A class of polynuclear metal catalysts, their preparation methods, and their application in the catalytic alcoholysis of polyester polymers.

Abstract

This invention discloses a class of polynuclear metal catalysts, their preparation methods, and their application in the catalytic alcoholysis of polyester polymers. The polynuclear metal catalyst comprises an organic ligand and metal ions (titanium ions, zirconium ions, or hafnium ions). The general chemical formula of the polynuclear metal catalyst is shown in formulas (I) and (II). The polynuclear metal catalyst of this invention can catalyze the rapid alcoholysis of general-purpose polyester polymers such as PET in alcohol solvents. The method is simple, safe, efficient, energy-saving, and yields high purity and high efficiency of the recovered monomers.

Description

Technical Field

[0001] This invention belongs to the field of polyester chemical recycling and degradation technology, specifically involving a class of polynuclear metal catalysts, their preparation methods, and their application in the catalytic alcoholysis of polyester polymers. Technical Background

[0002] Plastics play a vital role in modern society, hailed as one of the greatest scientific discoveries of the 20th century and a symbol of modern industry. Currently, global plastic production is increasing by 3%-4% annually, projected to reach 1.2 billion tons per year by 2060. The waste generated from these plastic products causes severe environmental pollution. Statistics show that $120 billion is spent globally annually on addressing plastic waste pollution. By 2040, approximately 600 million tons of plastic waste will be dumped into the environment annually. Polyethylene terephthalate (PET) is a linear thermoplastic polymer, widely used in plastic packaging bottles, films, and synthetic fibers due to its low cost, airtightness, transparency, good compressive strength, low energy consumption, and good processing performance. To date, global annual PET production has exceeded 70 million tons, making it the third largest plastic category after polyethylene and polypropylene. PET waste accounts for nearly 12% of existing plastic waste. Furthermore, the raw materials for PET production come from finite and non-renewable fossil resources. Meanwhile, PET and similar products are largely unable to undergo complete natural degradation, producing harmful microplastics and chemicals during the slow decomposition process that are detrimental to plants, animals, and the surrounding environment. Currently, only 10% of PET products are recycled, with the remainder being incinerated or landfilled. To minimize environmental pollution caused by excessive plastic production and incineration, the effective recycling of PET and other plastic products has become a significant social issue.

[0003] The recycling methods for PET and other plastic waste mainly include physical recycling and chemical recycling. Currently, most PET waste is recycled through physical recycling. This technology can be used for most PET bottle products. However, repeated physical recycling often leads to a decrease in product viscosity below food grade, and repeatedly recycled products can only be downgraded for use, such as in the manufacture of polyester fibers. Based on considerations of material recycling, energy recycling, and economic recycling, chemical recycling is a scientifically sound closed-loop recycling method that can depolymerize polymers into monomers and use them to synthesize high-purity virgin polymers.

[0004] Chemical degradation and recycling mainly include pyrolysis, hydrolysis, and alcoholysis. Methanol alcoholysis is currently the main chemical recycling method for degrading PET into the monomer dimethyl terephthalate (DMT). The degraded DMT can be easily purified by recrystallization, and the purified DMT can be used as a raw material for synthesizing PET or higher value-added polyesters, thus the demand for DMT is gradually increasing. Traditional methanol alcoholysis of PET degrades it into DMT and ethylene glycol under high temperature and high pressure conditions. This process requires a temperature of 180-220℃ and a pressure of 2-4 MPa (Chem. Eng. J. 2015, 270, 535-541; Polym. Degrad. Stab. 2003, 79, 529-533). To effectively degrade PET, researchers have adopted a series of enhancement methods. The main enhancement methods include supercritical enhancement, microwave enhancement, and co-solvent enhancement. Methanol hydrolysis under supercritical conditions can significantly reduce the degradation time of PET to within 1 hour and increase the DMT yield to about 90% in a short time, but this requires a pressure of 9-11 MPa and a temperature of 260-2270 °C (Ind. Eng. Chem. Res. 2005, 44, 3894-3900.). In addition, microwave-assisted methods can also reduce the degradation time of PET. Using zinc acetate as a catalyst under microwave conditions, PET can achieve 100% degradation and 80% DMT yield at 160 °C for 30 minutes (J. Appl. Polym. Sci. 2010, 118, 3066-3073.). Although both methods can achieve rapid degradation of PET in a short time, the reactions must be carried out under high temperature and high pressure, and these two enhanced methods have high requirements for reaction equipment, making industrial production difficult. Nomura's group degraded PET in ethanol using CpTiCl3 as a catalyst. The degradation of PET and the yield of monomers reached more than 99% after 24 hours of reaction at 170°C (Catalysts 2023, 13(2), 421). Compared with the two enhancement methods mentioned above, this strategy has relatively safe reaction conditions, energy saving and high monomer recovery rate, but the disadvantage is that the catalytic efficiency of the catalyst is low.

