Process for recycling plastics comprising the separation of impurities from a polymer solution by decantation

Abstract

The present invention relates to a process for treating a plastic feedstock, comprising: a) dissolution of the plastic feedstock in a dissolution solvent, between 100°C and 300°C and between 1.0 and 100.0 MPa absolute, to obtain a crude polymer solution; b) decantation of the crude polymer solution, to obtain a decanted polymer solution and a tailings fraction, step b) being carried out at 100-300°C and at 1.0-100.0 MPa absolute and using at least one decanter, an effluent enriched in polymer solution being recovered at the outlet of the or each decanter so as to constitute said decanted polymer solution, a tailings stream being recovered at the outlet of the or each decanter so as to constitute said tailings fraction, the liquid surface velocity in said decanter ranging between 1x10-7 and 1.000x10-2 m / s; c) solvent-polymer separation, to obtain a stream of purified thermoplastics. The present invention also relates to a device for carrying out such a process.

Description

[0001] PROCESS FOR RECYCLING PLASTICS COMPRISING SEPARATION BY

[0002] DECANTATION OF IMPURITIES FROM A POLYMER SOLUTION

[0003] TECHNICAL FIELD

[0004] The present invention relates to a method for treating plastics, in particular used plastics, in order to obtain a stream of purified thermoplastic polymers which can be recovered, for example, in the manufacture of new plastic objects. More particularly, the present invention relates to a method for purifying a plastic load, in particular from plastic waste, comprising thermoplastic polymers and in particular polyolefins, for example polyethylene and / or polypropylene, by dissolving the targeted thermoplastics in a solvent and then purifying the polymer solution obtained. Said method comprises in particular a step of purifying the polymer solution obtained by decanting at least some of the impurities, thus making it possible to recover a stream of purified thermoplastics at the outlet of the process according to the invention.

[0005] PRIOR TECHNIQUE

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

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

[0008] So-called chemical recycling aims to reform at least some monomers according to a generally complex sequence of steps. For example, plastic waste can undergo a pyrolysis step, and the recovered pyrolysis oil, generally after purification, can be converted at least in part, for example, into olefins by steam cracking. These olefins can then be polymerized. This type of sequence can be adapted for poorly sorted loads or rejects from sorting centers, but it generally requires significant energy consumption, particularly due to high-temperature treatments.Another way of recycling plastic waste consists of dissolving, at least in part, the plastics, in particular thermoplastics, in order to purify them, by eliminating impurities, for example additives such as fillers, dyes, pigments, and metals and / or polymers of the filler other than the one(s) targeted.

[0009] Several studies thus present different methods of treating plastic waste by dissolution and purification.

[0010] Document US 2017 / 002110 describes a particular method of purifying a polymer charge, in particular from plastic waste, by dissolving the polymer in a solvent, under particular temperature and pressure conditions, then contacting the polymer solution obtained with a solid.

[0011] WO 2018 / 114047 proposes a method for selectively dissolving a particular polymer of a plastic in a solvent at a dissolution temperature close to the boiling point of the solvent. However, the method of WO 2018 / 114047 does not allow for the efficient treatment and separation of impurities, for example additives.

[0012] US 2018 / 0208736 proposes a method for treating thermoplastics by liquefaction in a solvent and then separating the insolubles and / or gases. The method of US 2018 / 0208736 does not allow for effective treatment of impurities, and in particular impurities soluble in the solvent. The objective of US 2018 / 0208736 is to provide a plastic composition that can be used in a cracking process, so high purity is not sought. Indeed, US 2018 / 0208736 indicates for example that approximately 2% by weight of impurities remains after treatment in a reactor of a charge (comprising approximately 3% by weight of solid foreign materials relative to the total weight of the solid compounds of the charge) by dissolution in docosane (which has a boiling temperature of 369°C) at 150-300°C and 1.1-1.5 bar (i.e. 0.11-0.15 MPa) then decantation in a non-stirred zone of said reactor.

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

[0014] The present invention aims to improve these methods of treating thermoplastics by dissolving them in a solvent. In particular, the present invention seeks to optimize the removal, advantageously continuously, of impurities from a plastic charge and to recover a flow of thermoplastics, in particular polyolefins, purified and in particular decolorized and deodorized, while limiting the number of operations in the process implemented, and in particular the number of separation and / or purification steps of said process.The present invention thus seeks to effectively remove impurities, for example additives, from a plastic filler, which in particular comprises thermoplastics, and in particular polyolefins, so as to continuously obtain a flow of purified thermoplastics, in particular a flow of purified polyolefins, which can be reused for example as a polymer base in the manufacture of new plastic objects instead of virgin resin, by implementing a continuous and simple process.

[0015] SUMMARY OF THE INVENTION

[0016] The invention relates to a method for treating a plastic filler, comprising: a) a step of dissolving the plastic filler in a dissolving solvent, step a) being carried out at a dissolution temperature of between 100°C and 300°C and at a dissolution pressure of between 1.0 and 100.0 MPa absolute, to obtain at least one crude polymer solution; b) a step of decanting the crude polymer solution, to obtain a decanted polymer solution and a residue fraction, step b) being carried out at a temperature of between 100°C and 300°C and a pressure of between 1.0 and 100.0 MPa absolute, and using at least one decanter, when step b) comprises several decanters, said decanters operate in series or in parallel, the decanter or the first decanter of the decanters in series or each decanter in parallel being supplied with at least one fraction of said crude polymer solution,in which an effluent enriched in polymer solution is recovered at the outlet of the or each decanter, the effluent enriched in polymer solution recovered at the outlet of said decanter or of the last decanter of the decanters operating in series or all of the effluents enriched in polymer solution recovered at the outlet of each decanter operating in parallel, constituting said decanted polymer solution, a residue stream being recovered at the outlet of the or each decanter, all of the recovered residue streams constituting said residue fraction, said at least one decanter having a liquid superficial velocity varying between 1x10, -7 and 1,000x10' 2 m / s; then c) a solvent-polymer separation step, to obtain at least one stream of purified thermoplastic polymers.

[0017] The advantage of the method according to the invention is to propose an efficient and simple treatment of a plastic load, and in particular of plastic waste in particular from collection and sorting channels, so as to recover the thermoplastic polymers, in particular polyolefins, or even selectively polypropylene or polyethylene, which it contains in order to be able to recycle them for any type of application. The method according to the invention, which comprises the dissolution of the thermoplastics followed by a particular decantation step, in particular continuously, in fact makes it possible to obtain in a simple and advantageously continuous manner, a flow of purified thermoplastics having a sufficiently low impurity content so that the flow of purified thermoplastics can be used in any type of plastic formulation instead of virgin resin.More particularly, the process according to the invention makes it possible to eliminate at least 70% by weight, preferably at least 80% by weight, of the impurities, and in particular inorganic impurities, contained in the plastic filler. The process according to the invention also makes it possible to eliminate organic compounds and polymers, in particular insoluble ones, other than the targeted thermoplastics. In addition, very advantageously, the flow of purified thermoplastics, in particular purified polyolefins, obtained at the end of the process is less colored, or even discolored, compared to the plastic filler which feeds the process according to the invention.In very specific cases, the process according to the invention makes it possible to obtain a flow of purified thermoplastics, in particular the flow of purified polyolefins, or even polypropylene or polyethylene, comprising 5% by weight of impurities or less, very advantageously 1.0% by weight of impurities or less, even more preferably having a content of less than or equal to 0.5% by weight of impurities.

[0018] The method according to the invention thus proposes a simple scheme corresponding to a sequence of operations, comprising in particular at least one dissolution and one decantation, which makes it possible to rid the plastic waste of at least part of its impurities, in particular at least part of the additives, and to recover purified thermoplastics, in particular the purified thermoplastics in question, comprising few impurities, and advantageously a very low solvent content (preferably less than or equal to 10% by weight, preferably less than or equal to 1% by weight), so as to be able to recover the plastic waste by recycling said purified thermoplastics.

[0019] The invention also has the advantage of contributing to the recycling of plastics and the preservation of fossil resources, by enabling the recovery of plastic waste. It enables, in fact, the purification of plastic waste in order to obtain a flow of purified thermoplastic polymers, in particular purified polyolefins, or even purified polypropylene or polyethylene, with a reduced content of impurities and in particular decolorized and deodorized, which can be reused to form new plastic objects. The purified thermoplastics obtained can thus be used directly in formulations mixed with additives, for example plasticizers, colorants, pigments, fillers, etc., instead of or mixed with virgin resins, in order to obtain plastic materials with usage, aesthetic, mechanical or rheological properties facilitating their reuse and recovery.

[0020] The present invention also relates to a device for treating a plastic load to obtain a flow of purified thermoplastic polymers, which comprises:

[0021] - means for bringing into contact and dissolving at least in part the plastic filler in a dissolving solvent, to obtain a crude polymer solution;

[0022] - a decanting device comprising at least one decanter in which a liquid surface velocity varies between 1x10 -7 and 1,000x10 -2m / s, and preferably in which the injection speed is less than or equal to 1.00 m / s, when the settling device comprises several settling tanks, said settling tanks operating in series or in parallel, said at least one settling tank being a vertical or horizontal settling tank, preferably of cylindrical or generally cylindrical shape, preferably having a ratio L / D between the total height or length L of the settling tank and the diameter D of the settling tank of between 0.5 and 12, preferably between 1.0 and 6.0, said settling tank(s) comprising a polymer solution feed point, said at least one settling tank comprising a first outlet for an effluent enriched in polymer solution and a second outlet for a residue stream, when the settling device comprises several settling tanks in series, the first outlet of the downstream settling tank is advantageously connected to the feed point of the settling tank directly upstream,except for the last decanter in the series for which the first outlet is connected to means located downstream of the decanting device, when the decanting device comprises several decanters in parallel, all of said first outlets of said decanters are connected to each other and to a mixing system for mixing all of the effluents enriched in polymer solution recovered at the outlet of said decanters in parallel, said mixing system being connected to means located downstream of the decanting device;,

[0023] - possibly an additional purification system, located downstream of the decantation device;

[0024] - solvent-polymer separation means, located downstream of the decantation device, for separating a solvent stream and a stream of purified thermoplastic polymers.

[0025] According to one embodiment, said at least one decanter is a vertical decanter, in which:

[0026] - the feed point of said decanter is located between a quarter of the height of said decanter and three quarters of the height of said decanter, said feed point then defining two zones in the vertical decanter considered, an upper zone located between the feed point and the head of the vertical decanter, and a lower zone located between the feed point and the bottom of the vertical decanter,

[0027] - the first outlet of said decanter is advantageously located in the upper zone of the vertical decanter considered, and the second outlet is located in the lower zone of the vertical decanter,

[0028] According to another embodiment, said at least one decanter is a horizontal decanter, in which:

[0029] - the feed point of said decanter is located towards one end of the horizontal decanter considered,

[0030] - the first outlet and the second outlet of said decanter are located towards the end opposite the feed point.

[0031] DESCRIPTION OF EMBODIMENTS

[0032] According to the present invention, the expressions "between ... and ..." and "between .... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this is not the case and the limit values ​​are not included in the range described, such precision will be provided by the present invention.

[0033] For the purposes of the present invention, the different parameter ranges for a given step such as pressure ranges and temperature ranges may be used alone or in combination. For example, for the purposes of the present invention, a range of preferred pressure values ​​may be combined with a range of more preferred temperature values.

[0034] In the following, particular embodiments of the invention are described. They can be implemented separately or combined with each other, without limitation of combinations when technically feasible.

[0035] According to the present invention, the pressures are absolute pressures and are given in absolute MPa (or MPa abs.).

[0036] The terms "upstream" and "downstream" are to be understood in relation to the general flow of the fluid(s) or stream(s) in question in the process.

