A method for preparing a doped carbon-supported single-site metal catalyst using nitrogen-containing waste plastics and applications thereof

Abstract

The application discloses a method for preparing a doped carbon supported unit point metal catalyst by using nitrogen-containing waste plastics. The nitrogen-containing waste plastics are first dispersed into water, and then pretreated under a hydrothermal condition. After solvent evaporation and drying, a solid product is obtained. The solid product is uniformly laid on a heat-resistant substrate, and a metal foam is placed on the substrate. In a tube furnace, the metal foam is reacted at 700-1200 DEG C under an inert atmosphere to obtain a doped carbon supported unit point metal catalyst with thermal catalytic performance. The obtained catalyst can be applied to microwave-assisted rapid catalytic degradation of polyester, polycarbonate, epoxy resin and polyurethane resin plastics.

Description

TECHNICAL FIELD

[0001] The application relates to a method for preparing a doped carbon-supported unit point metal catalyst from nitrogen-containing waste plastics and application of the doped carbon-supported unit point metal catalyst in microwave-assisted rapid degradation of polyester, polycarbonate and polyurethane resin plastics, and belongs to the field of plastic solid waste recycling and resource utilization. BACKGROUND

[0002] Plastic recycling and chemical upgrading are the focus of renewable resource research in recent years. Nitrogen-containing waste plastics account for a large proportion of total waste plastics in the world. The nitrogen-containing waste plastics used in the application include melamine resin, urea-formaldehyde resin, melamine-urea-formaldehyde resin and polyurethane.

[0003] Melamine-formaldehyde resin (MFR), also known as melamine-formaldehyde resin, is a cross-linked polymer obtained by condensation polymerization of melamine and formaldehyde, and is a thermosetting plastic with a repeating methylene-linked triazine ring structure, which is widely used in tableware, toys and imitation glaze handicrafts. Urea-formaldehyde resin (UF), also known as urea-formaldehyde resin, is a high polymer with -NH2-CO- structural unit formed by condensation polymerization of urea and formaldehyde under the action of a catalyst. Initial urea-formaldehyde resin is mainly used as an adhesive. Final urea-formaldehyde resin is a cross-linked thermosetting plastic, which is mainly used in electrical appliances, soundproofing and thermal insulation materials, etc. Melamine-urea-formaldehyde resin (MUF) is a thermosetting plastic obtained by condensation polymerization of melamine, urea and formaldehyde, which is mainly used as an adhesive and melamine-urea-formaldehyde foaming foam. Polyurethane (PU), also known as polyurethane, is a high molecular material with urethane segment (-NHCOO-) formed by condensation polymerization of polyol and polyisocyanate. It is mainly used as soft / hard foam plastic, elastomer, fiber plastic, adhesive, etc. in textile, building, shoemaking industry and medical industry, etc. These nitrogen-containing waste plastics will slowly decompose to generate toxic and harmful pollutants such as formaldehyde and organic ammonia when landfilled Molecules 2020, 25 (16), 3629). A large amount of toxic gas is also generated in the incineration process. In addition, chemical recycling can only obtain a mixture, which is difficult to separate and purify and consumes a large amount of energy Green Chemistry 2021, 23 (19), 7816-7824; Green Chemistry , 2024, 26(3), 1132).

[0004] Metal single-site catalysts are supported catalysts composed of metal single-atom sites and carriers with isolated metal single-atom sites as active centers. The utilization rate of metal atoms reaches 100%. It has excellent catalytic activity and selectivity and can be applied in the fields of energy, petrochemicals and environmental protection. At present, the main methods for synthesizing metal single atoms include wet chemical method (CN202311718095; CN202410431144), defect design strategy ( ACS Catalysis 2018, 8,4044-4048) and electrochemical deposition ( Nature Communications 2016, 7, 10667) and high-temperature pyrolysis (CN202410186099; Chemical Reviwes 2020, 120, 21, 11900-11955) and so on. Among them, the wet chemical method requires precise control of the ratio of metal salts, support precursors and solvents, and the metal loading per unit point is low. The electrochemical deposition method requires the support to have good conductivity, and the reduction process easily forms metal particle agglomerates. The single atom required by the defect design strategy is specifically adsorbed on a metal oxide support with rich oxygen vacancies. Li Yadong used high-temperature pyrolysis to convert the zeolite imidazole skeleton into a metal unit-site catalyst. This process requires precise control of the metal ratio and the pyrolysis rate of the zeolite imidazole skeleton. Subsequently, Li Yadong and Wu Yuen used pyrolysis of small organic molecules or zeolite imidazole skeletons to obtain ammonia molecules coordinated with bulk metals to form M(NH3) x , which is then captured by the defects of the nitrogen-rich carbon support to obtain a metal single-site catalyst ( Nature Catalysis 2018, 1, 781-786). This process requires precise control of the pyrolysis rate of small organic molecules, the generation rate of nitrogen-rich carbon supports, and the relative distance between the ammonia precursor and the bulk metal. It also consumes small organic molecules and is uneconomical. In summary, these methods often require specialized equipment or complex support preparation and pre-modification, resulting in poor economics and severely limiting the large-scale preparation and practical application of single-atom catalysts.

