Preparation Method and Application of a Catalyst for Alcoholysis of Waste Polyester

Abstract

The present invention discloses a preparation method and application of a waste polyester alcoholysis catalyst. The preparation method of the present invention comprises the following steps: (1) fully dissolving a certain amount of boron source, nitrogen source and metal source in an appropriate amount of deionized water, heating to a certain temperature, and fully stirring until the solution evaporates to obtain a precursor solid; (2) grinding the precursor solid and calcining it in a tube furnace to obtain metal-doped boron nitride. The present invention has the advantages of simple preparation method, low cost, stable catalyst and mild reaction conditions, and overcomes the shortcomings of traditional PET alcoholysis catalysts such as low cycle number and poor catalytic effect. It provides a new idea for the efficient treatment of PET waste and has great practical application prospects.

Description

Technical Field

[0001] The present invention relates to a method for preparing a catalyst, and particularly to a method for preparing a catalyst for alcoholysis of waste polyester, belonging to the field of degradation and regeneration of waste polyester. Background Art

[0002] Polyethylene terephthalate (PET) is a semi-crystalline thermoplastic polyester with excellent chemical and physical properties, and is widely used in the fields of textiles, packaging bottles, electronic devices, mechanical equipment manufacturing, etc. It is currently the polyester material with the highest usage worldwide. According to statistics, about 70 million tons of PET are produced globally every year, and the production is continuously increasing. However, only 15% of PET is recycled, and most of the rest are piled up in landfills or dumped into the ocean as waste. Since PET is very stable, it is difficult to degrade naturally in the environment, thus causing serious environmental pollution. Therefore, it is necessary to recycle and reuse PET to reduce the amount of waste polyester in the cycle and reduce environmental pollution.

[0003] Traditional PET recycling methods are mainly divided into physical and chemical methods. Physical recycling refers to the method of regranulating waste PET through separation, crushing, washing and drying processes. In this process, mechanical stress and high-temperature environment during processing can cause PET molecular chain breakage, increase side reactions, and result in disadvantages such as a decrease in the viscosity and molecular weight of recycled PET. Chemical recycling is to depolymerize the PET molecular chain with a solvent, convert it into monomers or oligomers, and then purify and reuse it as chemical raw materials, which can achieve true recycling. Since the ester bonds in PET are easily depolymerized by many nucleophiles, according to the type of solvent, chemical recycling can be divided into hydrolysis method, alcoholysis method and ammonolysis method, etc. At present, the alcoholysis method of PET is more studied and widely used. Among them, alcoholysis is the most commonly used method in the alcoholysis process. Alcoholysis uses ethylene glycol (EG) as the alcoholysis solvent, has mild reaction conditions and low requirements for equipment, and takes bis(2-hydroxyethyl) terephthalate (BHET), the monomer that makes up PET, as the final product, which is easy for continuous production and is currently the most widely used method for PET chemical recycling. The patent with the application number CN202210195323.5 discloses a method for catalyzing the depolymerization of polyethylene terephthalate with a cyanamide compound: using a cyanamide compound as a catalyst and ethylene glycol as the alcoholysis solvent, performing an alcoholysis reaction on the PET raw material to obtain the monomer BHET. Under the influence of the hydrogen bond between the catalyst and EG, the O-H bond length of the hydroxyl group in ethylene glycol increases, making it easier for ethylene glycol to initiate a nucleophilic attack on PET, thus achieving the effect of degrading PET. The patent with the application number CN202111264266.3 discloses the application of phosphazene base in catalyzing the alcoholysis of polyethylene terephthalate: phosphazene base is a type of non-protic strong base, and its structure contains at least one P atom and four N atoms, and the P atom and N atoms are combined by covalent bonds. The biggest feature of such substances is their extremely strong basicity, which is stronger than that of other amine or amidine bases. This invention uses phosphazene base as a catalyst to alcoholyze waste PET, providing a new method for the recycling of waste PET. However, the above catalysts for catalyzing PET degradation have poor stability in the alcoholysis system and contain certain toxicity. Therefore, in view of the related problems in the process of catalyzing PET alcoholysis, it is necessary to develop new alcoholysis catalysts, which can reduce the toxicity of the catalyst while catalyzing PET alcoholysis, and at the same time ensure the stability of the catalyst in the reaction system and have good reusability.

