Method for treating used plastics by polymer dissolution and purification by extraction

Abstract

Disclosed is a method for processing a plastic feedstock, the method comprising the steps of: (a) a dissolution step comprising contacting the plastic feedstock with a dissolution solvent at a dissolution temperature of 100°C to 300°C and a dissolution pressure of 1 to 20.0 MPa (absolute) to dissolve at least a portion of the polymer of the plastic feedstock and obtain a crude polymer solution; (b) an extraction step comprising contacting the crude polymer solution with an extraction solvent at a temperature of 100°C to 300°C, a pressure of 1 to 20.0 MPa (absolute) and a mass ratio of the mass flow rate of the extraction solvent to the mass flow rate of the crude polymer solution of 0.05 to 20.0; obtaining an extracted polymer solution and spent solvent; and then (c) recovering the polymer; obtaining a solvent fraction and a purified polymer fraction.

Description

[Technical Field]

[0001] The present invention relates to a method for processing used plastics to obtain a purified stream of plastics that can, for example, be utilized as new plastic objects. More specifically, the present invention relates to a method for processing plastic feedstocks, especially those obtained from plastic waste, especially those containing thermoplastics, such as polyolefins, comprising a step of extracting the polymer solution to at least partially remove impurities, especially additives traditionally used in plastic-based materials, such as dyes, pigments, organic and inorganic fillers, and separating out the polymers, especially thermoplastics, that the feedstock contains, thereby allowing the plastic feedstock to be upgraded, recovered, and reused. [Background technology]

[0002] The plastics obtained from the collection and sorting channel can be upgraded through various channels.

[0003] "Mechanical" recycling allows some waste to be partially reused, either directly in new objects or by mixing a mechanically sorted plastic waste stream with a virgin polymer stream. This type of upgrading is limited because, although mechanical sorting makes it possible to improve the purity of a given type of polymer stream, it generally does not make it possible to sufficiently remove impurities, such as additives, such as fillers, dyes, pigments and metals, that are at least partially trapped in the polymer matrix.

[0004] "Chemical" recycling is generally directed toward at least partial modification of monomers through a complex series of steps. For example, plastic waste may undergo a pyrolysis process, and pyrolysis oil, typically recovered after refining, may be at least partially converted, for example, to olefins by steam cracking. These olefins may then be polymerized. While this type of sequence may be suitable for feedstocks that have undergone little sorting or waste from sorting centers, it generally requires high energy consumption, especially due to the high temperature treatment.

[0005] Another route for recycling plastic waste consists in at least partially dissolving plastics, in particular thermoplastics, with the aim of purifying them by removing the polymer(s) of the feedstock other than the targeted one(s) and / or impurities, such as additives, e.g., fillers, dyes, pigments and metals.

[0006] Several studies have therefore presented various methods for treating plastic waste by dissolution and purification. Patent document 1 describes a specific method for purifying a polymer feedstock, in particular a polymer feedstock obtained from plastic waste, by dissolving the polymer in a solvent under specific temperature and pressure conditions and then placing the resulting polymer solution in contact with a solid.

[0007] Patent Document 2 partially proposes a method for dissolving plastics in a solvent at a dissolution temperature close to the boiling point of the solvent, but the method of Patent Document 2 does not allow for efficient treatment of impurities other than polymers.

[0008] Patent Document 3 proposes a treatment method in which thermoplastic plastics are liquefied in a solvent and then insoluble substances and / or gases are separated and removed. The method of Patent Document 3 does not enable efficient treatment of impurities that are soluble in the solvent.

[0009] The present invention is directed to overcoming these drawbacks and to the recycling of plastics, in particular thermoplastics. More particularly, the present invention is directed to proposing a method for treating plastic feedstocks, in particular those obtained from plastic waste, in order to efficiently remove at least a portion of the impurities, in particular additives conventionally added to plastic materials, more particularly impurities that are particularly soluble in organic solvents, so that the plastic feedstocks, in particular plastic waste, can be upgraded by separating out and recovering polymers, in particular thermoplastics, which can be used, for example, as a polymer base for new plastic objects. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] US Patent Application Publication No. 2017 / 002110 [Patent Document 2] International Publication No. 2018 / 114047 [Patent Document 3] US Patent Application Publication No. 2018 / 0208736 Summary of the Invention [Means for solving the problem]

[0011] (Summary of the Invention) The present invention relates to a method for processing a feedstock, the method comprising the steps of: a) a dissolution step comprising contacting a plastic feedstock with a dissolution solvent at a dissolution temperature of 100°C to 300°C and a dissolution pressure of 1.0 to 20.0 MPa (absolute); obtaining at least one crude polymer solution; b) a step of extraction by placing the crude polymer solution obtained from step a) in contact with an extraction solvent at a temperature of 100°C to 300°C, a pressure of 1.0 to 20.0 MPa (absolute) and a mass ratio between the mass flow rate of the extraction solvent and the mass flow rate of the crude polymer solution of 0.05 to 20.0; obtaining at least one extracted polymer solution and at least one spent solvent; then c) recovering the polymer; obtaining at least one solvent fraction and at least one purified polymer fraction.

[0012] The advantage of the method of the present invention is that it proposes a method for efficiently processing feedstocks containing plastics, in particular plastic waste, especially plastic waste obtained from collection and sorting channels, to recover polymers, in particular thermoplastics, allowing them to be recycled for any type of application. The method of the present invention actually makes it possible to obtain purified polymer, in particular purified thermoplastic, and in particular purified polyolefin, e.g., polyethylene and polypropylene, streams, advantageously containing negligible or at least sufficiently low impurity contents so that the purified polymer, in particular purified thermoplastic, streams can be incorporated into any plastic blend instead of virgin polymer resin. For example, the purified polymer, in particular purified thermoplastic, and in particular purified polyolefin streams obtained at the end of the method of the present invention advantageously contain less than 5% by weight of impurities, highly advantageously less than 1% by weight of impurities.

[0013] The process according to the invention therefore proposes a series of operations which allow the removal of at least a portion of the impurities, in particular additives, from plastic waste and the recovery of a purified polymer which can then be recycled to upgrade the plastic waste. Advantageously, depending on the conditions used in the process steps, compounds present in the plastic feedstock may be soluble or insoluble in the solvent(s) used throughout the process according to the invention, allowing for efficient purification of the polymer.

[0014] The present invention has the additional advantage of contributing to the recycling of plastics and the conservation of fossil resources by enabling the upgrading of plastic waste, specifically to obtain purified polymer fractions with reduced impurity content, particularly decolorized and deodorized, which can be reused to form new plastic objects. The resulting purified polymer fractions can therefore be used directly in formulations as additives, e.g., in admixture with dyes, pigments or other polymers, in place of or in admixture with virgin polymer resins, with the aim of obtaining plastic products with aesthetic, mechanical or rheological processing properties that facilitate their reuse and upgrading.

[0015] The present invention also allows for the recovery of the solvent(s) used to treat the plastic feedstock of the process and recycling them after purification in the process, avoiding excessive consumption of the solvent(s).

[0016] The present invention is therefore directed to the purification of plastic feedstocks, in particular plastic waste, to obtain polymers, in particular thermoplastics, more particularly polyolefins, such as polyethylene and polypropylene, which are purified to allow their use in any application, in particular as a replacement for virgin polymers. The purification method proposed by the present invention therefore relies on dissolving the target polymers, i.e., separating them out and purifying them. More particularly, the present invention is directed to proposing a method comprising a dissolution step followed by at least one specific purification step, more particularly at least one extraction step b), possibly in combination with other intermediate purification steps, to obtain a purified polymer solution from which the purified polymer may be recovered. DETAILED DESCRIPTION OF THE INVENTION

[0017] (Description of the embodiment) According to the present invention, the expressions "comprised between ... and ..." and "between A and B or A to B (between ... and ...)" are equivalent and mean that both limits of the interval are included in the range of values ​​stated. If this is not the case and if both limits are not included in the range stated, such clarification is given by the present invention.

[0018] For purposes of the present invention, various ranges of parameters for a given process, such as pressure ranges and temperature ranges, may be used alone or in combination. For example, for purposes of the present invention, a range of preferred pressure values ​​may be combined with a range of more preferred temperature values.

[0019] In the following text, specific embodiments of the present invention may be described, which may be implemented separately or in combination together, without any limitation on the combination where this is technically feasible.

[0020] According to the present invention, pressure is absolute pressure and is given in MPa (absolute) (or MPa abs).

[0021] The terms "upstream" and "downstream" should be understood relative to the general flow of the fluid(s) or stream(s) under consideration in the method.

[0022] The term "additive" is a term commonly used in the field of polymers, particularly in the field of polymer blends. Additives introduced into polymer blends may be, for example, plasticizers, fillers (organic or inorganic solid compounds used to modify the physical, thermal, mechanical and / or electrical properties of polymer materials or to reduce their cost), reinforcing agents, dyes, pigments, curing agents, flame retardants, flame retardants, stabilizers, antioxidants, UV absorbers, antistatic agents, etc.

