Process for preparing purified and decolorized diester monomers by depolymerization of polyester feedstock

Abstract

The present invention relates to a process for depolymerizing a polyester feedstock containing PET, comprising the steps of: a) conditioning the polyester feedstock to produce a conditioned feed stream; b) depolymerizing the conditioned feed stream in the presence of a diol at a temperature of 150-300° C. to produce a diol to diester weight ratio in the feedstock of 0.3-8.0; producing a reaction effluent; c) separating the diol from the reaction effluent; producing at least one liquid monomer effluent; d) separating the liquid monomer effluent into a heavy impurities effluent and a pre-purified monomer effluent; and e) purifying the pre-purified monomer effluent; comprising an adsorption substep e1) carried out at a temperature of 50-200° C. and a crystallization substep e2) to produce at least one decolorized purified diester monomer effluent.

Description

[Technical field]

[0001] The present invention relates to a process for the preparation of a diester monomer effluent by depolymerization by glycolysis of a polyester feedstock, in particular comprising colored and / or opaque and / or multi-layer polyethylene terephthalate (PET), with the aim of recycling it to its polymerization unit. More particularly, the present invention relates to a process for the depolymerization by glycolysis of a polyester feedstock, preferably comprising at least colored and / or opaque PET, comprising a step of adsorption of the diester monomers followed by a step of purification of the diester effluent, comprising a step of crystallization, to obtain a purified and decolorized diester monomer effluent. [Background technology]

[0002] The chemical recycling of polyesters, and in particular polyethylene terephthalate (PET), has been the subject of numerous studies aimed at breaking down polyesters recovered in waste form into monomers that could then be used again as feedstock for polymerization processes.

[0003] A large number of polyesters are obtained from networks for collecting and sorting materials. In particular, polyester, and in particular PET, may originate from the collection of bottles, container trays, films, resins and / or fibres (e.g. textile fibres, tyre fibres) made of polyester. Polyesters obtained from collection and sorting channels are called polyesters eligible for recycling.

[0004] PET eligible for recycling can be divided into four main categories: - Clear PET: composed mainly of colorless transparent PET (generally at least 60% by weight) and pale blue transparent PET, does not contain pigments and can be used in mechanical recycling processes; - dark or colored (green, red, etc.) PET: generally may contain up to 0.1% by weight of a dye or pigment, but remains transparent or translucent; - Opaque PET: contains a significant amount of pigment, typically with a content varying between 0.25% and 5.0% by weight, which renders the polymer opaque. Opaque PET is increasingly used, for example, in the manufacture of food containers, such as milk bottles, in the composition of bottles for cosmetics, plant protection products or dyes; - Multilayer PET: containing layers of polymers other than PET or layers of recycled PET with virgin PET (i.e. not recycled PET) or films, for example of aluminium, between the layers. Multilayer PET is used after thermoforming to produce packaging materials, for example container trays.

[0005] The collection channels feed into the recycling channels, the structure of which differs from country to country. They vary according to the nature and volume of the streams, as well as the sorting technology, to maximize the amount of plastic upgraded from waste. The channels for recycling these streams generally consist of a first step of conditioning in flake form, during which bales of raw packaging material are washed, refined, sorted and crushed, and then refined again and sorted to give rise to a flake stream containing generally less than 1% by weight of "macroscopic" impurities (glass, metals, other plastics, wood, paper, cardboard, inorganic elements), preferentially less than 0.2% by weight, and even more preferentially less than 0.05% by weight.

[0006] The clear PET flakes may then undergo an extrusion-filtration process to produce extrudates that can then be reused as a mixture with virgin PET to produce new products (bottles, fibers, films). A process of solid state polymerization (known by the abbreviation SSP) under vacuum is necessary for food applications. This type of recycling is known as mechanical recycling.

[0007] Dark (or colored) PET flakes can also be recycled mechanically. However, the color of the extrudates formed from the colored stream limits the applications: dark PET is generally used to manufacture packaging straps or fibers. The outlets are therefore more limited compared to those of clear PET.

[0008] The presence of opaque PET with a high pigment content in recycled PET presents a problem for recyclers, since opaque PET has a negative effect on the mechanical properties of the recycled PET. Opaque PET is currently collected together with colored PET and is found in the colored PET stream. In terms of the development of applications for opaque PET, the content of opaque PET in the colored PET stream to be recycled is currently 5-20% by weight and is tending to increase. It will be possible to reach a content of opaque PET in the colored PET stream of 20-30% by weight or more within a period of a few years. However, it has been shown that with more than 10-15% opaque PET in the colored PET stream, the mechanical properties of the recycled PET are negatively affected (see Impact du developpement du PET opaque blanc sur le recyclage des emballages en PET [Impact of the increase in white opaque PET on the recycling of PET packaging], preliminary report of COTREP of 5 / 12 / 13), preventing recycling in the form of fibers, which is the main outlet channel for colored PET.

[0009] Dyes are natural or synthetic substances, which are particularly soluble in polyester materials and are used to color the materials into which they are introduced. Commonly used dyes have different properties and often contain heteroatoms of the O and N type, and conjugated unsaturation, for example quinone, methine or azo groups, or molecules, for example pyrazolones and quinophthalones. Pigments are finely divided substances, which are particularly insoluble in polyester materials and are used to color and / or opacify the materials into which they are introduced. The main pigments used to color and / or opacify polyesters, and in particular PET, are metal oxides, for example TiO2, CoAl2O4 or Fe2O3, silicates, polysulfides and carbon black. Pigments are particles with a size generally between 0.1 and 10 μm, mainly between 0.4 and 0.8 μm. The complete removal of these pigments is necessary to envisage recycling opaque PET, but the complete removal of these pigments by filtration is technically difficult because they have an extremely high blocking capacity.

[0010] Recycling of colored and opaque PET is therefore extremely problematic.

[0011] Patent document 1 describes a method for the depolymerization by glycolysis of colored PET, in particular that resulting from the recovery of green colored PET bottles. The feedstock treated by this method takes the form of colored PET flakes and is contacted with ethylene glycol in a reactor at a temperature of 180-280° C. for several hours. The product of glycolysis obtained at the end of the depolymerization step is purified by passage over activated carbon at a temperature above 170° C. and subsequent extraction of the residual dyes, in particular the yellow dyes, with a solvent, which may be an alcohol, for example methanol, or a glycol, for example ethylene glycol. The BHET crystallizes in the extraction solvent and is then separated by filtration.

[0012] In WO 2005 / 023111, post-consumer PET comprises a mixture of different PETs, e.g. clear PET and colored PETs, e.g. blue PET, green PET and / or amber PET, in the form of flakes, which are depolymerized by glycolysis in a batchwise manner in a reactor at 150-250°C in the presence of ethylene glycol and an amine catalyst. The diester monomer obtained is purified by direct filtration, then adsorption on activated carbon and finally passage over an ion exchange resin, in particular at a temperature of 80-90°C, followed by crystallization and recovery by filtration. WO 2005 / 023111 discloses another method for the purification of the diester monomer obtained by short path distillation at 200°C.

[0013] Patent document 3 likewise describes the purification of a solution of crude BHET dissolved in methanol or ethylene glycol, which comprises at least a series of contacts between said solution and activated carbon, an anion exchange resin and a cation exchange resin at temperatures between 40 and 120° C., in particular equal to 60° C., 65° C. or 80° C. In particular, this patent indicates that contact with activated carbon alone under said conditions is not particularly sufficient for completely decolorizing the solution, since the residual color, in particular the yellow color, persists, whereas after successive passes over activated carbon and anion and cation exchange resins the yellow coloration is no longer visible.

[0014] In patent 4, a method for the depolymerization of polyesters, especially colored polyesters, such as green PET, comprises the steps of depolymerization in a reactor at temperatures between 180 and 240° C. in the presence of a diol, especially ethylene glycol, and optionally evaporation in a thin-film evaporator, dissolution in a hot solvent, and filtration to separate out insoluble impurities with a size of more than 50 μm. The low proportion of pigments in colored PET allows separation by filtration. However, this technique cannot operate with the amount of pigments present in opaque PET, because these pigments quickly clog the filters.

[0015] US Pat. No. 5,399,663 describes the production of purified BHET from PET in flake form. The depolymerization step consists of glycolysis of PET flakes in solid form, which have been previously pretreated by washing with water at 180° C., followed by 195-200° C., in the presence of ethylene glycol and a catalyst, in a stirred reactor. The depolymerization step is followed by steps of prepurification by cooling, filtration, adsorption and treatment on ion exchange resins, which are presented as crucial and which take place before the evaporation of the glycol and the purification of the BHET. According to US Pat. No. 5, the prepurification makes it possible to prevent the repolymerization of BHET in the subsequent purification steps. However, going through the steps of filtration and ion exchange resins can be extremely problematic when the feedstock contains a large amount of very small solid particles, such as pigments and / or polymeric compounds other than PET, such as polyolefins or polyamines, and this is the case when the feedstock to be treated contains a significant proportion of opaque PET and / or multi-layer preformed PET, especially in a significant proportion (more than 10% by weight of opaque PET and / or multi-layer preformed PET).

[0016] In parallel, US Pat. No. 5,399,633 discloses a process for the depolymerization of polyesters including a step of glycolysis in the presence of ethylene glycol and a process for the purification of solutions of BHET on cation and anion exchange resins.

[0017] Finally, US Pat. No. 5,399,666 describes a method for the depolymerization of opaque PET, in particular polyester feedstocks containing 0.1% to 10% by weight of pigment, by glycolysis in the presence of ethylene glycol. A purified bis(2-hydroxyethyl) terephthalate (BHET) effluent is obtained after certain steps of separation and purification by adsorption. However, the BHET effluent obtained by the depolymerization method described in US Pat. No. 5,399,666 may have a drawback: the obtained BHET effluent acquires coloration particularly quickly, despite having passed through a column of adsorbent.

