PROCESS FOR RECYCLING POLYOLEFIN-BASED PLASTICS USING A SIMULATED STEREO EXCLUSION MOVING BED DEVICE

Abstract

The present invention relates to a process for purifying a plastic feedstock to obtain a stream of purified polyolefins, comprising: a) a dissolution step by contacting the plastic feedstock with a dissolving solvent; then b) a size exclusion extraction step, employing beds of a size exclusion solid in series and fed with the polymer solution from a) at an injection point (F) and with an eluent at an injection point (S) and employing a withdrawal of an extract at a withdrawal point (E) and a withdrawal of a raffinate comprising a purified polymer solution at a withdrawal point (R), the injection and withdrawal points being distinct and offset over time by one bed according to a determined frequency; then c) a polymer-solvent separation step, to obtain a stream of purified polyolefins.The invention also relates to a device for carrying out step b) and a device for carrying out the purification process. Figure 1 to be published.

Description

Title of the invention: METHOD FOR RECYCLING POLYOLEFIN-BASED PLASTICS USING A SIMULATED STEREO EXCLUSION MOVING BED DEVICE technical field

[0001] The invention relates to the field of recycling polyolefin-based plastics, in particular (co)polypropylene and / or (co)polyethylene, in order to obtain a stream of purified polyolefins that can be used, for example, in the manufacture of new plastic products. More particularly, the present invention relates to a process for treating a plastic feedstock, particularly one derived from plastic waste, comprising polyolefins, in particular (co)polypropylene and / or (co)polyethylene.The process advantageously comprises dissolving polyolefins in a solvent, in particular an organic solvent, especially hydrocarbon, at least one step of purifying the resulting polymer solution by simulated moving bed extraction by steric extrusion, in order to remove at least part of the impurities, in particular the additives conventionally used in plastic-based materials, and a step of separating the polymer and the solvent, to recover a stream of purified polyolefins, so as to be able to reuse the purified polyolefins in the manufacture of new objects and thus valorize the plastic filler, in particular from waste. Previous technique

[0002] Plastic recycling is a major environmental challenge for the coming century. There are several ways to recycle and recover value from plastics collected and sorted through recycling channels.

[0003] First, there is so-called mechanical recycling: mechanical recycling allows for the partial reuse of certain waste materials, either directly (after melting and shaping the thermoplastics) in new objects, or by mixing mechanically sorted plastic waste streams with streams of virgin polymers. This type of recovery is limited because mechanical sorting improves the purity of a plastic stream into a given type of polymer, but it generally does not sufficiently eliminate impurities that are at least partially trapped in the polymer matrix, such as additives like fillers, colorants, pigments, and metals, used in mixtures with polymers to give the material the desired properties.

[0004] Chemical recycling, on the other hand, primarily aims to eliminate additives and, depending on the processes applied, to chemically modify the polymer chains of the plastics in question to varying degrees (for example, recovery of the intact polymer, depolymerization of the latter, or obtaining mixtures of compounds including carbon and hydrogen after non-selective chain breaking of various polymers). These various options involve generally complex sequences of steps. For example, plastic waste may undergo a pyrolysis step, and the recovered pyrolysis oil, generally after purification, may be converted, at least in part, for example, into olefins by steam cracking. These olefins may then be polymerized or transformed into monomers before the latter are polymerized.This type of processing can be adapted for poorly sorted loads or sorting center rejects, but it generally requires significant energy consumption, particularly due to high-temperature treatments.

[0005] Among the various possible approaches, the deformulation of plastic materials based on thermoplastics, particularly polyolefins such as (co)polypropylenes and (co)polyethylenes, appears advantageous: it consists of dissolving the polymer in a solvent and removing the additives without altering the polymer chains. Preserving the polymer structure reduces the effort required to reuse the material and explains the good performance of this approach, particularly in terms of energy consumption.

[0006] When impurities contained in the plastic filler, such as additives, are insoluble in the solvent, they can potentially be separated by solid-liquid separation, for example by filtration. In contrast, solvent-soluble additives are particularly difficult to separate. One approach, the most conventional, may consist of separating them based on specific physicochemical properties, such as their polarity, solubility, boiling point, density, etc., but this can lead to a multiplication of purification steps given the plurality and diversity of the impurities present. The present invention proposes another approach based on exploiting the difference in size, more precisely the hydrodynamic volume, between the polymer macromolecules and the impurity molecules, such as those of the additives.

[0007] Size separation already exists and is commonly used as an analytical method to determine the molecular weight of polymers. This method, called size exclusion chromatography (or SEC), operated discontinuously (in batch mode), consists of using a fixed bed with several porosity levels. Small molecules explore this fixed bed down to the smallest porosities. Small pores result in long elution times, while large molecules, such as polymers, only pass through the largest pores and exhibit short elution times, allowing for selective separation of different molecules. Since additives commonly used in plastic formulations (colorants, plasticizers, antioxidants, stabilizers, etc.) are an order of magnitude smaller than polymers, particularly polyolefins, size exclusion chromatography can be applied to plastic purification. However, implementing a process using this chromatography principle is batch-based, which can be problematic for industrial applications.Furthermore, such a batch process would require a significant consumption of eluent to ensure efficient separation, which directly impacts the profitability, productivity, and environmental footprint of the process.

[0008] Simulated Moving Bed (SMB) technology, a concept invented in 1961, allows for the continuous operation of a batch chromatographic process, particularly by adsorption, with increased productivity and reduced eluent consumption, while ensuring efficient separation. Numerous industrial applications of this technology exist, particularly for adsorption separations used notably for xylene separation with the ELUXYL® or PAREX® processes (see the book Simulated Moving Bed Technology: Principles, Design and Process Applications, AE Rodrigues, Elsevier, 2015).The only large-scale application of a simulated moving bed with size exclusion chromatography (SMB-SEC) concerns the separation of n-paraffins from isoparaffins, as detailed in US patent 2985589. Recent publications mention the use of SMB-SEC technology for the fractionation of polyethylene glycols of varying molecular weights (MT Liang et al., J. Chromatogr. A, 2012, 1229, 107) or for protein separation (EJ Freydell et al., Chem. Eng. Sc, 2010, 65, 4701). More specifically, US patent 6551512 proposes a method for separating proteins of liquid composition, such as milk, by size exclusion in a simulated moving bed.Finally, a publication mentions the use of SMB-SEC in a recycling process for materials used in WEEE (waste electrical and electronic equipment). WEEE is polycarbonate-based and also includes poly(styrene-co-acetonitrile) (SAN) and additives such as flame retardants. It is these latter components that Weeden's team is trying to separate from a ternary solution containing SAN and two flame-retardant compounds, bis-. resorcinol diphenylphosphate and bisphenol A bis-diphenylphosphate, in a mixture of acetone-dichloromethane solvents (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 a stream of purified polyolefins, in particular a stream of polypropylene, polyethylene, their copolymers or mixtures thereof, has never been proposed.

[0010] The present invention thus aims to overcome the problems of the prior art and to contribute to the recycling of plastics. More particularly, it aims to provide an efficient, simple, and economically viable process for treating a polyolefin-based plastic filler, especially one derived from plastic waste, for example, from collection and sorting streams, in order to remove at least some of the impurities it contains, in particular at least some of the additives conventionally added to plastics, so as to be able to recover value from said polyolefin-based plastic filler. The present invention seeks, in effect, to efficiently separate the impurities from the polyolefins contained in used plastics and to recover the purified polyolefins, so that they can be used, for example, in the manufacture of new plastic objects, particularly as a replacement for virgin resin. Summary of the invention

[0011] The present invention thus relates to a process for purifying a plastic feedstock to obtain a stream of purified polyolefins, said process comprising:

[0012] a) a dissolution step comprising bringing the plastic feedstock into contact with a dissolving solvent, to obtain at least a crude polymer solution;

[0013] b') optionally a step of separating the insolubles from the polymer solution crude from step a), to obtain at least one clarified polymer solution;

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

[0015] said steric exclusion extraction step employing at least one train of n fixed beds of a steric exclusion solid, n being an integer greater than or equal to 4, the n beds being in series,

[0016] said fixed bed train of step b) being fed with crude or clarified polymer solution at at least one injection point F of the polymer solution and with an eluent at at least one injection point S of the eluent,

[0017] said fixed bed train of step b) implementing at least one withdrawal of a extract at at least one withdrawal point E of the extract, and at least one withdrawal of a refinery at at least one withdrawal point R of the refinery,

[0018] the injection points of the polymer solution and the eluent and the withdrawal points of the extract and the raffinate being distinct from each other, and distributed so as to determine at least three, preferably four, successive main operating zones of the n fixed beds:

[0019] - a zone I for elution of impurities, located between an injection point of the eluent and a point for extracting the extract;

[0020] - a zone II for the elution of polyolefins, located between the extraction withdrawal point and an injection point for the polymer solution;

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

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

[0023] the injection and withdrawal points being shifted over time from a fixed bed of steric exclusion solid according to a frequency determined by a predetermined permutation period,

[0024] said raffinate being recovered to constitute, at least in part, the purified polymer solution;

[0025] c) a polymer-solvent separation step, to obtain at least one stream of purified polyolefins and at least one solvent fraction comprising the dissolving solvent.

[0026] The advantage of the process of the invention is that it provides an efficient method for treating a feedstock comprising polyolefin-based plastics, particularly plastic waste from collection and sorting streams, in order to recover the polyolefins it contains for recycling into all types of applications. The process according to the invention makes it possible to obtain a stream of purified polyolefins, in particular a stream of polypropylene, polyethylene, their copolymers, or mixtures thereof, which is advantageously less colored than the initial plastic feedstock, or even colorless, and preferably deodorized. The purified polymer stream obtained preferably has negligible levels of prohibited or regulated substances, for example, those regulated by the REACH Regulation (see Annexes XIV and XVII of Regulation (EC) No 1907 / 2006 of the European Parliament and of the Council of 18 December 2006).In particular, the purified polyolefin stream obtained at the end of the process according to the invention very advantageously comprises a content of impurities, and in particular of additives, and a content of solvent, in particular of dissolving solvent and / or eluent, which is negligible or at least sufficiently low so that the purified polyolefin stream can be introduced into any plastics formulation instead. of virgin polymer resins. For example, the purified polyolefin stream obtained at the end of the process according to the invention advantageously comprises an impurity content of less than or equal to 5% by weight, very advantageously less than or equal to 1% by weight, or even less than or equal to 0.5% by weight, and advantageously a solvent content (in particular of dissolving solvent and eluent) of less than or equal to 5% by weight of solvent, preferably less than or equal to 1% by weight, preferably less than or equal to 0.1% by weight.

