Method for recycling plastics comprising separation of impurities from polymer solution by decantation

Abstract

The invention relates to a method for treating a plastic feedstock, comprising: a) dissolving the plastic feedstock in a dissolving solvent, at 100 DEG C to 300 DEG C and at a pressure of 1.0 to 100.0 MPa absolute, to obtain a crude polymer solution; b) decanting the crude polymer solution to obtain a decanted polymer solution and a tailing fraction, step b) being carried out at 100-300 DEG C and at a pressure of 1.0-100.0 MPa absolute and using at least one decanter, an effluent rich in polymer solution being recovered at the outlet of the or each decanter to form the decanted polymer solution, and step b) being carried out at a temperature of 100-300 DEG C and at a pressure of 1.0-100.0 MPa absolute and using at least one decanter. A tailing stream is recovered at the outlet of the or each decanter to form the tailing portion, the liquid surface velocity in the decanter ranging from 1 * 10 <-7 > to 1.000 * 10 <-2 > m / s; c) solvent-polymer separation to obtain a stream of purified thermoplastic. The invention also relates to a device for carrying out such a method.

Description

TECHNICAL FIELD

[0001] The present invention relates to a process for treating plastics, in particular waste plastics, to obtain a purified stream of thermoplastic polymers which can be upgraded, for example, in the manufacture of new plastic articles. More particularly, the present invention relates to a process for purifying a plastic feedstock, in particular obtained from a plastic waste, comprising thermoplastic polymers, and in particular polyolefins, such as polyethylene and / or polypropylene, by dissolving the target thermoplastic plastics in a solvent and then purifying the obtained polymer solution. The process in particular comprises a step of purifying the polymer solution by decanting at least some of the impurities, thereby making it possible to recover a stream of purified thermoplastic plastics at the outlet of the process according to the invention. PRIOR ART

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

[0003] “Mechanical” recycling makes it possible to partially reuse certain waste, either directly in new articles or by mixing the stream of mechanically sorted plastic waste with a stream of virgin polymers. This type of upgrading is limited because, although it is possible to obtain streams concentrated in a specific type of polymer, mechanical sorting does not make it possible to remove at least part of the impurities, such as additives, such as fillers, colorants, pigments and metals, which are trapped in the polymer matrix. Indeed, additives are compounds which are conventionally introduced into polymer formulations to impart desired properties to the material, and therefore to the final article, such as high mechanical strength, a specific color, etc.

[0004] “Chemical” recycling aims to at least partially reform the monomers via a generally complex series of steps. For example, plastic waste can undergo a pyrolysis step, and the pyrolysis oil which is generally recovered after purification can be converted into olefins, at least partially, for example by steam cracking. These olefins can then be polymerized. This type of sequence can be suitable for feedstocks which have undergone little sorting or sorting center waste, but in particular requires a large amount of energy consumption, due to the high-temperature treatment.

[0005] Another way for recycling plastic waste consists in at least partially dissolving the plastics, in particular thermoplastic plastics, in order to purify them by removing impurities, such as additives, such as fillers, colorants, pigments and metals, and / or polymers, from the feedstock other than the target polymer(s).

[0006] Several studies thus present various methods for treating plastic waste by dissolution and purification.

[0007] US 2017 / 002110 describes a specific method for purifying a polymeric feedstock, in particular obtained from plastic waste, by dissolving the polymer in a solvent at specific temperature and pressure conditions, followed by placing the obtained polymer solution in contact with a solid.

[0008] WO 2018 / 114047 proposes a method for selectively dissolving specific polymers of plastics in a solvent at a dissolution temperature close to the solvent boiling point. However, the method of document WO 2018 / 114047 does not allow efficiently treating and separating impurities, such as additives.

[0009] US 2018 / 0208736 proposes a treatment method by liquefying a thermoplastic plastic in a solvent, then separating insoluble matter and / or gases. The method of US 2018 / 0208736 is not able to efficiently treat impurities, and in particular impurities soluble in the solvent. The aim of US 2018 / 0208736 is to provide a plastic composition that can be used in a cracking method, thus not seeking a high purity. Indeed, US 2018 / 0208736 indicates that, for example, about 2 wt% of impurities remain after treatment in a reactor of a feedstock (comprising about 3 wt% of solid foreign matter relative to the total weight of solid compounds of the feedstock) after dissolution in dodecane (which has a boiling point of 369°C) at 150-300°C and 1.1-1.5 bar (i.e. 0.11-0.15 MPa), and then decanting in an unagitated zone of the reactor.

[0010] WO 2018 / 118579 describes a method for purifying a polymeric feedstock, in particular obtained from plastic waste, by dissolving the polymer in a solvent in a stirred reactor, followed by a settling step. More specifically, WO 2018 / 118579 shows purifying a feedstock consisting of post-consumer polypropylene by dissolving it in n-butane in an agitated autoclave at 140°C and 900 psig (6.21 MPa), followed by a settling phase after the agitation in the autoclave has stopped. The obtained polymer solution is optionally passed through a solid bed, and then depressurized in order to be able to separate at least some of the butane solvent from the polypropylene.

[0011] The present invention relates to improving these processes for treating thermoplastic plastics by dissolving in a solvent. In particular, the present invention relates to optimizing the removal of impurities from a plastic feedstock, advantageously continuously removing impurities from a plastic feedstock, and recovering a purified and in particular decolorized and deodorized thermoplastic plastic stream, in particular a polyolefin stream, while at the same time limiting the number of operations in the process carried out and in particular limiting the number of separation and / or purification steps of the process. The present invention thus relates to efficiently removing impurities (e.g. additives) from a plastic feedstock, in particular comprising a thermoplastic plastic and in particular a polyolefin, in order to continuously obtain a purified thermoplastic plastic stream, in particular a purified polyolefin stream, which can be reused as a replacement for virgin resin in the manufacture of new plastic articles by performing a continuous and simple process. SUMMARY

[0012] The present invention relates to a process for treating a plastic feedstock, comprising: a) a step of dissolving said plastic feedstock in a dissolving solvent, step a) being carried out at a dissolution temperature between 100 °C and 300 °C and at a dissolution pressure between 1.0 and 100.0 MPa absolute pressure, to obtain at least one crude polymer solution; b) a step of decanting said crude polymer solution to obtain a decanted polymer solution and a tailings fraction, step b) being operated at a temperature between 100 °C and 300 °C and at a pressure between 1.0 and 100.0 MPa absolute pressure, and using at least one decanter, when step b) comprises several decanters, said decanters being operated in series or in parallel, the decanter or a first decanter of the decanters in series or each decanter in parallel being fed with at least a portion of said crude polymer solution, wherein a polymer solution-enriched effluent is recovered at the outlet of said decanter or of each decanter, wherein the polymer solution-enriched effluent recovered at the outlet of said decanter or of the last decanter of the decanters operated in series or all the polymer solution-enriched effluents recovered at the outlet of each decanter of the decanters operated in parallel constitute said decanted polymer solution, a tailings stream is recovered at the outlet of the decanter or of each decanter, all the recovered tailings streams constituting said tailings fraction, said at least one decanter having a liquid superficial velocity between 1 x 10 -7 and 1.000 x 10 -2 m / s, then; c) a step of solvent / polymer separation to obtain at least one stream of purified thermoplastic polymer.

[0013] The method according to the application has the advantage of proposing a simple and efficient treatment of plastic feedstocks, and in particular plastic waste obtained in particular from collection and sorting channels, in order to recover the thermoplastic polymers, in particular polyolefins, or even selectively polypropylene or polyethylene, contained therein, so as to be able to recycle them into any type of application. The method according to the application, which comprises the dissolution of the thermoplastic plastics, then a specific decanting step, in particular continuously, in fact makes it possible to simply and advantageously obtain a stream of purified thermoplastic plastics having a sufficiently low content of impurities, so that the stream of purified thermoplastic plastics can be used as a substitute for virgin resins for any type of plastic formulation. More particularly, the method according to the application allows the removal of at least 70% by weight, preferably at least 80% by weight, of impurities, and in particular inorganic impurities contained in the plastic feedstock. The method according to the application also makes it possible to remove organic compounds and in particular insoluble polymers other than the target thermoplastic plastics. Furthermore, very advantageously, the stream of purified thermoplastic plastics, in particular purified polyolefins, obtained at the end of the method is less coloured or even discoloured with respect to the plastic feedstock fed to the method according to the application. In very particular cases, the method according to the application makes it possible to obtain a stream of purified thermoplastic plastics, in particular a stream of purified polyolefins, or even polypropylene or polyethylene, containing 5% by weight or less of impurities, very advantageously 1.0% by weight or less of impurities, even more preferentially having a content of impurities of less than or equal to 0.5% by weight.

[0014] Thus, the method according to the application proposes a simple scheme corresponding to a series of operations, in particular comprising at least dissolution and decanting, which makes it possible to remove at least some impurities, in particular at least some additives, from the plastic waste and to recover a purified thermoplastic plastic, in particular the target purified thermoplastic plastic, containing very little impurities and advantageously a very low content of solvent (preferably less than or equal to 10% by weight, preferentially less than or equal to 1% by weight) so as to be able to upgrade the plastic waste by recycling said purified thermoplastic plastic.

[0015] The present application also has the advantage of participating in plastic recycling and saving fossil resources by enabling the upgrading of plastic waste. In particular, it allows the purification of plastic waste, in order to obtain a stream of purified thermoplastic polymers, in particular purified polyolefins or even purified polypropylene or polyethylene, with reduced impurity content, and in particular decolorized and deodorized, which can be reused to form new plastic articles. The purified thermoplastic thus obtained can be used directly in formulations as a mixture with additives (e.g. plasticizers, colorants, pigments, fillers, etc.), instead of virgin resins or as a mixture with virgin resins, in order to obtain plastic products with aesthetic, mechanical or rheological working properties that facilitate their reuse and their upgrading.

[0016] The present application also relates to a device for treating a plastic feedstock to obtain a stream of purified thermoplastic polymers, comprising: - a device for placing in contact and at least partially dissolving the plastic feedstock in a dissolving solvent, to obtain a crude polymer solution; - a decanting device comprising at least one decanter, wherein the liquid superficial velocity ranges between 1 x 10 -7 and 1.000 x 10 -2 m / s, and preferably the injection velocity is less than or equal to 1.00 m / s, wherein the decanting device comprises several decanters operating in series or in parallel, said at least one decanter being a vertical or horizontal decanter, preferably shaped as a cylinder or substantially cylindrical, preferably wherein the ratio L / D between the total height or length L of the decanter and the diameter D of the decanter is between 0.5 and 12, preferably between 1.0 and 6.0, said decanter(s) comprising a polymer solution feed point, said at least one decanter comprising a first outlet for the effluent rich in polymer solution and a second outlet for the tail stream, when the decanting device comprises several decanters in series, the first outlet of the downstream decanter is advantageously connected to the feed point of the decanter directly upstream, except for the last decanter in series, whose first outlet is connected to a device located downstream of the decanting device, when the decanting device comprises several decanters in parallel, all said first outlets of said decanters are connected to each other and to a mixing system for mixing all the effluents rich in polymer solution recovered at the outlets of said decanters in parallel, said mixing system being connected to a device located downstream of the decanting device; - an optional additional purification system located downstream of the decanting device; - a solvent-polymer separation device, located downstream of the decanting device, for separating a solvent stream and a purified thermoplastic polymer stream.

[0017] According to one embodiment, the at least one decanter is a vertical decanter, wherein: - the feed point of the decanter is located between a quarter of the height of the decanter and three quarters of the height of the decanter, the feed point then defining two zones in the vertical decanter in question, an upper zone between the feed point and the top of the vertical decanter and a lower zone between the feed 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.

[0018] According to another embodiment, the at least one decanter is a horizontal decanter, wherein: - the feed point of the decanter is located towards one end of the horizontal decanter in question, - the first outlet and the second outlet of the decanter are located towards the end opposite the feed point.

[0019] Description of the embodiments According to the application, the expressions "of between... and..." and "between... and..." are equivalent and mean that the limits of the interval are included in the range of values described. If this is not the case and if the limits are not included in the range described, the application introduces such information.

[0020] For the purposes of the application, the various ranges of parameters for a given step, such as ranges of pressure and ranges of temperature, can be used individually or in combination. For example, a range of preferred pressure values can be combined with a range of more preferred temperature values for the purposes of the application.

