A method for regenerating waste PET by alcoholysis based on intermediate polymer

Abstract

The present invention relates to a waste PET alcoholysis regeneration method based on intermediate polymer, wherein the melt obtained by melting the waste PET is transported to a closed reactor, superheated diol steam is introduced into the closed reactor to depolymerize the waste PET to obtain intermediate polymer, and then the intermediate polymer is sent to the polymerization stage of the original polyester for reaction, and the reaction is terminated to prepare the regenerated polyester; the degree of polymerization of the intermediate polymer is 3 to 30, and the molecular weight distribution PDI is less than 3. The present invention can realize depolymerization in a homogeneous state, avoid the process of gradual depolymerization of solid-phase PET from the surface layer to the inner layer, realize the preparation of intermediate polymer by controlling the degree of polymerization of the depolymerization product, and increase the uniformity after repolymerization.

Description

Technical Field

[0001] The invention belongs to the technical field of polymerization and relates to a method for regenerating waste PET by alcoholysis based on a medium polymer. Background Art

[0002] Ethylene terephthalate (PET) is the most commonly used engineering plastic and fiber raw material. It has good chemical stability in the natural environment, but it cannot be naturally degraded. The continuous accumulation in the environment after disposal will cause microplastic and toxin pollution problems. Therefore, the recycling and reuse of PET has gradually become a research hotspot in recent years. Chemical recycling can depolymerize PET into terephthalic acid, ethylene glycol and other derivative chemicals at the molecular level, which can be "recycled" or "upgraded" after separation and purification. Ethylene glycol is one of the raw materials for polyester polymerization reaction, and it can also be used as a nucleophilic reagent to depolymerize polyester. After alcoholysis, no other chemical components will be introduced, making it an ideal PET chemical depolymerizer.

[0003] For example, patent CN113214458A discloses a method for preparing recycled polyester by efficient alcoholysis of waste polyester, reporting the use of oligomers and ethylene glycol to depolymerize PET to BHET and then repolymerize it to form recycled polyester. Patent CN115141363A discloses a method for preparing recycled cationic polyester using waste polyester, depolymerizing PET to BHET copolymerized cationic recycled polyester by diol. Patent CN117999305A discloses a method for manufacturing recycled polyester resin, reporting the one-step addition of polycarboxylic acid and polyol during depolymerization, followed by direct esterification, and then polycondensation to prepare recycled PET, and the direct regeneration after depolymerization is achieved by adding polyvalent raw materials.

[0004] At present, alcoholysis recycling of PET uses one or more diols and polyols as solvents to depolymerize waste PET. The target product of depolymerization is BHET or alcoholysis solution, which is then regenerated by polycondensation or functionalization. From the perspective of chemical structure, the repolymerization of mixed alcoholysis solution belongs to secondary regeneration, the polymer structure is difficult to control, and the physical and chemical properties are changed; from the perspective of the depolymerization process, the alcoholysis temperature is usually between 190 and 210 ° C, PET usually depolymerizes in the solid phase at the current temperature, depolymerization occurs from the surface, the degree of polymerization of the alcoholysis solution is difficult to control, and the molecular weight distribution is wide. In addition, the current target product of alcoholysis regeneration of PET is small molecule high-purity BHET or DMT, the cost is much higher than that of virgin polyester, which limits its large-scale promotion and application.

[0005] Therefore, it is of great significance to study a method for alcoholysis regeneration of waste PET based on intermediate polymers to solve the problems of difficult control of polymer structure, wide molecular weight distribution, and limited large-scale promotion and application in the existing technology. Summary of the invention

[0006] The purpose of the invention is to solve the problems existing in the prior art and provide a method for regenerating waste PET by alcoholysis based on a medium polymer.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for regenerating waste PET by alcoholysis based on intermediate polymers, wherein the melt obtained by melting the waste PET is transported to a closed reactor, superheated diol steam is introduced into the closed reactor to depolymerize the waste PET to obtain intermediate polymers, and then the intermediate polymers are sent to the polymerization stage of virgin polyester for reaction, and the regenerated polyester is prepared after the reaction is completed;

[0009] The degree of polymerization of the mesopolymer is 3~30, and the molecular weight distribution PDI is <3.

[0010] In the prior art, PET alcoholysis recovery is mainly through the depolymerization of PET in a diol solution. The depolymerization temperature is usually below the melting point of PET. Due to the different depolymerization efficiencies from the outside to the inside, in order to make the alcoholysis solution depolymerize evenly, the final target of alcoholysis is mainly BHET and DMT. The depolymerization is carried out with excess diol as the medium. If the chemical method of PET to PET is used for recovery, then alcoholysis to monomers such as BHET or DMT is not the best recovery solution. The method of repolymerizing PET from PET to intermediate polymers has a short process, low energy consumption and high efficiency. The existing method of using excessive diol for depolymerization cannot achieve the degree of polymerization control of the intermediate polymer; the PET alcoholysis adopted by the present invention is to pass the superheated diol vapor into the polyester melt to achieve alcoholysis, pass the superheated diol vapor into the closed reactor, inject the polyester melt into the closed reactor, and depolymerize at a certain temperature. The saturated vapor pressure can make the diol content in the melt consistent and evenly distributed, so as to depolymerize to obtain the intermediate polymer with uniform molecular weight distribution, realize homogenization, and avoid the uneven depolymerization from the surface layer to the inner layer in the solid state.

