Bis (2-hydroxyethyl) terephthalate solids having specific crystalline forms

Abstract

The present invention relates to a solid material consisting essentially of BHET having a crystalline form with a specific X-ray diffraction pattern, to a process for the preparation thereof, to a composition comprising said material, and to the use of said composition for the preparation of polyesters.

Description

Technical Field

[0001] The present invention relates to a solid material mainly composed of bis(2-hydroxyethyl) terephthalate (BHET), which presents a new crystal form. This crystal form enables the advantageous obtaining of a needle-like morphology of the solid material, thus facilitating its drying. The present invention also relates to a composition comprising said solid material, and the use of this composition for the production of terephthalate polyesters, such as polyethylene terephthalate (PET). Background Art

[0002] Bis(2-hydroxyethyl) terephthalate (BHET) is a monomer of terephthalate polyesters, and in particular of polyethylene terephthalate (PET).

[0003] BHET can be obtained by the direct esterification of terephthalic acid with ethylene glycol or by the transesterification between dimethyl terephthalate and ethylene glycol, these methods conventionally corresponding to the first reaction stage of a conventional PET production process. BHET can also be obtained by the depolymerization of polyesters, especially polyethylene terephthalate (PET), in the presence of ethylene glycol. This is known as the chemical recycling of polyesters, especially PET, since polyester waste, especially PET waste, is chemically treated (depolymerized) to obtain monomeric compounds, which are then reused to produce polyesters again, especially PET, and more particularly r-PET.

[0004] For example, patent application FR 3 053 691 describes a method for the depolymerization of a polyester raw material containing in particular 0.1% to 10% by weight of pigments by glycolysis in the presence of ethylene glycol. The bis(2-hydroxyethyl) terephthalate (BHET) monomer effluent obtained after specific separation and purification stages can be fed to the polymerization stage to produce PET. Patent JP3715812 describes the production of purified BHET from PET, and the obtained BHET can be used as a starting material in a plastic production process.

[0005] Although they disclose the polymerization of monomeric products (especially BHET) resulting from the depolymerization of PET by glycolysis, the cited documents do not give any information on the quality of the intermediates resulting from the depolymerization of PET, nor on the difficulty of the purification stages (especially the washing and drying stages) of the BHET-based intermediates.

[0006] In fact, the drying of BHET crystals is known to be problematic. For example, as explained in patent US 3668235, the drying time of solid BHET is very long, which affects the quality of BHET, especially the tendency to discolor and crystal aggregation.

[0007] To facilitate drying and thus limit the degradation of the product, it is important to reduce the operating time of drying. The residual moisture level of the filter cake after leaving the filtration constitutes a good indicator of the ease of drying the filter cake, since drying will become easier as the amount of water to be removed decreases.

[0008] Techniques known to those skilled in the art for reducing the water content of a solid material cake are to use a centrifugal dryer for liquid / solid separation, which achieves a residual moisture level 2 to 3 times lower than that of simple filtration. The residual moisture level corresponds to the balance between capillary force and centrifugal force (see M. Robatel et al., Centrifugation: Généralités, Théories [Centrifugation: General Points and Theories], Techniques de l’Ingénieur, A5550V1, 1989, 10 - 17).

[0009] Patent application WO 2021 / 032826 shows that the moisture level of the BHET crystal cake produced by filtration is generally 20 - 50 wt%. Subsequently, this document proposed granulating the BHET crystals to facilitate the drying of the solid, relying on the porosity of the granules to promote the transfer of matter and heat.

[0010] In addition, it is known that the needle - like morphology of solid material crystals enables better performance in terms of filterability than other morphologies (such as the platelet morphology) (see D. Bourcier et al., "Influence of Particle Size and Shape Properties on Cake Resistance and Compressibility during Pressure Filtration", Chemical Engineering Science, 2016, 144, 176 - 187).

[0011] Patent JP 5189266 confirmed the influence of the needle - like morphology of BHET on the quality of BHET, and in particular on the residual solvent content of the solid BHET obtained after crystallization and solid / liquid separation. However, this document did not give information on the crystal form of the obtained BHET.

