Method for producing benzene by directionally depolymerizing PET (Polyethylene Terephthalate) by utilizing RuWZr catalyst and application of method

Abstract

The invention discloses a method for producing benzene by directionally depolymerizing PET (Polyethylene Terephthalate) by utilizing a RuWZr catalyst and application of the method, and belongs to the technical field of solid waste recycling, the method comprises the following steps: constructing a reaction system by utilizing PET, the RuWZr catalyst and a solvent, and carrying out depolymerization and decarboxylation reaction on the reaction system in a hydrogen atmosphere to obtain benzene after the reaction is finished; a carrier in the RuWZr catalyst is amorphous tungsten-zirconium oxide, ruthenium is loaded on the amorphous tungsten-zirconium oxide in the form of zero-valent ruthenium, the molar ratio of tungsten to zirconium is (0.1-2): 1, and the loading amount of ruthenium is 0.2 wt%-5.0 wt%. According to the method, the RuWZr catalyst catalyzes PET directional one-pot depolymerization and selective decarboxylation reaction, upgrading conversion from waste PET to high-value aromatic compound benzene is achieved through a one-step method, and compared with a traditional technical path of producing benzene through coal or petroleum, the environment burden and the production cost are greatly reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solid waste recycling, and particularly relates to a method for producing benzene by directional depolymerization of PET using a RuWZr catalyst and application thereof. BACKGROUND

[0002] Plastic waste pollution has become a core problem of environmental governance. At present, only a small part of plastic garbage is recycled, and the rest is landfilled, incinerated or directly discharged into the natural environment, causing long-term harm to soil, water and ecosystems. Among the many plastics, the annual output of polyethylene terephthalate (PET) ranks first. It is widely used in the production of plastic packaging boxes, fiber textiles and other products, but its service life is relatively short, which can cause serious environmental pollution. In the industrialization process of recycling, utilizing and upgrading waste PET, the problem of resource waste is still prominent and needs to be solved urgently. Traditional mechanical physical recycling methods usually lead to a decrease in plastic performance, and the conversion efficiency of biodegradation technology is limited, and the application conditions are not yet fully mature. Therefore, it is crucial to develop fine high-value utilization technology of waste PET, and important chemicals can be prepared by directional preparation, which can convert waste PET into petroleum products and realize carbon resource recycling at the molecular level.

[0003] In the chemical upgrading and recycling process of waste PET, the preparation of high-value chemicals usually involves two key steps: first, depolymerizing waste PET into small molecule monomers; second, converting these small molecule monomers into high-value chemicals through catalytic conversion. At present, chemical depolymerization of waste PET mainly adopts methods such as methanolysis, hydrolysis, glycolysis, ammonolysis, etc., to generate small molecule compounds such as dimethyl terephthalate, terephthalic acid, etc. (Chinese patent documents with publication numbers CN119371305A, CN114835551A, CN117339593A, etc.). Subsequently, these small molecule compounds will be further processed and upgraded to convert into higher value-added products. From the perspective of molecular structure, PET plastic has a benzene ring structure. If it is further hydrogenated or cracked, not only a large amount of hydrogen and energy will be consumed, but also the valuable structure originally possessed by PET plastic will be destroyed, resulting in resource waste. In order to realize one-step directional depolymerization of waste PET and direct conversion into aromatic chemicals, a high-performance catalyst system must be developed, which can selectively break C-C bonds while avoiding hydrogenation of benzene rings.

