Monomer recovery from polyester

Abstract

The present invention relates to a process for the preparation of a polyester having repeating units [−A''−B''] of formula [−O−R 1 −OOC−R 2 −CO−], comprising the following steps: heating a recovered monomer product obtained from depolymerization of a polyester together with 3-50% by weight of water to a temperature higher than the melting point of said condensation monomers in a reactor at a pressure higher than ambient pressure by at least 0.5 bar to obtain a modified recovered monomer product having an increased concentration of COOH end groups. The present invention also relates to the use of a polyester prepared from said modified recovered monomer product for a solid state polycondensation reaction.

Description

[0001] The present invention relates to a method for regenerating monomers from condensation polymers that are polyesters, and a method for manufacturing polyesters from the recycled monomer products.

[0002] The preparation of polymers from polymer monomers is well-known and has been achieved on a large scale. Traditionally, the monomers used are derived from fossil resources. The utilization of fossil resources is based on a linear product stream from fossil resources to polymers and then to waste. In the long run, such a linear product stream is unsustainable. As an alternative, it has been proposed to use monomers derived from renewable resources to construct a more circular product stream. However, the resulting cycle from polymers to carbon dioxide and water to plant-based renewable resources and then back to polymers is a time-consuming and energy-intensive method for producing polymers.

[0003] Condensation polymers have the particular advantage of being depolymerized into their monomers and then repolymerized from these recycled monomers. According to the depolymerization technique, the same monomers typically used to prepare the original polymer can be obtained. In other cases, the recycled monomers may have different compositions, thus limiting their application in existing large-scale production processes. Such limiting differences may be the melting point of solid monomers, the viscosity of liquid monomers, or the energy required to melt or evaporate monomers. In particular, differences arise from the predetermined molar ratio of the reacting monomers.

[0004] Polyesters have a general structure consisting of repeating units. They are typically produced on a large scale by polymerizing monomers, which are diols and diacids.

[0005] Polyesters are typically prepared on a large scale by polymerizing diol monomers with substituted diacid monomers. Alternatively, polyesters can be prepared on a large scale by polymerizing cyclic dimers, trimers, or oligomers obtained from diol and diacid monomers. Polyesters are formed through ring-opening polymerization.

[0006] These polyesters can be regenerated by depolymerization with the addition of diol monomers. Depolymerization yields a recycled monomer product, which comprises products having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomers, where R 1 and R 2 As defined below.

[0007] The depolymerization of polyesters using glycol monomers is well-known and documented for use in both industrial and post-consumer waste. Particularly in the case of post-consumer waste, it is essential to remove organic contaminants that may have migrated into the polyester or may have bound to polyester molecules and subsequently been released during depolymerization. Such removal is described in Welle: Safety Evaluation of PolyethyleneTerephthalate Chemical Recycling Processes; Sustainability 2021, 13, 12854, 1-10. Following depolymerization, various washing steps achieve the removal of organic contaminants. A typical washing step is based on crystallization and subsequent filtration. This results in the monomer product containing a significant amount of residual liquid, which must be removed to obtain pure condensed monomers.

[0008] Typically, these cleaning steps are performed under conditions that prevent the decomposition of the aforementioned condensation monomers, in the case of glycolysis of PET with ethylene glycol, wherein the condensation monomers are bis(β-hydroxyethyl) terephthalate (BHET).

[0009] For example, US-3,668,235 (Teijin) describes a method for removing a volatile liquid medium from a solid BHET wetted with a volatile liquid medium and recovering the dried BHET. The method includes heating and melting the solid BHET wetted with the volatile liquid medium into a molten substance, the volatile liquid medium having a boiling point at atmospheric pressure not lower than 40°C but lower than the boiling point of ethylene glycol, and evaporating the volatile liquid medium from the melt without causing degradation of the BHET.

[0010] WO2022 / 180563A1 (Garbo) describes a method for preparing liquid BHET by depolymerization of polyethylene terephthalate (PET). The method comprises: depolymerizing PET with ethylene glycol, purifying and crystallizing the resulting BHET, and melting the resulting crystalline form of BHET (which is impregnated with a solvent) at a temperature below or equal to 90°C and above or equal to 70°C to obtain a solution of BHET in the solvent. The BHET solution is described as very stable, with no oligomer formation, and the BHET monomer content decreases only slightly due to hydrolysis after two weeks of heating, resulting in an increase in acidity (formation of 2.1 mol% carboxyl end groups). It is considered that the higher acidity of BHET is advantageous from the perspective of PET production because it increases the time reactivity of BHET and thus the polycondensation rate. However, the amount of free carboxyl groups (CEG), as measured according to ASTM D7409-15, should be 40 to 100 mmol / kg (less than 3 mol%), more preferably 60 to 80 mmol / kg. Therefore, WO2022 / 180563A1 only implies that the small amount of free carboxyl groups formed during the process described herein should not be disadvantageous. It does not imply that this amount can be significantly increased without any adverse effect on the properties of the desired product, BHET.

[0011] As discussed above, polyesters with low carboxyl end-group content are typically obtained from BHET as described in the prior art. A disadvantage of such polyesters is that they can only undergo slow solid-state polycondensation reactions, primarily based on transesterification, to produce diol monomer A as the condensation product.

[0012] The problem of this invention is to provide an improved method for preparing polyester from recycled monomer products.

[0013] The above-mentioned problems are solved by the present invention.

[0014] Specifically, the present invention relates to a method for preparing a polyester having repeating units [-A''-B''], wherein the repeating units [-A''-B''] have the formula [-OR 1 -OOC-R 2 [-CO-], which includes the following steps:

[0015] a1) Providing a waste stream comprising polyester having repeating units [-A''-B''], said repeating units [-A''-B''] having the formula [-OR 1 -OOC-R 2 -CO-], where R 1 and R 2The same or different, and selected from aliphatic hydrocarbons containing 1 to 15 carbon atoms, aromatic hydrocarbons containing 1 to 3 aromatic rings, cyclic hydrocarbons containing 4 to 10 carbon atoms, and heterocycles containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms.

[0016] a2) Forming a mixture comprising the waste stream and at least one diol monomer HO-R capable of reacting with the polyester. 1 Blends of -OH groups

[0017] a3) The blend obtained in step a2) is exposed in a reaction vessel to conditions suitable for the depolymerization of the polyester to obtain a depolymerization solution containing a recycled monomer product, said recycled monomer product containing at least 50% by dry weight condensed monomer having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH,

[0018] b1) Heating the regenerated monomer product together with 3-50% by weight of water in a reactor at a pressure at least 0.5 bar above ambient pressure but not exceeding 10 bar to a temperature above the melting point of the condensed monomer; and

[0019] b2) Heating the modified recycled monomer product from step b1), preferably under reduced pressure, to obtain a polyester polymer.

[0020] It has been found that the modified recycled monomer products obtained according to the present invention are more suitable for producing polyesters with higher intrinsic viscosity by solid-state polymerization.

[0021] The regenerated monomer products obtained through steps a1) to a3) of the method of the present invention mainly contain substances with OH end groups, and very few COOH end groups. Even after step a3) of the method of the present invention, the remaining or formed products with one OH end group and one COOH end group have the formula [HO-R]. 1 -OOC-R 2 The condensation monomers of [-COOH] will also have their content reduced by separating the recycled monomer product in the preferred optional step a6). Typically, the recycled monomer product recovered from the depolymerization of polyester using diol monomers will have less than 10 mol%, preferably less than 5 mol%, more preferably less than 3 mol% of COOH end groups.

[0022] According to the method of the present invention, in step b1), the regenerated monomer product is converted into a modified regenerated monomer product by heating under pressure. The modified regenerated monomer product optionally contains its low molecular weight reaction product, the concentration of its COOH end group being at least 9 mol%, preferably at least 14 mol%, and more preferably at least 19 mol% higher than the concentration of the COOH end group of the regenerated monomer product.

[0023] If the converted monomer product is used for the polymerization of polyester without the further addition of diol monomer A, the concentration of COOH end groups must not exceed 50 mol.

[0024] The modified regenerated monomer product is obtained by heating under pressure a regenerated monomer product containing 50% to 97% by weight of condensed monomer and 3% to 50% by weight of water until it has fully reacted to contain at least an increased COOH end group content of 9%, wherein the condensed monomer has the formula HO-R. 1 -OOC-R 2 -COO-R 1 -OH. Preferably, the heating of the regenerated monomer product with water is carried out at a temperature above the melting point of the condensation monomer and at a pressure at least 0.5 bar higher than ambient pressure, but not exceeding 10 bar.

[0025] The present invention also relates to a modified regenerated monomer product obtainable by the method of the present invention, comprising having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomers and having the formula [HO-R] 1 -OOC-R 2 A blend of modified condensation monomers of [-COOH], wherein R 1 and R 2 As defined above, the modified regenerated monomer product is characterized by having a COOH end group concentration ranging from 10 mol% to 50 mol%, preferably from 15 mol% to 45 mol%, and particularly preferably from 20 mol% to 40 mol.

[0026] The regenerated monomer product provided to step b1) contains, on a dry weight basis, at least 50% and at most 100%, more preferably at least 70%, most preferably at least 80%, and preferably less than 95%, most preferably less than 90% of condensed monomers having the formula HO-R. 1 -OOC-R 2 -COO-R 1 -OH; and 3% to 50%, preferably greater than 5%, more preferably greater than 10%, and preferably less than 40% water by weight, wherein the water content is based on the total weight of the recycled monomer product plus water. In a preferred embodiment of the invention, the modified recycled monomer product comprises at least 10 mol%, more preferably at least 15 mol%, and most preferably 20 mol% of a modified condensation monomer having polyester repeating units [-A''-B''] with OH and COOH end groups, having the formula [HO-R 1 -OOC-R 2 -COOH].

[0027] Optionally, the recycled monomer product may contain other substances, such as diol monomer A or its dimer or diacid B, dimers or low molecular weight oligomers of condensation monomers or comonomers, which react with the major condensation monomer at R 1 Or R 2 There are some differences.

[0028] In step b1), the regenerated monomer product is heated to a temperature above the melting point of the condensation monomer, preferably above 120°C, and more preferably above 135°C. Heating to the reaction temperature can be achieved by a separate heat exchanger and / or a heated reaction vessel.

[0029] As a result of the heating described in step b1), the pressure increases. According to the invention, the heating results in a pressure at least 0.5 bar above ambient pressure, preferably at least 1.2 bar, more preferably at least 2.0 bar, but not exceeding 10 bar, and preferably not exceeding 7 bar. To maintain the pressure within the desired range, excess gas phase can be released. The reaction conditions can be maintained for a longer period by increasing the temperature before removing the excess gas phase.

[0030] The reaction time for preparing the modified regenerated monomer product in step b1) depends on the initial water content and reaction temperature. It is determined according to the requirements described above. Typically, the reaction time ranges from 5 minutes to 10 hours, preferably less than 4 hours. The conditions must be sufficient to promote the desired reaction, allowing water to react with the condensation monomer or its low molecular weight reaction product.

[0031] Optionally, a catalyst may be added to the regenerated monomer product to promote its conversion into the modified regenerated monomer product in step b1.