[0012] The paper by Miyake (A. Miyake, “Polymorphism of Bis-β-Hydroxyethyl Terephthalate”, Bulletin of the Chemical Society of Japan, 1957, 30(4), 361-363) discloses four crystal forms of BHET: the α crystal form (which appears to be the most stable) and the β, γ, and δ forms. However, the paper gives no indication of their macroscopic morphology and their properties (in particular, filterability and / or ease of drying). According to the paper by Alvarez-Castillo (A. Alvarez-Castillo et al., "Studies on the Crystallization of Polyethylene Terphthalate Oligomer", Journal of Materials Science Letters, 14, 1995, 139-141), it appears that the α crystal form of BHET can impart a needle-like morphology to BHET crystals.

[0013] The object of the present invention is high-quality BHET, and in particular BHET crystals having as low a moisture and / or residual solvent content as possible. Thus, surprisingly, the inventors have discovered a new crystal form of BHET which necessarily results in a needle-like morphology and thus improves the filterability and drying properties of BHET crystals. Summary of the Invention

[0014] The subject of the present invention is a solid material mainly composed of BHET, having a crystal form presenting the following X-ray diffraction pattern, the X-ray diffraction pattern having the following average value of 2θ and a relative intensity I greater than or equal to 5% rel of the average value:

[0015] Table 1

[0016] 2θ (°) <![CDATA[I rel > 10.85 vw 18.35 vw 19.17 vs 21.76 vw 29.19 w 29.62 vw 38.82 vw 40.34 vw 49.18 vw

[0017] where vs = very strong; s = strong; m = medium; mw = medium-weak; w = weak; vw = very weak. The relative intensity I rel is given with reference to a relative intensity scale, where the value of the strongest line of the X-ray diffraction pattern is assigned 100: vw < 15; 15 ≤ w < 30; 30 ≤ mw < 50; 50 ≤ m < 65; 65 ≤ s < 85; vs ≥ 85.

[0018] The advantages of the present invention lie in the fact that the specific crystal form is beneficial to the filterability and drying of BHET. This is because the solid material according to the present invention exhibits a reduced residual moisture level after filtration compared to other crystal forms and is thus easier to dry. In addition, the crystal form of the solid BHET material according to the present invention has a repetitive structure, which induces a needle-like morphology of the crystals, enabling better filterability and improved crystal washing.

[0019] In addition, another advantage of the present invention lies in the fact that the specific crystal form of BHET is stable, especially thermally stable.

[0020] Another advantage of the present invention lies in the source of the solid BHET material and the composition containing the solid BHET material, as it can be obtained both by directly synthesizing BHET from terephthalic acid or dimethyl terephthalate and ethylene glycol and can also advantageously originate from the plastic recycling cycles established in recent years by national and international organizations to combat plastic pollution. This is because the solid BHET material of the present invention and the composition containing the solid BHET material can be very advantageously obtained at the end of a process of depolymerizing polyesters (such as PET) by glycolysis in the presence of diols, which process includes a purification stage, especially a BHET crystallization stage. The BHET produced by these depolymerization processes is called r-BHET, and the PET prepared by polymerizing r-BHET is called r-PET (as opposed to virgin resin or PET produced by direct polymerization of fresh ethylene glycol and terephthalic acid). Thus, the present invention contributes to combating plastic pollution.

[0021] Therefore, the present invention also relates to the use of a composition containing a solid BHET material for the preparation of polyesters, preferably PET. Description of the Drawings

[0022] Figure 1 Image of solid A of Example 1 observed by optical microscopy.

[0023] Figure 2 Image of solid B of Example 1 observed by optical microscopy.

[0024] Figure 3 XRD pattern obtained for solid A of Example 1.

[0025] Figure 4 XRD pattern of solid B of Example 1.

[0026] Figure 5 XRD pattern of solid C of Example 1.

[0027] Figure 6 XRD pattern of solid D of Example 1. Detailed Description

[0028] According to the present invention, the terms "bis(2-hydroxyethyl) terephthalate" and "BHET" denote the same compound and are interchangeable. Similarly, the terms "bis(2-hydroxyethyl) isophthalate" and "BHEI" denote the same compound and are interchangeable. The term "2-(2-hydroxyethoxy)ethyl 2-hydroxyethyl terephthalate" and "deg-BHET" denote the same compound and are also interchangeable with each other.

