EP4669695A1

EP4669695A1 - METHOD FOR RECYCLING A STREAM FROM POLYESTER WASTE MATERIAL AND SYSTEM FOR APPLYING THE METHOD

Info

Publication number: EP4669695A1
Application number: EP24708261.3A
Authority: EP
Inventors: Bram Wolfgang SCHMIDT; Johan Albert Frans Kunst; Layo VAN HET GOOR; Marco BRONS; Markus Anton RUESINK; Nikolaos PATSOS
Original assignee: Cure Technology BV
Current assignee: Cure Technology BV
Priority date: 2023-02-20
Filing date: 2024-02-19
Publication date: 2025-12-31
Also published as: KR20250151635A; AU2024224667A1; NL2034182B1; TW202442782A; JP2026506972A; WO2024177502A1; CN120731245A

Abstract

The present invention pertains to a process to recycle a stream of polyester waste material by depolymerising the polyester by alcoholysis into a liquid mixture comprising oligomeric esters having between 5 and 20 subunits and feeding the liquid mixture of oligomeric esters in a continuous manner to a reactor wherein the liquid mixture is present in combination with a gaseous head space, the reactor having means to increase the interface between the liquid mixture and the gaseous head space at least 5 times with respect to a horizontal cross section of the reactor, wherein the pressure in the head space is kept below 20 mbar, thereby repolymerising the oligomeric ester into a polyester having an intrinsic viscosity of at least 0.3 dL/g in less than 120 minutes residence time of the mixture in the reactor. The invention also pertains to a system for applying this method.

Description

A METHOD TO RECYCLE A STREAM OF POLYESTER WASTE MATERIAL AND A SYSTEM FOR APPLYING THE METHOD

GENERAL FIELD OF THE INVENTION

The invention pertains to the field of recycling polyester waste material, in particular material comprising semi-crystalline polyester such as polyethylene terephthalate (PET), and to systems for applying a recycling process.

BACKGROUND OF THE INVENTION

Polyester, such as PET as commonly used for soda bottles and yarn materials for producing textiles, is commonly recycled. The post-consumer polyester recycling industry started as a result of environmental pressure to improve waste management. The other aspect that acts as driving force for polyester recycling industry is that polyester products have a slow rate of natural decomposition. Many polyesters are non- degradable plastics in normal conditions since there is no known organism that can consume its relatively large molecules. Complicated and expensive procedures need to be operated in order for polyester to degrade biologically.

The first recycling effort of polyester waste material (i.e. post-consumer polyester objects or material) in the world was in the 1970’s but the development of adequate recycling processes evolved quickly. As an example, the total consumption of PET in Australia for the year 2000 was 88,258 tons, in which 28,113 tons were recovered demonstrating a recovery rate of about 32%. Many researchers reported that in order to achieve successful PET recycling, PET flakes should meet certain minimum requirements. The major factor affecting the suitability of post-consumer PET flakes for recycling is the level and nature of contaminants present in the flakes. Minimizing the amount of these contaminants leads to better rPET (i.e. recycled PET) quality. PET is contaminated with many substances such as acid producing contaminants, water, colouring contaminants, acetaldehyde and other contaminants such as detergents, fuel, pesticides, etc. due to the use of PET bottles for storing these substances.

Various distinct types of processes have been applied in order to recycle polyester waste materials, each having their pros and cons.

A first class of processes for recycling polyester waste material is so-called energetic recycling such as pyrolysis and carbonization. Pyrolysis of polyester waste was first described in the early 1980’s. It is an alternative to PET disposal in landfills. In general, polyester waste is pyrolysed without further purification of the plastic waste. The majority of pyrolyses are conducted to produce aliphatic and aromatic hydrocarbons as an alternative for fossil fuels or as a source for chemicals. Carbonization is a second method of pyrolyzing polyester waste materials.

A second class of processes for recycling polyester waste material is the mere sorting of the polyester waste material, followed by use of the sorted materials as additive in stone mastic asphalt, cementitious materials, mortars or concrete composites. Since polyester waste may be supplied in mixtures with other polymers, the polyester material has to be separated from these polymers prior to re-processing. Therefore, several methods have been developed including froth flotation, wet shaking table, swelling or thermomechanical procedures

Next to this, there is a class of processes that are based on (thermo-) mechanical methods to recycle polyester waste material. The simplest way of thermo-mechanical recycling is re-melting the sorted polyester waste. This method is applied for example in bottle-to-bottle technologies, where sorted PET-bottles are re-melted in crushed shape and reprocessed to bottles as beverage packaging. Several studies have been conducted on thermal re-processing PET. During this process, the polymer is exposed to high temperatures, shear forces and pressures. Thus, thermal degradation of PET occurs. As a consequence, reduced thermal and mechanical properties of the reprocessed material typically occur. Hence, a repeated thermal re-processing of polyester waste leads to a downcycling of the material. The problem of unwanted colouration of the recycled polyester material is typically overcome by using additives. Since the collection of polyester waste entails generally a mixture of differently coloured polyester materials, such thermally re-processed material leads to undesired colouration of recycled polyester. Therefore, the addition of complementary colours to polyester waste has been applied to mask discolouration. Although being an approved procedure, this method severely limits the use of the recycled polyester, in particular as a food packaging material.

A fourth class of processes to recycle polyester waste are the so-called chemical recycling (chemolysis) processes, wherein recycling of polyester waste material is enabled by depolymerisation into monomers and/or oligomers. This class can be divided in numerous sub-classes depending on the type of reactant used for the chemolysis.

An example is the application of ionic liquids for de-polymerization, first described around the year 2000. This method was developed to avoid the drawbacks of other methods like alcoholysis (high pressure and temperature as well as a heterogeneous reaction product) or acidic and alkaline hydrolysis (pollution problems) to provide an eco-friendly degrading agent for polymers and to enable degradation under moderate reaction conditions. However, no application of the obtained reaction products has hitherto been described.

As an alternative castor oil is applied for de-polymerisation. This method was developed to provide a renewable substitute of petrochemical agents (for example, glycols) for PET de-polymerization. After de-polymerization, the reaction products were aimed for the preparation of polyurethane systems. However, it appears to be very difficult to determine characteristic molecular weights due to the excessive amount of applied castor oil. Also, even with precise control of the reaction temperature a heterogeneous mixture of reaction products is obtained.

