PROCESSING PROCEDURES FOR PLASTIC MATERIALS AND EQUIPMENT FOR PROCESSING THESE MATERIALS

Abstract

The invention relates to a method for processing plastic material, including: a) dissolving this plastic material in a solvent, at a temperature between 100°C and 300°C and an absolute pressure between 0.1 and 100.0 MPa, to obtain a crude polymer solution; b) refining this crude polymer solution to obtain a refined polymer solution; and c) separating the solvent-polymer to obtain a stream of refined thermoplastic polymer, using one or more series gas-liquid separation chambers, operating at an inlet temperature between 100°C and 300°C, and at a pressure lower than the outlet pressure of b), and each part producing a gas stream and a liquid waste stream, the liquid waste stream obtained from that part or from a final gas-liquid separation chamber forming the aforementioned refined thermoplastic polymer stream. The invention also relates to an apparatus for performing the aforementioned method.

Description

[0001] PROCESS FOR RECYCLING PLASTICS BY DISSOLUTION AND SEPARATION

[0002] OPTIMIZED SOLVENT-POLYMERS

[0003] TECHNICAL FIELD

[0004] The present invention relates to a method for purifying and recycling plastics, in particular used plastics, in order to obtain a stream of purified thermoplastic polymers which can be recovered, for example, in the manufacture of new plastic objects. More particularly, the present invention relates to a method for treating a plastic load, in particular from plastic waste, comprising thermoplastics and in particular polyolefins, for example polyethylene and / or polypropylene, by dissolving the targeted thermoplastics in a solvent, purifying the polymer solution obtained, then separating the polymer from the solvent using a succession of gas-liquid separation sections operated under particular conditions.This process thus makes it possible, after purification of the polymer solution, to simply but very effectively separate the dissolution solvent used from the polymer stream and therefore to recover a stream of purified thermoplastics with very low residual solvent contents.

[0005] PRIOR TECHNIQUE

[0006] Plastics from collection and sorting channels can be recycled through different channels.

[0007] So-called mechanical recycling allows some waste to be partially reused either directly in new objects or by mixing mechanically sorted plastic waste streams with virgin polymer streams. This type of recovery is limited since, even if it allows for a plastic stream concentrated in a particular type of polymer, mechanical sorting does not eliminate impurities that are at least partly trapped in the polymer matrix, such as additives such as fillers, dyes, pigments, plasticizers, and metals. Indeed, additives are compounds conventionally introduced into polymer formulations to give the material, and therefore the final objects, the desired properties, for example high mechanical strength, a particular color, etc.

[0008] So-called chemical recycling aims firstly to eliminate additives and, depending on the processes applied, to more or less chemically modify the macromolecular chains of the polymers in question (for example, recovery of the intact polymer, depolymerization of the latter or non-selective breaking of the chains of various polymers to obtain mixtures of compounds comprising carbon and hydrogen). These various chemical recycling options involve generally complex sequences of steps. For example, plastic waste can undergo a pyrolysis step, and the recovered pyrolysis oil, generally after purification, can be converted at least in part, for example, into olefins by steam cracking. These olefins can then be polymerized or transformed into monomers before polymerization of the latter.This type of chain can be adapted for poorly sorted loads or sorting center rejects, but it generally requires significant energy consumption, particularly due to high-temperature treatments.

[0009] Another way of recycling plastic waste consists of the deformulation of plastic materials, based on thermoplastics, in particular polyolefins such as (co)polypropylenes and (co)polyethylenes, which appears more virtuous. Indeed, this way of recycling plastic waste consists of dissolving the target polymer in a solvent and removing impurities, for example additives such as fillers, dyes, pigments, plasticizers, and metals and / or polymers of the filler other than the target one(s), without modifying the macromolecular chains of the target polymer. The preservation of the polymeric structure reduces the effort required and explains the good performance of this recycling approach, particularly in terms of energy consumption.

[0010] Several studies thus present different methods of treating plastic waste by dissolution and purification.

[0011] Document US 2017 / 002110 describes a particular method for purifying a polymer charge, in particular from plastic waste, by dissolving the polymer in a solvent, under particular temperature and pressure conditions, then contacting the polymer solution obtained with a solid. The method described in application US 2017 / 002110 finally comprises a step of separating the purified polymer from the solvent at temperature and pressure conditions in which said polymer precipitates.

[0012] WO 2018 / 114047 proposes a method for selectively dissolving a particular polymer of a plastic in a solvent at a dissolution temperature close to the boiling temperature of the solvent. The polymer solution is then centrifuged and the polymer is then separated from the solvent, for example by flash.

[0013] Document WO2018 / 118579 describes a method for purifying a polymer feedstock, in particular from plastic waste, by dissolving the polymer in a solvent in a stirred reactor, followed by a sedimentation step. More particularly, WO2018 / 118579 illustrates the purification of a feedstock composed of post-consumer polypropylene by dissolving in n-butane in an autoclave stirred at 140°C and 900 psig (6.21 MPa), followed by a sedimentation phase after stopping the stirring in the autoclave. The resulting polymer solution is sent or not through beds of solids and then depressurized so as to be able to separate at least a portion of the butane solvent from the polypropylene.

[0014] The present invention aims to improve these methods of treating thermoplastics by dissolving in a solvent and in particular the separation of the solvent used from the purified polymer. In particular, the present invention seeks, in a method of purifying a plastic filler comprising thermoplastics by dissolving in a solvent, to optimize the separation of solvents, in particular of the dissolving solvent used, from said purified thermoplastics, so as to recover a stream of thermoplastics, in particular polyolefins, purified and in particular decolorized and deodorized, and having a residual solvent content of less than or equal to 5% by weight, preferably very low. The present invention particularly seeks to efficiently and simply separate the purified thermoplastics, preferably the purified polyolefins, from the solvent in which they are dissolved.

[0015] SUMMARY OF THE INVENTION

[0016] The invention relates to a method for treating a plastic filler comprising thermoplastics, said method comprising: a) a step of dissolving the plastic filler in a dissolving solvent, step a) being carried out at a dissolving temperature of between 100°C and 300°C and at a dissolving pressure of between 0.1 and 100.0 MPa absolute, to obtain at least one crude polymer solution; b) a step of purifying the crude polymer solution, to obtain a purified polymer solution, comprising: b1) a sub-step of separating the insolubles; and / or b2) a sub-step of washing, by contact with a dense solution; and / or b3) an extraction sub-step, by contact with an extraction solvent; and / or b4) a sub-step of adsorption of the impurities by contact with an adsorbent; then c) a step of solvent-polymer separation of the purified polymer solution, to obtain a stream of purified thermoplastic polymers and at least one stream of solvent,said solvent-polymer separation step c) using a gas-liquid separation section or several gas-liquid separation sections operating in series, said gas-liquid separation section or each of the gas-liquid separation sections being operated at an inlet temperature of between 100°C and 300°C and at a pressure lower than the outlet pressure of step b), when step c) uses several gas-liquid separation sections, the pressure of the later section being lower than that of the earlier section, the purified polymer solution, obtained at the end of purification step b), feeding said gas-liquid separation section or the first gas-liquid separation section of the series, said gas-liquid separation section or each of the gas-liquid separation sections producing a gas effluent, which corresponds to said at least one solvent stream, and a liquid effluent,when step c) uses several gas-liquid separation sections, the liquid effluent from the previous section feeding the subsequent section, the liquid effluent from said gas-liquid separation section or from the last gas-liquid separation section of the series constituting said flow of purified thermoplastic polymers.,

[0017] Said at least one solvent stream advantageously comprises the solvent(s) used in the process. In particular, it comprises dissolution solvent and optionally extraction solvent and / or dense solution.

[0018] The advantage of the method according to the invention is to propose a method for recycling, by dissolution, thermoplastics, preferably polyolefins, such as polypropylene, polyethylene, their copolymers, or their mixtures, included in a plastic load and in particular in plastic waste, for example post-consumer, making it possible to recover a stream of purified thermoplastics, i.e. freed from at least part of the impurities contained in the plastic load, and having a very low residual solvent content, in particular less than or equal to 5% by weight, preferably less than or equal to 1.00% by weight, preferably less than or equal to 0.10% by weight, preferably less than or equal to 500 ppm by weight of solvent relative to the total weight of the stream of purified thermoplastics.Indeed, the recycling process according to the invention, which is based on the principle of dissolving the targeted thermoplastics and purifying the polymer solution obtained, has the advantage, in addition to eliminating at least part of the organic and inorganic impurities contained in the plastic charge, for example additives introduced into the polymer materials by the formulators, of proposing a simple and effective scheme for separating the thermoplastics freed from the impurities of the solvent of the polymer solution, in particular the dissolution solvent used.

[0019] Thus, the method according to the invention has the advantage of proposing a simple method for recycling thermoplastics, and in particular polyolefins, such as polypropylene, polyethylene, their copolymers, or their mixtures, included in a plastic load for example from post-consumer waste, with an optimized solvent-polymer separation step, so as to obtain a stream of thermoplastics, in particular polyolefins, purified and in particular decolorized and deodorized, having sufficiently low residual contents of impurities and solvent so that the purified thermoplastics can be used in any type of plastic formulation instead of virgin resin.In particular, the method according to the invention makes it possible to recover a flow of purified thermoplastics, in particular a flow of purified polyolefins, or even polypropylene or polyethylene, comprising at most 5% by weight of impurities, very advantageously at most 1.0% by weight of impurities, preferably at most 0.5% by weight of impurities, relative to the total weight of the flow of purified thermoplastics.

[0020] The invention also has the advantage of contributing to the recycling of plastics and the preservation of fossil resources, by enabling the recovery of plastic waste. It enables, in fact, the purification of plastic waste in order to obtain a flow of purified thermoplastic polymers, in particular purified polyolefins, or even purified polypropylene or polyethylene, with a reduced content of impurities and in particular decolorized and deodorized, which can be reused to form new plastic objects. The purified thermoplastics obtained can thus be used directly in formulations mixed with additives, for example plasticizers, colorants, pigments, fillers, etc., instead of or mixed with virgin resins, in order to obtain plastic materials with usage, aesthetic, mechanical or rheological properties facilitating their reuse and recovery.

[0021] The present invention also relates to a device for treating a plastic load to obtain a flow of purified thermoplastic polymers, said device comprising:

[0022] - dissolution means for bringing into contact and dissolving at least partially the plastic filler in a dissolution solvent, and obtaining a crude polymer solution;

[0023] - purification means for purifying the crude polymer solution and obtaining a purified polymer solution;

[0024] - a solvent-polymer separation device, located downstream of said purification means, for separating the purified polymer solution into a stream of purified thermoplastic polymers and at least one solvent effluent, characterized in that said solvent-polymer separation device comprises: a gas-liquid separation section or several gas-liquid separation sections operating in series, preferably at least two, preferably between two and five, for example three or four, successive gas-liquid separation sections, at least one pressure control system in said gas-liquid separation section or in each gas-liquid separation section of the series, so as to adjust the pressure in said gas-liquid separation section or in each gas-liquid separation section of the series to a value lower than the operating pressure at the outlet of the purification means,and when said solvent-polymer separation device comprises several gas-liquid separation sections, so as to adjust the pressure in the later section to a lower value than that in the earlier section, said gas-liquid separation section or each gas-liquid separation section of the series comprising a feed system, a liquid withdrawal system and a gas withdrawal system, the feed system of said gas-liquid separation section or of the first gas-liquid separation section of the series being connected to at least one of the purification means and allowing the supply of purified polymer solution to said solvent-polymer separation device, when said solvent-polymer separation device comprises several gas-liquid separation sections, the feed system of the later section being connected to the liquid withdrawal system of the earlier section,the liquid withdrawal system of said gas-liquid separation section or of the last gas-liquid separation section of the series making it possible to recover said stream of purified thermoplastic polymers, the gas withdrawal system of said gas-liquid separation section or of each gas-liquid separation section of the series making it possible to recover said at least one solvent effluent, said at least one solvent effluent comprising dissolution solvent.,

[0025] DESCRIPTION OF EMBODIMENTS

[0026] In this description, the expressions "between ... and ..." and "between .... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this is not the case and the limit values ​​are not included in the range described, such clarification will be provided by this description.

[0027] In this description, the expression "greater than ..." is understood as strictly greater than, and symbolized by the sign ">", and the expression "less than ..." as strictly less than, and symbolized by the sign "<". When the limit is understood, the precision will be provided by the respective expressions "greater than or equal to ..." (and corresponding to the sign ">") and "less than or equal to" (corresponding to the sign "<").

[0028] For the purposes of the present invention, the different parameter ranges for a given step 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 preferred pressure values ​​may be combined with a range of more preferred temperature values.

[0029] In the following description, particular embodiments of the invention are described. They can be implemented separately or combined with each other, without limitation of combinations when this is technically feasible.

[0030] According to the present invention, the pressures are absolute pressures and are given indifferently in MPa or in absolute MPa (or MPa abs.).

[0031] The terms "upstream" and "downstream" are to be understood in relation to the general flow of the fluid(s) or stream(s) in question in the process, in particular in relation to the flow of the stream which includes the thermoplastics to be purified.

[0032] In this description, the terms "polymer", "thermoplastic polymer" and "thermoplastic" may be used interchangeably in place of each other.

[0033] The term "polyolefins" refers to any type of homopolymers and / or copolymers, and their mixtures, having olefins as their unit unit. More specifically, polyolefins can be polyethylene homopolymers, designated by the acronym PE, of any range (for example high density, also called HDPE, or low density, called LDPE), polypropylene homopolymers, designated by the acronym PP, their copolymers and / or their mixtures.

[0034] The term "additives" is a term conventionally used in the field of polymers and in particular in the field of polymer formulations. The additives introduced into polymer formulations may be, for example, plasticizers, fillers (which are solid organic or mineral compounds, making it possible to modify the physical, thermal, mechanical and / or electrical properties of polymer materials or to lower their cost price), reinforcing agents, colorants, plasticizers, pigments, hardeners, flame retardants, combustion retardants, stabilizing agents, antioxidants, UV absorbers, antistatic agents, etc.

[0035] The additives correspond to at least part of the impurities of the plastic load to be treated and which the treatment method according to the invention makes it possible to eliminate at least in part. Other types of impurities eliminated during the method according to the invention may be usual impurities, such as for example metallic impurities, paper / cardboard, biomass, polymers other than the targeted polymer(s), etc.

[0036] Thus, according to the invention, the impurities that the method according to the invention makes it possible to eliminate at least in part include the additives conventionally used in polymer formulations, and in particular thermoplastic formulations, and also possibly usage impurities resulting from the life cycle of plastic materials and objects, and / or resulting from the waste collection and sorting circuit. The latter may be metallic, organic or mineral impurities; they may be packaging residues, food residues or compostable residues (biomass).These usage impurities may also include glass, wood, cardboard, paper, aluminum, iron, metals, tires, rubber, silicones, rigid polymers, thermosetting polymers, thermoplastics of a nature different from that of the thermoplastics in question (in particular that of the polyolefins in question), household, chemical or cosmetic products, used oils, water, etc.

