Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
  • C08J11/18—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material
  • C08J11/22—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
  • C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/16—Dicarboxylic acids and dihydroxy compounds
  • C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
  • C08G63/181—Acids containing aromatic rings
  • C08G63/183—Terephthalic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/78—Preparation processes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/78—Preparation processes
  • C08G63/82—Preparation processes characterised by the catalyst used
  • C08G63/85—Germanium, tin, lead, arsenic, antimony, bismuth, titanium, zirconium, hafnium, vanadium, niobium, tantalum, or compounds thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/88—Post-polymerisation treatment
  • C08G63/90—Purification; Drying
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/91—Polymers modified by chemical after-treatment
  • C08G63/914—Polymers modified by chemical after-treatment derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/916—Dicarboxylic acids and dihydroxy compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
  • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2377/00—Characterised by the use of polyamides obtained by reactions forming a carboxylic amide link in the main chain; Derivatives of such polymers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/62—Plastics recycling; Rubber recycling

Definitions

• the present invention relates to a process for recovery and exploitation of polyesters and polyamides from waste polymeric artifacts.
• the technology is presented below with reference to a specific polymer of great industrial importance, polyethylene terephthalate (PET).
• BACKGROUND ART PET is currently produced from bis-2-hydroxyethylterephthalate (BHET) by poly condensation (PC).
• PC poly condensation
• This reaction requires the 3 steps shown in Figure 1: one in the liquid state, one in the molten state and one in the solid state.
• This evolution of the reaction reflects the progressive increase in the viscosity of the polymer, which results in long reaction times and removal of the by-products (especially ethylene glycol, EG) of the reaction. At high viscosities, such removal becomes extremely slow, requiring 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 the diagram in Figure 2).
• This process involves an initial stage of cyclic oligomer formation by cyclo-depolymerization (CDP) requiring high dilution. Exploiting the resulting low viscosity, the removal of by- products becomes very easy. The cyclic oligomers thus synthesized are then recovered, purified and polymerized by ROP in about one hour, drastically decreasing the polymerization reaction times. From an industrial point of view, however, this process is not economically attractive because the production of cyclic oligomers is thermodynamically favoured only at high dilutions (typical concentrations 10 g/1). Such conditions lead to the need for very high solvent volumes which are difficult to handle economically.
• the process which uses polycondensation as a synthesis method is the most widely used in the industry.
• the polymeric product is marketed in the form of pellets and then processed by manufacturing companies.
• the degree of polymerization achieved during the polymerization step (and thus the corresponding chemical-physical properties), several commercial uses are possible.
• the pellets will then be used to prepare synthetic fibres, laminates, trays, bottles and high- performance technical materials.
• Chemical recycling processes include the depolymerization of PET until its complete transformation into the monomers forming the same. In some cases, depolymerization is only partial, but the polymer thus recovered still needs an adequate repolymerization to bring the molecular weight thereof back to the values necessary to make bottles. In many cases, the monomers recovered for reasons of cost, quality and purity must be mixed with virgin monomers in order to meet market and process requirements. Chemical recycling processes have several advantages: they use mixed flakes, potentially also fibres, laminates, and films. They are versatile from the point of view of the products (possibility of returning to different monomers and also to different chemical compounds) and allow to remove contaminants.
• the recycling process subject of the present invention is (i) applicable not only to high-quality polyesters for bottles (PET) but also to polyester and polyamide fibres and (ii) does not have the drawbacks of the technologies described above.
• EP3778744 Al discloses processes for recycling post-consumer polyethylene terephthalate (PET), comprising the partial depolymerization of the post-consumer PET to produce PET oligomers, followed by repolymerization of the partially depolymerized PET with PET oligomers.
• PET post-consumer polyethylene terephthalate
• 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.
• EP3606980 Al discloses a process for the preparation of cyclic oligomers, which involves the reaction of a polyester cyclic oligomer composition comprising a polyester cyclic oligomer having two to five furan units. The process involves reacting a bifunctional derivative of furan and a diol in a linear oligomerization stage, to produce a linear oligomeric composition, followed by a stage in which the linear oligomer composition is reacted in a distillation-assisted cyclization (DA-C) step, to form a polyester cyclic oligomer composition and removal of a diol by-product by evaporation.
