A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent

Abstract

The present invention proposes a method for preparing paraxylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent. The method comprises the following steps: (1) placing sugars, melamine and metal salts in deionized water, stirring evenly to obtain a catalyst precursor solution, transferring the catalyst precursor solution to a reaction vessel for hydrothermal reaction, washing, drying and grinding the solid obtained by the hydrothermal reaction, microwave treatment, calcining in an argon atmosphere, cooling to room temperature, and obtaining a carbon-coated bimetallic catalyst; (2) first adding a hydrogen-rich solvent to the reaction vessel, then adding PET plastic and the carbon-coated bimetallic catalyst, stirring and reacting under a nitrogen atmosphere, and collecting and detecting the liquid phase product after natural cooling. The present invention provides a cleaner, more economical, safer and more efficient disposal method for the recycling and upgrading of PET, which has good economic, social and environmental benefits.

Description

Technical field:

[0001] The invention relates to the field of waste treatment, and in particular to a method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent. Background technology:

[0002] Since the beginning of this century, human society's demand for plastic products has been growing. According to statistics, the global production of plastic products in 2021 was 390 million tons, of which more than 90% came from derivatives of the petrochemical industry. Polyethylene terephthalate (PET) is one of the most common and widely used plastics. Its natural degradation cycle can last for hundreds of years, so it is necessary to develop efficient and clean recycling methods to reduce economic losses and environmental pollution. At present, there are three mainstream recycling methods for waste PET: energy recovery, mechanical recovery and chemical recovery. Energy recovery is to recover the heat energy of PET through combustion and other forms. This method is often accompanied by the emission of huge amounts of greenhouse gases and toxic gases, so it is not recommended. Mechanical recovery is to recycle and use waste PET in other fields without changing its chemical composition through physical means (melting, extrusion molding, etc.), but this method will lead to a decrease in the mechanical properties of PET, and the application of recycled recycled PET is limited, and efficient circulation of resources cannot be achieved. Chemical recycling is the process of converting waste PET into high-purity monomers or fine chemicals through chemical means (thermochemistry, catalysis, etc.). These products can be used as synthetic raw materials for PET or other chemical products. They have high recycling rates, low pollution, and extremely high economic and environmental benefits. Therefore, developing a cheap, stable, and efficient catalyst for the catalytic conversion of waste PET is the focus and difficulty of the current PET recycling field.

[0003] Carbon materials are widely used in the preparation of various catalysts due to their wide sources and low cost. Carbon coating gives the catalyst a three-dimensional structure, which can improve the diffusion of raw materials in the catalyst, increase the contact between active sites and reactions, and reduce catalyst deactivation. Traditional catalytic reduction reactions usually require the addition of high-pressure hydrogen, which introduces additional costs and potential safety risks to the recycling of PET. Summary of the invention:

[0004] The present invention solves the problems existing in the prior art and provides a method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent. The present invention adopts a hydrothermal method to prepare a carbon-coated catalyst with different metal active sites, and hydrogenates and reduces waste PET raw materials in various hydrogen-rich solvents, so as to directly convert PET into p-xylene, a basic chemical raw material with a wide range of application scenarios, thereby realizing the coupling of PET depolymerization and in-situ hydrogenation without the participation of exogenous hydrogen, and providing a cleaner, safer and more economically efficient solution for the comprehensive recycling and upgrading of PET waste plastics.

[0005] The object of the present invention is to provide a method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent, comprising the following steps:

[0006] (1) placing sugar, melamine and metal salt in deionized water and stirring them to obtain a catalyst precursor solution, wherein the molar concentration of the metal in the metal salt is 2-8 mmol / g based on the mass of the sugar, the mass ratio of the sugar to the melamine is 1-5:1, the metal in the metal salt is composed of copper and a transition metal, and the transition metal is selected from one of cerium (Ce), zinc (Zn), nickel (Ni) and cobalt (Co), transferring the catalyst precursor solution to a reaction vessel for hydrothermal reaction, cooling to room temperature after the hydrothermal reaction, washing, drying and grinding the solid obtained by the hydrothermal reaction, adding a small amount of deionized water and subjecting it to microwave treatment, then grinding the precursor again, calcining it in an argon atmosphere, and cooling it to room temperature to obtain a carbon-coated bimetallic catalyst aM@CxN-P / T, where a represents the molar amount of the added metal salt, M represents the metal type, x represents the type of sugar, P represents the microwave power, and T represents the calcination temperature;

