A method of degrading a polyester

Abstract

The application discloses a polyester degradation method. Specifically, the polyester degradation method comprises the following steps: degrading the polyester under the action of a carboxylic acid and a catalyst, namely, the polyester is degraded; the polyester comprises repeating units formed by a dibasic carboxylic acid and a dihydric alcohol; and the catalyst is a Lewis acid and / or a sulfonic acid organic acid. The degradation method has wide application range, the obtained product dicarboxylic acid is simple to separate and can be used for resynthesis of the polyester, the catalyst can be recycled and reused, the obtained product dihydric alcohol dicarboxylic acid ester can be reduced by hydrogenation to form a carboxylic acid, and the carboxylic acid and the catalyst in the degradation solution are repeatedly used for degradation of the polyester, so that the industrial benefits of the polyester degradation are maximized.

Description

Technical Field

[0001] This invention belongs to the field of organic chemistry and relates to a method for the degradation of polyester. Background Technology

[0002] Polyesters are a general term for polymers obtained by the condensation polymerization of polyols and polycarboxylic acids. They are a class of engineering plastics with excellent properties and wide applications, and can also be made into polyester fibers and polyester films. Specific types of polyesters include: polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polypropylene terephthalate (PTT), polyethylene 2,5-furandicarboxylate (PEF), and various modified polyester-based fibers, among which PET polyester is the most widely used.

[0003] PET polyester is an excellent crystalline thermoplastic polyester material widely used in food packaging, textiles, films, and synthetic fibers. However, due to its difficulty in being degraded by microorganisms in the environment, the disposal of waste PET polyester has become increasingly prominent with the rapid growth in PET polyester production and consumption. Recycling waste PET polyester can not only reduce environmental pollution but also achieve resource recycling. The main recycling methods for PET polyester are physical and chemical methods. Among them, monomers or intermediates obtained from chemical degradation can be used as raw materials to re-prepare high-performance polyester materials, achieving efficient resource regeneration.

[0004] Currently, the main chemical degradation methods for PET polyester include alcoholysis, hydrolysis, and ammonolysis. Alcoholysis uses various alcohols such as methanol and ethylene glycol as alcoholysis agents, degrading PET polyester into terephthalate (DMT, BHET) and ethylene glycol through different processes. Alcoholysis yields products with high purity, operates under relatively mild conditions, and is easily implemented for continuous industrial production, such as DuPont's low-pressure methanol alcoholysis process for PET polyester. This process first cuts the PET polyester into fragments, then feeds them into a reaction vessel containing molten DMT, controlling the reactor temperature at 220°C to ensure complete dissolution of the PET polyester in the solution. The resulting solution is then poured into the reactor, and methanol at a temperature of 260–300°C and a pressure of 0.34–0.65 MPa is blown into the reactor to react with the PET polyester solution in the reactor, causing a depolymerization reaction. Other methods include the three-stage continuous methanol depolymerization process for PET polyester used by Eastman Kodak. Alcoholysis has been extensively studied and the process is relatively mature, typically involving high temperatures above 200°C or various medium- and high-pressure controls. Hydrolysis is a method that uses water as a solvent to catalytically degrade PET polyester, depolymerizing it into monomers terephthalic acid (TPA) and ethylene glycol. The obtained TPA monomer can be directly used in the reprocessing of PET polyester. Neutral hydrolysis is typically carried out at temperatures ranging from 245 to 300°C, with pressures usually controlled between 1 and 4 MPa. The supercritical water hydrolysis process for PET developed by Kobe Steel in Japan belongs to this category. Alkaline hydrolysis is usually conducted in an aqueous solution of sodium hydroxide and potassium hydroxide, typically at temperatures ranging from 200 to 250°C, with reaction pressures controlled between 1.4 and 2 MPa, and a reaction time of 3 to 5 hours. The main products of this method are sodium terephthalate or potassium terephthalate and ethylene glycol. High-purity terephthalic acid can be obtained through acidification. However, the subsequent treatment of the waste liquid generated is complex and can easily pollute the environment. Amine hydrolysis involves reacting PET polyester with different types of amines to produce the corresponding benzamides. However, due to the slow reaction of PET and the large number of byproducts, PET amine hydrolysis has not yet been industrialized.