[0037] In this description, the terms "polymer", "thermoplastic polymer" and "thermoplastic" may be used interchangeably in place of each other.

[0038] The term "polyolefins" refers to any type of homopolymers and / or copolymers, and their mixtures, having olefins as their unit unit. More specifically, polyolefins can be polyethylene homopolymers, designated by the acronym PE, of any range (for example high density, also called HDPE, or low density, called LDPE), polypropylene homopolymers, designated by the acronym PP, their copolymers and / or their mixtures.

[0039] The term "additives" is a term conventionally used in the field of polymers and in particular in the field of polymer formulations. The additives introduced into polymer formulations may be, for example, plasticizers, fillers (which are solid organic or mineral compounds, making it possible to modify the physical, thermal, mechanical and / or electrical properties of polymer materials or to lower their cost price), reinforcing agents, colorants, plasticizers, pigments, hardeners, flame retardants, combustion retardants, stabilizing agents, antioxidants, UV absorbers, antistatic agents, etc.

[0040] The additives correspond to at least part of the impurities of the plastic load to be treated and which the treatment method according to the invention makes it possible to eliminate at least in part. Other types of impurities may be usual impurities, such as for example metallic impurities, paper / cardboard, biomass, polymers other than the targeted polymer(s), etc.

[0041] Thus, according to the invention, the impurities that the method according to the invention makes it possible to eliminate at least in part include the additives conventionally used in polymer formulations and generally usage impurities originating from the life cycle of plastic materials and objects, and / or originating from the waste collection and sorting circuit. The latter may be metallic, organic or mineral impurities; they may be packaging residues, food residues or compostable residues (biomass). These usage impurities may also include glass, wood, cardboard, paper, aluminum, iron, metals, tires, rubber, silicones, rigid polymers, thermosetting polymers, thermoplastics of a nature different from that of the targeted thermoplastics (in particular that of the targeted polyolefins), household, chemical or cosmetic products, used oils, water.

[0042] According to the invention, a polymer solution is a solution comprising the dissolution solvent and at least the targeted thermoplastic polymers, in particular the targeted polyolefins, dissolved (i.e. in particular solvated and dispersed) in said dissolution solvent, the dissolved polymers being initially present in the feedstock. The polymer solution may further comprise insoluble impurities (and in suspension in the polymer solution) and optionally soluble impurities (and solubilized in the dissolution solvent). Depending on the steps of the method according to the invention, said polymer solution may therefore comprise impurities in the form of insoluble particles which are advantageously in suspension in said polymer solution, optionally soluble impurities dissolved in the dissolution solvent, and / or optionally another liquid phase immiscible with said polymer solution.

[0043] 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 compound in question, in particular of the dissolving solvent, is understood to be the boiling point of said compound, in particular of said dissolving solvent, at atmospheric pressure (in particular equal to 0.1 MPa). Thus, the boiling point which characterizes the dissolving solvent must be understood to be the boiling point of said dissolving solvent at atmospheric pressure (in particular equal to 0.1 MPa).

[0044] The critical temperature and critical pressure of a solvent, in particular the dissolving solvent, are specific to said solvent and depend on the nature of the solvent considered. For a pure body, the critical temperature and critical pressure of a pure body are respectively the temperature and pressure of the critical point of said pure body. As well known to those skilled in the art, at the critical point and beyond, the pure body considered is in supercritical form or in the supercritical state; it can then be called a supercritical fluid. The invention thus relates to a method for treating a plastic filler, preferably composed of plastic waste, and advantageously comprising thermoplastic polymers, more particularly polyolefins, said method comprising, preferably consisting of: a) a step of dissolving the plastic filler in a dissolving solvent,preferably comprising at least one hydrocarbon compound, preferably aliphatic and preferably paraffinic, advantageously having a boiling point of between -50 and 250°C, preferably between -15 and 150°C, preferentially between -1 and 110°C and preferably between 20 and 100°C, preferably according to a weight ratio between the dissolution solvent and the plastic filler, of between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, even more preferentially between 3.0 and 7.0, to obtain at least one crude polymer solution, step a) being advantageously carried out at a dissolution temperature of between 100°C and 300°C, preferably between 150 and 250°C, and at a dissolution pressure of between 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 residue fraction, step b) being carried out at a temperature between 100°C and 300°C, preferably between 150 and 250°C, and a pressure between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferentially between 1.5 and 18.0 MPa absolute and very preferably between 2.0 and 15.0 MPa absolute, step b) using at least one decanter, preferably between one and ten decanters, preferentially between two and five decanters, advantageously operating in series or in parallel, preferably in parallel, the (or each) decanter being in particular a vertical or horizontal decanter, advantageously of cylindrical or generally cylindrical shape, preferably having an L / D ratio between the total height or length L of the decanter and the diameter or width D of the decanter 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 being supplied with at least a fraction, or all, of said raw polymer solution, advantageously at a supply point located on the decanter in question, an effluent enriched in polymer solution being recovered at the outlet of the or each decanter, the effluent enriched in polymer solution recovered at the outlet of said decanter or of the last decanter of the decanters in series or all of the effluents enriched in polymer solution recovered at the outlet of each decanter in parallel constituting said decanted polymer solution, a residue stream being recovered, in particular continuously or discontinuously, at the outlet of the or each decanter, all of the recovered residue streams constituting said residue fraction, said decanter(s) having:,

[0045] - a liquid surface speed varying between 1x10' 7 and 1,000x10 -2 m / s, preferably between 1.0x10 -6 and 1,000x10' 2 m / s, preferably between 1.0x10' 5 and 6,000x10' 3 m / s, preferably between 2.0x10' 5 and 5,000x10 -3 m / s, most preferably between 2.0x10' 5 and 9.00x10 -4 m / s, especially between 2.0x10 -5 and 5.00x10' 4 m / s,

[0046] - preferably an injection speed 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 being operated very advantageously for a residence time between 1 and 200 hours, preferably between 1 hour and 50 hours, and preferably with a filling rate of between 70% and 100% of the total volume of the decanter in question; b') optionally a step of purification of the decanted polymer solution, comprising: b'1) an additional solid-liquid separation sub-step, making it possible to obtain at least one clarified polymer solution; and / or b'2) washing of the decanted or optionally clarified polymer solution, by contact with a dense solution, making it possible to obtain at least one washing effluent and one washed polymer solution;and / or b'3) an extraction of the impurities by an extraction solvent, making it possible to obtain at least one extracted polymer solution and one used solvent; and / or b'4) an adsorption of the impurities by contact with a solid adsorbent, to obtain at least one refined polymer solution; the purification step making it possible to obtain a purified polymer solution which advantageously corresponds to a clarified or washed or extracted or refined polymer solution; then c) a solvent-polymer separation step, to obtain at least one stream of purified thermoplastic polymers, more particularly at least one stream of purified polyolefins, or even at least one stream of purified polypropylene or at least one stream of purified polyethylene.;

[0047] The charge

[0048] The feedstock of the process according to the invention, called plastic feedstock, comprises plastics which themselves more particularly comprise thermoplastic polymers, such as polyolefins. Preferably, the plastic feedstock comprises between 50 and 100% by weight, preferably between 70% and 100% by weight of plastics.

[0049] The plastics included in the feedstock of the process according to the invention are generally production scrap and / or “post-consumer” waste from plastic objects, in particular household plastic waste, plastic waste from construction, automotive plastic waste or waste from any type of transport or waste from electrical and electronic equipment. Preferably, the plastic waste comes from collection and sorting channels. The plastics or plastic materials comprise polymers which are mixed with additives in order to provide specific properties to the materials, with a view to constituting, after shaping, various objects (for example injection-molded parts, tubes, films, fibers, fabrics, mastics, coatings, etc.). The additives used in the plastics can be organic compounds or inorganic compounds.These include, for example, fillers, colorants, pigments, plasticizers, property modifiers, flame retardants, etc.

[0050] The feedstock of the process according to the invention comprises in particular thermoplastic polymers, preferably at least 50% by weight, preferably at least 70% by weight, more preferably at least 80% by weight and very preferably at least 90% by weight of 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 invention may be alkene polymers, diene polymers, vinyl polymers and / or styrenic polymers. Preferably, the thermoplastic polymers included in the plastic feedstock and targeted by the process according to the invention are polyolefins, such as polyethylene (PE), polypropylene (PP) and / or copolymers of ethylene and propylene or their mixtures.Preferably, the plastic filler comprises at least 80% by weight, preferably at least 85% by weight, more preferably at least 90% by weight, of polyolefins relative to the total weight of the plastic filler, 100% advantageously being the maximum upper limit. The method according to the invention thus aims in particular to purify and recover the polyolefins contained in the filler in order to be able to reuse them in different applications. According to a particular embodiment, the plastic filler comprises a mixture of polypropylene (PP) and polyethylene (PE), in particular at least 80% by weight, preferably at least 85% by weight, more preferably at least 90% by weight, of a mixture of polypropylene (PP) and polyethylene (PE), relative to the total weight of the plastic filler. The polyethylene may more particularly be high-density polyethylene (HDPE).In this particular embodiment, said mixture comprises for example between 5 and 95% by weight of PP and between 5 and 95% by weight of PE, in particular HDPE, or between 50 and 95% by weight of PP and between 5 and 50% by weight of PE, in particular HDPE. In this particular embodiment, the method according to the invention then aims to purify and specifically recover the PP and / or the PE.

[0051] The plastic filler may comprise mixtures of polymers, in particular thermoplastics other than the targeted polyolefins, additives advantageously used to formulate the plastic material and generally usage impurities resulting from the life cycle of plastic materials and objects, and / or resulting from the waste collection and sorting circuit, all of these compounds being considered as impurities. The feedstock of the process according to the invention generally comprises less than 50% by weight of impurities, preferably less than 20% by weight of impurities, more preferably less than 10% by weight of impurities. The plastic filler may comprise, for example, at least 1% by weight of impurities, or even at least 5% by weight of impurities.

[0052] The plastic filler may advantageously be pretreated upstream of the process so as to at least eliminate all or part of the so-called coarse impurities, i.e. impurities in the form of particles of a size greater than or equal to 10 mm, preferably greater than or equal to 5 mm, or even greater than or equal to 1 mm, for example impurities of the wood, paper, biomass, iron, aluminum, glass, etc. type, and so as to shape it generally in the form of divided solids so as to facilitate treatment in the process. This pretreatment may comprise a grinding step, a washing step at atmospheric pressure and / or a drying step. This pretreatment may be carried out on a different site, for example in a waste collection and sorting center, or on the same site where the treatment method according to the invention is implemented.Preferably, this pretreatment makes it possible to reduce the impurity content to less than 20% by weight, preferably less than 15% by weight, preferably less than 10% by weight, the percentages being given relatively to the weight of the plastic filler treated by the method according to the invention. At the end of the pretreatment, the filler is generally stored in the form of divided solids, for example in the form of ground materials, flakes or powder, or even granules, so as to facilitate handling and transport to the process.

[0053] Step a) of dissolution

[0054] According to the invention, the method comprises a dissolution step a) in which the plastic filler is brought into contact with a dissolution solvent and the thermoplastics it contains, and the separation and purification of which are advantageously targeted, in particular the polyolefins it contains, are dissolved in the dissolution solvent, to obtain at least one, preferably one, crude polymer solution.

[0055] Dissolution means any phenomenon leading to the production of at least one solution of thermoplastic polymers, i.e. a liquid (or fluid) comprising the targeted thermoplastic polymers dissolved in the dissolution solvent. A person skilled in the art is well aware of the phenomenon(s) involved in the dissolution of polymers and which includes at least mixing, solvation, dispersion, homogenization, and disentanglement of the thermoplastic polymer chains.