[0032] Suitable catalysts are:

[0033] - Inorganic acids, such as phosphoric acid,

[0034] - Inorganic bases, such as sodium hydroxide; inorganic bicarbonates, such as sodium bicarbonate; hydrotalcite;

[0035] - Organic acids or organic bases, such as ammonium bicarbonate, dimethylaminopyridine, ethylenediamine, and triethylamine.

[0036] - Metal salts, such as acetates or other carboxylates of alkali metals, titanium, aluminum, antimony, tin, or zinc.

[0037] - Metal complexes, such as glycolates of titanium, aluminum, antimony, tin, or zinc, or

[0038] - Metal oxides, such as zinc oxide or antimony oxide, hydrated metal oxides or mixed metal oxides, such as titanates as described in US5656716.

[0039] Optionally, the catalyst may be deactivated before transferring the modified regenerated monomer product to step b2). Deactivation may be carried out by neutralization, evaporation, or chemical deactivation, such as by chelation. Alternatively, the catalyst may be removed by filtration or magnetic separation, or it may be present in the form of a catalyst bed through which the solution is transported.

[0040] As a result of the conversion reaction in step b1), glycol monomer A is generated. Some glycol monomer A also exists in the gas phase, thus achieving monomer removal. This allows for the recovery of glycol monomer A on-site and reduces the need to remove excess glycol monomer A during polymer production.

[0041] In step b2), the modified recycled monomer product thus obtained is heated under reduced pressure to obtain a polyester polymer, as will be discussed below.

[0042] According to the present invention, it has been found that the polyester obtained after step b2) can be used as a starting polyester for solid-state polycondensation (SSP), wherein a high-viscosity polyester with a viscosity at least 0.1 dl / g higher than that of the starting polyester is prepared in the solid-state polycondensation, and the solid-state polycondensation reaction is based on esterification and transesterification reactions, wherein the ratio of esterification reaction to the total amount of esterification and transesterification reactions is higher than 25%, preferably higher than 30%, more preferably higher than 35%, and in some cases even higher than 50%.

[0043] The ratio of the above reactions was determined by conventional methods, such as by calculating the intrinsic viscosity and COOH end groups, or by measuring the COOH and OH end groups.

[0044] The polyester obtained by the above method is essentially free of contaminants and is suitable for preparing packaging materials that come into direct contact with food, such as bottles, cans, trays or films, even if the waste stream comes from non-food applications.

[0045] Another advantage of this invention is that it achieves an increased concentration of COOH terminal groups without adding any orthoacid monomers such as TPA, which explains the improvement observed in subsequent SSP reactions. Therefore, this invention provides improved regenerability.

[0046] In the method of this invention, any bisphenol A (BPA) that may be present in the recycled monomer product and / or modified recycled monomer product is inserted as a structural unit into the final polyester obtained after step b2). The presence of BPA in the recycled monomer product and / or modified recycled monomer product is harmless.

[0047] The following names will be used in this article to refer to condensation polymers, their depolymerization products and monomers.

[0048] Monomer: A general term for the structural unit of a polymer. For condensation polymers, monomers include single monomers, substituted monomers, and condensation monomers.

[0049] Individual monomer: The basic structural unit of a polymer existing in its unreacted form. According to the present invention, monomer A is a polymer having the formula HO-R. 1 Diol with -OH group, monomer B is a diol with the general formula HOOC-R 2 -COOH diacids, where R 1 and R 2 Throughout this specification, they may be the same or different, and are selected from aliphatic hydrocarbons containing 1 to 15 carbon atoms, aromatic hydrocarbons containing 1 to 3 aromatic rings, cyclic hydrocarbons containing 4 to 10 carbon atoms, or heterocycles containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms.

[0050] Replacement monomer: Monomer C, as a separate monomer B HOOC-R 2 -COOH and two capped molecules R 3 The condensation product of -OH was obtained, wherein the end-capped molecule R 3 -OH does not constitute part of the repeating unit of the relevant condensation polymer, meaning it is eliminated during the condensation reaction that forms the polymer, and R... 3 It is an aliphatic hydrocarbon containing 1 to 15 carbon atoms. According to the present invention, the substituted monomer has the C formula R. 3 OOC-R 2 -COOR 3 In one implementation, the end-capping molecule R 3 -OH can be methanol, thus yielding a substituted monomer C of type H3COOC-R. 2 -COOCH3.

[0051] Condensation monomer: A short-chain condensation product of individual monomers A and B, with the formula A'-B''-A', where A' and B'' have the following definitions. More specifically, the condensation monomer A'-B''-A' is HO-R 1 -OOC-R 2 -COO-R 1 -OH, where R 1 and R 2 Defined as described above.

[0052] Reacted monomers: The structural units of a polymer, existing in the reacted form within any larger molecule. Possible forms are A', A'', B', and B'', where A' is identical to H'-A'' and B' is identical to H'-B''.

[0053] According to the present invention

[0054] The A' unit represents the reacted monomer A, which is a diol with one reacted terminal group and one unreacted -OH terminal group, with the formula HO-R. 1 -O-;

[0055] The A'' unit represents the reacted monomer A, which is a diol with two reacted end groups, and its formula is -OR. 1 -O-,

[0056] The reacted A unit represents the sum of all reacted monomer units A' and A''.

[0057] The total number of A units represents the sum of all reacted and unreacted monomer units A, A', and A''.

[0058] According to the present invention

[0059] The B' unit represents the reacted monomer B, which is a diacid with one reacted terminal group and one unreacted -COOH terminal group, and its formula is HOOC-R. 2 -CO-;

[0060] The B'' unit represents a reacted monomer B having two reacted end groups, preferably a diacid having two reacted end groups, with the formula -OC-R. 2 -CO-, where

[0061] The reacted B unit represents the sum of all reacted monomer units B' and B'', and

[0062] The total number of B units represents the sum of all reacted and unreacted monomer units B, B', and B''.

[0063] For example, the total number of B units refers to the total number of B units in a given product, which is the sum of the products of the number of moles of all molecules containing B units multiplied by the number of B units in the corresponding molecule. For example, for a product containing monomer B and A'-B''-A' and dimer A'-B''-A'-B''-A', the total number of B units is = molB + 1*molA'-B''-A' + 2*molA'-B''-A'-B''-A'.

[0064] The following terms include the molar amount of each of the listed substances:

[0065]

[0066] Repeating unit: A condensation product consisting of one individual monomer A and one monomer B. Possible forms include -A''-B''-, with the formula [-OR 1 -OOC-R 2[-CO-] will provide the repeating structure in the middle of the molecule; or A'-B''- and -B''-A', which will provide the structure at the ends of the molecule. A repeating unit also exists in the condensation monomer A'-B'.

[0067] Dimer: A condensation product of two separate monomers containing two repeating units. Possible forms are A'-B''-A''-B''-A' and B'-A''-B''-A''-B'. The condensation product B'-A''-B''-A''-B' is considered a trimer and is therefore part of the oligomer family.

[0068] Oligomers: Condensation products of two separate monomers A and B containing several repeating units, with the formula E[-A''-B''] n -E, where 3<=n<=9, the expression for -A''-B''- is [-OR 1 -OOC-R 2 -CO-], and E=H', A' or B'.

[0069] Condensation polymer: A condensation product of two separate monomers having a large number of repeating units, with the formula E[-A''-B'']. n -E, where n>9, the molecular formula of -A''-B''- is [-OR 1 -OOC-R 2 -CO-], E = H', A', or B'. According to the present invention, the condensation polymer is a polyester.

[0070] Polyesters are produced through polycondensation and the elimination of a low-molecular-weight reaction product. Polycondensation can occur directly between monomers. It can also be carried out via intermediates, which subsequently undergo transesterification and the elimination of a low-molecular-weight reaction product, or via ring-opening polymerization.

[0071] The resulting polyester has a basically linear polymer chain. However, a small number of branches may also form.

[0072] The preferred polyester according to the present invention is a thermoplastic polyester.

[0073] Polyester is typically made of the general formula HO-R 1 The diol component of -OH and the general formula is HOOC-R 2 The polymer is prepared by condensation polymerization of the dicarboxylic acid component of -COOH, wherein R 1 and R 2Typically, the dicarboxylic acid component is an aliphatic hydrocarbon containing 1 to 15 carbon atoms, an aromatic hydrocarbon containing 1 to 3 aromatic rings, a cyclic hydrocarbon containing 4 to 10 carbon atoms, or a heterocyclic hydrocarbon containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms. Linear or cyclic diol components are typically used, as well as typically linear, aromatic, or heterocyclic dicarboxylic acid components. The corresponding diester, usually its dimethyl ester, can also be used instead of the dicarboxylic acid. Preferred examples of such polyesters include: polyethylene terephthalate (PET), typically made from terephthalic acid (TPA) and ethylene glycol (EG); polybutylene terephthalate (PBT), made from terephthalic acid (TPA) and 1,4-butanediol (BD); polypropylene terephthalate (PTT), made from terephthalic acid (TPA) and 1,3-propanediol (PB); polyethylene furanate (PEF), made from 2,5-furandicarboxylic acid (FDCA) and ethylene glycol (EG); and polytrimethylene furanate (p...). Polybutylene succinate (PTF); polybutylene succinate (PBS) made from succinic acid (SA) and 1,4-butanediol (BD); polybutylene adipate (PBA) made from adipic acid (AdA) and 1,4-butanediol (BD); polybutylene adipate-terephthalate (PBAT) made from adipic acid (AdA), terephthalic acid (TPA) and 1,4-butanediol (BD); and polyethylene naphthalate (PEN) made from naphthalene-2,6-dicarboxylic acid and ethylene glycol, wherein all of the above polyesters may exist in the form of homopolymers or copolymers.

[0074] This invention describes a method for preparing a polyester from monomers of a polyester, wherein at least one monomer is a recycled monomer product obtained from the polyester. The polyester prepared from the recycled monomer product may have the same composition or may have a different composition from the polyester from which the recycled monomer product is provided. The difference in composition may arise from the use of different monomers and / or different amounts of the same monomer in the preparation of the polyester. The difference in composition may also arise from the blending of different polyesters. According to the invention, at least one identical monomer is present in both the polyester from which the recycled monomer product is provided and the polyester prepared from the recycled monomer product.

[0075] For example, butanediol can be used as a reaction partner to depolymerize PET, and the resulting recycled monomer product can be repolymerized to form PBT. Alternatively, ethylene glycol can be used as a reaction partner to depolymerize PET copolymers containing a high content of glycol comonomers, and the resulting recycled monomer product can be repolymerized to form PET with a lower comonomer content.

[0076] The polyester according to the invention comprises repeating units [A''-B''-], specifically of the form [-OR]. 1 -OOC-R2 The general structure of [-CO-]. These polyesters can be produced by adding HO-R... 1 The -OH diol monomer A is regenerated by depolymerization. The depolymerization reaction produces a regenerated monomer product containing a condensation monomer, as described above, in the form of A'-B''-A', specifically, with the formula HO-R. 1 -OOC-R 2 -COO-R 1 -OH.

[0077] This invention describes a method for preparing a polyester from its monomers, wherein at least one monomer is a modified recycled monomer product obtained from the polyester. The modified recycled monomer product is obtained by reacting the recycled monomer with water. As described above, the recycled monomer product comprises a condensation monomer in the form of A'-B''-A', specifically, having the formula HO-R. 1 -OOC-R 2 -COO-R 1 -OH. The resulting modified regenerated monomer product contains a modified condensation monomer in the form of A'-B', specifically, with the formula HO-R. 1 -OOC-R 2 -COOH.

