Cracking catalysts, their preparation methods, and their application in the direct conversion of waste plastics to low-carbon olefins.

Abstract

This invention relates to the fields of catalysts and polymer material recycling, and discloses a cracking catalyst, its preparation method, and its application in the direct conversion of waste plastics to low-carbon olefins. The cracking catalyst comprises a composite support and modified oxides supported on the composite support. The composite support comprises a hydrogen-form Y-type molecular sieve and a KIT-6 all-silica mesoporous molecular sieve. Based on the total weight of the cracking catalyst, the content of the hydrogen-form Y-type molecular sieve is 8-32% by weight, the content of the KIT-6 all-silica mesoporous molecular sieve is 54-90% by weight, and the content of the modified oxide is 2-14% by weight. This preparation method not only solves the problem of waste plastic recycling but also increases the production of important chemical raw materials such as low-carbon olefins.

Description

Technical Field

[0001] This invention relates to the fields of catalysts and polymer recycling, specifically to a cracking catalyst, its preparation method, and its application in the direct conversion of waste plastics into low-carbon olefins. Background Technology

[0002] Plastic products are widely used in various fields due to their lightweight, high strength, corrosion resistance, good chemical stability, ease of processing, and aesthetic appeal. However, plastics are difficult to degrade naturally. While conventional landfill technology requires less investment and is simple to operate, it occupies large amounts of land and causes soil pollution. Incineration technology can achieve volume reduction requirements and recover some energy, but this process easily releases large amounts of hydrocarbons, nitrogen oxides, sulfides, and highly toxic substances, directly threatening human and environmental health. Therefore, the recycling and high-value utilization of waste plastics is a measure to save energy and protect the environment, and it has received widespread attention from countries around the world. Methods for recycling and utilizing waste plastics mainly include sorting and recycling, producing monomer raw materials, producing clean fuels, and using them for power generation.

[0003] In existing technologies, the main chemical recycling scheme for waste plastics is waste plastic pyrolysis technology. Waste plastic pyrolysis includes three basic methods: thermal pyrolysis (one-stage method), catalytic pyrolysis (one-stage method), and thermal pyrolysis-catalytic modification (two-stage method). The earliest developed waste plastic pyrolysis technology was thermal pyrolysis. This technology refers to a thermal conversion process in which a thermochemical decomposition reaction occurs under high-temperature, oxygen-free conditions, converting the large molecular weight organic matter in waste plastic products into small molecular weight liquids, fuel gas, and coke. The reaction temperature in this process is generally controlled between 350-900℃. Adding a catalyst during the thermal pyrolysis process results in catalytic thermal pyrolysis, which not only lowers the pyrolysis temperature but also improves product performance. The thermal pyrolysis-catalytic modification method, an improvement on catalytic pyrolysis, uses a catalyst to catalytically modify the pyrolysis gas after the waste plastic pyrolysis. This method produces higher quality products, is more flexible in operation, and has lower operating costs than thermal pyrolysis and catalytic pyrolysis, but the process is more complex.

[0004] Cracking technology for treating waste plastics offers great flexibility and good energy recovery, making it one of the most promising waste plastic treatment technologies. In existing technologies, one-step thermal cracking and one-step catalytic cracking primarily produce fuel oil, yielding only small amounts of low-carbon olefins (ethylene, propylene, butene). If a large quantity of low-carbon olefins is required, a two-stage process of thermal cracking followed by catalytic reforming is necessary.

[0005] Therefore, exploring a new chemical recycling process to produce pure and high-quality final products is an important research direction for plastic waste treatment. Summary of the Invention

[0006] The purpose of this invention is to address the current situation where the low content of low-carbon olefins in the products of catalytic cracking of waste plastics is relatively low, and to provide a cracking catalyst, its preparation method, and its application in the direct conversion of waste plastics to low-carbon olefins. This preparation method not only solves the problem of waste plastic recycling, but also increases the production of low-carbon olefins, an important chemical raw material.

[0007] To achieve the above objectives, a first aspect of the present invention provides a cracking catalyst, wherein the cracking catalyst comprises a composite support and a modified oxide supported on the composite support, the composite support comprising a hydrogen-type Y-type molecular sieve and a KIT-6 all-silica mesoporous molecular sieve, and based on the total weight of the cracking catalyst, the content of the hydrogen-type Y-type molecular sieve is 8-32% by weight, the content of the KIT-6 all-silica mesoporous molecular sieve is 54-90% by weight, and the content of the modified oxide is 2-14% by weight.

[0008] A second aspect of the present invention provides a method for preparing a cracking catalyst, wherein the preparation method includes:

[0009] Hydrogen-type Y-type molecular sieves, KIT-6 all-silica mesoporous molecular sieves, and aqueous solutions of modified oxide precursors were mixed and reacted; then, after dehydration, drying, and calcination, a cracking catalyst was obtained.

[0010] A third aspect of the present invention provides a pyrolysis catalyst prepared by the preparation method described above.

[0011] The fourth aspect of this invention provides the application of the aforementioned pyrolysis catalyst in the direct conversion of waste plastics to low-carbon olefins.

[0012] The technical solution of the present invention has the following advantages through the above technical solution:

[0013] (1) The cracking catalyst provided by the present invention has readily available raw materials, a simple preparation method, easy-to-control conditions, and good product repeatability.

[0014] (2) The pyrolysis catalyst provided by the present invention includes acidic zeolite molecular sieves and large-pore mesoporous materials, which have stable structure, good high temperature resistance, and facilitate the diffusion of raw material and product molecules during the pyrolysis reaction.

[0015] (3) The pyrolysis catalyst provided by this invention can convert waste plastics into low-carbon olefins in one step when used in the direct conversion of waste plastics into low-carbon olefins. This is a new method for the chemical recycling of waste plastics. It not only solves the problem of waste plastic recycling, but also increases the production of important chemical raw materials such as low-carbon olefins, thus having good economic benefits.

[0016] (4) The cracking catalyst provided by the present invention has mild process conditions, is easy to operate and has low requirements for reaction equipment when used for the direct conversion of waste plastics to low carbon olefins.

[0017] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0019] Figure 1 This is the small-angle X-ray diffraction (XRD) pattern of the pyrolysis catalyst A prepared in Example 1;

[0020] Figure 2 This is the wide-angle X-ray diffraction (XRD) spectrum of the cracking catalyst A prepared in Example 1. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] As previously stated, the first aspect of the present invention provides a cracking catalyst, wherein the cracking catalyst comprises a composite support and a modified oxide supported on the composite support, the composite support comprising a hydrogen-type Y-type molecular sieve and a KIT-6 all-silica mesoporous molecular sieve, and based on the total weight of the cracking catalyst, the content of the hydrogen-type Y-type molecular sieve is 8-32% by weight, the content of the KIT-6 all-silica mesoporous molecular sieve is 54-90% by weight, and the content of the modified oxide is 2-14% by weight.

