PROCESS FOR PRODUCING A POLYESTER HAVING A REDUCED CRYSTALLIZATION TEMPERATURE

Abstract

The present invention relates to a process for producing a polyester, comprising: a) a step of esterification of a mixture comprising a monomer A of formula 1 and a monomer B of formula 2, or a monomer A of formula 1, a monomer B of formula 2 and isophthalic acid, formula 1 formula 2 in which R1 is selected from the group consisting of: - (CH2)n-, with n an integer between 2 and 4, - (CH2-CHR2)-, with R2 selected from linear or branched alkyl groups, comprising between 1 and 6 carbon atoms (C1-C6) and a phenyl group; then b) a polycondensation step.

Description

Title of the invention: METHOD FOR PRODUCING A POLYESTER HAVING A REDUCED CRYSTALLIZATION TEMPERATURE Technical field

[0001] The invention relates to a process for producing a polyester, in particular a thermoplastic polyester, suitable in particular for applications in bottles, packaging or coatings, for example food containers. More particularly, the invention relates to a process for producing a polyester from a mixture of at least two dihydroxy aromatic diester monomers. Very advantageously, at least one of the two dihydroxy aromatic diester monomers is derived from a polyester recycling process, in particular from a process for depolymerizing a polyester feedstock, comprising for example waste and / or post-consumer polyesters. 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.

[0003] The process of polymerization, 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.

[0004] In particular, US patent 4,001,187 discloses processes for producing high-quality PET, comprising a step of continuously feeding ethylene glycol and terephthalic acid into the esterification medium comprising bis(2-hydroxyethyl) terephthalate (BHET). US patent application 2019 / 0002632 proposes a process comprising the esterification of a mixture of BHET and an aromatic polycarboxylic acid. Documents 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.Document US2020055982 discloses the production of a polyester polyol by polycondensation of a diol composition comprising a dihydroxyalkyl terephthalate monomer, in . in particular BHET, and a short-chain C2-C9 diol, in particular ethylene glycol or diethylene glycol, with a dicarboxylic acid, such as phthalic acid. Finally, patent application US 2018 / 0340041 proposes a process for producing a polyester by polymerization, in two reaction phases, of a mixture comprising a first diol terephthalate monomer, in the majority in the mixture, and a second monomer consisting of 2-(2-hydroxyethoxy) ethyl 2-hydroxyethyl terephthalate (BHET-DEG), in the minority in the mixture, the first esterification phase being carried out at a moderate temperature.

[0005] These documents propose the polymerization of mixtures of BHET with diol and / or carboxylic acid compounds but do not teach the preparation of polyester by reaction of said BHET, bis(2-hydroxyethyl) terephthalate, with its meta isomer, i.e. bis(2-hydroxyethyl) isophthalate, nor on how to adjust the proportion of meta-aromatic units during the esterification phase.

[0006] 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, to obtain a polyester. 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 high-quality polyester, the BHET being obtained by depolymerization of a polyester.

[0007] Although they disclose the polymerization of products resulting from the depolymerization of PET by glycolysis, the cited documents do not provide any information on the quality of the intermediate products resulting from the depolymerization of PET, in particular on the presence of para and meta isomers of dihydroxy aromatic diester monomers.

[0008] In Scheirs J., Long TE, "Modern Polyesters: Chemistry and Technology of Polyesters and Copolyesters" Chichester, John Wiley & Sons Ltd, 2003, 750 p. (Wiley Series in Polymer Science), the authors report that isophthalic acid (IPA) is a co-monomer that affects the crystallization behavior of PET. It is introduced into PET in amounts up to 5 mol%, in order to suppress crystallization behavior during injection molding and stretch blow molding, resulting in clear and glossy bottles. Patent application US2020079900 confirms that in order to provide acceptable optical clarity for bottle packaging, conventional PET resins often contain a co-monomer such as isophthalic acid (IPA). The comonomer functions to disrupt the linearity of the PET chains, thus reducing the tendency to crystallize.Reducing crystallization leads to improved haze (e.g., reduced haze value) and optical properties (e.g., increased brightness and / or visible light transmission). Small amounts of IPA comonomer, e.g., 1-10 wt%, can significantly alter polymer properties.

