Method for recycling polyolefin-based plastics using size exclusion simulated moving bed device

Abstract

The invention relates to a process for purifying a plastic feedstock to obtain a purified polyolefin stream, comprising: a) a dissolution step in which the plastic feedstock is contacted with a dissolution solvent; then b) a size exclusion extraction step, in which a series of size exclusion solid beds are used and the polymer solution obtained from a) is fed at an injection point (F) and an eluent is fed at an injection point (S), and an 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 different and a bed is moved over time according to the determined frequency; and then c) a polymer-solvent separation step, wherein a purified polyolefin stream is obtained. The invention also relates to a device for carrying out step b) and to a device for carrying out said purification method.

Description

Technical Field

[0001] The present invention relates to recycled polyolefin-based plastics, in particular in the field of (co)polypropylene and / or (co)polyethylene, to obtain a purified polyolefin stream which can be economically upgraded, for example for the manufacture of new plastic objects. More particularly, the present invention relates to a method for treating a plastic feedstock comprising polyolefins, in particular (co)polypropylene and / or (co)polyethylene, obtained in particular from plastic waste. The method advantageously comprises dissolving the polyolefin in a solvent, in particular an organic solvent, in particular a hydrocarbon solvent, at least one step of purifying the resulting polymer solution by extraction in a size exclusion simulated moving bed to at least partially remove impurities, in particular additives conventionally used in plastics-based materials, and separating the polymer and the solvent to recover a purified polyolefin stream so as to be able to reuse the purified polyolefin in the manufacture of new objects and thus economically upgrade the plastic feedstock obtained in particular from waste. Background Art

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

[0003] First, there is "mechanical" recycling: Mechanical recycling enables some waste to be partially reused - either directly (after melting and subsequent formation of the thermoplastic) in new objects or by mixing the mechanically sorted plastic waste stream with virgin polymer streams. This type of economic upgrading is limited because mechanical sorting enables the purity of the plastic stream of a given type of polymer to be improved, but generally does not sufficiently remove impurities at least partially trapped in the polymer matrix, such as additives, such as fillers, dyes, pigments and metals used in admixture with the polymer to impart the desired properties to the material.

[0004] "Chemical" recycling itself mainly aims to remove additives and, depending on the method applied, more or less chemically modifies the polymer chains of the plastics considered (for example recovering the intact polymer, depolymerizing it or obtaining a mixture of compounds containing carbon and hydrogen obtained after non-selective scission of the chains of various polymers). These various options involve a sequence of steps which are generally complex. For example, plastic waste can undergo a pyrolysis step and the recovered pyrolysis oil can generally be at least partially converted, after purification, into olefins by steam cracking. These olefins can then be polymerized or converted into monomers before polymerization. This type of sequence can be applied to feedstocks which have undergone little sorting or to sorting center waste, but it generally requires a large amount of energy, especially due to the high temperature treatment.

[0005] Among the various possible approaches, the deformulation of thermoplastic-based plastic materials, particularly polyolefins such as (co)polypropylene and (co)polyethylene, seems to be beneficial: it consists in dissolving the polymer in a solvent and removing the additives without altering the polymer chains. The preservation of the polymer structure reduces the effort required to recycle the material and explains the good performance of this method, particularly in terms of energy consumption.

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

[0007] Separation based on size already exists and is generally used as an analytical method for determining the molecular weight of polymers. This method, called size exclusion chromatography (or SEC), which is carried out discontinuously (“in batch mode”), consists in using a fixed bed with several porosity levels. Small molecules enter the said fixed bed up to the smallest porosity, and the associated elution time is thus high, while large molecules such as polymers only pass through the largest pores and exhibit a short elution time, which makes it possible to selectively separate various molecules. Considering that the size of the additives (colorants, plasticizers, antioxidants, stabilizers, etc.) commonly used in the formulation of plastics is much smaller (by an order of magnitude) than that of polymers, particularly polyolefins, the principle of size exclusion chromatography can thus be used for the purification of plastics. However, the implementation of methods using this chromatography principle is in batch mode, which can be problematic in an industrial context. In addition, this batch-mode method requires a significant 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, a concept invented in 1961, enables discontinuous “chromatography” methods (particularly by adsorption) to operate continuously, in order to increase productivity and limit the amount of eluent consumed, while ensuring efficient separation. There are many industrial references on this technology, particularly for separation by adsorption, which is particularly used 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 illustrated in patent US2985589. 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 US6551512 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 the recycling process of materials contained in WEEE (waste electrical and electronic equipment). 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 attempted 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] There has never been proposed the application of SMB-SEC technology as a method for purifying polyolefin-based plastic waste to obtain a purified polyolefin stream, particularly a stream of polypropylene, polyethylene, their copolymers or their mixtures.

[0010] The present invention thus aims to overcome the problems of the prior art and to participate in the recycling of plastics. More particularly, it aims to provide an efficient, simple and economically viable method for treating polyolefin-based plastic raw materials, said plastic raw materials being particularly obtained from, for example, plastic waste originating from collection and sorting channels, in order to remove at least some of the impurities contained therein, particularly at least some of the additives conventionally added to plastics, so as to enable said polyolefin-based plastic raw materials to be economically upgraded. The present invention particularly attempts to efficiently separate impurities from the polyolefins contained in used plastics and to recover purified polyolefins so that they can be used, for example, in the manufacture of new plastic objects, particularly in place of virgin resins. SUMMARY OF THE INVENTION

[0011] The present invention thus relates to a method for purifying a plastic raw material to obtain a purified polyolefin stream, the 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 optional step b’) to obtain a purified polymer solution,

[0015] 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,

[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 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:

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

[0020] - a polyolefin elution zone II, located between the extract removal point and the polymer solution injection point;

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

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

[0023] 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,

[0024] wherein 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 purified polyolefin stream and at least one solvent fraction containing the dissolved solvent.

[0026] The advantage of the method of the present invention is that it provides a method for efficiently treating a raw material containing polyolefin-based plastics, especially plastic waste particularly obtained from collection and sorting channels, to recover the polyolefins contained therein so that they can be recycled into any type of application. This is because the method according to the present invention makes it possible to obtain a purified polyolefin stream, especially a stream of polypropylene, polyethylene, their copolymers or mixtures thereof, which is very advantageously less colored than the initial plastic raw material, even colorless and preferably deodorized. The resulting purified polymer stream preferably has a negligible content of prohibited or regulated substances, such as according to the REACH regulation (see Annex XIV and XVII of Regulation (EC) No. 1907 / 2006 of the European Parliament and of the Council of 18 December 2006). In particular, the purified polyolefin stream 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, so that the purified polyolefin stream can replace virgin polymer resin in any plastic formulation. For example, the purified polyolefin stream obtained at the end of the method according to the present invention advantageously contains an impurity content of 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 a solvent content of less than or equal to 5% by weight, preferably less than or equal to 1% by weight, preferably less than or equal to 0.1% by weight (especially dissolved solvent and eluent).

[0027] The method according to the present invention thus provides a simple scheme corresponding to a minimized operation sequence, which makes it possible to remove at least some impurities, especially at least some additives, from plastic waste based on polyolefins, especially based on polypropylene, polyethylene, their copolymers or mixtures thereof, and to recover purified polyolefins, which advantageously contain little or even no solvent, so as to be able to economically upgrade plastic waste by recycling the purified polyolefins.

[0028] The present invention also has the advantage of participating in plastic recycling and fossil resource conservation by achieving the economic upgrading of plastic waste, especially polyolefin-based plastic waste. Specifically, it is capable of purifying plastic waste to obtain purified polyolefins with reduced impurity content, especially decolorized and deodorized polyolefins, which can be reused to form new plastic objects. The resulting purified polyolefin fraction can thus be used directly in formulations as a mixture with additives, such as dyes, pigments or other polymers, instead of or as a mixture with virgin polypropylene or polyethylene resins or their mixtures, to obtain plastic products with aesthetic, mechanical or rheological working properties that promote their reuse and their economic upgrading.