[0005] While significant breakthroughs have been made in the chemical recycling of plastic waste such as PET, most studies still face challenges including high energy consumption, high production costs, low efficiency, and complex conversion processes. Therefore, the development of efficient and low-cost catalysts is crucial for achieving safe, energy-saving, and efficient chemical recycling of waste such as PET. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a class of polynuclear metal catalysts, their preparation methods, and their application in the catalytic alcoholysis of polyester polymers.

[0007] One of the objectives of this invention is to provide a class of polynuclear metal catalysts.

[0008] The second objective of this invention is to provide a method for preparing the aforementioned polynuclear metal catalyst.

[0009] The third objective of this invention is to provide the application of the above-mentioned polynuclear metal catalyst in the catalytic alcoholysis of general polyester polymers such as PET.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A class of polynuclear metal catalysts, comprising an organic ligand and a metal ion; the general chemical formulas of the polynuclear metal catalysts are shown in (I) and (II) below:

[0012]

[0013] In this context, R1, R2, R3, R4, and R5 each independently represent hydrogen, halogen, alkyl, alkoxy, alkenyl, aryl, nitro, haloalkyl, silyl, and cycloalkyl, respectively, and M independently represents titanium ions (Ti). 4+ ), zirconium ions (Zr) 4+ or hafnium ions (Hf) 4+ X represents a coordination solvent independently.

[0014] Preferably, the alkyl group has 1-10 carbon atoms; the alkoxy group has 1-10 carbon atoms; the haloalkyl group has 1-10 carbon atoms; the alkenyl group has 2-10 carbon atoms; and the aryl group has 6-10 carbon atoms.

[0015] Preferably, R1, R2, R3, R4, and R5 are each independently hydrogen, fluorine, chlorine, bromine, iodine, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, sec-pentyl, isopentyl, cyclopentyl, n-hexyl, sec-hexyl, isohexyl, cyclohexyl, n-heptyl, cycloheptyl, methoxy, ethoxy, isopropoxy, tert-butyloxy, benzyl, phenyl, p-ethylphenyl, o-ethylphenyl, meta-ethylphenyl, or silyl.

[0016] Preferably, each of the X's independently represents coordinated methanol, ethanol, isopropanol, or tetrahydrofuran.

[0017] Preferably, the chemical formula of the polynuclear metal catalyst is as follows:

[0018] (Titanium metal catalyst)

[0019]

[0020] (Zirconium metal catalyst)

[0021]

[0022] (Hafnium metal catalyst)

[0023]

[0024]

[0025] The preparation method of the above-mentioned polynuclear metal catalyst includes the following steps:

[0026] The polynuclear metal catalyst formula (I) is obtained by in-situ synthesis of a compound of an organic phenolic ligand and a metal ion M in a non-coordinating organic solvent, or by further reaction with a coordinating solvent X to obtain the polynuclear metal catalyst formula (I); wherein the organic phenolic ligand is R-OH;

[0027] Polynuclear metal catalyst (I) is reacted in methanol to give polynuclear metal catalyst (II).

