Method for recycling and processing used plastics by dissolving in a solvent with staggered solvent addition

Abstract

The present invention relates to a method for processing a plastics feedstock, the method comprising: a) a dissolution step, implementing: i) a section for bringing the plastics feedstock into contact with at least some of a dissolution solvent, comprising at least one static or dynamic mixer, each mixer being fed with a plastics stream and a fraction of the dissolution solvent so that each mixer has a volume dilution ratio of dissolution solvent of between 3% and 70%, each mixer being run at a temperature of between 100°C and 300°C; then ii) a dissolution section run at a temperature of between 100°C and 300°C and a pressure of between 1.0 and 100.0 MPa absolute; then b) a purification step; then c) a solvent-polymer separation step, in order to obtain at least one fraction of purified thermoplastic polymers.

Description

[0001] PROCESS FOR RECYCLING AND TREATMENT OF USED PLASTICS BY DISSOLUTION IN A SOLVENT WITH STAGED INTRODUCTION OF THE SOLVENT

[0002] TECHNICAL FIELD

[0003] 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 filler, in particular from plastic waste, comprising thermoplastic polymers, 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 a staged mixing of the solvent with the plastic filler, to obtain a homogeneous mixture, preferably having a viscosity of less than or equal to 50 mPa.s, and very advantageously a concentration variation coefficient less than or equal to 10%, so as to optimize the dissolution of the targeted thermoplastics and the purification of the polymer solution obtained to recover a flow of purified thermoplastics.

[0004] PRIOR TECHNIQUE

[0005] Plastics from collection and sorting channels can be recycled through different channels.

[0006] 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 because, even if it allows a stream concentrated in a particular type of polymer to be obtained, 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.

[0007] 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.

[0008] Several studies thus present different methods of treating plastic waste by dissolution and purification. Document US 2017 / 0021 10 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 resulting polymer solution with a solid.

[0009] 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 other than polymers, for example additives.

[0010] Document 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 document US 2018 / 0208736 does not allow for effective treatment of impurities soluble in the solvent.

[0011] 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 methods of removing impurities from a plastic filler, by particularly improving the phase of bringing the solvent into contact with the plastic filler to be treated. The present invention thus aims to obtain a homogeneous mixture advantageously having a sufficiently low viscosity, thus allowing optimal dissolution of the targeted thermoplastics, in particular in terms of dissolution time, stirring power required for mixing in the reactor and operating cost.Very advantageously, the elimination of impurities can thus be maximized in order to 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, in particular in place of virgin resin. SUMMARY OF THE INVENTION.

[0012] The invention relates to a method for treating a plastic filler, comprising: a) a step of dissolving the plastic filler in a dissolving solvent, to obtain at least one raw polymer solution, the dissolving step a) implementing: i) a section for bringing the plastic filler into contact with at least a portion of the dissolving solvent, comprising at least one static or dynamic mixer, to produce a conditioned filler, each static or dynamic mixer being operated at a temperature of between 100°C and 300°C, each static or dynamic mixer being supplied with a plastic flow, comprising the plastic filler, and with a fraction of at least said portion of the dissolving solvent, so that each mixer has a volume dilution rate of dissolving solvent of between 3% and 70%,the volume dilution rate in dissolution solvent being the ratio between the volume flow rate of the fraction of at least said part of the dissolution solvent which feeds the static or dynamic mixer considered and the sum of the volume flow rates of the fraction of at least said part of the dissolution solvent and of the plastic flow which feed the static or dynamic mixer considered; ii) a dissolution section fed at least by the conditioned charge coming from the contacting section and operated at a dissolution temperature of between 100°C and 300°C and a dissolution pressure of between 1.0 and 100.0 MPa absolute; then b) a step of purifying the crude polymer solution to obtain a purified polymer solution, said purification step comprising: b1) a sub-step of separating the insolubles; and / or b2) a sub-step of washing, by contact with a dense solution; and / or b3) an extraction sub-step,by contact with an extraction solvent; and / or b4) a sub-step of adsorption of impurities by contact with a solid adsorbent; then, c) a step of solvent-polymer separation, to obtain at least a fraction of purified thermoplastic polymers.,

[0013] The advantage of the method of the invention is to propose a method for the efficient treatment of a plastic load, and in particular plastic waste, in particular from collection and sorting channels, so as to recover the thermoplastic polymers, in particular polyolefins, which it contains in order to be able to recycle them for all types of applications. The method according to the invention makes it possible more particularly to improve the phase of bringing the plastic load into contact with the dissolving solvent in order to obtain a homogeneous mixture advantageously having a viscosity preferably less than or equal to 50 mPa.s, preferably less than or equal to 20 mPa.s, very preferably less than or equal to 5 mPa.s, very preferably less than or equal to 1 mPa.s. Very advantageously, said homogeneous mixture has a coefficient of variation (CoV) of concentration preferably less than or equal to 10%, preferably less than or equal to 5%.Such a mixture has the advantage of thus leading to a sufficiently low effective viscosity in the dissolution reactor, thus participating in the dispersion and homogenization of the plastic feedstock - dissolution solvent mixture. The dissolution of the thermoplastics that one seeks to separate and recover is then optimal, without requiring excessively high stirring powers and / or while allowing the use of various stirring systems, such as mechanical stirring and / or stirring by recirculation loop. At the same time, the residence time necessary to effectively dissolve the targeted thermoplastics can also be advantageously reduced, which can result in the use of equipment, for example the dissolution reactor, of optimized size.

[0014] The present invention thus makes it possible to efficiently pre-mix the plastic filler with the dissolution solvent (or at least part of the dissolution solvent), while respecting technical constraints imposed by the mixing equipment used, in particular by the stirring system of the dissolution section but also by equipment used in the contacting section, for example static mixers. Generally, static mixers are used to mix fluids whose viscosity ratio between said fluids varies up to 1000 (i.e. < 1000). However, the present invention makes it possible to efficiently mix a plastic filler comprising thermoplastics, in particular polyolefins, whose viscosity in the molten state is typically between 300 and 20,000 Pa.s, with a solvent whose viscosity varies between 1 and 0.01 mPa.s, in particular between 0.2 and 0.03 mPa.s, in the temperature range at which the mixture is operated, i.e. a viscosity ratio between these two fluids in a range of approximately 10. 5 -10 9 , which is very high and usually incompatible with the technical constraints of static or dynamic mixers.

[0015] The process according to the invention, which comprises a dissolution step and in particular improved contacting of the solvent and the filler, thus makes it possible to obtain a stream of purified thermoplastics, advantageously comprising a content of impurities, and in particular additives, which is negligible or at least sufficiently low so that the stream of purified thermoplastic polymers can be used in any type of plastic formulation instead of virgin resin. For example, the stream of purified thermoplastics and in particular the stream of purified polyolefins, 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 of impurities, very advantageously less than or equal to 1.0% by weight of impurities, even more preferably a content of less than or equal to 0.5% by weight of impurities.

[0016] The method according to the invention thus proposes a simple scheme corresponding to a sequence of operations, which makes it possible to rid the plastic waste of at least some of its impurities, in particular at least some of the additives, and to recover purified thermoplastic polymers, advantageously comprising little or no solvent, so as to be able to recover the plastic waste by recycling said purified thermoplastics. Depending on the conditions implemented in the steps of the method, the additives present in the plastic feedstock can advantageously be soluble or insoluble in the solvent used throughout the method according to the invention, allowing efficient purification and separation of the polymers.

[0017] 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 fractions of purified thermoplastic polymers, in particular purified polyolefins, with a reduced content of impurities, in particular decolorized and deodorized thermoplastic fractions, which can be reused to form new plastic objects. The purified thermoplastic fractions obtained can thus be used directly in formulations mixed with additives, for example dyes, pigments, other polymers, instead of or mixed with virgin polymer resins, in order to obtain plastic products with usage, aesthetic, mechanical or rheological properties facilitating their reuse and recovery.

[0018] DESCRIPTION OF EMBODIMENTS

[0019] 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.

[0020] In the sense of the present invention, the different parameter ranges for a given step such as pressure ranges and temperature ranges can be used alone or in combination. For example, in the sense of the present invention, a range of preferred pressure values ​​can be combined with a range of more preferred temperature values. In the following, particular embodiments of the invention can be described. They can be implemented separately or combined with each other, without limitation of combinations when this is technically feasible.