[0005] Polyester plastics are linear polymers connected by ester bonds. Due to their excellent properties such as high strength, high heat resistance, acid and alkali resistance, etc., they are widely used in packaging, textile, automobile and other industries. Polyurethane is a high molecular material with urethane segments (-NHCOO-) formed by the polycondensation of polyols and polyisocyanate, mainly used in textile, construction, shoemaking industry and medical industry, etc. Polycarbonate is a polymer with carbonate groups. Due to its excellent optical properties, it is widely used in glass assembly industry, automobile industry, electronic and electrical industry, etc. Epoxy resin is an organic polymer containing two or more epoxy groups. It can be crosslinked with organic amine, polyamide, acid anhydride and other curing agents to form a thermosetting polymer with a network structure. It is widely used in mechanical and electronic, aerospace, automotive and military industries. However, the large-scale use and disposal of polyester, polycarbonate, epoxy resin and polyurethane plastics seriously pollute the environment and waste resources. Green Chemical Engineering , 2024, 5(2), 257-265; Polymer , 2017, 117(19), 183-197; Green Chemistry , 2024, 26, 1132). However, the above process requires the use of inorganic and organic acid (or base) catalysts, and the reaction time is long and the energy consumption is large.

[0006] Therefore, it is urgent to develop a simple and easy-to-control upgrading method for nitrogen-containing waste plastics, which reduces the use of organic solvents, does not require complex pretreatment and chemical synthesis, and has high product added value. At the same time, it is urgent to develop a method for rapidly degrading and catalytically degrading polyester, polycarbonate, epoxy resin and polyurethane plastics. SUMMARY

[0007] In view of the shortcomings of environmental pollution, toxic gas release during pyrolysis and difficulty in separating chemical degradation products during landfill treatment of waste nitrogen-containing waste plastics, the present application develops a simple and efficient method for preparing a carbon-doped metal unit point catalyst from nitrogen-containing waste plastics, and applies it to microwave-assisted rapid catalytic degradation of polyester, polycarbonate, epoxy resin and polyurethane plastics.

[0008] In order to achieve the above purpose, the application adopts the following technical scheme:

[0009] A method for preparing a carbon-doped metal unit point catalyst from nitrogen-containing waste plastics, comprising the following steps:

[0010] The nitrogen-containing waste plastics are crushed and dispersed in water, and then hydrothermally pretreated at 120-280℃ in a sealed container.

[0011] After evaporation of the solvent and drying, a solid product is obtained;

[0012] (3) The solid product is evenly spread on a heat-resistant substrate, and a metal foam is placed on it, and a doped carbon supported single-site metal catalyst is obtained by reacting at 700-1200°C under an inert atmosphere.

[0013] In the above step (1), the nitrogen-containing waste plastics are dispersed in water, and the mass of the nitrogen-containing waste plastics to the volume of water is R 0.2-0.01 g·mL -1 , and the nitrogen-containing waste plastics are selected from melamine resin, melamine urea-formaldehyde resin, urea-formaldehyde resin, and polyurethane.

[0014] In the above step (1), the pretreatment is carried out at 120-280°C for 2-4 h.

[0015] In the above step (2), the evaporation of the solvent is preferably carried out by evaporating the pretreated mixture at 50-80°C with air bubbling to promote water evaporation and reduce material loss.

[0016] In the above step (3), the metal foam is selected from foam iron, foam nickel, foam cobalt, foam copper, foam silver, foam nickel-iron, or foam nickel-cobalt. The mass ratio of the metal foam to the plastic solid is W 0.01-0.2.

[0017] In the above step (3), the metal loading mass fraction in the obtained doped carbon supported single-site metal catalyst is 10-20%.

[0018] In the above step (3), the inert atmosphere is an inert gas such as nitrogen or argon. The temperature is raised to 700-1200°C at a rate of 2-10°C / min -1 , and the doped carbon supported single-site metal catalyst is obtained by holding the temperature for 5-30 min.

[0019] The doped carbon supported single-site metal catalyst prepared by the above method can catalyze the degradation of polyester, polycarbonate (PC), epoxy resin (EP), and polyurethane (PU) waste plastics.