[0028] Preferably, the molar ratio of the organic phenolic ligand to the metal ion M is 1 to 4:1;

[0029] Preferably, the molar ratio of the metal ion M compound to the coordinating solvent X is 1:1 to 40.

[0030] Preferably, the noncoordinating organic solvent is at least one of cyclohexane, n-hexane, and toluene.

[0031] Preferably, the in-situ synthesis is carried out at room temperature.

[0032] The above-mentioned polynuclear metal catalysts are used in the catalytic alcoholysis of polyester polymers.

[0033] Preferably, the alcoholyzed polyester polymer is one or more of PET, PBT, PBS, PBA, and PES.

[0034] More preferably, the PET is a PET water bottle, PET polyester fiber clothing, or PET sound insulation board.

[0035] Preferably, the alcoholysis is carried out in an alcohol solvent; the alcoholysis temperature is 50-260°C; the alcoholysis pressure is 0-10 MPa; and the molar ratio of the polynuclear metal catalyst to the repeating unit of the polyester polymer in the alcoholysis is 0.01-100:100.

[0036] More preferably, the alcohol solvent is at least one selected from methanol, ethanol, isopropanol, ethylene glycol, and butanediol.

[0037] Technical concept of the present invention:

[0038] Given the current problems of high energy consumption, high industrial costs, low efficiency, and complex conversion processes in the recycling of waste polyester such as PET, the development of highly active catalysts is an important aspect of achieving efficient and rapid alcoholysis of PET. While ensuring monomer yield and quality, it is essential to significantly reduce the large energy consumption and high production costs of the alcoholysis solution, decrease solvent usage, and shorten the recycling cycle to achieve large-scale production of waste PET polyester through alcoholysis, bringing considerable social and economic benefits. This invention provides a catalyst synthesis and chemical recovery method for the catalytic degradation and recycling of waste PET, consisting of two main parts: catalyst synthesis and catalytic chemical recovery of waste PET polyester. For catalyst synthesis, a novel metal polynuclear complex is synthesized through transesterification of organic ligands with a metal. The complex is prepared at room temperature in an organic solvent using a metal compound and a corresponding amount of organic ligand, and the structure of the polynuclear compound is characterized. Chemical degradation utilizes alcoholysis. At 120°C, the synthesized metal complex catalyzes the rapid alcoholysis of PET in a small amount of alcohol. The method is simple, efficient, energy-saving, and yields high purity and high output of recovered monomers. The catalyst of this invention is inspired by hydrolytic enzymes and can activate general-purpose polyester plastics such as PET under the synergistic effect of metals. The biomimetic site combines the plastic substrate and the nucleophile to endow the alcoholysis process with intramolecular properties to stabilize key intermediates. By utilizing two metal centers, the proximity effect can be used to accelerate various alcoholysis processes to the maximum extent.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The polynuclear metal catalyst of the present invention has inexpensive and readily available ligand raw materials and is simple to prepare. The novel polynuclear metal complex catalyst can be synthesized by transesterification of a simple organic ligand with a metal compound.

[0041] (2) The multinuclear metal catalyst of the present invention is stable and has high catalytic activity, which can meet the needs of scientific research and industrial departments and has broad application prospects.