[0037] According to the invention, a polymer solution is a solution comprising the dissolution solvent and at least the targeted thermoplastic polymers, in particular the targeted polyolefins, dissolved, i.e. in particular solvated and dispersed, in said dissolution solvent, the dissolved polymers being initially present in the plastic filler. The polymer solution may further comprise insoluble impurities (and in suspension in the polymer solution) and optionally soluble impurities (and solubilized in the dissolution solvent). Depending on the steps of the method according to the invention implemented, said polymer solution may therefore comprise, in addition to the dissolved targeted thermoplastics, impurities in the form of insoluble particles which are advantageously in suspension in said polymer solution, optionally soluble impurities dissolved in the dissolution solvent, and / or optionally another liquid phase immiscible with said polymer solution.

[0038] It is well known that the boiling point of a compound varies with the operating pressure. However, without further indication, in particular without indication of the pressure, the boiling point of the compound in question, in particular of the dissolving solvent, is understood to be the boiling point of said compound, in particular of said dissolving solvent, at atmospheric pressure (in particular equal to 0.1 MPa). Thus, the boiling point which characterizes the dissolving solvent must be understood to be the boiling point of said dissolving solvent at atmospheric pressure (in particular equal to 0.1 MPa). The critical temperature and the critical pressure of a solvent, in particular of the dissolving solvent, are specific to said solvent and depend on the nature of the solvent in question.For a pure body, the critical temperature and critical pressure of a pure body are respectively the temperature and pressure of the critical point of said pure body. As well known to those skilled in the art, at the critical point and beyond, the pure body considered is in supercritical form or in the supercritical state; it can then be called a supercritical fluid.

[0039] The invention thus relates to a method for treating a plastic filler, comprising thermoplastics, more particularly polyolefins, said method comprising, preferably consisting of: a) a step of dissolving the plastic filler in a dissolving solvent, preferably comprising at least one hydrocarbon compound, preferably aliphatic and preferably paraffinic, advantageously having a boiling point of between -50 and 250°C, preferably between -15 and 200°C, preferably between 15 and 160°C and preferably between 20 and 120°C, preferably according to a weight ratio between the dissolving solvent and the plastic filler, of between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, even more preferably between 3.0 and 7.0, to obtain at least one crude polymer solution,step a) being advantageously carried out at a dissolution temperature of between 100°C and 300°C, preferably between 150 and 250°C, and at a dissolution pressure of between 0.1 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferentially between,

[0040] 1.5 and 18.0 MPa absolute and very preferably between 2.0 and 15.0 MPa absolute; b) a step of purifying the crude polymer solution, comprising: b1) a sub-step of separating the insolubles, making it possible to obtain at least one clarified polymer solution; and / or b2) a sub-step of washing, by contact with a dense solution, making it possible to obtain a washed polymer solution; and / or b3) a sub-step of extracting the impurities by an extraction solvent, making it possible to obtain at least one extracted polymer solution; and / or b4) a sub-step of adsorbing the impurities by contact with an adsorbent, to obtain at least one refined polymer solution; the purification step making it possible to obtain a purified polymer solution which advantageously corresponds to a clarified or washed or extracted or refined polymer solution; then c) a step of solvent-polymer separation of the purified polymer solution,to obtain at least one stream of purified thermoplastic polymers, more particularly at least one stream of purified polyolefins, and at least one stream of solvent, said solvent-polymer separation step c) using a gas-liquid separation section or several gas-liquid separation sections operating in series, preferably solvent-polymer separation step c) using at least two successive gas-liquid separation sections, said gas-liquid separation section or each of the gas-liquid separation sections being operated at an inlet temperature of between 100°C and 300°C, preferably between 110 and 275°C, preferably between 150 and 250°C, and at a pressure lower than that at the outlet of step b), preferably at a pressure lower than 100.0 MPa absolute, preferably lower than 25.0 MPa absolute, preferably lower than 18.0 MPa absolute, preferably lower than 15.0 MPa absolute,when step c) uses several gas-liquid separation sections, the pressure of the later section being lower than that of the earlier section, preferably the pressure in the gas-liquid separation section or each of the gas-liquid separation sections being greater than or equal to 0.000005 MPa absolute, in particular greater than or equal to 0.00001 MPa absolute, in particular greater than or equal to 0.0001 MPa absolute, more particularly greater than or equal to 0.0005 MPa, and in particular greater than or equal to 0.0008 MPa, said purified polymer solution, obtained at the end of purification step b), feeding said gas-liquid separation section or the first gas-liquid separation section of the series, said gas-liquid separation section or each of the gas-liquid separation sections producing a gas effluent, which corresponds to said at least one solvent stream and which advantageously comprises at least dissolution solvent,and a liquid effluent which advantageously comprises the targeted thermoplastics, when step c) uses several gas-liquid separation sections, the liquid effluent from the previous section feeding the subsequent section, the liquid effluent from said gas-liquid separation section or from the last gas-liquid separation section of the series constituting said flow of purified thermoplastic polymers, the or each gas effluent produced being able to be, in whole or in part, purged and / or purified and / or fractionated and / or recycled to step a) and / or optionally to step b), optionally step c) comprising the introduction of at least one additive, in particular an antioxidant, optionally step c) also using an intermediate liquid-liquid or supercritical-liquid separation section, located upstream of the gas-liquid separation section or of the series of gas-liquid separation sections.,

[0041] The charge

[0042] The feedstock of the process according to the invention, called plastic feedstock, comprises plastics which themselves more particularly comprise thermoplastic polymers, such as polyolefins. Preferably, the plastic feedstock comprises between 50 and 100% by weight, preferably between 70% and 100% by weight of plastics relative to the total weight of the plastic feedstock.

[0043] The plastics included in the feedstock of the process according to the invention are generally production scrap and / or “post-consumer” waste from plastic objects, in particular household plastic waste, plastic waste from construction, automotive plastic waste or waste from any type of transport or waste from electrical and electronic equipment. Preferably, the plastic waste comes from collection and sorting channels. Plastics or plastic materials are generally compositions (or formulations) comprising polymers which are mixed with additives in order to provide specific properties to the materials, with a view to constituting, after shaping, various objects (for example injection-molded parts, tubes, films, fibers, fabrics, mastics, coatings, etc.). The additives used in plastics can be organic compounds or inorganic compounds.These are, for example, fillers, colorants, pigments, plasticizers, property modifiers, flame retardants, etc.

[0044] The feedstock of the process according to the invention (i.e. the plastic feedstock) comprises in particular thermoplastic polymers, preferably at least 50% by weight, preferably at least 70% by weight, more preferably at least 80% by weight and very preferably at least 90% by weight of thermoplastics, relative to the total weight of the plastic feedstock, 100% advantageously being the maximum upper limit. The thermoplastics targeted by the process according to the invention and included in the plastic feedstock may be alkene (or olefin) polymers, diene polymers, vinyl polymers and / or styrenic polymers. Preferably, the thermoplastics targeted by the process according to the invention and included in the plastic feedstock are polyolefins, such as polyethylene (PE), polypropylene (PP) and / or copolymers of ethylene and propylene or their mixtures.Preferably, the plastic filler comprises at least 80% by weight, preferably at least 85% by weight, more preferably at least 90% by weight, of polyolefins relative to the total weight of the plastic filler, 100% advantageously being the maximum upper limit. The method according to the invention thus aims in particular to purify and recover the polyolefins contained in a plastic filler, in particular from plastic waste, in order to be able to reuse them in different applications. According to a particular embodiment, the plastic filler comprises a mixture of polypropylene (PP) and polyethylene (PE), in particular at least 80% by weight, preferably at least 85% by weight, more preferably at least 90% by weight, of a mixture of polypropylene (PP) and polyethylene (PE), relative to the total weight of the plastic filler. The polyethylene may more particularly be high-density polyethylene (HDPE).In this particular embodiment, said mixture comprises for example between 5 and 95% by weight of PP and between 5 and 95% by weight of PE, in particular HDPE, or between 50 and 95% by weight of PP and between 5 and 50% by weight of PE, in particular HDPE.

[0045] The plastic filler may comprise mixtures of polymers, in particular thermoplastics other than the targeted thermoplastics, and in particular other than the targeted polyolefins, additives advantageously used to formulate the plastic material and possibly usage impurities resulting from the life cycle of the plastic materials and objects and / or resulting from the waste collection and sorting circuit, all of these compounds being considered as impurities. The feedstock of the process according to the invention generally comprises less than 50% by weight of impurities, preferably less than 20% by weight of impurities, more preferably less than 10% by weight of impurities. The plastic filler may comprise, for example, at least 1% by weight of impurities, or even at least 5% by weight of impurities.

[0046] The plastic filler may advantageously be pretreated upstream of the process according to the invention so as to at least eliminate all or part of the so-called coarse impurities, i.e. impurities in the form of particles of a size greater than or equal to 10 mm, preferably greater than or equal to 5 mm, or even greater than or equal to 1 mm, for example impurities of the wood, paper, biomass, iron, aluminum, glass, etc. type, and so as to generally form it in the form of divided solids so as to facilitate treatment in the process. This pretreatment may comprise a grinding step, a washing step at atmospheric pressure and / or a drying step. This pretreatment may be carried out on a different site, for example in a waste collection and sorting center, or on the same site where the treatment method according to the invention is implemented.Preferably, this pretreatment makes it possible to reduce the impurity content to less than 20% by weight, preferably less than 15% by weight, preferably less than 10% by weight, the percentages being given relatively to the weight of the plastic filler treated by the method according to the invention. At the end of the pretreatment, the filler is generally stored in the form of divided solids, for example in the form of ground materials, flakes or powder, or even granules, so as to facilitate handling and transport to the process.

[0047] Step a) of dissolution

[0048] According to the invention, the method comprises a dissolution step a) in which the plastic filler is brought into contact with a dissolution solvent, to obtain at least one, preferably one, crude polymer solution. Indeed, this step advantageously allows the dissolution of at least a part, preferably all, of the targeted thermoplastics, preferably the targeted polyolefins, present in the plastic filler.

[0049] Dissolution means any phenomenon leading to the production of at least one solution of thermoplastic polymers, i.e. a liquid (or fluid) comprising the targeted thermoplastic polymers dissolved in the dissolution solvent. A person skilled in the art is well aware of the phenomena involved in the dissolution of polymers: these phenomena include at least mixing, solvation, dispersion, homogenization, and disentanglement of the thermoplastic polymer chains.

[0050] During and at the end of dissolution step a), the pressure and temperature conditions make it possible to maintain the dissolution solvent, at least in part and preferably in full, in the liquid state or possibly in the supercritical state, while the soluble fraction of the plastic filler, in particular the targeted thermoplastic polymers, for example the targeted polyolefins, and possibly (or even generally) at least part of the impurities, is advantageously dissolved, at least in part and preferably in full, in the dissolution solvent. In other words, the temperature and pressure conditions in step a) make it possible to avoid or at least limit the dissolution solvent being in gaseous form, which makes it possible to optimize the dissolution of the targeted thermoplastics.

[0051] The dissolving solvent is an organic solvent or a mixture of organic solvents. Advantageously, the dissolving solvent comprises, preferably consists of, at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic (i.e. saturated), preferably linear, branched or cyclic, preferably non-aromatic. Preferably, the dissolving solvent comprises at least 80% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear, branched or cyclic, preferably non-aromatic, the percentages being expressed relative to the total weight of the dissolving solvent (100% being the maximum).Preferably, the dissolving solvent comprises, preferably consists of, at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, having a boiling point (at atmospheric pressure, in particular at 0.1 MPa) of between -50 and 250°C, preferably between -15 and 200°C, preferentially between 15 and 160°C and preferably between 50 and 120°C. Preferably, said at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear, branched or cyclic, preferentially non-aromatic, has between 3 and 12 carbon atoms, preferably between 4 and 10 carbon atoms, preferentially between 5 and 8 carbon atoms, and very preferably has 6, 7 or 8 carbon atoms.For example, said at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear, branched or cyclic, preferably non-aromatic, may be chosen from the isomers of butane, pentane, hexane, heptane, octane, nonane, decane, and mixtures thereof, preferably from the isomers of hexane, heptane, octane and mixtures thereof. Thus, the dissolution solvent may comprise at least 80% by weight, preferably at least 95% by weight, more preferably at least 98% by weight, of an isomer or a mixture of isomers of butane, pentane, hexane, heptane, octane, nonane and / or decane, or of an isomer or a mixture of isomers of hexane, heptane and / or octane, the percentages being expressed relative to the total weight of the dissolution solvent (100% being the maximum).

[0052] Preferably, step a) of dissolution is supplied with the plastic filler and said dissolution solvent, according to a weight ratio between the dissolution solvent and the plastic filler, of between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, even more preferably between 3.0 and 7.0.

[0053] Advantageously, the dissolution solvent which feeds the dissolution step a) is in liquid or possibly supercritical form. It can advantageously be preheated, preferably to a temperature between 100 and 300°C, preferably between 150 and 250°C, prior to its introduction into step a), in particular prior to its introduction into the contacting section and possibly into the dissolution section, in order to facilitate the heating of the plastic charge and / or avoid a drop in temperature of the material flow during the contacting and dissolution in step a).

[0054] Advantageously, the dissolution solvent comprises, preferably consists of, fresh solvent (or a fresh solvent top-up) and / or a recycled solvent stream from a subsequent step of the process, preferably at least partly from step c) of solvent-polymer separation. Very advantageously, the dissolution step is carried out at a temperature, called the dissolution temperature, of between 100°C and 300°C, preferably between 150 and 250°C, and preferably a pressure, called the dissolution pressure, of between 0.1 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute and very preferably between 2.0 and 15.0 MPa absolute.The temperature and pressure may vary during the dissolution step from atmospheric conditions or the conditions of introduction of the plastic filler and / or the dissolution solvent into the process, until the dissolution conditions are reached, i.e. the dissolution temperature, in particular between 100 and 300°C, preferably between 150 and 250°C, and the dissolution pressure, in particular between 0.1 and 100.0 MPa, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute and very preferably between 2.0 and 15.0 MPa absolute. Very advantageously, at the end of the dissolution step, the raw polymer solution is at the dissolution temperature and at the dissolution pressure.

[0055] Limiting the temperature in dissolution step a) to a temperature less than or equal to 300°C, preferably less than or equal to 250°C, makes it possible to avoid or limit the thermal degradation of the targeted thermoplastics, in particular the targeted polyolefins, but also to limit the energy requirement of the process, thus contributing to limiting the operating costs of the process. Advantageously, the dissolution temperature is greater than or equal to the melting temperature of the targeted thermoplastics, in particular the targeted polyolefins, and very advantageously lower than the evaporation temperature at the dissolution pressure of the dissolution solvent, so as to promote their dissolution and very advantageously reduce the residence time necessary to effectively dissolve said thermoplastics in the dissolution solvent.Very preferably, the temperature in dissolution step a) is less than or equal to the critical temperature of the dissolution solvent, so as to avoid the formation of a supercritical phase during dissolution step a) which could disrupt the dissolution.

