Method for recycling and treatment of used plastics by dissolving in a solvent and step

Abstract

The invention relates to a method for treating a plastic feedstock, comprising: a) a dissolution step involving: i) a section in which the plastic feedstock is placed in contact with at least a portion of a dissolution solvent, said section comprising at least one static or dynamic mixer, each mixer feeding a plastic stream and a fraction of the dissolution solvent, each mixer has a volume-based dilution with the dissolving solvent of 3% to 70%, each mixer operating at a temperature of 100 DEG C to 300 DEG C; and then ii) a dissolution section operating at a temperature of from 100 DEG C to 300 DEG C and a pressure of from 1.0 to 100.0 MPa absolute; and then b) a purification step; and then c) a solvent / polymer separation step to obtain at least one fraction of purified thermoplastic polymer.

Description

Technical Field

[0001] The present invention relates to a method for treating plastics, in particular used plastics, to obtain a purified thermoplastic polymer stream that can be economically upgraded, for example, in the manufacture of new plastic products. More specifically, the present invention relates to a method for purifying a plastic feedstock, in particular derived from plastic waste, that contains a thermoplastic polymer, especially a polyolefin, such as polyethylene and / or polypropylene, by dissolving the target thermoplastic in a solvent and then purifying the resulting polymer solution. The method includes gradually mixing the solvent with the plastic feedstock to obtain a homogeneous mixture, preferably having a viscosity less than or equal to 50 mPa·s and very advantageously a coefficient of variation of concentration less than or equal to 10%, thereby optimizing the dissolution of the target thermoplastic and the purification of the resulting polymer solution to recover a purified thermoplastic polymer stream. Prior Art

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

[0003] "Mechanical" recycling can reuse some waste fractions, either directly for new articles or by mixing the mechanically sorted plastic waste stream with the virgin polymer stream. Such an economical upgrading method is limited, although a concentrated stream of a particular type of polymer can be obtained, mechanical sorting cannot remove at least some of the impurities trapped in the polymer matrix, such as additives (e.g., fillers, colorants, pigments, and metals).

[0004] "Chemical" recycling refers to at least partially reforming monomers through a series of generally complex steps. For example, plastic waste can undergo a pyrolysis step, and the recovered pyrolysis oil (usually after purification) can be at least partially converted (e.g., into olefins) by steam cracking. These olefins can then be polymerized. Such sequences can be applied to almost unsorted feedstock or to sorting center waste, but they generally require a particularly large amount of energy consumption due to the high-temperature treatment.

[0005] Another way to recycle plastic waste lies in at least partially dissolving the plastic, especially a thermoplastic, with the aim of purifying it by removing impurities (such as additives, e.g., fillers, colorants, pigments, and metals, and / or feedstock polymers other than one or more target polymers).

[0006] Thus, several studies have proposed various methods for treating plastic waste by dissolution and purification. US2017 / 002110 describes a specific method for purifying polymer raw materials (especially obtained from plastic waste) by dissolving the polymer in a solvent under specific temperature and pressure conditions and then allowing the obtained polymer solution to come into contact with a solid.

[0007] WO 2018 / 114047, for its part, proposes a method of selectively dissolving a specific polymer in 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 treat and separate impurities other than the polymer, such as additives.

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

[0009] The present invention relates to improving these methods for treating thermoplastics by dissolution in a solvent. Specifically, the present invention attempts to optimize the method for removing impurities from plastic raw materials by most particularly improving the stage of bringing the solvent into contact with the plastic raw material to be treated. Thus, the present invention aims to obtain a homogeneous mixture advantageously having a sufficiently low viscosity so as to optimize the dissolution process of the target thermoplastic, especially in terms of dissolution time, the stirring power required for mixing in the reactor, and operating costs. Very advantageously, impurities can thus be removed to a maximum extent to obtain a purified thermoplastic stream, especially a purified polyolefin stream, which can be reused, for example, in the manufacture of new plastic products as a base polymer, especially in place of virgin resin. Summary of the Invention

[0011] The present invention relates to a method for treating plastic raw materials, which comprises:

[0012] a) a step of dissolving the plastic raw material in a dissolution solvent to obtain at least one crude polymer solution, and the dissolution step a) comprises:

[0013] i) A section where the plastic raw material is placed in contact with at least a portion of the dissolving solvent, the section including at least one static or dynamic mixer to produce a conditioned feedstock, each static or dynamic mixer operating at a temperature of 100°C to 300°C, each static or dynamic mixer being fed with a plastic stream containing the plastic raw material and a fraction of at least the said portion of the dissolving solvent, such that each mixer has a volume-based dilution with the dissolving solvent of 3% to 70%, the volume-based dilution with the dissolving solvent being the ratio of the volume flow rate of the fraction of at least the said portion of the dissolving solvent fed to the static or dynamic mixer under consideration to the sum of the volume flow rates of the fraction of at least the said portion of the dissolving solvent and the plastic stream fed to the static or dynamic mixer under consideration;

[0014] ii) A dissolving section which is fed with at least the conditioned feedstock obtained from the contacting section and operates at a dissolving temperature of 100°C to 300°C and a dissolving pressure of 1.0 to 100.0 MPa absolute pressure; and then

[0015] b) A step of purifying the crude polymer solution to obtain a purified polymer solution, the purification step including:

[0016] b1) A sub-step of separating out insolubles; and / or

[0017] b2) A washing sub-step, carried out by contacting with a high-density solution; and / or

[0018] b3) An extraction sub-step, carried out by contacting with an extraction solvent; and / or

[0019] b4) An impurity adsorption sub-step, carried out by contacting with a solid adsorbent; and then

[0020] c) A solvent / polymer separation step to obtain at least one fraction of purified thermoplastic polymer.

[0021] The advantages of the method according to the invention are that it provides a method for the efficient treatment of plastic raw materials (and in particular plastic waste specifically obtained from collection and sorting channels) in order to recover the thermoplastic polymers contained therein, in particular polyolefins, and to be able to recycle them to any type of application. The method according to the invention can more specifically improve the stage of bringing the plastic raw material into contact with the dissolving solvent in order to obtain a homogeneous mixture which advantageously has a viscosity preferably less than or equal to 50 mPa·s, preferably less than or equal to 20 mPa·s, very preferably less than or equal to 5 mPa·s, very preferably less than or equal to 1 mPa·s. Very advantageously, the homogeneous mixture has a coefficient of variation of concentration (CoV) preferably less than or equal to 10%, preferably less than or equal to 5%. Such a mixture has the advantage that it thus results in a sufficiently low effective viscosity in the dissolving reactor, thus contributing to the dispersion and homogenization of the plastic raw material / dissolving solvent mixture. The dissolution of the thermoplastic plastic to be separated and recovered is then optimal, without the need to provide excessive stirring power and / or while allowing the use of various stirring systems, such as mechanical stirring and / or stirring via a recirculation loop. At the same time, the residence time required for the efficient dissolution of the target thermoplastic can also be advantageously shortened, which can be reflected in the use of equipment with optimized dimensions (such as a dissolving reactor).

[0022] Thus, the invention makes it possible to efficiently premix the plastic raw material with the dissolving solvent (or at least a part of the dissolving solvent), while complying with the technical limitations imposed by the mixing equipment used (in particular the stirring system in the dissolving section), as well as by the equipment used in the contact section (such as a static mixer). Generally, static mixers are used to mix fluids which have a viscosity ratio of at most 1000 (i.e. ≤1000) between said fluids. However, the invention can efficiently mix a plastic raw material containing a thermoplastic (in particular a polyolefin) having a melt viscosity generally from 300 to 20000 Pa·s with a solvent having a viscosity in the range from 1 to 0.01 mPa·s, particularly from 0.2 to 0.03 mPa·s, at the temperature at which the mixing takes place, that is to say, the viscosity ratio between these two fluids is in the range of about 5 to 9 which is very high and is generally incompatible with the technical limitations of static or dynamic mixers.

[0023] Thus, according to the method of the present invention (including the dissolution step and in particular the improved contact between the solvent and the raw material), a purified thermoplastic plastic stream can be obtained, which advantageously contains negligible or at least low enough impurities and in particular the content of additives such that the purified thermoplastic polymer stream can replace virgin resin in any type of plastic formulation. For example, the purified thermoplastic plastic stream obtained at the end of the method according to the present invention, and in particular the purified polyolefin stream, advantageously has an impurity content of less than or equal to 5% by weight of impurities, very advantageously less than or equal to 1.0% by weight of impurities, and even more preferably less than or equal to 0.5% by weight of impurities.

[0024] Thus, the method according to the present invention presents a simple scheme corresponding to a series of operations that can remove at least some impurities, in particular at least some additives, from plastic waste and recover a purified thermoplastic polymer (which advantageously contains a small amount of solvent or even no solvent), thereby enabling the economic upgrading of plastic waste by recycling the purified thermoplastic. Depending on the conditions used in the steps of the method, the additives present in the plastic raw material can advantageously be soluble or insoluble in the solvent used throughout the method according to the present invention, allowing for the efficient purification and separation of the polymer.

[0025] The present invention also has the advantage of participating in the recycling of plastics and protecting fossil resources by enabling the economic upgrading of plastic waste. Specifically, the present invention allows for the purification of plastic waste in order to obtain a purified thermoplastic polymer fraction, in particular a purified polyolefin, which has a reduced impurity content, which is in particular a decolorized and deodourized thermoplastic fraction that can be reused to form new plastic products. Thus, the obtained purified thermoplastic fraction can replace virgin polymer resin or be used as a mixture with virgin polymer resin as a mixture with additives (such as colorants, pigments or other polymers) directly in formulations in order to obtain plastic products with aesthetic, mechanical or rheological processing properties that facilitate their reuse and their economic upgrading.

[0026] Description of Embodiments

[0027] According to the present invention, the expressions "comprising between... and..." and "between... and..." are equivalent and mean that the limits of the interval are included within the range of the values described. If this were not the case and if the limits were not included within the described range, the present invention would state so.

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

[0029] Hereinafter, specific embodiments of the present invention may be described. When technically feasible, they can be implemented alone or in combination without limitation of the combination.

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

[0031] The terms “upstream” and “downstream” should be understood to vary with the general flow of the fluid(s) or stream(s) considered in the method.

[0032] In the present specification, the terms “polymer”, “thermoplastic polymer” and “thermoplastic” can be used interchangeably.

[0033] The terms “static or dynamic mixer” and “mixer” can be used interchangeably and correspond to the mixing devices known to those skilled in the art as static mixers or dynamic mixers.

[0034] According to the present invention, the viscosity is defined as the dynamic viscosity, especially using a viscometer at a temperature of 200 °C and a shear rate of 0.1 s -1 and preferably measured using a plate viscometer (e.g., DHR3 type from TA Instruments).

[0035] According to the present invention, the coefficient of variation of concentration (CoV) is calculated by dividing the standard deviation of z concentration measurements by the average concentration and is expressed as a percentage:

[0036]

[0037] where: standard deviation of the concentration measurements:

[0038] average concentration:

[0039] n represents the total number of concentration measurements in these mathematical formulas,

[0040] xi represents the concentration value determined at the i-th measurement; and

[0041] z is an integer greater than or equal to 2, preferably greater than or equal to 4, and generally less than or equal to 10000, preferably less than or equal to 1000,

[0042] The concentration can be determined by any method known to those skilled in the art, for example, by visualizing the color of a mixture of fluids with different colors, by measuring the content of a specific compound in the samples taken (especially z samples), for example, by liquid chromatography (or HPLC) or gas chromatography.