[0018] The object of the present invention is to improve these processes, in particular the process described in patent application WO 2005 / 023363, for the depolymerization by glycolysis of polyester feedstocks containing PET, preferably colored and / or opaque PET, in order to improve the purification, and more particularly the decolorization, of the diester effluents obtained after separation of heavy solid impurities, such as oligomers and pigments.The object of the present invention is in particular to obtain diester effluents, in particular BHET effluents, having a high purity and decolorized appearance by depolymerization of polyester feedstocks containing PET, preferably colored and / or opaque PET. [Prior art documents] [Patent documents]

[0019] [Patent Document 1] US Patent Application Publication No. 2006 / 0074136 [Patent Document 2] US Patent Application Publication No. 2015 / 0105532 [Patent Document 3] U.S. Patent No. 6,642,350 [Patent Document 4] European Patent No. 0865464 [Patent Document 5] Patent No. 3715812 [Patent Document 6] European Patent Application Publication No. 1120394 [Patent Document 7] French Patent Application Publication No. 3053691 Summary of the Invention [Means for solving the problem]

[0020] (Summary of the invention) An object of the present invention is therefore a process for the depolymerization of a polyester feedstock containing polyethylene terephthalate, comprising the following steps: a) a conditioning step; feeding at least said polyester feedstock; producing a conditioned feedstock stream; b) a step of depolymerization by glycolysis, feeding at least a conditioned feed stream and operating in the presence of diols at a temperature between 150 and 300° C. with a residence time between 0.1 and 10 hours, the weight ratio between the total amount of diols present in step b) and the amount of diesters contained in the conditioned feed stream being between 0.3 and 8.0; generating a reaction effluent; c) a step of separation of diols; feeding at least the reaction effluent from step b) and operating at a temperature between 60 and 250° C. and at a pressure lower than that of step b); giving rise to at least a diol effluent and a liquid monomer effluent; Said step of separation of diols is carried out in one gas-liquid separation section or in a series of 2 to 5 consecutive gas-liquid separation sections, each of which produces a gaseous effluent and a liquid effluent, the liquid effluent from the preceding section being fed to the succeeding section, the liquid effluent obtained from the last gas-liquid separation section constituting the liquid monomer effluent and one or more gaseous effluents being recovered to constitute said one or more diol effluents; d) separation of the liquid monomer effluent from step c) into a heavy impurities effluent and a pre-purified monomer effluent; operating at a temperature below 250° C., a pressure below 0.001 MPa and a liquid residence time below 10 minutes; e) a step of purification of the pre-purified monomer effluent, comprising an adsorption substep e1) and a crystallization substep e2); resulting in at least one decolorized purified diester monomer effluent; adsorption substep e1) is operated at a temperature of 50-200° C. and a pressure of 0.1-1.0 MPa, carrying out at least one section for mixing with a solvent and at least one section for adsorption in the presence of at least one adsorbent, The crystallization substep e2) is carried out in a solid production section, operating at a temperature between 0 and 100° C. and a pressure between 0.00001 and 1.00 MPa, followed by a solid-liquid separation section.

[0021] Preferably, step e) of purification of the pre-purified monomer effluent of the process according to the invention comprises an adsorption substep e1) followed by a crystallization substep e2), resulting in at least one decolorized purified diester monomer effluent and a used solvent effluent, in which an adsorption substep e1) is operated at a temperature between 50 and 200° C. and a pressure between 0.1 and 1.0 MPa, carrying out at least one section for mixing the prepurified monomer effluent from step d) with a solvent and at least one section for adsorption in the presence of at least one adsorbent, to obtain a pre-adsorbed monomer effluent, The crystallization substep e2) implements a solid production section, which at least feeds the adsorption-pretreated monomer effluent and operates at a temperature of 0-100° C. and a pressure of 0.00001-1.00 MPa, followed by a solid-liquid separation section, resulting in a decolorized purified diester monomer effluent and a spent solvent effluent.

[0022] One advantage of the present invention is to obtain from a polyester feedstock at least comprising polyethylene terephthalate (PET), particularly colored and / or opaque PET, a diester monomer effluent, particularly a bis(2-hydroxyethyl) terephthalate (BHET) effluent, which is purified and decolorized, more particularly a white colored purified solid diester monomer effluent, which meets the CIE 1976 L * a * b * It denotes color parameters expressed in a reference system, which is determined by chromaticity measurement (in accordance with the ASTM D6290 2019 method), preferably having: - Lightness (or luminance) parameter L * : close to 100, more particularly greater than 90.00, preferably greater than 92.00 (100.00 being the maximum); - Parameter a * (corresponding to the green-red axis); close to 0, more particularly between -1.50 and +1.50, preferably between -1.00 and +1.00; and - Parameter b * (corresponding to the blue-yellow axis); closer to 0, more precisely -2.50 to +2.50, even more precisely -1.00 to +1.50.

[0023] Advantageously, the process according to the invention makes it possible to obtain a diester monomer effluent, in particular a bis(2-hydroxyethyl) terephthalate (BHET) effluent, which is purified and decolorized and which, when characterized by UV-visible spectroscopy, does not show any significant absorption bands (i.e. distinguishable from background noise) in the visible wavelength range, i.e., between 400 and 800 nm.

[0024] The advantage of the present invention is therefore that any type of polyester waste, which increasingly contains pigments and dyes, can be treated, for example colored, opaque and even multi-layered PET. The method according to the invention is particularly suitable for treating opaque PET, making it possible to remove the pigments and dyes and recover the diester monomers, in particular the bis(2-hydroxyethyl) terephthalate (BHET) monomers, by chemical reactions and specific purification steps. The diester monomers obtained may be repolymerized to give polymers that do not differ from virgin polyester, in particular virgin PET, and therefore make it possible to reach the full range of uses of virgin PET. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] (List of Drawings) Figure 1 represents a particular embodiment of the invention. A polyester feedstock (1), containing colored and / or opaque PET, is conditioned in a conditioning step a), which also feeds a diol stream (11). The conditioned feedstock stream (2) is introduced into a depolymerization step b) by glycolysis, which is also fed another diol stream (12).

[0026] The reaction effluent (3) obtained after depolymerization is sent to a step c) for the separation of diols, resulting in a liquid monomer effluent (4) and a diol effluent (10). The liquid monomer effluent (4) is sent to a step d) for the separation of BHET. The diol effluent (10) recovered at the end of step c) is, after addition of a fresh diol feed (14) external to the process, divided into a diol stream (11) which is fed to step a), another diol stream (12) which is fed to step b) and a third diol stream (13) which is fed to step e).

[0027] Step d) implements in particular a short-path evaporator for producing a pre-purified monomer effluent (5) and a heavy impurities effluent (8). The heavy impurities effluent (8) may be at least partially recycled to the reaction step (step b)). The pre-purified monomer effluent (5) is sent to a purification step e).

[0028] In the purification step e), the prepurified monomer effluent (5) is fed to an adsorption section e1), which also feeds a diol stream (13), resulting in an adsorption-pretreated monomer effluent (6). The adsorption-pretreated monomer effluent (6) is then fed to a crystallization section e2), where crystallization of the diester monomer and then separation of the formed crystals are implemented, resulting in a decolorized purified diester monomer effluent (7) and a spent diol solvent stream (9). Optionally, the crystallization section may be fed with a stream of crystallization solvent (15), e.g. a diol or water. The spent diol solvent stream (9) may optionally be recovered in whole or in part and recycled to steps e1), a) and / or b), and / or optionally to step e2), where the recovered spent diol solvent stream (9) can be optionally purified before recycling.

[0029] Figure 2 represents a particular embodiment of the invention. A polyester feedstock (1), containing colored and / or opaque PET, is conditioned in a conditioning step a), which also feeds a diol stream (11). The conditioned feedstock stream (2) is introduced into a step b) of depolymerization by glycolysis, which in turn feeds another diol stream (12).

[0030] The reaction effluent (3) obtained after depolymerization is sent to a step c) for the separation of diols, which results in a liquid monomer effluent (4) and a diol effluent (10). The liquid monomer effluent (4) is sent to a step d) for the separation of BHET. The diol effluent (10) recovered at the end of step c) is, after addition of a fresh diol feed (14) external to the process, divided into a diol stream (11) which is fed to step a) and another diol stream (12) which is fed to step b).

[0031] Step d) implements in particular a short-path evaporator for producing a pre-purified monomer effluent (5) and a heavy impurities effluent (8). The heavy impurities effluent (8) may be at least partially recycled to the reaction step b). The pre-purified monomer effluent (5) is sent to the purification step e).

[0032] The purification step e) comprises: - an adsorption section e1; which is fed with said prepurified monomer effluent (5) and a solvent stream (13) external to the process, in particular a water stream; which produces an adsorption-pretreated monomer effluent (6); and - crystallization section e2); fed with the adsorption-pretreated monomer effluent (6) and optionally with a stream of crystallization solvent, for example water, and implementing the crystallization of the diester monomer and subsequent separation of the formed crystals; giving rise to a decolorized purified diester monomer effluent (7) and a spent solvent stream (9), in particular a water stream. Optionally, the crystallization section may be fed with a stream of crystallization solvent (15), for example a diol or water. The spent solvent stream (9) may optionally be totally or partially recovered and recycled to section e1) and / or optionally to section e2), with the possibility of optionally purifying the recovered spent solvent stream before recycling.

[0033] FIG. 3 shows the UV-visible spectra determined for the solids obtained by the methods described in Example 1 (grey) and Example 2 (black).

[0034] (Description of the embodiment) According to the present invention, polyethylene terephthalate or poly(ethylene terephthalate), also simply referred to as PET, comprises a diester (particularly a terephthalic acid diester) and has a basic repeat unit that is of the following formula:

[0035] [ka]

[0036] Traditionally, PET is obtained by the polycondensation of terephthalic acid (PTA) or dimethyl terephthalate (DMT) with ethylene glycol.

[0037] In the remainder of the text, the expression "per mole of diester in said polyester feedstock" corresponds to the number of moles of -[O-CO-O-(CH)-CO-O-CH-CH]- units in said polyester feedstock, in particular in the PET contained in said polyester feedstock, which are diester units resulting from the reaction of PTA with ethylene glycol, in particular in the PET contained in said polyester feedstock.

[0038] According to the present invention, the term "monomer" or "diester monomer" advantageously refers to a repeat unit of a polyester in a polyester feedstock, in particular a polyester in a polyethylene terephthalate PET in a polyester feedstock, and defines a diester of a dicarboxylic acid, preferably an aromatic dicarboxylic acid, preferentially terephthalic acid, and a diol, preferably a diol containing 2 to 12 carbon atoms, preferentially 2 to 4 carbon atoms (the preferred diol is ethylene glycol). More specifically, the "monomer" or "diester monomer" corresponds to the product targeted by the method of the present invention. Thus, according to one embodiment of the present invention, the "monomer" or "diester monomer" (the product targeted by the method of the present invention) is a diester of HOC n H 2n -CO2-(Aro)-CO2-C n H 2nOH type chemical formula, where n=2-12, preferably n=2-4, and -(Aro)-=-(C6H4)- represents an aromatic ring. Preferably, the term "monomer" or "diester monomer" refers to bis(2-hydroxyethyl) terephthalate (BHET), the target product of the depolymerization of PET in the presence of ethylene glycol, with chemical formula HOC2H4-CO2-(C6H4)-CO2-C2H4OH, where -(C6H4)- represents an aromatic ring.

[0039] The term "oligomer" typically refers to a small sized polymer, generally consisting of 2-20 basic repeat units. According to the present invention, the term "ester oligomer" or "BHET oligomer" refers to a terephthalate ester oligomer containing 2-20, preferably 2-5, basic repeat units of the formula -[O-CO-(CH)-CO-O-CH]-, where -(CH)- is an aromatic ring.

[0040] According to the present invention, the terms "diol" and "glycol" are used interchangeably and correspond to compounds containing two hydroxyl groups -OH and preferably containing from 2 to 12 carbon atoms, preferentially from 2 to 4 carbon atoms. A suitable diol is ethylene glycol, also called monoethylene glycol or MEG.

[0041] Thus, the diol or diol effluent stream used in the steps of the process of the invention preferably comprises ethylene glycol (or MEG) in an amount advantageously greater than 40% by weight, preferentially greater than 50% by weight and preferably equal to or greater than 60% by weight of the total weight of said diol or diol effluent stream.