[0056] At the same time, the dissolution pressure in dissolution step a) is greater than the saturated vapor pressure of the dissolution solvent, at the dissolution temperature, so that the dissolution solvent is at least partly, and preferably entirely, in liquid or possibly supercritical form, at the dissolution temperature, and thus to prevent the dissolution solvent from being partly in gaseous form. Under these operating conditions, in particular temperature and pressure, the dissolution of the targeted thermoplastics, in particular the targeted polyolefins, is optimized, in particular in terms of quality and operating time.Very advantageously, the dissolution temperature and pressure conditions reached in dissolution step a) are adjusted so that the mixture (dissolution solvent + targeted thermoplastics) is single-phase at the end of step a), said mixture possibly including insoluble impurities suspended in said mixture.

[0057] Advantageously, said dissolution step a) is carried out for a residence time preferably between 1 and 600 minutes, preferably between 2 and 300 minutes, more preferably between 2 and 180 minutes. The residence time is understood to be the residence time at the dissolution temperature and at the dissolution pressure, i.e. the time during which the plastic filler and the dissolution solvent are at the dissolution temperature and at the dissolution pressure, in step a).

[0058] The dissolution step a) is at least supplied with the plastic filler, in particular in the form of one or more plastic filler streams, and with the dissolution solvent, in particular in the form of one or more dissolution solvent streams, advantageously by means of one or more transport devices. The plastic filler stream(s) may be separate from the dissolution solvent stream(s). Part or all of the plastic filler may also be supplied to step a) in a mixture with part or all of the dissolution solvent, the remainder of the solvent and / or filler, where appropriate, being able to be supplied to step a) separately.

[0059] When bringing the plastic filler into contact with the dissolving solvent, the dissolving solvent is advantageously at least partly, and preferably entirely, in liquid or possibly supercritical form, while the plastic filler, which comprises the targeted thermoplastics, may be in solid or liquid form and may optionally comprise suspended solid particles. The plastic filler may also optionally be injected into the dissolving equipment, mixed with the dissolving solvent, in the form of a suspension in the dissolving solvent, the preparation and injection of the suspension being able to be continuous or discontinuous.

[0060] In order to allow contact between the dissolving solvent and the plastic filler and, above all, an efficient and homogeneous dissolution of the targeted thermoplastics in the dissolving solvent, step a) of dissolution can advantageously use different types of equipment such as mixing, transport and heating devices, and such as, for example, a reactor, a pump, a transport circuit, a stirring system, an oven, an exchanger, a mixer, etc. In particular, step a) advantageously uses at least one piece of dissolving equipment, and possibly at least one device for preparing the filler, a mixing device and / or a transport device.The equipment and / or devices used in step a) may be, for example, one or more static or dynamic mixers, an extruder, a pump, a reactor, a co- or counter-current column and / or transport devices, advantageously connected to each other. The transport devices, in particular for fluids, such as gases, liquids or solids, are well known to those skilled in the art. In a non-limiting manner, the transport devices may comprise at least one of the following devices: a compressor, a pump, an extruder, a vibrating tube, a worm screw, a valve. The equipment and / or devices used in step a) may also comprise or be associated with heating systems (for example, furnace, exchanger, tracing, etc.) to achieve the conditions necessary for dissolution.

[0061] Preferably, the dissolution step a) uses at least one means for melting at least partially the plastic filler, preferably an extruder, optionally at least one means for mixing at least a portion of the dissolution solvent and the plastic filler, advantageously at least partially melted, such as one or a series of two to ten mixer(s) (preferably one to ten static mixer(s)), and dissolution equipment, for example at least one continuously stirred reactor, also called "Continuous Stirred Tank Reactor" (CSTR) according to English terminology, equipped with at least one mechanical stirring system. In this case, the plastic filler feeds the melting means, in particular the extruder, so that, at the outlet of said means, at least a portion and preferably all of the targeted thermoplastics, included in the plastic filler, are in the molten state.The plastic filler can then be injected into the dissolution equipment, for example a reactor of the continuously stirred reactor (or CSTR) type, or possibly into a system comprising a mixer or a series of mixer(s) advantageously followed by a reactor, for example of the continuously stirred reactor (or CSTR) type. The plastic filler, at least partly in the molten state, can also be pumped using a pump dedicated to viscous fluids, often called a melt pump or gear pump. The plastic filler, at least partly in the molten state, can also be, at the outlet of said melting means, filtered using a filtration device, possibly in addition to the melt pump, in order to eliminate the largest particles; generally, the mesh size of this filter is between 10 μm (micrometer) and 1 mm (millimeter), preferably between 20 and 200 μm.At the same time, the dissolving solvent is directly fed to the dissolving equipment, said melting means, in particular the extruder, and / or the series of mixer(s).

[0062] Preferably, step a) uses, prior to at least one CSTR type reactor, an extruder followed by at least one static mixer into which at least a fraction of the dissolving solvent is injected, so as to promote shearing and intimate mixing between the dissolving solvent and the plastic filler, which contributes to the dissolution of the targeted thermoplastics.

[0063] Very advantageously, the raw polymer solution obtained at the end of dissolution step a) comprises at least the dissolution solvent and the targeted thermoplastics, in particular the targeted polyolefins, dissolved in the dissolution solvent. In general, the raw polymer solution also comprises soluble impurities also dissolved in the dissolution solvent and / or insoluble impurities in suspension. The raw polymer solution obtained at the end of dissolution step a) may optionally also comprise polymers, for example in the molten state, dissolved or not.

[0064] Step b) purification of the polymer solution

[0065] The purification method according to the invention comprises a step of purifying the crude polymer solution resulting from step a). This purification step b) comprises at least one of the sub-steps b1), b2), b3), b4) described below: b1) a sub-step of separating the insolubles, b2) a washing sub-step, by contact with a dense solution, b3) an extraction sub-step, by contact with an extraction solvent, b4) a sub-step of adsorption of the impurities by contact with an adsorbent.

[0066] The different sub-steps b1), b2), b3) and b4) can be operated continuously, discontinuously (or batch mode) or in fed-batch mode.

[0067] Preferably, the purification step b) comprises at least one sub-step b1) of separation of the insolubles. Preferably, the purification step b) comprises several (i.e. at least two) sub-steps chosen from sub-steps b1), b2), b3) and b4), in series with each other, and preferably at least one sub-step b1) of separation of the insolubles and for example one sub-step b4) of adsorption, and very advantageously in the order b1) then b4). The combination of at least two sub-steps chosen from b1), b2), b3) and b4) advantageously allows optimal purification of the polymer solution, which consequently makes it possible to obtain a flow of purified thermoplastics having very low impurity contents, preferably less than or equal to 5% by weight, preferably less than or equal to 1.0% by weight, preferably less than or equal to 0.5% by weight, relative to the total weight of the flow of purified thermoplastics.

[0068] The polymer solution obtained at the end of step b) is a purified polymer solution which comprises the targeted thermoplastics, in particular the targeted polyolefins, dissolved in the dissolution solvent. This purified polymer solution may correspond to a clarified polymer solution resulting from a sub-step b1) of separation of insolubles, a washed polymer solution resulting from a washing sub-step b2), an extracted polymer solution resulting from an extraction sub-step b3) or a refined polymer solution resulting from a sub-step b4) of adsorption of impurities.

[0069] Preferably, the temperature and pressure in step b) are adjusted so as to obtain at the outlet of step b), a polymer solution, i.e. the purified polymer solution, in liquid form.

[0070] Sub-step b1) of separation of insolubles

[0071] The purification process may comprise a sub-step b1) of separating the insolubles, in particular by solid-liquid separation, to advantageously obtain at least one clarified polymer solution (i.e. free of at least a portion, preferably all, of the insoluble impurities of the crude polymer solution), and preferably at least one insoluble fraction. Said at least one insoluble fraction advantageously comprises, at least in part, preferably all, of the insoluble impurities, in particular in suspension in the crude polymer solution resulting from step a), possibly the dissolution solvent and optionally soluble impurities.

[0072] The sub-step b1) of separating the insolubles thus makes it possible to eliminate at least a portion, preferably all, of the insoluble impurities present in suspension in the raw polymer solution resulting from step a). The insoluble impurities eliminated during the sub-step b1) of separating the insolubles are, for example, pigments, mineral compounds, packaging residues (glass, wood, cardboard, paper, aluminum) and insoluble polymers. When it is implemented, this sub-step b1) of separation advantageously makes it possible, in addition to the elimination of at least a portion of the insoluble impurities, to limit the operating problems, in particular of the clogging and / or erosion type, of the process steps located downstream of such a sub-step b1), while contributing to the purification of the plastic feedstock.

[0073] Sub-step b1) of separating the insolubles is advantageously carried out at a temperature of between 100 and 300°C, preferably between 150 and 250°C, preferentially between 160 and 225°C, very preferentially between 165 and 210°C, and preferably between 170 and 195°C, and at a pressure of between 0.1 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferentially between 1.0 and 18.0 MPa absolute and very preferably between 1.5 and 15.0 MPa absolute. Very advantageously, sub-step b1) of separation of the insolubles is carried out at the temperature and pressure conditions at the outlet of step a) of dissolution, i.e. at the dissolution temperature and the dissolution pressure as defined above, optionally with a lowered pressure, preferably from 0.01 to 10.0 MPa, preferably from 0.1 to 5.0 MPa due to the pressure losses experienced between step a) and sub-step b1).

[0074] When integrated into the process, sub-step b1) of separation of insolubles is preferably fed with the raw polymer solution from step a) or any other polymer solution from a sub-step b2), b3) or b4) possibly located upstream of sub-step b1). According to a preferred embodiment, sub-step b1) is fed with the raw polymer solution from step a). According to another embodiment, sub-step b1) can be fed with a washed polymer solution from a washing sub-step b2), located upstream of sub-step b1).

[0075] Advantageously, sub-step b1) implements any solid-liquid separation step known to those skilled in the art for separating insolubles, solids (such as additives of the mineral filler or pigment type) or liquids (for example polymers in molten form and of a nature different from that of the targeted thermoplastics), for example a separation step by decantation, filtration, centrifugation, electrostatic separation, etc.

[0076] Preferably, sub-step b1) comprises at least one, preferably between one and five, preferentially between two and five, solid-liquid separation step(s) (or solid-liquid-liquid separation, in particular in the case where the effluent obtained at the end of the dissolution step comprises, in addition to the polymer solution and the solid impurities, impurities and / or polymers in liquid form and with little or no solubility, and of a different nature than that of the thermoplastics in question). When implemented, sub-step b1) preferably comprises several, i.e. between two and five, solid-liquid separation steps (or solid-liquid-liquid separation) in series and / or in parallel. The presence of at least two solid-liquid separation steps in series makes it possible to improve the elimination of insolubles, while the presence of several solid-liquid separation steps in parallel makes it possible to manage the maintenance of the equipment and / or the unclogging operations.According to a preferred embodiment, sub-step b1) of separation of insolubles implements a step of solid-liquid separation by decantation and / or at least one, preferably between one and four, steps of solid-liquid separation by filtration.

[0077] Said at least one solid-liquid separation step preferably uses at least one solid-liquid separation equipment, for example a separator flask, a decanter, a centrifugal decanter, a centrifuge, a filter, a sand filter, a tangential filter notably using a membrane and / or a depth filter, an eddy current separator, an electrostatic separator, a triboelectric separator, and preferably a decanter, a filter, a sand filter and / or an electrostatic separator. Advantageously, a self-cleaning filter can be used, the cleaning or unclogging allowing the elimination of insolubles being carried out using a solvent flow. During sub-step b1), filter aids (for example diatomaceous earth or sand) can optionally be added prior to a decantation step and / or a filtration separation step.

[0078] Depending on the nature of the feed, the polymer solution which feeds sub-step b1), preferably the raw polymer solution, may optionally also comprise a second liquid phase, for example consisting of molten polymers, these polymers being of a different nature from that of the thermoplastics targeted. According to another particular embodiment, sub-step b1) advantageously uses a solid-liquid-liquid separation section, using equipment allowing the separation of two liquid phases and one solid phase, preferably by means of at least one two-phase or three-phase separator.

[0079] Said at least one insoluble fraction is preferably removed or treated so as to separate and recover compounds of interest, for example polymers, in particular thermoplastics, the dissolution solvent that it may contain. The removal or treatment of said at least one insoluble fraction may be facilitated by equipment allowing the transport and / or separation of polymer and / or solvent possibly present in the insoluble fraction, for example a conveyor, a vibrating tube, a worm screw, an extruder, a stripper. Sub-step b1) may use transport and / or separation equipment to remove and / or treat said at least one insoluble fraction.Advantageously, sub-step b1) comprises the separation and recovery of at least a portion of the solvent, in particular the dissolving solvent, contained in said at least one insoluble fraction, said at least a portion of the solvent, in particular the dissolving solvent, being able to be recycled in the process, in particular in step a).

[0080] Certain insoluble impurities, in particular certain pigments and mineral fillers, conventionally added during the formulation of polymers, may be in the form of particles smaller than 1 μm. This is for example the case of titanium dioxide, calcium carbonate and carbon black. According to a particular embodiment of sub-step b1), said sub-step b1) of separation of the insolubles advantageously uses an electrostatic separator, which makes it possible to effectively eliminate, at least in part, the insoluble particles smaller than 1 μm. According to another particular embodiment of sub-step b1), the sub-step b1) of the insolubles uses a sand filter, to eliminate particles of different sizes and in particular particles smaller than 1 μm.According to yet another particular embodiment, sub-step b1) of the insolubles uses a tangential filter notably using a membrane and / or a depth filter, possibly in the presence of filtration aids such as, for example, diatomaceous earth.

[0081] Sub-step b2) of washing

[0082] The treatment method may optionally comprise a sub-step b2) of washing with a dense solution, to advantageously obtain a washed polymer solution and preferably at least one washing effluent. The washed polymer solution obtained at the end of sub-step b2) advantageously comprises the targeted thermoplastics, dissolved in the dissolution solvent. Optionally, the washed polymer solution may also comprise residual impurities, in particular soluble in the dissolution solvent and / or possibly traces of the washing solvent when sub-step b2) is carried out.

[0083] The washing sub-step b2) can be integrated upstream or downstream, preferably downstream, of a sub-step b1) of separation of insolubles, when these two sub-steps are integrated into the treatment method according to the invention.

[0084] When integrated into the process, the washing sub-step b2) is fed with a dense solution and with the polymer solution resulting from the step or sub-step directly upstream of b2), in particular with the raw polymer solution resulting from step a) or the clarified polymer solution resulting from a sub-step b1). The polymer solution which feeds the washing sub-step b2), in particular the raw or optionally clarified polymer solution, may comprise insoluble impurities in suspension and / or solubilized impurities. These suspended or solubilized impurities may, in part or in whole, be eliminated during the washing sub-step b2) by dissolution or precipitation and / or by entrainment in the dense solution. Thus, when implemented, this sub-step b2) contributes to the treatment of the plastic feedstock and more particularly to the purification of the polymer solution.