[0004] The unique polarity of the boron-nitrogen bond in boron nitride and the high specific surface area of ​​hexagonal boron nitride give it good catalytic activity. Among them, the coexistence of boron atoms as Lewis acidic sites and nitrogen atoms as basic sites can produce various types of chemical interactions between BN and PET: nitrogen atoms as basic sites can enhance the nucleophilic attack of ethylene glycol by extracting hydrogen from hydroxyl groups, and boron atoms as acidic sites promote the electrophilic properties of PET carbonyl groups, making them more susceptible to attack by nucleophilic reagents EG. At the same time, as a graphene-like material, boron nitride can also produce π-π-like interactions with PET, making the reaction conditions milder. Studies have shown that the 3d orbitals of transition metals can produce strong interactions with the 2p orbitals of the corresponding available B or N sites in BN, enhancing the catalytic activity of the material. Therefore, doping transition metals in the boron nitride matrix is ​​expected to further improve the alcoholysis efficiency of PET. Summary of the invention

[0005] In order to solve the shortcomings of low catalytic efficiency and poor repeatability of catalysts in traditional PET alcoholysis systems, the present invention provides a method for preparing a waste polyester alcoholysis catalyst. BN is used as a matrix material, and metal atoms are anchored on boron nitride vacancies by metal atom doping, thereby obtaining a catalyst for the alcoholysis of polyethylene terephthalate catalyzed by transition metal-doped boron nitride. Studies have found that the catalyst has acid-base synergy, and nitrogen atoms as basic sites can enhance the nucleophilic attack of ethylene glycol by extracting hydrogen from hydroxyl groups, and boron atoms as acidic sites enhance the electrophilic properties of PET carbonyl groups, making them more susceptible to attack by nucleophilic reagents EG. The 3d orbital of the transition metal has a strong interaction with the 2p orbital of the corresponding B or N site in BN, which can enhance the catalytic activity. In addition, the excellent thermal properties of BN enhance the stability of the catalyst in the reaction system. The catalyst has the advantages of high catalytic efficiency, strong stability, good cycle performance, and low cost investment, providing a new idea for alcoholysis of PET and having great application prospects.

[0006] A method for preparing a waste polyester alcoholysis catalyst, the specific steps of which are as follows:

[0007] (1) dissolving a certain amount of boron source, nitrogen source, and metal source in an appropriate amount of deionized water, heating to a certain temperature, and stirring until the solution evaporates to obtain a precursor solid;

[0008] (2) The precursor solid is ground and then calcined in a tube furnace to obtain metal-doped boron nitride.

[0009] Preferably, the boron source in step (1) is one or more of boric acid, metaboric acid, and ammonia borane, the nitrogen source is one or more of urea, melamine, and dicyandiamide, and the metal source is one or more of nickel sulfate, cobalt sulfate, iron sulfate, and copper sulfate.

[0010] Preferably, the mass ratio of the boron source, nitrogen source, and metal source is 1:0.1 - 10:0.01 - 1.

[0011] Preferably, the concentration of the mixed solution is 10 - 50 g / L, and the evaporation temperature of the mixed solution is 50 - 100 °C.

[0012] An application of a waste polyester alcoholysis catalyst is applicable to a preparation method of a waste polyester alcoholysis catalyst, which is characterized in that: a certain amount of PET, EG, and boron nitride doped with metal are placed in a three-necked flask connected with a thermometer, a condenser, a stirrer, and nitrogen. Slowly heat up to a suitable temperature. After a certain reaction time, cool the reacted solution to 80 - 160 °C and filter while it is hot to separate the unpolymerized PET. Rinse the filtered solid with deionized water, dry it and weigh it to obtain the mass of the unpolymerized PET. Add a large amount of deionized water to the above filtrate, stir and heat to 40 - 110 °C, filter while it is hot to obtain a mixed solution of BHET, EG, and water. Cool this mixed solution to room temperature and then place it at a low temperature of 3 - 15 °C for 5 - 24 h, filter by suction and dry to obtain BHET, and weigh it to obtain the actual yield of BHET. The present invention combines the acidic sites and basic sites of boron nitride with transition metals at the same time. The doping of transition metals enables the 3d orbitals of the metals to interact well with the 2p orbitals of the corresponding B or N sites in boron nitride, enhancing the catalytic activity, and synergistically enhancing the catalytic activity with the acid-base sites that have catalytic effects themselves.