[0027] The process according to the invention thus proposes a simple scheme corresponding to a minimum sequence of operations, which makes it possible to remove from plastic waste based on polyolefins, in particular based on polypropylene, polyethylene, their copolymers or mixtures, at least part of their impurities, in particular at least part of the additives, and to recover purified polyolefins, advantageously comprising little or no solvent, so as to be able to recover plastic waste by recycling said purified polyolefins.

[0028] The invention also has the advantage of contributing to plastic recycling and the preservation of fossil resources by enabling the recovery of plastic waste, particularly polyolefin-based waste. It allows, in effect, the purification of plastic waste to obtain purified polyolefins with reduced impurity content, including decolorized and deodorized polyolefins, which can be reused to form new plastic objects. The purified polyolefin fractions obtained can thus be used directly in formulations mixed with additives, for example, colorants, pigments, or other polymers, either instead of or in combination with virgin polypropylene, polyethylene resins, or mixtures thereof, in order to obtain plastic products with performance, aesthetic, mechanical, or rheological properties that facilitate their reuse and recovery.

[0029] According to a second aspect, the present invention also relates to a device for extracting polyolefins from a polymer solution by size exclusion, said device comprising: - n fixed beds of a size exclusion solid, n being an integer greater than or equal to 4, preferably between 4 and 30, said size exclusion solid having a volume mean pore diameter preferably between 1 and 500 nm, preferably between 2 and 100 nm, preferably between 2 nm and 50 nm, preferably between 3 and 30 nm and preferably being a silica gel, a grafted silica, a carbon molecular sieve, or mixtures thereof,

[0030] the n fixed beds of the size exclusion solid being distributed in one or more column(s), the n beds being connected in series and preferably in a closed loop, - N injection systems for the polymer solution, N injection systems for an eluent, N extraction systems for an extract and N extraction systems for a raffinate, N being an integer preferably equal to n, said injection and extraction systems being located between two consecutive beds or possibly upstream of the first bed,

[0031] the injection systems for the polymer solution and the eluent and / or the extraction systems for the extract and the raffinate located at the same position being distinct or identical, - each injection and withdrawal system comprising at least one valve adapted to allow or prevent the passage of a flow of polymer solution and / or eluent and / or extract and / or raffinate, preferably a series of on / off valves controlled by an automatic sequence, or a single rotary valve, such that:

[0032] - to define, at a time t, an injection point of the polymer solution, a point injection point of the eluent, a withdrawal point of the extract, a withdrawal point of the raffinate, said injection and withdrawal points being distinct from each other and determining at least three, preferably four, successive main operating zones of the n fixed beds:

[0033] - a zone I for elution of impurities, comprising between an injection point of the eluent and a point for extracting the extract;

[0034] - a zone II for the elution of polyolefins, comprising the withdrawal point of the extract and an injection point of the polymer solution;

[0035] - an impurity retention zone III, located between the injection point of the polymer solution and a raffinate withdrawal point; and

[0036] - possibly a zone IV included between the point of withdrawal of the raffinate and the eluent injection point, - and to allow, over time, a shift in the injection and withdrawal points, synchronously or non-synchronously, according to a frequency determined by a predetermined permutation period, of a fixed bed of steric exclusion solid per permutation period.

[0037] The present invention further relates, according to a third aspect, to a device for processing a plastic feedstock to obtain a stream of purified polyolefins, comprising:

[0038] - means for bringing the plastic filler into contact with a dissolving solvent in order to dissolve at least part of the plastic filler in a dissolving solvent, to obtain a crude polymer solution; - possibly suitable solid-liquid separation methods to separate insolubles suspended in the crude polymer solution; - at least one size exclusion extraction device according to the invention; - means of separating the dissolving solvent and possibly the eluent from a stream of purified polyolefins. List of figures [Fig 1]

[0039] Fig. 1 represents a particular embodiment of the size exclusion extraction step of the present invention, at a given time t of the process, in which said size exclusion extraction step uses 15 fixed beds of size exclusion solid, of the silica gel type, distributed in a single column, said beds being connected to each other in series with respect to each other and in a closed circuit, a pump located between bed No. 15 and bed No. 1 making it possible to connect bed No. 15 and bed No. 1 in series.

[0040] In this particular embodiment and at this time t:

[0041] - the crude polymer solution from step a) of dissolution (not shown in the [Fig.l]) or possibly the clarified polymer solution from step b') of solid-liquid separation possibly integrated into the process (not shown in [Fig.l]) is introduced at the injection point F located between bed no. 9 and bed no. 10, these two beds being consecutive,

[0042] - an eluent is introduced at the injection point S located between bed no. 15 and bed no. 1, these two beds being consecutive,

[0043] - an extract, comprising at least some of the impurities present in the solution The polymer that feeds the column is drawn off at the withdrawal point E located between bed no. 6 and bed no. 7, these two beds being consecutive.

[0044] - a raffinate, composed, at least in part, of a purified polymer solution including the polyolefins present in the polymer solution that feeds the column, is drawn off at the drawing-off point R located between bed no. 13 and bed no. 14, these two fixed beds being consecutive.

[0045] The set of injection and withdrawal points thus defines 4 operating zones:

[0046] - a zone I for elution of impurities, located between the injection of the eluent and the withdrawal from the extract, including 6 beds,

[0047] - a zone II for the elution of polyolefins, located between the withdrawal of the extract and the injection of the polymer solution, comprising 3 beds,

[0048] - an impurity retention zone III, located between the injection of the solution polymer and the raffinate extraction, comprising 4 beds, and

[0049] - a zone IV, located between the withdrawal of the raffinate and the injection of the eluent, including 2 beds. [Fig 2]

[0050] Figure 2 represents another particular embodiment of the size exclusion extraction step of the present invention, at a given time t of the process, in which said size exclusion extraction step comprises 4 fixed beds of size exclusion solid, of silica gel type, each distributed in a column (i.e. one bed per column), said columns being connected to each other in series with respect to each other and in a closed circuit, a pump located between column no. 4 and column no. 1 allowing column no. 4 and column no. 1 to be connected in series.

[0051] In this particular embodiment and at time t:

[0052] - the polymer solution that feeds the size exclusion extraction step is in introduced at injection point F located between column 2 and column 3,

[0053] - an eluent is introduced at the injection point S located between column 4 and column 1,

[0054] - an extract, comprising at least some of the impurities present in the solution The polymer that feeds the size exclusion extraction step is withdrawn at withdrawal point E located between column 1 and column 2.

[0055] - a raffinate, composed, at least in part, of a purified polymer solution including the polyolefins present in the polymer solution which feeds the size exclusion extraction step, is withdrawn at the withdrawal point R located between column 3 and column 4. [Fig 3]

[0056] Figure 3 shows the concentration profile obtained in Example 1 for polyethylene (PE) and the Igrafos® 168 additive, by simulation along the length of the simulated moving bed, which comprises 15 fixed silica gel beds in a 6 / 3 / 4 / 2 configuration. By convention, the eluent injection is located upstream of bed 1 (and downstream of bed 15). The PE concentration profile as a function of the beds is represented by a solid black line, and the Igrafos® 168 additive concentration profile as a function of the beds is represented by the dashed line. Description of the implementation methods

[0057] According to the present invention, the expressions "between ... and ..." and "between ... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this is not the case and the limit values ​​are not included in the range described, such clarification will be provided by the present invention.

[0058] In this description, the expression "greater than..." is understood to mean strictly greater than, and symbolized by the sign ">", and the expression "less than" means strictly less than, and symbolized by the sign "<". When the limit is included, the precision will be provided by the respective expressions "greater than or equal to..." (corresponding to the sign ">") and "less than or equal to" (corresponding to the sign "<").

[0059] In the sense of the present invention, the different parameter ranges for a Given the step, pressure ranges and temperature ranges can be used alone or in combination. For example, in the sense of the present invention, a preferred pressure range can be combined with a more preferred temperature range.

[0060] In the following, particular embodiments of the invention are described. They can be implemented separately or in combination with each other, without limitation of combinations where technically feasible.

[0061] The terms "upstream" and "downstream" are to be understood in relation to the overall flow of the fluid(s) or stream(s) in question in the process. More specifically, the terms "upstream" and "downstream" are defined in relation to the flow of the stream that includes the polymers to be purified, in particular polyolefins. For example, the terms "upstream" and "downstream" are defined in the size exclusion step with respect to the polymer solution stream, that is to say, either at the feed of said step with crude (or clarified) polymer solution or at the outlet point of the purified polymer solution (i.e., the raffinate withdrawal point).

[0062] The term "additives" is a term classically 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 solid organic or mineral compounds that modify the physical, thermal, mechanical and / or electrical properties of polymer materials or reduce their cost), reinforcing agents, colorants, pigments, plasticizers, hardeners, flame retardants, combustion retardants, stabilizing agents, antioxidants, UV absorbers, antistatic agents, etc.

[0063] The additives correspond to at least some of the impurities in the plastic feed to be treated, which the treatment process according to the invention makes it possible to eliminate at least in part. Other types of impurities may be present in the plastic feed to be treated, such as impurities from use, for example metallic impurities, paper / cardboard, biomass, polymers other than the polymer(s) targeted, etc.

[0064] Thus, according to the invention, the impurities that the process according to the invention makes it possible to eliminate, at least in part, include the additives conventionally used in polymer formulations, in particular polyolefin-based formulations, and also possibly impurities from use arising from the life cycle of plastic materials and objects, and / or from the waste collection and sorting system. These latter impurities may be metallic, organic, or mineral; they may include packaging residues, food residues, or compostable residues (biomass). These impurities from use may also include glass, wood, cardboard, paper, aluminum, iron, metals, tires, rubber, silicones, rigid polymers, thermosetting polymers, household, chemical or cosmetic products, used oils, water, etc.

[0065] According to the invention, a polymer solution is a solution comprising a dissolving solvent and at least the polyolefins referred to, in particular polypropylene, polyethylene, their copolymers or mixtures thereof, dissolved, that is to say in particular solvated and dispersed, in said dissolving solvent, the dissolved polyolefins being initially present in the plastic filler. The polymer solution may further comprise soluble impurities (and solubilized in the dissolving solvent) and / or insoluble impurities (and suspended in the polymer solution; in the case of insoluble impurities of nanometric size, they will then be referred to as colloidal solutions).Depending on the steps of the process according to the invention, said polymer solution may therefore comprise, in addition to the polyolefins referred to dissolved in the dissolving solvent, impurities in the form of insoluble particles which are advantageously suspended in said polymer solution, soluble impurities dissolved in the dissolving solvent, and / or possibly another liquid phase immiscible with said polymer solution.

