Process for the recovery and utilization of polyesters and polyamides from waste polymer processing

Abstract

A method for recovering polyesters and polyamides from the corresponding polymer wastes, comprising: a) depolymerizing polyesters / polyamides to obtain linear and / or cyclic oligomers and / or monomers, b) recovering and purifying the products from step a), c) polymerizing the products from step b) by polycondensation and / or ring-opening polymerization. In step a), the depolymerization is partial, resulting in a mixture of oligomers, in particular including cyclic oligomers, and the aforementioned steps are carried out in polar and / or non-polar aprotic solvents at temperatures in the vicinity of the solvent boiling point between 100 and 300° C., in the presence of a catalyst, with simultaneous distillation of the reaction solvent and the volatile by-products dissolved therein.

Description

[Technical field]

[0001] The present invention relates to a process for the recovery and utilization of polyesters and polyamides from waste polymer processing. The technology is presented below with respect to a particular polymer of great industrial importance: polyethylene terephthalate (PET). [Background technology]

[0002] PET is currently produced from bis-2-hydroxyethyl terephthalate (BHET) by polycondensation (PC). This reaction requires three steps, shown in Figure 1: a step in the liquid state, a step in the molten state, and a step in the solid state. This progression of the reaction reflects a gradual increase in the viscosity of the polymer, resulting in long reaction times and the removal of the by-products of the reaction (especially ethylene glycol, EG). At high viscosities, such removal becomes extremely slow, taking times of the order of tens of hours for its completion. An alternative method proposed in the literature is ring-opening polymerization (ROP, shown in Figure 2). This process involves an initial stage of cyclic oligomer formation by cyclodepolymerization (CDP), which requires high dilution. Taking advantage of the resulting low viscosity, the removal of the by-products becomes very easy. The cyclic oligomers thus synthesized are then recovered, purified, and polymerized by ROP in about one hour, greatly shortening the polymerization reaction time. However, from an industrial point of view, this process is economically unattractive because the formation of cyclic oligomers is thermodynamically favorable only at high dilutions (typically concentrations of 10 g / l). Such conditions result in the need for very large quantities of solvents that are difficult to handle economically.

[0003] The processes using polycondensation as the synthesis method are the most widely used in industry. The polymer products are sold in the form of pellets and then processed by the manufacturing companies. Depending on the degree of polymerization achieved during the polymerization step (and therefore the corresponding physicochemical properties), several commercial applications are possible. In order of increasing quality, the pellets are used for the preparation of synthetic fibers, laminates, trays, bottles, and high-performance industrial materials.

[0004] Concerning the end-of-life fate of these polymer products, especially PET bottles, it should be noted that this will become plastic waste regardless of the process by which the polymer was generated. At this point, there are steps of collection, separation (not only by type of plastic but also by color, use and origin), washing and shredding to obtain so-called flakes. The quality (and therefore the cost) of these flakes depends precisely on the effectiveness of the previous separation, and therefore these materials will have different types of processing, as shown in Figure 3. The less valuable flakes are complete blends of different polymers, called PLASMIX. Such mixtures can be landfilled or incinerated or decomposed by pyrolysis into mixtures of low molecular weight compounds. Alternatively, by sorting and separation processes, it is possible to separate what is recovered from the separate waste collection into plastic materials of different qualities. In order of increasing quality, the inventors found that the following are synthetic fibers, multi-layer films and trays, opaque containers, colored bottles and transparent bottles. The latter are currently attracting strong interest, since they are the materials most in demand by recyclers, since they meet most of the requirements necessary for the effective operation of the different recycling systems.

[0005] The different flakes are the raw material for subsequent recycling processes that can be divided into two broad categories: chemical recycling and mechanical recycling.

[0006] Chemical recycling processes involve the depolymerization of PET up to its complete conversion into the monomers that form it. In some cases, the depolymerization is only partial, but the polymer thus recovered still requires sufficient repolymerization to return its molecular weight to the value required to make bottles. Often, the monomers recovered for cost, quality, and purity reasons must be mixed with virgin monomers to meet market and process demands. Chemical recycling processes have some advantages, using mixed flakes, and potentially also fibers, laminates, and films. They are versatile in terms of products (possibility of going back to different monomers, and even different compounds) and allow the removal of contaminants. On the other hand, they are generally operated by chemical companies, the only entities that can manage the plants that require large use of solvents, complex purification systems, and long process times. Moreover, the developers of these technologies are the same ones that produce and sell the virgin monomers and polymers. It is therefore a versatile and advantageous recycling system for those that already have a classical polycondensation system, since it allows the integration of the monomer supply with various proportions of recycled monomers. For the same reason, plants based on chemical recycling operate with high productivity, i.e. large volumes and very complex equipment. Currently, these processes constitute only a small percentage of recycling plants, still more at the prototype stage or on a laboratory and pilot scale. Although this type of process has several advantages, such as the possibility of recycling colored PET flakes, the removal of contaminants and its versatility in terms of products, it also has important drawbacks, especially related to the use of several chemical solvents that must then be properly recycled and disposed of.

[0007] For processes based on mechanical recycling, the inventors can distinguish two macro techniques, still shown in Figure 3: in their simplest application, they directly extrude the flakes to obtain PET in the form of pellets that may have different applications. However, mechanical recycling involves the pyrolysis of the polymer, thus obtaining PET of lower molecular weight than the starting PET. Typically starting from bottle flakes, a material is obtained that can be used for lower value products such as synthetic fibers. Such recycling systems are therefore called "open", or more explicitly "bottle to fiber". To overcome this limitation, the latest mechanical recycling processes, called Superclean, include a repolymerization step (solid state polymerization) immediately before or after the last extrusion step. Thereby, the final polymer is returned in a state of sufficient quality for the production of bottles, making the recycling system "closed" or "bottle to bottle". The strengths of this method are its cost-effectiveness, ease of implementation (no solvents required) and the process scale that can be adapted to the recycling needs (small scales are possible). On the other hand, no purification can be performed (except for partial removal of the most volatile contaminants), which forces the use of only high quality and expensive monochromatic flakes, making the process less flexible. Currently, over 80% of recycled bottles use mechanical recycling processes. Other forms of PET are too degraded by mechanical processes and therefore are not recycled.

[0008] It should be noted that the recycling process of the subject of the present invention (i) is applicable not only to high quality polyester (PET) for bottles, but also to polyester and polyamide fibers, and (ii) does not suffer from the drawbacks of the techniques described above.

[0009] Kamau SD et al.: “Cyclo-depolymerization of poly(propylene terephthalate): some ring-opening polymerizations of the cyclic oligomers produced polymers for advanced technologies, Wiley & Sons, Bognor Regis, GB, vol. 14, no. 7, 1 July 2003 (2003-07-01), p. 492-501 discloses a method for recycling polyester, in which the polyester polymer is first subjected to a cyclodepolymerization process to produce a mixture of cyclic oligomers that are used as starting monomers for the ring-opening polymerization.

[0010] EP3778744 A1 discloses a process for recycling post-consumer polyethylene terephthalate (PET) comprising partially depolymerizing the post-consumer PET to produce PET oligomers, followed by repolymerizing the partially depolymerized PET with the PET oligomers. The process produces a polymeric PET material comprising recycled PET oligomers. The process can also be combined or integrated with a virgin PET manufacturing process to produce a polymeric PET material composed of recycled PET oligomers and virgin PET monomers.

[0011] Hodge Philip ED - Liou guey-Sheng et al.: “Cyclodepolymerization as a method for the synthesis of macrocyclic oligomers”, Reactive and Functional Polymers, vol. 80, pp. 21-32, describes the preparation of macrocyclic oligomers by cyclodepolymerization of condensation polymers. This approach can provide a one-step synthesis of many macrocyclic molecules.

