Method for recycling waste polypropylene-based plastics using a light hydrocarbon solvent

Abstract

The invention relates to a method for purifying a plastics feedstock comprising polypropylene, said method comprising the steps of: a) dissolving the plastics feedstock in a dissolution solvent comprising a hydrocarbon compound having a boiling point of between -15°C and 100°C, at a dissolution temperature of between 150°C and 250°C and a dissolution pressure of between 1.0 and 18.0 MPa absolute, in order to obtain a crude polymer solution; b) purifying the crude polymer solution, comprising: b1) separating the insoluble substances; and / or b2) washing, using a dense solution; and / or b3) extraction, using an extraction solvent; and / or b4) adsorbing impurities; then c) solvent-polymer separation, using a supercritical separation section, at a temperature of between 160 and 300°C and a pressure of between 2.7 and 10.0 MPa absolute, followed by at least one solvent recovery section, in order to obtain purified polypropylene.

Description

[0001] PROCESS FOR RECYCLING USED POLYPROPYLENE-BASED PLASTICS USING A LIGHT HYDROCARBON SOLVENT

[0002] TECHNICAL FIELD

[0003] The present invention relates to a process for recycling used plastics, mainly comprising polypropylene (or PP) in order to obtain a stream of purified polypropylene which can be used, 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 polymers and in particular polypropylene, said method comprising dissolving the polymers in a light hydrocarbon solvent, in particular based on alkane(s), having a boiling point between -15°C and 100°C, at least one step of purifying the polymer solution obtained, in order to at least partially eliminate the impurities, in particular the additives conventionally used in plastic-based materials, and an optimized step of separating the purified polypropylene and the solvent, so as to be able to reuse the recovered purified polypropylene and thus recover the plastic filler.

[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 since mechanical sorting improves the purity of a stream in a given type of polymer, but generally it does not sufficiently 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 due in particular to high-temperature treatments.Another way of recycling plastic waste consists of dissolving, at least in part, the plastics, in particular thermoplastics, with a view to purifying them by eliminating the polymers from the load other than the one(s) targeted and / or impurities, for example additives such as fillers, colorants, pigments, and metals.

[0008] Several studies thus present different methods for treating plastic waste by dissolution and purification. Document US 2017 / 0021 10 describes a particular method for 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 dissolving 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 effectively treat impurities other than polymers.

[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 overcome these drawbacks and to contribute to the recycling of plastics. More particularly, it aims to propose an efficient, simple and economically viable method for treating a polypropylene-based plastic filler, in particular from plastic waste, in order to eliminate at least in part the impurities it contains, in particular at least in part the additives it contains and which are conventionally added to plastic materials, so as to be able to recover said plastic filler and more particularly plastic waste. The present invention seeks in fact to effectively separate the impurities from the polymers, and in particular from the polypropylene, which the used plastic materials contain, and to recover the purified polypropylene, in order to be able to use it for example as a polymer base in the manufacture of new plastic objects, in particular instead of virgin resin.

[0012] SUMMARY OF THE INVENTION

[0013] The invention relates to a method for purifying a plastic filler which comprises polypropylene, said method comprising: a) a dissolution step comprising bringing the plastic filler into contact with a dissolution solvent comprising at least one hydrocarbon compound having a boiling point of between -15°C and 100°C, at a dissolution temperature of between 150°C and 250°C, and a dissolution pressure of between 1.0 and 18.0 MPa absolute, to obtain at least one crude polymer solution; b) a step of purifying the crude polymer solution to obtain a purified polymer solution, 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 the impurities by contact with an adsorbent;then c) a solvent-polymer separation step, using at least one supercritical separation section operated at a temperature between 160 and 300°C and at a pressure (Psupercritical) between 2.7 and 10.0 MPa absolute, followed by at least one solvent recovery section, to obtain at least one fraction of purified polypropylene.;

[0014] The advantage of the method of the invention is to propose a method for the efficient treatment of a polypropylene-based plastic load, and in particular polypropylene-based plastic waste, in particular from collection and sorting channels, so as to recover the polypropylene it contains in order to be able to recycle it for any type of application. The method according to the invention makes it possible to obtain a purified polypropylene stream advantageously comprising negligible or at least sufficiently low levels of impurities, in particular additives, and solvent, in particular dissolving solvent, so that the purified polypropylene stream can be introduced into any type of plastic formulation instead of virgin polypropylene resin.For example, the purified polypropylene stream obtained at the end of the process according to the invention advantageously comprises less than 5% by weight of impurities, very advantageously less than 1% by weight of impurities and very advantageously less than 5% by weight of solvent (in particular of dissolving solvent), preferably less than 1% by weight of solvent, more preferably less than 0.1% by weight of solvent.

[0015] The process according to the invention thus proposes a simple scheme corresponding to a sequence of operations, which makes it possible to rid the polypropylene-based plastic waste of at least some of its impurities, in particular at least some of the additives, and to recover purified polypropylene, advantageously comprising little or no solvent, so as to be able to recover the plastic waste by recycling the purified polypropylene. Advantageously, depending on the conditions implemented in the steps of the process, the additives present in the plastic feedstock may be soluble or insoluble in the solvent used throughout the process according to the invention, allowing efficient purification and separation of the polymers.

[0016] Furthermore, the process according to the invention proposes a sequence of operations implemented under operating conditions, in particular temperatures and pressures, which are optimal, to effectively separate the impurities and solvents from the polypropylene, but reasonable, thus limiting the energy consumption of the process and, consequently, making said process economically attractive.

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

[0018] The present invention also makes it possible to efficiently and advantageously at lower cost separate the polypropylene from the solvent used (in particular the dissolving solvent), while limiting the thermal degradation of the polypropylene. Thus, the solvent used to treat the plastic filler, in particular the dissolving solvent, is recovered at least in part, and can be recycled to one of the stages of the process, which makes it possible to avoid excessive consumption of solvent, hence the ecological and economic interest of the process.

[0019] Thus, the present invention aims to purify a plastic load, in particular plastic waste, to obtain purified polypropylene, so as to be able to use it in any application, in particular as a replacement for virgin resins.

[0020] More particularly, the present invention aims to propose a process comprising a dissolution step followed by at least one purification step and then an optimized solvent / polymer separation, to obtain a purified polypropylene stream.

[0021] DESCRIPTION OF EMBODIMENTS

[0022] 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 described range of values. If this is not the case and the limit values ​​are not included in the described range, such clarification will be provided by the present invention. For the purposes 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, for the purposes of the present invention, a range of preferred pressure values ​​can be combined with a range of more preferred temperature values.

[0023] In the following, particular embodiments of the invention may be described. They may be implemented separately or combined with each other, without limitation of combinations when technically feasible.

[0024] According to the present invention, the pressures are absolute pressures and are given in absolute MPa (or MPa abs.).

[0025] 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.

[0026] 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.

[0027] The additives correspond to at least part of the impurities in the plastic load to be treated and which the process 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 polypropylene (such as for example polyethylene), etc.

[0028] 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, thermoplastic polymers other than polypropylene, thermosetting polymers, household, chemical or cosmetic products, used oils, water.

[0029] According to the invention, a polymer solution is a solution comprising the dissolution solvent and at least the targeted polypropylene, dissolved (i.e. in particular solvated and dispersed) in said dissolution solvent, the dissolved polypropylene 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.

[0030] The critical temperature and critical pressure of a solvent, in particular the dissolving solvent, are specific to said solvent and depend on the chemical nature of the solvent in question. 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 is well known to those skilled in the art, at the critical point and beyond, the pure substance in question is in supercritical form or in the supercritical state; it can then be called a supercritical fluid.