• D-C distillation-assisted cyclization
• the applicant has now found a process which, while being a chemical process as it contemplates a partial cyclo-depolymerization associated with a simultaneous distillation of the solvent, is a fast process capable of removing most of the by-products and contaminants. Moreover, by operating in the presence of a catalyst and at an appropriate dilution, the polymer is only partially degraded and the degradation products are essentially cyclic oligomers. Thereby, the material which is recovered is ready to be re polymerized by ROP, reaching bottle grade in less than 30 minutes.
• this approach has the indisputable advantage that complete depolymerization is not required. Furthermore, by reducing the complexity of the process and the number of solvents to be used compared to a traditional chemical recycling process, it is achievable not only by large industrial companies but also by small and medium-sized industries.
• An object of the present invention is therefore a process for recovering polyesters and polyamides from the corresponding polymeric waste products, comprising the following steps: a) Total and/or partial depolymerization of the polyester/polyamide and obtaining the linear and/or cyclic oligomers and/or monomers; b) Recovery and purification of the products from step a); b) Polymerization of the product from step b).
• step a) is conducted in a polar and/or apolar aprotic solvent starting from concentrations of said polymeric product in said solvent between 10 and 800g/l at the temperature close to the solvent boiling point, between 100 and 300°C, and in the presence of a catalyst, simultaneously distilling the reaction solvent and the volatile by-products dissolved therein. Only by carrying out step a) in this manner is it possible to conduct a partial depolymerization in which the mixture of oligomers consists mainly of cyclic oligomers.
• Figure 1 shows the traditional pattern of industrial polymerization of PET by poly condensation.
• Figure 2 shows the pattern of polymerization of PET by ring-opening polymerization (ROP).
• ROI ring-opening polymerization
• Figure 3 shows the current, separation and treatment chain of the different polymer fractions.
• the materials suitable for the different treatments are identified.
• Figure 4 shows the conversion results and the number average molecular weight as a function of time obtained using conventional cyclo-depolymerization (CDP) and distillation-assisted cyclo-depolymerization (DA-CDP) according to the present invention, at different initial PET concentrations.
• CDP cyclo-depolymerization
• D-CDP distillation-assisted cyclo-depolymerization
• Figure 5 shows a block diagram of the process of the following invention with greater detail related to the second step of the process (purification and recovery of the product).
• process bl the system for the selective separation and purification of the polymeric and oligomeric fractions is diagrammed; in process b2) a direct crystallization process with multi-step washing is diagrammed by means of a single solvent or mixture of solvents at constant and/or variable temperature; in process b3) a direct crystallization process with counter-current washing is diagrammed.
• Figure 6 shows:
• step c products exiting the third step of the process of the present invention from polymer/oligomer mixtures obtained after the recovery and purification step according to different methods (step b).
• Such mixtures are referred to as raw, hot , cold , and mix (cold hot), and their features will be explained below.
• the definition comprising does not exclude the presence of additional components or steps not expressly mentioned after such a definition.
• cyclo-depolymerization means a depolymerization which results in a mixture of polymers of different molecular weights, in particular high molecular weight polymers and low molecular weight cyclic oligomers.
• partial depolymerization means a depolymerization reaction in which the fraction of depolymerized polymer is between 0.1% and 80%, preferably between 0.1% and 40% by weight on the total weight of the starting polymer.
• polycondensation means a polymerization reaction involving the bonding of two linear chains of any length with the release of a low molecular weight by-product
• polymer chemolysis means the depolymerization reaction opposite to polycondensation, which involves the polymer breaking into two shorter chains favoured by the insertion in the chain of one or more molecules which promote the polymer chain breaking
• polymer decomposition means the depolymerization reaction opposite to polycondensation and involving the breakage of the polymer into two shorter chains due to degradation of the polymer chain (e.g., mechanical, thermal, physical stress, oxidation, irradiation, etc.);
• ring opening polymerization or ROP is instead the polymerization reaction by opening a cyclic oligomer;
• back biting refers to a cyclo-depolymerization reaction opposite to ROP, which therefore involves the breakage of the polymer with the formation of a shorter linear chain
• the PET is mainly produced in two qualities: fibre grade and bottle grade. These standards differ mainly in the average molecular weight and in the production recipes such as the amount and type of comonomers, dyes and stabilizers.
