Depolymerization method of waste polyester and regeneration method after depolymerization

Abstract

The invention relates to a depolymerization method of waste polyester and a regeneration method after depolymerization, and the depolymerization method comprises the following steps: mixing waste polyester, a first catalyst and water, and carrying out a hydrolysis reaction to obtain a hydrolysis product; mixing dihydric alcohol and the hydrolysis product, and carrying out alcoholysis reaction to obtain a depolymerization product; the first catalyst comprises a carrier and an acidic active component loaded on the carrier; the carrier comprises an Hbeta-25 molecular sieve and / or activated carbon; the acidic active component comprises phosphotungstic acid; according to the depolymerization method, the conversion rate of the waste polyester is preferably as high as 98.20% or above, the yield of the depolymerization product is preferably as high as 93.52% or above, the reaction conditions of the depolymerization method are mild, the regenerated polyester obtained by regeneration after subsequent depolymerization has excellent mechanical properties, and high value-added recycling of the waste polyester is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of waste polyester recycling, in particular to a depolymerization method of waste polyester and a regeneration method after depolymerization. Background Art

[0002] Polyester, a thermoplastic polymer with excellent properties, is widely used in various fields of life, such as chemical fibers, packaging, medicine, and electronic devices. With the rapid growth in polyester use, the accumulation of large amounts of waste polyester products has become an increasingly prominent environmental pollution problem. Nearly 70% of polyester is discarded due to lack of proper recycling, and more than half is landfilled or dumped into the ocean, resulting in a significant waste of petroleum resources and significant damage to ecological resources. Therefore, recycling waste polyester not only helps alleviate the pressure on polyester resources but also protects ecological and green resources.

[0003] Polyester recycling can be divided into two types based on different recycling characteristics: physical recycling and chemical recycling. Physical recycling involves remelting and granulating pre-treated waste polyester to regenerate the polyester. Pre-treatment includes impurity removal, crushing, alkaline washing, and drying. This method is characterized by low recycling costs and relatively simple application technology. However, due to thermal oxidative degradation and the presence of acidic substances during the remelting process, molecular chain breakage and impurity generation, the recycling rate is limited. Currently, there are three main depolymerization methods for chemically recycling polyester: hydrolysis, methanol depolymerization, and diol depolymerization. The hydrolysis method has problems such as easy equipment corrosion, harsh reaction conditions, excessively slow reaction, or unstable catalysts. The methanol depolymerization method often requires high temperature and high pressure, which places high demands on production equipment and poor industrial production safety. Although the diol depolymerization method has mild reaction conditions, its utilization rate of waste polyester, namely depolymerization efficiency, product yield, and purity, still has considerable room for improvement.

[0004] For example, CN113444284A discloses a method for acid-catalyzed hydrolysis of waste PET plastics, wherein the basic unit for constructing PET plastics (terephthalic acid) is used as a catalyst to catalyze the hydrolysis of waste PET plastics. The hydrolysis products of this method are terephthalic acid and ethylene glycol, which have low added value. The method does not involve related methods for regenerating polyester, and fails to achieve efficient resource utilization of waste polyester.

[0005] Therefore, how to develop a new depolymerization method for waste polyester and a regeneration method after depolymerization to achieve high value-added recycling of waste polyester and solve its pollution to the ecological environment is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a new depolymerization method for waste polyester and a regeneration method after depolymerization, which realizes the efficient and green degradation of waste polyester and obtains high-value-added depolymerization products, solving the current problems of low depolymerization efficiency, many side reactions, low product purity and yield, complex process flow and high depolymerization cost of waste polyester.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for depolymerizing waste polyester, the depolymerization method comprising the following steps:

[0009] (1) mixing waste polyester, a first catalyst and water to carry out a hydrolysis reaction to obtain a hydrolyzate;

[0010] (2) mixing the diol and the hydrolyzate of step (1) to carry out alcoholysis reaction to obtain a depolymerized product;

[0011] Step (1) The first catalyst comprises a carrier and an acidic active component supported on the carrier;

[0012] The carrier includes Hβ-25 molecular sieve and / or activated carbon; and the acidic active component includes phosphotungstic acid.

[0013] The present invention selects a first catalyst including a carrier and an acidic active component loaded on the carrier, selects Hβ-25 molecular sieve and / or activated carbon as the carrier, and selects the phosphotungstic acid as the acidic active component, that is, selects Hβ-25 molecular sieve loaded with phosphotungstic acid and / or activated carbon loaded with phosphotungstic acid as the first catalyst to perform a hydrolysis reaction. The first catalyst has a high specific surface area and abundant active sites, thereby improving the catalytic activity of the catalytic hydrolysis reaction and improving the hydrolysis reaction efficiency. The catalyst is then combined with subsequent ethylene glycol for further alcoholysis reaction, and the two are combined to realize a dual depolymerization process, significantly improving the depolymerization efficiency of waste polyester, improving the utilization rate of waste polyester, and reducing side reactions, thereby improving the yield and purity of the depolymerization product.

[0014] Compared with other catalysts, the carrier of the first catalyst of the present invention has a larger specific surface area and the loaded acidic active components have more active sites, thus having higher catalytic activity and promoting the hydrolysis of waste polyester. In addition, the first catalyst has strong stability and simple recovery, and can be recycled multiple times, thereby reducing the depolymerization cost. Compared with monohydric alcohols, the depolymerization product BHET obtained by the alcoholysis reaction of dihydric alcohols in the present invention has wider applications, higher added value, and milder reaction conditions.

[0015] Preferably, the waste polyester in step (1) comprises any one of waste polyethylene terephthalate, waste polypropylene terephthalate, waste polybutylene terephthalate, waste polylactic acid, waste polycaprolactone, waste polycarbonate, waste nylon 66, waste polyadipate / butylene terephthalate, waste polyurethane, waste poly-1,4-cyclohexanedimethanol terephthalate, waste polymethyl methacrylate or waste polyurethane, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of waste polyethylene terephthalate and waste polypropylene terephthalate, a combination of waste polybutylene terephthalate and waste polylactic acid, or a combination of waste polyethylene terephthalate and waste nylon 66, etc., preferably waste polyethylene terephthalate.

[0016] Preferably, the depolymerization method further comprises pre-treating the waste polyester before the mixing in step (1).

[0017] Preferably, the pretreatment includes crushing.

[0018] Preferably, the crushing process includes crushing the waste polyester into particles of 3 to 50 mm, for example, 3 mm, 5 mm, 8 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm or 50 mm.

