A method for recycling polyolefin-based plastics implementing a size-exclusion simulated moving bed device

Abstract

The present invention relates to a method 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; b) a size exclusion extraction step in which size exclusion solid beds are arranged in series, the polymer solution obtained in step a) is fed at injection point F, the eluate is fed at injection point S, the extract is withdrawn at withdrawal point E, and a raffinate containing the purified polymer is withdrawn at withdrawal point R, the injection and withdrawal points shifting by one bed over time at a frequency determined by a predetermined changeover period; and c) a step of separating the polymer and the solvent to obtain a purified polyolefin stream. The present invention also relates to a device for processing step b) and a device for processing the purification step.

Description

[Technical Field]

[0001] The present invention relates to the field of recycling polyolefin-based plastics, in particular (co)polypropylene and / or (co)polyethylene, to obtain a purified polyolefin stream that can be economically upgraded, for example, in the production of new plastic articles. More specifically, the present invention relates to a method for treating a plastic feedstock, in particular obtained from plastic waste, comprising polyolefins, in particular (co)polypropylene and / or (co)polyethylene. The method advantageously comprises dissolving the polyolefin in a solvent, in particular an organic solvent, in particular a hydrocarbon solvent, and at least one step of purifying the obtained polymer solution by extraction in a simulated moving bed by size exclusion to at least partially remove impurities, in particular additives conventionally used in plastic-based materials, and a step of separating the polymer from the solvent to recover the purified polyolefin stream, so that the purified polyolefin can be reused in the production of new articles, thus making it possible to economically upgrade plastic feedstocks, in particular obtained from waste. [Background technology]

[0002] Plastics recycling is a major environmental issue for the coming century. There are several approaches for the recycling and economic upgrading of plastics obtained from collection and sorting channels.

[0003] First, there is "mechanical" recycling, which allows the partial reuse of certain waste materials, either directly in new articles (after melting and then forming a thermoplastic resin) or by mixing mechanically separated plastic waste streams with virgin polymer streams. Although mechanical sorting makes it possible to improve the purity of plastic streams of a given type of polymer, this type of economic upgrading is generally limited, since it does not allow the impurities at least partially trapped in the polymer matrix to be sufficiently removed, such as additives such as fillers, dyes, pigments and metals used as a mixture with the polymer, to give the material the desired properties.

[0004] "Chemical" recycling primarily involves eliminating additives and, depending on the method applied, chemically modifying the polymer chains of the plastics under consideration to a greater or lesser extent (e.g., recovering the intact polymer, depolymerizing it, or obtaining a mixture of carbon- and hydrogen-containing compounds obtained after non-selective cleavage of the various polymer chains). These various options generally involve a complex sequence of steps. For example, plastic waste may undergo a pyrolysis step, and the recovered pyrolysis oil, generally after purification, may be at least partially converted, for example, into olefins by steam cracking. These olefins may then be polymerized or converted into monomers before being polymerized. This type of sequence may be suitable for feedstocks that have undergone little sorting or for waste from sorting centers, but generally requires a large amount of energy consumption, especially due to the high temperature treatment.

[0005] Among the various possible routes, the transformation of thermoplastic plastic materials, especially polyolefins such as (co)polypropylene and (co)polyethylene, appears to be the most viable, specifically consisting of dissolving the polymer in a solvent and removing the additives without modifying the polymer chain. The preservation of the polymer structure reduces the effort required to recycle the material and explains the good performance of this approach, especially in terms of energy consumption.

[0006] Impurities contained in plastic feedstocks, such as additives, may optionally be separated by solid / liquid separation, for example, by filtration, if they are insoluble in the solvent. However, additives that are soluble in the solvent are particularly difficult to separate. One of the most conventional approaches involves separating them based on physicochemical properties such as their polarity, solubility, boiling point, density, etc. However, this can lead to an increase in purification steps, given the multiple additives present and their diversity. The present invention proposes an alternative approach based on utilizing the size difference, more precisely, the hydrodynamic volume, between polymer macromolecules and impurity molecules, such as additive molecules.

[0007] Size-based separation already exists and is commonly used as an analytical method for determining the molecular weight of polymers. This method, called size-exclusion chromatography (SEC), is performed discontinuously ("batch mode") and consists of implementing a fixed bed with several porosity levels. Small molecules explore the fixed bed down to the smallest porosity, resulting in long associated elution times. However, large molecules, such as polymers, migrate only through the largest pores and exhibit short elution times, allowing for selective separation of various molecules. To the extent that additives commonly used in plastic formulations (colorants, plasticizers, antioxidants, stabilizers, etc.) have sizes that are an order of magnitude smaller than those of polymers, particularly polyolefins, the principles of size-exclusion chromatography can be applied to the purification of plastics. However, implementation of methods using such chromatographic principles is batch mode, which can be problematic in industrial settings. Furthermore, such methods in batch mode require significant consumption of eluate to ensure efficient separation, which directly affects the profitability, productivity, and ecological footprint of the method.

[0008] Simulated moving bed (SMB) technology, a concept invented in 1961, allows for the continuous functioning of discontinuous "chromatographic" processes, particularly by adsorption, with increased productivity and limited eluent consumption while ensuring efficient separation. There are numerous industrial references to this technology, particularly in the context of adsorption separations, used in particular for the separation of xylenes by the Eluxyl® or Parex® processes (see the 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 beds (or SMB-SEC, in the case of simulated moving beds with size-exclusion chromatography) is for the separation of n-paraffins from isoparaffins, as outlined in U.S. Pat. No. 2,985,589. Recent publications have mentioned the use of size-exclusion simulated moving bed (SMB-SEC) technology for the fractionation of polyethylene glycols of various 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 specifically, U.S. Pat. No. 6,551,512 proposes a method for the separation of proteins from liquid compositions such as milk by size exclusion in a simulated moving bed. Finally, one publication mentions the use of SMB-SEC in a method for the recycling of materials contained in the composition of WEEE (Waste Electrical and Electronic Equipment). WEEE is based on polycarbonate and also contains additives such as poly(styrene-co-acetonitrile) (SAN) and flame retardants. The latter is what the Weeden team is attempting 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 (GS Weeden et al., Journal of Chromatography A, 2015, 1422, 99).

[0009] The application of SMB-SEC technology as a method for purifying polyolefin-based plastic waste to obtain purified polyolefin streams, in particular streams of polypropylene, polyethylene, their copolymers or mixtures thereof, has not previously been proposed. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 2,985,589 [Patent Document 2] U.S. Patent No. 6,551,512 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention therefore aims to overcome the problems of the prior art and to address the recycling of plastics. More specifically, the present invention aims to provide an efficient, simple and economically feasible method for treating polyolefin-based plastic feedstock, in particular obtained from plastic waste, for example from collection and sorting channels, so as to remove at least some of the impurities contained in said polyolefin-based plastic feedstock, in particular at least some of the additives conventionally added to plastics, in order to enable economical upgrading of said polyolefin-based plastic feedstock. The present invention specifically aims 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 articles, in particular in place of virgin resin. [Means for solving the problem]

[0012] The present invention therefore provides a process for purifying a plastic feedstock to obtain a purified polyolefin stream, comprising the steps of: a) a dissolution step comprising contacting a plastic feedstock with a dissolution solvent to obtain at least one crude polymer solution; b') optionally separating insoluble material from the crude polymer solution obtained from step a) to obtain at least one clarified polymer solution; b) a step of extraction by size exclusion of the crude polymer solution obtained at the end of step a) or, optionally, of the clarified polymer solution obtained at the end of optional step b'), in order to obtain a purified polymer solution, The step of extracting by size exclusion comprises at least one column of n fixed beds of size exclusion solids, n being an integer greater than or equal to 4, and the n beds being in series; The train of fixed beds of step b) is fed with a crude or optionally clarified polymer solution at at least one injection point F for the polymer solution and with an effluent at at least one injection point S for the effluent, The fixed bed train of step b) implements at least one extraction of the extract at at least one extraction point E of the extract and at least one extraction of the raffinate at at least one extraction point R of the raffinate, The injection points of the polymer solution and the eluate, and the withdrawal points of the extract and the raffinate, are different from one another and are separated into at least three, preferably four, successive main operating zones of n fixed beds: a zone I of elution of impurities, located between the injection point of the eluate and the withdrawal point of the extract; - a zone II of polyolefin elution, located between the extraction point and the injection point of the polymer solution; a zone III of retention of impurities, located between the injection point of the polymer solution and the withdrawal point of the raffinate; and optionally distributed to define a zone IV located between the withdrawal point of the raffinate and the injection point of the eluate, the injection and withdrawal points are shifted over time through one fixed bed of size exclusion solids according to a frequency determined by a predetermined turnover period; an extraction step in which the raffinate is recovered to at least partially constitute a purified polymer solution; (c) polymer-solvent separation of the purified polymer solution to obtain at least one stream of purified polyolefin and at least one solvent fraction comprising the dissolving solvent; The present invention relates to a method, including:

[0013] The advantage of the method of the present invention is that it proposes an efficient method for treating feedstocks containing polyolefin-based plastics, particularly plastic waste obtained from collection and sorting channels, to recover the polyolefins contained therein so that they can be recycled for any type of application. This is because the method of the present invention makes it possible to obtain a purified polyolefin stream, in particular a stream of polypropylene, polyethylene, their copolymers, or mixtures thereof, which is highly advantageously less colored than the initial plastic feedstock, practically even colorless, and preferably deodorized. The obtained purified polymer stream preferably has a negligible content of substances prohibited or restricted, for example, by the REACH regulation (see Annexes XIV and XVII of Regulation (EC) 1907 / 2006 of the European Parliament and of the Council of December 18, 2006). In particular, the purified polyolefin stream obtained at the end of the method of the present invention highly advantageously has a negligible, or at least sufficiently low, content of impurities, in particular additives, and solvents, in particular dissolution and / or elution solvents, so that the purified polyolefin stream can be incorporated into any plastic formulation instead of virgin polymer resin. For example, the purified polyolefin stream obtained at the end of the process according to the invention advantageously comprises a content of impurities 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 advantageously a content of solvents (in particular dissolution solvents and eluates) 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.

[0014] The process according to the invention therefore proposes a simple scheme corresponding to a minimum sequence of operations which makes it possible to remove at least some of the impurities, in particular at least some of the additives, from plastic waste based on polyolefins, in particular polypropylene, polyethylene, their copolymers or mixtures thereof, and to recover purified polyolefins which are advantageously little or even free from solvent, and which make it possible to economically upgrade the plastic waste by recycling said purified polyolefins.