[0021] Hereinafter, particular embodiments of the application are described. They can be used individually or in combination, when this is technically possible, without limiting the combinations.

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

[0023] The terms "upstream" and "downstream" are understood to vary with the general flow of the fluid(s) or stream(s) considered in the process.

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

[0025] The term "polyolefin" means any type of homo- and / or copolymer having an olefin as a basic unit and mixtures thereof. More specifically, the polyolefin can be any range of polyethylene homo- polymers denoted by the acronym PE (e.g. high density, also known as HDPE or low density, known as LDPE), polypropylene homo-polymers denoted by the acronym PP, copolymers thereof and / or mixtures thereof.

[0026] The term "additive" is a term conventionally used in the field of polymers and in particular in the field of polymer formulations. The additives introduced into the polymer formulations can be, for example, plasticizers, fillers, which are organic or mineral solid compounds used to modify the physical, thermal, mechanical and / or electrical properties of the polymeric material or to reduce its cost price, reinforcing agents, colorants, plasticizers, pigments, hardeners, flame retardants, flame retarders, stabilizers, antioxidants, UV absorbers, antistatic agents, etc.

[0027] The additives correspond to at least some of the impurities of the plastic raw material to be treated, and the treatment method according to the present application makes it possible to at least partially remove them. Other types of impurities can be use-related impurities, such as metal impurities, paper / board, biomass, polymers different from the target polymer(s), etc.

[0028] Thus, according to the present application, the impurities that can be at least partially removed according to the method of the present application comprise additives conventionally used in polymer formulations and use-related impurities generally derived from the life cycle of plastic articles and materials and / or from the use of waste collection and sorting circuits. Said impurities can be metal, organic or mineral type impurities; they can be packaging residues, food residues or compostable residues (biomass). These use-related impurities can also comprise glass, wood, paperboard, paper, aluminum, iron, metals, tires, rubber, silicones, rigid polymers, thermoset polymers, thermoplastic polymers of different nature than the target thermoplastic polymers, in particular different from the target polyolefins, household products, chemical or cosmetic products, waste oils, water.

[0029] According to the present application, the polymer solution is a solution comprising a dissolving solvent and at least a target thermoplastic polymer, in particular a target polyolefin, dissolved, i.e. in particular solvated and dispersed, in said dissolving solvent, the dissolved polymer being initially present in a raw material. The polymer solution can also comprise insoluble (and suspended in the polymer solution) and optionally soluble (and dissolved in the dissolving solvent) impurities. Depending on the steps of the process according to the present application, said polymer solution can thus comprise impurities in the form of insoluble particles, which are advantageously suspended in said polymer solution, optionally soluble impurities, dissolved in the dissolving solvent, and / or optionally another liquid phase immiscible with said polymer solution.

[0030] It is well known that the boiling point of a compound varies with the operating pressure. However, without further indication, i.e. without indication of the pressure, the boiling point of the considered compound, in particular of the dissolving solvent, is understood to be the boiling point of said compound, in particular of said dissolving solvent, at atmospheric pressure, in particular equal to 0.1 MPa. Thus, the boiling point characterizing the dissolving solvent is understood to be the boiling point of said dissolving solvent at atmospheric pressure, in particular equal to 0.1 MPa.

[0031] The critical temperature and the critical pressure of a solvent, in particular of a dissolving solvent, are specific to said solvent and depend on the nature of the considered solvent. For a pure substance, the critical temperature and the critical pressure of the pure substance are respectively the temperature and the pressure of the critical point of said pure substance. As well known by the person skilled in the art, at and above the critical point, the considered pure substance is in a supercritical form or state; it can then be referred to as a supercritical fluid.

[0032] The present application thus relates to a process for treating a plastic raw material, the plastic raw material preferably consisting of plastic waste and advantageously comprising a thermoplastic polymer, more particularly a polyolefin, said process comprising and preferably consisting of: a) a step of dissolving the plastic raw material in a dissolving solvent, said dissolving solvent preferably comprising at least one hydrocarbon-based compound, preferably aliphatic and preferably paraffinic, advantageously having a boiling point of between -50 and 250°C, preferably between -15 and 150°C, preferably between -1 and 110°C and preferably between 20 and 100°C, preferably a weight ratio between the dissolving solvent and the plastic raw material of between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, even more preferably between 3.0 and 7.0, to obtain at least one crude polymer solution, Step a) is advantageously operated at a dissolution temperature between 100°C and 300°C, preferably between 150°C and 250°C, and at a dissolution pressure between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute, and very preferably between 2.0 and 15.0 MPa absolute; b) a step of decanting the crude polymer solution to obtain a decanted polymer solution and a tailings fraction, Step b) is operated at a temperature between 100°C and 300°C, preferably between 150 and 250°C, and at a pressure between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute, and very preferably between 2.0 and 15.0 MPa absolute; Step b) involves at least one decanter, preferably one to ten decanters, preferably two to five decanters, advantageously operated in series or in parallel, preferably in parallel, The (or each) decanter is in particular a vertical or horizontal decanter, advantageously shaped as a cylinder or substantially as a cylinder, preferably wherein the ratio L / D between the overall height or length L of the decanter and the diameter or width D of the decanter is between 0.5 and 12, preferably between 1.0 and 6.0, Said decanter or the first decanter of the decanters in series, or each decanter in parallel, is fed with at least a part or the whole of said crude polymer solution, advantageously at a feed point located on the considered decanter.

[0033] The polymer-rich solution effluent is recovered at the outlet of the decanter or of each decanter, the polymer-rich solution effluent recovered at the outlet of said decanter or at the outlet of the last decanter of the decanters in series, or all the polymer-rich solution effluents recovered at the outlet of each decanter in parallel, constitutes said decanted polymer solution, A tailings stream, in particular continuously or batchwise, is recovered at the outlet of the decanter or of each decanter, all the recovered tailings streams constituting said tailings fraction, Said (one or more) decanter(s) have: - a liquid superficial velocity between 1 x 10 -7 and 1.000 x 10 -2 m / s, preferably between 1.0 x 10 -6 and 1.000 x 10 -2 m / s, preferably between 1.0 x 10 -5 and 6.000 x 10 -3 m / s, preferably between 2.0 x 10 -5between 2.0 x 10 -3 between 2.0 x 10 -5 between 2.0 x 10 -4 between 2.0 x 10 -5 between 2.0 x 10 -4 between 2.0 x 10 - Preferably, the injection speed is less than or equal to 1.00 m / s, preferably less than or equal to 0.10 m / s, preferably less than or equal to 0.05 m / s, and preferably greater than or equal to 0.001 m / s; Each decanter is advantageously operated with a residence time between 1 and 200 hours, preferably between 1 hour and 50 hours, and preferably with a filling rate between 70% and 100% of the total volume of the decanter considered; b’) optionally, a step of purifying the decanted polymer solution, comprising: b’1) a further solid-liquid separation step to obtain at least one clarified polymer solution; and / or b’2) washing the decanted or optionally clarified polymer solution by contact with a dense solution to obtain at least one washing effluent and a washed polymer solution; and / or b’3) extracting impurities with an extraction solvent to obtain at least one extracted polymer solution and one used solvent; and / or b’4) adsorbing impurities by contact with a solid adsorbent to obtain at least one refined polymer solution; The purification step makes it possible to obtain a purified polymer solution, which advantageously corresponds to a clarified or washed or extracted or refined polymer solution; and then c) a solvent-polymer separation step to obtain at least one stream of purified thermoplastic polymer, more particularly at least one stream of purified polyolefin, or even at least one stream of purified polypropylene or at least one stream of purified polyethylene.

[0034] Raw material The raw material of the process according to the application, called plastic raw material, comprises plastics, which itself more particularly comprises thermoplastic polymers, such as polyolefins. Preferably, the plastic raw material comprises between 50% and 100% by weight, and preferably between 70% and 100% by weight, of plastics.

[0035] The plastics included in the feedstock of the process according to the application are generally production waste and / or "post-consumer" waste plastic articles, in particular household plastic waste, plastic waste from the construction industry, plastic waste from motor vehicles or plastic waste from any type of transport or electrical and electronic equipment waste. Preferably, the plastic waste is obtained from collection and sorting channels. The plastics or plastic materials comprise polymers mixed with additives in order to provide the material with specific properties with the aim of constituting various articles (for example injection-moulded parts, pipes, films, fibres, fabrics, mastics, envelopes, etc.) after shaping into a shape. The additives used in the plastics can be organic or inorganic compounds. They are for example fillers, colouring agents, pigments, plasticizers, property modifiers, flame retardants, etc.

[0036] The feedstock of the process according to the application comprises in particular thermoplastic polymers, 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 thermoplastic polymers, 100% advantageously being the maximum upper limit. The thermoplastic polymers included in the plastic feedstock and targeted by the process according to the application can be olefin polymers, diene polymers, vinyl polymers and / or styrene polymers. Preferably, the thermoplastic polymers included in the plastic feedstock and targeted by the process according to the application are polyolefins, for example polyethylene (PE), polypropylene (PP) and / or copolymers of ethylene and propylene, or mixtures thereof. Preferably, the plastic feedstock comprises at least 80% by weight, preferably at least 85% by weight, preferably at least 90% by weight of polyolefins relative to the total weight of the plastic feedstock, 100% advantageously being the maximum upper limit. The process according to the application thus most particularly relates to the purification and recovery of polyolefins included in the feedstock in order to be able to reuse them in various applications. According to a particular embodiment, the plastic feedstock comprises a mixture of polypropylene (PP) and polyethylene (PE), in particular at least 80% by weight, preferably at least 85% by weight, preferably at least 90% by weight of a mixture of polypropylene (PP) and polyethylene (PE) relative to the total weight of the plastic feedstock. The polyethylene can in particular be high-density polyethylene (HDPE). In this particular embodiment, the mixture comprises for example between 5% and 95% by weight of PP and between 5% and 95% by weight of PE, in particular HDPE, or between 50% and 95% by weight of PP and between 5% and 50% by weight of PE, in particular HDPE. In this particular embodiment, the process according to the application thus aims to purify and recover PP and / or PE exclusively.

[0037] The plastic feedstock can comprise a mixture of polymers, in particular thermoplastics other than the target polyolefin, advantageously additives used for formulating the plastic material and impurities typically associated with the use originating from the life cycle of the plastic material and of the manufactured body and / or from the waste collection and sorting circuit, these compounds being collectively referred to as impurities. The feedstock of the process according to the application typically comprises less than 50% by weight of impurities, preferably less than 20% by weight of impurities, preferably less than 10% by weight of impurities. The plastic feedstock can comprise for example at least 1 % by weight of impurities, or even at least 5% by weight of impurities.

[0038] The plastic feedstock can advantageously be pre-treated before the process, in order to remove at least all or some of the "coarse" impurities, i.e. impurities in the form of particles having a size greater than or equal to 10 mm, preferably greater than or equal to 5 mm, or even greater than or equal to 1 mm, such as wood, paper, biomass, iron, aluminium, glass, etc., and in order to bring it into a certain form, typically into the form of separate solids, in order to be treated in the process. This pre-treatment can comprise a grinding step, a step of washing at atmospheric pressure and / or a drying step. This pre-treatment can be carried out at a different site, for example at a waste collection and sorting centre, or at the same site where the treatment process according to the application is carried out. Preferably, this pre-treatment makes it possible to reduce the content of impurities to less than 20% by weight, preferably less than 15% by weight, preferably less than 10% by weight, this percentage being given with respect to the weight of the plastic feedstock treated by the process according to the application. At the end of the pre-treatment, the feedstock is typically stored in the form of separate solids, for example in the form of ground material, flakes or powder or particles, in order to be treated and transported into the process.

[0039] Dissolution step a) According to the application, the process comprises a dissolution step a) in which the plastic feedstock is brought into contact with a dissolution solvent and the thermoplastics contained therein, advantageously for their separation and purification; in particular, the polyolefins contained therein are dissolved in the dissolution solvent, in order to obtain at least one, preferably one, crude polymer solution.

