Method for producing a terephthalate polyester from a monomer mixture containing diesters

Abstract

The subject of the present invention is a process for producing terephthalate polyesters, comprising a step a) of preparing an esterification feedstock, comprising at least one mixing section to which at least one terephthalic acid feedstock and one diester monomer feedstock are fed, the ratio of the total number of moles of diol units introduced into said mixing section to the total number of moles of terephthalic acid units introduced into said mixing section being between 1.0 and 2.0, said mixing section being operated at a temperature between 25°C and 250°C and at a pressure of at least 0.1 MPa, an esterification step b) to produce at least one reaction effluent and an aqueous effluent, a polycondensation step c) to obtain an effluent comprising at least said terephthalate polyesters and at least one diol monomer, and a diol treatment step d) to obtain a purified diol stream.

Description

Technical Field

[0001] The present invention relates to a method for producing a polyester, particularly a terephthalate polyester such as polyethylene terephthalate (PET), from a mixture containing at least terephthalic acid and a diester of terephthalic acid and a diol. The diester is preferably a diester derived from a method for recycling polyester materials, i.e., a diester obtained at the end of a method for depolymerizing a polyester material to be recycled.

[0002] The chemical recycling of polyesters, particularly polyethylene terephthalate (PET), has been the subject of numerous investigations. These studies aim to decompose polyesters collected in the form of waste into monomers that can be reused as feedstocks for polymerization methods.

[0003] Numerous polyesters are generated by the cycle of collecting and sorting materials. In particular, polyesters, especially PET, can be derived from the collection of bottles, containers, films, resins, and / or fibers made of polyester (e.g., textile fibers, tire fibers). Polyesters derived from the collection and sorting industry are known as polyesters to be recycled.

[0004] PET to be recycled can be mainly classified into four categories: - Clear PET. Transparent PET that is not colored (generally at least 60% by weight), with a predominance of transparent PET colored in sky blue. It does not contain pigments and can be fed into mechanical recycling methods; - Dark or colored (green, red, etc.) PET. It can generally contain up to 0.1% by weight of dyes or pigments but remains transparent or translucent; -Opaque PET. To make the polymer opaque, it contains a significant amount of pigment. The content typically varies in the range of 0.25% to 5.0% by weight. For example, in the manufacture of food containers such as milk bottles, and increasingly in the compositions of bottles for cosmetics, plant protection agents, or dyes, more and more opaque PET is being used; -Multi-layer PET. It includes layers of polymers other than PET or layers of recycled PET between layers of virgin PET (i.e., PET that has not been recycled), or includes, for example, a film of aluminum. Multi-layer PET is used after thermoforming for manufacturing packages such as containers.

[0005] The collection industries enabling supply to the recycling industry are structured differently by country. The collection industries are evolving to maximize the amount of plastic recovered from waste in terms of its value, depending on the nature and flow volume of the waste and its sorting technology. The industry that recycles the waste stream generally consists of a first stage of conditioning in the form of flakes. In this stage, the bales of untreated packages are washed, purified, sorted, shredded, and then purified and sorted again. This results in a flake stream containing generally less than 1% by weight of "visible" impurities (glass, metal, other plastics, wood, paper, cardboard, inorganic elements), preferentially less than 0.2%, and even more preferentially less than 0.05% of "visible" impurities.

[0006] The clear PET flakes can then be subjected to an extrusion-filtration stage. This stage makes it possible to produce an extrudate that can be reused later as a mixture with virgin PET, thereby manufacturing new products (bottles, fibers, films). For use in food, a stage of solid-state polymerization under vacuum (known under the acronym SSP) is necessary. This type of recycling is known as mechanical recycling.

[0007] It is also possible to subject dark (or colored) PET flakes to mechanical recycling. However, its use is restricted due to the coloring of the extrudate formed from the colored stream: dark PET is generally used to produce packaging tapes and packaging fibers. Thus, its outlets are more restricted compared to those of clear PET.

[0008] If there is opaque PET containing a high content of pigments in the PET to be recycled, this opaque PET poses a problem to recyclers because it has an adverse effect on the mechanical properties of the PET to be recycled. Opaque PET is currently collected together with colored PET and found in the stream of colored PET. The content of opaque PET in the stream of colored PET to be recycled is currently 5 - 20% by weight, but considering that the uses of opaque PET are being developed, it tends to increase further. Within a few years, the content of opaque PET in the stream of colored PET may reach over 20 - 30% by weight. In fact, when the opaque PET in the stream of colored PET exceeds 10 - 15%, it has been shown that it has an adverse effect on the mechanical properties of the PET to be recycled (see Impact du developpement du PET opaque blanc sur le recyclage des emballages en PET (Impact of the increase in white opaque PET on the recycling of PET packages), Preliminary Report of COTREP, issued on December 5, 2013), and in the above case, due to the mechanical properties of the PET to be recycled, the recycling in the form of fibers, which is the main outlet of the industry for colored PET, is hindered.

[0009] Dyes are natural or synthetic substances that are particularly soluble in polyester materials and are introduced into the materials to color them. Commonly used dyes have different properties and often have O - type and N - type heteroatoms and conjugated unsaturated bonds. Examples include molecules such as quinone, methine, or azo functional groups, or pyrazolone and quinophthalone. FaceThe material is a finely divided substance that is insoluble, particularly in polyester materials, and is introduced into the material and used to color and / or opacify the material. The main pigments used to color and / or opacify polyester, particularly PET, are metal oxides such as TiO2, CoAl2O4, or Fe2O3, silicates, polysulfides, and carbon black. The pigments are generally particles having a size of 0.1 to 10 μm, predominantly 0.4 to 0.8 μm. Although it is necessary to completely remove these pigments by filtration for the recycling process of opaque PET, it is technically difficult because the pigments have extremely high blocking properties.

[0010] The recycling processes of colored PET and opaque PET thus involve extremely difficult problems.

[0011] Improvements in the method for the polymerization of PET also form the subject of numerous investigations. Some of these investigations relate to improvements in the preparation stage of mixtures of monomers, whether derived from the recycling industry or not.

[0012] In particular, Patent Document 1 discloses the production of high-quality polyester. It includes a method for depolymerizing PET flakes by glycolysis at atmospheric pressure in the presence of ethylene glycol in a bis(2-hydroxyethyl) terephthalate (BHET) base. The intermediate product obtained at the end of the depolymerization stage is filtered through a sintering system, whereby particles of at least 25 μm are retained before being introduced into the polymerization reactor, and as a result, high-quality polyester is obtained. However, Patent Document 1 does not disclose adding terephthalic acid to the polymerization reactor together with its intermediate.

[0013] Patent Document 2 discloses, in particular, a method for depolymerization by glycolysis of colored PET derived from the recovery of green-colored PET bottles. The stream of BHET obtained at the end of the glycolysis stage is purified by passing it through activated carbon to separate a predetermined dye such as a blue dye, and then extracting residual dyes such as a yellow dye with alcohol or water. BHET crystallizes from the extraction solvent and is then separated for the purpose of being usable in the PET polymerization process. In Patent Document 3, post-consumption PET containing a mixture of variously colored PETs such as clear PET, blue PET, green PET, 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 passing through activated carbon, and then crystallized and recovered by filtration, and thus polymerized to reform polyester. However, these two patent application documents do not detail the steps of the (re)polymerization process.