[0078] According to a preferred embodiment, the polyester is polyethylene terephthalate (PET) or a copolymer thereof. Preferably, ethylene glycol is used as glycol monomer A for depolymerization. In this case, the recycled monomer product comprises BHET as a condensation monomer and mono(2-hydroxyethyl) terephthalate (MHET) as a modified condensation monomer.

[0079] Depolymerization can generate a variety of byproducts, including those with a general structure of A'-B', specifically those with the formula HO-R. 1 -OOC-R 2 -COOH byproducts, or those with the formula HOOC-R 2 The diacid monomer B containing -COOH, and some depolymerization products, including dimers and oligomers. Other variants of the above-mentioned byproducts containing comonomers may also be generated.

[0080] Preferably, the regenerated monomer product comprises at least 50% by weight of the condensed monomer in the form of A'-B''-A', specifically, having the formula HO-R. 1 -OOC-R 2 -COO-R 1-OH. Preferably, the regenerated monomer product comprises at least 50%, more preferably at least 70%, and most preferably at least 80% of the condensed monomer on a dry basis, while the remainder may be present in the form of dimers, oligomers, and other byproducts. In a preferred embodiment, the dried regenerated monomer product comprises less than 90% of the condensed monomer on a dry basis. As used herein, "dry basis" means the total solids content of the regenerated monomer product free of any liquids such as residual glycols, water, or inert solvents.

[0081] This is sufficient to obtain high-quality recycled monomer products while reducing yield losses due to the removal of oligomers and dimers.

[0082] Generally, all monomer products containing more than 50% by weight of regenerated monomer units are considered regenerated monomer products. Water or inert solvents that may be present in the monomer product are not included in the calculation.

[0083] An inert solvent is any liquid that dissolves or disperses at least a portion of a solid substance and does not react with the solid substance or reacts with it at least to a small extent at the temperature at which the solution or dispersion is formed.

[0084] Preferably, the method of the present invention uses a monomer product containing more than 70% by weight of recycled monomer units.

[0085] Typically, condensation monomers are solids under ambient conditions. Ambient conditions refer to standard temperature and pressure (293.15 K, absolute pressure 101.325 kPa). Typical condensation monomers have melting points above 50°C. More typical condensation monomers have melting points above 70°C. Melting point refers to the temperature at which a pure condensation monomer melts. The actual melting temperature of a condensation monomer may be lower; for example, the presence of certain substances that are liquid under ambient conditions may lower its melting temperature.

[0086] According to the present invention, the modified recycled monomer product obtained in step b1) of the method of the present invention is used for the polymerization of polyester in step b2) of the method of the present invention.

[0087] In a preferred embodiment of the invention, after step b1), the pressure is reduced to remove the gaseous phase containing water and diol monomer A. The removal of the gaseous phase can be performed in multiple steps and can be aided by further increasing the temperature. In a preferred embodiment, the pressure is released to obtain ambient pressure. In an optional preferred embodiment, the pressure is reduced to a pressure below ambient pressure. Preferably, the pressure reduction reaches an absolute pressure of 0.5 to 0.05 bar.

[0088] Typically, in step b1), as more condensation monomers are converted by water, more diol monomer A is obtained. Given that diol monomer A generally has a higher boiling point than water, higher temperatures and / or lower pressures are required to reduce the liquid content. If the recycled monomer product is converted into solid particles, the residual liquid content, in this case, the content of diol monomer A and water, must be sufficiently low to make the particles suitable for bulk material handling. Therefore, the solid particles preferably contain less than 10% by weight, more preferably less than 6% by weight of a substance that is liquid under normal conditions. This percentage is expressed as the ratio of liquid to the weight of the particles including the liquid.

[0089] The process of preparing the modified recycled monomer product in step b1) can be a process step before the slurry preparation step of the melt phase polymerization device.

[0090] If the modified recycled monomer product obtained in step b1) is directly used for polymerization in the subsequent step b2), then step b1) can be integrated as a process step into the melt phase polymerization apparatus. In a preferred embodiment of the invention, the reactor for step b1), provided with the recycled monomer product and water, is integrated into the melt phase polymerization apparatus, which has previously been used to prepare polyester from diol monomer A and diacid monomer B. Preferably, this reactor, provided with the recycled monomer product and water, has previously been used for the esterification of diol monomer A and diacid monomer B, and is commonly referred to as an esterification reactor. Such an esterification reactor can be a separate vessel or a section within a vessel that combines the esterification reaction with further processing steps. If two separate esterification reactors are provided for primary and secondary esterification, the reactor used for primary esterification is preferred.

[0091] In this case, polyesters with a COOH end-group concentration higher than 10 mol% are prepared by a method including the following steps:

[0092] - The regenerated monomer product with less than 10 mol% COOH end groups obtained by steps a1) to a3) of the method of the present invention is provided to the esterification reactor;

[0093] - Supply water to the esterification reactor;

[0094] - Subsequently, step b1 of the method of the present invention is performed at a temperature of 120°C to 170°C in the presence of provided water by heating the regenerated monomer product in the esterification reactor and exposing it to a high pressure of 0.5 to 10 bar above atmospheric pressure.

[0095] - The pressure was then reduced to allow water and glycol monomer A to evaporate;

[0096] - Subsequently, the pressure is further reduced and the temperature is increased to conditions suitable for polymerization, thereby performing step b2 of the method of the present invention.

[0097] The amount of water supplied to the esterification reactor is equal to 3% to 50% of the total weight of the regenerated monomer product plus water.

[0098] In the above embodiment, water is supplied from a source located outside the reactor producing polyester. It can be supplied in the form of wet condensation monomers, or it can be supplied as a separate stream. The amount of water supplied does not include water that may be generated by the reaction, such as water produced by the reaction of diol monomer A with diacid monomer B.

[0099] According to a preferred embodiment of the present invention, in step b2) of the method of the present invention, a polyester with a COOH end-group concentration of at least 10 mol%, preferably at least 15 mol%, more preferably at least 20 mol% but not exceeding 45 mol% is prepared using the modified recycled monomer product. The preferred polyester has an intrinsic viscosity range of 0.4 to 0.9 dl / g, preferably higher than 0.5 dl / g, more preferably higher than 0.55 dl / g, and preferably lower than 0.8 dl / g, more preferably lower than 0.75 dl / g.

[0100] Methods for preparing polyesters have been described in detail. Various methods for preparing polyesters are described in the book "Modern Polyesters; Wiley Series in Polymer Science; 2003; Edited by John Scheirs" (typical examples in Chapters 2, 8, 9 and 11).

[0101] The typical preparation process involves the direct reaction of equal amounts of individual monomers A and B to generate a repeating unit structure [A''-B''-]. n Polyesters, specifically, have the formula [-OR 1 -OOC-R 2 -CO-] n The polyester, at the end can be A' (HO-R) 1 -O-) and / or B' unit (-OC-R) 2 -COOH) end capping. During the reaction, low molecular weight reaction products may be generated, which must be removed by evaporation.

[0102] Other so-called "two-step" processes use monomer B (HOOC-R²-COOH) alone and an excess of monomer A (HO-R) alone in the first step. 1 -OH), to form a prepolymer with a repeating unit structure [A''-B''-]n, specifically, with the formula [-OR 1 -OOC-R 2 -CO-]n, where n is a small number, preferably less than 20, and it is mainly composed of A' units (HO-R)1 -O-) end capping. During the reaction, low molecular weight reaction products may form, which must be removed by evaporation.

[0103] In the second step, the prepolymer continues to react, generating a repeating unit structure of [A''-B''-]. n Polyesters, specifically, have the formula [-OR 1 -OOC-R 2 -CO-] n The polyester can be made from A'(HO-R) 1 -O-) and / or B' unit (-OC-R) 2 -COOH) end-capping. During the second stage, excess monomer A (HO-R) is used. 1 -OH) is removed by evaporation.

[0104] An alternative to the two-step method is to use substituted monomer C and an excess of monomer A alone (HO-R). 1 -OH groups form a prepolymer with a repeating unit structure of [A''-B''-]. n Specifically, its formula is [-OR 1 -OOC-R 2 -CO-] n Where n is a small number, preferably less than 20, and it is mainly composed of A' units (HO-R). 1 -O-) end capping. During the reaction, low-molecular-weight reaction products may be generated, which must be removed by evaporation. In the second step, the prepolymer continues to react, generating a [A''-B''-] unit structure. n Polyesters, specifically, have the formula [-OR 1 -OOC-R 2 -CO-] n The polyester can be in A' unit (HO-R) 1 -O-) and / or B' unit (-OC-R) 2 -COOH) terminal capping. During the second stage, excess monomer A (HO-R) 1 -OH) is removed by evaporation.

[0105] Many polyesters contain at least one monomer, A or B, which is liquid under ambient conditions. Typically, the diol-type monomer A (HO-R) is... 1 -OH) is in a liquid state. This allows these individual monomers to be fed into the polyester polymerization reaction in liquid form. If one monomer is liquid and the second monomer is solid, the solid monomer can be dispersed in the liquid monomer to form a monomer slurry, which is then fed into the polyester polymerization reaction.

[0106] Therefore, a conventional apparatus designed to prepare polyesters from their individual monomers A and B includes a unit configured to prepare a slurry from the individual monomers A and B. This slurry preparation unit has corresponding supply units that provide individual monomer A in liquid form and individual monomer B in solid form. The resulting slurry is then fed into subsequent polyester polymerization steps.

[0107] Conventional apparatus designed to prepare polyesters from their individual monomers A and B also includes a unit configured to facilitate the esterification of the supplied monomers A and B. This esterification unit typically operates under ambient or high pressure and releases the water generated during the esterification reaction. This unit has corresponding supply units that provide monomers in liquid form, typically as a slurry. The resulting reaction product, typically a low molecular weight oligomer, is then fed into subsequent polyester polymerization steps.

[0108] According to the present invention, the recycled monomer product is obtained by depolymerization of polyester in steps a1) to a3) of the method according to the present invention.

[0109] In a preferred embodiment of the present invention, before performing step b1) of the method of the present invention, the following steps are also performed:

[0110] a5) Cool the solution to a temperature that causes the regenerated monomer product containing the condensed monomer to precipitate, and

[0111] a6) Recover the precipitated regenerated monomer product from the solution.

[0112] In another preferred embodiment of the invention, the following additional steps are performed between step a3) and step a5):

[0113] a4) Mix the depolymerization solution from step a3) with water or an inert solvent to obtain a diluted solution.

[0114] According to the preferred embodiment, the regenerated monomer product obtained in step a6) contains water and is provided to step b1).

[0115] The waste stream in step a1) of the method of the present invention can be any waste stream primarily comprising polyester. This waste stream may also contain contaminants. Contaminants include solid matter mixed with the polyester particles, typically metal, paper, or heterogeneous plastic. Contaminants include solid or liquid matter adhering to the surface of the polyester particles. These are typically residues from previous use, such as sugar or cooking oil, or cross-contaminants from collection, sorting, and pre-washing, such as sand, gravel, or detergent chemicals. Contaminants also include matter within the polyester particles. These are typically adsorbed volatile substances from previous use, such as fragrances, household chemicals, or solvents. They are also typically mixed contaminants, such as additives, colorants, inorganic fillers, or organic additive carriers. They are also typically mixed contaminants, such as different polymers in polymer blends or blends with natural fibers such as cotton. Contaminants also include water and organic matter adhering to the surface of the waste particles or absorbed by the waste particles. Such liquids can be removed by a pre-drying step. However, it is preferred to avoid such a drying step and provide a waste stream containing this liquid.

