Polyester depolymerization method

Abstract

This polyester depolymerization method includes subjecting a polyester to a depolymerization reaction in the presence of an alcohol and a homogeneous iron catalyst. The depolymerization reaction is preferably carried out in the presence of an additive, and the additive is preferably at least one selected from the group consisting of a nitrogen atom-containing cyclic compound or pyrimidine, imidazole and benzimidazole. The homogeneous iron catalyst is preferably at least one selected from the group consisting of iron (III) chloride (FeCl3), iron (III) bromide (FeBr3), and iron (III) iodide (FeI3).

Description

Method for depolymerizing polyester

[0001] This application claims priority to U.S. patent application Ser. No. 63 / 649,952, filed May 21, 2024, the contents of which are incorporated herein by reference.

[0002] Chemical recycling, which chemically converts used plastics into raw materials (monomers), is recognized as an important technology for solving the plastic waste problem, but its rate is still low globally.Upcycling, which converts plastic waste into high-value-added chemicals, is recognized as an important technology not only from the perspective of establishing basic technologies for establishing a recycling-oriented society, but also from the perspective of developing chemical processes from new alternative resources to fossil fuels such as petroleum.

[0003] Polyesters, such as polyethylene terephthalate (PET), are widely used general-purpose thermoplastics. PET is collected, sorted, washed, melted, and reprocessed, and then reused as transparent bottles through so-called mechanical recycling. However, because recycled PET resin is inferior in quality to virgin petroleum-derived resin, there is a strong demand for increased use of "bottle-to-bottle recycling," or "closed-loop recycling." Therefore, the importance of chemical recycling, which converts recycled PET resin into resins of the same quality as virgin petroleum-derived resins, has become widely recognized in recent years.

[0004] Many studies have been reported on the depolymerization of polyesters, including PET. However, most of these studies require harsh conditions (high temperature and high pressure) in the presence of excess bases, acids, and / or inorganic salts. For example, methods for recovering and purifying dimethyl terephthalate (DMT) or bis(2-hydroxyethyl) terephthalate (BHET), which have been put to practical use, require excess inorganic or organic bases, acids, and additives (e.g., inorganic salts, ionic liquids) (see, for example, Non-Patent Document 1). This process requires separation and purification of the target product and by-products, neutralization, removal of metal ions, wastewater treatment, and other procedures. These procedures reduce the quality of the recycled material, and current processes increase the price of recycled products.

[0005] Furthermore, in some methods, the alcohol that can be used is limited to methanol, and the efficiency decreases when other alcohols are used. Therefore, when other alcohols are used, more bases or acids and / or more severe conditions are required. For example, in the depolymerization with ethylene glycol (EG) (glycolysis method), PET is depolymerized using Zn(OAc) ２ (zinc acetate) catalyst and Na ２ CO ３ (196°C), 1,3-dimethylurea (190°C), or a mixture of an acid and a base (5 mol%, 180°C) (see, for example, Non-Patent Documents 2 to 4). In addition, depolymerization with methanol (methanolysis method) requires harsh conditions of high temperature (e.g., 280 to 310°C) and high pressure (about 4 MPa). To alleviate this, inorganic bases (e.g., K ２ CO ３ The coexistence of ZnCl and other amines was effective (see, for example, Non-Patent Documents 5 to 8). ２ and [HO ３ S-(CH ２ ) ３ -NET ３]Cl ((3-sulfonic acid)propyltriethylammonium chloride) at 205°C (Non-Patent Document 9). Therefore, the development of an efficient acid / base-free catalyst for the chemical recycling of polyester is considered an important challenge, and its development is expected to contribute greatly to the simplification of the purification and separation process to obtain recycled resins with high efficiency. In other words, such a catalyst and catalytic process would be more suitable for achieving horizontal recycling, or closed-loop chemical recycling, of PET.

[0006] Recently, the present inventors have demonstrated a strategy to solve the above-mentioned decomposition and repolymerization (polycondensation) problem by developing an efficient transesterification catalyst, since the decomposition and repolymerization (polycondensation) are transesterification reactions. Therefore, the present inventors have developed a catalyst for the transesterification of aliphatic fatty acid esters (FAEs), Cp'TiCl ３ (Cp' is a cyclopentadienyl group Cp or a pentamethylcyclopentadienyl ligand Cp ＊ This study focused on the application of calcium oxide (CaO), which is known as a catalyst for the transesterification of triglycerides (vegetable oils) with FAE, to the depolymerization of aliphatic polyesters. As a result, it was demonstrated that these catalysts can be used with various alcohols to promote the depolymerization of not only polyethylene adipate (PEA) and polybutylene adipate (PBA), but also PET and polybutylene terephthalate (PBT) (Non-Patent Documents 10-13). Furthermore, La(acac) ３ (acac stands for acetylacetonate) depolymerizes polyesters such as PET when treated with methanol (Non-Patent Documents 14 and 15).