[0085] The washing sub-step b2) advantageously comprises bringing the polymer solution which feeds sub-step b2), in particular the raw or clarified polymer solution, into contact with a dense solution. Advantageously, the dense solution has a higher density than the polymer solution (i.e. the mixture comprising at least the target thermoplastics and the dissolving solvent in which the target thermoplastics are dissolved), in particular greater than or equal to 0.85, preferably greater than or equal to 0.9, preferentially greater than or equal to 1.0. The dense solution may be an aqueous solution, which preferably comprises at least 50% by weight of water, preferably at least 75% by weight of water, very preferably at least 90% by weight of water. The pH of the aqueous solution may be adjusted using an acid or a base so as to promote the dissolution of certain impurities.The dense solution may also optionally be a solution comprising, preferably consisting of, an organic solvent with a density advantageously greater than or equal to 0.85, preferably greater than or equal to 0.9, preferentially greater than or equal to 1.0, and in which the polymers of the plastic filler remain insoluble under the temperature and pressure conditions of sub-step b2). Thus, the dense solution may comprise, in particular consist of, an organic solvent, for example chosen from sulfolane or N-methylpyrrolidone (NMP), optionally mixed with water. Very preferably, the dense solution is an aqueous solution which preferably comprises at least 50% by weight of water, preferably at least 75% by weight of water, very preferably at least 90% by weight of water.

[0086] Washing sub-step b2) is advantageously carried out at a temperature between 100 and 300°C, preferably between 150 and 250°C, and very advantageously at a pressure between 0.1 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.0 and 18.0 MPa absolute and very preferably between 1.5 and 15.0 MPa absolute. Very advantageously, washing sub-step b2) is carried out at the dissolution temperature and the dissolution pressure, optionally with a lowered pressure, preferably from 0.01 to 10.0 MPa, preferably from 0.1 to 5.0 MPa, due to the pressure losses experienced between step a) and sub-step b2).

[0087] In the washing sub-step b2), when integrated into the process, the mass ratio between the mass flow rate of the dense solution relative to the mass flow rate of the polymer solution, which feeds the sub-step b2), in particular the raw or clarified polymer solution, is advantageously between 0.05 and 20.0, preferably between 0.1 and 10.0 and more preferably between 0.5 and 3.0. The contacting between the polymer solution, in particular raw or clarified, and the dense solution can be carried out at several points of the equipment(s) used, i.e. by several injections of the polymer solution and / or the dense solution at different points along the equipment(s), it is then the sum of the injected flows which is taken into account in the calculation of the mass ratio.

[0088] Sub-step b2) may implement one or more washing equipment allowing the polymer solution to be brought into contact with the dense solution, and / or one or more separation equipment allowing at least one washing effluent and one washed polymer solution to be recovered. These equipments are well known to those skilled in the art: they are, for example, stirred reactors, static mixers, decanter mixers, two-phase or three-phase separator drums, co- or counter-current washing columns, tray columns, stirred columns, packed columns, pulsed columns, etc., each type of equipment being able to comprise one or more equipments used alone or in combination with equipments of another type.

[0089] According to a preferred embodiment, the washing sub-step b2) is carried out in a countercurrent washing column. In this preferred embodiment, the dense solution is advantageously injected into the upper part of the column, preferably into the upper half, preferably the upper third, of the column (the upper part of the column meaning the part closest to the column head), on the one hand, and the polymer solution, in particular raw or clarified, is injected into the lower part of the column, preferably into the lower half, preferably the lower third, of the column (the lower part of the column meaning the part closest to the column bottom), on the other hand. According to this embodiment, it is possible to recover at least one washed polymer solution, preferably at the column head, and a washing effluent, preferably at the column bottom.According to a very particular mode, the flows entering and / or leaving the washing column can be divided and injected at several injection points along the column and / or withdrawn at several withdrawal points along the column.

[0090] According to another embodiment, the washing sub-step b2) is carried out in a mixer-decanter comprising an agitated mixing zone, to bring the dense solution and the polymer solution, in particular raw or clarified, into contact, and a decantation zone, making it possible to recover a washed polymer solution and a washing effluent.

[0091] At the end of the washing sub-step b2), the washing effluent obtained advantageously comprises impurities solubilized in the dense solution and / or insoluble and entrained in the washing effluent. The washing effluent can be reprocessed in a washing treatment section, on the one hand to separate at least in part the solubilized and / or entrained impurities and optionally purify the washing effluent, to obtain a purified dense solution, and on the other hand to recycle at least a portion of the purified dense solution. This optional washing treatment section can use one or more well-known solid-liquid separation equipment, for example a separator drum, a decanter, a centrifugal decanter, a centrifuge, a filter. The washing effluent can also be sent outside the process, for example to a wastewater treatment plant when the dense solution is an aqueous solution.

[0092] Step b3) extraction

[0093] The method according to the invention may comprise a sub-step b3) of extraction advantageously by bringing the polymer solution which feeds sub-step b3) into contact with an extraction solvent, to obtain at least one extracted polymer solution and preferably a used solvent. The extracted polymer solution obtained at the end of sub-step b3) advantageously comprises the targeted thermoplastic polymers, dissolved in the dissolution solvent. The used solvent is advantageously loaded with impurities. Optionally, the extracted polymer solution may also comprise residual impurities, in particular soluble in the dissolution solvent and / or traces of the washing solvent and / or the extraction solvent if sub-step(s) b2) and / or b3) is (are) carried out.

[0094] When integrated into the treatment process according to the invention, the extraction sub-step b3) is very advantageously located downstream of a sub-step b1) of separation of insolubles, and possibly upstream or downstream of a washing sub-step b2) and / or an adsorption sub-step b4) when the latter are also integrated into the process.

[0095] The extraction sub-step b3) is advantageously supplied with an extraction solvent and with the polymer solution resulting from the step or sub-step directly upstream of b3), in particular with the crude polymer solution resulting from step a), the clarified polymer solution resulting from sub-step b1), the washed polymer solution resulting from sub-step b2) or the refined polymer solution resulting from a sub-step b4). The polymer solution which supplies sub-step b3), in particular the crude, clarified, washed or refined polymer solution, may comprise impurities, in particular solubilized impurities which may be partially or completely removed during the extraction sub-step b3) by contacting with an extraction solvent.

[0096] When integrated into the method according to the invention, the extraction sub-step b3) advantageously uses at least one extraction section, preferably between one and five extraction section(s), very preferably one extraction section.

[0097] Advantageously, the mass ratio between the mass flow rate of the extraction solvent relative to the mass flow rate of the polymer solution which feeds b3), is between 0.05 and 20.0, preferably between 0.1 and 10.0 and more preferably between 0.2 and 5.0. The contact between the polymer solution which feeds sub-step b3) and the extraction solvent can be carried out at several points in the extraction section, i.e. by several injections of the polymer solution and / or the extraction solvent at different points along the extraction section, it is then the sum of the injected flows which is taken into account in the calculation of the mass ratio.

[0098] Preferably, the extraction solvent used in extraction sub-step b3) comprises an organic solvent or a mixture of organic solvents. Preferably, the extraction solvent comprises, preferably consists of, at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic (i.e. saturated), preferably linear, branched or cyclic, preferably non-aromatic. Preferably, the extraction solvent comprises at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear, branched or cyclic, preferably non-aromatic, the percentages being expressed relative to the total weight of the dissolution solvent (100% being the maximum.Preferably, the extraction solvent comprises, preferably consists of, at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, having a boiling point of between - 50 and 250°C, preferably between - 15 and 200°C, preferentially between 15 and 160°C and preferably between 50 and 120°C (at atmospheric pressure, in particular at 0.1 MPa). Preferably, said at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear, branched or cyclic, preferentially non-aromatic, has between 3 and 12 carbon atoms, preferably between 4 and 10 carbon atoms, preferentially between 5 and 8 carbon atoms, and very preferably has 6, 7 or 8 carbon atoms.For example, said at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear, branched or cyclic, preferably non-aromatic, may be chosen from the isomers of butane, pentane, hexane, heptane, octane, nonane, decane, and mixtures thereof, preferably from the isomers of hexane, heptane, octane and mixtures thereof. Thus, the extraction solvent may comprise at least 80% by weight, preferably at least 95% by weight, more preferably at least 98% by weight, of an isomer or a mixture of isomers of butane, pentane, hexane, heptane, octane, nonane and / or decane, or of an isomer or a mixture of isomers of hexane, heptane and / or octane, the percentages being expressed relative to the total weight of the dissolution solvent (100% being the maximum).

[0099] Very preferably, the extraction solvent used in sub-step b3) when it is integrated into the process according to the invention is of the same nature as that of the dissolution solvent used in step a), possibly in a different physical state (for example the extraction solvent in the supercritical state compared to the dissolution solvent in the liquid state), so as to facilitate the management of the solvents and in particular their purification and their recycling in particular towards the dissolution step a) and possibly towards the extraction sub-step b3).Another advantage of using identical dissolution and extraction solvents, in identical or different physical states, in addition to facilitating solvent management (i.e. in particular the recovery, treatment and recycling of the solvents used in the process), is to limit energy consumption and costs, in particular those generated by the treatment and purification of the solvents.

[0100] The extraction section(s) of sub-step b3) may comprise one or more extraction equipment(s), allowing contact with the extraction solvent, and / or separation equipment allowing recovery of at least one used solvent, in particular loaded with impurities, and an extracted polymer solution. This equipment is well known to those skilled in the art: they are, for example, stirred reactors, static mixers, decanter mixers, two-phase or three-phase separator drums, co- or counter-current washing columns, tray columns, stirred columns, packed columns, pulsed columns, etc., each type of equipment being able to comprise one or more equipment used alone or in combination with equipment of another type.

[0101] According to a preferred embodiment of b3), the extraction is carried out in a countercurrent extraction column. In this preferred embodiment, the extraction solvent is advantageously injected into the upper part of the column, preferably into the upper half, preferably the upper third, of the column (the upper part of the column meaning the part closest to the column head), on the one hand, and the polymer solution which feeds sub-step b3) is injected into the lower part of the column, preferably into the lower half, preferably the lower third, of the column (the lower part of the column meaning the part closest to the column bottom), on the other hand. According to this embodiment, it is possible to recover at least one extracted polymer solution, preferably at the column head, and a used solvent, in particular loaded with impurities, preferably at the column bottom.The inlet and / or outlet flows of the countercurrent extraction column can be divided into several injection and / or withdrawal points along the column.

[0102] According to another embodiment of b3), the extraction is carried out in a mixer-decanter which advantageously comprises a stirred mixing zone to bring the extraction solvent and the polymer solution which feeds b3) into contact, and a decantation zone making it possible to recover an extracted polymer solution on the one hand and a used solvent on the other hand.

[0103] Advantageously, the extraction sub-step b3) is carried out under temperature and pressure conditions different from the temperature and pressure conditions of the dissolution step a).

[0104] According to a preferred embodiment, the extraction sub-step b3) when integrated into the treatment method implements a liquid / liquid extraction section. Preferably, said liquid / liquid extraction section is operated between 100°C and 300°C, preferably between 150°C and 250°C, and at a pressure between 0.1 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferentially between 1.0 and 18.0 MPa absolute and very preferably between 1.5 and 15.0 MPa absolute. In all cases, in this embodiment, the temperature and pressure conditions are adjusted so that the extraction solvent is in the liquid state, the dissolution solvent preferably also being in the liquid state.Very advantageously, the liquid / liquid extraction, in particular when the extraction solvent is the same as the dissolution solvent, is carried out under temperature and pressure conditions different from the dissolution conditions reached in step a), in particular at a temperature higher than the dissolution temperature and / or at a pressure lower than the dissolution pressure, so as to thus be placed in a two-phase zone of the corresponding polymer-solvent mixing diagram.

[0105] According to another preferred embodiment, the extraction sub-step b3) implements an extraction section under particular temperature and pressure conditions in which the extraction solvent is advantageously at least partly in supercritical form. Such extraction may be called supercritical extraction. In this embodiment, the extraction is carried out by bringing the polymer solution which feeds b3) into contact with an extraction solvent which is at least partly, preferably entirely, in the supercritical state (preferably at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight of the extraction solvent is in supercritical form).Such a sub-step b3) of supercritical extraction advantageously allows an efficient purification of the polymer solution, in particular thanks to the very strong affinity of organic impurities, such as certain additives, in particular certain colorants, plasticizers, etc., for the supercritical phase. The use of an extraction solvent in the supercritical state also makes it possible to create a significant density difference between the supercritical phase and the polymer solution in liquid form, which facilitates a separation by decantation between the supercritical phase advantageously loaded with impurities, and the liquid phase which comprises the targeted thermoplastics, and consequently which contributes to the purification of the polymer solution.

[0106] In this other preferred embodiment, sub-step b3) uses an extraction solvent comprising at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of at least one aliphatic paraffinic hydrocarbon compound (or alkane) (100% being the maximum, the percentages being expressed relative to the total weight of the extraction solvent) having a critical temperature preferably between 95 and 350°C, preferably between 130 and 320°C, preferably between 180 and 300°C.Advantageously, the supercritical extraction sub-step b3) of this other preferred embodiment is carried out at a temperature between 100 and 350°C, preferably between 130°C and 320°C, preferably between 180°C and 280°C, and at a pressure preferably between 2.0 and 100.0 MPa absolute, preferably between 2.0 and 25.0 MPa absolute, preferably between 2.0 and 18.0 MPa absolute, very preferably between 2.7 and 15.0 MPa absolute and very preferably between 3.0 and 7.5 MPa absolute, or even between 3.0 and 5.5 MPa absolute. In all cases, in this embodiment, the temperature and pressure conditions are adjusted, in particular in an adjustment section implemented in extraction sub-step b3) upstream of the extraction section, so that the extraction solvent is at least partly in the supercritical state in the extraction section.

[0107] In a particular embodiment, the extraction sub-step b3) implements a supercritical extraction and the extraction solvent is the same as that of the dissolution solvent, except that the extraction solvent is at least partly in the supercritical state. In this case of supercritical extraction, the dissolution solvent can become at least partly in supercritical form, advantageously optimizing the decantation during the extraction step, more particularly at each extraction phase or tray, between the liquid phase and the supercritical phase, which thus makes it possible to maximize the purification.

[0108] Advantageously, at the end of extraction sub-step b3), the used solvent obtained is in particular loaded with soluble impurities. It can be reprocessed in an organic treatment section making it possible, on the one hand, to separate at least part of the impurities and purify the solvent to obtain a purified extraction solvent, and on the other hand to recycle at least part of the purified extraction solvent at the inlet of b3), and / or at the inlet of dissolution step a) in the case where the dissolution solvent and the extraction solvent are of identical nature. The used solvent can be treated according to any method known to those skilled in the art, such as one or more methods among distillation, evaporation, extraction, adsorption, crystallization and precipitation of insolubles, or by purging.

[0109] Sub-step b4) adsorption

[0110] The treatment method according to the invention may comprise an adsorption sub-step b4), to obtain a refined polymer solution. The refined polymer solution obtained at the end of sub-step b4) advantageously comprises the targeted thermoplastic polymers, in particular the targeted polyolefins, dissolved in the dissolution solvent. When integrated into the method according to the invention, adsorption sub-step b4) is advantageously carried out by bringing the polymer solution which feeds it into contact with one or more adsorbents.

