Method for efficiently degrading and recycling waste PET polyester based on imidazole ring eutectic solvent

Abstract

The invention discloses a method for efficiently degrading polyethylene glycol terephthalate (PET) based on a deep eutectic solvent (DES), which mainly comprises the following steps: synthesizing a proper imidazole ring deep eutectic solvent by taking waste PET as a raw material, and degrading the PET for 30-90 minutes under the conditions that the temperature is 80-180 DEG C and the mass ratio of the DES to the PET is (0.5: 5)-(0.75: 5); the method has the advantages that no metal is contained, the subsequent metal removal operation is reduced, the solvent dosage is small, the degradation temperature is low, the PET degradation rate is high, and the monomer selectivity is good.

Description

Technical Field

[0001] The invention relates to the technical field of waste resource recycling, and in particular to a method for degrading waste PET polyester based on a low eutectic solvent using an imidazole ring as a hydrogen bond acceptor. Background Art

[0002] Polyethylene terephthalate (PET) is a thermoplastic polymer with a wide range of applications. Its excellent oxygen, carbon dioxide, and moisture barriers, combined with its lightweight, high durability, good abrasion resistance, excellent thermal stability, good chemical resistance, and high tensile strength, have enabled its development in numerous fields.

[0003] In recent years, many studies have focused on the sustainable degradation of traditionally non-biodegradable plastics using various catalysts to reduce the reaction time for polymer recycling, also through green pathways. In recent decades, a new generation of ionic solvents has emerged, the so-called deep eutectic solvents (DESs). They combine most of the advantages of ionic solvents (liquid at room temperature, low vapor pressure, and good solvent capacity), are easy to prepare, low in cost, low in toxicity, and are biodegradable and biocompatible. Therefore, they play an important role in the field of sustainable chemistry.

[0004] "Reduce, reuse, and recycle" should always be the focus of waste management, but in reality, while PET production is increasing, only a small portion of PET items are recycled, with the rest ending up in landfills or incineration. Currently, the primary methods for PET degradation and recycling are chemical recycling, primarily through amine / ammoniolysis, hydrolysis, and alcoholysis. Existing solvent degradation methods suffer from high reaction temperatures, long reaction times, high solvent usage, and poor product selectivity.

[0005] Therefore, we can consider using green and environmentally friendly low-eutectic solvents to degrade PET. The degradation process has low energy consumption and is green and environmentally friendly. The products can continue to be used in real life, realizing resource recycling. Summary of the Invention

[0006] In order to solve the problems raised in the above background technology, the purpose of the present invention is to provide a method for degrading waste PET polyester based on a low eutectic solvent with imidazole ring as a hydrogen bond acceptor, and directly mix the sample with DES for heating and stirring to degrade it.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a method for degrading waste PET polyester based on a deep eutectic solvent, comprising the following steps:

[0009] S1, mixing an imidazole ring deep eutectic solvent with waste PET polyester, heating and stirring, and degrading to obtain a degradation liquid;

[0010] S2. Deionized water or hot water is added to the degradation solution, and the product N,N'-bis(2-hydroxyethyl)terephthalamide is precipitated by recrystallization at room temperature, or bis(hydroxyethyl)terephthalate is obtained by recrystallization at 4°C;

[0011] S3. After centrifugation for 10-30 seconds in step (2), the undegraded waste PET polyester in the lower layer is washed with deionized water, dried, and then weighed.

[0012] Furthermore, in step S1, the imidazole ring deep eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor, the hydrogen bond acceptor is one of imidazole, 1-methylimidazole, and 2-methylimidazole, and the hydrogen bond donor is one of ethanolamine and ethylene glycol.

[0013] Preferably, when the hydrogen bond donor is ethanolamine as the deep eutectic solvent, the hydrogen bond acceptor is 1-methylimidazole; when the hydrogen bond donor is ethylene glycol as the deep eutectic solvent, the hydrogen bond acceptor is 2-methylimidazole.

[0014] Furthermore, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:4-1:8. The hydrogen bond acceptor and the hydrogen bond donor are stirred at a certain temperature to synthesize an imidazole ring deep eutectic solvent.

