A method for catalytic degradation of polyesters to cyclic anhydrides

Abstract

The application discloses a method for catalytically degrading ester into cyclic anhydride, and relates to the technical field of polyester degradation. The method comprises the following steps: using a Lewis acid catalyst to degrade waste or retired polyester polymer formula (II) in a solvent or under a solvent-free condition to obtain a degradation product; and obtaining cyclic anhydride monomer formula (I) through distillation or reduced-pressure sublimation of the degradation product. The application uses a Lewis acid salt as a catalyst, mixes waste or retired polyester with the Lewis acid salt, and heats to realize polymer degradation under a conventional solvent or a solvent-free condition, with a catalyst feeding amount of 1% to 20% (mass ratio). The degradation product comprises small molecules such as cyclic anhydride. Pure cyclic anhydride monomer (purity > 99%) is separated through distillation and a reduced-pressure sublimation process, and the cyclic anhydride recovery rate is 40% to 99%. The process realizes a chemical recycling conversion process of polyester polymer.

Description

Technical Field

[0001] The present invention relates to the technical field of polyester degradation, and in particular to a method for catalytically degrading polyester into cyclic acid anhydride. Background Art

[0002] Polyesters are a class of engineering plastics with excellent performance and a wide range of applications, offering advantages such as excellent chemical stability, abrasion resistance, light resistance, and heat resistance. However, waste or retired polyester plastics are often discarded, incinerated, or landfilled, resulting in low recycling value and environmental damage. Polymer chemical recycling is an important approach to achieving sustainable polymer recycling, but currently, the polyester materials that can be chemically recycled are primarily prepared by ring-opening polymerization of cyclic lactones, such as γ-butyrolactone and its derivatives (Hong, M.; Chen, EY Nat. Chem. 2016, 8, 42-49; Zhu, JB; Watson, EM; Tang, J.; Chen, EY Science 2018, 360, 398-403), valerolactone and its derivatives (Li, XL; Clarke, RW; Jiang, JY; Xu, TQ; Chen, EY Nat. Chem. 2023, 15, 278-285), and caprolactone and its derivatives. Alternating copolyesters are an important component of polyester materials, but to date, research on the chemical recycling of alternating copolyesters such as polyethylene phthalate, polyethylene succinate and other polymers into high-purity fine chemicals is still in its infancy. The development of highly active and highly selective catalysts is the key to achieving the chemical conversion and degradation of polyesters. Summary of the Invention

[0003] In view of the shortcomings of the above-mentioned background technology, the present invention mainly solves the problem that the research on efficient chemical recovery of alternating copolyesters to prepare high-purity fine chemicals in the prior art is still in its infancy. This is due to the large number of side reactions in the polymer degradation process, the variety of by-products, and the lack of effective separation measures. The present invention provides a method for catalytically degrading polyester to cyclic anhydrides. The method uses Lewis acid salt as a catalyst, mixes discarded or retired polyester with Lewis acid salt, adds 1%-20% (mass ratio) of catalyst, and heats in a conventional solvent or solvent-free condition to achieve polymer degradation. The degradation products include small molecules such as cyclic anhydrides. Pure cyclic anhydride monomers (purity>99%) are obtained by distillation to recover the solvent and separation through a reduced pressure sublimation process. The cyclic anhydride recovery rate is 40-99%. This process realizes the chemical recovery and conversion process of polyester polymers.

[0004] The first object of the present invention is to provide a method for catalytically degrading polyester to cyclic anhydride, comprising the following steps:

[0005] Using a Lewis acid catalyst, the discarded or retired polyester polymer of formula (II) is degraded in a solvent or without a solvent to obtain a degradation product;

[0006] The degradation product is distilled or sublimed under reduced pressure to obtain a cyclic anhydride monomer of formula (I);

[0007] Wherein, the discarded or retired polyester polymer includes a fat region segment and an aromatic region segment;

[0008] The synthetic route is:

[0009]

[0010] Preferably, the degradation temperature is 160-250° C., and the reaction time is 1-24 hours.

[0011] Preferably, the molar ratio of the Lewis acid catalyst to the polyester polymer is 1:1-100.

[0012] Preferably, the Lewis acid catalyst includes one or more of metal halides, metal acetates, and metal sulfates.

[0013] Preferably, the metal halide is a chloride salt or a bromide salt; the metal elements in the metal halide, metal acetate or metal sulfate include one or more of magnesium, calcium, aluminum, iron, manganese, zinc and niobium.

