance are, respectively, the temperature and pressure of the critical point of the pure substance. As is well known to those skilled in the art, above the critical point, the pure substance under consideration is in a supercritical form or in a supercritical state; it may be called a supercritical fluid.

[0030] The present invention relates to a method for purifying a plastic feedstock, preferably composed of plastic waste, and advantageously containing a thermoplastic polymer, more particularly a polyolefin, said method comprising, preferably consisting of, the following steps: a) Dissolution step; including contacting a plastic feedstock with a dissolution solvent containing at least one hydrocarbon-based compound; the hydrocarbon-based compound is preferably aliphatic, preferably paraffinic, and has a boiling point of -15 to 100 °C, preferably 8 to 100 °C, preferentially 25 to 69 °C, highly preferentially 25 to 61 °C, preferably 25 to 40 °C; the dissolution temperature during contact is 120 °C to 250 °C, preferably 130 to 225 °C, preferentially 150 °C to 210 °C, preferably 150 °C to 195 °C, and the dissolution pressure is 1.0 to 25.0 absolute MPa, preferably 1.0 to 20.0 absolute MPa, preferably 3.0 to 18.0 absolute MPa, preferentially 5.0 to 18.0 absolute MPa, preferably 6.0 to 17.0 absolute MPa; obtaining at least one crude polymer solution; then, b) Step of purifying the crude polymer solution; including at least one of the following sub-steps: b1) Sub-step of separating out insolubles; obtaining at least one clarified polymer solution and preferably an insoluble fraction; and / or b2) Sub-step of washing by contact with a concentrated solution; obtaining at least one washed polymer solution and preferably a wash effluent; and / or b3) Sub-step of extraction by contact with an extraction solvent; obtaining at least one extracted polymer solution and preferably a used solvent; and / or b4) Sub-step of adsorbing impurities by contact with an adsorbent; obtaining at least one refined and purified polymer solution; The purification step enables the obtaining of a purified polymer solution; the purified polymer solution preferably corresponds to a clarified and / or washed and / or extracted and / or refined and purified polymer solution; then, c) Solvent-polymer separation step; using at least one supercritical separation section; the temperature during operation is 160 to 300 °C, preferably 190 to 250 °C, preferentially 200 to 230 °C, and the pressure (P supercritical) at that time is 2.7 to 10.0 absolute MPa, preferably 3.0 to 6.0 absolute MPa, preferentially 3.0 to 5.0 absolute MPa, preferably 3.0 to 4.0 absolute MPa; continued by at least one solvent recovery section, particularly the temperature during operation is 160 to 300 °C, and the pressure is preferably between P supercritical and 0.000005 MPa (i.e., 5 Pa), preferentially 2.7 MPa to 0.000005 MPa, particularly 1.0 MPa to 0.000005 MPa; obtaining at least one fraction of the purified thermoplastic polymer, more specifically, at least one fraction of the purified polyolefin, advantageously the solvent fraction.

[0031] (Feedstock) The feedstock of the method according to the present invention is known as a plastic feedstock, and the feedstock contains plastic, and the plastic itself more specifically contains a thermoplastic polymer. Preferably, the plastic feedstock contains 50% to 100% by weight, preferably 70% to 100% by weight of plastic.

[0032] The plastic contained in the feedstock of the method according to the present invention generally includes production waste and / or waste plastic objects at the end of their life, particularly household plastic waste, plastic waste from the construction industry, plastic waste from vehicles or any type of transportation or electrical and electronic equipment waste. Preferably, the plastic waste is from collection and sorting channels. The plastic or plastic material contains a polymer, which after shaping is mixed with additives for the purpose of constituting various materials and objects (injection molded parts, tubes, films, fibers, fabrics, mastics, coatings, etc.). The additives used in plastics can be organic compounds or inorganic compounds. They are, for example, fillers, colorants, pigments, plasticizers, property modifiers, flame retardants, etc.

[0033] Preferably, the feedstock for the process according to the invention comprises, in particular, a thermoplastic polymer, preferably at least 50% by weight, preferentially at least 70% by weight, preferably at least 80% by weight, very preferably at least 90% by weight of thermoplastic polymer, relative to the total weight of the plastic feedstock. The thermoplastic polymer comprised in the plastic feedstock may be an alkene polymer, a diene polymer, a vinyl polymer and / or a styrene polymer. Preferably, the thermoplastic polymer comprised in the plastic feedstock is a polyolefin, for example polyethylene (PE), polypropylene (PP) and / or a copolymer of ethylene and propylene. Preferably, the plastic feedstock comprises at least 80% by weight, preferably at least 85% by weight, preferably at least 90% by weight of polyolefin, relative to the total weight of the plastic feedstock, the polyolefin being in particular a mixture of polyolefins and / or olefin copolymers, in particular a mixture of polyethylene (PE), polypropylene (PP) and / or a copolymer of ethylene and propylene. Advantageously, according to the invention, the polyolefin of the plastic feedstock is not mainly composed of polyethylene (PE) or polypropylene (PP), but is in fact a mixture of polyethylene (PE) and polypropylene (PP) and / or a copolymer of ethylene and propylene. The term "mainly" should be understood here to mean at least 80% by weight. The polyolefin of the plastic feedstock thus comprises less than 80% by weight of polyethylene or less than 80% by weight of polypropylene. Thus, more particularly, the plastic feedstock comprises at least 80% by weight, preferably at least 85% by weight, preferably at least 90% by weight of a mixture of polyethylene, polypropylene and / or a copolymer of ethylene and propylene, the percentages being given relative to the total weight of the plastic feedstock, said mixture comprising less than 80% by weight of polyethylene and less than 80% by weight of polypropylene.The plastic feedstock may thus contain polyethylene at a content of less than 80% by weight, preferably less than 72% by weight, preferentially less than 68% by weight, preferably less than 64% by weight, and polypropylene at a content of less than 80% by weight, preferably less than 72% by weight, preferentially less than 68% by weight, preferably less than 64% by weight. The percentages are given relative to the weight of the plastic feedstock to be treated by the method according to the invention. The method according to the invention thus aims, in particular, at purifying and recovering the polyolefins contained in the feedstock, in particular mixtures of polyolefins or their copolymers, so that they can be reused for various applications.

[0034] The plastic feedstock may contain impurities, for example polymers other than the targeted thermoplastic, additives, preferably those used for compounding the plastic material, and may also contain use-related impurities, which generally originate from the life cycle of the material and plastic objects and / or from the waste collection and sorting circuits. These compounds are collectively regarded as impurities. The plastic feedstock of the method according to the invention may contain up to 50% by weight of impurities, preferably up to 20% by weight of impurities, preferably up to 10% by weight of impurities. The plastic feedstock may contain, for example, at least 5% by weight of impurities.

[0035] The plastic feedstock may advantageously be pretreated prior to the method to remove at least some, and generally all, of the "coarse" impurities, i.e., impurities in the form of particles with a size of 10 mm or more, preferably 5 mm or more, more preferably 1 mm or more, such as wood, paper, biomass, iron, aluminum, glass, etc., and generally shaping it into the form of divided solids (or particles) to facilitate the treatment in the method. This pretreatment may include a grinding step, a washing step at atmospheric pressure, and / or a drying step. This pretreatment may be carried out at different sites, for example, at waste collection and sorting centers, or at the same site where the treatment method according to the invention is carried out. Preferably, this pretreatment can reduce the impurity content to less than 20% by weight, preferably less than 15% by weight, preferably less than 10% by weight, and the percentage is given relative to the weight of the plastic feedstock to be treated by the method according to the invention. At the end of the pretreatment, the feedstock is generally stored in the form of divided solids, for example, in the form of ground material or powder, to facilitate handling and transportation to the method.

[0036] (Dissolution step a)) According to the present invention, the method includes a dissolution step a), in which the plastic feedstock is placed in contact with a dissolution solvent to obtain at least one, preferably one crude polymer solution. Specifically, this step advantageously enables the dissolution of at least a part, preferably all, of the targeted thermoplastic polymer contained in the plastic feedstock, and most particularly the targeted polyolefin.

[0037] The term "dissolution" should be understood to mean any phenomenon leading to the formation of at least one polymer solution, i.e., a liquid containing a thermoplastic polymer dissolved in a solvent, more particularly in a dissolution solvent. Those skilled in the art are well aware of the phenomena involved in polymer dissolution, including at least mixing, dispersion, homogenization, solvation, and disentangling of the thermoplastic polymer chains.

[0038] During and at the end of the dissolution step a), depending on the pressure and temperature conditions, it is possible to maintain the dissolution solvent at least partially, preferably entirely, in liquid form, optimizing the dissolution of the targeted thermoplastic, in particular the targeted polyolefin.

[0039] Due to the nature of the dissolution solvent, advantageously, the use of operating conditions, in particular temperature and pressure conditions, especially pressure conditions, is possible, which are, firstly, reasonable for ensuring the maintenance of at least a partial, preferably total, liquid phase of the dissolution solvent not only in the dissolution step a), but also advantageously in the purification step b), and thus enabling optimal dissolution of the targeted polymer or polymers and advantageously efficient purification of the polymer solution, and secondly, reasonable for ensuring the passage of at least a portion of the dissolution solvent into a supercritical state in the solvent-polymer separation step c), allowing for demixing and thus separation of at least a portion of the dissolution solvent, optionally evaporation of at least a portion of the residual dissolution solvent, thereby making it possible to achieve a very low solvent content in the purified thermoplastic polymer recovered at the end of the process (advantageously, the content is less than 5% by weight of the solvent relative to the total weight of the purified thermoplastic polymer fraction, preferably 1% by weight of the solvent, preferably less than 0.1% by weight of the solvent). In fact, a very light alkane with a boiling point below -15°C, for example propane, which could be advantageous for its relatively mild critical conditions (temperature and pressure), would require the use of high pressure to maintain the dissolution solvent at least partially, preferably entirely, in liquid form throughout the dissolution step a) and the purification step b), which would involve significant costs, especially investment costs. Conversely, the use of a heavy solvent, for example an alkane with a boiling point above 100°C, would require very stringent operating conditions in step c) to achieve the critical conditions of said heavy solvent and to obtain said solvent in at least a partially supercritical state.

