Process for preparation of polyesters

Abstract

The present invention relates to a process for preparing a polyester comprising the steps of providing a monomer slurry from a recycled monomer product and at least one diacid monomer wherein the monomer product contains from 50% to 97% of a condensed monomer and from 3% to 50% by weight of a substance that is liquid under ambient conditions, and using the monomer slurry for the polymerization of the polyester, wherein the step of preparing the monomer slurry is performed in a manner that allows the monomer slurry to be maintained in liquid form. The invention also relates to solid particles comprising a recycled monomer product and a diacid monomer B, the molar ratio of s ''units-OC-R2-CO-to the diacid HOOC-R2-COOH ranging from 5: 1 to 1: 5. Further, the present invention relates to a process for providing a recycled monomer product wherein the monomer product contains from 50% to 97% by weight of a condensed monomer and from 3% to 50% by weight of a substance that is liquid under ambient conditions.

Description

Technical Field

[0001] The present invention relates to a method for recycling monomers from polycondensates, namely polyesters, and further relates to particles recycled from polycondensates, namely polyesters. Background Art

[0002] The preparation of polymers from their monomers is well known and established on a large scale. The monomers used traditionally originate from fossil resources. The use of fossil resources is based on a linear product flow from fossil resources to polymers and then to waste. For a long time, this linear product flow was unsustainable. As an alternative, it has been proposed to use monomers derived from renewable resources to produce a more circular product flow. However, the resulting product flow from polymer to CO 2 The cycle of water to plant-based renewable resources to polymers is a lengthy and energy-intensive method of providing polymers.

[0003] In particular, polycondensates have the advantage that they can be depolymerized into their monomers and repolymerized from such recycled monomers. Depending on the depolymerization technique, the same monomers that are generally used to prepare the original polymer can be obtained. In other cases, recycled monomers may have different compositions, so their use in existing large-scale manufacturing processes is limited. Such limiting differences may be the melting point of the solid monomer, the viscosity of the liquid monomer or the energy required for melting or evaporating the monomer. In particular, the difference is caused by the predefined molar ratio of the reacting monomers.

[0004] Polyesters have a general structure comprising repeating units. They are generally prepared on a large scale by polymerizing monomers with one another, wherein the monomers are diols and diacids.

[0005] Polyesters are generally 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 as a result of ring-opening polymerization.

[0006] These polyesters can be recycled by depolymerization by adding diol monomers. Depolymerization produces a recycled monomer product comprising a monomer having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer, where R 1 and R 2 Condensation monomers may be introduced into conventional polyester preparation processes starting with diol and diacid monomers.

[0007] However, the addition of recycled monomer product changes the molar ratio of the total A and B units as defined below. Therefore, the amount of individual diol monomer A must be reduced and / or the amount of individual diol monomer A evaporated from the process must be increased. Both of these are possible in conventional polyester production processes, but only to a limited extent, since the heating capacity for evaporation is limited and if the ratio of individual diol monomer A to individual diacid monomer B is reduced, the viscosity of the monomer feed changes.

[0008] GB-610136 is an early description of depolymerizing polyesters with diol monomers and repolymerizing them from the depolymerized solution.

[0009] Various methods have been developed to clean the monomer product obtained by depolymerization. See US-4,609,680, US-6,642,350, US-2006 / 074136 and US-6,630,601.

[0010] The typical washing step is based on crystallization and subsequent filtration. This results in a monomer product with a significant amount of residual liquid which must be eliminated to obtain pure condensation monomer.

[0011] The formation of solid condensation monomer particles is described in EP-2 838 941 A1. Here, flash evaporation is used to reduce the liquid content before the particle formation process. This evaporation step is energy intensive and is not necessary in many cases, because the equipment used to repolymerize the condensation monomers to polyesters, for example, has sufficient capacity to evaporate residual liquid in the esterification step. In addition, this patent is limited to particle formation of condensation monomers and does not provide for the formation of particles from a slurry containing condensation monomers and diacid monomers.

[0012] WO 2021 / 032826 A1 describes a method for obtaining granules with a high BHET content and a high dry weight by granulation and fluidized bed drying of crystallized BHET, which granules have the particular property of a large pore volume. The large pore volume is said to facilitate dissolution in EG or molten BHET.

[0013] WO 2021 / 032826 A1 describes the option of adding solid terephthalic acid to crystalline BHET. However, even if this is done after granulation, this will result in a dry blend, since granulation is defined as being compatible with the maintenance of the crystalline form. Such an inhomogeneous and brittle dry blend is not suitable for transport. Solid particles containing those ingredients in specific ratios are not disclosed.

[0014] Condensation products free of liquid residues can also be obtained by evaporation and condensation of the condensation monomers after evaporation of all liquid components. This is described in US Pat. No. 10,544,276, wherein after depolymerization, a step of evaporating all diols is carried out. This leads to the risk that the equilibrium of the depolymerization product shifts significantly back to a higher oligomer content; repolymerization occurs to some extent. This risk is reduced by reducing the pressure and operating the evaporation in a temperature range below the depolymerization temperature.

[0015] US-2020 / 0127416A1 describes that, in order to produce PET, BHET is added as a condensation monomer to TPA (terephthalic acid) and EG (ethylene glycol) at high temperature, the latter representing a diacid monomer and a diol monomer. BHET is not introduced as a solid into a slurry containing TPA and EG.

[0016] In view of the preparation of BHET, which includes the energy-intensive steps of evaporating all volatile liquids from BHET and subsequently evaporating BHET itself, BHET is inevitably used as a pure substance and must therefore be kept above its melting temperature to prevent solidification. This is confirmed by the 110°C mixing temperature used in US-2020 / 0127416A1. The BHET supplied to the slurry preparation does not contain (and due to the conditions applied cannot be) any substance that is liquid under ambient conditions.

[0017] Particular difficulties arise from contaminants that are liquid during depolymerization but solidify at lower temperatures.

[0018] WO 2021 / 089803 A1 describes a method in which a depolymerization solution inside a depolymerization reactor is separated into a first homogeneous part and a second part containing agglomerates. The agglomerates contain contaminants. The parts are then taken out of the reaction vessel separately. This requires separation at the temperature of depolymerization or cooling inside the reaction vessel, which causes solidification of such contaminants in the presence of liquefied contaminants and brings the risk of serious blockage inside the reactor.

[0019] WO 2021 / 089809 A1 describes a method in which pollutants are separated from a depolymerization solution by density separation in a separation vessel. In the process, the entire depolymerization solution is first cooled to precipitate the pollutants. Only then can the pollutants be separated and collected. Thus, the pollutants can only be separated after they have solidified based on the density difference between their solid form and the dilute solution. Summary of the invention

[0020] The problem of the present invention is to provide an improved method which overcomes the disadvantages of the above-mentioned methods. This problem is solved by the method of the present invention.

[0021] In detail, according to claim 1, the present invention provides a method for efficiently preparing and using a monomer product containing residual liquid.

[0022] According to claim 9, the present invention further provides a method for preparing pulp particles which are particularly suitable for preparing polyesters.

[0023] According to claim 11, the present invention further provides pulp particles which are particularly suitable for preparing polyesters.

[0024] According to claims 15 and 17, the present invention further provides a method for adjusting the depolymerization process to promote the return of the used solvent and at the same time reduce the formation of by-products.

[0025] According to claims 15 and 21, the invention further provides a method for optimizing the addition of cooling liquid to the depolymerization solution in such a way that the formation of by-products is reduced.

[0026] According to claims 15 and 22, the invention further provides a method for optimizing the separation of pollutants which are liquid under the depolymerization conditions and solidify during cooling to room temperature.

[0027] Specifically, the above problem is solved by a process for preparing a polyester having a repeating unit [-A"-B"] having the formula [-OR 1 -OOC-R 2 -CO-], the method comprising the following steps:

[0028] a) providing a recycled monomer product, wherein the monomer product contains 50 wt % to 97 wt % of monomers having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer, and 3% to 50% by weight of a substance that is liquid under ambient conditions, wherein the substance is selected from a diol having a melting point below 20° C., water and an inert solvent,

[0029] b) at least one compound having the formula HOOC-R 2 -COOH diacid monomer B is added to the recycled monomer product of step a) to obtain a monomer slurry,

[0030] c) using the monomer syrup from step b) for the polymerization of a polyester having repeating units [-A"-B"] of the formula [-OR 1 -OOC-R 2 -CO-],

[0031] Where R 1 and R 2are 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 heterocyclic rings containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms,

[0032] It is characterized in that the step of preparing the monomer slurry in step b) is performed in a manner allowing the monomer slurry to be maintained in liquid form.

[0033] The present invention also provides recycled monomer products, as they are obtained from the depolymerization, in a form that allows them to be effectively used in the preparation of polyesters and thus create an effective recycling loop for polyesters. Therefore, the present invention further relates to solid particles comprising:

[0034] a) a recycled monomer product, wherein the recycled monomer product contains 50% to 100% by weight of monomers having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer,

[0035] b) having the formula HOOC-R 2 -COOH diacid monomer B, where the B" unit -OC-R 2 -CO- and diacid HOOC-R 2 The molar ratio of -COOH ranges from 5:1 to 1:5,

[0036] Where R 1 and R 2 The same or different, 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 heterocyclic rings containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms.

[0037] The present invention also provides a (separate) process for providing a recycled monomer product, wherein the monomer product contains 50% to 97% by weight of monomers having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer, where R 1 and R 2 As defined above, the method comprises the following steps:

[0038] a1) providing a waste stream comprising polyesters having repeating units [-A"-B"] of the formula [-OR 1 -OOC-R 2 -CO-],

[0039] a2) forming a polyester containing a waste stream and at least one diol monomer HO-R1 -OH blends,

[0040] a3) exposing the blend obtained in step a2) to conditions suitable for depolymerization of the polyester in a reaction vessel to obtain a depolymerization solution containing recycled monomer product, wherein the monomer product contains a polyester having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer,

[0041] a4) mixing the depolymerization solution from step a3) with water or an inert solvent to obtain a diluted solution,

[0042] a5) cooling the diluted solution from step a4) to a temperature at which the recycled monomer product comprising the condensation monomers precipitates, and

[0043] a6) recovering the precipitated recycled monomer product from the solution to obtain a recycled monomer product containing 3 to 50% by weight of a substance that is liquid under ambient conditions, wherein the substance is selected from the group consisting of a glycol having a melting point below 20° C., water and an inert solvent,

[0044] Characterized in that the ratio of the sum of all diol monomers added in step a2) to the polyester repeating units [-A"-B"] contained in the waste stream from step a1) ranges from 5:1 to 15:1, and the ratio of diol monomers to the polyester repeating units [-A"-B"] contained in the depolymerization solution in step a3) ranges from 4:1 to 14:1, wherein the ratios are molar ratios.

[0045] The following nomenclature will be used herein for the polycondensates, their depolymerization products and their monomers.

[0046] Monomer: A general term for the structural unit of a polymer. For condensation polymers, monomer includes individual monomers, substituted monomers, and condensation monomers.

[0047] Single monomer: The basic structural unit of a polymer in unreacted form. According to the present invention, monomer A is a monomer having the formula HO-R 1 -OH diol, monomer B is a diol having the general formula HOOC-R 2 -COOH diacid, wherein R 1 and R 2 The same or different, 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 heterocyclic rings containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms.

[0048] Substituted monomer: As single monomer B HOOC-R 2 -COOH and two end-capping molecules R 3-OH, the end-capping molecule will not form part of the recurring units of the relevant polycondensate, i.e. the end-capping molecule will be eliminated during the polycondensation reaction to produce the polycondensate, and wherein R 3 is an aliphatic hydrocarbon containing 1 to 15 carbon atoms. According to the invention, the substituted monomer C has the formula R 3 OOC-R 2 -COOR 3 In one embodiment, the end-capping molecule R 3 -OH may be methanol, so that the resulting substituted monomer C is H 3 COOC-R 2 -COOCH 3 .

[0049] Condensation monomer: A short condensation product from both individual monomers A and B, having the formula A'-B"-A', wherein 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 As defined above.

[0050] Reactive Monomer: A structural unit of a polymer in any reactive form within a larger molecule. Possible forms are A', A", B', and B", where A' is equivalent to H'-A", and B' is equivalent to H'-B".

[0051] According to the present invention

[0052] A' unit represents a reactive monomer A, which has one reactive terminal group and one unreacted -OH terminal group and has the formula HO-R 1 -O-diols;

[0053] A" unit represents a reactive monomer A, which has two reactive end groups and has the formula -OR 1 -O-diol,

[0054] Reactive A units represent the sum of all reactive monomer units A' and A", and

[0055] Total A units refer to the sum of all reacted and unreacted monomer units A, A' and A".

[0056] According to the present invention

[0057] The B' unit represents a reactive monomer B having one reactive terminal group and one unreacted -COOH terminal group and having the formula HOOC-R 2 -CO- diacid;

[0058] B" unit represents a reactive monomer B having two reactive end groups, preferably having two reactive end groups and having the formula -OC-R 2 -CO- diacid, where

[0059] The reactive B unit represents the sum of all reactive monomer units B' and B", and

[0060] Total B units refers to the sum of all reacted and unreacted monomer units B, B' and B".

[0061] For example, total B units is the total amount of B units in a given product and is the sum of the moles of all molecules containing B units multiplied by the number of B units in each molecule. For example, the total amount of B units for a product containing monomers B and A'-B"-A' and dimer A'-B"-A"-B"-A' = mol B + 1*mol A'-B"-A' + 2*mol A'-B"-A"-B"-A'.

[0062] The following terms include the listed molar amounts of each substance:

[0063]

[0064]

[0065] Repeating unit: The condensation product of each of the individual monomers A and B. Possible forms are those having the formula [-OR 1 -OOC-R 2 -CO-], which provides a repeating structure in the middle of the molecule, or A'-B"- and -B"-A', which provide structure at the ends of the molecule. A single repeating unit is also present in the condensation monomer A'-B'.

[0066] Dimer: A condensation product of two individual monomers having 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 therefore part of an oligomer.

[0067] Oligomer: The condensation product of two monomers A and B with several repeating units, with the general formula E[-A"-B"] n _ E, wherein 3≤n≤9, -A"-B"- has the formula [-OR 1 -OOC-R 2 -CO-], and E=H', A' or B'.

[0068] Condensation polymer: A condensation product of two individual monomers with a large number of repeating units, with the general formula E[-A"-B"] n-E, wherein n>9, -A"-B"- has the formula [-OR 1 -OOC-R 2 -CO-], and E=H', A' or B'. According to the invention, the polycondensate is a polyester.

[0069] Polyesters are obtained by polycondensation with simultaneous elimination of low molecular weight reaction products. The polycondensation can be carried out directly between the monomers. The polycondensation can also be carried out via intermediate products, which are subsequently reacted by transesterification with simultaneous elimination of low molecular weight reaction products, or by ring-opening polymerization.

[0070] The polyesters thus obtained have a substantially linear polymer chain. However, small amounts of branches may form.

[0071] Preferred polyesters according to the invention are thermoplastic polyesters.

[0072] Polyester is usually composed of a general formula HO-R 1 -OH diol component and having the general formula HOOC-R 2 -COOH dicarboxylic acid component obtained by polycondensation, wherein R 1 and R 2 Typically, it 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 heterocycle containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms. Typically, a linear or cyclic diol component and a generally linear, aromatic or heterocyclic dicarboxylic acid component are used. Instead of a dicarboxylic acid, its corresponding diester, generally its dimethyl ester, may also be used. Preferred examples of such polyesters are polyethylene terephthalate (PET) generally obtained from terephthalic acid (TPA) and ethylene glycol (EG), polybutylene terephthalate (PBT) obtained from terephthalic acid (TPA) and 1,4-butanediol (BD), polytrimethylene terephthalate (PTT) obtained from terephthalic acid (TPA) and 1,3-propylene glycol (PB), polyethylene furandicarboxylate (PEE) obtained from 2,5-furandicarboxylic acid (FDCA ... poly(ethylene furandicarboxylate) (PEE) obtained from 2,5-furandicarboxylic acid (FDCA) and propylene glycol (PB), and poly(ethylene furandicarboxylate) (PEE) obtained from 2,5-furandicarboxylic acid (FDCA) and propylene glycol (PB). Poly(propylene furandicarboxylate) (PTE), poly(butylene succinate) (PBS) obtained from succinic acid (SA) and butane 1,4-diol (BD), poly(butylene adipate) (PBA) obtained from adipic acid (AdA) and 1,4-butanediol (BD), poly(butylene adipate terephthalate) (PBAT) obtained from adipic acid (AdA) terephthalic acid (TPA) and 1,4-butanediol (BD), and polyethylene naphthalate (PEN) obtained from naphthalene-2,6-dicarboxylic acid and ethylene glycol, wherein all of the above polyesters may be present in the form of homopolymers or copolymers.

[0073] The present invention describes a method for preparing polyesters from their monomers, wherein at least one monomer is a recycled monomer product obtained from polyesters. The polyester prepared from the recycled monomer product and the polyester providing a source for the recycled monomer product may be the same or different in composition. The difference in composition may be caused by the use of different monomers and / or the use of different amounts of common monomers when preparing the polyester. The difference in composition may also be caused by blends of different polyesters. According to the present invention, at least one common monomer is present in the polyester providing a source of the recycled monomer product and in the polyester prepared from the recycled monomer product.

[0074] For example, PET can be depolymerized using butanediol as a reaction partner, and the resulting recycled monomer product can be repolymerized to form PBT. Alternatively, PET copolymers with a large amount of diol comonomer can be depolymerized using ethylene glycol as a reaction partner, and the resulting recycled monomer product can be repolymerized to form PET with a lower comonomer content.

[0075] The polyester according to the invention has a 1 -OOC-R 2 -CO-] of the repeating unit [A"-B"-]. These polyesters can be prepared by adding a repeating unit having the formula HO-R 1 The depolymerization produces a recycled monomer product comprising condensation monomers of the form A'-B"-A' as defined above and specifically having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH.

[0076] Depolymerization can result in various byproducts, including those having specifically the formula HO-R 1 -OOC-R 2 -COOH byproducts of the general structure A'-B', or with the formula HOOC-R 2 -COOH diacid monomer B, and partial depolymerization products, including dimers and oligomers.

[0077] Other variations of the above-mentioned by-products containing comonomer may also be formed.

[0078] According to the present invention, the recycled monomer product comprises at least 50% by weight of the A'-B"-A' form and specifically has the formula HO-R 1 -OOC-R 2 -COO-R 1In one embodiment, the recycled monomer product of drying comprises at least 50%, more preferably at least 70%, and most preferably at least 80% of the condensation monomer, and the remainder can be in the form of dimer, oligomer and other by-products. In a preferred embodiment, the recycled monomer product of drying comprises less than 90% of the condensation monomer. This is enough to obtain a good quality recycled monomer product while reducing the yield loss caused by removing oligomer and dimer. The percentage is calculated as the mole % of the total amount based on the B unit. Drying refers to the solid content in the recycled monomer product without any liquid, such as residual glycol, water or inert solvent.

