Plastic recycling methods including separation of impurities from polymer solutions by decantation.

Abstract

The present invention relates to a method for processing plastic feedstock, comprising the steps of: a) dissolving the plastic feedstock in a dissolving solvent at 100°C to 300°C and an absolute pressure of 1.0 to 100.0 MPa to obtain a crude polymer solution; and b) decanting the crude polymer solution to obtain a decanted polymer solution and a tailing portion, wherein step b) is carried out at 100 to 300°C and an absolute pressure of 1.0 to 100.0 MPa using at least one decanter, wherein a polymer solution-rich effluent is collected at the decanter or the outlet of each decanter so as to constitute the decanted polymer solution, and a tailing flow is collected at the decanter or the outlet of each decanter so as to constitute a tailing portion, and the liquid level velocity in the decanter is 1 × 10⁻⁶ 7 ~1,000 x 10 2 The process includes steps a) m / s and c) solvent-polymer separation to obtain a stream of purified thermoplastic resin. The present invention also relates to an apparatus for carrying out such a method.

Description

[Technical Field]

[0001] The present invention relates to a method for processing plastics, particularly used plastics, to obtain a stream of purified thermoplastic polymer, which can be upgraded, for example, to the manufacture of new plastic objects. More specifically, the present invention relates to a method for purifying a plastic feedstock, in particular a plastic feedstock obtained from plastic waste, which includes thermoplastic polymers, particularly polyolefins, such as polyethylene and / or polypropylene, by dissolving the targeted thermoplastic plastic in a solvent and then purifying the resulting polymer solution. The method includes, in particular, a step of purifying the polymer solution obtained by decanting at least a portion of the impurities, thereby enabling the recovery of a stream of purified thermoplastic plastic at the outlet of the method according to the present invention. [Background technology]

[0002] Plastics obtained through collection and sorting channels can be upgraded according to various channels.

[0003] "Mechanical" recycling allows for the direct reuse of certain waste materials in new objects or partial reuse by mixing a stream of mechanically separated plastic waste with a stream of virgin polymers. This type of upgrade is limited because, while it allows for the acquisition of a stream concentrated with respect to certain types of polymers, mechanical separation does not allow for the removal of impurities, such as additives like fillers, colorants, and pigments, and metals, that are at least partially trapped in the polymer matrix. In fact, additives are compounds that have been conventionally introduced into polymer formulations to give the material, and therefore the final object, desired properties, such as high mechanical strength or specific color.

[0004] "Chemical" recycling generally leans towards modifying monomers at least partially through a complex series of processes. For example, plastic waste may undergo a pyrolysis process, and the recovered pyrolysis oil may, after generally refining, be converted at least partially to, for example, olefins by steam decomposition. These olefins may then be polymerized. While this type of sequence may be suitable for supply materials or sorting center waste that have undergone little sorting, it generally requires a large amount of energy consumption, particularly due to the energy consumption resulting from high-temperature processing.

[0005] Another route for recycling plastic waste involves at least partially dissolving plastics, particularly thermoplastics. This is done for the purpose of purifying them by removing impurities, such as additives like fillers, colorants, pigments, and metals, and / or polymers from the supply material other than the targeted one or more polymers.

[0006] Several studies have therefore proposed various methods for treating plastic waste by dissolution and purification.

[0007] Patent Document 1 describes a specific method for purifying polymer feedstock obtained in particular from plastic waste, the method comprising dissolving the polymer in a solvent under specific temperature and pressure conditions, and then contacting the resulting polymer solution with a solid.

[0008] Patent Document 2 proposes, as part of its scope, a method for selectively dissolving a specific polymer of plastic in a solvent at a dissolution temperature close to the boiling point of the solvent. However, the method in Patent Document 2 does not allow for the effective treatment and separation of impurities, such as additives.

[0009] Patent Document 3 proposes a treatment method by liquefying a thermoplastic plastic in a solvent and then separating and removing insoluble substances and / or gases. In the method of Patent Document 3, it is not possible to efficiently treat impurities, particularly impurities soluble in the solvent. The purpose of Patent Document 3 is to provide a plastic composition that can be used in a decomposition method, and therefore, high purity is not required. In fact, Patent Document 3 shows that, for example, after dissolution in docosane (boiling point 369 °C) at 150 to 300 °C and 1.1 to 1.5 bar (i.e., 0.11 to 0.15 MPa) in a reactor for a feedstock (containing about 3% by weight of solid foreign matter relative to the total weight of the solid compound of the feedstock) and subsequent treatment by decantation in the non-agitated zone of the reactor, about 2% by weight of impurities remain.

[0010] Patent Document 4 describes a method for purifying a polymer feedstock, particularly a polymer feedstock obtained from plastic waste. The method is carried out by dissolving the polymer in a solvent in a stirred reactor and then performing a sedimentation step. More specifically, Patent Document 4 exemplifies the purification of a feedstock composed of post-consumer polypropylene, which is carried out by dissolving it in n-butane in an autoclave stirred at 140 °C and 900 psig (6.21 MPa), followed by a sedimentation phase after stirring in the autoclave is stopped. The resulting polymer solution is optionally passed through a solid bed and then depressurized so that at least a portion of the butane solvent can be separated from the polypropylene.

[0011] The present invention is directed towards improving these methods for treating thermoplastic plastics by dissolution in a solvent. In particular, the present invention optimizes the removal of impurities from the plastic feedstock, advantageously a continuous removal, while recovering a purified, in particular decolorized and deodorized, stream of thermoplastic plastics, especially polyolefins, and at the same time is directed towards limiting the number of operations in the method carried out, especially the number of separation and / or purification steps of said method. The present invention is therefore directed towards efficiently removing impurities, such as additives, from a plastic feedstock, especially a thermoplastic plastic, especially a plastic feedstock containing polyolefins, so as to continuously obtain a stream of purified thermoplastic plastics, especially a stream of purified polyolefins, which stream of purified thermoplastic plastics can, for example, be reused as a base polymer in the manufacture of new plastic articles instead of virgin resin by carrying out a continuous and simple method.

Prior art documents

Patent documents

[0012]

Patent document 1

Patent document 2

Patent document 3

Patent document 4

Summary of the invention

Means for solving the problems

[0013] (Summary of the invention) The present invention relates to a method for treating a plastic feedstock, the method comprising the following steps: a) A step of dissolving the plastic supply material in a dissolving solvent; the dissolution temperature during this process is 100°C to 300°C, and the dissolution pressure is 1.0 to 100.0 absolute MPa; at least one crude polymer solution is obtained; b) A step of decanting the crude polymer solution; obtaining the decanted polymer solution and the tailing portion. The temperature during process b) is 100°C to 300°C, the pressure is 1.0 to 100.0 absolute MPa, and at least one decanter is used. If step b) includes several decanters, the decanters are operated in series or in parallel. Each decanter, either a first decanter in a series of decanters or in parallel, is fed at least a portion of the crude polymer solution. The effluent, concentrated with the polymer solution, is collected at the decanter or at the outlet of each decanter. The polymer solution-enriched spillage recovered at the outlet of the decanter or the last decanter in a series of decanters, or all the polymer solution-enriched spillage recovered at the outlets of each decanter in parallel, constitute the decanted polymer solution. The tailing flow is collected at the decanter or the outlet of each decanter, and all of the collected tailing flow constitutes the tailing portion. The liquid surface velocity of at least one of the decanters is 1 × 10⁻⁶ -7 ~1,000 × 10 -2 Over the range of m / s; then, c) Solvent / polymer separation step; obtain at least one stream of purified thermoplastic polymer.

[0014] The advantage of the method according to the present invention lies in offering a simple and efficient treatment of plastic feedstock, in particular plastic waste, especially plastic waste obtained from collection and sorting channels, allowing for the selective recovery of thermoplastic polymers, particularly polyolefins, and even polypropylene or polyethylene, contained therein, enabling their recycling into any type of application. The method according to the present invention particularly comprises a continuous step of dissolving thermoplastics and a subsequent specific decantation step, and the method according to the present invention makes it possible to obtain a stream of purified thermoplastics with a sufficiently low impurity content in a simple and advantageous continuous manner, and as a result, the stream of purified thermoplastics can be used in place of virgin resin in any type of plastic compound. More specifically, the method according to the present invention makes it possible to remove at least 70% by weight, and preferably at least 80% by weight, of impurities, particularly inorganic impurities, contained in the plastic feedstock. The method according to the present invention also makes it possible to remove organic compounds other than the targeted thermoplastics, in particular insoluble polymers. Furthermore, and highly advantageously, the purified thermoplastic, particularly purified polyolefin, stream obtained at the end of this method is less colored, or even decolorized, compared to the plastic feed material supplied to the method according to the present invention. In highly specific cases, the method according to the present invention makes it possible to obtain a purified thermoplastic, particularly purified polyolefin, and even more preferably polypropylene or polyethylene, stream containing 5% by weight or less of impurities, more preferably 1.0% by weight or less of impurities, and more preferably with an impurity content of 0.5% by weight or less.

[0015] The method according to the present invention therefore proposes a simple scheme that corresponds to a series of operations, particularly dissolution and decantation, which makes it possible to remove at least some of the impurities, in particular at least some of the additives, from plastic waste and to recover purified thermoplastics, in particular purified thermoplastics that are targeted, contain almost no impurities, and preferably contain a very low concentration of solvent (preferably 10% by weight or less, preferably 1% by weight or less), thereby upgrading the plastic waste by recycling the purified thermoplastics.

[0016] The present invention also has the advantage of contributing to plastic recycling and fossil resource conservation by enabling the upgrading of plastic waste. Specifically, it enables the purification of plastic waste for the purpose of obtaining purified thermoplastic polymers, particularly purified polyolefins, and even purified polypropylene or polyethylene flows, with a lower impurity content, and above all, decolorized and deodorized, which can be reused to form new plastic objects. The obtained purified thermoplastics may therefore be used directly in formulations, either in place of or in mixture with virgin resins, as a mixture with additives such as plasticizers, colorants, pigments or fillers, for the purpose of obtaining plastic products with aesthetic, mechanical or rheological processing properties that facilitate their reuse and upgrading.

[0017] The present invention also relates to a device for processing plastic feedstock to obtain a stream of purified thermoplastic polymer, which comprises the following: - Means for bringing plastic supply material into contact with a dissolving solvent and dissolving it at least partially in the dissolving solvent to obtain a crude polymer solution; - Decanting device with at least one decanter; liquid surface velocity is 1 × 10⁻⁶ -7~1,000 × 10 -2 Preferably, the injection rate is 1.00 m / s or less, over the range of m / s. The decanting device comprises several decanters, which are operated in series or in parallel. The at least one decanter is a vertical or horizontal decanter, preferably cylindrical or substantially cylindrical in shape, and preferably the ratio L / D between the total height or total length L of the decanter and the diameter D of the decanter is 0.5 to 12, preferably 1.0 to 6.0. The one or more decanters include a polymer solution feeding point. The at least one decanter includes a first outlet for polymer solution-enriched spillage and a second outlet for tailing flow, If the decanting device comprises several decanters in series, the first outlets of the downstream decanters are, advantageously, connected to the feeding point of the immediately upstream decanter, with the exception of the last decanter in series whose first outlet is connected to a means located downstream of the decanting device. If the decanting device comprises several decanters in parallel, all of the first outlets of the decanters are connected to a mixing system for mixing all of the effluent enriched with the polymer solution recovered at the outlets of the parallel decanters, and the mixing system is connected to a means located downstream of the decanting device; - Optionally, an additional purification system; located downstream of the decanting device; - A means for separating solvent and polymer; located downstream of the decanting device, it separates the solvent flow from the purified thermoplastic polymer flow.

[0018] According to one embodiment, the at least one decanter is a vertical decanter, - The feeding point of the decanter is located between 1 / 4 of the decanter's height and 3 / 4 of the decanter's height, and the feeding point defines two zones within the vertical decanter in question: an upper zone between the feeding point and the top of the vertical decanter, and a lower zone between the feeding point and the bottom of the vertical decanter. - The first outlet of the decanter is advantageously located in the upper zone of the vertical decanter in question, and the second outlet is located in the lower zone of the vertical decanter.

[0019] According to another embodiment, the at least one decanter is a horizontal decanter, - The feeding point of the decanter is located toward one end of the horizontal decanter in question, - The first and second outlets of the decanter are located toward the end opposite the feeding point. [Modes for carrying out the invention]

[0020] (Description of the embodiment) According to the present invention, the expressions "of between...and..." and "between...and..." are equivalent and mean that both upper and lower limits of the interval fall within the stated range of values. If this is not the case, and if both limits do not fall within the stated range, such information is introduced by the present invention.

[0021] For the purposes of the present invention, various ranges of parameters for a given process, such as pressure ranges and temperature ranges, can be used individually or in combination. For example, for the purposes of the present invention, a range of suitable pressure values ​​can be combined with a range of more suitable temperature values.

