Method and reactor system for depolymerizing polymers using a reusable catalyst

Abstract

A method and reactor system for depolymerizing a polymer is described. The method includes the steps of providing a polymer and a solvent in a reactor to obtain a reaction mixture, the solvent capable of reacting with the polymer to degrade the polymer into at least repeat units, providing a reusable catalyst in the reaction mixture capable of catalyzing said decomposition, decomposing the polymer in the reaction mixture under decomposition reaction conditions to obtain a depolymerized mixture containing at least light oligomers having 2 to 4 repeat units, inclusive, removing unreacted polymer, solid particles, and optionally superheavy oligomers from the depolymerized mixture after exiting the reactor, recovering at least a portion of the reusable catalyst from the depolymerized mixture, and recovering the light oligomers from the depolymerized mixture. During recovery of the reusable catalyst, the depolymerized mixture contains heavy oligomers having at least 5 repeat units.

Description

[Technical field]

[0001] The present invention relates to a method for depolymerizing a polymer using a reactive solvent for decomposing the polymer and a reusable catalyst, which catalyzes the decomposition reaction of the polymer, in which a relatively large amount of the applied reusable catalyst can be recovered and reused. The present invention also relates to a reactor system in which the method of the present invention can be carried out. [Background technology]

[0002] In order to prevent an increase in the amount of waste polymers, there is a growing awareness that the large amounts of polymers currently used for various purposes should be recycled.

[0003] Incineration is one possibility, but is undesirable for obvious reasons. Mechanical shredding and grinding of used polymers could be another solution to the problem of accumulating waste polymers. However, the recycled polymer properties are then degraded and often become fillers for other materials. Closed loop recycling (chemical recycling) is clearly the optimal solution. In closed loop recycling, the polymer to be recycled is depolymerized to its repeating units, e.g. the monomeric units from which the polymer was made. The depolymerization process can also give light oligomers, i.e. oligomers with 2 to 4 repeating units inclusive (dimers, trimers and tetramers). The monomers resulting from the decomposition reaction, and optionally the light oligomers, can be used again in the preparation of new polymers.

[0004] The decomposition of used polymers can be hindered by the fact that such polymers are usually present in products that may contain multiple materials, and suitable separation methods should be provided to separate the recycled polymer from the product. As a result, a significant amount of used polymers is still used as fuel and burned. The polymers may contain fillers and other additives to enhance the properties of the polymer. The polymers may be natural or man-made. The polymers may also be combined with other polymers in a polymer blend or form copolymers. It is also possible to combine polymers with other materials such as metals, glass and even rock. All of this makes recycling more difficult.

[0005] Furthermore, chemical recycling of polymers, such as polyethylene terephthalate (PET), is considered cost-effective only if carried out on a relatively large scale, for example with high capacity recycling lines of at least 50 kilotonnes per year, which can then be combined with the polymer producer's polymer production sites, which also tend to be on a large scale.

[0006] A further difficulty appears to be to ensure a consistent and continuous sourcing of waste, such as bottles and textiles, in the wide range of quantities required, for example, at one single site. However, even if the problem of separation of the desired polymer to be recycled from the product is satisfactorily solved, there may be a further concern that the process of decomposition of the polymer into monomers and optionally light oligomers has proven difficult. Many known methods are not selective enough or are insufficient in terms of too low conversion. Efficient conversion of the polymer into the desired product (monomers and / or light oligomers) is desirable, but at the same time it is also desirable to minimize the production of waste in terms of by-products. In other words, a relatively high yield (selectivity multiplied by conversion) is the desired target value of the depolymerization process.

[0007] The depolymerization reaction itself may be carried out in various types of reactors, including batch and continuous reactors, the latter utilizing flow chemistry in which the chemical depolymerization reaction proceeds in a continuously flowing medium, as opposed to what occurs in batch production.

[0008] Catalysts are often used in the synthesis of polymers, but are not often used in the decomposition of waste polymers. This is because the catalytic activity is sensitive to contaminants that are usually present in the waste polymers. Catalysts can only function properly under relatively pure and clean conditions. As a result, catalysts used in the decomposition process may need to be replaced periodically.

[0009] To catalyze the cracking reaction and increase the yield, either heterogeneous or homogeneous catalysts are usually used. When heterogeneous catalysts are used, the selectivity and conversion may be lower than when homogeneous catalysts are used, and the amount of available catalyst that can be selected is quite limited. However, homogeneous catalysts tend to have low recoverability, which may lead to contamination of the reaction product, which is undesirable.

[0010] The catalyst is usually prepared in a reactive solvent capable of reacting with the polymer in order to decompose the polymer into its monomers and light oligomers. Because the catalyst can be quite expensive, it is desirable to be able to recover a relatively large amount of the catalyst after decomposing the polymer in the reaction mixture containing the polymer, the reactive solvent and the catalyst. The catalyst thus recovered can then be reused a second time, and preferably more times.

[0011] Catalysts exist that are specialized for catalysis of depolymerization reactions, such as those described in International Patent Application No. 2016 / 105200 and in US Patent Application No. 2018 / 0371206. The catalysts disclosed therein relate to catalytic complexes that include three distinguishable elements: nanoparticles, a bridging moiety in contact with the nanoparticles, such as, but not limited to, a covalent bond, and a catalytic body in contact with the bridging moiety, such as, but not limited to, a covalent bond. The catalysts have been shown to be highly selective and produce relatively high yields in depolymerization.

[0012] The nanoparticles may preferably be magnetic in nature or may be magnetized to a sufficient degree under a relatively mild magnetic field. The use of magnetic nanoparticles improves the recovery of the catalyst, for example by magnetic forces after use.

[0013] A method for depolymerizing polymers, particularly terephthalate polymers, is also disclosed in International Patent Application No. 2021 / 089803. The disclosed method includes feeding waste material containing a polymer and a solvent into a reactor vessel and heating the waste material to depolymerize the polymer into monomers, dimers, trimers and / or oligomers. A catalyst complex may be added to catalyze the depolymerization. The method forms a first portion and a second portion in the reactor vessel, the second portion containing relatively heavy agglomerates, including, for example, polyolefins that were present in the waste material. The first portion of the liquid containing the monomers, dimers, trimers and / or oligomers is fed through a heat exchanger and then to a separator. The second portion is also fed to a separator where the second portion phase separates from the first portion. A centrifuge downstream from the separator then separates the first phase from the second phase, and the catalyst can be recovered from the second phase containing the polymer.

[0014] Although the above-exemplified catalysts can be recovered to a satisfactory extent, it remains an important goal to recover significant amounts of other catalysts while maintaining the catalytic activity of the recovered catalyst, and to improve the recovery of the exemplified catalysts. Small amounts of catalyst waste may be acceptable, for example on the order of a few percent or less of catalyst, for example less than 5% by weight, more preferably less than 4% by weight, even more preferably less than 2% by weight, even more preferably less than 1% by weight. However, substantially complete recovery of the catalyst is most preferred. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] International Patent Application No. 2016 / 105200 [Patent Document 2] U.S. Patent Application No. 2018 / 0371206 [Patent Document 3] International Patent Application No. 2021 / 089803 Summary of the Invention [Problem to be solved by the invention]

[0016] Thus, a need exists for a method and reactor system for depolymerizing polymers in which a substantial amount of the catalyst used in the depolymerization reaction can be recovered and reused. [Means for solving the problem]

[0017] In relation to the above, according to the present invention, a) providing a polymer and a solvent in a reactor to obtain a reaction mixture, the solvent being capable of reacting with the polymer to decompose the polymer into its monomers and oligomers; b) providing in the reaction mixture a reusable catalyst capable of catalyzing said decomposition; c) decomposing the polymer in the reaction mixture under decomposition reaction conditions to obtain a depolymerized mixture containing monomer and at least light oligomers having from 2 to 4 repeat units, and removing unreacted polymer, solid particles, and optionally superheavy oligomers having more than 200 repeat units from the depolymerized mixture upon exiting the reactor; d) recovering at least a portion of the reusable catalyst from the depolymerized mixture; e) recovering monomers and optionally light oligomers from the depolymerized mixture; Including, A method for depolymerizing polymers is provided, wherein during recovery of reusable catalyst in step d), the depolymerized mixture further contains heavy oligomers having at least 5 repeat units and at most 200 repeat units.

[0018] In another aspect of the present invention, there is provided a reactor system for recycling waste materials containing polymers suitable for depolymerization, said reactor system comprising: - a first reactor vessel having at least one inlet for waste material and another inlet for supplying said first reactor vessel with a reusable catalyst capable of catalyzing a depolymerization reaction of a polymer, and an outlet configured to depolymerize said polymer into its monomers and oligomers, said outlet configured to discharge the depolymerized mixture; - a first filter unit disposed downstream of said outlet and configured to remove unreacted polymer, solid particles, and extra-heavy oligomers having more than 200 repeat units from the depolymerized mixture after exiting the first reactor vessel, such that at least monomer and light oligomers having 2 to 4 repeat units, and heavy oligomers having at least 5 and at most 200 repeat units remain in said depolymerized mixture; a heat exchanger downstream of the outlet and the first filter unit; - a separation unit downstream of the heat exchanger, preferably comprising at least one centrifuge, adapted to recover at least a portion of the reusable catalyst from the depolymerized mixture and / or to recover monomers and light oligomers having 2 to 4 repeat units from the depolymerized mixture; - a conduit system connecting the components of the reactor system and a pressure means for circulation through the conduit system, the conduit system including a feedback conduit for feeding back a recovered portion of the reusable catalyst into the first reactor vessel; Equipped with.

[0019] The reactor system described above is particularly suitable for carrying out the process of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] According to the present invention, a) providing a polymer and a solvent in a reactor to obtain a reaction mixture, the solvent being capable of reacting with the polymer to decompose the polymer into its monomers and oligomers; b) providing in the reaction mixture a reusable catalyst capable of catalyzing said decomposition; c) decomposing the polymer in the reaction mixture under decomposition reaction conditions to obtain a depolymerized mixture containing monomer and at least light oligomers having from 2 to 4 repeat units, and removing unreacted polymer, solid particles, and extra-heavy oligomers having more than 200 repeat units from the depolymerized mixture upon exiting the reactor; d) recovering at least a portion of the reusable catalyst from the depolymerized mixture; e) recovering monomers and light oligomers from the depolymerized mixture. Including, During recovery of the reusable catalyst in step d), the depolymerized mixture further contains heavy oligomers having at least 5 repeat units and at most 200 repeat units. A method for depolymerizing a polymer is provided.

[0021] The inventors have found that, although the presence of a polymer may improve catalyst recovery during the step of recovering reusable catalyst from the depolymerized mixture as disclosed by International Patent Application No. 2021 / 089803, the step of preparing heavy oligomers having only up to 200 repeat units in the depolymerized mixture in step d) surprisingly improves catalyst recovery significantly, as demonstrated in the experimental section of the present disclosure. In other words, the molecular weight of the heavy oligomers in the depolymerized mixture in step d) should not be too high, since this would reduce the catalyst recovery. Maintaining the molecular weight of the heavy oligomers in the depolymerized mixture during recovery step d) between the claimed limits, i.e., having at least 5 repeat units and up to 200 repeat units, allows for improved, even substantially complete, reuse of the catalyst, significantly reducing the cost of depolymerization and increasing its efficiency. The catalysts may be homogeneous or heterogeneous, the latter being preferred.