[0015] Furthermore, when the hydrogen bond donor is ethanolamine; S1, mixing an imidazole ring low eutectic solvent with waste PET polyester, heating and stirring, and degrading at 80-120° C. to obtain a degradation liquid; S2, centrifuging the degradation liquid, taking the supernatant, adding deionized water, and recrystallizing and precipitating the product N,N'-bis(2-hydroxyethyl)terephthalamide (BHETA) at room temperature.

[0016] Preferably, in step S1, the degradation temperature is 100°C.

[0017] Furthermore, when the hydrogen bond donor is ethylene glycol; S1, mixing an imidazole ring low eutectic solvent with waste PET polyester, heating and stirring, and degrading at 140-180°C to obtain a degradation liquid; S2, centrifuging the degradation liquid, taking the supernatant, adding 100°C deionized water, and refrigerating at 4°C to recrystallize and precipitate the product bis(hydroxyethyl terephthalate) (BHET).

[0018] Preferably, in step S1, the degradation temperature is 160°C.

[0019] Furthermore, in step S1, the mass ratio of the imidazole ring deep eutectic solvent to the waste PET polyester is 5:0.5-5:0.75; and the degradation time is 30-90 minutes.

[0020] Furthermore, in step S2, deionized water or hot water (100° C. deionized water) twice the volume of the degradation solution is added and allowed to stand for 6-12 hours.

[0021] After the reaction is completed, the conversion rate of PET polyester and the yield of the product can be calculated by formulas (1), (2) and (3):

[0022]

[0023] Where M0 is the initial mass of PET, and M1 is the remaining mass of PET after degradation is completed;

[0024] W BHETA is the actual mass of BHETA, M PET is the molar mass of PET unit, M BHETA is the molar mass of BHETA, W PET The remaining PET mass after degradation is completed;

[0025] W BHET is the actual mass of BHET, M BHET is the molar mass of BHET.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The reaction system is at normal pressure, the degradation temperature is low, and the reaction time is short, ensuring the safety and efficiency of the experiment.

[0028] (2) The imidazole ring is used as a low eutectic solvent hydrogen bond acceptor, which is green and low-toxic. It is easy to separate from the product after the reaction is completed, and the product has high purity and good selectivity.

[0029] (3) The present invention provides a new approach for developing green, sustainable, and efficient methods for degrading PET, thereby minimizing environmental pollution and promoting the application of low eutectic solvents in the degradation of PET polyester.

[0030] (4) In the imidazole ring structure, the key role is played by the negative nitrogen center at position 3 and the positive nitrogen center at position 1. The negative nitrogen center can form hydrogen bonds with the amino group on ethanolamine and the hydroxyl group on ethylene glycol, making the nucleophilic groups of the amino group on ethanolamine and the hydroxyl group on ethylene glycol more nucleophilic. The positive center can attract the electrons on the carbonyl oxygen on PET, causing the electrons on the carbonyl carbon to transfer to the carbonyl oxygen, making the positive center on the carbonyl carbon more susceptible to attack by nucleophiles, effectively promoting the reaction rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a process flow chart of the method for efficiently degrading PET polyester based on a deep eutectic solvent of the present invention;

[0032] Figure 2 This is a data graph showing the degradation rate and product yield of PET polyester efficiently degraded using a deep eutectic solvent in Comparative Example 1 and Examples 1-3 of the present invention;

[0033] Figure 3 This is a data graph showing the degradation rate and product yield of PET polyester efficiently degraded using a deep eutectic solvent in Comparative Example 2 and Examples 4-6 of the present invention;

[0034] Figure 4 The data graphs of the degradation rate and product yield of PET polyester efficiently degraded by a deep eutectic solvent according to Examples 7-11 of the present invention are as follows;

[0035] Figure 5 The data graphs of the degradation rate and product yield of PET polyester efficiently degraded by deep eutectic solvents according to Examples 12-16 of the present invention are as follows;

[0036] Figure 6 The data graphs of degradation rate and product yield of PET polyester efficiently degraded by deep eutectic solvents according to Examples 17-21 of the present invention are as follows;

[0037] Figure 7 The data graphs of degradation rate and product yield of PET polyester efficiently degraded by deep eutectic solvents according to Examples 22-26 of the present invention are as follows;

