Catalyst for waste plastic cracking and preparation method and application thereof

Abstract

The application provides a catalyst for waste plastic cracking and a preparation method and application thereof, and the preparation method comprises the following steps: step 1, roasting FCC waste catalyst, then mixing with an inorganic acid solution to perform acid treatment; step 2, mixing the acid-treated FCC waste catalyst obtained in step 1 with sodium metaaluminate, adjusting the pH value to 7-10 to perform reaction; step 3, mixing and beating the material obtained in step 2 with an active component, drying and roasting to obtain the catalyst for waste plastic cracking. The FCC waste catalyst is subjected to acid treatment to extract part of alumina, then is reacted with sodium metaaluminate under certain pH and temperature, the matrix pore structure and cracking activity are improved; the active component ZSM-5 and beta molecular sieve increase the shape-selective catalytic reaction, and the selectivity and yield of low-carbon olefins are improved.

Description

Technical Field

[0001] This invention relates to the field of waste plastic pyrolysis, and particularly to a catalyst for the pyrolysis of waste plastics to produce more low-carbon olefins, a method for preparing the catalyst, and the application of the catalyst in the pyrolysis of waste plastics. Background Technology

[0002] Plastics are an important component of modern materials science, widely used worldwide due to their low cost and good overall performance. However, while plastic products bring convenience to people's lives, they also generate a large amount of waste, and "white pollution" has become a prominent environmental problem.

[0003] In addition, FCC catalysts are used in the largest quantities among oil refining catalysts, generating a large amount of spent catalysts annually. FCC spent catalysts have low activity and contain a certain amount of heavy metals. Currently, most FCC spent catalysts are disposed of through landfill. The reactivation of a few spent catalysts mainly involves methods such as acid washing, carbonylation-chlorination, sulfidation-oxidation, and magnetic rotation, aiming to remove heavy metals and restore activity. However, these methods are cumbersome and costly. How to properly dispose of spent catalysts has always been a concern for industry professionals.

[0004] The process for producing low-carbon olefins by catalytic pyrolysis of waste plastics and the catalysts used have been reported in existing technologies, for example:

[0005] Patent CN113398982 discloses a catalyst for the catalytic cracking of waste plastics to produce low-carbon olefins, comprising a silica-alumina matrix and a molecular sieve. The silica-alumina matrix includes silicon-containing and aluminum-containing materials, and the molecular sieve includes ZSM-5 molecular sieve and / or ZSM-11 molecular sieve. The prepared catalyst, applied to the catalytic cracking of waste plastics to produce low-carbon olefins, improves the yield of low-carbon olefins and simultaneously improves gasoline quality. However, the silica-alumina matrix in this patent is prepared by mixing boehmite with alkali metal hydroxides, then mixing with silicates, and finally adding diammonium hydrogen phosphate to form a precipitate, followed by filtration and washing. This process is complex and costly.

[0006] Patent CN112316986 discloses a catalyst, its preparation method, and its application. The catalyst's raw materials include a heat carrier and first to third active components. The heat carrier contains an oxide of at least one element selected from Si, Al, alkali metals, and alkaline earth metals. The first active component contains an oxide of at least one element selected from Zn, Cu, Ni, Mn, La, Ce, and Ti. The second active component is selected from oxides of alkali metals and / or alkaline earth metals. The third active component is selected from an oxide of at least one element selected from Zn, Ga, P, Cr, Ag, and K. Its application in the pyrolysis of waste plastics to produce low-carbon olefins and aromatics yields high yields. However, the catalyst composition in this patent is complex, resulting in high costs.

[0007] Patent CN108587668 discloses a method for producing light oil and gas by cracking and reducing viscosity of waste plastics from low-quality heavy oil. The steps are as follows: Low-quality heavy oil, waste plastics, and / or mixtures thereof are subjected to high-temperature roasting and modification of waste FCC catalyst discharged from a refinery catalytic converter. Harmful impurities are removed, and active components and additives are loaded onto the catalyst. This catalyst is then used as a catalyst for cracking, isomerization, desulfurization, pour point depressurization, and viscosity reduction under hydrogen-exposed or non-hydrogen-exposed conditions to produce high-value-added oil and gas products with a high yield of light oil. However, in this patent, the FCC waste catalyst is directly loaded with active components after roasting, and the catalyst performance needs improvement.

