Process for depolymerizing polyester feedstock including staged premixing of the polyester feedstock - Patents.com

Abstract

The present invention relates to a process for depolymerizing polyester filler, comprising: a) conditioning the filler by implementing a means for at least partially melting the filler and at least one mixer; feeding the mixers with the filler and a diol stream, the weight ratio of diol stream to filler being between 0.01 and 6.00, and the volumetric dilution level of diol in each mixer being between 3% and 70%; b) depolymerizing the polyester filler at 150-300°C, resulting in a weight ratio of diol to diester in step b) being between 0.3 and 8.0; c) optionally isolating the diol at a temperature between 60-250°C and at a pressure lower than in step b).

Description

[Technical field]

[0001] The present invention relates to a process for the depolymerization of polyesters, preferably polyesters containing polyethylene terephthalate (PET), to obtain a diester monomer stream, more particularly a bis(2-hydroxyethyl) terephthalate (BHET) stream. More particularly, the present invention relates to a process for the depolymerization of a polyester feedstock, preferably a polyester feedstock containing PET, comprising the specific step of conditioning said polyester feedstock by staged premixing of said feedstock with an alcohol stream to obtain a conditioned feedstock in the form of a conditioned, advantageously homogeneous, mixture exhibiting a viscosity below 50 mPa·s, which is then passed to a depolymerization reaction unit. [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 collection and sorting networks. 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) composed of polyester. Polyesters obtained from collection and sorting channels are called polyester or PET eligible for recycling.

[0004] PET eligible for recycling can be divided into four main categories: - Clear PET: consists mainly of colorless transparent PET (generally at least 60% by weight) and pale blue transparent PET, does not contain pigments and may 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 cosmetic, plant protection or dye bottles; - Multilayer PET: containing layers of polymers other than PET or layers of recycled PET with virgin PET (i.e. PET not subject to recycling) or films, e.g. of aluminium, between the layers. Multilayer PET is used after thermoforming to produce packaging materials, e.g. 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, particularly soluble in polyester materials, used to color the materials in which they are introduced. Commonly used dyes have different natures and often contain heteroatoms of the O and N type and conjugated unsaturation, such as quinone, methine or azo groups, or molecules such as pyrazolones and quinophthalones.

[0010] Pigments are finely divided substances, particularly insoluble in polyester materials, which are used to colour and / or opacify the materials into which they are introduced. The main pigments used to colour and / or opacify polyesters, and in particular PET, are metal oxides, such as TiO2, CoAl2O4 or Fe2O3, silicates, polysulfides and carbon black. Pigments are particles generally with a size 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.

[0011] Recycling of colored and opaque PET is therefore extremely problematic.

[0012] 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 PET flakes and is contacted with ethylene glycol in a reactor at a temperature of 180-280° C. for several hours. The BHET obtained at the end of the glycolysis step is purified on activated carbon to separate out certain dyes, for example blue dyes, followed by extraction of the remaining dyes, for example yellow dyes, with alcohol or water. The BHET is crystallized in the extraction solvent and then separated in order to be used in the polymerization process.

[0013] In US Pat. No. 5,399,636, 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, whereupon the resulting diester monomers are purified by filtration, ion exchange and / or passage over activated carbon, before being crystallized and recovered by filtration.

[0014] Patent document 3 describes the production of purified BHET from PET in the form of flakes. The depolymerization step consists of glycolysis of PET flakes in solid form, previously pretreated by washing with water, in a stirred reactor in the presence of ethylene glycol and a catalyst at 180°C to remove the residual water, then at 195-200°C. The depolymerization is followed by steps of preliminary purification of the reaction effluent by cooling, filtration, adsorption and treatment on ion exchange resins, which are presented as being of great importance, before evaporation of the glycol and purification of the BHET. The preliminary purification makes it possible to prevent repolymerization of BHET in the subsequent purification steps.

[0015] Finally, US Pat. No. 5,399,633 describes a method for the depolymerization of opaque PET, in particular polyester feedstocks containing 0.1% to 10% by weight of pigments, by glycolysis in the presence of ethylene glycol. A purified BHET effluent is obtained after certain steps of separation and purification. The patent application envisages the possibility of reactive extrusion in the first step of conditioning the feedstock to initiate the depolymerization reaction.

[0016] The object of the present invention is to improve these processes for the depolymerization by alcoholysis or glycolysis of polyester feedstocks, in particular the process of US Pat. No. 5,399,633. More particularly, it is an object of the present invention to improve the stage of conditioning the polyester feedstock upstream of the depolymerization step and mixing it with at least one alcohol stream as depolymerization agent, in order to obtain a homogeneous stream exhibiting a sufficiently low viscosity, in particular a viscosity below 50 mPa·s, thus allowing an optimal reaction step (i.e. the depolymerization step), in particular in terms of efficiency of the reaction, the required stirring power and operating costs. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] US Patent Application Publication No. 2006 / 0074136 [Patent Document 2] US Patent Application Publication No. 2015 / 0105532 [Patent Document 3] Patent No. 3715812 [Patent Document 4] French Patent Application Publication No. 3053691 Summary of the Invention [Means for solving the problem]

[0018] (Summary of the invention) An object of the present invention is therefore a process for the depolymerization of a polyester feedstock, comprising the steps of: a) a conditioning step using a means for at least partially melting the polyester feedstock and at least one static or dynamic mixer disposed downstream of the means for at least partially melting the polyester feedstock; producing a conditioned feed stream; the conditioning step a) is carried out at a temperature between 200 and 300° C., at least a polyester feedstock and an alcohol stream containing an alcohol compound are fed, the weight ratio of the alcohol stream relative to the polyester feedstock being between 0.03 and 6.00, The means for at least partially melting the polyester feedstock is fed with at least the polyester feedstock; Each static or dynamic mixer is fed with at least a portion of the alcohol stream and with a polyester stream, the volumetric dilution with the alcohol compound being between 3% and 70%, the volumetric dilution with the alcohol compound being the ratio between the volumetric flow rate of the portion of the alcohol stream fed to the static or dynamic mixer under consideration and the sum of the volumetric flow rates of the portion of the alcohol stream fed to the static or dynamic mixer under consideration and the polyester stream, the polyester feedstock fed to the static or dynamic mixer comprises the polyester feedstock and all of the portion of the alcohol stream introduced upstream of the static or dynamic mixer under consideration in step a), b) a step of depolymerization, at which the conditioned feed stream obtained from step a) is fed and operated at a temperature of 150-300° C., a residence time of 0.1-10 hours and a weight ratio between the total amount of alcohol compounds present in step b) and the amount of diesters contained in the conditioned feed stream of 0.3-8.0.