[0007] (2) First, add a hydrogen-rich solvent to a reaction vessel, then add PET plastic and the carbon-coated bimetallic catalyst prepared in step (1), empty the reaction vessel, raise the temperature to a preset temperature in a nitrogen atmosphere, stir and react, collect the liquid phase product after natural cooling and detect it, and obtain the target product, p-xylene. The step of emptying the reaction vessel is: introduce 1MPa nitrogen and then slowly discharge it, repeat three times, introduce 1MPa nitrogen and close the exhaust valve.

[0008] The hydrogen-rich solvents such as methanol, ethylene glycol, and 1,4-dioxane proposed in the present invention can provide hydrogen required for PET reduction in situ through reforming in the reaction system, which is a safer and more economical solution. At the same time, a carbon-coated bimetallic catalyst is used to achieve the coupling of PET depolymerization and in-situ hydrogenation in the hydrogen-rich solvent to obtain high-purity and high-yield p-xylene.

[0009] Preferably, the sugar in step (1) is selected from sucrose, maltose, lactose, and trehalose, each of which is C s , C m , C l , C t express.

[0010] Preferably, the molar ratio of copper to transition metal in step (1) is 1:1-4:1.

[0011] Preferably, the molar concentration of the metal in the catalyst precursor solution in step (1) is 5 mmol / g (based on the mass of the sugar), and the mass ratio of the sugar to melamine is 2:1.

[0012] More preferably, the metal salt in step (1) is a metal nitrate, chloride, sulfate or acetate.

[0013] Preferably, the hydrothermal reaction conditions of step (1) are: heating to 140°C-160°C at a heating rate of 1.5-2.5°C / min for 6-24h. The hydrothermal reaction is a tumbling hydrothermal reaction with a tumbling rate of 20-80rpm. More preferably, the hydrothermal reaction conditions are: heating to 150°C at 2°C / min for 12h with a tumbling rate of 50rpm.

[0014] Preferably, the calcination conditions in step (1) are: calcination temperature 400°C-700°C, calcination time 2-8h. More preferably, the calcination temperature is 550°C, and the calcination time is 4h.

[0015] Preferably, the microwave conditions in step (1) are: microwave power 0.5-1 kW, microwave time 0.5-2 min. More preferably, the microwave time is 1 min.

[0016] Preferably, the hydrogen-rich solvent in step (2) is selected from one of methanol, ethanol, isopropanol, 1,4-dioxane, tetrahydrofuran and cyclohexane.

[0017] Preferably, the mass volume ratio of the PET plastic to the hydrogen-rich solvent in step (2) is 0.1:10-30 g / mL, and the mass ratio of the catalyst to the PET plastic is 0.5-2:1. More preferably, the mass volume ratio of the PET plastic to the hydrogen-rich solvent is 0.1:20 g / mL, and the mass ratio of the catalyst to the PET plastic is 1:1.

[0018] Preferably, the reaction temperature in step (2) is 150° C.-260° C., the reaction stirring rate is 400-800 rpm, and the reaction time is 1-6 h.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1) The present invention uses relatively low-priced sugars as raw materials to prepare carbon-coated catalysts, which is economical and has no pollutant emissions during the preparation process. In addition, the coating method can effectively prevent the catalyst from deactivating while increasing the exposure opportunities of metal active sites, and has good reusability. The introduction of melamine also adds additional nitrogen-containing functional groups to the catalyst, further improving the catalytic activity;

[0021] 2) The present invention uses a hydrogen-rich solvent instead of H2 as a reducing agent, making the reaction system safer. The hydrogen-rich solvent also promotes the dispersion of raw materials and the reforming hydrogen supply, thereby improving the reaction efficiency;

[0022] 3) The present invention provides a resource-based and harmless disposal method for the recycling and upgrading of waste PET, a typical organic solid waste, thereby realizing the recycling of resources and significantly reducing the large amount of carbon emissions generated by traditional recycling methods.