[0056] During and at the end of dissolution step a), the pressure and temperature conditions make it possible to maintain the dissolution solvent, at least in part and preferably in full, in the liquid state or possibly in the supercritical state, while the soluble fraction of the plastic filler, in particular the targeted thermoplastic polymers and very particularly the targeted polyolefins, and for example at least part of the impurities, is advantageously dissolved, at least in part and preferably in full, in the dissolution solvent. In other words, the temperature and pressure conditions in step a) make it possible to avoid or at least limit the dissolution solvent being in gaseous form.

[0057] The dissolving solvent is an organic solvent or a mixture of organic solvents. Advantageously, the dissolving solvent comprises, preferably consists of, at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic (i.e. saturated), preferably linear or branched. Preferably, the dissolving solvent comprises at least 80% by weight, preferably at least 95% by weight, more preferably at least 98% by weight of at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear or branched, the percentages being expressed relative to the total weight of the dissolving solvent (100% being the maximum).Preferably, the dissolution solvent comprises at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, having a boiling point (at atmospheric pressure, in particular at 0.1 MPa) of between - 50 and 250°C, preferably between - 15 and 150°C, preferentially between - 1 and 110°C and preferably between 20 and 100°C. Preferably, the dissolution solvent comprises, preferably consists of, at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear or branched, having between 3 and 12 carbon atoms, preferentially between 4 and 8 carbon atoms, and very preferably having 6, 7 or 8 carbon atoms. For example, the dissolution solvent comprises a compound chosen from the isomers of butane, pentane, hexane, heptane and octane.The dissolution solvent may comprise, preferably consist of, a mixture of isomers of butane, pentane, hexane, heptane and / or octane, and preferably has a content of said mixture of isomers in the dissolution solvent 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, relative to the total weight of the dissolution solvent. According to a highly preferred embodiment, the dissolution solvent comprises, preferably consists of, an isomer or a mixture of isomers of hexane, heptane and / or octane. Very advantageously, a preferred hydrocarbon compound for the dissolution solvent comprises a paraffinic aliphatic compound, having a critical temperature (temperature at the critical point of said pure hydrocarbon compound) preferably between 95 and 350°C, preferentially between 130 and 300°C, preferably between 180 and 285°C.

[0058] Preferably, dissolution step a) is supplied with the plastic filler and a dissolution solvent, according to a weight ratio between the dissolution solvent and the plastic filler, of between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, even more preferably between 3.0 and 7.0.

[0059] Advantageously, the dissolution solvent which feeds the dissolution step a) is in liquid or possibly supercritical form. It can advantageously be preheated, preferably to a temperature between 100 and 300°C, preferably between 150 and 250°C, prior to its introduction into step a), in particular prior to its introduction into the contacting section and possibly into the dissolution section, in order to facilitate the heating of the plastic charge and / or avoid a drop in temperature of the material flow in the contacting and possibly dissolution sections of step a).

[0060] Advantageously, the dissolution solvent comprises, preferably consists of, fresh solvent (or a fresh solvent top-up) and / or a recycled solvent stream from a subsequent step of the process, preferably at least partly from step c) of solvent-polymer separation. Very advantageously, the dissolution step is carried out at a temperature, called the dissolution temperature, of between 100°C and 300°C, preferably between 150 and 250°C, and preferably a pressure, called the dissolution pressure, of between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferentially between 1.5 and 18.0 MPa absolute and very preferably between 2.0 and 15.0 MPa absolute.The temperature and pressure may vary during the dissolution step from atmospheric conditions or the conditions of introduction of the plastic filler and / or the dissolution solvent into the process, until the dissolution conditions are reached, i.e. the dissolution temperature, in particular between 100 and 300°C, preferably between 150 and 250°C, and advantageously the dissolution pressure, in particular between 1.0 and 100.0 MPa, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute and very preferably between 2.0 and 15.0 MPa absolute. Very advantageously, at the end of the dissolution step, the raw polymer solution is at the dissolution temperature and at the dissolution pressure.

[0061] Limiting the temperature in dissolution step a) to a temperature less than or equal to 300°C, preferably less than or equal to 250°C, makes it possible to avoid or limit the thermal degradation of the targeted thermoplastics, in particular the targeted polyolefins, but also to limit the energy requirement of the process, thus contributing to limiting the operating costs of the process. Advantageously, the dissolution temperature is greater than or equal to the melting temperature of the targeted thermoplastics, in particular the targeted polyolefins, so as to promote their dissolution and very advantageously reduce the residence time necessary to effectively dissolve said thermoplastics in the dissolution solvent.Very preferably, the temperature in dissolution step a) is less than or equal to the critical temperature of the dissolution solvent, so as to avoid the formation of a supercritical phase during dissolution step a) which could disrupt the dissolution.

[0062] At the same time, the dissolution pressure in the dissolution step is higher than the saturated vapor pressure of the dissolution solvent, at the dissolution temperature, so that the dissolution solvent is at least partly, and preferably entirely, in liquid or possibly supercritical form, at the dissolution temperature, and thus to avoid the dissolution solvent being partly in gaseous form. Thus, the dissolution of the targeted thermoplastics, in particular the targeted polyolefins, is optimized, in particular in terms of quality and operating time.

[0063] Advantageously, said dissolution step a) is carried out for a residence time preferably between 1 and 600 minutes, preferably between 2 and 300 minutes, more preferably between 2 and 180 minutes. The residence time is understood to be the residence time at the dissolution temperature and at the dissolution pressure, i.e. the time of implementation of the plastic charge with the dissolution solvent at the dissolution temperature and at the dissolution pressure, in step a).

[0064] In order to allow contact between the dissolving solvent and the plastic filler and, above all, an efficient and homogeneous dissolution of the targeted thermoplastics in the dissolving solvent, the dissolving step a) can advantageously implement different types of equipment such as mixing, transport, heating devices, and such as, for example, a reactor, a pump, a transport circuit, a stirring system, an oven, an exchanger, a mixer, etc. In particular, step a) advantageously implements at least one dissolution equipment, and possibly at least one filler preparation device, a mixing device and / or a transport device. These equipment and / or devices can be, for example, one or more static or dynamic mixers, an extruder, a pump, a reactor, a co- or counter-current column, or in a combination of lines 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 may comprise at least one of the following devices: a compressor, a pump, an extruder, a vibrating tube, a worm screw, a valve. The equipment and / or devices implemented in step a) may also comprise or be associated with heating systems (for example, furnace, exchanger, tracing, etc.) to achieve the conditions necessary for dissolution.

[0065] The dissolution step a) is at least supplied with the plastic filler, in particular in the form of one or more plastic filler streams, and with the dissolution solvent, in particular in the form of one or more dissolution solvent streams, advantageously by means of one or more transport devices. The plastic filler stream(s) may be separate from the dissolution solvent stream(s). Part or all of the plastic filler may also be supplied to step a) in a mixture with part or all of the dissolution solvent, the remainder of the solvent and / or filler, where appropriate, being able to be supplied to step a) separately.

[0066] When bringing the plastic filler into contact with the dissolving solvent, the dissolving solvent is advantageously at least partly, and preferably entirely, in liquid or possibly supercritical form, while the plastic filler, which comprises the targeted thermoplastics, may be in solid or liquid form and may optionally comprise suspended solid particles. The plastic filler may also optionally be injected into the dissolving equipment, mixed with the dissolving solvent, in the form of a suspension in the dissolving solvent, the preparation and injection of the suspension being able to be continuous or discontinuous.

[0067] Preferably, the dissolution step a) uses at least one means for melting at least partially the plastic filler, preferably an extruder, optionally at least one means for mixing at least a portion of the dissolution solvent and the plastic filler, advantageously at least partially melted, such as one or a series of two to ten mixer(s) (preferably one to ten static mixer(s)), and dissolution equipment, for example at least one continuously stirred reactor, also called "Continuous Stirred Tank Reactor" (CSTR) according to English terminology, equipped with at least one mechanical stirring system. In this case, the plastic filler feeds the melting means, in particular the extruder, so that, at the outlet of said means, at least a portion and preferably all of the targeted thermoplastics, included in the plastic filler, are in the molten state.The plastic filler can then be injected into the dissolution equipment or possibly into a system comprising a mixer or a series of mixer(s) advantageously followed by dissolution equipment. The plastic filler, at least partly in the molten state, can also be pumped using a pump dedicated to viscous fluids often called a melt pump or gear pump. The plastic filler, at least partly in the molten state, can also be, at the outlet of said melting means, filtered using a filtration device, possibly in addition to the melt pump, in order to eliminate the largest particles, generally the mesh size of this filter is between 10 μm (micrometer) and 1 mm (millimeter), preferably between 20 and 200 μm. At the same time, the dissolution solvent directly feeds the dissolution equipment or possibly the series of mixer(s).

[0068] Preferably, step a) uses, prior to at least one CSTR type reactor, an extruder and at least one static mixer into which at least a fraction of the dissolving solvent is injected, so as to promote shearing and intimate mixing between the dissolving solvent and the plastic filler, which contributes to the dissolution of the targeted thermoplastics.

[0069] Very advantageously, the raw polymer solution obtained at the end of dissolution step a) comprises at least the dissolution solvent and the targeted thermoplastics, in particular the targeted polyolefins, dissolved in the dissolution solvent. In general, the raw polymer solution also comprises soluble impurities also dissolved in the dissolution solvent and / or insoluble impurities in suspension. The raw polymer solution obtained at the end of dissolution step a) may optionally also comprise polymers, for example in the molten state, dissolved or not. Step b) of decanting the polymer solution

[0070] The method according to the invention comprises a step b) of decanting the crude polymer solution obtained at the end of step a) of dissolution, to generate, at least, a so-called decanted polymer solution and a residue fraction.

[0071] Indeed, the decantation step b) makes it possible, by acting on the differences in densities of the compounds present in the raw polymer solution, to separate at least a portion of the insoluble impurities which may be present in the raw polymer solution, in the form of solid particles, in particular in suspension, or in the form of a liquid phase, for example comprising a molten polymer, and possibly at least a portion of the soluble impurities, dissolved in the dissolution solvent. The decantation step b) thus makes it possible to recover a decanted polymer solution which is freed, at least in part, from the impurities present in the raw polymer solution which feeds said step b).The decantation step b) thus also generates a residue fraction which comprises at least a portion, preferably all, of the insoluble impurities of the crude polymer solution from step a) and optionally soluble impurities, and possibly the dissolving solvent which may, in part, be entrained with the impurities. The insoluble impurities removed during the decantation step b) are, for example, pigments, mineral compounds, packaging residues (glass, wood, cardboard, paper, aluminum) and polymers other than the targeted thermoplastics, in particular other than the targeted polyolefins.

[0072] According to one embodiment of the invention, the decanted polymer solution comprises a portion of the polyolefins contained in the initial plastic feedstock, for example the polypropylene of the plastic feedstock, while the residue fraction comprises polymer impurities, in particular thermoplastics other than the targeted polyolefins, and / or another portion of the polyolefins 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 other portion of the polyolefins may in particular not have been solubilized in the dissolution step a).The residue fraction can then advantageously be recovered and treated in another process, for example a second process according to the invention, so as to purify said thermoplastics, in particular said other part of the polyolefins of the initial plastic charge and separated in the residue fraction.

[0073] Another advantage of the decantation step b) of the process according to the invention lies in the fact that it allows efficient purification of the polymer solution, in continuous mode. This aspect is interesting since the yield of purified target thermoplastics, in particular purified target polyolefins, is then optimal.

[0074] Advantageously, the decantation step b) also makes it possible, in addition to the continuous elimination of at least part of the impurities, to limit the operating problems, in particular of the clogging and / or erosion type, of the process steps located downstream, while contributing effectively to the purification of the plastic load.

[0075] Advantageously, step b) is carried out at a temperature between 100°C and 300°C, preferably between 150 and 250°C, and a pressure between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferentially 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 under the temperature and pressure conditions of dissolution step a).

