Process for treating waste plastics by dissolving the polymers and purifying by washing

Abstract

The present invention relates to a process for treating a plastic feedstock comprising a polymer, comprising: a) a dissolution step involving contacting the plastic feedstock with a dissolution solvent at a dissolution temperature of 100 to 300 °C and a dissolution pressure of 1 to 20.0 MPa abs, to dissolve at least a portion of the polymer of the plastic feedstock and to obtain a crude polymer solution; b) a washing step by contacting the crude polymer solution with a high density solution at a temperature of 100 to 300 °C, a pressure of 1 to 20.0 MPa abs and at a mass ratio between the high density solution and the crude polymer solution of 0.05 to 20.0, to obtain a washed polymer solution and a washing effluent; and subsequently c) a step of recovering the polymer, to obtain a solvent fraction and a purified polymer fraction.

Description

Technical Field

[0001] This invention relates to a method for processing waste plastics to obtain purified plastic streams that can be used, for example, as new plastic articles. More particularly, this invention relates to a method for processing plastic raw materials, especially those obtained from plastic waste, particularly containing thermoplastics such as polyolefins, the method comprising the step of washing a polymer solution with a dense solution (e.g., an aqueous solution) to at least partially remove impurities, especially additives (e.g., dyes, pigments, organic fillers, and inorganic fillers) conventionally used in plastic-based materials, so as to enable the upgrading of the plastic raw materials by separating the polymers (especially thermoplastics) contained therein, thereby enabling their recycling and reuse. Existing technology

[0002] Plastics obtained from collection and sorting can be improved through various channels.

[0003] Mechanical recycling allows for the partial reuse of certain waste materials, either directly in new articles or by mixing mechanically sorted plastic waste streams with virgin polymer streams. This type of improvement is limited because mechanical sorting can improve the purity of a given type of polymer stream, but it typically cannot adequately remove impurities, such as additives like fillers, dyes, pigments, and metals, that are at least partially trapped in the polymer matrix.

[0004] "Chemical" recycling involves at least partial reformation of monomers via a series of typically complex steps. For example, plastic waste can undergo a pyrolysis step, and the recovered pyrolysis oil (usually after purification) can be at least partially converted into olefins, for example, by steam cracking. These olefins can then be polymerized. This type of sequence can be applied to feedstocks that have undergone little sorting or to waste from sorting centers, but it typically requires significant energy consumption, especially due to the high temperatures involved.

[0005] Another approach to recycling plastic waste involves at least partially dissolving the plastic, particularly thermoplastics, with the aim of purifying them by removing polymers and / or impurities other than the target polymer, such as additives like fillers, dyes, pigments, and metals.

[0006] Therefore, several studies have proposed various methods for treating plastic waste by dissolving and purifying it. US 2017 / 002110 describes a specific method for purifying polymer raw materials (especially polymer raw materials obtained from plastic waste) by dissolving the polymer in a solvent under specific temperature and pressure conditions and then contacting the resulting polymer solution with a solid.

[0007] WO 2018 / 114047, in itself, proposes a method for dissolving plastics in a solvent at a dissolution temperature close to the solvent's boiling point. However, the method in WO 2018 / 114047 is not effective at handling impurities other than polymers.

[0008] US 2018 / 0208736 discloses a treatment method that involves liquefying thermoplastics in a solvent and subsequently separating insoluble substances and / or gases. The method in US 2018 / 0208736 is not effective at handling impurities soluble in solvents.

[0009] This invention aims to overcome these drawbacks and participate in the recycling of plastics (especially thermoplastics). More specifically, this invention aims to provide a method for processing plastic raw materials (especially those obtained from plastic waste) to effectively remove at least some impurities, especially additives conventionally added to plastic materials, and more particularly impurities significantly soluble in organic solvents, so as to enable the upgrading of plastic raw materials and, more particularly, plastic waste by separating and recycling polymers (especially thermoplastics), thereby enabling their use, for example, as polymer bases for new plastic articles. Summary of the Invention

[0010] This invention relates to a method for processing plastic raw materials, comprising:

[0011] a) A dissolution step, which involves contacting the plastic raw material with a dissolving solvent at a dissolution temperature of 100°C to 300°C and a dissolution pressure of 1.0 to 20.0 MPa absolute pressure to obtain at least one crude polymer solution.

[0012] b) A washing step, which is carried out by contacting the crude polymer solution obtained from step a) with a high-density solution at a temperature of 100°C to 300°C, a pressure of 1.0 to 20.0 MPa absolute, and a mass ratio between the mass flow rate of the high-density solution and the mass flow rate of the crude polymer solution supplied in step b) of 0.05 to 20.0, to obtain at least one washed polymer solution and at least one washed effluent; and subsequently

[0013] c) A step of recovering the polymer to obtain at least one solvent fraction and at least one purified polymer fraction.

[0014] The advantage of the method of the present invention is that it provides a method for effectively treating raw materials containing plastics, particularly plastic waste, especially plastic waste obtained from collection and sorting channels, in order to recover the polymers contained in said plastic waste that can be recycled into any type of application, more particularly thermoplastics. The method according to the invention makes it possible to obtain purified polymer streams, more particularly purified thermoplastic streams, especially purified polyolefin streams such as polyethylene and polypropylene, advantageously containing negligible or at least sufficiently small impurity content, so that said purified polymer streams, more particularly purified thermoplastic streams, can be introduced into any plastic formulation in place of virgin polymer resins. For example, the purified polymer streams, more particularly purified thermoplastic streams, especially purified polyolefin streams obtained at the end of the method according to the invention advantageously contain less than 5% by weight of impurities, and very advantageously less than 1% by weight of impurities.

[0015] Therefore, the method according to the invention provides a series of operations for removing at least a portion of impurities, particularly additives, from plastic waste, and for recovering the purified polymer, so that the plastic waste can be upgraded by recycling the purified polymer. Advantageously, depending on the conditions used in the steps of the method, compounds present in the plastic raw material may be soluble or insoluble in one or more solvents used throughout the method according to the invention, thereby allowing for efficient purification of the polymer.

[0016] A further advantage of this invention is its contribution to plastic recycling and the conservation of fossil resources by upgrading plastic waste. Specifically, it enables the purification of plastic waste to obtain purified polymer fractions with reduced impurity content, significantly decolorized and deodorized, which can be reused to form new articles. Therefore, to obtain plastic products with aesthetic, mechanical, or rheological processing properties, the resulting purified polymer fractions can be used directly in formulations, as mixtures with additives such as dyes, pigments, or other polymers, in place of virgin polymer resins, or as mixtures with virgin polymer resins, whose aesthetic, mechanical, or rheological processing properties facilitate their reuse and upgrading.

[0017] The present invention also enables the recovery of one or more solvents used in the method for treating plastic raw materials and their recycling after purification in the method, thereby avoiding excessive consumption of one or more solvents.

[0018] Therefore, this invention relates to purifying plastic raw materials, particularly plastic waste, to obtain polymers, especially thermoplastics, and more particularly polyolefins such as polyethylene and polypropylene, purifying them so that they can be used in any application, especially as a substitute for virgin polymers. Thus, this invention proposes a purification method by dissolving the target polymers, i.e., separating and purifying them. More specifically, this invention relates to a method comprising a dissolution step, followed by at least one specific purification step, more particularly at least step b) of washing the polymer solution, optionally combined with other intermediate purification steps, to obtain a purified polymer solution from which the purified polymer can be recovered. Detailed Implementation

[0019] According to the present invention, the expression "included between..." and "between..." and "(...to...") are equivalent, and mean that the limit of the interval is included within the range of the described values. If this is not the case, and if the limit is not included within the described range, the present invention will provide such clarification.

[0020] For the purposes of this invention, various parameter ranges for a given step, such as pressure ranges and temperature ranges, can be used individually or in combination. For example, for the purposes of this invention, a preferred range of pressure values ​​can be combined with a more preferred range of temperature values.

[0021] Specific embodiments of the invention may be described below. They may be implemented individually or combined when technically feasible, without limiting the scope of the combination.

[0022] According to the present invention, the pressure is absolute pressure and is given in MPa absolute pressure (or MPa absolute pressure).

[0023] The terms “upstream” and “downstream” should be understood to vary with the general flow of the fluid or material being considered in the method.

[0024] The term "additive" is a commonly used term in the polymer field, particularly in the field of polymer formulations. Additives introduced into polymer formulations can be, for example, plasticizers, fillers (which are organic or inorganic solid compounds used to modify the physical, thermal, mechanical, and / or electrical properties of polymer materials or to reduce their cost), reinforcing agents, dyes, pigments, curing agents, flame retardants, combustion retardants, stabilizers, antioxidants, UV absorbers, antistatic agents, etc.

[0025] The additive corresponds to a portion of the impurities in the plastic raw material to be treated, and the treatment method according to the invention allows for at least partial removal of the additive. Other types of impurities may be impurities or plastic materials related to the use of the material, such as metallic impurities, paper / cardboard, biomass, other polymers, such as thermosetting or thermoplastic polymers, etc.

