Preparation method and application of catalyst applied to alcoholysis of waste polyester

Abstract

This invention discloses a method for the alcoholysis of waste polyester and its application, including a method for preparing an alcoholysis catalyst. The preparation method includes the following steps: adding a certain mass of hexagonal boron nitride, an amino group, a metal source, and a ball milling liquid medium into a ball mill jar, and then placing the ball mill jar in a planetary ball mill for ball milling to obtain metal-doped aminated boron nitride, which serves as the alcoholysis catalyst of this invention. This invention simultaneously grafts amino groups onto the surface of boron nitride and introduces metals into the vacancies of boron nitride through a one-step ball milling method. The preparation method is simple, low-cost, and produces a highly efficient and stable catalyst under mild reaction conditions. It overcomes the shortcomings of traditional PET alcoholysis catalysts, such as complex preparation processes and high costs, providing a new approach for the efficient treatment of PET waste and showing great promise for practical applications.

Description

Technical Field

[0001] This invention relates to a method for preparing catalysts, and particularly to a method for alcoholysis of waste polyester, belonging to the field of waste polyester degradation and regeneration. Background Technology

[0002] Polyethylene terephthalate (PET) is the most important type of thermoplastic polyester, commonly known as polyester resin. It possesses excellent chemical and physical properties and is in high demand in industries such as industry, agriculture, food, and medicine, making it the most widely used polyester material globally. PET materials generally have a short lifespan; PET plastic bottles, plastic cups, and some medical supplies are all disposable consumer goods. Due to the stability of PET's chemical structure, waste PET can take decades or even centuries to fully degrade in the natural environment. Failure to recycle waste PET will lead to incalculable environmental pollution problems. Statistics show that in 2020, global production of bottle-grade PET reached 27.45 million tons, and global demand continues to increase, leading to the accumulation of waste PET products in nature. Currently, the overall recycling rate of PET is less than 15%, with the majority ending up in landfills or being dumped into the ocean, causing serious environmental pollution. Therefore, it is necessary to recycle and reuse PET to reduce the amount of waste polyester in the cycle and mitigate environmental pollution.

[0003] Currently, the main methods for recycling waste PET are physical and chemical methods. Physical methods are simple to operate and low in cost, but due to the complex composition of waste PET, it is difficult to effectively remove impurities using only physical means, making it impossible to obtain stable and high-quality recycled polyester products. Chemical methods use solvents such as methanol (MA) and ethylene glycol (EG) under the action of a catalyst to depolymerize PET macromolecules to the monomer level. The purified depolymerized monomers can be used to prepare high-value-added products with diverse functions and wide applications, offering greater potential for product value enhancement compared to physical methods. Therefore, chemical depolymerization has received widespread research and application in recent years. Simultaneously, with changing consumer attitudes and increased environmental awareness, high-value-added recycled polyester products are gradually gaining consumer recognition, becoming a fashion trend and demonstrating enormous market potential. Patent application CN114849714A discloses a method for preparing a solid base catalyst for the alcoholysis of PET: magnesium chloride, β-alanine, and nickel chloride are dissolved in deionized water to obtain a mixed aqueous solution; sodium hydroxide and sodium bicarbonate are dissolved in deionized water to obtain an alkaline solution; the alkaline solution is added to the mixed aqueous solution, and the mixture is then stirred to obtain a suspension. This suspension is reacted to obtain a reaction solution containing magnesium-nickel bimetallic hydroxide. After solid-liquid separation, the solid portion is washed and vacuum dried to obtain a solid base catalyst precursor. The obtained solid base catalyst precursor is then calcined to obtain the final catalyst. However, this catalyst suffers from problems such as high metal content, a high risk of metal ion leakage, and low product purity. Patent application CN115055175A discloses a method for preparing defective zinc oxide nanosheet catalysts for the alcoholysis of PET: zinc chloride and a surfactant are added to a first mixed solvent, stirred, and reacted to obtain a mixed reaction solution containing Zn-CTAB. An aqueous ethanolamine solution and a second mixed solvent are then added to the Zn-CTAB mixed reaction solution. After stirring, solid-liquid separation, and other steps, a defective ZnO nanosheet precursor is obtained, which is then calcined to obtain the catalyst. The defective zinc oxide nanosheets prepared by this invention can be used as a catalyst for the alcoholysis of waste PET. However, the preparation process of the above catalyst is relatively complex, energy-intensive, and has a high metal content, with metal overflow affecting the purity of the alcoholysis products. Therefore, to address the aforementioned problems in the catalytic PET alcoholysis process, it is necessary to develop novel alcoholysis catalysts that can ensure the stability of the catalyst in the reaction system while catalyzing PET alcoholysis. Simultaneously, the catalyst preparation process should be simplified to reduce energy consumption, making the entire alcoholysis process more environmentally friendly.