• fibre grade PET is intended as polyethylene terephthalate having a molecular weight between 15000 and 20000 g/mol and an intrinsic viscosity between 0.55 and 0.67 dl/g.
• Fibre PET for technical yarns such as tyre cords has a higher molecular weight (intrinsic viscosity 0.95 dl/g).
• bottle grade PET is intended as polyethylene terephthalate having a molecular weight between 24000 and 36000 g/mol and an intrinsic viscosity between 0.75 and 1 dl/g.
• high molecular weight polymer means a polymer having a number average molecular weight between 20000 and 40000 g/mol.
• Low to medium molecular weight oligomers are defined as oligomers with a molecular weight between 1000 and 3500 g/mol.
• Very low molecular weight oligomers are defined as oligomers with a molecular weight between 200 and 1000 g/mol.
• polyester polymer products are understood as all compounds having a percentage of polyester between 1 and 100%.
• polyamide polymer products are understood as all compounds having a percentage of polyamide between 1 and 100%.
• polyester means all the polymers belonging to such a chemical category such as: polyethylene terephthalate (PET), polyethylenefuranoate (PEF), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), poly(butyleneadipate-terephthalate) (PBAT), polytrimethylene terephthalate (PTT), polybutylene succinate (PBS), unsaturated polyesters (UPE), polylactic acid (PLA), polyhydroxyalkanoates (PHA), etc.
• PET polyethylene terephthalate
• PBT polyethylenefuranoate
• PBT polybutylene terephthalate
• PEN polyethylene naphthalate
• PBAT poly(butyleneadipate-terephthalate)
• PTT polytrimethylene terephthalate
• PBS polybutylene succinate
• UEE unsaturated polyesters
• PLA polylactic acid
• PHA polyhydroxyalkanoates
• polyamide means all the polymers belonging to such a chemical category 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, po!yarylamide, polyaramides (Kevlar®), polyphthalamide, poly ami doamines, etc.
• flakes of polyethylene terephthalate bottles i.e., the shredding/grinding products of PET bottles
• Other waste products used as starting material are containers for packaging in polyester such as: food trays, films, etc.
• waste products used as a starting material are polyamide plastic products such as: automotive components, tubes, containers, packaging, technical materials, etc.
• polyester fibres such as: shoes, clothes, covers, cords, etc.
• polyamide fibres such as Nylon 6, Nylon 6,6, Kevlar, etc.
• stabilizers are those antioxidant compounds such as poly-substituted phenols, phosphites, etc., usually used to prevent the degradation of the polymer during processing.
• perfomers are those compounds capable of modifying the rheological and mechanical properties of the polymer.
• step a) the cyclo-depolymerization is carried out by simultaneously distilling the solvent.
• the low boiling by-products are also removed which, in the specific case of PET, comprise ethylene glycol and water.
• the aprotic polar solvent is preferably selected from a diaryl ether, mono/di/tri-Cl-C3- alkoxy -benzene, aryl-C 1 -C3 -alkyleneoxy-C 1 -C5-alkane, di-(aryl-C 1 -C3 -alkylene)- ether, aryl-C l-C3-alkylene-oxo-benzene, C4-C6 cycloalkyl-ketone, in which the aryl is a phenyl or a phenyl substituted with one or more linear or branched C1-C3 alkyl residues.
• the solvent is selected from: diphenyl ether, 1,3 dimethoxybenzene, benzyl methyl ether, benzyl butyl ether, di-benzyl ether, cyclohexanone, benzophenone, more preferably diphenyl ether.
• the apolar solvent is preferably a C5-C8 linear hydrocarbon, more preferably it is n- hexane.
• the step a) of the process according to the present invention is preferably conducted at a pressure between 100 and 1000 mbar, more preferably between 200 and 500 mbar, more preferably in the presence of inert gas, even more preferably under nitrogen.
• the catalyst is selected from cyclic tin octanoate, dibutyltin oxide, 2-ethylhexanoate tin, more preferably it is 2-ethylhexanoate tin.
• the concentration of the catalyst is preferably between 0.001 and 0.5% weight/weight of the polymer product.