[0012] EP3606980 A1 discloses a process for the preparation of cyclic oligomers which involves reacting a polyester cyclic oligomer composition comprising polyester cyclic oligomers having 2 to 5 furan units. The process involves reacting a difunctional derivative of furan with a diol in a linear oligomerization step to produce a linear oligomer composition, followed by reacting the linear oligomer composition in a distillation-assisted cyclization (DA-C) step to form a polyester cyclic oligomer composition and removing the diol by-product by evaporation. Summary of the Invention

[0013] Applicant has now discovered a chemical process that contemplates partial cyclodepolymerization with simultaneous distillation of the solvent, yet is a fast process that can remove most of the by-products and contaminants. Moreover, by operating in the presence of a catalyst and at appropriate dilution, the polymer only partially decomposes, and the decomposition products are essentially cyclic oligomers. The recovered material is then ready to be repolymerized by ROP, reaching bottle grade in less than 30 minutes.

[0014] With respect to conventional chemical processes, this approach has the undisputed advantage that complete depolymerization is not required. Moreover, by reducing the process complexity and the number of solvents used compared to traditional chemical recycling processes, it is achievable not only by large industrial companies but also by small and medium-sized companies.

[0015] An object of the present invention is therefore a process for the recovery of polyesters and polyamides from the corresponding polymer waste, comprising the following steps: a) complete and / or partial depolymerization of polyester / polyamide to obtain linear and / or cyclic oligomers and / or monomers, b) recovery and purification of the product from step a); c) Polymerization of the product from step b). This process is characterized in that step a) is carried out in polar and / or non-polar aprotic solvents, starting from a concentration of said polymer product in said solvent of 10-800 g / l, at temperatures close to the boiling point of the solvent, between 100 and 300° C., in the presence of a catalyst, with simultaneous distillation of the reaction solvent and the volatile by-products dissolved therein. Only by carrying out step a) in this way is it possible to carry out a partial depolymerization, in which the mixture of oligomers consists mainly of cyclic oligomers. [Brief description of the drawings]

[0016] [Figure 1] The traditional pattern of industrial polymerization of PET by polycondensation is shown. [Diagram 2] The polymerization pattern of PET by ring-opening polymerization (ROP) is shown. [Diagram 3] The current separation and processing chain of the different polymer moieties is shown. In particular, materials suitable for the different processes are identified. [Figure 4] 1 shows the conversion results and number average molecular weights as a function of time obtained using conventional cyclodepolymerization (CDP) and distillation-assisted cyclodepolymerization according to the invention (DA-CDP) at different initial PET concentrations. [Diagram 5] More detailed block diagrams of the inventive processes are given below with regard to the second step of the process (purification and recovery of the product): in particular: in process b1) a system for selective separation and purification of polymeric and oligomeric fractions is illustrated; in process b2) a direct crystallization process with multi-stage washing with a single solvent or a mixture of solvents at constant and / or variable temperature is illustrated; in process b3) a direct crystallization process with countercurrent washing is illustrated. [Figure 6] With respect to the product leaving the third step of the process object of the present invention, Figure 6 shows: Conversion to PET as a function of reaction time, Number average molecular weight of the polymer as a function of reaction time, Number average molecular weight as a function of conversion to PET, on two different scales. [Figure 7]FIG. 7 is a block diagram illustrating one preferred embodiment of the continuous process of the present invention. [Figure 8] FIG. 8 is a diagram illustrating a preferred embodiment of a system in which the continuous process contemplated in FIG. 7 may be carried out. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] All these results refer to products leaving the third step (step c) of the process of the invention from polymer / oligomer mixtures obtained after recovery and purification steps (step b) by different methods. Such mixtures are called raw, hot, cold and mixed (cold + hot) and their characteristics are explained below.

[0018] For the purposes of the present invention, a definition of comprising does not exclude the presence of additional elements or steps not expressly stated following such definition.

[0019] For the purposes of the present invention, the definitions consisting of and consisting in do not exclude the presence of further elements or steps than those listed after such definition.

[0020] For purposes of this invention, cyclodepolymerization means a depolymerization that results in a mixture of polymers of different molecular weights, particularly high molecular weight polymers and low molecular weight cyclic oligomers.

[0021] For the purposes of the present invention, partial depolymerization means a depolymerization reaction in which the proportion of depolymerized polymer is between 0.1% and 80% by weight, preferably between 0.1% and 40% by weight, of the total weight of the starting polymer.

[0022] For the purposes of this invention, a) Polycondensation refers to a polymerization reaction involving the joining of two linear chains of any length with the release of low molecular weight by-products; b) Polymer chemical degradation refers to the depolymerization reaction, which is the opposite of polycondensation, and involves the cleavage of a polymer into two shorter chains, favored by the insertion into the chain of one or more molecules that promote polymer chain scission; c) polymer decomposition refers to the depolymerization reaction, which is the opposite of polycondensation, and involves the breaking of a polymer into two shorter chains by degradation of the polymer chain (e.g., mechanical, thermal, physical stress, oxidation, irradiation, etc.); d) Ring-opening polymerization or ROP is, alternatively, a polymerization reaction by cleavage of cyclic oligomers; e) Backbiting refers to the reverse cyclodepolymerization reaction of ROP and therefore involves scission of the polymer with the formation of shorter linear chains and cyclic oligomers; f) End-biting is a cyclodepolymerization reaction involving head-to-tail ring closure of oligomeric linear chains to form cyclic oligomers and low molecular weight by-products, while the reverse reaction is a ring-opening reaction triggered by the low molecular weight by-products to form oligomers with the same repeat units as the starting cyclic oligomer.

[0023] PET is produced in two main qualities: fiber grade and bottle grade. These standards differ primarily in their production recipes, such as average molecular weight, and the amounts and types of comonomers, pigments, and stabilizers.

[0024] For the purposes of this invention, fiber grade PET is intended to mean polyethylene terephthalate having a molecular weight of 15,000-20,000 g / mol and an intrinsic viscosity of 0.55-0.67 dl / g. Fiber PET for industrial yarns such as tire cords has a higher molecular weight (intrinsic viscosity 0.95 dl / g).

[0025] For purposes of this invention, bottle grade PET is intended to mean polyethylene terephthalate having a molecular weight of 24000-36000 g / mol and an intrinsic viscosity of 0.75-1 dl / g.

[0026] For the purposes of the present invention, high molecular weight polymers means polymers having a number average molecular weight of 20 000 to 40 000 g / mol.

[0027] Low to medium molecular weight oligomers are defined as oligomers having a molecular weight between 1000 and 3500 g / mol.

[0028] Very low molecular weight oligomers are defined as oligomers having a molecular weight between 200 and 1000 g / mol.

[0029] In the process according to the invention, polyester polymer products are understood to be all compounds having a proportion of polyester between 1 and 100%.

[0030] In the process according to the invention, polyamide polymer products are understood to be all compounds having a proportion of polyamide between 1 and 100%.

[0031] In the process according to the invention, polyester means all polymers belonging to the chemical categories polyethylene terephthalate (PET), polyethylene furanoate (PEF), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), poly(butylene adipate-terephthalate) (PBAT), polytrimethylene terephthalate (PTT), polybutylene succinate (PBS), unsaturated polyester (UPE), polylactic acid (PLA), polyhydroxyalkanoates (PHA), etc.

