Depolymerization method of polyethylene glycol terephthalate and application thereof

Abstract

The invention discloses a depolymerization method of polyethylene glycol terephthalate and application of the depolymerization method. The depolymerization method of polyethylene glycol terephthalate comprises the following steps: 1) dispersing magnetic catalyst powder in ethylene glycol to obtain a magnetic catalyst dispersion liquid; and 2) heating the magnetic catalyst dispersion liquid in a magnetic induction heating device until the magnetic catalyst dispersion liquid is boiled, adding polyethylene glycol terephthalate powder, and carrying out a depolymerization reaction to obtain a reaction liquid containing bis (2-hydroxyethyl) terephthalate, a bis (2-hydroxyethyl) terephthalate dimer and a bis (2-hydroxyethyl) terephthalate oligomer. The polyethylene glycol terephthalate depolymerization method disclosed by the invention has the advantages of simplicity and convenience in operation, quick reaction start, mild reaction conditions, easiness in reaction control, easiness in catalyst recovery, low cost, high efficiency and the like, and is suitable for large-scale industrial application in the field of polyester recovery.

Description

Technical Field

[0001] The present invention relates to the technical field of polyester recovery, and in particular to a depolymerization method of polyethylene terephthalate and application thereof. Background Art

[0002] Polyethylene terephthalate (PET), a thermoplastic polyester with excellent mechanical properties and chemical resistance, has been widely used in numerous fields. However, with the increasing demand for polyester materials and the rapid growth of polyester production, a large amount of waste polyester accumulates in the wild and cannot be degraded, seriously affecting the ecological environment. Therefore, how to effectively degrade and recycle polyester materials is an urgent problem that needs to be solved.

[0003] At present, the degradation and recycling methods of PET plastics are mainly divided into the following two types: 1) physical recycling: mainly including mechanical recycling and thermal recycling. This method will cause irreversible performance loss of the material itself, and the quality of secondary PET products made from the recycled PET will be significantly reduced; 2) chemical recycling: mainly including hydrolysis, alcoholysis, diol alcoholysis and aminolysis. It is to first convert PET into the corresponding monomers by adding a reaction solvent for chemical depolymerization, and then repolymerize the monomers into PET. There is no problem of deterioration in the quality of PET products. However, this method has problems such as complex operation, harsh reaction conditions, high cost, and low efficiency. It is still difficult to fully meet the requirements of practical applications.

[0004] Therefore, it is of great significance to develop a polyethylene terephthalate depolymerization method with simple operation, mild reaction conditions, low cost and high efficiency. Summary of the Invention

[0005] The purpose of the present invention is to provide a depolymerization method of polyethylene terephthalate and application thereof.

[0006] The technical solution adopted by the present invention is:

[0007] A method for depolymerizing polyethylene terephthalate comprises the following steps:

[0008] 1) dispersing magnetic catalyst powder in ethylene glycol to obtain a magnetic catalyst dispersion;

[0009] 2) The magnetic catalyst dispersion is placed in a magnetic induction heating device and heated to boiling, and then polyethylene terephthalate powder is added to carry out a depolymerization reaction to obtain a reaction solution containing bis(hydroxyethyl) terephthalate, bis(hydroxyethyl) terephthalate dimer, and bis(hydroxyethyl) terephthalate oligomer.

[0010] Preferably, the mass ratio of the magnetic catalyst powder to the polyethylene terephthalate powder is 1 to 4:3.

[0011] Preferably, the mass ratio of the ethylene glycol to the polyethylene terephthalate powder is 2 to 10:1.

[0012] More preferably, the mass ratio of the ethylene glycol to the polyethylene terephthalate powder is 2 to 7:1.

[0013] Preferably, the magnetic catalyst powder in step 1) is at least one of ferroferric oxide powder, iron oxide powder, iron cobalt oxide powder and iron manganese oxide powder.

[0014] More preferably, the magnetic catalyst powder in step 1) is at least one of ferroferric oxide powder and iron cobalt oxide powder.

[0015] Preferably, the particle size of the magnetic catalyst powder in step 1) is 15 nm to 30 nm.

[0016] Preferably, the magnetic field frequency of the magnetic induction heating device in step 2) is 100kHz to 500kHz, and the induced current is 10A to 24A.

