A method for preparing liquid fuel from waste plastics and a catalyst for cracking waste plastics and use thereof

Abstract

The application provides a method for preparing liquid fuel from waste plastics and a catalyst for cracking waste plastics and application thereof, and the method comprises the following steps: taking a complex containing zinc oxide and at least one selected from nickel oxide and cobalt oxide as a catalyst precursor, mixing the catalyst precursor with the waste plastics at a mass ratio of 1:(0.1-30) to perform a thermal catalytic cracking reaction, then cooling the reaction product, dissolving the reaction product in an organic solvent, performing solid-liquid separation, and collecting the liquid. The application can not only convert waste plastics into liquid fuel, but also construct a metal-support interaction catalyst in situ from the catalyst precursor during the thermal catalytic cracking reaction, thereby improving the activity and stability of the catalyst. The application has the advantages of low cost, green environmental protection, stable process, simple operation and the like, can significantly improve the yield of liquid fuel and aviation kerosene components, and has significant popularization value.

Description

Technical Field

[0001] This invention relates to the field of liquid fuel and waste plastic resource recycling technology, and in particular to a method for preparing liquid fuel from waste plastics and a catalyst for pyrolyzing waste plastics and its application. Background Technology

[0002] Against the backdrop of energy transition and carbon reduction goals, small-scale powered transportation devices are gradually being replaced by new energy equipment. However, the aviation industry, as a key transportation sector, faces unique power requirements that make a simple transition from fuel-based systems to new energy equipment difficult. Sustainable development in the aviation industry has become a crucial issue for the future energy landscape.

[0003] Globally, over 400 million tons of plastic are produced annually, but only 9% is effectively recycled. The remaining waste plastics are disposed of through landfills or incineration, leading to soil pollution and secondary atmospheric emissions (such as dioxins). Meanwhile, the aviation industry is a major carbon emitter, and driven by the 2050 net-zero emissions target, the demand for "sustainable aviation fuel (SAF)" is increasing dramatically. The EU has mandated a 2% SAF blending ratio by 2025, and China's demand for SAF is also rising year by year.

[0004] Post-consumer waste plastics are low-value waste, with their molecular structure mainly composed of carbon (C) and hydrogen (H). Polyethylene, polypropylene, and polystyrene, in particular, which are produced and disposed of in large quantities, are high-quality raw materials for SAF (Styrene-Altered Plastic) production. The carbon-reducing properties of waste plastics in SAF production, coupled with the high value of SAF itself, make this pathway more competitive and economically valuable.

[0005] Commonly used methods for preparing aviation kerosene components from waste plastics, such as pyrolysis and hydrogenolysis, suffer from low yields, high costs, and poor stability. For example, pyrolysis often requires temperatures of 450-700℃, and the resulting aviation kerosene components are mostly olefin compounds, leading to poor thermal stability, easy oxidation, and coking, which increases energy consumption and subsequent processing costs. Hydrogenolysis is often used to produce liquid alkane components for aviation kerosene, but it faces problems such as the involvement of precious metals, the need for high-pressure, high-risk hydrogen as a co-reactant, and poor catalyst stability, resulting in low practicality (e.g., CN113502174A).

[0006] Nickel and cobalt are commonly used materials for the catalytic decomposition of waste plastics and can be used as alternatives to precious metals. However, during use, nickel and cobalt are prone to particle agglomeration and surface carbon accumulation, which causes the catalyst to lose its activity and has poor stability, resulting in low yield of aviation kerosene components.

[0007] Therefore, this invention is proposed. Summary of the Invention

[0008] This invention provides a method for preparing liquid fuel from waste plastics, a catalyst for pyrolyzing waste plastics, and its application, in order to solve the above-mentioned problems existing in the prior art.

[0009] In a first aspect, the present invention provides a method for preparing liquid fuel from waste plastics, comprising the following steps: using a composite containing zinc oxide and at least one selected from nickel oxide and cobalt oxide as a catalyst precursor, mixing the catalyst precursor with the waste plastics at a mass ratio of 1:(0.1-30), carrying out a thermocatalytic cracking reaction, then cooling the reaction product and dissolving it in an organic solvent, then performing solid-liquid separation, and collecting the liquid.

