Liquid regenerated polyester-based diol based on waste pet and method for preparing the same

Abstract

The present application relates to a kind of liquid regeneration polyester-based diols based on waste PET and its preparation method.The liquid regeneration polyester-based diols are composed of bis (2-hydroxyethyl) terephthalamide, epsilon-caprolactone, third copolymer component, organic solvent, catalyst, hydrogen bond donor.Bis (2-hydroxyethyl) terephthalamide obtained by waste PET aminolysis and epsilon-caprolactone are used as raw materials, and third copolymer component is introduced, and ring-opening copolymerization is carried out under the action of catalyst and hydrogen bond donor, to obtain liquid regeneration polyester-based diols.The advantages of the present application are that bis (2-hydroxyethyl) terephthalamide obtained by waste PET aminolysis is used to prepare liquid regeneration polyester-based diols, the crystallization phenomenon of traditional polyester-based diols at room temperature is inhibited, the flowability problem is improved, and it is used for industrial polyurethane slow-rebound sponge foaming, which can improve the physical and mechanical properties of slow-rebound sponge.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of waste PET recycling, and particularly relates to a liquid regenerated polyester-based diol based on waste PET and a preparation method thereof. BACKGROUND

[0002] Polyethylene terephthalate (PET) is one of the five major engineering plastics in the world, and the global production capacity has exceeded 800 million tons / year by the end of 2023. With the continuous growth and increase of the use of PET in the fields of packaging, clothing, building materials, biological medicine and the like, if the waste PET is not properly disposed, it will cause problems such as resource waste and environmental pollution. Therefore, under the background of “double carbon”, the recycling of waste PET becomes very important. According to the recycling path and the final product, the waste PET recycling technology is mainly divided into mechanical recycling, biological recycling and chemical recycling. The mechanical recycling process is simple but has the problem of performance degradation of the recycled material, the biological recycling is environmentally friendly but the degradation efficiency is limited. Chemical recycling can depolymerize waste PET into monomers and derivatives through a degradation reaction, but it faces the challenge of high cost of catalysts. Although a large number of studies have focused on the degradation of waste PET, especially the realization of complete degradation and effective separation of products, only part of the work focuses on the subsequent high-value utilization of depolymerized monomers. Therefore, if a strategy that is energy-saving and realizes the high-value utilization of depolymerized monomers can be developed, it will open up a new way for the recycling of waste PET.

[0003] Polyester-based polyol is one of the key raw materials in the production of polyurethane slow-rebound sponge, and its properties directly affect the elasticity and recovery force of the sponge. The molecular weight of polyester-based polyol is closely related to the crystallinity. When the molecular weight is relatively high (such as more than 2000), the chain segment regularity is enhanced, and it is easier to form crystals; and when the molecular weight is relatively low (such as less than 2000), the crystallinity may be weakened due to the shorter chain segment and loose structure. Moreover, the crystalline polyester-based polyol which is solid at room temperature is very inconvenient to use in the foaming process of polyurethane sponge, directly affecting the rebound performance and compression performance of the slow-rebound sponge. Therefore, through molecular structure design, the crystallization performance of polyester-based polyol at room temperature is inhibited, so that it has good fluidity at room temperature, which is crucial for preparing high-performance polyurethane slow-rebound sponge. Therefore, by using waste PET as a starting raw material, a polyester-based polyol with good fluidity at room temperature is synthesized through chemical reaction, which not only realizes the recycling of waste PET, but also can be used as a raw material for the foaming of polyurethane slow-rebound sponge. SUMMARY

[0004] The technical problem solved by the present application is to provide a liquid regenerated polyester-based diol based on waste PET and a preparation method thereof, which can solve the problems of limited subsequent high-value recycling of depolymerized monomers of waste PET, inconvenience in using solid crystalline polyester-based polyols in the polyurethane sponge foaming process, and direct impact on the rebound performance and compression performance of slow rebound sponges.

[0005] To solve the above technical problems, the technical scheme of the present application is that the structural formula of the liquid regenerated polyester-based diol based on waste PET is:

[0006] ,

[0007] In the formula, R is any one of methyl, butyl, and allyl;

[0008] x = 0.1~0.2,y = 0.1~0.4,z = 0.4~0.8。

[0009] Further, the number average molecular weight of the liquid regenerated polyester-based diol based on waste PET is 1400~6000.

