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WO2025219922A1 - Procédé de dégradation de produits plastiques contenant des polyesters - Google Patents

Procédé de dégradation de produits plastiques contenant des polyesters

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Publication number
WO2025219922A1
WO2025219922A1 PCT/IB2025/054032 IB2025054032W WO2025219922A1 WO 2025219922 A1 WO2025219922 A1 WO 2025219922A1 IB 2025054032 W IB2025054032 W IB 2025054032W WO 2025219922 A1 WO2025219922 A1 WO 2025219922A1
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WO
WIPO (PCT)
Prior art keywords
pet
depolymerization
process according
polymer
cyclic alkyl
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/IB2025/054032
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English (en)
Inventor
Francesco MILLUCCI
Raimondo Germani
Silvia COREZZI
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Universita degli Studi di Perugia
Original Assignee
Universita degli Studi di Perugia
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Filing date
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Application filed by Universita degli Studi di Perugia filed Critical Universita degli Studi di Perugia
Publication of WO2025219922A1 publication Critical patent/WO2025219922A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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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
    • C08J11/14—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 steam or water
    • 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
    • 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
    • C08J11/06—Recovery or working-up of waste materials of polymers without chemical reactions
    • C08J11/08—Recovery or working-up of waste materials of polymers without chemical reactions using selective solvents for polymer components
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J11/00—Recovery or working-up of waste materials
    • C08J11/04—Recovery or working-up of waste materials of polymers
    • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
    • C08J11/18—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material
    • C08J11/22—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds
    • C08J11/24—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds containing hydroxyl groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • 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
    • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
    • C08J2367/04—Polyesters derived from hydroxy carboxylic acids, e.g. lactones
    • 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
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
    • 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

  • Object of the present invention is a novel environmentally friendly process for the degradation of plastic materials containing polyesters.
  • the process provides for a pre-treatment of dissolution/precipitation of the plastic material in appropriate solvents, aimed at facilitating the subsequent depolymerization step of the polyester.
  • the process according to the invention enables the recovery of monomers and/or oligomers that can be reused for the ex-novo synthesis of plastic materials with properties unchanged from the virgin material.
  • Such methodology can be easily implemented in industrial settings dedicated to recycling plastic waste, with the potential to produce significant benefits in terms of energy efficiency and environmental sustainability.
  • PET polyethylene terephthalate
  • Mechanical recycling is undoubtedly the most established approach for the treatment of post-consumer plastic materials. This process relies on melting and extruding waste to create recycled granules that can be used as raw material for new applications.
  • the main disadvantage of this technology is that the combined effect of repeated heating and frequent mechanical stresses can lead to a reduction in the molecular weight of the recycled polymer, thus reducing its mechanical and thermal qualities with each reprocessing.
  • mechanical recycling does not allow for the separation of mixed waste in which, in addition to polyester, other polymers and/or additives or contaminants of a different nature are present.
  • a strategy that has recently emerged in the literature to significantly accelerate the chemical depolymerization process of polymeric materials recalcitrant to degradation is to pre-treat the polymer by using solvents.
  • the degradation of polymers, and polyesters in particular is indeed an interface phenomenon that initially involves only the outer surface of the polymer and then extends deep into the material. Such mechanism is significantly hampered by the high level of crystallinity (about 30-40%) of most post-consumer manufactured products.
  • Several studies have shown that through the diffusion of solvent molecules into the polymer matrix, it is possible to weaken the interactions between the polyester chains and increase the specific surface area of the polymer, thus facilitating the access of depolymerizing agents to the reaction sites, resulting in a reduction of depolymerization time.
  • pre-treatment of polyesters appears to be a promising solution to reduce time and energy costs associated with the chemical depolymerization process, further efforts are needed to discover more efficient, recyclable and low-toxicity solvents to make chemical recycling competitive with traditional methods.
  • Object of the present invention is to provide a process for degrading plastic products containing polyesters that is efficient and sustainable.
  • Further object of the present invention is to provide a process for degrading plastic products containing polyesters, which uses environmentally friendly "green” solvents widely used in cosmetics and pharmaceuticals.
