PROCESS FOR RECYCLING POLYETHYLENE TEREPHTHALATE BY GLYCOLYSIS INCLUDING OPTIMIZED EVAPORATION OF BHET

Abstract

The present invention relates to a process for preparing bis-(2-hydroxyethyl) terephthalate by depolymerization of a plastic filler comprising PET, comprising: a) a step of depolymerization of the PET in the presence of a diol, so as to have a weight ratio between the diol and the PET of the plastic filler of between 0.3 and 8.0, said step a) comprising a reaction phase operated between 150 and 300°C, b) a step of evaporation of the BHET to produce a BHET-rich stream and a heavy impurity stream, step b) using an evaporator comprising an evaporation zone and a zone for withdrawing the heavy impurity stream, and a section for discharging the heavy impurity stream located downstream of the evaporator, the evaporator being operated at a pressure less than or equal to 0.0010 MPa,and in which the evaporation zone is operated between 120 and 300°C and the heavy impurity stream withdrawal zone and the heavy impurity stream discharge section at a temperature greater than 250°C and less than or equal to 300°C.,

Description

Title of the invention: PROCESS FOR RECYCLING POLYETHYLENE TEREPHTHALATE BY GLYCOLYSIS INCLUDING OPTIMIZED EVAPORATION OF BHET Technical field

[0001] The invention relates to a process for preparing bis-(2-hydroxyethyl) terephthalate (BHET) by depolymerization of a plastic filler comprising polyethylene terephthalate (PET), said BHET obtained being in particular intended to be (re)polymerized to produce a polyester, more particularly PET (or rPET), and thus participate in the recycling of PET-based plastics. More particularly, the invention relates to a process for preparing bis-(2-hydroxyethyl) terephthalate (BHET) from a plastic filler comprising PET, said process comprising a step of glycolysis of the PET contained in the plastic filler which feeds said process and an optimized step of evaporation of the BHET generated. Prior art

[0002] Plastic recycling is a major environmental issue for the coming century. The collection channels, which feed the recycling channels, are structured differently depending on the country. They are evolving in such a way as to maximize the quantity of plastic recovered in waste depending on the nature and quantity of the flows and the sorting technologies. There are several ways of recycling and recovering plastics from the collection and sorting channels.

[0003] First of all, there is so-called mechanical recycling: mechanical recycling makes it possible to partially reuse certain waste, either directly (after passing into the molten state and then shaping the thermoplastics) in new objects, or by mixing the mechanically sorted plastic waste streams with virgin polymer streams.

[0004] Another possible route is the deformulation of plastic materials, in particular based on thermoplastics: it consists of dissolving the polymer, in particular the targeted thermoplastic, in a solvent and eliminating the additives without modification of the polymer chains using non-destructive purification methods.

[0005] So-called chemical recycling, for its part, aims firstly to eliminate the additives and, depending on the processes applied, to more or less chemically modify the polymer chains of the plastics considered (for example recovery of the intact polymer, depolymerization of the latter or obtaining mixtures of compounds comprising carbon and hydrogen obtained after non-selective breaking of the chains of various polymers). These various options involve generally complex sequences of steps.

[0006] Plastics from collection and sorting channels are called plastics for recycling. PET for recycling can come in particular from the collection of bottles, trays, films, resins and / or fibers made of polyester (such as textile fibers, tire fibers).

[0007] PET to be recycled can be classified into four main categories:

[0008] - clear PET, consisting mainly of colorless transparent PET (generally less than 60% by weight) and transparent azure PET, which does not contain pigments and can be used in mechanical recycling processes,

[0009] - dark or colored PET (green, red, etc.), which can generally contain up to 0.1% by weight of colorants or pigments but remains transparent, or translucent;

[0010] - opaque PET, which contains a significant amount of pigments at levels typically varying between 0.25 and 5.0% by weight to opacify the polymer. Opaque PET is increasingly used, for example, in the manufacture of food containers, such as milk bottles, in the composition of cosmetic, phytosanitary or dye bottles. Textile fibers can also be assimilated to this category of opaque PET;

[0011] - multi-layer PET or in a mixture with polymers other than PET or a A layer of recycled PET between layers of virgin PET (i.e., PET that has not been recycled), or an aluminum film, for example. Multi-layer PET is used after thermoforming to make packaging such as trays. PET mixed with other polymers is used, for example, in the textile industry.

[0012] In particular, the recycling process for plastic flows from packaging collection and sorting processes generally comprises a first conditioning step in the form of flakes during which bales of raw packaging are unpackaged and the containers washed, sorted and crushed, then purified and sorted again to produce a flow of flakes generally containing less than 5% by mass of “macroscopic” impurities (glass, metals, other plastics, wood, cardboard, mineral elements), for example less than 1% by mass of “macroscopic” impurities, preferably less than 0.2% by mass of “macroscopic” impurities and even more preferably less than 0.05% by mass.

[0013] The clear PET flakes can then undergo an extrusion-filtration step to produce extrudates which are then reusable in a mixture with virgin PET to make new products (bottles, fibers, films). A solid state vacuum polymerization step (known by the acronym SSP for Solid State Polymerization) is necessary for food uses. This type of recycling corresponds to mechanical recycling.

[0014] Dark (or colored) PET flakes are also mechanically recyclable. However, the coloring of the extradited products formed from colored streams limits its uses: dark PET is most often used to produce fibers or packaging strips. The outlets are therefore more limited compared to those of clear PET.

[0015] The presence of opaque PET containing pigments at significant levels in the PET to be recycled poses problems for recyclers because opaque PET impairs the mechanical properties of the recycled PET. Opaque PET is currently collected with colored PET and ends up in the colored PET stream. Given the development of uses for opaque PET, the opaque PET contents in the colored PET stream to be recycled are currently between 5-20% by weight and are tending to increase further. In a few years, it will be possible to achieve opaque PET contents in the colored PET stream higher than 20-30% by weight. However, it has been shown that beyond 10-15% of opaque PET in colored PET streams, the mechanical properties of the recycled PET are impaired (cf.“Impact of the development of white opaque PET on the recycling of PET packaging”, preliminary note from COTREP dated 5 / 12 / 13) and prevent recycling in the form of fibers, the main outlet for the sector for colored PET.

[0016] Dyes are natural or synthetic substances, soluble in particular in polyester material and used to color the material into which they are introduced. The dyes generally used are of different natures and often contain heteroatoms of type O and N, and conjugated unsaturations, such as for example quinone, methine, azo functions, or molecules such as pyrazolone and quinophthalone. Pigments are finely divided substances, insoluble in particular in polyester material, used to color and / or opacify the material into which they are introduced. The main pigments used to color and / or opacify polyesters, in particular PET, are metal oxides such as TiO 2, CoA12O4, Fe2O3, silicates, polysulfides, and carbon black. Pigments are particles generally between 0.1 and 10 pm in size, and mostly between 0.4 and 0.8 pm.The complete elimination of these pigments by filtration, necessary to consider recycling opaque PET, is technically difficult because they are extremely clogging.

[0017] The mechanical recycling of colored and opaque PET is therefore extremely delicate.

[0018] The chemical recycling of polyester, in particular polyethylene terephthalate (PET), has been the subject of numerous studies aimed at decomposing the polyester recovered in the form of waste into monomers which can again be used as feedstock for a polymerization process.