[0011] As the preferred technical solution:

[0012] A method for alcoholysis regeneration of waste PET based on intermediate polymer as described above, wherein the waste PET is waste PET bottle flakes, polyester waste yarn, polyester waste cloth or waste textiles containing polyester; the melting temperature of the waste PET is 250-270°C; single-component waste PET such as waste PET bottle flakes, polyester waste yarn, polyester waste cloth can be directly depolymerized and regenerated; waste textiles containing polyester include colored polyester textiles and polyester-cotton blended textiles, and the colored polyester textiles need to be decolorized before being recycled to prepare recycled PET or blended with masterbatch before spinning to complement the color to prepare dark recycled PET, and the polyester-cotton blended textiles need to filter out the cotton component before the intermediate polymer melt is conveyed (the cotton filtration is a three-stage filtration with filtration precisions of 500 mesh, 200 mesh and 100 mesh respectively) for recycling and reuse;

[0013] In the above-mentioned method for alcoholysis regeneration of waste PET based on intermediate polymer, the diol is ethylene glycol, 1,3-propylene glycol, 1,4-butanediol or 1,5-pentanediol.

[0014] In the above-mentioned method for alcoholysis regeneration of waste PET based on intermediate polymer, the temperature of superheated diol vapor is 250-270°C, the mass ratio of superheated diol vapor to melt is 2-10:1, and the depolymerization time is 10-30 min.

[0015] As described above, a method for alcoholysis regeneration of waste PET based on a mid-polymer, the general structural formula of the mid-polymer is:

[0016] ;

[0017] Where x = 3~30, R is (CH 2 ) z , z=2~5; by controlling the mass ratio of superheated diol vapor to melt and the depolymerization time, the value range of x can be controlled, thereby regulating the polymerization degree of the intermediate polymer.

[0018] The above-mentioned method for alcoholysis regeneration of waste PET based on intermediate polymer has the following specific process: the waste PET is melted and transported to a closed reactor, and then superheated diol vapor is introduced into the closed container to depolymerize the waste PET to obtain intermediate polymer, and then the intermediate polymer is sent to different polymerization stages of virgin PET according to the degree of polymerization of the intermediate polymer, so as to polymerize and obtain recycled polyester; wherein the addition amount of the intermediate polymer is 10-100wt% of the recycled polyester (when the addition amount is 100wt%, there is no virgin PET);

[0019] By controlling the flow rate and residence time of superheated diol vapor, PET can be controllably depolymerized into intermediate polymers with a certain degree of polymerization; according to different degrees of polymerization, the intermediate polymers transport the original PET to different polymerization stages to achieve polyester regeneration.

[0020] The above-mentioned method for regenerating waste PET by alcoholysis based on intermediate polymer, the polymerization of virgin PET includes 5 polymerization stages, which is a five-reactor polymerization, and the devices used include a first esterification reactor, a second esterification reactor, a first precondensation reactor, a second precondensation reactor and a final polycondensation reactor;

[0021] When x is 3-5, the intermediate polymer is sent to the first esterification reactor of the virgin PET;

[0022] When x is 6-12, the intermediate polymer is sent to the second esterification reactor of the virgin PET;

[0023] When x is 13-25, the intermediate polymer is sent to the first precondensation reactor of the virgin PET;

[0024] When x is 26-30, the intermediate polymer is sent to the second precondensation reactor of the original PET.

[0025] In the above-mentioned method for alcoholysis regeneration of waste PET based on intermediate polymer, the temperature of the first esterification kettle and the second esterification kettle is 240~260℃, and the pressure is 0~0.5MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final condensation kettle is 260~280℃, and the pressure is <200Pa.

[0026] As described in the above item, a method for regenerating waste PET by alcoholysis based on intermediate polymer, the degree of polymerization of the obtained recycled PET is 100-150, the intrinsic viscosity is 0.65-0.90 dl / g, and the melting point is 250-260°C.

[0027] At present, in the prior art, PET alcoholysis recovery is mainly through the depolymerization of PET in a diol solution. The depolymerization temperature is usually below the melting point of PET. Due to the different depolymerization efficiencies from the outside to the inside, in order to make the alcoholysis solution depolymerize evenly, the final target of alcoholysis is mainly BHET and DMT, and the depolymerization is carried out with excess diol as the medium. If you want to obtain functionalized recycled polyester, use BHET or DMT as the raw material and polymerize it with the functionalized monomer. Since the chemical method of functionalized PET is limited by complex components, it is difficult to recycle functionalized PET, because the BHET or DMT obtained after depolymerization will contain small molecules produced by the depolymerization of the functional components, which affects the purity of BHET or DMT. Even if the purity of BHET or DMT is improved by purification, it will increase the difficulty of the process and still waste the original functional components in the raw materials;

[0028] The alcoholysis of PET used in the present invention is to pass the superheated diol vapor into the waste functionalized PET to realize alcoholysis; the hot diol vapor is directly passed into the closed reactor to carry out alcoholysis on the waste functionalized PET melt to realize homogenization, avoiding the uneven depolymerization from the surface layer to the inner layer in the solid state; at this time, the intermediate polymer obtained by alcoholysis is an intermediate polymer with functional components, and then the functional monomer can be added according to the demand to adjust the proportion of the functional components (functional monomers different from the functional components in the raw materials can also be added), so as to obtain the functionalized recycled polyester desired by the technicians. Therefore, the method of the present invention not only effectively recovers the waste functionalized PET, shortens the process, but also makes full use of the functional components therein.