[0008] Patent CN103357431 discloses a catalyst for the pyrolysis of waste plastics to produce automotive fuel, its preparation method, and its application. This catalyst is formed by molding small-grained rare earth ZSM-5 / ZSM-11 molecular sieves with a binder and then further modified. The binder is alumina or silica; the ratio of molecular sieve to (molecular sieve + binder) is 30–85 wt%; the weight percentage of ZnO in the catalyst is 1.0–5.0 wt%, and the weight percentage of P2O5 is 0.5–6.0 wt%. This catalyst, used in the pyrolysis and conversion of polyolefin waste plastics to produce automotive fuel, features high activity, low reaction temperature, high gasoline and LPG yields, good gasoline product distribution (high content of aromatics and isoalkanes), and high octane number. However, since this catalyst is directly molded and modified from molecular sieves and binders, its pore structure needs further improvement.

[0009] Patent CN202010553447.7 provides a method for revitalizing spent catalytic cracking catalyst, comprising: calcining a spent catalytic cracking catalyst containing contaminating metals; leaching the calcined product in an alkaline solution containing a structure protectant; and sequentially washing the leached product with water and acid to obtain a revitalized catalytic cracking catalyst. The revitalized catalyst exhibits improved crystallinity (1%–10%), vanadium removal rate (50%–80%), and micro-reaction activity (10–15%) compared to the spent catalytic cracking equilibrium agent. The resulting catalyst maintains good activity stability even after multiple cycles of regeneration. However, this catalyst revitalization requires alkaline leaching, water washing, and acid washing, resulting in the discharge of large amounts of alkaline and acid solutions. Summary of the Invention

[0010] The main objective of this invention is to provide a catalyst for the pyrolysis of waste plastics, its preparation method, and its application, so as to overcome the defects of existing catalysts for the pyrolysis of waste plastics, such as complex preparation process, high cost, and poor performance.

[0011] To achieve the above objectives, the present invention provides a method for preparing a catalyst for the pyrolysis of waste plastics, comprising the following steps:

[0012] Step 1: Roast the spent FCC catalyst and then mix it with an inorganic acid solution for acid treatment;

[0013] Step 2: Mix the acid-treated FCC waste catalyst obtained in Step 1 with sodium aluminate, adjust the pH value to 7-10, and carry out the reaction.

[0014] Step 3: Mix the substance obtained in Step 2 with the active component, slurry, dry and calcine to obtain a catalyst for the pyrolysis of waste plastics.

[0015] The method for preparing the catalyst for waste plastic pyrolysis according to the present invention further includes a step of grinding the FCC waste catalyst, wherein the particle size of the ground FCC waste catalyst is less than 10 μm, and the ground FCC waste catalyst is calcined at a temperature of 600-900℃ for 1-10 hours.

[0016] The method for preparing the catalyst for waste plastic pyrolysis according to the present invention, wherein the weight ratio of the inorganic acid in the inorganic acid solution to the FCC waste catalyst is 0.05:1 to 0.1:1, and the inorganic acid is one or more of hydrochloric acid, phosphoric acid and sulfuric acid.

[0017] The method for preparing the catalyst for waste plastic pyrolysis according to the present invention includes an acid treatment at a temperature of 50–90°C for a time of 1–3 hours.

[0018] The method for preparing the catalyst for waste plastic pyrolysis according to the present invention, wherein the sodium aluminate is calculated as alumina, and the weight ratio of the sodium aluminate to the FCC waste catalyst is 0.05:1 to 0.1:1.