[0004] The unique polarity of the boron-nitrogen bond in boron nitride (BN) and the high specific surface area of ​​hexagonal boron nitride endow it with excellent catalytic activity. Specifically, the boron atom, acting as a Lewis acidic site, and the nitrogen atom, acting as a basic site, enable various types of chemical interactions between BN and PET: the nitrogen atom, as a basic site, can enhance the nucleophilic attack of ethylene glycol by extracting hydrogen from the hydroxyl group; the boron atom, as an acidic site, promotes the electrophilic properties of the PET carbonyl group, making it more susceptible to attack by the nucleophile ethylene glycol. Furthermore, the amino group, as an acidic site, can further enhance the electrophilic properties of the carbonyl group in PET. Grafting amino groups onto the surface of boron nitride through ball milling can effectively improve the efficiency of PET depolymerization by ethylene glycol. Ball milling also creates vacancies in boron nitride, facilitating the doping of metal ions; the introduction of a small amount of metal can further enhance the catalytic efficiency. Therefore, using boron nitride as a matrix, grafting amino groups onto the surface of boron nitride through ball milling while simultaneously introducing a small amount of metal ions holds promise for significantly improving the performance of hexagonal boron nitride in catalyzing the depolymerization of PET. Summary of the Invention

[0005] To address the shortcomings of traditional PET alcoholysis systems, such as low catalytic efficiency, poor catalyst stability, and complex preparation processes, this invention provides a method for the alcoholysis of waste polyester. Using boron nitride (BN) as the matrix material, a metal is anchored to vacancy in boron nitride using a one-step ball milling method. Simultaneously, amino groups are grafted onto the surface of boron nitride, resulting in a metal-doped aminated boron nitride catalyst for the alcoholysis of PET. Research revealed that this catalyst exhibits a synergistic acid-base effect. The nitrogen atom, acting as a basic site, enhances the nucleophilic attack of ethylene glycol by extracting hydrogen from the hydroxyl group. The boron atom, acting as an acidic site, improves the electrophilic properties of the PET carbonyl group, making it more susceptible to attack by the nucleophile ethylene glycol. Building upon the synergistic acid-base effect of boron nitride itself, the introduction of an amino group as a new acidic site, along with metal doping, provides a novel approach to PET alcoholysis with significant application potential.

[0006] A method for preparing a catalyst for the alcoholysis of waste polyester comprises the following steps:

[0007] A certain mass of hexagonal boron nitride, amino-based substances, metal source, and ball milling liquid medium are added together into a ball milling jar, and the ball milling jar is placed in a planetary ball mill for ball milling to obtain metal-doped ammoniated boron nitride.

[0008] Preferably, the amino group is one of isopropylamine, ethylenediamine, aniline, melamine, or urea.

[0009] Preferably, the metal source is one of manganese acetate, zinc acetate, copper sulfate, cobalt nitrate, or ferric sulfate.

[0010] Preferably, the ball milling liquid medium is one of ethanol, water, or isopropanol.

[0011] Preferably, the mass ratio of the hexagonal boron nitride, amino-based substances, and metal source is 1:1-20:0.01-2.