[0005] Numerous studies have been conducted on the degradation of PET polyester, and relatively mature processes exist. However, due to various limitations, there is still significant room for improvement in the chemical recycling of PET polyester. Furthermore, with the continuous development of the polyester industry, various polyester materials with different structures and functions have emerged in recent years. The industrial production and use of these functional polyesters will inevitably face the issue of waste recycling.

[0006] In conclusion, it is of great significance to develop a new, universal method for polyester degradation with higher industrial added value. Summary of the Invention

[0007] The technical problem this invention aims to solve is to overcome the shortcomings of existing polyester degradation methods, such as their limited variety and narrow applicability, and to provide a new method for polyester degradation. Unlike traditional degradation methods, this invention uses carboxylic acids to degrade polyester, resulting in a wider range of applications. The products obtained by the degradation method of this invention are easy to separate. The degradation product, diol dicarboxylic ester, obtained by this invention can be converted into diols using conventional methods for polyester resynthesis, or used directly as a chemical in other chemical transformations. The catalyst can be recycled and reused, or it can be hydrogenated and reduced to form carboxylic acids, which, together with the catalyst in the degradation solution, can be used for repeated polyester degradation, thereby maximizing the industrial benefits of polyester degradation.

[0008] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0009] This invention provides a method for degrading polyester, comprising the following steps: degrading the polyester under the action of a carboxylic acid and a catalyst; wherein the polyester comprises repeating units formed by dicarboxylic acids and diols; and wherein the catalyst is a Lewis acid and / or a sulfonic acid.

[0010] In some embodiments of the present invention, the structure of the repeating unit may be as shown in Formula I:

[0011]

[0012] Among them, ring A is C6-C 10 Aromatic rings, or 5-6 membered heteroaromatic rings with heteroatoms selected from one or more of N, O and S, and the number of heteroatoms being 1-2;

[0013] n is an integer from 1 to 9.

[0014] In some embodiments of the present invention, in ring A, C6-C 10 The aromatic ring can be a benzene ring (e.g.) ) or naphthalene ring.

[0015] In some embodiments of the present invention, in ring A, the 5-6 membered heteroaromatic ring "selected from one or more of N, O and S, with 1-2 heteroatoms" can be a 5-6 membered heteroaromatic ring "with O as the heteroatom and 1-2 heteroatoms", or it can be a furan ring (e.g. ).

[0016] In some embodiments of the present invention, n can be an integer from 1 to 5, or 1, 2 or 3.

[0017] In some embodiments of the present invention, ring A may be

[0018] In some embodiments of the present invention, the structure of the repeating unit may be as follows:

[0019] In some embodiments of the present invention, the repeating unit of the polyester may have the structure shown in Formula I:

[0020]

[0021] The definitions of ring A and n are the same as described above.

[0022] In some embodiments of the present invention, the degradation products include dicarboxylic acids and diol dicarboxylic acid esters.

[0023] In some embodiments of the present invention, the structure of the dicarboxylic acid may be as shown in Formula P1.

[0024]

[0025] The definition of ring A is the same as described above.

[0026] In some embodiments of the present invention, the structure of the dicarboxylic acid may be as follows:

[0027] In some embodiments of the present invention, the structure of the diol dicarboxylic acid ester may be as shown in Formula P2.

[0028]

[0029] Among them, R 1 It is a C1-C6 alkyl group;

[0030] The definition of n is the same as described above.

[0031] In some embodiments of the present invention, R 1 In this context, the C1-C6 alkyl group can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, or tert-butyl, for example, methyl, ethyl, or n-propyl.

[0032] In some embodiments of the present invention, the structure of the diol dicarboxylic acid ester may be as follows:

[0033] In some embodiments of the present invention, the Lewis acid may be a perfluoroalkyl sulfonate M(C m F 2m+1 SO3) x Where M is Sc ion, Y ion, Ce ion, Yb ion, Lu ion, Ti ion, Zr ion, Hf ion, V ion, Nb ion, Ta ion, Mo ion, W ion, Cu ion, Al ion, Fe ion, Ga ion, In ion, Sn ion or Bi ion, m is an integer from 1 to 8, and x is an integer from 1 to 6.