[0019] One advantage of the present invention lies in the advantage of improving the conditioning step of the polyester feedstock to improve the homogenization of the mixture of the polyester feedstock with at least one depolymerization agent, in particular with an alcohol stream, and to obtain a homogenous polyester-depolymerization agent mixture at the outlet of the conditioning section, advantageously having a viscosity of 50 mPa·s or less, preferably 30 mPa·s or less, and highly preferentially 15 mPa·s or less. Such a mixture therefore has the advantage of providing a sufficiently low effective viscosity in the reaction section, making it possible to use reasonable (i.e. limited) stirring powers in the reaction section, in particular in the reactors directly connected to the conditioning unit, which promotes the operability of the depolymerization process and limits the costs required for its implementation. The process according to the invention thus promotes the dispersion and homogenization of the feedstock with at least one alcohol stream, which makes it possible to improve the efficiency of the depolymerization reaction while reducing the stirring powers required for this dispersion and homogenization in the reaction section.

[0020] The invention thus makes it possible to effectively premix the polyester feedstock with at least a part of the depolymerization agents, in particular monoalcohols or diols, required for the depolymerization of polyesters, in particular PET, while observing the technical constraints imposed by the mixing equipment used, in particular the stripping system of the reaction section, but also by the equipment used in the conditioning section, for example static or dynamic mixers, which are recommended to avoid excessive viscosity differences between the fluids to be mixed. Typically, static mixers are used to mix fluids having a viscosity ratio between said fluids ranging up to 1000 (i.e. less than or equal to 1000). However, the invention makes it possible to effectively mix a polyester feedstock containing PET, the viscosity of which in the molten state is typically between 300 and 800 Pa·s, with an alcohol stream, in particular a methanol stream or an ethylene glycol stream, having a viscosity varying between 1 and 0.1 mPa·s in the range of temperatures at which the mixing is carried out, i.e. the viscosity ratio between these two fluids is about 1×105 ~1×10 6 , which is very high and usually has little compatibility with the technical constraints of static or dynamic mixers.

[0021] Finally, one advantage of the present invention is that it can process any type of polyester waste, which increasingly contains pigments, dyes and other polymers, such as bluish, opaque and multi-layered PET. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] (List of Drawings) FIG. 1 represents one particular embodiment of the method according to the invention, in which the depolymerization by glycolysis is carried out in the presence of ethylene glycol and comprises: Step (a): Conditioning a polyester feedstock (1), preferably a polyester feedstock (1) comprising PET: at least partially melting the polyester feedstock to produce the at least partially melted polyester feedstock (1). * ), and four static mixers (M1), (M2), (M3), (M4) in series, each mixed with a portion (2), (4), (6) and (8) of the ethylene glycol stream (11), each producing a respective polyester stream (3), (5), (7) and (9), each containing at least partially molten polyester feedstock (1) and mixed with one or more portions of the ethylene glycol stream previously introduced therein; Depolymerization step (b): receiving the conditioned feedstock (9) obtained from the conditioning step (a) and the diol effluent (12); and Step (c): Allows to separate the diol stream (10), the diester monomer stream (13) and the BHET effluent, the diol stream (10) being purified and capable of being mixed with the external diol stream (14) before being recycled to the conditioning (a) and depolymerization (b) steps.

[0023] FIG. 2 represents another particular embodiment of the method according to the invention, in which the depolymerization is carried out by glycolysis in the presence of ethylene glycol and comprises the following steps: a step (a) of conditioning a polyester feedstock (1), preferably comprising PET; using an extruder (A) followed by two static mixers (M1), (M2) in series; the extruder (A) is fed with the polyester feedstock (1) and a portion (2) of an ethylene glycol stream (11) to produce a mixture (3), and the static mixers (M1), (M2) are fed, respectively, with portions (4) and (6) of the ethylene glycol stream (11) to produce respective polyester streams (5) and (7), which contain at least partially molten polyester feedstock (1) and are mixed with one or more portions of the ethylene glycol stream previously introduced; a depolymerization step (b); receiving the conditioned feedstock (7) obtained from the conditioning step (a) and the diol effluent (12); and Step (c) allows to separate the diol stream (10), the diester monomer stream (13) and the BHET output; the diol stream (10) can be purified and mixed with an external diol stream (14) before being recycled to the conditioning (a) and depolymerization (b) steps.

[0024] (Description of the embodiment) According to the present invention, polyester terephthalate or poly(ethylene terephthalate), also simply called PET, has the basic repeating unit of the formula:

[0025] [ka]

[0026] Traditionally, PET is obtained by polycondensation of terephthalic acid (PTA) or dimethyl terephthalate (DMT) with ethylene glycol.

[0027] Hereinafter, 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 the polyester feedstock, which are in particular diester units resulting from the reaction of PTA with ethylene glycol.

[0028] According to the present invention, the term "monomer" or "diester monomer" or alternatively "diester" advantageously refers to a repeat unit of a polyester polymer.

[0029] According to a preferred embodiment of the present invention, the term "monomer" or "diester monomer" or alternatively "diester" is defined as a diester of a dicarboxylic acid, preferably a 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). According to this embodiment, the term "monomer" or "diester monomer" preferably refers to bis(2-hydroxyethyl)terephthalate (BHET) of formula HOC2H4-CO2-(C6H4)-CO2-C2H4OH, where -(C6H4)- denotes an aromatic ring, which is in particular the diester unit obtained from the reaction of PTA with ethylene glycol.

[0030] According to another embodiment of the invention, the term "monomer" or "diester monomer" may define a diester of a dicarboxylic acid, preferably a diester of a dicarboxylic acid, preferentially terephthalic acid, with a monoalcohol, preferably containing 1 to 10 carbon atoms, preferentially 1 to 3 carbon atoms, suitably methanol, ethanol, propanol, or a mixture thereof. According to this embodiment, the term "monomer" or "diester monomer" highly preferably refers to dimethyl terephthalate (DMT) of the formula CH3-CO2-(CH4)-CO2-CH3, where -(CH4)- represents an aromatic ring.

[0031] The term "oligomer" typically refers to a small sized polymer, generally consisting of 2-20 base repeat units, for example 2-5 base repeat units. Preferably, the term "ester oligomer" or "BHET oligomer" refers to a terephthalate ester oligomer containing 2-20, preferably 2-5, base repeat units of the formula -[O-CO-(CH)-CO-O-CH]-, where -(CH)- is an aromatic ring.