[0010] Further, the polydispersity index of the liquid regenerated polyester-based diol based on waste PET is 1.42~1.84.

[0011] Further, the liquid regenerated polyester-based diol based on waste PET is composed of the following components: bis(2-hydroxyethyl) terephthalamide obtained by aminolysis of waste PET, ε-caprolactone, a third copolymer component, an organic solvent, a catalyst, and a hydrogen bond donor.

[0012] The third copolymer component is any one of ε-decalactone, 6-allyl-ε-caprolactone, and 6-methyl-ε-caprolactone; preferably, the third copolymer component is one of ε-decalactone and 6-allyl-ε-caprolactone.

[0013] The molar ratio of bis(2-hydroxyethyl) terephthalamide, ε-caprolactone, and the third copolymer component is 1:2~10:5~25; preferably, the molar ratio of bis(2-hydroxyethyl) terephthalamide, ε-caprolactone, and the third copolymer component is 1:2~9:5~22.

[0014] The molar ratio of the catalyst, the hydrogen bond donor, and bis(2-hydroxyethyl) terephthalamide is 0.005~0.01:0.005~0.01:1.

[0015] Further, the catalyst is any one of benzene sulfonic acid, p-toluenesulfonic acid, methanesulfonic acid, and trifluoromethanesulfonic acid; preferably, the catalyst is one of p-toluenesulfonic acid and methanesulfonic acid.

[0016] the hydrogen bond donor is any one of N,N'-dicyclohexylurea, N,N'-diphenylurea, 1-(3,5-ditrifluoromethylphenyl)-3-cyclohexylthiourea, thiourea; preferably, the hydrogen bond donor is one of N,N'-dicyclohexylurea, thiourea;

[0017] the organic solvent is any one of dimethyl sulfoxide, toluene, tetrahydrofuran and acetonitrile; preferably, the organic solvent is one of toluene, tetrahydrofuran.

[0018] A preparation method of liquid regenerated polyester-based diol based on waste PET, characterized in that it comprises the following steps:

[0019] S1, the bis(2-hydroxyethyl)terephthalamide obtained by aminolysis of waste PET, ε-caprolactone and a catalyst, a hydrogen bond donor are added to a ceramic vacuum reactor with a vacuum degree of 0.1 MPa for dehydration, and replaced with nitrogen three times;

[0020] S2, a third copolymer component is added to the ceramic vacuum reactor, and the molar ratio of bis(2-hydroxyethyl)terephthalamide, ε-caprolactone and the third copolymer component is controlled;

[0021] S3, an organic solvent is added to the ceramic vacuum reactor, and the polymerization reaction temperature is controlled to be 0-60 ℃;

[0022] The polymerization reaction temperature is set according to the difficulty of polymerization process operation and product yield and other factors. The polymerization reaction at room temperature is relatively easy to operate, and the temperature also affects the molecular weight distribution of the polymer; preferably, the polymerization reaction temperature is 10-30 ℃;

[0023] The polymerization time is 1-6 hours;

[0024] The polymerization time affects the synthesis efficiency and effect. Short polymerization time leads to violent polymerization reaction, which is not conducive to control. Long polymerization time leads to low synthesis efficiency. Therefore, suitable polymerization time is very important for synthesis efficiency and effect. Preferably, the polymerization time is 1-3 hours;

[0025] After the polymerization reaction is completed, the catalyst and the hydrogen bond donor are removed by alkaline washing and water washing, and then the organic solvent is removed by drying to obtain the liquid regenerated polyester-based diol.

[0026] The application has the advantages that: the application takes bis (2-hydroxyethyl) terephthalamide obtained by amineolysis of waste PET and epsilon-caprolactone as starting materials, introduces a third copolymer component, and performs ring-opening copolymerization under the action of a catalyst and a hydrogen bond donor to obtain liquid regenerated polyester-based diols based on waste PET, greatly inhibiting the phenomenon of crystallization at room temperature of traditional polyester-based diols, improving the flowability problem in industrial production, and realizing subsequent high-value cyclic utilization of depolymerized monomers of waste PET.