[0031] The invention relates to a method for purifying a plastic filler, preferably composed of plastic waste, and comprising polypropylene, said method comprising, preferably consisting of: a) a dissolution step comprising bringing the plastic filler into contact with a dissolution solvent comprising at least one advantageously aliphatic and preferably paraffinic hydrocarbon compound, having a boiling point of between -15 and 100°C, preferably between 8 and 100°C, preferentially between 25 and 69°C, preferably between 25 and 61°C and very preferably between 25 and 40°C, at a dissolution temperature of between 150°C and 250°C, preferably between 160 and 225°C, preferentially between 165°C and 210°C and preferably between 170 and 195°C, and a dissolution pressure of between 1.0 and 18.0 MPa abs., preferably between 1.0 and 12.0 MPa abs., preferably between 3.0 and 11.0 MPa abs.,preferably between 5.0 and 11.0 MPa abs. and very preferably between 6.0 and 10.0 MPa abs., to obtain at least one crude polymer solution; then b) a step of purifying the crude polymer solution, comprising at least one of the following sub-steps: b1) a sub-step of separating the insolubles making it possible to obtain at least one clarified polymer solution and preferably an insoluble fraction; and / or b2) a washing sub-step, by contact with a dense solution, making it possible to obtain at least one washed polymer solution and preferably a washing effluent; 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 preferably a used solvent; and / or b4) a sub-step of adsorption of the impurities by contact with an 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 and / or washed and / or extracted and / or refined polymer solution; then, c) a solvent-polymer separation step using at least one supercritical separation section operated at a temperature between 160 and 300°C, preferably between 190 and 250°C, preferentially between 200 and 230°C, and at a pressure (Psupercritical) between 2.7 and 10.0 MPa abs., preferably between 3.0 and 6.0 MPa abs., preferentially between 3.0 and 5.0 MPa abs. and preferably between 3.0 and 4.0 MPa abs., followed by at least one solvent recovery section, in particular operated at a temperature between 160 and 300°C and a pressure between Psupercritical and 0.000005 MPa (i.e. 5 Pa), preferably between 2.7 MPa and 0.000005 MPa, and in particular between 1.0 MPa and 0.000005 MPa,to obtain at least a fraction of purified polypropylene and advantageously a fraction of solvent.,

[0032] The charge

[0033] The feedstock of the process according to the invention, called plastic feedstock, comprises plastics which themselves more particularly comprise polypropylene. Preferably, the plastic feedstock comprises between 50 and 100% by weight, more preferably between 70% and 100% by weight of plastics.

[0034] The plastics included in the feedstock of the process according to the invention are polypropylene-based and are generally production scrap and / or waste from end-of-life plastic objects, in particular household plastic waste, plastic waste from construction, automotive plastic waste or waste from any type of transport, or waste from electrical and electronic equipment. Preferably, the plastic waste comes from collection and sorting channels. In general, plastics or plastic materials comprise polymers which are mixed with additives, in order to constitute, after shaping, various materials and 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.

[0035] Preferably, the feedstock of the process according to the invention comprises at least 80% by weight, preferably at least 85% by weight, preferably at least 90% by weight, of polypropylene relative to the total weight of the plastic feedstock. The process according to the invention thus aims in particular to purify and recover the polypropylene contained in the feedstock in order to be able to reuse it in different applications.

[0036] The plastic filler may further comprise impurities, such as for example polymers, in particular thermoplastics, other than polypropylene, additives advantageously used to formulate the plastic material and also generally usage impurities resulting from the life cycle of plastic materials and objects, and / or resulting from the waste collection and sorting circuit. The plastic filler of the method according to the invention may comprise up to 20% by weight of impurities, preferably up to 15% by weight of impurities, more preferably up to 10% by weight of impurities. The plastic filler may comprise for example at least 5% by weight of impurities.

[0037] The plastic filler may advantageously be pretreated upstream of the process so as to at least eliminate all or part of the so-called coarse impurities, i.e. impurities in the form of particles of a size greater than or equal to 10 mm, preferably greater than or equal to 5 mm, or even greater than or equal to 1 mm, for example impurities of the wood, paper, biomass, iron, aluminum, glass, etc. type, and to shape it generally in the form of divided solids (or particles) so as to facilitate treatment in the process. This pretreatment may comprise a grinding step, a washing step at atmospheric pressure and / or a drying step. This pretreatment may be carried out on a different site, for example in a waste collection and sorting center, or on the same site where the treatment method according to the invention is implemented.Preferably, this pretreatment makes it possible to reduce the impurity content to less than 20% by weight, preferably less than 15% by weight, preferably less than 10% by weight, the percentages being given relatively to the weight of the plastic filler treated by the method according to the invention. At the end of the pretreatment, the filler is generally stored in the form of divided solids, for example in the form of ground material or powder, so as to facilitate handling and transport to the process.

[0038] Step a) of dissolution According to the invention, the method comprises a step a) of dissolution in which the plastic filler is brought into contact with a dissolution solvent, to obtain at least one, preferably one, crude polymer solution. This step in fact advantageously allows the dissolution of at least a part, preferably all, of the polypropylene of the plastic filler.

[0039] By dissolution is meant any phenomenon leading to the obtaining of at least one polymer solution, in particular a polypropylene solution, that is to say a liquid comprising polymers, in particular polypropylene, dissolved in a solvent, more particularly in the dissolution solvent. A person skilled in the art is well aware of the phenomena involved in the dissolution of polymers and which include at least mixing, dispersion, homogenization, solvation and disentanglement of the polymer chains, and more particularly of the polypropylene chains.

[0040] 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 its entirety, in the liquid state, so as to optimize the dissolution of the targeted polypropylene.

[0041] The nature of the dissolving solvent advantageously allows the use of operating conditions, in particular temperature and pressure conditions, in particular pressure, which are reasonable to ensure, on the one hand in step a) of dissolution but also advantageously in step b) of purification, the maintenance in the liquid phase, at least in part, preferably in full, of the dissolving solvent, thus allowing optimal dissolution of the targeted polypropylene and advantageously effective purification of the polymer solution, and, on the other hand in step c) of solvent-polymer separation, the passage to the supercritical state of at least a part of said dissolving solvent, to allow the demixing and therefore the separation of at least a part of said dissolving solvent, and possibly the evaporation of the residual dissolving solvent, at least in part,which thus makes it possible to achieve a very low solvent content in the purified polypropylene recovered at the end of the process (advantageously a content of less than 5% by weight of solvent, preferably less than 1% by weight of solvent, more preferably less than 0.1% by weight of solvent relative to the total weight of the purified polypropylene fraction). Indeed, a solvent composed of very light alkanes with a boiling point below -15°C, such as propane, which could be of interest in particular for its relatively mild critical conditions (temperature and pressure), would require the use of high pressure to keep the dissolution solvent at least in part, preferably in full, in liquid form throughout the duration of steps a) of dissolution and b) of purification, which would entail significant costs, in particular investment costs. Conversely, the use of a heavy solvent,like alkanes having a boiling point above 100°C, would require very severe operating conditions in step c) to reach the critical conditions of said heavy solvent and to be able to obtain said solvent at least partly in the supercritical state.,

[0042] Advantageously, the dissolving solvent comprises, preferably consists of, at least one hydrocarbon compound advantageously aliphatic and preferably paraffinic (i.e. saturated), preferably at least one alkane, having a boiling point of between -15 and 100°C, preferably between 8 and 100°C, preferentially between 25 and 69°C, preferably between 25 and 61°C and very preferably between 25 and 40°C.Preferably, the dissolution solvent comprises predominantly, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of a hydrocarbon compound which is advantageously aliphatic, preferably paraffinic (or alkane) (100% being the maximum, the percentages being expressed relative to the total weight of the dissolution solvent) having a boiling point of between -15 and 100°C, preferably between 8 and 100°C, preferably between 25 and 69°C, preferably between 25 and 61°C and very preferably between 25 and 40°C.Very advantageously, the predominantly aliphatic, preferably paraffinic, hydrocarbon compound of the dissolution solvent has a critical temperature (temperature at the critical point of said pure hydrocarbon compound) of between 130 and 285°C, preferably between 158 and 285°C, preferentially between 185 and 245°C, preferably between 185 and 230°C and very preferably between 185 and 200°C. In a very particular manner, the predominantly paraffinic hydrocarbon compound of the dissolution solvent has a critical pressure of between 2.5 and 5.0 MPa, preferably between 2.7 and 4.6 MPa, preferentially between 3.0 and 3.8 MPa, and preferably between 3.0 and 3.5 MPa.According to a preferred embodiment, the dissolution solvent comprises predominantly, preferably at least 80% by weight, preferentially at least 95% by weight, preferably 98% by weight of an aliphatic paraffinic hydrocarbon compound, preferably linear or branched, having a boiling point of between -15 and 100°C, preferably between 8 and 100°C, preferentially between 25 and 69°C, preferably between 25 and 61°C and very preferably between 25 and 40°C, and containing between 4 and 7 carbon atoms (i.e. C4-C7), preferably 5, 6 or 7 carbon atoms (respectively C5, C6 or C7), preferentially containing 5 or 6 carbon atoms (C5 or C6) and very preferably containing 5 carbon atoms (C5).