[0014] Patent Document 4 discloses a method for preparing glycol-modified polyethylene terephthalate (r-PETG). This method includes a depolymerization stage of PET in the presence of a mixture of monoethylene glycol (MEG) and neopentyl glycol, and a subsequent polymerization stage of the reaction effluent immediately thereafter.

[0015] Patent Document 5 describes a method for depolymerizing a polyester feedstock containing, inter alia, 0.1 to 10% by weight of a pigment. This depolymerization is carried out by glycolysis in the presence of ethylene glycol. The effluent of the bis(2-hydroxyethyl) terephthalate (BHET) monomer is obtained after specific separation and purification steps and can be fed to the polymerization step for the purpose of producing PET without specifying any conditions.

[0016] Patent Document 6 describes the production of purified BHET from PET, and the obtained BHET can be used as a starting material in the production method of plastic products. Similarly, Patent Document 7 discloses that high-purity bis(2-hydroxyethyl) terephthalate can be used as a starting material for regenerating high-quality polyester, if necessary. For this purpose, Patent Document 7 describes a method for depolymerizing polyester in more detail, but does not elaborate on the downstream stages of polymerization.

[0017] Patent Document 8 discloses a method for producing high-quality PET, which includes a step of continuously supplying ethylene glycol and terephthalic acid to an esterification medium containing bis(2-hydroxyethyl) terephthalate, where the amounts of the introduced acid and diol depend on parameters related to the viscosity of the mixture (slurry). Patent Document 9 discloses a method for producing PET, which includes a step of continuously supplying recycled ethylene glycol to a reaction medium. Patent Document 10 details a method for preparing a slurry in part, and its viscosity is improved by incorporating crystals of terephthalic acid pretreated by abrasion.

Prior Art Documents

Patent Documents

[0018]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

Summary of the Invention

Problems to be Solved by the Invention

[0019] None of the documents provides a method for producing an improved polyester in a mixture of terephthalic acid and diol monomer. Such a method would make it possible to reduce the solid content of the mixture, and thus facilitate subsequent processes, particularly the transportation process, and reduce the consumption of starting materials, particularly diols.

[0020] The subject of the present invention is a method for the production of terephthalate polyester, the method comprising the following steps: a) A step of preparing an esterification feedstock, the preparation step comprising at least one mixing section, the mixing section being supplied with at least one terephthalic acid feedstock and one diester monomer feedstock, the amounts of at least the terephthalic acid feedstock and the diester monomer feedstock introduced into the mixing section in the mixing being adjusted such that the ratio of the total number of moles of diol units of the formula -[C (n+1) H (2n+2) O2]-(wherein n is an integer of 1 or more) introduced into the mixing section to the total number of moles of terephthalic acid units of the formula -[CO-(C6H4)-CO]- introduced into the mixing section is 1.0 to 2.0, and the mixing section is operated at a temperature of 25°C to 250°C and a pressure of 0.1 MPa or more, the preparation step, b) The esterification stage of the esterification feedstock derived from stage a), whereby at least one reaction effluent and one aqueous effluent are produced. The esterification stage includes at least one reaction section and at least one separation section. This reaction section is an esterification stage operated at a temperature of 150°C to 400°C, a pressure of 0.05 to 1 MPa, and a residence time of 1 to 10 hours. c) The polycondensation stage of the reaction effluent obtained in stage b), whereby at least the terephthalate polyester and a diol effluent are obtained. The polycondensation stage includes at least one reaction section. This reaction section includes at least one reactor in which polycondensation is carried out. The reactor is operated at a temperature of 200°C to 400°C, a pressure of 0.0001 to 0.1 MPa, and a residence time of 0.1 to 5 hours. The reaction section also includes at least one extraction of the diol effluent. Polycondensation stage, and d) The diol treatment stage, which includes a recovery section to which at least all or part of the diol effluent derived from stage c) is supplied to obtain the diol effluent to be treated, and a purification section of the diol effluent to be treated to obtain a purified diol stream. Treatment stage, including.

[0021] Preferably, the present invention relates to a method for producing a terephthalate polyester from at least one polyester feedstock to be recycled. This method consists of the above stages a), b), c), and d).

Advantages of the Invention

[0022] One advantage of the present invention lies in the optimized preparation of the monomer feedstock. The reason is that the present invention enables at least partially replacing the monomer feedstock of the conventional method for producing terephthalate polyester with a terephthalic acid diester compound, that is, terephthalic acid and a diol.

[0023] Accordingly, the present invention has the advantage of preparing a monomer feedstock that exhibits a reduced solids content compared to a mixture of monomer feedstocks in the conventional process for producing terephthalate polyesters in which the diester monomer cannot be incorporated. According to the present invention, the solids content is the volume-based solids content defined as the ratio of the solid volume to the total volume of the two-phase monomer feedstock (i.e., the esterification feedstock according to the present invention). Thus, the present invention makes it possible to facilitate the steps of preparing and transporting the two-phase mixture, particularly during the polyester production process.

[0024] Another advantage of the present invention is that, while maintaining the operability of the preparation stage, i.e., without impairing the quality or preparation conditions of the mixture of monomer feedstocks, the amount of diol monomer introduced into the polyester production process is reduced compared to the conventional polyester production process. Since the amount of excess diol introduced into the process is reduced, the amount of diol that is recovered, treated, and recycled at the end of the polymerization is thus reduced, resulting in a reduction in the consumption of diol starting materials and in addition, inducing a reduction in the energy consumption of the process.

[0025] Furthermore, when the diester monomer incorporated into the mixture is advantageously the liquid diester intermediate obtained at the end of the polyester depolymerization process, the intermediate corresponding to the specifications of the polymerization process is directly incorporated into the mixture of step a). This is done without additionally providing a purification stage and / or a stage for conditioning the intermediate (e.g., the solidification stage of the diester obtained by depolymerization of the polyester). Thus, in particular, the energy consumption is considerably limited and, therefore, meets the expectations of society from an environmental protection perspective. **DETAILED DESCRIPTION OF THE INVENTION**

[0026] The present invention relates to a process for producing terephthalate polyesters, which process particularly includes the step of preparing a specific polymerization feedstock.

[0027] According to the present invention, the terms "polyester" and "terephthalate polyester" are interchangeable and mean polyalkylene terephthalate. Very generally, polyalkylene terephthalate is the result of the polycondensation of a diol (or glycol) monomer and a terephthalic acid (or dimethyl terephthalate) monomer. The terephthalate polyester according to the present invention is, inter alia, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), or any other polymer, the repeating unit of the main chain of which contains an ester functional group and an aromatic ring derived from terephthalic acid (or one of its esters, especially dimethyl terephthalate). According to the present invention, the preferred terephthalate polyester is polyethylene terephthalate, i.e., poly(ethylene terephthalate), also simply known as PET. Its basic repeating unit is shown in the following formula:

[0028] [Chemical formula]

[0029] Conventionally, PET has been obtained by the polycondensation of terephthalic acid (PTA) or dimethyl terephthalate (DMT) with ethylene glycol.

[0030] According to the present invention, the expression "to be recycled" describes any material, especially including polyester, derived from the industry of collecting and sorting plastic waste. In contrast, virgin polyester is derived only from the polymerization of a monomer feedstock containing at least one dicarboxylic acid (e.g., terephthalic acid, PTA) or one dicarboxylic acid ester (e.g., dimethyl terephthalate, DMT) and at least one compound of diols or glycols (e.g., ethylene glycol).

