Application of sulfonic acid / sulfuric acid and zinc salt in chemical recovery of polyester and chemical recovery method of polyester

Abstract

The invention discloses application of sulfonic acid / sulfuric acid and zinc salt in chemical recovery of polyester and a chemical recovery method of polyester, relates to the technical field of polymer recovery, and solves the problems of complex process flow and limited product application of the existing chemical recovery technology. The invention firstly provides an application of sulfonic acid / sulfuric acid in chemical recovery of polyester. The sulfonic acid / sulfuric acid is applied to chemical recovery of polyester as a catalyst to synthesize cyclic anhydride and aldehyde / ketone. Meanwhile, the invention provides application of the zinc salt in chemical recovery of polyester. The zinc salt can also be used as a catalyst to be applied to chemical recovery of polyester to synthesize cyclic anhydride and aldehyde / ketone. Adding a catalyst and polyester into the reaction container for reaction under anhydrous and anaerobic conditions, and carrying out reduced pressure distillation to separate aldehyde / ketone; and after the reaction is finished, recrystallizing the mixture to separate the cyclic anhydride. According to the chemical polyester recovery technology provided by the invention, waste polyester can be efficiently recovered into cyclic anhydride and aldehyde / ketone with high additional value, and efficient and sustainable utilization of resources is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer recovery, in particular to an application of sulfonic acid / sulfuric acid and zinc salt in polyester chemical recovery and a polyester chemical recovery method. Background Art

[0002] Chemical recycling technologies for polymer materials play a key role in achieving sustainable development in a circular economy. Efficiently converting waste polymer materials into recycled raw materials or upcycling them into high-value-added chemicals has become a key strategic direction in the global chemical industry. Polyester, a versatile polymer material, holds an irreplaceable position in packaging materials, textile fibers, and biomedical devices due to its excellent processing performance and tunable physical and chemical properties.

[0003] Ring-opening copolymerization of epoxides and cyclic anhydrides is an important polyester synthesis method, enabling flexible manipulation of material performance and functional properties. However, this synthetic strategy imparts extremely high thermodynamic stability to the polyester molecular chain, making depolymerization and regeneration of the material into monomers a significant challenge. Traditional chemical recycling typically involves hydrolysis to break down polyester into diols and dibasic acid monomers, but these monomers require multi-step functional group conversion to regenerate epoxides or cyclic anhydrides. This not only complicates the process but also results in significant energy consumption and carbon emissions.

[0004] To address this technical bottleneck, the Williams research team first reported a chemical recovery method for propylene oxide and succinic anhydride / glutaric anhydride copolyesters in 2025 (Angew. Chem. Int. Ed. 2025, e202423478). They used stannous (II) octoate as a catalyst to successfully achieve the efficient conversion of these polyesters into macrolides. However, the substrate universality of this method is still limited by the specific structure of the polyester, and the resulting macrolides have not yet shown significant advantages in industrial applications. The development of more universal depolymerization pathways is urgently needed.

[0005] It is worth noting that cyclic anhydrides, as key monomers in polymer synthesis and modification, have an annual global demand exceeding tens of millions of tons. Aldehydes / ketones are both important building blocks for organic synthesis and ideal precursors for the preparation of high-performance polymers. Therefore, developing innovative technologies for directly converting polyester waste into cyclic anhydrides and aldehydes / ketones would not only overcome the technical barriers of existing recycling systems but also potentially create a new industrial value chain, which would have a dual benefit in achieving carbon neutrality. Summary of the Invention

[0006] In order to solve the problems of complex process flow and limited product application of existing chemical recovery technology, the present invention proposes the application of sulfonic acid / sulfuric acid and zinc salt in polyester chemical recovery and a polyester chemical recovery method.

[0007] The technical solutions of the present invention are as follows:

[0008] An application of sulfonic acid / sulfuric acid in polyester chemical recovery, wherein the general structural formula of the sulfonic acid / sulfuric acid is as follows:

[0009]

[0010] Wherein R is selected from one of hydroxyl, alkyl, aralkyl, and perfluoroalkyl;

[0011] The sulfonic / sulfuric acid is used as a catalyst in the chemical recovery of polyester to synthesize cyclic anhydrides and aldehydes / ketones.

