Method for recycling plastic using size exclusion simulated moving bed device

Abstract

The invention relates to a method for purifying a plastic feedstock to obtain a purified polymer stream, comprising: a) a dissolution step in which the plastic feedstock is brought into contact with a dissolution solvent; followed by b) an extraction step by means of size exclusion, in which beds of size exclusion solids are used in series, the polymer solution from a) is fed at an injection point (F) and an eluent is fed at an injection point (S), and the extract is removed at a removal point (E) and a raffinate comprising the purified polymer solution is removed at a removal point (R), the injection point and the extraction point are separated and are moved by one bed along with time according to a given frequency; followed by c) a polymer-solvent separation step to obtain a stream of purified polymer. The invention also relates to a device for carrying out step b) and to a device for carrying out said purification method.

Description

Field of the Invention

[0001] The present invention relates to the field of plastic recycling, and more particularly to the recycling of polymers, more particularly thermoplastics, and more particularly thermoplastics other than polyolefin and polyvinyl chloride (or PVC) polymers. More particularly, the present invention relates to a method for treating plastic feedstock, particularly plastic feedstock obtained from plastic waste, which contains polymers, particularly thermoplastics, and particularly thermoplastics other than polyolefin and polyvinyl chloride (or PVC), to obtain a stream of purified polymer that can be economically upgraded, for example, in the manufacture of new plastic articles. The method very advantageously comprises dissolving the target polymer in a suitable solvent, performing at least one purification step on the obtained polymer solution by extraction in a size exclusion simulated moving bed so as to at least partially remove impurities, particularly additives conventionally used in plastic-based materials, and a step of separating the target polymer and the solvent to recover a stream of purified polymer, preferably a stream of purified thermoplastic, and preferably having chemical properties other than polyolefin or PVC properties. Prior Art

[0002] Plastic recycling is a major environmental challenge for the next century. There are several methods for recycling and economically upgrading plastics obtained from collection and sorting channels.

[0003] First, there is "mechanical" recycling: Mechanical recycling enables some waste materials to be partially reused in new articles either directly (after melting and subsequent formation of thermoplastics) or by mixing a mechanically sorted plastic waste stream with a virgin polymer stream. This type of economic upgrading is limited because mechanical sorting allows for improving the purity of the plastic stream of a given type of polymer, but generally does not allow for fully removing at least some of the impurities trapped in the polymer matrix, such as additives, like fillers, dyes, pigments, and metals, which are used in combination with the polymer to impart the desired properties to the material.

[0004] "Chemical" recycling per se is mainly directed toward eliminating additives and, depending on the method applied, more or less chemically modifies the polymer chains of the plastics under consideration (e.g., recovering intact polymers, depolymerizing them or obtaining a mixture of compounds containing carbon and hydrogen obtained after non-selectively breaking the chains of various polymers). These different options involve a generally complex sequence of steps. For example, plastic waste can undergo a pyrolysis step and the recovered pyrolysis oil can generally be at least partially converted into olefins, e.g., by steam cracking, after purification. These olefins can be polymerized or converted into monomers before polymerization. This type of sequence can be applied to feedstock or sorting center refuse that has undergone little sorting, but it generally requires a large amount of energy consumption, especially due to the high-temperature treatment.

[0005] Among the various possible routes, the deformulation of plastic materials, especially those based on thermoplastics, seems to be a virtuous approach: it consists of dissolving the polymer in a solvent and removing the additives without changing the polymer chains. The preservation of the polymer structure reduces the effort required for the reuse of the material and explains the good performance of this method, especially in terms of energy consumption.

[0006] When the impurities (such as additives) contained in the plastic feedstock are insoluble in the solvent, they can optionally be separated by solid / liquid separation, e.g., by filtration. However, additives that are soluble in the solvent are particularly difficult to separate. One of the most conventional methods can include separating them based on specific physicochemical properties (such as their polarity, solubility, boiling point, density, etc.), but this can lead to an increase in the purification steps considering the plurality and diversity of the impurities present. The present invention proposes another method based on taking advantage of the size difference, more precisely the difference in hydrodynamic volume, between polymer macromolecules and impurity molecules (such as additive molecules).

[0007] Size-based separation already exists and is commonly used as an analytical method for determining the molecular weight of polymers. This method, known as size-exclusion chromatography (or SEC), is carried out discontinuously (“in batch mode”) and involves using a fixed bed with several porosity levels. Small molecules explore the fixed bed until the smallest pores, so the associated elution time is long, while large molecules such as polymers only pass through the largest pores and exhibit a short elution time, thus achieving the selective separation of various molecules. Since the size of the additives (colorants, plasticizers, antioxidants, stabilizers, etc.) commonly used in plastic formulations is much smaller than the size of the polymer chains, by an order of magnitude, the principle of size-exclusion chromatography can be applied to the purification of plastics. However, the implementation of methods using this chromatographic principle is carried out in batch mode, which can be problematic in an industrial context. In addition, this batch-mode method would require a large consumption of eluent to ensure efficient separation, which directly affects the profitability, productivity, and ecological footprint of the method.

[0008] The simulated moving bed (SMB) technology is a concept invented in 1961 that enables discontinuous “chromatography” methods to operate continuously, particularly through adsorption, to increase productivity and limit the amount of eluent consumed while ensuring efficient separation. There are many industrial references to this technology, particularly for separation by adsorption, which is used specifically for or Process for separating xylenes (see publication Simulated Moving Bed Technology: Principles, Design and Process Applications, A.E. Rodrigues, Elsevier, 2015). The only large-scale application of size-exclusion simulated moving bed (or SMB-SEC, i.e., Simulated Moving Bed with Size Exclusion Chromatography) involves the separation of normal paraffins from isoparaffins, the general situation of which is described in patent US2 985 589. Recent publications mention the use of size-exclusion simulated moving bed (SMB-SEC) technology for the fractionation of polyethylene glycols of different molecular weights (M.T. Liang et al., J. Chromatogr. A, 2012, 1229, 107) or for the separation of proteins (E.J. Freydell et al., Chem. Eng. Sc., 2010, 65, 4701). More particularly, patent US 6 551 512 proposes a method for separating proteins from a liquid composition, such as milk, by size exclusion in a simulated moving bed. Finally, publications mention the use of SMB-SEC in recycling methods for materials contained in the composition of WEEE (Waste Electrical and Electronic Equipment). The WEEE is based on polycarbonate and also contains poly(styrene-co-acrylonitrile) (SAN) and additives such as flame retardants. The latter are precisely what the Weeden team tried to separate from a ternary solution containing SAN and two flame retardant compounds, resorcinol bis(diphenyl phosphate) and bisphenol A bis(diphenyl phosphate), in an acetone-dichloromethane solvent mixture (G.S. Weeden et al., Journal of Chromatography A, 2015, 1422, 99).

[0009] Accordingly, the present invention relates to overcoming the problems of the prior art and participating in the recycling of plastics. More particularly, it relates to providing an efficient, simple and economically viable method for treating plastic raw materials, especially plastic raw materials based on thermoplastics, and more particularly thermoplastics other than polyolefins and PVC, said plastic raw materials being particularly obtained from plastic waste, such as plastic waste obtained from collection and sorting channels, in order to remove at least a part of the impurities contained therein, especially at least a part of the additives conventionally added to plastics. The present invention specifically attempts to efficiently separate the target polymer contained in the used plastics from the impurities and to economically upgrade all types of plastic raw materials, especially plastic raw materials containing thermoplastics, and especially thermoplastics other than polyolefins and PVC, by recycling the purified target polymer, so as to be able to use it, for example, for manufacturing new plastic objects, such as replacing virgin resin. Summary of the Invention

[0011] Accordingly, the present invention relates to a method for purifying a plastic raw material to obtain a stream of purified polymer, said method comprising:

[0012] a) a dissolution step, which comprises bringing the plastic raw material into contact with a dissolution solvent to obtain at least one crude polymer solution;

[0013] b’) optionally, a step of separating insoluble materials from the crude polymer solution obtained from step a) to obtain at least one clarified polymer solution;

[0014] b) a size exclusion extraction step of the crude polymer solution obtained at the end of step a) or optionally the clarified polymer solution obtained at the end of the optional step b’) to obtain a purified polymer solution,

[0015] wherein said size exclusion extraction step uses at least one series of n size exclusion solid fixed beds, n being an integer greater than or equal to 4, said n beds being in series,

[0016] The series of fixed beds of step b) is fed with the crude polymer solution or optionally the clarified polymer solution at at least one polymer solution injection point F and with an eluent at at least one eluent injection point S,

[0017] wherein the series of fixed beds of step b) performs at least one extract removal at at least one extract removal point E and at least one raffinate removal at at least one raffinate removal point R,

[0018] wherein the polymer solution injection point, the eluent injection point, the extract withdrawal point, and the raffinate withdrawal point are different from each other and are distributed such that they define at least three, preferably four, successive main operating zones of the n fixed beds:

[0019] - an impurity elution zone I, which is located between the eluent injection point and the extract withdrawal point;

[0020] - an elution zone II of the target polymer, which is located between the extract withdrawal point and the polymer solution injection point;

[0021] - an impurity retention zone III, which is located between the polymer solution injection point and the raffinate withdrawal point; and

[0022] - optionally, a zone IV, which is located between the raffinate withdrawal point and the eluent injection point,

[0023] wherein the injection points and the withdrawal points are moved by one size-excluding solid fixed bed of the fixed bed over time according to a frequency determined by a predetermined switching cycle (permutation),

[0024] the raffinate is recovered to at least partially constitute the purified polymer solution;

[0025] c) a polymer-solvent separation step of the purified polymer solution to obtain at least one stream of purified polymer and at least one solvent fraction containing the dissolved solvent.

[0026] The advantages of the method of the present invention are that it provides a method for efficiently processing a raw material containing plastics, especially plastics based on thermoplastics, in particular plastic waste especially obtained from collection and sorting channels, in order to recover the polymers contained therein so that they can be recycled into all types of applications. This is because the method according to the present invention enables a stream of purified polymers to be obtained, especially a stream of purified thermoplastics and preferably excluding polyolefins and PVC, advantageously less colored than the initial plastic raw material, in fact even colorless and preferably deodorized. The stream of purified polymers obtained preferably has a negligible content of prohibited or regulated substances, such as the prohibited or regulated substances of the REACH regulation (see Appendices XIV and XVII of Regulation (EC) No. 1907 / 2006 of the European Parliament and of the Council of 18 December 2006). In particular, the stream of purified polymers obtained at the end of the method according to the present invention very advantageously contains a negligible or at least low enough impurity content, especially additive content, and solvent content, especially dissolved solvent and / or eluent solvent content, such that the stream of purified polymers can replace virgin polymer resin in any plastic formulation. For example, the stream of purified polymers obtained at the end of the method according to the present invention advantageously contains an impurity content of less than or equal to 10% by weight, preferably less than or equal to 5% by weight, very advantageously less than or equal to 1% by weight, or even less than or equal to 0.5% by weight, and an solvent (especially dissolved solvent and eluent) content of less than or equal to 10% by weight, preferably less than or equal to 5% by weight of the solvent, preferably less than or equal to 1% by weight.

[0027] Thus, the method according to the present invention provides a simple scheme corresponding to a minimized sequence of operations, which makes it possible to remove at least a part of its impurities, especially at least a part of the additives, from the plastic waste and to recover the purified target polymer, especially the purified target thermoplastic, and especially the purified thermoplastic excluding polyolefins and PVC, so as to be able to economically upgrade the plastic waste by recycling the purified polymers.