[0040] The term "dissolution" is understood to mean any phenomenon leading to the production of at least one thermoplastic polymer solution, i.e. a liquid (or fluid) comprising the target thermoplastic polymer dissolved in a dissolution solvent. The person skilled in the art is perfectly aware of the phenomenon(s) involved in the dissolution of polymers and which involve at least mixing, solvation, dispersion, homogenization and disentangling of the chains of thermoplastic polymers.

[0041] During and at the end of the dissolving step a), the pressure and temperature conditions are such that it is possible to keep the dissolving solvent at least partly and preferably entirely in liquid form or optionally in supercritical form, while the plastic feedstock, in particular the target thermoplastic polymer, and most particularly the target polyolefin, and for example at least a soluble fraction of the impurities, are advantageously at least partly and preferably completely dissolved in the dissolving solvent. In other words, the temperature and pressure conditions in step a) avoid or at least limit the possibility for the dissolving solvent to be 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 and in particular paraffinic, preferably straight-chain or branched, hydrocarbon-based compound. Preferably, the dissolving solvent comprises at least 80% by weight, preferably at least 95% by weight, preferably at least 98% by weight, of at least one preferably aliphatic and in particular paraffinic, preferably straight-chain or branched, hydrocarbon-based compound, the percentages being expressed with respect to the total weight of the dissolving solvent (100% being the maximum). Preferably, the dissolving solvent comprises at least one preferably aliphatic and in particular paraffinic hydrocarbon-based compound having a boiling point (at atmospheric pressure, in particular at 0.1 MPa) of between -50°C and 250°C, preferably between -15°C and 150°C, preferably between -1°C and 110°C, and preferably between 20°C and 100°C. Preferably, the dissolving solvent comprises and preferably consists of at least one preferably aliphatic and in particular paraffinic, preferably straight-chain or branched, hydrocarbon-based compound containing between 3 and 12 carbon atoms, preferably between 4 and 8 carbon atoms, and very preferably containing 6, 7 or 8 carbon atoms. For example, the dissolving solvent comprises a compound chosen from butane, pentane, hexane, heptane and isomers of octane. The dissolving solvent can comprise and preferably consists of a mixture of isomers of butane, pentane, hexane, heptane and / or octane, and preferably the content of said mixture of isomers in the dissolving solvent is greater than or equal to 80% by weight, preferably greater than or equal to 95% by weight, preferably greater than or equal to 98% by weight, with respect to the total weight of the dissolving solvent. According to a very preferred embodiment, the dissolving solvent comprises and preferably consists of hexane, heptane and / or octane isomers or a mixture of isomers. Very advantageously, the preferred hydrocarbon-based compounds for the dissolving solvent comprise paraffinic aliphatic compounds having a critical temperature (the temperature of the pure hydrocarbon-based compound at the critical point) preferably of between 95 and 350°C, preferably between 130 and 300°C, preferably between 180 and 285°C.

[0043] Preferably, the dissolving step a) is fed with the plastic feedstock and the dissolving solvent, the weight ratio between the dissolving solvent and the plastic feedstock being between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, even more preferably between 3.0 and 7.0.

[0044] Advantageously, the dissolution solvent fed to the dissolution step a) is in liquid or possibly supercritical form. Advantageously, it can be preheated, preferably to a temperature between 100°C and 300°C, preferably between 150°C and 250°C, before its introduction in step a), in particular before its introduction in the contact section and optionally in the dissolution section, in order to facilitate the heating of the plastic feedstock and / or to avoid a temperature drop of the material stream in the contact section and optionally in the dissolution section of step a).

[0045] Advantageously, the dissolution solvent comprises, and preferably consists of, fresh solvent (or a supply of fresh solvent) and / or a stream of recycled solvent obtained from a subsequent step of the process, preferably at least partially from the solvent-polymer separation step c).

[0046] Very advantageously, the dissolution step is operated at a temperature (referred to as the dissolution temperature) between 100°C and 300°C, preferably between 150°C and 250°C, and preferably at a pressure (referred to as the dissolution pressure) between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute, and very preferably between 2.0 and 15.0 MPa absolute. During the dissolution step, the temperature and the pressure can be changed from atmospheric conditions or from the conditions under which the plastic feedstock and / or the dissolution solvent are introduced into the process, to reach the dissolution conditions (i.e. the dissolution temperature, in particular between 100°C and 300°C, preferably between 150°C and 250°C, and advantageously the dissolution pressure, in particular between 1.0 MPa and 100.0 MPa, preferably between 1.0 MPa and 25.0 MPa absolute, preferably between 1.5 MPa and 18.0 MPa absolute, and very preferably between 2.0 MPa and 15.0 MPa absolute). Very advantageously, at the end of the dissolution step, the crude polymer solution is at the dissolution temperature and the dissolution pressure.

[0047] Limiting the temperature in the dissolution step a) to a temperature less than or equal to 300°C, preferably less than or equal to 250°C, makes it possible to avoid or limit the thermal degradation of the target thermoplastic plastic, in particular the target polyolefin, but also to limit the energy requirements of the process, thereby helping to limit the operating costs of the process. Advantageously, the dissolution temperature is greater than or equal to the melting point of the target thermoplastic plastic, in particular the target polyolefin, in order to facilitate its dissolution and very advantageously to reduce the residence time required to effectively dissolve said thermoplastic plastic in the dissolution solvent. Very preferably, the temperature in the dissolution step a) is less than or equal to the critical temperature of the dissolution solvent, in order to avoid the formation of a supercritical phase during the dissolution step a) which tends to disrupt the dissolution.

[0048] At the same time, the dissolution pressure in the dissolution step is higher than the saturation vapor pressure of the dissolution solvent at the dissolution temperature, so that the dissolution solvent is at least partially and preferably completely in liquid or possibly supercritical form at the dissolution temperature and thus the possibility of the dissolution solvent being partially in gaseous form is avoided. Thus, the dissolution of the target thermoplastic, in particular the target polyolefin, is optimized in particular with regard to quality and operating time.

[0049] Advantageously, the residence time in which the dissolution step a) is carried out is preferably between 1 and 600 minutes, preferably between 2 and 300 minutes, preferably between 2 and 180 minutes. The residence time is understood to be the residence time at the dissolution temperature and the dissolution pressure, i.e. the time in which the plastic feedstock is subjected to the dissolution solvent at the dissolution temperature and the dissolution pressure in step a).

[0050] In order to enable the dissolution solvent and the plastic feedstock to be placed in contact with each other and, in particular, in order to enable the target thermoplastic to be dissolved efficiently and uniformly in the dissolution solvent, the dissolution step a) can advantageously involve various types of equipment, such as mixing, transport and heating devices, for example reactors, pumps, transport circuits, stirring systems, ovens, exchangers, mixers, etc. In particular, step a) advantageously involves at least one dissolution equipment piece, and optionally at least one feedstock preparation device, mixing device and / or transport device. These equipment and / or device pieces can be, for example, one or more static or dynamic mixers, extruders, pumps, reactors, co-current or counter-current columns, or combinations of pipes and equipment. Devices for transporting in particular fluids (such as gases, liquids or solids) are well known to those skilled in the art. In a non-limiting manner, the transport devices can comprise at least one of the following devices: a compressor, a pump, an extruder, a vibrating pipe, an endless screw or a valve. The equipment pieces and / or device pieces used in step a) can also comprise or be combined with heating systems (such as ovens, exchangers, tracings, etc.) to achieve the conditions required for dissolution.

[0051] The dissolution step a) is fed at least with the plastic feedstock, in particular in the form of one or more streams of plastic feedstock, and with the dissolution solvent, in particular in the form of one or more streams of dissolution solvent, advantageously by means of one or more transport devices. The stream(s) of plastic feedstock can be different from the stream(s) of dissolution solvent. Some or all of the plastic feedstock can also be fed mixed with some or all of the dissolution solvent to step a), the remainder of the solvent and / or the feedstock possibly being fed separately to step a) if appropriate.

[0052] During the contact of the plastic feedstock with the dissolving solvent, the dissolving solvent is advantageously at least partially and preferably entirely in the liquid or possibly supercritical form, while the plastic feedstock comprising the target thermoplastic plastic can be in solid or liquid form, optionally comprising suspended solid particles. The plastic feedstock can also optionally be injected into the dissolving device as a mixture with the dissolving solvent in the form of a suspension in the dissolving solvent, the preparation and injection of the suspension possibly being continuous or batchwise.

[0053] Preferably, the dissolving step a) involves at least one device for at least partially melting the plastic feedstock (preferably an extruder), optionally at least one device for mixing at least partially the dissolving solvent and the plastic feedstock, advantageously at least partially melted (for example one or a series of two to ten mixers, preferably one to ten static mixers) and a dissolving device, for example at least one continuous stirred tank reactor (CSTR) equipped with at least one mechanical stirring system. In this case, the plastic feedstock is fed to the melting device, in particular to the extruder, so that at the outlet of said device at least some and preferably all of the target thermoplastic plastic comprised in the plastic feedstock is in molten form. The plastic feedstock can then be subsequently injected into the dissolving device or optionally into a system comprising one mixer or a series of mixers, advantageously followed by the dissolving device. The plastic feedstock at least partially in molten form can also be pumped by means of a pump specific for viscous fluids, commonly known as melt pump or gear pump. The plastic feedstock at least partially in molten form at the outlet of said melting device can also be filtered by means of a filtering device (optionally in addition to the melt pump), with the aim of removing the coarsest particles; generally, the mesh size of this filter is between 10 pm (micrometers) and 1 mm (millimeters), preferably between 20 and 200 pm. At the same time, the dissolving solvent is fed directly to the dissolving device or possibly to the mixer or series of mixers.

[0054] Preferably, step a) implements an extruder and at least one static mixer (at least part of the dissolving solvent is injected therein) before at least one CSTR type reactor, in order to promote the shearing and intimate mixing between the dissolving solvent and the plastic feedstock, thus promoting the dissolution of the target thermoplastic plastic.

[0055] Very advantageously, the crude polymer solution obtained at the end of the dissolving step a) comprises at least the dissolving solvent and the target thermoplastic plastic (in particular the target polyolefin) dissolved in the dissolving solvent. Generally, the crude polymer solution also comprises soluble impurities and / or suspended insoluble impurities also dissolved in the dissolving solvent. The crude polymer solution obtained at the end of the dissolving step a) can also optionally comprise polymers, for example in molten form, dissolved form or undissolved form.

[0056] Step b) of decanting the polymer solution The process according to the present application comprises a step b) of decanting the crude polymer solution obtained at the end of the dissolving step a) to produce at least one "decan ted" polymer solution and a tailings fraction.

[0057] In fact, the decanting step b) makes it possible to separate at least some of the insoluble impurities that can be present in the crude polymer solution, in the form of solid particles, in particular in suspension, or in the form of a liquid phase, for example comprising molten polymer, and optionally at least some of the soluble impurities, by varying the density difference of the compounds present in the crude polymer solution. The decanting step b) thus makes it possible to recover a decanted polymer solution that is at least partially free of the impurities present in the crude polymer solution fed to said step b). The decanting step b) thus also produces a tailings fraction comprising at least some, preferably all, of the insoluble impurities of the crude polymer solution obtained from step a), and possibly soluble impurities, and possibly the dissolving solvent that can be partially entrained with the impurities. The insoluble impurities removed during the decanting step b) are for example pigments, mineral compounds, packaging residues (glass, wood, cardboard, paper, aluminium) and polymers other than the target thermoplastic (in particular other than the target polyolefin).

[0058] According to one embodiment of the present application, the decanted polymer solution comprises a fraction of the polyolefin contained in the initial plastic feedstock, for example polypropylene of the plastic feedstock, and the tailings fraction comprises polymer impurities, in particular thermoplastic other than the target polyolefin, and / or another fraction of the polyolefin contained in the initial plastic feedstock (for example polyethylene), and in particular high-density polyethylene (HDPE) of the plastic feedstock. Said polymer impurities and / or said another fraction of the polyolefin can in particular not have been dissolved in the dissolving step a). The tailings fraction can then advantageously be recovered and treated in another process, for example a second process according to the present application, in order to purify said thermoplastic, in particular said another fraction of the polyolefin of the initial plastic feedstock, and separate it in the tailings fraction.

[0059] Another advantage of the decanting step b) of the process according to the present application lies in the fact that it allows a high-performance, continuous purification of the polymer solution. This aspect is advantageous because the yield of the purified target thermoplastic, in particular of the purified target polyolefin, is then optimal.