[0010] This invention, when preparing liquid fuel from waste plastics, uses a composite containing zinc oxide and at least one selected from nickel oxide and cobalt oxide as a catalyst precursor. In this precursor, zinc oxide serves as the support, and nickel oxide and cobalt oxide are the metal components. During the thermocatalytic cracking reaction, in-situ reduction can be achieved using reducing media such as hydrogen and carbon monoxide generated from plastic decomposition, transforming nickel oxide and cobalt oxide into nickel and cobalt nanoparticles or clusters. Compared to nickel and cobalt oxide, zinc oxide requires a higher temperature to be reduced. In the reducing environment, zinc oxide undergoes etching and atomic migration during reduction. A small amount of zinc oxide forms a thin oxide layer, coating the nickel and cobalt nanoparticles / clusters, creating a tightly bonded interface between the active metal and zinc oxide. This spontaneously forms a metal-support interaction catalyst, effectively dispersing the active metals (nickel and cobalt) and preventing particle agglomeration and surface carbon accumulation, thus improving the catalyst's activity and stability, significantly increasing the yield of liquid fuel, and simultaneously reducing the yield of olefin compounds in the liquid fuel. This method, without the need for external hydrogenation, precious metals, solvents, or co-reactants, not only constructs a catalyst through in-situ reduction of catalyst precursors, but also achieves the conversion of waste plastics into liquid fuels, particularly the stable, efficient, and selective conversion of high-value aviation kerosene components, under the action of the constructed catalyst. It has many advantages such as low cost, environmental friendliness, robust process, and simple operation, and can significantly improve the yield of aviation kerosene components, thus having significant promotional value.

[0011] Furthermore, the catalyst precursor is a complex containing zinc oxide, nickel oxide and cobalt oxide, wherein the mass ratio of zinc oxide, nickel oxide and cobalt oxide in the complex is 1:(0.01~1):(0.01~1).

[0012] And / or, the catalyst precursor is a complex containing zinc oxide and nickel oxide, wherein the mass ratio of zinc oxide to nickel oxide in the complex is 1:(0.01~1).

[0013] And / or, the catalyst precursor is a complex containing zinc oxide and cobalt oxide, wherein the mass ratio of zinc oxide to cobalt oxide in the complex is 1:(0.01~1).

[0014] This invention has found that when the mass ratio of zinc oxide, nickel oxide, and cobalt oxide in the catalyst precursor is controlled within the above-mentioned range, the coating effect of zinc oxide on nickel and cobalt nanoparticles / clusters can be improved. This can more effectively disperse the active metals (nickel and cobalt), avoid the phenomenon of nickel and cobalt particle agglomeration and surface carbon accumulation, improve the activity and stability of the catalyst, and thus improve the yield of liquid fuel and aviation kerosene components.

[0015] Furthermore, the temperature of the thermocatalytic cracking reaction is 200~400℃, and the reaction time is 1~40h. In the reaction system containing the catalyst precursor of the present invention, controlling the reaction temperature within the above-mentioned reasonable range can not only effectively reduce energy consumption, but also regulate the degree of cracking, avoiding the problem of product distribution being light or heavy due to excessive cracking and / or insufficient cracking, thereby improving the yield of liquid fuel and aviation kerosene components.

[0016] Preferably, the cooling method involves first cooling to room temperature, and then placing it at -20 to 10°C for 0.1 to 1 hour. This invention employs a further cooling method after cooling to room temperature, which can further condense low-boiling-point compounds (such as C4-C6) and improve the yield of liquid fuel.

[0017] Preferably, the cooling method is to first cool to room temperature, and then place it at 0°C for 10 minutes.

[0018] Preferably, the thermocatalytic cracking reaction is carried out under an oxygen-free atmosphere.

[0019] More preferably, the oxygen-free atmosphere is achieved by filling the atmosphere with nitrogen, argon, or helium at 0.1 MPa at room temperature.

[0020] Preferably, before mixing the waste plastic with the catalyst precursor, the process further includes drying the waste plastic at 80-90°C for 4-5 hours, and then crushing it to a particle size of less than 2 cm.

[0021] Furthermore, the method for preparing the catalyst precursor includes: directly mixing zinc oxide powder with at least one selected from nickel oxide powder and cobalt oxide powder.

[0022] Furthermore, the preparation method of the catalyst precursor includes: mixing a zinc source for providing zinc oxide and a nickel salt for providing nickel oxide and / or a cobalt salt for providing cobalt oxide to obtain a metal salt, and then pretreating the metal salt before calcining it at 200~600℃ for 1~5h.

[0023] Preferably, when the zinc source is mixed with any one of the nickel salt and cobalt salt, the mass ratio of the zinc source to the nickel salt or the zinc source to the cobalt salt is (0.001~200):1.

[0024] Preferably, when the zinc source, nickel salt and cobalt salt are mixed, the mass ratio of the zinc source, nickel salt and cobalt salt is (0.001~200):(0.001~200):1.