[0028] The present invention also has the advantage of participating in plastic recycling and fossil resource conservation by achieving an economic upgrade of plastic waste. Specifically, it allows the purification of plastic waste to obtain purified polymers with a reduced impurity content, which are especially decolorized and deodorized polymers, which can be reused to form new plastic objects. Thus, the purified polymers obtained can be used directly in formulations, either in place of or in admixture with the virgin resin of the corresponding polymer, as a mixture with additives such as dyes, pigments, other polymers, to obtain plastic products with use properties, aesthetic properties, mechanical properties or rheological properties that promote their reuse and their economic upgrade.

[0029] According to a second aspect, the present invention also relates to a device for extracting dissolved polymers from a polymer solution by size exclusion, said device comprising:

[0030] - a fixed bed of n size-exclusion solids, where n is an integer greater than or equal to 4, preferably between 4 and 30, said size-exclusion solids having a volume-average pore diameter preferably between 1 and 500 nm, preferably between 2 and 100 nm, preferably between 2 nm and 50 nm, preferably between 3 and 30 nm, and preferably being silica gel, grafted silica, carbon molecular sieve or a mixture thereof,

[0031] the fixed bed of said n size-exclusion solids is distributed in one or more towers, said n beds being connected in series and preferably in a closed loop,

[0032] - N polymer solution injection systems, N eluent injection systems, N extract removal systems and N raffinate removal systems, where N is an integer preferably equal to n, said injection and removal systems being located between two consecutive beds or optionally upstream of the first bed,

[0033] wherein the polymer solution injection system and the eluent injection system and / or the extract removal system and the raffinate removal system located at the same position are different or the same,

[0034] - each injection and removal system comprises at least one valve adapted to allow or not allow the flow of polymer solution and / or the flow of eluent and / or the flow of extract and / or the flow of raffinate liquid to pass through, preferably a series of switching valves controlled by an automatic sequence or a single rotary valve, so as to:

[0035] - define at time t a polymer solution injection point, an eluent injection point, an extract removal point and a raffinate removal point, said injection points and removal points being different from each other and determining at least three, preferably four consecutive main operating zones of said n fixed beds:

[0036] - an impurity elution zone I, which is included between the eluent injection point and the extract removal point;

[0037] - an elution zone II of the target polymer, which is included between the extract removal point and the polymer solution injection point;

[0038] - an impurity retention zone III, which is included between the polymer solution injection point and the raffinate removal point; and

[0039] - optionally, a zone IV, which is included between the raffinate removal point and the eluent injection point,

[0040] - and such that there is a bed of size - exclusion solids that can be moved, per switching cycle, in synchronism or out of synchronism with time, at a frequency determined by a predetermined switching cycle, by one size - exclusion solid dimension per switching cycle, the injection point and the withdrawal point being moved.

[0041] According to a third aspect, the present invention also relates to an apparatus for treating a plastic raw material to obtain a stream of purified polymer, comprising:

[0042] - a dissolving tool for bringing the plastic raw material into contact with a dissolving solvent to at least partially dissolve the plastic raw material in the dissolving solvent to obtain a crude polymer solution;

[0043] - optionally, a solid - liquid separation tool adapted to separate insoluble materials suspended in the crude polymer solution;

[0044] - at least one size - exclusion extraction device according to the present invention;

[0045] - a tool for separating the dissolving solvent and optionally the eluent from the stream of purified polymer.

[0046] List of the drawings

[0047] Figure 1 Shows a particular embodiment of the size - exclusion extraction step of the present invention at a given moment t of the method, in which the size - exclusion extraction step uses 15 fixed beds of size - exclusion solids of silica - gel type, distributed in a single column, the beds being connected in series with respect to each other and in a closed loop, and a pump located between bed no. 15 and bed no. 1 makes it possible to connect bed no. 15 and bed no. 1 in series.

[0048] In this particular embodiment and at this moment t:

[0049] - the crude polymer solution obtained from the dissolving step a) ( Figure 1 not shown) or, optionally, the clarified polymer solution obtained from the optional solid - liquid separation step b') ( Figure 1 not shown) incorporated into the method is introduced at an injection point F located between bed no. 9 and bed no. 10, these two beds being consecutive,

[0050] - the eluent is introduced at an injection point S located between bed no. 15 and bed no. 1, these two beds being consecutive,

[0051] - an extract containing at least a portion of the impurities present in the polymer solution fed to the column is withdrawn at a withdrawal point E located between bed no. 6 and bed no. 7, these two beds being consecutive,

[0052] - a raffinate consisting at least in part of a purified polymer solution is withdrawn at a withdrawal point R located between bed no. 13 and bed no. 14, these two fixed beds being consecutive.

[0053] The combined injection and withdrawal points thus define four operating zones:

[0054] - An impurity elution zone I, which is located between the eluent injection and the extract withdrawal and contains six beds,

[0055] - An elution zone II for the target polymer, which is located between the extract withdrawal and the polymer solution injection and contains three beds,

[0056] - An impurity retention zone III, which is located between the polymer solution injection and the raffinate withdrawal and contains four beds, and

[0057] - A zone IV, which is located between the raffinate withdrawal and the eluent injection and contains two beds.

[0058] Figure 2 Represents another specific embodiment of the size exclusion extraction step of the present invention at a given moment t of the method, wherein the size exclusion extraction step comprises four fixed beds of size exclusion solids of the silica type, each distributed in a column (i.e., one bed per column), the columns being connected in series relative to each other and in a closed loop, and a pump located between column 4 and column 1 enables the series connection of column 4 and column 1.

[0059] In this specific embodiment and at this moment t:

[0060] - The polymer solution fed into the size exclusion extraction step is introduced at an injection point F located between column 2 and column 3,

[0061] - The eluent is introduced at an injection point S located between column 4 and column 1,

[0062] - An extract containing at least a portion of the impurities present in the polymer solution fed into the size exclusion extraction step is withdrawn at a withdrawal point E located between column 1 and column 2,

[0063] - A raffinate consisting of at least part of the polymer solution is withdrawn at a withdrawal point R located between column 3 and column 4.

[0064] Figure 3 Represents the concentration profiles of polyethylene terephthalate (PET) and dye blue 104 obtained by simulation along the entire length of a simulated moving bed in the case of Example 1, the simulated moving bed comprising 15 silica beds according to a 6 / 3 / 4 / 2 configuration. By convention, the eluent injection is located upstream of bed 1 (and downstream of bed 15). The concentration profile of PET as a function of the bed is represented by a solid black line, and the concentration profile of the dye as a function of the bed is represented by a dashed line.

[0065] Description of the embodiment

[0066] According to the present invention, the expressions "between... and..." and "from... to..." are equivalent and mean that the limiting values of the interval are included in the described range of values. If this is not the case and if the limiting values are not included in the said range, such a clarification will be given by the present invention.

[0067] In the present specification, the expression "greater than..." is understood to be strictly greater than and is represented by the symbol ">", and the expression "less than" is understood to be strictly less than and is represented by the symbol "<". When the limiting values are included, this detail will be indicated by the corresponding expressions "greater than or equal to..." (and corresponding to the symbol "≥") and "less than or equal to" (corresponding to the symbol "≤").

[0068] 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, for the purposes of the present invention, a range of preferred pressure values can be combined with a range of more preferred temperature values.

[0069] Hereinafter, specific embodiments of the present invention are described. They can be carried out alone or in combination, and when this is technically feasible, the combination is not limited.

[0070] The terms "upstream" and "downstream" should be understood according to the general flow of the fluid or stream considered in the method. More particularly, the terms "upstream" and "downstream" are defined according to the flow of the stream containing the polymer to be purified. For example, the terms "upstream" and "downstream" are defined with respect to the stream of the polymer solution in a size exclusion step, that is, with respect to the feeding of the crude (or clarified) polymer solution to said step, or with respect to the outlet point of the purified polymer solution (i.e., the raffinate withdrawal point).

[0071] The term "additive" is a term conventionally used in the field of polymers and in particular in the field of polymer formulations. Additives introduced into a polymer formulation can be, for example, plasticizers, fillers (which are organic or inorganic (mineral) solid compounds used to modify the physical, thermal, mechanical and / or electrical properties of the polymer material or to reduce its cost price), reinforcing agents, dyes, pigments, hardeners, plasticizers, flame retardants, combustion retardants, stabilizers, antioxidants, UV absorbers, antistatic agents, etc.

[0072] The additives correspond to at least a part of the impurities of the plastic raw material to be treated, and the treatment method according to the present invention makes it possible to remove at least part of these impurities. Other types of impurities may be present in the plastic raw material to be treated, such as impurities related to its use, such as metal impurities, paper / cardboard, biomass, polymers other than the target polymer, etc.

[0073] Thus, according to the present invention, the impurities that can be removed at least in part by the method include additives conventionally used in polymer formulations, especially those based on thermoplastics, and may also be use-related impurities obtained from the life cycle of plastic objects and materials, and / or use-related impurities obtained from waste collection and sorting circuits. The impurities can be of metallic, organic or inorganic 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, water, etc.

[0074] According to the present invention, a polymer solution is a solution containing a dissolving solvent and at least a target polymer, especially a thermoplastic other than polyolefins and PVC, which is dissolved (i.e., especially solvated and dispersed) in the dissolving solvent, and the dissolved polymer initially exists in the plastic raw material. The polymer solution may additionally contain soluble impurities (which are dissolved in the dissolving solvent) and / or insoluble impurities (which are suspended in the polymer solution; in the case of nano-scale insoluble impurities, reference will be made to colloidal solutions). Depending on the steps of the method according to the present invention carried out, the polymer solution can thus contain, in addition to the target polymer dissolved in the dissolving solvent, impurities in the form of insoluble particles advantageously suspended in the polymer solution, soluble impurities dissolved in the dissolving solvent, and / or another liquid phase that may be immiscible with the polymer solution.

[0075] In this specification, the term "room temperature" (r.t.) is understood to mean a temperature generally of 20°C ± 5°C, and the term "atmospheric pressure" is understood to mean a pressure of 0.101325 MPa.

[0076] The present invention relates to a method for purifying a plastic raw material, which preferably consists of plastic waste and advantageously contains polymers, preferably thermoplastics, and preferably thermoplastics other than polyolefins and PVC. The method comprises the following steps and preferably consists of the following steps:

[0077] a) A dissolving step, which includes bringing the plastic raw material into contact with a dissolving solvent to obtain at least one crude polymer solution;

[0078] b’) An optional step of separating insoluble materials from the crude polymer solution, especially performing solid / liquid separation on the crude polymer solution obtained from step a), to advantageously obtain a clarified polymer solution and preferably an insoluble fraction;

[0079] b) A size-exclusion extraction step of the crude polymer solution obtained at the end of step a) or optionally the clarified polymer solution obtained at the end of an optional step b'), to obtain a purified polymer solution,

[0080] wherein the size-exclusion extraction step uses at least one series of n fixed beds of size-exclusion solids, n being an integer greater than or equal to 4, preferably between 4 and 30, preferably between 8 and 24, very preferably between 8 and 21, and preferably between 12 and 15,

[0081] wherein advantageously, the n fixed beds of size-exclusion solids are distributed in one or more towers, preferably in M towers, M being an integer between 1 and the total number n of fixed beds of size-exclusion solids, the n beds being in series relative to each other and preferably in a closed loop,

[0082] The at least one series of fixed beds of step b) is fed with the crude polymer solution or the clarified polymer solution at at least one polymer solution injection point F and with an eluent at at least one eluent injection point S,

[0083] wherein the at least one series of fixed beds of step b) performs at least one extract removal at at least one extract removal point E and at least one raffinate removal at at least one raffinate removal point R,

[0084] wherein the polymer solution injection point, the eluent injection point, the extract removal point and the raffinate removal point are different from each other, advantageously located between two successive beds or optionally upstream of the first bed, and are distributed such that they define at least three, preferably four successive main operating zones of the n fixed beds:

[0085] - An impurity elution zone I, which is located between the eluent injection point and the extract removal point;

[0086] - An elution zone II of the target polymer, which is located between the extract removal point and the polymer solution injection point;

[0087] - An impurity retention zone III, which is located between the polymer solution injection point and the raffinate removal point; and

[0088] - Optionally and preferably, a zone IV, which is located between the raffinate removal point and the eluent injection point,

[0089] wherein the injection points and the removal points are moved by one fixed bed of size-exclusion solids over time according to a frequency determined by a predetermined switching cycle,

[0090] wherein the raffinate is recovered to form at least a part, preferably all, of the purified polymer solution;

[0091] c) The polymer-solvent separation step of the purified polymer solution to obtain at least one stream of purified polymer, in particular a stream of purified thermoplastic, and more particularly a stream of purified thermoplastic other than polyolefins and PVC, and at least one solvent fraction comprising the dissolved solvent and possibly an eluent.