[0042] (3) The multi-core metal catalyst of the present invention can catalyze the rapid alcoholysis of general polyester polymers such as PET in alcohol solvents such as methanol. The method is simple, safe, efficient, low energy consumption, and the recovered monomer has high purity and yield. Attached Figure Description

[0043] Figure 1 Catalyst 1 in Example 1 1 H NMR spectrum;

[0044] Figure 2 Catalyst 2 in Example 2 1 H NMR spectrum;

[0045] Figure 3Catalyst 14 in Example 14 1 H NMR spectrum;

[0046] Figure 4 This is the single-crystal diffraction pattern of catalyst 1 in Example 1;

[0047] Figure 5 This is a single-crystal diffraction pattern of catalyst 14 in Example 14;

[0048] Figure 6 For the recovery of DMT in application example 14 1 H NMR spectrum; Detailed Implementation

[0049] The present invention will be specifically described below with reference to the embodiments, but the implementation and protection scope of the present invention are not limited to the following embodiments.

[0050] Example 1

[0051] Synthesis of Catalyst 1

[0052] 2 g (7 mmol) of tetraisopropyl titanate was added to a 100 mL round-bottom flask, followed by a 20 mL solution of 2.64 g (28 mmol) of phenol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed by vacuum distillation to obtain a yellow solid (3 g, 89%).

[0053]

[0054] 1 H NMR spectrum as shown Figure 1 Single-crystal diffraction pattern as follows: Figure 4 .

[0055] 1 H NMR (400MHz, Chloroform-d): δ7.23 (d, J = 7.7Hz, 8H), 6.93 (t, J = 7.4Hz, 4H), 6.84 (d, J = 7.9Hz, 8H), 4.07 (p, J = 6.1Hz, 1H), 1.22 (d, J = 6.1Hz, 6H).

[0056] Example 2

[0057] Synthesis of Catalyst 2

[0058] 2 g (7 mmol) of tetraisopropyl titanate was added to a 100 ml round-bottom flask, followed by a 20 ml solution of 3 g (28 mmol) of p-cresol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (3.4 g, 92%).

[0059]

[0060] 1 H NMR spectrum as shown Figure 2 .

[0061] 1 H NMR (400MHz, Chloroform-d): δ7.06 (d, J=7.9Hz, 8H), 6.76 (d, J=7.9Hz, 8H), 4.11–4.05 (m, 1H), 2.30 (s, 12H), 1.24 (d, J=6.2Hz, 6H).

[0062] Example 3

[0063] Synthesis of Catalyst 3

[0064] 2 g (7 mmol) of tetraisopropyl titanate was added to a 100 ml round-bottom flask, followed by a 20 ml solution of 4.2 g (28 mmol) of p-tert-butylphenol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (4.4 g, 90%).

[0065]

[0066] 1 H NMR (400MHz, Chloroform-d): δ7.37–7.19(m,8H),6.85–6.73(m,8H),4.06(p,J=6.2Hz,1H),1.30(s,36H),1.22(d,J=6.1Hz,6H).

[0067] Example 4

[0068] Synthesis of Catalyst 4

[0069] 2 g (7 mmol) of tetraisopropyl titanate was added to a 100 ml round-bottom flask, followed by a 20 ml solution of 3.6 g (28 mmol) of p-chlorophenol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (3.8 g, 88%).

[0070]

[0071] 1 H NMR (400MHz, Chloroform-d): δ7.18(d,J=8.3Hz,8H), 6.76(d,J=8.3Hz,8H), 4.07(h,J=6.2Hz,1H), 1.21(d,J=6.1Hz,6H).

[0072] Example 5

[0073] Synthesis of Catalyst 5

[0074] 2 g (7 mmol) of tetraisopropyl titanate was added to a 100 ml round-bottom flask, followed by a 20 ml solution of 4.84 g (28 mmol) of p-bromophenol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (5.1 g, 91%).

[0075]

[0076] 1 H NMR (400MHz, Chloroform-d): δ7.35(d,J=8.3Hz,8H), 6.70(d,J=8.3Hz,8H), 4.07(h,J=6.2Hz,1H), 1.21(d,J=6.1Hz,6H).

[0077] Example 6

[0078] Synthesis of Catalyst 6

[0079] 2 g (7 mmol) of tetraisopropyl titanate was added to a 100 ml round-bottom flask, followed by a 20 ml solution of 5.6 g (28 mmol) of p-iodophenol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (6.5 g, 94%).