[0013] Preferably, the mass of PET is 0.5 - 6.0 g, the volume of EG is 5 - 40 mL, the mass of the catalyst is 0.1 - 1.5 g, the alcoholysis temperature is 150 - 260 °C, and the alcoholysis time is 3 - 15 h.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] (1) The catalyst is simple to prepare, low in cost, and has good catalytic performance, and is a stable alcoholysis catalyst.

[0016] (2) The doping of transition metals enables the 3d orbitals of the metals to interact well with the 2p orbitals of the corresponding B or N sites in BN, enhancing the catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the XRD pattern of the metal-doped boron nitride catalyst prepared by the present invention;

[0018] Figure 2 It is the SEM pattern of the metal-doped boron nitride catalyst prepared by the present invention;

[0019] Figure 3The PET depolymerization rate and BHET yield of polyethylene terephthalate alcoholysis catalyzed by the metal-doped boron nitride prepared in the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with specific examples. These implementation cases are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, after reading the content taught by the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the appended claims of the application.

[0021] Embodiment 1:

[0022] (1) dissolving a certain amount of boric acid, melamine, and cobalt sulfate in a mass ratio of 1:1:0.1 in 100 mL of deionized water, heating to 85° C., and stirring until the solution evaporates to obtain a precursor solid;

[0023] (2) The precursor solid is ground and placed in a tube furnace and heated to 900°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at this temperature for 2 h to obtain metal cobalt-doped boron nitride ( Figure 1 and Figure 2 ).

[0024] An application of a waste polyester alcoholysis catalyst is applicable to a preparation method of a waste polyester alcoholysis catalyst: 1.0g PET, 15.0mL EG, and 0.15g BN-Co are placed in a three-necked flask connected to a thermometer, a condenser, a stirrer, and nitrogen, and the temperature is slowly raised to 200°C, and the reaction time is set to 5h. The conversion rate of PET is 100%, and the BHET yield is 86% ( Figure 3 ).

[0025] Embodiment 2:

[0026] (1) dissolving a certain amount of metaboric acid, urea, and cobalt sulfate in a mass ratio of 1:1:0.1 in 100 mL of deionized water, heating to 85° C., and stirring until the solution evaporates to obtain a precursor solid;

[0027] (2) The precursor solid is ground and placed in a tube furnace. The temperature is increased to 900°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at this temperature for 2 h to obtain metal cobalt-doped boron nitride.

[0028] An application of a waste polyester alcoholysis catalyst is applicable to a preparation method of a waste polyester alcoholysis catalyst: 1.0g PET, 15.0mL EG, and 0.15g BN-Co are placed in a three-necked flask connected to a thermometer, a condenser, a stirrer, and nitrogen, and the temperature is slowly raised to 180°C, and the reaction time is set to 5h. The conversion rate of PET is 88%, and the yield of BHET is 75%.

[0029] Example 3:

[0030] (1) A certain amount of boric acid, melamine, and cobalt sulfate were fully dissolved in 100 mL of deionized water at a mass ratio of 1:1:0.5 and heated to 85 °C, and stirred thoroughly until the solution evaporated to obtain a precursor solid;

[0031] (2) The precursor solid was ground and then placed in a tube furnace. Under a nitrogen atmosphere, it was heated to 900 °C at a heating rate of 5 °C / min and held for 3 h to obtain boron nitride doped with cobalt metal.

[0032] The application of a waste polyester alcoholysis catalyst is applicable to a preparation method of a waste polyester alcoholysis catalyst: 1.0 g of PET, 15.0 mL of EG, and 0.15 g of BN-Co were placed in a three-necked flask connected to a thermometer, a condenser, a stirrer, and nitrogen, and slowly heated to 160 °C. The reaction time was set to 5 h. The conversion rate of PET was 68%, and the yield of BHET was 69%.

