BIS(2-HYDROXYETHYL) TEREPHTHALATE HAVING LOW NITROGEN CONTENT

Abstract

The invention relates to a composition comprising mainly BHET and having a nitrogen content of less than or equal to 10 ppm by weight, the nitrogen content being determined according to a chemiluminescence method, with an ozone flow at 35 cm3 / min, after oxidative combustion of a sample in liquid form, prepared by dilution of the composition in tetrahydrofuran, at a temperature of 1050-1100°C and in the presence of an oxidizing mixture composed of oxygen and helium, and using a calibration curve carried out using a diphenylamine standard diluted in toluene.

Description

Title of the invention: BIS(2-HYDROXYETHYL) TEREPHTHALATE HAVING A LOW NITROGEN CONTENT Technical field

[0001] The invention relates to a composition, in particular resulting from a process for depolymerizing a polyester, more particularly from a process for depolymerizing PET, comprising mainly bis(2-hydroxyethyl) terephthalate (BHET) and having a low nitrogen content, in particular less than or equal to 10 ppm by weight, said content being measured by a chemiluminescence method, said composition making it possible to produce a polyester, more particularly an r-PET or recycled PET, having little or no coloring. The invention also relates to the use of said composition for producing a polyester and a process for producing a colorless polyester. Prior art

[0002] The chemical recycling of polyester, in particular polyethylene terephthalate (PET), has been the subject of numerous studies aimed at decomposing the polyester, recovered in the form of waste, into monomers which can then be used as feedstock for a polymerization process. The polymerization process, in particular of products resulting from the depolymerization of polyester, such as diol, diacid or diester monomers or even oligomers, to obtain PET has also been the subject of numerous studies.

[0003] For example, US patent 4,001,187 discloses processes for producing PET, comprising a step of continuously feeding ethylene glycol and terephthalic acid into the esterification medium comprising bis(2-hydroxyethyl) terephthalate (BHET). US 2019 / 0106567 and US2020031992 disclose processes for preparing flame-retardant and dyed polyesters, respectively, by esterification of a bis-hydroxy alkyl terephthalate monomer with diacid mixtures followed by polycondensation, the diacid mixtures comprising an aromatic dicarboxylic acid, preferably terephthalic acid, and respectively a carboxy-phosphinic acid and a dyed aromatic dicarboxylic acid containing a sulfonate group, for example sulfoterephthalic acid.Patent application US 2018 / 0340041 proposes a process for producing a polyester by polymerization, in two reaction phases, of a mixture comprising a first monomer terephthalate diol, in the majority in the mixture, and a second monomer consisting of 2-(2-hydroxyethoxy) ethyl 2-hydroxyethyl terephthalate. (BHET-deg), a minority in the mixture, the first esterification phase being carried out at a moderate temperature.

[0004] In parallel, document MX 2007 / 004429 discloses the production of a polyester, comprising the depolymerization by glycolysis of PET flakes 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 step is filtered on a frit to retain particles of at least 25 μm before being introduced into the polymerization reactor. Patent application WO 2017 / 006217 discloses the process for preparing a modified polyethylene terephthalate glycol (r-PETG) comprising a step of depolymerization of a PET in the presence of a mixture of monoethylene glycol (MEG) and neopentyl glycol, followed directly by a step of polymerization of the reaction effluent.Patent application FR 3053691 describes a process for depolymerizing a polyester filler comprising in particular from 0.1 to 10% by weight of pigments, by glycolysis in the presence of ethylene glycol. An effluent of bis-(2-hydroxyethyl) terephthalate (BHET) monomer, obtained after specific separation and purification steps, can feed a polymerization step to produce PET. Patent JP3715812 describes the production of refined BHET from PET, the BHET obtained being able to be used as a raw material in a process for producing plastic products. Patent EP 1 120 394 discloses the possible use of high-purity bis-(2-hydroxyethyl) terephthalate (BHET) as a raw material for the production of a polyester, the BHET being obtained by depolymerization of a polyester.

[0005] Although they disclose the polymerization of monomeric products, in particular BHET, resulting from the depolymerization of PET by glycolysis, the cited documents do not, however, provide any information on the quality of the intermediate products resulting from the depolymerization of PET, to enable an r-PET (i.e. a recycled PET and more particularly obtained after chemical recycling of polyester materials) of good quality and in particular little colored, or even colorless, to be obtained.