[0022] In the context of this application, a monomer is defined as a molecule containing one repeat unit of a polymer, while an oligomer contains a molecule containing at least two repeat units. The light oligomers relate to molecules containing 2 to 4 repeat units, including both ends, such as dimers, trimers and tetramers, while the heavy oligomers are defined as having at least 5 repeat units. Since the heavy oligomers are still oligomers, their average molecular weight is not too high. It has been determined that heavy oligomers with too high a molecular weight have the effect of reducing the catalyst recovery. Therefore, an optimal molecular weight range for the heavy oligomers appears to be effective. In a preferred embodiment, therefore, the upper limit of the amount of repeat units in the heavy oligomer is 200, more preferably 100, even more preferably 50, even more preferably 40, even more preferably 30, and most preferably 20. A super heavy oligomer is defined as an oligomer having more repeat units than a heavy oligomer, i.e. having an amount of repeat units greater than the upper limit defined above. It should also be mentioned that the heavy oligomers may exhibit a molecular weight distribution. Thus, defining heavy oligomers having 5 to 200 repeat units does not necessarily mean that they must contain molecules with 5 repeat units, or 200 repeat units. However, in this embodiment, they have molecules with lengths that fall within the range of 5 to 200 repeat units. For example, for the PET being depolymerized, the molecular weight of the pentamer (with two carboxyl end groups) is 934 g / mole, and the molecular weight of the 200mer (with two glycol end groups) is 38462 g / mole.

[0023] The diagram below illustrates the depolymerization of PET using, for example, ethylene glycol as reactive solvent, in which case the heavy oligomers are represented by oligomers with m≧5, preferably m≦200.

[0024] [ka]

[0025] The depolymerized mixture is the mixture remaining after the decomposition step c). Depending on the reaction conditions and according to an embodiment of the present invention, the depolymerized mixture may contain monomers, light oligomers and heavy oligomers containing more than 5 repeat units. The depolymerized mixture may further contain unreacted polymer and / or the superheavy oligomers. Other materials present in the waste polymer feedstock may be present in the depolymerized mixture upon leaving the reactor vessel. Such other materials may include, for example, polyolefins, possibly other radically polymerized polymers such as PVC and polystyrene, as well as metals such as aluminum, glass and rock particles. Condensation polymers other than the one being depolymerized are also examples of such other materials. In a preferred embodiment, the main polymer depolymerized is polyethylene terephthalate (PET). However, the present invention is not limited in principle to the depolymerization of PET, and the method can be used to depolymerize other polymers and polyesters as well.

[0026] The heavy oligomers present in the depolymerized mixture during the recovery of the reusable catalyst in step d) may come from different sources. They may for example come from the depolymerized mixture itself, or from another depolymerized polymer, or may be provided as such. In one embodiment, a method is provided in which the heavy oligomers comprise repeat units of the polymer to be degraded. In other words, the heavy oligomers come from the polymer to be degraded. They may be provided separately or may come from the depolymerized mixture. In another embodiment, the heavy oligomers may come from another polymer, or may be synthetically added to the depolymerized mixture in step d), i.e. the step of recovering at least a portion of the reusable catalyst from the depolymerized mixture. It is also possible to combine different sources of heavy oligomers.

[0027] In a preferred embodiment, a method is provided in which the monomers and oligomers are formed by degrading the polymer in the reaction mixture under degrading reaction conditions during step c) In another embodiment, a method is provided in which the degrading reaction in step c) is stopped early by removing the degrading reaction conditions to promote the formation of heavy oligomers and prevent further degrading of these heavy oligomers to light oligomers.

[0028] The decomposition reaction conditions can be relieved by a number of means. In one embodiment, a method is provided in which the decomposition reaction temperature is reduced below the decomposition reaction temperature required for complete decomposition of the polymer into its monomers and light oligomers. In another embodiment, a method is provided in which the decomposition reaction time is reduced below the decomposition reaction time required for complete decomposition of the polymer into its monomers and light oligomers, including dimers, trimers and / or tetramers. In yet another embodiment, a method is provided in which the decomposition reaction temperature and decomposition reaction time are reduced below the decomposition reaction temperature and decomposition reaction time required for complete decomposition of the polymer into its monomers and light oligomers.

[0029] In a preferred method according to the embodiment, the degradation reaction time is at most 0.95 times, more preferably at most 0.8, and even more preferably at most 0.5 times the degradation reaction time required for complete degradation of the polymer into its monomers and light oligomers.

[0030] The heavy oligomer does not have to be derived from the polymer to be degraded. For example, a method according to an embodiment may be provided in which the heavy oligomer also comprises another heavy oligomer having at least 5 repeat units, preferably up to 200 repeat units, of another polymer different from the polymer to be degraded. It is also possible that the polymer to be degraded is a block copolymer, and that certain blocks of the copolymer form the heavy oligomer after degradation.

[0031] The other polymer may, for example, be decomposable by the solvent under the decomposition reaction conditions and may include a condensation polymer added to the reaction mixture. The other heavy oligomer may also be derived from another polymer after the other polymer is decomposed in a separate process. The heavy oligomer may also be synthesized in a separate oligomerization process. In such an embodiment, the heavy oligomer is available through a separate source in such cases.

[0032] According to yet another embodiment of the present invention, a method is provided in which the heavy oligomers (originating from the polymer to be degraded or from another source) are added to the depolymerized mixture after step c) and before or during step d). This embodiment provides additional flexibility. It is also possible that the heavy oligomers originate from the decomposition reaction of the polymer to be degraded and also from a polymer originating from another source.

[0033] In yet another preferred embodiment, the decomposition step c) c1) substantially completely decomposing the polymer of step a) to form monomers and / or light oligomers having 2 to 4 repeat units; c2) adding an additional amount of said polymer to said reaction mixture after step c1); c3) decomposing said additional quantity of polymer such that said depolymerized mixture contains said heavy oligomers from said additional quantity of polymer; A method is provided that includes:

[0034] The amount of heavy oligomers in the depolymerized mixture is not particularly critical. The yield of heavy oligomers in the depolymerized mixture should not be too high, as this may reduce the yield of monomer and light oligomers in the depolymerized mixture. The yield of heavy oligomers in the depolymerized mixture should not be too low, as this would adversely affect the amount of catalyst recovered.

[0035] A preferred embodiment provides the claimed process, wherein the amount of said heavy oligomers in catalyst recovery step d) ranges from 0.1 to 50 wt.-%, preferably from 1 to 30 wt.-%, more preferably from 5 to 25 wt.-%, based on the total weight of monomers and light oligomers in the depolymerized mixture.

[0036] According to another embodiment of the above process, the amount of monomer in the depolymerized mixture ranges from 5 to 95 wt.%, preferably from 10 to 85 wt.%, more preferably from 15 to 75 wt.%, based on the total weight of monomer, light oligomers, and heavy oligomers in the depolymerized mixture.

[0037] For the decomposition, the solid polymer is prepared in a reactive solvent for the monomer. Thus, the method can be considered as a solid-liquid decomposition process supported by the addition of a recoverable catalyst. As reactive solvent, for example, alcohols can be used. The alcohol is preferably selected from the group of aliphatic alcohols. Preferably, alcohols with a boiling point above 150° C. are used, which can further participate as a reagent in the decomposition of the polymer. In this respect, polyols are preferred. Suitable polyols are for example glycerol, propylene glycol and ethylene glycol. The most preferred alcohol is ethylene glycol. This results in glycolysis of the polymer, more particularly of the condensation polymer, for example polyester. Due to the presence of two alcohol groups per molecule, the monomer has one free alcohol group, which can react again with an acid to form an ester. It is said that the free alcohol group is not available when using monoalcohols such as methanol. However, the claimed method is not limited to the use of glycolysis, but also works with depolymerization methods based on hydrolysis and / or methanolysis, or other depolymerization principles. The use of mixtures of alcohols is not excluded. Mixtures of alcohols with other polar organic solvents, such as ketones or aldehydes, are not excluded, but it is preferred that only one alcohol can participate as a reagent in the decomposition, to prevent the formation of additional monomers.

[0038] Preferably, the polymer to be degraded is a condensation polymer, for example selected from polyesters, polyethers, polycarbonates, polyimides and polyamides, representative examples being PET (polyethylene terephthalate), PEF (polyethylene furanoate), PTT (polytrimethylene terephthalate), PBT (polybutylene terephthalate), PLA (polylactic acid).

[0039] More generally, the polymer may be selected from natural polymers, bio-based polymers, biodegradable polymers, polymers formed (directly or indirectly) from fossil fuels, and combinations thereof. In an illustrative example, the polymer is at least one of a polyester, a polyether, such as polyoxymethylene (POM), polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), polyethylene oxide (PEO), polypropylene oxide (PPO), polytetrahydrofuran (PTHF), and polytetramethylene ether glycol (PTMEG), a polypeptide, a polyamide, a polyamine, a polycondensate, preferably a polyester, such as a polycarboxylic acid ester, the polycarboxylic acid ester being polyethylene terephthalate (PET), Preferably, the polymer is selected from polyethylene furanoate (PEF), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyethylene adipate (PEA), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene naphthalate (PEN), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and polycondensates of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid (VECTRAN). In other words, a wide variety of polymers can be decomposed by the method. Some adjustments may be necessary, for example in terms of the catalyst used, the temperature applied, the solvent used, etc. The method is optimal for decomposition systems using glycolysis, such as polyesters and polyethers, especially PET and PEF. Preferably, the polymeric material to be decomposed is obtained from polymer waste materials, such as bottles or textiles. The waste material may contain one or more additives, such as colorants.

[0040] The present invention is particularly useful for the depolymerization of terephthalate polymers. Terephthalate polymers are a group of polyesters with terephthalate in the backbone. The most common example of a terephthalate polymer is polyethylene terephthalate, also known as PET. Alternative examples include polybutylene terephthalate, polypropylene terephthalate, polyethylene isophthalate, polypentaerythrityl terephthalate, and copolymers thereof, such as copolymers of ethylene terephthalate with polyglycols, such as copolymers of polyoxyethylene glycol with poly(tetramethylene glycol). PET is one of the most common polymers, and recycling PET into reusable raw materials by its depolymerization is highly desirable.

[0041] One preferred means of depolymerization is catalyzed glycolysis. Usually, as a result of the use of an alcohol such as ethylene glycol, a reaction mixture containing bis(2-hydroxyethyl) terephthalate (BHET) monomer and its light oligomers can be formed. The amount of light oligomers formed can depend on many process parameters, such as the polymer:solvent ratio, i.e., the PET:EG ratio when PET is depolymerized using EG as a reactive solvent. According to the degradation process, the terephthalate polymer is depolymerized by glycolysis in the presence of a catalyst. At the end of the depolymerization process, water may be added and phase separation may occur. This allows the first phase containing the BHET monomer units and light oligomers to be separated from the second phase containing the catalyst, the heavy oligomers, and optionally other additives, such as colorants. The first phase may contain impurities in dissolved form and as dispersed particles. The BHET monomer can be recovered, for example, by crystallization methods.

[0042] High purity of monomers and light oligomers is required in order to reuse them in polymerization. As is known, any contaminants from the raw materials may affect the subsequent polymerization reaction. Furthermore, since terephthalate polymers are used in food and even pharmaceutical applications, strict regulations are applied to prevent health problems.

[0043] A preferred method for the depolymerization, preferably condensation, of a polymer, such as PET, comprises several steps, usually including the preparation of a catalyst, a polymer and a reactive solvent, such as an alcohol, and heating to a high enough temperature to achieve an acceptable reaction rate. The solid polymer is dispersed in a reactive solvent (the dispersion usually also includes at least some depolymerization), in which the polymer is decomposed into oligomers and monomers. Then, a separation is performed of the solution, which contains, on the one hand, the dissolved monomers, and any dissolved light oligomers, and, on the other hand, a sparingly soluble or insoluble fraction. The sparingly soluble or insoluble fraction usually contains the catalyst, and, as it turns out, also the heavy oligomers. The further insoluble fraction may contain any pigments, dyes or other colorants and fillers present in the solid polymer.

[0044] The depolymerization process may be carried out batchwise, continuously, semi-continuously, and combinations thereof, with the continuous configuration being preferred.