[0043] Advantageously, dissolution step a) is carried out at a dissolution temperature of between 150 and 250°C, preferably between 160 and 225°C, very preferably between 165 and 210°C and preferably between 170 and 195°C, and a dissolution pressure of between 1.0 and 18.0 MPa absolute, preferably between 1.0 and 12.0 MPa absolute, preferably between 3.0 and 11.0 MPa absolute, preferably between 5.0 and 11.0 MPa absolute, very preferably between 6.0 and 10.0 MPa absolute.More particularly, the temperature and pressure may vary throughout step a), from the conditions of introduction of the plastic filler and / or the dissolution solvent, for example from ambient conditions, i.e. a temperature between 10 and 30°C and atmospheric pressure (0.1 MPa), until reaching the dissolution conditions, i.e. the dissolution temperature, in particular between 150 and 250°C, preferably between 160 and 225°C, very preferably between 165 and 210°C and preferably between 170 and 195°C, and the dissolution pressure, in particular between 1.0 and 18.0 MPa absolute, preferably between 1.0 and 12.0 MPa absolute, preferably between 3.0 and 11.0 MPa absolute, preferably between 5.0 and 11.0 MPa absolute. and very preferably between 6.0 and 10.0 MPa absolute.Very advantageously, at the end of dissolution step a), the flow of dissolved polymer, in particular the polymer solution, is at the dissolution temperature and at the dissolution pressure.

[0044] Limiting the temperature in step a) to a temperature less than or equal to 250°C, preferably less than or equal to 225°C, preferably less than or equal to 210°C or even 195°C, makes it possible to avoid or limit the thermal degradation of the polymers, in particular polypropylene, but also to limit the energy requirement of the process, thus contributing to limiting the operating costs and the carbon footprint of the process. Preferably, the dissolution temperature is greater than or equal to the melting temperature of the polypropylene, so as to promote its dissolution.

[0045] At the same time, the dissolution pressure is advantageously greater 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 form, at the dissolution temperature, so as to optimize the dissolution of the targeted polypropylene.

[0046] Very advantageously, the dissolution temperature and pressure conditions reached in step a) are adjusted so that the mixture (dissolution solvent + polypropylene) is homogeneous and very preferably single-phase, said mixture possibly including insoluble impurities suspended in said mixture.

[0047] Preferably, the weight ratio (filler / solvent) between the plastic filler and the dissolution solvent (or the ratio between the mass flow rate of the plastic filler and the mass flow rate of the dissolution solvent, at the inlet of dissolution step a)) is between 0.01 and 2.0, preferably between 0.05 and 1.0, more preferably between 0.10 and 0.8.

[0048] Advantageously, dissolution step a) 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 to be the residence time at the dissolution temperature and at the dissolution pressure, i.e. the time of implementation of the plastic charge with the dissolution solvent at the dissolution temperature and at the dissolution pressure, in step a).

[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 from step c) of solvent-polymer separation.

[0050] The contacting between the dissolving solvent and the plastic filler to dissolve at least in part, preferably in full, the polypropylene of the plastic filler in the dissolving solvent can be carried out in a line and / or equipment and / or between two pieces of equipment. Thus, step a) advantageously uses at least one piece of dissolving equipment, and optionally at least one device for preparing the filler, a mixing device and / or a transport device. These pieces of equipment and / or devices can be, for example, a static mixer, an extruder, a pump, a reactor, a co- or counter-current column, or in a combination of lines and pieces of equipment. The transport devices, in particular for fluids, such as liquids or solids, are well known to those skilled in the art. In a non-limiting manner, the transport devices can comprise a pump, an extruder, a vibrating tube, a worm screw, a valve.The equipment and / or devices may also include or be associated with heating systems (e.g. furnace, exchanger, tracing, etc.) to achieve the conditions necessary for dissolution. Dissolution step a) may be carried out continuously, discontinuously (or in batch mode) or in fed-batch mode.

[0051] The dissolution step a) is at least supplied with the plastic filler, in particular in the form of one or more plastic filler streams, and with the dissolution solvent, in particular in the form of one or more dissolution solvent streams, advantageously by means of one or more transport devices. The plastic filler stream(s) may be separate from the dissolution solvent stream(s). Part or all of the plastic filler may also be supplied to step a) in a mixture with part or all of the dissolution solvent, the remainder of the solvent and / or filler, where appropriate, being able to be supplied to step a) separately.

[0052] When bringing the plastic filler into contact with the dissolving solvent, the dissolving solvent is advantageously at least partly, and preferably entirely, in liquid form, while the plastic filler, which comprises polypropylene, may be in solid or liquid form optionally comprising suspended solid particles. The plastic filler may also optionally be injected into the dissolving equipment, mixed with the dissolving solvent, in the form of a suspension in the dissolving solvent, the preparation and injection of the suspension being able to be continuous or discontinuous.

[0053] According to a particular embodiment of the invention, step a) may use an extruder and possibly at least one other dissolution equipment. In this case, the plastic feedstock, possibly with at least a fraction of the dissolution solvent, feeds the extruder so that, at the outlet of the extruder, at least a portion and preferably all of the targeted polypropylene, included in the feedstock, is in the molten state (or at least partly dissolved). The plastic feedstock, possibly mixed with at least a fraction of the dissolution solvent, is then injected into dissolution equipment, for example of the reactor type, at least partly in the molten state (or partly dissolved). The plastic feedstock, at least partly in the molten state (and / or partly dissolved) at the outlet of the extruder, may also be pumped using a pump dedicated to viscous fluids, often called a "melt" pump or gear pump.The plastic filler, at least partly in the molten state (or partly dissolved) can also be, at the extruder outlet, filtered using a filtration device, possibly in addition to the "melt" pump, in order to eliminate the largest particles, generally the mesh size of this filter is between 10 microns and 1 mm, preferably between 20 and 200 microns.

[0054] Preferably, step a) uses an extruder into which the dissolving solvent is injected, advantageously at several points, so as to promote shearing and therefore intimate mixing between the dissolving solvent and the plastic filler, which contributes to the dissolution of the polypropylene.

[0055] Optionally, the treatment method may comprise an intermediate adsorption step a'), located during the dissolution step a) or directly downstream of the dissolution step a), and which comprises the introduction of an adsorbent, preferably of the alumina, silica, silica-alumina, activated carbon or bleaching earth type, in the form of divided particles, into the raw polymer solution obtained at the end of step a) or optionally during the dissolution step a). The adsorbent may then be removed during the purification step b), for example during a sub-step b1) of separation of the insolubles and / or a washing sub-step b2). This optional adsorption step a') in the presence of an adsorbent in divided form makes it possible to optimize the purification of the polymer solution.

[0056] The raw polymer solution obtained at the end of dissolution step a) comprises at least the dissolution solvent, the polypropylene that the present invention seeks to recover purified, dissolved in the dissolution solvent. In general, the raw polymer solution also comprises soluble impurities also dissolved in the dissolution solvent. The raw polymer solution may optionally further comprise insoluble impurities or compounds in suspension. The raw polymer solution obtained at the end of step a) may optionally also comprise polymers, other than the targeted polypropylene, for example in the molten state.