[0038] Figure 8 The data graphs of the degradation rate and product yield of PET polyester efficiently degraded by deep eutectic solvents according to Examples 27-31 of the present invention are as follows;

[0039] Figure 9 The data graphs of degradation rate and product yield of PET polyester efficiently degraded by deep eutectic solvents according to Examples 32-36 of the present invention are as follows;

[0040] Figure 10 The data graphs of degradation rate and product yield of PET polyester efficiently degraded by deep eutectic solvents according to Examples 37-42 of the present invention are as follows;

[0041] Figure 11 The data graphs of degradation rate and product yield of PET polyester efficiently degraded by deep eutectic solvents according to Examples 43-48 of the present invention are as follows;

[0042] Figure 12 This is a data graph showing the degradation rate and product yield of Comparative Examples 3-5 of the present invention using a deep eutectic solvent for efficient degradation of PET polyester;

[0043] Figure 13 This is a data graph showing the degradation rate and product yield of Comparative Examples 6-8 of the present invention using a deep eutectic solvent for efficient degradation of PET polyester;

[0044] Figure 14 IR spectra of the products obtained in Examples 1-6 of the present invention;

[0045] Figure 15The NMR spectra of the product BHETA obtained in Examples 1-3 of the present invention are shown in Figures 1-3, (a) is a H-NMR spectrum, and (b) is a C-NMR spectrum;

[0046] Figure 16 The NMR spectra of the product BHET obtained in Examples 4-6 of the present invention are as follows: (a) is the H NMR spectrum, and (b) is the C NMR spectrum. DETAILED DESCRIPTION

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0048] Examples 1-3

[0049] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0050] (2) Prepare low eutectic solvents with a molar ratio of imidazole:ethanolamine, 1-methylimidazole:ethanolamine, and 2-methylimidazole:ethanolamine of 1:6, heat and stir at 80°C for 1 hour and set aside.

[0051] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.5:5, heated to 100°C, and then condensed and refluxed for 60 minutes.

[0052] (4) After the reaction, the unreacted PET bottle flakes were separated by centrifugation at a speed of 5000 rpm, and excess deionized water was added to precipitate the product BHETA, which was separated by centrifugation at a speed of 9000 rpm and dried at 80°C for 12 h.

[0053] (5) The mass of the product BHETA and the remaining PET was weighed, and the yield of BHETA and the conversion rate of PET were calculated.

[0054] The effects of different deep eutectic solvents on the degradation reaction of waste PET bottle flakes are detailed in Table 1, No. 1-3 and Figure 2 .

[0055] Table 1 Effects of different deep eutectic solvents in Examples 1-3 on the degradation reaction of waste PET bottle flakes

[0056] Example Deep eutectic solvents PET degradation rate% BHETA yield % 1 Imidazole:ethanolamine (1:6) 55.27 54.83 2 1-Methylimidazole:ethanolamine (1:6) 100 81.34 3 2-Methylimidazole:ethanolamine (1:6) 42.87 52.05

[0057] The infrared spectra of the products obtained in Examples 1-6 of the present invention are as follows: Figure 14 As shown, the infrared spectrum of BHETA is 3373 cm-1 The peak at 3288 cm corresponds to NH in hydrogen bonding, while the peak at 3288 cm -1 The peak at 1622 cm corresponds to the bending of the amide-NH plane. -1 The peak at 1557 cm corresponds to the C=O bend in the amide bond. -1 The peak at 1054 cm represents the secondary amide stretching vibration. -1 The peak at 3446 cm represents the stretching vibration of primary alcohol as shown in the infrared spectrum of BHET. -1 The peak at 2963 cm is the OH stretching vibration peak. -1 The peak at 2880 cm is the CH antisymmetric stretching vibration peak. -1 The peak at 1715 cm is the CH symmetric stretching vibration peak. -1 The peak at 1282 cm is the stretching vibration peak of the ester group C=O. -1 The peak at 1073 cm is the COC stretching vibration peak of the ester group. -1 The peak at 728 cm is the CO stretching vibration peak of the hydroxyl group. -1 The peak at is the out-of-plane bending vibration peak of the CH ring of the benzene ring, which is basically consistent with the characteristic peak of the standard infrared spectrum.