[0009] However, none of the prior art documents proposes a simple process for producing a polyester having a formulation compatible with packaging applications, and more particularly with bottle-type applications, using in particular raw materials which can be derived from the recycling of plastics and in particular polyesters. Summary of the invention

[0010] The subject of the invention is a process for producing a polyester, comprising:

[0011] a) a step of esterification of a mixture comprising a monomer A of formula 1 and a monomer B of formula 2 or a monomer A of formula 1, a monomer B of formula 2 and isophthalic acid, to obtain an oligomeric intermediate,

[0012] formula 1

[0013] [Chem.l] O / =. O RO ^_7 OR HO OH

[0014] formula 2

[0015] [Chem.2]

[0016] in which R1 is chosen from the group consisting of: -(CH2)n-, with n an integer between 2 and 4, -(CH2-CHR2)-, with R2 chosen from linear or branched alkyl groups, comprising between 1 and 6 carbon atoms (C1-C6) and a phenyl group;

[0017] b) a step of polycondensation of the oligomeric intermediate.

[0018] The present invention has the advantage of proposing a simple process for producing polyester having a meta- unit content corresponding to a reduced crystallization behavior and melting point and at least suitable for injection-molding and / or injection-blow molding processes, thus making it compatible with packaging applications, and more particularly with bottle-type applications. In particular, the meta- unit content of the polyester, preferably PET, obtained using the process according to the invention is advantageously between 0.1 and 10.0 mol%, preferably between 0.25 and 7.0 mol%, preferentially between 0.5 and 5.0 mol% relative to all the elementary units of the polyester.Bottles can then be manufactured with the polyester obtained according to the process of the present invention by known injection-stretch-blow molding processes and the manufactured bottles have a clear and transparent appearance.

[0019] Another advantage of the present invention lies in the origin of the raw materials, and in particular of the dihydroxy aromatic diester monomers, which can come from any known source and in particular from the plastic recycling circuits set up in recent years by national and international organizations to combat plastic pollution. Indeed, at least one of the, or both, dihydroxy aromatic diester monomers used to prepare the polyester according to the present invention can be derived from polyester depolymerization processes, such as PET, in the presence of diol or methanol. Thus, the process according to the present invention can participate in the recycling of polyester materials and therefore in the fight against plastic pollution. Description of the embodiments

[0020] According to the invention, the terms “diester monomer”, “aromatic diester monomer” and “dihydroxyl aromatic diester monomer” are interchangeable and denote monomeric compounds that can be condensed with each other to form the polyester in question. More particularly, the diester monomer according to the invention is a diester compound derived from terephthalic or isophthalic acid and a diol, preferably a mono- or polyalkylene glycol, preferably monoalkylene glycol, the term derivative meaning in this case that the compound can result from the condensation of terephthalic or isophthalic acid with said diol. Thus, the diester monomer according to the invention comprises an aromatic ring doubly substituted in the para or meta position by ester groups each comprising a hydroxyl group. Particular diester monomers according to the invention are in particular monomer A of formula 1, monomer B of formula 2 and monomer C of formula 3:

[0021] formula 1

[0022] [Chem.l] OO -< HO OH,

[0023] formula 2

[0024] [Chem.2] O HO

[0025] formula 3

[0026] [Chem.3] ho' oh

[0027] in which: R1 is chosen from the group consisting of: - (CH2)n-, with n an integer between 2 and 4, preferably equal to 2, - (CH2-CHR2)-, with R2 chosen from linear or branched alkyl groups, comprising between 1 and 6 carbon atoms (C1-C6), preferably between 1 and 3 carbon atoms (C1-C3), preferably 2 carbon atoms (C2), and a phenyl group