[0022] Specific embodiments of the present invention are described below. They can be used separately or in combination, and there are no restrictions on the combination, as long as it is technically feasible.

[0023] According to the present invention, the pressure is an absolute pressure and is given in absolute MPa (MPa absolute or MPa abs).

[0024] The terms “upstream” and “downstream” should be understood in relation to the general flow of one or more fluids or flows under consideration in this method.

[0025] In this specification, the terms "polymer," "thermoplastic polymer," and "thermoplastic plastic" may be used interchangeably.

[0026] The term "polyolefin" refers to any type of homopolymer and / or copolymer, as well as mixtures thereof, having an olefin as the basic unit. More specifically, polyolefins can be any range of polyethylene homopolymers designated by the abbreviation PE (e.g., high-density ones, also called HDPE, or low-density ones, called LDPE), polypropylene homopolymers designated by the abbreviation PP, copolymers thereof, and / or mixtures thereof.

[0027] The term "additive" is a term that has been conventionally used in the field of polymers, particularly in the field of polymer formulations. Additives introduced into polymer formulations may include, for example, plasticizers, fillers (these are organic or mineral solid compounds used to modify the physical, thermal, mechanical, and / or electrical properties of polymer materials, or to reduce their cost), reinforcing agents, colorants, pigments, curing agents, flame retardants, combustion retardants, stabilizers, antioxidants, UV absorbers, and antistatic agents.

[0028] The additives correspond to at least some of the impurities in the plastic supply material to be processed, which can be removed at least partially by the processing method according to the present invention. Other types of impurities may be impurities related to use, such as metallic impurities, paper / cardboard, biomass, and polymers other than the one or more targeted polymers.

[0029] Therefore, according to the present invention, impurities that can be removed at least partially by the method of the present invention include additives conventionally used in polymer formulations, as well as general use-related impurities derived from the lifecycle of plastic objects and materials, and / or from waste collection and sorting circuits. The impurities may be of the type of metal, organic, or mineral; they may be packaging residues, food residues, or compostable residues (biomass). These use-related impurities may include glass, wood, cardboard, paper, aluminum, iron, metals, tires, rubber, silicone, rigid polymers, thermosetting polymers, thermoplastics with properties different from those of the target thermoplastic (particularly the target polyolefin), household goods, chemical products, or cosmetics, used oils, and water.

[0030] According to the present invention, the polymer solution is a solution comprising a dissolving solvent and at least a target thermoplastic polymer, in particular a target polyolefin, wherein the target thermoplastic polymer is dissolved (i.e., particularly solvated and dispersed) in the dissolving solvent, and the dissolved polymer is initially present in the feed material. The polymer solution may contain impurities, which may be insoluble (suspended in the polymer solution) and, in some cases, soluble (dissolved in the dissolving solvent). Depending on the steps of the method according to the present invention, the polymer solution may therefore contain impurities in the form of insoluble particles advantageously suspended in the polymer solution, optionally soluble impurities dissolved in the dissolving solvent, and / or optionally another liquid phase immiscible with the polymer solution.

[0031] It is well known that the boiling point of a compound changes with operating pressure. However, in the absence of further instructions, i.e., pressure instructions, the boiling point of the compound under consideration, in particular the dissolving solvent, should be understood as the boiling point of the compound, in particular the dissolving solvent, at atmospheric pressure (especially equal to 0.1 MPa). Therefore, the boiling point characterizing the dissolving solvent should be understood as the boiling point of the dissolving solvent at atmospheric pressure (especially equal to 0.1 MPa).

[0032] The critical temperature and critical pressure of a solvent, particularly a dissolving solvent, are specific to the solvent and depend on the properties of the solvent under consideration. For pure substances, the critical temperature and critical pressure of the pure substance are the temperature and pressure at the critical point of the pure substance, respectively. As is well known to those skilled in the art, above the critical point, the pure substance under consideration is in a supercritical form or supercritical state; it may then be called a supercritical fluid.

[0033] The present invention therefore relates to a method for processing plastic feedstock, preferably consisting of plastic waste, and advantageously comprising a thermoplastic polymer, more particularly a polyolefin, the method comprising, preferably comprising the following steps: a) A step of dissolving the plastic supply material in a dissolving solvent; the dissolving solvent preferably contains at least one hydrocarbon-based compound, preferably an aliphatic compound, preferably a paraffinic compound, and advantageously has a boiling point of -50 to 250°C, preferably -15 to 150°C, preferredly -1 to 110°C, preferably 20 to 100°C, and the weight ratio of the dissolving solvent to the plastic supply material is preferably 0.2 to 100.0, preferably 0.3 to 20.0, preferably 1.0 to 10.0, and more preferably 3.0 to 7.0; at least one crude polymer solution is obtained. The dissolution temperature when performing step a) is advantageously 100°C to 300°C, preferably 150°C to 250°C, and the dissolution pressure is 1.0 to 100.0 absolute MPa, preferably 1.0 to 25.0 absolute MPa, more preferably 1.5 to 18.0 absolute MPa, and very preferably 2.0 to 15.0 absolute MPa; b) A step of decanting the crude polymer solution; obtaining the decanted polymer solution and the tailing portion; The temperature during step b) is 100°C to 300°C, preferably 150°C to 250°C, and the pressure is 1.0 to 100.0 absolute MPa, preferably 1.0 to 25.0 absolute MPa, more preferably 1.5 to 18.0 absolute MPa, and very preferably 2.0 to 15.0 absolute MPa. Step b) involves at least one decanter, preferably 1 to 10 decanters, more preferably 2 to 5 decanters, and is advantageously operated in series or in parallel, preferably in parallel. Said (or each) decanter is particularly a vertical or horizontal decanter, advantageously having a cylindrical or substantially cylindrical shape, and preferably the ratio L / D between the total height or length L of the decanter and the diameter or width D of the decanter is 0.5 to 12, preferably 1.0 to 6.0. The decanter or the first decanter of a plurality of decanters in series or each decanter in parallel is fed with at least part or all of the crude polymer solution, advantageously at the feed point located on the decanter under consideration. The effluent enriched with the polymer solution is recovered at the outlet of said decanter or each decanter. The effluent enriched with the polymer solution is recovered at the outlet of said decanter or the last decanter of the decanters in series, or alternatively all the effluents enriched with the polymer solution are recovered at the outlets of each decanter in parallel, constituting the decanted polymer solution. The tailing stream is recovered, particularly continuously or batchwise, at the outlet of said decanter or each decanter, and all the recovered tailing streams constitute the tailing portion. One or more of said decanters have the following: - The liquid surface velocity is 1×10 -7 ~1.000×10 -2 m / s, preferably 1.0×10 -6 ~1.000×10 -2 m / s, more preferably 1.0×10 -5 ~6.000×10 -3 m / s, preferably 2.0×10 -5 ~5.000×10 -3 m / s, most preferably 2.0×10 -5 ~9.00×10 -4 m / s, particularly in the range of 2.0×10 -5 ~5.00×10 -4 m / s. - Preferably, the injection rate is 1.00 m / s or less, preferably 0.10 m / s or less, more preferably 0.05 m / s or less, and preferably 0.001 m / s or more; Each decanter is operated for a residence time of 1 to 200 hours, preferably 1 to 50 hours, and the filling rate is preferably 70% to 100% of the total volume of the decanter under consideration; b') Optionally, a step of purifying the decant polymer solution; including: b'1) Additional solid-liquid separation sub-step; obtain at least one clarified polymer solution; and / or b'2) A step of washing the decanted or optionally clarified polymer solution; by contact with a high-density solution; to obtain at least one washed effluent and the washed polymer solution; and / or b'3) Step of extraction of impurities with an extraction solvent; obtain at least one extracted polymer solution and at least one used solvent; and / or b'4) Step of adsorption of impurities; carried out by contact with a solid adsorbent; to obtain at least one refined and purified polymer solution; The purification process makes it possible to obtain a purified polymer solution; the purified polymer solution advantageously corresponds to a clarified, washed, extracted, or refined polymer solution; then c) Solvent-polymer separation step; obtain at least one stream of purified thermoplastic polymer, more specifically at least one stream of purified polyolefin, and furthermore, at least one stream of purified polypropylene or at least one stream of purified polyethylene.

[0034] (Feed material) The feedstock of the method according to the present invention is known as a plastic feedstock and comprises a plastic, which in itself comprises a thermoplastic polymer, for example, a polyolefin. Preferably, the plastic feedstock contains 50% to 100% by weight of plastic, preferably 70% to 100% by weight.

[0035] The plastics included in the raw materials supplied by the method according to the present invention are generally production waste and / or “post-consumer” waste plastic objects, in particular household plastic waste, plastic waste from the construction industry, plastic waste from automobiles or any type of transport or electrical and electronic equipment waste. Preferably, the plastic waste is obtained from collection and sorting channels. The plastic or plastic material comprises a polymer mixed with additives to provide material-specific properties for the purpose of forming various objects (injection molded parts, tubes, films, fibers, fabrics, mastics, coatings, etc.) after shaping. The additives used in the plastic may be organic or inorganic compounds. They are, for example, fillers, colorants, pigments, plasticizers, property modifiers, and combustion retarders.

[0036] The feedstock of the method according to the present invention particularly comprises a thermoplastic polymer, preferably at least 50% by weight, preferably at least 70% by weight, preferably at least 80% by weight, and very preferably at least 90% by weight of the thermoplastic polymer, with 100% being the advantageous maximum upper limit. The thermoplastic polymer contained in the plastic feedstock and targeted by the method according to the present invention may be an alkene polymer, a diene polymer, a vinyl polymer, and / or a styrene polymer. Preferably, the thermoplastic polymer contained in the plastic feedstock and targeted by the method according to the present invention is a polyolefin, such as polyethylene (PE), polypropylene (PP), and / or a copolymer of ethylene and propylene, or a mixture thereof. Preferably, the plastic feedstock contains at least 80% by weight, preferably at least 85% by weight, and preferably at least 90% by weight of polyolefin relative to the total weight of the plastic feedstock, with 100% being the advantageous maximum upper limit. The method according to the present invention is therefore most specifically directed toward purifying and recovering the polyolefin contained in the feedstock so that they can be reused for various applications. According to a particular embodiment, the plastic feedstock comprises a mixture of polypropylene (PP) and polyethylene (PE), in particular, a mixture of polypropylene (PP) and polyethylene (PE) in an amount of at least 80% by weight, preferably at least 85% by weight, and preferably at least 90% by weight, relative to the total weight of the plastic feedstock. The polyethylene may be high-density polyethylene (HDPE) in particular. In this particular embodiment, the mixture comprises, for example, 5% to 95% by weight of PP and 5% to 95% by weight of PE, in particular HDPE, or 50% to 95% by weight of PP and 5% to 50% by weight of PE, in particular HDPE. In this particular embodiment, the method according to the present invention is therefore specifically aimed at purifying and recovering PP and / or PE.

[0037] The plastic supply material may contain a mixture of polymers, particularly thermoplastics other than the target polyolefin, additives advantageously used for compounding the plastic material, and general-use related impurities originating from the lifecycle of the plastic material and objects, and / or from the waste collection and sorting circuit, and these compounds are collectively considered impurities. The supply material for the method according to the present invention generally contains less than 50% by weight of impurities, preferably less than 20% by weight of impurities, and preferably less than 10% by weight of impurities. The plastic supply material may contain, for example, a minimum of 1% by weight of impurities, and even a minimum of 5% by weight of impurities.

[0038] The plastic feed material may be advantageously pre-treated before the method to remove at least some of the “crude” impurities, i.e., impurities in the form of particles 10 mm or larger, preferably 5 mm or larger, and even more preferably 1 mm or larger, such as wood, paper, biomass, iron, aluminum, glass, etc., and to make it generally in the form of a divided solid to facilitate processing in the method. This pre-treatment may include a grinding step, a washing step at atmospheric pressure, and / or a drying step. This pre-treatment may be performed in different locations, for example, at a waste collection and sorting center, or in the same location where the processing method according to the present invention is performed. Preferably, this pre-treatment makes it possible to reduce the impurity content to less than 20% by weight, preferably less than 15% by weight, and preferably less than 10% by weight, the percentage being given relative to the weight of the plastic feed material processed by the method according to the present invention. At the end of the pre-treatment, the feed material is generally stored in the form of a divided solid, for example, in the form of ground material, flakes, powder, or granules to facilitate handling and transport to the method.

[0039] (melting step a)) According to the present invention, the method comprises a dissolution step a), in which a plastic supply material is placed in contact with a dissolution solvent and contains a thermoplastic plastic which is advantageously targeted for separation and purification; in particular, polyolefins contained therein dissolve in the dissolution solvent to obtain at least one, preferably one, crude polymer solution.