[0029] According to a second aspect, the present invention also relates to a device for extracting polyolefins 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 the n size exclusion solids is distributed in one or more towers, the 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] where 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 includes at least one valve suitable for allowing or not allowing the polymer solution stream and / or the eluent stream and / or the extract stream and / or the raffinate stream to pass through, preferably a series of on-off valves controlled automatically in sequence, or a single rotary valve, so that:

[0035] - at time t, define the polymer solution injection point, the eluent injection point, the extract removal point and the 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 the n fixed beds:

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

[0037] - Polyolefin elution zone II, which is included between the extract withdrawal point and the polymer solution injection point;

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

[0039] - Optionally, zone IV, which is included between the raffinate withdrawal point and the eluent injection point,

[0040] - And enabling the injection point and the withdrawal point to 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.

[0041] According to a third aspect, the present invention also relates to a device for treating plastic raw materials to obtain a purified polyolefin stream, which includes:

[0042] - A dissolving tool for bringing the plastic raw materials into contact with a dissolving solvent to at least partially dissolve the plastic raw materials 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 purified polyolefin stream. Description of the Drawings

[0046] Figure 1 Represents a 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 uses 15 fixed beds of size-exclusion solids of the silica gel type, distributed in a single column, the beds being connected in series with each other and in a closed loop, and a pump located between bed No. 15 and bed No. 1 enables bed No. 15 and bed No. 1 to be connected in series.

[0047] In this specific embodiment and at this moment t:

[0048] - The crude polymer solution obtained from the dissolving step a) ( Figure 1 not shown therein) or optionally, the clarified polymer solution obtained from the optional solid-liquid separation step b') ( Figure 1 not shown therein) is introduced at the injection point F located between bed No. 9 and bed No. 10, and these two beds are consecutive,

[0049] - The eluent is introduced at the injection point S located between bed No. 15 and bed No. 1, and these two beds are consecutive,

[0050] - An extract containing at least some of the impurities present in the polymer solution fed into the column is withdrawn at withdrawal point E located between bed 6 and bed 7, these two beds being consecutive.

[0051] - The raffinate, consisting at least in part of a purified polymer solution containing polyolefins present in the polymer solution fed into the column, is withdrawn at withdrawal point R located between bed 13 and bed 14, these two fixed beds being consecutive.

[0052] The combined injection and withdrawal points thus define 4 operating zones:

[0053] - Impurity elution zone I, located between the eluent injection and the extract withdrawal, containing 6 beds.

[0054] - Polyolefin elution zone II, located between the extract withdrawal and the polymer solution injection, containing 3 beds.

[0055] - Impurity retention zone III, located between the polymer solution injection and the raffinate withdrawal, containing 4 beds, and

[0056] - Zone IV, located between the raffinate withdrawal and the eluent injection, containing 2 beds.

[0057] Figure 2 Represents another specific embodiment of the size exclusion extraction step of the present invention at a given moment t of the process, wherein the size exclusion extraction step comprises 4 fixed beds of size exclusion solids of silica gel type, each distributed in a column (i.e., one bed per column), the columns being connected in series with respect to each other and in a closed loop, and a pump located between column 4 and column 1 makes it possible to connect column 4 and column 1 in series.

[0058] In this specific embodiment and at this moment t:

[0059] - The polymer solution fed into the size exclusion extraction step is introduced at injection point F located between column 2 and column 3.

[0060] - The eluent is introduced at injection point S located between column 4 and column 1.

[0061] - An extract containing at least some of the impurities present in the polymer solution fed into the size exclusion extraction step is withdrawn at withdrawal point E located between column 1 and column 2.

[0062] - The raffinate, consisting at least in part of a purified polymer solution containing polyolefins present in the polymer solution fed into the size exclusion extraction step, is withdrawn at withdrawal point R located between column 3 and column 4.

[0063] Figure 3Represents the concentration profiles of polyethylene (PE) and additive 168 obtained by simulation along the entire length of the simulated moving bed in the case of Example 1. The simulated moving bed contains 15 silica gel fixed 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 PE varying with the bed is represented by a solid black line, and the additive 168 concentration profile varying with the bed is represented by a dashed line. Detailed Description

[0064] According to the present invention, the expressions "of between... and..." and "between... and..." are equivalent and mean that the limiting values of the interval are included within the described numerical range. If this is not the case and if the limiting values are not included within the described range, the present invention will state so.

[0065] In this 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 "≤").

[0066] For 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 present invention, a range of preferred pressure values can be combined with a range of more preferred temperature values.

[0067] Hereinafter, specific embodiments of the present invention are described. When technically feasible, they can be implemented alone or in combination without limitation on the combination.

[0068] 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 (especially polyolefin). 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 supply of the crude (or clarified) polymer solution to the said step, or with respect to the outlet point of the purified polymer solution (i.e., the raffinate withdrawal point).

[0069] The term "additive" is a term commonly used in the field of polymers, particularly in the field of polymer formulations. Additives introduced into polymer formulations can be, for example, plasticizers, fillers (which are organic or inorganic solid compounds used to modify the physical, thermal, mechanical, and / or electrical properties of polymer materials or to reduce their cost price), reinforcing agents, dyes, pigments, plasticizers, hardeners, flame retardants, combustion retardants, stabilizers, antioxidants, UV absorbers, antistatic agents, etc.

[0070] The additives correspond to at least some of the impurities in the plastic raw material to be treated, and the treatment method according to the present invention makes it possible to remove at least a part of them. Other types of impurities may be present in the plastic raw material to be treated, such as use-related impurities, such as metal impurities, paper / cardboard, biomass, polymers other than the target polymer, etc.

[0071] Thus, according to the present invention, the impurities that can be at least partially removed by the method according to the present invention include additives commonly used in polymer formulations, particularly polyolefin-based formulations, and use-related impurities that may come from the life cycle of plastic objects and materials and / or from waste collection and sorting circuits. The impurities may be of metal, organic or inorganic type; they may be packaging residues, food residues or compostable residues (biomass). These use-related impurities may also include glass, wood, cardboard, paper, aluminum, iron, metal, tires, rubber, silicone, rigid polymers, thermosetting polymers, household products, chemical products or beauty products, waste oil, water, etc.

[0072] According to the present invention, a polymer solution is a solution containing a dissolving solvent and at least a target polyolefin, particularly polypropylene, polyethylene, their copolymers or mixtures thereof, dissolved (i.e., particularly solvated and dispersed) in the dissolving solvent, and the dissolved polyolefin 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-insoluble impurities, reference is thus made to colloidal solutions). Depending on the steps of the method according to the present invention carried out, the polymer solution may thus contain, in addition to the target polyolefin 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.

[0073] As is well known, the boiling point of a compound varies with the operating pressure. However, in the absence of further indication, i.e., in the absence of an indication of pressure, the boiling point of the compound under consideration, particularly that of the dissolving solvent, is understood to be the boiling point of the compound, particularly the dissolving solvent, at atmospheric pressure (particularly equal to 0.1 MPa). Therefore, characterizing the boiling point of the dissolving solvent should be understood as the boiling point of the dissolving solvent at atmospheric pressure (particularly equal to 0.1 MPa).