[0014] Preferably, the discarded or retired polyester polymer has the following structural formula:

[0015]

[0016] Where, segment A For the fat area segment, segment B It is a fragment of the fat region or the aromatic region.

[0017] Preferably, the segment A comprises one of the following structural formulas:

[0018]

[0019] Wherein, R is NO3, F, CN, MeO, Me, Et, i Pr or t Bu group.

[0020] Preferably, the segment B comprises one of the following structural formulas:

[0021]

[0022] Preferably, when the polymer degradation is carried out in a solvent, the solvent includes one or more of toluene, acetonitrile, propionitrile, 1,4-dioxane, nitroethane, pyridine, acetic acid, ethylene glycol monomethyl ether, octane, butyl acetate, morpholine, chlorobenzene, p-(m-)xylene, acetic anhydride, o-xylene, N,N-dimethylformamide, and cyclohexanone.

[0023] The second object of the present invention is to provide a cyclic acid anhydride.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a method for catalytically degrading polyester to cyclic anhydrides. Using a Lewis acid salt as a catalyst, the method involves mixing discarded or retired polyester with the Lewis acid salt, adding 1% to 20% (by mass) of the catalyst, and heating in a conventional solvent or without a solvent to achieve polymer degradation. The degradation products include small molecules such as cyclic anhydrides. Pure cyclic anhydride monomers (purity >99%) are obtained by distillation to recover the solvent and then undergoing vacuum sublimation to achieve a cyclic anhydride recovery rate of 40-99%. This process achieves chemical recovery and conversion of polyester polymers.

[0026] Compared to conventional polyester recycling methods, which alkalize and then acidify the polymer to produce the corresponding diacid and diol, and then condense and polymerize it, this method uses mild reaction conditions, produces the monomer in a single step, consumes less energy, and is more environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the H-NMR spectrum of the cyclic anhydride obtained by degradation in Example 1.

[0028] Figure 2 This is the H-NMR spectrum of the cyclic anhydride obtained by degradation in Example 15.

[0029] Figure 3 This is the H-NMR spectrum of the cyclic anhydride obtained by degradation in Example 20.

[0030] Figure 4 This is the H-NMR spectrum of the cyclic anhydride obtained by degradation in Example 24. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0032] A first aspect of the present invention provides a method for catalytically degrading polyester to cyclic anhydride, comprising the following steps:

[0033] Using a Lewis acid catalyst, the discarded or retired polyester polymer of formula (II) is degraded in a solvent or without a solvent to obtain a degradation product;

[0034] The degradation product is distilled or sublimed under reduced pressure to obtain a cyclic anhydride monomer of formula (I);

[0035] Wherein, the discarded or retired polyester polymer includes a fat region segment and an aromatic region segment;

[0036] The synthetic route is:

[0037]

[0038] The present invention utilizes a Lewis acid salt as a catalyst. Discarded or retired polyester is mixed with the Lewis acid salt, with a catalyst dosage of 1% to 20% (by mass), and heated in a conventional solvent or without solvent to degrade the polymer. The degradation products include small molecules such as cyclic anhydrides. Pure cyclic anhydride monomers (purity >99%) are obtained through solvent recovery by distillation and separation by vacuum sublimation, with a cyclic anhydride recovery rate of 40-99%. This process achieves chemical recovery and conversion of polyester polymers.

[0039] The degradation temperature is 160-250° C., and the reaction time is 1-24 hours.

[0040] The molar ratio of the Lewis acid catalyst to the polyester polymer is 1:1-100.

[0041] The Lewis acid catalyst comprises one or more of a metal halide, a metal acetate, and a metal sulfate. The metal halide is a chloride salt or a bromide salt; and the metal element in the metal halide, metal acetate, or metal sulfate comprises one or more of magnesium, calcium, aluminum, iron, manganese, zinc, and niobium.

[0042] The discarded or retired polyester polymer structural formula is as follows:

[0043]

[0044] Where, segment A For the fat area segment, segment B It is a fragment of the fat region or the aromatic region.

[0045] The A segment includes one of the following structural formulas:

[0046]

[0047] Wherein, R is NO3, F, CN, MeO, Me, Et, i Pr or t Bu group.