[0045] The temperature and pressure of the above process can be selected according to the polymer to be decomposed and the catalyst used.Usually, a slightly higher temperature is preferred from the viewpoint of reaction rate, but a lower temperature is preferred from the viewpoint of energy consumption.Similarly, a higher pressure is preferred, but a lower pressure, for example a pressure of about 100 kPa, can be preferred from the viewpoint of reducing the complexity of the reactor system.

[0046] The elevated temperature used in the depolymerization can be selected depending on the polymer and catalyst by routine experimentation, and is usually selected to be at most 20°C lower than the boiling point of the reactive solvent used. In the case of depolymerization of polyesters such as PET, ethylene glycol is the preferred reactive solvent, and the elevated temperature is suitably selected within the range of 150 to 250°C, more preferably within the range of 180 to 220°C, most preferably within the range of 190 to 210°C. To stop the decomposition reaction, the temperature can be reduced, for example, to below 160°C or even lower. Typical reaction times range from 30 seconds to 24 hours or more, depending on the selection of other conditions. In the process, the dispersion of the solid polymer and the decomposition of the polymer into oligomers and monomers can occur simultaneously.

[0047] A further advantage of the method is that it is relatively insensitive (e.g., in terms of yield) to the use of mixed polymers. Mixed polymers can refer to combinations of two or more different polymers, such as different polyesters, such as PET, polyethylene furanoate (PEF), polytrimethylene terephthalate (PTT), and polybutylene terephthalate (PBT), or combinations of one polymer with different properties, such as color, origin, etc., and combinations thereof. The method is also relatively insensitive to contaminants, including additives, such as pigments, fillers, etc., present in the polymer being degraded.

[0048] In a preferred embodiment, a process is provided which includes the additional step of removing unreacted polymer and optionally superheavy oligomers having more repeat units than the heavy oligomers from the depolymerized mixture after step c) and before step d). The step of removing said materials from the depolymerized mixture can significantly increase the amount of catalyst recovered.

[0049] A method for using said removed material to advantage in a method according to a useful embodiment is provided, in which the removed unreacted polymer and any extra-heavy oligomers are depolymerized in a separate second reactor vessel with substantially complete conversion to monomer and light oligomers by applying steps a) to c) of claim 1. The completely depolymerized mixture resulting from the depolymerization in the second reactor vessel can then be introduced into the depolymerized mixture, preferably prior to step d).

[0050] It has also been found to be advantageous for the recovery yield of the catalyst to provide a process according to yet another embodiment, in which further materials present in the depolymerized mixture, such as polyolefins, are at least partially, preferably completely, removed from the depolymerized mixture after step c) and before step d).

[0051] There are several methods for recovering the catalyst from the depolymerized mixture. If the catalyst contains, for example, magnetic particles, the catalyst can be removed by exposing the depolymerized mixture to a magnetic field. However, an improved embodiment relates to a method in which the catalyst recovery step d) comprises a phase formation step comprising forming a first phase containing mainly monomers and light oligomers and a second phase containing mainly heavy oligomers and catalyst, the phase formation step comprising cooling the depolymerized mixture from the reaction temperature, preferably to a temperature below 160° C. In this process, the heavy oligomers can be first dissolved in the reaction mixture during the decomposition step c) and can be at least partially precipitated from the depolymerized mixture during the phase formation step. The above reveals that heavy oligomers with an upper limit of the repeat unit amount of 200, more preferably 100, even more preferably 50, even more preferably 40, even more preferably 30, most preferably 20, work optimally in terms of an increased amount of catalyst being able to be recovered.

[0052] In the phase formation step, it may be possible to add water to the depolymerized mixture to create a hydrophilic solution as a first phase substantially containing monomers and light oligomers, and a second phase substantially containing heavy oligomers and the catalyst, however, preferred embodiments relate to a process in which the phase formation step is carried out without substantially adding water to the depolymerized mixture.

[0053] The inventors have surprisingly found that the precipitated heavy oligomers contain a significant amount of catalyst. The present embodiment allows the heavy oligomers to be removed together with the catalyst from the depolymerized mixture, for example by centrifugation. After decomposition, the resulting mixture may be cooled, preferably to a temperature of 50 to 150° C., more preferably to 80 to 110° C. At this temperature, separation is carried out, notably by centrifugation. To further increase the recovered catalyst yield, separation can be carried out in a number of centrifuges arranged in series. Advantageously, disc stack centrifuges can also be used. In disc stack centrifuges, the separating means rotate at high speeds while generating high g-forces.

[0054] In an embodiment, the step of providing a reusable catalyst preferably comprises the step of reusing the recovered catalyst from said second phase by adding said recovered catalyst to the reaction mixture.

[0055] According to a preferred embodiment of the invention, the process further comprises a step of separating said first phase mainly containing monomers and light oligomers from said second phase mainly containing said heavy oligomers and catalyst, said separation step being carried out at a temperature below 100° C., preferably by centrifugation.

[0056] In another embodiment of the process, the monomer is obtained in a crystallization step, and the monomer is crystallized from the first phase, which mainly contains the monomer and light oligomers, after a separation step. The formed crystals (e.g. BHET crystals) are then removed from the mother liquor, for example by filtration. Any reactive solvent remaining after the claimed process, which is usually a mixture of alcohol and any water, can be recovered and recycled after reducing any water content to about zero water content.

[0057] The present invention can be carried out using any catalyst suitable for the purpose. Suitable catalysts are reusable and recoverable, and preferably contain heterogeneous catalysts. In the depolymerization method according to the embodiment, the catalyst then forms a dispersion in the reaction mixture during step c).

[0058] Some possible different depolymerization catalysts are based on ferromagnetic and / or ferrimagnetic materials. Also antiferromagnetic, synthetic magnetic, paramagnetic, superparamagnetic materials can be used, such as Fe, Co, Ni, Gd, Dy, Mn, Nd, Sm, and preferably O, B, C, N, such as iron oxides, such as ferrites, such as magnetite, hematite, and maghemite. The catalyst particles may contain nanoparticles.

[0059] The catalyst particles catalyze a depolymerization reaction in which individual molecules of polymer are released out of the solid polymer via catalytic reaction, the polymer being, for example, semi-crystalline. This release results in the dispersion of the polymeric material into the reactive solvent and / or dissolution of the individual polymer molecules into the reactive solvent. It is believed that the dispersion and / or dissolution further enhances the depolymerization of the polymer into monomers and oligomers.

[0060] One group of suitable catalysts includes transition metals in their metallic or ionic form. The ionic forms include free ions in solution and ions in ionic or covalent bonds. Ionic bonds form when one atom donates one or more electrons to another atom. Covalent bonds form interatomic bonds resulting from the sharing of electron pairs between two atoms. The transition metals can be selected from the first row of transition metals, also known as 3d orbital transition metals. More specifically, the transition metals are selected from iron, nickel and cobalt. However, iron and nickel particles are most preferred because cobalt is harmful to the body and iron and nickel particles can be formed in pure form. Additionally, alloys of the individual transition metals can be used.

[0061] If the catalyst particles are made of metal, they may be provided with an oxide surface, which may further enhance the catalytic activity. The oxide surface may form by itself on contact with air or water, or the oxide surface may be intentionally applied.

[0062] The use of iron particles is most preferred: besides being magnetic, it has been found that they catalyze the depolymerization of, for example, PET to monomers with 70 to 90% conversion within an acceptable reaction time of up to 6 hours, depending on other process factors such as catalyst dosage and PET / solvent ratio.

[0063] Non-porous metal particles, particularly transition metal particles, may be suitably prepared by thermal decomposition of carbonyl complexes such as iron pentacarbonyl and nickel tetracarbonyl. Alternatively, iron and nickel oxides may be prepared via exposure of the metals to oxygen at elevated temperatures, e.g., above 400°C. Non-porous particles may be more suitable than porous particles because they may be less exposed to alcohol, so they may corrode less and they may be reused for catalysis more frequently. Furthermore, because of the limited surface area, any oxidation at the surface may reduce the amount of metal ions, thereby removing low concentrations of ions present in the product stream as leached contaminants.

[0064] Another group of suitable catalysts includes particles based on alkaline earth elements selected from beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba), and their oxides. A preferred alkaline earth metal oxide is magnesium oxide (MgO). Other suitable metals include, but are not limited to, titanium (Ti), zirconium (Zr), manganese (Mn), zinc (Zn), aluminum (Al), germanium (Ge) and antimony (Sb), and their oxides, and also their alloys. Noble metals, such as palladium (Pd) and platinum (Pt), are also suitable. MgO and ZnO have been found to catalyze the depolymerization of, for example, PET to monomers at 70 to 90% conversion within acceptable reaction times, again depending on other process factors such as catalyst dosage and PET / solvent ratio. Suitable catalysts based on hydrotalcite are also contemplated.

[0065] Preferably, the catalyst particles are selected to be substantially insoluble in the (alcoholic) reactive solvent and at elevated temperatures above 100° C. One oxide that tends to dissolve easily in alcohols such as glycols at elevated temperatures is less suitable, such as amorphous SiO2.

[0066] The preferred concentration of catalyst is 1 wt% or less relative to the amount of PET. Good results have been achieved with catalyst loadings of less than 0.2 wt%, or even less than 0.1 wt%, relative to the amount of PET. The low catalyst loadings are highly advantageous, as the method of the present invention allows for the recovery of increased amounts of nanoparticle catalyst.

[0067] The surface area of ​​the non-porous particles according to the invention is preferably less than 10 m 2 / g, more preferably up to 5m 2 / g, and even more preferably at most 1m 2 In another embodiment, the surface area is at least 3 m 2 / g. The porosity is preferably 10 -2 cm3 / g or up to, for example, 10 -3 cm 3 / g. Porous particles can also be used, which usually exhibit a relatively large surface area.

[0068] Nanoparticles can also be used as or in depolymerization catalysts. The nanoparticles have small diameters and surface areas of 10 to 1000 m. 2 / g, more preferably 50 to 500m 2 / g, most preferably 80 to 150m 2 / g or more. It is believed that condensation polymers are significantly adsorbed to these types of nanoparticles, which results in faster depolymerization and therefore an economically viable process. Many options are available for separating the above nanoparticles.

[0069] The catalytic nanoparticles preferably have magnetic properties, either by containing a magnetic material or by being sufficiently magnetized under a relatively gentle magnetic field, as applied in the present method. Preferably, the magnetic nanoparticles contain iron, nickel and / or cobalt, or a combination thereof, in the form of their oxides or metals, such as iron oxide, but preferably in the form of Fe304. Another preferred example is α-Fe203 and / or γ-Fe203. A preferred example of an alloy is CoFe204. Other preferred examples are NiFe204, Ni2Fe205 or NiO.

[0070] It has been found that the nanoparticles need to be 17enzotrently small in order for the catalyst complex to function as a catalyst, thereby breaking down the polymer into smaller units, but with a yield of these smaller units, specifically their monomers, that is high enough for commercial reasons. It has further been found that the nanoparticles need to be large enough to allow the catalyst of the invention to be recovered and reused. It is economically undesirable that the catalyst can be removed either with the waste or with the resulting decomposition products. The average diameter of the suitable nanoparticles is in the range of 2 to 500 nm, more preferably in the range of 3 to 200 nm, even more preferably in the range of 4 to 100 nm. It has been found that particles with a somewhat smaller diameter, for example 5 to 50 nm, are optimal, for example in terms of yield and recovery of the catalyst complex. It should be noted that the term "size" refers to the average size of the particles, the actual diameter of the particles may vary somewhat depending on their characteristics. Furthermore, aggregates may be formed, for example in the solution. The size of these aggregates is usually in the range of 50 to 200 nm, for example 80 to 150 nm, for example around 100 nm. It is preferred to use nanoparticles containing iron oxide.

[0071] Particle size and its distribution can be measured by light scattering, for example using a Malvern dynamic light scattering instrument, e.g. NS500 series. In a more laborious approach, usually applicable to relatively small particle sizes but equally applicable to larger sizes, a representative electron microscope image is taken and the size of the individual particles is measured on the image. For the average particle size, a number average can be taken. In an approximation, the average can be considered as the size of the most abundant particle or the median size.