[0012] The invention discloses an application of a zinc salt in polyester chemical recycling. The zinc salt is used as a catalyst in the polyester chemical recycling to synthesize cyclic anhydrides and aldehydes / ketones.

[0013] Preferably, the structural formula of the polyester is one of the following:

[0014]

[0015] Preferably, the structural formula of the polyester is one of the following:

[0016]

[0017] Preferably, the structural formula of the sulfonic acid / sulfuric acid is one of the following:

[0018]

[0019] Preferably, the structural formula of the zinc salt is one of the following:

[0020]

[0021] The present invention also provides a chemical recovery method for polyester, comprising the following steps:

[0022] S1. Adding a catalyst and polyester to a reaction vessel under anhydrous and oxygen-free conditions and reacting at a specific temperature; the catalyst is sulfonic acid / sulfuric acid or zinc salt;

[0023] S2. During the reaction, performing reduced pressure distillation to separate the generated aldehyde / ketone;

[0024] S3. After the reaction is completed, the mixture obtained by the reaction is recrystallized to separate the generated cyclic anhydride.

[0025] Preferably, the mass ratio of sulfonic acid / sulfuric acid to polyester is 0.5:100 to 20:100.

[0026] Preferably, the mass ratio of the zinc salt to the polyester is 0.5:100 to 20:100.

[0027] Preferably, the specific temperature is 40-200° C., and the reaction time is 1-100 h.

[0028] Compared with the prior art, the present invention has the following specific beneficial effects:

[0029] The technical solution provided by the present invention uses sulfonic acid / sulfuric acid or zinc salts as catalysts to catalyze the chemical recovery of epoxide / cyclic anhydride copolyesters into cyclic anhydrides and aldehydes / ketones. This solves the problem of the high thermodynamic stability of these polyesters, which makes chemical recovery difficult. It also addresses the limitations of polyester substrate applicability and the limited application of recycled products in existing technologies. The polyester chemical recovery technology provided by the present invention can efficiently recover high-value-added cyclic anhydrides and aldehydes / ketones from discarded polyester, achieving efficient and sustainable resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 1 is a comparison chart of H NMR spectra of commercially available phthalic anhydride and phthalic anhydride recovered in Example 1;

[0031] Figure 2 is the isobutyraldehyde recovered in Example 1 1 H NMR spectra;

[0032] Figure 3 This is a diagram of phthalic anhydride before and after recrystallization in Example 7. DETAILED DESCRIPTION

[0033] In order to make the technical solution of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the specification of the present invention. It should be noted that the following embodiments are only used to better understand the technical solution of the present invention and should not be understood as limiting the present invention.

[0034] It should be noted that the present invention has no particular limitation on the source and synthesis method of the polyester, and the polyester can be synthesized by the ring-opening copolymerization method of epoxide and cyclic anhydride reported in the literature or by the condensation polymerization method of diol and dibasic acid reported in the literature.

[0035] The present invention has no particular limitation on the source of the catalyst, and commercially available products may be used.

[0036] In the present invention, the obtained polyester is preferably dried and then subjected to chemical recovery reaction.

[0037] In the present invention, the obtained catalyst is preferably dried before undergoing a chemical recovery reaction.

[0038] In the present invention, polyester is used as the reaction substrate without the use of additional solvent.

[0039] The present invention has no particular limitation on the methods of recrystallization and (reduced pressure) distillation. Cyclic anhydrides and aldehydes / ketones can be obtained in high yields by using the techniques of recrystallization and (reduced pressure) distillation well known to those skilled in the art.

[0040] Example 1.

[0041] Under anhydrous and oxygen-free conditions, polyester poly(IBO-alt-PA) (2.00 g) and p-toluenesulfonic acid (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 150°C for 5 hours. During the reaction, the generated isobutyraldehyde was collected by distillation. After the reaction, the reaction mixture was recrystallized from ethyl acetate to separate the generated phthalic anhydride. The polyester conversion was >99%, the isobutyraldehyde yield was 60%, and the phthalic anhydride yield was 94%.

[0042] The obtained phthalic anhydride was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0043] 1 H NMR (500MHz, CDCl3 TMS): δ8.06-8.02(m,2H),7.95-7.92(m,2H).

