A method for hydrolyzing and regenerating waste PET products based on intermediate polymers

Abstract

The present invention belongs to the technical field of polymer material preparation and recycling, and relates to a method for hydrolyzing and regenerating waste PET products based on intermediate polymers, wherein superheated water vapor is introduced into the melt of waste PET products in a closed reactor, and then the intermediate polymer is kept warm to obtain the intermediate polymer, and then the intermediate polymer is added to the polymerization reaction system of PET, and the regenerated PET is obtained after the polymerization reaction is completed. The present invention realizes efficient hydrolysis and regeneration of PET at a relatively low temperature and in a relatively short time, reduces energy consumption and cost, combines hydrolysis and regeneration with polymerization technology to simplify the process, improves efficiency and economic benefits, and uses water vapor as a depolymerizing agent to realize environmental protection and efficient recycling and reuse of waste resources.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material preparation and recycling, and relates to a method for hydrolyzing and regenerating waste PET products based on mesomers. Background Art

[0002] Polyethylene terephthalate (PET) is the most commonly used engineering plastic and fiber raw material. It has excellent chemical stability in the natural environment and is difficult to degrade naturally. After being discarded, the continuous accumulation of PET in the environment will cause microplastic and toxin pollution problems. In recent years, the recycling and reuse of polyester materials has gradually become a research hotspot.

[0003] Chemical recycling technology, through molecular-level operations, can depolymerize waste PET products into derivative chemicals such as terephthalic acid and ethylene glycol. After separation and purification, these products can be "recycled" or "upgraded", which is currently recognized as the only recycling method that can achieve sustainable development. Among the many depolymerization agents, water is regarded as one of the ideal polyester chemical depolymerization agents because of its clean, easy-to-separate, pollution-free characteristics, and its effectiveness as a nucleophilic agent in PET depolymerization.

[0004] For example, patent CN103664513B discloses a method for hydrolyzing and recovering monomers of aromatic polyester composite materials. The method uses caustic soda aqueous solution and polar solvent as reaction medium, takes monomer recovery as the ultimate goal, and realizes the recovery of substances such as biphenyl diphenol. Patent application CN116769231A discloses a recovery method for mild and efficient selective hydrolysis of waste polymer materials based on polyester. The method uses a reaction solvent composed of diols, water, polar aprotic solvents or ethers as a medium, aiming to achieve selective separation and monomer recovery. Patent application CN115650848A discloses a method for recovering waste PET. The method first uses ethylene glycol for alcoholysis, and then adds water and heats for further hydrolysis. The ultimate goal is to achieve separation and recovery of high-purity BHET. Patent application CN101372810A discloses a method for preparing polyester multifunctional finishing agent for polyester using recycled polyester waste as raw material. The method prepares a multifunctional finishing agent with a certain molecular weight by hydrolysis, polymerization and sulfonation in the aqueous phase.

[0005] However, the hydrolysis of PET currently still faces the problems of high reaction temperature and harsh reaction conditions, which limits its widespread application. Therefore, the hydrolysis process is often used for selective separation and recovery, mainly focusing on the recovery of PTA and ethylene glycol monomers.

[0006] Therefore, there is an urgent need to develop a new PET hydrolysis recycling pathway with mild hydrolysis conditions and short process, and to combine it with the existing virgin polyester process to achieve flexible preparation of partial or full regeneration, thereby helping the management of waste plastics and environmental protection. Summary of the invention

[0007] The purpose of the present invention is to solve the problems existing in the prior art and provide a method for hydrolyzing and regenerating waste PET products based on a mesomer.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A method for hydrolyzing and regenerating waste PET products based on intermediate polymers, wherein superheated water vapor is introduced into a waste PET product melt in a closed reactor and then the melt is kept warm to obtain an intermediate polymer, and then the intermediate polymer is added to a PET polymerization reaction system, and regenerated PET is obtained after the polymerization reaction is completed, wherein the mass ratio of the superheated water vapor to the waste PET product melt is 2-10:1, and the structural formula of the intermediate polymer is as follows:

[0010] ;

[0011] In the formula, x is the degree of polymerization of the mesopolymer, x=3~7;

[0012] The polymerization reaction system of PET is a 5-reactor polymerization reaction system, including esterification 1 reactor, esterification 2 reactors, polycondensation 1 reactor, polycondensation 2 reactors, and final polycondensation reactor;