[0079] Furthermore, the recycled monomer product comprising at least 50% by weight of the condensation monomer, ie, the recycled monomer product in a wet state, contains remainders in the form of dimers, oligomers and other by-products.

[0080] Typically, all monomer products containing more than 50% by weight of recycled monomer units are considered recycled monomer products. The calculation does not take into account any water or inert solvents that may be present in the monomer product.

[0081] An inert solvent is any liquid which dissolves or disperses at least a portion of the solid matter and which does not react with the solid matter or at least reacts with the solid matter only to a small extent at the temperature at which the solution or dispersion is formed.

[0082] Preferably, a monomer product containing more than 70% by weight of recycled monomer units is used in the process of the invention.

[0083] For example, using a compound specifically having the formula HO-R 1 -OH recycled diol monomer A is depolymerized and can be recycled having a specific formula [-OR 1 -OOC-R 2 -CO-], producing a polyester having a repeating unit [A"-B"-] of the formula [HO-R 1 -OOC-R 2 -COOR 1 -OH] condensation monomer A'-B"-A'. All monomer units A'(HO-R 1 -O-) and all monomer units B" (-OC-R 2 -CO-) are recycled. For this calculation, the monomer unit A'(HO-R 1 -O-) and the weight of monomer unit B" (-OC-R 2 -CO-) and divided by the weight of the condensation monomer A'-B"-A'[HO-R 1 -OOC-R 2 -COOR 1-OH] weight. Water is not taken into account. If specifically having the formula HO-R 1 A monomer A having a molecular weight of [HO-R 1 -OOC-R 2 -COOR 1 -OH], during which elimination of the glycol monomer A occurs, or wherein the glycol monomer is recycled from a process in which it has previously been used as a solvent.

[0084] For example, using a compound specifically having the formula HO-R 1 -OH of the original diol monomer A is depolymerized and can be recycled to have a specific formula [-OR 1 -OOC-R 2 -CO-], producing a polyester having a repeating unit [A"-B"-] of the formula [HO-R 1 -OOC-R 2 -COOR 1 -OH] condensation monomer A'-B'-A'. In this case, 50% of the monomer units A'(HO-R 1 -O-) and all monomer units B" (-OC-R 2 -CO-) are recycled. For this calculation, 50% of the monomer units A'(HO-R 1 -O-) and the weight of monomer unit B" (-OC-R 2 -CO-) and divided by the weight of the condensation monomer A'-B"-A'[HO-R 1 -OOC-R 2 -COOR 1 -OH] by weight. For this calculation, the atoms of the linking groups A' and B" (specifically, the linking O atom in the A' group) are divided equally into two units. In the case of bishydroxyethyl terephthalate (BHET) obtained from PET and virgin ethylene glycol as monomer A, the recycled content would be 79%.

[0085] In addition, specifically having the formula [HO-R 1 -OOC-R 2 -COO-R 1 The condensation monomer product of the A'-B"-A' form of [-OH] obtained in an amount exceeding 50% as a reaction product involving recycled monomer A and / or recycled monomer B is considered to be a recycled monomer product.

[0086] For example, using monomer X for depolymerization, it is possible to recycle monomer X having the formula [-OR 1 -OOC-R 2 -CO-], resulting in a substituted monomer X'-B"-X'. In a subsequent step, the substituted monomer X'-B"-X' is reacted with the original monomer A to produce a polyester having the formula [HO-R 1 -OOC-R 2 -COO-R 1 -OH] condensation monomer A'-B"-A'. All monomer units B" (-OC-R 2 -CO-) are recycled. For this calculation, monomer unit B" (-OC-R 2 -CO-) divided by the weight of the condensation monomer A'-B"-A'[HO-R 1 -OOC-R 2 -COO-R 1 -OH] by weight. For this calculation, the atoms of the linking groups A' and B", specifically the linking O atom in the A' group, are divided equally into two units. In the case of bishydroxyethyl terephthalate (BHET) obtained from PET and virgin ethylene glycol as monomer A, the recycled content would be 58%. If, however, 50% of monomer A comes from the depolymerization of the initial polymer, the recycled content is again 79%.

[0087] Typically, the condensation monomer is solid at ambient conditions. Ambient conditions refer to normal temperature and pressure (293.15K, 101.325 kPa absolute). Typical condensation monomers have a melting point above 50°C. More typically, a melting point above 70°C. The melting point is the temperature at which the pure condensation monomer melts. The actual temperature of the molten condensation monomer may be lower because, for example, the presence of a substance that is liquid at ambient conditions may reduce the melting temperature.

[0088] According to the present invention, the recycled monomer product is maintained in liquid form during the preparation of the monomer slurry.

[0089] Recycled monomer products having a melting temperature above ambient conditions require heating, so that in the process of the invention, such recycled monomer products in liquid form are in a molten state. This can be obtained by melting solid recycled monomer products obtained in a previous manufacturing step, or by supplying the recycled monomer products in liquid form from a previous manufacturing step, wherein conditions are applied under which the recycled monomer products are in a liquid state. Such a previous manufacturing step preferably comprises a depolymerization step of the polyester.

[0090] Such previous manufacturing steps as described above may be performed at different locations, or may be performed at the same location. If the previous manufacturing steps are performed at different locations, then the recycled monomer product must be transported. Transport includes any form in which the monomer product is stationary in a transport container that is moved from one location to another. This includes transport in boxes, containers, or tanks.

[0091] If the previous manufacturing steps are carried out at the same location, the recycled monomer product can preferably be transported from one reaction vessel to another reaction vessel. This includes movement by conveyor belts, bucket conveyors, chain conveyors, pneumatic conveying or pumping.

[0092] The recycled monomer product can be supplied at any temperature. It can be in a solid or molten (i.e. liquid) state. If the recycled monomer product is supplied in solid form, it must be melted to convert it into a suitable liquid form. The temperature of the recycled monomer product in liquid form is preferably at least 5°C, more preferably 15°C, higher than the melting temperature of the recycled monomer product to prevent unwanted solidification. It is also preferred that the recycled monomer product is maintained at a temperature lower than the melting temperature of the polyester obtained from the recycled monomer product. Since the recycled monomer product is used to prepare a slurry that is sensitive to thermal oxidative degradation, it is preferred to maintain the temperature as low as possible.

[0093] In a preferred embodiment, the temperature of the recycled monomer product in liquid form is supplied at a temperature at or below the melting temperature of the condensation monomers.

[0094] According to the present invention, a HOOC-R 2 The diacid monomer B containing -COOH is added to the recycled monomer product. The diacid monomer B can be added as a solid, preferably as a powder or granules. The typical particle size of the diacid monomer B used according to the present invention is 0.1 to 2000 μm, preferably 0.5 to 500 μm, while the median particle size is preferably 10 to 300 μm, preferably 30 to 200 μm. The median particle size (also referred to as D 50 value) is the particle size at which half the particles are smaller and half the particles are larger.

[0095] Alternatively, with the formula HOOC-R 2 The diacid monomer B having a carbonyl group-COOH may be added to the recycled monomer product in the form of a dispersion in a liquid such as water, a glycol or an inert solvent. However, the amount of liquid should be limited because water, an inert solvent and excess glycol must be evaporated before or during the subsequent polymerization of the polyester. According to a preferred embodiment of the present invention, the monomer slurry having the formula HOOC-R 2The -COOH diacid monomer B is added without diol or in an amount of diol less than the amount of diacid monomer B, preferably less than 80% of the amount of diacid monomer B, wherein the calculation is based on the molar amounts of each component.

[0096] With HOOC-R 2 The diacid monomer B containing -COOH should be added to the recycled monomer product so that the recycled monomer product remains above its melting temperature. Therefore, it is preferred to heat the diacid monomer B to above the melting temperature of the recycled monomer product, or if added at a lower temperature, to heat the recycled monomer product sufficiently to prevent it from solidifying.

[0097] Since the diacid monomer B is insoluble or only partially soluble in the recycled monomer product, a slurry is formed in which solid particles of the diacid monomer B are dispersed in the recycled monomer product. The liquid in which the diacid monomer B reacts with the recycled monomer product and / or the diol monomer A and is thus completely dissolved in the recycled monomer product is no longer considered a slurry.

[0098] The recycled monomer product should be stirred well to form a uniform slurry. The formation of agglomerates should be avoided.

[0099] According to the present invention, the compound having the formula HOOC-R 2 The amount of -COOH diacid monomer B added depends on the B" unit (-OC-R 2 -CO-) and has the formula HOOC-R 2 The amount of diacid monomer B containing -COOH.

[0100] Preferably, a compound having the formula HOOC-R is added 2 -COOH diacid monomer B, so that after adding it, the B" unit (-OC-R 2 -CO-) and single monomer B(HOOC-R 2 The molar ratio of -COOH) is in the range of 5:1 to 1:5. The amount of single monomer B is the sum of single monomer B in the recycled monomer product and added single monomer B. The amount of B" units in the slurry is equal to the B" units in the recycled monomer product.

[0101] If only an incidental amount of the individual diacid monomer B is present in the recycled monomer product (<1 wt %), then it may be convenient to calculate the ratio of B" units in the recycled monomer product to the individual diacid monomer B added.

[0102] If the B" unit (-OC-R 2 -CO-) and the single diacid monomer B(HOOC-R 2 -COOH) ratio is high, a large amount of specifically having the formula HO-R1 -OH single diol monomer A.

[0103] For example, if 5 moles of a compound having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer A'-B"-A' and 1 mole of a single diacid monomer B (HOOC-R 2 -COOH) are combined, then complete polymerization will produce a specific having the formula HO-R 1 -OOC-R 2 -CO-[OR 1 -OOC-R 2 -CO] 5 -OR 1 -OH'-B"-[A"-B"-] 5 -A' and 3 moles specifically have the formula HO-R 1 -OH, the latter will have to evaporate during the polyester preparation.

[0104] If the B" unit in the slurry [-OC-R 2 -CO-] with a single diacid monomer B(HOOC-R 2 -COOH), a smaller amount of the specific HO-R 1 -OH diol monomer A. For example, if 4 moles of a diol monomer having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer A'-B"-A' and 2 moles of a single diacid monomer B (HOOC-R 2 -COOH) are combined, then complete polymerization will produce a specific having the formula HO-R 1 -OOC-R 2 -CO-[OR 1 -OOC-R 2 -CO] 5 -OR 1 -OH'-B"-[A"-B"-] 5 -A' and only 1 mol specifically of the formula HO-R 1 -OH diol monomer A, which will have to evaporate during polyester preparation. Since less monomer A must be evaporated, less energy is consumed during the polymerization process. Therefore, it is advantageous to keep the B" units (-OC-R 2 -CO-) and single monomer B(HOOC-R 2The molar ratio of -COOH) is lower than 4:1, preferably lower than 3:1, more preferably lower than 2:1.

[0105] If the B" unit (-OC-R 2 -CO-) and single monomer B(HOOC-R 2 -COOH) ratio is low, then a small amount of HO-R 1 -OOC-R 2 -COO-R 1 The recycled condensation monomers A'-B"-A' of -OH are used to prepare polyesters.

[0106] For example, if 1 mol of a compound having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer A'-B"-A' and 5 moles of a single diacid monomer B (HOOC-R 2 -COOH) are combined, then complete polymerization will produce a specific having the formula HO-R 1 -OOC-R 2 -CO-[OR 1 -OOC-R 2 -CO] 5 -OR 1 -OH'-B"-[A"-B"-] 5 -A'. This requires the addition of 5 moles of a compound having the formula HO-R 1 -OH diol monomer A alone produces only 1 / 6 of the B" units (-OC-R 2 -CO-) from recycled monomer products. If the B" unit (-OC-R 2 -CO-) and single monomer B(HOOC-R 2 -COOH) ratio is higher, the greater the amount of 1 -OOC-R 2 -COO-R 1 The recycled condensation monomers A'-B"-A' of -OH are used to prepare polyesters.

[0107] For example, if 2 moles of a compound having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer A'-B"-A' and 4 moles of a single diacid monomer B (HOOC-R 2 -COOH) are combined, then complete polymerization will produce a specific having the formula HO-R 1 -OOC-R 2 -CO-[OR 1-OOC-R 2 -CO] 5 -OR 1 -OH'-B"-[A"-B"-] 5 -A'. This only requires the addition of 3 moles of a compound having the formula HO-R 1 -OH diol monomer A, which produces 1 / 3 of the B" units (-OC-R 2 -CO-) from the polymer of the recycled monomer product. Therefore, it is advantageous to maintain the B" units (-OC-R 2 -CO-) and single monomer B(HOOC-R 2 -COOH) is higher than 1:4 (ie the ratio should not become less than 0.25), preferably higher than 1:3, more preferably higher than 1:2.

[0108] From the above calculations and according to one embodiment of the present invention, it can be seen that it may be necessary to prepare the slurry so that the slurry contains specifically having the formula HO-R 1 -OH. The single diol monomer A may already be present in the recycled monomer product. The single diol monomer A may also be added to the single diacid monomer B (HOOC- 2 -COOH) is added to the recycled monomer product before or after. Optionally, the separate diol monomer A can be added to the recycled monomer product together with the separate diacid monomer B. The amount of separate diol monomer A added should be limited to limit the required evaporation of the separate diol monomer A in the subsequent polymerization reaction. Although a small amount of evaporation of the separate diol monomer A is an indispensable part of the polymerization process, excessive such evaporation should be avoided to minimize energy consumption.

[0109] According to a preferred embodiment of the present invention, specifically having the formula HO-R 1 The required amount of the single diol monomer A of -OH depends on the B" units (-OC-R 2 -CO-) and the amount of the single diacid monomer B (HOOC-R 2 -COOH). Specifically, it has the formula HO-R 1 The required amount of the single diol monomer A of -OH is the minimum value A 最小 To maximum value A 最大 ,

[0110] Among them A 最小 =1.05*diacid-0.95*B" unit,

[0111] A 最小 ≥0

[0112] And A 最大 =1.75*diacid-0.25*B" unit

[0113] Among them, single diol, A 最小 , A 最大 , B" units and diacids are expressed in molar amounts.

[0114] A 最小 The lower limit of is 0. In this case, there are enough 1 -OOC-R 2 -COO-R 1 -OH condensation monomers A'-B"-A' to supply all the required amounts of reactive A units (A' and A").

[0115] A 最大 The upper limit is in the B" unit (-OC-R 2 -CO-) and diacid monomer B(HOOC-R 2 This is achieved with a molar ratio of 1:5 to 8.5 moles of monomer A per 6 moles of total B units.

[0116] A 最大 A more preferred value is 6.5 moles of individual monomer A (HO-R) per 6 moles of total B units. 1 -OH) 最大 The more preferred upper limit is in the B" unit (-OC-R 2 -CO-) and single monomer B(HOOC-R 2 -COOH) at a molar ratio of 1:2 or higher.

[0117] More preferably, A 最大 =1.5*monomer B(HOOC-R 2 -COOH)-0.5*B” unit (-OC-R 2 -CO-).

[0118] This results in the B" unit (-OC-R 2 -CO-) and single monomer B(HOOC-R 2 -COOH) is 1:5, A 最大 The upper limit is 7 moles of individual monomer A (HO-R) per 6 moles of total B units 1 -OH).

[0119] The most preferred is A 最大 The upper limit is 0.8 moles of individual monomer A (HO-R 1 -OH).

[0120] According to the present invention, the above-mentioned monomer syrup is used for the polymerization of polyester.

[0121] The preparation of polyesters is well described. Various methods for the preparation of polyesters are described in "Modern Polyesters; Wiley Series in polymer Science; 2003; edited by John Scheirs" (Chapters 2, 8, 9 and general examples in Chapter 11).

[0122] The general preparation process involves direct reaction of equal amounts of separate monomers A and B to produce a product having a specific formula [-OR 1 -OOC-R 2 -CO-] n The repeating unit structure [A”-B”-] n The polyester can be composed of A'(HO-R 1 -O-) and / or B' units (-OC-R 2 During the reaction, low molecular weight reaction products may form which have to be removed by evaporation.

[0123] Other so-called two-step processes use a single monomer B (HOOC-R 2 -COOH) and excess of a single monomer A (HO-R 1 -OH) to form a compound having the formula [-OR 1 -OOC-R 2 -CO-] n The repeating unit structure [A”-B”-] n A prepolymer wherein n is a decimal preferably less than 20 and which is mostly composed of A' units (HO-R 1 During the reaction, low molecular weight reaction products may form which have to be removed by evaporation.

[0124] In the second step, the prepolymer is further reacted to produce a polymer having the formula [-OR 1 -OOC-R 2 -CO-] n The repeating unit structure [A”-B”-] n The polyester can be composed of A'(HO-R 1 -O-) and / or B' units (-OC-R 2 During the second stage, the excess of the individual monomers A (HO-R 1 -OH).

[0125] An alternative option for a two-step process uses a substituted monomer C and an excess of a single monomer A (HO-R 1 -OH) to form a compound having the formula [-OR1 -OOC-R 2 -CO-] n The repeating unit structure [A”-B”-] n A prepolymer wherein n is a decimal preferably less than 20 and which is mostly composed of A' units (HO-R 1 During the reaction, low molecular weight reaction products may be formed which must be removed by evaporation. In a second step, the prepolymer is further reacted to produce a prepolymer having specifically the formula [-OR 1 -OOC-R 2 -CO-] n The repeating unit structure [A”-B”-] n The polyester can be composed of A'(HO-R 1 -O-) and / or B' units (-OC-R 2 During the second stage, the excess of the individual monomers A (HO-R 1 -OH).

[0126] Many polyesters have at least one single monomer A or B that is liquid under ambient conditions. Typically, the diol single monomer A (HO-R 1 -OH) is a liquid. This allows the individual monomers to be fed as liquids to the polyester polymerization. If one monomer is a liquid and the second monomer is a solid, the solid monomer can be dispersed in the liquid monomer to form a slurry of the individual monomers and fed to the polyester polymerization.

[0127] Thus, a conventional plant designed to prepare polyester from its individual monomers A and B comprises a unit configured to prepare a slurry from the individual monomers A and B. This slurry preparation unit has an associated supply unit which allows the supply of the individual monomers A in liquid form and the individual monomers B in solid form. The resulting slurry is then fed to the subsequent step of the polyester polymerization.