[0006] However, depending on the intended applications, several types of additives can be introduced into the final polyester. These include organic molecules comprising one or more nitrogen atoms, such as the light stabilizers described by Li et al. (Bo Li, Study of the Migration of Stabilizer and Plasticizer from Polyethylene Terephthalate into Food Simulants, Journal of Chromatography Science, 2016, Vol. 54, No. 6, 939-951), chain extenders or flame retardants (Swoboda Benjamin Swoboda. Improvement of the fire behavior of recycled PET and PET / PC alloys. Chemistry of Materials. University doctoral thesis. Montpellier: University of Montpellier II, 2007, 280 p.), anthranilamide scavenger of acetaldehyde as described in patent US6274212. Furthermore, in order to improve the oxygen barrier properties, the polyester used in the manufacture of food containers can be combined with other polymers such as Nylon-MXD6, the generic name given to a range of crystalline polyamides. This combination also introduces the presence of molecules containing nitrogen atoms.

[0007] It is known that additives introduced into polymer formulations depending on the intended applications can be detrimental and influence the type of recycling to be considered for the recycling of plastic materials. Indeed, these additives can influence the mechanical properties of recycled polymers, preventing mechanical recycling, or even influence the coloring of polymers, in particular polyesters recycled chemically, in particular by depolymerization then repolymerization of the monomers obtained.

[0008] The color of the polyester obtained can be characterized according to a colorimetric method as described in ASTM D6290 2019. The measurements are expressed in the CIE L*a*b* reference system. The parameter L* represents the lightness (or luminance) which increases as it approaches 100. The values ​​of the parameter a* correspond to a color ranging from green (negative values) to red (positive values). Finally, the values ​​of the parameter b* correspond to a color varying from blue (negative values) to yellow (positive values). US patent 8,431,202 discloses that the desirable color for a polyester is generally indicated by an a* coordinate value preferably ranging from minus 4.4 (-4.4) to plus 1.6 (+1.6) and a b* coordinate value preferably ranging from minus 8.6 (-8.6) to plus 10.2 (+10.2).

[0009] Thus, the inventors of the applicant have discovered that the quality of BHET, monomer of PET and in particular the quality of r-BHET which is derived from the depolymerization of a PET filler, and more particularly its nitrogen content, strongly influences the quality, in particular the coloring, of the r-PET prepared. Summary of the invention

[0010] The subject of the invention is a composition comprising mainly BHET and having a nitrogen content of less than or equal to 10 ppm by weight, the nitrogen content being determined according to a chemiluminescence method, with an ozone flow at 35 cm3 / min, after oxidative combustion of a sample in liquid form, prepared by dilution of the composition in tetrahydrofuran, at a temperature of 1050-1100°C and in the presence of an oxidizing mixture composed of oxygen and helium, and using a calibration curve carried out using a diphenylamine standard diluted in toluene.

[0011] The advantage of the present invention lies in the fact that the BHET-based composition makes it possible to obtain, after polymerization, a polyester, in particular a PET, having a low coloration or even being colorless. The clear polyester thus obtained can be used in very varied applications, applications in which the polyester-based material will be very colorful for which the polyester will be integrated into very colorful formulations, and not only gray, up to applications such as bottles for example for which the material can be transparent colorless or slightly azure.

[0012] Another advantage of the present invention lies in the origin of the BHET-based composition which advantageously comes from the plastic recycling circuits, set up in recent years by national and international organizations to combat plastic pollution. Indeed, the BHET-based composition of the present invention is very advantageously obtained at the end of depolymerization processes by glycolysis of polyester such as PET, in the presence of diol. The BHET resulting from these depolymerization processes is then called r-BHET and the PET prepared by polymerization from r-BHET is called r-PET (as opposed to PET or virgin resin resulting from the direct polymerization of terephthalic acid and fresh ethylene glycol). Thus, the present invention contributes to the fight against plastic pollution.

[0013] The present invention therefore also relates to the use of said composition for preparing a polyester, preferably a PET. It also relates to a process for producing a polyester, comprising: a) a step of esterification of a filler comprising at least the composition according to one of claims 1 to 4, and optionally at least one dicarboxylic acid, preferably chosen from terephthalic acid and isophthalic acid, and / or at least one diol, preferably chosen from ethylene glycol, diethylene glycol, butylene glycol, cyclohexane dimethanol, neopentyl glycol or mixtures thereof, the preferred diol being ethylene glycol; then b) a polycondensation step. Description of the embodiments

[0014] According to the invention, the terms "bis(2-hydroxyethyl) terephthalate" and "BHET" designate the same compound and are interchangeable. Similarly, the terms "bis(2-hydroxyethyl) isophthalate" and "BHEI" designate the same compound and are interchangeable. The terms "2-(2-hydroxyethoxy) ethyl 2-hydroxyethyl terephthalate" and "BHET-deg" designate the same compound and are also interchangeable.