• the concentration of the polymer in the solvent in step a) is preferably between 10 and 800 g/1, more preferably between 50 g/1 and 400 g/1.
• step a) is conducted by using diphenyl ether as solvent, at a reaction temperature preferably between 100° and 240°C, at pressures between 100 and 1000 mbar, preferably in inert gas, more preferably nitrogen, and for a time between 1 and 5 hours.
• the solvent in step a) is diphenyl ether and step a) is conducted at temperatures between 200 and 224°C, at pressures between 200 and 600 mbar, for a time between 2 and 4 hours.
• Step a) of the process is depolymerization.
• This treatment causes a decrease in the molecular weight of the polymer due to chemolysis and back-biting (or cyclo depolymerization) reactions.
• a normal cyclo-depolymerization without evaporation of solvent involves a progressive decrease in the production of cyclic oligomers as the concentration of the PET increases.
• This behaviour is shown in Figure 4 (left graphs) and is a consequence of the fact that the back-biting reactions are disadvantaged with increasing PET concentration. At very high dilutions, such a depolymerization is virtually complete, with almost exclusively cyclic oligomer formation.
• Step b) of the process of the present invention comprises several solutions for purifying the product of step a).
• the first possibility bl) allows the separation of the polymer and oligomers and preferably comprises four stages in series, of which the latter is optional.
• the second possible route b2) comprises a direct purification system with cross-flow multistage washes.
• the third possible option b3) comprises a direct purification process with counter-flow multistage washes with preferably a continuous washing and extraction process.
• the possible purification system bl is called "Hot-Cold separation and purification system”. This comprises the selective separation of high, medium, low, and very low molecular weight compounds by operating with a selective precipitation and washing of the collected fractions.
• the first (step bl.l) comprises a step of eliminating the insoluble impurities, preferably by filtration, centrifugation or decanting of the reaction mixture from step a) at the solvent boiling temperature.
• insoluble impurities are different, 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).
• the subsequent step bl.2) comprises a cooling process of the reaction mixture to the temperature at which the high molecular weight polymer fraction (not depolymerized) precipitates, which is recovered by filtration; in the case of PET, this temperature is between 140 and 180°C, preferably between 140 and 160°C.
• a subsequent step bl.3) comprises a system in which the permeate is subjected to further cooling to about room temperature. Low and medium molecular weight cyclic oligomers are precipitated at this temperature, which are still recovered by filtration.
• the method of the invention can include a step bl.4) in which the filtered solution from step bl.3) is added with a hydrocarbon solvent, preferably n-hexane, to allow the precipitation of the lower molecular weight oligomers.
• a hydrocarbon solvent preferably n-hexane
• the possible purification system b2) is called "direct separation and purification system with cross-flow washing". This process allows to directly obtain a polymer-oligomer mixture by operating with cross-flow purification.
• the first (step b2.1) comprises a step of eliminating the insoluble impurities, preferably by filtration, centrifugation or decanting of the reaction mixture from step a) at the solvent boiling temperature.
• These insoluble impurities are different, 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).
• the next step b2.2) comprises a process of cooling the reaction mixture to about room temperature with precipitation of the high molecular weight (non-depolymerized) polymer fraction together with the low and medium molecular weight cyclic oligomers.
• the solid material from step b2.2) is then washed and purified with a cross-flow multistage process.
• the contaminant-rich solvent from step a) is initially removed and the residual solid product obtained is washed with pure solvent.
• the successive washes can be carried out with the same solvent or/and with a different solvent than that used by step a).
• the multiple wash process can be carried out with a variable washing solvent temperature, for example increasing or decreasing along the wash process.
• the temperatures typically used cover the range between ambient temperature and the boiling point of the washing solvent used. This process allows for greater flexibility in the purification and washing process.
• the possible purification system b3) is called "direct separation and purification system with counter-current washing". This process allows to directly obtain a polymer-oligomer mixture by operating with counter-current purification.
• the first (step b3.1) comprises a step of eliminating the insoluble impurities, preferably by filtration, centrifugation or decanting of the reaction mixture from step a) at the solvent boiling temperature.
• These insoluble impurities are different, 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).
• the next step b3.2) comprises a process of cooling the reaction mixture to about room temperature with precipitation of the high molecular weight (non-depolymerized) polymer fraction together with the low and medium molecular weight cyclic oligomers.