The degradation of polyester polymers using enzymes was first described in the 1970’s. As the use of ionic liquids and castor oil, this bio-chemical method was developed to provide an eco-friendly procedure of polymer recycling in contrast to conventional chemical recycling methods. However, efficiency is rather low with respect to complete de-polymerization of the polyester and hence quantitative recovery of homogeneous reaction products for re-use is not possible.

Alcoholysis for de-polymerization of PET was first described in the early 1990’s. This method was developed to avoid the drawbacks of the acidic and alkaline hydrolysis (pollution problems) to provide a renewable and more eco-friendly degrading agent for polymers. Generally, polyester is de-polymerised with an excess of an alcohol to yield corresponding esters of the corresponding acid and ethylene glycol. Among the alcoholysis methods, reaction with methanol has gained special importance because of the low price and the availability of methanol. Also ethylene glycol (a diol, the use of which is sometimes classed separately as “glycolysis”, although it falls in the class of alcoholysis) is used mainly in reactive extrusion to produce low molecular weight oligomers. However, these oligomers have to be separated and purified for further processing, since the crude reaction product consists of a heterogeneous mixture of monomer, oligomers and polymers. Various other alcohols are described to be useful such as pentaerythritol, 1-butanol, 1-pentanol and 1-hexanol and 2-ethyl-1 - hexanol. Also other diols than ethylene glycol, like BHET, neopentyl glycol (NPG), tetraethylene glycol (TEEG), polyethyleneglycol, polytetramethylene oxide and terpoly[poly(oxyethylene)-poly-(oxypropylene)-poly(oxyethylene) are described in the art for depolymerizing polyester by alcoholysis. However, in all cases mixtures of undefined low molecular weight oligomers are typically obtained. Another serious downside of alcoholysis is the need for a catalyst. The most important catalysts have been zinc acetate and manganese. Further catalysts are cobalt and lead acetate. The need of such catalysts hamper the wide application of alcoholysis for recycling polyester waste material.

Aminolysis and ammonolyis were developed for polyester recycling, since the reactivity of the amine-group is higher than the hydroxyl-group or alcohols used alcoholysis of polyester. However, as far alcoholysis, the need for a metal catalyst remains.

Lastly, an alternative chemical recycling of polyester is given by the controlled depolymerization of polyester using blocking chain scission with defined amounts of the de-polymerization agent (see Geyer et al. in eXPRESS Polymer Letters Vol.10, No.7 (2016) 559-586). This method produces polyester oligomers of well-defined molecular weights in a greater range than existing chemical methods like alcoholysis. However, this method requires sorted polyester material, which has to be free of contaminants.

While energetic and thermo-mechanical recycling entail downcycling of the material, chemical recycling requires considerable amounts of chemicals, and chemical recycling has as a main disadvantage its high costs, the variability of the end product (which largely depends on the type of waste material), the need for using a (metal) catalyst and the difficulty of removing colourants. Therefore, a need exists for improved methods, systems and process to enable the recycling of polyester waste materials.

OBJECT OF THE INVENTION

It is an object of the present invention to devise a process and system that allows in an economic advantageous way the recycling of polyester waste materials, into to a high grade polyester.

SUMMARY OF THE INVENTION

In order to meet the object of the invention a process was developed to recycle a stream of polyester waste material by firstly depolymerising the polyester by alcoholysis into a liquid mixture comprising oligomeric esters having between 5 and 20 subunits, and thereafter feeding this liquid mixture of oligomeric esters in a continuous manner to a reactor wherein the liquid mixture is present in combination with a gaseous head space, the reactor having means to increase the interface between the liquid mixture and the gaseous head space at least 5 times with respect to a horizontal cross section of the reactor, wherein the pressure in the head space is kept below 20 mbar, thereby repolymerising the oligomeric ester into a polyester having an intrinsic viscosity of at least 0.3 dL/g in less than 120 minutes residence time of the mixture in the reactor.

The process of depolymerising a polyester by alcoholysis into a liquid mixture comprising oligomeric esters having between 5 and 20 subunits as such is known form the prior art, such as e.g. from WO 2022/003084 (assigned to Cure Technology BV). Also, it is described that for repolymerisation of the oligomers, the mixture may be exposed in a so called condensation reactor to a low pressure. However, as indicated, a combination of two of these condensation reactors is typically needed. In the present invention, a pre-condensation step is no longer necessary.

It was recognised by the present inventors that the known process has several disadvantages. Firstly, the process of repolymerisation in a condensation reactor takes a lot of time, typically around 8-10 hours or more. This means that the process, realising that the mixture has to be kept above its melting temperature, requires large amounts of energy and is thus relatively expensive to perform. However, it has always been believed that this in an inherent issue which cannot be avoided: high amounts of the alcohol monomer have to be removed in order to induce repolymerisation and that process simply takes time. Importantly however, the present invention recognised another major disadvantage. It appears that oligomers that are the result of a depolymerisation reaction are more prone to thermal degradation that oligomers made of virgin materials. The reason for this is unclear, but the result is that the known process may lead to a partly degraded polymer, which shows as a slight, yellowish discolouration, making the material less suitable, or even unsuitable for high end applications.

The inventors surprisingly found now, that despite the low intrinsic viscosity (iv) of oligomeric esters having between 5 and 20 subunits, viz. around 0.1 dL/g, such a mixture can be repolymerised by directly feeding it into a so-called finisher reactor. In traditional industrial polycondensation processes, a common feature is that multiple reaction stages are employed using several reactors in series, wherein the sequential reaction procedure includes (a) monomers, low molecular weight oligomers, and low molecular weight prepolymers being synthesized in regular condensation reactors, and (b) the prepolymers are then polymerized to higher molecular weight polymers in finishing polymerization reactors (often rotating disc reactors; See e.g. US 3,728,083 assigned to Allied Chemical Corporation) where large vapor-liquid surface areas are provided (increasing the interface between the liquid mixture and the gaseous head space at least 5 times with respect to a horizontal cross section of the reactor) to extract the final alcohols. It is commonly known that the first stages are needed to increase the viscosity (lowering the amount of volatile monomers) to at least an iv of 0.3, since otherwise in the finisher the required low pressure cannot be obtained. The stepwise increase of the viscosity to at least 0.3 is deemed necessary for a stable and effective polymerisation process.