[0076] Step b) uses at least one decanting device, also called a decanter. Preferably, step b) uses between one and ten decanters, preferably between two and five decanters. When step b) uses several decanters, i.e. between two and ten, preferably between two and five decanters, said decanters can operate in series and / or in parallel, preferably in parallel.

[0077] Said decanter(s) is (are) preferably of cylindrical or generally cylindrical shape, closed at each end, in particular by hemispherical or conical ends, and advantageously comprising orifices for example for the supply of raw polymer solution and for the outlet of the different separated flows. The term "generally cylindrical" means that the shape of the decanter is a cylinder closed at the ends, in particular by hemispherical ends or by a first hemispherical end and a second end of conical shape. In a very particular manner, the decanter(s) used in step b) may be of multi-cylindrical shape. The expression "multi-cylindrical" means that the decanter considered may have several cylindrical sections of different diameters. For example, a first cylindrical zone of diameter D1 and a second cylindrical zone of diameter D2, with D1 greater than D2.

[0078] The or each decanter implemented in step b) may be a vertical or horizontal decanter. In other words, the or each decanter which is preferably of generally cylindrical shape is operated so that the cylinder is positioned respectively vertically or horizontally.

[0079] Preferably, said decanter(s) implemented in step b), which preferably is (are) cylindrical or generally cylindrical in shape, has a ratio L / D between the total length L of the decanter considered (i.e. the total length of the closed cylinder, the ends being included) and the diameter (or width) D of the decanter considered being between 0.5 and 12, preferably between 1.0 and 6.0.

[0080] In a very particular manner, the decanter(s) implemented in step b) may be one or more vertical decanters (or verticals) of multi-cylindrical shape. The expression “multi-cylindrical” means that the decanter considered may have several cylindrical sections of different diameters. For example, a first cylindrical zone of diameter D1 and a second cylindrical zone of diameter D2, with D1 greater than D2, the second cylindrical zone of diameter D2 preferably being located above (i.e. on the side of the head of the decanter) the first cylindrical zone of diameter D1. In this very particular embodiment, the diameter D to be considered is the diameter of the widest cylindrical section of said decanter considered, i.e. the diameter D1 of the decanter of the example cited above.

[0081] Step b) is fed with at least a fraction, or all, of the raw polymer solution from step a). In the embodiment in which step b) uses a single decanter or several decanters in series, the entire raw polymer solution obtained at the end of step a) feeds said decanter or the first decanter in the series. In the embodiment in which step b) uses several decanters in parallel, the raw polymer solution obtained at the end of step a) feeds each decanter operating in parallel. In this latter embodiment, the raw polymer solution is advantageously divided into several partial streams of raw polymer solution, in particular into as many partial streams as there are decanters in parallel.

[0082] The (or each) decanter used in step b) is supplied with polymer solution, in particular with raw polymer solution or with an effluent enriched with polymer solution, at a supply point located on the decanter in question.

[0083] When the decanter in question is a vertical decanter, said polymer solution feed point is advantageously located between the upper quarter of the height of said decanter and the upper three-quarters of the height of said decanter, preferably between the upper third of the height of said decanter and the upper two-thirds of the height of said decanter. Said polymer solution feed point then defines two zones in the vertical decanter in question, an upper zone located between the polymer solution feed point and the head of the vertical decanter, and a lower zone located between the polymer solution feed point and the bottom of the vertical decanter.

[0084] When the decanter in question is a horizontal decanter, said polymer solution feed point is preferably located on one side of the horizontal decanter, i.e. at one of the ends of the horizontal decanter or close to one of the ends of the horizontal decanter, preferably in an area between one of the two ends of the horizontal decanter and one third of the length of said decanter from said end, preferably between one of the two ends of the horizontal decanter and one quarter of the length of said decanter from said end.

[0085] The (or each) decanter comprises an outlet for an effluent enriched in polymer solution, i.e. an effluent comprising the polymer solution freed from at least some of the impurities. Thus, an effluent enriched in polymer solution is recovered at the outlet of the or each decanter implemented in step b). The effluent enriched in polymer solution can be recovered by withdrawal or overflow. When step b) uses a single decanter, the effluent enriched in polymer solution recovered at the outlet of said decanter therefore constitutes the decanted polymer solution. When step b) uses several decanters in parallel, all of the effluents enriched in polymer solution and recovered at the outlet of each decanter constitutes the decanted polymer solution.Finally, when step b) uses several decanters in series with each other, the effluent enriched with polymer solution recovered at the outlet of the upstream decanter advantageously directly feeds the downstream decanter with polymer solution and the effluent enriched with polymer solution recovered at the outlet of the last decanter in the series constitutes the decanted polymer solution.

[0086] When the decanter considered is a vertical decanter, the outlet of the effluent enriched in polymer solution is advantageously located in the upper zone of the vertical decanter considered, that is to say in a zone between the polymer solution feed point and the head of the decanter.

[0087] When the decanter in question is a horizontal decanter, the outlet for the effluent enriched in polymer solution 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 which is opposite the end towards which the polymer solution feed point is located, preferably said outlet for the effluent enriched in polymer solution being located in an area between the end of the decanter opposite the end towards 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 towards which the polymer solution feed point is located and one quarter of the length of the decanter from said opposite end.

[0088] The (or each) decanter also comprises an outlet for a residue stream. Thus, a residue stream is recovered at the outlet of the or each decanter implemented in step b). When step b) uses a single decanter, the residue stream recovered at the outlet of said decanter therefore constitutes said residue fraction obtained at the end of step b). When step b) uses several decanters in parallel or in series, all of the residue streams recovered at the outlet of each decanter constitutes said residue fraction obtained at the end of step b).

[0089] The residue stream in the decanter under consideration may be recovered, or purged, continuously or discontinuously. When the residue stream is purged discontinuously, the purge frequency may vary between 0.01 and 20.0 mHz, preferably 0.1 and 10.0 mHz, preferably between 0.5 and 1.0 mHz.

[0090] When the decanter considered is a vertical decanter, the outlet of the residue flow is advantageously located in the lower zone of the decanter (i.e. in the zone between the polymer solution feed point and the bottom of the decanter), preferably in the bottom of the decanter considered, for example in the bottom of the conical end of the vertical decanter.

[0091] When the decanter in question is a horizontal decanter, the outlet of the residue flow is located in the bottom of the decanter in question and advantageously on the side of the decanter opposite the polymer solution feed point, i.e. close to the end of the decanter which is opposite the end towards which the polymer solution feed point is located, preferably in an area between the end of the decanter opposite the end towards 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 towards which the polymer solution feed point is located and one quarter of the length of the decanter from said opposite end.

[0092] Said at least one decanter implemented in step b) is preferably operated with a filling rate of between 70% and 100% of the total volume of the decanter considered. The term “filling rate” corresponds to the ratio between the total volume of material (polymer solution and residues) present in the decanter and the total volume of the decanter (i.e. geometric volume of the decanter).

[0093] In said at least one decanter implemented in step b), there is a liquid surface velocity (also called empty barrel velocity, in particular ascending) which varies between 1x10' 7 and 1,000x10 -2 m / s, preferably between 1.0x10' 6 and 1,000x10' 2 m / s, preferably between 1.0x10 -5 and 6,000x10 -3 m / s, preferably between 2.0x10 -5 and 5,000x10' 3 m / s, very preferably between 2.0x10 -5 and 9.00x10' 4 m / s, especially between 2.0x10 -5 and 5.00x10'4m / s. This liquid surface velocity, called VSL (or Q / S), is well known to those skilled in the art and corresponds to the flow rate Q of liquid freed from at least part of the impurities divided by the area S of the section of the decanter (in particular of the widest section in the case of a multi-cylindrical decanter). In the case of a vertical decanter, the liquid surface velocity is adjusted so as to be less than or equal to a value equal to 0.85 times the sedimentation velocity, preferably 0.80 times the sedimentation velocity. In the case of a horizontal decanter, the liquid surface velocity is a function of the sedimentation velocity but also of the length L of the horizontal decanter. The sedimentation velocity advantageously corresponds to the speed, or average speed, at which the impurity particles sediment in the polymer solution.The sedimentation rate is therefore more particularly a function of the gravitational force, the density, the diameter and concentration of the impurity particles considered and the viscosity of the medium, i.e. of the polymer solution.

[0094] Very advantageously, said decanter(s) have(s) an injection speed of the polymer solution, in particular of the raw polymer solution or of the effluent enriched with polymer solution, less than or equal to 1.00 m / s, preferably less than or equal to 0.10 m / s, preferentially 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.

[0095] Thus, in each decanter, the residence time can be adjusted between 1 and 200 hours, preferably between 1 hour and 50 hours. The residence time here corresponds to the residence time in the decanter, namely, the ratio between the useful volume of the decanter (i.e. the volume of material in the decanter which is a function of the filling rate of the decanter considered) and the volume flow rate of polymer solution (raw polymer solution or effluent enriched in polymer solution) feeding the decanter considered.

[0096] The residue fraction can be recovered and treated to recover any solvent it may contain.

[0097] According to one embodiment of the invention, the residue fraction may comprise polymeric impurities, in particular thermoplastics other than the targeted polyolefins, or even polyolefins, for example polyethylene (PE) and in particular high-density polyethylene (HDPE), which were contained in the plastic feedstock but which are not the specific targeted polyolefins. The residue fraction may then advantageously be recovered and treated in another process, for example in a second process according to the invention, so as to purify said thermoplastics, in particular said polyolefins from the residue fraction.

[0098] According to a particular embodiment, the method according to the invention aims to recover and purify the polypropylene (PP) from the plastic filler, said plastic filler being able to comprise other thermoplastics, or even other polyolefins, for example PE and in particular HDPE. Step a) is adjusted to allow selective dissolution of said polypropylene from the plastic filler. It is understood by selective dissolution that the majority of the PP, and possibly a minor fraction of PE, in particular HDPE, contained in the initial plastic filler, is (are) dissolved in the dissolution solvent, while the majority of the PE, in particular HDPE, and possibly a minor fraction of PP, contained in the initial plastic filler, is (are) undissolved.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 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 separate at least in part, preferably in full, the thermoplastics other than the targeted PP, for example makes it possible to separate PE or HDPE. The residue fraction recovered at the bottom of the decanter then advantageously comprises the thermoplastics, other than the targeted PP, for example comprises PE and in particular HDPE. Said residue fraction is then very advantageously recovered and treated in a process, for example another recycling process according to the invention, to separate and recover said thermoplastics, for example said PE or HDPE, in purified form.

[0099] The decanted polymer solution recovered at the end of step b) may optionally undergo a purification step or be sent directly to step c) of solvent-polymer separation. Preferably, the decanted polymer solution recovered at the end of step b) is sent to a purification step b'), which very preferably comprises an additional solid-liquid separation and / or an adsorption of impurities, in particular soluble ones.

[0100] Optional step b') of purification of the polymer solution

[0101] The treatment method according to the invention may also comprise an additional purification step of 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) an additional solid-liquid separation sub-step, b'2) a washing sub-step, by contact with a dense solution, b'3) an extraction sub-step, by contact with an extraction solvent, b'4) a sub-step of adsorption of the impurities by contact with an adsorbent solid.

[0102] The integration into the process according to the invention of such a step b') and in particular of one or more of the sub-steps b'1), b'2), b'3), b'4) very advantageously allows maximum purification of the polymer solution and thus contributes to achieving the objective of purity of the flow of purified thermoplastics recovered at the outlet of the process, i.e. obtaining an impurity content of the flow of purified thermoplastics 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 so-called purified polymer solution, which corresponds to a clarified polymer solution resulting from an additional solid-liquid separation sub-step b'1), a washed polymer solution resulting from a washing sub-step b'2), an extracted polymer solution resulting from an extraction sub-step b'3) or a refined polymer solution resulting from an impurity adsorption sub-step b'4).

