FR3142760A1 - METHOD FOR RECYCLING WASTE BASED ON PVC PLASTICS USING A DEVICE FOR EXTRACTING POLYMER CHAINS IN A SIMULATED MOVING BED WITH STERIC EXCLUSION - Google Patents

Abstract

The present invention relates to a method for recovering a PVC stream, comprising: a) a dissolution step by bringing a plastic filler into contact with a dissolution solvent; then b) an extraction step by steric exclusion, using fixed beds of a steric exclusion solid in series and supplied with the polymer solution resulting from a) at an injection point (F) and at a eluting at an injection point (S) and implementing 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 staggered over the time of a bed according to a determined frequency; then c) a polymer-solvent separation step, to obtain a purified PVC flow. The present invention also relates to a device for carrying out step b) and a device for carrying out the recovery process. Figure 1 to be published

Description

PROCESS FOR RECYCLING PVC PLASTIC WASTE USING A DEVICE FOR EXTRACTION OF POLYMER CHAINS IN A SIMULATED MOVING BED WITH STERIC EXCLUSION

The invention relates to the field of recycling of polyvinyl chloride (PVC) plastics, in particular a method for treating a plastic load from PVC-based plastic waste in order to obtain a flow of at least one purified PVC polymer allowing its reuse in the manufacture of new plastic objects. More specifically, the invention relates to a method for treating a plastic load, in particular from PVC-based plastic waste, comprising the dissolution of at least one PVC polymer in a solvent, at least one step of purifying the polymer solution thus obtained and the separation of at least one PVC polymer and at least one solvent in order to recover a flow of at least one purified PVC polymer for subsequent recovery.

By definition, a plastic is a mixture consisting of a basic polymeric material and numerous additives, the whole being capable of being molded or shaped (generally hot and/or under pressure), in order to produce a semi-finished product or an object. A commonly accepted practice is to name said plastic by the name of the polymer that constitutes it. Thus, poly(vinyl chloride) plastic or PVC for polyvinyl chloride according to the Anglo-Saxon name actually corresponds to the combination of the PVC polymer, sometimes referred to in the remainder of the description as “PVC resin”, with various additives chosen according to the functionalities required for said plastic. Said additives can be organic (macro)molecules or inorganic (nano)particles and are used according to the desired properties for the PVC plastic: resistance to heat, light or mechanical stress, flexibility, ease of processing, coloring, etc.

There are several methods for recycling PVC plastics: so-called conventional methods involving simple mechanical recycling of plastics, methods involving modifications to their composition (with possible chemical transformations of the initial constituents), etc.

Since the middle of the ^20th century, the recycling of PVC plastic involving a physical process has been the subject of numerous studies aimed, in a first step, at solubilizing the PVC resin with a variable proportion of additives and then, in a second step, at recovering said resin using various processes (precipitation, evaporation, etc.) in the presence of all or part of the soluble additives. For example, we cite patents EP0945481 and EP1268628 on the one hand, and EP2276801 on the other hand, which aim to recycle respectively various PVC-based objects (flexible or rigid pipes, window frames, cables, etc.) and specifically PVC-based objects reinforced with fibers (tarpaulins, floor coverings, etc.) according to a process implementing a step of dissolving the PVC resin and soluble additives in an organic solvent, followed by a step of precipitation with water vapor allowing the recovery of the PVC resin and the majority of the additives.

However, maintaining these additives in the PVC thus recovered for recycling is not always desirable. For example, the evolution over time of the regulations that concern them has an impact. Thus, certain plasticizers belonging to the phthalate family, notably widely used to formulate so-called "soft" PVCs around forty years ago, have been gradually subject to authorization in Europe on the basis of the REACH regulation which aims, since the end of 2006, to secure the manufacture and use of chemical substances in European industry and, finally, gradually excluded from usable additives (Annexes XIV and XVII of Regulation (EC) No 1907/2006 of the European Parliament and of the Council of 18 December 2006). Following the same trend, the use of Cd-based metal stabilizers in PVC plastic formulations, notably called PVC compounds (in particular so-called "rigid" PVC plastics), was banned by an amendment to Annex XVII (Regulation 494/2011 of 20 May 2011). Similarly, lead-based stabilizers were subject to restrictions (Annex XV) that were detailed and adopted between December 2017 and March 2018 by the Risk Assessment Committee (RAC) and Socio-Economic Analysis Committee (SEAC) of ECHA. Thus, over the last 20 years, several families of additives have seen their field of use restricted, a phenomenon that is likely to increase in the years to come.

These new regulations now lead to the banning of the presence of many additives in recycled raw materials (RPM), in particular through the establishment of very restrictive limit thresholds in terms of authorized quantities (for example, the quantity of phthalates subject to authorization and considered in a mixture must not exceed more than 1000 ppm of the final composition of the RPM concerned). Taking into account the often very long lifespan of PVC-based objects (several decades), PVC-based objects formulated before the end of 2006 and now at the end of their life cannot be recycled via regeneration methods leading to the retention of these prohibited additives, whether said methods are conventional, such as mechanical recycling processes, or not, such as the examples of dissolution/precipitation processes mentioned above.

Given, on the one hand, current and future regulatory constraints and, on the other hand, the limitation of fossil resources which highlights the need to move towards a so-called "circular" economy, producing a purified polymer resin (i.e. free as much as possible from additives) from plastic waste for reuse as an MPR equivalent to a virgin resin from petroleum is today a major challenge in meeting the environmental challenges of the ^21st century.

Many processes have been considered to enable the extraction of various families of plastic additives, including PVC plastic in particular. For example and in a non-exhaustive manner, patents EP1311599 and JP2007191586 both propose a first step of dissolving the PVC resin and at least one family of additives among phthalate-type plasticizers, flame retardants or lead-based metal stabilizers by a first organic solvent, followed by one or more step(s) of liquid-liquid extraction of at least one family of additives from the solution obtained previously via the use of at least one other solvent (organic and/or aqueous) different from the first organic solvent. Patent JP2007092035 discloses another example of possible implementation with a dissolution of the PVC resin and at least the phthalate-type additives via the use of a mixture of solvents under supercritical conditions and the recovery of said phthalates in this same mixture of solvents after “breaking” of said supercritical conditions, then a step of extraction of the lead-based additives from the residual solid phase containing the PVC resin via the use of at least one liquid surfactant.

Despite these advances, removing all additives from a PVC plastic, and even more so from a mixture of PVC-based plastics from various formulations (e.g. constituting post-consumer waste), still represents a scientific and industrial challenge today. The dissolution step mentioned above is primarily interesting for removing some of the additives that are not soluble in the chosen solvent(s). On the other hand, additives that are soluble in the solvent(s) are particularly difficult to separate, particularly due to their very varied chemical nature. A first approach may consist of extracting them on the basis of physicochemical properties such as their polarity, solubility, boiling point, density, etc., but this may lead to a multiplication of purification steps given the plurality and diversity of the additives present. Furthermore, obtaining a flow of at least one purified PVC polymer is generally not a sufficient condition to ensure the economic viability of a process for regenerating PVC-based objects. The main reason frequently put forward is the difficulty in finding an economically viable balance between the resale cost (equivalent to the added value) of the products obtained and the cost of the unit operations implemented in said regeneration process, which is all the more true if the separation steps envisaged are numerous. Finally, treating a plastic load from PVC-based plastic waste involves proposing a robust and versatile process to take into account the variability of the additives present depending on the origin of the waste considered (in terms of intended use and production date).

The present invention thus proposes another approach to respond to the problems explained above, based on the exploitation of the difference in size, more precisely of the hydrodynamic volume, between the polymeric macromolecules and the molecules of impurities such as those of the additives.

The present invention therefore makes it possible, from a polymer solution containing at least one PVC polymer dissolved in a dissolution medium and the associated soluble additives, to selectively extract said PVC polymer from the medium, regardless of the nature of said additives.

The size separation technique already exists and is commonly used as an analysis method to determine the molecular weight of polymers. This method, called size exclusion chromatography (SEC), consists of implementing a fixed bed operated discontinuously (called “batch”) and comprising several levels of porosity. Small molecules explore said fixed bed down to the lowest porosities, the associated elution times then being high, while large molecules, such as polymers, only travel through the largest pores and have low elution times, thus inducing the desired separation. Since the additives commonly used for PVC-based plastic formulations have a size an order of magnitude smaller than that of the polymer chains of the PVC resin, the principle of size exclusion chromatography can thus be applied for the purification of PVC-based plastics. However, the industrial implementation of a process using such a principle is problematic, mainly because of the discontinuous aspect of the batch process. In addition, such a process in discontinuous mode would require a significant consumption of eluent to ensure effective separation, which directly impacts the profitability, productivity and ecological footprint of the process.

Simulated Moving Bed (SMB) technology, a concept invented in 1961, allows the continuous passage of a “chromatographic” process, in particular by adsorption, discontinuously, with an increase in productivity and a limitation of the quantity of eluent consumed, while ensuring efficient separation. Many industrial references of this technology exist, in particular for adsorption separations used in particular for the separation of xylenes with the ELUXYL® or PAREX® processes (see the book Simulated Moving Bed technology: Principles, Design and Process Applications, A. E. Rodrigues, Elsevier, 2015). The only large-scale application of a simulated moving bed with size exclusion (SMB - SEC) concerns the separation of n-paraffins from iso-paraffins, the outlines of which are specified in patent US2985589. Recent publications mention the use of simulated moving bed with size exclusion (SMB - SEC) technology for the fractionation of polyethylene glycols of various molecular weights (M. T. Liang et al., J. Chromatogr. A, 2012, 1229, 107) or for the separation of proteins (E. J. Freydell et al., Chem. Eng. Sc, 2010, 65, 4701). More specifically, patent US6551512 proposes a method for separating proteins of liquid composition, such as milk, by size exclusion in a simulated moving bed. Finally, one publication mentions the use of SMB-SEC in a recycling process for materials used in WEEE (waste electrical and electronic equipment). WEEE is based on polycarbonate and also includes poly(styrene-co-acetonitrile) (SAN) and additives such as flame retardants. It is these that Weeden’s team is seeking to separate from a ternary solution containing SAN and two flame retardant compounds, resorcinol bis-diphenylphosphate and bisphenol A bis-diphenylphosphate, in an acetone-dichloromethane solvent mixture (G. S. Weeden et al., Journal of Chromatography A, 2015, 1422, 99).

The application of SMB-SEC technology as a method for purifying PVC-based plastic waste to obtain a purified PVC polymer stream that can be reused as MPR for the manufacture of new plastic objects has never been proposed.