[0028] R3 is chosen from the group consisting of: the group R1, a group -(CH2)n-(O-(CH2)n)m- , with m and n being whole numbers, m being between 1 and 4, preferably equal to 1 or 2, and n being between 2 and 4, preferably equal to 2, preferably the group -(CH2)n-(O-(CH2)n)m- is a derivative of (i.e. derived from) diethylene glycol (i.e. -CH2-CH2-O-CH2-CH2-) or a derivative of (i.e. derived from) triethylene glycol (i.e. -CH2-CH2-(O-CH2-CH2)2-), a group -(CH2-CH(CH3)2-CH2)- , and a group -CH2-C6Hi0-CH2-, in which -C6Hi0- is advantageously a bi-substituted cy-clohexyl,

[0029] R4 is chosen from the group consisting of: a group -(CH2)n-(O-(CH2)n)m- , with m and n being whole numbers, m being between 1 and 4, preferably equal to 1 or 2, and n being between 2 and 4, preferably equal to 2, preferably the group -(CH2)n-(O-(CH2)n)m- is a derivative of (i.e. derived from) diethylene glycol (i.e. -CH2-CH2-O-CH2-CH2-) or a derivative of (i.e. derived from) triethylene glycol (i.e. -CH2-CH2-(O-CH2-CH2)2-), a group -(CH2-CH(CH3)2-CH2)- , and a group -CH2-C6Hi0-CH2-, in which -C6Hi0- is advantageously a bi-substituted cy-clohexyl.

[0030] Very preferably, monomer A is bis(2-hydroxyethyl) terephthalate (BHET) and monomer B is bis(2-hydroxyethyl) isophthalate (BHEI).

[0031] According to the invention, the terms “terephthalate unit” and “para- unit” are interchangeable and designate the units of the polyester or of the monomers comprising an aromatic nucleus (therefore units called aromatic units) and in which the aromatic nucleus is substituted in the para position.

[0032] According to the invention, the terms “isophthalate unit” and “meta- unit” are interchangeable and designate the units of the polyester or of the monomers comprising an aromatic nucleus (therefore units called aromatic units) and in which the aromatic nucleus is substituted in the meta position.

[0033] According to the invention, the term "polyester" designates a thermoplastic polymer, advantageously saturated (as opposed to thermosetting polyesters) having as elementary repeating units diol esters, and more particularly at least alkylene terephthalate units, the alkylene ester groups of which are located para on the aromatic ring, and alkylene isophthalate units, the alkylene ester groups of which are located meta on the aromatic ring. Preferably, the alkylene terephthalate units are in the majority in the main polymer chain compared to the alkylene isophthalate units, which means that the alkylene terephthalate units represent at least 60 mol%, preferably at least 80 mol%, preferentially at least 90 mol%, preferably at least 95 mol% of the elementary units present in the polymer chain, relative to the alkylene phthalate units (i.e. relative to all the alkylene terephthalate and alkylene isophthalate units). Preferably, the alkylene isophthalate units, which are in the minority in the main polymer chain relative to the alkylene terephthalate units, represent between 0.1 and 10.0 mol%, preferably between 0.25 and 7.0 mol%, preferentially between 0.5 and 5.0 mol% of the elementary units present in the polymer chain, relative to the alkylene phthalate units (i.e. relative to all the alkylene terephthalate and alkylene isophthalate units). Thus, according to the invention, the term "polyester" is used to designate a poly(alkylene terephthalate) (or polyalkylene terephthalate, according to anglicized terminology) in the chain of which there are alkylene isophthalate units.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), each of these polyesters also comprising alkylene isophthalate units, respectively ethylene isophthalate, butylene isophthalate, trimethylene isophthalate units. The polyester according to the invention may also comprise on its main polymer chain other units, 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, whose majority repeating para-elementary unit is of formula 4 and which comprises at least one minority meta-elementary unit of formula 5 on the main polymer chain:

[0034] formula 4

[0035] [Chem.4].

[0036] formula 5

[0037] [Chem.5]

[0038] According to the invention, the terms “diol” and “glycol” are used interchangeably and cor correspond to compounds comprising 2 hydroxyl groups -OH and preferably comprising between 2 and 12 carbon atoms, preferably between 2 and 4 carbon atoms. The preferred diol is ethylene glycol, also called mono-ethylene glycol or MEG.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] According to the invention, the pressures are absolute pressures and are given in MPa.