[0080]

[0081] 1 H NMR (400MHz, Chloroform-d): δ7.66(d,J=8.3Hz,8H), 6.58(d,J=8.3Hz,8H), 4.07(h,J=6.2Hz,1H), 1.21(d,J=6.1Hz,6H).

[0082] Example 7

[0083] Synthesis of Catalyst 7

[0084] 1 g (3.5 mmol) of tetraisopropyl titanate was added to a 100 ml round-bottom flask, followed by a 20 ml solution of 4.7 g (14 mmol) of p-triphenylmethyl in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (4.9 g, 95%).

[0085]

[0086] 1 H NMR (400MHz, Chloroform-d): δ7.37–7.31(m,24H),7.27–7.22(m,12H),7.13–

[0087] 7.09(m,24H),7.03–6.98(m,8H),6.93–6.89(m,8H),4.07(h,J=6.2Hz,1H),1.21(d,J=6.1Hz,6H).

[0088] Example 8

[0089] Synthesis of Catalyst 8

[0090] 2.7 g (7 mmol) of zirconium isopropoxide-isopropanol complex was added to a 100 mL round-bottom flask, followed by a 20 mL solution of 2.64 g (28 mmol) of phenol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (3.3 g, 88%).

[0091]

[0092] 1 H NMR (400MHz, Chloroform-d): δ7.23 (d, J = 7.7Hz, 8H), 6.93 (t, J = 7.4Hz, 4H), 6.84 (d, J = 7.9Hz, 8H), 4.07 (p, J = 6.1Hz, 1H), 1.22 (d, J = 6.1Hz, 6H).

[0093] Example 9

[0094] Synthesis of Catalyst 9

[0095] 2.7 g (7 mmol) of zirconium isopropoxide-isopropanol complex was added to a 100 mL round-bottom flask, followed by a 20 mL solution of 3.0 g (28 mmol) of p-cresol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (3.6 g, 90%).

[0096]

[0097] 1 H NMR (400MHz, Chloroform-d): δ7.06 (d, J=7.9Hz, 8H), 6.76 (d, J=7.9Hz, 8H), 4.11–4.05 (m, 1H), 2.30 (s, 12H), 1.24 (d, J=6.2Hz, 6H).

[0098] Example 10

[0099] Synthesis of Catalyst 10

[0100] 2.7 g (7 mmol) of zirconium isopropoxide-isopropanol complex was added to a 100 mL round-bottom flask, followed by a 20 mL solution of 4.2 g (28 mmol) of p-tert-butylphenol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (4.6 g, 88%).

[0101]

[0102] 1 H NMR (400MHz, Chloroform-d): δ7.37–7.19(m,8H),6.85–6.73(m,8H),4.06(p,J=6.2Hz,1H),1.30(s,36H),1.22(d,J=6.1Hz,6H).

[0103] Example 11

[0104] Synthesis of Catalyst 11

[0105] 2.7 g (7 mmol) of zirconium isopropoxide-isopropanol complex was added to a 100 mL round-bottom flask, followed by a 20 mL solution of 3.6 g (28 mmol) of p-chlorophenol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (4.2 g, 91%).

[0106]

[0107] 1 H NMR (400MHz, Chloroform-d): δ7.18(d,J=8.3Hz,8H), 6.76(d,J=8.3Hz,8H), 4.07(h,J=6.2Hz,1H), 1.21(d,J=6.1Hz,6H).

[0108] Example 12

[0109] Synthesis of Catalyst 12

[0110] 2.7 g (7 mmol) of zirconium isopropoxide-isopropanol complex was added to a 100 mL round-bottom flask, followed by a 20 mL solution of 4.8 g (28 mmol) of p-bromophenol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (5.2 g, 89%).

