Process for recycling waste polypropylene-based plastics using light hydrocarbon solvent

Abstract

The present invention relates to a method for purifying a plastic raw material comprising polypropylene, the method comprising the steps of: a) dissolving the plastic raw material in a dissolving solvent comprising a hydrocarbyl compound having a boiling point of-15 DEG C to 100 DEG C at a dissolving temperature of 150 DEG C to 250 DEG C and a dissolving pressure of 1.0 to 18.0 MPa absolute to obtain a crude polymer solution; b) purifying the crude polymer solution, comprising: b1) separating insoluble substances; and / or b2) washing with a high-density solution; and / or b3) extracting with an extraction solvent; and / or b4) adsorbing impurities; followed by c) separating the solvent-polymer using a supercritical separation section at a temperature of 160 to 300 DEG C and at a pressure of 2.7 to 10.0 MPa absolute, followed by at least one solvent recovery section to obtain purified polypropylene.

Description

Technical Field

[0001] The present invention relates to a method for recycling waste plastics mainly comprising polypropylene (or PP) to obtain a purified polypropylene stream that can be economically upgraded, for example for use in the manufacture of new plastic articles. More particularly, the present invention relates to a method for purifying a plastic raw material, in particular obtained from plastic waste, comprising a polymer and in particular polypropylene, said method comprising dissolving the polymer in a light hydrocarbon solvent, in particular based on alkanes with a boiling point ranging from -15°C to 100°C, at least one step of purifying the polymer solution obtained, in order to at least partially remove impurities, in particular additives conventionally used for plastic-based materials, and an optimized step of separating the purified polypropylene from the solvent, in order to be able to reuse the recovered purified polypropylene and thus economically upgrade the plastic raw material. Prior art

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

[0003] "Mechanical" recycling allows the partial reuse of certain wastes, either directly in new articles or by mixing a mechanically sorted plastic waste stream with a stream of virgin polymers. This type of economic upgrading is limited, since mechanical sorting allows the purity of a given type of polymer stream to be improved, but it is generally not possible to adequately remove impurities, such as additives, such as fillers, colorants, pigments and metals, which are at least partially trapped in the polymer matrix.

[0004] "Chemical" recycling involves at least partial reforming of monomers via a generally complex series of steps. For example, plastic waste can undergo a pyrolysis step, and the pyrolysis oil, which is usually recovered after purification, can be at least partially converted into, for example, olefins by steam cracking. These olefins can then be polymerized. This type of sequence can be suitable for almost unsorted feedstocks or for sorting central waste, but it generally requires the consumption of a large amount of energy, in particular due to the high temperature treatment.

[0005] Another route to recycle plastic waste involves at least partially dissolving the plastics, especially thermoplastics, with the aim of purifying them by removing polymers other than the target polymer and / or impurities (e.g. additives such as fillers, colorants, pigments and metals) in the feedstock.

[0006] Several studies have thus proposed various methods for treating plastic waste by dissolution and purification. US2017 / 002110 describes a specific method for purifying polymer raw materials, in particular polymer raw materials obtained from plastic waste, by dissolving the polymer in a solvent under specific temperature and pressure conditions and then contacting the obtained polymer solution with a solid.

[0007] WO 2018 / 114047, for its part, 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 cannot effectively process impurities other than polymers.

[0008] US2018 / 0208736 proposes a treatment method by liquefying thermoplastics in a solvent and then separating insoluble matter and / or gas. The method of US2018 / 0208736 cannot effectively treat impurities soluble in the solvent.

[0009] The present invention aims to overcome these drawbacks and to participate in the recycling of plastics. More particularly, the present invention aims to propose an effective, simple and economically viable method for treating a plastic raw material based on polypropylene, in particular obtained from plastic waste, in order to at least partially eliminate the impurities it contains, in particular the additives it contains and conventionally added to plastics, so as to be able to economically upgrade the plastic raw material and more particularly the plastic waste. The present invention in fact seeks to effectively separate impurities from the polymers contained in the waste plastics, and in particular from the polypropylene, and to recover purified polypropylene, so as to be able to use it as a polymer base, for example, in the manufacture of new plastic articles, in particular to replace virgin resins. SUMMARY OF THE INVENTION

[0011] The present invention relates to a method for purifying a plastic raw material containing polypropylene, the method comprising:

[0012] a) a dissolving step, which involves contacting the plastic raw material with a dissolving solvent comprising at least one hydrocarbon-based compound having a boiling point of -15 to 100° C. at a dissolving temperature of 150° C. to 250° C. and at a dissolving pressure of 1.0 to 18.0 MPa absolute pressure to obtain at least one crude polymer solution;

[0013] b) a step of purifying the crude polymer solution to obtain a purified polymer solution, comprising:

[0014] b1) a sub-step of separating insoluble matter; and / or

[0015] b2) a sub-step of washing by contact with a dense solution; and / or

[0016] b3) a sub-step of extracting by contacting with an extraction solvent; and / or

[0017] b4) a sub-step of adsorbing impurities by contact with an adsorbent; and subsequently

[0018] c) a solvent-polymer separation step using at least one supercritical separation section operated at a temperature ranging from 160 to 300° C. and at a pressure ranging from 2.7 to 10.0 MPa absolute (Psupercritical), followed by at least one solvent recovery section, to obtain at least one purified polypropylene fraction.

[0019] The process of the invention has the advantage of proposing a method for the efficient treatment of polypropylene-based plastic raw materials, and in particular polypropylene-based plastic waste, obtained in particular from collection and sorting channels, so as to recover the polypropylene it contains in order to be able to recycle it into any type of application. The process according to the invention makes it possible to obtain a purified polypropylene stream, which advantageously contains a content of impurities (in particular additives) and solvents (in particular dissolved solvents) that is negligible or at least low enough to be able to introduce the purified polypropylene stream into any type of plastic formulation in place of virgin polypropylene resin. For example, the purified polypropylene stream obtained at the end of the process according to the invention advantageously contains 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 solvents (in particular dissolved solvents), preferably less than 1% by weight of solvents, preferably less than 0.1% by weight of solvents.

[0020] The process according to the invention thus proposes a simple scheme corresponding to a series of operations which makes it possible to remove at least a portion of the impurities, in particular at least some of the additives, from plastic waste based on polypropylene and to recover purified polypropylene which advantageously contains little or even no solvent, so as to be able to upgrade the plastic waste economically by recycling it. Advantageously, depending on the conditions used in the steps of the process, the additives present in the plastic raw material may be soluble or insoluble in the solvent used throughout the process according to the invention, allowing an effective purification and separation of the polymer.

[0021] Furthermore, the process according to the present invention proposes a series of operations carried out under optimal operating conditions, particularly in terms of temperature and pressure, to effectively separate impurities and solvents from polypropylene, but the operating conditions are reasonable, thereby limiting the energy consumption of the process and thus making the process economically advantageous.

[0022] The invention also has the advantage of participating in the recycling of plastics and the saving of fossil resources by achieving an economic upgrading of plastic waste. In particular, it allows the purification of plastic waste to obtain a purified polypropylene fraction with a reduced impurity content, in particular a decolorized and deodorized polypropylene fraction, which can be reused to form new plastic articles. The purified polypropylene fraction obtained can thus be used directly in formulations as a mixture with additives (such as colorants, pigments or other polymers) to replace virgin resins or as a mixture with virgin resins, with the aim of obtaining plastic products with aesthetic, mechanical or rheological processing properties, which facilitate their reuse and their economic upgrading.

[0023] The invention also enables efficient and advantageously low-cost separation of polypropylene from the solvent used, in particular the dissolving solvent, while limiting thermal degradation of the polypropylene. Thus, the solvent used to treat the plastic raw material, in particular the dissolving solvent, is at least partially recovered and can be recycled to one of the steps of the process, thereby avoiding excessive solvent consumption, thereby obtaining ecological and economic advantages of the process.

[0024] The present invention thus aims at purifying plastic raw materials, in particular plastic waste, in order to obtain purified polypropylene, thus being able to use it in any application, in particular for replacing virgin resins.

[0025] More particularly, the present invention aims at proposing a process comprising a dissolution step, followed by at least one purification step and then an optimized solvent / polymer separation, in order to obtain a purified polypropylene stream. DETAILED DESCRIPTION OF THE INVENTION

[0027] According to the present invention, the expressions "included between ... and ..." and "between ... and ... (... to ...)" are equivalent and mean that the limits of the interval are included in the range of values ​​described. If this is not the case, and if the limits are not included in the range described, the present invention will give such clarification.

[0028] For the purposes of the present invention, various ranges of parameters of a given step, such as pressure ranges and temperature ranges, can be used alone or in combination. For example, within the meaning of the present invention, a range of preferred pressure values ​​can be combined with a range of more preferred temperature values.

[0029] Hereinafter, specific embodiments of the present invention may be described. They may be implemented individually or combined together when the combination is technically feasible without limiting the combination.

[0030] According to the present invention, the pressure is an absolute pressure and is given in MPa absolute (or MPa abs).

[0031] The terms "upstream" and "downstream" should be understood as varying with the general flow of the fluid or stream under consideration in the process.

[0032] The term "additive" is a term conventionally used in the field of polymers, and in particular in the field of polymer formulations. The additive introduced into the polymer formulation may be, for example, a plasticizer, a filler (which is an organic or inorganic solid compound used to change the physical, thermal, mechanical and / or electrical properties of a polymer material or to reduce its cost price), a reinforcing agent, a colorant, a pigment, a hardener, a flame retardant, a combustion retardant, a stabilizer, an antioxidant, a UV absorber, an antistatic agent, etc.

[0033] The additive corresponds to at least a portion of the impurities of the plastic raw material to be processed, and the method according to the invention makes it possible to at least partially remove the additive. Other types of impurities may be use-related impurities, such as metal impurities, paper / cardboard, biomass, polymers other than the target polypropylene (e.g. polyethylene), etc.

[0034] Thus, according to the invention, the impurities that the method according to the invention makes it possible to remove at least partially include additives conventionally used in polymer formulations and generally use-related impurities originating from the life cycle of plastic objects and materials and / or from waste collection and sorting circuits. The impurities may be impurities of metallic, organic or mineral type; they may be packaging residues, food residues or compostable residues (biomass). These use-related impurities may also contain glass, wood, cardboard, paper, aluminum, iron, metal, tires, rubber, silicone, rigid polymers, thermoplastic polymers other than polypropylene, thermosetting polymers, household, chemical or cosmetic products, waste oils and water.