[0043] The invention thus relates to a process for producing a polyester, comprising, preferably consisting of:

[0044] a) a step of esterification of a mixture comprising a monomer A of formula 1 and a monomer B of formula 2 or of a mixture comprising a monomer A of formula 1, a monomer B of formula 2 and isophthalic acid (IPA), preferably in a molar ratio (meta- / [meta- + para-]) of the aromatic units substituted in meta- relative to all the aromatic units (in particular substituted in meta- and para-) present in the mixture, of between 0.1 and 10.0 mol%, preferably between 0.25 and 7.0 mol%, preferentially between 0.5 and 5.0 mol%, said molar ratio corresponding more particularly to the ratio between the number of moles of monomer B and isophthalic acid present in the mixture and the total number of moles of monomers present in the mixture and having an aromatic cycle, and therefore in particular the total number of moles of monomer A, monomer B and isophthalic acid, to obtain an oligomeric intermediate,

[0045] formula 1

[0046] [Chem.6] HO OH

[0047] formula 2

[0048] [Chem.7]

[0049] in which R1 is chosen from the group consisting of: -(CH2)n-, with n an integer between 2 and 4, preferably equal to 2 such that R1 is an ethyl group, -(CH2-CHR2)-, with R2 chosen from linear or branched alkyl groups, comprising between 1 and 6 carbon atoms (C1-C6), preferably between 1 and 3 carbon atoms (C1-C3), preferably 2 carbon atoms (C2), and a phenyl group;

[0050] b) a step of polycondensation of the oligomeric intermediate.

[0051] The mixture of step a) may comprise the monomer B in a molar ratio of the monomer B relative to the total of the monomers A and B (monomer B / [monomer A + monomer B]) less than or equal to 10 mol%, more particularly between 0.01 and 10.0 mol%, preferably between 0.05 and 7.00 mol%, more preferably between 0.05 and 5.00 mol%. If the amount of monomer B in the mixture of step a) is too low, in particular if the molar ratio (monomer B / [monomer A + monomer B]) of monomer B relative to all of the monomers A and B present in the mixture of step a), is less than 0.1 mol %, then the mixture of step a) comprises isophthalic acid, in addition to monomers A and B, so as to achieve a molar ratio (meta- / [meta- + para-]) of the mixture of between 0.1 and 10.0 mol %, preferably between 0.25 and 7.0 mol %, preferentially between 0.5 and 5.0 mol %.At the same time, if the molar ratio (monomer B / [monomer A + monomer B]) of monomer B relative to all of the monomers A and B present in the mixture of step a) is between 0.1 and 10.0 mol%, preferably between 0.25 and 7.0 mol%, preferentially between 0.5 and 5.0 mol%, the mixture of step a) may comprise only the monomers A and B or it may additionally comprise isophalic acid so as to adjust the molar ratio (meta- / [meta- + para-]) of the mixture to a precise value and between 0.1 and 10.0 mol%, preferably between 0.25 and 7.0 mol%, preferentially between 0.5 and 5.0 mol%.

[0052] According to a preferred embodiment of the invention, monomer A is bis(2-hydroxyethyl) terephthalate (BHET) and monomer B is bis(2-hydroxyethyl) isophthalate (BHEI), the group R1 then being an ethyl group -(CH2-CH2)-. Preferably, the BHEI is present in the mixture of step a) in a molar quantity of between 0.01 and 10.00 mol %, preferably between 0.05 and 7.00 mol %, more preferably between 0.05 and 5.00 mol %, relative to the molar quantity of all the BHET and BHEI monomers present in said mixture of step a). In this case, the polyester produced by the process according to the invention is a poly(ethylene terephthalate), also called polyethylene terephthalate or PET, advantageously composed of ethylene terephthalate units (substitution of the aromatic ring in para) and comprising ethylene isophthalate units (substitution of the aromatic ring in meta-). Such PET advantageously has a lower crystallization rate and melting point than a PET not comprising ethylene isophthalate units.Thus, a PET which includes ethylene isophthalate units in addition to ethylene terephthalate units is compatible with packaging applications and in particular with bottle applications, since it is suitable for injection-blow molding processes and makes it possible to obtain clear and transparent bottles.