• the solid material from step b3.2) is then washed and purified with a counter-current multistage process.
• the contaminant-rich solvent from step a) is initially removed and the residual solid product obtained 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 contaminants can be carried out continuously with a variable washing solvent temperature, for example increasing or decreasing along the washing process.
• the temperatures typically used cover the range between ambient temperature and the boiling point of the washing solvent used. This process allows greater flexibility in the purification and washing process and a strong reduction in the volumes of solvent used.
• the polymerization reaction or step c) of the process is preferably carried out at a temperature between 220 and 280 °C, with nitrogen flow and without the addition of further catalyst.
• the two hot and cold precipitates already described the raw precipitate and one obtained by mixing hot and cold ⁇ mix) in proportions such as to reproduce the content of PET and cyclic oligomers of the raw product.
• the latter material thus represents the equivalent of the raw material but is free of residual solvent, dyes and other impurities.
• Figure 6 shows the number average molecular weight data measured as a function of the conversion to polymer obtained by ROP from the various materials now described. In all cases, it was possible to produce a recycled polymer capable of meeting the specific bottle grades.
• Figure 6 graph at the bottom right the hot material repolymerizes almost exclusively by polycondensation while the cold one by ROP. If the mixture called mix ⁇ hot + cold) 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 solvent whose evaporation limits the reaction temperature in the first steps, followed however by fast kinetics.
• step c) of repolymerization can be conducted using any of the products of step b) in its possible variants:
• step c) of the inventive process can be carried out starting from mixtures of the products detailed in the above list.
• dyes, stabilizers and additives are preferably added in order to allow to obtain a final polymer with the same application properties as virgin polymers.
• the Applicant has further found that the food contaminants associated with the normal use of the polymer, e.g., for PET bottles, can also be removed by the method of the invention. This is achieved in the process in which polymer precipitation is performed followed by washing the precipitate with a solvent such as diphenyl ether.
• a solvent such as diphenyl ether.
• Regulation (EC) no. 282/2008 was followed, which calls for the challenge test , i.e., the introduction of known quantities of polluting compounds (surrogates) and the tracking of the subsequent removal up to residual concentration values which do not represent a risk for human health.
• the removal efficiency was quantified by defining the following three parameters: the PET/impurity ratio, the purity of the PET and the residual solvent/PET ratio (diphenyl ether was used as solvent in these tests).
• the PET/impurity ratio the purity of the PET
• the residual solvent/PET ratio diphenyl ether was used as solvent in these tests.
• the impurities constituted by the residual solvent are eliminated during the polymerization or step c).
• the traces of residual solvent reached values lower than the sensitivity threshold of NMR 300 Mhz used for characterization. Accordingly, it can be stated that the final solvent concentration is lower than the sensitivity of the state of the art, estimated at 10 ppm.
• step b) after the hot precipitation of the by-products a direct cold filtration is carried out and a subsequent washing with pure solvent, in step c) of polymerization a removal of the semi -volatile compounds up to 99.5%, up to 97% for heavy compounds and greater than 99.9% for the solvent is also obtained.
• a further object of the present invention is the process of the invention in which at least one of the steps a) - c) is conducted continuously,
• a further object of the present invention is the process of the invention in which at least two of the steps a) - c) are conducted continuously.
• DACDP One preferred embodiment of the continuous process of the invention is shown in the block diagram of figure 7.
• the plastic waste is introduced together with the solvent premixed with the catalyst into the first continuously operating reactor called DACDP.
• This reactor consists of a continuously operating system in which the cyclo- depolymerization reaction occurs with distillation.
• the type of reactor can, for example, be of the continuous stirring tank reactor (CSTR) type, such as a reactor chosen from a paddle mixer reactor, a ribbon mixer reactor, etc. designed to ensure an effective removal of the volatile ingredients and the solvent.
• CSTR continuous stirring tank reactor
• the product obtained at the bottom of the reactor consisting of the unreacted polymer together with its solvent-solubilized oligomers is pumped to a continuous and/or semi -continuous filtration system such as membrane filtration, permeation, press-filter, filter press, etc. to separate the solid stream (polymer + oligomers) from the solvent rich in non-volatile contaminants.