[0020] Specifically, the method for catalytic degradation of waste plastics is as follows: a catalytic amount of the doped carbon supported single-site metal catalyst is added to a waste plastic dispersion liquid, and after ultrasonic dispersion, a solid-liquid dispersion slurry is formed, and catalytic degradation is carried out under microwave assistance.

[0021] The solvent in the waste plastic dispersion liquid is selected from water, methanol, ethanol, acetic acid, ethylene glycol, and diethylene glycol, and the mass of the waste plastics (g) to the volume of the solvent (mL) is R , R = m(waste plastics) V (solvent), R 0.01~0.5 g∙ mL -1 .

[0022] The microwave power of the microwave-assisted catalytic degradation is 500~2000 W, the reaction temperature is 100~280℃, the reaction time is 0.5~20 min, and the reaction pressure is 0.1~2 MPa.

[0023] The polyester plastics are polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and polycaprolactone (PCL).

[0024] Advantages and beneficial effects of the present application: (1) The present application aims at the shortcomings of waste nitrogen-containing waste plastics landfill pollution environment, pyrolysis release of toxic gases and difficult separation of chemical degradation products, and develops a method for preparing a carbon-doped metal unit point catalyst using nitrogen-containing waste plastics; nitrogen-containing small molecules generated by pyrolysis of waste nitrogen-containing waste plastics are captured by foam metal to form a carbon-doped metal unit point catalyst; the interaction between waste nitrogen-containing waste plastics and foam metal is strong due to the high pyrolysis temperature of waste nitrogen-containing waste plastics and the relatively slow release rate of nitrogen-containing small molecules, so that the preparation conditions and parameters of the synthesized unit point metal catalyst are simple and controllable; the pretreatment and preparation process is simple, and there is no need to synthesize a carrier and a precursor; using nitrogen-containing waste plastics as raw materials, the carbon-doped metal unit point catalyst can be obtained with low cost and environmental protection, and high value-added products can be obtained.(2) The present application aims at the problem of slow degradation rate of waste polyester, polycarbonate, epoxy resin and polyurethane resin plastics, and develops a rapid microwave-assisted catalytic degradation method, which realizes rapid and efficient degradation of waste polyester, polycarbonate, epoxy resin and polyurethane resin plastics by using the prepared carbon-doped metal unit point catalyst.(3) The carbon-doped metal unit point catalyst generates in-situ thermal effect under microwave irradiation, so that rapid and efficient degradation of waste polyester, polycarbonate, epoxy resin and polyurethane resin plastics can be realized at a lower reaction temperature and pressure; a microwave high-pressure continuous flow reactor is used to realize continuous degradation. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a schematic diagram of pyrolysis of foam metal covered waste plastic hydrothermal treatment product;

[0026] Figure 2 High-angle annular dark field scanning transmission electron micrograph of example 1;

[0027] Figure 3 High-angle annular dark field scanning transmission electron micrograph of example 4;

[0028] Figure 4 Transmission electron micrograph of example 11;

[0029] Figure 5 Transmission electron microscopy image of Example 12;

[0030] Figure 6 High-angle annular dark-field scanning transmission electron microscopy image of Example 13;

[0031] Figure 7 Infrared comparison of the degradation product terephthalic acid in Example 15 and the commercially available product. DETAILED DESCRIPTION

[0032] Below in conjunction with specific embodiment of the present invention, technical solution of the present invention is clearly and completely described, it is obvious that described embodiment is only a part of embodiment of the present invention, rather than whole embodiment.The reagent, method and equipment adopted in the present invention are conventional reagents, methods and equipment in the art.Based on the embodiment in the present invention, the every other embodiment that those of ordinary skill in the art obtain under the premise of not making creative work, all belong to the scope of protection of the present invention.

[0033] Example 1

[0034] Disperse 5.0 g of melamine resin in 500 mL of water. R = 0.01, the dispersion was transferred to a sealed container and pretreated at 200 ° C for 3 hours. The resulting mixture was evaporated at 60 ° C. During the evaporation process, auxiliary air bubbling was used to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum drying oven at 90 ° C for 8 h. Figure 1 As shown, 0.2 g of solid product was evenly spread in a porcelain boat crucible, and 0.02 g of nickel foam was placed on it. W = 0.1. In a tube furnace, under nitrogen atmosphere (flow rate 50 mL∙min -1 ), at 2℃ min -1 The temperature was raised to 800°C at a constant temperature and under this atmosphere. After calcination for 1 hour, 0.08 g of nitrogen-oxygen-doped carbon-supported single-site Ni catalyst was obtained, with a loading of 11.3%. High-angle annular dark-field scanning transmission electron microscopy images showed that Ni was dispersed on the nitrogen-oxygen-doped carbon as isolated metal single-atom sites ( Figure 2 ).