[0040] The term “dissolution” should be understood to mean any phenomenon that leads to the formation of at least one solution of a thermoplastic polymer, i.e., a liquid (or fluid) containing the target thermoplastic polymer dissolved in a dissolving solvent. Those skilled in the art are well aware of one or more phenomena involved in the dissolution of polymers, including at least mixing, solvation, dispersion, homogenization, and disentangling of thermoplastic polymer chains.

[0041] During and at the end of dissolution step a), the pressure and temperature conditions make it possible to maintain the dissolution solvent in liquid form or possibly supercritical form, at least partially, preferably completely, while the soluble portion of the plastic feed material, particularly the target thermoplastic polymer, most specifically the target polyolefin, and, for example, impurities, are advantageously, at least partially, preferably completely dissolved in the dissolution solvent. In other words, the temperature and pressure conditions of step a) avoid or at least limit the possibility that the dissolution solvent is in gaseous form.

[0042] The dissolving solvent is an organic solvent or a mixture of organic solvents. Advantageously, the dissolving solvent comprises, and preferably consists of, at least one, preferably aliphatic, particularly paraffinic (i.e., saturated), preferably linear or branched hydrocarbon-based compound. Preferably, the dissolving solvent contains at least 80% by weight, preferably at least 95% by weight, preferably at least 98% by weight, of at least one, preferably aliphatic, particularly paraffinic, preferably linear or branched hydrocarbon-based compound, where the percentage is expressed relative to the total weight of the dissolving solvent (100% being the maximum). Preferably, the boiling point (at atmospheric pressure, particularly 0.1 MPa) of at least one, preferably aliphatic, particularly paraffinic hydrocarbon-based compound contained in the dissolving solvent is -50 to 250°C, preferably -15 to 150°C, preferably -1 to 110°C, preferably 20 to 100°C. Preferably, the dissolving solvent comprises, and preferably consists of, at least one, preferably aliphatic, particularly paraffinic, preferably linear or branched hydrocarbon-based compound, wherein the hydrocarbon-based compound contains 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms, and more preferably 6, 7, or 8 carbon atoms. For example, the dissolving solvent comprises a compound selected from isomers of butane, pentane, hexane, heptane, and octane. The dissolving solvent may preferably contain a mixture of isomers of butane, pentane, hexane, heptane, and / or octane, preferably in a content of the mixture of isomers in the dissolving solvent: 80% by weight or more, preferably 95% by weight or more, and more preferably 98% by weight or more, relative to the total weight of the dissolving solvent, and may preferably consist of, and preferably consist of, isomers or mixtures of isomers of hexane, heptane, and / or octane. A significant advantage is that suitable hydrocarbon-based compounds for dissolution include paraffinic aliphatic compounds, and the critical temperature (the temperature at the critical point of the pure hydrocarbon compound) is preferably 95 to 350°C, more preferably 130 to 300°C, and most preferably 180 to 285°C.

[0043] Preferably, in the dissolution step a), the plastic supply material and the dissolution solvent are supplied at a weight ratio of 0.2 to 100.0, preferably 0.3 to 20.0, preferably 1.0 to 10.0, and more preferably 3.0 to 7.0 between the dissolution solvent and the plastic supply material.

[0044] Advantageously, the dissolving solvent supplied to the dissolution step a) is in liquid form, and possibly in supercritical form. Advantageously, it can be preheated before its introduction to step a), particularly to the contact section, and possibly to the dissolution section, preferably to a temperature of 100-300°C, preferredly 150-250°C, to facilitate heating of the plastic feed material and / or avoid temperature drops in the material flow in the contact and possibly dissolution sections of step a).

[0045] Advantageously, the dissolving solvent includes, preferably consists of, a fresh solvent (or fresh feed solvent) and / or a recycled solvent stream obtained from a subsequent step of the Method, preferably at least partially obtained from step c) of the solvent-polymer separation.

[0046] Much more advantageously, the temperature known as the dissolution temperature when the dissolution process is operated is 100°C to 300°C, preferably 150°C to 250°C, and the pressure known as the dissolution pressure is preferably 1.0 to 100.0 absolute MPa, preferably 1.0 to 25.0 absolute MPa, preferredly 1.5 to 18.0 absolute MPa, and very preferably 2.0 to 15.0 absolute MPa. The temperature and pressure can be varied during the dissolution process from atmospheric conditions or the conditions for introducing the plastic feed material and / or dissolution solvent into the method, to reach dissolution conditions, i.e., the dissolution temperature, particularly 100 to 300°C, preferably 150 to 250°C, and advantageously, the dissolution pressure, particularly 1.0 to 100.0 MPa, preferably 1.0 to 25.0 absolute MPa, preferredly 1.5 to 18.0 absolute MPa, and very preferably 2.0 to 15.0 absolute MPa. Much more advantageously, at the end of the dissolution process, the crude polymer solution is at the dissolution temperature and dissolution pressure.

[0047] By limiting the temperature in dissolution step a) to 300°C or lower, preferably 250°C or lower, it is possible not only to avoid or limit the thermal degradation of the target thermoplastic, particularly the target polyolefin, but also to limit the energy requirements of the method, and thus help to limit the operating costs of the method. Advantageously, the dissolution temperature is above the melting point of the target thermoplastic, particularly the target polyolefin, which promotes their dissolution and, much more advantageously, shortens the residence time required to effectively dissolve the thermoplastic in the dissolution solvent. Much more preferably, the temperature in dissolution step a) is below the critical temperature of the dissolution solvent, which avoids the formation of a supercritical phase in dissolution step a) that can easily interfere with dissolution.

[0048] At the same time, the dissolution pressure in the dissolution process is higher than the saturated vapor pressure of the dissolution solvent at the dissolution temperature. As a result, the dissolution solvent is at least partially, preferably completely, in liquid form at the dissolution temperature, and possibly in supercritical form, thus avoiding the possibility of the dissolution solvent being partially in gaseous form. Therefore, the dissolution of target thermoplastics, particularly target polyolefins, is optimized, especially with respect to quality and operating time.

[0049] Advantageously, the dissolution step a) is carried out over a residence time of preferably 1 to 600 minutes, preferably 2 to 300 minutes, and preferably 2 to 180 minutes. The residence time is understood to be the residence time at the dissolution temperature and pressure, i.e., the time during which the plastic supply material is dissolved by the solvent at the dissolution temperature and pressure in step a).

[0050] To enable the dissolution solvent and the plastic feed material to be in contact with each other, and in particular to enable the target thermoplastic to be efficiently and uniformly dissolved in the dissolution solvent, dissolution step a) may advantageously include various types of equipment, such as mixing, transport and heating devices, e.g., reactors, pumps, transport circuits, stirring systems, ovens, exchangers, mixers, etc. In particular, step a) may advantageously include at least one dissolution apparatus, and optionally at least one feed material preparation device, mixing device and / or transport device. These apparatus and / or devices may be, for example, one or more static or dynamic mixers, extruders, pumps, reactors, parallel or countercurrent columns, or combinations of lines and equipment. Devices for transport, in particular devices for transporting fluids, e.g., gases, liquids or solids, are well known to those skilled in the art. Non-limitingly, the transport device may comprise at least one of the following devices: compressors, pumps, extruders, vibrating tubes, endless screws or valves. The equipment and / or devices used in step a) may include, or be combined with, a heating system (e.g., an oven, a changer, a tracer, etc.) to achieve the conditions necessary for dissolution.

[0051] Dissolution step a) is advantageously supplied by one or more transport devices, comprising at least one plastic feed material, particularly in the form of a stream of one or more plastic feed materials, and a dissolving solvent, particularly in the form of a stream of one or more dissolving solvents. The streams of one or more plastic feed materials may be different from the streams of one or more dissolving solvents. Some or all of the plastic feed material may be supplied to step a) as a mixture with some or all of the dissolving solvent, the remainder of the solvent and / or the remainder of the feed material, and may be supplied separately to step a) as needed.

[0052] While the plastic feed material is in contact with the dissolving solvent, the dissolving solvent is, advantageously, at least partially, preferably completely, in liquid form, or possibly in supercritical form, while the plastic feed material contains the target thermoplastic plastic, which may be in solid or liquid form, and possibly contains solid particles in a suspension. The plastic feed material may optionally be injected into the dissolution equipment as a mixture with the dissolving solvent, or as a suspension in the dissolving solvent, and the preparation and injection of the suspension may be continuous or batch.

[0053] Preferably, the dissolution step a) includes at least one means for at least partially melting the plastic feed material, preferably an extruder; optionally, at least one means for mixing at least a portion of the dissolution solvent and, advantageously, the at least partially melted plastic feed material, for example, one or a series of 2 to 10 mixers (preferably 1 to 10 static mixers); and dissolution equipment, for example, at least one Continuous Stirred Tank Reactor (CSTR) with at least one mechanical stirring system. In this case, the plastic feed material is fed to the dissolution means, in particular the extruder, so that at least a portion, preferably all, of the target thermoplastic contained in the plastic feed material is in a molten form at the outlet of the means. The plastic feed material can then be injected into dissolution equipment, or optionally into a system comprising a mixer or a series of mixers and, advantageously, subsequent dissolution equipment. The plastic feed material, in at least a partially melted form, may be pumped by a pump specifically designed for viscous fluids, often known as a melt pump or gear pump. The plastic feed material, in at least a partially molten form, may be filtered at the outlet of the melting means, optionally in addition to the melting pump, by a filtration device for the purpose of removing the coarsest particles; generally, the mesh size of this filter is 10 μm (micrometers) to 1 mm (millimeter), preferably 20 to 200 μm. At the same time, the dissolution solvent is supplied directly to the dissolution equipment or optionally to a mixer or a series of mixers.

[0054] Preferably, step a) involves installing an extruder and at least one static mixer before at least one CSTR-type reactor, to which at least a portion of the dissolving solvent is injected. This promotes shear and close mixing between the dissolving solvent and the plastic feed material, and therefore contributes to the dissolution of the target thermoplastic.

[0055] Much to the advantage, the crude polymer solution obtained at the end of dissolution step a) comprises at least the dissolving solvent and the target thermoplastic, particularly the target polyolefin, dissolved in the dissolving solvent. Generally, the crude polymer solution also contains soluble impurities that are also soluble in the dissolving solvent and / or insoluble impurities in the suspension. The crude polymer solution obtained at the end of dissolution step a) may optionally contain the polymer in, for example, a molten form, a dissolved form or an insoluble form.

[0056] (Step b: Decantation of polymer solution) The method according to the present invention comprises step b) decanting the crude polymer solution obtained at the end of step a) to produce at least one “decanted” polymer solution and tailing portion.

[0057] In fact, the decantation step b) makes it possible to separate at least some of the insoluble impurities and, optionally, at least some of the soluble impurities dissolved in the dissolving solvent by altering the density differences of the compounds present in the crude polymer solution. Insoluble impurities may be present in the crude polymer solution in the form of solid particles, particularly suspended or in the liquid phase, or in the liquid phase, for example, including molten polymer. The decantation step b) therefore makes it possible to recover a decanted polymer solution in which the impurities present in the crude polymer solution fed to step b) are at least partially removed. The decantation step b) therefore also generates a tailing portion, which contains at least some, preferably all, of the insoluble impurities in the crude polymer solution obtained from step a), optionally at least some, preferably all, of the soluble impurities, and optionally at least some, preferably all, of the dissolving solvent, which may optionally be partially encombined with the impurities. Insoluble impurities removed during decantation step b) include, for example, pigments, mineral compounds, packaging residues (glass, wood, cardboard, paper, aluminum), and polymers other than the target thermoplastic, particularly polymers other than the target polyolefin.

[0058] According to one embodiment of the present invention, the decanted polymer solution contains a portion of the polyolefin contained in the initial plastic feedstock, for example, polypropylene of the plastic feedstock, while the tailing portion contains polymer impurities, particularly thermoplastics other than the target polyolefin, and / or other portions of the polyolefin contained in the initial plastic feedstock, for example, polyethylene of the plastic feedstock, particularly high-density polyethylene (HDPE). The polymer impurities and / or the other portions of the polyolefin may not be particularly solubilized in dissolution step a). The tailing portion can then be advantageously recovered and processed by another method, for example, a second method according to the present invention, to purify the thermoplastic, particularly the other portions of the polyolefin of the initial plastic feedstock, and separate them into the tailing portion.

[0059] Another advantage of the decantation step b) of the method according to the present invention is that it enables efficient and continuous purification of the polymer solution. This embodiment is advantageous because the yield of the purified target thermoplastic, in particular the purified target polyolefin, is optimal in this case.

[0060] Advantageously, the decantation process (b) allows for the continuous removal of at least some of the impurities, while simultaneously limiting operational problems in downstream processing steps, particularly clogging and / or erosion, and efficiently contributing to the purification of the plastic feedstock.