[0066] It is well known that the boiling point of a compound varies with the operating pressure. However, without further specification, i.e., without specifying the pressure, the boiling point of the compound in question, in particular the dissolving solvent, is understood to be the boiling point of said compound, in particular said dissolving solvent, at atmospheric pressure (in particular 0.1 MPa). Thus, the boiling point that characterizes the dissolving solvent must be understood as the boiling point of said dissolving solvent at atmospheric pressure (in particular 0.1 MPa).

[0067] The invention relates to a method for purifying a plastic feedstock, preferably composed of plastic waste, and advantageously comprising polyolefins, said method preferably comprising:

[0068] a) a dissolution step comprising bringing the plastic filler into contact with a dissolving solvent, to obtain at least one crude polymer solution;

[0069] b') optionally a step for separating insolubles from the polymer solution crude, in particular by solid / liquid separation, of the crude polymer solution from step a), to advantageously obtain a clarified polymer solution and preferably an insoluble fraction;

[0070] b) a size exclusion extraction step of the crude polymer solution obtained at the end of step a) or optionally of the clarified polymer solution obtained at the end of the optional step b'), to obtain a purified polymer solution,

[0071] said size exclusion extraction step employing at least one train of n fixed beds of a size exclusion solid, n being an integer greater than or equal to 4, preferably between 4 and 30, preferably between 8 and 24, most preferably between 8 and 21 and preferably between 12 and 15,

[0072] the n fixed beds of the steric exclusion solid being advantageously distributed in one or more column(s), preferably in M ​​column(s), M being an integer between 1 and the total number n of fixed beds of the exclusion solid, the n beds being in series with respect to each other and preferably in a closed loop,

[0073] said at least one fixed bed train of step b) being fed with crude or clarified polymer solution at at least one injection point F of the polymer solution and with an eluent at at least one injection point S of the eluent,

[0074] said at least one fixed bed train of step b) implementing at least one withdrawal of an extract at at least one withdrawal point E of the extract, and at least one withdrawal of a raffinate at at least one withdrawal point R of the raffinate,

[0075] the injection points of the polymer solution and the eluent and the withdrawal points of the extract and the raffinate being distinct from each other, advantageously located between two consecutive beds or possibly upstream of the first bed, and distributed so that they determine at least three, preferably four, successive main operating zones of the n fixed beds: - a zone I for elution of impurities, located between an injection point of the eluent and a withdrawal point of the extract; - a zone II for the elution of polyolefins, located between the point of withdrawal of the extract and a point of injection of the polymer solution; - a zone III for impurity retention, located between the point of injection of the polymer solution and a point of withdrawal of the raffinate; and - optionally, and preferably, a zone IV located between the raffinate withdrawal point and the eluent injection point,

[0076] the injection and withdrawal points being shifted over time from a fixed bed of steric exclusion solid according to a frequency determined by a predetermined permutation period,

[0077] said raffinate being recovered to constitute at least a part, preferably all, of the purified polymer solution;

[0078] c) a polymer-solvent separation step, to obtain at least one stream of purified polyolefins, in particular a stream of purified polypropylene, a stream of purified polyethylene, a stream of their copolymers or a stream of a purified mixture of polypropylene and polyethylene, and at least one solvent fraction comprising the dissolving solvent and optionally the eluent. Charge

[0079] The feedstock of the process according to the invention, referred to as the plastic feedstock, comprises plastics which themselves comprise, in particular, polymers and more particularly polyolefins, such as polypropylene, polyethylene, their copolymers or mixtures thereof. Preferably, the plastic feedstock comprises between 50 and 100% by weight, and more preferably between 70% and 100% by weight, of plastics.

[0080] The plastics included in the feedstock of the process according to the invention are generally production by-products and / or post-consumer waste, including household waste, construction waste, automotive waste, and waste electrical and electronic equipment. Preferably, the plastic waste comes from collection and sorting channels. Plastics or plastic materials are generally compositions (or formulations) comprising polymers, particularly polyolefins, which are most often mixed with additives to impart specific properties to the materials, in order to form, after shaping, various objects (injection-molded parts, tubes, films, fibers, fabrics, sealants, coatings, etc.). The additives used in plastics can be organic or inorganic compounds.These include, for example, fillers, colorants, pigments, plasticizers, property modifiers, combustion retardants, etc.

[0081] The plastic filler of the process according to the invention therefore comprises polymers, and in particular polyolefins, such as polypropylene, polyethylene, their copolymers, or mixtures thereof. Preferably, the plastic filler comprises at least 50% by weight, preferably at least 80% by weight, preferably at least 85% by weight, and preferably at least 90% by weight, of polyolefins relative to the total weight of the plastic filler. The process according to the invention is thus particularly aimed at purifying and recovering the polyolefins contained in the plastic filler so that they can be reused in various applications.

[0082] The plastic filler may include other polymers, other than the polyolefins referred to, and other impurities, in particular additives typically used to formulate the plastic material and generally impurities resulting from the life cycle of plastic materials and articles and / or from the waste collection and sorting system. The plastic filler of the process according to the invention generally comprises less than 50% by weight of impurities, preferably less than 20% by weight of impurities, and more preferably less than 10% by weight of impurities. The plastic filler may include, for example, 1% by weight of impurities or more, in particular 5% by weight of impurities or more.

[0083] The plastic filler comprising polyolefins, treated by the process according to the invention, can advantageously be pretreated upstream of the process according to the invention, so as to at least eliminate all or part of the so-called impurities Coarse impurities, that is, impurities in the form of particles 10 mm or larger, preferably 5 mm or larger, or even 1 mm or larger, such as wood, paper, biomass, iron, aluminum, glass, etc., are pretreated to generally form them into divided solids to facilitate processing in the method according to the invention. This pretreatment may include a grinding step, an atmospheric pressure washing step, and / or a drying step. This pretreatment may be carried out at a different site, for example, at a waste collection and sorting center, or at the same site where the purification process according to the invention is implemented. Preferably, this pretreatment reduces the impurity content to less than 6% by weight relative to the total weight of the plastic feedstock.Following pretreatment, the plastic feedstock is generally stored in the form of divided solids, for example as chips, powder, flakes or granules, in order to facilitate handling and transport to the process. Step a) of dissolution

[0084] According to the invention, the process comprises a dissolution step a) in which the plastic filler is contacted with a dissolving solvent to obtain at least one, preferably a single, crude polymer solution. This step advantageously allows the dissolution of at least some, preferably all, of the targeted polymers, preferably the targeted polyolefins, present in the plastic filler.

[0085] By dissolution, we mean any phenomenon leading to the obtaining of at least one solution of polymers (in particular polyolefins), that is to say, a liquid (or possibly a supercritical fluid) comprising polymers (in particular polyolefins) dissolved in a solvent, more particularly in the dissolving solvent. Those skilled in the art are well acquainted with the phenomenon(ies) involved in the dissolution of polymers, the phenomenon(ies) comprising at least one mixing, dispersion, homogenization, solvation, and disentanglement of polymer chains, and more particularly of thermoplastic chains.

[0086] During and at the end of step a) of dissolution, the pressure and temperature conditions allow the dissolving solvent, at least in part and preferably all of the dissolving solvent, to be maintained in a liquid or possibly supercritical state, while the soluble fraction of the feed, in particular the polymers concerned, especially the polyolefins concerned, and at least part of the impurities, is advantageously dissolved at least in part and preferably in full.

[0087] The dissolving solvent is an organic solvent or a mixture of organic solvents, preferably chosen so that its Hansen parameters lie within the Hansen sphere of the target polymer, in particular the target polyolefins. The theory Hansen's law allows the prediction of the solubility of a polymer, particularly a thermoplastic such as polyolefins (polyethylene and / or polypropylene), in a solvent by determining the Hansen parameters and solubility sphere for the solvent and the polymer, respectively, as a function of several parameters, especially their polar, hydrogen bonding, and dispersion parameters. If a solvent or solvent mixture exhibits Hansen parameters within the Hansen sphere of the target polymer, the polymer should be at least partially, and preferably completely, soluble in the solvent. Advantageously, the dissolving solvent comprises, and preferably consists of, at least one hydrocarbon compound, preferably aliphatic and 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, and preferably 98% by weight of at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear or branched, the percentages being 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 and in particular paraffinic, having a boiling point (at atmospheric pressure, in particular at 0.1 MPa) between -50 and 250°C, preferably between -15 and 150°C, preferably between -1 and 110°C, and preferably between 20 and 100°C.Preferably, the dissolving solvent comprises, or preferably consists of, at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear or branched, having between 3 and 12 carbon atoms, preferably between 4 and 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, or preferably consist of, a mixture of isomers of butane, pentane, hexane, heptane, and / or octane, and such that the content of said mixture in the dissolving solvent is greater than or equal to 80% by weight, preferably greater than or equal to 95% by weight, and preferably greater than or equal to 98% by weight, relative to the total weight of the dissolving solvent.Most advantageously, a preferred hydrocarbon compound for the dissolving solvent is a paraffinic aliphatic compound, having a critical temperature (temperature at the critical point of said pure hydrocarbon compound) preferably between 95 and 350°C, preferably between 130 and 300°C, and preferably between 180 and 285°C.

[0088] Preferably, step a) of dissolution is fed with the plastic filler and a dissolving solvent, in a weight ratio of the dissolving solvent to the plastic filler, between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, even more preferably between 3.0 and 7.0.

[0089] Advantageously, the dissolving solvent that feeds the dissolution step a) is in liquid or possibly supercritical form. It can advantageously be preheated, preferably to a temperature between 100 and 300°C, preferably between 150 and 250°C, prior to its introduction into step a), in particular prior to its introduction into the contacting section and possibly into the dissolving section, in order to facilitate the heating of the plastic filler and / or a temperature drop of the material flow in the contacting and possibly dissolving sections of step a).

[0090] Advantageously, the dissolving solvent comprises, preferably consists of, fresh solvent (or a fresh solvent top-up) and / or a recycled solvent stream from a later step of the process, for example at least partly from step c) of solvent-polymer separation.