[0035] Comparison Examples

[0036] The process of this comparative example is the same as that of Example 1, except that no foamed nickel is placed during the roasting process, and only 0.07 g of nitrogen and oxygen-doped carbon is obtained by roasting.

[0037] Example 2

[0038] 1.0 g melamine resin was dispersed in 20 mL water, R = 0.05, the dispersion was transferred to a closed container and pre-treated at 280 °C for 2.5 hours. The resulting mixture was evaporated at 70°C, with the assistance of air bubbling to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum oven at 90°C for 8 h. 0.5 g of the solid product was evenly spread in a porcelain boat crucible and 0.075 g of foam cobalt was placed on top W = 0.15. In a tube furnace, under a nitrogen atmosphere (flow rate 100 mL min -1 -1) the temperature was increased at a rate of 8°C min -1 -1 to 900°C. After 0.5 h of isothermal calcination at this temperature and in this atmosphere, 0.21 g of a nitrogen-oxygen doped carbon supported single-site Co catalyst was obtained, with a loading of 15.1%.

[0039] Example 3

[0040] 3.0 g polyurethane was dispersed in 30 mL water, R = 0.1, the dispersion was transferred to a closed container and pre-treated at 120 °C for 4 hours. The resulting mixture was evaporated at 50°C, with the assistance of air bubbling to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum oven at 120°C for 2 h. 0.3 g of the solid product was evenly spread in a porcelain boat crucible and 0.015 g of foam zinc was placed on top W = 0.05. In a tube furnace, under an argon atmosphere (flow rate 150 mL min -1 -1) the temperature was increased at a rate of 2°C min -1 -1 to 700°C. After 6 h of isothermal calcination at this temperature and in this atmosphere, 0.11 g of a nitrogen-oxygen doped carbon supported single-site Zn catalyst was obtained, with a loading of 10.1%.

[0041] Example 4

[0042] 4.0 g polyurethane was dispersed in 200 mL water, R = 0.02, the dispersion was transferred to a closed container and pre-treated at 150 °C for 3 hours. The resulting mixture was evaporated at 60°C, with the assistance of air bubbling to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum oven at 100°C for 4 h. 0.4 g of the solid product was evenly spread in a porcelain boat crucible and 0.004 g of foam copper was placed on top W = 0.01. In a tube furnace, under a nitrogen atmosphere (flow rate 50 mL min-1 ) to 800 °C at a rate of 5 °C min -1 After 5 h of isothermal calcination at this temperature and atmosphere, 0.16 g of nitrogen-oxygen doped carbon supported single-site Cu catalyst with a loading of 12.8% was obtained.

[0043] Example 5

[0044] 0.8 g of urea-formaldehyde resin was dispersed in 50 mL of water, R = 0.016, the dispersion was transferred to a closed container and pre-treated at 180 °C for 3 h. The resulting mixture was evaporated at 70 °C, with the assistance of air bubbling to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum oven at 110 °C for 3 h. 0.2 g of the solid product was evenly spread in a porcelain boat crucible, and 0.04 g of foamed nickel was placed on top W = 0.2. In a tube furnace, under nitrogen atmosphere (flow rate 10 mL min -1 ), the temperature was increased to 900 °C at a rate of 7 °C min -1 After 4 h of isothermal calcination at this temperature and atmosphere, 0.06 g of nitrogen-oxygen doped carbon supported single-site Ni catalyst with a loading of 12.4% was obtained.

[0045] Example 6

[0046] 2.4 g of urea-formaldehyde resin was dispersed in 80 mL of water, R = 0.03, the dispersion was transferred to a closed container and pre-treated at 210 °C for 3.5 h. The resulting mixture was evaporated at 50 °C, with the assistance of air bubbling to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum oven at 110 °C for 12 h. 0.3 g of the solid product was evenly spread in a porcelain boat crucible, and 0.03 g of foamed iron was placed on top W = 0.1. In a tube furnace, under argon atmosphere (flow rate 150 mL min -1 ), the temperature was increased to 1000 °C at a rate of 10 °C min -1 After 2 h of isothermal calcination at this temperature and atmosphere, 0.09 g of nitrogen-oxygen doped carbon supported single-site Fe catalyst with a loading of 10.5% was obtained. High-angle annular dark-field scanning transmission electron microscopy images showed that Fe was dispersed as isolated metal single-atom sites on the nitrogen-oxygen doped carbon ( Figure 3 ).