[0004] Benzene is an important basic chemical in the chemical industry and the core raw material of the aromatic hydrocarbon industry chain, with an annual global production of over 50 million tons. It is widely used in manufacturing industries to produce clothing, packaging, automobile parts, building materials, pharmaceuticals, cosmetics, etc. Currently, benzene is mainly produced through catalytic reforming of petroleum and coal, steam cracking, and toluene disproportionation processes. However, these methods have problems such as harsh conditions and high energy consumption. Therefore, it is particularly important to develop a mild and sustainable strategy for producing benzene based on renewable resources, which will reduce dependence on fossil resources and have significant industrial and social significance. SUMMARY

[0005] To solve the above problems in the prior art, the present application provides a method for producing benzene by directional depolymerization of PET using a RuWZr catalyst. The RuWZr catalyst is a heterogeneous solid catalyst that can be recycled and used to catalyze the directional one-pot depolymerization and selective decarboxylation of PET. This one-step process achieves the upgrading and conversion of waste PET to high-value aromatic compounds such as benzene. The reaction conditions are relatively mild and environmentally friendly.

[0006] The specific technical solutions adopted are as follows: A method for producing benzene by directional depolymerization of PET using a RuWZr catalyst, comprising: constructing a reaction system using PET, a RuWZr catalyst, and a solvent, and performing a depolymerization and decarboxylation reaction under a hydrogen atmosphere to obtain benzene. The support in the RuWZr catalyst is amorphous tungsten-zirconium oxide, and ruthenium is loaded on the amorphous tungsten-zirconium oxide in the form of zero-valent ruthenium. The molar ratio of tungsten to zirconium is 0.1-2:1, and the ruthenium loading is 0.2 wt%-5.0 wt%, as determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The RuWZr catalyst is prepared by impregnation using ruthenium chloride, amorphous tungsten-zirconium oxide, and water as raw materials. The amorphous tungsten-zirconium oxide is prepared by impregnation using ammonium metatungstate, zirconium hydroxide, and water as raw materials.

[0007] The RuWZr catalyst can catalyze PET depolymerization and promote in situ decarboxylation of terephthalic acid in the reaction intermediate to selectively produce benzene. The catalyst is relatively stable in high-temperature systems and can be reused multiple times through reduction and regeneration, maintaining good catalytic activity and good recyclability.

[0008] Specifically, PET can be in the form of sheets, particles, or powder, and waste PET or pure PET chemicals can be used to construct the reaction system.

[0009] Preferably, the solvent is a mixture of dodecane and water, and the volume ratio of dodecane to water is preferably 0.2-5:1.

[0010] Preferably, the mass ratio of PET to RuWZr catalyst is 1:0.1-2, and the amount ratio of PET to mixed solvent is 1 g:10-250 mL.

[0011] Further preferably, the volume ratio of dodecane and water in the mixed solvent is 2:1, the molar ratio of tungsten to zirconium elements in the RuWZr catalyst used is 0.4:1, and the ruthenium loading is 0.5 wt%; under the above conditions and parameters, the RuWZr catalyst has a good catalytic effect and can produce the product benzene in high yield, which helps to efficiently utilize the carbon resources in PET.

[0012] Specifically, the depolymerization and decarboxylation reaction equation can be expressed as: Preferably, the depolymerization and decarboxylation reaction is carried out under a hydrogen pressure of 0.1-2 MPa, the depolymerization and decarboxylation reaction temperature is 220-380 ° C, and the depolymerization and decarboxylation reaction time is 8-24 h.

[0013] Further preferably, the conditions for the depolymerization and decarboxylation reaction are 0.4 MPa, 300 ° C, and 16 h.

[0014] Preferably, the preparation method of amorphous tungsten-zirconium oxide is as follows: preparing a mixture comprising ammonium metatungstate, zirconium hydroxide and deionized water, stirring the mixture at room temperature until dry, then heating and further drying the mixture, crushing the dried solid and calcining it in an air atmosphere at 500-700 ° C for 2-6 h to obtain amorphous tungsten-zirconium oxide as a catalyst carrier.

[0015] Preferably, the preparation method of the RuWZr catalyst is: preparing a mixture comprising ruthenium chloride, amorphous tungsten zirconium oxide and deionized water, stirring the mixture at room temperature until dry, then heating and further drying it, crushing the dried solid and calcining it in a reducing atmosphere at 300-500 ° C for 3-6 h to obtain the RuWZr catalyst.