[0116] Waste logistics can originate from post-industrial or post-consumer waste. Such waste can be in the form of articles such as containers or fabrics; or it can be in the form of intermediate products such as sheets, fiber rolls or container preforms; or it can be in the form of raw materials such as pellets or shredded solid solutions.

[0117] Waste streams may have undergone pre-cleaning steps, such as optical sorting or separation by mechanical means such as density separation or sieving, to remove heterogeneous polymers and non-polymers.

[0118] Waste materials may have undergone a pre-cleaning step, such as washing with hot or cold water, optionally containing corrosive substances and / or cleaning agents, to remove surface contaminants.

[0119] Waste streams may have undergone pre-cleaning steps, such as drying at high temperatures to remove moisture and / or volatile organic pollutants.

[0120] Waste streams can be cut into granules, or they can be in the form of dust or powder. Typical granule sizes range from 0.1 mm to several centimeters. For ease of handling, granules larger than 1 mm are preferred, and to prevent undissolved granules from clogging pipes, granules smaller than 5 cm, especially smaller than 3 cm, are preferred.

[0121] The waste stream may contain liquefied contaminants. A liquefied contaminant is defined as a substance that is solid at room temperature but is liquid and insoluble in the depolymerization solution formed in step a3) under the conditions of step a3). Liquefied contaminants may be present at a concentration of 0.1% to 48% by weight based on the total amount of the waste stream. "Insoluble" means that no part of the substance dissolves in a given amount. Small amounts of dissolved components are not considered.

[0122] The waste stream may contain solid contaminants. Solid contaminants are defined as substances that are solid and insoluble in the depolymerization solution formed in step a3) under the conditions of step a3). Solid contaminants may be present at a concentration of 0.1% to 48% by weight based on the total amount of the waste stream. "Insoluble" means that no part of the substance dissolves in a given amount. Small amounts of dissolved components are not considered. According to the invention, the total polyester content is greater than 50%. If the concentration of the liquefied contaminant plus the solid contaminant is greater than 1%, more preferably greater than 2%, and most preferably greater than 5%, the preferred embodiment is most suitable.

[0123] Waste streams containing large amounts of liquefied contaminants include, for example, polyester sheets with polyolefin layers or silicone release layers, or polyester containers with polyolefin-based barrier layers such as EVOH.

[0124] Waste streams containing high levels of solid contaminants include, for example, polyester fibers mixed with non-melting fibrous materials such as cotton. Other sources of polyester waste streams with high contaminant levels may originate from the mixing portion of the cleaning steps in polymer sorting or cleaning facilities.

[0125] The formation of the blend in step a2) includes any form of mixing and blending apparatus suitable for mixing a typical solid or liquid waste stream and a typical liquid glycol monomer. Alternatively, it includes any form of mixing and blending apparatus suitable for mixing a typical solid waste stream and a solid glycol monomer. In both cases, heating can be implemented to promote blend formation. Typically, the waste stream is supplied to the mixing apparatus in a controlled amount. This can include any weight or volume metering device, such as a loss-in-weight feeder, belt scale, or airlock. The supply of the solid waste stream can include pneumatic conveying, screw conveying, belt conveying, and / or gravimetric feeding. The liquid waste stream can be supplied using an extruder with or without a metering pump and / or melt filter. In this case, it is preferable to supply the liquid waste stream to a position in the mixing apparatus below the waste stream fill level to promote immediate contact between the waste stream and the glycol. Preferably, the supply of the liquid waste stream is made through multiple openings, thereby providing a large surface contact area between the waste stream and the glycol monomer. This is particularly important if the melting point of the liquid waste stream is higher than the boiling temperature of the glycol monomer.

[0126] According to the present invention, at least one diol monomer HO-R capable of reacting with polyester is used. 1-OH. Typically, only one glycol monomer is used. Using different glycol monomers will result in a mixture of recycled depolymerization products, which may only be useful for a particular copolyester. However, any glycol monomer may contain trace amounts of impurities, such as its dimer. Typically, the glycol monomer is supplied to the mixing unit in a controlled quantity. This can include any weight or volume metering device. Alternatively, the weight or volume difference from the supply tank can be utilized. Typically, the glycol monomer is supplied in liquid form via a pump.

[0127] The ratio of solid waste stream to glycol monomers has a significant impact on the final composition of the recycled monomer product after depolymerization and the economics of the recycling process. In a preferred embodiment, the ratio of the total amount of all glycol monomers added in step a2) to the polyester repeating units contained in the waste stream of step a1) ranges from 5:1 to 15:1, where the ratio is a molar ratio.

[0128] The blend may also contain a catalyst to facilitate the subsequent depolymerization reaction. Such a catalyst can be in the form of a metal salt or an organic compound. Alternatively, organometallic complexes can be used. The catalyst can be added as a pure substance in solid or liquid form, or in solution form. When using a solution, the diol monomer is the most suitable solvent.

[0129] The formation of blends can be accomplished either continuously or by preparing individual batches.

[0130] One option is to use a stirred vessel to form the blend. Depending on the liquid-to-solid ratio and the bulk density of the solid, the solid may not be completely submerged in the liquid. In this case, forming the blend may require some depolymerization and partial dissolution of the solid in the liquid to form a homogeneous blend. In this case, steps a2) and a3) overlap. In a continuous process, steps a2) and a3) also overlap, where the glycol monomer and waste stream are supplied to a depolymerization reactor that has already undergone depolymerization. US-4,609,680 describes such a procedure.

[0131] Another option is to use an extruder to melt the polyester and mix it with glycol monomers.

[0132] Step a3) involves depolymerizing the blend obtained in step a2). Conditions suitable for polyester depolymerization in waste streams are well-known in industry. For example, "Recycling of Polyethylene Terephthalate Bottles; Elsevier; 1" stVarious PET depolymerization methods are described in "ed. 2018, Edited by Sabu Thomas". According to the present invention, the depolymerization conditions must be sufficient to obtain a monomer product mainly composed of condensed monomers with the structure A'-B''-A', which have the formula HO-R. 1 -OOC-R 2 -COO-R 1 -OH.

[0133] As previously mentioned, the mixing in step a2) and the depolymerization in step a3) may overlap, as depolymerization may have already begun during mixing. In a preferred embodiment, the hot glycol monomer is mixed with the waste stream to preheat the waste stream to a temperature sufficient to initiate depolymerization. A suitable temperature is typically above 130°C and at least 20°C lower than the boiling point of the glycol monomer. In either case, the final degree of depolymerization is obtained in step a3). Depolymerization takes place in a reaction vessel. One option is to use a stirred vessel for depolymerization. In batch processes, this can be the same vessel used in step a2). In continuous processes, a single stirred vessel or a series of stirred vessels is preferred. Alternatively, a tubular reactor can be used instead of one or more stirred vessels. Typically, the reaction vessel includes heating devices, such as a heating mantle, internal heating coils, or an external heat exchanger, through which a portion of the depolymerization solution is pumped and returned to the vessel.

[0134] The container is heated to conditions suitable for polyester depolymerization. Typically, temperatures exceeding 170°C are required to achieve sufficient depolymerization. Preferably, the temperature is raised to the boiling point of the glycol monomer. The glycol monomer may contain other liquids; therefore, the boiling point may be lower than the glycol monomer's boiling point. As the other liquids evaporate from the depolymerization solution, the boiling point increases. As the recycled monomer product is generated and dissolved in the glycol monomer, the glycol monomer's boiling point rises above its initial boiling point. Preferably, sufficient heating is provided to maintain boiling. The reaction vessel is typically operated in a pressure range of 500 mbar to 5 bar. However, it is preferable to operate the reaction vessel at near atmospheric pressure in the range of 1 bar ± 100 mbar. Particularly preferably, the reaction vessel is operated at slightly overpressure, up to 100 mbar, so that the evaporated liquids can be transferred to subsequent process steps. Unless otherwise specified, all pressures refer to absolute pressures.

[0135] In a series of reaction vessels, temperature and pressure can vary from one vessel to the next. Especially when an extruder is used in step a2), higher temperatures and pressures can be initially used. However, according to the invention, such extruded blends are subsequently transferred to a reactor conforming to the above specifications.

[0136] A preferred series of reactors is used: a first reactor with a pressure close to atmospheric pressure and a temperature at the boiling point of the solution; a second reactor with an overpressure of up to 5 bar and a higher temperature compared to the first reactor; and a third reactor with a pressure lower than the second reactor, preferably close to atmospheric pressure. This series of reactors allows depolymerization to occur in the first reactor while removing volatile contaminants. Then, the depolymerization rate is increased in the second reactor, and some diol monomers are evaporated from the third reactor.

[0137] Depolymerization continues until a depolymerization solution is formed. Except for certain contaminants, the waste stream should be completely dissolved in the depolymerization solution. Prolonged reactions at high temperatures should be avoided, as this leads to the formation of byproducts, such as dimers of the diol monomer. The total residence time for steps a2) and a3) is typically between 20 minutes and 6 hours. In step a3), where the diol monomer boils and the reaction is carried out at near-ambient pressure, a residence time of 1 to 5 hours is preferred. When the waste stream is preheated according to the above method, the residence time, including such preheating, can be up to 24 hours.

[0138] The depolymerization solution contains regenerated monomer products, wherein the monomer products contain substances with the formula HO-R 1 -OOC-R 2 -COO-R 1 Condensation monomers of -OH groups.

[0139] Depolymerization is typically carried out under reflux. This is usually done to maintain a constant ratio of polyester repeating units to diol monomers. This means that most organic contaminants remain in the depolymerization solution. According to a preferred embodiment of the invention, the blend in step a2) contains at least one volatile organic contaminant.

[0140] In a preferred embodiment, the present invention provides a method for directly removing volatile organic pollutants during the depolymerization process, thereby reducing the pollutant load in subsequent cleaning steps. While such removal of volatile pollutants with extremely low boiling points or extremely low solubility can be achieved by limiting the effectiveness of reflux, it is impossible to remove volatile organic pollutants with high solubility in glycol monomer A under depolymerization conditions in a system retaining glycol monomer A. In this context, volatile pollutants with extremely low boiling points are considered to be pollutants with boiling points below 80°C, and volatile pollutants with extremely low solubility are considered to be pollutants with a solubility in glycol monomer A of less than 10 grams per liter of solution under depolymerization conditions. In this context, volatile pollutants with high solubility in glycol monomer A are considered to have a solubility in glycol monomer A of more than 100 grams per liter of solution under depolymerization conditions.

[0141] It has been found that the removal of organic pollutants can be promoted by evaporating these pollutants and glycol monomer A. This leads to a decrease in the ratio of glycol monomer A to polyester repeating units, or the need to replace the evaporated glycol monomer A with separately purified glycol monomer A, or a combination of the two.

[0142] Volatile organic pollutants (VOCs) are a group of low-boiling-point substances. There is no definitive definition for the term "volatile." In the context of this invention, the term is used to refer to organic pollutants whose normal boiling point is more than 50°C lower than the boiling point of the diol monomer A used in depolymerization step a3). Water is a volatile substance but not a volatile organic pollutant. Other low-boiling-point diols are volatile organic substances but not volatile organic pollutants.