[0019] The method for preparing the catalyst for waste plastic pyrolysis according to the present invention, wherein the reaction temperature in step 2 is 50-90°C and the reaction time is 1-3 hours.

[0020] The method for preparing the catalyst for waste plastic pyrolysis according to the present invention, wherein the active component is one or a mixture of ZSM-5 molecular sieve and β molecular sieve.

[0021] The method for preparing a catalyst for pyrolysis of waste plastics according to the present invention, wherein the weight ratio of the active component to the FCC waste catalyst is 0.2:1 to 2:1, preferably 0.5:1 to 1:1.

[0022] To achieve the above objectives, the present invention also provides a catalyst for the pyrolysis of waste plastics obtained by the above preparation method.

[0023] To achieve the above objectives, the present invention further provides the application of the above-mentioned catalyst in the pyrolysis of waste plastics, wherein the pyrolysis conditions are a pyrolysis temperature of 450-600°C, a pressure of 0.1-1.0 MPa, and a catalyst accounting for 2-15 wt% of the mass of the waste plastics.

[0024] The beneficial effects of this invention are:

[0025] (1) Catalytic cracking is an acidic catalytic reaction. In order to generate more low-carbon olefins, the catalyst is required to have high olefin selectivity, low hydrogen transfer activity, and high matrix cracking activity. In this invention, the FCC waste catalyst is acid-treated to extract some alumina, and then reacted with sodium aluminate at a certain pH to improve the matrix pore structure and cracking activity. The active components ZSM-5 and β molecular sieves increase shape-selective catalytic reaction, thereby improving the low-carbon olefin selectivity and yield.

[0026] (2) The catalyst preparation process of this invention has no harmful emissions, and truly realizes the complete recycling and reuse of FCC waste catalyst. It is an efficient, green, environmentally friendly and economical method for recycling and reusing waste catalyst. Detailed Implementation

[0027] The technical solution of the present invention will be described in detail below. The following embodiments are implemented under the premise of the technical solution of the present invention and a detailed implementation process is given. However, the protection scope of the present invention is not limited to the following embodiments. Structures or experimental methods that do not specify specific conditions in the following embodiments are generally performed under conventional conditions.

[0028] This invention provides a method for preparing a catalyst for the pyrolysis of waste plastics, comprising the following steps:

[0029] Step 1: Roast the spent FCC catalyst and then mix it with an inorganic acid solution for acid treatment;

[0030] Step 2: Mix the acid-treated FCC waste catalyst obtained in Step 1 with sodium aluminate, adjust the pH value to 7-10, and carry out the reaction.

[0031] Step 3: Mix the substance obtained in Step 2 with the active component, slurry, dry and calcine to obtain a catalyst for the pyrolysis of waste plastics.

[0032] The present invention involves extracting a portion of inactive alumina from FCC waste catalyst through acid treatment, then reacting it with sodium aluminate to improve alumina activity, thereby improving matrix pore structure and cracking activity. The resulting catalyst is then mixed with active components and used for the catalytic cracking of waste plastics, exhibiting high selectivity and high yield of low-carbon olefins.

[0033] This invention does not specifically limit the use of waste plastics. The catalyst of this invention can be used to catalyze the pyrolysis of any waste plastics, such as one or a mixture of waste low-density polyethylene (relative molecular weight of 0.910 to 0.925), high-density polyethylene (relative molecular weight of 0.941 to 0.965), polypropylene, and polystyrene.

[0034] This invention does not specifically limit the use of FCC waste catalysts, as long as they are FCC catalysts, such as catalytic cracking catalysts discharged from industrial catalytic cracking units, or deactivated catalytic cracking catalysts.

[0035] In one embodiment, the FCC waste catalyst is ground before calcination. The grinding method is not particularly limited; for example, a ball mill can be used. After grinding, the particle size of the FCC waste catalyst is less than 10 μm. The ground FCC waste catalyst is then calcined at a temperature of 600–900°C for 1–10 hours, preferably 1–3 hours. Calcination activates the alumina in the FCC waste catalyst, facilitating the subsequent acid extraction of ionic Al.