[0035] According to the present invention, the polymer solution is a solution comprising a dissolving solvent and at least a target polypropylene, the target polypropylene being dissolved (i.e., in particular solvated and dispersed) in the dissolving solvent, the dissolved polypropylene being initially present in the raw material. The polymer solution may also contain soluble impurities (which are dissolved in the dissolving solvent) and / or insoluble impurities (which are suspended in the polymer solution). As a function of the steps of the method according to the present invention that have been performed, the polymer solution may thus contain insoluble particles advantageously suspended in the polymer solution, soluble impurities dissolved in the dissolving solvent, and / or impurities in the form of another liquid phase that is optionally immiscible with the polymer solution.

[0036] The critical temperature and critical pressure of a solvent, in particular a dissolving solvent, are specific to the solvent and depend on the chemical properties of the solvent under consideration. For a pure substance, the critical temperature and critical pressure of a pure substance are the temperature and pressure, respectively, of the critical point of the pure substance. As is well known to those skilled in the art, at or above the critical point, the pure substance under consideration is in supercritical form or in a supercritical state; it may then be referred to as a supercritical fluid.

[0037] The present invention relates to a method for purifying a plastic raw material, preferably consisting of plastic waste and containing polypropylene, the method comprising the following steps and preferably consisting of the following steps:

[0038] a) a dissolving step, which comprises contacting the plastic raw material with a dissolving solvent comprising at least one hydrocarbon-based compound, advantageously aliphatic and preferably paraffinic, having a boiling point of -15 to 100° C., preferably 8 to 100° C., preferably 25 to 69° C., preferably 25 to 61° C. and very preferably 25 and 40° C., at a dissolving temperature of 150 to 250° C., preferably 160 to 225° C., preferably 165 to 210° C., and preferably 170 to 195° C., and at a dissolving pressure of 1.0 to 18.0 MPa absolute, preferably 1.0 to 12.0 MPa absolute, preferably 3.0 to 11.0 MPa absolute, preferably 5.0 to 11.0 MPa absolute and very preferably 6.0 to 10.0 MPa absolute, to obtain at least one crude polymer solution; and subsequently

[0039] b) a step of purifying the crude polymer solution, comprising at least one of the following sub-steps:

[0040] b1) a sub-step of separating off the insoluble matter to obtain at least a clear polymer solution and preferably an insoluble fraction; and / or

[0041] b2) a sub-step of washing by contacting with a high density solution to obtain at least one washed polymer solution and preferably a wash effluent; and / or

[0042] b3) a sub-step of extracting by contacting with an extraction solvent to obtain at least one extracted polymer solution and preferably spent solvent; and / or

[0043] b4) a sub-step of adsorbing impurities by contacting with an adsorbent to obtain at least one purified polymer solution;

[0044] This purification step makes 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; and subsequently

[0045] c) a solvent-polymer separation step using at least one supercritical separation section operated at a temperature of 160 to 300° C., preferably 190 to 250° C., preferably 200 to 230° C. and at a pressure (P supercritical ) of 2.7 to 10.0 MPa absolute, preferably 3.0 to 6.0 MPa absolute, preferably 3.0 to 5.0 MPa absolute and preferably 3.0 to 4.0 MPa absolute, followed by at least one solvent recovery section operated in particular at a temperature of 160 to 300° C. and a pressure of P supercritical to 0.000005 MPa (i.e. 5 Pa), preferably 2.7 MPa to 0.000005 MPa, and in particular 1.0 MPa to 0.000005 MPa, to obtain at least one purified polypropylene fraction and advantageously a solvent fraction.

[0046] raw material

[0047] The raw material of the process according to the invention, called plastic raw material, comprises plastic, which itself more particularly comprises polypropylene. Preferably, the plastic raw material comprises 50% to 100% by weight and preferably 70% to 100% by weight of plastic.

[0048] The plastics contained in the raw materials of the method according to the invention are based on polypropylene and are generally production waste and / or waste plastic articles at the end of their life, in particular household plastic waste, plastic waste from the construction industry, plastic waste from cars or from any type of transport or electrical and electronic equipment waste. Preferably, the plastic waste comes from collection and sorting channels. Typically, plastics or plastic materials contain polymers mixed with additives to form various materials and articles (injection molded parts, pipes, films, fibers, fabrics, adhesives (mastics), coatings (coatings) etc.) after forming. The additives used for plastics can be organic compounds or inorganic compounds. They are, for example, fillers, colorants, pigments, plasticizers, property modifiers, flame retardants, etc.

[0049] Preferably, the feedstock of the process according to the invention comprises at least 80% by weight, preferably at least 85% by weight and preferably at least 90% by weight of polypropylene relative to the total weight of the plastic feedstock. The process according to the invention thus most particularly relates to the purification and recovery of the polypropylene contained in the feedstock in order to be able to reuse it in various applications.

[0050] The plastic raw material may also contain impurities, such as polymers other than polypropylene (in particular thermoplastics), additives advantageously used for the formulation of plastic materials, and impurities generally associated with use which originate from the life cycle of the material and plastic articles and / or from waste collection and sorting circuits. The plastic raw material according to the process of the invention may contain up to 20% by weight of impurities, preferably up to 15% by weight of impurities, preferably up to 10% by weight of impurities. The plastic raw material may contain, for example, at least 5% by weight of impurities.

[0051] The plastic raw material may advantageously be pretreated before the process so as to remove at least all or some of the "coarse" impurities, i.e. impurities in the form of particles with a size greater than or equal to 10 mm, preferably greater than or equal to 5 mm, or even greater than or equal to 1 mm, such as impurities such as wood, paper, biomass, iron, aluminum, glass, etc., and shape it, usually in the form of a comminuted (divided) solid (or particles), to facilitate the treatment in the process. The pretreatment may comprise a grinding step, a washing step at atmospheric pressure and / or a drying step. This pretreatment may be carried out at different locations, for example at a waste collection and sorting center, or at the same location where the treatment process according to the invention is implemented. Preferably, the pretreatment makes it possible to reduce the content of impurities to less than 20% by weight, preferably less than 15% by weight, preferably less than 10% by weight, the percentage being given relative to the weight of the plastic raw material treated by the process according to the invention. At the end of the pretreatment, the raw material is usually stored in the form of a comminuted solid, for example in the form of a ground material or powder, so as to facilitate handling and transport to the process.

[0052] Dissolution step a)

[0053] According to the invention, the method comprises a dissolving step a) in which the plastic raw material is contacted with a dissolving solvent to obtain at least one, preferably one, crude polymer solution. In particular, this step advantageously enables dissolving at least a portion and preferably all of the polypropylene in the plastic raw material.

[0054] The term "dissolution" is understood to mean any phenomenon leading to the production of at least one polymer solution, in particular a polypropylene solution, i.e. a liquid comprising the polymer, in particular polypropylene, dissolved in a solvent, more in particular in a dissolving solvent. The phenomena involved in polymer dissolution are well known to those skilled in the art and include at least mixing, dispersion, homogenization, solvation and disentanglement of polymer chains, and more in particular polypropylene chains.

[0055] During and at the end of the dissolving step a), the pressure and temperature conditions are such as to keep the dissolving solvent at least partially and preferably completely in liquid form, in order to optimize the dissolution of the target polypropylene.

[0056] The properties of the dissolving solvent advantageously allow the use of reasonable operating conditions, and in particular temperature and pressure conditions, in particular pressure conditions, ensuring firstly that in the dissolving step a) but advantageously also in the purification step b) the dissolving solvent remains at least partially and preferably completely in the liquid phase, thereby allowing optimal dissolution of the target polypropylene and advantageously efficient purification of the polymer solution, and secondly that in the solvent-polymer separation step c) at least a portion of said dissolving solvent enters a supercritical state, allowing demixing and thus separation of at least a portion of the dissolving solvent, and optionally at least partial evaporation of the residual dissolving solvent, which thereby makes it possible to achieve very low solvent contents (advantageously a content of less than 5 wt.-% solvent, preferably less than 1 wt.-% solvent, preferably less than 0.1 wt.-% solvent relative to the total weight of the purified polypropylene fraction) in the purified polypropylene recovered at the end of the process. In fact, a solvent consisting of very light alkanes with a boiling point below -15°C (e.g. propane) - which may be advantageous in particular due to their relatively mild critical conditions (temperature and pressure) - would require the use of high pressures in order to keep the dissolving solvent at least partially and preferably completely in liquid form throughout the dissolving step a) and the purification step b), which would entail significant costs, in particular investment costs. On the contrary, the use of heavy solvents, such as alkanes with a boiling point above 100°C, would require very strict operating conditions in step c) in order to reach the critical conditions of said heavy solvent and to be able to obtain said solvent at least partially in a supercritical state.

[0057] Advantageously, the dissolving solvent comprises, preferably consists of, at least one hydrocarbon-based compound, advantageously aliphatic and preferably paraffinic (i.e. saturated), preferably at least one alkane, with a boiling temperature of from -15 to 100° C., preferably from 8 to 100° C., preferably from 25 to 69° C., preferably from 25 to 61° C. and very preferably from 25 to 40° C. Preferably. The dissolving solvent comprises mainly, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight, hydrocarbon-based compounds, advantageously aliphatic, preferably paraffinic (or alkane) (100% being a maximum, the percentage being expressed relative to the total weight of the dissolving solvent), with a boiling point of from -15 to 100° C., preferably from 8 to 100° C., preferably from 25 to 69° C., preferably from 25 to 61° C. and very preferably from 25 to 40° C. Very advantageously, the hydrocarbyl compound, which is advantageously aliphatic, preferably paraffinic, which forms the main amount of the dissolving solvent, has a critical temperature (the temperature at the critical point of the pure hydrocarbyl compound) of 130 to 285° C., preferably 158 to 285° C., preferably 185 to 245° C., preferably 185 to 230° C. and very preferably 185 to 200° C. Very particularly, the paraffinic hydrocarbyl compound forming the main amount of the dissolving solvent has a critical pressure of 2.5 to 5.0 MPa, preferably 2.7 to 4.6 MPa, preferably 3.0 to 3.8 MPa and preferably 3.0 to 3.5 MPa. According to a preferred embodiment, the dissolving solvent mainly comprises, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight, aliphatic chain alkane compounds, which are preferably linear or branched, have a boiling point of -15 to 100°C, preferably 8 to 100°C, preferably 25 to 69°C, preferably 25 to 61°C and very preferably 25 to 40°C, and contain 4 to 7 carbon atoms (i.e. C4-C7), preferably 5, 6 or 7 carbon atoms (C5, C6 or C7, respectively), preferably 5 or 6 carbon atoms (C5 or C6) and very preferably 5 carbon atoms (C5).

