A method for the short process production of pet copolyesters

Abstract

The application discloses a kind of short process preparation PET copolyester method.The method includes: waste PET polyester, alcoholysis agent and catalyst are mixed, alcoholysis reaction is carried out in closed reaction kettle, when the number average molecular weight of oligomer obtained by controlling alcoholysis reaction is 5000-7000g / mol, the polymerization degree is 25-35, the reaction is stopped, then the polycondensation reaction is completed under high vacuum condition, and PET copolyester is obtained.The method is under the action of alcoholysis agent ethylene glycol and catalyst (such as titanium double metal catalyst) waste PET polyester is alcoholized reaction, by adjusting reaction temperature and reaction time accurately control the oligomer obtained by alcoholysis reaction is in the state of number average molecular weight 5000-7000g / mol, the polymerization degree is 25-35, then directly using alcoholysis reaction product carries out polycondensation reaction and prepares PET copolyester, realizes the recycling of PET waste.At the same time, after alcoholysis reaction, the system does not need any separation step, directly carries out polycondensation reaction, greatly simplifies process flow, shortens time cost.

Description

Technical Field

[0001] This invention relates to the field of waste material recycling. More specifically, it relates to a short-process method for preparing PET copolyester. Background Technology

[0002] Polyethylene terephthalate (PET) is a widely used thermoplastic polyester material, commonly used in beverage bottles, food packaging, and textiles due to its excellent mechanical properties, heat resistance, and chemical stability. However, the widespread use of PET has also brought significant environmental problems, especially the accumulation of waste caused by its non-degradable nature. Therefore, developing effective PET recycling technologies is crucial. Currently, PET recycling methods are mainly divided into physical recycling and chemical recycling. Physical recycling regenerates PET materials through processes such as washing, crushing, and melting, but its recycling efficiency is limited by the purity and impurity content of the raw materials. Chemical recycling, on the other hand, converts waste PET into its raw material monomers through chemical reactions, enabling efficient processing of complex and mixed PET waste and improving recycling efficiency.

[0003] Chemical recycling technologies include various methods such as hydrolysis, alcoholysis, and pyrolysis. Hydrolysis decomposes PET into terephthalic acid and ethylene glycol through a reaction with water under high temperature and pressure. Alcoholysis utilizes alcohols (such as methanol, ethanol, and ethylene glycol) to react with PET to produce alcohol esters and monomers. Pyrolysis decomposes PET into low-molecular-weight compounds through high-temperature treatment in an oxygen-deficient or anaerobic environment. These methods not only effectively recycle waste PET but also produce high-purity raw material monomers to meet higher application standards. Compared to physical recycling, chemical recycling offers advantages such as higher recovery rates, greater tolerance to pollutants, and the possibility of achieving closed-loop recycling, thus playing a positive role in reducing environmental burden.

[0004] Patent CN118374057A discloses a method for preparing PET copolyester through alcoholysis and polymerization of waste PET. However, different catalysts are required in the alcoholysis and polymerization stages, and stabilizers and antioxidants need to be added to the polymerization system, making the operation complex. Patent CN112441917A discloses a method for recovering terephthalic acid esters by transesterification of waste PET with alkyl alcohols, but the product requires multiple processing steps, resulting in a complex process and high energy consumption. Therefore, a simpler method for PET recycling is needed. Summary of the Invention

[0005] To address the above problems, one objective of this invention is to provide a short-process method for preparing PET copolyester. This method, by selecting suitable alcoholysis agents and catalysts and accurately controlling the reaction endpoint of the alcoholysis reaction, allows for the direct use of the alcoholysis products for polycondensation to prepare PET copolyester. No additional catalysts or other materials are required during the process, nor are any separation or esterification steps necessary. This method is simple to operate, requires minimal catalyst, has a short process route, low energy consumption, and achieves the recycling of waste PET polyester.

[0006] Another object of the present invention is to provide a PET copolyester.

[0007] To achieve the first objective mentioned above, the present invention adopts the following technical solution:

[0008] This invention discloses a method for preparing PET copolyester from waste PET polyester, comprising the following steps:

[0009] Waste PET polyester, alcoholysis agent and catalyst are mixed and alcoholysis reaction is carried out in a closed reactor. The reaction is stopped when the number average molecular weight of the oligomers obtained by alcoholysis reaction is 5000-7000 g / mol and the degree of polymerization is 25-35. Then, polycondensation reaction is completed under high vacuum to obtain PET copolyester.