[0060] Advantageously, in addition to removing at least some of the impurities continuously, the decanting step b) is able to limit the operating problems of the downstream process steps, in particular for example clogging and / or erosion, while at the same time effectively contributing to the purification of the plastic feedstock.

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

[0062] Step b) uses at least one decanting device piece (also referred to as decanter). Preferably, step b) uses one to ten decanters, preferably two to five decanters. When step b) uses several decanters (i.e. two to ten), preferably two to five decanters, the decanters can be operated in series and / or in parallel, preferably in parallel.

[0063] The decanter(s) are preferably shaped as a cylinder or substantially as a cylinder, closed at each end, in particular by hemispherical or conical ends, and advantageously comprise orifices, for example for supplying the crude polymer solution and for the outlets of the various separated streams. The term "substantially as a cylinder" means that the shape of the decanter is a cylinder closed at the ends, in particular by a hemispherical end or by a first hemispherical end and a second conical end. Very particularly, the decanter(s) used in step b) can be multicylinder. The expression "multicylinder" means that the decanter in question can have several cylinder segments of different diameters; for example, a first cylinder region of diameter D1 and a second cylinder region of diameter D2, with D1 being greater than D2.

[0064] The decanter or decanters used in step b) can be vertical or horizontal decanters. In other words, the decanter or decanters are operated in a substantially cylindrical shape such that the cylinder is positioned vertically or horizontally, respectively.

[0065] Preferably, the decanter(s) used in step b), which are preferably shaped as a cylinder or substantially as a cylinder, have a 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, which is between 0.5 and 12, preferably between 1.0 and 6.0.

[0066] Very particularly, the decanter(s) used in step b) can be one or more vertical decanters of the multi-cylinder type. The expression "multi-cylinder" means that the decanter in question can have several cylinder sections of different diameters; for example a first cylinder section of diameter D1 and a second cylinder section of diameter D2, with D1 being greater than D2, the second cylinder section of diameter D2 being preferably located above the first cylinder section of diameter D1 (i.e. on the top side of the decanter). In this very specific embodiment, the diameter D to be considered is the diameter of the widest cylinder section of the decanter in question, i.e. the diameter D1 of the decanter of the above example.

[0067] At least a part or all of the crude polymer solution obtained in step a) is fed to step b). In embodiments in which a single decanter or several decanters in series are used in step b), all of the crude polymer solution obtained at the end of step a) is fed to the decanter or to the first decanter in series. In embodiments in which several decanters are used in parallel in step b), the crude polymer solution obtained at the end of step a) is fed to each of the decanters operating in parallel. In this latter embodiment, the crude polymer solution is advantageously divided into several partial streams of crude polymer solution, in particular as many partial streams as there are decanters in parallel.

[0068] The decanter(s) used in step b) is fed with polymer solution, in particular crude polymer solution or polymer-rich solution effluent, at a feed point located on the decanter in question.

[0069] When the decanter in question is a vertical decanter, said feed point for feeding the polymer solution is advantageously located between the upper quarter of the height of the decanter and the upper three quarters of the height of the decanter, preferably between the upper third of the height of the decanter and the upper two thirds of the height of the decanter. Said polymer solution feed point then defines two zones in the vertical decanter in question, an upper zone between the polymer solution feed point and the top of the vertical decanter, and a lower zone between the polymer solution feed point and the bottom of the vertical decanter.

[0070] When the decanter in question is a horizontal decanter, said polymer solution feed point is preferably located at one side of the horizontal decanter, that is to say at or close to one end of the horizontal decanter, preferably between one of the two ends of the horizontal decanter and one third of the length of the decanter from said end, preferably between one of the two ends of the horizontal decanter and one quarter of the length of the decanter from said end.

[0071] The (or each) decanter comprises an outlet for a polymer solution-enriched effluent, i.e. an effluent comprising a polymer solution free of at least some impurities. The polymer solution-enriched effluent is thus recovered at the outlet of the (or each) decanter used in step b). The polymer solution-enriched effluent can be recovered by withdrawal or overflow. When step b) uses a single decanter, the polymer solution-enriched effluent recovered at the outlet of said decanter thus constitutes the decanted polymer solution. When step b) uses several decanters in parallel, all the effluents recovered at the outlet of each decanter, which are polymer solution-enriched, constitute the decanted polymer solution. Finally, when step b) uses several decanters in series, one after the other, the polymer solution-enriched effluent recovered at the outlet of an upstream decanter is advantageously directly fed to the downstream decanter, and the polymer solution-enriched effluent recovered at the outlet of the last decanter in series constitutes the decanted polymer solution.

[0072] When the decanter considered is a vertical decanter, the outlet for a polymer solution-enriched effluent is advantageously located in the upper region of the vertical decanter in question, i.e. in the region between the polymer solution feed point and the top of the decanter.

[0073] When the decanter considered is a horizontal decanter, the outlet for a polymer solution-enriched effluent is advantageously located on the side of the decanter opposite the polymer solution feed point, i.e. at or near the end of the decanter opposite the end at which the polymer solution feed point is located, said outlet for a polymer solution-enriched effluent preferably being in the region between the end of the decanter opposite the end at which the polymer solution feed point is located and one third of the length of the decanter from said opposite end, preferably between the end of the decanter opposite the end at which the polymer solution feed point is located and one quarter of the length of the decanter from said opposite end.

[0074] The (or each) decanter also comprises a tail stream outlet. The tail stream is thus recovered from the outlet of the or each decanter used in step b). When step b) uses a single decanter, the tail stream recovered at the outlet of said decanter thus constitutes the tail fraction obtained at the end of step b). When step b) uses several decanters in parallel or in series, all the tail streams recovered at the outlet of each decanter constitute the tail fraction obtained at the end of step b).

[0075] The tail stream in the decanter considered can be recovered or purged continuously or batchwise. When the tail stream is purged batchwise, the purge frequency can vary between 0.01 and 20.0 mHz, preferably between 0.1 and 10.0 mHz, preferably between 0.5 and 1.0 mHz.

[0076] When the decanter under consideration is a vertical decanter, the outlet for the tailings stream is advantageously located in the lower region of the decanter (i.e. in the region between the point of feed of the polymer solution and the bottom of the decanter), preferably in the bottom of the decanter under consideration, for example in the bottom of the conical end of the vertical decanter.

[0077] When the decanter under consideration is a horizontal decanter, the outlet for the tailings stream is located in the bottom of the decanter under consideration and is advantageously in the side of the decanter opposite the point of feed of the polymer solution, i.e. close to the end of the decanter opposite the end in which the point of feed of the polymer solution is located, preferably in the region between the end of the decanter opposite the end in which the point of feed of the polymer solution is located and one third of the length of the decanter from said opposite end, preferably between the end of the decanter opposite the end in which the point of feed of the polymer solution is located and one quarter of the length of the decanter from said opposite end.

[0078] The at least one decanter used in step b) is preferably operated with a fill rate between 70% and 100% of the total volume of the decanter under consideration. The term "fill rate" corresponds to the ratio between the total volume of material (polymer solution and tailings) 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 is a liquid superficial velocity (also known as knockout drum velocity), in particular upwards, ranging between 1 x 10 -7 and 1.000 x 10 - 2 m / s, preferably between 1.0 x 10 -6 and 1.000 x 10 -2 m / s, preferably between 1.0 x 10 -5 and 6.000 x 10 -3 m / s, preferably between 2.0 x 10 -5 and 5.000 x 10 -3 m / s, very preferably between 2.0 x 10 -5 and 9.00 x 10 -4 m / s, in particular between 2.0 x 10 -5 and 5.00 x 10 -4between 0.0001 and 1.00 m / s, preferably between 0.001 and 0.10 m / s, and preferably between 0.005 and 0.05 m / s. The liquid surface velocity, called LSV (or Q / S), is well known to the person skilled in the art and corresponds to the flow rate Q of the liquid, free of at least some of the impurities, divided by the cross-sectional area S of the decanter, in particular the widest cross-section in the case of a multi-cylinder decanter. In the case of a vertical decanter, the liquid surface velocity is adjusted so as to be at most equal to 0.85 times the settling rate, preferably 0.80 times the settling rate. In the case of a horizontal decanter, the liquid surface velocity varies with the settling rate but also with the length L of the horizontal decanter. The settling rate advantageously corresponds to the speed or average speed at which the impurity particles settle in the polymer solution. Thus, the settling rate more particularly varies with the gravity, density, diameter and concentration of the impurity particles considered, and with the viscosity of the medium, i.e. the polymer solution.

[0080] Very advantageously, the decanter(s) have an injection velocity of the polymer solution, in particular of the crude polymer solution or of the effluent enriched in polymer solution, of less than or equal to 1.00 m / s, preferably less than or equal to 0.10 m / s, preferably less than or equal to 0.05 m / s, and preferably greater than or equal to 0.0001, or even greater than or equal to 0.001 m / s.

[0081] Thus, in each decanter, the residence time can be adjusted to be between 1 and 200 hours, preferably between 1 hour and 50 hours. The residence time here corresponds to the ratio between the working volume of the decanter, i.e. the volume of material in the decanter, which varies with the degree of filling of the decanter considered, and the volumetric flow rate of the polymer solution, crude polymer solution or effluent enriched in polymer solution, fed to the decanter in question.

[0082] The tailings fraction can be recovered and treated in order to recover any solvent it can contain.

[0083] According to one embodiment of the application, the tailings fraction can contain a polymer impurity, in particular a thermoplastic plastic other than the target polyolefin, or even a polyolefin, such as polyethylene (PE), and in particular high-density polyethylene (HDPE), which is contained in the plastic feedstock but is not the specific polyolefin that is targeted. The tailings fraction can then advantageously be recovered and treated in another process, for example in a second process according to the application, in order to purify said thermoplastic plastic, in particular said polyolefin of the tailings fraction.

[0084] According to a particular embodiment, the aim of the process according to the application is to recover and purify the polypropylene (PP) of a plastic feedstock, possibly comprising other thermoplastics or even other polyolefins, such as PE and in particular HDPE. The conditioning step a) is adjusted so as to make it possible to selectively dissolve the polypropylene of 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, in particular HDPE, contained in the initial plastic feedstock, is dissolved in the dissolution solvent, while the majority of the PE, in particular 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 between 170 and 230°C, preferably between 180 and 220°C, and the dissolution pressure is preferably between 1.5 and 10.0 MPa absolute, preferably between 2.0 and 8.0 MPa absolute. Step b) then makes it possible to at least partially, and preferably completely, separate the thermoplastics other than the target PP, for example to make it possible to separate the PE or the HDPE. The tailings fraction recovered at the bottom of the decanter then advantageously comprises the thermoplastics other than the target PP, for example the PE and in particular the HDPE. Said tailings fraction is then very advantageously recovered and processed in a process, for example according to another recycling process according to the application, to separate and recover said thermoplastics, for example said PE or HDPE, in purified form.

[0085] The decanted polymer solution recovered at the end of step b) can optionally be subjected to a purification step or directly to the solvent-polymer separation step c). Preferably, the decanted polymer solution recovered at the end of step b) is subjected to a purification step b') which very preferably comprises a further solid-liquid separation and / or in particular the adsorption of soluble impurities.

[0086] Optional purification of the polymer solution step b') The treatment process according to the application can also comprise a further step of purifying the decanted polymer solution. This optional purification step b') comprises at least one of the sub-steps b'1), b'2), b'3) and b'4) described below: b'1) a further solid-liquid separation sub-step, b'2) a washing sub-step, by contact with a high-density solution, b'3) an extraction sub-step, by contact with an extraction solvent, b'4) a sub-step of adsorbing impurities, by contact with a solid adsorbent.

[0087] The incorporation of one or more of such steps b' and in particular sub-steps b'1 ), b'2), b'3), b'4) into the process according to the application very advantageously allows a maximum purification of the polymer solution and thus contributes to achieving the purity targets of the purified thermoplastic plastic stream recovered at the outlet of the process, i.e. to obtain an impurity content of the purified thermoplastic plastic stream of less than or equal to 5% by weight, preferably less than or equal to 1.0% by weight, preferably less than or equal to 0.5% by weight. This optional step b' thus makes it possible to obtain a "purified" polymer solution, which corresponds to a clarified polymer solution obtained from the additional solid-liquid separation sub-step b'1 ), to a washed polymer solution obtained from the washing sub-step b'2), to an extracted polymer solution obtained from the extraction sub-step b'3) or to a refined polymer solution obtained from the impurity adsorption sub-step b'4).