[0029] According to the present invention, the term "polyester" denotes a thermoplastic polymer which is advantageously saturated (as opposed to thermosetting polyesters), having diol diesters as the basic repeating unit, and more particularly having at least alkylene terephthalate units. The polymer chain may also contain alkylene isophthalate and / or dialkyl terephthalate units. Thus, according to the present invention, the term "polyester" is used to denote poly(alkylene terephthalate) (or alkylene terephthalate polymer). The polyester according to the present invention may be, for example, poly(ethylene terephthalate) (or polyethylene terephthalate, PET), poly(butylene terephthalate) (or polybutylene terephthalate, PBT) or poly(propylene terephthalate) (or polypropylene terephthalate, PTT). The polyester according to the present invention may also contain other units in its main polymer chain, such as vinyl or polyol units, depending on the desired final properties of the polymer and on the target application. According to the present invention, the preferred polyester is polyethylene terephthalate or poly(ethylene terephthalate), also simply referred to as PET.

[0030] According to the present invention, the use of the terms "diol" and "glycol" makes no difference, and they correspond to compounds containing 2 hydroxy - OH groups, and preferably contain 2 to 12 carbon atoms, preferably 2 to 4 carbon atoms. The preferred diol is ethylene glycol, also known as monoethylene glycol or MEG.

[0031] A crystal is a solid in which atoms, ions or molecules are arranged in a three-dimensional space through a periodically repeating structure. The crystal form corresponds to the description of this repeating structure. Solids can exist in different crystal forms: this is called polymorphism. During the crystallization process, the formation of one form rather than another is directed by the choice of solvent and / or the way in which the crystallization process is carried out. Each form is typically characterized by X-ray diffraction (XRD). The set of peaks in the diffraction pattern obtained by XRD, in particular their positions and preferably their intensities, characterize the crystal form. In the case of BHET, four crystal forms are known: the α, β, γ and δ forms (see A. Miyake, "Polymorphism of Bis-β-Hydroxyethyl Terephthalate", Bulletin of the Chemical Society of Japan, 1957, 30(4), 361-363).

[0032] According to the present invention, the expressions “… to …” and “between … and …” are equivalent and mean that the limiting values of the interval are included within the range of the values described. If this is not the case and if the limiting values are not included within the said range, the present invention will provide such information.

[0033] Within the meaning of the present invention, the various parameter ranges of a given stage (such as a pressure range and a temperature range) can be used alone or in combination. For example, in the context of the present invention, a preferred pressure value range can be combined with a more preferred temperature value range.

[0034] Subsequently, specific embodiments of the present invention can be described. When this is technically feasible, these embodiments can be implemented alone or in combination with each other, without being limited by the combination.

[0035] According to the present invention, the pressure is the absolute pressure and is given in MPa.

[0036] Thus, the present invention relates to a solid material mainly composed of BHET, which preferably contains BHET in an amount of greater than or equal to 50% by weight, preferably greater than or equal to 70% by weight, preferably greater than or equal to 90% by weight, very preferably greater than or equal to 95% by weight, preferably in a manner greater than or equal to 98% by weight, and actually even greater than or equal to 99% by weight (the percentage is based on the total weight of the dry matter, that is, without moisture or other solvents such as ethylene glycol or methanol or glycol ethers used during the preparation of such solids and especially during the crystallization stage), which has a crystal form presenting an X-ray diffraction pattern (or XRD pattern), and the X-ray diffraction pattern has the following average value of 2θ and a relative intensity I of greater than or equal to 5% rel The average value of:

[0037] Table 1

[0038] 2θ (°) <![CDATA[I rel > 10.85 vw 18.35 vw 19.17 vs 21.76 vw 29.19 w 29.62 vw 38.82 vw 40.34 vw 49.18 vw

[0039] where vs = very strong; s = strong; m = medium; mw = medium - weak; w = weak; vw = very weak. The relative intensity I rel is given with reference to a relative intensity scale, where the value of the strongest line of the X - ray diffraction pattern is designated as 100: vw < 15; 15 ≤ w < 30; 30 ≤ mw < 50; 50 ≤ m < 65; 65 ≤ s < 85; vs ≥ 85.