[0043] The lower the coefficient of variation (CoV) of the concentration, the better the quality of the mixture, that is, the more homogeneous the mixture.

[0044] The term "additive" is a commonly used term in the field of polymers and especially in the field of polymer formulations. Additives introduced into polymer formulations can be, for example, plasticizers, fillers (organic or mineral solid compounds used to change the physical, thermal, mechanical, and / or electrical properties of polymer materials or to reduce their cost price), reinforcing agents, colorants, pigments, hardeners, flame retardants, stabilizers, antioxidants, UV absorbers, antistatic agents, etc.

[0045] The additives correspond to at least a part of the impurities in the plastic raw materials to be processed, and at least a part of them can be removed according to the treatment method of the present invention. Other types of impurities can be impurities related to the use, such as metal impurities, paper / cardboard, biomass, polymers other than the target polymer(s), etc.

[0046] Therefore, according to the present invention, the impurities that can be at least partially removed by the method according to the present invention include the additives commonly used in polymer formulations and the impurities generally related to the use, which are derived from the life cycle of plastic products and materials and / or from waste collection and sorting channels. The impurities can be of metal, organic, or mineral type; they can be packaging residues, food residues, or compostable residues (biomass). These use-related impurities can also include glass, wood, cardboard, paper, aluminum, iron, metal, tires, rubber, silicone, rigid polymers, thermosetting polymers, household items, chemicals or cosmetics, waste oil, and water.

[0047] According to the present invention, a polymer solution is a solution comprising a dissolution solvent and at least a target thermoplastic polymer (in particular a target polyolefin), which polymers are dissolved (i.e., in particular solvated and dispersed) in the dissolution solvent, and the dissolved polymers are initially present in the feedstock. The polymer solution may also comprise soluble impurities (which are dissolved in the dissolution solvent) and / or insoluble impurities (which are suspended in the polymer solution). Thus, depending on the steps of the method according to the present invention that have been carried out, the polymer solution may comprise impurities in the form of insoluble particles (which particles are advantageously suspended in the polymer solution), soluble impurities dissolved in the dissolution solvent, and / or optionally another liquid phase immiscible with the polymer solution.

[0048] It is well known that the boiling point of a compound varies with the operating pressure. However, in the absence of further indication (i.e., without specifying the pressure), the boiling point of the compound under consideration (in particular the dissolution solvent) should be understood as the boiling point of said compound (in particular said dissolution solvent) at atmospheric pressure (in particular 0.1 MPa). Thus, the boiling point characterizing the dissolution solvent should be understood as the boiling point of the dissolution solvent at atmospheric pressure (in particular 0.1 MPa).

[0049] The critical temperature and critical pressure of a solvent (in particular the dissolution solvent) are specific to said solvent and depend on the nature of the solvent under consideration. For a pure substance, its critical temperature and critical pressure are respectively the temperature and pressure of the critical point of said pure substance. As is well known to those skilled in the art, at and above the critical point, the pure substance under consideration is in a supercritical form or supercritical state; then it can be referred to as a supercritical fluid.

[0050] Accordingly, the present invention relates to a method for treating a plastic feedstock, which plastic feedstock preferably consists of plastic waste and advantageously contains a thermoplastic polymer, more specifically a polyolefin, the method comprising the following steps and preferably consisting of:

[0051] a) a step of dissolving the plastic feedstock in a dissolution solvent, which dissolution solvent preferably comprises at least one compound preferably being an aliphatic, hydrocarbon-based compound, preferably having a boiling point of from -50 °C to 250 °C, preferably from -15 °C to 150 °C, preferably from -1 °C to 110 °C, and preferably from 20 °C to 100 °C, and the weight ratio between the dissolution solvent and the plastic feedstock is preferably from 0.2 to 100.0, preferably from 0.3 to 20.0, preferably from 1.0 to 10.0, and even more preferably from 3.0 to 7.0, to obtain at least one crude polymer solution, and this dissolution step a) involves:

[0052] i) A section where the plastic raw material is placed in contact with at least a part of the dissolving solvent, which section includes at least one, preferably one to ten, preferably two to six, preferably two to five static or dynamic mixers, advantageously in series, to produce a modulated raw material, and each static or dynamic mixer operates at a temperature of 100°C to 300°C, preferably 150 to 250°C.

[0053] The feed to each static or dynamic mixer comprises a plastic stream containing the plastic raw material and a fraction of at least said part of the dissolving solvent, such that each mixer has a volume-based dilution with the dissolving solvent of 3% to 70%, preferably:

[0054] - When the viscosity ratio between the plastic stream fed to the considered static or dynamic mixer and the fraction of at least said part of the dissolving solvent is greater than or equal to 3500, preferably greater than or equal to 3000, the volume-based dilution with the dissolving solvent is 3% to 50%, preferably 10% to 35%, and very preferably 15% to 30%.

[0055] - When the viscosity ratio between the plastic stream fed to the considered static or dynamic mixer and the fraction of at least said part of the dissolving solvent is less than 3500, preferably less than 3000, the volume-based dilution with the dissolving solvent is 10% to 70%, preferably 20% to 65%, very preferably 30% to 65%, or even 35% to 65%.

[0056] For each considered static or dynamic mixer, the volume-based dilution with the dissolving solvent is the ratio of the volume flow rate of the fraction of at least said part of the dissolving solvent fed to the considered static or dynamic mixer to the sum of the volume flow rates of the fraction of at least said part of the dissolving solvent and the plastic stream fed to the considered static or dynamic mixer.

[0057] The contact section may include a device for at least partially melting the plastic raw material upstream of the first static or dynamic mixer, which melting device feeds the plastic raw material and optionally also feeds a fraction of at least said part of the dissolving solvent, for example 0.02% to 4.0% by weight, or even 0.1% to 1.0% by weight, based on the total weight of the dissolving solvent introduced in step a).

[0058] ii) A dissolving section, which feeds at least the modulated raw material obtained from the contact section and optionally another part of the dissolving solvent, and operates at a dissolving temperature of 100°C to 300°C, preferably 150 to 250°C and at a dissolving pressure of 1.0 to 100.0 MPa absolute, preferably 1.0 to 25.0 MPa absolute, preferably 1.5 to 18.0 MPa absolute and very preferably 2.0 to 15.0 MPa absolute; and then

[0059] b) A step of purifying the crude polymer solution, which comprises:

[0060] b1) A sub-step of separating out insolubles to obtain at least one clarified polymer solution and an insoluble fraction; and / or

[0061] b2) A washing sub-step, by contacting with a high-density solution, to obtain at least one washing effluent and a washed polymer solution; and / or

[0062] b3) An extraction sub-step, by contacting with an extraction solvent, to obtain at least one extracted polymer solution and a spent solvent; and / or

[0063] b4) An impurity adsorption sub-step, by contacting with a solid adsorbent, to obtain at least one refined polymer solution;

[0064] The purification step can obtain a purified polymer solution, which advantageously corresponds to the clarified polymer solution or the washed polymer solution or the extracted polymer solution or the refined polymer solution; and then

[0065] c) A solvent-polymer separation step to obtain at least one fraction of purified thermoplastic polymer, more specifically at least one fraction of purified polyolefin.

[0066] Raw materials

[0067] The raw material according to the method of the present invention, called plastic raw material, contains plastics, which itself more specifically contains thermoplastic polymers, such as polyolefins. Preferably, the plastic raw material contains 50% to 100% by weight and preferably 70% to 100% by weight of plastics.

[0068] The plastics included in the raw material according to the method of the present invention are usually production wastes and / or "post-consumer" waste plastic products, especially household plastic wastes, plastic wastes from the construction industry, plastic wastes from motor vehicles or from any type of transportation or electrical and electronic equipment wastes. Preferably, the plastic wastes are derived from collection and sorting channels. The plastics or plastic materials contain polymers mixed with additives to endow the materials with specific properties for the purpose of forming various products (injection molded parts, pipes, films, fibers, fabrics, mastics, coatings, etc.) after plastic shaping. The additives used in plastics can be organic compounds or inorganic compounds. For example, they are fillers, colorants, pigments, plasticizers, property modifiers, flame retardants, etc.

[0069] The starting materials according to the method of the present invention especially contain thermoplastic polymers, preferably at least 50% by weight, preferably at least 70% by weight, preferably at least 80% by weight, and very preferably at least 90% by weight of thermoplastic polymers. The thermoplastic polymers included in the plastic starting materials can be olefin polymers, diolefin polymers, vinyl polymers, and / or styrene polymers. Preferably, the thermoplastic polymers included in the plastic starting materials are polyolefins, such as polyethylene (PE), polypropylene (PP), and / or copolymers of ethylene and propylene, or mixtures thereof. Preferably, the plastic starting materials contain at least 80% by weight, preferably at least 85% by weight, and preferably at least 90% by weight of polyolefins based on the total weight of the plastic starting materials. Therefore, the method according to the present invention most specifically relates to purifying and recovering the polyolefins contained in the starting materials so as to be able to reuse them in various applications.

[0070] The plastic starting materials can contain mixtures of polymers (especially mixtures of thermoplastics and / or mixtures of thermoplastics and other polymers), additives advantageously used for formulating plastic materials, and impurities usually related to the use (which originate from the life cycle of plastic materials and products, and / or from waste collection and sorting channels, and these compounds are collectively referred to as impurities). The starting materials according to the method of the present invention usually contain less than 50% by weight of impurities, preferably less than 20% by weight of impurities, preferably less than 10% by weight of impurities. The plastic starting materials can contain, for example, at least 1% by weight of impurities, or even at least 5% by weight of impurities.

[0071] The plastic starting materials can be advantageously pretreated before the method in order 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, even greater than or equal to 1 mm, such as impurities like wood, paper, biomass, iron, aluminum, glass, etc., and shape them, usually in the form of dispersed solids, in order to facilitate the treatment in the method. The pretreatment can include a grinding step, a washing step under atmospheric pressure, and / or a drying step. The pretreatment can be carried out at different sites, for example, at a waste collection and sorting center, or at the same site where the treatment method according to the present invention is carried out. Preferably, the pretreatment can reduce the impurity content to less than 20% by weight, preferably less than 15% by weight, more preferably less than 10% by weight, and this percentage is given based on the weight of the plastic starting materials treated by the method according to the present invention. At the end of the pretreatment, the starting materials are usually stored in the form of dispersed solids (such as in the form of ground materials, flakes or powders, or granules) in order to facilitate their treatment and transportation to the method.

[0072] Dissolution step a)

[0073] According to the present invention, the method comprises a dissolution step a), in which a plastic raw material is brought into contact with a dissolution solvent and which contains a thermoplastic, advantageously for the separation and purification of the thermoplastic; specifically, the polyolefin contained therein is dissolved in the dissolution solvent to obtain at least one (preferably one) crude polymer solution. Subsequently, the dissolution step a) involves: i) a section in which the plastic raw material is brought into contact with some or all of the dissolution solvent, the contact being advantageously carried out by gradually introducing the dissolution solvent; and ii) a dissolution section in which at least part of the plastic raw material, preferably at least part of the target thermoplastic, preferably all of the target thermoplastic, in particular the target polyolefin, is dissolved in the dissolution solvent. The contact section and the dissolution section can be separate and consecutive sections, with the contact section preceding the dissolution section, or combined and simultaneous sections.