[0007] In particular, the depolymerization of polyester with alcohol using both titanium and calcium catalysts yielded only the raw material (monomer) (both conversion and selectivity were over 99%). This discovery made it possible to carry out one-pot closed-loop chemical recycling (one-pot depolymerization-repolymerization) of PBT depolymerization with ethanol (Non-Patent Document 12). Furthermore, Cp'TiCl ３By using a catalyst, it became possible to produce amides by aminolysis of polyesters (Non-Patent Document 16).

[0008] A. McNeeley and YA Liu, Ind. Eng. Chem. Res., 2024, 63, 3355–3399. Polymer Degradation and Stability, 2010, 95, 2011; 1022-1028B. Liu, W. Fu, X. Lu, Q. Zhou and S. Zhang, ACS Sustainable Chemistry & Engineering, 2018, 7, 3292–3300S. Kaiho, AAR Hmayed, KR Delle Chiaie, JC Worch and AP Dove, Macromolecules, 2022, 55, 10628-10639R. D. Allen and MI James, in Circular Economy of Polymers: Topics in Recycling Technologies, ed. DI Collias, MI James and JM Layman, ACS Symposium Series; American Chemical Society , Washington , DC , 2021 , pp . 61-80D. Paszun and T. Speech, Ind. Eng. Chem. Res., 1997, 36, 1373-1383Damayanti and HS Wu, Polymers, 2021, 13, 1475A. McNeeley and YA Liu, Ind. (1999). Eng. Chem. Res., 2024, 63, 3355–3399S. https: / / doi.org / 10.1103 / PhysRevLett.1840.011302 , Google Scholar Crossref , CAS 10. Liu, Z. Wang, L. Li, S. Yu, C. Xie and F. Liu. Nomura , T. Aoki , Y. Ohki , S. Kikkawa and S. Aoki .Yamazoe, ACS Sustainable Chemistry & Engineering, 2022, 10, 12504-12509S. Sudhakaran, SH Siddiki, B. Kitiyanan and K. Nomura, ACS Sustainable Chemistry & Engineering, 2022, 10, 12864-12872Y. Ohki, Y. Ogiwara and K. Nomura, Catalysts, 2023, 13, 421P. Unruean, P. Padungros, K. Nomura and B. Kitiyanan, Journal of Material Cycles and Waste Management, 2024, 26, 731-740R. Abe, N. Komine, K. Nomura and M. Hirano, Chemical Communications, 2022, 58, 8141-8144N. Kobayashi, N. Komine, K. Nomura, H. Hirano and M. Hirano, Bulletin of the Chemical Society of Japan, 2023, 96, 1324-1330Y. Ogiwara and K. Nomura, ACS Organic & Inorganic Au, 2023, 3, 377-383.

[0009] However, in order to further promote the decomposition and recycling of polyester on a global scale, it has been desired to develop a method for depolymerizing polyester that not only enables one-pot closed-loop chemical recycling of polyester but also uses an easily available and inexpensive polyester decomposition catalyst.

[0010] The inventors used commercially available FeCl ３ and FeBr ３We have already reported that this catalyst is an effective transesterification catalyst for the transesterification of FAE (methyl 1-undecenoate), and we have investigated its potential as a homogeneous catalyst for the depolymerization of polyesters such as PET with alcohol. As a result, we demonstrated that this homogeneous catalyst enables efficient depolymerization of polyester with alcohol, enabling the selective depolymerization of polyester from plastic mixtures (polyester and polyethylene) and polyester fiber waste (a mixture of PET and cotton, which also contains dyes commonly used in clothing). This makes it applicable to actual chemical recycling processes (obtaining raw materials) from waste. We have found that this could enable the efficient chemical recycling of textile (fabric and clothing) waste, another important challenge toward realizing a circular economy. Furthermore, we found that the addition of a small amount of amine further improves catalytic activity and reaction efficiency while maintaining selectivity.

