Method for producing a terephthalate polyester from a monomeric mixture comprising a diester

Abstract

The aim of the invention is a method for producing a terephthalate polyester, comprising a step a) of preparing an esterification charge comprising at least one mixing section fed with at least one terephthalic acid charge and a diester monomer charge, so that the ratio of the total number of moles of diol units introduced into said mixing section to the total number of moles of terephthalate units introduced into said mixing section is between 1.0 and 2.0, said mixing section being operated at a temperature between 25 and 250°C and at a pressure that is greater than or equal to 0.1 MPa; a step b) of esterification for producing at least one reaction effluent and one aqueous effluent; a step c) of polycondensation for obtaining at least said terephthalate polyester and an effluent comprising at least one diol monomer; and a step d) of treating diols in order to obtain a purified diol stream.

Description

[0001] Process for producing polyester terephthalate from a mixture

[0002] monomeric comprising a diester

[0003] technical field

[0004] The invention relates to a process for producing a polyester, in particular a polyester terephthalate such as polyethylene terephthalate (PET), from a mixture comprising at least terephthalic acid and a diester of terephthalic acid and a diol. Said diester is preferably a diester obtained from a polyester material recycling process, that is to say, a diester obtained from a depolymerization process of a polyester material to be recycled.

[0005] Previous technique

[0006] The chemical recycling of polyester, particularly polyethylene terephthalate (PET), has been the subject of much work aimed at breaking down polyester recovered as waste into monomers that can again be used as a filler in a polymerization process.

[0007] Many polyesters are sourced from material collection and sorting systems. In particular, polyester, especially PET, can come from the collection of bottles, trays, films, resins, and / or fibers composed of polyester (such as textile fibers or tire fibers). Polyester from collection and sorting streams is called recyclable polyester.

[0008] Recyclable PET can be classified into four main categories:

[0009] - Clear PET, consisting mainly of colorless transparent PET (generally at least 60% by weight) and azure colored transparent PET, which does not contain pigments and can be used in mechanical recycling processes,

[0010] - dark PET, or colored PET (green, red, etc.), which can generally contain up to 0.1% by weight of dyes or pigments but remains transparent, or translucent;

[0011] - 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, and in the composition of cosmetic, plant protection product, or dye bottles;

[0012] - Multilayer PET, which consists of layers of polymers other than PET or a layer of recycled PET sandwiched between layers of virgin PET (i.e., PET that has not undergone recycling), or an aluminum film, for example. Multilayer PET is used after thermoforming to make packaging such as trays. The collection systems that feed the recycling streams are structured differently depending on the country. They are evolving to maximize the amount of plastic recovered from waste, based on the nature and volume of the waste streams and the sorting technologies used.The recycling process for these streams generally consists of a first stage of conditioning in the form of flakes during which raw packaging bales are washed, purified and sorted, shredded and then purified and sorted again to produce a stream of flakes generally containing less than 1% by mass of "macroscopic" impurities (glass, metals, other plastics, wood, paperboard, mineral elements), preferably less than 0.2% of "macroscopic" impurities and even more preferably less than 0.05%.

[0013] The clear PET flakes can then undergo an extrusion-filtration process to produce extrudates that can be reused by blending them with virgin PET to make new products (bottles, fibers, films). A solid-state vacuum polymerization (SSP) step is required for food-grade applications. This type of recycling is called mechanical recycling.

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

[0015] The presence of opaque PET containing significant amounts of pigments in recycled PET poses problems for recyclers because opaque PET alters 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 increasing uses of opaque PET, the levels of opaque PET in the colored PET stream are currently between 5-20% by weight and are tending to increase further. Within a few years, it will be possible to reach opaque PET levels in the colored PET stream exceeding 20-30% by weight. However, it has been shown that beyond 10-15% opaque PET in colored PET streams, the mechanical properties of the recycled PET are altered."Impact of the development of opaque white 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 colored PET in the sector.

[0016] Dyes are natural or synthetic substances, soluble in materials such as polyester, used to color the materials into which they are incorporated. Dyes commonly used are of various types and often contain O and N heteroatoms, and conjugated unsaturates, such as quinone, methine, and azo groups, or molecules like pyrazolone and quinophthalone. Pigments are finely divided substances, insoluble in materials such as polyester, used to color and / or opacify the materials into which they are incorporated. The main pigments used to color and / or opacify polyesters, particularly PET, are metal oxides such as TiO2, CoAl2O4, and Fe2O3, as well as silicates, polysulfides, and carbon black. Pigments are particles generally between 0.1 and 10 µm in size, with the majority being between 0.4 and 0.8 µm.The complete removal of these pigments by filtration, necessary to consider recycling opaque PET, is technically difficult because they are extremely clogging.

[0017] Recycling colored and opaque PET is therefore extremely delicate.

[0018] The improvement of the PET polymerization process has also been the subject of much research. Part of this research concerns improving the preparation phase of the monomer mixture, whether or not the monomers come from the recycling stream.

[0019] In particular, patent application MX 2007 / 004429 discloses the production of a high-quality polyester, comprising a process for the atmospheric-pressure glycolysis depolymerization of PET flakes in the presence of ethylene glycol in a bis(2-hydroxyethyl) terephthalate (BHET) base. The intermediate product obtained from the depolymerization step is filtered through a sintering system to retain particles of at least 25 µm before being introduced into the polymerization reactor to obtain a high-quality polyester. However, document MX 2007 / 004429 does not disclose the addition of terephthalic acid and its intermediate to the polymerization reactor.

[0020] US patent application 2006 / 0074136 describes a glycolytic depolymerization process for colored PET, specifically PET recovered from green PET bottles. The BHET stream obtained from the glycolysis step is purified over activated carbon to separate certain colorants, such as blue dyes, and then residual colorants, such as yellow dyes, are extracted with an alcohol or water. The BHET that crystallizes in the extraction solvent is then separated for use in a PET polymerization process. In US patent application 2015 / 0105532, post-consumer PET, comprising a mixture of different colored PETs such as clear, blue, green, and / or amber PET, is depolymerized by glycolysis in the presence of an amine catalyst and alcohol.The resulting diester monomer can be purified by filtration, ion exchange, and / or passage through activated carbon before being crystallized and recovered by filtration for polymerization to reform a polyester. However, these two patent applications do not detail the steps of the (re)polymerization process.

[0021] Patent application WO 2017 / 006217 discloses a process for preparing a modified polyethylene terephthalate glycol (r-PETG) comprising a PET depolymerization step in the presence of a mixture of monoethylene glycol (MEG) and neopentyl glycol, followed directly by a polymerization step of the reaction effluent. Patent application FR 3053691 describes a process for depolymerizing a polyester filler, including, in particular, 0.1 to 10 wt% pigments, by glycolysis in the presence of ethylene glycol. A bis-(2-hydroxyethyl) terephthalate (BHET) monomer effluent, obtained after specific separation and purification steps, can feed a polymerization step to produce PET, without any further conditions being specified.