[0111]

[0112] 1 H NMR (400MHz, Chloroform-d): δ7.35(d,J=8.3Hz,8H), 6.70(d,J=8.3Hz,8H), 4.07(h,J=6.2Hz,1H), 1.21(d,J=6.1Hz,6H).

[0113] Example 13

[0114] Synthesis of Catalyst 13

[0115] 2.9 g (7 mmol) of hafnium isopropoxide complex was added to a 100 mL round-bottom flask, followed by a 20 mL solution of 2.63 g (28 mmol) of phenol in n-hexane. The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum to obtain a yellow solid (6.0 g, 92%).

[0116]

[0117] 1 H NMR (400MHz, Chloroform-d): δ7.23 (d, J = 7.7Hz, 8H), 6.93 (t, J = 7.4Hz, 4H), 6.84 (d, J = 7.9Hz, 8H), 4.07 (p, J = 6.1Hz, 1H), 1.22 (d, J = 6.1Hz, 6H).

[0118] Example 14

[0119] Synthesis of Catalyst 14

[0120] Catalyst 1 (1 g, 1 mmol) was added to a 100 ml round-bottom flask, followed by methanol (0.67 g, 20 mmol). The mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum, and the mixture was recrystallized from toluene to give a yellow solid (0.7 g, 90%).

[0121]

[0122] 1 H NMR spectrum as shown Figure 3 Single-crystal diffraction pattern as follows: Figure 5 .

[0123] 1 H NMR (400MHz, Chloroform-d): δ7.25 (t, J = 7.7Hz, 28H), 6.94 (t, J = 7.4Hz, 14H), 6.84 (d, J = 8.0Hz, 28H), 3.51 (s, 6H).

[0124] Example 15

[0125] Synthesis of Catalyst 15

[0126] Catalyst 8 (1 g, 1 mmol) was added to a 100 ml round-bottom flask, followed by methanol (1.3 g, 40 mmol), and the mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum, and the mixture was recrystallized from toluene to give a yellow solid (0.8 g, 93%).

[0127]

[0128] 1 H NMR (400MHz, Chloroform-d): δ7.25 (t, J = 7.7Hz, 28H), 6.94 (t, J = 7.4Hz, 14H), 6.84 (d, J = 8.0Hz, 28H), 3.51 (s, 6H).

[0129] Example 16

[0130] Synthesis of Catalyst 16

[0131] Catalyst 13 (1 g, 0.8 mmol) was added to a 100 ml round-bottom flask, followed by methanol (1 g, 32 mmol), and the mixture was stirred at room temperature for 2 hours. After the reaction was complete, all volatiles were removed under vacuum, and the mixture was recrystallized from toluene to give a yellow solid (0.76 g, 92%).

[0132]

[0133] 1 H NMR (400MHz, Chloroform-d): δ7.25 (t, J = 7.7Hz, 28H), 6.94 (t, J = 7.4Hz, 14H), 6.84 (d, J = 8.0Hz, 28H), 3.51 (s, 6H).

[0134] Example 17

[0135] Synthesis of Catalyst 17

[0136] 2 g (7 mmol) of tetraisopropyl titanate was added to a 100 mL round-bottom flask, followed by a 20 mL solution of 2.64 g (28 mmol) of phenol in n-hexane. The mixture was stirred at room temperature for 2 hours, and then 2 g (28 mmol) of tetrahydrofuran was added and reacted for 1 hour. After the reaction was completed, all volatiles were removed by vacuum distillation to obtain a yellow solid (3.2 g, 92%).

[0137]

[0138] 1H NMR (400MHz, Chloroform-d): δ7.23(d,J=7.7Hz,8H), 6.93(t,J=7.4Hz,4H), 6.84(d,J=7.9Hz,8H), 3.83–3.75(m,4H), 1.93–1.83(m,4H).