[0061] Advantageously, the temperature during step b) is 100°C to 300°C, preferably 150°C to 250°C, and the pressure is 1.0 to 100.0 absolute MPa, preferably 1.0 to 25.0 absolute MPa, preferredly 1.5 to 18.0 absolute MPa, and very preferably 2.0 to 15.0 absolute MPa. Preferably, step b) is carried out under the temperature and pressure conditions of the dissolution step a).

[0062] Step b) uses at least one decanting device, also known as a decanter. Preferably, step b) uses 1 to 10 decanters, preferably 2 to 5 decanters. When step b) uses several decanters, i.e., 2 to 10, preferably 2 to 5 decanters, the decanters can be operated in series and / or in parallel, preferably in parallel.

[0063] One or more of the decanters are preferably cylindrical or substantially cylindrical in shape, with each end closed, particularly by a hemispherical or conical end, and advantageously include orifices, e.g., for supplying crude polymer solutions and outlets for various separated flows. The term “substantially cylindrical” means that the shape of the decanter is cylindrical with ends closed, particularly by a hemispherical end, or by a first hemispherical end and a second conical end. In very detail, one or more decanters used in step b) may be polycylindrical. The expression “polycylindrical” means that the decanter in question may have several cylindrical cross-sections of different diameters; for example, having a first cylindrical zone of diameter D1 and a second cylindrical zone of diameter D2, where D1 is greater than D2.

[0064] The decanter or each decanter used in step b) may be a vertical or horizontal decanter. In other words, the decanter or each decanter, which is preferably in a substantially cylindrical shape, is operated so that the cylinder is positioned vertically or horizontally, respectively.

[0065] Preferably, the one or more decanters used in step b) are preferably cylindrical or substantially cylindrical in shape, and the ratio L / D between the total length L of the decanter in question (i.e., the total length of the closed cylinder, including the ends) and the diameter (or width) D of the decanter in question is 0.5 to 12, preferably 1.0 to 6.0.

[0066] More specifically, the one or more decanters used in step b) may be one or more vertical decanters in a polycylindrical form. The expression “polycylindrical” means that the decanter in question may have several cylindrical sections of different diameters; for example, having a first cylindrical zone of diameter D1 and a second cylindrical zone of diameter D2, where D1 is greater than D2, and the second cylindrical zone of diameter D2 is preferably located above the first cylindrical zone of diameter D1 (i.e., towards the top of the decanter). In this very particular embodiment, the diameter D to be considered is the diameter of the widest cylindrical section of the decanter being considered, i.e., the diameter D1 of the decanter in the example above.

[0067] Step b) is fed at least part or all of the crude polymer solution obtained from step a). In embodiments where step b) uses a single decanter or several decanters in series, all of the crude polymer solution obtained at the end of step a) is fed to the decanter or the first decanter in series. In embodiments where step b) uses several decanters in parallel, the crude polymer solution obtained at the end of step a) is fed to each decanter operating in parallel. In this latter embodiment, the crude polymer solution is advantageously divided into several partial flows of the crude polymer solution, in particular, into the same number of partial flows as there are decanters in parallel.

[0068] The decanter used in step b) is used to deliver the polymer solution, in particular the crude polymer solution or the polymer solution-enriched effluent, to a delivery point located on the decanter in question.

[0069] If the decanter in question is a vertical decanter, the feeding point for feeding the polymer solution is advantageously located between the upper quarter and the upper three-quarters of the decanter's height, preferably between the upper one-third and the upper two-thirds of the decanter's height. The feeding point for the polymer solution then defines two zones within the vertical decanter in question, the upper zone located between the feeding point for the polymer solution and the top of the vertical decanter, and the lower zone located between the feeding point for the polymer solution and the bottom of the vertical decanter.

[0070] If the decanter in question is a horizontal decanter, the feeding point for the polymer solution is preferably located on one side of the horizontal decanter, i.e., at or near one end of the horizontal decanter, preferably in the zone between one of the two ends of the horizontal decanter and one-third of the length of the decanter, starting from that end, and preferably between one of the two ends of the horizontal decanter and one-quarter of the length of the decanter, starting from that end.

[0071] The decanter or each decanter is provided with an outlet for polymer solution-enriched effluent, i.e., effluent containing a polymer solution free of at least some impurities. Therefore, the polymer solution-enriched effluent is recovered at the outlet of the decanter or each decanter used in step b). The polymer solution-enriched effluent can be recovered by drawing or overflowing. If step b) uses a single decanter, the polymer solution-enriched effluent recovered at the outlet of the decanter therefore constitutes a decanted polymer solution. If step b) uses several decanters in parallel, all of the polymer solution-enriched effluent recovered at the outlet of each decanter constitutes a decanted polymer solution. Finally, if step b) uses several decanters in series sequentially, the polymer solution-enriched effluent recovered at the outlet of the upstream decanter is advantageously fed directly to the downstream decanter along with the polymer solution, and the polymer solution-enriched effluent recovered at the outlet of the last decanter in the series constitutes the decanted polymer solution.

[0072] If the decanter under consideration is a vertical decanter, the outlet for the polymer solution-enriched effluent is advantageously located in the upper zone of the vertical decanter in question, i.e., the zone between the polymer solution feeding point and the top of the decanter.

[0073] If the decanter under consideration is a horizontal decanter, the outlet for the polymer solution-enriched effluent is advantageously located on the side of the decanter opposite to the polymer solution feeding point, i.e., the end of the decanter opposite to the end where the polymer solution feeding point is located, and the outlet for the polymer solution-enriched effluent is preferably located in the zone between the end of the decanter opposite to the end where the polymer solution feeding point is located and one-third of the length of the decanter from the opposite end, and preferably between the end of the decanter opposite to the end where the polymer solution feeding point is located and one-quarter of the length of the decanter from the opposite end.

[0074] Each of the decanters also has an outlet for the tailing flow. Therefore, the tailing flow is recovered from the decanter or the outlet of each decanter used in step b). If step b) uses a single decanter, the tailing flow recovered at the outlet of that decanter therefore constitutes the tailing portion obtained at the end of step b). If step b) uses several decanters in parallel or in series, all the tailing flow recovered at the outlet of each decanter constitutes the tailing portion obtained at the end of step b).

[0075] The tailing flow in the decanter under consideration may be recovered or purged continuously or in batches. If the tailing flow is purged in batches, the purge frequency may vary between 0.01 and 20.0 mHz, preferably between 0.1 and 10.0 mHz, and more preferably between 0.5 and 1.0 mHz.

[0076] If the decanter under consideration is a vertical decanter, the outlet for tailing flow is advantageously located in the lower zone of the decanter (i.e., the zone between the polymer solution feeding point and the bottom of the decanter), preferably at the bottom of the decanter under consideration, for example, at the bottom of the conical end of a vertical decanter.

[0077] If the decanter under consideration is a horizontal decanter, the outlet for tailing flow is located at the bottom of the decanter under consideration, advantageously on the side of the decanter opposite to the polymer solution feeding point, i.e., near the end of the decanter opposite to the end where the polymer solution feeding point is located, preferably in the zone between the end of the decanter opposite to the end where the polymer solution feeding point is located and one-third of the length of the decanter from the opposite end, and more preferably in the zone between the end of the decanter opposite to the end where the polymer solution feeding point is located and one-quarter of the length of the decanter from the opposite end.

[0078] The at least one decanter used in step b) is preferably operated with a filling density of 70% to 100% of the total volume of the decanter under consideration. The term “filling density” corresponds to the ratio between the total volume of the material (polymer solution and tailing) present in the decanter and the total volume of the decanter (i.e., the geometric volume of the decanter).

[0079] In the at least one decanter used in step b), there exists a liquid surface velocity (also known as knockout drum velocity, particularly upward knockout drum velocity), which is 1 × 10⁻⁶ -7 ~1,000 × 10 -2 m / s, preferably 1.0 × 10 -6 ~1,000 × 10 -2 m / s, preferably 1.0 × 10 -5 ~6,000 x 10 -3 m / s, preferably 2.0 × 10 -5 ~5,000 x 10 -3 m / s, very preferably 2.0 × 10 -5 ~9.00 x 10 -4 m / s, especially 2.0 × 10⁻⁶ -5 ~5.00 x 10 -4 This is m / s. This liquid surface velocity is known as LSV (or Q / S), is well known to those skilled in the art, and corresponds to the flow rate Q of the liquid, with at least some impurities removed, divided by the cross-sectional area S of the decanter (especially the widest cross-section in the case of a multi-cylindrical decanter). In the case of a vertical decanter, the liquid surface velocity is adjusted to be no more than or equal to 0.85 times the settling velocity, preferably no more than or equal to 0.80 times the settling velocity. In the case of a horizontal decanter, the liquid surface velocity depends on the settling velocity, but also on the length L of the horizontal decanter. The settling velocity advantageously corresponds to the rate at which impurity particles settle in the polymer solution, or the average velocity. The settling velocity, therefore, depends more specifically on gravity, the density, diameter, and concentration of the impurity particles under consideration, and the viscosity of the medium, i.e., the polymer solution.

[0080] Much more advantageously, the injection rate of the polymer solution, particularly the crude polymer solution or polymer solution-enriched effluent, from the one or more decanters is 1.00 m / s or less, preferably 0.10 m / s or less, preferredly 0.05 m / s or less, and preferably 0.0001 m / s or more, and even more preferably 0.001 m / s or more.

[0081] Therefore, in each decanter, the residence time can be adjusted to 1 to 200 hours, preferably 1 to 50 hours. Here, the residence time corresponds to the ratio between the residence time in the decanter, i.e., the working volume of the decanter (i.e., the volume of material in the decanter depending on the degree of filling of the decanter under consideration) and the volumetric flow rate of the polymer solution (crude polymer solution or polymer solution-enriched effluent) supplied to the decanter in question.

[0082] The tailing portion can be recovered and processed to recover any solvents it may contain.

[0083] According to one embodiment of the present invention, the tailing portion may contain polymer impurities, particularly thermoplastics other than the target polyolefin, and furthermore, polyolefins, such as polyethylene (PE), particularly high-density polyethylene (HDPE), which were present in the plastic supply material but are not the specific polyolefin to be targeted. The tailing portion can then be advantageously recovered and processed in another manner, for example, in a second method according to the present invention, to purify the thermoplastic, particularly the polyolefin of the tailing portion.

[0084] According to a particular embodiment, the object of the method according to the present invention is the recovery and purification of polypropylene (PP) from a plastic feedstock, which may also contain other thermoplastics, and even other polyolefins, such as PE, particularly HDPE. The adjustment in step a) is made to enable the selective dissolution of the polypropylene in the plastic feedstock. The term “selective dissolution” is understood to mean that the majority of the PP, and possibly a small portion of the PE, particularly HDPE, contained in the initial plastic feedstock is dissolved in the dissolution solvent, while the majority of the PE, particularly HDPE, and possibly a small portion of the PP contained in the initial plastic feedstock is not dissolved. According to this particular embodiment, the dissolution temperature is preferably 170 to 230°C, preferably 180 to 220°C, and the dissolution pressure is preferably 1.5 to 10.0 absolute MPa, preferably 2.0 to 8.0 absolute MPa. Step b) makes it possible to separate, at least partially, preferably completely, thermoplastics other than the target PP, for example, PE or HDPE. The tailing portion recovered at the bottom of the decanter may, in this case, be advantageously composed of thermoplastics other than the target PP, such as PE, particularly HDPE. The tailing portion may, in this case, be recovered and processed in a certain manner, for example, another recycling method according to the present invention, to separate and recover the thermoplastics, such as the PE or HDPE, in a purified form.

[0085] The decanted polymer solution recovered at the end of step b) may optionally undergo a purification step or be sent directly to a solvent-polymer separation step c). Preferably, the decanted polymer solution recovered at the end of step b) is sent to a purification step b'), which greatly preferentially includes additional solid-liquid separation and / or adsorption of soluble impurities in particular.

[0086] (Optional step b' for purifying the polymer solution) The processing method according to the present invention may include a further step of purifying the decanted polymer solution. This optional purification step b') includes at least one of the substeps b'1), b'2), b'3), and b'4) described below: b'1) Additional solid-liquid separation sub-step, b'2) A sub-step of washing by contact with a high-density solution, b'3) Sub-step of extraction by contact with extraction solvent, b'4) A sub-step of adsorption of impurities by contact with a solid adsorbent.

