Green recycling method of polyester plastic

Abstract

The application discloses a green recycling method of polyester plastics. The method comprises the following steps: using a heteropoly acid and / or a reducing metal ion as a catalyst, and using an organic acid as a solvent to decompose polyester plastics into monomers, such as TPA and EG. The method provided by the application has a high degradation rate of polyester plastics, a mild reaction process, no need of pressurization, and is green and environment-friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of waste resource recycling, and more specifically, to a green recycling method for polyester plastics. Background Art

[0002] Polyester plastics are widely used in a variety of applications, including packaging, textile fibers, construction, electronics, and healthcare. Polyethylene terephthalate (PET) is the most representative polyester plastic, with an annual production volume exceeding 70 million tons. Currently, the disposal of plastic waste has become a serious global issue.

[0003] The chemical recycling and high-value utilization of waste plastics is a significant research area. Its implementation pathways include alcoholysis, acetolysis, aminolysis, hydrogenolysis, and hydrolysis. Because water is a green and sustainable depolymerization agent, hydrolysis has become an environmentally friendly and clean way to recycle waste PET. However, due to the high hydrophobicity of PET, hydrolysis under neutral conditions requires high temperatures (200–300°C) and high pressures (1–4 MPa) to overcome the kinetic barriers to depolymerization. To reduce reaction conditions, the addition of alkali (such as NaOH or KOH) can effectively accelerate the hydrolysis of PET. This is because the generated terephthalic acid (TPA) dissolves to form terephthalate salts, thereby promoting reaction kinetics. However, this approach presents several challenges: the alkali is continuously consumed during the reaction, and the resulting terephthalate salt product cannot be directly used for PET repolymerization. Furthermore, the regeneration of TPA requires the consumption of a large amount of acid to neutralize the terephthalate salt. This not only increases chemical consumption but also generates large amounts of wastewater, resulting in serious environmental pollution. Furthermore, the hydrolysis of PET under acidic conditions also faces significant difficulties. For example, PET has a high tolerance to dilute acid, so a high concentration of strong acid (such as 13 mol·L -1 of nitric acid or 7 mol·L -1 To improve hydrolysis efficiency, the use of sulfuric acid (e.g., sulfuric acid) or pure organic acids is required, and harsh reaction conditions (high temperature and high pressure) are required. Such high acidity operating conditions pose dual challenges in industrial applications, both in terms of safety and environmental impact, further limiting their feasibility for large-scale deployment.

[0004] Chinese patent CN119098218A reports a method for hydrolyzing PET using a solid acid modified with an asymmetric diquaternary ammonium surfactant as a catalyst. However, the reaction requires a temperature above 180°C for at least 24 hours. Therefore, there is an urgent need to develop a method for efficiently and economically treating PET waste, transforming it into valuable resources and achieving integrated resource utilization. Summary of the Invention

[0005] The present invention aims to provide an environmentally friendly recycling method for polyester plastics. By using a heteropoly acid as a catalyst and an organic acid as a solvent, the polyester plastics can be decomposed at relatively low temperatures to produce high-value-added terephthalic acid (TPA), ethylene glycol (EG), and 1,4-butanediol (BDO).

[0006] The first aspect of the present invention provides a green recycling method for polyester plastics, comprising: using a heteropoly acid as a catalyst and an organic acid as a solvent to decompose the polyester plastic into TPA, EG, and BDO.

[0007] The amount of the heteropoly acid is 0.1-0.4 mol·L -1 .

[0008] Preferably, the heteropoly acid is any one of Keggin-type phosphotungstic acid, Keggin-type silicotungstic acid, Dawson-type phosphotungstic acid, Dawson-type silicotungstic acid, and Keggin-type phosphotungstic acid monosubstituted with copper, cobalt, nickel, iron, manganese, or zinc, and Keggin-type silicotungstic acid monosubstituted with iron or copper.

[0009] Preferably, the phosphotungstic acid comprises H3PW 12 O 40 、PW 12 、P2W 18 Any one of .

[0010] Preferably, the organic acid includes any one of formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, trifluoroacetic acid or trichloroacetic acid.

[0011] Preferably, the water content of the organic acid is less than 10%.

[0012] Preferably, the hydrolysis temperature is ≤120°C.

[0013] Preferably, the decomposition temperature is 100°C.

[0014] Preferably, the decomposition time is 4-8 hours.

[0015] Preferably, the method further comprises: using reducing metal ions as co-catalysts.