The present invention thus aims to overcome the problems of the prior art and to participate in the recycling of plastics, in particular the recycling of PVC plastics. More particularly, it aims to provide an efficient, simple and economically viable method for treating all types of PVC loads to obtain a purified PVC polymer flow, compatible with the regulations in force and reusable in the manufacture of new plastic objects. The present invention seeks to effectively separate impurities from used PVC plastic materials and to recover purified PVC resins, which can be used in the manufacture of new PVC-based objects, using a method with a limited number of unit steps, thus making it possible to limit the costs of the method and improve its ecological performance.

Thus, the present invention proposes, according to a first aspect, a method for recovering a flow of at least one purified PVC polymer from a plastic load, comprising:

a) a dissolution step comprising bringing the plastic filler into contact with a dissolution solvent, to obtain at least one raw polymer solution;

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

b) a step of extraction by steric exclusion of the crude polymer solution obtained at the end of step a) or optionally of the clarified polymer solution obtained at the end of step b'), to obtain a purified polymer solution,

said steric exclusion extraction step implementing 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 fixed beds of the steric exclusion solid being in series,

said fixed bed train of step b) being supplied with raw 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 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 that they determine at least three, preferably four, successive main operating zones of the n fixed beds:

- an impurity elution zone I, located between the eluent injection point and the extract withdrawal point;

- a zone II for elution of at least one PVC polymer, located between the point of withdrawal of the extract and the point of injection of the polymer solution;

- a zone III for retaining impurities, located between the injection point of the polymer solution and the point of withdrawal of the raffinate; and

- optionally a zone IV located between the raffinate withdrawal point and the eluent injection point,

the injection and withdrawal points being offset over time of a fixed bed of steric 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, for separating the purified polymer solution into a purified PVC polymer stream and at least one solvent fraction comprising dissolving solvent.

The advantage of the method of the invention is to propose an efficient method for treating a load comprising PVC-based plastics, in particular plastic waste, in particular from collection and sorting channels, so as to recover the PVC resins it contains in order to be able to recycle them for all types of applications. The method according to the invention makes it possible to obtain a purified PVC polymer flow, very advantageously less colored than the plastic load, or even colorless, and preferably deodorized. In particular, the purified PVC polymer flow, obtained at the end of the method according to the invention, advantageously comprises a content of impurities, and in particular additives, and a content of solvent, in particular dissolution solvent and/or eluent, which are negligible or at least sufficiently low so that the purified PVC polymer flow complies with the regulations in force and can be introduced into any plastic formulation in place of virgin PVC resins. For example, the purified PVC polymer flow obtained presents (contents expressed in weight percentages relative to or total weight of the purified PVC polymer flow obtained):

- a content of less than 0.1% by weight of phthalates subject to authorization by the REACH regulation in Europe (Annex XIV of Regulation (EC) No. 1907/2006 of the European Parliament and of the Council of December 18, 2006),

- a content of less than 0.1% by weight of the lead element,

- a content of less than 0.1% by weight, and preferably less than or equal to 0.01% by weight, of the element cadmium,

- more generally a content of less than or equal to 10% by weight, preferably less than or equal to 5% by weight, preferentially less than or equal to 1.0% by weight, and even more preferably less than or equal to 0.5% by weight, or even less than or equal to 0.1% by weight, of impurities, and

- more generally a content of less than or equal to 10% by weight, preferably less than or equal to 5% by weight, preferentially less than or equal to 1.0% by weight, and even more preferably less than or equal to 0.1% by weight of solvent.

The method according to the invention thus proposes a simple scheme corresponding to a minimum sequence of operations, which makes it possible to rid PVC-based plastic waste of at least some of its impurities, in particular at least some of the additives, and to recover at least one purified PVC polymer, so as to be able to recover PVC plastic waste by recycling said purified PVC polymer.

The invention also has the advantage of participating in the recycling of plastics and the preservation of fossil resources, by allowing the recovery of plastic waste, particularly PVC-based. It allows, in fact, the purification of PVC plastic waste in order to obtain purified PVC polymer flows with a reduced impurity content, which can be reused to form new objects. The purified PVC polymer flows obtained can thus be used directly in formulations mixed with additives, for example dyes, pigments, other polymers, instead of or mixed with virgin PVC resins, in order to obtain plastic products with usage, aesthetic, mechanical or rheological properties facilitating their reuse and recovery.

The present invention also relates, according to a second aspect, to a device for extraction by steric exclusion of PVC polymer from a polymer solution, said device comprising:

- n fixed beds of a steric exclusion solid, n being an integer greater than or equal to 4, preferably between 4 and 30, more preferably between 12 and 15, said steric exclusion solid having a volume average pore diameter preferably between 1 and 500 nm, preferably between 2 and 100 nm, more preferably between 2 and 50 nm, more preferably between 3 and 30 nm, and more preferably being a silica gel, a grafted silica, a carbon molecular sieve, or mixtures thereof,

the n fixed beds of the steric exclusion solid being distributed in one or more columns, 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 raffinate withdrawal systems, 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 polymer solution and eluent injection systems and/or the extract and raffinate withdrawal systems located at the same position being distinct or identical,

- each injection and withdrawal system comprising valves adapted to allow or not allow a flow of polymer solution and/or eluent and/or extract and/or raffinate to pass, preferably a series of on/off valves, controlled by an automatic sequence, or a single rotary valve, so that:

- to define, at a time t, a polymer solution injection point, an eluent injection point, an extract withdrawal point and a raffinate withdrawal point, 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, between an injection point of the eluent and a point of withdrawal of the extract;

- a zone II for elution of at least one PVC polymer, between the point of withdrawal of the extract and a point of injection of the polymer solution;

- a zone III for retaining impurities, between the injection point of the polymer solution and a raffinate withdrawal point; and

- possibly a zone IV between the raffinate withdrawal point and the eluent injection point,

- 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.

The present invention also relates, according to a third aspect, to a device for treating a plastic load to obtain a flow of purified PVC polymer, comprising:

- means for bringing the plastic filler and a dissolving solvent into contact, so as to at least partially dissolve said plastic filler in said dissolving solvent and to obtain a raw polymer solution;

- possibly solid-liquid separation means suitable for separating insolubles suspended in the raw polymer solution;

- at least one steric exclusion extraction device according to the invention;

- means for separating the dissolution solvent and possibly the eluent from a flow of purified PVC polymer.

List of figures [Fig 1]

There represents a particular embodiment of the steric exclusion extraction step of the present invention, at a given time t of the process, in which said steric exclusion extraction step uses 15 fixed beds of steric 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.

In this particular embodiment and at this time t:

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

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

- an extract, comprising at least part of the impurities present in the polymer solution which feeds the column, is drawn off at draw-off point E located between bed no. 6 and bed no. 7, these two beds being consecutive,

- a raffinate, composed, at least in part, of a purified polymer solution comprising at least one PVC resin present in the polymer solution which feeds the column, is drawn off at the draw-off point R located between bed no. 13 and bed no. 14, these two beds being consecutive.

All the injection and withdrawal points thus define 4 operating zones:

- a zone I for elution of impurities, located between the injection of the eluent and the withdrawal of the extract, comprising 6 beds,

- a zone II for elution of at least one PVC polymer, located between the extraction of the extract and the injection of the polymer solution, comprising 3 beds,

- a zone III for retaining impurities, located between the injection of the polymer solution and the withdrawal of the raffinate, comprising 4 beds, and

- a zone IV, located between the raffinate withdrawal and the eluent injection, comprising 2 beds.

[Fig 2]

There represents another particular embodiment of the steric exclusion extraction step of the present invention, at a given time t of the process, in which said steric exclusion extraction step comprises 4 fixed beds of steric exclusion solid, of the silica gel type, each distributed in a column (i.e. one bed per column), said columns being connected together in series with each other and in a closed circuit, a pump located between column no. 4 and column no. 1 making it possible to connect column no. 4 and column no. 1 in series.

In this particular embodiment and at time t:

- the polymer solution which feeds the steric exclusion extraction step is introduced at injection point F located between column 2 and column 3,

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

- an extract, comprising at least part of the impurities present in the polymer solution which feeds the steric exclusion extraction step, is drawn off at draw-off point E located between column 1 and column 2,

- a raffinate, composed, at least in part, of a purified polymer solution comprising at least one PVC resin present in the polymer solution which feeds the steric exclusion extraction step, is drawn off at the draw-off point R located between column 3 and column 4.

[Fig 3]

There represents the concentration profile obtained in Example 1, for a PVC resin and the additive di-decyl phthalate (DiDP), by simulation throughout the simulated moving bed which comprises 15 fixed beds of silica gel in a 6/3/4/2 configuration. By convention, the injection of the eluent is located upstream of bed 1 (and downstream of bed 15). The concentration profile of the PVC resin as a function of the beds is represented by a solid black line and the concentration profile of the additive didecyl phthalate (DiDP) as a function of the beds is represented by the dotted line.

Terminology

Some definitions and/or clarifications are given below, although more details on the objects defined below may be given later in the description.

A PVC-based object is understood to mean an object, generally a consumer object, which comprises, and preferably consists of, at least one PVC plastic.

Polyvinyl chloride plastic, also called PVC plastic, is understood to mean the combination of a PVC polymer, also called PVC resin, with various additives chosen according to the functionalities required for the PVC plastic, themselves chosen according to the intended applications.

PVC polymer is traditionally produced by the radical polymerization of vinyl chloride (VCM), a monomer itself obtained from chlorine and ethylene. The present invention allows the treatment of any type of PVC plastic load and the recycling of any grade of PVC polymer.