[0011] An object of the present invention is to provide a method for depolymerizing polyesters, which enables decomposition into raw material monomers with very high selectivity and yield under acid / base-free conditions using an easily available and inexpensive homogeneous catalyst, even if the polyester is contained in a mixture with a substance other than polyester.

[0012] The present invention has the following aspects. [1] A method for depolymerizing a polyester, comprising subjecting the polyester to a depolymerization reaction in the presence of an alcohol and a homogeneous iron catalyst. [2] The method for depolymerizing a polyester according to [1], wherein the depolymerization reaction is carried out further in the presence of an additive. [3] The method for depolymerizing a polyester according to [2], wherein the additive is a nitrogen-atom-containing cyclic compound. [4] The method for depolymerizing a polyester according to [2], wherein the additive is at least one selected from the group consisting of pyrimidine, imidazole, and benzimidazole. [5] The method for depolymerizing a polyester according to any one of [1] to [4], wherein the polyester has at least one ester bond in the repeating unit of the polymer. [6] The method for depolymerizing a polyester according to any one of [1] to [5], wherein the polyester is at least one selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene isosorbide terephthalate (PEIT), polylactic acid (PLA), polyhydroxyalkanoate (PHA), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), polyethylene furanoate (PEF), polycaprolactone (PCL), poly(ethylene adipate) (PEA), polyethylene naphthalate (PEN), polycyclohexylene dimethylene terephthalate (PCT), polyethylene succinate (PES), poly(butylene succinate-co-terephthalate) (PBST), and poly(butylene succinate / terephthalate / isophthalate)-co-(lactate) (PBSTIL). [7] The method for depolymerizing a polyester according to [6], wherein the polyester is polyethylene terephthalate (PET). [8] The method for depolymerizing a polyester according to any one of [1] to [6], wherein the polyester is a polyester contained in a mixture of a polyester and a substance other than a polyester. [9] The method for depolymerizing a polyester according to any one of [1] to [6], wherein the homogeneous iron catalyst is iron(III) chloride (FeCl ３ ), iron(III) bromide (FeBr ３ ) and iron(III) iodide (FeI ３

[10] The method for depolymerizing a polyester according to any one of [1] to [8], wherein the homogeneous iron catalyst is at least one selected from the group consisting of iron(III) chloride (FeCl ３ ) is at least one selected from the group consisting of methanol, ethanol, ethylene glycol, n-butanol, and isopropanol.

[11] The method for depolymerizing a polyester according to any one of [1] to

[10] , wherein the alcohol is at least one selected from the group consisting of methanol, ethanol, ethylene glycol, n-butanol, and isopropanol.

[12] The method for depolymerizing a polyester according to any one of [1] to

[11] , wherein the amount of the homogeneous iron catalyst relative to the amount of the alcohol (100 mol%) is 0.5 to 15.0 mol%, preferably 1.0 to 10 mol%, and more preferably 2.0 to 8.0 mol%.

[13] The method for depolymerizing a polyester according to any one of [1] to

[12] , wherein the reaction temperature of the depolymerization reaction is 110 to 220°C, preferably 120 to 210°C, and more preferably 150 to 190°C.

[14] The method for depolymerizing a polyester according to any one of [1] to

[13] , wherein the reaction pressure of the depolymerization reaction is 0.2 to 4 MPa, and preferably 0.2 to 3 MPa.

[0013] According to the present invention, there can be provided a method for depolymerizing polyester, which enables decomposition of polyester into raw material monomers with very high selectivity and yield under acid / base-free conditions using an easily available and inexpensive homogeneous catalyst, even if the polyester is contained in a mixture with a substance other than polyester.

[0014] In Example 1 １ H and １３ C-NMR spectra of FeCl under various conditions. ３ 1 shows a photograph of the reaction mixture in the depolymerization of PET by Example 8. １３ 1 is a chart showing the time course of monitoring by C-NMR spectrum. It is an enlarged view of a part of the chart shown in FIG. 3. １ H and １３1 shows a C-NMR spectrum; 2 shows a photograph showing the color change of the reaction mixture in the examples; 3 shows a photograph of the fiber waste sample used in Examples 21 to 25; 4 shows the NMR spectrum after removing volatiles from the reaction mixture in Examples 22, 23 and 25; and 5 shows photographs of the reaction mixture in Examples 26 and 27. １３ The C-NMR spectrum is shown.