[0027] The application does not require high-temperature and high-pressure polymerization conditions, has a shorter polymerization time, high selectivity, controllable molecular weight, and narrow molecular weight distribution, and the liquid regenerated polyester-based diols obtained by polymerization have a number average molecular weight of 1400-6000, and can be used for industrial polyurethane slow-rebound sponge foaming to improve the physical and mechanical properties of the slow-rebound sponge. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described in detail below in combination with specific embodiments. The following embodiments can enable a person skilled in the art to more fully understand the application, but the application is not limited in the scope of the embodiments.

[0029] The specific embodiment adopts the following technical scheme: the structural formula of the liquid regenerated polyester-based diols based on waste PET is as follows:

[0030] ,

[0031] In the formula, R is any one of a methyl group, a butyl group and an allyl group;

[0032] x = 0.1-0.2, y = 0.1-0.4, and z = 0.4-0.8.

[0033] The number average molecular weight of the liquid regenerated polyester-based diols based on waste PET is 1400-6000.

[0034] The polydispersity index of the liquid regenerated polyester-based diols based on waste PET is 1.42-1.84.

[0035] The liquid regenerated polyester-based diols based on waste PET are composed of the following components: bis (2-hydroxyethyl) terephthalamide obtained by amineolysis of waste PET, epsilon-caprolactone, a third copolymer component, an organic solvent, a catalyst and a hydrogen bond donor.

[0036] The third copolymer component is any one of epsilon-decalactone, 6-allyl-epsilon-caprolactone and 6-methyl-epsilon-caprolactone; preferably, the third copolymer component is one of epsilon-decalactone and 6-allyl-epsilon-caprolactone.

[0037] The molar ratio of bis (2-hydroxyethyl) terephthalamide, epsilon-caprolactone and the third copolymer component is 1:2-10:5-25; preferably, the molar ratio of bis (2-hydroxyethyl) terephthalamide, epsilon-caprolactone and the third copolymer component is 1:2-9:5-22.

[0038] The molar ratio of the catalyst, the hydrogen bond donor and bis (2-hydroxyethyl) terephthalamide is 0.005-0.01:0.005-0.01:1.

[0039] The catalyst is any one of benzene sulfonic acid, p-toluene sulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid; preferably, the catalyst is one of p-toluene sulfonic acid, methanesulfonic acid.

[0040] The hydrogen bond donor is any one of N,N'-dicyclohexylurea, N,N'-diphenylurea, 1-(3,5-ditrifluoromethylphenyl)-3-cyclohexyl thiourea, thiourea; preferably, the hydrogen bond donor is one of N,N'-dicyclohexylurea, thiourea.

[0041] The organic solvent is any one of dimethyl sulfoxide, toluene, tetrahydrofuran and acetonitrile; preferably, the organic solvent is one of toluene, tetrahydrofuran.

[0042] A preparation method of liquid regenerated polyester-based diol based on waste PET, characterized in that it comprises the following steps:

[0043] S1, bis (2-hydroxyethyl) terephthalamide obtained by aminolysis of waste PET, epsilon-caprolactone, catalyst and hydrogen bond donor are added into a ceramic reactor with a vacuum degree of 0.1 MPa for dehydration, and replaced with nitrogen three times;

[0044] S2, the third copolymer component is added into the ceramic vacuum reactor, and the molar ratio of bis (2-hydroxyethyl) terephthalamide, epsilon-caprolactone and the third copolymer component is controlled.

[0045] S3, the organic solvent is added into the ceramic vacuum reactor, the polymerization reaction temperature is controlled at 0-60℃, and the polymerization time is 1-6 hours; after the polymerization reaction is completed, the catalyst and the hydrogen bond donor are removed by alkaline washing and water washing, and then the organic solvent is removed after drying, to obtain the liquid regenerated polyester-based diol.

[0046] Preferably, the polymerization reaction temperature is 10-30℃, and the polymerization time is 1-3 hours.