[0022] Patent JP3715812 describes the production of refined BHET from PET, the resulting BHET being usable as a raw material in a plastic product manufacturing process. Concurrently, patent EP 1 120 394 discloses the potential use of high-purity bis-(2-hydroxyethyl) terephthalate as a raw material for the re-production of a high-quality polyester. To this end, patent EP 1 120 394 specifically describes a polyester depolymerization process without detailing the downstream polymerization steps.

[0023] US patent 4,001,187 discloses a process for producing high-quality PET, including a step of continuously feeding ethylene glycol and terephthalic acid into the esterification medium comprising bis(2-hydroxyethyl)terephthalate, the amounts of acid and diol introduced being a function of a parameter related to the viscosity of the mixture (the "slurry"). US patent 6,815,525 discloses a process for producing PET, including a step of continuously feeding recycled ethylene glycol into the reaction medium. US patent 4,334,090 details a process for preparing the slurry, the viscosity of which is improved by incorporating pre-treated terephthalic acid crystals.None of these documents proposes a polyester production process with an improvement in the mixture of terephthalic acid and diol monomers, allowing the solids content of said mixture to decrease and thus facilitate subsequent operations, particularly transport, and reduce the consumption of raw materials, especially diol.

[0024] Summary of the invention

[0025] The invention relates to a process for producing a polyester terephthalate, comprising: a) a step of preparing an esterification feed comprising at least one mixing section fed with at least one terephthalic acid feed and one diester monomer feed, the amounts of at least said terephthalic acid feed and said diester monomer feed introduced into said mixing section in said mixture being adjusted so that the ratio of the total number of moles of diol units of formula - [C (n+i) H ( 2 n+ 2) 02]-, n being an integer greater than or equal to 1, introduced into said mixing section, relative to the total number of moles of terephthalate motifs of formula - [CO-(C6H4)-CO]-, introduced into said mixing section, is between 1.0 and 2.0, said mixing section being operated at a temperature between 25 and 250°C and at a pressure greater than or equal to 0.1 MPa,

[0026] b) an esterification step of said esterification feed from step a), to produce at least one reaction effluent and one aqueous effluent, said esterification step comprising at least one reaction section operated at a temperature between 150 and 400°C, at a pressure between 0.05 and 1 MPa, and with a residence time between 1 and 10 h, and at least one separation section,

[0027] (c) a polycondensation step of said reaction effluent obtained in step (b) to obtain at least said polyester terephthalate and a diol effluent, said step comprising at least one reaction section including at least one reactor in which the polycondensation is carried out and being operated at a temperature between 200 and 400°C, at a pressure between 0.0001 and 0.1 MPa, with a residence time between 0.1 and 5 h, said reaction section also comprising at least one withdrawal of a diol effluent,

[0028] d) a diol treatment step, comprising a recovery section fed at least by all or part of the diol effluent from step c), to obtain a diol effluent for treatment, and a purification section for said diol effluent to obtain a purified diol stream. Preferably, the present invention relates to a process for producing polyester terephthalate from at least one polyester feedstock to be recycled, consisting of steps a), b), c), and d), described above.

[0029] One advantage of the invention lies in the optimized preparation of the monomeric filler. Indeed, the present invention allows the substitution, at least in part, of the monomeric fillers, i.e. terephthalic acid and diol, of the conventional processes for the production of terephthalic polyesters, by a terephthalic diester compound.

[0030] Thus, the present invention has the advantage of preparing a monomeric feedstock with a reduced solids content compared to monomeric feedstock mixtures used in conventional polyester terephthalate production processes in which no diester monomers are incorporated. The solids content is a volumetric solids content defined, according to the invention, as the ratio of the solids volume to the total volume of the two-phase monomeric feedstock (i.e., the esterification feedstock according to the invention). The present invention therefore facilitates the preparation and transport of the two-phase mixture, particularly during the polyester production process.

[0031] Another advantage of the present invention is the reduction in the amount of diol monomer introduced into the polyester production process compared to conventional polyester production processes, while maintaining the operability of the preparation step, i.e., without degrading the preparation conditions or the quality of the monomer filler mixture. Since the amount of excess diol introduced into the process is reduced, the amount of diol recovered, processed, and recycled at the end of polymerization is also reduced, thereby leading not only to a reduction in diol raw material consumption but also to a reduction in the process's energy consumption.

[0032] Furthermore, when the diester monomer incorporated into the mixture is advantageously a liquid diester intermediate obtained from a polyester depolymerization process, said intermediate meeting the specifications of the polymerization process is incorporated directly into the mixture of step a), without an additional purification and / or intermediate conditioning step (for example a solidification step of the diester obtained by polyester depolymerization), thus limiting, among other things, significant energy consumption and thus meeting an ecological expectation of society.

[0033] Description of the implementation methods

[0034] The invention relates to a process for producing a polyester terephthalate comprising in particular a step of preparing a particular polymerization charge.

[0035] According to the invention, the terms "polyester" and "polyester terephthalate" are interchangeable and refer to a polyalkylene terephthalate. Typically, a polyalkylene terephthalate is the result of the polycondensation of a diol (or glycol) monomer with a terephthalic acid (or dimethyl terephthalate) monomer. The polyester terephthalate according to the invention is, in particular, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), or any other polymer whose main chain repeating unit contains an ester function and an aromatic ring derived from terephthalic acid (or one of its esters, in particular dimethyl terephthalate). According to the invention, the preferred polyester terephthalate is polyethylene terephthalate or poly(ethylene terephthalate), also simply called PET, whose repeating unit has the following formula:

[0036] Classically, PET is obtained by polycondensation of terephthalic acid (PT A), or dimethyl terephthalate (DMT), with ethylene glycol.

[0037] According to the invention, the term "recyclable" refers to any material, particularly one containing polyester, originating from plastic waste collection and sorting channels. In contrast, virgin polyester is solely derived from the polymerization of monomer fillers comprising at least one dicarboxylic acid (e.g., terephthalic acid, PTA) or a dicarboxylate ester (e.g., dimethyl terephthalate, DMT) and at least one compound from the diol or glycol family (e.g., ethylene glycol).

[0038] According to the invention, the term "diester monomer" refers to a terephthalate ester compound with the chemical formula H0C (m+1) H (2m+2) -CO2-(C6H4)-CO2-C (n+i) H (2n+2)OH, in which: -(C6H4)- represents an aromatic ring; n and m are integers, identical or different, preferably identical (i.e., n = m), and greater than or equal to 1, preferably between 1 and 5, preferably between 1 and 3. A diester monomer molecule corresponds to a compound that would result from the esterification of a terephthalic acid molecule HOOC-(C6H4)-COOH (where -(-(C6H4)- represents an aromatic ring) with two molecules of at least one diol (or glycol), more particularly with a molecule of a diol with the chemical formula HO-C (n+i) H ( n+ ) -OH and a molecule of a diol with the chemical formula HO-C (m+1) H ( 2 m+ 2 ) -OH. The preferred diester monomer is bis(2-hydroxyethyl) terephthalate (BHET).