[0087] The incorporation of one or more of such steps b'), particularly sub-steps b'1), b'2), b'3), b'4) into the method according to the present invention, greatly advantageously, enables maximum purification of the polymer solution and thus helps achieve the purity objective of the purified thermoplastic stream recovered at the outlet of the method, i.e., obtaining an impurity content of 5% by weight or less, preferably 1.0% by weight or less, and preferentially 0.5% by weight or less in the purified thermoplastic stream. This optional step b') thus makes it possible to obtain a “purified” polymer solution, which corresponds to a clarified polymer solution obtained from an additional solid-liquid separation sub-step b'1), a washed polymer solution obtained from a washing sub-step b'2), an extracted polymer solution obtained from an extraction sub-step b'3), or a refined purified polymer solution obtained from an impurity adsorption sub-step b'4).

[0088] Preferably, when incorporated into a method according to the present invention, the purification step b') includes an additional solid-liquid separation sub-step b'1) and / or impurity adsorption sub-step b'4). According to a very specific embodiment, the method according to the present invention includes an additional solid-liquid separation sub-step b'1) and / or impurity adsorption sub-step b'4), more specifically an additional solid-liquid separation sub-step b'1), followed by an impurity adsorption sub-step b'4).

[0089] (Optional additional solid-liquid separation sub-step b'1)) This purification method may include an additional solid-liquid separation sub-step b'1), which advantageously yields at least one clarified polymer solution. Sub-step b'1) allows for the removal of impurities that are typically insoluble in the dissolving solvent and were not separated in decantation step b). In fact, insoluble impurities exist in the form of suspended particles in the crude polymer solution and may have densities lower than or too close to the density of the polymer solution, and therefore cannot be separated, or at least effectively separated, during decantation step b); they may therefore remain suspended in the decanted polymer solution at the end of step b). Sub-step b'1) may thus allow for increased efficiency in the purification of the polymer solution, particularly in the separation of insoluble impurities, when incorporated into the method according to the present invention.

[0090] An optional sub-step b'1) may result in the formation of insoluble material in addition to the clarified polymer solution. This insoluble material, if present, advantageously contains impurities that are typically insoluble and not separated in the decantation step b).

[0091] The temperature at which the optional sub-step b'1) is advantageously performed is 100 to 300°C, preferably 150 to 250°C, and the pressure at which it is advantageous is preferably 1.0 to 100.0 absolute MPa, preferably 1.0 to 25.0 absolute MPa, more preferably 1.5 to 18.0 absolute MPa, and very preferably 2.0 to 15.0 absolute MPa. Much more advantageously, the sub-step b'1) for separating insoluble material is performed under the temperature and pressure conditions at the outlet of the dissolution step a), i.e., at the dissolution temperature and dissolution pressure defined above.

[0092] If a sub-step b'1) is incorporated into this method, it is preferably fed the decanted polymer solution obtained from the decantation step b). According to another embodiment, the sub-step b'1) may be fed the washed polymer solution obtained from the washing sub-step b'2).

[0093] Advantageously, an optional sub-step b'1) includes a section comprising at least one solid-liquid separation apparatus, which is selected from, for example, filters, sand filters, tangential filters, particularly membranes and / or deep filters, which may optionally use in the presence of a filtration adjuvant (e.g., diatomaceous earth), eddy current separators, electrostatic separators, triboelectric separators, preferably filters, sand filters and / or electrostatic separators. Advantageously, self-cleaning filters may be used, which allow for the removal of insoluble matter using a solvent flow by washing or declogging.

[0094] According to a particular embodiment, an optional sub-step b'1) comprises at least two, and generally fewer than five, solid-liquid separation devices in series and / or parallel. The presence of at least two solid-liquid separation devices in series allows for improved removal of insoluble matter, while the presence of parallel devices allows for control over the maintenance and / or declogging operations of the devices.

[0095] Certain insoluble impurities, particularly certain pigments and mineral fillers, are conventionally added during polymer formulation and may be introduced in the form of particles smaller than 1 μm in size. This is the case, for example, of titanium dioxide, calcium carbonate, and carbon black. According to one particular embodiment, the sub-step b'1) for separating insoluble materials advantageously uses an electrostatic separator, which makes it possible to efficiently remove at least some of the insoluble particles smaller than 1 μm. According to another particular embodiment, the sub-step b'1) for separating insoluble materials includes a sand filter to remove particles of different sizes, in particular particles smaller than 1 μm. According to yet another particular embodiment, the sub-step b'1) for separating insoluble materials uses a tangential filter, in particular using a membrane and / or depth filter, in the presence of a filtration adjuvant, such as diatomaceous earth.

[0096] Depending on the properties of the raw materials supplied, the polymer solution, preferably the decanted polymer solution, to be fed to sub-step b'1) may, in some cases, contain a second liquid phase, which consists, for example, of a molten polymer, and whose density is not significantly different from that of the polymer solution to be separated in step b). According to another particular embodiment, sub-step b'1) advantageously includes equipment for separating the second liquid phase, preferably by at least one two-phase or three-phase separator.

[0097] (Optional washing sub-step b'2)) The processing method may optionally include a sub-step b'2) of washing with a high-density solution, which is advantageous in obtaining at least one washing effluent and at least one washed polymer solution. The washed polymer solution obtained at the end of sub-step b'2) advantageously contains the target thermoplastic that the present invention seeks to recover and purify dissolved in the dissolving solvent. Optionally, the washed polymer solution may contain residual impurities, which are particularly soluble in trace amounts of washing solvent if sub-step b'2) is performed, in the dissolving solvent and / or optionally.

[0098] The washing sub-step b'2) may be incorporated upstream or downstream, preferably downstream, of the additional solid-liquid separation sub-step b'1) when these two sub-steps are incorporated into the processing method according to the present invention.

[0099] If a washing sub-step b'2) is incorporated into this method, it is fed a high-density solution and a decanted polymer solution obtained from step b) or optionally a clarified polymer solution obtained from sub-step b'1). The polymer solution fed to the washing sub-step b'2), particularly the decanted or optionally clarified polymer solution, may contain suspended insoluble and / or soluble impurities that are not separated in step b). These suspended or soluble impurities may be partially or completely removed during the washing sub-step b'2) by dissolution or precipitation and / or entrainment in the high-density solution. Therefore, if performed, this sub-step b'2) contributes to the processing of the plastic feedstock, more specifically to the purification of the polymer solution.

[0100] The washing sub-step b'2) advantageously includes bringing the decanted or optionally clarified polymer solution, which is to be fed to sub-step b'2), into contact with the high-density solution. Advantageously, the high-density solution has a higher density than the polymer solution (i.e., a mixture containing at least the target thermoplastic and the solvent in which the target thermoplastic is dissolved), particularly 0.85 or higher, preferably 0.9 or higher, and preferentially 1.0 or higher. The high-density solution may be an aqueous solution, which preferably contains at least 50% by weight of water, preferably at least 75% by weight of water, and much more preferably at least 90% by weight of water. The pH of the aqueous solution may be adjusted using an acid or base to facilitate the dissolution of a given impurity. The high-density solution may optionally contain, and preferably consist of, an organic solvent, the density of which is advantageously 0.85 or higher, preferably 0.9 or higher, and more preferably 1.0 or higher, and the polymer of the plastic supply material remains insoluble under the temperature and pressure conditions of sub-step b'2). For example, the organic solvent is selected from sulfolane or N-methylpyrrolidone (NMP), and optionally as a mixture with water. Much preferably, the high-density solution is an aqueous solution, which preferably contains at least 50% by weight of water, preferably at least 75% by weight of water, and very preferably at least 90% by weight of water.

[0101] The temperature at which the sub-step b'2) of washing is advantageously carried out is 100 to 300°C, preferably 150 to 250°C, and much more advantageously, the pressure at which it is 1.0 to 100.0 absolute MPa, preferably 1.0 to 25.0 absolute MPa, preferredly 1.5 to 15.0 absolute MPa, and very more preferably 2.0 to 15.0 absolute MPa. Much more advantageously, the sub-step b'2) of washing is carried out at the dissolution temperature and the aforementioned dissolution pressure.

[0102] In the washing sub-step b'2), if it is incorporated into the method, the mass ratio between the mass flow rate of the high-density solution and the mass flow rate of the decanted or optionally clarified polymer solution supplied to sub-step b'2) is advantageously 0.05 to 20.0, preferably 0.1 to 10.0, and preferably 0.5 to 3.0. The contact arrangement between the decanted or optionally clarified polymer solution and the high-density solution may be carried out at several points within the equipment used, i.e., by several injections of the decanted or clarified polymer solution and / or high-density solution at different points along the equipment; in that case, the total of the injected flows is taken into consideration in the calculation of the ratio.

[0103] Sub-step b'2) may be performed in one or more washing devices that allow contact placement with the high-density solution and / or separation equipment, enabling the recovery of at least one washing effluent and at least one washed polymer solution. This equipment is well known and includes, for example, agitated reactors, static mixers, decant mixers, two-phase or three-phase separation vessels, parallel or counter-flow washing columns, plate columns, agitated columns, packed columns, pulsed columns, etc., and each type of equipment may include one or more devices used alone or in combination with another type of equipment.

[0104] According to a preferred embodiment, the washing sub-step b'2) is performed in a countercurrent washing column, in which, on the one hand, a high-density solution is injected into preferably half, preferably one-third, of the column closest to the top of the column, and on the other hand, a decanted or clarified polymer solution is injected into preferably half, preferably one-third, of the column closest to the bottom of the column. According to this embodiment, it is possible to recover at least one washed polymer solution and at least one washing effluent.

[0105] According to a very specific embodiment, the flow at the inlet and / or outlet of the washing column may be divided and injected at several injection points along the column, and / or withdrawn at several withdrawal points along the column.

[0106] According to another embodiment, the washing sub-step b'2) is performed in a mixer decanter, which includes an agitated mixing zone for bringing a high-density solution into contact with a decanted or clarified polymer solution, and a decantation zone that allows for the recovery of the washed polymer solution and washing effluent.

[0107] At the end of the washing sub-step b'2), the resulting washing effluent advantageously contains impurities dissolved in the high-density solvent and / or insoluble impurities entrained in the washing effluent. The washing effluent may be reprocessed in a washing effluent treatment section, on the one hand separating at least partially the dissolved and / or entrained impurities, and optionally purifying the washing effluent to obtain a purified high-density solution, and on the other hand recycling a portion of the purified washing solution. This washing treatment section may be equipped with one or more instruments known for solid-liquid separation, such as separation vessels, decanters, centrifugal decanters, centrifuges, or filters. The washing effluent may be sent outside of this method, for example, to a spent water treatment station if the high-density solution is an aqueous solution.

[0108] (Sub-step b'3 of arbitrary selection extraction) The method according to the present invention may include a sub-step b'3) of extraction by contacting with an extraction solvent to obtain at least one extracted polymer solution and at least one spent solvent. The extracted polymer solution obtained at the end of sub-step b'3) preferably contains the target thermoplastic polymer that the present invention seeks to recover and purify dissolved in the dissolving solvent. The spent solvent is preferably filled with impurities. In some cases, the extracted polymer solution may contain residual impurities, which are soluble in particular the dissolving solvent and / or trace amounts of washing solvent and / or extraction solvent if one or more sub-steps b2) and / or b3) are performed.

[0109] If the extraction sub-step b'3) is incorporated into the method according to the present invention, it is advantageously located between the decantation step b) and the solvent-polymer separation step c), and optionally upstream or downstream of the adsorption sub-step b'4) if the adsorption sub-step b'4) is also incorporated into the method, preferably downstream of an additional solid-liquid separation sub-step b'1).

[0110] The extraction substep b'3) is advantageously fed with the extraction solvent and the decanted polymer solution obtained from step b), the clarified polymer solution obtained from substep b'1), the washed polymer solution obtained from substep b'2), or the refined and purified polymer solution obtained from the adsorption substep b'4). The polymer solution fed to substep b'3), preferably the decanted polymer solution or optionally the clarified, washed, or refined solution, may therefore contain dissolved impurities. These dissolved impurities may be partially or completely removed by being in contact with the extraction solvent during the extraction substep b'3).

[0111] If the method according to the present invention incorporates a sub-step of extraction (b'3), the extraction advantageously includes at least one extraction section, preferably 1 to 5 extraction sections, and more preferably 1 extraction section.

[0112] The mass ratio between the mass flow rate of the extraction solvent and the mass flow rate of the polymer solution to be fed to b'3), preferably a decanted polymer solution or optionally a clarified, washed, or refined polymer solution, is advantageously 0.05 to 20.0, preferably 0.1 to 10.0, and preferably 0.2 to 5.0. The contact arrangement between the polymer solution to be fed to substep b'3) and the extraction solvent may be carried out by several injections of the polymer solution and / or extraction solvent at several points within the extraction section, i.e., at different points along the extraction section; in that case, the total injected flow is taken into consideration in the calculation of the ratio.