[0015] The method for depolymerizing polyester of the present invention comprises subjecting polyester to a depolymerization reaction in the presence of a monohydric alcohol and a homogeneous iron catalyst. The depolymerization reaction in the method of the present invention is a transesterification reaction, in which the polyester is decomposed into a polycarboxylic acid ester (an ester with the monohydric alcohol) and a polyhydric alcohol. For example, when the polyester is polyethylene terephthalate (PET) and the monohydric alcohol is ethanol, the PET is decomposed into diethyl terephthalate (DET) and ethylene glycol (EG).

[0016] <Polyester> Generally, polyester is a condensation polymer synthesized by dehydration condensation of a polycarboxylic acid and a polyhydric alcohol to form an ester bond. Examples of the polyester include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene isosorbide terephthalate (PEIT), polylactic acid (PLA), polyhydroxyalkanoate (PHA), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), polyethylene furanoate (PEF), polycaprolactone (PCL), poly(ethylene adipate) (PEA), polyethylene naphthalate (PEN), polycyclohexylene dimethylene terephthalate (PCT), polyethylene succinate (PES), poly(butylene succinate-co-terephthalate) (PBST), and poly(butylene succinate / terephthalate / isophthalate)-co-(lactate) (PBSTIL). Of these, polyethylene terephthalate (PET) is preferred, as it is widely used in a variety of applications, including PET bottles used as beverage containers, base materials for films and magnetic tapes, and fibers for clothing (fleece, etc.).

[0017] In a preferred embodiment of the present invention, the polyester is a polyester contained in a mixture of polyester and a substance (foreign matter) other than polyester (hereinafter, also referred to as a "polyester mixture"). Examples of the substance other than polyester include polyvinyl chloride (PVC), polyvinyl acetal, polyvinyl butyral (PVB), polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), cotton, polyolefin, polyethylene, polypropylene, polystyrene, polycarbonate, spandex, natural fibers, cellulose ester, polyacrylate, polymethacrylate, polyamide, nylon, poly(lactic acid), polydimethylsiloxane, polysilane, calcium carbonate, titanium dioxide, inorganic fillers, dyes, pigments, color toners, colorants, plasticizers, adhesives, flame retardants, metals, aluminum, iron, and combinations thereof. The amount of polyester and non-polyester substances (foreign matter) in the polyester mixture is not particularly limited, but may be, for example, about 0.01% to about 50% by weight, about 0.01% to about 40% by weight, about 0.01% to about 30% by weight, about 0.01% to about 20% by weight, about 0.01% to about 15% by weight, about 0.01% to about 10% by weight, about 0.01% to about 7.5% by weight, about 0.01% to about 5% by weight, about 0.01% to about 2.5% by weight, or about 0.01% to about 1.0% by weight, based on the weight of the polyester in the polyester mixture. According to the method of the present invention, raw material monomers can be obtained with very high selectivity and yield by directly subjecting the polyester mixture to a depolymerization reaction without performing pretreatment or the like to remove foreign matter from the polyester mixture. Specifically, selectivity and yield of nearly 100% (>99%) are achievable.

[0018] <Homogeneous iron catalyst> The homogeneous iron catalyst is iron (III) chloride (FeCl ３ ), iron(III) bromide (FeBr ３ ) and iron(III) iodide (FeI ３In particular, from the viewpoint of reaction efficiency in PET depolymerization, iron(III) chloride (FeCl ３ These homogeneous iron catalysts can be produced by known methods, and commercially available products may also be used.

[0019] <Alcohol> The alcohol is preferably at least one monohydric alcohol selected from the group consisting of methanol, ethanol, ethylene glycol, n-butanol, and isopropanol. From the viewpoint of yield, the alcohol is preferably methanol or ethanol. The amount of the homogeneous iron catalyst relative to the amount of the alcohol (100 mol%) is preferably 0.5 to 15.0 mol%, more preferably 1.0 to 10 mol%, and even more preferably 0.5 to 5.0 mol%. When the amount of the homogeneous iron catalyst is equal to or greater than the lower limit, the decomposition rate is advantageously high. When the amount of the homogeneous iron catalyst is equal to or less than the upper limit, the catalyst cost can be reduced and the catalytic efficiency is advantageously high.

