A method for preparing aromatic hydrocarbon and ethylene glycol by depolymerization of waste polyester plastic coupled with ethylene carbonate hydrogenolysis

Abstract

The application discloses a method for preparing aromatic hydrocarbon and ethylene glycol by depolymerization and coupling ethylene carbonate hydrogenolysis of waste polyester plastic, and a Cu-based supported catalyst is used as a catalyst and prepared by an ammonia evaporation method and a low-temperature hydrogen reduction method. The waste polyester plastic is used as raw material, dioxane is used as a solvent, and the coupling ethylene carbonate hydrogenolysis reaction is carried out at 120-200 DEG C, so that the depolymerization rate of the polyester reaches 100%, the yield of the aromatic hydrocarbon converted from the polyester by further complete deoxygenation reaches 100%, and the yield of the ethylene glycol reaches 99%. The method realizes the resource utilization of the waste polyester plastic and the high-value conversion of the low-price ethylene carbonate under mild conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the resource utilization of solid waste waste polyester plastic, and in particular to a method for preparing aromatic hydrocarbon and ethylene glycol by depolymerization and coupling of waste polyester plastic and hydrogenolysis of ethylene carbonate. BACKGROUND

[0002] Since the 1950s, plastic products have been widely used due to their convenience and excellent performance. Currently, the oil resources required for plastic production account for 8% of the total global oil resources, and the carbon emissions during the production and use of plastics account for 3.8% of the total global carbon emissions. Due to the durability and decomposition resistance of plastics, the widespread use of plastics has led to the prevalence of improper management of waste plastics and "white pollution", which has gradually threatened the natural environment and human living environment. In 2020, the total amount of plastics worldwide exceeded 8 billion tons, and the cumulative amount of waste plastics reached 6.3 billion tons. The recycling rate of plastic waste is about 10%, and about 90% of waste plastics are directly landfilled or accumulated in the natural environment, seriously polluting the environment and causing harm to human health. Therefore, recycling waste plastics not only can control "white pollution", but also can reduce carbon dioxide emissions. How to achieve efficient and clean disposal of waste plastics and reasonable resource recovery has become a challenge faced by the global economy.

[0003] Landfill, incineration energy and resource utilization are the main disposal methods of waste plastics. The aging of plastics in the landfill process produces toxic and harmful substances that leach into the soil and spread, and also leads to the emission of a large amount of greenhouse gases. Incineration disposal has low requirements for raw material pretreatment, is easy to operate, has high disposal efficiency, and relatively low cost. However, waste plastic incineration is accompanied by the production of toxic organic gases such as polycyclic aromatic hydrocarbons, dioxins and furans, which can easily cause secondary pollution of the environment. More importantly, the raw materials for the production of most plastics are extremely important chemical raw materials, especially polyarylate plastics, which can be depolymerized and deoxygenated to produce high-value aromatic hydrocarbons, and have high value for recycling and reuse. Therefore, a variety of pyrolysis methods have been used for the resource utilization of waste plastics. For example, Chinese invention CN114436806A provides a method for preparing disodium terephthalate from polyester waste plastic PET by one-step low-temperature conversion. PET and catalyst are added to a NaOH solution to completely convert disodium terephthalate in one step. Chinese invention CN114436806A discloses a method for preparing monocyclic aromatic hydrocarbons by converting PET-based plastics in cooperation with natural gas hydrates. A titanium dioxide-supported Pt-Ni bimetallic catalyst is prepared by impregnation method, and the depolymerization of PET and the reforming of natural gas hydrates are coupled. One or more of the products obtained at 250℃-400℃ are monocyclic aromatic hydrocarbons benzene, toluene and p-xylene. Literature 1 [Nat Catal, 5, 673] reports an automated high-throughput direct evolution method for engineering plastic polymer-degrading enzymes, which can more effectively depolymerize semi-crystalline PET. Literature 2 [Nat Sustain, 2023, 6: 965] reports a binuclear zinc catalyst for polyester depolymerization, which has a recycling activity of 577 g PET d -1 g catal -1 for catalyzing PET degradation at pH 13 and 90℃. Literature 3 [Nat Commun, 2022, 13: 3343] reports that Cu / SiO2 prepared by hydrothermal method can catalyze the complete conversion of PET to p-xylene, but the catalyst needs to be modified by Na and reduced by hydrogen at 450℃.