[0058] The NMR spectra of the product BHETA obtained in Examples 1-3 of the present invention are as follows: Figure 15 Figure a shows the H NMR spectrum of BHETA. A triplet peak at 8.49 ppm corresponds to the CO-NH protons. A triplet peak at 7.88 ppm corresponds to the same ortho-substituted aromatic compound, namely, the four phenyl hydrogen protons. Another triplet peak at 4.69 ppm corresponds to the hydroxyl functional group, which is present at the end of BHETA. The two methyl groups in the BHETA structure do not appear in the same position in the NMR spectrum. This is due to the different electronegativity of the nitrogen and oxygen atoms. Therefore, the two methyl groups appear as two distinct peaks at 3.49 ppm and 3.31 ppm, respectively. Figure b shows the C NMR spectrum of BHETA. As shown, there is a peak at 166.13 ppm, which is due to the carbonyl carbon attached to the aromatic ring. The peaks at 137.10 ppm and 127.53 ppm correspond to carbon atoms on the aromatic ring, respectively. The peak at 60.11 ppm is associated with the aliphatic carbon attached to the hydroxyl group, and the peak at 42.67 ppm is associated with the unsaturated double-bonded carbon attached to the amino group.

[0059] The NMR spectra of the product BHET obtained in Examples 4-6 of the present invention are as follows: Figure 16Figure a shows the H NMR spectrum of BHET. The singlet peak at 8.11 ppm corresponds to hydrogen on the benzene ring, the triplet peak at 4.96-4.98 ppm corresponds to the active hydrogen of the hydroxyl group, and the quartet peak at 3.72-3.75 ppm corresponds to the methylene hydrogen attached to the hydroxyl group. Figure b shows the C NMR spectrum of BHET. The peak at 165.63 ppm corresponds to the carbonyl carbon, the peak at 134.19 ppm corresponds to the carbon of the substituted benzene ring, the peak at 129.95 ppm corresponds to the carbon of the unsubstituted benzene ring, the peak at 67.47 ppm corresponds to the methylene carbon attached to the ester group, and the peak at 59.4 ppm corresponds to the methylene carbon attached to the hydroxyl group.

[0060] Examples 4-6

[0061] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0062] (2) Prepare deep eutectic solvents with a molar ratio of imidazole:ethylene glycol, 1-methylimidazole:ethylene glycol, and 2-methylimidazole:ethylene glycol of 1:6, heat and stir at 80°C for 1 hour and set aside.

[0063] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.5:5, heated to 160°C, and then condensed and refluxed for 60 minutes.

[0064] (4) After the reaction is completed, add 100°C boiling water to dissolve it, and then centrifuge at 5000 rpm to separate the unreacted PET bottle flakes. The precipitated product BHET is refrigerated at 4°C, separated by centrifugation at 9000 rpm, and freeze-dried for 12 hours.

[0065] (5) The mass of the product BHET and the remaining PET was weighed, and the yield of BHET and the conversion rate of PET were calculated.

[0066] The effects of different deep eutectic solvents on the degradation reaction of waste PET bottle flakes are detailed in Table 2, No. 4-6 and Figure 3 .

[0067] Table 2 Effects of different deep eutectic solvents in Examples 4-6 on the degradation reaction of waste PET bottle flakes

[0068]

[0069]

[0070] Examples 7-11

[0071] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0072] (2) Prepare a low eutectic solvent with a molar ratio of 1-methylimidazole to ethanolamine of 1:4-1:8, heat and stir at 80°C for 1 hour and set aside.

[0073] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.75:5, heated to 100°C, and then condensed and refluxed for 60 minutes.

[0074] (4) After the reaction, the unreacted PET bottle flakes were separated by centrifugation at a speed of 5000 rpm, and the product BHETA was precipitated by adding excess deionized water at room temperature. The product was separated by centrifugation at a speed of 9000 rpm and dried at 80°C for 12 h.

[0075] (5) The mass of the product BHETA and the remaining PET was weighed, and the yield of BHETA and the conversion rate of PET were calculated.

[0076] The effects of the molar ratio of hydrogen bond acceptors to hydrogen bond donors of different deep eutectic solvents on the degradation reaction of waste PET bottle flakes are detailed in Table 3, No. 7-11 and Figure 4 .