[0015] The present invention also has the advantage of contributing to the recycling of plastics and the conservation of fossil resources by enabling the economic upgrading of plastic waste, particularly polyolefin-based plastic waste. Specifically, it allows the purification of plastic waste to obtain purified polyolefins with a reduced content of impurities, particularly decolorized and deodorized polyolefins, which can be reused to form new plastic articles. The resulting purified polyolefin fraction can therefore be used directly in formulations, as a mixture with additives such as dyes, pigments or other polymers, in place of or in combination with virgin polypropylene or polyethylene resins or mixtures thereof, to obtain plastic products with aesthetic, mechanical or rheological working properties that facilitate their reuse and economic upgrading.

[0016] The present invention also relates, according to a second aspect, to a device for extracting polyolefins from a polymer solution by size exclusion, comprising: - n fixed beds of size exclusion solids, n being an integer greater than or equal to 4, preferably between 4 and 30, said size exclusion solids preferably having a volume average pore size of 1 to 500 nm, preferably between 2 and 100 nm, preferentially between 2 and 50 nm, preferentially between 3 and 30 nm, preferably being silica gel, grafted silica, carbon molecular sieves or mixtures thereof, n fixed beds of size exclusion solids distributed in one or more columns, the n beds being connected in series, preferably in a closed loop; N injection systems for the polymer solution, N injection systems for the eluate, N withdrawal systems for the extract, and N withdrawal systems for the raffinate, where N is an integer preferably equal to n, said injection systems and said withdrawal systems being located between two successive beds or, optionally, upstream of the first bed, Injection and withdrawal systems for the polymer solution and eluate, and / or the extract and raffinate, are located in one and the same position, and are different or identical; Equipped with each injection and withdrawal system comprises at least one valve suitable for allowing or disabling the passage of the polymer solution and / or eluate and / or extract and / or raffinate streams, preferably a series of open / close valves controlled by an automatic sequence, or a single rotary valve, whereby At a time t, an injection point for the polymer solution, an injection point for the eluate, a withdrawal point for the extract and a withdrawal point for the raffinate are defined, said injection points and said withdrawal points being different from one another, and comprising at least three, preferably four, successive main operating zones of n fixed beds: - a zone I of elution of impurities, which is comprised between the injection point of the eluate and the withdrawal point of the extract; - Zone II of polyolefin dissolution, which is comprised between the extraction point of the extract and the injection point of the polymer solution; a zone III of retention of impurities contained between the injection point of the polymer solution and the withdrawal point of the raffinate, and - optionally determining a zone IV comprised between the withdrawal point of the raffinate and the injection point of the eluate, - Also relates to a device that allows the shifting of injection and withdrawal points over time, synchronously or asynchronously, with one fixed bed of size exclusion solids per transfer period, according to a frequency determined by the given transfer period.

[0017] The present invention also provides, according to a third aspect, a device for the treatment of a plastic feedstock to obtain a stream of purified polyolefins, comprising: - dissolving means for contacting the plastic feedstock and the dissolving solvent so as to at least partially dissolve the plastic feedstock in the dissolving solvent to obtain a crude polymer solution; - optionally solid-liquid separation means suitable for separating insoluble materials in suspension in the crude polymer solution; at least one device for extraction by size exclusion according to the invention, - means for separating the dissolution solvent and optionally an eluate from the purified polyolefin stream; The present invention relates to a device comprising: [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram illustrating the step of extraction by size exclusion at a given time t of a method according to an embodiment of the invention. [Figure 2] FIG. 2 shows a diagram of the step of extraction by size exclusion at a given time t of a method according to another embodiment of the invention. [Figure 3] FIG. 1 shows the concentration profiles obtained in the context of Example 1 for polyethylene (PE) and the additive Irgafos® 168 by simulation along the entire length of a simulated moving bed comprising 15 fixed beds of silica gel in a 6 / 3 / 4 / 2 configuration. DETAILED DESCRIPTION OF THE INVENTION

[0019] FIG. 1 represents a specific embodiment of the size-exclusion extraction step of the present invention at a given time t of the method, said size-exclusion extraction step implementing 15 fixed beds of silica gel type size-exclusion solid distributed in a single column, said beds being connected together in series with respect to each other, and a pump located between bed No. 15 and bed No. 1 in a closed circuit making it possible to connect bed No. 15 and bed No. 1 in series.

[0020] In this particular embodiment, at this time t, the crude polymer solution obtained from the dissolution step a) (not shown in FIG. 1) or the clarified polymer solution obtained from the solid-liquid separation step b') optionally incorporated in the process (not shown in FIG. 1) is introduced at an injection point F located between beds No. 9 and 10, these two beds being consecutive, the effluent is introduced at an injection point S located between bed No. 15 and bed No. 1, these two beds being consecutive; an extract containing at least a portion of the impurities present in the polymer solution feeding the column is withdrawn at a withdrawal point E located between bed No. 6 and bed No. 7, these two beds being consecutive; A raffinate, at least partly composed of the purified polymer solution containing the polyolefins present in the polymer solution feeding the column, is withdrawn at a withdrawal point R located between beds No. 13 and 14, these two beds being consecutive. The combined injection and withdrawal points therefore form four operating zones: a zone I for elution of impurities located between the injection of the eluate and the withdrawal of the extract, the zone I comprising six beds; a polyolefin elution zone II located between the extraction of the extract and the injection of the polymer solution, said zone II comprising three beds; - a zone III of retention of impurities located between the injection of the polymer solution and the withdrawal of the raffinate, the zone III comprising four beds; - defining a zone IV located between the withdrawal of the raffinate and the injection of the eluate, the zone IV comprising two beds.

[0021] FIG. 2 represents another specific embodiment of the size exclusion extraction step of the present invention at a given time t of the method, said size exclusion extraction step comprising four fixed beds of silica gel type size exclusion solids each distributed in a column (i.e., one bed per column), said columns being connected together in series with respect to each other, and a pump positioned between column no. 4 and column no. 1 in a closed circuit making it possible to connect column no. 4 and column no. 1 in series.

[0022] In this particular embodiment, at time t: the polymer solution feeding the step of extraction by size exclusion is introduced at injection point F located between columns 2 and 3, - an eluate is introduced at an injection point S located between column 4 and column 1, an extract comprising at least a portion of the impurities present in the polymer solution feeding the step of extraction by size exclusion is withdrawn at a withdrawal point E located between columns 1 and 2, A raffinate, at least partially composed of a purified polymer solution comprising the polyolefins present in the polymer solution feeding the step of extraction by size exclusion, is withdrawn at a withdrawal point R located between columns 3 and 4.

[0023] Figure 3 represents the concentration profiles obtained in the context of Example 1 for polyethylene (PE) and the additive Irgafos® 168 by simulation along the entire length of a simulated moving bed comprising 15 fixed beds of silica gel in a 6 / 3 / 4 / 2 configuration. By convention, the injection of the eluate is positioned upstream of bed 1 (and downstream of bed 15). The concentration profile of PE as a function of bed number is represented by the solid black line, and the concentration profile of the additive Irgafos® 168 as a function of bed number is represented by the dotted line.

[0024] According to the present invention, the expressions "of between... and..." and "between... and..." are equivalent and mean that the limits of the interval are included in the range of values ​​stated. If this is not the case and if the limit is not included in the range stated, such clarification is given by the present invention.

[0025] In this document, the expression "greater than" is understood to mean strictly greater than and is represented by the symbol ">", and the expression "less than" is understood to mean strictly less than and is represented by the symbol <". If a limitation is included, this specification is indicated by the respective expressions "greater than or equal to" (and corresponding to the symbol '≧') and "less than or equal to" (corresponding to the symbol '≦').

[0026] For purposes of the present invention, various ranges of parameters of a given process, such as pressure ranges and temperature ranges, may be used alone or in combination. For example, for purposes of the present invention, a range of preferred pressure values ​​may be combined with a range of more preferred temperature values.

[0027] Below, specific embodiments of the present invention are described, which may be implemented separately or in combination with one another, without limiting the combination, if technically feasible.

[0028] The terms "upstream" and "downstream" should be understood as a function of the general flow of the fluid(s) or stream(s) being considered in the process. More specifically, the terms "upstream" and "downstream" are defined according to the flow of the stream containing the polymer, particularly polyolefin, to be purified. For example, the terms "upstream" and "downstream" are defined in a size exclusion step either with respect to the stream of the polymer solution, i.e., the feeding of the crude (or clarified) polymer solution to said step, or with respect to the outlet point of the purified polymer solution (i.e., the withdrawal point of the raffinate).

[0029] The term "additive" is a term conventionally used in the field of polymers, and in particular in the field of polymer formulations. Additives introduced into 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), reinforcing agents, dyes, pigments, plasticizers, curing agents, flame retardants, flame retardants, stabilizers, antioxidants, UV absorbers, antistatic agents, etc.

[0030] The additives address at least some of the impurities of the plastic feedstock being treated, which the treatment method according to the invention allows to at least partially remove. Other types of impurities may be present in the plastic feedstock being treated, such as use-related impurities, e.g. metal impurities, paper / cardboard, biomass, polymers other than the targeted polymer(s), etc.

[0031] Thus, according to the present invention, the impurities that the method according to the present invention allows for at least partial removal include additives conventionally used in polymer formulations, especially polyolefin-based formulations, and possibly use-related impurities arising from the life cycle of plastic articles and materials and / or from waste collection and sorting circuits. These impurities may be metallic, organic, or mineral impurities, and may be packaging residues, food residues, or compostable residues (biomass). These use-related impurities may also include glass, wood, cardboard, paper, aluminum, iron, metals, tires, rubber, silicone, hard polymers, thermosetting polymers, household, chemical, or cosmetic products, waste oil, water, etc.

[0032] According to the present invention, a polymer solution is a solution comprising a dissolving solvent and at least the target polyolefin, in particular polypropylene, polyethylene, their copolymers or mixtures thereof, dissolved, i.e., particularly solvated and dispersed, in the dissolving solvent, the dissolved polyolefin initially present in the plastic feedstock. The polymer solution may additionally contain soluble impurities (dissolved in the dissolving solvent) and / or insoluble impurities (in the case of nanometer-sized insoluble impurities suspended in the polymer solution, this is referred to as a colloidal solution). Thus, depending on the steps of the method according to the present invention being carried out, the polymer solution may contain, in addition to the target polyolefin dissolved in the dissolving solvent, impurities advantageously in the form of insoluble particles suspended in the polymer solution, soluble impurities dissolved in the dissolving solvent, and / or possibly another liquid phase immiscible with the polymer solution.