[0026] Therefore, according to the invention, the method according to the invention enables impurities that can be at least partially removed from the stream of the target polymer to include additives conventionally used in polymer formulations and generally use-related impurities originating from the life cycle of plastic articles and materials, and / or from waste collection and sorting loops. These impurities can be metallic, organic, or mineral-type impurities; they can be packaging residues, food scraps, or compostable residues (biomass). These use-related impurities may also include glass, wood, cardboard, paper, aluminum, iron, metals, tires, rubber, silicone resins, rigid polymers, thermosetting polymers, household, chemical or cosmetic, waste oil, and water.

[0027] According to the invention, the polymer solution is a solution comprising a dissolving solvent and at least a polymer, preferably a target polymer, more particularly a target thermoplastic, especially a target polyolefin, dissolved in the dissolving solvent, the dissolved polymer initially present in the raw material. The polymer solution may also contain soluble and / or insoluble impurities. As a function of the steps already performed according to the method of the invention, the polymer solution may contain impurities in the form of insoluble particulate matter advantageously suspended in the polymer solution, soluble impurities dissolved in the dissolving solvent, and / or optionally another liquid phase immiscible with the polymer solution.

[0028] The critical temperature and critical pressure of a solvent, particularly a dissolving solvent and / or an extracting solvent, are inherent to the solvent and are respectively the temperature and pressure of the solvent's critical point. As is well known to those skilled in the art, at or above the critical point, a solvent is in a supercritical form or in a supercritical state, and the temperature and pressure operating conditions are the supercritical conditions of the solvent; thus, it can be called a supercritical fluid.

[0029] This invention relates to a method for preparing a plastic raw material, which preferably consists of plastic waste and advantageously includes a polymer, preferably a thermoplastic, and more particularly a polyolefin. The method comprises the following steps, preferably:

[0030] a) a dissolution step, which involves contacting the raw material with a solvent to obtain at least one crude polymer solution; and subsequently

[0031] E1) Optionally, the step of separating insoluble substances to obtain at least one clarified polymer solution and at least one insoluble fraction;

[0032] b) A washing step, which is carried out by contact with a high-density solution to obtain at least one washing effluent and at least one washed polymer solution;

[0033] E2) Optionally, the extraction step is carried out by contacting an extraction solvent to obtain at least one extracted polymer solution and at least one waste solvent.

[0034] E3) Optionally, the step of adsorbing impurities by contacting an adsorbent solid to obtain at least one purified polymer solution; and finally

[0035] c) A step of recovering the polymer to obtain at least one solvent fraction and at least one purified polymer fraction.

[0036] raw material

[0037] The raw materials used in the method according to the invention, referred to as plastic raw materials, comprise plastics, and more particularly, polymers. Preferably, the plastic raw materials comprise 50% to 100% by weight, more preferably 70% to 100% by weight of plastics.

[0038] The plastics included in the raw materials of the method according to the invention are typically production waste and / or waste, particularly household waste, construction waste, or electrical and electronic equipment waste. Preferably, the plastic waste originates from collection and sorting channels. Plastics or plastic materials are typically polymers, which are usually mixed with additives to form various materials and articles (injection-molded parts, tubes, films, fibers, fabrics, adhesives, coatings, etc.) after molding. The additives used for the plastics can be organic or inorganic compounds. They are, for example, fillers, dyes, pigments, plasticizers, property modifiers, flame retardants, etc.

[0039] Therefore, the raw materials used in the method according to the invention comprise polymers, particularly thermoplastics. The polymers contained in the plastic raw materials can be olefin polymers, diene polymers, vinyl polymers, and / or styrene polymers. Preferably, the polymers contained in the plastic raw materials are polyolefins, such as polyethylene (PE), polypropylene (PP), and / or copolymers of ethylene and propylene. Very preferably, the polymers in the plastic raw materials comprise at least 80% by weight, preferably at least 85% by weight, preferably at least 90% by weight, and most preferably at least 94% by weight of polyolefins relative to the total weight of the raw materials. Therefore, the method according to the invention most particularly relates to purifying and recovering the polyolefins contained in the raw materials so that they can be reused in a variety of applications.

[0040] Plastic raw materials may comprise mixtures of polymers, particularly mixtures of thermoplastics and / or mixtures of thermoplastics with other polymers, as well as impurities, particularly additives advantageously used in the formulation of plastic materials and generally use-related impurities originating from the life cycle of the material and plastic articles, and / or from waste collection and sorting loops. Raw materials according to the method of the invention typically contain less than 50% by weight of impurities, preferably less than 20% by weight, and most preferably less than 10% by weight.

[0041] The plastic-containing raw material can advantageously be pretreated prior to the method to remove at least all or some of the "coarse" impurities, i.e., impurities in particulate form with a size greater than or equal to 10 mm, preferably greater than or equal to 5 mm, or even greater than or equal to 1 mm, such as impurities like wood, paper, biomass, iron, aluminum, glass, etc., and to shape it, typically into a dispersed solid form, for processing in the method. This pretreatment may include a grinding step, a washing step under atmospheric pressure, and / or a drying step. This pretreatment can be carried out at different locations, such as at a waste collection and sorting center, or at the same location where the processing method according to the invention is performed. Preferably, the pretreatment reduces the impurity content to less than 6% by weight. At the end of the pretreatment, the raw material is typically stored in a dispersed solid form, such as as ground material or powder, for easy processing and transport to the method.

[0042] Dissolving step a)

[0043] According to the invention, the method includes a dissolution step a), wherein the plastic raw material is contacted with a dissolving solvent at a dissolution temperature of 100°C to 300°C and a dissolution pressure of 1.0 to 20.0 MPa absolute pressure to obtain at least one, preferably a crude polymer solution. Specifically, this step advantageously dissolves at least a portion of the polymer, preferably all of the polymer, preferably thermoplastics, and most particularly polyolefins, such as polyethylene and / or polypropylene.

[0044] The term "dissolution" should be understood to refer to any phenomenon that results in the formation of at least one polymer solution, i.e., a liquid containing a polymer dissolved in a solvent, and more particularly, dissolved in the solvent. Those skilled in the art are well aware of the phenomena involved in polymer dissolution, and that it includes at least the mixing, dispersion, homogenization, and detangling of polymer chains, and more particularly thermoplastic chains.

[0045] During and at the end of dissolution step a), the pressure and temperature conditions are such that the dissolving solvent (at least a portion and preferably all of the dissolving solvent) is kept in liquid form, while the soluble fractions of the raw material, particularly the target polymer, preferably the target thermoplastic, preferably the target polyolefin, and at least a portion of the impurities are advantageously at least partially and preferably completely dissolved.

[0046] Contacting the dissolving solvent with the plastic raw material to dissolve the polymer of the plastic raw material at least partially and preferably completely in the dissolving solvent can be carried out in one line and / or item of the equipment and / or between two items of the equipment. Therefore, step a) advantageously involves at least one item of a dissolving device, and optionally at least one raw material preparation device, mixing device, and / or conveying device. These items and / or devices can be, for example, static mixers, extruders, pumps, reactors, co-current or counter-current towers, or combinations of lines and equipment. Devices for conveying, particularly fluids (e.g., gases, liquids, or solids), are well known to those skilled in the art. In a non-limiting manner, conveying devices may include compressors, pumps, extruders, vibrating tubes, endless screws, or valves. The items and / or devices of the equipment may also include a heating system (e.g., oven, exchanger, a tracing element, etc.) or in combination with a heating system to achieve the conditions required for dissolution.

[0047] In dissolving step a), at least the plastic raw material (particularly in the form of one or more plastic raw material streams) and the dissolving solvent (particularly in the form of one or more dissolving solvent streams) are supplied, advantageously via one or more conveying devices. The plastic raw material streams (one or more) may differ from the dissolving solvent streams (one or more). Where appropriate, a portion or all of the plastic raw material may also be supplied to step a) as a mixture with a portion or all of the dissolving solvent, the remainder of the solvent, and / or the remainder of the raw material, or step a) may be supplied separately.

[0048] During the contact of the plastic raw material with the dissolving solvent, the dissolving solvent is advantageously at least partially, preferably entirely, in liquid form, while the plastic raw material containing polymers, particularly thermoplastics, especially polyolefins, can be in solid or liquid form, optionally containing suspended solid particles. The plastic raw material can also optionally be injected into the dissolving apparatus as a mixture with the dissolving solvent in the form of a suspension in the dissolving solvent; the preparation and injection of the suspension can be continuous or intermittent.

[0049] Preferably, step a) includes at least one extruder and a melting device. In this case, the plastic raw material is supplied to the extruder in such a way that at the extruder outlet, at least a portion, preferably all, of the target polymer, particularly the target thermoplastic, and more particularly polyolefin, contained in the raw material is in molten form. The plastic raw material, at least partially in molten form, is then injected into the melting device. The plastic raw material, at least partially in molten form, can also be pumped by a pump specifically designed for viscous fluids, commonly referred to as a melt pump or gear pump. The plastic raw material, at least partially in molten form, can also optionally be filtered at the extruder outlet using a filter device other than the melt pump to remove the coarsest particles; typically, the filter mesh size is from 10 micrometers to 1 millimeter, preferably from 20 to 200 micrometers.