[0029] A method for alcoholysis regeneration of waste functionalized PET based on intermediate polymer, wherein the melt obtained by melting the waste functionalized PET is transported to a closed reactor, superheated diol steam is introduced into the closed reactor to depolymerize the waste functionalized PET to obtain intermediate polymer, and then functional monomers and diols are added to the closed reactor to co-esterify the intermediate polymer, and the co-esterified product is sent to the polymerization stage of the original polyester for reaction, and the functionalized regenerated polyester is prepared after the reaction is completed;

[0030] The degree of polymerization of the mesopolymer is 3~30, and the molecular weight distribution PDI is <3.

[0031] As the preferred technical solution:

[0032] A method for alcoholysis regeneration of waste functionalized PET based on a mid-polymer as described above, wherein the waste functionalized PET is flame-retardant PET or cationic dye-dyeable PET; the melting temperature of the waste functionalized PET is 220-240°C;

[0033] In the above-mentioned method for alcoholysis regeneration of waste functionalized PET based on intermediate polymer, the diol is one or more of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol and 1,5-pentanediol.

[0034] In the above-mentioned method for alcoholysis regeneration of waste functionalized PET based on intermediate polymer, the functional monomer is sodium 5-sulfonate of isophthalic acid, 3-hydroxyphenylphosphatidyl propionic acid, [(6-oxy-6H-dibenzo-(C,E)(1,2)-oxaphosphorin-6-one)-methyl]-succinic acid or isophthalic acid.

[0035] As described above, in the alcoholysis regeneration method of waste functionalized PET based on the intermediate polymer, the temperature of the superheated diol vapor is 250-270°C, the mass ratio of the superheated diol vapor to the melt is 2-10:1, and the depolymerization time is 10-30 min; the co-esterification temperature is 220-240°C, the co-esterification time is 2-4 h, the co-esterification pressure is 0.2-0.5 MPa, the amount of functional monomer added is 5-10 wt% of the intermediate polymer, and the alcohol-acid ratio of the diol added after depolymerization to obtain the intermediate polymer to the functional monomer is 1.1-1.3:1.

[0036] As described above, the alcoholysis regeneration method of waste functionalized PET based on the intermediate polymer has the general structural formula of:

[0037]

[0038] Among them, x = 3~30, by controlling the mass ratio of superheated diol vapor to melt and the depolymerization time, the value range of x can be controlled, thereby regulating the degree of polymerization of the intermediate polymer, R is (CH 2 ) z , z = 2~5, R0 It is a functional component, and the raw material corresponding to the functional component is a functional monomer. The functional monomer corresponding to the functional component in the mesopolymer may be the same substance as the functional monomer added after depolymerization to obtain the mesopolymer, or it may not be.

[0039] The above-mentioned method for alcoholysis regeneration of waste functionalized PET based on intermediate polymer has the following specific process: the waste functionalized PET is melted and transported to a closed reactor, and then superheated diol steam is introduced into the closed container to depolymerize the waste PET to obtain intermediate polymer, and then functional monomers and diols are added to the closed reactor to co-esterify with the intermediate polymer, and then the co-esterified product is sent to different polymerization stages of virgin PET according to the degree of polymerization of the intermediate polymer, so as to polymerize and obtain regenerated functional polyester; wherein the addition amount of the intermediate polymer is 10-100wt% of the functionalized regenerated polyester, and when the addition amount is 100wt%, there is no virgin PET;

[0040] By controlling the inflow rate and residence time of superheated diol vapor, PET can be controllably depolymerized into intermediate polymers with a certain degree of polymerization; according to different degrees of polymerization, the intermediate polymers are transported to the same polymerization stage of the original PET to achieve polyester regeneration.

[0041] The above-mentioned method for alcoholysis regeneration of waste functionalized PET based on intermediate polymer, the polymerization of virgin PET includes 5 polymerization stages, which is a five-reactor polymerization, and the devices used include a first esterification reactor, a second esterification reactor, a first precondensation reactor, a second precondensation reactor and a final polycondensation reactor;

[0042] When x is 3-5, the intermediate polymer is sent to the first esterification reactor of the virgin PET;

[0043] When x is 6-12, the intermediate polymer is sent to the second esterification reactor of the virgin PET;

[0044] When x is 13-25, the intermediate polymer is sent to the first precondensation reactor of the virgin PET;

[0045] When x is 26-30, the intermediate polymer is sent to the second precondensation reactor of the original PET.