[0077] Table 3 Effect of the molar ratio of hydrogen bond acceptors to hydrogen bond donors of deep eutectic solvents of Examples 7-11 on the degradation reaction of waste PET bottle flakes

[0078] Example molar ratio PET degradation rate% BHETA yield % 7 1:4 95.36 78.76 8 1:5 97.79 80.05 9 1:6 98.63 80.82 10 1:7 93.11 77.09 11 1:8 93.08 78.92

[0079] Examples 12-16

[0080] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0081] (2) Prepare a low eutectic solvent with a molar ratio of 2-methylimidazole to ethylene glycol of 1:4-1:8, heat and stir at 80°C for 1 hour and set aside.

[0082] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.75:5, heated to 160°C, and then condensed and refluxed for 60 minutes.

[0083] (4) After the reaction is completed, add 100°C boiling water to dissolve it, and then centrifuge at 5000 rpm to separate the unreacted PET bottle flakes. The precipitated product BHET is refrigerated at 4°C, separated by centrifugation at 9000 rpm, and freeze-dried for 12 hours.

[0084] (5) The mass of the product BHET and the remaining PET was weighed, and the yield of BHET and the conversion rate of PET were calculated.

[0085] The effects of the molar ratio of hydrogen bond acceptors to hydrogen bond donors of different deep eutectic solvents on the degradation reaction of waste PET bottle flakes are detailed in Table 4, No. 12-16 and Figure 5 .

[0086] Table 4 Effect of the molar ratio of hydrogen bond acceptors to hydrogen bond donors of deep eutectic solvents of Examples 12-16 on the degradation reaction of waste PET bottle flakes

[0087] Example molar ratio PET degradation rate% BHET yield % 12 1:4 85.99 63.30 13 1:5 90.64 65.48 14 1:6 92.27 70.27 15 1:7 90.24 61.41 16 1:8 82.63 58.04

[0088] Examples 17-21

[0089] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0090] (2) Prepare a low eutectic solvent with a molar ratio of 1-methylimidazole to ethanolamine of 1:6, heat and stir at 80°C for 1 hour and set aside.

[0091] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.5:5, heated to 80-120°C, and then condensed and refluxed for 60 minutes.

[0092] (4) After the reaction, the unreacted PET bottle flakes were separated by centrifugation at a speed of 5000 rpm, and the product BHETA was precipitated by adding excess deionized water at room temperature. The product was separated by centrifugation at a speed of 9000 rpm and dried at 80°C for 12 h.

[0093] (5) The mass of the product BHETA and the remaining PET was weighed, and the yield of BHETA and the conversion rate of PET were calculated.

[0094] The effects of different reaction temperatures of deep eutectic solvents on the degradation reaction of waste PET bottle flakes are detailed in Table 5, No. 17-21 and Figure 6 .

[0095] Table 5 Effect of reaction temperature on degradation of waste PET bottle flakes by deep eutectic solvents in Examples 17-21

[0096] Example Temperature PET degradation rate% BHETA yield % 17 80 31.23 18.62 18 90 88.58 69.46 19 100 100 81.34 20 110 100 78.75 21 120 100 74.21

[0097] Examples 22-26

[0098] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0099] (2) Prepare a low eutectic solvent with a molar ratio of 2-methylimidazole to ethylene glycol of 1:4-1:8, heat and stir at 80°C for 1 hour and set aside.

[0100] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.5:5, heated to 140-180°C, and then condensed and refluxed for 60 minutes.

[0101] (4) After the reaction is completed, add 100°C boiling water to dissolve it, and then centrifuge at 5000 rpm to separate the unreacted PET bottle flakes. The precipitated product BHET is refrigerated at 4°C, separated by centrifugation at 9000 rpm, and freeze-dried for 12 hours.

[0102] (5) The mass of the product BHET and the remaining PET was weighed, and the yield of BHET and the conversion rate of PET were calculated.

[0103] The effects of different deep eutectic solvents on the degradation reaction of waste PET bottle flakes are detailed in Table 6, No. 22-26 and Figure 7 .