[0047] Example 7

[0048] Disperse 1.0 g of melamine urea-formaldehyde resin in 100 mL of water. R = 0.01, the dispersion was transferred to a sealed container and pretreated at 160 ° C for 3 hours. The resulting mixture was evaporated at 50 ° C. During the evaporation process, auxiliary air bubbling was used to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum drying oven at 110 ° C for 3 h. 0.4 g of the solid product was evenly spread in a porcelain boat crucible, and 0.06 g of foamed copper was placed on it. W = 0.15. In a tube furnace, under argon atmosphere (flow rate 200 mL∙min -1 ), at 15℃ min -1 The temperature was raised to 1100°C at a rate of 100°C. After constant temperature calcination for 1 hour at this temperature and atmosphere, 0.17 g of nitrogen-oxygen-doped carbon-supported single-site Cu catalyst was obtained with a loading of 12.5%.

[0049] Example 8

[0050] Disperse 1.6 g of melamine urea-formaldehyde resin in 20 mL of water. R = 0.08, transfer the dispersion into a sealed container and heat at 250 The mixture was pretreated at 400 °C for 2 hours. The resulting mixture was evaporated at 60 °C. During the evaporation process, auxiliary air bubbling was used to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum drying oven at 80 °C for 2 h. 0.5 g of the solid product was evenly spread in a porcelain boat crucible, and 0.02 g of foamed silver was placed on it. W = 0.04. In a tube furnace, under nitrogen atmosphere (flow rate 180 mL∙min -1 ), at 20℃ min -1 The temperature was raised to 1200°C at a rate of 100°C. After constant temperature calcination for 0.5 h at this temperature and atmosphere, 0.16 g of nitrogen-oxygen-doped carbon-supported single-site Ag catalyst was obtained with a loading of 10.3%.

[0051] Example 9

[0052] Disperse 1.0 g of melamine resin and 1.0 g of urea-formaldehyde resin in 10 mL of water. R = 0.2, transfer the dispersion into a sealed container and heat at 260 The mixture was pretreated at 70°C for 2 hours. During the evaporation process, air was bubbling to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum drying oven at 80°C for 2 hours. 0.3 g of the solid product was evenly spread in a porcelain boat crucible, and 0.03 g of foamed iron-nickel was placed on it. W= 0.1. In a tube furnace, under argon atmosphere (flow rate 100 mL min -1 -1), the temperature was increased to 700°C at a rate of 6°C min -1 -1. After 6 h of isothermal calcination at this temperature and under this atmosphere, 0.15 g of nitrogen-oxygen doped carbon supported single-site Fe, Ni catalysts were obtained, with loadings of 1.7% and 8.5%, respectively.

[0053] Example 10

[0054] 1.4 g of polyurethane and 1.4 g of urea-formaldehyde resin were dispersed in 20 mL of water, R = 0.14, and the dispersion was transferred to a closed container and pre-treated at 230 °C for 2 h. The resulting mixture was evaporated at 80°C, with the assistance of air bubbling to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum oven at 60°C for 2 h. 0.4 g of the solid product was uniformly spread in a porcelain boat crucible, and 0.06 g of foamed nickel-cobalt was placed on top W = 0.15. In a tube furnace, under argon atmosphere (flow rate 160 mL min -1 -1), the temperature was increased to 900°C at a rate of 7°C min -1 -1. After 3 h of isothermal calcination at this temperature and under this atmosphere, 0.14 g of nitrogen-oxygen doped carbon supported single-site Ni, Co catalysts were obtained, with loadings of 7.7% and 2.4%, respectively.

[0055] Example 11

[0056] 0.5 g of polyethylene terephthalate was dispersed in 50 mL of water, R = 0.01, and the dispersion was transferred to a closed container and pre-treated at 200 °C for 3 h. The resulting mixture was evaporated at 60°C, with the assistance of air bubbling to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum oven at 90°C for 8 h. 0.2 g of the solid product was uniformly spread in a porcelain boat crucible, and 0.02 g of foamed nickel was placed on top W = 0.1. In a tube furnace, under nitrogen atmosphere (flow rate 50 mL min -1 -1), the temperature was increased to 800°C at a rate of 2°C min -1 -1. After 1 h of isothermal calcination at this temperature and under this atmosphere, 0.06 g of oxygen-doped carbon supported Ni nanoparticles were obtained, with a loading of 10.5%. Transmission electron micrographs showed that Ni was dispersed as metallic nanoparticles on the nitrogen-oxygen doped carbon (Fig. 4). Figure 4