However, it was found now that the oligomeric product that results from an alcoholysis, even when the polymerisation level is between 5 and 20 subunits, and thus the iv is very low (around 0.1) can be directly fed to such a finishing reactor. To an even greater surprise, the total amount of time needed to remove the volatiles can be kept below 120 minutes. This means that the novel process is far more economic, requiring substantially less energy, but also, since the time needed to expose the materials to the high melt temperatures (above 250°) is considerably shorter and thus the thermal degradation of these material is at a very low level if existent at all.

The reason that the low viscosity oligomeric esters can be fed directly into a finishing reactor and be able and (re-)polymerise the oligomers in a relatively short amount of time is not 100% understood. It is believed that one of the reasons is that the oligomer esters are the product of a de-polymerising alcoholysis, such as the one known form the ‘084 patent application identified here above. Another reason is believed to be that the process is restricted to a continuous feed and repolymerisation process. A discontinuous process was found to be less stable and may even led to a failure in repolymerisation in short timeframe. Also, the amount of polymerisation of the oligomer, i.e. the number of subunits, is important. Below 5 the amount of volatiles is too high to be able and removed in a single stage process, let alone in a finisher with a high liquidgas interface. Above 20, the oligomer is too viscous to allow a pre-polymerisation purification and thus, may lead to a lower quality product.

In the finisher, an iv of up to 0.65 can be reached in a relatively short time frame, making the material ideally suitable for direct use, or as a starting material for even higher grade polyesters. The iv reached is a matter of time. Also, the design of a finisher (pump type and capacity, outlet diameter etc) allows a maximum iv which is still able to be processed.

It is noted that instead of one large volume finisher, the finishers can be composed of two or more sub-finishers in line, as long as each of these sub-finishers have means to increase the interface between the liquid mixture and the gaseous head space at least 5 times with respect to a horizontal cross section of the reactor (i.e. the respective subfinisher), and the pressure in the head space is kept below 20 mbar.

It was found that the invention is effective for different types of polyesters, since the chemistry is basically the same. Correspondingly, the type of alcohol is not essential to the depolymerisation process as such, and thus to obtain an oligomeric ester of between 5 and 20 units for repolymerising in a finisher. Depending on the type of polyester, type and amount of alcohol, one may arrive at different levels of de- and repolymerisation (when the other circumstances, such as residence time, are the same), or vary the circumstances to arrive at a predetermined level of de- or repolymerisation. This can be controlled i.a. by measuring the viscosity of the (partly depolymerised) polyester mixture, residence time in the various reactors and other circumstances such as temperature and pressure. For any type of polyester at its various stages of de- and repolymerisation by a particular alcohol, a reference curve can be made beforehand that defines e.g. the relationship between viscosity and grade of polymerisation such that the required level of polymerisation can be obtained.

It is noted that in the art processes are known partly use features of the present invention. For example, CZ 299244 (assigned to Sirek Milan) discloses a process of basic hydrolysis of waste PET based on the principle of two-stage chemolytic decomposition to terephthalic acid salt and ethylene glycol, wherein in the first stage of the process the PET waste is degraded by simultaneously running extrusion hydrolysis and glycolysis, and wherein in the second stage a melt of the resulting oligomeric products of the PET reactive extrusion leaving the first stage, is subjected in a continuous sequence and under continuous dosing of aqueous solution of alkali metal hydroxide and/or ammonium hydroxide to basic hydrolysis in the presence of a catalyst. The resulting product is then used for repolymerisation.

US 4620032 (assigned to Celanese Corporation) also discloses a two-stage depolymerisation process, aiming at repolymerisation to a high grade polyester, but the process is based on hydrolysis. In particular, in the known process the polyester is intimately mixed with a depolymerizing agent which is either one of the products resulting from the complete hydrolytic depolymerization of the condensation polymer or water. The depolymerization agent is mixed with the polyester for a time sufficient that the molecular weight of the polyester in a first stage is reduced by at least 50%. The treated condensation polymer of lower molecular weight is thereafter subjected in a second stage to neutral hydrolysis to effect complete hydrolytic depolymerization to a monomeric material, which material that can be used for repolymerization.

WO9720886 (assigned to Eastman Chemical Company) discloses a one stage batch process wherein postconsumer or scrap polyester is reacted with glycol to produce a monomer or low molecular weight oligomer by depolymerization of the polyester. The monomer or oligomer, as the case may be, is then purified using one or more of a number of steps including filtration, crystallization, and optionally adsorbent treatment or evaporation to be able and used in a subsequent repolymerisation process to arrive at a polyester.

The present invention also pertains to a process for repolymerising an oligomeric ester having between 5 and 20 subunits, comprising feeding a liquid mixture comprising the oligomeric ester in a continuous manner to a reactor wherein the liquid mixture is present in combination with a gaseous head space, the reactor having means to increase the interface between the liquid mixture and the gaseous head space at least 5 times with respect to a horizontal cross section of the reactor, wherein the pressure in the head space is kept below 20 mbar, thereby repolymerising the oligomeric ester into a polyester having an intrinsic viscosity of at least 0.3 dL/g in less than 120 minutes residence time of the mixture in the reactor.

The invention also pertains to a system for recycling a stream of polyester waste material, the system comprising in consecutive order 1) an extruder, 2) a continuous stirred tank reactor (CSTR) and 3) a finishing reactor wherein a liquid content can be present in combination with a gaseous head space, the system further comprising means to supply a first amount of alcohol into the extruder and a second amount of alcohol into the CSTR, the reactor having means to increase the interface between the liquid and the gaseous head space at least 5 times with respect to a horizontal cross section of the reactor, and wherein the pressure in the head space is able to be kept below 20 mbar, wherein the extruder, the CSTR and the finishing reactor are operatively coupled such that a stream of polyester waste material is able to flow from an entrance of the extruder to an outlet of the finishing reactor in a continuous manner.