[0039] According to the invention, the "diester monomer filler" comprises a diester monomer as defined above. The "diester monomer filler" according to the invention may also comprise at least one diol (or glycol), preferably corresponding to the diol moiety(ies) contained in said diester monomer of said filler. Advantageously, said diester monomer filler preferably comprises at least 10% by weight of diester monomer, preferably at least 20% by weight.

[0040] The term "dye" refers to a substance soluble in polyester material and used to color it. Dyes can be of natural or synthetic origin.

[0041] The term "pigment," and more specifically coloring and / or opacifying pigment, refers to a finely divided substance insoluble in polyester. Pigments are in the form of particles generally ranging in size from 0.1 to 10 µm, and predominantly between 0.4 and 0.8 micrometers. They are often mineral in nature. Typically, pigments, particularly opacifying pigments, are metal oxides such as TiO2, CoAl2O4, and Fe2O3, as well as silicates, polysulfides, and carbon black.

[0042] According to the present invention, the expression "between ... and ..." means that the limit values ​​of the interval are included within the described range of values. If this were not the case and the limit values ​​were not included within the described range, this clarification will be provided by the present invention.

[0043] Charges

[0044] According to the invention, said process is fed with at least one terephthalic acid feed and one diester monomer feed.

[0045] The terephthalic acid filler is advantageously in powder form, i.e., as solid particles of terephthalic acid. The terephthalic acid particles incorporated into the monomer mixture preferably have an average diameter between 1 and 1000 µm, particularly between 30 and 500 µm, and especially between 80 and 200 µm. The average diameter of the terephthalic acid particles is determined by any particle size analysis method known to those skilled in the art, such as laser diffraction or sieving, preferably by sieving through a column of suitable sieves according to a technique known to those skilled in the art.

[0046] The terephthalic acid used in the terephthalic acid filler can advantageously be produced by oxidation of para-xylene, by depolymerization of polyesters, or by any other process that yields a terephthalic acid filler with the specifications required by the polymerization processes. The terephthalic acid can be derived from fossil hydrocarbon sources or biomass.

[0047] According to the invention, the diester monomer filler comprises a diester monomer, as defined above, corresponding to a terephthalate diester compound of chemical formula H0C (m+1) H (2m+2) -CO2-(C6H4)-CO2-C (n+i) H (2n+2)OH, wherein: -(C6H4)- represents an aromatic ring; n and m are integers, identical or different, preferably identical (i.e., n = m), and greater than or equal to 1, preferably between 1 and 5, most preferably between 1 and 3. The diester monomer preferably comprises the repeating units of polyester terephthalate produced by the process according to the invention. Most preferably, the diester monomer feedstock comprises bis(2-hydroxyethyl) terephthalate (BHET) as the diester monomer. The diester monomer feedstock according to the invention may also comprise at least one diol, preferably corresponding to the diol unit(s) contained in said diester monomer of said feedstock. Said diester monomer feedstock preferably comprises at least 10% by weight of diester monomer, preferably at least 20% by weight.

[0048] According to the invention, the diester monomer feedstock can be in liquid or solid form, preferably the diester monomer feedstock is in liquid form.

[0049] In an advantageous embodiment of the invention, said monomer diester feed of step a) comprises at least a fraction, preferably comprises the whole, of a purified diester effluent, obtained from a depolymerization process of a polyester feed to be recycled, in particular obtained from the depolymerization processes of a polyester feed to be recycled of patents JP 3715812 and FR 3053691, and of application WO 01 / 10812.

[0050] Advantageously, said purified biodiesel effluent is obtained by a depolymerization process of a recyclable polyester feedstock comprising at least the following steps:

[0051] (i) a depolymerization step comprising at least one reaction section fed with said polyester feedstock to be recycled and a glycol stream, to obtain a depolymerization reaction effluent,

[0052] ii) a separation-purification step comprising a separation section to obtain glycol effluent and at least one purification section to obtain purified diester effluent, at least a fraction of said purified diester effluent obtained in step ii) is sent to said step a).

[0053] In this embodiment, the polyester filler to be recycled originates from waste collection and sorting channels, particularly for plastic waste. Preferably, the polyester filler to be recycled is a polyethylene terephthalate (PET) filler to be recycled.

[0054] The polyester feedstock to be recycled, which feeds the depolymerization step i), can be in the form of flakes (or semacles), the longest of which is less than 10 cm, preferably between 5 and 25 mm, or in the form of micronized solids, i.e., particles preferably with a size between 10 microns and 1 mm. The polyester feedstock to be recycled preferably comprises less than 2% by weight, preferably less than 1% by weight, of "macro" impurities such as waste glass, metal, plastic other than polyester terephthalate, wood, paperboard, and mineral elements.The polyester feedstock to be recycled may also be in the form of fibers, such as textile fibers, optionally pretreated to remove cotton, polyamide, or any other non-polyester textile fibers, or such as tire fibers, optionally pretreated to remove, in particular, polyamide fibers or rubber or polybutadiene residues. The polyester feedstock to be recycled, which feeds the depolymerization step (i), advantageously contains more than 50% by weight of polyalkylene terephthalate, preferably more than 70% by weight, and preferably more than 90% by weight of polyalkylene terephthalate.

[0055] The polyester filler to be recycled may be obtained from polyester terephthalate waste, preferably PET, clear, colored, opaque, dark, and / or multilayer. It advantageously comprises at least one polyester terephthalate, preferably PET, opaque, dark, or multilayer. Preferably, it comprises at least 10% by weight of opaque polyester terephthalate, preferably opaque PET, and most preferably at least 15% by weight of opaque polyester terephthalate, preferably PET. The polyester filler to be recycled may contain up to 10% by weight of pigments, in particular between 0.1% and 10% by weight of pigments, in particular between 0.1% and 5% by weight of pigments, and / or up to 1% by weight of dyes, in particular between 0.05% and 1% by weight of dyes, in particular between 0.05% and 0.2% by weight of dyes.

[0056] The polyester filler to be recycled may also contain elements used as polymerization catalysts and / or as stabilizing agents in polyester production processes, such as antimony, titanium, and tin.

[0057] Advantageously, depolymerization step i) carries out, in the reaction section, a glycolysis reaction of the polyalkylene terephthalate of said polyester feedstock to be recycled, in the presence of said glycol stream, in one or more reactors. Said glycol stream preferably comprises a diol monomer corresponding to the diol unit in the composition of the repeating unit of the polyester terephthalate produced by the production process according to the invention. Preferably, said glycol stream is an ethylene glycol stream. Advantageously, said glycol stream that feeds depolymerization step i) preferably comprises at least a fraction of said purified diol stream obtained at the end of step d) of the polyester terephthalate production process according to the invention.The said reaction section of step i) of depolymerization is carried out at a temperature between 150 and 400°C, preferably between 180 and 300°C, preferably between 200°C and 280°C, at an operating pressure of at least 0.1 MPa, preferably at least 0.4 MPa, and with a residence time per reactor of between 0.05 and 10 h, preferably between 0.1 and 6 h, preferably between 0.5 and 4 h, said residence time per reactor being defined as the ratio of the liquid volume of the reactor by the volumetric flow rate of the stream that feeds said reactor. The glycol stream feeds the reaction section in such a way that the amount of the glycol compound contained in said glycol stream is adjusted from 1 to 20 moles of diol of said glycol stream per mole of repeating elementary motif of polyester contained in said polyester feed to be recycled, preferably from 3 to 10 moles of diol of said glycol stream per mole of diester in said polyester feed to be recycled.