[0021] According to the present invention, the pressures are absolute pressures and are given in absolute MPa (or MPa abs.).

[0022] 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.

[0023] In this description, the terms "polymer", "thermoplastic polymer" and "thermoplastic" may be used interchangeably in place of each other.

[0024] The terms “static or dynamic mixer” and “mixer” are used interchangeably and correspond to mixing equipment well known to those skilled in the art such as static mixer or dynamic mixer.

[0025] According to the invention, viscosity is defined as being a dynamic viscosity, in particular measured at a temperature of 200°C and at a shear rate of 0.1 s -1 , using a viscometer, preferably using a plate-plate type viscometer, for example type DHR3 from TA Instrument.

[0026] According to the invention, the coefficient of variation (CoV) of concentration is calculated by dividing the standard deviation of z concentration measurements by the average concentration, expressed as a percentage: with the standard deviation on the concentration measurements: a the average concentration: x = n representing in these mathematical formulas, the total number of concentration measurements, xi representing the concentration value determined at measurement i; and z being an integer greater than or equal to 2, preferably greater than or equal to 4, and generally less than or equal to 10,000, preferably less than or equal to 1,000, the concentration being determined by any method known to those skilled in the art, for example by visualizing the color of a mixture of fluids of different colors, by measuring the content of a particular compound in samples taken (in particular z samples) and determined for example by liquid chromatography (or HPLC) or gas chromatography. The lower the concentration coefficient of variation (CoV), the better the quality of the mixture, i.e. the more homogeneous the mixture.

[0027] 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, dyes, pigments, hardeners, flame retardants, combustion retardants, stabilizing agents, antioxidants, UV absorbers, antistatic agents, etc.

[0028] 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.

[0029] 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 resulting from the life cycle of plastic materials and objects, and / or resulting from the waste collection and sorting circuit. The latter may be metallic, organic or mineral impurities; they may be packaging residues, food residues or compostable residues (biomass). These usage impurities may also include glass, wood, cardboard, paper, aluminum, iron, metals, tires, rubber, silicones, rigid polymers, thermosetting polymers, household, chemical or cosmetic products, used oils, water.

[0030] 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 soluble (and solubilized in the dissolution solvent) and / or insoluble (and suspended in the polymer solution) impurities. Depending on the steps of the process according to the invention undergone, said polymer solution may therefore comprise impurities in the form of insoluble particles which are advantageously suspended in said polymer solution, soluble impurities dissolved in the dissolution solvent, and / or possibly another liquid phase immiscible with said polymer solution.

[0031] 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).

[0032] 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 substance, the critical temperature and critical pressure of a pure substance are respectively the temperature and pressure of the critical point of said pure substance. As well known to those skilled in the art, at the critical point and beyond, the pure substance considered is in supercritical form or in the supercritical state; it can then be called a supercritical fluid.

[0033] 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 preferably aliphatic hydrocarbon compound, preferably having a boiling point of between -50 and 250°C, preferably between -15 and 150°C, preferably between -1 and 110°C and preferably between 20 and 100°C, preferably according to a weight ratio between the dissolving solvent and the plastic filler of between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, even more preferably between 3.0 and 7.0, to obtain at least one crude polymer solution,step a) of dissolution implementing: i) a section for bringing the plastic charge into contact with at least a portion of the dissolution solvent, comprising at least one, preferably between one and ten, preferably between two and six, preferably between two and five, static or dynamic mixer(s), advantageously in series, to produce a conditioned charge, each static or dynamic mixer being operated at a temperature between 100°C and 300°C, preferably between 150 and 250°C, each static or dynamic mixer being supplied with a plastic flow, comprising the plastic charge, and with a fraction of at least said portion of the dissolution solvent so that each mixer has a volume dilution rate in dissolution solvent between 3% and 70%, preferably between:,

[0034] - between 3% and 50%, preferably between 10% and 35%, and very preferably between 15% and 30%, when the ratio of the viscosities between the plastic flow and the fraction of at least said part of the dissolving solvent, which feeds the static or dynamic mixer considered, is greater than or equal to 3500, preferably greater than or equal to 3000,

[0035] - between 10% and 70%, preferably between 20% and 65%, very preferably between 30% and 65%, or even between 35% and 65%, when the ratio of the viscosities between the plastic flow and the fraction of at least said part of the dissolving solvent, which feeds the static or dynamic mixer in question, is less than 3500, preferably less than 3000, the volume dilution rate in dissolving solvent, for each static or dynamic mixer in question, being the ratio between the volume flow rate of the fraction of at least said part of the dissolving solvent which feeds the static or dynamic mixer in question and the sum of the volume flow rates of said fraction of at least said part of the dissolving solvent and of the plastic flow which feeds the static or dynamic mixer in question, the contacting section being able to comprise a means for melting at least in part the plastic charge, located upstream of the first static or dynamic mixer,the melting means then being advantageously supplied with the plastic charge and optionally also being supplied with a fraction of at least said part of the dissolution solvent, for example between 0.02 and 4.0% by weight, or even between 0.1 and 1.0% by weight, of the weight of dissolution solvent introduced in step a); ii) a dissolution section supplied at least with the conditioned charge from the contacting section, and optionally with another part of the dissolution solvent, and operated at a dissolution temperature of between 100°C and 300°C, preferably between 150 and 250°C, and a 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; then b) a step of purification of the crude polymer solution,comprising: b1) a sub-step of separating the insolubles making it possible to obtain at least one clarified polymer solution and one insoluble fraction; and / or b2) a washing sub-step, by contact with a dense solution, making it possible to obtain at least one washing effluent and one washed polymer solution; and / or b3) an extraction sub-step, by contact with an extraction solvent, making it possible to obtain at least one extracted polymer solution and one used solvent; and / or b4) a sub-step of 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 fraction of purified thermoplastic polymers, more particularly at least one fraction of purified polyolefins.,

[0036] The charge

[0037] 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.

[0038] 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 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 (injection-molded parts, tubes, films, fibers, fabrics, mastics, coatings, etc.). The additives used in plastics can be organic compounds or inorganic compounds.These include, for example, fillers, colorants, pigments, plasticizers, property modifiers, flame retardants, etc.

[0039] 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. The thermoplastic polymers included in the plastic feedstock may be alkene polymers, diene polymers, vinyl polymers and / or styrenic polymers. Preferably, the thermoplastic polymers included in the plastic feedstock are polyolefins, such as polyethylene (PE), polypropylene (PP) and / or copolymers of ethylene and propylene or mixtures thereof. Preferably, the plastic feedstock comprises at least 80% by weight, preferably at least 85% by weight, more preferably at least 90% by weight, of polyolefins relative to the total weight of the plastic feedstock.The process according to the invention thus aims in particular to purify and recover the polyolefins contained in the feedstock in order to be able to reuse them in different applications.

[0040] The plastic filler may comprise polymer blends, in particular blends of thermoplastics and / or blends of thermoplastics and other polymers, additives advantageously used to formulate the plastic material and generally usage impurities from the life cycle of plastic materials and objects, and / or 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.

[0041] The plastic filler can advantageously be pretreated upstream of the process so as to at least eliminate all or part of the so-called coarse impurities, that is to say 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 type, etc., and to shape it generally in the form of divided solids so as to facilitate treatment in the process. This pretreatment can comprise a grinding step, a washing step at atmospheric pressure and / or a drying step. This pretreatment can 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.

[0042] Step a) of dissolution

[0043] 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, 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. Dissolution step a) then implements i) a section for bringing the plastic filler into contact with part or all of the dissolution solvent, said contacting being advantageously carried out by staged introduction of the dissolution solvent, and ii) a dissolution section allowing the dissolution of at least part of the plastic filler, preferably at least part of the targeted thermoplastics, preferably all of the targeted thermoplastics, in particular the targeted polyolefins, in the dissolution solvent.The contacting section and the dissolving section may be separate and successive sections, with the contacting section preceding the dissolving section, or joint and simultaneous sections.