[0019] Preferably, the crushing process further includes a first washing and a first drying performed in sequence.

[0020] Preferably, the loading amount of the acidic active component in the first catalyst in step (1) is 50-60 wt%, for example, 50 wt%, 52 wt%, 55 wt%, 58 wt% or 60 wt%.

[0021] The present invention further preferably has a loading amount of the acidic active component in the first catalyst in step (1) of 50 to 60 wt %, which is conducive to the sufficient hydrolysis of waste polyester while ensuring low cost. If the loading amount of the acidic active component in the first catalyst is too low, the hydrolysis will be incomplete, the utilization rate of the waste polyester will be reduced, and the depolymerization efficiency will be reduced. If the loading amount of the acidic active component in the first catalyst is too high, the depolymerization efficiency of the waste polyester will not be significantly improved, but the depolymerization cost will be increased.

[0022] Preferably, the mass ratio of the waste polyester, the first catalyst and water in step (1) is 1:(0.01-0.05):(1-12), for example, it can be 1:0.01:1, 1:0.02:2, 1:0.03:5, 1:0.04:8, 1:0.05:10 or 1:0.05:12, etc.

[0023] The present invention further preferably adopts a mass ratio of the waste polyester, the first catalyst and water in step (1) of 1: (0.01-0.05): (1-12), which is conducive to the full hydrolysis of the waste polyester and improves the depolymerization efficiency; if the mass ratio of the waste polyester and the first catalyst is too high, that is, the addition amount of the first catalyst is too low, the depolymerization efficiency will be reduced; if the mass ratio of the waste polyester and the first catalyst is too low, that is, the addition amount of the first catalyst is too high, the depolymerization efficiency cannot be significantly improved, but the first catalyst will be wasted, and the depolymerization cost will be increased.

[0024] Preferably, the hydrolysis reaction in step (1) is carried out in a first protective gas atmosphere.

[0025] Preferably, the first protective gas comprises nitrogen.

[0026] Preferably, the temperature of the hydrolysis reaction in step (1) is 180-240°C, for example, it can be 180°C, 190°C, 200°C, 210°C, 220°C, 230°C or 240°C.

[0027] Preferably, the pressure of the hydrolysis reaction in step (1) is 0.15 to 0.30 MPa, for example, 0.15 MPa, 0.18 MPa, 0.20 MPa, 0.22 MPa, 0.25 MPa, 0.28 MPa or 0.30 MPa.

[0028] Preferably, the hydrolysis reaction time in step (1) is 15 to 60 min, for example, it can be 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min.

[0029] Preferably, the hydrolysis reaction in step (1) is accompanied by a first stirring.

[0030] Preferably, the first stirring speed is 100-200 r / min, for example, 100 r / min, 120 r / min, 140 r / min, 160 r / min, 180 r / min or 200 r / min.

[0031] Preferably, the diol in step (2) comprises any one or a combination of at least two of ethylene glycol, 1,3-propylene glycol or 1,4-butanediol, wherein typical but non-limiting combinations include a combination of ethylene glycol and 1,3-propylene glycol, a combination of 1,3-propylene glycol and 1,4-butanediol or a combination of ethylene glycol and 1,4-butanediol, etc., preferably ethylene glycol.

[0032] Preferably, the mass ratio of the diol in step (2) to the waste polyester in step (1) is (3-8):1, for example, it can be 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1 or 8:1, etc.

[0033] Preferably, the alcoholysis reaction in step (2) is carried out in a second protective gas atmosphere.

[0034] Preferably, the second protective gas comprises nitrogen.

[0035] Preferably, the temperature of the alcoholysis reaction in step (2) is 180-240°C, for example, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C or 240°C.

[0036] Preferably, the pressure of the alcoholysis reaction in step (2) is 0.15 to 0.30 MPa, for example, 0.15 MPa, 0.18 MPa, 0.20 MPa, 0.22 MPa, 0.25 MPa, 0.28 MPa or 0.30 MPa.

[0037] Preferably, the alcoholysis reaction time in step (2) is 60 to 120 min, for example, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min or 120 min.

[0038] Preferably, the alcoholysis reaction in step (2) is accompanied by a second stirring.

[0039] Preferably, the second stirring speed in step (2) is 100 to 200 r / min, for example, it can be 100 r / min, 120 r / min, 140 r / min, 160 r / min, 180 r / min or 200 r / min.

[0040] Preferably, the depolymerization method further comprises post-processing the depolymerization product of step (2).

[0041] Preferably, the post-treatment includes cooling, first filtration, crystallization, second filtration, second washing, second drying and rectification.

[0042] As a further preferred technical solution of the present invention, the depolymerization method of waste polyester comprises the following steps:

[0043] (1) first crushing waste polyester into waste polyester fragments with a particle size of 3 to 50 mm, then sequentially washing and drying the waste polyester fragments; then mixing the first dried waste polyester fragments, a first catalyst, and water in a mass ratio of 1:(0.01 to 0.05):(1 to 12), and performing a hydrolysis reaction for 15 to 60 minutes in a first protective gas atmosphere at 180 to 240° C., 0.15 to 0.30 MPa, and 100 to 200 r / min to obtain a hydrolyzate;

[0044] (2) mixing a diol and the hydrolysis product of step (1), and performing an alcoholysis reaction for 60 to 120 minutes under second stirring conditions of 180 to 240° C., 0.15 to 0.30 MPa, and 100 to 200 r / min in a second protective gas atmosphere to obtain a depolymerized product; wherein the first catalyst in step (1) comprises a carrier and an acidic active component supported on the carrier; the loading amount of the acidic active component in the first catalyst is 50 to 60 wt%; the carrier comprises Hβ-25 molecular sieve and / or activated carbon; the acidic active component comprises phosphotungstic acid; and the first protective gas comprises nitrogen;

[0045] The waste polyester in step (1) includes any one of waste polyethylene terephthalate, waste polypropylene terephthalate, waste polybutylene terephthalate, waste polylactic acid, waste polycaprolactone, waste polycarbonate, waste nylon 66, waste polybutylene adipate / terephthalate, waste polyurethane, waste poly(1,4-cyclohexanedimethanol terephthalate), waste polymethyl methacrylate or waste polyurethane, or a combination of at least two thereof;

[0046] The diol in step (2) includes any one of ethylene glycol, 1,3-propylene glycol or 1,4-butanediol, or a combination of at least two of them; the mass ratio of the diol in step (2) to the waste polyester in step (1) is (3 to 8):1; and the second protective gas includes nitrogen.