[0004] However, the solvent is very critical in the PET degradation process. As reported in document 4 [Chem Eng Sci, 2020, 220, 115642], when methanol and ethylene glycol are used as solvents, the products of PET degradation by zinc oxide, a homogeneous catalyst, are dimethyl terephthalate and bis-hydroxyethyl terephthalate, respectively. Document 5 [Angew Chem Int Ed, 2022, 61, e202117205] reports a new process for one-pot conversion of CO2 and PET into high-value chemicals through reaction series. The hydrogenation product of CO2, methanol, is consumed in situ in the PET alcoholysis. The above indicates that the hydrogenation product of CO2, alcohol, has a great influence on PET degradation. Based on this, Cu-based supported catalysts are prepared by ammonia evaporation method and low-temperature hydrogen reduction method. In the process of converting waste polyester plastics into aromatic hydrocarbons, the hydrogenolysis reaction of ethylene carbonate is coupled, the free radicals generated in the hydrogenolysis process of ethylene carbonate are used to promote the alcoholysis of polyester, and the monomers generated are further deoxidized to generate aromatic hydrocarbons, realizing the one-step conversion of waste polyester plastics into aromatic hydrocarbons. The method realizes the recycling of waste polyester plastics and the high-value conversion of low-cost ethylene carbonate in the process of preparing ethylene glycol from ethylene carbonate hydrogenolysis, and has good industrial application prospect. SUMMARY

[0005] In view of the harsh reaction conditions, low conversion rate and low product selectivity in the process of converting waste polyester plastics into aromatic hydrocarbons, the present application provides a method for preparing aromatic hydrocarbons and ethylene glycol by depolymerization of waste polyester plastics coupled with hydrogenolysis of ethylene carbonate. Under the action of Cu-based supported catalyst, the active species generated by hydrogenolysis of ethylene carbonate first alcoholizes waste polyester plastics into monomers, and then further converts into aromatic hydrocarbons. The method has low reaction temperature, fast reaction rate and high product yield, and the catalyst is cheap, the preparation method is simple, green and environment-friendly.

[0006] The technical scheme of the present application is as follows:

[0007] A method for preparing aromatic hydrocarbons and ethylene glycol by depolymerization of waste polyester plastics coupled with hydrogenolysis of ethylene carbonate, using Cu-based supported catalyst, using waste polyester plastics as raw material, ethylene carbonate as depolymerization assistant, dioxane as solvent, and carrying out reaction in hydrogen environment to obtain aromatic hydrocarbons and ethylene glycol, realizing the recycling and recycling of waste polyester plastics and the high-value conversion of low-cost ethylene carbonate.

[0008] Further, the carrier of the Cu-based supported catalyst is one or more of silicon dioxide, zirconium dioxide, cerium dioxide and aluminum oxide, and the loading amount of Cu is 5-40wt%.

[0009] Further, the Cu-based supported catalyst is prepared by loading Cu onto the carrier by ammonia evaporation method, and then prepared by low-temperature hydrogen reduction method.

[0010] Further, the low-temperature hydrogen reduction method is carried out in a reduction furnace, the reduction atmosphere is hydrogen, the reduction temperature is 50-250℃, and the reduction time is 2-8 h.

[0011] Further, the waste and old polyester plastic is one or two or more of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate (PC), and polydiallyl phthalate (PDAP).

[0012] Further, the mass ratio of the waste and old polyester plastic to the catalyst is 10:1-1:1, and the mass ratio of the waste and old polyester plastic to the ethylene carbonate is 1:2-1:10.