[0074] The present invention relates to a method for purifying plastic raw materials, which are preferably composed of plastic waste and advantageously contain polyolefins, and the method comprises the following steps, preferably consisting of the following steps:

[0075] a) A dissolution step, which includes bringing the plastic raw materials into contact with a dissolving solvent to obtain at least one crude polymer solution;

[0076] b’) Optionally, a step of separating insoluble materials from the crude polymer solution, particularly by solid / liquid separation of the crude polymer solution obtained from step a), to advantageously obtain a clarified polymer solution and preferably an insoluble fraction;

[0077] 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,

[0078] wherein the size exclusion extraction step uses at least one series of n fixed beds of size exclusion solids, and 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;

[0079] Advantageously, the n fixed beds of size exclusion solids are distributed in one or more towers, preferably in M towers, where M is an integer between 1 and the total number n of fixed beds of size exclusion solids, and the n beds are in series with respect to each other and preferably in a closed loop;

[0080] 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;

[0081] wherein the at least one series of fixed beds of 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;

[0082] The polymer solution injection point, the eluent injection point, the extract take-out point, and the raffinate take-out point are different from each other and are advantageously located between two consecutive beds or optionally upstream of the first bed, and are distributed so as to define at least three, preferably four consecutive main operating zones of the n fixed beds:

[0083] - Impurity elution zone I, located between the eluent injection point and the extract take-out point;

[0084] - Polyolefin elution zone II, located between the extract take-out point and the polymer solution injection point;

[0085] - Impurity retention zone III, located between the polymer solution injection point and the raffinate take-out point; and

[0086] - Optionally and preferably, zone IV, located between the raffinate take-out point and the eluent injection point,

[0087] wherein the injection points and the take-out points are moved by one size-exclusion solid fixed bed over time according to a frequency determined by a predetermined switching cycle,

[0088] wherein the raffinate is recovered to constitute at least a part, preferably all, of the purified polymer solution;

[0089] c) The polymer-solvent separation step of the purified polymer solution to obtain at least one purified polyolefin stream, in particular a purified polypropylene stream, a purified polyethylene stream, a stream of its copolymers or a stream of a purified polypropylene / polyethylene mixture, and at least one solvent fraction containing the dissolved solvent and possibly the eluent.

[0090] Feedstock

[0091] The feedstock of the process according to the invention, referred to as "plastic feedstock", contains plastics, which in themselves particularly contain polymers, more particularly polyolefins, such as polypropylene, polyethylene, their copolymers or their mixtures. Preferably, the plastic feedstock contains plastics in an amount between 50% and 100% by weight, preferably between 70% and 100% by weight.

[0092] The plastics contained in the raw materials of the method according to the invention are generally production rejects and / or "post-consumer" waste, especially household waste, construction waste, waste from the automotive industry or waste electrical and electronic equipment. Preferably, the plastic waste is obtained from collection and sorting channels. The plastics or plastic materials are generally compositions (or formulations) containing polymers, especially polyolefins, which are usually mixed with additives to impart specific properties to the material so as to form various objects after shaping (such as injection molded parts, pipes, films, fibers, fabrics, putties, coatings, etc.). The additives used in the plastics can be organic compounds or inorganic compounds. They are, for example, fillers, dyes, pigments, plasticizers, modifiers, flame retardants, etc.

[0093] The plastic raw materials of the method according to the invention thus contain polymers, especially polyolefins, such as polypropylene, polyethylene, their copolymers or their mixtures. Preferably, based on the total weight of the plastic raw materials, the plastic raw materials contain at least 50% by weight, preferably at least 80% by weight, preferably at least 85% by weight, preferably at least 90% by weight of polyolefins, 100% advantageously being the maximum upper limit. The method according to the invention thus most particularly aims to purify and recycle the polyolefins contained in the plastic raw materials so that they can be reused in various applications.

[0094] The plastic raw materials may contain other polymers and other impurities in addition to the target polyolefins, especially the additives usually used in formulating plastic materials, and the use-related impurities usually from the life cycle of plastic materials and objects and / or from the waste collection and sorting circuits. The plastic raw materials of the method according to the invention generally contain less than 50% by weight of impurities, preferably less than 20% by weight of impurities, preferably less than 10% by weight of impurities. The plastic raw materials may contain, for example, more than 1% by weight of impurities, especially more than 5% by weight of impurities.

[0095] The plastic raw material containing polyolefins processed by the method according to the present invention can be advantageously pretreated before the method according to the present invention 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 of wood, paper, biomass, iron, aluminum, glass, etc., and shaped into the form of usually crushed solids to facilitate processing in the method according to the present invention. Such pretreatment may include a grinding step, a washing step under atmospheric pressure, and / or a drying step. Such 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 method according to the present invention is carried out. Preferably, such pretreatment makes it possible to reduce the impurity content to less than 6% 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 crushed solids, such as in the form of ground materials, powders, flakes or granules, for ease of operation and transportation to the method.

[0096] Dissolution step a)

[0097] According to the present 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 the dissolution of at least part, preferably all, of the target polymer, preferably the target polyolefin, present in the plastic raw material.

[0098] The term "dissolution" should be understood to mean any phenomenon that results in the production of at least one polymer solution (especially a polyolefin solution), i.e., a liquid (or possibly a supercritical fluid) containing a polymer (especially a polyolefin) 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 include at least the mixing, dispersion, homogenization, solvation, and disentanglement of polymer chains, more particularly thermoplastic chains.

[0099] During and at the end of the dissolution step a), the pressure and temperature conditions make it possible to keep the dissolution solvent (at least part, preferably all of the dissolution solvent) in a liquid or possibly supercritical state (the temperature and pressure conditions in step a) make it possible to avoid or at least limit the dissolution solvent being present in gaseous form), while the soluble part of the raw material, especially the target polymer, most particularly the target polyolefin, and at least some of the impurities are advantageously at least partially and preferably completely dissolved.

[0100] The dissolving solvent is an organic solvent or a mixture of organic solvents, preferably selected such that its Hansen parameters are within the Hansen sphere of the target polymer, in particular the target polyolefin. By determining the Hansen solubility parameters and Hansen spheres of the solvent and the polymer respectively according to several parameters, in particular their polarity, hydrogen bonding and dispersion parameters, the Hansen theory makes it possible to predict the solubility of polymers, in particular thermoplastics such as polyolefins (polyethylene and / or polypropylene) in solvents. 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. Advantageously, the dissolving solvent contains at least one hydrocarbon compound, preferably consists of at least one hydrocarbon compound, which hydrocarbon compound is preferably aliphatic, in particular an alkane (i.e., saturated), preferably straight-chain or branched-chain. Preferably, the dissolving solvent contains at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of at least one hydrocarbon compound, which is preferably aliphatic, in particular an alkane, preferably straight-chain or branched-chain, the percentage being expressed relative to the total weight of the dissolving solvent (100% being the maximum). Preferably, the dissolving solvent contains at least one hydrocarbon compound, which is preferably aliphatic, in particular an alkane, having a boiling point (at atmospheric pressure, in particular at 0.1 MPa) between -50 and 250 °C, preferably between -15 and 150 °C, preferably between -1 and 110 °C, preferably between 20 and 100 °C. Preferably, the dissolving solvent contains at least one hydrocarbon compound, preferably consists of at least one hydrocarbon compound, which hydrocarbon compound is preferably aliphatic, in particular an alkane, preferably straight-chain or branched-chain, containing 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms, such as 4, 5, 6, 7 or 8 carbon atoms. For example, the dissolving solvent contains a hydrocarbon compound selected from isomers of butane, pentane, hexane, heptane and octane. The dissolving solvent may contain, preferably consists of, a mixture of isomers of butane, pentane, hexane, heptane and / or octane, and the content of the mixture in the dissolving solvent is preferably greater than or equal to 80% by weight, preferably greater than or equal to 95% by weight, preferably greater than or equal to 98% by weight relative to the total weight of the dissolving solvent. Very advantageously, the preferred hydrocarbon compound for the dissolving solvent is an aliphatic alkane compound having a critical temperature (the temperature at the critical point of the pure hydrocarbon compound) preferably between 95 and 350 °C, preferably between 130 and 300 °C, preferably between 180 and 285 °C.

[0101] 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 more preferably between 3.0 and 7.0.