[0058] The depolymerization reaction can be carried out with or without the addition of a catalyst. When the depolymerization reaction is carried out after the addition of a catalyst, the catalyst can be homogeneous or heterogeneous and chosen from among the esterification catalysts known to those skilled in the art, such as complexes of oxides and salts of antimony, tin, and titanium; alkoxides of metals from groups (I) and (IV) of the periodic table of elements; organic peroxides; and acid-base metal oxides. Preferably, the depolymerization reaction is carried out without the addition of a catalyst.

[0059] The depolymerization reaction can also advantageously be carried out in the presence of a solid adsorbent agent in powder or shaped form, the function of which is to capture at least part of the impurities, in particular colored impurities, thus relieving the purification phase of step ii). Said solid adsorbent agent is in particular an activated carbon.

[0060] The depolymerization reaction effluent obtained at the end of depolymerization step i) comprises a mixture of diester monomers and oligomers comprising between 1 and 5, preferably between 1 and 3, elementary units of the formula -[0-CO-(C6H4)-CO-0-C (n+i) H ( n+ 2 )]-, with n an integer between 1 and 5, preferably between 1 and 5, of diol compounds, impurities possibly present in said polyester feedstock, and compounds possibly produced as a result of secondary reactions such as etherification or degradation reactions. The diol compounds are advantageously the diol monomers and co-monomers forming part of the polyester feedstock to be recycled and released at the end of the depolymerization reaction, and those unreacted from the glycol stream feeding step i) of depolymerization. Said depolymerization reaction effluent may also contain unconverted polyesters and other polymers. The depolymerization reaction effluent obtained at the end of step i) of depolymerization feeds step ii) of separation-purification, which includes at least one glycol effluent separation section and at least one purification section to obtain a purified diester effluent.

[0061] The said separation and purification sections may be in one order or another relative to each other. The said separation and purification sections may also be interconnected when step ii) includes a section for purifying the depolymerization reaction effluent to obtain a purified depolymerization reaction effluent, a section for separating said purified depolymerization reaction effluent to obtain a glycol effluent and a diester effluent, and a section for purifying said diester effluent to obtain a purified diester effluent.

[0062] In a preferred embodiment, step ii) includes a section for separating said depolymerization reaction effluent to obtain a glycol effluent, advantageously comprising the diol from the glycol stream of step i) that has not reacted, and a diester effluent, and a section for purifying said diester effluent to obtain a purified diester effluent.

[0063] The glycol effluent obtained from the separation section of step ii) advantageously comprises more than 50% by weight, preferably more than 70% by weight, and preferably more than 90% by weight of diols. The separation section advantageously allows for the recovery of unreacted diol from the glycol stream of step i). The diester effluent obtained from the separation section is preferably in liquid form and advantageously comprises more than 10% by weight, preferably more than 25% by weight, and preferably more than 50% by weight of diester monomers and oligomers.

[0064] Advantageously, the separation section comprises one or more separation devices to allow the recovery of an effluent enriched in diols (the glycol effluent), and optionally, an effluent enriched in light impurities and an effluent enriched in heavy impurities. Any physical, chemical, or physicochemical separation method known to those skilled in the art may be used, such as gas-liquid separation, distillation, evaporation, solvent extraction coupled or not with a chemical reaction, crystallization followed by filtration or centrifugation, or a combination of such separation methods.Preferably, said separation section comprises a succession of gas-liquid separations, preferably 1 to 5 gas-liquid separations, operated at a temperature between 100 and 250°C, preferably between 110 and 220°C, preferably between 120 and 210°C, and at a pressure between 0.00001 and 0.2 MPa, preferably between 0.00004 and 0.15 MPa, preferably between 0.00004 and 0.1 MPa.

[0065] Preferably, all or part of said glycol effluent recovered at the end of step ii) is advantageously sent to step d) of treatment of the process according to the invention.

[0066] All or part of the glycol effluent recovered from step ii) may be pre-purified in a diol pre-purification section included in step ii) to remove some of the impurities carried along with the glycol effluent, such as dyes, pigments, or other solid particles. The pre-purification section fed with all or part of the glycol effluent may include, but is not limited to, solid adsorption (e.g., on activated carbon) and a filtration system. At least a fraction of the pre-purified glycol effluent may be directly recycled to the depolymerization step i). Separation of the various diols that may be present in the glycol effluent may be carried out in the pre-purification section.

[0067] The diester effluent purification phase consists of separating at least one purified diester monomer effluent from all or part of the following compounds from step i of depolymerization: diester oligomers, possibly unconverted polyester, impurities possibly present in the polyester feed to be recycled such as other polymers, pigments, dyes, polymerization catalysts or any other inorganic compound composing said polyester feed to be recycled or formed during step i) of depolymerization, while minimizing the loss of diester monomer.

[0068] The purification of said diester effluent is advantageously carried out by any physical, chemical, or physicochemical method known to those skilled in the art, enabling the recovery of a purified diester monomer effluent with a diester monomer yield greater than or equal to 50% by weight, preferably greater than or equal to 70% by weight, and preferably greater than or equal to 80% by weight. Yield is understood to mean the quantity of diester monomer in said purified diester monomer stream relative to the total quantity of diester monomer introduced into the purification section. Preferably, said purified diester monomer effluent is free from dyes or inorganic impurities such as pigments, depolymerization catalysts, and ions. Preferably, the purified diester monomer comprises diester monomer molecules and optionally oligomers of said diester with a degree of polymerization between 2 and 5.

[0069] The purification of said diester effluent (and / or said depolymerization reaction effluent) advantageously employs one or more purification operations, such as filtration, evaporation, distillation, membrane separation, precipitation or crystallization, adsorption onto a collection mass, treatment with an ion-exchange resin, or solvent extraction. For example, in patent EP 0865464, the purification of the diester effluent comprises a series of operations involving dissolution in a hot solvent followed by precipitation and filtration to separate impurities larger than 50 µm, and the separation of diester monomers and oligomers in a thin-film evaporator. Optionally, the purification section of step ii) may comprise at least two purification operations (or two phases):

[0070] - a first purification phase which allows the separation of impurities insoluble in said diester effluent (and / or said depolymerization reaction effluent), or which have become insoluble after cooling or partial evaporation of said effluent or addition of a third substance such as for example a flocculating agent or solvent promoting precipitation;

[0071] - a second purification phase which allows the separation of impurities soluble in said diester effluent (and / or said depolymerization reaction effluent) or which have become soluble after heating or addition of a solvent.