[0034] Preferably, M is Sc ion, Hf ion, Zr ion, Al ion or Fe ion, more preferably Hf ion;

[0035] Preferably, m is 1, 2, or 3;

[0036] Preferably, x is 3 or 4;

[0037] Preferably, the Lewis acid is trifluoromethanesulfonate M(CF3SO3). x The definitions of M and x are as described above;

[0038] Preferably, the trifluoromethanesulfonate is Hf(OTf)4, Al(OTf)3, Fe(OTf)3 or Sc(OTf)3, more preferably Hf(OTf)4.

[0039] In some embodiments of the present invention, the sulfonic acid organic acid may be perfluoroalkyl sulfonic acid HC. m’ F 2m’+1 SO3, where m' is an integer from 1 to 8, preferably 1, 2 or 3, such as TfOH.

[0040] In some embodiments of the present invention, the carboxylic acid may be a C2-C6 carboxylic acid, preferably acetic acid, propionic acid or butyric acid.

[0041] In some embodiments of the present invention, the molar ratio of the carboxylic acid and the dicarboxylic acid monomer contained in the polyester may be 2:1 to 30:1, preferably 5:1 to 15:1, for example 6:1, 7:1, 11:1 or 13:1.

[0042] In some embodiments of the present invention, the amount of catalyst used may be 0.1 to 20 mol%, preferably 1 to 10 mol%, for example 2 mol%, 5 mol%, or 10 mol%, based on the amount of dicarboxylic acid monomer contained in the polyester.

[0043] In some embodiments of the present invention, the degradation can be carried out with the participation of water. There are no particular restrictions on the amount of water used, as long as it does not affect the degradation of the polyester.

[0044] In some embodiments of the present invention, the degradation can be carried out at a temperature of 140–180°C, for example, 150°C.

[0045] In some embodiments of the present invention, the degree of degradation can be monitored by conventional means in the art (e.g., infrared spectroscopy, mass spectrometry, nuclear magnetic resonance, etc.), and the degradation time can be 8 to 24 hours, for example 8 to 12 hours.

[0046] In some embodiments of the present invention, the post-degradation treatment may include the following steps: filtration, washing, and drying to obtain dicarboxylic acid. The washing reagent may be an alcohol solvent (e.g., ethanol).

[0047] The filtrate obtained from filtration can be further processed as follows: water and an organic solvent are added to the filtrate, and the organic phase is extracted. The solvent in the organic phase is then removed to obtain a diol dicarboxylic acid ester. The organic solvent can be an ester solvent (e.g., ethyl acetate). The organic phase can also be dried with a drying agent (e.g., anhydrous sodium sulfate, anhydrous magnesium sulfate, etc.). The method for removing the solvent from the organic phase can be a conventional method in the art, such as vacuum concentration or evaporation.

[0048] In some embodiments of the present invention, the filtrate obtained by filtration may be further subjected to the following operation: catalytic hydrogenation reaction of the filtrate obtained by filtration with a hydrogen source under the action of a heterogeneous hydrogenation catalyst.

[0049] Preferably, the heterogeneous hydrogenation catalyst is Pd / C.

[0050] Preferably, the hydrogen source is hydrogen gas.

[0051] Preferably, the molar ratio of the heterogeneous hydrogenation catalyst to the catalyst in the aforementioned polyester degradation method is 1:5 to 1:15, for example, 1:10.

[0052] Preferably, the temperature of the catalytic hydrogenation reaction is 150–200°C, for example, 180°C.

[0053] In some embodiments of the present invention, the catalytic hydrogenation reaction may further include the following steps: after the catalytic hydrogenation reaction is completed, the reaction solution is filtered, and the filter cake and filtrate are collected.

[0054] In the catalytic hydrogenation reaction, the filter cake contains a recyclable heterogeneous hydrogenation catalyst that can be repeatedly used in the catalytic hydrogenation reaction, for example, in the catalytic hydrogenation reaction described above.

[0055] In the catalytic hydrogenation reaction, the filtrate contains the aforementioned catalyst and carboxylic acid, and can be repeatedly used for the degradation of the aforementioned polyester.

[0056] Preferably, the catalytic hydrogenation reaction is as follows:

[0057]

[0058] The definitions of R1, n, and catalyst are as described above, wherein the catalyst is the catalyst contained in the filtrate obtained from the aforementioned filtration and does not need to be added separately; the catalyst is preferably the aforementioned Lewis acid, such as the aforementioned trifluoromethanesulfonate M(CF3SO3). x For example, Fe(OTf)3.