[0017] Further preferably, the magnetic field frequency of the magnetic induction heating device in step 2) is 300kHz to 500kHz, and the induced current is 20A to 24A.

[0018] Preferably, the particle size of the polyethylene terephthalate powder in step 2) is 150 μm to 180 μm.

[0019] Preferably, the depolymerization reaction in step 2) is carried out under standard atmospheric pressure.

[0020] Preferably, the depolymerization reaction in step 2) is carried out under stirring.

[0021] Preferably, the depolymerization reaction time in step 2) is 5 min to 120 min.

[0022] More preferably, the depolymerization reaction time in step 2) is 15 min to 120 min.

[0023] Application of the above-mentioned polyethylene terephthalate depolymerization method in the field of polyester recovery.

[0024] The beneficial effects of the present invention are as follows: the polyethylene terephthalate depolymerization method of the present invention has the advantages of simple operation, fast reaction start-up, mild reaction conditions, easy reaction control, easy catalyst recovery, low cost, high efficiency, etc., and is suitable for large-scale industrial application in the field of polyester recovery.

[0025] Specifically:

[0026] 1) The present invention utilizes electromagnetic induction heating of a magnetic catalyst to catalyze the depolymerization of PET, thereby recovering bis(hydroxyethyl) terephthalate (BHET) monomer. Compared to conventional heating methods, the non-contact direct heating of the magnetic catalyst by electromagnetic induction significantly improves the depolymerization reaction rate and monomer yield.

[0027] 2) The present invention uses electromagnetic induction heating to generate a local high temperature on the surface of the magnetic material to form a hot spot (the magnetic material can absorb electromagnetic energy in an alternating magnetic field), thereby accelerating the chemical reaction rate at the hot spot, and can promote the smooth occurrence of reactions that have high activation energy and are difficult to occur. The method has the advantages of fast reaction start-up, mild reaction conditions, easy reaction control, and high efficiency. It can also achieve efficient catalytic alcoholysis of PET diol using electrical energy.

[0028] 3) The polyethylene terephthalate depolymerization method of the present invention is simple to operate, low in cost, and highly efficient, and is suitable for large-scale industrial application in the field of polyester recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the magnetic induction heating device and the depolymerization reaction device. DETAILED DESCRIPTION

[0030] The present invention will be further explained and illustrated below with reference to specific embodiments.

[0031] Example 1:

[0032] A method for depolymerizing polyethylene terephthalate, comprising the following steps:

[0033] 1) Add 1 g of ferroferric oxide powder (particle size 15 nm to 20 nm) and 30 g of ethylene glycol to a three-necked flask, and then install a mechanical stirring device on the three-necked flask to stir to obtain a magnetic catalyst dispersion;

[0034] 2) Place the three-necked flask (containing the magnetic catalyst dispersion) in the coil attached to the magnetic induction heating device, turn on the magnetic induction heating device and heat to boiling. The magnetic field frequency of the magnetic induction heating device is 300 kHz and the induced current is 10 A. Then, add 3 g of polyethylene terephthalate powder (particle size of 150 μm to 180 μm), control the reaction pressure to 1 atm, and stir under condensation reflux for 60 minutes (depolymerization reaction; the structural diagram of the magnetic induction heating device and the depolymerization reaction device is shown in FIG. Figure 1 As shown; Figure 1 wherein a is a magnetic induction heating device and b is a depolymerization reaction device), heating is stopped and the mixture is naturally cooled to room temperature to obtain a reaction solution containing bis(hydroxyethyl) terephthalate, bis(hydroxyethyl) terephthalate dimer and bis(hydroxyethyl) terephthalate oligomer.

[0035] PET conversion rate and BHET yield test:

[0036] The reaction solution containing bis(hydroxyethyl terephthalate), bis(hydroxyethyl terephthalate) dimer and bis(hydroxyethyl terephthalate) oligomer was filtered, the solid was dried and weighed to calculate the PET conversion rate, and the filtrate was analyzed by high performance liquid chromatography to calculate the BHET yield.