[0031] According to the present invention, the term "diester monomer" has the chemical formula HOC (m+1) H (2m+2) -CO2-(C6H4)-CO2-C(n+1) H (2n+2) The terephthalic acid ester compound of OH means. In this chemical formula, -(C6H4)- represents an aromatic ring, and n and m are the same or different integers, preferably the same integer (i.e., n = m), and are integers of 1 or more, preferably 1 to 5, more preferably 1 to 3. The molecule of the diester monomer corresponds to a compound derived from the esterification of one molecule of terephthalic acid, HOOC-(C6H4)-COOH (wherein -(C6H4)- represents an aromatic ring) and two molecules of at least one diol (or glycol). More specifically, the two molecules refer to one molecule of the diol of the chemical formula HO-C (n+1) H (2n+2) -OH and one molecule of the diol of the chemical formula HO-C (m+1) H (2m+2) -OH. A preferred diester monomer is bis(2-hydroxyethyl) terephthalate (BHET).

[0032] According to the present invention, the "diester monomer feedstock" includes a diester monomer as defined above. The "diester monomer feedstock" according to the present invention may also preferably contain at least one diol (or glycol) corresponding to the diol unit(s) present in the diester monomer of the feedstock. Advantageously, the diester monomer feedstock preferably contains at least 10% by weight, preferably at least 20% by weight of the diester monomer.

[0033] The term "dye" is understood to mean a substance that is soluble in the polyester material and is used to color the polyester material. The dye may be of natural or synthetic origin.

[0034] The term "pigment", more specifically, a coloring pigment and / or an opacifying pigment, is understood to mean a finely divided substance that is insoluble in the polyester material. The form of the pigment is generally particles having a size of 0.1 to 10 μm, predominantly 0.4 to 0.8 μm. Pigments often have the properties of inorganic substances. Conventionally used pigments, especially opacifying pigments, are metal oxides such as TiO2, CoAl2O4 or Fe2O3, silicates, polysulfides, and carbon black.

[0035] According to the present invention, the expression "··· to ···" means that within the range of the two described values, the limit values at both ends of the interval are included. In the case where this is not so, i.e., where the limit values are not included in the described range, the present invention will accurately describe to that effect.

[0036] (Feedstock) According to the present invention, at least one terephthalic acid feedstock and one diester monomer feedstock are supplied to the said method.

[0037] The terephthalic acid feedstock is preferably in the form of a powder, i.e., in the form of solid terephthalic acid particles. Preferably, the terephthalic acid particles incorporated into the monomer mixture preferably exhibit an average diameter of 1 to 1000 μm, especially 30 to 500 μm, particularly 80 to 200 μm. The average diameter of the terephthalic acid particles can be determined by any method of particle size analysis known to those skilled in the art, for example, by laser diffraction or sieving, preferably by sieving on a column of an appropriate sieve known to those skilled in the art.

[0038] The terephthalic acid of the terephthalic acid feedstock can advantageously be produced by the oxidation of paraxylene, by the depolymerization of polyester, or by any other method that enables the production of a terephthalic acid feedstock conforming to the specifications required by the polymerization process. Terephthalic acid can be derived from a fossil hydrocarbon source or biomass.

[0039] According to the present invention, the diester monomer feedstock includes a diester monomer as defined above and has the chemical formula HOC (m+1) H (2m+2) -CO2-(C6H4)-CO2-C (n+1) H (2n+2) OH (wherein, -(C6H4)- represents an aromatic ring, n and m are the same or different, preferably the same (i.e., n = m) integers, and are integers of 1 or more, preferably 1 to 5, more preferably 1 to 3), corresponding to a terephthalic acid diester compound. The diester monomer preferably contains a repeating unit that forms the basis of the terephthalate polyester produced by the method according to the present invention. Most preferably, the diester monomer feedstock contains bis(2-hydroxyethyl) terephthalate (BHET) as the diester monomer. The diester monomer feedstock according to the present invention may also preferably contain at least one diol corresponding to the diol unit(s) present in the diester monomer of the feedstock. The diester monomer feedstock preferably contains at least 10% by weight, preferably at least 20% by weight of the diester monomer.

[0040] According to the present invention, the diester monomer feedstock may be in liquid form or in solid form. Preferably, the diester monomer feedstock is in liquid form.

[0041] In an advantageous embodiment of the present invention, the diester monomer feedstock in step a) is obtained at the end of the depolymerization method of the polyester feedstock to be recycled, in particular, at the end of the depolymerization method of the polyester feedstock to be recycled as described in Patent No. 3715812, French Patent Invention No. 3053691, and International Publication No. 01 / 10812 Pamphlet, and includes at least a fraction of the purified diester effluent, preferably all of the effluent.

[0042] Advantageously, the purified diester effluent is obtained by a process for the depolymerization of the polyester feedstock to be recycled. This process comprises at least the following steps: i) a depolymerization step comprising at least one reaction section to which a stream of the polyester feedstock to be recycled and a glycol are fed to obtain a depolymerization reaction effluent, and ii) a separation / purification step comprising a separation section for obtaining a glycol effluent and at least one purification section for obtaining a purified diester effluent; in step ii), a fraction of the purified diester effluent is sent at least to step a).

[0043] In this embodiment, the polyester feedstock to be recycled is derived from industries for collecting and sorting waste, in particular plastic waste. Preferably, the polyester feedstock to be recycled is a polyethylene terephthalate (PET) feedstock to be recycled.

[0044] The polyester feedstock to be recycled and supplied to the depolymerization step i) may be in the form of flakes. The flakes have a maximum length of less than 10 cm, preferably 5 - 25 mm, or are in the form of ultrafine ground solids, i.e., preferably in the form of particles with a size of 10 microns to 1 mm. The polyester feedstock to be recycled preferably contains less than 2% by weight, preferably less than 1% by weight, of "macro" impurities (such as glass, metal, plastics other than terephthalate polyester, wood, paper, cardboard, or waste formed from inorganic elements, etc.). The polyester feedstock to be recycled may also be in the form of textile fibers, such as textile fibers optionally pretreated to remove cotton, polyamide fibers, or any other textile fibers other than polyester fibers, or in particular, tire fibers optionally pretreated to remove residues of polyamide fibers, rubber, or polybutadiene. The polyester feedstock to be recycled and supplied to the depolymerization step i) advantageously contains more than 50% by weight of polyalkylene terephthalate, preferably more than 70% by weight, more preferably more than 90% by weight of polyalkylene terephthalate.

[0045] The polyester feedstock to be recycled can be obtained from waste of clear, colored, opaque, dark, and / or multilayered terephthalate polyester, preferably PET. It advantageously contains at least one opaque, dark, or multilayered terephthalate polyester, preferably PET. Preferably, it contains at least 10% by weight of opaque terephthalate polyester, preferably opaque PET, very preferably at least 15% by weight of opaque terephthalate polyester, preferably PET. The polyester feedstock to be recycled may also contain up to 10% by weight of pigments, especially 0.1% - 10% by weight of pigments, particularly 0.1% - 5% by weight of pigments, and / or up to 1% by weight of dyes, especially 0.05% - 1% by weight of dyes, particularly 0.05% - 0.2% by weight of dyes.

[0046] The polyester feedstock to be recycled may also contain elements, such as antimony, titanium, or tin, etc., which are used as polymerization catalysts and / or stabilizers in the polyester manufacturing process.