[0072] Preferably, the purification of said diester effluent (and / or said depolymerization reaction effluent) employs a separation section comprising a falling film or scraped film evaporation system, or a short-path falling film or scraped film distillation, or a succession of several evaporations and / or short-path falling film or scraped film distillations, operated at a temperature of 250°C or lower, preferably 230°C or lower, preferably 200°C or lower, and at a pressure of 0.001 MPa or lower, preferably 0.0001 MPa or lower, preferably 0.00005 MPa or lower, followed by a decolorization section operated at a temperature between 100 and 250°C, preferably between 110 and 200°C, and preferably between 120 and 180°C, and at a pressure between 0.1 and 1.0 MPa, preferably between 0.2 and 0.8 MPa, and preferably between 0.3 and 0.5 MPa, in the presence of an adsorbent,preferably activated charcoal.

[0073] Advantageously, the purified diester effluent obtained at the end of step ii) comprises at least

[0074] 10% by weight of diester monomer, preferably at least 20% by weight of diester monomer.

[0075] 11 preferably contains less than 1% by weight, preferably less than 0.1% by weight, of pigments introduced into the process with the polyester feed to be recycled and less than 10% by weight, preferably less than 1% by weight, of dyes introduced into the process with the polyester feed to be recycled.

[0076] This step (ii) may also produce an ester impurity effluent composed of oligomers and optionally of polymers not converted in the depolymerization step (i). This ester impurity effluent may advantageously be wholly or partly recycled back to step (i) or purged and sent to an incineration system. If so, the fraction of this ester impurity effluent recycled back to step (i) may undergo at least one separation operation, preferably a filtration operation, to reduce the amount of pigments and / or other solid impurities that may be present in the ester impurity effluent.Optionally, all or part of at least a fraction of the glycol effluent from step ii) or step d) of the process according to the invention may advantageously be mixed with said fraction of the recycled ester impurity effluent so as to decrease the viscosity of said fraction of said ester impurity effluent and facilitate its transport to step i) and optionally its treatment in an optional filtration step.

[0077] Preferably, the purified diester effluent is recovered at the end of step ii) in liquid form or in solid form, preferably in liquid form.

[0078] Advantageously, at least a fraction of said purified diester effluent obtained in step ii) is sent to step a) of the process for producing a polyester terephthalate according to the invention.

[0079] Step a) preparation of the esterification charge

[0080] According to the invention, the process for producing a polyester terephthalate includes a step a) of preparing an esterification feedstock. Said step a) includes at least one mixing section fed with at least one terephthalic acid feedstock, and a diester monomer feedstock.

[0081] The esterification feedstock, according to the invention, which is obtained at the end of step a), is a homogeneous two-phase mixture, comprising at least terephthalic acid, a diester monomer and optionally a diol (or glycol) of chemical formula HO-C (n+i) H (2n+ 2 )- OH, where n is an integer greater than or equal to 1, preferably between 1 and 5, and more preferably between 1 and 3. "Biphasic" advantageously means a suspension of a solid phase in a liquid or paste phase. "Homogeneous" means that the solid phase, suspended in the liquid or paste phase, is distributed homogeneously throughout the liquid or paste phase. More particularly, the esterification charge according to the invention is a mixture of solid terephthalic acid particles, typically with a diameter between 1 and 1000 µm, in particular between 80 and 300 µm, distributed homogeneously in a liquid or paste phase comprising the diol monomers and the diester monomers.

[0082] Advantageously, the quantities of the monomer fillers, that is, the quantities of at least the terephthalic acid filler and the diester monomer filler, introduced into said section of the mixture, are adjusted so that the ratio of the total number of moles of diol motifs of formula -[C (n+i) H ( 2 n+ 2 )

[02] -, n being an integer greater than or equal to 1, introduced into said mixing section, relative to the total number of moles of terephthalate motifs of formula -[CO-(C6H4)-CO]-, introduced into said mixing section, is between 1.0 and 2.0, preferably between 1.0 and 1.5, and preferably between 1.0 and 1.3. Preferably, the mixing section of step a) is fed with diester monomer feed in liquid form. When the diester monomer feed intended to feed the mixing section is in solid form, step a) of the process of the invention may optionally include a conditioning section, located upstream of the mixing section, to obtain a liquid diester monomer feed.The said conditioning section is at least supplied with the monomer diester feedstock in solid form and operated at a temperature above the liquefaction temperature of said monomer diester feedstock, preferably between 25 and 250°C, and at a pressure greater than or equal to 0.1 MPa. The pressure of said mixing section is very advantageously less than or equal to 5 MPa.

[0083] In a preferred embodiment of the invention, the mixing section of step a) of the process according to the invention is further supplied with a diol monomer feedstock, preferably comprising a diol monomer corresponding to the diol unit(s) contained in the diester monomer of said diester monomer feedstock. It predominantly comprises the diol monomer that forms part of the repeating unit of the polyester terephthalate produced by the process according to the invention. Preferably, the diol monomer feedstock comprises at least 70 mol%, preferably at least 90 mol%, and most preferably 99.5 mol%, of a diol monomer that forms part of the repeating unit of the polyester terephthalate referred to. Preferably, the diol monomer feedstock comprises ethylene glycol. Said diol monomer feedstock is preferably in liquid form.

[0084] Preferably, said diol monomer feed may be, at least in part, a fraction of the purified diol stream obtained in step d) of the process according to the invention. Said diol monomer feed may optionally include an external diol source.

[0085] When a diol monomer filler is incorporated into the mixing section of step a), the amount of said diol filler introduced into the mixing section of step a) is adjusted so that the ratio of the number of diol motifs to the number of terephthalate motifs in the mixture of step a), as defined above, is between 1.0 and 2.0, preferably between 1.0 and 1.5 and preferably between 1.0 and 1.3.

[0086] Advantageously, the amount of diester monomer molecules contained in the diester monomer feed introduced into the mixing section of step a) represents at least 5% by weight relative to the weight of terephthalic acid (PTA), preferably at least 15% by weight.

[0087] A diester monomer molecule in the diester monomer filler comprises two diol units and one terephthalate unit. A terephthalic acid molecule comprises one terephthalate unit. A diol molecule comprises one diol unit. Thus, the incorporation of one mole of diester monomer, for example, one mole of bis(2-hydroxyethyl) terephthalate (BHET), in a mixture with the terephthalic acid and diol monomer fillers, preferably a diol corresponding to the diol unit contained in said diester monomer, such as ethylene glycol, allows for the substitution of a portion of said terephthalic acid filler and all or part of said diol filler.

[0088] Advantageously, said mixing section in step a) of the process according to the invention is operated at a temperature between 25 and 250°C, preferably between 60 and 200°C, most preferably between 100 and 150°C, and at a pressure greater than or equal to 0.1 MPa. The pressure of said mixing section is very advantageously less than or equal to 5 MPa. One or more polymerization catalysts may, moreover, be incorporated into the mixture in step a) of the process according to the invention.

[0089] Other monomeric (or co-monomer) compounds can also be advantageously introduced into the mixture and constitute part of the esterification feedstock. These other monomeric compounds, by way of example, may include dicarboxylic acids such as isophthalic acid and diols such as 1,4-dihydroxymethylcyclohexane and diethylene glycol.