[0036] The calcined FCC waste catalyst is mixed with an inorganic acid solution for acid treatment. In one embodiment, the inorganic acid in the solution is a strong or moderately strong acid, such as one or more of hydrochloric acid, phosphoric acid, and sulfuric acid, preferably phosphoric acid. The weight ratio of the inorganic acid to the FCC waste catalyst is 0.05:1 to 0.1:1, where the FCC waste catalyst is on a dry basis. In another embodiment, the acid treatment temperature is 50–90°C, and the treatment time is 1–3 hours. Acid treatment converts inactive alumina into an ionic state, which then reacts with sodium aluminate.

[0037] Step 2 involves mixing the acid-treated FCC waste catalyst obtained in Step 1 with sodium aluminate, adjusting the pH value to 7-10, and then reacting.

[0038] In one embodiment, sodium aluminate is calculated as Al2O3, and the weight ratio of sodium aluminate to FCC waste catalyst is 0.05:1 to 0.1:1, wherein the FCC waste catalyst is calculated on a dry basis.

[0039] In one embodiment, sodium aluminate is first formed into a solution and then mixed with the acid-treated FCC waste catalyst obtained in step 1. The present invention does not particularly limit the concentration of the sodium aluminate solution, as long as the sodium aluminate in the sodium aluminate solution and the FCC waste catalyst satisfy the above-mentioned weight relationship.

[0040] This invention does not specifically limit the method of pH adjustment; for example, ammonia can be used. In one embodiment, the reaction temperature of the acid-treated FCC waste catalyst with sodium aluminate is 50–90°C, and the reaction time is 1–3 hours. After acid extraction, the FCC waste catalyst reacts with sodium aluminate to form an active aluminum structure, which has better thermal stability and lower cost.

[0041] Step 3 involves mixing the substance obtained in step 2 with the active component, pulping, drying, and calcining to obtain a catalyst for the pyrolysis of waste plastics.

[0042] In one embodiment, the active component is one or a mixture of ZSM-5 and β-zeolite, and the weight ratio of the active component to the FCC waste catalyst is 0.2:1 to 2:1, preferably 0.5:1 to 1:1, wherein the FCC waste catalyst is on a dry basis. This invention does not particularly limit the choice of ZSM-5 or β-zeolite.

[0043] This invention does not specifically limit the drying method, for example, spray drying. This invention does not specifically limit the calcination temperature in step 3; conventional calcination conditions in the art are sufficient.

[0044] In one specific embodiment, the method for preparing the catalyst for waste plastic pyrolysis of the present invention includes the following steps:

[0045] (1) After grinding the FCC waste catalyst into powder using a ball mill, it is calcined at 600-900℃ for 1-10 hours.

[0046] (2) Mix the above-mentioned roasted waste catalyst with an inorganic acid solution, and after acid treatment at 50-90°C for 1-3 hours, add sodium aluminate solution, adjust the pH value to 7-10 with ammonia water, and continue the reaction at 50-90°C for 1-3 hours.

[0047] (3) The above-treated FCC waste catalyst is mixed with the active component, slurryed, spray-dried and calcined, and washed with water to obtain the waste plastic cracking catalyst that produces more low-carbon olefins.

[0048] The catalyst for waste plastic pyrolysis obtained by the above preparation method of the present invention is used in the waste plastic pyrolysis process under the following conditions: pyrolysis temperature 450-600℃, pressure 0.1-1.0MPa, and catalyst accounting for 2-15wt% of waste plastic mass.

[0049] Therefore, this invention involves acid extraction of FCC waste catalyst, followed by reaction with sodium aluminate to form an active aluminum structure, which is then combined with active components to obtain a catalyst for waste plastic pyrolysis. When used for waste plastic pyrolysis, it exhibits good pyrolysis performance, good selectivity for target products, and high yield of low-carbon olefins. At the same time, it achieves complete recycling and reuse of waste catalyst, thereby improving resource utilization.