[0040] Advantageously, the dissolution solvent contains, preferably consists of, at least one hydrocarbon-based compound, which is advantageously aliphatic, preferably paraffinic (i.e., saturated), preferably at least one alkane, with a boiling temperature of -15 to 100 °C, preferably 8 to 100 °C, preferably 25 to 69 °C, highly preferably 25 to 61 °C, preferably 25 to 40 °C. Preferably, the dissolution solvent mainly, preferably contains at least 80% by weight, preferably at least 95% by weight, preferably up to 98% by weight of hydrocarbon-based compounds, which are advantageously aliphatic, preferably paraffinic (or alkane) (with a maximum of 100%, and the percentage is expressed relative to the total weight of the dissolution solvent), and the boiling point is -15 to 100 °C, preferably 8 to 100 °C, preferably 25 to 69 °C, highly preferably 25 to 61 °C, preferably 25 to 40 °C. Most advantageously, the critical temperature of the hydrocarbon-based compound (advantageously aliphatic, preferably paraffinic, forming the main amount of the dissolution solvent) (the temperature at the critical point of the high-purity hydrocarbon-based compound) is 130 to 285 °C, preferably 158 to 285 °C, preferably 185 to 245 °C, highly preferably 185 to 230 °C, preferably 185 to 200 °C. In great detail, the critical pressure of the main paraffinic hydrocarbon-based compound of the dissolution solvent is 2.5 to 5.0 MPa, preferably 2.7 to 4.6 MPa, preferably 3.0 to 3.8 MPa, most preferably 3.0 to 3.5 MPa. According to a preferred embodiment, the dissolution solvent mainly, preferably contains at least 80% by weight, preferably at least 95% by weight, preferably up to 98% by weight of aliphatic paraffinic hydrocarbon-based compounds, which are preferably linear or branched, with a boiling point of -15 to 100 °C, preferably 8 to 100 °C, preferably 25 to 69 °C, highly preferably 25 to 61 °C, preferably 25 to 40 °C, containing 4 to 7 carbon atoms (i.e., C4 - C7), preferably 5, 6 or 7 carbon atoms (C5, C6 or C7 respectively), preferably containing 5 or 6 carbon atoms (C5 or C6), highly preferably containing 5 carbon atoms (C5).

[0041] Advantageously, the melting temperature when performing the melting step a) is 120°C to 250°C, preferably 130°C to 225°C, preferentially 150°C to 210°C, preferably 150°C to 195°C, and the melting pressure is 1.0 to 25.0 MPa (absolute), preferably 1.0 to 20.0 MPa (absolute), preferentially 3.0 to 18.0 MPa (absolute), highly preferentially 5.0 to 18.0 MPa (absolute), preferably 6.0 to 17.0 MPa (absolute). More specifically, the temperature and pressure may vary over the entire process a) from the conditions of introducing the plastic feedstock and / or the melting solvent, for example, ambient conditions, i.e., a temperature of 10 to 30°C and atmospheric pressure (0.1 MPa), to the melting conditions, i.e., the melting temperature, in particular 120°C to 250°C, preferably 130 to 225°C, preferentially 150°C to 210°C, preferably 150 to 195°C and the melting pressure, in particular 1.0 to 25.0 MPa (absolute), preferably 1.0 to 20.0 MPa (absolute), preferably 3.0 to 18.0 MPa (absolute), preferentially 5.0 to 18.0 MPa (absolute), highly preferably 6.0 to 17.0 MPa (absolute) until they are achieved. Highly advantageously, at the end of the melting step a), the flow of the melted polymer is at the melting temperature and the melting pressure.

[0042] By restricting the temperature in step a) to 250°C or lower, preferably 225°C or lower, preferentially 210°C or lower, and further 195°C or lower, it is possible not only to avoid or limit the thermal degradation of the polymer, in particular, thermoplastic plastics, more specifically polyolefins, but also to limit the energy requirements of the method, and thus contribute to limiting the operating costs and carbon dioxide emissions of the method. Preferably, the melting temperature is above the melting point of the polymer, in particular thermoplastic plastics, more specifically polyolefins, and promotes their melting.

[0043] In parallel, the melting pressure is advantageously higher than the saturated vapor pressure of the melting solvent at the melting temperature, and as a result, the melting solvent is at least partially, preferably entirely, in liquid form at the melting temperature, optimizing the melting of the targeted thermoplastic plastic.

[0044] Advantageously, the temperature and pressure conditions of the dissolution achieved in step a) are adjusted such that the mixture (dissolution solvent + target thermoplastic) is homogeneous and, most preferably, single-phase, and the mixture may contain insoluble impurities suspended therein.

[0045] Preferably, the weight ratio between the plastic feedstock and the dissolution solvent ((feedstock / solvent), or the ratio between the mass flow rate of the plastic feedstock and the mass flow rate of the dissolution solvent at the inlet of the dissolution step a)) is from 0.01 to 2.0, preferably from 0.05 to 1.0, preferably from 0.10 to 0.8.

[0046] Advantageously, the dissolution step a) is carried out over a residence time of from 1 to 600 minutes, preferably from 2 to 300 minutes, preferably from 5 to 180 minutes. The residence time is understood as the residence time at the dissolution temperature and dissolution pressure in step a), i.e., the time of implementation of the plastic feedstock with the dissolution solvent at the dissolution temperature and dissolution pressure.

[0047] Advantageously, the dissolution solvent comprises and preferably consists of a fresh solvent feed and / or a recycled solvent stream obtained from a subsequent step of the process, preferably from the solvent-polymer separation step c).

[0048] Bringing the dissolving solvent into contact with the plastic feedstock to at least partially, preferably entirely, dissolve the thermoplastic polymer of the plastic feedstock in the dissolving solvent may be carried out in a line and / or in a device and / or between two devices. Therefore, step a) advantageously includes at least one dissolving device, optionally at least one feedstock preparation device, mixing device and / or transport device. These devices and / or apparatuses may be, for example, static mixers, extruders, pumps, reactors, co-current or counter-current columns, or a combination of lines and installations. Devices for transport, especially for fluids, for example for the transport of liquids or solids, are well known to those skilled in the art. By way of non-limiting example, the transport device may include pumps, extruders, vibrating tubes, endless screws or valves. The devices and / or apparatuses may include or be combined with a heating system (for example, an oven, exchanger, trace, etc.) to achieve the conditions required for dissolution. The dissolution step a) may be carried out continuously, in batch mode or in fed-batch mode.

[0049] The dissolution step a) feeds the plastic feedstock, in particular in the form of one or more streams of the plastic feedstock, at least, and the dissolving solvent, in particular in the form of one or more streams of the dissolving solvent, advantageously by one or more transport devices. One or more streams of the plastic feedstock may be different from one or more streams of the dissolving solvent. Part or all of the plastic feedstock may be fed to step a) as a mixture with part or all of the dissolving solvent, and the remainder of the solvent and / or feedstock may optionally be fed separately to step a).

[0050] While the plastic feedstock is in contact with the dissolving solvent, the dissolving solvent is preferably at least partially, and preferably entirely, in liquid form, whereas the plastic feedstock, which includes thermoplastic polymers, particularly polyolefins, may be in solid or liquid form and may, in some cases, contain solid particles in suspension. The plastic feedstock may, in some cases, be injected into the dissolving facility in the form of a suspension in the dissolving solvent as a mixture with the dissolving solvent, and the preparation and injection of the suspension may be continuous or batchwise.

[0051] According to a particular embodiment of the invention, step a) may be carried out using an extruder and optionally at least one other dissolving device. In this case, the plastic feedstock may, in some cases, feed at least part of the dissolving solvent into the extruder, and at the outlet of the extruder, at least part, preferably all, of the targeted thermoplastic polymer contained in the feedstock, more particularly polyolefin, is in molten form (and / or at least partially dissolved form). The plastic feedstock may, in some cases, be mixed with at least part of the dissolving solvent and then injected into the dissolving device, such as a reactor, in at least partially molten form (or partially dissolved form). The plastic feedstock leaves the extruder in at least partially molten form (or partially dissolved form), and this may be pumped by a pump dedicated to viscous fluids, often known as a melt pump or a gear pump. The plastic feedstock may, in at least partially molten form (or partially dissolved form), at the outlet of the extruder, be filtered using a filtering device, and in some cases in addition to the melt pump, for the purpose of removing the coarsest particles; generally, the mesh size of this filter is from 10 microns to 1 mm, preferably from 20 to 200 microns.

[0052] Preferably, step a) advantageously includes an extruder into which the dissolving solvent is injected, which promotes shearing and thus promotes intimate mixing between the dissolving solvent and the plastic feedstock, which contributes to dissolving the thermoplastic, more particularly the polyolefin.

[0053] Optionally, the process may include an intermediate adsorption step a'), which is located during or directly downstream of the dissolution step a), and which comprises the introduction of a solid adsorbent, preferably in the form of divided particles, such as, for example, alumina, silica, silica-alumina, activated carbon or bleaching earth, into the crude polymer solution obtained at the end of step a) or, optionally, during the dissolution step a). The solid adsorbent may be removed during the purification step b), for example, during the step b1) of separating out the insoluble matter and / or during the washing step b2). This optional step a') of adsorption in the presence of the solid adsorbent in divided form makes it possible to optimize the purification of the polymer solution.