[0058] Advantageously, the dissolution step a) is carried out at a dissolution temperature of 150 to 250° C., preferably 160 to 225° C., very preferably 165 to 210° C. and preferably 170 to 195° C., and at a dissolution pressure of 1.0 to 18.0 MPa absolute, preferably 1.0 to 12.0 MPa absolute, preferably 3.0 to 11.0 MPa absolute, preferably 5.0 to 11.0 MPa absolute and very preferably 6.0 to 10.0 MPa absolute. More particularly, the temperature and pressure can be varied throughout step a) from the conditions under which the plastic raw material and / or the dissolving solvent are introduced, for example from ambient conditions, i.e. a temperature of 10 to 30° C. and atmospheric pressure (0.1 MPa), until dissolving conditions are reached, i.e. a dissolving temperature, in particular 150 to 250° C., preferably 160 to 225° C., very preferably 165 to 210° C. and preferably 170 to 195° C., and a dissolving pressure, in particular 1.0 to 18.0 MPa absolute, preferably 1.0 to 12.0 MPa absolute, preferably 3.0 to 11.0 MPa absolute, preferably 5.0 to 11.0 MPa absolute and very preferably 6.0 to 10.0 MPa absolute. Very advantageously, at the end of dissolving step a), the stream of dissolved polymer, in particular the polymer solution, is at the dissolving temperature and the dissolving pressure.

[0059] 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 thermal degradation of the polymer, in particular polypropylene, and also limits the energy requirements 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 point of polypropylene, so as to promote its dissolution.

[0060] 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 partially, and preferably completely, in liquid form at the dissolution temperature to optimize the dissolution of the target polypropylene.

[0061] Very advantageously, the dissolution temperature and pressure conditions achieved in step a) are adjusted so that the mixture (dissolving solvent+polypropylene) is homogeneous and very preferably single-phase, said mixture possibly comprising insoluble impurities suspended in said mixture.

[0062] Preferably, the weight ratio between the plastic raw material and the dissolving solvent (raw material / solvent) (or the ratio between the mass flow rate of the plastic raw material and the mass flow rate of the dissolving solvent at the inlet of the dissolving step a)) is 0.01 to 2.0, preferably 0.05 to 1.0, preferably 0.10 to 0.8.

[0063] Advantageously, the dissolution step a) is carried out for a residence time of 1 to 600 minutes, preferably 2 to 300 minutes, preferably 5 to 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 during which the plastic raw material is treated with the dissolution solvent at the dissolution temperature and at the dissolution pressure in step a).

[0064] Advantageously, the dissolving solvent comprises and preferably consists of a supply of fresh solvent and / or a stream of recycled solvent obtained from a subsequent step of the process, preferably from the solvent-polymer separation step c).

[0065] Contacting the dissolving solvent with the plastic raw material so that the polypropylene of the plastic raw material is at least partially and preferably completely dissolved in the dissolving solvent can be carried out in a pipeline and / or item in the equipment and / or between two items in the equipment. Thus, step a) advantageously involves at least one item of dissolving equipment, and optionally at least one raw material preparation device, mixing device and / or conveying device. The items and / or devices of these equipment can be, for example, static mixers, extruders, pumps, reactors, co-current or countercurrent towers, or a combination of pipelines and equipment. Devices for conveying, in particular, fluids (such as liquids or solids) are well known to those skilled in the art. In a non-limiting manner, the conveying device can include a pump, an extruder, a vibrating tube, an endless screw or a valve. The items and / or devices of the equipment can also include a heating system (such as an oven, an exchanger, a heating element (atracing)), etc.) or be combined with a heating system to achieve the conditions required for dissolution. The dissolving step a) can be carried out continuously, in batch mode or in a fed-batch mode.

[0066] Advantageously, at least the plastic raw material (in particular in the form of one or more plastic raw material streams) and the dissolving solvent (in particular in the form of one or more dissolving solvent streams) are fed to the dissolving step a) with the aid of one or more conveying devices. The plastic raw material stream may be different from the dissolving solvent stream. Part or all of the plastic raw material may also be fed to step a) as a mixture with part or all of the dissolving solvent, the remaining solvent and / or the raw material or, where appropriate, may be fed to step a) separately.

[0067] In the process of contacting the plastic raw material with the dissolving solvent, the dissolving solvent is advantageously at least partially and preferably completely in liquid form, and the plastic raw material comprising polypropylene can be in solid or liquid form optionally containing suspended solid particles. The plastic raw material can also be optionally injected into the dissolving device as a mixture with the dissolving solvent in the form of a suspension in the dissolving solvent, and the preparation and injection of the suspension can be continuous or intermittent.

[0068] According to a particular embodiment of the invention, step a) may use an extruder and optionally at least one other item of dissolving equipment. In this case, the plastic raw material is optionally fed to the extruder together with at least a portion of the dissolving solvent, so that at the outlet of the extruder, at least a portion and preferably all of the target polypropylene contained in the raw material is in molten form (or in at least partially dissolved form). Subsequently, the plastic raw material optionally mixed with at least a portion of the dissolving solvent is injected at least partially in molten form (or partially dissolved form) into an item of dissolving equipment, such as a reactor. The plastic raw material that leaves the extruder at least partially in molten form (and / or partially dissolved form) can also be pumped by means of a pump dedicated to viscous fluids (commonly referred to as a melt pump or gear pump). Optionally, in addition to the melt pump, the plastic raw material that is at least partially in molten form (or partially dissolved form) can also be filtered at the outlet of the extruder using a filtering device to remove the coarsest particles; typically, the mesh size of the filter is 10 microns to 1 mm, preferably 20 to 200 microns.

[0069] Preferably, step a) comprises an extruder into which the dissolving solvent is advantageously injected at several points to promote shear and thereby intimate mixing between the dissolving solvent and the plastic feedstock, which helps to dissolve the polypropylene.

[0070] Optionally, the treatment process may comprise an intermediate adsorption step a') during or directly downstream of the dissolution step a) and which comprises introducing into the crude polymer solution obtained at the end of step a) or optionally during the dissolution step a) an adsorbent in the form of pulverized particles, such as preferably alumina, silica-alumina, activated carbon or bleaching clay. This adsorbent can subsequently be removed during the purification step b), for example during the sub-step b1) of separating off the insolubles and / or the washing sub-step b2). This optional adsorption step a') in the presence of the adsorbent in pulverized form makes it possible to optimize the purification of the polymer solution.

[0071] The crude polymer solution obtained at the end of the dissolving step a) comprises at least the dissolving solvent, the purified polypropylene that the present invention attempts to recover dissolved in the dissolving solvent. Typically, the crude polymer solution also comprises soluble impurities that are also dissolved in the dissolving solvent. The crude polymer solution may optionally also comprise suspended insoluble impurities or compounds. The crude polymer solution obtained at the end of step a) may also optionally comprise polymers other than the target polypropylene, for example in molten form.

[0072] At the end of the dissolution step carried out under such operating conditions (in particular in terms of temperature and pressure), the polypropylene of the plastic raw material is advantageously completely or partially dissolved in the dissolving solvent; the polypropylene solution obtained (i.e. the crude polymer solution) will be able to undergo a purification step b) and a subsequent solvent-polymer separation step c) in order to recover the polypropylene from the plastic raw material in a purified form, having a very low content of impurities and residual solvents, which is compatible with any type of subsequent application. Thus, the process according to the invention allows the recovery of polypropylene from plastic waste in an optimal manner and under completely rational operating conditions (in particular a bounded, i.e. limited, dissolution pressure), and thus with controlled energy consumption and therefore limited costs.

[0073] Purification step b) of the polymer solution

[0074] The purification method according to the present invention comprises a step of purifying the crude polymer solution obtained from step a). The purification step b) comprises at least one of the following sub-steps b1), b2), b3) and b4):

[0075] b1) a sub-step of separating insoluble matter,

[0076] b2) a sub-step of washing by contact with a high-density solution,

[0077] b3) a sub-step of extraction by contact with an extraction solvent,

[0078] b4) a sub-step of adsorbing impurities by contacting with an adsorbent.

[0079] The various substeps b1), b2), b3) and b4) which may be carried out in purification step b) may be operated continuously, in batch mode or in fed-batch mode.

[0080] Preferably, the purification step b) comprises at least one substep b1) of separating off insolubles. The purification step b) preferably comprises several (i.e. at least two) consecutive substeps selected from the substeps b1), b2), b3) and b4), and preferably at least one substep b1) of separating off insolubles and, for example, one adsorption substep b4), very advantageously in this order. The combination of at least two substeps selected from b1), b2), b3) and b4) advantageously allows an optimal purification of the polymer solution.

[0081] The polymer solution obtained at the end of step b) is a purified polymer solution and comprises polypropylene dissolved in at least a dissolving solvent. This purified polymer solution may correspond to the clarified polymer solution obtained from the sub-step b1) of separating off the insolubles, the washed polymer solution obtained from the washing sub-step b2), the extracted polymer solution obtained from the extraction sub-step b3), or the refined polymer solution obtained from the sub-step b4) of adsorbing impurities.

[0082] Sub-step b1) of separating insoluble matter

[0083] The purification process may comprise a sub-step b1) of separating out the insolubles by solid-liquid separation, so as to advantageously obtain at least one clarified polymer solution (in other words at least partially, preferably completely free of the insolubles contained in the crude polymer solution) and preferably an insoluble fraction. The insoluble fraction advantageously comprises at least a part, and preferably all, of the insoluble impurities, in particular the insoluble impurities suspended in the crude polymer solution obtained in step a).