[0103] Preferably, when integrated into the process according to the invention, the purification step b') comprises an additional sub-step b'1) of solid-liquid separation and / or a sub-step b'4) of adsorption of impurities. According to a very particular embodiment, the process according to the invention comprises an additional sub-step b'1) of solid-liquid separation and / or a sub-step b'4) of adsorption of impurities, and more particularly an additional sub-step b'1) of solid-liquid separation followed by a sub-step b'4) of adsorption of impurities.

[0104] Optional sub-step b'1) of additional solid-liquid separation

[0105] The purification process may comprise an additional solid-liquid separation sub-step b'1), to advantageously obtain at least one clarified polymer solution. Sub-step b'1) makes it possible to eliminate impurities that are typically insoluble in the dissolution solvent, which would not have been separated in the decantation step b). Indeed, insoluble impurities, in the form of particles suspended in the raw polymer solution, may have densities that are lower than or too close to the polymer solution and therefore cannot be separated, or at least not effectively separated, during the decantation step b); they may thus remain in suspension in the decanted polymer solution at the end of step b). Sub-step b'1) may then make it possible, when integrated into the process according to the invention, to increase the efficiency of the purification of the polymer solution and in particular the efficiency of the separation of the insoluble impurities.

[0106] The optional sub-step b'1) may generate, in addition to the clarified polymer solution, an insoluble fraction. The insoluble fraction when generated advantageously comprises impurities, typically insoluble and not separated in the decantation step b).

[0107] 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, preferentially 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 separation of the insolubles is carried out at the temperature and pressure conditions at the outlet of the dissolution step a), i.e. at the dissolution temperature and the dissolution pressure as defined above.

[0108] When integrated into the process, sub-step b'1) is preferably fed with the decanted polymer solution from decantation step b). According to another embodiment, sub-step b'1) can be fed with a washed polymer solution from a washing sub-step b'2).

[0109] Advantageously, the optional sub-step b'1) implements a section comprising at least one solid-liquid separation equipment, for example chosen from a filter, a sand filter, a tangential filter notably using a membrane and / or a depth filter possibly in the presence of filtration aids (for example diatomaceous earth), an eddy current separator, an electrostatic separator, a triboelectric separator, preferably a filter, a sand filter and / or an electrostatic separator. Advantageously, a self-cleaning filter can be used, the cleaning or unclogging allowing the elimination of insolubles being carried out using a solvent flow.

[0110] According to a particular embodiment, the optional sub-step b'1) implements at least two, and generally less than five, solid-liquid separation equipment in series and / or in parallel. The presence of at least two solid-liquid separation equipment in series makes it possible to improve the elimination of insolubles while the presence of equipment in parallel makes it possible to manage the maintenance of said equipment and / or unclogging operations.

[0111] Certain insoluble impurities, in particular certain pigments and mineral fillers, conventionally added during the formulation of polymers, can be introduced in the form of particles smaller than 1 μm. This is for example the case of titanium dioxide, calcium carbonate and carbon black. According to a particular embodiment, said sub-step 'b1) of separation of the insolubles advantageously uses an electrostatic separator, which makes it possible to effectively eliminate at least in part, the insoluble particles smaller than 1 μm. According to another particular embodiment, sub-step b'1) of separation of the insolubles uses a sand filter, to eliminate particles of different sizes and in particular particles smaller than 1 μm.According to yet another particular embodiment, sub-step b'1) of separation of insolubles uses a tangential filter notably using a membrane and / or a depth filter, possibly in the presence of filtration aids such as diatomaceous earth.

[0112] Depending on the nature of the feed, the polymer solution which feeds sub-step b'1), preferably the decanted polymer solution, may optionally also comprise a second liquid phase, for example consisting of molten polymers, and the density of which is not sufficiently different from that of the polymer solution to be separated during step b). According to another particular embodiment, sub-step b'1) advantageously uses equipment allowing the separation of a second liquid phase, preferably by means of at least one two-phase or three-phase separator.

[0113] Sub-Step b'2) optional washing

[0114] The treatment method may optionally further comprise a sub-step b'2) of washing with a dense solution, to advantageously obtain at least one washing effluent and a washed polymer solution. The washed polymer solution obtained at the end of sub-step b'2) advantageously comprises the targeted thermoplastics that the present invention seeks to recover purified, dissolved in the dissolving solvent.

[0115] Optionally, the washed polymer solution may also include residual impurities, in particular soluble in the dissolution solvent and / or possibly traces of the washing solvent if sub-step b'2) is carried out.

[0116] The washing sub-step b'2) can be integrated upstream or downstream, preferably downstream, of an additional solid-liquid separation sub-step b'1), when these two sub-steps are integrated into the treatment method according to the invention.

[0117] When integrated into the process, the washing sub-step b'2) is fed with a dense solution and with the decanted polymer solution from step b) or possibly the clarified polymer solution from a sub-step b'1). The polymer solution which feeds the washing sub-step b'2), in particular the decanted or possibly clarified polymer solution, may comprise insoluble impurities in suspension and / or solubilized impurities, and not separated in step b). These suspended or solubilized impurities may, in part or in whole, be eliminated during the washing sub-step b'2) by dissolution or precipitation and / or by entrainment in the dense solution. Thus, when implemented, this sub-step b'2) contributes to the treatment of the plastic load and more particularly to the purification of the polymer solution.

[0118] The washing sub-step b'2) advantageously comprises bringing the decanted or optionally clarified polymer solution, which feeds sub-step b'2), into contact with a dense solution. Advantageously, the dense solution has a higher density than the polymer solution (i.e. the mixture comprising at least the targeted thermoplastics and the dissolving solvent in which the targeted thermoplastics are dissolved), in particular greater than or equal to 0.85, preferably greater than or equal to 0.9, preferentially greater than or equal to 1.0. The dense solution may be an aqueous solution, which preferably comprises at least 50% by weight of water, preferably at least 75% by weight of water, very preferably at least 90% by weight of water. The pH of the aqueous solution may be adjusted using an acid or a base so as to promote the dissolution of certain impurities.The dense solution may also optionally be a solution comprising, preferably consisting of, an organic solvent with a density advantageously greater than or equal to 0.85, preferably greater than or equal to 0.9, preferentially greater than or equal to 1.0, and in which the polymers of the plastic filler remain insoluble under the temperature and pressure conditions of sub-step b'2), for example an organic solvent chosen from sulfolane or N-methylpyrrolidone (NMP), optionally mixed with water. Very preferably, the dense solution is an aqueous solution which preferably comprises at least 50% by weight of water, preferably at least 75% by weight of water, very preferably at least 90% by weight of water.

[0119] 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, preferentially 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 the dissolution temperature and the dissolution pressure.

[0120] In the washing sub-step b'2), when it is integrated into the process, the mass ratio between the mass flow rate of the dense solution and the mass flow rate of the polymer solution, decanted or possibly clarified, which feeds the sub-step b'2) is advantageously between 0.05 and 20.0, preferably between 0.1 and 10.0 and more preferably between 0.5 and 3.0. The contact between the polymer solution, decanted or possibly clarified, and the dense solution can be carried out at several points of the equipment(s) used, i.e. by several injections of the decanted or clarified polymer solution and / or of the dense solution at different points along the equipment(s), it is then the sum of the injected flows which is taken into account in the calculation of the ratio.

[0121] Sub-step b'2) can be carried out in one or more washing equipment allowing contact with the dense solution and / or with separation equipment allowing recovery of at least one washing effluent and a washed polymer solution. This equipment is well known, for example stirred reactors, static mixers, decanter mixers, two-phase or three-phase separator drums, co- or counter-current washing columns, tray column, stirred column, packed column, pulsed column, etc., each type of equipment being able to comprise one or more equipment used alone or in combination with equipment of another type.According to a preferred embodiment, the washing sub-step b'2) is carried out in a countercurrent washing column in which the dense solution is injected, preferably into half, preferably one third, of the column closest to the column head, on the one hand and the decanted or clarified polymer solution is injected, preferably into half, preferably one third, of the column closest to the column bottom, on the other hand. According to this embodiment, it is possible to recover at least one washed polymer solution and one washing effluent.

[0122] According to a very particular mode, the flows entering and / or leaving the washing column can be divided and injected at several injection points along the column and / or withdrawn at several withdrawal points along the column.

[0123] According to another embodiment, the washing sub-step b'2) is carried out in a mixer-decanter comprising an agitated mixing zone, to bring the dense solution and the decanted or clarified polymer solution into contact, and a decantation zone, making it possible to recover a washed polymer solution and a washing effluent.

[0124] At the end of the washing sub-step b'2), the washing effluent obtained advantageously comprises impurities solubilized in the dense and / or insoluble solvent and entrained in the washing effluent. The washing effluent can be reprocessed in a washing treatment section, on the one hand to separate at least in part the solubilized and / or entrained impurities and optionally purify the washing effluent, to obtain a purified dense solution, and on the other hand to recycle at least a portion of the purified washing solution. This washing treatment section can implement one or more well-known solid-liquid separation equipment, for example a separator drum, a decanter, a centrifugal decanter, a centrifuge, a filter. The washing effluent can also be sent outside the process, for example to a wastewater treatment plant when the dense solution is an aqueous solution.

[0125] Step b'3) optional extraction

[0126] The method according to the invention may comprise a sub-step b'3) of extraction by contacting with an extraction solvent, to obtain at least one extracted polymer solution and a used solvent. The extracted polymer solution obtained at the end of sub-step b'3) advantageously comprises the targeted thermoplastic polymers that the present invention seeks to recover purified, dissolved in the dissolution solvent. The used solvent is advantageously loaded with impurities. Optionally, the extracted polymer solution may also comprise residual impurities, in particular soluble in the dissolution solvent and / or traces of the washing solvent and / or the extraction solvent if sub-step(s) b2) and / or b3) is (are) carried out.When integrated into the process according to the invention, the extraction sub-step b'3) is advantageously located between the decantation step b) and the solvent-polymer separation step c), and optionally upstream or downstream of an adsorption sub-step b'4) if the latter is also integrated into the process, and preferably downstream of an additional solid-liquid separation sub-step b'1).

[0127] The extraction sub-step b'3) is advantageously supplied with an extraction solvent and with the decanted polymer solution from step b), the clarified polymer solution from sub-step b'1), the washed polymer solution from sub-step b'2) or the refined polymer solution from an adsorption sub-step b'4). The polymer solution which supplies sub-step b'3), preferably the decanted polymer solution or possibly the clarified, washed or refined solution, may therefore also comprise solubilized impurities. These solubilized impurities may be partially or completely removed during the extraction sub-step b'3) by contacting with an extraction solvent.

[0128] When integrated into the method according to the invention, the extraction sub-step b'3) advantageously implements at least one extraction section, preferably between one and five extraction section(s), very preferably one extraction section.

[0129] The mass ratio between the mass flow rate of the extraction solvent and the mass flow rate of the polymer solution which feeds b'3), preferably the decanted polymer solution or possibly the clarified, washed or refined polymer solution, is advantageously between 0.05 and 20.0, preferably between 0.1 and 10.0 and more preferably between 0.2 and 5.0. The contact between the polymer solution which feeds sub-step b'3) and the extraction solvent can be carried out at several points in the extraction section, i.e. by several injections of the polymer solution and / or the extraction solvent at different points along the extraction section, it is then the sum of the injected flows which is taken into account in the calculation of the ratio.