[0074] The term "dissolution" should be understood to mean any phenomenon that results in the production of at least one thermoplastic polymer solution (i.e., a liquid (or fluid) containing the target thermoplastic polymer dissolved in the dissolution solvent). Those skilled in the art are well aware of the phenomena involved in polymer dissolution, and it involves at least the mixing, solvation, dispersion, homogenization, and disentangling of thermoplastic polymer chains.

[0075] During and at the end of the dissolution step a), the pressure and temperature conditions are such that the dissolution solvent can be maintained at least partially and preferably completely in liquid form or optionally in supercritical form, while the soluble fraction of the plastic raw material, in particular the target thermoplastic polymer, and most particularly the target polyolefin, and also, for example, at least part of the impurities, are advantageously at least partially and preferably completely dissolved in the dissolution solvent.

[0076] The dissolving solvent is an organic solvent or a mixture of organic solvents. Advantageously, the dissolving solvent comprises at least one, preferably aliphatic and in particular paraffinic (i.e., saturated), preferably straight-chain or branched hydrocarbon-based compound, preferably consisting of it. Preferably, the dissolving solvent comprises at least 80% by weight, preferably at least 95% by weight, preferably at least 98% by weight of at least one, preferably aliphatic and in particular paraffinic, preferably straight-chain or branched hydrocarbon-based compound, this percentage being expressed relative to the total weight of the dissolving solvent (100% being the maximum). Preferably, the dissolving solvent comprises at least one, preferably aliphatic and in particular paraffinic, hydrocarbon-based compound having a boiling point of -50°C to 250°C, preferably -15°C to 150°C, preferably -1°C to 110°C and preferably 20°C to 100°C (at atmospheric pressure, in particular at 0.1 MPa). Preferably, the dissolving solvent comprises at least one, preferably aliphatic and in particular paraffinic, preferably straight-chain or branched hydrocarbon-based compound (which contains 3 to 12, preferably 4 to 8 carbon atoms), preferably consisting of it. For example, the dissolving solvent comprises compounds selected from the isomers of butane, pentane, hexane, heptane and octane. The dissolving solvent may comprise a mixture of isomers of butane, pentane, hexane, heptane and / or octane, preferably consisting of it, and preferably the content of the mixture in the dissolving solvent is greater than or equal to 80% by weight, preferably greater than or equal to 95% by weight, preferably greater than or equal to 98% relative to the total weight of the dissolving solvent. Very advantageously, the preferred hydrocarbon-based compound for the dissolving solvent comprises a paraffinic aliphatic compound having a critical temperature of preferably 95 to 350°C, preferably 130 to 300°C, preferably 180 to 285°C (the temperature of the pure hydrocarbon-based compound at the critical point).

[0077] Preferably, in the dissolving step a), the plastic raw material and the dissolving solvent are fed in a weight ratio between the dissolving solvent and the plastic raw material of 0.2 to 100.0, preferably 0.3 to 20.0, preferably 1.0 to 10.0, and even more preferably 3.0 to 7.0.

[0078] Advantageously, the dissolving solvent fed to the dissolving step a) is in liquid or optionally supercritical form. Advantageously, it can be preheated, preferably to a temperature of 100°C to 300°C, preferably 150°C to 250°C, before being introduced into step a), especially before being introduced into the contact section and optionally the dissolving section, in order to promote the heating of the plastic raw material and / or the temperature drop of the material stream in the contact section and optionally the dissolving section of step a).

[0079] Advantageously, the dissolving solvent comprises a make-up of fresh solvent and / or a recycled solvent stream obtained from subsequent steps of the process, preferably at least partially obtained from the solvent-polymer separation step c), and preferably consists of it.

[0080] i) Contact section:

[0081] According to the present invention, the section where the plastic raw material is brought into contact with at least a part of the dissolving solvent includes at least one static or dynamic mixer, preferably one to ten, preferably two to six, very preferably two to five static or dynamic mixers, preferably static mixers. When the contact section contains several (i.e., at least two) static or dynamic mixers, the static or dynamic mixers are advantageously connected in series (or continuously) with each other. Advantageously, each static or dynamic mixer operates at a temperature preferably of 100°C to 300°C, preferably 150°C to 250°C.

[0082] Each static or dynamic mixer feed comprises a plastic stream containing the plastic raw material and a fraction of the dissolution solvent that dissolves at least said part (i.e., the fraction of the dissolution solvent fed to contact zone i), preferably all of the fraction), such that in each mixer, the volume-based dilution with the dissolution solvent is from 3% to 70%. According to the invention, the volume-based dilution with the dissolution solvent in a static or dynamic mixer corresponds to the ratio of the volume flow rate of the fraction of the dissolution solvent fed to the considered static or dynamic mixer (more precisely, the fraction of this part of the dissolution solvent fed to contact zone i) to the sum of the volume flow rates of the said fraction of the dissolution solvent fed to the considered static or dynamic mixer (i.e., at least this part of the fraction of the dissolution solvent fed to zone i) and the plastic stream. The term "plastic stream" corresponds to any stream in contact zone i) of the dissolution step a) that comprises at least the plastic raw material and all of the dissolution solvent part (i.e., at least this part of the fraction of the dissolution solvent fed to this zone i), which is introduced into the contact zone upstream of the considered static or dynamic mixer. In other words, the plastic stream fed to a static or dynamic mixer corresponds to a material stream containing the plastic raw material and preferably consisting of it, the plastic raw material being advantageously at least partially molten and supplemented with all of the dissolution solvent fraction (i.e., at least this part of the fraction of the dissolution solvent fed to zone i), which is introduced into the (one or more) static or dynamic mixer(s) upstream of the considered static or dynamic mixer and optionally into a device for at least partially melting the plastic raw material that is optionally located upstream of the first static or dynamic mixer. Thus, the plastic stream fed to contact zone i) corresponds to the plastic raw material; the plastic stream at the outlet of contact zone i) corresponds to the conditioned raw material stream and contains the plastic raw material and at least a part of the dissolution solvent. The plastic stream fed to the first static or dynamic mixer contains the plastic raw material in molten form (or at least partially molten form), or a premix containing at least a part of the plastic raw material in molten form and a fraction of the dissolution solvent, consisting especially of it: then the plastic stream fed to the first static or dynamic mixer is especially in the form of a viscous fluid. The expression "viscous fluid" means that the considered stream is a fluid having a certain viscosity (especially dynamic viscosity), typically from 0.5 to 20000 Pa·s, or even more particularly from 1.0 to 4000 Pa·s. The said viscosity, especially the dynamic viscosity, is measured at a temperature of 200 °C and a shear rate of 0.1 s -1 using a viscometer, preferably a plate viscometer (e.g., type DHR3 from TA Instruments).

[0083] Preferably, the volume-based dilution with the dissolution solvent in each static or dynamic mixer comprises:

[0084] - When the viscosity ratio between the plastic stream fed to the static or dynamic mixer under consideration and at least this part of the fraction of the dissolving solvent (i.e., the fraction fed to section i)) of the dissolving solvent is greater than or equal to 3500, preferably greater than or equal to 3000, the volume-based dilution of the dissolving solvent is 3% - 50%, preferably 10% - 35%, and very preferably 15% - 30%.

[0085] - When the viscosity ratio between the plastic stream fed to the static or dynamic mixer under consideration and the fraction of the dissolving solvent (i.e., the fraction fed to section i)) of the dissolving solvent is less than 3500, preferably less than 3000, the volume-based dilution of the dissolving solvent is 10% - 70%, preferably 20% - 65%, very preferably 30% - 65%, or even 35% - 65%.

[0086] Preferably, the dissolving solvent fed to dissolving step a) is divided into n sub-streams of the dissolving solvent, where n is an integer equal to m or equal to m + 1 or m + 2, and m is an integer equal to the number of static or dynamic mixers used in contacting section i). One of the sub-streams of the dissolving solvent is fed to each static or dynamic mixer, such that in each static or dynamic mixer, the volume-based dilution of the dissolving solvent is 3% - 70%, and preferably:

[0087] - When the viscosity ratio between the plastic stream fed to the static or dynamic mixer under consideration and the sub-stream of the dissolving solvent (i.e., the fraction of the dissolving solvent) is greater than or equal to 3500, preferably greater than or equal to 3000, the volume-based dilution of the dissolving solvent is 3% - 50%, preferably 10% - 35%, and very preferably 15% - 30%; or

[0088] - When the viscosity ratio between the plastic stream fed to the static or dynamic mixer under consideration and the sub-stream of the dissolving solvent (i.e., the fraction of the dissolving solvent) is less than 3500, preferably less than 3000, the volume-based dilution of the dissolving solvent is 10% - 70%, preferably 20% - 65%, very preferably 30% - 65%, or even 35% - 65%.

[0089] Optionally, the sub-stream of the dissolving solvent (i.e., the fraction of the dissolving solvent) can be fed to a device for at least partially melting the plastic raw material located upstream of the first static or dynamic mixer, and / or the sub-stream of the dissolving solvent (i.e., the fraction of the dissolving solvent) can be directly fed to dissolving section ii).

[0090] Each static or dynamic mixer is preferably implemented with a residence time of less than or equal to 20 minutes, preferably from 0.01 seconds to 20 minutes, preferably from 0.1 seconds to 10 minutes, preferably from 0.5 seconds to 5 minutes, which residence time is defined herein as the ratio between the volume of liquid (or viscous fluid) in the considered static or dynamic mixer relative to the sum of the volume flows of the plastic stream and the dissolved solvent fraction fed to the considered static or dynamic mixer.

[0091] According to a specific embodiment of the invention, the contacting section i) may further comprise means for at least partially melting the plastic raw material, preferably at least partially melting the target thermoplastic, preferably completely melting the target thermoplastic. When the contacting section comprises means for at least partially melting the plastic raw material, said means are located upstream of the (one or more) static or dynamic mixers, preferably upstream of the first static or dynamic mixer of the series. Preferably, the means for at least partially melting the polyester raw material is a single-screw or twin-screw extruder.