[0102] Advantageously, the dissolution solvent fed into dissolution step a) is in liquid or possibly supercritical form. Advantageously, it can be preheated, preferably to a temperature between 100 and 300 °C, preferably between 150 and 250 °C, before being introduced into step a), in particular before being introduced into the contacting section and optionally into the dissolution section, to promote the heating of the plastic raw material and / or to avoid a temperature drop of the material stream in the contacting section and optionally the dissolution section of step a).

[0103] Advantageously, the dissolution solvent comprises and preferably consists of a fresh solvent (or a supply of fresh solvent) and / or a stream of recycled solvent obtained from subsequent steps of the process, for example at least partially obtained from the solvent-polymer separation step c).

[0104] Very advantageously, the dissolution step is carried out at a temperature (referred to as the dissolution temperature) between 100 °C and 300 °C, preferably between 150 °C and 250 °C, and a pressure (referred to as the dissolution pressure) between 1.0 and 100.0 MPa absolute pressure, preferably between 1.0 and 25.0 MPa absolute pressure, preferably between 1.5 and 18.0 MPa absolute pressure, very preferably between 2.0 and 15.0 MPa absolute pressure. The temperature and pressure can be changed from the introduction conditions of the plastic raw material and / or the dissolution solvent to the dissolution conditions during the dissolution step, i.e. in particular a dissolution temperature between 100 and 300 °C, preferably between 150 and 250 °C, and a dissolution pressure in particular between 1.0 and 100.0 MPa absolute pressure, preferably between 1.0 and 25.0 MPa absolute pressure, preferably between 1.5 and 18.0 MPa absolute pressure, very preferably between 2.0 and 15.0 MPa absolute pressure. Very advantageously, at the end of the dissolution step, the crude polymer solution is at the dissolution temperature and the dissolution pressure.

[0105] 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 polyolefin and also limits the energy requirement of the process, thus contributing to limiting the operating costs of the process. Advantageously, the dissolution temperature is greater than or equal to the melting point of the target polyolefin to promote their dissolution and very advantageously to reduce the residence time required for effective dissolution of the target polyolefin. Very preferably, the temperature in dissolution step a) is less than or equal to the critical temperature of the dissolution solvent to avoid the formation of a supercritical phase during dissolution step a) that is liable to disrupt the dissolution.

[0106] At the same time, the dissolution pressure in the dissolution step is higher than the saturation vapour pressure of the dissolution solvent at the dissolution temperature so 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 polyolefin, in particular in terms of quality and operating time.

[0107] 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.

[0108] Advantageously, the dissolution step a) is carried out with a residence time preferably between 1 and 600 minutes, more preferably between 2 and 300 minutes, even more preferably between 2 and 180 minutes. The residence time is understood to be the residence time at the dissolution temperature and dissolution pressure in step a), i.e., the time during which the plastic raw material is processed with the dissolution solvent at the dissolution temperature and dissolution pressure.

[0109] In order for the dissolution solvent and the plastic raw material to be able to contact each other, and in particular for the target polyolefin to be dissolved efficiently and uniformly 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 a combination of pipelines and equipment. Devices for particularly conveying fluids such as gases, liquids, or solids are well known to those skilled in the art. Without limitation, the conveying device can include compressors, pumps, extruders, vibrating tubes, screw conveyors (endless screws), or valves. The devices and / or apparatuses used in step a) can also include a heating system (such as a furnace, exchanger, tracing cable, etc.) or be combined with a heating system to achieve the conditions required for dissolution.

[0110] At least a plastic raw material is fed into the dissolution step a), particularly in the form of one or more plastic raw material streams, and a dissolution solvent is fed in, particularly in the form of one or more dissolution solvent streams, advantageously by means of one or more conveying devices. The plastic raw material stream can be different from the dissolution solvent stream. Some or all of the plastic raw materials can also be fed into step a) as a mixture with some or all of the dissolution solvent, and the remaining solvent and / or remaining raw material can possibly be fed into step a) separately as appropriate.

[0111] During the contact of the plastic raw material with the dissolution solvent, the dissolution solvent is advantageously at least partially and preferably completely in liquid or possibly supercritical form, while the plastic raw material containing a polymer, particularly a polyolefin, can be in solid or liquid form and optionally contain suspended solid particles. The plastic raw material can also optionally be injected into the dissolution device as a mixture with the dissolution solvent, in the form of a suspension in the dissolution solvent, and the preparation and injection of the suspension can be continuous or batchwise.

[0112] Preferably, the dissolution step a) uses at least one extruder and dissolution equipment, 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 so that at the outlet of the extruder, at least a part and preferably all of the target polyolefin contained in the plastic raw material is in a molten state. Then the plastic raw material is injected into the dissolution equipment at least partially in a molten form. At least a part of the plastic raw material in a molten state can also be pumped by a pump dedicated to viscous fluids (usually called a melt pump or a gear pump). At least a part of the plastic raw material in a 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 this filter is between 10 μm (micrometers) and 1 mm (millimeters), preferably between 20 and 200 μm.

[0113] Preferably, step a) uses at least one static mixer and an extruder before at least one CSTR-type reactor, and at least a part of the dissolution solvent is injected therein to promote shear and fine mixing between the dissolution solvent and the plastic raw material, thus contributing to the dissolution of the polyolefin.

[0114] Very advantageously, the crude polymer solution obtained at the end of the dissolution step a) contains at least the dissolution solvent and the target polyolefin dissolved in the dissolution solvent. Generally, the crude polymer solution also contains soluble impurities that are also dissolved in the dissolution solvent and optionally suspended insoluble impurities. The crude polymer solution obtained at the end of the dissolution step a) may also optionally contain polymers other than the target polyolefin, such as in a molten state, a dissolved state or an undissolved state.

[0115] Optional step b') of separating insoluble materials

[0116] The method according to the invention may optionally include a step b') of separating insoluble materials from the crude polymer solution, in particular by solid-liquid separation, which is advantageously 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 said step b') of separating insoluble materials also makes it possible to advantageously separate an insoluble fraction, which contains at least a part, preferably all, of the insoluble impurities particularly 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.

[0117] Advantageously, when performing step b') of separating insoluble materials, it is located upstream of the size exclusion extraction step b) and generally downstream of the dissolution step a). When performing this separation step b'), in addition to removing at least a portion of the insoluble impurities, it also advantageously makes it possible to limit the operating problems of 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 includes step b') of separating insoluble materials.

[0118] 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 100 °C and 300 °C, preferably between 150 and 250 °C, and at a pressure between 1.0 and 100.0 MPa absolute pressure, preferably between 1.0 and 25.0 MPa absolute pressure, preferably between 1.5 and 18.0 MPa absolute pressure, very preferably between 2.0 and 15.0 MPa absolute pressure.

[0119] When incorporated into the method, preferably the crude polymer solution obtained from step a) is fed to step b') of separating insoluble materials.

[0120] Advantageously, the 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 with a filter aid such as diatomaceous earth or sand), a vortex separator, an electrostatic separator, a triboelectric separator, preferably a decanter, a filter, a sand filter, and / or an electrostatic separator. Advantageously, a self-cleaning filter can be used, especially cleaned or unclogged using a solvent stream, so as to be able to remove insoluble materials.

[0121] Removal of the insoluble fraction may require the use of a device capable of conveying and optionally capable of removing the solvent that may be entrained in the separated insoluble fraction. For example, step b') can use a conveyor, a vibrating tube, a screw conveyor, an extruder, or a stripper. Step b') can thus use a conveying device 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 method.

[0122] According to a particular embodiment, the step b') of separating the insoluble material uses at least two, usually less than five, solid-liquid separation devices in series and / or in parallel. The presence of at least the solid-liquid separation devices in series makes it possible to improve the removal of the insoluble material, while the presence of the parallel devices makes it possible to manage the maintenance of the devices and / or the operation of clearing blockages.