[0053] Very advantageously, at least one of the monomers A and B can be obtained by processes for depolymerizing thermoplastic polyesters preferably from collection and sorting channels (i.e. from channels belonging to waste recycling systems, particularly plastic waste), in particular in the presence of diol.In a very particular manner, the mixture of step a) comprises BHET and BHEI, of which at least the BHET, preferably the BHET and the BHEI, is (are) derived from a process for treating polyester, preferably PET, comprising the depolymerization of the polyester, preferably comprising PET, in the presence of diol, preferably ethylene glycol, or in the presence of methanol, preferably in the presence of diol, in particular in the presence of ethylene glycol, said treatment process optionally comprising purification steps so as to obtain a BHET or a mixture of BHET and BHEI that is purified and compatible with the polymerization steps of the process according to the invention.

[0054] According to a particular embodiment of the invention, the mixture of step a) may further comprise a monomer C of formula 3:

[0055] formula 3

[0056] [Chem.7] HO OH,

[0057] in which: - R3 is chosen from the group consisting of: - the R1 group, - a group -(CH2)n-(O-(CH2)n)m-

[0058] [Chem. 8]

[0059] with m and n being integers, m being between 1 and 4, preferably equal to 1 or 2, and n being between 2 and 4, preferably equal to 2, preferably the group -(CH2)n-(O-(CH2)n)m- is a derivative of diethylene glycol (i.e. -CH2-CH2 -O-CH2-CH2-) or a derivative of triethylene glycol (i.e. -CH2-CH2-(O-CH2-CH2)2-),

[0060] - a group -(CH2-CH(CH3)2-CH2)-

[0061] [Chem.9]

[0062] and

[0063] - a group -CH2-C6Hi0-CH2-

[0064] [Chem. 10]

[0065] in which -C6Hi0- is advantageously a bi-substituted cyclohexyl,

[0066] - R4 is chosen from the group consisting of: - a group -(CH2)n-(O-(CH2)n)m-, with m and n being whole numbers, m being between 1 and 4, preferably equal to 1 or 2, and n being between 2 and 4, preferably equal to 2, preferably the group -(CH2)n-(O-(CH2)n)m- being a derivative of diethylene glycol, such as -CH2-CH2-O-CH2-CH2-, or a derivative of triethylene glycol, such as -CH2-CH2-(O-CH2-CH2)2-, - a group -(CH2-CH(CH3)2-CH2)-, and - a group -CH2-C6Hi0-CH2-, in which -C6Hi0- is advantageously a bi-substituted cyclohexyl.

[0067] Very preferably, R3 is the group R1, in particular an ethyl group -CH2-CH2-, and R4 is a derivative of diethylene glycol, i.e. -CH2-CH2 -O-CH2-CH2-,

[0068] In this particular embodiment, the mixture in step a) comprises the monomer C preferably in a molar ratio of the monomer C relative to the set of monomers A and C (monomer C / [monomer A + monomer C]) present in the mixture of step a), between 0.05 and 10.00 mol%, preferably 0.10 and 10.00 mol%, preferentially between 0.25 and 7.00 mol%, preferably between 0.50 and 5.00 mol%.

[0069] According to another particular embodiment, the mixture of step a) may further comprise at least one dicarboxylic acid other than isophthalic acid, such as terephthalic acid (PTA), or one of its dialkyl diesters, such as its dimethyl diester, for example dimethyl terephthalate, and / or at least one diol, preferably chosen from ethylene glycol, diethylene glycol, butylene glycol, cyclohexane dimethanol, neopentyl glycol, and mixtures thereof. Preferably, the mixture of step a) further comprises terephthalic acid (PTA) and optionally at least ethylene glycol.