[0111] When integrated into the process according to the invention, the adsorption sub-step b4) is preferably carried out in the purification step b), upstream of the solvent-polymer separation step c). However, it can be carried out during the dissolution step a), by introducing adsorbent particles mixed with the crude polymer solution, said adsorbent particles being removed during the purification step b), optionally during a sub-step b1) of separation of the insolubles or a washing sub-step b2). The adsorption sub-step b4) can also be carried out during the purification step b), preferably downstream of a sub-step b1) of separation of the insolubles and optionally upstream or downstream of an extraction sub-step b3).

[0112] The adsorption sub-step b4) advantageously uses an adsorption section operated in the presence of at least one adsorbent, preferably solid, and in particular in the form of a fixed bed, an entrained bed (or slurry, i.e. in the form of particles introduced into the flow to be purified and entrained with this flow) or in the form of an ebullating bed, preferably in the form of a fixed bed or an entrained bed, or in the form of adsorbent particles dispersed in the polymer solution. The adsorbent(s) used in sub-step b4) is (are) preferably an alumina, a silica, a silica-alumina, an activated carbon, a bleaching earth, or their mixtures, preferably an activated carbon, a bleaching earth or their mixtures, preferably in the form of a fixed bed or an entrained bed, the circulation of the flows being able to be ascending or descending through said bed.

[0113] Advantageously, when integrated into the process, the adsorption sub-step b4) is carried out at a temperature between 100 and 300°C, preferably between 150 and 250°C, and at a pressure between 0.1 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferentially between 1.0 and 18.0 MPa absolute and very preferably between 1.5 and 15.0 MPa absolute. Very advantageously, the adsorption sub-step b4) is carried out at the dissolution temperature and pressure conditions, i.e. at the dissolution temperature and dissolution pressure reached in step a), optionally with a lowered pressure, preferably from 0.01 to 10.0 MPa, preferably from 0.1 to 5.0 MPa due to the pressure losses experienced between step a) and sub-step b4).Preferably, in sub-step b4), the hourly volumetric flow rate (or WH), which corresponds to the ratio between the volumetric flow rate of the polymer solution which feeds b4) and the volume of adsorbent, advantageously in operation in b4), is between 0.05 and 10 h. 1 , preferably between 0.1 and 5.0 h -1. According to a particular embodiment of sub-step b4), the adsorption section may comprise one or more fixed bed(s) of adsorbent, for example in the form of adsorption column(s), preferably at least two adsorption columns, preferentially between two and four adsorption columns, containing said adsorbent(s). When the adsorption section comprises two adsorption columns, an operating mode may be an operation called "swing", according to the established Anglo-Saxon term, in which one of the columns is online, i.e. in operation, while the other column is in reserve. When the adsorbent of the online column is used up, this column is isolated while the reserve column is put online, i.e. in operation.The spent adsorbent can then be regenerated in situ and / or replaced with fresh adsorbent so that the column containing it can be brought back online once the other column has been isolated.

[0114] Another mode of operation of this particular embodiment of b4) is to have at least two adsorbent columns operating in series. When the adsorbent of the column placed at the head is used up, this first column is isolated and the used adsorbent is regenerated in situ or replaced by fresh adsorbent. The column is then put back online in the last position and so on. This operation is called permutable mode, or according to the English term "PRS" for Permutable Reactor System or "lead and lag" according to the established Anglo-Saxon term. The association of at least two adsorption columns makes it possible to overcome the possible and possibly rapid poisoning and / or clogging of the adsorbent under the joint action of impurities, contaminants and insolubles possibly present in the flow to be treated.The presence of at least two adsorption columns facilitates the replacement and / or regeneration of the adsorbent, advantageously without stopping the process, and also makes it possible to control costs and limit adsorbent consumption.

[0115] Step c) solvent-polymer separation

[0116] According to the invention, the method comprises a step c) of solvent-polymer separation, to obtain at least one stream of purified thermoplastic polymers, more particularly at least one stream of purified polyolefins, and preferably at least one stream of solvent. This step c) is located downstream of the purification step b). It is advantageously supplied with the purified polymer solution obtained at the end of the purification step b).

[0117] Step c) of solvent-polymer separation aims to separate, at least in part, preferably mainly, or even in full, the solvent(s), in particular the dissolution solvent, contained in the purified polymer solution which feeds step c), so as to recover the targeted thermoplastics, freed at least in part, preferably in full, of impurities and the dissolution solvent, and preferably also of the other solvent(s) possibly used in particular during step b) of the process (i.e. the extraction solvent and / or the dense solution).By majority, it is necessary to understand at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, very preferably at least 95% by weight, relative to the weight of the solvent(s) contained in the purified polymer solution which feeds step c), in particular of the dissolution solvent and optionally of the extraction solvent and / or of the dense solution contained in the purified polymer solution which feeds step c).

[0118] Thus, step c) of solvent-polymer separation implements a gas-liquid separation section or several gas-liquid separation sections operating in series. The expression "several gas-liquid separation sections" means, according to the present description, at least two gas-liquid separation sections, and preferably between two and ten, preferentially between two and five, for example three or four, gas-liquid separation sections. Preferably, step c) of solvent-polymer separation implements at least two, preferentially between two and ten, very preferentially between two and five, for example three or four, successive gas-liquid separation sections. In other words, step c) of solvent-polymer separation preferably implements N gas-liquid separation sections, N being an integer greater than or equal to two, preferably between two and ten, preferentially between two and five, N being for example three or four.

[0119] The principle of separation in said gas-liquid separation section or in the gas-liquid separation sections of the series is based on the evaporation, at least in part, of the solvent, in particular the dissolving solvent, present in the polymer solution which feeds said section or each of said sections; and said solvent (or the fraction of said solvent) then in gas form is separated from the polymer solution which is in liquid form.

[0120] Thus, the gas-liquid separation section or each of the gas-liquid separation sections produces a gas effluent, which advantageously comprises solvent, in particular dissolving solvent, in gas form, and a liquid effluent which advantageously comprises the target thermoplastics possibly dissolved in the residual dissolving solvent. When the liquid effluent comprises residual solvent, in particular residual dissolving solvent, said target thermoplastics are dissolved in the residual solvent and the liquid effluent therefore corresponds to a polymer solution.Very advantageously, the liquid effluent from said gas-liquid separation section or from the last gas-liquid separation section of the series preferably comprises at most 5% by weight, preferably at most 1.00% by weight, very preferably at most 0.10% by weight, or even at most 500 ppm by weight of solvent, relative to the total weight of said liquid effluent, and advantageously constitutes said stream of purified thermoplastic polymers.

[0121] The purified polymer solution, obtained at the end of purification step b), feeds said gas-liquid separation section or the first gas-liquid separation section of the series. When step c) uses several gas-liquid separation sections, the liquid effluent from the previous section feeds the subsequent section. In other words, when step c) uses N successive gas-liquid separation sections, with N an integer greater than or equal to two, preferably between two and ten, preferentially between two and five, for example N being three or four: the purified polymer solution, obtained at the end of purification step b), feeds the first gas-liquid separation section of the series, which produces a first gas effluent and a first liquid effluent;the first liquid effluent obtained at the end of the first gas-liquid separation section feeds the second gas-liquid separation section of the series which produces a second gas effluent and a second liquid effluent; the second liquid effluent obtained at the end of the second gas-liquid separation section feeds the third gas-liquid separation section of the series which produces a third gas effluent and a third liquid effluent; and so on up to the Nth section which is fed by the (N-1)th liquid effluent obtained at the end of the (N - 1)th gas-liquid separation section of the series and which produces an Nth gas effluent and an Nth liquid effluent, the Nth liquid effluent obtained at the end of the Nth gas-liquid separation section advantageously constitutes the flow of purified thermoplastic polymers.;

[0122] The gas effluent produced by said gas-liquid separation section or the gas effluents produced by the gas-liquid separation sections of the series is (are) recovered and may be, in whole or in part, purged and / or purified and / or fractionated and / or recycled, directly or after purification, to step a) and / or possibly to step b). For example, the gas effluent produced by said gas-liquid separation section or the gas effluents produced by the gas-liquid separation sections of the series may be entirely purged; or partly purged and partly recycled directly to step a); or entirely recycled directly to step a) with a total purge at regular frequency and for a fixed time; or at least partly purified and then recycled to step a).According to another embodiment, at least a portion of the gas effluent produced by said gas-liquid separation section or the gas effluents produced by the gas-liquid separation sections of the series can be recovered and sent to the purification step b) and be used as a cleaning solvent for at least one purification equipment, for example for cleaning filters.

[0123] Said gas-liquid separation section or each of the gas-liquid separation sections, implemented in step c), is operated at an inlet temperature (i.e. at the inlet of said section or each section) of between 100°C and 300°C, preferably between 110 and 275°C, preferably between 150 and 250°C, and at a pressure lower than the pressure of step b) and preferably at the outlet pressure of step b), in particular at a pressure lower than 100.0 MPa absolute, preferably lower than 25.0 MPa absolute, preferably lower than 18.0 MPa absolute, preferably lower than 15.0 MPa absolute. Preferably, in the gas-liquid separation section or in each of the gas-liquid separation sections, the pressure is greater than or equal to 0.000005 MPa absolute (i.e. greater than or equal to 5 Pa absolute), in particular greater than or equal to 0.00001 MPa absolute (i.e.greater than or equal to 10 Pa absolute), in particular greater than or equal to 0.0001 MPa absolute (i.e. greater than or equal to 0.1 kPa absolute), more particularly greater than or equal to 0.0005 MPa absolute (i.e. greater than or equal to 0.5 kPa absolute). Very advantageously, the temperature is adjusted, in the gas-liquid separation section or in each of the gas-liquid separation sections, so as to have an operating temperature greater than or equal to the evaporation temperature of the solvent, in particular of the dissolving solvent, and advantageously greater than or equal to the melting temperature of the thermoplastics in question, at the operating pressure of the gas-liquid separation section in question.

[0124] When step c) uses several gas-liquid separation sections, the pressure of the subsequent section is lower than that of the previous section. In other words, when step c) uses N successive gas-liquid separation sections, N being an integer greater than or equal to two, preferably between two and ten, preferentially between two and five, for example N being chosen from three and four, the pressure of the second section of the series is lower than that of the first section of the series, the pressure of the third section of the series is lower than that of the second section of the series, and so on up to the Nth section in which the pressure is lower than the pressure of the (N-1)th section of the series, the pressure of the first section of the series being lower than the pressure of step b), preferably than the pressure at the outlet of step b). In particular,the first gas-liquid separation section can be operated at an inlet temperature of between 100 and 300°C, preferably between 110 and 275°C, and at a pressure of less than 100.0 MPa absolute, preferably less than 25.0 MPa absolute, preferably less than 15.0 MPa absolute, and advantageously greater than or equal to 0.0008 MPa absolute (i.e. greater than or equal to 0.8 kPa absolute or greater than or equal to 8 mbar absolute); while the Nth section can be operated at an inlet temperature of between 100 and 300°C, preferably between 110 and 275°C, and at a pressure of between 0.000005 and 1.00 MPa absolute (i.e. between 5 Pa absolute and 1.00 MPa absolute or between 0.05 mbar and 10.0 bar), preferably between 0.00001 and 1.00 MPa absolute (i.e. between 10 Pa absolute and 1.00 MPa absolute, or between 0.1 mbar and 10.0 bar), preferably between 0.0001 and 1.00 MPa absolute (i.e. between 1 mbar and 10.0 bar), preferably between 0.0001 and 0.10 MPa absolute (i.e. between 1 mbar and 1.0 bar), preferably between 0.0005 and 0.10 MPa absolute (i.e. between 5 mbar and 1.0 bar), preferably between 0.0005 and 0.050 MPa absolute (i.e. between 5 mbar and 0.50 bar), preferably between 0.0005 and 0.0050 MPa absolute (i.e. between 5 mbar and 50 mbar), very preferably between 0.0005 and 0.0020 MPa absolute (i.e. between 5 mbar and 20 mbar) and very preferably between 0.0008 and 0.0010 MPa absolute (i.e. between 8 mbar and 10 mbar). In this particular case, the pressure in each intermediate section, located between the first and the Nth section, if applicable, that is to say when it(they) is(are) implemented, is adjusted in a decreasing manner and between the pressure of the first section and the pressure of the last section.

[0125] According to a very particular embodiment, the thermoplastic targeted is polypropylene and the dissolution solvent is an isomer or a mixture of isomers of hexane, heptane and / or octane. In this particular embodiment, dissolution step a) is carried out at a dissolution temperature of between 150 and 250°C, preferably between 160 and 225°C, preferentially between 170 and 200°C, and at a dissolution pressure of between 1.0 and 25.0 MPa absolute, preferably between 1.0 and 12.0 MPa absolute, preferentially between 1.5 and 6.0 MPa absolute, preferably between 2.0 and 5.0 MPa absolute. According to this particular embodiment, step b) is carried out in the same temperature and pressure ranges and makes it possible to obtain a purified polymer solution comprising the targeted polypropylene and which is sent to step c) of solvent-polymer separation.In this embodiment, step c) implements for example four successive gas-liquid separation sections, in which:

[0126] - the first section is preferably operated at an inlet temperature between 165 and 275°C, preferably between 170 and 275°C, and at a pressure between 0.5 and 4.0 MPa, preferably between 0.5 and 2.0 MPa absolute, preferably between 0.5 and 1.0 MPa absolute,

[0127] - the fourth section is preferably operated at an inlet temperature between 165 and 275°C, preferably between 170 and 275°C, and at a pressure between 0.000005 and 0.0050 MPa absolute (i.e. between 0.05 and 50 mbar), preferably between 0.00001 and 0.0050 MPa absolute (i.e. between 0.1 and 50 mbar), preferably between 0.0001 and 0.0050 MPa absolute (i.e. between 1 and 50 mbar), very preferably between 0.0005 and 0.0020 MPa absolute (i.e. between 5 and 20 mbar), very preferably between 0.0008 and 0.0010 MPa absolute (i.e. between 8 and 10 mbar), or at a pressure between 0.000005 and 1.0 MPa absolute (i.e. between 0.05 mbar and 10 bar) in the presence of a stripping agent introduced at the level of the fourth gas-liquid separation section;

[0128] - the second and third gas-liquid separation sections (i.e. the intermediate gas-liquid separation sections) are operated at an inlet temperature between 165 and 275°C, preferably between 170 and 275°C, and at a pressure lower than that of the first gas-liquid separation section and higher than that of the fourth gas-liquid separation section, and more particularly: for the second gas-liquid separation section, at a pressure lower than the pressure of the first gas-liquid separation section and higher than that of the third gas-liquid separation section; and for the third gas-liquid separation section, at a pressure lower than the pressure of the second gas-liquid separation section and higher than that of the fourth gas-liquid separation section.