[0091] Most advantageously, the dissolution step is carried out at a temperature, called the dissolution temperature, between 100°C and 300°C, preferably between 150°C and 250°C, and at a pressure, called the dissolution pressure, between 1.0 and 100.0 MPa absolute, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute and most preferably between 2.0 and 15.0 MPa absolute. The temperature and pressure can evolve during the dissolution step, from the conditions of introduction of the plastic filler and / or the dissolving solvent, until reaching the dissolution conditions, i.e. the dissolution temperature, in particular between 100 and 300°C, preferably between 150 and 250°C, and the dissolution pressure, in particular between 1.0 and 100.0 MPa, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute and very preferably between 2.0 and 15.0 MPa absolute.Advantageously, at the end of the dissolution step, the crude polymer solution is at the dissolution temperature and dissolution pressure.

[0092] Limiting the temperature in step a) of dissolution to a temperature less than or equal to 300°C, preferably less than or equal to 250°C, prevents or limits the thermal degradation of the polyolefins, and also reduces the energy requirement of the process, thus contributing to limiting the operating costs of the process. Advantageously, the dissolution temperature is greater than or equal to the melting temperature of the polyolefins in question, so as to promote their dissolution and very advantageously reduce the residence time required to dissolve the polyolefins in question efficiently. Most preferably, the temperature in step a) of dissolution is less than or equal to the critical temperature of the dissolving solvent, so as to avoid the formation of a supercritical phase during step a) of dissolution which could disrupt the dissolution.

[0093] In parallel, the dissolution pressure in the dissolution step is greater than the saturated vapor pressure of the dissolution solvent, at the dissolution temperature, so that the dissolution solvent is at least partly, and preferably entirely, in liquid or possibly supercritical form, at the dissolution temperature, which allows the dissolution of polyolefins to be optimized, in particular in terms of quality and operating time.

[0094] Most advantageously, the temperature and pressure conditions of dissolution reached in step a) of dissolution are adjusted so that the mixture (dissolving solvent + targeted thermoplastics) is single-phase at the end of step a), said mixture possibly including insoluble impurities suspended in said mixture.

[0095] Advantageously, said step a) of dissolution is carried out for a residence time preferably of between 1 and 600 minutes, preferably between 2 and 300 minutes, most preferably between 2 and 180 minutes. Residence time is understood as the residence time at the dissolution temperature and dissolution pressure, i.e. the time of implementation of the plastic filler with the dissolving solvent at the dissolution temperature and dissolution pressure, in step a).

[0096] In order to allow contact between the dissolving solvent and the plastic feedstock, and especially to ensure efficient and homogeneous dissolution of the targeted polyolefins in the dissolving solvent, the dissolution step may advantageously employ various types of equipment such as mixing, conveying, and heating devices, and, for example, a reactor, a pump, a conveying circuit, an agitation system, a furnace, a heat exchanger, a mixer, etc. In particular, step a) advantageously employs at least one piece of dissolving equipment, and optionally at least one feedstock preparation device, a mixing device, and / or a conveying device. This equipment and / or these devices may be, for example, static mixer(s), an extruder, a pump, a reactor, a co-current or counter-current column, or a combination of lines and equipment.Transport devices, particularly for fluids such as gases, liquids, or solids, are well known to those skilled in the art. These devices may include, but are not limited to, a compressor, a pump, an extruder, a vibrating tube, a screw conveyor, and a valve. The equipment and / or devices used in step a) may also include or be combined with heating systems (e.g., furnace, heat exchanger, heat treatment, etc.) to achieve the conditions necessary for dissolution.

[0097] Step a) of dissolution is at least supplied by the plastic filler, in particular in the form of one or more plastic filler streams, and by the solvent of dis The solution, in particular in the form of one or more dissolving solvent streams, advantageously by means of one or more conveying devices. The plastic filler stream(s) may be separate from the dissolving solvent stream(s). Some or all of the plastic filler may also feed step a) mixed with some or all of the dissolving solvent, the remainder of the solvent and / or filler, if any, feeding step a) separately.

[0098] When the plastic filler is brought into contact with the dissolving solvent, the dissolving solvent is advantageously at least partially, and preferably entirely, in liquid or possibly supercritical form, while the plastic filler, which comprises polymers, particularly polyolefins, may be in solid or liquid form and may optionally include suspended solid particles. The plastic filler may also optionally be injected into the dissolving equipment, mixed with the dissolving solvent, or as a suspension in the dissolving solvent; the preparation and injection of the suspension may be continuous or discontinuous.

[0099] Preferably, step a) of dissolution employs at least one extruder and dissolution equipment, for example, 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 such that, at the extruder outlet, at least some, and preferably all, of the targeted polyolefins contained in the plastic feedstock are in a molten state. The plastic feedstock is then injected into the dissolution equipment, at least partially in molten form. The plastic feedstock, at least partially in a molten state, can also be pumped using a pump designed for viscous fluids, often called a melt pump or gear pump.The plastic charge, at least partly in a molten state, can also be filtered at the extruder outlet using a filtration device, possibly in addition to the melt pump, in order to remove the largest particles; generally the mesh size of this filter is between 10 pm (micrometers) and 1 mm (millimeter), preferably between 20 and 200 pm.

[0100] Preferably, step a) implements, prior to at least one CSTR type reactor, at least one static mixer and one extruder in which at least a fraction of the dissolving solvent is injected, so as to promote shearing and intimate mixing between the dissolving solvent and the plastic filler, which contributes to the dissolution of the polyolefins.

[0101] Most advantageously, the crude polymer solution obtained at the end of step a) of dissolution comprises at least the dissolving solvent and the targeted polyolefins dissolved in the dissolving solvent. In general, the crude polymer solution It also includes soluble impurities that are also dissolved in the dissolving solvent and possibly insoluble impurities in suspension. The crude polymer solution obtained at the end of step a) of dissolution may also include polymers, other than the polyolefins concerned, for example in a melted, dissolved or undissolved state.

[0102] Optional step b') of separation of insolubles

[0103] The process according to the invention may optionally include a step b') for separating insolubles from the crude polymer solution, in particular by solid-liquid separation, advantageously located upstream of the size-exclusion extraction step b). This step b') for separating insolubles advantageously allows, when integrated into the process according to the invention, the separation of an insoluble fraction, which includes at least some, preferably all, of the insoluble impurities, in particular those suspended in the crude polymer solution obtained from step a). The insoluble impurities removed during the optional step b') for separating insolubles are, for example, additives initially present in the plastic filler (pigments, fillers, other polymers, etc.) and / or impurities from use (such as mineral compounds, glass, wood, paper, metal, other polymers, or degradation products).

[0104] Step b') of separating the insolubles thus makes it possible, when integrated into the process according to the invention, to advantageously obtain a clarified polymer solution, which is a polymer solution from which at least some, and preferably all, of the insoluble impurities have been removed. Preferably, step b') also makes it possible to obtain an insoluble fraction.

[0105] Advantageously, step b') of insoluble separation, when implemented, is located upstream of step b) of size exclusion extraction and typically downstream of step a) of dissolution. When implemented, this separation step b') advantageously allows, in addition to the removal of at least some of the insoluble impurities, the limitation of operational problems, in particular clogging and / or erosion, in the downstream process steps, while also contributing to the purification of the plastic feedstock. Preferably, the process according to the invention comprises a step b)' of insoluble separation.

[0106] Step b') of separating the insolubles is advantageously carried out under temperature and pressure conditions close to those of step a). Most advantageously, step b') of separating the insolubles is carried out under the temperature and pressure conditions of step a) of dissolution, that is to say, at the dissolution temperature and dissolution pressure as defined above. Thus, most advantageously, step b') is carried out at a temperature between 100°C and 300°C, preferably between 150°C and 250°C, and a pressure between 1.0 and 100.0 MPa. preference 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.

[0107] When integrated into the process, step b') of separating insolubles is preferably fed with the crude polymer solution from step a).

[0108] Advantageously, the optional step b') may implement a section comprising at least one solid-liquid separation device, for example a separator flask, a decanter, a decanter centrifuge, a centrifuge, a filter, a sand filter, a tangential flow filter incorporating a membrane and / or a depth filter possibly with filter aids (for example, diatomaceous earth or sand), an eddy current separator, an electrostatic separator, a triboelectric separator, preferably a decanter, a filter, a sand filter and / or an electrostatic separator. Advantageously, a self-cleaning filter may be used, with cleaning or unclogging to remove insolubles being carried out using a solvent stream.

[0109] Removing the insoluble fraction may require the use of equipment for transporting and possibly removing any solvent that may be carried along with the separated insoluble fraction. For example, step b') may use a conveyor, a vibrating tube, a screw conveyor, an extruder, or a stripper. Step b') may therefore use transport equipment to remove the insoluble fraction and / or for removing any solvent carried along with the separated insoluble fraction. Advantageously, at least some of the solvent carried along with the separated insoluble fraction is recovered and recycled in the process.

[0110] According to a particular embodiment, step b') of insoluble separation uses at least two, and generally fewer than five, solid-liquid separation units in series and / or in parallel. The presence of at least two solid-liquid separation units in series improves the removal of insolubles, while the presence of units in parallel facilitates the maintenance of said units and / or unclogging operations.

[0111] Certain insoluble impurities, particularly certain pigments and mineral fillers, conventionally added during polymer formulation, may be introduced as particles smaller than 1 pm. This is the case, for example, with titanium dioxide, calcium carbonate, and carbon black. In one embodiment, said step b') of separating the insolubles advantageously employs an electrostatic separator, which makes it possible to efficiently remove, at least partially, the insoluble particles smaller than 1 pm. In another embodiment, the step b') of separating the insolubles employs a sand filter to remove particles of various sizes, and in particular particles of size in less than 1 pm. According to yet another embodiment, step b') of separating insolubles uses a tangential filter including a membrane and / or a depth filter, possibly in the presence of filtration aids such as diatomaceous earth.

[0112] Depending on the nature of the plastic filler, the polymer solution that feeds into step b'), preferably the crude polymer solution, may optionally also include a second liquid phase, for example, consisting of molten polymers other than the polyolefins of interest. According to another particular embodiment, step b' advantageously employs equipment enabling the separation of this second liquid phase, preferably by means of at least one three-phase separator.

[0113] According to the invention, said optional step b') of insolubles separation allows, when integrated into the process, the obtaining of at least one clarified polymer solution comprising at least the dissolving solvent, at least the polyolefins referred to, dissolved in said solvent. Thus, at least a part, and preferably all, of the insoluble impurities potentially present in suspension in the crude polymer solution obtained at the end of step a) of the process according to the invention is removed from the polymer solution in step b'). Step b) of size exclusion extraction

[0114] The process according to the invention comprises a size exclusion extraction step (b), which is in particular fed with an eluent and the crude polymer solution from step (a) or optionally with the clarified polymer solution from step (b') of insoluble separation. Advantageously, the size exclusion step (b) makes it possible to obtain at least one purified polymer solution, and preferably a used solvent, in particular one containing impurities.