[0040] In the following part of the present specification, the solid material mainly composed of BHET according to the present invention may also be referred to as BHET material or solid BHET.

[0041] According to a specific embodiment of the present invention, a solid material mainly composed of BHET having a crystalline form with the XRD pattern presented in Table 1 presents a single crystalline form. In other words, it only presents the crystalline form of the X - ray diffraction pattern having the average value of 2θ and the average value of relative intensity given in Table 1. Preferably, the BHET material having a single crystalline form with the XRD pattern presented in Table 1 does not have an amorphous form.

[0042] According to another specific embodiment of the present invention, the solid material is mainly composed of BHET, which presents a crystalline form having an X - ray diffraction pattern represented by the 2θ values and relative intensity values greater than or equal to 5% in Table 1, and another crystalline form of BHET preferably selected from the α - form, β - form, δ - form or γ - form of BHET and combinations of at least two of these crystalline forms. The XRD patterns of the α, β, δ and γ forms of BHET are as Figure 1 shown and were determined by the Miyake group (A. Miyake, “Polymorphism of Bis - β - Hydroxyethyl Terephthalate”, Bulletin of the Chemical Society of Japan, 1957, 30(4), 361 - 363). According to this specific embodiment of the present invention, the BHET material may also have an amorphous form. Preferably, the BHET material of this specific embodiment does not contain an amorphous form.

[0043] According to the present invention, X-ray diffraction (XRD) analysis of the BHET material makes it possible to confirm the presence of the BHET crystal form. According to the present invention, the X-ray diffraction pattern of the solid BHET material includes at least the lines listed in Table 1. Preferably, the X-ray diffraction pattern does not contain other lines with significant intensity other than the lines listed in Table 1 (that is, the intensity is greater than or equal to 5% of the intensity of the strongest line of the XRD pattern). For those skilled in the art, the basic feature on the XRD pattern is the position of the peaks (2θ value); the relative intensities given are usually used to provide information.

[0044] The X-ray diffraction pattern (or XRD pattern) is obtained by using the conventional powder method, using copper Kα 1 radiation and performing radiocrystallographic analysis with a diffractometer. The position of the diffraction peaks (or lines) is represented by the angle 2θ. The absolute error Δ(2θ) assigned to the 2θ measurement is generally accepted to be equal to ±0.1°. The relative intensity I hkl assigned to each d rel value is measured according to the height of the corresponding diffraction peak (or line). According to the present invention, the X-ray diffraction pattern of the solid material mainly containing BHET includes at least the lines given in Table 1.

[0045] Very advantageously, the solid material according to the present invention is in the form of needles.

[0046] The present invention also relates to a composition comprising the BHET material according to the present invention. Preferably, the composition comprising the BHET material according to the present invention is in solid form or liquid form (that is, a composition that is macroscopically in liquid form, such as a suspension or slurry of a composition in liquid form), and more particularly in solid form, slurry form or suspension form in which solid particles of the BHET material according to the present invention are suspended in a solvent. Therefore, the composition comprising the BHET material according to the present invention can be in solid or liquid (suspension or slurry) form and additionally contains a solvent, which is preferably selected from aqueous solvents, especially water, alcohol solvents, such as methanol or diols, such as ethylene glycol, or solvents composed of glycol mono- or diether; preferably, the solvent is water.

[0047] According to a specific embodiment of the present invention, the composition comprising the BHET material according to the present invention is a solid composition and additionally contains a solvent, and the content of the solvent is preferably less than or equal to 20% by weight, preferably less than or equal to 15% by weight, preferably less than or equal to 10.0% by weight, and more particularly less than or equal to 5.0% by weight, and actually even less than or equal to 1.0% by weight.

[0048] According to another specific embodiment of the present invention, the composition comprising the BHET material according to the present invention is a composition in liquid form, more particularly a composition of the slurry or suspension type, which comprises a solvent and solid particles of the BHET material according to the present invention. The solid material according to the present invention is preferably from 1% to 75% by weight, preferably from 5% to 45% by weight, and preferably from 15% to 35% by weight, based on the total weight of the composition.