[0104] Table 6 Effect of reaction temperature on degradation of waste PET bottle flakes by deep eutectic solvents in Examples 22-26

[0105] Example Temperature PET degradation rate% BHET yield % 22 140 6.23 8.13 23 150 42.38 23.20 24 160 100 70.27 25 170 100 69.59 26 180 100 70.48

[0106] Examples 27-31

[0107] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0108] (2) Prepare a low eutectic solvent with a molar ratio of 1-methylimidazole to ethanolamine of 1:6, heat and stir at 80°C for 1 hour and set aside.

[0109] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.5:5, heated to 100°C, and then condensed and refluxed for 30-90 minutes.

[0110] (4) After the reaction, the unreacted PET bottle flakes were separated by centrifugation at a speed of 5000 rpm, and the product BHETA was precipitated by adding excess deionized water at room temperature. The product was separated by centrifugation at a speed of 9000 rpm and dried at 80°C for 12 h.

[0111] (5) The mass of the product BHETA and the remaining PET was weighed, and the yield of BHETA and the conversion rate of PET were calculated.

[0112] The effects of different reaction times of deep eutectic solvents on the degradation reaction of waste PET bottle flakes are detailed in Table 7, No. 27-31 and Figure 8 .

[0113] Table 7 Effect of reaction time on degradation of waste PET bottle flakes by deep eutectic solvents in Examples 27-31

[0114] Example Time min PET degradation rate% BHETA yield % 27 30 74.93 72.17 28 45 82.38 73.29 29 60 100 81.34 30 75 100 80.96 31 90 100 81.04

[0115] Examples 32-36

[0116] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0117] (2) Prepare a low eutectic solvent with a molar ratio of 2-methylimidazole to ethylene glycol of 1:6, heat and stir at 80°C for 1 hour and set aside.

[0118] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.5:5, heated to 160°C, and then condensed and refluxed for 30-90 minutes.

[0119] (4) After the reaction is completed, add 100°C boiling water to dissolve it, and then centrifuge at 5000 rpm to separate the unreacted PET bottle flakes. The precipitated product BHET is refrigerated at 4°C, separated by centrifugation at 9000 rpm, and freeze-dried for 12 hours.

[0120] (5) The mass of the product BHET and the remaining PET was weighed, and the yield of BHET and the conversion rate of PET were calculated.

[0121] The effects of different reaction times of deep eutectic solvents on the degradation reaction of waste PET bottle flakes are detailed in Table 8, No. 32-36 and Figure 9 .

[0122] Table 8 Effect of reaction time of Examples 32-36 on degradation of waste PET bottle flakes by deep eutectic solvent

[0123] Example Time min PET degradation rate% BHET yield % 32 30 56.93 23.43 33 45 98.47 58.81 34 60 100 70.27 35 75 100 70.89 36 90 100 69.93

[0124] Examples 37-42

[0125] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0126] (2) Prepare a low eutectic solvent with a molar ratio of 1-methylimidazole to ethanolamine of 1:6, heat and stir at 80°C for 1 hour and set aside.

[0127] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.5:5-0.75:5, heated to 100°C, and then condensed and refluxed for 60 minutes.

[0128] (4) After the reaction, the unreacted PET bottle flakes were separated by centrifugation at a speed of 5000 rpm, and the product BHETA was precipitated by adding excess deionized water at room temperature. The product was separated by centrifugation at a speed of 9000 rpm and dried at 80°C for 12 h.

[0129] (5) The mass of the product BHETA and the remaining PET was weighed, and the yield of BHETA and the conversion rate of PET were calculated.

[0130] The effects of different solid-liquid ratio deep eutectic solvents on the degradation reaction of waste PET bottle flakes are detailed in Table 9, No. 37-42 and Figure 10 .

[0131] Table 9 Effect of solid-liquid ratio in reaction of Examples 37-42 on degradation of waste PET bottle flakes by deep eutectic solvent

[0132]

[0133]

[0134] Examples 43-48

[0135] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0136] (2) Prepare a low eutectic solvent with a molar ratio of 2-methylimidazole to ethylene glycol of 1:6, heat and stir at 80°C for 1 hour and set aside.

[0137] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.5:5-0.75:5, heated to 160°C, and then condensed and refluxed for 60 minutes.