[0092] Feedstock

[0093] The feedstock for the process according to the invention, referred to as "plastic feedstock", comprises plastics which themselves contain polymers, in particular thermoplastics, and more particularly thermoplastics other than polyolefins (such as polypropylene, polyethylene and their copolymers) and PVC. Preferably, the plastic feedstock contains between 50% and 100% by weight, and preferably between 70% and 100% by weight, of plastics.

[0094] The plastics contained in the feedstock for the process according to the invention are generally production rejects and / or "post-consumer" waste, in particular domestic waste, construction waste, waste from the automotive industry or end-of-life electrical and electronic equipment. Preferably, the plastic waste is obtained from collection and sorting channels. Plastics or plastic materials are generally compositions (or formulations) containing polymers, in particular thermoplastics, which are generally mixed with additives to impart specific properties to the material in order to form various objects after shaping (such as injection-molded parts, pipes, films, fibres, fabrics, mastics, coatings, etc.). The additives used in plastics can be organic or inorganic compounds. For example, they are fillers, dyes, pigments, plasticizers, property modifiers, flame retardants, etc.

[0095] Thus, the plastic raw material according to the method of the present invention comprises polymers, in particular thermoplastics, and more particularly thermoplastics other than polyolefins and PVC. Preferably, relative to the total weight of the plastic raw material, the plastic raw material comprises at least 50% by weight, preferably at least 70% by weight, preferably at least 80% by weight, preferably at least 90% by weight (100% is advantageously the maximum upper limit) of polymers, in particular thermoplastics, and in particular thermoplastics other than polyolefins and PVC. Thus, the method according to the present invention particularly relates to purifying and recovering the said polymers, in particular the said thermoplastics, and in particular the said thermoplastics other than polyolefins and PVC contained in the plastic raw material so as to be able to reuse them in various applications. The polymers which are very particularly targeted are preferably polyesters such as polyethylene terephthalate (or PET) and its copolymers, polystyrene and its copolymers, polycarbonate and its copolymers, polyamides and its copolymers such as nylon, methyl polyacrylates and polymethacrylates such as PMMA (polymethyl methacrylate), polyalkyloxide or polyalkyl glycol and its copolymers such as polyethylene oxide or polyethylene glycol (PEO or PEG respectively), cellulose (co)polymers, silicones or polysiloxanes such as polydimethylsiloxane, or mixtures thereof.

[0096] The plastic raw material may comprise a plurality of polymers other than the target polymer, in particular the target thermoplastic. For example, the plastic raw material may optionally comprise polyolefins (such as polyethylene and / or polypropylene homopolymers or copolymers) and / or PVC as a mixture with the target polymer, in particular the target thermoplastic. The plastic raw material may also comprise other impurities, in particular additives which are commonly used to formulate plastic materials and which are generally impurities related to use obtained from the life cycle of plastic materials and objects and / or obtained from waste collection and sorting circuits. The plastic raw material according to the method of the present invention generally comprises less than 50% by weight of impurities, preferably less than 30% by weight of impurities, preferably less than 20% by weight of impurities, preferably less than 10% by weight of impurities. The plastic raw material may comprise, for example, 1% by weight or more of impurities or indeed even 5% by weight or more of impurities.

[0097] The plastic raw material can be pretreated before the method according to the invention in order to remove at least all or part of the "coarse" impurities, i.e., impurities in the form of particles with a size greater than or equal to 10 mm, preferably greater than or equal to 5 mm, or even greater than or equal to 1 mm, such as impurities like wood, paper, biomass, iron, aluminum, glass, etc., and to shape it, usually in the form of a divided solid, in order to facilitate the treatment in the method according to the invention. This pretreatment can include a grinding step, a washing step under atmospheric pressure, and / or a drying step. This pretreatment can be carried out at different locations, for example, at a waste collection and sorting center, or at the same location where the purification according to the method of the invention is carried out. Preferably, this pretreatment enables the impurity content to be reduced to less than 11% by weight relative to the total weight of the plastic raw material. At the end of the pretreatment, the plastic raw material is usually stored in the form of a divided solid, for example, in the form of ground material, powder, flakes, or granules, for easy handling and transportation to the process.

[0098] Dissolution step a)

[0099] According to the invention, the method comprises a dissolution step a) in which the plastic raw material is brought into contact with a dissolution solvent to obtain at least one, preferably only one, crude polymer solution. Specifically, this step advantageously enables at least a part and preferably all of the target polymer, preferably the target thermoplastic, present in the plastic raw material to be dissolved.

[0100] The term "dissolution" should be understood to mean any phenomenon that results in the production of at least one polymer solution (especially a thermoplastic solution), i.e., a liquid (or possibly a supercritical fluid) containing a polymer (especially a thermoplastic) dissolved in a solvent, more particularly in a dissolution solvent. Those skilled in the art are fully aware of the phenomena involved in polymer dissolution, which phenomena include at least the mixing, dispersion, homogenization, solvation, and disentanglement of polymer chains and more particularly thermoplastic chains.

[0101] During and at the end of the dissolution step a), the pressure and temperature conditions are such that the dissolution solvent can be kept, at least in part and preferably entirely, in a liquid or possibly supercritical state (the temperature and pressure conditions in step a) are such that the presence of the dissolution solvent in gaseous form can be avoided or at least limited), while the soluble part of the raw material, especially the target polymer, most especially the target thermoplastic, and at least a part of the impurities are advantageously at least partially and preferably completely dissolved.

[0102] The dissolution solvent is a solvent or a solvent mixture, in particular an organic solvent, preferably selected such that its Hansen parameters are within the Hansen sphere of the target polymer. The Hansen theory enables the prediction of the solubility of polymers, in particular thermoplastics, in solvents by determining the Hansen solubility parameters and spheres of the solvent and the polymer respectively based on multiple parameters, in particular their polarity, hydrogen bonding and dispersion parameters. If the solvent or solvent mixture exhibits Hansen parameters within the Hansen sphere of the target polymer, the polymer should be at least partially, preferably completely soluble in the solvent. Preferably, the dissolution solvent is a solvent or a solvent mixture, in particular an organic solvent, preferably selected from hydrocarbons, in particular straight-chain or cyclic paraffinic, olefinic or aromatic hydrocarbons; alcohols, in particular monoalcohols and polyalcohols; straight-chain or cyclic esters; straight-chain or cyclic ethers; straight-chain or cyclic ketones; vinyl compounds; nitrile compounds; straight-chain or cyclic amine and amide compounds; organic sulfur compounds; chlorinated compounds; organic acids in pure form or in aqueous solution; and mixtures thereof, and preferably contains 1 to 12 carbon atoms, preferably 2 to 8 carbon atoms.For example, the dissolving solvent may comprise a mixture of hydrocarbons derived from petroleum fractions, particularly C2 to C8 petroleum fractions; isomers or mixtures of isomers of alkanes, particularly aliphatic or cyclic C3 to C7 hydrocarbons, such as one or more isomers of butane, pentane, hexane or heptane; aromatic hydrocarbons, such as toluene or xylene; C2 to C8 alcohols or mixtures of C2 to C8 alcohols, such as ethanol, propanol or isopropanol, butanol; glycol (or diol), such as ethylene glycol or diethylene glycol; linear or cyclic esters, such as ethyl acetate, propyl acetate, butyl acetate, pentyl acetate, 2-butoxyethanol acetate, butyl propionate, propyl propionate, methyl propionate, allyl acetate, 2-(2-butoxyethoxy)ethyl acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, butyl benzoate, ethyl lactate, γ-butyrolactone (GBL), γ-valerolactone (GVL), caprolactone; aliphatic or cyclic ketones, such as methyl ethyl ketone (MEK); diethyl ketone (DEK); methyl propyl ketone; 4-heptanone; 2,4-dimethyl-3-pentanone; methyl isobutyl ketone (MIBK); diisobutyl ketone; methyl isopentyl ketone; 4-hydroxy-4-methylpentan-2-one; cyclopentanone; cyclohexanone; isophorone; aliphatic or cyclic C3 to C8 ethers, such as methoxycyclopentane, propylene glycol phenyl ether, diethylene glycol butyl ether, dipropylene glycol butyl ether, propylene glycol methyl ether, propylene glycol butyl ether, dipropylene glycol methyl ether, ethylene glycol butyl ether, tetrahydrofuran (THF), 1,3-dioxolane, 2-hydroxymethyloxolane; linear or cyclic amides, such as N,N-diethylformamide; N,N-dimethylacetamide; N,N-dimethylformamide (DMF), 2-pyrrolidone; N-methyl-2-pyrrolidone (NMP); organic acids such as acetic acid alone or in aqueous solution; organic sulfur compounds such as dimethyl sulfoxide (DMSO), sulfolane; chlorinated compounds, such as dichloromethane; trichloromethane (chloroform); carbon tetrachloride; trichloroethylene; dihydrolevoglucosenone and mixtures thereof. The dissolving solvent may also optionally contain inorganic acids, particularly sulfuric acid, alone or in aqueous solution.

[0103] Preferably, the plastic raw material and the dissolving solvent are fed into the dissolving step a), and the weight ratio of the dissolving solvent to the plastic raw material is between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, and even more preferably between 3.0 and 7.0.

[0104] Advantageously, the dissolution solvent fed into dissolution step a) is in liquid or possibly in supercritical form. Advantageously, it can be preheated, preferably to a temperature between 40 and 300 °C, preferably between 40 and 250 °C, before being introduced into step a), in particular before being introduced into the contacting section and optionally into the dissolution section, in order to promote the heating of the plastic raw material and / or to avoid a temperature drop of the material flow in the contacting section and optionally the dissolution section of step a).

[0105] Advantageously, the dissolution solvent comprises and preferably consists of a stream of fresh solvent (or supply of fresh solvent) and / or a recycle solvent obtained from subsequent steps of the process (e.g. at least partially obtained from the solvent-polymer separation step c)).

[0106] Very advantageously, the dissolution step is carried out at a temperature (referred to as the dissolution temperature) between room temperature and 300 °C, preferably between 20 and 300 °C, preferably between 40 and 250 °C and at a pressure between atmospheric pressure and 100.0 MPa absolute pressure, preferably between 0.1 and 100.0 MPa absolute pressure, preferably between 0.1 and 25.0 MPa absolute pressure, preferably between 0.1 and 15.0 MPa absolute pressure and very preferably between 0.1 and 5.0 MPa absolute pressure (referred to as the dissolution pressure). During the dissolution step, the temperature and pressure can vary from the conditions of introduction of the plastic raw material and / or the dissolution solvent to the dissolution conditions, i.e. the dissolution temperature and the dissolution pressure. Very advantageously, at the end of the dissolution step, the crude polymer solution is at the dissolution temperature and the dissolution pressure.