[0046] In the above-mentioned method for alcoholysis regeneration of waste functionalized PET based on intermediate polymer, the temperature of the first esterification kettle and the second esterification kettle is 240~260℃, and the pressure is 0~0.5MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final condensation kettle is 260~280℃, and the pressure is <200Pa.

[0047] As described in the above item, a method for alcoholysis regeneration of waste functionalized PET based on intermediate polymer, the degree of polymerization of the obtained recycled PET is 100-150, the intrinsic viscosity is 0.65-0.85 dl / g, and the melting point is 230-250°C.

[0048] Beneficial effects:

[0049] (1) The present invention provides a method for regenerating waste PET by alcoholysis based on intermediate polymers. First, the waste PET is melted and then transported to a reactor. Subsequently, superheated diol is introduced into the melt. Depolymerization can be achieved in a homogeneous state, thereby avoiding the process in which the solid phase PET gradually depolymerizes from the surface layer to the inner layer. The degree of polymerization of the depolymerization product can be controlled to prepare the intermediate polymer, and the uniformity can be increased after polymerization.

[0050] (2) The present invention is a method for regenerating waste PET by alcoholysis based on intermediate polymers. Diol is used as one of the raw materials for polyester synthesis. The introduction of diol as a depolymerizing agent into the molecular chain does not affect its repolymerization. The chemical structure of the alcoholysis product is mainly a hydroxyl alcohol structure, and can directly undergo ester exchange to achieve polycondensation reaction.

[0051] (3) In the alcoholysis regeneration method of waste PET based on intermediate polymer of the present invention, diol is not directly used as a medium, but is directly passed into the melt in the form of superheated steam. The degree of polymerization of the intermediate polymer is controlled by flow rate and time. Under superheated conditions, excess diol vapor overflows from the melt and directly accumulates at the upper end of the reactor, where it can be directly recovered and reused, thereby greatly reducing costs.

[0052] (4) In the alcoholysis regeneration method of waste PET based on intermediate polymers of the present invention, intermediate polymers with different polymerization degrees can be added to the first esterification kettle, the second esterification kettle, the first pre-polycondensation kettle, the second pre-polycondensation kettle and the final polycondensation kettle, which are connected with the original polyester preparation process, and can realize partial addition or full regeneration process. The addition ratio of recycled polyester can be adjusted according to actual needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 The schematic diagram of a method for alcoholysis regeneration of waste PET based on intermediate polymer;

[0054] Figure 2 The schematic diagram is a method for alcoholysis regeneration of waste functionalized PET based on intermediate polymer; wherein y is the original degree of polymerization of the functional PET before depolymerization. DETAILED DESCRIPTION

[0055] 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.

[0056] The test methods involved in the performance indicators of the present invention are as follows:

[0057] Degree of polymerization: Calculated by viscosity-average molecular weight; calculation formula: [η] = KM α , x = M / 228; where K and α are solvent constants; the test solvent is phenol / tetrachloroethane with a mass ratio of 1:1; at 25°C, K = 2.1×10 -4 , α=0.82), [η] is the test relative viscosity, M is the average molecular weight of the polymer, and x is the degree of polymerization. Intrinsic viscosity: tested using an Ubbelohde viscometer with a capillary diameter of 0.7~0.8mm. Use an electronic balance to take 0.25g of the sample to be tested and dissolve it in a phenol-tetrachloroethane solvent with a mass ratio of 1:1. Use a 50ml volumetric flask to prepare a solution with a concentration of 0.005g / ml, and dissolve it completely in a 60~70℃ water bath. Then put the prepared solution into a 25℃ constant temperature water bath for ten minutes; the temperature of the constant temperature water bath is 25±0.1℃. Observe and record the solution flowing through the upper and lower scale lines of the Ubbelohde viscometer, take the average of three tests for each sample as the final result, and the calculation process is according to the following formula.

[0058] Formula (1);

[0059] Formula (2);

[0060] Formula (3);

[0061] Where: —Relative viscosity; —Solution flow time (s); —Solvent flow time (s); — specific viscosity; ]—Intrinsic viscosity.

[0062] Molecular weight distribution PDI: The number average molecular weight and molecular weight distribution (PDI) of the samples were tested using a GPC-50 gel permeation chromatograph produced by PL Company of the United Kingdom. The equipment was equipped with a differential refractometer and a PL gel column (5µm mixed-C), with 1,1,1,3,3,3-hexafluoro-2-propanol as the eluent and a flow rate of 1mL / min. During the test, the sample was dried and dissolved in hexafluoroisopropanol to prepare a 1.0mg / mL solution, and the test was carried out when the column temperature reached 40±1℃.

[0063] The raw materials in the embodiments of the present invention are derived from bulk chemical raw materials.