[0092] Advantageously, the device for at least partially melting the plastic starting material allows the mixing and at least partial melting of the plastic starting material, and more particularly, at least partial melting, preferably complete melting, of the target thermoplastic of the plastic starting material. Thus, the melting device (preferably the extruder) is advantageously used at a temperature of from 100 °C to 300 °C, preferably from 150 °C to 250 °C. Accordingly, the plastic starting material is fed to the optional melting device (such as an extruder), in which the plastic starting material is advantageously heated to a temperature of from 100 °C to 300 °C, preferably from 150 °C to 250 °C, and particularly to a temperature close to or even slightly above the melting point of the target thermoplastic (such as the target polyolefin), so as to be in the form of a viscous fluid at the outlet of the melting device. When introduced into the melting device, the plastic starting material may already be at a temperature of from 100 °C to 300 °C, preferably from 150 °C to 250 °C, or at ambient temperature, such as from 10 °C to 30 °C. Accordingly, the plastic starting material is advantageously heated to or maintained at a temperature of from 100 °C to 300 °C, preferably from 150 °C to 250 °C, in the melting device in order to at least partially melt. Very advantageously, at least 70% by weight of the plastic starting material, preferably at least 80% by weight of the plastic starting material, preferably at least 90% by weight of the plastic starting material is in the form of a viscous fluid at the outlet of the melting device (such as an extruder). Thus, when integrated into the contact section, the device for at least partially melting the plastic starting material feeds the plastic starting material, for example in the form of solid particles, and a stream in the form of a viscous fluid can be obtained, which generally has a dynamic viscosity of from 0.5 to 20,000 Pa·s, or even more particularly from 1.0 to 3,000 Pa·s. The optional device for at least partially melting the plastic starting material advantageously brings the plastic starting material to a temperature of from 100 °C to 300 °C, preferably from 150 °C to 250 °C and to a pressure of preferably atmospheric pressure (i.e. 0.1 MPa) to 20 MPa absolute pressure, preferably from 0.15 MPa to 15 MPa absolute pressure, under which conditions the plastic starting material is advantageously at least partially melted, and particularly under these conditions, the target thermoplastic comprised in the plastic starting material is at least partially melted, preferably completely melted.

[0093] The feeding of the plastic starting material to the melting device can advantageously be carried out by any method known to the person skilled in the art, such as via a feed hopper, and it can be inerted in order to limit the introduction of oxygen into the process.

[0094] According to a very particular embodiment of the present invention, the contacting section comprises a melting device, preferably an extruder, which feeds the plastic raw material and which can also feed a fraction of the solvent for dissolution, which can contribute to reducing the viscosity of the plastic stream at the outlet of said device, and thus participate in the overall homogenization of the at least partially molten plastic raw material with the solvent for dissolution, and advantageously allows the degradation of the target thermoplastic, in particular the target polyolefin, to be limited. Another advantage of this very particular embodiment lies in fact in the fact that this embodiment (i.e., introducing a fraction of the solvent for dissolution into the melting device) can improve the efficiency of the mixer, in particular the efficiency of the first mixer, and thus can reduce the number of static or dynamic mixers required to achieve a dynamic viscosity of the conditioned raw material stream (i.e., the mixture [plastic raw material + solvent for dissolution] at the end of the contacting section) of less than or equal to 50 mPa·s, preferably less than or equal to 20 mPa·s, very preferably less than or equal to 5 mPa·s, very preferably less than or equal to 1 mPa·s, and very advantageously, the coefficient of variation of concentration (CoV) is preferably less than or equal to 10%, preferably less than or equal to 5%. When introducing a fraction of the solvent for dissolution into the device for at least partially melting the plastic raw material, the amount of the fraction of the solvent for dissolution fed to said device is preferably adjusted such that the weight ratio between the fraction of the solvent for dissolution fed to said device and the plastic raw material fed to said device is from 0.001 to 0.20000, preferably from 0.001 to 0.100, more preferably from 0.003 to 0.050, very preferably from 0.005 to 0.030. For example, when introducing a fraction of the solvent for dissolution into the device for at least partially melting the plastic raw material, the amount of the fraction of the solvent for dissolution fed to said device preferably corresponds to 0.02% to 4.0% by weight, or even 0.1% to 1.0% by weight, of the total weight of the solvent for dissolution introduced in step a).

[0095] Preferably, the residence time in the device for at least partially melting the plastic raw material (optionally applied in the contacting section i) is advantageously less than or equal to 1 hour, preferably less than or equal to 5 minutes, preferably less than or equal to 2 minutes, and preferably greater than or equal to 0.5 second, preferably greater than or equal to 1 second, very preferably greater than or equal to 10 seconds. The residence time is defined herein as the available volume in the device divided by the volume flow rate of the plastic raw material.

[0096] The possible device for at least partially melting the plastic raw material can advantageously be connected to a vacuum extraction system in order to remove impurities present in the raw material, such as dissolved gases, light organic compounds and / or moisture.

[0097] The possible melting device (preferably an extruder) may also advantageously include a filtration system at the outlet, thus allowing the removal of solid particles larger than 20 μm and preferably smaller than 2 cm, such as sand, wood chips or metal particles. For example, the device (preferably an extruder) for at least partially melting the plastic raw material is directly connected to a first filtration system (especially a filter) at the outlet, which is suitable for removing solid particles with a size generally greater than or equal to 1000 μm, preferably greater than or equal to 500 μm, preferably greater than or equal to 400 μm, preferably greater than or equal to 300 μm. Subsequently, a melt pump or a gear pump is provided to maintain and / or increase the pressure, followed by a second filtration system, which is suitable for removing solid particles with a size generally greater than or equal to 60 μm, preferably greater than or equal to 20 μm.

[0098] At the end of the contact section i), i.e., at the outlet of the last static mixer, the obtained plastic stream advantageously corresponds to the modulated raw material, which is very advantageously in liquid form and preferably has a viscosity less than or equal to 50 mPa·s, preferably less than or equal to 20 mPa·s, very preferably less than or equal to 5 mPa·s, very preferably less than or equal to 1 mPa·s. Very advantageously, at the end of the contact section, the modulated raw material also has a coefficient of variation of concentration (CoV) preferably less than or equal to 10%, preferably less than or equal to 5%.

[0099] The modulated raw material can then be defined as a homogeneous mixture, which contains a polymer solution of a thermoplastic (especially a polyolefin, and more particularly polypropylene and / or polyethylene) in a dissolving solvent, preferably at a weight ratio of the dissolving solvent to the plastic raw material of 0.2 to 100.0, preferably 0.3 to 20.0, preferably 1.0 to 10.0, even more preferably 3.0 to 7.0, and contains soluble and / or insoluble impurities, and the homogeneous mixture has a viscosity less than or equal to 50 mPa·s, preferably less than or equal to 20 mPa·s, very preferably less than or equal to 5 mPa·s, very preferably less than or equal to 1 mPa·s.

[0100] ii) Dissolution section:

[0101] The modulated raw material obtained from the contact section is fed to the dissolution section in dissolution step a). The dissolution section may also be fed with a portion of the dissolving solvent, especially when not all of the dissolving solvent has been introduced into the contact section i). The stream recovered at the outlet of the dissolution section corresponds to a polymer solution, especially a crude polymer solution.

[0102] Very advantageously, the dissolution section operates at a dissolution temperature of from 100 °C to 300 °C, preferably from 150 °C to 250 °C, and a dissolution pressure of from 1.0 to 100.0 MPa absolute pressure, preferably from 1.0 to 25.0 MPa absolute pressure, preferably from 1.5 to 18.0 MPa absolute pressure and very preferably from 2.0 to 15.0 MPa absolute pressure. The temperature and pressure in the dissolution section can vary from the introduction conditions of the conditioned feedstock from the contacting section and / or the dissolution solvent fraction that may be introduced into the dissolution section until the dissolution conditions are reached, i.e., the dissolution temperature, in particular from 100 to 300 °C, preferably from 150 to 250 °C, and the dissolution pressure, in particular from 1.0 to 100.0 MPa absolute pressure, preferably from 1.0 to 25.0 MPa absolute pressure, preferably from 1.5 to 18.0 MPa absolute pressure, and very preferably from 2.0 to 15.0 MPa absolute pressure. Very advantageously, at the end of the dissolution section, the crude polymer solution is at the dissolution temperature and the dissolution pressure.

[0103] Limiting the temperature in the dissolution section and more generally in dissolution step a) to a temperature of less than or equal to 300 °C, preferably less than or equal to 250 °C, makes it possible to avoid or limit the thermal degradation of the thermoplastic, and more particularly of the polyolefin, and also makes it possible to limit the energy requirement of the process, thus contributing to limiting the operating costs of the process. Advantageously, the dissolution temperature is greater than or equal to the melting point of the thermoplastic, and more particularly of the polyolefin, in order to promote its dissolution and very advantageously to shorten the residence time required for efficient dissolution of the target thermoplastic. Preferably, the temperature in the dissolution section and more generally in dissolution step a) is less than or equal to the critical temperature of the dissolution solvent in order to avoid the formation of a supercritical phase during dissolution step a), which is liable to disrupt the dissolution.

[0104] At the same time, the dissolution pressure in the dissolution section is higher than the saturated vapour pressure of the dissolution solvent at the dissolution temperature, such that the dissolution solvent is at least partially, and preferably entirely, in liquid or optionally supercritical form at the dissolution temperature, thereby optimizing the dissolution of the target thermoplastic, and more particularly of the polyolefin, especially in terms of quality and operating time.

[0105] Very advantageously, the dissolution temperature and dissolution pressure conditions reached in dissolution section ii) are adjusted such that the mixture (dissolution solvent + target thermoplastic) is single-phase at the end of step a), said mixture possibly containing insoluble impurities suspended in the mixture.

[0106] Advantageously, dissolution section ii) operates with a residence time of from 1 to 600 minutes, preferably from 2 to 300 minutes, preferably from 5 to 180 minutes. In this case, the residence time should be understood as the residence time at the dissolution temperature and the dissolution pressure, i.e., in the dissolution section, the time during which the dissolution solvent acts on the plastic feedstock at the dissolution temperature and the dissolution pressure.

[0107] The dissolution section ii) can employ different types of equipment, such as mixing, conveying, heating devices, and for example, reactors, pumps, conveying circuits, stirring systems, furnaces, exchangers, mixers, etc.

[0108] According to a particular embodiment, the dissolution section employs a continuous stirred tank reactor (CSTR) or a series of continuous stirred tank reactors (CSTR), which series may comprise two to five CSTRs, preferably two or three CSTRs, and each continuous stirred tank reactor (CSTR) advantageously comprises a mechanical stirring system. In fact, according to the method of the present invention, a conditioned feedstock is obtained that comprises, in particular, the contacting section as described above and that enables a viscosity of preferably less than or equal to 50 mPa·s, preferably less than or equal to 20 mPa·s, very preferably less than or equal to 5 mPa·s, very preferably less than or equal to 1 mPa·s, which allows for the use of reasonable (i.e., limited) mechanical stirring power in the dissolution reactor, thus facilitating the operability of the dissolution section, while at the same time limiting the costs required for its implementation, and while ensuring the best homogenization of the mixture and the maximum dissolution of the target thermoplastic in the plastic raw material in the dissolution solvent.

[0109] The dissolution section can employ any reactor stirred by any stirring system. In fact, at the end of the contacting section i), a conditioned feedstock is obtained that has a viscosity of preferably less than or equal to 50 mPa·s, preferably less than or equal to 20 mPa·s, very preferably less than or equal to 5 mPa·s, very preferably less than or equal to 1 mPa·s and, very advantageously, a coefficient of variation of concentration (CoV) of preferably less than or equal to 10%, preferably less than or equal to 5%, which allows for the use of reasonable (i.e., limited) stirring power in the dissolution reactor, thus facilitating the operability of the dissolution section, which allows for the use of any stirring system, while advantageously allowing for a shortening of the mixing time (i.e., the residence time in the dissolution section) and / or the use of a wide range of operating pressures, and while ensuring the best homogenization of the mixture and thus the maximum dissolution of the target thermoplastic in the plastic raw material in the dissolution solvent.