[0138] (4) After the reaction is completed, add 100°C boiling water to dissolve it, and then centrifuge at 5000 rpm to separate the unreacted PET bottle flakes. The precipitated product BHET is refrigerated at 4°C, separated by centrifugation at 9000 rpm, and freeze-dried for 12 hours.

[0139] (5) The mass of the product BHET and the remaining PET was weighed, and the yield of BHET and the conversion rate of PET were calculated.

[0140] The effects of different solid-liquid ratio deep eutectic solvents on the degradation reaction of waste PET bottle flakes are detailed in Table 10, No. 43-48 and Figure 11 .

[0141] Table 10 Effect of solid-liquid ratio of reaction of Examples 43-48 on degradation of waste PET bottle flakes by deep eutectic solvent

[0142] Example Solid-liquid ratio (g / g) PET degradation rate% BHETA yield % 43 0.5:5 100 70.27 44 0.55:5 100 72.33 45 0.6:5 99.02 72.32 46 0.65:5 95.58 71.00 47 0.7:5 92.87 69.80 48 0.75:5 92.27 67.09

[0143] Comparative Example 1

[0144] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0145] (2) PET bottle flakes and ethanolamine were added into the reactor at a mass ratio of 0.5:5, heated to 100°C, and then condensed and refluxed for 60 minutes.

[0146] (3) After the reaction, the unreacted PET bottle flakes were separated by centrifugation at a speed of 5000 rpm, and the product BHETA was precipitated by adding excess deionized water at room temperature. The product was separated by centrifugation at a speed of 9000 rpm and dried at 80°C for 12 h.

[0147] (4) The mass of the product BHETA and the remaining PET was weighed, and the yield of BHETA and the conversion rate of PET were calculated. The effect of conventional solvents on the degradation of waste PET bottle flakes in Comparative Example 1 is shown in Tables 11 and Figure 2 .

[0148] Table 11 Comparative Example 1 Effect of traditional solvents on the degradation of waste PET bottle flakes

[0149]

[0150]

[0151] Comparative Example 2

[0152] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0153] (2) PET bottle flakes and ethylene glycol were added into the reactor at a mass ratio of 0.5:5, heated to 160°C, and then condensed and refluxed for 60 minutes.

[0154] (3) After the reaction is completed, 100°C boiling water is added to dissolve the product, and the unreacted PET bottle flakes are separated by centrifugation at a speed of 5000 rpm. The precipitated product BHET is refrigerated at 4°C, separated by centrifugation at a speed of 9000 rpm, and then freeze-dried for 12 hours.

[0155] (4) The mass of the product BHET and the remaining PET was weighed and the yield of BHET and the conversion rate of PET were calculated. The effect of conventional solvents on the degradation of waste PET bottle flakes in Comparative Example 2 is shown in Tables 12 and Figure 3 .

[0156] Table 12 Comparative Example 2 Effect of traditional solvents on the degradation of waste PET bottle flakes

[0157] Comparative Example PET degradation rate% BHET yield % 2 12.73 16.11

[0158] Comparative Examples 3-5

[0159] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0160] (2) Prepare a low eutectic solvent of acetamide:ethanolamine, choline chloride:ethanolamine, 1-(2-hydroxyethyl)-3-methylimidazole chloride:ethanolamine in a molar ratio of 1:6, heat and stir at 80°C for 1 hour and set aside.

[0161] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.5:5, heated to 100°C, and then condensed and refluxed for 60 minutes.

[0162] (4) After the reaction, the unreacted PET bottle flakes were separated by centrifugation at a speed of 5000 rpm, and excess deionized water was added to precipitate the product BHETA, which was separated by centrifugation at a speed of 9000 rpm and dried at 80°C for 12 h.

[0163] (5) The mass of the product BHETA and the remaining PET was weighed and the yield of BHETA and the conversion rate of PET were calculated. The effects of other deep eutectic solvents on the degradation of waste PET bottle flakes in Examples 3-5 are detailed in Tables 13 and Figure 12 .

[0164] Table 13 Effect of other deep eutectic solvents in comparative examples 3-5 on the degradation of waste PET bottle flakes

[0165] Comparative Example PET degradation rate% BHETA yield % 3 41.83 37.54 4 55.86 42.76 5 78.72 50.11

[0166] Comparative Examples 6-8

[0167] (1) Use scissors to cut the Wahaha mineral water bottle into 0.3 cm × 0.3 cm pieces, clean them with ethanol ultrasonically, and dry them for later use.