[0057] ​Example 12

[0058] 5.0 g melamine resin was dispersed in 500 mL water, R = 0.01, the dispersion was transferred into a closed container and pre-treated at 200 °C for 3 hours. The resulting mixture was evaporated at 60 °C, with the assistance of air bubbling to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum oven at 90 °C for 8 h. 0.2 g of the solid product and 0.02 g of foamed nickel were placed in a porcelain boat crucible (1.5 cm x 4 cm) with the solid product close to the gas inlet end and the foamed nickel close to the gas outlet end, with a distance of 1 cm between them, W = 0.1. In a tube furnace, under a nitrogen atmosphere (flow rate 50 mL min -1 -1) at a rate of 2 °C min -1 -1 to 800 °C. After 1 h of isothermal calcination at this temperature and under this atmosphere, 0.07 g of nitrogen-oxygen-doped carbon supported Ni nanoclusters were obtained, with a loading of 11.5%. Transmission electron micrographs showed that Ni was dispersed on the nitrogen-oxygen-doped carbon in the form of metal nanoclusters (Fig. 2). Figure 5

[0059] Example 13

[0060] 5.0 g melamine resin was dispersed in 500 mL water, R = 0.01, the dispersion was transferred into a closed container and pre-treated at 200 °C for 3 hours. The resulting mixture was evaporated at 60 °C, with the assistance of air bubbling to promote water evaporation and reduce material loss. Subsequently, the solid product was dried in a vacuum oven at 90 °C for 8 h. 0.2 g of the solid product and 0.02 g of foamed nickel were placed in a porcelain boat crucible (1.5 cm x 4 cm) with the solid product close to the gas inlet end and the foamed nickel close to the gas outlet end, with a distance of 1 cm between them, W = 0.1. In a tube furnace, under a nitrogen atmosphere (flow rate 50 mL min -1 -1) at a rate of 2 °C min -1 -1 to 800 °C. After 1 h of isothermal calcination at this temperature and under this atmosphere, 0.01 g of nitrogen-oxygen-doped carbon supported single-site Ni catalyst was obtained, with a loading of 1.5%. High-angle annular dark-field scanning transmission electron micrographs showed that Ni was dispersed on the nitrogen-oxygen-doped carbon in the form of isolated metal single-atom sites (Fig. 3). Figure 6 Comparing with Figure 2 and Figure 6 , the content of Ni was significantly reduced compared to Example 1.

[0061] Example 14

[0062] ​0.5 g of polyethylene terephthalate was dispersed in 50 mL of acetic acid, R = 0.01. 0.005 g of catalyst of Example 1 was added, C = 0.1%. The mixture was ultrasonically dispersed for 10 min to form a solid-liquid dispersion slurry. The slurry was transferred to a 100 mL microwave reaction tank for microwave-assisted catalytic degradation. The microwave power was 500 W, the reaction temperature was 160°C, the reaction pressure was 1.2 MPa, and the reaction time was 20 min. The conversion rate of polyethylene terephthalate was 99%. The degradation products were terephthalic acid and ethylene glycol diacetate, the selectivity of terephthalic acid was 100%, and the yield was 99%.

[0063] Comparative Example

[0064] The procedure of this comparative example was the same as that of Example 13, except that the nitrogen-oxygen doped carbon obtained from the comparative example of Example 1 was used as the catalyst. The conversion rate of polyethylene terephthalate was 9.5%. The degradation products were terephthalic acid and ethylene glycol diacetate, the selectivity of terephthalic acid was 100%, and the yield was 9.5%.

[0065] Example 15

[0066] 5 g of polyethylene terephthalate was dispersed in 100 mL of pure water, R = 0.05. 0.025 g of catalyst of Example 2 was added, C = 0.5%. The mixture was ultrasonically dispersed for 5 min to form a solid-liquid dispersion slurry. The slurry was transferred to a microwave reaction tank at a flow rate of 0.5 mL·min -1 The slurry was pumped into a 1 mm diameter and 10 m long engineering plastic reaction coil system at a flow rate of 0.5 mL·min -1 The slurry was pumped into a 1 mm diameter and 10 m long engineering plastic reaction coil system at a flow rate of 0.5 mL·min Figure 7 The infrared absorption of the degraded terephthalic acid was consistent with that of the commercial product. Among them, the infrared absorption peak of the degraded terephthalic acid at > 3400 cm -1 The results showed that the purity of the degraded terephthalic acid was high, close to that of the commercial terephthalic acid.

[0067] Example 16

[0068] 10 g of polybutylene terephthalate was dispersed in 20 mL of methanol, R = 0.5. 0.1 g of the catalyst of Example 3 was added, C = 1%. The mixture was ultrasonically dispersed for 20 min to form a solid-liquid dispersion slurry. The slurry was transferred to a 100 mL microwave reaction tank for microwave-assisted catalytic degradation. The microwave power was 800 W, the reaction temperature was 150°C, the reaction pressure was 2 MPa, and the reaction time was 12.5 min. The conversion rate of polybutylene terephthalate was 98%. The degradation products were dimethyl terephthalate and butanediol, the selectivity of dimethyl terephthalate was 100%, and the yield was 98%.