[0113] The extraction solvent used in the extraction sub-step b'3) preferably comprises an organic solvent or a mixture of organic solvents. Preferably, the extraction solvent comprises, and preferably consists of, at least one preferably aliphatic, particularly paraffinic (i.e., saturated), preferably linear or branched hydrocarbon-based compound. Preferably, the extraction solvent comprises at least 80% by weight, preferably at least 95% by weight, and preferably at least 98% by weight, of at least one preferably aliphatic, particularly paraffinic, preferably linear or branched hydrocarbon-based compound, the percentage expressed relative to the total weight of the dissolving solvent (100% being the maximum). Preferably, the boiling point (at atmospheric pressure, particularly 0.1 MPa) of at least one preferably aliphatic, particularly paraffinic hydrocarbon-based compound contained in the extraction solvent is -50 to 250°C, preferably -15 to 150°C, preferably -1 to 110°C, and preferably 20 to 100°C. Preferably, the extraction solvent comprises, and preferably consists of, at least one aliphatic, particularly paraffinic, preferably linear or branched hydrocarbon-based compound, wherein the hydrocarbon-based compound preferably contains 3 to 12 carbon atoms, and more preferably 4 to 8 carbon atoms. For example, the extraction solvent comprises a compound selected from isomers of butane, pentane, hexane, and heptane. The extraction solvent may preferably contain a mixture of isomers of butane, pentane, hexane, heptane, and octane, preferably in a content of the mixture of isomers in the extraction solvent: 80% by weight or more, more preferably 95% by weight or more, and more preferably 98% by weight or more, relative to the total weight of the extraction solvent, and may preferably consist of, and preferably consists of, these. Preferably, the extraction solvent is a paraffinic aliphatic compound, and its critical temperature (the temperature at the critical point of the pure hydrocarbon-based compound) is 95 to 350°C, more preferably 130 to 300°C, and more preferably 180 to 285°C.

[0114] Much more preferably, the extraction solvent used in the optional sub-step b'3) is the same solvent as the dissolution solvent used in step a), but in a different physical state (e.g., the dissolution solvent is in liquid form while the extraction solvent is in supercritical form), to facilitate the management of the solvent, in particular its purification and recycling into the dissolution step a) and optionally the extraction sub-step b'3). Another advantage of using the same dissolution and extraction solvents in the same or different physical states is that, in addition to facilitating the management of the solvents involved in the method according to the present invention, in particular its recovery, processing and recycling into at least one of the steps of the method, it limits energy consumption, in particular the costs incurred by the processing and purification of the solvents.

[0115] One or more extraction sections of the optional sub-step b'3) may be equipped with one or more extraction instruments, which may be arranged in contact with separation equipment for recovering the extraction solvent and / or at least one spent solvent, particularly the one filled with impurities and the extracted polymer solution. This equipment is well known and may include, for example, agitated reactors, static mixers, decant mixers, two-phase or three-phase separation vessels, parallel or counter-flow washing columns, plate columns, agitated columns, packed columns, pulsed columns, etc., and each type of equipment may be equipped with one or more instruments, which may be used alone or in combination with other types of equipment.

[0116] According to a preferred embodiment of b'3), the extraction is performed in a countercurrent extraction column, where the extraction solvent is injected on the one hand and the polymer solution to be fed to sub-step b'3) is injected on the other hand. According to this embodiment, it is possible to recover, on the one hand, at least one extracted polymer solution and on the other hand, the spent solvent, in particular the spent solvent packed with impurities. Preferably, the polymer solution to be fed to b'3), preferably a decanted, or optionally clarified, washed, or refined polymer solution, is injected into the upper half of the column, preferably the upper third, i.e., the half closest to the top of the countercurrent extraction column, preferably the first third, while the extraction solvent is injected into the lower half of the column, preferably the lower third, i.e., the half closest to the bottom of the countercurrent extraction column, preferably the first third.

[0117] The flow at the inlet and / or outlet of a countercurrent extraction column may be divided at several injection and / or extraction points along the column.

[0118] According to another embodiment of b'3), the extraction is carried out in a mixer decanter, which advantageously includes a stirring and mixing zone for bringing the extraction solvent into contact with the polymer solution to be fed to b'3), preferably a decanted or optionally clarified, washed or refined polymer solution, and a decantation zone that allows for the recovery of the extracted polymer solution on the one hand and the used solvent on the other.

[0119] Advantageously, the extraction sub-step b'3) is carried out under different temperature and pressure conditions than those of the dissolution step a).

[0120] According to a preferred embodiment of b'3), the extraction sub-step b'3) includes a liquid / liquid extraction section. Preferably, the liquid / liquid extraction section is operated at a temperature of 100°C to 300°C, preferably 150°C to 250°C, and a pressure of 1.0 to 100.0 absolute MPa, preferably 1.0 to 25.0 absolute MPa, preferredly 1.5 to 18.0 absolute MPa, and much more preferably 2.0 to 15.0 absolute MPa. In any case, in this embodiment, the temperature and pressure conditions are adjusted so that the extraction solvent is in liquid form and the dissolving solvent is also preferably in liquid form. Much to the advantage, the liquid / liquid extraction is performed under different temperature and pressure conditions than those achieved in step a), particularly at a temperature higher than its dissolution temperature and / or at a pressure lower than its dissolution pressure, especially when the extraction solvent is the same as the dissolving solvent, and therefore in the two-phase zone of the corresponding polymer-solvent mixture diagram.

[0121] According to another preferred embodiment of b'3), the sub-step b'3) of extraction includes a section for extraction under specific temperature and pressure conditions in which the extraction solvent is advantageously at least partially in a supercritical state. Such extraction may be called supercritical extraction. In this embodiment, extraction is carried out by bringing a polymer solution, preferably decanted or optionally clarified, washed or refined polymer solution, into contact with an extraction solvent under temperature and pressure conditions that allow for obtaining a supercritical phase consisting mainly (i.e., preferably at least 50% by weight, preferredly at least 70% by weight, preferably at least 90% by weight) of the extraction solvent. In other words, in this embodiment, extraction is carried out by bringing a polymer solution, preferably decanted or optionally clarified, washed or refined polymer solution, into contact with an extraction solvent that is at least partially, preferably fully, in a supercritical state. Such a sub-step b'3) of supercritical extraction advantageously allows for the efficient purification of the polymer solution. This is primarily due to the extremely high affinity of organic impurities, such as some additives, particularly certain colorants and plasticizers, to the supercritical phase. The use of an extraction solvent in a supercritical state also makes it possible to create a substantial density difference between the supercritical phase and the polymer solution in liquid form, thereby facilitating decantation separation between the supercritical and liquid phases, which in turn contributes to the purification of the polymer solution.

[0122] In another preferred embodiment, the extraction solvent used in substep b'3) contains at least 80% by weight, preferably at least 95% by weight, and most preferably at least 98% by weight of at least one aliphatic paraffinic hydrocarbon-based compound (or alkane) (100% is the maximum, and the percentage is expressed relative to the total weight of the extraction solvent), and its critical temperature is preferably 95 to 350°C, preferably 130 to 300°C, and most preferably 180 to 285°C.

[0123] Advantageously, the temperature during which the sub-step b'3) of supercritical extraction in this other particular embodiment is performed is preferably 150°C to 300°C, preferably 180°C to 280°C, and the pressure is preferably 2.0 to 100.0 absolute MPa, preferably 2.0 to 25.0 absolute MPa, preferably 2.0 to 18.0 absolute MPa, and much more preferably 3.0 to 15.0 absolute MPa. Much more preferably, the operating pressure of such sub-step b'3) of supercritical extraction is 2.7 absolute MPa to 7.5 absolute MPa, preferredly 3.0 absolute MPa to 5.5 absolute MPa. In any case, in this embodiment, the temperature and pressure conditions are controlled, in particular, in a control section upstream of the extraction section implemented in the sub-step b'3) of extraction, and the extraction solvent is at least partially supercritical in the extraction section.

[0124] In certain embodiments, the extraction sub-step b'3) is supercritical extraction, and the extraction solvent is the same as the dissolving solvent, except that the extraction solvent is at least partially in the supercritical phase. In this case of supercritical extraction, the dissolving solvent may be at least partially in the supercritical form, which is advantageous because it is possible to optimize decantation during the extraction step, more specifically in each extraction phase or plateau between the liquid phase and the supercritical phase, and thus maximize the purification.

[0125] Advantageously, at the end of sub-step b'3) of extraction, the obtained spent solvent is packed, in particular, with soluble impurities. It may be reprocessed in an organic processing section, which on the one hand separates at least partially the impurities and purifies the solvent to obtain a purified extraction solvent, and on the other hand, it is possible to recycle at least a portion of the purified extraction solvent to the inlet of sub-step b'3) of extraction and / or to the inlet of dissolution step a) in the case that the dissolution solvent and the extraction solvent are the same. The spent solvent may be treated by any method known to those skilled in the art, e.g., one or more of distillation, evaporation, extraction, adsorption, crystallization and precipitation of insoluble matter, or by purging.

[0126] (Optional adsorption sub-step b'4)) The processing method according to the present invention may include an adsorption sub-step b'4) to obtain a refined and purified polymer solution. The refined and purified polymer solution obtained at the end of the optional sub-step b'4) advantageously contains a target thermoplastic polymer, particularly a target polyolefin, dissolved in a dissolving solvent.

[0127] If the method according to the present invention incorporates an adsorption sub-step b'4), it is preferably performed downstream of the decantation step b) and upstream of the solvent-polymer separation step c). However, it may be performed upstream of the decantation step b) and / or during the dissolution step a) by introducing adsorbent particles as a mixture with the crude polymer solution, the adsorbent particles being removed during the decantation step b) and optionally during an additional solid-liquid separation sub-step b'1), and even during the washing sub-step b'2). The adsorption sub-step b'4) may optionally be performed upstream or downstream of the extraction sub-step b'3). Therefore, if the method according to the present invention incorporates an adsorption sub-step b'4), it is performed by contacting the polymer solution fed to this step with one or more adsorbents.

[0128] An optional adsorption sub-step b'4) advantageously includes an adsorption section, which is operated in the presence of at least one adsorbent, which is preferably solid and in particular in the form of a fixed bed, a jet bed (or slurry, i.e., a form of particles introduced into and accompanied by the flow to be purified) or a boiling bed, preferably in the form of a fixed bed or a jet bed. The one or more adsorbents used in sub-step b) are preferably alumina, silica, silica-alumina, activated carbon, bleached earth, or mixtures thereof, preferably activated carbon, bleached earth, or mixtures thereof, preferably in the form of a fixed bed or a jet bed, and the flow of the flow may be rising or falling.

[0129] Advantageously, when incorporated into the present method, the temperature during the adsorption sub-step b'4) is 100-300°C, preferably 150-250°C, and the pressure is 1.0-100.0 absolute MPa, preferably 1.0-25.0 absolute MPa, preferredly 1.5-18.0 absolute MPa, and very preferably 2.0-15.0 absolute MPa. Much more advantageously, the adsorption sub-step b'4) is carried out under the conditions of dissolution temperature and pressure, i.e., at the dissolution temperature and pressure achieved in step a). Preferably, in the optional sub-step b'4), the space-time velocity (or HSV) corresponds to the ratio between the volumetric flow rate of the polymer solution supplied to b'4) and the volume of the adsorbent advantageously operated in b'4), which is 0.05-10h -1 Prioritizing 0.1 to 5.0 hours -1 That is the case.

[0130] According to a particular embodiment of sub-step b'4), the adsorption section may comprise one or more fixed beds of adsorbent, which may take the form of, for example, adsorption columns, preferably at least two, preferably two to four, adsorption columns, containing the one or two types of adsorbent. If the adsorption section comprises two adsorption columns, one operating mode may be called a “swing” operation according to specialized terminology, where one column is online, i.e., operational, while the other column is in standby mode. When the adsorbent in the online column is used up, this column is isolated, while the standby column is brought online, i.e., operational. The used adsorbent can then be regenerated in situ and / or replaced with fresh adsorbent, and as a result, the column containing it can be brought online again, where the other column has been isolated.

[0131] Another functionalization mode of this particular embodiment of b'4) involves functionalizing at least two adsorbent columns in series. When the adsorbent in the top-positioned column is used up, this first column is isolated, and the used adsorbent is regenerated in situ or replaced with fresh adsorbent. This column is then brought back online at the last position, and so on. This operation is called the read-and-lag mode, or PRS (permutable reactor system). The combination of at least two adsorbent columns makes it possible to overcome the potential for rapid poisoning and / or clogging of the adsorbent due to the combined action of impurities, contaminants, and insolubles that may be present in the flow to be processed. The reason for this is that the presence of at least two adsorbent columns makes it easier to replace and / or regenerate the adsorbent, which is advantageous as it does not interrupt the process, allows for cost control, and limits adsorbent consumption.

[0132] (Step c: Separation of solvent and polymer) According to the present invention, the method comprises a solvent-polymer separation step c), to obtain at least one purified thermoplastic polymer stream, more specifically at least one purified polyolefin stream, and preferably at least one solvent portion. This step c) is downstream of the decantation step b), or optionally downstream of step b') for purifying the decanted polymer solution.