[0032] In the process according to the invention, polyamide means all polymers belonging to the chemical categories such as polyamide 6 (nylon 6), polyamide 11 (nylon 11), polyamide 12 (nylon 12), polyamide 66 (nylon 66), polyamide 610 (nylon 610), polyamide 66 / 610 (nylon 66 / 610), polyamide 6 / 12 (nylon 6 / 12), polyamide 666 (nylon 666 or 6 / 66), polyamide 6 / 69 (nylon 6 / 69), nylon 1010, nylon 1012, polyarylamides, polyaramids (Kevlar®), polyphthalamides, polyamidoamines, etc.

[0033] In the method according to the invention, flakes of polyethylene terephthalate bottles, i.e. shredded / crushed PET bottles, are preferably employed as polymer waste.

[0034] Other waste materials used as starting materials are polyester packaging containers such as food trays, films, etc.

[0035] Other waste materials used as starting materials are polyamide plastic products such as automotive parts, tubes, containers, packaging, industrial materials, etc.

[0036] Other waste materials used as starting materials are shredded polyester fibres such as from shoes, clothing, covers, cords etc., and polyamide fibres such as Nylon 6, Nylon 6,6 and Kevlar.

[0037] For purposes of this invention, stabilizers are antioxidant compounds, such as polysubstituted phenols, phosphites, and the like, commonly used to prevent degradation of polymers during processing.

[0038] For the purposes of this invention, a performer is a compound capable of modifying the rheological and mechanical properties of a polymer.

[0039] In the process according to the invention, in step a), the cyclodepolymerization is carried out by simultaneous distillation of the solvent, whereby in addition to the solvent, low-boiling by-products, including ethylene glycol and water in the particular case of PET, are also removed.

[0040] The aprotic polar solvent is preferably selected from diaryl ethers, mono / di / tri-C1-C3-alkoxybenzenes, aryl-C1-C3-alkyleneoxy-C1-C5-alkanes, di-(aryl-C1-C3-alkylene)-ethers, aryl-C1-C3-alkylene-oxo-benzenes, C4-C6 cycloalkyl-ketones, where aryl is phenyl or phenyl substituted with one or more linear or branched C1-C3 alkyl residues.

[0041] More preferably, the solvent is selected from diphenyl ether, 1,3-dimethoxybenzene, benzyl methyl ether, benzyl butyl ether, dibenzyl ether, cyclohexanone, benzophenone, more preferably diphenyl ether.

[0042] The non-polar solvent is preferably a C5 to C8 linear hydrocarbon, more preferably n-hexane.

[0043] Step a) of the process according to the invention is preferably carried out at a pressure between 100 and 1000 mbar, more preferably between 200 and 500 mbar, more preferably in the presence of an inert gas, even more preferably under nitrogen.

[0044] The catalyst is selected from cyclic tin octoate, dibutyltin oxide, tin 2-ethylhexanoate, more preferably tin 2-ethylhexanoate. The concentration of the catalyst is preferably 0.001-0.5% weight / weight of the polymer product.

[0045] The concentration of the polymer in the solvent in step a) is preferably between 10 and 800 g / l, more preferably between 50 g / l and 400 g / l.

[0046] In particular when the polymer waste is PET bottle flakes or polyester fibres, step a) is preferably carried out by using diphenyl ether as solvent at a reaction temperature of 100-240° C., at a pressure of 100-1000 mbar, preferably in an inert gas, more preferably in nitrogen, for a time period of 1-5 hours.

[0047] According to a particularly preferred solution, when the starting polymeric material consists of colored polyethylene terephthalate bottle flakes, the solvent of step a) is diphenyl ether and step a) is carried out at a temperature of 200-224°C, at a pressure of 200-600 mbar and for a time of 2-4 hours.

[0048] Step a) of the process is the depolymerization. This treatment causes a reduction in the molecular weight of the polymer, due to chemical degradation and backbiting (or cyclodepolymerization) reactions. As already known in the literature (and verified experimentally), normal cyclodepolymerization without evaporation of the solvent is accompanied by a progressive decrease in the production of cyclic oligomers as the PET concentration increases. This behavior is shown in Figure 4 (left graph) and is a consequence of the fact that backbiting reactions become less favorable with increasing PET concentration. At very high dilutions, such depolymerization is practically complete, forming almost exclusively cyclic oligomers.

[0049] If the same reaction is carried out with simultaneous distillation (Figure 4, right graph), several advantages are obtained: 1) Elimination of volatile contaminants originally present in the waste polymer as well as any volatile impurities associated with the use of the polymer during its life (mechanical degradation, absorption of contaminants, flavorings, etc.). 2) Distillation can eliminate the by-products of the aforementioned reactions, such as ethylene glycol and water, increasing the conversion to cyclic oligomers. This occurs because the elimination of the by-products favors the end-biting reaction. For example, working with a polymer concentration of 100 g / l (yellow line), the cyclic oligomer content goes from about 20% in the case of cyclodepolymerization alone to about 40% in the case of distillation-assisted cyclodepolymerized DA-CDP. 3) At the same time, elimination of the by-products provides a second benefit: by removing the reaction by-products, polycondensation reactions are favored which increase the molecular weight of the undepolymerized polymer even beyond that required for bottle grades.

[0050] In other words, the classical process of cyclodepolymerization involves the depolymerization of polymers with the formation of cyclic oligomers supported by high dilution. Under the same operating conditions, the combined use of distillation results in (i) an increase in the yield of cyclic oligomers, (ii) an increase in the molecular weight of the residual polymer, and (iii) the elimination of volatile contaminants.

[0051] Step b) of the process of the invention comprises several solutions for purifying the product of step a). The first possibility b1) allows the separation of polymers and oligomers and comprises preferably four stages in succession, the latter being optional. The second possible route b2) comprises a direct purification system with cross-flow multi-stage washing. The third possible option b3) comprises a direct purification process with countercurrent multi-stage washing, preferably with successive washing and extraction processes. An exemplary diagram summarizing the different possible options is shown in FIG. 5.

[0052] A possible purification system b1) is called "high-low temperature separation and purification system". It involves the selective separation of high, medium, low and very low molecular weight compounds by operating on selective precipitation and washing of the collected fractions.

[0053] The first (step b1.1) preferably comprises the elimination of insoluble impurities by filtration, centrifugation or decantation of the reaction mixture from step a) at the solvent boiling point. These insoluble impurities are different and can be, for example, inorganic fillers (additives added to facilitate the processing of the polymer during the preparation of the product), metals (typically catalysts added during the synthesis of the polymer) and other insoluble plastics in the reaction solvent (residues of different polymers due to incomplete separation of the flakes).

[0054] The subsequent step b1.2) comprises the process of cooling the reaction mixture to a temperature at which the high molecular weight polymer fraction (not depolymerized) precipitates and is recovered by filtration; for PET this temperature is between 140 and 180°C, preferably between 140 and 160°C.

[0055] After removal of the polymer, the subsequent step b1.3) involves a system in which the permeate undergoes further cooling to about room temperature. Low and medium molecular weight cyclic oligomers precipitate at this temperature and are still recovered by filtration.

[0056] Finally, the process of the present invention may comprise a step b1.4) in which a hydrocarbon solvent, preferably n-hexane, is added to the filtered solution from step b1.3) to allow precipitation of lower molecular weight oligomers.

[0057] If the waste material is polyethylene terephthalate flakes and the solvent in step a) is diphenyl ether, the cooling temperature in step b1.2) is 140-160°C and the temperature at which the product is washed in step b1.2) is 90-120°C.

[0058] Both the precipitate consisting essentially of unreacted polymer recovered at boiling point (high temperature) and the oligomers precipitated at room temperature (low temperature) appear as white powders, since any dyes remain in solution. The slight color is associated with the residue of solvent containing the original dyes of the waste polymer. If the precipitation is carried out by direct cooling to room temperature, a solid powder consisting of PET and cyclic oligomers is obtained, which retains all non-volatile impurities and dyes. Such a product is designated as unpurified before solvent removal.