  • Still an object of the present invention is to provide a process for degrading plastic products containing polyesters that uses "green” solvents that are also cost- effective when used on an industrial scale.
  • Yet an object of the present invention is to provide a process for degrading plastic products containing polyesters that allows their chemical depolymerization in extremely short time and also allows the use of minimal amounts of catalysts.
  • Object of the present invention is a process for chemical depolymerization of plastic materials containing polyesters, comprising: a pre-treatment step of the plastic material with cyclic alkyl carbonates, resulting in the dissolution and precipitation of said polyesters in the form of pre-treated material, a washing step of said pre-treated material with deionized water and/or at least one organic solvent free of ester functionalities, resulting in a washed pretreated material, a subsequent chemical depolymerization step of said pre-treated washed material, resulting in monomers and/or oligomers.
  • the inventors have surprisingly found that the pre-treatment step carried out according to the present invention, by altering the physical structure of the polyesters, allows their subsequent chemical depolymerization in an extremely short time even in the presence of any minimal amounts of catalyst.
  • the plastic material containing polyesters undergoes pre-treatment with cyclic alkyl carbonates according to the invention, precipitation of the dissolved polyesters in said cyclic alkyl carbonates is induced by cooling, resulting in a "gel", in which the solvent molecules (cyclic alkyl carbonate) remain trapped inside the polymer matrix.
  • the cyclic alkyl carbonate used in the aforementioned pre-treatment step can be extracted from that matrix by repeated washing in water without altering the gel structure of the polymer, which, thanks to the increased specific surface area, is easily degraded in the subsequent chemical depolymerization step.
  • the process according to the present invention is of considerable interest to chemical industries operating in the recycling sector, thus providing practical help in solving the current crisis caused by the accumulation of plastics.
  • Figure 1 shows bottles containing 1 g PET from the following samples (a) VIRGIN PET, (b) WET PET 25, (c) DRY PET 25.
  • Figure 2 shows the PET conversion percentages and TPA yields for (a) virgin (VIRGIN PET), (b) pre-treated (Experiment la) without removing the wash water contained inside the polymer (WET PET 25), (c) pre-treated (Experiment la) and dried in an oven at 70°C (DRY PET 25), high crystallinity PET powder (Poliplast S.r.l. - Bergamo, Italy).
  • FIG 3 shows PET conversion percentages and TPA yields at different reaction times (Experiment 1c) at 90°C (Figure 3a) and 25°C (Figure 3b).
  • Figure 4 shows PET conversion percentages and TPA yields after 5 minutes of reaction at varying temperature (Experiment 1c).
  • Figure 5 shows the relationship between linearized PET conversion (Jander's model) at different temperatures and reaction time ( Figure 5a), and the Arrenhius relationship for the alkaline hydrolysis process of PET ( Figure 5b).
  • Figure 6 shows the PET conversion percentages (Figure 6a) and TPA yields (Figure 6b) for the samples prepared at 25 wt% and 15 wt% at different reaction times (1 g highly crystalline PET powder, 1.2 equivalents of NaOH, 90°C).
  • Figure 7 shows the ATR-IR spectra of (a) TPA obtained by depolymerization of highly crystalline PET powder and (b) commercial standard of TPA.
  • Figure 8 shows the X H NMR (DMSO-de) spectrum of the reaction product (TPA) isolated from the depolymerization of highly crystalline PET powder.
  • Figure 9 shows the recyclability of propylene carbonate, showing the efficiency of four subsequent reaction cycles (Figure 9a), along with the ATR-IR spectrum of propylene carbonate as received and after the fourth recovery cycle ( Figure 9b).
  • Figure 10 shows the effect of the treatment with activated carbon for decolorization of reaction products.
  • Figure 11 shows the TGA curve of water swollen PET (WET PET).
  • Figure 12 shows: (a) the SEM image of the surface of virgin PET, (b)-(c) the CRYO-SEM images of the cryo-fractured surface of WET PET 25 after 3 and 10 minutes of ice sublimation at -110 °C, respectively, (d) the SEM image of the surface of DRY PET 25.