[0047] Example 1:

[0048] The polymerization reaction formula in this example is as follows:

[0049]

[0050] The bis(2-hydroxyethyl)terephthalamide (2.52 g, 10 mmol), ε-caprolactone (2.85 g, 25 mmol), p-toluenesulfonic acid (142.36 mg, 0.25 mmol), N,N'-dicyclohexylurea (112.17 mg, 0.5 mmol) were added into a ceramic vacuum reactor, vacuum dehydration, and replaced with nitrogen 3 times, ε-decalactone (9.87 g, 58 mmol) and tetrahydrofuran 5 mL, control the polymerization temperature at 25 ℃, stirring for 2.5 hours. After the polymerization was completed, the catalyst and hydrogen bond donor were removed, to obtain the liquid regenerated polyester-based diol based on waste PET, the yield was 87.5%, the number average molecular weight was 1468, the polydispersity index was 1.47, the hydroxyl value was 87 mgKOH / g, and the viscosity was 220-350 mPa·s.

[0051] Example 2:

[0052] The polymerization reaction formula in this example is as follows:

[0053]

[0054] The bis(2-hydroxyethyl)terephthalamide (2.52 g, 10 mmol), ε-caprolactone (5.71 g, 50 mmol), p-toluenesulfonic acid (284.7 mg, 0.5 mmol), N,N'-dicyclohexylurea (224.34 mg, 1.0 mmol) were added into a ceramic vacuum reactor, vacuum dehydration, and replaced with nitrogen 3 times, ε-decalactone (19.7 g, 116 mmol) and tetrahydrofuran 10 mL, control the polymerization temperature at 25 ℃, stirring for 3 hours. After the polymerization was completed, the catalyst and hydrogen bond donor were removed, to obtain the liquid regenerated polyester-based diol based on waste PET, the yield was 92.6%, the number average molecular weight was 2943, the polydispersity index was 1.43, the hydroxyl value was 57 mgKOH / g, and the viscosity was 450-800 mPa·s.

[0055] Example 3:

[0056] The polymerization reaction formula in this example is as follows:

[0057]

[0058] The bis (2-hydroxyethyl) terephthalamide (2.52 g, 10 mmol), ε-caprolactone (9.70 g, 85 mmol), p-toluenesulfonic acid (455.5 mg, 0.8 mmol), N, N'-dicyclohexyl urea (358.9 mg, 1.6 mmol) were added into a ceramic vacuum reactor, vacuum dehydration, and replaced with nitrogen 3 times, ε-decalactone (33.71 g, 198 mmol) and tetrahydrofuran 20 mL, the polymerization temperature was controlled at 25 ℃, and stirred for 3 hours. After the polymerization was completed, the catalyst and hydrogen bond donor were removed, to obtain a liquid regenerated polyester-based diol based on waste PET, with a yield of 90.8%, a number average molecular weight of 5034, a polydispersity index of 1.63, a hydroxyl value of 45 mgKOH / g, and a viscosity of 950-1100 mPa·s.

[0059] Example 4:

[0060] The polymerization reaction formula in this example is as follows:

[0061]

[0062] The bis (2-hydroxyethyl) terephthalamide (2.52 g, 10 mmol), ε-caprolactone (2.85 g, 25 mmol), p-toluenesulfonic acid (142.36 mg, 0.25 mmol), thiourea (38.06 mg, 0.5 mmol) were added into a ceramic vacuum reactor, vacuum dehydration, and replaced with nitrogen 3 times, ε-decalactone (9.87 g, 58 mmol) and tetrahydrofuran 5 mL, the polymerization temperature was controlled at 25 ℃, and stirred for 2.5 hours. After the polymerization was completed, the catalyst and hydrogen bond donor were removed, to obtain a liquid regenerated polyester-based diol based on waste PET, with a yield of 83.3%, a number average molecular weight of 1443, a polydispersity index of 1.54, a hydroxyl value of 91 mgKOH / g, and a viscosity of 240-400 mPa·s.

[0063] Example 5:

[0064] The polymerization reaction formula in this example is as follows:

[0065]

[0066] bis(2-hydroxyethyl)terephthalamide (2.52 g, 10 mmol), ε-caprolactone (2.85 g, 25 mmol), methanesulfonic acid (24.02 mg, 0.25 mmol), N,N'-dicyclohexylurea (112.17 mg, 0.5 mmol) were added into a ceramic vacuum reactor, vacuum dehydration, and replaced with nitrogen 3 times, ε-decalactone (9.87 g, 58 mmol) and tetrahydrofuran 5 mL were added, the polymerization temperature was controlled at 25 °C, and stirring was carried out for 2.5 hours. After the polymerization was completed, the catalyst and hydrogen bond donor were removed, to obtain a liquid regenerated polyester-based diol based on waste PET, with a yield of 89.4%, a number average molecular weight of 1441, a polydispersity index of 1.45, a hydroxyl value of 83 mgKOH / g, and a viscosity of 230-390 mPa·s.