[0059] In this invention, the catalysts referred to are all catalysts in the aforementioned degradation reaction, which are different from the heterogeneous hydrogenation catalysts mentioned above. The heterogeneous hydrogenation catalysts mentioned above refer to the heterogeneous hydrogenation catalysts in the aforementioned catalytic hydrogenation reaction.

[0060] Unless otherwise specified, the terms used in this invention have the following meanings:

[0061] The term "polyester" refers to a polymer in which repeating units are linked by ester functional groups. The repeating units of a "polyester" can be ester structures formed from dicarboxylic acids and diols.

[0062] Examples of “polyester” include, but are not limited to, polyethylene terephthalate (PET), polypropylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene terephthalate co-isosorbide terephthalate (PEIT), polylactic acid (PLA), poly(L-lactic acid) (PLLA), poly(D-lactic acid) (PDLA), poly(D,L-lactic acid) (PDLLA), PLA stereopolymer composite (scPLA), polyhydroxyalkanoate (PHA), and poly( 3-Hydroxybutyrate)(P(3HB) / PHB), Poly(3-Hydroxyvalerate)(P(3HV) / PHV), Poly(3-Hydroxyhexanoate)(P(3HHx)), Poly(3-Hydroxyoctanoate)(P(3HO)), Poly(3-Hydroxydecanoate)(P(3HD)), Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate)(P(3HB-co-3HV) / PHBV), Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate)(P(3HB-co-3HHx) ) / (PHBHHx)), poly(3-hydroxybutyrate-co-4-hydroxybutyrate)(P(3HB-co-4HB)), poly(3-hydroxybutyrate-co-5-hydroxyvalerate)(PHB5HV), poly(3-hydroxybutyrate-co-3-hydroxypropionate)(PHB3HP), polyhydroxybutyrate-co-hydroxyoctanoate (PHBO), polyhydroxybutyrate-co-hydroxyoctadecanoate (PHBOd), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxybutyrate) Polybutylene succinate (PBS), polybutylene succinate co-butylene adipate (PBSA), polybutylene adipate co-butylene terephthalate (PBAT), polyethylene furanate dicarboxylate (PEF), polycaprolactone (PCL), polyethylene adipate (PEA), and blends / mixtures of two or more of the above, also covering polyester segments in copolymers such as polyurethane (PU) and unsaturated polyester resins.

[0063] The term "polymer" refers to a macromolecule whose structure consists of multiple repeating units linked by covalent chemical bonds. In the context of this invention, the term polymer covers natural and synthetic polymers composed of a single type of monomer (i.e., homopolymers) or natural and synthetic polymers composed of two or more different types of monomers (i.e., copolymers).

[0064] The term "alkyl" refers to a straight-chain or branched alkyl group having a specified number of carbon atoms (e.g., C1-C6). Alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, isobutyl, sec-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, etc.

[0065] The term "aromatic ring" refers to a ring with a specified number of carbon atoms (e.g., C6-C).10 An aromatic ring is a cyclic group consisting solely of carbon atoms, which can be monocyclic or polycyclic, and at least one ring is aromatic (conforming to Hückel's rule). The aromatic ring is connected to other segments of the molecule through an aromatic or non-aromatic ring. Aromatic rings include, but are not limited to, benzene rings and naphthalene rings.

[0066] The term "heteroaromatic ring" refers to a cyclic group having a specified number of ring atoms (e.g., 5-6 members), a specified number of heteroatoms (e.g., 1 or 2), and a specified type of heteroatom (one or more of N, O, and S). It can be monocyclic or polycyclic, and at least one ring is aromatic (conforming to Hückel's rule). Heteroaromatic rings are linked to other segments of a molecule through aromatic or non-aromatic rings. Heteroaromatic rings include, but are not limited to, furan rings, pyrrole rings, thiophene rings, pyrazole rings, imidazole rings, oxazole rings, thiazole rings, pyridine rings, and pyrimidine rings.

[0067] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0068] The reagents and raw materials used in this invention are all commercially available.