[0015] According to the invention, the term "polyester" designates a thermoplastic polymer, advantageously saturated (as opposed to thermosetting polyesters) having as elementary repeating units diol diesters, and more particularly at least alkylene terephthalate units. The polymer chain can also comprise alkylene isophthalate and / or dialkyl terephthalate units. Thus, according to the invention, the term "polyester" is used to designate a poly(alkylene terephthalate) (or polyalkylene terephthalate, according to anglicized terminology). The polyester according to the invention may, for example, be poly(ethylene terephthalate) (or polyethylene terephthalate, PET), poly(butylene terephthalate) (or polybutylene terephthalate, PBT), poly(trimethylene terephthalate) (or polytrimethylene terephthalate, PTT). The polyester according to the invention may also comprise other units on its main polymer chain, such as vinyl or polyol units, depending on the final properties desired for the polymer and depending on the intended applications. According to the invention, the preferred polyester is polyethylene terephthalate or poly(ethylene terephthalate), also simply called PET.

[0016] According to the invention, the terms "diol" and "glycol" are used interchangeably and correspond to compounds comprising 2 hydroxyl groups -OH and preferably comprising between 2 and 12 carbon atoms, preferentially between 2 and 4 carbon atoms. The preferred diol is ethylene glycol, also called monoethylene glycol or MEG.

[0017] According to the present invention, the expressions "between ... and ..." and "between .... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this is not the case and the limit values ​​are not included in the range described, such precision will be provided by the present invention.

[0018] In the sense of the present invention, the different parameter ranges for a given step such as pressure ranges and temperature ranges can be used alone or in combination. For example, in the sense of the present invention, a range of preferred pressure values ​​can be combined with a range of more preferred temperature values.

[0019] In the following, particular embodiments of the invention may be described. They may be implemented separately or combined with each other, without limitation of combinations when this is technically feasible.

[0020] According to the invention, the pressures are absolute pressures and are given in MPa.

[0021] The invention thus relates to a composition comprising mainly BHET, in particular at least 90% by weight of BHET, preferably at least 95% by weight of BHET and more preferably at least 98% by weight of BHET, and having a nitrogen content of less than or equal to 10 ppm by weight, preferably less than or equal to 5 ppm by weight and very advantageously less than 3 ppm by weight. The nitrogen content is advantageously determined according to a chemiluminescence method, in particular using a PAC-Antek Multitek VNS type device, in particular equipped with a vertical furnace, syringe injection and a CTC type sample changer. Analytics PAL System 748. More particularly, the nitrogen content is determined by chemiluminescence with an ozone flow preferably at 35 cm3 / min, after oxidative combustion of a sample in liquid form, advantageously prepared by dilution of the composition in tetrahydrofuran (THF) in particular according to a 10-fold dilution, preferably 10 μl or 20 μl of said sample in liquid form advantageously contained in a quartz tube, at a temperature of 1050-1100°C and in the presence of an oxidizing mixture composed of oxygen and helium (preferably under an oxygen flow at 450 cm3 / min and helium at 130 cm3 / min), and using a calibration curve carried out using a diphenylamine standard diluted in toluene.

[0022] More generally, the principle of chemiluminescence analysis lies in the decomposition of a sample comprising nitrogen, in liquid form, heated to a high temperature, for example 1050-1100°C. Said sample undergoes oxidative combustion in the presence of oxygen. The products resulting from this combustion are CO2, H2O, nitrogen oxides NOx, SO2. The nitrogen compounds obtained are then detected by chemiluminescence, based on the fact that NO reacts with ozone to produce nitrogen dioxide in an excited state (NO2*), according to the reactions:

[0023] NO + O3 NO2* + O2, and NOs* ■ ■ -NOî + -photon-^jg)

[0024] The light emitted by the return of NO2* to its ground state is detected by a photomultiplier. The electrical signal obtained is a function of the quantity of nitrogen contained in the sample tested. The intensity of the signals obtained is related to the nitrogen concentration using a preliminary calibration curve carried out using a standard, such as diphenylamine, diluted in a solvent, such as toluene, to obtain different total nitrogen contents.