[0032] According to the present invention, the term "monoalcohol" refers to a compound containing a single hydroxyl group -OH and preferably containing 1 to 10 carbon atoms, preferentially 1 to 3 carbon atoms. Preferably, the monoalcohol is selected from methanol, ethanol, propanol and mixtures thereof, the preferred monoalcohol being methanol.

[0033] 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.

[0034] According to the present invention, the term "alcohol compound" refers to a monoalcohol or diol as defined above. The alcohol compound is advantageously the depolymerization agent required for the depolymerization by alcoholysis or glycolysis of the polyester feedstock. According to a highly preferred embodiment, the alcohol compound is a diol containing from 2 to 12 carbon atoms, preferentially from 2 to 4 carbon atoms, and highly preferentially ethylene glycol. According to another embodiment of the invention, the alcohol compound is a monoalcohol, preferably containing from 1 to 10 carbon atoms, preferentially from 1 to 3 carbon atoms, and preferably chosen from methanol, ethanol, propanol and mixtures thereof, the preferred monoalcohol being methanol.

[0035] The alcohol stream used in the process of the invention comprises, preferably consists of, alcohol compounds, advantageously as defined above. The alcohol stream preferentially comprises at least 95% by weight of alcohol compounds, in particular at least 95% by weight of monoalcohols or diols. Highly preferably, the alcohol stream comprises at least 95% by weight of ethylene glycol.

[0036] Highly preferably, the alcohol compound is ethylene glycol, the alcohol stream is therefore a diol stream, more precisely an ethylene glycol stream, and the target diester monomer is BHET.

[0037] 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.

[0038] 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.

[0039] The terms "upstream" and "downstream" are to be understood relative to the general flow of streams in the process.

[0040] The terms "static or dynamic mixer" and "mixer" are used interchangeably and refer to mixing equipment known to those skilled in the art as static mixers or dynamic mixers.

[0041] According to the present invention, the viscosity is defined as being the kinematic viscosity, in particular at a temperature of 250° C. and at 100 s-1 at a shear rate of 100 rpm using a viscometer, preferably a plate-plate type viscometer, for example a DHR3 type manufactured by TA Instruments.

[0042] 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.

[0043] 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.

[0044] 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 one another without any restriction on the combination.

[0045] (Feed material) The process according to the invention is fed with a polyester feedstock which comprises at least one polyester, i.e. a polymer, the repeat units of whose backbone contain ester groups. The polyester feedstock preferably comprises polyethylene terephthalate (PET), for example clear PET and / or pigmented PET and / or opaque PET.

[0046] 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.

[0047] Preferably, the polyester feedstock comprises a minimum of 50% by weight polyethylene terephthalate (PET), preferably a minimum of 70% by weight, suitably a minimum of 90% by weight, with a maximum of 100% by weight PET.

[0048] Preferably, the polyester feedstock comprises at least one PET selected from clear, tinted, opaque, dark and multi-layered PET, and mixtures thereof. Very particularly, the polyester feedstock comprises at least 10% by weight of opaque PET, highly preferably at least 15% by weight of opaque PET, advantageously opaque PET to be recycled, i.e. PET obtained from collection and sorting segments. The polyester feedstock may comprise 100% by weight of opaque PET, highly preferably less than 70% by weight of opaque PET.

[0049] The polyester feedstock may comprise a pigment and / or a dye. For example, the polyester feedstock may comprise 0.1% to 10% by weight of a pigment, in particular 0.1% to 5% by weight of a pigment. It may in particular comprise 0.005% to 1% by weight of a dye, preferably 0.01% to 0.2% by weight of a dye.

[0050] 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.

[0051] 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 in particular to remove cotton or polyamide fibers, or any textile fiber other than polyester, or even other fibers, such as tire fibers, optionally pretreated to remove, inter alia, polyamide fibers or rubber or polybutadiene residues. The polyester feedstock may also include polyesters obtained from production rejects from polyester polymerization and / or conversion processes. The polyester feedstock may also include elements used as polymerization catalysts and stabilizers in PET production processes, such as antimony, titanium or tin.

[0052] (Conditioning process a) The process according to the invention comprises a conditioning step a) which at least uses means for at least partially melting the polyester feedstock and at least one static or dynamic mixer arranged downstream of the means for at least partially melting the polyester feedstock. The conditioning step a) makes it possible to obtain a conditioned feedstock stream.

[0053] The assembly comprising, and preferably consisting of, the means for at least partially melting the polyester feedstock and one or more static or dynamic mixers constitutes a section referred to as the conditioning section.

[0054] Said conditioning section of step a) thus makes it possible, on the one hand, to heat and pressurize said polyester feedstock to the operating conditions of the depolymerization step b), and, on the other hand, to contact and premix the polyester feedstock with at least a portion of the alcohol compounds required for the depolymerization.

[0055] Advantageously, the conditioning step a) is fed with a polyester feedstock and an alcohol stream such that the weight ratio of the alcohol stream relative to the polyester feedstock, i.e. the ratio between the flow rate by weight of the alcohol stream fed to step a) and the flow rate by weight of the polyester feedstock fed to step a), is 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 alcohol stream corresponds to at least a portion of the alcohol effluent obtained from optional step c). The temperature at which step a) is implemented, in particular the temperature in the means for at least partially melting the polyester feedstock and in the static or dynamic mixer or mixers, is advantageously between 200 and 300° C., preferentially 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. Preferably, the conditioning section is operated under an inert atmosphere to limit the introduction of oxygen into the system and thus oxidation of the polyester feedstock.

[0056] Advantageously, the means for at least partially melting the polyester feedstock make it possible to at least partially mix and melt the polyester feedstock, more particularly to at least partially melt the PET of the polyester feedstock. Preferably, the means for at least partially melting the polyester feedstock is an extruder, in particular a twin-screw extruder or a single-screw extruder. Said means is advantageously carried out at a temperature between 200 and 300°C, preferentially between 250 and 290°C.