[0069] The positive and progressive effects of this invention are as follows:

[0070] (1) Unlike traditional degradation methods, this invention uses carboxylic acids (such as acetic acid, propionic acid, n-butyric acid, etc.) to degrade polyesters, which is applicable to a variety of polyesters, such as PET polyester, PTT polyester, PBT polyester, PEF polyester, etc., and has a wide range of applications.

[0071] (2) The product obtained by this invention is easy to separate.

[0072] (3) The degradation product of the present invention, diol dicarboxylic acid ester, can be converted into diol by conventional methods and used for the resynthesis of polyester. The catalyst can be recycled and reused, which is conducive to maximizing the industrial benefits of polyester degradation.

[0073] (4) The filtrate after recovering phthalic acid from the degradation solution of the present invention can also undergo further catalytic hydrogenation to convert the diol dicarboxylic acid ester in it into carboxylic acid, and continue to be used together with the catalyst in the degradation solution for the degradation of polyester. The catalyst in the catalytic hydrogenation reaction can also be recycled and reused, which is conducive to maximizing the industrial benefits of polyester degradation. Detailed Implementation

[0074] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0075] In the following embodiments, the structure of the repeating unit of the polyester involved is as follows:

[0076]

[0077]

[0078] General steps:

[0079] Add 96 mg of PET polyester fragments and 0.2 mL of glacial acetic acid (molar ratio of raw materials approximately 1:6) sequentially to a 5 mL sample vial. Add the trifluoromethanesulfonic acid metal salt catalyst, seal the vial, heat to 150 °C, and stir for an appropriate time. After the reaction is complete, filter the solution. Wash the resulting solid with a small amount of ethanol and dry it to obtain pure terephthalic acid P1-A. The filtrate can be re-added with PET fragments and glacial acetic acid for repeated degradation reactions. After multiple reactions, ethylene glycol diacetate can be recovered by distillation or extraction.

[0080] Examples 1-8

[0081] The specific conditions and yields of the embodiments are shown in Table 1.

[0082] Table 1

[0083]

[0084] Examples 1-9 above mainly yielded the degradation product terephthalic acid P1-A. 1 H NMR(500MHz,DMSO)δ13.26(s,2H),8.04(s,4H),HR-MS(ESI-TOF)C8H7O6 + [M+H] + The calculated value is 167.0344, and the measured value is 167.0337.

[0085] Ethylene glycol diacetate P2-A, 1 H NMR (500MHz, CDCl3) δ4.28 (s, 4H), 2.09 (s, 6H), HR-MS (ESI-TOF) C6H 11 O4 + [M+H] + The calculated value is 147.0657, and the measured value is 147.0653.

[0086] Example 10

[0087] 96 mg of PET polyester flakes, 0.2 mL of glacial acetic acid (molar ratio of raw materials approximately 1:6), and 18 mg of hafnium trifluoromethanesulfonate were added sequentially to a 5 mL sample vial. The vial was sealed and heated to 150 °C, and the reaction was stirred for 8–12 hours. After the reaction was complete, the sample was filtered, and the resulting solid was washed with a small amount of ethanol and dried to obtain 76.9 mg of terephthalic acid P1-A, with a separation yield of 94%. 96 mg of PET and 0.1 mL of glacial acetic acid were added to the filtrate again, and the sample was sealed and heated to 150 °C. After stirring for 8–12 hours, the sample was filtered, the solid was washed, and dried to obtain 76.7 mg of terephthalic acid P1-A, with a separation yield of 94%. This process was repeated to separate 79.0 mg of terephthalic acid P1-A, with a yield of 95%. Water and ethyl acetate were added to the final filtrate and separated. The aqueous phase was extracted multiple times with ethyl acetate. The organic phases were combined, dried, and the solvent was evaporated to obtain ethylene glycol diacetate P2-A. 190 mg was collected, with a yield of 87% of the total amount added in three batches.

[0088] Example 11

[0089] 96 mg of PET polyester flakes, 0.5 mL of propionic acid (molar ratio of raw materials approximately 1:13), and 18 mg of hafnium trifluoromethanesulfonate were added sequentially to a 5 mL sample vial. The vial was sealed and heated to 150 °C, and the reaction was stirred for 8–12 hours. After the reaction was complete, the sample was filtered, and the resulting solid was washed with a small amount of ethanol and dried to obtain 71.4 mg of terephthalic acid P1-A, with a separation yield of 86%. Water and ethyl acetate were added to the filtrate for separation. The aqueous phase was extracted multiple times with ethyl acetate, and the organic phases were combined, dried, and the solvent was evaporated to obtain ethylene glycol dipropionate P2-B, of which 76.9 mg was collected, with a yield of 89%.