[0023] The additives represent a portion of the impurities of the plastic feedstock to be treated that the treatment method according to the invention allows to at least partially remove. Other types of impurities may be use-related impurities or plastic materials, such as metal impurities, paper / cardboard, biomass, other polymers, such as those of the thermoset or thermoplastic type, etc.

[0024] Thus, according to the present invention, the impurities that can be at least partially removed from the target polymer stream by the method according to the present invention include additives traditionally used in polymer formulations, as well as general use-related impurities originating from the life cycle of plastic objects and materials and / or impurities originating from waste collection and sorting circuits. These impurities may be metallic, organic, or mineral impurities; they may be packaging residues, food residues, or compostable residues (biomass). These use-related impurities may include glass, wood, cardboard, paper, aluminum, iron, metals, tires, rubber, silicone, rigid polymers, thermosetting polymers, household products, chemical products, cosmetics, used oil, and water.

[0025] According to the present invention, a polymer solution is a solution comprising a dissolution solvent and at least a polymer, preferably a target polymer, in particular a target thermoplastic, in particular a target polyolefin, dissolved in the dissolution solvent, the dissolved polymer initially being present in the feedstock. The polymer solution may contain soluble and / or insoluble impurities. Depending on the steps of the method according to the present invention that have been carried out, the polymer solution may contain impurities in the form of insoluble particles, advantageously suspended in the polymer solution, soluble impurities dissolved in the dissolution solvent, and / or possibly another liquid phase immiscible with the polymer solution.

[0026] The critical temperature and critical pressure of a solvent, particularly a dissolving solvent and / or an extracting solvent, are specific to said solvent and are the temperature and pressure, respectively, of the solvent's critical point. As is well known to those skilled in the art, above its critical point, the solvent is in a supercritical form or state, and the operating conditions of temperature and pressure are the solvent's supercritical conditions; it may be referred to as a supercritical fluid.

[0027] The present invention relates to a method for preparing a plastic feedstock, preferably made up of plastic waste and advantageously containing a polymer, preferably a thermoplastic, in particular a polyolefin, said method comprising, and preferably consisting of, the following steps: a) a dissolving step comprising placing the feedstock in contact with a solvent; obtaining at least one crude polymer solution; and then E1) optionally separating off insoluble matter; obtaining at least one clarified polymer solution and at least one insoluble fraction; E2) optionally a washing step by contact with a concentrated solution; obtaining at least one washing effluent and at least one washed polymer solution; b) an extraction step by contact with an extraction solvent, obtaining at least one extracted polymer solution and at least one spent solvent, in particular containing impurities; E3) optionally a step of adsorption of impurities by contact with an adsorbent solid; obtaining at least one purified polymer solution, and finally c) recovering the polymer; obtaining at least one solvent fraction and at least one purified polymer fraction.

[0028] (Feed material) The feedstock for the process according to the invention is known as a plastic feedstock and comprises plastics, which themselves comprise more particularly polymers. Preferably, the plastic feedstock comprises between 50% and 100% by weight of plastics, preferably between 70% and 100% by weight.

[0029] The plastics contained in the feedstock for the process according to the invention are generally manufacturing rejects and / or waste, in particular household waste, construction waste or waste electrical and electronic equipment. Preferably, the plastic waste comes from collection and sorting channels. Plastics or plastic materials are generally polymers that are usually mixed with additives for the purpose of forming them into shapes and then constructing various materials and objects (injection-molded parts, tubes, films, fibers, fabrics, mastics, coatings, etc.). The additives used in plastics can be organic or inorganic compounds. They are, for example, fillers, dyes, pigments, plasticizers, property modifiers, flame retardants, etc.

[0030] The feedstock for the process according to the invention therefore comprises polymers, in particular thermoplastics. The polymers contained in the plastic feedstock may be alkene polymers, diene polymers, vinyl polymers, and / or styrene polymers. Preferably, the polymers contained in the plastic feedstock are polyolefins, such as polyethylene (PE), polypropylene (PP), and / or copolymers of ethylene and propylene. Highly preferably, the polymers of the plastic feedstock comprise at least 80 wt. %, preferably at least 85 wt. %, preferably at least 90 wt. %, and highly preferably at least 94 wt. % polyolefins, relative to the total weight of the feedstock. The process according to the invention is therefore most particularly directed to purifying and recovering the polyolefins contained in the feedstock so that they can be reused in various applications.

[0031] The plastic feedstock may comprise a mixture of polymers, in particular a mixture of thermoplastic resins and / or a mixture of thermoplastic resins with other polymers, and additives advantageously used to blend impurities, in particular plastic materials and commonly used impurities originating from the life cycle of materials and plastic objects and / or from waste collection and sorting circuits. The feedstock for the process according to the invention generally contains less than 50% by weight of impurities, preferably less than 20% by weight of impurities, preferably less than 10% by weight of impurities.

[0032] The plastic-containing feedstock may advantageously be pretreated prior to the present process to remove at least part of the "coarse" impurities, i.e., impurities in the form of particles of 10 mm or more, preferably 5 mm or more, or even 1 mm or more in size, such as wood, paper, biomass, iron, aluminum, glass, etc., and generally form it into a divided solid form to facilitate processing in the present process. This pretreatment may include a crushing step, a washing step at atmospheric pressure, and / or a drying step. This pretreatment may be carried out at a different location, for example, at a waste collection and sorting center, or it may be carried out at the same location as the processing method according to the present invention. Preferably, this pretreatment makes it possible to reduce the impurity content to less than 6% by weight. At the end of the pretreatment, the feedstock is generally stored in divided solid form, for example, in the form of crushed material or powder, to facilitate handling and transport to the present process.

[0033] (melting step a)) According to the present invention, the process comprises a dissolution step a) in which a plastic feedstock is placed in contact with a dissolution solvent at a dissolution temperature of 100°C to 300°C and a dissolution pressure of 1.0 to 20.0 MPa (absolute) to obtain at least one, preferably one crude polymer solution. Specifically, this step advantageously allows for at least partial, preferably complete dissolution of a polymer, preferably a thermoplastic, most preferably a polyolefin, such as polyethylene and / or polypropylene.

[0034] The term "dissolution" should be understood as meaning any phenomenon that leads to the creation of at least one polymer solution, i.e., a liquid containing a polymer dissolved in a solvent, more particularly a dissolution solvent. Those skilled in the art are well aware of the phenomena involved in the dissolution of polymers and that include at least the mixing, dispersion, homogenization and dissociation of the polymer chains, in particular the thermoplastic chains.

[0035] During and at the end of dissolution step a), the pressure and temperature conditions make it possible to maintain the dissolution solvent at least partially, preferably completely, in liquid form, while the soluble fraction of the feedstock, in particular the target polymer, preferably the target thermoplastic, preferably the target polyolefin, and at least part of the impurities, are advantageously at least partially, preferably completely dissolved.

[0036] The contacting of the dissolution solvent with the plastic raw material to at least partially, preferably completely dissolve the polymer of the plastic feedstock in the dissolution solvent may be carried out in a line and / or equipment and / or between two pieces of equipment. Therefore, step a) advantageously includes at least one dissolution equipment, and optionally at least one feedstock preparation device, mixing device, and / or transport device. These equipment and / or devices may be, for example, static mixers, extruders, pumps, reactors, cocurrent or countercurrent columns, or a combination of lines and equipment. These equipment and / or devices may be, for example, static mixers, extruders, pumps, reactors, cocurrent or countercurrent columns, or a combination of lines and equipment. Devices for transporting, especially fluids such as gases, liquids, or solids, are well known to those skilled in the art. In a non-limiting embodiment, the transport device may include a compressor, pump, extruder, vibrating tube, endless screw, or valve. The equipment and / or device may include or be combined with a heating system (eg, oven, exchanger, trace, etc.) to achieve the conditions required for lysis.

[0037] The dissolution step a) advantageously comprises one or more transport devices for transporting at least the plastic feedstock, in particular in the form of one or more streams of plastic feedstock, and the dissolution solvent, in particular in the form of one or more streams of dissolution solvent. The plastic feedstock stream(s) may be different from the dissolution solvent stream(s). Part or all of the plastic feedstock may be fed to step a) in a mixture with part or all of the dissolution solvent, and the remainder of the solvent and / or feedstock may, if appropriate, be fed to step a) separately.

[0038] During the contacting of the plastic feedstock with the dissolving solvent, the dissolving solvent is advantageously at least partially, preferably completely, in liquid form, while the plastic feedstock comprising a polymer, in particular a thermoplastic, especially a polyolefin, may be in solid or liquid form, optionally containing solid particles in suspension. The plastic feedstock may be injected into the dissolving facility in the form of a suspension in the dissolving solvent, optionally as a mixture with the dissolving solvent, and the preparation and injection of the suspension may be continuous or batchwise.