[0072] Preferred heterogeneous catalysts that can be used in the present invention are catalyst complexes containing catalyst particles, such as those disclosed above, and catalyst bodies that are attached to or in contact with the catalyst particles via a linking group, said catalyst bodies containing cationic moieties with positive charges and negative moieties with negative charges. The catalyst particles are preferably nanoparticles, and the catalyst particles may themselves exhibit some catalytic activity.

[0073] The catalyst complex (ABC) comprises three distinguishable elements: a (nano)particle (A), a linking group (B) that is in contact with the particle chemically, e.g., covalently, or physically, e.g., by adsorption, and a catalyst entity (C) that may be chemically, e.g., covalently, associated with the linking group. The linking group preferably does not completely cover the nanoparticle surface, as in core-shell particles.

[0074] The particles of the catalyst complex are preferably based on ferromagnetic and / or ferrimagnetic materials. Also antiferromagnetic, synthetic, paramagnetic, superparamagnetic materials, such as materials containing at least one of Fe, Co, Ni, Gd, Dy, Mn, Nd, Sm, and preferably at least one of O, B, C, N, such as iron oxides, such as ferrites, such as hematite (Fe2O3), magnetite (Fe3O4), and maghemite (Fe2O3, γ-Fe2O3), can be used. From a cost perspective, even if the catalyst complex of the invention is completely or largely recovered, relatively cheap particles, such as particles containing Fe, are preferred. A further advantage of iron or iron oxide particles is that they have the highest saturation magnetization, making it easy to separate the particles via a magnetic separator. Even more importantly, the iron oxide nanoparticles have a positive effect on the decomposition reaction. The iron oxide may further contain additional elements, such as cobalt and / or manganese, such as CoFe2O4.

[0075] The catalyst particles used in the catalyst complex according to the invention can be at least partially coated with a protective coating. For example, Fe3O4 particles can be coated with said materials to promote the formation of a stable suspension and, finally, to protect the particles from oxidation to Fe2O3, which may have different magnetic properties. Thus, at least a part of the surface of the catalyst particles may be coated with materials such as polyethyleneimine (PEI), polyethylene glycol (PEG), silicon oil, fatty acids such as oleic acid or stearic acid, silanes, mineral oils, amino acids, or polyacrylic acid or polyvinylpyrrolidone (PVP). Carbon is also a possible coating material. The coating can be removed before or during the catalytic reaction. The technique for removing the coating can include, for example, a separate solvent washing step before using it in the reactor, or a step of burning in air. However, removing the coating is not essential.

[0076] The catalyst body of the present invention comprises at least two parts. The first part refers to a part with a positive charge (cation). The second part refers to a part, usually a salt complex part, with a negative charge (anion). The negative and positive charges usually balance each other. It has been found that the positive and negative charged parts have a synergistic and enhancing effect on the decomposition process of waste terephthalate polymer in terms of conversion and selectivity.

[0077] The positively charged moiety (cation) may be aromatic or aliphatic and / or heterocyclic. The cationic moiety may be aliphatic and is preferably selected from guanidine (carbamimidoyl azanium), ammonium, phosphonium and sulfonium. The non-aromatic or aromatic heterocyclic moiety preferably comprises a heterocycle having at least one, preferably at least two, heteroatoms. The heterocycle may have 5 or 6 atoms, preferably 5 atoms. The positively charged moiety may preferably be an aromatic moiety which stabilizes the positive charge. Usually, the cationic moiety carries the positive charge on a heteroatom. The heteroatom may be, for example, nitrogen N, phosphorus P or sulfur S. Suitable aromatic heterocycles are pyrimidine, imidazole, piperidine, pyrrolidine, pyridine, pyrazole, oxazole, triazole, thiazole, benzotriazo, benzotriazole, isoquinol and viologen-based compounds (having two interlocking pyridine ring structures). In particular, the imidazole structure is preferred, resulting in an imidazolium ion. Suitable cationic moieties with N as a heteroatom include imidazolium (5-membered ring with two N), piperidinium (6-membered ring with one N), pyrrolidinium (5-membered ring with one N), and pyridinium (6-membered ring with one N). A preferred imidazolium cationic moiety is butylmethylimidazolium (bmim + ), ethylimidazolium, or butylimidazolium (bim + Other suitable cationic moieties include, but are not limited to, triazolium (a five-membered ring with three N's), thiazolium (a five-membered ring with an N and an S), and (iso)quinolinium (two six-membered rings with N's (naphthalene)).

[0078] In a preferred method, the cationic moiety of the catalyst is selected from at least one of an imidazolium group, a piperidinium group, a pyridinium group, a pyrrolidinium group, a sulfonium group, an ammonium group, and a phosphonium group.

[0079] The cationic moiety may have one or more substituents, which are preferably selected alkyl moieties. In certain embodiments, the alkyl moiety is C1-C6 in length, for example C2-C4 in length. In specific examples, the imidazolium group has two substituents R1, R2 adjacent to one of the two nitrogen atoms, the piperidinium group has two substituents R1, R2 adjacent to the nitrogen atom, the pyridinium group has two substituents R1, R2 adjacent to the nitrogen atom, the pyrrolidinium group has two substituents R1, R2 adjacent to the nitrogen atom, the sulfonium group has three substituents R1, R2, R3 adjacent to the sulfur atom, the ammonium group has four substituents R1, R2, R3, R4 adjacent to the nitrogen atom, and the phosphonium group has four substituents R1, R2, R3, R4 adjacent to the phosphorus atom.

[0080] The negatively charged moiety (anion) may relate to an anionic complex or to a simple ion such as a halide ion. The negatively charged moiety (anion) may relate to a salt complex moiety, preferably a divalent or trivalent metal cation, such as Fe 3+ , Al 3+ , Ca 2+ , Zn 2+ and Cu 2+ , and a negatively charged counter ion, such as a halide ion, e.g., Cl - , F - , and Br - In an example, the salt may be a metal salt complex moiety having a halide ion or the like. 3+ , for example FeCl4 - Alternatively, a counter ion without a metal salt complex can be used, such as a halide ion as is known.

[0081] The linking group may include a bridging moiety where the catalyst body contacts the catalyst particle. The catalyst body and particles of the present invention are combined by the bridging moiety whereby the catalyst body contacts the catalyst particle. The linking typically involves a combination of bridging moieties and a physical or chemical bond between the catalyst body on the one hand and the catalyst particle on the other hand. In particular, a plurality of bridging moieties contact or bond with the surface of the catalyst particle of the present invention. Suitable bridging moieties include weak organic acids, silyl-containing groups, and silanols. More specifically, for this, the bridging moiety includes a functional group that bonds with the oxide of the particle and a second linking group that bonds with the catalyst body. The functional group may be, for example, a carboxylic acid, an alcohol, a silicic acid group, or a combination thereof. Other acids such as organic sulfonic acids are not excluded. The linking group may include, for example, a terminal alkylene chain with an alkylene chain between C1 and C6, for example propylene and ethylene, which is in contact with a cationic moiety. The linking group may be in contact with a cationic moiety, such as a preferred imidazolium moiety. In the above mentioned contact state, the BC complex then comprises, for example, an imidazolium having two alkyl groups, for example butylmethylimidazolium (bmim+) or illustratively ethylmethylimidazolium.

[0082] The bridging moiety is preferably provided as a reagent with which the linking group is functionalized for chemical reaction with the aid of a catalyst. For example, a suitable functionalization of the linking group is the provision of a substituted alkyl halide. Suitable reagents include, for example, 2-chloropropyltrialkoxysilane and 2-bromopropyltrialkoxysilane. The alkoxy group is preferably ethoxy, but methoxy or propoxy are not excluded. It is preferred to use trialkoxysilanes, but dialkyldialkoxysilanes and trialkyl-monoalkoxysilanes are not excluded. In the latter case, the alkyl group is preferably a lower alkyl, for example a C1-C4 alkyl. At least one of the alkyl groups is subsequently functionalized, for example with a halide as described above.

[0083] The reagent is then reacted with a catalyst. Preferably, this reaction produces a positive charge on the cationic moiety, more specifically on the heteroatom in the cationic moiety, preferably the heterocyclic ring. The reaction is, for example, of a (substituted) alkyl halide with a heteroatom, such as nitrogen, containing a cationic moiety, resulting in a bond between the heteroatom and the alkyl group. The heteroatom is then positively charged and the halide negatively charged. The negatively charged halide can then be enhanced by the addition of a Lewis acid to form a metal salt complex. One example is the conversion of chloride to FeCl4 - It is a transformation into.

[0084] According to the present invention, the bridging moiety and the catalytic body bound thereto are (mol bridging moiety / gr magnetic particle) 5 * 10 -6 -0.1, preferably 1 * 10 -5 -0.01, more preferably 2 * 10 -5 -10 -3 , e.g. 4 * 10 -5 -10 -4 It is preferred that a relatively large amount be available in view of any efficient recovery of the catalyst complex, while in view of the amount of catalyst and its cost, a somewhat smaller amount may be more preferred.

[0085] In a preferred embodiment, the catalyst complex is used in a weight ratio of catalyst complex to polymer ranging from 0.001:10 to 1.0:10, preferably from 0.005:10 to 0.5:10.

[0086] Another aspect of the present invention relates to a reactor system for recycling waste materials containing polymers suitable for depolymerization, said reactor system comprising: - a first reactor vessel having at least one inlet for waste material and another inlet for supplying said first reactor vessel with a reusable catalyst capable of catalyzing a depolymerization reaction of a polymer, and an outlet configured to depolymerize said polymer into its monomers and oligomers, said outlet configured to discharge the depolymerized mixture; - a first filter unit disposed downstream of said outlet and configured to remove unreacted polymer, solid particles, and optionally superheavy oligomers from the depolymerized mixture after exiting the first reactor vessel such that at least light oligomers having 2 to 4 repeat units, inclusive, and heavy monomers having at least 5, and optionally up to 200, repeat units remain in the depolymerized mixture; a heat exchanger downstream of the outlet and the first filter unit; - a separation unit downstream of the heat exchanger, preferably comprising at least one centrifuge, configured to recover at least a portion of the reusable catalyst from the depolymerized mixture and / or to recover monomers and light oligomers having 2 to 4 repeat units, inclusive, from the depolymerized mixture; - a conduit system connecting the components of the reactor system and a pressure means for circulation through the conduit system, the conduit system including a feedback conduit for feeding back a recovered portion of the reusable catalyst into the first reactor vessel; Equipped with.

[0087] The reactor system described above is particularly suitable for carrying out the process of the present invention.

[0088] An improved embodiment of the reactor system is characterized in that the first filter unit is configured to remove very heavy oligomers having more than 200 repeat units from the depolymerized mixture after exiting the first reactor vessel, more preferably configured to remove very heavy oligomers having more than 100, even more preferably more than 50, even more preferably more than 40, even more preferably more than 30, and most preferably more than 20 repeat units from the depolymerized mixture after exiting the first reactor vessel. A suitable filter unit may comprise a strainer or another unit capable of performing a filtration function.

[0089] Those skilled in the art may be able to design the first filter unit to pass heavy oligomers and retain unreacted polymers, solid particles, and superheavy oligomers having more than 200 repeat units. The same considerations apply to the optional second filter unit and the third filter unit described further below. A suitable method for selecting the retention capacity of a filter unit (e.g., its mesh size) may be to pass the depolymerized mixture through the filter unit and collect the retentate and filtrate. By measuring the (number or weight) average molecular weight of the retentate, the filter unit allows correlation of the retention capacity of the filter unit with the desired average molecular weight of the retentate and / or filtrate. Any method may be used to measure the average molecular weight, and suitable methods include gel permeation chromatography (GPC) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDITOFMS). It has been found that suitable mesh sizes may be in the range of from 20 μm to 1000 μm, more preferably from 50 μm to 800 μm, even more preferably from 100 μm to 600 μm, and most preferably from 150 μm to 500 μm.