[0057] The means for at least partially melting the polyester feedstock are advantageously fed with at least the polyester feedstock, for example in the form of flakes, which makes it possible to obtain a viscous liquid flow, typically having a viscosity of 0.5 to 600 Pa·s, or in practice more particularly of 1.0 to 500 Pa·s. The viscosity is in particular the kinematic viscosity, which at a temperature of 250° C. and 100 s -1 The viscosity is measured at a shear rate of 100 MPa using a viscometer, preferably a plate-plate viscometer, for example of the type DHR3 from TA Instruments. In the means for at least partially melting the polyester feedstock, for example an extruder, the polyester feedstock is advantageously gradually heated to a temperature between 200 and 300° C., preferentially between 250 and 290° C., in particular close to or even slightly above the melting point of the polyester, for example PET, which it contains, so that it becomes at least partially liquid (i.e. at least partially melted) at the outlet of said means. Highly advantageously, at least 70% by weight of the polyester feedstock, preferably at least 80% by weight, preferentially at least 90% by weight and suitably at least 95% by weight of the polyester feedstock is in liquid form when it leaves said means, for example an extruder, of step a).

[0058] More specifically, the polyester feedstock is fed to a means for at least partially melting the polyester feedstock, said means being preferably an extruder. The feeding of the polyester feedstock is advantageously carried out by any technique known to the person skilled in the art, for example via a feed hopper, which may be inactivated so as to limit the introduction of oxygen into the process. Advantageously, the means for at least partially melting the feedstock, preferably an extruder, makes it possible to bring the polyester feedstock to a temperature of 200 to 300°C, preferentially 250 to 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, under such conditions the polyester feedstock is advantageously at least partially melted, and in particular under such conditions the PET, which may be contained in the polyester feedstock, is at least partially melted, preferably completely melted.

[0059] According to a preferred embodiment of the invention, the means for at least partially melting the polyester feedstock, preferably an extruder, may be fed with a portion of the alcohol stream fed to step a), which may aid in the at least partial liquefaction of the polyester feedstock and thus contribute to a decrease in the viscosity of the stream at the outlet of said means, thus contributing to an overall homogenization of the at least partially melted polyester feedstock and the alcohol compounds, in particular in the conditioning step a) and also in the depolymerization step b). Another advantage of this embodiment (i.e. introducing a portion of the alcohol stream fed to the conditioning step a) into the melting means) lies in the fact that this implementation may make it possible to reduce the number of static or dynamic mixers required to achieve a viscosity of the [polyester feedstock+alcohol compounds] mixture (corresponding to the conditioned feedstock stream) at the end of step a): 50 mPa·s or less, preferably 30 mPa·s or less, highly preferentially 15 mPa·s or less. If part of the alcohol stream fed to step a) is introduced into a means for at least partially melting the polyester feedstock, the adjustment of the amount of alcohol compound fed to said means is preferably carried out in such a way that the weight ratio between said part of the alcohol stream fed to said means and the polyester feedstock fed to said means is between 0.001 and 0.100, preferably between 0.003 and 0.050, highly preferably between 0.005 and 0.030.

[0060] Preferably, the residence time in the means for at least partially melting the polyester feedstock is advantageously equal to or less than 5 minutes, preferably equal to or less than 2 minutes, and suitably equal to or greater than 1 second, preferentially equal to or greater than 10 seconds, said residence time being defined as the volume available in said means divided by the volumetric flow rate of the polyester feedstock.

[0061] The means for at least partially melting the polyester feedstock may advantageously be connected to a vacuum extraction system to remove impurities present in the feedstock, such as dissolved gases, light organic compounds and / or moisture.

[0062] The means for at least partially melting the polyester feedstock, preferably an extruder, may advantageously comprise a filtration system at the outlet, thus making it possible to remove solid particles having a size greater than 20 μm and preferably less than 2 cm, such as particles of sand, wood or metal.

[0063] According to a particular embodiment, the means for at least partially melting the polyester feedstock, preferably an extruder, is directly connected at its outlet to a first filtration system, in particular a filter, designed to remove solid particles having a size typically of 1000 μm or more, preferably 500 μm or more, preferably 400 μm or more and preferentially 300 μm or more, followed by a melt or gear pump making it possible to maintain and / or increase the pressure, followed by a second filtration system designed to remove solid particles having a size typically of 60 μm or more, preferably 20 μm or more. Thus, in this particular embodiment, the conditioning section comprises: - means for at least partially melting the polyester feedstock, preferably an extruder, making it possible to obtain an at least partially molten polyester feedstock, preferably at a pressure typically between 0.1 MPa and 15.0 MPa, suitably between 0.15 MPa and 1.5 MPa, then a first filtration system, in particular a filter, designed to remove from the at least partially molten feedstock obtained from said means solid particles having a size typically greater than or equal to 1000 μm, preferably greater than or equal to 500 μm, preferably greater than or equal to 400 μm and preferentially greater than or equal to 300 μm, then a melt pump or a gear pump, which in particular makes it possible to maintain and / or increase the pressure in the conditioning section to a pressure equal to or greater than the pressure at the outlet of the means for at least partially melting the polyester feedstock, preferably between 0.1 MPa and 15.0 MPa, preferentially between 1 MPa and 15.0 MPa and suitably between 1 MPa and 7.0 MPa, then a second filtration system, in particular a filter; designed to remove solid particles whose size is typically greater than or equal to 60 μm, preferably greater than or equal to 20 μm, then at least one static or dynamic mixer, advantageously as described below.

[0064] According to another particular embodiment, a system for separation of metals may be installed upstream of the means for at least partially melting the polyester feedstock to remove any metal impurities in the polyester feedstock.

[0065] Advantageously, in the conditioning step a) a means for at least partially melting the polyester feedstock is used, preferably an extruder, and at least one, preferably 1 to 5, suitably 2 to 5 and highly preferably 2 to 4 static or dynamic mixers, preferentially a static mixer. The static or dynamic mixer or mixers are advantageously arranged downstream of the means for at least partially melting the polyester feedstock. When the conditioning section comprises more than one static or dynamic mixer, the static or dynamic mixers are advantageously in series with one another. Preferably, in the conditioning step a) an extruder and 2 to 5, preferably 2 to 4 static or dynamic mixers are used, the extruder being preferably operated at a temperature of 200 to 300° C., preferentially 250 to 290° C., and the static or dynamic mixers being operated in series and preferably carried out at a temperature of 200 to 300° C., preferentially 250 to 290° C.