[0110] Optionally, an adsorbent can be introduced into the polymer solution in the dissolution section ii), particularly in the dissolution reactor, and the adsorbent is advantageously a solid, preferably in the form of shaped or unshaped dispersed particles. In this case, the purification method includes an intermediate adsorption step a') during the dissolution step a). The adsorbent is preferably selected from alumina, silica, silica-alumina, activated carbon, or decolorizing earth. Subsequently, the solid adsorbent can be removed during the purification step b), for example, during the sub-step b1) of separating the insoluble matter and / or the washing sub-step b2). This optional adsorption step a') in the presence of the solid adsorbent in dispersed form can optimize the purification of the polymer solution.

[0111] According to a preferred embodiment of the present invention, the dissolution step a) is carried out: i) a section where the plastic raw material is brought into contact with at least a part of the dissolution solvent, the dissolution solvent having a boiling point of -50°C to 250°C, preferably -15°C to 150°C, preferably 20°C to 100°C; and ii) a dissolution section. In this preferred embodiment, the contact section i) operates at a temperature of 150°C to 250°C and uses an extruder, optionally with a filtration system at the extruder outlet, and then three, four or five static mixers are operated in series with each other, and the dissolution section ii) uses a continuously stirred tank reactor with mechanical stirring (i.e., of the CSTR type), operating at a temperature of 150 to 250°C and a pressure of 1.5 to 18.0 MPa absolute pressure. The dissolution solvent is divided into n sub-streams of the dissolution solvent, where n is a natural number, and the number n of the sub-streams of the dissolution solvent is equal to the number m of the static mixers used in the contact section i) (in this embodiment, m is an integer equal to three, four or five) or equal to m + 1 or m + 2. In this embodiment, the plastic raw material is fed into the extruder to obtain a plastic stream composed of at least partially molten plastic raw material, where the target thermoplastic in the plastic raw material, in particular the target polyolefin, is advantageously molten, and optionally one of the sub-streams of the dissolution solvent is fed into the extruder, such that the weight ratio between the dissolution solvent fraction fed into the extruder (i.e., the sub-stream of the dissolution solvent) and the plastic raw material fed into the extruder is, for example, 0.001 to 0.200, preferably 0.001 to 0.100, preferably 0.003 to 0.050, very preferably 0.005 to 0.030. For example, such that the sub-stream of the dissolution solvent fed into the extruder preferably accounts for 0.02 wt% to 4.0 wt%, or even 0.1 wt% to 1.0 wt% of the total weight of the dissolution solvent introduced in step a). In this preferred embodiment, each static mixer is fed with the plastic stream and one of the sub-streams of the dissolution solvent, such that in each static mixer, the volume-based dilution with the dissolution solvent comprises:

[0112] - When the viscosity ratio between the plastic stream fed into the considered static mixer and the sub-stream of the dissolution solvent is greater than or equal to 3500, preferably greater than or equal to 3000, the volume-based dilution with the dissolution solvent is 3% - 50%, preferably 10% - 35%, and very preferably 15% - 30%;

[0113] - When the viscosity ratio between the plastic stream fed into the considered static mixer and the sub-stream of the dissolution solvent is less than 3500, preferably less than 3000, the volume-based dilution with the dissolution solvent is 10% - 70%, preferably 20% - 65%, very preferably 30% - 65%, or even 35% - 65%.

[0114] Preferably, in this preferred embodiment, the residence time in the extruder (defined as the volume available in the extruder divided by the volumetric flow rate of the feedstock) is from 0.5 seconds to 1 hour, preferably from 0.5 seconds to 5 minutes, more preferably from 1 second to 2 minutes, or from 10 seconds to 2 minutes.

[0115] Then, a plastic stream obtained from the last static mixer of the contacting section i) is fed to the dissolution section ii), in particular a CSTR-type reactor, of this same preferred embodiment, and optionally a sub-stream of the dissolution solvent is also fed.

[0116] The polymer solution obtained at the end of the dissolution step a) (advantageously referred to as the "crude" polymer solution) contains at least the dissolution solvent and the polymer dissolved in this dissolution solvent (in particular the target thermoplastic polymer that the present invention seeks to recover and purify). Generally, the polymer solution obtained at the end of the dissolution step a) also contains soluble impurities that are also dissolved in the dissolution solvent. It may also optionally contain insoluble impurities in suspension. The polymer solution obtained at the end of step a) (advantageously referred to as the "crude" polymer solution) may also optionally contain polymers other than the target polymer, for example in molten form.

[0117] Step b) for purifying the polymer solution

[0118] The treatment method according to the present invention comprises a step of purifying the crude polymer solution obtained from step a). This purification step b) comprises at least one of the following sub-steps b1), b2), b3) and b4):

[0119] b1) A sub-step of separating out insolubles,

[0120] b2) A washing sub-step, carried out by contacting with a high-density solution;

[0121] b3) An extraction sub-step, carried out by contacting with an extraction solvent,

[0122] b4) An impurity adsorption sub-step, carried out by contacting with a solid adsorbent.

[0123] Preferably, the purification step b) includes at least one sub-step b1) of separating insoluble matters. The purification step b) preferably includes several (i.e., at least two) sub-steps (in sequence) selected from sub-step b1), sub-step b2), sub-step b3) and sub-step b4), and preferably includes at least one sub-step b1) of separating insoluble matters and, for example, one adsorption sub-step b4), very preferably in this order. The combination of at least two sub-steps selected from b1), b2), b3) and b4) advantageously allows for the optimal purification of the polymer solution. The polymer solution obtained at the end of step b) is a purified polymer solution and contains the target thermoplastic dissolved in the dissolution solvent. The purified polymer solution can correspond to a clarified polymer solution obtained from the sub-step b1) of separating insoluble matters, a washed polymer solution obtained from the washing sub-step b2), an extracted polymer solution obtained from the extraction sub-step b3), or a refined polymer solution obtained from the sub-step b4) of adsorbing impurities.

[0124] Sub-step b1) for separating insoluble matters

[0125] The purification method may include a sub-step b1) of separating insoluble matters by solid-liquid separation to advantageously obtain at least one clarified polymer solution and preferably obtain an insoluble fraction. The insoluble fraction advantageously contains at least a part, and preferably all, of the insoluble impurities, especially those suspended in the crude polymer solution obtained from step a).

[0126] Thus, the sub-step b1) of separating insoluble matters makes it possible to remove at least a part, preferably all, of the insoluble impurity particles in the dissolution solvent, which are suspended in the crude polymer solution obtained from step a). The insoluble impurities removed during the sub-step b1) of separating insoluble matters are, for example, pigments, mineral compounds, packaging residues (glass, wood, cardboard, paper, aluminum), and insoluble polymers.

[0127] When performing this separation sub-step b1), in addition to removing at least a part of the insoluble impurities, advantageously, this separation sub-step b1) makes it possible to limit the operational problems of downstream method steps, especially such as clogging and / or corrosion, while contributing to the purification of the plastic raw material.

[0128] The sub-step b1) of separating insoluble matters is advantageously carried out at a temperature of 100 °C to 300 °C, preferably 150 °C to 250 °C, and at an absolute pressure of 1.0 to 100.0 MPa, preferably 1.0 to 25.0 MPa, preferably 1.5 to 18.0 MPa, and very preferably 2.0 to 15.0 MPa. Very advantageously, the sub-step b1) of separating insoluble matters is carried out under 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.

[0129] When the sub-step b1) of separating the insoluble matter is incorporated into the process, it preferably feeds the crude polymer solution obtained from step a). According to another embodiment, the sub-step b1) can feed the washed polymer solution obtained from the washing sub-step b2).

[0130] Advantageously, the sub-step b1) includes a section comprising at least one solid-liquid separation device, said separation device being selected, for example, from separation vessels, decanters, centrifugal decanters, centrifuges, filters, sand filters, in particular tangential filters using membranes and / or depth filters (optionally in the presence of a filter aid such as diatomaceous earth), hydrocyclones, electrostatic separators, triboelectric separators, preferably decanters, filters, sand filters and / or electrostatic separators. Advantageously, self-cleaning filters can be used, which are cleaned or unblocked using a solvent stream, allowing the removal of insoluble matter.

[0131] The removal of the insoluble fraction can be facilitated by a device for conveying and / or removing trace solvents that may be present in the insoluble fraction, said device being, for example, a conveyor, a vibrating tube, an endless screw, an extruder or a stripper. Thus, the sub-step b1) can include a device for conveying and / or removing trace solvents to remove the insoluble fraction. Advantageously, at least a portion of the solvent recovered in the sub-step b1) is recycled to the process.

[0132] According to a specific embodiment, the sub-step b1) of separating the insoluble matter includes at least two (and generally fewer than five) solid-liquid separation devices in series and / or in parallel. The presence of at least two solid-liquid separation devices in series allows for improved removal of insoluble matter, while the presence of devices in parallel allows for the management of the maintenance of said devices and / or the unblocking operation.

[0133] Certain insoluble impurities, especially certain additives, such as pigments and mineral fillers, which are usually added during the formulation of the polymer, can be introduced in the form of particles with a size less than 1 μm. For example, this is the case for titanium dioxide, calcium carbonate and carbon black. According to a specific embodiment of the sub-step b1), the sub-step b1) of separating the insoluble matter advantageously includes an electrostatic separator, which allows for the efficient removal of at least a portion of the insoluble particles with a size less than 1 μm. According to another specific embodiment of the sub-step b1), the sub-step b1) of separating the insoluble matter includes a sand filter to remove particles of different sizes, and especially particles with a size less than 1 μm. According to yet another specific embodiment of the sub-step b1), the sub-step b1) of separating the insoluble matter involves a tangential filter using membranes and / or depth filters, optionally in the presence of a filter aid such as diatomaceous earth.

[0134] Depending on the nature of the raw materials, the polymer solution (preferably a crude polymer solution) fed to sub-step b1) may also optionally contain a second liquid phase, for example consisting of molten polymer. According to another specific embodiment, sub-step b1) advantageously includes a device for separating out this second liquid phase, preferably by means of at least one two-phase or three-phase separator.

[0135] Sub-step b2) for washing

[0136] The treatment method may also optionally include a washing sub-step b2) with a high-density solution to advantageously obtain at least one washing effluent and a washed polymer solution. The washed polymer solution obtained at the end of sub-step b2) advantageously contains the purified target polymer to be recovered according to the present invention dissolved in the dissolution solvent. Optionally, if sub-step b2) is carried out, the washed polymer solution may also contain residual impurities (which may be particularly soluble in the dissolution solvent) and / or optionally trace amounts of the washing solvent.

[0137] When the washing sub-step b2) and the sub-step b1) of separating out insoluble matter are incorporated into the purification step b), the washing sub-step b2) can be integrated upstream or downstream of the sub-step b1) of separating out insoluble matter, preferably downstream.

[0138] When the washing sub-step b2) is incorporated into the method, the washing sub-step b2) is fed a high-density solution and the crude polymer solution obtained from step a) or from an optional intermediate adsorption step a'), or the clarified polymer solution obtained from b1). The polymer solution fed to the washing sub-step b2), in particular the crude polymer solution or the clarified polymer solution, may contain suspended insoluble impurities and / or dissolved impurities. These suspended or dissolved impurities can be partially or completely removed during the washing sub-step b2) by dissolution or precipitation and / or by entrainment in the said high-density solution. Thus, when the washing sub-step b2) is carried out, this sub-step b2) contributes to the treatment of the plastic raw material, and more specifically, it contributes to the purification of the polymer solution.