[0033] It is well known that the boiling point of a compound varies with the operating pressure. However, without further indication, i.e., without pressure indication, the boiling point of the compound under consideration, particularly the dissolving solvent, should be understood as the boiling point of said compound, particularly the dissolving solvent, at atmospheric pressure (particularly equal to 0.1 MPa). Therefore, the boiling point characterizing a dissolving solvent should be understood as the boiling point of said dissolving solvent at atmospheric pressure (particularly equal to 0.1 MPa).

[0034] The present invention provides a method for purifying a plastic feedstock, preferably consisting of plastic waste, advantageously comprising polyolefins, comprising the steps of: a) a dissolution step comprising contacting a plastic feedstock with a dissolution solvent to obtain at least one crude polymer solution; b') an optional step of separating insoluble material from the crude polymer solution, in particular by solid / liquid separation of the crude polymer solution obtained from step a), in order to advantageously obtain a clarified polymer solution, preferably an insoluble fraction; b) a step of extraction by size exclusion of the crude polymer solution obtained at the end of step a) or, optionally, of the clarified polymer solution obtained at the end of optional step b'), in order to obtain a purified polymer solution, The step of extraction by size exclusion comprises at least one fixed bed of size exclusion solids, n being an integer greater than or equal to 4, preferably between 4 and 30, preferentially between 8 and 24, very preferentially between 8 and 21, and preferably between 12 and 15; Advantageously, the n fixed beds of size exclusion solids are distributed in one or more columns, preferably M columns, where M is an integer between 1 and the total number n of fixed beds of exclusion solids, the n beds being in series with one another, preferably in a closed loop; The at least one fixed bed of step b) is fed with a crude or clarified polymer solution at at least one injection point F for the polymer solution and with an effluent at at least one injection point S for the effluent, The at least one row of fixed beds of step b) implements at least one withdrawal of the extract at at least one withdrawal point E of the extract and at least one withdrawal of the raffinate at at least one withdrawal point R of the raffinate, The injection points of the polymer solution and the eluate, and the withdrawal points of the extract and the raffinate, are different from one another and are advantageously located between two successive beds or, optionally, upstream of the first bed, and are arranged in at least three, preferably four, successive main operating zones of n fixed beds: a zone I of elution of impurities, located between the injection point of the eluate and the withdrawal point of the extract; - a zone II of polyolefin elution, located between the extraction point and the injection point of the polymer solution; a zone III of retention of impurities, located between the injection point of the polymer solution and the withdrawal point of the raffinate; and optionally and preferably distributed so as to define a zone IV located between the withdrawal point of the raffinate and the injection point of the eluate, the injection and withdrawal points are shifted over time through one fixed bed of size exclusion solids according to a frequency determined by a predetermined turnover period; an extraction step in which the raffinate is recovered to constitute at least a portion, preferably all, of a purified polymer solution; c) a step of polymer-solvent separation of the purified polymer solution to obtain at least one stream of purified polyolefin, in particular a stream of purified polypropylene, a stream of purified polyethylene, a stream of copolymers thereof or a stream of a purified mixture of polypropylene and polyethylene, and at least one solvent fraction comprising the dissolution solvent and optionally an eluate; The present invention relates to a method comprising, and preferably consisting of, the steps of:

[0035] feedstock The feedstock for the process according to the invention, referred to as "plastic feedstock", itself comprises plastics, in particular polymers, more particularly polyolefins, such as polypropylene, polyethylene, copolymers thereof or mixtures thereof. Preferably, the plastic feedstock comprises 50% to 100% by weight, preferably 70% to 100% by weight, of plastics.

[0036] The plastics contained in the feedstock for the process according to the invention are generally production waste and / or "post-consumer" waste, in particular waste from household waste, construction waste, the automotive sector, or waste electrical and electronic equipment. Preferably, the plastic waste is obtained from collection and sorting channels. Plastics or plastic materials are generally compositions (or formulations) containing polymers, in particular polyolefins, which are usually mixed with additives to give the material specific properties for the purpose of forming various articles (e.g., injection-molded parts, tubes, films, fibers, fabrics, mastics, coatings, etc.). The additives used in plastics can be organic or inorganic compounds. They are, for example, fillers, dyes, pigments, plasticizers, property modifiers, flame retardants, etc.

[0037] The plastic feedstock of the process according to the invention therefore comprises a polymer, in particular a polyolefin, such as polypropylene, polyethylene, copolymers thereof or mixtures thereof. Preferably, the plastic feedstock comprises at least 50% by weight, preferably at least 80% by weight, preferably at least 85% by weight, preferably at least 90% by weight of polyolefin relative to the total weight of the plastic feedstock, advantageously with 100% being the maximum upper limit. The process according to the invention is therefore most particularly directed to purifying and recovering the polyolefins contained in the plastic feedstock so that they can be reused in various applications.

[0038] The plastic feedstock may contain other polymers than the targeted polyolefin, and other impurities, particularly additives typically used to formulate plastic materials, as well as use-related impurities generally resulting from the life cycle of plastic materials and articles and / or from waste collection and sorting circuits. The plastic feedstock for the process according to the invention generally contains less than 50 wt.% impurities, preferably less than 20 wt.% impurities, preferably less than 10 wt.% impurities. The plastic feedstock may, for example, contain 1 wt.% or more impurities, particularly 5 wt.% or more impurities.

[0039] The polyolefin-containing plastic feedstock to be treated by the process according to the invention can advantageously be pretreated before the process according to the invention to remove at least all or part of the "crude" impurities, i.e., impurities in the form of particles with a size of 10 mm or more, preferably 5 mm or more, or even 1 mm or more, such as wood, paper, biomass, iron, aluminum, glass, etc., and to bring it into a form, generally in the form of a divided solid, to facilitate treatment by the process according to the invention. This pretreatment can include a grinding step, a washing step at atmospheric pressure, and / or a drying step. This pretreatment can be carried out at a different location, for example, at a waste collection and sorting center, or at the same location where the purification process according to the invention is carried out. Preferably, this pretreatment allows the content of impurities to be reduced to less than 6% by weight, based on the total weight of the plastic feedstock. At the end of the pretreatment, the plastic feedstock is generally stored in the form of a divided solid, for example, in the form of crushed material, powder, flakes, or granules, to facilitate handling and transportation to the process.

[0040] Dissolution step a) According to the invention, the method comprises a dissolution step a) in which the plastic feedstock is brought into contact with a dissolution solvent in order to obtain at least one, preferably only one, crude polymer solution. In particular, this step advantageously allows the dissolution of at least part, preferably all, of the target polymer, preferably the target polyolefin, present in the plastic feedstock.

[0041] The term "dissolution" should be understood to mean any phenomenon leading to the production of at least one polymer solution (particularly a polyolefin solution), i.e. a liquid (or possibly a supercritical fluid) comprising a polymer (particularly a polyolefin) dissolved in a solvent, more particularly a dissolution solvent. The skilled person is well aware of the phenomenon / phenomena involved in the dissolution of a polymer, which phenomenon / phenomena include at least the mixing, dispersion, homogenization, solvation, and disentanglement of the polymer chains, more particularly thermoplastic chains.

[0042] During and at the end of the dissolution step a), the pressure and temperature conditions make it possible to maintain at least partly, preferably all, of the dissolution solvent in a liquid or possibly supercritical state (the temperature and pressure conditions of step a) make it possible to avoid or at least limit the presence of the dissolution solvent in gaseous form), while the feedstock, in particular the soluble fraction of the target polymer, most particularly the target polyolefin, and at least part of the impurities, are advantageously at least partly, preferably completely dissolved.

[0043] The dissolving solvent is preferably an organic solvent or a mixture of organic solvents selected so that its Hansen parameters are within the Hansen sphere of the target polymer, particularly the target polyolefin. Hansen theory makes it possible to predict the solubility of polymers, particularly thermoplastics such as polyolefins (polyethylene and / or polypropylene), in a solvent by determining the Hansen solubility parameters and spheres for each solvent and polymer as a function of several parameters, particularly their polarity, hydrogen bonding, and dispersion parameters. If a solvent or a mixture of solvents exhibits a Hansen parameter 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 comprises, and preferably consists of, at least one hydrocarbon compound, preferably aliphatic, particularly paraffinic (i.e., saturated), preferably linear or branched. Preferably, the dissolving solvent comprises at least 80% by weight, preferably at least 95% by weight, preferably at least 98% by weight, of at least one hydrocarbon compound, preferably aliphatic, particularly paraffinic, preferably linear or branched, percentages expressed relative to the total weight of the dissolving solvent (100% being the maximum). Preferably, the dissolving solvent comprises at least one hydrocarbon compound, preferably aliphatic, particularly paraffinic, having a boiling point (at atmospheric pressure, particularly 0.1 MPa) of -50 to 250°C, preferably -15 to 150°C, preferentially -1 to 110°C, preferably 20 to 100°C. Preferably, the dissolving solvent comprises, or preferably consists of, at least one hydrocarbon compound, preferably aliphatic, particularly paraffinic, preferably linear or branched, containing 3 to 12 carbon atoms, preferentially 4 to 8 carbon atoms, e.g., 4, 5, 6, 7, or 8 carbon atoms. For example, the dissolving solvent comprises a hydrocarbon compound selected from the isomers of butane, pentane, hexane, heptane, and octane. The dissolving solvent may comprise, and preferably consist of, a mixture of isomers of butane, pentane, hexane, heptane and / or octane, and preferably the content of said mixture in the dissolving solvent is greater than or equal to 80% by weight, preferentially 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 hydrocarbon compounds preferred for the dissolving solvent are paraffinic aliphatic compounds having a critical temperature (the temperature at the critical point of said pure hydrocarbon compounds) preferably between 95 and 350°C, preferentially between 130 and 300°C, preferably between 180 and 285°C.

[0044] Preferably, in the dissolving step a) the plastic feedstock and dissolving solvent are fed in a weight ratio of dissolving solvent to plastic feedstock of 0.2 to 100.0, preferably 0.3 to 20.0, preferably 1.0 to 10.0, even more preferentially 3.0 to 7.0.

[0045] Advantageously, the dissolution solvent fed to the dissolution step a) is in liquid or possibly supercritical form. Advantageously, the dissolution solvent can be preheated to a temperature preferably between 100 and 300°C, preferentially between 150 and 250°C, before its introduction into step a), in particular into the contacting section and optionally the dissolution section, in order to facilitate heating of the plastic feedstock and / or to avoid a temperature drop of the material stream in the contacting and optionally dissolving section of step a).

[0046] Advantageously, the dissolution solvent comprises, preferably consists of, a stream of fresh solvent (or a feed of fresh solvent) and / or recycled solvent obtained from a subsequent step of the process, e.g. obtained at least in part from the solvent-polymer separation step c).