[0044] By dissolution, it is necessary to understand any phenomenon leading to the obtaining of at least one solution of thermoplastic polymers, that is to say a liquid (or fluid) comprising the targeted thermoplastic polymers dissolved in the dissolution solvent. The person skilled in the art is well aware of the phenomenon(s) involved in the dissolution of polymers and which comprises at least a mixing, a solvation, a dispersion, a homogenization, a disentanglement of the thermoplastic polymer chains.

[0045] 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 thermoplastic polymers targeted and very particularly the polyolefins targeted, and for example at least part of the impurities, is advantageously dissolved, at least in part and preferably in full, in the dissolution solvent.

[0046] 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. For example, the dissolution solvent comprises a compound chosen from the isomers of butane, pentane, hexane, heptane and octane.The dissolving solvent may comprise, preferably consist of, a mixture of isomers of butane, pentane, hexane, heptane and / or octane, and preferably at a content of said mixture in the dissolving 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 dissolving solvent. Very advantageously, a preferred hydrocarbon compound for the dissolving 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, preferably between 130 and 300°C, preferably between 180 and 285°C.

[0047] 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.

[0048] 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 a drop in temperature of the material flow in the contacting and possibly dissolution sections of step a).

[0049] Advantageously, the dissolution solvent comprises, preferably consists of, 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. i) the contacting section:

[0050] According to the invention, the section for bringing the plastic filler into contact with at least part of the dissolving solvent comprises at least one static or dynamic mixer, preferably between one and ten, preferably between two and six, very preferably between two and five static or dynamic mixer(s), preferably static. When the contacting section comprises several (i.e. at least two) static or dynamic mixers, the static or dynamic mixers are advantageously in series with each other (or successive). Advantageously, each static or dynamic mixer is operated at a temperature preferably between 100°C and 300°C, preferably between 150 and 250°C.Each static or dynamic mixer is fed with a plastic flow, comprising the plastic feed, and with a fraction of at least said part of the dissolving solvent (i.e. a fraction of the part, preferably all, of the dissolving solvent which feeds the contacting section i)) so that, in each mixer, the volume dilution rate of dissolving solvent is between 3% and 70%. The volume dilution rate of dissolving solvent in a static or dynamic mixer corresponds, according to the invention, to the ratio between the volume flow rate of the fraction of dissolving solvent which feeds the static or dynamic mixer in question (more precisely of the fraction of the part of the dissolving solvent which feeds the contacting section i) and the sum of the volume flow rates of said fraction of dissolving solvent (i.e.of the fraction of at least the part of the dissolution solvent which feeds section i)) and of the plastic flow which feeds the static or dynamic mixer considered. The term "plastic flow" corresponds to any flow in the contacting section i) of the dissolution step a), which comprises at least the plastic feed and all of the dissolution solvent fractions (i.e. fractions of at least the part of the dissolution solvent which feeds section i)) introduced into the contacting section upstream of the static or dynamic mixer considered. In other words, the plastic flow, which feeds a static or dynamic mixer, corresponds to a material flow comprising, preferably consisting of, the plastic feed, advantageously at least partly melted, added to all of the dissolution solvent fractions (i.e.fractions of at least the part of the dissolving solvent which feeds section i)) introduced into the static or dynamic mixer(s) located upstream of the static or dynamic mixer in question and possibly into a means for melting at least in part the plastic charge possibly located upstream of the first static or dynamic mixer. Thus the plastic flow which feeds the contacting section i) corresponds to the plastic charge; the plastic flow at the outlet of the contacting section i) corresponds to a flow of conditioned charge and comprises the plastic charge and at least part of the dissolving solvent.The plastic flow which feeds the first static or dynamic mixer comprises, in particular consists of, the plastic filler which is in molten form (or at least partly in molten form) or a premix comprising the plastic filler at least partly in molten form and a fraction of the dissolving solvent: the plastic flow which feeds the first static or dynamic mixer is then in particular in the form of a viscous fluid. The expression "viscous fluid" means that the flow considered is a fluid having a viscosity, in particular a dynamic viscosity, typically between 0.5 and 20,000 Pa.s, or more particularly between 1.0 and 4,000 Pa.s. The viscosity, in particular a dynamic viscosity, is measured at a temperature of 200°C and a shear rate of 0.1 s. -1, using a viscometer, preferably using a plate-plate type viscometer, for example type DHR3 from TA Instrument. Preferably, the volume dilution rate of dissolution solvent in each static or dynamic mixer is:

[0051] - between 3% and 50%, preferably between 10% and 35%, and very preferably between 15% and 30%, when the ratio of the viscosities between the plastic flow and the fraction of dissolution solvent (i.e. the fraction of at least the part of the dissolution solvent which feeds section i)), which feeds the static or dynamic mixer considered, is greater than or equal to 3500, preferably greater than or equal to 3000,

[0052] - between 10% and 70%, preferably between 20% and 65%, very preferably between 30% and 65%, or even between 35% and 65%, when the ratio of the viscosities between the plastic flow and the fraction of dissolution solvent (i.e. the fraction of at least the part of the dissolution solvent which feeds section i), which feeds the static or dynamic mixer considered, is less than 3500, preferably less than 3000.

[0053] Preferably, the dissolution solvent which feeds the dissolution step a) is divided into n partial flows of dissolution solvent, n being an integer equal to m, to m+1 or m+2, m being an integer equal to the number of static or dynamic mixers used in the contacting section i), each static or dynamic mixer being fed by one of the partial flows of dissolution solvent so that, in each static or dynamic mixer, the volume dilution rate of dissolution solvent is between 3% and 70%, and preferably:

[0054] - between 3% and 50%, preferably between 10 and 35%, and very preferably between 15% and 30%, when the ratio of the viscosities between the plastic flow and the partial flow of dissolution solvent (i.e. the fraction of dissolution solvent), which feeds the static or dynamic mixer considered, is greater than or equal to 3500, preferably greater than or equal to 3000; or

[0055] - between 10% and 70%, preferably between 20 and 65%, very preferably between 30% and 65%, or even between 35% and 65%, when the ratio of the viscosities between the plastic flow and the partial flow of dissolution solvent (i.e. the fraction of dissolution solvent), which feeds the static or dynamic mixer considered, is less than 3500, preferably less than 3000.

[0056] Optionally, a partial flow of dissolving solvent (i.e. a fraction of dissolving solvent) may feed a means for at least partially melting the plastic charge located upstream of the first static or dynamic mixer, and / or a partial flow of dissolving solvent (i.e. a fraction of dissolving solvent) may directly feed the dissolution section ii). Each static or dynamic mixer is preferably implemented with a residence time of less than or equal to 20 minutes, preferably between 0.01 seconds and 20 minutes, preferably between 0.1 seconds and 10 minutes, preferably between 0.5 seconds and 5 minutes, the residence time being defined here as the ratio between the volume of liquid (or viscous fluid) in the static or dynamic mixer considered relative to the sum of the volume flow rates of the plastic flow and the fraction of dissolving solvent which feed the static or dynamic mixer considered.

[0057] According to a particular embodiment of the invention, the contacting section i) may also comprise a means for melting at least in part the plastic filler, preferably at least in part the targeted thermoplastics, preferably all of the targeted thermoplastics. When the contacting section comprises a means for melting at least in part the plastic filler, said means is located upstream of the static or dynamic mixer(s), preferably upstream of the first static or dynamic mixer in the series. Preferably, the means for melting at least in part the polyester filler is a single- or twin-screw extruder.