[0088] Preferably, when it is incorporated into the process according to the application, the purification step b' comprises the additional solid-liquid separation sub-step b'1 ) and / or the impurity adsorption sub-step b'4). According to a very particular embodiment, the process according to the application comprises the additional solid-liquid separation sub-step b'1 ) and / or the impurity adsorption sub-step b'4), and more particularly the additional solid-liquid separation sub-step b'1 ), followed by the impurity adsorption sub-step b'4).

[0089] Optional additional solid-liquid separation sub-step b'1 ) The purification process can comprise the additional solid-liquid separation sub-step b'1 ) to advantageously obtain at least one clarified polymer solution. The sub-step b'1 ) allows the removal of impurities that are generally not soluble in the dissolution solvent, which were not separated out during the decanting step b). Indeed, the insoluble impurities in the form of particles suspended in the crude polymer solution can have a density lower than or too close to the density of the polymer solution and thus cannot be separated, at least not efficiently, during the decanting step b); they can thus remain suspended in the decanted polymer solution at the end of step b). When it is incorporated into the process according to the application, the sub-step b'1 ) then makes it possible to improve the purification efficiency of the polymer solution and in particular the separation efficiency of the insoluble impurities.

[0090] In addition to the clarified polymer solution, the optional sub-step b'1 ) can produce an insoluble fraction. When an insoluble fraction is produced, it advantageously comprises the impurities that are generally insoluble and that were not separated out during the decanting step b).

[0091] The optional sub-step b'1 ) is advantageously carried out at a temperature between 100 and 300°C, preferably between 150 and 250°C, and preferably at a pressure between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute, and very preferably between 2.0 and 15.0 MPa absolute. Very advantageously, the sub-step b'1 ) of separating insoluble material is carried out under the temperature and pressure conditions at the outlet of the dissolution step a), i.e. at the dissolution temperature and dissolution pressure as defined above.

[0092] When it is incorporated into the process, the sub-step b'1 ) is preferably fed with the decanted polymer solution obtained from the decanting step b). According to another embodiment, the sub-step b'1 ) can be fed with the washed polymer solution obtained from the washing sub-step b'2).

[0093] Advantageously, the optional sub-step b'1 ) comprises a section comprising at least one solid-liquid separation device, for example selected from the group consisting of filters, sand filters, tangential filters, in particular using membranes and / or depth filters, optionally in the presence of a filtration aid such as diatomaceous earth, vortex separators, electrostatic separators, triboelectric separators, preferably filters, sand filters and / or electrostatic separators. Advantageously, self-cleaning filters can be used, cleaning or un-clogging allowing the removal of insoluble material using a solvent stream.

[0094] According to a particular embodiment, the optional sub-step b'1 ) comprises at least two, and generally less than five, solid-liquid separation devices in series and / or in parallel. The presence of at least two solid-liquid separation devices in series makes it possible to improve the removal of insoluble material, while the presence of devices in parallel makes it possible to manage maintenance and / or un-clogging operations of said devices.

[0095] Certain insoluble impurities, in particular certain pigments and mineral fillers, generally introduced during the formulation of the polymer, can be introduced in the form of particles of size less than 1 pm. This is the case, for example, for titanium dioxide, calcium carbonate and carbon black. According to one particular embodiment, the sub-step b'1 ) of separating insoluble material advantageously employs an electrostatic separator, which makes it possible to remove at least partially insoluble particles of size less than 1 pm. According to another particular embodiment, the sub-step b'1 ) of separating insoluble material comprises a sand filter to remove particles of different sizes, and in particular of size less than 1 pm. According to yet another particular embodiment, the sub-step b'1 ) of separating insoluble material employs a tangential filter, in particular using membranes and / or depth filters, optionally in the presence of a filtration aid such as diatomaceous earth.

[0096] The polymer solution, preferably the decanted polymer solution, fed to sub-step b'1 ) can also optionally comprise a second liquid phase, for example consisting of molten polymer, depending on the nature of the feedstock, and whose density is not sufficiently different from that of the polymer solution to be separated in step b). According to another particular embodiment, sub-step b'1 ) advantageously comprises a device for separating out the second liquid phase, preferably by means of at least one two- or three-phase separator.

[0097] Optional washing sub-step b'2) The treatment process can also optionally comprise a washing sub-step b'2) with a high-density solution, to advantageously obtain at least one washing effluent and one washed polymer solution. The washed polymer solution obtained at the end of sub-step b'2) advantageously comprises the purified target thermoplastic plastic sought to be recovered according to the application, dissolved in the dissolution solvent. Optionally, if sub-step b'2) is performed, the washed polymer solution can also comprise residual impurities, which are in particular soluble in the dissolution solvent and / or optionally traces of washing solvent.

[0098] When these two sub-steps are incorporated into the treatment process according to the application, washing sub-step b'2) can be incorporated upstream or downstream, preferably downstream, of the additional solid-liquid separation sub-step b'1 ).

[0099] When it is incorporated into the process, washing sub-step b'2) is fed with a high-density solution and the decanted polymer solution obtained from step b) or optionally the clarified polymer solution obtained from sub-step b'1 ). The polymer solution, in particular the decanted or optionally clarified polymer solution, fed to washing sub-step b'2) can comprise suspended insoluble impurities and / or dissolved impurities, which were not separated out in step b). These suspended or dissolved impurities can be partially or totally removed during washing sub-step b'2) by dissolution or precipitation and / or by entrainment in the high-density solution. Thus, when it is performed, this sub-step b'2) contributes to the treatment of the plastic feedstock and more particularly to the purification of the polymer solution.

[0100] The washing sub-step b'2) advantageously involves placing in contact the decanted or optionally clarified polymer solution (which is fed to sub-step b'2)) with a high density solution. Advantageously, the high density solution has a higher density than the polymer solution (i.e. the mixture comprises at least a target thermoplastic and a dissolving solvent, the target thermoplastic being dissolved in the dissolving solvent), in particular greater than or equal to 0.85, preferably greater than or equal to 0.9, preferably greater than or equal to 1.0. The high density solution can be an aqueous solution, which preferably comprises at least 50 wt% of water, preferably at least 75 wt% of water, very preferably at least 90 wt% of water. The pH of the aqueous solution can be adjusted with an acid or a base in order to promote the dissolution of certain impurities. The high density solution can also optionally be a solution comprising, preferably consisting of, an organic solvent having a density advantageously greater than or equal to 0.85, preferably greater than or equal to 0.9, preferably greater than or equal to 1.0, and in which the polymers of the plastic feedstock remain insoluble under the temperature and pressure conditions of sub-step b'2), for example an organic solvent selected from sulfolane or N-methylpyrrolidone (NMP), optionally as a mixture with water. Very preferably, the high density solution is an aqueous solution, which preferably comprises at least 50 wt% of water, preferably at least 75 wt% of water, very preferably at least 90 wt% of water.

[0101] The washing sub-step b'2) is advantageously carried out at a temperature between 100 and 300°C, preferably between 150 and 250°C, and very advantageously at a pressure between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 15.0 MPa absolute, and very preferably between 2.0 and 15.0 MPa absolute. Very advantageously, the washing sub-step b'2) is carried out at a dissolution temperature and a dissolution pressure.

[0102] In the washing sub-step b'2), when it is incorporated into the process, 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 fed to sub-step b'2) is advantageously between 0.05 and 20.0, preferably between 0.1 and 10.0, and preferably between 0.5 and 3.0. The placing in contact between the decanted or optionally clarified polymer solution and the high density solution can be carried out at several points in the equipment used, i.e. via several injections of the decanted or clarified polymer solution and / or of the high density solution at different points along the equipment; the sum of the injected streams is then taken into account when calculating the ratio.

[0103] Sub-step b'2) can be carried out in one or more pieces of equipment, placed in contact with the high-density solution and / or with separation equipment, so that at least one wash effluent and one washed polymer solution can be recovered. This equipment is well known, such as stirred reactors, static mixers, decanting mixers, two- or three-phase separation vessels, co- or counter-current washing columns, plate columns, stirred columns, packed columns, pulse columns, etc., each type of equipment possibly comprising one or more pieces of equipment used alone or in combination with another type of equipment.

[0104] According to a preferred embodiment, washing sub-step b'2) is carried out in a counter-current washing column, in which the high-density solution is injected, preferably in one half, preferably one third, of the column closest to the top of the column, and the decanted or clarified polymer solution is injected, preferably in one half, preferably one third, of the column closest to the bottom of the column. According to this embodiment, at least one washed polymer solution and one wash effluent can be recovered.

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

[0106] According to another embodiment, washing sub-step b'2) is carried out in a mixer-decanter comprising a mixing zone (to place the high-density solution and the decanted or clarified polymer solution in contact) and a decanting zone (so that it is possible to recover the washed polymer solution and the wash effluent).

[0107] At the end of washing sub-step b'2), the wash effluent obtained advantageously comprises the impurities dissolved in the high-density solvent and / or the insoluble impurities entrained in the wash effluent. The wash effluent can be reprocessed in a washing treatment section, on the one hand at least partially separating the dissolved and / or entrained impurities and optionally purifying the wash effluent to obtain a purified high-density solution, and on the other hand to recycle at least a portion of the purified wash solution. This washing treatment section can comprise one or more pieces of equipment well known for solid-liquid separation, such as separation vessels, decanters, centrifugal decanters, centrifuges or filters. When the high-density solution is an aqueous solution, the wash effluent can also be sent outside the process, for example to a wastewater treatment station.

[0108] Optional extraction step b'3) The process according to the present application can comprise an extraction substep b'3) by contact placement with an extraction solvent to obtain at least one extracted polymer solution and one spent solvent. The extracted polymer solution obtained at the end of substep b'3) advantageously comprises the purified target thermoplastic polymer sought to be recovered according to the present application, dissolved in the dissolving solvent. The spent solvent advantageously is charged with impurities. Optionally, if substeps b2) and / or b3) are performed, the extracted polymer solution can also comprise residual impurities, which can be soluble in the dissolving solvent and / or traces of the washing solvent and / or the extraction solvent, in particular.

[0109] When it is incorporated in the process according to the present application, extraction substep b'3) is advantageously located between decantation step b) and solvent-polymer separation step c), optionally upstream or downstream of adsorption substep b'4) if the latter is also incorporated in the process, and preferably downstream of the further solid-liquid separation substep b'1).

[0110] Extraction substep b'3) is advantageously fed with an 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 polymer solution obtained from adsorption substep b'4). The polymer solution, preferably the decanted polymer solution or the optionally clarified, washed or refined solution, fed to substep b'3) can thus also comprise dissolved impurities. These dissolved impurities can be partially or totally removed during extraction substep b'3) by contact placement with the extraction solvent.

[0111] When it is incorporated in the process according to the present application, extraction substep b'3) advantageously involves at least one extraction section, preferably between one and five extraction sections, very preferably one extraction section.

[0112] The mass flow rate of the extraction solvent and the mass flow rate of the polymer solution, preferably the decanted polymer solution or the optionally clarified, washed or refined polymer solution, fed to b'3) are advantageously in a mass ratio between 0.05 and 20.0, preferably between 0.1 and 10.0 and preferably between 0.2 and 5.0. The contact placement between the polymer solution and the extraction solvent fed to substep b'3) can be performed at several points in the extraction section, i.e. via several injections of the polymer solution and / or the extraction solvent at different points along the extraction section; the sum of the injected streams is then considered when calculating the ratio.