[0016] Furthermore, during the preparation of the amorphous tungsten zirconium oxide and the RuWZr catalyst, the temperature is raised to 80-120 °C and further dried for 10-24 h.

[0017] Furthermore, during the preparation of amorphous tungsten zirconium oxide, the heating rate of calcination in an air atmosphere is 2-10 °C / min; during the preparation of RuWZr catalyst, the reducing atmosphere is a hydrogen-argon mixed atmosphere, and the heating rate of calcination in a reducing atmosphere is 1-5 °C / min.

[0018] The present invention also provides application of the method for producing benzene by directional depolymerization of PET using RuWZr catalyst in the treatment of waste plastics, wherein the main component of the waste plastics is PET.

[0019] Specifically, the above method can be used to process waste PET, including but not limited to PET bottles, PET film, PET trays, PET ribbons, PET twine, PET non-woven fabrics, and blends of PET with cotton, spandex, and other ingredients. The method is suitable for recycling and upgrading various forms of PET waste, offering high efficiency and adaptability.

[0020] Furthermore, the waste PET is pre-cleaned and pre-crushed before treatment. The pre-cleaning and pre-crushing operations can prevent other pollutants from interfering with and poisoning the RuWZr catalyst, thereby ensuring the conversion effect of the waste PET.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) RuWZr catalyst is a heterogeneous solid catalyst. As the core of the method of the present invention, it has the advantages of good catalytic activity, high catalytic efficiency, convenient recovery and good recyclability. It can accurately break the C-C bond while avoiding the hydrogenation of the benzene ring, and realize the upgrading conversion of waste PET to the high-value aromatic compound benzene in one step.

[0022] (2) The high-value PET conversion solution provided by the present invention offers the advantages of rapid reaction, simple process, and excellent catalytic performance. It enables efficient, one-step production of high-value benzene, breaking through the thermodynamic limitations of PET depolymerization. Compared with traditional coal or petroleum-based benzene production technologies, this green catalytic system significantly reduces environmental burden and production costs, effectively alleviating reliance on non-renewable resources.

[0023] (3) The method of the present invention has wide applicability and can be used to process a variety of waste PET raw materials, including PET water bottles, PET films, PET trays, PET ribbons, PET ropes, PET non-woven fabrics, and blended fabrics of PET and other components such as cotton and spandex, etc., and can efficiently complete targeted upgrading and conversion in a short time. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Figure 2 shows the XRD characterization results of fresh RuWZr catalyst and RuWZr catalyst after five cycles of use.

[0025] Figure 2 This is the gas chromatography (GC) spectrum of benzene obtained in Example 1.

[0026] Figure 3 This is the mass spectrum (MS) of benzene obtained in Example 1. DETAILED DESCRIPTION

[0027] In order to make the objects, features and advantages of the present invention more clearly understood, a detailed description is given below using specific embodiments. In the following description, many specific details are set forth to fully understand the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0028] The procedures for the following examples, in which specific conditions are not specified, generally follow conventional conditions or those recommended by the manufacturer. Any material not described in detail in this specification belongs to the prior art known to those skilled in the art. The experimental materials used in the following examples, unless otherwise specified, can be purchased from conventional biochemical reagent companies.

[0029] The RuWZr catalysts in the following examples were prepared using the following impregnation method: In a 100 mL beaker, add ammonium metatungstate, zirconium hydroxide, and a small amount (5-10 mL) of deionized water. Stir the mixture at room temperature until dry, then heat it to 110 °C and dry it for 12 hours. Grind the dried solid evenly and calcine it in a muffle furnace at 600 °C in air for 3 hours (heating rate: 5 °C / min) to obtain the catalyst support—an amorphous tungsten-zirconium oxide.