[0090] In another embodiment, the reactor system further comprises a separate second reactor vessel adapted to receive the unreacted polymer and any super-heavy oligomers removed from the first filter unit, the second reactor adapted to depolymerize the removed unreacted polymer and any super-heavy oligomers to monomer and light oligomers with substantially complete conversion. Preferably, the second reactor vessel has an outlet adapted to discharge the fully depolymerized mixture and a conduit connecting the outlet to a heat exchanger. The conduit connecting the outlet to the heat exchanger preferably has a third filter unit disposed downstream of the outlet and adapted to remove solid particles from the fully polymerized mixture.

[0091] Another useful embodiment of the present invention provides a reactor system further comprising a second filter unit downstream of the heat exchanger and upstream of the separation unit, configured for at least partially, preferably completely, removing other materials present in the depolymerized mixture, such as, for example, polyolefins, from said depolymerized mixture.

[0092] Yet another embodiment provides a reactor system further comprising a source of heavy oligomers other than the first reactor vessel, the source being provided with an outlet configured for discharging heavy oligomers from the source, and a conduit connected to said outlet and configured for adding said heavy oligomers to the depolymerized mixture in or downstream of said heat exchanger and / or in or upstream from said separation unit. This embodiment provides further flexibility to adjust the desired amount of heavy oligomers in the depolymerized mixture for improved catalyst recovery.

[0093] The separation unit downstream of the heat exchanger preferably comprises at least one centrifuge. The separation unit is configured to recover at least a portion of the reusable catalyst from the depolymerized mixture and / or to recover light oligomers having 2 to 4 repeat units, inclusive, from the depolymerized mixture. According to the invention, the separation unit may be configured for substantially complete recovery of the reusable catalyst from the depolymerized mixture. A further improved reactor system according to an embodiment is characterized in that the separation unit comprises a plurality of centrifuges arranged in series, any centrifuge may more preferably comprise a disk stack centrifuge.

[0094] Another practical embodiment provides a reactor system, in which at least one solvent buffer vessel is arranged upstream of the first reactor vessel and / or the second reactor vessel, the inlet of the at least one solvent buffer vessel being connected to a feedback conduit and its outlet being connected to the first reactor vessel and / or the second reactor vessel.

[0095] These and other aspects of the method and reactor system of the present invention will be further explained with reference to the figures, which are purely schematic and are not drawn to scale. [Brief description of the drawings]

[0096] [Figure 1] FIG. 1 illustrates a reactor system according to an embodiment of the present invention. [Diagram 2] FIG. 2 illustrates a reactor system according to another embodiment of the present invention. [Diagram 3] FIG. 1 shows a photograph of the polyethylene terephthalate (PET) waste material used. [Figure 4] FIG. 4 shows a graph of the concentration of iron (Fe) in BHET and mother liquor obtained after depolymerization of the material of FIG. 3 using an Fe-based catalyst and after separation of the BHET for a number of embodiments in accordance with the invention and for a number of comparative examples. [Diagram 5]FIG. 1 shows a graph of separation efficiency of Fe-based catalysts for a number of embodiments in accordance with the present invention and for a number of comparative examples. [Figure 6] FIG. 13 shows a photograph of another polyethylene terephthalate (PET) scrap material used. [Figure 7] FIG. 7 shows a graph of the concentration of iron (Fe) in BHET and mother liquor obtained after depolymerization of the material of FIG. 6 using an Fe-based catalyst and after separation of the BHET for a number of embodiments in accordance with the invention and for a number of comparative examples. [Figure 8] FIG. 1 shows a graph of separation efficiency of Fe-based catalysts for a number of embodiments in accordance with the present invention and for a number of comparative examples. [Figure 9] FIG. 1 shows photographs of heavy oligomers before (image a) and after (image b) separation of the catalyst of the material used in Example 5. [Figure 10] FIG. 7 shows a graph of the concentration of Mg in BHET and mother liquor obtained after depolymerization of the material of FIG. 6 using a Mg-based catalyst and after separation of BHET for a number of embodiments according to the invention and for a number of comparative examples. [Figure 11] FIG. 1 shows a graph of separation efficiency of Mg-based catalysts for a number of embodiments according to the present invention and for a number of comparative examples. [Figure 12] FIG. 13 shows a photograph of yet another polyethylene terephthalate (PET) scrap material used. [Figure 13] FIG. 13 shows a graph of iron (Fe) concentration in BHET and mother liquor after depolymerization of the material of FIG. 12 with an Fe-based catalyst and after separation of the BHET for embodiments in accordance with the invention and comparative examples. [Figure 14] Finally, FIG. 1 shows a graph of the separation efficiency of Fe-based catalysts for embodiments according to the invention and comparative examples.

[0097] DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS In the following, identical or corresponding parts in different figures are referred to by the same reference numerals. The illustrated embodiments are intended to be illustrative and explanatory, and are not intended to limit the scope of the claims.

[0098] FIG. 1 shows a reactor system 100 according to a first embodiment, comprising a reactor vessel 10 provided with a first inlet 11, a second inlet 12 and a third inlet 13, and an outlet 21. The reactor vessel 10 is adapted to depolymerize a polymer, in particular a condensation polymer, said depolymerized mixture leaving the vessel 10 through the outlet 21. Other materials present in the feedstock may also be separated from the outlet 21. Such other materials include, for example, polyolefins, possibly other radically polymerized polymers such as PVC and polystyrene, as well as metals such as aluminum, glass and rocks. Also, other condensation polymers than the one to be depolymerized are illustrative of said other materials. The main condensation polymer to be depolymerized is polyethylene terephthalate (PET) in a preferred embodiment. However, the invention is not limited in principle to the depolymerization of PET, and said reactor system may also be used to depolymerize other polymers and polyesters.

[0099] The reactor system 100 shown in FIG. 1 is configured as a continuous system in which the reactor vessel 10 is continuously fed with polymer waste material, solvent and catalyst to sustain the depolymerization reaction. In such a continuous system, it may be desirable to use a cascade of reactors. The polymer material, solvent and catalyst constitute a reaction mixture whose composition changes along the path of depolymerization. According to an embodiment of the present invention, the conditions in the first reactor vessel 10 are such that the primary polymer (the polymer to be degraded) added to the first reactor vessel is only partially depolymerized, i.e., depolymerized to non-complete conversion. In this way, only a portion of the primary polymer, e.g., PET, is depolymerized to light oligomers and monomers, while another portion is depolymerized to heavy oligomers. Furthermore, some undissolved polymer may exit the first reactor vessel 10. The waste material fed to the reactor vessel 10 via the first inlet 11 is usually in the form of flakes. The solvent added to the vessel 10 through the second inlet 12 is preferably an alcohol, more preferably ethylene glycol. The catalyst may be any catalyst suitable for the purpose, for example based on magnetic nanoparticles or their aggregates functionalized with ionic liquid. Preferred magnetic nanoparticles are iron oxide particles and cobalt-iron oxide particles. Besides iron and / or cobalt, the presence of other metals is not excluded. Any aggregates of magnetic nanoparticles are preferably porous and more preferably have a size that allows their separation in the centrifuge 60. If alternative catalysts are used, the catalysts are again preferably selected with a size that allows their separation in the centrifuge 60. The polymeric material is preferably introduced into the reactor vessel 10 in a ratio with the solvent in the range of 10:1 to 1:10. The order of addition of the components (catalyst, waste material and solvent) is irrelevant. However, it appears advantageous to add the catalyst as a dispersion in the solvent, so as to add it to the vessel 10 together with the solvent through the second inlet 12. Furthermore, the solvent may be preheated. Alternatively, the reactor system 100 may be designed as a batch system.

[0100] As shown in FIG. 1, the reactor vessel 10 is provided with a first outlet 21 configured for removal of the depolymerized mixture 31. The partially depolymerized mixture contains monomers and light and heavy oligomers, and may also contain unreacted polymers and other materials as defined above. The partially depolymerized mixture 31 is guided through a first filter unit 20, for example with a strainer. The first filter unit 20 separates solid particles, such as metals, glass, and rocks, and / or unreacted polymers from the depolymerized mixture 31. The thus cleaned partially depolymerized mixture leaves the first filter unit as stream 32a. The partially depolymerized mixture stream 32 is mainly liquid and is transferred by means of a pump 41 to a heat exchanger 30, where the partially depolymerized mixture stream 32 is cooled. The resulting cooled partially depolymerized mixture stream 32b is then passed through a second filter unit 40 and further fed downstream into a vessel 50, which may be provided with an inlet 51 for adding water or an aqueous solution. The second filter unit 40 may also be embodied as a strainer and serves to optionally separate polyolefins and other polymers from the partially depolymerized mixture stream 32b. The separated materials leave the second filter unit 40 as stream 33. As shown in FIG. 1, a further vessel 35 may be provided upstream of the second filter unit 40 in some embodiments. The further vessel 35 may optionally be provided with an inlet 36 for adding water or an aqueous solution. The further vessel 35 aids in the separation of polyolefins and other polymers from the partially depolymerized mixture stream 32b in the second filter unit 40.

[0101] The downstream vessel 50 may, in embodiments, be provided with mixing means to ensure sufficient mixing of the cooled partially depolymerized mixture 32 with the optionally provided water or aqueous solution. Typically, said mixing means include a mixing chamber and an agitator of any form. However, the agitator may not be strictly required depending on the flow regime of the cooled partially depolymerized mixture stream 32b. Indeed, the cooled depolymerized mixture stream 32b may be provided as a turbulent flow, and a mixing chamber without an agitator may be sufficient in that case. The mixing chamber is preferably part of the downstream vessel, but may alternatively be implemented as a chamber upstream of the downstream vessel 50. Similar remarks may be made for any other vessel 35.

[0102] Said optional water or aqueous solution added to the vessel 50 (and optionally to the further vessel 35) may act as a coolant. It may be provided at room temperature or at any elevated temperature, preferably liquid. It is not excluded that a separate cooling means is provided and / or the obtained stream may pass through another heat exchanger downstream of the vessel 50 or in the further vessel 35. To ensure a sufficiently low temperature, it is also possible to provide a temperature sensor in the downstream vessel 50, integrated in a controller arranged to control the heat exchanger 30. Due to the cooling or addition of any water or aqueous solution, two phases may appear, the first being an aqueous phase containing the solvent, monomer and at least light oligomers as defined in the present invention. The second phase is a slurry containing the solvent, catalyst and heavy oligomers as defined in the present invention. Said phases leave the vessel 50 as stream 32c, said phases are then separated in a centrifuge 60, resulting in a first separated phase 61 which is further processed to obtain the product to be depolymerized, e.g. BHET, and a second separated phase 62 which is recycled. In FIG. 1, the second phase 62 is shown to be recycled directly to the reactor vessel 10 via the solvent buffer vessel 70. According to the invention, the second phase 62 contains an alcoholic solvent, more preferably ethylene glycol, water, heavy oligomers, optionally colorants, and a (heterogeneous) catalyst. The second phase 62 may further contain small amounts of light oligomers and monomers. The inventors have found that by feeding the heavy oligomers into the depolymerized mixture stream 32c and into the centrifuge 60, a larger amount of the (heterogeneous) catalyst is separated in the second phase 62 than is possible according to the prior art. The amount of the (heterogeneous) catalyst recycled to the reactor vessel 10 is then also increased. As a result, a smaller amount of the (heterogeneous) catalyst is separated and lost in the first phase 61.

[0103] In one implementation, the recycle line through which the second phase 62 is directed to the first solvent buffer vessel 70 includes a distillation step to reduce the water content of the second phase 62. Preferably, the second phase 62 is ultimately fed back into the reactor vessel 10 with a water content of less than 10% by weight, more preferably less than 5% by weight or less than 2% by weight, or even less than 1%.