[0129] According to another particular embodiment, the thermoplastic in question is polyethylene and the dissolution solvent is preferably an isomer or a mixture of isomers of butane, pentane, hexane, heptane and / or octane. In this particular embodiment, dissolution step a) is carried out at a dissolution temperature of between 120 and 300°C, preferably between 130 and 275°C, preferentially between 150 and 250°C, and at a dissolution pressure of between 0.1 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferentially between 1.5 and 18.0 MPa absolute, preferably between 2.0 and 15.0 MPa absolute. Step b) is carried out in the same temperature and pressure ranges and makes it possible to obtain a purified polymer solution comprising the targeted polyethylene and which is sent to step c) of solvent-polymer separation.In this other particular embodiment, step c) can implement for example four successive gas-liquid separation sections, in which:

[0130] - the first section is preferably operated at an inlet temperature between 130 and 300°C, preferably between 150 and 275°C, and at a pressure greater than or equal to 0.1 MPa absolute and less than the outlet pressure of step b), the temperature and pressure being advantageously adjusted so as to evaporate part of the dissolution solvent, present in the purified polymer solution which feeds the first section;

[0131] - the fourth section is preferably operated at an inlet temperature between 130 and 300°C, preferably between 150 and 275°C, and at a pressure between 0.000005 and 0.0500 MPa absolute (i.e. between 0.05 and 500 mbar), preferably between 0.00001 and 0.0100 MPa absolute (i.e. between 0.1 and 100 mbar), preferably between 0.0001 and 0.0050 MPa absolute (i.e. between 1 and 50 mbar);

[0132] - the second and third gas-liquid separation sections (i.e. the intermediate gas-liquid separation sections) are operated at an inlet temperature between 130 and 300°C, preferably between 150 and 275°C, and at a pressure lower than that of the first gas-liquid separation section and higher than that of the fourth gas-liquid separation section, and more particularly: for the second gas-liquid separation section, at a pressure lower than the pressure of the first gas-liquid separation section and higher than that of the third gas-liquid separation section; and for the third gas-liquid separation section, at a pressure lower than the pressure of the second gas-liquid separation section and higher than that of the fourth gas-liquid separation section.

[0133] Said gas-liquid separation section or sections may implement any type of device known to those skilled in the art for separating gas and liquid, possibly accompanied by means for adjusting the temperature and pressure, for example means for heating, means for adjusting and controlling the pressure above atmospheric pressure, means for adjusting and controlling the pressure below atmospheric pressure (to obtain a vacuum), etc.; mechanical means for setting the gas and liquid phases in motion and in contact.For example, said gas-liquid separation section or said gas-liquid separation sections may implement one or more pieces of equipment chosen from: a separator drum, a column, a distillation column, a stripper, equipment comprising internals and / or packing facilitating the separation between the gas and the liquid, an evaporator, a thin-film evaporator, a scraped film evaporator, a falling film evaporator, a blade evaporator, a rotating disc reactor or column, a reactor, a stirred reactor, an extruder, a kneading reactor, a devolatilizer. According to a very particular embodiment, said gas-liquid separation section or said gas-liquid separation sections may implement a gas-liquid separator comprising:.

[0134] - an enclosure comprising a cylindrical upper part and a cylindrical lower part extending into a bottom with a decreasing section, said lower part advantageously comprising a liquid guard zone at the bottom of the enclosure,

[0135] - an inlet pipe, for supplying said separator with a gas / liquid flow, said inlet pipe opening at one end into the lower part of said enclosure and said end being advantageously bent (i.e. the internal end being advantageously bent), - an outlet pipe located in the bottom of said enclosure, for discharging a flow of liquid separated from said gas-liquid separator,

[0136] - a gas-liquid separation system which can be:

[0137] - a cyclone with a cylindro-conical body, internal to said enclosure, and comprising a tangential inlet tube for supplying said cyclone with a gas / liquid mixture, said tube being located in the upper part of said enclosure, an outlet tube for discharging a separate gas flow, said outlet tube located at the top of said cylindro-conical body, said outlet tube opening outside the enclosure of the gas-liquid separator, and an opening at the base of said cylindro-conical body, said opening being connected to a return leg for a liquid flow, said return leg opening into said liquid guard zone at the bottom of the enclosure of said gas-liquid separator; and / or

[0138] - a gas-liquid separation device equipped with a helical spiral located in the upper part of said enclosure, said gas-liquid separation device being topped with an upper cap which comprises at its upper end a gas discharge conduit and at its lower end a vertical conduit concentric with the inlet conduit allowing the return of the separated liquid to the liquid guard zone at the bottom of the enclosure of said gas-liquid separator;

[0139] - possibly means for injecting a driving agent and / or inert gas flow.

[0140] According to this particular embodiment, the lower part of the enclosure, and more particularly the liquid guard zone at the bottom of the enclosure, can be equipped with an agitator. Still according to this particular embodiment, a pump, in particular a pump capable of driving viscous fluids, also called a melt pump, can be implemented at the external end (at said gas-liquid separator) of said outlet pipe located at the bottom of the enclosure.

[0141] A stripping agent (or entraining agent) may optionally be introduced into the gas-liquid separation section or the last (i.e. the Nth) gas-liquid separation section of the series, to assist the vaporization of the residual solvent present in the polymer solution at the inlet of said last section. The addition of a stripping agent thus makes it possible to optimize the solvent-polymer separation in the last gas-liquid separation section. It makes it possible to achieve very low residual solvent contents in the purified thermoplastic stream, in particular less than or equal to 5% by weight, preferably less than or equal to 1.00% by weight, preferably less than or equal to 0.10% by weight, preferably less than or equal to 500 ppm by weight of solvent relative to the total weight of the purified thermoplastic stream, without the need to achieve a high vacuum in the last section, i.e.without reaching a pressure between 0.000005 and 1.00 MPa absolute, in particular between 0.00001 and 1.00 MPa absolute, in particular between 0.0001 and 1.00 MPa absolute, more particularly between 0.0005 and 0.0020 MPa absolute, or even very particularly between 0.0008 and 0.0010 MPa absolute. The entraining agent possibly introduced is a compound lighter than the dissolution solvent, i.e. a compound having a boiling point lower than that of the dissolution solvent (at atmospheric pressure), for example water, nitrogen, hydrogen. Preferably, the quantity of entraining agent possibly introduced represents between 10% and 0.1% by weight of entraining agent relative to the thermoplastics in question.

[0142] Optionally, a flow of inert gas, preferably a flow of nitrogen, may be introduced into the gas-liquid separation section or the first gas-liquid separation section of the series, to assist the vaporization and therefore the removal of the solvent, in particular the dissolution solvent, present in the purified polymer solution which feeds step c). The presence of inert gas modifies the phase diagram. The presence of the inert gas, in particular the presence of nitrogen, may therefore promote the evaporation of the solvent, in particular the dissolution solvent, present in the purified polymer solution which feeds step c), and thus make it possible to limit the operating temperatures in said section or first section, while optimizing the evaporation of the solvent.At the outlet of the gas-liquid separation section or the first gas-liquid separation section of the series, the inert gas is then advantageously found in a mixture with the gaseous dissolving solvent in the gas effluent. The presence of the inert gas, in particular the presence of nitrogen, can also modify the phase diagram in such a way that the solvent, in particular the dissolving solvent, present in the purified polymer solution, is at least partly in the supercritical state. In this situation, the fraction of the solvent, in particular the dissolving solvent, which is in supercritical form, can be separated from the polymer solution by density difference, for example by decantation in particular in a settling tank.The presence of the inert gas, in particular the presence of nitrogen, can also modify the phase equilibrium of the purified polymer solution which can demix and become biphasic with a first liquid phase which comprises the thermoplastics and a liquid phase composed essentially of solvent, in particular dissolving solvent. In the case of the presence of an inert gas flow, in particular a nitrogen flow, said inert gas flow is introduced in such a quantity that the weight ratio between the flow rate of the inert gas flow and the flow rate of the purified polymer solution is between 0.000001 and 1.00, preferably 0.0001 and 0.50. Optionally, the solvent-polymer separation step c) can comprise an intermediate separation upstream of the successive gas-liquid separation(s). Thus, step c) can implement an intermediate separation section, located upstream of the successive gas-liquid separation section(s).This intermediate separation may be a liquid-liquid separation, which then advantageously uses an intermediate liquid-liquid separation section, or a supercritical-liquid separation, which then advantageously uses an intermediate supercritical-liquid separation section. The optional intermediate liquid-liquid or supercritical-liquid separation section is advantageously supplied with the purified polymer solution from step b), and optionally with a flow of inert gas, in particular a flow of nitrogen.It makes it possible to produce a liquid phase which comprises the targeted thermoplastics in particular dissolved in the residual dissolution solvent, and a second liquid phase or a supercritical phase which comprises dissolution solvent, respectively in the liquid state or at least partially supercritical, and which is advantageously low in targeted thermoplastics, preferably which contains less than 5% by weight, preferably less than 1.00% by weight, preferably less than 0.10% by weight, or even less than 500 ppm by weight of targeted thermoplastics relative to the total weight of said second liquid phase or supercritical phase, or which is even free of targeted thermoplastics. Said possible flow of inert gas can in fact help the demixing of the purified polymer solution to form a two-phase liquid system, or help at least part of the dissolution solvent to pass into the supercritical state.

[0143] When an intermediate liquid-liquid separation is integrated into step c), said intermediate liquid-liquid separation advantageously comprises (i) an adjustment of the temperature and / or the pressure so as to obtain the demixing of the purified polymer solution, then (ii) a separation by density difference, in particular by decantation, of a first liquid phase, which comprises the targeted thermoplastics in particular dissolved in the residual dissolution solvent, and of a second liquid phase, which is poor in targeted thermoplastics, that is to say which comprises less than 5% by weight, preferably less than 1.00% by weight, preferentially less than 0.10% by weight, or even less than 500 ppm by weight of targeted thermoplastics relative to the total weight of said second liquid phase.Thus, when step c) comprises an intermediate liquid-liquid separation, the temperature and / or the pressure are adjusted in the intermediate liquid-liquid separation section, so as to form from the purified polymer solution, optionally in the presence of a flow of inert gas, a two-phase system. Preferably, the temperature in the intermediate liquid-liquid separation section is adjusted to a value lower than the critical temperature of the dissolution solvent (but higher than the melting temperature of the target thermoplastics).And preferably, the pressure in the intermediate liquid-liquid separation section is adjusted to a value less than or equal to the bubble point pressure of the dissolving solvent at the operating temperature, preferably adjusted to a value between a pressure 1.0 MPa less than the bubble point pressure or equal to said bubble point pressure of the dissolving solvent at the operating temperature.

[0144] When an intermediate supercritical-liquid separation is integrated in step c), said intermediate supercritical-liquid separation preferably comprises (i) an adjustment of the temperature and / or the pressure in the intermediate supercritical-liquid separation section, optionally in the presence of an inert gas flow, so that the dissolving solvent is at least partially in the supercritical state, then (ii) a separation by density difference, in particular by decantation, of a liquid phase which comprises the targeted thermoplastics in particular dissolved in the residual dissolving solvent, and of a supercritical phase which comprises dissolving solvent in the supercritical state.The possible intermediate supercritical-liquid separation can in particular be integrated into step c) when the dissolution solvent is sufficiently light, in particular when the dissolution solvent has a boiling point (at atmospheric pressure, in particular at 0.1 MPa) of between -50 and 100°C, preferably between -50 and 70°C, preferentially between -45 and 50°C.

[0145] The liquid phase which comprises the targeted thermoplastics obtained at the end of the possible intermediate liquid-liquid or supercritical-liquid separation section feeds the gas-liquid separation section or the first gas-liquid separation section, advantageously in place of the purified solution.

[0146] For example, the thermoplastic in question is polyethylene and the dissolving solvent is preferably an isomer or a mixture of isomers of butane, pentane, hexane, heptane and / or octane. In this particular case, the dissolving step a) is carried out at a dissolving temperature of between 120 and 300°C, preferably between 130 and 275°C, preferentially between 150 and 250°C, and at a dissolving pressure of between 0.1 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferentially between 1.5 and 18.0 MPa absolute, preferably between 2.0 and 15.0 MPa absolute. Step b) is carried out in the same temperature and pressure ranges and makes it possible to obtain a purified polymer solution comprising the targeted polyethylene and which is sent to step c) of solvent-polymer separation. In this particular case,step c) may implement at least one intermediate liquid-liquid or supercritical-liquid separation section and two or three successive gas-liquid separation sections, for example in the following manner: - the intermediate liquid-liquid or supercritical-liquid separation section, preferably supercritical-liquid, is operated at an inlet temperature between 130 and 300°C, preferably between 150 and 275°C, and at a pressure greater than or equal to between 3.0 and 10.0 MPa absolute, preferably between 3.0 and 100.0 MPa absolute, the temperature and pressure being advantageously adjusted so as to obtain a two-phase liquid-liquid system or so as to have at least part of the dissolution solvent in the supercritical state,present in the purified polymer solution which feeds the first section; said intermediate liquid-liquid or supercritical-liquid separation section thus produces a liquid effluent which comprises polyethylene and which is sent to the first gas-liquid separation section, and another liquid effluent or a supercritical effluent, preferably a supercritical effluent, which comprises dissolving solvent;,

[0147] - the first gas-liquid separation section is operated at an inlet temperature between 130 and 300°C, preferably between 150 and 275°C, and at a pressure greater than or equal to 0.1 MPa absolute and less than the pressure at the outlet of the intermediate liquid-liquid or supercritical-liquid separation section;

[0148] - the last gas-liquid separation section is operated at an inlet temperature between 130 and 300°C, preferably between 150 and 275°C, and at a pressure between 0.000005 and 0.0500 MPa absolute (i.e. between 0.05 and 500 mbar), preferably between 0.00001 and 0.0100 MPa absolute (i.e. between 0.1 and 100 mbar), preferably between 0.0001 and 0.0050 MPa absolute (i.e. between 1 and 50 mbar);

[0149] - the possible intermediate gas-liquid separation section is operated at an inlet temperature between 130 and 300°C, preferably between 150 and 275°C, and at a pressure lower than that of the first gas-liquid separation section and higher than that of the last gas-liquid separation section.