[0057] At the end of the dissolution step carried out under such operating conditions, in particular temperature and pressure, the polypropylene of the plastic filler is advantageously dissolved, in whole or in part, in the dissolution solvent; the polypropylene solution obtained (i.e. the raw polymer solution) will be able to undergo step b) of purification then step c) of solvent-polymer separation, so as to recover the polypropylene of the plastic filler, in purified form, with very low impurity and residual solvent contents compatible with any type of subsequent application. Thus, the method according to the invention makes it possible to recover polypropylene from plastic waste in an optimal manner and under entirely reasonable operating conditions (in particular a well-limited, i.e. limited, dissolution pressure), and therefore with controlled energy consumption and consequently a limited cost.

[0058] The purification 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.

[0059] The different sub-steps b1), b2), b3) and b4) which can be implemented in the purification step b) can be operated continuously, discontinuously (or in batch mode) or in fed-batch mode.

[0060] 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 polypropylene dissolved in at least 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.

[0061] Sub-Step b1) of separation of insolubles

[0062] The purification process may comprise a sub-step b1) of separating the insolubles by solid-liquid separation, to advantageously obtain at least one clarified polymer solution (i.e. devoid of at least a portion, preferably all, of the insolubles that the crude polymer solution comprises) 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).

[0063] Sub-step b1) of separating the insolubles thus makes it possible to eliminate at least a portion, preferably all, of the particles of compounds insoluble in the dissolution solvent, present in suspension in the raw polymer solution resulting from step a) or from a possible step a'). The insoluble compounds (or 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.

[0064] When implemented, this separation sub-step b1) advantageously makes it possible, in addition to eliminating at least part of the insoluble impurities, to limit the operating problems, in particular of the clogging and / or erosion type, of the process steps located downstream of such a sub-step b1), while contributing to the purification of the plastic load.

[0065] Sub-step b1) of separating the insolubles is advantageously carried out at a temperature preferably between 150 and 250°C, preferably between 160 and 225°C, very preferably between 165 and 210°C, and preferably between 170 and 195°C, and at a pressure between 1.0 and 18.0 MPa absolute, preferably between 1.0 and 12.0 MPa absolute, preferably between 3.0 and 11.0 MPa absolute, preferably between 5.0 and 11.0 MPa absolute, very preferably between 6.0 and 10.0 MPa absolute. Very advantageously, sub-step b1) of separation of 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.

[0066] When integrated into the process, sub-step b1) of separation of insolubles is preferably fed with the raw polymer solution from step a) or from a possible intermediate adsorption step a'). According to another embodiment, sub-step b1) can be fed with a washed polymer solution from a washing sub-step b2).

[0067] Advantageously, sub-step b1) implements at least one solid-liquid separation section (or solid-liquid-liquid separation, in particular in the case where the effluent obtained at the end of the dissolution step comprises, in addition to the polymer solution and the solid impurities, impurities and / or polymers of a different nature than the targeted polypropylene, in liquid form and with little or no solubility). The solid-liquid separation section comprises at least one piece of solid-liquid separation equipment, for example a separator drum, a decanter, a centrifugal decanter, a centrifuge, a filter, a sand filter, a tangential filter using in particular a membrane and / or a depth filter, 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. Preferably, sub-step b1) uses at least one decantation section advantageously comprising at least one decanter and / or at least one filtration section. During sub-step b1), filtration aids (for example diatomaceous earth or sand) can optionally be added prior to the decantation and / or filtration.

[0068] 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.

[0069] 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.

[0070] Certain insoluble compounds, in particular certain pigments and mineral fillers, conventionally added during the formulation of polymers, may be 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, 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.

[0071] 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, these polymers being of a different nature from that of polypropylene. According to another particular embodiment, sub-step b1) advantageously uses a solid-liquid-liquid separation section, using equipment allowing the separation of two liquid phases from a solid phase, preferably by means of at least one two-phase or three-phase separator.

[0072] Sub-step b2) of washing

[0073] The purification process may optionally comprise a sub-step b2) of washing with a dense solution, to advantageously obtain at least one washed polymer solution and preferably a washing effluent. The washed polymer solution obtained at the end of sub-step b2) advantageously comprises the polypropylene that the present invention seeks to recover purified, dissolved in the dissolution solvent. Optionally, the washed polymer solution may still comprise residual impurities, in particular soluble in the dissolution solvent and / or possibly traces of the washing solvent (i.e. dense solution) if sub-step b2) is carried out.

[0074] 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).

[0075] 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 impurities in the form of insoluble compounds in suspension and / or in the form of solubilized compounds. These suspended or solubilized compounds may, in part or in full, be removed 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 filler and more particularly to the purification of the polymer solution.

[0076] The washing sub-step b2) advantageously comprises bringing the polymer solution which feeds sub-step b2), i.e. the raw or clarified polymer solution, 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 polypropylene and the dissolving solvent in which the targeted polypropylene is dissolved). In particular, the dense solution has a density preferably greater than or equal to 0.85, preferably greater than or equal to 0.9, preferentially greater than or equal to 1.0, and preferably less than or equal to 1.5. 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 compounds. 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 polypropylene of the plastic filler remains 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.

[0077] The washing sub-step b2) is advantageously carried out at a temperature preferably between 150 and 250°C, preferably between 160 and 225°C, very preferably between 165 and 210°C, and preferably between 170 and 195°C, and at a pressure between 1.0 and 18.0 MPa absolute, preferably between 1.0 and 12.0 MPa absolute, preferably between 3.0 and 11.0 MPa absolute, preferably between 5.0 and 11.0 MPa absolute, very preferably between 6.0 and 10.0 MPa absolute. Very advantageously, the washing sub-step b2) is carried out at the dissolution temperature and the dissolution pressure.

[0078] In the washing sub-step b2), when integrated into the process, the mass ratio (dense solution / polymer solution) between the mass flow rate of the dense solution and the mass flow rate of the 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 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 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 mass ratio (dense solution / polymer solution).

[0079] 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.

[0080] 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 the upper half, preferably the third, of the column, preferably closest to the column head, on the one hand, and the crude or clarified polymer solution is injected, preferably into the lower half, preferably the third, of the column, preferably 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 advantageously a washing effluent.

[0081] According to a very particular mode, the flows entering and / or leaving the washing column can be divided and injected at several injection points along the column and / or withdrawn at several withdrawal points along the column.

[0082] According to another embodiment, the washing sub-step b2) is carried out in a mixer-decanter comprising an agitated mixing zone, to bring the dense solution and the raw or clarified polymer solution into contact, and a decantation zone, making it possible to recover a washed polymer solution and advantageously a washing effluent.

[0083] At the end of the washing sub-step b2), the washing effluent advantageously obtained comprises in particular compounds solubilized in the dense and / or insoluble solution and entrained in the washing effluent. The washing effluent can be reprocessed in a washing effluent treatment section, on the one hand to separate at least in part the solubilized and / or entrained compounds 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 dense solution. This washing effluent 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.

[0084] Step b3) extraction

[0085] 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 preferably a used solvent in particular loaded with impurities. The extracted polymer solution obtained at the end of sub-step b3) advantageously comprises the polypropylene that the present invention seeks to recover purified, dissolved in the dissolution solvent. Optionally, the extracted polymer solution may still comprise residual impurities in particular soluble in the dissolution solvent and / or traces of dense solution and / or of the extraction solvent if sub-step(s) b2) and / or b3) is (are) carried out.

[0086] 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), preferably downstream of a sub-step b1) of separation of insolubles and possibly upstream or downstream of an adsorption sub-step b4) if the latter is also integrated into step b).

[0087] 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 comprise, in addition to polypropylene, possibly solubilized compounds or solubilized impurities.These solubilized compounds 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 optionally a washing sub-step b2) and / or an adsorption sub-step b4) allows improved purification of the polymer solution, using both the affinity of the impurities for the extraction solvent and optionally for the dense solution and / or an adsorbent.

[0088] When integrated into the method according to the invention, the extraction sub-step b3) advantageously uses at least one extraction section, preferably between one and five extraction section(s), very preferably one extraction section.

[0089] The mass ratio (extraction solvent / polymer solution) 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 mass ratio (extraction solvent / polymer solution).