[0019] US patent application 2004 / 0147624 describes a method for preparing purified BHET by decomposition of polyester in the presence of ethylene glycol (i.e., glycolytic depolymerization of the polyester). More particularly, the Document US 2004 / 0147624 describes a process for producing purified BHET from PET bottles (clear PET and colored PET), comprising a step of depolymerization of the PET in the presence of ethylene glycol, followed by a succession of steps of purification of the reaction effluent by filtration, by contact with ion exchange resins and adsorbents, by crystallization, then finally by evaporation of the BHET in a falling film type molecular evaporator operated at a temperature of 208°C and a pressure of 13 Pa, and with an internal condenser at 118°C. Application US 2004 / 0147624 does not mention the recovery of a residue stream at the evaporation step and therefore even less the problems of fouling of the system for recovering said stream and a fortiori the solutions for limiting this fouling.

[0020] Patent JP3715812 describes the production of refined BHET from PET in the form of flakes, by depolymerization by glycolysis of the PET flakes followed by a step of pre-purification of the reaction effluent by cooling, filtration, adsorption and treatment on ion exchange resin, said pre-purification step being presented as very important and carried out before the evaporation of the glycol then the evaporation of the BHET carried out between 190°C and 250°C under vacuum (between 0.1 and 0.5 mmHg, i.e. between approximately 13 Pa and approximately 67 Pa or between approximately 0.13 mbar and 0.67 mbar). Patent JP3715812 explains that the pre-purification makes it possible to avoid the re-polymerization of the BHET in the subsequent evaporation steps.

[0021] Korean patent applications KR20230069611 and KR20230127720 also describe methods for obtaining purified BHET from PET waste, comprising a step of evaporating the BHET. These Korean applications disclose that the evaporation of the BHET is preferably carried out by thin-film evaporation in an evaporator whose internal pressure is, for example, between 0.005 Torr and 5.0 Torr (i.e., between approximately 0.0067 mbar and approximately 6.7 mbar) and whose internal temperature of the thin film in the upper part of the evaporator is at a temperature greater than or equal to 100°C and less than or equal to 250°C, and preferably between 150°C and 250°C or 180°C and 220°C. Applications KR20230069611 and KR20230127720 explain that evaporation of BHET allows the removal of BHET dimers and trimers.

[0022] Document FR 3053691 A1 describes a process for depolymerizing a polyester filler comprising opaque PET and in particular from 0.1 to 10% by weight of pigments, by glycolysis in the presence of ethylene glycol. A purified bis-(2-hydroxyethyl) terephthalate (BHET) effluent is obtained after separation and purification steps: separation of at least a portion of the ethylene glycol, then evaporation of the generated BHET and finally decolorization of the recovered BHET stream, for example by adsorption. The BHET evaporation step is carried out under vacuum, at a temperature less than or equal to 250°C, and with a short residence time (less than or equal to 10 minutes), and allows the recovery of a BHET stream, which then undergoes a decolorization step, and a residue stream comprising heavy compounds, such as PET oligomers not fully converted during depolymerization or generated during the evaporation steps.

[0023] Document FR 3105236 describes an improvement to the process for depolymerization by glycolysis of a polyester feedstock comprising PET and in particular that of document FR 3053691. The improvement consists in particular in recycling an effluent comprising at least a fraction of the oligomeric residues, separated during a step downstream of the depolymerization, in the presence of diol, upstream of the depolymerization step. If document FR 3105236 explains that the recycling of at least a fraction of the residues in the presence of diol makes it possible, in addition to increasing the overall yield of the process, to simplify the operability of transporting said fraction of residues to the reaction section, it remains silent as to possible problems of fouling of the evaporator and a fortiori as to the solutions making it possible to remedy them.

[0024] The present invention seeks to improve the processes for preparing BHET by glycolytic depolymerization of a polyester feedstock, of the prior art. More particularly, the present invention seeks to improve the evaporation step of the BHET monomer, so as to limit fouling and therefore blockage problems in the evaporator, in particular at the residue withdrawal zone, and preferably in the withdrawal line located downstream. Summary of the invention

[0025] The present invention relates to a process for preparing bis-(2-hydroxyethyl) terephthalate BHET by depolymerization of a plastic filler comprising polyethylene terephthalate PET, said process comprising:

[0026] a) a step of depolymerizing the PET of the plastic filler, in the presence of a diol, with a quantity of diol adjusted so as to have a weight ratio between the quantity of diol and the quantity of PET contained in the plastic filler between 0.3 and 8.0,

[0027] said depolymerization step comprising a reaction phase carried out at a temperature between 150 and 300°C,

[0028] said depolymerization step producing a reaction effluent comprising BHET,

[0029] b) a BHET evaporation step to produce a BHET-rich stream and a heavy impurity stream,

[0030] said evaporation step implementing i) an evaporator having a wall with an internal surface and an external surface and comprising an evaporation zone and a zone for withdrawing the heavy impurity stream, and ii) a stream discharge section heavy impurities located downstream of the heavy impurity flow withdrawal zone from the evaporator,

[0031] the evaporator being operated at a pressure less than or equal to 0.0010 MPa, and in which:

[0032] the evaporation zone of the evaporator is operated at a temperature of the external surface of the wall of the evaporator at the level of the evaporation zone less than or equal to 300°C and greater than or equal to 120°C and the zone for withdrawing the heavy impurity stream and the section for discharging the heavy impurity stream being operated at a heating temperature greater than 250°C and less than or equal to 300°C.

[0033] The method according to the invention makes it possible to limit the fouling of the evaporator used to evaporate the BHET generated during the step of depolymerization by glycolysis of the PET of a plastic feedstock, for example plastic waste, in particular at the level of the residue withdrawal zone (which mainly comprise heavy impurities, in particular dense and / or whose molar mass is higher than that of the targeted BHET), and of the withdrawal line located downstream of the evaporator. Thus, by limiting the fouling of the evaporator, the present invention makes it possible to reduce the operational shutdowns of the BHET evaporation unit and therefore contributes to the optimization of the overall process from both a technical and economic point of view. Description of the embodiments

[0034] According to the invention, polyethylene terephthalate or poly(ethylene terephthalate), also simply called PET, has an elementary repeating unit of formula:

[0035] Conventionally, PET is obtained by polycondensation of terephthalic acid (PTA), or dimethyl terephthalate (DMT), with ethylene glycol.

[0036] In the remainder of the text, the expression "per mole of diester in said plastic filler" corresponds to the number of moles of -[O-CO-O-(C6H4)-CO-O-CH2 -CH2]- unit in the plastic filler, and which is in particular the diester unit resulting from the reaction of PTA and ethylene glycol.

[0037] In the remainder of the description, the term “monomer” or “BHET monomer” or “BHET” designates bis(2-hydroxyethyl) terephthalate (BHET) of chemical formula HOC2H4-CO2-(C6H4)-CO2-C2H4OH, in which -(C6H4)- represents an aromatic cycle, and which is in particular the diester unit resulting from the esterification reaction of PTA with ethylene glycol.