[0115] The polymer solution which feeds the size exclusion extraction step b), in particular the crude polymer solution from step a) or possibly the clarified polymer solution from the insoluble separation step b'), generally includes solubilized impurities, which are advantageously eliminated at least in part, preferably in full, during size exclusion extraction, in particular by contacting a size exclusion solid in the presence of an eluent.Indeed, step b) of size exclusion extraction allows for the separation of compounds present in the crude or possibly clarified polymer solution, in particular the separation of dissolved polyolefins and solubilized impurities, according to their size, notably at the molecular level (or rather their hydrodynamic volume), by simulated countercurrent chromatography or simulated moving bed chromatography, hereinafter referred to as the "LMS" process or "SMB" for Simulated Mobile Bed according to Anglo-Saxon terminology. This extraction step b) is very advantageous. The process allows for the selective separation of polyolefins, dissolved in the dissolving solvent, from the solubilized impurities present in the polymer solution that feeds said step b), i.e., the crude or clarified polymer solution. Step b) thus produces a purified polymer solution, said purified polymer solution being a polymer solution free of at least some, preferably all, of the soluble impurities present in the polymer solution that feeds said step b), i.e., those present in the crude or clarified polymer solution.

[0116] Preferably, the eluent that feeds step b) is a solvent, in particular an organic solvent, preferably such that its Hansen parameters are within the Hansen sphere of the target polymers. Preferably, the eluent is a solvent, or mixture of solvents, preferably organic(s), comprising at least 80 wt%, preferably at least 95 wt%, preferably 98 wt% of a hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear or branched, the percentages being expressed relative to the total weight of the dissolving solvent (100% being the maximum), preferably having a boiling point (at atmospheric pressure) between -50 and 250°C, preferably between -15 and 150°C, preferably between -1 and 110°C and preferably between 20 and 100°C.Preferably, the dissolving solvent comprises, or preferably consists of, a hydrocarbon compound, preferably aliphatic and in particular paraffinic, preferably linear or branched, having between 3 and 12 carbon atoms, preferably between 4 and 8 carbon atoms. For example, the dissolving solvent comprises a hydrocarbon compound selected from the isomers of butane, pentane, hexane, heptane, and octane. Most preferably, the eluent is of the same chemical nature, or even the same solvent, as the dissolving solvent.

[0117] Advantageously, step b) of size exclusion extraction employs at least one train, preferably a single train, of several fixed beds of a size exclusion solid, preferably in operation. Said train(s) is / are advantageously fed with the crude polymer solution from step a) or optionally the clarified polymer solution from the optional step b'), and with the eluent.When step b) includes several, in particular between two and four, fixed bed trains of size-exclusion solid, in operation, these fixed bed trains operate in parallel with each other and are each fed with a fraction of the polymer solution that feeds step b), in particular the crude polymer solution from step a) or possibly the clarified polymer solution from the optional step b'), and with a fraction of the eluent that feeds step b), said polymer solution that feeds step b) being then divided into as many partial streams of crude or possibly clarified polymer solution as there are fixed bed trains in operation, and similarly said eluent that feeds step b). being divided into as many partial flows of eluent as there are trains of fixed beds in operation.

[0118] Optionally, the process may also include, in particular in parallel with step b), at least one fixed bed train of steric exclusion solid (as described below), which is (are) not in operation, in particular which is stopped in standby and / or in regeneration and / or backup mode.

[0119] The fixed bed train (or each fixed bed), advantageously in operation, of step b) of size exclusion extraction comprises n fixed beds of a size exclusion solid, n being an integer greater than or equal to 4, preferably between 4 and 30, preferably between 8 and 24, most preferably between 8 and 21, and most preferably between 12 and 15. The number of fixed beds must be sufficient to allow efficient separation, and reasonable so as to limit costs, particularly investment costs. The n fixed beds are advantageously in series with respect to each other. The n fixed beds of size exclusion solid can operate in a closed loop or in an open loop.Preferably, the n fixed beds of size exclusion solid operate in a closed loop, that is to say, the n fixed beds are connected to each other successively and preferably in a closed loop (the first is connected to the second, the second to the third, etc., and the nth to the first), thus allowing continuous operation of the size exclusion extraction and advantageously a reduction in eluent consumption, since the eluent is advantageously partly regenerated and recycled continuously.

[0120] The n fixed beds of size exclusion solid are advantageously distributed in one or more columns, preferably in M ​​columns, where M is an integer between 1 and the total number of fixed beds of size exclusion solid in the train considered, i.e., M being between 1 and n. Thus, the (or each) fixed bed train of the size exclusion extraction step b) can implement between 1 and n columns, each comprising one or more fixed beds of size exclusion solid. For example, the (or each) fixed bed train of the size exclusion extraction step b) can implement one column (or tower), preferably of large capacity (volume), which includes the n fixed beds, or two columns, each of which includes n / 2 fixed beds. Both configurations allow for a significant reduction in investment costs but require unloading the entire column, i.e.n fixed beds or n / 2 fixed beds, when there is a problem on one of the beds in the column. According to another embodiment, the (or each) fixed bed train of step b) of steric exclusion extraction uses n columns (or towers), preferably each of the columns being of lower capacity (volume) than in the previous case, each of the columns comprising a fixed bed of steric exclusion solid, thus facilitating the maintenance and / or cleaning and / or bypass in particular of one bed among the n beds. This is operational because in this configuration, only one column (containing a single bed) needs to be unloaded and / or bypassed, not a group of beds. However, this latter configuration entails significant investment costs.

[0121] Preferably, the size exclusion solid is in the form of solid particles. It may also be called a granular medium. The size exclusion solid is chosen to be inert with respect to the polymer solution to be treated, i.e., the dissolving solvent and the polyolefins to be treated, and with respect to the eluent. It is also chosen to allow efficient separation of the compounds present, particularly dissolved compounds, in the treated polymer solution, and more specifically, efficient separation of the impurities solubilized in the dissolving solvent from the dissolved polyolefins.The steric exclusion solid is advantageously a porous solid which can be organic (generally polymeric) and / or inorganic, and preferably having a volume average pore diameter preferably between 1 nm and 500 nm, preferably between 2 nm and 100 nm, very preferably between 2 nm and 50 nm, and preferably between 3 nm and 30 nm.Advantageously, the size exclusion solid comprises silica (such as silica gel, also called silica, or grafted silica), a carbon molecular sieve, a polymeric molecular sieve (of a chemical nature other than polyolefinic), a porous polymer gel, a carbon replica, a preferably dealuminized zeolite (e.g., USY type), a preferably calcined alumina, a metal-organic framework (MOF) material, or mixtures thereof. Preferably, the size exclusion solid comprises, or preferably consists of, silica gel, grafted silica, a carbon molecular sieve, or mixtures thereof.Advantageously, the steric exclusion solid preferably has a pore volume between 0.01 and 3.0 ml / g, preferably between 0.1 and 2.0 ml / g, and preferably between 0.3 and 1.2 ml / g. The mean pore diameter and pore volume of the steric exclusion solid are determined by mercury porosimetry and, more specifically, measured by mercury porosimetry intrusion according to ASTM D4284-83 at a maximum pressure of 4000 bar, using a surface tension of 484 dyne / cm and a contact angle of 140°. The wetting angle used was 140°, following the recommendations of the book "Techniques de l'ingénieur, traité analyse et caractérisation", 1950, by J. Charpin and B. Rasneur. To obtain better accuracy, the value of mercury volume in ml / g given corresponds to the value of total mercury volume in ml / g measured on the sample minus the value of mercury volume in ml / g measured on the . The same sample was tested at a pressure of 30 psi (approximately 2 bar). These same parameters, and in particular the volumes and diameters of the solid within the mesoporosity range (2–50 nm), can also be measured by nitrogen adsorption / desorption volumetry (also called nitrogen adsorption isotherm), a complementary analytical method. This analysis involves the physical adsorption of nitrogen molecules into the material's porosity through a gradual increase in pressure at constant temperature and provides information on textural characteristics. In particular, it allows access to the mesoporous distribution of the steric extrusion solid. Thus, the representative pore distribution of a pore population centered within a range of 2 to 50 nm is determined by the Barrett-Joyner-Halenda (BJH) model.The nitrogen adsorption-desorption isotherm according to the BJH model is described in the periodical "The Journal of American Society", 73, 373, (1951) written by EP Barrett, LG Joyner and PP Halenda.

[0122] The size-exclusion solid particles preferably have a volume-equivalent mean diameter (preferably determined by laser granulometry, i.e., by laser diffraction using a particle size analyzer) of between 20 and 5000 pm, preferably between 50 and 1500 pm, preferably between 100 and 800 pm, and even more preferably between 300 and 600 pm. Advantageously, the solid particles are substantially spherical.

[0123] According to the invention, the fixed bed train (or each fixed bed train) of step b) of size exclusion extraction is fed with crude or clarified polymer solution at at least one injection point F of the polymer solution and with at least one eluent at one injection point S of the eluent. Preferably, the fixed bed train considered is fed with crude or clarified polymer solution at one injection point F of the polymer solution and with an eluent at one injection point S of the eluent.

[0124] Preferably, the eluent and the polymer solution feed the (or each) fixed bed train of step b) of size exclusion extraction at a ratio of the volumetric flow rates of the eluent 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, preferably between 0.8 and 2.0, such a ratio being also called the solvent ratio. Such a solvent ratio, i.e. such a setting of the volumetric flow rates of the crude or clarified polymer solution and of the eluent, for the (or each) train, contributes to the efficiency of the size exclusion separation of polyolefins from the impurities present in the polymer solution that feeds step b).

[0125] When the fixed bed train includes several injection points Fi of the polymer solution, for example two injection points Fl and F2 of the polymer solution, the flow of the crude or clarified polymer solution that feeds said fixed bed train is divided into as many partial flows of polymer solution to feed said train of fixed beds at said injection points Fi, said partial flows of polymer solution having equal or different flow rates between them.

[0126] When the fixed bed train includes several injection points Si of eluent, for example two injection points SI and S2, the total flow of eluent which feeds said fixed bed train is divided into as many partial flows of eluent to feed said fixed bed train at said injection points Si, said partial flows of eluent having equal or different flow rates between them.