[0090] 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, advantageously aliphatic and preferably paraffinic, preferably at least one alkane, having a boiling point of between -15 and 100°C, preferably between 8 and 100°C, preferentially between 25 and 69°C, preferably between 25 and 61°C and very preferably between 25 and 40°C.Preferably, the extraction solvent comprises predominantly, preferably at least 80% by weight, preferentially at least 95% by weight, preferably 98% by weight of a hydrocarbon compound, preferably aliphatic paraffinic (or alkane) (100% being the maximum, the percentages being expressed relative to the total weight of the dissolution solvent), having a boiling point of between -15 and 100°C, preferably between 8 and 100°C, preferentially between 25 and 69°C, preferably between 25 and 61°C and very preferably between 25 and 40°C.Very advantageously, the hydrocarbon compound, advantageously aliphatic, preferably paraffinic, which is the majority of the extraction solvent, has a critical temperature (temperature at the critical point of said pure hydrocarbon compound) of between 130 and 285°C, preferably between 158 and 285°C, preferentially between 185 and 245°C, preferably between 185 and 230°C and very preferably between 185 and 200°C.According to a preferred embodiment, the extraction solvent comprises predominantly, preferably at least 80% by weight, preferentially at least 95% by weight, preferably 98% by weight of an aliphatic paraffinic hydrocarbon compound, preferably linear or branched, having a boiling point of between -15 and 100°C, preferably between 8 and 100°C, preferentially between 25 and 69°C, preferably between 25 and 61°C and very preferably between 25 and 40°C, and containing between 4 and 7 carbon atoms (from C4 to C7), preferably 5, 6 or 7 carbon atoms (respectively in C5, C6 or C7), preferentially containing 5 or 6 carbon atoms (in C5 or C6) and very preferably containing 5 carbon atoms (in C5).

[0091] 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, lies in addition to facilitating the management of the solvents used in the process according to the invention, in particular the recovery of the solvents, their treatment and their recycling to at least one of the stages of the process, in limiting energy consumption and costs in particular generated by the treatment and purification of the solvents.

[0092] 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.

[0093] 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 the upper half, preferably the third, of the column, preferably closest to the head of the countercurrent extraction column, while the extraction solvent is injected into the lower half, preferably the third, of the column, preferably closest to the bottom of the countercurrent extraction column.

[0094] The inlet and / or outlet flows of the countercurrent extraction column can be divided into several injection and / or withdrawal points along the column.

[0095] According to another embodiment of b3), the extraction is carried out in a mixer-decanter which advantageously comprises a stirred mixing zone for, on the one hand, bringing into contact the extraction solvent and the polymer solution which feeds b3), preferably the clarified, washed or refined polymer solution, and on the other hand a decantation zone making it possible to recover an extracted polymer solution on the one hand and a used solvent on the other hand.

[0096] 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).

[0097] 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 150 and 250°C, preferably between 160 and 225°C, very preferably between 165 and 210°C, and more preferably between 170 and 195°C, and at a pressure of between 1.0 and 18.0 MPa absolute, preferably between 1.0 and 12.0 MPa absolute, preferably between 3.0 and 11.0 MPa absolute, preferably between 5.0 and 11.0 MPa absolute, very preferably between 6.0 and 10.0 MPa absolute. In any case, in this embodiment, the temperature and pressure conditions are adjusted so that the extraction solvent is in the liquid state, the dissolution solvent preferably also being in the liquid state.Very advantageously, the liquid / liquid extraction, in particular when the extraction solvent is the same as the dissolution solvent, is carried out under temperature and pressure conditions different from the dissolution conditions of 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 mixture diagram.

[0098] 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 in part, in supercritical form. Such extraction may be called supercritical extraction. In this embodiment, the extraction is carried out by bringing the polymer solution which feeds b3), 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 which feeds b3), 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 colorants or plasticizers, for the supercritical phase.The use of a supercritical extraction solvent also allows for the creation of a significant density difference between the supercritical phase and the polymer solution in liquid form, which facilitates demixing and separation by decantation between the two phases, i.e. between the supercritical phase and the liquid phase, which consequently contributes to the efficiency of the purification of the polymer solution.

[0099] In this other preferred embodiment, sub-step b3) uses an extraction solvent comprising predominantly, preferably at least 80% by weight, preferentially at least 95% by weight, preferably 98% by weight of a hydrocarbon compound, preferably aliphatic paraffinic (or alkane), (100% being the maximum, the percentages being expressed relative to the total weight of the dissolution solvent), having a critical temperature preferably between 130 and 285°C, preferably between 158 and 285°C, preferentially between 185 and 245°C, very preferentially between 185 and 230°C and preferably between 185 and 200°C.Very preferably, in such a supercritical extraction sub-step b3), the extraction solvent comprises predominantly, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of a paraffinic aliphatic hydrocarbon compound having a boiling point of between -15 and 100°C, preferably between 8 and 100°C, preferably between 25 and 69°C, very preferably between 25 and 61°C and preferably between 25 and 40°C, and containing between 4 and 7 carbon atoms (i.e. C4-C7), preferably 5, 6 or 7 carbon atoms (respectively C5, C6 or C7), preferably containing 5 or 6 carbon atoms (C5 or C6) and very preferably containing 5 carbon atoms (C5).In a very particular manner, the majority of the paraffinic aliphatic hydrocarbon compound in the extraction solvent has a critical pressure of between 2.5 and 5.0 MPa, preferably between 2.7 and 4.6 MPa, preferentially between 3.0 and 3.8 MPa, and preferably between 3.0 and 3.5 MPa.

[0100] Advantageously, the supercritical extraction sub-step b3) of this particular embodiment is carried out at a temperature preferably between 160°C and 300°C, preferably between 190 and 250°C, preferably between 200°C and 230°C, and at a pressure preferably between 2.7 and 10.0 MPa absolute, preferably between 3.0 and 6.0 MPa absolute, preferably between 3.0 and 5.0 MPa absolute and very preferably between 3.0 and 4.0 MPa absolute. According to a very particular embodiment of this embodiment of sub-step b3), the pressure at which the supercritical extraction is carried out is very advantageously between the critical pressure (PC(extraction solvent)) of the majority paraffinic aliphatic hydrocarbon compound of the extraction solvent (that is to say, preferably, the critical pressure of the majority paraffinic aliphatic hydrocarbon compound having a boiling point of between -15 and 100°C, preferably between 8 and 100°C,preferably between 25 and 69°C, very preferably between 25 and 61°C and more preferably between 25 and 40°C, and containing between 4 and 7 carbon atoms, preferably 5, 6 or 7 carbon atoms, preferably containing 5 or 6 carbon atoms and very preferably containing 5 carbon atoms, as defined above) and a pressure equal to 3.0 MPa above the critical pressure of the majority paraffinic aliphatic hydrocarbon compound of the extraction solvent (i.e.: PC(extraction solvent) + 3.0 MPa), preferably between the critical pressure of the majority paraffinic aliphatic hydrocarbon compound of the extraction solvent (PC(extraction solvent)) and a pressure equal to 1.5 MPa above the critical pressure of the majority paraffinic aliphatic hydrocarbon compound of the extraction solvent (i.e.: PC(extraction solvent) + 1.5 MPa),preferably between the critical pressure of the majority paraffinic aliphatic hydrocarbon compound of the extraction solvent (PC(extraction solvent)) and a pressure equal to 0.5 MPa above the critical pressure of the majority paraffinic aliphatic hydrocarbon compound of the extraction solvent (i.e.: equal to PC(extraction solvent) + 0.5 MPa), the pressures being absolute pressures. 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,the adjustment of the temperature and pressure of the extraction solvent in said adjustment section being advantageously carried out by means known to those skilled in the art (by using for example a pump and / or valve and / or turbine and / or exchanger and / or oven).,

[0101] In a very preferred embodiment of b3), the extraction sub-step b3) uses a supercritical extraction and the extraction solvent is the same as the dissolution solvent (or comprises the same major compound as the dissolution solvent and possibly impurities), except that the extraction solvent is at least partly in the supercritical phase. Advantageously, at the end of the 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 may be treated by any method known to those skilled in the art, such as for example one or more of the following methods: distillation, evaporation, extraction, adsorption, crystallization and precipitation of insolubles, or by purging.