[0012] Preferably, the ball milling conditions are: total ball milling time 8-36h, forward rotation time 5-60min, reverse rotation time 5-60min, and interval time 30-500s.

[0013] An application of an alcoholysis method for waste polyester, characterized by: placing a certain amount of PET, EG, and metal-doped ammoniated boron nitride in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen gas; slowly heating to a specified temperature; reacting for a specified time; cooling the reaction solution to 100-180℃ and filtering while hot to separate undepolymerized PET; washing the filtered solid with deionized water; drying and weighing to obtain the mass of undepolymerized PET; adding a large amount of deionized water to the filtrate; stirring and heating to 40-120℃; filtering while hot to obtain a mixed solution of diethyl terephthalate (BHET), EG, and water; cooling the mixed solution to room temperature and then placing it at a low temperature of 3-15℃ for 5-24 hours; filtering and drying to obtain BHET; and weighing to obtain the actual yield of BHET.

[0014] Preferably, the mass of PET is 0.5-20.0g, the volume of EG is 5-200mL, the mass of catalyst is 0.1-2.0g, the alcoholysis temperature is 120-260℃, and the alcoholysis time is 0.5-8h.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) The catalyst is prepared by simultaneously grafting amino groups and introducing metals through a one-step ball milling method, which is simple and low in cost.

[0017] (2) The introduction of amino groups further enhances the electrophilic properties of carbonyl groups in PET, and the introduction of a small amount of metals also enhances the alcoholysis efficiency of PET ethylene glycol hydrolysis, making it a highly efficient and environmentally friendly catalyst. Detailed Implementation

[0018] The present invention will be further illustrated below with specific examples. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0019] Example 1:

[0020] Hexagonal boron nitride, melamine, zinc acetate, and isopropanol were added to a ball mill jar in a mass ratio of 1:5:0.1:30. The jar was then placed in a planetary ball mill for ball milling. The ball milling conditions were: a total ball milling time of 16 hours, a forward rotation time of 30 minutes, a reverse rotation time of 30 minutes, and an interval of 300 seconds. This yielded zinc-doped aminated boron nitride, which can be used as a catalyst for alcoholysis.

[0021] An application of an alcoholysis method for waste polyester is described, applicable to the following method: 5.0 g PET, 80.0 mL EG, and 0.2 g catalyst are placed in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen atmosphere. The temperature is slowly raised to 200 °C, and the reaction time is set to 3 hours. The PET conversion rate is 100%, and the BHET yield is 85.6%.

[0022] Example 2:

[0023] Hexagonal boron nitride, urea, ferric sulfate, and isopropanol were added to a ball mill jar in a mass ratio of 1:6:0.2:50. The jar was then placed in a planetary ball mill for ball milling. The ball milling conditions were: total ball milling time of 18 hours, forward rotation time of 40 minutes, reverse rotation time of 40 minutes, and interval time of 400 seconds. Iron-doped ammoniated boron nitride was obtained and used as a catalyst for alcoholysis.

[0024] An application of an alcoholysis method for waste polyester is described, applicable to the following method: 3.0 g PET, 60.0 mL EG, and 0.2 g catalyst are placed in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen atmosphere. The temperature is slowly raised to 200 °C, and the reaction time is set to 4 h. The PET conversion rate is 100%, and the BHET yield is 85.1%.

[0025] Example 3:

[0026] Hexagonal boron nitride, ethylenediamine, cobalt nitrate, and ethanol were added to a ball mill jar in a mass ratio of 1:4:0.2:45. The jar was then placed in a planetary ball mill for ball milling under the following conditions: total milling time of 12 hours, forward rotation time of 35 minutes, reverse rotation time of 35 minutes, and interval time of 350 seconds. This yielded cobalt-doped aminated boron nitride, which can be used as a catalyst for alcoholysis.

[0027] An application of an alcoholysis method for waste polyester is described, applicable to the following method: 3.5g PET, 60.0mL EG, and 0.15g catalyst are placed in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen gas. The temperature is slowly raised to 200℃, and the reaction time is set to 4 hours. The PET conversion rate is 94.5%, and the BHET yield is 77.8%.