[0047] In a second aspect, the present invention provides a method for regenerating waste polyester after depolymerization, the method comprising mixing a second catalyst and the depolymerization product obtained by the depolymerization method described in the first aspect to obtain a mixed system, and sequentially subjecting the mixed system to an esterification reaction and a polycondensation reaction to obtain regenerated polyester.

[0048] The present invention achieves the regeneration of waste polyester by mixing the second catalyst and the depolymerization product obtained by the depolymerization method described in the first aspect, and undergoing esterification reaction and polycondensation reaction. The obtained regenerated polyester has high mechanical properties, solves the problem of waste polyester polluting the ecological environment, and realizes efficient and green resource recycling of waste polyester.

[0049] The post-depolymerization regeneration method of the present invention does not impose any restrictions on the depolymerization method for obtaining the depolymerization product, and is applicable to regenerating the depolymerization product obtained by the depolymerization method described in the first aspect of the present invention, and is also applicable to regenerating depolymerization products obtained by other solutions.

[0050] Preferably, the post-depolymerization regeneration method further comprises mixing the polymer raw materials.

[0051] Preferably, the polymeric raw material comprises a diol, a dibasic acid or a polyol.

[0052] Preferably, the diol includes any one of ethylene glycol, 1,3-propylene glycol or 1,4-butanediol, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of ethylene glycol and 1,3-propylene glycol, a combination of ethylene glycol and 1,4-butanediol, or a combination of 1,3-propylene glycol and 1,4-butanediol, etc.

[0053] Preferably, the dibasic acid comprises any one of terephthalic acid, isophthalic acid or phthalic acid, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of terephthalic acid and isophthalic acid, a combination of isophthalic acid and phthalic acid, or a combination of terephthalic acid and phthalic acid, etc.

[0054] Preferably, the polyol comprises any one of polyether polyol, polycarbonate polyol or acrylic polyol, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of polyether polyol and polycarbonate polyol, a combination of polyether polyol and acrylic polyol, or a combination of polycarbonate polyol and acrylic polyol.

[0055] Preferably, the polyether polyol comprises polytetramethylene ether glycol and / or polytrimethylene ether glycol.

[0056] Preferably, the polycarbonate polyol includes polypropylene carbonate diol and / or polypropylene carbonate triol.

[0057] Preferably, the acrylic polyol includes acrylic diol and / or acrylic triol.

[0058] The present invention can flexibly obtain different types of polyesters or polyester elastomers by further mixing polymerization raw materials into the depolymerization product.

[0059] Preferably, the amount of the second catalyst added is 0.01% to 0.02% of the mass of the depolymerization product, for example, 0.01%, 0.012%, 0.015%, 0.018% or 0.02%.

[0060] Preferably, the second catalyst comprises any one or a combination of at least two of an antimony-based catalyst, a titanium-based catalyst or a germanium-based catalyst, wherein typical but non-limiting combinations include a combination of an antimony-based catalyst and a titanium-based catalyst, a combination of a titanium-based catalyst and a germanium-based catalyst, or a combination of an antimony-based catalyst and a germanium-based catalyst, etc.

[0061] Preferably, the antimony-based catalyst includes any one or a combination of at least two of ethylene glycol antimony, antimony acetate or antimony trioxide, wherein typical but non-limiting combinations include a combination of ethylene glycol antimony and antimony acetate, a combination of antimony acetate and antimony trioxide, or a combination of ethylene glycol antimony and antimony trioxide.

[0062] Preferably, the titanium-based catalyst includes any one of tetraisopropyl titanate, tetra-n-butyl titanate or titanium ethylene glycol, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of tetraisopropyl titanate and tetra-n-butyl titanate, a combination of tetra-n-butyl titanate and titanium ethylene glycol, or a combination of tetraisopropyl titanate and titanium ethylene glycol, etc.

[0063] Preferably, the germanium-based catalyst includes germanium acetate and / or germanium dioxide.

[0064] Preferably, the mixing in the post-depolymerization regeneration method further comprises adding a heat stabilizer.

[0065] Preferably, the amount of the thermal stabilizer added is 0.005% to 0.05% of the mass of the depolymerization product, for example, it can be 0.005%, 0.008%, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045% or 0.05%, etc.

[0066] Preferably, the heat stabilizer includes any one or a combination of at least two of trimethyl phosphate, dimethyl phosphate, triphenyl phosphate, diphenyl phosphate, triphenyl phosphite, diphenyl phosphite, ammonium phosphite, ammonium dihydrogen phosphate, phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid or ammonium phosphate, wherein typical but non-limiting combinations include a combination of trimethyl phosphate and dimethyl phosphate, a combination of triphenyl phosphate, diphenyl phosphate and triphenyl phosphite, or a combination of ammonium phosphite and ammonium dihydrogen phosphate, etc.

[0067] Preferably, in the post-depolymerization regeneration method, the mixing is performed in a third protective gas atmosphere.

[0068] Preferably, the third protective gas comprises nitrogen.

[0069] Preferably, the mixing temperature in the post-depolymerization regeneration method is 220-240°C, for example, 220°C, 225°C, 230°C, 235°C or 240°C.

[0070] Preferably, the mixing pressure in the post-depolymerization regeneration method is 0.4 to 0.6 MPa, for example, 0.4 MPa, 0.42 MPa, 0.45 MPa, 0.48 MPa, 0.5 MPa, 0.52 MPa, 0.55 MPa, 0.58 MPa or 0.6 MPa.

[0071] Preferably, the mixing time in the post-depolymerization regeneration method is 30 to 60 minutes, for example, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes or 60 minutes.

[0072] Preferably, the mixing process in the post-depolymerization regeneration method is accompanied by a third stirring.

[0073] Preferably, the third stirring speed is 80-100 r / min, for example, 80 r / min, 85 r / min, 90 r / min, 95 r / min or 100 r / min.

[0074] Preferably, the temperature of the esterification reaction is 240-250°C, for example, 240°C, 242°C, 245°C, 248°C or 250°C.

[0075] Preferably, the esterification reaction time is 15 to 30 minutes, for example, 15 minutes, 18 minutes, 20 minutes, 22 minutes, 25 minutes, 28 minutes or 30 minutes.

[0076] Preferably, during the esterification reaction, the mixed system undergoes a first uniform pressure reduction.