[0023] The inventors of this invention discovered that the main components of the pyrolysis catalysts disclosed in the prior art are microporous zeolite molecular sieves (including beta, ZSM-11, ZSM-35, or ZRP). Although microporous molecular sieves have an ordered and stable structure, their pore sizes are relatively narrow, generally between 0.4-0.8 nm. Waste plastic products have large molecular weights and relatively long molecular chains. During the pyrolysis reaction of waste plastic products, the diffusion of larger reactant and product molecules between the narrow pores is difficult, which not only affects the contact between reactants and active centers but also easily leads to side reactions such as deep dehydrogenation. KIT-6 all-silica mesoporous molecular sieve has the structural advantages of large specific surface area and large pore volume, as well as high-temperature resistance (KIT-6 mesoporous molecular sieve can withstand calcination at 600℃ during preparation while maintaining a regular mesoporous structure). However, the silica surface, which is composed of silicon and oxygen as the basic framework, does not contain functional groups and has poor activity in the pyrolysis reaction. The inventors of this invention discovered during their research and development of catalysts for waste plastic pyrolysis that by comprehensively utilizing the structural advantages of all-silica mesoporous inorganic materials and the surface acidic centers of zeolite molecular sieves (it should be noted that the surface acidity of zeolite molecular sieves can be characterized by the NH3-TPD experiment, in which the surface of silica-alumina zeolite molecular sieves must contain L acidic centers, and the surface of hydrogen-form silica-alumina zeolite molecular sieves must contain both Brønsted acid and L acidic centers), and by mixing and modifying a certain amount of KIT-6 all-silica mesoporous molecular sieves with hydrogen-form Y zeolite molecular sieves as the main component of the catalyst for the pyrolysis reaction of waste plastics, not only can the activity of the pyrolysis catalyst be effectively improved, but the selectivity of low-carbon olefins can also be increased.

[0024] According to the present invention, the Y-type molecular sieve framework structure is fixed, and the most basic structural unit constituting the framework is silicon-oxygen and aluminum-oxygen tetrahedra. These tetrahedra form secondary structural units such as four-membered rings, six-membered rings, and eight-membered rings through Si-O or Al-O bonds. These secondary structural units are then assembled to form β cages. The eight β cages are arranged in a diamond crystal pattern, and adjacent β cages are connected by six-membered rings with Si-O-Si(Al) bonds to form octahedral zeolite cages. The octahedral zeolite cages are interconnected by twelve-membered rings along three crystal axes. The twelve-membered rings are the main windows of the Y-type molecular sieve, with a pore size of approximately 0.74 nm. Compared with the narrow-pore Y-type molecular sieves, the KIT-6 all-silica mesoporous molecular sieve has an average pore size between 4-10 nm and a specific surface area higher than 600 m². 2 / g. Mixing an appropriate amount of KIT-6 all-silica mesoporous molecular sieve with hydrogen-type Y molecular sieve facilitates the smooth diffusion of reactant and product molecules with larger molecular volumes, and can effectively avoid the occurrence of side reactions.

[0025] According to the present invention, preferably, based on the total weight of the pyrolysis catalyst, the content of the hydrogen-form Y-type molecular sieve is 12-28% by weight, the content of the KIT-6 all-silica mesoporous molecular sieve is 60-84% by weight, and the content of the modified oxide is 4-12% by weight. More preferably, based on the total weight of the pyrolysis catalyst, the content of the hydrogen-form Y-type molecular sieve is 16-24% by weight, the content of the KIT-6 all-silica mesoporous molecular sieve is 66-78% by weight, and the content of the modified oxide is 6-10% by weight. In the present invention, by using the aforementioned specific contents of each component, the prepared pyrolysis catalyst can exhibit better catalytic activity and higher low-carbon olefin selectivity when used in the direct conversion of waste plastics to produce low-carbon olefins.

[0026] According to the present invention, the modified oxide is selected from one or more of alkaline earth metal oxides, transition metal oxides, and rare earth metal oxides; preferably, the modified oxide is selected from one or more of calcium oxide, magnesium oxide, strontium oxide, barium oxide, zinc oxide, cerium oxide, lanthanum oxide, and zirconium dioxide. In this invention, the specific modified oxides selected from the present invention have the advantage of improving the electron distribution on the molecular sieve surface and selectively covering some excessively acidic centers, making the catalyst surface properties more suitable for the catalytic cracking reaction of waste plastics.

[0027] According to the present invention, the hydrogen-type Y-type molecular sieve is a HY molecular sieve and / or a HUSY molecular sieve. In this invention, the HY molecular sieve or the HUSY molecular sieve can be commercially available. Specifically, the HY molecular sieve is more preferably: HY molecular sieve of model NKF-8-20 (molar ratio of SiO2 to Al2O3 is 20, produced by Nankai University Catalyst Factory) or HY molecular sieve of model NKF-7-2-40FY (molar ratio of SiO2 to Al2O3 is 43, produced by Nankai University Catalyst Factory); the HUSY molecular sieve is more preferably: HUSY molecular sieve of model NKF-7-2 (molar ratio of SiO2 to Al2O3 is 12, produced by Nankai University Catalyst Factory).

[0028] According to the present invention, the inventors use a mixture of hydrogen-form Y-type molecular sieve and KIT-6 all-silica mesoporous molecular sieve with a silicon-to-aluminum molar ratio (Si / Al) of 5-60 as the main active component, and introduce metal oxides as a modifying component, thereby improving both catalyst activity and low-carbon olefin selectivity. Preferably, when the silicon-to-aluminum molar ratio of the hydrogen-form Y-zeolite molecular sieve is 12-43, both catalyst activity and low-carbon olefin selectivity are significantly improved.

[0029] According to the present invention, the KIT-6 all-silica mesoporous molecular sieve has an average pore size of 4-10 nm and a specific surface area of ​​600-800 m². 2 / g, pore volume 0.7-1.5cm³ 3 / g; Preferably, the KIT-6 all-silica mesoporous molecular sieve has an average pore size of 6.5-8.5 nm and a specific surface area of ​​650-780 m². 2 / g, pore volume 1.2-1.4cm³ 3 / g. In this invention, the use of KIT-6 all-silica mesoporous molecular sieve with the aforementioned specific parameters enables the prepared cracking catalyst to exhibit better catalytic activity and higher selectivity when used in the direct conversion of waste plastics to produce low-carbon olefins.

[0030] According to the present invention, the preparation method of the KIT-6 all-silica mesoporous molecular sieve includes:

[0031] Under hydrolysis gelation conditions, template agent, silicon source, n-butanol and hydrochloric acid are mixed to obtain a gel mixture; the gel mixture is then subjected to crystallization, solid-liquid separation, washing, drying and calcination treatments to obtain KIT-6 all-silica mesoporous molecular sieve.