[0054] The crude polymer solution obtained at the end of the dissolution step a) contains at least the dissolving solvent and the polymer to be recovered and purified according to the invention, in particular the thermoplastic polymer, dissolved in the dissolving solvent. Generally, the crude polymer solution also contains soluble impurities that are soluble in the dissolving solvent. The crude polymer solution may optionally contain insoluble impurities or compounds in suspension. The crude polymer solution obtained at the end of step a) may optionally contain polymers other than the targeted polymer, for example in molten form.

[0055] At the end of such a dissolution process, which is carried out, in particular, under operating conditions relating to temperature and pressure, the targeted thermoplastic of the plastic feedstock, in particular polyolefin, is advantageously dissolved, in whole or in part, in the dissolution solvent. The resulting thermoplastic solution (i.e., crude polymer solution) can undergo a purification step b), and then a solvent-polymer separation step c), recovering the thermoplastic from the plastic feedstock in a purified form, with the impurity and residual solvent contents being at a very low level and suitable for any type of subsequent application. Therefore, the method according to the invention enables the recovery of thermoplastics, in particular polyolefins, from plastic waste in an optimal and overall rational way under operating conditions (in particular, sufficiently restricted, i.e., restricted dissolution pressure), and thus the energy consumption is controlled and, as a result, the cost is restricted.

[0056] (Step b) of purifying the polymer solution) The purification method according to the invention comprises a step of purifying the crude polymer solution obtained from step a). This purification step b) includes at least one of the following sub-steps b1), b2), b3) and b4): b1) Sub-step of separating out insolubles, b2) Sub-step of washing by contact with a concentrated solution, b3) Sub-step of extraction by contact with an extraction solvent, b4) Sub-step of adsorption of impurities by contact with an adsorbent.

[0057] The various sub-steps b1), b2), b3) and b4) that may be carried out in the purification step b) may be operated continuously, in batch mode or in fed-batch mode.

[0058] Preferably, the purification step b) includes at least one sub-step b1) for separating out insoluble impurities. The purification step b) preferably includes several (i.e., at least two) sub-steps selected from sub-steps b1), b2), b3) and b4) in series, preferably including at least one sub-step b1) for separating out impurities and, for example, at least one adsorption sub-step b4) in this order very advantageously. By combining at least two sub-steps selected from b1), b2), b3) and b4), preferably, optimal purification of the polymer solution can be achieved.

[0059] The polymer solution obtained at the end of step b) is a purified polymer solution, containing at least the target thermoplastic dissolved in the dissolution solvent. This purified polymer solution may correspond to a clarified polymer solution obtained from the sub-step b1) for separating out impurities, a washed polymer solution obtained from the washing sub-step b2), an extracted polymer solution obtained from the extraction sub-step b3) or a refined purified polymer solution obtained from the sub-step b4) for adsorbing impurities.

[0060] (Sub-step b1) for separating out impurities) This purification method may include a sub-step b1) for separating out insoluble impurities by solid-liquid separation, preferably obtaining at least one polymer solution and preferably an insoluble fraction, and the polymer solution is clarified (in other words, free from at least a part, preferably all of the insoluble impurities contained in the crude polymer solution). The insoluble fraction preferably contains at least a part, preferably all of the insoluble impurities, especially in a suspended state in the crude polymer solution obtained from step a).

[0061] By the sub-step b1) of separating out insolubles, it is thus possible to remove at least a part, preferably all, of the particles of the insoluble compounds in the dissolution solvent that are present in suspension in the crude polymer solution obtained from step a) or from the optional step a’). The insoluble compounds (or impurities) removed during the sub-step b1) of separating out insolubles are, for example, pigments, mineral compounds, packaging residues (glass, wood, cardboard, paper, aluminum) and insoluble polymers.

[0062] When it is carried out, this separation sub-step b1) advantageously, in addition to removing at least a part of the insoluble impurities, makes it possible to limit operational problems in the treatment steps downstream of such a sub-step b1), in particular clogging and / or erosion, etc., while at the same time contributing to the purification of the plastic feedstock.

[0063] The temperature at which the sub-step b1) of separating out insolubles is advantageously carried out is 120 °C to 250 °C, preferably 130 °C to 225 °C, preferentially 150 °C to 210 °C, preferably 150 °C to 195 °C, and the pressure is 1.0 to 25.0 MPa (absolute), preferably 1.0 to 20.0 MPa (absolute), preferentially 3.0 to 18.0 MPa (absolute), preferably 5.0 to 18.0 MPa (absolute), most preferably 6.0 to 17.0 MPa (absolute). Most advantageously, the sub-step b1) of separating out insolubles is carried out under the temperature and pressure conditions at the outlet of the dissolution step a), that is, at the dissolution temperature and dissolution pressure as defined above.

[0064] When it is incorporated into the method, the sub-step b1) of separating out insolubles is preferably fed with the crude polymer solution obtained from step a) or from the optional intermediate adsorption step a’). According to another embodiment, the sub-step b1) may be fed with the washed polymer solution obtained from the washing sub-step b2).

[0065] Advantageously, the secondary step b1) includes at least one solid-liquid separation section (or solid-liquid-liquid separation section; in particular, in the case where the effluent obtained at the end of the dissolution step contains, in addition to the polymer solution and solid impurities, impurities and / or polymers with properties different from the target thermoplastic in liquid form and are contained with little or no solubility). The solid-liquid separation section includes at least one piece of solid-liquid separation equipment, for example, a separation vessel, a decanter, a centrifugal decanter, a centrifuge, a filter, a sand filter, a tangential filter, in particular, those using a membrane and / or a depth filter, a vortex current separator, an electrostatic separator, a triboelectric separator, preferably including a decanter, a filter, a sand filter and / or an electrostatic separator. Advantageously, a self-cleaning filter may be used, and the cleaning or clogging elimination enabling the removal of insoluble matter is carried out using a solvent stream. Preferably, the secondary step b1) includes at least one sedimentation section advantageously including at least one decanter and / or at least one filtration section. In the secondary step b1), a filter aid (for example, diatomaceous earth or sand) may optionally be added before decanting and / or filtration.

[0066] The removal of the insoluble fraction may be facilitated by equipment for transporting and / or removing traces of the solvent that may be present in the insoluble fraction, such as a conveyor, a vibrating tube, an endless screw, an extruder or a stripper. The secondary step b1) may therefore include equipment for transporting and / or removing traces of the solvent to remove the insoluble fraction. Advantageously, at least a part of the solvent recovered in the secondary step b1) is recycled to the process.

[0067] According to certain embodiments, the sub-step b1) of separating out insolubles includes at least two and generally less than five solid-liquid separation devices in series and / or in parallel. The presence of at least two solid-liquid separation devices in series enables the improvement of the removal of insolubles, while the presence of the parallel equipment enables the management of the maintenance and / or clogging elimination operations of the said equipment.

[0068] Certain insoluble compounds that are conventionally added during the polymer formulation, in particular certain pigments and mineral fillers, may be in the form of particles with a size of less than 1 μm. This is the case, for example, for titanium dioxide, calcium carbonate and carbon black. According to a particular embodiment of sub-step b1), the said sub-step b1) of separating out insolubles advantageously includes an electrostatic separator, whereby at least a part of the insoluble particles with a size of less than 1 μm can be efficiently removed. According to another particular embodiment of sub-step b1), the sub-step b1) of separating out insolubles includes a sand filter, which removes particles of different sizes, in particular particles with a size of less than 1 μm. According to yet another particular embodiment, the sub-step b1) of separating out insolubles includes a tangential filter, in particular one using a membrane and / or a depth filter, which may in some cases be included in the presence of a filter aid, such as diatomaceous earth, etc.

[0069] Depending on the nature of the feedstock, the polymer solution, preferably the crude polymer solution, fed to sub-step b1) may in some cases include a second liquid phase, for example a liquid phase consisting of a molten polymer that is different in nature from that of the target thermoplastic. According to another particular embodiment, sub-step b1) advantageously includes a solid-liquid-liquid separation section, using equipment for separating out two liquid phases and one solid phase, preferably by means of at least one two-phase or three-phase separator.

[0070] (Washing sub-step b2)) This purification method may optionally include a sub-step b2) of washing with a concentrated solution, and advantageously, at least one washed polymer solution and preferably a wash effluent are obtained. The washed polymer solution obtained at the end of sub-step b2) advantageously contains the target thermoplastic polymer that the present invention seeks to recover and purify dissolved in a dissolution solvent. Optionally, the washed polymer solution may further contain residual impurities (which are particularly soluble in the dissolution solvent) and / or, optionally, traces of the washing solvent (i.e., traces of the concentrated solution) if sub-step b2) is carried out.

[0071] When these two sub-steps are integrated into the purification step b), the washing sub-step b2) may be integrated upstream or downstream, preferably downstream, of the sub-step b1) that separates out the insoluble matter.

[0072] When it is integrated into the method, the washing sub-step b2) is fed with a concentrated solution and the crude polymer solution obtained from step a) or optionally from an intermediate adsorption step a’), or alternatively the clarified polymer solution obtained from b1). The polymer solution fed to the washing sub-step b2), particularly the crude or clarified polymer solution, may contain impurities in the form of suspended insoluble compounds and / or dissolved compounds. These suspended or dissolved compounds may be partially or entirely removed during the washing sub-step b2) by dissolution or precipitation and / or entrainment in the concentrated solution. Therefore, when it is carried out, this sub-step b2) contributes to the treatment of the plastic feedstock and, more particularly, to the purification of the polymer solution.