[0028] Example 4:

[0029] Hexagonal boron nitride, aniline, zinc acetate, and isopropanol were added to a ball mill jar in a mass ratio of 1:3:0.2:50. The jar was then placed in a planetary ball mill for ball milling under the following conditions: total ball milling time of 16 hours, forward rotation time of 30 minutes, reverse rotation time of 30 minutes, and interval time of 200 seconds. This yielded zinc-doped ammoniated boron nitride, which can be used as a catalyst for alcoholysis.

[0030] An application of an alcoholysis method for waste polyester is described, applicable to the following method: 3.0 g PET, 60.0 mL EG, and 0.15 g catalyst are placed in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen gas. The temperature is slowly raised to 200 °C, and the reaction time is set to 4 h. The PET conversion rate is 78.6%, and the BHET yield is 59.4%.

[0031] Example 5:

[0032] Hexagonal boron nitride, isopropylamine, copper sulfate, and isopropanol were added to a ball mill jar in a mass ratio of 1:2:0.1:50. The jar was then placed in a planetary ball mill for ball milling under the following conditions: total ball milling time of 20 hours, forward rotation time of 60 minutes, reverse rotation time of 60 minutes, and interval time of 500 seconds. Copper-doped ammoniated boron nitride was obtained and used as a catalyst for alcoholysis.

[0033] An application of an alcoholysis method for waste polyester is described, applicable to the following method: 3.0 g PET, 60.0 mL EG, and 0.1 g catalyst are placed in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen atmosphere. The temperature is slowly raised to 190 °C, and the reaction time is set to 3 h. The PET conversion rate is 74.2%, and the BHET yield is 55.1%.

[0034] Example 6:

[0035] Hexagonal boron nitride, melamine, copper sulfate, and water were added to a ball mill jar in a mass ratio of 1:2:0.1:40. The jar was then placed in a planetary ball mill for ball milling. The ball milling conditions were: total ball milling time of 20 hours, forward rotation time of 50 minutes, reverse rotation time of 50 minutes, and interval time of 300 seconds. Copper-doped ammoniated boron nitride was obtained and used as a catalyst for alcoholysis.

[0036] An application of an alcoholysis method for waste polyester is described, applicable to the following method: 3.0 g PET, 60.0 mL EG, and 0.1 g catalyst are placed in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen gas. The temperature is slowly raised to 190 °C, and the reaction time is set to 1 h. The PET conversion rate is 72.6%, and the BHET yield is 53.5%.

[0037] Example 7:

[0038] Hexagonal boron nitride, ethylenediamine, manganese acetate, and isopropanol were added to a ball mill jar in a mass ratio of 1:5:0.15:50. The jar was then placed in a planetary ball mill for ball milling under the following conditions: total ball milling time of 14 hours, forward rotation time of 30 minutes, reverse rotation time of 30 minutes, and interval time of 60 seconds. This yielded manganese-doped ammoniated boron nitride, which can be used as a catalyst for alcoholysis.

[0039] An application of a method for the alcoholysis of waste polyester is described, applicable to the following method: 5.0 g PET, 50.0 mL EG, and 0.1 g catalyst are placed in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen gas. The temperature is slowly raised to 180 °C, and the reaction time is set to 5 h. The PET conversion rate is 61.8%, and the BHET yield is 43.3%.

[0040] Example 8:

[0041] Hexagonal boron nitride, ethylenediamine, manganese acetate, and water were added to a ball mill jar in a mass ratio of 1:1:0.1:40. The jar was then placed in a planetary ball mill for ball milling. The ball milling conditions were: total ball milling time of 10 hours, forward rotation time of 30 minutes, reverse rotation time of 30 minutes, and interval time of 300 seconds. This yielded manganese-doped aminated boron nitride, which can be used as a catalyst for alcoholysis.