DEFINITIONS

A polyester is a polymer in which the monomer units are linked together by an ester group. They are typically formed by polymerizing a polyhydric alcohol with a polybasic acid, and used mainly in the manufacture of resins, plastics, and textile fibres. It is well known that polyesters may be prepared by a condensation polymerisation process in which monomers providing the “acid component” (including ester-forming derivatives thereof) are reacted with monomers providing a “hydroxyl component”. If desired the polyesters may also comprise other linking groups such as for example a proportion of carbonylamino linking groups -C(=O)-NH- (i.e. amide linking group) or -C(=O)-N-R²- (tertiary amide linking group). Polyester as used in ever-day live can be aliphatic, semiaromatic or aromatic. Typical examples are polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3- hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polyethylene furanoate (PEF) and Vectran, a polycondensation product of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid. Of these PET, also abbreviated as PETE, or the obsolete PETP or PET-P, is the most common thermoplastic polymer resin of the polyester family and the virgin material is considered as one of the most important engineering polymers of the past decades. It is regarded an excellent material for many applications and is used in fibres for clothing, containers for liquids and foods, thermoforming for manufacturing, and in combination with glass fibre for engineering resins. It is also referred to by brand names such as Terylene, Arnite, Eastapac, Mylar, Lavsan, Dacron etc. A polyester may contain up to 50% (w/w) of non-polyester polymer chains (e.g. 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50%) while still being referred to as a polyester material.

The melting temperature of a polyester is the temperature above which the polyester has the properties of a liquid. Since many polymers typically do not have a very sharp melting point, the melting temperature may be the highest temperature of a fairly broad temperature range in which the polymer slowly becomes "leathery," then "tacky," and then finally liquid.

A polyester waste material is a post-consumer material at or after the end of its consumer life-time, i.e. the time during which it is used by a consumer for practical or esthetical purposes., which in essence is composed of polyester and up to 10% (e.g. 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10) of additives like fillers (e.g. fibrous like material or particulate matter), stabilisers, colourants etc.

Depolymerising means to lower molecular weight, by breaking down the original polyester molecules to shorter length molecules down to for example oligomers.

A continuous process is a flow production process used to process materials without interruption. In such a process the materials, for example dry bulk or fluids are continuously in motion, undergoing chemical reactions and/or subject to mechanical or heat treatment. A continuous process is contrasted with a batch process.

Alcohol is a hydrocarbon substance or mixture of such substances formed when a hydroxyl group is substituted for a hydrogen atom in the hydrocarbon. The alcohol can be monovalent, divalent (i.e. a diol), etc.

Intrinsic viscosity is a measure of a solute's contribution to the viscosity q of a solution, see “Progress in Biophysics and Molecular Biology" (Harding 1997). The IV (or iv) can be measured according to DIN/ISO 1628. Typically, a concentration of 1% for the polymer is used and m-cresol as solvent, wherein the IV can be expressed in dL/g (often presented without the latter dimension). A practical method for the determination of intrinsic viscosity is by using an Ubbelohde viscometer.

Two consecutive stages means that the respective first and second stage follow in a continuous manner, thus without interruption. This however does not exclude that one or more additional intermediate process steps takes place in between the two stages.

A mixture is a composition of two or more different substances combined or blend into one mass. Mixing two compounds does not exclude that the compounds react while being mixed to form other compounds in the mixture.

An oligomer having between 5 and 20 subunits is any oligomer from pentamer to eicosamer.

The interface between gas and liquid is a surface dimension, thus a unit in m².

The cross section of reactor is its footprint, thus its measures when projected on a horizontal surface.

FURTHER EMBODIMENTS OF THE INVENTION

In a first further embodiment of the process according to the invention the liquid mixture comprises oligomeric esters having between 5-14 subunits (thus 5, 6, 7, 8, 9, 10, 11 , 12, 13 or 14 subunits), preferably between 8 and 10 subunits (8, 9 or 10). The higher lower limit means that the time for repolymerisation can be further decreased, increasing the economics of the process and the quality of the resulting polymer. The lower upper limit is advantageous from a handling point of view of the feed stream, including any purification treatments, into the finishing reactor. It was even more surprising to see that the material, despite a very low polymerisation rate of 14 subunits or below, was able to be repolymerised directly in the finisher within 120 minutes.

In another embodiment of the process according to the invention, the pressure in the head space is kept below 10 mbar. This way the time needed for repolymerisation can be further decreased. Preferably the pressure in the head space is kept between 1 and 3 mbar, such as 2 mbar.

In yet another embodiment of the process according to the invention, the reactor has means to increase the interface between the liquid mixture and the gaseous head space at least 10 times with respect to the cross section of the reactor, preferably at least 20- 100 times. An increase interface between the liquid mixture and the gaseous head space means that the repolymerisation can take place at a higher speed. Downside is that the reactor is typically of a more complicated construction and needs a higher pump capacity. This means the process becomes more expensive. Still, this may be compensated for by a higher quality of the end-product meaning that a higher price can be obtained.

In again another embodiment of the process according to the invention, the oligomeric ester is repolymerised into a polyester having an intrinsic viscosity of at least 0.3 dL/g in less than 100 minutes, preferably less than 80 minutes, most preferably in less than 60 minutes. Less time correspond to less thermal degradation and is thus advantageous. The time can be gradually decreased (in the 1-60 minute range) by various means such as a lower pressure, a higher liquid-gas interface etc. This is a matter of finisher design which is within the toolbox of the skilled practitioner.

In still another embodiment of the process according to the invention, the oligomeric ester is repolymerised into a polyester having an intrinsic viscosity of at least 0.4 dL/g, preferably at least 0.5 or even 0.6 dL/g. For a given finisher configuration, a higher iv can be obtained by applying a higher residence time. In order to increase the iv for a constant residence time, the finisher configuration has to be adapted (higher pump capacity; increase in liquid-gas interface etc.) Advantageously, the process of depolymerizing the polyester in the stream of polyester waste material by alcoholysis comprises a first stage of depolymerisation and a separate second consecutive stage of depolymerisation, to which first and second stages the stream of polymer waste material is subjected in a continuous manner, wherein in the first stage of the two consecutive stages, the stream of polyester waste material is continuously fed to an extruder operated at a temperature above the melting temperature of the polyester, while a first amount of alcohol is co-fed to the extruder, in order to produce a fluid mixture comprising a melt of the at least partly depolymerised polyester; and in the second stage, the said fluid mixture is continuously fed to a continuously stirred tank reactor (CSTR) operated at a temperature above the melting temperature of the polyester, while co-feeding a second amount of alcohol to the CSTR, wherein a residence time in the CSTR is used to provide at the outlet of the CSTR a continuous stream of polyester depolymerised into an oligomeric ester.