[0102] Sub-Step b4) of adsortion

[0103] 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 polypropylene that the present invention seeks to recover purified, dissolved in the dissolution solvent.

[0104] 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, the adsorption sub-step b4) is implemented by bringing the polymer solution which feeds it, in particular the raw polymer solution from step a), the clarified polymer solution from b1) or washed from b2) or even the extracted polymer solution from b3), into contact with one or more adsorbent(s).

[0105] 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 a bubbling bed, preferably in the form of a fixed bed or an entrained bed. Each adsorbent used in sub-step b4) is 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.Advantageously, when integrated into the process, the adsorption sub-step b4) is carried out at a temperature preferably between 150 and 250°C, preferably between 160 and 225°C, very preferably between 165 and 210°C, and preferably between 170 and 195°C, and at a pressure between 1.0 and 18.0 MPa absolute, preferably between 1.0 and 12.0 MPa absolute, preferably between 3.0 and 11.0 MPa absolute, preferably between 5.0 and 11.0 MPa absolute, very preferably between 6.0 and 10.0 MPa absolute. Very advantageously, the adsorption sub-step b4) is carried out under the dissolution temperature and pressure conditions, i.e. at the dissolution temperature and dissolution pressure of 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 .

[0106] According to a particular embodiment of sub-step b4), the adsorption section may comprise one or more fixed bed(s) of adsorbent(s), 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.

[0107] Another mode of operation of this particular embodiment of b4), comprising one or more fixed bed(s) of adsorbent(s), 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 either regenerated in situ or replaced with 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 the consumption of adsorbent. According to this particular embodiment of sub-step b4) of adsorption in a fixed bed of adsorbent(s), sub-step b4) is preferably carried out downstream of a sub-step b1) of separation of insolubles and / or a sub-step b2) of washing, and possibly 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 a sub-step b2) of washing, and possibly a sub-step b3) of extraction, with a sub-step b4) of adsorption allows an improved purification of the polymer solution, using both the affinity of the residual impurities for the adsorbent and for the extraction solvent and possibly a dense solution.

[0108] 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 sub-step b1) of separation of the insolubles or to a sub-step b2) of washing. Such an implementation of the adsorption sub-step b4), by introduction of the adsorbent particles then solid / liquid separation, advantageously corresponds to the possible intermediate adsorption step a'), described further in this description.

[0109] According to the invention, the process comprises a step c) of solvent-polymer separation, to obtain at least one fraction of purified polypropylene and preferably a solvent fraction.

[0110] Solvent-polymer separation step c) advantageously uses at least one supercritical separation section, followed by at least one solvent recovery section, preferably between one and five solvent recovery section(s), in series. Solvent-polymer separation step c), more particularly the supercritical separation section, in particular the first supercritical separation section, is fed with the purified polymer solution from purification step b).

[0111] Step c) of solvent-polymer separation thus aims firstly 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 polypropylene freed at least in part, preferably mainly and preferentially completely, of the 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%, 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 method of separating the solvent from the polymers 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.

[0112] The purified polypropylene fraction obtained at the end of step c) may correspond to a concentrated polypropylene solution or to liquid (i.e., molten) or solid purified polypropylene. The solvent-polymer separation step c) may optionally further comprise a conditioning section for conditioning the recovered purified polypropylene, in solid form and more particularly in the form of solid granules. In this optional conditioning section, the recovered purified polypropylene is cooled, advantageously to a temperature below the melting temperature of the polypropylene, to obtain a fraction comprising polypropylene in the solid state.

[0113] 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%, 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 also 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).

[0114] Step c) of solvent-polymer separation thus uses a supercritical separation section which makes it possible to separate at least a portion of the dissolution solvent, and possibly the extraction solvent and the dense solution, and possibly a portion of the residual impurities which would not have been eliminated during step b), under temperature and pressure conditions adjusted so as to be placed in supercritical conditions, i.e. beyond the critical point of the solvent(s) to be separated, in particular beyond the critical point of the dissolution solvent, more particularly beyond the critical point of the majority hydrocarbon compound of the dissolution solvent, which advantageously makes it possible to easily separate and recover at least a portion of the solvent, in particular of the dissolution solvent.This supercritical separation section in particular uses a fluid system which consists of a supercritical phase comprising mainly solvent, in particular dissolving solvent, and a liquid phase comprising polypropylene. The term "mainly" here means 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 stream in question, i.e. the supercritical phase. The separation can then be called supercritical separation of the solvent(s).The supercritical separation of the solvent(s) makes it possible to efficiently separate on the one hand at least a portion of the solvent(s) and in particular the dissolving solvent and on the other hand the polypropylene or a concentrated polypropylene solution, the supercritical separation being advantageously enabled by the significant difference in density between the two phases, the supercritical phase comprising mainly solvent, in particular dissolving solvent, and the liquid phase comprising polypropylene. In addition, the supercritical separation of the solvent(s) advantageously makes it possible to present a significantly reduced energy and environmental cost compared to a simple vaporization of the solvent, since during the transition to the supercritical state, there is no latent heat of vaporization.

[0115] The supercritical separation section is advantageously operated at a temperature of between 160°C and 300°C, preferably between 190 and 250°C, preferably between 200°C and 230°C, and at a pressure (Psupercritical) of between 2.7 and 10.0 MPa absolute, preferably between 3.0 and 6.0 MPa absolute, preferably between 3.0 and 5.0 MPa absolute and preferably between 3.0 and 4.0 MPa absolute.

[0116] According to a particular embodiment, the supercritical separation section of step c) is carried out at a pressure (Psupercritical) between the critical pressure of the majority hydrocarbon compound of the dissolution solvent (PC(solvent dissolution)) and a pressure equal to 3.0 MPa above the critical pressure of the majority hydrocarbon compound of the dissolution solvent (i.e.: PC(solvent dissolution) + 3.0 MPa), preferably between the critical pressure of the majority hydrocarbon compound of the dissolution solvent (PC(solvent dissolution)) and a pressure equal to 1.5 MPa above the critical pressure of the majority hydrocarbon compound of the dissolution solvent (i.e.: PC(solvent dissolution) + 1.5 MPa), preferably between the critical pressure of the majority hydrocarbon compound of the dissolution solvent (PC(solvent)) and a pressure equal to 0.5 MPa above the critical pressure of the majority hydrocarbon compound of the dissolution solvent (i.e.: equal to PC(dissolution solvent) + 0.5 MPa), the pressures being absolute pressures, the majority hydrocarbon compound of the dissolution solvent being an advantageously aliphatic, preferably paraffinic, hydrocarbon compound having a boiling point of between -15 and 100°C, preferably between 8 and 100°C, preferentially between 25 and 69°C, very preferentially between 25 and 61°C and most preferably between 25 and 40°C, and preferably containing between 4 and 7 carbon atoms, preferably 5, 6 or 7 carbon atoms, preferentially containing 5 or 6 carbon atoms and very preferentially containing 5 carbon atoms, as described in detail in the description of step a) above.,

[0117] The supercritical separation section of step c) is preferably carried out by demixing and then decanting the liquid phase (comprising the polypropylene) and the supercritical phase (composed of solvent). Advantageously, the supercritical phase from the supercritical separation section constitutes at least in part the solvent fraction obtained at the end of step c). The liquid phase which comprises the polypropylene is preferably sent to a solvent recovery section or a series of solvent recovery sections.

[0118] Step c) may optionally comprise one or more successive supercritical separation sections, in particular between one and five, more particularly one, two or three. The liquid phase which comprises the polypropylene and which comes from a supercritical separation section may therefore also be fed to another subsequent supercritical separation section, the liquid phase from the last supercritical separation section being advantageously sent to a solvent recovery section or a series of solvent recovery sections. Very preferably, step c) comprises a supercritical separation section.

[0119] Very advantageously, the supercritical separation of the solvent makes it possible to further reduce the residual impurity content of the purified polypropylene fraction.