[0044] Figure 1 This is a comparison of the H NMR spectra of commercially available phthalic anhydride and the phthalic anhydride recovered in Example 1. The benzene ring proton signals of the recovered phthalic anhydride basically overlap with those of the commercial product, indicating that the main structure is successfully retained and the anhydride functional groups are not significantly damaged.

[0045] The obtained isobutyraldehyde was analyzed by nuclear magnetic resonance hydrogen spectrum test, the spectrum is shown in Figure 2 As shown, the results are as follows:

[0046] 1 H NMR (500MHz, CDCl3 TMS): δ9.65 (d, J = 1.3 Hz, 1H), 2.44 (pd, J = 7.1, 1.3 Hz, 1H), 1.13 (d, J = 7.1 Hz, 6H).

[0047] It can be proved that this embodiment successfully converts polyester into isobutyraldehyde and phthalic anhydride through the chemical recovery method of the present invention, and the conversion rate is relatively high.

[0048] When the catalyst p-toluenesulfonic acid was replaced with an equal weight of sulfuric acid, while other components remained unchanged, the polyester conversion rate was >99%, the isobutyraldehyde yield was 54%, and the phthalic anhydride yield was 92%.

[0049] When the catalyst p-toluenesulfonic acid was replaced with an equal weight of methanesulfonic acid, while other components remained unchanged, the polyester conversion rate was >99%, the isobutyraldehyde yield was 58%, and the phthalic anhydride yield was 91%.

[0050] The above catalyst p-toluenesulfonic acid was replaced by an equal weight of β-naphthalenesulfonic acid, while the other factors remained unchanged. The conversion rate of polyester was 89%, the yield of isobutyraldehyde was 63%, and the yield of phthalic anhydride was 70%.

[0051] When the catalyst p-toluenesulfonic acid was replaced with an equal weight of trifluoromethanesulfonic acid, while other factors remained unchanged, the polyester conversion rate was >99%, the isobutyraldehyde yield was 43%, and the phthalic anhydride yield was 85%.

[0052] The catalyst p-toluenesulfonic acid was replaced with an equal weight of 4-dodecylbenzenesulfonic acid, while the other factors remained unchanged. The conversion rate of polyester was 70%, the yield of isobutyraldehyde was 36%, and the yield of phthalic anhydride was 54%.

[0053] When the catalyst p-toluenesulfonic acid was replaced with an equal weight of camphorsulfonic acid, while other components remained unchanged, the polyester conversion rate was >99%, the isobutyraldehyde yield was 67%, and the phthalic anhydride yield was 87%.

[0054] Example 2.

[0055] Under anhydrous and oxygen-free conditions, the polyester poly(IBO-alt-PA) (2.00 g) and trifluoromethanesulfonic acid (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 100°C for 5 hours. During the reaction, the generated isobutyraldehyde was collected by distillation. After the reaction, the resulting phthalic anhydride was separated by recrystallization from ethyl acetate. The polyester conversion was >99%, the isobutyraldehyde yield was 51%, and the phthalic anhydride yield was 89%.

[0056] Example 3.

[0057] Under anhydrous and oxygen-free conditions, the polyester poly(IBO-alt-PA) (2.00 g) and trifluoromethanesulfonic acid (0.02 g, 1 wt%) were added to a distillation apparatus and reacted at 100°C for 10 hours. During the reaction, the generated isobutyraldehyde was collected by distillation. After the reaction, the reaction mixture was recrystallized from ethyl acetate to separate the generated phthalic anhydride. The polyester conversion was 97%, the isobutyraldehyde yield was 66%, and the phthalic anhydride yield was 83%.

[0058] Example 4.

[0059] Under anhydrous and oxygen-free conditions, polyester poly(IBO-alt-PA) (2.00 g) and ZnCl2 (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 170°C for 5 hours. During the reaction, the generated isobutyraldehyde was collected by distillation. After the reaction, the reaction mixture was recrystallized from ethyl acetate to separate the generated phthalic anhydride. The polyester conversion was >99%, the isobutyraldehyde yield was 79%, and the phthalic anhydride yield was 94%.

[0060] Example 5.