[0047] Highly advantageously, the dissolution step is carried out at a temperature known as the dissolution temperature, between 100°C and 300°C, preferably between 150°C and 250°C, and at a pressure known as the dissolution pressure, between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferentially between 1.5 and 18.0 MPa absolute, and very preferably between 2.0 and 15.0 MPa absolute. The temperature and pressure can vary during the dissolution step from the conditions at which the plastic feedstock and / or dissolution solvent were introduced to the dissolution conditions, i.e., a dissolution temperature, in particular between 100°C and 300°C, preferably between 150 and 250°C, and a dissolution pressure, in particular between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferentially between 1.5 and 18.0 MPa absolute, and very preferably between 2.0 and 15.0 MPa absolute. Highly advantageously, at the end of the dissolution step, the crude polymer solution is at the dissolution temperature and dissolution pressure.

[0048] Limiting the temperature in dissolution step a) to a temperature of 300°C or less, preferably 250°C or less, makes it possible to avoid or limit thermal degradation of the polyolefin, but also makes it possible to limit the energy requirements of the process, and thus helps to limit the operating costs of the process. Advantageously, the dissolution temperature is above the melting point of the targeted polyolefins, thereby facilitating their dissolution and, very advantageously, shortening the residence time required to effectively dissolve the targeted polyolefins. Very preferably, the temperature in dissolution step a) is below the critical temperature of the dissolution solvent, to avoid the formation of supercritical phases during dissolution step a), which would tend to interfere with dissolution.

[0049] At the same time, the dissolution pressure in the dissolution step is higher than the saturated vapor pressure of the dissolution solvent at the dissolution temperature, so that the dissolution solvent is at least partially, preferably completely, in liquid or possibly supercritical form at the dissolution temperature, which makes it possible to optimize the targeted dissolution of the polyolefin, in particular with regard to quality and operating time.

[0050] Highly advantageously, the dissolution temperature and pressure conditions reached in the dissolution step a) are adjusted so that the mixture (dissolution solvent + target thermoplastic resin) is in a single phase at the end of step a), said mixture optionally containing insoluble impurities suspended in said mixture.

[0051] Advantageously, said dissolution step a) is preferably carried out with a residence time of 1 to 600 minutes, preferably 2 to 300 minutes, preferably 2 to 180 minutes, where residence time is understood to be the residence time at the dissolution temperature and dissolution pressure, i.e. the treatment time of the plastic feedstock with the dissolution solvent at the dissolution temperature and dissolution pressure in step a).

[0052] To allow the dissolution solvent and the plastic feedstock to come into contact with each other, and in particular to allow the targeted polyolefin to be efficiently and uniformly dissolved in the dissolution solvent, the dissolution step can advantageously implement various types of equipment, such as mixing, transport, and heating devices, for example, reactors, pumps, transport circuits, stirring systems, furnaces, exchangers, mixers, etc. In particular, step a) advantageously implements at least one dissolution device and, optionally, at least one feedstock preparation device, mixing device, and / or transport device. These equipment and / or devices may be, for example, one or more static mixers, extruders, pumps, reactors, cocurrent or countercurrent columns, or a combination of lines and equipment. Devices for transporting fluids, particularly gases, liquids, or solids, are well known to those skilled in the art. Without limitation, the transport device may comprise a compressor, pump, extruder, vibrating tube, endless screw, or valve. The equipment and / or devices implemented in step a) may also include or be combined with a heating system (e.g., furnace, exchanger, heat tracing cable, etc.) to achieve the conditions required for dissolution.

[0053] To the dissolution step a) at least the plastic feedstock, in particular in the form of one or more streams of plastic feedstock, and the dissolution solvent, in particular in the form of one or more streams of dissolution solvent, are fed, advantageously by one or more transport devices. The plastic feedstock stream(s) may be different from the dissolution solvent stream(s). Part or all of the plastic feedstock may also be fed to step a) as a mixture with part or all of the dissolution solvent, the remainder of the solvent and / or the remainder of the feedstock, or optionally fed separately to step a), if desired.

[0054] During contact of the plastic feedstock with the dissolution solvent, the dissolution solvent is advantageously at least partially, preferably completely, in liquid or optionally supercritical form, while the plastic feedstock comprising the polymer, in particular the polyolefin, may be in solid or liquid form and may optionally comprise solid particles in suspension. The plastic feedstock may also optionally be injected into the dissolution equipment in the form of a suspension in the dissolution solvent, as a mixture with the dissolution solvent, the preparation and injection of the suspension being optionally continuous or batchwise.

[0055] Preferably, the melting step a) implements at least one extruder and melting equipment, such as at least one continuous stirred tank reactor (CSTR) and at least one mechanical stirring system. In this case, the plastic feedstock is fed into the extruder so that at least a portion, preferably all, of the target polyolefin contained in the plastic feedstock is in a molten state at the extruder outlet. The plastic feedstock is then injected into the melting equipment in at least a partially molten form. The plastic feedstock, in an at least partially molten state, may be pumped by a pump dedicated to viscous fluids, often known as a melt pump or gear pump. The at least partially molten plastic feedstock may be filtered at the extruder outlet, optionally in addition to the melt pump, through a filtration device to remove the coarsest particles; typically, the mesh size of this filter is between 10 μm (micrometers) and 1 mm (millimeters), preferably between 20 and 200 μm.

[0056] Preferably, step a) implements, prior to the at least one CSTR-type reactor, at least one static mixer and an extruder into which at least a portion of the dissolving solvent is injected to promote shear and intimate mixing between the dissolving solvent and the plastic feedstock, thus contributing to the dissolution of the polyolefin.

[0057] Very advantageously, the crude polymer solution obtained at the end of the dissolution step a) comprises at least the dissolution solvent and the target polyolefin dissolved in the dissolution solvent. Generally, the crude polymer solution also comprises soluble impurities also dissolved in the dissolution solvent and optionally insoluble impurities in suspension. The crude polymer solution obtained at the end of the dissolution step a) may optionally also comprise polymers other than the target polyolefin, for example in a molten, dissolved or undissolved state.

[0058] Optional step b') of separating insoluble material The method according to the invention may optionally comprise a step b') of separating insoluble materials from the crude polymer solution, in particular by solid-liquid separation, advantageously located upstream of the step b) of extraction by size exclusion. Thus, when incorporated into the method according to the invention, the step b') of separating insoluble materials advantageously allows for obtaining a clarified polymer solution, which is a polymer solution from which at least some, preferably all, insoluble impurities have been removed. The above-mentioned step b') of separating insoluble materials also advantageously allows for the separation of an insoluble fraction, in particular, when incorporated into the method according to the invention, comprising at least some, preferably all, of the insoluble impurities in suspension 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 originally present in the plastic feedstock (pigments, fillers, other polymers, etc.) and / or use-related impurities (e.g., mineral compounds, glass, wood, paper, metals, other polymers or degradation products). Preferably, step b') also allows for the obtaining of a clarified polymer solution and an insoluble fraction.

[0059] Advantageously, step b') of separation of insoluble materials, if carried out, is located upstream of step b) of extraction by size exclusion, typically downstream of step a) of dissolution. If carried out, this separation step b') advantageously makes it possible to limit operational problems of downstream method steps, in particular clogging and / or erosion type, while contributing to the purification of the plastic feedstock, in addition to removing at least a portion of the insoluble impurities. Preferably, the method according to the invention comprises step b') of separation of insoluble materials.

[0060] Step b') of separating the insoluble material is advantageously carried out under temperature and pressure conditions close to those of step a). Very advantageously, step b') of separating the insoluble material is carried out under the temperature and pressure conditions of dissolution step a), i.e., the dissolution temperature and dissolution pressure defined above. Very advantageously, step b') is therefore 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, preferably between 1.0 and 25.0 MPa absolute, preferentially between 1.5 and 18.0 MPa absolute, and very advantageously between 2.0 and 15.0 MPa absolute.

[0061] When incorporated into the process, step b') of separation of insoluble material is preferably fed with the crude polymer solution obtained from step a).

[0062] Advantageously, optional step b') may implement at least one solid-liquid separation device, such as a knockout drum, a decanter, a centrifugal decanter, a centrifuge, a filter, a sand filter, in particular a tangential filter implementing a membrane and / or a depth filter, an eddy current separator, an electrostatic separator, a triboelectric separator, optionally in the presence of a filter aid (for example diatomaceous earth or sand), preferably a section comprising a decanter, a filter, a sand filter and / or an electrostatic separator. Advantageously, self-cleaning filters may be used, the cleaning or declogging allowing the removal of insoluble materials, in particular using a solvent stream.

[0063] The removal of the insoluble fraction may require the use of equipment that allows transport and, optionally, removal of solvent that may be entrained in the separated insoluble fraction. For example, step b') may implement a conveyor, a vibrating tube, an endless screw, an extruder, or a stripper. Step b') may therefore implement a transport device to discharge the insoluble fraction and / or to remove solvent that may be entrained in the separated insoluble fraction. Advantageously, at least a portion of the solvent that may be entrained in the separated insoluble fraction is recovered and recycled to the method.

[0064] According to a particular embodiment, step b') of separating insoluble material implements at least two, generally less than five, solid-liquid separation devices in series and / or parallel. The presence of at least one solid-liquid separation device in series makes it possible to improve the removal of insoluble material, while the presence of parallel devices makes it possible to manage the maintenance and / or unclogging operations of said devices.

[0065] Certain insoluble impurities, particularly certain pigments and mineral fillers, that are conventionally added during polymer compounding may be introduced in the form of particles less than 1 μm in size. This is the case, for example, with titanium dioxide, calcium carbonate, and carbon black. According to one embodiment, step b') of the separation of insoluble materials advantageously employs an electrostatic separator, which allows for at least partial and efficient removal of insoluble particles less than 1 μm in size. According to another embodiment, step b') of the separation of insoluble materials employs a sand filter to remove particles of different sizes, particularly particles less than 1 μm in size. According to yet another embodiment, step b') of the separation of insoluble materials employs a tangential filter, particularly a membrane and / or depth filter, optionally in the presence of a filter aid such as diatomaceous earth.

[0066] Depending on the nature of the plastic feedstock, the polymer solution, preferably crude polymer solution, fed to step b') may also optionally comprise a second liquid phase, for example consisting of a molten polymer other than the targeted polyolefin. According to another particular embodiment, step b') advantageously implements equipment allowing the separation of this second liquid phase, preferably by means of at least one three-phase separator.

[0067] According to the invention, said optional separation step b') of insoluble materials, when incorporated into the process, makes it possible to obtain at least one clarified polymer solution comprising at least a dissolution solvent and at least the target polyolefin(s) dissolved in said solvent. Thus, at least part, preferably all, of the insoluble impurities that may be present in suspension in the crude polymer solution obtained at the end of step a) of the process according to the invention are removed from the polymer solution in step b').