[0042] The term "dye" defines a substance that is soluble in polyester material and is used to color it. Dyes can be of natural or synthetic origin.

[0043] According to the present invention, the term "pigment", more particularly opacifying and / or coloring pigments, defines finely divided substances that are particularly insoluble in polyester materials. Pigments are in the form of solid particles and generally have a size between 0.1 and 10 μm, predominantly between 0.4 and 0.8 μm. They are often of inorganic nature. Commonly used pigments, especially those used for opacifying, are metal oxides, such as TiO2, CoAl2O4 or Fe2O3, silicates, polysulfides and carbon black.

[0044] According to the present invention, the expressions "of between A and B" and "between A and B" are equivalent and mean that both limits of the interval (A, B) are included in the stated range of values. If this is not the case and if both limits are not included in the stated range, such an explanation will be given by the present invention.

[0045] For the purposes of the present invention, various ranges of parameters for a given process, such as pressure ranges and temperature ranges, may be used alone or in combination, for example, a range of preferred pressure values ​​may be combined with a more preferred range of temperature values ​​within the meaning of the present invention.

[0046] In the following text, specific embodiments of the present invention may be described, which may be implemented separately or, where technically feasible, in combination with each other without any restriction on the combination.

[0047] The terms "upstream" and "downstream" should be understood according to the general flow of the streams in the process.

[0048] According to the invention, pressure is absolute pressure and is given in MPa or MPa (absolute) (or MPa (absolute)).

[0049] (Feed material) The process according to the invention comprises a polyester feedstock which comprises polyethylene terephthalate (PET), preferably comprising at least opaque PET, pigmented PET, multi-layer PET or mixtures thereof, suitably comprising at least opaque PET and / or pigmented PET, and optionally multi-layer PET.

[0050] The polyester feedstock is advantageously a recycled polyester feedstock obtained from waste, in particular plastic waste, collection and sorting channels. The polyester feedstock may originate, for example, from the collection of bottles, container trays, films, resins and / or fibres consisting of polyethylene terephthalate.

[0051] The polyester feedstock advantageously comprises at least 50% by weight polyethylene terephthalate (PET), preferably at least 70% by weight, suitably at least 90% by weight, with a maximum being 100% by weight PET.

[0052] The polyester feedstock preferably comprises at least one PET selected from opaque, dark or pigmented and multi-layered PET, and mixtures thereof. Very particularly, the polyester feedstock comprises at least 10% by weight of opaque PET, very preferably at least 15% by weight of opaque PET, advantageously opaque PET to be recycled, i.e. PET obtained from collection and sorting channels. The polyester feedstock may comprise 100% by weight of opaque PET. More particularly, it may comprise up to 70% by weight of opaque PET.

[0053] The polyester feedstock advantageously comprises from 0.1% to 10% by weight of pigment, advantageously from 0.1% to 5% by weight of pigment. It preferably also comprises from 0.005% to 1% by weight of dye, especially from 0.01% to 0.20% by weight of dye.

[0054] In the collection and sorting channel the polyester waste is washed and ground and then constitutes the polyester feedstock for the process according to the invention.

[0055] The polyester feedstock may be wholly or partly in the form of flakes, the longest length of which is less than 10 cm, preferentially between 5 and 25 mm, or in the form of finely divided solids, i.e. in the form of particles, the particles preferably having a size between 10 micrometers (μm) and 1 mm. The feedstock may contain "macroscopic" impurities, preferably less than 5% by weight, preferentially less than 3% by weight, such as glass, metal, plastics other than polyester (e.g. PP, PEHD, etc.), wood, paper, cardboard or inorganic elements. The polyester feedstock may be wholly or partly in the form of fibers, such as textile fibers, optionally pretreated to remove cotton or polyamide fibers, or any textile fibers other than polyester, such as tire fibers, optionally pretreated to remove polyamide fibers or rubber or polybutadiene residues, among others. The polyester feedstock may comprise polyester obtained from production rejects from the polyester polymerization and / or conversion process. The polyester feedstock may also contain elements such as antimony, titanium or tin that are used as polymerization catalysts and stabilizers in the PET production process.

[0056] (Conditioning process a) The process according to the invention comprises a conditioning step a) to which the polyester feedstock is at least fed to produce a conditioned feed stream.

[0057] Said step a) makes it possible, on the one hand, in particular to heat and pressurize said polyester feedstock to the operating conditions of the depolymerization step b).

[0058] In the conditioning step a), the polyester feedstock is gradually heated to a temperature close to or even slightly above its melting point so as to become at least partially liquid. Advantageously, at least 70% by weight of the polyester feedstock, highly advantageously at least 80% by weight, preferably at least 90% by weight and preferentially at least 95% by weight of the polyester feedstock is in liquid form at the end of step a). The temperature at which step a) is implemented is advantageously between 200 and 300° C., preferably between 250 and 290° C. This temperature is kept as low as possible to minimize thermal degradation of the polyester, but must be sufficient to at least partially melt the polyester feedstock.

[0059] The conditioning step a) may advantageously be operated in an inert atmosphere to limit the introduction of oxygen into the system and oxidation of the polyester feedstock.

[0060] Advantageously, the pressure at which step a) is implemented is preferably between atmospheric pressure (ie 0.1 MPa) and 20 MPa, preferably between 0.15 MPa and 10 MPa.

[0061] Advantageously, step a) may be fed with a diol stream, preferably an ethylene glycol stream, the weight ratio of the diol stream relative to the polyester feedstock, i.e. the ratio between the flow rate by weight of the diol stream fed to step a) and the flow rate by weight of the polyester feedstock fed to step a), being between 0.03 and 6.00, preferably between 0.05 and 5.00, preferentially between 0.10 and 4.00, and suitably between 0.50 and 3.00. Highly advantageously, the diol stream fed to step a) corresponds to at least a portion of the (preferably purified) diol effluent obtained from step c), possibly in admixture with a fresh diol feed external to the process according to the invention. The effect of contacting the polyester feedstock with the diol stream is to initiate the depolymerization reaction of the polyester feedstock before its introduction into the depolymerization step b). It also makes it possible to reduce the viscosity of the polyester feedstock, thereby promoting the homogenization of the feedstock-diol mixture and, as a consequence, the depolymerization reaction.

[0062] According to a preferred embodiment of the invention, step a) implements an extruder, optionally followed by at least one static or dynamic mixer.

[0063] Preferably, the residence time in said extruder, defined as the volume of said extruder divided by the volumetric flow rate of the polyester feedstock, is advantageously at most 5 minutes, preferably at most 2 minutes, and suitably greater than 1 second, preferentially at least 10 seconds. Advantageously, the extruder makes it possible to bring the polyester feedstock to a temperature of between 200 and 300°C, preferentially between 250 and 290°C, and a pressure preferably between atmospheric pressure (i.e. 0.1 MPa) and 20 MPa, preferably between 0.15 MPa and 10 MPa, conditions under which said polyester feedstock is advantageously at least partially melted.

[0064] The extruder is advantageously connected to a vacuum extraction system to remove impurities present in the feed, such as dissolved gases, light organic compounds and / or moisture. A filtration system may be advantageously implemented at the outlet of the extruder, advantageously upstream of step b), to remove solid particles, such as sand particles, having a size of more than 40 μm and preferably less than 2 cm. The feeding of the polyester feedstock to the extruder is advantageously carried out by any method known to the person skilled in the art, for example through a feeding hopper, which may advantageously be inerted to limit the introduction of oxygen into the system.

[0065] The polyester feedstock may advantageously be mixed in the conditioning step a) with at least a portion of the heavy impurities effluent obtained from step d).

[0066] The conditioned feed stream obtained from the conditioning section is advantageously sent to the depolymerization step b).

[0067] (Depolymerization step b)) The process according to the invention comprises a step b) of depolymerization by glycolysis, advantageously of the feedstock polyethylene terephthalate (PET) in the presence of a diol.

[0068] The diol present in step b) advantageously functions not only as a depolymerization agent but also as a solvent, thus making it possible to reduce the viscosity of the reaction medium and to accelerate the reaction and thus the depolymerization. The diol present in step b) is introduced in step a) or in step b), or in steps a) and b). The diol is advantageously monoethylene glycol.

[0069] The depolymerization step b) is fed at least with the conditioned feed stream obtained from the conditioning step a) and optionally with a feed of diol obtained in particular from a diol effluent internal or external to the process according to the invention, in such a way that the weight ratio between the amount by weight of diol introduced in step a) and / or step b) and the total amount by weight of diol present in step b), which corresponds to the sum of the amount by weight of diester contained in the conditioned feed stream (i.e. contained in the polyester feed, in particular in the PET in the polyester feed; the amount by weight of diester therefore corresponds more precisely to the weight of polyester, in particular PET in the polyester feed), is between 0.3 and 8.0, preferably between 1.0 and 7.0, suitably between 1.5 and 6.0. In other words, the depolymerization step b) is fed with the conditioned feed stream resulting from the conditioning step a) and, optionally, with a feed of diol, such that the molar ratio of the total molar amount of diol introduced in step a) and / or step b) relative to the total molar amount of diester contained in the conditioned feed stream (i.e. contained in the polyester feed) is between 1.0 and 24.0, preferably between 3.0 and 21.0, suitably between 4.5 and 18.0, respectively.

[0070] Preferably, the depolymerization step b) is fed with the conditioned feed stream obtained from step a) and with a feed of diol, preferably a feed of ethylene glycol, advantageously obtained from a diol effluent internal or external to the process according to the invention, so that the weight ratio of the total amount of diol introduced in step b) and optionally in step a) relative to the total amount of diester contained in the conditioned feed stream (i.e. contained in the polyester feedstock: therefore, more precisely, the weight of polyester, in particular PET in the polyester feedstock) is between 0.3 and 8.0, preferably between 1.0 and 7.0, advantageously between 1.5 and 6.0 (i.e. the molar ratio of diol relative to diester is respectively between 1.0 and 24.0, preferably approximately between 3.0 and 21.0, advantageously between 4.5 and 18.0).

[0071] Advantageously, the depolymerization step b) advantageously implements one or several reaction sections, preferably at least two reaction sections, suitably between two and four reaction sections, preferably working in series. Each reaction section may comprise a reactor, more particularly any type of reactor known to the skilled person making it possible to carry out the reactions of depolymerization or transesterification, preferably a reactor stirred by a mechanical stirring system and / or a recirculation loop and / or fluidization. In each reaction section, the reactor may optionally comprise a conical base making it possible to remove impurities. Advantageously, said depolymerization step b) implements at least two reaction sections, preferably from 2 to 4 reaction sections, functioning in series, one or more reaction sections being operated at mutually identical or different temperatures, starting from the second reaction section, which are preferably lower than or equal to the temperature of the first reaction section, preferably lower relative to the temperature of the first reaction section, preferentially by 10 to 50° C. lower, even by 20 to 40° C. lower.