[0143] According to a preferred embodiment of the invention, the blend in step a2) contains at least one volatile organic compound (VOC), and during depolymerization step a3), at least 15% but no more than 150% by weight of the glycol monomer A supplied to step a2) is evaporated. The evaporated glycol monomer A may result in a reduction in the content of glycol monomer A in depolymerization step a3). Alternatively, the evaporated glycol monomer A, or a portion thereof, may be replaced by high-purity glycol monomer A introduced into step a3). Such high-purity glycol monomer A cannot be obtained by a simple reflux cooler. It requires separate purification equipment such as a distillation column and / or membrane filtration unit. Preferably, the amount of VOC introduced into depolymerization step a3) due to the replacement of glycol monomer A is less than the amount of VOC introduced from step a2) into depolymerization step a3). An evaporation percentage of 100% or more is feasible only when replenishment is made.

[0144] To obtain a low concentration of volatile organic pollutants in the depolymerization solution following step a3), it is preferable to evaporate at least 20%, more preferably at least 25%, and more preferably at least 30% of the glycol monomer A by weight. To limit the energy consumption associated with evaporation, it is preferable to evaporate no more than 100%, more preferably no more than 80%, and more preferably no more than 70% of the glycol monomer A by weight.

[0145] According to a preferred embodiment of the invention, during depolymerization step a3), at least 15% but no more than 60% by weight of the diol monomer A is evaporated and removed. Evaporation occurs due to heating of the diol monomer A, and after depolymerization begins, it occurs due to heating of the depolymerization solution to its pressure-dependent boiling point.

[0146] According to another preferred embodiment of the invention, the removal of glycol monomer A is sufficient to raise the boiling point of the depolymerization solution by at least 5°C, more preferably at least 8°C, and most preferably at least 10°C, compared to the pressure-dependent boiling point of glycol monomer A.

[0147] "Removed" means that the post-evaporation stream is directed away from the step in which evaporation occurs. This does not include liquid reflux from the reflux cooler. In batch processes, the mass content decreases due to evaporation. In continuous processes, the mass balance between the input and output streams must be maintained. However, "removed" means that there is no direct feedback stream from which vapor is directed to the unit where evaporation occurs. The percentage calculation is based on the amount of diol monomer initially added in step a2), including the water content in the diol monomer, expressed as a weight percentage.

[0148] However, it is important to limit the evaporation rate so that the molar ratio is not shifted too much towards a higher oligomer content in the depolymerization solution. Therefore, the ratio of diol monomers to polyester repeating units in the depolymerization solution should be maintained above 4:1. Taking into account the upper limit and the depolymerization reaction, this upper limit is reduced to 14:1.

[0149] In a continuous process using a single reactor, the residual water content remains slightly high. If a series of continuously operating reactors are used, and ethylene glycol is evaporated sequentially, a residual water content similar to that of a batch process can be achieved. Evaporation can be initiated simply by heating at a given pressure, applying reduced pressure at a given temperature, or by compression followed by heating and decompression, the latter being called flash evaporation.

[0150] In a preferred embodiment, the evaporated liquid is directed to a separation unit configured to obtain a regenerated diol monomer stream, and at least a portion of the regenerated diol monomer is subsequently used in step a2.

[0151] The preferred method described above for removing organic pollutants and diol monomer A by evaporation can also be advantageously applied in the following process, wherein the produced recycled monomer product is not converted into a modified recycled monomer product in the subsequent step b1).

[0152] Therefore, the present invention also provides a method for preparing a polyester having repeating units [-A''-B''], wherein the repeating units [-A''-B''] have the formula [-OR 1 -OOC-R 2 [-CO-], which includes the following steps:

[0153] a1) Providing a waste stream comprising polyester having repeating units [-A''-B''], said repeating units [-A''-B''] having the formula [-OR 1 -OOC-R 2 -CO-], where R 1 and R 2The same or different, and selected from aliphatic hydrocarbons containing 1 to 15 carbon atoms, aromatic hydrocarbons containing 1 to 3 aromatic rings, cyclic hydrocarbons containing 4 to 10 carbon atoms, and heterocycles containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms.

[0154] a2) Forming a mixture comprising the waste stream and at least one diol monomer HO-R capable of reacting with the polyester. 1 Blends of -OH groups

[0155] a3) Expose the blend obtained in step a2) in a reaction vessel to conditions suitable for the depolymerization of the polyester to obtain a depolymerization solution containing a recycled monomer product, said recycled monomer product containing at least 50% by dry weight a condensed monomer of the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH,

[0156] b2) Heating the recycled monomer product to obtain a polyester polymer.

[0157] The blend formed in step a2) is characterized in that it contains at least one volatile organic pollutant, and during step a3), at least 15% but no more than 150% by weight of the diol monomer A supplied to step a2) is evaporated.

[0158] In the method described, step b1 is omitted.

[0159] According to the method of the present invention, the depolymerization solution obtained in step a3) can be further processed directly in step b1) to obtain the modified regenerated monomer product.

[0160] According to a preferred embodiment of the invention, prior to further processing in step b1), the depolymerization solution obtained in step a3) may undergo other processing steps a4), a5) and a6) which will be discussed below.

[0161] In optional step a4), the depolymerization solution from step a3) is mixed with water or an inert solvent to obtain a diluted solution. Any mixing apparatus suitable for mixing two different liquids can be used. In a batch process, it can be the same container used in step a3), or it can be a subsequent container. In a continuous process, a separate apparatus is preferred. The ratio of the amount of water or inert solvent to the amount of glycol monomer ranges from 5:1 to 1:3. A preferred mixing ratio is less than 3:1. A preferred mixing ratio is greater than 1:1.5. The mixing ratio is expressed as a volume ratio based on the amount of glycol monomer in the depolymerization solution at the start of water addition. Most preferably, the amount of water added is equal to or greater than the amount of glycol monomer added in step a2).

[0162] Mixing may include adding all the water or inert solvent to the entire amount of the depolymerization solution at one location. Mixing may also include adding portions of water or inert solvent sequentially at different locations. Mixing may include adding all the water or inert solvent to only a portion of the depolymerization solution, and then mixing it with the remaining depolymerization solution.

[0163] Alternatively, mixing may include adding all the depolymerization solution to the full volume of water or inert solvent at one location. Mixing may also include sequentially adding portions of the depolymerization solution or inert solvent at different locations. Mixing may include adding only a portion of the depolymerization solution to the full volume of water or inert solvent before mixing with the remaining depolymerization solution.

[0164] Alternatively, mixing may include adding the depolymerizer to a premixed, diluted depolymerization solution. The required water may be added simultaneously, before, or after the addition of the depolymerization solution. Similarly, various liquids may be supplied to one or more locations.

[0165] Alternatively, mixing may include mixing a continuous stream of depolymerization solution with a continuous stream of water or an inert solvent.

[0166] Alternatively, mixing may include mixing a continuous stream of depolymerization solution with a continuous stream of premixed diluted depolymerization solution.

[0167] In any case, the mixing process should avoid overcooling of the depolymerization solution to prevent premature crystallization of the condensation monomers, their dimers, and / or oligomers.

[0168] In a preferred embodiment, the flow rates and temperatures of the two liquid streams should be adjusted before mixing so that the resulting diluted solution reaches a temperature below its boiling point but above the precipitation temperature of the condensation monomers without evaporation. In the case of a depolymerization solution produced from polyethylene terephthalate and ethylene glycol, the preferred temperature of the diluted solution is above 60°C and below 110°C. A more preferred temperature is above 70°C and below 100°C. Some water vapor or inert solvent vapor may form during mixing. Typically, these vapors are condensed and returned to the diluted solution or transferred to a solvent recovery unit.

[0169] Generally, any sudden cooling should be avoided. However, it is also necessary to prevent the formation of excessive amounts of byproducts with the universal structure A'-B', especially those with the formula HO-R. 1 -OOC-R 2 -COOH is a byproduct. This requires rapid cooling to below 90°C. Therefore, water is preferably added in such a manner that the solution temperature reaches below 90°C within 1 hour after the start of water addition. Preferably, the solution temperature reaches below 90°C within 30 minutes.

[0170] In a preferred embodiment of the invention, water is added in such a way that the solution is present in the stirring container and water is added to the container at multiple locations.

[0171] In another preferred embodiment, water is added by the solution flowing through a pipe, and water is injected into the pipe.

[0172] In one preferred embodiment, the diluted solution from step a4) is cooled in step a5). In another preferred embodiment, the depolymerization solution from step a3) is cooled directly in step a5), without performing step a4).

[0173] Any cooling device suitable for cooling liquids and inducing precipitation of dissolved solids can be used. Typically, a stirred vessel is used. The vessel usually includes a cooling device, such as a cooling jacket, internal cooling coils, or an external heat exchanger, through which a portion of the diluted solution is pumped and returned to the vessel. Alternatively, at least partial cooling can be carried out in a plate or tube heat exchanger. Cooling must be sufficient to precipitate most of the dissolved monomeric products, particularly the contained condensed monomers. However, cooling must keep the diluted solution liquid. Therefore, cooling is limited to the melting point of the diluted solution. Under water cooling conditions, a cooling temperature between 0°C and 25°C, preferably below 15°C, and more preferably below 10°C, is used. The cooling time must be long enough for most of the dissolved monomeric products to precipitate. Since the cooling rate is a significant factor in the crystal size development of the precipitated solid, a longer cooling time is preferred to facilitate easy filtration of solid particles. Typical cooling times range from 1 to 16 hours. Cooling can be carried out by isothermal heating, by stepped heating, or by holding the temperature for a period after heating. Stirring is preferred during cooling to prevent the formation of large gel-like masses. The stirring must be strong enough to reach the entire liquid volume throughout the cooling process. At the same time, high friction should be avoided to prevent breakage of the precipitated solids. Typical stirrers are paddle stirrers or cup stirrers. At least 80%, preferably at least 90%, of the precipitated solids (by weight) should have a particle size greater than 20 µm.

[0174] Because precipitated solids of varying particle sizes may form, it is advantageous to employ the following process steps: liquid from a cooling unit is introduced into a dynamic separation device, which separates the liquid into a first liquid fraction and a second liquid fraction, wherein the second liquid fraction contains a majority of particles smaller than the critical size, and wherein the second liquid fraction is returned to the cooling unit, while the first liquid fraction is directed for further processing. The second liquid fraction may be combined with the dilution solution from step a4) before entering the cooling unit. Preferably, the second liquid fraction contains more than 70% particles smaller than the critical size. The critical size particles are less than 10 µm, preferably less than 20 µm, and most preferably less than 30 µm. The dynamic separation device can be any device that separates particles in a liquid based on the particle's response to gravity. Typical devices include, for example, decanters, centrifuges, hydrocyclones, or simple sedimentation tanks. Preferred dynamic separation devices such as decanters, centrifuges, or hydrocyclones achieve separation in less than 5 minutes.

[0175] The advantage of using such a dynamic separation device lies not only in returning small, difficult-to-filter particles to an earlier stage of the process, but also in simultaneously creating a separation tendency to provide a first liquid fraction with a higher solids content compared to the second liquid fraction. Therefore, the solid-liquid ratio of the liquid entering the dynamic separation device is lower compared to devices that do not perform particle return. This lower solid-liquid ratio subsequently facilitates separation by particle size.