[0066] Advantageously, each static or dynamic mixer is fed with at least a portion of the alcohol stream fed to step a) and with the polyester stream such that in each mixer the volumetric dilution with alcohol compound is between 3% and 70%. The volumetric dilution with alcohol compound in the static or dynamic mixer corresponds according to the invention to the ratio between the volumetric flow rate of the portion of the alcohol stream fed directly to the static or dynamic mixer under consideration and the sum of the volumetric flow rates of the portion of the alcohol stream and the polyester stream fed to the static or dynamic mixer under consideration. For each static or dynamic mixer, the polyester stream advantageously corresponds to a stream comprising, preferably consisting of, at least partially melted polyester feedstock and the entire portion of the alcohol stream introduced in step a) upstream of the static or dynamic mixer under consideration. In other words, the polyester stream feeding the static or dynamic mixer corresponds to a stream of material comprising and preferably consisting of the (advantageously at least partially molten) polyester feedstock, supplemented with the entire portion of the alcohol stream introduced into one or more static or dynamic mixers arranged upstream of the static or dynamic mixer under consideration, possibly into the means for at least partially melting the polyester feedstock. For example, if the static or dynamic mixer under consideration is the first static or dynamic mixer of the conditioning section and the means for at least partially melting the polyester feedstock are not fed with an alcohol compound, the polyester stream corresponds to the (advantageously at least partially molten) polyester feedstock.

[0067] Preferably, the volumetric dilution with alcohol compound in each static or dynamic mixer is as follows: - from 3% to 50%, preferably from 10% to 35%, highly preferably from 15% to 30%, when the viscosity ratio between the polyester stream and the alcohol stream portions feeding the static or dynamic mixer under consideration is greater than or equal to 3500, preferably greater than or equal to 3000; - 10% to 70%, preferably 20% to 65%, highly preferably 30% to 65%, or even 35% to 65%, when the viscosity ratio between the polyester stream and the alcohol stream portions feeding the static or dynamic mixer under consideration is less than 3500, preferably less than 3000.

[0068] Preferably, the alcohol stream fed to the conditioning step a) is divided into n partial streams of alcohol compounds (i.e. n portions of the alcohol stream), n being an integer equal to m or m+1, m being an integer equal to the number of static or dynamic mixers used in the conditioning step a), each static or dynamic mixer being fed one of the partial streams of alcohol compounds (i.e. one of the portions of the alcohol stream fed to the conditioning step a), In each static or dynamic mixer, the volumetric dilution with the alcohol compound is preferably performed in the following manner so as to be 3% to 70%: - between 3% and 50%, preferably between 10% and 35%, highly preferably between 15% and 30%, when the viscosity ratio between the polyester stream and the alcohol stream portions feeding the static or dynamic mixer under consideration is greater than or equal to 3500, preferably greater than or equal to 3000; or - if the viscosity ratio between the polyester stream and the alcohol stream portions fed to the static or dynamic mixer under consideration is less than 3500, preferably less than 3000, it is fed in such a way that it is between 10% and 70%, preferably between 20% and 65%, highly preferably between 30% and 65% or even between 35% and 65%.

[0069] Optionally, a partial stream of the alcohol compound (ie, a portion of the alcohol stream) may be fed to a melting means.

[0070] Advantageously, each static or dynamic mixer is operated at a temperature between 200 and 300° C., preferentially between 250 and 290° C., with a residence time preferably between 0.5 seconds and 20 minutes, preferably between 1 second and 5 minutes, suitably between 3 seconds and 1 minute, the residence time being defined here as the ratio of the volume of liquid in the static or dynamic mixer with respect to the sum of the volumetric flow rates of the polyester stream and the portion of the alcohol stream feeding the static or dynamic mixer under consideration.

[0071] The alcohol stream fed to the conditioning step a) may advantageously be heated, preferably to a temperature between 200 and 300° C., preferentially between 250 and 290° C., before being introduced into step a), in particular into the means for at least partially melting the polyester feedstock and / or into the static or dynamic mixer(s), to help bring the polyester feedstock to the desired temperature.

[0072] According to a preferred embodiment of the invention, the conditioning step a) uses an extruder, an optional filtration system at the extruder outlet and then 2, 3 or 4 static or dynamic mixers operating in series with one another. In this preferred embodiment, the extruder is fed with the polyester feedstock and preferably with a portion of the alcohol stream such that the weight ratio between said portion of the alcohol stream fed to the extruder and the polyester feedstock fed to the extruder is between 0.001 and 0.100, preferably between 0.003 and 0.050, and preferably between 0.005 and 0.030. The other portion of the alcohol stream is divided into 2, 3 or 4 partial streams of alcohol compounds, respectively, the number of partial streams of alcohol compounds being equal to the number of static or dynamic mixers used, each of the static or dynamic mixers being fed with the polyester stream and one of the partial streams of alcohol compounds, in each static or dynamic mixer the volumetric dilution with alcohol compounds is between 3% and 70% and is as follows: i) suitably between 3% and 50%, preferably between 10% and 35%, highly preferably between 15% and 30%, when the viscosity ratio between the polyester stream and the partial stream of alcohol compound feeding the static or dynamic mixer under consideration is greater than or equal to 3500, preferably greater than or equal to 3000; or ii) When the viscosity ratio between the polyester stream and the alcohol compound part stream feeding the static or dynamic mixer under consideration is less than 3500, preferably less than 3000, suitably between 10% and 70%, preferably between 20% and 65%, highly preferably between 30% and 65% or even between 35% and 65%.

[0073] Preferably, the residence time in the extruder, defined as the volume available in the extruder divided by the volumetric flow rate of the feedstock, is from 0.5 seconds to 1 hour, preferably from 0.5 seconds to 5 minutes, preferably from 1 second to 2 minutes, or from 10 seconds to 2 minutes.

[0074] At the end of the conditioning step a), a conditioned feed stream is advantageously obtained. Highly advantageously, the conditioned feed stream is in liquid form and exhibits a viscosity of preferably less than or equal to 50 mPa·s, preferably less than or equal to 30 mPa·s and highly preferentially less than or equal to 15 mPa·s.

[0075] (Depolymerization step b)) The process according to the invention comprises a depolymerisation step b) More particularly, the depolymerisation of the polyester feedstock, in particular of the PET it comprises, is carried out by glycolysis, if the alcohol compound is a diol, or by alcoholysis, if the alcohol compound is a monoalcohol.

[0076] 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 alcohol compounds, such that the weight ratio between the total amount of alcohol compounds present in step b), which corresponds to the sum of the amounts by weight of alcohol compounds introduced in step a) and optional step b), and the amount by weight of diesters contained in the conditioned feed stream (i.e. the amount by weight of diesters contained in the polyester feedstock, according to a particular embodiment the amount by weight of PET contained in the polyester feedstock) 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 obtained from the conditioning step a) and with an optional feed of alcohol compound such that the molar ratio of the total molar amount of alcohol compound introduced in step a) and in the optional step b) to the total molar amount of diester contained in the conditioned feed stream (i.e. contained in the polyester feed) is respectively between 0.9 and 24.0, preferably between 3.0 and 21.0, suitably between 4.5 and 18.0.