[0049] Advantageously, the composition according to the present invention can be obtained by a process for treating a polyester raw material (preferably comprising PET), preferably obtained by a process which comprises a depolymerization stage of the polyester raw material (especially the PET contained therein), and preferably followed by at least one separation-purification stage. The depolymerization stage can be carried out by glycolysis in the presence of ethylene glycol or by methanolysis in the presence of methanol. In the latter case, an additional transesterification stage is required in the presence of ethylene glycol. Preferably, the depolymerization stage is carried out by glycolysis in the presence of ethylene glycol. The process for treating a polyester raw material (preferably comprising PET) can, for example, comprise a purification stage of the effluent obtained by depolymerization of the polyester raw material, especially a stage of crystallizing BHET from water, from ethylene glycol or from glycol monoethers or diethers, preferably from water.

[0050] According to a specific embodiment of the present invention, the composition according to the present invention can additionally comprise bis(2-hydroxyethyl) isophthalate (BHEI), preferably in a molar amount such that the molar ratio of the number of moles of BHEI present in the composition to the combined number of moles of BHET and BHEI (BHEI / [BHET + BHEI]) is less than or equal to 10.0 mol%, preferably less than or equal to 5.0 mol%, preferably less than or equal to 1.0 mol%, and preferably less than or equal to 0.5 mol%. In addition, if the composition comprises BHEI, the (BHEI / [BHET + BHEI]) molar ratio is greater than or equal to 0.001 mol%, preferably greater than or equal to 0.01 mol%, preferably greater than or equal to 0.05 mol%.

[0051] According to another specific embodiment of the invention, the BHET-based composition according to the invention may additionally comprise 2-(2-hydroxyethoxy)ethyl 2-hydroxyethyl terephthalate (deg-BHET), preferably in a molar amount such that the molar ratio of the number of moles of deg-BHET present in the composition relative to the number of moles of the combination of BHET and deg-BHET (deg-BHET / [BHET + deg-BHET]) is less than or equal to 10.0 mol%, preferably less than or equal to 5.0 mol%, preferably less than or equal to 1.0 mol%. Additionally, if the composition comprises deg-BHET, the (deg-BHET / [BHET + deg-BHET]) molar ratio is greater than or equal to 0.001 mol%, preferably greater than or equal to 0.05 mol%, preferably greater than or equal to 0.10 mol%, and preferably greater than or equal to 0.50 mol% in a preferred manner.

[0052] It may be found that one or the other or both of these specific embodiments of the invention are cases of products obtained at the end of a polyester raw material treatment process comprising a depolymerization stage.

[0053] Therefore, the invention relates to a method for preparing a composition according to the invention, the method comprising:

[0054] - a depolymerization stage of a polyester raw material, said polyester raw material preferably comprising PET, by depolymerization by glycolysis in the presence of ethylene glycol or by methanolysis in the presence of methanol, preferably by depolymerization by glycolysis in the presence of ethylene glycol; and then

[0055] - at least one purification stage, preferably comprising a stage of crystallization from water, from ethylene glycol or from a glycol monoether or diether, preferably from water.

[0056] Very advantageously, the preparation method comprises the depolymerization method described in patent FR 3 053 691, consists of the depolymerization method described in patent FR 3 053 691, the decolorization stage of which comprises an adsorption stage and may additionally comprise a purification stage by crystallization of BHET from water, from ethylene glycol or from a glycol monoether or diether, preferably from water.

[0057] The BHET material according to the invention has a specific crystal form, the XRD pattern of which is shown in Table 1, advantageously such that the composition according to the invention containing this BHET material can be filtered and dried, and the composition is obtained at the end of such a preparation method. With the facilitation of these filtration and drying stages, the solid according to the invention obtained at the end of such stages advantageously contains a reduced residual solvent content, in particular a reduced residual moisture content, which makes it possible to use it in the polymerization stage without incurring high additional energy-consuming treatments.

[0058] The composition according to the invention comprising BHET material very advantageously makes it possible to obtain, after polymerization, a polyester, preferably PET, and in particular r-PET, which exhibits a light coloration, in fact even a colorless coloration.