[0025] Preferably, the composition based on bis(2-hydroxyethyl) terephthalate (BHET) is obtained by a process for depolymerizing a polyester filler, preferably comprising PET. For example, the composition based on BHET is the product obtained at the end of the depolymerization process described in patent FR 3053691. Advantageously, the polyester filler of the depolymerization processes in question comes from the collection and sorting channels which are themselves integrated into a recycling system, in particular for plastics. Said polyester filler therefore comprises in particular waste and / or post-consumer products, based on polyester, in particular PET. The product obtained at the end of the processes for treating such polyester fillers which comprise a depolymerization step, preferably by glycolysis in the presence of diol, preferably ethylene glycol, or by methanolysis in the presence of methanol, typically comprises mainly BHET and may be called r-BHET. Very advantageously, the composition according to the invention is one of these products, obtained at the end of the processes for treating such polyester fillers, preferably comprising PET, which comprise a depolymerization step, preferably by glycolysis in the presence of diol, preferably ethylene glycol or by methanolysis in the presence of methanol, preferably by glycolysis in the presence of ethylene glycol.

[0026] According to a particular embodiment of the invention, the BHET-based composition according to the invention may further comprise bis(2-hydroxyethyl) isophthalate (BHEI), preferably in a molar amount such that the molar ratio (BHEI / [BHET + BHEI]) between the number of moles of BHEI relative to the number of moles of the BHET and BHEI combination present in the composition is less than or equal to 10.0 mol%, preferably less than or equal to 5.0 mol%, preferentially 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 molar ratio (BHEI / [BHET + BHEI]) is greater than or equal to 0.001 mol%, preferably greater than or equal to 0.01 mol%, preferentially greater than or equal to 0.05 mol%.

[0027] According to another particular embodiment of the invention, the BHET-based composition according to the invention may further comprise 2-(2-hydroxyethoxy) ethyl 2-hydroxyethyl terephthalate (BHET-deg), preferably in a molar amount such that the molar ratio (BHET-deg / [BHET + BHET-deg]) between the number of moles of BHET-deg relative to the number of moles of the BHET and BHET-deg combination present in the composition is less than or equal to 10.0 mol%, preferably less than or equal to 5.0 mol%, preferentially less than or equal to 1.0 mol%. In addition, if the composition comprises BHET-deg, the molar ratio (BHET-deg / [BHET + BHET-deg]) 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%, more preferably greater than or equal to 0.50 mol%.

[0028] One or the other or these two particular embodiments of the invention may possibly be the case(s) of products obtained at the end of the processes for treating polyester fillers, which comprise a depolymerization step preferably by glycolysis in the presence of diol, preferably ethylene glycol or by methanolysis in the presence of methanol, preferably by glycolysis in the presence of ethylene glycol.

[0029] A composition according to the invention thus very advantageously makes it possible to obtain, after polymerization, a polyester, preferably a PET, and in particular an r-PET having a light or even colorless coloring.

[0030] Thus the invention also relates to the use of the composition according to the invention, optionally mixed with at least one dicarboxylic acid, preferably chosen from terephthalic acid and isophthalic acid, and / or at least one diol, preferably chosen from ethylene glycol, diethylene glycol, butylene glycol, cyclohexane dimethanol, neopentyl glycol or mixtures thereof, the preferred diol being ethylene glycol, to prepare a polyester, preferably a PET.

[0031] The invention also relates to a process for producing a polyester, comprising, preferably consisting of:

[0032] a) a step of esterification of a filler comprising at least the composition according to the invention, and optionally at least one dicarboxylic acid, preferably chosen from terephthalic acid and isophthalic acid, and / or at least one diol, preferably chosen from ethylene glycol, diethylene glycol, butylene glycol, cyclohexane dimethanol, neopentyl glycol or mixtures thereof, the preferred diol being ethylene glycol; then

[0033] b) a polycondensation step.

[0034] Advantageously, step a) is carried out at a temperature between 150 and 350°C, preferably between 200 and 300°C, more preferably between 250 and 285°C. Preferably, step a) is carried out at a pressure between 0.05 and 1.0 MPa, preferably between 0.1 and 0.5 MPa. Very advantageously, step a) is carried out with a residence time between 0.5 and 10.0 hours, preferably between 1.0 and 6.0 hours, the residence time being defined here as the ratio of the reaction volume of a reactor carried out in step a) to the volume flow rate of the liquid stream leaving said reactor.