[0025] Preferably, the zinc source is selected from any one or more of zinc oxide and zinc salts.

[0026] Preferably, the nickel salt may be selected from one or more of nickel chloride, nickel nitrate, nickel acetate, nickel acetylacetonate, and nickel carbonate; the cobalt salt may be selected from one or more of cobalt acetate, cobalt nitrate, cobalt chloride, cobalt acetylacetonate, and cobalt oxalate; and the zinc salt may be selected from one or more of zinc acetate, zinc acetylacetonate, zinc carbonate, zinc chloride, and zinc nitrate.

[0027] Furthermore, the pretreatment method is selected from any one of microwave method, impregnation method and hydrothermal method.

[0028] Preferably, when microwave pretreatment is used, the zinc source used to obtain the metal salt is a zinc salt, and the steps of the microwave method include: adding water and an alkaline medium to the metal salt and stirring evenly, then placing it under microwave heating at 100~2000W and 40~90℃ for 0.5~5h, and after the reaction is completed, cooling, filtering, washing and drying are performed.

[0029] Preferably, the mass ratio of the metal salt, water, and alkaline medium is 1:(0.01~100):(0.01~100).

[0030] Preferably, when the impregnation method is used for pretreatment, the zinc source used to obtain the metal salt is zinc oxide, and the steps of the impregnation method include: adding water to the metal salt, stirring and impregnating for 0.5 to 6 hours, and then removing the water.

[0031] Preferably, when a hydrothermal method is used for pretreatment, the zinc source used to obtain the metal salt is a zinc salt, and the steps of the hydrothermal method include: adding urea and water to the metal salt and stirring evenly, and hydrothermally reacting at 100~260℃ for 6~30h; after the reaction is completed, cooling, filtering, washing, and drying.

[0032] Preferably, the mass ratio of the metal salt, water, and urea is 1:(0.01~100):(0.01~100).

[0033] An unexpected discovery of this invention is that, compared to the method of directly mixing zinc oxide with at least one selected from nickel oxide and cobalt oxide, pre-mixing the corresponding raw materials and then pre-treating them by any one of microwave, impregnation or hydrothermal methods can further improve the yield of liquid fuel and aviation kerosene components and reduce the yield of olefin compounds.

[0034] Furthermore, the waste plastics include one or more of polyethylene, polypropylene, polystyrene, and mixed waste plastics from landfills.

[0035] Preferably, the organic solvent includes one or more of dichloromethane, tetrahydrofuran, and trichloromethane.

[0036] Furthermore, the collected liquid is subjected to rotary evaporation to remove organic solvents from the liquid.

[0037] In a second aspect, the present invention provides a liquid fuel prepared by the method described above.

[0038] Preferably, the mass percentage of aviation kerosene component in the liquid fuel is 70% to 90%.

[0039] A third aspect of the present invention provides a catalyst for pyrolyzing waste plastics, prepared by the method described above, wherein the catalyst is a solid obtained after solid-liquid separation.

[0040] The catalyst of this invention can be obtained during the preparation of liquid fuel from waste plastics. It corresponds to the solid obtained from solid-liquid separation during liquid fuel preparation, with the liquid obtained being the liquid fuel. The catalyst uses a complex of nickel oxide and at least one selected from cobalt oxide and zinc oxide as a catalyst precursor. During the thermocatalytic cracking reaction of preparing liquid fuel from waste plastics, the catalyst precursor is reduced in situ by reducing media such as hydrogen and carbon monoxide generated from plastic decomposition to form a catalyst with metal-zinc oxide support interaction. This catalyst can efficiently and selectively convert waste plastics, even mixed waste plastics, into liquid fuel with a high proportion of aviation kerosene components, achieving a yield of 40-80% aviation kerosene components. It possesses numerous advantages such as high stability, high catalytic efficiency, low cost, and safety, and has significant application potential.

[0041] Preferably, the catalyst is calcined and regenerated in an air atmosphere during use or after a long period of use, and the calcination and regeneration temperature is 300~700℃ for 1~5h.

[0042] A fourth aspect of the invention provides the use of the catalyst described above in the preparation of liquid fuels.

[0043] Preferably, the catalyst is used in the preparation of liquid fuel from waste plastics.

[0044] Furthermore, the method of application includes: using waste plastic as raw material, adding the catalyst to carry out the thermocatalytic cracking reaction, then cooling the reaction product and dissolving it with an organic solvent, and then performing solid-liquid separation, wherein the liquid obtained from the solid-liquid separation is the liquid fuel containing organic solvent.

[0045] Furthermore, the mass ratio of the catalyst to the waste plastic is 1:(0.1~30).