[0059] Therefore, the present invention also relates to the use of a composition according to the invention, which composition is optionally mixed with at least one dicarboxylic acid and / or at least one diol to prepare a polyester, preferably PET. The dicarboxylic acid is preferably selected from terephthalic acid and isophthalic acid, and the diol is preferably selected from ethylene glycol, diethylene glycol, butanediol, cyclohexanedimethanol, neopentyl glycol or a mixture thereof, and the preferred diol is ethylene glycol.

[0060] Therefore, the present invention also relates to a method for producing a polyester, which method comprises the following stages, preferably consists of the following stages:

[0061] a) A stage of esterifying the raw materials, said raw materials comprising at least the composition according to the invention, and optionally comprising at least one dicarboxylic acid and / or at least one diol, the dicarboxylic acid being preferably selected from terephthalic acid and isophthalic acid, the diol being preferably selected from ethylene glycol, diethylene glycol, butanediol, cyclohexanedimethanol, neopentyl glycol or a mixture thereof, and the preferred diol being ethylene glycol, and then

[0062] b) A polycondensation stage.

[0063] Advantageously, stage a) is carried out at a temperature of 150 to 350 °C, preferably 200 to 300 °C, and in a preferred manner at 250 to 285 °C. Preferably, stage a) is carried out at a pressure of 0.05 to 1.0 MPa, preferably 0.1 to 0.5 MPa. Very advantageously, stage a) is carried out with a residence time of 0.5 to 10.0 hours, preferably 1.0 to 6.0 hours, the residence time being defined herein as the ratio of the reaction volume of the reactor used in stage a) to the volumetric flow rate of the liquid stream leaving said reactor.

[0064] A polymerization catalyst can optionally be introduced in step a), which polymerization catalyst is preferably based on antimony, titanium, germanium, aluminum, zinc acetate, calcium acetate and / or manganese acetate.

[0065] The reaction carried out in step a) generates a diol compound, which diol compound is advantageously separated during stage a), for example by extraction, distillation and / or adsorption. Water can also be formed. The water formed then itself is also advantageously separated during stage a).

[0066] Advantageously, the process for producing a polyester according to the invention comprises a polycondensation stage b) at the end of stage a). Stage b) can advantageously employ one or more, preferably one or two, polycondensation sub-stages, such as at least one, preferably one, liquid-phase or melt-phase polycondensation sub-stage, optionally followed by at least one, preferably one, solid-phase polycondensation sub-stage.

[0067] Very advantageously, the polycondensation stage b) employs at least one polymerization zone, preferably one or two polymerization zones, which advantageously operate in the liquid phase or in the melt phase, said polymerization zone at a temperature higher than the temperature of stage a), preferably at a temperature of 190 to 400 °C, preferably 220 to 350 °C, in a preferred manner at a temperature of 265 to 300 °C, preferably at a pressure of 0.01 to 100.00 kPa, preferably 0.05 to 10.00 kPa, and in a preferred manner with a residence time of 0.1 to 5.0 hours, preferably 0.5 to 4 hours, preferably 1.0 to 3.0 hours. The residence time in the polymerization zone of stage b) is defined as the ratio of the reaction volume of the reactor employed in the polymerization zone to the volumetric flow rate of the liquid stream containing the produced polyester leaving the reactor.

[0068] The polymerization reaction can optionally be continued in a solid-phase polycondensation zone located downstream of the polymerization zone and operating in the solid phase, and this polymerization reaction is preferably carried out at a temperature (in particular the product temperature) of 190 to 250 °C, preferably 200 to 230 °C, depending on whether the operation is carried out in continuous mode or in batch mode. The polycondensation zone can preferably operate under an inert atmosphere, for example under a nitrogen stream, at a pressure close to atmospheric pressure or under vacuum (in particular at a pressure of 0.01 to 100 kPa, in fact even at a pressure of 0.01 to 10 kPa). The residence time (defined as the time during which the product is subjected to polycondensation conditions in the polycondensation zone) is 5 to 20 hours, preferably 10 to 16 hours. Advantageously, a crystallization zone can be provided in front of the polycondensation zone, so the crystallization zone is located between the polymerization zone and the polycondensation zone, in which the polyester formed at the end of the polymerization zone advantageously crystallizes, and said crystallization zone can operate at a temperature of preferably 110 to 210 °C and a residence time of preferably 0.5 to 6 hours (defined as the time during which the product is subjected to crystallization conditions in the zone).