  • Figure 13 shows the ATR-IR spectra of virgin PET (gray line) and DRY PET 25 (black line).
  • Figure 14 shows the TGA curves of virgin and DRY PET 25.
  • the lower panel shows the derivative of the two curves.
  • Figure 15 shows the GPC curves depicting the distribution of the mass fraction between the molecular weights of virgin (gray line) and DRY (black line) PET 25.
  • Figure 16 shows the multi -peak fit of WAXD spectra of virgin (top panel) and DRY (bottom panel) PET 25.
  • the dark bands depict the crystalline peaks, whereas the enlarged light band is the amorphous material.
  • Figure 17 shows the DSC curves of first heating, cooling, and second heating at the rate of 10 °C/min for virgin PET (gray curves) and DRY PET (black curves).
  • Figure 18 shows the band decomposition of the ATR-IR spectra in the 1320- 1425 cm' 1 region for virgin (gray) and DRY (black) PET 25.
  • the absorption bands of the glycol segments in trans-extended (1340 cm' 1 ) and gauche-twisted (1370 cm' 1 ) conformations are highlighted with a darker color.
  • Figure 19 shows the WAXD spectrum of the recovered TPA.
  • the reference model for TPA PDF 00-031-1916 is shown with gray bars.
  • polymers molecules with a high molecular weight consisting of a large number of repeated structural units called “monomers”, covalently linked together to form a long chain.
  • Some common examples of polymers are polyethylene terephthalate (PET), polyethylene (PE), polystyrene (PS) and polypropylene (PP).
  • PET polyethylene terephthalate
  • PE polyethylene
  • PS polystyrene
  • PP polypropylene
  • polyethylene terephthalate is the polymer resulting from the polycondensation reaction of two monomers, terephthalic acid (TPA) and ethylene glycol (EG), according to the following structure:
  • oligomers refers to a class of molecules intermediate in size between monomers and polymers.
  • oligomers derived from polyethylene terephthalate typically contain 2 to 20 monomers.
  • polyester means polymers that contain at least one ester group in the main chain. Some of the most common examples of polyesters are: polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) and polylactic acid (PLA).
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PEN polyethylene naphthalate
  • PLA polylactic acid
  • plastic product containing polyesters or equivalently "plastic article containing polyesters" means a plastic manufactured product or article consisting of at least one polymer, which is polyester.
  • plastic objects containing polyesters include, for example, water bottles, textile fibers, shopping bags, packaging films or plastic components for electronics.
  • the plastic product containing polyesters may also further contain contaminants or additives, including plasticizers, pigments, dyes, organic and inorganic fillers or other polymers.
  • mixed plastic waste refers to plastic products containing two or more different polymers, or one polymer and additives and/or contaminants, combined in a way that is extremely difficult to mechanically separate and recycle.
  • Typical examples of mixed plastic waste are, for example, multilayer packaging or polymer blends commonly used in carpet or textile production.
  • polyester degradation and “depolymerization” of polyester are used equivalently to refer to the process of fragmentation of polyester polymer chains into smaller units such as monomers or oligomers.
  • (chemical) recycling process means a process during which at least one of the polymers in the starting material undergoes a depolymerization reaction. Through this process, it is possible to recover monomers and/or oligomers that can be reused for the synthesis of new plastic materials.
  • gel means a two-phase material consisting of a liquid phase embedded in a solid matrix.
  • cyclic alkyl carbonate is the liquid phase whereas polyester is the solid phase.
  • crystallinity means the degree of order with which, when aligned together, the polymer chains are arranged in ordered structures.
  • Polymers can exist in forms characterized by several degrees of crystallinity ranging from fully amorphous (randomly oriented chains) to semi-crystalline (ordered regions coexisting with amorphous regions), or fully crystalline.
  • the degree of crystallinity of a polymer can be estimated by several analytical techniques, of which, the most commonly used are differential scanning calorimetry (DSC) and X-ray diffraction (XRD). According to the present invention, the degree of crystallinity of polyester inside a plastic material product corresponds to that measured by DSC according to following formula (2): 100 (2) where:
  • AHfioo% is the melting enthalpy of the examined polyester in the fully crystalline state
  • AHfioo% to be substituted in formula II for given polyester, can be deduced from the scientific literature.