[0139] Example 18

[0140] Synthesis of Catalyst 18

[0141] 2 g (7 mmol) of tetraisopropyl titanate was added to a 100 mL round-bottom flask, followed by a solution of 2.64 g (28 mmol) of phenol in 20 mL of hexane. The mixture was stirred at room temperature for 2 hours, and then 1.3 g (28 mmol) of ethanol was added and the mixture was reacted for 1 hour. After the reaction was completed, all volatiles were removed under vacuum and the mixture was recrystallized in toluene to obtain a yellow solid (0.7 g, 75%).

[0142]

[0143] 1 H NMR (400MHz, Chloroform-d): δ7.23(d,J=7.7Hz,8H), 6.93(t,J=7.4Hz,4H), 6.84(d,J=7.9Hz,8H), 3.69(d,J=4.9Hz,2H), 1.25(s,3H).

[0144] The PET used in the following application examples is common recycled PET water bottles.

[0145] Application Example 1

[0146] The PET alcoholysis was catalyzed using catalyst 1 synthesized in Example 1. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 1 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 H NMR ( Figure 1 Characterized by GC-MS, the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0147] Application Example 2

[0148] The PET alcoholysis was catalyzed using catalyst 2 synthesized in Example 2. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 2 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0149] Application Example 3

[0150] The PET alcoholysis was catalyzed using catalyst 3 synthesized in Example 3. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 3 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0151] Application Example 4

[0152] The PET alcoholysis was catalyzed using catalyst 4 synthesized in Example 4. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 4 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0153] Application Example 5

[0154] The PET alcoholysis was catalyzed using catalyst 5 synthesized in Example 5. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 5 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0155] Application Example 6

[0156] The PET alcoholysis was catalyzed using catalyst 6 synthesized in Example 6. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 6 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0157] Application Example 7

[0158] The catalyst 7 synthesized in Example 7 was used to catalyze the alcoholysis of PET. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 7 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0159] Application Example 8

[0160] The PET alcoholysis was catalyzed using catalyst 8 synthesized in Example 8. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 8 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0161] Application Example 9

[0162] The PET alcoholysis was catalyzed using catalyst 9 synthesized in Example 9. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 9 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0163] Application Example 10

[0164] The PET alcoholysis was catalyzed using catalyst 10 synthesized in Example 10. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 10 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield and purity of dimethyl terephthalate (DMT) were above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0165] Application Example 11

[0166] The PET alcoholysis was catalyzed using catalyst 11 synthesized in Example 11. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 11 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0167] Application Example 12

[0168] The PET alcoholysis was catalyzed using catalyst 12 synthesized in Example 12. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 12 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization was above 99%.

[0169] Application Example 13

[0170] The PET alcoholysis was catalyzed using catalyst 13 synthesized in Example 13. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 13 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0171] Application Example 14

[0172] The PET alcoholysis was catalyzed using catalyst 14 synthesized in Example 14. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 14 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 H NMR ( Figure 6 Characterized by GC-MS, the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0173] Application Example 15

[0174] The PET alcoholysis was catalyzed using catalyst 15 synthesized in Example 15. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 15 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0175] Application Example 16

[0176] The PET alcoholysis was catalyzed using catalyst 16 synthesized in Example 16. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 6 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%, and the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0177] Application Example 17

[0178] The PET alcoholysis was catalyzed using catalyst 17 synthesized in Example 17. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 17 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0179] Application Example 18

[0180] The PET alcoholysis was catalyzed using catalyst 18 synthesized in Example 18. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of catalyst 18 and 2 ml of methanol. After alcoholysis at 120°C for 1 hour, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was above 99%; the purity of DMT obtained by direct recrystallization from the mother liquor was above 99%.

[0181] Application Example 19

[0182] Tetraisopropyl titanate was used as a catalyst for the alcoholysis of PET. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of tetraisopropyl titanate and 2 ml of methanol. After alcoholysis at 120 °C for 2 hours, the system changed from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by HNMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was 90%, and the DMT obtained by direct recrystallization of the mother liquor contained methanol titanium impurities.