[0139] Washing sub-step b2) advantageously involves bringing into contact the crude polymer solution or the clarified polymer solution fed to sub-step b2) with a high-density solution. Advantageously, the high-density solution has a density higher than that of the polymer solution (i.e., a mixture comprising at least the target thermoplastic and the dissolution solvent that dissolves the target thermoplastic), specifically greater than or equal to 0.85, preferably greater than or equal to 0.9, and preferably greater than or equal to 1.0. The high-density solution can be an aqueous solution, which preferably contains at least 50% by weight of water, preferably at least 75% by weight of water, and very preferably at least 90% by weight of water. The pH of this aqueous solution can be adjusted using an acid or a base to promote the dissolution of certain impurities. The high-density solution can also optionally be an organic solvent (e.g., an organic solvent selected from sulfolane or N-methylpyrrolidone (NMP), optionally present in the form of a mixture with water) having a density advantageously greater than or equal to 0.85, preferably greater than or equal to 0.9, more preferably greater than or equal to 1.0, and in which the polymer of the plastic raw material remains insoluble under the temperature and pressure conditions of sub-step b2), preferably a solution composed of it. Very preferably, the high-density solution is an aqueous solution, which preferably contains at least 50% by weight of water, preferably at least 75% by weight of water, and very preferably at least 90% by weight of water.

[0140] Advantageously, washing sub-step b2) is carried out at a temperature of 100 °C to 300 °C, preferably 150 °C to 250 °C, and at an absolute pressure of 1.0 to 100.0 MPa, preferably 1.0 to 25.0 MPa, more preferably 1.5 to 15.0 MPa, and very preferably 2.0 to 15.0 MPa. Very advantageously, washing sub-step b2) is carried out at the dissolution temperature and dissolution pressure.

[0141] In washing sub-step b2), when incorporated into the method, the mass ratio between the mass flow rate of the high-density solution fed to sub-step b2) and the mass flow rate of the crude polymer solution or the clarified polymer solution is advantageously 0.05 to 20.0, preferably 0.1 to 10.0, and more preferably 0.5 to 3.0. The bringing into contact of the crude polymer solution or the clarified polymer solution with the high-density solution can be carried out at several sites of the equipment used, i.e., by injecting the crude polymer solution or the clarified polymer solution and / or the high-density solution several times at different sites along the equipment; then the sum of the injected streams is considered when calculating the ratio.

[0142] Sub-step b2) can be carried out in one or more washing apparatuses such that contact placement can be made with the high-density solution and / or with the separation apparatus, such that at least one washing effluent and one washed polymer solution can be recovered. Such apparatuses are well known, such as stirred reactors, static mixers, decantation mixers, two-phase or three-phase separation vessels, co-current or counter-current washing towers, plate towers, stirred towers, packed towers, pulsed towers, etc., and each type of apparatus may include one or more apparatuses used alone or in combination with another type of apparatus.

[0143] According to a preferred embodiment, the washing sub-step b2) is carried out in a counter-current washing tower, in which on the one hand the high-density solution is injected, preferably into the upper half, preferably the upper third, of the tower closest to the top of the tower, and on the other hand, the crude or clarified polymer solution is injected, preferably into the lower half, preferably the lower third, of the tower closest to the bottom of the tower. According to this embodiment, at least one washed polymer solution and one washing effluent can be recovered.

[0144] According to a very specific embodiment, the streams at the inlet and / or outlet of the washing tower can be separated and injected at several injection points along the tower and / or withdrawn at several withdrawal points along the tower.

[0145] According to another embodiment, the washing sub-step b2) is carried out in a mixer-decanter, which mixer-decanter includes a stirred mixing zone for contact placement of the high-density solution and the crude or clarified polymer solution, and a decantation zone that enables the recovered washed polymer solution and washing effluent.

[0146] At the end of the washing sub-step b2), the obtained washing effluent advantageously contains impurities dissolved in the high-density solvent and / or insoluble compounds entrained in the washing effluent. The washing effluent can be reprocessed in a washing treatment section, on the one hand at least partially separating the dissolved and / or entrained impurities and optionally purifying the washing effluent to obtain a purified high-density solution, and on the other hand at least partially recycling a part of the purified washing solution. This washing treatment section can include one or more well-known apparatuses for solid-liquid separation, such as separation vessels, decanters, centrifugal decanters, centrifuges or filters. When the high-density solution is an aqueous solution, the washing effluent can also be sent out of the method, for example, to a wastewater treatment station.

[0147] Sub-step b3) for extraction

[0148] Step b) of the method according to the invention may include an extraction sub-step b3) carried out by contacting and placing with an extraction solvent to obtain at least one extracted polymer solution and, in particular, a used solvent containing impurities. The extracted polymer solution obtained at the end of sub-step b3) advantageously contains the purified target thermoplastic polymer dissolved in the dissolution solvent that the present invention attempts to recover. Optionally, if sub-step(s) b2) and / or b3) are carried out, the extracted polymer solution may also contain residual impurities that are particularly soluble in the dissolution solvent and / or traces of the washing solution and / or the extraction solvent.

[0149] When the extraction sub-step b3) is integrated into the method according to the invention, the extraction sub-step b3) is advantageously located between the dissolution step a) and the solvent-polymer separation step c), and optionally upstream or downstream of the adsorption sub-step b4) (if the adsorption sub-step b4) is also integrated into step b), and preferably downstream of the sub-step b1) for separating insoluble matter.

[0150] Advantageously, the extraction sub-step b3) feeds the extraction solvent and the polymer solution, in particular the crude polymer solution obtained from step a), the clarified polymer solution obtained from sub-step b1), the washed polymer solution obtained from sub-step b2), or the refined polymer solution obtained from the adsorption sub-step b4). Preferably, the extraction sub-step b3) feeds the extraction solvent and the clarified polymer solution obtained from sub-step b1), the washed polymer solution obtained from sub-step b2), or optionally the refined polymer solution obtained from the adsorption sub-step b4). Thus, the polymer solution fed to sub-step b3), preferably the clarified polymer solution, the washed polymer solution, or the refined polymer solution, may also contain dissolved impurities. These dissolved impurities can be partially or completely removed during the extraction sub-step b3) by contacting and placing with the extraction solvent. Very advantageously, the combination of the extraction sub-step b3) with the sub-step b1) for separating insoluble matter and the optional adsorption sub-step b4) allows for the improvement of the purification of the polymer solution, by optionally taking advantage of the affinity of the impurities for both the adsorbent and the extraction solvent.

[0151] When the extraction sub-step b3) is incorporated into the method according to the invention, the extraction sub-step b3) advantageously involves at least one extraction zone, preferably one to five extraction zones, and very preferably one extraction zone.

[0152] The mass ratio between the mass flow rate of the extraction solvent and the mass flow rate of the polymer solution fed to step b3) (preferably a clarified polymer solution, a washed polymer solution or a refined 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 a clarified polymer solution, a washed polymer solution or a refined polymer solution) fed to sub-step b3) and the extraction solvent can be carried out at several sites in the extraction section, i.e., by injecting the polymer solution and / or the extraction solvent several times at different sites along the extraction section; then the sum of the injected streams is considered when calculating the ratio.

[0153] The extraction solvent used in extraction sub-step b3) advantageously comprises an organic solvent or a mixture of organic solvents. Preferably, the extraction solvent comprises at least one hydrocarbon-based compound which is preferably aliphatic and in particular an alkane (i.e., saturated), preferably straight-chain or branched-chain, and is preferably composed of the same. Preferably, the extraction solvent comprises at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of at least one hydrocarbon-based compound which is preferably aliphatic and in particular an alkane, preferably straight-chain or branched-chain, this percentage being expressed relative to the total weight of the dissolution solvent (100% being the maximum). Preferably, the extraction solvent comprises at least one hydrocarbon-based compound which is preferably aliphatic and in particular an alkane, having a boiling point of -50 °C to 250 °C, preferably -15 °C to 150 °C, preferably -1 °C to 110 °C, and preferably 20 °C to 100 °C (at atmospheric pressure, in particular at 0.1 MPa). Preferably, the extraction solvent comprises at least one aliphatic, and in particular an alkane, preferably straight-chain or branched-chain, hydrocarbon-based compound having 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms, and is preferably composed of the same. For example, the extraction solvent comprises compounds selected from the isomers of butane, pentane, hexane, heptane and octane. The extraction solvent may comprise a mixture of isomers of butane, pentane, hexane, heptane and / or octane, preferably composed of the same, and the content of the mixture of isomers in the extraction solvent is preferably greater than or equal to 80% by weight, preferably greater than or equal to 95% by weight, preferably greater than or equal to 98% by weight relative to the total weight of the extraction solvent. Preferably, the extraction solvent comprises an alkane aliphatic compound having a critical temperature of preferably 95 °C to 350 °C, preferably 130 °C to 300 °C, preferably 180 °C to 285 °C (the temperature of the pure hydrocarbon-based compound at the critical point).

[0154] Very preferably, the extraction solvent used in b3) is the same as the dissolution solvent used in step a), optionally in a different physical state (e.g., the extraction solvent is in a supercritical form relative to the dissolution solvent in liquid form), in order to facilitate the management of the solvent, and in particular the purification and recovery of the solvent, in particular for recycling to the dissolution step a) and optionally to the extraction sub-step b3). In addition to facilitating the management of the solvents involved in the process according to the invention (in particular the recovery of solvents, the treatment of solvents and the recycling of solvents to at least one step of the process), another advantage of using the same dissolution solvent and extraction solvent in the same or different physical states is to limit the energy consumption and in particular the costs generated by the treatment and purification of the solvents.

[0155] The extraction section(s) of b3) may include one or more extraction devices capable of being placed in contact with the extraction solvent and / or with the separation device to recover at least one used solvent, in particular a solvent containing impurities, and the extracted polymer solution. Such devices are well known, such as stirred reactors, static mixers, decantation mixers, two-phase or three-phase separation vessels, co-current or counter-current scrubbing towers, plate columns, stirred columns, packed columns, pulsed columns, etc., and each type of device may include one or more devices used alone or in combination with another type of device.

[0156] According to a preferred embodiment of b3), the extraction is carried out in a counter-current extraction column, into which on the one hand the extraction solvent is injected and on the other hand the polymer solution fed to sub-step b3) is injected. According to this embodiment, on the one hand at least one extracted polymer solution can be recovered and on the other hand a used solvent containing in particular impurities can be recovered. Preferably, the polymer solution fed to b3) (preferably a clarified, washed or refined polymer solution) is injected into the upper half, preferably the upper third, of the column closest to the top of the counter-current extraction column, while the extraction solvent is injected into the lower half, preferably the lower third, of the column closest to the bottom of the counter-current extraction column.

[0157] The streams at the inlet and / or outlet of the counter-current extraction column can be divided into several injection sites and / or withdrawal sites along the column.

[0158] According to another embodiment of b3), the extraction is carried out in a mixer-decanter which advantageously comprises: a stirred mixing zone for bringing the extraction solvent into contact with the polymer solution fed to b3), preferably a clarified, washed or refined polymer solution; and a decantation zone which can recover on the one hand the extracted polymer solution and on the other hand the used solvent.