[0038] The term “oligomer” typically denotes a small polymer, generally consisting of 2 to 20 elementary repeating units, for example between 2 and 5 elementary repeating units. In the present description, the term “oligomer”, "PET oligomer", "ester oligomer" or "BHET oligomer" are used interchangeably and designates a terephthalate ester oligomer, comprising between 2 and 20, preferably between 2 and 5, elementary repeating units of formula -[O-CO-(C6H4)-CO-O-C2H4]-, with -(C6H4)- an aromatic cycle.

[0039] In the present description, the terms "diol" and "glycol" are used interchangeably and correspond to compounds comprising 2 hydroxyl groups -OH and preferably comprising between 2 and 12 carbon atoms, preferentially between 2 and 8 carbon atoms. The preferred diol is ethylene glycol, also called mono-ethylene glycol or MEG.

[0040] The diol stream, used in the steps of the process of the invention, comprises, preferably consists of, the diol advantageously defined above. The diol stream preferably comprises at least 95% by weight of diol. Very preferably, the diol stream comprises at least 95% by weight of ethylene glycol.

[0041] The terms “upstream” and “downstream” are to be understood in relation to the general flow of the stream in the process.

[0042] According to the present invention, the pressures are absolute pressures and are given in absolute MPa (or MPa abs.) or in absolute mbar (or mbar abs).

[0043] According to the invention, the times and durations are expressed in hours (h), in minutes (min) and / or in seconds (sec).

[0044] In the present description, the expressions "between ... and..." and "between ... and..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this were not the case and the limit values ​​were not included in the range described, such precision will be provided by the present invention.

[0045] In the sense of the present invention, the different parameter ranges for a given step such as pressure ranges and temperature ranges may be used alone or in combination. For example, in the sense of the present invention, a range of preferred pressure values ​​may be combined with a range of more preferred temperature values.

[0046] In the following, particular embodiments of the invention may be described. They may be implemented separately or combined with each other, without limitation of combinations when this is technically feasible. Charge

[0047] The method according to the invention is fed with a plastic charge comprising at least polyethylene terephthalate (PET).

[0048] Said plastic load is advantageously a plastic load to be recycled, in particular from waste collection and sorting channels. Said plastic load may come, for example, from the collection of bottles, trays, films, resins and / or fibers made of pure or mixed polyethylene terephthalate.

[0049] Advantageously, the plastic filler comprises at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight of polyethylene terephthalate (PET). In particular, the plastic filler comprises at least one PET chosen from clear, colored, opaque, dark, multi-layer PET and their mixtures. According to a particular embodiment, the plastic filler comprises at least 10% by weight of opaque PET, very preferably at least 15% by weight of opaque PET, said opaque PET advantageously being opaque PET to be recycled, i.e. from collection and sorting channels. The plastic filler may comprise from 0.1% to 10% by weight of pigments, advantageously from 0.1% to 5% by weight. It may also comprise in particular from 0.01% to 5% by weight of colorants, in particular 0.05% to 1% by weight of colorants, preferably from 0.05% to 0.2% by weight of colorants.

[0050] In the collection and sorting channels, the plastic packaging waste is washed and crushed before constituting the plastic load of the process according to the invention. The polyester textile waste can be smoothed (hard points such as buttons and fasteners removed) before being shredded and possibly densified (or shaped) in the form of granules or popcom so that it can be mechanically introduced into the process according to the invention.

[0051] The plastic filler may therefore be, in whole or in part, in the form of granules or flakes, the greatest length of which is less than 10 mm, preferably between 5 and 25 mm, or in the form of a micronized solid, i.e. in the form of particles preferably having a size between 10 microns and 1 mm.

[0052] According to a particular embodiment, the plastic filler comprises polyester textile waste which can be pretreated, for example de-smoothed and shredded, and possibly densified in the form of granules or popcorn.

[0053] The plastic filler may, in addition, comprise polyester, in particular PET, from production waste from the polymerization and / or transformation processes of the polyester material.

[0054] The plastic filler may also comprise “macroscopic” impurities, preferably less than 5% by weight, preferably less than 3% by weight of “macroscopic” impurities, such as glass, metal, plastics other than polyester (for example PP, HDPE, etc.), wood, cardboard, mineral elements. Said polyester filler may also be, in whole or in part, in the form of fibers, such as textile fibers, optionally pretreated to remove cotton fibers, polyamide fibers, or any other textile fiber other than polyester, or such as tire fibers, optionally pretreated to remove in particular polyamide fibers or rubber or polybutadiene residues. The plastic filler may also include elements, for example metallic elements, used as polymerization catalysts and as stabilizing agents in PET production processes, such as antimony, titanium, tin. Step a) of depolymerization

[0055] The process according to the invention comprises a step of depolymerization of the PET contained in the plastic filler, in the presence of a diol and preferably in the presence of ethylene glycol, to produce a reaction effluent comprising BHET.

[0056] The reaction carried out in step a) corresponds to a reaction of depolymerization of PET by glycolysis.

[0057] Depolymerization step a) advantageously comprises a reaction phase.

[0058] Step a) is advantageously supplied with said plastic filler and at least one diol stream, preferably an ethylene glycol stream. The amount of diol introduced in step a), and in particular present in the reaction phase of step a), is adjusted so as to have a weight ratio between the weight amount of diol, preferably ethylene glycol, present in the reaction phase of step a), relative to the weight amount of PET contained in the plastic filler of between 0.3 and 8.0, preferably between 1.0 and 7.0, more preferably between 1.5 and 6.0.In other words, the depolymerization step a) is fed by the plastic feedstock and by at least one diol flow, so that the molar ratio between the total quantity of moles of diol, preferably ethylene glycol, introduced in step a), and therefore present in the reaction phase of a), relative to the total quantity of moles of diester units of the PET contained in the plastic feedstock is respectively between 0.9 and 24.0, preferably between 3.0 and 21.0, more preferably between 4.5 and 18.0.

[0059] Advantageously, said reaction phase of depolymerization step a) may implement one or more reaction sections, preferably at least two reaction sections, preferably between two and four reaction sections, preferably operating in series. Each reaction section advantageously comprises a reactor, more particularly any type of reactor known to those skilled in the art for carrying out a depolymerization or transesterification reaction, and preferably a reactor stirred by a mechanical stirring system and / or by a recirculation loop and / or by fluidization. In each reaction section, the reactor may optionally comprise a conical bottom for purging impurities.Preferably, depolymerization step b) uses at least two reaction sections, preferably between two and four reaction sections, operating in series, the reaction section(s) from the second reaction section being operated at a temperature which is identical or different from each other, and preferably lower than or equal to the temperature of the first reaction section, preferably lower and preferentially lower. from 10 to 50°C, or even 20 to 40°C lower, compared to the temperature of the first reaction section.

[0060] Advantageously, the reaction phase of step a) is carried out at a temperature between 150 and 300°C, preferably between 170 and 290°C, more preferably between 180 and 270°C, in particular in the liquid phase. The operating pressure of the reaction phase of step a) is advantageously adjusted so as to maintain the reaction system in the liquid phase, the expression "reaction system" meaning all of the constituents and phases present within said reaction phase of step a). Preferably, the reaction phase of step a) is carried out at a pressure of at least 0.1 MPa, preferably at least 0.4 MPa, and preferably less than 5 MPa. Preferably, the reaction phase of step a) is carried out with a residence time of between 0.1 and 10 hours, preferably between 0.25 and 8 hours, between 0.5 and 6 hours.The residence time in the reaction phase of step a) is defined here as the ratio of the volume of liquid present in the reaction phase, i.e. the total volume of the reaction system, to the volume flow rate of the flow leaving said reaction phase. Thus, if the reaction phase of step b) uses several reactors, preferably in series, the residence time in the reaction phase is then defined as the ratio of the total volume of liquid present in all the reactors used, in particular in series, to the volume flow rate of the flow leaving the last reactor in the series.