Said additives entering into the composition of a PVC plastic can be organic molecules or macromolecules or inorganic (nano)particles and are used according to the properties that they confer on the PVC resin. In general and non-exhaustively, the formulation of a PVC plastic involves at least one family of additives described below:

- stabilizers to limit the degradation of polymer chains by dehydrochlorination and/or oxidation under the effect of heat, light, oxygen and/or mechanical stress. The nature of these stabilizers (metallic compounds (Pb, Sn, Ca, Zn, Cd) or organic) depends on the required properties and therefore the intended applications. Here are some examples of stabilizers frequently used in the past or currently: lead stearate, dibasic lead stearate, dibasic lead phthalate, zinc stearate, calcium stearate, etc., taken alone or in a mixture. Co-stabilizers can also be considered, for example epoxidized oils,

- plasticizers to induce flexible behavior and better impact and cold resistance of PVC plastic, the most widely used being part of the phthalate family. The latter are obtained by reaction between a phthalic anhydride and alcohols with more or less long carbon chains and are composed of a benzene nucleus and two carboxylic ester groups placed in the ortho position of the benzene nucleus. Dioctyl or diethylhexyl phthalate (DOP or DEHP), diisononyl phthalate (DINP) and diisodecyl phthalate (DIDP) are examples of phthalates very widely used in the past or currently. Other non-phthalic plasticizers are used today such as bis(2-ethylhexyl) adipate (DEHA) or cyclohexane-1,2-dicarboxylic acid diisononyl ester (DINCH),

- lubricants to control intermolecular friction forces within the polymer itself (internal lubricants such as stearic acid, etc.) or between the polymer and the metal walls of the processing tools (external lubricants such as paraffins, polyethylene waxes, etc.),

- inert charges or “fillers”, most of the time mineral (CaCO ₃ , carbon black, Kaolin, etc.), which act as diluents or to improve certain mechanical, electrical, thermal properties, etc.,

- dyes and/or pigments ( _TiO2 , carbon black), the latter being insoluble in the polymer and therefore present in the form of particles dispersed in the PVC plastic,

- shock-resistant agents, generally polymers (such as polyacrylates) and copolymers (such as MBS for methacrylate-butadiene-styrene), whose role is to reduce the fragility of PVC, particularly at low temperatures,

- other adjuvants: antioxidants, anti-UV, biocides, antistatics, flame retardants, reinforcements, etc.

Impurities are understood to mean all elements other than PVC resins constituting a plastic load, in particular from PVC-based plastic waste that the process according to the invention proposes to treat. Said impurities correspond at least in part to the additives previously mentioned and described. Other types of impurities may be usage impurities resulting from the life cycle of PVC-based objects and/or from the collection and sorting circuit, or even from pre-treatment operations of PVC-based plastic waste. These usage impurities may be metallic, organic or mineral impurities. They may be residues of materials (other than PVC plastics) constituting PVC-based objects or other objects that have been in contact with PVC-based objects, dirt (food, biomass, earth/rubble, glue, etc.), etc. These usage impurities may thus and in a non-exhaustive manner include glass, wood, cardboard, paper, metal, rubber, silicones, plastics other than PVC (for example PET, etc.), mineral elements, etc. Any degradation products of the additives formed over time during the life of the PVC-based product are also considered to be impurities.

In the present description, the expression “purified PVC polymer stream” represents the main and recoverable product obtained after treatment of a plastic load, in particular from PVC-based plastic waste, by the process according to the invention. It comprises at least one PVC resin of a given grade, preferably a mixture of PVC resins of the same chemical nature but of variable grades. The term “purified” means in particular that the PVC polymer stream obtained at the end of the process according to the invention comprises negligible or at least very low contents, in all cases in accordance with the regulations in force, of impurities (including additives) as described above and of at least one solvent as used according to the process of the invention. Thus, more particularly, the stream of at least one purified PVC polymer has a content (contents expressed as weight percentages relative to the total weight of the final product, i.e. of the purified PVC polymer stream obtained):

- a content of less than 0.1% by weight of phthalates subject to authorization by the REACH regulation in Europe (Annex XIV of Regulation (EC) No. 1907/2006 of the European Parliament and of the Council of 18 December 2006), in particular less than 0.1% by weight of phthalates chosen from the list constituted by the following phthalates: dibutyl phthalate (DBP), dioctyl or diethylhexyl phthalate (DOP or DEHP), benzyl butyl phthalate (BBP), dibutyl phthalate (DBP), diisobutyl phthalate (DIBP), dipentyl phthalate (DPP), diisopentyl phthalate, n-pentyl isopentyl phthalate, dihexyl phthalate, bis(2-methoxyethyl) phthalate, alone or in mixture,

- a content of less than 0.1% by weight of the element lead, in particular said lead contained in additives of the metallic stabilizer type assessed under the REACH regulation and subject to restrictions (Annex XV) detailed and adopted between December 2017 and March 2018 by the Risk Assessment Committee (RAC) and Socio-Economic Analysis Committee (SEAC) of ECHA,

- a content of less than 0.1% by weight, and preferably less than 0.01% by weight, of the element cadmium, in particular said cadmium contained in additives of the metallic stabilizer type prohibited by the REACH regulation according to the amendment of Annex XVII (Regulation 494/2011 of May 20, 2011),

- more generally a content of less than or equal to 10% by weight, preferably less than or equal to 5% by weight, preferentially less than 1.0% by weight, even more preferably less than or equal to 0.5% by weight, or even less than or equal to 0.1% by weight, of impurities, and

- more generally a content less than or equal to 10% by weight, preferably less than or equal to 5% by weight, preferentially less than or equal to 1.0% by weight and even more preferably less than or equal to 0.1% by weight of at least one solvent used in the process according to the invention.

In the present description, the expression “polymer solution” refers to a liquid medium comprising a dissolution solvent and at least one dissolved PVC polymer, i.e. solvated and dispersed, in said dissolution solvent, the dissolved PVC polymer being initially present in the plastic filler treated by the method according to the invention. The polymer solution may further comprise soluble impurities (and solubilized in the dissolution solvent) and/or insoluble impurities (and suspended in the polymer solution). Depending on the steps of the method according to the invention implemented, said polymer solution may therefore comprise impurities in the form of insoluble particles which are advantageously suspended in said polymer solution (in the case of insoluble impurities of nanometric size, we will then speak of colloidal solutions), soluble impurities dissolved in the dissolution solvent and/or possibly another liquid phase immiscible with said polymer solution.

In this description, the expression “greater than…” is understood as strictly greater than, and symbolized by the sign ">", and the expression “less than” as strictly less than, and symbolized by the sign “<”. When the limit is understood, the precision will be provided by the respective expressions “greater than or equal to…” (and corresponding to the sign “≥”) and “less than or equal to” (corresponding to the sign “≤”).

In this description, ambient temperature (Tamb) is understood to mean a temperature typically of 20°C ± 5°C, and atmospheric pressure is understood to mean a pressure of 0.101325 MPa.

In this description, the term “understand” is synonymous with (means the same thing as) “comprise”, “include” and “contain”, and is inclusive or open and does not exclude other elements that are not mentioned. It is understood that the term “understand” includes the exclusive and closed term “consist”.

In this description, the expression “between … and …” means that the limit values of the interval are included in the range of values described, unless otherwise specified.

In the present description, the different parameter ranges for a given step such as pressure ranges and temperature ranges may be used alone or in combination. For example, in the present description, a range of preferred pressure values may be combined with a range of more preferred temperature values.

In the following, particular embodiments of the invention are described. They can be implemented separately or combined with each other, without limitation of combinations when this is technically feasible.

In the following, we speak of a step to designate an operation or a group of similar operations carried out on a given flow at a certain point in the process. The process is described in its different steps taken in the order of flow of the flows or products.

Finally, the terms “upstream” and “downstream” are to be understood in relation to the general 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 PVC resins. For example, the terms “upstream” and “downstream” are defined in the steric exclusion step in relation to the stream of polymer solution, i.e. either at the feed of said step b) in raw (or clarified) polymer solution or at the outlet point of the polymer solution extracted during this step b) (i.e. raffinate withdrawal point).

The description of the method according to the invention below refers to the diagrams in Figures 1 to 2, illustrating different implementations of the method according to the invention.

In accordance with the invention, the method for recovering a flow of at least one reusable purified PVC polymer from a plastic load advantageously derived from PVC-based plastic waste, comprises, and may consist of, the following steps:

a) a dissolution step comprising bringing the plastic filler into contact with at least one dissolution solvent to obtain at least one crude polymer solution; then

b’) an optional step of separating the insolubles from the crude polymer solution, advantageously making it possible to obtain a clarified polymer solution and preferably an insoluble fraction; then

b) a step of extraction by steric exclusion of the crude polymer solution obtained at the end of step a) or possibly of the clarified polymer solution obtained at the end of the optional step b'), making it possible to obtain a purified polymer solution,

said steric exclusion extraction step using at least one train of n fixed beds of a steric exclusion solid, n being an integer greater than or equal to 4, preferably between 4 and 30, preferentially between 8 and 24, very preferentially between 8 and 21 and more preferably between 12 and 15,

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 each other and preferably in a closed loop,

said at least one train of fixed beds of step b) being supplied with raw 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 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,

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:

- an impurity elution zone I, located between an eluent injection point and an extract withdrawal point;

- a zone II for elution of at least one PVC polymer, located between the point of withdrawal of the extract and a point of injection of the polymer solution;

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

- optionally, and preferably, a zone IV located between the raffinate withdrawal point and the eluent injection point,

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

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

c) a polymer-solvent separation step, to obtain at least one fraction of at least one solvent, comprising in particular dissolution solvent and optionally eluent, and a flow of at least one purified PVC polymer.

Charge

The method according to the invention is fed with a plastic feedstock, in particular PVC-based, and more particularly derived from PVC-based plastic waste. It may also be called a “PVC feedstock” and comprises at least one PVC plastic.

Said plastic load is advantageously a PVC load to be recycled of the “production scraps” type, i.e. waste from the production processes of the PVC polymer during its polymerization or of the PVC plastic during its formulation/shaping or of the PVC-based object during its production, or of the “post-consumer waste” type, i.e. waste generated after consumption by the user of said PVC-based object. In particular, the plastic load to be recycled may come from any existing collection and sorting channels or networks for production scraps and/or post-consumer waste making it possible to isolate a flow based on at least one PVC plastic, in particular the collection and sorting channels or networks specific to plastic waste.

Thus, the plastic filler, which is typically of the “production scraps” type and/or of the “post-consumer waste” type, generally comes from the major fields of application using PVC plastic such as, but not limited to, the fields of building and construction, packaging, automotive, electrical and electronic equipment, sports, medical equipment, etc. Preferably, the PVC filler comes from the field of building and construction. More specifically, PVC-based objects are generally used in these fields as profiles (windows, doors, blinds, roller shutter boxes), pipes and fittings, various rigid materials and bottles, rigid plates and films, flexible films and sheets, flexible tubes and profiles, cables, floor coverings, coated fabrics, etc.

Advantageously, the plastic filler comprises at least 50% by mass, preferably at least 70% by mass, more preferably at least 90% by mass and even more preferably at least 95% by mass of PVC plastic.