[0032] According to the present invention, in the preparation method of KIT-6 all-silica mesoporous molecular sieve, the template agent can be various nonionic surfactants conventionally used in the art; in the present invention, preferably, the template agent is a polyoxyethylene-polyoxypropylene-polyoxyethylene amphoteric triblock copolymer; more preferably, the template agent is P123 (molecular formula EO). 20 PO 70 EO 20 ).

[0033] According to the present invention, in the preparation method of KIT-6 all-silica mesoporous molecular sieve, the silicon source can be a silicon-containing organic compound and / or a silicon-containing inorganic compound; in the present invention, preferably, the silicon source is selected from one or more of methyl orthosilicate, ethyl orthosilicate, isopropyl orthosilicate and silica sol; more preferably, the silicon source is ethyl orthosilicate.

[0034] According to the present invention, in the preparation method of KIT-6 all-silica mesoporous molecular sieve, the molar ratio of the template agent, the silicon source, n-butanol, hydrochloric acid and water is 1:(10-150):(20-200):(200-1200):(5000-20000); preferably 1:(30-100):(50-120):(500-900):(8000-13500).

[0035] In this invention, the inventors discovered that mixing a template agent, a silicon source, n-butanol, and hydrochloric acid yields a gel mixture. The template agent acts as a guiding agent for forming specific pore structures, the silicon source provides the necessary elements for the basic framework structure of the mesoporous molecular sieve, n-butanol assists in the formation of the mesoporous structure, and hydrochloric acid ensures the synthesis reaction proceeds under acidic conditions. The combined use of the template agent, silicon source, n-butanol, and hydrochloric acid is essential for the synthesis of the desired KIT-6 mesoporous molecular sieve.

[0036] According to the present invention, in the preparation method of KIT-6 all-silica mesoporous molecular sieve, the conditions for hydrolysis gelation include: a temperature of 20-50℃ and a time of 5-30h; preferably, a temperature of 30-40℃ and a time of 20-24h.

[0037] According to the present invention, in the preparation method of KIT-6 all-silica mesoporous molecular sieve, the crystallization conditions include: a temperature of 80-120℃ and a time of 10-40h; preferably, a temperature of 90-110℃ and a time of 20-30h.

[0038] According to the present invention, the solid-liquid two-phase separation process in the preparation method of KIT-6 all-silica mesoporous molecular sieve does not have special requirements and can be a separation method known in the art, including gravity filtration, pressure filtration, vacuum filtration, or centrifugal filtration. Preferably, the separation process specifically includes: using a vacuum flask to create a vacuum at the bottom of a funnel or using a centrifugal filter.

[0039] According to the present invention, in the preparation method of KIT-6 all-silica mesoporous molecular sieve, the washing conditions are not particularly limited. For example, the washing process may include: after filtration, a solid product is obtained, and the solid product is repeatedly washed with distilled water (the number of washing times may be 2-10), and then vacuum filtered.

[0040] According to the present invention, in the preparation method of KIT-6 all-silica mesoporous molecular sieve, the drying conditions include: a temperature of 70-140℃ and a time of 4-20h.

[0041] According to the present invention, in the preparation method of KIT-6 all-silica mesoporous molecular sieve, the calcination conditions include: a temperature of 400-600℃ and a time of 8-60h; preferably, a temperature of 450-550℃ and a time of 20-30h.

[0042] According to the present invention, the specific surface area of ​​the cracking catalyst is 570-750 m². 2 / g, pore volume 0.5-1.5cm³ 3 / g; preferably, the specific surface area of ​​the pyrolysis catalyst is 651-739m². 2 / g, pore volume 0.9-1.4cm³3 / g.

[0043] A second aspect of the present invention provides a method for preparing a cracking catalyst, wherein the preparation method includes:

[0044] Hydrogen-type Y-type molecular sieves, KIT-6 all-silica mesoporous molecular sieves, and aqueous solutions of modified oxide precursors were mixed and reacted; then, after dehydration, drying, and calcination, a cracking catalyst was obtained.

[0045] According to the present invention, the modified oxide precursor is selected from one or more of the nitrates, chlorides, acetates or sulfates of alkaline earth metals, transition metals and rare earth metals, preferably one or more of the nitrates of calcium, magnesium, strontium, barium, zinc, cerium, lanthanum and zirconium.

[0046] According to the present invention, the mass concentration of the modified component aqueous solution can be 1-20%, preferably 2-10%.

[0047] According to the present invention, the weight ratio of the aqueous solution of the hydrogen-type Y molecular sieve, the KIT-6 all-silica mesoporous molecular sieve and the modified oxide precursor is 1:(1.5-12.0):(3-30), preferably 1:(3.5-7.0):(6-20).

[0048] According to the present invention, the conditions for the contact reaction include: a temperature of 10-100°C, preferably 30-80°C; and a time of 0.5-50 h, preferably 2-20 h. Preferably, to achieve better mixing, rapid stirring or ultrasonic means can be used to improve mixing efficiency during the mixing of the aqueous solution of the hydrogen-type Y-type molecular sieve, KIT-6 all-silica mesoporous molecular sieve, and the modified oxide precursor.

[0049] According to the present invention, the water removal method is not particularly limited and can be any water removal method known in the art, such as using a rotary evaporator to evaporate water or using a heating and stirring method to remove water.

[0050] According to the present invention, the drying conditions include: a temperature of 60-150°C, preferably 80-130°C; and a time of 1-30 hours, preferably 3-20 hours.

[0051] According to the present invention, the calcination conditions include: a temperature of 400-700℃, preferably 500-600℃; and a time of 2-20h, preferably 3-10h.

[0052] A third aspect of the present invention provides a pyrolysis catalyst prepared by the preparation method described above.

[0053] The fourth aspect of this invention provides the application of the aforementioned pyrolysis catalyst in the direct conversion of waste plastics to low-carbon olefins.

[0054] According to the present invention, the method of applying the catalyst includes: contacting waste plastic powder with the pyrolysis catalyst under specific conditions.

[0055] In this invention, the contact conditions between the waste plastic powder and the pyrolysis catalyst include: the contact temperature can be 420-580℃, preferably 450-540℃; the contact pressure can be 0.01-1.0 MPa, preferably 0.05-0.5 MPa; the contact time can be 0.5-12 h, preferably 1-5 h; and the weight ratio of the pyrolysis catalyst to the waste plastic powder can be 1:0.5-50, preferably 1:2-30.

[0056] The present invention will be described in detail below through embodiments.

[0057] In the following examples and comparative examples:

[0058] Small-angle XRD tests of the samples were performed on a BRUKER AXS D8 ADVANCE high-power rotating target X-ray diffractometer, with a scanning range of 0.5-10°.

[0059] Wide-angle XRD tests of the samples were performed on a Philips X'Pert MPD X-ray powder diffractometer with a Cu Kα target and a scanning range of 2θ = 5-90°.

[0060] The pore structure parameters of the samples were analyzed using an ASAP2020-M+C adsorption analyzer manufactured by Micromeritics, USA. Before measurement, the samples were degassed under vacuum at 350℃ for 4 hours. The specific surface area of ​​the samples was calculated using the BET method, and the pore volume was calculated using the BJH model.