[0130] The extraction solvent used in extraction sub-step b'3) advantageously comprises an organic solvent or a mixture of organic solvents. Preferably, the extraction solvent comprises, preferably consists of, at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic (i.e. saturated), preferably linear or branched. Preferably, the extraction solvent comprises at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear or branched, the percentages being expressed relative to the total weight of the dissolution solvent (100% being the maximum.Preferably, the extraction solvent comprises at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, having a boiling point of between - 50 and 250°C, preferably between - 15 and 150°C, preferentially between - 1 and 110°C and preferably between 20 and 100°C (at atmospheric pressure, in particular at.

[0131] 0.1 MPa). Preferably, the extraction solvent comprises, preferably consists of, at least one aliphatic hydrocarbon compound, in particular paraffinic, preferably linear or branched, having between 3 and 12 carbon atoms, preferably between 4 and 8 carbon atoms. For example, the extraction solvent comprises a compound chosen from the isomers of butane, pentane, hexane and heptane. The extraction solvent may comprise, preferably consist of, a mixture of isomers of butane, pentane, hexane, heptane and octane, and preferably has a content of said mixture of isomers in the extraction solvent 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, relative to the total weight of the extraction solvent.Preferably, the extraction solvent is a paraffinic aliphatic compound, having a critical temperature (temperature at the critical point of said pure hydrocarbon compound) preferably between 95 and 350°C, preferably between 130 and 300°C, preferably between 180 and 285°C.

[0132] Very preferably, the extraction solvent used in the optional sub-step b'3) is the same solvent as the dissolution solvent used in step a), possibly in a different physical state (for example the extraction solvent in the supercritical state compared to the dissolution solvent in the liquid state), so as to facilitate the management of the solvents and in particular their purification and their recycling in particular to the dissolution step a) and possibly to the extraction sub-step b'3).Another advantage of using identical dissolution and extraction solvents, in identical or different physical states, is, in addition to facilitating the management of the solvents used in the process according to the invention, in particular the recovery of the solvents, their treatment and their recycling to at least one of the stages of the process, to limit energy consumption and costs in particular generated by the treatment and purification of the solvents.

[0133] The extraction section(s) of optional sub-step b'3) may comprise one or more extraction equipment(s), allowing contact with the extraction solvent and / or with separation equipment allowing recovery of at least one used solvent, in particular loaded with impurities, and an extracted polymer solution. This equipment is well known, for example stirred reactors, static mixers, decanter mixers, two-phase or three-phase separator drums, co- or counter-current washing columns, tray column, stirred column, packed column, pulsed column etc., each type of equipment being able to comprise one or more equipments used alone or in combination with equipments of another type.

[0134] According to a preferred embodiment of b'3), the extraction is carried out in a countercurrent extraction column where the extraction solvent is injected, on the one hand, and the polymer solution which feeds sub-step b'3) is injected, on the other hand. According to this embodiment, it is possible to recover at least one extracted polymer solution, on the one hand, and a used solvent, in particular loaded with impurities, on the other hand.Preferably, the polymer solution which feeds b'3), preferably the 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, and preferably the third, closest to the head of the countercurrent extraction column while the extraction solvent is injected into the lower half, preferably the lower third, of the column, i.e. the half, and preferably the third, closest to the bottom of the countercurrent extraction column.

[0135] The inlet and / or outlet flows of the countercurrent extraction column can be divided into several injection and / or withdrawal points along the column.

[0136] According to another embodiment of b'3), the extraction is carried out in a mixer-decanter which advantageously comprises a stirred mixing zone to bring the extraction solvent and the polymer solution which feeds b'3) into contact, preferably the decanted or optionally clarified, washed or refined polymer solution, and a decantation zone making it possible to recover an extracted polymer solution on the one hand and a used solvent on the other hand.

[0137] Advantageously, the extraction sub-step b'3) is carried out under temperature and pressure conditions different from the temperature and pressure conditions of the dissolution step a).

[0138] According to a preferred embodiment of b'3), the extraction sub-step b'3) implements a liquid / liquid extraction section. Preferably, the liquid / liquid extraction section is operated 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, preferentially between 1.5 and 18.0 MPa absolute and very preferably between 2.0 and 15.0 MPa absolute. In any case, in this embodiment, the temperature and pressure conditions are adjusted so that the extraction solvent is in the liquid state, the dissolution solvent preferably also being in the liquid state.Very advantageously, the liquid / liquid extraction, in particular when the extraction solvent is the same as the dissolution solvent, is carried out under temperature and pressure conditions different from the dissolution conditions reached in step a), in particular at a temperature higher than the dissolution temperature and / or at a pressure lower than the dissolution pressure, so as to thus be placed in a two-phase zone of the corresponding polymer-solvent mixing diagram.

[0139] According to another preferred embodiment of b'3), the extraction sub-step b'3) implements an extraction section under particular temperature and pressure conditions in which the extraction solvent is advantageously at least partly in supercritical form. Such extraction may be called supercritical extraction. In this embodiment, the extraction is carried out by bringing the polymer solution, preferably the decanted or optionally clarified, washed or refined polymer solution, into contact with an extraction solvent, advantageously under temperature and pressure conditions which make it possible to obtain a supercritical phase composed mainly (i.e. preferably at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight) of the extraction solvent.In other words, in this embodiment, the extraction is carried out by bringing the polymer solution, preferably the decanted or optionally clarified, washed or refined polymer solution, into contact with an extraction solvent which is at least partly, preferably entirely, in the supercritical state. Such a supercritical extraction sub-step b'3) advantageously allows efficient purification of the polymer solution, in particular due to the very strong affinity of organic impurities, such as some of the additives, in particular certain dyes, plasticizers, etc., for the supercritical phase. The use of an extraction solvent in the supercritical state also makes it possible to create a significant density difference between the supercritical phase and the polymer solution in liquid form, which facilitates separation by decantation between the supercritical phase and the liquid phase, and consequently which contributes to the purification of the polymer solution.

[0140] In this other preferred embodiment, sub-step b'3) uses an extraction solvent comprising at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of at least one aliphatic paraffinic hydrocarbon compound (or alkane) (100% being the maximum, the percentages being expressed relative to the total weight of the extraction solvent) having a critical temperature preferably between 95 and 350°C, preferably between 130 and 300°C, preferably between 180 and 285°C.

[0141] Advantageously, the supercritical extraction sub-step b'3) of this other particular embodiment is carried out at a temperature preferably between 150°C and 300°C, preferably between 180°C and 280°C, and at a pressure preferably between 2.0 and 100.0 MPa absolute, preferably between 2.0 and 25.0 MPa absolute, preferably between 2.0 and 18.0 MPa absolute and very preferably between 3.0 and 15.0 MPa absolute. Very preferably, the operating pressure of such a supercritical extraction sub-step b'3) is between 2.7 MPa and 7.5 MPa absolute, preferably between 3.0 MPa and 5.5 MPa absolute. In all cases, in this embodiment, the temperature and pressure conditions are adjusted, in particular in an adjustment section implemented in extraction sub-step b'3) upstream of the extraction section, so that the extraction solvent is at least partly in the supercritical state in the extraction section.

[0142] In a particular embodiment, the extraction sub-step b'3) implements a supercritical extraction and the extraction solvent is the same as the dissolution solvent, except that the extraction solvent is at least partly in the supercritical phase. In this case of supercritical extraction, the dissolution solvent can become at least partly in supercritical form, advantageously optimizing the decantation during the extraction step, more particularly at each extraction phase or tray, between the liquid phase and the supercritical phase, which thus makes it possible to maximize the purification.

[0143] Advantageously, at the end of extraction sub-step b'3), the used solvent obtained is in particular loaded with soluble impurities. It can be reprocessed in an organic treatment section making it possible, on the one hand, to separate at least part of the impurities and purify the solvent to obtain a purified extraction solvent, and on the other hand to recycle at least part of the purified extraction solvent at the inlet of extraction b'3), and / or at the inlet of dissolution step a) in the case where the dissolution solvent and the extraction solvent are identical. The used solvent can be treated according to any method known to those skilled in the art, such as one or more methods among distillation, evaporation, extraction, adsorption, crystallization and precipitation of insolubles, or by purging.

[0144] Sub-step b'4) optional adsorption

[0145] The treatment method according to the invention may comprise an adsorption sub-step b'4), to obtain a refined polymer solution. The refined polymer solution obtained at the end of the optional sub-step b'4) advantageously comprises the targeted thermoplastic polymers, in particular the targeted polyolefins, dissolved in the dissolution solvent.

[0146] When integrated into the process according to the invention, the adsorption sub-step b'4) is preferably carried out downstream of the decantation step b) and upstream of the solvent-polymer separation step c). However, it can be carried out upstream of the decantation step b) and / or during the dissolution step a), by introducing adsorbent particles mixed with the raw polymer solution, said adsorbent particles being removed during the decantation step b) and possibly during an additional solid-liquid separation sub-step b'1) or even during a washing sub-step b'2). The adsorption sub-step b'4) can also be carried out upstream or downstream of an extraction sub-step b'3). Thus, when integrated into the process according to the invention, the adsorption sub-step b'4) is implemented by bringing the polymer solution which feeds it into contact with one or more adsorbents.

[0147] The optional adsorption sub-step b'4) advantageously implements an adsorption section operated in the presence of at least one adsorbent, preferably solid, and in particular in the form of a fixed bed, an entrained bed (or slurry, i.e. in the form of particles introduced into the flow to be purified and entrained with this flow) or in the form of an ebullating bed, preferably in the form of a fixed bed or an entrained bed. The adsorbent(s) used in sub-step b) is (are) preferably an alumina, a silica, a silica-alumina, an activated carbon, a bleaching earth, or their mixtures, preferably an activated carbon, a bleaching earth or their mixtures, preferably in the form of a fixed bed or an entrained bed, the circulation of the flows being able to be ascending or descending.

[0148] Advantageously, when integrated 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, preferentially 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 dissolution temperature and pressure conditions, i.e. at the dissolution temperature and dissolution pressure reached in step a). Preferably, in the possible sub-step b'4), the hourly volumetric velocity (or WH), which corresponds to the ratio between the volumetric flow rate of the polymer solution which feeds b'4) and the volume of adsorbent, advantageously in operation in b'4), is between 0.05 and 10 h -1 , preferably between 0.1 and 5.0 h -1 .

[0149] According to a particular embodiment of sub-step b'4), the adsorption section may comprise one or more fixed bed(s) of adsorbent, for example in the form of adsorption column(s), preferably at least two adsorption columns, preferably between two and four adsorption columns, containing said adsorbent(s). When the adsorption section comprises two adsorption columns, an operating mode may be a so-called "swing" operation, according to the established English term, in which one of the columns is online, i.e. in operation, while the other column is in reserve. When the adsorbent of the online column is used up, this column is isolated while the reserve column is put online, i.e. in operation.The spent adsorbent can then be regenerated in situ and / or replaced with fresh adsorbent so that the column containing it can be brought back online once the other column has been isolated.

[0150] Another mode of operation of this particular embodiment of b'4) is to have at least two adsorbent columns operating in series. When the adsorbent of the column placed at the head is used up, this first column is isolated and the used adsorbent is regenerated in situ or replaced by fresh adsorbent. The column is then put back online in the last position and so on. This operation is called permutable mode, or according to the English term "PRS" for Permutable Reactor System or "lead and lag" according to the established Anglo-Saxon term. The association of at least two adsorption columns makes it possible to overcome the possible and possibly rapid poisoning and / or clogging of the adsorbent under the joint action of impurities, contaminants and insolubles possibly present in the flow to be treated.The presence of at least two adsorption columns facilitates the replacement and / or regeneration of the adsorbent, advantageously without stopping the process, and also makes it possible to control costs and limit adsorbent consumption.

[0151] Step c) solvent-polymer separation

[0152] According to the invention, the method comprises a step c) of solvent-polymer separation, to obtain at least one stream of purified thermoplastic polymers, more particularly at least one stream of purified polyolefins, and preferably at least one solvent fraction. This step c) is located downstream of step b) of decantation, or possibly of a step b') of purification of the decanted polymer solution.