[0064] Example 1

[0065] A method for regenerating waste PET by alcoholysis based on intermediate polymer, such as Figure 1 As shown, the specific steps are as follows:

[0066] (1) Preparation of raw materials:

[0067] Waste PET: Waste PET bottle flakes;

[0068] Diol: ethylene glycol;

[0069] (2) The waste PET is melted at 250°C to obtain a melt which is transported to a closed reactor, and then superheated diol vapor at 250°C is introduced into the closed container to depolymerize the waste PET for 30 minutes to obtain a polymer having a degree of polymerization of 3 and a molecular weight distribution (PDI) of 1.3;

[0070] Among them, the mass ratio of superheated diol vapor to melt is 10:1; the structural formula of the intermediate polymer is:

[0071] ;

[0072] (3) According to the degree of polymerization of the intermediate polymer, the intermediate polymer is sent to the first esterification kettle of the virgin PET for polymerization reaction. The polymerization of the virgin PET includes 5 polymerization stages. The equipment used includes the first esterification kettle, the second esterification kettle, the first pre-polycondensation kettle, the second pre-polycondensation kettle and the final polycondensation kettle. After the reaction is completed, the recycled polyester is prepared;

[0073] Among them, the addition amount of the intermediate polymer is 100wt% of the recycled polyester; the temperature of the first esterification kettle and the second esterification kettle is 240℃, and the pressure is 0.5MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final condensation kettle is 260℃, and the pressure is 100Pa.

[0074] The degree of polymerization of the recycled PET finally obtained is 150, the intrinsic viscosity is 0.9 dl / g, and the melting point is 260°C.

[0075] Example 2

[0076] A method for regenerating waste PET by alcoholysis based on intermediate polymer, the specific steps are as follows:

[0077] (1) Preparation of raw materials:

[0078] Waste PET: waste polyester yarn;

[0079] Diol: 1,3-propylene glycol;

[0080] (2) The waste PET is melted at a temperature of 255°C to obtain a melt which is transported to a closed reactor, and then superheated diol vapor at 255°C is introduced into the closed container to depolymerize the waste PET for 25 minutes to obtain a polymer having a degree of polymerization of 8 and a molecular weight distribution (PDI) of 1.7;

[0081] Among them, the mass ratio of superheated diol vapor to melt is 6:1; the structural formula of the intermediate polymer is:

[0082] ;

[0083] (3) According to the degree of polymerization of the intermediate polymer, the intermediate polymer is sent to the second esterification kettle of the virgin PET for polymerization reaction. The polymerization of the virgin PET includes 5 polymerization stages. The equipment used includes the first esterification kettle, the second esterification kettle, the first pre-polycondensation kettle, the second pre-polycondensation kettle and the final polycondensation kettle. After the reaction is completed, the recycled polyester is prepared;

[0084] Among them, the addition amount of the intermediate polymer is 75wt% of the recycled polyester; the temperature of the first esterification kettle and the second esterification kettle is 245℃, and the pressure is 0.4MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final condensation kettle is 265℃, and the pressure is 100Pa.

[0085] The degree of polymerization of the recycled PET finally obtained is 130, the intrinsic viscosity is 0.82 dl / g, and the melting point is 257°C.

[0086] Example 3

[0087] A method for regenerating waste PET by alcoholysis based on intermediate polymer, the specific steps are as follows:

[0088] (1) Preparation of raw materials:

[0089] Waste PET: Waste polyester fabric;

[0090] Diol: 1,4-butanediol;

[0091] (2) The waste PET is melted at 260°C to obtain a melt which is transported to a closed reactor, and then superheated diol vapor at 260°C is introduced into the closed container to depolymerize the waste PET for 20 minutes to obtain a polymer with a degree of polymerization of 21 and a molecular weight distribution (PDI) of 2.3;

[0092] Among them, the mass ratio of superheated diol vapor to melt is 4:1; the structural formula of the intermediate polymer is:

[0093] ;

[0094] (3) According to the degree of polymerization of the intermediate polymer, the intermediate polymer is sent to the first pre-condensation reactor of the virgin PET for polymerization reaction. The polymerization of the virgin PET includes 5 polymerization stages. The equipment used includes the first esterification reactor, the second esterification reactor, the first pre-condensation reactor, the second pre-condensation reactor and the final condensation reactor. After the reaction is completed, the recycled polyester is prepared;

[0095] Among them, the addition amount of the intermediate polymer is 50wt% of the recycled polyester; the temperature of the first esterification kettle and the second esterification kettle is 250℃, and the pressure is 0.2MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final condensation kettle is 270℃, and the pressure is 100Pa.

[0096] The degree of polymerization of the recycled PET finally obtained is 125, the intrinsic viscosity is 0.78 dl / g, and the melting point is 255°C.

[0097] Example 4

[0098] A method for regenerating waste PET by alcoholysis based on intermediate polymer, the specific steps are as follows:

[0099] (1) Preparation of raw materials:

[0100] Waste PET: Colored polyester waste textiles;

[0101] Diol: 1,5-pentanediol;

[0102] (2) The waste PET was melted at 265°C to obtain a melt which was transported to a closed reactor, and then superheated diol vapor at 270°C was introduced into the closed container to depolymerize the waste PET for 15 minutes to obtain a polymer with a degree of polymerization of 28 and a molecular weight distribution (PDI) of 2.7;

[0103] Among them, the mass ratio of superheated diol vapor to melt is 2:1; the structural formula of the intermediate polymer is:

[0104] ;

[0105] (3) According to the degree of polymerization of the intermediate polymer, the intermediate polymer is sent to the second pre-polycondensation kettle of the virgin PET for polymerization reaction. The polymerization of the virgin PET includes five polymerization stages. The equipment used includes a first esterification kettle, a second esterification kettle, a first pre-polycondensation kettle, a second pre-polycondensation kettle and a final polycondensation kettle. After the reaction is completed, the recycled polyester is prepared.