[0061] Elemental analysis of the samples was performed on an Eagle III energy-dispersive X-ray fluorescence spectrometer manufactured by EDAX Corporation in the United States.

[0062] The rotary evaporator was manufactured by IKA GmbH in Germany, and its model number is RV10 digital.

[0063] The drying oven was manufactured by Shanghai Yiheng Scientific Instruments Co., Ltd., model DHG-9030A.

[0064] The muffle furnace is manufactured by CARBOLITE, model CWF1100.

[0065] The HY molecular sieves (NKF-8-20, SiO2 to Al2O3 molar ratio of 20), HY molecular sieves (NKF-7-2-40FY, SiO2 to Al2O3 molar ratio of 43), and HUSY molecular sieves (NKF-7-2, SiO2 to Al2O3 molar ratio of 12) used in the examples and comparative examples were all purchased from the Catalyst Factory of Nankai University; the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (P123) used in the examples and comparative examples were purchased from Sigma-Aldrich Chemistry; and all other reagents used in the examples and comparative examples were purchased from Sinopharm Chemical Reagent Co., Ltd., and the reagent purity was analytical grade.

[0066] Example 1

[0067] This embodiment illustrates the cracking catalyst prepared using the preparation method of the present invention and its application.

[0068] (1) Preparation of KIT-6 all-silica mesoporous molecular sieve

[0069] At 35°C, 11.6 g of triblock copolymer surfactant P123 was dissolved in 411 g of 3.9 M hydrochloric acid solution and stirred for 4 h until P123 was completely dissolved, forming a transparent solution. Then, 11.8 g of n-butanol was added to this solution and stirring continued for 1 h. Next, 25 g of tetraethyl orthosilicate was slowly added dropwise to the solution, and the mixture was stirred at 35°C for 24 h to obtain a gel mixture. The gel mixture was transferred to a hydrothermal reactor and crystallized at 100°C for 24 h. The crystallized product was repeatedly washed with deionized water and filtered to obtain a KIT-6 mesoporous material filter cake. The KIT-6 mesoporous material filter cake was dried at 100°C for 12 h and calcined at 500°C for 24 h to remove the template agent, yielding KIT-6 mesoporous molecular sieve A.

[0070] The specific surface area of ​​KIT-6 all-silica mesoporous molecular sieve A is 724 m². 2 / g, pore volume 1.3cm³ 3 / g, with an average pore size of 7.8nm.

[0071] (2) Preparation of cracking catalyst

[0072] 14.1 g of calcium nitrate and 20.5 g of magnesium nitrate hexahydrate were dissolved in 400 g of distilled water to prepare an aqueous solution. 20 g of NKF-8-20 HY molecular sieve (molar ratio of SiO2 to Al2O3 of 20) and 72 g of KIT-6 all-silica mesoporous molecular sieve A were added to the above aqueous solution. After stirring at 60 °C for 5 h, the water was removed using a rotary evaporator. The solid product was dried at 110 °C for 8 h and then calcined at 550 °C for 6 h to obtain cracking catalyst A.

[0073] Catalyst A has a specific surface area of ​​651 m². 2 / g, pore volume 0.9cm³ 3 / g.

[0074] Based on the total weight of catalyst A, the content of HY molecular sieve is 20% by weight, the content of KIT-6 all-silica mesoporous molecular sieve is 72% by weight, the content of calcium oxide is 4.8% by weight, and the content of magnesium oxide is 3.2% by weight.

[0075] Figure 1 This is the small-angle X-ray diffraction (XRD) pattern of the pyrolysis catalyst A prepared in Example 1; from Figure 1 It can be observed that the sample exhibits a strong diffraction signal and a clearly distinguishable shoulder peak in the range of 2θ = 0.5°–1.5°, and two weaker diffraction signals between 2θ = 1.5°–2.0°. These diffraction signals correspond to a typical three-dimensional cubic mesoporous structure. This indicates that the KIT-6 all-silica mesoporous molecular sieve, after being prepared into a catalyst, still retains a relatively regular mesoporous channel structure, and the catalyst preparation process did not damage the basic structure of the mesoporous molecular sieve.

[0076] Figure 2 This is the wide-angle X-ray diffraction (XRD) pattern of the pyrolysis catalyst A prepared in Example 1; from Figure 2 It can be seen from the spectrum that the X-ray diffraction angles of this sample are mainly: 2θ = 6.1°, 10.0°, 11.9°, 15.6°, 18.7°, 20.4°, 23.7°, 27.0°, 30.7°, 31.8°, and 34.0°. These eleven diffraction signals are consistent with the diffraction patterns of Y-type molecular sieves, indicating that the HY molecular sieve in catalyst A still maintains the typical Y-type molecular sieve crystal phase structure after calcination at 550℃, and the basic structure of the zeolite molecular sieve was not destroyed during the catalyst preparation process. In addition, no diffraction signals corresponding to the modified oxides appeared in the wide-angle XRD pattern, indicating that the modified oxides are uniformly dispersed on the catalyst.

[0077] (3) Evaluation of the reaction performance of direct conversion of waste plastics to low-carbon olefins

[0078] The performance of the catalyst in the catalytic cracking of waste plastics was evaluated using a fixed-bed reactor. The catalyst loading was 10.0 g, the waste polyethylene plastic loading was 50.0 g, the reaction temperature was 500℃, the reaction pressure was 0.1 MPa, and the reaction time was 2 hours. After product cooling and gas-liquid separation, the gas composition was analyzed using an Agilent 6890 gas chromatograph equipped with an Al2O3-S capillary column and a flame ionization detector (FID), with programmed temperature ramping and quantitative analysis using correction factors. The liquid composition was analyzed using an Agilent 6890 gas chromatograph equipped with a PONA column. The reaction results are shown in Table 1.

[0079] Example 2

[0080] This embodiment illustrates the cracking catalyst prepared using the preparation method of the present invention and its application.

[0081] (1) Preparation of KIT-6 all-silica mesoporous molecular sieve

[0082] At 25°C, 11.6 g of triblock copolymer surfactant P123 was dissolved in 320 g of 3.1 M hydrochloric acid solution and stirred for 4 h until P123 was completely dissolved, forming a transparent solution. Then, 7.4 g of n-butanol was added to this solution and stirring continued for 1 h. Next, 12.5 g of tetraethyl orthosilicate was slowly added dropwise to the solution, and the mixture was stirred at 25°C for 30 h to obtain a gel mixture. The gel mixture was transferred to a hydrothermal reactor and crystallized at 90°C for 32 h. The crystallized product was repeatedly washed with deionized water and filtered to obtain a KIT-6 mesoporous material filter cake. The KIT-6 mesoporous material filter cake was dried at 90°C for 20 h and calcined at 450°C for 30 h to remove the template agent, yielding KIT-6 mesoporous molecular sieve B.