[0123] Certain insoluble impurities that are conventionally added during polymer formulation, in particular certain pigments and mineral fillers, may be introduced in the form of particles with a size of less than 1 μm. For example, this is the case for titanium dioxide, calcium carbonate, and carbon black. According to one embodiment, the step b') of separating the insoluble material advantageously uses an electrostatic separator, which makes it possible to efficiently remove at least partially the insoluble particles with a size of less than 1 μm. According to another embodiment, the step b') of separating the insoluble material uses a sand filter to remove particles of different sizes, in particular particles with a size of less than 1 μm. According to yet another embodiment, the step b') of separating the insoluble material uses a tangential filter, which particularly uses membranes and / or depth filters, optionally in the presence of a filter aid such as diatomaceous earth.

[0124] 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 polyolefin. According to another particular embodiment, step b') advantageously uses a device capable of separating this second liquid phase, preferably by means of at least one three-phase separator.

[0125] According to the present invention, when incorporated into the method, the optional step b') of separating the insoluble material makes it possible to obtain at least one clarified polymer solution, which contains at least the dissolved solvent and at least the target polyolefin dissolved in the 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 is removed from the polymer solution.

[0126] Size exclusion extraction step (b)

[0127] The method according to the present invention includes a size exclusion extraction step b), in particular fed with an eluent and the crude polymer solution obtained from step a) or optionally fed with the clarified polymer solution obtained from the step b') of separating the insoluble material. Advantageously, the size exclusion extraction step b) makes it possible to obtain at least one purified polymer solution and preferably a waste solvent, in particular a waste solvent carrying impurities.

[0128] The polymer solution fed into 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, preferably completely removed, during the size-exclusion extraction, in particular by bringing the crude polymer solution or the optionally clarified polymer solution into contact with size-exclusion solids in the presence of an eluent. Specifically, size-exclusion extraction step b) can separate the compounds present in the crude polymer solution or the optionally clarified polymer solution according to their size, in particular their size at the molecular scale (or rather, their hydrodynamic volume), by simulated countercurrent chromatography or simulated moving bed (hereinafter referred to as the "SMB" method). Very advantageously, this extraction step b) of the method enables the selective separation of the polyolefin dissolved in the dissolution solvent from the dissolved impurities present in the polymer solution fed into step b) (i.e., the crude polymer solution or the optionally clarified polymer solution). Step b) thus makes it possible to produce a purified polymer solution which is a polymer solution from which at least a part, preferably all, of the soluble impurities present in the polymer solution fed into step b), i.e., present in the crude polymer solution or the optionally clarified polymer solution, have been removed.

[0129] Preferably, the eluent fed into step b) is a solvent, in particular an organic solvent, preferably a solvent whose Hansen parameters are within the Hansen sphere of the target polymer. Preferably, the eluent is a solvent, preferably an organic solvent, or a solvent mixture, preferably an organic solvent mixture, which contains at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of hydrocarbon compounds, preferably aliphatic, in particular alkanes, preferably straight-chain or branched-chain hydrocarbon compounds, the percentage being expressed relative to the total weight of the eluent (100% being the maximum), and preferably having a boiling point (at atmospheric pressure) between -50 and 250 °C, preferably between -15 and 150 °C, preferably between -1 and 110 °C, preferably between 20 and 100 °C. Preferably, the eluent contains, preferably consists of, hydrocarbon compounds which are preferably aliphatic, in particular alkanes, preferably straight-chain or branched-chain hydrocarbon compounds, containing 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms, such as 4, 5, 6, 7 or 8 carbon atoms. For example, the dissolution solvent contains hydrocarbon compounds selected from the isomers of butane, pentane, hexane, heptane and octane. Very preferably, the eluent has the same chemical nature as the dissolution solvent, even being the same solvent.

[0130] Advantageously, the size exclusion extraction step b) uses at least one series, preferably a single series, of several fixed beds of size exclusion solids, especially during operation. Advantageously, the said series is fed with the crude polymer solution obtained from step a) or, optionally, with the clarified polymer solution obtained from an optional step b'), and with an eluent. When step b) comprises several, especially 2 to 4, series of fixed beds of size exclusion solids during operation, these series of fixed beds operate in parallel with one another and each is fed with a part of the polymer solution fed to step b), especially the crude polymer solution obtained from step a) or, optionally, with the clarified polymer solution obtained from an optional step b'), and with a part of the eluent fed to step b). In this case, the said polymer solution fed to step b) is then divided into as many sub-streams of crude polymer solution or optional clarified polymer solution as there are series of fixed beds in operation, and similarly, the said eluent fed to step b) is then divided into as many sub-streams of eluent as there are series of fixed beds in operation.

[0131] Optionally, the method may also comprise, especially in parallel with step b), at least one series of fixed beds of size exclusion solids (as described below) that is not in operation, especially in a stationary standby state and / or in a regeneration and / or standby mode.

[0132] The said (or each) series of fixed beds in 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 to enable efficient separation and reasonable to limit costs, especially investment costs. The said n fixed beds are connected in series relative to one another. The said n fixed beds of size exclusion solids may operate in a closed loop or an open loop. Preferably, the said n fixed beds of size exclusion solids operate in a closed loop, i.e. the said n fixed beds are connected to one another successively and preferably in a closed loop (the first is connected to the second, the second to the third, and so on, and the nth to the first), thus enabling the size exclusion extraction to operate continuously and advantageously reducing the consumption of eluent since the eluent is then partially continuously regenerated and recycled.

[0133] In one (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 in question, i.e., 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 columns, 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 a column, the entire column, i.e., n fixed beds or n / 2 fixed beds, needs to be unloaded. 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) per column than in the previous case, each column containing one fixed bed of size-exclusion solid, thus facilitating maintenance and / or cleaning and / or bypassing, especially of one of the n beds in operation, since in this configuration, it is only one column (which contains only one bed) rather than a group of beds that needs to be unloaded and / or bypassed. However, the latter configuration requires a considerably higher investment cost.

[0134] 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 dissolving solvent and the polyolefin to be treated) and with respect to the eluent. It is also selected so as to be able to efficiently separate the compounds present, especially dissolved in the treated polymer solution, and more particularly the impurities dissolved in the dissolving solvent with respect to the dissolved polyolefin. Advantageously, the size exclusion solid is a porous solid, which can be organic (usually polymeric) and / or inorganic, and preferably has a volume average pore diameter preferably between 1 nm and 500 nm, preferably between 2 nm and 100 nm, very preferably between 2 nm and 50 nm and preferably between 3 nm 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 polyolefins), porous polymer gels, carbon replicas, preferably dealuminated zeolites (such as USY type), preferably calcined alumina, MOF (metal-organic framework) type materials or mixtures thereof. Preferably, the size exclusion solid comprises, preferably consists of silica gel (or silica), grafted silica, carbon molecular sieves or mixtures thereof. Very advantageously, the size exclusion solid preferably has 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, more particularly by mercury intrusion porosimetry according to standard ASTM D4284-83 at a maximum pressure of 4000 bar using a surface tension of 484 dynes / cm and a contact angle of 140°. According to the recommendation on page 1050 of the publication "Techniques del’ingénieur, traitéanalyse etcaractérisation" [Engineering Techniques, Analysis and Characterization Treatise] by J. Charpin and B. Rasneur, 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, especially the volume and diameter of the solid in the mesoporous range (2 - 50 nm), can also be measured by nitrogen adsorption / desorption volumetry (also known as nitrogen adsorption isotherm), which is an analytical method complementary to the above method. This analysis corresponds to the physical adsorption of nitrogen molecules in the pores of the material by gradually increasing the pressure at a constant temperature and provides information on the texture characteristics.In particular, it makes it possible to obtain the mesopore distribution of size-excluding solids. Thus, the representative pore distribution of the pore population centered in the range from 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.

[0135] 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, more preferably between 300 and 600 μm (preferably determined by laser particle size analysis, i.e., by laser diffraction using a particle size analyzer). Advantageously, the solid particles are substantially spherical.