[0090] Example 12

[0091] 96 mg of PET polyester flakes, 0.5 mL of n-butyric acid (molar ratio of raw materials approximately 1:11), and 18 mg of hafnium trifluoromethanesulfonate were added sequentially to a 5 mL sample vial. The vial was sealed and heated to 150 °C, and the reaction was stirred for 8–12 hours. After the reaction was complete, the sample was filtered, and the resulting solid was washed with a small amount of ethanol and dried to obtain 61.0 mg of terephthalic acid P1-A, with a separation yield of 74%. Water and ethyl acetate were added to the filtrate for separation. The aqueous phase was extracted multiple times with ethyl acetate, and the organic phases were combined, dried, and the solvent was evaporated to obtain ethylene glycol di-n-butyrate P2-C, of ​​which 86.4 mg was collected, with a yield of 86%.

[0092] Example 13

[0093] 103 mg of PTT polyester fragments, 0.2 mL of glacial acetic acid (molar ratio of raw materials approximately 1:6), and 18 mg of hafnium trifluoromethanesulfonate were added sequentially to a 5 mL sample vial. The vial was sealed and heated to 150 °C, and the reaction was stirred for 8–12 hours. After the reaction was complete, the sample was filtered, and the resulting solid was washed with a small amount of ethanol and dried to obtain 76.3 mg of terephthalic acid P1-A, with a separation yield of 92%. Water and ethyl acetate were added to the filtrate for separation. The aqueous phase was extracted multiple times with ethyl acetate, and the organic phases were combined, dried, and the solvent was evaporated to obtain propylene glycol diacetate P2-D, of which 64.8 mg was collected, with a yield of 80%.

[0094] Example 14

[0095] 110 mg of PBT polyester fragments, 0.2 mL of glacial acetic acid (molar ratio of raw materials approximately 1:6), and 18 mg of hafnium trifluoromethanesulfonate were added sequentially to a 5 mL sample vial. The vial was sealed and heated to 150 °C, and the reaction was stirred for 8–12 hours. After the reaction was complete, the sample was filtered, and the resulting solid was washed with a small amount of ethanol and dried to obtain 78.0 mg of terephthalic acid P1-A, with a separation yield of 94%. Water and ethyl acetate were added to the obtained filtrate for separation. The aqueous phase was extracted multiple times with ethyl acetate, and the organic phases were combined, dried, and the solvent was evaporated to obtain 68.0 mg of butanediol diacetate P2-E, with a yield of 78%.

[0096] Example 15

[0097] 92 mg of PEF polyester flakes, 0.2 mL of acetic acid (raw material ratio fixed at 1:6), and 18 mg of hafnium trifluoromethanesulfonate were added sequentially to a 5 mL sample vial. The vial was sealed and heated to 150 °C, and the reaction was stirred for 8–12 hours. After the reaction was complete, the sample was filtered, and the resulting solid was washed with a small amount of ethanol and dried to obtain 55.6 mg of 2,5-furandicarboxylic acid P1-B, with a separation yield of 67%. 1 ¹H NMR (500MHz, DMSO) δ 13.53 (s, 2H), 7.28 (s, 2H). The filtrate can be reused repeatedly as described above to recover ethylene glycol diacetate.

[0098] Example 16

[0099] 96 mg of PET polyester fragments, 0.2 mL of glacial acetic acid (molar ratio of raw materials approximately 1:6), and 5 mol% Fe(OTf)3 were added sequentially to a 5 mL sample vial. The vial was sealed and heated to 150 °C, and the mixture was stirred for 8 h. After the reaction was complete, the vial was filtered, and the resulting solid was washed with a small amount of ethanol and dried to obtain pure terephthalic acid P1-A, with a separation yield of 81%. Approximately 3 mL of the reaction filtrate was placed in a reactor, and 10% loaded Pd / C (molar ratio of Pd to Fe(OTf)3 approximately 1:10) was added. Hydrogen gas was introduced at 15 bar, the vial was sealed, and the reactor was heated to 180 °C and reacted at 180 °C for 2 h. After the reaction was completed and cooled to room temperature, the reaction solution was filtered, and the solid collected was the recovered Pd / C powder. After drying, it could be reused in hydrogenation experiments. The resulting filtrate was a mixed solution of Fe(OTf)3, acetic acid, and ethylene glycol diacetate, which could be repeatedly used for PET degradation. The yield of acetic acid in this step can be determined by nuclear magnetic resonance internal standard quantification, with a typical yield of approximately 88%.