[0037] The PET conversion rate is calculated as follows: PET conversion rate (%) = (initial PET weight - unreacted PET weight) / initial PET weight × 100%, where the initial PET weight refers to the weight of the PET before the reaction (in g), and the unreacted PET weight refers to the weight of the solid matter (undecomposed PET) obtained by filtration (in g).

[0038] The BHET yield is calculated as follows: BHET yield (%) = weight of BHET in the filtrate / theoretical BHET weight × 100%, where theoretical BHET weight = (initial PET weight - unreacted PET weight) × M BHET / M PET , M BHET refers to the molar mass of BHET (254 g / mol), M PET Refers to the molar mass of the repeating unit in PET (192 g / mol).

[0039] According to the test, the PET conversion rate in this embodiment is 9.25%, and the BHET yield is 5.56%.

[0040] Example 2:

[0041] A method for depolymerizing polyethylene terephthalate is identical to that of Example 1 except that the induction current in step 2) is adjusted from 10 A to 14 A.

[0042] After testing, the PET conversion rate in this embodiment was 37.12%, and the BHET yield was 27.14%.

[0043] Example 3:

[0044] A method for depolymerizing polyethylene terephthalate is identical to that of Example 1 except that the induction current in step 2) is adjusted from 10 A to 18 A.

[0045] After testing, the PET conversion rate in this embodiment was 53.89%, and the BHET yield was 42.10%.

[0046] Example 4:

[0047] A method for depolymerizing polyethylene terephthalate is identical to that of Example 1 except that the induction current in step 2) is adjusted from 10 A to 20 A.

[0048] After testing, the PET conversion rate in this embodiment was 67.34%, and the BHET yield was 59.20%.

[0049] Example 5:

[0050] A method for depolymerizing polyethylene terephthalate is identical to that of Example 1 except that the induction current in step 2) is adjusted from 10 A to 22 A.

[0051] After testing, the PET conversion rate in this embodiment was 75.82%, and the BHET yield was 64.10%.

[0052] Example 6:

[0053] A method for depolymerizing polyethylene terephthalate is identical to that of Example 1 except that the induction current in step 2) is adjusted from 10 A to 24 A.

[0054] After testing, the PET conversion rate in this embodiment was 88.00%, and the BHET yield was 82.00%.

[0055] Example 7:

[0056] A method for depolymerizing polyethylene terephthalate is identical to Example 1, except that the magnetic catalyst powder in step 1) is replaced with an equal mass of iron cobalt oxide powder (particle size of 15 nm to 22 nm) instead of ferrosoferric oxide powder (particle size of 15 nm to 22 nm) and the induced current in step 2) is adjusted from 10 A to 24 A.

[0057] After testing, the PET conversion rate in this embodiment was 89.25%, and the BHET yield was 84.00%.

[0058] Example 8:

[0059] A method for depolymerizing polyethylene terephthalate is identical to Example 1, except that the magnetic catalyst powder in step 1) is replaced with an equal mass of iron oxide powder (particle size of 15 nm to 25 nm) instead of ferrosoferric oxide powder (particle size of 15 nm to 25 nm) and the induced current in step 2) is adjusted from 10 A to 24 A.

[0060] According to the test, the PET conversion rate in this embodiment is 29.94%, and the BHET yield is 6.36%.

[0061] Example 9:

[0062] A method for depolymerizing polyethylene terephthalate is identical to Example 1, except that the magnetic catalyst powder in step 1) is replaced with an equal mass of ferromanganese oxide powder (particle size of 20 nm to 30 nm) instead of ferroferric oxide powder (particle size of 15 nm to 20 nm) and the induced current in step 2) is adjusted from 10 A to 24 A.

[0063] After testing, the PET conversion rate in this embodiment was 60.34%, and the BHET yield was 46.12%.

[0064] Example 10:

[0065] A method for depolymerizing polyethylene terephthalate is identical to Example 1 except that the magnetic field frequency in step 2) is adjusted from 300 kHz to 100 kHz and the induced current in step 2) is adjusted from 10 A to 24 A.

[0066] After testing, the PET conversion rate in this embodiment was 29.45%, and the BHET yield was 19.18%.

[0067] Example 11:

[0068] A method for depolymerizing polyethylene terephthalate is identical to Example 1 except that the magnetic field frequency in step 2) is adjusted from 300 kHz to 200 kHz and the induced current in step 2) is adjusted from 10 A to 24 A.