[0168] (2) Prepare a low eutectic solvent of acetamide:ethylene glycol, choline chloride:ethylene glycol, and 1-(2-hydroxyethyl)-3-methylimidazole chloride:ethylene glycol in a molar ratio of 1:6, heat and stir at 80°C for 1 hour and set aside.

[0169] (3) PET bottle flakes and DES were added into the reactor at a mass ratio of 0.5:5, heated to 160°C, and then condensed and refluxed for 60 minutes.

[0170] (4) After the reaction is completed, add 100°C boiling water to dissolve it, and then centrifuge at 5000 rpm to separate the unreacted PET bottle flakes. The precipitated product BHET is refrigerated at 4°C, separated by centrifugation at 9000 rpm, and freeze-dried for 12 hours.

[0171] (5) The mass of the product BHET and the remaining PET was weighed and the yield of BHET and the conversion rate of PET were calculated. The effects of other deep eutectic solvents on the degradation of waste PET bottle flakes in Comparative Examples 6-8 are detailed in Tables 14 and Figure 13 .

[0172] Table 14 Effect of other deep eutectic solvents in comparative examples 6-8 on the degradation of waste PET bottle flakes

[0173] Comparative Example PET degradation rate% BHET yield % 6 57.09 35.11 7 77.81 45.79 8 80.72 57.76

[0174] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0175] It should be noted that the above content merely illustrates the technical idea of the present invention and cannot be used to limit the scope of protection of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for degrading waste PET polyester based on a deep eutectic solvent, characterized in that: The following steps are involved: S1, mixing an imidazole ring deep eutectic solvent with waste PET polyester, heating and stirring, and degrading to obtain a degradation liquid; S2. Deionized water or hot water is added to the degradation solution to recrystallize and precipitate the product N,N'-bis(2-hydroxyethyl)terephthalamide or bis(hydroxyethyl)terephthalate; S3: After centrifugation in step S2, the undegraded waste PET polyester in the lower layer is washed with deionized water and dried.

2. The method for degrading waste PET polyester based on a deep eutectic solvent according to claim 1, characterized in that: In step S1, the imidazole ring deep eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor, the hydrogen bond acceptor is one of imidazole, 1-methylimidazole, and 2-methylimidazole, and the hydrogen bond donor is one of ethanolamine and ethylene glycol.

3. The method for degrading waste PET polyester based on a deep eutectic solvent according to claim 2, characterized in that: The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:4-1:

8.

4. The method for degrading waste PET polyester based on a deep eutectic solvent according to claim 2, characterized in that: When the hydrogen bond donor is ethanolamine; S1, mixing the imidazole ring deep eutectic solvent with the waste PET polyester, heating and stirring, Degradation is performed at 80-120° C. to obtain a degradation solution; S2. The degradation solution is centrifuged, the supernatant is taken, deionized water is added, and the product N,N'-bis(2-hydroxyethyl)terephthalamide is precipitated by recrystallization at room temperature.

5. The method for degrading waste PET polyester based on a deep eutectic solvent according to claim 2, characterized in that: When the hydrogen bond donor is ethylene glycol; S1, mixing the imidazole ring deep eutectic solvent with the waste PET polyester, heating and stirring, Degradation at 140-180°C to obtain a degradation liquid; S2, adding 100°C deionized water to the degradation liquid, centrifuging to separate the undegraded PET polyester solid, and refrigerating the supernatant at 4°C to recrystallize and precipitate the product bis(hydroxyethyl) terephthalate.

6. A method for degrading waste PET polyester based on a deep eutectic solvent according to any one of claims 1 to 5, characterized in that: In step S1, the mass ratio of the imidazole ring deep eutectic solvent to the waste PET polyester is 5:0.5-5:0.75; and the degradation time is 30-90 minutes.

7. The method for degrading waste PET polyester based on a deep eutectic solvent according to claim 1, characterized in that: In step S2, deionized water or boiling water twice the volume of the degradation solution is added and the mixture is allowed to stand for 6-12 hours.

Images