[0083] The specific surface area of ​​KIT-6 all-silica mesoporous molecular sieve B is 739 m². 2 / g, pore volume 1.4cm³ 3 / g, with an average pore size of 8.0nm.

[0084] (2) Preparation of cracking catalyst

[0085] 11.4 g of calcium nitrate and 7.7 g of zinc nitrate hexahydrate were dissolved in 600 g of distilled water to prepare an aqueous solution. 16 g of HY molecular sieve NKF-7-2-40FY (molar ratio of SiO2 to Al2O3 of 4:3) and 78 g of KIT-6 all-silica mesoporous molecular sieve B were added to the above aqueous solution. After stirring at 80 °C for 2 h, the water was removed using a rotary evaporator. The solid product was dried at 130 °C for 3 h and then calcined at 600 °C for 3 h to obtain the cracking catalyst B.

[0086] Catalyst B has a specific surface area of ​​687 m². 2 / g, pore volume 1.0cm³ 3 / g.

[0087] Based on the total weight of catalyst B, the content of HY molecular sieve is 16% by weight, the content of KIT-6 all-silica mesoporous molecular sieve is 78% by weight, the content of calcium oxide is 3.9% by weight, and the content of zinc oxide is 2.1% by weight.

[0088] The reaction performance of catalyst B was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1. The evaluation results are listed in Table 1.

[0089] Example 3

[0090] This embodiment illustrates the cracking catalyst prepared using the preparation method of the present invention and its application.

[0091] (1) Preparation of KIT-6 all-silica mesoporous molecular sieve

[0092] At 50°C, 11.6 g of the triblock copolymer surfactant P123 was dissolved in 500 g of 3.6 M hydrochloric acid solution and stirred for 2 h until P123 was completely dissolved, forming a transparent solution. Then, 17.7 g of n-butanol was added to this solution and stirring continued for 1 h. Next, 41.6 g of tetraethyl orthosilicate was slowly added dropwise to the solution, and the mixture was stirred at 50°C for 7 h to obtain a gel mixture. The gel mixture was transferred to a hydrothermal reactor and crystallized at 120°C for 10 h. The crystallized product was repeatedly washed with deionized water and filtered to obtain a KIT-6 mesoporous material filter cake. The KIT-6 mesoporous material filter cake was dried at 130°C for 6 h and calcined at 600°C for 8 h to remove the template agent, yielding KIT-6 mesoporous molecular sieve C.

[0093] The specific surface area of ​​KIT-6 all-silica mesoporous molecular sieve C is 703 m². 2 / g, pore volume 1.2cm³ 3 / g, with an average pore size of 7.5nm.

[0094] (2) Preparation of cracking catalyst

[0095] An aqueous solution was prepared by dissolving 8.6 g of anhydrous strontium nitrate, 6.6 g of lanthanum nitrate, and 11.5 g of zirconium nitrate pentahydrate in 300 g of distilled water. 24 g of HUSY molecular sieve (NKF-7-2, molar ratio of SiO2 to Al2O3 1:2) and 66 g of KIT-6 all-silica mesoporous molecular sieve C were added to the aqueous solution. After stirring at 30 °C for 20 h, the water was removed using a rotary evaporator. The solid product was dried at 80 °C for 20 h and then calcined at 500 °C for 10 h to obtain the cracking catalyst C.

[0096] Catalyst C has a specific surface area of ​​644 m². 2 / g, pore volume 0.7cm³ 3 / g.

[0097] Based on the total weight of catalyst C, the content of HUSY molecular sieve is 24 wt%, the content of KIT-6 all-silica mesoporous molecular sieve is 66 wt%, the content of strontium oxide is 4.2 wt%, the content of lanthanum oxide is 2.5 wt%, and the content of zirconium dioxide is 3.3 wt%.

[0098] The reaction performance of catalyst C was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1. The evaluation results are listed in Table 1.

[0099] Example 4

[0100] This embodiment illustrates the cracking catalyst prepared using the preparation method of the present invention and its application.

[0101] The pyrolysis catalyst was prepared according to the same preparation method as in Example 1, wherein KIT-6 all-silica mesoporous molecular sieve A was prepared according to step (1) in Example 1.

[0102] The cracking catalyst D was prepared according to step (2) in Example 1, except that the preparation conditions were changed. The specific process is as follows:

[0103] 6.0 g of cerium nitrate and 10.2 g of magnesium nitrate hexahydrate were dissolved in 400 g of distilled water to prepare an aqueous solution. 12 g of NKF-8-20 HY molecular sieve (molar ratio of SiO2 to Al2O3 of 20) and 84 g of KIT-6 all-silica mesoporous molecular sieve A were added to the above aqueous solution. After stirring at 60 °C for 5 h, the water was removed using a rotary evaporator. The solid product was dried at 110 °C for 8 h and then calcined at 550 °C for 6 h to obtain the cracking catalyst D.

[0104] The specific surface area of ​​catalyst D is 693 m². 2 / g, pore volume 1.0cm³ 3 / g.

[0105] Based on the total weight of catalyst D, the content of HY molecular sieve is 12% by weight, the content of KIT-6 all-silica mesoporous molecular sieve is 84% ​​by weight, the content of cerium oxide is 2.4% by weight, and the content of magnesium oxide is 1.6% by weight.

[0106] The reaction performance of catalyst D was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1. The evaluation results are listed in Table 1.

[0107] Example 5

[0108] This embodiment illustrates the cracking catalyst prepared using the preparation method of the present invention and its application.

[0109] The pyrolysis catalyst was prepared according to the same preparation method as in Example 3, wherein KIT-6 all-silica mesoporous molecular sieve C was prepared according to step (1) in Example 3.

[0110] The cracking catalyst E was prepared according to step (2) in Example 3, except that the preparation conditions were changed. The specific process is as follows:

[0111] 13.3 g of barium nitrate and 15.4 g of zinc nitrate hexahydrate were dissolved in 300 g of distilled water to prepare an aqueous solution. 28 g of HUSY molecular sieve (NKF-7-2, molar ratio of SiO2 to Al2O3 1:2) and 60 g of KIT-6 all-silica mesoporous molecular sieve C were added to the aqueous solution. After stirring at 30 °C for 20 h, the water was removed using a rotary evaporator. The solid product was dried at 80 °C for 20 h and then calcined at 500 °C for 10 h to obtain the cracking catalyst E.

[0112] Catalyst E has a specific surface area of ​​612 m². 2 / g, pore volume 0.6cm³ 3 / g.

[0113] Based on the total weight of catalyst E, the content of HUSY molecular sieve is 28% by weight, the content of KIT-6 all-silica mesoporous molecular sieve is 60% by weight, the content of barium oxide is 7.8% by weight, and the content of zinc oxide is 4.2% by weight.

[0114] The reaction performance of catalyst E was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1, and the evaluation results are listed in Table 1.

[0115] Example 6

[0116] This embodiment illustrates the cracking catalyst prepared using the preparation method of the present invention and its application.