[0136] According to the invention, the (or each) series of fixed beds in 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 the eluent injection point S. Preferably, the series of fixed beds in question 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.

[0137] Preferably, the eluent and the polymer solution are fed to the (or each) series of fixed beds in the size-excluding extraction step b) according to a volume flow rate ratio of the eluent to 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. It is also possible to refer to this ratio as the solvent level. For the (or each) series under consideration, this solvent level, i.e., this regulation 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 polyolefin and impurities present in the polymer solution fed to step b).

[0138] When the series of fixed beds comprises several polymer solution injection points Fi, for example two polymer solution injection points F1 and F2, the stream of the crude polymer solution or the clarified polymer solution fed to the series of fixed beds under consideration is divided into as many sub-streams of polymer solution as there are injection points Fi for feeding the series of fixed beds, and the sub-streams of polymer solution exhibit the same or different flow rates from each other.

[0139] When the fixed bed of the series comprises several eluent injection points Si, for example two injection points S1 and S2, the total eluent stream fed to the fixed bed of the considered series is divided into the same number of sub-streams of eluent (i.e., into i sub-streams of eluent, where i is an integer equal to the number of eluent injection points Si) for feeding into the fixed bed of the series at the injection points Si, and the sub-streams of eluent exhibit the same or different flow rates with respect to one another.

[0140] The (or each) series of fixed beds of the size exclusion extraction 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. Preferably, the (or each) series of fixed beds of the size exclusion extraction step b) performs extract removal at the extract removal point E and raffinate removal at the raffinate removal point R.

[0141] The polymer solution injection point F, the eluent injection point S, the extract removal point E, and the raffinate removal point R are different from one another. They are advantageously located between two consecutive 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 consecutive). However, in the case of a particular embodiment of the process, on average during the operating cycle, they can be located in the middle of or within the fixed bed. The polymer solution injection point, the eluent injection point, the extract removal point, and the raffinate removal point are distributed relative to one another 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 comprised between the eluent injection point S and the extract removal point E;

[0142] - A polymer (particularly the target polyolefin) elution zone II, which is comprised between the extract removal point E and the polymer solution injection point F;

[0143] - An impurity retention zone III, which is comprised between the polymer solution injection point F and the raffinate removal point R; and

[0144] - Optionally and preferably, a zone IV, which is comprised between the raffinate removal point R and the eluent injection point S.

[0145] - Optionally and preferably, a zone IV, which is comprised between the raffinate removal point R and the eluent injection point S.

[0146] When there are several polymer solution injection points Fi and / or several eluent injection points Si and / or several extract withdrawal points and / or several raffinate withdrawal points, zones I, II, III and optionally IV start at the first injection point and / or withdrawal point of the stream(s) under consideration (eluent, polymer solution, extract or raffinate), the term "first" being defined herein as the most upstream point among all the injection points and / or withdrawal points of the stream(s) under consideration. When there are several polymer solution injection points Fi and / or several eluent injection points Si and / or several extract withdrawal points and / or several 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.

[0147] When the n fixed beds of the series under consideration in step b) operate in an open circuit, an eluent is introduced at the eluent injection point S, a crude polymer solution or optionally a clarified polymer solution is introduced at the polymer solution injection point F, an extract is withdrawn at the extract withdrawal point E, and all the residue is withdrawn at the raffinate withdrawal point R. Thus, the injection 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 an eluent to polymer solution volume flow rate ratio between 2.0 and 50.0, preferably between 5.0 and 20.0, and even between 5.0 and 10.0.

[0148] When the n fixed beds of the series under consideration in step b) operate in a closed circuit, an eluent is introduced at the eluent injection point S, a crude polymer solution or optionally a clarified polymer solution is introduced at the polymer solution injection point F, an extract is withdrawn at the extract withdrawal point E, a raffinate is withdrawn at the 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 and withdrawal points define four successive main operating zones, namely zones I, II, III and IV, zone IV possibly being 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 an eluent to polymer solution volume flow rate ratio between 0.1 and 10, preferably between 0.2 and 5.0, and even between 0.8 and 2.0.

[0149] Advantageously, in the case of a closed loop of n fixed beds, the n size-excluding solid beds are distributed in zones I to IV, preferably according to the a / b / c / d type configuration. With respect to the total number n of size-excluding solid beds, the distribution of the size-excluding solid beds in zones I to IV is such that:

[0150] - a is the number of size-excluding solid beds in zone I,

[0151] - b is the number of size-excluding solid beds in zone II,

[0152] - c is the number of size-excluding solid beds in zone III, and

[0153] - d is the number of size-excluding solid beds in zone IV,

[0154] And wherein:

[0155] - a = (n * 0.30) * (1 ± 0.40, preferably 1 ± 0.30),

[0156] - b = (n * 0.15) * (1 ± 0.40, preferably 1 ± 0.30),

[0157] - c = (n * 0.25) * (1 ± 0.40, preferably 1 ± 0.30), and

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

[0159] It is obvious to those 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 under consideration in the operation. Thus, the 6 / 3 / 4 / 2 configuration means that there are 15 fixed beds of size-excluding 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.

[0160] Very advantageously, the bulk density of each of the n fixed beds of size-excluding 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 and preferably between 300 and 1000 kg / m 3 and preferably between 400 and 800 kg / m 3 and vary between.

[0161] 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 over time at a frequency determined by a predetermined switching period. The switching period can be defined as the time between two successive displacements (or movements) of the injection and withdrawal points over a 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 particularly makes it possible to define the operating cycle and also advantageously to define the cycle time, which corresponds to the time required for the injection and withdrawal points to return to their initial positions, i.e., which corresponds to the number of beds n multiplied by the switching period.

[0162] When the n fixed beds of size-exclusion solids operate in a closed loop, the operating cycle thus advantageously includes the same number of switching periods as there are size-exclusion solid beds present in the closed separation loop. For example, the operating cycle of a series of 12 fixed beds of size-exclusion solids includes 12 switching periods. Thus, in a preferred embodiment where the n fixed beds of size-exclusion solids of the considered series of fixed beds operate in a closed loop, the switching period is preferably adjusted 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 polyolefins and impurities present in the polymer solution fed in step b).

[0163] In the case of the embodiment where the n fixed beds operate in an open loop (i.e., 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.

[0164] The displacement of the injection points F and S and the withdrawal points E and R can be achieved by installing a series of switching valves controlled by an automatic sequence or by installing a single rotary valve.

[0165] 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), i.e., from upstream to downstream, and may be referred to as 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). Upon switching (or shifting of the injection and withdrawal points), the injection and withdrawal points are moved one bed 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, i.e., when the downward liquid flow is equal to the upward liquid flow, a stop flow can 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 varies with the bulk density of the size-excluding solid in the fixed bed and the particle density of the size-excluding solid. More particularly, the interstitial volume (V (颗粒间) ) of the size-excluding solid can be calculated by the following formula:

[0166] V (颗粒间) =V (床) x(1 - d (堆积) / d (颗粒) ) + V 死区

[0167] where:

[0168] V (颗粒间) : The interstitial volume of the size-excluding solid in the bed (in m 3 );

[0169] V (床) : The geometric volume of the bed (in m 3 );

[0170] 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, i.e., the mass of the solid / unit volume of the bed. As a first method, based on the principles derived from standards D4164 and D4180 applicable to the case of catalysts, 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 down by vibration;

[0171] d (颗粒) : The particle density of the size-excluding solid, usually determined by mercury porosimetry (in kg / m 3 );

[0172] V 死区 : The volume of the device through which the fluid flows, especially the polymer solution, without the size-excluding solid (in m 3calculate (e.g., the volume of the upstream pipeline, downstream pipeline, etc.).

[0173] Stopping the flow rate (which is a volumetric flow rate) makes it possible to calculate 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, 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, preferably between 1.0 and 1.25. Thus, the stopping flow rate helps to regulate the extraction step and thus the separation efficiency.