[0059] A possible purification system b2) is called "Direct separation and purification system in cross-flow washing". This process makes it possible to directly obtain a polymer-oligomer mixture by operating in cross-flow purification. The first (step b2.1) comprises a step of eliminating insoluble impurities, preferably by filtration, centrifugation or decantation of the reaction mixture from step a) at the solvent boiling point. These insoluble impurities are different and are, for example, inorganic fillers (additives added to facilitate the processing of the polymer during the preparation of the product), metals (typically catalysts added during the synthesis of the polymer) and other insoluble plastics in the reaction solvent (residues of different polymers due to incomplete separation of the flakes).

[0060] The next step b2.2) involves cooling the reaction mixture to approximately room temperature and precipitating the high molecular weight (non-depolymerized) polymer fraction together with the low and medium molecular weight cyclic oligomers. After crystallization, the solid from step b2.2) is then washed and purified in a cross-flow multi-stage process. In the latter step, the contaminant-rich solvent from step a) is first removed and the resulting residual solid product is washed with pure solvent. Successive washes can be performed with the same solvent or / and different solvents as used in step a). Multiple washing processes can be performed with variable washing solvent temperatures, for example increasing or decreasing along the washing process. Typically used temperatures cover the range from ambient temperature to the boiling point of the washing solvent used. This process allows for greater flexibility in the purification and washing processes.

[0061] A possible purification system b3) is called "direct separation and purification system with countercurrent washing". This process makes it possible to directly obtain a polymer-oligomer mixture by operating in countercurrent purification. The first (step b3.1) comprises a step of eliminating insoluble impurities, preferably by filtration, centrifugation or decantation of the reaction mixture from step a) at the solvent boiling point. These insoluble impurities are different and are, for example, inorganic fillers (additives added to facilitate the processing of the polymer during the preparation of the product), metals (typically catalysts added during the synthesis of the polymer) and other insoluble plastics in the reaction solvent (residues of different polymers due to incomplete separation of the flakes).

[0062] The next step b3.2) involves the cooling of the reaction mixture to approximately room temperature and the precipitation of the high molecular weight (non-depolymerized) polymer fraction together with the low and medium molecular weight cyclic oligomers. After crystallization, the solid from step b3.2) is then washed and purified in a countercurrent multi-stage process. In the latter step, the contaminant-rich solvent from step a) is first removed and the resulting residual solid product is washed with pure solvent. The washing can be carried out with the same solvent or / and with a different solvent than that used in step a). The process of washing and extracting the contaminants can be carried out continuously, for example with a variable washing solvent temperature that increases or decreases along the washing process. Typically used temperatures cover the range from ambient temperature to the boiling point of the washing solvent used. This process allows for greater flexibility in the purification and washing process as well as a significant reduction in the amount of solvent used.

[0063] The polymerization reaction or step c) of the process is preferably carried out at a temperature between 220 and 280° C., with a nitrogen flow and without the addition of further catalyst.

[0064] To study the influence of the starting materials on the progress of the reaction, four different starting materials were tested: the two already described hot and cold precipitates, an unpurified precipitate, and one obtained by mixing hot and cold in a ratio such as to reproduce the PET and cyclic oligomers content of the unpurified product (mixture). The latter material therefore represents the equivalent of the unpurified material, but without residual solvents, pigments, and other impurities.

[0065] Figure 6 shows the number average molecular weight data measured as a function of conversion from the various materials described here to polymers obtained by ROP. In all cases it was possible to produce recycled polymers capable of meeting the specified bottle grades. As expected from the average molecular weight data as a function of conversion (Figure 6, bottom right graph), the high temperature material repolymerizes almost exclusively by polycondensation, while the low temperature material repolymerizes by ROP. If a mixture, called mixed (high temperature + low temperature), is used as a reagent, both polymerization reactions are present. The raw material has a short initial induction period (Figure 6, conversion-time graph), probably due to the presence of a solvent whose evaporation limits the reaction temperature in the first step, but is followed by fast kinetics. The molecular weight increase is also very fast, but is followed by a rapid deterioration purely, which is surely due to the presence of residual contaminants.

[0066] Based on these results, it was determined that the most promising material would precipitate as a purified mixture (mixture) of PET and cyclic oligomers. It was then verified that such a material could also be obtained by direct precipitation at a temperature that would ensure good recovery of the polymer and oligomers while keeping the solvent-soluble dyes and other impurities or additives in solution. In this case, if the waste is PET flakes or fibers, the preferred temperature is 25-30°C. Finally, it is preferable to rinse the precipitate with hot solvent, preferably at a temperature of 90-120°C, to eliminate impurities.

[0067] According to the invention, the repolymerization step c) can be carried out using any of the products of step b) in its possible variants: the high molecular weight polymer from step b1.2), low / medium molecular weight oligomers from step b1.3), the lower molecular weight oligomers from step b1.4), the polymer-oligomer mixture from purification method b2), · Polymer-oligomer mixtures from purification method b3).

[0068] Alternatively, step c) of the process of the invention can be carried out starting from a mixture of the products detailed in the list above.

[0069] Finally, in step c), dyes, stabilizers and additives (performers) are preferably added in order to make it possible to obtain a final polymer with the same applicability as the virgin polymer.

[0070] The physicochemical equivalence between the polyester obtained by the process according to the invention without additives and the virgin polymer is confirmed by the equal transmittance values ​​of the two materials.

[0071] Applicants have further found that food contaminants associated with normal use of the polymer, for example in PET bottles, can also be removed by the method of the present invention. This is achieved in a process where precipitation of the polymer is carried out followed by washing the precipitate with a solvent such as diphenyl ether.

[0072] To verify this, we followed Regulation (EC) no. 282 / 2008, which requires challenge tests, i.e. the introduction of known amounts of contaminating compounds (surrogates) and tracking of their subsequent removal until residual concentration values ​​that do not indicate a risk to human health.

[0073] For the test, two cases were chosen to study: one with a low contamination level and one with a high contamination level. To simulate the absorption of food flavors in PET, the flakes were soaked in a 2.5% solution of limonene and methanol, left at 50 °C for 12 to 72 hours. The stabilizer was instead inserted directly into the reaction environment, at 0.15% in one case and 0.5% in the other. The results of the analysis on the distillate allowed the verification of how, after 5 hours of reaction, not only EG and water but also a small amount of the volatile additive methanol (boiling point 209 °C) were eliminated, the removal of which was estimated at 81% in the low contamination case.

[0074] Considering the overlap of the characteristic peaks of the flavorings and stabilizers, the removal efficiency was quantified by defining the following three parameters: PET / impurity ratio, PET purity, and residual solvent / PET ratio (diphenyl ether was used as the solvent for these tests).

[0075] By simply rinsing with pure solvent, preferably at temperatures between 90 and 120 °C, the "dirty" solvent remaining in the filtered polymer can be replaced by "clean", i.e. solvent free of impurities (flavorings and stabilizers of the polymer). Thereby, an overall removal of impurities of 84 and 97% was estimated in two cases. Moreover, the total removal of methanol in the two process steps a) (DA-CDP) and b) (filtration) reaches values ​​between 95 and 99.5%.

[0076] Finally, impurities constituted by residual solvents are eliminated during the polymerization or step c). Indeed, after 10 minutes of reaction under nitrogen flow, 99.99% of the solvent was seen to be removed, and after another 20 minutes under vacuum, traces of residual solvent reached values ​​below the sensitivity threshold of the NMR 300 Mhz used for characterization. It can therefore be stated that the final solvent concentration is estimated at 10 ppm, lower than the state-of-the-art sensitivity.