[0047] Advantageously, the depolymerization step i) employs a glycolysis reaction of the polyalkylene terephthalate of the polyester feedstock to be recycled in one or more reactors in the presence of a stream of the glycol in the reaction section. The stream of the glycol preferably contains a diol monomer, which corresponds to the diol unit in the composition of the repeating unit that forms the basis of the terephthalate polyester produced by the manufacturing method according to the present invention. Preferably, the stream of the glycol is a stream of ethylene glycol. Advantageously, the stream of the glycol fed to the depolymerization step i) contains at least a fraction of the stream of the purified diol obtained at the end of step d) of the manufacturing method of the terephthalate polyester according to the present invention, and preferably consists only of this fraction.

[0048] The reaction section of the depolymerization step i) is carried out at a temperature of 150°C to 400°C, preferably 180°C to 300°C, more preferably 200°C to 280°C, an operating pressure of at least 0.1 MPa, preferably at least 0.4 MPa, and a residence time per reactor of 0.05 to 10 hours, preferably 0.1 to 6 hours, more preferably 0.5 to 4 hours. The residence time per reactor is defined as the ratio of the liquid volume of the reactor to the volumetric flow rate of the stream fed to the reactor. The stream of the glycol is fed to the reaction section and is adjusted such that the amount of the glycol compound contained in the stream of the glycol is 1 to 20 moles of diol per mole of the repeating unit that forms the basis of the polyester in the polyester feedstock to be recycled, and preferably 3 to 10 moles of diol per mole of the diester in the polyester feedstock to be recycled.

[0049] 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 is selected from known esterification catalysts for those skilled in the art, such as complexes, oxides, and salts of antimony, tin, or titanium, alkoxides of metals from Groups (I) and (IV) of the Periodic Table of the Elements, organic peroxides, or acidic / basic metal oxides, etc. Preferably, the depolymerization reaction is carried out without the addition of a catalyst.

[0050] The depolymerization reaction can also advantageously be carried out in the presence of a solid adsorbent in powder form or in a shaped form. The role of the solid adsorbent is to capture at least a part of the impurities, especially the colored impurities, and thus to relieve the burden on the purification step in step ii). The solid adsorbent is especially activated carbon.

[0051] The depolymerization reaction effluent obtained at the end of the depolymerization step i) comprises a diester monomer, and an oligomer containing 1 to 5, preferably 1 to 3, basic units of the formula -[O-CO-(C6H4)-CO-O-C (n+1) H (2n+2) -(wherein n is an integer from 1 to 5, preferably an integer from 1 to 5), a diol compound, optionally impurities present in the polyester feedstock, and optionally compounds resulting from side reactions (such as etherification or decomposition reactions, etc.). The diol compound is preferably the diol monomer and comonomer that make up the composition of the polyester feedstock to be recycled and released at the end of the depolymerization reaction, and the unreacted ones derived from the glycol stream are fed to the depolymerization step i). The depolymerization reaction effluent may also contain unreacted polyester and other polymers.

[0052] The depolymerization reaction effluent obtained at the end of the depolymerization step i) is fed to the separation / purification step ii). The separation / purification step ii) includes at least one glycol effluent separation section and at least one purification section to obtain a purified diester effluent.

[0053] The separation and purification sections may be in any order relative to each other. When step ii) includes a section for purifying the depolymerization reaction effluent to obtain a purified depolymerization reaction effluent, a section for separating the purified depolymerization reaction effluent to obtain a glycol effluent and a diester effluent, and a section for purifying the diester effluent to obtain a purified diester effluent, the separation and purification sections may also be connected to each other.

[0054] In a preferred embodiment, step ii) advantageously includes a section for separating the depolymerization reaction effluent to obtain a glycol effluent containing unreacted diol of the glycol stream of step i) and a diester effluent, and a section for purifying the diester effluent to obtain a purified diester effluent.

[0055] The glycol effluent obtained at the outlet of the separation section of step ii) advantageously contains more than 50% by weight, preferably more than 70% by weight, more preferably more than 90% by weight of diol. Advantageously, the separation section enables the recovery of the unreacted diol of the glycol stream of step i). The diester effluent obtained at the outlet of the separation section is preferably in liquid form and advantageously contains more than 10% by weight, preferably more than 25% by weight, more preferably more than 50% by weight of diester monomers and oligomers.

[0056] Advantageously, the separation section includes one or more separation devices, whereby it is possible to recover an effluent rich in diol (glycol effluent) and, optionally, an effluent rich in light impurities and an effluent rich in heavy impurities. Any physical, chemical, or physical / chemical separation method known to those skilled in the art can be used, and the methods include, for example, gas / liquid separation, distillation, evaporation, extraction with a solvent, etc., which may or may not be carried out together with a chemical reaction, crystallization and subsequent filtration or centrifugation, or a combination of the separation methods. Preferably, the separation section includes a series of gas / liquid separations, preferably 1 to 5 gas / liquid separations, which are carried out at a temperature of 100 to 250 °C, preferably 110 to 220 °C, more preferably 120 to 210 °C, and a pressure of 0.00001 to 0.2 MPa, preferably 0.00004 to 0.15 MPa, preferably 0.00004 to 0.1 MPa.

[0057] Preferably, all or part of the glycol effluent recovered at the end of step ii) is advantageously sent to treatment step d) of the method according to the invention.

[0058] All or part of the glycol effluent recovered at the end of step ii) can be pre-purified in a section for pre-purifying the diol contained in step ii), whereby part of the impurities (such as dyes, pigments, or other solid particles, etc.) entrained with the glycol effluent are removed. The pre-purification section to which all or part of the glycol effluent is supplied can include, as non-limiting examples, adsorption on a solid (such as activated carbon) and a filtration system. The fraction of the pre-purified glycol effluent can be recycled directly to at least the depolymerization step i). Separation of different types of diols that may be contained in the glycol effluent can be carried out in the pre-purification section.

[0059] The purification step of the diester effluent consists of separating at least one purified diester monomer effluent from all or part of the following compounds derived from the depolymerization step i), while minimizing the loss of diester monomers: diester oligomers, optionally unreacted polyester, impurities (other polymers, pigments, dyes, polymerization catalysts, etc.) that may be present in the polyester feedstock to be recycled, or any other inorganic compounds that constitute the polyester feedstock to be recycled or are formed during the depolymerization step i).

[0060] The diester effluent is preferably purified by physical, chemical, or physical / chemical methods known to those skilled in the art. This makes it possible to recover a purified diester monomer effluent with a yield of the diester monomer of 50% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more. The term "yield" is understood to mean the amount of diester monomer in the flow of the purified diester monomer relative to the total amount of diester monomer introduced into the purification section. Preferably, the purified diester monomer effluent is free of dyes or inorganic impurities (pigments, depolymerization catalysts, and ions, etc.). Preferably, the purified diester monomer contains diester monomer and, optionally, molecules of oligomers of said diester with a degree of polymerization of 2 to 5.

[0061] The purification of the diester effluent (and / or the depolymerization reaction effluent) preferably employs one or more purification operations (e.g., filtration, evaporation, distillation, membrane separation, precipitation, crystallization, adsorption onto a trapping mass, treatment on an ion exchange resin, or extraction with a solvent, etc.). For example, in European Patent No. 0865464, the purification of the diester effluent includes a series of dissolution operations in a hot solvent, followed by precipitation and filtration, whereby impurities having a size greater than 50 μm are separated, and diester monomers and oligomers in a thin-film evaporator are separated. Optionally, the purification section of step ii) may include at least two purification operations (or steps): - A first purification step that enables the separation of impurities that are insoluble in the diester effluent (and / or the depolymerization reaction effluent), or become insoluble after cooling, or partial evaporation of the effluent, or addition of a third body (such as a flocculant or a solvent that promotes precipitation). - A second purification step that enables the separation of impurities that are soluble in the diester effluent (and / or the depolymerization reaction effluent), or become soluble after heating or addition of a solvent.