[0010] Furthermore, the alcoholysis agent is selected from ethylene glycol; the catalyst is selected from one or more of antimony-based catalysts, germanium-based catalysts, rare earth catalysts, and titanium-based catalysts, preferably a titanium-based bimetallic catalyst. The titanium-based bimetallic catalyst is prepared according to CN108034046A. The titanium-based bimetallic catalyst selected in this invention can catalyze both the alcoholysis of PET polyester and the synthesis of copolyesters, making it a highly efficient catalyst with dual catalytic activity.

[0011] Furthermore, the amount of the alcoholysis agent used is 0.5-10 times the mass of the waste PET polyester.

[0012] Further, the amount of catalyst used is 0.01-0.5% of the mass of waste PET polyester. Exemplarily, the amount of catalyst used can also be 0.01-0.1%, 0.01-0.2%, 0.01-0.3%, 0.01-0.4%, 0.05-0.1%, 0.05-0.2%, 0.05-0.3%, 0.05-0.4%, 0.05-0.5%, 0.1-0.2%, 0.1-0.3%, 0.1-0.4%, 0.1-0.5%, 0.2-0.3%, 0.2-0.4%, 0.2-0.5%, 0.3-0.4%, 0.3-0.5%, 0.4-0.5%, etc., of the mass of waste PET polyester.

[0013] Furthermore, the reaction temperature of the alcoholysis reaction is 180-230℃, and the reaction time of the alcoholysis reaction is 1.0-8.0h.

[0014] Furthermore, the reaction temperature of the polycondensation reaction is 240-260℃, and the reaction time of the polycondensation reaction is 0.5-5.0h.

[0015] Furthermore, the vacuum level in the polycondensation reaction is controlled at 10-100 Pa.

[0016] Furthermore, the waste PET polyester is selected from one or more of waste PET bottles, waste PET films and waste PET fibers, and its number average molecular weight is 10-40 kg / mol.

[0017] To achieve the second objective mentioned above, the present invention adopts the following technical solution:

[0018] This invention discloses a PET copolyester prepared using the method described above.

[0019] The beneficial effects of this invention are as follows:

[0020] This invention provides a rapid and effective method for preparing PET copolyester from waste PET polyester. The method involves alcoholystolysis of waste PET polyester using ethylene glycol as an alcoholysis agent and a catalyst (e.g., a titanium-based bimetallic catalyst). By precisely controlling the reaction temperature and time, the alcoholysis reaction is achieved, resulting in oligomers with a number average molecular weight of 5000-7000 g / mol and a degree of polymerization of 25-35. The alcoholysis products are then directly used for polycondensation to prepare PET copolyester, thus realizing the recycling of PET waste.

[0021] After the alcoholysis reaction, the system requires no separation steps and can skip the esterification stage to directly carry out the polycondensation reaction. The oligomers after alcoholysis have moderate fluidity in the melt state, which is not too restrictive to the subsequent collision of end groups to carry out polycondensation reaction, thus ensuring that the product has a good molecular weight distribution; at the same time, it is not too low to consume too much energy, which can greatly simplify the process and shorten the time cost.

[0022] The catalyst selected in this invention (e.g., a titanium-based bimetallic catalyst) can catalyze both the alcoholysis of PET polyester and the synthesis of copolyesters. This allows for a successful transition from alcoholysis to polycondensation without the need for secondary addition of a polycondensation catalyst throughout the process. Furthermore, the relatively small amount of catalyst used in the alcoholysis reaction and the absence of additional catalyst in the subsequent polycondensation reaction ensures a low metal content in the recovered polymer.

[0023] The waste PET polyester used in this invention has a wide range of sources, including waste PET bottles, waste PET films, and waste PET fibers. This method realizes the recycling of PET waste into polymer products. Detailed Implementation

[0024] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0025] The molecular weight and distribution of the polymer were determined using gel permeation chromatography (GPC, e2695, Waters, USA) with chloroform and o-chlorophenol as a mixed solvent, chloroform as the mobile phase, and PMMA as the reference standard.

[0026] The content of metal elements in the polymer was determined using an inductively coupled plasma mass spectrometer (ICP-MS-2030, Shimadzu, Japan) with trifluoroacetic acid as the solvent.

[0027] The titanium-based bimetallic catalysts used in the following specific examples of the present invention were prepared according to the preparation conditions of Example 1 in CN108034046A.