[0127] The fixed bed train (or each) of the size exclusion extraction step (b) implements at least one withdrawal of an extract at at least one withdrawal point E of the extract, and at least one withdrawal of a raffinate at at least one withdrawal point R of the raffinate. Preferably, the fixed bed train (or each) of the size exclusion extraction step (b) implements one withdrawal of an extract at a withdrawal point E of the extract, and one withdrawal of a raffinate at a withdrawal point R of the raffinate.

[0128] The injection points F of the polymer solution and S of the eluent, and the withdrawal points E of the extract and R of the raffinate, are distinct from one another. They are advantageously located between two consecutive beds, or possibly upstream of the first bed, particularly in the case of an open circuit (in the case of a closed loop of n fixed beds, the nth bed being connected to the first bed, these two beds are considered consecutive). However, in one embodiment, particularly according to a VARICOL® process, they may be located, on average over an operating cycle, in the middle of a fixed bed or within a fixed bed. The injection points of the polymer solution and the eluent, and the withdrawal points of the extract and the raffinate, are distributed relative to one another so as to define at least three, preferably four, successive main operating zones of the n fixed beds:

[0129] - a zone I for elution of impurities, located between the injection point S of the eluent and the extraction point E of the extract;

[0130] - a zone II for polymer elution (in particular of the polyolefins concerned), comprising between the extraction point E of the extract and the injection point F of the polymer solution;

[0131] - an impurity retention zone III, comprising the injection point F of the polymer solution and the raffinate withdrawal point R; and

[0132] - optionally, and preferably, a zone IV comprising between the point of withdrawal R of the raffinate and the injection point S of the eluent.

[0133] When there are several injection points Fi of the polymer solution and / or Si of the eluent and / or several withdrawal points of the extract and / or raffinate, zones I, II, III and possibly IV, begin at the first injection and / or withdrawal point of the stream considered (eluent, polymer solution, extract or raffinate), the term "first" being defined here as the one furthest upstream of all the injection points. and / or withdrawal of said flux considered. When there are several injection points Fi of the polymer solution and / or Si of the eluent and / or several withdrawal points of the extract and / or the raffinate, secondary operating zones can also be defined, in particular within zones I, II, III and possibly IV which are the main operating zones.

[0134] When the n fixed beds of the train considered in step b) operate in open circuit, the eluent is introduced at the eluent injection point(s) S, the crude or possibly clarified polymer solution is introduced at the polymer solution injection point(s) F, the extract is withdrawn at the extract withdrawal point(s) E, and everything else is withdrawn at the raffinate withdrawal point(s) R. The injection and withdrawal points thus define three main successive operating zones, zones I, II, and III. In this embodiment, a significant quantity of eluent relative to the polymer solution is generally required to maximize separation. For example, this open-circuit operating mode requires a ratio of the volumetric flow rates of the eluent relative to the polymer solution of between 2.0 and 50.0, preferably between 5.0 and 20.0, or even between 5.0 and 10.0.

[0135] When the n fixed beds of the considered train in step b) operate in a closed loop, the eluent is introduced at the eluent injection point(s) S, the crude or possibly clarified polymer solution is introduced at the polymer solution injection point(s) F, an extract is withdrawn at the extract withdrawal point(s) E, a raffinate is withdrawn at the raffinate withdrawal point(s) R, and at least a portion of the introduced eluent advantageously remains circulating in the closed loop of the n beds (this is referred to as eluent recycling). In this embodiment, the injection and withdrawal points then define four main successive operating zones, zones I, II, III, and IV, with zone IV being designated as the eluent regeneration and recycling zone. In this particular embodiment, the eluent supply requirements (i.e.The quantities of eluent introduced in S) are very advantageously less important than in the case of an open-circuit operating mode to ensure efficient separation. For example, this closed-loop operating mode requires a volumetric flow rate ratio of the eluent to the polymer solution between 0.1 and 10, preferably between 0.2 and 5.0, or even between 0.8 and 2.0.

[0136] Advantageously, in the case of a closed loop of n fixed beds, the n steric exclusion solid beds are distributed in zones I to IV, preferably according to a so-called a / b / c / d type configuration, the distribution of the steric exclusion solid beds in zones I to IV with respect to the total number n of steric exclusion solid beds being such that:

[0137] - a, is the number of steric exclusion solid beds in zone I,

[0138] - b, the number of steric exclusion solid beds in zone II,

[0139] - c, the number of steric exclusion solid beds in zone III, and

[0140] - d, the number of steric exclusion solid beds in zone IV,

[0141] and in which:

[0142] - a = (n * 0.30) * (1 ± 0.40, preferably 1 ± 0.30),

[0143] - b = (n * 0.15) * (1 ± 0.40, preferably 1 ± 0.30),

[0144] - c = (n * 0.25) * (1 ± 0.40, preferably 1 ± 0.30), and

[0145] - d = (n * 0.30) * (1 ± 0.40, preferably 1 ± 0.30).

[0146] It is obvious to those skilled in the art that the sum of the number of fixed beds in zones I, II, III, and IV (i.e., a+b+c+d) is advantageously equal to n, the total number of fixed beds in the operating train of fixed beds considered. Thus, a 6 / 3 / 4 / 2 configuration means that there are 15 fixed beds of steric exclusion solid distributed as follows: 6 fixed beds in zone I, 3 fixed beds in zone II, 4 fixed beds in zone III, and 2 beds in zone IV.

[0147] Most advantageously, the filling density of each of the n fixed beds of steric exclusion solid, expressed as mass of steric exclusion solid per unit bed volume (i.e. per kg of solid per m3 of bed) can vary between 100 and 1500 kg / m3, preferably between 300 and 1000 kg / m3, preferably between 400 and 800 kg / m3.

[0148] According to the invention, the injection points F and S and the withdrawal points E and R are shifted over time in a bed of steric exclusion solid at a frequency determined by a predetermined permutation period. A permutation period can be defined as the time between two successive displacements (or shifts) of the injection and withdrawal points in a fixed bed. The periodic displacement (or shift) of the injection points F and S and the withdrawal points E and R can be performed synchronously or asynchronously, the latter case (asynchronous) being known as VARICOL®.The periodic movement of the injection and withdrawal points along the n fixed beds makes it possible in particular to define an operating cycle and also advantageously a cycle time which corresponds to the time required for the injection and withdrawal points to return to their initial position, i.e. to the number of beds n multiplied by the permutation period.

[0149] When the n fixed beds of exclusion solid operate in a closed loop, an operating cycle advantageously comprises as many permutation periods as there are beds of steric exclusion solid present in the closed separation loop. For example, an operating cycle of a train comprising 12 fixed beds of steric exclusion solid includes 12 permutation periods. Thus, in the preferred embodiment in which the n fixed beds of exclusion solid of the considered fixed bed train operate in a closed loop, the permutation period is preferably adjusted to define a cycle time, which corresponds to the time required for the injection and withdrawal points to return to their initial position, ranging from 1 minute to 600 minutes, preferably from 5 minutes to 200 minutes, and preferably from 10 minutes to 90 minutes. Such a cycle time contributes to the efficiency of the steric exclusion separation of polyolefins and impurities present in the polymer solution that feeds step b).

[0150] In the case of the embodiment in which the n fixed beds operate in open circuit (i.e. that everything is drawn off with the extract and the raffinate), the cycle time can also be between 1 minute and 600 minutes, preferably between 5 minutes and 200 minutes, preferably between 10 minutes and 90 minutes.

[0151] The movement of the injection points F and S and of the withdrawal points E and R can be done by the installation of a series of on / off valves, controlled by an automatic sequence, or even of a single rotary valve.

[0152] In general, the liquid flow in the fixed beds is advantageously 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, and may be called downward liquid flow even if the presence of pump(s) is / are necessary (particularly between the nth bed and the first bed in the case of closed-loop operation where the n beds are in a column). At the time of the switchover (or relocation of the injection and withdrawal points), the injection and withdrawal points are moved one bed, located downstream of the previous bed, thus creating / simulating a countercurrent liquid flow, possibly called an upward flow. A cutoff flow rate can then be defined when the two countercurrent liquid flows are equal, i.e., when the downward liquid flow rate is equal to the upward liquid flow rate.This stopping flow rate can be calculated by dividing the intergranular volume of the size exclusion solid in the beds by the permutation period, the intergranular volume of the size exclusion solid in the beds being a function of the filling density of the fixed beds of size exclusion solid and the density of the size exclusion solid particles. More specifically, the intergranular volume (V(intergranular)) of the size exclusion solid can be calculated by the following formula: .

[0153] V(intergranular) X (1 - d(filling) / d(grain)) + Vmort

[0154] with:

[0155] Intergranular) ■ The intergranular volume of the steric exclusion solid in the beds (in m3);

[0156] V(iitS): the geometric volume of the beds (in m3);

[0157] (^filling): the filling density of the size exclusion solid in the beds (in kg / m3), corresponding to the actual filling density of the size exclusion solid, i.e., the mass of said solid per unit volume of the bed. As a first approximation, it can be likened to the packed filling density which consists of the mass of solid occupied by a given volume after compaction by vibration of said solid, according to a principle derived from standards D4164 and D4180 applied to the case of catalysts;

[0158] d(grain): the grain density of the steric exclusion solid, typically measured by mercury porosimetry (in kg / m3);

[0159] Vmort: the volume (in m3) of the equipment without steric exclusion solid but through which the fluid concerned flows, in particular the polymer solution (for example the volume of the upstream, downstream lines, etc.).

[0160] The cutoff flow rate, which is a volumetric flow rate, allows the calculation of dimensionless parameters, particularly those relating to zones II and IV, specifically the ratio between the volumetric flow rate in zone II and the cutoff flow rate, and the ratio between the volumetric flow rate in zone IV and the cutoff flow rate. Preferably, the ratio of the volumetric flow rate of zone IV divided by the cutoff flow rate is less than or equal to 2, preferably between 0.5 and 1.5, and even more preferably between 0.8 and 1.0; preferably, the ratio of the volumetric flow rate of zone II divided by the cutoff flow rate is between 0.5 and 3.0, preferably between 0.9 and 1.5, and preferably between 1.0 and 1.25. Thus, the cutoff flow rate helps in adjusting the extraction stage and therefore in the efficiency of the separation.