[0174] Furthermore, very advantageously, it is possible to adjust the superficial velocity in the fixed bed of the operating zone - 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 the superficial velocity is between 0.01 and 10.0 cm / s, preferably between 0.05 and 2.5 cm / s. Adjusting the superficial velocity in the fixed bed advantageously makes it possible to particularly control the particle wear of the size-exclusion solids and thus regulate the operation of the series of fixed beds in step b) to avoid large pressure drops (encountered particularly at high speeds) and / or dispersion problems (encountered particularly at low speeds).

[0175] Preferably, the size-exclusion extraction step b) is carried out at a temperature between 100 and 300 °C, preferably between 150 °C and 250 °C, and at a pressure between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute, very preferably between 2.0 and 15.0 MPa absolute. Under these operating conditions, the polyolefin 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 per se. Preferably, the temperature and pressure conditions of step b) are the same as those of the dissolution step a).

[0176] 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 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 recovered at the end of step b). This purified polymer solution is then preferably at least partially, preferably completely, sent to the polymer-solvent separation step c). However, if necessary, it can be sent to at least one additional purification step to optimize the purification of the target polyolefin (if required). This size-exclusion extraction step b) thus makes it possible to efficiently and continuously separate impurities, especially soluble impurities, from a crude polymer solution or an optionally clarified polymer solution containing a polyolefin dissolved in a dissolution solvent.

[0177] Size-exclusion extraction, especially in the case of a closed loop of a fixed bed, makes it possible to efficiently separate impurities from polyolefins in continuous mode, which makes it possible to limit the labor required for carrying out the step while promoting its operability. It is also capable of achieving high productivity, especially compared to size-exclusion chromatography operations in batch mode, while providing relatively low eluent consumption.

[0178] Polymer-solvent separation step c)

[0179] According to the invention, the method comprises a polymer-solvent separation step c) of a purified polymer solution to obtain at least one purified polyolefin stream, especially a purified polypropylene stream, a purified polyethylene stream, a stream of its copolymers, a stream of a purified polypropylene / polyethylene mixture, and at least one solvent fraction containing the dissolution solvent.

[0180] The polymer-solvent separation step c) advantageously uses at least one solvent recovery section, preferably 1 to 5 solvent recovery sections.

[0181] Advantageously, the purified polymer solution obtained at the end of step b) or optionally the final purified polymer solution obtained from an additional purification step located downstream of the size-exclusion extraction step b) is fed to step c).

[0182] 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 polymer solution fed into step c), more particularly the purified polymer solution or optionally, the final purified polymer solution obtained from an additional purification step, from the target polyolefin contained therein, so as to recover at least partially, preferably mainly, preferably completely the polyolefin from which the dissolved solvent and optionally the eluent still present in the polymer solution fed into 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, still more preferably at least 95% by weight, based on the weight of the solvent contained in the purified polymer solution fed into 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, atomization, stripping, backmixing, density difference, in particular decantation or centrifugation.

[0183] The at least one purified polyolefin stream thus obtained can correspond to a polymer solution of concentrated polyolefin or to polyolefin in liquid (or viscous) or solid form. Preferably, the polymer-solvent separation step c) additionally comprises a conditioning section for conditioning the purified polyolefin in solid form, more particularly in particulate form.

[0184] The polymer-solvent separation step c) also aims to at least partially, preferably mainly, preferably completely recover the solvent contained in the purified polymer solution fed into 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, still more preferably at least 95% by weight, based on the weight of the solvent contained in the purified polymer solution fed into step c).

[0185] 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.

[0186] Thus, the method according to the invention makes it possible to efficiently and continuously recover polyolefins from plastic feedstocks with high productivity and a limited number of operations. Very advantageously, the method according to the invention makes it possible to obtain a polyolefin stream with a high purity, 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 polyolefin, relative to the total weight of the recovered purified stream), from any type of plastic feedstock. Another advantage of the method according to the invention also lies in the fact that it is possible to efficiently separate the impurities present in the plastic feedstock, in particular additives, while the solvents, in particular the dissolution solvent and the eluent, can be reasonably consumed, and the energy consumption is lower than that of more conventional "thermal" separations, such as that required for crystallization. The method according to the invention thus makes it possible to obtain a purified polyolefin stream that is less colored than the plastic feedstock to be treated, even colorless and very advantageously deodorized. The resulting purified polymer stream preferably has a negligible content of prohibited or regulated substances, for example according to the REACH regulation. More particularly, the method according to the invention makes it possible to obtain a purified polyolefin stream that removes at least a part, preferably all of the impurities present in the plastic feedstock, such as additives and at least partially, even completely removes the solvents, in particular the dissolution solvent and the eluent.

[0187] Thus, the method according to the invention advantageously makes it possible to obtain a purified polyolefin stream having an impurity content of less than or equal to 5% by weight, preferably less than or equal to 1% by weight, more preferably less than or equal to 0.5% by weight of impurities, and very advantageously, a solvent content of less than or equal to 5% by weight, preferably less than or equal to 1% by weight, preferably less than or equal to 0.1% by weight of solvents (in particular the dissolution solvent and the eluent), the percentages being given relative to the total weight of the purified polyolefin stream.

[0188] Size exclusion extraction device

[0189] The invention also relates to a size exclusion extraction device suitable for separating polyolefins from the impurities contained in a polymer solution. The device comprises:

[0190] - 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, preferably between 12 and 15, 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 (or silicon dioxide), grafted silica, carbon molecular sieve or a mixture thereof,

[0191] The fixed beds of the n size-exclusion solids are distributed in one or more towers, preferably in M towers, where M is an integer between 1 and the total number n of fixed beds of size-exclusion solids, and the n beds are connected in series and preferably in a closed loop.

[0192] - 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, and the injection and removal systems are located between two consecutive beds or optionally upstream of the first bed.

[0193] Where 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, i.e., between the same two consecutive beds or optionally upstream of the first bed, are different or the same (the term "the same" should be understood to mean that the valve system can make it possible to introduce a polymer solution or an eluent, or remove one or the other stream, i.e., remove the extract or the raffinate).

[0194] - Each injection and removal system includes at least one valve suitable for allowing or not allowing the passage of a polymer solution stream and / or an eluent stream and / or an extract stream and / or a raffinate stream, preferably i) a series of switching valves controlled by an automatic sequence, or ii) a single rotary valve, so that:

[0195] At time t, the polymer solution injection point, the eluent injection point, the extract removal point and the raffinate removal point are defined, and the injection points and removal points are different from each other and determine at least three, preferably four consecutive main operating zones of the n fixed beds:

[0196] - An impurity elution zone I, which is included between the eluent injection point and the extract removal point;

[0197] - A polyolefin elution zone II, which is included between the extract removal point and the polymer solution injection point;

[0198] - An impurity retention zone III, which is included between the polymer solution injection point and the raffinate removal point; and

[0199] - Optionally, a zone IV, which is included between the raffinate removal point and the eluent injection point;

[0200] And makes it possible to move the injection points and removal points synchronously or asynchronously by one fixed bed of size-exclusion solids over time per switching cycle according to the frequency determined by a predetermined switching cycle.

[0201] Device for treating plastic raw materials

[0202] Such a size exclusion extraction device can be incorporated into a more comprehensive plastic raw material processing device to obtain a purified polyolefin stream, the device comprising:

[0203] - A dissolution tool for contacting the plastic raw material with a dissolution solvent to at least partially dissolve the plastic raw material in the dissolution solvent to obtain a crude polymer solution, the dissolution tool being any type of equipment for contacting and dissolving the plastic raw material with the dissolution solvent, such as an extruder, one or more static mixers, one or more continuous stirred tank reactors (CSTRs) equipped with a suitable stirring system;

[0204] - Optionally, a solid-liquid separation tool, in particular any type of solid-liquid separation equipment, suitable for separating insoluble materials suspended in the crude polymer solution;

[0205] - At least one size exclusion extraction device according to the present invention and as described above, advantageously connected to the dissolution tool for contacting and dissolving or optionally connected to at least one of the solid-liquid separation tools;

[0206] - A tool for separating the dissolution solvent and optionally an eluent from the purified polyolefin stream, in particular any type of equipment for separating the dissolution solvent and optionally an eluent from the purified polyolefin stream, advantageously connected to the at least one size exclusion extraction device.