[0077] In particular, if in step b) high-temperature precipitation of the by-products is followed by direct low-temperature filtration and subsequent washing with pure solvent, in step c) of the polymerization up to 99.5% removal of semi-volatile compounds, up to 97% removal of heavy compounds and even more than 99.9% removal of solvent are obtained.

[0078] A further object of the invention is a process according to the invention, wherein at least one of steps a) to c) is carried out continuously.

[0079] A further object of the invention is a process according to the invention, wherein at least two of steps a) to c) are carried out successively.

[0080] A further subject of the invention is a process according to the invention, in which all steps a) to c) are carried out continuously.

[0081] One preferred embodiment of the continuous process of the present invention is shown in the block diagram of FIG.

[0082] After passing through the separation process, the plastic waste is introduced into the first continuously operating reactor, called DACDP, together with the catalyst and premixed solvent. This reactor consists of a continuously operating system in which the cyclodepolymerization reaction occurs along with distillation. The type of reactor can be of the continuous stirred tank reactor (CSTR) type, for example a reactor selected from paddle mixer reactors, ribbon mixer reactors, etc., designed to ensure effective removal of volatile components and solvents.

[0083] After a residence time of 20 min to 2 h, the product obtained at the bottom of the reactor, consisting of unreacted polymer and its solvent-solubilized oligomers, is pumped through continuous and / or semi-continuous filtration systems such as membrane filtration, permeation, press filters, filter presses, etc., to separate the solid stream (polymer + oligomers) from the solvent rich in non-volatile contaminants.

[0084] The polymer thus collected is then sent to a repolymerization system which may consist of a drying system (e.g., a drum) and subsequently undergoes direct repolymerization in an extruder or a combined drying-repolymerization system operating in conjunction with an extruder including a degassing and devolatilization system.

[0085] All solvent streams are conveyed to a solvent regeneration system that may operate by distillation, microfiltration, or adsorption, so that the regenerated solvent can be reused in a closed loop within the described process.

[0086] FIG. 8 shows the layout of a preferred embodiment of a system in which the continuous process contemplated in FIG. 7 may take place.

[0087] As can be seen from the diagram, the solvent coming from the storage tank (solvent storage) is partly sent to the reactor where it is mixed with the catalyst before entering the DACDP depolymerization plant. The polymer recycled from the associated tank (polymer storage) is also fed to the reactor through line 6. The depolymerized product leaves the bottom of the DACDP reactor together with the unreacted polymer and is subsequently sent, after cooling, to the solid solvent separator. The recovered solids are passed through a filter (washing filter) and washed with solvent, partly coming from the storage tank (lines 2 and 15) and partly from the solvent separated in the solvent solid separator. The solid product leaving the wash is sent to the reaction extruder through line 11 and then to the recycled polymer storage tank.

[0088] The distilled solvent stream in the DACP (line 13), that of the solvent leaving the solvent solids separator (line 14) and that coming from the wash (line 16) are sent to the solvent regenerator, from where the regenerated solvent leaves overhead and is sent to a storage tank through line 18, while all waste and impurities are conveyed to a waste tank through line 19.

[0089] Some examples of the process of the invention carried out discontinuously are given below for the purpose of illustrating, but not limiting, the process according to the invention.

[0090] I) Materials used in the reactions and related analyses described in the Examples: Swiss Alpina Bottle, CocaCola® Bottle, Sprite® Bottle, Fant® Bottle, Valser® Bottle, Rivella Fresh® Bottle, 2-Isopropyl-5-methylcyclohexanol (Menthol, Merck, 98%), p-Mentha-1,8-diene (Limonene, Merck, 98%), Irganox® B 561 FF (BASF), Irgafos® 126 (BASF), Dibutyltin Oxide (Bu2SnO, Merck, 98%), Anhydrous Ethylene Glycol (EG, Sigma Aldrich, 99.8%), Diphenyl Ether (DPhE, Aldrich, Reagent Plus®, 99%), trifluoroacetic acid (TFA, Fluorochem, 99%) and potassium trifluoroacetate (K-TFAc, Aldrich, 98%), dichloromethane (DCM, Fisher, 99.99%), hexafluoroisopropanol (HIP, Fluorochem, 99.9%). Chloroform-d (CDCl3, Armar Chemicals, 99.8%) and trifluoroacetic acid-d (TFA-d, Cambridge Isotope Laboratories, 99.5%) were mixed in a ratio of 3:1. The initiator and dibutyltin oxide were stored in a glove box under nitrogen atmosphere. To compare the recycled PET (r-PET) obtained by the process of the present invention with bottle-grade PET, a sample of the latter was taken from a PET bottle.

[0091] To estimate the accuracy of the molecular weight analysis method, PET and PMMA standards were obtained from PSS (Polymer Standards Service, Germany).

[0092] II) Analysis 1H NMR (300 MHz) spectra were recorded on a Bruker Avance III spectrometer. The NMR spectra were compared with those of residual solvent. The conversion values ​​and the weight and number average molecular weights Mn and Mw of the PET samples were determined by size exclusion chromatography (SEC). An Agilent 1100 GPC / SEC unit equipped with a PFG M(PSS) linear column connected to an Agilent 1100 VWD / UV detector operating at 313 nm, a DAWN HELEOS II multi-angle laser followed by an Optilab TrEX RI refractive index detector (both from Wyatt Technology Europe) was used for this purpose. The samples were eluted with HFIP spiked with 0.03 M K-TFAc at 1 mL / min at room temperature. The conversion was measured as the percentage of PET to the total UV signal area using WinGPC Unichrom PSS software. The absolute molecular weight was measured using Wyatt ASTRA software (dn / dc(PET)=0.249 mL / g). NMR measurements were performed using PET samples at a concentration of 0.4 mg / mL dissolved in pure TFA-d or in a 1:3 volume ratio of TFA-d / CDCl3.

[0093] Example 1. Distillation-assisted partial (cyclization) depolymerization of PET bottles A four-neck flask equipped with a magnetic stirrer or alternatively with a mechanical stirrer through one of the necks was used and heated by a heating mantle. The first neck was used to measure the reaction temperature. A second side neck was used to take reaction samples with a spatula during the reaction. These samples were then dried in an oven at 120°C. The center neck was fitted with a Vigreux column with a condenser on top, to which the flask was connected to collect the vapours. The latter was previously oven dried and used to measure the condensate collection rate, i.e. the distillation rate. The composition of the collected distillate was measured by NMR.

[0094] Diphenyl ether solutions with different PET flake concentrations (1, 5, 10, and 20 g PET in 100 mL DPhE, corresponding to 10, 50, 100, and 200 g / l, respectively) were prepared. The PET flakes were previously obtained from the corresponding bottles, cut into square flakes with a size of about 1 cm, and dried in a vacuum oven at 130° C. for 30 min.

[0095] The reaction temperature was raised to the boiling point of the solvent and, after complete dissolution of the PET, the catalyst was added at a concentration of 0.01-0.1%. The reaction was allowed to proceed at the boiling point, under magnetic stirring at 600 rpm, for 6 hours at a pressure of 300-500 mbar. This reaction time was in excess of what was required and a more complex kinetic analysis was considered.

[0096] During the reaction, the pressure was regulated by a vacuum pump. Both the reaction temperature and the temperature inside the Vigreux column were measured with two K-type thermocouples.

[0097] At the end of the reaction, the reaction product was recovered according to the procedure reported in Example 3.