[0033] Example 4:

[0034] (1) A certain amount of ammonia borane, dicyandiamide, and zinc sulfate were fully dissolved in 100 mL of deionized water at a mass ratio of 1:1:0.1 and heated to 90 °C, and stirred thoroughly until the solution evaporated to obtain a precursor solid;

[0035] (2) The precursor solid was ground and then placed in a tube furnace. Under a nitrogen atmosphere, it was heated to 1000 °C at a heating rate of 5 °C / min and held for 2 h to obtain boron nitride doped with zinc metal.

[0036] The application of a waste polyester alcoholysis catalyst is applicable to a preparation method of a waste polyester alcoholysis catalyst: 1.0 g of PET, 15.0 mL of EG, and 0.15 g of BN-Zn were placed in a three-necked flask connected to a thermometer, a condenser, a stirrer, and nitrogen, and slowly heated to 200 °C. The reaction time was set to 5 h. The conversion rate of PET was 93%, and the yield of BHET was 78%.

[0037] Example 5:

[0038] (1) A certain amount of boric acid, melamine, and copper sulfate were fully dissolved in 100 mL of deionized water at a mass ratio of 1:2:0.1 and heated to 85 °C, and stirred thoroughly until the solution evaporated to obtain a precursor solid;

[0039] (2) The precursor solid was ground and then placed in a tube furnace. Under a nitrogen atmosphere, it was heated to 900 °C at a heating rate of 5 °C / min and held for 2 h to obtain boron nitride doped with copper metal.

[0040] Application of a waste polyester alcoholysis catalyst, applicable to a preparation method of a waste polyester alcoholysis catalyst: Put 1.0 g of PET, 15.0 mL of EG, and 0.15 g of BN-Cu into a three-necked flask connected with a thermometer, a condenser, a stirrer, and nitrogen, slowly heat up to 200 °C, and set the reaction time to 5 h. The conversion rate of PET is 90%, and the yield of BHET is 75%.

[0041] Example 6:

[0042] (1) Dissolve a certain amount of boric acid, melamine, and copper sulfate in a mass ratio of 1:1:0.05 in 100 mL of deionized water and heat to 70 °C, stir well until the solution evaporates to obtain a precursor solid;

[0043] (2) Grind the precursor solid and place it in a tube furnace. Under a nitrogen atmosphere, heat it to 900 °C at a heating rate of 5 °C / min and keep it for 2 h to obtain boron nitride doped with metallic copper.

[0044] Application of a waste polyester alcoholysis catalyst, applicable to a preparation method of a waste polyester alcoholysis catalyst: Put 1.5 g of PET, 20.0 mL of EG, and 0.15 g of BN-Cu into a three-necked flask connected with a thermometer, a condenser, a stirrer, and nitrogen, slowly heat up to 180 °C, and set the reaction time to 5 h. The conversion rate of PET is 85%, and the yield of BHET is 70%.

[0045] Example 7:

[0046] (1) Dissolve a certain amount of metaboric acid, urea, and nickel sulfate in a mass ratio of 1:1:0.1 in 80 mL of deionized water and heat to 85 °C, stir well until the solution evaporates to obtain a precursor solid;

[0047] (2) Grind the precursor solid and place it in a tube furnace. Under a nitrogen atmosphere, heat it to 900 °C at a heating rate of 5 °C / min and keep it for 3 h to obtain boron nitride doped with metallic nickel.

[0048] Application of a waste polyester alcoholysis catalyst, applicable to a preparation method of a waste polyester alcoholysis catalyst: Put 1.5 g of PET, 20.0 mL of EG, and 0.2 g of BN-Ni into a three-necked flask connected with a thermometer, a condenser, a stirrer, and nitrogen, slowly heat up to 160 °C, and set the reaction time to 5 h. The conversion rate of PET is 75%, and the yield of BHET is 61%.