[0058] Advantageously, the means for melting at least in part the plastic filler makes it possible to mix and melt at least in part the plastic filler, and more particularly to melt at least in part, preferably in full, the targeted thermoplastics of the plastic filler. Said means for melting, preferably said extruder, is therefore advantageously used at a temperature of between 100°C and 300°C, preferably between 150 and 250°C. The plastic filler thus feeds said optional means for melting, for example an extruder, in which it is advantageously heated to a temperature of between 100°C and 300°C, preferably between 150 and 250°C, and in particular to a temperature close to or even slightly higher than the melting temperature of the targeted thermoplastics, for example the targeted polyolefins, so as to become in the form of a viscous fluid, at the outlet of said means for melting.When introduced into the melting means, the plastic filler may already be at a temperature between 100°C and 300°C, preferably between 150 and 250°C, or at room temperature, for example between 10 and 30°C. It is therefore advantageously heated or maintained at a temperature between 100°C and 300°C, preferably between 150 and 250°C, in the melting means, so as to be at least partially melted. Very advantageously, at least 70% by weight of the plastic filler, preferably at least 80% by weight, preferably at least 90% by weight, of the plastic filler is in the form of a viscous fluid at the outlet of said melting means, for example from the extruder. Thus, when it is integrated into the contacting section, the means for at least partially melting the plastic filler is supplied by the plastic filler, for example in the form of solid particles, and makes it possible to obtain a flow in the form of a viscous fluid, typically with a dynamic viscosity between 0.5 and 20,000 Pa.s, or more particularly between 1.0 and 3000 Pa.s. The possible means for at least partially melting the plastic filler advantageously makes it possible to bring the plastic filler to a temperature of between 100°C and 300°C, preferably between 150 and 250°C, and to a pressure preferably between atmospheric pressure (i.e. 0.1 MPa) and 20 MPa absolute, preferably between 0.15 MPa and 15 MPa absolute, conditions in which said plastic filler is advantageously at least partially melted, and in particular in which the thermoplastics in question, included in the plastic filler, are at least partially melted, preferably completely melted.

[0059] The feeding of the melting means with the plastic charge can advantageously be carried out by any method known to those skilled in the art, for example via a feed hopper, and can be inerted in order to limit the introduction of oxygen into the process.

[0060] According to a very particular embodiment of the invention, the contacting section comprises a means for melting, preferably an extruder, which is fed by the plastic charge and which can also be fed by a fraction of the dissolving solvent, which can help to reduce the viscosity of the plastic flow at the outlet of said means, thus participating in the overall homogenization of the plastic charge at least partly melted with the dissolving solvent, and advantageously making it possible to limit the degradation of the targeted thermoplastics, in particular the targeted polyolefins. Another advantage of this very particular embodiment lies in the fact that this implementation (i.e.introduction of a fraction of the dissolving solvent into the melting means) can improve the efficiency of the mixers, in particular the first mixer, and thus allow a reduction in the number of static or dynamic mixers required to achieve a dynamic viscosity of the conditioned feed stream, i.e. of the mixture [plastic feed + dissolving solvent] at the end of the contacting section, less than or equal to 50 mPa.s, preferably less than or equal to 20 mPa.s, very preferably less than or equal to 5 mPa.s, very preferably less than or equal to 1 mPa.s, and very advantageously a coefficient of variation (CoV) of concentration preferably less than or equal to 10%, preferably less than or equal to 5%.When a fraction of the dissolving solvent is introduced into the means for at least partially melting the plastic filler, the amount of said dissolving solvent fraction which feeds said means is preferably adjusted so that the weight ratio between the dissolving solvent fraction which feeds said means and the plastic filler which feeds said means is between 0.001 and 0.20000, preferably between 0.001 and 0.100, preferentially between 0.003 and 0.050, very preferably between 0.005 and 0.030. For example, a fraction of the dissolving solvent is introduced into the means for at least partially melting the plastic filler, the amount of said dissolving solvent fraction which feeds said means preferably corresponding to between 0.02 and 4.0% by weight, or even between 0.1 and 1.0% by weight, of the total weight of dissolving solvent introduced in step a).

[0061] Preferably, the residence time in the means for at least partially melting the plastic filler, optionally implemented in section i) of contacting, is advantageously less than or equal to 1 hour, preferably less than or equal to 5 min, preferably less than or equal to 2 min, and preferably greater than or equal to 0.5 seconds, preferably greater than or equal to 1 second, very preferably greater than or equal to 10 seconds. Said residence time is defined here as the volume available in said means divided by the volume flow rate of the plastic filler.

[0062] The possible means for at least partially melting the plastic filler may advantageously be connected to a vacuum extraction system, so as to remove impurities such as dissolved gases, light organic compounds and / or moisture present in the filler.

[0063] Said possible means for melting, preferably an extruder, may also advantageously comprise at the outlet a filtration system thus making it possible to eliminate solid particles of a size greater than 20 pm, and preferably less than 2 cm, such as particles of sand, wood, metal.For example, the means for melting at least partially the plastic filler, preferably an extruder, is directly connected, at the outlet, to a first filtration system, in particular a filter, adapted to remove solid particles of a size typically greater than or equal to 1000 pm, preferably greater than or equal to 500 pm, preferably greater than or equal to 400 pm, preferably greater than or equal to 300 pm, followed by a melt pump (or "melt pump" according to the established English term) or a gear pump (or gear pump according to the English term) making it possible to maintain and / or increase the pressure, followed by a second filtration system adapted to remove solid particles of a size typically greater than or equal to 60 pm, preferably greater than or equal to 20 pm.

[0064] At the end of the contacting section i), i.e. at the outlet of the last static mixer, the plastic flow obtained advantageously corresponds to the conditioned charge, which is very advantageously in liquid form, and preferably has a viscosity less than or equal to 50 mPa.s, preferably less than or equal to 20 mPa.s, very preferably less than or equal to 5 mPa.s, very preferably less than or equal to 1 mPa.s. Very advantageously, at the end of the contacting section, the conditioned charge also has a concentration variation coefficient (CoV) preferably less than or equal to 10%, preferably less than or equal to 5%.The conditioned charge can then be defined as a homogeneous mixture comprising a polymer solution of thermoplastics, in particular polyolefins and more particularly polypropylene and / or polyethylene, in a dissolving solvent, preferably in a weight ratio between the dissolving solvent and the plastic charge 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, and comprising soluble and / or insoluble impurities, said homogeneous mixture having a viscosity and viscosity less than or equal to 50 mPa.s, preferably less than or equal to 20 mPa.s, very preferably less than or equal to 5 mPa.s, very preferably less than or equal to 1 mPa.s. ii) the dissolution section:.

[0065] The conditioned feed from the contacting section feeds the dissolution section in dissolution step a). The dissolution section may also be fed with a portion of dissolution solvent, particularly when not all of the dissolution solvent has been introduced into contacting section i). The stream recovered at the outlet of the dissolution section corresponds to a polymer solution, particularly a raw polymer solution.

[0066] Very advantageously, the dissolution section is operated at a dissolution temperature of between 100°C and 300°C, preferably between 150 and 250°C, and a 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 can vary in the dissolution section, from the conditions of introduction of the conditioned charge from the contacting section and / or of the dissolution solvent fraction possibly introduced into the dissolution section, until reaching the dissolution conditions, i.e. the dissolution temperature, in particular between 100 and 300°C, preferably between 150 and 250°C, and the dissolution pressure, in particular between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute and very preferably between 2.0 and 15.0 MPa absolute. Very advantageously, at the end of the dissolution section, the raw polymer solution is at the dissolution temperature and at the dissolution pressure.

[0067] Limiting the temperature in the dissolution section and more generally 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 thermoplastics and more particularly of the 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 thermoplastics and more particularly of the polyolefins, so as to promote their dissolution and very advantageously reduce the residence time necessary to effectively dissolve the targeted thermoplastics.Preferably, the temperature in the dissolution section and more generally 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) likely to disrupt the dissolution.

[0068] At the same time, the dissolution pressure in the dissolution section 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, which makes it possible to optimize the dissolution of the targeted thermoplastics and more particularly of the polyolefins, in particular in terms of quality and operating time.

[0069] Very advantageously, the dissolution temperature and pressure conditions reached in dissolution section ii) are adjusted so that the mixture (dissolution solvent + targeted thermoplastics) is single-phase at the end of step a), said mixture possibly including insoluble impurities suspended in said mixture.

[0070] Advantageously, dissolution section ii) is carried out for a residence time of between 1 and 600 minutes, preferably between 2 and 300 minutes, more preferably between 5 and 180 minutes. The residence time is understood, in this case, as 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 the dissolution section.

[0071] Section ii) of dissolution can implement different types of equipment such as mixing, transport, heating devices, and for example a reactor, a pump, a transport circuit, a stirring system, a furnace, an exchanger, a mixer, etc.