[0107] Limiting the temperature in dissolution step a) to a temperature less than or equal to 300 °C, preferably less than or equal to 250 °C, makes it possible to avoid or limit the thermal degradation of the polymer and also to limit the energy requirements of the process, thereby contributing to limiting the operating costs of the process. Advantageously, the dissolution temperature is greater than or equal to the melting point of the target polymer in order to promote its dissolution and very advantageously to reduce the residence time required for efficient dissolution of the target polymer. Very preferably, the temperature 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) that can disrupt the dissolution.

[0108] At the same time, the dissolution pressure in the dissolution step 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 completely in liquid or possibly supercritical form at the dissolution temperature, which makes it possible to optimize the dissolution of the target polymer, in particular in terms of quality and operating time.

[0109] Very advantageously, the dissolution temperature and pressure conditions achieved in dissolution step a) 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.

[0110] Advantageously, the dissolution step a) is carried out with a residence time preferably between 1 and 600 minutes, preferably between 2 and 300 minutes, preferably between 2 and 180 minutes. In step a), the residence time is understood to be the residence time at the dissolution temperature and at the dissolution pressure, i.e., the time during which the plastic raw material is processed with the dissolution solvent at the dissolution temperature and at the dissolution pressure.

[0111] In order for the dissolution solvent and the plastic raw material to be able to contact each other, and most importantly, for the target polymer to be dissolved efficiently and homogeneously in the dissolution solvent, the dissolution step can advantageously use various types of equipment, such as mixing, conveying and heating devices, for example reactors, pumps, conveying circuits, stirring systems, furnaces, exchangers, mixers, etc. In particular, step a) advantageously uses at least one dissolution device, and optionally at least one raw material preparation device, mixing device and / or conveying device. These devices and / or apparatuses can be, for example, one or more static mixers, extruders, pumps, reactors, co-current or counter-current towers, or combinations of pipelines and equipment. Devices for conveying specific fluids (such as gases, liquids or solids) are well known to those skilled in the art. By way of non-limiting example, the conveying device can include compressors, pumps, extruders, vibrating tubes, endless screws or valves. The devices and / or apparatuses used in step a) can also include a heating system (such as a furnace, exchanger, heat tracing cable, etc.) or be combined with a heating system to achieve the conditions required for dissolution.

[0112] Into the dissolution step a), there are advantageously fed at least the plastic raw material, in particular in the form of one or more streams of plastic raw material, and the dissolution solvent, in particular in the form of one or more streams of dissolution solvent, by means of one or more conveying devices. The stream of plastic raw material can be different from the stream of dissolution solvent. Part or all of the plastic raw material can also be fed into step a) as a mixture with part or all of the dissolution solvent, and the remainder of the solvent and / or raw material can be fed into step a) separately, where appropriate.

[0113] During the contact of the plastic raw material with the dissolving solvent, the dissolving solvent is advantageously at least partially, and preferably completely, in liquid or possibly supercritical form, while the plastic raw material containing polymers, especially thermoplastics, can be in solid or liquid form and optionally contains suspended solid particles. The plastic raw material can also optionally be injected into the dissolving device as a mixture with the dissolving solvent in the form of a suspension in the dissolving solvent, and the preparation and injection of the suspension can be continuous or batchwise.

[0114] Preferably, for the dissolving step a), at least one extruder and a dissolving device are used, such as at least one Continuous Stirred Tank Reactor (CSTR) and at least one mechanical stirring system. In this case, the plastic raw material is fed into the extruder such that at the outlet of the extruder, at least part, preferably all, of the target polymer contained in the plastic raw material is in a molten state. Subsequently, at least part of the plastic raw material in molten form is injected into the dissolving device. At least part of the plastic raw material in molten state can also be pumped by a pump dedicated to viscous fluids (commonly referred to as a melt pump or a gear pump). At least part of the plastic raw material in molten state can also be filtered at the outlet of the extruder by a filtering device (optionally in addition to the melt pump) to remove the coarsest particles; generally, the mesh size of such a filter is between 10 μm (micrometers) and 1 mm (millimeters), preferably between 20 and 200 μm.

[0115] Preferably, at least one static mixer and an extruder are used before at least one CSTR-type reactor in step a), where at least part of the dissolving solvent is injected to promote shear and intimate mixing between the dissolving solvent and the plastic raw material, thereby facilitating the dissolution of the target polymer.

[0116] Very advantageously, the crude polymer solution obtained at the end of the dissolving step a) contains at least the dissolving solvent and the target polymer dissolved in the dissolving solvent. Generally, the crude polymer solution also contains soluble impurities that are also dissolved in the dissolving solvent and optionally suspended insoluble impurities. The crude polymer solution obtained at the end of the dissolving step a) can also optionally contain polymers other than the target polymer, such as in molten state, dissolved state or undissolved state.

[0117] Optional step b') of separating insoluble materials

[0118] The method according to the invention may optionally comprise a step b') of separating insoluble materials from the crude solution, in particular by solid-liquid separation, which advantageously is located upstream of the size-exclusion extraction step b). Thus, when incorporated into the method according to the invention, the step b') of separating insoluble materials makes it possible to advantageously obtain a clarified polymer solution, which is a polymer solution from which at least a part, preferably all, of the insoluble impurities have been removed. When incorporated into the method according to the invention, the step b') of separating insoluble materials also makes it possible to advantageously separate an insoluble fraction, which contains in particular a part, and preferably all, of the insoluble impurities suspended in the crude polymer solution obtained from step a). The insoluble impurities removed during the optional step b') of separating insoluble materials are, for example, additives (pigments, fillers, other polymers, etc.) initially present in the plastic raw material and / or impurities associated with use (such as inorganic compounds, glass, wood, paper, metal, other polymers or degradation products). Preferably, step b') also makes it possible to obtain a clarified polymer solution and an insoluble fraction.

[0119] Advantageously, when the step b') of separating insoluble materials is carried out, it is located upstream of the size-exclusion extraction step b) and generally downstream of the dissolution step a). When this separation step b') is carried out, in addition to removing at least a part of the insoluble impurities, it also advantageously makes it possible to limit operating problems in the downstream method steps, in particular problems of the clogging and / or erosion type, while contributing to the purification of the plastic raw material. Preferably, the method according to the invention comprises the step b') of separating insoluble materials.

[0120] The step b') of separating insoluble materials is advantageously carried out under temperature and pressure conditions close to those of step a). Very advantageously, the step b') of separating insoluble materials is carried out under the temperature and pressure conditions of the dissolution step a), i.e. at the dissolution temperature and dissolution pressure as defined above. Thus, very advantageously, step b') is carried out at a temperature between room temperature and 300 °C, preferably between 20 and 300 °C, preferably between 40 and 250 °C, and at a pressure between atmospheric pressure and 100.0 MPa absolute pressure, preferably between 0.1 and 100.0 MPa absolute pressure, preferably between 0.1 and 25.0 MPa absolute pressure, preferably between 0.1 and 15.0 MPa absolute pressure and very preferably between 0.1 and 5.0 MPa absolute pressure.

[0121] When incorporated into the method, it is preferred to feed the crude polymer solution obtained from step a) to the step b') of separating insoluble materials.

[0122] Advantageously, optional step b') can use a section comprising at least one solid-liquid separation device, such as a knockout drum, a decanter, a centrifugal decanter, a centrifuge, a filter, a sand filter, a tangential filter (especially using membranes and / or depth filters, optionally in the presence of a filter aid such as diatomaceous earth or sand), a hydrocyclone, an electrostatic separator, a triboelectric separator, preferably a decanter, a filter, a sand filter and / or an electrostatic separator. Advantageously, a self-cleaning filter can be used, especially cleaned or unblocked using a solvent stream so that insoluble material can be removed.

[0123] Removal of the insoluble fraction may require the use of equipment that enables conveyance and optionally enables removal of the solvent that may be entrained in the separated insoluble fraction. For example, step b') can use a conveyor, a vibrating tube, a worm, an extruder or a stripper. Step b') can thus use conveying equipment to discharge the insoluble fraction and / or remove the solvent that may be entrained with the separated insoluble fraction. Advantageously, at least a portion of the solvent that may be entrained with the separated insoluble fraction is recovered and recycled to the process.

[0124] According to a particular embodiment, step b') of separating the insoluble material uses 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 enables improved removal of the insoluble material, while the presence of parallel devices enables management of the maintenance and / or unblocking operations of the devices.

[0125] Certain insoluble impurities that are routinely added during polymer formulation, especially certain pigments and inorganic fillers, may be introduced in the form of particles smaller than 1 μm in size. For example, this is the case for titanium dioxide, calcium carbonate and carbon black. According to one embodiment, step b') of separating the insoluble material advantageously uses an electrostatic separator, which enables efficient removal of at least a portion of the insoluble particles smaller than 1 μm in size. According to another embodiment, step b') of separating the insoluble material uses a sand filter to remove particles of different sizes, and especially particles smaller than 1 μm in size. According to yet another embodiment, step b') of separating the insoluble material uses a tangential filter, which especially uses membranes and / or depth filters, optionally in the presence of a filter aid such as diatomaceous earth.

[0126] Depending on the nature of the plastic raw material, the polymer solution fed to step b'), preferably the crude polymer solution, may also optionally contain a second liquid phase, for example consisting of a molten polymer other than the target polymer. According to another particular embodiment, step b') advantageously uses equipment that enables separation of this second liquid phase, preferably by means of at least one three-phase separator.

[0127] According to the present invention, when incorporated into the method, the optional step b') of separating insoluble materials makes it possible to obtain at least one clarified polymer solution comprising at least a dissolved solvent and at least the target polymer dissolved in said solvent. Thus, in step b'), at least a part, preferably all, of the insoluble impurities that may be suspended in the crude polymer solution obtained at the end of step a) of the method according to the present invention are removed from the polymer solution.

[0128] Size exclusion extraction step (b)

[0129] The method according to the present invention comprises a size exclusion extraction step b), in particular feeding an eluent and the crude polymer solution obtained from step a) or optionally feeding the clarified polymer solution obtained from step b') of separating insoluble materials. Advantageously, the size exclusion extraction step b) makes it possible to obtain at least one purified polymer solution and preferably waste solvent, in particular waste solvent carrying impurities.

[0130] The polymer solution fed to the size exclusion extraction step b), in particular the crude polymer solution obtained from step a) or optionally, the clarified polymer solution obtained from step b') of separating insoluble materials, generally contains dissolved impurities which are advantageously at least partially removed during size exclusion extraction and preferably completely removed, in particular by bringing said crude polymer solution or optionally clarified polymer solution into contact with size exclusion solids in the presence of an eluent. Specifically, the size exclusion extraction step b) allows the separation of the compounds present in the crude polymer solution or optionally clarified polymer solution according to their size, in particular at the molecular scale (or more precisely, their hydrodynamic volume), in particular separating the dissolved target polymer and the dissolved impurities. Very advantageously, this extraction step b) of the method allows the selective separation of the target polymer dissolved in the dissolved solvent from the dissolved impurities present in the polymer solution fed to step b) (i.e., the crude polymer solution or optionally clarified polymer solution). Step b) thus makes it possible to produce a purified polymer solution which is a polymer solution free from at least a part, preferably all, of the soluble impurities present in the polymer solution fed to step b), that is to say present in the crude polymer solution or optionally clarified polymer solution.