[0023] In summary, the present invention proposes an efficient conversion scheme for preparing p-xylene from waste PET using a carbon-coated bimetallic catalyst, using cheap sugars as carbon sources and melamine as nitrogen sources to prepare a carbon-coated transition metal catalyst rich in nitrogen-containing functional groups, and realizing in-situ hydrogenation of waste PET to produce p-xylene in a hydrogen-rich solvent. This provides a cleaner, more economical, safer and more efficient disposal method for the recycling and upgrading of PET, with good economic, social and environmental benefits. Specific implementation method:

[0024] The following examples are provided to further illustrate the present invention, rather than to limit the present invention.

[0025] Unless otherwise defined, all professional terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the experimental materials and reagents herein are conventional commercial products in the art. In the following embodiments, the PET plastic is crushed to more than 100 mesh.

[0026] Embodiment 1:

[0027] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0028] (1) 2 g of sucrose, 1 g of melamine, 5 mmol of copper nitrate, and 5 mmol of cerium nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The obtained solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.6 kW microwave for 0.5 min. The mixture was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 5Cu5Ce@C s N-0.6.

[0029] (2) 0.1 g of waste PET powder and 5Cu5Ce@C s0.1 g of N-0.6 catalyst and 20 mL of methanol were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 230°C and stirred at a stirring rate of 600 rpm for 2 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 72.63%, as shown in Table 1.

[0030] Comparative Example 1:

[0031] The same as Example 1, except that no carbon-coated bimetallic catalyst was added during the reaction process, and no p-xylene was produced in the product.

[0032] Comparative Example 2:

[0033] The same as Example 1, except that the metal salt added during the catalyst preparation was 10 mmol of copper nitrate, and no cerium nitrate was added. The final yield of p-xylene was 23.47%.

[0034] Comparative Example 3:

[0035] The same as Example 1, except that the metal salt added during the catalyst preparation was 10 mmol of cerium nitrate, and no copper nitrate was added. The final p-xylene yield was 11.05%.

[0036] Comparative Example 4:

[0037] The same as Example 1, except that microwave treatment was not performed during catalyst preparation, and the final p-xylene yield was 36.51%.

[0038] Comparative Example 5:

[0039] The same as Example 1, except that no calcination treatment was performed during catalyst preparation, and the final p-xylene yield was 4.76%.

[0040] It can be seen from Example 1 and Comparative Example 1 that the carbon-coated bimetallic catalyst has an excellent catalytic effect on the in-situ hydrogenation of PET to produce p-xylene.

[0041] It can be seen from Example 1 and Comparative Examples 2-3 that the bimetallic loading has a synergistic promoting effect on the catalyst activity. Compared with a single loaded catalyst, the catalytic effect of the bimetallic loaded catalyst is significantly improved.

[0042] It can be seen from Example 1 and Comparative Examples 4-5 that the synergistic effect of microwave treatment and calcination results in a lower temperature gradient and a richer pore structure in the catalyst precursor, which significantly improves the diffusion of raw materials in the catalyst pores and the heat and mass transfer during the reaction process, increases the contact opportunities between reactants and catalytic active sites, and significantly improves the catalytic effect on the in-situ hydrogenation reaction of PET.

[0043] Embodiment 2:

[0044] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0045] (1) 2 g of maltose, 1 g of melamine, 5 mmol of copper nitrate, and 5 mmol of cerium nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.6 kW microwave for 0.5 min. The solid product was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 5Cu5Ce@C m N-0.6.

[0046] (2) 0.1 g of waste PET powder and 5Cu5Ce@C m 0.1 g of N-0.6 catalyst and 20 mL of methanol were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 230°C and stirred at a stirring rate of 600 rpm for 2 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 68.42%, as shown in Table 1.