  • fully crystalline PET has a AHfioo% of 140.1 J/g.
  • the level of crystallinity significantly affects the recyclability of polymers. Highly crystalline polymers are generally more difficult to recycle than their amorphous homologues.
  • dissolution/precipitation process means a procedure used to alter the physical properties of a polymer and consists of dissolving this polymer in a solvent and then precipitating it from the solution. In the context of the invention, this process is used to separate the polyester from other polymers and additives and/or contaminants and to facilitate the subsequent depolymerization step.
  • cyclic alkyl carbonates or simply “alkyl carbonates” is used in the text to refer to a class of molecules with the following 5-membered cyclic structure: where possible substituents were denoted by the letters Ri, R2, R3, and R4, wherein Ri, R2, R3, and R4 can be the same or different from each other and selected from: H and C1-C4 alkyl chains, preferably selected from H, CH3, C2H5, C3H7 or C4H9. According to the present invention, cyclic alkyl carbonates can also be different and in mixture with each other.
  • cyclic alkyl carbonates are frequently used in industrial applications as solvents, lubricants or electrolytes. Furthermore, they have recently attracted significant interest in the context of "green chemistry” or “eco-friendly chemistry", since they can be synthesized by cycloaddition of CO2 to epoxides, a process that allows highly polluting greenhouse gases to be transformed into high value-added materials.
  • the plastic material product subjected to the process of the invention contains polyethylene terephthalate (PET).
  • PET polyethylene terephthalate
  • the plastic material product subjected to the process of the invention contains at least one of the following polymers: polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polyethylene isophthalate (PEI), polycaprolactone (PCL), polyglycolic acid (PGA), poly-lactic acid (PLA), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA), polyethylene furanoate (PEF).
  • the plastic material product can also consist of an appropriate blend of the aforementioned polymers.
  • the plastic material product undergoing the process may contain, in addition to at least one polyester, other polymers including: polyamide 6 (PA6), polyamide 66 (PA66), polyethylene (PE), polypropylene (PP) or cellulose.
  • PA6 polyamide 6
  • PA66 polyamide 66
  • PE polyethylene
  • PP polypropylene
  • the plastic material product subjected to the process of the invention may also contain contaminants or additives such as, for example, greases, lubricants, plasticizers, flame retardants, pigments, dyes, antistatic agents, organic and inorganic fillers, even in mixtures with each other.
  • contaminants or additives such as, for example, greases, lubricants, plasticizers, flame retardants, pigments, dyes, antistatic agents, organic and inorganic fillers, even in mixtures with each other.
  • the plastic material product subjected to the process of the invention can be pulverized by various techniques, including: mechanical crushing, dry or cryogenic grinding, ultrasonic crushing, micronization or heat treatment.
  • the purpose of the pulverization process is to reduce the size of the material to be treated and increase its surface area.
  • the plastic material product subjected to the process of the invention is appropriately preliminarily treated by washing and disinfecting to remove possible contaminants.
  • the plastic material product is properly dried beforehand to remove any residual moisture.
  • the material to be subjected to dissolution/precipitation treatment must not have residual moisture, which could lead to even partial hydrolysis of the cyclic alkyl carbonate and thus a reduction in its solubilizing power.
  • This drying step preferably occurs in an oven under an inert atmosphere (e.g., under nitrogen) or, alternatively, by vacuum drying.
  • the drying temperature is between 70°C and 180°C.
  • the process according to the present invention is carried out by loading cyclic alkyl carbonate, which serves as the solvent in this pre-treatment step of the starting plastic material, into a thermostated reactor that is gradually heated to a temperature between 100°C and the boiling point of the cyclic alkyl carbonate, in order to remove any residual moisture retained in the solvent.
  • the plastic material product containing polyesters is then added to the preheated cyclic alkyl carbonate inside the reactor, respecting a weight percentage ratio between 5 and 70 wt% of polymer to total polymer-solvent.