• a continuous and/or semi -continuous filtration system such as membrane filtration, permeation, press-filter, filter press, etc. to separate the solid stream (polymer + oligomers) from the solvent rich in non-volatile contaminants.
• the polymer thus collected is then sent to the re-polymerization system which can consist of a drying system (e.g., drum) and is subsequently subjected to a direct re-polymerization in an extruder or a combined drying-repolymerization system operated with an extruder including degassing and devolatilization system.
• a drying system e.g., drum
• All the solvent streams are conveyed to a solvent regeneration system which can work by distillation, microfiltration, adsorption. Thereby the regenerated solvent can be reused in a closed loop within the described process.
• Figure 8 shows the layout of a preferred embodiment of the system in which the continuous process contemplated in figure 7 is conducted.
• the solvent coming from the storage tank (solvent storage) is sent in part to the reactor where it is mixed together with the catalyst before entering the DACDP depolymerization plant.
• the polymer to be recycled from the relative tank (Polymer storage) is also supplied to the reactor through line 6.
• the depolymerized products exit from the bottom of the DACDP reactor together with the unreacted polymer, which are subsequently sent after cooling to a solid solvent separator.
• the recovered solid is passed over filter (Washing filter), is washed with solvent coming partly from the storage tank (lines 2 and 15) and partly from the solvent separated in the solvent solid separator.
• the solid product exiting the wash is sent through line 11 to the reactive extruder and subsequently sent to the recycled polymer storage tank.
• EXAMPLE 1 Partial (cvcleVdepolymerization of PET bottles assisted by distillation) of PET bottles assisted by distillation A four-necked flask was used, heated by a heating mantle provided with magnetic stirring or alternatively fitted with mechanical stirring through one of the necks. The first neck was used to measure the reaction temperature. The second lateral neck was used during the reaction to take the reaction samples by means of a spatula. These samples were then dried in an oven at 120°C. In the central neck a Vigreux column was installed with a condenser in the head to which a flask was connected to collect the vapours. The latter was previously oven-dried and was used to measure the condensate collection rate, i.e., the distillation rate.
• the composition of the collected distillate was measured by NMR.
• Diphenyl ether solutions at different concentrations of PET flakes (1, 5, 10 and 20 g of PET in 100 mL of DPhE, corresponding to 10, 50, 100 and 200 g/1 respectively) were prepared.
• the PET flakes were previously obtained from the corresponding bottles, cutting them into square flakes about 1 cm in size, dried for 30 minutes in an oven at 130°C in vacuum.
• the reaction temperature was increased to the boiling temperature of the solvent and, after complete dissolution of the PET, the catalyst was added at concentrations of 0.01- 0.1 %.
• the reaction was allowed to proceed at boiling temperature under magnetic stirring at 600 rpm for 6 hours and at a pressure of 300-500 mbar. This reaction time is in excess with respect to what is necessary and has been considered for a more complete kinetic analysis.
• the pressure was adjusted by vacuum pump. Both the reaction temperature and the temperature inside the Vigreux column were measured with two Re type thermocouples.
• EXAMPLE 1-A Conventional cvclo-depolymerization of PET bottle flakes A 250-mL three-necked flask, heated by an oil bath placed on a magnetic heating plate, was used as a reactor. The first lateral neck was used to measure the temperature by means of a thermocouple. The second lateral neck was used during the course of the reaction to withdraw the reaction samples by means of a spatula. These samples were then dried in a 120°C oven.
• a spillway was installed on the central neck to condense the vapours.
• Diphenyl ether solutions at different concentrations of PET flakes (1, 5, 10 and 20 g of PET in 100 mL of DPhE, corresponding to 10, 50, 100 and 200 g/1 respectively) were prepared.
• the PET flakes were previously obtained from the corresponding bottles, cutting them into square flakes about 1 cm in size, dried for 30 minutes in an oven at 130°C in vacuum.
• the temperature was increased until boiling and, after complete dissolution of the PET, the catalyst was added at concentrations of 0.01- 0.1 %.
• the reaction was kept under stirring at 600 rpm for 6 hours at the boiling temperature. Then the reaction was quenched by cooling and the final solution was filtered.