[0150] Optionally, at least one additive may be introduced in step c), and / or optionally upstream of step c), in particular upstream of step a) of dissolution, in step a) of dissolution or even in step b) and more particularly in a sub-step b1) of separation of the insolubles. For example, an antioxidant agent may be introduced in step c), and / or optionally upstream of step c), for example upstream of step a) of dissolution, in step a) of dissolution or even in step b) and more particularly in a sub-step b1) of separation of the insolubles, so as to limit, or even avoid, any degradation of the targeted thermoplastics. A person skilled in the art will be able to choose said at least one additive, in particular said antioxidant agent, depending on the targeted thermoplastics. For example, the antioxidant agent may be chosen from the compounds marketed under the trademarks Irganox® and Irgafos®,and in particular among the following commercial compounds: Irganox® 1010, Irgafos® 168, Irgafos® 168 oxidized. A person skilled in the art will also know how to adjust the quantity of said at least one additive, in particular of said antioxidant agent to be introduced, depending on the thermoplastics targeted and the desired properties. For example, the antioxidant agent can be introduced so as to adjust the content of said antioxidant agent between 100 and 10,000 ppm by weight, preferably between 500 and 5,000 ppm by weight of antioxidant agent relative to the weight of the thermoplastics targeted. In the case where an additive, in particular an antioxidant agent, is introduced in step c), and when step c) uses a single gas-liquid separation section, said additive, in particular antioxidant agent, is preferably introduced upstream of said gas-liquid separation section,more particularly in the purified polymer solution resulting from b) or possibly in the liquid phase resulting from the intermediate liquid-liquid or supercritical-liquid separation section optionally implemented upstream of said gas-liquid separation section. In the case where an additive, in particular an antioxidant, is introduced in step c), and when step c) uses several successive gas-liquid separation sections, said additive, in particular antioxidant, is preferably introduced downstream of the first gas-liquid separation section of the series, individually or in fractions, more particularly in at least one of the liquid effluents produced by the gas-liquid separation sections of the series (including the first section), and preferably in one of the liquid effluents produced by one of the sections upstream of the last gas-liquid separation section of the series. In the case where an additive,in particular an antioxidant, is introduced in step c), and when step c) uses an intermediate liquid-liquid or supercritical-liquid separation section and one or more successive gas-liquid separation sections and, said additive, in particular an antioxidant, is preferably introduced downstream of said intermediate section, in a unitary or fractional manner, more particularly in the liquid phase from said intermediate section and / or in the liquid effluent produced by the gas-liquid separation section or in at least one of the liquid effluents produced by the gas-liquid separation sections of the series (including the first section),and preferably in the liquid phase from said intermediate section and / or in the liquid effluent produced by the gas-liquid separation section or in one of the liquid effluents produced by one of the sections upstream of the last gas-liquid separation section in the series.,

[0151] Thus, the process according to the invention makes it possible to obtain a stream of purified thermoplastics, and more particularly of purified polyolefins, having a very low residual solvent content (in particular of dissolving solvent), and in particular less than or equal to 5% by weight, preferably less than or equal to 1.00% by weight, preferably less than or equal to 0.10% by weight, or even a content less than or equal to 500 ppm by weight, relative to the total weight of the stream of purified thermoplastics. More particularly, the stream of purified thermoplastics, and more particularly of purified polyolefins, obtained at the end of the process according to the invention has a volatile organic compound (VOC) content less than or equal to 5% by weight, preferably less than or equal to 1.00% by weight, preferably less than or equal to 0.10% by weight, or even a content less than or equal to 500 ppm by weight, relative to the total weight of the stream of purified thermoplastics.The VOC content gives a good indication of the solvent content and in particular the residual solvent content in the resulting purified thermoplastic stream.

[0152] Preferably, the content of volatile organic compounds (VOCs) is determined by gas chromatography with headspace extraction (or HS for headspace according to the English term) coupled with mass spectrometry (MS) or with a flame ionization detector (FID), preferably coupled with mass spectrometry (MS).

[0153] The stream of purified thermoplastic polymers obtained at the end of the process according to the invention also very advantageously has an impurity content of less than or equal to 5% by weight of impurities, preferably less than or equal to 1.0% by weight of impurities, preferably a content of less than or equal to 0.5% by weight of impurities relative to the total weight of the stream of purified thermoplastics. The stream of purified thermoplastic polymers obtained at the end of the process according to the invention can then be used in any application, for example as a replacement for the same polymers in the virgin state.

[0154] Device

[0155] The present invention also relates to a device for treating a plastic load to obtain a flow of purified thermoplastic polymers, which comprises:

[0156] A) dissolution means for bringing into contact and dissolving at least in part the plastic filler in a dissolution solvent, and obtaining a raw polymer solution, said dissolution means advantageously being any type of industrial equipment allowing said bringing into contact and said dissolution, for example an extruder, one or more static or dynamic mixers, and / or one or more continuously stirred reactors, also called “Continuous Stirred Tank Reactor” (CSTR) according to English terminology, and equipped with suitable stirring system(s);

[0157] B) purification means for purifying the raw polymer solution, and obtaining a purified polymer solution, said purification means advantageously being any type of industrial equipment for purifying the raw polymer solution, said purification means being able to comprise: solid-liquid (or solid-liquid-liquid) separation means, said solid-liquid separation means advantageously being any type of industrial equipment for separating solids and one or two liquids, such as separation equipment by decantation, filtration, centrifugation and / or static electricity, to obtain a clarified polymer solution; a washing device for bringing the raw or clarified polymer solution into contact with a dense solution, in particular an aqueous solution, to obtain a washed polymer solution;an extraction device allowing the raw or clarified or washed polymer solution to be brought into contact with an organic solvent in the liquid state or at least partially in the supercritical state, to obtain an extracted polymer solution; and / or an adsorption device allowing the raw or clarified or washed or extracted polymer solution to be brought into contact with at least one adsorbent, in particular at least one adsorbent bed or adsorbent particles in divided form, and allowing the recovery of a refined polymer solution, said clarified, washed, extracted or refined polymer solution constituting the purified polymer solution;

[0158] C) a solvent-polymer separation device, located downstream of said purification means, for separating the purified polymer solution into a stream of purified thermoplastic polymers and at least one solvent effluent advantageously comprising dissolving solvent, characterized in that said solvent-polymer separation device comprises: a gas-liquid separation section or several gas-liquid separation sections operating in series, preferably at least two, preferably between two and ten, very preferably between two and five, for example three or four, successive gas-liquid separation sections, at least one pressure control system in said gas-liquid separation section or in each gas-liquid separation section of the series,so as to adjust the pressure in said gas-liquid separation section or each gas-liquid separation section of the series to a value lower than the pressure at the outlet of the purification means, and when said solvent-polymer separation device comprises several gas-liquid separation sections, so as to adjust the pressure in the later section to a value lower than that of the earlier section, optionally at least one system for controlling the temperature, in particular the inlet temperature, of said gas-liquid separation section or of each gas-liquid separation section of the series, said gas-liquid separation section or each gas-liquid separation section of the series comprising a feed system, a liquid withdrawal system and a gas withdrawal system,the feed system of said gas-liquid separation section or of the first gas-liquid separation section of the series being connected to at least one of the purification means and allowing the feed of purified polymer solution to said solvent-polymer separation device, when said solvent-polymer separation device comprises several gas-liquid separation sections, the feed system of the later section being connected to the liquid withdrawal system of the earlier section, the liquid withdrawal system of said gas-liquid separation section or of the last gas-liquid separation section of the series making it possible to recover said stream of purified thermoplastic polymers, the gas withdrawal system of said gas-liquid separation section or of each gas-liquid separation section of the series making it possible to recover said at least one solvent effluent which comprises dissolution solvent,and the gas withdrawal system of said section or of each gas-liquid separation section possibly being able to be connected directly or indirectly to devices for condensing, for purifying, for fractionating and / or for recycling one or more solvent effluents to said dissolution means and / or possibly to said purification means.,

[0159] Said gas-liquid separation section or said gas-liquid separation sections may implement any type of device, in particular any type of industrial equipment, known to those skilled in the art for separating gas and liquid, possibly accompanied by devices for adjusting the temperature, in particular the inlet temperature, and the pressure, for example equipment for heating, equipment for adjusting and controlling the pressure above atmospheric pressure, equipment for adjusting and controlling the pressure below atmospheric pressure (to obtain a vacuum), etc.; equipment for setting the gas and liquid phases in motion and in contact.For example, said gas-liquid separation section or said gas-liquid separation sections may implement one or more pieces of equipment chosen from: a separator drum, a column, a distillation column, a stripper, equipment comprising internals and / or packing facilitating the separation between the gas and the liquid, an evaporator, a thin-film evaporator, a scraped film evaporator, a falling film evaporator, a blade evaporator, a rotating disc reactor or column, a reactor, a stirred reactor, an extruder, a kneading reactor, a devolatilizer. According to a very particular embodiment, said gas-liquid separation section or said gas-liquid separation sections may implement a gas-liquid separator comprising:.

[0160] - an enclosure comprising a cylindrical upper part and a cylindrical lower part extending into a bottom with a decreasing section, said lower part advantageously comprising a liquid guard zone at the bottom of the enclosure,

[0161] - an inlet pipe, for supplying said separator with a gas / liquid flow, said inlet pipe opening at one end into the lower part of said enclosure and said end being advantageously bent (i.e. the internal end being advantageously bent),

[0162] - an outlet pipe located in the bottom of said enclosure, for evacuating a flow of liquid separated from said gas-liquid separator,

[0163] - a gas-liquid separation system which can be:

[0164] - a cyclone with a cylindro-conical body, internal to said enclosure, and comprising a tangential inlet tube for supplying said cyclone with a gas / liquid mixture, said tube being located in the upper part of said enclosure, an outlet tube for discharging a separate gas flow, said outlet tube located at the top of said cylindro-conical body, said outlet tube opening outside the enclosure of the gas-liquid separator, and an opening at the base of said cylindro-conical body, said opening being connected to a return leg for a liquid flow, said return leg opening into said liquid guard zone at the bottom of the enclosure of said gas-liquid separator; and / or

[0165] - a gas-liquid separation device equipped with a helical spiral located in the upper part of said enclosure, said gas-liquid separation device being topped with an upper cap which comprises at its upper end a gas discharge conduit and at its lower end a vertical conduit concentric with the inlet conduit allowing the return of the separated liquid to the liquid guard zone at the bottom of the enclosure of said gas-liquid separator;

[0166] - possibly means for injecting a driving agent and / or inert gas flow. According to this particular embodiment, the lower part of the enclosure, and more particularly the liquid guard zone at the bottom of the enclosure, can be equipped with an agitator. Still according to this particular embodiment, a pump, in particular a pump capable of driving viscous fluids, also called a melt pump, can be implemented at the external end (to said gas-liquid separator) of said outlet pipe located in the bottom of the enclosure.

[0167] According to a preferred embodiment, said purification means B) comprise at least solid-liquid separation means advantageously followed by an adsorption device. In this particular embodiment, said solid-liquid separation means comprise in particular at least one decanter optionally followed by at least one other solid-liquid separation means, for example at least one filter.

[0168] Optionally, the solvent-polymer separation device C) may comprise an intermediate liquid-liquid or supercritical-liquid separation section, upstream of said gas-liquid separation section or the first gas-liquid separation section of the series. In this particular embodiment, said liquid-liquid or supercritical-liquid separation section is connected to at least one of the purification means, and the supply system of said gas-liquid separation section or the first gas-liquid separation section of the series is connected to said liquid-liquid or supercritical-liquid separation section, and not to at least one of the purification means.The optional intermediate supercritical-liquid separation section preferably comprises at least temperature and pressure adjustment systems, devices for separation by density difference, for example decantation equipment, of two liquid phases of different density or of a liquid phase and a supercritical phase, and systems for withdrawing a liquid phase comprising the targeted thermoplastics and systems for withdrawing another liquid phase and a supercritical phase, essentially composed of solvent and in particular of dissolving solvent.

[0169] Optionally, the gas-liquid separation section or the first intermediate gas-liquid separation section and / or the possible intermediate liquid-liquid or supercritical-liquid separation section, may comprise a system for introducing a flow of inert gas.

[0170] The treatment device according to the invention may optionally further comprise at least one additive introduction system, for example an antioxidant agent. In particular, said at least one additive introduction system is included in the solvent-polymer separation device, and is preferably located upstream of said gas-liquid separation section or upstream of the last gas-liquid separation section of the series. Preferably, when said polymer solvent separation device comprises said at least one additive introduction system and several gas-liquid separation sections, said at least one additive introduction system is located downstream of the first gas-liquid separation section.

[0171] Said device for processing a plastic load also advantageously comprises transport equipment between said means, devices and systems.

[0172] Such a treatment device very advantageously makes it possible to recycle any type of plastic load comprising thermoplastics, in particular polyolefins, and to recover a flow of purified thermoplastics, in particular a flow of purified polyolefins, having a very low residual solvent content (in particular dissolving solvent).

[0173] The following examples and figures illustrate the invention, in particular particular embodiments of the invention, without limiting its scope.

[0174] LIST OF FIGURES

[0175] Figure 1 represents a particular embodiment of the method according to the invention. The particular embodiment of Figure 1 corresponds to the method described in Example 1.

[0176] Figure 2 represents a preferred embodiment of the method according to the invention. The embodiment of Figure 2 corresponds to the method described in Example 2.

[0177] Figure 3 represents a particular embodiment of the method according to the invention. The embodiment of Figure 3 corresponds to the method described in Example 3.

[0178] EXAMPLES

[0179] In the examples below, the analyses carried out on the load and the products obtained are as follows:

[0180] - the content of volatile organic compounds (VOCs), which gives an indication of the solvent content, in particular residual solvent in the flow of thermoplastics in question, is determined by gas chromatography with headspace extraction (or HS for headspace according to the Anglo-Saxon term) coupled with mass spectrometry;

[0181] - the ash content, which gives an indication of the inorganic impurity content, is determined by thermogravimetric analysis (TGA). The ash content is determined by thermogravimetric analysis (TGA), using a Perkin Elmer TGA 8000 device, according to ISO 11358-1 (2014). A sample of 10-20 mg of material is placed on a platinum plate. The temperature is equilibrated at 50°C for 10 minutes, then increased at a heating rate of 20°C / min to 950°C under nitrogen flow. The ash content corresponds to the weight determined at 850°C relative to the weight of the initial sample, expressed as a weight percentage (wt%);

[0182] - the color parameters are expressed in the CIE L*a*b* reference system (defined by the International Commission on Illumination (CIE)), determined by colorimetry (according to the ISO 11664-4 standard), with:

[0183] - a parameter L* of clarity (or luminance), such that the closer L* is to 100, the clearer or more transparent the analyzed solid is; on the contrary, the closer L* is to 0, the more opaque the analyzed solid is;

[0184] - a parameter a* (corresponding to a green-red axis), which measures the color ranging from green (negative values) to red (positive values); a target value of a* is a value approaching 0;

[0185] - a parameter b* (corresponding to a blue-yellow axis), which measures the color ranging from blue (negative values) to yellow (positive values); a target value of b* is a value approaching 0.

[0186] L*a*b* values ​​are determined using a Standard Konica / Minolta Colorimeter CM-3700A device, on solid samples of approximately 20 g of cryogenically ground material. They represent a first indicator of the purity of the polyolefin-based product.

[0187] Example 1 (in accordance with the invention)

[0188] The process of Example 1 is illustrated schematically in Figure 1.

[0189] Step a) of dissolution:

[0190] A filler 1 derived from plastic waste and containing 95% by weight of polypropylene (PP) is introduced in the form of flakes into an extruder heated to 200°C. At the extruder outlet, the filler is at least partly in molten form and is mixed with n-heptane 2 used as a dissolving solvent and previously heated to 200°C, according to a solvent / filler weight ratio of 4 / 1. The mixture comprising the solvent and the filler is introduced into a stirred reactor at 190°C and maintained at 190°C and 2.0 MPa absolute for a residence time of 1 hour. A crude polymer solution 3 is then obtained.

[0191] Step b) purification:

[0192] The raw polymer solution 3, which is continuously recovered from the stirred reactor, is injected into a decanter operated at 190°C and 2.0 MPa. The residence time in the decanter is 1 hour, the residence time corresponding to the ratio between the useful volume of the decanter (i.e. the volume of material in the decanter which is a function of the filling rate of the decanter) and the volume flow rate of raw polymer solution 3 feeding the decanter. Impurities are deposited at the bottom of the decanter, to form a “cake” which is purged discontinuously (flow 5). At the outlet of the decanter, the recovered polymer solution is filtered through a 10 μm mesh filter and then through a 1 μm mesh filter.