[0073] The cleaning sub-step b2) advantageously includes contacting the polymer solution fed to the sub-step b2), i.e., the crude or clarified polymer solution, with a dense solution. Advantageously, the dense solution has a higher density than the polymer solution (i.e., the mixture contains at least the target thermoplastic polymer and a dissolving solvent, and the target polypropylene is dissolved in the dissolving solvent). In particular, the density of the dense solution is preferably 0.85 or more, preferably 0.9 or more, preferentially 1.0 or more, and preferably 1.5 or less. The dense solution may be an aqueous solution, which preferably contains at least 50% by weight of water, preferably at least 75% by weight of water, and most preferably at least 90% by weight of water. The pH of the aqueous solution may be adjusted using an acid or a base to promote the dissolution of certain compounds. The dense solution may optionally contain an organic solvent and may preferably consist of a solution with a density that is advantageously 0.85 or more, preferably 0.9 or more, preferentially 1.0 or more, and the polymer of the plastic feedstock remains insoluble under the temperature and pressure conditions of the sub-step b2). For example, the organic solvent is selected from sulfolane or N-methylpyrrolidone (NMP), optionally as a mixture with water. Most preferably, the dense solution is an aqueous solution preferably containing at least 50% by weight of water, preferably at least 75% by weight of water, and most preferably at least 90% by weight of water.

[0074] When the cleaning sub-step b2) is advantageously carried out, the temperature is 120°C to 250°C, preferably 130°C to 225°C, preferentially 150°C to 210°C, preferably 150°C to 195°C, and the pressure at that time is 1.0 to 25.0 MPa (absolute), preferably 1.0 to 20.0 MPa (absolute), preferentially 3.0 to 18.0 MPa (absolute), preferably 5.0 to 18.0 MPa (absolute), and most preferably 6.0 to 17.0 MPa (absolute). Most advantageously, the cleaning sub-step b2) is carried out at the dissolution temperature and dissolution pressure.

[0075] In the case where it is incorporated into this method in the washing sub-step b2), the mass ratio (concentrated solution / polymer solution) between the mass flow rate of the concentrated solution and the mass flow rate of the polymer solution fed to the sub-step b2) is preferably from 0.05 to 20.0, more preferably from 0.1 to 10.0, and most preferably from 0.5 to 3.0. Placing the polymer solution and the concentrated solution in contact with each other may be carried out at several points in the equipment used, i.e., through several injections of the polymer solution and / or the concentrated solution at different points along the equipment; what is taken into account in the calculation of the mass ratio (concentrated solution / polymer solution) is the total of the injected flows.

[0076] The sub-step b2) may be carried out in one or more washing apparatuses that allow placement in contact with the concentrated solution and / or by separation equipment that allows recovery of at least one washing effluent and at least one washed polymer solution. This equipment is well-known and includes, for example, stirred reactors, static mixers, decanting mixers, two-phase or three-phase separation vessels, co-current or counter-current washing columns, plate columns, stirred columns, packed columns, pulsed columns, etc., and each type of equipment may include one or more pieces of equipment used alone or in combination with another type of equipment.

[0077] According to a preferred embodiment, the washing sub-step b2) is carried out in a counter-current washing column, in which the concentrated solution is preferably injected, on the one hand, into the preferably upper half, preferably the upper third of the column closest to the top of the column, and on the other hand, the crude or clarified polymer solution is preferably injected into the preferably lower half, preferably the lower third of the column closest to the bottom of the column. According to this embodiment, it is possible to recover at least one washed polymer solution and, advantageously, the washing effluent.

[0078] According to a very special embodiment, the flow at the inlet and / or outlet of the washing column may be split and injected at several injection points along the column and / or withdrawn at several withdrawal points along the column.

[0079] According to another embodiment, the washing sub-step b2) is carried out in a mixer-decanter, which mixer-decanter includes a stirring type mixing zone arranged such that a concentrated solution is in contact with a crude or clarified polymer solution, and a decantation zone enabling the recovery of the washed polymer solution and advantageously the washing effluent.

[0080] At the end of the washing sub-step b2), a washing effluent is advantageously obtained, which washing effluent contains, in particular, compounds dissolved in the concentrated solution and / or insoluble compounds entrained in the washing effluent. The washing effluent may be reprocessed in a washing effluent treatment section, on the one hand, at least partially separating out the dissolved and / or entrained compounds, and optionally purifying the washing effluent to obtain a purified concentrated solution, and on the other hand, at least partially recycling a part of the purified concentrated solution. This washing effluent treatment section may include one or more devices well-known for solid-liquid separation, for example, a separation vessel, a decanter, a centrifugal decanter, a centrifuge or a filter. The washing effluent may be sent outside the method, for example, to a used water treatment station when the concentrated solution is an aqueous solution.

[0081] (Extraction sub-step b3)) Step b) of the method according to the invention may include a sub-step b3) of extraction by placing it in contact with an extraction solvent, obtaining at least one extracted polymer solution and, preferably, a used solvent, in particular one filled with impurities. The extracted polymer solution obtained at the end of sub-step b3) advantageously contains the target thermoplastic polymer to be recovered and purified by the invention dissolved in a dissolution solvent. Optionally, the extracted polymer solution may further contain residual impurities that are particularly soluble in the dissolution solvent and / or traces of the concentrated solution and / or the extraction solvent if sub-steps b2) and / or b3) are carried out.

[0082] When it is integrated into the method according to the invention, extraction sub-step b3) is advantageously located between the dissolution step a) and the solvent-polymer separation step b), preferably downstream of the sub-step b1) for separating out insoluble substances, or, optionally, upstream or downstream of the adsorption sub-step b4) if the adsorption sub-step b4) is also integrated into step b).

[0083] The extraction sub-step b3) is preferably fed with an extraction solvent and a polymer solution, in particular, the crude polymer solution obtained from step a), the clarified polymer solution obtained from sub-step b1), the washed polymer solution obtained from sub-step b2) or the refined polymer solution obtained from the adsorption sub-step b4). Preferably, the extraction sub-step b3) is fed with an extraction solvent and the clarified polymer solution obtained from sub-step b1) and the washed polymer solution obtained from sub-step b2), or, optionally, the refined polymer solution obtained from the adsorption sub-step b4). The polymer solution fed to sub-step b3), preferably the clarified polymer solution, the washed polymer solution or the refined polymer solution, may therefore optionally contain dissolved compounds or dissolved impurities. These dissolved compounds may be partially or wholly removed by placing them in contact with the extraction solvent during the extraction sub-step b3). Very advantageously, the combination of sub-step b1) for separating out the insolubles in the extraction sub-step b3) and optionally the washing sub-step b2) and / or the adsorption sub-step b4) enables improved purification of the polymer solution and exploits the affinity of impurities for both the extraction solvent and, optionally, the concentrated solution and / or the adsorbent.

[0084] When it is incorporated into the process according to the invention, the extraction sub-step b3) advantageously includes at least one extraction section, preferably from 1 to 5 extraction sections, very preferably 1 extraction section.

[0085] The mass ratio (extraction solvent / polymer solution) between the mass flow rate of the extraction solvent and the mass flow rate of the polymer solution fed to sub-step b3), preferably a clarified polymer solution, a washed polymer solution or a refined polymer solution, is advantageously from 0.05 to 20.0, preferably from 0.1 to 10.0, preferably from 0.2 to 5.0. Placing the polymer solution fed to sub-step b3), preferably a clarified polymer solution, a washed polymer solution or a refined polymer solution, in contact with the extraction solvent may be carried out at several points in the extraction section, i.e. via several injections of the polymer solution and / or the extraction solvent at different points along the extraction section; what is taken into account in the calculation of the mass ratio (extraction solvent / polymer solution) is the sum of the flows injected.

[0086] The extraction solvent used in the extraction sub-process b3) advantageously comprises an organic solvent or a mixture of organic solvents. Preferably, the extraction solvent comprises, preferably consists of, at least one hydrocarbon-based compound, and the hydrocarbon-based compound is advantageously aliphatic, preferably paraffinic, preferably at least one alkane, and the boiling point is -15 to 100 °C, preferably 8 to 100 °C, preferentially 25 to 69 °C, preferably 25 to 61 °C, most preferably 25 to 40 °C. Preferably, the extraction solvent mainly, preferably at least 80% by weight, preferentially at least 95% by weight, preferably up to at least 98% by weight, preferably paraffinic aliphatic hydrocarbon-based compounds (or alkanes) (with 100% being the maximum, and the percentage being expressed relative to the total weight of the dissolving solvent), and the boiling point is -15 to 100 °C, preferably 8 to 100 °C, preferentially 25 to 69 °C, preferably 25 to 61 °C, most preferably 25 to 40 °C. Most advantageously, the hydrocarbon-based compound is advantageously aliphatic, preferably paraffinic, forms the majority of the extraction solvent, and its critical temperature (the temperature at the critical point of the high-purity hydrocarbon-based compound) is 130 to 285 °C, preferably 158 to 285 °C, preferentially 185 to 245 °C, preferably 185 to 230 °C, most preferably 185 to 200 °C. According to a preferred embodiment, the extraction solvent mainly, preferably at least 80% by weight, preferentially at least 95% by weight, preferably up to at least 98% by weight of aliphatic paraffinic hydrocarbon-based compounds, which are preferably linear or branched, and the boiling point is -15 to 100 °C, preferably 8 to 100 °C, preferentially 25 to 69 °C, preferably 25 to 61 °C, most preferably 25 to 40 °C, contains 4 to 7 carbon atoms (C4-C7), preferably 5, 6 or 7 carbon atoms (each being C5, C6 or C7), preferably contains 5 or 6 carbon atoms (C5 or C6), and preferentially contains 5 carbon atoms (C5).

[0087] Preferably, the extraction solvent used in b3) is the same solvent as the dissolution solvent used in step a), and in some cases, it is in a different physical state (for example, the extraction solvent is in a supercritical form, while the dissolution solvent is in a liquid form), which facilitates the management of the solvents, especially their purification and their recycling, particularly to the dissolution step a) and, optionally, to the extraction sub-step b3). Another advantage of using the same dissolution and extraction solvents in the same or different physical states is that it facilitates the management of the solvents included in the method according to the invention, especially the recovery of the solvents, their treatment, and their recycling to at least one of the steps of the method, in addition to limiting the energy consumption and costs resulting especially from the treatment and purification of the solvents.