[0131] Preferably, the eluent fed to step b) is a solvent, in particular an organic solvent or a mixture of solvents, preferably a mixture of organic solvents, preferably a solvent whose Hansen parameters are within the Hansen sphere of the target polymer. Preferably, the eluent is a solvent or a solvent mixture, in particular an organic solvent, preferably selected from hydrocarbons, in particular straight-chain or cyclic alkanes, olefins or aromatics; alcohols, in particular monoalcohols and polyols; straight-chain or cyclic esters; straight-chain or cyclic ethers; straight-chain or cyclic ketones; vinyl compounds; nitrile compounds; straight-chain or cyclic amines and amide compounds; organic sulfur compounds; chlorinated compounds; and mixtures thereof, and preferably contains 1 to 12 carbon atoms, preferably 2 to 8 carbon atoms. For example, the eluent may comprise a mixture of hydrocarbons derived from petroleum fractions, in particular C2 to C8 petroleum fractions:; alkanes, in particular isomers or mixtures of isomers of aliphatic or cyclic C3 to C7 hydrocarbons, such as one or more isomers of butane, pentane, hexane or heptane; aromatics, such as toluene or xylene; C2 to C8 alcohols or mixtures of C2 to C8 alcohols, such as ethanol, propanol or isopropanol, butanol; glycols (or diols), such as ethylene glycol or diethylene glycol; straight-chain or cyclic esters, such as ethyl acetate, propyl acetate, butyl acetate, pentyl acetate, 2-butoxyethyl acetate, butyl propionate, propyl propionate, methyl propionate, allyl acetate, 2-(2-butoxyethoxy)ethyl acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, butyl benzoate, ethyl lactate, γ-butyrolactone (GBL), γ-valerolactone (GVL), caprolactone; aliphatic or cyclic ketones, such as methyl ethyl ketone (MEK), diethyl ketone (DEK), methyl propyl ketone, 4-heptanone, 2,4-dimethyl-3-pentanone, methyl isobutyl ketone (MIBK), diisobutyl ketone, methyl isopentyl ketone, 4-hydroxy-4-methylpentan-2-one, cyclopentanone, cyclohexanone, isophorone; aliphatic or cyclic C3 to C8 ethers, such as methoxycyclopentane, propylene glycol phenyl ether, diethylene glycol butyl ether, dipropylene glycol butyl ether, propylene glycol methyl ether, propylene glycol butyl ether, dipropylene glycol methyl ether, ethylene glycol butyl ether, tetrahydrofuran (THF), 1,3-dioxolane, 2-hydroxymethyloxolane; straight-chain or cyclic amides, such as N,N-diethylformamide, N,N-dimethylacetamide, N,N-dimethylformamide (DMF), 2-pyrrolidone, N-methyl-2-pyrrolidone (NMP); organic acids such as acetic acid alone or in aqueous solution; organic sulfur compounds such as dimethyl sulfoxide (DMSO), sulfolane; chlorinated compounds, such as dichloromethane, chloroform, carbon tetrachloride, trichloroethylene; dihydrolevoglucosenone; and mixtures thereof, or sulfuric acid alone or in aqueous solution. Very preferably, the eluent has the same chemical properties as the dissolving solvent, in fact even the same solvent.

[0132] Advantageously, the size-exclusion extraction step b) uses at least one series, preferably a single series, of a plurality of fixed beds of size-exclusion solids during operation. Advantageously, the series is fed with the crude polymer solution obtained from step a) or optionally the clarified polymer solution obtained from optional step b'), and with an eluent. When step b) comprises a plurality of, especially 2 to 4, series of fixed beds of size-exclusion solids during operation, these series of fixed beds are run in parallel with one another, and each is fed with a portion of the polymer solution fed to step b), especially the crude polymer solution obtained from step a) or optionally the clarified polymer solution obtained from optional step b'), and with a portion of the eluent fed to step b). In this case, the polymer solution fed to step b) is subsequently divided into as many partial streams of crude polymer solution or optionally clarified polymer solution as there are series of fixed beds in operation, and similarly, the eluent fed to step b) is subsequently divided into as many partial streams of eluent as there are series of fixed beds in operation.

[0133] Optionally, the method may further comprise, especially in parallel with step b), at least one series of fixed beds of size-exclusion solids that is not in operation, especially in a standby state and / or in a regeneration and / or standby mode (as described below).

[0134] The fixed bed (or each fixed bed) of the size-exclusion extraction step b) that is advantageously in operation comprises n fixed beds of size-exclusion solids, where n is an integer greater than or equal to 4, preferably between 4 and 30, preferably between 8 and 24, very preferably between 8 and 21, and preferably between 12 and 15. The number of fixed beds must be sufficient so that efficient separation can be achieved and reasonable to limit costs, especially investment costs. The n fixed beds are connected in series relative to one another.

[0135] The n fixed beds of size-exclusion solids can be run in a closed loop or an open loop. Preferably, the n fixed beds of size-exclusion solids are run in a closed loop, that is, the n fixed beds are connected to one another successively and preferably in a closed loop (the first to the second, the second to the third, and so on, and the nth to the first), so that size-exclusion extraction can be run continuously and advantageously reduce the consumption of the eluent, since the eluent is subsequently partially continuously regenerated and recycled.

[0136] In a (or each) series of fixed beds, the fixed beds of the n size-exclusion solids are advantageously distributed in one or more columns, preferably in M columns, where M is an integer between 1 and the total number of fixed beds of the size-exclusion solids of the series under consideration, that is to say M is between 1 and n. Thus, the (or each) series of fixed beds of the size-exclusion extraction step b) can use from 1 to n columns, each containing one or more fixed beds of size-exclusion solids. For example, the (or each) series of fixed beds of the size-exclusion extraction step b) can use a single column (or tower), preferably with a large capacity (volume), which contains n fixed beds; or two towers, each containing n / 2 fixed beds. These two configurations make it possible to significantly limit the investment costs, but when there is a problem with one bed in the tower, it is necessary to unload the entire tower, i.e., n fixed beds or n / 2 fixed beds. According to another embodiment, the (or each) series of fixed beds of the size-exclusion extraction step b) uses n columns (or towers), preferably with a smaller capacity (volume) for each tower than in the previous case, each tower containing a fixed bed of size-exclusion solid, thus facilitating maintenance and / or cleaning and / or by-passing, especially of one of the n beds in operation, since in this configuration, it is only one tower (which contains only one bed) rather than an assembly of beds that has to be unloaded and / or by-passed. However, the latter configuration requires a large amount of capital costs.

[0137] Preferably, the size exclusion solid is provided in the form of solid particles. It can also be referred to as a particulate medium. The size exclusion solid is selected to be inert with respect to the polymer solution to be treated (i.e., the dissolution solvent and the polymer to be treated) and with respect to the eluent. It is also selected to be capable of efficiently separating compounds present in, in particular dissolved in, the treated polymer solution, and more particularly impurities dissolved in the dissolution solvent with respect to the dissolved target polymer. Advantageously, the size exclusion solid is a porous (mesoporous and / or macroporous) solid, which can be organic (usually polymeric) and / or inorganic, and preferably has a volume average pore diameter preferably between 1 and 500 nm, preferably between 2 and 100 nm, very preferably between 2 nm and 50 nm (mesoporous solid), and preferably between 3 and 30 nm. Advantageously, the size exclusion solid comprises silica (such as silica gel, also known as silica, and / or grafted silica), carbon molecular sieves, polymer molecular sieves (chemically different from the target polymer), porous polymer gels, preferably dealuminated zeolites (such as USY type), carbon replicas, preferably calcined alumina, MOF (metal organic framework) type materials or mixtures thereof. Preferably, the size exclusion solid comprises silica gel (or silica), grafted silica, carbon molecular sieves or mixtures thereof, preferably consisting of silica gel (or silica), grafted silica, carbon molecular sieves or mixtures thereof. Very advantageously, the size exclusion solid preferably exhibits a pore volume between 0.01 and 3.0 ml / g, preferably between 0.1 and 2.0 ml / g, preferably between 0.3 and 1.2 ml / g. The average pore diameter and pore volume of the size exclusion solid are determined by mercury porosimetry, and more particularly by mercury intrusion porosimetry using a surface tension of 484 dynes / cm and a contact angle of 140° at a maximum pressure of 4000 bar according to standard ASTM D4284-83. According to the recommendation on page 1050 of the publication "Techniques de l’ingénieur, traité analyse et caractérisation" by J. Charpin and B. Rasneur [Engineering Techniques, Analysis and Characterization Treatise], the wetting angle taken is equal to 140°. For better accuracy, a given value of the mercury volume in ml / g corresponds to the total mercury volume value in ml / g measured on the sample minus the mercury volume value in ml / g measured on the same sample at a pressure corresponding to 30 psi (about 2 bar).These same parameters, and in particular the volume and diameter of solids in the mesoporous range (2 - 50 nm), can also be measured by the nitrogen adsorption / desorption volumetry method (also known as nitrogen adsorption isotherm), which is an analytical method complementary to the above-mentioned method. This analysis corresponds to the physical adsorption of nitrogen molecules in the pores of the material via a gradually increasing pressure at a constant temperature and provides information on the texture characteristics. In particular, it enables the acquisition of the mesoporous distribution of size-excluding solids. Thus, the representative pore distribution of pore groups centered in the range of 2 to 50 nm is determined by the Barrett-Joyner-Halenda (BJH) model. The nitrogen adsorption-desorption isotherm according to the BJH model is described in the journal "The Journal of the American Chemical Society", 73, 373 (1951) by E.P. Barrett, L.G. Joyner, and P.P. Halenda.

[0138] The particles of the size-excluding solid preferably have a volume-average equivalent diameter between 20 and 5000 μm, preferably between 50 and 1500 μm, preferably between 100 and 800 μm, and even more preferably between 300 and 600 μm (preferably determined by laser particle size analysis, that is, by laser diffraction using a particle size analyzer). Advantageously, the solid particles are substantially spherical.

[0139] According to the invention, the said (or each) series of fixed beds of the size-excluding extraction step b) is fed with a crude polymer solution or an optionally clarified polymer solution at at least one polymer solution injection point F and with at least one eluent at an eluent injection point S. Preferably, the said series of fixed beds under consideration is fed with a crude polymer solution or an optionally clarified polymer solution at the polymer solution injection point F and with an eluent at the eluent injection point S.

[0140] Preferably, the eluent and the polymer solution are fed to the said (or each) series of fixed beds of the size-excluding extraction step according to a ratio of the volume flow rate of the eluent to the volume flow rate of the polymer solution between 0.1 and 50.0, preferably between 0.2 and 10.0, preferably between 0.5 and 5.0, preferably between 0.8 and 2.0. This ratio can also be referred to as the solvent level. For the said (or each) series under consideration, this solvent level, that is, this adjustment of the volume flow rate of the crude polymer solution or the optionally clarified polymer solution and the volume flow rate of the eluent, contributes to the efficiency of the size-excluding separation of the target thermoplastic and impurities present in the polymer solution fed in step b).

[0141] When the series of fixed beds includes a plurality of polymer solution injection points Fi, for example, two polymer solution injection points F1 and F2, the stream of crude polymer solution or clarified polymer solution fed to the series of fixed beds under consideration is divided into the same number of sub-streams of polymer solution to be fed to the series of fixed beds at the injection points Fi, and the sub-streams of polymer solution exhibit the same or different flow rates from each other.