[0077] Preferably, the endpoint pressure of the first uniform pressure reduction is 0.8-1.2 kPa, for example, it can be 0.8 kPa, 0.85 kPa, 0.9 kPa, 0.95 kPa, 1.0 kPa, 1.05 kPa, 1.1 kPa, 1.15 kPa or 1.2 kPa.

[0078] The present invention further prefers that the endpoint pressure of the first uniform pressure reduction is 0.8 to 1.2 kPa, which is conducive to the complete esterification of the depolymerization product and the added monomer into oligomers such as dimers or trimers, and the molecular weight distribution of the recycled polyester is uniform and the performance is excellent; if the endpoint pressure of the first uniform pressure reduction is too low, the esterification reaction will be too fast, and macromolecular products will be generated in the esterification stage, resulting in uneven molecular weight distribution of the recycled polyester and uneven distribution of mechanical properties of the recycled polyester, affecting the performance and service life; if the endpoint pressure of the first uniform pressure reduction is too high, the esterification rate will be reduced, unreacted monomers will be present, the molecular weight distribution of the recycled polyester will be uneven, small molecular substances will remain, the recycled polyester will have poor mechanical properties, poor color value, and low melting point.

[0079] Preferably, the reduction rate of the first uniform pressure reduction is 5 to 10 kPa / min, for example, it can be 5 kPa / min, 5.5 kPa / min, 6 kPa / min, 6.5 kPa / min, 7 kPa / min, 7.5 kPa / min, 8 kPa / min, 8.5 kPa / min, 9 kPa / min, 9.5 kPa / min or 10 kPa / min, etc.

[0080] The present invention further preferably has a reduction rate of 5 to 10 kPa / min for the first uniform pressure reduction, which is beneficial for controlling the speed of the esterification reaction and ensuring complete esterification of the depolymerization product with the raw material. If the reduction rate of the first uniform pressure reduction is too low, the water discharge time will be longer, the esterification reaction speed will be reduced, and the by-products generated by the side reaction diol etherification will affect the color value of the regenerated polyester. If the reduction rate of the first uniform pressure reduction is too high, the pre-condensation stage will start too early, resulting in the generation of macromolecular products and uneven molecular weight distribution of the regenerated polyester.

[0081] Preferably, the esterification reaction is accompanied by a fourth stirring.

[0082] Preferably, the fourth stirring speed is 80-100 r / min, for example, 80 r / min, 85 r / min, 90 r / min, 95 r / min or 100 r / min.

[0083] Preferably, the polymerization reaction temperature is 265-290°C, for example, 265°C, 270°C, 275°C, 280°C, 285°C or 290°C.

[0084] Preferably, the polymerization reaction time is 10 to 60 minutes, for example, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes or 60 minutes.

[0085] Preferably, during the polymerization reaction, the mixed system undergoes a second uniform pressure reduction.

[0086] Preferably, the endpoint pressure of the second uniform pressure reduction is ≤100 Pa, for example, it can be 100 Pa, 95 Pa, 90 Pa, 85 Pa, 80 Pa, 75 Pa or 70 Pa.

[0087] Preferably, the reduction rate of the second uniform pressure reduction is 0.5-1 kPa / min, for example, it can be 0.5 kPa / min, 0.6 kPa / min, 0.7 kPa / min, 0.8 kPa / min, 0.9 kPa / min or 1 kPa / min.

[0088] Preferably, the polymerization reaction is accompanied by a fifth stirring.

[0089] The present invention further prefers that the reduction rate of the second uniform pressure reduction is 0.5 to 1 kPa / min, which is beneficial to the discharge of ethylene glycol and low molecules in the material system, promotes the reaction in the positive direction, increases the molecular chain segments of the recycled polyester, and increases the viscosity; if the reduction rate of the second uniform pressure reduction is too low, the condensation reaction rate will be slow, the small molecules in the system will be difficult to be discharged in time, the reaction time will be long, the reaction will proceed in the reverse direction, the product will degrade, the product viscosity will decrease, and the polyester melt quality will be poor; if the reduction rate of the second uniform pressure reduction is too high, the condensation reaction rate will be accelerated, the side reactions will increase accordingly, the residence time will remain unchanged, and the color value b value will tend to increase.

[0090] Preferably, the fifth stirring speed is 80-100 r / min, for example, 80 r / min, 85 r / min, 90 r / min, 95 r / min or 100 r / min.

[0091] As a further preferred technical solution of the present invention, the method for regenerating waste polyester after depolymerization comprises the following steps:

[0092] The depolymerization product of the first aspect, the second catalyst, and the thermal stabilizer are mixed under third stirring conditions of 220-240° C., 0.4-0.6 MPa, and 80-100 r / min for 30-60 minutes to obtain a mixed system; then, under fourth stirring conditions of 240-250° C. and 80-100 r / min, the mixed system is first uniformly depressurized at a reduction rate of 5-10 kPa / min to an end pressure of 0.8-1.5 kPa, and an esterification reaction is carried out for 15-30 minutes; and then, under fifth stirring conditions of 265-290° C. and 80-100 r / min, the mixed system is second uniformly depressurized at a reduction rate of 0.5-1 kPa / min to an end pressure of ≤100 Pa, and a polycondensation reaction is carried out for 10-60 minutes to obtain a regenerated polyester;

[0093] Wherein, the third protective gas includes nitrogen;

[0094] The second catalyst comprises any one or a combination of at least two of an antimony-based catalyst, a titanium-based catalyst or a germanium-based catalyst; the antimony-based catalyst comprises any one or a combination of at least two of ethylene glycol antimony, antimony acetate or antimony trioxide; the titanium-based catalyst comprises any one or a combination of at least two of tetraisopropyl titanate, tetra-n-butyl titanate or ethylene glycol titanium; the germanium-based catalyst comprises germanium acetate and / or germanium dioxide; the amount of the second catalyst added is 0.01% to 0.02% of the mass of the depolymerization product;

[0095] The heat stabilizer includes any one of trimethyl phosphate, dimethyl phosphate, triphenyl phosphate, diphenyl phosphate, triphenyl phosphite, diphenyl phosphite, ammonium phosphite, ammonium dihydrogen phosphate, phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid or ammonium phosphate, or a combination of at least two thereof; the addition amount of the heat stabilizer is 0.005% to 0.05% of the mass of the depolymerization product.