[0048] The B segment includes one of the following structural formulas:

[0049]

[0050] According to the present invention, when polymer degradation is carried out in a solvent, the solvent includes one or more of toluene, acetonitrile, propionitrile, 1,4-dioxane, nitroethane, pyridine, acetic acid, ethylene glycol monomethyl ether, octane, butyl acetate, morpholine, chlorobenzene, p-(m-)xylene, acetic anhydride, o-xylene, N,N-dimethylformamide, and cyclohexanone.

[0051] In one embodiment, a method for catalytically degrading polyester to cyclic anhydride is provided, wherein the synthetic route is:

[0052]

[0053] The specific steps include: using a Lewis acid salt as a catalyst, mixing the catalyst with discarded or retired polyester, and degrading the polymer in a solvent or in the absence of a solvent; the degradation products include small-molecule monomers such as cyclic anhydrides, which are then recovered by distillation or reduced-pressure sublimation to obtain the cyclic anhydride monomers. It should be noted that the absence of a solvent simply refers to mixing the polymer with the salt solid.

[0054] After recovering the solvent by distillation, the solid matter is sublimed to obtain the cyclic anhydride (purity>99%) with a yield of 40-99%.

[0055] A second aspect of the present invention provides a cyclic anhydride.

[0056] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0057] A method for catalytically degrading polyester to cyclic anhydride, the synthetic route is:

[0058]

[0059] The specific steps include: 1.0 g of polyethylene phthalate and 50 mg of catalyst are mixed and ground evenly in a mortar, placed in a 10 ml reaction bottle, and degraded at 180°C;

[0060] The different catalysts, degradation times and cyclic anhydride yields used in each example are shown in Table 1;

[0061] Table 1 Comparison of different catalysts used in various examples

[0062]

[0063] As shown in Table 1, without adding a catalyst, the polymer remains stable at 180°C. After adding a catalyst, the degradation efficiency of the polyester can be significantly improved. The most effective catalyst is ZnCl2 (Example 1).

[0064] In each example, the solvent-free method was used: ZnCl2 was used as a catalyst (50 mg), and different polyester polymers (1.0 g) were ground and mixed uniformly in a mortar. The degradation time and cyclic anhydride yield are shown in Table 2.

[0065] Table 2 Comparison of different polyester polymers used in various examples

[0066]

[0067]

[0068]

[0069]

[0070] As shown in Table 2, ZnCl2 can realize the degradation process of various polyesters and prepare cyclic anhydride compounds.

[0071] The sublimed cyclic anhydrides of Examples 1-14, 15-19, 20-23 and 24-28 were analyzed by nuclear magnetic resonance spectroscopy. The results are shown in Table 1. Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 As shown, from Figures 1 to 4 It can be seen that there are no obvious impurity peaks.

[0072] The present invention describes preferred embodiments and their effects. However, those skilled in the art, once informed of the basic inventive concept, may make additional changes and modifications to these embodiments. Therefore, it is intended that the appended claims be interpreted to include the preferred embodiments as well as all changes and modifications that fall within the scope of the invention.

[0073] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for catalytically degrading polyester to cyclic anhydride, characterized in that: The following steps are involved: Using a Lewis acid catalyst, the discarded or retired polyester polymer of formula (II) is degraded under solvent-free conditions to obtain a degradation product; The degradation product is distilled or sublimed under reduced pressure to obtain a cyclic anhydride monomer of formula (I); The synthetic route is: ； The degradation temperature is 160-250° C., and the reaction time is 1-24 hours; The molar ratio of the Lewis acid catalyst to the polyester polymer is 1:1 to 100; The Lewis acid catalyst is one or more of metal halides, metal acetates, and metal sulfates; The metal halide is a chloride salt or a bromide salt; The metal element in the metal halide, metal acetate or metal sulfate is magnesium or zinc; Or the metal halide is FeCl3; The discarded or retired polyester polymer includes segment A and segment B, and has the following structural formula: The A segment is one of the following structural formulas: ， ， ， ， ， ， ， ， ， ， ； Wherein, R is NO3, F, CN, MeO, Me, Et, i Pr or t Bu group; The segment B is one of the following structural formulas: ， ， ， ， ， ， ， ， 。 2. The method for catalytically degrading polyester to cyclic anhydride according to claim 1, wherein: When polymer degradation is carried out in a solvent, the solvent is one or more of toluene, acetonitrile, propionitrile, 1,4-dioxane, nitroethane, pyridine, acetic acid, ethylene glycol monomethyl ether, octane, butyl acetate, morpholine, chlorobenzene, acetic anhydride, o-xylene, N,N-dimethylformamide, and cyclohexanone.

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