[0104] Further processing of the first phase 61 includes, for example, treatment with activated carbon and one or more crystallization treatments to arrive at a crystalline raw material suitable for polymerization. Most preferably, the raw material is BHET, but it is also feasible to collect crystalline light oligomers, such as dimers, trimers and tetramers.

[0105] Although not shown in Figure 1, the lines connecting the different units may be equipped with valves to control the flow of the different mixture streams. It can be understood that said valves are under the control of a controller, none of which is shown.

[0106] As further shown in FIG. 1 , the solid particles and unreacted polymer stream 33 is directed to a second reactor vessel 80. The second reactor vessel 80 is disposed downstream of the first outlet 21 of the first reactor vessel 10. As such, the purpose of the second reactor vessel 80 is to effect further depolymerization of the unreacted polymer entering the second reactor vessel 80 through its inlet 81. The conditions in the second reactor vessel 80 are preferably maintained such that substantially complete conversion of the polymer to monomer is achieved in the second reactor vessel 80. This is in contrast to the conditions imposed in the first reactor vessel 10 according to embodiments where the depolymerization in the first reactor vessel 10 is only partially carried out with non-complete conversion of the polymer such that heavy oligomers and, ultimately, further polymer are still present upon leaving the first reactor vessel 10 as stream 31. It has been found in the experiments leading to this embodiment of the invention that the presence of heavy oligomers is advantageous for separation in centrifuge 60 of homogeneous or heterogeneous catalysts even when water or another aqueous solution is not added as a phase separation additive in mixing vessel 50. Thus, in a preferred embodiment, vessel 50 does not include an inlet 51 for water or another aqueous solution.

[0107] As further shown in FIG. 1, the second reactor vessel 80 is provided with an outlet 82 configured for removal of the substantially completely depolymerized mixture 52. The depolymerized mixture contains monomers (and possibly some light oligomers) and may also contain other materials as defined above. The fully depolymerized mixture 52 is guided through a third filter unit 90, which may for example include a strainer. The third filter unit 90 separates the remaining solid particles, such as metal, glass, and rock, from the depolymerized mixture 52 and discharges them as stream 53. The thus cleaned depolymerized mixture leaves the third filter unit 90 as stream 54. The substantially completely depolymerized mixture stream 54 is primarily liquid and is transferred to the heat exchanger 30 where the substantially completely depolymerized mixture stream 54 is combined with the partially depolymerized mixture stream 32a and cooled. The resulting cooled depolymerized mixture stream 32b is then passed through the second filter unit 40 and fed further downstream into the vessel 50, as described above.

[0108] At least one further inlet 83 may be provided in the second reactor vessel 80. This inlet 83 may be configured, for example, to optionally add a solvent and / or catalyst, or even more waste polymer material to the second reactor vessel 80.

[0109] The second reactor vessel 80 may be provided with a further inlet 84 connecting to an upstream second solvent buffer vessel 71. The second solvent buffer vessel 71 is provided upstream via line 72 and connected to a first solvent buffer vessel 70 receiving recycled solvent and (heterogeneous) catalyst via line 63. Optionally, the first solvent buffer vessel 70 is also fed with recycled solvent via line 64 or with raw solvent and catalyst via line 65.

[0110] In one implementation of the reaction system and its use for depolymerization, the second reactor vessel 80 is arranged as a batch reactor. This is the preferred option to ensure that substantially all of the unreacted polymer originating from the first reactor vessel 10 can be depolymerized. To this end, the depolymerization temperature in the second reactor vessel 90 may be maintained, for example, in the range of 170 to 250° C.

[0111] A second embodiment of the invention is shown in Figure 2 as reactor system 101. In this embodiment, a separate source of heavy oligomers 45 is provided, as well as a line or conduit 46 connecting the heavy oligomer source 45 with one of streams 32b and / or 32c. The conduit 46 may be connected to the product stream to be depolymerized at location 32b between the heat exchanger 30 and the second filter unit 40, or alternatively between the second filter unit 40 and the vessel 50, or alternatively between just upstream of the centrifuge 60 and downstream of the vessel 50. The latter embodiment is shown in Figure 2. The source of heavy oligomers 45 may contain synthesized heavy oligomers, or alternatively heavy oligomers obtained by partial depolymerization of a primary polymer, or by partial depolymerization of another polymer.

[0112] In this embodiment, the conditions in the first reactor vessel 10 may be selected to only partially depolymerize the primary polymer, as described above. Further polymerization is then carried out in the second reactor vessel 80. The additional heavy oligomers are then fed to the centrifuge 60 via line 46. In another embodiment, it may also be possible to select reaction conditions such that the primary polymer is substantially completely depolymerized at full conversion in the first reactor vessel 10. In that case, substantially all of the heavy oligomers required to achieve the desired high recovery level of the (heterogeneous) catalyst are fed to the centrifuge 60 via line 46. In this embodiment, it may also be possible to close the second reactor vessel 80. The solid particles exiting the first reactor vessel 10 as stream 33 may then be stored elsewhere.

[0113] The present invention will now be described in more detail with reference to the following examples, which are not intended to limit the invention but are merely presented as exemplary embodiments of the invention. EXAMPLES

[0114] Tests were performed on colored and uncolored PET. The results are of the same order of magnitude for both conversion and selectivity to BHET. As a result, the inventors conclude that there is little or no effect of color additives in this respect. Furthermore, additives, such as pigments, can be easily removed from the decomposition products.

[0115] The sourced raw materials (PET) may include polyester clothing, PET carpets, PET material originating from the automotive industry, recycled PET, and multi-layered PET trays containing other polymers such as PE and PP. Again, the results are of the same order of magnitude for both conversion and selectivity.

[0116] The average residence time of the polymer in the reactor during the decomposition can be selected from 30 seconds to 5 hours, preferably 60 seconds to 2 hours, more preferably 2 to 60 minutes, for example 5 to 30 minutes. Longer or shorter times can be used, depending for example on the size and boundary conditions of the reactor. For example, high pressure (500 to 3000 kPa) processes at temperatures between 150° C. and 350° C. can lead to very short decomposition times, on the order of minutes.

[0117] Said reactors are selected from (semi)continuous types, such as continuous stirred tank reactors (CSTR), and tubular reactors, such as loop reactors, plug flow reactors, oscillatory flow reactors, N-unit loop reactor systems, and batch reactors, and combinations thereof.

[0118] In exemplary embodiments of the present process, the decomposition is carried out at a temperature of from 50° C. to 500° C., preferably from 90° C. to 350° C., more preferably from 150° C. to 250° C., even more preferably from 170° C. to 220° C., such as from 180° C. to 210° C., for example, between 185° C. and 200° C. It is believed that the preferred ranges result in relatively milder temperatures than prior art processes, particularly those carried out at temperatures above 300° C.

[0119] In the exemplary process, the pressure is 90 kPa to 10,000 kPa, preferably 100 kPa to 8,000 kPa, more preferably 200 kPa to 2,000 kPa. The mild pressure in the exemplary process is an advantage over some prior art processes that often need to be carried out at relatively high pressures, e.g., 1000 kPa, in combination with high temperatures. In selecting a combination of temperature and pressure, [T,P] in the range of [180°C, 60 kPa] to [450°C, 8,200 kPa] can be selected.

[0120] In the exemplary method, the amount of catalyst is 0.001 to 35 wt.%, preferably 0.005 to 20 wt.%, more preferably 0.01 to 10 wt.%, even more preferably 0.05 to 0.15 wt.%, based on the total weight of the polymer fed. If the amount of catalyst is relatively high, a shorter reaction time can be obtained, but if the amount is relatively low, a longer reaction time is usually required. Depending on further boundary conditions, one can vary the amount of catalyst.

[0121] In the case of depolymerization of PET, the catalyst may for example be used in a catalyst:PET ratio (weight to weight) of 1:5 to 1:2500, such as 1:1000 to 1:1500. Further, for example, the amount of ethylene glycol:PET may vary from 1:2 to 1:20, such as 1:3 to 1:8. The waste polymer may relate to a single type of polymer, such as PET, PEF, PA, etc., and also mixtures thereof. It usually contains 50 to 99.9% by weight of a particular polymer, such as PET, with the remainder being impurities, other polymers, other compounds, etc.

[0122] Comparative experiment A: Complete conversion (FC) Depolymerization experiments were carried out using a 500 ml flask. A quantity of 0.027 g of ABC complex catalyst containing catalyst body C, iron containing nanoparticles A, and bridging moieties B connecting catalyst body C to the magnetic iron nanoparticles A was used in combination with 33.4 g of spent mixed-color polyethylene terephthalate (PET) flakes (approximately 10×10 mm pieces) and 250 g of ethylene glycol (EG). This resulted in a weight ratio of catalyst complex to PET of 1:1250 or 0.08 wt%. Figure 3 shows a photograph of the polyethylene terephthalate (PET) flakes used.

[0123] The round bottom flask was placed in a heating setup. Heating was started and after 20 minutes the reaction mixture reached a reaction temperature of 197° C. After 300 minutes at 197° C. the reaction was stopped by cooling to below 160° C.

[0124] The reaction mixture was transferred through a sieve filter into a centrifuge flask to remove residual solids. The residual solids present in the feedstock were collected in the amount of 1.3 g (non-PET material, e.g., polyethylene, polypropylene).

[0125] Water was added to the centrifuge bottle to give a water:EG ratio of 1:1. The mixture was centrifuged at 4000 rpm for 3 minutes. The supernatant was separated by decantation and cooled to crystallize the BHET product. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0126] To estimate the separation feasibility, the dried BHET and mother liquor were analyzed by XRF. As shown under A.FC in Figure 4, iron was detected in the dried BHET and mother liquor in amounts of 279 ppm and 18 ppm, respectively. The amount of dried BHET was 36.4 g. The separation efficiency was calculated to be 39%.

[0127] Comparative experiment B: Complete conversion without adding water (FC (anhydrous)) A similar procedure to that described for the depolymerization reaction in Comparative Experiment A was used.

[0128] After 300 minutes at 197° C., the reaction was stopped by cooling to below 160° C. Residual solids were removed by transferring the reaction mixture through a sieve filter into a centrifuge flask. 0.5 g of residual solids present in the feed were collected (non-PET materials, e.g., polyethylene, polypropylene).

[0129] The mixture was centrifuged at 4000 rpm for 3 minutes. The supernatant was separated by decantation and cooled to crystallize the BHET product. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0130] To estimate the separation feasibility, the dried BHET and mother liquor were analyzed by XRF. As shown under B.FC (anhydrous) in Figure 4, iron was detected in the dried BHET and mother liquor in amounts of 377 ppm and 2 ppm, respectively. The amount of dried BHET was 35.2 g. The separation efficiency was calculated to be 22%.

[0131] Example 1 Non-Complete Conversion (NFC) A similar procedure to that described for the depolymerization reaction in Comparative Experiment A was used.

[0132] After 120 minutes at 197° C., the reaction was stopped by cooling to below 160° C. Residual solids were removed by transferring the reaction mixture through a sieve filter into a centrifuge flask. 16.5 g of residual solids were collected consisting of unreacted PET and non-PET materials (e.g., polyethylene, polypropylene) present in the feed.

[0133] Water was added to the centrifuge bottle to give a water:EG ratio of 1:1. The mixture was centrifuged at 4000 rpm for 3 minutes. A clear layer of oligomers (containing the catalyst) was observed. The supernatant was separated by decantation and cooled to crystallize the BHET product. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0134] To estimate the separation feasibility, the dried BHET and mother liquor were analyzed by XRF. As shown under 1.NFC in Figure 4, 46 ppm and 2 ppm of iron were detected in the dried BHET and mother liquor, respectively. The amount of dried BHET was 17.2 g. The separation efficiency was calculated to be 90%.