[0050] Preferably, step a) includes an extruder into which the dissolving solvent is injected at several points to promote shearing and thus promote close mixing between the dissolving solvent and the plastic raw material, which helps to dissolve the polymer, especially thermoplastics, and more particularly polyolefins.

[0051] The dissolving solvent used in dissolving step a) is advantageously an organic solvent or a solvent mixture of preferred organic solvents. Preferably, the dissolving solvent is selected from organic solvents, preferably containing one or more hydrocarbons, preferably composed of one or more hydrocarbons, said hydrocarbons having a boiling point of -50°C to 250°C, preferably -15°C to 150°C, preferably 20°C to 110°C. Preferably, the dissolving solvent contains one or more hydrocarbons, preferably composed of one or more hydrocarbons, very preferably one or more alkanes, said hydrocarbons having 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms, very preferably 5 to 7 carbon atoms, such as pentane, hexane, and heptane isomers. Preferably, it is very advantageous to be an organic solvent, preferably a hydrocarbon dissolving solvent having a critical temperature of 90 to 400°C, preferably 130 to 300°C, preferably 180 to 290°C, and a critical pressure of 1.5 to 5.0 MPa absolute pressure, preferably 2.0 to 4.3 MPa absolute pressure, preferably 2.4 to 4.2 MPa absolute pressure. According to one embodiment, the dissolving solvent has a boiling point greater than 70°C, preferably between 80°C and 220°C, and / or the solvent contains, preferably, an alkane having at least seven carbon atoms. According to another preferred embodiment, the dissolving solvent has a boiling point less than 50°C or greater than 150°C.

[0052] Advantageously, dissolution is carried out at a dissolution temperature of 100°C to 300°C and a dissolution pressure of 1.0 to 20.0 MPa absolute. More particularly, throughout step a), the temperature and pressure begin to change from ambient conditions (i.e., the temperature of the plastic raw material is 10 to 30°C and the atmospheric pressure is 1 bar (0.1 MPa)) until the dissolution conditions are reached, more particularly the dissolution temperature and dissolution pressure. Specifically, the dissolution temperature is 100 to 300°C, preferably 150 to 250°C, and the dissolution pressure is 1.0 to 20.0 MPa absolute, preferably 1.5 to 15.0 MPa absolute, and very preferably 2.0 to 10.0 MPa absolute. Very advantageously, at the end of dissolution step a), the stream of dissolved polymer is at the dissolution temperature and dissolution pressure. Preferably, the weight ratio between the plastic raw material and the dissolving solvent is 0.01 to 5.0, preferably 0.05 to 3.0, and more preferably 0.10 to 1.0.

[0053] The temperature in step a) is limited to less than or equal to 300°C, preferably less than or equal to 250°C, to prevent or limit the thermal degradation of the polymer, particularly thermoplastics, and more particularly polyolefins. Preferably, the dissolution temperature is greater than or equal to the melting point of the polymer, particularly thermoplastics, and more particularly polyolefins, to promote their dissolution. Preferably, the temperature in dissolution step a) is less than or equal to the critical temperature of the dissolving solvent to avoid the formation of a supercritical phase that is easily destructive to dissolution during dissolution step a).

[0054] Simultaneously, the dissolution pressure is greater than the saturated vapor pressure of the dissolving solvent at the dissolution temperature, such that the dissolving solvent is at least partially, preferably entirely, in liquid form at the dissolution temperature. Advantageously, the dissolution pressure is greater than or equal to the critical pressure of the dissolving solvent, so that recovery step c) can be carried out, particularly under conditions where at least a portion of the solvent is in a supercritical form, without significantly increasing the pressure between steps a) and c), especially between the outlet of step a) and step c). When the dissolution pressure in step a) is greater than or equal to the critical pressure of the dissolving solvent, the dissolution temperature is less than the critical temperature of the dissolving solvent, so as to maintain the dissolving solvent at least partially in liquid form.

[0055] Advantageously, the dissolution temperature and pressure conditions achieved in step a) are adjusted so that the mixture (dissolved solvent + target polymer) is a single-phase mixture.

[0056] Advantageously, the dissolution step a) is carried out for a residence time of 1 to 600 minutes, preferably 2 to 300 minutes, and more preferably 2 to 180 minutes. The residence time is understood to be the residence time at the dissolution temperature and dissolution pressure, i.e., the time taken in step a) to dissolve the plastic raw material with the dissolving solvent at the dissolution temperature and dissolution pressure.

[0057] Advantageously, the dissolving solvent used in step a) comprises, preferably, a supply of fresh solvent and / or a stream of recycled solvent obtained from the recovery step c).

[0058] Optionally, the treatment method may include an intermediate adsorption step a′) located during or directly downstream of the dissolution step a), and it includes introducing an adsorbent solid (preferably, for example, alumina, silica, silica-alumina, activated carbon, or decolorizing earth) in dispersed particulate form into the crude polymer solution obtained at the end of step a) or optionally during the dissolution step a). The adsorbent solid can then be removed during the washing step b) and / or during one of the optional intermediate purification steps, such as in the optional step E1) for separating insoluble substances. This optional adsorption step a′) in the presence of the adsorbent solid in a separated form allows for optimization of the purification of the polymer solution.

[0059] The crude polymer solution obtained at the end of dissolution step a) contains at least a dissolving solvent, a polymer dissolved in the dissolving solvent, and, in particular, the target polymer that the present invention seeks to recover and purify. Typically, the crude polymer solution also contains soluble impurities and / or suspended insoluble impurities or compounds also dissolved in the dissolving solvent. The crude polymer solution obtained at the end of step a) may also optionally contain polymers other than the target polymer, such as polymers in molten form.

[0060] Optional step E1 for separating insoluble substances

[0061] The processing method may optionally include step E1) of separating insoluble substances by solid-liquid separation, which may be an additional purification step to advantageously obtain at least one clarified polymer solution and at least one insoluble fraction. When incorporated into the method according to the invention, step E1) of separating insoluble substances is located between dissolution step a) and polymer recovery step c), and upstream or downstream of washing step b), preferably upstream of washing step b). The obtained insoluble fraction advantageously contains at least a portion, preferably all, of the insoluble impurities, especially the insoluble impurities suspended in the crude polymer solution obtained from step a).

[0062] Therefore, step E1) of separating insoluble substances allows at least a portion, preferably all, of the particles of the insoluble compound in the dissolving solvent to be removed under the temperature and pressure conditions of step a), which can be suspended in the polymer solution, preferably in the crude polymer solution obtained from step a) or optionally from step a′). The insoluble impurities removed in the optional step E1) of separating insoluble substances are, for example, pigments, mineral compounds, packaging residues (glass, wood, cardboard, paper, aluminum), and insoluble polymers.

[0063] When this separation step E1 is performed, it advantageously allows for the limitation of operational problems in downstream process steps, particularly such as clogging and / or corrosion, while also contributing to the purification of the plastic raw material.

[0064] When incorporated into the method, step E1) of separating the insoluble substance is advantageously carried out at a temperature of 100 to 300°C, preferably 150 to 250°C, and an absolute pressure of 1.0 to 20.0 MPa, preferably 1.5 to 15.0 MPa, and most preferably 2.0 to 10.0 MPa. It is also highly advantageous that step E1) of separating the insoluble substance is optionally carried out at the dissolution temperature and pressure conditions, i.e., at the temperature and pressure conditions at the outlet of step a).

[0065] When incorporated into the method, step E1) of separating insoluble substances preferably supplies a crude polymer solution obtained from step a or optionally from intermediate adsorption step a′). According to another embodiment, step E1) may optionally supply a washed polymer solution obtained from washing step b).

[0066] When incorporated into the method, step E1) advantageously includes a section comprising at least one solid-liquid separation device, such as a separating flask, decanter, centrifugal decanter, centrifuge, filter, sand filter, eddy current separator, electrostatic separator, triboelectric separator, preferably a decanter, filter, sand filter and / or electrostatic separator.

[0067] The removal of insoluble fractions can be facilitated by devices (e.g., conveyors, vibrating tubes, worm gears, extruders, or strippers) used for conveying and / or removing trace amounts of solvent that may be present in the insoluble fraction. Therefore, step E1) may include devices for conveying and / or removing trace amounts of solvent to remove the insoluble fraction.

[0068] According to one specific embodiment of optional step E1), step E1) for separating insoluble substances includes at least two, and typically fewer than five, solid-liquid separation devices connected in series and / or in parallel. The presence of at least two solid-liquid separation devices connected in series allows for improved removal of insoluble substances, while the presence of devices connected in parallel allows for the management of maintenance and / or deblocking operations of said devices.