[0061] Under anhydrous and oxygen-free conditions, the polyester poly(SO-alt-PA) (2.00 g) and 4-dodecylbenzenesulfonic acid (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 150°C for 6 hours. During the reaction, the generated phenylacetaldehyde was collected by vacuum distillation. After the reaction, the resulting phthalic anhydride was separated by recrystallization from ethyl acetate. The polyester conversion was >99%, the phenylacetaldehyde yield was 32%, and the phthalic anhydride yield was 93%.

[0062] The obtained phenylacetaldehyde was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0063] 1 H NMR (500MHz, CDCl3 TMS): δ9.75 (t, J = 2.4 Hz, 1H), 7.39 (t, J = 7.4 Hz, 2H), 7.33 (t, J = 7.3 Hz, 1H), 7.24 (d, J = 7.2 Hz, 2H), 3.69 (d, J = 2.4 Hz, 1H).

[0064] The obtained phthalic anhydride was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0065] 1 H NMR (500MHz, CDCl3 TMS): δ8.03-7.99(m,2H),7.92-7.89(m,2H).

[0066] Example 6.

[0067] Under anhydrous and oxygen-free conditions, polyester poly(SO-alt-PA) (2.00 g) and ZnCl2 (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 170°C for 6 hours. During the reaction, the generated phenylacetaldehyde was collected by vacuum distillation. After the reaction, the resulting phthalic anhydride was separated by recrystallization from ethyl acetate. The polyester conversion was >99%, the phenylacetaldehyde yield was 43%, and the phthalic anhydride yield was 91%.

[0068] When the catalyst ZnCl2 was replaced with an equal weight of ZnBr2, while the other factors remained unchanged, the conversion rate of polyester was 83%, the yield of phenylacetaldehyde was 37%, and the yield of phthalic anhydride was 72%.

[0069] When the catalyst ZnCl2 was replaced with an equal weight of ZnSO4, with the rest remaining unchanged, the conversion of polyester was >99%, the yield of phenylacetaldehyde was 41%, and the yield of phthalic anhydride was 86%.

[0070] When the catalyst ZnCl2 was replaced with an equal weight of Zn(NO3)2, with the rest remaining unchanged, the conversion rate of polyester was >99%, the yield of phenylacetaldehyde was 47%, and the yield of phthalic anhydride was 88%.

[0071] When the catalyst ZnCl2 was replaced with an equal weight of Zn(OAc)2, while the other factors remained unchanged, the conversion of polyester was 64%, the yield of phenylacetaldehyde was 15%, and the yield of phthalic anhydride was 51%.

[0072] When the catalyst ZnCl2 was replaced with an equal weight of ZnGA, while the other factors remained unchanged, the conversion rate of polyester was 58%, the yield of phenylacetaldehyde was 12%, and the yield of phthalic anhydride was 42%.

[0073] Example 7.

[0074] Under anhydrous and oxygen-free conditions, polyester poly(VIO-alt-PA) (2.00 g) and p-toluenesulfonic acid (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 150°C for 5 hours. During the reaction, the generated (trans)-crotonaldehyde was collected by distillation. After the reaction, the reaction mixture was recrystallized from ethyl acetate to separate the generated phthalic anhydride. The polyester conversion was 67%, the (trans)-crotonaldehyde yield was 12%, and the phthalic anhydride yield was 58%.

[0075] The obtained (trans)-butenal was subjected to nuclear magnetic resonance hydrogen spectrum analysis and the results were as follows:

[0076] 1 H NMR (500MHz, CDCl3 TMS): δ9.50 (d, J = 7.9 Hz, 1H), 6.87 (dq, J = 15.4, 6.9 Hz, 1H), 6.15 (ddq, J = 15.5, 7.9, 1.6 Hz, 1H), 2.04 (dd, J = 6.8, 1.6 Hz, 3H).

[0077] The obtained phthalic anhydride was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0078] 1H NMR (500MHz, CDCl3 TMS): δ8.06-8.01(m,2H),7.95-7.91(m,2H).

[0079] Example 8.

[0080] Under anhydrous and oxygen-free conditions, polyester poly(VIO-alt-PA) (2.00 g) and p-toluenesulfonic acid (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 120°C for 12 hours. During the reaction, the generated (trans)-crotonaldehyde was collected by distillation. After the reaction, the reaction mixture was recrystallized from ethyl acetate to separate the generated phthalic anhydride. The polyester conversion was 43%, the (trans)-crotonaldehyde yield was 10%, and the phthalic anhydride yield was 26%.