[0133] The solvent-polymer separation step c) is directed towards separating at least partially, preferably mainly or even completely, one or more solvents, particularly the dissolving solvent, contained in the decanted or purified polymer solution fed to step c), and recovering the target thermoplastic such that impurities and the dissolving solvent, and optionally one or more other solvents used in the Method (i.e., the extraction solvent and / or high-density solution), are at least partially, preferably completely. The term “mainly” should be understood to mean at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, and very preferably at least 95% by weight, relative to the weight of one or more solvents, particularly the dissolving solvent, contained in the decanted or purified polymer solution fed to step c), and optionally the extraction solvent and / or high-density solution contained in the decanted or purified polymer solution fed to step c).

[0134] Any solvent-polymer separation method known to those skilled in the art may be performed, in particular any method that allows for a phase change of the polymer or one or more solvents. One or more solvents can be separated, for example, by flash evaporation, atomization, stripping of the solvent, crystallization and solid-liquid separation of the polymer, demixing, density difference, in particular decantation or centrifugation. Step c) may involve carrying out several separation operations in series. For example, step c) may include solvent-polymer separation by demixing at least a portion of one or more solvents in a supercritical state, where one or more solvents are brought to a supercritical state after the temperature and / or pressure conditions in step c), preferably by adjusting the pressure and maintaining the temperature at 100-300°C, preferably 150-250°C, so that at least one compound of one or more solvents is under supercritical conditions, followed by at least one separation of the residual solvent by evaporation, which can be carried out under pressure conditions lower than the pressure used for the transition of the solvent to the supercritical state, particularly 4-0.000005 MPa (i.e., 5 Pa), preferably 3-0.000005 MPa (i.e., 5 Pa), and the temperature can be maintained at 100-300°C, preferably 150-250°C.

[0135] The stream of purified thermoplastic polymer obtained at the end of step c) may correspond to a concentrated polymer solution or a liquid (i.e., molten) or solid purified thermoplastic polymer. The solvent-polymer separation step c) may optionally include a conditioning section for conditioning the recovered thermoplastic, in particular the target polyolefin, into a solid form, more specifically into a solid granular form. In this possible conditioning section, the recovered purified thermoplastic polymer is advantageously cooled to a temperature below the melting point of the polymer to obtain the portion containing the thermoplastic in a solid form.

[0136] The solvent-polymer separation step c) is also directed towards recovering at least partially, preferably primarily, and preferably completely, one or more solvents contained in the decanted or purified polymer solution fed to step c), particularly the dissolving solvent and / or optionally the extraction solvent and / or the high-density solution. The term “primarily” should be understood to mean at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, and very preferably at least 95% by weight, relative to the weight of one or more solvents contained in the decanted or purified polymer solution fed to step c). Thus, by step c), it is advantageously possible to obtain at least one solvent portion. The solvent-polymer separation step c) is also optionally directed towards purifying the recovered solvent portion and recycling it, among other things, upstream of the dissolving step a), and possibly upstream of sub-steps b'2) and / or sub-steps b'3).

[0137] Much to our advantage, the solvent portion recovered at the end of step c) may be processed in an organic processing section located at the end of step c) to purify it and obtain a purified solvent, in particular a purified dissolving solvent and optionally a highly purified solution and / or a purified extraction solvent, which can be advantageously recycled to dissolving step a) and / or optionally to a washed sub-step b'2) or an extraction sub-step b'3). The optional organic processing section at the end of step c) may use any method known to those skilled in the art, such as one or more of distillation, evaporation, liquid-liquid extraction, adsorption, crystallization and precipitation of insoluble matter, or by purging.

[0138] Therefore, the method according to the present invention makes it possible to obtain a stream of purified thermoplastic polymer, more specifically purified polyolefin, from any type of plastic feedstock, in particular plastic waste. In particular, the method according to the present invention makes it possible to remove at least 70% by weight, and preferably at least 80% by weight, of impurities, particularly inorganic impurities, contained in the plastic feedstock. The method according to the present invention also makes it possible to remove organic compounds other than the target thermoplastic, in particular insoluble polymers. Furthermore, and highly advantageously, the stream of purified thermoplastic, in particular purified polyolefin, obtained at the end of the method is less colored or even decolorized compared to the plastic feedstock fed into the method according to the present invention. The stream of purified thermoplastic polymer obtained at the end of the method according to the present invention can then be used in any application, for example, as a substitute for the same polymer in virgin form. The impurity content of the stream of purified thermoplastic polymer obtained continuously through the method according to the present invention is therefore low enough to be used in any application.

[0139] Much more preferably, the stream of purified thermoplastic polymer obtained at the end of the method according to the present invention contains impurities in an amount of 5% by weight or less, much more preferably 1.0% by weight or less, or even more preferably 0.5% by weight or less. Much more preferably, the stream of purified thermoplastic polymer obtained at the end of the method according to the present invention contains residual solvent (particularly dissolving solvent) in an amount of 5% by weight or less, preferably 1.0% by weight or less, preferably 0.1% by weight or less, or even more preferably 500 ppm by weight or less, relative to the total weight of the stream of purified thermoplastic.

[0140] (device) The present invention also relates to a device for processing plastic feedstock to obtain a stream of purified thermoplastic polymer, the device comprising: - Means for bringing the plastic supply material into contact with a dissolving solvent and dissolving it at least partially; for example, an extruder, one or more static mixers, one or more continuous stirring tank reactors (CSTRs), etc.; one or more suitable stirring systems are provided; to obtain a crude polymer solution; - Decanting device; comprising at least one decanter (also called a static decanter), preferably 1 to 10 decanters, and more preferably 2 to 5 decanters; If the decanting device has several decanters, the decanters are operated in series or in parallel, preferably in parallel. The one or more decanters are vertical or horizontal decanters, preferably cylindrical or substantially cylindrical, or even more polycylindrical in shape, and preferably the ratio L / D between the total height or total length L of the decanter and the diameter (or width) D of the decanter is 0.5 to 12, preferably 1.0 to 6.0. The one or more decanters are equipped with a feeding point and are fed polymer solutions, particularly crude polymer solutions or polymer solution-enriched effluents. Advantageously, the feeding point of a first decanter of a decanter or a series of decanters, or the feeding points of each decanter in parallel, are connected to the means for contact and dissolution, and at least part or all of the crude polymer solution is fed to the one or more decanters. Preferably, if the decanter in question is a vertical decanter, the feeding point of the decanter is advantageously located between one-quarter of the decanter's height from the top (or upper end) of the vertical decanter and three-quarters of the decanter's height from the top (or upper end) of the vertical decanter, preferably between one-third of the decanter's height from the top (or upper end) of the vertical decanter and the upper two-thirds of the decanter's height from the top (or upper end) of the vertical decanter, and the feeding point then defines two zones within the vertical decanter in question: an upper zone located between the feeding point and the top (or upper end) of the vertical decanter, and a lower zone located between the feeding point and the bottom (or lower end) of the vertical decanter. Preferably, if the decanter in question is a horizontal decanter, the feeding point of the decanter is advantageously located toward one end of the horizontal decanter in question, i.e., at or near one end of the horizontal decanter, preferably in the zone between one of the two ends of the horizontal decanter and one-third of the length of the decanter, starting from that end, and preferably between one of the two ends of the horizontal decanter and one-quarter of the length of the decanter, starting from that end. The one or more decanters comprises a first outlet for the polymer solution-enriched effluent and a second outlet for tailing flow. If the decanting device comprises several decanters in series, the first outlet of the downstream decanters (i.e., the outlet for the polymer solution-enriched effluent) is advantageously connected to the feeding point of the immediately upstream decanter, except for the last decanter in series (i.e., the first outlet of decanter i is connected to the feeding point of decanter i+1), and at the last decanter in series, the first outlet (i.e., the outlet for the polymer solution-enriched effluent) is connected to a means located downstream of the decanting device, in particular a solvent-polymer separation means, or optionally an additional purification system. If the decanting device comprises several decanters in parallel, all of the first outlets of the decanters (i.e., outlets for polymer solution-enriched effluents) are connected to a mixing system for mixing all polymer solution-enriched effluents with each other and recovered at the outlets of the parallel decanters, the mixing system being, much to its advantage, connected to means located downstream of the decanting device, in particular solvent-polymer separation means, or optionally an additional purification system. Preferably, if the decanter in question is a vertical decanter, the first outlet of the decanter (i.e., the outlet for the polymer solution-enriched effluent) is advantageously located in the upper zone of the vertical decanter in question, i.e., the zone between the feeding point and the top (or upper end) of the vertical decanter, and the second outlet is advantageously located in the lower zone of the vertical decanter, preferably at the bottom (or lower end) of the vertical decanter. Preferably, if the decanter in question is a horizontal decanter, the first outlet of the decanter (i.e., the outlet for the polymer solution-enriched effluent), and preferably the second outlet, are advantageously located toward the end opposite the feeding point, i.e., the end opposite to the end where the feeding point is located, or near the end, and preferably the first outlet and preferably the second outlet are located in the area between the end opposite the feeding point and one-third of the length of the decanter, starting from the opposite end, and preferably the area between the end opposite the feeding point and one-quarter of the length of the decanter, starting from the opposite end. The one or more decanters described above are as follows: - The liquid surface velocity is 1 × 10⁻⁶ -7 ~1,000 × 10 -2 m / s, preferably 1.0 × 10 -6 ~1,000 × 10 -2 m / s, preferably 1.0 × 10 -5 ~6,000 x 10 -3 m / s, preferably 2.0 × 10 -5 ~5,000 x 10 -3 m / s, very preferably 2.0 × 10 -5 ~9.00 x 10 -4 m / s, especially 2.0 × 10⁻⁶ -5 ~5.00 x 10 -4 It spans the range of m / s. - Preferably, the injection rate is 1.00 m / s or less, preferably 0.10 m / s or less, more preferably 0.05 m / s or less, and preferably 0.001 m / s or more; - In some cases, an additional purification system is located downstream of the decanting device, and in particular comprises additional solid-liquid separation means, such as filters, washing means, extraction means and / or adsorption means. If the additional purification system comprises several means, these means operate in series with respect to one another; - A solvent-polymer separation means is located downstream of the decanting device, which is for separating the solvent stream, particularly containing the dissolving solvent, from the stream of purified thermoplastic polymer, particularly the stream of purified polyolefin, and the solvent-polymer separation means is advantageously connected to the decanting device, or optionally to the additional purification system.

[0141] Preferably, the processing device comprises at least one additional purification system, preferably additional solid-liquid separation means, such as a filter and / or adsorption means, and more preferably additional solid-liquid separation means, followed by adsorption means.

[0142] The device for processing plastic supply materials also, advantageously, includes means for transport between the means and the device.

[0143] The following examples and drawings illustrate the present invention, and in particular specific embodiments of the present invention, and do not limit the scope of the present invention.

[0144] (List of drawings) Figure 1 shows a diagram of a decanter used according to an embodiment of the method of the present invention, the decanter being a substantially cylindrical vertical decanter, the bottom of which is conical, and the top end being hemispherical. The decanter has a length L and a diameter D. It is fed a polymer solution at feeding point (1). The effluent enriched with the polymer solution is collected at point (2), and the tailing is purged at point (3).

[0145] Figure 2 shows a diagram of a decanter used according to another embodiment of the method of the present invention, the decanter being a horizontal decanter, substantially cylindrical in shape, and having hemispherical ends. The decanter has length L and diameter D. It is fed a polymer solution at feeding point (1). The effluent enriched with the polymer solution is collected at point (2), and the tailing is purged at point (3).

[0146] (Examples) In the following examples, the analyses performed on the raw materials and the resulting products are as follows: - The ash content provides an indicator of the inorganic impurity content, which is determined by thermogravimetric analysis (or TGA). The ash content is determined by thermogravimetric analysis (or TGA) using a Perkin Elmer TGA 8000 instrument, according to ISO 11358-1 standard (2014). A sample of 10-20 mg of the material is placed on a platinum plate.

[0147] The temperature is equilibrated at 50°C for 10 minutes, and then raised to 950°C at a heating rate of 20°C / min under a nitrogen flow. The ash content is expressed as a weight percentage (Wt%), corresponding to the weight measured at 850°C relative to the starting sample weight: - The content of organic compounds, particularly Irganox® 1010, Irgafos® 168, and Irgafos® 168 oxide, is determined by high-performance liquid chromatography (HPLC): - Color parameters, CIE L * a * b * Expressed in a reference system (defined by the International Commission on Illumination (CIE)) and determined by colorimetric methods (according to ISO 11664-4 standard), where: • Brightness (or luminance) parameter L * L * The closer L is to 100, the clearer or more transparent the analyzed solid will be; conversely, * The closer the value is to 0, the more opaque the analyzed solid becomes; • Parameter a * (The green-red axis corresponds to the range of colors from green (negative values) to red (positive values); a * The target value is close to 0; • Parameter b * (Corresponding to the blue-yellow axis) measures the range of colors from blue (negative values) to yellow (positive values); b * The target value is close to 0.