[0069] Declogging of equipment, particularly electrostatic separators or filters, can be performed using a solvent injected during backflush. The declogging solvent can be an aqueous solution or an organic solution, preferably an organic solvent with the same properties as the organic solvent used in dissolving step a) and / or washing step b). According to one specific embodiment, the declogging solvent has the same properties as the high-density solution used in washing step b).

[0070] Some insoluble compounds, particularly pigments and mineral fillers, can be introduced in the form of particles smaller than 1 μm in size. This is true for titanium dioxide, calcium carbonate, and carbon black, for example. According to one embodiment of optional step E1), step E1) advantageously includes an electrostatic separator, which allows for the efficient removal of at least a portion, preferably all, of the insoluble particles smaller than 1 μm. According to another embodiment of optional step E1), step E1) includes a sand filter to remove particles of varying sizes, particularly those smaller than 1 μm.

[0071] Depending on the properties of the raw material, the polymer solution supplied in step E1) is preferably a crude polymer solution, and may optionally contain a second liquid phase, such as a second liquid phase composed of molten polymer. According to another specific embodiment of optional step E1), step E1) advantageously includes equipment for separating the second liquid phase, preferably by at least one three-phase separator.

[0072] Selecting step b)

[0073] According to the invention, the treatment method includes step b) of washing with a high-density solution to advantageously obtain at least one wash effluent and at least one washed polymer solution. The washed polymer solution obtained at the end of step b) advantageously contains the target polymer that the invention seeks to recover and purify, dissolved in the dissolving solvent. Optionally, it may still contain residual impurities particularly soluble in the dissolving solvent and / or trace amounts of the washing solvent.

[0074] Advantageously, in washing step b), a high-density solution and a polymer solution are supplied, preferably a crude polymer solution obtained from step a) or from an optional intermediate adsorption step a′), or a clarified polymer solution obtained from an optional step E1). The polymer solution supplied in optional step b) may also optionally be a refined polymer solution obtained from an optional adsorption step E3), which is specifically carried out by adding the adsorbent as a mixture with the polymer solution. Preferably, in washing step b), a high-density solution and a polymer solution are supplied, preferably a crude polymer solution obtained from step a) or from an optional intermediate adsorption step a′), or a clarified polymer solution obtained from an optional step E1. The polymer solution supplied in washing step b), more particularly the crude or clarified polymer solution, may contain impurities in the form of suspended insoluble compounds and / or dissolved compounds. These suspended or dissolved compounds can be partially or completely removed during washing step b) by dissolution or precipitation and / or by entrainment in the high-density solution. Therefore, step b) facilitates the treatment of plastic raw materials and, more particularly, the purification of polymer solutions.

[0075] Washing step b) advantageously involves contacting the crude or clarified polymer solution from step b) with a high-density solution. Advantageously, the high-density solution has a higher density than the polymer solution (i.e., a mixture containing at least the target polymer and a dissolving solvent in which the target polymer is dissolved). Specifically, the density of the high-density solution is greater than or equal to 0.85, preferably greater than or equal to 0.9, and more preferably greater than or equal to 1.0. The high-density solution may also advantageously be polar or at least more polar than the dissolving solvent in order to improve the purification efficiency of the polymer solution, particularly for polar impurities.

[0076] The high-density solution can be an aqueous solution, preferably containing at least 50% by weight of water, preferably at least 75% by weight of water, preferably at least 90% by weight of water, and very preferably at least 95% by weight of water. The pH of the aqueous solution can be adjusted with acid or base to promote the dissolution of certain compounds. The high-density solution may also optionally be a solution containing an organic solvent, preferably composed of, an organic solvent such as sulfolane or N-methylpyrrolidone (NMP), selected for its organic solvent, and optionally as a mixture with water. Preferably, the high-density solution in washing step b) is an aqueous solution, preferably containing at least 90% by weight of water, and very preferably at least 95% by weight of water.

[0077] Washing step b) is advantageously carried out at a temperature of 100 to 300°C, preferably 150 to 250°C, and at an absolute pressure of 1.0 to 20.0 MPa, preferably 1.5 to 15.0 MPa, and most preferably 2.0 to 10.0 MPa. It is also highly advantageous that washing step b) is carried out at a dissolution temperature and dissolution pressure.

[0078] Advantageously, the mass ratio between the mass flow rate of the high-density solution and the mass flow rate of the crude or clarified polymer solution supplied in step b) is preferably 0.05 to 20.0, more preferably 0.1 to 10.0, and even more preferably 0.5 to 3.0. Contact between the crude or clarified polymer solution and the high-density solution can be carried out at several points in the equipment used, i.e., by injecting the crude or clarified polymer solution and / or the high-density solution several times along different points in the equipment; the sum of the injected streams is then taken into account when calculating the ratio.

[0079] Step b) may be carried out in a project using one or more washing devices that enable contact with the high-density solution and / or with the separation equipment, thereby allowing the recovery of at least one washing effluent and at least one washed polymer solution. Such devices are well known, such as stirred reactors, static mixers, decanter mixers, two-phase or three-phase separation flasks, co-current or countercurrent washing towers, plate towers, stirred towers, packed towers, pulsed towers, etc., and each type of device may include projects using one or more devices alone or in combination with another type of device.

[0080] According to a preferred embodiment, washing step b) is carried out in a countercurrent washing tower, wherein a high-density solution is injected on one side, preferably into the half of the tower closest to the top, more preferably one-third, and a crude or clarified polymer solution is injected on the other side, preferably into the half of the tower closest to the bottom, more preferably one-third. According to this embodiment, at least one washed polymer solution and at least one wash effluent can be recovered.

[0081] According to a very specific implementation, the stream at the inlet and / or outlet of the washing tower can be separated and injected at several injection points along the tower and / or withdrawn at several withdrawal points along the tower.

[0082] According to another embodiment, the washing step b) is carried out in a mixer-decanter, which includes a stirring mixing zone and a decanting zone, the stirring mixing zone being used to contact the high-density solution with the crude or clarified polymer solution, and the decanting zone allowing the recovery of the washed polymer solution and the wash effluent.

[0083] At the end of washing step b), the obtained wash effluent advantageously contains compounds dissolved in the high-density solvent and / or insoluble compounds entrained in the wash effluent. The wash effluent may be further processed in a washing treatment section to, on the one hand, at least partially separate the dissolved and / or entrained compounds, and optionally purify the wash effluent to obtain a purified high-density solution, and on the other hand, at least partially recycle a portion of the purified wash solution. This washing treatment section may include items from one or more devices well known for solid-liquid separation, such as separation flasks, decanters, centrifugal decanters, centrifuges, or filters. The wash effluent may also be sent outside the process, for example, to a wastewater treatment plant when the high-density solution is an aqueous solution.

[0084] According to one specific embodiment, and where the method according to the invention includes optional step E1), the clogging stream optionally generated in step E1) comprising at least a portion of the insoluble fraction obtained from step E1) is at least partially mixed with the washing effluent to remove the insoluble impurities removed in steps E1) and b) in a common section.

[0085] Optional extraction step E2)

[0086] The method according to the invention may optionally include an extraction step E2), which is carried out by contacting an extraction solvent to obtain at least one extracted polymer solution and at least one waste solvent particularly loaded with impurities. The extracted polymer solution obtained at the end of the optional step E2) advantageously contains the target polymer that the invention seeks to recover and purify, dissolved in the dissolving solvent. Optionally, if step E2) is performed, it may still contain residual impurities particularly soluble in the dissolving solvent and / or trace amounts of washing solvent and / or extraction solvent.

[0087] When incorporated into the method according to the invention, the extraction step E2) is advantageously located between the washing step b) and the polymer recovery step c). In the optional extraction step E2), a polymer solution, preferably the washed polymer solution obtained from step b) or optionally the purified polymer solution obtained from the optional adsorption step E3), and an extraction solvent are advantageously supplied.

[0088] The polymer solution supplied in optional step E2), preferably the washed polymer solution obtained from step b) or the purified polymer solution obtained from optional step E3), may optionally contain dissolved compounds or dissolved impurities. These dissolved compounds can be partially or completely removed during extraction step E2) by contact with the extraction solvent. Most advantageously, the combination of washing step b) and extraction step E2) allows for improved purification of the polymer solution by utilizing the affinity of impurities for both the high-density solvent of optional polarity and the extraction solvent.

[0089] Optional extraction step E2) advantageously involves at least one extraction section, preferably one to five extraction sections, and most preferably one extraction section. Optional extraction step E2) is preferably carried out at a temperature of 100 to 300°C, preferably 150 to 250°C. Optional extraction step E2) is preferably carried out at a pressure of 1.0 to 20.0 MPa absolute pressure, preferably 1.5 to 15.0 MPa absolute pressure, and most preferably 2.0 to 10.0 MPa absolute pressure. According to a preferred embodiment of optional step E2), extraction step E2) is carried out at temperature and pressure conditions different from those of step a).

[0090] The mass ratio between the mass flow rate of the extraction solvent and the mass flow rate of the polymer solution supplied in step E2) is advantageously from 0.05 to 20.0, preferably from 0.1 to 10.0, and more preferably from 0.2 to 5.0. Contact between the polymer solution supplied in optional step E2) and the extraction solvent can be carried out at several points within the extraction section, i.e., by injecting the polymer solution and / or extraction solvent several times at different points along the extraction section; the total amount of injected streams is then taken into account when calculating the ratio.