[0081] Example 9.

[0082] Under anhydrous and oxygen-free conditions, polyester poly(PO-alt-PA) (2.00 g) and p-toluenesulfonic acid (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 180°C for 6 hours. During the reaction, the generated propionaldehyde was collected by distillation. After the reaction, the resulting phthalic anhydride was separated by recrystallization from ethyl acetate. The polyester conversion was 52%, the propionaldehyde yield was 10%, and the phthalic anhydride yield was 44%.

[0083] The obtained propionaldehyde was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0084] 1 H NMR (500MHz, CDCl3 TMS): δ9.78 (t, J = 1.3 Hz, 1H), 2.46 (qd, J = 7.4, 1.4 Hz, 2H), 1.09 (t, J = 7.3 Hz, 3H).

[0085] The obtained phthalic anhydride was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0086] 1 H NMR (500MHz, CDCl3 TMS): δ8.05-8.01(m,2H),7.94-7.89(m,2H).

[0087] Example 10.

[0088] Under anhydrous and oxygen-free conditions, polyester poly(CHO-alt-PA) (2.00 g) and p-toluenesulfonic acid (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 190°C for 6 hours. During the reaction, cyclohexanone was collected by distillation. After the reaction, the resulting phthalic anhydride was separated by recrystallization from ethyl acetate. The polyester conversion was 68%, the cyclohexanone yield was 43%, and the phthalic anhydride yield was 49%.

[0089] The obtained cyclohexanone was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0090] 1 H NMR (500MHz, CDCl3 TMS): δ2.35 (t, J = 6.6 Hz, 4H), 1.88 (p, J = 6.2 Hz, 4H), 1.76-1.70 (m, 2H).

[0091] The obtained phthalic anhydride was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0092] 1 H NMR (500MHz, CDCl3 TMS): δ8.04-7.99(m,2H),7.93-7.88(m,2H).

[0093] Example 11.

[0094] Under anhydrous and oxygen-free conditions, the polyester poly(LO-alt-PA) (2.00 g) and p-toluenesulfonic acid (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 140°C for 13 hours. During the reaction, the generated (R)-dihydrocarvone was collected by vacuum distillation. After the reaction, the resulting phthalic anhydride was separated by recrystallization from ethyl acetate. The polyester conversion was 78%, the (R)-dihydrocarvone yield was 41%, and the phthalic anhydride yield was 62%.

[0095] The obtained cyclohexanone was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0096] 1 H NMR (500MHz, CDCl3 TMS): δ4.76(m,1H),4.73(s,1H),2.47-2.41(m,1H),2.40-2.29(m,3H),2.16-2.11(m,1H),1 .96-1.92(m,1H),1.73(s,3H),1.69-1.63(m,1H),1.42-1.33(m,1H),1.04(d,J=6.7Hz,3H).

[0097] The obtained phthalic anhydride was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0098] 1 H NMR (500MHz, CDCl3 TMS): δ8.03-7.99(m,2H),7.91-7.88(m,2H).

[0099] Example 12.

[0100] Under anhydrous and oxygen-free conditions, the polyester poly(IBO-alt-MA) (2.00 g) and p-toluenesulfonic acid (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 70°C for 72 hours. During the reaction, the generated isobutyraldehyde was collected by distillation. After the reaction, the reaction mixture was recrystallized from ethyl acetate to separate the generated maleic anhydride. The polyester conversion was >99%, the isobutyraldehyde yield was 63%, and the maleic anhydride yield was 83%.

[0101] The obtained isobutyraldehyde was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0102] 1 H NMR (500MHz, CDCl3 TMS): δ9.66 (d, J = 1.3 Hz, 1H), 2.45 (pd, J = 7.0, 1.3 Hz, 1H), 1.14 (d, J = 7.1 Hz, 6H).

[0103] The obtained maleic anhydride was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0104] 1 H NMR (500MHz, CDCl3 TMS): δ7.04 (s, 2H).

[0105] Example 13.