[0039] Preferably, step a) comprises at least one extruder and a melting facility. In this case, the plastic feedstock is fed into the extruder, so that at least a portion, preferably all, of the target polymer, particularly the target thermoplastic, especially the polyolefin, contained in the feedstock is in a molten form outside the extruder. The plastic feedstock is injected into the melting facility in at least a partially molten form. The plastic feedstock in an at least partially molten state may be pumped by a pump dedicated to viscous fluids, commonly known as a melt pump or a gear pump. In addition to the melt pump, the plastic feedstock in at least a partially molten form may optionally be filtered at the extruder outlet using a filtering device to remove the coarsest particles; the mesh size of this filter is generally between 10 microns and 1 mm, preferably between 20 and 200 microns.

[0040] Preferably, step a) comprises an extruder into which the dissolving solvent is advantageously injected at several points to promote shear and therefore intimate mixing between the dissolving solvent and the plastic feedstock, which contributes to dissolving the polymer, in particular the thermoplastic, in particular the polyolefin.

[0041] The dissolution solvent used in the dissolution step a) is advantageously an organic solvent or a mixture of solvents, preferably organic. Preferably, the dissolution solvent is chosen from organic solvents, preferably comprising, and preferentially consisting of, one or more hydrocarbons, the boiling point of which is between -50°C and 250°C, preferably between -15°C and 150°C, preferably between 20°C and 110°C. Preferably, the dissolution solvent comprises, and preferably consists of, one or more hydrocarbons, highly preferably one or more alkanes, containing 3 to 12 carbon atoms, preferentially 4 to 8 carbon atoms, highly preferably 5 to 7 carbon atoms, such as the isomers of pentane, hexane and heptane. The dissolving solvent is highly advantageously an organic solvent, preferably a hydrocarbon, preferably having a critical temperature of 90-400°C, preferably 130-300°C, preferably 180-290°C, and a critical pressure of 1.5-5.0 MPa (absolute), preferably 2.0-4.3 MPa (absolute), preferably 2.4-4.2 MPa (absolute). According to certain embodiments, the dissolving solvent has a boiling point above 70°C, preferably 80-220°C, and / or the solvent comprises, preferably consists of, an alkane containing at least 7 carbon atoms. According to other preferred embodiments, the dissolving solvent has a boiling point below 50°C or above 150°C.

[0042] Advantageously, the melting temperature when melting is carried out is between 100°C and 300°C, and the melting pressure is between 1.0 and 20.0 MPa (absolute). More particularly, the temperature and pressure evolve throughout step a) from ambient conditions, i.e., a temperature of the plastic feedstock of 10-30°C and atmospheric pressure of 1 bar (0.1 MPa), until melting conditions are reached, more particularly the melting temperature and the melting pressure. In particular, the melting temperature is between 100 and 300°C, preferably between 150 and 250°C, and the melting pressure is between 1.0 and 20.0 MPa (absolute), preferably between 1.5 and 15.0 MPa (absolute), and very particularly between 2.0 and 10.0 MPa (absolute). Highly advantageously, at the end of the melting step a), the melted polymer stream is at the melting temperature and the melting pressure. Preferably, the weight ratio between the plastic feedstock and the dissolving solvent is between 0.01 and 5.0, preferably between 0.05 and 3.0, preferably between 0.10 and 1.0.

[0043] By limiting the temperature in step a) to a temperature below 300°C, preferably below 250°C, it is possible to prevent or limit thermal degradation of the polymer, in particular thermoplastics, more particularly polyolefins. Preferably, the dissolution temperature is above the melting point of the polymer, in particular thermoplastics, more particularly polyolefins, to promote their dissolution. Preferably, the temperature in dissolution step a) is below the critical temperature of the dissolution solvent to avoid the formation of supercritical phases during dissolution step a), which would tend to interfere with dissolution.

[0044] In parallel, the dissolution pressure is greater than the saturated vapor pressure of the dissolution solvent at the dissolution temperature, so that the dissolution solvent is at least partially, preferably completely, in liquid form at the dissolution temperature. Advantageously, the dissolution pressure is greater than or equal to the critical pressure of the dissolution solvent, allowing extraction step b) and / or recovery step c) to be carried out under conditions in which at least part of the solvent is in supercritical form, so that it is not necessary to significantly increase the pressure between step a), in particular the outlet of step a) and steps b) and / or c). When the dissolution pressure in step a) is greater than or equal to the critical pressure of the dissolution solvent, the dissolution temperature is less than the critical temperature of the dissolution solvent, so that the dissolution solvent remains at least partially in liquid form.

[0045] Highly advantageously, the dissolution temperature and pressure conditions reached in step a) are adjusted so that the mixture (dissolving solvent+target polymer) is a one-phase mixture.

[0046] Advantageously, said dissolution step a) is carried out over a residence time of 1 to 600 minutes, preferably 2 to 300 minutes, preferably 2 to 180 minutes, residence time being understood as the residence time at the dissolution temperature and dissolution pressure, i.e. the time of the treatment of the plastic feedstock in step a) with the dissolution solvent at the dissolution temperature and dissolution pressure.

[0047] Advantageously, the dissolution solvent used in step a) comprises, preferably consists of, a fresh solvent supply and / or a recycled solvent stream obtained from recovery step c).

[0048] Optionally, the treatment method may include an intermediate adsorption step a'), which is located during or immediately downstream of dissolution step a) and involves introducing an adsorbent solid, preferably alumina, silica, silica-alumina, activated carbon or bleaching earth, in the form of divided particles, into the crude polymer solution obtained at the end of step a) or, optionally, during dissolution step a). The adsorbent solid may then be removed during one of the optional intermediate purification steps, for example, during optional step E1) of separation of insoluble matter and / or optional washing step E2). This optional adsorption step a') makes it possible to optimize the purification of the polymer solution in the presence of the adsorbent solid in divided form.

[0049] The crude polymer solution obtained at the end of the dissolution step a) contains at least the dissolution solvent and the polymer, particularly the target polymer to be recovered and purified by the present invention, dissolved in the dissolution solvent. Generally, the crude polymer solution also contains soluble impurities and / or suspended insoluble impurities or compounds that are also soluble in the dissolution solvent. The crude polymer solution obtained at the end of step a) may optionally contain polymers other than the target polymer, for example, polymers in molten form.

[0050] (Optional step E1) of separating out insoluble matter) The process may optionally comprise an optional step E1) in which insoluble matter is separated off by solid-liquid separation to advantageously obtain at least one clarified polymer solution and at least one insoluble fraction, said step E1) being located between the dissolution step a) and the extraction step b), which advantageously comprises at least part, preferably all, of the insoluble impurities suspended in the crude polymer solution, in particular resulting from step a).

[0051] Step E1) of separating out insoluble substances thus makes it possible to remove at least some, preferably all, of the particles of compounds insoluble in the dissolution solvent under the temperature and pressure conditions of step a), which may be present in suspension in the polymer solution, preferably the crude polymer solution, obtained from step a) or optional step a'). Insoluble impurities removed during optional step E1) of separating out insoluble substances are, for example, pigments, mineral compounds, packaging residues (glass, wood, cardboard, paper, aluminum) and insoluble polymers.

[0052] If it is implemented, this separation step E1) advantageously makes it possible to limit operational problems of downstream process steps, such as clogging and / or corrosion, while at the same time contributing towards the purification of the plastics feedstock.

[0053] When it is incorporated into the process, step E1) of separating off insoluble matter is advantageously carried out at a temperature of 100 to 300° C., preferably 150 to 250° C., and at a pressure of 1.0 to 20.0 MPa (absolute), preferably 1.5 to 15.0 MPa (absolute), highly preferably 2.0 to 10.0 MPa (absolute). Highly advantageously, the optional step E1) of separating off insoluble matter is carried out under the temperature and pressure conditions of dissolution, i.e. under the temperature and pressure conditions at the outlet of step a).

[0054] If it is incorporated into the process, said step E1) of separating off insoluble matter is preferably fed with the crude polymer solution obtained from step a) or from the optional intermediate adsorption step a').

[0055] When it is incorporated into the method, said step E1) advantageously comprises a section comprising at least one solid-liquid separation device, such as a separating flask, a decanter, a centrifugal decanter, a centrifuge, a filter, a sand filter, an eddy current separator, an electrostatic separator, a triboelectric separator, preferably a decanter, a filter, a sand filter and / or an electrostatic separator.

[0056] The removal of the insoluble fraction may be facilitated by equipment for transporting and / or removing traces of solvent that may be present in the insoluble fraction, such as a conveyor, a vibrating tube, an endless screw, an extruder or a stripper. Optional step E1) may therefore comprise equipment for transporting and / or removing traces of solvent in order to remove the insoluble fraction.

[0057] According to a particular embodiment of optional step E1), step E1) of separating out insoluble matter comprises at least two, and generally less than five, solid-liquid separation devices in series and / or parallel. The presence of at least two solid-liquid separation devices in series makes it possible to improve the removal of insoluble matter, while the presence of devices in parallel makes it possible to manage the maintenance and / or unclogging operations of said devices.