[0047] Embodiment 3:

[0048] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0049] (1) 2 g of lactose, 1 g of melamine, 5 mmol of copper nitrate, and 5 mmol of cerium nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The obtained solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.6 kW microwave for 0.5 min. The mixture was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was recorded as 5Cu5Ce@C l N-0.6.

[0050] (2) 0.1 g of waste PET powder and 5Cu5Ce@C l0.1 g of N-0.6 catalyst and 20 mL of methanol were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 230°C and stirred at a stirring rate of 600 rpm for 2 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 56.77%, as shown in Table 1.

[0051] Embodiment 4:

[0052] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0053] (1) 2 g of trehalose, 1 g of melamine, 5 mmol of copper nitrate, and 5 mmol of cerium nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction, the mixture was cooled to room temperature. The solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.6 kW microwave for 0.5 min. The product was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 5Cu5Ce@C t N-0.6.

[0054] (2) 0.1 g of waste PET powder and 5Cu5Ce@C t 0.1 g of N-0.6 catalyst and 20 mL of methanol were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 230°C and stirred at a stirring rate of 600 rpm for 2 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 65.12%, as shown in Table 1.

[0055] Embodiment 5:

[0056] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0057] (1) 2 g of sucrose, 1 g of melamine, 5 mmol of copper nitrate, and 5 mmol of nickel nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.6 kW microwave for 0.5 min. The product was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 5Cu5Ni@C s N-0.6.

[0058] (2) 0.1 g of waste PET powder and 5Cu5Ni@C s 0.1 g of N-0.6 catalyst and 20 mL of methanol were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 230°C and stirred at a stirring rate of 600 rpm for 2 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 34.09%, as shown in Table 1.

[0059] Embodiment 6:

[0060] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0061] (1) 2 g of sucrose, 1 g of melamine, 5 mmol of copper nitrate, and 5 mmol of zinc nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.6 kW microwave for 0.5 min. The product was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 5Cu5Zn@C s N-0.6.

[0062] (2) 0.1 g of waste PET powder and 5Cu5Zn@C s0.1 g of N-0.6 catalyst and 20 mL of methanol were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 230°C and stirred at a stirring rate of 600 rpm for 2 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 55.62%, as shown in Table 1.

[0063] Embodiment 7:

[0064] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0065] (1) 2 g of sucrose, 1 g of melamine, 5 mmol of copper nitrate, and 5 mmol of cobalt nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The obtained solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.6 kW microwave for 0.5 min. The mixture was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 5Cu5Co@C s N-0.6.

[0066] (2) 0.1 g of waste PET powder and 5Cu5Co@C s 0.1 g of N-0.6 catalyst and 20 mL of methanol were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 230°C and stirred at a stirring rate of 600 rpm for 2 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 67.23%, as shown in Table 1.

[0067] Embodiment 8:

[0068] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0069] (1) 2 g of sucrose, 1 g of melamine, 8 mmol of copper nitrate, and 2 mmol of cerium nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.6 kW microwave for 1 min. The solid product was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 8Cu2Ce@C s N-0.6.

[0070] (2) 0.1 g of waste PET powder and 8Cu2Ce@C s 0.1 g of N-0.6 catalyst and 20 mL of methanol were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 230°C and stirred at a stirring rate of 600 rpm for 2 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 86.94%, as shown in Table 1.

[0071] Embodiment 9:

[0072] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0073] (1) 2 g of sucrose, 1 g of melamine, 8 mmol of copper nitrate, and 2 mmol of cerium nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.6 kW microwave for 1 min. The solid product was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 8Cu2Ce@C s N-0.6.

[0074] (2) 0.1 g of waste PET powder and 8Cu2Ce@C s0.1 g of N-0.6 catalyst and 20 mL of 1,4-dioxane were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 230 ° C and stirred at a stirring rate of 600 rpm for 2 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 95.33%, as shown in Table 1.

[0075] Embodiment 10:

[0076] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0077] (1) 2 g of sucrose, 1 g of melamine, 8 mmol of copper nitrate, and 2 mmol of cerium nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.6 kW microwave for 1 min. The solid product was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 8Cu2Ce@C s N-0.6.