[0046] The present invention provides a method for preparing liquid fuel from waste plastics, a catalyst for pyrolyzing waste plastics, and the beneficial effects of their application, including at least the following: The present invention uses waste plastics as raw materials and employs a composite containing zinc oxide and at least one selected from nickel oxide and cobalt oxide as a catalyst precursor for thermocatalytic pyrolysis. This not only converts waste plastics into liquid fuels, but also allows the catalyst precursor to be reduced in situ to form a metal-support interaction catalyst during the thermocatalytic pyrolysis process, thereby improving the catalyst's activity and stability. It has many advantages such as low cost, environmental friendliness, robust process, and simple operation, and can significantly improve the yield of liquid fuels and aviation kerosene components, thus having significant promotional value. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0048] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0050] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0051] Example 1 This embodiment provides a method for preparing liquid fuel from waste plastics, and its process flow diagram is as follows: Figure 1 As shown, the waste plastic is polypropylene centrifuge tube waste plastic (material is polypropylene, wherein the polypropylene content is 97wt%), and the method includes the following steps: (1) Dry the waste plastic at 80℃ for 5 hours and crush it to a particle size of less than 2cm; then mix the crushed waste plastic with the catalyst precursor at a mass ratio of 2:1 to obtain a mixture.

[0052] (2) Weigh 30g of the mixture and place it in the reactor. First, purge the reactor with nitrogen gas three times or more. Then, fill the reactor with 0.1MPa of nitrogen gas at room temperature and seal the reactor.

[0053] (3) Set the temperature of the reactor to 300℃ and allow the mixture to undergo thermal catalytic cracking reaction at this temperature for 16 hours. After the reaction is completed, allow the reaction products in the reactor to cool naturally to room temperature, and then place them at 0℃ for further cooling for 10 minutes.

[0054] (4) Open the gas outlet of the reactor and collect the non-condensable gas. Then, open the reactor, collect the reaction products, add dichloromethane to the reaction products, dissolve the reaction products at 50°C, and then filter to obtain a solid (i.e., the catalyst) and a liquid. The collected liquid is then subjected to rotary evaporation at 30°C to remove the dichloromethane and obtain liquid fuel. The composition of the obtained liquid fuel is analyzed, and the results are shown in Table 1.

[0055] The catalyst precursor was prepared using a microwave method. The preparation steps included: stirring 5g of nickel nitrate, 100g of zinc nitrate, 2L of deionized water, and 60mL of ammonia water until homogeneous; then placing the mixture in a microwave reactor and reacting it at 300W and 70℃ for 2 hours; after the reaction, cooling, filtering, washing, drying at 100℃ for 3 hours, and then calcining at 300℃ for 3 hours to obtain the catalyst precursor. The mass ratio of zinc oxide to nickel oxide in the catalyst monomer was 21:1.

[0056] This embodiment also provides a catalyst for pyrolyzing waste plastics. The catalyst is a nickel-zinc-zinc oxide composite, which is obtained by in-situ reduction and reconstruction of catalyst precursors and waste plastics as raw materials during the preparation of liquid fuel. The preparation method also adopts the method of steps (1) to (4). The solid obtained in step (4) is the catalyst.

[0057] Example 2 This embodiment provides a method for preparing liquid fuel from waste plastics. The steps are basically the same as in Embodiment 1. The waste plastic used is polyethylene plastic bag waste plastic (material is polyethylene, wherein the polyethylene content is 97wt%). The difference in the steps is: (1) Dry the waste plastic at 80℃ for 5 hours and crush it to a particle size of less than 2cm; then mix the crushed waste plastic with the catalyst precursor at a mass ratio of 1:1 to obtain a mixture.

[0058] (3) Set the temperature of the reactor to 320℃ and allow the mixture to undergo thermal catalytic cracking reaction at this temperature for 24 hours. After the reaction is completed, allow the reaction products in the reactor to cool naturally to room temperature, and then place them at -10℃ for further cooling for 10 minutes.

[0059] The catalyst precursor was prepared by an impregnation method, the preparation steps of which included: mixing 2.5g of cobalt chloride, 100g of zinc oxide, and 500mL of deionized water, impregnating and stirring at room temperature for 4h, then heating to 100℃ and stirring to remove moisture, drying at 80℃ for 6h to obtain a solid product; then calcining the solid product at 400℃ for 2h, and cooling to obtain the catalyst precursor. The mass ratio of zinc oxide to cobalt oxide in the catalyst monomer was 20:1.