[0117] The pyrolysis catalyst was prepared according to the same preparation method as in Example 1, wherein KIT-6 all-silica mesoporous molecular sieve A was prepared according to step (1) in Example 1.

[0118] The cracking catalyst F was prepared according to step (2) in Example 1, except that the preparation conditions were changed. The specific process is as follows:

[0119] 3.0 g of strontium nitrate and 5.1 g of magnesium nitrate hexahydrate were dissolved in 400 g of distilled water to prepare an aqueous solution. 8 g of NKF-8-20 HY molecular sieve (SiO2 to Al2O3 molar ratio of 20) and 90 g of KIT-6 all-silica mesoporous molecular sieve A were added to the above aqueous solution. After stirring at 60 °C for 5 h, the water was removed using a rotary evaporator. The solid product was dried at 110 °C for 8 h and then calcined at 550 °C for 6 h to obtain the cracking catalyst F.

[0120] The specific surface area of ​​catalyst F is 711 m². 2 / g, pore volume 1.1cm³ 3 / g.

[0121] Based on the total weight of catalyst F, the content of HY molecular sieve is 8 wt%, the content of KIT-6 all-silica mesoporous molecular sieve is 90 wt%, the content of strontium oxide is 1.2 wt%, and the content of magnesium oxide is 0.8 wt%.

[0122] The reaction performance of catalyst F was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1. The evaluation results are listed in Table 1.

[0123] Example 7

[0124] This embodiment illustrates the cracking catalyst prepared using the preparation method of the present invention and its application.

[0125] The pyrolysis catalyst was prepared according to the same preparation method as in Example 3, wherein KIT-6 all-silica mesoporous molecular sieve C was prepared according to step (1) in Example 3.

[0126] The cracking catalyst G was prepared according to step (2) in Example 3, except that the preparation conditions were changed. The specific process is as follows:

[0127] 14.3 g of barium nitrate and 20.5 g of zinc nitrate hexahydrate were dissolved in 600 g of distilled water to prepare an aqueous solution. 32 g of HUSY molecular sieve (NKF-7-2, with a SiO2 to Al2O3 molar ratio of 1:2) and 54 g of KIT-6 all-silica mesoporous molecular sieve C were added to the above aqueous solution. After stirring at 30 °C for 20 h, the water was removed using a rotary evaporator. The solid product was dried at 80 °C for 20 h and then calcined at 500 °C for 10 h to obtain the cracking catalyst G.

[0128] The specific surface area of ​​catalyst G is 571 m². 2 / g, pore volume 0.5cm³ 3 / g.

[0129] Based on the total weight of catalyst G, the content of HUSY molecular sieve is 32% by weight, the content of KIT-6 all-silica mesoporous molecular sieve is 54% by weight, the content of barium oxide is 8.4% by weight, and the content of zinc oxide is 5.6% by weight.

[0130] The reaction performance of catalyst G was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1, and the evaluation results are listed in Table 1.

[0131] Comparative Example 1

[0132] The pyrolysis catalyst was prepared according to the same preparation method as in Example 1, wherein KIT-6 all-silica mesoporous molecular sieve A was prepared according to step (1) in Example 1.

[0133] The cracking catalyst D1 was prepared according to step (2) in Example 1, except that the preparation conditions were changed. The specific process is as follows:

[0134] 1.8 g of calcium nitrate and 2.5 g of magnesium nitrate hexahydrate were dissolved in 400 g of distilled water to prepare an aqueous solution. 4 g of NKF-8-20 HY molecular sieve (SiO2 to Al2O3 molar ratio of 20) and 95 g of KIT-6 all-silica mesoporous molecular sieve A were added to the above aqueous solution. After stirring at 60 °C for 5 h, the water was removed using a rotary evaporator. The solid product was dried at 110 °C for 8 h and then calcined at 550 °C for 6 h to obtain the cracking catalyst D1.

[0135] The specific surface area of ​​catalyst D1 is 719 m². 2 / g, pore volume 1.2cm³ 3 / g.

[0136] Based on the total weight of catalyst D1, the content of HY molecular sieve is 4% by weight, the content of KIT-6 all-silica mesoporous molecular sieve is 95% by weight, the content of calcium oxide is 0.6% by weight, and the content of magnesium oxide is 0.4% by weight.

[0137] The reaction performance of catalyst D1 was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1, and the evaluation results are listed in Table 1.

[0138] Comparative Example 2

[0139] The pyrolysis catalyst was prepared according to the same preparation method as in Example 3, wherein KIT-6 all-silica mesoporous molecular sieve C was prepared according to step (1) in Example 3.

[0140] (2) Preparation of cracking catalyst

[0141] 27.3 g of barium nitrate and 23.9 g of lanthanum nitrate hexahydrate were dissolved in 800 g of distilled water to prepare an aqueous solution. 45 g of HUSY molecular sieve (NKF-7-2, molar ratio of SiO2 to Al2O3 1:2) and 30 g of KIT-6 all-silica mesoporous molecular sieve C were added to the aqueous solution. After stirring at 30 °C for 20 h, the water was removed using a rotary evaporator. The solid product was dried at 80 °C for 20 h and then calcined at 500 °C for 10 h to obtain the cracking catalyst D2.

[0142] The specific surface area of ​​catalyst D2 is 496 m². 2 / g, pore volume 0.4cm³ 3 / g.

[0143] Based on the total weight of catalyst D2, the content of HUSY molecular sieve is 45 wt%, the content of KIT-6 all-silica mesoporous molecular sieve is 30 wt%, the content of barium oxide is 16.0 wt%, and the content of lanthanum oxide is 9.0 wt%.

[0144] The reaction performance of catalyst D2 was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1. The evaluation results are listed in Table 1.

[0145] Comparative Example 3

[0146] The pyrolysis catalyst was prepared according to the same preparation method as in Example 2, wherein KIT-6 all-silica mesoporous molecular sieve B was prepared according to step (1) in Example 2.

[0147] The cracking catalyst D3 was prepared according to step (2) in Example 2, except that the preparation conditions were changed and hydrogen-type Y-type molecular sieves were not used. The specific process is as follows:

[0148] 11.4 g of calcium nitrate and 7.7 g of zinc nitrate hexahydrate were dissolved in 600 g of distilled water to prepare an aqueous solution. 94 g of KIT-6 all-silica mesoporous molecular sieve B was added to the above aqueous solution, and the mixture was stirred at 80 °C for 2 h. The water was removed using a rotary evaporator, and the solid product was dried at 130 °C for 3 h, and then calcined at 600 °C for 3 h to obtain the cracking catalyst D3.

[0149] Based on the total weight of catalyst D3, the KIT-6 all-silica mesoporous molecular sieve contains 94 wt% calcium oxide, 3.9 wt% calcium oxide, and 2.1 wt% zinc oxide.

[0150] The reaction performance of catalyst D3 was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1. The evaluation results are listed in Table 1.