The plastic filler treated in the process for recovering a reusable purified PVC polymer stream according to the invention is in the form of particles. Thus, if the PVC filler is in an initial form which is that specific to production scraps or post-consumer waste, in particular in the latter case in the initial form of PVC-based objects, it may undergo, beforehand, a conditioning step (as described below) comprising at least one grinding or shredding to form a PVC filler in the form of particles. Depending on the sectors and/or networks from which these production scraps and/or end-of-life PVC-based objects come, the PVC waste may be ground and/or washed and/or undergo any other conditioning step as described below, in order to form the PVC filler in the form of particles suitable for the process according to the invention. For example, the PVC filler may advantageously be in the form of ground material, optionally washed, the largest dimension of which is less than or equal to 20 cm, preferably less than or equal to 10 cm, more preferably less than or equal to 1 cm and even more preferably less than or equal to 5 mm. The PVC filler may also advantageously be in the form of a micronized solid, i.e. in the form of particles preferably having an average size of less than 1 mm, for example between 10 micrometers (µm) and 800 micrometers (µm). The average size advantageously corresponds to the average diameter of the spheres circumscribed by said particles.

Thus, the plastic charge which feeds the process according to the invention is advantageously in the form of particles, typically having an average size of between 10 µm and 20 cm, for example particles of the ground material type having an average size of between 1 mm and 20 cm, preferably between 1 mm and 10 cm, more preferably between 1 mm and 1 cm, even more preferably between 1 mm and 5 mm, or particles resulting from micronization (very fine grinding to produce a powder) with an average size of less than 1 mm, preferably between 10 µm and 800 µm.

As already mentioned, the PVC filler may also comprise usage impurities, often “macroscopic”, such as glass, wood, cardboard, paper, metal, rubber, silicones, plastics other than PVC (e.g. PET, etc.), mineral elements, etc. Advantageously, the PVC filler comprises at most 50% by mass, preferably at most 30% by mass, preferably at most 10% by mass and even more preferably at most 5% by mass of “macroscopic” impurities. A possible prior conditioning step may make it possible, in addition to putting the filler mentioned above into particles, to eliminate all or part of said usage impurities.

The different stages of the process according to the invention leading to the flow of at least one reusable purified PVC polymer are detailed in the following paragraphs.

Optional preliminary step of conditioning the PVC load

According to the invention, the method may comprise a prior step of conditioning the PVC feedstock (not shown in Figures 1 and 2) comprising at least one step of grinding or shredding or micronizing the PVC feedstock to form a PVC feedstock in the form of solid particles as defined above, capable of being sent to dissolution step a). This prior conditioning step may also comprise one or more steps mentioned in the following non-exhaustive list: grinding by micronization, sorting, over-sorting, washing, drying, etc. Depending on the nature of the PVC feedstock treated, the step or steps, as well as their possible frequencies and sequences, involved in the prior conditioning step are chosen in particular by the person skilled in the art so as to limit the quantity of usual impurities and to reduce the size of the solid elements initially making up the PVC feedstock.

For example, the prior conditioning step makes it possible to provide a PVC charge in the form of particles, for example crushed, washed, with an average size of less than or equal to 5 mm, preferably between 1 mm and 5 mm, the content of use impurities of which is preferably at most 10% by mass, and more preferably at most 5% by mass. Said previously conditioned PVC charge may also be in the form of micronized solid particles, i.e. in the form of particles having an average size of less than 1 mm, for example between 10 µm and 800 µm.

The preliminary step of conditioning the PVC load may include a step of drying the PVC load.

Step a) dissolution

The method according to the invention comprises a dissolution step a) in which the PVC filler (or plastic filler), advantageously in the form of particles, is brought into contact with a dissolution solvent, to obtain at least one, preferably a single, raw polymer solution. This step advantageously allows the dissolution of at least a portion, preferably all, of the PVC resins contained in the plastic filler.

Dissolution means any phenomenon leading to the production of at least one polymer solution, i.e. a liquid comprising at least the PVC resins dissolved in a solvent, more particularly in the dissolution solvent. The person skilled in the art is well aware of the phenomenon(s) involved in the dissolution of polymers, the phenomenon(s) comprising at least one mixing, homogenization, solvation, disentangling and dispersion of the polymer chains and more particularly here of the PVC polymer chains.

The dissolution solvent is chosen, due to its physicochemical properties, for its ability to solvate, disentangle and disperse the PVC polymer chains. In this respect, a person skilled in the art can rely on knowledge of the Hildebrand and/or Hansen solubility parameters of the solvents to define, in relation to these same parameters specific to PVC resins, the most suitable solvent or mixture of solvents for carrying out dissolution step a) of the process according to the invention. More particularly, the dissolution solvent is a solvent or a mixture of solvents, in particular organic, preferably chosen so that its Hansen parameters are within the Hansen sphere of the targeted PVC polymer. Hansen's theory allows to predict the solubility of a polymer, in particular a thermoplastic such as PVC, in a solvent, by determining the Hansen parameters and solubility sphere for the solvent and the polymer respectively, as a function of several parameters, in particular their polar, hydrogen bonding and dispersion parameters. If a solvent or a mixture of solvents has Hansen parameters in the Hansen sphere of the PVC polymer, said PVC polymer should be at least partially, preferably completely, soluble in said solvent. Thus, the dissolution solvent is advantageously an organic solvent or a mixture of organic solvents, preferably chosen from: ketones (acetone; methyl ethyl ketone or MEK; diethyl ketone or DEK; methyl propyl ketone; 4-heptanone; 2,4-dimethyl-3-pentanone; methyl isobutyl ketone or MIBK; diisobutyl ketone; methyl isoamyl ketone; 4-hydroxy-4-methylpentan-2-one; etc.), cyclic ketones (cyclopentanone; cyclohexanone; isophorone; etc.), amides (N,N-diethyl formamide; N,N-dimethyl acetamide; N,N-dimethyl formamide or DMF; etc.), cyclic amides (2-pyrrolidone; N-methyl-2-pyrrolidone or NMP; etc.), esters (methyl acetate; ethyl acetate; propyl acetate; butyl acetate; amyl acetate; 2-butoxyethanol acetate; n-butyl propionate; propyl propionate; methyl propionate; allyl acetate; 2-(2-butoxyethoxy)ethyl acetate; propylene glycol methyl ether acetate; propylene glycol ethyl ether acetate; butyl benzoate; benzyl benzoate; ethyl lactate; etc.), cyclic esters (γ-butyrolcatone or GBL; γ-valerolactone or GVL; caprolactone; etc.), ethers (methoxycyclopentane or CPME; propylene glycol phenyl ether; diethylene glycol butyl ether; dipropylene glycol butyl ether; propylene glycol methyl ether; propylene glycol butyl ether; dipropylene glycol methyl ether; ethylene glycol butyl ether; etc.), cyclic ethers (tetrahydrofuran or THF; 1,3-dioxolane; 2-hydroxymethyloxolane; etc.), chlorinated solvents (dichloromethane; trichloromethane or chloroform; tetrachloromethane; trichloroethylene; etc.), hydrocarbons (xylene; toluene; limonene; isohexane; cyclohexane; etc.), sulfur-containing solvents (dimethylsulfoxide or DMSO; sulfolane; etc.), nitrogenous solvents (1-nitropropane; etc.), dihydrolevoglucosenone or cyrene, etc. Preferably, the dissolution solvent is selected from ketones, cyclic ketones and cyclic esters, such as MEK, DEK, 4-heptanone, 2,4-dimethyl-3-pentanone, MIBK, cyclopentanone, GBL, GVL, taken alone or as a mixture. Even more preferably, the dissolution solvent is selected from DEK, 4-heptanone, 2,4-dimethyl-3-pentanone, GBL and GVL, taken alone or as a mixture.

Step a) of dissolving the PVC filler is preferably carried out at a dissolution temperature between room temperature and 200°C, preferably between 20°C and 200°C, preferably between 40°C and 180°C, more preferably between 60°C and 150°C, and advantageously at a dissolution pressure between atmospheric pressure and 11.0 MPa absolute, preferably between 0.1 and 11.0 MPa absolute, preferably between 0.1 and 5.0 MPa absolute, more preferably between 0.1 and 2.0 MPa absolute. The operating conditions of pressure and temperature are thus chosen so as to maintain the dissolution solvent, at least in part and preferably in its entirety, in the liquid state, while the soluble fraction of the PVC feedstock, in particular the PVC resins and at least part of the impurities, is advantageously dissolved at least in part and preferably in its entirety. Very advantageously, the temperature and pressure conditions of dissolution step a) are adjusted so that the mixture (dissolution solvent + PVC resin(s)) is single-phase, with insoluble impurities possibly being suspended in said mixture.

Very advantageously, dissolution step a) is carried out with a residence time of between 1 minute (min) and 10 hours (h), preferably between 10 min and 4 h, more preferably between 10 min and 2 h. The residence time is understood as the residence time at the dissolution temperature and at the dissolution pressure, i.e. the time for implementing the plastic charge with the dissolution solvent at the dissolution temperature and at the dissolution pressure, in step a).

Preferably, step a) is supplied with said plastic filler and said dissolving solvent, such that the weight quantity of PVC resin(s) present in the plastic filler, relative to the weight of the dissolving solvent, is between 2 and 30% by weight, preferably between 5 and 20% by weight, and even more preferably between 10 and 15% by weight.

In order to allow the dissolution solvent to come into contact with the plastic filler and to dissolve in the dissolution solvent at least a portion, preferably all, of the PVC resins contained in the plastic filler, dissolution step a) may use different equipment. Thus, step a) may advantageously use at least one piece of dissolution equipment, one piece of mixing equipment and/or one piece of transport equipment. These pieces of equipment (or devices) may be, for example, a static mixer, an extruder, a pump, a reactor, a co- or counter-current column. Transport equipment, in particular for fluids such as liquids or solids, is well known to those skilled in the art. In a non-limiting manner, the transport equipment may comprise a compressor, a pump, an extruder, a vibrating tube, a worm screw, a valve. The equipment may also comprise or be associated with heating systems (for example, oven, exchanger, tracing, etc.) to achieve the conditions necessary for dissolution. In a very particular manner, dissolution step a) can use a reactor stirred by a mechanical stirring system and/or by recirculation loop and/or by fluidization, for example a perfectly stirred batch or continuous reactor, or a rotating drum type reactor.

Dissolution step a) is at least supplied with the plastic feedstock (or PVC feedstock) and with the dissolution solvent, in particular in the form of one or more flows of dissolution solvent, advantageously by means of one or more transport device(s). The PVC feedstock may be introduced in the form of a flow of solid particles separate from the flow(s) of dissolution solvent. Part or all of the PVC feedstock may also be supplied to step a) in a mixture with part or all of the dissolution solvent, in particular in the form of a suspension of solid particles in the liquid solvent, the remainder of the solvent and/or feedstock, where appropriate, being able to be supplied to step a) separately.