[0035] A polymerization catalyst, preferably based on antimony, titanium, germanium, aluminum, zinc acetate, calcium acetate and / or manganese acetate, may optionally be introduced in step a).

[0036] The reaction carried out in step a) generates a diol compound which is advantageously separated during step a), for example by withdrawal, distillation and / or adsorption. Water may also be formed. The water then formed is also advantageously separated during step a).

[0037] Advantageously, the process for producing a polyester according to the invention comprises a step b) of polycondensation at the end of step a). Step b) may advantageously implement one or more, preferably one or two, sub-steps of polycondensation, for example at least, preferably one, sub-step of polycondensation in liquid or molten phase, optionally followed by at least one, preferably one, sub-step of polycondensation in solid phase.

[0038] Very advantageously, the polycondensation step b) uses at least one polymerization section, preferably one or two polymerization sections, advantageously operated in liquid or molten phase, said polymerization section(s) being carried out at a temperature higher than the temperature at which step a) is carried out, preferably at a temperature between 190 and 400°C, preferably between 220 and 350°C, preferably between 265 and 300°C, preferably at a pressure between 0.01 and 100.00 kPa, preferably between 0.05 and 10.00 kPa, and preferably with a residence time between 0.1 and 5.0 hours, preferably between 0.5 and 4 hours, preferably between 1.0 and 3.0 hours. According to the invention, the residence time in the polymerization section of step b) is defined as the ratio of the reaction volume of a reactor used in said polymerization section to the volume flow rate of the liquid stream, comprising the polyester produced, leaving said reactor.

[0039] The polymerization reaction may optionally be continued in a polycondensation section located downstream of the polymerization section and operated in solid phase, preferably at a temperature (in particular a product temperature) of between 190 and 250°C, preferably between 200 and 230°C. Depending on whether this operation is carried out in continuous mode or in batch mode. The polycondensation section may preferably be operated under an inert atmosphere, for example under a nitrogen flow at a pressure close to atmospheric pressure, or under vacuum (in particular at a pressure of between 0.01 and 100 kPa, or even between 0.01 and 10 kPa). The residence time (defined as the time during which the product is subjected to the polycondensation conditions in said polycondensation section) is between 5 and 20 hours, preferably between 10 and 16 hours.Said polycondensation section may advantageously be preceded by a crystallization section, thus located between the polymerization section and the polycondensation section, in which the polyester formed, obtained at the end of the polymerization section, is advantageously crystallized, said crystallization section being able to be operated at a temperature preferably between 110 and 210°C, and for a residence time (defined as the time during which the product is subjected to the crystallization conditions in said section) preferably between 0.5 and 6 hours.

[0040] Step b) is preferably carried out in the presence of a polymerization catalyst, in particular based on antimony, titanium, germanium, aluminum, zinc acetate, calcium acetate and / or manganese acetate.

[0041] Additives may be introduced in step b) of polycondensation. The additives optionally introduced in step b) may be, for example: agents for inhibiting secondary etherification reactions, such as, for example, amines (n-butylamine, diisopropylamine or triethylamine), sodium hydroxide or organic hydroxides or lithium carbonate, stabilizing agents such as phosphites or phosphates, and polyamide-type compounds to reduce the amount of degradation product such as acetaldehyde.

[0042] The method according to the invention, advantageously implementing the polymerization of the BHET-based composition according to the invention whose nitrogen content, determined by the chemiluminescence method developed above, is less than or equal to 10 ppm by weight, preferably less than or equal to 5 ppm by weight, very advantageously less than 3 ppm by weight, thus makes it possible to obtain a polyester, preferably a PET, which is slightly colored, or even colorless. Very advantageously, the present invention makes it possible to obtain, by polymerization of the BHET-based composition according to the invention, a polyester, preferably a PET having a b* coordinate value, determined by colorimetry as described in ASTM D6290 2019, advantageously between -10.0 and +10.0, preferably between -8.0 and +8.0.

[0043] US patent 8431202 mentions that the addition of cobalt additives or organic toners (otherwise known as color correctors) makes it possible to minimize or eliminate the yellow color, measured in b*, of the resin. Thus, the method according to the invention, implementing the polymerization of a BHET-based composition having a nitrogen content measured by chemiluminescence of less than or equal to 10 ppm by weight, preferably less than or equal to 5 ppm by weight, very advantageously less than 3 ppm by weight, makes it possible to reduce the proportion of color correctors necessary in view of the intended application for the polyester.