[0070] In this embodiment, the amount of terephthalic acid (PTA) introduced into the mixture of step a) is such that the molar proportion (meta- units / [meta- units + para- units]) of meta- units, in particular provided by monomer B and isophthalic acid (IPA), relative to all the aromatic units, in particular provided by monomer A, PTA, monomer B, IPA and optionally monomer C if it is present in the mixture of step a), is preferably between 0.1 and 10.0 mol%, preferentially between 0.25 and 7.0 mol%, more preferably between 0.5 and 5.0 mol%.

[0071] 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 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, comprising the oligomeric intermediate, leaving said reactor.

[0072] 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).

[0073] 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, in particular when the mixture of step a) comprising the monomers A and B, and optionally C, further comprises a dicarboxylic acid, such as for example isophthalic and / or terephthalic acid. The water then formed is also advantageously separated during step a).

[0074] Advantageously, the process for producing a polyester according to the invention comprises a step b) of polycondensation of the oligomeric intermediate obtained from step a), step b) may advantageously comprise one or more, preferably one or two, polycondensation sub-step(s), for example at least one, preferably one, polycondensation sub-step in liquid or molten phase, optionally followed by at least one, preferably one, polycondensation sub-step in solid phase.

[0075] Very advantageously, the polycondensation step b) implements at least one polymerization section, preferably one or two polymerization sections, advantageously operated in the liquid or molten phase, said polymerization section(s) being implemented at a temperature higher than the temperature at which step a) is implemented, 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.

[0076] 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.

[0077] 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.

[0078] 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 for reducing the amount of degradation product such as acetaldehyde.

[0079] The process according to the invention thus makes it possible to obtain a polyester, advantageously having a content of meta- units between 0.1 and 10.0 mol%, preferably between 0.25 and 7.0 mol%, preferentially between 0.5 and 5.0 mol%, relative to all the elementary units of the polyester obtained, which allows the polyester obtained to have a reduced crystallization rate and melting point while retaining satisfactory mechanical properties or at least suitable for injection-molding and / or injection-blow molding processes, which thus makes it compatible with packaging applications and more particularly with bottle-type applications. In particular, the process according to the invention can be integrated into plastic waste recycling channels, since it can advantageously use monomers resulting from the depolymerization of polyesters to prepare the targeted polyester in a simple manner.

[0080] The following examples illustrate the invention without limiting its scope. EXAMPLES

[0081] Example 1 (According to the invention):

[0082] A mixture of BHET and BHEI such that BHEI / [BHET + BHEI] = 2.2 + / - 0.1 mol% is engaged in an esterification step a) carried out at 275°C under 0.15 MPa in the presence of 250 ppm of Sb2O3 catalyst for 99 minutes.

[0083] 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 105 min.

[0084] The polyester obtained at the end of this first polycondensation step has a proportion of meta- units relative to all the aromatic units of 2.2% mol + / - 0.1% mol.

[0085] 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.

[0086] The polyester obtained at the end of the second polycondensation step has a proportion of meta- units relative to all the aromatic units of 2.2% mol + / - 0.1%, which is fully compatible with packaging applications, in particular type of bottles.

[0087] Example 2 (Not in accordance with the invention):

[0088] A mixture of BHET and BHEI such that BHEI / [BHET + BHEI] = 0.2 mol% is engaged in an esterification step a) carried out at 275°C under 0.15 MPa in the presence of 250 ppm of Sb2O3 catalyst for 75 minutes.

[0089] 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 120 min.

[0090] The polyester obtained at the end of this first polycondensation step has a proportion of meta- units relative to all the aromatic units of 0.2 mol%.

[0091] 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 205°C, at atmospheric pressure under nitrogen circulation.

[0092] The polyester obtained at the end of the second polycondensation stage has a proportion of meta- units relative to all the aromatic units of 0.2 mol%, which is a low proportion, not very compatible with packaging applications, particularly of the bottle type.

[0093] Example 3 (According to the invention):

[0094] A mixture of BHET and BHEI such that BHEI / [BHET + BHEI] = 0.2 mol% is used in an esterification step a), carried out at 275°C under 0.15 MPa for 86 minutes, in the presence of 250 ppm of Sb2O3 catalyst and IPA such that (BHEI + IPA) / (BHEI + IPA + BHET) = 2.3 mol%.