[0072] The depolymerization step b) is operated at a temperature between 150 and 300° C., preferably between 180 and 290° C., suitably between 210 and 270° C., in particular in the liquid phase. Advantageously, step b) is implemented with a residence time in each reaction section of 0.1 to 10 h, preferably between 0.25 and 8 h, 0.5 to 6 h. The residence time in a reaction section is defined as the ratio of the liquid volume of said reaction section to the volumetric flow rate of the stream leaving said reaction section.

[0073] The operating pressure of the reaction section or sections of step b) is determined so as to keep the reaction system in the liquid phase. This pressure is advantageously at least 0.1 MPa, preferentially at least 0.4 MPa and preferably less than 5 MPa. The term "reaction system" means all the components and phases present in said step b).

[0074] The glycolysis reaction may be carried out in the presence or absence of a catalyst.

[0075] If the glycolysis reaction is carried out in the presence of a catalyst, this catalyst may be homogeneous or heterogeneous and is selected from esterification catalysts known to those skilled in the art, such as complexes, oxides and salts of antimony, tin or titanium, alkoxides of metals from groups (I) and (IV) of the periodic table of the elements, organic peroxides or acidic / basic metal oxides.

[0076] A suitable heterogeneous catalyst advantageously comprises at least 50% by weight, preferentially at least 70% by weight, advantageously at least 80% by weight, highly advantageously at least 90% by weight and even more advantageously at least 95% by weight of a solid solution, relative to the total weight of the catalyst. This solid solution preferably comprises at least 50% by weight of a solid solution of formula Z x AlO (3+x)wherein x is between 0 (except for the limiting value) and 1, and Z is selected from Co, Fe, Mg, Mn, Ti and Zn, and contains up to 50% by weight of alumina and oxide of element Z. The preferred heterogeneous catalyst advantageously contains up to 10% by weight of a dopant. The dopant is selected from silicon, phosphorus and boron, used alone or in mixture. For example, and without limitation, the solid solution may consist of a mixture of spinel ZnAl2O4 and spinel CoAl2O4, or else of a mixture of spinel ZnAl2O4, spinel MgAl2O4 and spinel FeAl2O4, or else of only spinel ZnAl2O4.

[0077] According to a particular embodiment of the invention, a catalyst, preferably selected from amines, preferably tertiary mono- and diamines such as tetramethylethylenediamine (TMEDA), pentamethyldiethylenetriamine (PMDETA), trimethyltriazacyclononane (TACN), triethylamine (TEA), 4-(N,N-dimethylamino)pyridine (DMAP), 1,4-diazabicyclo[2.2.2]octane (DABCO), N-methylimidazole (NMI), and alkali metal or alkaline earth metal hydroxides such as Mg(OH)2 and NaOH, may be added to the conditioned feed stream in the depolymerization step b).

[0078] The depolymerization step is preferably carried out without the addition of an external catalyst to the polyester feedstock.

[0079] Said depolymerization step may be carried out in the presence of a solid adsorbent, advantageously in powder form or in shaped form, whose function is to capture at least a portion of the colouring impurities, thereby easing the burden of the purification step. Said solid adsorbent is advantageously activated carbon.

[0080] Step b) may be fed with at least a portion of the heavy impurities effluent obtained from step d).

[0081] The glycolysis reaction makes it possible to convert the polyester of the polyester feedstock, in particular the PET of the polyester feedstock, and possibly its oligomers, into diester monomers and oligomers, advantageously the PET into at least the monomer bis(2-hydroxyethyl) terephthalate (BHET) and oligomers of BHET. The conversion of the polyester feedstock, and more particularly the PET of the polyester feedstock, in the depolymerization step b) is greater than 50%, preferably greater than 70%, and advantageously greater than 85%. Advantageously, the molar BHET yield is greater than 50%, preferably greater than 70%, and advantageously greater than 85%. The molar BHET yield corresponds to the molar flow rate of BHET at the outlet of step b) versus the number of moles of diester present in the polyester feedstock fed to said step a).

[0082] An internal recirculation loop may advantageously be implemented in step b) to withdraw a portion of the reaction system from the reaction section, filter this portion and reinject said filtered portion into said reaction section of step b), this internal loop making it possible to remove "macroscopic" solid impurities that may be present in the reaction liquid.

[0083] Advantageously, the depolymerization step b) makes it possible to obtain a reaction effluent, advantageously in essentially liquid form, which is sent to a step c) of separation of the diol.

[0084] (Step c) of isolating the diol) The process according to the invention comprises a step c) of separation of the diol from the reaction effluent obtained from step b). Step c) is therefore advantageously fed with at least the reaction effluent obtained from step b) and operated at a temperature between 60 and 250° C. and at a pressure lower than that of step b) to give at least a diol effluent and a liquid monomer effluent. The main function of step c) is to recover all or part of the unreacted diol and / or the diol formed during the depolymerization step.

[0085] Advantageously, step c) is operated at a pressure lower than that of step b) and comprises evaporating a portion of the reaction effluent from step b) to obtain one or more gas effluents, said one or more gas effluents obtained at the end of step c) consisting of more than 40% by weight of diol, preferably more than 50% by weight of diol, suitably more than 60% by weight of diol, the preferred diol being ethylene glycol (MEG), constituting one or more diol effluents.

[0086] Advantageously, step c) implements one gas-liquid separation section or a series of gas-liquid separation sections, advantageously 2 to 5 successive separation sections, for example 3 gas-liquid separation sections. Each of the gas-liquid separation sections produces a liquid effluent and a gaseous effluent. The liquid effluent from the preceding section is fed to the following section. The liquid effluent obtained from the last gas-liquid separation section constitutes the liquid monomer effluent. The gaseous effluent or effluents are recovered to constitute said diol effluent or effluents.

[0087] Advantageously, at least a portion of the at least one gaseous effluent produced may be condensed to give at least one liquid diol effluent. The diol effluent or effluents may contain other compounds, such as dyes, light alcohols, water or diethylene glycol. All or a portion of the diol effluent or effluents obtained from step c) that remain in gaseous state or are condensed to liquid form may be sent, each independently or as a mixture, to a step of diol purification to produce at least one purified diol effluent that is then recycled. Optionally, all or a portion of the diol effluent or effluents obtained from step c) may be recycled to step a) and / or step b) and / or sent to step e), preferably after condensation, after purification or directly, advantageously, optionally as a mixture with a diol supplement external to the process according to the invention.

[0088] According to a preferred embodiment of the present invention, the diol effluent(s) obtained from step c), advantageously kept in gaseous state and / or after condensation, are sent to a purification step to produce at least a purified diol effluent, which is then recycled in whole or in part to steps a) and / or b) and / or to step e). In this embodiment, said steps of purification of the diol effluent(s) may non-exhaustively comprise adsorption on solids (e.g. activated carbon) to remove dyes, and / or one or more distillations to separate impurities, such as diethylene glycol, water and other alcohols.

[0089] Advantageously, at least one of the gas-liquid separation sections may be implemented in a falling film evaporator or thin film evaporator or short path distillation. Step c) may implement at least one separation section performing a short path distillation.

[0090] The operation of step c) is carried out in such a way that the temperature of the liquid effluent is maintained above a lower value below which the target diester monomer precipitates and below a higher value above which the diester monomer undergoes significant repolymerization, depending on the diol / monomer molar ratio. The operating temperature in step c) is between 60 and 250° C., preferably between 90 and 220° C., and suitably between 100 and 210° C. It is particularly advantageous to implement a series of gas-liquid separations, advantageously a series of 2 to 5 successive separations, since it makes it possible to adjust the temperature of the liquid effluent in each separation in response to the abovementioned constraints.

[0091] The regulation of the pressure in step c), preferably in each separation section, is advantageously carried out so as to allow evaporation of the diol at a defined temperature in each separation section, while minimizing repolymerization and allowing optimal integration in terms of energy, which is generally between 0.00001 and 0.2 MPa, preferably between 0.00004 and 0.15 MPa, and advantageously between 0.00004 and 0.1 MPa.

[0092] The gas-liquid separation section or sections are advantageously agitated by any method known to those skilled in the art.

[0093] (Step d) of separating the monomers) The process according to the invention comprises a step d) of separation of the liquid monomer effluent obtained from step c) into a heavy impurities effluent and a pre-purified monomer effluent.

[0094] Said step d) is advantageously operated at a temperature below 250°C, preferably below 230°C, highly preferably below 200°C and preferably above 110°C, a pressure below 0.001 MPa, preferably below 0.0005 MPa, preferably below 0.00005 MPa and preferably above 0.000001 MPa and a liquid residence time below 10 minutes, preferably below 5 minutes, preferably below 1 minute and preferably above 0.1 seconds.

[0095] The purpose of this separation step d) is to separate the vaporized diester monomers, especially BHET, from the oligomers that were not completely converted during the depolymerization step and remain liquid, thus also trapping heavy impurities, e.g. pigments, as well as from the unconverted polyester polymer, from other polymers that may be present in the polyester feedstock, and from the polymerization catalyst, while minimizing the loss of monomers due to repolymerization. Some oligomers may possibly be entrained with monomers, especially those with small size (i.e. those with low molar mass, e.g. dimers). Heavy impurities, such as pigments, unconverted polyester polymer, other polymers that may be present in the polyester feedstock, and the polymerization catalyst are advantageously located together with the oligomers in the heavy impurities effluent.

[0096] Due to the possible presence of polymerization catalysts in the polyester feedstock, the separation must be carried out with very short liquid residence times and at temperatures below 250° C., limiting any risk of repolymerization of the monomers, and more particularly of the BHET, during this step. Separation by simple atmospheric distillation is therefore not considered.

[0097] Advantageously, the separation step d) implements a falling film or thin film evaporation system or a falling film or thin film short path distillation system, preferably a falling film or thin film short path distillation system.

[0098] Very low operating pressures, advantageously less than 0.001 MPa, preferably less than 0.0005 MPa, suitably less than 0.00005 MPa and preferably more than 0.000001 MPa, are necessary in order to make it possible to operate step d) at temperatures below 250° C., preferably below 230° C., whilst allowing the monomers to vaporize. A polymerization inhibitor may advantageously be mixed with the liquid monomer effluent before feeding it to said step d).

[0099] A solvent may be advantageously mixed with the liquid monomer effluent before being fed to said step d) to facilitate the removal of heavy impurities, such as pigments, at the bottom of the short-path distillation or evaporation system. This solvent must have a much higher boiling point than the target diester monomers, especially BHET, under the operating conditions of step d). It may be, for example, polyethylene glycol, or PET oligomers.

[0100] In particular, the heavy impurities effluent comprises pigments, oligomers and possibly unseparated BHET. The heavy impurities effluent is advantageously recycled in whole or in part to conditioning step a) and / or step b). A portion of the heavy impurities effluent may advantageously be recycled directly to step a) and / or step b), alone or in a mixture with the diol effluent. The heavy impurities effluent may advantageously undergo at least one purification step, preferably a filtration step, before its recycling, so as to reduce the amount of pigments and / or other solid impurities. The separated heavy impurities effluent portion having a high pigment content may advantageously be purged from the treatment process and sent to an incineration system. The heavy impurities effluent portion is preferably recycled to step a) and / or step b) without prior separation of solid impurities.