[0161] Furthermore, and very advantageously, the surface velocity in the fixed beds of an operating zone, which corresponds to the volumetric flow rate in the zone considered divided by the cross-section of said zone (i.e., of the column in which the beds of said zone are located), can be adjusted so that this surface velocity is between 0.01 and 10.0 cm / s and preferably between 0.05 and 2.5 cm / s. Adjusting the surface velocity in the fixed beds advantageously allows, in particular, control of the attrition of the steric exclusion solid particles and thus allows adjustment of the operation of the fixed bed train in step b) so as to avoid large pressure losses (particularly encountered at high velocities) and / or dispersion problems (particularly encountered at low velocities).

[0162] Preferably, step b) of size exclusion extraction is carried out at a temperature between 100 and 300°C, preferably between 150°C and 250°C, and at a pressure between 1.0 and 100.0 MPa, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute, and most preferably between 2.0 and 15.0 MPa absolute. Under these operating conditions, the polyolefins remain dissolved in the dissolving solvent and optionally in the eluent, the latter (i.e., the dissolving solvent and the eluent) being at least partially in liquid form. Preferably, the temperature and pressure conditions of step b) are the same as those of step a) of dissolution.

[0163] Step b) of size exclusion extraction thus makes it possible to recover at least one an extract comprising at least some, preferably all, of the impurities present in the polymer solution that feeds said step b), and at least one raffinate comprising a polymer solution freed at least some, preferably all, of impurities. Said raffinate recovered at the end of the size-exclusion extraction step b) constitutes in part or in whole the purified polymer solution, which is recovered at the outlet of step b). This purified polymer solution is then preferably sent, at least some, preferably all, to the polymer-solvent separation step c). However, if necessary, it may be sent to at least one additional purification step, so as to optimize, if needed, the purification of the targeted polyolefins.This step b) of size exclusion extraction thus makes it possible to efficiently and continuously separate impurities, particularly soluble ones, from the crude or clarified polymer solution, comprising the polyolefins dissolved in the dissolving solvent.

[0164] Size exclusion chromatography, particularly in the case of a closed-loop fixed-bed system, allows for the efficient separation of impurities from polyolefins in a continuous manner, thereby reducing the labor required for this step while facilitating its operation. It also offers high productivity, especially compared to batch size exclusion chromatography, while providing relatively low eluent consumption. Step c) Polymer-solvent separation

[0165] According to the invention, the process includes a step c) of polymer-solvent separation, to obtain at least one stream of purified polyolefins, in particular a stream of purified polypropylene, a stream of purified polyethylene, or a stream of their copolymers, a stream of a purified mixture of polypropylene and polyethylene, and at least one solvent fraction comprising the dissolving solvent.

[0166] Step c) of polymer-solvent separation advantageously implements at least one solvent recovery section and preferably between one and five solvent recovery section(s).

[0167] Advantageously, step c) is fed with the purified polymer solution obtained at the end of step b) or possibly a final purified polymer solution from an additional purification step located downstream of step b) of size exclusion extraction.

[0168] Step c) of polymer-solvent separation thus aims first to separate at least partially, preferably predominantly, the dissolving solvent and possibly the eluent of the targeted polyolefin(s), contained in the polymer solution that feeds step c), more particularly the purified polymer solution or possibly a final purified polymer solution from a higher purification step additionally, so as to recover at least the polyolefins, freed at least partially, preferably predominantly, and preferably completely, of the dissolving solvent, and possibly the eluent, still present in the polymer solution that feeds step c). By predominantly, we mean at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight, and even more preferably at least 95% by weight, relative to the weight of the solvent(s) contained in the purified polymer solution that feeds step c), in particular the dissolving solvent and possibly the eluent contained in said purified polymer solution. Any solvent / polymer separation method known to those skilled in the art may be used, in particular any method allowing a phase change of the polymer(s) and / or solvent(s).The solvent(s) can be separated, for example, by precipitation or crystallization of polymers, evaporation of solvents by flash, atomization, stripping, demixing, density difference and in particular decantation or centrifugation, etc.

[0169] Said at least one stream of purified polyolefins thus obtained may correspond to a concentrated polymer solution of polyolefins or to polyolefins in liquid (or viscous) or solid form. Preferably, step c) of polymer-solvent separation further comprises a conditioning section for conditioning the purified polyolefins in solid form and more particularly in the form of granules.

[0170] Step c) of polymer-solvent separation also aims to recover at least partially, preferably predominantly, and preferably entirely, the solvent(s) contained in the purified polymer solution that feeds step c). Step c) of polymer-solvent separation also aims optionally to purify and recycle the recovered solvent fraction, particularly upstream of step a) of dissolution. By predominantly, it should be understood as at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight, and even more preferably at least 95% by weight relative to the weight of the solvent(s) contained in the purified polymer solution that feeds step c).

[0171] 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, in order to obtain at least one solvent fraction and one purified polymer fraction.

[0172] Thus, the process according to the invention makes it possible to efficiently and continuously recover polyolefins from a plastic feedstock, with high productivity and a limited number of operations. Most advantageously, the process according to the invention makes it possible to obtain a polyolefin stream exhibiting high purity, preferably greater than or equal to 95%, preferably greater than or equal to 99%, preferably greater than or equal to up to 99.5% (by weight of polyolefins relative to the total weight of the recovered purified stream), from any type of plastic feedstock. Another advantage of the process according to the invention lies in the fact that efficient separation of impurities, particularly additives, present in the plastic feedstock is possible, while allowing for reasonable solvent consumption, especially of dissolving solvent and eluent, and lower energy consumption than that required for more conventional, so-called thermal separations, such as crystallization. The process according to the invention thus makes it possible to obtain a stream of purified polyolefins that is less colored than the plastic feedstock being treated, or even colorless, and very advantageously deodorized. The resulting purified polymer stream preferably has negligible levels of prohibited or regulated substances, for example, those regulated by the REACH regulation.More particularly, the process according to the invention makes it possible to obtain a stream of purified polyolefins free of at least some, preferably all, of the impurities, such as additives, present in the plastic filler, and free, at least some or even all, of solvent, in particular the dissolving solvent and the eluent.

[0173] Thus, the process according to the invention advantageously makes it possible to obtain a stream of purified polyolefins comprising an impurity content of less than or equal to 5% by weight, preferably less than or equal to 1% by weight and even more preferably less than or equal to 0.5% by weight of impurities, and very advantageously a solvent content (in particular dissolving solvent and eluent) of less than or equal to 5% by weight of solvent, 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 stream of purified polyolefins. Size exclusion extraction device

[0174] The present invention also relates to a size exclusion extraction device adapted for separating polyolefins from impurities contained in a polymer solution. Said device comprises:

[0175] - n fixed beds of a steric exclusion solid, n being an integer greater than or equal to 4, preferably between 4 and 30, preferably between 8 and 24, most preferably between 8 and 21 and preferably between 12 and 15, said size-exclusion solid having a volume mean pore diameter preferably between 1 nm and 500 nm, preferably between 2 nm and 100 nm, preferably between 2 nm and 50 nm, preferably between 3 and 30 nm and preferably being a silica gel (or silica), a grafted silica, a carbon molecular sieve, or mixtures thereof,

[0176] the n fixed beds of the steric exclusion solid being distributed in one or more column(s), preferably in M ​​column(s), M being an integer between 1 and the total number n of fixed beds of the exclusion solid, the n beds being connected in series and preferably in a closed loop,

[0177] - N injection systems, preferably distinct from each other, for the polymer solution, N injection systems, preferably distinct from each other, for an eluent, N withdrawal systems, preferably distinct from each other, for an extract and N withdrawal systems, preferably distinct from each other, for a refiner, N being an integer preferably equal to n, said injection and withdrawal systems being located between two consecutive beds or possibly upstream of the first bed,

[0178] the injection systems for the polymer solution and the eluent and / or the withdrawal systems for the extract and the raffinate located in the same position, i.e. between the same two consecutive beds or possibly upstream of the first bed, being distinct or identical (by identical, it must be understood that a valve system can allow either the introduction of the polymer solution or that of the eluent, or the withdrawal of one or the other flow, i.e. of the extract or the raffinate),

[0179] - each injection and withdrawal system comprising at least one suitable valve to allow or prevent the passage of a flow of polymer solution and / or eluent and / or extract and / or raffinate, preferably i) a series of on / off valves controlled by an automatic sequence, or ii) a single rotary valve, so as:

[0180] to define, at a time t, an injection point of the polymer solution, an injection point of the eluent, a withdrawal point of the extract and a withdrawal point of the raffinate, said injection and withdrawal points being distinct from each other and determining at least three, preferably four, successive main operating zones of the n fixed beds:

[0181] - a zone I for elution of impurities, comprising between an injection point of the eluent and a point for extracting the extract;

[0182] - a zone II for the elution of polyolefins, comprising between the withdrawal point of the extract and an injection point of the polymer solution;

[0183] - an impurity retention zone III, comprising between the injection point of the polymer solution and a raffinate withdrawal point; and

[0184] - possibly a zone IV between the raffinate withdrawal point and the eluent injection point;

[0185] and to allow, over time, a shift of the injection and withdrawal points, synchronously or non-synchronously, according to a frequency determined by a predetermined permutation period, of a fixed bed of steric exclusion solid per permutation period. Plastic filler processing device

[0186] Such a size-exclusion extraction device can be integrated into a more comprehensive device for processing a plastic feedstock to obtain a flow of po- purified lyolefins, which include:

[0187] - means for bringing the plastic filler into contact with a dissolving solvent in order to dissolve at least part of said plastic filler in said dissolving solvent, such as an extruder, static mixer(s), continuous stirred tank reactor(s), also called "Continuous Stirred Tank Reactor" (CSTR) according to Anglo-Saxon terminology, equipped with suitable stirring system(s), to obtain a crude polymer solution;

[0188] - possibly suitable solid-liquid separation means for separating insoluble in suspension in the crude polymer solution;

[0189] - at least one size exclusion extraction device according to the invention and as described above, advantageously connected to said means for contacting and dissolving or possibly to at least one of said solid-liquid separation means;

[0190] - means for separating the dissolving solvent and optionally the eluent of a stream of purified polyolefins, advantageously connected to at least one size exclusion extraction device.

[0191] Said device for processing a plastic feed to obtain a stream of purified polyolefins also advantageously includes means for transporting said means and devices.

[0192] Such a device makes it very advantageous to recover polyolefins with high purity from a plastic feed which may include a multitude of impurities.

[0193] The following example and figures illustrate the invention, in particular particular embodiments of the invention, without limiting its scope. EXAMPLES Example 1

[0194] This example is the result of numerical simulations carried out on the basis of experiments carried out in the laboratory.