[0135] Example 2 Incomplete conversion without adding water (NFC (anhydrous)) A similar procedure to that described for the depolymerization reaction in Comparative Experiment A was used.

[0136] After 120 minutes at 197° C., the reaction was stopped by cooling to below 160° C. Residual solids were removed by transferring the reaction mixture through a sieve filter into a centrifuge flask. 12.3 g of residual solids were collected consisting of unreacted PET and non-PET materials (e.g., polyethylene, polypropylene) present in the feed.

[0137] The mixture was centrifuged at 4000 rpm for 3 minutes. A clear layer of oligomers (containing the catalyst) was observed. The supernatant was separated by decantation and cooled to crystallize the BHET product. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0138] To estimate the separation feasibility, the dried BHET and mother liquor were analyzed by XRF. As shown under 2.NFC (anhydrous) in Figure 4, 28 ppm and 3 ppm of iron were detected in the dried BHET and mother liquor, respectively. The amount of dried BHET was 21 g. The calculated separation efficiency was 89%.

[0139] Example 3 Fully converted + non-fully converted (FC / NFC) A similar procedure to that described for the depolymerization reaction in Comparative Experiment A was used.

[0140] After 300 minutes at 197°C, the reaction was stopped by cooling to room temperature. 33.4 g of raw, post-consumer mixed-color polyethylene terephthalate (PET) flakes (approximately 10x10 mm pieces) were added to the reaction mixture. Heating was started and after 20 minutes the reaction mixture reached a reaction temperature of 197°C.

[0141] After 120 minutes at 197° C., the reaction was stopped by cooling to below 160° C. 14.1 g of residual solids consisting of unreacted PET and non-PET materials (e.g., polyethylene, polypropylene) present in the feed were collected.

[0142] Water was added to the centrifuge bottle to give a water:EG ratio of 1:1. The mixture was centrifuged at 4000 rpm for 3 minutes. A clear layer of oligomers (containing the catalyst) was observed. The supernatant was separated by decantation and cooled to crystallize the BHET product. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0143] To estimate the separability, the dried BHET and mother liquor were analyzed by XRF. As shown under 3.FC / NFC in Figure 4, 31 ppm and 4 ppm of iron were detected in the dried BHET and mother liquor, respectively. The amount of dried BHET was 50.95 g.

[0144] The results are summarized in Figures 4 and 5. Figure 4 shows the concentration of Fe (in ppm) found in the recovered BHET and in the mother liquor. Figure 5 shows the separation efficiency in percentage (%). The results show that in the process according to the invention the iron-based catalyst is recovered in a significant amount, i.e. at least 10 times more than in the prior art process. Indeed, only 28 to 46 ppm of catalyst remains in the obtained dried BHET and 2 to 4 ppm in the mother liquor, whereas according to the known process 279 to 377 ppm of catalyst are lost in the dried BHET. The catalyst separation efficiency is 80 to 90%, whereas in the prior art process it is only 22 to 39%.

[0145] Comparative experiment C: Complete conversion (FC) of transparent, colorless PET The depolymerization experiments were carried out using a 500 ml flask. A quantity of 0.027 g of ABC complex catalyst was used in combination with 33.4 g of transparent polyethylene terephthalate (PET) flakes (10×2 mm pieces) and 250 g of ethylene glycol (EG). Figure 6 shows a photograph of the transparent polyethylene terephthalate (PET) flakes used.

[0146] The round bottom flask was placed in a heating setup. Heating was started and after 20 minutes the reaction mixture reached a reaction temperature of 197°C. After 300 minutes at 197°C the reaction was stopped by cooling to below 160°C. The reaction mixture was transferred through a sieve filter into a centrifuge flask to remove residual solids. No residual solids were collected indicating complete conversion of the PET feedstock.

[0147] Water was added to the centrifuge bottle to give a water:EG ratio of 1:1. The mixture was centrifuged at 4000 rpm for 3 minutes. The supernatant was separated by decantation and cooled to crystallize the BHET product. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0148] To estimate the separation feasibility, the dried BHET and mother liquor were analyzed by XRF. As shown under C.FC in Figure 7, 161 ppm and 22 ppm of iron were detected in the dried BHET and mother liquor, respectively. The amount of dried BHET was 37.45 g. The calculated separation efficiency was 14%.

[0149] Example 4 Transparent colorless PET: Non-complete conversion (NFC) A similar procedure to that described for the depolymerization reaction in Comparative Experiment C was used.

[0150] After 180 minutes at 197° C., the reaction was stopped by cooling to below 160° C. Residual solids were removed by transferring the reaction mixture through a sieve filter into a centrifuge flask. Residual solids consisting of unreacted PET were collected in the amount of 8.36 g.

[0151] Water was added to the centrifuge bottle to give a water:EG ratio of 1:1. The mixture was centrifuged at 4000 rpm for 3 minutes. A clear layer of oligomers (containing the catalyst) was observed.

[0152] The supernatant was separated by decantation and cooled to crystallize the BHET product. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0153] To estimate the separation feasibility, the dried BHET and mother liquor were analyzed by XRF. As shown under 4.NFC in Figure 7, 75 ppm and 3.2 ppm of iron were detected in the dried BHET and mother liquor, respectively. The amount of dried BHET was 25.3 g. The separation efficiency was calculated to be 82%.

[0154] Example 5 Transparent, colorless PET: incomplete conversion and addition of preformed oligomers (NFC) Oligomers were made in a non-complete conversion NFC-depolymerization reaction. The experiment was carried out using a 500 ml flask. Zinc(II) acetate catalyst in an amount of 0.014 g was used in combination with 33.4 g of transparent polyethylene terephthalate (PET) flakes (10×2 mm pieces) and 250 g of ethylene glycol (EG). The round-bottom flask was placed in a heating setup. Heating was started and after 20 min the reaction mixture reached a reaction temperature of 197° C. After 120 min at 197° C., the reaction was stopped by cooling to below 160° C. The reaction mixture was transferred to a centrifuge flask through a sieve filter to remove residual solids. 10.9 g of residual solids consisting of unreacted PET were collected. Water was added to the centrifuge bottle to achieve a water:EG ratio of 1:1. The mixture was centrifuged at 4000 rpm for 3 min. The white precipitate layer consisting of (heavy) oligomers was collected at the bottom of the centrifuge jar (28.6 g) along with EG and water. Figure 9a shows a photograph of the preformed oligomer-containing centrifuge precipitate.

[0155] The same procedure was used for the depolymerization reaction described in Comparative Experiment C. After 300 min at 197° C., the reaction was stopped by cooling to room temperature.

[0156] A quantity of 28.6 g of white precipitate obtained from the NFC reaction with zinc(II) acetate was added to the reaction mixture as heavy oligomers. Heating was started and after 10 minutes the reaction mixture reached a temperature of 160° C. and the added oligomers dissolved. The reaction mixture was transferred through a sieve filter to a centrifuge flask to remove residual solids. No residual solids were collected, indicating complete conversion of the PET feedstock and complete dissolution of the added oligomers.

[0157] Water was added to the centrifuge bottle to achieve a water:EG ratio of 1:1. The mixture was centrifuged at 4000 rpm for 3 minutes. A clear layer of oligomers (containing the catalyst) was observed. The color of the precipitate changed from white to brown, as shown in the photograph in Figure 9.

[0158] Indeed, Figure 9 shows photographs of a) pre-prepared oligomer centrifuge precipitates and b) oligomer centrifuge precipitates after full conversion (FC) depolymerization / separation. The supernatant was separated by decantation and cooled to crystallize the BHET product. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0159] To estimate the separation feasibility, the dried BHET and mother liquor were analyzed by XRF. As shown in Figure 7 under 5.FC+ oligomers, 78 ppm and 2 ppm of iron were detected in the dried BHET and mother liquor, respectively. The amount of dried BHET was 37.3 g. The separation efficiency was calculated to be 80%.

[0160] The results are summarized in Figures 7 and 8. They show that in the process according to the invention, the iron-based catalyst is recovered in substantial quantities, i.e. more than in the prior art process. Indeed, only 75-78 ppm of catalyst remain in the obtained dried BHET and 2-3 ppm in the mother liquor, whereas according to the known process 161 ppm of catalyst are lost in the dried BHET. The catalyst separation efficiency is 80-82%, whereas in the prior art process it is only 14%.

[0161] Comparative experiment D: Transparent colorless PET: Full conversion (FC) Depolymerization experiments were carried out in a 500 ml flask using 0.034 g of MgO catalyst in combination with 33.4 g of transparent polyethylene terephthalate (PET) flakes (10×2 mm pieces) and 250 g of ethylene glycol (EG).

[0162] The round bottom flask was placed in a heating setup. Heating was started and after 20 minutes the reaction mixture reached a reaction temperature of 197° C. After 300 minutes at 197° C. the reaction was stopped by cooling to below 160° C.

[0163] The reaction mixture was transferred through a sieve filter into a centrifuge flask to remove residual solids. No residual solids were collected, indicating complete conversion of the PET feedstock. Water was added to the centrifuge bottle to achieve a 1:1 water:EG ratio. The mixture was centrifuged at 4000 rpm for 3 minutes. The supernatant was separated by decantation and cooled to crystallize the BHET product. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0164] To estimate the separation feasibility, the dried BHET and mother liquor were analyzed by XRF. As shown under D.FC(MgO) in Figure 10, 74 ppm and <10 ppm magnesium were detected in the dried BHET and mother liquor, respectively. The amount of dried BHET was 34.1 g. The calculated separation efficiency was 64%.

[0165] Example 6 Transparent colorless PET: Non-complete conversion (NFC) A similar procedure to that described for the depolymerization reaction in Comparative Experiment D was used.

[0166] After 120 minutes at 197° C., the reaction was stopped by cooling to below 160° C. Residual solids were removed by transferring the reaction mixture through a sieve filter into a centrifuge flask. 5.8 g of residual solids were collected, consisting of unreacted PET.

[0167] Water was added to the centrifuge bottle to give a water:EG ratio of 1:1. The mixture was centrifuged at 4000 rpm for 3 minutes. The supernatant was separated by decantation and cooled to crystallize the BHET product. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0168] To estimate the separation feasibility, the dried BHET and mother liquor were analyzed by XRF. As shown in Figure 10 under 6.NFC(MgO), 25 ppm and <10 ppm magnesium were detected in the dried BHET and mother liquor, respectively. The amount of dried BHET was 29.5 g. The separation efficiency was calculated to be 74%.

[0169] The results are summarized in Figures 10 and 11. They show that in the method according to the invention, the MgO catalyst is recovered in a significant amount, i.e. more than in the prior art method. Indeed, only 25 ppm of catalyst remains in the obtained dried BHET, whereas according to the known method 74 ppm of catalyst is lost in the dried BHET. The amount of MgO catalyst in the mother liquor was below the measurement limit and therefore could not be measured. The separation efficiency of the MgO catalyst is 74%, whereas in the prior art method it is 64%.

[0170] Comparative experiment E: Colored textile PET: Full conversion (FC) The depolymerization experiments were carried out using a 500 ml flask. An amount of 0.034 g of ABC complex catalyst was used in combination with 33.4 g of mixed-color polyethylene terephthalate (PET) textile (2.5×2.5 cm piece) and 250 g of ethylene glycol (EG). Figure 12 shows a photograph of the PET textile piece used.

[0171] The round bottom flask was placed in a heating setup. Heating was started and after 20 minutes the reaction mixture reached a reaction temperature of 197°C. After 180 minutes at 197°C the reaction was stopped by cooling to below 160°C. The reaction mixture was transferred through a sieve filter into a centrifuge flask to remove residual solids. No residual solids were collected indicating complete conversion of the PET feedstock.