[0090] The process according to the invention, by incorporating a diester monomer, for example BHET monomers, into the esterification feedstock, makes it possible to substitute a portion of the terephthalic acid, which is a compound in the form of a powder of solid particles, in the two-phase mixture of monomers for polyester production. The solids content of this two-phase mixture can therefore be reduced compared to conventional polyester production processes, thus facilitating subsequent industrial operations, particularly its transport. The presence of a diester monomer, especially BHET, can also promote an increase in the esterification rate of terephthalic acid.The substitution of part of the terephthalic acid and all or part of the diol with diester monomers in the process according to the invention also allows, with the same solids content in the two-phase reaction mixture as in conventional polyester production processes, a reduction in the amount of excess ethylene glycol introduced into the mixture. This leads to a reduction in costs, particularly raw material costs, but also a significant reduction in the energy consumption of the polyester production process, due to a greatly reduced quantity of material to be processed and recycled. Step b) Esterification.

[0091] According to the invention, the process for producing a polyester terephthalate includes a step b) of esterifying the esterification feedstock obtained at the end of step a), to produce at least one reaction effluent and one aqueous effluent.

[0092] The reaction effluent advantageously comprises diesters and ester oligomers. Preferably, the diesters in the reaction effluent are of the same nature as the diester monomer incorporated in the mixture of step a). Preferably, the ester oligomers in the reaction effluent advantageously consist of elementary units corresponding to the repeating elementary units of the polyester terephthalate produced by the process according to the invention.

[0093] Advantageously, said esterification step b) includes at least one reaction section and at least one separation section to separate said reaction effluent and said aqueous effluent.

[0094] The reaction carried out in step b) advantageously comprises an esterification reaction consisting of a condensation reaction of at least the hydroxyl groups (-OH) of the diester monomer of the diester monomer feed incorporated into the esterification feed in step a), and of any diol monomers present in the esterification feed, with at least the carboxyl groups (-COOH) of the terephthalic acid of the terephthalic acid feed incorporated into the esterification feed in step a). This esterification reaction produces diester monomer molecules, for example bis(2-hydroxyethyl) terephthalate (BHET), and diester oligomers advantageously comprising 2 to 5 terephthalate units. It also releases water.The reaction implemented in step b) of the process according to the invention also advantageously includes transesterification reactions consisting of the condensation reaction of diester monomer molecules with each other, thereby releasing diol molecules.

[0095] The reaction section is operated at a temperature between 150 and 400°C, preferably between 200 and 300°C, at a pressure between 0.05 and 1 MPa, preferably between 0.1 and 0.3 MPa, and with a residence time between 0.5 and 10 h, preferably between 1 and 5 h. According to the invention, the residence time in the esterification step (b) is defined as the ratio of the reaction volume of a reactor in the reaction section to the volumetric flow rate of the liquid exiting the reactor. The esterification reaction is advantageously carried out in one or more stirred reactors in series or parallel, in one or more tubular reactors in series or parallel, or in a combination of stirred and tubular reactors in series or parallel.

[0096] In the separation section of step b), the water formed during the esterification reaction is separated. Advantageously, the reaction section also includes at least one withdrawal of a water- and diol-rich effluent. The water is separated, in particular, by difference in volatility, for example by distillation, or by adsorption from the effluent withdrawn from the reaction medium containing at least some of the diol and released water present in the reaction medium.

[0097] Advantageously, a polymerization catalyst known to those skilled in the art, possibly mixed with a diol flux, feeds a finishing section of esterification step b). Polymerization catalysts include, but are not limited to, catalysts based on antimony, titanium, germanium or aluminum, zinc acetate, calcium or manganese.

[0098] The incorporation of the diester monomer feedstock into the monomer feedstocks of the polymerization process according to the invention makes it possible to substitute at least part of the terephthalic acid feedstock and all or part of the diol feedstock, thereby reducing the amount of water formed and consequently the effluent withdrawn from the reaction medium to be treated. Energy consumption is thus advantageously reduced.

[0099] Step c) of polycondensation

[0100] According to the invention, the process for producing a polyester terephthalate comprises a step c) of polycondensation of the reaction effluent obtained in step b), to obtain at least said polyester terephthalate and a diol effluent. Said diol effluent comprises at least one diol monomer advantageously corresponding to the diol motif, of formula -[C (n+i) H (2n+2)02]-, n being an integer greater than or equal to 1, included at least in the diester of the monomer diester feed which feeds the mixing section in step a) of the process according to the invention.

[0101] Step c) of polycondensation consists of carrying out a condensation reaction between the monomers and diester oligomers obtained in step b) of esterification to obtain a polyester with a given degree of polymerization and the desired physicochemical properties (e.g., viscosity index, crystallinity, color, mechanical properties, etc.). This condensation reaction releases diol compounds, possibly water, and co-products, which must be removed.

[0102] Step c) of polycondensation comprises at least one reaction section including at least one reactor in which the polycondensation is carried out and at least one withdrawal of a diol effluent, advantageously comprising at least one monomer corresponding to the diol motif of formula -[C (n+i) H ( 2 n+ 2 ) 02]-, n being an integer greater than or equal to 1, included at least in the diester of the monomer diester feed which feeds the mixing section in step a) of the process according to the invention.

[0103] Advantageously, said reaction section is carried out in one or more reactors, operating in series or in parallel, at a temperature of 200 to 400°C, preferably between 250 and 300°C, at a pressure between 0.0001 and 0.1 MPa, preferably between 0.0004 and 0.01 MPa, with a residence time between 0.1 and 5 h, preferably between 0.5 and 3 h. According to the invention, the residence time in said polycondensation step c) is defined as the ratio of the reaction volume of a reactor in said reaction section to the volumetric flow rate of the liquid exiting said reactor. The condensation reaction in polycondensation step c) can be carried out in two successive reaction steps: a molten-phase condensation step followed by a solid-phase post-condensation step.

[0104] Advantageously, polymerization additives and catalysts can be introduced in step c) of polycondensation. These additives may include, but are not limited to, agents that inhibit secondary etherification reactions, such as amines (n-butylamine, diisopropylamine, or triethylamine), sodium hydroxide, organic hydroxides, or lithium carbonate; stabilizing agents such as phosphites or phosphates; and polyamide compounds to reduce the amount of degradation products like acetaldehyde. Commonly used polymerization catalysts include, for example, catalysts based on antimony, titanium, germanium, or aluminum, zinc acetate, calcium acetate, or manganese acetate.Advantageously, the withdrawal of said diol effluent is carried out using one or more withdrawal systems, advantageously connected to the reactor(s) of the reaction section of said step c), and allows the separation of the diol monomer released during the condensation reaction and optionally water and other co-products possibly released during the condensation reaction. Preferably, the diol effluent, withdrawn from the reactor(s) of step c), is a gaseous effluent which is then advantageously cooled to a temperature between 0 and 100°C and condensed to obtain a liquid effluent, said liquid effluent comprising at least the diol monomer.

[0105] Preferably, at least a fraction of the effluent comprising at least the diol monomer, preferably in liquid form, is sent to step d) of the process according to the invention. Advantageously, said effluent comprising at least the diol monomer, preferably in liquid form, can be wholly or partly recycled directly to step a) of preparing an esterification feedstock.