[0013] The preparation steps of recycled PET are as follows:

[0014] (1) reacting the intermediate polymer with a degree of polymerization of 3-4 and the intermediate polymer with a degree of polymerization of 5-7 with EG at 240-260°C and 0-0.5 MPa for 90-150 min to obtain ester 1 and ester 2, respectively;

[0015] (2) PTA, EG, and esterified product 1 (i.e., all esterified product 1 obtained in step (1)) are added to an esterification reactor 1, and reacted at 240-260° C. and 0-0.5 MPa for 120-180 min to obtain an intermediate product a;

[0016] (3) Add the intermediate product a (i.e., all the intermediate products a obtained in step (2)) and the esterified product 2 (i.e., all the esterified product 2 obtained in step (1)) into the esterification reactor 2, and react at 240-260° C. and 0-0.5 MPa for 120-180 min to obtain the intermediate product b. The structural formula of the intermediate product b is as follows:

[0017] ;

[0018] Wherein, y is the degree of polymerization of the intermediate product b, y=12~25;

[0019] (4) Add the intermediate product b into the polycondensation reactor 1, and react at 260-280°C and <200Pa for 60-90min to obtain the intermediate product c;

[0020] (5) Add the intermediate product c into the polycondensation reactor 2, and react at 260-280°C and <200Pa for 90-120min to obtain the intermediate product d;

[0021] (6) The intermediate product d is added into the final polycondensation reactor and reacted at 260-280°C and <200Pa for 90-120min to obtain recycled PET.

[0022] The present invention introduces superheated water vapor into a closed reactor and performs depolymerization at a certain temperature. The saturated steam pressure can make the superheated water vapor content in the melt of the waste PET product consistent and evenly distributed. With the appropriate amount of superheated water vapor, an intermediate polymer can be obtained after hydrolysis. The regeneration of the intermediate polymer has the characteristic of efficient preparation, that is, the intermediate polymer with a certain molecular weight is already in an intermediate state during the polymerization process. Compared with the regeneration process of the monomer, the condensation polymerization time can be greatly shortened.

[0023] If the closed reactor is replaced with a non-closed reactor, the system changes significantly. Non-closed containers allow superheated steam to continue to exist during the circulation process, but when a small amount of steam is used for depolymerization, the steam distribution in the melt becomes uneven due to the different positions where the steam is introduced, especially when the depolymerization time is short. Although increasing the amount of steam can improve the distribution, excess steam will cause some depolymers to further depolymerize into monomer products. In extreme cases, completely excessive steam will make the final product all monomer PTA. In contrast, closed reactors can ensure uniform dispersion of steam in the melt when a small amount of steam is introduced by precisely controlling the saturated steam pressure. This uniformity is crucial for controlling the degree of depolymerization and promoting the formation of intermediate polymers.

[0024] As the preferred technical solution:

[0025] In the above-mentioned method for hydrolyzing and regenerating waste PET products based on intermediate polymers, the temperature of the superheated water vapor is 110-130°C, the insulation temperature is 250-280°C, and the insulation time is 50-80 minutes.

[0026] In the above-mentioned method for hydrolyzing and regenerating waste PET products based on intermediate polymers, superheated water vapor is introduced into the melt of the waste PET products from the bottom or side of the closed reactor.

[0027] As described above, in the method for hydrolyzing and regenerating waste PET products based on intermediate polymers, the waste PET product melt is formed by melting the waste PET products, and the melting temperature is 250-270°C. The waste PET products include polyester bottle flakes, polyester waste silk, polyester textiles and polyester-cotton blended textiles, wherein the polyester textiles may be colored, and these colored polyester textiles need to be decolorized before recycling, or blended with masterbatches before spinning to adjust the color, thereby preparing dark-colored recycled PET; when the processed waste PET products are polyester-cotton blended textiles, it is necessary to first separate the cotton component through three-stage filtration (the filtration precision is 500 mesh, 200 mesh and 100 mesh, respectively), and then add the remaining PET components into the PET polymerization reaction system.