[0078] (2) 0.1 g of waste PET powder and 8Cu2Ce@C s 0.1 g of N-0.6 catalyst and 20 mL of tetrahydrofuran were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 230°C and stirred at a stirring rate of 600 rpm for 2 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 60.47%, as shown in Table 1.

[0079] Embodiment 11:

[0080] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0081] (1) 2 g of sucrose, 1 g of melamine, 8 mmol of copper nitrate, and 2 mmol of cerium nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.6 kW microwave for 1 min. The solid product was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 8Cu2Ce@C s N-0.6.

[0082] (2) 0.1 g of waste PET powder and 8Cu2Ce@C s 0.1 g of N-0.6 catalyst and 20 mL of cyclohexane were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 230°C and stirred at a stirring rate of 600 rpm for 2 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 90.52%, as shown in Table 1.

[0083] Embodiment 12:

[0084] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0085] (1) 2 g of sucrose, 1 g of melamine, 8 mmol of copper nitrate, and 2 mmol of cerium nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.5 kW microwave for 0.5 min. The product was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 8Cu2Ce@C s N-0.5.

[0086] (2) 0.1 g of waste PET powder and 8Cu2Ce@C s0.5 g of N-0.5 catalyst and 15 mL of 1,4-dioxane were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 180°C and stirred at a stirring rate of 600 rpm for 1 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 30.04%, as shown in Table 1.

[0087] Embodiment 13:

[0088] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0089] (1) 2 g of sucrose, 1 g of melamine, 8 mmol of copper nitrate, and 2 mmol of cerium nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for a tumbling hydrothermal reaction for 12 h at a tumbling rate of 50 rpm. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 1 kW microwave for 2 min. The solid product was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 8Cu2Ce@C s N-1.

[0090] (2) 0.1 g of waste PET powder and 8Cu2Ce@C s 0.2 g of N-1 catalyst and 30 mL of 1,4-dioxane were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 260°C and stirred at a stirring rate of 600 rpm for 6 hours. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 79.68%, as shown in Table 1.

[0091] Embodiment 14:

[0092] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0093] (1) 2 g of sucrose, 1 g of melamine, 8 mmol of copper nitrate, and 2 mmol of cerium nitrate were placed in 50 mL of deionized water, stirred thoroughly, and then ultrasonically treated for 30 min. The mixture was then transferred to a reactor and heated to 150 °C at 2 °C / min for tumbling hydrothermal treatment for 12 h at a tumbling rate of 50 rpm. After the hydrothermal treatment, the mixture was cooled to room temperature. The solid product was washed with water, dried in a vacuum oven at 60 °C, ground, and then treated with a 0.8 kW microwave for 1 min. The product was then heated to 550 °C at 2 °C / min in an argon atmosphere and calcined. The mixture was kept warm for 4 h, cooled to room temperature, ground, and stored for later use. The obtained carbon-coated bimetallic catalyst was designated as 8Cu2Ce@C s N-0.8.

[0094] (2) 0.1 g of waste PET powder and 8Cu2Ce@C s 0.1 g of N-0.8 catalyst and 20 mL of 1,4-dioxane were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 240 ° C and stirred at a stirring rate of 600 rpm for 3 h. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 96.83%, as shown in Table 1.

[0095] Embodiment 15:

[0096] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0097] (1) The reaction was carried out under the same conditions as in Example (14). After the reaction, the catalyst was washed, filtered, dried, ground, and then a small amount of deionized water was added dropwise and treated with a 0.8 kW microwave for 1 min. The catalyst was then heated to 550° C. at 2° C. / min in an argon atmosphere and re-calcined to obtain a catalyst 8Cu2Ce@C that had been used once. s N-0.8-R1.

[0098] (2) 0.1 g of waste PET powder and 8Cu2Ce@C s 0.1 g of N-0.8-R1 catalyst and 20 mL of 1,4-dioxane were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 240 ° C and stirred at a stirring rate of 600 rpm for 3 hours. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 92.09%, see Table 1 for details.