[0091] The extraction solvent used in the optional extraction step E2) is advantageously an organic solvent or a solvent mixture of preferred organic solvents. Preferably, the extraction solvent is selected from organic solvents, preferably containing one or more hydrocarbons, preferably composed of one or more hydrocarbons, said hydrocarbons having a boiling point of -50°C to 250°C, preferably -15°C to 150°C, preferably 20°C to 110°C. Preferably, the extraction solvent contains one or more hydrocarbons, preferably composed of one or more hydrocarbons, very preferably one or more alkanes, said hydrocarbons having 3 to 12 carbon atoms, preferably 4 to 8 carbon atoms, very preferably 5 to 7 carbon atoms, such as pentane, hexane, and heptane isomers. Preferably, the critical temperature of the extraction solvent (preferably an organic solvent, preferably a hydrocarbon) is 90 to 400°C, preferably 130 to 300°C, preferably 180 to 290°C, and the critical pressure of the extraction solvent is 1.5 to 5.0 MPa absolute pressure, preferably 2.0 to 4.3 MPa absolute pressure, preferably 2.4 to 4.2 MPa absolute pressure. According to one embodiment, the extraction solvent has a boiling point greater than 70°C, preferably between 80°C and 220°C, and / or the solvent contains at least 7 carbon atoms. According to another preferred embodiment, the extraction solvent has a boiling point less than 50°C or greater than 150°C.

[0092] Very preferably, the extraction solvent used in optional step E2) is the same solvent as the dissolving solvent used in step a), optionally in a different physical state (e.g., the extraction solvent is in a supercritical form relative to the liquid form of the dissolving solvent), in order to facilitate solvent management, especially their purification and recycling, particularly recycling to the dissolving step a) and optionally to the extraction step E2). Another advantage of using the same dissolving and extraction solvents in the same or different physical states is that, in addition to facilitating the technical management of the solvents involved in the method according to the invention, particularly the recovery, treatment and recycling of the solvents, they also limit energy consumption and, in particular, the costs arising from the treatment and purification of the solvents.

[0093] Optional step E2) may include one or more extraction sections that enable contact with an extraction solvent and / or with a separation device for recovering at least one waste solvent, particularly a waste solvent loaded with impurities, and the extracted polymer solution. Such equipment is well-known, such as stirred reactors, static mixers, decanters, two-phase or three-phase separation flasks, co-current or countercurrent scrubbing columns, plate columns, stirred columns, packed columns, pulse columns, etc., and each type of equipment may include one or more items used alone or in combination with another type of equipment.

[0094] According to a preferred embodiment of optional step E2), the extraction is carried out in a countercurrent extraction column, wherein the extraction solvent is injected on one side and the polymer solution supplied in step E2) is injected on the other. According to this embodiment, at least one extracted polymer solution can be recovered, and waste solvent, especially that loaded with impurities, can also be recovered. Preferably, the polymer solution supplied in step E2) is injected into the column to the half closest to the top of the countercurrent extraction column, preferably one-third, while the extraction solvent is injected into the half closest to the bottom of the countercurrent extraction column, preferably one-third.

[0095] The stream at the inlet and / or outlet of the countercurrent extraction column can be separated at several injection and / or extraction points along the column.

[0096] According to another embodiment, the extraction is carried out in a mixer-decanter, which advantageously includes a stirring mixing zone and a decanting zone. The stirring mixing zone is used to contact the extraction solvent and the polymer solution, preferably a washed polymer solution or optionally a purified polymer solution, and the decanting zone allows for the recovery of the extracted polymer solution on the one hand and the recovery of the waste solvent on the other.

[0097] According to a preferred embodiment of optional step E2), step E2) involves a liquid / liquid extraction section. In this embodiment, the extraction solvent is preferably selected from pentane, hexane, and heptane isomers, more preferably from pentane and hexane isomers, and very preferably from pentane isomers. Preferably, the liquid / liquid extraction section is operated at 100°C to 300°C, preferably 150°C to 250°C, and at a pressure of 1.0 to 20.0 MPa absolute, preferably 1.5 to 15.0 MPa absolute, and very preferably 2.0 to 10.0 MPa absolute. In any case, in this embodiment, the temperature and pressure conditions are adjusted such that the extraction solvent is in liquid form, and the dissolving solvent itself is also preferably in liquid form. It is highly advantageous that liquid / liquid extraction, particularly when the extraction solvent and the dissolving solvent are the same, is carried out under temperature and pressure conditions different from the dissolution conditions achieved in step a), particularly at temperatures above the dissolution temperature and / or at pressures below the dissolution pressure, thereby taking place in the two-phase region of the respective polymer-solvent mixture phase diagram.

[0098] According to another preferred embodiment of optional step E2), step E2) includes an extraction section under specific temperature and pressure conditions, wherein the extraction solvent is advantageously at least partially in a supercritical form. Such extraction can be referred to as supercritical extraction. In this embodiment, extraction is carried out by contacting the polymer solution, preferably a washed or optionally purified polymer solution, with the extraction solvent, advantageously at temperature and pressure conditions that allow obtaining a supercritical phase consisting mainly (i.e., preferably at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight) of the extraction solvent. In other words, in this embodiment, extraction is carried out by contacting the polymer solution, preferably a washed or purified polymer solution, with an extraction solvent that is at least partially, preferably entirely, in a supercritical form. Such a supercritical extraction step E2) advantageously allows for the efficient purification of the polymer solution, especially due to the very high affinity of organic impurities such as some additives, particularly certain dyes, plasticizers, etc., for the supercritical phase. Using a supercritical form of extraction solvent also allows for a significant density difference to be generated between the supercritical phase and the liquid form of the polymer solution, which facilitates separation between the supercritical and liquid phases by decantation, and thus aids in the purification of the polymer solution.

[0099] In this particularly preferred embodiment, the optional extraction step E2) uses an extraction solvent having a critical temperature preferably from 130 to 300°C and preferably from 180 to 290°C, and a critical pressure preferably from 2.0 to 4.3 MPa and preferably from 2.4 to 4.2 MPa. Most advantageously, in such a supercritical extraction step E2), the extraction solvent is selected from hydrocarbons preferably containing 4 to 8 carbon atoms, preferably 5 to 7 carbon atoms. The extraction solvent used for supercritical extraction can be, for example, a pentane isomer, a hexane isomer, a heptane isomer, or cyclopentane, cyclohexane, or methylcyclopentane.

[0100] Advantageously, the optional supercritical extraction step E2) is carried out at a temperature preferably from 150°C to 300°C, more preferably from 180°C to 280°C, and at a pressure preferably from 2.0 to 20.0 MPa absolute, more preferably from 2.0 to 15.0 MPa absolute, and very preferably from 3.0 to 10.0 MPa absolute. In any case, in this embodiment, the temperature and pressure conditions are adjusted, particularly in the conditioning section included in the extraction step E2) upstream of the extraction section, such that the extraction solvent is at least partially in a supercritical form within the extraction section.

[0101] In a highly preferred embodiment of optional step E2), the extraction step E2) involves supercritical extraction, and the extraction solvent is the same as the dissolving solvent, except that the extraction solvent is at least partially in the supercritical phase. In this highly advantageous case of supercritical extraction, the dissolving solvent can be made to be at least partially in a supercritical form, advantageously optimizing decantation during the extraction process, more particularly at each extraction phase or plateau between the liquid phase and the supercritical phase, thereby maximizing purification.

[0102] Advantageously, at the end of extraction step E2), the resulting waste solvent is particularly loaded with impurities. It can be reprocessed in the organic treatment section such that, on the one hand, the impurities can be at least partially separated and the solvent purified to obtain a purified extraction solvent; on the other hand, at least a portion of the purified extraction solvent can be recycled to the inlet of optional extraction step E2), and / or, if the dissolving solvent and extraction solvent are the same, recycled to the inlet of dissolution step a). The waste solvent can be treated according to any method known to those skilled in the art, such as one or more of distillation, evaporation, extraction, adsorption, crystallization, and precipitation of insoluble substances, or by purging.

[0103] Optional adsorption step E3)

[0104] The processing method may also optionally include an adsorption step E3), which is located between the dissolution step a) and the polymer recovery step c). Depending on the quality of the starting plastic raw material and the impurities it contains, it may be advantageous to complete the purification of the polymer solution with the optional adsorption step E3), so that at least one purified polymer solution can be obtained.

[0105] When incorporated into the method according to the invention, the adsorption step E3) is carried out downstream of the dissolution step a) and upstream of the polymer recovery step c), advantageously upstream or downstream of the washing step b). Optionally, the adsorption step E3) may be carried out upstream or downstream of the optional extraction step E2).