[0128] Therefore, it is also desirable to provide the monomer slurry of the present invention in liquid form to the polyester polymerization. However, in contrast to conventional equipment, feeding the monomer slurry of the present invention requires more heating to obtain and / or maintain the monomer slurry in liquid form. At a minimum, the monomer slurry must be maintained at a temperature above the melting temperature of the recycled monomer product containing the monomer having the formula HO-R 1 -OOC-R 2 -COO-R 1Generally, when fed to the polyester polymerization, the monomer slurry should be at a temperature of 70°C or higher up to 200°C, preferably at 90°C or higher, more preferably at 105°C or higher, preferably below 160°C, more preferably below 140°C. Most preferably, when the slurry is fed to the polyester polymerization, the monomer slurry is above the temperature of the monomer having the formula HO-R 1 -OOC-R 2 -COO-R 1 Melting point of the condensation monomer with -OH.

[0129] Therefore, it is preferred to maintain the unit for preparing the slurry at a temperature of 70°C or above up to 200°C, preferably at 90°C or above, more preferably at 105°C or above, preferably below 160°C, more preferably below 140°C. Most preferably, the unit is maintained above the temperature of the slurry having the formula HO-R 1 -OOC-R 2 -COO-R 1 Melting point of the condensation monomer with -OH.

[0130] In order to maintain the desired temperature, the unit for preparing the slurry is equipped with a heating device sufficient to maintain the temperature at 70°C or above up to 200°C, preferably at 90°C or above, more preferably at 105°C or above, preferably below 160°C, more preferably below 140°C. Most preferably, the heating device is sufficient to maintain the temperature above 100°C. 1 -OOC-R 2 -COO-R 1 Melting point of the condensation monomer with -OH.

[0131] Compared to conventional equipment, a supply unit is required that allows the recycled monomer product to be fed in solid form at a temperature below its melting temperature or at a temperature sufficient to supply the recycled monomer product in molten form, which needs to be at a temperature of 70°C or above up to 200°C, preferably at 90°C or above, more preferably at 105°C or above.

[0132] The supply unit for the solid recycled monomer product may be any unit that allows providing the solid recycled monomer product in controlled amounts while maintaining the recycled monomer product in solid form. Examples are screws, rotary air locks, chain conveyors or pneumatic conveying systems.

[0133] The supply unit for the liquid recycled monomer product can be any unit that allows to provide the liquid recycled monomer product in controlled amounts while maintaining the recycled monomer product in liquid form. Examples are an extruder, a pump or a container with an outlet valve controlling the downstream from the container. Preferably, the supply unit is also equipped with an incorporated or downstream heating device to melt the monomer product.

[0134] As mentioned above, the recycled monomer product may be solid under ambient conditions. In a preferred embodiment of the present invention, the slurry preparation unit of the plant designed to prepare polyester is performed in a manner that allows melting the monomer product and maintaining the monomer product in a molten state while forming a monomer slurry.

[0135] Alternatively, a supply unit is provided that supplies the recycled monomer product in a molten state. In this case, the slurry preparation unit of the apparatus designed to prepare polyester is performed in a manner that allows the recycled monomer product to be maintained in a molten state while forming the monomer slurry.

[0136] In a further preferred embodiment of the present invention, the monomer slurry of the present invention can be added as a solid to the slurry preparation unit. In this case, the monomer slurry is solidified before being added to the polyester production unit. If the slurry must be stored or transported to a different location, such intermediate solidification may be desirable.

[0137] In this embodiment of the present invention, the slurry preparation unit of the apparatus designed to prepare polyester is performed in a manner allowing the monomer slurry to be melted and maintained in a molten state.

[0138] According to the present invention, the monomer slurry may contain 2 to 40 wt % of water and / or inert solvent, based on the total amount of the slurry. According to the present invention, it is preferred to evaporate at least a portion of the water and / or inert solvent. Therefore, the slurry preparation unit is performed in a manner that allows the monomer slurry to be maintained in a molten state while evaporating at least a portion of the water and / or inert solvent.

[0139] The monomer slurry may contain additives such as catalysts, colorants, antioxidants, stabilizers or inorganic fillers. These additives may be added during the production of the recycled monomer product. These additives may also be added to the recycled monomer product stream or to the diacid monomer B (HOOC-R) entering the slurry preparation unit. 2 -COOH) stream. Alternatively, additives may also be added to the slurry. The additives may be added in pure form, as a blend of additives or with a liquid. Typically, such additives are dissolved or dispersed in the individual monomers A (HO-R 1 -OH).

[0140] After the slurry is prepared, the polymerization of the polyester begins in the same or at least very similar manner to the known polymerization of the original polymer. Different molar ratios affecting the evaporation of the volatile components may lead to minor differences. Different (generally higher) feed temperatures of the monomer slurry may lead to other differences. In particular, when a large amount of monomers with the formula HO-R 1 -OOC-R 2 -COO-R 1 When the condensation monomer A'-B"-A of -OH is carried out, the first step of the reaction is accelerated, resulting in shorter residence time, smaller amounts of evaporated reaction products, the possibility of reducing the reaction pressure and thus the possibility of obtaining higher productivity.

[0141] According to a preferred embodiment of the present invention, the recycled monomer product is obtained by depolymerization of polyester. According to a preferred embodiment of the present invention, obtaining the recycled monomer product comprises the following steps:

[0142] a1) providing a waste stream comprising polyesters having repeating units [-A"-B"] of the formula [-OR 1 -OOC-R 2 -CO-],

[0143] a2) forming a waste stream and at least one diol monomer HO-R 1 -OH or end-capping molecule R 3 -OH blends, where R 3 is an aliphatic hydrocarbon group containing 1 to 15 carbon atoms capable of reacting with polyester,

[0144] a3) exposing the blend obtained in step a2) to conditions suitable for depolymerization of the polyester in a reaction vessel to obtain a depolymerization solution containing a recycled monomer product, wherein the monomer product contains a condensation monomer having the formula HO-R1-OOC-R2-COO-R1-OH,

[0145] a4) mixing the depolymerization solution from step a3) with water or an inert solvent to obtain a diluted solution,

[0146] a5) cooling the solution from step a4) to a temperature at which the recycled monomer product comprising the condensation monomers precipitates, and

[0147] a6) recovering the precipitated recycled monomer product from the solution to obtain a recycled monomer product containing 3 to 50 wt% of a substance that is liquid under ambient conditions, wherein the substance is selected from a glycol having a melting point below 20°C, water and an inert solvent.

[0148] The waste stream of step a1) can be any stream mainly containing polyester. It can also contain pollutants. The pollutants include solid substances mixed with polyester particles. Generally, they are metals, paper or foreign plastics. Pollutants include solid or liquid substances adhering to the surface of polyester particles. Generally, they are residues of previous use, such as sugar or edible oil, or residues of cross-contamination during collection, sorting and pre-cleaning, such as sand, stones or washing chemicals. Pollutants also include substances inside polyester particles. Generally, they are volatile substances absorbed from previous use, such as aromatic substances, household chemicals or solvents. Generally, there are also mixed pollutants, such as additives, such as colorants, inorganic fillers or organic additive carriers. Generally, there are also mixed pollutants, such as different polymers in polymer blends or blends with natural fibers such as cotton. Pollutants also include water and organic substances adhering to the surface of waste particles or absorbed by waste particles. This liquid can be removed by a pre-drying step. However, it is preferred to avoid this drying step and provide a waste stream containing liquid.

[0149] Waste streams may be generated from post-industrial or post-consumer waste. Such waste may be in the form of an article, such as a container or fabric, or it may be in the form of an intermediate product, such as a sheet, fiber roll or preform for a container, or it may be in the form of a raw material, such as pellets or chopped solidified melt. The waste stream may undergo a pre-cleaning step, such as optical sorting or separation by mechanical means, such as density separation or screening, to remove foreign polymeric and non-polymeric substances.

[0150] The waste stream may be subjected to a pre-cleaning step, such as washing with hot or cold water, optionally containing caustic substances and / or detergents, to remove surface contaminants.

[0151] The waste stream may undergo a pre-cleaning step, such as drying at elevated temperatures, to remove moisture and / or volatile organic contaminants.

[0152] The waste stream may be cut into particles, or it may be in the form of dust or powder. Typical particle sizes are from 0.1 mm up to several centimeters. For ease of handling, particles larger than 1 mm are preferred, and to prevent undissolved particles from clogging pipes, sizes smaller than 5 cm, especially smaller than 3 cm, are preferred.

[0153] According to a preferred embodiment of the present invention, the waste stream may contain liquefied pollutants. Liquefied pollutants are defined as substances that are solid at room temperature but liquid under the conditions of step a3) and are insoluble in the depolymerization solution formed in step a3). Liquefied pollutants may be present in a concentration of 0.1% to 48% by weight based on the total amount of the waste stream. Insoluble means that any part of the substance given its amount is not dissolved. Trace amounts that enter the solution are not taken into account.

[0154] According to a preferred embodiment of the present invention, the waste stream may contain solid contaminants. Solid contaminants are defined as substances that are solid under the conditions of step a3) and are insoluble in the depolymerization solution formed in step a3). Solid contaminants may be present in a concentration of 0.1% to 48% by weight based on the total amount of the waste stream. Insoluble means that any part of the substance given its amount is insoluble. Trace amounts that enter the solution are not taken into account. According to the present invention, the total content of polyester is higher than 50%. If the content concentration of liquefaction plus solid contaminants is higher than 1%, more preferably higher than 2%, and most preferably higher than 5%, it is most appropriate to use the preferred embodiment.

[0155] Waste streams with large amounts of liquefied contaminants are, for example, polyester sheets with a polyolefin layer or a silicone release layer or polyester containers with a polyolefin-based barrier layer such as EVOH.

[0156] Waste streams with high amounts of solid contaminants are for example polyester fibres mixed with non-melting fibre materials such as cotton.Other sources of polyester waste streams with high levels of contaminants are mixed fractions that may result from cleaning steps in polymer sorting or washing facilities.

[0157] Forming the blend in step a2) includes any form of mixing and mixing equipment that can be used to mix general solid or liquid waste streams and general liquid diol monomers. Alternatively, it includes any form of mixing and mixing equipment that can be used to mix general solid waste streams and solid diol monomers. In both cases, heating can be applied to promote the formation of the blend. Generally, the waste stream is supplied to the mixing device in a controlled amount. This can include any weight or volume dosing equipment, such as a loss-in-weight feeder, a belt scale or an air lock. The supply of the solid form of the waste stream can include pneumatic conveying, screw conveying, belt conveying and / or gravity feeding. An extruder with or without a dosing pump and / or a melt filter can be used to supply the liquid form of the waste stream. In this case, the liquid waste stream is preferably supplied to the mixing device at a position below the filling level of the waste stream to promote direct contact between the waste stream and the diol. Preferably, the supply of the liquid waste stream is carried out through multiple ports, providing a large surface contact area between the waste stream and the diol monomer. This is particularly important if the melting point of the liquid waste stream is higher than the boiling point of the diol monomer.

[0158] According to the present invention, at least one diol monomer HO-R1-OH capable of reacting with polyester is used. Generally, only one diol monomer is used. Using different diol monomers will produce mixed recycled depolymerization products, which may only be used for a particular copolyester. However, any diol monomer may contain a small amount of impurities, such as its dimer. Generally, the diol monomer is supplied to the mixing device in a controlled amount. This can include any gravity or volumetric dosing device. Alternatively, a weight or volume difference with a supply tank is used. Generally, the diol monomer is supplied in liquid form by a pump.

[0159] The ratio of solid waste stream to diol monomer 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 sum of all diol monomers added in step a2) to the polyester repeating units contained in the waste stream from step a1) ranges from 5:1 to 15:1, wherein the ratio is a molar ratio.

[0160] The blend may also contain a catalyst to promote the subsequent depolymerization reaction. Such a catalyst may be in the form of a metal salt or in the form of an organic substance. In addition, an organometallic complex may be used. The catalyst may be added as a pure substance or in solution in solid or liquid form. When a solution is used, the diol monomer is the most suitable solvent. Forming the blend may be accomplished in a continuous manner or by preparing separate batches.

[0161] One option is to use a stirred vessel to form the blend. Depending on the ratio of liquid to solid and the bulk density of the solid, the solid may not be completely immersed in the liquid. In this case, forming the blend may require some depolymerization and partial dissolution of the solid in the liquid before a uniform blend is formed. In this case, steps a2) and a3) overlap. Steps a2) and a3) also overlap in a continuous process, where the diol monomer and the waste stream are supplied to a depolymerization reactor, where depolymerization is already in progress. Such a procedure is explained in US4609680.

[0162] Another option is to use an extruder to melt the polyester and mix it with the diol monomer.

[0163] Step a3) comprises the depolymerization of the blend obtained in step a2). Conditions suitable for depolymerizing polyesters in waste streams are well known in the industry. As an example, various methods for depolymerizing PET are described in "Recycling of Polyethylene Terephthalate Bottles; Else-vier; 1st edition, 2018, by Sabu Thomas". According to the present invention, the depolymerization conditions must be sufficient to obtain polyesters consisting mainly of the formula HO-R 1 -OOC-R2 -COO-R 1 The monomer product is composed of condensation monomers of the structure A'-B"-A' with -OH.

[0164] As previously mentioned, the mixing of step a2) and the depolymerization of step a3) can overlap, since depolymerization may have already begun during mixing. In a preferred embodiment, hot diol monomers are mixed with the waste stream to preheat the waste stream to a temperature sufficient to initiate depolymerization. Suitable temperatures are generally above 130°C and at least 20°C lower than the boiling point of the diol monomers. In any case, the final depolymerization level is obtained in step a3). The depolymerization is carried out in a reaction vessel. One option is to use a stirred vessel for depolymerization. In a batch process, this may be the same as the container used in step a2). In a continuous process, a separate stirred vessel or a series of stirred vessels are preferred. Alternatively, a tubular reactor can be used instead of one or more stirred vessels. Generally, the reaction vessel includes a heating device, such as a hood heating, an internal heating coil or an external heat exchanger, through which a portion of the depolymerization solution is pumped and returned to the container.

[0165] The container is heated to conditions suitable for depolymerization of the polyester. Generally, a temperature exceeding 170° C. must be achieved to achieve sufficient depolymerization. Preferably, the temperature is raised to the boiling point of the diol monomer. The diol monomer may contain other liquids. Therefore, the boiling point can be lower than the boiling point of the diol monomer. When other liquids evaporate from the depolymerization solution, the boiling point increases. When the recycled monomer product is formed and dissolved in the diol monomer, the boiling point of the diol monomer increases to above its initial boiling point. Preferably, sufficient heating is provided to maintain boiling. The reaction vessel is generally operated at a pressure range of 500 mbar to 5 bar. However, it is preferred to operate the reaction vessel at an atmospheric pressure of about 1 bar ± 100 mbar. It is particularly preferred to operate the reaction vessel at a slight overpressure of up to 100 mbar to allow the evaporated liquid to be transferred to subsequent process steps. If there is no different annotation, the pressure refers to the absolute pressure.

[0166] In a series of reaction vessels, the temperature and pressure may vary from one vessel to the next. In particular, if an extruder is used in step a2), higher temperatures and pressures may be used initially. However, according to the invention, this extruded blend will then be transferred to a reactor of the above specifications.

[0167] A preferred series of reactors uses a first reactor at about atmospheric pressure at the boiling point of the solution, a second reactor at a temperature higher than the first reactor at an overpressure of up to 5 bar, and a third reactor at a pressure lower than the second reactor, preferably at about atmospheric pressure. This series allows depolymerization in the first reactor while removing volatile contaminants. It then allows an increase in the rate of depolymerization in the second reactor and allows some of the diol monomer to evaporate from the third reactor.

[0168] Depolymerization is continued until a depolymerization solution has been formed. Except for some pollutants, the waste stream should be completely dissolved in the depolymerization solution. Long reactions at high temperatures should be avoided because they lead to the formation of by-products, such as the formation of dimers of diol monomers. The residence time of steps a2) and a3) together is generally 20 minutes to 6 hours. In the case where step a3) is carried out with boiling diol monomers at approximately ambient pressure, the preferred residence time is 1 to 5 hours. In the case of preheating the waste stream as described above, the residence time including this preheating may be up to 24 hours.

[0169] The depolymerization solution contains a recycled monomer product, wherein the monomer product contains a condensation monomer having the formula HO-R1-OOC-R2-COO-R1-OH.

[0170] In step a4), the depolymerization solution from step a3) is mixed with water or an inert solvent to obtain a diluted solution. Any mixing device suitable for mixing two different liquids can be used. In a batch process, this may be the same container used in step a3). In a continuous process, a separate device is preferred. The amount of water or inert solvent is 5:1 to 1:3 compared to the amount of diol monomer. It is preferred that the mixing ratio is lower than 3:1. It is preferred that the mixing ratio is higher than 1:1.5. The mixing ratio is expressed as a volume ratio based on the amount of diol monomer in the depolymerization solution when the water is added. Most preferably, water is added that is equal to or exceeds the amount of diol monomer added to step a2). Mixing can include adding all the water or inert solvent to the total amount of depolymerization solution at one location. Mixing can also involve adding portions of water or inert solvent sequentially at different locations. Mixing can include adding all the water or inert solvent to only a portion of the depolymerization solution, followed by mixing with the remaining depolymerization solution. In any case where a distinction can be made, especially in batch processes, it is preferred to add water or an inert solvent to the depolymerization solution rather than adding the depolymerization solution to water or an inert solvent. This prevents initial supercooling of part of the depolymerization solution.

[0171] In a preferred embodiment, the flow rates and temperatures of the two liquid streams should be adjusted before mixing so that the resulting dilute solution reaches a temperature below its boiling point but above the temperature at which the condensation monomers begin to precipitate without the need for evaporation. In the case of a depolymerization solution obtained from polyethylene terephthalate and ethylene glycol, it is preferred that the temperature of the dilute solution is above 60° C. and below 110° C. More preferred is a temperature above 70° C. and below 100° C. During the mixing process, some water vapor or inert solvent may be formed. Typically, these vapors are condensed and returned to the dilute solution or transferred to a solvent recovery unit.

[0172] Generally, any quenching should be avoided. However, it is also necessary to prevent the formation of excessive amounts of 1 -OOC-R 2 Byproducts of the general structure A'-B' of -COOH. This requires rapid cooling to below 90°C. Therefore, it is preferred that the water addition is carried out so that the solution reaches a temperature below 90°C within 1 hour after the start of water addition. Preferably, the solution reaches a temperature below 90°C within 30 minutes.

[0173] In a preferred embodiment of the invention, the water addition is carried out such that the solution is present in a stirred vessel and the water is added to the vessel at multiple locations.

[0174] In another preferred embodiment, the water addition is performed such that the solution flows through a conduit into which water is injected.