[0098] The mole fractions of each component in both the reaction mixture and the distillate were determined by 1H-NMR (in CDCl3 and CDCl3 / TFA-d 3:1, respectively).

[0099] Example 1-A. Conventional Cyclodepolymerization of PET Bottle Flakes A 250 mL three-neck flask heated by an oil bath placed on a magnetic heating plate was used as the reactor. The first side neck was used to measure the reaction temperature using a thermocouple. The second side neck was used to remove reaction samples with a spatula during the course of the reaction. These samples were then dried in an oven at 120° C. An outlet was attached to the center neck to condense the vapors.

[0100] Diphenyl ether solutions with different PET flake concentrations (1, 5, 10, and 20 g PET in 100 mL DPhE, corresponding to 10, 50, 100, and 200 g / l, respectively) were prepared. PET flakes were previously obtained from the corresponding bottles, cut into square flakes with a size of about 1 cm, and dried in a vacuum oven at 130 °C for 30 min. During the reaction, the temperature was increased to boiling and after complete dissolution of the PET, the catalyst was added at a concentration of 0.01-0.1%. The reaction was maintained at the boiling point for 6 h under stirring at 600 rpm. The reaction was then quenched by cooling and the final solution was filtered. The distillate compositions, such as those of the reaction mixtures, were measured by 1H-NMR (in CDCl3 and CDCl3 / TFA-d 3:1, respectively) as described in Example 1.

[0101] The results obtained in this example are reported and compared with those obtained with the method of the invention reported in Figure 5. The advantages emerging from the analysis of these graphs have been discussed above (pages 10-11, lines 25-33 and 1-12).

[0102] Example 2. Distillation-assisted partial (cyclo)depolymerization of PET bottles to remove contaminants A 250 mL electrically heated three-neck flask equipped with a magnetic stirrer was used as the reactor. The first side neck was used to measure the reaction temperature. Samples of the reaction mixture were taken from the second side neck during the reaction using a spatula pre-dried in an oven at 120° C. A Vigreux column was fitted to the center neck. A condenser was placed on top of the aforementioned column to condense the vapors and collect the condensate in a flask pre-dried in an oven at 120° C. The amount collected over time was weighed and the distillation rate was measured while the composition of the distillate was evaluated by NMR.

[0103] Diphenyl ether solutions were prepared with different PET flake concentrations. The PET flakes were previously obtained from the corresponding bottles, cut into square flakes with a size of about 1 cm, dried in a vacuum oven at 130 °C for 30 minutes, then left to soak in an aqueous solution of 2.5% m / m methanol and 2.5% m / m limonene at 50 °C under stirring for 24-72 hours. The addition of Irganox® B 561 FF and Irgafos® 126 in concentrations of 0.15-0.5% was made directly in the reactor at the same time as the addition of the flakes. The temperature was increased to boiling and after complete dissolution of the PET, the catalyst was added in concentrations of 0.1-0.05%. The reaction mixture was kept stirred at 600 rpm with a magnetic stirrer at boiling point at 300-500 mbar for 6 hours. The pressure was controlled by a vacuum pump.

[0104] The reaction was then switched off. The reaction products were collected according to the operating methods described in Examples 3 and 4. The temperatures in the Vigreux column and in the reaction column were measured with two K-type thermocouples. The composition of the distillate and the composition of the reaction mixture were measured by 1H-NMR in CDCl3 and CDCl3 / TFA-d 3:1, respectively.

[0105] Example 3. Separation method for selective thermal precipitation (step b1) After the assisted cyclodepolymerization (DA-CDP), the reaction mixtures of Examples 1 and 1A are filtered at the boiling point of the solvent to eliminate insoluble products such as inorganic fillers, metals, and any other polymer residues that are insoluble in the reaction solvent. The solution is then cooled to 150-160°C. At these temperatures, the high molecular weight compounds precipitate, which are then separated by filtration through a Buchner filter. The filtered solution is then further cooled to a temperature of 25-30°C. At this temperature, the low / medium molecular weight oligomers precipitate, which are recovered by filtration through a Buchner filter. The filtered solution is treated with n-hexane to precipitate the very low molecular weight oligomers, which are finally separated by filtration.

[0106] Example 4. Separation method for direct cryoprecipitation (steps b2) and b3) After the assisted cyclodepolymerization (DA-CDP), the reaction mixtures of Examples 1 and 1A are filtered at the boiling point of the solvent to eliminate insoluble products such as inorganic fillers, metals, and any other polymer residues that are insoluble in the reaction solvent.

[0107] The solution is then cooled to 25-30° C. At this temperature, both the high molecular weight polymer and the low / medium molecular weight oligomers precipitate. The precipitate is separated by filtration on a Büchner filter. The retentate collected on the filter is treated with DPhE to wash the solids, preferably at a temperature of 20-120° C., to eliminate residual contaminants by a multiple wash (as in variant b2) of step b) described above) or countercurrent (as in variant b3) of step b) described above) system.

[0108] The contaminant content was assessed by NMR analysis using CDCl3 / TFA-d in a volume ratio of 3:1 as the solvent.

[0109] Example 5. Polymerization and characterization of the product 500 mg of the reaction mixture obtained as described in Examples 3 and 4 was placed in a 5 ml Schlenk tube reactor and 1500 mg of the same mixture was placed in a 10 ml Schlenk tube reactor. Both reactors were placed in a heater block and dried under vacuum for about 30 minutes. The reactors were removed from the heater block and the vacuum was replaced with nitrogen.

[0110] Set the desired temperature (240-280 °C) with the heater block and return the reactor to the heater block.

[0111] Samples are taken during the reaction using a spatula previously dried in an oven at 120 °C. After the desired time (10-60 min), the reaction is quenched by immersing the Schlenk tube in ice water.

[0112] The resulting polymer (hereafter referred to as r-PET to distinguish it from virgin polymer) is dissolved in pure HFIP and subsequently precipitated by the addition of THF. The product is then collected by filtration or centrifugation.

[0113] An alternative methodology involves dissolving the reaction product in pure HFIP, followed by evaporation of the solvent overnight under an exhaust hood. The solid is dried under vacuum at 80° C. to give a white product. The solid is analyzed by NMR (1H NMR (300 MHz, 25° C., TFAd) (ppm)=7.45 (s, 2H, -CH-Ar-), 4.88 (s, 4H, -CH2-CH2-O-).

[0114] Gas Permeability The gas permeability of rPET was measured at 25°C and 50% relative humidity using a MOCON Ox-Tran instrument for thicknesses of 12–90 μm and 5–50 cm. 2 of surface area, and 10 cm 3 The device was evaluated using a polymer film with a gas flow rate of 100 s / min. The device was calibrated with a standard PET film supplied by the manufacturer.

[0115] Films were prepared for transmittance analysis by pouring a 150 mg / mL solution of rPET in HFIP onto a glass plate heated to 60° C. in a ventilated stove to allow the solvent to evaporate. After this step, the transmittance of the film was measured, and thickness measurements were also taken both before and after the transmittance measurements to verify the integrity of the film itself.

[0116] The results demonstrate that rPET exhibits transmittance quite similar to that of non-recycled PET, as highlighted on page 16, lines 11-13 of this disclosure.

[0117] Mechanical testing Freeze grinding The rPET was dried for 1 day in a vacuum oven at 130° C. The dried polymer was milled under liquid nitrogen in a Freeze / Mill 6770 machine at 15 Hz for 3 cycles of 5 min.