It was found that the process as known from the above identified ‘084 international patent application is advantageously suitable for arriving at the required liquid oligomeric ester mixture.

Preferably in the second stage of this process, the amount of alcohol fed to the CSTR is below 6% w/w, preferably below 3.5 % w/w, even more preferably between 0 and 2% w/w. The total amount of alcohol of the first and second amount of alcohol (thus both amounts added up), is between 3 and 12% w/w with respect to the stream of polyester material. Although it is described in the ‘084 patent that in the CSTR the upper limit of alcohol is less critical than in an extruder, a preferred total amount of alcohol used to depolymerize the polyester in the CSTR was found to be preferably below 6% w/w, more preferably below 3.5 % w/w, even more preferably between 0 and 2% w/w with respect to the stream of polyester waste material, to be used in the present process. It is noted however, that the total amount of alcohol used in the overall process (thus all alcohol used for the alcoholytic degradation of the polyester) is preferably above 2.5% (w/w), in particular when MEG is used, against the believe that the less alcohol is used, the faster the repolymerization process is. The preferred minimum amount of alcohol (i.e. 2.5%) is a feature of the invention in its broadest scope, thus not restricted to the particular embodiment of the use of an extruder and CSTR.

In yet again another embodiment of the process according to the invention, the two consecutive stages are preceded by a step wherein the stream of polyester waste material is subjected to a drying process to reduce the amount of water in the stream to less than 5000 ppm (i.e. less than 0.5% w/w of water with respect to the stream of polyester waste material), preferably between 10 and 1000 ppm, more preferably between 20 and 100 ppm. The presence of water in the process inevitably leads to free carboxyl groups due to hydrolysis. A high level of free carboxyl groups, i.e. above 45 mmol/kg at the end of the initial repolymerisation process (i.e. the process wherein the oligomeric ester is repolymerised into a polyester, typically having an iv of between 0.4 and 0.6), is less advantageous in the present process. The type of pre-drying process is not essential. Pre-drying can be done in different ways, e.g. by simply blowing hot air at 120°C through a bed of polyester flakes or agglomerates, which may already suffice to reduce the moisture content below 5000ppm. However, since this still may require quite a low vacuum in the extruder to remove any additional moist if desired, it is preferred to use more vigorous methods like a desiccant air dryer with hot air at 150°C, or a dryer applying a (low) vacuum. Advantageously, the amount of water in the stream lies between 10 and 1000 ppm, preferably between 20 and 100 ppm, most preferably around 50 ppm.

In an embodiment the alcoholysis comprises the use of a diol, preferably a diol selected from the group of ethylene glycol, 1,3-propanediol, butanediol, cyclohexane dimethanol and neopentyl glycol. The use of a diol leads to a further decrease in time needed for repolymerisation in the finisher.

In yet again a further embodiment, in which embodiment the polyester is polyethylene terephthalate (PET), the oligomeric ester for over 50% w/w, preferably over 60, 70, 80 or even 90% w/w, comprises oligomers of 5 to 20 Bis(2-Hydroxyethyl) terephthalate (BHET) units, preferably 6 to15 (BHET) units, most preferably, 8 to10 BHET units.

The above does not exclude any variants from the process or additional process steps. For example, additional (pre-)purification/filtration steps can be added. Also, the invention is not restricted to particular types of filters, although screen changer type filters are believed to be ideally suitable for a continuous process as claimed since depending on the amount of particulate matter present in the polyester waste material, filters may need to be changed every few hours. Also, when applying a filter, this may very well be a cascade of two, three or more separate consecutive filters of descending mesh size in order to withstand pressure differences over the filters. Next to this, in order to be able and fully remove all colourants and dies, the melted material may advantageously be pumped through a bed filled with (activated) carbon granules, SiC>2 granules, or any other small molecule absorbing material.

It is also foreseen to introduce copolymerization in the repolymerization in the finisher. For example, a slurry of a pure diacid and a pure diol can be prepared, and/or other monomer can be formed which can be added to the finisher to which the purified oligomeric mixture is added. When the diacid and/or diol differs from the monomers as present in the polyester waste material, a copolymer is being produced. Such monomers could for example be bio-based, to further reduce the CO2 footprint or could be e.g. isophthalic acid, succinic acid, neo pentyl glycol, to obtain other product characteristics of the ultimate polyester to be produced, adapted to the intended application. Typically, the comonomer is pre-polymerized before it is fed to the finisher and mixed with the recycled oligomer.

Any of the above further embodiments can also embodied in the system of the invention. The invention will now be further illustrated using the following non-limiting figures and examples.

EXAMPLES

Figure 1 schematically depicts an overview of a process for de- and re-polymerising as known from the art.

Figure 2 schematically depicts a typical re-polymerisation configuration for industrial application.

Figure 3 schematically depicts a de- and repolymerisation configuration for a stream of polyester waste using prior art technology.

Figure 4 schematically depicts a de- and repolymerisation configuration according to the invention.

Example 1 provides various experiments, comparing the prior art with the invention.

Figure 1

Figure 1 schematically depicts an overview a process for de- and re-polymerising as known from WO 2022/003084). In this process PET is depolymerised and repolymerised in a continuous process through steps 1 - 8. Step 9 is an additional repolymerisation step including solid-state polymerisation, to arrive at a desired IV well above 0.6.

The process is based on the commonly known equilibrium reaction of PET in an alcoholysis based on mono ethylene glycol (MEG):

BHET [PET]x + ¹/₂ x MEG

In this process, by adding MEG to the polyester melt, the equilibrium shift to the left, resulting in shorter polymer chains, ultimately oligomers (less than 100 repeating BHET units, in particular less than 50, 40,30, 20 or even 10 units) and decreasing viscosity. By removing MEG, for example by using a vacuum or nitrogen, the short chains react with each other to form a polyester again. By controlling the depolymerisation rate, and thus the oligomer length, the viscosity of the material is controlled. This chemistry is in principle the same for any industrial polymerisation process for arriving at a polyester or a corresponding oligomer.