  • the weight percentage ratio of polymer to total polymer-solvent is between 15 and 30 wt%.
  • the plastic material product to be treated contains impurities, additives or polymers other than polyesters, which do not dissolve in the cyclic alkyl carbonate, an operation can be carried out to separate and remove these impurities from the polyester, for example, by hot filtration of the solution.
  • the polyester component of the plastic material product to be treated is completely dissolved, its precipitation is caused by cooling the reactor. It is preferred that the reactor temperature in this step is brought to a range between 140°C and 20°C; the "cooling" temperature will depend on the cyclic alkyl carbonate selected as the solvent in the pre-treatment step.
  • the pre-treated material obtained from the pre-treatment step of the process according to the present invention, appears as an easily deformable uniform solid consisting of a porous polymer matrix inside which cyclic alkyl carbonate solvent is retained.
  • the consistency and deformability of the resulting solid strongly depend on the polymer-solvent ratio selected for dissolution. Higher proportions of polymer to the solvent result in greater resistance to deformation of the resulting pre-treated material or precipitated solid.
  • the solid obtained from the pre-processing step is suitably pulverized by known techniques such as, for example: mechanical crushing, dry or cryogenic grinding, ultrasonic crushing, micronization or heat treatment. Pulverization of the pre-treated material obtained from said pre-treatment step facilitates subsequent washing and removal of the solvent from the pre-treated polymer.
  • the resulting powder is repeatedly washed to remove residual solvent, for example, the powder is washed in deionized water.
  • organic solvents such as acetone, ethanol, methanol or other organic solvents can be used to wash the pre-treated material.
  • This last step plays a key role in the next step of depolymerization. Indeed, the solvent used for washing becomes intercalated directly into the polymer, replacing the cyclic alkyl carbonate used for dissolution, which otherwise could interfere with the depolymerization process, since it is also has ester functionalities.
  • the cyclic alkyl carbonate is then separated by distillation from the washing solvent.
  • the pre-treated material is directly subjected to the depolymerization step without being dried first.
  • the depolymerization step consists of a hydrolysis reaction, preferentially an alkaline hydrolysis.
  • depolymerization can be carried out according to any of the known solvolitic processes of polyester degradation.
  • the solvent selected for washing should correspond to the solvolitic agent used for depolymerization (for example, water for hydrolysis, ethylene glycol for glycolysis, ethanol or methanol for alcoholysis, etc).
  • said depolymerization step is carried out in the presence of a catalyst selected, for example, from the group comprising: NaOH, Na2CCh, KOH, K2CO3 and LiOH.
  • a catalyst selected, for example, from the group comprising: NaOH, Na2CCh, KOH, K2CO3 and LiOH.
  • phase-transfer catalysts for example, quaternary ammonium or phosphonium salts
  • the depolymerization step is a biological depolymerization carried out by using depolymerase capable of hydrolyzing the ester bond.
  • Depolymerase preferably belongs to the cutinase, lipase, esterase, petase or carboxylesterase groups.
  • the pre-treated material is directly loaded into a thermostated reactor together with the catalyst.
  • reduced amounts of water or organic solvent can be added, depending on the solvolitic process selected.
  • stirring is provided by mechanical stirrer.
  • the duration of the depolymerization process, as well as the optimal temperature, may depend on the nature of the product to be degraded, the type and amounts of catalyst that may be used, and the type of solvolitic process selected.
  • the monomers and/or oligomers obtained can be separated and purified by using different methodologies, including, for example: solvent extraction, filtration, distillation, column chromatography or precipitation.
  • the monomers and/or oligomers obtained from the depolymerization step can be used to re-synthesize the starting polyester with unaltered chemical and physical properties compared to the virgin material.
  • the monomers and/or oligomers obtained from the depolymerization step can be used for the synthesis of new polymers different from the starting polyester, or for the synthesis of other high value-added substances.
  • the non-depolymerized portion of the material undergoing degradation can be separated from the reaction products by filtration, centrifugation or solvent extraction.