[0077] Preferably, the depolymerization step b) is fed with the conditioned feed stream obtained from step a) and with a feed of alcohol compounds, highly preferably with a feed of methanol or ethylene glycol, such that the weight ratio of the total amount by weight of alcohol compounds introduced in steps a) and b) relative to the total amount by weight of diesters contained in the conditioned feed stream (i.e. the total amount by weight of diesters contained in the polyester feedstock, according to a particular embodiment the amount of PET contained in the polyester feedstock) is between 0.3 and 8.0, preferably between 1.0 and 7.0, better still between 1.5 and 6.0 (i.e. the molar ratio of alcohol compounds relative to diesters is, respectively, between 0.9 and 24.0, preferably between 3.0 and 21.0 approximately, better still between 4.5 and 18.0).

[0078] Advantageously, in said depolymerization step b), advantageously one or more reaction sections, preferably at least two reaction sections, suitably two to four reaction sections, are used, preferably operated 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 a depolymerization or transesterification reaction, 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 bottom making it possible to remove impurities. Advantageously, the depolymerization step b) is carried out in at least two reaction sections, preferably two to four reaction sections, operated 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 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.

[0079] 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 carried out with a residence time in each reaction section: 0.1 to 10 hours, preferably 0.25 to 8 hours, 0.5 to 6 hours. 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.

[0080] 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 10 MPa, preferentially less than 5 MPa. The term "reaction system" means all the components and phases present in said step b).

[0081] The depolymerization reaction may be carried out in the presence or absence of a catalyst.

[0082] If the depolymerization reaction is carried out in the presence of a catalyst, this 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, acidic / basic metal oxides, compounds based on manganese, zinc, titanium, lithium, magnesium, calcium or cobalt.

[0083] 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 is of the 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.

[0084] According to a particular embodiment of the present invention, a homogeneous catalyst may be added in the depolymerization step b), preferably selected from amines, preferably tertiary monoamines 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.

[0085] The depolymerization step is preferably carried out without the addition of an external catalyst to the polyester feedstock.

[0086] Said depolymerization step may be carried out in the presence of a solid adsorbent, advantageously in powder or shaped form, to capture at least a portion of the colouring impurities, thereby easing the burden of any possible purification step, said solid adsorbent being advantageously activated carbon.

[0087] The depolymerization reaction allows the polyester feedstock to be converted into monomers and / or oligomers. Preferably, the depolymerization step allows the polyester of the polyester feedstock, preferably the PET of the polyester feedstock, and optionally its oligomers, to be converted into at least one diester monomer, preferably bis(2-hydroxyethyl) terephthalate (BHET) or dimethyl terephthalate (DMT), and optionally its oligomers. The conversion of the polyester of the polyester feedstock, preferably PET, is greater than 50%, preferably greater than 70%, preferably greater than 85%, at the end of the depolymerization step b). Preferably, the molar yield of the diester monomer, highly preferably BHET, is greater than 50%, preferably greater than 70%, preferably greater than 85%. The molar yield of the diester monomer corresponds to the molar flow rate of the diester monomer at the outlet of step b) (i.e. in the reaction effluent) related to the number of moles of diester in the polyester feedstock fed to step a).

[0088] In parallel, the depolymerization reaction typically also produces diols, particularly ethylene glycol.

[0089] An internal recirculation loop may advantageously be implemented in step b), performing the withdrawal of a portion of the reaction system, the filtration of this portion and the reinjection of said filtered portion into said step b), this internal loop making it possible to remove "macroscopic" solid impurities that may be present in the reaction liquid.

[0090] Advantageously, the depolymerization step b) makes it possible to obtain a reaction effluent, advantageously in essentially liquid form, which contains the target diester monomer, highly preferably BHET. The reaction effluent may be sent to a purification step to separate the diester monomer, highly preferably BHET, from other compounds present in the reaction effluent, such as unreacted alcohol compounds, the diol formed during the depolymerization, preferably the ethylene glycol formed, impurities, such as pigments and / or dyes, or other by-products that may be formed, such as dimers or trimers of the diol and their derivatives (such as esters of the diol dimers), to obtain a purified diester monomer effluent. In particular, the reaction effluent may be sent to an optional separation step c) to recover an alcohol effluent, preferably an alcohol effluent essentially composed of alcohol compounds.

[0091] (Optional separation step c)) The process according to the invention may comprise a separation step c) to which is fed at least the reaction effluent obtained from step b) and which gives rise to at least an alcohol effluent and a diester monomer effluent.

[0092] The main role of the optional step c) is to recover all or part of the unreacted alcohol compounds, which are then advantageously recycled to steps a) and / or b). The optional step c) may also make it possible to recover all or part of the diols generated during the depolymerization.

[0093] Optional step c) is advantageously carried out in one or a series of several gas-liquid separation sections, advantageously in 2 to 5 successive gas-liquid separation sections. Each of the gas-liquid separation sections produces a liquid phase and a gas phase. The liquid phase from the preceding gas-liquid separation section feeds the subsequent gas-liquid separation section. All of the gas phase is recovered and constitutes the alcohol effluent. The liquid phase obtained from the last gas-liquid separation section constitutes the diester monomer effluent.

[0094] 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. Optional step c) may implement at least one short path distillation separation section.

[0095] Advantageously, the operation in step c) is carried out in such a way that the temperature of the liquid phase is maintained above a lower temperature value below which the diester monomer, preferably the BHET monomer, precipitates and below an upper temperature value above which the diester monomer undergoes significant repolymerization. The temperature in step c) is advantageously between 60 and 250° C., preferably between 90 and 220° C., suitably between 100 and 210° C. The operation as 2 to 5 successive gas-liquid separations in succession is particularly advantageous, since it makes it possible to adjust the temperature of the liquid phase within each separation in accordance with the abovementioned constraints.

[0096] The pressure in the optional step c) is preferably below the pressure in step b) and evaporates a part of the reaction effluent obtained from step b). The pressure in the optional step c) is therefore advantageously adjusted to minimize the repolymerization of the monomers and to allow optimal integration in terms of energy, while allowing evaporation of the diol at a given temperature in each separation section. It is preferably between 0.00001 and 0.2 MPa, preferentially between 0.00004 and 0.15 MPa, and suitably between 0.00004 and 0.1 MPa.

[0097] The gas-liquid separation section or sections are advantageously agitated by any method known to those skilled in the art.