[0068] Size exclusion extraction step (b) The method according to the invention comprises a step b) of extraction by size exclusion, which in particular is fed with the eluate and crude polymer solution obtained from step a) or, optionally, with the clarified polymer solution obtained from step b') of separation of insoluble materials. Advantageously, step b) of extraction by size exclusion makes it possible to obtain at least one purified polymer solution and preferably the used solvent, in particular full of impurities.

[0069] The polymer solution fed to step b) of extraction by size exclusion, in particular the crude polymer solution obtained from step a) or the clarified polymer solution optionally obtained from step b') of separation of insoluble materials, generally contains dissolved impurities, which are advantageously at least partially, preferably completely, removed during size exclusion extraction, in particular by contacting the crude or optionally clarified polymer solution with a size exclusion solid in the presence of an eluent. Specifically, step b) of extraction by size exclusion allows the separation of compounds present in the crude or optionally clarified polymer solution, in particular the separation of the dissolved target polyolefin and dissolved impurities, according to their size on 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 allows the selective separation of polyolefins dissolved in a dissolving solvent from the dissolved impurities present in the polymer solution (i.e., the crude or optionally clarified polymer solution) fed to step b). Step b) thus makes it possible to produce a purified polymer solution, said purified polymer solution being a polymer solution from which at least some, preferably all, of the soluble impurities present in the polymer solution fed to said step b), i.e. present in the crude or optionally clarified polymer solution, have been removed.

[0070] Preferably, the eluate fed to step b) is a solvent, particularly an organic solvent, preferably one whose Hansen parameter is within the Hansen sphere of the target polymer. Preferably, the eluate is a solvent, preferably an organic solvent, or a mixture of solvents, preferably a mixture of organic solvents, comprising at least 80% by weight, preferentially at least 95% by weight, preferably 98% by weight, of hydrocarbon compounds, preferably aliphatic and especially paraffinic, preferably linear or branched-chain hydrocarbon compounds, preferably having a boiling point (at atmospheric pressure) of -50 to 250°C, preferably -15 to 150°C, preferentially -1 to 110°C, preferably 20 to 100°C, percentages expressed relative to the total weight of the eluate (100% being the maximum). Preferably, the eluate comprises, or preferably consists of, hydrocarbon compounds, preferably aliphatic, especially paraffinic, preferably linear or branched-chain hydrocarbon compounds, containing 3 to 12 carbon atoms, preferentially 4 to 8 carbon atoms, for example 4, 5, 6, 7, or 8 carbon atoms. For example, the dissolving solvent comprises a hydrocarbon compound selected from the isomers of butane, pentane, hexane, heptane and octane. Highly preferably, the eluent is of the same chemical nature as the dissolving solvent, indeed even the same solvent.

[0071] Advantageously, step b) of extraction by size exclusion is implemented, in particular in operation, by at least one train of several fixed beds of size exclusion solids, preferably a single train, to which the crude polymer solution obtained from step a) or, optionally, the clarified polymer solution obtained from optional step b') and the eluate are advantageously fed. If step b) comprises several, in particular 2 to 4, trains of fixed beds of size exclusion solids, in operation, these trains of fixed beds operate in parallel with one another and are respectively fed with a fraction of the polymer solution to be fed to step b), in particular the crude polymer solution obtained from step a), or, optionally, the clarified polymer solution obtained from optional step b'), and a fraction of the eluate to be fed to step b). In this case, the polymer solution fed to step b) is then divided into as many partial streams of crude or optionally clarified polymer solution as there are rows of fixed beds in operation, and similarly, the effluent fed to step b) is then divided into as many partial streams of effluent as there are rows of fixed beds in operation.

[0072] Optionally, the method may also include, particularly in parallel with step b), at least one train of fixed beds of size exclusion solids (as described below) that is not in operation, particularly in standby, shut down and / or in regeneration and / or backup mode.

[0073] The fixed bed train (or each train) advantageously operating in step b) of extraction by size exclusion comprises n fixed beds of size exclusion solids, where n is an integer greater than or equal to 4, preferably between 4 and 30, preferentially between 8 and 24, very preferentially between 8 and 21, and preferably between 12 and 15. The number of fixed beds must be sufficient to allow efficient separation and reasonable to limit costs, especially capital costs. The n fixed beds are in series with one another. The n fixed beds of size exclusion solids can be operated in a closed loop or an open circuit. Preferably, the n fixed beds of size exclusion solids are operated in a closed loop, i.e., the n fixed beds are connected to one another in series, preferably in a closed loop (the first is connected to the second, the second to the third, etc., and the nth is connected to the first), thus allowing continuous operation of extraction by size exclusion and advantageously reducing eluate consumption, since the eluate is subsequently partially continuously regenerated and reused.

[0074] In one (or each) fixed bed column, n fixed beds of size exclusion solids are advantageously distributed over one or more columns, preferably M columns, where M is an integer between 1 and the total number of fixed beds of exclusion solids in the column under consideration, i.e., M is between 1 and n. Thus, the fixed bed column (or each column) of step b) of extraction by size exclusion may comprise 1 to n columns, each of which comprises one or more fixed beds of size exclusion solids. For example, the fixed bed column (or each column) of step b) of extraction by size exclusion may comprise a single column (or tower), preferably of large capacity (volume), containing n fixed beds, or two columns, each containing n / 2 fixed beds. These two configurations allow for significant capital cost reduction, but if there is a problem with one of the beds in a column, the entire column, i.e., n or n / 2 fixed beds, must be removed. According to another embodiment, the (or each) train of fixed beds of step b) of extraction by size exclusion is implemented with n columns (or towers), preferably each of which has a smaller capacity (volume) than in the previous case, each of which contains a fixed bed of size exclusion solids, thus facilitating the maintenance and / or cleaning and / or bypass of one in particular of the n beds during operation, since in this configuration only one column (containing only one bed) must be removed and / or bypassed, rather than an assembly of beds. However, the latter configuration involves considerable capital costs.

[0075] Preferably, the size exclusion solid is provided in the form of solid particles. The size exclusion solid is sometimes called a granular medium. The size exclusion solid is selected so as to be inert to the polymer solution to be treated, i.e., the dissolving solvent and the polyolefin to be treated, as well as to the eluate. The size exclusion solid is also selected so as to enable efficient separation of the compounds present in the polymer solution to be treated, in particular the dissolved compounds, more particularly the impurities dissolved in the dissolving solvent from the dissolved polyolefin. The size exclusion solid may advantageously be organic (generally polymeric) and / or inorganic, and is preferably a porous solid having a volume average pore size of preferably 1 nm to 500 nm, preferentially 2 nm to 100 nm, very preferentially 2 nm to 50 nm, and preferably 3 nm to 30 nm. Advantageously, the size exclusion solid comprises silica (e.g., silica gel, also called silica, and / or grafted silica), carbon molecular sieves, polymeric molecular sieves (other than polyolefin-based in chemistry), porous polymer gels, carbon replicas, preferably dealuminated zeolites (e.g., 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 has a pore volume of preferably 0.01 to 3.0 ml / g, preferably 0.1 to 2.0 ml / g, preferentially 0.3 to 1.2 ml / g. The average pore size and pore volume of the size-excluded solids are determined by mercury porosimetry, more specifically measured by mercury intrusion porosimetry at a maximum pressure of 4000 bar, using a surface tension of 484 dynes / cm and a contact angle of 140°, according to standard ASTM D4284-83.Following the recommendation on page 1050 of the publication "Techniques de l'ingenieur, trait analyze et characterization" [Engineering Techniques, Analysis and Characterization Treatise] by J. Charpin and B. Rasneur, the wetting angle was taken equal to 140 degrees. For better accuracy, a given value of mercury volume (ml / g) corresponds to the total mercury volume (ml / g) measured on the sample minus the mercury volume (ml / g) measured on the same sample at a pressure equivalent to 30 psi (approximately 2 bar). These same parameters, especially the volume and diameter of solids in the mesoporous range (2-50 nm), can also be measured by nitrogen adsorption / desorption volumetrics (also known as nitrogen adsorption isotherms), a complementary analytical method to the one mentioned above. This analysis corresponds to the physical adsorption of nitrogen molecules in the porosity of a material via a gradual increase in pressure at a constant temperature, providing information on textural properties. In particular, it allows access to the mesoporous distribution of size-excluded solids. Therefore, the pore distribution, which represents a population of pores centered in the 2-50 nm range, 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.

[0076] The particles of the size-excluded solid preferably have a volume-average equivalent diameter (preferably determined by laser particle size analysis, i.e. laser diffraction using a particle size analyzer) of 20 to 5000 μm, preferably 50 to 1500 μm, preferentially 100 to 800 μm, even more preferably 300 to 600 μm. Advantageously, the solid particles are substantially spherical.

[0077] According to the invention, the (or each) train of fixed beds of step b) of extraction by size exclusion is fed with a crude or optionally clarified polymer solution at at least one injection point F for the polymer solution and with at least one eluate at injection point S for the eluate. Preferably, the train of fixed beds under consideration is fed with a crude or optionally clarified polymer solution at injection point F for the polymer solution and with the eluate at injection point S for the eluate.

[0078] Preferably, the eluate and the polymer solution are fed to the (each) fixed-bed column of step b) of extraction by size exclusion in a ratio of the volumetric flow rate of the eluate to the polymer solution of 0.1 to 50.0, preferably 0.2 to 10.0, preferably 0.5 to 5.0, preferentially 0.8 to 2.0, such ratio also being referred to as the solvent level. Such solvent level, i.e., such adjustment of the volumetric flow rate of the crude or optionally clarified polymer solution and the volumetric flow rate of the eluate for the (each) column under consideration, contributes to the efficiency of the separation by size exclusion of the polyolefins and impurities present in the polymer solution fed to step b).

[0079] If the train of fixed beds comprises several injection points Fi of the polymer solution, for example two injection points F1 and F2 of the polymer solution, the stream of crude or clarified polymer solution feeding the train of fixed beds considered above is divided into partial streams of polymer solution for feeding the train of fixed beds at the injection points Fi, the partial streams of polymer solution exhibiting the same or different flow rates from each other.

[0080] If a train of fixed beds comprises several injection points Si for eluate, for example two injection points S1 and S2, the total stream of eluate feeding the train of fixed beds considered above is divided into partial streams of eluate (i.e., into i partial streams of eluate, where i is an integer equal to the number of injection points Si for eluate) for feeding the train of fixed beds at the injection points Si, said partial streams of eluate exhibiting the same or different flow rates from one another.