[0101] Said pre-purified monomer effluent (also called pre-purified diester monomer effluent) obtained from the separation section of step d) is advantageously sent to a purification step e).

[0102] Optionally, said pre-purified monomer effluent obtained from the separation section of step d) may be sent before step e) to a gas / liquid separation section, operated in any installation known to the skilled person at a temperature between 100 and 250° C., preferably between 110 and 200° C., suitably between 120 and 180° C., and at a pressure between 0.00001 and 0.1 MPa, preferably between 0.00001 and 0.01 MPa, suitably between 0.00001 and 0.001 MPa. In a preferred embodiment of the present invention, separation step d) is implemented in a system of evaporation by falling film or thin film short path distillation, said optional gas-liquid separation section being integrated into the evaporation system. The optional gas-liquid separation section allows the separation of the gaseous diol effluent and the liquid pre-purified monomer effluent, further reducing the amount of diol remaining in the pre-purified monomer effluent and even removing the residual diol by recovering in the gaseous diol effluent more than 50% by weight, preferably more than 70% by weight, and preferably more than 90% by weight of the diol that may be entrained in the pre-purified monomer effluent in step d). The amount of monomer entrained in the gaseous diol effluent is preferably less than 1% by weight, preferably less than 0.1% by weight, and more preferably less than 0.01% by weight, relative to the amount by weight of monomer present in the pre-purified monomer effluent. The gaseous diol effluent is then advantageously condensed and optionally pretreated in a purification step, alone or in a mixture with one or more diol effluents obtained from step c), recycled to step a) and / or step b) and / or recycled as a mixture to step e). If the process comprises this optional gas-liquid separation section, it is the liquid pre-purified monomer effluent obtained at the end of said optional gas-liquid section that is sent to step e).

[0103] (purification process e)) The process according to the invention comprises a step of purification of the pre-purified monomer effluent obtained from step d) to yield at least one decolorized purified diester monomer effluent and a spent solvent effluent.

[0104] Said purification step e) advantageously makes it possible to remove residual dyes from the prepurified monomer effluent, in particular those whose boiling point is below the cut point, i.e. in particular under the temperature and pressure conditions carried out in step d) of the separation of the monomers, since these residual dyes entrained with the prepurified monomer effluent in which they are coloured can be effectively removed in said purification step e). Purification step e) also advantageously makes it possible to remove residual organic or inorganic, in particular colourless, impurities which may still be present in the prepurified monomer effluent obtained from step d), such as residual salts, compounds derived from diol dimers, in particular ethylene glycol dimers, i.e. compounds derived from diethylene glycol, such as diethylene glycol esters (e.g. 2-(2-hydroxyethoxy)ethyl terephthalate 2-hydroxyethyl) and other comonomers of the diester monomers (e.g. positional isomers of BHET) which were not removed by distillation.

[0105] The purification step e) comprises an adsorption substep e1) and a crystallization substep e2), the substeps e1) and e2) being explained below. Preferably, the purification step e) comprises an adsorption substep e1) followed by a crystallization substep e2).

[0106] (Adsorption sub-process e1) Advantageously, the adsorption substep e1) implements at least one section for mixing the prepurified monomer effluent obtained from step d) or optionally the liquid prepurified monomer effluent with a solvent and at least one adsorption section. The adsorption substep e1) makes it possible to obtain an adsorption-pretreated monomer effluent, which is advantageously at least partially decolorized.

[0107] The mixing section of substep e1) makes it possible to obtain a monomer-solvent mixture, which is fed with the liquid prepurified monomer effluent obtained from step d) or optionally with the liquid prepurified monomer effluent and with a solvent, preferably chosen from water, alcohols, diols and mixtures thereof, preferably from water, diols, such as ethylene glycol and mixtures thereof. Preferably, the solvent fed to the mixing section of substep e1) comprises, preferably consists of, water and / or diol, more particularly the same diol used for the depolymerization by glycolysis, i.e. the same diol, such as ethylene glycol, fed to steps a) and / or b).

[0108] Advantageously, the solvent fed to the mixing section of substep e1) comprises, preferably consists of, a portion of the diol effluent obtained from step c), all or part of the optionally purified solvent effluent obtained from the spent solvent effluent obtained at the outlet of the solid-liquid separation section of substep e2), a supply of solvent, preferably diol and / or water, external to the process according to the invention, or a mixture thereof. According to a particular embodiment of the invention, this solvent comprises, preferably consists of, all or part of the purified or unpurified solvent effluent obtained from the spent solvent effluent obtained at the outlet of the solid-liquid separation section of substep e2), optionally supplemented by a supply of solvent external to the process according to the invention.

[0109] Preferably, the adjustment of the amount of solvent introduced into the mixing section of substep e1) is carried out in such a way that the pre-purified monomer effluent, or optionally the liquid pre-purified monomer effluent, represents between 20% and 90% by weight, preferentially between 30% and 80% by weight, preferably between 40% and 75% by weight, even more preferably between 40% and 60% by weight of the total weight of the monomer-solvent mixture in said mixing section.

[0110] Advantageously, the mixing section of substep e1) is operated at a temperature between 50 and 200°C, preferably between 70 and 170°C, and preferably between 80 and 150°C, and at a pressure between 0.1 and 1.0 MPa, preferably between 0.1 and 0.8 MPa, and preferably between 0.1 and 0.5 MPa. The solvent may be heated prior to said mixing section, preferably to a temperature between 50 and 200°C, preferably between 70 and 170°C, and preferably between 80 and 150°C, at which the mixing section is operated.

[0111] The mixing section of sub-step e1) may possibly implement a static or dynamic mixer, in particular a static mixer.

[0112] Advantageously, the monomer-solvent mixture obtained at the end of the mixing section of substep e1) is fed to at least one adsorption section, preferably 1 to 10, better still 1 to 4 adsorption sections. Each adsorption section of substep e1) is advantageously operated at a temperature of 50 to 200° C., preferably 70 to 170° C., preferentially 80 to 150° C., better still 80 to 120° C., and highly advantageously at a pressure of 0.1 to 1.0 MPa, in particular 0.1 to 0.8 MPa, more particularly 0.1 to 0.5 MPa, in the presence of at least one adsorbent.

[0113] Each adsorption section advantageously comprises at least one adsorber (e.g. reactor or column), preferably up to four adsorber. Highly advantageously, the residence time in each adsorber of the adsorption step is between 20 min and 40 h, preferably between 1 h and 30 h, preferably between 1 h and 20 h. The residence time is defined here as the ratio between the internal volume of the adsorber and the volumetric flow rate of the monomer-solvent mixture obtained from the mixing section. If the adsorption section or sections comprise more than one adsorber, i.e. between 2 and 4 adsorber, the adsorber are arranged in series or in parallel with one another in each section.

[0114] Each adsorption section is operated in the presence of at least one adsorbent, and preferably up to 5 different adsorbents. According to a very particular embodiment, each adsorption section implements one or two different adsorbents. According to the invention, the adsorbents are said to be different if they are different in their nature and / or their composition and / or their different particle size and / or their textural properties, such as pore volume. Preferably, the different adsorbents are of different nature. The reason is that it may be advantageous to combine two or more different adsorbents, in particular adsorbents of different nature, to optimize the removal of residual dyes, which may themselves be of very different nature. Indeed, since the polyester feedstock of the present process is obtained from polyester waste, for example PET packaging or plastic bottle waste, it may contain a very large number of colored and / or opaque PET and therefore a very large number of different dye compounds. The color of the effluent obtained from step d) may also originate from the decomposition or transformation of the compounds constituting the feedstock during the conditioning step a), the depolymerization step b), the diol separation step c) and the monomer separation step d).

[0115] When the adsorption section comprises 2 to 5 different adsorbents, said different adsorbents are in a mixture or arranged in series within said adsorption section, preferably arranged in series, more preferentially each of the adsorbents is in a different adsorbent (e.g. reactor or column) arranged in series or in parallel, preferably arranged in series.

[0116] Advantageously, the adsorbent or adsorbents are in particular in solid form. Preferably, the adsorbent or adsorbents are chosen from activated carbon, alumina and clay. The activated carbon is obtained, for example, from petroleum coke, bituminous coal or any other fossil origin, or from biomass, for example wood, coconut or any other biomass source. Different starting materials may be mixed to obtain an activated carbon that may be used as an adsorbent in said adsorption section. The clay may be a layered double hydroxide or a natural or converted clay, for example, as known to those skilled in the art as bleaching earth. Preferably, at least one adsorbent is activated carbon. Thus, when the adsorption section comprises a single type of adsorbent, said adsorbent is activated carbon, and when the adsorption section comprises two or more different adsorbents, one adsorbent is activated carbon and one or more others are another activated carbon, alumina and / or clay, preferably activated carbon and / or clay, more particularly clay.

[0117] Preferably, the pore volume (Vp) of each adsorbent, determined by mercury porosimetry, is greater than or equal to 0.25 mL / g, preferentially greater than or equal to 0.40 mL / g, suitably greater than or equal to 0.50 mL / g, and preferably less than or equal to 5 mL / g.

[0118] Preferably, each adsorption section of substep e1) is implemented as follows: - in a flow-through fixed bed mode, i.e. in at least one adsorber containing a fixed bed of one or more adsorbents, in particular in at least one column of one or more adsorbents; operation is possible in upflow or downflow mode, preferably in upflow mode, or - stirred systems, advantageously in at least one continuously stirred reactor; also known as continuous stirred tank reactor (CSTR).

[0119] If the adsorption section is implemented in stirred mode in at least one stirred reactor of the CSTR type, the reactor or reactors are followed by a filtration system for recovering said adsorbent or adsorbents present in suspension in the treated liquid. Preferably, the adsorption section is implemented in flow-through fixed bed mode.

[0120] Preferably, when each adsorption section comprises at least two different adsorbents, the adsorbents may be: - all present in a mixture or in succession of fixed beds in each column of one or more adsorption sections; or - used in each of the adsorption subsections of one or more adsorption sections, the subsections being placed in series with one another, each adsorption subsection comprising, preferably consisting of, 1 to 4, preferably 2 to 4, fixed bed adsorbent columns.

[0121] Highly advantageously, each of the adsorption sections or subsections comprises 2 to 4 fixed bed columns, in particular at least 2 fixed bed columns, preferably 2 to 4 fixed bed columns of the same adsorbent or adsorbents. When an adsorption section or subsection comprises two columns of the same adsorbent or adsorbents, the adsorption section may be operated according to a "swing" operation mode, in which one of the columns is on-line while the other column is in reserve. When the adsorbent in the on-line column is exhausted, this column is isolated while the in-reserve column is placed on-line. The used adsorbent of the isolated column may then be regenerated in situ and / or replaced with fresh adsorbent and placed back on-line again where the other column was isolated. Another way to operate the adsorbent columns is to have at least two columns operating in series: when the adsorbent in the lead column (i.e. the first column in the series) becomes worn out, this first column is isolated, the spent adsorbent is regenerated in-situ or replaced with fresh adsorbent, said column is then put back on-line at the last position in the series of columns, etc. This operation is called "lead-lag". Highly preferably, each adsorption section implements at least two columns of the same adsorbent, preferably two to four columns of the same adsorbent, preferentially two columns of the same adsorbent, operating in a "lead-lag" manner.