[0061] A depolymerization catalyst may optionally feed the depolymerization step a).

[0062] When a depolymerization catalyst is introduced in step a), said depolymerization catalyst may be homogeneous or heterogeneous and chosen from esterification catalysts known to those skilled in the art such as oxide complexes and salts of antimony, tin, titanium, alkoxides of metals from groups (I) and (IV) of the periodic table of elements, organic peroxides, acid-base metal oxides.

[0063] A preferred heterogeneous catalyst advantageously comprises at least 50% by mass relative to the total mass of the catalyst, preferably at least 70% by mass, advantageously at least 80% by mass, very advantageously at least 90% by mass, and even more advantageously at least 95% by mass of a solid solution consisting of at least one spinel of formula ZXA12O(3+X) in which x is between 0 (limit excluded) and 1, and Z is chosen from Co, Fe, Mg, Mn, Ti, Zn, and comprising at most 50% by mass of alumina and oxide of element Z. Said preferred heterogeneous catalyst advantageously contains at most 10% by mass of dopants chosen from silicon, phosphorus and boron taken alone or as a mixture. For example, and in a non-limiting manner, said solid solution may consist of a mixture of spinel ZnAl2O4 and CoA12O4 spinel, or be made of a mixture of ZnAl 2O4 spinel, MgAl2O4 spinel and FeAl2O4 spinel, or be made of ZnAl2O4 spinel only.

[0064] A homogeneous catalyst may be chosen from amines, preferably tertiary mono- and di-amines, such as for example tetramethylethylenediamine (TMEDA), pentamethyldiethylenetriamine (PMDETA), trimethyl triaza cyclononane (TACN), triethylamine (TEA), 4-(N,N-dimethylamino) pyridine (DMAP), 1,4-diazabicyclo (2,2,2)octane (DABCO), N-methyl imidazole (NMI), and alkali or alkaline earth hydroxides, such as for example Mg(OH)2 and NaOH, may be added to depolymerization step b).

[0065] A preferred homogeneous catalyst may be chosen from acetates, carbonates, oxides, hydroxides, and their derivatives, of a metal, the metal being able to be an alkali metal, an alkaline earth metal or a transition metal.

[0066] According to one embodiment, the depolymerization step is carried out without adding an external catalyst to the plastic filler.

[0067] The reaction phase of the depolymerization step can be carried out in the presence of a solid adsorbent agent in the form of particles, for example in the form of powder or shaped in particular in the form of granules, so as to capture at least part of the impurities, in particular dyes, thus relieving any subsequent purification steps. Said solid adsorbent agent is advantageously an activated carbon.

[0068] The depolymerization reaction advantageously makes it possible to convert the PET of the plastic filler into at least the bis(2-hydroxyethyl) terephthalate (BHET) monomer and BHET oligomers. The conversion of the PET of the plastic filler in depolymerization step a) is greater than 50%, preferably greater than 70%, more preferably greater than 85%. The molar yield of BHET monomer is greater than 50%, preferably greater than 70%, more preferably greater than 80%. The molar yield of BHET monomer corresponds to the molar flow rate of BHET at the outlet of step a) relative to the molar flow rate of diester (i.e. diester units) in the PET of the plastic filler which feeds step b).

[0069] An internal recirculation loop can advantageously be implemented in step a): a fraction of the reaction system of the reaction phase is withdrawn, then filtered and finally reinjected into the reaction phase of step a). Step a) can implement several recirculation loops. For example, when the reaction phase of step a) implements several reaction sections, said reaction phase can implement several recirculation loops and each of the recirculation loops can carry out a withdrawal in a reaction section and a reinjection in the same reaction section or in a reaction section different. This (these) internal recirculation loop(s) allows the elimination of solid impurities, in particular “macroscopic” impurities, possibly introduced with the plastic load.

[0070] Depolymerization step a) optionally comprises a phase of conditioning the plastic filler, located upstream of the reaction phase. When step a) of the process according to the invention comprises a conditioning phase, the latter is advantageously supplied with the plastic filler and optionally with at least one diol flow, and makes it possible to produce a flow of conditioned filler.

[0071] Said conditioning phase makes it possible in particular to heat and pressurize said plastic filler under the operating conditions of the reaction phase of the depolymerization step. More particularly, when it is integrated into step a), the conditioning phase of step a) may comprise a heating phase for melting at least partly the plastic filler and / or a pre-mixing phase for mixing the plastic filler, optionally at least partly melted, with at least part of the diol present in the reaction phase of step a) of depolymerization.

[0072] Advantageously, during the heating phase of the possible conditioning phase, the plastic filler is progressively heated preferably to a temperature close to or even slightly higher than the melting temperature of the PET contained in said plastic filler, so as to make it at least partly liquid. Advantageously, at least 70% by weight of the PET of the plastic filler, very advantageously at least 80% by weight, preferably at least 90% by weight, preferentially at least 95% by weight of the PET of the plastic filler, or even all of the PET of the plastic filler, is melted and in liquid form at the end of the possible conditioning phase of step a).

[0073] During the pre-mixing phase of the conditioning phase, at least a fraction of the total diol present in the reaction phase of step a) is introduced, in particular in the form of one or more diol streams, and mixed with the plastic filler, optionally at least partly melted. According to one embodiment and when step a) comprises a conditioning phase with a pre-mixing phase, only a fraction of the total diol present in the reaction phase of step a) is introduced to the pre-mixing phase and the second fraction feeds the reaction phase. According to another embodiment and when step a) comprises a conditioning phase with a pre-mixing phase, all of the total diol present in the reaction phase of step a) is introduced to the pre-mixing phase.

[0074] The conditioning phase of step a) is advantageously carried out at a temperature of between 150 and 300°C, preferably between 225 and 275°C, more preferably between 250 and 290°C. This temperature is kept as low as possible to minimize thermal degradation of the PET polymer, and can be ... sufficiently sufficient to melt at least partially the PET of the plastic filler. The conditioning phase can be carried out under an inert atmosphere to limit the introduction of oxygen into the system and the oxidation of the plastic filler. Advantageously, the conditioning phase of step a) is carried out at a pressure preferably between atmospheric pressure (i.e. 0.1 MPa) and 20 MPa, preferably between 0.15 MPa and 10 MPa.

[0075] The conditioning phase of step a) can implement any type of equipment known to those skilled in the art for heating and pressurizing a plastic charge and / or for mixing said plastic charge with a solvent, in particular diol. For example, the conditioning phase, when integrated into step a) can implement an extruder, in particular single-screw or twin-screw, solid and liquid feed systems, one or more static or dynamic mixers. It can also implement a batch, semi-batch or continuous PET melting capacity which makes it possible to feed the reaction phase with a controlled flow rate and temperature.

[0076] When integrated into step a), a conditioned feedstock, advantageously at least partly in liquid form, is obtained at the end of the conditioning phase and feeds the reaction phase. When step a) does not include a conditioning phase, the reaction phase is directly fed with the plastic feedstock and all of the diol.