In step 1 , a polyester waste material comprising pieces of (pure) PET carpet and flakes of PET bottles is dried to a moisture level of 50 ppm. Then, in step 2 the dried stream of waste material is fed to a conical co-rotating twin screw extruder. Due to the conical shape of the extruder the opening for feeding the material is bigger than with a conventional twin-screw extruder so feeding is easier and it generates less shear due to a more gentle natural compression giving less thermal damage to the polymer. Thermal degradation generates undesirable side reactions and formation of end groups giving an inferior end-product quality. The extruder is operated at 280°C to melt the polyester completely. Adjacent the end of the conical twin screw extruder (at 10% of its length) an injection point for dosing MEG (indicated as arrow 50) is provided to obtain the first step in depolymerization, thus reducing the viscosity. For this, about 1% of MEG (w/w) is dosed. The reduction of the IV also helps to minimize the pressure difference over the first filtration step 3 to make it possible to filtrate with a mesh size of 80 micrometre. The filter also acts as a static mixer to homogenize the mixture and distribute the added glycol with the molten polymer to react completely with shorter polymer chains and a molecular weight distribution at equilibrium (dispersion grade of about 2) as a result. Process parameters are chosen such that the MEG is (almost) fully reacted and no (hardly any) free MEG is present anymore. The partly depolymerized and filtered material is fed to a single screw extruder in step 4. The design of the screw (see WO 2022/003084, figure 2) aims at maximising the percentage glycol which can be dosed (preventing the melt from becoming inhomogeneous). This maximum is increased by adjusting common process parameters like screw speed, pressure build up, etc. Typically, about 3-4% of MEG is dosed in this extruder (indicated by arrow 50’). At the end of the extruder the viscosity of the melt is measured. The level of the viscosity is controlled by an automated control loop (not indicated in figure 1) controlling the level of MEG being dosed in the single screw extruder. This automated control loop results in a consistent viscosity, typically an IV between 0.1 and 0.2, independent of the IV of the starting material. Due to the inherent transesterification reaction which takes place in the extruder, the polydispersity may remain low, preferably around 2-3, depending mainly on the residence time in the extruder (which may be adjusted in the process by controlling initial feed and extruder speed).

The depolymerized material filtered for a second time in step 5. Due to the IV of about 0.15 the filtration size can be reduced in comparison to the first filter, preferable being 40 micrometre, without a pressure difference over the filter being too high.

The material with an IV of about 0.15 (0.1 -0.2) is continuously added to the CSTR in step 6. In this CSTR also MEG is added (indicated by arrow 50”) to further depolymerize the material to the required viscosity/oligomer length. Due to the fact that the material already has a low (controlled) viscosity upon entry, the difference in viscosity with the added MEG is not so big that homogeneous mixing is critical. 4-6% of MEG can be homogeneously mixed easily. The residence time in the CSTR is long enough (typically 25-45 minutes) to depolymerize the material to the required oligomer length, but also to have enough time for the transesterification reaction to obtain a polydispersity of 2. At the end of the reactor the viscosity is measured and with an automated control loop controlling the addition of MEG in the reactor. This results in an extremely stable continuous process hardly dependent on the type (IV) of the starting material.

In the CSTR, decolouration takes place by adding activated carbon, indicated by arrow 60. The activated carbon may be pre-selected for the best performance to absorb the colourants present in the polyester waste. After the CSTR, the low viscous oligomer/activated carbon mixture is pumped through a three-step micro filtration (20/10/5 micrometre) step 7 to remove the carbon particles loaded with colourant from the oligomers. A parallel set of three filters is installed so that in case of a pressure difference over the filter that is too high, the melt can be pumped through the parallel set, while the first filter set can be cleaned.

After the filtration while the melt having an IV of around 0.1 (the number of subunits in the oligomeric mixite being on average about 10) is still at an elevated temperature of about 250°C, the melt is pumped to a condensation reactor (step 8) which is operated under vacuum at 2 mbar, at a temperature of about 260°C, to remove the MEG, with the result that the equilibrium of the BHET/PET equilibrium shifts to the right forming the PET polymer. In the reactor a polyester with an IV between 0.4 and 0.6 can be obtained. The polymer is removed from the reactor and pumped through a die-plate provide with holes, thus generating polymer strands. These strands are cooled down and cut into amorphous granules.

The amorphous granules may undergo an off-line crystallisation process by subjecting the granules to a temperature of 130 - 180°C which leads to a crystallisation process. The partly crystallised granules are subjected to a solid-state polymerisation process wherein the polyester is heated to an elevated temperature below the melting temperature of this polyester while subjected to a vacuum or an inert gas. This way a solid state additional repolymerisation is induced, to arrive at an IV above 0.6. The obtained IV can be adjusted by processing parameters in a way that the IV matches the required IV for the intended application, having any value between 0.65 and 1.0 typically.

Figure 2

Figure 2 schematically depicts a typical re-polymerisation configuration for industrial application. This set-up is the so-called 2 reactor polycondensation technology, in which the polymerisation takes place in two consecutive polymerisation reactors. The first one, indicated with reference number 8 is a standard condensation reactor. The second one, indicated with reference number 30, is a so-called finisher, having the means to increase the liquid-gas interface in the reactor at least 5 times with respect to the footprint of the reactor.

The reactor 8 is the same as known from WO 2022/003084. For laboratory test purposes, the use of such a standard condensation reactor alone is often sufficient since time is not a principle issue. However, for industrial application, a standard condensation reactor is always followed by a finisher to allow faster repolymerisation. In this typical set-up, the oligomer mixture having a typical IV value of around 0.1 is fed (22) into the reactor 8 and forms a gas-liquid interface 23 halfway the reactor. The reactor is provided with a mixing means 21 that is driven by a motor 20. The alcohol is pumped away via means 24. This way, the oligomeric mixture can be polymerised to a higher grade (the number of units being 25 or higher) to an IV of at least 0.2 - 0.3, such as to be able and fed (25) into the finisher 30, forming a gas-liquid interface 230. In the example, the finisher is provided with a rotating disc mixer 210, driven by motor 200. Since the gas-liquid interface is established half-way the rotating discs, rotating of the discs and therewith elevating liquid film (on both sides of the discs) into the open gaseous space, will lead to a substantial increase of the gas-liquid interface, in this case about a factor 10 with respect to the footprint of finisher reactor 30. This way, the alcohol can be removed faster (240) leading to a stream of polyester 250 with in IV around 0.6 in a relatively short time frame.