[0060] This embodiment also provides a catalyst for pyrolyzing waste plastics. The catalyst is a cobalt-zinc-zinc oxide composite, which is obtained by in-situ reduction and reconstruction of catalyst precursors and waste plastics during the preparation of liquid fuel. The preparation method is the same as the method in steps (1) to (4) of this embodiment. The solid obtained in step (4) is the catalyst.

[0061] Example 3 This embodiment provides a method for preparing liquid fuel from waste plastics. The steps are basically the same as in Embodiment 1. The waste plastic used is polyethylene agricultural film waste plastic (material is polyethylene, wherein the polyethylene content is 95wt%). The difference in the steps is: (1) Dry the waste plastic at 80°C for 5 hours and crush it to a particle size of less than 2 cm; then mix the crushed waste plastic with the catalyst precursor at a mass ratio of 5:1 to obtain a mixture.

[0062] (3) Set the temperature of the reactor to 300℃ and allow the mixture to undergo thermal catalytic cracking reaction at this temperature for 32 hours. After the reaction is completed, allow the reaction products in the reactor to cool naturally to room temperature, and then place them at -5℃ for further cooling for 10 minutes.

[0063] The catalyst precursor was prepared using a microwave method. The preparation steps included: stirring 13g of nickel chloride, 88g of zinc acetate, 1.6L of deionized water, and 10g of sodium hydroxide until homogeneous; then placing the mixture in a microwave reactor and reacting it at 500W and 80℃ for 3 hours; after the reaction, cooling, filtering, washing, drying at 100℃ for 3 hours, and calcining at 420℃ for 1 hour to obtain the catalyst precursor. The mass ratio of zinc oxide to nickel oxide in the catalyst monomer was 4.5:1.

[0064] This embodiment also provides a catalyst for pyrolyzing waste plastics. The catalyst is a nickel-zinc-zinc oxide composite, which is obtained by in-situ reduction and reconstruction of catalyst precursors and waste plastics as raw materials during the preparation of liquid fuel. The preparation method also adopts the method of steps (1) to (4). The solid obtained in step (4) is the catalyst.

[0065] Example 4 This embodiment provides a method for preparing liquid fuel from waste plastics. The steps are basically the same as in Embodiment 1. The waste plastics used are polyethylene agricultural film waste plastics (material is polyethylene, wherein the polyethylene content is 95wt%), polyethylene medicine bottle waste plastics (material is polyethylene, wherein the polyethylene content is 97wt%), and polypropylene centrifuge tube waste plastics (material is polypropylene, wherein the polypropylene content is 97wt%). The difference in the steps is as follows: (1) The waste plastics of polyethylene agricultural film, waste plastics of polyethylene medicine bottles and waste plastics of polypropylene centrifuge tubes are dried at 80℃ for 5 hours, then crushed to a particle size of less than 2cm, and then the crushed waste plastics are mixed in a mass ratio of 3:2:5; then the mixed waste plastics are mixed with the catalyst precursor in a mass ratio of 2:1 to obtain the mixture.

[0066] (3) Set the temperature of the reactor to 250°C and allow the mixture to undergo a thermal catalytic cracking reaction at this temperature for 30 hours. After the reaction is completed, allow the reaction products in the reactor to cool naturally to room temperature, and then place them at -10°C for a further cooling of 10 minutes.

[0067] The catalyst precursor was prepared by a hydrothermal method, comprising the following steps: mixing 1g of cobalt acetylacetonate, 4g of nickel acetylacetonate, 50g of zinc acetylacetonate, 10g of urea, and 200mL of deionized water, stirring thoroughly, and then hydrothermally reacting at 180℃ for 20h. After the reaction, the mixture was cooled to room temperature, filtered, washed, dried at 100℃ for 3h, and then calcined at 500℃ for 4h to obtain the catalyst precursor. The mass ratio of zinc oxide, nickel oxide, and cobalt oxide in the catalyst monomer was 23:2:1.

[0068] This embodiment also provides a catalyst for pyrolyzing waste plastics. The catalyst is a cobalt-nickel-zinc-zinc oxide composite, which is obtained by in-situ reduction and reconstruction of catalyst precursors and waste plastics during the preparation of liquid fuel. The preparation method also adopts the method of steps (1) to (4). The solid obtained in step (4) is the catalyst.