[0175] In step a5), the diluted solution from step a4) is cooled. Any cooling device suitable for cooling the liquid and inducing the precipitation of dissolved solids can be used. Generally, a stirred container is used. Generally, the container includes a cooling device, such as a cooling hood, an internal cooling coil or an external heat exchanger, through which a portion of the diluted solution is pumped and returned to the container. Alternatively, at least a portion of the cooling can be carried out in a plate or tube heat exchanger. The cooling must be sufficient to precipitate most of the dissolved monomer products, especially the condensed monomers contained. However, the cooling must maintain the diluted solution in liquid form. Therefore, the cooling is limited to the melting temperature of the diluted solution. In the presence of water cooling, a temperature of 0°C to 25°C, preferably less than 15°C, more preferably less than 10°C is used. The cooling time must be long enough to precipitate most of the dissolved monomer products. Since the cooling rate is an important factor in the crystal size of the precipitated solid, a longer cooling time is preferred to achieve easy filtering of solid particles. The general cooling time is 1 to 16 hours. The cooling can be carried out by a constant temperature ramp, by a stepped temperature ramp or by a temperature ramp followed by a certain time. Agitation is preferably used during cooling to prevent the formation of large gelatinous masses. Agitation must be strong enough to reach the total liquid volume throughout the cooling process. At the same time, high friction should be avoided to prevent the precipitated solids from breaking. Typical agitators are bled agitators or cup agitators. At least 80%, preferably at least 90%, of the precipitated solids (by weight) should have a particle size greater than 20 μm.

[0176] Since precipitated solids of different particle sizes can be formed, it is advantageous to adopt such a process step in which the liquid from the cooling device is directed to a dynamic separation device, which separates the liquid into a first liquid portion and a second liquid portion, wherein the second liquid portion contains most of the particles below the critical size, and wherein the second liquid portion is directed back to the cooling device and the first liquid portion is directed to further processing. The second liquid portion can be combined with the dilution solution from step a4) before entering the cooling device. Preferably, the second liquid portion contains more than 70% of the particles with a particle size below the critical size. The particles with the critical size are below 10 μm, preferably below 20 μm, and most preferably below 30 μm. The dynamic separation device can be any device that separates particles in a liquid based on their response to gravity. General equipment is, for example, a decanter, a centrifuge, a hydrocyclone or a simple settling tank. It is preferred to allow dynamic separation equipment such as a decanter, a centrifuge or a hydrocyclone that can be separated in less than 5 minutes. The advantage of utilizing such a dynamic separation device is not only the return of small and difficult to filter particles to an earlier stage in the process, but also the tendency for simultaneous separation to provide a first liquid portion having a higher solids content than the second liquid portion. Thus, the solids to liquid ratio of the liquid entering the dynamic separation device is reduced compared to an arrangement without such particle return. The reduced solids to liquid ratio subsequently facilitates separation by particle size.

[0177] The precipitated solids containing the recycled monomer product from step a5) are separated from the solution of step a6) by any method suitable for mechanical solid-liquid separation. This includes filtration, sedimentation or centrifugation. It does not include thermal methods in which the solution is completely evaporated. The advantage of mechanical separation is to remove pollutants that are soluble in the solution and are therefore separated from the precipitated solids. General suitable filtering equipment includes filter presses, belt filters or drum filters. Separation can be carried out in an intermittent or continuous manner. In the absence of suitable continuous equipment, an alternating intermittent system will be used. After separation, two material fractions are obtained: a solid recycled monomer product containing condensation monomers and a liquid solution. The solution contains diol monomers, water and / or an inert solvent as well as pollutants, residual catalysts and soluble components from polyester depolymerization, such as condensation monomers, dimers, oligomers and other by-products of depolymerization.

[0178] Some residual solution is retained in the recycled monomer product, which is considered to be wet solids. The liquid content in the wet solid is generally 50% to 200% based on the dry solid weight. Due to the presence of unwanted substances in the liquid, it is desirable to remove the liquid by mechanical means. Similarly, thermal separation by evaporation will cause the dissolved substances to be retained in the recycled monomer product. The separation can include air flow purging, compression to remove the liquid or the technology of liquid exchange due to washing. This technology can be combined and repeated in a variety of sequences. It is especially desirable to wash the solid multiple times, followed by at least one purge stage. Diol monomers, water or inert solvents as washing liquids can be used. Since each subsequent washing stage produces a liquid stream of higher purity, the liquid stream from one stage can be used as washing liquid in the previous washing stage.

[0179] In a preferred embodiment, the following sequence is used to clean the obtained wet solids:

[0180] - placing the wet solids of the recycled monomer product on a filtration device;

[0181] - at least two water washing steps are subsequently carried out such that fresh water is used in a step other than the first washing step and the water filtrate from the fresh water washing step is used as washing solution in the preceding washing step;

[0182] - using at least a first air purge step after the fresh water wash step;

[0183] - Optionally after the water washing step and before or after the first air purge step, a diol monomer A washing step may be used;

[0184] - Optionally after the diol monomer A washing step, a second air purge step is used.

[0185] An advantage of the above procedure is that a minimum amount of water is used, which reduces the amount of water that must be recovered.

[0186] In another preferred embodiment, the following sequence is used to clean the obtained wet solid:

[0187] - placing the wet solids of the recycled monomer product on a filtration device;

[0188] - subsequently performing at least two diol monomer A washing steps such that fresh diol monomer is used in a step other than the first washing step and the diol monomer filtrate from the fresh diol monomer washing step is used as the washing solution in the preceding washing step;

[0189] - After the fresh diol monomer washing step, at least a first air purge step is used.

[0190] Embodiments using diol monomers further reduce the amount of water used and, by displacement, reduce the amount of water that must be removed by evaporation from the recycled monomer product.

[0191] The solid particles are particularly advantageous when they are made from recycled monomer products where there is a lower risk of agglomeration during storage with diol monomers compared to water.

[0192] One option is to direct all or part of the liquid stream after washing to a separation unit configured such that a recycle diol monomer stream is obtained.

[0193] In a preferred alternative, in step a5), at least a portion of the liquid after washing is directed to a cooling device. The advantage of this return of washing liquid is that residual condensation monomers in dissolved form or in the form of small particles are returned to the process step where precipitation occurs, and thus the recovery of such condensation monomers is facilitated. In addition, as mentioned above, the return of additional liquid supports possible particle size separation.

[0194] If there are special requirements with regard to heat capacity or inertness, the so-called air purge step can be performed with other gases such as nitrogen or CO 2 to execute.

[0195] Several additional clean-up steps may be used in the preparation of the recycled monomer product.

[0196] These cleaning steps can be applied in step a) of the process according to the invention for preparing polyesters, as well as in a separate process according to the invention for providing a recycled monomer product.

[0197] These cleaning steps can be performed sequentially or in combination. They include:

[0198] - Evaporation of volatile contaminants from any material stream of any of steps a1) to a6), in particular from step a3). This requires directing the vapors away from the step where the evaporation occurs. Optionally, a portion of the vapors is condensed and returned to the process step. The term "material stream" relates to all materials used, generated or processed in any of steps a1) to a6), including the waste stream of step a1), the blend formed in step a2) from the waste stream of a1) and the added diol monomer, the depolymerization solution obtained from the blend in step a3), the diluted solution obtained in step a4) from the depolymerization solution mixed with water or an inert solvent, and the precipitated recycled monomer product obtained in step a5).

[0199] - Mechanical separation such as filtration of solid contaminants from any solution obtained in any of steps a3) to a5). This can be done in one or more steps. The separation comprises filtration, which may comprise a first filtration step with a mesh size of 0.1 to 3 mm and a second fine filtration with a pore size of 0.1 μm to 0.1 mm.

[0200] - Mechanically separating, such as filtering, the precipitated oligomer particles from any solution obtained in any of steps a3) to a5). This is preferably done after step a4) at a temperature that allows the oligomers to precipitate but allows the majority of dimers and condensation monomers to remain in solution. Filter aids may be used to facilitate filtration.

[0201] - Mechanically separate the dimer particles, such as by filtration, from any solution obtained in any of steps a3) to a5). This is preferably done after step a4) at a temperature that allows precipitation of the dimer but allows most of the condensed monomers to remain in solution. A filter aid may be used to facilitate filtration. A specific separation procedure for this dimer is explained in WO 2021 / 032821.

[0202] According to a preferred embodiment, the mechanical separation of oligomer and / or dimer is so limited that the amount of oligomer and dimer retained in the solution accounts for more than 10% of the solid weight, preferably less than 20%. This can be achieved by setting the precipitation temperature high enough to keep some oligomers and dimers in solution. Alternatively, this can be achieved by limiting the mechanical separation, for example, by a sufficiently large mesh size, allowing small particles to pass. This second option leaves nucleation in the solution, which helps subsequent crystallization or condensation monomers.

[0203] - Colorants and other high boiling point organic contaminants are removed by using activated carbon and subsequently separating the activated carbon 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, or it can be used as a packed bed through which the solution is passed. A filter aid can be used to facilitate the filtration. The cleaning step with activated carbon can also be used after redissolving the recycled monomer product. The procedure for removing color with activated carbon is explained in US-6,642,350 and US-2006 / 074136.

[0204] - Removal of metals by using an ion exchanger and subsequently separating the ion exchanger from any solution obtained in any of steps a3) to a5). The ion exchangers can be mixed with the solution in powder or granular form and subsequently filtered, or they can be used as a packed bed through which the solution is passed. Filter aids can be used to facilitate filtration. A cleaning step using an ion exchanger can also be used after redissolving the recycled monomer product. Ion exchange procedures are explained in US, 6,642,350 and US, 6,630,601.

[0205] - redissolving the obtained recycled monomer product in the diol monomer, water or an inert solvent or a mixture thereof, followed by precipitation of the recycled monomer product and mechanical separation from the solution.

[0206] - purging and / or washing the filter cake obtained in step a6) with air, water, the individual monomers and / or an inert solvent.

[0207] The above cleaning steps can be combined. For example, oligomer removal, activated carbon removal and / or ion exchanger removal can be combined into one separation step.

[0208] According to a preferred embodiment of the present invention, after the depolymerization and cleaning steps are completed, a recycled monomer product is obtained containing 3% to 50% by weight of substances that are liquid under ambient conditions, wherein the substances are selected from glycols having a melting point below 20° C., water and inert solvents. Preferably, the substances that are liquid under ambient conditions are selected from glycols having a melting point below 20° C. and water.

[0209] The diol monomers, water and inert solvent can be collected from any of the above steps. Those streams can be in liquid or gaseous form. The streams generally contain other materials such as pollutants, residual catalysts and soluble components from the depolymerization of the polyester, such as condensation monomers, dimers, oligomers and other by-products of the depolymerization.

[0210] It may be desirable to recover a separate purified liquid stream for reuse in any of steps a1) to a6). Typical methods of recovering the liquid are membrane filtration or distillation.

[0211] According to a preferred embodiment of the invention, the blend in step a2) contains 2 to 10 wt. % of water and at least 15 wt. % but not more than 60 wt. % of the diol monomers are evaporated and removed during step a3).

[0212] By "removal" is meant that the evaporation stream is directed away from the step where evaporation occurs. This excludes liquid returning from the reflux cooler. In a batch process, the contained mass decreases due to evaporation. In a continuous process, the mass balance between the input and output streams must be in equilibrium. However, by "removal" is meant that there is no direct feedback flow from the unit where the vapor is directed to the unit where evaporation occurs. The percentages are calculated 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. More preferably, at least 20% of the diol monomer is evaporated and removed. More preferably, no more than 50% of the diol monomer is evaporated and removed. As an example, 1 part of a waste stream containing 1% water can be mixed with 3 parts of diol monomer containing 5% water. This exemplary blend contains an average of 4% water. Evaporating 1 part of EG (=33.3% by weight of diol) from a batch process simultaneously removes more than 90% of the water. Preferably, more than 95%, even more preferably more than 98% of the water is removed. Due to the presence of residual water, it is possible to produce a waste stream having specifically the formula HO-R 1 -OOC-R 2 Since the by-product of the general structure A'-B' of -COOH is difficult to recover, it is desirable to limit the residual amount of water in the depolymerization solution directed to step a4) to a value below 0.5% by weight, more preferably below 0.25%, even more preferably below 0.1%. However, it is important to limit the evaporation so that the molar ratio does not shift in such a way that the equilibrium in the depolymerization solution is shifted too much towards a higher oligomer content. Therefore, the ratio of diol monomers to polyester repeating units contained in the depolymerization solution should be kept higher than 4 to 1. Taking into account the upper limit and the depolymerization reaction, the lower limit is reduced to 14 to 1.

[0213] In a continuous process in a single reactor, the residual water content remains slightly higher. If a series of continuously operated reactors is used and the EG is evaporated sequentially, a residual water content similar to that of a batch process can be achieved. The evaporation can be initiated simply by heating at a given pressure, by applying reduced pressure at a given temperature, or by compression followed by heating and decompression, the latter being called flash evaporation.

[0214] In a preferred embodiment, the evaporated liquid is directed to a separation unit configured such that a recycled diol monomer stream having a water content of 2 to 12 wt. % is obtained, at least a portion of which is subsequently used in step a2).

[0215] In a preferred embodiment, a liquid stream is obtained from one or more steps comprising step a5) and after step a5), wherein the liquid stream comprises water and diol monomer, and wherein the liquid stream is directed to a separation unit configured such that a recycled diol monomer stream having a water content of 2 to 12 wt.-% is obtained, and subsequently at least a portion of the recycled diol monomer is used in step a2).

[0216] In a preferred embodiment, a vapour stream is obtained during step a3) and a liquid stream is obtained from one or more steps including and after step a5). Both streams comprise water and diol monomer and both streams are directed to a common separation unit configured such that a recycled diol monomer stream is obtained.

[0217] The common separation unit preferably comprises at least one distillation column which allows heat exchange between the vapor stream and the liquid stream.

[0218] The separation unit may further be configured to recover other liquids, in particular water, into a separate purified liquid stream.

[0219] An advantage of the present invention is that the recovered diol monomer can contain up to 13% by weight, preferably 2% to 12% residual water when combined with the waste stream in step a2). This simplifies liquid recovery compared to systems where dry diol monomer must be used. At the same time, most of the energy required for evaporation is recovered for heating purposes in the separation unit, especially the distillation column.

[0220] Therefore, it is preferred to direct the liquid collected in liquid form from step a6) and the liquid collected in gaseous form from step a3) to a common distillation column, and return at least a portion of the recovered diol monomer having a residual water content of 2% to 12% to step a2).

[0221] Alternatively, the evaporated liquid is directed to a waste stream of step a1).The mass ratios and temperature ratios are chosen such that a major part of the diol monomers condenses and a major part of the water remains in vapor form.

[0222] This heat exchange and mass exchange can be carried out in a fixed bed vessel, where both inlet streams enter from the top. At the bottom, the vapor stream can be separated from the solid waste stream, and a portion of the condensed glycol monomers remain in the waste stream. Optionally, the heat exchange can be carried out indirectly in a heat exchanger such as a reactor with a heating mantle having heating coils. The resulting condensate can be combined with the waste stream.

[0223] In a preferred embodiment of the present invention, recycled diol monomers are used to dissolve the oligomers obtained from the polyester waste stream. Subsequently, in step a2), recycled diol monomers containing dissolved oligomers are used. Generally, oligomers are obtained from any additional cleaning step in steps a3) to a5). Oligomers may be present as pollutants, absorbents and / or filter aids. In this case, the oligomer solution can be separated from the solid particles. Optional absorbents and filter aids are also returned to step a2). Together with oligomers, other depolymerization products such as condensation monomers and diols are also recovered.

[0224] According to a preferred embodiment, for the mixing with water in step a4), the amount of water or inert solvent is 5:1 to 1:3 compared to the amount of diol monomer, and one or more of the following conditions are met:

[0225] - Water is added to the solution;

[0226] - the temperature of the two liquid streams to be mixed should be adjusted before mixing so that the resulting dilute solution reaches a temperature below its boiling point but above the temperature at which the condensation monomers begin to precipitate without evaporation;

[0227] - the water addition is carried out such that the solution reaches a temperature of less than 90° C. within 1 hour after the start of the water addition;

[0228] - the water addition is carried out in such a way that the solution is present in a stirred vessel, the water being added to the vessel at a plurality of locations;

[0229] - water addition is carried out so that the solution flows through the pipes and water is injected into the pipes;

[0230] - the water addition is carried out such that the solution is maintained at a temperature above 70° C.;

[0231] - The water addition is carried out such that the solution reaches a temperature below 105°C.

[0232] In a preferred embodiment of the invention, the waste stream in step a1) contains liquefied pollutants in a concentration of 0.1% to 48% by weight, based on the total amount of the waste stream, wherein liquefied pollutants are defined as substances that are solid at room temperature but liquid under the conditions of step a3) and are insoluble in the depolymerization solution formed in step a3). The depolymerization solution formed in step a3) is divided into two parts, while the liquefied pollutants are maintained in a liquid state. The two parts can be divided into two separate, mechanically separated streams. Preferably, the two parts are stacked on top of each other. The first part contains the liquefied pollutants and the second part is substantially free of liquefied pollutants. In the case where the distinction between the individual parts is not clearly visible, the distinction is made based on the fact that the first part contains 90% or more of the total amount of the liquefied pollutants and the second part contains at most 10% by weight of the total amount of the liquefied pollutants.

[0233] According to this preferred embodiment, the liquefied pollutants in the first part are solidified by contact with a cooling liquid selected from diol monomers, water or an inert solvent in the presence of at least a portion of the depolymerization solution and then removed from the diluted solution in solid form. The second part is then combined with the first part.

[0234] This part can have different volumes or flow rates. The initial accumulation of liquefied pollutants is caused by the density difference between the depolymerization solution and the liquefied pollutants in liquid form. The solidification of the cooling liquid and the liquefied pollutants generally reduces the density difference. The cooling liquid is added after sufficient accumulation has occurred in the first part. The upper limit of the water or inert solvent added to the first part is the total amount of water or inert solvent added in step a4). If a diol monomer is used as a cooling liquid, the upper limit is only given by the dilution effect of the diol monomer and the subsequent recovery cost. The lower limit of the diol monomer, water or inert solvent added to the first part is the amount of diol monomer, water or inert solvent required for the first part to be cooled to a sufficiently low temperature to solidify the liquefied pollutants. General liquefied pollutants such as polyolefins need to be cooled to less than 110°C. For some low melting point polyolefin copolymers, a temperature as low as 80°C may be required. The solidified liquefied pollutants are preferably removed by a screen that allows the solution to pass but retains most of the liquefied pollutants in solid form. Smaller particles and particles with a smaller density difference with the dilute solution are separated more slowly by density difference and may remain suspended. Therefore, the solidified liquefied pollutants are preferably removed by a screen assembled inside the separation container. In order to facilitate the cleaning of the screen, it is desirable to reduce the temperature sufficiently to prevent the liquefied pollutants from adhering to the screen. The screen holes must be wide enough to allow small particles of the precipitated depolymerization product to pass through the screen.