[0020] <Additives> The depolymerization reaction is preferably carried out in the presence of an additive. The presence of an appropriate additive enables decomposition into raw material monomers with higher selectivity and yield. Examples of the additive include nitrogen-containing cyclic compounds. Specific examples of the nitrogen atom-containing cyclic compound include pyrrole, pyrazole, triazole, tetrazole, oxazole, isoxazole, isothiazole, oxadiazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, dihydropyrrolopyrrole, furopyrrole, thienopyrrole, indoline, indole, isoindole, indolizine, indazole, benzimidazole, azaindole, pyrazolopyrimidine, purine, benzisoxazole, benzisothiazole, benzoxazole, benzthiazole, adenine, guanine, tetrahydroquinolinoline, dihydroisoquinolinoline, quinoline, isoquinoline, quinoxaline, fusalazine, quinazoline, cinnoline, naphtholidine, pyridopyrimidine, pyridopyrazine, pteridine, quinolinone, isoquinolinone, carbesol, acridine, benzoxazine, phenazine, phenoxazine, and phenothiazine. Among these, from the viewpoints of the selectivity and yield of the raw material monomers, it is preferable to use at least one additive selected from the group consisting of pyrimidine, imidazole, and benzimidazole. From the viewpoints of the selectivity and yield of the raw material monomers, the amount of the additive is preferably 0.5 to 30 molar equivalents, more preferably 0.5 to 10 molar equivalents, and even more preferably 1 to 5 molar equivalents.

[0021] <Reaction Conditions> The reaction temperature of the depolymerization reaction is preferably 110 to 220°C, more preferably 120 to 210°C, and even more preferably 150 to 190°C. When the reaction temperature is equal to or higher than the lower limit, the energy required for heating is reduced. When the reaction temperature is equal to or lower than the upper limit, the reaction proceeds rapidly. The reaction pressure of the depolymerization reaction is preferably 0.2 to 4 MPa, and more preferably 0.2 to 3 MPa. The reaction time of the depolymerization reaction varies depending on the type and amount of catalyst, but is preferably 1 to 24 hours, more preferably 1 to 18 hours, and even more preferably 3 to 12 hours. When the reaction time is equal to or higher than the lower limit, no unreacted material remains.

[0022] <Optional Pretreatment of Polyester Blend> As described above, in the method of the present invention, even when a polyester blend containing foreign matter is used, the polyester blend can be directly subjected to a depolymerization reaction without any pretreatment to remove the foreign matter, and the polyester can be decomposed into raw material monomers with a selectivity and yield of nearly 100% (>99%). Therefore, pretreatment is not necessary, but the polyester blend may be subjected to an optional pretreatment before the depolymerization reaction. The pretreatment may include any type of treatment to remove a portion of the optional foreign matter from the polyester blend and / or recover one or more polyesters from a mixed feedstock, e.g., a feedstock containing the above-mentioned foreign matter. For example, in one aspect, the optional pretreatment may include exposing the polyester blend to one or more solvents to selectively dissolve the polyesters in the polyester blend (or at least a portion of the foreign matter in the polyester blend) and enable separation between at least a portion of the foreign matter and one or more polyesters in the polyester blend. In one example aspect, the optional pretreatment may include exposing the polyester blend to one or more solvents, e.g., one or more solvents capable of causing dissolution of the polyesters in the polyester blend. For example, the one or more solvents can include, but are not limited to, 4-methylcyclohexanemethanol (MCHM), ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), 1,4-cyclohexanedimethanol (CHDM), poly(ethylene glycol) (PEG), neopentyl glycol (NPG), propanediol (PDO), butanediol (BDO), 2-methyl-2,4-pentanediol (MPdiol), poly(tetramethylene ether) glycol (PTMG), dibutyl terephthalate (DBT), dioctyl terephthalate (DOTP), ethylene carbonate (EC), dimethyl carbonate (DMC), dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), or combinations thereof. In the same or alternative aspect, the polyester blend may be exposed to one or more solvents at a specific temperature to effect dissolution of one or more components.In various aspects, the pretreatment process may include one or more dissolution and separation steps using various solvents and / or temperatures to achieve a desired level of contaminant removal and / or PET purity level. For example, one aspect may utilize dissolution and separation using one solvent at a particular temperature to, e.g., remove one or more contaminants, followed by subsequent dissolution and separation of the polyester fraction using another solvent at a particular temperature to, e.g., remove one or more other contaminants. The dissolution and / or separation in this optional pretreatment step may utilize any suitable system, reactor, vessel, and / or separation technique to achieve the desired pretreated polyester mixture.