[0069] After testing, the PET conversion rate in this embodiment was 46.78%, and the BHET yield was 33.37%.

[0070] Example 12:

[0071] A method for depolymerizing polyethylene terephthalate is identical to Example 1 except that the magnetic field frequency in step 2) is adjusted from 300 kHz to 400 kHz and the induced current in step 2) is adjusted from 10 A to 24 A.

[0072] After testing, the PET conversion rate in this embodiment was 89.25%, and the BHET yield was 82.90%.

[0073] Example 13:

[0074] A method for depolymerizing polyethylene terephthalate is identical to Example 1 except that the magnetic field frequency in step 2) is adjusted from 300 kHz to 500 kHz and the induced current in step 2) is adjusted from 10 A to 24 A.

[0075] After testing, the PET conversion rate in this embodiment was 91.32%, and the BHET yield was 85.95%.

[0076] Example 14:

[0077] A method for depolymerizing polyethylene terephthalate is identical to Example 1, except that the magnetic catalyst powder in step 1) is replaced with an equal mass of iron cobalt oxide powder (particle size of 15 nm to 22 nm) instead of ferrosoferric oxide powder (particle size of 15 nm to 22 nm), the magnetic field frequency in step 2) is adjusted from 300 kHz to 500 kHz, and the induced current in step 2) is adjusted from 10 A to 24 A.

[0078] After testing, the PET conversion rate in this embodiment was 95.24%, and the BHET yield was 90.23%.

[0079] Example 15:

[0080] A method for depolymerizing polyethylene terephthalate is identical to Example 1, except that the magnetic catalyst powder in step 1) is replaced with an equal mass of iron oxide powder (particle size of 15 nm to 25 nm) instead of ferrosoferric oxide powder (particle size of 15 nm to 25 nm), the magnetic field frequency in step 2) is adjusted from 300 kHz to 500 kHz, and the induced current in step 2) is adjusted from 10 A to 24 A.

[0081] After testing, the PET conversion rate in this embodiment was 39.14%, and the BHET yield was 17.66%.

[0082] Example 16:

[0083] A method for depolymerizing polyethylene terephthalate is identical to Example 1, except that the magnetic catalyst powder in step 1) is replaced with an equal mass of ferromanganese oxide powder (particle size of 20 nm to 30 nm) instead of ferroferric oxide powder (particle size of 15 nm to 20 nm), the magnetic field frequency in step 2) is adjusted from 300 kHz to 500 kHz, and the induced current in step 2) is adjusted from 10 A to 24 A.

[0084] After testing, the PET conversion rate in this embodiment was 70.51%, and the BHET yield was 51.63%.

[0085] Example 17:

[0086] A method for depolymerizing polyethylene terephthalate, comprising the following steps:

[0087] 1) Add 1 g of ferroferric oxide powder (particle size 15 nm to 20 nm) and 6 g of ethylene glycol to a three-necked flask, and then install a mechanical stirring device on the three-necked flask to stir to obtain a magnetic catalyst dispersion;

[0088] 2) A three-necked flask (containing the magnetic catalyst dispersion) was placed in a coil attached to a magnetic induction heating apparatus. The magnetic induction heating apparatus was turned on and heated to boiling at a magnetic field frequency of 300 kHz and an induced current of 24 A. 3 g of polyethylene terephthalate powder (particle size of 150 μm to 180 μm) was then added. The reaction pressure was controlled to 1 atm, and the mixture was stirred and refluxed for 15 minutes. The heating was stopped, and the mixture was naturally cooled to room temperature to obtain a reaction solution containing bis(hydroxyethyl) terephthalate, bis(hydroxyethyl) terephthalate dimer, and bis(hydroxyethyl) terephthalate oligomers.

[0089] After testing, the PET conversion rate in this embodiment was 85.90%, and the BHET yield was 67.30%.

[0090] Example 18:

[0091] A method for depolymerizing polyethylene terephthalate is identical to Example 17 except that the amount of ethylene glycol in step 1) is adjusted from 6 g to 10 g.

[0092] After testing, the PET conversion rate in this embodiment was 91.50%, and the BHET yield was 77.00%.