[0058] The declogging of the equipment, in particular the electrostatic separator or filter, can be carried out using a backflushing injection solvent. The declogging solvent can be an aqueous or organic solution, preferably an organic solvent of the same nature as that used in the dissolution step a) and / or extraction step b). According to a particular embodiment, the declogging solvent is of the same nature as the concentrated solution used in the optional washing step E2). Some insoluble compounds, in particular some pigments and mineral fillers traditionally added to polymer formulations, can be introduced in the form of particles with a size of less than 1 μm. This is the case, for example, for titanium dioxide, calcium carbonate, and carbon black. According to a particular embodiment of optional step E1), said step E1) of separating out insoluble substances advantageously comprises an electrostatic separator, which allows for the efficient removal of at least a portion, preferably all, of the insoluble particles with a size of less than 1 μm. According to another particular embodiment of optional step E1), step E1) of separating out insoluble matter comprises a sand filter to remove particles of different sizes, in particular particles with a size below 1 μm.

[0059] Depending on the nature of the feedstock, the polymer solution, preferably crude polymer solution, fed to step E1) may optionally comprise a second liquid phase, which may consist, for example, of molten polymer. According to another particular embodiment of optional step E1), step E1) advantageously comprises equipment for separating out this second liquid phase, which is preferably carried out by means of at least one three-phase separator.

[0060] (Optional washing step E2) The present treatment method may optionally comprise a step E2) of washing with a concentrated solution, which step E2) is located between the dissolution step a) and the extraction step b), and advantageously obtains at least one washing effluent and at least one washed polymer solution. The washed polymer solution obtained at the end of the optional step E2) advantageously contains the target polymer that the present invention aims to recover and purify, dissolved in the dissolution solvent. Optionally, it may still contain residual impurities that are particularly soluble in the dissolution solvent and / or traces of the washing solvent, if step E2) is optionally performed.

[0061] When incorporated into the process, washing step E2) is fed with the concentrate solution and a polymer solution, preferably the crude polymer solution obtained from step a) or the optional intermediate adsorption step a'), or the clarified polymer solution obtained from optional step E1). The polymer solution fed to step E2) may optionally be a purified polymer solution obtained from optional adsorption step E3), in particular by adding an adsorbent in a mixture with the polymer solution. The polymer solution fed to optional washing step E2), i.e., the crude polymer solution, the clarified polymer solution, or otherwise optionally purified polymer solution, may contain impurities in the form of suspended insoluble and / or dissolved compounds. These suspended or dissolved compounds may be partially or completely removed during washing step E2) by dissolution or precipitation and / or entrainment in the concentrate solution. Therefore, when implemented, this step E2) contributes to the treatment of the plastic feedstock, more particularly to the purification of the polymer solution.

[0062] The optional washing step E2) advantageously comprises placing the polymer solution (crude polymer solution, clarified polymer or otherwise optionally purified polymer solution) fed to step E2) in contact with a concentrated solution. Advantageously, the concentrated solution has a higher density than the polymer solution (i.e., a mixture comprising at least the target polymer and a dissolution solvent in which the target polymer is dissolved), in particular 0.85 or more, preferably 0.9 or more and preferentially 1.0 or more. The concentrated solution may be an aqueous solution, which preferably comprises at least 50% by weight of water, preferably at least 75% by weight of water and highly preferably at least 90% by weight of water. The pH of the aqueous solution may be adjusted using an acid or a base to facilitate the dissolution of some compounds. The dope solution may optionally be a solution comprising, preferably consisting of, an organic solvent advantageously having a density of 0.85 or more, preferably 0.9 or more, preferentially 1.0 or more, in which the polymer of the plastic feedstock remains insoluble under the temperature and pressure conditions of optional step E2), for example the organic solvent is selected from sulfolane or N-methylpyrrolidone (NMP), optionally in a mixture with water. Highly preferably, the dope solution is an aqueous solution, preferably containing at least 50% by weight of water, preferably at least 75% by weight of water, highly preferably at least 90% by weight of water.

[0063] The optional washing step E2) is advantageously carried out at a temperature of 100 to 300°C, preferably 150 to 250°C, and at a pressure of 1.0 to 20.0 MPa (absolute), preferably 1.5 to 15.0 MPa (absolute), highly preferably 2.0 to 10.0 MPa (absolute). Highly advantageously, the optional washing step E2) is carried out at the dissolution temperature and pressure.

[0064] In the optional washing step E2), the mass ratio between the mass flow rate of the dope solution and the mass flow rate of the crude or clarified polymer solution fed to step E2) is advantageously between 0.05 and 20.0, preferably between 0.1 and 10.0, preferably between 0.5 and 3.0. The contacting arrangement between the crude or clarified polymer solution and the dope solution may be carried out at several points in the installation used, i.e. via several injections of the crude or clarified polymer solution and / or the dope solution at different points along the installation: it is the sum of the injected flows that is taken into account in calculating the ratio.

[0065] The optional step E2) may be carried out in one or more washing devices that can be placed in contact with the concentrated solution and / or by means of separation equipment that allows at least one washing effluent and at least one washed polymer solution to be recovered. This equipment is well known and includes, for example, stirred reactors, static mixers, decanting mixers, two- or three-phase separation flasks, cocurrent or countercurrent washing columns, plate columns, stirred columns, packed columns, pulse columns, etc., each type of equipment possibly comprising one or more devices used alone or in combination with other types of equipment.

[0066] According to a preferred embodiment, the optional washing step E2) is carried out in a countercurrent washing column, in which, on the one hand, the concentrated solution is injected into the half, preferably the third, of the column closest to the top of the column, and, on the other hand, the crude or clarified polymer solution is injected into the half, preferably the third, of the column closest to the bottom of the column. According to this embodiment, it is possible to recover at least one washed polymer solution and at least one washing effluent.

[0067] According to very particular embodiments, the flow at the inlet and / or outlet of the wash column may be split and injected at several injection points along the column and / or withdrawn at several withdrawal points along the column.

[0068] According to another embodiment, the optional washing step E2) is carried out in a mixer-decanter, which comprises an agitation mixing zone for placing the concentrated solution and the crude or clarified polymer solution in contact, and a decantation zone making it possible to recover the washed polymer solution and the wash effluent.

[0069] At the end of the washing step E2), the wash effluent obtained advantageously contains the compounds dissolved in the rich solvent and / or the insoluble compounds entrained in the wash effluent. The wash effluent may be reprocessed in a washing treatment section, whereby the dissolved and / or entrained compounds are at least partially separated off and the wash effluent is optionally purified to obtain a purified rich solution, while part of the purified wash solution is at least partially recycled. This washing treatment section may comprise one or more devices known for solid-liquid separation, such as, for example, a separating flask, a decanter, a centrifugal decanter, a centrifuge or a filter. The wash effluent may also be sent outside the process, for example, to a used water treatment station if the rich solution is an aqueous solution.

[0070] (Extraction step b)) The method according to the invention comprises an extraction step b), which advantageously comprises feeding the extraction solvent and the crude polymer solution obtained from step a), or optionally the clarified polymer solution obtained from optional step E1), the washed polymer solution obtained from optional step E2), or the purified solution obtained from optional adsorption step E3), to obtain at least one extracted polymer solution and at least one used solvent, in particular one containing impurities. The extracted polymer solution obtained at the end of step b) advantageously comprises the target polymer that the invention aims to recover and purify, dissolved in the dissolution solvent. In some cases, it may still contain residual impurities that are particularly soluble in the dissolution solvent and / or traces of the extraction solvent, and, if step E2) is carried out, optionally traces of the washing solvent.

[0071] The dissolved polymer-containing streams fed to step b), i.e. preferably the crude polymer solution obtained from step a), the clarified polymer solution obtained from optional step E1), the washed polymer solution obtained from optional step E2) or the purified polymer solution obtained from optional step E3), may therefore optionally contain dissolved compounds or dissolved impurities, which may be partially or totally removed during extraction step b) by contacting with an extraction solvent.

[0072] Extraction step b) advantageously comprises at least one extraction section, preferably 1 to 5 extraction sections, and highly preferably 1 extraction section. The temperature at which extraction step b) is carried out is 100 to 300°C, preferably 150 to 250°C. The pressure at which extraction step b) is carried out is 1.0 to 20.0 MPa (absolute), preferably 1.5 to 15.0 MPa (absolute), and highly preferably 2.0 to 10.0 MPa (absolute). According to a preferred embodiment of the invention, the process according to the invention comprises extraction step b) under temperature and pressure conditions different from those of step a).

[0073] The mass ratio between the mass flow rate of the extraction solvent and the mass flow rate of the polymer solution fed to step b) is advantageously between 0.05 and 20.0, preferably between 0.1 and 10.0, preferably between 0.2 and 5.0. The contact arrangement between the polymer solution fed to step b), preferably the crude polymer solution or optionally clarified, washed or purified polymer solution, and the extraction solvent may be carried out at several points in the extraction section, i.e. at different points along the extraction solvent, via several injections of the polymer solution and / or the extraction solvent fed to step b): it is the sum of the injected flows that is taken into account in calculating the ratio.