[0106] Among them, the addition amount of the intermediate polymer is 25wt% of the recycled polyester; the temperature of the first esterification kettle and the second esterification kettle is 255°C, and the pressure is 0.1MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final condensation kettle is 275°C, and the pressure is 150Pa.

[0107] The degree of polymerization of the recycled PET finally obtained is 110, the intrinsic viscosity is 0.71 dl / g, and the melting point is 253°C.

[0108] Example 5

[0109] A method for regenerating waste PET by alcoholysis based on intermediate polymer, the specific steps are as follows:

[0110] (1) Preparation of raw materials:

[0111] Waste PET: polyester-cotton blended waste textiles (polyester / cotton ratio is 80 / 20);

[0112] Diol: ethylene glycol;

[0113] (2) The waste PET is melted at 270°C to obtain a melt which is transported to a closed reactor, and then superheated diol vapor at 250°C is introduced into the closed container to depolymerize the waste PET for 10 minutes to obtain a polymer with a degree of polymerization of 15 and a molecular weight distribution (PDI) of 2.0;

[0114] Among them, the mass ratio of superheated diol vapor to melt is 8:1; the structural formula of the intermediate polymer is:

[0115] ;

[0116] (3) According to the degree of polymerization of the intermediate polymer, the intermediate polymer is sent to the first pre-condensation reactor of the virgin PET for polymerization reaction. The polymerization of the virgin PET includes 5 polymerization stages. The equipment used includes the first esterification reactor, the second esterification reactor, the first pre-condensation reactor, the second pre-condensation reactor and the final condensation reactor. After the reaction is completed, the recycled polyester is prepared;

[0117] Among them, the addition amount of the intermediate polymer is 10wt% of the recycled polyester; the temperature of the first esterification kettle and the second esterification kettle is 260℃, and the pressure is 0MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final polycondensation kettle is 280℃, and the pressure is 150Pa.

[0118] 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.

[0119] Example 6

[0120] A method for regenerating waste functionalized PET by alcoholysis based on intermediate polymer, such as Figure 2 As shown, the specific steps are as follows:

[0121] (1) Preparation of raw materials:

[0122] Waste functionalized PET: flame retardant PET;

[0123] Diol: ethylene glycol;

[0124] Functional monomer: 3-hydroxyphenylphosphinopropionic acid;

[0125] (2) The waste functionalized PET was melted at 230°C and transported to a closed reactor. Then, superheated diol vapor at 250°C was introduced into the closed container to depolymerize the waste PET for 30 min to obtain a polymer with a degree of polymerization of 3 and a molecular weight distribution (PDI) of 1.6. Subsequently, functional monomers and diols were added to the closed reactor to co-esterify the polymer at 220°C and 0.2 MPa for 4 h.

[0126] The mass ratio of superheated diol vapor to melt is 10:1; the amount of functional monomer added is 8wt% of the intermediate polymer; the ratio of diol added after depolymerization to the functional monomer is 1.15:1; the structural formula of the intermediate polymer is:

[0127] ; R 0 is a functional component, and the raw material corresponding to the functional component is a functional monomer;

[0128] (3) According to the degree of polymerization of the intermediate polymer, the co-esterified product is sent to the first esterification kettle of the virgin PET for polymerization reaction. The polymerization of the virgin PET includes 5 polymerization stages. The equipment used includes the first esterification kettle, the second esterification kettle, the first pre-polycondensation kettle, the second pre-polycondensation kettle and the final polycondensation kettle. After the reaction is completed, the functionalized recycled polyester is prepared.

[0129] Among them, the addition amount of the intermediate polymer is 50wt% of the functionalized recycled polyester; the temperature of the first esterification kettle and the second esterification kettle is 240°C, and the pressure is 0.5MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final condensation kettle is 260°C, and the pressure is 100Pa.

[0130] 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 240°C.

[0131] Example 7

[0132] A method for alcoholysis regeneration of waste functionalized PET based on mid-polymer, the specific steps are as follows:

[0133] (1) Preparation of raw materials:

[0134] Waste functionalized PET: Cationic dyes can dye PET;

[0135] Diol: 1,3-propylene glycol;

[0136] Functional monomer: sodium 5-sulfonisophthalate;

[0137] (2) The waste functionalized PET was melted at 240°C and transported to a closed reactor. The superheated diol vapor at 255°C was introduced into the closed container to depolymerize the waste PET for 25 min to obtain a polymer with a degree of polymerization of 6 and a molecular weight distribution (PDI) of 1.9. Subsequently, the functional monomer and diol were added to the closed reactor to co-esterify the polymer at 225°C and 0.3 MPa for 3.5 h.