[0028] In the above-mentioned method for hydrolyzing and regenerating waste PET products based on intermediate polymers, the total mass of intermediate polymers with a degree of polymerization of 3-4 and intermediate polymers with a degree of polymerization of 5-7 is 10-100wt% of the mass of PTA, the mass ratio of intermediate polymers with a degree of polymerization of 3-4 and intermediate polymers with a degree of polymerization of 5-7 is 1-4:1-4, and the reaction molar ratio of intermediate polymers with a degree of polymerization of 3-4, intermediate polymers with a degree of polymerization of 5-7 or PTA to EG is 1:1.1-1.3. The reaction molar ratio refers to the ratio of two substances that react. Taking step (1) as an example, In step (1), the intermediate polymer with a degree of polymerization of 3 to 4 and the intermediate polymer with a degree of polymerization of 5 to 7 react with EG respectively, which is equivalent to the presence of two portions of EG (one portion reacts with the intermediate polymer with a degree of polymerization of 3 to 4, denoted as EG1, and the other portion reacts with the intermediate polymer with a degree of polymerization of 5 to 7, denoted as EG2). The reaction molar ratio of the intermediate polymer with a degree of polymerization of 3 to 4 and EG refers to the molar ratio of the intermediate polymer with a degree of polymerization of 3 to 4 and EG1, and the reaction molar ratio of the intermediate polymer with a degree of polymerization of 5 to 7 and EG refers to the molar ratio of the intermediate polymer with a degree of polymerization of 5 to 7 and EG2.

[0029] In the above-mentioned method for hydrolyzing and regenerating waste PET products based on intermediate polymers, the polymerization degree of the recycled PET is 100-150, the intrinsic viscosity is 0.65-0.90 dl / g, and the melting point is 250-260°C.

[0030] Beneficial effects:

[0031] (1) The present invention achieves efficient hydrolysis regeneration of PET at a lower reaction temperature and in a shorter reaction time, significantly reducing energy consumption and production costs.

[0032] (2) The present invention combines the hydrolysis regeneration process with the PET polymerization process, simplifies the recycling process, and improves production efficiency and economic benefits.

[0033] (3) The present invention uses water as a depolymerizing agent and superheated water vapor to participate in the reaction, thereby reducing pollution to the environment and achieving efficient recycling and reuse of waste resources. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0035] The following are the test methods for the relevant performance indicators in each embodiment:

[0036] Intrinsic viscosity: The test was conducted using an Ubbelohde viscometer with a capillary diameter of 0.7-0.8 mm. The specific process was as follows: 0.25 g of recycled PET sample was weighed using an electronic balance and dissolved in a phenol-tetrachloroethane mixed solvent with a mass ratio of 1:1. The solution was prepared into a concentration of 0.005 g / ml using a 50 ml volumetric flask and heated in a water bath at 60 to 70 °C to ensure that the sample was completely dissolved. After that, the prepared solution was transferred to a constant temperature water bath at 25 °C and kept for 10 min. The time required for the solution to flow through the upper and lower scale lines of the Ubbelohde viscometer was observed and recorded. Each sample was tested three times and the average value was taken as the final result. The following formula was used to calculate the intrinsic viscosity:

[0037] ;

[0038] ;

[0039] [ ]= ;

[0040] In the formula, is the relative viscosity, is the solution flow time (s), is the solvent flow time (s), is the specific viscosity, [ ] is the intrinsic viscosity, is the solution concentration (g / 100mL).

[0041] Degree of polymerization: The degree of polymerization is determined by calculating the viscosity average molecular weight. The specific process is: first, the intrinsic viscosity of the intermediate polymer, intermediate product b or recycled PET sample is measured using an Ubbelohde viscometer with a capillary diameter of 0.7~0.8mm. ], then, using the known solvent constants K, α (K = 2.1x10 -4, α=0.82) to calculate the viscosity average molecular weight M of the sample (calculation formula: [ ]=KM α ), finally, calculate the degree of polymerization of the sample (calculation formula: degree of polymerization = M / 228).

[0042] Melting point: The test was conducted using a Q-20 differential scanning calorimeter (DSC) from TA, USA. The specific process was as follows: after the recycled PET sample was vacuum dried at 80°C for 12 hours, 5-10 mg was weighed and placed in a DSC crucible; in a 50 mL / min nitrogen atmosphere, the temperature was raised to 200°C at 20°C / min and kept for 3 minutes to observe the thermal effect, then the temperature was lowered to -40°C at 10°C / min and kept for another 3 minutes, and finally the temperature was raised to 40°C at 10°C / min to complete the test cycle.