[0013] Further, the reaction temperature is 120-200℃, the hydrogen pressure is 3-8 MPa, and the reaction time is 1-24 h.

[0014] In the above method for preparing aromatic hydrocarbons by converting waste and old polyester plastic, the yield of the waste and old polyester plastic converted into aromatic hydrocarbons reaches 100%, and the yield of ethylene glycol prepared by hydrogenolysis of ethylene carbonate reaches 99%.

[0015] The present application has the following advantages:

[0016] In the Cu-based supported catalyst prepared by the ammonia evaporation method and the low-temperature hydrogen reduction method, Cu is uniformly dispersed and coexists with Cu 0 and Cu + , the active species generated by the hydrogenolysis of ethylene carbonate is used to promote the degradation of the waste and old polyester plastic into corresponding monomers, and then the monomers are converted into aromatic hydrocarbons under the synergistic catalysis of Cu 0 and Cu + . This method can reduce the reaction temperature to 120℃, the depolymerization rate of the waste and old polyester plastic reaches 100%, the yield of the completely deoxygenated aromatic hydrocarbons reaches 100%, and the yield of ethylene glycol reaches 99%. This method couples the PET depolymerization-hydrodeoxygenation for preparing aromatic hydrocarbons and the hydrogenolysis of ethylene carbonate for preparing ethylene glycol, and realizes the recycling utilization of the waste and old polyester plastic and the high-value conversion of low-price ethylene carbonate under mild conditions. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The XRD patterns of the Cu / SiO2 supported catalyst prepared by the ammonia evaporation method and the low-temperature hydrogen reduction method are shown in the figure, which are the catalyst precursor (Cu / SiO2-N), the catalyst reduced at 100℃ (Cu / SiO2-100) and the catalyst reduced at 250℃ (Cu / SiO2-250). DETAILED DESCRIPTION

[0018] The present application will be further described in detail below with reference to specific embodiments, but the present application is not limited thereto.

[0019] The reagents used in the examples are all of analytical purity, and the water is deionized water. Example 1

[0020] A Cu / SiO2 supported catalyst with a Cu mass content of 30wt% was prepared. Cu(NO3)2·3H2O was dissolved in 50 mL of deionized water, an ammonia solution was added to adjust the pH to 11, and silica sol was added and stirred. The mixture was then transferred to a water bath and heated to 90°C to perform ammonia evaporation until the pH value decreased to 7. The precipitate was then separated by filtration, dried, and calcined. The target catalyst was obtained by reducing the calcined product under pure hydrogen at 100°C for 4 hours. 0.1 g of the above catalyst, 0.2 g of PET, 1 g of ethylene carbonate, and 15 g of dioxane were added to a high-pressure reaction kettle. The air in the kettle was removed by displacement, and hydrogen was injected to a pressure of 4 MPa. After reacting at 160°C for 2 hours, the yield of p-xylene was 100%, and the yield of ethylene glycol was 96.8%. Example 2

[0021] A Cu / SiO2 supported catalyst with a Cu mass content of 5wt% was prepared. Cu(NO3)2·3H2O was dissolved in 50 mL of deionized water, an ammonia solution was added to adjust the pH to 11, and silica sol was added and stirred. The mixture was then transferred to a water bath and heated to 90°C to perform ammonia evaporation until the pH value decreased to 7. The precipitate was then separated by filtration, dried, and calcined. The target catalyst was obtained by reducing the calcined product under pure hydrogen at 250°C for 2 hours. 0.02 g of the above catalyst, 0.2 g of PET, 0.4 g of ethylene carbonate, and 15 g of dioxane were added to a high-pressure reaction kettle. The air in the kettle was removed by displacement, and hydrogen was injected to a pressure of 4 MPa. After reacting at 200°C for 4 hours, the yield of p-xylene was 100%, and the yield of ethylene glycol was 75.7%. Example 3