[0235] An advantage of the present invention is that by limiting the cooling to the first part, less cooling capacity is required to solidify the liquefied contaminant. This allows the amount of cooling liquid to be reduced and allows the temperature of the cooling liquid to be increased, which is necessary to prevent quenching. If not all of the diol monomer, water or inert solvent is added to the first layer, the remaining liquid can be added to any part before or after the first and second parts are combined but before step a5).

[0236] In a specific preferred embodiment of the present invention, the density of the liquefied pollutant in liquid form is lower than that of the depolymerization solution formed in step a3). The separation into two parts is carried out in a separation container having at least one supply port for the depolymerization solution containing the liquefied pollutant on one side, at least one removal port for the depolymerization solution on the other side, a separation zone between the two ports, and a cooling zone between the separation zone and the removal port. In the separation zone, the depolymerization solution is separated into an upper layer of a first phase containing the liquefied pollutant and a lower layer of a second phase substantially free of the liquefied pollutant. The glycol monomer, water or an inert solvent is added to the upper layer in the cooling zone in an amount sufficient to solidify the liquefied pollutant. A general apparatus for this separation step is shown in Figure 1 The general specifications provided can be applied to any device suitable for separation.

[0237] According to a further preferred embodiment of the present invention, a liquefied substance is added to the depolymerization solution before the cooling zone. The liquefied substance comprises a melting point higher than 90°C but lower than the temperature at which the depolymerization solution is supplied to the separation container, a density lower than 1 g / cm 3 , preferably less than 0.96 g / cm 3 and is substantially insoluble in the depolymerization solution. A suitable liquefying substance is, for example, a low density polyethylene having a melt flow index higher than 10 g / min, measured at 190° C. The advantage of such an intentionally added liquefying substance lies in the fact that it will act as a suspending agent for the small droplets of liquefied contaminants during the separation stage. It also acts as a scavenger for non-polar contaminants with low solubility in the glycol monomers, water or inert solvents. This is of primary importance if recycled condensation monomers are used to manufacture materials that come into direct contact with food.

[0238] According to a further preferred embodiment of the present invention, a liquefied substance is added to the depolymerization solution before the cooling zone, wherein the liquefied substance comprises a liquid having a melting point higher than 90°C but lower than the temperature at which the depolymerization solution is supplied to the separation container and a density lower than 1 g / cm 3 And substances that are insoluble in the depolymerization solution.

[0239] In another preferred embodiment of the invention, the waste stream in step a1) contains solid pollutants in a concentration of 0.1 wt.-% to 48 wt.-%, based on the total amount of the waste stream, wherein solid pollutants are defined as substances which are solid under the conditions of step a3) and which are insoluble in the depolymerization solution formed in step a3). The solid pollutants are removed from the diluted solution together with the liquefied pollutants. In order to ensure that the solid pollutants are separated as described, independently of their density, it is necessary to assemble the screen so that both sinking and floating particles are captured.

[0240] Any solid particles removed will generally contain residues of the depolymerization solution. It is therefore preferred to recover as much solution as possible. This can be done via an air stream or a wash solution.

[0241] The advantage of this combined removal is the flexibility to operate the system with very different waste streams without having to configure the system specifically for those waste streams. Another advantage is a single waste stream which facilitates treatment and solution recovery.

[0242] According to one embodiment of the present invention, the recycled monomer product contains a substance that is liquid under normal conditions. This liquid contains individual monomers A (HO-R) with a melting point below 20°C. 1 -OH), water or an inert solvent. The amount of this liquid should be limited to 50% by weight of the total recycled monomer product, because water, inert liquid and excess individual monomer A must be evaporated before or during the polyester polymerization.

[0243] Preferably, the amount of such liquid is limited to 35% by weight of the total recycled monomer product. However, the presence of such liquids may be desirable because they reduce the melting point of the recycled monomer product. In order to sufficiently reduce the melting point, at least 3%, preferably more than 5%, more preferably more than 7%, and most preferably at least 10% of liquid based on the total amount of recycled monomer product is required.

[0244] In a preferred embodiment of the present invention, below the 1 -OOC-R 2 -COO-R 1 The recycled monomer product is stored as a liquid at a temperature below the melting point of the condensation monomer A'-B"-A' having the formula HO-R 1 -OOC-R 2 -COO-R 1 The recycled monomer product is transported as a liquid from the first location to the second location at a temperature at which the condensation monomer A'-B"-A' of the formula HO-R 1 -OOC-R 2 -COO-R 1 Such reduced transportation or storage temperatures are desirable because side reactions may occur during transportation and storage time at the melting temperature of the condensation monomers A'-B"-A' of -OH.

[0245] In a preferred embodiment of the present invention, below the 1 -OOC-R 2 -COO-R 1The recycled monomer product is released from the transport or storage container as a liquid at a second location at a temperature lower than the melting temperature of the condensation monomer A'-B"-A' of -OH. This reduced release temperature is desirable for rapidly liquefying recycled monomer products that are in the form of a sticky solid or paste and thus make extraction from the transport or storage container difficult.

[0246] In a preferred embodiment of the present invention, below the 1 -OOC-R 2 -COO-R 1 -OH condensation monomer A'-B"-A' at a temperature of the melting temperature, the diacid monomer B (HOOC-R 2 -COOH) is added to the recycled monomer product in liquid form. This reduced mixing temperature is desirable to increase the viscosity of the monomer product, which facilitates the dispersion of monomer B in the monomer product.

[0247] The material that is liquid under ambient conditions and contained in the recycled monomer product may be a residual liquid from the preparation of the recycled monomer product, such as a residual reactant or a liquid used in a step of purifying the recycled monomer product. This liquid may also originate from monomer A (HO-R 1 -OH) or from the addition of additives dissolved or dispersed in the liquid.

[0248] The substances which are liquid at ambient conditions and are contained in the recycled monomer product can be added to the monomer B (HOOC-R 2 -COOH). This is of particular interest if the liquid comprises water or an inert solvent which is not required for the subsequent polyester polymerization.

[0249] In a preferred embodiment of the invention, the recycled monomer product is obtained by crystallization from a solution containing water and / or an inert solvent. After filtering and optionally washing, the recycled monomer product contains up to 50% by weight of residual water and / or inert solvent, based on the total amount of the recycled monomer product. The wet recycled monomer product is melted to provide the recycled monomer product in liquid form. 2 -COOH) is added to the wet recycled monomer product melt to obtain a monomer slurry. Preferably, before adding the separate monomer B (HOOC-R 2Before and / or during the polymerization of the polyester (A'-B"-COOH), water and / or inert solvent are evaporated. The evaporation of water and / or inert solvent does not have to be complete, since some water and / or inert solvent can generally evaporate during the polymerization of the polyester. Water and inert solvents having a boiling point above 100° C. and below the boiling point of the condensation monomers A'-B"-A' can be evaporated at temperatures close to their pressure-dependent boiling points without the risk of unwanted evaporation of the condensation monomers A'-B"-A'. As the content of water and / or inert solvent decreases, the temperature needs to be increased to at least the melting point of the condensation monomers A'-B"-A'.

[0250] In a preferred embodiment, evaporation of water and / or inert solvent and recycling of monomer product and monomer B (HOOC-R 2 -COOH) is mixed in subsequent vessels. The first vessel is designed to evaporate most of the water and / or inert solvent. The second vessel is designed to mix the recycled monomer product with monomer B (HOOC-R 2 -COOH) are mixed. The two containers can be directly connected.

[0251] This first vessel is preferably equipped with an inlet for recycled monomer product in liquid or solid form. The port is preferably located at the upper end of the vessel.

[0252] The first container may further be equipped with an outlet for the monomer product in liquid form. The port is preferably located at the lower end of the container, typically at the opposite end of the inlet for the recycled monomer product. The port is preferably controllable by a valve to regulate the slurry flow from the container.

[0253] The first container may further be equipped with an outlet for substances in gaseous form under the conditions required to provide the recycled monomer product in a molten state. This port is preferably connected to a condensing device that allows the recovery of evaporated liquid.

[0254] The first container may be further equipped with a mixing and beating device. Such a mixing and beating device may include blades or paddles on a rotating shaft, or a single screw or parallel screws.

[0255] The first container may further be equipped with a heating device. Such a heating device may constitute a heating mantle or a heating element inside the container. The heating device must be designed to provide sufficient heating to promote evaporation of water and / or inert solvent. If the recycled monomer product is provided in solid form, sufficient heating device should be provided to allow the recycled monomer product to melt.

[0256] This second vessel is preferably equipped with an inlet for the recycled monomer product in liquid or solid form, and for the separate monomer B (HOOC-R 2 -COOH) entrance.

[0257] The second vessel may further be equipped with an outlet for the monomer slurry in liquid form. This outlet is preferably located at the opposite end of the inlet for the recycled monomer product.

[0258] The second container may further be equipped with a mixing device. Such a mixing device may include blades or paddles on a rotating shaft, or a single screw or parallel screws.

[0259] The second vessel may further be equipped with a heating device. The heating device must be designed to provide sufficient heating to maintain the monomer slurry in liquid form.

[0260] In a preferred embodiment, evaporation of water and / or inert solvent and recycling of monomer product and monomer B (HOOC-R 2 -COOH) are mixed in a common container.

[0261] Such a vessel is preferably equipped with an inlet for the recycled monomer product in liquid or solid form, and for the separate monomer B (HOOC-R 2 If the recycled monomer product is provided in solid form, sufficient distance between the inlets should be provided to allow for the addition of the separate monomer B (HOOC-R 2 -COOH). However, it is possible that the separate monomer B (HOOC-R 2 -COOH) can be combined with the recycled monomer product which is still in solid form, provided that the recycled monomer product is subsequently melted in the same vessel.

[0262] Another embodiment of the present invention comprises the step of mixing the recycled monomer product and the separate monomer B (HOOC-R) in solid form. 2 -COOH) were premixed, then melted and mixed to obtain a monomer slurry.

[0263] The container may further be equipped with an outlet for the monomer slurry in liquid form. The outlet is preferably located at the lower end of the container, typically at the opposite end of the inlet for the recycled monomer product. The outlet is preferably controllable by a valve to regulate the slurry flow from the container.

[0264] The container may further be equipped with an outlet for substances in gaseous form under the conditions required to provide the recycled monomer product in the molten state. This port is preferably connected to a condensing device that allows the recovery of evaporated liquid.

[0265] The container may further be equipped with a mixing device. Such a mixing device may include stirring blades or paddles on a rotating shaft, or a single screw or parallel screws.

[0266] The container may further be equipped with a heating device. Such a heating device may constitute a heating mantle or heating element inside the container. The heating device must be designed to provide sufficient heating to promote evaporation of water and / or inert solvent and maintain the monomer slurry in liquid form. If the recycled monomer product is provided in solid form, sufficient heating devices should be provided to allow the recycled monomer product to melt. Optionally, the reflux of the heated slurry can support the heating.

[0267] The container for preparing the monomer slurry can be a supplement to the process design for making polyester. In this case, the container becomes part of the recycled monomer product supply unit.

[0268] Alternatively, the container can replace the single monomer A (HO-R) used to prepare the conventional process of making polyester mainly composed of 1 -OH) and single monomer B (HOOC-R 2 In a preferred embodiment of the present invention, an existing container for preparing a monomer slurry made mainly of single monomer A and single monomer B is equipped with an additional heating device to allow the preparation of a monomer slurry according to the present invention.

[0269] In a preferred embodiment of the present invention, the recycled monomer product is obtained by crystallization from a solution containing water and / or an inert solvent. After filtration, the monomer product contains up to 50% by weight of residual water and / or inert solvent, based on the total amount of the recycled monomer product. In order to reduce the amount of water, the crystallized recycled monomer product can be mixed with monomer A (HO-R 1 -OH) and separated from excess liquid by additional filtration. The wet recycled monomer product obtained is melted to provide the recycled monomer product in liquid form. The additional filtration step reduces the amount of evaporation required during slurry formation and / or polyester polymerization.

[0270] In a preferred embodiment of the invention, the slurry is cooled, solidified and converted into granules. The conversion into granules can be carried out before (eg by spray or droplet technology), during or after solidification.

[0271] The particles can be formed by any suitable particle forming technique. This includes granulation such as hot die face cutting, droplet granulation or spray congealing. It involves contacting the material to be solidified with a cold surface, such as rotational forming or drum tableting. The particles can be in the form of pellets, flakes or powders. The particles can be further processed to provide particles of a defined size range. This includes grinding, sieving or air screening.

[0272] Typical particle sizes are in the range of a few micrometers to a few centimeters. For handling, storage and transportation, a defined particle size of 0.3 mm to 3 cm is preferred.

[0273] Solidified particles can be brittle or ductile, depending on the amount of material that is liquid under ambient conditions and present in the particles. They can be free-flowing or sticky with a tendency to form agglomerates. Free-flowing particles are preferred for dry handling, storage and transportation.

[0274] An advantage of the present invention is that the preparation of a monomer slurry made predominantly of recycled monomer product and monomer B alone and optionally monomer A alone allows the slurry preparation step to be omitted from the polymerization process.

[0275] An advantage of the present invention is that preparing a solid monomer slurry made primarily of recycled monomer product and monomer B alone results in reduced brittleness compared to recycled monomer product alone.

[0276] An advantage of the present invention is that the recycled monomer product with residual liquid may initially tend to form agglomerates, but after adding the diacid monomer B (HOOC-R 2 -COOH), a slurry is obtained which does not exhibit the same viscosity after curing. This free-flowing slurry can be stored and transported without the risk of agglomeration.

[0277] Another advantage of the present invention is that in the single monomer B (HOOC-R 2 -COOH) and the polyesters derived therefrom are produced at different locations. 2 Producing the slurry at the site of production of the polyester (-COOH) can simplify the logistics of recycled monomer and virgin monomer to the polyester manufacturing facility.

[0278] Single monomer A (HO-R 1 -OH) contains a group of diols in unreacted form, the monomer unit A'(HO-R 1 -O-) and A”(-OR 1 -O-) contains a reactive diol unit. 2 -COOH) contains a group of diacids in unreacted form, monomer unit B'(HOOC-R 2 -CO-) and B”(-OC-R 2 -CO-) contains a reactive diacid unit.

[0279] A preferred embodiment of the present invention requires monomer A (HO-R 1 -OH) contains at least 90% ethylene glycol (EG), wherein the percentages are calculated as molar percentages of the total amount of monomer A alone, and monomer B (HOOC- 2 -COOH) contains at least 90% terephthalic acid (TPA), wherein the percentages are calculated as molar percentages of the total amount of monomers B alone.

[0280] Other suitable forms of the monomers may include any comonomers commonly used to make polyesters, such as isophthalic acid (IRA), cyclohexanedimethanol (CHDM), or diethylene glycol (DEG).

[0281] The polyesters made from these monomers belong to the group of polyethylene terephthalate and their copolymers (PET) having the main repeating unit [TPA-EG-].

[0282] When depolymerization is performed using PET with EG as the sole monomer A, the main monomer product will be bis(hydroxyethyl)terephthalate (BHET). Obviously, in the presence of comonomers, comonomer-substituted BHET can be formed. For example, DEG can replace EG as the reactive monomer A' or A". Upon repolymerization, PET will be obtained again. According to the present invention, PET is formed by adding TPA to BHET.

[0283] As an alternative, monomer R 3 -OH, preferably methanol, for depolymerization. Upon reaction with EG, BHET will be obtained again.

[0284] The depolymerization products from PET and EG may also contain dimers and oligomers of BHET. Although most of these dimers and oligomers are terminated by OH end groups, some COOH end groups will be present. The depolymerization products may also contain monohydroxyethyl terephthalate (MHET) and TPA. Obviously, in the presence of comonomers and by-products, dimers and oligomers may contain a portion of comonomers. In particular, DEG can replace EG as reactive monomer A' or A". Optionally, the purification step after depolymerization may include a step to reduce the amount of MHET. Furthermore, optionally, the purification step after depolymerization may include a step to reduce the amount of BHET and oligomers thereof substituted by DEG, CHDM and / or IPA. Optionally, this reduction is the result of dissolving, crystallizing and filtering the depolymerization product enriched in BHET. In a preferred embodiment of the present invention, BHET contains 3 wt.% to 50 wt.% of substances that are liquid under ambient conditions, preferably water and / or ethylene glycol. More preferably, BHET contains more than 5 wt.%, more preferably more than 7 wt.%, and especially 10 wt.% or more of substances that are liquid under ambient conditions, preferably water and / or ethylene glycol. The same preferred ranges for depolymerization, various cleaning steps, and slurry preparation and subsequent PET production as defined above apply to general polyesters.

[0285] Specifically, for the supply of BHET containing water and / or ethylene glycol, a temperature of 70°C to 100°C is preferred, and for slurry preparation, a temperature of 100°C to 130°C is preferably maintained.

[0286] A preferred embodiment of the present invention relates to solid particles comprising:

[0287] - a recycled monomer product, wherein the recycled monomer product contains 50 to 100% by weight of monomers having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer,

[0288] -With HOOC-R 2 -COOH diacid monomer B, B' unit -OC-R 2 -CO- with single diacid monomer B HOOC-R 2 The molar ratio of -COOH ranges from 5:1 to 1:5, where R 1 and R 2 The same or different, 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 heterocyclic rings containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms.

[0289] Preferably, the B" unit -OC-R 2 -CO- and single monomer B HOOC-R 2 The molar ratio of -COOH is lower than 4:1, more preferably lower than 3:1. As the molar ratio decreases from the upper limit, the amount of the individual monomer A (HO-R 1 -OH) is reduced.

[0290] Preferably, the B" unit -OC-R 2 -CO- and single monomer B HOOC-R 2 The molar ratio of -COOH is higher than 1:3 (i.e., greater than about 0.33), more preferably higher than 1:2. As the molar ratio increases from the lower limit, the amount of the individual monomer A (HO-R 1 At the same time, the recycled content in the resulting polyester increases.

[0291] In which the solid particles are unit A" (-OR 1 -O-) and B”(-OC-R 2 -CO-) and the only source of monomer A (HO-R 1 Ideally, under the general limitations of existing polymerization equipment, the molar ratio ranges from 2:1 to 1:1.

[0292] According to a preferred embodiment of the present invention, the solid particles comprise:

[0293] - a recycled monomer product, wherein the recycled monomer product contains 50 to 100% by weight of monomers having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer,

[0294] -With HOOC-R 2 -COOH diacid monomer B, B' unit -OC-R 2 -CO- with single diacid monomer B HOOC-R 2 The molar ratio of -COOH ranges from 3:1 to 1:4, where R 1 and R 2 are 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 heterocyclic rings containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms,

[0295] -Diol Monomer A(HO-R 1 -OH), the total amount of B units is equal to the single monomer A (HO-R 1 The molar ratio of -OH) ranges from 6:1 to 1:1.35.