[0062] Preferably, the purification of the diester effluent (and / or the depolymerization reaction effluent) employs a separation section including a falling film or thin film evaporation system, a short-path falling film or thin film distillation, or a series of several short-path falling film or thin film evaporation and / or distillation operations that are operated at a temperature of 250 °C or lower, preferably 230 °C or lower, preferentially 200 °C or lower, and a pressure of 0.001 Mpa or lower, preferably 0.0001 MPa or lower, more preferably 0.00005 MPa or lower. Then, a decolorization section is operated at a temperature of 100 - 250 °C, preferably 110 - 200 °C, more preferably 120 - 180 °C, and a pressure of 0.1 - 1.0 MPa, preferably 0.2 - 0.8 Mpa, more preferably 0.3 - 0.5 Mpa, in the presence of an adsorbent, preferably activated carbon.

[0063] Advantageously, the purified diester effluent obtained at the end of step ii) contains at least 10 wt% of diester monomer, preferably at least 20 wt% of diester monomer. It preferably contains less than 1 wt%, preferably less than 0.1 wt% of the pigment introduced into the process together with the polyester feedstock to be recycled, and less than 10 wt%, preferably less than 1 wt% of the dye introduced into the process together with the polyester feedstock to be recycled.

[0064] Said step ii) may also give rise to an effluent of ester impurities consisting of oligomers and optionally polymers not converted in depolymerization step i). Said effluent of ester impurities is preferably recycled, either completely or partially, to step i) or withdrawn and sent to an incineration system. Where appropriate, said fraction of the effluent of ester impurities recycled to step i) may be subjected to at least one separation operation, preferably a filtration operation, which reduces the amount of other solid impurities which may optionally be present in said effluent of ester impurities and / or pigments. Optionally, at least a fraction, whole or part, of the glycol effluent resulting from step ii) or step d) according to the invention is preferably mixed with said recycled fraction of the effluent of ester impurities, thereby reducing the viscosity of said fraction of the effluent in the ester impurities. This makes it easier to transport it to step i) and easier to process it in the optional filtration step.

[0065] Preferably, the purified diester effluent is recovered at the end of step ii) in liquid form or in solid form, preferably in liquid form.

[0066] 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 terephthalate polyester according to the invention.

[0067] Step a) of preparing the esterification feedstock According to the invention, a process for producing a terephthalate polyester comprises a step a) of preparing an esterification feedstock. Said step a) comprises at least one mixing section. At least one terephthalic acid feedstock and one diester monomer feedstock are fed to the mixing section.

[0068] The esterification feedstock according to the invention obtained at the end of step a) comprises at least terephthalic acid, a diester monomer, and optionally the chemical formula HO-C(n+1) H (2n+2) -OH (wherein n is an integer of 1 or more, preferably 1 to 5, more preferably 1 to 3), and is a homogeneous two-phase mixture containing a diol (or glycol). The term "two-phase" is preferably understood to mean a state in which a solid phase is suspended in a liquid or paste-like phase. The term "homogeneous" should be understood to mean that the solid phase suspended in the liquid or paste-like phase is homogeneously distributed throughout the liquid or paste-like phase. More specifically, the esterification feedstock according to the present invention is a mixture of solid terephthalic acid particles having a diameter typically of 1 to 1000 μm, particularly 80 to 300 μm, which are homogeneously distributed in a liquid or paste-like phase containing a diol monomer and a diester monomer.

[0069] Advantageously, the amount of the monomer feedstock introduced into the mixing section, i.e., at least the amount of the terephthalic acid feedstock and the diester monomer feedstock, is such that the ratio of the total number of moles of diol units of the formula -[C (n+1) H (2n+2) O2] - (wherein n is an integer of 1 or more) introduced into the mixing section to the total number of moles of terephthalic acid units of the formula -[CO-(C6H4)-CO]- introduced into the mixing section is adjusted to be 1.0 to 2.0, preferably 1.0 to 1.5, more preferably 1.0 to 1.3.

[0070] Preferably, a diester monomer feedstock in liquid form is fed to the mixing section of step a). If the diester monomer feedstock intended to be fed to the mixing section is in solid form, step a) of the process of the present invention may optionally include a conditioning section located upstream of the mixing section, whereby a liquid diester monomer feedstock is obtained. At least a solid form of the diester monomer feedstock is fed to the optional conditioning section, and this section is operated at a temperature above the liquefaction temperature of the diester monomer feedstock, preferably from 25°C to 250°C and at a pressure of 0.1 MPa or more. The pressure in the mixing section is very preferably 5 MPa or less.

[0071] In a preferred embodiment of the present invention, a diol monomer feedstock is additionally fed to the mixing section of step a) of the process according to the present invention. This diol monomer feedstock preferably contains a diol monomer corresponding to the diol unit(s) contained in the diester monomer of the diester monomer feedstock. It predominantly contains the diol monomer that constitutes the composition of the repeating unit that forms the basis of the terephthalate polyester produced by the process according to the present invention. Preferably, the diol monomer feedstock contains at least 70 mol%, preferably at least 90 mol%, very preferably 99.5 mol% of the diol monomer that constitutes the composition of the individual units of the terephthalate polyester intended. Preferably, the diol monomer feedstock contains ethylene glycol. The diol monomer feedstock is preferably in liquid form.

[0072] Preferably, the diol monomer feedstock can be at least in part a fraction of the purified diol stream obtained in step d) of the process according to the present invention. The diol monomer feedstock may optionally contain an external diol source.

[0073] When the diol monomer feedstock is incorporated into the mixing section of step a), as defined above, the amount of the diol feedstock introduced into the mixing section of step a) is adjusted such that the ratio of the number of diol units to the number of terephthalic acid units in the mixture of step a) is 1.0 to 2.0, preferably 1.0 to 1.5, more preferably 1.0 to 1.3.

[0074] Advantageously, the molecular weight of the diester monomer contained in the diester monomer feedstock introduced into the mixing section of step a) represents at least 5% by weight, preferably at least 15% by weight, based on the weight of terephthalic acid (PTA).

[0075] The molecule of the diester monomer of the diester monomer feedstock contains two diol units and one terephthalic acid unit. One terephthalic acid molecule contains one terephthalic acid unit. One diol molecule contains one diol unit. Thus, by incorporating 1 mole of a diester monomer, for example, 1 mole of bis(2-hydroxyethyl) terephthalate (BHET), as a mixture with the feedstocks of terephthalic acid monomer and diol monomer (preferably, this diol corresponds to the unit of a diol such as ethylene glycol contained in the diester monomer), it becomes possible to replace a part of the terephthalic acid feedstock and all or part of the diol feedstock.

[0076] Advantageously, the mixing section in step a) of the method according to the invention is operated at a temperature of 25 to 250 °C, preferably 60 to 200 °C, more preferably 100 to 150 °C, and a pressure of 0.1 Mpa or more. The pressure of the mixing section is very advantageously 5 MPa or less.

[0077] In addition, one or more polymerization catalysts can be incorporated into the mixture in step a) of the method according to the invention.

[0078] Advantageously, other monomer (or comonomer) compounds may also be incorporated into the mixture and may be found in the esterification feedstock. As non-limiting examples, said other monomer compounds may be, for example, dicarboxylic acids such as isophthalic acid and diols such as 1,4-dihydroxymethylcyclohexane and diethylene glycol.