[0120] Preferably, the supercritical section, optionally the series of supercritical separation sections, is followed by at least one, preferably between one and five, solvent recovery section(s), preferably successive.The first solvent recovery section is fed with the liquid phase comprising the polypropylene and coming from the supercritical separation section, possibly the series of supercritical separation sections and in particular from the last supercritical separation section, and, in the case where the separation section comprises at least two solvent recovery sections, each of the following solvent recovery sections, i.e. from the second solvent recovery section, is fed with the liquid phase comprising the polypropylene and coming from the previous solvent recovery section, for example the second solvent recovery section being fed with the liquid phase comprising the targeted thermoplastic polymers coming from the first solvent recovery section.The liquid phase containing the polypropylene, from the last solvent recovery section, constitutes the purified polypropylene fraction, obtained at the end of step c).

[0121] The phase or set of phases containing only solvent, originating from the solvent recovery sections, together with the supercritical phase originating from the supercritical separation section, possibly from the series of supercritical separation sections, constitutes the solvent fraction(s) advantageously recovered at the end of step c). The phase or set of phases containing only solvent originating from the solvent recovery sections is (or are) preferably in gaseous form and can be condensed and possibly mixed with the supercritical phase originating from the supercritical separation section, the temperature and pressure conditions of which have advantageously been previously adjusted to be in liquid form.

[0122] Each solvent recovery section is operated at a temperature advantageously operated at a temperature between 160 and 300°C (and preferably at a temperature higher than the melting temperature of the polypropylene) and a pressure between the pressure used in the supercritical separation section(s) (Psupercritical) and 0.000005 MPa (i.e. 5 Pa). Preferably, each solvent recovery section is operated at a temperature between 160 and 300°C and at a pressure between the pressure of the previous section of step c) and 0.000005 MPa.Thus, when step c) implements a supercritical separation section and several (at least two) solvent recovery sections, the first solvent recovery section S1, which directly follows the supercritical separation section, is implemented at a pressure P(S1) between the pressure (Psupercritical) implemented in the supercritical separation section (advantageously directly preceding) and 0.000005 MPa; the second solvent recovery section S2, which directly follows the solvent recovery section S1, is implemented at a pressure P(S2) between the pressure P(S1) implemented in the first solvent recovery section S1 and 0.000005 MPa, and so on for the following sections.According to a preferred embodiment, each solvent recovery section is operated at a temperature advantageously operated at a temperature between 160 and 300°C and a pressure between the pressure of the previous section of step c) and 0.000005 MPa and preferably at a pressure between 10.0 MPa and 0.000005 MPa, preferably between 5.0 MPa and 0.000005 MPa, preferably between 2.7 MPa and 0.000005 MPa. Preferably, the temperature and pressure conditions are adjusted in each solvent recovery section to act on the volatility of the solvent(s) still present in the polymer phase which is advantageously in the form of a concentrated polypropylene solution or in the form of molten or solid polypropylene.

[0123] In the case where several different solvents have been used in the purification process according to the invention, in particular in step a) of dissolution and possibly in a sub-step b3) of extraction, step c) can use several solvent recovery sections, for example two, three or four solvent recovery sections, so as to recover separately, sequentially and / or successively the different solvents, in particular the dissolution solvent and possibly the extraction solvent.

[0124] Advantageously, the supercritical separation and solvent recovery sections of step c) can be implemented continuously, discontinuously (or in batch mode) or in fed-batch mode.

[0125] 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 at least one purified solvent, in particular at least one purified dissolution solvent, in order to be able to advantageously recycle it to the dissolution step a), and 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.

[0126] The process according to the invention thus makes it possible to obtain a purified polypropylene stream from plastic waste, which can be used in any application, for example as a replacement for virgin resins. The purified polypropylene stream, i.e. the purified polypropylene fraction, obtained by the process according to the invention thus has sufficiently low impurity and residual solvent contents to be able to be used in any application. Preferably, the purified polypropylene stream obtained at the end of the process according to the invention advantageously comprises less than 5% by weight of impurities, very advantageously less than 1% by weight of impurities, and very advantageously less than 5% by weight of residual solvent (in particular dissolution solvent), preferably less than 1% by weight of residual solvent, more preferably less than 0.1% by weight of residual solvent.

[0127] According to a preferred embodiment of the invention, the method for purifying the plastic filler, which comprises polypropylene, comprises, preferably consists of: a) a step of dissolution in a dissolution solvent comprising at least one paraffinic aliphatic hydrocarbon compound, having a boiling point of between -15 and 100°C, preferably between 8 and 100°C, preferentially between 25 and 69°C, very preferentially between 25 and 61°C and preferably between 25 and 40°C, carried out at a dissolution temperature of between 150 and 250°C, preferentially between 160 and 225°C, very preferentially between 165 and 210°C, and preferably between 170 and 195°C, and at a dissolution pressure of between 1.0 and 18.0 MPa absolute, preferably 1.0 and 12.0 MPa absolute, preferably between 3.0 and 11.0 MPa absolute, preferably between 5.0 and 11.0 MPa absolute, very preferably between 6.0 and 10.0 MPa absolute,to obtain at least one crude polymer solution; then b) a step of purifying the polymer solution, comprising: b1) a sub-step of separating the insolubles to obtain a clarified polymer solution and an insoluble fraction; then b4) a sub-step of adsorption of the impurities by contact of the clarified polymer solution with an adsorbent, to obtain at least one refined polymer solution; then c) a solvent-polymer separation step using at least one supercritical separation section operated at a temperature between 160 and 300°C, preferably between 190 and 250°C, preferentially between 200 and 230°C, and at a pressure (Psupercritical) between 2.7 and 10.0 MPa abs., preferably between 3.0 and 6.0 MPa abs., preferentially between 3.0 and 5.0 MPa abs. and preferably between 3.0 and 4.0 MPa abs., followed by at least one solvent recovery section,operated at a temperature between 160 and 300°C and a pressure between the pressure of the supercritical separation section (Psupercritical) and 0.000005 MPa (i.e. 5 Pa), to obtain at least one fraction of purified polypropylene.,

[0128] According to another aspect, the present invention relates to a device for purifying a plastic filler, which comprises polypropylene, said device comprising, preferably consisting of: a) a section for dissolving the plastic filler in a dissolving solvent advantageously comprising at least one paraffinic aliphatic hydrocarbon compound, carried out at a dissolution temperature of between 150 and 250°C, preferably between 160 and 225°C, very preferably between 165 and 210°C, and preferably between 170 and 195°C, and at a dissolution pressure of between 1.0 and 18.0 MPa absolute, preferably 1.0 and 12.0 MPa absolute, preferably between 3.0 and 11.0 MPa absolute, preferably between 5.0 and 11.0 MPa absolute, very preferably between 6.0 and 10.0 MPa absolute, to obtain at least one crude polymer solution;then b) a section for purifying the crude polymer solution, comprising: b1) a subsection for separating the insolubles; and / or b2) a washing subsection, by contact with a dense solution; and / or b3) an extraction subsection, by contact with an extraction solvent; and / or b4) a subsection for adsorbing the impurities by contact with an adsorbent;then c) a solvent-polymer separation section comprising at least one supercritical separation section operated at a temperature between 160 and 300°C, preferably between 190 and 250°C, preferentially between 200 and 230°C, and at a pressure (Psupercritical) between 2.7 and 10.0 MPa abs., preferably between 3.0 and 6.0 MPa abs., preferentially between 3.0 and 5.0 MPa abs. and preferably between 3.0 and 4.0 MPa abs., followed by at least one solvent recovery section, operated at a temperature between 160 and 300°C and a pressure between the pressure of the supercritical separation section (Psupercritical) and 0.000005 MPa (i.e. 5 Pa), to obtain at least one fraction of purified polypropylene.;

[0129] Preferably, the purification section b) comprises: b1) a subsection for separating the insolubles to obtain a clarified polymer solution and an insoluble fraction; then b4) a subsection for adsorbing the impurities by contact of the clarified polymer solution with an adsorbent, to obtain at least one refined polymer solution.

[0130] The following examples illustrate the invention, in particular particular embodiments of the invention, without limiting its scope.