[0069] Example 17

[0070] 5 g of polybutylene terephthalate was dispersed in 50 mL of acetic acid, R = 0.1. 0.125 g of the catalyst of Example 4 was added, C = 2.5%. The mixture was ultrasonically dispersed for 60 min to form a solid-liquid dispersion slurry. The slurry was transferred to a microwave reaction tank at a flow rate of 1 mL·min -1 The slurry was pumped into a 1 mm diameter and 10 m long engineering plastic reaction coil system at a flow rate of 1 mL·min

[0071] Example 18

[0072] 6 g of polycaprolactone was dispersed in 200 mL of ethanol, R = 0.03. 0.24 g of the catalyst of Example 5 was added, C = 4%. The mixture was ultrasonically dispersed for 15 min to form a solid-liquid dispersion slurry. The slurry was transferred to a 500 mL microwave reaction tank for microwave-assisted catalytic degradation. The microwave power was 1000 W, the reaction temperature was 100°C, the reaction pressure was 0.8 MPa, and the reaction time was 12 min. The conversion rate of polycaprolactone was 97.5%. The degradation product was ethyl caproate, the selectivity was 100%, and the yield was 97.5%.

[0073] Example 19

[0074] 2 g polycarbonate was dispersed in 25 mL glycerol, R = 0.08. 0.016 g catalyst of Example 6 was added, C = 0.8%. The mixture was ultrasonically dispersed for 40 min to form a solid-liquid dispersion slurry. The slurry was transferred to a 100 mL microwave reaction tank for microwave-assisted catalytic degradation. The microwave power was 1600 W, the reaction temperature was 280°C, the reaction pressure was 0.1 MPa, and the reaction time was 2 min. The conversion rate of polycarbonate was 95.5%. The degradation products were bisphenol A and glycerol carbonate, and the selectivity of bisphenol A was 95% with a yield of 91%.

[0075] Example 20

[0076] 0.15 g bisphenol A diglycidyl ether (DER311) and methyl-5-norbornene-2,3-dicarboxylic anhydride cured thermosetting epoxy resin powder were dispersed in 15 mL pure water, R = 0.01. 0.005 g catalyst of Example 7 was added, C = 0.1%. The mixture was ultrasonically dispersed for 10 min to form a solid-liquid dispersion slurry. The slurry was transferred to a 100 mL microwave reaction tank for microwave-assisted catalytic degradation. The microwave power was 500 W, the reaction temperature was 200°C, the reaction pressure was 1.8 MPa, and the reaction time was 20 min. The conversion rate of thermosetting epoxy resin was 98%. The degradation products were bisphenol A and cis-5-norbornene-endo-2,3-dicarboxylic acid oligomers with a yield of 95%.

[0077] Example 21

[0078] 4 g toluene isocyanate and thermoplastic polyurethane soft polyurethane based on polyethylene glycol were dispersed in 15 mL ethylene glycol, R = 0.267. 0.008 g catalyst of Example 8 was added, C = 0.2%. The mixture was ultrasonically dispersed for 15 min to form a solid-liquid dispersion slurry. The slurry was transferred to a 50 mL microwave reaction tank for microwave-assisted catalytic degradation. The microwave power was 2000 W, the reaction temperature was 280°C, the reaction pressure was 0.3 MPa, and the reaction time was 0.5 min. The conversion rate of polyurethane was 97%. The degradation product was polyether polyol with a yield of 89%.

[0079] Example 22

[0080] 2 g 1, 4-diphenylmethane diisocyanate and thermoplastic polyurethane hard polyurethane based on butanediol were dispersed in 50 mL ethylene glycol-water solution (V 乙二醇 :V水 = 1:1) and R = 0.04, C = 0.04 g / L. R = 0.04. 0.04 g of the catalyst of Example 9 was added, C = 2%. The mixture was ultrasonically dispersed for 25 min to form a solid-liquid dispersion slurry. The slurry was transferred to a 100 mL microwave reaction tank for microwave-assisted catalytic degradation. The microwave power was 1500 W, the reaction temperature was 180°C, the reaction pressure was 0.9 MPa, and the reaction time was 1 min. The conversion rate of the polyurethane was 100%. The degradation product was a polyether polyol with a yield of 84%.