[0081] The (or each) train of fixed beds of step b) of extraction by size exclusion implements at least one withdrawal of the extract at at least one withdrawal point E for the extract and at least one withdrawal of the raffinate at at least one withdrawal point R for the raffinate. Preferably, the (or each) train of fixed beds of step b) of extraction by size exclusion implements a withdrawal of the extract at the extraction point E for the extract and a withdrawal of the raffinate at the raffinate withdrawal point R.

[0082] The injection points F of the polymer solution and S of the eluate, as well as the withdrawal points E of the extract and R of the raffinate, are different from one another. They are advantageously located between two successive beds, especially in the case of an open circuit, or optionally upstream of the first bed (in the case of a closed loop of n fixed beds, these two beds are considered to be successive, since the nth bed is connected to the first bed). However, they may also be located in the middle of the fixed bed or in the fixed bed, on average over the operating cycle, especially in the case of an embodiment according to the VARICOL® process. The injection points of the polymer solution and the eluate and the withdrawal points of the extract and the raffinate are such that they are located in at least three, preferably four, successive main operating zones of the n fixed beds: a zone I of elution of impurities, comprised between the injection point S of the eluate and the withdrawal point E of the extract; - a zone II of elution of the polymer (in particular the targeted polyolefin) contained between the extraction point E of the extract and the injection point F of the polymer solution; a zone III of retention of impurities, comprised between the injection point F of the polymer solution and the withdrawal point R of the raffinate, and Optionally, a zone IV preferably included between the withdrawal point R of the raffinate and the injection point S of the eluate. are distributed relative to one another to determine

[0083] If there are several injection points Fi of the polymer solution and / or several injection points Si of the eluate and / or several withdrawal points of the extract and / or raffinate, zones I, II, III and optionally IV start at the first injection and / or withdrawal point of the stream under consideration (eluate, polymer solution, extract or raffinate), the term "first" being defined here as being the furthest upstream of all injection and / or withdrawal points of said stream under consideration. If there are several injection points Fi of the polymer solution and / or several injection points Si of the eluate and / or several withdrawal points of the extract and / or raffinate, secondary operating zones may also be defined, in particular inside the main operating zones, zones I, II, III and optionally IV.

[0084] When the n fixed beds of the train under consideration in step b) are operated in an open circuit, the eluate is introduced at eluate injection point(s) S, the crude or optionally clarified polymer solution is introduced at polymer solution injection point(s) F, the extract is withdrawn at extract withdrawal point(s) E, and the remainder is withdrawn at raffinate withdrawal point(s) R. The injection and withdrawal points thus define three successive main operating zones: Zones I, II, and III. In this embodiment, a large amount of eluate relative to the polymer solution is generally required to maximize separation. For example, this mode of operation in an open circuit requires a volumetric flow ratio of eluate to polymer solution of 2.0 to 50.0, preferably 5.0 to 20.0, and in practice even 5.0 to 10.0.

[0085] When the n fixed beds of the train under consideration in step b) are operated in a closed loop, the eluate is introduced at eluate injection point(s) S, the crude or optionally clarified polymer solution is introduced at polymer solution injection point(s) F, the extract is withdrawn at extract withdrawal point(s) E, and the raffinate is withdrawn at raffinate withdrawal point(s) R, with at least a portion of the introduced eluate advantageously remaining circulating within the closed loop of the n beds (the expression used is then eluate recycle). In this embodiment, the injection and withdrawal points then define four successive main operating zones, zones I, II, III, and IV, with zone IV being referred to as the zone for eluate regeneration and recycle. In this particular embodiment, the eluate supply requirement (i.e., the amount of eluate introduced at S) is advantageously much smaller than in the case of an open-circuit operating mode, ensuring efficient separation. For example, this mode of operation in closed loop requires a ratio of volumetric flow rate of eluate to polymer solution of 0.1 to 10, preferably 0.2 to 5.0, and in practice even 0.8 to 2.0.

[0086] Advantageously, in the case of a closed loop of n fixed beds, the n beds of size-exclusion solids are distributed in zones I to IV, preferably according to an a / b / c / d type configuration, the distribution of the beds of size-exclusion solids in zones I to IV relative to the total number n of beds of size-exclusion solids being: - a is the number of beds of size-excluded solids in zone I, - b is the number of beds of size-excluded solids in zone II, - c is the number of beds of size-excluded solids in zone III, - d is the number of beds of size-excluded solids in zone IV, where: - 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) It is as if.

[0087] It will be clear 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, the total number of fixed beds in the train of fixed beds considered in operation. Thus, a 6 / 3 / 4 / 2 configuration means that there are 15 fixed beds of size-excluded solids 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.

[0088] Very advantageously, the size exclusion is determined by the mass of size-excluded solids per unit volume of bed (i.e., per m of bed). 3 The packing density of each of the n fixed beds of size-excluded solids, expressed in kg of solids per m, is between 100 and 1500 kg / m 3 , preferably 300 to 1000 kg / m 3 , preferentially 400-800 kg / m 3 It can change.

[0089] According to the invention, the injection points F and S and the withdrawal points E and R are shifted over time by one bed of size-excluded solids according to a frequency determined by a predetermined transfer period. A transfer period can be defined as the period between two successive displacements (or shifts) of the injection and withdrawal points by one fixed bed. The periodic displacements (or shifts) of the injection points F and S and the withdrawal points E and R can be carried out synchronously or asynchronously, the latter case (asynchronous) being known under the name VARICOL®. The periodic displacement of the injection and withdrawal points along the entire length of n fixed beds makes it possible in particular to define an operating cycle and also advantageously a cycle time corresponding to the period required for the injection and withdrawal points to return to their initial position, i.e., a cycle time corresponding to the number n of beds multiplied by the transfer period.

[0090] When n fixed beds of rejection solids operate in a closed loop, the operating cycle therefore advantageously includes as many transfer periods as there are beds of size exclusion solids present in the closed separation loop. For example, the operating cycle of a train including 12 fixed beds of size exclusion solids includes 12 transfer periods. Therefore, in a preferred embodiment in which n fixed beds of rejection solids of the considered fixed bed train operate in a closed loop, the transfer periods are preferably adjusted to define a cycle time of 1 to 600 minutes, preferably 5 to 200 minutes, preferably 10 to 90 minutes, corresponding to the time required for the injection and withdrawal points to return to their initial positions. Such a cycle time contributes to the efficiency of the separation by size exclusion of polyolefins and impurities present in the polymer solution fed to step b).

[0091] In the case of an embodiment in which the n fixed beds operate in an open circuit (i.e., all are withdrawn together with the extract and raffinate), the cycle time may also be from 1 minute to 600 minutes, preferably from 5 minutes to 200 minutes, preferably from 10 minutes to 90 minutes.

[0092] The displacement of the injection points F and S and the withdrawal points E and R may be carried out by the installation of a series of open / close valves controlled by an automatic sequence, or equally by the installation of a single rotary valve.

[0093] In general, the liquid in the fixed beds advantageously flows from bed i to bed i+1, where i is an integer between 1 and n, the total number of fixed beds, i.e., from upstream to downstream. This flow may be referred to as downward liquid flow, even if a pump(s) is required (especially between the nth bed and the first bed in closed-loop operation, where n beds are in a column). At the time of changeover (or displacement of the injection and withdrawal points), the injection and withdrawal points are displaced by a bed located downstream of the preceding bed, thus creating / simulating a countercurrent liquid flow, optionally referred to as upward liquid flow. A stop flow rate can then be defined when the two countercurrent liquid flow rates are equal, i.e., when the downward liquid flow rate is equal to the upward liquid flow rate. This stop flow rate can be calculated by dividing the interparticle volume of the size-excluded solids in the bed by the changeover period, where the interparticle volume of the size-excluded solids in the bed is a function of the packing density of the fixed bed of size-excluded solids and the particle density of the size-excluded solids. More specifically, the intergranular volume of the size-excluded solid (V( 粒間 )) can be calculated by the following formula:

[0094] V (粒間) =V (床) ×(1-d (充填) / d (粒) )+V dead where: V (粒間) : Intergranular volume of size-excluded solids in the bed (m 3 ), V (床) : Geometric volume of floor (m 3 ), d (充填) : the true packing density of the size-excluded solids, i.e. the packing density (kg / m3) of the size-excluded solids in the bed, corresponding to the mass of said solids per unit volume of the bed. As a first approach, this can be analogized to the tapped packing density, which consists of the mass of solids that occupies a given volume after tapping said solids by vibration, according to principles derived from standards D4164 and D4180, which apply in the case of catalysts.

[0095] d (粒): Particle density (kg / m) of size-excluded solids, typically measured by mercury porosimetry 3 ), V dead : The volume (m) of the device through which no size-excluded solids flow but which is subject to associated fluids, especially polymer solutions. 3 ) (e.g., volume of the line upstream, downstream, etc.).

[0096] The stop flow rate, which is a volumetric flow rate, allows for the calculation of dimensionless parameters, particularly for zones II and IV, such as the ratio of the volumetric flow rate of zone II to the stop flow rate and the ratio of the volumetric flow rate of zone IV to the stop flow rate. Preferably, the ratio of the volumetric flow rate of zone IV divided by the stop flow rate is less than or equal to 2, preferentially 0.5 to 1.5, and more preferably still 0.8 to 1.0. Preferably, the ratio of the volumetric flow rate of zone II divided by the stop flow rate is 0.5 to 3.0, preferentially 0.9 to 1.5, and preferably 1.0 to 1.25. The stop flow rate thus allows for the adjustment of the extraction step and thus the efficiency of the separation.

[0097] Furthermore, very advantageously, the superficial velocity in the fixed bed of said operating zone, which corresponds to the volumetric flow rate in the zone under consideration divided by the cross section of the operating zone (i.e. of the column in which the bed of said zone under consideration is located), can be adjusted so that this superficial velocity is between 0.01 and 10.0 cm / s, preferentially between 0.05 and 2.5 cm / s. Adjusting the superficial velocity in the fixed bed advantageously makes it possible to adjust the operation of the column of fixed beds of step b) in order to control in particular the attrition of the size-excluded solid particles and thus to avoid large pressure drops (encountered in particular at high velocities) and / or dispersion problems (encountered in particular at low velocities).

[0098] Preferably, step b) of extraction by size exclusion is carried out at a temperature of 100 to 300°C, preferably 150 to 250°C, and at a pressure of 1.0 to 100.0 MPa absolute, preferably 1.0 to 25.0 MPa absolute, preferentially 1.5 to 18.0 MPa absolute, and very preferably 2.0 to 15.0 MPa absolute. Under these operating conditions, the polyolefin remains dissolved in the dissolution solvent and, optionally, in the eluate, the latter (i.e., the dissolution solvent and the eluate), some of which are at least partially in liquid form. Preferably, the temperature and pressure conditions of step b) are the same as those of the dissolution step a).