[0095] The reaction medium is then subjected in a first polycondensation step, to a temperature of 285°C and a pressure of 0.1 kPa) for 73 min.

[0096] The polyester obtained at the end of this first polycondensation step has a proportion of meta- units relative to all the aromatic units of 2.3 mol%.

[0097] 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 205°C, at atmospheric pressure under nitrogen circulation.

[0098] The polyester obtained at the end of the second polycondensation step has a proportion of meta- units relative to all the aromatic units of 2.3 mol%, which is fully compatible with packaging applications.

Claims

1. Claims A process for producing a polyester, comprising: a) a step of esterification of a mixture comprising a monomer A of formula 1 and a monomer B of formula 2 or a monomer A of formula 1, a monomer B of formula 2 and isophthalic acid, to obtain an oligomeric intermediate, formula 1 [Chem 11] HO OH formula 2

2.

3. in which R1 is chosen from the group consisting of: -(CH2)n-, with n an integer between 2 and 4, -(CH2-CHR2)-, with R2 chosen from linear or branched alkyl groups, comprising between 1 and 6 carbon atoms (C1-C6), and a phenyl group; b) a polycondensation step of the oligomeric intermediate; and wherein the mixture of step a) comprises monomer A and monomer B or monomer A, monomer B and isophthalic acid in a molar ratio (meta- / [meta- + para-]) of meta- units relative to all the aromatic units present in the mixture, of between 0.1 and 10.0 mol%. Process according to claim 1, in which the mixture of step a) comprises monomer A and monomer B or monomer A, monomer B and isophthalic acid in a molar ratio (meta- / [meta- + para-]) of the meta- units relative to all the aromatic units present in the mixture, of between 0.25 and 7.0 mol%, preferably between 0.5 and 5.0 mol%. A method according to claim 1 or 2, wherein R1 is an ethyl group.

4. Process according to one of claims 1 to 3, in which the mixture of step a) comprises a monomer C of formula 3, formula 3 [Chem 13] OO 4 4 RO OR HO OH in which: R3 is chosen from the group consisting of: the group R1, a group -(CH2)n-(O-(CH2)n)m-, with m and n integers, m being between 1 and 4, preferably equal to 1 or 2, and n being between 2 and 4, preferably equal to 2, a group -(CH2-CH(CH3)2-CH2)-, and a group -CH2-C6Hi0-CH2-, R4 is chosen from the group consisting of: a group -(CH2)n-(O-(CH2)n)m-, with m and n integers, m being between 1 and 4, preferably equal to to 1 or 2, and n being between 2 and 4, preferably equal to 2, a group -(CH2-CH(CH3)2-CH2)- and a group -CH2-C6Hi0-CH2-.

5. Process according to claim 4, in which the mixture of step a) comprises the monomer C present in a molar ratio of the monomer C relative to all the monomers A and C present in the mixture of step a), of between 0.05 and 10.00 mol%, preferably 0.10 and 10.00 mol%, preferentially between 0.25 and 7.00 mol%, preferably between 0.50 and 5.00 mol%.

6. Process according to one of the preceding claims, in which the mixture of step a) comprises a dicarboxylic acid other than isophthalic acid, such as terephthalic acid, or one of its dialkyl diesters, such as its dimethyl diester, for example dimethyl terephthalate, and / or at least one diol, preferably chosen from ethylene glycol, diethylene glycol, butylene glycol, cyclohexane di-methanol, neopentyl glycol or mixtures thereof, the preferred diol being ethylene glycol.

7. Method according to one of the preceding claims, in which step a) is carried out at a temperature between 150 and 350°C, preferably between 200 and 300°C, preferably between 250 and 285°C.

8. Method according to one of the preceding claims, wherein step a) is carried out at a pressure between 0.05 and 1.0 MPa, preferably between 0.1 and 0.5 MPa.

9. Method according to one of the preceding claims, in which step b) comprises 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.

10. Method according to one of the preceding claims, in which step b) implements at least one polymerization section, operated in liquid or molten phase, at a temperature higher than the temperature at which step a) is implemented, 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.

11. Method according to one of the preceding claims, 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.