[0151] Comparative Example 4

[0152] The pyrolysis catalyst was prepared using the same method as in Example 3, except that the preparation conditions were changed and KIT-6 all-silica mesoporous molecular sieve was not used. The specific process is as follows:

[0153] 26.9 g of magnesium nitrate hexahydrate, 6.6 g of lanthanum nitrate, and 11.5 g of zirconium nitrate pentahydrate were dissolved in 300 g of distilled water to prepare an aqueous solution. 90 g of HUSY molecular sieve (NKF-7-2, with a SiO2 to Al2O3 molar ratio of 12) was added to the aqueous solution. After stirring at 30 °C for 20 h, the water was removed using a rotary evaporator. The solid product was dried at 80 °C for 20 h and then calcined at 500 °C for 10 h to obtain the cracking catalyst D4.

[0154] Based on the total weight of catalyst D4, the content of HUSY molecular sieve is 90 wt%, the content of magnesium oxide is 4.2 wt%, the content of lanthanum oxide is 2.5 wt%, and the content of zirconium dioxide is 3.3 wt%.

[0155] The reaction performance of catalyst D4 was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1. The evaluation results are listed in Table 1.

[0156] Comparative Example 5

[0157] The pyrolysis catalyst was prepared according to the same preparation method as in Example 1, wherein KIT-6 all-silica mesoporous molecular sieve A was prepared according to step (1) in Example 1.

[0158] The cracking catalyst D5 was prepared according to step (2) in Example 1, except that the preparation conditions were changed and no modified oxide was added. The specific process is as follows:

[0159] 22g of NKF-8-20 HY molecular sieve (with a molar ratio of SiO2 to Al2O3 of 20) and 78g of KIT-6 all-silica mesoporous molecular sieve A were added to 400g of distilled water. After stirring at 60℃ for 5h, the water was removed using a rotary evaporator. The solid product was dried at 110℃ for 8h and then calcined at 550℃ for 6h to obtain the cracking catalyst D5.

[0160] Based on the total weight of catalyst D5, the content of HY molecular sieve is 22% by weight, and the content of KIT-6 all-silica mesoporous molecular sieve is 78% by weight.

[0161] The reaction performance of catalyst D5 was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1. The evaluation results are listed in Table 1.

[0162] Comparative Example 6

[0163] The pyrolysis catalyst was prepared according to the same preparation method as in Example 1, wherein KIT-6 all-silica mesoporous molecular sieve A was prepared according to step (1) in Example 1.

[0164] The cracking catalyst D6 was prepared according to step (2) in Example 1, except that the preparation conditions were changed and the modified oxide was changed to sodium oxide. The specific process is as follows:

[0165] 21.9 g of sodium nitrate was dissolved in 400 g of distilled water to prepare an aqueous solution. 20 g of NKF-8-20 HY molecular sieve (molar ratio of SiO2 to Al2O3 of 20) and 72 g of KIT-6 all-silica mesoporous molecular sieve A were added to the above aqueous solution. After stirring at 60 °C for 5 h, the water was removed using a rotary evaporator. The solid product was dried at 110 °C for 8 h and then calcined at 550 °C for 6 h to obtain the cracking catalyst D6.

[0166] Based on the total weight of catalyst D6, the content of HY molecular sieve is 20% by weight, the content of KIT-6 all-silica mesoporous molecular sieve is 72% by weight, and the content of sodium oxide is 8.0% by weight.

[0167] The reaction performance of catalyst D6 was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1. The evaluation results are listed in Table 1.

[0168] Comparative Example 7

[0169] The pyrolysis catalyst was prepared according to the same preparation method as in Example 1, wherein KIT-6 all-silica mesoporous molecular sieve A was prepared according to step (1) in Example 1.

[0170] The cracking catalyst D7 was prepared according to step (2) in Example 1, except that the preparation conditions were changed and the modified oxide was changed to nickel oxide. The specific process is as follows:

[0171] 31.1 g of nickel nitrate hexahydrate was dissolved in 400 g of distilled water to prepare an aqueous solution. 20 g of NKF-8-20 HY molecular sieve (with a molar ratio of SiO2 to Al2O3 of 20) and 72 g of KIT-6 all-silica mesoporous molecular sieve A were added to the above aqueous solution. After stirring at 60 °C for 5 h, the water was removed using a rotary evaporator. The solid product was dried at 110 °C for 8 h and then calcined at 550 °C for 6 h to obtain the cracking catalyst D7.

[0172] Based on the total weight of catalyst D7, the content of HY molecular sieve is 20% by weight, the content of KIT-6 all-silica mesoporous molecular sieve is 72% by weight, and the content of nickel oxide is 8.0% by weight.

[0173] The reaction performance of catalyst D7 was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low-carbon olefins in step (3) of Example 1. The evaluation results are listed in Table 1.

[0174] Table 1

[0175] Example or comparative example catalyst Waste plastic conversion rate (%) Total yield of low-carbon olefins (%) Example 1 Catalyst A 100 42.2 Example 2 Catalyst B 100 41.9 Example 3 Catalyst C 100 41.7 Example 4 Catalyst D 100 40.2 Example 5 Catalyst E 100 39.8 Example 6 Catalyst F 100 38.5 Example 7 Catalyst G 100 38.2 Comparative Example 1 Catalyst D1 84 22.0 Comparative Example 2 Catalyst D2 100 24.7 Comparative Example 3 Catalyst D3 52 6.1 Comparative Example 4 Catalyst D4 100 25.7 Comparative Example 5 Catalyst D5 100 27.0 Comparative Example 6 Catalyst D6 100 27.9 Comparative Example 7 Catalyst D7 100 24.5

[0176] The results above demonstrate that the pyrolysis catalyst provided by this invention can directly catalytically convert waste plastics into low-carbon olefins. The waste plastic conversion rate is 100%, and the low-carbon olefin yield is high.

[0177] In Comparative Example 1, the content of KIT-6 all-silica mesoporous molecular sieve was too high, the content of hydrogen-type Y-type molecular sieve was too low, and the content of modified components was not within the scope of protection claimed in this invention. Due to the small number of acidic centers on the catalyst and insufficient activation sites during the reaction, the feed conversion rate and the yield of low-carbon olefins were low.

[0178] In Comparative Example 2, the content of KIT-6 all-silica mesoporous molecular sieve was too low, the content of hydrogen-type Y-type molecular sieve was too high, and the content of modified components was not within the scope of protection claimed in this invention. Due to the limited number of macropores in the catalyst, the diffusion of reactant and product molecules was hindered during the reaction, resulting in a low yield of low-carbon olefins.

[0179] In Comparative Example 3, the catalyst did not contain hydrogen-type Y-type molecular sieves, but only KIT-6 all-silica mesoporous molecular sieves. Due to the almost complete absence of acidic centers on the catalyst and the severe lack of activation sites during the reaction, the feed conversion rate was very low and the yield of low-carbon olefins was also low.