Step a) may be fed continuously or discontinuously with said plastic filler and/or said dissolving solvent, in mixture or separately.

Preferably, dissolution step a) is carried out in a reactor of the stirred type by a mechanical stirring system and/or by recirculation loop and/or by fluidization and/or by ultrasound, for example a perfectly stirred batch or continuous reactor, or a rotating drum type reactor. In addition, the introduction of the PVC charge in the form of a flow of solid particles, independent of the dissolution solvent flow(s), is preferred.

Advantageously, the dissolution solvent used in step a) comprises, preferably consists of, fresh solvent (or an addition of fresh solvent) and/or a stream of recycled solvent from a subsequent step of the process, in particular from at least part of recovery step c).

According to the invention, said dissolution step a) makes it possible to obtain at least one, preferably only one, polymer solution, herein called raw polymer solution, comprising at least the dissolution solvent and at least the PVC resin(s) dissolved in said solvent. In general, the raw polymer solution also comprises soluble impurities also dissolved in the dissolution solvent and possibly insoluble impurities in suspension.

Optional step b’) separation of insolubles

The method according to the invention may optionally comprise a step b') of separating the insolubles from the raw polymer solution, in particular by solid-liquid separation, advantageously located upstream of the step b) of extraction by steric exclusion. Said step b') of separating the insolubles advantageously makes it possible, when it is integrated into the method according to the invention, to separate an insoluble fraction, which comprises at least in part, preferably all, of the insoluble impurities in particular in suspension in the raw polymer solution resulting from step a). The insoluble impurities removed during step b') of separating the insolubles are, for example, additives initially present in the PVC plastics (pigments, fillers, other polymers, etc.), usage impurities (mineral compounds, glass, wood, paper, metal, other polymers) and/or degradation products, as described above in this description.

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

When implemented, this separation step b') advantageously makes it possible, in addition to eliminating at least part of the insoluble impurities, to limit the operating problems, in particular of the clogging and/or erosion type, of the process steps located downstream, while contributing to the purification of the PVC feedstock. Preferably, the process according to the invention comprises a step b') of separating the insolubles.

Advantageously, the step of separating the insoluble materials, when it is implemented, is located upstream of step b) of extraction by steric exclusion and typically downstream of step a) of dissolution.

Step b') of separating the insolubles is advantageously carried out under temperature and pressure conditions close to those of step a). Very advantageously, step b') of separating the insolubles is carried out under the temperature and pressure conditions of step a) of dissolution, as defined above. Thus, very advantageously, step b') is carried out at a temperature between room temperature and 200°C, preferably between 20°C and 200°C, preferably between 40°C and 180°C, more preferably between 60°C and 150°C, and advantageously at a pressure between atmospheric pressure and 11.0 MPa absolute, preferably between 0.1 and 11.0 MPa absolute, preferably between 0.1 and 5.0 MPa absolute, more preferably between 0.1 and 2.0 MPa absolute.

When integrated into the process, step b') of separation of insolubles is preferably fed with the raw polymer solution from step a).

Advantageously, the optional step b') can implement a section comprising at least one solid-liquid separation equipment, for example a separator flask, a decanter, a centrifugal decanter, a centrifuge, a filter, a sand filter, a tangential filter notably implementing a membrane and/or a depth filter optionally in the presence of filtration 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 can be used, the cleaning or unclogging allowing the elimination of insolubles being carried out using a solvent flow.

The evacuation of the insoluble fraction may require the implementation of equipment allowing the transport and possibly allowing the elimination of solvent which may be impregnated in the separated insoluble fraction. For example, step b') may implement a conveyor, a vibrating tube, an endless screw, an extruder, stripping. Step b') may therefore implement transport equipment to evacuate the insoluble fraction and/or to eliminate the solvent possibly entrained with the separated insoluble fraction. Advantageously, at least part of the solvent possibly entrained with the separated insoluble fraction is recovered and recycled in the process.

According to a particular embodiment, step b') of separating the insolubles uses at least two, and generally less than five, solid-liquid separation equipment in series and/or in parallel. The presence of at least two solid-liquid separation equipment in series makes it possible to improve the elimination of the insolubles while the presence of equipment in parallel makes it possible to manage the maintenance of said equipment and/or unclogging operations.

Certain insoluble impurities, in particular certain pigments and mineral fillers, conventionally added during the formulation of polymers, can be introduced in the form of particles smaller than 1 µm. This is the case, for example, for titanium dioxide, calcium carbonate and carbon black. According to one embodiment, said step b') of separating the insolubles advantageously uses an electrostatic separator, which makes it possible to effectively eliminate, at least in part, the insoluble particles smaller than 1 µm. According to another embodiment, step b') of separating the insolubles uses a sand filter, to eliminate particles of different sizes and in particular particles smaller than 1 µm. According to yet another embodiment, step b') of separating the insolubles uses a tangential filter using in particular a membrane and/or a depth filter, optionally in the presence of filtration aids such as diatomaceous earth.

According to the invention, said optional step b’) of separating the insolubles allows, when it is integrated into the process, the obtaining of at least one clarified polymer solution comprising at least the dissolution solvent and at least the PVC resin(s) dissolved in said solvent. Thus, at least a portion, and preferably all, of the insoluble impurities potentially present in suspension in the raw polymer solution obtained at the end of step a) of the process according to the invention is eliminated from the polymer solution in step b’).

Step b) steric exclusion extraction

The method according to the invention comprises a step b) of extraction by steric exclusion, which is in particular supplied with an eluent and the raw polymer solution from step a) or optionally with the clarified polymer solution from step b') of separation of the insolubles. Advantageously, step b) of extraction by steric exclusion makes it possible to obtain at least one purified polymer solution, and preferably a used solvent, in particular loaded with impurities.

The polymer solution which feeds step b) of extraction by steric exclusion, in particular the crude polymer solution resulting from step a) or possibly the clarified polymer solution resulting from step b') of separation of the insolubles, generally comprises solubilized impurities, which are advantageously eliminated at least in part, preferably in full, during step b), in particular by contacting with a steric exclusion solid in the presence of an eluent. Indeed, step b) of extraction by steric exclusion allows a separation of the compounds present in the raw or possibly clarified polymer solution, in particular the separation of the dissolved PVC resin(s) and the solubilized impurities, according to their size in particular at the molecular scale (or rather their hydrodynamic volume), by simulated counter-current chromatography or simulated moving bed, hereinafter referred to as the “LMS” or “SMB” process for Simulated Mobile Bed according to the English terminology. Very advantageously, this extraction step of the process according to the invention allows the selective separation of the PVC resin(s), dissolved in the dissolution solvent, from the solubilized impurities, present in the polymer solution which feeds said step b), i.e. the raw or clarified polymer solution. Step b) thus makes it possible to produce a purified polymer solution, said purified polymer solution being a polymer solution freed from at least part, preferably all, of the soluble impurities present in the polymer solution which feeds said step b), i.e. present in the raw or clarified polymer solution.

Preferably, the eluent which feeds the extraction step b) is a solvent, in particular an organic solvent or a mixture of organic solvents, preferably chosen so that its Hansen parameters are within the Hansen sphere of the targeted PVC polymer. Preferably, the eluent which feeds the extraction step b) is a solvent, in particular an organic solvent or a mixture of organic solvents chosen from: ketones (acetone; methyl ethyl ketone or MEK; diethyl ketone or DEK; methyl propyl ketone; 4-heptanone; 2,4-dimethyl-3-pentanone; methyl isobutyl ketone or MIBK; diisobutyl ketone; methyl isoamyl ketone; 4-hydroxy-4-methylpentan-2-one; etc.), cyclic ketones (cyclopentanone; cyclohexanone; isophorone; etc.), amides (N, N-diethyl formamide; N, N-dimethyl acetamide; N, N-dimethyl formamide or DMF; etc.), cyclic amides (2-pyrrolidone; N-methyl-2-pyrrolidone or NMP; etc.), esters (acetate methyl acetate; ethyl acetate; propyl acetate; butyl acetate; amyl acetate; 2-butoxyethanol acetate; n-butyl propionate; propyl propionate; methyl propionate; allyl acetate; 2-(2-butoxyethoxy)ethyl acetate; propylene glycol methyl ether acetate; propylene glycol ethyl ether acetate; butyl benzoate; benzyl benzoate; ethyl lactate; etc.), cyclic esters (γ-butyrolcatone or GBL; γ-valerolactone or GVL; caprolactone; etc.), ethers (methoxycyclopentane or CPME; propylene glycol phenyl ether; diethylene glycol butyl ether; dipropylene glycol butyl ether; propylene glycol methyl ether; propylene glycol butyl ether; dipropylene glycol methyl ether; ethylene glycol butyl ether; etc.), cyclic ethers (tetrahydrofuran or THF; 1,3-dioxolane; 2-hydroxymethyloxolane; etc.), chlorinated solvents (dichloromethane; trichloromethane or chloroform; tetrachloromethane; trichloroethylene; etc.), hydrocarbons (xylene; toluene; limonene; isohexane; cyclohexane; etc.), sulfur-containing solvents (dimethylsulfoxide or DMSO; sulfolane; etc.), nitrogenous solvents (1-nitropropane; etc.), dihydrolevoglucosenone or cyrene, etc. Preferably, the eluent is chosen from ketones, cyclic ketones and cyclic esters, such as MEK, DEK, 4-heptanone, 2,4-dimethyl-3-pentanone, MIBK, cyclopentanone, GBL, GVL, taken alone or as a mixture. Preferably, the eluent is chosen from DEK, 4-heptanone, 2,4-dimethyl-3-pentanone, GBL and GVL, taken alone or as a mixture. Very preferably, the eluent is of the same chemical nature, or even the same solvent, as the dissolution solvent.

Advantageously, step b) of extraction by steric exclusion uses at least one train, preferably a single train, of several fixed beds of a steric exclusion solid, in operation. Said train(s) is (are) advantageously supplied with the raw polymer solution from step a) or possibly the clarified polymer solution from the optional step b'), and with the eluent. When step b) comprises several, in particular between two and four, trains of fixed beds of steric exclusion solid, in operation, these trains of fixed beds operate in parallel with each other and are each supplied with a fraction of the polymer solution which supplies step b), in particular the raw polymer solution resulting from step a) or possibly the clarified polymer solution resulting from the optional step b'), and with a fraction of the eluent which supplies step b), said polymer solution which supplies step b) then being divided into as many partial flows of raw or possibly clarified polymer solution as there are trains of fixed beds in operation, and similarly said eluent which supplies step b) then being divided into as many partial flows of eluent as there are trains of fixed beds in operation.