[0106] The optional adsorption step E3) advantageously comprises an adsorption section operating in the presence of at least one adsorbent, preferably a solid, particularly in the form of a fixed bed, an entrained bed (or slurry, i.e., in the form of particles introduced into and entrained by the stream to be purified), or a fluidized bed. The adsorption section advantageously operates in the presence of at least one adsorbent, preferably alumina, silica, silica-alumina, activated carbon, or decolorizing clay, preferably in the form of a fixed bed or an entrained bed, and the circulation of the stream can be ascending or descending. When the method according to the invention includes an optional adsorption step E3) upstream of washing step b), the adsorption section preferably operates in the presence of an adsorbent in the form of an entrained bed (i.e., in the form of dispersed particles introduced into the polymer solution). When the method according to the invention includes an adsorption step E3) downstream of washing step b), the adsorption section is very preferably operated in the presence of an adsorbent in the form of a fixed bed.

[0107] The optional adsorption step E3) is advantageously carried out at a temperature of 100 to 300°C, preferably 150 to 250°C, and at a pressure of 1.0 to 20.0 MPa absolute, preferably 1.5 to 15.0 MPa absolute, and most preferably 2.0 to 10.0 MPa absolute. Very advantageously, step E3) is carried out at the dissolution temperature and pressure conditions, i.e., at the dissolution temperature and pressure reached in step a). Preferably, in step E3), the space velocity (or HSV), which corresponds to the ratio between the volumetric flow rate of the polymer solution supplied in step E3) and the volume of the adsorbent, is 0.05 to 10 h⁻¹. -1 Preferably 0.1 to 5.0 h -1 .

[0108] According to one specific embodiment of optional step E3), the adsorption section may include one or more adsorbent fixed beds, for example, in the form of an adsorption tower containing said adsorbent, preferably at least two adsorption towers, more preferably two to four adsorption towers. When the adsorption section includes two adsorption towers, one operating mode may be a mode known in technical terms as “swing” operation, where one tower is online, i.e., in use, while the other tower is on standby. When the adsorbent in the online tower runs out, that tower is isolated, and the standby tower is brought online, i.e., put into use. The used adsorbent can then be regenerated in situ and / or replaced with fresh adsorbent, so that once the other tower is isolated, the tower containing the aforementioned adsorbent can be brought online again.

[0109] Another operating mode of this specific embodiment, including step E3) comprising one or more adsorbent fixed beds, is to have at least two towers operating in series. When the adsorbent in the first tower is depleted, the first tower is isolated, and the used adsorbent is regenerated in situ or replaced with fresh adsorbent. The last tower is then brought back online, and so on. This operating mode is called a displaceable mode, or PRS for displaceable reactor systems, or, according to the specialized terminology, “lead and lag.” The combination of at least two adsorption towers allows for overcoming the potential and possible rapid adsorbent poisoning and / or clogging due to the combined effects of impurities, contaminants, and insoluble substances that may be present in the stream to be treated. This is because the presence of at least two adsorption towers facilitates adsorbent replacement and / or regeneration, and advantageously allows for cost control and limitation of adsorbent consumption without halting the process.

[0110] Advantageously, the combination of washing step b) and optional adsorption step E3) enables improved purification of the polymer solution by utilizing the affinity of residual impurities for both the high-density solvent and the adsorbent solid.

[0111] According to another embodiment, the adsorption section of optional step E3) may involve adding adsorbent particles to the polymer solution, particularly a crude polymer solution, the particles being separated from the polymer solution by a step of removing the adsorbent particles downstream of the adsorption section, for example, during washing step b) if optional step E3) is upstream of step b). This embodiment of optional adsorption step E3) by introducing adsorbent particles, followed by solid / liquid separation, advantageously corresponds to the optional intermediate adsorption step a′ described above in this specification.

[0112] Step c) of polymer recycling

[0113] According to the present invention, the method includes step c) of recovering the polymer to obtain at least one solvent fraction and at least one purified polymer fraction.

[0114] Polymer recovery step c) advantageously includes at least one solvent recovery section, preferably one to five solvent recovery sections. In polymer recovery step c), a washed polymer solution or optionally an extracted or purified polymer solution is supplied.

[0115] Therefore, polymer recovery step c) primarily involves at least partially, preferably substantially, separating the solvent(s), particularly the dissolving solvent and optionally the washing solvent, or even the extraction solvent, contained in the polymer solution supplied in step c) (i.e., the washed polymer solution or optionally the extracted polymer solution or the purified polymer solution), in order to recover the polymer that is at least partially, preferably substantially, and preferably entirely free of the dissolving solvent and (one or more) other solvents that may still be present in the polymer solution supplied in step c). The term "substantially" should be understood to mean at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, and very preferably at least 95% by weight, relative to the weight of the solvent(s) contained in the polymer solution supplied in step c), particularly the dissolving solvent and optionally the washing solvent contained in the polymer solution supplied in step c). Any method known to those skilled in the art for separating the solvent from the polymer can be used, especially any method capable of causing a phase change in the polymer or (one or more) solvents. The (one or more) solvents can be separated, for example, by evaporation, stripping, layering, density difference (especially decantation or centrifugation), etc.

[0116] The obtained purified polymer fraction may correspond to a concentrated polymer solution or to purified polymer in solid form. Preferably, polymer recovery step c) further includes a conditioning section for conditioning the polymer in solid form, more particularly for polymer in solid particulate form.

[0117] Polymer recovery step c) also involves at least partially, preferably substantially and preferably entirely, the recovery of one or more solvents contained in the washed polymer solution or optionally extracted or purified polymer solution of supply step c), particularly the dissolving solvent and optionally the washing solvent, or even the extraction solvent. Polymer recovery step c) also optionally involves purifying and recycling the recovered solvent fraction, particularly upstream of dissolving step a) and / or washing step b) and / or extraction step E2). The term "substantially" should be understood to mean at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, and very preferably at least 95% by weight, relative to the weight of one or more solvents contained in the washed polymer solution or optionally extracted or purified polymer solution of supply step c).

[0118] The polymer recovery step c) advantageously includes at least one solvent recovery section at a temperature of 0 to 350°C, preferably 5 to 300°C, preferably 10 to 250°C, and at an absolute pressure of 0.1 to 20.0 MPa, preferably 0.1 to 15.0 MPa, very preferably 0.1 to 10.0 MPa.

[0119] Advantageously, polymer recovery step c) includes at least one solvent recovery section, each preferably comprising equipment operating at different temperatures and pressures to obtain at least one solvent fraction and at least one purified polymer fraction. In the processing method according to the invention, particularly when several different solvents are used in dissolution step a) and washing step b) and optionally extraction step E2), step c) may include several solvent recovery sections, such as two, three, or four, to recover various solvents separately, sequentially, and / or successively, particularly dissolution solvents, washing solvents, and optionally extraction solvents.

[0120] According to one specific embodiment of the present invention, the method of the present invention advantageously includes, sequentially or simultaneously:

[0121] - Solvent recovery section c1), in which the polymer solution is preferably heated to a temperature above the melting point of the polymer to obtain a solvent fraction and a purified polymer fraction.

[0122] - Conditioning section c2), in which the purified polymer fraction, which is advantageously separated from (one or more) solvents, is advantageously cooled to a temperature below the polymer melting point to obtain a fraction containing polymer in solid form.

[0123] According to a preferred embodiment of the invention, step c) comprises a section of step c) where the solvent is recovered under temperature and pressure conditions adjusted to be supercritical (i.e., above the critical point of the solvent(one or more) to be separated, particularly above the critical point of the dissolving solvent), advantageously allowing for the easy separation and recovery of at least a portion of the solvent, particularly the dissolving solvent. In this embodiment, the solvent recovery section specifically comprises a fluid system consisting of a supercritical phase primarily containing the solvent, particularly the dissolving solvent, and a liquid phase containing the polymer. The term "primarily" herein refers to at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, and very preferably at least 95% by weight, relative to the weight of the stream under consideration (i.e., the supercritical phase). This separation can thus be referred to as supercritical separation of the solvent(one or more). Supercritical separation of the solvent(one or more) allows for the efficient separation of the solvent(one or more), particularly the dissolving solvent, on the one hand, and the efficient separation of the polymer or optionally concentrated polymer solutions on the other hand, advantageously achieved through a significant difference in density between the two phases. Furthermore, supercritical separation of (one or more) solvents is advantageous over simple evaporation of the solvent, enabling a significant reduction in energy and environmental costs, since there is no latent heat of vaporization during the process of entering the supercritical state.

[0124] According to one specific embodiment of the present invention, at least a portion of the purified polymer fraction obtained at the end of step c) can be recycled to the dissolution step a) to undergo the processing cycle again, thereby improving the polymer purification efficiency.

[0125] Advantageously, the solvent fraction recovered at the end of step c) can be processed in an organic treatment section located at the end of step c) to purify it and obtain a purified solvent, particularly a purified dissolving solvent, so that it can advantageously be recycled to dissolving step a) and / or optionally to washing step b) and / or optional extraction step E2). The optional organic treatment section at the end of step c) can be performed using any method known to those skilled in the art, such as one or more methods selected from distillation, evaporation, liquid-liquid extraction, adsorption, crystallization and precipitation of insoluble substances, or by rinsing.