[0106] In a very particular embodiment, said effluent comprising at least the diol monomer, preferably in liquid form, can be wholly or partly recycled directly to step b) of esterification.

[0107] Step d) of diol treatment

[0108] According to the invention, the process for producing a polyester terephthalate includes a step d) of treating diols, comprising a recovery section fed at least by all or part of the diol effluent, from step c), to obtain a diol effluent to be treated, and a purification section of said diol effluent to be treated to obtain a purified diol stream.

[0109] Advantageously, the recovery section of step d) is fed at least by all or part of the diol effluent obtained in step c), preferably in liquid form. It may also be fed by all or part of the glycol effluent from the separation section of step ii) of the process for depolymerizing a polyester feedstock to be recycled, in the case of the advantageous embodiment of the invention in which the monomer diester feedstock of step a) comprises at least a fraction of the purified diester effluent obtained at the end of the process for depolymerizing a polyester feedstock to be recycled. Optionally, the recovery section of step d) of the process according to the invention may also be fed by an external diol supplement. Advantageously, the recovery section may include one or more filtration operations for the various streams comprising at least the diol monomer.

[0110] A diol effluent to be treated is obtained at the end of the recovery section of step d) of the process according to the invention and is sent to said purification section to obtain a purified diol stream.

[0111] The purification section comprises at least one separation system enabling the implementation of any physical, physicochemical, or chemical separation method known to those skilled in the art, such as gas-liquid separation, distillation, or adsorption. Preferably, the purification of the diol effluent to be treated employs at least one distillation column, preferably a series of distillation columns, operated at a temperature between 50 and 250°C, preferably between 70 and 220°C, and at a pressure between 0.001 and 0.2 MPa, preferably between 0.01 and 0.1 MPa. Preferably, the purification section comprises a separation phase for impurities lighter than the diol monomer in the diol effluent to be treated and a separation phase for impurities heavier than the diol monomer in the diol effluent to be treated, preferably in a series of distillation columns.

[0112] Advantageously, said step (d) may also include a section for removing volatile organic compounds by thermal or catalytic combustion of said compounds to prevent their release into the environment. By way of example, said impurity treatment section may include filtration if solid particles are present and a catalytic or non-catalytic combustion system.

[0113] The process according to the invention thus makes it possible to obtain a polyester terephthalate, advantageously having the desired degree of polymerization and the desired physicochemical properties, from an improved mixture of monomers that limits the consumption of diol monomer and reduces the amount of diol monomer potentially introduced in excess into the monomer mixture (i.e., the esterification charge) that has not been converted. This reduced diol consumption thus limits the amount of diol to be recycled and therefore reduces the energy consumption of the process.

[0114] The process also allows, by substituting an acid monomer and two diol monomers with a diester monomer, to reduce the solids content of the starting monomer mixture for polymerization, thus facilitating subsequent operations, in particular the transport of this two-phase mixture.

[0115] The following examples illustrate the invention without limiting its scope.

[0116] Examples

[0117] EXAMPLE 1 - Comparison

[0118] 5.5 t / h of terephthalic acid (PTA) are introduced into a mixing flask equipped with mechanical stirring and mixed at 110°C with 2.5 t / h of a monoethylene glycol (MEG) stream comprising 2.13 t / h of MEG from a storage tank and 0.37 t / h of recycled MEG from the MEG purification section.

[0119] The quantities of PTA and MEG introduced correspond to a PTA / MEG molar ratio of 1.23. At 110°C, 1% by mass of the initially introduced PTA is solubilized in the MEG, and the volume solids content, defined as the ratio of the volume of solids to the total volume of the paste (solid + liquid), is 60.7% by volume. The resulting mixture forms a viscous paste.

[0120] The resulting mixture is then transferred using a suitable pump to a first esterification reactor operated at 260°C, 0.5 MPa, with a residence time of 1.25 h. 1.4 t / h of a steam effluent comprising 71 wt. water and 29 wt. MEG is drawn off and sent to a reflux column to separate the water formed by the esterification reaction from the MEG. The MEG is then returned to the reactor. A PTA conversion of 85% is achieved in the first reactor.

[0121] The liquid effluent from the first reactor is then sent to a second esterification reactor operated at 260°C and 0.2 MPa with a residence time of 1.25 h. 140 kg / h of a steam effluent comprising 40 wt. water and 60 wt. MEG is drawn from the second reactor and sent to the reflux column. A PTA conversion of 92% is achieved at the outlet of the second reactor.

[0122] The liquid effluent from the second esterification reactor is sent to a third reactor operated at 275°C and 0.033 MPa with a residence time of 0.5 h, which allows for a 95.8% conversion of PTA and the initiation of polycondensation. Antimony trioxide is added as a polymerization catalyst at the inlet of the third reactor at a concentration of 220 ppm wt. A vapor effluent comprising 70 wt% MEG, 16.5 wt% water, 5.5 wt% acetaldehyde, 2.5 wt% diethylene glycol, and 5.5 wt% oligomers is drawn from the third reactor, partially condensed, and then sent to the MEG purification section.

[0123] The liquid effluent from the third reactor is sent to a fourth reactor (polycondensation reactor) operated at 275°C and 0.0066 MPa with a residence time of 0.5 h. A vapor effluent with a composition of 60% wt. of MEG, 25% wt. of water, 6% wt. of acetaldehyde, 3% wt. of diethylene glycol and 6% wt. of oligomers is drawn from the fourth reactor and partially condensed then sent to the MEG purification section.

[0124] The liquid effluent from the fourth reactor is sent to a final reactor (polycondensation reactor) operated at 280°C and 0.000013 MPa with a residence time of 1 h. A vapor effluent with a composition of 57% wt. MEG and 43% wt. water is drawn off and partially condensed then sent to the MEG purification section.

[0125] The MEG purification section comprises a first distillation column with 25 trays, operating at 145°C and 0.02 MPa, to separate diethylene glycol. The bottom of the first distillation column is sent to a second distillation column with 17 trays, operating at 100°C and 0.1 MPa, to separate lighter compounds such as water and acetaldehyde. The MEG recovered from these two distillations has a purity greater than 99.8% and is then recycled to the mixing vessel. 6.25 t / h of PET are produced. The total primary energy consumption for PET production is 5.8 MMkcal / h.

[0126] EXAMPLE 2 - According to the invention

[0127] BHET production by glycolysis of recyclable PET flakes

[0128] 4 t / h of flakes from recycled PET feedstock, shredded and washed, consisting of 50% opaque PET and 50% colored PET by weight, are melted in an extruder at 250°C and mixed with 11.4 t / h of ethylene glycol (MEG). The resulting mixture is injected into a stirred reactor, maintained at 220°C and a pressure of 0.4 MPa, for a residence time of 4 h. At the reactor outlet, the reaction effluent comprises 66% MEG by weight, 27.4% BHET by weight, 1.7% diethylene glycol (DEG) by weight, 0.2% water by weight, and 4.7% oligomers, pigments, and other heavy compounds by weight.