[0084] Sub-step b1) of separating out the insolubles thus makes it possible to remove at least a portion, and preferably all, of the particles of insoluble compounds dissolved in the solvent, which particles are present in suspension in the crude polymer solution obtained from step a) or optional step a'). Insoluble compounds (or impurities) removed during sub-step b1) of separating out the insolubles are, for example, pigments, mineral compounds, packaging residues (glass, wood, cardboard, paper, aluminum) and insoluble polymers.

[0085] When it is carried out, this separation substep b1) advantageously makes it possible, besides removing at least part of the insoluble impurities, to limit operating problems of the process steps downstream of such substep b1), such as in particular clogging and / or corrosion, while at the same time contributing to the purification of the plastic raw material.

[0086] The sub-step b1) of separating off the insolubles is advantageously carried out at a temperature of preferably 150° C. to 250° C., preferably 160° C. to 225° C., very preferably 165° C. to 210° C. and preferably 170° C. to 195° C. and at a pressure of 1.0 to 18.0 MPa absolute, preferably 1.0 to 12.0 MPa absolute, preferably 3.0 to 11.0 MPa absolute, preferably 5.0 to 11.0 MPa absolute and very preferably 6.0 to 10.0 MPa absolute. Very advantageously, the sub-step b1) of separating off the insolubles is carried out at the temperature and pressure conditions at the outlet of the dissolution step a), i.e. at the dissolution temperature and dissolution pressure as defined above.

[0087] When incorporated into the process, substep b1) of separating off insolubles is preferably fed with the crude polymer solution obtained from step a) or from the optional intermediate adsorption step a'). According to another embodiment, substep b1) can be fed with the washed polymer solution obtained from the washing substep b2).

[0088] Advantageously, sub-step b1) comprises at least one section for solid-liquid separation (or solid-liquid-liquid separation, in particular in the case where the effluent obtained from the dissolution step contains, in addition to the polymer solution and solid impurities, impurities in liquid or barely soluble or insoluble form and / or polymers of properties different from the target polypropylene). The solid-liquid separation section comprises at least one item of solid-liquid separation equipment, such as a separation vessel, 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, allowing the use of a solvent stream for cleaning or dredging to remove insolubles. Preferably, sub-step b1) comprises at least one decanting section, advantageously comprising at least one decanter, and / or at least one filtration section. During sub-step b1), a filtering aid (such as diatomaceous earth or sand) can be optionally added before decanting and / or filtering.

[0089] The removal of the insoluble fraction can be facilitated by a device for conveying and / or removing trace amounts of solvent that may be present in the insoluble fraction, such as a conveyor, a vibrating tube, a worm, an extruder or a stripping tower. Sub-step b1) can thus comprise a device for conveying and / or removing trace amounts of solvent to remove the insoluble fraction. Advantageously, at least a portion of the solvent recovered in sub-step b1) is recycled into the method.

[0090] According to a particular embodiment, the sub-step b1) of separating the insolubles comprises at least two, and generally less than five, items of solid-liquid separation equipment connected in series and / or in parallel. The presence of at least two items of solid-liquid separation equipment connected in series makes it possible to improve the removal of insolubles, while the presence of parallel equipment makes it possible to manage the maintenance and / or declogging operations of the equipment.

[0091] Certain insoluble compounds routinely added during the formulation of polymers, in particular certain pigments and mineral fillers, may be in the form of particles having a size less than 1 μm. This is the case, for example, with titanium dioxide, calcium carbonate and carbon black. According to a particular embodiment of sub-step b1), the sub-step b1) of separating out the insolubles advantageously comprises an electrostatic separator which makes it possible to effectively remove at least a portion of the insoluble particles having a size less than 1 μm. According to another particular embodiment of sub-step b1), the sub-step b1) of separating out the insolubles comprises a sand filter to remove particles of different sizes, and in particular particles having a size less than 1 μm. According to yet another particular embodiment, the sub-step b1) of separating out the insolubles comprises a tangential filter, in particular using a membrane and / or a depth filter, optionally in the presence of a filtering aid such as, for example, diatomaceous earth.

[0092] Depending on the nature of the raw materials, the polymer solution, preferably the crude polymer solution, fed to sub-step b1) may also optionally contain a second liquid phase, for example consisting of molten polymers, which have different properties from the polypropylene. According to another particular embodiment, sub-step b1) advantageously comprises a solid-liquid-liquid separation section, comprising a device for separating two liquid phases and one solid phase, preferably by means of at least one two-phase or three-phase separator.

[0093] Washing sub-step b2)

[0094] The purification process may optionally comprise a sub-step b2) of washing with a high density 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 purified polypropylene that the present invention seeks to recover dissolved in the dissolving solvent. Optionally, if sub-step b2) is carried out, the washed polymer solution may further comprise residual impurities that are particularly soluble in the dissolving solvent and / or optionally traces of washing solvent (i.e. traces of high density solution).

[0095] When these two sub-steps are integrated into the purification step b), the washing sub-step b2) can be integrated upstream or downstream of the sub-step b1) for separating off the insolubles, preferably downstream.

[0096] When it is integrated into the process, the washing substep b2) is fed with a high-density solution and with a crude polymer solution obtained from step a) or from an optional intermediate adsorption step a'), or with a clarified polymer solution obtained from b1). The polymer solution, in particular the crude polymer solution or the clarified polymer solution, feeding the washing substep b2) may contain impurities in the form of suspended insoluble compounds and / or dissolved compounds. During the washing substep b2), these suspended compounds or dissolved compounds may be partially or completely removed by dissolution or precipitation and / or by entrainment in the high-density solution. Thus, when it is carried out, the substep b2) contributes to the processing of the plastic raw material and more particularly to the purification of the polymer solution.

[0097] Washing sub-step b2) advantageously comprises making the polymer solution of feed sub-step b2), i.e. crude polymer solution or clarified polymer solution contact with high density solution. Advantageously, this high density solution has higher density than polymer solution (i.e. mixture of dissolving solvent in which at least target polypropylene and target polypropylene are dissolved). In particular, this high density solution has a density preferably greater than or equal to 0.85, preferably greater than or equal to 0.9, preferably greater than or equal to 1.0 and preferably less than or equal to 1.5. High density solution can 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. Acid or alkali can be used to adjust the pH of the aqueous solution to promote the dissolution of certain compounds. The high density solution may also optionally be a solution comprising, preferably consisting of, an organic solvent having a density advantageously greater than or equal to 0.85, preferably greater than or equal to 0.9, preferably greater than or equal to 1.0 and in which the polypropylene of the plastic raw material remains insoluble under the temperature and pressure conditions of sub-step b2), for example an organic solvent selected from sulfolane or N-methylpyrrolidone (NMP), optionally as a mixture with water. Very preferably, the high density solution is an aqueous solution preferably comprising at least 50% by weight of water, preferably at least 75% by weight of water, very preferably at least 90% by weight of water.

[0098] The washing substep b2) is advantageously carried out at a temperature of preferably 150° C. to 250° C., preferably 160° C. to 225° C., very preferably 165° C. to 210° C. and preferably 170° C. to 195° C., and at a pressure of 1.0 to 18.0 MPa absolute, preferably 1.0 to 12.0 MPa absolute, preferably 3.0 to 11.0 MPa absolute, preferably 5.0 to 11.0 MPa absolute and very preferably 6.0 to 10.0 MPa absolute. Very advantageously, the washing substep b2) is carried out at the dissolution temperature and dissolution pressure.

[0099] In the washing sub-step b2), when it is incorporated into the process, the mass ratio between the mass flow of high-density solution and the mass flow of polymer solution feeding sub-step b2) (high-density solution / polymer solution) is advantageously between 0.05 and 20.0, preferably between 0.1 and 10.0 and preferably between 0.5 and 3.0. The contact between the polymer solution and the high-density solution can be carried out at several points in the equipment used, i.e. via several injections of polymer solution and / or high-density solution at different points along the equipment; the sum of the injected streams is then taken into account when calculating the mass ratio (high-density solution / polymer solution).

[0100] Sub-step b2) may be carried out in one or more items of washing equipment which allow contact with a high density solution and / or with a separation device, making it possible to recover at least one washing effluent and a washed polymer solution. Such equipment is well known, such as stirred reactors, static mixers, decanting mixers, two-phase or three-phase separation vessels, co-current or countercurrent washing towers, plate towers, stirred towers, packed towers, pulse towers, etc., each type of equipment may include items of one or more equipment used alone or in combination with another type of equipment.

[0101] According to a preferred embodiment, the washing substep b2) is carried out in a countercurrent washing column, wherein the high density solution is injected on the one hand, preferably into the upper half, preferably the upper third, of the column, preferably closest to the top of the column, and the crude polymer solution or clarified polymer solution is injected on the other hand, preferably into the lower half, preferably the lower third, of the column, preferably closest to the bottom of the column. According to this embodiment, at least one washed polymer solution and advantageously a washing effluent can be recovered.

[0102] According to a very particular embodiment, the stream at the inlet and / or outlet of the wash column can be split and injected at several injection points along the column and / or withdrawn at several withdrawal points along the column.

[0103] According to another embodiment, the washing substep b2) is carried out in a mixer-decanter comprising an agitated mixing zone, which brings the high-density solution into contact with the crude polymer solution or the clarified polymer solution, and a decanting zone, which makes it possible to recover the washed polymer solution and advantageously the washing effluent.

[0104] At the end of washing sub-step b2), the wash effluent advantageously obtained comprises the compound dissolved in the high density solution and / or the insoluble compound carried by oneself in the wash effluent. Wash effluent can be reprocessed in the wash effluent treatment section, at least partially separates the compound dissolved and / or carried by oneself and optionally purifies this wash effluent on the one hand, to obtain the high density solution of purifying, and on the other hand at least partially recirculates the high density solution of a part of purifying. This wash effluent treatment section can comprise the project of one or more equipments known for solid-liquid separation, for example separation vessel, decanter, centrifugal decanter, centrifuge or filter. When the high density solution was the aqueous solution, the wash effluent also can be delivered to outside the method, for example, deliver to a wastewater treatment station.