[0016] Preferably, the reducing metal ions include Fe 2+ 、Ni 2+ 、Zn 2+ Cr 3+ 、Co 3+ 、Fe 3+ Any one of .

[0017] In practical applications, the reducing metal ions may be water-soluble metal salts, such as chloride salts.

[0018] Preferably, the polyester plastic includes PET or PBT.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0020] (1) The present invention utilizes the catalytic depolymerization ability of heteropolyacids on polyester plastics. Through the catalytic ability of low-concentration heteropolyacids and the synergistic swelling effect of organic acids on polyesters, the polyesters can be completely hydrolyzed to produce corresponding monomers under mild conditions.

[0021] (2) Since the system is acidic, TPA precipitates directly and can be separated directly from the reaction system by filtration, avoiding post-neutralization treatment. Compared with the alkaline hydrolysis process, the energy consumption of neutralization purification is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The XRD spectra of the product TPA in the present invention and commercially available TPA are shown in FIG.

[0023] Figure 2 The infrared spectra of the product TPA in the present invention and commercially available TPA are shown in FIG.

[0024] Figure 3 In formic acid solvent, PET and PW 12 The solution after reaction 1 H NMR.

[0025] Figure 4 In formic acid solvent, PBT and PW 12 The solution after reaction 1 H NMR. DETAILED DESCRIPTION

[0026] The following description sets forth numerous specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific implementations disclosed below.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. It should be noted that the reagents used in the present embodiment are all common commercially available products.

[0028] Example 1 Different PW 12 Effect of concentration on the hydrolysis of polyester plastics in formic acid solvent

[0029] In the polyester hydrolysis experiment, the total solution volume was 10 mL (formic acid as solvent, ≤10% water, 0.1-0.3 mol·L - 1 PW 12 ), 0.5 g of PET or PBT powder (100 mesh) was added to a glass bottle with a screw cap for reaction at 100°C for 8 hours. To prevent the influence of oxygen, the air in the container was purged with pure N2 gas before heating. After the reaction was completed, the reaction mixture was poured into about 40 mL of distilled water for precipitation and separation of terephthalic acid (TPA). In order to calculate the polyester conversion rate and TPA yield, the precipitate was treated with NaOH aqueous solution (1 mol·L -1 ) and then dissolved. The unreacted polyester that is insoluble in the alkaline medium is removed by filtration, and the generated TPA is treated with 1 mol·L -1 The specific reaction conditions and results are shown in Table 1.

[0030] Table 1 Different PWs 12 Effect of concentration on the hydrolysis of polyester plastics in formic acid

[0031]

[0032] Example 2 Hydrolysis Effects of Different Heteropolyacids on Polyester in Formic Acid

[0033] Repeat Example 1, 0.3 mol·L -1 The heteropolyacid was reacted with 0.5 g of PET or PBT powder in formic acid (1% water content). All other steps remained the same. Specific reaction conditions and results are shown in Table 2.

[0034] Table 2 Hydrolysis effect of different heteropolyacids on polyester in formic acid

[0035]

[0036]

[0037] Example 3PW 12 Effects of different reducing metal salts on the hydrolysis of polyester in formic acid

[0038] Repeat Example 1, 0.3 mol·L -1 PW 12 With 0.1 mol·L -1 The metal salt was dissolved in formic acid and reacted with 0.5 g of PET or PBT powder. All other steps remained unchanged. Specific reaction conditions and results are shown in Table 3.

[0039] Table 3 PW 12 Effects of different metal salts on the hydrolysis of polyester in formic acid

[0040]

[0041]

[0042] Example 4PW 12 Hydrolysis effect of polyester plastics in different organic acids

[0043] Repeat Example 1, using formic acid, acetic acid, propionic acid or butyric acid as solvent (1% water, 0.3 mol·L - 1 PW 12 ), reacted with 0.5g PET or PBT powder. Other operation steps remain unchanged. Specific reaction conditions and results are shown in Table 4. 12 When used with different organic acids as catalysts, it has a good degradation effect on polyester plastics, with a conversion rate of over 80%.