[0148] L * a * b * The value is determined using a standard Konica / Minolta CM-3700A colorimeter for a solid sample of approximately 20g of cryomyl material.

[0149] (Example 1 (Conforms to the present invention)) (melting step a)) A feedstock from plastic waste containing 95% by weight polypropylene (PP) is introduced in flake form into an extruder heated to 200°C. At the extruder outlet, the feedstock is in at least a partially molten state and is mixed with n-heptane, used as the solvent, and preheated to 200°C at a solvent / feedstock weight ratio of 5 / 1. The mixture containing the solvent and feedstock is introduced into a stirred reactor, heated to 200°C, and maintained at 2.0 absolute MPa for a residence time of 1 hour. A crude polymer solution is obtained.

[0150] (Decantation process b)) The crude polymer solution obtained from dissolution step a) is then subjected to decantation step b).

[0151] The crude polymer solution is continuously withdrawn from a stirred reactor and poured into a static vertical decanter having a nearly cylindrical shape with a height-to-diameter ratio L / D3.1. The decanter is operated under the following conditions: - Temperature 200℃ - Pressure 2.0 MPa - Injection speed 0.04m / s - Upward knockout drum speed 0.07 mm / s - Stay duration: 1 hour.

[0152] A "cake-like substance" accumulates at the bottom of the decanter: it contains insoluble compounds, inorganic solids, parts of the solvent, and organic elements. This "cake-like substance" is sequentially purged at a frequency of 0.8 mHz.

[0153] (Step c: Separation of solvent and polymer) At the decanter outlet, the decanted polymer solution obtained from step b) is then subjected to the solvent-polymer separation step c).

[0154] At the outlet of this method, solid A is obtained at ambient temperature and atmospheric pressure. Solid A is composed of polypropylene (PP). Solid A is analyzed. The results are summarized in Table 1 below. Table 1 compares the measured properties of the feedstock and the obtained solid A, in particular the ash content (giving an indicator of the inorganic impurity content), colorimetric parameters L, a and b, and the relative weights of three organic compounds (Irganox® 1010, Irgafos® 168, and Irgafos® 168 oxide).

[0155] [Table 1]

[0156] The resulting solid A, composed of polypropylene (PP), is refined relative to the plastic supply raw materials for the following reasons (see Table 1); - More than 80% by weight of inorganic impurities (100 × (1.09 - 0.2) / 1.09 = 81.65%) has been removed (Solid A contains less than 80% by weight of inorganic impurities relative to the plastic supply raw material); - The content of the three tested organic impurities (Irganox® 1010, Irgafos® 168, and Irgafos® 168 Oxide) was also lower in Solid A (194 ppm, 138 ppm, and 505 ppm, respectively) compared to the plastic supply raw materials (1831 ppm, 628 ppm, and 1899 ppm, respectively); - Solid A is less colored than the supply material: the luminosity parameter L increases in solid A (88.65) and is close to 100 relative to what was measured for the supply material (57.47), but parameters a and b are closer to 0 in solid A (a=1.23 and b=7.76) compared to the supply material (14.68 and 10.83, respectively).

[0157] (Example 2 (Conforms to the present invention)) A feedstock from the same type of plastic waste as in Example 1, containing 95% by weight of polypropylene (PP), is introduced in flake form into an extruder heated to 200°C. At the outlet of the extruder, the feedstock is in at least a partially molten state, and this is mixed with n-heptane used as the solvent and preheated to 200°C at a solvent / feedstock weight ratio of 5 / 1. The mixture is then introduced into a stirred reactor, heated to 200°C, and maintained at 2.0 absolute MPa for a residence time of 1 hour. A crude polymer solution is obtained.

[0158] The crude polymer solution is continuously withdrawn from a stirred reactor and poured into a static vertical decanter having a ratio of L / D3.1 between the total height of the decanter and the diameter of a roughly cylindrical decanter. The decanter is operated under the following conditions: - Temperature 200℃ - Pressure 2.0 MPa - Injection speed 0.04m / s - Upward knockout drum speed 0.07 mm / s - Stay duration: 1 hour.

[0159] Impurities accumulate at the bottom of the decanter, forming a "cake-like" or "bed," which is then purged in batches at a frequency of 0.8 mHz.

[0160] At the decanter outlet, the decanted polymer solution is filtered through a filter with a 10 μm mesh opening, and then filtered again through a filter with a 1 μm mesh opening.

[0161] The filtered polymer solution is then fed into an adsorption column containing an activated carbon bed and operated at 200°C and 2.0 MPa.

[0162] The adsorbed polymer solution is collected at the outlet of the adsorption column and then subjected to a solvent-polymer separation step.

[0163] At the exit of the method, solid B is obtained at ambient temperature and atmospheric pressure. Solid B is composed of polypropylene (PP). Solid B is analyzed in the same manner as solid A in Example 1. The results are summarized in Table 2 below, which compares the measured properties of the feedstock and the obtained solid B, in particular the ash content (giving an indicator of the inorganic impurity content), colorimetric parameters L, a and b, and the relative weights of three organic compounds (Irganox® 1010, Irgafos® 168, and Irgafos® 168 oxide).

[0164] [Table 2]

[0165] The resulting solid B, composed of polypropylene (PP), is refined relative to the plastic supply raw materials for the following reasons (see Table 2): - Approximately 100% by weight of inorganic impurities (100 × (1.1 - 0.0) / 1.1 = 100%) have been removed; - The content of the three tested organic impurities (Irganox® 1010, Irgafos® 168, and Irgafos® 168 Oxide) was also lower in Solid B (158 ppm, 113 ppm, and 494 ppm, respectively) compared to the plastic supply raw materials (1831 ppm, 628 ppm, and 1899 ppm, respectively); - Solid B shows less coloration and improved colorimetric parameters compared to the supply material: the luminosity parameter L increases in solid B (98.89) and is close to 100 relative to what was measured for the supply material (57.47), but parameters a and b are close to 0 in solid B (a=-0.29 and b=4.61) relative to the supply material (14.68 and 10.83, respectively). [Brief explanation of the drawing]

[0166] [Figure 1] This diagram shows a decanter used according to an embodiment of the method of the present invention. [Figure 2] This diagram shows a decanter used according to another embodiment of the method of the present invention.

Claims

1. A method for processing plastic supply raw materials, comprising the following steps: a) A step of dissolving the plastic supply material in a dissolving solvent; the dissolution temperature during this process is 100°C to 300°C, and the dissolution pressure is 1.0 to 100.0 absolute MPa; at least one crude polymer solution is obtained; b) A step of decanting the crude polymer solution; obtaining the decanted polymer solution and the tailing portion. The operating temperature is 100°C to 300°C, the pressure is 1.0 to 100.0 absolute MPa, and at least one decanter is used. If step b) includes several decanters, the decanters are operated in series or in parallel, At least a portion of the crude polymer solution is supplied to each of the first decanter or parallel decanters in a series of decanters, The effluent enriched with the polymer solution is collected in the decanter or at the outlet of each decanter. The polymer solution-enriched spillage recovered at the outlet of the last decanter in a series of decanters, or all the polymer solution-enriched spillage recovered at the outlet of each decanter in a parallel operation, constitute the decanted polymer solution. The tailing flow is collected at the decanter or the outlet of each decanter, and all of the collected tailing flow constitutes the tailing portion. The liquid surface velocity of at least one of the decanters is 1 × 10⁻⁶ －７ ~1,000 x 10 －２ Over the range of m / s; then c) Solvent / polymer separation step; obtain at least one stream of purified thermoplastic polymer.

2. The method according to claim 1, wherein the dissolving solvent and the plastic supply material are supplied to step a) in a weight ratio of 0.2 to 100.0, preferably 0.3 to 20.0, preferably 1.0 to 10.0, and more preferably 3.0 to 7.

0.

3. The method according to claim 1 or 2, wherein the dissolving solvent comprises at least one hydrocarbon-based compound, and the boiling point of the dissolving solvent is -50°C to 250°C, preferably -15°C to 150°C, more preferably -1°C to 110°C, and more preferably 20°C to 100°C.

4. The method according to any one of claims 1 to 3, wherein the dissolving solvent comprises, preferably, a mixture of isomers of butane, pentane, hexane, heptane and / or octane, more preferably an isomer or mixture of isomers of hexane, heptane and / or octane.

5. The method according to any one of claims 1 to 4, wherein step b) uses 1 to 10 decanters, preferably 2 to 5 decanters.

6. The method according to any one of claims 1 to 5, wherein each decanter in step b) is cylindrical or substantially cylindrical in shape, and the ratio L / D between the total length L of the decanter and the diameter D is 0.5 to 12, preferably 1.0 to 6.

0.

7. The liquid surface velocity in each decanter is 1.0 × 10⁻⁶. －６ ~1,000 x 10 －２ m / s, preferably 1.0 × 10 －５ ~6,000 x 10 －３ , more preferably 2.0 × 10 －５ ~9.00 x 10 －４ The method according to any one of claims 1 to 6, in the range of m / s.

8. The method according to any one of claims 1 to 7, wherein the injection speed of each decanter is 1.00 m / s or less, preferably 0.10 m / s or less, more preferably 0.05 m / s or less, and preferably 0.001 m / s or more.

9. The method according to any one of claims 1 to 8, wherein each decanter is filled to a capacity of 70% to 100% of the total volume of the decanter under consideration.

10. The method according to any one of claims 1 to 9, comprising the step of purifying a decanted polymer solution to obtain a purified polymer solution, wherein the purification step includes the following sub-steps: b'1) Additional solid-liquid separation sub-steps; and / or b'2) A sub-step of washing by contact with a high-density solution; and / or b'3) A sub-step of extraction by contact with an extraction solvent; and / or b'4) A sub-step of adsorption of impurities by contact with a solid adsorbent.

11. The method according to any one of claims 1 to 10, wherein the plastic supply material comprises a thermoplastic polymer, more particularly a polyolefin.

12. A device for processing plastic supply raw materials to obtain a stream of purified thermoplastic polymer, comprising: - Means for obtaining a crude polymer solution by bringing a plastic supply material into contact with a dissolving solvent and dissolving it at least partially in the dissolving solvent; - A decantation device equipped with at least one decanter; the liquid surface velocity ranges from 1×10 －７ to 1.000×10 －２ m / s, and preferably the injection velocity is 1.00 m / s or less. The decanting device comprises several decanters, which are operated in series or in parallel. The at least one decanter is a vertical or horizontal decanter, preferably cylindrical or substantially cylindrical in shape, and preferably the ratio L / D between the total height or total length L of the decanter and the diameter D of the decanter is 0.5 to 12. The one or more decanters include a polymer solution dispensing point. The at least one decanter includes a first outlet for effluent enriched with a polymer solution and a second outlet for tailing flow. If the decanting device comprises several decanters in series, the first outlet of the downstream decanters is advantageously connected to the feeding point of the immediately upstream decanter, except for the last decanter in series whose first outlet is connected to a means located downstream of the decanting device. If the decanting device comprises several decanters in parallel, all of the first outlets of the decanters are connected to a mixing system for mixing all of the effluent enriched with the polymer solution recovered at the outlets of the parallel decanters, and the mixing system is connected to a means located downstream of the decanting device; - Optionally, an additional purification system; located downstream of the decanting device; - A means for separating solvent and polymer; located downstream of the decanting device, it separates the flow of solvent from the flow of purified thermoplastic polymer.

13. The liquid surface velocity in at least one of the decanters is 1.0 × 10⁻⁶ －６ ~1,000 x 10 －２ m / s, preferably 1.0 × 10 －５ ~6,000 x 10 －３ , more preferably 2.0 × 10 －５ ~9.00 x 10 －４ The device according to claim 12, which operates in the range of m / s.

14. The device according to claim 12 or 13, wherein the at least one decanter is a vertical decanter, as follows: - The feeding point of the decanter is located between one-quarter of the decanter's height and three-quarters of the decanter's height, and the feeding point defines two zones within the vertical decanter in question: an upper zone between the feeding point and the top of the vertical decanter, and a lower zone between the feeding point and the bottom of the vertical decanter. - The first outlet of the decanter is located in the upper zone of the vertical decanter in question, and the second outlet is located in the lower zone of the vertical decanter.

15. The device according to claim 12 or 13, wherein the at least one decanter is a horizontal decanter, as follows: - The feeding point of the decanter is located toward one end of the horizontal decanter in question, - The first and second outlets of the decanter are located toward the end opposite the feeding point.

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