[0099] Thus, step b) of extraction by size exclusion allows the recovery of at least one extract containing at least partially, preferably completely, the impurities present in the polymer solution fed to step b), and at least one raffinate containing a polymer solution from which impurities have been at least partially, preferably completely removed. The raffinate recovered at the end of step b) of extraction by size exclusion 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 step c) of polymer-solvent separation. However, if necessary, the purified polymer solution may be sent to at least one additional purification step to optimize the purification of the target polyolefin, if necessary. This step b) of extraction by size exclusion therefore allows the efficient and continuous separation of, in particular, soluble impurities from a crude or optionally clarified polymer solution containing polyolefin dissolved in a dissolution solvent.

[0100] Extraction by size exclusion, especially in the case of a fixed-bed closed loop, allows for the efficient separation of impurities from polyolefins in a continuous mode, which makes it possible to limit the effort required to carry out said step and at the same time facilitate its operability, and also allows for a high productivity, especially compared to size exclusion chromatography operation in batch mode, while providing a relatively low consumption of eluent.

[0101] Polymer-solvent separation step c) According to the invention, the process comprises a step c) of polymer-solvent separation of the purified polymer solution to obtain at least one stream of purified polyolefin, in particular a stream of purified polypropylene, a stream of purified polyethylene or a stream of copolymers thereof, a stream of a purified mixture of polypropylene and polyethylene, and at least one solvent fraction comprising the dissolving solvent.

[0102] The polymer-solvent separation step c) advantageously implements at least one solvent recovery section, preferably between 1 and 5 solvent recovery sections.

[0103] Advantageously, step c) is fed with the purified polymer solution obtained at the end of step b) or with the final purified polymer solution obtained from an additional purification step, optionally located downstream of step b) of extraction by size exclusion.

[0104] Thus, the polymer-solvent separation step c) is primarily intended to separate at least partly, preferably for the most part, the dissolving solvent and optionally the eluate from the target polyolefin(s) contained in the polymer solution fed to step c), more particularly the purified polymer solution, or the final purified polymer solution optionally obtained from an additional purification step, in order to recover at least the polyolefins from which the dissolving solvent and optionally the eluate still present in the polymer solution fed to step c) have been at least partly, preferably for the most part, and preferentially completely removed. The term "for the most part" should be understood to mean at least 50% by weight, preferentially at least 70% by weight, more preferably at least 90% by weight, and even more preferably at least 95% by weight, based on the weight of the solvent(s) contained in the purified polymer solution fed to step c), in particular the dissolving solvent and optionally the eluate contained in said purified polymer solution. Any method of solvent(s) / polymer(s) separation known to those skilled in the art can be carried out, in particular any method that allows a phase change of the polymer(s) and / or solvent(s). The solvent(s) can be separated, for example, by precipitation or crystallization of the polymer, flash evaporation of the solvent, atomization, stripping, demixing, density differences, especially decantation or centrifugation, and the like.

[0105] The at least one purified polyolefin stream thus obtained may correspond to a polyolefin-enriched polymer solution or to polyolefin in liquid (i.e. viscous) or solid form. Preferably, step c) of polymer-solvent separation additionally comprises a conditioning section for conditioning the purified polyolefin in solid form, more particularly in granular form.

[0106] The polymer-solvent separation step c) also aims at at least partially, preferably for the most part, and preferentially completely, recovering the solvent(s) contained in the purified polymer solution fed to step c), in particular the dissolution solvent and optionally the eluate. The polymer-solvent separation step c) also aims, optionally, at purifying and recycling the recovered solvent fraction, in particular upstream of the dissolution step a). The term "for the most part" should be understood to mean at least 50% by weight, preferentially at least 70% by weight, more preferably at least 90% by weight, even more preferably at least 95% by weight, relative to the weight of the solvent(s) contained in the purified polymer solution fed to step c).

[0107] Advantageously, step c) of polymer-solvent separation implements at least one solvent recovery section, the latter preferably comprising equipment operated at different temperatures and different pressures with the aim of obtaining at least one solvent fraction and one purified polymer fraction.

[0108] The process according to the invention thus allows for efficient and continuous recovery of polyolefins from plastic feedstocks with high productivity and a limited number of operations. Very advantageously, the process according to the invention makes it possible to obtain, starting from any type of plastic feedstock, a polyolefin stream exhibiting a high purity, preferably greater than 95%, preferably greater than 99%, and preferentially greater than 99.5% (weight of polyolefin relative to the total weight of the recovered purified stream). Another advantage of the process according to the invention lies in the fact that it allows for efficient separation of impurities, especially additives, present in the plastic feedstock, while allowing for reasonable consumption of solvents, especially dissolving solvents and eluents, and lower energy consumption than that required for more conventional "thermal" separations, such as crystallization. The process according to the invention therefore makes it possible to obtain a purified polyolefin stream that is less colored than the plastic feedstock being treated, practically even colorless, and is very advantageously deodorized. The resulting purified polymer stream preferably has a negligible content of substances prohibited or restricted, for example, by the REACH regulation. More specifically, the process according to the invention makes it possible to obtain a purified polyolefin stream from which at least some, preferably all, of the impurities, such as additives, present in the plastic feedstock have been removed, and from which solvents, in particular dissolution solvents and eluates, have been at least partially, indeed even completely, removed.

[0109] The process according to the invention therefore advantageously makes it possible to obtain a purified polyolefin stream having an impurity content of impurities of less than or equal to 5% by weight, preferably less than or equal to 1% by weight, more preferably even less than or equal to 0.5% by weight, and very advantageously a solvent content (in particular dissolution solvents and eluates) 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, the percentages being given relative to the total weight of the purified polyolefin stream.

[0110] Device for extraction by size exclusion The present invention also relates to a device for extraction by size exclusion suitable for separating polyolefins from impurities contained in a polymer solution, said device comprising: - n fixed beds of size exclusion solids, n being an integer greater than or equal to 4, preferably between 4 and 30, preferentially between 8 and 24, very preferentially between 8 and 21, preferably between 12 and 15, said size exclusion solids preferably having a volume average pore size of between 1 nm and 500 nm, preferably between 2 nm and 100 nm, preferentially between 2 nm and 50 nm, preferentially between 3 and 30 nm, preferably being silica gel (or silica), grafted silica, carbon molecular sieves or mixtures thereof, n fixed beds of size exclusion solids distributed in one or more columns, preferably M columns, where M is an integer between 1 and the total number n of fixed beds of exclusion solids, and the n beds are connected in series, preferably in a closed loop; N injection systems, preferably different from one another, for the polymer solution, N injection systems, preferably different from one another, for the eluate, N withdrawal systems, preferably different from one another, for the extract, and N withdrawal systems, preferably different from one another, for the raffinate, where N is an integer preferably equal to n, said injection and withdrawal systems being located between two successive beds or optionally upstream of the first bed, the injection and withdrawal systems of the polymer solution and eluate, and / or the extract and raffinate, located in one and the same position, i.e. between the same two successive beds or optionally upstream of the first bed, being different or identical (the term "identical" should be understood to mean that the system of valves can either allow the introduction of the polymer solution or the eluate, or the withdrawal of one or the other stream, i.e. the extract or the raffinate), and Equipped with each injection and withdrawal system comprises at least one valve suitable for allowing or disabling the passage of the polymer solution and / or eluate and / or extract and / or raffinate streams, preferably i) a series of open / close valves controlled by an automatic sequence, or ii) a single rotary valve, whereby At a time t, an injection point for the polymer solution, an injection point for the eluate, a withdrawal point for the extract and a withdrawal point for the raffinate are defined, said injection points and withdrawal points being different from one another, and comprising at least three, preferably four, consecutive main operating zones of n fixed beds: - a zone I of elution of impurities, which is comprised between the injection point of the eluate and the withdrawal point of the extract; - Zone II of polyolefin dissolution, which is comprised between the extraction point of the extract and the injection point of the polymer solution; a zone III of retention of impurities contained between the injection point of the polymer solution and the withdrawal point of the raffinate, and - optionally determining a zone IV comprised between the withdrawal point of the raffinate and the injection point of the eluate; It also allows for the shifting of injection and withdrawal points over time, synchronously or asynchronously, with one fixed bed of size-excluded solids per transfer period, according to a frequency determined by the given transfer period.

[0111] Device for processing plastic feedstock Such a device for extraction by size exclusion can be incorporated into a more comprehensive device for the processing of plastic feedstocks to obtain a stream of purified polyolefins, which device comprises: - a dissolving means for contacting a plastic feedstock with a dissolving solvent to at least partially dissolve said plastic feedstock in said dissolving solvent, said dissolving means being any type of equipment for contacting and dissolving a plastic feedstock with a dissolving solvent to obtain a crude polymer solution, such as an extruder, one or more static mixers, one or more continuous stirred tank reactors (CSTR) equipped with appropriate agitation system(s); - optionally solid-liquid separation means, in particular any type of equipment for solid-liquid separation, optionally suitable for separating insoluble materials in suspension in the crude polymer solution, at least one device for extraction by size exclusion according to the invention and, as described above, advantageously connected to said dissolution means for contacting and dissolving or optionally to at least one of said solid-liquid separation means, - means for separating the dissolution solvent and optionally the eluate from the stream of purified polyolefins, in particular any type of equipment for separating the dissolution solvent and optionally the eluate from the stream of optionally purified polyolefins, advantageously connected to at least one device for extraction by size exclusion as described above; Equipped with.

[0112] Said device for treating a plastic feedstock to obtain a stream of purified polyolefins also advantageously comprises transport means between said means and the device.

[0113] Such a device very advantageously allows for the recovery of polyolefins at high purity from plastic feedstocks that may contain numerous impurities.

[0114] The following examples and figures illustrate the invention and in particular certain embodiments of the invention without limiting its scope.

[0115] Example Example 1 This example is the result of a digital simulation based on experiments carried out in the laboratory.

[0116] The feedstock to be processed consists of 95% by weight of polyethylene (PE) with a volume-average molar mass MW=650,000 g / mol and 5% by weight of the additive Irgafos® 168, which is conventionally used as a stabilizer in polyolefin blends.

[0117] The feedstock is first dissolved in heptane at 200° C. and 1.0 MPa (i.e., 10 bar) to form a homogeneous crude polymer solution comprising 80 wt. % heptane and 20 wt. % polyethylene and additive-containing feedstock.

[0118] The crude polymer solution formed is introduced into a simulated moving bed consisting of 15 beds containing silica gel, distributed in a 6 / 3 / 4 / 2 configuration (see FIG. 1). The eluent is heptane.