[0069] Example 5 This embodiment provides a method for preparing liquid fuel from waste plastics. The steps are basically the same as in Embodiment 1. The waste plastics used are polyethylene water pipe waste plastic (material is polyethylene, wherein the polyethylene content is 97wt%), polypropylene car bumper waste plastic (material is polypropylene, wherein the polypropylene content is 97wt%), and polystyrene foam waste plastic (material is polystyrene, wherein the polystyrene content is 97wt%). The difference in the steps is as follows: (1) The waste plastics of polyethylene water pipes, polypropylene car bumpers and polystyrene foam were dried at 80°C for 5 hours, then crushed to a particle size of less than 2 cm, and then the crushed waste plastics were mixed in a mass ratio of 4:5:1; then the mixed waste plastics were mixed with the catalyst precursor in a mass ratio of 1:2 to obtain the mixture.

[0070] (3) Set the temperature of the reactor to 350°C and allow the mixture to undergo a thermal catalytic cracking reaction at this temperature for 24 hours. After the reaction is completed, allow the reaction products in the reactor to cool naturally to room temperature, and then place them at -15°C for a further cooling of 10 minutes.

[0071] The catalyst precursor was prepared using a microwave method. The preparation steps included: mixing 10g of nickel chloride, 8g of cobalt chloride, 50g of zinc chloride, 500mL of deionized water, and 15g of potassium hydroxide until homogeneous. The mixture was then placed in a microwave reactor and microwaved at 1500W and 85℃ for 4 hours. After the reaction, the mixture was cooled, filtered, washed, dried at 100℃ for 3 hours, and calcined at 500℃ for 2 hours to obtain the catalyst precursor. The mass ratio of zinc oxide, nickel oxide, and cobalt oxide in the catalyst monomer was 52:1:25.

[0072] This embodiment also provides a catalyst for pyrolyzing waste plastics. The catalyst is a cobalt-nickel-zinc-zinc oxide composite, which is obtained by in-situ reduction and reconstruction of catalyst precursors and waste plastics during the preparation of liquid fuel. The preparation method also adopts the method of steps (1) to (4). The solid obtained in step (4) is the catalyst.

[0073] Example 6 This embodiment provides a method for preparing liquid fuel from waste plastics, the steps of which are basically the same as those in Embodiment 1. The waste plastics used are mixed waste plastics from landfills (containing 50wt% polyethylene and 45wt% polypropylene). The difference in the steps is as follows: (1) Dry the mixed waste plastics in the landfill at 80°C for 5 hours, then crush them to a particle size of less than 2 cm; then mix the waste plastics with the catalyst precursor at a mass ratio of 6:1 to obtain the mixture.

[0074] (3) Set the temperature of the reactor to 350°C and allow the mixture to undergo thermal catalytic cracking reaction at this temperature for 30 hours. After the reaction is completed, allow the reaction products in the reactor to cool naturally to room temperature, and then place them at -18°C for further cooling for 10 minutes.

[0075] The catalyst precursor was prepared by a hydrothermal method, comprising the following steps: mixing 10g cobalt acetate, 60g zinc acetate, 8g urea, and 60mL deionized water until homogeneous, then reacting hydrothermally at 220℃ for 26h. After the reaction, cooling to room temperature, filtering, washing, drying at 100℃ for 3h, and then calcining at 350℃ for 4h to obtain the catalyst precursor. The mass ratio of zinc oxide to cobalt oxide in the catalyst monomer is 17:1.

[0076] This embodiment also provides a catalyst for pyrolyzing waste plastics. The catalyst is a cobalt-zinc oxide composite, which is obtained by in-situ reduction and reconstruction of catalyst precursors and waste plastics as raw materials during the preparation of liquid fuel. The preparation method also adopts the method of steps (1) to (4). The solid obtained in step (4) is the catalyst.

[0077] Example 7 This embodiment provides a method for preparing liquid fuel from waste plastics. The steps are basically the same as those in Embodiment 1, except that the temperature of the thermocatalytic cracking reaction is 500°C and the time is 16 hours.

[0078] Example 8 This embodiment provides a method for preparing liquid fuel from waste plastics. The steps are basically the same as those in Example 1, except that zinc oxide and nickel oxide are directly mixed at a mass ratio of 21:1 to obtain a catalyst monomer for catalytic cracking.

[0079] Example 9 This embodiment provides a method for preparing liquid fuel from waste plastics. The steps are basically the same as those in Embodiment 2, except that zinc oxide and cobalt oxide are directly mixed at a mass ratio of 20:1 to obtain a catalyst monomer for catalytic cracking.

[0080] Example 10 This embodiment provides a method for preparing liquid fuel from waste plastics. The steps are basically the same as those in Embodiment 4, except that zinc oxide, nickel oxide and cobalt oxide are directly mixed in a mass ratio of 23:2:1 to obtain a catalyst monomer for catalytic cracking.