[0030] In a 100 mL beaker, ruthenium chloride, the amorphous tungsten zirconium oxide prepared in the above steps, and a small amount (5-10 mL) of deionized water were added. The mixture was stirred at room temperature until dry, then heated to 110 °C and dried for 12 h. The dried solid was ground uniformly and then calcined in a tube furnace at 400 °C in a reducing atmosphere for 4 h (reducing gas: 5% H2 / 95% Ar; heating rate: 2 °C / min; gas flow rate: 30 mL / min) to obtain the RuWZr catalyst.

[0031] The carrier in the RuWZr catalyst is amorphous tungsten zirconium oxide. The molar ratio of tungsten to zirconium and the ruthenium loading can be controlled by modifying the feed amount of ammonium metatungstate, zirconium hydroxide and ruthenium chloride. The molar ratio of tungsten to zirconium is generally 0.1-2:1, and the ruthenium loading is generally controlled to be 0.2 wt%-5.0 wt%. It is obtained by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) testing. The test shows that the best catalytic performance of depolymerization and decarboxylation reaction can be achieved when the molar ratio of tungsten to zirconium is 0.4:1 and the ruthenium loading is 0.5 wt%. The XRD characterization results of the RuWZr catalyst before the reaction and after five cycles of reaction are shown in Figure 2. Figure 1As shown, it is proved that the ruthenium is successfully loaded on the amorphous tungsten-zirconium oxide in the form of zero-valent ruthenium, and the tungsten-zirconium is in the form of WZrO x (mixture of pentavalent and hexavalent tungsten, mixture of trivalent and tetravalent zirconium).

[0032] Example 1 In a high-pressure reactor equipped with a magnetic stirrer, a thermocouple, and a program-controlled temperature instrument, 0.03 g of PET powder, 0.015 g of RuWZr catalyst (Ru loading amount is 0.5 wt%, W / Zr molar ratio = 0.4:1), 4 mL of dodecane, and 2 mL of water were added. After the high-pressure reactor was sealed, the gas in the high-pressure reactor was replaced with hydrogen three times, and then the hydrogen was pressurized to 0.4 MPa at ambient temperature. The stirring and heating were turned on, and the reaction system was heated to 300 °C, and reacted at this temperature for 16 h. After the reaction was completed, the high-pressure reactor was quenched to ambient temperature in an ice water bath. The liquid phase was extracted with dodecane three times, and hexadecane was used as an internal standard, and then mass spectrometry was used for qualitative analysis, gas chromatography (GC) was used for quantitative analysis, and mass spectrometry (MS) was used for qualitative analysis. The results show that the benzene yield of this example is 83.3%, and the toluene yield is 9.7% (toluene is one of the reaction by-products, which comes from the incomplete breaking of carboxyl groups, i.e. part of the carboxyl groups undergoes hydrogenation and deoxidation reaction to form methyl groups). After simple distillation, the GC and MS graphs of the separated benzene are shown in Figures 1 and 2, respectively. Figure 2 and Figure 3 As shown.

[0033] In addition, in order to test the recyclability of the RuWZr catalyst, the post-reaction catalyst RuWZr was recycled and treated as follows: the solid catalyst was recovered by filtration, washed with dodecane and acetone, and dried at 60 °C. It was first calcined in a muffle furnace at 600 °C in air for 3 h, and then calcined and reduced in a tube furnace at 400 °C in a reducing atmosphere for 4 h (reducing gas: 5% H2 / 95% Ar; heating rate: 2 °C / min; gas flow rate: 30 mL / min). The treated catalyst was used in the next cycle experiment. The test results show that the recovered and treated RuWZr catalyst can be reused in the next cycle, and after being reused for 6 times, the RuWZr catalyst still has high catalytic efficiency, and the yields of benzene and toluene reach 50.9% and 5.4%, respectively.