[0050] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0051] Raw material or equipment sources: hydrochloric acid (36 mg%), phosphoric acid (85 mg%), sulfuric acid (75 mg%), FCC waste catalyst (specific surface area 113.7 m²). 2 / g, pore volume is 0.127cm³ 3 The following substances were used: sodium aluminate solution (Al2O3 100g / L), ammonia (28wt%), ZSM-5 molecular sieve (loss on ignition 2.3% (water content 2.3wt%), SiO2 / Al2O3 molar ratio 30-300), and β molecular sieve (loss on ignition 2.6% (water content 2.6wt%), SiO2 / Al2O3 molar ratio 30-200). All of these were industrial products and were sourced from the catalyst plant of Lanzhou Petrochemical Company.

[0052] Evaluation and analysis methods: The surface area and pore volume of the catalyst were determined by low-temperature nitrogen adsorption-desorption method. (For analytical methods, please refer to "Analytical Methods in Petrochemical Industry (RIPP Experimental Methods)", edited by Yang Cuiding et al., Science Press, 1990). The catalyst reaction performance was evaluated using a small fixed fluidized bed.

[0053] Example 1

[0054] 303g of pulverized FCC waste catalyst (dry basis) was calcined at 650℃ for 2.5h, then mixed with 50g hydrochloric acid and 1198g deionized water, and reacted at 60℃ for 1.5h. Then, 227ml sodium aluminate solution was added, the pH was adjusted to 8.2 with ammonia water, and the reaction continued for 2h. Then, 307g of ZSM-5 molecular sieve (silicon-aluminum ratio 50) was added, mixed and pulped, spray dried and shaped, calcined, washed, filtered and dried to obtain waste plastic pyrolysis catalyst C-1 that produces more light oil.

[0055] Using waste polypropylene as raw material, under reaction conditions of 455℃, 0.1MPa, and catalyst C-1:polypropylene ratio of 9.0wt%, the yield of ethylene + propylene + butene was 49.9%, and the yield of gasoline was 34.1%.

[0056] Example 2

[0057] 395g of pulverized FCC waste catalyst (dry basis) was calcined at 850℃ for 1.5h, then mixed with 41.8g of phosphoric acid and 1103g of deionized water, and reacted at 80℃ for 1h. Then, 198ml of sodium aluminate solution was added, and the pH was adjusted to 7.8 with ammonia water. The reaction was continued for 1h. Then, 206g of β molecular sieve (silicon-to-aluminum ratio 45) was added and mixed and pulped. The mixture was spray-dried and shaped. After calcination, washing, filtration and drying, the waste plastic pyrolysis catalyst C-2, which produces more light oil, was obtained.

[0058] Using waste plastics as raw materials (low-density polyethylene (relative molecular weight 0.910-0.925), high-density polyethylene (relative molecular weight 0.941-0.965), and polypropylene: 20wt%, 32wt%, and 48wt%), under reaction conditions of 490℃, 0.35MPa, and catalyst C-2:waste plastic = 5.5wt%, the yield of ethylene + propylene + butene was 48.1%, and the yield of gasoline was 35.7%.

[0059] Example 3

[0060] 353g of pulverized FCC waste catalyst (dry basis) was calcined at 600℃ for 9h, then mixed with 23.5g of sulfuric acid and 1400g of deionized water, reacted at 70℃ for 2h, then 317ml of sodium aluminate solution was added, the pH was adjusted to 9.5 with ammonia water, and the reaction continued for 1.5h. Then 93g of ZSM-5 (silicon-aluminum ratio 280) and 189.4g of β molecular sieve (silicon-aluminum ratio 30) were added and mixed and pulped, spray-dried and shaped, calcined, washed, filtered and dried to obtain waste plastic pyrolysis catalyst C-3 for producing more light oil.