[0088] One or more extraction sections of b3) may include one or more pieces of extraction equipment and may be arranged to be in contact with a separation facility for recovering the extraction solvent and / or at least one used solvent, especially one filled with impurities, and the extracted polymer solution. This equipment is well-known and includes, for example, stirred reactors, static mixers, decanting mixers, two-phase or three-phase separation vessels, co-current or counter-current washing columns, plate columns, stirred columns, packed columns, pulsed columns, etc., and each type of equipment may include one or more pieces of equipment used alone or in combination with another type of equipment.

[0089] According to a preferred embodiment of b3), the extraction is carried out in a countercurrent extraction column, where on the one hand an extraction solvent is injected and on the other hand a polymer solution fed to the sub-step b3) is injected. According to this embodiment, it is possible to recover on the one hand at least one extracted polymer solution and on the other hand a spent solvent, in particular one filled with impurities. Preferably, the polymer solution fed to b3), preferably a clarified, washed or refined polymer solution, is injected into the upper half of the column closest to the top of the countercurrent extraction column, preferably the upper third, while the extraction solvent is preferably injected into the lower half of the column closest to the bottom of the countercurrent extraction column, preferably the lower third.

[0090] The flow at the inlet and / or outlet of the countercurrent extraction column may be split at several injection and / or withdrawal points along the column.

[0091] According to another embodiment of b3), the extraction is carried out in a mixer-decanter, which advantageously comprises on the one hand a stirred mixing zone for placing the extraction solvent in contact with the polymer solution fed to the sub-step b3), preferably a clarified, washed or refined polymer solution, and on the other hand a decantation zone enabling the recovered extracted polymer solution to be recovered on the one hand and the spent solvent on the other hand.

[0092] Advantageously, the extraction sub-step b3) is carried out under temperature and pressure conditions different from those of the dissolution step a).

[0093] According to a preferred embodiment of b3), the extraction sub-step b3) includes a liquid / liquid extraction section. Preferably, when the liquid / liquid extraction section is operated, the temperature is 120°C to 250°C, preferably 130°C to 225°C, preferentially 150°C to 210°C, preferably 150°C to 195°C, and the pressure is 1.0 to 25.0 MPa (absolute), preferably 1.0 to 20.0 MPa (absolute), preferentially 3.0 to 18.0 MPa (absolute), preferably 5.0 to 18.0 MPa (absolute), most preferably 6.0 to 17.0 MPa (absolute). In any case, in this embodiment, the temperature and pressure conditions are adjusted so that the extraction solvent is in a liquid form, and the dissolution solvent is also preferably in a liquid form. Most advantageously, the liquid / liquid extraction is carried out, particularly when the extraction solvent is the same as the dissolution solvent, under temperature and pressure conditions different from those of the dissolution in step a), particularly at a temperature above the dissolution temperature and / or a pressure below the dissolution pressure, so that it is in the two-phase zone of the corresponding polymer-solvent mixing diagram.

[0094] According to another preferred embodiment of b3), the extraction sub-step b3) includes a section for extraction under specific temperature and pressure conditions where the extraction solvent is advantageously at least partially in a supercritical form. Such extraction may be referred to as supercritical extraction. In this embodiment, the extraction is advantageously mainly (i.e., preferably at least 50% by weight, preferentially at least 70% by weight, preferably at least 90% by weight) by placing the polymer solution fed to b3), preferably a clarified, washed or refined polymer solution, in contact with the extraction solvent under temperature and pressure conditions that enable the formation of a supercritical phase composed mainly of the extraction solvent. In other words, in this embodiment, the extraction is carried out by placing the polymer solution fed to b3), preferably a clarified, washed or refined polymer solution, in contact with the extraction solvent that is at least partially, preferably entirely, in a supercritical form. Such a supercritical extraction sub-step b3) advantageously enables efficient purification of the polymer solution, particularly due to the very high affinity of organic impurities, such as some additives, especially certain colorants or plasticizers, for the supercritical phase. The use of the extraction solvent in a supercritical form also makes it possible to create a substantial density difference between the supercritical phase and the polymer solution in liquid form, which facilitates separation by demixing and decantation between the two phases, i.e., the supercritical phase and the liquid phase, and thus contributes to the efficiency of the purification of the polymer solution.

[0095] In this other preferred embodiment, the extraction solvent used in sub-step b3) mainly preferably contains at least 80% by weight, preferentially at least 95% by weight, preferably up to at least 98% by weight of a paraffinic aliphatic hydrocarbon-based compound (or alkane) (where 100% is the maximum and the percentage is expressed relative to the total weight of the dissolution solvent), and the critical temperature is preferably 130 - 285°C, preferably 158 - 285°C, preferentially 185 - 245°C, preferably 185 - 230°C, most preferably 185 - 200°C. Most preferably, in such a supercritical extraction sub-step b3), the extraction solvent mainly preferably contains at least 80% by weight, preferentially at least 95% by weight, preferably up to at least 98% by weight of a paraffinic aliphatic hydrocarbon-based compound, the boiling point is -15 - 100°C, preferably 8 - 100°C, preferentially 25 - 69°C, most preferentially 25 - 61°C, preferably 25 - 40°C, contains 4 - 7 carbon atoms (i.e., C4 - C7), preferably 5, 6 or 7 carbon atoms (C5, C6 or C7 respectively), preferentially contains 5 or 6 carbon atoms (C5 or C6), and most preferentially contains 5 carbon atoms (C5). Very particularly, the critical pressure of the main paraffinic aliphatic hydrocarbon-based compound of the extraction solvent is 2.5 - 5.0 MPa, preferably 2.7 - 4.6 MPa, preferentially 3.0 - 3.8 MPa, and most preferably 3.0 - 3.5 MPa.

[0096] Advantageously, when the supercritical extraction sub-step b3) of this specific embodiment is carried out, the temperature is preferably 160°C to 300°C, preferentially 190 to 250°C, preferably 200°C to 230°C, and the pressure at that time is preferably 2.7 to 10.0 MPa (absolute), preferentially 3.0 to 6.0 MPa (absolute), preferably 3.0 to 5.0 MPa (absolute), and most preferably 3.0 to 4.0 MPa (absolute). According to the highly detailed mode of this preferred embodiment of sub-step b3), when the supercritical extraction is carried out, the pressure is highly advantageously between the critical pressure of the extraction solvent, which is mainly a paraffin-based aliphatic hydrocarbon-based compound (CP (extraction solvent)) (that is, as defined above, preferably having a boiling point of -15 to 100°C, preferably 8 to 100°C, preferentially 25 to 69°C, most preferentially 25 to 61°C, preferably 25 to 40°C, containing 4 to 7 carbon atoms, preferably 5, 6 or 7 carbon atoms, preferentially containing 5 or 6 carbon atoms, and most preferentially containing 5 carbon atoms, mainly a paraffin-based aliphatic hydrocarbon-based compound) and a pressure 3.0 MPa higher than the critical pressure of the extraction solvent, which is mainly a paraffin-based aliphatic hydrocarbon-based compound (that is: CP (extraction solvent) + 3.0 MPa), preferably between the critical pressure of the extraction solvent, which is mainly a paraffin-based aliphatic hydrocarbon-based compound (CP (extraction solvent)) and a pressure 1.5 MPa higher than the critical pressure of the extraction solvent, which is mainly a paraffin-based aliphatic hydrocarbon-based compound (that is: CP (extraction solvent) + 1.5 MPa), preferably between the critical pressure of the extraction solvent, which is mainly a paraffin-based aliphatic hydrocarbon-based compound (CP (extraction solvent)) and a pressure 0.5 MPa higher than the critical pressure of the extraction solvent, which is mainly a paraffin-based aliphatic hydrocarbon-based compound (that is, equal to CP (extraction solvent) + 0.5 MPa), and the pressure is absolute pressure.In any case, in this embodiment, the adjustment of the temperature and pressure conditions is carried out, in particular, in an adjustment section which is carried out upstream of the extraction section in the extraction sub-step b3). As a result, the extraction solvent is at least partially in a supercritical state in the extraction section. The adjustment of the temperature and pressure of the extraction solvent in the adjustment section is preferably carried out by means known to those skilled in the art (for example, using pumps and / or valves and / or turbines and / or heat exchangers and / or ovens).

[0097] In a highly preferred embodiment, the extraction sub-step b3) includes supercritical extraction. Apart from the fact that the extraction solvent is at least partially in a supercritical phase, the extraction solvent is the same as the dissolution solvent (or contains the same main compound as the dissolution solvent and may contain impurities).

[0098] Advantageously, at the end of the extraction sub-step b3), the used solvent obtained is particularly filled with impurities. It may be reprocessed in an organic treatment section, which on the one hand makes it possible to at least partially separate out the impurities and purify the solvent to obtain a purified extraction solvent, and on the other hand makes it possible to recycle at least a part of the purified extraction solvent to the inlet of the extraction sub-step b3) and / or, in the case where the dissolution solvent and the extraction solvent are the same, to the inlet of the dissolution step a). The used solvent may be treated according to any method known to those skilled in the art, for example, one or more of the following methods: distillation, evaporation, extraction, adsorption, crystallization and precipitation of insoluble substances, or purge.

[0099] (Adsorption sub-step b4)) The step b) of the treatment method according to the present invention may include an adsorption sub-step b4) to obtain at least one refined and purified polymer solution. The refined and purified polymer solution obtained at the end of the sub-step b4) preferably contains the thermoplastic polymer targeted for recovery and purification by the present invention dissolved in the dissolution solvent.