[0034] Example 2 In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.03 g of PET powder, 0.015 g of RuWZr catalyst (Ru loading of 0.5 wt%, W / Zr molar ratio = 0.4:1), 4 mL of dodecane, and 2 mL of water were added. After sealing the autoclave, the atmosphere was replaced with hydrogen three times. Then, hydrogen was pressurized to 0.2 MPa at ambient temperature. Stirring and heating were initiated, and the reaction system was heated to 300°C and allowed to react at this temperature for 16 hours. After completion of the reaction, the autoclave was quenched in an ice-water bath to ambient temperature. The liquid phase was extracted three times with dodecane, using hexadecane as an internal standard. Qualitative analysis was performed by mass spectrometry, and quantitative analysis was performed by gas chromatography (GC). The results showed that the benzene yield in this example was 73.6%, and the toluene yield was 8.9%.

[0035] Example 3 In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.03 g of PET powder, 0.015 g of RuWZr catalyst (Ru loading of 0.5 wt%, W / Zr molar ratio = 0.4:1), 4 mL of dodecane, and 3 mL of water were added. After sealing the autoclave, the atmosphere was replaced with hydrogen three times. Then, hydrogen was pressurized to 0.4 MPa at ambient temperature. Stirring and heating were initiated, and the reaction system was heated to 300°C and allowed to react at this temperature for 16 hours. After completion of the reaction, the autoclave was quenched in an ice-water bath to ambient temperature. The liquid phase was extracted three times with dodecane, using hexadecane as an internal standard. Qualitative analysis was performed by mass spectrometry, and quantitative analysis was performed by gas chromatography (GC). The results showed that the benzene yield in this example was 65.8%, and the toluene yield was 15.2%.

[0036] Example 4 In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.03 g of PET powder, 0.015 g of RuWZr catalyst (Ru loading of 0.5 wt%, W / Zr molar ratio = 0.4:1), 4 mL of dodecane, and 2 mL of water were added. After sealing the autoclave, the atmosphere was replaced with hydrogen three times. Then, hydrogen was pressurized to 0.4 MPa at ambient temperature. Stirring and heating were initiated, and the reaction system was heated to 310 °C and allowed to react at this temperature for 16 h. After completion of the reaction, the autoclave was quenched in an ice-water bath to ambient temperature. The liquid phase was extracted three times with dodecane, using hexadecane as an internal standard. The resulting mixture was then qualitatively analyzed by mass spectrometry and quantitatively analyzed by gas chromatography (GC). The results showed that the benzene yield in this example was 73.3%, and the toluene yield was 7.6%.

[0037] Example 5 In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.03 g of PET powder, 0.015 g of RuWZr catalyst (Ru loading of 0.5 wt%, W / Zr molar ratio = 0.3:1), 4 mL of dodecane, and 2 mL of water were added. After sealing the autoclave, the atmosphere was replaced with hydrogen three times. Then, hydrogen was pressurized to 0.4 MPa at ambient temperature. Stirring and heating were initiated, and the reaction system was heated to 300°C and allowed to react at this temperature for 16 hours. After completion of the reaction, the autoclave was quenched in an ice-water bath to ambient temperature. The liquid phase was extracted three times with dodecane, using hexadecane as an internal standard. Qualitative analysis was performed by mass spectrometry, and quantitative analysis was performed by gas chromatography (GC). The results showed that the benzene yield in this example was 74.4%, and the toluene yield was 8.9%.

[0038] Example 6 In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.03 g of PET powder, 0.015 g of RuWZr catalyst (Ru loading of 0.5 wt%, W / Zr molar ratio = 0.4:1), 4 mL of dodecane, and 2 mL of water were added. After sealing the autoclave, the atmosphere was replaced with hydrogen three times. Then, hydrogen was pressurized to 0.4 MPa at ambient temperature. Stirring and heating were initiated, and the reaction system was heated to 300°C and allowed to react at this temperature for 14 hours. After completion of the reaction, the autoclave was quenched in an ice-water bath to ambient temperature. The liquid phase was extracted three times with dodecane, using hexadecane as an internal standard. Qualitative analysis was performed by mass spectrometry, and quantitative analysis was performed by gas chromatography (GC). The results showed that the benzene yield in this example was 81.6%, and the toluene yield was 9.4%.