[0138] The mass ratio of superheated diol vapor to melt is 7:1; the amount of functional monomer added is 10wt% of the intermediate polymer; the ratio of diol added after depolymerization to the functional monomer is 1.1:1; the structural formula of the intermediate polymer is:

[0139] ; R 0 is a functional component, and the raw material corresponding to the functional component is a functional monomer;

[0140] (3) According to the degree of polymerization of the intermediate polymer, the co-esterified product is sent to the second esterification kettle of the virgin PET for polymerization reaction. The polymerization of the virgin PET includes five polymerization stages. The equipment used includes a first esterification kettle, a second esterification kettle, a first pre-polycondensation kettle, a second pre-polycondensation kettle and a final polycondensation kettle. After the reaction is completed, the functionalized recycled polyester is prepared.

[0141] Among them, the addition amount of the intermediate polymer is 70wt% of the functionalized recycled polyester; the temperature of the first esterification kettle and the second esterification kettle is 245°C, and the pressure is 0.1MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final condensation kettle is 265°C, and the pressure is 100Pa.

[0142] The degree of polymerization of the recycled PET finally obtained is 120, the intrinsic viscosity is 0.7 dl / g, and the melting point is 245°C.

[0143] Example 8

[0144] A method for alcoholysis regeneration of waste functionalized PET based on mid-polymer, the specific steps are as follows:

[0145] (1) Preparation of raw materials:

[0146] Waste functionalized PET: flame retardant PET;

[0147] Diol: 1,4-butanediol;

[0148] Functional monomer: [(6-oxo-6H-dibenzo-(C,E)(1,2)-oxaphosphorin-6-one)-methyl]-succinic acid;

[0149] (2) The waste functionalized PET was melted at 220°C and transported to a closed reactor. The superheated diol vapor at 260°C was introduced into the closed container to depolymerize the waste PET for 20 min to obtain a polymer with a degree of polymerization of 26 and a molecular weight distribution (PDI) of 2.9. Subsequently, the functional monomer and diol were added to the closed reactor to co-esterify with the polymer at 230°C and 0.35 MPa for 3 h.

[0150] The mass ratio of superheated diol vapor to melt is 2:1; the amount of functional monomer added is 5wt% of the intermediate polymer; the ratio of diol added after depolymerization to the functional monomer is 1.3:1; the structural formula of the intermediate polymer is:

[0151] ; R 0 is a functional component, and the raw material corresponding to the functional component is a functional monomer;

[0152] (3) According to the degree of polymerization of the intermediate polymer, the co-esterified product is sent to the second pre-condensation reactor of the virgin PET for polymerization reaction. The polymerization of the virgin PET includes five polymerization stages. The equipment used includes a first esterification reactor, a second esterification reactor, a first pre-condensation reactor, a second pre-condensation reactor and a final condensation reactor. After the reaction is completed, the functionalized recycled polyester is prepared.

[0153] Among them, the addition amount of the intermediate polymer is 25wt% of the functionalized recycled polyester; the temperature of the first esterification kettle and the second esterification kettle is 250°C, and the pressure is 0.4MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final condensation kettle is 270°C, and the pressure is 100Pa.

[0154] The degree of polymerization of the recycled PET finally obtained is 135, the intrinsic viscosity is 0.78 dl / g, and the melting point is 235°C.

[0155] Example 9

[0156] A method for alcoholysis regeneration of waste functionalized PET based on mid-polymer, the specific steps are as follows:

[0157] (1) Preparation of raw materials:

[0158] Waste functionalized PET: Cationic dyes can dye PET;

[0159] Diol: 1,5-pentanediol;

[0160] Functional monomer: isophthalic acid;

[0161] (2) The waste functionalized PET was melted at 230°C and transported to a closed reactor. The superheated diol vapor at 270°C was introduced into the closed container to depolymerize the waste PET for 15 min to obtain a polymer with a degree of polymerization of 19 and a molecular weight distribution (PDI) of 2.4. Subsequently, the functional monomer and diol were added to the closed reactor to co-esterify the polymer at 235°C and 0.4 MPa for 2.5 h.

[0162] The mass ratio of superheated diol vapor to melt is 6:1; the amount of functional monomer added is 6wt% of the intermediate polymer; the ratio of diol added after depolymerization to the functional monomer is 1.25:1; the structural formula of the intermediate polymer is:

[0163] ; R 0 is a functional component, and the raw material corresponding to the functional component is a functional monomer;

[0164] (3) According to the degree of polymerization of the intermediate polymer, the co-esterified product is sent to the first pre-condensation reactor of the virgin PET for polymerization reaction. The polymerization of the virgin PET includes five polymerization stages. The equipment used includes the first esterification reactor, the second esterification reactor, the first pre-condensation reactor, the second pre-condensation reactor and the final condensation reactor. After the reaction is completed, the functionalized recycled polyester is prepared.

[0165] Among them, the addition amount of the intermediate polymer is 10wt% of the functionalized recycled polyester; the temperature of the first esterification kettle and the second esterification kettle is 255°C, and the pressure is 0.2MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final condensation kettle is 275°C, and the pressure is 150Pa.

[0166] The degree of polymerization of the recycled PET finally obtained is 145, the intrinsic viscosity is 0.83 dl / g, and the melting point is 250°C.