[0074] The extraction solvent used in extraction step b) is advantageously an organic solvent or a mixture of solvents, preferably organic. Preferably, the extraction solvent is chosen from organic solvents, preferably comprising, and preferentially consisting of, one or more hydrocarbons, having a boiling point between -50°C and 250°C, preferably between -15°C and 150°C, preferably between 20°C and 110°C. Preferably, the extraction solvent comprises, and preferably consists of, one or more hydrocarbons, highly preferably one or more alkanes, containing 3 to 12 carbon atoms, preferentially 4 to 8 carbon atoms, highly preferably 5 to 7 carbon atoms, such as the isomers of pentane, hexane and heptane. Preferably, the critical temperature of the extraction solvent (highly advantageously an organic solvent, preferably a hydrocarbon) is 90-400°C, preferably 130-300°C, preferably 180-290°C, and the critical pressure of the extraction solvent is 1.5-5.0 MPa (absolute), preferably 2.0-4.3 MPa (absolute), preferably 2.4-4.2 MPa (absolute). According to a particular embodiment, the boiling point of the extraction solvent is above 70°C, preferably 80-220°C, and / or the solvent contains at least 7 carbon atoms. According to another preferred embodiment, the boiling point of the extraction solvent is below 50°C or above 150°C.

[0075] Highly preferably, the extraction solvent used in step b) is the same solvent as the dissolution solvent used in step a), optionally in a different physical state (e.g. the dissolution solvent is in liquid form while the extraction solvent is in a supercritical state), facilitating the management of the solvents, in particular their purification and their recycling, in particular recycling to dissolution step a) and extraction step b).Another advantage of using the same dissolution and extraction solvent in the same or different physical states, in addition to facilitating the management of the solvents involved in the process according to the invention, is the advantage of limiting the energy consumption and costs incurred in particular by the recovery of the solvents, their treatment and their recycling to at least one step of the process, as well as the treatment and purification of the solvents.

[0076] The extraction section(s) of step b) may comprise one or more extraction devices, allowing the extraction solvent and / or at least one used solvent, in particular the solvent containing impurities, to be placed in contact with separation equipment for recovering the extracted polymer solution. This equipment is well known and includes, for example, stirred reactors, static mixers, decanting mixers, two- or three-phase separation flasks, cocurrent or countercurrent wash columns, plate columns, stirred columns, packed columns, pulse columns, etc., each type of equipment may comprise one or more devices used alone or in combination with other types of equipment.

[0077] According to a preferred embodiment of the present invention, extraction step b) comprises a countercurrent extraction column into which the extraction solvent is injected on the one hand and the polymer solution to be fed to step b) is injected on the other hand. This embodiment makes it possible to recover at least one extracted polymer solution on the one hand and the spent solvent, especially the spent solvent containing impurities, on the other hand. Preferably, the polymer solution to be fed to step b), preferably the crude polymer solution or the optionally clarified, washed or purified polymer solution, is injected into the half, preferably the third, of the countercurrent extraction column closest to the top, while the extraction solvent is injected into the half, preferably the third, of the countercurrent extraction column closest to the bottom.

[0078] The flow at the inlet and / or outlet of the countercurrent extraction column may be split at several injection and / or withdrawal points along the column.

[0079] According to another embodiment of the invention, the extraction is carried out in a mixer-decanter, which advantageously comprises an agitated mixing zone for placing the extraction solvent and the polymer solution in contact, and a decantation zone making it possible to recover, on the one hand, the extracted polymer solution and, on the other hand, the used solvent.

[0080] According to a preferred embodiment of the present invention, the extraction step b) comprises a liquid / liquid extraction section. In this embodiment, the extraction solvent is preferably selected from the isomers of pentane, hexane, and heptane, preferably from the isomers of pentane and hexane, and most preferably from the isomers of pentane. The liquid / liquid extraction section is preferably operated at a temperature of 100°C to 300°C, preferably from 150°C to 250°C, and at a pressure of 1.0 to 20.0 MPa (absolute), preferably from 1.5 to 15.0 MPa (absolute), and most preferably from 2.0 to 10.0 MPa (absolute). In any case, in this embodiment, the temperature and pressure conditions are adjusted so that the extraction solvent is in liquid form, and the dissolving solvent itself is preferably in liquid form. Highly advantageously, the liquid / liquid extraction is carried out under temperature and pressure conditions different from the dissolution conditions achieved in step a), in particular when the extraction solvent is identical to the dissolution solvent, in particular at a temperature higher than the dissolution temperature and / or at a pressure lower than the dissolution pressure, thus resulting in the two-phase zone of the corresponding polymer-solvent mixing diagram.

[0081] According to another particularly preferred embodiment of the present invention, extraction step b) comprises a section for extraction under specific temperature and pressure conditions, the extraction solvent being advantageously at least partially in supercritical form. Such extraction may be called supercritical extraction. In this embodiment, extraction is carried out by contacting the polymer solution, preferably crude, clarified, washed or purified polymer solution, fed to step b) with the extraction solvent, advantageously under temperature and pressure conditions that allow obtaining a supercritical phase composed mainly of the extraction solvent (i.e., preferably at least 50% by weight, preferentially at least 70% by weight, preferably at least 90% by weight). In other words, extraction is carried out by contacting the polymer solution, preferably crude, clarified, washed or purified polymer solution fed to step b), with the extraction solvent, which is at least partially, preferably completely in supercritical form. Such a supercritical extraction step b) advantageously allows for an efficient purification of the polymer solution, due in particular to the very high affinity of organic impurities, such as some of the additives, especially dyes, some of the plasticizers, etc., for the supercritical phase. The use of an extraction solvent in supercritical form also makes it possible to create a substantial density difference between the supercritical phase and the polymer solution in liquid form, which facilitates separation by decantation between the supercritical and liquid phases and thus contributes to the purification of the polymer solution.

[0082] In this particularly preferred embodiment, extraction step b) uses an extraction solvent whose supercritical temperature is preferably between 130 and 300°C, preferably between 180 and 290°C, and whose supercritical pressure is preferably between 2.0 and 4.3 MPa (absolute), preferably between 2.4 and 4.2 MPa (absolute). Highly advantageously, in such a supercritical extraction step b), the extraction solvent is chosen from hydrocarbons, preferentially containing 4 to 8 carbon atoms, preferably 5 to 7 carbon atoms. The extraction solvent for the supercritical extraction may be, for example, a pentane isomer, in particular n-pentane, 2-methylbutane (or isopentane) or 2,2-dimethylpropane, a hexane isomer, in particular n-hexane, 2-methylpentane (or isohexane), 2,2-dimethylbutane or 2,3-dimethylbutane, or a heptane isomer, in particular n-heptane, 2-methylhexane (or isoheptane), 3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane, 2,2,3-trimethylbutane, or cyclopentane, cyclohexane or methylcyclopentane.

[0083] Advantageously, the supercritical extraction step b) is carried out at a temperature of preferably 150°C to 300°C, preferably 180°C to 280°C, and at a pressure of preferably 2.0 to 20.0 MPa (absolute), preferably 2.0 to 15.0 MPa (absolute), highly preferably 3.0 to 10.0 MPa (absolute). In any case, in this embodiment, the temperature and pressure conditions are adjusted, inter alia, in a regulation section comprised in extraction step b) upstream of the extraction step, so that the extraction solvent is at least partially in supercritical form in the extraction section.

[0084] In a highly preferred embodiment of the present invention, extraction step b) comprises supercritical extraction, in which the extraction solvent is identical to the dissolution solvent, except for the fact that the extraction solvent is at least partially in the supercritical phase. In this highly advantageous case of supercritical extraction, the dissolution solvent can be at least partially in supercritical form, which advantageously optimizes decantation during the extraction step, and more particularly between the liquid and supercritical phases at each extraction phase or plateau, thereby making it possible to maximize purification.

[0085] Advantageously, at the end of extraction step b), the spent solvent obtained contains, in particular, impurities. It may be reprocessed in an organic processing section, which, on the one hand, makes it possible to at least partially separate out the impurities and purify the solvent to obtain a purified extraction solvent, and, on the other hand, makes it possible to recycle at least a portion of the purified extraction solvent to the inlet of extraction step b) and / or, possibly, to the inlet of dissolution step a), in cases where the dissolution solvent and the extraction solvent are identical. If a mixture of organic solvents is used as the extraction solvent, this organic processing section may make it possible to at least partially recover the organic solvent separately. The spent solvent may be processed according to any method known to those skilled in the art, for example by one or more of the following methods: distillation, evaporation, extraction, adsorption, crystallization, precipitation of insoluble substances, or purging.

[0086] In the specific case where the extraction solvent is the same as the dissolution solvent, the advantage of using an extraction solvent that is the same as the dissolution solvent lies in the fact that an organic processing section does not need to ensure separation between the dissolution solvent and the extraction solvent, and both can be entrained in the spent solvent, which represents a significant savings in terms of investment and energy consumption. Furthermore, this organic processing section may be interchanged with the section for processing the solvent fraction recovered at the end of step c), thus at least reducing the investment costs and energy consumption associated with the processing of the organic solvent stream resulting from the process. Furthermore, limiting the number of different solvents used in the process according to the invention, or even reducing it to one or two, simplifies the plastic feedstock processing process, minimizes utility consumption, and optimizes the solvent recovery, purification, and recycling steps, while allowing for efficient purification of the polymer solution to obtain a purified polymer.