[0183] Application Example 20

[0184] The alcoholysis of PET was catalyzed using a zirconium isopropoxide-isopropanol complex. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of the zirconium isopropoxide-isopropanol complex and 2 ml of methanol. After alcoholysis at 120 °C for 2 hours, the system transitioned from heterogeneous to homogeneous. The mother liquor was then...1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was 89%, and the DMT obtained by direct recrystallization of the mother liquor contained methazine zirconium impurities.

[0185] Application Example 21

[0186] The alcoholysis of PET was catalyzed using a hafnium isopropanol-isopropanol complex. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of the hafnium isopropanol-isopropanol complex and 2 ml of methanol. After alcoholysis at 120 °C for 2 hours, the system transitioned from heterogeneous to homogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was 91%; the DMT obtained by direct recrystallization from the mother liquor contained methanol hafnium impurities.

[0187] Application Example 22

[0188] Titanium dioxide was used as a catalyst for the alcoholysis of PET. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of titanium dioxide and 2 ml of methanol. After alcoholysis at 120°C for 2 hours, the system remained heterogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was 0.

[0189] Application Example 23

[0190] Titanium tetrachloride was used as a catalyst for the alcoholysis of PET. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of titanium tetrachloride and 2 ml of methanol. After alcoholysis at 120°C for 2 hours, the system remained heterogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was less than 5%.

[0191] Application Example 24

[0192] Titanium dichlorophenocene was used as a catalyst for the alcoholysis of PET. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of titanium dichlorophenocene and 2 ml of methanol. After alcoholysis at 120 °C for 2 hours, the system remained heterogeneous. The mother liquor was then... 1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was less than 5%.

[0193] Application Example 25

[0194] The PET alcoholysis was catalyzed using trichlorotitanium. 500 mg of PET was added to a 4 ml thick-walled pressure-resistant bottle, followed by 50 mg of trichlorotitanium and 2 ml of methanol. After alcoholysis at 120°C for 2 hours, the system remained heterogeneous. The mother liquor was then...1 Characterization by 1H NMR and GC-MS showed that the yield of dimethyl terephthalate (DMT) was less than 5%.

[0195] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A class of polynuclear metal catalysts, characterized in that, The chemical formula of the polynuclear metal catalyst is as follows:

2. The method for preparing the polynuclear metal catalyst according to claim 1, characterized in that, The following steps are involved: The polynuclear metal catalyst is obtained by in-situ synthesis of a compound of an organic phenolic ligand and a metal ion M in a non-coordinating organic solvent, or by further reaction with a coordinating solvent; the organic phenolic ligand is R-OH; the coordinating solvent is methanol, ethanol, isopropanol, or tetrahydrofuran. The polynuclear metal catalyst is obtained by reacting it in methanol.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the organic phenolic ligand and the metal ion M is 1 to 4:1; The molar ratio of the metal ion M compound to the coordinating solvent X is 1:1 to 40.

4. The preparation method according to claim 3, characterized in that, The noncoordinating organic solvent is at least one of cyclohexane, n-hexane, and toluene.

5. The application of the polynuclear metal catalyst according to claim 1 in the catalytic alcoholysis of polyester polymers.

6. The application according to claim 5, characterized in that, The alcoholyzed polyester polymers are one or more of PET, PBT, PBS, PBA, and PES.

7. The application according to claim 5, characterized in that, The alcoholysis is carried out in an alcohol solvent; the alcoholysis temperature is 50-260℃; the alcoholysis pressure is 0-10MPa; and the molar ratio of the polynuclear metal catalyst to the repeating unit of the polyester polymer in the alcoholysis is 0.01-100:

100.

8. The application according to claim 5, characterized in that, The alcohol solvent is at least one of methanol, ethanol, isopropanol, ethylene glycol, and butanediol.

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