This two-stage se-up is commonly used since it is known that a mixture with a low iv of around 0.1 cannot be directly fed into a finisher: the bulk of the alcohol has to removed before entering a finisher, otherwise a low pressure cannot be obtained in the finisher and thus polycondensation will hardly take place. In many cases even a three-stage setup is used in the industry (adding an extra condensation reactor 8 before the finisher 30) for the stepwise reduction of the amount of alcohol and therewith stepwise increase in the IV until the mixture is suitable for feeding into the last stage finisher.

Figure 3

Figure 3 schematically depicts a de- and repolymerisation configuration for a stream of polyester waste using prior art technology. In this set-up, the depolymerisation technology as known from WO 2022/003084 is used. In particular, as described in WO 2022/003084 in the examples section (which section is incorporated herein by reference), the waste stream is fed into a first extruder 2, then into a second extruder 4 and then into a CSTR 6. This corresponds to steps 1 through 6 in figure 1 . Then the resulting oligomer mixture having an IV of around 0.1 is fed into condensation reactor 8. The remainder of the process is identical to what is depicted in figure 2. Figure 4

Figure 4 schematically depicts a de- and repolymerisation configuration according to the invention. In principle, the set-up is the same as that of figure 3, albeit that the oligomer mixture that comes from CSTR 6 is fed directly into the finisher 30.

Example 1

In this example a direct comparison is made between a process based on prior art technology as depicted in figure 3, versus a process using the set-up of figure 4, i.e. where the oligomer mixture resulting from the depolymerization of a stream of polyester waste material is fed directly into a finisher. For this comparison a lab-type finisher was used, being able to only process a liquid up to an IV of 0.3-0.35. It is estimated that in order to arrive at an IV of about 0.6 in an industrial finisher about twice the amount of time is needed. However, this extra time needed is expected to be fully compensated by the fact that in an industrial finisher a pressure as low as 1-2 mbar can be obtained whereas in the laboratory set-up this was about 10 mbar. This means that the time needed in the laboratory finisher to reach an IV of about 0.3 is expected to be the same as needed in an industrial finisher to reach an IV of about 0.6.

For the comparison experiment a polyester material, consisting of PET granules (RamaPET N180; IV 0.8 dL/g), was melted and depolymerized with monoethylene glycol (MEG; fibre grade, obtained from Vivochem) into a liquid mixture of oligomeric esters having an average polymerization grade between 5 and 20 (5-20 subunits of BHET per molecule) at a throughput of about 30 kg/hr. Since the filling level in the CSTR was maintained at ca. 48%, the average residence of the partially depolymerized polyester material in the CSTR was 30 minutes. In these depolymerization and repolymerization trials, the virgin polyester material was used as such, and, thus, was not dried beforehand.

In a first experiment, the resulting oligomer was repolymerized in the set-up of figure 2, thus the process being in line with that as shown in figure 3. In a second series of experiments the resulting oligomer was repolymerized by directly feeding the oligomer mixture into the finisher, as shown in figure 4. In the latter series the amount of MEG as used in the depolymerization process was varied in order to arrive at oligomers with a varying grade of polymerization. In this respect it is noted that the use of about 10% MEG leads to an x (= degree of polymerization = number of subunits in the oligomer) of about 8-10; 7.5% MEG leads to an x of about 11-12; 4.5-6% MEG leads to an x of about 15-16 and 2.5% MEG leads to an x of about 20. Melting and depolymerization of the polyester material and subsequent repolymerization of the liquid depolymerized polyester material were executed under conditions depicted in Table 1. For each of these experiments the depolymerization process as described in WO 2022/003084 was used. In the first extruder the temperature was kept in each case to about 288°C, no MEG was added. The amount of MEG added to the second extruder was in each case 2.4% and the temperature was kept at about 268°C. In the CSTR the amount of MEG added is indicated in the table here above. The temperature in de condensation reactor was about 258°C. In the finisher the temperature was kept to about 271 °C. Table 1 De- and repolymerization experiments In experiment 1 partial depolymerization of the molten virgin polyester material went smoothly in the presence of 10 w/w% MEG versus PET in total for Extruder II and CSTR, in a time frame of about 20-25 minutes. Intermediate sampling before repolymerization showed that a white depolymerized polyester material with a degree of polymerization (DP) ca. 8-10 (or molecular weight Mw 1500-1950 Dalton) was formed. The liquid depolymerized polyester oligomer was repolymerized in the set-up of figure 2 yielding a pale, yellow liquid recycled polyester material (Lab value above threshold) with an intrinsic viscosity IV 0.31 dL/g after about 9 hours of polymerization. The yellow colouration was indicative of significant thermal degradation.

In the experiments 2-16 various continuous depolymerization-repolymerization experiments were performed, excluding the standard condensation reactor and directly feeding the liquid oligomer mixture into the finisher, thus, without the contribution of a pre-polymerization reactor. The obtained liquid recycled polyester material was cooled down in a water bath and cut into solid polyester granules. In these experiments, apart from assessing the total time needed to arrive at the same degree of polymerization as arrived at in the first experiment, the influence of the amount of MEG during the depolymerization step and residence time in the finisher on the physical properties of the obtained polymer as expressed in intrinsic viscosity, and colour values was investigated. The conditions and settings of the individual reactors in the continuous depolymerization-repolymerization line and the result of this experiment in terms of intrinsic viscosity (IV) and colour values (L*a*b*) are listed in the table as far as relevant.

Experiments 2 and 3 in the table show that a reduction in the amount of MEG to 5.1 w/w% in the CSTR and therewith, the total amount of MEG to 7.5 w/w%, yield recycled polyester material from liquid polyester oligomers at a residence of about 1 hour in the finisher. Apart from the omitting the pre-polymerization reactor, the one hour residence is significantly shorter than the 5 hours in experiment 1. From the recycled polyester material polyester granules were obtained with intrinsic viscosities of about 0.3 dL/g (at the level of viscosity of the recycled polyester material obtained in the repolymerization process comprising a pre-polymerization reactor and finisher; experiment 1) but at a significantly reduced time and at significantly reduced colour, indicating less thermal degradation.

A reduction in residence time to 0.5 hour in the finisher (see experiments 4 to 8) while maintaining the total amount of MEG of 7.5 w/w% for the partial depolymerization reaction in Extruder II and the CSTR to polyester oligomers, yields recycled polyester granules with intrinsic viscosities that are higher when compared to experiments 2 and 3. The reduction in residence time in the finisher improves the colour of the recycled polyester granules as indicated by the lower b* values of around 5.