[0105] Extraction sub-step b3)

[0106] Step b) of the process according to the invention may comprise a sub-step b3) of extraction by contact with an extraction solvent to obtain at least one extracted polymer solution and preferably a spent solvent particularly loaded with impurities. The extracted polymer solution obtained at the end of sub-step b3) advantageously comprises the purified polypropylene that the invention seeks to recover dissolved in the dissolving solvent. Optionally, if sub-steps b2) and / or b3) are carried out, the extracted polymer solution may further comprise residual impurities that are particularly soluble in the dissolving solvent and / or traces of the high-density solution and / or the extraction solvent.

[0107] When it is 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 the sub-step b1) for separating off the insolubles, and if the adsorption sub-step b4) is also integrated into step b), it may be upstream or downstream of the adsorption sub-step b4).

[0108] The extraction substep b3) is advantageously fed with an extraction solvent and with a polymer solution, in particular a crude polymer solution obtained from step a), a clarified polymer solution obtained from substep b1), a washed polymer solution obtained from substep b2), or a refined polymer solution obtained from adsorption substep b4). Preferably, the extraction substep b3) is fed with an extraction solvent and with a clarified polymer solution obtained from substep b1), a washed polymer solution obtained from substep b2), or optionally with a refined polymer solution obtained from adsorption substep b4). The polymer solution of the feed substep b3), preferably a clarified polymer solution, a washed polymer solution or a refined polymer solution, may optionally contain dissolved compounds or dissolved impurities in addition to the polypropylene. These dissolved compounds may be partially or completely removed during the extraction substep b3) by contact with the extraction solvent. Very advantageously, the combination of the extraction sub-step b3) with the sub-step b1) of separating off the insolubles and optionally the washing sub-step b2) and / or the adsorption sub-step b4) allows an improved purification of the polymer solution, taking advantage of the affinity of the impurities for the extraction solvent and possibly for the high density solution and / or the adsorbent.

[0109] When it is incorporated into the process according to the invention, the extraction sub-step b3) advantageously involves at least one extraction section, preferably one to five extraction sections, very preferably one extraction section.

[0110] The mass ratio between the mass flow of the extraction solvent and the mass flow of the polymer solution (preferably clarified polymer solution, washed polymer solution or refined polymer solution) fed to substep b3) (extraction solvent / polymer solution) is advantageously between 0.05 and 20.0, preferably between 0.1 and 10.0 and preferably between 0.2 and 5.0. The contact between the polymer solution (preferably clarified polymer solution, washed polymer solution or refined polymer solution) fed to substep b3) and the extraction solvent can be carried out at several points in the extraction section, i.e. via several injections of the polymer solution and / or the extraction solvent at different points along the extraction section; the sum of the injected streams is then taken into account when calculating the mass ratio (extraction solvent / polymer solution).

[0111] The extraction solvent used in the 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-based compound, advantageously aliphatic and preferably paraffinic, preferably at least one alkane, with a boiling point of -15 to 100° C., preferably 8 to 100° C., preferably 25 to 69° C., preferably 25 to 61° C., and very preferably 25 to 40° C. Preferably, the extraction solvent mainly comprises, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight, preferably paraffinic aliphatic hydrocarbon compounds (or alkanes) (100% being a maximum, the percentage being expressed relative to the total weight of the dissolved solvent), whose boiling point is from -15 to 100°C, preferably from 8 to 100°C, preferably from 25 to 69°C, preferably from 25 to 61°C and very preferably from 25 to 40°C. Very advantageously, the hydrocarbon compounds forming the majority of the extraction solvent - which are advantageously aliphatic, preferably paraffinic - have a critical temperature (the temperature at the critical point of the pure hydrocarbon compounds) of 130 to 285°C, preferably from 158 to 285°C, preferably from 185 to 245°C, preferably from 185 to 230°C and very preferably from 185 to 200°C. According to a preferred embodiment, the extraction solvent mainly comprises, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight, aliphatic chain-alkane-based compounds, which are preferably linear or branched, have a boiling point of -15 to 100°C, preferably 8 to 100°C, preferably 25 to 69°C, preferably 25 to 61°C and very preferably 25 to 40°C, and contain 4 to 7 carbon atoms (C4-C7), preferably 5, 6 or 7 carbon atoms (C5, C6 or C7, respectively), preferably contain 5 or 6 carbon atoms (C5 or C6) and very preferably contain 5 carbon atoms (C5).

[0112] Very preferably, the extraction solvent used for b3) is the same solvent as the dissolution solvent used for step a), optionally in a different physical state (e.g. the extraction solvent is in supercritical form with respect to the dissolution solvent in liquid form) to facilitate the management of the solvents and in particular their purification and their recycling, in particular to the dissolution step a) and optionally to the extraction sub-step b3). Another advantage of using the same dissolution and extraction solvents in the same or different physical state, in addition to facilitating the management of the solvents involved in the process according to the invention, in particular their recovery, their treatment and their recycling to at least one step of the process, is that the energy consumption and the costs resulting in particular from the treatment and purification of the solvents are limited.

[0113] The extraction section of b3) may comprise one or more items of extraction equipment, enabling contact with the extraction solvent and / or with the separation equipment, in order to recover at least one waste solvent, in particular a waste solvent loaded with impurities, and the extracted polymer solution. Such equipment is well known, for example stirred reactors, static mixers, decanting mixers, two-phase or three-phase separation vessels, co-current or counter-current washing columns, plate columns, stirred columns, packed columns, pulse columns, etc., each type of equipment may comprise one or more items of equipment used alone or in combination with another type of equipment.

[0114] According to a preferred embodiment of b3), the extraction is carried out in a countercurrent extraction column, into which the extraction solvent is injected on the one hand and the polymer solution of the feed substep b3) is injected on the other hand. According to this embodiment, at least one extracted polymer solution can be recovered on the one hand and the spent solvent, which is particularly loaded with impurities, can be recovered on the other hand. Preferably, the polymer solution of the feed b3), preferably the clarified, washed or refined polymer solution, is injected into the upper half, preferably the upper third, of the countercurrent extraction column, which is closest to the top of the column, while the extraction solvent is injected into the lower half, preferably the lower third, of the column, which is preferably closest to the bottom of the countercurrent extraction column.

[0115] The stream at the inlet and / or outlet of the countercurrent extraction column may be split at several injection and / or withdrawal points along the column.

[0116] According to another embodiment of b3), the extraction is carried out in a mixer-decanter which advantageously comprises, on the one hand, a stirred mixing zone for contacting the extraction solvent and the polymer solution, preferably clarified, washed or refined polymer solution, fed to substep b3), and, on the other hand, a decantation zone which makes it possible to recover the extracted polymer solution on the one hand and the spent solvent on the other hand.

[0117] Advantageously, the extraction sub-step b3) is carried out under temperature and pressure conditions different from those of the dissolution step a).

[0118] According to a preferred embodiment of b3), the extraction substep b3) comprises a liquid / liquid extraction section. Preferably, the liquid / liquid extraction section is operated at 150° C. to 250° C., preferably 160° C. to 225° C., very preferably 165° C. to 210° C. and preferably 170° C. to 195° C., and at a pressure of 1.0 to 18.0 MPa absolute, preferably 1.0 to 12.0 MPa absolute, preferably 3.0 to 11.0 MPa absolute, preferably 5.0 to 11.0 MPa absolute and very preferably 6.0 to 10.0 MPa absolute. In any case, in this embodiment, the temperature and pressure conditions are adjusted so that the extraction solvent is in liquid form and the dissolving solvent is preferably also in liquid form. Very advantageously, the liquid / liquid extraction, in particular when the extraction solvent is the same as the dissolving solvent, is carried out under temperature and pressure conditions that are different from the dissolving conditions of step a), in particular at a temperature above the dissolving temperature and / or at a pressure below the dissolving pressure, and thus in the two-phase region of the corresponding polymer-solvent mixture diagram.

[0119] According to another preferred embodiment of b3), the extraction sub-step b3) includes a section of extraction under specific temperature and pressure conditions, wherein the extraction solvent is advantageously, at least partially, in supercritical form. Such extraction can be referred to as supercritical extraction. In this embodiment, the polymer solution of feed b3), preferably a clarified, washed or refined polymer solution, is contacted with the extraction solvent, advantageously under temperature and pressure conditions that allow a supercritical phase consisting 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 to be obtained. In other words, in this embodiment, the extraction is carried out by contacting the polymer solution of feed b3), preferably a clarified, washed or refined polymer solution, with an extraction solvent that is at least partially, preferably completely in supercritical form. Such supercritical extraction sub-step b3) advantageously allows effective purification of the polymer solution, particularly due to the very high affinity of organic impurities (e.g., some additives, particularly certain colorants or plasticizers) for the supercritical phase. The use of a supercritical form of the extraction solvent also allows a significant density difference to be created between the supercritical phase and the polymer solution in liquid form, which facilitates demixing and decantation separation between the two phases, i.e., the supercritical phase and the liquid phase, which therefore contributes to the effectiveness of purification of the polymer solution.

[0120] In this other preferred embodiment, sub-step b3) uses an extraction solvent which mainly comprises, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight, preferably paraffinic aliphatic hydrocarbon compounds (or alkanes) (100% is the maximum, the percentage being expressed relative to the total weight of the dissolved solvent), and whose critical temperature is preferably from 130 to 285°C, preferably from 158 to 285°C, preferably from 185 to 245°C, very preferably from 185 to 230°C and preferably from 185 to 200°C. Very preferably, in such supercritical extraction sub-step b3), the extraction solvent mainly comprises, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight, of alkanaliphatic hydrocarbon-based compounds having a boiling point of -15 to 100° C., preferably 8 to 100° C., preferably 25 to 69° C., very preferably 25 to 61° C. and preferably 25 to 40° C. and containing 4 to 7 carbon atoms (i.e. C4-C7), preferably 5, 6 or 7 carbon atoms (respectively C5, C6 or C7), preferably 5 or 6 carbon atoms (C5 or C6) and very preferably 5 carbon atoms (C5). Very particularly, the alkanaliphatic hydrocarbon-based compounds constituting the main part of the extraction solvent have a critical pressure of 2.5 to 5.0 MPa, preferably 2.7 to 4.6 MPa, preferably 3.0 to 3.8 MPa and preferably 3.0 to 3.5 MPa.