[0153] Step c) of solvent-polymer separation aims to separate, at least in part, preferably mainly, or even in full, the solvent(s), in particular the dissolution solvent, contained in the decanted or purified polymer solution which feeds step c), so as to recover the targeted thermoplastics freed at least in part, preferably in full, of impurities and the dissolution solvent, and possibly of the other solvent(s) used in the process (i.e. the extraction solvent and / or the dense solution).By predominantly, it is necessary to understand at least 50% by weight, preferably at least 70% by weight, more 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 which feeds step c), in particular the dissolution solvent and possibly the extraction solvent and / or the dense solution contained in the decanted or purified polymer solution which feeds step c). Any solvent-polymer separation method known to those skilled in the art can be implemented, in particular all methods allowing a phase change of the polymers or solvent(s). The solvent(s) can be separated, for example, by flash evaporation of the solvents, atomization, stripping, crystallization of the polymers and solid-liquid separation, demixing, density difference and in particular decantation or centrifugation, etc.Step c) can implement several separation operations in series.For example, step c) may comprise a solvent-polymer separation by demixing at least a portion 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 the temperature being maintained between 100 and 300°C, preferably between 150 and 250°C, so as to be in the supercritical conditions of at least one of the compounds of the solvent(s), followed by at least one separation of the residual solvent by evaporation, in particular under pressure conditions lower than the pressure used for the transition to the supercritical state of the solvent, in particular at a pressure between 4 and 0.000005 MPa (i.e. 5 Pa), preferably between 3 and 0.000005 MPa (i.e. 5 Pa), the temperature being able to be maintained between 100 and 300°C, preferably between 150 and 250°C.

[0154] The stream of purified thermoplastic polymers obtained at the end of step c) may correspond to a concentrated polymer solution or to purified liquid (i.e. molten) or solid thermoplastic polymers. The solvent-polymer separation step c) may optionally further comprise a conditioning section for conditioning the recovered thermoplastics, in particular the targeted polyolefins, in solid form and more particularly in the form of solid granules. In this optional conditioning section, the recovered purified thermoplastic polymers are cooled, advantageously to a temperature below the melting temperature of the polymers, to obtain a fraction comprising thermoplastics in the solid state.

[0155] Step c) of solvent-polymer separation also aims to recover at least in part, preferably mainly and preferentially in full, the solvent(s) contained in the decanted or purified polymer solution which feeds step c), and in particular the dissolution solvent and possibly the extraction solvent and / or the dense solution. By mainly, it is necessary to understand at least 50% by weight, preferably at least 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 which feeds step c). Thus, step c) advantageously makes it possible to obtain at least a fraction of solvent.Step c) of solvent-polymer separation also possibly aims to purify the recovered solvent fraction and to recycle it in particular upstream of step a) of dissolution and possibly upstream of sub-step b'2) and / or sub-step b'3).

[0156] 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), so as to purify it and obtain a purified solvent, in particular a purified dissolution solvent and optionally a purified dense solution and / or a purified extraction solvent, in order to be able to advantageously recycle it 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 implement any method known to those skilled in the art, for example one or more methods among distillation, evaporation, liquid-liquid extraction, adsorption, crystallization and precipitation of insolubles, or by purging.

[0157] Thus, the process according to the invention makes it possible to obtain a stream of purified thermoplastic polymers, and more particularly purified polyolefins, from any type of plastic filler and in particular plastic waste. In particular, the process according to the invention makes it possible to eliminate at least 70% by weight, preferably at least 80% by weight, of the impurities, and in particular inorganic impurities, contained in the plastic filler. The process according to the invention also makes it possible to eliminate organic compounds and polymers, in particular insoluble ones, other than the targeted thermoplastics. In addition, very advantageously, the stream of purified thermoplastics, in particular purified polyolefins, obtained at the end of the process is less colored or even discolored compared to the plastic filler which is fed by the process according to the invention.The stream of purified thermoplastic polymers obtained at the end of the process according to the invention can then be used in any application, for example as a replacement for the same polymers in the virgin state. The stream of purified thermoplastic polymers, obtained continuously by the process according to the invention, thus has a sufficiently low impurity content to be able to be used in any application.

[0158] Very preferably, the stream of purified thermoplastic polymers obtained at the end of the process according to the invention advantageously has an impurity content of less than or equal to 5% by weight, very advantageously an impurity content of less than or equal to 1.0% by weight of impurities, or even a content of less than or equal to 0.5% by weight of impurities. Very advantageously, the stream of purified thermoplastic polymers obtained at the end of the process according to the invention (has a residual solvent content (in particular dissolving 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, or even a content of less than or equal to 500 ppm by weight, relative to the total weight of the stream of purified thermoplastics.

[0159] Device

[0160] The present invention also relates to a device for treating a plastic load to obtain a flow of purified thermoplastic polymers, which comprises:

[0161] - means for bringing into contact and dissolving at least in part the plastic filler in a dissolving solvent, such as an extruder, one or more static mixers, one or more continuously stirred reactors, also called “Continuous Stirred Tank Reactor” (CSTR) according to English terminology, equipped with suitable stirring system(s), to obtain a crude polymer solution;

[0162] - a settling device comprising at least one settling tank (also called a static settling tank), preferably between one and ten settling tanks, preferably between two and five settling tanks; when the settling device comprises several settling tanks, said settling tanks operate in series or in parallel, preferably in parallel, said settling tank(s) being vertical or horizontal, preferably cylindrical or generally cylindrical in shape, or even multi-cylindrical in shape, preferably having a ratio L / D between the total height or length L of the settling tank and the diameter (or width) D of the settling tank of between 0.5 and 12, preferably between 1.0 and 6.0, said settling tank(s) comprising a feed point, to be fed with polymer solution, in particular with raw polymer solution or with an effluent enriched with polymer solution,advantageously the feed point of the decanter or of the first decanter of the decanters in series or of each decanter in parallel being connected to said means for contacting and dissolving to feed said decanter(s) with at least a fraction, or all, of said raw polymer solution, 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 said decanter, from the head (or upper end) of said vertical decanter, and three quarters of the height of said decanter, from the head (or upper end) of said vertical decanter, preferably between a third of the height of said decanter, from the head (or upper end) of said vertical decanter, and the upper two thirds of the height of said decanter, from the head (or upper end) of said vertical decanter,said feed point then defining two zones in the vertical decanter considered, an upper zone located between the feed point and the head (or upper end) of the vertical decanter, and a lower zone located between the feed point and the bottom (or lower end) of the vertical decanter, preferably when the decanter considered is a horizontal decanter, the feed point of said decanter is advantageously located towards one end of the horizontal decanter considered, that is to say at one of the ends of the horizontal decanter or close to one of the ends of the horizontal decanter, preferably in a zone between one of the two ends of the horizontal decanter and a third of the length of said decanter from said end, preferably between one of the two ends of the horizontal decanter and a quarter of the length of said decanter from said end,said decanter(s) comprising a first outlet for an effluent enriched in polymer solution and a second outlet for a residue stream, when the decanting device comprises several decanters in series, the first outlet (i.e. the outlet of the effluent enriched in polymer solution) of the downstream decanter is advantageously connected to the feed point of the decanter directly upstream (i.e. the first outlet of decanter i is connected to the feed point of decanter i+1), except for the last decanter in the series for which the first outlet (i.e. the outlet of the effluent enriched in polymer solution) is connected to means located downstream of the decanting device, in particular solvent-polymer separation means or possibly an additional purification system, when the decanting device comprises several decanters in parallel,all of said first outlets (i.e. the outlets of the effluent enriched in polymer solution) of said decanters are connected to each other and to a mixing system for mixing all of the effluents enriched in polymer solution recovered at the outlet of said decanters in parallel, said mixing system being very advantageously connected to means located downstream of the decanting device, in particular solvent-polymer separation means or possibly an additional purification system, preferably when the decanter considered is a vertical decanter, the first outlet (i.e. the outlet of the effluent enriched in polymer solution) of said decanter is advantageously located in the upper zone of the vertical decanter considered, i.e. in a zone between the feed point and the head (or upper end) of the vertical decanter, and the second outlet is advantageously located in the lower zone 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 (i.e. outlet of the effluent enriched in polymer solution) of said decanter and preferably the second outlet, is (are) advantageously located towards the end opposite the feed point, i.e. at the end or close to the end which is opposite the end towards which the feed point is located, preferably said first outlet and preferably said second outlet, is (are) located in an area between the end opposite the feed point and one third of the length of the decanter from said opposite end, preferably between the end opposite the feed point and one quarter of the length of the decanter from said opposite end, said decanter(s) having a design so as to have:,

[0163] - a liquid surface velocity varying between 1x10" 7 and 1,000x10" 2 m / s, preferably between 1.0x10' 6 and 1,000x10' 2 m / s, preferably between 1.0x10" 5 and 6,000x10' 3 m / s, preferably between 2.0x10 -5 and 5,000x10' 3 m / s, very preferably between 2.0x10 -5 and 9.00x10" 4 m / s, especially between 2.0x10" 5 and 5.00x10" 4 m / s,

[0164] - preferably an injection speed 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;

[0165] - possibly an additional purification system, located downstream of the decantation device, and comprising in particular additional solid-liquid separation means, for example filters, washing means, extraction means and / or adsorption means, when said additional purification system comprises several means, said means operate in series with each other;

[0166] - solvent-polymer separation means, located downstream of the decantation device, for separating a solvent flow comprising in particular the dissolution solvent and a flow of purified thermoplastic polymers, in particular a flow of purified polyolefins, said solvent-polymer separation means being advantageously connected to said decantation or possibly to said additional purification system.

[0167] Preferably, the treatment device comprises at least one additional purification system, preferably comprising additional solid-liquid separation means, for example filters and / or adsorption means, preferably additional solid-liquid separation means and then adsorption means. Said device for treating a plastic load also advantageously comprises transport means between said means and devices.

[0168] The following examples and figures illustrate the invention, in particular particular embodiments of the invention, without limiting its scope.

[0169] LIST OF FIGURES

[0170] Figure 1 represents the diagram of a decanter implemented according to an embodiment of the method of the present invention, in which the decanter is a vertical decanter, generally cylindrical, the bottom of said decanter being conical and the head end being hemispherical in shape. The decanter has a length L and a diameter D. It is fed with a polymer solution at the feed point 1. The effluent enriched with polymer solution is recovered at point 2 and the residues purged at point 3.

[0171] Figure 2 shows the diagram of a decanter implemented according to another embodiment of the method of the present invention, in which the decanter is a horizontal, generally cylindrical decanter, with hemispherical ends. The decanter has a length L and a diameter D. It is fed with a polymer solution at feed point 1. The effluent enriched with polymer solution is recovered at point 2 and the residues purged at point 3.

[0172] EXAMPLES

[0173] In the examples below, the analyses carried out on the load and the products obtained are as follows:

[0174] - the ash content, which gives an indication of the inorganic impurity content, is determined by thermogravimetric analysis (TGA). The ash content is determined by thermogravimetric analysis (TGA), using a Perkin Elmer TGA 8000 device, according to ISO 11358-1 (2014). A sample of 10-20 mg of material is placed on a platinum plate. The temperature is equilibrated at 50°C for 10 minutes, then increased at a heating rate of 20°C / min to 950°C under nitrogen flow. The ash content corresponds to the weight determined at 850°C relative to the weight of the initial sample, expressed as a weight percentage (% by weight);

[0175] - the contents of organic compounds, in particular Irganox® 1010, Irgafos® 168, oxidized Irgafos® 168, are 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 ISO 11664-4), with: o a parameter L* of lightness (or luminance), such that the closer L* is to 100, the clearer or more transparent the analyzed solid is; conversely, the closer L* is to 0, the more opaque the analyzed solid is; o a parameter a* (corresponding to a green-red axis), which measures the color ranging from green (negative values) to red (positive values); a target value of a* is a value approaching 0; o a parameter b* (corresponding to a blue-yellow axis), which measures the color ranging from blue (negative values) to yellow (positive values); a target value of b* is a value approaching 0.