[0119] The silica gel of the bed is in the form of beads and has the following characteristics:

[0120] -Bead diameter = 500 μm -Pore size=6~10nm -Pore volume=0.80ml / g - Packing density = solids 530kg / bed m 3 -Extragranular porosity=0.4 Each bed is modeled by a 1D piston fixed-bed model with axial dispersion and a Fick model for intragranular migration. The radius of gyration for polyethylene is estimated to be 32 nm, so the polymer is considered to exist only in the extragranular phase. The additives and solvents have a radius of gyration less than 1 nm and can therefore diffuse into the intragranular porosity. The medium within the bed is considered isothermal (200 °C) and the density of the polymer solution is constant (477 kg / m). 3 Finally, all beds are modeled and the cycle is dynamically solved until the concentration profile converges.

[0121] The extraction is adjusted using the following settings:

[0122] Cycle time = 15 minutes The ratio of the volumetric flow rate of the eluent (heptane) to the volumetric flow rate of the polymer solution, S / F, is 1.08. Zone IV flow rate / stop flow rate = 0.92 Zone II flow rate / stop flow rate = 1.10 Maximum sky speed=1.80cm / s The concentration profiles obtained by simulation for PE and additive along the entire length of the simulated moving bed, by conventional injection of effluent upstream of bed 1 (and downstream of bed 15), are shown in Figure 3. In Figure 3, the concentration profile of PE is represented by the solid black line, and the concentration profile of the additive Irgafos® 168 is represented by the dotted line. The concentrations along the entire length of the bed are given as the weight percentage of the following compound, i.e., PE or additive, relative to the weight of heptane.

[0123] From Figure 3 it is clear that the polyethylene (PE), which does not explore the intragranular porosity, is entrained towards the raffinate and is drawn off between beds 13 and 14. The additives, being smaller, are able to diffuse into the intragranular porosity and are entrained towards the extract which is drawn off between beds 6 and 7.

[0124] The step of PE extraction carried out in a simulated moving bed makes it possible to obtain the following performance qualities: - polyethylene purity = 99.99 wt.% (this 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 additives in the raffinate, excluding solvent, i.e. excluding heptane), - polyethylene yield = 100% (this corresponds to the weight flow rate of PE extracted in the raffinate divided by the weight flow rate of PE extracted in the extract + raffinate combination), Productivity = 170 kg / h of PE extracted in the raffinate / m of silica gel bed 3 .

[0125] The raffinate at the outlet of the simulated moving bed for extraction by size exclusion can then be recovered and sent to a polymer-solvent separation section, in particular to a section for evaporation of the solvent heptane.

Claims

1. 1. A process for purifying a plastic feedstock to obtain a purified polyolefin stream, comprising: a) a dissolution step comprising contacting said plastic feedstock with a dissolution solvent to obtain at least one crude polymer solution; b') optionally separating insoluble material from said crude polymer solution obtained from step a) to obtain at least one clarified polymer solution; b) a step of extraction by size exclusion of said crude polymer solution obtained at the end of step a) or optionally of said clarified polymer solution obtained at the end of optional step b') in order to obtain a purified polymer solution, The step of extracting by size exclusion implements at least one train of n fixed beds of size exclusion solids, n being an integer greater than or equal to 4, and the n beds being in series; The train of fixed beds of step b) is fed with a crude or optionally clarified polymer solution at at least one injection point F for the polymer solution and with the eluate at at least one injection point S for the eluate, The train of fixed beds of step b) implements at least one withdrawal of the extract at at least one withdrawal point E of the extract and at least one withdrawal of the raffinate at at least one withdrawal point R of the raffinate, The injection points of the polymer solution and the eluate, and the withdrawal points of the extract and the raffinate are different from each other and are located in at least three, preferably four, successive main operating zones of the n fixed beds: a zone I of elution of the impurities, located between the injection point of the eluate and the withdrawal point of the extract; a zone II of elution of the polyolefin located between the withdrawal point of the extract and the injection point of the polymer solution; a zone III of retention of the impurities, located between the injection point of the polymer solution and the withdrawal point of the raffinate; and optionally distributed to define a zone IV located between the withdrawal point of the raffinate and the injection point of the eluate, the injection point and the withdrawal point are shifted over time by one fixed bed of size exclusion solids according to a frequency determined by a predetermined turnover period; an extraction step in which the raffinate is recovered to at least partially constitute the purified polymer solution; c) polymer-solvent separation of said purified polymer solution to obtain at least one stream of purified polyolefin and at least one solvent fraction comprising the dissolving solvent; A method comprising:

2. 2. The method according to claim 1, wherein the dissolving solvent comprises at least one hydrocarbon compound which is preferably aliphatic and especially paraffinic, very preferably an aliphatic paraffinic hydrocarbon compound, containing 3 to 12 carbon atoms, very preferably 4 to 8 carbon atoms, with a boiling point of -50 to 250°C, preferably -15 to 150°C, preferentially -1 to 110°C, preferably 20 to 100°C.

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

4. 4. The method according to claim 1, wherein step b) of extraction by size exclusion implements at least one train of n fixed beds of size exclusion solids, n being an integer between 4 and 30, preferably between 12 and 15.

5. 5. The method according to any one of claims 1 to 4, wherein the size-excluded solid is a porous solid having a volume-average pore diameter of 1 to 500 nm, preferably 2 to 100 nm, preferentially 2 nm to 50 nm, preferentially 3 to 30 nm.

6. The method of any one of claims 1 to 5, wherein the size exclusion solid comprises silica gel, grafted silica, carbon molecular sieve, or a mixture thereof.

7. 7. The method according to any one of claims 1 to 6, wherein the eluate and the polymer solution are fed to step b) according to a volumetric flow ratio of the eluate to the polymer solution of between 0.1 and 50.0, preferably between 0.2 and 10.0, preferably between 0.5 and 5.0, preferentially between 0.8 and 2.

0.

8. 8. The process according to claim 1, wherein the injection points of the polymer solution and the eluate and the withdrawal points of the extract and the raffinate are located between two successive beds or, optionally, upstream of the first bed.

9. The n beds of size-exclusion solids operate in a closed loop and are distributed among four main operating zones, zones I to IV, according to an a / b / c / d type configuration, and the distribution of the beds of size-exclusion solids in zones I to IV relative to the total number n of beds of size-exclusion solids preferably comprises: - a is the number of beds of size-excluded solids in zone I, - b is the number of beds of size-excluded solids in zone II, -c is the number of beds of size-excluded solids in zone III; - d is the number of beds of size-excluded solids in zone IV; where: - 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) The method according to any one of claims 1 to 8, wherein

10. 10. The method according to any one of claims 1 to 9, wherein the n beds are in a closed loop and the transfer periods are preferably adjusted to define a cycle time corresponding to the time required for the injection and withdrawal points to return to their initial positions, said cycle time being between 1 and 600 minutes, preferably between 5 and 200 minutes, preferably between 10 and 90 minutes.

11. 11. The method according to any one of claims 1 to 10, wherein step a) is carried out at a dissolution temperature of 100°C to 300°C, preferably 150 to 250°C, and at a dissolution pressure of 0.1 to 100.0 MPa absolute, preferably 1.0 to 25.0 MPa absolute, preferably 1.5 to 18.0 MPa absolute, very preferably 2.0 to 15.0 MPa absolute.

12. 12. The method according to any one of claims 1 to 11, wherein in step a) the plastics feedstock and the dissolving solvent are fed at a weight ratio between the dissolving solvent and the plastics feedstock of 0.2 to 100.0, preferably 0.3 to 20.0, preferably 1.0 to 10.0, more preferentially 3.0 to 7.

0.

13. 13. The method according to any one of claims 1 to 12, wherein step b) of extraction by size exclusion is carried out at a temperature of from 100°C to 300°C, preferably from 150 to 250°C, and at a pressure of from 1.0 to 100.0 MPa absolute, preferably from 1.0 to 25.0 MPa absolute, preferably from 1.5 to 18.0 MPa absolute, very preferably from 2.0 to 15.0 MPa absolute.

14. 1. A device for extracting polyolefins from a polymer solution by size exclusion, comprising: - n fixed beds of size exclusion solids, n being an integer greater than or equal to 4, preferably between 4 and 30, said size exclusion solids preferably having a volume average pore diameter between 1 and 500 nm, preferably between 2 and 100 nm, preferentially between 2 and 50 nm, preferentially between 3 and 30 nm, preferably being silica gel, grafted silica, carbon molecular sieves or mixtures thereof, n fixed beds of size exclusion solids distributed in one or more columns, the n beds being connected in series, preferably in a closed loop; N injection systems for the polymer solution, N injection systems for the eluate, N withdrawal systems for the extract and N withdrawal systems for the raffinate, N being an integer preferably equal to n, said injection systems and said withdrawal systems being located between two successive beds or, optionally, upstream of said first bed, an injection system and a withdrawal system for the polymer solution and the eluate, and / or the withdrawal system for the extract and the raffinate, located in one and the same position, being different or the same; Equipped with each injection and withdrawal system comprises at least one valve suitable for allowing or disabling the passage of the polymer solution and / or eluate and / or extract and / or raffinate streams, preferably a series of open / close valves controlled by an automatic sequence, or a single rotary valve, so that At a time t, an injection point for the polymer solution, an injection point for the eluate, a withdrawal point for the extract and a withdrawal point for the raffinate are defined, said injection points and said withdrawal points being different from one another, and comprising at least three, preferably four, consecutive main operating zones of said n fixed beds: a zone I of elution of said impurities, comprised between the injection point of said eluate and the withdrawal point of said extract; a zone II of elution of the polyolefin contained between the withdrawal point of the extract and the injection point of the polymer solution; a zone III of retention of said impurities contained between the injection point of said polymer solution and the withdrawal point of said raffinate, and - optionally determining a zone IV comprised between the withdrawal point of the raffinate and the injection point of the eluate, A device that also allows the shifting of the injection and withdrawal points over time, synchronously or asynchronously, by one fixed bed of size exclusion solids per transfer period, according to a frequency determined by the given transfer period.

15. 1. A device for the processing of a plastic feedstock to obtain a purified polyolefin stream, comprising: - dissolving means for contacting said plastic feedstock with a dissolving solvent so as to at least partially dissolve said plastic feedstock in the dissolving solvent to obtain a crude polymer solution; - optionally solid-liquid separation means suitable for separating insoluble materials in suspension in said crude polymer solution; - at least one device for extraction by size exclusion according to claim 14, - means for separating said dissolution solvent and optionally said eluate from a purified polyolefin stream; A device comprising:

Images