[0067] Example 6

[0068] The polymerization reaction formula in this example is as follows:

[0069]

[0070] bis(2-hydroxyethyl)terephthalamide (2.52 g, 10 mmol), ε-caprolactone (2.85 g, 25 mmol), methanesulfonic acid (24.02 mg, 0.25 mmol), thiourea (38.06 mg, 0.5 mmol) were added into a ceramic vacuum reactor, vacuum dehydration, and replaced with nitrogen 3 times, ε-decalactone (9.87 g, 58 mmol) and tetrahydrofuran 5 mL were added, the polymerization temperature was controlled at 25 °C, and stirring was carried out for 2.5 hours. After the polymerization was completed, the catalyst and hydrogen bond donor were removed, to obtain a liquid regenerated polyester-based diol based on waste PET, with a yield of 91.4%, a number average molecular weight of 1567, a polydispersity index of 1.42, a hydroxyl value of 84 mgKOH / g, and a viscosity of 260-420 mPa·s.

[0071] Example 7

[0072] The polymerization reaction formula in this example is as follows:

[0073]

[0074] The bis (2-hydroxyethyl) terephthalamide (2.52 g, 10 mmol), ε-caprolactone (5.71 g, 50 mmol), methanesulfonic acid (48.06 mg, 0.5 mmol), N, N'-dicyclohexyl urea (224.34 mg, 1.0 mmol) were added into a ceramic vacuum reactor, vacuum dehydration, and replaced with nitrogen 3 times, ε-decalactone (9.87 g, 58 mmol) and tetrahydrofuran 10 mL were added, and the polymerization temperature was controlled at 25°C, and stirred for 3 hours. After the polymerization was completed, the catalyst and hydrogen bond donor were removed, to obtain a liquid regenerated polyester-based diol based on waste PET, with a yield of 93.2%, a number average molecular weight of 2789, a polydispersity index of 1.51, a hydroxyl value of 57 mgKOH / g, and a viscosity of 430-780 mPa·s.

[0075] Example 8:

[0076] The polymerization reaction formula in this example is as follows:

[0077]

[0078] The bis (2-hydroxyethyl) terephthalamide (2.52 g, 10 mmol), ε-caprolactone (9.70 g, 85 mmol), methanesulfonic acid (81.69 mg, 0.85 mmol), N, N'-dicyclohexyl urea (224.34 mg, 1.0 mmol) were added into a ceramic vacuum reactor, vacuum dehydration, and replaced with nitrogen 3 times, ε-decalactone (33.71 g, 198 mmol) and tetrahydrofuran 20 mL were added, and the polymerization temperature was controlled at 25°C, and stirred for 3 hours. After the polymerization was completed, the catalyst and hydrogen bond donor were removed, to obtain a liquid regenerated polyester-based diol based on waste PET, with a yield of 87.6%, a number average molecular weight of 4589, a polydispersity index of 1.449, a hydroxyl value of 46 mgKOH / g, and a viscosity of 860-1250 mPa·s.

[0079] Example 9:

[0080] The polymerization reaction formula in this example is as follows:

[0081]

[0082] Bis(2-hydroxyethyl)terephthalamide (2.52 g, 10 mmol), ε-caprolactone (2.85 g, 25 mmol), p-toluenesulfonic acid (142.36 mg, 0.25 mmol), N,N'-dicyclohexylurea (112.17 mg, 0.5 mmol) were added into a ceramic vacuum reactor, vacuum dehydration, and replaced with nitrogen 3 times, ε-decalactone (9.87 g, 58 mmol) and tetrahydrofuran 5 mL, control the polymerization temperature at 10 ℃, stirring for 2 hours. After the polymerization, the catalyst and hydrogen bond donor were removed, to obtain the liquid waste PET-based regenerated polyester-based diol, the yield was 93.5%, the number average molecular weight was 1573, the polydispersity index was 1.56, the hydroxyl value was 82 mgKOH / g, and the viscosity was 240-340 mPa·s.