[0176] In a preferred embodiment, the precipitated solid containing the regenerated monomer product from step a5) is separated from the solution from step a6) by any suitable method for mechanical solid-liquid separation. These methods include filtration, sedimentation, or centrifugation. Thermal methods that completely evaporate the solution are excluded. The advantage of mechanical separation is the removal of soluble contaminants from the solution, thereby separating them from the precipitated solid. Suitable filtration equipment typically includes filter presses, belt filters, or rotary drum filters. Separation can be carried out intermittently or continuously. If no suitable continuous equipment is available, an alternating intermittent system is used. The separation yields two material fractions: a solid regenerated monomer product containing condensed monomers and a liquid solution. This solution contains glycol monomers, water and / or inert solvents, contaminants, and residual catalysts and soluble components such as condensed monomers, dimers, oligomers, and other depolymerization byproducts from polyester depolymerization.

[0177] One option is to direct all or a portion of the liquid stream after washing to a separation unit configured to obtain a regenerated diol monomer stream.

[0178] Several additional washing steps can be used when preparing the regenerated monomer product.

[0179] These cleaning steps can be performed sequentially or in combination. They include:

[0180] - Vaporizing contaminants from any material stream in any of steps a1) to a6), particularly from the material stream in step a3). This requires directing the vapor away from the step in which the evaporation occurs. Optionally, a portion of the vapor is condensed and returned to the process step. The term "material stream" includes all materials used, generated, or processed in any of steps a1) to a6), including the waste stream of step a1), blends formed from the waste stream from step a1) and the diol monomers added in step a2), the depolymerization solution obtained from the blend in step a3), the diluted solution obtained by mixing the depolymerization solution with water or an inert solvent in step a4), and the precipitated regenerated monomer product obtained in step a5).

[0181] - Mechanical separation from any solution obtained in any of steps a3) through a5), such as filtering solid contaminants. This process may be performed in one or more steps. Separation includes filtration, which may include a first sieving step using a sieve size of 0.1 to 3 mm and a second fine filtration using a pore size of 0.1 µm to 0.1 mm.

[0182] - Mechanical separation from any solution obtained in any of steps a3) to a5), such as filtering the precipitated oligomer particles. This is preferably carried out after step a4) at a temperature that allows for oligomer precipitation but retains most of the dimers and condensation monomers in solution. Filter aids may be used to facilitate filtration.

[0183] - Mechanical separation from any solution obtained in any of steps a3) to a5), such as filtering the precipitated dimer particles. This is preferably carried out after step a4) at a temperature that allows dimer precipitation but retains most of the condensed monomers in solution. Filter aids may be used to facilitate filtration.

[0184] - Mechanical separation from any solution obtained from any of steps a3) to a5), such as filtering the precipitated dimer particles. This is preferably carried out after step a4) at a temperature that allows dimer precipitation but retains most of the condensed monomers in solution. Filter aids may be used to facilitate filtration. Such methods for the separation of specific dimers are explained in WO2021 / 032821. Preferably, the mechanical separation of oligomers and / or dimers should be limited such that the amount of residual oligomers and dimers in solution is greater than 5% on a dry basis, preferably less than 20%. This can be achieved by setting a sufficiently high precipitation temperature that allows some oligomers and dimers to remain in solution. Alternatively, this can be achieved by limiting mechanical separation, for example by using a sufficiently large sieve size, allowing small particles to pass through.

[0185] - Activated carbon is used to remove colorants and other high-boiling-point organic contaminants, and the activated carbon is subsequently separated from any solution obtained in any of steps a3) to a5). The activated carbon can be mixed with the solution in powder or granular form and then filtered; alternatively, it can be used as a packed bed through which the solution passes. Filter aids can be used to facilitate filtration. A washing step using activated carbon can also be employed after the regenerated monomer product has been redissolved. Procedures for removing color using activated carbon are described in US6,642,350 and US2006 / 074136.

[0186] - Metals are removed using an ion exchanger, and the ion exchanger is subsequently separated from any solution obtained in any of steps a3) through a5). The ion exchanger may be mixed with the solution in powder or granular form and then filtered; alternatively, it may be used as a packed bed through which the solution passes. Filter aids may be used to facilitate filtration. A washing step using an ion exchanger may also be employed after the regenerated monomer product has been redissolved. Ion exchange procedures are described in US6,642,350 and US6,630,601.

[0187] - The obtained regenerated monomer product is redissolved in a glycol monomer, water, or an inert solvent or a mixture thereof, and then the regenerated monomer product is precipitated and mechanically separated from the solution.

[0188] - The filter cake obtained in step a6) is purged and / or washed with air, water, a single monomer and / or an inert solvent.

[0189] The above cleaning steps can be combined. For example, oligomer removal, activated carbon removal, and / or ion exchanger removal can be combined into a single separation step.

[0190] After completing the depolymerization and cleaning steps, a regenerated monomer product is obtained, which contains 3% to 50% by weight, preferably greater than 5%, more preferably greater than 10%, and more preferably less than 40% by weight of a substance that is liquid under ambient conditions, wherein the substance is selected from glycols, water, and inert solvents with melting points below 20°C. Preferably, the substance that is liquid under ambient conditions is selected from glycols and water with melting points below 20°C.

[0191] Diol monomers, water, and inert solvents can be collected from any of the steps described above. These streams can be in liquid or gaseous form. These streams typically contain other substances such as contaminants, residual catalysts from polyester depolymerization, and soluble components such as condensation monomers, dimers, oligomers, and other depolymerization byproducts.

[0192] It is desirable to recover the individual purified liquid streams for reuse in any of steps a1) through a6) or other cleaning steps. Common liquid recovery methods include membrane filtration or distillation.

[0193] In a preferred embodiment, a liquid stream is obtained from one or more steps including step a5) and steps following step a5), wherein the liquid stream comprises water and diol monomers, and wherein the liquid stream is directed to a separation unit configured such that a regenerated diol monomer stream is obtained, and at least a portion of the regenerated diol monomers is subsequently used in step a2).

[0194] In a preferred embodiment, a vapor stream is obtained during step a3), and a liquid stream is obtained from one or more steps including and following step a5). Both streams contain water and diol monomers, and both streams are directed to a common separation unit configured to obtain a regenerated diol monomer stream.

[0195] The common separation unit preferably includes at least one distillation column that enables heat exchange between the vapor stream and the liquid stream.

[0196] The separation unit can also be further configured to recover other liquids, especially water, into a separate purified liquid stream.

[0197] The depolymerization and subsequent crystallization of the regenerated monomer product results in a precipitated solid suspended in the solution. These precipitated solids, containing the regenerated monomer product, are separated from the solution by any suitable mechanical solid-liquid separation method. However, after step a6), some residual solution remains in the regenerated monomer product, which is considered a wet solid. Due to undesirable substances in the liquid, it is desirable to remove the liquid mechanically, thereby displacing the liquid in the wet solid. Methods known in the art include washing with a clean solution or other liquid to achieve such displacement. However, displacement is not complete, and undesirable substances tend to adhere to the solid surface. Using multiple washing steps further reduces the amount of undesirable substances, but also increases the amount of washing liquid that must ultimately be recovered, and increases the loss of regenerated monomer product. Furthermore, undesirable substances may be trapped between or within the voids of multiple solid particles, to which additional washing steps have little effect.

[0198] The liquid content in wet solids typically ranges from 50% to 200% based on the weight of the dry solids. Due to undesirable substances in the liquid, it is desirable to remove the liquid mechanically, thereby displacing it from the wet solids. Similarly, thermal separation by evaporation results in dissolved substances remaining in the regenerated monomer product, while displacement removes such substances along with the solution. This separation can include techniques such as purge with airflow, compression dehydration, or washing with liquid replacement.

[0199] It has been found that using a higher temperature washing solution can improve the removal of unwanted substances; at the same time, losses can be limited by reusing such washing solution in previous process steps.

[0200] According to a preferred embodiment of the invention, displacement washing and redissolution washing are combined. Such techniques can be used in combination and repeated in multiple sequences. It is particularly desirable to perform multiple washes of the solid followed by at least one purging stage. Diol monomers, water, or inert solvents can be used as washing solutions.

[0201] In a preferred embodiment, the inlet temperature of the washing liquid in the first washing step is lower than the inlet temperature of the washing liquid in subsequent washing steps. Preferably, at least one subsequent washing step is carried out at a washing liquid inlet temperature 10°C higher than the inlet temperature of the washing liquid in the first washing step, more preferably 15°C higher, and most preferably 20°C higher or higher. Optionally, the washing liquid in at least one subsequent washing step is washing liquid vapor, such as water vapor, which condenses upon contact with the regenerated monomer product. Increasing the washing liquid temperature will increase the solubility of contaminants and optionally residual catalyst. Therefore, the removal of contaminants and optionally residual catalyst is improved. Due to the higher solubility of the regenerated monomer product, some of the regenerated monomer product redissolves in the washing solution, thereby releasing trapped contaminants or residual catalyst, thus further improving the removal of contaminants and optionally residual catalyst.

[0202] A washing step with a higher inlet temperature yields a filtrate with a higher outlet temperature.

[0203] In a preferred embodiment, the temperature of the washing solution in the first washing step is close to the temperature of the filtered regenerated monomer product. Preferably, the temperature of the washing solution in the first washing step is no more than 10°C higher or lower than the temperature of the filtered regenerated monomer product, more preferably no more than 5°C. Although a washing solution with a temperature significantly higher than that of the regenerated monomer product can be used, it is preferable to use the first washing step as a displacement step, resulting in minimal redissolution for highly contaminated residual solutions. This minimizes the total redissolution amount.

[0204] Preferably, the total amount of fresh washing solution used is limited to limit the redissolution of the regenerated monomer product. Since each subsequent washing stage produces filtrate of higher purity, filtrate from one stage can be used as washing solution for the previous washing stage.

[0205] According to the present invention, the washing liquid from the subsequent washing step has higher inlet and outlet temperatures, and thus produces a filtrate containing more dissolved regenerated monomer products.

[0206] When this filtrate is reused as a washing liquid, it needs to be cooled by at least 10°C, which causes precipitation of the regenerated monomer product. At least a portion of this cooling occurs due to contact with the regenerated monomer product. In this way, heat from the washing liquid is transferred to the solids, which reduces the overall energy consumption of the process.

[0207] Further cooling conditions should be selected, preferably not exceeding 1°C / min, to allow the crystals to grow sufficiently and to separate those crystals in the early washing step without obstructing the flow of the washing liquid.

[0208] Alternatively, the filtrate can be reused in process steps prior to separation in step a6). A preferred use is for diluting the depolymerization solution in step a4). Furthermore, in this case, the solution undergoes some cooling due to contact with the regenerated monomer product, and energy is transferred to the solid.

[0209] The advantage of both return schemes is that additional dissolved regenerated monomer products will be returned to earlier steps.

[0210] Generally, the amount of washing liquid should range from 0.1 to 10 times the amount of the regenerated monomer product. Preferably, the amount is less than 5 times the amount of the regenerated monomer product, particularly preferably less than 3 times. Preferably, the amount is more than 0.3 times the amount of the regenerated monomer product, particularly preferably less than 0.5 times.