[0081] Comparative Example 1 This comparative example provides a method for preparing liquid fuel from waste plastics, the steps of which are basically the same as those in Example 1, except that: The preparation method of the catalyst precursor includes: stirring 100g of zinc nitrate, 2L of deionized water and 60mL of ammonia water evenly, then placing it in a microwave reactor and microwaving it at 300W and 70℃ for 2h. After the reaction is completed, the mixture is cooled, filtered, dried at 100℃ for 3h, and calcined at 300℃ for 3h to obtain the catalyst precursor.

[0082] This comparative example also provides a catalyst for pyrolyzing waste plastics. The catalyst is a zinc-zinc oxide composite, which is obtained by in-situ reduction and reconstruction of catalyst precursors and waste plastics during the preparation of liquid fuel. The preparation method also adopts the method of steps (1) to (4). The solid obtained in step (4) is the catalyst.

[0083] Comparative Example 2 This comparative example provides a method for preparing liquid fuel from waste plastics, the steps of which are basically the same as those in Example 2, except that: The catalyst preparation method includes: mixing 100g of zinc oxide and 500mL of deionized water, impregnating and stirring at room temperature for 4h, then heating to 100℃ and stirring to remove water, drying at 80℃ for 6h to obtain a solid product; then calcining the solid product at 400℃ for 2h, and cooling to obtain the catalyst precursor.

[0084] This embodiment also provides a catalyst for pyrolyzing waste plastics. The catalyst is a zinc-zinc oxide composite, which is obtained by in-situ reduction and reconstruction of catalyst precursors and waste plastics as raw materials during the preparation of liquid fuel. The preparation method is the same as the method in steps (1) to (4) of this embodiment. The solid obtained in step (4) is the catalyst.

[0085] Experimental Example 1 This experimental example compares the yield and C8-C content of liquid fuels prepared by the methods of the embodiments and comparative examples. 16 The yields of aviation kerosene components and the olefin content in the liquid fuel were determined, and the results are shown in Table 1: Table 1. Yields and olefin contents of liquid fuel and aviation kerosene components prepared by the methods of Example 1 and the comparative examples.

[0086] As shown in Table 1, Examples 1-10 used a complex containing zinc oxide and at least one of nickel oxide and cobalt oxide as a catalyst precursor to prepare liquid fuel. Compared with Comparative Examples 1 and 2, which only used zinc oxide, this significantly improved the yield of liquid fuel and aviation kerosene components and reduced the olefin content. In particular, when Examples 1-6 were prepared by combining microwave, impregnation and hydrothermal methods for pretreatment, the corresponding effects of improving the yield of liquid fuel, aviation kerosene components and reducing the olefin content were more significant.

[0087] Experiment Example 2 In this experimental example 2, based on the examples and comparative examples, the catalyst prepared in the examples and comparative examples was added at least once to the same fresh waste plastic as in the comparative and examples for a thermocatalytic cracking reaction. The mass ratio of catalyst to waste plastic was the same as that of catalyst monomer to waste plastic in the examples and comparative examples. The yield of liquid fuel produced from the catalyst that was reused 10 times, and the C8-C content were measured. 16 The yields of aviation kerosene components and the olefin content in the liquid fuel were determined, and the results are shown in Table 2. Table 2. Yields and olefin contents of the liquid fuel and aviation kerosene components prepared in Example 2.

[0088] In Table 2, the catalysts obtained in the examples and comparative examples for preparing liquid fuels were not reused in the examples and comparative examples, corresponding to 0 times, which corresponds to the data in Table 1. As can be seen from Table 2, the catalysts prepared in Examples 1-10 have higher stability after use than those in Comparative Examples 1 and 2, indicating that the catalysts obtained in this invention for preparing liquid fuels not only have high catalytic activity but also strong stability and can be reused more than 30 times.

[0089] The calculation formulas for the above liquid fuel yield, aviation kerosene component yield and olefin content in liquid fuel are as follows. The detection method for olefins and alkanes in the corresponding carbon fractions of liquid fuel is chromatography-mass spectrometry, and the detection standards refer to NB / T 11687-2024 and NB / T 11687-2024.

[0090] Olefin content (%) in liquid fuel = (mass of olefins in liquid fuel / total mass of olefins and alkanes in liquid fuel) × 100%; Liquid fuel yield (%) = (mass of liquid fuel / mass of waste plastic) × 100%; Aviation kerosene component yield (%) = (mass of aviation kerosene component in liquid fuel / mass of waste plastics) × 100%. Wherein, the mass of aviation kerosene component refers to the C8-C content of the liquid fuel. 16 The sum of the masses of the compounds.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing liquid fuel from waste plastics, characterized in that, The process includes the following steps: using a complex containing zinc oxide and at least one selected from nickel oxide and cobalt oxide as a catalyst precursor, mixing the catalyst precursor with the waste plastic at a mass ratio of 1:(0.1~30) to carry out a thermocatalytic cracking reaction, then cooling the reaction product and dissolving it in an organic solvent, followed by solid-liquid separation and collecting the liquid.