[0077] Advantageously, depolymerization step a) makes it possible to obtain a reaction effluent comprising BHET. Optional pre-purification step a')

[0078] Optionally, the process according to the invention may comprise a step of pre-purification of the reaction effluent, located downstream of the depolymerization step and upstream of step b) of evaporation of the BHET.

[0079] This intermediate step makes it possible to eliminate at least a portion of the compounds other than the targeted BHET and present in the reaction effluent, such as diol, in particular ethylene glycol, solid impurities (macroscopic impurities, pigments, inorganic fillers, etc.), dyes, polymerization and / or depolymerization catalysts, ethylene glycol, etc. This optional step of pre-purification of the reaction effluent makes it possible to obtain a pre-purified effluent, comprising the BHET generated during the depolymerization step a). When it is integrated into the process, it is the pre-purified effluent which feeds the evaporation step b); otherwise (i.e. when the process does not include an optional step a'), it is the reaction effluent from step a) which feeds step b).

[0080] In particular, said optional pre-purification step may comprise one or more sub-steps chosen from:

[0081] - at least one filtration, for example by means of one or more filters, in series or not, with a mesh size which can be between 1 and 1000 pm, preferably between 1 and 500 pm, for example between 1 and 250 pm;

[0082] - precipitation of impurities (such as pigments or dyes), for example by cooling the optionally filtered reaction effluent, then by filtration of the cooled effluent, in particular by passing it through a filter of size, for example, between 1 and 50 pm, and preferably between 1 and 10 pm;

[0083] - adsorption, by contact with at least one adsorbent, for example chosen from activated carbons, aluminas and clays;

[0084] - an ionic treatment by contact with at least one ion exchange resin, in particular with at least one cation exchange resin and / or with at least one anion exchange resin;

[0085] - crystallization and / or precipitation of BHET, for example by cooling and / or contact with a solvent (for example water), advantageously followed by solid-liquid separation for example by filtration;

[0086] - a separation of the diol, in particular by gas-liquid separation, or even a gas-liquid separation sequence, the recovered liquid phase comprising the BHET, the gas phase comprising the diol.

[0087] A person skilled in the art will be able to choose the purification method(s) best suited for this optional pre-purification step. For example, he or she may choose from the purification steps disclosed in document US2004 / 0147624, patent JP3715812, patent FR3053691 and / or applications KR20230069611 and KR20230127720. Step b) evaporation of the BHET monomer

[0088] The process according to the invention comprises a step b) of evaporation of the BHET advantageously generated during step a) of depolymerization, to produce a stream rich in BHET and a stream of heavy impurities.

[0089] This step b) of evaporation of the BHET aims to separate all or part of the BHET monomer, which is vaporized, from the oligomers, not entirely converted, possibly from the unconverted PET polymer, and also from the impurities, such as pigments, other polymers possibly present, polymerization catalysts and possibly depolymerization catalysts, while minimizing the loss of monomers by re-polymerization.

[0090] The term "BHET-rich" here means that the stream under consideration comprises BHET at a higher concentration than the BHET concentration of the stream which feeds step b). Preferably, said BHET-rich stream comprises at least 50% by weight of BHET monomer, preferably at least 70% by weight of BHET monomer, preferentially at least 80% by weight of BHET monomer, preferably at least 90% by weight of BHET monomer, relative to the total weight of said BHET-rich stream. The BHET-rich stream may optionally comprise residual impurities such as dyes, and / or other monomers such as 2-(2-hydroxyethoxy) ethyl 2-hydroxyethyl terephthalate (BHETdeg), mono-2-hydroxyethyl terephthalate, terephthalic acid or bis(2-hydroxyethyl) isophthalate (BHEI), BHET dimers or trimers, or compounds consisting in particular of BHET monomer altered for example by thermal or thermo-oxidative degradation reactions.

[0091] Preferably, the heavy impurity stream comprises heavy compounds, in particular PET oligomers not entirely converted, unconverted PET polymer, impurities, in particular heavy impurities, such as pigments, other polymers possibly present in particular in the plastic filler (in particular polymers of a nature different from that of PET), polymerization catalysts and possibly depolymerization catalysts. Preferably, the heavy impurity stream may comprise at least 15% by weight of heavy compounds, in particular at least 25% by weight of heavy compounds, or even at least 40% by weight of heavy compounds, relative to the total weight of said heavy impurity stream. The heavy impurity stream may also comprise BHET monomer, not separated.

[0092] According to the invention, step b) advantageously uses an evaporator and a section for discharging the heavy impurity flow. The section for discharging the heavy impurity flow is advantageously located downstream of the evaporator and in particular allows the discharge of the heavy impurity flow to the outside of the evaporator; it may correspond, for example, to a flow circulation line located downstream of the evaporator and which allows the withdrawal of said flow.

[0093] More particularly, the evaporator of step b) is a device capable of separating a flow, preferably in liquid form at the inlet of said device, by evaporation of at least a fraction of said flow, preferably in the form of a film along the walls of said device, and preferably being operated under vacuum. Preferably, said evaporator implemented in step b) is any equipment known to those skilled in the art allowing such separation, in particular any type of evaporator provided with a heated side wall and equipped with an internal rotor, said rotor being known to limit the thickness of the film on the heated wall. Said evaporator preferably comprises a condensation zone, located inside or outside the evaporator (i.e. the enclosure or volume of the evaporator, enclosure / volume delimited by the internal wall of said evaporator).This type of evaporator makes it possible to reduce the residence time and maximize the evaporation surface. This type of evaporator advantageously makes it possible to reduce the residence time of the products of interest inside the evaporator, and therefore at high temperatures, and to maximize the evaporation surface. In a very particular way, the evaporator implemented at . step b) is advantageously a thin film evaporator (TFE) or a short path evaporator (SPE). It is known to those skilled in the art that the difference between the thin film evaporator and the short path evaporator lies in the location of the condensation zone of the evaporated flow which is located outside the equipment comprising the evaporation zone in the case of the thin film evaporator (TFE) and which is located inside the equipment which comprises the evaporation zone in the case of the short path evaporator (SPE). The short path evaporator can also be called a short path distiller (SPD).The evaporator used in step b) may also be a falling film evaporator or a wiped film evaporator. The condensation zone of the evaporated stream may be operated at a temperature between 100°C and 170°C, preferably between 110 and 150°C and more preferably between 115°C and 140°C.

[0094] More particularly, the evaporator implemented in step b) has a wall with an internal surface and an external surface. The internal surface of the wall of the evaporator can be defined as the surface of the wall which delimits a volume, called the internal volume of the evaporator, inside which the evaporation of the BHET and the separation are advantageously carried out. The internal surface of the wall of the evaporator can also be defined as the surface of the wall of the evaporator of which at least a portion is in contact with at least the flow of heavy impurities. Conversely, the external surface of the wall of the evaporator is the surface of the wall of the evaporator which has no contact with the products of interest, in particular with the flow of heavy impurities or the flows comprising BHET (i.e. the flow feeding step b) and the flow rich in BHET obtained at the end of step b).The external surface is the surface of the wall which is advantageously directly heated and therefore which is preferably in contact with a heating means, for example an electrical source or a heat transfer fluid. Preferably, the external surface of the wall of the evaporator is in contact with a heat transfer fluid such as an oil.