[0061] Using waste plastics as raw materials (low-density polyethylene (relative molecular weight 0.910-0.925), high-density polyethylene (relative molecular weight 0.941-0.965), polypropylene, and polystyrene by mass percentage: 20wt%, 18wt%, 46wt%, and 16wt%), under reaction conditions of 555℃, 0.15MPa, and catalyst C-3: 9wt% waste plastic, the yield of ethylene + propylene + butene was 47.5%, and the yield of gasoline was 36.8%.

[0062] Example 4

[0063] 419g of pulverized FCC waste catalyst (dry basis) was calcined at 700℃ for 5h, then mixed with 34.5g of phosphoric acid and 1739g of deionized water, and reacted at 90℃ for 1.2h. Then, 251ml of sodium aluminate solution was added, and the pH was adjusted to 8.9 with ammonia water. The reaction continued for 1.8h. Then, 377.1g of ZSM-5 molecular sieve (silicon-aluminum ratio 120) was added, mixed and pulped, spray-dried and shaped, calcined, washed, filtered and dried to obtain C-4, a waste plastic pyrolysis catalyst for producing more light oil.

[0064] Using waste plastics as raw materials (high-density polyethylene (relative molecular weight 0.941-0.965), polypropylene: 50wt%, 50wt%), under reaction conditions of 475℃, 0.5MPa, and catalyst C-4: waste plastic 5wt%, the yield of ethylene + propylene + butene was 50.1%, and the yield of gasoline was 33.9%.

[0065] Example 5

[0066] 521g of pulverized FCC waste catalyst (dry basis) was calcined at 890℃ for 1h, then mixed with 61.3g of phosphoric acid and 1484g of deionized water, and reacted at 75℃ for 2.4h. Then, 416ml of sodium aluminate solution was added, the pH was adjusted to 7.5 with ammonia water, and the reaction continued for 2.8h. Then, 156.3g of β molecular sieve (silicon-aluminum ratio 180) was added, mixed and pulped, spray-dried and shaped, calcined, washed, filtered and dried to obtain waste plastic pyrolysis catalyst C-5 for producing more light oil.

[0067] Using waste plastics as raw materials (polystyrene and polypropylene: 30wt% and 70wt%, respectively), under reaction conditions of 595℃, 0.5MPa, and catalyst C-5: waste plastic 4.5wt%, the yield of ethylene + propylene + butene was 45.3%, and the yield of gasoline was 38.8%.

[0068] Comparative Example 1

[0069] After calcining 303g of powdered FCC waste catalyst (dry basis) at 650℃ for 2.5h, it was mixed with 307g of ZSM-5 molecular sieve (silicon-aluminum ratio 50) and pulped. The mixture was then spray-dried and shaped. After calcination, washing, filtration and drying, the waste plastic pyrolysis catalyst D-1, which produces more light oil, was obtained.

[0070] Using waste polypropylene (same as in Example 1) as raw material, under reaction conditions of 455°C, 0.1 MPa, and catalyst D-1:polypropylene ratio of 9.0 wt%, the yield of ethylene + propylene + butene was 39.3%, and the yield of gasoline was 31.5%.

[0071] Comparative Example 2

[0072] After calcining 353g of powdered FCC waste catalyst (dry basis) at 600℃ for 9h, it was mixed with 23.5g of sulfuric acid and 1400g of deionized water and reacted at 70℃ for 2h. Then, 93g of ZSM-5 (silicon-aluminum ratio 280) and 189.4g of β molecular sieve (silicon-aluminum ratio 30) were added and mixed into a pulp. The mixture was spray-dried and shaped, then calcined, washed, filtered and dried to obtain waste plastic pyrolysis catalyst D-2 for producing more light oil.

[0073] Using waste plastics (same as in Example 3) as raw materials (low-density polyethylene (relative molecular weight 0.910-0.925), high-density polyethylene (relative molecular weight 0.941-0.965), polypropylene, and polystyrene by mass percentage: 20%, 18%, 46%, and 16%), under reaction conditions of 555°C, 0.15 MPa, and catalyst D-2: waste plastic 9 wt%, the yield of ethylene + propylene + butene was 37.8%, and the yield of gasoline was 39.6%.