[0100] When incorporated into the process according to the invention, the adsorption sub-step b4) is advantageously carried out downstream of the dissolution step a) and upstream of the polymer-solvent separation step c). It may be carried out upstream of the sub-step b1) for separating out insolubles and / or the washing sub-step b2), and may particularly correspond to an optional intermediate adsorption step a’). Preferably, it is carried out downstream of the sub-step b1) for separating out insolubles and, optionally, downstream of the washing sub-step b2), which sub-step b2) itself is preferably downstream of the sub-step b1). It may also be carried out upstream or downstream of, for example, the extraction sub-step b3). Therefore, the adsorption sub-step b4) is carried out by placing the polymer solution fed thereto, in particular the crude polymer solution obtained from step a), the clarified polymer solution obtained from b1), the washed polymer solution obtained from b2) or the extracted polymer solution obtained from b3) otherwise, in contact with one or more adsorbents.

[0101] The adsorption sub-step b4) advantageously includes an adsorption section which is operated in the presence of at least one adsorbent which is preferably solid and is in particular in the form of a fixed bed, a fluidized bed (or slurry, i.e. in the form of particles introduced into the stream to be purified and entrained with this stream) or a boiling bed, preferably in the form of a fixed bed or a fluidized bed. Each adsorbent used in the sub-step b4) is preferably alumina, silica, silica-alumina, activated carbon, bleaching earth, or a mixture thereof, preferably activated carbon, bleaching earth or a mixture thereof, preferably in the form of a fixed bed or a fluidized bed, and the flow-through of the stream may be upward or downward.

[0102] Advantageously, when it is incorporated into the present method, the temperature during the adsorption sub-step b4) is 120°C to 250°C, preferably 130°C to 225°C, preferentially 150°C to 210°C, preferably 150°C to 195°C, and the pressure is 1.0 to 25.0 MPa (absolute), preferably 1.0 to 20.0 MPa (absolute), preferentially 3.0 to 18.0 MPa (absolute), preferably 5.0 to 18.0 MPa (absolute), most preferably 6.0 to 17.0 MPa (absolute). Most advantageously, the adsorption sub-step b4) is carried out under the temperature and pressure conditions of dissolution, i.e., at the dissolution temperature and dissolution pressure of step a). Preferably, in the optional sub-step b4), the hourly space velocity (HSV) corresponds to the ratio between the volumetric flow rate of the polymer solution fed to b4) and the volume of the adsorbent, and advantageously, it is operated in b4) at 0.05 to 10 h -1 , preferentially 0.1 to 5.0 h -1 .

[0103] According to a specific embodiment of the sub-step b4), the adsorption section may include one or more fixed beds of one or more adsorbents, for example, in the form of adsorption columns, preferably at least two adsorption columns, preferentially 2 to 4 adsorption columns, and contains one or more of the said adsorbents. When the adsorption section includes two adsorption columns, one mode of operation may be what is referred to as a "swing" operation in technical terms, where one of the columns is on-line, i.e., in service, while the other column is in reserve. When the adsorbent in the on-line column is exhausted, this column is isolated, while the reserve column is put on-line, i.e., put into service. The used adsorbent can then be regenerated in situ and / or exchanged with fresh adsorbent, and the column containing it is put on-line again when the other column is isolated.

[0104] Another mode of functionalization of this particular embodiment of b4) involves one or more fixed beds of one or more adsorbents and functionalizing at least two columns in series. When the adsorbent in the first column placed at the head is exhausted, this first column is isolated and the used adsorbent is either regenerated on-site or replaced with fresh adsorbent. The column is then returned online in the last position and this is repeated. This operation is known as the variable array mode or by the term PRS (Permutable Reactor System) or also as "lead and lag". The combination of at least two adsorption columns makes it possible to overcome the potentially rapid poisoning and / or clogging of the adsorbent due to the combined action of impurities, contaminants and insolubles that may be present in the stream to be treated. The reason for this is that the presence of at least two adsorption columns facilitates the replacement and / or regeneration of the adsorbent, preferably without stopping the treatment, and also makes it possible to control costs and limit the consumption of the adsorbent.

[0105] According to this particular embodiment of the adsorption sub-step b4) in a fixed bed of one or more adsorbents, the sub-step b4) is preferably carried out downstream of the sub-step b1) for separating out insolubles and / or the washing sub-step b2) and, optionally, upstream or downstream of the extraction sub-step b3). Advantageously, the combination of the sub-step b1) for separating out insolubles and / or the washing sub-step b2) and, optionally, the extraction sub-step b3) with the adsorption sub-step b4) enables improved purification of the polymer solution by taking advantage of the affinity of the residual impurities for both the adsorbent and the extraction solvent and, optionally, the concentrated solution.

[0106] According to another embodiment, the adsorption section of b4) may consist of adding adsorbent particles to a polymer solution, particularly a crude polymer solution, and the particles may be separated from the polymer solution via a step of removing the adsorbent particles located downstream of the adsorption section. The removal of the adsorbent particles may preferably correspond to the sub-step b1) of separating out insolubles or the washing sub-step b2). Such an implementation of the adsorption sub-step b4) preferably corresponds to the optional intermediate adsorption step a’) described earlier herein by introducing the adsorbent particles and subsequently performing solid-liquid separation.

[0107] (Step c) of solvent-polymer separation) According to the present invention, the method includes a solvent-polymer separation step c) to obtain at least one purified thermoplastic polymer fraction, more particularly at least one purified polyolefin fraction, and preferably a solvent fraction.

[0108] The solvent-polymer separation step c) preferably includes at least one supercritical separation section, followed in series by at least one solvent recovery section, preferably 1 to 5 solvent recovery sections. The solvent-polymer separation step c), more particularly the supercritical separation section, especially the first supercritical separation section, is fed with the purified polymer solution obtained from the purification step b).

[0109] The solvent-polymer separation step c) is thus initially directed towards, at least partially, preferably predominantly, even more preferably entirely, separating out one or more solvents, in particular the dissolving solvent, contained in the purified polymer solution fed to step c), in order to recover the thermoplastic polymer. The thermoplastic polymer is at least partially, preferably mainly, preferentially entirely, freed from impurities and the dissolving solvent, and optionally also from one or more other solvents (i.e., the extraction solvent and / or the concentrated solution) used in the process. The term "predominantly" is to be understood as meaning at least 50% by weight, preferentially preferably at least 70% by weight, preferably at least 90% by weight, very preferably at least 95% by weight, relative to the weight of one or more solvents, in particular the dissolving solvent, contained in the purified polymer solution fed to step c), and optionally also the extraction solvent and / or the concentrated solution. Any method known to the person skilled in the art for separating a solvent from a polymer may be carried out, in particular any method that enables a phase change of the polymer or of one or more solvents. The one or more solvents may be separated out, for example, by evaporation, stripping, demixing, density difference, in particular by decantation or centrifugation, etc.

[0110] The fraction of the purified thermoplastic polymer obtained at the end of step c) may correspond to a concentrated polymer solution or to a purified thermoplastic polymer in liquid (i.e., molten) or solid form. The solvent-polymer separation step c) may optionally include a conditioning section for conditioning the recovered thermoplastic plastic in solid form, more particularly in the form of solid granules. In this possible conditioning section, the recovered purified thermoplastic polymer is advantageously cooled to a temperature below the melting point of the polymer to obtain a fraction containing the polymer in solid form.

[0111] The solvent-polymer separation step c) is also directed towards at least partially, preferably mostly, preferentially entirely recovering one or more solvents contained in the purified polymer solution fed to step c), in particular the dissolving solvent, optionally the extraction solvent and / or the concentrated solution. The term "predominantly" should be understood to mean at least 50% by weight, preferentially preferably at least 70% by weight, preferably at least 90% by weight, highly preferably at least 95% by weight relative to the weight of one or more solvents contained in the purified polymer solution fed to step c). Therefore, step c) also advantageously makes it possible to obtain at least one solvent fraction. The solvent-polymer separation step c) is also directed, in some cases, towards purifying the recovered solvent fraction and recycling it, in particular upstream of the dissolving step a), optionally upstream of the washing sub-step b2) and / or the extraction sub-step b3).

[0112] The solvent-polymer separation step c) thus includes a supercritical separation section, whereby at least part of the dissolved solvent, optionally the extraction solvent and / or the dense solution, and optionally also part of the residual impurities not removed during step b), are separated under supercritical conditions, i.e., at a temperature and pressure adjusted to be above the critical point of one or more solvents to be separated out, in particular above the critical point of the dissolved solvent, and more particularly above the critical point of the main hydrocarbon-based compound of the dissolved solvent. This enables, advantageously, the easy separation and recovery of at least part of the solvent, in particular the dissolved solvent. This supercritical separation section particularly includes a fluid system composed of a supercritical phase mainly containing the solvent, in particular the dissolved solvent, and a liquid phase containing the thermoplastic polymer. The term "predominantly" here means at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, and most preferably at least 95% by weight relative to the weight of the flow under consideration, i.e., the supercritical phase. The separation may be referred to as the supercritical separation of one or more solvents. By the supercritical separation of one or more solvents, on the one hand, at least part of one or more solvents, in particular the dissolved solvent, and on the other hand, the thermoplastic polymer or the concentrated polymer solution can be efficiently separated. The supercritical separation is advantageously made possible by a significant density difference between the two phases, namely the supercritical phase and the liquid phase containing the thermoplastic polymer. Furthermore, the supercritical separation of one or more solvents advantageously enables a significant reduction in energy and environmental costs relative to the simple evaporation of the solvent, because there is no latent heat of evaporation during the transition to the supercritical state.

[0113] The temperature at which the supercritical separation section is advantageously operated is from 160 °C to 300 °C, preferentially from 190 to 250 °C, preferably from 200 °C to 230 °C, and the pressure (Psupercritical) at that time is from 2.7 to 10.0 MPa (absolute), preferably from 3.0 to 6.0 MPa (absolute), preferentially from 3.0 to 5.0 MPa (absolute), preferably from 3.0 to 4.0 MPa (absolute).