[0122] The combination of at least two columns of the same adsorbent makes it possible in particular to improve the possibly rapid saturation and / or clogging of the adsorbent. In particular, the presence of at least two adsorbent columns advantageously facilitates the replacement and / or regeneration of the adsorbent without shutting down the adsorption unit (e1) and thus the treatment process, thus reducing the risk of clogging, preventing unit shutdowns due to adsorbent saturation, controlling costs and limiting adsorbent consumption, while ensuring continuous production of purified diester monomer. This combination of at least two adsorbent columns also advantageously makes it possible to maximize the adsorption capacity of said adsorbent in each adsorption unit, in particular when operating in the "lead-lag" mode.

[0123] In a very particular embodiment of the invention, each adsorption section comprises two different adsorbents, and each adsorption section very preferentially comprises a first subsection comprising at least two, preferably from two to four, fixed bed columns of activated carbon and a second subsection comprising at least two, preferably from two to four, fixed bed columns of another adsorbent, preferably chosen from another activated carbon or a clay, the first subsection operating in swing or reed-lag mode and the second subsection operating in particular in swing or reed-lag mode and being located upstream or downstream of the first subsection of fixed bed activated carbon columns.

[0124] Preferably, each sorbent is in the form of granules, extrudates or powder. Preferably, each sorbent is in the form of: in the form of granules or extrudates, if the adsorption section or sections are implemented in a flow-through fixed bed mode, and - in the form of a powder, when the adsorption section or sections are implemented in a stirred reactor of the CSTR type.

[0125] The size of the at least one adsorbent, especially when it is in the form of granules or extrudates, is such that the smallest dimension of the at least one adsorbent (corresponding to the diameter of the circle circumscribing the basis of the granules or lobe extrudates, or the diameter of the cylinder circumscribing the basis of the cylinder of cylindrical type extrudates; this dimension is also called "diameter") is preferably between 0.1 and 5 mm, preferentially between 0.3 and 2 mm. For example, activated carbon extrudates with a diameter of 0.8 mm sold by Cabot Norit, or granules in the size range of 0.4 to 1.7 mm sold by Chemviron may be suitable as adsorbents in the adsorption section of substep e1).

[0126] The adsorption substep e1) may advantageously comprise a step of regeneration of said adsorbent(s).

[0127] An adsorption-pretreated monomer effluent is obtained at the end of each adsorption section and is advantageously fed to the crystallization subsection e2). If substep e1) implements more than one adsorption section, i.e. 2 to 10, preferably 2 to 4 adsorption sections, the monomer effluents resulting at the outlet of the adsorption sections may advantageously be recombined to constitute the adsorption-pretreated monomer effluent, which is then fed to the crystallization substep e2).

[0128] (Crystallization sub-step e2) Advantageously, the crystallization substep e2) implements at least one solid production section and at least one solid-liquid separation section. The crystallization substep e2) makes it possible to obtain a decolorized purified diester monomer effluent and a spent solvent effluent.

[0129] Advantageously, the crystallization substep e2) implements one or more crystallization or precipitation operations and one or more solid-liquid separation operations. According to a particular embodiment of the invention, the crystallization substep e2) implements a solid production section as described below followed by a solid-liquid separation section as further detailed below. According to another particular embodiment of the invention, the crystallization substep e2) implements two or more solid production sections as described below, preferably between two and five solid production sections, each of which is followed by a solid-liquid separation section as further detailed below.

[0130] The solids-producing section of substep e2) is fed with the pre-purified monomer effluent from step d) or with the adsorption-pretreated monomer effluent from substep e1), preferably with the adsorption-pretreated monomer effluent from substep e1). Optionally, the solids-producing section may be fed with a crystallization solvent, which may be the same or different from the solvent introduced into the mixing section of substep e1). The crystallization solvent is advantageously selected from water, monoalcohols, diols, ethers, aldehydes, esters, hydrocarbons and mixtures of at least two of these compounds belonging to the same or different chemical families. Preferably, said crystallization solvent is selected from water, monoalcohols having 1 to 12 carbon atoms, such as methanol or ethanol, diols having 1 to 12 carbon atoms, aromatic hydrocarbons, such as monoaromatic compounds or mixtures of monoaromatic compounds, and mixtures of at least two of said compounds. Highly advantageously, the crystallization solvent is water, a monoalcohol having 1 to 12 carbon atoms, such as methanol or ethanol, a diol having 1 to 12 carbon atoms, such as ethylene glycol, a monoaromatic compound, such as xylene, or a mixture thereof.Preferably, the crystallization solvent is water, a diol having 1 to 12 carbon atoms, preferably ethylene glycol, or a mixture thereof.

[0131] According to a preferred embodiment of the invention, the crystallization solvent comprises, and preferably consists of, all or part of the solvent effluent obtained from the spent solvent effluent obtained at the end of the solid-liquid separation section of substep e2), which may be purified or unpurified, optionally supplemented by a supply of solvent external to the process according to the invention.

[0132] Preferably, in case a crystallization solvent is introduced in substep e2), the amount of crystallization solvent introduced into the solids production section is adjusted so that the pre-purified monomer effluent fed to substep e1) represents between 1% and 75% by weight, preferentially between 5% and 45% by weight, preferably between 15% and 35% by weight of the total weight of the mixture in said solids production section (i.e. the mixture comprising the pre-purified monomer effluent, the solvent introduced in substep e1) and the crystallization solvent introduced in substep e2).

[0133] Before being introduced into the solids production section, all or part of the crystallization solvent may preferably be heated or cooled to the temperature at which the adsorption section is operated, in particular to a temperature of preferably 0 to 120°C, preferably 5 to 100°C, suitably 10 to 90°C.

[0134] Advantageously, the temperature at which the solids production section of substep e2) is operated (i.e. the temperature of the effluent obtained from said solids production section) is between 0 and 100° C., preferably between 5 and 80° C., and preferably between 10 and 70° C. More precisely, in the solids production section, the adsorption-pretreated monomer effluent is cooled, optionally in a mixture with the crystallization solvent, from the temperature at which the adsorption section is operated, i.e. a temperature of between 50 and 200° C., preferably between 70 and 170° C., preferentially between 80 and 150° C., and preferably between 80 and 120° C., to a temperature of between 0 and 100° C., preferably between 5 and 80° C., and preferably between 10 and 70° C.

[0135] The cooling may be implemented according to any method known to the skilled person. For example, in particular in the batch mode, the realization of the cooling of the temperature may be without regulation of the temperature drop (i.e. without imposed temperature ramp; therefore only the initial and final temperatures are controlled) or according to at least one decreasing temperature gradient, in particular according to a decreasing temperature gradient of 5-30° C. / h, more particularly 8-15° C. / h, or else according to both modes linked together in series, i.e. without control for one part of the cooling and according to a decreasing temperature gradient for another part of the cooling. According to another example, the cooling may simply result from the introduction of the stream to be cooled from the adsorption step b), i.e. the adsorption-pretreated monomer effluent obtained from the adsorption step e1) or the mixture containing the adsorption-pretreated monomer effluent and the crystallization solvent, into a reservoir having a volume advantageously adapted to the flow rate of the stream to be cooled and kept at a temperature of 0-100° C., preferably 5-80° C., suitably 10-70° C.

[0136] The pressure at which the solids-producing section is advantageously operated is between 0.00001 and 1.00 MPa, preferably between 0.0001 and 0.50 MPa, and suitably between 0.001 and 0.20 MPa. According to a particular embodiment of the invention, the solids-producing section is operated under vacuum, preferably at a pressure between 0.0001 and 0.10 MPa, preferentially between 0.001 and 0.01 MPa. According to another particular embodiment, the solids-producing section is advantageously operated in a jacketed reactor, at a pressure between 0.01 and 1.00 MPa, preferably between 0.05 and 0.20 MPa, and suitably at atmospheric pressure, i.e. 0.10 MPa.

[0137] Advantageously, the purpose of the solids-producing section is at least in part to solidify, i.e. to crystallize or precipitate, the diester monomer, preferably BHET, in particular present in the adsorption-pretreated monomer effluent obtained from substep e1). The solids-producing section therefore comprises, preferably consists of, a precipitation or crystallization stage, implemented by any precipitation or crystallization technique known to the skilled person. The solids-producing section is preferably a section for crystallization, for example by cooling or concentration, implemented in any equipment known to the skilled person, for example as defined in the journal Techniques de l'Ingenieur, "Cristallisation industrielle - Aspects pratiques" [Industrial Crystallization - Practical Aspects], ref. J2788 V1, followed by liquid-solid separation.

[0138] According to a preferred embodiment of the present invention, water is mixed as crystallization solvent with the adsorption-pretreated monomer effluent obtained from substep e1) and the solids production section is operated under conditions such that the temperature of the effluent obtained from said solids production section is between 5 and 50°C, preferably between 10 and 40°C.

[0139] According to another preferred embodiment of the present invention, the crystallization solvent introduced and mixed with the adsorption-pretreated monomer effluent obtained from substep e1) is ethylene glycol and the solids production section is operated under conditions such that the temperature of the effluent obtained from said solids production section is between 5 and 50°C, preferably between 10 and 40°C.

[0140] Advantageously, said section for producing solids, preferably by crystallization, comprises one or more crystallization operations, operating in series or in parallel, which are carried out batchwise or continuously, preferably continuously.

[0141] The solid production section makes it possible to obtain a heterogeneous effluent comprising a solid phase and a liquid phase of the diester monomer, which is advantageously sent to a solid-liquid separation section.

[0142] In the solid-liquid separation section, the diester monomer, preferably BHET, advantageously in solid form, in particular in crystalline form, is separated from a liquid phase comprising all or part of the solvent introduced in the mixing section of substep e1) and the crystallization solvent optionally introduced in the solid-producing section. The solid-liquid separation section advantageously implements any means of solid-liquid separation known to the person skilled in the art, in particular at least one filtration, decantation and / or centrifugation system. The solid diester monomer thus separated constitutes the decolorized purified diester monomer effluent and the liquid phase constitutes the spent solvent effluent.

[0143] According to a particular embodiment of the invention, the decolorized purified diester monomer effluent, recovered in solid form, preferably by filtration or centrifugation, may further advantageously undergo all or part of the following operations, carried out one or more times without a predefined chronological sequence: rinsing with a solvent identical or different to that feeding the mixing section or, optionally, the solid-producing section; additional filtration or centrifugation; removal of residual solvent by any method known to the skilled person, for example by evaporation to dryness; shaping, for example into powder or granules; and storage of the solid.

[0144] According to another embodiment of the invention, the decolorized purified diester monomer effluent is recovered in a solid-liquid separation section, preferably by filtration or centrifugation, and then sent directly (i.e. without a stage of solid storage) to a polymerization process known to those skilled in the art, optionally followed by an operation of rinsing of the solid purified diester monomer effluent with water or a diol effluent, such as ethylene glycol, preferably with water, prior to the polymerization reaction, and subsequently heating the rinsed solids for the purposes of melting.