2. The method for preparing liquid fuel from waste plastics according to claim 1, characterized in that, The catalyst precursor is a complex containing zinc oxide, nickel oxide and cobalt oxide, wherein the mass ratio of zinc oxide, nickel oxide and cobalt oxide in the complex is 1:(0.01~1):(0.01~1). And / or, the catalyst precursor is a complex containing zinc oxide and nickel oxide, wherein the mass ratio of zinc oxide to nickel oxide in the complex is 1:(0.01~1). And / or, the catalyst precursor is a complex containing zinc oxide and cobalt oxide, wherein the mass ratio of zinc oxide to cobalt oxide in the complex is 1:(0.01~1).

3. The method for preparing liquid fuel from waste plastics according to claim 1 or 2, characterized in that, The temperature of the thermocatalytic cracking reaction is 200~400℃, and the reaction time is 1~40h; Preferably, the cooling method is to first cool to room temperature, and then place it at -20~10℃ for 0.1~1h; Preferably, the thermocatalytic cracking reaction is carried out under an oxygen-free atmosphere.

4. The method for preparing liquid fuel from waste plastics according to any one of claims 1 to 3, characterized in that, The method for preparing the catalyst precursor includes: directly mixing zinc oxide powder with at least one selected from nickel oxide powder and cobalt oxide powder.

5. The method for preparing liquid fuel from waste plastics according to any one of claims 1 to 3, characterized in that, The method for preparing the catalyst precursor includes: mixing a zinc source for providing zinc oxide and a nickel salt and / or a cobalt salt for providing nickel oxide to obtain a metal salt, and then pretreating the metal salt before calcining it at 200~600℃ for 1~5h; Preferably, when the zinc source is mixed with any one selected from the nickel salt and cobalt salt, the mass ratio of the zinc source to the nickel salt or the zinc source to the cobalt salt is (0.001~200):1; Preferably, when the zinc source, nickel salt, and cobalt salt are mixed, the mass ratio of the zinc source, nickel salt, and cobalt salt is (0.001~200):(0.001~200):1; Preferably, the zinc source is selected from any one or more of zinc oxide and zinc salts.

6. The method for preparing liquid fuel from waste plastics according to claim 5, characterized in that, The pretreatment method is selected from any one of microwave method, impregnation method and hydrothermal method; Preferably, when microwave pretreatment is used, the zinc source used to obtain the metal salt is a zinc salt, and the steps of the microwave method include: adding water and an alkaline medium to the metal salt and stirring evenly, then placing it under microwave heating at 100~2000W and 40~90℃ for 0.5~5h, and after the reaction is completed, cooling, filtering, washing and drying are performed. Preferably, the mass ratio of the metal salt, water, and alkaline medium is 1:(0.01~100):(0.01~100). Preferably, when the impregnation method is used for pretreatment, the zinc source used to obtain the metal salt is zinc oxide, and the steps of the impregnation method include: adding water to the metal salt, stirring and impregnating for 0.5 to 6 hours, and then removing the water; Preferably, when a hydrothermal method is used for pretreatment, the zinc source used to obtain the metal salt is a zinc salt, and the steps of the hydrothermal method include: adding urea and water to the metal salt and stirring until homogeneous, and then hydrothermally reacting at 100~260℃ for 6~30h; after the reaction is completed, cooling, filtering, washing, and drying are performed. Preferably, the mass ratio of the metal salt, water, and urea is 1:(0.01~100):(0.01~100).

7. The method for preparing liquid fuel from waste plastics according to any one of claims 1 to 6, characterized in that, The waste plastics include one or more of polyethylene, polypropylene, polystyrene, and mixed waste plastics from landfills; Preferably, the organic solvent includes one or more of dichloromethane, tetrahydrofuran, and trichloromethane.

8. A liquid fuel, characterized in that, Prepared by the method described in any one of claims 1 to 7; Preferably, the mass percentage of aviation kerosene component in the liquid fuel is 70% to 90%.

9. A catalyst for pyrolyzing waste plastics, characterized in that, The catalyst is prepared by the method according to any one of claims 1 to 7, wherein the catalyst is a solid obtained after solid-liquid separation.

10. The use of the catalyst according to claim 9 in the preparation of liquid fuels.

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