[0167] Example 10

[0168] A method for alcoholysis regeneration of waste functionalized PET based on mid-polymer, the specific steps are as follows:

[0169] (1) Preparation of raw materials:

[0170] Waste functionalized PET: flame retardant PET;

[0171] Diol: a mixed solution of 1,4-butanediol and 1,5-pentanediol in a volume ratio of 1:1;

[0172] Functional monomer: 3-hydroxyphenylphosphinopropionic acid;

[0173] (2) The waste functionalized PET was melted at 225°C and transported to a closed reactor. The superheated diol vapor at 260°C was introduced into the closed container to depolymerize the waste PET for 25 min to obtain a polymer with a degree of polymerization of 15 and a molecular weight distribution (PDI) of 2.1. Subsequently, the functional monomer and diol were added to the closed reactor to co-esterify the polymer at 240°C and 0.5 MPa for 2 h.

[0174] The mass ratio of superheated diol vapor to melt is 4:1; the amount of functional monomer added is 8wt% of the intermediate polymer; the ratio of diol added after depolymerization to the functional monomer is 1.2:1; the structural formula of the intermediate polymer is:

[0175] ; R 0 is a functional component, and the raw material corresponding to the functional component is a functional monomer;

[0176] (3) According to the degree of polymerization of the intermediate polymer, the co-esterified product is sent to the first pre-condensation reactor of the virgin PET for polymerization reaction. The polymerization of the virgin PET includes five polymerization stages. The equipment used includes the first esterification reactor, the second esterification reactor, the first pre-condensation reactor, the second pre-condensation reactor and the final condensation reactor. After the reaction is completed, the functionalized recycled polyester is prepared.

[0177] Among them, the addition amount of the intermediate polymer is 100wt% of the functionalized recycled polyester; the temperature of the first esterification kettle and the second esterification kettle is 260°C, and the pressure is 0MPa; the temperature of the first precondensation kettle, the second precondensation kettle and the final polycondensation kettle is 280°C, and the pressure is 150Pa.

[0178] The degree of polymerization of the recycled PET finally obtained is 150, the intrinsic viscosity is 0.90 dl / g, and the melting point is 230°C.

Claims

1. A method for regenerating waste PET by alcoholysis based on intermediate polymer, characterized in that: The melt obtained by melting the waste PET is transported to a closed reactor, superheated diol steam is introduced into the closed reactor to depolymerize the waste PET to obtain a medium polymer, and the medium polymer is sent to the polymerization stage of the original polyester for reaction, and the reaction is completed to prepare the recycled polyester; The temperature of the superheated glycol vapor is 250-270°C, the mass ratio of the superheated glycol vapor to the melt is 2-10:1, and the depolymerization time is 10-30 minutes; The degree of polymerization of the mesopolymer is 3 to 30, and the molecular weight distribution PDI is <3.

2. A method for regenerating waste PET by alcoholysis based on medium polymer according to claim 1, characterized in that: Waste PET includes waste PET bottle flakes, waste polyester yarn, waste polyester cloth or waste textiles containing polyester; the melting temperature of waste PET is 250-270℃.

3. A method for regenerating waste PET by alcoholysis based on medium polymer according to claim 1, characterized in that: The diol is ethylene glycol, 1,3-propylene glycol, 1,4-butanediol or 1,5-pentanediol.

4. A method for regenerating waste PET by alcoholysis based on medium polymer according to claim 1, characterized in that: The general structural formula of the mesopolymer is: Wherein, x=3-30, R is (CH2) z , z=2~5.

5. A method for regenerating waste PET by alcoholysis based on medium polymer according to claim 4, characterized in that: The specific process of the alcoholysis regeneration method of waste PET based on intermediate polymer is: the waste PET is transported to a closed reactor after being melted, and then superheated diol vapor is introduced into the closed container to depolymerize the waste PET to obtain intermediate polymer, and then the intermediate polymer is sent to different polymerization stages of the original PET according to the polymerization degree of the intermediate polymer, thereby polymerizing to obtain recycled polyester; wherein the addition amount of the intermediate polymer is 10 to 100 wt% of the recycled polyester.

6. The method for regenerating waste PET by alcoholysis based on intermediate polymer according to claim 5, characterized in that: The polymerization of virgin PET includes five polymerization stages, and the devices used include a first esterification kettle, a second esterification kettle, a first pre-polycondensation kettle, a second pre-polycondensation kettle, and a final polycondensation kettle; When x is 3 to 5, the intermediate polymer is sent to the first esterification reactor of the virgin PET; When x is 6 to 12, the intermediate polymer is sent to the second esterification reactor of the virgin PET; When x is 13 to 25, the intermediate polymer is sent to the first precondensation reactor of the virgin PET; When x is 26-30, the intermediate polymer is sent to the second precondensation reactor of the original PET.

7. The method for regenerating waste PET by alcoholysis based on intermediate polymer according to claim 6, characterized in that: The temperature of the first esterification kettle and the second esterification kettle is 240-260°C, and the pressure is 0-0.5MPa; the temperature of the first pre-polycondensation kettle, the second pre-polycondensation kettle and the final polycondensation kettle is 260-280°C, and the pressure is <200Pa.

8. A method for alcoholysis regeneration of waste PET based on intermediate polymer according to any one of claims 1 to 7, characterized in that: The polymerization degree of the obtained 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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