[0121] Advantageously, the supercritical extraction substep b3) of this particular embodiment is carried out at a temperature preferably of 160° C. to 300° C., preferably of 190 to 250° C., preferably of 200 to 230° C., and at a pressure preferably of 2.7 to 10.0 MPa absolute, preferably of 3.0 to 6.0 MPa absolute, preferably of 3.0 to 5.0 MPa absolute and very preferably of 3.0 to 4.0 MPa absolute. According to a very particular mode of this embodiment of sub-step b3), the supercritical extraction is carried out at a pressure which is very advantageously between the critical pressure of the main alkanaliphatic hydrocarbon compounds of the extraction solvent (CP(extraction solvent)) (i.e. preferably the critical pressure of the main alkanaliphatic hydrocarbon compounds having a boiling point of -15 to 100° C., preferably 8 to 100° C., preferably 25 to 69° C., very preferably 25 to 61° C. and preferably 25 to 40° C. and containing 4 to 7 carbon atoms, preferably 5, 6 or 7 carbon atoms, preferably 5 or 6 carbon atoms and very preferably 5 carbon atoms, as defined above) and above the critical pressure of the main alkanaliphatic hydrocarbon compounds of the extraction solvent equal to 3. 0 MPa (i.e. CP (extraction solvent) + 3.0 MPa), preferably between the critical pressure of the main paraffinic aliphatic hydrocarbon compounds of the extraction solvent (CP (extraction solvent)) and a pressure equal to 1.5 MPa above the critical pressure of the main paraffinic aliphatic hydrocarbon compounds of the extraction solvent (i.e. CP (extraction solvent) + 1.5 MPa), preferably between the critical pressure of the main paraffinic aliphatic hydrocarbon compounds of the extraction solvent (CP (extraction solvent)) and a pressure equal to 0.5 MPa above the critical pressure of the main paraffinic aliphatic hydrocarbon compounds of the extraction solvent (i.e. equal to CP (extraction solvent) + 0.5 MPa), the pressure being an absolute pressure. In any case, in this embodiment, the temperature and pressure conditions are adjusted, in particular in the adjustment section carried out in the extraction sub-step b3) upstream of the extraction section, so that the extraction solvent is at least partially in a 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 in a manner known to the person skilled in the art (using, for example, pumps and / or valves and / or turbines and / or exchangers and / or ovens).

[0122] In a very preferred embodiment of b3), the extraction sub-step b3) comprises supercritical extraction and the extraction solvent is the same as the dissolving solvent (or comprises the same main compounds and possible impurities as the dissolving solvent), except that the extraction solvent is at least partly in the supercritical phase.

[0123] Advantageously, at the end of the extraction sub-step b3), the spent solvent obtained is particularly loaded with impurities. It can be reprocessed in the organic treatment section so that it is possible, on the one hand, to at least partially separate the impurities and purify the solvent to obtain a purified extraction solvent, and on the other hand, at least a portion of the purified extraction solvent is recycled to the inlet of the extraction sub-step b3) and / or to the inlet of the dissolution step a), in the case where the dissolving solvent and the extraction solvent are identical. The spent solvent can be treated according to any method known to those skilled in the art, for example one or more of the following methods: distillation, evaporation, extraction, adsorption, crystallization and precipitation of insolubles, or by purging.

[0124] Adsorption sub-step b4)

[0125] Step b) of the treatment process according to the invention may comprise an adsorption sub-step b4) for obtaining at least one purified polymer solution. The purified polymer solution obtained at the end of sub-step b4) advantageously comprises the purified polypropylene that the invention seeks to recover, dissolved in a dissolving solvent.

[0126] When it is incorporated into the process according to the invention, the adsorption sub-step b4) is advantageously carried out downstream of the dissolution step a) and upstream of the polymer-solvent separation step c). It can be carried out upstream of the sub-step b1) for separating off the insolubles and / or the washing sub-step b2), and can correspond in particular to the optional intermediate adsorption step a'). Preferably, it is carried out downstream of the sub-step b1) for separating off the insolubles and of the possible washing sub-step b2), said sub-step b2) itself preferably being downstream of the sub-step b1). It can also be carried out, for example, upstream or downstream of the extraction sub-step b3). Thus, the adsorption sub-step b4) is carried out by contacting the polymer solution fed thereto, in particular the crude polymer solution obtained from step a), the clarified polymer solution obtained from b1) or the washed polymer solution obtained from b2) or the extracted polymer solution obtained from b3), with one or more adsorbents.

[0127] The adsorption sub-step b4) advantageously comprises 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 a slurry, i.e. in the form of particles introduced into the stream to be purified and entrained with this stream) or an ebullating bed, preferably in the form of a fixed bed or an entrained bed. Each adsorbent used in sub-step b4) is preferably alumina, silica, silica-alumina, activated carbon, bleaching clay or a mixture thereof, preferably activated carbon, bleaching clay or a mixture thereof, preferably in the form of a fixed bed or an entrained bed, the circulation of which stream may be ascending or descending.

[0128] Advantageously, when it is incorporated into the process, the adsorption substep b4) is carried out at a temperature preferably between 150° C. and 250° C., preferably between 160° C. and 225° C., very preferably between 165° C. and 210° C. and preferably between 170° C. and 195° C., and at a pressure of 1.0 to 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, the adsorption substep b4) is carried out under dissolution temperature and pressure conditions, i.e. at the dissolution temperature and dissolution pressure of step a). Preferably, in the optional substep b4), the hourly space velocity (or HSV), which corresponds to the ratio between the volume flow of the polymer solution fed b4) and the volume of the adsorbent, advantageously operating in b4), is between 0.05 and 10 h -1 , preferably 0.1 to 5.0h -1 .

[0129] According to a particular embodiment of sub-step b4), the adsorption section may comprise one or more fixed beds of one or more adsorbents, for example in the form of an adsorption tower containing said adsorbent, preferably at least two adsorption towers, preferably two to four adsorption towers. When the adsorption section comprises two adsorption towers, an operating mode may be a mode of operation according to the special terminology known as "swing", in which one tower is online, i.e. in use, and the other tower is on standby. When the adsorbent of the online tower is exhausted, the tower is isolated and the standby tower is put online, i.e. put into use. The exhausted adsorbent can then be regenerated in situ and / or replaced with fresh adsorbent so that once the other tower is isolated, the tower containing the above adsorbent can be put online again.

[0130] Another operating mode of this particular embodiment of b4) comprising one or more fixed beds of one or more adsorbents is to have at least two towers operating in series. When the adsorbent of the tower located at the head is exhausted, the first tower is isolated and the exhausted adsorbent is regenerated in situ or replaced with fresh adsorbent. The tower at the last position is then restored online, and so on. This operation is called replaceable mode, or according to the term PRS (replaceable reactor system), or also called "lead and lag". The combination of at least two adsorption towers makes it possible to overcome the possible and potential rapid poisoning and / or blockage of the adsorbent caused by the combined action of impurities, pollutants and insolubles that may be present in the logistics to be treated. The reason is that the presence of at least two adsorption towers facilitates the replacement and / or regeneration of the adsorbent, and advantageously there is no need to stop the method, and it also makes it possible to control costs and limit the consumption of adsorbents.

[0131] According to this particular embodiment of the adsorption sub-step b4) in a fixed bed of one or more adsorbents, sub-step b4) is preferably carried out downstream of the sub-step b1) of separating off the insolubles and / or the washing sub-step b2), and optionally upstream or downstream of the extraction sub-step b3). Advantageously, the combination of the sub-step b1) of separating off the insolubles, and / or the washing sub-step b2), and the optional extraction sub-step b3) with the adsorption sub-step b4) allows to improve the purification of the polymer solution by exploiting the affinity of the residual impurities for the adsorbent and the extraction solvent and optionally the high-density solution.

[0132] According to another embodiment, the adsorption section of b4) may comprise the addition of adsorbent particles to the polymer solution, in particular to the crude polymer solution, said particles being separable from the polymer solution via a step of removing the adsorbent particles downstream of said adsorption section. The removal of the adsorbent particles may then advantageously correspond to a sub-step b1) of separating out the insolubles or to a washing sub-step b2). Such an embodiment of the adsorption sub-step b4) advantageously corresponds to the optional intermediate adsorption step a') described earlier in this specification, by introducing adsorbent particles and subsequently carrying out a solid / liquid separation.

[0133] Solvent-polymer separation step c)

[0134] According to the present invention the process comprises a solvent-polymer separation step c) to obtain at least one purified polypropylene fraction and preferably a solvent fraction.

[0135] The solvent-polymer separation step c) advantageously comprises in series at least one supercritical separation section followed by at least one solvent recovery section, preferably one to five solvent recovery sections. The 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 obtained from the purification step b).

[0136] The solvent-polymer separation step c) thus first involves at least partially, preferably predominantly or even completely separating the solvent contained in the purified polymer solution of feeding step c), in particular the dissolving solvent, in order to recover polypropylene from which impurities and the dissolving solvent and possibly other solvents used in the process, i.e. the extraction solvent and / or the high density solution, have been at least partially, preferably predominantly and preferably completely removed. The term "predominantly" is understood to mean at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, very preferably at least 95% by weight, relative to the weight of the solvent contained in the purified polymer solution of feeding step c), in particular the dissolving solvent and the optional extraction solvent and / or the high density solution contained in the purified polymer solution of feeding step c). Any method known to the person skilled in the art for separating solvents from polymers, in particular any method capable of causing a phase change of the polymer or the solvent, can be carried out. The solvent can be separated out, for example, by evaporation, stripping, demixing, density differences, in particular decantation or centrifugation.

[0137] The fraction of purified polypropylene obtained at the end of step c) may correspond to a concentrated polypropylene solution or to a liquid (i.e. molten) or solid purified polypropylene. The solvent-polymer separation step c) may also optionally comprise a conditioning section for conditioning the recovered purified polypropylene in solid form and more particularly in the form of solid particles. In this possible conditioning section, the recovered purified polypropylene is cooled, advantageously to a temperature below the melting point of the polypropylene, to obtain a fraction comprising the polypropylene in solid form.