[0106] Under anhydrous and oxygen-free conditions, the polyester poly(IBO-alt-SA) (2.00 g) and p-toluenesulfonic acid (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 70°C for 72 hours. During the reaction, the generated isobutyraldehyde was collected by distillation. After the reaction, the resulting succinic anhydride was separated by recrystallization from ethyl acetate. The polyester conversion was >99%, the isobutyraldehyde yield was 58%, and the succinic anhydride yield was 78%.

[0107] The obtained isobutyraldehyde was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0108] 1H NMR (500MHz, CDCl3 TMS): δ9.64 (d, J = 1.3 Hz, 1H), 2.44 (pd, J = 7.1, 1.4 Hz, 1H), 1.13 (d, J = 7.1 Hz, 6H).

[0109] The obtained succinic anhydride was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0110] 1 H NMR (500MHz, CDCl3 TMS): δ2.94 (s, 4H).

[0111] Example 14.

[0112] Under anhydrous and oxygen-free conditions, the polyester poly(IBO-alt-GA) (2.00 g) and p-toluenesulfonic acid (0.1 g, 5 wt%) were added to a distillation apparatus and reacted at 70°C for 72 hours. During the reaction, the generated isobutyraldehyde was collected by distillation. After the reaction, the resulting glutaric anhydride was separated by recrystallization from ethyl acetate. The polyester conversion was >99%, the isobutyraldehyde yield was 56%, and the glutaric anhydride yield was 82%.

[0113] The obtained isobutyraldehyde was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0114] 1 H NMR (500MHz, CDCl3 TMS): δ9.65 (d, J = 1.3 Hz, 1H), 2.44 (pd, J = 7.1, 1.3 Hz, 1H), 1.14 (d, J = 7.1 Hz, 6H).

[0115] The obtained glutaric anhydride was subjected to nuclear magnetic resonance hydrogen spectrum analysis test, and the results were as follows:

[0116] 1 H NMR (500MHz, CDCl3 TMS): δ2.74 (t, J=6.7Hz, 4H), 2.01 (q, J=6.7Hz, 2H).

[0117] As can be seen from the above examples, the present invention uses sulfonic acid / sulfuric acid or zinc salt as a catalyst to solve the high thermodynamic stability of epoxide / cyclic anhydride copolyesters and can achieve efficient chemical recovery of such polyesters into cyclic anhydrides and aldehydes / ketones.

[0118] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. An application of sulfonic acid / sulfuric acid in polyester chemical recovery, characterized in that: The general structural formula of the sulfonic acid / sulfuric acid is as follows: Wherein R is selected from one of hydroxyl, alkyl, aryl, and perfluoroalkyl; The sulfonic / sulfuric acid is used as a catalyst in the chemical recovery of polyester to synthesize cyclic anhydrides and aldehydes / ketones.

2. An application of zinc salt in polyester chemical recovery, characterized in that: The zinc salt is used as a catalyst in the chemical recovery of polyester to synthesize cyclic anhydrides and aldehydes / ketones.

3. The use according to claim 1 or 2, characterized in that The structural formula of the polyester is one of the following:

4. The use according to claim 1 or 2, characterized in that The structural formula of the polyester is one of the following:

5. The use according to claim 3, characterized in that The structural formula of the sulfonic acid / sulfuric acid is one of the following:

6. The use according to claim 3, characterized in that The structural formula of the zinc salt is one of the following:

7. A chemical recovery method for polyester, characterized in that: The steps include: S1. Adding a catalyst and polyester to a reaction vessel under anhydrous and oxygen-free conditions and reacting at a specific temperature; the catalyst is sulfonic acid / sulfuric acid or zinc salt; S2. During the reaction, performing reduced pressure distillation to separate the generated aldehyde / ketone; S3. After the reaction is completed, the mixture obtained by the reaction is recrystallized to separate the generated cyclic anhydride.

8. The chemical recovery method of polyester according to claim 7, characterized in that: The mass ratio of the sulfonic acid / sulfuric acid to the polyester is 0.5:100 to 20:

100.

9. The chemical recovery method of polyester according to claim 7, characterized in that: The mass ratio of the zinc salt to the polyester is 0.5:100 to 20:

100.

10. The chemical recovery method of polyester according to claim 7, characterized in that: The specific temperature is 40-200° C., and the reaction time is 1-100 hours.

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