[0043] Example 1

[0044] A method for hydrolyzing and regenerating waste PET products based on medium polymer, the specific steps are as follows:

[0045] (1) Preparation of raw materials;

[0046] Waste PET product melt a: melted from waste PET products, with a melting temperature of 250°C;

[0047] Waste PET product melt b: melted from waste PET products, with a melting temperature of 270°C;

[0048] EG;

[0049] PTA;

[0050] (2) preparing mesopolymer a and mesopolymer b respectively;

[0051] The preparation process of the intermediate polymer a is as follows: after superheated water vapor with a temperature of 110° C. is introduced into the waste PET product melt a in the closed reactor from the bottom of the closed reactor, the temperature is kept at 280° C. for 55 minutes to obtain the intermediate polymer a with a polymerization degree of 3; wherein the mass ratio of the superheated water vapor to the waste PET product melt is 2:1;

[0052] The preparation process of the intermediate polymer b is as follows: after superheated water vapor with a temperature of 110° C. is introduced into the waste PET product melt b in the closed reactor from the side of the closed reactor, the temperature is kept at 275° C. for 50 minutes to obtain the intermediate polymer b with a polymerization degree of 5; wherein the mass ratio of the superheated water vapor to the waste PET product melt is 4:1;

[0053] (3) Preparation of recycled PET;

[0054] (3.1) Mesopolymer a and mesopolymer b were reacted with EG at 240°C and 0.5 MPa for 150 min to obtain ester 1 and ester 2 respectively;

[0055] (3.2) PTA, EG and ester 1 were added to the esterification reactor 1, and reacted at 250°C and 0.2 MPa for 155 min to obtain intermediate product a;

[0056] (3.3) Add the intermediate product a and esterification product 2 into the esterification reactor 2, and react at 250°C and 0.2 MPa for 155 min to obtain the intermediate product b with a degree of polymerization of 25;

[0057] (3.4) Add intermediate product b into polycondensation reactor 1 and react at 280°C and 100 Pa for 60 min to obtain intermediate product c;

[0058] (3.5) Add the intermediate product c into the polycondensation reactor 2 and react at 280°C and 100 Pa for 90 min to obtain the intermediate product d;

[0059] (3.6) The intermediate product d is added to the final polycondensation reactor and reacted at 280°C and 150 Pa for 90 min to obtain recycled PET;

[0060] In steps (3.1) to (3.6), the total mass of polymer a and polymer b is 10wt% of the mass of PTA, the mass ratio of polymer a to polymer b is 4:1, the reaction molar ratio of polymer a to EG is 1:1.1, the reaction molar ratio of polymer b to EG is 1:1.1, and the reaction molar ratio of PTA to EG is 1:1.3.

[0061] The degree of polymerization of the finally obtained recycled PET is 150, the intrinsic viscosity is 0.90 dl / g, and the melting point is 260°C.

[0062] Example 2

[0063] A method for hydrolyzing and regenerating waste PET products based on medium polymer, the specific steps are as follows:

[0064] (1) Preparation of raw materials;

[0065] Waste PET product melt a: melted from waste PET products, with a melting temperature of 255°C;

[0066] Waste PET product melt b: melted from waste PET products, with a melting temperature of 265°C;

[0067] EG;

[0068] PTA;

[0069] (2) preparing mesopolymer a and mesopolymer b respectively;

[0070] The preparation process of the intermediate polymer a is as follows: after superheated water vapor with a temperature of 130° C. is introduced into the waste PET product melt a in the closed reactor from the side of the closed reactor, the temperature is kept at 275° C. for 60 minutes to obtain the intermediate polymer a with a polymerization degree of 3; wherein the mass ratio of the superheated water vapor to the waste PET product melt is 4:1;

[0071] The preparation process of the intermediate polymer b is as follows: after superheated water vapor with a temperature of 125° C. is introduced into the waste PET product melt b in the closed reactor from the bottom of the closed reactor, the temperature is kept at 270° C. for 65 minutes to obtain the intermediate polymer b with a polymerization degree of 5; wherein the mass ratio of the superheated water vapor to the waste PET product melt is 5:1;

[0072] (3) Preparation of recycled PET;

[0073] (3.1) Mesopolymer a and mesopolymer b were reacted with EG at 260°C and 0 MPa for 90 min to obtain ester 1 and ester 2 respectively;

[0074] (3.2) PTA, EG and ester 1 were added to the esterification reactor 1, and reacted at 240°C and 0.5 MPa for 180 min to obtain intermediate product a;