[0093] Example 19:

[0094] A method for depolymerizing polyethylene terephthalate is identical to Example 17 except that the amount of ethylene glycol in step 1) is adjusted from 6 g to 15 g.

[0095] After testing, the PET conversion rate in this embodiment was 88.50%, and the BHET yield was 78.50%.

[0096] Example 20:

[0097] A method for depolymerizing polyethylene terephthalate is identical to Example 17 except that the amount of ethylene glycol in step 1) is adjusted from 6 g to 20 g.

[0098] After testing, the PET conversion rate in this embodiment was 85.90%, and the BHET yield was 78.40%.

[0099] Example 21:

[0100] A method for depolymerizing polyethylene terephthalate is identical to Example 17 except that the amount of ethylene glycol in step 1) is adjusted from 6 g to 30 g.

[0101] After testing, the PET conversion rate in this embodiment was 43.40%, and the BHET yield was 39.90%.

[0102] Example 22:

[0103] A method for depolymerizing polyethylene terephthalate is identical to Example 17, except that the magnetic catalyst powder in step 1) is replaced with "ferroferric oxide powder (particle size of 15 nm to 20 nm)" of equal mass and the amount of ethylene glycol in step 1) is adjusted from "6 g" to "20 g".

[0104] According to the test, the PET conversion rate in this embodiment is 87.41%, and the BHET yield is 81.92%.

[0105] Example 23:

[0106] A method for depolymerizing polyethylene terephthalate is identical to Example 17, except that the magnetic catalyst powder in step 1) is replaced with an equal mass of iron oxide powder (particle size of 15 nm to 25 nm) from "ferrosoferric oxide powder (particle size of 15 nm to 25 nm)" and the amount of ethylene glycol in step 1) is adjusted from "6 g" to "20 g".

[0107] After testing, the PET conversion rate in this embodiment was 25.34%, and the BHET yield was 15.49%.

[0108] Example 24:

[0109] A method for depolymerizing polyethylene terephthalate is identical to Example 17, except that the magnetic catalyst powder in step 1) is replaced with an equal mass of ferromanganese oxide powder (particle size of 20 nm to 30 nm) instead of ferroferric oxide powder (particle size of 15 nm to 20 nm) and the amount of ethylene glycol in step 1) is adjusted from 6 g to 20 g.

[0110] After testing, the PET conversion rate in this embodiment was 46.36%, and the BHET yield was 33.25%.

[0111] Example 25:

[0112] A method for depolymerizing polyethylene terephthalate, comprising the following steps:

[0113] 1) Add 2 g of ferroferric oxide powder (particle size 15 nm to 20 nm) and 20 g of ethylene glycol into a three-necked flask, and then install a mechanical stirring device on the three-necked flask to stir to obtain a magnetic catalyst dispersion;

[0114] 2) A three-necked flask (containing the magnetic catalyst dispersion) was placed in a coil attached to a magnetic induction heating apparatus. The magnetic induction heating apparatus was turned on and heated to boiling at a magnetic field frequency of 300 kHz and an induced current of 24 A. 3 g of polyethylene terephthalate powder (particle size of 150 μm to 180 μm) was then added. The reaction pressure was controlled to 1 atm, and the mixture was stirred and refluxed for 15 minutes. The heating was stopped, and the mixture was naturally cooled to room temperature to obtain a reaction solution containing bis(hydroxyethyl) terephthalate, bis(hydroxyethyl) terephthalate dimer, and bis(hydroxyethyl) terephthalate oligomers.

[0115] After testing, the PET conversion rate in this embodiment was 100%, and the BHET yield was 98.20%.

[0116] Example 26:

[0117] A method for depolymerizing polyethylene terephthalate is identical to that of Example 25, except that the amount of ferrosoferric oxide powder in step 1) is adjusted from 2 g to 3 g.

[0118] After testing, the PET conversion rate in this embodiment was 100%, and the BHET yield was 98.10%.

[0119] Example 27:

[0120] A method for depolymerizing polyethylene terephthalate is identical to Example 25 except that the amount of ferrosoferric oxide powder in step 1) is adjusted from 2 g to 4 g.