[0099] Embodiment 16:

[0100] A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent comprises the following steps:

[0101] (1) The reaction was carried out under the same conditions as in Example (14). After the reaction, the catalyst was washed, filtered, dried, ground, and then a small amount of deionized water was added dropwise and treated with a 0.8 kW microwave for 1 min. The catalyst was then heated to 550° C. at 2° C. / min in an argon atmosphere and re-calcined. The steps were repeated three times to obtain the catalyst 8Cu2Ce@C after three uses. s N-0.8-R3.

[0102] (2) 0.1 g of waste PET powder and 8Cu2Ce@C s 0.1 g of N-0.8-R3 catalyst and 20 mL of 1,4-dioxane were added to a 100 mL reactor, and 1 MPa nitrogen was introduced and slowly discharged. After repeating three times, 1 MPa nitrogen was introduced and the exhaust valve was closed. The reaction was heated to 240 ° C and stirred at a stirring rate of 600 rpm for 3 hours. After natural cooling, the liquid phase product was collected and tested. The yield of p-xylene was 90.41%, see Table 1 for details.

[0103] Table 1

[0104]

[0105]

[0106] The description of the above embodiments is only used to help understand the technical solution and core ideas of the present invention. It should be pointed out that for technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention. These improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing p-xylene by in-situ hydrogenation of PET plastic in a hydrogen-rich solvent, characterized in that: The following steps are involved: (1) placing sugar, melamine and metal salt in deionized water and stirring them to obtain a catalyst precursor solution, wherein the molar concentration of the metal in the metal salt is 2-8 mmol / g based on the mass of the sugar, the mass ratio of the sugar to the melamine is 1-5:1, the metal in the metal salt is composed of copper and a transition metal, and the transition metal is selected from one of cerium, zinc, nickel and cobalt, the catalyst precursor solution is transferred to a reaction container and subjected to a hydrothermal reaction, after which the temperature is cooled to room temperature, the solid obtained by the hydrothermal reaction is washed with water, dried and ground, and then subjected to microwave treatment, calcined in an argon atmosphere, and cooled to room temperature to obtain a carbon-coated bimetallic catalyst, wherein the sugar is selected from one of sucrose, maltose, lactose and trehalose, and the molar ratio of the copper to the transition metal is 1:1-4:1; (2) First, a hydrogen-rich solvent is added to a reaction container, wherein the hydrogen-rich solvent is selected from one of methanol, ethanol, isopropanol, 1,4-dioxane, tetrahydrofuran and cyclohexane, and then PET plastic and the carbon-coated bimetallic catalyst prepared in step (1) are added. Under a nitrogen atmosphere, the temperature is raised to a preset temperature for stirring and reacting. After natural cooling, the liquid phase product is collected and tested to obtain the target product, p-xylene.

2. The method according to claim 1, characterized in that The molar concentration of the metal in the catalyst precursor solution of step (1) is 0.2 mol / L, the mass ratio of the sugar to melamine is 2:1, and the molar ratio of melamine to the metal salt is 0.794:

1.

3. The method according to claim 1, characterized in that The hydrothermal reaction conditions of step (1) are: heating to 140°C-160°C at a heating rate of 1.5-2.5°C / min and reacting for 6-24 h.

4. The method according to claim 1, characterized in that: The calcination conditions in step (1) are: calcination temperature 400°C-700°C, calcination time 2-8 h.

5. The method according to claim 1, characterized in that The microwave treatment conditions in step (1) are: microwave power 0.5-1 kW, microwave time 0.5-2 min.

6. The method according to claim 1, characterized in that The mass volume ratio of the PET plastic to the hydrogen-rich solvent in step (2) is 0.1:10-30 g / mL, and the mass ratio of the catalyst to the PET plastic is 0.5-2:

1.

7. The method according to claim 1, characterized in that The reaction temperature in step (2) is 150°C-260°C, the reaction stirring rate is 400-800 rpm, and the reaction time is 1-6 h.

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