[0113] The extraction solvent used in sub-step b'3) advantageously comprises an organic solvent or a mixture of organic solvents. Preferably, the extraction solvent comprises, and preferably consists of, at least one organic compound, preferably aliphatic and in particular alkane, preferably linear or branched, based on hydrocarbons. Preferably, the extraction solvent comprises at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight, of at least one organic compound, preferably aliphatic and in particular alkane, preferably linear or branched, based on hydrocarbons, the percentages being expressed with respect to the total weight of the solvent dissolved (maximum value of 100%). Preferably, the extraction solvent comprises at least one organic compound, preferably aliphatic and in particular alkane, based on hydrocarbons, having a boiling point of between -50 and 250°C, preferably between -15 and 150°C, preferably between -1 and 110°C and preferably between 20 and 100°C (at atmospheric pressure, in particular at 0.1 MPa). Preferably, the extraction solvent comprises, preferably consists of, at least one organic compound, preferably aliphatic and in particular alkane, preferably linear or branched, based on hydrocarbons, containing between 3 and 12 carbon atoms, preferably between 4 and 8 carbon atoms. For example, the extraction solvent comprises a compound chosen from butane, isomers of pentane, hexane and heptane. The extraction solvent can comprise, preferably consist of, a mixture of butane, isomers of pentane, hexane, heptane and octane, and preferably the content of said mixture of isomers in the extraction solvent is greater than or equal to 80% by weight, preferably greater than or equal to 95% by weight, preferably greater than or equal to 98% by weight, with respect to the total weight of the extraction solvent. Preferably, the extraction solvent is an alkane aliphatic compound having a critical temperature (temperature of the critical point of said pure hydrocarbon-based compound) preferably between 95 and 350°C, preferably between 130 and 300°C, preferably between 180 and 285°C.

[0114] Very preferably, the extraction solvent used in optional sub-step b'3) is the same solvent as the dissolution solvent used in step a), optionally in a different physical state (for example supercritical form with respect to the dissolution solvent in liquid form), in order to facilitate the management of the solvents and in particular their purification and their recycling to in particular the dissolution step a) and optionally to the extraction sub-step b'3). Another advantage of using the same dissolution solvent and extraction solvent in the same or different physical state is, in addition to facilitating the management of the solvents involved in the process according to the application, in particular the recovery of the solvents, their treatment and their recycling to at least one step of the process, and to limit the energy consumption and in particular the costs generated by the treatment and purification of the solvents.

[0115] The extraction section(s) of optional sub-step b'3) can comprise one or more pieces of equipment for placing in contact with the extraction solvent and / or with a separation device for recovering at least one spent solvent, in particular loaded with impurities, and an extracted polymer solution. Such equipment is well known, for example stirred reactors, static mixers, decanting mixers, two- or three-phase separation vessels, co- or counter-current washing columns, plate columns, stirred columns, packed columns, pulse columns, etc., each type of equipment possibly comprising one or more pieces of equipment used alone or in combination with another type of equipment.

[0116] According to a preferred embodiment of b'3), the extraction is carried out in a counter-current extraction column into which the extraction solvent is injected on the one hand and the polymer solution fed to sub-step b'3) on the other hand. According to this embodiment, at least one extracted polymer solution on the one hand and a spent solvent, in particular loaded with impurities, on the other hand can be recovered. Preferably, the polymer solution fed to b'3) (preferably a decanted or optionally clarified, washed or refined polymer solution) is injected into the upper half, preferably the upper third, of the column (i.e. the half, preferably the third, closest to the top of the counter-current extraction column), while the extraction solvent is injected into the lower half, preferably the lower third, of the column (i.e. the half, preferably the third, closest to the bottom of the counter-current extraction column).

[0117] The streams at the inlet and / or outlet of the counter-current extraction column can be divided along several injection points and / or withdrawal points of the column.

[0118] According to another embodiment of b'3), the extraction is carried out in a mixer-decanter advantageously comprising a stirred mixing zone for placing in contact the extraction solvent and the polymer solution fed to b'3) (preferably a decanted or optionally clarified, washed or refined polymer solution) and a decanting zone making it possible to recover on the one hand an extracted polymer solution and on the other hand a spent solvent.

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

[0120] According to a preferred embodiment of b'3), the sub-step b'3) of extraction involves a liquid / liquid extraction section. Preferably, the liquid / liquid extraction section is operated at a temperature between 100 °C and 300 °C, preferably between 150 °C and 250 °C, and at a pressure between 1.0 and 100.0 MPa absolute pressure, preferably between 1.0 and 25.0 MPa absolute pressure, preferably between 1.5 and 18.0 MPa absolute pressure, and very preferably between 2.0 and 15.0 MPa absolute pressure. In any case, in this embodiment, the temperature and pressure conditions are adjusted such that the extraction solvent is in liquid form and the dissolving solvent is preferably also in liquid form. Very advantageously, especially when the extraction solvent is identical to the dissolving solvent, the liquid / liquid extraction is carried out at different temperature and pressure conditions than the dissolving conditions achieved in step a), in particular at a temperature higher than the dissolving temperature and / or at a pressure lower than the dissolving pressure, so as to thus be in the two-phase region of the corresponding polymer-solvent diagram.

[0121] According to another preferred embodiment of b'3), the sub-step b'3) of extraction comprises a section for extraction at specific temperature and pressure conditions, wherein the extraction solvent is advantageously at least partially in supercritical form. Such extraction can be referred to as supercritical extraction. In this embodiment, the extraction is carried out by placing the polymer solution, preferably the decanted or optionally clarified, washed or refined polymer solution, in contact with the extraction solvent, advantageously at temperature and pressure conditions such that it is possible to obtain mainly a supercritical phase consisting of the extraction solvent, i.e. preferably at least 50 wt%, preferably at least 70 wt%, preferably at least 90 wt%. In other words, in this embodiment, the extraction is carried out by placing the polymer solution, preferably the decanted or optionally clarified, washed or refined polymer solution, in contact with an extraction solvent which is at least partially, preferably entirely, in supercritical form. Such supercritical extraction sub-step b'3) advantageously allows an efficient purification of the polymer solution, in particular due to the very high affinity of organic impurities, such as some additives, in particular certain colorants, plasticizers, etc., for the supercritical phase. The use of an extraction solvent in supercritical form also enables to generate a significant density difference between the supercritical phase and the polymer solution in liquid form, which facilitates the separation by decanting between the supercritical phase and the liquid phase, and which thus contributes to the purification of the polymer solution.

[0122] In this other preferred embodiment, the sub-step b'3) uses an extraction solvent comprising at least 80 wt%, preferably at least 95 wt%, preferably 98 wt%, of at least one aliphatic paraffinic hydrocarbon-based compound (or alkane) (100% being the maximum, said percentages being expressed with respect to the total weight of the extraction solvent), said extraction solvent having a critical temperature of preferably between 95 and 350 °C, preferably between 130 and 300 °C, preferably between 180 and 285 °C.

[0123] Advantageously, the supercritical extraction sub-step b'3) of this other particular embodiment is carried out at a temperature of preferably between 150 and 300°C, preferably between 180 and 280°C, and at a pressure of preferably between 2.0 and 100.0 MPa absolute, preferably between 2.0 and 25.0 MPa absolute, preferably between 2.0 and 18.0 MPa absolute, and very preferably between 3.0 and 15.0 MPa absolute. Very preferably, the operating pressure of this supercritical extraction sub-step b'3) is between 2.7 and 7.5 MPa absolute, preferably between 3.0 and 5.5 MPa absolute. In any case, in this embodiment, the temperature and pressure conditions are adjusted, in particular in the conditioning section provided in the extraction sub-step b'3) upstream of the extraction section, so that the extraction solvent is at least partially in a supercritical state in the extraction section.

[0124] In a particular embodiment, the extraction sub-step b'3) implements a supercritical extraction, and the extraction solvent is identical to the dissolution solvent, except for the fact that the extraction solvent is at least partially in a supercritical phase. In this case of supercritical extraction, the dissolution solvent can at least partially become in a supercritical form, advantageously optimizing the decantation during the extraction step, more particularly at each extraction phase or plateau between the liquid and supercritical phases, which thus makes it possible to maximize the purification.

[0125] Advantageously, at the end of the extraction sub-step b'3), the waste solvent obtained carries, in particular, the soluble impurities. It can be reprocessed in the organic treatment section, so that, on the one hand, the impurities can be at least partially separated and the solvent purified to obtain a purified extraction solvent, and, on the other hand, at least part of the purified extraction solvent is recycled to the inlet of the extraction b'3) and / or to the inlet of the dissolution step a), in the case where the dissolution solvent and the extraction solvent are identical. The waste solvent can be treated according to any method known to the person skilled in the art, for example one or more of distillation, evaporation, extraction, adsorption, crystallization and precipitation of insoluble substances, or by purging.

[0126] Optional adsorption sub-step b'4) The treatment process according to the application can comprise an adsorption sub-step b'4) for obtaining a refined polymer solution. The refined polymer solution obtained at the end of the optional sub-step b'4) advantageously comprises the target thermoplastic polymer, in particular the target polyolefin, dissolved in the dissolution solvent.

[0127] When it is incorporated into the process according to the application, the adsorption sub-step b'4) is preferably carried out downstream of the decanting step b) and upstream of the solvent-polymer separation step c). However, it can be carried out upstream of the decanting step b) and / or during the dissolving step a), by introducing the adsorbent particles as a mixture with the crude polymer solution, the said adsorbent particles being removed during the decanting step b) and possibly during the additional solid-liquid separation sub-step b'1) or even during the washing sub-step b'2). The adsorption sub-step b'4) can also optionally be carried out upstream or downstream of the extraction sub-step b'3). Thus, when it is incorporated into the process according to the application, the adsorption sub-step b'4) is carried out by contacting the polymer solution fed to the adsorption sub-step b'4) with one or more adsorbents.

[0128] The optional adsorption sub-step b'4) advantageously comprises an adsorption section operated in the presence of at least one adsorbent, which is preferably solid and in particular in the form of a fixed bed, an entrained bed (or slurry, i.e. in the form of particles introduced into and entrained in the stream to be purified) or in the form of a boiling bed, preferably in the form of a fixed bed or an entrained bed. The adsorbent(s) used in the sub-step b) is preferably alumina, silica, silica-alumina, activated carbon, decolorizing earth, or a mixture thereof, preferably activated carbon, decolorizing earth, or a mixture thereof, preferably in the form of a fixed bed or an entrained bed, the circulation of the said stream possibly being ascending or descending.

[0129] Advantageously, when it is incorporated into the process, the adsorption sub-step b'4) is carried out at a temperature between 100 and 300°C, preferably between 150 and 250°C, and at a pressure between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute, and very preferably between 2.0 and 15.0 MPa absolute. Very advantageously, the adsorption sub-step b'4) is carried out at the dissolving temperature and pressure conditions, i.e. at the dissolving temperature and dissolving pressure reached in step a). Preferably, in the optional sub-step b'4), the hourly space velocity (or HSV), which corresponds to the ratio between the volumetric flow rate of the polymer solution fed to b'4) and the volume of adsorbent, is between 0.05 and 10 h -1 -1 Advantageously in b'4).

[0130] ​According to a particular embodiment of sub-step b'4), the adsorption section can comprise one or more fixed bed adsorbents, for example in the form of an adsorption tower, preferably at least two adsorption towers, preferably two to four adsorption towers, said adsorption towers comprising said adsorbent(s). When the adsorption section comprises two adsorption towers, one mode of operation can be a mode according to the specific terminology called "swing" operation, wherein one tower is on-line, i.e. in use, while the other tower is on standby. When the adsorbent of the on-line tower is exhausted, this tower is isolated, while the tower on standby is put on-line, i.e. in use. The spent adsorbent can then be regenerated in situ and / or replaced with fresh adsorbent, so that the tower containing this adsorbent can be brought on-line again as soon as the other tower is isolated.

[0131] Another mode of operation of this particular embodiment b'4) is to have at least two adsorption towers operating in series. When the adsorbent of the tower placed in first position is exhausted, this first tower is isolated and the spent adsorbent is regenerated in situ or replaced with fresh adsorbent. This tower is then re-introduced on-line with the last position, and so on. This mode of operation is called the Permutable mode, or PRS for Permutable Reactor System, or called "lead and lag". The combination of at least two adsorption towers makes it possible to overcome possible and potential rapid poisoning and / or clogging of the adsorbent due to the combined effect of impurities, contaminants and insolubles that can be present in the stream to be treated. The presence of at least two adsorption towers is justified by the fact that it facilitates the replacement and / or regeneration of the adsorbent, advantageously without interruption of the process, but also makes it possible to control the costs and limit the consumption of adsorbent.