[0118] Compression Molding The compression molding step was achieved using a commercial hot press (Rondol Technology Ltd, Stoke-on-trent, UK). The freeze-ground rPET powder as described above was placed in a square mold, to which a force of about 3 kN was applied for 3 minutes using the aforementioned hot press at a temperature of 260 °C, sufficient to melt the powder. Cooling was then obtained by placing the mold under a cold press equipped with a water cooling system operating at 8 °C. A 0.06-0.08 ± 0.001 mm thick rPET film suitable for the transmittance test was then obtained.

[0119] Behavior under stress Dumbbell (or dogbone) shaped specimens with a width of 1.25 mm and a length of 5 mm were cut by compression molding (ISO 527-2, Type 5B). Uniaxial stress / strain curves were plotted at 0.5 s -1 The results were made starting from stress measurements of 100 nm to 150 nm. Calculated mechanical properties such as Young's modulus, yield stress, and breaking strength are the average of at least five measurements. All mechanical tests were performed at room temperature (25°C). Stresses in all figures are taken as nominal stresses. All tests were performed both parallel and perpendicular to the visible fibers.

[0120] These tests demonstrate that the polymers obtained by the process of the invention are brittle and therefore it is preferable to add, in step c), conventional stabilizers and performers to make it possible to obtain polymers with properties such as elongation at break comparable to those of the same type of polymer prepared from scratch.

[0121] Example 6. Recovery and recycling of PET from multi-colored bottles The experimental set-up for performing DA-CDP includes a thermal heating mantle, a 250 ml flask, a Vigreux column, a Liebig condenser, a distillate collection flask, a vacuum pump, and a stirring system (mechanical or magnetic).

[0122] 100 ml of DPhE and 10-40 g of pre-shredded bottles are placed in the aforementioned 250 ml flask. The pressure is set to about 400 mbar to ensure a solvent evaporation temperature of about 218 °C. The heating mantle is turned on and heated to boiling point. At this point, all of the polymer is completely dissolved except for the coarse insoluble foreign matter that can be easily removed. Then 0.05% catalyst (antimony oxide) is added and vapor removal by distillation is maintained at about 3 g / h, assuming a reaction time of 2-4 hours. During this step, the by-products of the reaction described above, as well as volatile contaminants resulting from the decomposition and absorption of the polymer during its normal life and use, are also distilled along with the solvent.

[0123] Example 7. Recovery and recycling of polyester from polyester fibers The experimental set up for carrying out DA-CDP includes a thermal heating mantle, a 250 ml flask, a Vigreux column, a Liebig condenser, a distillate collection flask, a vacuum pump, and a stirring system (mechanical or magnetic). 100 ml of pre-chopped fiber DPhE solution, with an estimated polyester content of 10-40 g, is placed in the aforementioned 250 ml flask. The pressure is set to about 400 mbar to ensure a solvent evaporation temperature of about 218 °C. The heating mantle is turned on and heated to boiling point. At this point, all the polymer is completely dissolved, except for coarse insoluble foreign matter that can be easily removed. It is in this step that the cotton fibers, elastane, etc. are then removed, then 0.05% of catalyst (e.g. antimony oxide) is added and the reaction is assumed for 2-4 hours, while maintaining a distillation flow rate of about 3 g / h. During this step, the by-products of the reactions described above, as well as volatile contaminants resulting from decomposition and absorption of the polymer during its normal life and use, are also distilled along with the solvent.

[0124] Example 8. Hot-cold filtration After the mixture reacts for the time indicated in Examples 6 and 7, the reaction mixture is transferred to a beaker after filtration at boiling point to remove foreign matter. The solution is then cooled to about 140°C, at which temperature the heaviest precipitation of the polymer occurs and is then separated. The remaining solution is then further cooled to room temperature, resulting in the precipitation of various lower molecular weight oligomers. This is followed by washing the resulting solid compound with 50 ml of pure solvent. The solids from the hot and cold precipitations are then pooled to obtain a cyclic oligomer-polymer blend ready to be repolymerized.

[0125] Example 9. Cold direct filtration After the mixture reacts for the time indicated in Examples 6 and 7, the polymer is transferred to a beaker after hot filtration to remove foreign matter. The solution is then cooled to room temperature until both the high molecular weight polymer and oligomer are completely precipitated. Following this, the resulting solid compound is washed with 100 ml of pure solvent preheated to about 100° C. to maximize the effectiveness of dye removal. The thus bleached solid, free of solvent-soluble dyes and heavy contaminants, constitutes the cyclic oligomer-polymer mixture ready to be repolymerized.

[0126] Example 10. Repolymerization The cyclic polymer-oligomer mixture is placed in a Schlenk tube reactor or flask under mechanical stirring. Operating under vacuum to remove residual solvent, the system is brought to a temperature of 240-280°C, at which the repolymerization reaction occurs. During this process step, both polycondensation and ring-opening polymerization (ROP) reactions occur simultaneously. Bottle grade is reached in 10 minutes, and maximum growth of polymer molecular weight is reached in 20-30 minutes.

[0127] Considering the high temperatures, after this time the usual phenomenon of thermal decomposition of the polymer sets in. To mitigate such a phenomenon it is sufficient to add conventional commercial antioxidants. Such addition may not be necessary if the reaction is stopped for a short time but still sufficient to produce a polymer ready to meet market needs.

[0128] Considering the high reaction rate, repolymerization can be anticipated by directly feeding the cyclic polymer-oligomer mixture into a commercial extruder operating at a temperature of 260 °C and a residence time of 10-15 min.

Claims

**Claim 1**: A process for partially depolymerizing polymer waste, wherein at least 20% of the polymer waste is converted into cyclic oligomers. **Claim 2**: The process according to claim 1, wherein at least 40% of the polymer waste is converted into cyclic oligomers. **Claim 3**: The process according to claim 1, wherein the depolymerization is carried out by distilling the reaction mixture of the polymer waste in an aprotic polar solvent. **Claim 4**: A process for partially depolymerizing polymer waste, wherein the depolymerization is carried out by distilling the reaction mixture of the polymer waste in an aprotic polar solvent, and which results in a mixture of cyclic oligomers, aliphatic oligomers, and polymers. **Claim 5**: The process according to claim 4, wherein distilling the reaction mixture includes simultaneously distilling the solvent. **Claim 6**: A process for preparing a polymer from the corresponding polymer waste, comprising: a) partially depolymerizing the polymer waste to obtain a solution of polymers and oligomers; b) purifying the product from step a) and recovering it in the form of a solid mixture; and c) polymerizing the solid mixture from step b), wherein: - in step a), the depolymerization is only partial and results in a mixture of cyclic oligomers, aliphatic oligomers, and starting polymers; - step a) is carried out by simultaneously distilling the reaction solvent in an aprotic polar solvent. **Claim 7**: The process according to claim 6, wherein the polymer waste has a starting concentration of 10 - 800 g / l. **Claim 8**: The process according to claim 6, wherein the depolymerization is carried out at or near the boiling point of the solvent. **Claim 9**: The process according to claim 6, wherein the boiling point of the solvent ranges from 100 to 300 °C.

10. A process for preparing a polymer from corresponding polymer waste, comprising the following: a) partially depolymerizing the polymer waste, thereby obtaining a solution of polymers and oligomers; b) purifying the product from step a) and recovering it in the form of a solid mixture; c) polymerizing the solid mixture from step b). The process includes: - In step a), the depolymerization is only partial, resulting in a mixture of cyclic oligomers, aliphatic oligomers, and the starting polymer; - Step a) is carried out in an aprotic polar solvent, starting from a concentration of 10 - 800 g / l of the polymer waste, at the boiling point of the solvent in the range of 100 - 300 °C, while simultaneously distilling the reaction solvent. Process.

11. The process according to any one of claims 1 - 10, wherein the depolymerization is carried out in the presence of a catalyst.