[0087] (Optional adsorption step E3) The treatment method may optionally comprise an optional adsorption step E3), located between the dissolution step a) and the polymer recovery step c). Depending on the quality of the starting plastic feedstock and the impurities it contains, it may in fact be advantageous to complete the purification of the polymer solution by an optional adsorption step E3), which makes it possible to obtain at least one purified polymer solution.

[0088] When it is incorporated into the process according to the invention, the adsorption step E3) is carried out downstream of the dissolution step a) and upstream of the polymer recovery step c). The optional adsorption step E3) may advantageously be carried out upstream or downstream of the extraction step b).

[0089] Said optional adsorption step E3) advantageously comprises an adsorption section, operated in the presence of at least one adsorbent, which is preferably solid, in particular in the form of a fixed bed, an entrained bed (or a slurry, i.e. in the form of particles introduced into the stream to be purified and entrained with this stream) or in the form of an ebullated bed, preferably in the form of a fixed or entrained bed. The adsorption section is advantageously operated in the presence of at least one adsorbent, preferably of the alumina, silica, silica-alumina, activated carbon or bleaching earth type, preferably in the form of a fixed or entrained bed, with the circulation of the stream optionally ascending or descending.

[0090] The optional adsorption step E3) is advantageously carried out at a temperature of 100 to 300°C, preferably 150 to 250°C, and at a pressure of 1.0 to 20.0 MPa (absolute), preferably 1.5 to 15.0 MPa (absolute), and highly preferably 2.0 to 10.0 MPa (absolute). Highly advantageously, step E3) is carried out under conditions of dissolution temperature and pressure, i.e., at the dissolution temperature and dissolution pressure reached in step a). Preferably, in optional step E3), the hourly space velocity (HSV), which corresponds to the ratio between the volumetric flow rate of the polymer solution fed to step E3) and the volume of the adsorbent, is 0.05 to 10 h -1 , preferentially 0.1~5.0h -1 is.

[0091] According to a particular embodiment of optional step E3), the adsorption section may comprise one or more fixed beds of adsorbent, for example in the form of adsorption columns, preferably at least two adsorption columns, preferentially two to four adsorption columns, containing said adsorbent. When the adsorption section comprises two adsorption columns, one mode of operation is, according to the terminology, called "swing" operation, in which one of the columns is online, i.e., in service, while the other column is in reserve. When the adsorbent of the online column becomes spent, this column is isolated, while the in-reserve column is brought online, i.e., in service. The spent adsorbent can then be regenerated in situ and / or replaced with fresh adsorbent, and the column containing it can be brought online again once the other column has been isolated.

[0092] Another mode of operation of this particular embodiment of step E3), which includes one or more fixed beds of adsorbent, is to have at least two columns. When the adsorbent in the first column is exhausted, this first column is isolated, and the spent adsorbent is either regenerated in situ or replaced with fresh adsorbent. The column is then brought back online in the rearmost position, and the process is repeated. This mode of operation is known as the permutable mode, or PRS for permutable reactor system, or "lead and lag" according to other technical terms. The combination of at least two adsorbent columns makes it possible to overcome possible and potential rapid poisoning and / or clogging of the adsorbent due to the combined action of impurities, contaminants, and insoluble substances that may be present in the stream to be treated. The reason for this is that the presence of at least two adsorbent columns advantageously facilitates adsorbent replacement and / or regeneration without shutting down the process, which also makes it possible to control costs and limit adsorbent consumption.

[0093] According to a particular embodiment of the optional step E3) of adsorption on a fixed bed of adsorbent, said optional step E3) is preferably carried out downstream of the optional step E1) of separation of insoluble matter and / or the optional washing step E2), and upstream or downstream of the extraction step b). Advantageously, the combination of the extraction step b) and the adsorption step E3) allows an improved purification of the polymer solution by taking advantage of the affinity of the residual impurities for both the extraction solvent and the adsorbent solid.

[0094] According to another embodiment, the adsorption section of the optional step E3) may consist of adding sorbent particles to the polymer solution, in particular the crude polymer solution, from which they may be separated via a step of removing the sorbent particles located downstream of the adsorption section. In this particular embodiment, the optional adsorption step E3) is advantageously carried out before the extraction step b) and in all cases after the dissolution step a). The removal of the sorbent particles may advantageously correspond to the step E1) of separating out insoluble substances or to the washing step E2). Such implementation of the optional adsorption step E3) advantageously corresponds to the optional intermediate adsorption step a'), which has been described herein above, by the introduction of the sorbent particles followed by a solid / liquid separation.

[0095] (Polymer recovery step c)) According to the invention, the process comprises a step c) of recovering the polymer, obtaining at least one solvent fraction and at least one purified polymer fraction.

[0096] The polymer recovery step c) advantageously comprises at least one solvent recovery section, preferably 1 to 5 solvent recovery sections, to which the extracted or optionally purified polymer solution is fed.

[0097] The polymer recovery step c) is therefore primarily aimed at at least partially, preferably predominantly, separating out the solvent(s), in particular the dissolving solvent and optionally the extraction solvent, contained in the polymer solution fed to step c), i.e., the extracted or optionally purified polymer solution, to recover a polymer that is at least partially, preferably predominantly and completely free of the dissolving solvent that may still be present in the polymer solution fed to step c) and other solvent(s) used in the method. The term "predominantly" should be understood to mean at least 50% by weight, preferentially preferably at least 70% by weight, preferably at least 90% by weight, and highly preferably at least 95% by weight, relative to the weight of the solvent(s) contained in the polymer solution fed to step c), in particular the dissolving solvent and optionally the extraction solvent contained in the extracted or optionally purified polymer solution fed to step c). Any method for separating the solvent from the polymer known to those skilled in the art may be used, in particular any method that allows a phase change of the polymer(s) or the solvent(s). The solvent(s) may be separated off, for example by evaporation, stripping, demixing, differences in density, in particular by decantation or centrifugation.

[0098] The purified polymer fraction obtained may correspond to a concentrated polymer solution or to a solid purified polymer. Preferably, the polymer recovery step c) also comprises a conditioning section for conditioning the polymer in solid form, more particularly in the form of solid granules.

[0099] The polymer recovery step c) is also directed towards at least partial, preferably predominantly and predominantly total, recovery of the solvent(s), in particular the dissolution solvent and optionally the extraction solvent, contained in the extracted or optionally purified polymer solution fed to step c). The polymer recovery step c) is also directed towards purifying and recovering the recovered solvent fraction, in particular upstream of the dissolution step a) and / or upstream of the extraction step b). The term "predominantly" is to be understood as meaning at least 50% by weight, preferentially preferably at least 70% by weight, preferably at least 90% by weight, and very preferably at least 95% by weight, relative to the weight of the solvent(s) contained in the extracted or optionally purified polymer solution fed to step c).

[0100] Said polymer recovery step c) advantageously comprises at least one solvent recovery section in which the temperature is between 0 and 350°C, preferably between 5 and 300°C, preferably between 10 and 250°C, and in which the pressure is between 0.1 and 20.0 MPa (absolute), preferably between 0.1 and 15.0 MPa (absolute), highly preferably between 0.1 and 10.0 MPa (absolute).

[0101] Advantageously, polymer recovery step c) comprises at least one solvent recovery section, each preferably comprising equipment operated at different temperatures and pressures, with the aim of obtaining at least one solvent fraction and at least one purified polymer fraction. In the case where several different solvents are used in the process according to the invention, in particular in dissolution step a) and extraction step b), step c) may comprise several solvent recovery sections, for example 2, 3 or 4 solvent recovery sections, so that the various solvents, in particular the dissolution solvent and the extraction solvent, are recovered separately, sequentially and / or continuously. Preferably, the dissolution solvent and the extraction solvent are the same, and polymer recovery step c) comprises a single solvent recovery section.

[0102] According to a particular embodiment of the invention, the method of the invention advantageously comprises, successively or simultaneously: - solvent recovery section c1); the polymer solution is preferably heated to a temperature above the melting point of the polymer to obtain a solvent fraction and a purified polymer fraction, - conditioning section c2); the purified polymer fraction (advantageously separated from the solvent(s)) is advantageously cooled to a temperature below the melting point of the polymer to obtain a fraction comprising the polymer in solid form.

[0103] According to a preferred embodiment of the present invention, step c) comprises a section for recovering the solvent of step c), the solvent(s) to be separated, in particular the dissolving solvent, under conditions of temperature and pressure adjusted to supercritical conditions, i.e., above the critical point, allowing for easy separation and recovery of at least a portion of the solvent, in particular the dissolving solvent. In this embodiment, the solvent recovery section particularly comprises a fluid system consisting of a supercritical phase containing predominantly the solvent, in particular the dissolving solvent, and a liquid phase containing the polymer. The term "predominantly" here means at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, and highly preferably at least 95% by weight, relative to the weight of the stream under consideration, i.e., the supercritical phase. The separation may be referred to as supercritical separation of the solvent(s). Supercritical separation of solvent(s) allows for efficient separation of solvent(s), in particular dissolving solvent, on the one hand, and polymer or possibly concentrated polymer solution, on the other hand, advantageously permitted by significant difference in density between the two phases. Furthermore, supercritical separation of solvent(s) allows for significantly reduced energy and environmental costs compared to simple vaporization of the solvent, since there is no latent heat of vaporization during the transition to the supercritical state.