[0114] According to a specific embodiment, the pressure (Psupercritical) when the supercritical separation section of step c) is carried out is between the critical pressure (CP(solvent)) of the main hydrocarbon-based compound of the dissolution solvent and a pressure 3.0 MPa higher than the critical pressure of the main hydrocarbon-based compound of the dissolution solvent (i.e., CP(solvent) + 3.0 MPa), preferably between the critical pressure (CP(solvent)) of the main hydrocarbon-based compound of the dissolution solvent and a pressure 1.5 MPa higher than the critical pressure of the main hydrocarbon-based compound of the dissolution solvent (i.e., CP(solvent) + 1.5 MPa), preferably between the critical pressure (CP(solvent)) of the main hydrocarbon-based compound of the dissolution solvent and a pressure 0.5 MPa higher than the critical pressure of the main hydrocarbon-based compound of the dissolution solvent (i.e., equal to CP(solvent) + 0.5 MPa). The pressure is an absolute pressure. The main hydrocarbon-based compound of the dissolution solvent is preferably an aliphatic, preferably paraffinic hydrocarbon-based compound, with a boiling point of -15 to 100 °C, preferably 8 to 100 °C, preferably 25 to 69 °C, most preferably 25 to 61 °C, preferably 25 to 40 °C, preferably containing 4 to 7 carbon atoms, preferably 5, 6 or 7 carbon atoms, preferably 5 or 6 carbon atoms, most preferably 5 carbon atoms, as detailed in the description of step a) above.

[0115] The supercritical separation section of step c) is preferably carried out by demixing the liquid phase (containing the thermoplastic polymer) and the supercritical phase (composed of the solvent) and then decanting. Advantageously, the supercritical phase from the supercritical separation section at least partially constitutes the solvent fraction obtained at the end of step c). The liquid phase containing the thermoplastic polymer is preferably sent to a solvent recovery section or a series of solvent recovery sections.

[0116] Step c) may optionally include one or a plurality of consecutive supercritical separation sections, in particular 1 to 5, more particularly 1, 2 or 3. The liquid phase containing polypropylene and obtained from the supercritical separation section may thus be fed to another subsequent supercritical separation section, and the liquid phase from the last supercritical separation section is preferably sent to one or a series of solvent recovery sections. Most preferably, step c) includes one supercritical separation section.

[0117] Most advantageously, the supercritical separation of the solvent further reduces the content of residual impurities in the purified thermoplastic polymer fraction, more particularly at least one purified polyolefin fraction.

[0118] Preferably, the supercritical separation section, optionally a series of supercritical separation sections, is followed by at least one, preferably 1 to 5, preferably consecutive solvent recovery sections. The first solvent recovery section is fed with the liquid phase containing the target thermoplastic polymer obtained from the supercritical separation section, optionally a series of supercritical separation sections, in particular from the last supercritical separation section. In the case where the separation section includes at least two solvent recovery sections, each of the subsequent solvent recovery sections, i.e., from the second solvent recovery section onwards, is fed with the liquid phase containing the target thermoplastic polymer obtained from the preceding solvent recovery section. For example, the second solvent recovery section is fed with the liquid phase containing the target thermoplastic polymer obtained from the first solvent recovery section. The liquid phase containing the thermoplastic polymer obtained from the last solvent recovery section constitutes the purified thermoplastic polymer fraction, more particularly the purified polyolefin fraction, obtained at the end of step c).

[0119] The phase or combination of phases containing only the solvent obtained from one or more solvent recovery sections constitutes, together with the supercritical phase obtained from the supercritical separation section, or in the case of a series of supercritical separation sections, one or more solvent fractions advantageously recovered at the end of step c). The phase or combination of phases containing only the solvent obtained from one or more solvent recovery sections is preferably in gaseous form. They may be condensed and, optionally, mixed with the supercritical phase obtained from the supercritical separation section, the temperature and pressure conditions of which are pre-adjusted to be in liquid form.

[0120] When each solvent recovery section is carried out, the temperature is preferably 160 - 300 °C (preferably, the temperature is higher than the melting point of the target thermoplastic polymer), and the pressure is between the pressure (Psupercritical) used in the supercritical separation section and 0.000005 MPa (i.e., 5 Pa). Most preferably, when each solvent recovery section is carried out, the temperature is 160 - 300 °C, and the pressure at that time is between the pressure of the preceding section of step c) and 0.000005 MPa. Therefore, when step c) includes a supercritical separation section and several (at least two) solvent recovery sections, the pressure P(S1) when the first solvent recovery section S1 directly following the supercritical separation section is carried out is between the pressure (Psupercritical) used in the supercritical separation section (preferably the immediately preceding section) and 0.000005 MPa; the pressure P(S2) when the second solvent recovery section S2 directly following the solvent recovery section S1 is carried out is between the pressure P(S1) used in the first solvent recovery section S1 and 0.000005 MPa, and the same applies to subsequent sections. According to a preferred embodiment, when each solvent recovery section is carried out, the temperature is preferably 160 - 300 °C, the pressure is between the pressure of the preceding section of step c) and 0.000005 MPa, preferably, the pressure at that time is 10.0 MPa - 0.000005 MPa, preferentially 5.0 MPa - 0.000005 MPa, preferably 2.7 MPa - 0.000005 MPa. Preferably, the temperature and pressure conditions are adjusted in each solvent recovery section, and preferably modify the volatility of one or more solvents still present in the polymer phase in the form of a concentrated polymer solution or in the form of a molten or solid polymer.

[0121] In cases where several different solvents are used in the purification method according to the invention, in particular, in the dissolution step a), optionally, in the extraction sub-step b3), step c) may include several solvent recovery sections, for example, 2, 3 or 4 solvent recovery sections, separately, sequentially and / or continuously recovering various solvents, in particular, the dissolution solvent, optionally, the extraction solvent.

[0122] Advantageously, the supercritical separation and solvent recovery section of step c) may be operated continuously, in batch mode or in fed-batch mode.

[0123] Most advantageously, the solvent fraction recovered at the end of step c) may be treated in an organic treatment section arranged at the end of step c) to purify it and obtain at least one purified solvent, in particular at least one purified dissolving solvent, and advantageously recycle it to the dissolution step a), optionally to the washing sub-step b2) or the extraction sub-step b3). The optional organic treatment section at the end of step c) may use any method known to those skilled in the art, for example, distillation, evaporation, liquid-liquid extraction, adsorption, crystallization and precipitation of insolubles, or one or more methods from among purging.

[0124] By the method according to the invention, it is thus possible to obtain a purified stream of thermoplastic, more particularly polyolefin, from plastic waste, which may be used in any application, for example, instead of the same polymer in virgin form. The content of impurities and residual solvents in the purified stream of thermoplastic obtained via the method according to the invention, i.e., the purified thermoplastic polymer fraction, is thus low enough to be used in any application. Preferably, the stream of purified thermoplastic polymer obtained at the end of the method according to the invention, in particular the stream of purified polyolefin, advantageously contains less than 5% by weight of impurities, most advantageously less than 1% by weight of impurities, and most advantageously less than 5% by weight of residual solvent (in particular, dissolving solvent), preferably less than 1% by weight of residual solvent, preferably less than 0.1% by weight of residual solvent.

[0125] According to a preferred embodiment of the invention, a method for purifying a plastic feedstock comprises the following steps, preferably consisting of them: a) A step of dissolving in a dissolution solvent; this dissolution solvent contains at least one aliphatic, paraffinic hydrocarbon-based compound, and the boiling point is -15 to 100 °C, preferably 8 to 100 °C, preferentially 25 to 69 °C, preferably 25 to 61 °C, most preferably 25 to 40 °C; the dissolution temperature when carried out is 120 °C to 250 °C, preferably 130 to 225 °C, preferentially 150 °C to 210 °C, preferably 150 °C to 195 °C, and the dissolution pressure is 1.0 to 25.0 absolute MPa, preferably 1.0 to 20.0 absolute MPa, preferentially 3.0 to 18.0 absolute MPa, preferably 5.0 to 18.0 absolute MPa, most preferably 6.0 to 17.0 absolute MPa; at least one crude polymer solution is obtained; and then, b) A step of purifying the crude polymer solution; including the following sub-steps; b1) A sub-step of separating out insoluble substances; a clarified polymer solution and an insoluble fraction are obtained; and then b4) A sub-step of adsorbing impurities by contacting the clarified polymer solution with an adsorbent; at least one refined and purified polymer solution is obtained; and then c) A solvent-polymer separation step; using at least one supercritical separation section; the temperature when this section is operated is 160 to 300 °C, preferably 190 to 250 °C, preferentially 200 to 230 °C, and the pressure (P supercritical) at that time is 2.7 to 10.0 absolute MPa, preferably 3.0 to 6.0 absolute MPa, preferentially 3.0 to 5.0 absolute MPa, preferably 3.0 to 4.0 absolute MPa; followed by at least one solvent recovery section, the temperature when operated is 160 to 300 °C, and the pressure is between the pressure of the supercritical separation section (P supercritical) and 0.000005 MPa (i.e., 5 Pa); at least one fraction of the purified thermoplastic polymer is obtained.