[0079] Thus, in the process according to the invention, by incorporating a diester monomer, such as a BHET monomer, into the esterification feedstock, it is possible to replace a part of terephthalic acid, which is a compound in the form of a powder of solid particles, in a two-phase mixture of monomers for the production of polyester. Thus, the solids content of this two-phase mixture can be reduced compared to conventional polyester production processes, and therefore the subsequent production steps, especially transportation, are facilitated. Also, the presence of the diester monomer, especially BHET, makes it possible to accelerate the esterification of terephthalic acid. Further, in the process according to the invention, by replacing a part of terephthalic acid and all or part of the diol with a diester monomer, if the solids content of the two-phase reaction mixture is the same as compared to conventional polyester production processes, it is possible to reduce the amount of ethylene glycol introduced in excess into the mixture. As a result, not only does this significantly reduce the amount of material to be treated and recycled, leading to a reduction in costs, especially the starting material costs, but it also considerably reduces the energy consumption of the polyester production process.

[0080] Esterification step b) According to the invention, the process for producing a terephthalate polyester comprises an esterification step b) of the esterification feedstock obtained at the end of step a). This results in at least one reaction effluent and one aqueous effluent.

[0081] The reaction effluent preferably contains diesters and ester oligomers. Preferably, the diesters in the reaction effluent are of the same nature as the diester monomers incorporated into the mixture in step a). Preferably, the ester oligomers in the reaction effluent advantageously consist of basic units corresponding to the basic repeating units of the terephthalate polyester produced by the process according to the invention.

[0082] Advantageously, the esterification step b) comprises at least one reaction section and at least one separation section for separating the reaction effluent and the aqueous effluent.

[0083] The reaction carried out in step b) advantageously includes an esterification reaction. The esterification reaction consists at least of the condensation reaction between the -OH groups of the diester monomers of the diester monomer feedstock incorporated into the esterification feedstock in step a) and the diol monomers optionally present in the esterification feedstock, and the -COOH groups of the terephthalic acid of the terephthalic acid feedstock incorporated into the esterification feedstock in step a). This esterification reaction gives rise, for example, to molecules of diester monomers such as bis(2-hydroxyethyl) terephthalate (BHET) and advantageously molecules of diester oligomers containing 2 to 5 terephthalic acid units. Water is also released in the esterification reaction. The reaction carried out in step b) of the process according to the invention also advantageously includes a transesterification reaction consisting of the condensation reaction between the molecules of diester monomers, and therefore releases diol molecules.

[0084] The reaction section is operated at a temperature of 150 to 400 °C, preferably 200 to 300 °C, a pressure of 0.05 to 1 MPa, preferably 0.1 to 0.3 Mpa, and a residence time of 0.5 to 10 hours, preferably 1 to 5 hours. According to the present invention, the residence time in the esterification step b) is defined as the ratio of the reaction volume of the reactor in the reaction section to the volumetric flow rate of the liquid stream exiting the reactor. The esterification reaction is preferably carried out in one or more stirred reactors in series or parallel, one or more tubular reactors in series or parallel, or a combination of stirred and tubular reactors in series or parallel.

[0085] The water generated during the esterification reaction is separated in the separation section of step b). Advantageously, the reaction section also includes at least one withdrawal of the withdrawn effluent rich in water and diol. The water is separated, in particular, by differences in volatility, for example by distillation or by adsorption starting from the effluent withdrawn from the reaction medium containing at least a portion of the released water and diol present in the reaction medium.

[0086] Advantageously, a polymerization catalyst known to those skilled in the art is fed to the final section of the esterification step b), optionally as a mixture with a diol stream. By way of non-limiting example, the polymerization catalyst is a catalyst based on antimony, titanium, germanium, aluminum, zinc acetate, calcium, or manganese.

[0087] By incorporating a diester monomer feedstock into the monomer feedstock of the polymerization process according to the present invention, it is possible to replace at least a portion of the terephthalic acid feedstock and all or a portion of the diol feedstock, thereby reducing the amount of water generated and, therefore, the amount of effluent to be withdrawn from the reaction medium to be treated. This advantageously reduces the energy consumption.

[0088] Polycondensation step c) According to the present invention, a method for producing a terephthalate polyester includes a polycondensation step c) of the reaction effluent obtained in step b), whereby at least said terephthalate polyester and a diol effluent are obtained. Said diol effluent contains at least one diol monomer, which advantageously corresponds to a diol unit of the formula -[C (n+1) H (2n+2) O2]-(wherein n is an integer of 1 or more), and this is contained at least in the diester of the diester monomer feedstock supplied to the mixing section of step a) of the method according to the present invention.

[0089] The polycondensation step c) consists in carrying out a condensation reaction of the diester monomer and oligomer obtained in the esterification step b), whereby a polyester having a given degree of polymerization and desired physicochemical properties (e.g., viscosity index, crystallinity, color, mechanical properties, etc.) is obtained. Said condensation reaction releases a diol compound, optionally water and by-products, which are preferably removed.

[0090] The polycondensation step c) includes at least one reaction section. The reaction section includes at least one reactor in which polycondensation is carried out and at least one extraction of the diol effluent. The diol effluent advantageously contains at least one monomer corresponding to a diol unit of the formula -[C (n+1) H (2n+2) O2]-(wherein n is an integer of 1 or more), which is contained at least in the diester of the diester monomer feedstock supplied to the mixing section in step a) of the method according to the present invention.

[0091] Advantageously, the reaction section is operated in one or more reactors operating in series or in parallel at a temperature of 200 to 400 °C, preferably 250 to 300 °C, a pressure of 0.0001 to 0.1 MPa, preferably 0.0004 to 0.01 MPa, and a residence time of 0.1 to 5 hours, preferably 0.5 to 3 hours. According to the present invention, the residence time in the polycondensation step c) is defined as the ratio of the reaction volume of the reactor in the reaction section to the volume flow rate of the liquid flow exiting the reactor. The condensation reaction in the polycondensation step c) can be carried out in two consecutive reaction stages, namely, a melt-phase condensation stage and a subsequent solid-phase post-condensation stage.

[0092] Advantageously, a polymerization additive and a catalyst can be introduced in the polycondensation step c) Lead to Non-limiting examples of additives include, for example, etherification side reaction inhibitors such as amines (n-butylamine, diisopropylamine, or triethylamine), sodium hydroxide, organic hydroxides, lithium carbonate, etc., stabilizers such as phosphites or phosphates, and polyamide-type compounds for reducing the amount of decomposition products such as acetaldehyde. Commonly used polymerization catalysts are, for example, catalysts based on antimony, titanium, germanium, aluminum, zinc acetate, calcium, manganese, etc.

[0093] Advantageously, the extraction of the diol effluent is carried out using one or more extraction systems preferably connected to the reactor(s) of the reaction section of step c), thereby enabling the separation of the diol monomer released during the condensation reaction, optionally water, and other by-products optionally released during the condensation reaction. Preferably, the diol effluent withdrawn from the reactor(s) of step c) is a gaseous effluent, which is then preferably cooled to a temperature of 0 to 100 °C and condensed, thereby obtaining an effluent in liquid form. The liquid effluent contains at least the diol monomer.

[0094] Preferably, at least the fraction of the effluent containing the diol monomer, preferably in liquid form, is sent at least to step d) of the process according to the invention.