[0126] Therefore, the method according to the invention enables the acquisition of purified streams of polymers, particularly thermoplastics, and more particularly polyolefins, from plastic waste, which can be used in any application, for example, as a substitute for the same polymer in its virgin form. Thus, the purified polymer streams obtained by the method according to the invention, i.e., the purified polymer fractions, have sufficiently low impurity content to be usable in any application.

[0127] According to a preferred embodiment of the present invention, a method for processing plastic raw materials includes the following steps, preferably consisting of the following steps:

[0128] - Step a) involves dissolving the polymer in a solvent to obtain at least one crude polymer solution;

[0129] - Step b) involves washing the crude polymer solution by contacting it with a high-density solution to obtain at least one wash effluent and at least one washed polymer solution;

[0130] - Extracting the washed polymer solution with an extraction solvent, preferably including supercritical extraction, to obtain at least one extracted polymer solution and at least one waste solvent (step E2); and

[0131] - Step c) involves recovering the polymer from the extracted polymer solution, preferably including supercritical separation of one or more solvents, particularly supercritical separation of the dissolving solvent, to obtain solvent fractions and purified polymer fractions.

[0132] The dissolving solvent and the extraction solvent are preferably the same.

[0133] According to another preferred embodiment of the present invention, a method for processing plastic raw materials includes the following steps, preferably consisting of the following steps:

[0134] - Step a) involves dissolving the polymer in a solvent to obtain at least one crude polymer solution;

[0135] - Step E1: Separating insoluble substances supplied along with the crude polymer solution to obtain at least one clarified polymer solution and at least one insoluble fraction;

[0136] - Step b) involves washing the clarified polymer solution by contacting it with a high-density solution to obtain at least one wash effluent and at least one washed polymer solution;

[0137] - Extracting the washed polymer solution with an extraction solvent, preferably including supercritical extraction, to obtain at least one extracted polymer solution and at least one waste solvent (step E2); and

[0138] - Step c) involves recovering the polymer from the extracted polymer solution, preferably including supercritical separation of one or more solvents to obtain solvent fractions and purified polymer fractions;

[0139] The dissolving solvent and the extraction solvent are preferably the same.

[0140] According to a preferred alternative embodiment of the present invention, a method for processing plastic raw materials includes the following steps, preferably consisting of the following steps:

[0141] - Step a) involves dissolving the polymer in a solvent to obtain at least one crude polymer solution;

[0142] - Step b) involves washing the crude polymer solution by contacting it with a high-density solution to obtain at least one wash effluent and at least one washed polymer solution;

[0143] - Step E1: Separating insoluble substances supplied along with the washed polymer solution to obtain at least one clarified polymer solution and at least one insoluble fraction;

[0144] - Extracting the clarified polymer solution with an extraction solvent, preferably including supercritical extraction, to obtain at least one extracted polymer solution and at least one waste solvent (step E2); and

[0145] - Step c) involves recovering the polymer from the extracted polymer solution, preferably including supercritical separation of one or more solvents to obtain solvent fractions and purified polymer fractions;

[0146] The dissolving solvent and the extraction solvent are preferably the same.

[0147] According to another specific embodiment of the present invention, a method for processing plastic raw materials includes the following steps, preferably consisting of the following steps:

[0148] - Step a) involves dissolving the polymer in a solvent to obtain at least one crude polymer solution;

[0149] - Step E1: Separating insoluble substances supplied along with the crude polymer solution to obtain at least one clarified polymer solution and at least one insoluble fraction;

[0150] - Step b) involves washing the clarified polymer solution by contacting it with a high-density solution to obtain at least one wash effluent and at least one washed polymer solution;

[0151] - Extract the washed polymer solution with an extraction solvent, preferably including supercritical extraction, to obtain at least one extracted polymer solution and at least one waste solvent (step E2);

[0152] - An adsorption step E3) in which the extracted polymer solution is contacted with an adsorbent, preferably an adsorbent in a fixed bed, to obtain at least one purified polymer solution; and

[0153] - Step c) involves recovering the polymer from the purified polymer solution obtained in step E3), preferably including supercritical separation of one or more solvents to obtain solvent fractions and purified polymer fractions.

[0154] The dissolving solvent and the extraction solvent are preferably the same.

[0155] According to another specific embodiment of the present invention, a method for processing plastic raw materials includes the following steps, preferably consisting of the following steps:

[0156] - Step a) involves dissolving the polymer in a solvent to obtain at least one crude polymer solution;

[0157] - Step b) involves washing the crude polymer solution by contacting it with a high-density solution to obtain at least one wash effluent and at least one washed polymer solution;

[0158] - Step E1: Separating insoluble substances supplied along with the washed polymer solution to obtain at least one clarified polymer solution and at least one insoluble fraction;

[0159] - Extract the clarified polymer solution with an extraction solvent, preferably including supercritical extraction, to obtain at least one extracted polymer solution and at least one waste solvent (step E2);

[0160] - An adsorption step E3) in which the extracted polymer solution is contacted with an adsorbent, preferably an adsorbent in a fixed bed, to obtain at least one purified polymer solution; and

[0161] - Step c) involves recovering the polymer from the purified polymer solution obtained in step E3), preferably including supercritical separation of one or more solvents to obtain solvent fractions and purified polymer fractions.

[0162] The dissolving solvent and the extraction solvent are preferably the same.

[0163] The following embodiments and accompanying drawings illustrate the present invention, particularly specific implementations of the invention, but do not limit its scope.

[0164] List of Attachments

[0165] about Figures 1 to 3 The information on the elements referenced herein enables a better understanding of the invention, but the invention is not limited to... Figures 1 to 3 The specific implementation schemes described herein. The various implementation schemes presented may be used individually or in combination with each other, without any limitation on the combination.

[0166] Figure 1 A flowchart illustrating one embodiment of the method of the present invention includes:

[0167] - Step a) involves dissolving the plastic raw material 1 containing the polymer in a dissolving solvent 2 to obtain a crude polymer solution 3;

[0168] - Step b) involves washing the crude polymer solution 3 with a high-density solution 6, preferably an aqueous solution 6, to obtain a washed polymer solution 8 and a wash effluent 7.

[0169] - Step c) recovers the polymer from the washed polymer solution 8 obtained in step b) to obtain solvent fraction 13 and purified polymer fraction 14.

[0170] Figure 2 yes Figure 1 Variations of embodiments of the method according to the present invention, as shown in the figure, include:

[0171] - Step a) involves dissolving the plastic raw material 1 containing the polymer in a dissolving solvent 2 to obtain a crude polymer solution 3;

[0172] - Step E1: Separating the insoluble substances supplied along with the crude polymer solution 3 to obtain the clarified polymer solution 5 and the insoluble fraction 4;

[0173] - Step b) involves washing the clarified polymer solution 5 by contacting it with a high-density solution 6 to obtain a wash effluent 7 and a washed polymer solution 8;

[0174] - Step E2: Extract the washed polymer solution 8 with extraction solvent 9 to obtain the extracted polymer solution 11 and waste solvent 10;

[0175] -Adsorption step E3: obtaining a purified polymer solution 12 by contacting the extracted polymer solution 11 with an adsorbent.

[0176] - Step c) recovers the polymer from the purified polymer solution 12 obtained in step E3) to obtain solvent fraction 13 and purified polymer fraction 14.

[0177] Figure 3 yes Figure 2 The variations of the embodiments of the method according to the present invention are shown in the figure. Figure 3 In the embodiment shown, the method includes an intermediate step a′) between step a) and step E1). The crude polymer solution 3 is contacted with an adsorbent in dispersed solid form to obtain a polymer solution 21 containing a suspended adsorbent, which is then supplied to separation step E1). The adsorbent previously introduced in step a′) is then separated and removed in an insoluble fraction 4.

[0178] Figures 1 to 3 Only the main steps involving the primary logistics are shown to provide a better understanding of the invention. It should be clearly understood that all the equipment required for operation (containers, pumps, exchangers, furnaces, towers, etc.) are present, even if they are not shown.

[0179] Example

[0180] Example 1 (according to the present invention)

[0181] 250 ml of n-pentane and 23 g of 5 mm diameter polypropylene-based pinkish-purple bead-like plastic material were introduced into a 500 ml autoclave equipped with a stirrer.

[0182] The autoclave was then sealed and heated at 180°C at a rate of 2°C / min while stirring at 500 rpm. Once the temperature of 180°C was reached, it was maintained at this temperature and stirred for 3 hours under an autogenous pressure of 26 bar (or 2.6 MPa). After 3 hours, all the polypropylene dissolved in n-pentane. A highly colored liquid phase, i.e., the crude polymer solution, was obtained.