[0296] Preferably, the B" unit (-OC-R 2 -CO-) and monomer B(HOOC-R 2 The molar ratio of the monomers A (HO-R) to the monomer product is less than 2:1, more preferably less than 1.5:1. As the molar ratio decreases from the upper limit, the individual monomers A (HO-R) that may be present in the monomer product 1 -OH) increases.

[0297] Preferably, the total amount of B units is equal to the total amount of monomer A (HO-R 1 The molar ratio of -OH) is lower than 3:1, more preferably lower than 2:1.

[0298] Preferably, the B" unit (-OC-R 2 -CO-) and single monomer B(HOOC-R 2 The molar ratio of the monomers A (HO-R) to the monomers B (HO-R) is higher than 1:3, more preferably higher than 1:2. As the molar ratio increases from the lower limit, the amount of recycled content in the resulting polyester increases. However, more of the individual monomers A (HO-R) must be evaporated during the polymerization. 1 -OH).

[0299] Preferably, the total amount of B units is equal to the amount of the individual monomers A (HO-R 1 The molar ratio of -OH) is higher than 1:1.25, more preferably higher than 1:1.

[0300] In which the solid particles are unit A" (-OR 1 -O-) and B”(-OC-R 2 -CO-) and the only source of monomer A (HO-R 1 -OH) is evaporated within the usual limits of existing polymerization equipment, the B" unit (-OC-R 2 -CO-) and single monomer B(HOOC-R 2 -COOH) in a molar ratio ranging from 1:2 to 1:1, and the total amount of B units is equal to the total amount of the single monomer A (HO-R 1 The molar ratio of -OH) is in the range of 1.5:1 to 3:1.

[0301] Based on the above range, the weight of the single monomer A in the condensation monomer may exceed the dry weight. However, it is preferred to limit the content of the single monomer A to 50%.

[0302] Based on a preferred embodiment of the present invention, the solid particles comprise 2 to 40% by weight of a substance that is liquid under normal conditions. In order to maintain free-flowing slurry particles, the solid particles contain less than 10% by weight, preferably less than 6% by weight of a substance that is liquid under normal conditions. The percentage is calculated as the ratio of liquid to the weight of particles including the liquid. In the range of obtaining free-flowing particles with residual liquid, it is possible to process by common bulk material means such as pneumatic conveying, and to store bulk materials in large silos, which requires free-flowing product characteristics while still allowing particles to be converted into liquids at low temperatures. In order to limit drying requirements, the solid particles preferably contain more than 5% by weight of a substance that is liquid under normal conditions. In this case, the percentage is calculated as the ratio of liquid to the BHET weight including liquid in the particles.

[0303] The descriptions, definitions and calculations for the recycled monomer products and the monomers therein and the associated polyesters and the monomer units therein plus their monomers and depolymerization products apply to the particles in a similar manner to the above procedures.

[0304] Preferred particles of the present invention comprise:

[0305] - 1 to 2 moles of recycled BHET;

[0306] - Add 1 mol of TPA;

[0307] - The water content is at most 50% by weight of the total granules.

[0308] Another preferred particle of the present invention comprises:

[0309] - 2 to 3 moles of recycled BHET;

[0310] - Add 3 to 4 moles of TPA;

[0311] - Add 2 to 4 moles of EG;

[0312] - The water content is at most 40% by weight, based on the weight of BHET.

[0313] Such particles may contain comonomers and by-products as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0314] The invention will now be described in more detail with reference to non-limiting examples and to the accompanying drawings.

[0315] Figure 1 A schematic diagram showing an embodiment of the device according to the invention is shown. DETAILED DESCRIPTION

[0316] Figure 1 A separation container 1 is shown with one or more supply ports 2 on one side of the separation container 1 and one or more removal ports 3 on the other side of the separation container 1. Optionally, the separation container 1 contains additional removal ports 4 and / or drain ports 5 at the bottom. A screen 6 is configured to be disposed in the separation container 1.

[0317] The supply port 2 is positioned so that the depolymerization solution can be provided to the supply zone 7. The port 2 can extend through the vessel wall, as shown, or can be positioned to supply the depolymerization solution from the top (not shown). The flow of the depolymerization solution is directed from the supply zone 7 toward the removal port 3. After the supply zone 7, the solution passes through the separation zone 8 and the cooling zone 9. In the supply zone 7, a plate 13 can be mounted to the reactor wall below the supply port. The plate 13 guides the solid particles to settle from the vessel wall onto the screen 6.

[0318] In the separation zone 8, the depolymerized solution separates into an upper first phase containing liquefied pollutants and a lower second phase substantially free of liquefied pollutants. The separation zone is designed so that minimal turbulence occurs.

[0319] In the cooling zone 9, the liquefied pollutants in the first layer are solidified by contact with water as a cooling liquid in the presence of a portion of the depolymerization solution. Water is added to the surface of the first phase or to the first phase through at least one supply pipe 10 so that mixing occurs throughout the upper layer. This mixing can be the result of the water velocity entering the solution, or it can be the result of a mixing device. The water temperature is selected so that the upper layer is sufficiently cooled to allow the liquefied pollutants to solidify. At the same time, it is high enough to prevent excessive supercooling. Generally, the water temperature is from room temperature to 70°C. The water can be supplied as a spray and / or one or more water jets. Preferably, the water flow is directed towards the removal port 3.

[0320] Screen 6 is so configured as to be arranged in separation vessel 1 that it allows depolymerization solution to pass but removes solid contaminants. Screen 6 can be static, which requires regular removal of solid contaminants, or it can be operated continuously, as shown in the figure, or graduated operation. The solid contaminants removed can be rinsed to recover the adhered recycled monomer product. This rinsing can be carried out offline, or it can be carried out in a separate rinse zone 11 on screen 6 as shown in the figure. For rinsing, use separate monomers and / or water. The rinse liquid temperature should be similar to or higher than the cooling water temperature to prevent additional precipitation or even redissolution of the recycled monomer product. At the same time, the water temperature must be low enough to prevent the solid contaminants from melting. Generally, the rinse liquid temperature is 40°C to 90°C. The rinse liquid is returned directly to the separation vessel 1, as shown in the figure, or returned to the process after separate collection. The advantage of separate collection is that additional cleaning steps are allowed, such as fine filtration.

[0321] Flushing may be followed by an air purge to reduce the amount of liquid adhering to the solid contaminants.

[0322] If a continuous screen or graduated screen 6 is used, various measures can be foreseen to clean the screen 6 to prevent the accumulation of solids, such as solid contaminants or precipitated depolymerization products. The solid contaminants are removed by falling off the screen 6. This can be supported by a scraper. In addition, the screen can be backwashed in the cleaning zone 12. The conditions for backwashing are similar to those for flushing. However, the backwashing liquid is preferably not returned to the process without additional cleaning.

[0323] As the depolymerized solution flows through the separation zone 8, the liquefied contaminants, which are less dense than the solution, move toward the top of the solution. This movement toward the top depends on the density difference and the particle size. As the depolymerized solution flows through the cooling zone 9, the stirring will cause some downward movement of the liquefied contaminants. Overall, the two layers formed (solution with and without liquefied contaminants) have no clear boundary and they change their layer thickness. Important for this process is the fact that in the entire layer where the liquefied contaminants are present, sufficient cooling is achieved to solidify those contaminants.

[0324] While the liquefied pollutant solidifies, part of the recycled monomer product may precipitate. The screen 6 must be designed so that the precipitated monomer product passes through the screen 6 together with the solution. The liquefied pollutant generally has a tendency to agglomerate, which helps to form larger particles and facilitates filtration. The general screen opening is 0.1 mm to 30 mm. The preferred screen opening is greater than 0.2 mm and less than 10 mm.

[0325] If the particles of the liquefied pollutants remain too small, additional liquefied product can be added before the separation zone 8. Most suitably, this additional liquefied product is added to the depolymerization solution. Suitable liquefied products are those having a melting point above 90° C. but below the temperature at which the depolymerization solution is supplied to the separation vessel 1 and a density below 1 g / cm 3 Any product that is insoluble in the depolymerization solution. Olefin-based oligomers or high MFI polymers are preferred. In addition to the ability to form larger agglomerates of liquefied pollutants in the separation vessel, the liquefied product can also serve as a means to reduce the viscosity of the liquefied pollutants during depolymerization and extract non-polar pollutants from the depolymerization solution.

[0326] One or more removal ports 3 are located behind the screen 6 and typically extend through the vessel wall.

[0327] A further removal opening 4 may extend through the container wall at a lower height.

[0328] If only removal port 3 is present, the total flow of the diluted depolymerization solution is directed to subsequent process steps. If multiple removal ports 3 and 4 are present, the upper layer is directed primarily toward removal port 3 and the lower layer is directed primarily toward port 4. By adjusting the flow rate, the thickness of the layer can be adjusted. At the removal ports, both layers are substantially free of liquefied contaminants, but have different temperatures and water contents. Both flows of the diluted depolymerization solution are directed to subsequent process steps. Subsequent process steps include pumping, mixing of the two flows, and filtration.

[0329] Optionally, there are one or more drains 5 at the bottom of the separation vessel 1. The drains 5 allow for periodic or continuous removal of solid particles having a density higher than that of the depolymerization solution.

[0330] The separation vessel 1 needs to be insulated to prevent heat loss. Optionally, the walls of the vessel are heated by microheating or jacketing. A hood or enclosure may be provided to prevent the evaporated water, which may contain some volatile contaminants, from escaping to the environment.

[0331] Water has been used as a coolant to provide Figure 1 Alternatively, diol monomers or inert solvents can be used. Independently of the type of cooling liquid, preference is given to using liquid which has been returned from one or more subsequent process steps and optionally after a cleaning or recovery step.

[0332] method:

[0333] All presented compositions were measured by high pressure liquid chromatography (HPLC) using THF as solvent and water / acetonitrile / methanol (ratios varied from 90 / 5 / 5 to 10 / 45 / 45) as eluents.

[0334] All metal contents reported were measured by inductively coupled plasma (TCP) using nitric acid and microwave digestion to prepare the measuring solutions.

[0335] All thermal analysis results were measured by differential scanning calorimetry (DSC) in 40 μl aluminum pans at a heating rate of 10°C / min.

[0336] All compression measurements were performed on screened samples. The samples were placed on a bottom surface of 10.2 cm 2 , fill the crucible with a height of 2 cm. 2 The piston is pressed into the crucible containing the sample at a constant speed. Once a piston resistance of 1 N is measured, the zero point of the compression experiment is set. The experiment is continued until a compression force of 50 N is obtained. The deviation at this point is recorded and divided by the initial filling height of the sample.

[0337] The water content in PET was measured by a halogen moisture analyzer, heating from 40°C to 200°C at 1°C / min.

[0338] The water content in EG was measured using IR spectroscopy and chemometrics based on a calibration curve of known EG / water mixtures.

[0339] Example 1

[0340] 192.4 g of PET flakes obtained from a transparent PET bottle with about 0.3 wt% water and flake size of 2-12 mm were mixed with 1.1 g of zinc acetate dihydrate as a depolymerization catalyst and 425 ml of ethylene glycol as a reactant and solvent. The molar ratio of EG to PET repeating units was 7.5:1. The mixture was heated under reflux conditions at atmospheric pressure for 4 hours. The liquid temperature increased over time from 197° C. to 204° C. A clear depolymerization solution was obtained.

[0341] Example 2

[0342] 100 ml of the thermal depolymerization solution from Example 1 was quickly poured into 75 ml of water precooled to 1° C. The resulting solution was turbid white and had a temperature of 66° C. The solution was heated to 70° C. and filtered through a filter with a pore size of 12-15 μm to separate the solidified oligomers from the solution. The filtration took 27 minutes and gave 13 g of isolated solid (after drying).

[0343] Example 3

[0344] 335 ml of water were added slowly to the remaining depolymerization solution from Example 1 so that the solution temperature remained above 100° C. Thereafter, the temperature was maintained at 100° C. to 105° C. until 1 hour after the start of the water addition. The resulting solution was almost clear. The solution was then cooled to 70° C. to give a cloudy white solution. 175 ml of this solution were filtered as described in Example 2. The filtration time was 8 minutes and 17 g of solids were obtained.

[0345] It can be seen from Examples 2 and 3 that filtration is improved if the water addition is performed such that rapid supercooling of the depolymerization solution is avoided.

[0346] Example 4

[0347] The procedure of Example 1 was repeated to obtain a depolymerization solution. 425 ml of water was added to the obtained depolymerization solution so slowly that the solution temperature remained above 100° C. Thereafter, the temperature was maintained at 100° C. to 105° C. until 1 hour after the start of water addition.

[0348] The solution contains:

[0349] MHET 9.9mg / g BHET, including comonomer-substituted BHET 204.2mg / g Dimers, including comonomer-substituted dimers 32.1mg / g Other oligomers 4.2mg / g

[0350] The solid content of the solution was 251 mg / g. The remaining weight was EG and water. The BHET content of the solid was 81.6%; and the additional contents were as follows: MHET 3.9%, dimer 12.8%, other oligomers 1.7%.

[0351] The solid content of 1.1% is DEG substituted BHET and dimer.

[0352] The solution was then cooled to 70°C and filtered through a filter with a pore size of 12-15 μm to separate the solidified oligomer from the solution.

[0353] The oligomer filter cake contains:

[0354] MHET 10.1mg / g BHET, including comonomer-substituted BHET 201.8mg / g Dimers, including comonomer-substituted dimers 214.8mg / g Other oligomers 37.7mg / g

[0355] The filtrate contained:

[0356]

[0357]

[0358] Example 5

[0359] The filtrate from Example 4 was cooled to room temperature and then placed in a refrigerator where it was cooled and maintained at 5°C while stirring throughout the 8 hour cooling period and vacuum filtered through a filter with a pore size of 12-15 μm to separate the solidified BHET from the solution.

[0360] The BHET-rich filter cake contains:

[0361] MHET 12.9mg / g BHET, including comonomer-substituted BHET 433.9mg / g Dimers, including comonomer-substituted dimers 26.2mg / g Other oligomers 1.3mg / g

[0362] The solid content of 0.8% is DEG substituted BHET and dimer.

[0363] The solid content of the BHET-rich filter cake was 474 mg / g. The remaining weight was EG and water.

[0364] The filtrate contained:

[0365] MHET 5.3mg / g BHET, including comonomer-substituted BHET 14.7mg / g Dimers, including comonomer-substituted dimers 0.8mg / g Other oligomers 0.03mg / g

[0366] Comparing the BHET-enriched filter cake from Example 5 with the depolymerized solution from Example 4, based on total solids content, the MHET content decreased from 3.9% to 2.7%, while the dimer and oligomer contents decreased from 12.8% to 5.5% and from 1.7% to 0.3%, respectively. At the same time, the DEG-substituted material decreased from 1.1% to 0.8%.

[0367] As can be seen from Examples 4 and 5, the crystallization procedure not only reduces the dimer and oligomer content of the monomer product, but also reduces the amount of monomer replaced by the copolymer.

[0368] Example 6

[0369] Repeat Example 4 and Example 5. 137 g of the oligomer solution after filtration and cooling was passed through a pore size of 20 μm and a surface area of ​​56 cm 2 When the filtrate flow rate decreases significantly, stop adding solution to the filter.

[0370] The vacuum was kept constant at 500 mbar. Once the surface of the filter cake looked dry, the vacuum and filtration were stopped. The total filtration time was 160 seconds. The filter cake obtained was 83 g and the filtrate was 54 g.

[0371] The filter cake contains:

[0372] MHET 4.7mg / g BHET, including comonomer-substituted BHET 285.5mg / g Dimers, including comonomer-substituted dimers 57.2mg / g Other oligomers 4.9mg / g

[0373] The solid content of the filter cake was 352 mg / g. The remaining weight was EG and water. The BHET content in the solid was 81%; the remaining components were as follows: MHET 1.3%, dimer 16.2%, other oligomers 1.4%.

[0374] After the initial filtration, the filter cake was washed 3 times by spraying 45 g of demineralized water on the filter cake each time. Each filtration was performed until the surface of the filter cake looked dry. This took 146 seconds, 61 seconds and 65 seconds, and each washing step gave 50 g, 49 g and 45.5 g of filtrate.

[0375] Finally, the filter cake was subjected to dehydration under vacuum for 120 seconds to obtain 30 g of filtrate.

[0376] After dehydration, the filter cake contains:

[0377] MHET 1.0mg / g BHET, including comonomer-substituted BHET 562.9mg / g Dimers, including comonomer-substituted dimers 70.6mg / g Other oligomers 8.0mg / g

[0378] The weight of the filter cake was 43.5 g. The solid content in the filter cake was 643 mg / g. The remaining weight was mainly water. The BHET content in the solid was 87.6%; the remaining components were as follows: MHET 0.2%, dimer 11%, other oligomers 1.3%. The antimony and zinc contents were 0.75 ppm and 1.6 ppm, respectively.

[0379] In the depolymerization solution, the initial zinc content was 274 ppm due to the addition of zinc acetate catalyst for depolymerization, and the initial antimony content was about 39 ppm due to the presence of antimony catalyst in PET. In the BHET-rich filter cake, the residual antimony content was less than 2% of the initial value, and the residual zinc content was less than 0.6% of the initial value.

[0380] As can be seen from Example 6, the washing step further improves the quality of the BHET-rich filter cake and reduces the amount of liquid contained therein.

[0381] Example 7

[0382] Example 6 was repeated, but without oligomer filtration after depolymerization. 72 g of solution were used.

[0383] The total filtration time was 115 seconds. The filter cake obtained was 47.5 g and the filtrate was 24.5 g. The amount of water used in the three washes was 28 g each. The filtration times for the washes were 95 seconds, 45 seconds and 50 seconds; the dehydration time was 120 seconds.

[0384] After dehydration, the filter cake contains:

[0385] MHET 1.9mg / g BHET, including comonomer-substituted BHET 604.8mg / g Dimers, including comonomer-substituted dimers 85.3mg / g Other oligomers 13.8mg / g

[0386] The weight of the filter cake was 24.6 g. The solid content in the filter cake was 706 mg / g. The remaining weight was mainly water. The BHET content in the solid was 85.7%; the remaining components were as follows: MHET 0.3%, dimer 12.1%, other oligomers 2.0%. The antimony and zinc contents were 1.5 ppm and 5.3 ppm, respectively.

[0387] Comparing Example 6 and Example 7, a higher quality of BHET and a better yield per unit filtration area are obtained by using oligomer filtration before recovering the BHET-rich product. The higher quality is not only suitable for the reduced oligomer content, but also for the reduced metal content.