[0104] According to a particular embodiment of the invention, at least a portion of the purified polymer fraction obtained at the end of step c) may be recycled to the dissolution step a) and again undergo a treatment cycle to increase the efficiency of polymer purification.

[0105] Highly advantageously, the solvent fraction recovered at the end of step c) may be treated in an organic processing section located at the end of step c) to purify it and obtain a purified solvent, in particular a purified dissolution solvent, which can be advantageously recycled to the dissolution step a) and / or the optional extraction step b). Said optional organic processing section at the end of step c) may use any method known to those skilled in the art, for example one or more of the following methods: distillation, evaporation, liquid-liquid extraction, adsorption, crystallization and precipitation of insoluble substances or by purging. In the particular case where the extraction solvent is identical to the dissolution solvent, the solvent fraction recovered at the end of step c) may be treated in the same organic processing section as the organic processing section for the used solvent obtained at the end of extraction step b). The used solvent obtained in step b) and the solvent fraction obtained in step c) are treated in the same organic treatment section, which makes it possible to simplify the process for treating the plastic feedstock, to minimize the consumption of utilities and to optimize the solvent recovery, purification and recycling processes, while at the same time allowing an efficient purification of the polymer solution to obtain a purified polymer.

[0106] The process according to the invention therefore makes it possible to obtain from plastic waste a purified stream of polymers, in particular thermoplastics, more particularly polyolefins, which may be used in any application, for example to replace the same polymer in virgin form. The purified stream of polymers, i.e. the purified polymer fraction, obtained via the process according to the invention therefore has a sufficiently low impurity content so that it can be used in any application.

[0107] According to a preferred embodiment of the present invention, the method for processing plastic feedstock comprises the steps of: - a step a of dissolving in a dissolution solvent); obtaining at least one crude polymer solution; - a step E1 of feeding a crude polymer solution and separating out insoluble matter; obtaining at least one clarified polymer solution and at least one insoluble matter fraction; - a step b of extraction of the clarified polymer solution with an extraction solvent; preferably involving supercritical extraction, to obtain at least one extracted polymer solution and at least one spent solvent; and - a step c) of recovering the polymer from the extracted polymer solution; preferably comprising supercritical separation of the solvent(s) to obtain a solvent fraction and a purified polymer fraction; and the dissolving solvent and the extracting solvent are preferably the same.

[0108] According to another preferred embodiment of the present invention, a method for processing plastic feedstock comprises the steps of: - a step a of dissolving in a dissolution solvent); obtaining at least one crude polymer solution; - a step E1 of feeding a crude polymer solution and separating out insoluble matter; obtaining at least one clarified polymer solution and at least one insoluble matter fraction; - a step E2 of washing the clarified polymer solution by contact with a concentrated solution); obtaining at least one wash effluent and at least one washed polymer solution; - a step b of extraction of the washed polymer solution with an extraction solvent; preferably involving supercritical extraction, obtaining at least one extracted polymer solution and at least one spent solvent; and - a step c) of recovering the polymer from the extracted polymer solution obtained from step b); preferably comprising supercritical separation of the solvent(s) to obtain a solvent fraction and a purified polymer fraction; and the dissolving solvent and the extracting solvent are preferably the same.

[0109] According to certain embodiments of the present invention, a method for processing plastic feedstock comprises the steps of: - a step a of dissolving in a dissolution solvent); obtaining at least one crude polymer solution; - a step E2 of washing the crude polymer solution by contact with a concentrated solution); obtaining at least one wash effluent and at least one washed polymer solution; - a step E1 of feeding the washed polymer solution and separating out insoluble matter; obtaining at least one clarified polymer solution and at least one insoluble fraction; - a step b of extraction of the clarified polymer solution with an extraction solvent; preferably involving supercritical extraction, to obtain at least one extracted polymer solution and at least one spent solvent; and - a step c) of recovering the polymer from the extracted polymer solution obtained from step b); preferably comprising supercritical separation of the solvent(s) to obtain a solvent fraction and a purified polymer fraction: and the dissolving solvent and the extracting solvent are preferably the same.

[0110] According to another preferred embodiment of the present invention, a method for processing plastic feedstock comprises the steps of: - a step a of dissolving in a dissolution solvent); obtaining at least one crude polymer solution; - a step E1 of feeding a crude polymer solution and separating out insoluble matter); obtaining at least one clarified polymer solution and at least one insoluble fraction; - a step E2 of washing the clarified polymer solution by contact with a concentrated solution); obtaining at least one wash effluent and at least one washed polymer solution; - step b) of extraction of the washed polymer solution with an extraction solvent; preferably involving supercritical extraction, obtaining at least one extracted polymer solution and at least one spent solvent; - a step E3 of adsorption by placing the extracted polymer solution in contact with an adsorbent, preferably in a fixed bed; obtaining at least one purified polymer solution; and - a step c) of recovering the polymer from the purified polymer solution obtained from step E3); preferably comprising a supercritical separation of the solvent(s) to obtain a solvent fraction and a purified polymer fraction: and the dissolving solvent and the extracting solvent are preferably the same.

[0111] According to another preferred alternative embodiment of the present invention, a method for processing plastic feedstock comprises the steps of: - a step a of dissolving in a dissolution solvent); obtaining at least one crude polymer solution; - a step E2 of feeding the crude polymer solution and separating out the insoluble matter); obtaining at least one clarified polymer solution and at least one insoluble fraction; - a step E2 of washing the clarified polymer solution by contact with a concentrated solution); obtaining at least one wash effluent and at least one washed polymer solution; - a step E3 of adsorption by placing the extracted polymer solution in contact with an adsorbent, preferably in a fixed bed; obtaining at least one purified polymer solution; - a step b of extraction of the purified polymer solution with an extraction solvent; preferably involving supercritical extraction, obtaining at least one extracted polymer solution and at least one spent solvent; and - a step c) of recovering the polymer from the extracted polymer solution; preferably comprising supercritical separation of the solvent(s) to obtain a solvent fraction and a purified polymer fraction; and the dissolving solvent and the extracting solvent are preferably the same.

[0112] The following examples and figures are illustrative of the present invention and in particular of certain embodiments of the present invention, but are not intended to limit the scope of the invention.

[0113] (List of drawings) The information regarding the elements referenced in Figures 1 to 3 is intended to enable a better understanding of the invention and is not intended to limit the invention to the specific embodiments shown in Figures 1 to 3. The various embodiments presented may be used alone or in combination with each other, without any limitations on the combinations.

[0114] FIG. 1 shows a scheme of one embodiment of the method of the present invention, comprising the following steps: - a step a of dissolving a plastic feedstock (1); the plastic feedstock (1) comprises a polymer in a dissolution solvent (2) to obtain a crude polymer solution (3); - step b of extraction of the crude polymer solution (3) with an extraction solvent (9); obtaining an extracted polymer solution (11) and a used solvent (10); - a step c) of recovering the polymer from the extracted polymer solution (11) obtained from step b), obtaining a solvent fraction (13) and a purified polymer fraction (14).

[0115] FIG. 2 shows a variant of the implementation of the method according to the invention shown in FIG. 1, which comprises the following steps: - a step a of dissolving a plastic feedstock (1); the plastic feedstock (1) comprises a polymer in a dissolution solvent (2) to obtain a crude polymer solution (3); - a step E1 of feeding the crude polymer solution (3) and separating out the insoluble matter; obtaining a clarified polymer solution (5) and an insoluble fraction (4); - a step E2 of washing the clarified polymer solution (5) by contacting it with a concentrated solution (6); obtaining a wash effluent (7) and a washed polymer solution (8); - step b of extraction of the washed polymer solution (8) with an extraction solvent (9); obtaining an extracted polymer solution (11) and a used solvent (10); - a step E3 of adsorption by placing the extracted polymer solution (11) in contact with an adsorbent; obtaining a purified polymer solution (12); - a step c) of recovering the polymer from the purified polymer solution (12) obtained from step E3); obtaining a solvent fraction (13) and a purified polymer fraction (14).

[0116] Figure 3 shows a variant of the implementation of the process according to the invention depicted in Figure 2. In the embodiment shown in Figure 3, the process comprises an intermediate step a') between step a) and step E1). The crude polymer solution (3) is brought into contact with the adsorbent in divided form, with the aim of obtaining a polymer solution (21) containing the adsorbent in suspension, which is then fed to the separation step E1). The adsorbent previously introduced in step a') is separated off in the insoluble fraction (4) and removed.

[0117] To allow a better understanding of the invention, only the main steps are shown together with the main flows in Figures 1 to 3. It is clearly understood that all the equipment necessary for functioning (vessels, pumps, exchangers, furnaces, columns, etc.) is present, even if not shown.