[0023] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0024] <Analytical Method> <Yield Evaluation> 0.2 g of mesitylene (1,3,5-trimethylbenzene) was added to the resulting reaction mixture as an internal standard, and the yield of diethyl terephthalate (DET) was evaluated by gas chromatography (GC) (quantitative analysis using a calibration curve for the internal standard). GC chromatograms were recorded using a gas chromatograph (GC-2014, Shimadzu Corporation) equipped with a flame ionization detector (FID) using nitrogen as the carrier gas. The analysis conditions were as follows: DB-1MS column: 30 m × 0.250 mm × 0.25 μm; column temperature: 80°C (4 min), then increased to 320°C (20°C / min) (injection 300°C, flow rate (column) 1.71 mL / min).

[0025] Evaluation of Conversion Rate: The reaction mixture obtained was dissolved in chloroform-d(CDCl) at 25°C. ３ ) in １ H (500.13 MHz) and １３ C{ １ H (125.77 MHz) NMR spectroscopy. １ H and １３C-NMR measurements were performed on a Bruker AV500 spectrometer (500.13 MHz and 125.77 MHz, respectively) at 25 °C. Chemical shifts were measured using tetramethylsilane (SiMe ４ The methyl group of the compound (C) was used as the reference (0.00 ppm) and the values ​​were recorded in ppm.

[0026] [Example 1] <FeCl ３ or FeBr ３ Catalytic Depolymerization of PET with Ethanol> Depolymerization of PET with ethanol was carried out in a sealed glass reaction tube containing a PET sheet, ethanol (EtOH) (5.0 mL), and the amount of FeCl shown in Table 1. ３ or FeBr ３ The reaction mixture was stirred magnetically at the temperature shown in Table 1. The reaction scheme for this depolymerization is shown below.

[0027]

[0028] Depolymerization was carried out in a dry box under a nitrogen atmosphere. PET sheets were prepared by cutting PET beverage bottles. Anhydrous ethanol (>99.5%, Kanto Chemical Co., Ltd.) was used. FeCl ３ (97.0%) and FeBr ３ (98.0%) was obtained from Aldrich Chemical Co. The specific procedure for depolymerization of PET by transesterification is as follows: FeCl in the amount shown in Table 1 ３ or FeBr ３ , 500 mg of PET sheet, and 5.0 mL of ethanol were loaded into an oven-dried 15.0 mL scale pressure tube with a screw cap under a nitrogen atmosphere. The reaction mixture was stirred for a predetermined time and temperature using an alumina bath. After the reaction was completed, the mixture was cooled to room temperature and CHCl ３ (approximately 3 mL). ３The solvents (e.g., ethanol) were removed under vacuum. Selective transesterification of PET from mixtures with polyethylene or cotton was carried out under similar conditions, except that 500 mg of PET sheet and 200 mg of cotton or polyethylene were used. Conversion and yield were measured using the methods described above. The results are shown in Table 1. In all examples, the conversion was determined to be greater than 99% (>99%), as no residual resonances due to carbonyl groups other than diethyl terephthalate (DET) were observed.

[0029]

[0030] FeCl ３ Depolymerization of PET with ethanol in the presence of ethanol (5.0 mol%) proceeded at 180°C, and DET was obtained with a selectivity and yield of nearly 100% (>99%) as determined by GC analysis (Examples 1 and 2). The calculated recovery yields of ethylene glycol (EG) and DET after careful removal of ethanol were very close. The fact that only DET and EG were produced was due to the １ H and １３ This was also confirmed by the C-NMR spectrum (Figure 1; additional NMR spectra are shown in Figure 10). ３ Reactions carried out in the presence of Fe (Examples 7-9) or at 160°C (Fe 5.0 mol%, Examples 3-5) showed similar results, and the results were reproducible (Examples 3 and 4). １３ After removal of volatiles (including EG), DET was obtained as the only product, as shown by the time course monitored by C-NMR spectroscopy.

[0031] In contrast, FeCl ３In the low loading reactions (1.0 mol%, Examples 10-12), the DET yield was low after 18 hours but increased over time, eventually reaching over 99% after 48 hours [DET yield 21% (18 hours), 97% (30 hours), >99% (48 hours)]. This is similar to what was observed in the depolymerization of PET with ethanol using Cp'TiCl and CaO catalysts. The reaction performed at 120 °C also resulted in a decrease in DET yield (Example 6). In both Examples 6 and 10, only one resonance attributed to the carbonyl group of DET was observed in the region around 155-170 ppm, which is attributed to the carbonyl carbon. Meanwhile, the reaction mixture after removal of volatiles was analyzed using CDCl. ３ Except that the mixture in CDCl showed two phases. ３ The solution was completely dissolved in the solution (Fig. 4, Example 6) and Fig. 5). １ The H-NMR spectrum is shown in FIG. １３ The C-NMR spectrum is shown (in chloroform solvent, 25°C). ３ The amount was 1.0 mol%, and the reaction times were 18 hours (Example 10), 30 hours (Example 11), and 48 hours (Example 12). Several resonances (probably due to oligomers) were observed in the spectra, and several additional peaks (with retention times longer than DET) were also observed in GC. These results indicate that Cp'TiCl ３ This suggests that PET was depolymerized to give a mixture of oligomers that were eventually converted to DET over time, as observed with catalytic depolymerization.