Optionally, the method may also comprise, in particular in parallel with step b), at least one train of fixed beds of steric exclusion solids (as described below), which is (are) not in operation, in particular which are stopped and/or in regeneration and/or emergency mode.

The (or each) train of fixed beds, advantageously in operation, of step b) of extraction by steric exclusion comprises n fixed beds of a steric exclusion solid, n being an integer greater than or equal to 4, preferably between 4 and 30, preferentially between 8 and 24, very preferentially between 8 and 21 and more preferably between 12 and 15. The number of fixed beds must be sufficient to allow effective separation, and reasonable so as to limit costs, particularly investment costs. The n fixed beds are advantageously in series with each other.

The n fixed beds of size exclusion solids can operate in a closed loop or in an open circuit. Preferably, the n fixed beds of size exclusion solids operate in a closed loop, that is to say that 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 the consumption of eluent, since the eluent is advantageously partly regenerated and recycled continuously.

The n fixed beds of steric exclusion solid are advantageously distributed in one or more columns, preferably in M columns, M being an integer between 1 and the total number of fixed beds of exclusion solid in the train considered, i.e. M being between 1 and n. Thus, the (or each) train of fixed beds of step b) of extraction by steric exclusion can implement between 1 and n columns, each comprising one or more fixed beds of steric exclusion solid. For example, the (or each) train of fixed beds of step b) can implement a column (or tower), preferably of large capacity (volume), which comprises the n fixed beds, or two columns each comprising n/2 fixed beds, these two configurations making it possible to significantly limit the cost of investments but requiring the entire column to be unloaded, i.e. n fixed beds or n/2 fixed beds, when there is a problem on one of the beds of the column. According to another embodiment, the (or each) fixed bed train of step b) implements 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 bypassing in particular of a bed among the n beds in operation since in this configuration, only one column (which comprises a single bed) must be discharged and/or bypassed and not a set of beds. However, this latter configuration generates higher investment costs.

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 so as to be inert with respect to the polymer solution to be treated, i.e. the dissolution solvent and the PVC resins to be treated, and with respect to the eluent. It is also chosen so as to allow effective separation of the compounds present, in particular dissolved, in the treated polymer solution, and more particularly effective separation of the impurities solubilized in the dissolution solvent with respect to the PVC resins which are also dissolved. The steric exclusion solid is advantageously a porous solid (meso and/or macroporous) 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 (mesoporous solid), and preferably between 3 nm and 30 nm. Advantageously, the steric exclusion solid comprises silica (such as a silica gel, also called silica, grafted silica, etc.), a carbon molecular sieve (or according to the English terminology Carbon Molecular Sieve), a carbon replica (carbon replica according to the English terminology), a polymeric molecular sieve (of a chemical nature other than PVC) (or polymeric molecular sieve, according to the English terminology), a porous polymer gel, a preferably dealuminated zeolite (for example of the USY type), a preferably calcined alumina, a material of the MOF type for metal organic framework, or mixtures thereof. Preferably, the steric exclusion solid comprises, preferably consists of, a silica gel (or silica), a grafted silica, a carbon molecular sieve (or according to the English terminology Carbon Molecular Sieve), or mixtures thereof. Very advantageously, the steric exclusion solid preferably has a pore volume of 0.01 and 3.0 ml/g, preferably between 0.1 and 2.0 ml/g, preferentially between 0.3 and 1.2 ml/g. The average pore diameter and the pore volume of the steric exclusion solid are determined by mercury porosimetry and more particularly measured by intrusion with a mercury porosimeter according to standard 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 that was taken is equal to 140° following the recommendations of the work "Techniques de l'ingénieur, traité analyse et caractérisation", 1050, by J. Charpin and B. Rasneur. In order to obtain better precision, the value of the mercury volume in ml/g given corresponds to the value of the total mercury volume in ml/g measured on the sample minus the value of the mercury volume in ml/g measured on the same sample for a pressure corresponding to 30 psi (approximately 2 bar). These same parameters, and in particular the volumes and diameter of the solid in the mesoporosity range, can also be measured by nitrogen adsorption/desorption volumetry (also called nitrogen adsorption isotherm), a complementary analysis method to that mentioned above. This analysis corresponds to the physical adsorption of nitrogen molecules in the porosity of the material via a progressive increase in pressure at constant temperature and provides information on the textural characteristics. In particular, it provides access to the mesoporous distribution of the steric extrusion solid. Thus, the representative pore distribution of a pore population centered in 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 E. P. Barrett, L. G. Joyner and P. P. Halenda.

The steric exclusion solid particles preferably have a volume equivalent mean diameter (preferably determined by laser granulometry, i.e. by laser diffraction using a granulometer) of between 20 and 5000 µm, preferably between 50 and 1500 µm, preferentially between 100 and 800 µm and even more preferably between 300 and 600 µm. Advantageously, the solid particles are substantially spherical.

According to the invention, the (or each) fixed bed train of step b) of steric exclusion extraction is supplied with raw or clarified polymer solution at at least one injection point F of the polymer solution and at least one eluent at an injection point S of the eluent. Preferably, the fixed bed train in operation considered is supplied with raw or clarified polymer solution at an injection point F of the polymer solution and at least one eluent at an injection point S of the eluent.

Preferably, the eluent and the polymer solution feed the (or each) fixed bed train of the steric exclusion extraction step according to a ratio of the volume 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, preferentially between 0.8 and 2.0, such a ratio being also called solvent rate. Such a solvent rate, i.e. such an adjustment of the volume flow rates of the polymer solution, raw or clarified, and of the eluent, for the (or each) train, contributes to the efficiency of the separation by steric exclusion of the PVC resins from the impurities present in the polymer solution which feeds the extraction step b).

When the fixed bed train comprises several injection points Fi of the polymer solution, for example two injection points F1 and F2 of the polymer solution, the flow of the raw or clarified polymer solution which feeds said fixed bed train considered in the extraction step is divided into as many partial flows of polymer solution to feed said fixed bed train at said injection points Fi, said partial flows of polymer solution having flow rates that are equal to or different from each other.

When the fixed bed train comprises several eluent injection points Si, for example two injection points S1 and S2, the total flow of eluent which feeds said fixed bed train in question 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 flow rates which are equal to or different from each other.

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

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 each other. They are advantageously located between two consecutive beds, or possibly upstream of the first bed, in particular 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 to be consecutive). However, they may be located, in the case of an embodiment in particular according to a Varicol® process (described below), on average over an operating cycle, in the middle of a fixed bed or in a fixed bed. The injection points of the polymer solution and of the eluent and the withdrawal points of the extract and of the raffinate are distributed relative to each other 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, between the injection point S of the eluent and the withdrawal point E of the extract;

- a zone II for elution of at least one PVC polymer, between the draw-off point E of the extract and the injection point F of the polymer solution;

- a zone III for retaining impurities, between the injection point F of the polymer solution and the withdrawal point R for withdrawing the raffinate; and

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

When there are several injection points F) 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 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 being the one furthest upstream of all the injection and/or withdrawal points of said stream 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 raffinate, secondary operating zones may also be defined, in particular within zones I, II, III and IV which are the main operating zones.

When the n fixed beds of the train considered in step b) operate in an open circuit, the eluent is introduced at the eluent injection point(s) S, the raw or optionally 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 all the remainder is withdrawn at the raffinate withdrawal point(s) R. The injection and withdrawal points thus define three successive main operating zones, zones I, II, III. In this embodiment, a significant amount of eluent relative to the polymer solution is, in general, necessary to be able to maximize the separation. For example, this open-circuit mode of operation requires a ratio of the volume flow rates of the eluent 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.

When the n fixed beds of the train considered in step b) operate in a closed loop, the eluent is introduced at the eluent injection point(s) S, the raw or optionally 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 part of the introduced eluent advantageously remains in circulation in the closed loop of the n beds (this is then referred to as recycling of the eluent). In this embodiment, the injection and withdrawal points then define four successive main operating zones, zones I, II, III and IV, with zone IV being able to be called the eluent regeneration and recycling zone. In this particular embodiment, the requirements for eluent supply (i.e. the quantities of eluent introduced in S) are very advantageously less significant than in the case of an open circuit operating mode to ensure efficient separation. For example, this closed loop operating mode requires a ratio of the volume flow rates of the eluent relative to the polymer solution of between 0.1 and 10, preferably between 0.2 and 5.0, or even between 0.8 and 2.0.

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

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

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

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

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

and in which:

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

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

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

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

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

Very advantageously, the filling density of each of the n fixed beds of steric exclusion solid, expressed in mass of steric exclusion solid per unit of 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 , preferentially between 400 and 800 kg/ ^m3 .

According to the invention, the injection points F and S and the withdrawal points E and R are shifted over time by a bed of steric exclusion solid according to a frequency determined by a predetermined permutation period. A permutation period can be defined as the period of time between two successive displacements (or shifts) of a fixed bed of the injection and withdrawal points. The periodic displacement (or shift) of the injection points F and S) and withdrawal points E and R can be carried out synchronously or non-synchronously, the latter case (non-synchronous) being known as VARICOL®. The periodic displacement of the injection and withdrawal points throughout 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. the number of beds n multiplied by the permutation period.

When the n fixed beds of steric exclusion solids operate in a closed loop, an operating cycle therefore advantageously includes as many permutation periods as there are beds of steric exclusion solids present in the closed separation loop. For example, an operating cycle of a train comprising 12 fixed beds of steric exclusion solids includes 12 permutation periods.

Thus, in the preferred embodiment in which the n fixed beds of exclusion solids of the train considered operate in a closed loop, the permutation 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, between 1 minute and 600 minutes, preferably between 5 minutes and 200 minutes, preferably between 10 minutes and 90 minutes. Such a cycle time contributes to the efficiency of the separation by steric exclusion of the PVC resins and the impurities present in the polymer solution which feeds the extraction step b).

In the case of the embodiment in which the n fixed beds operate in open circuit (i.e. 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, more preferably between 10 minutes and 90 minutes.