In experiments 9 and 10 to 14, the amount of MEG in the CSTR is reduced to 3.4 and 1.7 w/w%, respectively, thereby reducing the total amount of MEG that is used in the partial depolymerization reaction < 5.8 w/w%. Repolymerization of these polyester oligomers for 1 hour in the finisher and subsequent granulation yields recycled polyester granules with intrinsic viscosities that are slightly higher than in previous experiments, varying around 0.33 dL/g, and also higher b* values.

An increase in residence time for the repolymerization process to 2 hours was investigated in experiments 15 and 16. In addition, also the amount of MEG in the CSTR was reduced to 0 w/w%. Repolymerization of depolymerized polyester material with a DP 20 to 25 over the course of 2 hours showed a further increase in intrinsic viscosity to 0.35 dL/g of the obtained recycled polyester granules. The polyester granules appeared more yellowish than in experiments 4 to 9, as confirmed by the higher b* values of about 9.

These experiments show that faster repolymerization can be achieved when using only a finisher in the repolymerization of polyester oligomers. The recycled polyester granules show comparable viscosities in significantly shorter residence times. The colour values of the recycled polyester granules shows that a shorter residence of polyester oligomers in the finisher leads to less thermal degradation.

Claims

1. A process to recycle a stream of polyester waste material by depolymerising the polyester by alcoholysis into a liquid mixture comprising oligomeric esters having between 5 and 20 subunits and feeding the liquid mixture of oligomeric esters in a continuous manner to a reactor wherein the liquid mixture is present in combination with a gaseous head space, the reactor having means to increase the interface between the liquid mixture and the gaseous head space at least 5 times with respect to a horizontal cross section of the reactor, wherein the pressure in the head space is kept below 20 mbar, thereby repolymerising the oligomeric ester into a polyester having an intrinsic viscosity of at least 0.3 dL/g in less than 120 minutes residence time of the mixture in the reactor.

2. A process according to claim 1 , characterised in that the liquid mixture comprises oligomeric esters having between 5-14 subunits

3. A process according to claim 1 or 2, characterised in that the liquid mixture comprises oligomeric esters having between 8 and 10 subunits.

4. A process according to any of the preceding claims, characterised in that the pressure in the head space is kept below 10 mbar.

5. A process according to claim 4, characterised in that the pressure in the head space is kept between 1 and 3 mbar.

6. A process according to any of the preceding claims, characterised in that the reactor has means to increase the interface between the liquid mixture and the gaseous head space at least 10 times with respect to the cross section of the reactor, preferably at least 20-100 times.

7. A process according to any of the preceding claims, characterised in that the oligomeric ester is repolymerised into a polyester having an intrinsic viscosity of at least 0.3 dL/g in less than 100 minutes, preferably less than 80 minutes, most preferably in less than 60 minutes.

8. A process according to any of the preceding claims, characterised in that the oligomeric ester is repolymerised into a polyester having an intrinsic viscosity of at least 0.4 dL/g, preferably at least 0.5 or even 0.6 dL/g.

9. A process according to any of the preceding claims, characterized in that the process of depolymerizing the polyester in the stream of polyester waste material by alcoholysis comprises a first stage of depolymerisation and a separate second consecutive stage of depolymerisation, to which first and second stages the stream of polymer waste material is subjected in a continuous manner, wherein in the first stage of the two consecutive stages, the stream of polyester waste material is continuously fed to an extruder operated at a temperature above the melting temperature of the polyester, while a first amount of alcohol is co-fed to the extruder, in order to produce a fluid mixture comprising a melt of the at least partly depolymerised polyester; in the second stage, the said fluid mixture is continuously fed to a continuously stirred tank reactor (CSTR) operated at a temperature above the melting temperature of the polyester, while co-feeding a second amount of alcohol to the CSTR, wherein a residence time in the CSTR is used to provide at the outlet of the CSTR a continuous stream of polyester depolymerised into an oligomeric ester.

10. A process according to claim 9, characterised in that in the second stage, the amount of alcohol fed to the CSTR is below 6% w/w, preferably below 3.5 % w/w, even more preferably between 0 and 2% w/w.

11. A process according to claim 9 or 10, characterized in that the two consecutive stages are preceded by a step wherein the stream of polyester waste material is subjected to a drying process to reduce the amount of water in the stream to less than 5000 ppm, preferably between 10 and 1000 ppm, more preferably between 20 and 100 ppm.

12. A process according to any of the preceding claims, characterised in that the alcoholysis comprises the use of a diol, preferably a diol selected from the group of ethylene glycol, 1,3-propanediol, butanediol, cyclohexane dimethanol and neopentyl glycol.

13. A process according to any of the preceding claims, wherein the polyester is polyethylene terephthalate (PET), characterised in that the oligomeric ester for over 50% w/w, preferably over 60, 70, 80 or even 90% w/w, comprises oligomers of 5 to 20 Bis(2-Hydroxyethyl) terephthalate (BHET) units, preferably 6 to15 (BHET) units, most preferably, 8 to10 BHET units.

14. A process for repolymerising an oligomeric ester having between 5 and 20 subunits, comprising feeding a liquid mixture comprising the oligomeric ester in a continuous manner to a reactor wherein the liquid mixture is present in combination with a gaseous head space, the reactor having means to increase the interface between the liquid mixture and the gaseous head space at least 5 times with respect to a horizontal cross section of the reactor, wherein the pressure in the head space is kept below 20 mbar, thereby repolymerising the oligomeric ester into a polyester having an intrinsic viscosity of at least 0.3 dL/g in less than 120 minutes residence time of the mixture in the reactor.

15. System for recycling a stream of polyester waste material, the system comprising in consecutive order 1) an extruder, 2) a continuous stirred tank reactor (CSTR) and 3) a finishing reactor wherein a liquid content can be present in combination with a gaseous head space, the system further comprising means to supply a first amount of alcohol into the extruder and a second amount of alcohol into the CSTR, the reactor having means to increase the interface between the liquid and the gaseous head space at least 5 times with respect to a horizontal cross section of the reactor, and wherein the pressure in the head space is able to be kept below 20 mbar, wherein the extruder, the CSTR and the finishing reactor are operatively coupled such that a stream of polyester waste material is able to flow from an entrance of the extruder to an outlet of the finishing reactor in a continuous manner.