[0042] An application of an alcoholysis method for waste polyester is described, applicable to the following method: 5.0 g PET, 50.0 mL EG, and 0.1 g catalyst are placed in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen atmosphere. The temperature is slowly raised to 180 °C, and the reaction time is set to 5 h. The PET conversion rate is 58.8%, and the BHET yield is 43.6%.

[0043] Comparative Example 1:

[0044] Hexagonal boron nitride, zinc acetate, and water were added to a ball mill jar in a mass ratio of 1:0.1:40. The jar was then placed in a planetary ball mill for ball milling. The ball milling conditions were: total ball milling time of 16 hours, forward rotation time of 60 minutes, reverse rotation time of 60 minutes, and interval time of 300 seconds. Zinc-doped boron nitride was obtained and used as a catalyst for alcoholysis.

[0045] An application of an alcoholysis method for waste polyester is described, applicable to the following method: 3.0 g PET, 50.0 mL EG, and 0.1 g catalyst are placed in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen gas. The temperature is slowly raised to 200 °C, and the reaction time is set to 3 h. The PET conversion rate is 31.8%, and the BHET yield is 13.6%.

[0046] Comparative Example 2:

[0047] Hexagonal boron nitride, ethylenediamine, and ethanol were added to a ball mill jar at a mass ratio of 1:0.1:50, and the jar was placed in a planetary ball mill for ball milling. The ball milling conditions were: total ball milling time 10 h, forward rotation time 30 min, reverse rotation time 30 min, and interval time 300 s. Amination-modified boron nitride was obtained and used as a catalyst for alcoholysis.

[0048] An application of an alcoholysis method for waste polyester is described, applicable to the following method: 3.0 g PET, 50.0 mL EG, and 0.1 g catalyst are placed in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen gas. The temperature is slowly raised to 200 °C, and the reaction time is set to 3 h. The PET conversion rate is 51.8%, and the BHET yield is 35.5%.

[0049] The examples were tested according to the evaluation criteria proposed above, and the test results are shown in Table 1. As can be seen from Table 1, analyzing the performance evaluation of Examples 1-8 reveals that the conversion rate of PET and the yield of BHET increase within a certain range with increasing amino content and metal doping amount. Simultaneously, the ball milling conditions also significantly affect the catalytic effect. Analyzing the performance differences between Comparative Examples 1-2 and the Examples shows that introducing metal while grafting hexagonal boron nitride with amino groups significantly improves catalytic performance compared to grafting amino groups alone or introducing metals alone.

[0050] The PET yield and BHET conversion rate under different conditions are shown in the table below:

[0051]

Claims

1. A method for preparing a catalyst for alcoholysis of waste polyester, characterized by, A certain mass of hexagonal boron nitride, amino-based substances, a metal source, and a ball milling liquid medium are added together into a ball milling jar, and the ball milling jar is placed in a planetary ball mill for ball milling to obtain metal-doped amino boron nitride; the ball milling liquid medium is one of ethanol, water, or isopropanol; the mass ratio of hexagonal boron nitride, amino-based substances, and metal source is 1:1-20:0.01-2; The amino-based substance is one of isopropylamine, ethylenediamine, aniline, melamine, or urea; The metal source is one of manganese acetate, zinc acetate, copper sulfate, cobalt nitrate, or ferric sulfate; The ball milling conditions are as follows: total ball milling time 8-36 h, forward rotation time 5-60 min, reverse rotation time 5-60 min, and interval time 30-500 s.

2. The catalyst obtained by the preparation method according to claim 1 is used in the alcoholysis of waste polyester, characterized in that: A certain amount of polyester, ethylene glycol, and metal-doped aminated boron nitride are placed in a three-necked flask connected to a thermometer, condenser, stirrer, and nitrogen gas. The temperature is slowly raised to a suitable temperature, and the reaction is allowed to proceed for the set time.

3. The application according to claim 2, characterized in that, The mass of polyester is 0.5-20.0 g, the volume of ethylene glycol is 5.0-200 mL, the mass of catalyst is 0.1-2.0 g, the alcoholysis temperature is 120-260℃, and the alcoholysis time is 0.5-8 h.

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