[0159] Advantageously, the extraction sub-step b3) is carried out under temperature and pressure conditions different from those of the dissolution step a).

[0160] According to a preferred embodiment of b3), the extraction sub-step b3) involves a liquid / liquid extraction section. Preferably, the liquid / liquid extraction section operates at a temperature of from 100 °C to 300 °C, preferably from 150 °C to 250 °C, and at an absolute pressure of from 1.0 to 100.0 MPa, preferably from 1.0 to 25.0 MPa, more preferably from 1.5 to 18.0 MPa, and very preferably from 2.0 to 15.0 MPa. In any case, in this embodiment, the temperature and pressure conditions are adjusted such that the extraction solvent is in liquid form and the dissolution solvent is also preferably in liquid form. Very advantageously, especially when the extraction solvent is the same as the dissolution solvent, the liquid / liquid extraction is carried out under temperature and pressure conditions different from those of the dissolution achieved in step a), in particular at a temperature higher than the dissolution temperature and / or at a pressure lower than the dissolution pressure, so as to be in the two-phase region of the corresponding polymer-solvent phase diagram.

[0161] According to another preferred embodiment of b3), the extraction sub-step b3) includes a section for carrying out the extraction under specific temperature and pressure conditions, wherein the extraction solvent is advantageously at least partially in supercritical form. Such an extraction can be referred to as supercritical extraction. In this embodiment, the extraction is carried out by contacting the polymer solution (preferably a clarified, washed or refined polymer solution) with the extraction solvent, advantageously under temperature and pressure conditions where a supercritical phase mainly (i.e., preferably at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight) composed of the extraction solvent can be obtained. In other words, in this embodiment, the extraction is carried out by bringing the polymer solution (preferably a clarified, washed or refined polymer solution) into contact with an extraction solvent that is at least partially, preferably entirely, in supercritical form. Such a supercritical extraction sub-step b3) advantageously allows for efficient purification of the polymer solution, especially because of the extremely high affinity of organic impurities (such as some additives, especially certain colorants, plasticizers, etc.) for the supercritical phase. Using an extraction solvent in supercritical form may also create a significant density difference between the supercritical phase and the polymer solution in liquid form, which promotes separation by decantation between the supercritical phase and the liquid phase, and thus contributes to the purification of the polymer solution.

[0162] In this another preferred embodiment, the sub-step b3) uses an extraction solvent that comprises at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of at least one chain alkane aliphatic hydrocarbon-based compound (or alkane) (100% being the maximum, the percentage being expressed relative to the total weight of the extraction solvent), which has a critical temperature preferably of from 95 °C to 350 °C, preferably from 130 °C to 300 °C, preferably from 180 °C to 285 °C.

[0163] Advantageously, the supercritical extraction sub-step b3) of this other specific embodiment is carried out at a temperature preferably of 150 °C to 300 °C, preferably 180 °C to 280 °C, and at a pressure preferably of 2.0 to 100.0 MPa absolute pressure, preferably 2.0 to 25.0 MPa absolute pressure, preferably 2.0 to 18.0 MPa absolute pressure, and very preferably 3.0 to 15.0 MPa absolute pressure. Very preferably, the operating pressure of such a supercritical extraction sub-step b3) is 2.7 MPa to 7.5 MPa absolute pressure, preferably 3.0 MPa to 5.5 MPa absolute pressure. In any case, in this embodiment, the temperature and pressure conditions are adjusted, especially in the adjustment section implemented in the extraction sub-step b3) upstream of the extraction section, such that the extraction solvent is at least partially in a supercritical state in the extraction section.

[0164] In a very preferred embodiment of b3), the extraction sub-step b3) comprises supercritical extraction, and the extraction solvent is the same as the dissolution solvent, except for the fact that the extraction solvent is at least partially in a supercritical phase. In such a very advantageous supercritical extraction, the dissolution solvent can become at least partially in a supercritical form, advantageously optimizing the decantation between the liquid phase and the supercritical phase, especially during the extraction step and more particularly during each extraction stage or plateau, so that purification can be maximized.

[0165] Advantageously, at the end of the extraction sub-step b3), the resulting used solvent contains impurities in particular. The solvent can be reprocessed in an organic treatment section, on the one hand, such that the impurities can be at least partially separated out and the solvent purified to obtain a purified extraction solvent; on the other hand, in the case where the dissolution solvent and the extraction solvent are the same, at least a part of the purified extraction solvent is recycled to the inlet of extraction b3), and / or to the inlet of the dissolution step a). The used solvent can be treated according to any method known to those skilled in the art, for example, from one or more of the following methods: distillation, evaporation, extraction, adsorption, crystallization, and precipitation of insoluble substances, or by purging.

[0166] Sub-step b4) for adsorption

[0167] Step b) of the treatment method according to the invention may comprise an adsorption sub-step b4) for obtaining at least one refined polymer solution. The refined polymer solution obtained at the end of the sub-step b4) advantageously contains the purified target thermoplastic polymer dissolved in the dissolution solvent that the present invention attempts to recover.

[0168] When the adsorption sub-step b4) 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). The adsorption sub-step b4) can be carried out upstream of the sub-step b1) for separating insoluble matters and / or the washing sub-step b2), and in particular can correspond to an optional intermediate adsorption step a'). Preferably, the adsorption sub-step b4) is carried out downstream of the sub-step b1) for separating insoluble matters and possibly downstream of the washing sub-step b2), and the washing sub-step b2) itself is preferably carried out downstream of the sub-step b1). The adsorption sub-step b4) can also be carried out upstream or downstream of, for example, the extraction sub-step b3). Thus, when the adsorption sub-step b4) is incorporated into the process according to the invention, the adsorption sub-step b4) is carried out by bringing the polymer solution fed to the adsorption sub-step b4) into contact with one or more adsorbents.

[0169] The adsorption sub-step b4) advantageously includes an adsorption section operating in the presence of at least one adsorbent, which is preferably solid and in particular in the form of a fixed bed, an entrained bed (or slurry, i.e., introduced in particulate form into the stream to be purified and entrained by the stream) or in the form of a fluidized bed, preferably in the form of a fixed bed or an entrained bed. The (one or more) adsorbents used in the sub-step b) are preferably alumina, silica, silica-alumina, activated carbon, decolorizing earth or a mixture thereof, preferably activated carbon, decolorizing earth, or a mixture thereof, preferably in the form of a fixed bed or an entrained bed, and the circulation of the stream can be upward or downward.

[0170] Advantageously, when the adsorption sub-step b4) is incorporated into the process, the adsorption sub-step b4) is carried out at a temperature of 100 °C to 300 °C, preferably 150 °C to 250 °C, and at an absolute pressure of 1.0 to 100.0 MPa, preferably 1.0 to 25.0 MPa, preferably 1.5 to 18.0 MPa, and very preferably 2.0 to 15.0 MPa. Very advantageously, the adsorption sub-step b4) is carried out under the dissolution temperature and pressure conditions, i.e., at the dissolution temperature and dissolution pressure reached in step a). Preferably, in the optional sub-step b4), the space velocity (or HSV), which corresponds to the ratio of the volume flow rate of the polymer solution fed to b4) to the volume of the adsorbent advantageously operating in b4), is 0.05 to 10 h -1 , preferably 0.1 to 5.0 h -1 .

[0171] According to a specific embodiment of sub-step b4), the adsorption section may comprise one or more fixed beds of adsorbent, for example in the form of an adsorption column containing (one or more) adsorbents, preferably at least two adsorption columns, preferably two to four adsorption columns. When the adsorption section comprises two adsorption columns, one operating mode may be the mode called "swing" operation according to the specialized terminology, in which one column is online, i.e., in use, while the other column is standby. When the adsorbent in the online column is exhausted, the column is isolated, and the standby column is put into operation, i.e., in use. Then, the spent adsorbent can be regenerated in situ and / or replaced with fresh adsorbent so that the column containing the adsorbent can be put online again once the other column is isolated.

[0172] Another operating mode of this specific embodiment of b4) is to have at least two columns operating in series. When the adsorbent in the first column in line is exhausted, the first column is isolated, and the spent adsorbent is regenerated in situ or replaced with fresh adsorbent. Subsequently, the column is put back into operation in the last position, and so on. This operating mode is called the permutation mode, or according to the term PRS, it represents a Permutable Reactor System, or also according to the specialized terminology called "lead and lag". The combination of at least two adsorption columns makes it possible to overcome the possible and potential rapid poisoning and / or clogging of the adsorbent due to the combined action of impurities, contaminants, and insolubles that may be present in the stream to be treated. The reason is that the presence of at least two adsorption columns helps with the replacement and / or regeneration of the adsorbent, advantageously without stopping the process, and also makes it possible to control costs and limit the consumption of the adsorbent.

[0173] According to this specific embodiment of the adsorption sub-step b4) carried out in the fixed bed of adsorbent, sub-step b4) is preferably carried out downstream of the sub-step b1) of separating insolubles and / or the washing sub-step b2), and upstream or downstream of the extraction sub-step b3). Advantageously, the combination of the sub-step b1) of separating insolubles and / or the washing sub-step b2) and the extraction sub-step b3) with the adsorption sub-step b4) allows for the improvement of the purification of the polymer solution by using the affinity of the residual impurities for both the adsorbent solid and the extraction solvent and optionally the high-density solution.

[0174] According to another embodiment, the adsorption section b4) may comprise adding adsorbent particles to a polymer solution, in particular a crude polymer solution, and the particles may be separated from the polymer solution by a step of removing the adsorbent particles located downstream of said adsorption section. The removal of the adsorbent particles may then advantageously correspond to the step b1) of separating out the insolubles or the washing step b2). This implementation of the adsorption sub-step b4) by introducing adsorbent particles followed by solid-liquid separation advantageously corresponds to the optional intermediate adsorption step a') previously described in this specification.

[0175] Step c) Solvent-polymer separation

[0176] According to the invention, the process comprises a solvent-polymer separation step c) to obtain at least one purified thermoplastic polymer fraction, more particularly at least one purified polyolefin fraction, and preferably at least one solvent fraction.

[0177] The solvent-polymer separation step c) involves at least partially, preferably mainly, or even completely separating out the (one or more) solvents, in particular the dissolved solvents, contained in the purified polymer solution fed to step c), in order to recover the thermoplastic that has been at least partially, preferably completely, freed from impurities and dissolved solvents and possibly from the (one or more) other solvents (i.e., extraction solvents and / or high-density solutions) used in the process. The term "mainly" should be 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, based on the weight of the (one or more) solvents (in particular the dissolved solvents) contained in the purified polymer solution fed to step c) and on the weight of the optional extraction solvents and / or high-density solutions contained in the purified polymer solution fed to step c). Any method known to those skilled in the art for separating solvents from polymers can be carried out, in particular any method capable of causing a phase change in the polymer or the (one or more) solvents. For example, the (one or more) solvents can be separated out by evaporation, stripping, layering, density difference and in particular decantation or centrifugation. Step c) can be carried out with several separation operations in series. For example, step c) can include solvent-polymer separation carried out by layering at least a part of the (one or more) solvents in supercritical form, after adjusting the temperature and / or pressure conditions in step c), the (one or more) solvents being in supercritical form, preferably adjusting the pressure and maintaining the temperature at 100 to 300 °C, preferably 150 to 250 °C, so that at least one compound of the (one or more) solvents is in supercritical conditions, and then carrying out at least one separation of the residual solvents by evaporation, in particular under pressure conditions lower than the pressure used to transform into the supercritical state of the solvent, in particular at a pressure of 4 to 0.000005 MPa (i.e., 5 Pa), preferably 3 to 0.000005 MPa (i.e., 5 Pa), and the temperature can be maintained at 100 to 300 °C, preferably 150 to 250 °C.