[0100] Example 17

[0101] Add 2 mmol of hexanoic acid and Fe(OTf)3 to a 5 mL sample vial to achieve a concentration of approximately 0.125 mol / L. Then add water to achieve a concentration of approximately 0.5 mol / L. Next, add 96 mg of PET polyester (0.5 mmol) fragments, seal the vial, heat to 150 °C, and stir for 8 hours. After the reaction is complete, filter the solution. The resulting solid is washed with a small amount of ethanol and dried to obtain pure terephthalic acid P1-A, with a separation yield of 95%. Place the filtrate to be treated in a reactor, add 10% loaded Pd / C (Pd element to Fe(OTf)3 molar ratio approximately 1:10), purge with 15 bar of hydrogen gas, seal the vial, heat the reactor to 180 °C, and react at 180 °C for 2 hours. After the reaction is complete and cooled to room temperature, filter the reaction solution and collect the solid as recovered Pd / C powder. After drying, it can be reused in hydrogenation experiments. The resulting filtrate is a mixed solution of Fe(OTf)3, hexanoic acid, and ethylene glycol dihexanoate, which can be repeatedly used for PET degradation. The remaining amount of hexanoic acid after this step can be determined by nuclear magnetic resonance internal standard quantification, with a typical content of approximately 95% of the initial amount added.

[0102] The filtrate collected in the above steps was reused with Pd / C for PET degradation: 96 mg of PET polyester (0.5 mmol) fragments were added to the filtrate, the mixture was sealed, heated to 150°C, and stirred for 8 hours. After the reaction was complete, the mixture was filtered, and the resulting solid was washed with a small amount of ethanol and dried to obtain pure terephthalic acid P1-A, with a separation yield of 88%. The reaction filtrate to be treated was placed in a reactor, the recovered Pd / C powder was added, hydrogen gas was introduced at 15 bar, the reactor was sealed, and the temperature was raised to 180°C, where it was reacted for 2 hours. After the reaction was completed and cooled to room temperature, the reaction solution was filtered, and the Pd / C powder and degradation solution could be collected again. At this time, the hexanoic acid content was approximately 92% of the initial amount added.

[0103] Comparative Example 1

[0104]

[0105] 220 mg of PBT polyester fragments, 183 mg of saccharin, 35 mg of hafnium trifluoromethanesulfonate, and 2 mL of toluene were added to a 15 mL reaction flask. The flask was sealed and heated to 150 °C, and the reaction was carried out with stirring for 24 hours. The PBT polyester fragments showed no change, and no degradation products were obtained.

[0106] Comparative Example 2

[0107] 96 mg of PET polyester fragments, 0.2 mL of glacial acetic acid (molar ratio of raw materials approximately 1:6), and 0.2 mL of water were added sequentially to a 5 mL sample vial. The vial was sealed and heated to 150 °C. After stirring for 24 hours, the PET polyester fragments were clearly visible with no significant morphological change. The solution was only slightly turbid, and the yields of degradation products P1-A and P2-A were below 5%.