[0142] When the series of fixed beds includes a plurality of eluent injection points Si, for example, two injection points S1 and S2, the total eluent stream fed to the series of fixed beds under consideration is divided into the same number of sub-streams of eluent (that is, divided into i sub-streams of eluent, where i is an integer equal to the number of eluent injection points Si) to be fed to the series of fixed beds at the injection points Si, and the sub-streams of eluent exhibit the same or different flow rates from each other.

[0143] The (or each) series of fixed beds in the size exclusion extraction step b) performs at least one extract withdrawal at at least one extract withdrawal point E and at least one raffinate withdrawal at at least one raffinate withdrawal point R. Preferably, the (or each) series of fixed beds in the size exclusion extraction step b) performs extract withdrawal at the extract withdrawal point E and raffinate withdrawal R at the raffinate withdrawal point R.

[0144] The polymer solution injection point F, the eluent injection point S, the extract withdrawal point E, and the raffinate withdrawal point R are different from each other. They are advantageously located between two successive beds or optionally upstream of the first bed, particularly in the case of an open circuit (in the case of a closed circuit of n fixed beds, since the nth bed is connected to the first bed, these two beds are considered to be successive). However, in particular according to In one embodiment of the process, on average during the operating cycle, they can be located in the middle of the fixed bed or in the fixed bed. The polymer solution injection point, the eluent injection point, the extract withdrawal point, and the raffinate withdrawal point are distributed relative to each other such that they define at least three, preferably four successive main operating zones of the n fixed beds:

[0145] - An impurity elution zone I, which is included between the eluent injection point S and the extract withdrawal point E;

[0146] - An elution zone II of the target polymer, which is included between the extract withdrawal point E and the polymer solution injection point F;

[0147] - An impurity retention zone III, which is included between the polymer solution injection point F and the raffinate withdrawal point R; and

[0148] - Optionally and preferably, zone IV, which is comprised between raffinate withdrawal point R and eluent injection point S.

[0149] When there are multiple polymer solution injection points Fi and / or multiple eluent injection points Si and / or multiple extract withdrawal points and / or multiple raffinate withdrawal points, zones I, II, III and optionally IV start at the first injection point and / or withdrawal point of the stream under consideration (eluent, polymer solution, extract or raffinate), the term "first" being defined herein as the most upstream point among all injection points and / or withdrawal points of the stream under consideration. When there are multiple polymer solution injection points Fi and / or multiple eluent injection points Si and / or multiple extract withdrawal points and / or multiple raffinate withdrawal points, secondary operating zones can also be defined, in particular within zones I, II, III and optionally IV which are the main operating zones.

[0150] When the n fixed beds of the considered series of step b) operate in an open circuit, an eluent is introduced at eluent injection point S, a crude polymer solution or optionally a clarified polymer solution is introduced at polymer solution injection point F, an extract is withdrawn at extract withdrawal point E, and all residues are withdrawn at raffinate withdrawal point R. Thus, the injection points and withdrawal points define three successive main operating zones, namely zones I, II, III. In this embodiment, a large amount of eluent is generally required relative to the polymer solution in order to be able to maximize the separation. For example, this operating mode in an open circuit requires a volume flow rate ratio of eluent to polymer solution between 2.0 and 50.0, preferably between 5.0 and 20.0, and in fact even between 5.0 and 10.0.

[0151] When the n fixed beds of the considered series of step b) operate in a closed circuit, an eluent is introduced at eluent injection point S, a crude polymer solution or optionally a clarified polymer solution is introduced at polymer solution injection point F, an extract is withdrawn at extract withdrawal point E, a raffinate is withdrawn at raffinate withdrawal point R, and at least a portion of the introduced eluent advantageously remains in circulation in the closed circuit of the n beds (the expression used is recycle of the eluent). In this embodiment, the injection points and withdrawal points thus define four successive main operating zones, namely zones I, II, III and IV, and zone IV can be referred to as the regeneration and recycle zone of the eluent. In this particular embodiment, in order to ensure efficient separation, the supply requirement of the eluent (i.e., the amount of eluent introduced at S) is very advantageously less than in the case of the open circuit operating mode. For example, this operating mode in a closed circuit requires a volume flow rate ratio of eluent to polymer solution between 0.1 and 10, preferably between 0.2 and 5.0, and in fact even between 0.8 and 2.0.

[0152] Advantageously, in the case of a closed loop of n fixed beds, the n size - exclusion solid beds are distributed in zones I to IV, preferably according to an a / b / c / d type configuration. With respect to the total number n of size - exclusion solid beds, the distribution of the size - exclusion solid beds in zones I to IV is such that:

[0153] - a is the number of size - exclusion solid beds in zone I,

[0154] - b is the number of size - exclusion solid beds in zone II,

[0155] - c is the number of size - exclusion solid beds in zone III, and

[0156] - d is the number of size - exclusion solid beds in zone IV,

[0157] And wherein:

[0158] - a=(n * 0.30)*(1 ± 0.40, preferably 1 ± 0.30),

[0159] - b=(n * 0.15)*(1 ± 0.40, preferably 1 ± 0.30),

[0160] - c=(n * 0.25)*(1 ± 0.40, preferably 1 ± 0.30), and

[0161] - d=(n * 0.30)*(1 ± 0.40, preferably 1 ± 0.30).

[0162] It is obvious to a person skilled in the art that the sum of the number of fixed beds in zones I, II, III and IV (i.e., a + b + c + d) is advantageously equal to n, i.e., the total number of fixed beds in the series of fixed beds in the considered operation. Thus, a 6 / 3 / 4 / 2 configuration means that there are 15 fixed beds of size - exclusion solids, which are divided into 6 fixed beds in zone I, 3 fixed beds in zone II, 4 fixed beds in zone III and 2 beds in zone IV.

[0163] Very advantageously, the bulk density of each of the n fixed beds of size - exclusion solids, expressed as the mass / unit volume of the bed (i.e., in kg solid / m 3 bed), can vary between 100 and 1500 kg / m 3 preferably between 300 and 1000 kg / m 3 preferably between 400 and 800 kg / m 3 and vary.

[0164] According to the present invention, the injection points F and S and the withdrawal points E and R are moved along a size exclusion solid bed at a frequency determined by a predetermined switching period over time. The switching period can be defined as the time between two successive displacements (or movements) of the injection and withdrawal points by one fixed bed. The periodic displacement (or movement) of the injection points F and S and the withdrawal points E and R can be carried out synchronously or asynchronously, and the latter case (asynchronous) may be known by the name of The periodic displacement of the injection and withdrawal points along the entire length of the n fixed beds in particular makes it possible to define the operating cycle and also advantageously defines the cycle time, which corresponds to the time required for the injection and withdrawal points to return to their initial positions, that is to say, which corresponds to the number of beds n multiplied by the switching period.

[0165] When the n fixed beds of size exclusion solids operate in a closed loop, the operating cycle thus advantageously contains the same number of switching periods as the size exclusion solid beds present in the closed separation loop. For example, the operating cycle of a series of fixed beds containing 12 size exclusion solids contains 12 switching periods.

[0166] Thus, in a preferred embodiment in which the n fixed beds of size exclusion solids of the considered series of fixed beds operate in a closed loop, it is preferred to adjust the switching period to define a cycle time, which corresponds to the time required for the injection and withdrawal points to return to their initial positions, which is between 1 minute and 600 minutes, preferably between 5 minutes and 200 minutes, preferably between 10 minutes and 90 minutes. Such a cycle time contributes to the efficiency of the size exclusion separation of the target polymer and impurities present in the polymer solution fed in step b).

[0167] In the case of an embodiment in which the n fixed beds operate in an open loop (that is to say all substances are withdrawn together with the extract and raffinate), the cycle time can also be between 1 minute and 600 minutes, preferably between 5 minutes and 200 minutes, preferably between 10 minutes and 90 minutes.

[0168] The displacement of the injection points F and S and the withdrawal points E and R can be achieved by installing a series of on-off valves controlled by an automatic sequence or by installing a single rotary valve.

[0169] Generally, the liquid flow in the fixed bed advantageously goes from bed i to bed i+1, where i is an integer between 1 and n (total number of fixed beds), that is, from upstream to downstream, and can be called downward liquid flow, even if a pump must be present (in the case of operation in a closed loop and in the case where the n beds are in a tower, especially between the nth bed and the first bed). At the moment of switching (or shifting of the injection and withdrawal points), the injection and withdrawal points are shifted by one bed, placed downstream of the previous bed, thereby establishing / simulating a countercurrent liquid flow, optionally called upward liquid flow. When the two countercurrent liquid flows are equal, that is, when the downward liquid flow is equal to the upward liquid flow, the stop flow can then be defined. The stop flow can be calculated by dividing the interstitial volume of the size-excluding solid in the bed by the switching period, and the interstitial volume of the size-excluding solid in the bed is a function of the bulk density of the fixed bed of the size-excluding solid and the particle density of the size-excluding solid. More particularly, the interstitial volume (V (颗粒间) ) can be calculated by the following formula:

[0170] V (颗粒间) = V (床) x (1 - d (堆积) / d (颗粒) ) + V 死区

[0171] Where:

[0172] V (颗粒间) : The interstitial volume of the size-excluding solid in the bed (in m 3 );

[0173] V (床) : The geometric volume of the bed (in m 3 );

[0174] d (堆积) : The bulk density of the size-excluding solid in the bed (in kg / m 3 ), corresponding to the true bulk density of the size-excluding solid, that is, the mass / unit volume of the bed of the solid. As a first method, according to the principles derived from standards D4164 and D4180 applicable to the catalyst case, it can be compared to the tapped bulk density, which consists of the mass of the solid that occupies a given volume after being tapped and compacted by vibration;

[0175] d (颗粒) : The particle density of the size-excluding solid, usually measured by mercury porosimetry (in kg / m 3 );

[0176] V 死区 : The volume of the device through which the fluid flows, especially the polymer solution, without the size-excluding solid (in m 3count (e.g., the volume of the upstream pipeline, downstream pipeline, etc.).

[0177] Stopping the flow rate (which is a volumetric flow rate) enables the calculation of dimensionless parameters, particularly those related to zones II and IV, specifically the ratio of the volumetric flow rate in zone II to the stopping flow rate, and the ratio of the volumetric flow rate in zone IV to the stopping flow rate. Preferably, the ratio of the volumetric flow rate in zone IV divided by the stopping flow rate is less than or equal to 2, preferably between 0.5 and 1.5, and even more preferably between 0.8 and 1.0. Preferably, the ratio of the volumetric flow rate in zone II divided by the stopping flow rate is between 0.5 and 3.0, preferably between 0.9 and 1.5, and preferably between 1.0 and 1.25. Thus, the stopping flow rate helps to regulate the extraction step and thus contributes to the separation efficiency.

[0178] Furthermore, very advantageously, the superficial velocity in the fixed bed of the operating zone can be adjusted - which corresponds to the volumetric flow rate in the considered zone divided by the cross-sectional area of the zone (i.e., the column in which the bed of the considered zone is located) - such that this superficial velocity is between 0.01 and 10.0 cm / s, and preferably between 0.05 and 2.5 cm / s. Adjusting the superficial velocity in the fixed bed advantageously enables the control of particle wear of the size-exclusion solids in particular, and thus the operation of the series of fixed beds in step b) can be adjusted to avoid large pressure drops (encountered especially at high speeds) and / or dispersion problems (encountered especially at low speeds).