  • the process according to the present invention allows a rapid depolymerization step to be carried out, for example, by alkaline hydrolysis under mild conditions, subsequent to the pre-treatment step of the starting plastic material.
  • One of the highly innovative aspects of the process subject-matter of the present invention is the washing step of the material obtained by precipitation during the pre-treatment step with cyclic alkyl carbonates, which allows the dissolution solvent intercalated in the precipitated material to be completely replaced with water, thus preventing re-compaction of the solid polymer matrix and promoting the diffusion of alkalis to the ester bonds.
  • the washed pretreated material remains swollen with water and, for example, by alkaline hydrolysis, completely depolymerizes into monomers within 5 minutes at 90 °C and before 2 hours at room temperature (25 °C), producing significantly improved results compared with conventional hydrolysis methods.
  • the process according to the present invention allows chemical depolymerization of plastic materials containing at least one polyester that is complete under unburdened conditions to be achieved and, in the case of depolymerization by alkaline hydrolysis with NaOH, with minimal NaOH consumption.
  • the process according to the present invention involves the use of propylene carbonate (PC), one of the most environmentally friendly and widely available solvents on the market.
  • PC propylene carbonate
  • the process exploits, in the pre-treatment step, the high solubility of PET in PC at high temperature for complete dissolution, whereas the subsequent cooling to room temperature triggers thermally induced phase separation, thus forming a porous solid matrix that retains the dissolution solvent.
  • the intercalated PC molecules can then be replaced by water, through said washing step, thus avoiding the recompaction of the polymer chains into a hydrophobic solid structure.
  • the resulting PET swollen with water is capable of retaining water up to about three times its mass.
  • Increased interfacial water stabilizes the separation of polymer chains and contributes to their depolymerization by significantly promoting the diffusion of alkali to ester bonds, thus minimizing NaOH consumption.
  • the depolymerization step for example, by alkaline hydrolysis reaction, is greatly enhanced because the problem posed by the hydrophobicity of PET is overcome thanks to the almost complete substitution by water of the pre-treatment solvent (cyclic alkyl carbonate - for example, PC). This substitution occurs without causing any chemical alteration to the polymer, but rather significantly contributing in facilitating the breakage of the polymer chains in the subsequent chemical depolymerization step, such as for example by alkaline hydrolysis.
  • the pre-treatment solvent cyclic alkyl carbonate - for example, PC
  • PET with a high level of crystallinity (42% C.I.) in granules and powder form (sieved at 1200 pm) was supplied by Poliplast S.p.a. (Bergamo, Italy) and used as received.
  • Post-consumer PET manufactured products such as bottles, textiles and containers were purchased from local retailers, washed with water and detergents, cut into approximately 2 cm x 2 cm fragments, and dried in an oven at 70°C.
  • a mix of different PET waste products was provided by a local landfill in the form of ground product. The material received was washed with water and detergents, and dried in an oven at 70°C prior to use.
  • PC Propylene carbonate
  • EC ethylene carbonate
  • NaOH >97.0% purity
  • H2SO4 >96.0% purity
  • TPA terephthalic acid
  • DSC Differential scanning calorimetry
  • TGA Thermogravimetric analyses
  • SEM images were acquired with a LEO 1525 ZEISS FE- SEM microscope, Cryo-SEM images were obtained with a Leo Crossbeam 1540 XBFIB-SEM ZEISS microscope.
  • GPC Gel permeation chromatography
  • Powdered PET supplied by Poliplast srl, with a high level of crystallinity (42% CI, measured by DSC) was used as the reference standard for performing the experiments set forth in this example.
  • the pre-treatment step in cyclic alkyl carbonates was performed on the received powder according to the following protocol. 60 g propylene carbonate was weighed and added to a 100-ml round- bottomed flask with two necks, equipped with a thermometer and mechanical stirrer. The flask was immersed in a silicone oil bath preheated to a temperature of about 200°C.
  • WET PET 25 wet porous powder
  • Figure 11 wet porous powder
  • the procedure was also repeated using 15 wt% and 40 wt% as the polymer-solvent ratio, taking 6 and 20 minutes for dissolution, respectively. Since the prepared 40 wt% solution is extremely viscous and difficult to stir, for reasons of operational convenience, only the samples prepared at 25 and 15 wt% were used for the subsequent experiments.