[0072] According to a particular embodiment, the dissolution section uses a continuously stirred reactor, also called a "Continuous Stirred Tank Reactor" (CSTR) according to English terminology, or a series of continuously stirred reactors (or CSTR reactors), said series being able to comprise between two and five CSTR reactors, preferably two or three CSTR reactors, each continuously stirred reactor (CSTR reactor) advantageously comprising a mechanical stirring system. Indeed, the method according to the invention, comprising in particular a contacting section as described above, which makes it possible to obtain a conditioned feedstock having a viscosity preferably less than or equal to 50 mPa.s, preferably less than or equal to 20 mPa.s, very preferably less than or equal to 5 mPa.s, very preferably less than or equal to 1 mPa.s, allows the use of reasonable (i.e. limited) mechanical stirring power in the dissolution reactor, thus facilitating the operability of the dissolution section while limiting the costs necessary for its implementation, and while ensuring optimal homogenization of the mixture and maximum dissolution of the targeted thermoplastics of the plastic filler in the dissolution solvent.

[0073] The dissolution section can use any reactor stirred by any stirring system. In fact, obtaining a conditioned charge having a viscosity preferably less than or equal to 50 mPa.s, preferably less than or equal to 20 mPa.s, very preferably less than or equal to 5 mPa.s, very preferably less than or equal to 1 mPa.s.s, and very advantageously a coefficient of variation (CoV) of concentration preferably less than or equal to 10%, preferably less than or equal to 5%, at the end of section i) of contacting allows the use of a reasonable (i.e. limited) stirring power in the dissolution reactor, thus facilitating the operability of the dissolution section, which allows the use of any stirring system, while advantageously allowing a reduction in the mixing time, i.e. the residence time in the dissolution section, and / or the use of a wide range of operating pressures, and ensuring optimal homogenization of the mixture and therefore maximum dissolution of the targeted thermoplastics of the plastic filler in the dissolution solvent.

[0074] Optionally, an adsorbent, advantageously solid, preferably in the form of divided particles, shaped or not, may be introduced into the polymer solution in dissolution section ii), in particular in the dissolution reactor. In this case, the purification process comprises an intermediate adsorption step a'), located during dissolution step a). The adsorbent is advantageously chosen from aluminas, silicas, silica-aluminas, activated carbons or bleaching earths. The solid adsorbent may then be removed during purification step b), for example during a sub-step b1) of separation of insolubles and / or a washing sub-step b2). This optional adsorption step a') in the presence of solid adsorbent in divided form makes it possible to optimize the purification of the polymer solution.

[0075] According to a preferred embodiment of the invention, step a) of dissolution implements: i) a section for bringing the plastic charge into contact with at least a portion of a dissolution solvent, having a boiling temperature of between -50 and 250°C, preferably between -15 and 150°C, preferably between 20 and 100°C, and ii) a dissolution section. In this preferred embodiment, the contacting section i) is operated at a temperature between 150 and 250°C and uses an extruder, possibly a filtration system at the extruder outlet, then three, four or five static mixers, operating in series with each other, and the dissolution section ii) uses a continuously stirred reactor by mechanical stirring (i.e. CSTR type) operated at a temperature between 150 and 250°C and a pressure between 1.5 and 18.0 MPa absolute.The dissolving solvent is divided into n partial flows of dissolving solvent, n being a natural integer and the number n of partial flows of dissolving solvent being equal to the number m of static mixers implemented in the contacting section i) (in this embodiment, m being an integer equal to three, four or five) or to a number m+1 or m+2. In this embodiment, the extruder is fed with the plastic feedstock, to obtain a plastic flow composed of the at least partly melted plastic feedstock, in which the targeted thermoplastics, in particular the targeted polyolefins, of the plastic feedstock are advantageously melted, and optionally one of the partial flows of dissolving solvent so that the weight ratio between the fraction of dissolving solvent (i.e.the partial flow of dissolving solvent) which feeds the extruder and the plastic feed which feeds the extruder is between 0.001 and 0.200, preferably between 0.001 and 0.100, preferentially between 0.003 and 0.050, very preferably between 0.005 and 0.030, for example so that the partial flow of dissolving solvent which feeds the extruder preferably represents between 0.02 and 4.0% by weight, or even between 0.1 and 1.0% by weight, of the total weight of dissolving solvent introduced in step a). In this preferred embodiment, each of the static mixers is fed by a plastic flow and one of the partial flows of dissolving solvent so that, in each static mixer, the volume dilution rate of dissolving solvent is between:

[0076] - between 3% and 50%, preferably between 10 and 35%, and very preferably between 15% and 30%, when the ratio of the viscosities between the plastic flow and the partial flow of dissolving solvent which feeds the static mixer considered is greater than or equal to 3500, preferably greater than or equal to 3000;

[0077] - between 10% and 70%, preferably between 20 and 65%, very preferably between 30% and 65%, or even between 35% and 65%, when the ratio of the viscosities between the plastic flow and the partial flow of dissolving solvent which feeds the static mixer in question is less than 3500, preferably less than 3000.

[0078] Preferably, in this preferred embodiment, the residence time in the extruder, defined as the volume available in said extruder divided by the feed volume flow rate, is between 0.5 seconds and one hour, preferably between 0.5 seconds and 5 minutes, preferably 1 second and 2 minutes, or between 10 seconds and 2 minutes.

[0079] The dissolution section ii), in particular the CSTR type reactor, of this same preferred embodiment is then supplied by the plastic flow from the last static mixer of the contacting section i) and possibly by a partial flow of dissolution solvent.

[0080] The polymer solution, advantageously referred to as crude, obtained at the end of dissolution step a) comprises at least the dissolution solvent, polymers, in particular the targeted thermoplastic polymers that the present invention seeks to recover purified, dissolved in the dissolution solvent. In general, the polymer solution obtained at the end of dissolution step a) also comprises soluble impurities also dissolved in the dissolution solvent. It may optionally further comprise insoluble impurities in suspension. The polymer solution, advantageously referred to as crude, obtained at the end of step a) may optionally also comprise polymers, other than the targeted polymers, for example in the molten state.

[0081] Step b) purification of the polymer solution

[0082] The treatment method according to the invention comprises a step of purifying the crude polymer solution resulting from step a). This purification step b) comprises at least one of the sub-steps b1), b2), b3), b4) described below: b1) a sub-step of separating the insolubles, b2) a washing sub-step, by contact with a dense solution, b3) an extraction sub-step, by contact with an extraction solvent, b4) a sub-step of adsorption of the impurities by contact with an adsorbent solid.

[0083] Preferably, the purification step b) comprises at least one sub-step b1) of separation of the insolubles. The purification step b) preferably comprises several (i.e. at least two) sub-steps chosen from sub-steps b1), b2), b3) and b4), in series, and preferably at least one sub-step b1) of separation of the insolubles and for example one sub-step b4) of adsorption, and very advantageously in this order. The combination of at least two sub-steps chosen from b1), b2), b3) and b4) advantageously allows optimal purification of the polymer solution. The polymer solution obtained at the end of step b) is a purified polymer solution and comprises the targeted thermoplastics dissolved in the dissolution solvent.This purified polymer solution may correspond to a clarified polymer solution resulting from a sub-step b1) of separation of insolubles, a washed polymer solution resulting from a sub-step b2) of washing, an extracted polymer solution resulting from a sub-step b3) of extraction or a refined polymer solution resulting from a sub-step b4) of adsorption of impurities.

[0084] Sub-step b1) of separation of insolubles The purification process may comprise a sub-step b1) of separation of insolubles by solid-liquid separation, to advantageously obtain at least one clarified polymer solution and preferably an insoluble fraction. The insoluble fraction advantageously comprises at least in part, preferably all, of the insoluble impurities, in particular in suspension in the crude polymer solution resulting from step a).

[0085] Sub-step b1) of separating the insolubles thus makes it possible to eliminate at least a portion, preferably all, of the particles of impurities insoluble in the dissolution solvent, present in suspension in the raw polymer solution resulting from step a). The insoluble impurities eliminated during sub-step b1) of separating the insolubles are, for example, pigments, mineral compounds, packaging residues (glass, wood, cardboard, paper, aluminum) and insoluble polymers.

[0086] When implemented, this sub-step b1) of separation makes it possible, in addition to the elimination of at least part of the insoluble impurities, advantageously to limit the operating problems, in particular of the clogging and / or erosion type, of the process steps located downstream, while contributing to the purification of the plastic load.