• a 250-mL, electrically heated, 3 -necks flask provided with magnetic stirring was used as a reactor.
• the first lateral neck was used to measure the reaction temperature.
• Samples of the reaction mixture were taken from the second lateral neck during the reaction by means of spatulas previously dried in an oven at 120°C.
• a Vigreux column was installed on the central neck.
• a condenser was arranged at the top of said column to condense the vapours and collect the condensate in a flask, previously dried in an oven at 120°C. Weighing the collected quantities over time, the distillation rate was measured, while the composition of the distillate was evaluated by NMR. Diphenyl ether solutions were prepared at different concentration of PET flakes.
• the PET flakes were previously obtained by the corresponding bottles, cutting them into square flakes about 1 cm in size, dried for 30 minutes in an oven at 130°C in vacuum and then left to macerate at 50°C under stirring in a solution at 2.5 %m/m Menthol and 2.5 %m/m Limonene in water for 24-72 h.
• the addition of Irganox® B 561 FF and Irgafos® 126 at a concentration of 0.15-0.5% was carried out directly in the reactor simultaneously with the addition of the flakes.
• the temperature was increased until boiling, and after complete dissolution of the PET, the catalyst was added at concentrations of 0.1-0.05%.
• the reaction mixture was kept stirred with a magnetic stirrer at 600 rpm for 6 hours at 300- 500 mbar and at boiling temperature.
• the pressure was controlled by vacuum pump.
• step b 144 After the assisted cyclo-depolymerization (DA-CDP), the reaction mixture of Examples 1 and 1A is filtered at the boiling temperature of the solvent to eliminate insoluble products such as inorganic fillers, metals, and any other polymer residues insoluble in the reaction solvent. The solution is then cooled to 150-160°C. At these temperatures high molecular weight components precipitate, which are then separated by filtration by Biichner filter. Then the filtered solution is further cooled to temperatures between 25 and 30°C. At this temperature the low/medium molecular weight oligomers are precipitated, which are recovered by filtration by Biichner filter. The filtered solution is treated with n-hexane to precipitate the very low molecular weight oligomers, which are finally separated by filtration.
• D-CDP assisted cyclo-depolymerization
• EXAMPLE 4 Separation method for direct cold precipitation (steps b2) and b3V) After the assisted cyclo-depolymerization (DA-CDP), the reaction mixture of Examples 1 and 1A is filtered at the boiling temperature of the solvent to eliminate insoluble products such as inorganic fillers, metals, and any other polymer residues insoluble in the reaction solvent.
• D-CDP assisted cyclo-depolymerization
• the solution is then cooled to 25 to 30°C. At this temperature, both high molecular weight polymers and low/medium molecular weight oligomers precipitate.
• the precipitates are separated by filtration with Biichner filter.
• the retentate collected on the filter is treated with DPhE to wash the solid, preferably at temperatures between 20 and 120°C, and eliminate the residual contaminants with a system of multiple washes (as in variant b2) of step b) described above) or counter-current (as in variant b3) of step b) described above).
• EXAMPLE 5 Polymerization and characterization of the product 500 mg of the reaction mixture obtained as described in Examples 4 and 5 was loaded into a 5 ml Schlenk tube reactor, and 1500 mg of the same mixture was loaded into a 10 ml Schlenk tube reactor. Both reactors were placed in a heater block and vacuum-dried for about 30 minutes. The reactors are removed from the heater block and the vacuum is replaced by nitrogen.
• the desired temperature (240-280°C) is set in the heater block and the reactors are returned to the heater block.
• the produced polymer (hereinafter referred to as r-PET to differentiate it from the virgin polymer) is dissolved in pure HFIP and subsequently precipitated by addition of THF. The product is then collected by filtration or centrifugation.
• Another methodology includes dissolving the reaction product in pure HFIP followed by nocturnal evaporation of the solvent under extracted hood.
• the solid is vacuum-dried at 80°C to yield a white product.
• the gas permeability of rPET was assessed at 25°C and 50% relative humidity using a MOCON Ox-Tran device using polymer films between 12 and 90 pm thick, with a surface area between 5 and 50 cm 2 and a gas flow rate of 1 OcvirVmin
• the calibration of the device was carried out with a standard PET supplied by the manufacturer.