[0180] In Comparative Example 4, the catalyst did not contain KIT-6 all-silica mesoporous molecular sieve, but only hydrogen-type Y-type molecular sieve. Because the catalyst contained almost no large-pore channels, the diffusion of reactant and product molecules was severely hindered during the reaction, resulting in a low yield of low-carbon olefins.

[0181] In Comparative Example 5, the catalyst did not contain modified oxides, resulting in a lower yield of low-carbon olefins.

[0182] In Comparative Examples 6 and 7, the modified oxides specifically defined in this invention were not used; instead, sodium oxide or nickel oxide were used. Due to the poor modification effect of other oxides, the yield of low-carbon olefins was low.

[0183] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. The application of a pyrolysis catalyst in the direct conversion of waste plastics to low-carbon olefins, the application comprising: The reaction involves contacting plastic powder with a pyrolysis catalyst, characterized in that the plastic powder is waste polyethylene plastic, and the pyrolysis catalyst comprises a composite support and modified oxides supported on the composite support; wherein the modified oxides are selected from one or more of alkaline earth metal oxides, transition metal oxides, and rare earth metal oxides; the composite support comprises hydrogen-type Y-type molecular sieves and KIT-6 all-silica mesoporous molecular sieves, and based on the total weight of the pyrolysis catalyst, the content of the hydrogen-type Y-type molecular sieves is 8-32% by weight, the content of the KIT-6 all-silica mesoporous molecular sieves is 54-90% by weight, and the content of the modified oxides is 2-14% by weight; the specific surface area of ​​the pyrolysis catalyst is 570-750 m² / g. 2 / g, pore volume 0.5-1.5cm³ 3 / g; The preparation methods of the cracking catalyst include: Hydrogen-type Y-type molecular sieves, KIT-6 all-silica mesoporous molecular sieves, and aqueous solutions of modified oxide precursors were mixed and reacted; then, after dehydration, drying, and calcination, a cracking catalyst was obtained.

2. The application according to claim 1, wherein, Based on the total weight of the cracking catalyst, the content of the hydrogen-type Y-type molecular sieve is 12-28% by weight, the content of the KIT-6 all-silica mesoporous molecular sieve is 60-84% by weight, and the content of the modified oxide is 4-12% by weight.

3. The application according to claim 2, wherein, Based on the total weight of the cracking catalyst, the content of the hydrogen-type Y-type molecular sieve is 16-24% by weight, the content of the KIT-6 all-silica mesoporous molecular sieve is 66-78% by weight, and the content of the modified oxide is 6-10% by weight.

4. The application according to claim 1, wherein, The modified oxide is selected from one or more of calcium oxide, magnesium oxide, strontium oxide, barium oxide, zinc oxide, cerium oxide, lanthanum oxide, and zirconium dioxide.

5. The application according to claim 1 or 3, wherein, The hydrogen-type Y-type molecular sieve includes HY molecular sieve and / or HUSY molecular sieve; And / or, the SiO2 / Al2O3 molar ratio of the hydrogen-type Y-type molecular sieve is 5-60.

6. The application according to claim 5, wherein, The SiO2 / Al2O3 molar ratio of the hydrogen-type Y-type molecular sieve is 12-43.

7. The application according to claim 1 or 3, wherein, The KIT-6 all-silica mesoporous molecular sieve has an average pore size of 4-10 nm and a specific surface area of ​​600-800 m². 2 / g, pore volume 0.7-1.5cm³ 3 / g.

8. The application according to claim 7, wherein, The KIT-6 all-silica mesoporous molecular sieve has an average pore size of 6.5-8.5 nm and a specific surface area of ​​650-780 m². 2 / g, pore volume 1.2-1.4cm³ 3 / g.

9. The application according to any one of claims 1, 3, and 8, wherein, The preparation method of the KIT-6 all-silica mesoporous molecular sieve includes: Under hydrolysis gelation conditions, template agent, silicon source, n-butanol and hydrochloric acid are mixed to obtain a gel mixture; the gel mixture is then subjected to crystallization, solid-liquid separation, washing, drying and calcination treatments to obtain KIT-6 all-silica mesoporous molecular sieve.

10. The application according to claim 9, wherein, The template agent is a nonionic surfactant; And / or, the silicon source is selected from organic silicon-containing compounds or inorganic silicon-containing compounds; And / or, the molar ratio of the template agent, the silicon source, n-butanol, hydrochloric acid and water is 1:(10-150):(20-200):(200-1200):(5000-20000); And / or, the conditions for hydrolysis gel preparation include: a temperature of 20-50°C and a time of 5-30 hours; And / or, the crystallization conditions include: a temperature of 80-120°C and a time of 10-40 hours; And / or, the calcination conditions include: a temperature of 400-600℃ and a time of 8-60h.

11. The application according to claim 10, wherein, The template agent is a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer; And / or, the silicon source is one or more of methyl orthosilicate, ethyl orthosilicate, isopropyl orthosilicate, and silica sol; And / or, the molar ratio of the template agent, the silicon source, n-butanol, hydrochloric acid and water is 1:(30-100):(50-120):(500-900):(8000-13500).

12. The application according to claim 11, wherein, The template agent is P123; And / or, the silicon source is tetraethyl orthosilicate.

13. The application according to claim 1, wherein, The specific surface area of ​​the cracking catalyst is 651-739 m². 2 / g, pore volume 0.9-1.4cm³ 3 / g.

14. The application according to claim 1, wherein, The modified oxide precursor is selected from one or more of the alkaline earth metals, transition metals and rare earth metals, including nitrates, chlorides, acetates and sulfates. And / or, the concentration of the aqueous solution of the modified oxide precursor is 1-20% by weight. And / or, the weight ratio of the aqueous solution of the hydrogen-type Y-type molecular sieve, the KIT-6 all-silica mesoporous molecular sieve, and the modified oxide precursor is 1:(1.5-12.0):(3-30); And / or, the conditions for the contact reaction include: a temperature of 10-100°C and a time of 0.5-50 h; And / or, the calcination conditions include: a temperature of 400-700℃ and a time of 2-20h.

15. The application according to claim 14, wherein, The modified oxide precursor is selected from one or more nitrates of calcium, magnesium, strontium, barium, zinc, cerium, lanthanum and zirconium; And / or, the weight ratio of the aqueous solution of the hydrogen-type Y-type molecular sieve, the KIT-6 all-silica mesoporous molecular sieve, and the modified oxide precursor is 1:(3.5-7.0):(6-20); And / or, the conditions for the contact reaction include: a temperature of 30-80°C and a time of 2-20 hours; And / or, the calcination conditions include: a temperature of 500-600℃ and a time of 3-10h.

16. The application according to claim 1, wherein, The conditions for reacting plastic powder with the pyrolysis catalyst include: a temperature of 420-580℃, a pressure of 0.01-1 MPa, and a contact time of 0.5-12 h. And / or, the weight ratio of the pyrolysis catalyst to the waste plastic powder is 1:(0.5-50).

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