[0044] The following examples illustrate the invention without limiting its scope. EXAMPLES Example 1:

[0045] A total nitrogen content of 14.0 ppm by weight is measured in a first batch of BHET, obtained by glycolytic depolymerization of a PET feedstock.

[0046] The nitrogen content is determined using a chemiluminescence method, using a PAC-Antek Multitek VNS type device, equipped with a vertical oven, syringe injection and a CTC Analytics PAL System 748 type sample changer, and by:

[0047] - introduction of 10 pL of sample in liquid form (prepared by 10-fold dilution in the THF of the first batch of BHET) in a quartz tube heated to 1050°C,

[0048] - oxidative combustion of the sample in the presence of an oxidizing flux composed of helium (130 cm3 / min) and oxygen (450 cm3 / min), producing CO2, H2O, NOx, SO2,

[0049] - detection by a photomultiplier of the light emitted following the reaction of NO obtained with an ozone flow (35 cm3 / min), producing nitrogen dioxide in an excited state (NO2*), followed by the return of NO2* to its ground state,

[0050] - determination of the quantity of nitrogen by comparison of the signal intensity electrical obtained from a calibration curve previously carried out using a diphenylamine standard diluted in toluene.

[0051] This BHET is engaged in an esterification step a), carried out at 275°C under 0.15 MPa for 90 minutes, in the presence of 250 ppm of Sb2O3 catalyst.

[0052] The reaction medium is then subjected in a first polycondensation step, at a temperature of 285°C and a pressure of 0.1 kPa, for 105 min.

[0053] Then, after a preliminary crystallization step of 2 hours at 125°C (i.e. at the temperature of the granules), the previous polyester obtained at the end of the first polycondensation step is engaged in a solid phase polycondensation step at 200°C, at atmospheric pressure under nitrogen circulation.

[0054] The PET obtained at the end of polycondensation is colored with a pronounced yellow appearance.

[0055] The average of 10 colorimetry measurements carried out according to ASTM D6290 2019 in reflectance gives the following value for the b* coordinate: b* = 18.4 Example 2:

[0056] A second batch of BHET is obtained according to a process of depolymerization of a PET charge in the presence of ethylene glycol. The total nitrogen content, measured on this second batch of BHET by the chemiluminescence method described above in Example 1, is less than 2.3 ppm by weight.

[0057] This BHET is engaged in an esterification step a), carried out at 275°C under 0.15 MPa for 93 minutes, in the presence of 250 ppm of Sb2O3 catalyst.

[0058] The reaction medium is then subjected in a first polycondensation step, at a temperature of 285°C and a pressure of 0.1 kPa, for 64 min.

[0059] Then, after a preliminary crystallization step of 2 hours at 125°C (i.e. at the temperature of the granules), the previous polyester obtained at the end of the first polycondensation step is engaged in a solid phase polycondensation step at 200°C, at atmospheric pressure under nitrogen circulation.

[0060] The PET obtained at the end of polycondensation is not very colored and has a less colored appearance than the PET obtained according to the process described in Example 1.

[0061] The average of 10 colorimetry measurements carried out according to ASTM D6290 2019 in reflectance gives the following value for the b* coordinate: b* = 7.37. Example 3:

[0062] Another batch of BHET is obtained according to a process of depolymerization of a PET charge in the presence of ethylene glycol. The total nitrogen content, measured on this batch of BHET by the chemiluminescence method described above in Example 1 is less than 2.3 ppm wt.

[0063] This BHET is engaged in an esterification step a), carried out at 275°C under 0.15 MPa for 90 minutes, in the presence of 250 ppm of Sb2O3 catalyst.

[0064] The reaction medium is then subjected to a first polycondensation step, at a temperature of 285°C and a pressure of 0.1 kPa, for 69 min.

[0065] Then, after a preliminary crystallization step of 2 hours at 125°C (i.e. at the temperature of the granules), the previous polyester obtained at the end of the first polycondensation step is engaged in a solid phase polycondensation step at 200°C, at atmospheric pressure under nitrogen circulation.

[0066] The PET obtained at the end of polycondensation is not very colored and has a less colored appearance than the PET obtained according to the process described in Example 1.