[0028] Examples 1-11

[0029] The steps for preparing PET copolyester by alcoholysis and polymerization of waste PET polyester are as follows:

[0030] (1) Alcohololysis: Waste PET polyester (100.0g), ethylene glycol (300.0g), and a certain amount of titanium-based bimetallic catalyst were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The stirring speed was 300rpm, and after reacting at a certain temperature for a certain time, oligomers with a number average molecular weight of about 5000-7000g / mol and a degree of polymerization of 25-35 were obtained.

[0031] (2) Polymerization: The pressure of the reaction system is reduced to below 100 Pa using an oil pump, and the stirring speed is increased to 450 rpm. Polycondensation reaction is carried out at a certain temperature. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30 N·cm, the reaction is considered to have reached the endpoint, and PET copolyester is obtained.

[0032] In Examples 1-11, the amount of catalyst, alcoholysis temperature, alcoholysis time, molecular weight of oligomer, polycondensation temperature and polycondensation time of each example are shown in Table 1, and the molecular weight of the PET copolyester obtained in each example is shown in Table 2.

[0033] Table 1. Reaction parameters in Examples 1-11

[0034]

[0035] Table 2. Molecular weight of PET copolyesters in Examples 1-11

[0036]

[0037]

[0038] Comparative Example 1

[0039] The preparation of PET copolyester by alcoholysis and polymerization of waste PET polyester differs from Example 7 in that the reaction time is extended to completely hydrolyze the PET polyester into monomers before polymerization. The steps are as follows:

[0040] (1) Alcohololysis: Waste PET (100.0 g), ethylene glycol (300.0 g), and titanium-based bimetallic catalyst (0.15 g) were added to a 500 mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200 °C and the stirring speed at 300 rpm. After 6.0 h of reaction, the yield of the monomer product diethyl terephthalate was 80.1%.

[0041] (2) Polymerization: Under normal pressure, esterification was carried out at 200-240℃ for 180 min with a stirring speed of 450 rpm. Subsequently, the pressure of the reaction system was reduced to below 100 Pa using an oil pump, and polycondensation was carried out at 250℃ for about 60 min. When the viscosity of the polymer increased significantly and the torque of the stirring device reached 30 N·cm, the reaction was considered to have reached its endpoint, and PET copolyester was obtained.

[0042] Comparative Example 2

[0043] The preparation of PET copolyester by alcoholysis and polymerization of waste PET polyester differs from Comparative Example 1 in that the PET polyester is hydrolyzed into oligomers with a molecular weight of approximately 2000 g / mol before polymerization. The steps are as follows:

[0044] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and titanium-based bimetallic catalyst (0.15g) were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200℃ and the stirring speed at 300rpm. After reacting for 3.0h, oligomers with a number average molecular weight of approximately 2000g / mol were obtained.

[0045] (2) Polymerization: The pressure of the reaction system is reduced to below 100 Pa using an oil pump, the temperature of the oil bath is raised to 250℃, and the stirring speed is increased to 450 rpm to carry out the polycondensation reaction. The polycondensation reaction lasts for about 80 minutes. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30 N·cm, the reaction is considered to have reached its endpoint, and PET copolyester is obtained.

[0046] Comparative Example 3

[0047] The preparation of PET copolyester by alcoholysis and polymerization of waste PET polyester differs from Comparative Example 1 in that the PET polyester is hydrolyzed into oligomers with a molecular weight of approximately 10,000 g / mol before polymerization. The steps are as follows:

[0048] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and titanium-based bimetallic catalyst (0.15g) were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200℃ and the stirring speed at 300rpm. After reacting for 1.5h, oligomers with a number average molecular weight of approximately 10000g / mol were obtained.

[0049] (2) Polymerization: The pressure of the reaction system is reduced to below 100 Pa using an oil pump, the temperature of the oil bath is raised to 250℃, and the stirring speed is increased to 450 rpm to carry out the polycondensation reaction. The polycondensation reaction lasts for about 60 minutes. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30 N·cm, the reaction is considered to have reached its endpoint, and PET copolyester is obtained.

[0050] The reaction parameters and product information for Examples 7 and Comparative Examples 1-3 are shown in Table 3.

[0051] Table 3. Reaction parameters and product information for Example 7 and Comparative Examples 1-3

[0052]

[0053] The comparison reveals that depolymerizing polyester into monomers or lower molecular weight oligomers before polymerization significantly prolongs the alcoholysis and polymerization times. Conversely, shortening the alcoholysis time to obtain oligomers with higher molecular weights results in higher oligomer viscosity, hindering the normal progress of the polycondensation reaction and leading to a wider molecular weight distribution in the copolyester.