[0022] A Cu / SiO2 supported catalyst with a Cu mass content of 40wt% was prepared. Cu(NO3)2·3H2O was dissolved in 50 mL of deionized water, an ammonia solution was added to adjust the pH to 11, and silica sol was added and stirred. The mixture was then transferred to a water bath and heated to 90°C to perform ammonia evaporation until the pH value decreased to 7. The precipitate was then separated by filtration, dried, and calcined. The target catalyst was obtained by reducing the calcined product under pure hydrogen at 50°C for 8 hours. 0.2 g of the above catalyst, 0.2 g of PET, 2.0 g of ethylene carbonate, and 15 g of dioxane were added to a high-pressure reaction kettle. The air in the kettle was removed by displacement, and hydrogen was injected to a pressure of 3 MPa. After reacting at 140°C for 5 hours, the yield of p-xylene was 100%, and the yield of ethylene glycol was 96.7%. Example 4

[0023] Cu / SiO2 supported catalyst was prepared with Cu mass content of 30wt%, Cu(NO3)2·3H2O was dissolved in 50 mL deionized water, ammonia solution was added to adjust pH to 11, silica sol was added and stirred, then it was transferred to a water bath to heat to 90 ℃ to evaporate ammonia until the pH value decreased to 7, then the precipitate was separated by filtration, dried and calcined, and then reduced at 100 ℃ under pure hydrogen for 4 h to obtain the target catalyst. 0.1 g of the above catalyst, 0.2 g of PET, 1.0 g of ethylene carbonate and 15 g of dioxane were added to a high-pressure reaction kettle, the air in the kettle was removed by displacement method, hydrogen was injected to a pressure of 4 MPa, and after reaction at 120 ℃ for 24 h, the yield of p-xylene was 100% and the yield of ethylene glycol was 99.1%. Example 5

[0024] Cu / SiO2 supported catalyst was prepared with Cu mass content of 30wt%, Cu(NO3)2·3H2O was dissolved in 50 mL deionized water, ammonia solution was added to adjust pH to 11, silica sol was added and stirred, then it was transferred to a water bath to heat to 90 ℃ to evaporate ammonia until the pH value decreased to 7, then the precipitate was separated by filtration, dried and calcined, and then reduced at 100 ℃ under pure hydrogen for 4 h to obtain the target catalyst. 0.1 g of the above catalyst, 0.2 g of PET, 1.0 g of ethylene carbonate and 15 g of dioxane were added to a high-pressure reaction kettle, the air in the kettle was removed by displacement method, hydrogen was injected to a pressure of 4 MPa, and after reaction at 120 ℃ for 24 h, the yield of p-xylene was 100% and the yield of ethylene glycol was 99.1%. Example 6

[0025] Cu / ZrO2 supported catalyst was prepared with Cu mass content of 30wt%, Cu(NO3)2·3H2O was dissolved in 50 mL deionized water, ammonia solution was added to adjust pH to 11, nano zirconia was added and stirred, then it was transferred to a water bath to heat to 90 ℃ to evaporate ammonia until the pH value decreased to 7, then the precipitate was separated by filtration, dried and calcined, and then reduced at 150 ℃ under pure hydrogen for 6 h to obtain the target catalyst. 0.1 g of the above catalyst, 0.2 g of PET, 1.0 g of ethylene carbonate and 15 g of dioxane were added to a high-pressure reaction kettle, the air in the kettle was removed by displacement method, hydrogen was injected to a pressure of 6 MPa, and after reaction at 180 ℃ for 3 h, the yield of p-xylene was 100% and the yield of ethylene glycol was 92.9%. Example 7

[0026] Cu / Al2O3 supported catalyst with Cu mass content of 30wt% was prepared by dissolving Cu(NO3)2·3H2O in 50 mL deionized water, adding ammonia solution to adjust pH to 11, adding nano-alumina and stirring, then transferring it to a water bath to heat to 90°C to perform ammonia evaporation until the pH value decreases to 7, then filtering and separating the precipitate, drying and calcining, and then reducing at 100°C under pure hydrogen for 4 hours to obtain the target catalyst. 0.1 g of the above catalyst, 0.2 g of PET, 1.0 g of vinyl carbonate and 15 g of dioxane were added to a high-pressure reaction kettle, the air in the kettle was removed by displacement method, hydrogen was injected to a pressure of 6 MPa, and after reaction at 180°C for 8 h, the yield of p-xylene was 100% and the yield of ethylene glycol was 90.3%. Example 8