  • the effectiveness of the treatment in increasing polymer degradability was evaluated by subjecting virgin PET powder, and material obtained after the treatment described in Experiment la prepared at a concentration of 25 wt% (polymer-solvent ratio), to an alkaline hydrolysis process under the same conditions.
  • the material obtained as described in Experiment la was used both in the form of wet powder ("WET PET 25") and after being dried in an oven for 24 h at 70°C (“DRY PET 25”), as shown in Figure 1.
  • the prepared solution was added to the hot flask.
  • the mixture formed having the consistency of slurry because of the high polymer/solvent ratio, was kept under mechanical stirring at 250 rpm for 10 minutes.
  • the hydrolysis reaction proceeds according to the following scheme: providing disodium terephthalate (Na2TP) and ethylene glycol (EG) as soluble products.
  • PET conversion PET conversion percentages
  • TPA yield terephthalic acid yields
  • the depolymerization step by alkaline hydrolysis on the "WET PET 25" sample was repeated at room temperature, by placing an amount of wet powder corresponding to 1 g together with 1 g (2.4 equivalent) NaOH in tablets into a 50 mL flask. Then 3 ml deionized water was added to the flask and the mixture was kept under stirring for 15 minutes. Thanks to the combined effect of the doubled amount of NaOH and the heat developed by its dissolution, a PET conversion of 95 ⁇ 2% and a TPA yield of 91 ⁇ 2% could be achieved at room temperature (25°C).
  • Example 2 1 g PET from a green fabric (see Example 2) was treated according to the protocol described in Experiment la of Example 1 and subjected to depolymerization by alkaline hydrolysis at 90°C for 10 min with 1.2 equivalents NaOH. After 10 minutes, 1 g activated carbon was added to the mixture, which was kept under stirring for additional 20 minutes. The activated carbon was then removed by filtration and the reaction products precipitated from the filtrate by acidification (see Example 1). The difference in the coloration of the final product can be observed in Figure 10, from which the bleaching action of activated carbon is clearly evident.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)

Abstract

L'objet de la présente invention concerne un nouveau procédé respectueux de l'environnement pour la dégradation de matières plastiques contenant des polyesters. Le procédé permet un prétraitement de dissolution/précipitation de la matière plastique dans des solvants appropriés, visant à faciliter l'étape de dépolymérisation ultérieure du polyester.
PCT/IB2025/054032 2024-04-18 2025-04-17 Procédé de dégradation de produits plastiques contenant des polyesters Pending WO2025219922A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0850982A2 (fr) * 1996-12-31 1998-07-01 Shell Internationale Researchmaatschappij B.V. Procédé de récupération de polyester solide microporeux à partir d'un courant de recyclage et produits fabriqués par ce procédé
WO2005118691A2 (fr) * 2004-06-04 2005-12-15 Chemical Products Corporation Separation de polyolefines de polyamides
US20060069170A1 (en) * 2004-09-27 2006-03-30 Chemical Products Corporation Decomposition of Polyester
US20230048275A1 (en) * 2019-12-19 2023-02-16 Carbios Process for degrading plastic products
US20230049607A1 (en) * 2019-12-19 2023-02-16 Carbios Process for degrading plastic products

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0850982A2 (fr) * 1996-12-31 1998-07-01 Shell Internationale Researchmaatschappij B.V. Procédé de récupération de polyester solide microporeux à partir d'un courant de recyclage et produits fabriqués par ce procédé
WO2005118691A2 (fr) * 2004-06-04 2005-12-15 Chemical Products Corporation Separation de polyolefines de polyamides
US20060069170A1 (en) * 2004-09-27 2006-03-30 Chemical Products Corporation Decomposition of Polyester
US20230048275A1 (en) * 2019-12-19 2023-02-16 Carbios Process for degrading plastic products
US20230049607A1 (en) * 2019-12-19 2023-02-16 Carbios Process for degrading plastic products

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