[0145] According to another particular embodiment of the invention, the purification step e) may comprise, as described above, a crystallization substep e2) followed by an adsorption substep e1), in particular as follows: - substep e2) is fed with the pre-purified monomer effluent obtained from step d) and, optionally, a crystallization solvent; - substep e2) results in a solid, which is fed to substep e1); - the solids resulting at the end of substep e2) are dissolved in the solvent of the mixing section of substep e1) to obtain a solution; - the solution obtained at the outlet of the mixing section of substep e1) is fed to one or more adsorption sections of substep e1); a decolorized purified diester monomer effluent is obtained in liquid form, which can be precipitated and / or recrystallized according to any one of the methods known to the person skilled in the art to obtain a decolorized purified diester monomer effluent in solid form.

[0146] Advantageously, the decolorized purified diester monomer effluent obtained at the end of the process according to the invention preferably comprises at least 90% by weight, preferentially at least 95% by weight, suitably at least 98% by weight of diester monomer (i.e. the product targeted by the process according to the invention), preferably BHET. The decolorized purified diester monomer effluent obtained at the end of the process according to the invention highly advantageously comprises less than 5% by weight, preferably less than 1% by weight, preferentially less than 0.5% by weight of impurities of the type of esters of dicarboxylic acids with dimers or trimers of at least one diol, for example ester compounds derived from diethylene glycol (for example 2-(2-hydroxyethoxy)ethyl 2-hydroxyethyl terephthalate).

[0147] Highly advantageously, the decolorized purified diester monomer effluent obtained at the end of the process according to the invention is a white solid. Purification step e) comprises a stage of treatment by adsorption of a monomer solution followed by a stage of crystallization of said monomer. Purification step e) thus makes it possible to fully decolorize the prepurified diester monomer effluent obtained from step d). In particular, dyes possibly present in the prepurified monomer effluent obtained from step d) remain captured by the adsorbent in the adsorption section during the solids formation operation or remain dissolved in the solvent or mixture of solvents (solvent introduced in substep e1) and possibly in substep e2)) and are therefore concentrated in the spent solvent effluent.

[0148] The decolorized purified diester monomer effluent obtained upon completion of purification step e) of the process of the invention is therefore advantageously a white solid in appearance.

[0149] The decolorized purified diester monomer effluent obtained at the end of step e) may be characterized by UV-visible spectroscopy to confirm the presence of an absorption band in the visible range, in particular 400-800 nm. According to this characterization method, the decolorized purified diester monomer effluent is preferably characterized by UV-visible spectroscopy, in particular at 400-800 nm, advantageously after dissolution in a liquid medium, i.e. advantageously in a suitable solvent, preferably at 0.1% to 10% by weight, at ambient temperature (typically 15-30° C., in particular 20-25° C.), using conventional laboratory benchtop UV-visible spectroscopy. Ethanol may be used as a suitable solvent, allowing dissolution of a sample of the decolorized purified diester monomer effluent. Conventional cuvettes with an optical path length of 1 cm or 1 inch may be used. Preferably, the UV-visible spectrum of the bleached purified diester monomer effluent is determined using a solution of the bleached purified diester monomer effluent prepared at 5% by weight in ethanol and a cuvette having an optical path length of 1 inch. According to this method, the bleached purified diester monomer effluent obtained by the method according to the invention advantageously exhibits a spectrum that does not display any significant absorption bands (i.e., cannot be distinguished from background noise) within the visible wavelength range, i.e., within the range of 400-800 nm.

[0150] The decolorized purified diester monomer effluent obtained at the end of step e) may be characterized according to the colorimetric method as described in ASTM D6290 2019. The light source chosen is Illuminant D65 and the measurements are made in reflection, in specular excluded mode, with a standard observer at 10°. The measurements are based on the CIE L * a * b * According to colorimetry, the decolorized purified diester monomer effluent obtained by the process according to the invention advantageously has a CIE L * a * b * Indicate the frame of reference: - Lightness (or luminance) parameter L *close to 100, more particularly greater than 90.00, preferably greater than 92.00 (100.00 being the maximum); - Parameter a * (corresponding to the green-red axis); close to 0, more particularly between -1.50 and +1.50, preferably between -1.00 and +1.00; and - Parameter b * (corresponding to the blue-yellow axis); close to 0, more specifically -2.50 to +2.50, more specifically -1.00 to +1.50.

[0151] The spent solvent effluent comprises all or part of the solvent introduced into the mixing section of substep e1) and the crystallization solvent optionally introduced into the solid production section. It may advantageously also comprise dyes and / or other residual impurities. Preferably, the spent solvent effluent comprises less than 20% by weight, preferentially less than 15% by weight, preferably less than 10% by weight, preferably less than 5% by weight of diester monomers (i.e. products targeted by the process according to the invention), preferably BHET monomers.

[0152] The spent solvent effluent may then be recycled to the mixing section of substep e1) or to the sections of steps a) and / or b) of the process in case the purified solvent is a diol of the same nature as that used for the depolymerization reaction, and / or to the section e2) as a crystallization solvent, as the case may be. The spent solvent effluent may be treated, at least in part, in particular to separate the dyes and / or impurities, for example by adsorption, and thus to recover the purified solvent, which may then be recycled to the mixing section of substep e1) or to the sections of steps a) and / or b) of the process in case the purified solvent is a diol of the same nature as that used for the depolymerization reaction, and / or to the section e2) as a crystallization solvent, as the case may be. The spent solvent effluent may, in addition to separation of the dye and / or impurities, undergo an operation for separation of the solvent, for example by distillation or decantation, if a crystallization solvent is introduced in substep e2) and which is different from the solvent introduced in the mixing section of substep e1), to obtain two separate solvents, one of which can be recycled to the mixing section of substep e1) and the other of which can be recycled to the solid-producing section of substep e2).

[0153] The bleached purified diester monomer effluent obtained at the end of the process according to the invention may therefore be fed directly or indirectly to a polymerization process known to the person skilled in the art, for the purpose of producing a polyester polymer, preferably a PET or a PET-based copolyester, which is indistinguishable from the corresponding virgin resin, said polymerization process may be fed, in addition to the bleached purified diester monomer effluent, with ethylene glycol, terephthalic acid or dimethyl terephthalate, or any other monomer, depending on the targeted (co)polymer.

[0154] The following figures and examples are illustrative of the present invention and are not intended to limit the scope of the invention.

[0155] (Example) In the following examples, the conditioning step a), the depolymerization step b), the diol separation step c) and the monomer separation step d) are identical and are described below. The only variation is in the purification step e) between the processes of Example 1 (in accordance with the invention) and Example 2 (not in accordance with the invention).

[0156] A polyester feedstock, specifically containing 20% ​​by weight of opaque PET, is obtained for processing from a collection and sorting channel.

[0157] The polyester feedstock comprises 20 wt% opaque PET, which itself contains 6.2 wt% TiO2 pigment. 4 kg / h of flakes of the polyester feedstock are brought to a temperature of 250°C and then injected into a first stirred reactor together with 11.5 kg / h of ethylene glycol (MEG), which is maintained at 250°C, and then into a second and third stirred reactor, which are maintained at 220°C. The reactors are maintained at a pressure of 0.4 MPa. The residence time, defined as the ratio of the liquid volume in the reactor to the sum of the liquid volumetric flow rates entering the reactors, is set to 20 minutes in the first reactor and 2.1 hours in the second and third reactors. At the outlet of the third reactor, the reaction effluent consisted of 67.7 wt. % diol composed very predominantly of ethylene glycol (MEG) (i.e., containing 95 wt. % or more of MEG), 25.8 wt. % diester monomer composed very predominantly of bis(2-hydroxyethyl) terephthalate (BHET) (i.e., containing 95 wt. % or more of BHET), 20.32 wt. % TiO, and 6.1 wt. % heavy compounds including, inter alia, dimers and / or oligomers of BHET.

[0158] The separation of the diols present in the reaction effluent is carried out by evaporation in a series of two flash vessels at temperatures ranging from 180° C. to 120° C. and pressures from 0.04 MPa to 0.004 MPa, followed by a thin-film evaporator operated at 175° C. and 0.0005 MPa. At the end of this evaporation step, a MEG-rich stream of 10.46 kg / h and a BHET-rich liquid stream of 5.02 kg / h are recovered. The MEG-rich stream corresponding to the diol effluent is sent to a step of purification by distillation to give a purified MEG stream, which may be recycled at least on the one hand to the depolymerization reactor. The BHET-rich liquid stream corresponding to the liquid monomer effluent consists of 79.6% by weight of BHET diester monomer, 0.6% by weight of MEG, 1.0% by weight of TiO2 and 18.8% by weight of heavy compounds, including dimers of BHET.

[0159] The BHET-rich liquid stream is then injected into a short-path evaporator, also called short-path distillation, which is operated at a pressure of 20 Pa. The hot oil at 215° C. allows the evaporation of BHET, which is subsequently condensed in the short-path evaporator at 130° C. to obtain a liquid stream of pre-purified BHET (corresponding to the pre-purified monomer effluent). The residence time in the short-path evaporator is 1 min. The liquid stream of pre-purified BHET exhibits a flow rate of 3.8 kg / h and is recovered as distillate from the short-path evaporator. It consists of 99% by weight of BHET diester monomer and does not contain any traces of TiO2. A heavy residue with a flow rate of 1.19 kg / h is recovered as residue from the short-path evaporator, which consists of 16.7% by weight of BHET diester monomer, 79.2% by weight of BHET oligomers and 4.1% by weight of TiO2. A portion of the heavy residue may be purged while another portion may be recycled to the reaction step.

[0160] Example 1 - In accordance with the invention (Adsorption sub-process e1) A liquid stream of pre-purified BHET containing 99% by weight of BHET diester is pressurized to 0.15 MPa and fed to a mixing section with a flow rate by weight of 3.8 kg / h, to which a stream of water is also fed. The feed rate of water is adjusted so that said liquid stream of pre-purified BHET represents 50% by weight of the mixture (liquid stream of pre-purified BHET + water). The mixing section is operated at 90° C. and a pressure of 0.15 MPa.

[0161] The resulting mixture is then fed to the adsorption section, which consists of two columns, each packed with adsorbent (i.e. having a fixed bed of adsorbent). The adsorption section is operated at 90° C. and a pressure of 0.15 MPa. One column is on-stream (i.e. in operation) and the other column remains in reserve. The adsorbent used to pack the two columns is activated carbon (reference ROY 0.8 from Cabot Norit) consisting of cylindrical extrudates with a diameter of 0.8 mm.

[0162] The residence time is fixed at 40 min in one column. The linear velocity of the empty column is 2.4 cm / min.

[0163] (Crystallization sub-step e2) A batch of 780 g of the liquid stream obtained at the end of the adsorption substep e1) is mixed with water in a stirred tank until a temperature of 60° C. is reached, so that the amount by weight of the liquid stream of pre-purified BHET introduced in substep e1) represents 20% by weight of the final mixture and the amount of water introduced in substeps e1) and e2) represents 80% by weight of the final mixture. The mixture is cooled to 50° C. over 1 hour while kept under stirring, then gradually cooled to 20° C. according to a gradient of 12° C. / h.