[0138] The solvent-polymer separation step c) also involves at least partial, preferably predominantly and preferably completely recovering the solvent contained in the purified polymer solution of the feeding step c), and in particular the dissolving solvent and optionally the extracting solvent and / or the high-density solution. The term "predominantly" is understood to mean at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, very preferably at least 95% by weight relative to the weight of the solvent contained in the purified polymer solution of the feeding step c). Thus, step c) advantageously also makes it possible to obtain at least one solvent fraction. The solvent-polymer separation step c) also optionally involves purifying the recovered solvent fraction and recycling it, in particular upstream of the dissolving step a) and possibly upstream of the sub-step b2) and / or sub-step b3).

[0139] The solvent-polymer separation step c) thus comprises a supercritical separation section, which makes it possible to at least partially separate the dissolving solvent, and possible extraction solvent and high density solution, and optionally some residual impurities not removed during step b) under temperature and pressure conditions adjusted to supercritical conditions (i.e., exceeding the critical point of the solvent to be separated, in particular exceeding the critical point of the dissolving solvent, more particularly exceeding the critical point of the main hydrocarbon-based compound of the dissolving solvent), which advantageously makes it possible to easily separate and recover at least a portion of the solvent, in particular the dissolving solvent. The supercritical separation section particularly comprises a fluid system consisting of a supercritical phase mainly comprising a solvent, in particular a dissolving solvent, and a liquid phase comprising polypropylene. The term "mainly" herein means at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, very preferably at least 95% by weight relative to the weight of the stream under consideration (i.e., the supercritical phase). This separation can then be referred to as supercritical separation of the solvent. The supercritical separation of the solvent allows efficient separation of at least a portion of the solvent, and in particular the dissolved solvent, on the one hand, and of the polypropylene or concentrated polypropylene solution on the other hand, the supercritical separation being advantageously allowed by the significant difference in density between the two phases, the supercritical phase comprising mainly the solvent, in particular the dissolved solvent, and the liquid phase comprising the polypropylene. Furthermore, the supercritical separation of the solvent advantageously enables significant reductions in energy and environmental costs relative to simple evaporation of the solvent, since there is no latent heat of evaporation during entry into the supercritical state.

[0140] The supercritical separation section is advantageously operated at a temperature of 160° C. to 300° C., preferably 190 to 250° C., preferably 200 to 230° C., and at a pressure (P supercritical ) between 2.7 and 10.0 MPa absolute, preferably 3.0 to 6.0 MPa absolute, preferably 3.0 to 5.0 MPa absolute and preferably 3.0 to 4.0 MPa absolute.

[0141] According to a specific embodiment, the supercritical separation section of step c) is between the critical pressure of the main hydrocarbon-based compounds of the dissolved solvent (CP (dissolved solvent)) and a pressure equal to 3.0 MPa above the critical pressure of the main hydrocarbon-based compounds of the dissolved solvent (i.e.: CP (dissolved solvent) + 3.0 MPa), preferably between the critical pressure of the main hydrocarbon-based compounds of the dissolved solvent (CP (dissolved solvent)) and a pressure equal to 1.5 MPa above the critical pressure of the main hydrocarbon-based compounds of the dissolved solvent (i.e.: CP (dissolved solvent) + 1.5 MPa), preferably between the critical pressure of the main hydrocarbon-based compounds of the dissolved solvent (CP (dissolved solvent)) and a pressure equal to 1.5 MPa above the critical pressure of the main hydrocarbon-based compounds of the dissolved solvent (i.e.: CP (dissolved solvent) + 1.5 MPa). The critical pressure of the main hydrocarbon compound of the dissolved solvent is equal to a pressure of 0.5 MPa (i.e., equal to CP (dissolved solvent) + 0.5 MPa) (P supercritical), which is an absolute pressure. The main hydrocarbon compound of the dissolved solvent is advantageously an aliphatic, preferably an alkane hydrocarbon compound, with a boiling point of -15 to 100°C, preferably 8 to 100°C, preferably 25 to 69°C, very preferably 25 to 61°C and preferably 25 to 40°C, and preferably contains 4 to 7 carbon atoms, preferably 5, 6 or 7 carbon atoms, preferably 5 or 6 carbon atoms and very preferably 5 carbon atoms, as described in detail in the description of step a) above.

[0142] The supercritical separation section of step c) is preferably carried out by separation and subsequent decanting of the liquid phase (comprising the polypropylene) and the supercritical phase (consisting of the solvent). Advantageously, the supercritical phase from the supercritical separation section constitutes at least part of the solvent fraction obtained at the end of step c). The liquid phase comprising the polypropylene is preferably sent to a solvent recovery section or a series of solvent recovery sections.

[0143] Step c) may optionally comprise one or more successive supercritical separation sections, in particular one to five, more particularly one, two or three. The liquid phase comprising polypropylene and obtained from the supercritical separation section can thus also be fed to another subsequent supercritical separation section, advantageously the liquid phase from the last supercritical separation section being sent to a solvent recovery section or a series of solvent recovery sections. Very preferably, step c) comprises one supercritical separation section.

[0144] Very advantageously, supercritical separation of the solvent makes it possible to reduce the content of residual impurities of the purified polypropylene fraction even further.

[0145] Preferably, the supercritical section (optionally a series of supercritical separation sections) is followed by at least one, preferably one to five, preferably consecutive, solvent recovery sections. The first solvent recovery section is fed with the liquid phase comprising polypropylene and obtained from the supercritical separation section, the optional series of supercritical separation sections and in particular from the last supercritical separation section, and in case the separation section comprises at least two solvent recovery sections, each of the subsequent solvent recovery sections, i.e. starting from the second solvent recovery section, is fed with the liquid phase comprising polypropylene and obtained from the previous solvent recovery section, e.g. the second solvent recovery section is fed with the liquid phase comprising the target thermoplastic polymer obtained from the first solvent recovery section. The liquid phase containing polypropylene obtained from the last solvent recovery section constitutes the purified polypropylene fraction obtained at the end of step c).

[0146] The phase or combination of phases containing only solvent obtained from the solvent recovery section together with the supercritical phase obtained from the supercritical separation section (optionally obtained from a series of supercritical separation sections) constitute the solvent fraction advantageously recovered at the end of step c). The phase or combination of phases containing only solvent obtained from the solvent recovery section is preferably in gaseous form and can be condensed and optionally mixed with the supercritical phase obtained from the supercritical separation section, the temperature and pressure conditions of which are advantageously adjusted in advance so as to be in liquid form.

[0147] Each solvent recovery section is advantageously implemented at a temperature of 160 to 300° C. (and preferably at a temperature above the melting point of polypropylene) and a pressure between the pressure used in the supercritical separation section (P supercritical ) and 0.000005 MPa (i.e. 5 Pa). Preferably, each solvent recovery section is implemented at a temperature of 160 to 300° C. and a pressure between the pressure of the previous section in step c) and 0.000005 MPa. Thus, when step c) comprises a supercritical separation section and several (at least two) solvent recovery sections, the first solvent recovery section S1 immediately following the supercritical separation section is implemented at a pressure P(S1) between the pressure used in the supercritical separation section (advantageously directly preceding) (Psupercritical) and 0.000005 MPa; the second solvent recovery section S2 immediately following the solvent recovery section S1 is implemented at a pressure P(S2) between the pressure P(S1) used in the first solvent recovery section S1 and 0.000005 MPa, and the subsequent sections are implemented by analogy. According to a preferred embodiment, each solvent recovery section is carried out at a temperature advantageously comprised between 160 and 300° C. and at a pressure comprised between the pressure of the previous section of step c) and 0.000005 MPa, and preferably 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 modify the volatility of the solvent still present in the polymer phase, advantageously in the form of a concentrated polypropylene solution or in the form of molten or solid polypropylene.

[0148] In the purification process according to the invention, in particular in case several different solvents are used in the dissolution step a) and optionally in the extraction sub-step b3), step c) may comprise several solvent recovery sections, for example two, three or four solvent recovery sections, in order to recover the various solvents, in particular the dissolution solvent and the optional extraction solvent, separately, sequentially and / or successively.

[0149] Advantageously, the supercritical separation and solvent recovery section of step c) can be carried out continuously, in batch mode or in fed-batch mode.

[0150] Very advantageously, the solvent fraction recovered at the end of step c) can be treated in an organic treatment section located at the end of step c) in order to purify it and obtain at least one purified solvent, in particular at least one purified dissolving solvent, so as to be advantageously able to recycle it to the dissolving step a) and optionally to the washing sub-step b2) or the extraction sub-step b3). Said optional organic treatment section at the end of step c) can use any method known to a person skilled in the art, for example one or more methods selected from distillation, evaporation, liquid-liquid extraction, adsorption, crystallization and precipitation of insolubles, or by washing.

[0151] The process according to the invention thus makes it possible to obtain a purified polypropylene stream from plastic waste, which can be used for any application, for example to replace virgin resin. The purified stream of polypropylene obtained via the process according to the invention, i.e. the purified polypropylene fraction, thus has a sufficiently low content of impurities and residual solvents to be able to be used for any application. Preferably, the stream of purified polypropylene obtained at the end of the process according to the invention advantageously contains 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 solvents (in particular dissolving solvents), preferably less than 1% by weight of residual solvents, preferably less than 0.1% by weight of residual solvents.

[0152] According to a preferred embodiment of the present invention, the method for purifying a plastic raw material comprising polypropylene comprises the following steps, and preferably consists of the following steps:

[0153] a) a dissolving step in a dissolving solvent comprising at least one aliphatic paraffin-based compound having a boiling point of -15 to 100°C, preferably 8 to 100°C, preferably 25 to 69°C, very preferably 25 to 61°C and preferably 25 to 40°C, the dissolving step being carried out at a dissolving temperature of 150 to 250°C, preferably 160 to 225°C, very preferably 165 to 210°C and preferably 170 to 195°C and a dissolving pressure of 1.0 to 18.0 MPa absolute pressure, preferably 1.0 to 12.0 MPa absolute pressure, preferably 3.0 to 11.0 MPa absolute pressure, preferably 5.0 to 11.0 MPa absolute pressure and very preferably 6.0 to 10.0 MPa absolute pressure, to obtain at least one crude polymer solution; and subsequently

[0154] b) a step of purifying the polymer solution, comprising:

[0155] b1) a sub-step of separating the insoluble matter to obtain a clear polymer solution and an insoluble fraction; and subsequently

[0156] b4) a sub-step of adsorbing impurities by contacting the clarified polymer solution with an adsorbent to obtain at least one purified polymer solution; and subsequently

[0157] c) a solvent-polymer separation step using at least one supercritical separation section operating at a temperature of 160 to 300° C., preferably 190 to 250° C., preferably 200 to 230° C. and a pressure (P supercritical ) of 2.7 to 10.0 MPa absolute, preferably 3.0 to 6.0 MPa absolute, preferably 3.0 to 5.0 MPa absolute and preferably 3.0 to 4.0 MPa absolute, followed by at least one solvent recovery section operating at a temperature of 160 to 300° C. and a pressure between the pressure of the supercritical separation section (P supercritical ) and 0.000005 MPa (i.e. 5 Pa), to obtain at least one purified polypropylene fraction.