[0039] Example 7 Waste PET (actual single-component product) (color tray) was pre-crushed to obtain PET flakes. 0.03 g of PET flakes, 0.015 g of RuWZr catalyst (Ru loading of 0.5 wt%, W / Zr molar ratio = 0.4:1), 4 mL of dodecane, and 2 mL of water were then added to an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller. The autoclave was sealed and the atmosphere was replaced with hydrogen three times. Then, hydrogen was pressurized to 0.4 MPa at ambient temperature. Stirring and heating were initiated, and the reaction system was heated to 300°C and allowed to react at this temperature for 16 hours. After the reaction, the autoclave was quenched in an ice-water bath to ambient temperature. The liquid phase was extracted three times with dodecane, using hexadecane as an internal standard. The resulting mixture was then analyzed qualitatively by mass spectrometry and quantitatively by gas chromatography (GC). The results showed a benzene yield of 71.4% and a toluene yield of 10.2% in this example.

[0040] Example 8 The waste PET actual single-component product (industrial polyester rope) was crushed in advance to obtain PET fragments, and then 0.03 g of the PET fragments, 0.015 g of a RuWZr catalyst (Ru loading amount: 0.5 wt%, W / Zr molar ratio = 0.4:1), 4 mL of dodecane and 2 mL of water were added into a high-pressure kettle reactor provided with an electromagnetic stirrer, a thermocouple and a program-controlled temperature instrument. After the high-pressure kettle reactor was sealed, the gas in the high-pressure kettle was replaced with hydrogen three times, and then the high-pressure kettle was pressurized with hydrogen to a pressure of 0.4 MPa at ambient temperature. The stirring and heating were started, the reaction system was heated to 300 °C, and the reaction was carried out at this temperature for 16 h. After the reaction was completed, the high-pressure kettle was quenched to ambient temperature in an ice-water bath. The liquid phase was extracted with dodecane three times, hexadecane was used as an internal standard, and then mass spectrometry was performed for qualitative analysis and gas chromatography (GC) was performed for quantitative analysis. The results show that the benzene yield of this example is 73.2% and the toluene yield is 7.4%.

[0041] Example 9 The waste PET actual multi-component product (black polyester cotton, 85% PET + 15% cotton) was crushed in advance to obtain PET fragments, and then 0.03 g of the PET fragments, 0.015 g of a RuWZr catalyst (Ru loading amount: 0.5 wt%, W / Zr molar ratio = 0.4:1), 4 mL of dodecane and 2 mL of water were added into a high-pressure kettle reactor provided with an electromagnetic stirrer, a thermocouple and a program-controlled temperature instrument. After the high-pressure kettle reactor was sealed, the gas in the high-pressure kettle was replaced with hydrogen three times, and then the high-pressure kettle was pressurized with hydrogen to a pressure of 0.4 MPa at ambient temperature. The stirring and heating were started, the reaction system was heated to 300 °C, and the reaction was carried out at this temperature for 16 h. After the reaction was completed, the high-pressure kettle was quenched to ambient temperature in an ice-water bath. The liquid phase was extracted with dodecane three times, hexadecane was used as an internal standard, and then mass spectrometry was performed for qualitative analysis and gas chromatography (GC) was performed for quantitative analysis. The results show that the benzene yield of this example is 81.6% and the toluene yield is 5.8%.

[0042] Example 10 Waste PET (an actual multi-component product) (orange woven fabric, 95% PET + 5% PU) was pre-crushed to obtain PET flakes. 0.03 g of PET flakes, 0.015 g of RuWZr catalyst (Ru loading of 0.5 wt%, W / Zr molar ratio = 0.4:1), 4 mL of dodecane, and 2 mL of water were then added to an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller. The autoclave was sealed and the atmosphere was replaced three times with hydrogen. Hydrogen was then pressurized to 0.4 MPa at ambient temperature. Stirring and heating were initiated, and the reaction system was heated to 300°C and allowed to react at this temperature for 16 hours. After the reaction, the autoclave was quenched in an ice-water bath to ambient temperature. The liquid phase was extracted three times with dodecane, using hexadecane as an internal standard. The resulting mixture was then qualitatively analyzed by mass spectrometry and quantitatively analyzed by gas chromatography (GC). The results showed a benzene yield of 79.2% and a toluene yield of 6.3% in this example.