[0027] Cu / SiO2 supported catalyst with Cu mass content of 30wt% was prepared by dissolving Cu(NO3)2·3H2O in 50 mL deionized water, adding ammonia solution to adjust pH to 11, adding silica sol and stirring, then transferring it to a water bath to heat to 90°C to perform ammonia evaporation until the pH value decreases to 7, then filtering and separating the precipitate, drying and calcining, and then reducing at 100°C under pure hydrogen for 4 hours to obtain the target catalyst. 0.1 g of the above catalyst, 0.2 g of PET, 1.0 g of polydiallyl terephthalate and 15 g of dioxane were added to a high-pressure reaction kettle, the air in the kettle was removed by displacement method, hydrogen was injected to a pressure of 4 MPa, and after reaction at 170°C for 4 h, the yield of p-xylene was 100% and the yield of ethylene glycol was 97.3%. Example 9

[0028] Cu / SiO2-CeO2 supported catalyst with Cu mass content of 20wt% was prepared by dissolving Cu(NO3)2·3H2O in 50 mL deionized water, adding ammonia solution to adjust pH to 11, adding nano-SiO2-CeO2 and stirring, then transferring it to a water bath to heat to 90°C to perform ammonia evaporation until the pH value decreases to 7, then filtering and separating the precipitate, drying and calcining, and then reducing at 200°C under pure hydrogen for 2 hours to obtain the target catalyst. 0.1 g of the above catalyst, 0.2 g of polycarbonate, 1.0 g of vinyl carbonate and 15 g of dioxane were added to a high-pressure reaction kettle, the air in the kettle was removed by displacement method, hydrogen was injected to a pressure of 5 MPa, and after reaction at 180°C for 4 h, the yield of 2,2-diphenylpropane was 98% and the yield of ethylene glycol was 98.8%. Example 10

[0029] Cu / SiO2-Al2O3 supported catalyst was prepared with Cu content of 30wt%, Cu(NO3)2·3H2O was dissolved in 50 mL deionized water, ammonia solution was added to adjust pH to 11, SiO2-Al2O3 powder was added and stirred, then it was transferred to a water bath to heat to 90 ℃ to perform ammonia evaporation until pH value decreased to 7, then the precipitate was separated by filtration, dried and calcined, then the target catalyst was obtained by reduction under pure hydrogen at 100 ℃ for 4 h. 0.1 g of the above catalyst, 0.2 g of polybutylene terephthalate, 1.0 g of ethylene carbonate and 15 g of dioxane were added into a high-pressure reaction kettle, air in the kettle was removed by displacement method, hydrogen was injected until the pressure reached 4 MPa, after reaction at 150 ℃ for 2 h, the yield of p-xylene was 100% and the yield of ethylene glycol was 98.0%.

[0030] As can be seen from the results of the above examples, the Cu-based supported catalyst exhibits very high activity, ethylene carbonate is mainly prepared from CO2 and ethylene oxide in industry, in the presence of ethylene carbonate, the yield of aromatic hydrocarbon can reach nearly 100% and the yield of ethylene glycol can reach 99% under mild conditions, the method realizes the resource utilization of waste polyester plastics and the conversion and emission reduction of CO2.