[0158] According to another aspect, the invention relates to a device for purifying a plastic raw material comprising polypropylene, the device comprising, preferably consisting of, the following components:

[0159] a) a section for dissolving the plastic raw material in a dissolving solvent which advantageously comprises at least one paraffinic aliphatic hydrocarbon-based compound, at a dissolving temperature of 150 to 250° C., preferably 160 to 225° C., very preferably 165 to 210° C. and preferably 170 to 195° C. and at a dissolving pressure of 1.0 to 18.0 MPa absolute, preferably 1.0 to 12.0 MPa absolute, preferably 3.0 to 11.0 MPa absolute, preferably 5.0 to 11.0 MPa absolute, very preferably 6.0 to 10.0 MPa absolute, to obtain at least one crude polymer solution; and subsequently

[0160] b) a section for purification of the crude polymer solution, comprising:

[0161] b1) an insoluble separation subsection; and / or

[0162] b2) passing through a washing sub-section in contact with a high density solution; and / or

[0163] b3) passing through an extraction sub-section in contact with an extraction solvent; and / or

[0164] b4) passing through an impurity adsorption sub-section in contact with an adsorbent; and subsequently

[0165] c) a solvent-polymer separation section comprising at least one supercritical separation section operating at a temperature of 160 to 300° C., preferably 190 to 250° C., preferably 200 to 230° C. and at a pressure (P supercritical ) of 2.7 to 10.0 MPa absolute, preferably 3.0 to 6.0 MPa absolute, preferably 3.0 to 5.0 MPa absolute and preferably 3.0 to 4.0 MPa absolute, followed by at least one solvent recovery section operating at a temperature of 160 to 300° C. and a pressure between the pressure of the supercritical separation section (P supercritical ) and 0.000005 MPa (i.e. 5 Pa), to obtain at least one purified polypropylene fraction.

[0166] Preferably, the purification section b) comprises:

[0167] b1) separating the insoluble matter sub-fraction to obtain a clear polymer solution and an insoluble fraction; then

[0168] b4) A subsection for adsorbing impurities by contacting the clarified polymer solution with an adsorbent to obtain at least one refined polymer solution.

[0169] The following examples illustrate the invention, particularly specific embodiments of the invention, without limiting the scope thereof. Example

[0170] Example 1 (according to the present invention)

[0171] Dissolution step a):

[0172] A raw material obtained from plastic waste and containing 95% by weight of polypropylene (PP) is fed in the form of flakes into an extruder heated to 180° C. Upon leaving the extruder, the raw material is at least partially in molten form and mixed with a solvent containing 99% of n-pentane and preheated to 180° C. at a solvent / raw material mass ratio of 9:1. The mixture of solvent and raw material is introduced into a stirred reactor and heated to 180° C. and maintained at a residence time of 1 hour at an absolute pressure of 7 MPa. A polymer solution is then obtained.

[0173] The polymer solution from the dissolution step a) is subsequently subjected to a purification step b):

[0174] The polymer solution was continuously withdrawn from the stirred reactor and passed through three filters placed in series, maintained at 180° C. and having cut-off diameters of 500 μm, 100 μm and 10 μm, respectively (in that order). The pressure drop across the filters was 0.05 MPa.

[0175] At the outlet of a series of filters, the clarified polymer solution passed through an adsorption section comprising an activated carbon particle bed with a contact time of 2 hours and subsequently passed through a filter to retain the activated carbon particles. The adsorption section was operated at 180°C, which resulted in a pressure drop of 0.2 MPa.

[0176] The purified polymer solution from purification step b) is subsequently subjected to a solvent-polymer separation step c) comprising a supercritical section:

[0177] The purified polymer solution from the adsorption section is then heated to 210°C at a pressure slightly less than 7 MPa (solution pressure minus the pressure drop induced in the section of purification step b)). The polymer solution is then expanded to 4 MPa absolute pressure and injected into a decanter maintained at 4 MPa absolute pressure and 210°C for a residence time of 5 minutes. Two phases are formed: the upper phase mainly comprises n-pentane solvent in a supercritical state, while the lower liquid phase comprises polypropylene dissolved in n-pentane solvent. The upper phase is discharged from the upper part of the decanter.

[0178] The lower liquid phase was subsequently subjected to evaporation of the residual solvent in two consecutive evaporation sections: firstly at a temperature of 210° C. and a pressure of 0.5 MPa for 5 minutes, and secondly at a temperature of 210° C. and a pressure of 0.01 MPa for 2 minutes.

[0179] At the end of the process, at atmospheric temperature and pressure, a solid A consisting of purified polypropylene (PP) is obtained. Solid A is analyzed.

[0180] The obtained solid A was almost colorless and almost translucent, and contained less than 5% by weight of impurities and less than 1% by weight of n-pentane.

[0181] Example 2 (non-compliant)

[0182] In this Example 2, the same starting material was processed and the dissolution step a) and the purification step b) were carried out in the same way as the method described in Example 1.

[0183] The purified polymer solution from purification step b) is subjected to a solvent-polymer separation step not including a supercritical section:

[0184] The purified polymer solution from the adsorption section was maintained at 180°C and expanded to an absolute pressure of 2 MPa, and then injected into a decanter maintained at an absolute pressure of 2 MPa and 180°C for a residence time of 5 minutes. Two phases were formed: a gaseous upper phase consisting of n-pentane solvent and a liquid lower phase containing polypropylene dissolved in the n-pentane solvent. The gas phase was discharged from the upper part of the decanter.

[0185] The lower liquid phase was subsequently subjected to evaporation of the residual solvent, initially at a temperature of 210° C. and a pressure of 0.5 MPa for 5 minutes and subsequently at a temperature of 210° C. and a pressure of 0.01 MPa for 2 minutes.

[0186] At the end of the process, at atmospheric temperature and pressure, a solid B consisting of purified polypropylene (PP) is obtained. Solid B is analyzed.

[0187] The obtained solid B was almost colorless and almost translucent, and contained less than 5% by weight of impurities and less than 1% by weight of n-pentane.

[0188] However, the content of impurities (organic compounds excluding the dissolved solvent) in the solid B is higher than the impurity content measured in the solid A obtained in Example 1 according to the present invention.

[0189] Furthermore, the energy consumption required for the polymer-solvent separation according to Example 2 is greater than the energy consumption required for the polymer-solvent separation of the method described in Example 1, ie when the polymer-solvent separation includes a supercritical phase section.

Claims

1. A method for purifying a plastic raw material containing polypropylene, the method comprising: a) a dissolving step, which involves contacting the plastic raw material with a dissolving solvent comprising at least one hydrocarbon-based compound having a boiling point of -15 to 100° C. at a dissolving temperature of 150° C. to 250° C. and at a dissolving pressure of 1.0 to 18.0 MPa absolute pressure 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 insoluble matter; and / or b2) a sub-step of washing by contact with a dense solution; and / or b3) a sub-step of extracting by contacting with an extraction solvent; and / or b4) a sub-step of adsorbing impurities by contact with an adsorbent; and subsequently c) a solvent-polymer separation step using at least one supercritical separation section operated at a temperature comprised between 160 and 300° C. and at a pressure comprised between 2.7 and 10.0 MPa absolute (Psupercritical), followed by at least one solvent recovery section, to obtain at least one purified polypropylene fraction.

2. The method according to claim 1, wherein the plastic raw material 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 raw material.

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

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

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

6. The method according to any one of the preceding claims, wherein the purification step b) comprises at least a sub-step b1) of separating off insolubles, optionally followed by a sub-step b2) of washing by contact with a high density solution, and / or a sub-step b3) of extracting by contact with an extraction solvent, and / or a sub-step b4) of adsorbing impurities by contact with an adsorbent.

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

8. The process according to claim 1, wherein the supercritical separation section in step c) is operated at a pressure (Psupercritical) of 3.0 to 6.0 MPa absolute, preferably 3.0 to 5.0 MPa absolute and preferably 3.0 to 4.0 MPa absolute.

9. The process according to claim 1 , wherein step c) comprises one to five solvent recovery sections, each solvent recovery section operating at a temperature of 160 to 300° C. and at a pressure of the supercritical separation section (P supercritical ) to 0.000005 MPa, preferably 2.7 MPa to 0.000005 MPa.

10. An apparatus for purifying a plastic feedstock comprising polypropylene, the apparatus comprising: a) a section for dissolving the plastic raw material in a dissolving solvent, which is operated at a dissolving temperature of 150 to 250° C. and at a dissolving pressure of 1.0 to 18.0 MPa absolute pressure to obtain at least one crude polymer solution; and subsequently b) a section for purifying the crude polymer solution, comprising: b1) an insoluble separation subsection; and / or b2) passing through a washing sub-section in contact with a high density solution; and / or b3) passing through an extraction sub-section in contact with an extraction solvent; and / or b4) passing through an impurity adsorption sub-section in contact with an adsorbent; and subsequently c) a solvent-polymer separation section comprising at least one supercritical separation section operating at a temperature of 160 to 300° C. and at a pressure P supercritical of 2.7 to 10.0 MPa absolute pressure, followed by at least one solvent recovery section operating at a temperature of 160 to 300° C. and at a pressure of between P supercritical of the supercritical separation section and 0.000005 MPa (i.e. 5 Pa) to obtain at least one purified polypropylene fraction.