[0096] Compared with the prior art, the present invention has at least the following beneficial effects:

[0097] (1) The depolymerization method of waste polyester provided by the present invention first performs a hydrolysis reaction by selecting a catalyst composed of a specific carrier and a specific acidic active component, and then combines it with a further alcoholysis reaction of a diol. The two act synergistically to achieve high-value-added conversion and utilization of waste polyester. The conversion rate of waste polyester is preferably as high as 98.20% or more, and the yield of depolymerization product is preferably as high as 93.52% or more. In addition, the depolymerization method has mild reaction conditions, a simple process flow, and low cost.

[0098] (2) The present invention provides a method for regenerating waste polyester after depolymerization, wherein the depolymerization method further polymerizes the depolymerization product obtained by the depolymerization method described in the first aspect to obtain regenerated polyester, and further optimizes the pressure reduction rate and the terminal pressure of each reaction stage in the polymerization process to further obtain regenerated polyester with excellent mechanical properties, wherein the tensile strength is preferably as high as 55.05 MPa or more, the elongation at break is preferably as high as 13.12% or more, and the flexural strength is preferably as high as 55.60 MPa or more. DETAILED DESCRIPTION

[0099] For the convenience of understanding the present invention, the present invention is given below with examples. It should be understood by those skilled in the art that the examples are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0100] The raw materials for preparing the Hβ-25 molecular sieve catalyst loaded with phosphotungstic acid used in the following examples or comparative examples include 30g of tetraethyl orthosilicate, 8g of aluminum sulfate, 30g of sodium oxide, 200g of deionized water, 50g of tetraethylammonium hydroxide and 213g of phosphotungstic acid; the preparation method specifically includes the following steps:

[0101] (1) Tetraethyl orthosilicate, aluminum sulfate, sodium oxide, deionized water and tetraethylammonium hydroxide were stirred for 30 minutes to mix evenly, and then dried at 120°C until all the water was evaporated. The resulting reactant was sent to a reactor and heated to 150°C and steam was introduced for 72 hours. Then, the temperature was raised to 700°C and maintained for 8 hours. The solid product was taken out and repeatedly rinsed with deionized water three times and dried to obtain a carrier.

[0102] (2) The dried carrier is impregnated with a certain mass concentration of phosphotungstic acid and stirred for 18 hours, and then the obtained solid is dried to obtain an Hβ-25 molecular sieve catalyst loaded with 55wt% phosphotungstic acid. By adjusting the raw material ratio, Hβ-25 molecular sieve catalysts with different phosphotungstic acid loading amounts are obtained.

[0103] The preparation method of the activated carbon catalyst loaded with phosphotungstic acid used in the following examples or comparative examples specifically includes the following steps:

[0104] 500g of coconut shells are crushed to 200 mesh, and the crushed powder is dried at 80°C until the moisture content is less than 15%. The coconut shell powder is then sent to a carbonization furnace. The temperature in the central area of the carbonization furnace is 500-550°C. The coconut shell powder is added to the carbonization furnace and sequentially dried, pyrolyzed, pre-carbonized and carbonized to remove volatile matter, and finally flows out from the storage bin; the carbonized coconut shells are then sent to a high-temperature reactor, activated by water vapor at 900°C for 2 hours, and then cooled and taken out to obtain an activated carbon carrier.

[0105] Take 50g of activated carbon carrier and dissolve it with 45% nitric acid by mass, treat it at 85℃ for 2h and then dry it. The dried activated carbon is immersed in the above-mentioned phosphotungstic acid, stirred for 24h and then dried to obtain an activated carbon catalyst loaded with 55wt% phosphotungstic acid. Different phosphotungstic acid loadings can be obtained by adjusting the raw material ratio.

[0106] It is worth noting that the present invention does not impose any restrictions on the preparation method of the Hβ-25 molecular sieve catalyst loaded with phosphotungstic acid and the preparation method of the activated carbon catalyst loaded with phosphotungstic acid. Other Hβ-25 molecular sieve catalysts and activated carbon catalysts that can prepare corresponding phosphotungstic acid loadings are also suitable for the depolymerization method of the present invention.

[0107] In the following examples and comparative examples, the depolymerization products obtained by the depolymerization process are purified and decolorized during the regeneration process of waste polyester after depolymerization.

[0108] 1. Implementation

[0109] Example 1

[0110] This embodiment provides a depolymerization method for waste polyethylene terephthalate, which comprises the following steps:

[0111] (1) first crushing waste polyethylene terephthalate to waste polyethylene terephthalate fragments with a particle size of 10 mm, then sequentially washing and drying the waste polyethylene terephthalate fragments; then mixing the first dried waste polyethylene terephthalate fragments, an Hβ-25 molecular sieve catalyst loaded with 55 wt% phosphotungstic acid, and water in a mass ratio of 1:0.03:4, and performing a hydrolysis reaction for 30 minutes under a nitrogen atmosphere at 200° C., 0.20 MPa, and 150 r / min first stirring conditions to obtain a hydrolyzate;

[0112] (2) mixing ethylene glycol and the hydrolysis product of step (1), and performing an alcoholysis reaction for 100 minutes under a second stirring condition of 200° C., 0.20 MPa and 150 r / min in a nitrogen atmosphere to obtain a depolymerization product, bis-β-hydroxyethyl terephthalate (BHET).

[0113] This embodiment also provides a method for regenerating waste polyethylene terephthalate after depolymerization, the method comprising the following steps:

[0114] The depolymerization product, antimony acetate, and trimethyl phosphate were mixed for 40 minutes under a nitrogen atmosphere at a third stirring condition of 230° C., 0.5 MPa, and 90 r / min to obtain a mixed system, wherein the amount of antimony acetate added was 0.015% by mass of the depolymerization product; and the amount of trimethyl phosphate added was 0.02% by mass of the depolymerization product. Subsequently, under a fourth stirring condition of 245° C. and 90 r / min, the mixed system was first uniformly depressurized at a reduction rate of 8 kPa / min to an end pressure of 1.0 kPa, and an esterification reaction was carried out for 20 minutes. Then, under a fifth stirring condition of 280° C. and 90 r / min, the mixed system was second uniformly depressurized at a reduction rate of 0.8 kPa / min to an end pressure of 100 Pa, and a polycondensation reaction was carried out for 30 minutes to obtain regenerated polyethylene terephthalate.