[0044] Table 4 PW 12 Hydrolysis effect of polyester plastics in different organic acids

[0045] Serial number Polyester type Organic acid type Polyester conversion rate (%) TPA yield (%) Example 4-1 PET Formic acid 95.04 92.96 Example 4-2 PET Acetic acid 82.44 80.79 Example 4-3 PET Propionic acid 92.25 90.89 Example 4-4 PET Butyric acid 93.04 89.67 Examples 4-5 PET Trifluoroacetic acid 92.05 88.66 Examples 4-5 PET Trichloroacetic acid 94.74 92.37 Examples 4-6 PET Isobutyric acid 94.12 92.61 Examples 4-7 PBT Formic acid 97.47 95.09 Examples 4-8 PBT Acetic acid 88.45 86.49 Examples 4-9 PBT Propionic acid 94.33 92.22 Examples 4-10 PBT Butyric acid 95.71 93.19 Examples 4-11 PBT Isobutyric acid 96.45 94.12 Examples 4-12 PBT Trifluoroacetic acid 94.12 92.11 Examples 4-13 PBT Trichloroacetic acid 96.12 94.71

[0046] Example 5 Effect of Temperature on the Hydrolysis of Polyester Plastics

[0047] Repeat Example 1, using formic acid as solvent (1% water, 0.3 mol·L -1 PW 12 ) was reacted with 0.5 g of PET powder at 80, 90, 100, 110, and 120°C for 8 hours. All other steps remained unchanged. Specific reaction conditions and results are shown in Table 5.

[0048] Table 5 Effect of temperature on the hydrolysis of polyester plastics

[0049]

[0050] Example 6

[0051] Repeat Case 1, using formic acid as solvent (1-10% water, 0.3 mol L -1 PW 12 ) was reacted with 0.5 g of PET or PBT powder at 100°C for 8 hours. All other steps remained unchanged. Specific reaction conditions and results are shown in Table 13.

[0052] Table 6 Effect of water content on the hydrolysis of polyester plastics

[0053]

[0054]

[0055] Example 7PW 12 Stability of polyester plastics to hydrolysis in formic acid

[0056] Repeat Example 1, using formic acid as solvent (1% water, 0.3 mol·L -1 PW 12 ) and 0.5 g of PET powder (temperature at 100°C, reaction time 8 hours. After the reaction is completed, PET and terephthalic acid (TPA) are precipitated and separated. The solution is used for the next reaction. Other operation steps remain unchanged. Repeat 10 times. Specific reaction conditions and results are shown in Table 7.

[0057] Table 7 PW 12 Stability of polyester plastics to hydrolysis in formic acid

[0058] Serial number Number of cycles PET conversion rate (%) TPA yield (%) Example 7-1 1 95.04 92.96 Example 7-2 2 93.23 91.78 Example 7-3 3 92.12 90.56 Example 7-4 4 93.01 90.9 Example 7-5 5 92.59 90.81 Example 7-6 6 91.22 88.12 Example 7-7 7 91.23 89.11 Examples 7-8 8 90.20 88.18 Examples 7-9 9 89.91 87.14 Examples 7-10 10 88.01 86.61

[0059] All the solid products TPA obtained in Example 7 were analyzed by XRD ( Figure 1 ) and infrared spectroscopy ( Figure 2 ) were characterized. The IR spectrum and XRD of the TPA prepared in the embodiment were no different. Compared with the commercial TPA, the characteristic peaks were basically the same, indicating that the polyester plastic was successfully decomposed into TPA in the embodiment of the present invention. In the liquid phase products of PET and PBT hydrolyzed by heteropolyacid in formic acid solvent, 1 HNMR results showed that, in addition to the solvent signal, there was only a single hydrolysis product, ethylene glycol (EG) ( Figure 3 ) and 1,4-butanediol (BDO) signal peaks ( Figure 4 ). This shows that the system has good polyester hydrolysis selectivity.

[0060] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A green recycling method for polyester plastics, characterized in that: include: Using heteropoly acid as catalyst and organic acid as solvent, polyester plastics are decomposed into TPA and EG; The heteropoly acid is PW 12 、P2W 18 、PW 11 Cu, PW 11 Co, PW 11 Ni, PW 11 Fe, PW 11 Mn, PW 11 Zn、SiW 12 、Si2W 18 、SiW 11 Fe、SiW 11 Any one of Cu; The amount of the heteropoly acid is 0.1-0.4 mol·L -1 ; The organic acid is any one of formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, trifluoroacetic acid and trichloroacetic acid; The decomposition temperature is 80-120°C; The polyester plastic is PET or PBT; It also includes: using a reducing metal salt as a co-catalyst; the reducing metal salt is any one of FeCl2, NiCl2, ZnCl2, CrCl3, CoCl3, CoCl3, and FeCl3.

2. The green recycling method according to claim 1, characterized in that: The water content of the organic acid is less than 10%.

3. The green recycling method according to claim 1, characterized in that: The decomposition time is 4-8 hours.

Images