[0098] The alcohol effluent obtained at the end of the optional step c) comprises unreacted alcohol compounds. It may contain the diol generated during the depolymerization, preferably ethylene glycol, and possibly other compounds, such as dyes, light alcohols, water or diethylene glycol. At least a portion of the alcohol effluent may be advantageously recycled, preferably after purification, suitably in liquid form (i.e. after condensation), to step a) and / or step b), possibly in a mixture with a supplement of alcohol compounds external to the process according to the invention.

[0099] All or part of the alcohol effluent may be recycled to steps a) and / or b), preferably in liquid form, after being treated in purification steps which may non-exhaustively include adsorption onto a solid (e.g. activated carbon) to remove the dye, and separation of impurities such as diethylene glycol, water and other alcohols by one or more distillations.

[0100] The diester monomer effluent obtained upon termination of optional step c) may be transferred to one or more purification steps to obtain a decolorized purified diester monomer effluent, highly preferably a decolorized purified BHET effluent, which may then be polymerized.

[0101] According to a particular embodiment, the depolymerization method according to the invention may be integrated into the method described in patent application FR 3053691. In this embodiment, the method according to the invention comprises an optional step c) of separation of diols and replaces the conditioning step a), the depolymerization step b) and the diol separation step c) of the method described in patent application FR 3053691. Thus, in this embodiment, the overall method comprises the depolymerization method according to the invention with the conditioning step a) and the depolymerization step b) and the above-mentioned optional step c), followed by a step d) of separation of monomers and a step e) of purification, in particular by decolorization, for example as described in application FR 3053691.

[0102] The process according to the invention thus makes it possible, in an optimized manner, starting from any type of polyester waste, for example one containing opaque PET, to obtain an effluent containing diester monomers, both in terms of process operability and operating costs. Said diester monomers obtained may then be polymerized, preferably after purification, in the presence or absence of ethylene glycol, terephthalic acid and / or dimethyl terephthalate, to give a PET that is visually indistinguishable from virgin PET.

[0103] The following figures and examples illustrate the invention but do not limit its scope.

[0104] (Example) In the following examples, only the conditioning step a) is strictly described.

[0105] (Example 1: In accordance with the present invention) In this example, the depolymerization method corresponds to the embodiment illustrated diagrammatically in FIG. 1, in which the conditioning section includes: - extruder A; containing a feed hopper through which the extruder is fed with the PET feedstock (1) obtained from the collection and sorting channels at a flow rate of 50 kg / h; followed by - 4 static mixers in series M1, M2, M3, M4.

[0106] The PET feedstock is in the form of flakes and contains 95.72% by weight PET; 1.24% by weight pigments; 0.04% by weight dyes; and 3.00% by weight impurities such as paper, wood, metal, sand, etc.

[0107] Each mixer M1, M2, M3, M4 is fed with a respective PET stream (1), (3), (5) and (7) and with a respective portion (2), (4), (6), (8) of the ethylene glycol stream (11) obtained from step c) of the separation of the diol (ethylene glycol or MEG).

[0108] The conditioning section is carried out at a temperature of 250° C. and a pressure of 1.0 MPa (10 bar).

[0109] Table 1 shows both the amount of ethylene glycol (MEG) introduced into each mixer and the change in viscosity of the PET stream at the inlet / outlet of each static mixer under the operating conditions of temperature and pressure. Table 1 also shows the viscosity ratio between the PET and MEG streams entering each static mixer. The volumetric dilution with MEG in each mixer corresponds to: for mixer M1, the dilution by MEG given for stream (3), for mixer M2, the dilution by MEG given for stream (5), for mixer M3, the dilution by MEG given for stream (7), For mixer M4, the dilution by MEG given for stream (9).

[0110] [Table 1]

[0111] The conditioning step a) involves the extrusion followed by four static mixers, gradually introducing MEG in a weight ratio of 2 with respect to the PET feedstock (2 parts MEG per 1 part PET feedstock), such that at the end of this conditioning step a) the viscosity of the conditioned feed stream is 1.5 mPa·s (i.e. less than 15 mPa·s), achieved whilst respecting the technical constraints imposed by the static mixers with regard to the viscosity of the streams involved. Such a viscosity then facilitates homogenization of the mixture in the reaction section following mixer M4.

[0112] (Example 2: In accordance with the present invention) In this example, the depolymerization method corresponds to the embodiment illustrated diagrammatically in FIG. 2, in which the conditioning section comprises: - extruder A: contains a feed hopper through which the extruder is fed with the PET feedstock (1) obtained from the collection and sorting channel at a flow rate of 50 kg / h; then - Two static mixers M1 and M2 in series.

[0113] The PET feedstock is the same as that of Example 1: it is in the form of flakes and contains: 95.72 wt% PET; 1.24 wt% pigment; 0.04 wt% dye; and 3.00 wt% impurities such as paper, wood, metal, sand, etc.

[0114] The extruder is fed with a portion (2) of the ethylene glycol stream (11) obtained from step c) of the separation of the diol (ethylene glycol or MEG).

[0115] Each mixer M1 and M2 is fed with a respective PET stream (3) and (5) and with a respective portion (4) and (6) of the ethylene glycol stream (11) obtained from step c) of the separation of the diol (ethylene glycol or MEG).

[0116] The conditioning section is carried out at a temperature of 250° C. and a pressure of 1.0 MPa (10 bar).

[0117] Table 2 shows both the amount of ethylene glycol (MEG) introduced into each mixer and the change in viscosity of the PET stream at the inlet / outlet of each static mixer under the operating conditions of temperature and pressure. Table 2 also shows the viscosity ratio between the PET and MEG streams entering the extruder and each static mixer. The volumetric dilution with MEG in each mixer and extruder corresponds to: - for extruder A, the dilution with MEG given for stream (3); - for mixer M1, the dilution by MEG given for flow (5); For mixer M2, the dilution by MEG given for stream (7).

[0118] [Table 2]

[0119] The conditioning step a) is carried out following the reactive extrusion by two static mixers, gradually introducing MEG in a weight ratio of 2 with respect to the PET feedstock (2 parts MEG for 1 part PET feedstock), such that at the conclusion of this conditioning step a), the viscosity of the conditioned feed stream is less than 10 mPa·s (8.8 mPa·s), which is achieved while respecting the technical constraints imposed by the static mixers with respect to the viscosity of the streams involved. Such a viscosity facilitates homogenization of the mixture in the reaction section following mixer M2. [Brief description of the drawings]

[0120] [Figure 1] 1 represents one particular embodiment of the method according to the invention. [Diagram 2] 4 illustrates another particular embodiment of the method according to the invention.