[0179] Preferably, the size-exclusion extraction step b) is carried out at a temperature between room temperature and 300 °C, preferably between 20 and 300 °C, preferably between 40 and 250 °C, and at a pressure between atmospheric pressure and 100.0 MPa absolute pressure, preferably between 0.1 and 100.0 MPa absolute pressure, preferably between 0.1 and 25.0 MPa absolute pressure, preferably between 0.1 and 15.0 MPa absolute pressure, and very preferably between 0.1 and 5.0 MPa absolute pressure. Under these operating conditions, the target polymer, particularly the target thermoplastic, and more particularly the thermoplastic other than polyolefin and PVC polymers, remains dissolved in the dissolution solvent and optionally dissolved in the eluent, the latter (i.e., the dissolution solvent and the eluent) being at least partially in liquid form by itself. Preferably, the temperature and pressure conditions of step b) are the same as those of the dissolution step a).

[0180] The size-exclusion extraction step b) thus makes it possible to recover at least one extract and at least one raffinate, the extract containing at least partially, preferably completely, the impurities present in the polymer solution fed to said step b), and the raffinate containing the polymer solution from which the impurities have been at least partially, preferably completely, removed. The raffinate recovered at the end of the size-exclusion extraction step b) partially or completely constitutes the purified polymer solution, which is recovered at the end of step b). Subsequently, this purified polymer solution is preferably fed at least partially, preferably completely, to the polymer-solvent separation step c). However, if necessary, it can be fed to at least one additional purification step to optimize the purification of the target polymer (if required). This size-exclusion extraction step b) thus makes it possible to efficiently and continuously separate impurities, in particular soluble impurities, from a crude polymer solution or an optionally clarified polymer solution containing the target polymer dissolved in a dissolution solvent, in particular a target thermoplastic, and more particularly a thermoplastic other than polyolefins and PVC.

[0181] Size-exclusion extraction, particularly in the case of a closed loop of a fixed bed, makes it possible to efficiently separate impurities from the target polymer in continuous mode, which makes it possible to limit the labor required for said step while promoting its operability. It also allows for high productivity, particularly compared to size-exclusion chromatography operations in batch mode, while providing a relatively low eluent consumption.

[0182] Polymer-solvent separation step c)

[0183] According to the invention, the method comprises a polymer-solvent separation step c) of the purified polymer solution to obtain at least one stream of purified polymer, in particular a stream of purified thermoplastic, and more particularly a stream of purified thermoplastic other than polyolefins and PVC, and at least one solvent fraction containing the dissolution solvent.

[0184] The polymer-solvent separation step c) advantageously uses at least one solvent recovery section, and preferably 1 to 5 solvent recovery sections.

[0185] Advantageously, the purified polymer solution obtained at the end of step b) or the finally purified polymer solution optionally obtained from an additional purification step located downstream of the size-exclusion extraction step b) is fed to step c).

[0186] The polymer-solvent separation step c) thus mainly aims to at least partially, preferably mainly, separate the dissolved solvent and optionally the eluent from the target polymer contained in the polymer solution fed to step c), more particularly the purified polymer solution or optionally the finally purified polymer solution obtained from an additional purification step, so as to recover at least partially, preferably mainly, and preferably completely the at least target polymer from which the dissolved solvent and optionally the eluent still present in the polymer solution fed to step c) have been removed. The term "mainly" should be understood to mean at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight, and even more preferably at least 95% by weight, based on the weight of the solvent contained in the purified polymer solution fed to step c), in particular the dissolved solvent and optionally the eluent contained in said purified polymer solution. Any solvent / polymer separation method known to those skilled in the art can be carried out, in particular any method that enables the polymer and / or the solvent to undergo a phase change. The solvent can be separated, for example, by precipitation or crystallization of the polymer, flash evaporation of the solvent, atomization (high-pressure jet, rotary atomizer, two-fluid nozzle, ultrasonic atomizer), stripping, stratification, density difference, and in particular by decantation or centrifugation, extrusion separation, etc.

[0187] The stream of the at least one purified polymer thus obtained can correspond to a polymer solution concentrated in the target polymer or to the target polymer in liquid (or viscous) or solid form. Preferably, the polymer-solvent separation step c) additionally comprises an adjustment section for adjusting the purified polymer in solid form, and more particularly in powder or granular form.

[0188] The polymer-solvent separation step c) also aims to at least partially, preferably mainly, and preferably completely recover the solvent contained in the purified polymer solution fed to step c), in particular the dissolved solvent and optionally the eluent. The polymer-solvent separation step c) also optionally aims to purify and recycle the recovered solvent fraction, in particular upstream of the dissolution step a). The term "mainly" should be understood to mean at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight, and even more preferably at least 95% by weight, based on the weight of the solvent contained in the purified polymer solution fed to step c).

[0189] Advantageously, the polymer-solvent separation step c) uses at least one solvent recovery section, which preferably comprises equipment operating at different temperatures and different pressures in order to obtain at least one solvent fraction and one purified polymer fraction.

[0190] Thus, the method according to the invention makes it possible to efficiently and continuously recover polymers, in particular thermoplastics, and more particularly thermoplastics other than polyolefins and PVC, from plastic feedstocks with high productivity and a limited number of operations. Very advantageously, the method according to the invention makes it possible to start from any type of plastic feedstock and obtain a stream of polymer with a high purity, preferably greater than or equal to 90%, preferably greater than or equal to 95%, preferably greater than or equal to 99%, preferably greater than or equal to 99.5% (by weight of the target polymer, in particular the target thermoplastic, and more particularly the thermoplastic other than polyolefins and PVC, relative to the total weight of the recovered and purified stream). Another advantage of the method according to the invention also lies in the fact that impurities present in the plastic feedstock, in particular additives, can be efficiently separated, while making it possible to reasonably consume solvents, in particular dissolution solvents and eluents, and the energy consumption is lower than that of more conventional "thermal" separations, such as the energy consumption required for crystallization. The method according to the invention thus makes it possible to obtain a stream of purified polymer that is less colored than the plastic feedstock to be treated, practically even colorless and very advantageously deodorized. The stream of purified polymer obtained preferably has a negligible content of prohibited or regulated substances, such as those prohibited or regulated by the REACH regulation. More particularly, the method according to the invention makes it possible to obtain a stream of purified polymer that removes at least a part, preferably all, of the impurities present in the plastic feedstock, such as additives and at least partially, practically even completely removes solvents, in particular dissolution solvents and eluents.

[0191] Thus, the method according to the invention advantageously makes it possible to obtain a stream of purified polymer having an impurity content of less than or equal to 10% by weight, preferably less than or equal to 5% by weight, preferably less than or equal to 1% by weight, and even more preferably less than or equal to 0.5% by weight of impurities, and very advantageously a solvent (in particular dissolution solvent and eluent) content of less than or equal to 10% by weight, preferably less than or equal to 5% by weight, and preferably less than or equal to 1% by weight, the percentages being given relative to the total weight of the stream of purified polymer.

[0192] Size exclusion extraction device

[0193] The invention also relates to a size exclusion extraction device suitable for separating dissolved polymers, in particular dissolved thermoplastics, and more particularly dissolved thermoplastics other than polyolefins and PVC, from the impurities contained in the polymer solution. The device comprises:

[0194] - A fixed bed of n size - exclusion solids, where n is an integer greater than or equal to 4, preferably between 4 and 30, more preferably between 8 and 24, very preferably between 8 and 21, and preferably between 12 and 15. The size - exclusion solids have a volume - average pore diameter preferably between 1 and 500 nm, preferably between 2 nm and 100 nm, preferably between 2 nm and 50 nm, preferably between 3 and 30 nm, and are preferably silica (or silicon dioxide), grafted silica, carbon molecular sieve, or a mixture thereof.

[0195] The fixed bed of the n size - exclusion solids is distributed in one or more towers, preferably in M towers, where M is an integer between 1 and the total number n of the fixed beds of size - exclusion solids. The n beds are connected in series and preferably in a closed loop.

[0196] - N polymer - solution injection systems (preferably different from each other), N eluent injection systems (preferably different from each other), N extract removal systems (preferably different from each other), and N raffinate removal systems (preferably different from each other), where N is an integer preferably equal to n. The injection and removal systems are located between two successive beds or optionally upstream of the first bed.

[0197] Among them, the polymer - solution injection system, the eluent injection system, and / or the extract removal system and the raffinate removal system located at the same position, that is, between the same two successive beds or optionally upstream of the first bed, can be different or the same (the term "the same" should be understood to mean that the valve system can allow the introduction of polymer solution or eluent, or the removal of one or the other stream, that is, the removal of extract or raffinate).

[0198] - Each injection and removal system includes at least one valve suitable for allowing or not allowing the flow of polymer solution and / or eluent flow and / or extract flow and / or raffinate flow to pass through. Preferably, i) a series of switching valves controlled by an automatic sequence, or ii) a single rotary valve, so that:

[0199] - At time t, define the polymer - solution injection point, the eluent injection point, the extract removal point, and the raffinate removal point. The injection points and removal points are different from each other and determine at least three, preferably four successive main operating zones of the n fixed beds:

[0200] - Impurity elution zone I, which is included between the eluent injection point and the extract removal point;

[0201] - Elution zone II of the target polymer, which is included between the extract removal point and the polymer - solution injection point;

[0202] - Impurity retention zone III, which is included between the polymer - solution injection point and the raffinate removal point; and

[0203] - Optionally, zone IV, which is located between the raffinate withdrawal point and the eluent injection point;

[0204] - And such that the injection point and the withdrawal point can be moved synchronously or asynchronously by one size-exclusion solid fixed bed per switching cycle over time according to a frequency determined by a predetermined switching cycle.

[0205] Device for processing plastic raw materials

[0206] Such a size-exclusion extraction device can be incorporated into a more encompassing plastic raw material processing device to obtain a purified polymer stream, preferably a purified thermoplastic other than polyolefin and PVC advantageously, and the device comprises:

[0207] - Dissolution means for bringing the plastic raw material into contact with a dissolution solvent to dissolve at least part of the plastic raw material in the dissolution solvent, and the dissolution means is any type of equipment for bringing the plastic raw material into contact with the dissolution solvent and dissolving it, such as an extruder, one or more static mixers, one or more continuous stirred tank reactors (CSTRs) equipped with a suitable stirring system, to obtain a crude polymer solution;

[0208] - Optionally, solid-liquid separation means, in particular any type of solid-liquid separation equipment optionally, which is suitable for separating insoluble materials suspended in the crude polymer solution;

[0209] - At least one size-exclusion extraction device according to the present invention and as described above, which is advantageously connected to the dissolution means for contacting and dissolving or optionally connected to at least one of the solid-liquid separation means;

[0210] - Means for separating the dissolution solvent and optionally the eluent from the purified polymer stream, in particular any type of equipment for separating the dissolution solvent and optionally the eluent from the purified polymer stream optionally, which is advantageously connected to the at least one size-exclusion extraction device.

[0211] The device for processing plastic raw materials to obtain a purified polymer stream also advantageously comprises means for conveying between the means and the device.

[0212] Such a device very advantageously enables the recovery of high-purity polymers, preferably purified thermoplastics other than polyolefins and PVC advantageously, from plastic raw materials that may contain many impurities.

[0213] The following examples and the accompanying drawings illustrate the present invention, in particular specific embodiments of the present invention, without limiting its scope. Examples

[0214] Example 1

[0215] This example is based on the results of digital simulations performed on experiments conducted in the laboratory.

[0216] The raw material to be processed consists of 97.9 wt% of polyethylene terephthalate (PET) with a number-average molar mass MW = 30000 g / mol, 2 wt% of titanium dioxide, and 0.1 wt% of solvent blue 104, which is an organic dye derived from anthraquinone and is commonly used in PET formulations.