[0183] 125 ml of water was then added to the system, while maintaining the temperature at 180°C, the pressure at 2.6 MPa, and the stirring at 500 rpm. These temperature, pressure, and stirring conditions were maintained for 5 minutes, after which stirring was stopped. Following the cessation of stirring, the system was then separated by sedimentation. After standing for 5 minutes, the fluid system within the autoclave separated by sedimentation to form two phases at the end of the washing step. The upper phase, containing the polymer and corresponding to the washed polymer solution, showed less discoloration compared to the mixture before the washing step.

[0184] Take 15 ml of the washed polymer solution and place it in a crystallizing dish. Then place the crystallizing dish in an oven at 180°C and atmospheric pressure, while purging with nitrogen for 6 hours.

[0185] Then, a slightly pinkish white solid was obtained in a crystallizing dish.

[0186] Example 2 (not based on the present invention)

[0187] 250 ml of n-pentane and 23 g of 5 mm diameter polypropylene-based pinkish-purple bead-like plastic material were introduced into a 500 ml autoclave equipped with a stirrer.

[0188] The autoclave was then sealed and heated at 180°C at a rate of 2°C / min while stirring at 500 rpm. Once the temperature of 180°C was reached, it was maintained at this temperature and stirred for 3 hours under an autogenous pressure of 2.6 MPa. After 3 hours, all the polypropylene dissolved in n-pentane. A highly colored liquid phase, i.e., the crude polymer solution, was obtained.

[0189] Take 15 ml of the crude polymer solution and place it in a crystallizing dish. Then place the crystallizing dish in an oven at 180°C and atmospheric pressure, while purging with nitrogen for 6 hours.

[0190] A pinkish-purple solid was then obtained in a crystallizing dish. The obtained solid had a color similar to that of the beads from the initial raw material.

Claims

1. Methods for processing plastic raw materials, including: a) A dissolution step, which involves contacting the plastic raw material with a dissolving solvent containing hydrocarbons at a dissolution temperature of 150°C to 250°C and a dissolution pressure of 1.0 to 20.0 MPa absolute pressure to obtain at least one crude polymer solution. b) A washing step, which is carried out by contacting the crude polymer solution obtained from step a) with a high-density solution having a density greater than or equal to 0.85 at a temperature of 150°C to 250°C, a pressure of 1.0 to 20.0 MPa absolute, and at a mass ratio between the mass flow rate of the high-density solution and the mass flow rate of the crude polymer solution supplied in step b) of 0.05 to 20.0, to obtain at least one washed polymer solution and at least one washed effluent; and subsequently c) A step of recovering the polymer to obtain at least one solvent fraction and at least one purified polymer fraction.

2. The method according to claim 1, wherein the dissolving solvent is selected from organic solvents with a boiling point of -50°C to 250°C.

3. The method according to claim 1, wherein the dissolving solvent is selected from organic solvents with a boiling point of -15°C to 150°C.

4. The method according to claim 1, wherein the dissolving solvent is selected from organic solvents with a boiling point of 20°C to 110°C.

5. The method according to any one of claims 1 to 4, wherein the dissolving solvent has a critical temperature of 90 to 400°C and a critical pressure of 1.5 to 5.0 MPa absolute pressure.

6. The method according to claim 5, wherein the dissolving solvent has a critical temperature of 180 to 290°C.

7. The method of claim 5, wherein the dissolving solvent has a critical pressure of 2.4 to 4.2 MPa absolute pressure.

8. The method according to any one of claims 1-4, wherein the dissolution pressure is 1.5 to 15.0 MPa absolute pressure.

9. The method according to claim 8, wherein the dissolution pressure is 2.0 to 10.0 MPa absolute pressure.

10. The method according to any one of claims 1 to 4, wherein the high-density solution used in step b) has a density greater than or equal to 0.

9.

11. The method of claim 10, wherein the high-density solution used in step b) has a density greater than or equal to 1.

0.

12. The method according to any one of claims 1 to 4, wherein the high-density solution used in step b) is an aqueous solution containing at least 50% by weight of water.

13. The method of claim 12, wherein the aqueous solution comprises at least 75% by weight water.

14. The method of claim 12, wherein the aqueous solution comprises at least 95% by weight water.

15. The method according to any one of claims 1 to 4, wherein the washing step b) is performed at the dissolution temperature and the dissolution pressure.

16. The method according to any one of claims 1 to 4, wherein the polymer recovery step c) comprises a solvent recovery section at a temperature of 0 to 350°C and a pressure of 0.1 to 20.0 MPa absolute pressure.

17. The method of claim 16, wherein the polymer recovery step c) comprises a solvent recovery section at a temperature of 10 to 250°C.

18. The method of claim 16, wherein the polymer recovery step c) comprises a solvent recovery section at a pressure of 0.1 to 10.0 MPa absolute pressure.

19. The method according to any one of claims 1 to 4, wherein the polymer recovery step c) comprises at least one solvent recovery section under temperature and pressure conditions adjusted to be under supercritical conditions of the dissolved solvent.

20. The method according to any one of claims 1 to 4, comprising an extraction step E2, which is carried out by contacting a washed polymer solution with an extraction solvent at a temperature of 100°C to 300°C and a pressure of 1.0 to 20.0 MPa absolute pressure at a mass ratio between the mass flow rate of the extraction solvent and the mass flow rate of the washed polymer solution of 0.05 to 20.0, to obtain at least one extracted polymer solution and at least one waste solvent.

21. The method of claim 20, wherein the extraction solvent is an organic solvent having a critical temperature of 90 to 400°C.

22. The method of claim 20, wherein the extraction solvent is an organic solvent having a critical temperature of 180 to 290°C.

23. The method of claim 20, wherein the extraction solvent is an organic solvent having a critical pressure of 1.5 to 5.0 MPa absolute pressure.

24. The method of claim 20, wherein the extraction solvent is an organic solvent having a critical pressure of 2.4 to 4.2 MPa absolute pressure.

25. The method of claim 20, wherein the extraction solvent is the same as the dissolving solvent and is at least partially in a supercritical form.

26. The method according to any one of claims 1 to 4, comprising step E1) separating insoluble substances, which is carried out by solid-liquid separation at a temperature of 100°C to 300°C and a pressure of 1.0 to 20.0 MPa absolute pressure, said step E1) being located between said dissolution step a) and said polymer recovery step c), and upstream or downstream of said washing step b).

27. The method of claim 26, wherein step E1) of separating insoluble substances comprises an electrostatic separator and / or a filter and / or a sand filter.

28. The method according to any one of claims 1 to 4, comprising an adsorption step E3) located between the dissolution step a) and the polymer recovery step c), and comprising an adsorption section operated in the presence of at least one adsorbent at a temperature of 100 to 300°C and a pressure of 1.0 to 20.0 MPa absolute pressure.

29. The method according to any one of claims 1 to 4, comprising: a) A dissolution step, which involves contacting the plastic raw material with a dissolving solvent containing hydrocarbons at a dissolution temperature of 150°C to 250°C and a dissolution pressure of 1.0 to 20.0 MPa absolute pressure to obtain at least one crude polymer solution. b) A washing step, which is carried out by contacting the crude polymer solution obtained from step a) with a high-density solution having a density greater than or equal to 0.85 at a temperature of 150°C to 250°C, a pressure of 1.0 to 20.0 MPa absolute, and a mass ratio between the mass flow rate of the high-density solution and the mass flow rate of the crude polymer solution of 0.05 to 20.0, to obtain at least one washed polymer solution and at least one washed effluent; E2) An extraction step, which is carried out by contacting the washed polymer solution obtained from step b) with an extraction solvent at a temperature of 100°C to 300°C, at a pressure of 1.0 to 20.0 MPa absolute pressure, and at a mass ratio between the mass flow rate of the extraction solvent and the mass flow rate of the washed polymer solution of 0.05 to 20.0, to obtain at least one extracted polymer solution and at least one waste solvent. and subsequently c) A polymer recovery step to obtain at least one solvent fraction and at least one purified polymer fraction.

30. The method of claim 29, wherein the high-density solution in step b) is an aqueous solution.

31. The method according to any one of claims 1 to 4, comprising: a) A dissolution step, which involves contacting the plastic raw material with a dissolving solvent containing hydrocarbons at a dissolution temperature of 150°C to 250°C and a dissolution pressure of 1.0 to 20.0 MPa absolute pressure to obtain at least one crude polymer solution. b) A washing step, which is carried out by contacting the crude polymer solution obtained from step a) with a high-density solution having a density greater than or equal to 0.85 at a temperature of 150°C to 250°C, a pressure of 1.0 to 20.0 MPa absolute, and a mass ratio between the mass flow rate of the high-density solution and the mass flow rate of the crude polymer solution of 0.05 to 20.0, to obtain at least one washed polymer solution and at least one washed effluent; E3) An adsorption step, which supplies the washed polymer solution obtained from step b), and includes an adsorption section operated in the presence of at least one adsorbent at a temperature of 100°C to 300°C and a pressure of 1.0 to 20.0 MPa absolute pressure to obtain at least one purified polymer solution; and subsequently c) A polymer recovery step to obtain at least one solvent fraction and at least one purified polymer fraction.

32. The method according to claim 31, wherein the high-density solution in step b) is an aqueous solution.

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