[0178] The purified thermoplastic polymer fraction obtained at the end of step c) can correspond to a concentrated polymer solution or to a purified thermoplastic polymer in liquid (i.e., molten) or solid form. The solvent-polymer separation step c) can also optionally include a conditioning section for conditioning the recovered thermoplastic polymer (in solid form, or more specifically in the form of solid particles). In this possible conditioning section, the recovered purified thermoplastic polymer is cooled, advantageously to a temperature below the melting point of the polymer, in order to obtain a fraction comprising the polymer in solid form.

[0179] The solvent-polymer separation step c) also involves at least partially, preferably predominantly, and preferably entirely recovering the (one or more) solvents, and in particular the dissolution solvent, and optionally the extraction solvent and / or the high-density solution, contained in the purified polymer solution fed to step c). The term "predominantly" should be 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, based on the weight of the (one or more) solvents contained in the purified polymer solution fed to step c). Thus, step c) advantageously 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 dissolution step a), and possibly upstream of sub-step b2) and / or sub-step b3).

[0180] 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 this solvent portion and obtain a purified solvent, in particular a purified dissolution solvent, so that it can advantageously be recycled to the dissolution step a) and / or optionally recycled to the washing sub-step b2) or the extraction sub-step b3). The said optional organic treatment section at the end of step c) can employ any method known to those skilled in the art, such as one or more of distillation, evaporation, liquid-liquid extraction, adsorption, crystallization, and precipitation of insolubles, or by purging.

[0181] Thus, the process according to the invention can obtain a purified thermoplastic polymer (especially polyolefin) stream from plastic waste, which stream can be used in any application, for example to replace the same polymer in its virgin form. The purified polymer stream obtained by the process according to the invention, i.e. the purified thermoplastic polymer fraction, thus has an impurity content low enough to be used in any application. Preferably, the purified thermoplastic polymer stream, especially the purified polyolefin stream (i.e. the purified thermoplastic polymer fraction) obtained at the end of the process according to the invention, advantageously has an impurity content of less than or equal to 5% by weight, very advantageously less than or equal to 1.0% by weight, or even less than or equal to 0.5% by weight. Very advantageously, the purified thermoplastic polymer stream (i.e. the purified thermoplastic polymer fraction) obtained at the end of the process has a residual solvent (especially the dissolution solvent) content, based on the total weight of the thermoplastic polymer stream, of less than or equal to 5% by weight of residual solvent, preferably less than or equal to 1.0% by weight of residual solvent, preferably less than or equal to 0.1% by weight of residual solvent, or even less than or equal to 500 ppm by weight of residual solvent.

[0182] The following examples and figures illustrate the invention, in particular specific embodiments thereof, without limiting its scope.

[0183] List of Drawings

[0184] Figure 1 A flowchart showing an embodiment of the method of the present invention, which includes:

[0185] - Step a) of dissolving plastic raw material 1 in dissolving solvent 19 to obtain crude polymer solution 12, and step a) includes:

[0186] - Section a-i), for bringing plastic raw material 1 into contact with dissolving solvent 19 to obtain conditioned raw material 11, said section a-i) using extruder (A) to obtain at least partially molten plastic raw material 1*, and five static mixers M1, M2, M3, M4, M5, with each mixer fed with a dissolving solvent sub-stream 2, dissolving solvent sub-stream 4, dissolving solvent sub-stream 6, dissolving solvent sub-stream 8, dissolving solvent sub-stream 10 obtained from the total dissolving solvent stream 19 and plastic streams 1*, plastic stream 3, plastic stream 5, plastic stream 7, plastic stream 9

[0187] - Dissolving section a-ii), particularly using a continuous stirred tank reactor of CSTR type, to obtain crude polymer solution 12

[0188] - Purification step b), preferably including separation of insolubles, followed by in particular an adsorption sub-step, to obtain purified polymer solution 13 and insoluble fraction 14

[0189] - Solvent-polymer separation step c), to obtain purified thermoplastic fraction 15, and more specifically purified polyolefin fraction, and solvent stream 16

[0190] This solvent stream 16 is advantageously purified, for example in distillation section d), to recover purified dissolving solvent stream 17, which is mixed with fresh solvent stream 18 to form dissolving solvent 19, and dissolving solvent 19 is divided into five dissolving solvent sub-streams 2, 4, 6, 8, 10 for feeding to static mixers M1, M2, M3, M4, M5 of section a-i) Examples

[0191] Example 1 (According to the present invention)

[0192] In this example, only the contact section i) of the purification method corresponding to the embodiment schematically presented was tested, and the contact section i) of the dissolving step a) includes: Figure 1 - Extruder A, which includes a feed hopper through which plastic raw material from the collection and sorting channel is fed into the extruder; then

[0193] - Extruder A, which includes a feed hopper through which plastic raw material from the collection and sorting channel is fed into the extruder; then

[0194] - Five static mixers M1, M2, M3, M4, M5 in series.

[0195] The plastic raw material contains: 95% by weight of polypropylene; 5% by weight of polyethylene and impurities, especially additives such as pigments, colorants, fillers, etc.

[0196] The contact section operates at a temperature of 200 °C and a pressure of 2.5 MPa (25 bar).

[0197] The flow rate of the plastic raw material introduced into extruder A is 50 kg / h. The raw material 1* is at least partially molten at the outlet of extruder A; more specifically, the polyolefins contained in the raw material and thus at least polypropylene are in a molten state at the outlet of the extruder.

[0198] The dissolution solvent used is n - heptane and a mixture 19 of a purified and recycled n - heptane stream 17 and a fresh n - heptane stream 18. The total flow rate of n - heptane 19 fed to the dissolution step a) is 250 kg / h.

[0199] Each of the static mixers M1, M2, M3, M4, M5 is fed with an n - heptane sub - stream 2, an n - heptane sub - stream 4, an n - heptane sub - stream 6, an n - heptane sub - stream 8, an n - heptane sub - stream 10 respectively, and is fed with a plastic stream 1*, a plastic stream 3, a plastic stream 5, a plastic stream 7, a plastic stream 9 containing at least molten polypropylene respectively. The coefficient of variation of the target concentration at the outlet of each static mixer is 5% (or 0.05).

[0200] Table 1 shows the amount of dissolution solvent introduced into each static mixer and the viscosity changes of the inlet / outlet streams of each static mixer under the operating conditions of this temperature and pressure. Table 1 also gives the viscosity ratio between the plastic stream and the n - heptane stream entering each static mixer, and also the volume - based dilution with n - heptane in each mixer.

[0201] Table 1

[0202]

[0203] At the end of the contact section a - i) of step a) using an extruder and then five static mixers fed with n - heptane sub - streams, the viscosity of the modulated feed stream is less than 1 mPa·s (0.95 mPa·s), while complying with the technical limitations imposed by the static mixer regarding the viscosity of the streams involved. Such a viscosity promotes the subsequent homogenization of the mixture in the CSTR - type dissolution reactor in the dissolution section, and the dissolution reactor is of the CSTR type.

Claims

1. A method for processing plastic raw materials, comprising: a) a step of dissolving the plastic raw materials in a dissolving solvent to obtain at least one crude polymer solution, and the dissolving step a) involves: i) a section for bringing at least a part of the plastic raw materials into contact with the dissolving solvent, which includes at least one static or dynamic mixer to produce a modulated raw material, each static or dynamic mixer operating at a temperature of 100°C to 300°C, and each static or dynamic mixer feeding a plastic stream containing the plastic raw materials and a fraction of at least said part of the dissolving solvent, such that each mixer has a volume-based dilution with the dissolving solvent of 3% to 70%, and the volume-based dilution with the dissolving solvent is the ratio of the volume flow rate of the fraction of at least said part of the dissolving solvent fed to the considered static or dynamic mixer to the sum of the volume flow rates of the fraction of at least said part of the dissolving solvent and the plastic stream fed to the considered static or dynamic mixer; ii) a dissolving section, which feeds at least the modulated raw material obtained from the contact section and operates at a dissolving temperature of 100°C to 300°C and a dissolving pressure of 1.0 to 100.0 MPa absolute pressure; And then b) a step of purifying the crude polymer solution to obtain a purified polymer solution, and the purification step includes: b1) a sub-step of separating out insoluble matters; and / or b2) a washing sub-step, carried out by contacting with a high-density solution; and / or b3) an extraction sub-step, carried out by contacting with an extraction solvent; and / or b4) an impurity adsorption sub-step, carried out by contacting with a solid adsorbent; and then c) a step of solvent / polymer separation to obtain at least one fraction of purified thermoplastic polymer.

2. The method according to claim 1, wherein the contact section includes one to ten, preferably two to six, preferably two to five, preferably serially connected static or dynamic mixers.

3. The method according to claim 1 or 2, wherein each mixer has the following volume-based dilution with the dissolving solvent: - When the viscosity ratio between the plastic stream fed to the considered static or dynamic mixer and the fraction of at least said part of the dissolving solvent is greater than or equal to 3500, preferably greater than or equal to 3000, the volume-based dilution with the dissolving solvent is 3% to 50%, preferably 10% to 35%, and very preferably 15% to 30%, - When the viscosity ratio between the plastic stream fed to the considered static or dynamic mixer and the fraction of at least said part of the dissolving solvent is less than 3500, preferably less than 3000, the volume-based dilution with the dissolving solvent is 10% to 70%, preferably 20% to 65%, very preferably 30% to 65%, or even 35% to 65%.

4. The method according to any one of the preceding claims, wherein the contact section includes a device for at least partially melting the plastic raw materials upstream of the first static or dynamic mixer, and the melting device is preferably an extruder.

5. The method according to any one of the preceding claims, wherein the dissolving solvent comprises at least one alkan aliphatic hydrocarbon group compound having a boiling point of -50 °C to 250 °C, preferably -15 °C to 150 °C, preferably -1 °C to 110 °C, and preferably 20 °C to 100 °C.

6. The method according to any one of the preceding claims, wherein the dissolving solvent and the plastic raw material are fed to step a) at a weight ratio of the dissolving solvent to the plastic raw material of 0.2 to 100.0, preferably 0.3 to 20.0, preferably 1.0 to 10.0, and even more preferably 3.0 to 7.

0.

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

8. The method according to any one of the preceding claims, wherein the dissolving section is operated at a dissolving temperature of 150 °C to 250 °C.

9. The method according to any one of the preceding claims, wherein the dissolving section is operated at a dissolving pressure of 1.0 to 25.0 MPa absolute pressure, preferably 1.5 to 18.0 MPa absolute pressure, and very preferably 2.0 to 15.0 MPa absolute pressure.

10. The method according to any one of the preceding claims, wherein the purification step b) comprises a sub-step b1) of separating out insoluble matters, preferably followed by at least one adsorption sub-step.

11. The method according to any one of the preceding claims, wherein the plastic raw material comprises a thermoplastic polymer, more specifically a polyolefin.

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