[0388] Example 8

[0389] The filter cake from Example 7 was washed twice more with 28 g of water. The filter cake weight was reduced to 24.2 g. The antimony and zinc contents were 1.2 ppm and 3.9 ppm, respectively.

[0390] Comparison of Example 6 and Example 8 continues to show that when an oligomer filtration step is used, the metal content is lower even when an additional washing step is applied. However, the additional washing step offsets some of the disadvantages of avoiding an oligomer filtration step.

[0391] Example 9

[0392] Example 1 was repeated except that water was added so that the moisture content of the PET was 2 wt%. The MHET content of the solution was determined to be 1.7%.

[0393] Example 10

[0394] Example 1 was repeated except that the PET was vacuum dried at 55°C for 5 days prior to depolymerization and pure ethylene glycol containing less than 0.1% water was used. The MHET content in the solution was determined to be 0.1%.

[0395] It can be seen from Examples 9 and 10 that MHET formation can be avoided if water is prevented from entering the depolymerization.

[0396] It is evident from Example 5 that more than 25% of the solids content in the final filtrate is MHET. This indicates that the formation of MHET directly leads to additional losses.

[0397] Therefore, if MHET formation is avoided due to the reduction of water in the feed stream, the losses can be reduced.

[0398] Embodiment 11

[0399] Example 1 was repeated using undried PET. The moisture content was determined to be approximately 0.3 wt%.

[0400] 425 ml of water were added to the thermal depolymerization solution in such a way that the solution temperature remained above 100° C. The water addition lasted for approximately 15 minutes.

[0401] The MHET content in the solution was determined to be 1.9%.

[0402] Thereafter, the temperature was maintained at 105° C. for 1 hour. The MHET content increased to 2.8%.

[0403] Comparing the MHET content of Example 11 (1.9%) with the expected MHET subtracted from Examples 9 and 10 (linearly interpolated to 0.27%), it can be seen that additional MHET was formed during the water addition and that subsequent heating resulted in the formation of additional MHET.

[0404] Therefore, if MHET formation is avoided due to a reduction in the contact time between the thermal depolymerization solution and water, the losses can be reduced.

[0405] Example 12

[0406] Example 9 was repeated. After depolymerization, 100 ml of the solution was heated under vacuum (800 mbar) to remove 32 ml of solvent (mainly ethylene glycol). The initial molar ratio of EG to PET repeating units was 7.5:1. Due to the depolymerization reaction, the molar ratio decreased to 6.6:1. Due to evaporation, 41% of the initially added ethylene glycol was removed. The final molar ratio decreased to 3.5:1. During evaporation, the temperature increased from 70°C to 140°C.

[0407] 65 ml of water are added to the thermal depolymerization solution in such a way that the solution temperature remains above 100° C. The addition of water lasts for about 15 minutes. The solution is then rapidly cooled, reaching below 60° C. within 15 minutes.

[0408] The solution contains:

[0409] MHET 3.3mg / g BHET, including comonomer-substituted BHET 239.2mg / g Dimers, including comonomer-substituted dimers 46.0mg / g Other oligomers 8.1mg / g

[0410] The solid content of the solution was 297 mg / g. The remaining weight was EG and water. The BHET content in the solid was 80.6%; the remaining components were as follows: MHET 1.1%, dimer 15.5%, other oligomers 2.7%.

[0411] The solid content of 1.2% is DEG substituted BHET and dimer.

[0412] Comparing Example 4 and Example 12 and considering the MHET formation discussed in Example 11, it can be seen that a reduced amount of MHET can be obtained as the solvent evaporates from the depolymerization solution. However, with the removal of solvent to such a low molar ratio, the content of dimers and oligomers increases by 1.7% and 1%, respectively.

[0413] Embodiment 13

[0414] 192.4 g of PET flakes with a flake size of 2-12 mm obtained from a transparent PET bottle were mixed with 1.1 g of zinc acetate dihydrate as a depolymerization catalyst and 601.9 ml of ethylene glycol as a reactant and solvent. PET contained 1 wt% water and EG contained 4.1 wt% water. The molar ratio of dry EG to dry PET repeating units was 10.2:1. The mixture was heated under boiling conditions at atmospheric pressure until 173 ml of EG and water had evaporated, which took about 100 minutes. Excluding water, this was equivalent to a 25.2% EG removal rate based on the initial EG amount. The reaction was continued under reflux conditions for a total reaction time of 4 hours. The final molar ratio was reduced to 6.8:1. The liquid temperature increased over time to 205°C. A clear depolymerization solution was obtained.

[0415] The solution contains:

[0416] MHET 1.0mg / g BHET, including comonomer-substituted BHET 312.5mg / g Dimers, including comonomer-substituted dimers 50mg / g Other oligomers 7.1mg / g

[0417] The solid content of the solution was 370.6 mg / g. The remaining weight was EG. The BHET content in the solid was 84.3%; the remaining components were as follows: MHET 0.3%, dimer 13.5%, other oligomers 1.9%.

[0418] The solid content of 0.9% is DEG substituted BHET and dimer.

[0419] 425 ml of water are added to the thermal depolymerization solution in such a way that the solution temperature remains above 100° C. The addition of water lasts for about 15 minutes. The solution is then slowly cooled to 80° C. for about 1 hour.

[0420] The solution contains:

[0421] MHET 4.9mg / g BHET, including comonomer-substituted BHET 186.8mg / g Dimers, including comonomer-substituted dimers 29.7mg / g Other oligomers 4.1mg / g

[0422] The solid content of the solution was 225.5 mg / g. The remaining weight was EG and water. The BHET content in the solid was 82.8%; the remaining components were as follows: MHET 2.2%, dimer 13.2%, other oligomers 1.8%.

[0423] The 1% solids content is DEG substituted BHET and dimer.

[0424] Comparison of Example 9 and Example 13 before the addition of water shows that when the solvent is evaporated during depolymerization, reduced amounts of MHET can be obtained despite the initial addition of large amounts of water.

[0425] This is also evident when comparing Example 4 and Example 13 after the addition of water. In addition, no negative effect on oligomer content was observed, in contrast to Example 12. As discussed in Example 11, the increase in MHET content during water addition in Example 13 compared to Example 12 is attributed to slower cooling.

[0426] Another advantage of the procedure used in Example 13 compared to Example 12 is the fact that no vacuum is required for operation.

[0427] Embodiment 14

[0428] The procedure of Example 6 was repeated. The wet BHET-rich product was dissolved in 70°C water and filtered to obtain a BHET solution with a minimum oligomer content. The received solution was cooled to 5°C and filtered. The filter cake was dried in a vacuum oven at 60°C. The sample contained 95.2% BHET, 0.5% MHET and 4.3% dimer. The sample was considered to be clean BHET. Its bulk density was 580 kg / m 3 .

[0429] The samples were prepared with the following composition (in wt%):

[0430] BHET% water% Ethylene glycol% Liquid content% Sample 14-1 100 Sample 14-2 99.6 0.4 0.4 Sample 14-3 94.8 5.2 5.2 Sample 14-4 85 15 15 Sample 14-5 78 22 22 Sample 14-6 63 37 37 Sample 14-7 39 61 61 Sample 14-8 93 7 7 Sample 14-9 88 12 12 Sample 14-10 78 22 22 Sample 14-11 58 42 42 Sample 14-12 47 53 53 Sample 14-13 96.8 3.2 3.2 Sample 14-14 98.1 1.9 1.9

[0431] The following measurements were taken:

[0432] DSC measurements: Samples 14-1 to 14-7 and 14-13 to 14-14 were scanned from -50 °C to 120 °C in a closed pan to prevent evaporation:

[0433] Peak [℃] Left border[℃] Right boundary[℃] End point [℃] Sample 14-1 110.9 87 119.3 113 Sample 14-2 111.0 87 118.4 114 Sample 14-3 92.2 38 99.7 98 Sample 14-4 62.2 40 86.7 85 Sample 14-5 61.3 44 79.3 71 Sample 14-6 61.0 44 75.1 67 Sample 14-7 61.1 46 72.2 65 Sample 14-13 95.0 37.3 101.7 100 Sample 14-14 102.4 43.1 110.0 106

[0434] Except for samples 14-1 to 14-2, all samples showed an ice peak, i.e., the melting peak of water.

[0435] BHET has a melting peak at 111° C. and a narrow melting range, with complete melting achieved at about 114° C. 1.9% water is sufficient to shift the melting peak temperature and significantly broaden the melting peak, indicating a dual structure.

[0436] At 3.2% water, complete melting as indicated by the endpoint was achieved, more than 10°C below the melting peak temperature of dry BHET. At 15% and above water content, the melting peak shifted to or slightly below 62°C, and the melting peak narrowed, indicating a uniform wet BHET structure. Complete melting occurred at 67°C to 85°C, depending on the amount of water from 15% to 37%.

[0437] In general, the addition of water liquefies BHET at temperatures significantly below its melting temperature.

[0438] DSC measurement: Samples 14-8 to 14-12 were scanned from -50 °C to 250 °C in a closed pan to prevent evaporation:

[0439] Peak [℃] Left border[℃] Right boundary[℃] End point [℃] Sample 14-1 110.9 87 119.3 113 Sample 14-8 106.1 56 115.0 110 Sample 14-9 100.3 26 110.6 106 Sample 14-10 84.9 23 101.8 92 Sample 14-11 72.2 19 96.5 90 Sample 14-12 70.0 23 90.9 87

[0440] Only sample 14-12 showed the expected ice peak at -13°C.

[0441] BHET has a melting peak and a narrow melting range at 111°C, and complete melting is achieved at about 114°C. 7% ethylene glycol is sufficient to change the melting peak temperature and broaden the melting peak, indicating a dual structure. At 42% and above ethylene glycol content, the melting peak shifts to 72°C or slightly below 72°C, and the melting peak narrows, indicating a uniform wet BHET structure. Complete melting occurs at 87°C to 92°C, depending on the amount of ethylene glycol from 22% to 53%.

[0442] In general, BHET is less sensitive to residual ethylene glycol than to water. However, it still shows the ability to reduce melting conditions.

[0443] Embodiment 15

[0444] Use cleaned BHET from Example 14. Add water or ethylene glycol to solid BHET at room temperature.

[0445] Samples were prepared with the following composition (wt%):

[0446] BHET% water% Ethylene glycol% TPA% Sample 15-1 70 30 Sample 15-2 80.4 19.6 Sample 15-3 52.3 12.8 34.9 Sample 15-4 44.2 10.8 45.0 Sample 15-5 67.1 32.9 Sample 15-6 52.1 22.4 25.5

[0447] A product with the following characteristics was obtained:

[0448]

[0449] The sensitivity of BHET to water can be used to prepare liquids at low temperatures.

[0450] Sample 15-1 was heated to 90° C. A clear liquid was obtained, although still 20° C. below the melting temperature of BHET. This liquid was used for viscosity measurements at 70° C., 75° C., 80° C., and 90° C. at shear rates of 10, 100, and 500 / sec.

[0451] T＝70℃ T＝75℃ T＝80℃ T＝90℃ 10[1 / sec] 270 130 97 63 100[1 / sec] 22 12 14 11 500[1 / sec] 8.9 6 6 6

[0452] The solution had very low temperature sensitivity. However, significant shear thinning was observed, indicating that slurry formation was reduced by agitation.

[0453] Sample 15-2 was heated to 90°C. Although still 20°C below the melting temperature of BHET, a clear liquid was obtained. This liquid was used for viscosity measurements at 80°C, 90°C, 100°C, and 120°C at shear rates of 10, 100, and 500 / sec. No shear thinning was observed.

[0454] T＝80℃ T＝90℃ T＝100℃ T＝120℃ 100[1 / sec] 42 27 17 9.5

[0455] Compared to Sample 15-1, water was observed to have a higher viscosity and higher temperature sensitivity.

[0456] In an attempt to prepare sample 15-3, sample 15-2 was tempered to 100°C and the required amount of cold (at room temperature) TPA in powder form was quickly added. The temperature dropped and caused the solution to partially solidify. Immediate formation of agglomerates was observed. Even with continuous stirring, it was not possible to break up the agglomerates.

[0457] In a second attempt to prepare sample 15-3, sample 15-2 was heated to 100°C and the required amount of cold (at room temperature) TPA in powder form was slowly added while continuously stirring and heating the resulting slurry. An opaque slurry (sample 15-3) was obtained, which was used for viscosity measurements at 100°C, 110°C, and 120°C at shear rates of 10, 100, and 500 / sec. No shear thinning was observed.

[0458] T＝100℃ T＝110℃ T＝120℃ 100[1 / sec] 116 92 67

[0459] The molar ratio of diol to diacid in the obtained slurry was 1.5:1, which was suitable for preparing PET. 50% of the diacid units in the obtained PET were derived from recycled BHET.

[0460] Compared to sample 15-2, an increase in viscosity was observed, which is seen as a result of the addition of TPA. Temperature sensitivity was maintained.

[0461] Sample 15-3 was used to add additional TPA as described above. An opaque slurry was obtained (Sample 15-4) which was used for viscosity measurements at 100° C., 110° C., and 120° C. at shear rates of 10, 100, and 500 / sec. No shear thinning was observed.

[0462] T＝100℃ T＝110℃ T＝120℃ 100[1 / sec] 348 263 193

[0463] The molar ratio of diol to diacid in the obtained slurry was 1.17:1, which was suitable for preparing PET. 39% of the diacid units in the obtained PET were derived from recycled BHET.

[0464] Compared to sample 15-3, a further increase in viscosity was observed, which is seen as a result of the addition of TPA. Temperature sensitivity remains.

[0465] The neat BHET from Example 14 was heated to 120°C and the required amount of cold (at room temperature) TPA in powder form was slowly added while continuously stirring and heating the obtained slurry. An opaque slurry (Sample 15-5) was obtained, which was used for viscosity measurements at 100°C, 110°C and 120°C at shear rates of 10, 100 and 500 / sec. No shear thinning was observed.

[0466] T＝120℃ 100[1 / sec] 100

[0467] The molar ratio of diol to diacid in the obtained slurry was 1.14:1, which was suitable for preparing PET. 57% of the diacid units in the obtained PET were derived from recycled BHET.

[0468] Despite the lower content of TPA compared to Sample 15-3, an increase in viscosity was observed, which is considered to be a result of the lack of liquid content in Sample 15-5.

[0469] Sample 15-1 was tempered to 90°C and cold (at room temperature) TPA in powder form was slowly added while continuously stirring and heating the resulting slurry. An opaque slurry (Sample 15-6) was obtained, which was used for viscosity measurements at 70°C, 75°C, 80°C and 90°C at shear rates of 10, 100 and 500 / sec.

[0470] T＝70℃ T＝75℃ T＝80℃ T＝90℃ 10[1 / sec] 296 134 143 95.9 100[1 / sec] 29.1 20.2 23.4 15.4 500[1 / sec] 15.5 14.5 12.8 7.1

[0471] The molar ratio of diol to diacid in the obtained slurry was 1.14:1, which was suitable for preparing PET. 57% of the diacid units in the obtained PET were derived from recycled BHET.

[0472] Compared to Sample 15-5, a decrease in viscosity was observed, which is believed to be a result of the inventive liquid component in Sample 15-6. Temperature sensitivity was maintained.

[0473] Overall, Example 15 demonstrates that low viscosity slurries can be prepared at reduced temperatures if the recycled BHET contains residual liquid. However, care must be taken to maintain the liquid state when adding TPA to avoid agglomeration due to negative cooling effects.

[0474] Example 16

[0475] The procedure of Example 6 was repeated. The wet BHET-rich product was dissolved in 70°C water and filtered to obtain a BHET solution with a minimum oligomer content. The obtained solution was cooled to 5°C and filtered. 10 g of the filter cake was heated to evaporate a portion of the contained water and a slurry was prepared with TPA. After heating for 4 minutes, a solution temperature of 100°C was reached and strong foaming was observed. Under strong stirring, 3.6 g of TPA in powder form was added within 2 minutes. The temperature was continued to increase and heating was stopped at approximately 105°C. The sample was poured onto a cold metal plate and ground through an 8 mm sieve to obtain a ground sample (Sample 16-1). The water content was determined to be 6.4% based on the total sample weight.

[0476] To further analyze the sensitivity to residual liquid, samples having compositions according to samples 14-1, 14-3 and 14-5 were heated to above their melting points and poured onto a cold metal plate to obtain solid sample plates. The sample plates were broken into pieces and ground through an 8 mm screen in a grinder to obtain three ground samples (respectively, samples 16-2, 16-3 and 16-4).

[0477] Another mixture was prepared by adding 0.8 g of ethylene glycol to 15 g of Sample 15-5 and converted as described above to obtain a ground sample (Sample 16-5).

[0478] Composition, in % by weight:

[0479] BHET% water% Ethylene glycol% TPA% Sample 16-1 62.8 6.4 30.8 Sample 16-2 100 Sample 16-3 94.8 5.2 Sample 16-4 78 22 Sample 16-5 63.7 5.1 31.2

[0480] A product with the following characteristics was obtained:

[0481]

[0482]

[0483] All samples were tested in compression experiments.

[0484] The experiment was carried out at different temperatures and up to 5N / cm 2 The results are given as % compression plus observation of the sample flow behavior during the measurement.

[0485]

[0486] Compression tests lead to an increase in bulk density, either due to densification caused by breaking the flakes or by compression of the flakes.

[0487] At lower temperatures, sample 16-2 exhibited brittle glass-like fracture behavior, while samples 16-1, 16-3, and 16-5 exhibited more ductile fracture. In all of these cases, compression was the result of a denser packing of fractured pieces. At higher temperatures, a transition to granular deformation was observed.

[0488] Sample 16-4 already exhibits a large portion of particle deformation at low temperatures, which leads to the observed densification.

[0489] As is apparent from Example 16, dry BHET exhibits low compressibility and viscosity under pressure even at elevated temperatures and is therefore considered suitable for storage as a free-flowing bulk material. At >20% water content, bulk storage is not feasible even at 30°C or above. At about 5% water or EG content, bulk storage at up to 70°C is considered feasible. Even with 9.3% water in BHET, granules can be formed with TPA that remain free-flowing in bulk storage up to 50°C. Overall, the sensitivity to EG is less than the sensitivity to water.

[0490] The bulk density of the granules so produced is significantly higher than that of the oven-dried BHET filter cake, which facilitates transportation and storage.

[0491] Embodiment 17

[0492] To further analyze the effect of added diacids and liquids on the brittleness of the solid particles, samples having compositions according to 15-5 (sample 17-1) and 15-4 (sample 17.2) were heated above their melting points and poured onto a cold metal plate to obtain solid sample plates. The sample plates were compared in a torsion experiment providing a stress-strain curve from which the fracture stress, fracture torsion angle and initial modulus can be reported.