[0129] The ethylene glycol present in the reaction effluent is separated by evaporation in a series of 5 flasks at temperatures ranging from 200°C to 124°C and pressures from 0.1 MPa to 0.00025 MPa. Following this evaporation step, a MEG stream of 10.95 t / h composed of 97% wt. MEG, 2.5% wt. DEG, 0.2% wt. water and 0.2% wt. BHET, and a BHET-rich liquid stream of 5.17 t / h, are recovered. The MEG stream is sent to a first distillation column equipped with 25 trays and operated at 0.02 MPa and 145°C to separate DEG and heavy products. It then passes into a second distillation column equipped with 17 trays and operated at 100°C and 0.1 MPa to separate the water and recover a purified MEG effluent, which can then be recycled to the depolymerization reactor mixed with fresh MEG. The BHET-rich liquid stream comprises 87.1% wt. BHET, 0.2% wt. MEG, 0.1% wt. DEG, and 12.6% wt. of oligomers, pigments, and other heavy compounds.

[0130] The BHET-rich liquid stream is then injected into a short-path distillation unit at a temperature of 205°C and a pressure of 0.00002 MPa. A pre-purified BHET liquid effluent with a flow rate of 4.46 t / h is recovered by cooling the vapors in the short-path distillation unit to 115°C. It comprises 99.8 wt% BHET, 0.1 wt% MEG, and 0.1 wt% DEG. A heavy residue comprising 93 wt% oligomers, pigments, and other heavy compounds, and 7 wt% BHET, is also recovered at a flow rate of 0.7 t / h from the short-path distillation unit.

[0131] The pre-purified BHET liquid stream is compressed to 0.5 MPa and then fed into a fixed bed of activated carbon with an adsorption capacity equal to 5% of its mass. Following this step, a decolorized and depigmented BHET liquid stream is recovered and reinjected into a monomer blending step as described in Example 1. The prepared blend then undergoes the various polymerization steps as in the process described in Example 1 to produce PET.

[0132] Table 1 below reports the quantities of PTA, MEG, and solid BHET monomers incorporated, the solid content in the feedstock mixture obtained at 110°C, and the ratio of diol to terephthalate repeat units for the production of 6.25 t / h of PET, taking into account the incorporation of BHET from the depolymerization process described above, for two diol to terephthalate repeat unit ratios (1.23 and 1.1). The results presented are calculated for different quantities of BHET introduced into the mixture, assuming that 1 mol of BHET replaces 1 mol of PTA and 2 mol of MEG in the mixture, and are based on process simulations incorporating solubility and thermodynamic data calibrated to experimental points.

[0133]

[0134] It appears that the solids content is significantly reduced when BHET is introduced into the two-phase monomer mixtures intended for polymerization (esterification fillers) of Examples 2a, 2b, and 2c, compared to the solids content of a two-phase monomer mixture of Example 1: a reduction in the volume solids content from approximately 15% to approximately 48%. More specifically, with an equivalent diol-to-terephthalate ratio, the solids content between the mixture of Example 1 and Examples 2a and 2b decreases from 60.7% vol. to 49.2% vol. (a decrease of approximately 19%) and 31.8% vol. (a decrease of approximately 48%), respectively, depending on the amount of BHET introduced into the monomer mixture.Example 2c, compared to Example 2a, shows that for the same quantity of BHET introduced into the monomer mixture (1.74 t / h), it is possible to prepare a two-phase monomer mixture with a reduced solids content compared to a mixture without BHET (51.5% by volume versus 60.7% by volume in Example 1), while also reducing the amount of ethylene glycol added (only 1.39 t / h in Example 2c compared to 1.65 t / h in Example 2a). Thus, the consumption of ethylene glycol raw material is reduced without compromising the quality of the two-phase mixture, which can then be easily transported to the polymerization operations.

Claims

A Process for producing a terephthalate polyester, comprising:a) a stage for preparing an esterification feedstock comprising at least one mixing section that is fed with at least one terephthalic acid feedstock and one diester monomer feedstock comprising bis(2-hydroxyethyl) terephthalate BHET and being in the liquid form, wherein the amounts of at least the said terephthalic acid feedstock and the said diester monomer feedstock, introduced into the said mixing section in the said mixture, are adjusted so that the ratio of the total number of moles of diol units of formula -[C(n+1)H(2n+2)O2]-, n being an integer greater than or equal to 1, introduced into the said mixing section, with respect to the total number of moles of terephthalate units of formula -[CO-(C6H4)-CO]- introduced into the said mixing section, is between 1.0 and 1.3, wherein the said mixing section is operated at a temperature of between 100°C and 150°C and at a pressure of greater than or equal to 0.1 MPa,b) a stage for esterifying the said esterification feedstock resulting from stage a), in order to produce at least one reaction effluent and one aqueous effluent, wherein the said esterification stage comprises at least one reaction section, operated at a temperature between 150°C and 400°C, at a pressure between 0.05 and 1 MPa, and with a residence time between 1 and 10 h, and at least one separation section,c) a stage of polycondensation of the said reaction effluent obtained in stage b) in order to obtain at least the said terephthalate polyester and a diol effluent, the said stage comprising at least one reaction section comprising at least one reactor in which the polycondensation is carried out and which is operated at a temperature between 200°C and 400°C, at a pressure between 0.0001 and 0.1 MPa, with a residence time between 0.1 and 5 h, the said reaction section also comprising at least one withdrawal of a diol effluent,d) a stage for treating the diols, comprising a recovery section that is fed at least with all or part of the diol effluent resulting from stage c), in order to obtain a diol effluent to be treated, and a section for purifying the said diol effluent to be treated, in order to obtain a purified diol stream.The Process for producing according to Claim 1, wherein the said mixing section of the said stage a) is additionally fed with a diol monomer feedstock which comprises at least 70 mol% of a diol monomer participating in the composition of the individual unit of the said terephthalate polyester.The Process for producing according to Claim 1, wherein the said diester monomer feedstock of stage a) comprises at least a fraction of a purified diester effluent obtained at the end of a process for the depolymerization of a polyester feedstock to be recycled.The Process for producing according to Claim 1, wherein the said purified diester effluent is obtained by a process for the depolymerization of a polyester feedstock to be recycled comprising at least the following stages:i) a depolymerization stage comprising at least one reaction section fed with the said polyester feedstock to be recycled and with a glycol stream, in order to obtain a depolymerization reaction effluent,ii) a separation / purification stage comprising a separation section, in order to obtain a glycol effluent, and a purification section, in order to obtain a purified diester effluent, iii) a stage for recycling at least a fraction of the said purified diester effluent obtained in stage ii) to the said stage a).The Process for producing according to Claim 1, in which the said preparation stage comprises a conditioning section, located upstream of the mixing section, fed at least with a diester monomer feedstock in the solid form and operated at a temperature of between 25°C and 250°C and at a pressure of greater than or equal to 0.1 MPa.The Process for producing according to Claim 1, wherein the said terephthalate polyester is polyethylene terephthalate and the said diester monomer is bis(2-hydroxyethyl) terephthalate (BHET).

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