[0049] Example 8:

[0050] (1) A certain amount of ammonia borane, melamine, and iron sulfate were fully dissolved in 90 mL of deionized water at a mass ratio of 1:1:0.05 and heated to 80 °C, and stirred thoroughly until the solution evaporated to obtain a precursor solid;

[0051] (2) The precursor solid was ground and placed in a tubular furnace, and heated to 1000 °C at a heating rate of 5 °C / min under a nitrogen atmosphere and held for 2 h to obtain boron nitride doped with metallic iron.

[0052] The application of a waste polyester alcoholysis catalyst is applicable to a preparation method of a waste polyester alcoholysis catalyst: 1.0 g of PET, 15.0 mL of EG, and 0.15 g of BN-Fe were placed in a three-necked flask connected to a thermometer, a condenser, a stirrer, and nitrogen, and slowly heated to 200 °C, and the reaction time was set to 3 h. The conversion rate of PET was 71%, and the yield of BHET was 63%.

[0053] Comparative Example 1:

[0054] (1) A certain amount of boron source and nitrogen source were fully dissolved in 100 mL of deionized water at a mass ratio of 1:1 and heated to 85 °C, and stirred thoroughly until the solution evaporated to obtain a precursor solid;

[0055] (2) The precursor solid was ground and placed in a tubular furnace, and heated to 900 °C at a heating rate of 5 °C / min under a nitrogen atmosphere and held for 2 h to obtain boron nitride.

[0056] 1.5 g of PET, 15.0 mL of EG, and 0.15 g of BN were placed in a three-necked flask connected to a thermometer, a condenser, a stirrer, and nitrogen, and slowly heated to 200 °C, and the reaction time was set to 3 h. The conversion rate of PET was 48%, and the yield of BHET was 34%.

[0057] Comparative Example 2:

[0058] (1) A certain amount of cobalt sulfate powder was fully dissolved in 100 mL of deionized water and heated to 85 °C, and stirred thoroughly until the solution evaporated to obtain a precursor solid;

[0059] (2) The precursor solid was ground and placed in a tubular furnace, and heated to 900 °C at a heating rate of 5 °C / min under a nitrogen atmosphere and held for 2 h to obtain a metal catalyst.

[0060] 1.0 g of PET, 20.0 mL of EG, and 0.15 g of the metal catalyst were placed in a three-necked flask connected to a thermometer, a condenser, a stirrer, and nitrogen, and slowly heated to 200 °C, and the reaction time was set to 3 h. The conversion rate of PET was 54%, and the yield of BHET was 38%.

Claims

1. Application of a waste polyester alcoholysis catalyst, characterized in that: A certain amount of PET, ethylene glycol, and metal-doped boron nitride are placed in a three-necked flask connected to a thermometer, a condenser, a stirrer, and nitrogen. Slowly heat the mixture to 150 - 240 °C and react for 3 - 15 h. That's it. The waste polyester alcoholysis catalyst is prepared by the following method: (1) Dissolve a certain amount of boron source, nitrogen source, and metal source in an appropriate amount of deionized water and heat to a certain temperature. Stir well until the solution evaporates to obtain a precursor solid. The boron source is one of boric acid, metaboric acid, ammonia borane, boron chloride, boron sulfide, boron oxide, or sodium borohydride. The nitrogen source is one of urea, melamine, dicyandiamide, sodium azide, or sodium amide. The metal source is one of nickel sulfate, cobalt sulfate, copper sulfate, or zinc sulfate. (2) Grind the precursor solid and place it in a tubular furnace. Calcinate it at 800 - 1200 °C for 2 - 5 h in a nitrogen atmosphere to obtain metal-doped boron nitride.

2. The application of a waste polyester alcoholysis catalyst according to claim 1, characterized in that, The mass ratio of the catalyst, PET, and ethylene glycol is 1 - 15:5 - 60:17 - 140.

3. The application of a waste polyester alcoholysis catalyst according to claim 1, characterized in that, The mass ratio of the boron source, nitrogen source, and metal source is 1:0.1 - 10:0.01 - 1.

4. Use of a waste polyester alcoholysis catalyst according to claim 1, characterized in that, In step (1), the evaporation temperature of the mixed solution is 50 - 100 °C.

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