[0118] (Example) Example 1 (according to the present invention) 125 mL of n-pentane and 23 g of plastic feedstock are introduced into a 500 mL autoclave equipped with a stirrer. The plastic feedstock is in the form of pink-purple colored beads of 5 mm diameter and is based on polypropylene.

[0119] The autoclave is then sealed and heated at a rate of 2°C per minute to 180°C with stirring at 500 revolutions per minute (rpm). Once a temperature of 180°C is reached, the temperature and stirring are maintained at an autogenous pressure of 2.6 MPa (absolute) for 3 hours. After 3 hours, all the polypropylene is dissolved in n-pentane. At the end of the dissolution process, a crude polymer solution is obtained, which is a highly colored liquid phase.

[0120] 125 mL of n-pentane is then added to the system, and the temperature is raised to 200°C at a rate of 20°C per hour while maintaining stirring at 500 rpm. The pressure inside the autoclave is then increased to 4.0 MPa (absolute). At 200°C and 4.0 MPa (absolute), the conditions are supercritical, i.e., above the critical temperature and at the critical pressure of n-pentane. These temperature, pressure and stirring conditions are then maintained for 15 minutes, after which the stirring is stopped. The system is then decanted in less than 5 seconds. At the end of the extraction step, two phases are obtained: the lower phase contains the polymer and corresponds to the extracted polymer solution, which upon decantation is slightly less colored than the mixture before the extraction step, and the upper phase is significantly colored.

[0121] 15 mL of the extracted polymer solution is taken and placed in a crystallizing dish, which is then placed in an oven at 180° C. and atmospheric pressure while being flushed with nitrogen for 6 hours.

[0122] A slightly pinkish white solid is then obtained in the crystallizing dish.

[0123] Example 2 (not in accordance with the present invention) 125 mL of n-pentane and 23 g of plastic feedstock are introduced into a 500 mL autoclave equipped with a stirrer. The plastic feedstock is in the form of pink-purple colored beads of 5 mm diameter and is based on polypropylene.

[0124] The autoclave is then sealed and heated at a rate of 2°C per minute to 180°C with stirring at 500 revolutions per minute (rpm). Once a temperature of 180°C is reached, the temperature and stirring are maintained at an autogenous pressure of 2.6 MPa (absolute) for 3 hours. After 3 hours, all the polypropylene is dissolved in n-pentane. At the end of the dissolution process, a crude polymer solution is obtained, which is a highly colored liquid phase.

[0125] 15 mL of the crude polymer solution is taken and placed in a crystallizing dish, which is then placed in an oven at 180° C. and atmospheric pressure while being flushed with nitrogen for 6 hours.

[0126] A pink-purple colored solid is thus obtained in the crystallizing dish, the color of which is close to that of the original feed beads. [Brief explanation of the drawings]

[0127] [Figure 1] 1 shows a scheme of one embodiment of the method of the present invention. [Figure 2] 2 is a variant of the implementation of the method according to the invention represented in FIG. 1; [Figure 3] 3 is a variant of the implementation of the method according to the invention represented in FIG. 2.

Claims

1. A method for processing a plastic supply material containing a polyolefin, comprising the following steps: a) A dissolution step comprising bringing the plastic supply material into contact with a dissolution solvent containing a hydrocarbon having 3 to 12 carbon atoms, at a dissolution temperature of 100°C to 300°C and a dissolution pressure of 1.0 to 20.0 MPa in absolute pressure; obtaining at least one crude polymer solution; b) Extraction step by contacting the crude polymer solution obtained in step a) with an extraction solvent containing a hydrocarbon having 3 to 12 carbon atoms at a temperature of 100°C to 300°C, an absolute pressure of 1.0 to 20.0 MPa, and a mass ratio of 0.05 to 20.0 between the mass flow rate of the extraction solvent and the mass flow rate of the crude polymer solution; obtaining at least one extracted polymer solution and at least one used solvent; then c) A step to recover the polymer; obtaining at least one solvent fraction and at least one purified polyolefin fraction.

2. The method according to claim 1, wherein the dissolving solvent is selected from organic solvents, and the boiling point of the organic solvent is -50°C to 250°C, or -15°C to 150°C, or 20°C to 110°C.

3. The method according to claim 1 or 2, wherein the critical temperature of the dissolving solvent is 90 to 400°C, or 130 to 300°C, or 180 to 290°C, and the critical pressure is 1.5 to 5.0 MPa, or 2.0 to 4.3 MPa, or 2.4 to 4.2 MPa.

4. The method according to any one of claims 1 to 3, wherein the dissolution temperature in step a) is 150 to 250°C, and the dissolution pressure is 1.5 to 15.0 MPa in absolute pressure, or 2.0 to 10.0 MPa in absolute pressure.

5. The method according to any one of claims 1 to 4, wherein the extraction solvent used in step b) is a hydrocarbon, its critical temperature is 90 to 400°C, or 130 to 300°C, or 180 to 290°C, and its critical pressure is 1.5 to 5.0 MPa in absolute pressure, or 2.0 to 4.3 MPa in absolute pressure, or 2.4 to 4.2 MPa in absolute pressure.

6. The method according to any one of claims 1 to 5, wherein the extraction solvent is the same as the dissolution solvent.

7. The method according to claim 1 or 2, wherein the extraction solvent is the same as the dissolution solvent but is in a different physical state.

8. The method according to any one of claims 1 to 7, wherein in step b), extraction is performed by placing the crude polymer solution obtained from step a) in contact with an extraction solvent that is at least partially or completely in a supercritical state.

9. The method according to claim 8, wherein the extraction solvent is a pentane isomer, a hexane isomer, or a heptane isomer.

10. The method according to claim 8 or 9, wherein the temperature during extraction step b) is 150°C to 300°C or 180°C to 280°C, and the pressure at that time is 2.0 to 20.0 MPa in absolute pressure, or 2.0 to 15.0 MPa in absolute pressure, or 3.0 to 10.0 MPa in absolute pressure.

11. The method according to any one of claims 1 to 10, wherein the polymer recovery step c) includes a solvent recovery section where the temperature therein is 0 to 350°C, or 5 to 300°C, or 10 to 250°C, and the pressure therein is 0.1 to 20.0 MPa in absolute pressure, or 0.1 to 15.0 MPa in absolute pressure, or 0.1 to 10.0 MPa in absolute pressure.

12. The method according to any one of claims 1 to 11, wherein step c) polymer recovery step includes at least one solvent recovery section under temperature and pressure conditions adjusted to bring the dissolving solvent under supercritical conditions.

13. The method according to any one of claims 1 to 12, comprising step E1) separating and removing insoluble substances by solid-liquid separation, wherein step E1) is located between a dissolution step a) and an extraction step b), the operating temperature is 100°C to 300°C, and the pressure is 1.0 to 20.0 MPa in absolute pressure.

14. The method according to claim 13, wherein step E1) includes an electrostatic separator, a filter, a sand filter, or a combination thereof.

15. The method according to any one of claims 1 to 14, comprising step E2) washing with a high-density solvent, wherein step E2) is located between step a) and step b), the operating temperature is 100°C to 300°C, the pressure is 1.0 to 20.0 MPa in absolute pressure, and the density of the high-density solvent is 0.85 or higher, or 0.9 or higher, or 1.0 or higher.

16. The method according to claim 15, wherein the high-density solvent is an aqueous solution.

17. The method according to any one of claims 1 to 16, comprising an adsorption step E3), the step E3) being located between a dissolution step a) and a polymer recovery step c), and comprising an adsorption section operated in the presence of at least one adsorbent, wherein the temperature during the operation is 100 to 300°C and the pressure is 1.0 to 20.0 MPa in absolute pressure.

18. A method according to any one of claims 1 to 17, comprising the following steps: a) A dissolution step in which plastic supply material is brought into contact with a dissolution solvent containing hydrocarbons having 3 to 12 carbon atoms, at a dissolution temperature of 100°C to 300°C and a dissolution pressure of 1.0 to 20.0 MPa in absolute pressure; at least one crude polymer solution is obtained; E1) A step of feeding the crude polymer solution obtained from step a) and separating and removing insoluble substances by solid-liquid separation at a temperature of 100°C to 300°C and an absolute pressure of 1.0 to 20.0 MPa; obtaining at least one clarified polymer solution and at least one insoluble fraction; b) Extraction step by contacting the clarified polymer solution obtained from step E1) with an extraction solvent containing a hydrocarbon having 3 to 12 carbon atoms at a temperature of 100 to 300°C, an absolute pressure of 1.0 to 20.0 MPa, and a mass ratio of the mass flow rate of the extraction solvent to the mass flow rate of the clarified polymer solution of 0.05 to 20.0; obtaining at least one extracted polymer solution and at least one used solvent, then c) Polymer recovery step: obtain at least one solvent fraction and at least one purified polyolefin fraction.

19. The method according to claim 18, wherein the polymer recovery step includes at least one solvent recovery section under temperature and pressure conditions adjusted to bring the dissolving solvent under supercritical conditions.

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