[0067] The average of 10 colorimetry measurements carried out according to ASTM D6290 2019 in reflectance gives the following value for the b* coordinate: b* = 6.74.

Claims

Claims

1. Composition comprising at least 90% by weight of BHET and having a nitrogen content of less than or equal to 5 ppm by weight, the nitrogen content being determined according to a chemiluminescence method, with an ozone flow at 35 cm3 / min, after oxidative combustion of a sample in liquid form, prepared by dilution of the composition in tetrahydrofuran, at a temperature of 1050-1100°C and in the presence of an oxidizing mixture composed of oxygen and helium, and using a calibration curve carried out using a diphenylamine standard diluted in toluene, said composition comprising 2-(2-hydroxyethoxy) ethyl 2-hydroxyethyl terephthalate, or BHET-deg, in a molar ratio (BHET-deg / [BHET + BHET-deg]) between the number of moles of BHET-deg relative to the number of moles of the whole BHET and BHET-deg less than or equal to 10.0 mol% and greater than or equal to 0.001 mol%.

2. Composition according to claim 1 in which the nitrogen content is less than or equal to 3 ppm by weight.

3. Composition according to one of claims 1 and 2 being obtained by a process for treating a polyester filler, preferably comprising PET, which comprises a step of depolymerization by glycolysis in the presence of ethylene glycol or by methanolysis in the presence of methanol.

4. Composition according to one of the preceding claims, comprising at least 95% by weight of BHET and preferably at least 98% by weight of BHET.

5. Composition according to one of the preceding claims, comprising BHEI, preferably in a molar ratio (BHEI / [BHET + BHEI]) between the number of moles of BHEI relative to the number of moles of the BHET and BHEI combination present in the composition less than or equal to 10.0%, preferably less than or equal to 5.0%, preferentially less than or equal to 1.0% and preferably less than or equal to 0.5%.

6. Composition according to one of the preceding claims, comprising BHET-deg in a molar ratio (BHET-deg / [BHET + BHET-deg]) between the number of moles of BHET-deg relative to the number of moles of the BHET and BHET-deg combination present in the composition is less than or equal to 5.0 mol%, preferably less than or equal to 1.0 mol%, preferably less than or equal to 0.5 mol%, and very preferably greater than or equal to 0.05 mol%, preferably greater than or equal to 0.10 mol%, preferably greater than or equal to 0.50 mol%.

7. Use of the composition according to one of claims 1 to 6, for preparing a polyester, preferably a PET.

8. Use according to claim 7, in which the composition according to one of claims 1 to 6 is mixed with at least one dicarboxylic acid, preferably chosen from terephthalic acid and isophthalic acid, and / or at least one diol, preferably chosen from ethylene glycol, diethylene glycol, butylene glycol, cyclohexane dimethanol, neopentyl glycol or mixtures thereof, the preferred diol being ethylene glycol.

9. A process for producing a polyester, comprising: a) a step of esterification of a filler comprising at least the composition according to one of claims 1 to 6, and optionally at least one dicarboxylic acid, preferably chosen from terephthalic acid and isophthalic acid, and / or at least one diol, preferably chosen from ethylene glycol, diethylene glycol, butylene glycol, cyclohexane dimethanol, neopentyl glycol or mixtures thereof, the preferred diol being ethylene glycol, said step a) being carried out at a temperature of between 150 and 350°C; then b) a polycondensation step.

10. Method according to the preceding claim, in which step a) is carried out at a temperature between 200 and 300°C, preferably between 250 and 285°C, and preferably at a pressure between 0.05 and 1.0 MPa, preferably between 0.1 and 0.5 MPa.

11. Method according to one of claims 9 and 10, in which step b) implements one or more polycondensation sub-step(s), for example at least one polycondensation sub-step in liquid or molten phase, optionally followed by at least one polycondensation sub-step in solid phase.

12. Method according to one of claims 9 to 11, in which step b) implements at least one polymerization section, advantageously operated in liquid or molten phase, and carried out at a temperature higher than the temperature at which step a) is carried out, preferably at a temperature between 190 and 400°C, preferably between 220 and 350°C, preferably between 265 and 300°C, and preferably at a pressure between 0.01 and 100.0 kPa, preferably between 0.05 and 10.00 kPa.

13. Process according to one of claims 9 to 12, in which step b) is carried out in the presence of a polymerization catalyst, preferably based on antimony, titanium, germanium, aluminum, zinc acetate, calcium acetate and / or manganese acetate.