[0176] L*a*b* values ​​are determined using a Standard Konica / Minolta Colorimeter CM-3700A device, on solid samples of approximately 20 g of cryo-ground material.

[0177] Example 1 (in accordance with the invention)

[0178] Step a) of dissolution:

[0179] A filler derived from plastic waste and containing 95% by weight of polypropylene (PP) is introduced in the form of flakes into an extruder heated to 200°C. At the extruder outlet, the filler is at least partly in molten form and is mixed with n-heptane used as solvent and previously heated to 200°C, according to a solvent / filler weight ratio of 5 / 1. The mixture comprising the solvent and the filler is introduced into a stirred reactor and heated to 200°C, and maintained at 2.0 MPa absolute, for a residence time of 1 hour. A crude polymer solution is then obtained.

[0180] Step b) decantation:

[0181] The raw polymer solution from dissolution step a) is then subjected to decantation step b):

[0182] The raw polymer solution is continuously withdrawn from the stirred reactor and injected into a static, vertical decanter, having an L / D ratio between the total height and the diameter of the generally cylindrical decanter of 3.1. Said decanter is operated according to the following conditions:

[0183] - A temperature of 200°C

[0184] - A pressure of 2.0 MPa

[0185] - An injection speed of 0.04 m / s - An upward empty barrel speed of 0.07 mm / s

[0186] - A stay of 1 hour.

[0187] A "cake" is deposited at the bottom of the decanter: it includes insoluble compounds, inorganic solids, a solvent fraction, and organic elements. This "cake" is purged sequentially at a frequency of 0.8 mHz.

[0188] Step c) solvent-polymer separation:

[0189] At the outlet of the decanter, the decanted polymer solution from step b) is then subjected to a solvent-polymer separation step c).

[0190] At the process outlet, at atmospheric temperature and pressure, a solid A is obtained. Solid A is composed of polypropylene (PP). Solid A is analyzed. The results are summarized in Table 1 below. Table 1 compares the characteristics measured for the feedstock and for the solid A obtained, including the ash content (which gives an indication of the inorganic impurity content), the colorimetry parameters L, a and b and the relative weight quantities of three organic compounds (Irganox® 1010, Irgafos® 168, Irgafos® 168 oxidized).

[0191] Table 1

[0192] The obtained solid A composed of polypropylene (PP) is purified compared to the plastic filler (see table 1) since: - more than 80% by weight of inorganic impurities (100x(1.09-0.2) / 1.09=81.65%) have been eliminated (solid A comprises more than 80% by weight less inorganic impurities compared to the plastic filler);

[0193] - the contents of the three organic impurities tested (Irganox® 1010, Irgafos® 168, oxidized Irgafos® 168) are also reduced in solid A (respectively 194 ppm weight, 138 ppm weight and 505 ppm weight) compared to the plastic filler (respectively 1831 ppm weight, 628 ppm weight and 1899 ppm weight);

[0194] - solid A is also less colored than the charge: the brightness parameter L is increased for solid A (88.65) and approaches 100 compared to that measured for the charge (57.47), while the parameters a and b are closer to the value 0 for solid A (a=1.23 and b=7.76) compared to the charge (respectively 14.68 and 10.83).

[0195] Example 2 (in accordance with the invention)

[0196] A filler from plastic waste, of the same type as that of Example 1, containing 95% by weight of polypropylene (PP), is introduced in the form of flakes into an extruder heated to 200°C. At the extruder outlet, the filler is at least partly in molten form and is mixed with n-heptane used as solvent and previously heated to 200°C, according to a solvent / filler weight ratio of 5 / 1. The mixture is then introduced into a stirred reactor and heated to 200°C, and maintained at 2.0 MPa absolute, for a residence time of 1 hour. A crude polymer solution is then obtained.

[0197] The raw polymer solution is continuously withdrawn from the stirred reactor and injected into a static, vertical decanter, having an L / D ratio between the total height of the decanter and the diameter of the generally cylindrical decanter of 3.1. Said decanter is operated under the following conditions:

[0198] - A temperature of 200°C

[0199] - A pressure of 2.0 MPa

[0200] - An injection speed of 0.04 m / s

[0201] - An upward empty barrel speed of 0.07 mm / s

[0202] - A stay of 1 hour.

[0203] Impurities settle at the bottom of the decanter, forming a “cake” or “bed” which is purged discontinuously at a frequency of 0.8 mHz.

[0204] At the outlet of the decanter, the decanted polymer solution is filtered through a 10 μm mesh filter and then through a 1 μm mesh filter. The filtered polymer solution is then sent to an adsorption column containing an activated carbon bed, and operated at 200°C and 2.0 MPa.

[0205] The adsorbed polymer solution, recovered at the outlet of the adsorption column, is then subjected to a solvent-polymer separation step.

[0206] At the process outlet, and at atmospheric temperature and pressure, a solid B is obtained. Solid B is composed of polypropylene (PP). Solid B is analyzed in the same way as solid A of Example 1. The results are summarized in Table 2 below, which compares the characteristics measured for the feedstock and the solid B obtained, in particular the ash content (which gives an indication of the inorganic impurity content), the colorimetry parameters L, a and b and the relative weight quantities of three organic compounds (Irganox® 1010, Irgafos® 168, oxidized Irgafos ®168).

[0207] Table 2

[0208] The obtained solid B, composed of polypropylene (PP), is purified with respect to the plastic filler (see table 2) since:

[0209] - approximately 100% by weight of inorganic impurities (100x(1,1 -0.0) / 1,1 =100%) were removed;

[0210] - the contents of the three organic impurities tested (Irganox® 1010, Irgafos® 168, oxidized Irgafos® 168) are also reduced in solid B (respectively 158 ppm by weight, 113 ppm by weight and 494 ppm by weight) compared to the plastic filler (respectively 1831 ppm by weight, 628 ppm by weight and 1899 ppm by weight); - solid B is also less colored than the filler and the colorimetry parameters are improved: the brightness parameter L is increased for solid B (98.89) and approaches 100 compared to that measured for the filler (57.47), while the parameters a and b are closer to the value 0 for solid B (a = -0.29 and b = 4.61) compared to the filler (respectively 14.68 and 10.83).

Claims

CLAIMS 1. A method for treating a plastic filler, comprising: a) a step of dissolving the plastic filler in a dissolving solvent, step a) being carried out at a dissolution temperature of between 100°C and 300°C and at a dissolution pressure of between 1.0 and 100.0 MPa absolute, to obtain at least one crude polymer solution; b) a step of decanting the crude polymer solution, to obtain a decanted polymer solution and a residue fraction, step b) being carried out at a temperature of between 100°C and 300°C and a pressure of between 1.0 and 100.0 MPa absolute, and using at least one decanter, when step b) comprises several decanters, said decanters operate in series or in parallel, the decanter or the first decanter of the decanters in series or each decanter in parallel being supplied with at least one fraction of said crude polymer solution,in which an effluent enriched in polymer solution is recovered at the outlet of the or each decanter, the effluent enriched in polymer solution recovered at the outlet of said decanter or of the last decanter of the decanters operating in series or all of the effluents enriched in polymer solution recovered at the outlet of each decanter operating in parallel, constituting said decanted polymer solution, a residue stream being recovered at the outlet of the or each decanter, all of the recovered residue streams constituting said residue fraction, said at least one decanter having a liquid superficial velocity varying between 1x10', 7 and 1,000x10 -2 m / s; then c) a solvent-polymer separation step, to obtain at least one stream of purified thermoplastic polymers.

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

0.

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

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

5. Method according to any one of the preceding claims, in which step b) uses between one and ten decanters, preferably between two and five decanters.

6. Method according to any one of the preceding claims, in which each decanter of step b) is of cylindrical or generally cylindrical shape, having a ratio L / D between the total length L and the diameter D of the decanter of between 0.5 and 12, preferably between 1.0 and 6.

0.

7. Method according to any one of the preceding claims, in which the liquid superficial velocity varies, in each decanter, between 1.0x10' 6 and 1,000x10 -2 m / s, preferably between 1.0x10 -5 and 6,000x10 -3 m / s, most preferably between 2.0x10' 5 and 9.00x10 -4 m / s.

8. Method according to any one of the preceding claims, in which each decanter has an injection speed less than or equal to 1.00 m / s, preferably less than or equal to 0.10 m / s, preferentially less than or equal to 0.05 m / s, and preferably greater than or equal to 0.001 m / s.

9. Method according to any one of the preceding claims, in which each decanter is operated with a filling rate of between 70% and 100% of the total volume of the decanter in question.

10. Method according to any one of the preceding claims, comprising a step of purifying the decanted polymer solution to obtain a purified polymer solution, said purification step comprising: b'1) an additional solid-liquid separation sub-step; and / or b'2) a washing sub-step, by contact with a dense solution; and / or b'3) an extraction sub-step, by contact with an extraction solvent; and / or b'4) a sub-step of adsorption of the impurities by contact with a solid adsorbent.

11. Method according to any one of the preceding claims, in which the plastic filler comprises thermoplastic polymers, more particularly polyolefins.

12. Device for treating a plastic load to obtain a flow of purified thermoplastic polymers, which comprises: - means for bringing into contact and dissolving at least in part the plastic filler in a dissolving solvent, to obtain a crude polymer solution; - a decanting device comprising at least one decanter in which a liquid surface velocity varies between 1x10' 7 and 1,000x10' 2 m / s and preferably in which the injection speed is less than or equal to 1.00 m / s, when the decanting device comprises several decanters, said decanters operating in series or in parallel, said at least one decanter being a vertical or horizontal decanter, preferably of cylindrical or generally cylindrical shape, preferably having a ratio L / D between the total height or length L of the decanter and the diameter D of the decanter of between 0.5 and 12, said decanter(s) comprising a polymer solution feed point, said at least one decanter comprising a first outlet for an effluent enriched in polymer solution and a second outlet for a residue 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 the series for which the first outlet is connected to means located downstream of the decanting device, when the decanting device comprises several decanters in parallel, all of said first outlets of said decanters are connected to each other and to a mixing system for mixing all of the effluents enriched in polymer solution recovered at the outlet of said decanters in parallel,said mixing system being connected to means located downstream of the decanting device; - possibly an additional purification system, located downstream of the decantation device; - solvent-polymer separation means, located downstream of the decantation device, for separating a solvent stream and a stream of purified thermoplastic polymers.

13. Device according to claim 12, wherein the liquid surface velocity in said at least one decanter varies between 1.0x10 -6 and 1,000x10' 2 m / s, preferably between 1.0x10' 5 and 6,000x10 -3 m / s, most preferably between 2.0x10' 5 and 9.00x10' 4 m / s.

14. Device according to claim 12 or 13, wherein said at least one decanter is a vertical decanter, wherein: - the feed point of said decanter is located between a quarter of the height of said decanter and three quarters of the height of said decanter, said feed point then defining two zones in the vertical decanter considered, an upper zone located between the feed point and the head of the vertical decanter, and a lower zone located between the feed point and the bottom of the vertical decanter, and - the first outlet of said decanter is located in the upper zone of the vertical decanter in question, and the second outlet is located in the lower zone of the vertical decanter.

15. Device according to claim 12 or 13, wherein said at least one decanter is a horizontal decanter, wherein: - the feed point of said decanter is located towards one end of the horizontal decanter considered, - the first outlet and the second outlet of said decanter are located towards the end opposite the feed point.

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