[0217] First, the raw material is dissolved in tetrahydrofuran (THF) at 190 °C and 1.8 MPa (or 18 bar) to form a homogeneous crude polymer solution containing 90 wt% of THF and 10 wt% of the raw material (which contains PET and additives).

[0218] The crude polymer solution is filtered to remove all insoluble additives such as titanium dioxide.

[0219] The resulting solution is introduced into a simulated moving bed consisting of 15 beds containing silica gel and distributed in a 6 / 3 / 4 / 2 configuration (see Figure 1 ). The eluent is THF.

[0220] The silica gel in the beds is in the form of beads and has the following characteristics:

[0221] The silica gel exhibits the following properties:

[0222] - Bead diameter = 500 μm;

[0223] - Pore diameter = 6 - 10 nm;

[0224] - Pore volume = 0.50 ml / g;

[0225] - Bulk density = 530 kg of solid / m 3 of the bed

[0226] - External particle porosity = 0.4.

[0227] Each bed is modeled by a 1D piston fixed-bed model with axial dispersion and a Fick model for intra-particle transfer. Since the radius of gyration of polyethylene terephthalate is estimated to be 14 nm, the polymer is considered to be present only in the external particle phase. The radius of gyration of the dye and the solvent is less than 1 nm and can therefore diffuse into the intra-particle pores. Size exclusion separation is carried out at 190 °C and 1.8 MPa (18 bar). All beds are modeled and the cycle is dynamically solved until the concentration profiles converge.

[0228] This extraction is adjusted by the following settings:

[0229] - Cycle time = 10 min

[0230] - The volume flow rate of the eluent (THF) relative to the volume flow rate of the polymer solution S / F = 1.42;

[0231] - Zone IV flow rate / stop flow rate = 0.94;

[0232] - Zone II flow rate / stop flow rate = 1.08;

[0233] - Maximum apparent velocity = 2.10 cm / s.

[0234] The concentration profiles of PET and the dye obtained by simulation along the entire length of the simulated moving bed are as Figure 3 shown, where the eluent is injected upstream of bed 1 (and downstream of bed 15) as a convention. In Figure 3 it, the concentration profile of PET is represented by a solid black line, while the concentration profile of the dye Blue 104 is represented by a dashed line. The concentration along the entire length of the bed is given as the mass fraction of the compound being traced.

[0235] From Figure 3 it is obvious that the polyethylene terephthalate (PET) that does not enter the intragranular pores is entrained into the raffinate and withdrawn between beds 13 and 14. Due to the smaller size of the additive, it can diffuse into the intragranular pores and be entrained into the extract, which is withdrawn between beds 6 and 7.

[0236] The steps of PET extraction carried out in the simulated moving bed make it possible to obtain the following performance qualities:

[0237] - The content of Blue 104 in the raffinate is equal to 0.66 ppm by weight (which corresponds to the weight of Blue 104 in the raffinate relative to the total weight of the dye and polyethylene terephthalate, excluding the solvent, i.e., excluding THF), while at the inlet of the process, the content of Blue 104 is 1019 ppm by weight relative to the total weight of the dye and PET in the crude polymer solution. Therefore, after size exclusion continuous extraction, the content of the dye in the raffinate is greatly reduced.

[0238] - The PET yield is 100% by weight (which corresponds to the weight flow rate of PET withdrawn in the raffinate divided by the weight flow rate of PET withdrawn in the combination of the extract + raffinate). All PET is located in the raffinate. There is no loss of PET in the extract. The PET yield is optimal.

[0239] - The productivity is 85 kg PET / h / m withdrawn in the raffinate 3 Silica gel bed

[0240] The raffinate at the outlet of the simulated moving bed used for size exclusion extraction can be subsequently recycled and fed into the polymer-solvent separation section, in particular the evaporation section of the solvent THF.

Claims

1. A method for purifying a stream of plastic raw materials to obtain a purified polymer stream, the method comprising: a) a dissolution step, which comprises contacting the plastic raw materials with a dissolution solvent to obtain at least one crude polymer solution; b’) optionally, a step of separating insoluble materials from the crude polymer solution obtained from step a) to obtain at least one clarified polymer solution; b) a size exclusion extraction step of the crude polymer solution obtained at the end of step a) or optionally the clarified polymer solution obtained at the end of optional step b’) to obtain a purified polymer solution, wherein the size exclusion extraction step uses at least one series of n fixed beds of size exclusion solids, n being an integer greater than or equal to 4, the n beds being in series, the series of fixed beds of step b) is fed with the crude polymer solution or optionally the clarified polymer solution at at least one polymer solution injection point F and with an eluent at at least one eluent injection point S, wherein the series of fixed beds of step b) performs at least one extract removal at at least one extract removal point E and at least one raffinate removal at at least one raffinate removal point R, wherein the polymer solution injection point and the eluent injection point and the extract removal point and the raffinate removal point are different from each other and are distributed such that they define at least three, preferably four, successive main operating zones of the n fixed beds: - an impurity elution zone I, which is located between the eluent injection point and the extract removal point; - an elution zone II of the target polymer, which is located between the extract removal point and the polymer solution injection point; - an impurity retention zone III, which is located between the polymer solution injection point and the raffinate removal point; and - optionally, a zone IV, which is located between the raffinate removal point and the eluent injection point, wherein the injection points and the removal points are moved by one fixed bed of size exclusion solids over time according to a frequency determined by a predetermined switching cycle, wherein the raffinate is recovered to at least partially constitute the purified polymer solution, c) a polymer-solvent separation step of the purified polymer solution to obtain at least one stream of purified polymer and at least one solvent fraction containing the dissolution solvent.

2. The method according to claim 1, wherein the stream of purified polymer is preferably a stream of purified thermoplastics other than polyolefins and PVC.

3. The method according to claim 1 or 2, wherein the eluent has the same chemical properties as the dissolution solvent.

4. The method according to any one of the preceding claims, wherein the size exclusion extraction step b) uses at least one series of n fixed beds of size exclusion solids, n being an integer between 4 and 30, and preferably between 12 and 15.

5. The method according to any one of the preceding claims, wherein the size exclusion solids are porous solids having a volume average pore diameter between 1 and 500 nm, preferably between 2 and 100 nm, preferably between 2 nm and 50 nm, preferably between 3 and 30 nm.

6. The method according to any one of the preceding claims, wherein the size exclusion solid comprises silica gel, grafted silica, carbon molecular sieve or a mixture thereof.

7. The method according to any one of the preceding claims, wherein the eluent and the polymer solution are fed into step b) according to a ratio of the volume flow rate of the eluent to the volume flow rate of the polymer solution that is between 0.1 and 50.0, preferably between 0.2 and 10.0, preferably between 0.5 and 5.0, preferably between 0.8 and 2.

0.

8. The method according to any one of the preceding claims, wherein the polymer solution injection point and the eluent injection point, and the extract withdrawal point and the raffinate withdrawal point are located between two successive beds or optionally upstream of the first bed.

9. The method according to any one of the preceding claims, wherein the n size exclusion solid beds operate in a closed loop and are distributed in four main operating zones, namely zones I to IV, according to a configuration of type a / b / c / d. With respect to the total number n of size exclusion solid beds, the distribution of the size exclusion solid beds in zones I to IV is preferably such that: - a is the number of size exclusion solid beds in zone I, - b is the number of size exclusion solid beds in zone II, - c is the number of size exclusion solid beds in zone III, and - d is the number of size exclusion solid beds in zone IV, and wherein: - a = (n * 0.30) * (1 ± 0.40, preferably 1 ± 0.30), - b = (n * 0.15) * (1 ± 0.40, preferably 1 ± 0.30), - c = (n * 0.25) * (1 ± 0.40, preferably 1 ± 0.30), and - d = (n * 0.30) * (1 ± 0.40, preferably 1 ± 0.30).

10. The method according to any one of the preceding claims, wherein the n beds are in a closed loop and preferably the switching period is adjusted to define a cycle time, which corresponds to the time required for the injection point and the withdrawal point to return to their initial positions, and which is between 1 and 600 minutes, preferably between 5 and 200 minutes, preferably between 10 and 90 minutes.

11. The method according to any one of the preceding claims, wherein step a) is carried out at a dissolution temperature between 20 °C and 300 °C, preferably between 40 °C and 250 °C, and at a dissolution pressure between 0.1 and 100.0 MPa absolute pressure, preferably between 0.1 and 25.0 MPa absolute pressure, preferably between 0.1 and 15.0 MPa absolute pressure, and very preferably between 0.1 and 5.0 MPa absolute pressure.

12. The method according to any one of the preceding claims, wherein step a) is fed with the plastic raw material and the dissolution solvent at a weight ratio of the dissolution solvent to the plastic raw material that is between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, more preferably between 3.0 and 7.

0.

13. The method according to any one of the preceding claims, wherein the size exclusion extraction step b) of step b) is carried out at a temperature between 20 °C and 300 °C, preferably between 40 and 250 °C, and at an absolute pressure between 0.1 and 100.0 MPa, preferably between 0.1 and 25.0 MPa, preferably between 0.1 and 15.0 MPa and very preferably between 0.1 and 5.0 MPa.

14. An apparatus for extracting dissolved polymer from a polymer solution by size exclusion, the apparatus comprising: - n fixed beds of size exclusion solids, where n is an integer greater than or equal to 4, preferably between 4 and 30, the size exclusion solids having a volume average pore diameter preferably between 1 and 500 nm, preferably between 2 and 100 nm, preferably between 2 nm and 50 nm, preferably between 3 and 30 nm, and preferably being silica gel, grafted silica, carbon molecular sieve or a mixture thereof, The n fixed beds of size exclusion solids are distributed in one or more towers, the n beds being connected in series and preferably in a closed loop, - N polymer solution injection systems, N eluent injection systems, N extract removal systems and N raffinate removal systems, where N is an integer preferably equal to n, the injection and removal systems being located between two successive beds or optionally upstream of the first bed, wherein the polymer solution injection system and the eluent injection system and / or the extract removal system and the raffinate removal system located at the same position are different or the same, - Each injection and removal system comprises at least one valve suitable for allowing or not allowing the flow of polymer solution and / or the flow of eluent and / or the flow of extract and / or the flow of raffinate to pass through, preferably a series of switching valves controlled automatically in sequence, or a single rotary valve, so that: - At time t, the polymer solution injection point, the eluent injection point, the extract removal point and the raffinate removal point are defined, the injection points and the removal points being different from each other and determining at least three, preferably four successive main operating zones of the n fixed beds: - An impurity elution zone I, which is included between the eluent injection point and the extract removal point; - An elution zone II of the target polymer, which is included between the extract removal point and the polymer solution injection point; - An impurity retention zone III, which is included between the polymer solution injection point and the raffinate removal point; and - Optionally, zone IV, which is included between the raffinate removal point and the eluent injection point, - And enabling the injection points and the removal points to be moved synchronously or asynchronously with time at a frequency determined by a predetermined switching period by one bed of size exclusion solids per switching period.

15. An apparatus for processing plastic raw materials to obtain a stream of purified polymer, which comprises: - Dissolving means for bringing the plastic raw material into contact with a dissolving solvent to dissolve at least part of the plastic raw material in the dissolving solvent to obtain a crude polymer solution; - Optionally, solid-liquid separation means suitable for separating the insoluble materials suspended in the crude polymer solution; - At least one size exclusion extraction device according to claim 14; - A tool for separating the dissolving solvent and optionally the eluent from the stream of purified polymer.

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