[0115] Example 2

[0116] This embodiment provides a depolymerization method for waste polyethylene terephthalate, which comprises the following steps:

[0117] (1) first crushing waste polyethylene terephthalate to waste polyethylene terephthalate fragments with a particle size of 5 mm, then sequentially washing and drying the waste polyethylene terephthalate fragments; then mixing the first dried waste polyethylene terephthalate fragments, an activated carbon catalyst loaded with 55 wt% phosphotungstic acid, and water in a mass ratio of 1:0.01:2, and performing a hydrolysis reaction for 15 minutes in a nitrogen atmosphere at 180° C., 0.15 MPa, and 200 r / min first stirring conditions to obtain a hydrolyzate;

[0118] (2) Ethylene glycol and the hydrolysis product of step (1) were mixed, and an alcoholysis reaction was carried out for 60 minutes under a second stirring condition of 180° C., 0.15 MPa and 200 r / min in a nitrogen atmosphere to obtain a depolymerization product, bis-β-hydroxyethyl terephthalate (BHET).

[0119] This embodiment also provides a method for regenerating waste polyethylene terephthalate after depolymerization, the method comprising the following steps:

[0120] The depolymerization product, tetraisopropyl titanate and triphenyl phosphate were mixed for 60 minutes under a nitrogen atmosphere at a third stirring condition of 220° C., 0.4 MPa and 100 r / min to obtain a mixed system, wherein the amount of tetraisopropyl titanate added was 0.01% by mass of the depolymerization product; and the amount of triphenyl phosphate added was 0.005% by mass of the depolymerization product. Subsequently, under a fourth stirring condition of 240° C. and 100 r / min, the mixed system was first uniformly depressurized at a reduction rate of 5 kPa / min to an end pressure of 0.8 kPa, and an esterification reaction was carried out for 30 minutes. Then, under a fifth stirring condition of 265° C. and 100 r / min, the mixed system was second uniformly depressurized at a reduction rate of 0.5 kPa / min to an end pressure of 80 Pa, and a condensation reaction was carried out for 60 minutes to obtain regenerated polyethylene terephthalate.

[0121] Example 3

[0122] This embodiment provides a depolymerization method for waste poly(trimethylene terephthalate), the depolymerization method comprising the following steps:

[0123] (1) first crushing waste poly (propylene glycol terephthalate) to waste poly (propylene glycol terephthalate) fragments with a particle size of 30 mm, then sequentially washing and drying the waste poly (propylene glycol terephthalate) fragments; then mixing the first dried waste poly (propylene glycol terephthalate) fragments, an Hβ-25 molecular sieve catalyst loaded with 60 wt% phosphotungstic acid, and water in a mass ratio of 1:0.05:12, and performing a hydrolysis reaction for 60 min in a nitrogen atmosphere at 240° C., 0.30 MPa, and 100 r / min under first stirring conditions to obtain a hydrolyzate;

[0124] (2) mixing ethylene glycol and the hydrolyzate of step (1), and performing an alcoholysis reaction for 120 min under a second stirring condition of 240° C., 0.30 MPa, and 100 r / min in a nitrogen atmosphere to obtain a depolymerization product, bis-β-hydroxypropyl terephthalate (BHPET).

[0125] The conversion rate of waste poly(trimethylene terephthalate) and the yield of bis-β-hydroxypropyl terephthalate (BHPET) in this embodiment are comparable to those in Example 1 and Example 2.

[0126] This embodiment also provides a method for regenerating waste poly(trimethylene terephthalate) after depolymerization, the method comprising the following steps:

[0127] The depolymerization product, germanium acetate and dimethyl phosphate were mixed for 30 minutes in a nitrogen atmosphere at a third stirring condition of 240° C., 0.6 MPa and 80 r / min to obtain a mixed system, wherein the amount of germanium acetate added was 0.02% by mass of the depolymerization product; and the amount of dimethyl phosphate added was 0.05% by mass of the depolymerization product. Subsequently, under a fourth stirring condition of 250° C. and 80 r / min, the mixed system was first uniformly depressurized at a reduction rate of 10 kPa / min to an end pressure of 1.5 kPa, and an esterification reaction was carried out for 15 minutes. Then, under a fifth stirring condition of 290° C. and 80 r / min, the mixed system was second uniformly depressurized at a reduction rate of 1 kPa / min to an end pressure of 90 Pa, and a polycondensation reaction was carried out for 20 minutes to obtain regenerated poly(trimethylene terephthalate).

[0128] The mechanical properties of the recycled poly(trimethylene terephthalate) obtained in this example are comparable to those of the recycled polyethylene terephthalate obtained in Examples 1 and 2.

[0129] Example 4

[0130] This embodiment provides a depolymerization method for waste polyethylene terephthalate. The depolymerization method is the same as that of Example 1, except that the loading amount of phosphotungstic acid in the first catalyst used is 45 wt%.

[0131] Example 5

[0132] This embodiment provides a depolymerization method for waste polyethylene terephthalate. The depolymerization method is the same as that of Example 1, except that the loading amount of phosphotungstic acid in the first catalyst used is 65 wt%.

[0133] Example 6

[0134] This embodiment provides a depolymerization method for waste polyethylene terephthalate. The depolymerization method is the same as that in Example 1, except that the mass ratio of the waste polyethylene terephthalate to the Hβ-25 molecular sieve catalyst loaded with 55 wt% phosphotungstic acid is 1:0.06.

[0135] Example 7

[0136] This embodiment provides a method for regenerating waste polyethylene terephthalate after depolymerization. The method is the same as that of Example 1 except that the endpoint pressure of the first uniform pressure reduction is 1.5 kPa.

[0137] Example 8

[0138] This embodiment provides a method for regenerating waste polyethylene terephthalate after depolymerization. The method is the same as that of Example 1 except that the endpoint pressure of the first uniform pressure reduction is 0.7 kPa.

[0139] Example 9

[0140] This embodiment provides a method for regenerating waste polyethylene terephthalate after depolymerization. The method is the same as that of Example 1 except that the reduction rate of the first uniform pressure reduction is 12 kPa / min.

[0141] Example 10

[0142] This embodiment provides a method for regenerating waste polyethylene terephthalate after depolymerization. The method is the same as that of Example 1 except that the reduction rate of the first uniform pressure reduction is 4 kPa / min.

[0143] Example 11

[0144] This embodiment provides a method for regenerating waste polyethylene terephthalate after depolymerization. The method is the same as that of Example 1 except that the reduction rate of the second uniform pressure reduction is 1.2 kPa / min.

[0145] Example 12

[0146] This embodiment provides a method for regenerating waste polyethylene terephthalate after depolymerization. The method is the same as that of Example 1 except that the reduction rate of the second uniform pressure reduction is 0.4 kPa / min.

