Green recovery method of polyester plastics

Abstract

The invention discloses a green recovery method of polyester plastics. The method comprises the following steps: by taking heteropoly acid and / or reducing metal ions as a catalyst and organic acid as a solvent, decomposing polyester plastic into monomers, such as TPA and EG. The method provided by the invention has the advantages of high degradation rate of polyester plastics, mild reaction process, no need of pressurization and environmental protection.

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 packaging, textile fibers, construction, electronics and medical fields. Polyethylene terephthalate (PET) is the most representative polyester plastic, with an annual output of more than 70 million tons. Currently, plastic waste disposal has become a serious global problem.

[0003] Chemical recycling and high-value utilization of waste plastics is an important research field, and its realization methods include alcoholysis, acetolysis, aminolysis, hydrogenolysis and hydrolysis. Since 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 needs to be carried out at high temperature (200–300°C) and high pressure (1–4MPa) to overcome its depolymerization kinetic barriers. In order to reduce the reaction conditions, the addition of alkali (such as NaOH or KOH) can effectively accelerate the hydrolysis process of PET. This is because the generated terephthalic acid (TPA) can dissolve to form terephthalate, thereby promoting the reaction kinetics. However, this method has some challenges: the alkali agent is continuously consumed in the reaction, the generated terephthalate product cannot be directly used for the repolymerization of PET, and the regeneration of TPA requires a large amount of acid to neutralize the terephthalate. This not only increases the consumption of chemicals, but also produces a large amount of wastewater, bringing serious environmental pollution problems. In addition, PET hydrolysis 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 Sulfuric acid) or pure organic acid is used to improve the hydrolysis efficiency, and harsh reaction conditions (high temperature and high pressure) are required. Such high acidity operating conditions pose dual challenges of safety and environmental impact in industrial applications, further limiting the feasibility of large-scale promotion.

[0004] Chinese patent CN119098218A reports a method for hydrolyzing PET, using a solid acid modified by an asymmetric diquaternary ammonium salt surfactant as a catalyst, but the reaction needs to be carried out at a temperature above 180°C for more than 24 hours. Therefore, it is urgent to develop a method that can efficiently and economically treat PET waste, turn PET waste into treasure, and realize the integrated utilization of resources. Summary of the invention

[0005] The purpose of the present invention is to provide a green recycling method for polyester plastics. By using heteropoly acid as a catalyst and organic acid as a solvent, polyester plastics can be decomposed under relatively high temperature conditions to produce terephthalic acid TPA, ethylene glycol EG, and 1,4-butanediol BDO with high added value.

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

[0007] The dosage 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, 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 comprises 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. The catalytic ability of low-concentration heteropolyacids and the swelling effect of organic acids on polyesters can be used to completely hydrolyze polyesters to produce corresponding monomers under mild conditions.

[0021] (2) Since the system is acidic, TPA is directly precipitated and can be directly separated from the reaction system by filtration, avoiding post-neutralization treatment. Compared with the alkaline hydrolysis process, the energy consumption of neutralization and 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 After the reaction, the solution 1 H NMR.

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

[0026] Many specific details are set forth in the following description to facilitate a full 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 can make similar improvements without violating the connotation of the present invention, so the present invention is not limited to the specific implementation 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 commercial 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 ), 0.5g PET or PBT powder (100 mesh) was added to a glass bottle with a screw cap for reaction, the reaction temperature was 100°C, and the reaction time was 8 hours. In order 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 40mL 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 ) was dissolved again. The unreacted polyester insoluble in the alkaline medium was removed by filtration, and the generated TPA was treated with 1 mol·L -1 The specific reaction conditions and results are shown in Table 1.

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

[0031]

[0032] Example 2 Effects of different heteropolyacids on the hydrolysis of polyester in formic acid

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

[0034] Table 2 Effects of different heteropolyacids on the hydrolysis of polyester in formic acid

[0035]

[0036]

[0037] Example 3 PW 12 Effect 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 solvent and reacted with 0.5 g PET or PBT powder. The other operation steps remained unchanged. The 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 4 PW 12 Hydrolysis effect of polyester plastics in different organic acids

[0043] Example 1 was repeated, using formic acid, acetic acid, propionic acid or butyric acid as the solvent (1% water, 0.3 mol·L - 1 PW 12 ), and reacted with 0.5g PET or PBT powder. The other operation steps remain unchanged. The specific reaction conditions and results are shown in Table 4. It can be seen that PW 12 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 Embodiment 4-5 PET Trifluoroacetic acid 92.05 88.66 Embodiment 4-5 PET Trichloroacetic acid 94.74 92.37 Embodiment 4-6 PET Isobutyric acid 94.12 92.61 Embodiment 4-7 PBT Formic acid 97.47 95.09 Embodiment 4-8 PBT Acetic acid 88.45 86.49 Embodiment 4-9 PBT Propionic acid 94.33 92.22 Embodiment 4-10 PBT Butyric acid 95.71 93.19 Embodiment 4-11 PBT Isobutyric acid 96.45 94.12 Embodiment 4-12 PBT Trifluoroacetic acid 94.12 92.11 Embodiment 4-13 PBT Trichloroacetic acid 96.12 94.71

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

[0047] Example 1 was repeated, using formic acid as the solvent (1% water, 0.3 mol·L -1 PW 12 ), reacted with 0.5 g PET powder at 80, 90, 100, 110 and 120 ° C. for 8 hours. Other operation steps remain 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 ), reacted with 0.5 g PET or PBT powder at 100° C. for 8 hours. Other operation 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 7 PW 12 Stability of polyester plastics to hydrolysis in formic acid

[0056] Example 1 was repeated, using formic acid as the solvent (1% water, 0.3 mol·L -1 PW 12 ) and 0.5 g 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. The other operation steps remain unchanged. Repeat 10 times. The 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 Cycle times 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 Embodiment 7-8 8 90.20 88.18 Embodiment 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 commercially available 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 product of the hydrolysis of PET and PBT 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 indicates that the system has good polyester hydrolysis selectivity.

[0060] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached 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.

2. The green recycling method according to claim 1, characterized in that: The heteropoly acid is any one of Keggin-type phosphotungstic acid, Keggin-type silicotungstic acid, Dawson-type phosphotungstic acid, Dawson-type silicotungstic acid, Keggin-type phosphotungstic acid monosubstituted with copper, cobalt, nickel, iron, manganese or zinc, and Keggin-type silicotungstic acid monosubstituted with iron or copper.

3. The green recycling method according to claim 1, characterized in that: The dosage of the heteropoly acid is 0.1-0.4 mol·L -1 .

4. The green recycling method according to claim 1, characterized in that: The organic acid includes any one of formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, trifluoroacetic acid and trichloroacetic acid.

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

6. The green recycling method according to claim 1, characterized in that: The hydrolysis temperature is 80-120°C.

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

8. The green recycling method according to any one of claims 1 to 7, characterized in that: Also includes: Reducing metal ions are used as co-catalysts.

9. The green recycling method according to claim 8, characterized in that: The reducing metal ions include Fe 2+ 、Ni 2+ 、Zn 2+ Cr 3+ 、Co 3+ , Fe 3+ Sn 4+ , Mn 2+ Sn 4+ Any one of .

10. The green recycling method according to claim 1, wherein the polyester plastic comprises PET or PBT.

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