[0172] Water was added to the centrifuge bottle to give a water:EG ratio of 1:1. The mixture was centrifuged at 4000 rpm for 3 minutes. The supernatant was separated by decantation and cooled to crystallize the BHET product. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0173] To estimate the separation feasibility, the dried BHET and mother liquor were analyzed by XRF. As shown under E.FC in Figure 13, 176 ppm and 2 ppm of iron were detected in the dried BHET and mother liquor, respectively. The amount of dried BHET was 35.8 g. The calculated separation efficiency was 12%.

[0174] Example 7 Colored textile PET: Non-complete conversion (NFC) A similar procedure to that described for the depolymerization reaction in Comparative Experiment E was used.

[0175] After 55 min at 197°C, the reaction was stopped by cooling to below 160°C. Water was added to the centrifuge bottle to give a 1:1 water:EG ratio. The mixture was centrifuged at 4000 rpm for 3 min. A clear layer of unreacted PET fibers and oligomers (containing catalyst) was observed. The supernatant was separated by decantation and cooled to crystallize the BHET product. The precipitate was collected in a vial. The BHET was filtered from the mother liquor using a Buchner filter and dried in a vacuum oven at 60°C.

[0176] To estimate the separation feasibility, the dried BHET and mother liquor were analyzed by XRF. As shown under 7.NFC in Figure 13, 8 ppm and 2 ppm of iron were detected in the dried BHET and mother liquor, respectively. The amount of dried BHET was 11.7 g. The separation efficiency was calculated to be 86%.

[0177] The results are summarized in Figures 13 and 14. They show that in the method according to the invention the iron catalyst is recovered in a significant amount, i.e. more than in the prior art method. Indeed, only 8 ppm of catalyst remains in the obtained dried BHET, whereas according to the known method 176 ppm of catalyst is lost in the dried BHET. The efficiency of separation of the iron catalyst is 86%, whereas in the prior art method it is 12%. [Explanation of symbols]

[0178] 10 Reactor vessel 11 First Entrance 12 Second Entrance 13 The Third Entrance 20 First filter unit 21 Exit 30 heat exchanger 31 mixture 32 Mixed logistics 32a Mixed logistics 32b Mixed logistics 32c mixed logistics 33 style 35 Another container 36 Entrance 40 Second Filter Unit 41 Pump 45 Source 46 Line 50 containers 51 Entrance 52 mixture 53 style 54 Mixed logistics 60 Centrifuge 61 First Separation Phase 62 Second Separation Phase 63 Line 64 lines 65 Line 70 Solvent Buffer Containers 71 Second Solvent Buffer Container 72 Line 80 Second reactor vessel 81 Entrance 82 Exit 83 Entrance 84 Entrance 90 Third Filter Unit 90 Reaction vessel 100 Reactor System 101 Reactor System

Claims

1. a) providing a polymer and a solvent in a reactor vessel to obtain a reaction mixture, the solvent being capable of reacting with the polymer to decompose the polymer into its monomers and oligomers; b) providing a reusable catalyst in the reaction mixture capable of catalyzing said decomposition; c) decomposing the polymer in the reaction mixture under decomposition reaction conditions to obtain a depolymerized mixture containing at least the monomer and light oligomers having 2 to 4 repeat units, inclusive; and removing unreacted polymer, solid particles, and superheavy oligomers having more than 200 repeat units from the depolymerized mixture upon exiting the reactor. d) recovering at least a portion of the reusable catalyst from the depolymerized mixture; e) recovering monomers and light oligomers from the depolymerized mixture; Including, During recovery of the reusable catalyst in step d), the depolymerized mixture contains heavy oligomers having at least 5 repeat units and at most 200 repeat units, 10. A method for depolymerizing a polymer, wherein the removal of unreacted polymer and superheavy oligomers having more than 200 repeat units from the depolymerized mixture after exiting the reactor is carried out before step d).

2. 2. The method according to claim 1, wherein during recovery of the reusable catalyst in step d), the depolymerized mixture contains heavy oligomers having at least 6 repeat units, preferably at least 8 repeat units.

3. 2. The process according to claim 1, wherein during recovery of the reusable catalyst in step d), the depolymerized mixture contains an upper limit of heavy oligomers of at most 100, even more preferably at most 50, even more preferably at most 40, even more preferably at most 30, and most preferably at most 20 repeat units.

4. The method of claim 1, wherein the heavy oligomer has repeating units of a polymer that are degraded.

5. 5. The method of claim 4, wherein the heavy oligomers are formed by decomposing the polymer in the reaction mixture under decomposition reaction conditions during step c).

6. 6. The method of claim 5, wherein the decomposition reaction in step c) is terminated early by removing the decomposition reaction conditions.

7. 7. The method of claim 5 or 6, wherein the decomposition reaction temperature and / or decomposition reaction time is reduced below that required for complete decomposition of the polymer into its monomers and light oligomers containing dimers, trimers, and tetramers.

8. 8. The method of claim 7, wherein the decomposition reaction time is at most 0.95 times, more preferably at most 0.8 times, more preferably at most 0.5 times the decomposition reaction time required for complete decomposition of the polymer into the monomers and light oligomers.

9. 10. The method of claim 1, wherein the heavy oligomers also contain oligomers having at least 5 repeat units of another polymer different from the polymer being degraded.

10. 10. The method of claim 9, wherein the other polymer comprises a condensation polymer that is decomposable by the solvent under the degradation reaction conditions.

11. 10. The method of claim 1, wherein the heavy oligomers are added to the depolymerized mixture after step c) and before or during step d).

12. 2. The process according to claim 1, wherein the amount of heavy oligomers in catalyst recovery step d) is in the range of 0.1 to 50% by weight, preferably 1 to 30% by weight, more preferably 5 to 25% by weight, based on the total weight of monomers and light oligomers in the depolymerized mixture.

13. 2. The method of claim 1, wherein the amount of monomers and light oligomers in the depolymerized mixture ranges from 5 to 95% by weight, preferably from 10 to 85% by weight, and more preferably from 15 to 75% by weight, based on the total weight of monomers, light oligomers, and heavy oligomers in the depolymerized mixture.

14. 2. The process of claim 1, wherein unreacted polymer and superheavy oligomers having more than 100 repeat units, preferably more than 50, even more preferably more than 40, even more preferably more than 30, and most preferably more than 20 repeat units are removed from the depolymerized mixture before step d).

15. 15. The method of claim 14, wherein the removed unreacted polymer and any extra-heavy oligomers are depolymerized in a separate second reactor vessel at substantially complete conversion to monomer and light oligomers by applying steps a) to c) of claim 1.

16. 16. The method of claim 15, wherein the fully depolymerized mixture resulting from the depolymerization in the second reactor vessel is introduced into the depolymerized mixture prior to step d).

17. 2. The method of claim 1, wherein other materials present in the depolymerized mixture, such as polyolefins, are at least partially, preferably completely, removed from the depolymerized mixture after step c) and before step d).

18. 2. The process of claim 1, wherein the catalyst recovery step d) comprises a phase formation step comprising forming a first phase containing mainly monomers and light monomers and a second phase containing mainly the heavy oligomers and catalyst, wherein the phase formation step comprises cooling the depolymerized mixture to a temperature preferably below 160°C.

19. 20. The method of claim 18, wherein the phase-forming step is carried out without substantially adding water to the depolymerized mixture.

20. 20. The method of claim 19, wherein the phase forming step is carried out using conditions such that the heavy oligomers at least partially precipitate from the reaction mixture.

21. 14. The method of claim 13, further comprising separating the first phase containing primarily monomers and light oligomers from the second phase containing primarily heavy oligomers and catalyst, wherein the separating step is carried out at a temperature less than 110°C.

22. 18. The method of claim 17, wherein the step e) of recovering the light monomers comprises, after the separation step, crystallizing the monomers and light oligomers from the first phase containing mainly light oligomers.

23. 2. The method of claim 1, wherein the step of providing a reusable catalyst comprises the step of recycling the recovered catalyst, preferably by adding the recovered catalyst from the second phase to the reaction mixture.

24. 10. The method of claim 1, wherein the step of providing a reusable catalyst further comprises adding heavy oligomers from the separate phase to the reaction mixture.

25. 2. The method of claim 1, wherein the solvent is a mono- or di-alcohol, optionally selected from ethylene glycol, propylene glycol and butylene glycol, preferably selected from ethylene glycol and diethylene glycol, more preferably ethylene glycol.

26. 2. The method of claim 1, wherein the polymer is a polycondensation polymer, preferably a terephthalate-containing homopolymer or copolymer.

27. The method of claim 1 , wherein the catalyst comprises a metal composition.

28. 27. The method of claim 26, wherein the catalyst comprises metal containing nanoparticles.

29. 27. The method of claim 26, wherein the catalyst comprises a catalyst complex containing a catalytic entity, a metal containing nanoparticle, and a bridging moiety connecting the catalytic entity with the magnetic nanoparticle.

30. - a first reactor vessel having at least one inlet for waste material and another inlet for supplying said first reactor vessel with a reusable catalyst capable of catalyzing a depolymerization reaction of a polymer, and an outlet configured to depolymerize said polymer into its monomers and oligomers, said outlet configured to discharge a depolymerized mixture; - a first filter unit disposed downstream of said outlet and configured to remove unreacted polymer, solid particles, and super-heavy oligomers having more than 200 repeat units from the depolymerized mixture after exiting the first reactor vessel, such that at least light oligomers having 2 to 4 repeat units, inclusive, and heavy monomers having at least 5 and at most 200 repeat units remain in the depolymerized mixture; a heat exchanger downstream of the outlet and the first filter unit; a separation unit downstream of the heat exchanger, preferably comprising at least one centrifuge, configured to recover at least a portion of the reusable catalyst from the depolymerized mixture and / or to recover monomers and light oligomers from the depolymerized mixture; - a conduit system connecting the reactor system components and pressure means for circulation through the conduit system, the conduit system including a feedback conduit for feeding back a recovered portion of the reusable catalyst into the first reactor vessel; 1. A reactor system for recycling waste materials containing polymers suitable for depolymerization, comprising:

31. 31. The reactor system of claim 30, wherein the first filter unit is configured to remove super heavy oligomers having more than 100 repeat units from the depolymerized mixture after exiting the first reactor vessel, even more preferably more than 50, even more preferably more than 40, even more preferably more than 30, and most preferably more than 20 repeat units.

32. 32. The reactor system of claim 30 or 31, further comprising a separate second reactor vessel adapted to receive the unreacted polymer and any super-heavy oligomers removed from the first filter unit, said second reactor configured to depolymerize the removed unreacted polymer and any super-heavy oligomers into monomer and light oligomers with substantially complete conversion.

33. 33. The reactor system of claim 32, wherein the second reactor vessel has an outlet configured to discharge the fully depolymerized mixture, and a conduit connecting the outlet with a heat exchanger.

34. 34. The reactor system of claim 33, wherein the conduit connecting the heat exchanger and the outlet comprises a third filter unit disposed downstream of the outlet and configured to remove solid particles from the fully polymerized mixture.

35. 31. The reactor system of claim 30, further comprising a second filter unit configured to at least partially, preferably completely, remove other materials present in the depolymerized mixture, such as, for example, polyolefins, from the depolymerized mixture, the second filter unit being located downstream of the heat exchanger and upstream of the separation unit.

36. 31. The reactor system of claim 30, further comprising: a source of heavy oligomers other than the first reactor vessel, the source having an outlet configured to discharge heavy oligomers from the source; and a conduit connected to the outlet and configured to add the heavy oligomers to the depolymerized mixture in or downstream of the heat exchanger and / or in or upstream from the separation unit.

37. 31. The reactor system according to claim 30, wherein at least one solvent buffer vessel is arranged upstream of the first reactor vessel and / or the second reactor vessel, and an inlet of the at least one solvent buffer vessel is connected to a feedback conduit and an outlet thereof is connected to the first reactor vessel and / or the second reactor vessel.

38. 31. The reactor system of claim 30, wherein the separation unit comprises a centrifuge or a plurality of centrifuges arranged in series, any of which may comprise a disc stack centrifuge.

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