• the preparation of the film for permeability analysis was carried out by pouring a solution of about 150mg/mL of rPET into HFIP on a glass plate heated to 60°C inside a ventilated stove to evaporate the solvent. After this step, the permeability of the film was measured, also performing thickness measurements both before and after the permeability measurement to verify the integrity of the film itself.
• the results demonstrate that rPET exhibits a permeability quite like that of non-recycled PET, as underlined on page 16, lines 11-13 of the present disclosure.
• the compression moulding step was accomplished using a commercial hot press (Rondol Technology Ltd, Stoke-on-trent, ETC).
• the cryo-milled r-PET powder as described above was placed in a square-shaped mould to which a force of about 3 kN was applied for 3 min by means of the aforesaid hot press at a temperature of 260°C, sufficient to melt the powder.
• Cooling is then obtained by placing the mould under a cold press equipped with a water cooling system operating at 8°C.
• rPET film of a thickness of 0.06 to 0.08 ⁇ 0.001 mm suitable for permeability testing is then obtained. Behaviour under stress
• Dumbbell (or dog bone) shaped samples 1.25 mm wide and 5 mm long were cut by compression moulding (ISO 527-2, type 5B).
• Uniaxial stress/strain diagrams were constructed starting from 0.5 sec 1 stress measurement.
• the calculated values of mechanical properties, such as Young's modulus, yield stress, and fracture strength, are the average of at least five measurements. All the mechanical tests were performed at room temperature (25 °C). The stress in all the diagrams is understood as the nominal stress. All the tests were performed both in parallel and perpendicular with respect to the visible fibres.
• step c) it is preferable to add conventional stabilizers and performers to allow to obtain a polymer with properties such as elongation at break comparable to those of polymers of the same type prepared from scratch.
• EXAMPLE 6 Recovering and recycling PET from multicolour bottles
• the experimental set to conduct the DA-CDP includes thermal -heating mantle, 250ml flask, Vigreux column, Liebig condenser, distillate collection flask, vacuum pump and stirring system (mechanical or magnetic).
• EXAMPLE 7 Polyester recovery and recycling from polyester fibres
• the experimental set to conduct the DA-CDP includes thermal -heating mantle, 250ml flask, Vigreux column, Liebig condenser, distillate collection flask, vacuum pump and stirring system (mechanical or magnetic). 100 ml of a DPhE solution of pre-shredded fibres with an estimated polyester content of 10 to 40 g are loaded into the aforesaid 250 ml flask. The pressure is set around 400mbar to ensure a solvent evaporation temperature of about 218°C. The heating mantle is lit and heat up to the boiling point. At this point, all the polymer is completely dissolved except for any coarse and insoluble foreign bodies, which can be easily removed.
• the reaction mixture is transferred to a beaker after filtration at the boiling temperature to remove any foreign bodies.
• the solution is then cooled to about 140°C, at which temperature the most massive precipitation of the polymer occurs and is then separated.
• the remaining solution is then further cooled to room temperature, so that various lower molecular weight oligomers precipitate.
• a washing of the solid compounds obtained with 50 ml of pure solvent follows.
• the solids from the hot and cold precipitation are then pooled to obtain the cyclic oligomer-polymer blend ready to be repolymerized.
• EXAMPLE 9 Cold direct filtration
• the cyclic polymer-oligomer mixture is charged under mechanical stirring in a Schlenk tube reactor or in a flask. Operating under vacuum to remove any residual solvent, the system is brought to a temperature between 240 and 280°C, at which temperature the repolymerization reaction occurs. During this method step, both polycondensation and ring opening polymerization (ROP) reactions occur simultaneously. In 10 minutes the bottle grade is reached and in 20-30 minutes the maximum growth of the molecular weight of the polymer is reached. Given the high temperature, after this time the normal phenomena of thermal decomposition of the polymer begin. To mitigate such phenomena, it is sufficient to add conventional commercial antioxidants. Such addition may not be necessary if the reaction is stopped at short times but still sufficient to produce a polymer ready to meet market needs.
• ROP ring opening polymerization
• repolymerization can be envisaged by feeding the cyclic polymer-oligomer mixture directly to a commercial extruder operating at temperatures of 260°C and with residence times of 10-15 minutes.

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