[0074] Comparative Example 3

[0075] After calcining 395g of powdered FCC waste catalyst (dry basis) at 850℃ for 1.5h, 198ml of sodium aluminate solution was added, the pH was adjusted to 7.8 with ammonia water, and the reaction was carried out for 1h. Then, 206g of β molecular sieve (silicon-to-aluminum ratio 45) was added and mixed and pulped. The mixture was spray-dried and shaped, and then calcined, washed, filtered and dried to obtain waste plastic pyrolysis catalyst D-3 for producing more light oil.

[0076] Using waste plastics (same as in Example 2) as raw materials (low-density polyethylene (relative molecular weight 0.910-0.925), high-density polyethylene (relative molecular weight 0.941-0.965), polypropylene: 20%, 32%, 48%), under reaction conditions of 490°C, 0.35 MPa, and catalyst D-3: waste plastic = 5.5 wt%, the yield of ethylene + propylene + butene was 39.8%, and the yield of gasoline was 33.2%.

[0077] Comparative Example 4

[0078] Using waste plastics as raw materials (high-density polyethylene (relative molecular weight 0.941-0.965), polypropylene: 50wt%, 50wt%), under reaction conditions of 475℃, 0.5MPa, and 5wt% FCC waste catalyst: waste plastic, the yield of ethylene + propylene + butene was 9.1%, and the yield of gasoline was 64.5%.

[0079] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a catalyst for the pyrolysis of waste plastics, characterized in that, Includes the following steps: Step 1: Roast the spent FCC catalyst and then mix it with an inorganic acid solution for acid treatment; Step 2: Mix the acid-treated FCC waste catalyst obtained in Step 1 with sodium aluminate, adjust the pH value to 7-10, and carry out the reaction. Step 3: Mix the substance obtained in Step 2 with the active component, slurry, dry and calcine to obtain a catalyst for the pyrolysis of waste plastics; The sodium aluminate is calculated as alumina, and the weight ratio of the sodium aluminate to the FCC waste catalyst is 0.05:1 to 0.1:1; the active component is one or a mixture of ZSM-5 molecular sieve and β molecular sieve.

2. The method for preparing the catalyst for waste plastic pyrolysis according to claim 1, characterized in that, It also includes the step of grinding the FCC waste catalyst, the particle size of the ground FCC waste catalyst is less than 10µm, and the ground FCC waste catalyst is calcined at a temperature of 600-900℃ for 1-10 hours.

3. The method for preparing the catalyst for waste plastic pyrolysis according to claim 1, characterized in that, The weight ratio of the inorganic acid in the inorganic acid solution to the FCC waste catalyst is 0.05:1 to 0.1:1, and the inorganic acid is one or more of hydrochloric acid, phosphoric acid, and sulfuric acid.

4. The method for preparing the catalyst for waste plastic pyrolysis according to claim 1, characterized in that, The acid treatment is performed at a temperature of 50–90°C for 1–3 hours.

5. The method for preparing the catalyst for waste plastic pyrolysis according to claim 1, characterized in that, The reaction temperature in step 2 is 50–90°C, and the reaction time is 1–3 hours.

6. The method for preparing the catalyst for waste plastic pyrolysis according to claim 1, characterized in that, The weight ratio of the active component to the FCC waste catalyst is 0.2:1 to 2:

1.

7. The method for preparing the catalyst for waste plastic pyrolysis according to claim 6, characterized in that, The weight ratio of the active component to the FCC waste catalyst is 0.5:1 to 1:

1.

8. The catalyst for pyrolysis of waste plastics obtained by the preparation method according to any one of claims 1-7.

9. The application of the catalyst according to claim 8 in the pyrolysis of waste plastics, characterized in that, The pyrolysis conditions are a pyrolysis temperature of 450–600℃, a pressure of 0.1–1.0 MPa, and a catalyst content of 2–15 wt% of the waste plastic.