[0054] Comparative Example 4

[0055] The preparation of PET copolyester by alcoholysis and polymerization of waste PET polyester differs from Example 7 in that the catalyst used in the reaction is tetrabutyl titanate, and the steps are as follows:

[0056] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and tetrabutyl titanate (0.19g) were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200℃ and the stirring speed at 300rpm. After reacting for 4.0h, oligomers with a number average molecular weight of approximately 6000g / mol were obtained.

[0057] (2) Polymerization: The pressure of the reaction system is reduced to below 100 Pa using an oil pump, the temperature of the oil bath is raised to 250℃, and the stirring speed is increased to 450 rpm to carry out the polycondensation reaction. The polycondensation reaction lasts for about 110 minutes. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30 N·cm, the reaction is considered to have reached its endpoint, and PET copolyester is obtained.

[0058] Comparative Example 5

[0059] The preparation of PETG copolyester by alcoholysis and polymerization of waste PET polyester differs from Comparative Example 4 in the amount of tetrabutyl titanate used. The steps are as follows:

[0060] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and tetrabutyl titanate (0.32g) were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200℃ and the stirring speed at 300rpm. After reacting for 2.0h, oligomers with a number average molecular weight of approximately 6000g / mol were obtained.

[0061] (2) Polymerization: The pressure of the reaction system is reduced to below 100 Pa using an oil pump, the temperature of the oil bath is raised to 250℃, and the stirring speed is increased to 450 rpm to carry out the polycondensation reaction. The polycondensation reaction lasts for about 70 minutes. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30 N·cm, the reaction is considered to have reached its endpoint, and PET copolyester is obtained.

[0062] Comparative Example 6

[0063] The preparation of PETG copolyester from waste PET polyester alcoholysis and polymerization differs from Comparison 5 in that tetrabutyl titanate is added twice during the alcoholysis and polymerization reactions, as follows:

[0064] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and tetrabutyl titanate (0.16g) were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200℃ and the stirring speed at 300rpm. After reacting for 4.5h, oligomers with a number average molecular weight of approximately 6000g / mol were obtained.

[0065] (2) Polymerization: Add tetrabutyl titanate (0.16 g) to the three-necked flask, reduce the pressure of the reaction system to below 100 Pa using an oil pump, raise the temperature of the oil bath to 250 °C, and increase the stirring speed to 450 rpm to carry out the polycondensation reaction. The polycondensation reaction lasts for about 70 min. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30 N·cm, the reaction is considered to have reached its endpoint, and PET copolyester is obtained.

[0066] The reaction parameters and product information for Examples 7 and Comparative Examples 4-6 are shown in Table 4.

[0067] Table 4. Reaction parameters and product information for Example 7 and Comparative Examples 4-6

[0068]

[0069] The comparison reveals that when tetrabutyl titanate is used as a catalyst, the reaction efficiency is relatively lower than that of titanium-based bimetallic catalysts. A longer alcoholysis time or more catalysts are required to obtain a copolyester comparable to that in the examples. However, increasing the amount of catalyst may result in a higher metal content in the prepared copolyester.

[0070] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A short-process method for preparing PET copolyester, characterized in that, Includes the following steps: Waste PET polyester, alcoholysis agent and catalyst are mixed and alcoholysis reaction is carried out in a closed reactor. The reaction is stopped when the number average molecular weight of the oligomers obtained by alcoholysis reaction is 5000-7000 g / mol and the degree of polymerization is 25-35. Then, polycondensation reaction is completed under high vacuum to obtain PET copolyester. The alcoholysis agent is selected from ethylene glycol; the catalyst is selected from titanium-based bimetallic catalysts. The amount of the alcoholysis agent used is 0.5-10 times the mass of the waste PET polyester; The amount of catalyst used is 0.01-0.5% of the mass of waste PET polyester; The reaction temperature of the alcoholysis reaction is 180-230℃, and the reaction time is 1.0-8.0 h.

2. The method according to claim 1, characterized in that, The reaction temperature of the polycondensation reaction is 240-260℃, and the reaction time is 0.5-5.0 h.

3. The method according to claim 1, characterized in that, The vacuum level in the polycondensation reaction is controlled at 10-100 Pa.

4. The method according to claim 1, characterized in that, The waste PET polyester is selected from one or more of waste PET bottles, waste PET films and waste PET fibers, and its number average molecular weight is 10-40 kg / mol.

5. PET copolyester, characterized in that, It is prepared by the method described in any one of claims 1-4.

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