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

In general, the liquid flow in the fixed beds is advantageously from bed i to bed i+1, i being an integer between 1 and n the total number of fixed beds, i.e. from upstream to downstream, possibly being called descending liquid flow even if the presence of pump(s) is necessary (in particular between the nth bed and first bed in the case of closed loop operation and where the n beds are in a column). At the time of the permutation (or displacement of the injection and withdrawal points), the feed and withdrawal points are moved by one bed, placed downstream of the previous bed, thus creating/simulating a countercurrent liquid flow, possibly called ascending. A stop flow can then be defined when the two countercurrent liquid flow rates are equal, i.e. when the descending liquid flow rate is equal to the ascending liquid flow rate. This stoppage 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 packing density of the fixed size exclusion solid beds 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:

V _{(intergranular)} = V _(beds) x (1 - d _(filling) / d _(grain) ) + V _dead

with :

V _{(intergranular)} : the intergranular volume of the steric exclusion solid in the beds (in m ³ );

V _(beds) : the geometric volume of the beds (in ^m3 );

d _(filling) : the packing density of the steric exclusion solid in the beds (in kg/m ³ ), corresponding to the actual packing density of the steric exclusion solid, i.e. the mass of said solid per unit volume of the bed. As a first approximation, it can be assimilated to the packed packing density which consists of the mass of solid that a given volume occupies after packing by vibration of said solid, according to a principle derived from standards D4164 and D4180 applied to the case of catalysts;

d _(grain) : the grain density of the steric exclusion solid, typically measured by mercury porosimetry (in kg/m ³ );

V _dead : the volume (in ^m3 ) of equipment without steric exclusion solid but traversed by the fluid concerned, in particular the polymer solution (for example the volume of the lines upstream, downstream, etc.).

The stop flow rate, which is a volume flow rate, makes it possible to calculate dimensionless parameters, in particular relating to zones II and IV, in particular the ratio between the volume flow rate in zone II and the stop flow rate, and the ratio between the volume flow rate in zone IV and the stop flow rate. Preferably, the ratio of the volume flow rate of zone IV divided by the stop 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 volume flow rate of zone II divided by the stop flow rate is between 0.5 and 3.0, preferably between 0.9 and 1.5 and even more preferably between 1.0 and 1.25. Thus, the stop flow rate makes it possible to assist in the adjustments of the extraction step b) and therefore in the efficiency of the separation.

Furthermore, very advantageously, the superficial velocity in the fixed beds of an operating zone, which corresponds to the volume flow rate in the zone considered divided by the section of said zone (i.e. of the column in which the beds of said zone considered are located) can be adjusted so that this superficial velocity is between 0.01 and 10.0 cm/s and preferably between 0.05 and 2.5 cm/s. Adjusting the superficial velocity in the fixed beds advantageously makes it possible to control in particular the attrition of the particles of steric exclusion solid and thus to adjust the operation of the train of fixed beds of the extraction step so as to avoid high pressure losses (in particular encountered at high speed) and/or dispersion problems (in particular encountered at low speed).

Preferably, the steric exclusion extraction step of step b) is carried out at a temperature between room temperature and 200°C, preferably between 20°C and 200°C, preferably between 40°C and 180°C, more preferably between 60°C and 150°C, and advantageously at a pressure between atmospheric pressure and 11.0 MPa absolute, preferably between 0.1 MPa and 11.0 MPa absolute, preferably between 0.1 MPa and 5.0 MPa absolute, more preferably between 0.1 MPa and 2.0 MPa absolute. Under these operating conditions, the PVC resins remain dissolved in the dissolution solvent and optionally in the eluent, the latter (i.e. the dissolution solvent and the eluent) being at least partly in liquid form. Preferably, the temperature and pressure conditions of step b) are the same as those of dissolution step a).

Step b) of extraction by steric exclusion thus makes it possible to recover at least one extract which comprises at least in part, preferably in full, the impurities present in the polymer solution which feeds said step b), and at least one raffinate which comprises a polymer solution freed at least in part, preferably in full, of impurities. Said raffinate recovered at the end of the step of extraction by steric exclusion constitutes at least in part, preferably in full, the purified polymer solution. This purified polymer solution is then preferably sent, at least in part, preferably in full, to step c) of polymer-solvent separation. However, if necessary, it can be sent to other possible purification steps, so as to optimize if necessary the purification of the targeted PVC resins. This steric exclusion extraction step thus makes it possible to efficiently and continuously separate impurities, particularly soluble ones, from the polymer solution, raw or clarified, comprising the PVC resin(s) dissolved in the dissolution solvent.

Size exclusion extraction, particularly in the case of a closed loop of fixed beds, makes it possible to effectively separate impurities from PVC polymers, in a continuous mode, which makes it possible to limit the labor required to carry out said step while facilitating its operability. It also allows high productivity, particularly compared to batch size exclusion chromatography operations, while offering relatively low eluent consumption.

Step c) polymer-solvent separation

According to the invention, the method comprises a step c) of polymer-solvent separation, to obtain at least one flow of at least one purified PVC polymer and at least one fraction of at least one solvent comprising the dissolution solvent.

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

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

The polymer-solvent separation step c) thus aims firstly to separate at least in part, preferably mainly, the dissolution solvent and possibly the eluent from the PVC polymer(s), contained in the polymer solution which feeds step c), more particularly the purified polymer solution or possibly a final purified polymer solution resulting from an additional purification step, so as to recover at least one PVC polymer, freed at least in part, preferably mainly and preferentially in full, of the dissolution solvent, and possibly of the eluent, still present in the polymer solution which feeds step c). By predominantly, it is necessary to understand the elimination of at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, more preferably at least 95% by weight, very preferably at least 99% by weight, or even at least 99.9% by weight, of the solvent(s) (i.e. the dissolution solvent and optionally the eluent) contained in the purified polymer solution, relative to the weight of the solvent(s) contained in the purified polymer solution which feeds step c), in particular the dissolution solvent and optionally the eluent contained in said purified polymer solution. Any solvent/polymer separation method known to those skilled in the art can be implemented, in particular all methods 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, flash devolatilization, atomization (high pressure nozzle, rotary atomizer, bi-fluid nozzle, ultrasonic atomizer), stripping, demixing, extrusion, density difference and in particular decantation or centrifugation, etc.

The flow of at least one purified PVC polymer thus obtained may correspond to a concentrated polymer solution or to at least one purified PVC resin in solid form. Preferably, step c) of polymer-solvent separation further comprises a conditioning section for conditioning at least one purified PVC resin in solid form and more particularly in the form of powder, beads or granules.

The polymer-solvent separation step c) also aims to recover at least in part, preferably mainly and preferentially in full, the solvent(s) contained in the purified polymer solution that feeds step c). The polymer-solvent separation step c) also optionally aims to purify and recycle the recovered solvent fraction, in particular upstream of the dissolution step a). By mainly, it is necessary to understand 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).

Advantageously, step c) of polymer-solvent separation uses 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.

Thus, the method according to the invention makes it possible to efficiently and continuously recover PVC polymers from a plastic feedstock, with high productivity and a limited number of operations. Very advantageously, the method according to the invention makes it possible to obtain a PVC polymer stream having a high purity, preferably greater than or equal to 90%, preferably greater than or equal to 95%, preferentially greater than or equal to 99%, and even more preferably strictly greater than 99.9% (by weight of PVC polymer relative to the total weight of the purified stream recovered), from any type of PVC-based plastic feedstock. Another advantage of the method according to the invention also lies in the fact that an efficient separation of impurities, in particular additives, present in the plastic feedstock, is possible, while allowing a reasonable consumption of solvents, in particular of dissolution solvent and eluent, and a lower energy consumption than that required for more conventional separations, known as thermal separations, for example crystallization. The method according to the invention thus makes it possible to obtain a flow of purified PVC polymer, less colored than the plastic load to be treated, or even colorless, and very advantageously deodorized. More particularly, the method according to the invention makes it possible to obtain a flow of purified PVC polymer freed from at least part, preferably all, of the impurities, such as additives, present in the plastic load, and freed, at least in part or even in total, of solvent, in particular the dissolution solvent and the eluent.

Thus, the method according to the invention advantageously makes it possible to obtain a purified PVC polymer stream comprising a solvent content, in particular dissolution solvent or eluent, of less than or equal to 10% by weight, preferably less than or equal to 5% by weight, preferentially less than or equal to 1.0% by weight and even more preferably less than or equal to 0.1% by weight, and very advantageously an impurity content of less than or equal to 10% by weight, preferably less than or equal to 5% by weight and preferentially less than or equal to 1.0% by weight, even more preferably less than or equal to 0.5% by weight, or even less than or equal to 0.1% by weight, the percentages being given relative to the total weight of the purified PVC polymer stream. In particular, the purified PVC polymer stream obtained very advantageously has contents:

- less than 0.1% by weight of phthalates subject to authorisation by the REACH regulation in Europe (Annex XIV of Regulation (EC) No 1907/2006 of the European Parliament and of the Council of 18 December 2006), in particular strictly less than 0.1% by weight of phthalates chosen from the list consisting of the following phthalates: dibutyl phthalate (DBP), dioctyl or diethylhexyl phthalate (DOP or DEHP), benzyl and butyl phthalate (BBP), dibutyl phthalate (DBP), diisobutyl phthalate (DIBP), dipentyl phthalate (DPP), diisopentyl phthalate, n-pentyl and isopentyl phthalate, dihexyl phthalate, bis(2-methoxyethyl) phthalate, alone or in a mixture,

- less than 0.1% by weight of the lead element, in particular said lead contained in additives of the metallic stabilizer type assessed under the REACH regulation and subject to restrictions (Annex XV) detailed and adopted between December 2017 and March 2018 by the Risk Assessment Committee (RAC) and Socio-Economic Analysis Committee (SEAC) of ECHA,

- less than 0.1% by weight, and preferably less than 0.01% by weight, of the element cadmium, in particular said cadmium contained in additives of the metallic stabilizer type prohibited by the REACH regulation according to the amendment of Annex XVII (Regulation 494/2011 of May 20, 2011).

Size exclusion extraction device

The present invention also relates to a size exclusion extraction device suitable for separating PVC polymers from impurities, included in a polymer solution. Said device comprises:

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

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,

- 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 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 systems for injecting the polymer solution and the eluent and/or the systems for withdrawing the extract and the raffinate located at 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 should 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. the extract or the raffinate),

- each injection and withdrawal system comprising at least one valve adapted to allow or not allow a flow of polymer solution and/or eluent and/or extract and/or raffinate to pass, preferably i) a series of on-off valves which are controlled by an automatic sequence, or ii) a single rotary valve, so that:

- to define, at a time t, a polymer solution injection point, an eluent injection point, an extract withdrawal point and a raffinate withdrawal point, 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, between an injection point of the eluent and a point of withdrawal of the extract;

- a zone II for elution of at least one PVC polymer, between the point of withdrawal of the extract and a point of injection of the polymer solution;

- a zone III for retaining impurities, between the injection point of the polymer solution and a raffinate withdrawal point; and

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

- 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.