[0095] Advantageously, the effluent containing at least the diol monomer, preferably in liquid form, can be recycled directly, either completely or partially, in the preparation step a) of the esterification feedstock.

[0096] In a very particular embodiment, the effluent containing at least the diol monomer, preferably in liquid form, can be recycled directly, either completely or partially, to the esterification step b).

[0097] Treatment step d) of the diol According to the invention, a process for producing a terephthalate polyester comprises a step d) of treating a diol. Step d) comprises a recovery section to which at least all or part of the diol effluent resulting from step c) is fed in order to obtain a diol effluent to be treated, and a purification section of said diol effluent to be treated in order to obtain a stream of purified diol.

[0098] Advantageously, in said recovery section of step d), at least all or part of the diol effluent obtained in step c) is fed, preferably in liquid form. In addition, in an advantageous embodiment of the invention, the diester monomer feedstock of step a) comprises at least a fraction of the purified diester effluent obtained at the end of the process for the depolymerization of the polyester feedstock to be recycled, then in said recovery section of step d), Again all or part of the glycol effluent resulting from the separation section of step ii) of the process for the depolymerization of the polyester feedstock to be recycled can be fed. Optionally, an externally-supplied diol can also be fed to said recovery section of step d) of the process according to the invention. Advantageously, the recovery section can include one or more operations of filtering different streams containing at least the diol monomer.

[0099] The diol effluent to be treated is obtained at the outlet of the recovery section of step d) of the process according to the invention and is sent to said purification section, whereby a stream of purified diol is obtained.

[0100] Said purification section includes at least one separation system, which makes it possible to carry out any physical, physicochemical or chemical separation method known to those skilled in the art, such as, for example, 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, which are operated at a temperature of 50 to 250°C, preferably 70 to 220°C, and a pressure of 0.001 to 0.2 MPa, preferably 0.01 to 0.1 MPa. Preferably, said purification section includes a stage for separating impurities lighter than the diol monomer of the diol effluent to be treated and a stage for separating impurities heavier than the diol monomer of the diol effluent to be treated, and preferably includes a series of distillation columns.

[0101] Advantageously, step d) may also include a section for removing compounds by thermal or catalytic combustion of said compounds in order to prevent volatile organic compounds from being discharged into the environment. As a non-limiting example, said section for treating impurities includes filtration when solid particles and a catalytic combustion system or a non-catalytic combustion system are present.

[0102] Thus, according to the process of the invention, it is possible to obtain a terephthalate polyester having an improved monomer mixture, advantageously having the desired degree of polymerization and the desired physicochemical properties, as a result of which it is possible to limit the consumption of diol monomers and the amount of excess diol monomers optionally introduced into the mixture of unconverted monomers (i.e., the esterification feedstock). By thus reducing the consumption of diol, the amount of diol to be recycled is limited, and for this reason, the energy consumption of the process is reduced.

[0103] Also, by replacing one acid monomer and two diol monomers with one diester monomer according to this method, it becomes possible to reduce the solid content of the starting polymerization monomer mixture, and therefore, subsequent operations, particularly the transportation of this two-phase mixture, become easier.

[0104] The following examples illustrate the present invention, but these examples do not limit the scope of the present invention.

[0105] Examples

[0106] Example 1 - Comparative Example

[0107] 5.5 t / hour of terephthalic acid (PTA) was introduced into a mixing vessel equipped with a mechanical stirrer and mixed with a flow of 2.5 t / hour of monoethylene glycol (MEG) at 110°C. This flow included 2.13 t / hour of MEG from a storage tank and 0.37 t / hour of recycled MEG from a section for the purification of MEG.

[0108] The amounts of introduced PTA and MEG corresponded to a PTA / MEG molar ratio of 1.23.

[0109] At 110°C, 1 wt% of the initially introduced PTA was dissolved in MEG. The volume-based solid content, defined as the ratio of the solid volume to the total volume of the paste (solid + liquid), was 60.7 vol%. The resulting mixture formed a viscous paste.

[0110] The resulting mixture was then transferred, using a suitable pump, to a first esterification reactor operating at 260°C, 0.5 MPa, with a residence time of 1.25 hours.

[0111] A vapor effluent of 1.4 t / h containing 71 wt% water and 29 wt% MEG was withdrawn and sent to a reflux column. Thereby, the water and MEG generated by the esterification reaction were separated. The MEG was then returned to the reactor. In the first reactor, the conversion rate of the obtained PTA was 85%.

[0112] The liquid effluent from the first reactor was then sent to a second esterification reactor operating at 260 °C, 0.2 Mpa with a residence time of 1.25 h. A vapor effluent of 140 kg / h containing 40 wt% water and 60 wt% MEG was withdrawn from the second reactor and sent to the reflux column. The conversion rate of PTA at the outlet of the second reactor achieved 92%.

[0113] The liquid effluent from the second esterification reactor was sent to a third reactor operating at 275 °C, 0.033 Mpa with a residence time of 0.5 h. Thereby, the conversion rate of PTA was brought to 95.8%, making it possible to start polycondensation. At the inlet of the third reactor, antimony trioxide at a ratio of 220 ppm by weight was added as a polymerization catalyst. A vapor effluent containing 70 wt% MEG, 16.5 wt% water, 5.5 wt% acetaldehyde, 2.5 wt% diethylene glycol, and 5.5 wt% oligomer was withdrawn from the third reactor, partially condensed, and then sent to a section for MEG purification.

[0114] The liquid effluent from the third reactor was sent to a fourth reactor (polycondensation reactor) operating at 275 °C, 0.0066 Mpa with a residence time of 0.5 h. A vapor effluent with a composition of 60 wt% MEG, 25 wt% water, 6 wt% acetaldehyde, 3 wt% diethylene glycol, and 6 wt% oligomer was withdrawn from the fourth reactor, partially condensed, and then sent to a section for MEG purification.

[0115] The liquid effluent from the fourth reactor was sent to the final reactor (polycondensation reactor) operating at 280 °C, 0.000013 Mpa with a residence time of 1 hour. A vapor effluent with a composition of 57 wt% MEG and 43 wt% water was withdrawn, partially condensed, and then sent to the section for the purification of MEG.

[0116] The section for the purification of MEG included a first distillation column with 25 plates operating at 145 °C and 0.02 Mpa at the top. This made it possible to separate diethylene glycol. The bottoms product from the first distillation column was sent to a second distillation column with 17 plates operating at 100 °C and 0.1 Mpa at the top. This made it possible to separate light components such as water and acetaldehyde. The MEG recovered at the end of these two distillations showed a purity of over 99.8%. This MEG was then recycled to the mixing vessel.

[0117] 6.25 t / hour of PET was produced. The total primary energy consumption for the production of PET was 5.8 MMkcal / hour.

[0118] Example 2 - Conforming to the present invention

[0119] Production of BHET by glycolysis of PET flakes to be recycled 4 t / hour of flakes from a crushed and washed PET feedstock to be recycled, consisting of 50 wt% opaque PET and 50 wt% colored PET, was melted in an extruder at 250 °C and mixed with 11.4 t / hour of ethylene glycol (MEG). The resulting mixture was injected into a stirred reactor, and the reactor was maintained at 220 °C and a pressure of 0.4 MPa for a residence time of 4 hours. At the outlet of the reactor, the reaction effluent contained 66 wt% MEG, 27.4 wt% BHET, 1.7 wt% diethylene glycol (DEG), 0.2 wt% water, 4.7 wt% oligomers, pigments, and other heavy compounds.