12. The process according to any one of claims 1 - 10, wherein the polymer waste is a polyester.

13. The polymer waste is colorless and colored flakes of polyethylene terephthalate bottles, polyester fibers, polyester trays or laminates, or polyethylene furanoate products, according to the process of claim 12.

14. The process according to any one of claims 1 - 10, wherein the polymer waste is a polyamide.

15. The process according to claim 14, wherein the polymer waste is polyamide fiber.

16. The solvent is selected from diaryl ethers, mono / di / tri-C1-C3-alkoxy-benzenes, aryl-C1-C3-alkyleneoxy-C1-C5-alkanes, di-(aryl-C1-C3-alkylene)-ethers, aryl-C1-C3-alkylene-oxo-benzenes, C4-C6 cycloalkyl-ketones, where the aryl is phenyl or phenyl substituted with one or more linear or branched C1-C3 alkyl residues, the process according to any one of claims 3 to 10.

17. The solvent is 1,3-dimethoxybenzene, benzyl methyl ether, benzyl butyl ether, dibenzyl ether, diphenyl ether, cyclohexanone, or benzophenone, the process according to claim 16.

18. The depolymerization is carried out at a reaction temperature between 100 °C and 240 °C, the process according to any one of claims 1 to 10.

19. The depolymerization is carried out at a pressure between 1 and 1000 mbar, the process according to any one of claims 1 to 10.

20. The depolymerization is carried out at a pressure between 200 and 500 mbar, the process according to any one of claims 1 to 10.

21. The depolymerization is carried out under an inert gas, the process according to any one of claims 1 to 10.

22. The depolymerization is carried out under nitrogen, the process according to any one of claims 1 to 10.

23. The depolymerization is carried out for 30 minutes to 5 hours, the process according to any one of claims 1 to 10.

24. Step a) is carried out at a reaction temperature of 100 to 240 °C, at a pressure of 1 to 1000 mbar, preferably in an inert gas, more preferably in nitrogen, for a time of 30 minutes to 5 hours by using diphenyl ether as the solvent, the process according to any one of claims 1 to 10.

25. The process according to claim 11, wherein the catalyst is selected from organometals and / or metal oxides.

26. The process according to claim 25, wherein the catalyst is cyclic tin oxanoate, dibutyltin oxide, or antimony oxide.

27. The process according to claim 26, wherein the catalyst is antimony oxide.

28. The process according to any one of claims 1 to 10, wherein at least 20% of the polymer waste is converted into cyclic oligomers.

29. The process according to any one of claims 1 to 10, wherein at least 40% of the polymer waste is converted into cyclic oligomers.

30. The process according to any one of claims 3 to 10, wherein distillation removes one or more by-products.

31. The process according to claim 30, wherein the one or more by-products include diol by-products.

32. The process according to claim 30, wherein the one or more by-products include ethylene glycol or water.

33. The process according to any one of claims 3 to 10, wherein distillation removes one or more volatile contaminants.

34. The process according to claim 33, wherein the one or more volatile contaminants are solvents.

35. The process according to any one of claims 1 to 10, including purifying one or more products of the depolymerization.

36. Step b) preferably includes step b1.1), or b2.1), or b3.1) of removing insoluble impurities by filtration, centrifugation, pressurization, or decantation of the reaction mixture from step a) at the solvent boiling point, The reaction mixture from step b1.1) includes the following steps: b1.2) cooling the reaction mixture to a temperature at which the unreacted polymer recovered by filtration precipitates, which temperature is 140 to 180 °C, preferably 140 to 160 °C in the case of PET; b1.3) after removal of the polymer, further cooling the permeate to room temperature, which is the temperature at which the low and medium molecular weight cyclic oligomers recovered by filtration, centrifugation, pressure or decantation precipitate; Optionally, b1.4) adding a hydrocarbon solvent, preferably n - hexane, to the filtered solution from step b1.3) to enable precipitation of the lower molecular weight oligomers and subjecting to a treatment comprising - the reaction mixture from step b2.1) is subjected to a cooling step b2.2) at a temperature of 20 to 40 °C, preferably 25 to 30 °C, at which temperature both the unreacted polymer and the oligomers precipitate and they are separated from the solvent by filtration and subsequently washed with pure solvent, preferably at a temperature of 90 to 120 °C, to eliminate coloring of the polymer and further impurities; - the filtrate from step b3.1) is subjected to cooling in step b3.2) to a temperature of 20 to 40 °C, preferably 25 to 30 °C, and the precipitate thus obtained is washed in step b3.3) in a counter - current manner with a ketone solvent (preferably acetone) at a temperature from 20 °C to the boiling point of the solvent to remove both the dye and contaminants; The process according to any one of claims 6 to 10.

37. The process according to claim 36, wherein the waste is polyethylene terephthalate flakes and the solvent in step a) is diphenyl ether, the cooling temperature in step b1.2) is 140 to 160 °C and the temperature at which the product is washed in step b1.3) is 90 to 120 °C.

38. The filtrate from step b3.1) is cooled in step b3.2) to a temperature of 20 to 40 °C, preferably 25 to 30 °C, and the precipitate thus obtained is washed in step b3.3) with a ketone solvent (preferably acetone) at a temperature of 20 °C to the boiling point of the solvent in countercurrent to remove both the said pigment and the said contaminants, the process according to claim 36.

39. The following products: (i) the high molecular weight polymer from step b1.2), (ii) the low / medium molecular weight oligomers from step b1.3), (iii) the lower molecular weight oligomers from step b1.4), (iv) the polymer-oligomer mixture from purification method b2-2), (v) the polymer-oligomer mixture from purification process b3-3) By using one or a mixture of them, bulk polymerization (step c)) is carried out at a temperature of 240 to 280 °C for a time of 10 to 30 minutes, the process according to claim 36.

40. By using one or more of the products (i) to (v) in a mixture with virgin PET, bulk polymerization (step c)) is carried out at a temperature of 240 to 280 °C for a time of 10 to 30 minutes, the process according to claim 39.

41. The polymerization is carried out in an extruder at 240 to 280 °C for a time of 10 to 15 minutes, the process according to claim 40.

42. Stabilizers, pigments and performers customarily used in this type of polymerization are added in step c), the process according to claim 39.

43. Step c) results in a polymer having a molecular weight substantially equal to that of the said polymer waste, the process according to any one of claims 6 to 10. **Claim 44**: The process according to any one of claims 6 to 10, wherein step c) results in a polymer having a number average molecular weight of 20,000 to 40,000 g / mol. **Claim 45**: The process according to any one of claims 6 to 10, wherein step c) results in a polymer having a number average molecular weight of 24,000 to 36,000 g / mol. **Claim 46**: The process according to any one of claims 6 to 10, wherein step c) results in a polymer having a number average molecular weight of 15,000 to 20,000 g / mol. **Claim 47** The process according to any one of claims 6 to 10, wherein at least one of steps a) to c) is carried out continuously. **Claim 48** The process according to claim 47, wherein at least two of steps a) to c) are carried out continuously. **Claim 49** The process according to claim 47, wherein all three steps a) to c) are carried out continuously. **Claim 50**: The process according to any one of claims 1 to 10, further comprising an initial step of separating the polymer waste by quality. **Claim 51**: The process according to any one of claims 1 to 10, further comprising removing a pigment. **Claim 52**: The process according to any one of claims 1 to 10, further comprising separating non-volatile contaminants. **Claim 53**: The process according to any one of claims 1 to 10, further comprising removing one or more insoluble impurities. **Claim 54**: The process according to claim 53, wherein the one or more insoluble impurities include cotton fibers or elastin. **Claim 55**: A product prepared by the process according to any one of claims 1 to 10.

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