Device for processing a plastic load

Such a size exclusion extraction device can be integrated into a more global device for treating a plastic load to obtain a purified PVC polymer flow, which includes:

- means for bringing the plastic filler and a dissolving solvent into contact so as to at least partially dissolve said plastic filler in said dissolving solvent and to obtain a raw polymer solution;

- possibly solid-liquid separation means suitable for separating insolubles suspended in the raw polymer solution;

- at least one steric 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;

- means for separating the dissolution solvent and possibly the eluent from a flow of purified PVC polymer, advantageously connected to said at least one steric exclusion extraction device.

Said device for treating a PVC load to obtain a flow of purified PVC polymer also advantageously comprises means of transport between said means and devices.

Such a device very advantageously makes it possible to recover PVC polymers with high purity from a PVC-based plastic load which may include a multitude of impurities.

The following example and the figures illustrate the invention, in particular particular embodiments of the invention, without limiting its scope.

EXAMPLES Example 1

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

The charge to be treated is composed of a Poly(Vinyl Chloride) or PVC resin (55% by weight) with a molar mass MW=120,000 g/mol, and a di-decyl phthalate (DiDP) additive (45% by weight), the percentages being given by weight relative to the total weight of the charge.

The filler is first dissolved in diethyl ketone (DEK) at 100°C, at atmospheric pressure, to form a homogeneous raw polymer solution comprising 80% by weight of DEK and 20% by weight of filler (polymer and additive).

The obtained raw polymer solution is introduced into a simulated moving bed, comprising 15 fixed beds of a solid consisting of silica gel. Said fixed beds are distributed according to a 6/3/4/2 configuration (cf. ). The eluent is diethyl ketone (DEK).

Silica gel has the following properties:

- ball diameter = 500 µm;

- pore diameter = 6 – 10 nm;

- pore volume = 0.50 ml/g of solid;

- filling density = 530 kg of solid /m ³ lit.

Each bed is modeled by a 1D fixed piston bed model with axial dispersion and a Fick model for intragranular transfer. Since the radius of gyration of PVC is estimated at 39 nm, the polymer is considered to be present only in the extragranular phase. The additives and the solvent have a radius of gyration less than 1 nm and can therefore diffuse into the intragranular porosity. The medium in the beds is considered isothermal (100 °C) and the density of the polymer solution is considered constant (800 kg/m ³ ).

The extraction is adjusted with the following settings:

- cycle time = 15 min, i.e. a permutation period of 60 seconds;

- volume flow rate of eluent relative to volume flow rate of polymer solution S/F = 1.32;

- Zone IV flow rate / stop flow rate = 0.97;

- Zone II flow rate / stop flow rate = 1.05;

- maximum surface velocity = 1.43 cm/s.

The concentration profiles obtained for PVC and the additive, by simulation, are illustrated in the which shows the concentration profile of PVC (solid line) and that of DiDP (dotted line). By convention, the injection of the eluent is carried out just upstream of bed 1. The concentrations throughout the bed are given as weight percentages of the compound monitored, i.e. PVC or additive, relative to the weight of DEK.

According to the , it appears that the PVC, which does not explore the intragranular porosity, is carried towards the raffinate and drawn off between beds 13 and 14. The DiDP additive being smaller, it diffuses into the intragranular porosity and is carried towards the extract with a draw off between beds 6 and 7.

The extraction carried out in a simulated moving bed allows the following performances to be obtained:

- purity of the separated PVC = 99.93% by weight (which corresponds to the weight, or weight flow, of PVC in the raffinate relative to the total weight, or total weight flow, of the PVC and additive assembly in the raffinate, excluding DEK solvent);

- yield of separated PVC = 99.95% (which corresponds to the weight flow of PVC extracted from the raffinate divided by the weight flow of PVC extracted from the extract + raffinate);

- productivity = 149 kg of PVC extracted in the raffinate/h/m ³ of bed.

The raffinate leaving the simulated moving bed of steric exclusion extraction can then be recovered and sent to a polymer-solvent separation section, in particular a DEK solvent evaporation section.

Claims (15)

Process for recovering a flow of at least one purified PVC polymer from a plastic load, comprising:
a) a dissolution step comprising bringing the plastic filler into contact with a dissolution solvent, to obtain at least one raw polymer solution;
b') optionally a step of separating the insoluble materials from the crude polymer solution obtained at the end of step a), to obtain at least one clarified polymer solution;
b) a step of extraction by steric exclusion of the crude polymer solution obtained at the end of step a) or optionally of the clarified polymer solution obtained at the end of step b'), to obtain a purified polymer solution,
said steric exclusion extraction step implementing 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 fixed beds of the steric exclusion solid being in series,
said fixed bed train of step b) being supplied with raw 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 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 that they determine at least three, preferably four, successive main operating zones of the n fixed beds:
- an impurity elution zone I, located between the eluent injection point and the extract withdrawal point;
- a zone II for elution of at least one PVC polymer, located between the point of withdrawal of the extract and the point of injection of the polymer solution;
- an impurity retention zone III, located between the polymer solution injection point and the 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 offset over time of a fixed bed of steric 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, for separating the purified polymer solution into a purified PVC polymer stream and at least one solvent fraction comprising dissolving solvent. The method of claim 1, wherein the dissolving solvent is an organic solvent selected from ketones, amides, esters, ethers, chlorinated solvents, sulfurous solvents, nitrogenous solvents, hydrocarbons, and mixtures thereof, preferably from methyl ethyl ketone, diethyl ketone, 4-heptanone, 2,4-dimethyl-3-pentanone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, N,N-diethyl formamide, 2-pyrrolidone, N-methyl-2-pyrrolidone, γ-butyrolcatone, γ-valerolactone, methoxycyclopentane, tetrahydrofuran, dichloromethane, dimethyl sulfoxide, xylene, isohexane, dihydrolevoglucosenone or cyrene, and mixtures thereof, in a very preferred among diethyl ketone, 4-heptanone, 2,4-dimethyl-3-pentanone, γ-butyrolcatone, γ-valerolactone, and mixtures thereof. Method according to claim 1 or 2, in which the eluent is an organic solvent of the same chemical nature as the dissolution solvent. Method according to one of the preceding claims, in which step b) of extraction by steric exclusion uses at least one train of n fixed beds of a steric exclusion solid, n being an integer between 4 and 30, and preferably between 12 and 15. Method according to one of the preceding claims, in which the steric exclusion solid is a porous solid having a volume average pore diameter of between 1 and 500 nm, preferably between 2 and 100 nm, preferentially between 2 nm and 50 nm, preferentially between 3 and 30 nm. A method according to any preceding claim, wherein the size exclusion solid comprises silica gel, grafted silica, carbon molecular sieve, or mixtures thereof. Method according to one of the preceding claims, in which the eluent and the polymer solution feed step b) according to a ratio of the volume 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, preferentially between 0.8 and 2.0. Method according to one of the preceding claims, in which 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. Method according to one of the preceding claims, in which the n beds of steric exclusion solid operate in a closed loop and are distributed in four main operating zones, zones I to IV, according to a configuration called a / b / c / d type, the distribution of the beds of steric exclusion solid in zones I to IV relative to the total number n of beds of steric exclusion solid being preferably such that:
- a, the number of beds of steric exclusion solid in zone I,
- b, the number of beds of steric exclusion solid in zone II,
- c, the number of steric exclusion solid beds in zone III, and
- d, the number of steric exclusion solid beds in zone IV
and in which:
- 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). Method according to one of the preceding claims, in which the n beds are in a closed loop and the permutation period is preferably adjusted so as to define a cycle time, which corresponds to the time necessary for the injection and withdrawal points to return to their initial position, between 1 and 600 minutes, preferably between 5 and 200 minutes, more preferably between 10 and 90 minutes. Process according to one of the preceding claims, in which step a) is carried out at a dissolution temperature between 20 and 200°C, preferably between 40 and 180°C, preferentially between 60 and 150°C, and a dissolution pressure between 0.1 and 11.0 MPa absolute, preferably between 0.1 and 5.0 MPa absolute, preferentially between 0.1 and 2.0 MPa absolute. Method according to one of the preceding claims, in which the weight quantity of PVC polymer of the plastic charge which feeds step a) represents between 2 and 30% by weight, preferably between 5 and 20% by weight, more preferably between 10 and 15% by weight, relative to the weight of the dissolution solvent. Process according to one of the preceding claims, in which step b) is carried out at a temperature between 20 and 200°C, preferably between 40 and 180°C, preferentially between 60 and 150°C, and a pressure between 0.1 and 11.0 MPa absolute, preferably between 0.1 and 5.0 MPa absolute, preferentially between 0.1 and 2.0 MPa absolute. Device for steric exclusion extraction of PVC polymer from a polymer solution, said device comprising:
- n fixed beds of a steric exclusion solid, n being an integer greater than or equal to 4, preferably between 4 and 30, more preferably between 12 and 15, said steric exclusion solid having a volume average pore diameter preferably between 1 and 500 nm, preferably between 2 and 100 nm, more preferably between 2 and 50 nm, more preferably between 3 and 30 nm, and more preferably being a silica gel, a grafted silica, a carbon molecular sieve, or mixtures thereof,
the n fixed beds of the steric exclusion solid being distributed in one or more columns, the n beds being connected in series and preferably in a closed loop,
- N systems for injecting the polymer solution, N systems for injecting an eluent, N systems for withdrawing an extract and N systems for withdrawing 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 polymer solution and eluent injection systems and/or the extract and raffinate withdrawal systems located at the same position being distinct or identical,
- each injection and withdrawal system comprising valves adapted to allow or not allow a flow of polymer solution and/or eluent and/or extract and/or raffinate to pass, preferably a series of on/off valves, controlled by an automatic sequence, or a single rotary valve, so that:
- to define, at a time t, a polymer solution injection point, an eluent injection point, an extract withdrawal point and a raffinate withdrawal point, 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:
- an impurity elution zone I, between an eluent injection point and an extract withdrawal point;
- a zone II for elution of at least one PVC polymer, between the point of withdrawal of the extract and a point of injection of the polymer solution;
- an impurity retention zone III, between the polymer solution injection point and a raffinate withdrawal point; and
- possibly a zone IV between the raffinate withdrawal point and the eluent injection point,
- 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. Device for treating a plastic load to obtain a flow of purified PVC polymer, comprising:
- means for bringing the plastic filler and a dissolving solvent into contact, so as to at least partially dissolve said plastic filler in said dissolving solvent and to obtain a raw polymer solution;
- possibly solid-liquid separation means suitable for separating insolubles suspended in the raw polymer solution;
- at least one steric exclusion extraction device according to claim 14;
- means for separating the dissolution solvent and possibly the eluent from a purified PVC polymer flow.