[0120] Ethylene glycol present in the reaction effluent was separated by evaporation in a series of five vessels at a temperature in the range of 200 °C to 124 °C and a pressure of 0.1 MPa ~0.00025 MPa . At the end of this evaporation stage, a stream of 10.95 t / h of MEG was recovered, consisting of a liquid stream rich in 97 wt% MEG, 2.5 wt% DEG, 0.2 wt% water, 0.2 wt% BHET, and 5.17 t / h of BHET. The MEG stream was sent to a first distillation having 25 plates and operating at 145 °C and 0.02 MPa . This separated the DEG and heavy products. It was then sent to a second distillation column having 17 plates and operating at 100 °C and 0.1 MPa . This separated the water and recovered a purified MEG effluent. The MEG effluent can then be recycled to the depolymerization reactor as a mixture with fresh MEG that has been supplemented. The liquid stream rich in BHET contained 87.1 wt% BHET, 0.2 wt% MEG, 0.1 wt% DEG, 12.6 wt% oligomers, pigments, and other heavy compounds.

[0121] The liquid stream rich in BHET was then injected into a short - process distillation at a temperature of 205 °C and a pressure of 0.00002 Mpa. A pre - purified liquid BHET effluent with a flow rate of 4.46 t / h was recovered by cooling the vapor to 115 °C in the short - process distillation. It contained 99.8 wt% BHET, 0.1 wt% MEG, and 0.1 wt% DEG. A heavy residue containing 93 wt% oligomers, pigments, other heavy compounds, and 7 wt% BHET was also recovered at a flow rate of 0.7 t / h at the outlet of the short - process distillation.

[0122] The flow of the preliminarily refined liquid BHET was compressed to 0.5 MPa and then fed to a fixed bed of activated carbon having an adsorption capacity equal to 5% by weight. As described in Example 1, at the end of this stage, the decolorized and pigment-removed liquid flow of BHET was recovered and reinjected into the preparation stage of the monomer mixture. The prepared mixture was then subjected to different polymerization stages as in the method described in Example 1 for the purpose of producing PET.

[0123] Table 1 below shows the amounts of PTA and MEG monomers, the amount of incorporated solid BHET monomer, the solids content in the feed mixture obtained at 110 °C, and the ratio of the number of diol units to the number of terephthalic acid units. This ratio is shown for two ratios (1.23 and 1.1) of diol units to terephthalic acid units for the production of 6.25 t / h of PET, taking into account the incorporation of BHET derived from the above depolymerization method. The results shown in the table are the calculated results for different amounts of BHET introduced into the mixture, and 1 mole of BHET is considered to replace 1 mole of PTA and 2 moles of MEG in the mixture. This result is based on a process simulation that integrates the solubility data and thermodynamic data set at the experimental points.

[0124]

Table 1

[0125] When BHET is introduced into the two-phase mixture (esterification feedstock) of monomers intended for the polymerization of Examples 2a, 2b, and 2c, it is clear that the solids content is significantly reduced compared to the solids content of the two-phase mixture of monomers in Example 1: the reduction in solids content by volume was from about 15% to about 48%. More specifically, when the ratio of diol units to terephthalic acid units is equivalent, the solids content of the mixture of Example 1 and the mixtures of Examples 2a and 2b changed from 60.7% by volume to 49.2% by volume (a reduction of about 19%) and 31.8% by volume (a reduction of about 48%), respectively, depending on the amount of BHET introduced into the monomer mixture. Example 2c, together with Example 2a, introduced the same type and amount of BHET (1.74 t / hour) into the monomer mixture, but it has been shown that it is possible to prepare a two-phase monomer mixture with a reduced solids content compared to the mixture without BHET (51.5% by volume compared to 60.7% by volume in Example 1). At the same time, it has also been shown that the amount of ethylene glycol supplied is reduced (only 1.39 t / hour in Example 2c compared to 1.65 t / hour in Example 2a). Therefore, the consumption of ethylene glycol starting material is reduced without impairing the quality of the two-phase mixture. This makes it possible to facilitate the transportation of the two-phase mixture to the polymerization step.

Claims

1. A method for producing a terephthalate polyester, comprising: the following steps: a) A preparation stage of an esterification feedstock, the preparation stage including at least one mixing section, the mixing section being supplied with at least one terephthalic acid feedstock and one diester monomer feedstock, the diester monomer feedstock including bis(2-hydroxyethyl) terephthalate (BHET) and being in liquid form, the mixing section being additionally supplied with a diol monomer feedstock, and the amounts of at least the terephthalic acid feedstock, the diester monomer feedstock, and the diol monomer feedstock introduced into the mixing section in the mixing are adjusted such that the ratio of the total number of moles of diol units of the formula -[C （ｎ＋１） H （２ｎ＋２） O ２ -(wherein n is an integer of 1 or more) introduced into the mixing section to the total number of moles of terephthalic acid units of the formula -[CO-(C ６ H ４ )-CO] is 1.0 to 1.3, and the mixing section is operated at a temperature of 100°C to 150°C and a pressure of 0.1 MPa or more, the preparation stage, Here, the diester monomer feedstock includes a fraction of a purified diester effluent obtained at the end of a depolymerization method of a polyester feedstock to be recycled, and the depolymerization method includes the following steps: i) A depolymerization step including at least one reaction section to which the polyester feedstock to be recycled and a glycol stream are fed to obtain a depolymerization reaction effluent; ii) A separation / purification step including a separation section for obtaining a glycol effluent and a purification section for obtaining a purified diester effluent; and iii) A recycling step of recycling at least a fraction of the purified diester effluent obtained in step ii) to step a); b) An esterification step of the esterification feedstock derived from step a), thereby producing at least one reaction effluent and one aqueous effluent, the esterification step including at least one reaction section and at least one separation section, the reaction section being operated at a temperature of 150°C to 400°C, a pressure of 0.05 to 1 MPa, and a residence time of 1 to 10 hours; c) A polycondensation step of the reaction effluent obtained in step b), thereby obtaining at least the terephthalate polyester and a diol effluent, the polycondensation step including at least one reaction section, the reaction section including at least one reactor in which polycondensation is carried out, the reactor being operated at a temperature of 250°C to 300°C, a pressure of 0.0004 to 0.01 MPa, and a residence time of 0.5 to 3 hours, and the reaction section also including at least one extraction of the diol effluent; d) A diol treatment step including a recovery section to which all or part of the diol effluent derived from step c) is at least fed to obtain a diol effluent to be treated, and a purification section of the diol effluent to be treated to obtain a purified diol stream. A manufacturing method comprising the above steps.

2. The manufacturing method according to claim 1, wherein the diol monomer feedstock contains at least 70 mol% of the diol monomer constituting the composition of the individual units of the terephthalate polyester.

3. The method for production according to claim 1 or 2, wherein the diol monomer feedstock contains at least 99.5 mol% of the diol monomer constituting the composition of each unit of the terephthalate polyester.

4. The preparation stage includes a conditioning section, the conditioning section being located upstream of the mixing section, and at least the diester monomer feedstock being supplied in solid form and operated at a temperature of 25°C to 250°C and a pressure of 0.1 MPa or more. The method for production according to any one of claims 1 to 3.

5. The method for production according to any one of claims 1 to 4, wherein the terephthalate polyester is polyethylene terephthalate.

6. The method for production according to any one of claims 1 to 5, wherein the diol monomer feedstock is at least partially a fraction of the stream of purified diol obtained in step d).

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