Claims

1. A method for degrading polyester, characterized in that, It includes the following steps: The polyester is degraded under the action of carboxylic acid and catalyst; the polyester contains repeating units formed by dicarboxylic acid and diol; the catalyst is Lewis acid and / or sulfonic acid organic acid. The carboxylic acid is acetic acid, propionic acid, butyric acid, or hexanoic acid; The structure of the repeating unit is shown in Equation I: Among them, ring A is C6-C 10 Aromatic rings, or 5-6 membered heteroaromatic rings with heteroatoms selected from one or more of N, O and S, and the number of heteroatoms being 1-2; n is an integer from 1 to 9; The Lewis acid is Hf(OTf)4, Al(OTf)3, Fe(OTf)3 or Sc(OTf)3; The sulfonic acid organic acid mentioned is TfOH; The degradation products include dicarboxylic acids and diol dicarboxylic acid esters; The structure of the diol dicarboxylic acid ester is shown in formula P2. ； R 1 It can be methyl, ethyl, n-propyl, or n-pentyl; The post-degradation treatment includes the following steps: filtration, washing, and drying to obtain dicarboxylic acid; the filtrate obtained by filtration is subjected to the following operation, which includes: catalytic hydrogenation reaction of the filtrate obtained by filtration with a hydrogen source under the action of a heterogeneous hydrogenation catalyst. In the post-treatment of the degradation, the catalytic hydrogenation reaction further includes the following steps: after the catalytic hydrogenation reaction is completed, the reaction solution is filtered, and the filter cake and filtrate are collected; the filter cake contains the heterogeneous hydrogenation catalyst and is repeatedly used in the catalytic hydrogenation reaction; the filtrate contains the catalyst and carboxylic acid and is repeatedly used for the degradation of the polyester. The catalytic hydrogenation reaction is as follows: 。 2. The method for degrading polyester as described in claim 1, characterized in that, In ring A, the C6-C 10 The aromatic ring is a benzene ring or a naphthalene ring; And / or, in ring A, the 5-6 membered heteroaromatic ring described as having "heteroatoms selected from one or more of N, O and S, and the number of heteroatoms being 1-2" is a 5-6 membered heteroaromatic ring described as having "heteroatoms of O and the number of heteroatoms being 1-2". And / or, n is an integer from 1 to 5.

3. The method for degrading polyester as described in claim 2, characterized in that, In ring A, the 5-6 membered heteroaromatic ring described as having "heteroatoms selected from one or more of N, O and S, with 1-2 heteroatoms" is a furan ring; And / or, n is 1, 2 or 3.

4. The method for degrading polyester as described in claim 2, characterized in that, Ring A is or .

5. The method for degrading polyester as described in claim 4, characterized in that, The structure of the repeating unit is as follows: , , or .

6. The method for degrading polyester as described in claim 1, characterized in that, The structure of the dicarboxylic acid is shown in formula P1. The definition of ring A is as described in any one of claims 2-5.

7. The method for degrading polyester as described in claim 6, characterized in that, The structure of the dicarboxylic acid is as follows: or ; And / or, when the structure of the diol dicarboxylic acid ester is as shown in formula P2, R 1 It can be methyl, ethyl, or n-propyl.

8. The method for degrading polyester as described in claim 7, characterized in that, When the structure of the diol dicarboxylic acid ester is as shown in formula P2, the structure of the diol dicarboxylic acid ester is: , , , or .

9. The method for degrading polyester as described in claim 1, characterized in that, The molar ratio of the carboxylic acid and the dicarboxylic acid monomer contained in the polyester is 2:1 to 30:1; And / or, based on the amount of dicarboxylic acid monomer contained in the polyester, the amount of catalyst used is 0.1~20 mol%; And / or, the degradation is carried out with the participation of water; And / or, the degradation is carried out at a temperature of 140~180°C; And / or, the degradation time is 8~24h.

10. The method for degrading polyester as described in claim 9, characterized in that, The carboxylic acid is acetic acid, propionic acid, or butyric acid; And / or, the molar ratio of the carboxylic acid to the dicarboxylic acid monomer contained in the polyester is 5:1 to 15:1; And / or, based on the amount of dicarboxylic acid monomer contained in the polyester, the amount of catalyst used is 1 to 10 mol.

11. The degradation method according to claim 1, characterized in that, It meets one or more of the following conditions: (1) The hydrogen source is hydrogen gas; (2) The heterogeneous hydrogenation catalyst is Pd / C; (3) The molar ratio of the heterogeneous hydrogenation catalyst to the catalyst is 1:5 to 1:15; (4) The temperature of the catalytic hydrogenation reaction is 150~200℃.

12. The degradation method according to claim 11, characterized in that, It meets one or two of the following conditions: (1) The molar ratio of the heterogeneous hydrogenation catalyst to the catalyst is 1:10; (2) The temperature of the catalytic hydrogenation reaction is 180℃.

13. The method for degrading polyester according to any one of claims 10 to 12, characterized in that, The Lewis acid mentioned is Hf(OTf)4.

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