Claims

Claim 1 A method for the depolymerization of a polyester feedstock, the method comprising the following steps: a) A conditioning step; using means for at least partially melting the polyester feedstock and at least one static or dynamic mixer arranged downstream of the means for at least partially melting the polyester feedstock; producing a conditioned feedstock stream. The temperature when operating the conditioning step a) is 200 to 300 °C, at least feeding the polyester feedstock and an alcohol stream containing an alcohol compound, and the weight ratio of the alcohol stream to the polyester feedstock is 0.03 to 6.

00. At least feed the polyester feedstock to the means for at least partially melting the polyester feedstock. To each static or dynamic mixer, at least a part of the alcohol stream and the polyester stream are fed, and the volume dilution degree by the alcohol compound is 3% to 70%. The volume dilution degree by the alcohol compound is the ratio between the volume flow rate of the part of the alcohol stream fed to the static or dynamic mixer under consideration and the sum of the volume flow rate of the part of the alcohol stream and the volume flow rate of the polyester stream fed to the static or dynamic mixer under consideration. The polyester feedstock fed to the static or dynamic mixer includes the polyester feedstock and all of the part of the alcohol stream introduced upstream of the static or dynamic mixer under consideration in step a). b) A depolymerization step; at least feeding the conditioned feedstock stream obtained from step a), the temperature when operating is 150 °C to 300 °C, the residence time is 0.1 to 10 hours, and the weight ratio between the total amount of the alcohol compound present in step b) and the amount of diester contained in the conditioned feedstock stream is 0.3 to 8.

0. Claim 2 The method according to claim 1, wherein in step a), the weight ratio of the alcohol stream to the polyester feedstock is 0.05 to 5.00, preferably 0.10 to 4.00, and suitably 0.50 to 3.

00. Claim 3 The alcohol compound is a monoalcohol, preferably methanol, ethanol, propanol, and mixtures thereof, preferably a monoalcohol selected from methanol, or a diol, such as ethylene glycol, in the method according to claim 1 or 2.

4. In the conditioning step a), 1 to 5 static or dynamic mixers, preferably 2 to 5 static or dynamic mixers, suitably 2 to 4 static or dynamic mixers are used, and the static or dynamic mixers are in series with each other, in the method according to claim 1.

5. In each static or dynamic mixer used in step a), the volume dilution degree by the alcohol compound is as follows, in the method according to claim 1: - When the viscosity ratio between the polyester stream fed to the static or dynamic mixer under consideration and the portion of the alcohol stream is 3500 or more, preferably 3000 or more, 3% to 50%, preferably 10% to 35%, most preferably 15% to 30%, - When the viscosity ratio between the polyester stream fed to the static or dynamic mixer under consideration and the portion of the alcohol stream is less than 3500, preferably less than 3000, 10% to 70%, preferably 20% to 65%, most preferably 30% to 65%, or even 35% to 65%.

6. The temperature when operating the conditioning step a) is 250 to 290 °C, in the method according to claim 1.

7. Means for at least partially melting the polyester feedstock, preferably an extruder, to which a portion of the alcohol stream fed to step a) is also fed, preferably the weight ratio between the portion of the alcohol stream fed to the means and the polyester feedstock fed to the means: 0.001 to 0.100, preferably 0.003 to 0.050, most preferably 0.005 to 0.030, in the method according to claim 1.

8. Means for at least partially melting the polyester feedstock, preferably the temperature when operating the extruder is 200 to 300 °C, preferably 250 to 290 °C, in the method according to claim 1.

9. Each static or dynamic mixer is operated at a temperature of 200 to 300 °C, preferably 250 to 290 °C, preferably for a residence time of 0.5 seconds to 20 minutes, preferably 1 second to 5 minutes, suitably 3 seconds to 1 minute, and the residence time is defined as the ratio to the total volumetric flow rate of the polyester stream and the alcohol stream portion fed to the static or dynamic mixer under consideration of the volume of liquid in the static or dynamic mixer, the method according to claim 1.

10. In the conditioning step a), an extruder and 2, 3 or 4 static or dynamic mixers arranged in series following it are used, the extruder is fed with a polyester feedstock and a portion of the alcohol stream, and the weight ratio between the portion of the alcohol stream fed to the extruder and the polyester feedstock fed to the extruder is made to be 0.001 to 0.100, preferably 0.003 to 0.050, most preferably 0.005 to 0.030, the other portion of the alcohol stream is divided into partial streams of 2, 3 or 4 alcohol compounds, the number of partial streams of alcohol compounds is equal to the number of static or dynamic mixers used, each static or dynamic mixer is fed with a polyester stream and one of the partial streams of alcohol compound, and in each static or dynamic mixer, the volumetric dilution with the alcohol compound is as follows, the method according to claim 1: - When the viscosity ratio between the polyester stream and the partial stream of alcohol compound fed to the static or dynamic mixer under consideration is 3500 or more, preferably 3000 or more, it is 3% to 50%, preferably 10% to 35%, most preferably 15% to 30%, or - When the viscosity ratio between the polyester stream and the partial stream of alcohol compound fed to the static or dynamic mixer under consideration is less than 3500, preferably less than 3000, it is 10% to 70%, preferably 20% to 65%, most preferably 30% to 65%, or even 35% to 65%.

11. The weight ratio between the total amount of alcohol compound 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, the method according to claim 1.

12. The temperature at which the depolymerization step b) is operated is 180 to 290 °C, preferably 210 to 270 °C, the method according to claim 1.

13. comprising a separation step c) for producing an alcohol effluent and a diester monomer effluent, feeding at least the reaction effluent obtained from step b) to step c), the temperature during operation of step c) being from 60 to 250 °C and the pressure during operation thereof being lower than the pressure of step b), step c) using from 1 to 5, preferably from 2 to 5, successive gas-liquid separation sections, each gas-liquid separation section producing a liquid phase and a gas phase, the liquid phase from the preceding gas-liquid separation section being fed to the subsequent gas-liquid separation section, the liquid phase obtained from the last gas-liquid separation section constituting the diester monomer effluent and all of the gas phase being recovered to at least partially constitute the alcohol effluent, the process according to claim 1. **Claim 14** The process according to claim 13, wherein the alcohol stream fed to step a) is at least part of the alcohol effluent obtained from step c). **Claim 15** The process according to claim 1, wherein the polyester feedstock comprises polyethylene terephthalate, advantageously at least 50% by weight, preferably at least 70% by weight, suitably at least 90% by weight of polyethylene terephthalate.

Images