[0087] Sub-step b1) of separating the insolubles is advantageously 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, sub-step b1) of separating the insolubles is carried out at the temperature and pressure conditions at the outlet of step a) of dissolution, i.e. at the dissolution temperature and the dissolution pressure as defined above.

[0088] When integrated into the process, sub-step b1) of separating the insolubles is preferably fed with the raw polymer solution from step a). According to another embodiment, sub-step b1) can be fed with a washed polymer solution from a washing sub-step b2).

[0089] Advantageously, sub-step b1) implements a section comprising at least one solid-liquid separation equipment, for example chosen from a separator flask, a decanter, a centrifugal decanter, a centrifuge, a filter, a sand filter, a tangential filter notably using a membrane and / or a depth filter possibly in the presence of filtration aids (for example diatomaceous earth), an eddy current separator, an electrostatic separator, a triboelectric separator, preferably a decanter, a filter, a sand filter and / or an electrostatic separator. Advantageously, a self-cleaning filter can be used, the cleaning or unclogging allowing the elimination of insolubles being carried out using a solvent flow.The removal of the insoluble fraction may be facilitated by equipment allowing the transport and / or elimination of traces of solvent possibly present in the insoluble fraction, for example a conveyor, a vibrating tube, a worm screw, an extruder, a stripper. Sub-step b1) may therefore use equipment for transporting and / or eliminating traces of solvent to remove the insoluble fraction. Advantageously, at least part of the solvent recovered during sub-step b1) is recycled in the process.

[0090] According to a particular embodiment, sub-step b1) of separating the insolubles uses 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 the insolubles while the presence of equipment in parallel makes it possible to manage the maintenance of said equipment and / or unclogging operations.

[0091] Certain insoluble impurities, in particular certain additives such as pigments and mineral fillers, conventionally added during the formulation of polymers, may 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 of sub-step b1), said sub-step b1) of separation of the insolubles advantageously uses an electrostatic separator, which makes it possible to effectively eliminate at least in part, the insoluble particles smaller than 1 μm. According to another particular embodiment of sub-step b1), the sub-step b1) of the insolubles uses a sand filter, to eliminate particles of different sizes and in particular particles smaller than 1 μm.According to yet another particular embodiment of sub-step b1), sub-step b1) of the insolubles uses a tangential filter notably using a membrane and / or a depth filter, possibly in the presence of filtration aids such as for example diatomaceous earth.

[0092] Depending on the nature of the feed, the polymer solution which feeds sub-step b1), preferably the raw polymer solution, may optionally also comprise a second liquid phase, for example consisting of molten polymers. According to another particular embodiment, sub-step b1) advantageously uses equipment allowing the separation of this second liquid phase, preferably by means of at least one two-phase or three-phase separator.

[0093] Sub-step b2) of washing

[0094] The treatment method may optionally further comprise a sub-step b2) 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 b2) advantageously comprises the targeted polymers that the present invention seeks to recover purified, dissolved in the dissolution solvent. Optionally, the washed polymer solution may also comprise residual impurities, in particular soluble in the dissolution solvent and / or possibly traces of the washing solvent if sub-step b2) is carried out.

[0095] The washing sub-step b2) can be integrated upstream or downstream, preferably downstream, of a sub-step b1) of separation of insolubles, when these two sub-steps are integrated into the purification step b).

[0096] When integrated into the process, the washing sub-step b2) is fed with a dense solution and with the raw polymer solution from step a) or from a possible intermediate adsorption step a'), or with the clarified polymer solution from b1). The polymer solution which feeds the washing sub-step b2), in particular the raw or clarified polymer solution, may comprise insoluble suspended impurities and / or solubilized impurities. These suspended or solubilized impurities may, in part or in full, be eliminated during the washing sub-step b2) by dissolution or precipitation and / or by entrainment in the dense solution. Thus, when implemented, this sub-step b2) contributes to the treatment of the plastic feedstock and more particularly to the purification of the polymer solution.

[0097] The washing sub-step b2) advantageously comprises bringing the raw or clarified polymer solution, which feeds sub-step b2), 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 b2), 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.

[0098] The washing sub-step b2) is advantageously 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 15.0 MPa absolute and very preferably between 2.0 and 15.0 MPa absolute. Very advantageously, the washing sub-step b2) is carried out at the dissolution temperature and the dissolution pressure.

[0099] In the washing sub-step b2), when integrated into the process, the mass ratio between the mass flow rate of the dense solution and the mass flow rate of the raw or clarified polymer solution which feeds the sub-step b2) 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 raw or clarified polymer solution and the dense solution can be carried out at several points of the equipment(s) used, i.e. by several injections of the raw or clarified polymer solution and / or the dense solution at different points along the equipment(s), it is then the sum of the injected flows which is taken into account in the calculation of the ratio.

[0100] Sub-step b2) 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.

[0101] According to a preferred embodiment, the washing sub-step b2) 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 crude 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.

[0102] According to a very particular embodiment, the inlet and / or outlet flows of 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. According to another embodiment, the washing sub-step b2) is carried out in a mixer-settler comprising a stirred mixing zone, to bring the dense solution and the crude or clarified polymer solution into contact, and a settling zone, making it possible to recover a washed polymer solution and a washing effluent.

[0103] At the end of the washing sub-step b2), 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 use one or more well-known solid-liquid separation equipment, for example a separator drum, a decanter, a centrifugal decanter, a centrifuge, a filter. The washing effluent can also be sent outside the process, for example to a wastewater treatment plant when the dense solution is an aqueous solution.

[0104] Step b3) extraction

[0105] Step b) of the method according to the invention may comprise a sub-step b3) of extraction by contacting with an extraction solvent, to obtain at least one extracted polymer solution and a used solvent, in particular loaded with impurities. The extracted polymer solution obtained at the end of sub-step b3) advantageously comprises the targeted thermoplastic polymers that the present invention seeks to recover purified, dissolved in the dissolution solvent. 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.

[0106] When integrated into the process according to the invention, the extraction sub-step b3) is advantageously located between the dissolution step a) and the solvent-polymer separation step c), and optionally upstream or downstream of an adsorption sub-step b4) if the latter is also integrated into step b), and preferably downstream of a sub-step b1) of separation of insolubles.

[0107] The extraction sub-step b3) is advantageously supplied with an extraction solvent and with the polymer solution, in particular the crude polymer solution from step a), the clarified polymer solution from sub-step b1), the washed polymer solution from sub-step b2) or the refined polymer solution from an adsorption sub-step b4). Preferably, the extraction sub-step b3) is supplied with an extraction solvent and with the clarified polymer solution from sub-step b1) or the washed polymer solution from sub-step b2), or possibly with a refined polymer solution from an adsorption sub-step b4). The polymer solution which supplies sub-step b3), preferably the clarified polymer solution, the washed polymer solution or the refined polymer solution, may therefore also comprise solubilized impurities.These solubilized impurities can be partially or completely removed during the extraction sub-step b3) by contacting with an extraction solvent. Very advantageously, the combination of an extraction sub-step b3) with a sub-step b1) of separation of the insolubles and possibly an adsorption sub-step b4) allows improved purification of the polymer solution, possibly using both the affinity of the impurities for the adsorbent and for the extraction solvent.

[0108] When integrated into the method according to the invention, the extraction sub-step b3) advantageously implements at least one extraction section, preferably between one and five extraction section(s), very preferably one extraction section.

[0109] The mass ratio between the mass flow rate of the extraction solvent and the mass flow rate of the polymer solution which feeds b3), preferably the clarified polymer solution, the washed polymer solution or the 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 contacting between the polymer solution which feeds sub-step b3), preferably the clarified polymer solution, the washed polymer solution or the refined polymer solution, 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.

[0110] The extraction solvent used in extraction sub-step b3) 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 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, preferentially between 4 and 8 carbon atoms. For example, the extraction solvent comprises a compound chosen from the isomers of butane, pentane, hexane, heptane and octane.The extraction 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 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 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, preferably between 130 and 300°C, preferably between 180 and 285°C.

[0111] Very preferably, the extraction solvent used in b3) 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 b3). 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 steps of the process, to limit the energy consumption and the costs in particular generated by the treatment and purification of the solvents.

[0112] The extraction section(s) of b3) 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, such as 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.