[0095] Inside the evaporator, different zones can be defined. More particularly, the evaporator comprises an evaporation zone and a heavy impurity flow withdrawal zone, advantageously defined inside said evaporator. Preferably, the heavy impurity flow withdrawal zone is located in the lower part of the evaporator, in particular in a part of the evaporator comprising the bottom of the evaporator, very particularly a part of the evaporator located between the bottom of the evaporator and three-quarters of the height of the evaporator (starting from the bottom of the evaporator), preferably between the bottom of the evaporator and the half the height of the evaporator (starting from the bottom of the evaporator), preferably between the bottom of the evaporator and a quarter of the height of the evaporator (starting from the bottom of the evaporator). Preferably, the evaporation zone is located above the heavy impurity stream withdrawal zone. Advantageously, the heavy impurity stream discharge section is located downstream of the heavy impurity stream withdrawal zone from the evaporator.

[0096] Very advantageously, the evaporator further comprises a supply of a stream comprising BHET (in particular the reaction effluent from step a), or a pre-purified effluent obtained at the end of an intermediate pre-purification step optionally), a device for withdrawing the heavy impurity stream which is preferably located in the zone for withdrawing the heavy impurity stream and a device for withdrawing the BHET-rich stream, which may be located above the evaporation zone in particular in the case of a thin film or layer evaporator (TFE) or below the evaporation zone in particular in the case of a short-path evaporator SPE. Preferably, in the case of a short-path evaporator, the evaporator also comprises a condensation zone, for example by implementing a condenser, inside said evaporator.The heavy impurity flow discharge section is very advantageously directly connected to the heavy impurity flow withdrawal device.

[0097] Advantageously, the evaporator is operated at a pressure less than or equal to 0.0010 MPa (i.e. less than or equal to 10 mbar), preferably less than or equal to 0.0005 MPa (i.e. less than or equal to 5 mbar), and preferably greater than or equal to 0.0000001 MPa (i.e. greater than or equal to 0.001 mbar), or even greater than or equal to 0.0000005 MPa (i.e. greater than or equal to 0.005 mbar).

[0098] According to the invention, the heavy impurity flow withdrawal zone and the heavy impurity flow discharge section are operated at a temperature, in particular a heating temperature (advantageously corresponding to the temperature of the external surface of the wall of the evaporator and to the temperature of the heavy impurity flow discharge section, i.e. advantageously to the temperature of the surface of the wall which is directly heated), greater than 250°C and less than or equal to 300°C, preferably operated at a temperature between 255 and 300°C, preferably between 260 and 290°C and preferably between 270 and 285°C. And advantageously, the evaporation zone is operated at a temperature adjusted so that the temperature of the external surface of the wall of the evaporator at the level of the evaporation zone is less than or equal to 300°C and preferably greater than or equal to 120°C, preferably greater than or equal to 150°C.Preferably, the evaporator is operated with a liquid residence time of less than or equal to 20 minutes, preferably less than or equal to 10 minutes, preferably less than or equal to 5. minutes, preferably less than or equal to 3 minutes, and preferably greater than or equal to 0.1 seconds. The liquid residence time is defined as the ratio of the liquid volume in the evaporator to the volume flow rate of the liquid stream feeding the evaporator.

[0099] According to a first preferred embodiment of the invention, the evaporation zone is operated at a temperature, in particular a temperature of the external surface of the wall of the evaporator at the evaporation zone, less than or equal to 250°C, preferably less than or equal to 245°C, and preferably at a temperature, in particular a temperature of the external surface of the wall of the evaporator at the evaporation zone, greater than or equal to 120°C, preferably greater than or equal to 150°C.According to this first preferred embodiment, the evaporator is operated at a pressure preferably less than or equal to 0.00015 MPa (less than or equal to 1.5 mbar), preferably less than or equal to 0.00010 MPa (less than or equal to 1.0 mbar), preferably less than or equal to 0.00008 MPa (i.e. less than or equal to 0.8 mbar), very preferably less than or equal to 0.00005 MPa (i.e. less than or equal to 0.5 mbar), and even more preferably less than or equal to 0.00004 MPa (i.e. less than or equal to 0.4 mbar). According to this embodiment, the evaporator is operated so as to obtain a BHET monomer yield greater than or equal to 80%, preferably greater than or equal to 85% and even more preferably greater than or equal to 90%.The BHET monomer yield can be defined as the ratio between the weight flow rate of BHET monomer in the BHET-rich stream - the distillate - divided by the weight flow rate of BHET monomer in the stream that feeds step b). The BHET monomer yield is advantageously adjusted by modifying the evaporation conditions. In particular, the BHET monomer yield increases when the exchange surface between the wall of the evaporator and the stream to be separated, i.e. in particular the internal surface, increases and / or when the temperature of the external wall surface increases and / or when the operating pressure of the evaporator decreases (within the temperature and pressure limits stated above). A person skilled in the art will be able to adjust the temperature and pressure conditions and the exchange surface to achieve the desired BHET yields.

[0100] According to a second preferred embodiment of the invention, the evaporation zone is operated at a temperature, in particular a temperature of the external surface of the wall of the evaporator at the evaporation zone, greater than 250°C, preferably greater than or equal to 255°C, preferentially greater than or equal to 260°C, preferably greater than or equal to 270°C, and preferably at a temperature, in particular a temperature of the external surface of the wall of the evaporator at the evaporation zone, less than or equal to 300°C. According to this second preferred embodiment, the evaporator is operated at a pressure of preferably greater than or equal to 0.00001 MPa (i.e. greater than or equal to 0.1 mbar), preferably greater than or equal to 0.00010 MPa (i.e. greater than or equal to 1.0 mbar), preferably greater than or equal to 0.00012 MPa (i.e. greater than or equal to 1.2 mbar), and preferably less than or equal to 0.0010 MPa (i.e. less than or equal to 10 mbar), preferably less than or equal to 0.0005 MPa (i.e. less than or equal to 5 mbar).

[0101] Under these operating conditions, in particular temperature and pressure, step b) allows efficient evaporation of the BHET, generated in step a) of depolymerization and contained in the flow which feeds step b), in particular the reaction effluent from step a) or a pre-purified effluent (from an intermediate step of pre-purification of the reaction effluent optionally located upstream of step b), while limiting, or even avoiding, the fouling of the zone for withdrawing the heavy impurity flow from the evaporator and of the section for discharging the heavy impurity flow.

[0102] The BHET-rich stream is recovered to be polymerized in particular in a PET production unit. The BHET-rich stream may also optionally be sent to a final purification step, before being sent to a PET production unit. Thus, the method according to the invention may further comprise an optional final purification step, in particular of the BHET-rich stream. Said final purification step may comprise, more particularly, a step of bringing the BHET-rich stream (optionally mixed with a solvent such as water, a diol, a mono-alcohol, etc.) into contact with a solid, for example an adsorbent such as activated carbon, for purification by adsorption, and / or purification by crystallization and / or precipitation of the BHET, for example by cooling and / or by introduction of a solvent (for example water).

[0103] Advantageously, the heavy impurity stream can be purged and / or recycled to the depolymerization step a).