[0069] Stage b) is preferably carried out in the presence of a polymerization catalyst, in particular a polymerization catalyst based on antimony, titanium, germanium, aluminum, zinc acetate, calcium acetate and / or manganese acetate.

[0070] Additives can be introduced during the polycondensation stage b). Additives optionally introduced in stage b) can be, for example: reagents for suppressing side etherification reactions, such as, for example, amines (n-butylamine, diisopropylamine or triethylamine), sodium hydroxide or organic hydroxides or lithium carbonate, stabilizers such as phosphites or phosphates, and polyamide-type compounds for reducing the amount of degradation products (such as acetaldehyde).

[0071] The following drawings and examples are used to illustrate the present invention without limiting its scope.

[0072] Examples

[0073] Example 1: Solids

[0074] At the end of the process of depolymerizing PET waste by glycolysis and purifying it by crystallization from water (temperature gradually decreasing from 60 °C to 20 °C), two solids, solid A and solid B, are obtained and recovered by filtration. The recovered solids A and B contain at least 98.5 wt% of BHET based on their dry solid weight. Subsequently, a part of solid B is dried in an oven at 30 °C for 15 hours to obtain solid C. Subsequently, a part of solid C is placed at 60 °C for 15 hours to obtain solid D.

[0075] Solids A and B are observed by optical microscopy. Figure 1 And Figure 2 Photographs of these observations of solids A and B are shown in

[0076] Solid A has a flake-like morphology ( Figure 1 ).

[0077] Solid B has a needle-like morphology ( Figure 2 ).

[0078] The XRD patterns of solids A, B, C, and D are determined by radiocrystallographic analysis using a diffractometer with the conventional powder method using copper Kα 1 radiation. The position of the diffraction peaks (or lines) is represented by the angle 2θ, measured with an absolute error Δ(2θ) equal to ±0.1°. The relative intensity I rel is measured by the height of the corresponding diffraction peak (or line). The XRD patterns of solids A, B, C, and D are shown in Figure 3 , 4 , 5, and 6, respectively, and presented in Table 2 below.

[0079] Table 2

[0080] Solid A Solid B Solid C Solid D 2θ (°) <![CDATA[I rel > 2θ (°) <![CDATA[I rel > 2θ (°) <![CDATA[I rel > 2θ (°) <![CDATA[I rel > 6.65 vw 10.80 w 10.87 vw 10.90 w 6.92 vs 11.13 vw 11.20 vw 13.87 vw 14.31 vw 23.37 vw 18.29 vw 18.39 vw 18.39 vw 35.16 vw 18.55 vw 18.62 vw 19.12 vs 19.19 vs 19.19 vs 21.73 vw 21.79 vw 21.79 vw 29.15 w 29.21 w 29.21 s 29.55 vw 29.65 vw 29.65 vw 38.77 vw 38.84 vw 38.84 vw 40.28 vw 40.38 vw 40.38 vw 49.13 vw 49.20 vw 49.20 vw

[0081] where vs = very strong; s = strong; m = medium; mw = medium-weak; w = weak; vw = very weak. Relative intensity I rel is given with reference to a relative intensity scale in which the value of the strongest line of the X-ray diffraction pattern is assigned a value of 100: vw < 15; 15 ≤ w < 30; 30 ≤ mw < 50; 50 ≤ m < 65; 65 ≤ s < 85; vs ≥ 85.

[0082] Solid A corresponds to the α form.

[0083] Solids B, C and D correspond to the crystalline forms according to the invention. It can be seen from the XRD patterns that the crystalline forms according to the invention are stable since the XRD patterns of solids C (drying solid for 15 h at 30 °C) and D (drying solid for 15 h at 30 °C and then drying solid for 15 h at 60 °C) do not change or only change slightly relative to solid B.