[0113] According to a preferred embodiment of b3), 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 b3) 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 b3), preferably the clarified, washed or refined polymer solution, is injected into half, preferably one third, of the column closest to the head of the countercurrent extraction column while the extraction solvent is injected into half, preferably one third, of the column closest to the bottom of the countercurrent extraction column.

[0114] The inlet and / or outlet flows of the countercurrent extraction column can be divided into several injection and / or withdrawal points along the column.

[0115] According to another embodiment of b3), the extraction is carried out in a mixer-decanter which advantageously comprises a stirred mixing zone for bringing the extraction solvent and the polymer solution which feeds b3) into contact, preferably the clarified, washed or refined polymer solution, and a decantation zone for recovering an extracted polymer solution on the one hand and a used solvent on the other hand.

[0116] Advantageously, the extraction sub-step b3) is carried out under temperature and pressure conditions different from the temperature and pressure conditions of the dissolution step a).

[0117] According to a preferred embodiment of b3), the extraction sub-step b3) 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, preferably between 1.5 and 18.0 MPa absolute and very preferably between 2.0 and 15.0 MPa absolute. In all cases, in this embodiment, the temperature and pressure conditions are adjusted so that the extraction solvent is in the liquid state, the dissolution solvent preferably also being in the liquid state.Very advantageously, the liquid / liquid extraction, in particular when the extraction solvent is the same as the dissolution solvent, is carried out under temperature and pressure conditions different from the dissolution conditions reached in step a), in particular at a temperature higher than the dissolution temperature and / or at a pressure lower than the dissolution pressure, so as to thus be placed in a two-phase zone of the corresponding polymer-solvent mixing diagram.

[0118] According to another preferred embodiment of b3), the extraction sub-step b3) implements an extraction section under particular temperature and pressure conditions in which the extraction solvent is advantageously at least partly in supercritical form. Such extraction may be called supercritical extraction. In this embodiment, the extraction is carried out by bringing the polymer solution, preferably the 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, 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 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 b3) advantageously allows efficient purification of the polymer solution, in particular due to the very strong affinity of organic impurities, such as for example certain 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.

[0119] In this other preferred embodiment, sub-step b3) uses an extraction solvent comprising at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of at least one aliphatic paraffinic hydrocarbon compound (or alkane) (100% being the maximum, the percentages being expressed relative to the total weight of the extraction solvent) having a critical temperature preferably between 95 and 350°C, preferably between 130 and 300°C, preferably between 180 and 285°C.

[0120] Advantageously, the supercritical extraction sub-step b3) 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 b3) 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 b3) upstream of the extraction section, so that the extraction solvent is at least partly in the supercritical state in the extraction section.

[0121] In a very preferred embodiment of b3), the extraction sub-step b3) 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 very advantageous 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.

[0122] Advantageously, at the end of extraction sub-step b3), the used solvent obtained is in particular loaded with 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 b3), 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, for example, one or more methods among distillation, evaporation, extraction, adsorption, crystallization and precipitation of insolubles, or by purging.

[0123] Sub-step b4) adsorption

[0124] Step b) of the treatment method according to the invention may comprise an adsorption sub-step b4), to obtain at least one refined polymer solution. The refined polymer solution obtained at the end of sub-step b4) advantageously comprises the targeted thermoplastic polymers that the present invention seeks to recover purified, dissolved in the dissolution solvent.

[0125] When integrated into the process according to the invention, the adsorption sub-step b4) is advantageously implemented downstream of the dissolution step a) and upstream of the solvent-polymer separation step c). It can be implemented upstream of a sub-step b1) of separation of the insolubles and / or b2) of washing and correspond in particular to the possible intermediate adsorption step a'). Preferably, it is implemented downstream of a sub-step b1) of separation of the insolubles and possibly of a washing sub-step b2), itself preferably downstream of the sub-step b1). It can also be implemented, for example, upstream or downstream of an extraction sub-step b3). Thus, when it is integrated into the process according to the invention, the adsorption sub-step b4) is implemented by bringing the polymer solution which feeds it into contact with one or more adsorbents.

[0126] The adsorption sub-step b4) advantageously uses an adsorption section operated in the presence of at least one adsorbent, preferably solid, and in particular in the form of a fixed bed, an entrained bed (or slurry, i.e. in the form of particles introduced into the flow to be purified and entrained with this flow) or in the form of an ebullating bed, preferably in the form of a fixed bed or an entrained bed. 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.

[0127] Advantageously, when integrated into the process, the adsorption sub-step b4) is carried out at a temperature between 100 and 300°C, preferably between 150 and 250°C, and at a pressure between 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 b4) is carried out at the dissolution temperature and pressure conditions, i.e. at the dissolution temperature and the dissolution pressure reached in step a). Preferably, in the possible sub-step b4), the hourly volumetric velocity (or WH), which corresponds to the ratio between the volumetric flow rate of the polymer solution which feeds b4) and the volume of adsorbent, advantageously in operation in b4), is between 0.05 and 10 h 1 , preferably between 0.1 and 5.0 h -1 .

[0128] According to a particular embodiment of sub-step b4), the adsorption section may comprise one or more fixed bed(s) of adsorbent, for example in the form of adsorption column(s), preferably at least two adsorption columns, 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.

[0129] Another mode of operation of this particular embodiment of b4) is to have at least two 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.

[0130] According to this particular embodiment of sub-step b4) of adsorption in a fixed bed of adsorbent, sub-step b4) is preferably carried out downstream of a sub-step b1) of separation of the insolubles and / or of a sub-step b2) of washing, and upstream or downstream of a sub-step b3) of extraction. Advantageously, the combination of a sub-step b1) of separation of the insolubles, and / or of a sub-step b2) of washing, and of a sub-step b3) of extraction with a sub-step b4) of adsorption allows an improved purification of the polymer solution, by using both the affinity of the residual impurities for the adsorbent solid and also for the extraction solvent and possibly a dense solution.

[0131] The adsorption section of b4) may, according to another embodiment, consist of an addition of adsorbent particles into the polymer solution, in particular the raw polymer solution, said particles being able to be separated from the polymer solution via a step of removing the adsorbent particles located downstream of said adsorption section. The removal of the adsorbent particles may then advantageously correspond to a step b1) of separating the insolubles or to the washing step b2). Such an implementation of the adsorption sub-step b4), by introducing the adsorbent particles then solid / liquid separation, advantageously corresponds to the possible intermediate adsorption step a'), described further in this description.

[0132] Step c) solvent-polymer separation

[0133] According to the invention, the process comprises a step c) of solvent-polymer separation, to obtain at least one fraction of purified thermoplastic polymers, more particularly at least one fraction of purified polyolefins, and preferably at least one fraction of solvent.

[0134] Step c) of solvent-polymer separation aims to separate, at least in part, preferably mainly, or even completely, the solvent(s), in particular the dissolution solvent, contained in the purified polymer solution which feeds step c), so as to recover the thermoplastics freed at least in part, preferably completely, 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 purified polymer solution which feeds step c), in particular the dissolution solvent and optionally the extraction solvent and / or the dense solution contained in the 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 the solvent(s). The solvent(s) can be separated, for example, by evaporation, stripping, 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.

[0135] The fraction of purified thermoplastic polymers obtained at the end of step c) may correspond to a concentrated polymer solution or to liquid (i.e. molten) or solid purified thermoplastic polymers. The solvent-polymer separation step c) may optionally further comprise a conditioning section for conditioning the recovered thermoplastics, 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 polymers in the solid state.

[0136] 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 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 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 b2) and / or sub-step b3).

[0137] Very advantageously, the solvent fraction recovered at the end of step c) can be treated in an organic treatment section located at the end of step c), so as to purify it and obtain a purified solvent, in particular a purified dissolution solvent, in order to be able to advantageously recycle it to the dissolution step a), and / or possibly to the washing sub-step b2) or the extraction sub-step b3). Said optional organic treatment section at the end of step c) can implement any method known to those skilled in the art, such as for example one or more methods among distillation, evaporation, liquid-liquid extraction, adsorption, crystallization and precipitation of insolubles, or by purging.