[0032] Figure 2 shows the FeCl under various conditions. ３ As shown in Figure 2a, a small amount of FeCl was added at 180 °C to depolymerize PET. ３The reaction mixture for the reaction performed in Example 1 initially turned cloudy and pale yellow after 18 hours (Figure 2a, left) and became a clear solution after 30 hours (Figure 2a, right). It can be seen that DET was produced with nearly 100% (>99%) selectivity and yield (as confirmed by GC and NMR spectra). A similar color change was observed in Figure 2b, where the reaction mixture with incomplete conversion to DET showed a cloudy pale yellow color and eventually changed color to a clear solution upon completion of conversion to DET. These observations support the above hypothesis that PET was first converted to an oligomer mixture and then ultimately converted to DET.

[0033] Similarly, the depolymerization of PET with ethanol was ３ The reaction proceeds in the presence of FeBr ３ In the reactions carried out with 3.0 and 5.0 mol % of FeBr, DET was stably obtained with a selectivity and yield of almost 100% (>99%) (Examples 13, 16, and 17). ３ The DET yield in the low loading (1.0 mol%) reaction was initially low (34%, Example 18) and reached a steady state after 48 hours (Example 20). However, the conversions at 160°C (Example 14) and 120°C (Example 15) were significantly higher than those at 1.0 mol% FeCl. ３ Therefore, FeCl was not used as a catalyst for PET depolymerization. ３ The color of the reaction mixture initially showed red, and then changed from a cloudy pale red to a clear solution in which DET was stably produced (Figure 6).

[0034] Examples 21 to 25 Selective depolymerization of PET from a mixture with polyethylene and textile waste using ethanol The reaction was carried out in the same manner as in Example 1, except that 200 mg of the textile waste sample shown in Table 2 and FIG. 7 was used instead of the PET sheet. The mass of cotton was measured after collecting the solid after filtering the reaction mixture and drying it under vacuum. The results are shown in Table 2.

[0035]

[0036] The textile waste samples (yellow, white, and black, see Figure 3) were treated with ethanol to remove FeCl ３As shown in Figure 7a and Table 2 (Examples 21 and 22), a yellow sample consisting of a mixture of PET (65%) and cotton (35%) was depolymerized with FeCl ３ Treatment with ethanol in the presence of EG (5.0 mol% relative to PET) afforded DET (>99% yield, traces of dye remaining), and cotton was also recovered in consistent high yields (>99% recovery yield). Complete conversion to DET was achieved in 16 hours (Example 22). Similarly, the reaction of the white sample (Figure 7b, 100% PET) and the black sample (Figure 7c, 100% PET) with ethanol also afforded PET (Examples 23-25), and the results were reproducible (Examples 23 and 24). Furthermore, as shown in Figure 8, after removal of volatiles from the reaction mixture, no other resonances attributed to DET were observed in the NMR spectrum (EG remained). Note that Figure 8 shows the results of the reaction at 180 °C with 5 mol% FeCl ３ of the mixture obtained by depolymerization of PET fabric by transesterification with ethanol using １３ C-NMR spectrum (25 °C, CDCl ３ Figure 8(a) shows the NMR spectrum for the white sample (Example 22, 100% PET), Figure 8(b) shows the NMR spectrum for the white sample (Example 23, 100% PET), and Figure 8(c) shows the NMR spectrum for the black sample (Example 25, 100% PET). These results clearly demonstrate that this acid- and base-free method can be applied to the chemical recycling of textile waste to produce raw materials without any products.

[0037] Examples 26 and 27 Selective depolymerization of PET from a mixture with cotton using ethanol The reaction was carried out in the same manner as in Example 1, except that a mixture of 500 mg of PET sheet and 200 mg of polyethylene (PE) or cotton fabric was used instead of the PET sheet. The mass of cotton was measured after filtering the reaction mixture, recovering it as a solid, and drying it in vacuo. The results are shown in Table 3. The changes in the reaction system during the reaction are also shown in Figure 9.