[0121] After testing, the PET conversion rate in this embodiment was 100%, and the BHET yield was 97.80%.

[0122] Example 28:

[0123] A method for depolymerizing polyethylene terephthalate is identical to Example 25, except that the magnetic catalyst powder in step 1) is replaced by an equal mass of "iron cobalt oxide powder (particle size of 15 nm to 22 nm)" instead of "ferroferric oxide powder (particle size of 15 nm to 22 nm)".

[0124] After testing, the PET conversion rate in this embodiment was 100%, and the BHET yield was 99.32%.

[0125] Example 29:

[0126] A method for depolymerizing polyethylene terephthalate is identical to Example 25, except that the magnetic catalyst powder in step 1) is replaced by an equal mass of "iron oxide powder (particle size of 15 nm to 20 nm)" instead of "ferrosoferric oxide powder (particle size of 15 nm to 25 nm)".

[0127] After testing, the PET conversion rate in this embodiment was 90.21%, and the BHET yield was 82.45%.

[0128] Example 30:

[0129] A method for depolymerizing polyethylene terephthalate is identical to Example 25, except that the magnetic catalyst powder in step 1) is replaced with an equal mass of ferromanganese oxide powder (particle size of 20 nm to 30 nm) instead of "ferroferric oxide powder (particle size of 15 nm to 20 nm)".

[0130] After testing, the PET conversion rate in this embodiment was 92.34%, and the BHET yield was 84.63%.

[0131] Example 31:

[0132] A method for depolymerizing polyethylene terephthalate, comprising the following steps:

[0133] 1) Add 2 g of ferroferric oxide powder (particle size 15 nm to 20 nm) and 20 g of ethylene glycol into a three-necked flask, and then install a mechanical stirring device on the three-necked flask to stir to obtain a magnetic catalyst dispersion;

[0134] 2) A three-necked flask (containing the magnetic catalyst dispersion) was placed in a coil attached to a magnetic induction heating apparatus. The magnetic induction heating apparatus was turned on and heated to boiling at a magnetic field frequency of 300 kHz and an induced current of 24 A. 3 g of polyethylene terephthalate powder (particle size of 150 μm to 180 μm) was then added. The reaction pressure was controlled to 1 atm, and the mixture was stirred and refluxed under condensation for 5 minutes. The heating was stopped, and the mixture was naturally cooled to room temperature to obtain a reaction solution containing bis(hydroxyethyl) terephthalate, bis(hydroxyethyl) terephthalate dimer, and bis(hydroxyethyl) terephthalate oligomers.

[0135] According to the test, the PET conversion rate in this embodiment is 3.60%, and the BHET yield is 0.60%.

[0136] Example 32:

[0137] A method for depolymerizing polyethylene terephthalate is identical to Example 31 except that the condensation reflux time in step 2) is adjusted from 5 min to 10 min.

[0138] After testing, the PET conversion rate in this embodiment was 63.40%, and the BHET yield was 54.80%.

[0139] Example 33:

[0140] A method for depolymerizing polyethylene terephthalate is identical to Example 31 except that the condensation reflux time in step 2) is adjusted from 5 min to 20 min.

[0141] After testing, the PET conversion rate in this embodiment was 100%, and the BHET yield was 97.80%.

[0142] Example 34:

[0143] A method for depolymerizing polyethylene terephthalate is identical to Example 31 except that the induction current in step 2) is adjusted from 24 A to 16 A and the condensation reflux time in step 2) is adjusted from 5 min to 30 min.

[0144] According to the test, the PET conversion rate in this embodiment is 20.34%, and the BHET yield is 15.96%.

[0145] Example 35:

[0146] A method for depolymerizing polyethylene terephthalate is identical to Example 31 except that the induction current in step 2) is adjusted from 24 A to 16 A and the condensation reflux time in step 2) is adjusted from 5 min to 60 min.

[0147] After testing, the PET conversion rate in this embodiment was 43.40%, and the BHET yield was 39.17%.

[0148] Example 36:

[0149] A method for depolymerizing polyethylene terephthalate is identical to Example 31 except that the induction current in step 2) is adjusted from 24 A to 16 A and the condensation reflux time in step 2) is adjusted from 5 min to 90 min.