[0147] 2. Comparative Example

[0148] Comparative Example 1

[0149] This comparative example provides a depolymerization method for waste polyethylene terephthalate, wherein the depolymerization method includes step (1) wherein the first catalyst is H + Except for the ZSM-5 catalyst, the rest are the same as those in Example 1.

[0150] This comparative example also provides a method for regenerating waste polyethylene terephthalate after depolymerization. The method is the same as Example 1 except that the depolymerization product obtained by the depolymerization method of this comparative example is regenerated.

[0151] Comparative Example 2

[0152] This comparative example provides a depolymerization method for waste polyethylene terephthalate. The depolymerization method is the same as Example 1 except that the ethylene glycol in step (2) is replaced by ethanol.

[0153] The depolymerization product obtained by the depolymerization method of this comparative example is diethyl terephthalate (DTP), with a yield of 37.64%.

[0154] This comparative example also provides a method for regenerating waste polyethylene terephthalate after depolymerization. In addition to regenerating the depolymerization product obtained by the depolymerization method described in this comparative example, the regeneration method also includes adding ethylene glycol to the mixing system. The amount of ethylene glycol added is 30% of the mass of the depolymerization product DTP. Otherwise, everything else is the same as in Example 1.

[0155] 3. Test and its results

[0156] ① The conversion rate of waste polyethylene terephthalate (PET) and the yield of the product bis-β-hydroxyethyl terephthalate (BHET) of the depolymerization methods provided in Examples 1, 2, 4 to 6, and Comparative Examples 1 and 2 were calculated respectively, specifically using Formula (1) and Formula (2). The results are shown in Table 1.

[0157]

[0158] Table 1

[0159]

[0160]

[0161] From the data in Table 1 we can see that:

[0162] (1) From Example 1 and Example 2, it can be seen that the depolymerization method of waste polyester provided by the present invention has high depolymerization efficiency, the conversion rate of PET is as high as over 98.20%, and the yield of the depolymerization product BHET is as high as over 93.52%, thereby achieving high value-added recycling of waste polyester.

[0163] (2) Combining Example 1 with Examples 4 to 6, it can be seen that the loading amount of phosphotungstic acid in the first catalyst in Example 4 is too low, resulting in the conversion rate of PET dropping to 97.43% and the yield of the depolymerization product BHET dropping to 91.21%; the loading amount of phosphotungstic acid in the first catalyst in Example 5 is too high, and does not significantly improve the conversion rate of PET and the yield of the product BHET; the mass ratio of the waste polyethylene terephthalate and the Hβ-25 molecular sieve catalyst loaded with 55wt% phosphotungstic acid in Example 6 is too low, that is, the addition amount of the Hβ-25 molecular sieve catalyst loaded with 55wt% phosphotungstic acid is too high, and does not significantly improve the depolymerization effect. Therefore, the present invention further prefers that the loading amount of the acidic active component in the first catalyst in the depolymerization method is 50-60wt%, and further prefers that the mass ratio of the waste polyester and the first catalyst is 1:(0.01-0.05), so as to further improve the depolymerization efficiency while reducing the depolymerization cost.

[0164] (3) Combining Example 1 with Comparative Examples 1 and 2, it can be seen that since the comparative example 1 uses H + @ZSM-5 catalyst, resulting in a relatively small specific surface area of the molecular sieve, a low acid catalyst loading, and a relatively low depolymerization efficiency and product yield; since ethanol was used for alcoholysis in Comparative Example 2, the product obtained by alcoholysis using ethanol was diethyl terephthalate, and ethanol alcoholysis had high requirements for reaction pressure. Under the same pressure conditions as in Example 1, the alcoholysis reaction was slow, and the depolymerization efficiency and product yield were low.

[0165] ② The mechanical properties of the regenerated polyester obtained by the depolymerization methods of waste polyester provided in the above examples and comparative examples were tested. The tensile properties (tensile strength and elongation at break) were tested according to GB / T528-2009, and the flexural properties (flexural strength) were tested according to GB / T9341-2000. The results are shown in Table 2.

[0166] Table 2

[0167] project Tensile strength / MPa Elongation at break / % Bending strength / MPa Example 1 55.20 20.92 61.40 Example 2 50.05 13.12 55.60 Example 3 52.38 15.03 58.01 Example 7 43.51 6.28 49.63 Example 8 44.45 7.52 49.86 Example 9 47.58 10.47 51.62 Example 10 46.99 9.56 53.22 Example 11 45.31 8.01 50.21 Example 12 42.29 3.23 46.51 Comparative Example 1 48.68 11.23 52.25 Comparative Example 2 36.67 10.96 13.48

[0168] From the data in Table 2 we can see that:

[0169] (1) It can be seen from Examples 1 to 3 that the depolymerization and regeneration method of waste polyester provided by the present invention successfully prepares recycled polyester with excellent mechanical properties, with a tensile strength of more than 50.05 MPa, an elongation at break of more than 13.12%, and a flexural strength of more than 55.60 MPa.

[0170] (2) Combining Example 1 with Example 7 and Example 8, it can be seen that the endpoint pressure of the first uniform pressure reduction in Example 7 is too high or the endpoint pressure of the first uniform pressure reduction in Example 8 is too low, both of which lead to a significant decrease in the mechanical properties of the obtained recycled polyethylene terephthalate; this shows that the present invention further prefers that the endpoint pressure of the first uniform pressure reduction is 0.8 to 1.2 kPa, which further improves the mechanical properties of the obtained recycled polyester.

[0171] (3) Combining Example 1 with Examples 9 to 12, it can be seen that no matter the reduction rate of the first uniform pressure reduction in Example 9 is too high or the reduction rate of the second uniform pressure reduction in Example 11 is too high, or the reduction rate of the first uniform pressure reduction in Example 10 is too low or the reduction rate of the second uniform pressure reduction in Example 12 is too low, all of them lead to a significant decrease in the mechanical properties of the obtained recycled polyethylene terephthalate; thus, the present invention further prefers that the reduction rate of the first uniform pressure reduction is 5 to 10 kPa / min, and further prefers that the reduction rate of the second uniform pressure reduction is 0.5 to 1 kPa / min, thereby further improving the mechanical properties of the obtained recycled polyester.