[0211] More preferably, the filter cake with a thickness ranging from 2 to 10 mm, and more preferably less than 8 mm, is washed.

[0212] Given the small amount of washing liquid and the thin filter cake in each cycle, it is necessary to distribute the washing liquid evenly. This is preferably achieved by spraying the washing liquid. Preferably, the washing liquid is distributed over the entire filter cake at a flow rate of 0.5 to 5 kg / m².

[0213] In a preferred embodiment, the resulting wet solids are cleaned in the following order:

[0214] - Place the wet solid of the recycled monomer product at a temperature of T F1 On the filter device;

[0215] - Washing of the regenerated monomer product includes the following steps in sequence: at temperature T W1 =T F1 The washing step using water and / or diol monomer A at + / -10°C, and the washing step at temperature T W2 >=T W1 Washing steps using water and / or glycol monomer A at +10°C;

[0216] - Optionally, after any of the cleaning steps described, at least one air purging step is performed;

[0217] - Optionally, use water and / or an additional washing step with diol monomer A;

[0218] - Optionally, at least two washing steps are then performed, such that fresh washing solution is used in a step that is not the first washing step, and the filtrate of that washing step is used as the washing solution in the previous washing step, if necessary, by lowering its temperature.

[0219] Optionally, the filtrate from a washing step, preferably from a solution obtained at temperature T W2 The filtrate from the washing step is used in a step prior to the filtration of the regenerated monomer product, preferably in step a4 for diluting the depolymerization solution.

[0220] The preferred washing and removal process in step a6) above can also be advantageously used in processes where the produced recycled monomer product is subsequently converted into a modified recycled monomer product without going through step b1).

[0221] In such cases, or in any situation where the liquid content in the regenerated monomer product is too high after step a6), it may be desirable to reduce the liquid content in BHET by evaporation.

[0222] As described in US3668235, the melt can be evaporated to an extremely low residual moisture content using a stirred vessel. However, the aforementioned patent neglects the loss of BHET (Boiler Energy Evaporation) due to liquid evaporation over time.

[0223] Partial drying to a liquid level of less than 30% by weight, or preferably less than 10% by weight, but more than 1% by weight, preferably more than 2% by weight, can also be achieved in a shorter residence time using a stirred vessel, or preferably by a thin-film evaporator, more preferably a stirred thin-film evaporator. Although the surface temperature of the evaporator may be high, the evaporation temperature of the BHET melt should be maintained below 130°C, preferably below 115°C. Evaporation can be assisted by pressures below ambient pressure, typically in the range of a few to several hundred millibars below ambient pressure. However, low vacuum levels below 100 millibars are undesirable, as this promotes the evaporation of BHET. The evaporated liquid can be condensed. In a preferred embodiment, the evaporated liquid is directed to a solvent recovery unit, where it can be combined with the liquid from a previous filtration or washing step.

[0224] Evaporation from the melt requires melting the wet recycled monomer product. This can be done in the same stirred vessel or in a separate melting vessel. After evaporation, the melt can be cooled and shaped into pellets using any suitable dry pelletizing equipment such as a flake machine, spray coagulant, rotational molding machine, or die pelletizer.

[0225] Further cleaning steps, such as melt filtration (preferably with a pore size of less than 3 µm, more preferably less than 1 µm), and / or decolorization in an absorption bed, such as an activated carbon bed, and / or ion exchange in an ion exchange bed, can be applied to the melt stream of the regenerated monomer product. This cleaning step can be performed before evaporation, as this allows for the use of a lower melting temperature, preferably below 110°C. It can also be performed after evaporation, as this limits the flow rate.

[0226] Although such cleaning steps may have been performed before step a6), it is also advantageous to perform them after step a6) because the volumetric flow rate is much smaller at this step, and final cleaning at the end of the process is desirable.

[0227] Therefore, the present invention also provides a method for preparing a polyester having repeating units [-A''-B''], wherein the repeating units [-A''-B''] have the formula [-OR 1 -OOC-R 2 [-CO-], which includes the following steps:

[0228] a1) Providing a waste stream comprising polyester having repeating units [-A''-B''], said repeating units [-A''-B''] having the formula [-OR 1 -OOC-R 2 -CO-], where R 1 and R 2 The same or different, and selected from aliphatic hydrocarbons containing 1 to 15 carbon atoms, aromatic hydrocarbons containing 1 to 3 aromatic rings, cyclic hydrocarbons containing 4 to 10 carbon atoms, and heterocycles containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms.

[0229] a2) Forming a mixture comprising the waste stream and at least one diol monomer HO-R capable of reacting with the polyester. 1 Blends of -OH groups

[0230] a3) Expose the blend obtained in step a2) in a reaction vessel to conditions suitable for the depolymerization of the polyester to obtain a depolymerization solution containing a recycled monomer product, said recycled monomer product containing at least 50% by dry weight a condensed monomer of the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH,

[0231] a5) Cool the solution to a temperature that causes the regenerated monomer product containing the condensed monomer to precipitate, and

[0232] a6) Recover the precipitated regenerated monomer product from the solution.

[0233] b2) Heating the recycled monomer product to obtain a polyester polymer.

[0234] The characteristic feature is that the regenerated monomer product of step a6) contains a residual solution containing undesirable substances, wherein washing for replacing the residual solution and washing for partially redissolving the regenerated monomer product are performed in at least two subsequent washing steps.

[0235] The preferred embodiment of the present invention requires monomer A (HO-R) 1 -OH) contains at least 90% ethylene glycol (EG), where this percentage is calculated as a molar percentage of the total amount of monomer A alone, and monomer B (HOOC-R) 2 The (-COOH) contains at least 90% terephthalic acid (TPA), where the percentage is calculated as a molar percentage of the total amount of monomer B alone.

[0236] Other suitable monomer forms may include any comonomer commonly used in polyester manufacturing, such as isophthalic acid (IPA), cyclohexanediol (CHDM), or diethylene glycol (DEG).

[0237] Polyesters made from these monomers belong to the polyethylene terephthalate and its copolymers (PET) group, with the main repeating unit being [TPA-EG-].

[0238] When EG is used as monomer A alone for PET depolymerization, the major monomer product is bis(hydroxyethyl) terephthalate (BHET). Clearly, in the presence of a comonomer, comonomer-substituted BHET may be formed. For example, DEG can replace EG as the reacted monomer A' or A''. Upon repolymerization, PET is obtained again. According to the present invention, PET is formed by adding TPA to BHET.

[0239] As an alternative, monomer R 3 -OH, preferably methanol, can be used for depolymerization. After reaction with ethylene glycol, BHET is obtained again.

[0240] Comparative Example 1

[0241] Polyester-polyethylene terephthalate (PET) with repeating units of [-A''-B''] was prepared using pure condensation monomer bis(2-hydroxyethyl) terephthalate (BHET) of the formula A'-B''-A'. Monomer A is primarily ethylene glycol, and monomer B is primarily terephthalic acid. BHET contains 15 mol / ton of COOH end groups, which is equivalent to approximately 0.3% by weight of mono(2-hydroxyethyl) terephthalate (MHET) or 0.2 mol% of COOH end groups.

[0242] The intrinsic viscosity (IV) of PET is 0.6 dl / g, corresponding to a molecular weight of 16400 g / mol. It has 122 end groups, and the amount of carboxyl end groups (COOH) is 10.7 mol / ton, which is equivalent to a COOH concentration of 8.8%.

[0243] For solid-phase polycondensation (SSP), the resulting PET was crystallized at 175°C, preheated to 195°C, and treated at 195°C under a continuous nitrogen flow, followed by cooling. An intrinsic viscosity of 0.75 dl / g was achieved in 18.6 hours. The COOH end-group content decreased to 7.7 mol / t, equivalent to a COOH concentration of 8.3%. Overall, the SSP reaction was based on 20.5% esterification. The final SSP reaction rate was 0.0081 dl / g / h.

[0244] The intrinsic viscosity was determined according to a standard method in a 50:50 mixture of phenol and dichlorobenzene.

[0245] Comparative Example 2

[0246] Comparative Example 1 was repeated. However, prior to PET preparation, BHET (containing 8.9 wt% BHET oligomer, mainly a dimer, 15 mol / t COOH end groups, which is equivalent to 0.2 mol% COOH end group content, and 40 to 50 wt% water (based on dry weight)) was preheated under reflux in the presence of water until approximately 100 mol / t COOH end groups were obtained, which is equivalent to approximately 2.1 wt% mono(2-hydroxyethyl) terephthalate (MHET) or 1.3 mol% COOH end group content.

[0247] The intrinsic viscosity of the PET obtained from the modified BHET is 0.63 dl / g, and the COOH end groups are 7 mol / t, which is equivalent to a COOH concentration of 6.1%.

[0248] Comparing Comparative Example 1 and Comparative Example 2 shows that a small increase in COOH end groups in BHET did not lead to an increase in COOH end groups in PET resin.

[0249] Example 1

[0250] PET with an intrinsic viscosity of 0.6 dl / g was prepared using the recycled BHET obtained by the method of the present invention. The BHET used as the starting material in Comparative Example 2 was heated at 150-160°C and a pressure below 7 barg for 4 hours to obtain a modified recycled monomer product. The resulting modified recycled monomer product contained 973 mol / t of COOH end groups, which is equivalent to approximately 20% by weight of mono(2-hydroxyethyl) terephthalate (MHET) or 12.3 mol% of COOH end groups, representing an increase of 11 mol%.

[0251] The PET made from the modified recycled monomer product has a carboxyl end group content of 15.3 mol / t, which is equivalent to a COOH concentration of 12.6%.

[0252] For solid-phase polycondensation (SSP), the resulting PET was crystallized at 175°C, preheated to 195°C, and treated at 195°C under a continuous nitrogen flow, followed by cooling. An intrinsic viscosity of 0.75 dl / g was achieved in 13.7 hours. The amount of carboxyl end groups decreased to 10.8 mol / t, equivalent to a carboxyl concentration of 11.6%. Overall, the SSP reaction was based on 31.2% esterification. The final SSP rate was 0.0109 dl / g / h.

[0253] Example 2

[0254] PET with an intrinsic viscosity of 0.6 dl / g was prepared using the recycled BHET obtained by the method of the present invention. A modified recycled monomer product was obtained as described in Example 1, but the processing time was extended until the COOH end-group content reached 32 mol%.

[0255] The PET prepared in this way has a carboxyl end group content of 28.5 mol / ton, which is equivalent to a COOH concentration of 23.4%.

[0256] For solid-phase polycondensation (SSP), the resulting PET was crystallized at 175°C, preheated to 195°C, and treated at 195°C under a continuous nitrogen flow, followed by cooling. An intrinsic viscosity of 0.75 dl / g was achieved in 8.6 hours. The amount of carboxyl end groups decreased to 20.8 mol / t, equivalent to a carboxyl concentration of 22.4%. Overall, the SSP reaction was based on 52.9% esterification. The final SSP rate was 0.0174 dl / g / h.

[0257] A comparison of embodiments and comparative embodiments according to the present invention shows that a significant increase in COOH end groups in BHET leads to an increase in COOH end groups in PET resin and consequently an increase in SSP rate.