[0104] Optional step c) of treatment of the heavy impurity flow

[0105] The process according to the invention may optionally comprise a step c) of treatment of the heavy impurity stream, which comprises the recycling of at least a fraction of the heavy impurity stream to the depolymerization step a) and / or the purging of at least a fraction of the heavy impurity stream. Preferably, the process according to the invention comprises said step c).

[0106] Advantageously, the recycling of at least a fraction of the heavy impurity stream from step b), to the depolymerization step a), is carried out by means of a transfer section while the purging of at least a fraction of the heavy impurity stream is carried out by means of a purge section. In other words, step c) implements a transfer section and / or a purge section, said transfer section being advantageously implemented between the flow discharge section heavy impurities implemented in step b) and a section implemented in step a) of depolymerization (for example a reaction section comprising at least one reactor, or possibly a conditioning section comprising in particular an extruder).

[0107] Said transfer section and said purge section may be directly or indirectly connected to said heavy impurity stream discharge section implemented in step b). Indeed, step c) may optionally further comprise a separation of the heavy impurity stream from step b) into a first fraction of the heavy impurity stream and a second fraction of the heavy impurity stream, said first fraction and said second fraction advantageously corresponding to the entire heavy impurity stream from step b). In this embodiment, step c) then comprises the recycling of said first fraction of the heavy impurity stream to the depolymerization step a) and the purging of said second fraction of the heavy impurity stream.Said possible separation is advantageously implemented in a separation section preferably located downstream of the heavy impurity flow discharge section of step b) and upstream of the transfer and purge sections. Thus, when step c) comprises a separation of the heavy impurity flow, the transfer section and the purge section are indirectly connected to the heavy impurity flow discharge section. According to another embodiment, in particular when the entire heavy impurity flow is recycled, the transfer section can therefore be directly connected to said heavy impurity flow discharge section. According to yet another embodiment, in particular when the entire heavy impurity flow is purged, the purge section can therefore be directly connected to said heavy impurity flow discharge section.

[0108] When step c) is integrated into the process according to the invention, the recycling and / or purging of at least a fraction of the heavy impurity stream, and optionally the separation of the heavy impurity stream, are carried out at a temperature preferably between 250 and 300°C, preferably between 250 and 270°C. In other words, the transfer section, the purging section and the optional separation section are implemented at a temperature preferably between 250 and 300°C, preferably between 250 and 270°C.

[0109] At this recycling and / or purging (and possibly separation) temperature, the PET oligomers, and possibly the PET polymer, included in the heavy impurity stream are in molten form and can easily be transported to step a) via the transfer section and / or removed from the process via the purging section, without fouling them or at least limiting their fouling.

[0110] Thus, the method according to the invention is an optimized method for producing BHET from a plastic load, for example plastic waste, which allows the reduction of fouling of these zones, without loss of BHET production yield, in particular when said process comprises the recycling of at least a fraction of the heavy impurity stream. Indeed, even if the risk of formation of PET oligomers may be greater at the operating temperature above 250°C, compared to a more conventional temperature (less than or equal to 250°C), the PET oligomers not entirely converted during step a) or possibly formed in the evaporator (or during possible intermediate steps of pretreatment of the reaction effluent), and possibly the PET polymer, present in the heavy impurity stream, are melted, i.e. in liquid form, which reduces the fouling of the zones in contact with said heavy impurity stream (the heavy impurity withdrawal zone of the evaporator, the discharge section and the transfer, purge and possibly separation sections).Conversely, at a temperature lower than or equal to 250°C, PET oligomers can be in solid form, in particular in the form of solid particles possibly suspended in the heavy impurity flow, which significantly increases the risks of blockage of these same areas in contact with the heavy impurity flow.

[0111] The following examples illustrate the invention without limiting its scope. EXAMPLES

[0112] In the following examples 1 to 3, the plastic feedstock which feeds the process is a polyester feedstock from the packaging collection and sorting channels, and comprising PET of which 20% by weight is opaque PET which itself contains 6.2% by weight of TiO2 pigment. The depolymerization and intermediate pre-purification steps (evaporation of the diol by gas-liquid separation) are identical for examples 1 to 3 and are described below.

[0113] 4 kg / h of polyester filler flakes comprising PET of which 20% by weight Opaque PET which itself contains 6.2% by weight of TiO2 pigment, are brought to a temperature of 250°C then injected with 11.5 kg / h of ethylene glycol (MEG) into a first stirred reactor maintained at 250°C then successively into a second and a third stirred reactor 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 volume flow rates entering the reactor, is set at 20 min in the first reactor and 2.1 h in the second and third reactors. At the outlet of the third reactor, the reaction effluent consists of 67.7% by weight of diol composed predominantly of ethylene glycol (MEG) (predominantly meaning here: comprising 95% by weight or more of MEG), 25.8% by weight of diester monomer composed predominantly of bis-(2-hydroxyethyl) terephthalate (BHET) (predominantly meaning here: comprising 95% by weight or more of BHET), 0.32% weight of TiO2, and 6.1% by weight of heavy compounds containing, among other things, dimers and / or oligomers.

[0114] The diol present in the reaction effluent is evaporated by gas-liquid separation in a succession of two flash drums at temperatures ranging from 180°C to 120°C and pressures of 0.04 MPa to 0.004 MPa followed by a scraped film evaporator operated at 175°C and 0.0005 MPa. At the end of this evaporation step, a MEG-rich stream (10.46 kg / h) and a BHET-rich liquid stream (5.02 kg / h) are recovered. The BHET-rich liquid stream, corresponding to the pre-purified effluent, consists of 79.6% by weight of BHET monomer, 0.6% by weight of MEG and 1.0% by weight of TiO2 and 18.8% by weight of heavy compounds containing, among other things, BHET dimers and / or oligomers. Example 1 (non-compliant)

[0115] The BHET-rich liquid stream is then injected into a short-path evaporator SPE (or short-path distiller SPD), the external surface of the wall of which is heated with hot oil, and which makes it possible to obtain a liquid stream of BHET and a stream of heavy impurities.

[0116] The short-path evaporator is operated at a pressure of 0.017 mbar (i.e. 0.0000017 MPa or 1.7 Pa), and at an oil temperature equal to 235°C at the evaporation zone and equal to 190°C at the bottom of the evaporator (i.e. at the heavy impurity flow withdrawal zone). The heavy impurity discharge section located downstream of the bottom of the short-path evaporator is at a temperature of 220°C. The condenser located inside the short-path evaporator is at a temperature of 120°C. The liquid residence time in the evaporator is 1 minute.

[0117] The evaporator is operated for 37 hours before being shut down due to blockage.

[0118] During the 37 hours of operation, the short-path evaporator made it possible to recover a liquid stream of BHET (which is the distillate of the evaporator), consisting of 99% by weight of BHET diester monomer and which is free of TiO2, at a flow rate of 3.8 kg / h, and a heavy residue, at a flow rate of 1.19 kg / h, which comprises 16.7% by weight of BHET diester monomer, 79.2% by weight of BHET oligomers and 4.1% by weight of TiO2. Example 2 (compliant)

[0119] The BHET-rich liquid stream is then injected into a short-path evaporator SPE (or short-path distiller SPD), the external surface of the wall of which is heated with hot oil, and which makes it possible to obtain a BHET liquid stream and a heavy impurity stream.