[0493]

[0494] It can be demonstrated that the blends with EG present have a softer, more elastic behavior. This indicates lower brittleness, which is considered to be beneficial for material handling and storage operations.

[0495] Embodiment 18

[0496] To further analyze the influence of the added diacid in the solid particles, ground samples having compositions according to Sample 14-1 (Sample 18-1) and 15-5 (Sample 18-2) were compared in an experiment demonstrating the mechanical sensitivity of the particles.

[0497] 35 g of each sample was placed on a stack of sieves with mesh sizes of 6.3 mm, 5 mm, 4 mm, 3.15 mm, 2 mm and 1 mm and separated according to their particle size. The content of each sieve was measured. The sieve stack was then placed on a vibration device and exposed to a vibration amplitude of 10 mm / g for 10 minutes and subsequently to a vibration amplitude of 15 mm / g. The content of the sieves was measured again and the difference of each fraction was calculated.

[0498]

[0499]

[0500] During the vibration, both samples experienced a transition from larger particles to smaller particles. In most cases, the largest category was reduced in favor of the lower and finest categories.

[0501] Pure BHET undergoes more transitions than BHET with TPA addition, indicating that the blends are more resistant to mechanical forces generated by material handling and storage operations.

[0502] Embodiment 19

[0503] 360 g of undried PET flakes with a flake size of 2-12 mm obtained from a light blue PET bottle were mixed with 2 g of zinc acetate dihydrate as a depolymerization catalyst and 1100 ml of ethylene glycol as a reactant and solvent. PET contained approximately 0.3 wt% of water. EG contained 4.1 wt% of water. The molar ratio of dry EG to dry PET repeating units was 10:1. The mixture was heated under boiling conditions at atmospheric pressure until 309 ml of EG and water had evaporated. This was equivalent to 28.1% of the initial wet EG amount or 24.6% EG removal rate based on the initial EG amount without water. The reaction was continued under reflux conditions for a total reaction time of 4 hours. The liquid temperature increased over time to 205°C. A clear depolymerization solution was obtained. The solution was cooled to 105°C and filtered through a filter with a pore size of 25 μm to separate the unreacted residue. The dry weight of the residue obtained was 3.6 g.

[0504] 800 ml of water are added to the depolymerization solution so slowly that the solution temperature remains above 100° C. Afterwards, the temperature is maintained at 100° C. to 105° C. until 30 minutes after the start of water addition. The solution is then cooled to 70° C. and filtered through a filter with a pore size of 25 μm to separate the solidified oligomers from the solution. The filtration is supported by an overpressure of 2 bar. 740 cm 2 A filtration area of ​​54.3 g of dry oligomer was obtained.

[0505] 3.2 g of activated carbon in powder form was added to the filtrate. The filtrate was heated again and maintained at 90° C. for 40 minutes. The solution was filtered through a filter with a pore size of 0.45 μm.

[0506] The resulting filtrate was cooled to room temperature and then placed in a refrigerator where it was cooled and maintained at a temperature of 5°C while stirring throughout the 8-hour cooling period. It was filtered through a filter with a pore size of 25 μm to separate the solidified BHET from the solution. The filtration was supported by an overpressure of 1 bar. 615 cm 2 filtration area.

[0507] After the initial filtration, the filter cake was washed 3 times by spraying 600 ml of demineralized water on the filter cake. 602 g of wet filter cake were obtained.

[0508] The filter cake contains:

[0509] MHET 1.5mg / g BHET, including comonomer-substituted BHET 548.2mg / g Dimers, including comonomer-substituted dimers 35.4mg / g Other oligomers 3.9mg / g

[0510] The solid content of the filter cake was 598 mg / g. The remaining weight was mainly water. The BHET content in the solid was 93.0%; the other components were as follows: MHET 0.3%, dimer 6.0%, other oligomers 0.7%. The antimony and zinc contents in the solid were 2.9 ppm and 3.5 ppm, respectively.

[0511] The wet BHET-rich filter cake was transferred to a one-liter flask and transported to a facility equipped for melt phase polymerization of PET. The flask was heated to liquefy the contents, and 176.3 g of TPA in powder form (molar ratio BHET:TPA=1:0.75) was added under constant heating and mixing, while some water was evaporated. 300 ppm of antimony catalyst was added, and the hot slurry was transferred to a polymerization reactor, where residual water and water and EG produced by the polymerization reaction were evaporated. The temperature was then raised to 290°C and the pressure was reduced to 2 mbar. The final polymer was poured onto a cold plate and ground into powder. The intrinsic viscosity of the resulting PET was 0.55 dl / g. Its L value was 91 and its b* value was 0.9.

[0512] Embodiment 20

[0513] Example 13 was repeated. 150 ml of the obtained solution was cooled to room temperature under stirring, resulting in precipitation of oligomers and BHET particles. The solution was left to settle overnight. The solution remained turbid almost all the time. It is assumed that no real sedimentation occurred because there was only enough liquid to fill the voids between the settled particles. At room temperature, a portion of the solution was filtered through a filter with a pore size of 12-15 μm to obtain a filtrate.

[0514] Repeat Example 13 again, and 150ml of the solution thus obtained is mixed with 50ml of the hot filtrate from the previous test. The ratio of EG to water in the filtrate is the same as the solution added, and contains BHET (saturated at room temperature). The solution obtained is cooled to room temperature under agitation, resulting in oligomer and BHET particle precipitation. 65g of the solution is filtered through a filter with a pore size of 12-15 μm. The filtration time is 1 minute 13 seconds. The remaining solution is left to settle overnight. Discard the upper half solution (comprising a small clear liquid layer and a larger turbid solution layer with particles). The lower half solution is mixed and filtered through a filter with a pore size of 12-15 μm, until a filter cake having been formed with the same amount of previous filtration. The filtration time is 55 seconds.

[0515] Comparison of the sedimentation of the original and diluted solutions shows that dilution results in improved separation.

[0516] Based on yield per unit filtration area and time, a 30% higher filtration rate was obtained when a dilution and settling step was used prior to filtration.

Claims

1. A method for preparing a polyester having a repeating unit [-A''-B''], wherein the repeating unit [-A''-B''] has the formula [-OR 1 -OOC-R 2 -CO-], the method comprising the following steps: a) providing a recycled monomer product, wherein the monomer product contains 50 wt % to 97 wt % of a monomer having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer, and 3% to 50% by weight of a substance that is liquid under ambient conditions, wherein the substance is selected from a diol having a melting point below 20° C., water and an inert solvent, b) at least one HOOC-R 2 The diacid monomer B containing -COOH is added to the recycled monomer product of step a) to obtain a monomer slurry, c) using the monomer syrup from step b) for the polymerization of a polyester having repeating units [-A''-B''] of the formula [-OR 1 -OOC-R 2 -CO-], Where R 1 and R 2 are 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 heterocyclic rings containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms, It is characterized in that the step of preparing the monomer slurry in step b) is performed in a manner allowing the monomer slurry to be maintained in liquid form.

2. The method according to claim 1, characterized in that The monomer slurry after step b): - B'' unit (-OC-R 2 -CO-) with the formula HOOC-R 2 The molar ratio of the diacid monomer B to -COOH ranges from 5:1 to 1:5, and - With HO-R 1 The amount of diol monomer A with -OH is the minimum value A 最小 To maximum value A 最大 , where A 最小 = 1.05 * diacid - 0.95 * B'' unit, A 最小 ≥0, And A 最大 = 1.75 * diacid - 0.25 * B'' units, Among them, single diol, A 最小 , A 最大 , B'' units and diacids are expressed in molar amounts.

3. The method according to any one of the preceding claims, characterized in that The diacid HOOC-R added to prepare the monomer slurry 2 -COOH in the absence of diol HO-R 1 -OH or in the case of diols HO-R 1 The amount of -OH is lower than that of diacid HOOC-R 2 The amount of -COOH added was calculated based on the molar amount.

4. The method according to any one of the preceding claims, characterized in that The step a) of providing the recycled monomer product comprises the following steps: a1) providing a waste stream comprising polyesters having repeating units [-A''-B''] of the formula [-OR 1 -OOC-R 2 -CO-], a2) forming a waste stream comprising the waste stream and at least one diol monomer HO-R 1 -OH or end-capping molecule R 3 -OH blends, where R 3 is an aliphatic hydrocarbon group containing 1 to 15 carbon atoms capable of reacting with the polyester, a3) exposing the blend obtained in step a2) to conditions suitable for depolymerization of the polyester in a reaction vessel to obtain a depolymerization solution containing recycled monomer products, wherein the monomer products contain a monomer having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer, a4) mixing the depolymerization solution from step a3) with water or an inert solvent to obtain a diluted solution, a5) cooling the solution from step a4) to a temperature at which recycled monomer product comprising the condensation monomers precipitates, and a6) recovering the precipitated recycled monomer product from the solution to obtain a recycled monomer product.

5. The method according to any one of the preceding claims, characterized in that The recycled monomer product provided in step a) is in liquid form and is below the monomeric form of the formula HO-R 1 -OOC-R 2 -COO-R 1 The temperature is the melting temperature of the condensation monomer of -OH.

6. The method according to any one of the preceding claims, characterized in that Do one of the following: - releasing said recycled monomer product from a transport or storage container, - transporting said recycled monomer product in a transport container, - Storing the recycled monomer product in a storage vessel In the case of a HO-R 1 -OOC-R 2 -COO-R 1 The condensation of -OH occurs at a temperature which is the melting temperature of the monomer and in which the recycled monomer product is in liquid form.

7. The method according to any one of the preceding claims, characterized in that At least a portion of the components of the recycled monomer product which are liquid at ambient conditions is evaporated before or during the preparation of the monomer slurry in step b).

8. The method according to any one of the preceding claims, characterized in that The slurry obtained in step b) contains 2% to 40% of water and / or an inert solvent, based on the total weight of the slurry, and the preparation of the slurry is performed in a manner allowing the monomer slurry to be maintained in a molten state while evaporating at least a portion of the water and / or inert solvent.

9. The method according to any one of the preceding claims, characterized in that Prior to being used in step c), the monomer syrup obtained in step b) is cooled, solidified and converted into particles, wherein the conversion into particles can be performed before, during or after solidification.

10. The method according to any one of the preceding claims, characterized in that The diol monomer A comprises more than 90% ethylene glycol, wherein the percentage is calculated as a mole percentage of the total amount of diol monomer A, and the diacid monomer B comprises more than 90% terephthalic acid, wherein the percentage is calculated as a mole percentage of the total amount of diacid monomer B.

11. A solid particle comprising: a recycled monomer product, wherein the recycled monomer product contains 50 to 100% by weight of a monomer having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer, b. With the formula HOOC-R 2 -COOH diacid monomer B, B'' unit -OC-R 2 -CO- and diacid HOOC-R 2 The molar ratio of -COOH ranges from 5:1 to 1:5, Where R 1 and R 2 The same or different, 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 heterocyclic rings containing 1 to 3 oxygen atoms and 3 to 10 carbon atoms.

12. Solid particles according to claim 11, characterised in that The molar ratio of B'' units to diacids ranges from 3:1 to 1:4, and the solid particles further comprise diol monomers A HO-R 1 The molar ratio of the total amount of -OH, B units to diol ranges from 6:1 to 1:1.

35.

13. Solid particles according to one of claims 11 and 12, characterised in that The particles contain 2 to 40% by weight of a substance which is liquid under normal conditions.

14. Solid particles according to any one of claims 11 to 13, characterised in that The diol monomer A comprises more than 90% ethylene glycol, wherein the percentage is calculated as a mole percentage of the total amount of diol monomer A, and the diacid monomer B comprises more than 90% terephthalic acid, wherein the percentage is calculated as a mole percentage of the total amount of diacid monomer B.

15. A method for providing a recycled monomer product, wherein the monomer product contains 50% to 97% by weight of monomers having the formula HO-R 1 -OOC-R 2 -COO-R 1 -OH condensation monomer, the method comprising the following steps: a1) providing a waste stream comprising polyesters having repeating units [-A''-B''] of the formula [-OR 1 -OOC-R 2 -CO-], a2) forming a polyester comprising the waste stream and at least one diol monomer HO-R 1 -OH blends, a3) exposing the blend obtained in step a2) to conditions suitable for depolymerization of the polyester in a reaction vessel to obtain a depolymerization solution containing recycled monomer products, wherein the monomer products contain a monomer having the formula HO-R 1 OOC-R 2 -COO-R 1 OH condensation monomer, a4) mixing the depolymerization solution from step a3) with water or an inert solvent to obtain a diluted solution, a5) cooling the diluted solution from step a4) to a temperature at which the recycled monomer product comprising the condensation monomers precipitates, and a6) recovering the precipitated recycled monomer product from the solution to obtain a recycled monomer product containing 3 to 50% by weight of a substance that is liquid under ambient conditions, wherein the substance is selected from the group consisting of a glycol having a melting point below 20° C., water and an inert solvent, Characterized in that the ratio of the sum of all added diol monomers to the polyester repeating units contained in the waste stream ranges from 5:1 to 15:1, and the ratio of the diol monomers to the polyester repeating units contained in the depolymerization solution ranges from 4:1 to 14:1, wherein the ratios are molar ratios.

16. The method according to claim 4 or 15, characterized in that Apply one or more of the following cleaning steps: - evaporation of volatile contaminants from any material stream of any of steps a1) to a6), in particular from step a3); - mechanical separation such as filtration of solid contaminants from any solution obtained in any of steps a3) to a5); - mechanically separating, such as by filtration, the precipitated oligomer particles from any solution obtained in any of steps a3) to a5); - mechanically separating, such as by filtration, the precipitated dimer particles from any solution obtained in any of steps a3) to a5); - removal of colorants and other high boiling point organic contaminants by using activated carbon and subsequently separating said activated carbon from any solution obtained in any of steps a3) to a5); - removing metals by using an ion exchanger and subsequently separating said ion exchanger from any solution obtained in any of steps a3) to a5); - redissolving the obtained recycled monomer product in diol monomer, water or an inert solvent or a mixture thereof, followed by precipitation of the recycled monomer product and mechanical separation from the solution; - purging and / or washing the filter cake obtained in step a6) with air, water, the individual monomers and / or an inert solvent.

17. The method according to claim 4 or 15, characterized in that The blend in step a2) contains 2 to 10% by weight of water, and at least 15% by weight but not more than 60% by weight of the diol monomers are evaporated and removed during step a3).

18. The method according to claim 4 or 15, characterized in that A liquid stream is obtained from one or more steps including and after step a5), wherein the liquid stream comprises water and diol monomer, and wherein the liquid stream is directed to a separation unit configured such that a recycled diol monomer stream having a water content of 2 to 12 wt. % is obtained, and subsequently at least a portion of the recycled diol monomer is used in step a2).

19. The method according to claim 4 or 15, characterized in that A vapour stream is obtained during step a3), wherein a liquid stream is obtained from one or more steps including and after step a5), wherein both streams comprise water and diol monomer, and wherein both streams are directed to a common separation unit configured such that a recycled diol monomer stream is obtained.

20. The method according to claim 4 or 15, characterized in that The recycled diol monomer is used to dissolve oligomers that have been obtained from a polyester waste stream and the recycled diol monomer containing the dissolved oligomers is subsequently used in step a2).

21. The method according to claim 4 or 15, characterized in that For the mixing with water in step a4), the amount of water or inert solvent is in the range of 5:1 to 1:3 compared to the amount of diol monomer, and one or more of the following conditions are met: - Water is added to the solution; - the temperature of the two liquid streams to be mixed should be adjusted before mixing so that the resulting dilute solution, without the need for evaporation, reaches a temperature below its boiling point but above the temperature at which the condensation monomers begin to precipitate; - the water addition is carried out such that the solution reaches a temperature of less than 90° C. within 1 hour after the start of the water addition; - the water addition is carried out such that the solution is present in a stirred vessel, the water being added to the vessel at a plurality of locations; - the water addition is carried out so that the solution flows through the pipe into which the water is injected; - water addition is carried out such that the solution is maintained at a temperature above 70° C.; - The water addition is carried out such that the solution reaches a temperature below 105°C.

22. The method according to claim 4 or 15, characterized in that The waste stream in step a1) contains liquefied contaminants in a concentration of 0.1 to 48% by weight, based on the total amount of the waste stream, wherein the liquefied contaminants are defined as substances that are solid at room temperature but liquid under the conditions of step a3) and are insoluble in the depolymerization solution formed in step a3), wherein the depolymerization solution formed in step a3) is divided into two parts while maintaining the liquefied contaminants in a liquid state, wherein the first part contains the liquefied contaminants and the second part is substantially free of liquefied contaminants, wherein the liquefied pollutants in the first portion are solidified by contact with a diol monomer, water or an inert solvent as a cooling liquid in the presence of at least a portion of the depolymerization solution and subsequently removed from the dilute solution in a solid form, and wherein the second part is subsequently merged with the first part.

23. The method according to claim 22, characterized in that The density of the liquefied pollutant in liquid form is lower than the depolymerized solution formed in step a3), wherein the separation into two parts is carried out in a separation container, which has at least one supply port for a depolymerization solution containing liquefied pollutants on one side, at least one removal port for the depolymerization solution on the other side, a separation zone between the two ports, and a cooling zone between the separation zone and the removal port, wherein the depolymerization solution is separated in the separation zone into an upper first phase containing the liquefied pollutant and a lower second phase substantially free of the liquefied pollutant, and wherein diol monomer, water or an inert solvent is added to the upper layer in the cooling zone in an amount sufficient to solidify the liquefied pollutants.

24. The method according to any one of claims 22 to 23, characterized in that the waste stream in step a1) contains solid contaminants in a concentration of 0.1 to 48% by weight, based on the total amount of the waste stream, wherein the solid contaminants are defined as substances that are solid under the conditions of step a3) and are insoluble in the depolymerization solution formed in step a3), The solid pollutants are removed from the dilute solution together with the liquefied pollutants.

25. The method according to any one of claims 22 to 24, characterized in that A liquefied substance is added to the depolymerization solution before the cooling zone, wherein the liquefied substance comprises a melting point higher than 90° C. but lower than the temperature at which the depolymerization solution is supplied to the separation container, a density lower than 1 g / cm 3 and substances that are insoluble in the depolymerization solution.

26. The method according to claim 4 or 15, characterized in that The liquid from the cooling device used in step a5) is directed to a dynamic separation device, preferably selected from a decanter, a centrifuge and a hydrocyclone, wherein the dynamic separation device separates the liquid into a first liquid portion and a second liquid portion, wherein the second liquid portion contains a majority of particles of a critical size below 10 μm, preferably below 20 μm, most preferably below 30 μm, and wherein the second liquid portion is directed back to the cooling device.

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