[0138] Thus, the process according to the invention makes it possible to obtain a purified stream of thermoplastic polymers and more particularly polyolefins, from plastic waste, which can be used in any application, for example as a replacement for the same polymers in the virgin state. The purified stream of polymers, i.e. the fraction of purified thermoplastic polymers, obtained by the process according to the invention thus has a sufficiently low impurity content to be able to be used in any application. Preferably, the stream of purified thermoplastic polymers and in particular the stream of purified polyolefins obtained at the end of the process according to the invention (i.e. the fraction of purified thermoplastic polymers) advantageously has an impurity content of less than or equal to 5% by weight of impurities, very advantageously impurities 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 (i.e. the fraction of purified thermoplastic polymers) has a residual solvent content (in particular dissolution solvent) of less than or equal to 5% by weight of residual solvent, preferably less than or equal to 1.0% by weight of residual solvent, preferably less than or equal to 0.1% by weight of residual solvent, or even a content of less than or equal to 500 ppm by weight of residual solvent, relative to the total weight of the stream of thermoplastic polymers.

[0139] The following examples and figures illustrate the invention, in particular particular embodiments of the invention, without limiting its scope.

[0140] LIST OF FIGURES

[0141] Figure 1 represents the diagram of an embodiment of the method of the present invention, comprising: - a step a) of dissolving the plastic filler 1 in a dissolving solvent 19, to obtain a crude polymer solution 12, step a) implementing:

[0142] - a section ai) for bringing the plastic charge 1 into contact with a dissolution solvent 19 to obtain a conditioned charge 11, said section ai) using an extruder (A) to obtain a plastic charge 1 * at least partly melted, and five static exchangers M1, M2, M3, M4, M5, each exchanger being supplied by a partial flow of dissolution solvent 2, 4, 6, 8, 10, from the total flow of dissolution solvent 19, and by a plastic flow 1 *, 3, 5, 7, 9,

[0143] - a dissolution section a-ii), in particular using a continuously stirred reactor of the CSTR type, to obtain a crude polymer solution 12,

[0144] - a purification step b), preferably comprising a separation of the insolubles followed in particular by an adsorption sub-step, to obtain a purified polymer solution 13 and an insoluble fraction 14,

[0145] - a step c) of solvent-polymer separation, to obtain a fraction of purified thermoplastics 15, and more particularly a fraction of purified polyolefins, and a solvent stream 16.

[0146] The solvent stream 16 is advantageously purified, for example in a distillation section d), to recover a purified dissolution solvent stream 17 which is mixed with a fresh solvent stream 18 to constitute the dissolution solvent 19, the latter being divided into five partial streams 2, 4, 6, 8, 10, of dissolution solvent to feed the static mixers M1, M2, M3, M4, M5 of section ai).

[0147] EXAMPLES

[0148] Example 1 (in accordance with the invention)

[0149] In this example, only the contacting section i) of a purification process corresponding to the embodiment shown schematically in Figure 1 is tested and in which the contacting section i) of the dissolution step a) comprises:

[0150] - an extruder A, which comprises a feed hopper through which the extruder is fed with plastic feed from the collection and sorting line; followed by

[0151] - five static mixers M1, M2, M3, M4, M5, in series.

[0152] The plastic filler comprises: 95% by weight of polypropylene; 5% by weight of polyethylene and impurities, in particular additives such as pigments, dyes, fillers, etc.

[0153] The contacting section is operated at a temperature of 200°C and at a pressure of 2.5 MPa (25 bars). The flow rate of plastic feed introduced into extruder A is 50 kg / h. The feed 1 * is melted at least in part at the outlet of extruder A; more particularly, the polyolefins, and therefore at least the polypropylene, which said feed contains, are in molten form at the outlet of the extruder.

[0154] The dissolution solvent used is n-heptane and a mixture 19 of a stream 17 of purified and recycled n-heptane with a stream of fresh n-heptane 18. The total flow rate of n-heptane 19, which feeds the dissolution step a), is 250 kg / h.

[0155] Each static mixer M1, M2, M3, M4, M5, is fed with a partial flow of n-heptane, respectively 2, 4, 6, 8, 10, and a plastic flow, respectively 1 *, 3, 5, 7, 9, which includes at least the molten polypropylene. The coefficient of variation of the concentration targeted at the outlet of each static mixer is 5% (or 0.05).

[0156] Table 1 shows both the quantities of dissolving solvent introduced into each static mixer and the evolution of the viscosity of the inlet / outlet streams of each static mixer under the operating conditions of temperature and pressure. Table 1 also gives the viscosity ratio between the plastic stream and the n-heptane stream entering each static mixer as well as the volume dilution rate of n-heptane in each mixer.

[0157] Table 1

[0158] At the end of the contacting section ai) of step a) using an extruder followed by five static mixers supplied with partial flows of n-heptane, the viscosity of the conditioned feed flow is less than 1 mPa.s (0.95 mPa.s), while respecting the technical constraints imposed by the static mixers relative to the viscosities of the flows involved. Such a viscosity then makes it possible to facilitate the homogenization of the mixture in a CSTR type dissolution reactor in the dissolution section, said dissolution reactor being of the CSTR type.

Claims

CLAIMS 1. Method for treating a plastic filler, comprising: a) a step of dissolving the plastic filler in a dissolving solvent, to obtain at least one raw polymer solution, the dissolving step a) implementing: i) a section for bringing the plastic filler into contact with at least a portion of the dissolving solvent, comprising at least one static or dynamic mixer, to produce a conditioned filler, each static or dynamic mixer being operated at a temperature between 100°C and 300°C, each static or dynamic mixer being supplied with a plastic flow, comprising the plastic filler, and with a fraction of at least said portion of the dissolving solvent so that each mixer has a volume dilution rate in dissolving solvent between 3% and 70%,the volume dilution rate in dissolution solvent being the ratio between the volume flow rate of the fraction of at least said part of the dissolution solvent which feeds the static or dynamic mixer considered and the sum of the volume flow rates of the fraction of at least said part of the dissolution solvent and of the plastic flow which feed the static or dynamic mixer considered; ii) a dissolution section fed at least by the conditioned charge coming from the contacting section and operated at a dissolution temperature of between 100°C and 300°C and a dissolution pressure of between 1.0 and 100.0 MPa absolute; then b) a step of purifying the crude polymer solution to obtain a purified polymer solution, said purification step comprising: b1) a sub-step of separating the insolubles; and / or b2) a sub-step of washing, by contact with a dense solution; and / or b3) an extraction sub-step,by contact with an extraction solvent; and / or b4) a sub-step of adsorption of impurities by contact with a solid adsorbent; then, c) a step of solvent-polymer separation, to obtain at least a fraction of purified thermoplastic polymers., 2. Method according to claim 1, in which the contacting section comprises between one and ten, preferably between two and six, more preferably between two and five, static or dynamic mixer(s), preferably in series.

3. Method according to claim 1 or 2, in which each mixer has a volume dilution rate in dissolution solvent of: - between 3% and 50%, preferably between 10% and 35%, and very preferably between 15% and 30%, when the ratio of the viscosities between the plastic flow and the fraction of at least said part of the dissolving solvent, which feeds the static or dynamic mixer considered, is greater than or equal to 3500, preferably greater than or equal to 3000, - between 10% and 70%, preferably between 20% and 65%, very preferably between 30% and 65%, or even between 35% and 65%, when the ratio of the viscosities between the plastic flow and the fraction of at least said part of the dissolving solvent, which feeds the static or dynamic mixer considered, is less than 3500, preferably less than 3000.

4. Method according to any one of the preceding claims, in which the contacting section comprises means for at least partially melting the plastic filler, located upstream of the first static or dynamic mixer, said means for melting preferably being an extruder.

5. Method according to any one of the preceding claims, in which the dissolving solvent comprises at least one paraffinic aliphatic hydrocarbon compound 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.

6. Method according to any one of the preceding claims, in which the dissolution solvent and the plastic filler feed step a) according to a weight ratio between the dissolution 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.

7. A method according to any one of the preceding claims, wherein each static or dynamic mixer is operated at a temperature between 150 and 250°C.

8. A method according to any preceding claim, wherein the dissolution section is operated at a dissolution temperature of between 150 and 250°C.

9. Method according to any one of the preceding claims, in which the dissolution section is operated at a dissolution pressure 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.

10. Method according to any one of the preceding claims, in which step b) of purification comprises a sub-step b1) of separation of the insolubles preferably followed by at least one sub-step of adsorption.

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

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