[0084] Example 2: Electrospinning of solid E (not according to the invention) and solid F (according to the invention)

[0085] Solids E and F were obtained by crystallizing BHET solutions in water by gradually reducing the temperature from 60 °C to 20 °C over 4 h and 6 h, respectively, and solids E and F were recovered after filtration, containing at least 98.5 wt% of BHET relative to their dry solid weight. They were observed under an optical microscope and their XRD patterns were determined according to the same method as described in detail in Example 1.

[0086] Solid E has a flake-like morphology and exhibits the α crystallographic form.

[0087] Solid F has a needle-like morphology and exhibits the crystalline form according to the invention.

[0088] Solid E and F were each subjected to washing with water such that each mixture was a suspension of 20 wt% solid in 80 wt% water and then solid-liquid separation was carried out by electrospinning at 20 °C.

[0089] The residual water content of each solid after washing was determined by the weight loss of the solid after drying in an oven at 40 °C under vacuum for 15 h.

[0090] The results obtained for the two solids E and F are presented in Table 3.

[0091] Table 3

[0092] Solid E Solid F BHET Content (%) 98.5 98.5 Crystal Form α According to the present invention Residual Moisture Content after Centrifugal Spinning (%) 26 10

[0093] The results show that the solid F having the crystal form according to the present invention and presenting a needle form enables a residual moisture content (10%) to be achieved, which is lower than the residual moisture content achieved by the solid E having an α crystal form and presenting a flake form. Thus, compared with the solid F, the solid F will be easier to dry because less water needs to be removed.

Claims

1. A solid material mainly composed of BHET, having a crystalline form presenting the following X-ray diffraction pattern, wherein the X-ray diffraction pattern has the following average value of 2θ and a relative intensity I greater than or equal to 5% rel average value of: Table 1 where vs = very strong; s = strong; m = medium; mw = medium-weak; w = weak; vw = very weak. Relative intensity I rel is given with reference to a relative intensity scale, where the value of the strongest line in the X-ray diffraction pattern is assigned 100: vw < 15; 15 ≤ w < 30; 30 ≤ mw < 50; 50 ≤ m < 65; 65 ≤ s < 85; vs ≥ 85.

2. The material according to claim 1, which presents a single crystal form.

3. The material according to claim 1, which has a crystal form presenting an X-ray diffraction pattern represented by the 2θ values and relative intensity values of Table 1 and another crystal form, said another crystal form being preferably selected from the α form, β form, δ form or γ form of BHET and combinations of at least two of these crystal forms.

4. The material according to any one of the preceding claims, which comprises BHET having said crystal form, in an amount greater than or equal to 90% by weight, preferably greater than or equal to 95% by weight, and preferably in a preferred manner greater than or equal to 98% by weight, said percentage being given relative to the total weight of the dry material.

5. The material according to any one of the preceding claims, which is in the form of needles.

6. A solid or liquid composition comprising the material according to any one of the preceding claims.

7. The composition according to claim 6, which additionally comprises a solvent, preferably an aqueous solvent, an alcohol solvent such as methanol, or a diol, or a diol monoether or diether, and the preferred solvent is water.

8. The solid composition according to claim 6 or 7, which additionally comprises a solvent, and preferably its content is less than or equal to 20% by weight, preferably less than or equal to 15% by weight, based on weight.

9. The composition according to any one of claims 6 to 8, which can be obtained by a method of treating a polyester raw material, said polyester raw material preferably comprising PET, said method comprising a stage of depolymerization by glycolysis in the presence of ethylene glycol, and preferably followed by at least one purification and / or separation stage, such as a stage comprising crystallization of BHET, especially crystallization of BHET from water.

10. A method for preparing the composition according to any one of claims 6 to 9, which comprises: - a stage of depolymerization of a polyester raw material, said polyester raw material preferably comprising PET, using depolymerization by glycolysis in the presence of ethylene glycol or depolymerization by methanolysis in the presence of methanol, preferably depolymerization by glycolysis in the presence of ethylene glycol; and then - at least one purification stage, preferably comprising a stage of crystallization from water, from ethylene glycol or from a diol monoether or diether, preferably from water.

11. Use of the composition according to any one of claims 6 to 9 for the preparation of a polyester, preferably PET.

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