[0164] During the course of cooling, solid particles are formed, giving a suspension of solid in liquid, which mainly contains water. The resulting suspension at 20° C. is then filtered to recover a solid cake and a colored liquid filtrate. The solid cake is rinsed with 1.5 L of water. The rinsed solid cake is recovered and then dried under vacuum at 40° C. overnight to give 320 g of a white solid containing 99% by weight of BHET diester (composition determined by liquid chromatography).

[0165] The recovered solid is white in color. UV-Vis spectroscopy is performed on a BHET solution prepared by dissolving a sample of the obtained white solid at 5 wt% in ethanol. UV-Vis spectroscopy is performed in a cuvette with a 1 inch path length using a Hach DR3900 laboratory benchtop UV-Vis spectrometer. The obtained UV-Vis spectrum does not display any significant absorption bands in the wavelength range of 400-800 nm (see Figure 3).

[0166] Colorimetric measurements are also performed on the obtained solid BHET according to the method of ASTM D6290 2019. A 5 g sample of the solid BHET product is pulverized by grinding in a mortar. 5 g of the ground BHET is placed in a cuvette made of optical quality glass with a diameter of 34 mm. Measurements are performed in reflection using a Konica Minolta CM-2300d colorimeter and SpectraMagic NX software under the following conditions: illuminant D65, specular reflection excluded, standard observer at 10°. Measurements are performed according to the CIE L * a * b * The results are expressed in the reference frame. The results are obtained by averaging the values ​​obtained in the ten measurements carried out on the sample. The results are shown in Table 1.

[0167] Example 2 - Not in accordance with the invention A batch of 780 g of the pre-purified BHET liquid stream obtained at the outlet of the short-path distillation is mixed with water in a stirred tank to achieve a final content of 20% by weight of pre-purified BHET liquid stream and 80% by weight of water, and a final temperature of 60° C. The mixture is cooled to 50° C. over 1 hour while kept under stirring, then gradually cooled to 20° C. according to a downward gradient of 12° C. / h.

[0168] During the course of cooling, solid particles are formed, giving a suspension of solids in a liquid that is composed very predominantly of water. The suspension is then filtered to recover a solid cake and a colored liquid filtrate. The solid cake is rinsed with 1.5 L of water. The rinsed solid cake is recovered and then dried under vacuum at 40° C. overnight to give 320 g of a white solid containing 99% by weight of the BHET diester.

[0169] UV-Visible spectroscopy measurements are performed on a BHET solution prepared by dissolving the resulting white BHET solid in ethanol at 5 wt%. UV-Visible spectroscopy measurements are performed in a cuvette with a 1 inch path length using a Hach DR3900 laboratory benchtop UV-Visible spectrometer. The obtained UV-Visible spectrum displays significant absorption bands in the wavelength range of 400-800 nm (see Figure 3).

[0170] Colorimetric measurements are also performed on the obtained solid BHET according to the method of ASTM D6290 2019. A 5 g sample of the solid BHET product is ground after grinding in a mortar. 5 g of BHET is placed in a cuvette made of optical quality glass with a diameter of 34 mm. Measurements are performed in reflection using a Konica Minolta CM-2300d colorimeter and SpectraMagic NX software under the following conditions: illuminant D65, specular reflection excluded, standard observer at 10°. Measurements are performed according to the CIE L * a * b * The results are expressed in the reference frame. The results are obtained by averaging the values ​​obtained in the 10 measurements carried out on the sample. The results are presented in Table 1.

[0171] [Table 1]

[0172] The results of measurements (by UV-Visible spectroscopy and colorimetry) carried out on the BHET obtained from the methods described in Examples 1 and 2 show the following: - there is no absorption band in the visible range (400-800 nm) for the BHET obtained from the method of Example 1, whereas the BHET obtained from the method of Example 2 displays a significant absorption band in the wavelength range from 400 to 800 nm (see Figure 3); - L reflecting the production of the product by the method described in Example 1 * a * b * The color measurement is "whiter" than that obtained by the method described in Example 2 or the smallest L * a * b * Chromaticity measurements are targeted at L * a * b * The values ​​match for the following reasons: - L of the solid BHET obtained by the method of Example 1 * The value was 93.02, which is greater than 92.00 and is the value (L * =90.02), of solid BHET obtained by the method of Example 1 (matched) * and b * The values ​​of a are 0.03 and 1.00, respectively, which are the values ​​obtained for the solid BHET obtained from the method of Example 2 (a * = 1.21 and b * =2.22), which is closer to 0 in absolute value.

[0173] Therefore, the process described in Example 1 in accordance with the invention, which includes a step of purification of BHET by adsorption followed by a crystallization step, makes it possible to obtain a decolorized purified BHET of better quality (because it is better decolorized) than the BHET obtained at the end of the process described in Example 2 (not in accordance), which includes only a crystallization step as purification step. [Brief description of the drawings]

[0174] [Figure 1] 1 represents a specific embodiment of the present invention. [Diagram 2] 1 represents a specific embodiment of the present invention. [Diagram 3] FIG. 1 shows the UV-visible spectra determined for the solids obtained by the methods described in Example 1 (grey) and Example 2 (black).

Claims

1. A method for the depolymerization of a polyester feedstock containing polyethylene terephthalate, the method comprising the following steps: a) Conditioning step; feeding at least said polyester feedstock; producing a conditioned feedstock stream; b) Depolymerization step by glycolysis; feeding at least the conditioned feedstock stream, operating at a temperature of 150 to 300 °C with a residence time of 0.1 to 10 hours in the presence of a diol, and setting the weight ratio between the total amount of diol present during step b) and the amount of diester contained in the conditioned feedstock stream to 0.3 to 8.0; producing a reaction effluent; c) Diol separation step; feeding at least the reaction effluent obtained from step b), operating at a temperature of 60 to 250 °C and a pressure lower than the pressure of step b); producing at least a diol effluent and a liquid monomer effluent; Implementing the step of separating the diol in one gas-liquid separation section or a series of 2 to 5 consecutive gas-liquid separation sections, each of the gas-liquid separation sections producing a gas effluent and a liquid effluent, feeding the liquid effluent from the preceding section to the subsequent section, the liquid effluent obtained from the last gas-liquid separation section constituting the liquid monomer effluent, and recovering one or more gas effluents to constitute the one or more diol effluents; d) Step of separating the heavy impurity effluent and the pre-purified monomer effluent from the liquid monomer effluent obtained from step c); the temperature during operation is less than 250 °C, the pressure is less than 0.001 MPa, and the liquid residence time is less than 10 minutes; and e) Step of purifying the pre-purified monomer effluent; comprising an adsorption sub-step e1) and a crystallization sub-step e2); producing at least one decolorized and purified diester monomer effluent; operating the adsorption sub-step e1) at a temperature of 50 to 200 °C and a pressure of 0.1 to 1.0 MPa, implementing at least one section for mixing with a solvent and at least one section for adsorption in the presence of at least one adsorbent, The crystallization sub-step e2) implements a solid formation section and operates at a temperature of 0 to 100 °C and a pressure of 0.00001 to 1.00 MPa, followed by a solid-liquid separation section.

2. The step e) of purifying the pre-purified monomer effluent includes an adsorption sub-step e1) and the subsequent crystallization sub-step e2), producing at least one decolorized and purified diester monomer effluent and a spent solvent effluent. The adsorption sub-step e1) is operated at a temperature of 50 to 200 °C and a pressure of 0.1 to 1.0 MPa, implementing at least one section for mixing the pre-purified monomer effluent obtained from step d) with a solvent and at least one section for adsorption in the presence of at least one adsorbent to obtain an adsorption-pretreated monomer effluent. The crystallization sub-step e2) implements a solid formation section, feeds at least the adsorption-pretreated monomer effluent, operates at a temperature of 0 to 100 °C and a pressure of 0.00001 to 1.00 MPa, followed by a solid-liquid separation section, producing a decolorized and purified diester monomer effluent and a spent solvent effluent, according to the method of claim 1.

3. Adjusting the amount of the solvent introduced into the mixing section of sub-step e1) such that the pre-purified monomer effluent obtained from step d) or the solid produced at the end of sub-step e2) accounts for 20 wt% to 90 wt%, preferably 30 wt% to 80 wt%, preferably 50 wt% to 75 wt%, and even more preferably 40 wt% to 60 wt% of the total weight of the mixture in the mixing section, according to the method of claim 1 or 2.

4. The solvent fed into the mixing section of sub-step e1) is selected from water, alcohol, diol, such as ethylene glycol and mixtures thereof, preferably diol, such as ethylene glycol, water, and mixtures thereof, according to the method of claim 1.

5. The temperature when operating sub-step e1) is 70 to 170 °C, preferably 80 to 150 °C, according to the method of claim 1.

6. The pressure when operating sub-step e1) is 0.1 to 0.8 MPa, preferably 0.1 to 0.5 MPa, according to the method of claim 1.

7. At least one adsorbent in the adsorption section of sub-step e1) is activated carbon, according to the method of claim 1.

8. The temperature during the operation of the solid formation section is 5 to 80 °C, preferably 10 to 70 °C, for the method according to claim 1.

9. The pressure during the operation of the solid formation section is 0.0001 to 0.50 MPa, preferably 0.001 to 0.20 MPa, for the method according to claim 1.

10. A crystallization solvent identical or different from the solvent introduced into the mixing section of sub-step e1) is fed to the solid formation section, and the amount of the crystallization solvent introduced into the solid formation section is adjusted such that the pre-purified monomer effluent fed to sub-step e1) accounts for 1 wt% to 75 wt%, preferably 5 wt% to 45 wt%, more preferably 15 wt% to 35 wt% of the total weight of the mixture in the solid formation section, for the method according to claim 1.

11. The polyester feedstock contains at least 50 wt%, preferably at least 70 wt%, suitably at least 90 wt% of polyethylene terephthalate, especially including opaque PET, colored PET, multilayer PET, or a mixture thereof, for the method according to claim 1.

12. The polyester feedstock contains 0.1 wt% to 10 wt% of a pigment, preferably 0.1 wt% to 5 wt% of a pigment and preferably 0.005 wt% to 1 wt% of a dye, especially 0.01 wt% to 0.2 wt% of a dye, for the method according to claim 1.

13. The temperature when implementing step a) is 200 to 300 °C, preferably 250 to 290 °C, and the pressure at that time is preferably 0.1 MPa to 20 MPa, suitably 0.15 MPa to 10 MPa, for the method according to claim 1.

14. A diol stream is fed to step a) at a weight ratio of the diol stream to the polyester feedstock: 0.03 to 6.00, preferably 0.05 to 5.00, preferably 0.10 to 4.00, suitably 0.50 to 3.00, for the method according to claim 1.

15. The weight ratio between the total amount of diol present in step b) and the amount of diester contained in the conditioned feedstock stream is 1.0 to 7.0, preferably 1.5 to 6.0, for the method according to claim 1.

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