[0081] Example 23

[0082] 10 g of a thermosetting polyurethane with 4,4'-dicyclohexyl methane diisocyanate, 1,2-hexanediol, and glycerol as raw materials was dispersed in 100 mL of diethylene glycol solution, R = 0.1. 0.1 g of the catalyst of Example 10 was added, C = 1%. The mixture was ultrasonically dispersed for 10 min to form a solid-liquid dispersion slurry. The slurry was transferred to a microwave reaction tank at a flow rate of 2 mL·min -1 The slurry was pumped into a 1 mm diameter and 10 m long engineering plastic reaction coil system at a flow rate of 2 mL·min

[0083] Example 24

[0084] 0.5 g of polyethylene terephthalate was dispersed in 50 mL of acetic acid, R = 0.01. 0.005 g of the catalyst of Example 11 was added, C = 0.1%. The mixture was ultrasonically dispersed for 10 min to form a solid-liquid dispersion slurry. The slurry was transferred to a 100 mL microwave reaction tank for microwave-assisted catalytic degradation. The microwave power was 500 W, the reaction temperature was 160°C, the reaction pressure was 1.2 MPa, and the reaction time was 20 min. The conversion rate of the polyethylene terephthalate was 40%. The degradation product was terephthalic acid and ethylene glycol diacetate, and the selectivity of terephthalic acid was 100% with a yield of 20%.

[0085] Example 25

[0086] 0.5 g of polyethylene terephthalate was dispersed in 50 mL of acetic acid, R= 0.01. 0.005 g of the catalyst of Example 12 was added, C = 0.1%. The mixture was ultrasonically dispersed for 10 min to form a solid-liquid dispersion slurry. The slurry was transferred to a 100 mL microwave reaction tank for microwave-assisted catalytic degradation. The microwave power was 500 W, the reaction temperature was 160°C, the reaction pressure was 1.2 MPa, and the reaction time was 20 min. The conversion rate of polyethylene terephthalate was 55%. The degradation products were terephthalic acid and ethylene glycol diacetate, the terephthalic acid selectivity was 100%, and the yield was 25%.

[0087] Example 26

[0088] 0.5 g of polyethylene terephthalate was dispersed in 50 mL of acetic acid, R = 0.01. 0.005 g of the catalyst of Example 13 was added, C = 0.1%. The mixture was ultrasonically dispersed for 10 min to form a solid-liquid dispersion slurry. The slurry was transferred to a 100 mL microwave reaction tank for microwave-assisted catalytic degradation. The microwave power was 500 W, the reaction temperature was 160°C, the reaction pressure was 1.2 MPa, and the reaction time was 20 min. The conversion rate of polyethylene terephthalate was 45%. The degradation products were terephthalic acid and ethylene glycol diacetate, the terephthalic acid selectivity was 100%, and the yield was 45%.

Claims

1. A method for preparing a carbon-doped single-site metal catalyst using nitrogen-containing waste plastics, characterized in that The following steps are involved: (1) crushing nitrogen-containing waste plastics and dispersing them in water, and hydrothermally pre-treating them at 120-280° C. in a sealed container, wherein the nitrogen-containing waste plastics are selected from melamine resin, melamine urea-formaldehyde resin, urea-formaldehyde resin, and polyurethane; (2) Evaporating the solvent and drying to obtain a solid product; (3) The solid product is evenly spread on a heat-resistant substrate, and metal foam is placed thereon, and reacted at 700-1200°C under an inert atmosphere to obtain a doped carbon-supported single-site metal catalyst, wherein the metal foam is selected from foamed iron, foamed nickel, foamed cobalt, foamed copper, foamed silver, foamed nickel-iron, or foamed nickel-cobalt.

2. The preparation method according to claim 1, wherein: In step (3), the metal loading mass fraction of the obtained carbon-doped supported unit-site metal catalyst is 10-20%.

3. The doped carbon-supported single-site metal catalyst prepared by the method of claim 1.

4. Use of the doped carbon-supported single-site metal catalyst according to claim 3 in the catalytic degradation of polyester, polycarbonate, epoxy resin and polyurethane waste plastics.

5. The application according to claim 4, characterized in that: A catalytic amount of doped carbon-supported single-site metal catalyst is added to a waste plastic dispersion, and after ultrasonic dispersion, a solid-liquid dispersion slurry is formed, which is then catalytically degraded under the assistance of microwaves.

6. The application according to claim 5, characterized in that: The solvent in the waste plastic dispersion is selected from water, methanol, ethanol, acetic acid, ethylene glycol, and diethylene glycol.

7. The use according to claim 5, characterized in that: The microwave power of microwave-assisted catalytic degradation is 500~2000W, the reaction temperature is 100~280℃, and the reaction pressure is 0.1~2 MPa.

8. The application according to claim 5, characterized in that: The polyester plastic is selected from polyethylene terephthalate, polybutylene terephthalate, and polycaprolactone.

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