[0132] Solvent-polymer separation step c) According to the present application, the process comprises a solvent-polymer separation step c) to obtain at least one stream of purified thermoplastic polymer, more particularly at least one stream of purified polyolefin, and preferably at least one solvent fraction. This step c) is downstream of the decanting step b), or possibly of the step b' of purification of the decanted polymer solution.

[0133] The solvent-polymer separation step c) involves at least partially, preferably mainly, or even completely separating the solvent(s) contained in the decanted or purified polymer solution fed to step c), in particular the solubilization solvent, so as to recover the target thermoplastic already at least partially, preferably completely, free of impurities and solubilization solvent and possibly free of the other solvent(s) used in the process, i.e. the extraction solvent and / or the high-density solution. The term "mainly" is understood to mean at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, very preferably at least 95% by weight, relative to the weight of the solvent(s) contained in the decanted or purified polymer solution fed to step c), in particular the weight of the solubilization solvent and optionally the weight of the extraction solvent and / or the high-density solution contained in the decanted or purified polymer solution fed to step c).

[0134] Any solvent-polymer separation process known to those skilled in the art can be carried out, in particular any process capable of causing a phase change of the polymer or the solvent(s). The solvent(s) can be separated, for example, by flashing of the solvent, atomization, stripping, crystallization of the polymer and solid-liquid separation, delamination, density difference and in particular decantation or centrifugation, etc. Step c) can be implemented with several separation operations in series. For example, step c) can comprise performing the solvent-polymer separation by delamination of at least part of the solvent(s) in supercritical form, the solvent(s) being in supercritical form after adjustment of the temperature and / or pressure conditions in step c), preferably adjustment of the pressure and temperature maintained between 100 and 300°C, preferably between 150 and 250°C, so as to place at least one compound of the solvent(s) in supercritical conditions, followed by at least one separation of the residual solvent by evaporation, in particular under pressure conditions lower than those used to transform the solvent into a supercritical state, in particular under a pressure of between 4 and 0.000005 MPa (i.e. 5 Pa), preferably between 3 and 0.000005 MPa (i.e. 5 Pa), the temperature possibly being maintained between 100 and 300°C, preferably between 150 and 250°C.

[0135] The stream of purified thermoplastic polymer obtained at the end of step c) can correspond to a concentrated polymer solution, or to a purified thermoplastic polymer in liquid (i.e. molten) or solid state. The solvent-polymer separation step c) can also optionally comprise a conditioning section for conditioning the thermoplastic, in particular the target polyolefin, recovered in solid form and more particularly in solid particulate form. In this possible conditioning section, the purified thermoplastic polymer recovered is cooled, advantageously to a temperature below the melting point of the polymer, so as to obtain a fraction comprising the thermoplastic in solid form.

[0136] The solvent-polymer separation step c) also involves at least partially, preferably predominantly, and preferably entirely, recovering the solvent(s) contained in the decanted or purified polymer solution fed to step c), and in particular the dissolution solvent, and optionally the extraction solvent and / or the high-density solution. The term "predominantly" is understood to mean at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, very preferably at least 95% by weight, relative to the weight of the solvent(s) contained in the decanted or purified polymer solution fed to step c). Step c) thus advantageously makes it possible to obtain at least one solvent fraction. The solvent-polymer separation step c) also optionally involves purifying the recovered solvent fraction and recycling it, in particular upstream of the dissolution step a), and possibly upstream of the sub-step b'2) and / or the sub-step b'3).

[0137] Very advantageously, the solvent fraction recovered at the end of step c) can be treated in an organic treatment section located at the end of step c) in order to purify it and obtain a purified solvent, in particular a purified dissolution solvent, and optionally a purified high-density solution and / or a purified extraction solvent, which can advantageously be recycled to the dissolution step a) and / or optionally to the washing sub-step b'2) or the extraction sub-step b'3). Said optional organic treatment section at the end of step c) can employ any method known to the person skilled in the art, such as one or more of distillation, evaporation, liquid-liquid extraction, adsorption, crystallization and precipitation of insolubles, or by draining.

[0138] The process according to the application thus makes it possible to obtain a stream of purified thermoplastic polymers (and more particularly a stream of purified polyolefins) from any type of plastic feedstock and in particular from plastic waste. In particular, the process according to the application makes it possible to remove at least 70% by weight, preferably at least 80% by weight, of impurities, and in particular inorganic impurities contained in the plastic feedstock. The process according to the application also makes it possible to remove organic compounds and in particular insoluble polymers other than the target thermoplastic plastic. Furthermore, very advantageously, the stream of purified thermoplastic plastic (in particular purified polyolefin) obtained at the end of the process is less colored or even discolored relative to the plastic feedstock fed to the process according to the application. The stream of purified thermoplastic polymers obtained at the end of the process according to the application can then be used in any application, for example as a substitute for the same polymer in virgin form. The stream of purified thermoplastic polymers obtained continuously via the process according to the application thus has a sufficiently low impurity content to enable it to be used in any application.

[0139] Very preferably, the stream of purified thermoplastic polymer obtained at the end of the process according to the application advantageously has an impurity content of less than or equal to 5% by weight, very advantageously less than or equal to 1.0% by weight of impurities or even less than or equal to 0.5% by weight of impurities. Very advantageously, the stream of purified thermoplastic polymer obtained at the end of the process according to the application has a residual solvent content (in particular the dissolved solvent) of less than or equal to 5% by weight, preferably less than or equal to 1.0% by weight, preferably less than or equal to 0.1% by weight, relative to the total weight of the stream of purified thermoplastic, a content of less than or equal to or even less than or equal to 500 ppm by weight.

[0140] Device The present application also relates to a device for treating a plastic feedstock to obtain a stream of purified thermoplastic polymer, comprising: - a device for contacting and at least partially dissolving the plastic feedstock in a dissolving solvent, to obtain a crude polymer solution, such as an extruder, static mixer(s), one or more continuous stirred tank reactors (CSTR) equipped with suitable stirring system(s); - a decanting device comprising at least one decanter (also called static decanter), preferably from one to ten decanters, preferably from two to five decanters; When the decanting device comprises several decanters, the decanters are operated in series or in parallel, preferably in parallel, the decanter(s) are vertical decanters or horizontal decanters, preferably the shape is a cylinder or substantially cylindrical, or even a multi-cylinder, preferably wherein the ratio L / D between the total height or length L of the decanter and the diameter (or width) D of the decanter is between 0.5 and 12, preferably between 1.0 and 6.0, the decanter(s) comprise a feed point for feeding the polymer solution, in particular for feeding the crude polymer solution or the effluent rich in polymer solution, Advantageously, the feed point of the decanter or of the first decanter of the series of decanters or alternatively the feed point of each decanter in parallel is connected to said device for contacting and dissolving, so as to feed at least a part or all of said crude polymer solution to the decanter(s), Preferably, when the decanter in question is a vertical decanter, the feed point of said decanter is advantageously located between a quarter of the height of the decanter (starting from the top (or upper end) of the vertical decanter) and three quarters of the height of the decanter (starting from the top (or upper end) of the vertical decanter), preferably between a third of the height of the decanter (starting from the top (or upper end) of the vertical decanter) and two thirds of the height of the decanter (starting from the top (or upper end) of the vertical decanter), said feed point then defining two zones in the vertical decanter in question, an upper zone between the feed point and the top (or upper end) of the vertical decanter, and a lower zone between the feed point and the bottom (or lower end) of the vertical decanter, Preferably, when the decanter in question is a horizontal decanter, the feed point of said decanter is advantageously located close to one end of the horizontal decanter in question, that is to say, at or close to one end of the horizontal decanter, preferably in the region between one of the two ends of the horizontal decanter and a third of the length of the decanter from said end, preferably between one of the two ends of the horizontal decanter and a quarter of the length of the decanter from said end.

[0141] The decanter(s) comprise a first outlet for the effluent of the polymer-rich solution and a second outlet for the tail stream, When the decanting device comprises several decanters in series, the first outlet of the downstream decanter (i.e. the outlet for the effluent of the polymer-rich solution) is advantageously connected to the feed point of the immediately upstream decanter (i.e. the first outlet of the decanter i is connected to the feed point of the decanter i+1), except for the last decanter in series, the first outlet of which (i.e. the outlet for the effluent of the polymer-rich solution) is connected to a device located downstream of the decanting device, in particular a solvent-polymer separation device or an optional additional purification system, When the decanting device comprises several decanters in parallel, all the first outlets of said decanters (i.e. the outlets for the effluent of the polymer-rich solution) are connected to each other and to a mixing system for mixing all the effluents of the polymer-rich solution recovered at the outlets of the decanters in parallel, said mixing system being very advantageously connected to a device located downstream of the decanting device, in particular a solvent-polymer separation device or an optional additional purification system, Preferably, when the decanter in question is a vertical decanter, the first outlet of said decanter, i.e. the outlet for the effluent enriched in polymer solution, is advantageously located in the upper region of the vertical decanter in question, that is to say in the region between the point of feed of the vertical decanter and the top (or upper end), and the second outlet is advantageously located in the lower region of the vertical decanter, preferably in the bottom (or lower end) of the vertical decanter, Preferably, when the decanter in question is a horizontal decanter, the first outlet of said decanter, i.e. the outlet for the effluent enriched in polymer solution, and preferably the second outlet, is advantageously located close to the end opposite the point of feed, that is to say at or close to the end opposite the end at which the point of feed is located, preferably said first outlet and preferably said second outlet being located in the region between the end opposite the point of feed and one third of the length of the decanter from said opposite end, preferably between the end opposite the point of feed and one quarter of the length of the decanter from said opposite end.

[0142] Said decanter(s) are designed to have: - a liquid superficial velocity ranging between 1 x 10 -7 and 1.000 x 10 -2 m / s, preferably between 1.0 x 10 -6 and 1.000 x 10 -2 m / s, preferably between 1.0 x 10 -5 and 6.000 x 10 -3 m / s, preferably between 2.0 x 10 -5 and 5.000 x 10 -3 m / s, very preferably between 2.0 x 10 -5 and 9.00 x 10 -4 m / s, in particular between 2.0 x 10 -5 and 5.00 x 10 -4 m / s, - preferably an injection velocity less than or equal to 1.00 m / s, preferably less than or equal to 0.10 m / s, preferably less than or equal to 0.05 m / s, and preferably greater than or equal to 0.001 m / s; - optionally an additional purification system, located downstream of the decanting device, and comprising in particular an additional solid-liquid separation device, such as a filter, a washing device, an extraction device and / or an adsorption device, When said additional purification system comprises several devices, said devices are operated in series with one another; - a solvent-polymer separation device, located downstream of the decanting device, for separating the stream comprising, in particular, the dissolved solvent and the purified thermoplastic polymer, in particular the purified polyolefin, said solvent-polymer separation device being advantageously connected to said decanting device or optionally to said additional purification system.

[0143] Preferably, the treatment device comprises at least one additional purification system, which preferably comprises an additional solid-liquid separation device, such as a filter and / or an adsorption device, preferably an additional solid-liquid separation device, and then an adsorption device.

[0144] The device for treating plastic raw material also advantageously comprises means for transporting between said device and device.

[0145] The following examples and figures illustrate the application, in particular specific embodiments of the application, without limiting the scope thereof.

[0146] List of figures Figure 1 Figure representing a decanter used according to an embodiment of the method according to the application, wherein the decanter is a vertical decanter of substantially cylindrical shape, the bottom of said decanter being conical and the top end being hemispherical in shape. The decanter has a length L and a diameter D. The polymer solution is fed at the feed point 1. The effluent enriched in polymer solution is recovered at point 2 and the tailings are purged at point 3.