[0131] EXAMPLES

[0132] Example 1 (in accordance with the invention)

[0133] Step a) of dissolution:

[0134] A filler derived from plastic waste and containing 95% by weight of polypropylene (PP) is introduced in the form of flakes into an extruder heated to 180°C. At the extruder outlet, the filler is at least partly in molten form and is mixed with a solvent comprising 99% n-pentane and previously heated to 180°C, according to a solvent / filler mass ratio of 9 / 1. The mixture of solvent and filler is introduced into a stirred reactor and heated to 180°C, and maintained at 7 MPa absolute, for a residence time of 1 hour. A polymer solution is then obtained. The polymer solution resulting from the dissolution step a) is then subjected to a purification step b):

[0135] The polymer solution is continuously withdrawn from the stirred reactor and passes through three filters placed in series, maintained at 180°C and having cut-off diameters of 500 pm, 100 pm and 10 pm respectively (in that order). The pressure drop across the filters is 0.05 MPa.

[0136] At the outlet of the filter series, the clarified polymer solution passes through an adsorption section comprising a bed of activated carbon particles with a contact time of 2 hours and then a filter to retain the activated carbon particles. This adsorption section is operated at 180°C. It leads to a pressure drop of 0.2 MPa.

[0137] The purified polymer solution from purification step b) is then subjected to a solvent-polymer separation step c) comprising a supercritical section:

[0138] The purified polymer solution from the adsorption section is then heated to 210°C, the pressure being slightly lower than 7 MPa (dissolution pressure less the pressure losses induced in the sections of purification step b). The polymer solution is then expanded to 4 MPa absolute and then injected into a decanter maintained at 4 MPa abs and 210°C and for a residence time of 5 minutes. Two phases are formed: an upper phase comprising mainly n-pentane solvent in the supercritical state and a lower liquid phase comprising polypropylene dissolved in n-pentane solvent. The upper phase is withdrawn from the upper part of the decanter.

[0139] The lower liquid phase is then subjected to evaporation of the residual solvent, in two successive evaporation sections: first at a temperature of 210°C and a pressure of 0.5 MPa for 5 minutes, then secondly at a temperature of 210°C and a pressure of 0.01 MPa for 2 minutes.

[0140] At the process outlet, at atmospheric temperature and pressure, a solid A composed of purified polypropylene (PP) is obtained. Solid A is analyzed.

[0141] The solid A obtained is almost colorless and almost translucent and comprises less than 5% by weight of impurities and less than 1% by weight of n-pentane.

[0142] Example 2 (non-compliant)

[0143] In this example 2, the same feedstock is treated and steps a) of dissolution and b) of purification are carried out in an identical manner to the process described in example 1.

[0144] The purified polymer solution from purification step b) is subjected to a solvent-polymer separation step not including a supercritical section: The purified polymer solution from the adsorption section is maintained at 180°C and expanded to 2 MPa absolute then injected into a decanter maintained at 2 MPa abs and 180°C, for a residence time of 5 minutes. Two phases are formed: an upper gaseous phase composed of n-pentane solvent and a lower liquid phase comprising polypropylene dissolved in n-pentane solvent. The gaseous phase is withdrawn from the upper part of the decanter.

[0145] The lower liquid phase is then subjected to evaporation of the residual solvent, initially at a temperature of 210°C and a pressure of 0.5 MPa for 5 minutes, then in a second stage at a temperature of 210°C and a pressure of 0.01 MPa for 2 minutes.

[0146] At the process outlet, at atmospheric temperature and pressure, a solid B composed of purified polypropylene (PP) is obtained. Solid B is analyzed.

[0147] The solid B obtained is almost colorless and almost translucent and comprises less than 5% by weight of impurities and less than 1% by weight of n-pentane.

[0148] However, the content of impurities (organic compounds excluding dissolution solvent) in solid B is higher than that measured in solid A obtained in example 1 in accordance with the invention.

[0149] Furthermore, according to Example 2, the energy consumption required for the polymer-solvent separation is greater than the energy consumption required for the polymer-solvent separation of the process described in Example 1, i.e. when the polymer-solvent separation includes a supercritical phase section.

Claims

DEMANDS 1. A process for purifying a plastic filler comprising polypropylene, said process comprising: a) a dissolution step comprising contacting the plastic filler with a dissolving solvent comprising at least one hydrocarbon compound having a boiling point between -15°C and 100°C, a dissolution temperature between 150°C and 250°C, and a dissolution pressure between 1.0 and 18.0 MPa absolute, to obtain at least one crude polymer solution; b) a purification step of the crude polymer solution to obtain a purified polymer solution, comprising: b1) a substep for separating insolubles; and / or b2) a washing substep, by contact with a dense solution; and / or b3) an extraction substep, by contact with an extraction solvent; and / or b4) a substep for adsorbing impurities by contact with an adsorbent;then c) a solvent-polymer separation step, employing at least one supercritical separation section operated at a temperature between 160 and 300°C and at a pressure (Psupercritical) between 2.7 and 10.0 MPa absolute, followed by at least one solvent recovery section, to obtain at least one fraction of purified polypropylene.

2. A method according to claim 1, wherein the plastic filler comprises at least 80% by weight, preferably at least 85% by weight, preferably at least 90% by weight, of polypropylene relative to the total weight of the plastic filler.

3. A process according to claim 1 or 2, wherein the dissolving solvent comprises an aliphatic hydrocarbon compound having a boiling point between 8 and 100°C, preferably between 25 and 69°C, preferably between 25 and 61°C and preferably between 25 and 40°C.

4. A method according to any one of the preceding claims, wherein the dissolution step a) is carried out at a dissolution temperature between 160 and 225°C, preferably between 165 and 210°C and preferably between 170 and 195°C.

5. A method according to any one of the preceding claims, wherein the dissolution step a) is carried out at a dissolution pressure of between 1.0 and 12.0 MPa absolute, preferably between 3.0 and 11.0 MPa absolute, preferably between 5.0 and 11.0 MPa absolute, preferably between 6.0 and 10.0 MPa absolute.

6. A process according to any one of the preceding claims, wherein the purification step b) comprises at least the substep b1) of separating insolubles, optionally followed by a substep b2) of washing by contact with a dense solution, and / or a substep b3) of extraction by contact with an extraction solvent, and / or a substep b4) of adsorption of impurities by contact with an adsorbent.

7. A method according to any one of the preceding claims, wherein the supercritical separation section in step c) is operated at a temperature between 190 and 250°C, preferably between 200 and 230°C.

8. A method according to any one of the preceding claims, wherein the supercritical separation section in step c) is operated at a pressure (Psupercritical) between 3.0 and 6.0 MPa absolute, preferably between 3.0 and 5.0 MPa absolute and preferably between 3.0 and 4.0 MPa absolute.

9. A method according to any one of the preceding claims, wherein step c) comprises between one and five solvent recovery sections, each solvent recovery section being operated at a temperature between 160 and 300°C and a pressure between the pressure of the supercritical separation section (Psupercritical) and 0.000005 MPa, preferably between 2.7 MPa and 0.000005 MPa.

10. A device for purifying a plastic filler, comprising polypropylene, said device comprising: a) a section for dissolving the plastic filler in a dissolving solvent, carried out at a dissolution temperature between 150 and 250°C, and at a dissolution pressure between 1.0 and 18.0 MPa absolute, to obtain at least one crude polymer solution; then b) a section for purifying the crude polymer solution, comprising: b1) a subsection for separating insolubles; and / or b2) a subsection for washing, by contact with a dense solution; and / or b3) a subsection for extraction, by contact with an extraction solvent; and / or b4) a subsection for adsorbing impurities by contact with an adsorbent;then c) a solvent-polymer separation section comprising at least one supercritical separation section operated at a temperature between 160 and 300°C, and at a supercritical pressure P between 2.7 and 10.0 MPa absolute, followed by at least one solvent recovery section, operated at a temperature between 160 and 300°C and a pressure between the pressure of the supercritical separation section; Psupercritical and 0.000005 MPa (i.e., 5 Pa), to obtain at least a fraction of purified polypropylene.

Images