[0258] Comparative Example 3: No washing

[0259] Depolymerization was initiated with 288 g of clear PET and 640 ml of ethylene glycol, followed by the addition of 640 ml of water, according to steps a1) to a6) of the present invention, including step a4, to prepare a regenerated BHET filter cake. After step a5) and before step a6), a red concentrate dissolved in ethylene glycol / water was added. The filter cake was dried. The chromaticity a* values ​​of the dried filter cake (reflectivity) and the filtrate (transmittance) were measured. The filtrate color was converted to equivalent concentrate volume (ECA) based on a calibration curve obtained from the diluted concentrate. The ECA of the filtrate was 27 ml, and the a* value of the filter cake was 8.4.

[0260] Comparative Example 4: One-step replacement washing process

[0261] Comparative Example 3 was repeated. Before drying, the filter cake was washed once with water at 5°C at a ratio of 2:1 (filter cake weight to washing liquid). The color a* values ​​of the dried filter cake and the washing filtrate were measured. The filtrate color was converted to equivalent concentrate volume (ECA). The ECA of the filtrate was 4.8 ml, and the a* value of the filter cake was 5.4. Compared to Comparative Example 3, washing resulted in the transfer of additional colorant into the filtrate.

[0262] Comparative Example 5: Two-step replacement washing process

[0263] Comparative Example 3 was repeated. Before drying, the filter cake was washed twice with water at 5°C at a ratio of 2:1 (filter cake weight to washing liquid). The color a* values ​​of the dried filter cake and the second washing filtrate were measured. The filtrate color was converted to equivalent concentrate volume (ECA). The ECA of the second filtrate was 0.6 ml, the combined ECA was 5.4 ml, and the a* value of the filter cake was 5.6. The BHET loss due to the two washing steps was 3.8%.

[0264] Compared to Comparative Example 4, the additional washing resulted in only a very small amount of additional colorant being transferred into the filtrate.

[0265] Example 3: One displacement washing step, one redissolution washing step

[0266] Comparative Example 3 was repeated. Before drying, the filter cake was washed once with water at 5°C and then once with water at 40°C at a 2:1 ratio of filter cake weight to washing liquid. Both filtrates were recovered below room temperature and remained clear. The color a* values ​​of the dried filter cake and the second washing filtrate were measured. The filtrate color was converted to equivalent concentrate volume (ECA). The ECA of the second washing filtrate was 3.2 ml, the combined ECA was 8.1 ml, and the color a* value of the filter cake was 4.3. The BHET loss due to the two washing steps was 2.6%.

[0267] Compared to Comparative Example 5, the additional washing resulted in additional colorant being transferred to the filtrate without causing additional yield loss. The second filtrate is suitable for use as a coolant in previous process steps such as step a4.

[0268] Comparative Example 6: Three Redissolution Washing Steps

[0269] Comparative Example 3 was repeated. Before drying, the filter cake was washed three times with water at 40°C at a 2:1 ratio of filter cake weight to washing liquid. When cooled to room temperature, the first filtrate remained clear, while the second and third filtrates became cloudy. The color a* values ​​of the dried filter cake and all washing filtrates were measured. The filtrate colors were converted to equivalent concentrate volumes (ECA). The combined ECA of all filtrates was 8.8 ml, and the a* value of the filter cake was 1.8. The BHET loss due to the two washing steps was 13%.

[0270] Compared to Example 3, the hot washing step resulted in additional colorant being transferred into the filtrate, but caused significant yield loss due to redissolution in the second and third washing steps.

Claims

1. A method for preparing a polyester having repeating units [-A''-B''], said repeating units [-A''-B''] having the formula [-OR 1 -OOC-R 2 [-CO-], which includes the following steps: a1) Providing a waste stream comprising polyester having repeating units [-A''-B''], said repeating units [-A''-B''] having the formula [-OR 1 -OOC-R 2 -CO-], where R 1 and R 2 The same or different, and selected from aliphatic hydrocarbons containing 1 to 15 carbon atoms, aromatic hydrocarbons containing 1 to 3 aromatic rings, cyclic hydrocarbons containing 4 to 10 carbon atoms, and heterocycles containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms. a2) Forming a mixture comprising the waste stream and at least one diol monomer HO-R capable of reacting with the polyester. 1 Blends of -OH groups a3) The blend obtained in step a2) is exposed in a reaction vessel to conditions suitable for the depolymerization of the polyester to obtain a depolymerization solution containing a recycled monomer product, said recycled monomer product containing at least 50% by dry weight condensed monomer having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH, b1) The regenerated monomer product is heated in a reactor with 3-50% by weight of water at a pressure at least 0.5 bar above ambient pressure but not exceeding 10 bar to a temperature above the melting point of the condensed monomer, in order to obtain the modified regenerated monomer product. as well as b2) Heating the modified recycled monomer product from step b1), preferably under reduced pressure, to obtain a polyester polymer.

2. The method according to claim 1, characterized in that, The polyester is polyethylene terephthalate (PET), the diol monomer added in step a2) is ethylene glycol, and the condensation monomer obtained in step a3) is BHET.

3. The method according to any one of claims 1 or 2, characterized in that, Perform the following steps before step b1): a5) Cool the solution to a temperature that causes the regenerated monomer product containing the condensed monomer to precipitate, and a6) Recover the precipitated regenerated monomer product from the solution.

4. The method according to claim 3, characterized in that, Perform the following steps between step a3) and step a5): a4) The depolymerization solution from step a3) is mixed with water or an inert solvent to obtain a diluted solution, wherein the regenerated monomer product obtained in step a6) contains water, and is provided to step b1).

5. The method according to any one of claims 1 to 4, characterized in that, The COOH end-group concentration of the regenerated monomer product provided to step b1) is less than 10 mol%, and the COOH end-group concentration of the modified regenerated monomer product obtained in step b1) is at least 9 mol higher than that of the regenerated monomer product obtained in step a3).

6. The method according to claim 5, characterized in that, The modified recycled monomer product obtained in step b1) contains at least 10 mol% of a modified condensation monomer having polyester repeating units [-A''-B''] with OH and COOH end groups, which have the formula [HO-R 1 -OOC-R 2 -COOH].

7. A method for preparing a polyester having repeating units [-A''-B''], said repeating units [-A''-B''] having the formula [-OR 1 -OOC-R 2 [-CO-], which includes the following steps: a1) Providing a waste stream comprising polyester having repeating units [-A''-B''], said repeating units [-A''-B''] having the formula [-OR 1 -OOC-R 2 -CO-], where R 1 and R 2 The same or different, and selected from aliphatic hydrocarbons containing 1 to 15 carbon atoms, aromatic hydrocarbons containing 1 to 3 aromatic rings, cyclic hydrocarbons containing 4 to 10 carbon atoms, and heterocycles containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms. a2) Forming a mixture comprising the waste stream and at least one diol monomer HO-R capable of reacting with the polyester. 1 Blends of -OH groups a3) Expose the blend obtained in step a2) in a reaction vessel to conditions suitable for the depolymerization of the polyester to obtain a depolymerization solution containing a recycled monomer product, said recycled monomer product containing at least 50% by dry weight condensed monomer having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH, b2) Heating the recycled monomer product to obtain a polyester polymer. The blend formed in step a2) is characterized in that it contains at least one volatile organic pollutant that has high solubility in diol monomer A, whose normal boiling point is more than 50°C lower than that of diol monomer A, and during step a3), at least 15% but no more than 150% by weight of diol monomer A supplied in step a2) is evaporated.

8. The method of claim 7, further comprising steps a5) and a6) as defined in claim 4).

9. The method according to claim 7, characterized in that, During step a3), the evaporation of diol monomer A results in a decrease in the content of diol monomer A in the depolymerization step a3), and the evaporated diol monomer A or a portion thereof is optionally replaced by high-purity diol monomer A.

10. The method according to any one of claims 7 to 9, characterized in that, By weight, at least 15% but no more than 60% of the diol monomer A supplied to step a2) is evaporated and removed during depolymerization step a3).

11. A method for preparing a polyester having repeating units [-A''-B''], said repeating units [-A''-B''] having the formula [-OR 1 -OOC-R 2 [-CO-], which includes the following steps: a1) Providing a waste stream comprising polyester having repeating units [-A''-B''], said repeating units [-A''-B''] having the formula [-OR 1 -OOC-R 2 -CO-], where R 1 and R 2 The same or different, and selected from aliphatic hydrocarbons containing 1 to 15 carbon atoms, aromatic hydrocarbons containing 1 to 3 aromatic rings, cyclic hydrocarbons containing 4 to 10 carbon atoms, and heterocycles containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms. a2) Forming a mixture comprising the waste stream and at least one diol monomer HO-R capable of reacting with the polyester. 1 Blends of -OH groups a3) Exposing the blend obtained in step a2) to conditions suitable for the depolymerization of the polyester in a reaction vessel to obtain a depolymerization solution containing a recycled monomer product, the recycled monomer product containing at least 50% by dry weight a condensed monomer having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH, a5) Cool the solution to a temperature that causes the regenerated monomer product containing the condensed monomer to precipitate, and a6) Recover the precipitated regenerated monomer product from the solution. b2) Heating the recycled monomer product to obtain a polyester polymer. The method is characterized in that the regenerated monomer product of step a6) contains a residual solution containing undesirable substances, wherein washing for replacing the residual solution and washing for partially redissolving the regenerated monomer product are performed in at least two subsequent washing steps, and the filtrate of one of the washing steps is used in the method steps prior to the recovery of step a6).

12. The method according to claim 11, characterized in that, The washing process includes a series of washing steps, wherein the inlet temperature of the washing liquid in one washing step is lower than the inlet temperature of the washing liquid in at least one subsequent washing step, preferably 10°C lower, more preferably 15°C lower, and most preferably 20°C or more lower.

13. The method according to claim 11 or 12, characterized in that, Step a4) is performed between steps a3) and a5), where the depolymerization solution from step a3) is mixed with water to obtain a diluted solution, wherein the filtrate from a washing step, preferably from at least one subsequent washing step, is used in step a4).

14. Use of the polyester obtained by the method according to any one of claims 1 to 6 as a starting polyester for solid-state polycondensation, wherein, The solid-state polycondensation reaction prepares a high-viscosity polyester with a viscosity at least 0.1 dl / g higher than that of the starting polyester, and the solid-state polycondensation reaction is based on esterification and transesterification reactions, wherein the esterification reaction accounts for more than 25% of the total esterification and transesterification reactions.

15. A modified recycled monomer product obtained by the method according to any one of claims 1 to 6, and having the inclusion formula HO-R 1 -OOC-R 2 -COO-R 1 The condensation monomer of -OH is [HO-R] 1 -OOC-R 2 A blend of modified condensation monomers of [-COOH], wherein R 1 and R 2 The hydrocarbons may be the same or different, and are selected from aliphatic hydrocarbons containing 1 to 15 carbon atoms, aromatic hydrocarbons containing 1 to 3 aromatic rings, cyclic hydrocarbons containing 4 to 10 carbon atoms, and heterocycles containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms, characterized in that... The concentration of COOH end groups in the modified regenerated monomer product is 10 mol% to 50 mol%, preferably 15 mol% to 45 mol%, and more preferably 20 mol% to 40 mol%.

16. Use of a melt-phase polymerization apparatus previously used to prepare polyester from diol monomer A and diacid monomer B, the use being for performing step b1 of the method according to any one of claims 1 to 6.

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