[0150] According to the test, the PET conversion rate in this embodiment is 87.29%, and the BHET yield is 80.70%.

[0151] Example 37:

[0152] A method for depolymerizing polyethylene terephthalate is identical to Example 31 except that the induction current in step 2) is adjusted from 24 A to 16 A and the condensation reflux time in step 2) is adjusted from 5 min to 120 min.

[0153] After testing, the PET conversion rate in this embodiment was 100%, and the BHET yield was 94.34%.

[0154] Comparative Example:

[0155] A method for depolymerizing polyethylene terephthalate, comprising the following steps:

[0156] 1) Add 2 g of ferroferric oxide powder (particle size 15 nm to 20 nm) and 20 g of ethylene glycol into a three-necked flask, and then install a mechanical stirring device on the three-necked flask to stir to obtain a magnetic catalyst dispersion;

[0157] 2) A three-necked flask (containing the magnetic catalyst dispersion) was placed in an oil bath and heated to boiling (the same temperature as in Example 25). 3 g of polyethylene terephthalate powder (particle size: 150 μm to 180 μm) was then added. The reaction pressure was controlled to 1 atm, and the mixture was stirred and refluxed for 15 min. Heating was stopped, and the mixture was naturally cooled to room temperature to obtain a reaction solution containing bis(hydroxyethyl) terephthalate, bis(hydroxyethyl) terephthalate dimer, and bis(hydroxyethyl) terephthalate oligomers.

[0158] After testing, the PET conversion rate in this example was 4.00%, and the BHET yield was 1.80% (the PET conversion rate and BHET yield of Example 25 were 100% and 98.20%, respectively. Example 25 and the comparative example only differed in the heating method, but the PET conversion rate and BHET yield of Example 25 were much higher than those of the comparative example, indicating that the catalytic depolymerization of PET by electromagnetic induction heating of the magnetic catalyst can indeed bring about a significant improvement in the monomer yield compared with the traditional heating method).

[0159] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for depolymerizing polyethylene terephthalate, characterized in that: The following steps are involved: 1) dispersing magnetic catalyst powder in ethylene glycol to obtain a magnetic catalyst dispersion; 2) The magnetic catalyst dispersion is placed in a magnetic induction heating device and heated to boiling, and then polyethylene terephthalate powder is added to carry out a depolymerization reaction to obtain a reaction solution containing bis(hydroxyethyl) terephthalate, bis(hydroxyethyl) terephthalate dimer, and bis(hydroxyethyl) terephthalate oligomer.

2. The method for depolymerizing polyethylene terephthalate according to claim 1, wherein: The mass ratio of the magnetic catalyst powder to the polyethylene terephthalate powder is 1 to 4:

3.

3. The method for depolymerizing polyethylene terephthalate according to claim 1, wherein: The mass ratio of the ethylene glycol to the polyethylene terephthalate powder is 2 to 10:

1.

4. The method for depolymerizing polyethylene terephthalate according to any one of claims 1 to 3, wherein: In step 1), the magnetic catalyst powder is at least one of ferroferric oxide powder, iron oxide powder, iron cobalt oxide powder, and iron manganese oxide powder.

5. The method for depolymerizing polyethylene terephthalate according to any one of claims 1 to 3, wherein: Step 1) The particle size of the magnetic catalyst powder is 15 nm to 30 nm.

6. The method for depolymerizing polyethylene terephthalate according to any one of claims 1 to 3, wherein: Step 2) The magnetic field frequency of the magnetic induction heating device is 100kHz to 500kHz, and the induced current is 10A to 24A.

7. The method for depolymerizing polyethylene terephthalate according to any one of claims 1 to 3, wherein: Step 2) The particle size of the polyethylene terephthalate powder is 150 μm to 180 μm.

8. The method for depolymerizing polyethylene terephthalate according to any one of claims 1 to 3, wherein: The depolymerization reaction in step 2) is carried out under standard atmospheric pressure.

9. The method for depolymerizing polyethylene terephthalate according to any one of claims 1 to 3, wherein: The depolymerization reaction time in step 2) is 5 min to 120 min.

10. Use of the polyethylene terephthalate depolymerization method according to any one of claims 1 to 9 in the field of polyester recovery.

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