[0038]

[0039] As can be seen from Table 3 and Figure 9, the method of this example can be applied to selectively depolymerize PET from a mixture of PET and cotton or PE. Cotton or PE was consistently recovered in high yields, and DET was consistently recovered from the reaction mixture with nearly 100% (>99%) selectivity and yield (Examples 26 and 27). These results also demonstrate that the acid / base-free method of this example can be applied to the chemical recycling of textile waste to recover raw materials without producing any products.

[0040] [Examples 28 to 41 and Comparative Example 1] <FeCl ３ Catalytic Depolymerization of PET with Ethanol> Depolymerization of PET with ethanol was carried out in a sealed glass reaction tube, into which a PET sheet (prepared by cutting a PET beverage bottle as in Example 1), ethanol (EtOH) (5.0 mL), and the amount of FeCl shown in Table 4 were placed. ３ Furthermore, the additives shown in Table 4 were added in the form of FeCl ３ The reaction mixture was stirred magnetically at the temperature shown in Table 4.

[0041]

[0042] [Examples 42 to 52 and Comparative Example 2] <FeCl ３ Depolymerization of PET with Various Alcohols Using a Catalyst> Depolymerization of PET with various alcohols shown in Table 5 was carried out in a sealed glass reaction tube, into which a PET sheet (prepared by cutting a PET beverage bottle in the same manner as in Example 1), alcohol (5.0 mL), and the amount of FeCl shown in Table 5 were placed. ３ Furthermore, the additives shown in Table 5 were added in the form of FeCl ３ The reaction mixture was stirred magnetically at the temperature shown in Table 5.

[0043]

[0044] As can be seen from Tables 4 and 5, the presence of certain additives in the reaction system further improves the yield of DET.

Claims

1. A method for depolymerizing polyester, comprising subjecting the polyester to a depolymerization reaction in the presence of an alcohol and a homogeneous iron catalyst.

2. The method for depolymerizing polyester according to claim 1, wherein the depolymerization reaction is carried out in the presence of an additive.

3. The method for depolymerizing polyester according to claim 2, wherein the additive is a nitrogen atom-containing cyclic compound.

4. The method for depolymerizing polyester according to claim 2, wherein the additive is at least one selected from the group consisting of pyrimidine, imidazole and benzimidazole.

5. The method for depolymerizing polyester according to claim 1 or 2, wherein the polyester has at least one ester bond in the repeating unit of the polymer.

6. The method for depolymerizing polyester according to claim 1 or 2, wherein the polyester is at least one selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene isosorbide terephthalate (PEIT), polylactic acid (PLA), polyhydroxyalkanoate (PHA), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), polyethylene furanoate (PEF), polycaprolactone (PCL), poly(ethylene adipate) (PEA), polyethylene naphthalate (PEN), polycyclohexylene dimethylene terephthalate (PCT), polyethylene succinate (PES), poly(butylene succinate-co-terephthalate) (PBST), and poly(butylene succinate / terephthalate / isophthalate)-co-(lactate) (PBSTIL).

7. The method for depolymerizing polyester according to claim 6, wherein the polyester is polyethylene terephthalate (PET).

8. The method for depolymerizing polyester according to claim 1 or 2, wherein the polyester is contained in a mixture of polyester and a substance other than polyester.

9. The homogeneous iron catalyst is iron(III) chloride (FeCl ３ ), iron(III) bromide (FeBr ３ ) and iron(III) iodide (FeI ３ 3. The method for depolymerizing a polyester according to claim 1 or 2, wherein the depolymerization agent is at least one selected from the group consisting of:

10. The homogeneous iron catalyst is iron(III) chloride (FeCl ３ 6. The method for depolymerizing a polyester according to claim 5, wherein 11. The method for depolymerizing polyester according to claim 1 or 2, wherein the alcohol is at least one selected from the group consisting of methanol, ethanol, ethylene glycol, n-butanol, and isopropanol.

12. The method for depolymerizing polyester according to claim 1 or 2, wherein the amount of the homogeneous iron catalyst relative to the amount (100 mol %) of the alcohol is 0.5 to 15.0 mol %.

13. The method for depolymerizing polyester according to claim 1 or 2, wherein the depolymerization reaction is carried out at a temperature of 110 to 220°C.

14. The method for depolymerizing polyester according to claim 1 or 2, wherein the reaction pressure of the depolymerization reaction is 0.2 to 4 MPa.

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