[0075] (3.3) Add the intermediate product a and esterification product 2 into the esterification reactor 2, and react at 240°C and 0.5 MPa for 180 min to obtain the intermediate product b with a degree of polymerization of 22;

[0076] (3.4) Add intermediate product b into polycondensation reactor 1 and react at 275°C and 100 Pa for 65 min to obtain intermediate product c;

[0077] (3.5) Add the intermediate product c into the polycondensation reactor 2 and react at 275°C and 100 Pa for 95 min to obtain the intermediate product d;

[0078] (3.6) The intermediate product d is added to the final polycondensation reactor and reacted at 275°C and 150 Pa for 100 min to obtain recycled PET;

[0079] In steps (3.1) to (3.6), the total mass of intermediate polymer a and intermediate polymer b is 60wt% of the mass of PTA, the mass ratio of intermediate polymer a to intermediate polymer b is 1:1, the reaction molar ratio of intermediate polymer a to EG is 1:1.3, the reaction molar ratio of intermediate polymer b to EG is 1:1.3, and the reaction molar ratio of PTA to EG is 1:1.1.

[0080] The degree of polymerization of the recycled PET finally obtained is 115, the intrinsic viscosity is 0.71 dl / g, and the melting point is 253°C.

[0081] Example 3

[0082] A method for hydrolyzing and regenerating waste PET products based on medium polymer, the specific steps are as follows:

[0083] (1) Preparation of raw materials;

[0084] Waste PET product melt a: melted from waste PET products, with a melting temperature of 270°C;

[0085] Waste PET product melt b: melted from waste PET products, with a melting temperature of 250°C;

[0086] EG;

[0087] PTA;

[0088] (2) preparing mesopolymer a and mesopolymer b respectively;

[0089] The preparation process of the intermediate polymer a is as follows: after superheated water vapor with a temperature of 118° C. is introduced into the waste PET product melt a in the closed reactor from the side of the closed reactor, the temperature is kept at 265° C. for 70 minutes to obtain the intermediate polymer a with a polymerization degree of 4; wherein the mass ratio of the superheated water vapor to the waste PET product melt is 6:1;

[0090] The preparation process of the intermediate polymer b is as follows: after superheated water vapor with a temperature of 120° C. is introduced into the waste PET product melt b in the closed reactor from the side of the closed reactor, the temperature is kept at 255° C. for 60 minutes to obtain the intermediate polymer b with a polymerization degree of 7; wherein the mass ratio of the superheated water vapor to the waste PET product melt is 6:1;

[0091] (3) Preparation of recycled PET;

[0092] (3.1) Mesopolymer a and mesopolymer b were reacted with EG at 255°C and 0.1 MPa for 110 min to obtain ester 1 and ester 2 respectively;

[0093] (3.2) PTA, EG and ester 1 were added to the esterification reactor 1, and reacted at 255°C and 0.1 MPa for 140 min to obtain intermediate product a;

[0094] (3.3) Add the intermediate product a and esterification product 2 into the esterification reactor 2, and react at 255°C and 0.1 MPa for 140 min to obtain the intermediate product b with a degree of polymerization of 19;

[0095] (3.4) Add intermediate product b into polycondensation reactor 1 and react at 270°C and 50 Pa for 75 min to obtain intermediate product c;

[0096] (3.5) Add the intermediate product c into the polycondensation reactor 2 and react at 270°C and 100 Pa for 105 min to obtain the intermediate product d;

[0097] (3.6) The intermediate product d was added to the final polycondensation reactor and reacted at 270°C and 150 Pa for 105 min to obtain recycled PET;

[0098] In steps (3.1) to (3.6), the total mass of polymer a and polymer b is 40wt% of the mass of PTA, the mass ratio of polymer a to polymer b is 1:4, the reaction molar ratio of polymer a to EG is 1:1.25, the reaction molar ratio of polymer b to EG is 1:1.25, and the reaction molar ratio of PTA to EG is 1:1.2.

[0099] The degree of polymerization of the finally obtained recycled PET is 100, the intrinsic viscosity is 0.65 dl / g, and the melting point is 250°C.