[0193] The filtered polymer solution is then sent to an adsorption column containing a bed of activated carbon, and operated at 190°C and 2.0 MPa absolute (i.e. at an adsorption column outlet pressure of 2.0 MPa).

[0194] The adsorbed polymer solution 4, recovered at the outlet of the adsorption column, is then subjected to a solvent-polymer separation step.

[0195] Step c) solvent-polymer separation:

[0196] The solvent-polymer separation step uses a gas-liquid separation section c1. An antioxidant 7, Irgafos® 168, is introduced into the adsorbed polymer solution 4, so as to represent 600 ppm by weight of antioxidant agent relative to the weight of polypropylene included in the adsorbed polymer solution 4. The mixture then feeds the gas-liquid separation section c1 which is operated at an inlet temperature of 180°C and a pressure of 0.14 MPa absolute.

[0197] At the outlet of gas-liquid separation section c1, a gas effluent g1 and a liquid effluent 11 are recovered. The gas effluent g1 can then be, in whole or in part, purged and / or recycled. The liquid effluent 11 is placed in atmospheric conditions, i.e. at a temperature of approximately 20°C and a pressure of approximately 0.1 MPa.

[0198] A solid A (flow 6) is obtained. It is analyzed according to the methods described above. The results are presented in Table 1.

[0199] Table 1

[0200] (1): the VOC content of the feedstock was not measured. Solid A is composed of polypropylene, purified since it has a reduced ash content (<1000 ppm by weight) (and despite the introduction of antioxidant in step c) compared to that of the feedstock (1.1% by weight) and Cielab colorimetry parameters also improved compared to those of the feedstock. Furthermore, solid A shows a satisfactory VOC content, and therefore a residual solvent content (5% by weight of volatile organic compounds VOCs relative to the weight of solid A).

[0201] Example 2 (in accordance with the invention)

[0202] The process detailed in Example 2 is illustrated schematically in Figure 2.

[0203] A load 1 identical to that of Example 1, i.e. derived from plastic waste and containing 95% by weight of polypropylene (PP), is treated in Example 2. The process of Example 2 comprises the same dissolution steps a) and purification b) as those described in Example 1.

[0204] Step c) solvent-polymer separation:

[0205] The adsorbed polymer solution 4, recovered at the outlet of the adsorption column, is then subjected to a solvent-polymer separation step c) which uses four successive gas-liquid separation sections (or stages) c1, c2, c3, c4. The gas-liquid separation sections (or stages) 1 to 4 (i.e. c1, c2, c3, c4) are operated under the following temperature (the temperatures given below being the inlet temperatures for each section) and pressure conditions (the pressures being absolute pressures in each section):

[0206] Stage d: T = 180°C, P = 0.79 MPa, Stage c2: T = 180°C, P = 0.61 MPa, Stage c3: T = 180°C, P = 0.14 MPa, Stage c4: T = 250°C, P = 0.0014 MPa (i.e. 1.4 kPa or 14 mbar).

[0207] The adsorbed polymer solution 4, recovered at the outlet of the adsorption column, feeds the first gas-liquid separation section c1. The liquid effluent 11 produced by the first gas-liquid separation section c1 feeds the second section c2. The liquid effluent I2 produced by the second gas-liquid separation section c2 feeds the third section c3. An antioxidant 7, Irgafos® 168, is introduced into the liquid effluent I3 produced by the third gas-liquid separation section c3, so as to represent 600 ppm by weight of antioxidant agent relative to the weight of polypropylene included in the liquid effluent I3, and the mixture then feeds the fourth gas-liquid separation section c4. At the outlet of the fourth gas-liquid separation section c4, a liquid effluent I4 is recovered and placed under atmospheric conditions, i.e. at a temperature of approximately 20°C and a pressure of approximately 0.1 MPa. A solid B (flow 6) is then obtained.It is analyzed according to the methods described above. The results are presented in Table 2.

[0208] Each gas-liquid separation section c1, c2, c3, c4 also produces a gas effluent, respectively the streams g1, g2, g3 and g4. The gas effluents g1, g2, g3 and g4 produced are recovered and can then be, in whole or in part, purged and / or recycled.

[0209] Table 2

[0210] (1) : the VOC content of the load was not measured.

[0211] Solid B is composed of polypropylene, purified since it has a reduced ash content (< 1000 ppm by weight) (and despite the introduction of antioxidant in step c) compared to that of the feedstock (1.1% by weight) and Cielab colorimetry parameters also improved compared to those of the feedstock. Furthermore, solid B shows a very low VOC content, and therefore a very low residual solvent content (200 ppm by weight of volatile organic compounds VOCs relative to the weight of solid B).

[0212] Example 3 (in accordance with the invention)

[0213] The process of Example 3 is illustrated schematically in Figure 3.

[0214] Step a) of dissolution:

[0215] A feedstock 1 derived from plastic waste and containing 95% by weight of polypropylene (PP) is introduced in the form of flakes into an extruder heated to 200°C. At the extruder outlet, the feedstock is at least partly in molten form and is mixed with n-pentane 2 used as a dissolving solvent and previously heated to 190°C, according to a solvent / feedstock weight ratio of 4 / 1. The mixture comprising the solvent and the feedstock is introduced into a stirred reactor at 190°C and maintained at 190°C and 10.0 MPa absolute for a residence time of 1 hour. A crude polymer solution 3 is then obtained. Step b) of purification:

[0216] The raw polymer solution 3, which is continuously recovered from the stirred reactor, is injected into a decanter operated at 190°C and 9.9 MPa. The residence time in the decanter is 1 hour, the residence time corresponding to the ratio between the useful volume of the decanter (i.e. the volume of material in the decanter which is a function of the filling rate of the decanter) and the volume flow rate of raw polymer solution 3 feeding the decanter.

[0217] Impurities settle at the bottom of the decanter, forming a "cake" which is purged discontinuously (flow 5). At the decanter outlet, the recovered polymer solution is filtered through a 10 μm mesh filter and then through a 1 μm mesh filter.

[0218] The filtered polymer solution is then sent to an adsorption column containing a bed of activated carbon, and operated at 190°C and 9.7 MPa absolute (i.e. at an adsorption column outlet pressure of 9.7 MPa).

[0219] The adsorbed polymer solution 4, recovered at the outlet of the adsorption column, is then subjected to a solvent-polymer separation step.

[0220] Step c) solvent-polymer separation:

[0221] The solvent-polymer separation step uses a section c1 of separation by supercritical decantation of the solvent. An antioxidant 7, Irgafos® 168, is introduced into the adsorbed polymer solution 4, so as to represent 600 ppm by weight of antioxidant agent relative to the weight of polypropylene included in the adsorbed polymer solution 4. The mixture then feeds the section c1 of separation by supercritical decantation of the solvent which is operated at an inlet temperature of 209°C and a pressure of 4.1 MPa absolute.

[0222] At the outlet of gas-liquid separation section c1, a supercritical effluent sc1 and a liquid effluent 11 are recovered. The supercritical effluent sc1 can then be, in whole or in part, purged and / or recycled. The liquid effluent 11 is then subjected to a gas-liquid separation section (or stage) c2 at 180°C and 1 MPa. The gas effluent g1 produced is recovered and can then be, in whole or in part, purged and / or recycled.

[0223] At the outlet of the gas-liquid separation section c2, a liquid effluent I2 is recovered and placed in atmospheric conditions, i.e. at a temperature of approximately 20°C and a pressure of approximately 0.1 MPa.

[0224] A solid C (flow 6) is then obtained. It is analyzed according to the methods described above. The results are presented in Table 3. Table 3

[0225] (1) : the VOC content of the load was not measured.

[0226] Solid C is composed of polypropylene, purified since it has a reduced ash content (<1000 ppm by weight) (despite the introduction of antioxidant in step c) compared to that of the feedstock (1.1% by weight) and Cielab colorimetry parameters also improved compared to those of the feedstock. Solid C shows a very low VOC content, and therefore a very low residual solvent content (200 ppm by weight of volatile organic compounds VOCs relative to the weight of solid C).

Claims

CLAIMS 1. Method for treating a plastic filler (1) comprising thermoplastics, said method comprising: a) a step of dissolving the plastic filler in a dissolving solvent (2), step a) being carried out at a dissolving temperature of between 100°C and 300°C and at a dissolving pressure of between 0.1 and 100.0 MPa absolute, to obtain at least one crude polymer solution (3); b) a step of purifying the crude polymer solution, to obtain a purified polymer solution (4), comprising: b1) a sub-step of separating the insolubles; and / or b2) a sub-step of washing, by contact with a dense solution; and / or b3) an extraction sub-step, by contact with an extraction solvent; and / or b4) a sub-step of adsorption of the impurities by contact with an adsorbent; then c) a step of solvent-polymer separation of the purified polymer solution, to obtain a stream of purified thermoplastic polymers (6) and at least one stream of solvent,said solvent-polymer separation step c) using a gas-liquid separation section (c1) or several gas-liquid separation sections (c1, c2, c3, c4) operating in series, said gas-liquid separation section (c1) or each of the gas-liquid separation sections (c1, c2, c3, c4) being operated at an inlet temperature of between 100°C and 300°C, and at a pressure lower than the outlet pressure of step b), when step c) uses several gas-liquid separation sections (c1, c2, c3, c4), the pressure of the later section being lower than that of the earlier section, the purified polymer solution, obtained at the end of the purification step b), feeding said gas-liquid separation section (c1) or the first gas-liquid separation section (c1) of the series, said gas-liquid separation section (c1) or each of the gas-liquid separation sections (c1, c2, c3, c4) gas-liquid separation (c1, c2, c3, c4) producing a gas effluent (g1, g2, g3, g4),which corresponds to said at least one solvent flow, and a liquid effluent (11, 12, 13, 14), when step c) uses several gas-liquid separation sections (c1, c2, c3, c4), the liquid effluent from the previous section feeding the subsequent section, the liquid effluent from said gas-liquid separation section (c1) or from the last gas-liquid separation section of the series (c4) constituting said flow of purified thermoplastic polymers (6).

2. Method according to claim 1, in which the dissolution solvent (2) and the plastic filler (1) feed step a) according to a weight ratio of the dissolution solvent relative to the plastic filler, between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, even more preferably between 3.0 and 7.

0.

3. Method according to claim 1 or 2, wherein the dissolving solvent comprises at least one hydrocarbon compound, said dissolving solvent having a boiling point of between -50 and 250°C, preferably between -15 and 200°C, preferentially between 15 and 160°C and preferably between 50 and 120°C.

4. A method according to any one of the preceding claims, wherein the dissolving solvent comprises an isomer or a mixture of isomers of butane, pentane, hexane, heptane, octane, nonane and / or decane, and preferably an isomer or a mixture of isomers of hexane, heptane and / or octane.

5. Method according to any one of the preceding claims, wherein the pressure in the gas-liquid separation section (c1) or each of the gas-liquid separation sections (c1, c2, c3, c4) is greater than or equal to 0.000005 MPa absolute, in particular greater than or equal to 0.00001 MPa absolute, in particular greater than or equal to 0.0001 MPa absolute, more particularly greater than or equal to 0.0005 MPa.

6. Method according to any one of the preceding claims, in which said solvent-polymer separation step c) uses several successive gas-liquid separation sections, preferably at least two, preferably between two and ten, very preferably between two and five, for example three or four successive gas-liquid separation sections.

7. The method of claim 6, wherein the first gas-liquid separation section is operated at an inlet temperature of between 100 and 300°C, preferably between 110 and 275°C, and at a pressure of less than 100.0 MPa absolute, preferably less than 25.0 MPa absolute, preferably less than 15.0 MPa absolute, and advantageously greater than or equal to 0.0008 MPa absolute; the last section is operated at an inlet temperature of between 100 and 300°C, preferably between 110 and 275°C, and at a pressure of between 0.000005 and 1.00 MPa absolute, preferably between 0.00001 and 1.00 MPa absolute, preferably between 0.0001 and 1.00 MPa absolute, very preferably between 0.0005 and 0.10 MPa absolute, very preferably between 0.0005 and 0.0020 MPa absolute; and the pressure in each intermediate section is adjusted in a decreasing manner between the pressure of the first section and the pressure of the last section.

8. Method according to any one of the preceding claims, in which the or each gas effluent produced is, in whole or in part, purged and / or purified and / or fractionated and / or recycled to step a) and / or optionally step b).

9. A method according to any one of the preceding claims, wherein step c) comprises an intermediate liquid-liquid or supercritical-liquid separation section, located upstream of the gas-liquid separation section or the series of gas-liquid separation sections, to obtain a liquid phase, which comprises the target thermoplastics, and a second liquid phase or a supercritical phase which comprises dissolving solvent, and wherein the liquid phase, which comprises the target thermoplastics, feeds the gas-liquid separation section or the first gas-liquid separation section, instead of the purified polymer solution.

10. Method according to any one of the preceding claims, in which step c) comprises the introduction of at least one additive, in particular an antioxidant agent. II. Method according to any one of the preceding claims, in which the purification step b) comprises a sub-step b1) of separation of the insolubles, advantageously followed by a sub-step b4) of adsorption.

12. A method according to any preceding claim, wherein the plastic filler comprises polyolefins.

13. Device for treating a plastic load to obtain a flow of purified thermoplastic polymers, said device comprising: - dissolution means for bringing into contact and dissolving at least partially the plastic filler in a dissolution solvent, and obtaining a crude polymer solution; - purification means for purifying the crude polymer solution and obtaining a purified polymer solution; - a solvent-polymer separation device, located downstream of said purification means, for separating the purified polymer solution into a stream of purified thermoplastic polymers and at least one solvent effluent, characterized in that said solvent-polymer separation device comprises: a gas-liquid separation section or several gas-liquid separation sections operating in series, preferably at least two, preferably between two and five, for example three or four, successive gas-liquid separation sections, at least one pressure control system in said gas-liquid separation section or in each gas-liquid separation section of the series, so as to adjust the pressure in said gas-liquid separation section or in each gas-liquid separation section of the series to a value lower than the operating pressure at the outlet of the purification means, and when said solvent-polymer separation device comprises several gas-liquid separation sections, so as to adjust the pressure in the later section to a value lower than that in the earlier section,said gas-liquid separation section or each gas-liquid separation section of the series comprising a feed system, a liquid withdrawal system and a gas withdrawal system, the feed system of said gas-liquid separation section or of the first gas-liquid separation section of the series being connected to at least one of the purification means and allowing the supply of purified polymer solution to said solvent-polymer separation device, when said solvent-polymer separation device comprises several gas-liquid separation sections, the feed system of the later section being connected to the liquid withdrawal system of the earlier section, the liquid withdrawal system of said gas-liquid separation section or of the last gas-liquid separation section of the series allowing the recovery of said flow of purified thermoplastic polymers,the gas withdrawal system of said gas-liquid separation section or of each gas-liquid separation section of the series making it possible to recover said at least one solvent effluent, said at least one solvent effluent comprising dissolution solvent., 14. Device according to claim 13, comprising an intermediate liquid-liquid or supercritical-liquid separation section, upstream of said gas-liquid separation section or of the first gas-liquid separation section of the series.

15. Device according to claim 13 or 14, comprising at least one additive introduction system.

Images