[0195] The charge to be treated is composed of 95% by weight of polyethylene (PE) with average molar mass by volume MW = 650,000 g / mol and 5% by weight of an additive, Igrafos® 168, which is classically used as a stabilizer in polyolefin formulations.

[0196] The filler is first dissolved in heptane at 200 °C and 1.0 MPa (or 10 bars), to form a homogeneous crude polymer solution comprising 80% by weight heptane and 20% by weight filler comprising polyethylene and the additive.

[0197] The crude polymer solution formed is introduced into a simulated moving bed, composed of 15 beds comprising silica gel and distributed in a 6 / 3 / 4 / 2 configuration (see [Fig. 1]). The eluent is heptane.

[0198] The silica gel of the beds is in the form of beads and has the following characteristics:

[0199] Ball diameter = 500 pm

[0200] Pore diameter = 6-10 nm.

[0201] Porous volume = 0.80 ml / g

[0202] Filling density = 530 kg solids / m³ bed

[0203] Extragranular porosity = 0.4.

[0204] Each bed is modeled by a 1D fixed-bed piston model with axial dispersion and a Fick model for intragranular transfer. Since the radius of gyration of polyethylene is estimated at 32 nm, the polymer is considered to be present only in the extragranular phase. The additive and the solvent have a radius of gyration of less than 1 nm and can therefore diffuse into the intragranular porosity. The medium in the beds is considered isothermal (200°C) and the density of the polymer solution is considered constant (477 kg / m³). Finally, all the beds are modeled and the cycles are solved dynamically until convergence of the concentration profile.

[0205] The extraction is adjusted with the following settings:

[0206] Cycle time = 15 min

[0207] Volumetric flow rate of eluent (heptane) relative to the volumetric flow rate of polymer solution S / F = 1.08

[0208] Zone IV flow rate / stop flow rate = 0.92

[0209] Zone II flow rate / stop flow rate = 1.10

[0210] Maximum surface velocity = 1.80 cm / s.

[0211] The concentration profiles obtained for the PE and the additive, by simulation, along the simulated moving bed, with conventional injection of the eluent upstream of bed 1 (and downstream of bed 15), are illustrated in [Fig. 3]. In [Fig. 3], the PE concentration profile is represented by a solid black line and the Igrafos® 168 additive concentration profile is represented by a dashed line. The concentrations along the bed are given as weight percentages of the tracked compound, i.e., PE or the additive, relative to the weight of heptane.

[0212] According to [Fig.3], it appears that polyethylene (PE), which does not explore the intragranular porosity, is carried towards the raffinate and withdrawn between bed 13 and bed 14. The additive being smaller, it can diffuse into the intragranular porosity and is carried towards the extract, withdrawn between bed 6 and bed 7.

[0213] The PE extraction step carried out in a simulated moving bed makes it possible to obtain the following performance:

[0214] - Polyethylene purity = 99.99% by weight (which corresponds to the weight, or flow rate weight, of PE in the raffinate relative to the total weight, or total weight flow, of PE and additive in the raffinate, excluding solvent, i.e. excluding heptane),

[0215] - Polyethylene efficiency = 100% (by weight) (which corresponds to the weight flow rate) of PE extracted from the raffinate divided by the weight flow rate of PE extracted in the whole extracted + raffinate),

[0216] - Productivity = 170 kg PE extracted in the raffinate / h / m3 of silica gel bed.

[0217] The raffinate exiting the simulated moving bed of size exclusion extraction can then to be recovered and sent to a polymer-solvent separation section, specifically a heptane solvent evaporation section.

Claims

Demands

1. A process for purifying a plastic feedstock to obtain a stream of purified polyolefins, said process comprising: a) a dissolution step comprising bringing the plastic filler into contact with a dissolving solvent, to obtain at least one crude polymer solution, said dissolving solvent being an organic solvent chosen such that its Hansen parameters are in the Hansen sphere of the polyolefins concerned; b') optionally a step of separating insolubles from the crude polymer solution obtained from step a), to obtain at least one clarified polymer solution; (b) a size exclusion extraction step of the crude polymer solution obtained at the end of step (a) or optionally of the clarified polymer solution obtained at the end of step (b') (optional), to obtain a purified polymer solution, said size exclusion extraction step employing at least one train of n fixed beds of a size exclusion solid, n being an integer greater than or equal to 4, the n beds being in series, said size exclusion solid comprising silica, a carbon molecular sieve, a polymeric molecular sieve of a chemical nature other than polyolefinic, a porous polymer gel, a carbon replica, a zeolite, alumina, a metal-organic framework or MOF type material, or mixtures thereof, said train of fixed beds of step (b) being fed with crude or clarified polymer solution at at least one injection point F of the polymer solution and with an eluent at at least one injection point S of the eluent,said eluent being an organic solvent whose Hansen parameters are within the Hansen sphere of the polyolefins concerned, said fixed bed train of step b) implementing at least one withdrawal of an extract at at least one withdrawal point E of the extract, and at least one withdrawal of a raffinate at at least one withdrawal point R of the raffinate, the injection points of the polymer solution and the eluent and the withdrawal points of the extract and the raffinate being distinct from each other, and distributed so as to determine at least three, preferably four, successive main operating zones of the n fixed beds: - a zone I for impurity elution, located between an injection point of the eluent and an extract withdrawal point; - a zone II for elution of polyolefins, located between the extract withdrawal point and a polymer solution injection point; - a zone III for retention of impurities, located between the polymer solution injection point and a raffinate withdrawal point; and - optionally a zone IV located between the raffinate withdrawal point and the eluent injection point, the injection and withdrawal points being shifted over time by a fixed bed of size exclusion solid according to a frequency determined by a predetermined permutation period, said raffinate being recovered to constitute, at least in part, the purified polymer solution; c) a polymer-solvent separation step, to obtain at least one stream of purified polyolefins and at least one solvent fraction comprising the dissolving solvent.

2. A process according to claim 1, wherein the dissolving solvent comprises at least one hydrocarbon compound, preferably aliphatic and in particular paraffinic, having a boiling point between -50 and 250°C, preferably between -15 and 150°C, preferably between -1 and 110°C and preferably between 20 and 100°C, most preferably a hydrocarbon compound, aliphatic paraffinic, having between 3 and 12 carbon atoms and most preferably between 4 and 8 carbon atoms.

3. A method according to claim 1 or 2, wherein the eluent is of the same chemical nature as the dissolving solvent.

4. A method according to any one of the preceding claims, wherein the size exclusion extraction step b) employs at least one train of n fixed beds of a size exclusion solid, n being an integer between 4 and 30, and preferably between 12 and 15.

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

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

7. A method according to any one of the preceding claims, wherein the eluent and the polymer solution feed into step b) in a ratio of the volumetric flow rates of the eluent relative 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, preferably between 0.8 and 2.

0.

8. A method according to any one of the preceding claims, wherein the injection points of the polymer solution and the eluent and the withdrawal points of the extract and the raffinate are located between two consecutive beds or possibly upstream of the first bed.

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

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

11. A method according to any one of the preceding claims, wherein step a) is carried out at a dissolution temperature between 100°C and 300°C, preferably between 150 and 250°C, and a dissolution pressure between 1.0 and 100.0 MPa, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute and most preferably between 2.0 and 15.0 MPa absolute.

12. A method according to any one of the preceding claims, wherein the step a) is fed by the plastic filler and the dissolving solvent, according to a weight ratio between the dissolving solvent and the plastic filler of between 0.2 and 100.0, preferably between 0.3 and 20.0, preferably between 1.0 and 10.0, more preferably between 3.0 and 7.

0.

13. A method according to any one of the preceding claims, wherein step b) of size exclusion extraction of step b) is carried out at a temperature between 100°C and 300°C, preferably between 150 and 250°C, and a pressure between 1.0 and 100.0 MPa, preferably between 1.0 and 25.0 MPa absolute, preferably between 1.5 and 18.0 MPa absolute and most preferably between 2.0 and 15.0 MPa absolute.

14. A device for processing a plastic feedstock to obtain a stream of purified polyolefins, comprising: - means for contacting the plastic feedstock and a dissolving solvent so as to dissolve at least part of the plastic feedstock in a dissolving solvent, to obtain a crude polymer solution; - suitable solid-liquid separation means for separating insolubles suspended in the crude polymer solution; - at least one size-exclusion extraction device, connected to at least one of said solid-liquid separation means; - means for separating the dissolving solvent and optionally the eluent from a stream of purified polyolefins, said means for separating the dissolving solvent being connected to said at least one size-exclusion extraction device;in which said at least one size exclusion extraction device comprises: - n fixed beds of a size exclusion solid, n being an integer greater than or equal to 4, preferably between 4 and 30, said size exclusion solid having a volume mean pore diameter preferably between 1 and 500 nm, preferably between 2 and 100 nm, preferably between 2 nm and 50 nm, preferably between 3 and 30 nm and preferably being a silica gel, a grafted silica, a carbon molecular sieve, or mixtures thereof, the n fixed beds of the size exclusion solid being distributed in one or more column(s), the n beds being connected in series and preferably in a closed loop, - N polymer solution injection systems, N eluent injection systems, N extract withdrawal systems and N systems of; withdrawal of a raffinate, N being an integer preferably equal to n, said injection and withdrawal systems being located between two consecutive beds or possibly upstream of the first bed, the injection systems of the polymer solution and the eluent and / or the withdrawal systems of the extract and the raffinate located at the same position being distinct or identical, - each injection and withdrawal system comprising at least one valve adapted to allow or prevent the passage of a flow of polymer solution and / or eluent and / or extract and / or raffinate, preferably a series of on / off valves controlled by an automatic sequence, or a single rotary valve, such that: To define, at a given time t, an injection point for the polymer solution, an injection point for the eluent, a withdrawal point for the extract, a withdrawal point for the raffinate, said injection and withdrawal points being distinct from each other and determining at least three, preferably four, successive main operating zones of the n fixed beds: - a zone I for elution of impurities, located between an injection point of the eluent and a withdrawal point of the extract; - a zone II for the elution of polyolefins, located between the point of withdrawal of the extract and a point of injection of the polymer solution; - a zone III for impurity retention, located between the point of injection of the polymer solution and a point of withdrawal of the raffinate; and - possibly a zone IV located between the point of withdrawal of the raffinate and the point of injection of the eluent, O and to allow, over time, a shift in the injection and withdrawal points, synchronously or non-synchronously, according to a frequency determined by a predetermined permutation period, of a fixed bed of steric exclusion solid per permutation period.

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