[0100] Example 4

[0101] A method for hydrolyzing and regenerating waste PET products based on medium polymer, the specific steps are as follows:

[0102] (1) Preparation of raw materials;

[0103] Waste PET product melt a: melted from waste PET products, with a melting temperature of 260°C;

[0104] Waste PET product melt b: melted from waste PET products, with a melting temperature of 260°C;

[0105] EG;

[0106] PTA;

[0107] (2) preparing mesopolymer a and mesopolymer b respectively;

[0108] The preparation process of the intermediate polymer a is as follows: after superheated water vapor with a temperature of 125° C. is introduced into the waste PET product melt a in the closed reactor from the bottom of the closed reactor, the temperature is kept at 250° C. for 80 minutes to obtain the intermediate polymer a with a polymerization degree of 4; wherein the mass ratio of the superheated water vapor to the waste PET product melt is 10:1;

[0109] The preparation process of the intermediate polymer b is as follows: after superheated water vapor with a temperature of 130° C. is introduced into the waste PET product melt b in the closed reactor from the bottom of the closed reactor, the temperature is kept at 250° C. for 70 minutes to obtain the intermediate polymer b with a polymerization degree of 6; wherein the mass ratio of the superheated water vapor to the waste PET product melt is 5:1;

[0110] (3) Preparation of recycled PET;

[0111] (3.1) Mesopolymer a and mesopolymer b were reacted with EG at 250°C and 0.2 MPa for 140 min to obtain ester 1 and ester 2, respectively;

[0112] (3.2) PTA, EG and ester 1 were added to the esterification reactor 1, and reacted at 260°C and 0 MPa for 120 min to obtain intermediate product a;

[0113] (3.3) Add the intermediate product a and esterification product 2 into the esterification reactor 2, and react at 260°C and 0 MPa for 120 min to obtain the intermediate product b with a degree of polymerization of 16;

[0114] (3.4) Add intermediate product b into polycondensation reactor 1 and react at 265°C and 50 Pa for 80 min to obtain intermediate product c;

[0115] (3.5) Add the intermediate product c into the polycondensation reactor 2 and react at 265°C and 150 Pa for 115 min to obtain the intermediate product d;

[0116] (3.6) The intermediate product d was added to the final polycondensation reactor and reacted at 265°C and 150 Pa for 110 min to obtain recycled PET;

[0117] In steps (3.1) to (3.6), the total mass of polymer a and polymer b is 80wt% of the mass of PTA, the mass ratio of polymer a to polymer b is 2:3, the reaction molar ratio of polymer a to EG is 1:1.2, the reaction molar ratio of polymer b to EG is 1:1.2, and the reaction molar ratio of PTA to EG is 1:1.25.

[0118] The degree of polymerization of the recycled PET finally obtained is 120, the intrinsic viscosity is 0.74 dl / g, and the melting point is 255°C.

[0119] Example 5

[0120] A method for hydrolyzing and regenerating waste PET products based on medium polymer, the specific steps are as follows:

[0121] (1) Preparation of raw materials;

[0122] Waste PET product melt a: melted from waste PET products, with a melting temperature of 265°C;

[0123] Waste PET product melt b: melted from waste PET products, with a melting temperature of 255°C;

[0124] EG;

[0125] PTA;

[0126] (2) preparing mesopolymer a and mesopolymer b respectively;

[0127] The preparation process of the intermediate polymer a is as follows: after superheated water vapor with a temperature of 114° C. is introduced into the waste PET product melt a in the closed reactor from the side of the closed reactor, the temperature is kept at 255° C. for 75 minutes to obtain the intermediate polymer a with a polymerization degree of 4; wherein the mass ratio of the superheated water vapor to the waste PET product melt is 9:1;

[0128] The preparation process of the intermediate polymer b is as follows: after superheated water vapor with a temperature of 115° C. is introduced into the waste PET product melt b in the closed reactor from the bottom of the closed reactor, the temperature is kept at 250° C. for 65 minutes to obtain the intermediate polymer b with a polymerization degree of 7; wherein the mass ratio of the superheated water vapor to the waste PET product melt is 3:1;

[0129] (3) Preparation of recycled PET;

[0130] (3.1) Mesopolymer a and mesopolymer b were reacted with EG at 245°C and 0.3 MPa for 120 min to obtain ester 1 and ester 2, respectively;

[0131] (3.2) PTA, EG and ester 1 were added to the esterification reactor 1, and reacted at 245°C and 0.3 MPa for 170 min to obtain intermediate product a;

[0132] (3.3) Add the intermediate product a and esterification product 2 into the esterification reactor 2, and react at 245°C and 0.3 MPa for 170 min to obtain the intermediate product b with a degree of polymerization of 12;