[0172] (4) From Example 1, Comparative Examples 1 and 2, it can be seen that since the depolymerization efficiency and product yield in Comparative Example 1 are relatively low, the product may be mixed with incompletely depolymerized macromolecules, resulting in uneven molecular weight distribution of the polymerized recycled polyester and decreased mechanical properties. Since the depolymerization product in Comparative Example 2 is diethyl terephthalate (DTP), it cannot be directly repolymerized to form polyethylene terephthalate, and ethylene glycol needs to be additionally added. The ester exchange reaction between DTP and ethylene glycol requires a longer reaction time than BHET esterification. Therefore, the reaction product contains a large amount of small molecular substances, resulting in uneven molecular weight distribution of the polymerized polyester and decreased mechanical properties.

[0173] In summary, the present invention provides a method for depolymerizing waste polyester and a method for regenerating waste polyester after depolymerization. First, a hydrolysis reaction is carried out using a catalyst containing a specific carrier and a specific acidic active component, which is combined with a further alcoholysis reaction using a diol to achieve a dual depolymerization effect, so that the waste polyester is fully depolymerized and a depolymerization product with high purity is obtained. Subsequently, the depolymerization product is further regenerated, and the pressure and pressure reduction rate during the regeneration process are further optimized to successfully regenerate recycled polyester with excellent mechanical properties, thereby achieving high-value-added recycling of waste polyester.

[0174] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for depolymerizing waste polyester, characterized in that: The depolymerization method comprises the following steps: (1) mixing waste polyester, a first catalyst and water to carry out a hydrolysis reaction to obtain a hydrolyzate; (2) mixing the diol and the hydrolyzate of step (1) to carry out alcoholysis reaction to obtain a depolymerized product; Step (1) The first catalyst comprises a carrier and an acidic active component supported on the carrier; The carrier includes Hβ-25 molecular sieve and / or activated carbon; and the acidic active component includes phosphotungstic acid.

2. The depolymerization method according to claim 1, characterized in that Step (1) The loading amount of the acidic active component in the first catalyst is 50 to 60 wt%; Preferably, the mass ratio of the waste polyester, the first catalyst and water in step (1) is 1:(0.01-0.05):(1-12).

3. The depolymerization method according to claim 1 or 2, characterized in that The hydrolysis reaction in step (1) is carried out in a first protective gas atmosphere; Preferably, the first protective gas comprises nitrogen; Preferably, the temperature of the hydrolysis reaction in step (1) is 180-240°C; Preferably, the pressure of the hydrolysis reaction in step (1) is 0.15 to 0.30 MPa; Preferably, the hydrolysis reaction time in step (1) is 15 to 60 minutes; Preferably, the hydrolysis reaction in step (1) is accompanied by a first stirring; Preferably, the first stirring speed is 100-200 r / min.

4. The depolymerization method according to any one of claims 1 to 3, characterized in that The diol in step (2) includes any one of ethylene glycol, 1,3-propylene glycol or 1,4-butanediol or a combination of at least two thereof, preferably ethylene glycol; Preferably, the mass ratio of the diol in step (2) to the waste polyester in step (1) is (3-8):

1.

5. The depolymerization method according to any one of claims 1 to 4, characterized in that The alcoholysis reaction in step (2) is carried out in a second protective gas atmosphere; Preferably, the second protective gas comprises nitrogen; Preferably, the temperature of the alcoholysis reaction in step (2) is 180-240°C; Preferably, the pressure of the alcoholysis reaction in step (2) is 0.15 to 0.30 MPa; Preferably, the alcoholysis reaction time in step (2) is 60 to 120 minutes; Preferably, the alcoholysis reaction in step (2) is accompanied by a second stirring; Preferably, the rotation speed of the second stirring in step (2) is 100-200 r / min.

6. A method for regenerating waste polyester after depolymerization, characterized in that: The post-depolymerization regeneration method comprises mixing a second catalyst and a depolymerization product obtained by the depolymerization method according to any one of claims 1 to 5 to obtain a mixed system, and sequentially subjecting the mixed system to an esterification reaction and a polycondensation reaction to obtain a regenerated polyester.

7. The post-depolymerization regeneration method according to claim 6, characterized in that: The amount of the second catalyst added is 0.01% to 0.02% of the mass of the depolymerization product; Preferably, the second catalyst comprises any one or a combination of at least two of an antimony-based catalyst, a titanium-based catalyst or a germanium-based catalyst; Preferably, the antimony-based catalyst comprises any one or a combination of at least two of antimony glycol, antimony acetate or antimony trioxide; Preferably, the titanium-based catalyst comprises any one of tetraisopropyl titanate, tetra-n-butyl titanate or titanium ethylene glycol, or a combination of at least two thereof; Preferably, the germanium-based catalyst includes germanium acetate and / or germanium dioxide; Preferably, the mixing in the post-depolymerization regeneration method further comprises adding a heat stabilizer; Preferably, the amount of the heat stabilizer added is 0.005% to 0.05% of the mass of the depolymerized product; Preferably, the heat stabilizer includes any one of trimethyl phosphate, dimethyl phosphate, triphenyl phosphate, diphenyl phosphate, triphenyl phosphite, diphenyl phosphite, ammonium phosphite, ammonium dihydrogen phosphate, phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid or ammonium phosphate, or a combination of at least two thereof.

8. The post-depolymerization regeneration method according to claim 6 or 7, characterized in that: The mixing in the post-depolymerization regeneration method is performed in a third protective gas atmosphere; Preferably, the third protective gas comprises nitrogen; Preferably, the mixing temperature in the post-depolymerization regeneration method is 220-240°C; Preferably, the mixing pressure in the post-depolymerization regeneration method is 0.4 to 0.6 MPa; Preferably, the mixing time in the post-depolymerization regeneration method is 30 to 60 minutes.

9. The post-depolymerization regeneration method according to any one of claims 6 to 8, characterized in that: The temperature of the esterification reaction is 240-250°C; Preferably, the esterification reaction time is 15 to 30 minutes; Preferably, during the esterification reaction, the mixed system undergoes a first uniform pressure reduction; Preferably, the endpoint pressure of the first uniform pressure reduction is 0.8-1.2 kPa; Preferably, the reduction rate of the first uniform pressure reduction is 5-10 kPa / min.

10. The post-depolymerization regeneration method according to any one of claims 6 to 9, characterized in that: The polymerization reaction temperature is 265-290°C; Preferably, the polymerization reaction time is 10 to 60 minutes; Preferably, during the polymerization reaction, the mixed system undergoes a second uniform pressure reduction; Preferably, the endpoint pressure of the second uniform pressure reduction is ≤100 Pa; Preferably, the reduction rate of the second uniform pressure reduction is 0.5-1 kPa / min.

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