[0043] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for producing benzene by directional depolymerization of PET using RuWZr catalyst, characterized in that: include: A reaction system is constructed using PET, RuWZr catalyst and solvent, and the reaction system is subjected to depolymerization and decarboxylation reaction under a hydrogen atmosphere, and benzene is obtained after the reaction is completed; The carrier of the RuWZr catalyst is an amorphous tungsten zirconium oxide, and ruthenium is loaded on the amorphous tungsten zirconium oxide in the form of zero-valent ruthenium. The molar ratio of tungsten to zirconium is 0.1-2:1, and the ruthenium loading is 0.2 wt%-5.0 wt%; The RuWZr catalyst is prepared by an impregnation method using ruthenium chloride, amorphous tungsten zirconium oxide and water as raw materials, and the amorphous tungsten zirconium oxide is prepared by an impregnation method using ammonium metatungstate, zirconium hydroxide and water as raw materials.

2. The method for producing benzene by directional depolymerization of PET using RuWZr catalyst according to claim 1, characterized in that: The solvent is a mixed solvent of dodecane and water, and the volume ratio of dodecane to water is 0.2-5:

1.

3. The method for producing benzene by directional depolymerization of PET using RuWZr catalyst according to claim 2, characterized in that: The mass ratio of PET to RuWZr catalyst is 1:0.1-2, and the amount ratio of PET to mixed solvent is 1 g:10-250 mL.

4. The method for producing benzene by directional depolymerization of PET using RuWZr catalyst according to claim 1, characterized in that: The depolymerization and decarboxylation reaction is carried out under a hydrogen pressure of 0.1-2 MPa, the depolymerization and decarboxylation reaction temperature is 220-380 ° C, and the depolymerization and decarboxylation reaction time is 8-24 h.

5. The method for producing benzene by directional depolymerization of PET using RuWZr catalyst according to claim 1, characterized in that: The preparation method of amorphous tungsten-zirconium oxide is as follows: preparing a mixture containing ammonium metatungstate, zirconium hydroxide and deionized water, stirring the mixture at room temperature until dry, then heating and further drying the mixture, crushing the dried solid and calcining it in an air atmosphere at 500-700 ° C for 2-6 hours to obtain amorphous tungsten-zirconium oxide as a catalyst carrier.

6. The method for producing benzene by directional depolymerization of PET using RuWZr catalyst according to claim 1, characterized in that: The RuWZr catalyst is prepared by preparing a mixture comprising ruthenium chloride, amorphous tungsten zirconium oxide and deionized water, stirring the mixture at room temperature until dry, then heating and further drying the mixture, crushing the dried solid and calcining and reducing it in a reducing atmosphere at 300-500 °C for 3-6 hours to obtain the RuWZr catalyst.

7. The method for producing benzene by directional depolymerization of PET using RuWZr catalyst according to claim 5, characterized in that: The heating rate of calcination in air atmosphere was 2-10 °C / min.

8. The method for producing benzene by directional depolymerization of PET using RuWZr catalyst according to claim 6, characterized in that: The reducing atmosphere is a hydrogen-argon mixed atmosphere, and the heating rate of calcination in the reducing atmosphere is 1-5 °C / min.

9. Use of the method for producing benzene by directed depolymerization of PET using RuWZr catalyst according to any one of claims 1 to 8 in the treatment of waste plastics.

10. The use according to claim 9, characterized in that The main component of waste plastics is PET, and the waste plastics are pre-cleaned and pre-crushed before processing.

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