[0133] (3.4) Add intermediate product b into polycondensation reactor 1 and react at 260°C and 100 Pa for 90 min to obtain intermediate product c;

[0134] (3.5) Add the intermediate product c into the polycondensation reactor 2 and react at 260°C and 150 Pa for 120 min to obtain the intermediate product d;

[0135] (3.6) The intermediate product d is added to the final polycondensation reactor and reacted at 260°C and 150 Pa for 120 min to obtain recycled PET;

[0136] In steps (3.1) to (3.6), the total mass of intermediate polymer a and intermediate polymer b is 100wt% of the mass of PTA, the mass ratio of intermediate polymer a to intermediate polymer b is 3:2, the reaction molar ratio of intermediate polymer a to EG is 1:1.2, the reaction molar ratio of intermediate polymer b to EG is 1:1.2, and the reaction molar ratio of PTA to EG is 1:1.2.

[0137] The degree of polymerization of the recycled PET finally obtained is 140, the intrinsic viscosity is 0.81 dl / g, and the melting point is 256°C.

Claims

1. A method for hydrolyzing and regenerating waste PET products based on intermediate polymers, characterized in that: Superheated water vapor is introduced into the waste PET product melt in a closed reactor and then kept warm to obtain a mesopolymer, which is then added to a PET polymerization reaction system. After the polymerization reaction is completed, recycled PET is obtained, wherein the mass ratio of the superheated water vapor to the waste PET product melt is 2 to 10:1, and the structure of the mesopolymer is as follows: Wherein, x is the degree of polymerization of the mesopolymer, x = 3 to 7; The temperature of superheated steam is 110-130℃, the insulation temperature is 250~280℃, and the insulation time is 50~80min; The polymerization reaction system of PET is a 5-reactor polymerization reaction system, including esterification 1 reactor, esterification 2 reactors, polycondensation 1 reactor, polycondensation 2 reactors, and final polycondensation reactor; The preparation steps of recycled PET are as follows: (1) reacting a mesopolymer having a degree of polymerization of 3 to 4 and a mesopolymer having a degree of polymerization of 5 to 7 with EG at 240 to 260° C. and 0 to 0.5 MPa for 90 to 150 min to obtain esters 1 and esters 2, respectively; (2) PTA, EG and esterification product 1 are added to an esterification reactor 1, and reacted at 240-260° C. and 0-0.5 MPa for 120-180 min to obtain an intermediate product a; (3) adding the intermediate product a and the esterified product 2 into the esterification reactor 2, and reacting at 240-260° C. and 0-0.5 MPa for 120-180 min to obtain the intermediate product b; (4) adding the intermediate product b into the polycondensation reactor 1, reacting at 260-280° C. and <200 Pa for 60-90 min to obtain the intermediate product c; (5) adding the intermediate product c into the polycondensation reactor 2, reacting at 260-280° C. and <200 Pa for 90-120 min to obtain the intermediate product d; (6) The intermediate product d is added to the final polycondensation reactor and reacted at 260-280° C. and <200 Pa for 90-120 min to obtain recycled PET.

2. The method for hydrolyzing and regenerating waste PET products based on intermediate polymer according to claim 1, characterized in that: Superheated water vapor is introduced into the melt of waste PET products from the bottom or side of the closed reactor.

3. The method for hydrolyzing and regenerating waste PET products based on intermediate polymer according to claim 1, characterized in that: The waste PET product melt is formed by melting the waste PET products, and the melting temperature is 250-270°C.

4. The method for hydrolyzing and regenerating waste PET products based on intermediate polymer according to claim 1, characterized in that: The total mass of the intermediate polymers with a degree of polymerization of 3 to 4 and the intermediate polymers with a degree of polymerization of 5 to 7 is 10 to 100 wt % of the mass of PTA, the mass ratio of the intermediate polymers with a degree of polymerization of 3 to 4 and the intermediate polymers with a degree of polymerization of 5 to 7 is 1 to 4:1 to 4, and the reaction molar ratio of the intermediate polymers with a degree of polymerization of 3 to 4, the intermediate polymers with a degree of polymerization of 5 to 7 or PTA to EG is 1:1.1 to 1.

3.

5. The method for hydrolyzing and regenerating waste PET products based on intermediate polymer according to claim 4, characterized in that: The polymerization degree of recycled PET is 100-150, the intrinsic viscosity is 0.65-0.90 dl / g, and the melting point is 250-260°C.

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