[0126] According to another aspect, the present invention relates to a device for purifying a plastic feedstock, and the device includes the following, preferably consisting of them; a) A section for dissolving the plastic feedstock in a dissolving solvent; the dissolving solvent preferably contains at least one paraffinic aliphatic hydrocarbon-based compound; the dissolving temperature during operation is 120 °C to 250 °C, preferably 130 to 225 °C, preferentially 150 °C to 210 °C, most preferably 150 to 195 °C, and the dissolving pressure at that time is 1.0 to 25.0 MPa (absolute), preferably 1.0 to 20.0 MPa (absolute), preferentially 3.0 to 18.0 MPa (absolute), preferably 5.0 to 18.0 MPa (absolute), most preferably 6.0 to 17.0 MPa (absolute); obtaining at least one crude polymer solution; and then b) A section for purifying the crude polymer solution; including the following: b1) A sub-section for separating insolubles; and / or b2) A washing sub-section by contact with a concentrated solution; and / or b3) An extraction sub-section by contact with an extraction solvent; and / or b4) An impurity adsorption sub-section by contact with an adsorbent; and then c) A solvent-polymer separation section; including at least one supercritical separation section; the temperature during operation is 160 to 300 °C, preferably 190 to 250 °C, preferentially 200 to 230 °C, and the pressure (Psupercritical) at that time is 2.7 to 10.0 absolute MPa, preferably 3.0 to 6.0 absolute MPa, preferentially 3.0 to 5.0 absolute MPa, preferably 3.0 to 4.0 absolute MPa; followed by at least one solvent recovery section; the temperature during operation is 160 to 300 °C, and the pressure is between the pressure of the supercritical separation section (Psupercritical) and 0.000005 MPa (i.e., 5 Pa); obtaining at least one purified thermoplastic polymer fraction.

[0127] Preferably, the purification section b) includes the following: b1) A sub-section for separating insolubles; obtaining a clarified polymer solution and an insoluble fraction; then Sub-section for the adsorption of impurities by contacting the clarified polymer solution with an adsorbent; obtaining at least one refined polymer solution.

[0128] The following examples illustrate the invention, in particular specific embodiments thereof, but do not limit the scope of the invention.

[0129] (Example) (Example 1 (in accordance with the present invention)) (Dissolution step a)) A colored plastic feedstock (containing 95 wt% of a 50 / 50 mixture of polypropylene and polyethylene) in the form of pellets of size less than 5 mm based on polyolefin, derived from plastic waste, is introduced into an extruder heated to 180 °C in the form of flakes. At the extruder outlet, the feedstock is in at least a partially molten form, which is mixed with a solvent containing 99% n-pentane and preheated to 180 °C at a solvent / feedstock mass ratio of 9:1. The mixture of the solvent and the feedstock is introduced into a stirred reactor, heated to 180 °C and maintained at 12 MPa (absolute) for a residence time of 1 hour. Then, a polymer solution is obtained.

[0130] The polymer solution from the dissolution step a) is then subjected to a purification step b): The polymer solution is continuously withdrawn from the stirred reactor and passed through three filters placed in series. These filters are maintained at 180 °C and the cut-off diameters are 500 μm, 100 μm and 10 μm respectively (in this order). The pressure drop across the filters is 0.05 MPa.

[0131] At the outlet of the series of filters, the clarified polymer solution passes through an adsorption section containing a bed of activated carbon particles for a contact time of 2 hours and then through a filter retaining the activated carbon particles. This adsorption section is operated at 180 °C. Thereby, a pressure drop of 0.2 MPa is generated.

[0132] The purified polymer solution from purification step b) is then subjected to a solvent-polymer separation step c) which includes a supercritical section.

[0133] The purified polymer solution from the adsorption section is then heated to 210 °C and the pressure is slightly lower than 12 MPa (the value obtained by subtracting the pressure drop induced in the section of purification step b) from the dissolution pressure). The polymer solution is then expanded to 4 MPa (absolute) and injected into a decanter. This decanter is maintained at 4 absolute MPa and 210 °C for a residence time of 5 minutes. Two phases are formed: an upper phase mainly containing the n-pentane solvent in a supercritical state and a lower liquid phase containing the polyolefin dissolved in the n-pentane solvent. The upper phase is withdrawn from the top of the decanter.

[0134] The lower liquid phase is then subjected to evaporation of the residual solvent in two consecutive evaporation sections: first at a temperature of 210 °C and a pressure of 0.5 MPa for 5 minutes, and then at a temperature of 210 °C and a pressure of 0.01 MPa for 2 minutes.

[0135] At the end of the method, a solid A composed of purified polyolefin (50 / 50 polypropylene and polyethylene) is obtained at atmospheric standard conditions. Solid A is analyzed.

[0136] The obtained solid A is almost colorless, almost translucent, contains less than 5 wt% impurities and less than 1 wt% n-pentane.

[0137] (Example 2 (non-compliant)) In this Example 2, the same feedstock is processed and the dissolution step a) and the purification step b) are carried out in the same manner as described in Example 1.

[0138] The purified polymer solution from purification step b) is subjected to a solvent-polymer separation step that does not include a supercritical section: The purified polymer solution from the suction section is maintained at 180 °C, expanded to 2 MPa (absolute), and then injected into a decanter. This decanter is maintained at 2 absolute MPa and 180 °C for a residence time of 5 minutes. Two phases are formed: the gaseous upper phase consists of the n-pentane solvent, and the liquid lower phase contains the polyolefin dissolved in the n-pentane solvent. The gas phase is withdrawn from the upper part of the decanter.

[0139] The lower liquid phase is then subjected to evaporation of the residual solvent, first at a temperature of 210 °C and a pressure of 0.5 MPa for 5 minutes, and then at a temperature of 210 °C and a pressure of 0.01 MPa for 2 minutes.

[0140] At the end of the process, a solid B composed of purified polyolefin (50 / 50 polypropylene and polyethylene) is obtained at atmospheric standard conditions. Solid B is analyzed.

[0141] The obtained solid B is almost colorless and almost translucent, containing less than 5 wt% impurities and less than 1 wt% n-pentane.

[0142] However, the content of impurities (organic compounds excluding the dissolved solvent) in solid B is higher than the content measured in solid A obtained in Example 1 that complies with the present invention.

[0143] Furthermore, according to Example 2, the energy consumption required for polymer-solvent separation is greater than the energy consumption required for the polymer-solvent separation in the method described in Example 1, i.e., when the polymer-solvent separation includes a supercritical phase section.

Claims

1. A method for refining plastic supply raw materials, comprising the following steps: a) Dissolution step; which includes placing the plastic supply material in contact with a dissolution solvent; the dissolution solvent comprises at least one hydrocarbon-based compound having a boiling point of -15 to 100°C; the dissolution temperature is 120°C to 250°C and the dissolution pressure is 1.0 to 25.0 MPa absolute pressure; at least one crude polymer solution is obtained; b) A step of purifying the crude polymer solution; obtaining a purified polymer solution; comprising the following sub-steps: b1) A sub-step for separating insoluble material; and / or b2) A sub-step of cleaning by contact with a high-density solution; and / or b3) Sub-step of extraction by contact with extraction solvent; and / or b4) A sub-step of adsorption of impurities by contact with an adsorbent; and then c) Solvent-polymer separation step; using at least one supercritical separation section; operating at a temperature of 160–300°C and a pressure (P supercritical) of 2.7–10.0 MPa absolute pressure; followed by at least one solvent recovery section; obtaining at least one purified thermoplastic polymer fraction.

2. The method according to claim 1, wherein the plastic supply material comprises, at least 80% by weight, preferably at least 85% by weight, preferably at least 90% by weight, of polyethylene, polypropylene and / or a mixture of copolymers of ethylene and propylene, relative to the total weight of the plastic supply material, the percentages being given relative to the total weight of the plastic supply material, and the mixture comprising less than 80% by weight of polyethylene and less than 80% by weight of polypropylene.

3. The method according to claim 1 or 2, wherein the dissolving solvent comprises an aliphatic paraffinic hydrocarbon-based compound, the boiling point of which is 8°C to 100°C, preferably 25°C to 69°C, and more preferably 25°C to 40°C.

4. The method according to claim 1 or 2, wherein the dissolution temperature when performing dissolution step a) is 130°C to 225°C, preferably 150°C to 210°C.

5. The method according to claim 1 or 2, wherein the dissolution pressure when performing dissolution step a) is 1.0 to 20.0 MPa absolute pressure, preferably 5.0 to 18.0 MPa absolute pressure, and more preferably 6.0 to 17.0 MPa absolute pressure.

6. The method according to claim 1 or 2, wherein the purification step b) comprises at least a sub-step b1) for separating insoluble matter, and optionally a sub-step b2) for washing by contact with a high-density solution, and / or a sub-step b3) for extraction by contact with an extraction solvent, and / or a sub-step b4) for adsorption of impurities by contact with an adsorbent.

7. The method according to claim 1 or 2, wherein the temperature when operating the supercritical separation section in step c) is 190 to 250°C, preferably 200 to 230°C.

8. The method according to claim 1 or 2, wherein the pressure (P supercritical) when operating the supercritical separation section in step c) is 3.0 to 6.0 MPa absolute pressure, preferably 3.0 to 5.0 MPa absolute pressure, and more preferably 3.0 to 4.0 MPa absolute pressure.

9. The method according to claim 1 or 2, wherein step c) comprises 1 to 5 solvent recovery sections, the temperature during operation of each solvent recovery section being 160 to 300°C, and the pressure being between the pressure of the supercritical separation section (P supercritical) and 0.000005 MPa, preferably 2.7 MPa to 0.000005 MPa.

10. A device for refining plastic supply raw materials, comprising: a) A section for dissolving the plastic supply material in a dissolving solvent; the dissolution temperature during the operation is 120°C to 250°C, and the dissolution pressure is 1.0 to 25.0 MPa absolute pressure; at least one crude polymer solution is obtained; and then b) A section for purifying the crude polymer solution; comprising: b1) Subsection for separating insoluble matter; and / or b2) Washing of subsections by contact with high-density solution; and / or b3) Extraction subsection by contact with extraction solvent; and / or b4) Sub-subsection for impurity adsorption by contact with adsorbent; and then c) Solvent-polymer separation section; comprising at least one supercritical separation section; operating temperature is 160–300°C and pressure (P supercritical) is 2.7–10.0 MPa absolute pressure; followed by at least one solvent recovery section, operating temperature is 160–300°C and pressure is between the pressure (P supercritical) of the supercritical separation section and 0.000005 MPa (i.e., 5 Pa); at least one purified thermoplastic polymer fraction is obtained.