WO2024177502A1 - Procédé de recyclage d'un courant de matériau de polyester usagé et système d'application du procédé - Google Patents

Procédé de recyclage d'un courant de matériau de polyester usagé et système d'application du procédé Download PDF

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Publication number
WO2024177502A1
WO2024177502A1 PCT/NL2024/050082 NL2024050082W WO2024177502A1 WO 2024177502 A1 WO2024177502 A1 WO 2024177502A1 NL 2024050082 W NL2024050082 W NL 2024050082W WO 2024177502 A1 WO2024177502 A1 WO 2024177502A1
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Prior art keywords
polyester
reactor
head space
stream
process according
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PCT/NL2024/050082
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English (en)
Inventor
Bram Wolfgang SCHMIDT
Johan Albert Frans Kunst
Layo VAN HET GOOR
Marco BRONS
Markus Anton RUESINK
Nikolaos PATSOS
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Cure Technology B.V.
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Publication of WO2024177502A1 publication Critical patent/WO2024177502A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J11/00—Recovery or working-up of waste materials
    • C08J11/04—Recovery or working-up of waste materials of polymers
    • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
    • C08J11/18—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material
    • C08J11/22—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds
    • C08J11/24—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds containing hydroxyl groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
    • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
    • C08G63/16—Dicarboxylic acids and dihydroxy compounds
    • C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
    • C08G63/181—Acids containing aromatic rings
    • C08G63/183—Terephthalic acids
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/78—Preparation processes
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
    • C08G63/78—Preparation processes
    • C08G63/785—Preparation processes characterised by the apparatus used
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/62—Plastics recycling; Rubber recycling

Definitions

  • 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.
  • PET polyethylene terephthalate
  • 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.
  • polyester waste material i.e. post-consumer polyester objects or material
  • the first recycling effort of polyester waste material was in the 1970’s but the development of adequate recycling processes evolved quickly.
  • 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%.
  • 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.
  • polyester waste material 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.
  • 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.
  • polyester waste material 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
  • 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.
  • 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.
  • 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.
  • 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.
  • polyester is de-polymerised with an excess of an alcohol to yield corresponding esters of the corresponding acid and ethylene glycol.
  • reaction with methanol has gained special importance because of the low price and the availability of methanol.
  • 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.
  • 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.
  • polyester oligomers of well-defined molecular weights in a greater range than existing chemical methods like alcoholysis.
  • this method requires sorted polyester material, which has to be free of contaminants.
  • 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 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.
  • oligomeric esters having between 5 and 20 subunits viz. around 0.1 dL/g
  • finisher reactor 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.
  • 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.
  • 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.
  • the oligomer is too viscous to allow a pre-polymerisation purification and thus, may lead to a lower quality product.
  • 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.
  • the design of a finisher (pump type and capacity, outlet diameter etc) allows a maximum iv which is still able to be processed.
  • 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.
  • 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.
  • the other circumstances such as residence time, are the same
  • 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.
  • 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.
  • 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.
  • 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 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.
  • CSTR continuous stirred tank reactor
  • 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.
  • PETE 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.
  • additives like fillers e.g. fibrous like material or particulate matter
  • stabilisers e.g. fibrous like material or particulate matter
  • 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.
  • 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.
  • 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 m 2 .
  • the cross section of reactor is its footprint, thus its measures when projected on a horizontal surface.
  • 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.
  • the pressure in the head space is kept below 10 mbar. This way the time needed for repolymerisation can be further decreased.
  • the pressure in the head space is kept between 1 and 3 mbar, such as 2 mbar.
  • 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.
  • 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.
  • 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.
  • 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.
  • a higher iv can be obtained by applying a higher residence time.
  • 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 continuously stirred tank reactor
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the amount of water in the stream lies between 10 and 1000 ppm, preferably between 20 and 100 ppm, most preferably around 50 ppm.
  • 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.
  • a diol preferably a diol selected from the group of ethylene glycol, 1,3-propanediol, butanediol, cyclohexane dimethanol and neopentyl glycol.
  • 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.
  • BHET Bis(2-Hydroxyethyl) terephthalate
  • the above does not exclude any variants from the process or additional process steps.
  • additional (pre-)purification/filtration steps can be added.
  • 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.
  • 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.
  • 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.
  • 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.
  • the comonomer is pre-polymerized before it is fed to the finisher and mixed with the recycled oligomer.
  • 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.
  • FIG. 1 schematically depicts an overview a process for de- and re-polymerising as known from WO 2022/003084).
  • 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):
  • 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.
  • 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.
  • common process parameters like screw speed, pressure build up, etc.
  • about 3-4% of MEG is dosed in this extruder (indicated by arrow 50’).
  • 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 material with an IV of about 0.15 (0.1 -0.2) is continuously added to the CSTR in step 6.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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 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.
  • a standard condensation reactor is always followed by a finisher to allow faster repolymerisation.
  • 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.
  • 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.
  • 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.
  • FIG 3 schematically depicts a de- and repolymerisation configuration for a stream of polyester waste using prior art technology.
  • the depolymerisation technology as known from WO 2022/003084 is used.
  • 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 .
  • 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 schematically depicts a de- and repolymerisation configuration for a stream of polyester waste using prior art technology.
  • the depolymerisation technology as known from WO 2022/003084 is used.
  • 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 .
  • the resulting oligomer mixture having an IV of around 0.1 is fed
  • Figure 4 schematically depicts a de- and repolymerisation configuration according to the invention.
  • 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.
  • 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.
  • MEG monoethylene glycol
  • 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.
  • the resulting oligomer was repolymerized by directly feeding the oligomer mixture into the finisher, as shown in figure 4.
  • the amount of MEG as used in the depolymerization process was varied in order to arrive at oligomers with a varying grade of polymerization.
  • MEG molecular weight average polyethylene glycol
  • 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.
  • DP degree of polymerization
  • a reduction in residence time to 0.5 hour in the finisher 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.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Polyesters Or Polycarbonates (AREA)

Abstract

La présente invention concerne un processus de recyclage d'un courant de matériau de polyester usagé par dépolymérisation du polyester par alcoolyse en un mélange liquide comprenant des esters oligomères ayant entre 5 et 20 sous-motifs et introduction du mélange liquide d'esters oligomères d'une manière continue dans un réacteur dans lequel le mélange liquide est présent en combinaison avec un espace de tête gazeux, le réacteur ayant des moyens pour augmenter l'interface entre le mélange liquide et l'espace de tête gazeux au moins 5 fois par rapport à une section transversale horizontale du réacteur, la pression dans l'espace de tête étant maintenue au-dessous de 20 mbar, repolymérisant ainsi l'ester oligomère en un polyester ayant une viscosité intrinsèque d'au moins 0,3 dL/g en moins de 120 minutes de temps de séjour du mélange dans le réacteur. L'invention concerne également un système pour appliquer ce procédé.
PCT/NL2024/050082 2023-02-20 2024-02-19 Procédé de recyclage d'un courant de matériau de polyester usagé et système d'application du procédé WO2024177502A1 (fr)

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