[0147] Figure 2 Figure representing a decanter used according to another embodiment of the method according to the application, wherein the decanter is a horizontal decanter of substantially cylindrical shape, having hemispherical shaped ends. The decanter has a length L and a diameter D. The polymer solution is fed at the feed point 1. The effluent enriched in polymer solution is recovered at point 2 and the tailings are purged at point 3. Example

[0148] In the following examples, the analyses carried out on the raw materials and on the products obtained are as follows: - ash content, which gives an indication of the inorganic impurities content, determined by thermogravimetric analysis (or TGA). The ash content is determined by thermogravimetric analysis (or TGA) using a Perkin Elmer TGA 8000 device according to the ISO 11358-1 standard (2014). A sample of 10-20 mg of material is placed on a platinum plate. The temperature is equilibrated at 50°C for 10 minutes, then increased to 950°C at a heating rate of 20°C / min under nitrogen flow. The ash content corresponds to the weight determined at 850°C relative to the weight of the starting sample, expressed as a percentage by weight (wt%); - content of organic compounds, in particular Irganox® 1010, Irgafos® 168, oxidized Irgafos® 168, determined by high performance liquid chromatography (HPLC); - the color parameters are expressed in the CIE L*a*b* reference system (defined by the International Commission on Illumination; CIE), determined by colorimetry (according to the ISO 11664-4 standard), wherein: o the luminance (or lightness) parameter L*, such that the closer L* is to 100, the clearer or more transparent the analyzed solid is; on the contrary, the closer L* is to 0, the more opaque the analyzed solid is; o the parameter a* (corresponding to the green-red axis), which measures the color range from green (negative values) to red (positive values); the target value for a* is a value close to 0; o the parameter b* (corresponding to the blue-yellow axis), which measures the color range from blue (negative values) to yellow (positive values); the target value for b* is a value close to 0.

[0149] The L*a*b* values were determined on a solid sample of about 20 g of cryogenically milled material using a standard Konica / Minolta Colorimeter CM-3700 A instrument.

[0150] Example 1 (according to the application) Dissolution step a): The raw material from plastic waste and containing 95 wt% of polypropylene (PP) was introduced in the form of flakes into an extruder heated to 200°C. At the outlet of the extruder, the raw material was at least partially in molten form and was mixed with n-heptane used as solvent and previously heated to 200°C at a solvent / raw material weight ratio of 5 / 1. The mixture comprising solvent and raw material was introduced into a stirred reactor and heated to 200°C and maintained at 2.0 MPa absolute pressure for a residence time of 1 hour. A crude polymer solution was then obtained.

[0151] Decantation step b): The crude polymer solution obtained from the dissolution step a) was then subjected to a decantation step b): The crude polymer solution was continuously withdrawn from the stirred reactor and injected into a static, vertical decanter, wherein the ratio L / D between the total height and the diameter of the substantially cylindrical decanter was 3.1. Said decanter was operated at: - a temperature of 200°C - a pressure of 2.0 MPa - an injection speed of 0.04 m / s - an upward separation tank speed of 0.07 mm / s - a residence time of 1 hour.

[0152] A "filter cake" is deposited at the bottom of the decanter: it comprises insoluble compounds, inorganic solids, a part of the solvent and organic elements. The "filter cake" is sequentially drained at a frequency of 0.8 mHz.

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

[0154] At the outlet of the process, a solid A is obtained at atmospheric temperature and pressure. Solid A consists of polypropylene (PP). Solid A is analyzed. The results are summarized in the following table 1. Table 1 compares the measured properties of the raw material and of the obtained solid A, in particular the ash content which gives an indication of the inorganic impurities content, the colorimetric parameters L, a and b and the relative weight amounts of the three organic compounds (Irganox® 1010, Irgafos® 168 and oxidized Irgafos® 168).

[0155] Table 1 .

[0156] The obtained solid A consisting of polypropylene (PP) is purified with respect to the plastic raw material (see table 1) because: - more than 80 wt% of inorganic impurities have been removed (100 x (1.09-0.2) / 1.09 = 81.65%) (solid A contains more than 80 wt% less inorganic impurities with respect to the plastic raw material); - the content of the three organic impurities tested (Irganox® 1010, Irgafos® 168 and oxidized Irgafos® 168) is reduced in solid A (194 wtppm, 138 wtppm and 505 wtppm, respectively) with respect to the plastic raw material (1831 wtppm, 628 wtppm and 1899 wtppm, respectively); - solid A is also less colored than the raw material: the luminosity parameter L for solid A (88.65) is increased and close to 100 with respect to the luminosity parameter measured for the raw material (57.47), while the parameters a and b for solid A (a = 1.23 and b = 7.76) are closer to the 0 value than for the raw material (14.68 and 10.83, respectively).

[0157] Example 2 (according to the application) A raw material from plastic waste, of the same type as in Example 1 (comprising 95 wt% of polypropylene (PP)) was introduced in the form of flakes into an extruder heated to 200°C. At the outlet of the extruder, the raw material was at least partially in molten form and was mixed with n-heptane used as solvent and preheated to 200°C in a solvent / raw material weight ratio of 5 / 1. The mixture was then introduced into a stirred reactor and heated to 200°C and maintained at 2.0 MPa absolute pressure for a residence time of 1 hour. A crude polymer solution was then obtained.

[0158] The crude polymer solution was continuously withdrawn from the stirred reactor and injected into a static vertical decanter, wherein the ratio L / D between the total height of the decanter and the diameter of the decanter which is substantially cylindrical, was 3.1. The decanter was operated at: - a temperature of 200°C - a pressure of 2.0 MPa - an injection velocity of 0.04 m / s - an upward velocity of the separation tank of 0.07 mm / s - a residence time of 1 hour.

[0159] The impurities were deposited at the bottom of the decanter, forming a "cake" or "bed" which was removed in batches at a frequency of 0.8 mHz.

[0160] At the outlet of the decanter, the decanted polymer solution was filtered through a filter having a 10 pm mesh aperture and then through a filter having a 1 pm mesh aperture.

[0161] The filtered polymer solution was then sent to an adsorption column containing a bed of activated carbon and operated at 200°C and 2.0 MPa.

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

[0163] At the outlet of the process and at atmospheric temperature and pressure, a solid B was obtained. Solid B consisted of polypropylene (PP). Solid B was analyzed in the same way as solid A of Example 1. The results are summarized in Table 2 below, which compares the measured properties of the raw material and of the obtained solid B, in particular the ash content which gives an indication of the inorganic impurities content, the colorimetric parameters L, a and b and the amounts of relative weights of the three organic compounds (Irganox® 1010, Irgafos® 168 and oxidized Irgafos® 168).

[0164] [Table 2] .

[0165] The solid B consisting of polypropylene (PP) obtained is purified with respect to the plastic feedstock (see Table 2) because: - about 100% by weight of inorganic impurities have been removed (100 x (1.1 - 0.0) / 1.1 = 100%); - the content of the three organic impurities tested (Irganox® 1010, Irgafos® 168 and oxidized Irgafos® 168) is also reduced in solid B (158 ppm by weight, 113 ppm by weight and 494 ppm by weight, respectively) with respect to the plastic feedstock (1831 ppm by weight, 628 ppm by weight and 1899 ppm by weight, respectively); - solid B is also less colored than the feedstock and the colorimetric parameters are improved: the lightness parameter L for solid B (98.89) increases and is close to 100 with respect to the lightness parameter measured for the feedstock (57.47), while the parameters a and b for solid B (a = -0.29 and b = 4.61) are closer to the 0 value with respect to the feedstock (14.68 and 10.83, respectively).

Claims

1. A method for treating plastic raw materials, comprising: a) The step of dissolving the plastic raw material in a dissolving solvent, wherein step a) is carried out at a dissolving temperature between 100°C and 300°C and at a dissolving pressure between 1.0 and 100.0 MPa absolute pressure, to obtain at least one crude polymer solution; b) The step of decanting the crude polymer solution to obtain a decanted polymer solution and a tailings portion. Step b) is operated at a temperature between 100°C and 300°C and a pressure between 1.0 and 100.0 MPa absolute pressure, and using at least one decanter. When step b) involves several decanters, the decanters may operate in series or in parallel. The decanter, or the first decanter of a series of decanters, or the decanters in parallel, feeds at least a portion of the crude polymer solution. The effluent rich in polymer solution is recovered at the outlet of the decanter or each decanter. The polymer-rich effluent recovered at the outlet of the decanter, or at the outlet of the last decanter in a series operation, or at the outlets of all polymer-rich effluents recovered in a parallel operation, constitutes the decanted polymer solution. The tailings stream is recovered at the outlet of the decanter or each decanter, and all recovered tailings stream constitutes the tailings portion. The at least one decanter has a liquid surface velocity range of 1x10. -7 Up to 1.000x10 -2 Between m / s; then c) A solvent / polymer separation step to obtain a stream of at least one purified thermoplastic polymer.

2. The method according to claim 1, wherein the dissolving solvent and the plastic raw material are fed to step a) at a weight ratio between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, and even more preferably between 3.0 and 7.

0.

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

4. The method according to any one of the preceding claims, wherein the dissolving solvent comprises, preferably, the following: A mixture of isomers of butane, pentane, hexane, heptane and / or octane, and preferably isomers or mixtures of isomers of hexane, heptane and / or octane.

5. The method according to any one of the preceding claims, wherein step b) uses one to ten decanters, preferably two to five decanters.

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

0.

7. The method according to any one of the preceding claims, wherein the liquid surface velocity in each decanter ranges from 1.0 x 10⁻⁶. -6 Up to 1.000x10 -2 Between m / s, preferably between 1.0 x 10 m / s -5 Up to 6.000x10 -3 Between, very preferably at 2.0 x 10 -5 Up to 9.00x10 -4 Between m / s.

8. The method according to any one of the preceding claims, wherein each decanter has an injection rate of less than or equal to 1.00 m / s, preferably less than or equal to 0.10 m / s, preferably less than or equal to 0.05 m / s, and preferably greater than or equal to 0.001 m / s.

9. The method according to any one of the preceding claims, wherein each decanter operates at a fill rate between 70% and 100% of the total volume of the decanter under consideration.

10. The method according to any one of the preceding claims, comprising the step of purifying the decanted polymer solution to obtain a purified polymer solution, the purification step comprising: b'1) Additional solid-liquid separation sub-steps; and / or b'2) Washing sub-step, through contact with a high-density solution; and / or b'3) Extraction sub-step, through contact with extraction solvent; and / or b'4) Sub-step of adsorbing impurities, through contact with solid adsorbent.

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

12. An apparatus for processing plastic raw materials to obtain a purified stream of thermoplastic polymer, comprising: - An apparatus for contacting and at least partially dissolving a plastic raw material in a dissolving solvent to obtain a crude polymer solution; - A decanting apparatus comprising at least one decanter, wherein the liquid surface velocity ranges from 1 × 10⁻⁶. -7 Up to 1.000×10 -2 The injection rate is between 1.00 m / s and preferably less than or equal to 1.00 m / s. The decanting device comprises several decanters, which operate 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 wherein the ratio L / D between the total height or length L of the decanter and the diameter D of the decanter is between 0.5 and 12. The decanter(s) includes a polymer solution feed point. The at least one decanter includes a first outlet for the effluent rich in polymer solution and a second outlet for the tailings stream. When the decantering apparatus comprises several decanters connected in series, the first outlet of the downstream decanter is advantageously connected to the feed point of the decanter directly upstream, except for the last decanter in series, whose first outlet is connected to a device located downstream of the decantering apparatus. When the decanting apparatus comprises several decanters connected in parallel, all the first outlets of the decanters are connected to each other and to a mixing system for mixing all effluents of the polymer-rich solution recovered at the outlets of the parallel decanters, the mixing system being connected to a device located downstream of the decanting apparatus; - An optional additional purification system, located downstream of the decanting unit; A solvent-polymer separation unit, located downstream of the decanter, is used to separate the solvent stream and the purified thermoplastic polymer stream.

13. The apparatus of claim 12, wherein the liquid surface velocity in the at least one decanter is in the range of 1.0 x 10⁻⁶. -6 Up to 1.000x10 -2 Between m / s, preferably between 1.0 x 10 m / s -5 Up to 6.000x10 -3 Between, very preferably at 2.0 x 10 -5 Up to 9.00x10 -4 between.

14. The apparatus according to claim 12 or 13, wherein the at least one decanter is a vertical decanter, wherein: - The feed point of the decanter is located between one-quarter and three-quarters of the height of the decanter. The feed point then defines two regions in the vertical decanter under discussion: an upper region between the feed point and the top of the vertical decanter, and a lower region between the feed point and the bottom of the vertical decanter. - The first outlet of the decanter is located in the upper region of the vertical decanter under discussion, and the second outlet is located in the lower region of the vertical decanter.

15. The apparatus according to claim 12 or 13, wherein the at least one decanter is a horizontal decanter, wherein: - The feed point of the decanter is located at one end close to the horizontal decanter under discussion. - The first and second outlets of the decanter are located near the end opposite the feed point.

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