[0120] The short-path evaporator is operated at a pressure of 0.32 mbar (i.e. 0.000032 MPa or 32 Pa), and at an oil temperature equal to 250°C at the zone evaporation and equal to 280°C at the bottom of the evaporator (i.e. at the level of the heavy impurity flow withdrawal zone). The heavy impurity discharge section located downstream of the bottom of the short-path evaporator is at a temperature of 280°C. The condenser located inside the short-path evaporator is at a temperature of 120°C. The liquid residence time in the evaporator is 1 minute.

[0121] The evaporator is operated for 72 hours without stopping.

[0122] During the operation period, the short-path evaporator allowed the recovery of a liquid stream of BHET (which is the distillate of the evaporator), consisting of 99% by weight of BHET diester monomer and which is free of TiO2 and a heavy residue, which comprises 16.7% by weight of BHET diester monomer, 79.2% by weight of BHET oligomers and 4.1% by weight of TiO2.

[0123] Under the operating conditions of Example 2 (in accordance with the invention), the evaporation was thus carried out without any blockage problem throughout the duration of the operation (for 72 hours) and made it possible to recover a distillate comprising a very large majority of BHET. Example 3 (compliant)

[0124] The BHET-rich liquid stream is then injected into a short-path evaporator SPE (or short-path distiller SPD), the external surface of the wall of which is heated with hot oil, and which makes it possible to obtain a liquid stream of BHET and a stream of heavy impurities.

[0125] The short-path evaporator is operated at a pressure of 1.5 mbar (i.e. 0.00015 MPa or 150 Pa), and at an oil temperature equal to 280°C at the evaporation zone and equal to 280°C at the bottom of the evaporator (i.e. at the heavy impurity flow withdrawal zone). The heavy impurity discharge section located downstream of the bottom of the short-path evaporator is at a temperature of 280°C. The condenser located inside the short-path evaporator is at a temperature of 120°C. The liquid residence time in the evaporator is 1 minute.

[0126] The evaporator is operated for 72 hours without stopping.

[0127] During the operation period, the short-path evaporator allowed the recovery of a liquid stream of BHET (which is the distillate of the evaporator), consisting of 99% by weight of BHET diester monomer and which is free of TiO2 and a heavy residue, which comprises 16.7% by weight of BHET diester monomer, 79.2% by weight of BHET oligomers and 4.1% by weight of TiO2.

[0128] Under the operating conditions of Example 3 (in accordance with the invention), the evaporation was thus carried out without any blockage problem throughout the duration of the operation (for 72 hours) and made it possible to recover a distillate comprising overwhelmingly from BHET.

Claims

Claims

1. A process for preparing bis-(2-hydroxyethyl) terephthalate BHET by depolymerization of a plastic filler comprising polyethylene terephthalate PET, said process comprising: a) a step of depolymerization of the PET of the plastic filler, in the presence of a diol, with an amount of diol adjusted so as to have a weight ratio between the amount of diol and the amount of PET contained in the plastic filler between 0.3 and 8.0, said depolymerization step comprising a reaction phase carried out at a temperature between 150 and 300°C, said depolymerization step producing a reaction effluent comprising BHET, b) a step of evaporation of the BHET to produce a BHET-rich stream and a heavy impurity stream, said evaporation step implementing i) an evaporator, having a wall with an internal surface and an external surface and comprising an evaporation zone and a withdrawal zone of the heavy impurity flow,and ii) a heavy impurity stream discharge section located downstream of the heavy impurity stream withdrawal zone of the evaporator, the evaporator being operated at a pressure less than or equal to 0.0010 MPa, and in which: the evaporation zone of the evaporator is operated at a temperature of the external surface of the wall of the evaporator at the level of the evaporation zone less than or equal to 300°C and greater than or equal to 120°C, and the heavy impurity stream withdrawal zone and the heavy impurity stream discharge section being operated at a heating temperature greater than 250°C and less than or equal to 300°C.,

2. Method according to claim 1, in which the heavy impurity flow withdrawal zone and the heavy impurity flow discharge section are operated at a heating temperature of between 255 and 300°C, preferably between 260 and 290°C and more preferably between 270 and 285°C.

3. Method according to claim 1 or 2, wherein the evaporator of step b) is operated at a pressure less than or equal to 0.0005 MPa, and preferably greater than or equal to 0.0000001 MPa, in particular greater than or equal to 0.0000005 MPa.

4. Method according to one of claims 1 to 3, in which the evaporator of step b) is implemented with a liquid residence time less than or equal to 20 min, preferably less than or equal to 10 min, preferably less than or equal to 5 min, more preferably less than or equal to 3 min.

5. Method according to one of claims 1 to 4, wherein said evaporation zone of the evaporator is operated at a temperature of the external surface of the wall of the evaporator at the evaporation zone less than or equal to 250°C, preferably less than or equal to 245°C, and preferably at a temperature greater than or equal to 150°C, and preferably at a pressure less than or equal to 0.00015 MPa, preferably less than or equal to 0.00010 MPa, preferably less than or equal to 0.00008 MPa, very preferably less than or equal to 0.00005 MPa.

6. Method according to one of claims 1 to 4, wherein said evaporation zone is operated at a temperature of the external surface of the wall of the evaporator at the level of the evaporation zone greater than 250°C, preferably greater than or equal to 255°C, preferentially greater than or equal to 260°C, preferably greater than or equal to 270°C, preferentially at a pressure greater than or equal to 0.00001 MPa, preferably greater than or equal to 0.00010 MPa, preferably greater than or equal to 0.00012 MPa.

7. Method according to one of the preceding claims, comprising a step c) of treatment of the heavy impurity stream comprising i) the recycling of at least a fraction of the heavy impurity stream to the depolymerization step a), by means of a transfer section, and / or ii) the purging of at least a fraction of the heavy impurity stream, by means of a purge section, in which the transfer section and the purge section are implemented at a temperature preferably between 250 and 300°C, preferably between 250 and 270°C.

8. A method according to claim 7, wherein step c) further comprises separating a first fraction of the heavy impurity stream and a second fraction of the heavy impurity stream and recycling said first fraction of the heavy impurity stream to depolymerization step a) and purging said second fraction of the heavy impurity stream, said separation being carried out at a temperature preferably between 250 and 300°C, preferably between 250 and 270°C.

9. Method according to one of the preceding claims, in which step a) of depolymerization comprises a phase of conditioning the plastic filler, located upstream of the reaction phase, the conditioning phase preferably comprising a heating phase to melt at least partly said plastic filler and / or a pre-mixing phase to mix said plastic filler, optionally at least partly melted, with at least part of the diol.

10. Method according to one of the preceding claims, comprising an intermediate step a') of pre-purification of the reaction effluent from step a), located upstream of step b) of evaporation, the pre-purification step a') comprising in particular: filtration; precipitation of impurities; ionic treatment by contact with at least one ion exchange resin; adsorption by contact with at least one adsorbent such as an activated carbon, an alumina or a clay; crystallization and / or precipitation of the BHET; and / or separation of the diol in particular by gas-liquid separation.

11. Method according to one of the preceding claims, further comprising at least one step of final purification of the BHET-rich stream, in particular by contact with a solid, for example by contact with at least one adsorbent; and / or by solidification of the BHET, in particular by crystallization and / or precipitation of the BHET.