Claims

1. A method for preparing aromatic hydrocarbon and ethylene glycol by depolymerization of waste polyester plastic coupled with ethylene carbonate hydrogenolysis, characterized in that, The Cu-based supported catalyst is prepared by an ammonia evaporation method and a low-temperature hydrogen reduction method, a carrier of the Cu-based supported catalyst is one or two or more of silica, zirconium dioxide, cerium dioxide and aluminum oxide, Cu is loaded on the carrier by the ammonia evaporation method, and then the Cu-based catalyst is prepared by the low-temperature hydrogen reduction method, and a reduction temperature is 50-250 DEG C. The Cu-based supported catalyst is prepared by an ammonia evaporation method and a low-temperature hydrogen reduction method, a carrier of the Cu-based supported catalyst is one or two or more of silica, zirconium dioxide, cerium dioxide and aluminum oxide, Cu is loaded on the carrier by the ammonia evaporation method, and then the Cu-based catalyst is prepared by the low-temperature hydrogen reduction method, and a reduction temperature is 50-250 DEG C. The Cu-based supported catalyst is prepared by an ammonia evaporation method and a low-temperature hydrogen reduction method, a carrier of the Cu-based supported catalyst is one or two or more of silica, zirconium dioxide, cerium dioxide and aluminum oxide, Cu is loaded on the carrier by the ammonia evaporation method, and then the Cu-based catalyst is prepared by the low-temperature hydrogen reduction method, and a reduction temperature is 50-250 DEG C.

2. The method for preparing aromatic hydrocarbon and ethylene glycol from waste polyester plastic by depolymerization coupled with ethylene carbonate hydrogenolysis according to claim 1, characterized in that, The Cu-based supported catalyst is prepared by an ammonia evaporation method and a low-temperature hydrogen reduction method, a carrier of the Cu-based supported catalyst is one or two or more of silica, zirconium dioxide, cerium dioxide and aluminum oxide, Cu is loaded on the carrier by the ammonia evaporation method, and then the Cu-based catalyst is prepared by the low-temperature hydrogen reduction method, and a reduction temperature is 50-250 DEG C.

3. The method for preparing aromatic hydrocarbon and ethylene glycol from waste polyester plastic by depolymerization coupled with ethylene carbonate hydrogenolysis according to claim 1, characterized in that, The Cu-based supported catalyst is prepared by an ammonia evaporation method and a low-temperature hydrogen reduction method, a carrier of the Cu-based supported catalyst is one or two or more of silica, zirconium dioxide, cerium dioxide and aluminum oxide, Cu is loaded on the carrier by the ammonia evaporation method, and then the Cu-based catalyst is prepared by the low-temperature hydrogen reduction method, and a reduction temperature is 50-250 DEG C.

4. The method for preparing aromatic hydrocarbon and ethylene glycol from waste polyester plastic by depolymerization coupled with ethylene carbonate hydrogenolysis according to claim 1, characterized in that, The Cu-based supported catalyst is prepared by an ammonia evaporation method and a low-temperature hydrogen reduction method, a carrier of the Cu-based supported catalyst is one or two or more of silica, zirconium dioxide, cerium dioxide and aluminum oxide, Cu is loaded on the carrier by the ammonia evaporation method, and then the Cu-based catalyst is prepared by the low-temperature hydrogen reduction method, and a reduction temperature is 50-250 DEG C.

5. The method for preparing aromatic hydrocarbon and ethylene glycol from waste polyester plastic by depolymerization, coupling ethylene carbonate and hydrogenolysis according to claim 1, characterized in that, The Cu-based supported catalyst is prepared by an ammonia evaporation method and a low-temperature hydrogen reduction method, a carrier of the Cu-based supported catalyst is one or two or more of silica, zirconium dioxide, cerium dioxide and aluminum oxide, Cu is loaded on the carrier by the ammonia evaporation method, and then the Cu-based catalyst is prepared by the low-temperature hydrogen reduction method, and a reduction temperature is 50-250 DEG C. The Cu-based supported catalyst is prepared by an ammonia evaporation method and a low-temperature hydrogen reduction method, a carrier of the Cu-based supported catalyst is one or two or more of silica, zirconium dioxide, cerium dioxide and aluminum oxide, Cu is loaded on the carrier by the ammonia evaporation method, and then the Cu-based catalyst is prepared by the low-temperature hydrogen reduction method, and a reduction temperature is 50-250 DEG C.

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