[0083] Example 10:

[0084] The polymerization reaction formula in this embodiment is as follows:

[0085]

[0086] Bis(2-hydroxyethyl)terephthalamide (2.52 g, 10 mmol), ε-caprolactone (2.85 g, 25 mmol), p-toluenesulfonic acid (142.36 mg, 0.25 mmol), N,N'-dicyclohexylurea (112.17 mg, 0.5 mmol) were added into a ceramic vacuum reactor, vacuum dehydration, and replaced with nitrogen 3 times, ε-decalactone (9.87 g, 58 mmol) and tetrahydrofuran 5 mL, control the polymerization temperature at 10 ℃, stirring for 2 hours. After the polymerization, the catalyst and hydrogen bond donor were removed, to obtain the liquid waste PET-based regenerated polyester-based diol, the yield was 93.5%, the number average molecular weight was 1573, the polydispersity index was 1.56, the hydroxyl value was 82 mgKOH / g, and the viscosity was 240-340 mPa·s.

[0087] The basic principles and main features of the present application and the advantages of the present application are shown and described above. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing liquid recycled polyester diol based on waste PET, characterized in that: Includes the following steps: S1. The bis(2-hydroxyethyl) terephthalamide, ε-caprolactone, catalyst, and hydrogen bond donor obtained from the amination of waste PET are added to a ceramic reactor with a vacuum of 0.1 MPa for dehydration and then purged with nitrogen three times. S2. Add the third copolymer component into the ceramic vacuum reactor and control the molar ratio of bis(2-hydroxyethyl) terephthalamide, ε-caprolactone and the third copolymer component; S3. Add organic solvent into the ceramic vacuum reactor, control the polymerization reaction temperature to 0~60 ℃, and the polymerization time to 1~6 hours; after the polymerization reaction is completed, remove the catalyst and hydrogen bond donor by alkaline washing and water washing, and then dry and remove the organic solvent to obtain liquid recycled polyester diol. The third copolymer component is any one of ε-decanolide, 6-allyl-ε-caprolactone, and 6-methyl-ε-caprolactone; The molar ratio of bis(2-hydroxyethyl) terephthalamide, ε-caprolactone, and the third copolymer component is 1:2~10:5~25; The molar ratio of the catalyst, hydrogen bond donor, and bis(2-hydroxyethyl) terephthalamide is 0.005~0.01∶0.005~0.01∶1.

2. The method for preparing liquid recycled polyester diol based on waste PET according to claim 1, characterized in that: The number-average molecular weight of the liquid recycled polyester diol based on waste PET is 1400–6000.

3. The method for preparing liquid recycled polyester diol based on waste PET according to claim 1, characterized in that: The polydispersity index of the liquid recycled polyester diol based on waste PET is 1.42 to 1.

84.

4. The method for preparing liquid recycled polyester diol based on waste PET according to claim 1, characterized in that: The catalyst is any one of benzenesulfonic acid, p-toluenesulfonic acid, methanesulfonic acid, and trifluoromethanesulfonic acid; the hydrogen bond donor is any one of N,N'-dicyclohexylurea, N,N'-diphenylurea, 1-(3,5-ditrifluoromethylphenyl)-3-cyclohexylthiourea, and thiourea; the organic solvent is any one of dimethyl sulfoxide, toluene, tetrahydrofuran, and acetonitrile.

5. The method for preparing liquid recycled polyester diol based on waste PET according to claim 1, characterized in that: The third copolymer component is one of ε-decanolide and 6-allyl-ε-caprolactone; the molar ratio of bis(2-hydroxyethyl) terephthalamide, ε-caprolactone and the third copolymer component is 1:2~9:5~22.

6. The method for preparing liquid recycled polyester diol based on waste PET according to claim 1, characterized in that: The catalyst is one of p-toluenesulfonic acid and methanesulfonic acid; the hydrogen bond donor is one of N,N'-dicyclohexylurea and thiourea; and the organic solvent is one of toluene and tetrahydrofuran.

7. The method for preparing liquid recycled polyester diol based on waste PET according to claim 1, characterized in that: The polymerization reaction temperature is 10~30 ℃; the polymerization time is 1~3 hours.

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