[0207] The device for processing the plastic raw material to obtain a purified polyolefin stream also advantageously includes a tool for conveying between the tools and the device.

[0208] Such a device very advantageously makes it possible to recover high-purity polyolefins from plastic raw materials that may contain many impurities.

[0209] The following examples and figures illustrate the present invention, in particular specific embodiments thereof, without limiting its scope.

[0210] Examples

[0211] Example 1

[0212] This example is based on the results of a numerical simulation carried out on experiments conducted in the laboratory.

[0213] The raw material to be processed consists of 95 wt% polyethylene (PE) with a volume average molar mass MW = 650000 g / mol and 5 wt% of an additive 168 (which is conventionally used as a stabilizer in polyolefin formulations).

[0214] First, the raw materials are dissolved in heptane at 200 °C and 1.0 MPa (or 10 bar) to form a homogeneous crude polymer solution containing 80 wt% heptane and 20 wt% raw materials containing polyethylene and additives.

[0215] The formed crude polymer solution is introduced into a simulated moving bed, which consists of 15 beds containing silica gel and is distributed in a 6 / 3 / 4 / 2 configuration (see Figure 1 ). The eluent is heptane.

[0216] The silica gel in the bed is in the form of beads and has the following characteristics:

[0217] Bead diameter = 500 μm

[0218] Pore diameter = 6 - 10 nm

[0219] Pore volume = 0.80 ml / g

[0220] Bulk density = 530 kg of solid / m 3 of the bed

[0221] External particle porosity = 0.4.

[0222] Each bed is modeled by a 1D piston fixed bed model with axial dispersion and a Fick model for intra-particle transfer. The radius of gyration of polyethylene is estimated to be 32 nm, so the polymer is considered to exist only in the external particle phase. The radii of gyration of the additives and the solvent are less than 1 nm, so they can diffuse into the intra-particle pores. The medium in the bed is considered to be isothermal (200 °C), and the density of the polymer solution is considered to be constant (477 kg / m 3 ). Finally, all the beds are modeled and the dynamics of these cycles are solved until the concentration profiles converge.

[0223] The extraction is adjusted by the following settings:

[0224] Cycle time = 15 min

[0225] The volume flow rate of the eluent (heptane) relative to the volume flow rate of the polymer solution S / F = 1.08;

[0226] Zone IV flow rate / stop flow rate = 0.92

[0227] Zone II flow rate / stop flow rate = 1.10

[0228] Maximum superficial velocity = 1.80 cm / s.

[0229] In the case where the eluent is injected upstream of bed 1 (and downstream of bed 15) as per convention, the concentration profiles of PE and additives obtained by simulation along the entire length of the simulated moving bed are shown inFigure 3 In Figure 3 , the concentration profile of PE is represented by the solid black line, and the concentration profile of additive 168 is represented by the dashed line. The concentration along the entire length of the bed is given as the weight percentage of the compound being traced (i.e., PE or additive) relative to the weight of heptane.

[0230] From Figure 3 it is evident that polyethylene (PE) that does not enter the intra-particle pores is entrained to the raffinate and withdrawn between beds 13 and 14. Due to the smaller size of the additive, it can diffuse into the intra-particle pores and is entrained to the extract, which is withdrawn between beds 6 and 7.

[0231] Performing the PE extraction step in a simulated moving bed makes it possible to obtain the following performance qualities:

[0232] - Polyethylene purity = 99.99 wt% (which corresponds to the weight or weight flow rate of PE in the raffinate relative to the total weight or total weight flow rate of PE and additive in the raffinate excluding the solvent, i.e., excluding heptane)

[0233] - Polyethylene yield = 100% (by weight) (which corresponds to the weight flow rate of PE withdrawn in the raffinate divided by the weight flow rate of PE withdrawn in the combination of extract + raffinate)

[0234] - Productivity = 170 kg of PE withdrawn in the raffinate / h / m 3 Silica gel bed

[0235] The raffinate at the outlet of the simulated moving bed used for size exclusion extraction can subsequently be recovered and fed to the polymer-solvent separation section, particularly the evaporation section of the solvent heptane.

Claims

1. A method for purifying a plastic raw material to obtain a purified polyolefin stream, the method comprising: 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; 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 withdrawal at at least one extract withdrawal point E and at least one raffinate withdrawal at at least one raffinate withdrawal point R, wherein the polymer solution injection point and the eluent injection point and 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: - An impurity elution zone I, located between the eluent injection point and the extract withdrawal point; - A polyolefin elution zone II, located between the extract withdrawal point and the polymer solution injection point; - An impurity retention zone III, located between the polymer solution injection point and the raffinate withdrawal point; and - Optionally, zone IV, located between the raffinate withdrawal point and the eluent injection point, wherein the injection points and the withdrawal 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 purified polyolefin stream and at least one solvent fraction containing the dissolution solvent.

2. The method according to claim 1, wherein the dissolution solvent comprises at least one hydrocarbon compound, which is preferably aliphatic, in particular an alkane, having a boiling point between -50 and 250 °C, preferably between -15 and 150 °C, preferably between -1 and 110 °C, preferably between 20 and 100 °C, very preferably an aliphatic alkane compound having 3 to 12 carbon atoms, very preferably 4 to 8 carbon atoms.

3. The method according to claim 1 or 2, wherein the eluent has the same chemical nature 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, preferably between 12 and 15.

5. The method according to any one of the preceding claims, wherein the size exclusion solid is a porous solid 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 volume flow rate ratio of the eluent to 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.

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 consecutive 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 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 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, 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 100 °C and 300 °C, preferably between 150 °C and 250 °C and at a dissolution pressure between 1.0 and 100.0 MPa absolute pressure, preferably between 1.0 and 25.0 MPa absolute pressure, preferably between 1.5 and 18.0 MPa absolute pressure, very preferably between 2.0 and 15.0 MPa absolute pressure.

12. The method according to any one of the preceding claims, wherein the plastic raw material and the dissolution solvent are fed to step a) at a weight ratio between the dissolution solvent and the plastic raw material of 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 100 °C and 300 °C, preferably between 150 °C and 250 °C and at a pressure between 1.0 and 100.0 MPa absolute pressure, preferably between 1.0 and 25.0 MPa absolute pressure, preferably between 1.5 and 18.0 MPa absolute pressure, very preferably between 2.0 and 15.0 MPa absolute pressure.

14. An apparatus for extracting polyolefins 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 consecutive 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 includes at least one valve adapted to allow or not allow the polymer solution stream and / or the eluent stream and / or the extract stream and / or the raffinate stream to pass through, preferably a series of switching valves controlled automatically in sequence, or a single rotary valve, so that: ○ 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 the removal points being different from each other and determining at least three, preferably four consecutive main operating zones of the n fixed beds: - Impurity elution zone I, which is included between the eluent injection point and the extract removal point; - Polyolefin elution zone II, which is included between the extract removal point and the polymer solution injection point; - 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 making it possible to move the injection points and the removal points synchronously or asynchronously by one fixed bed of size exclusion solids over time per switching cycle according to a frequency determined by a predetermined switching cycle.

15. An apparatus for treating a plastic raw material to obtain a purified polyolefin stream, which comprises: - A dissolving tool for bringing a 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; - Optionally, a solid-liquid separation tool adapted to separate 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 an eluent from the purified polyolefin stream.

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