Dual-channel composite catalysts, their preparation methods, and their application in the direct catalytic cracking of waste plastics to produce low-carbon olefins.

Abstract

This invention relates to the fields of catalysts and polymer material recycling, and discloses a dual-pore composite catalyst, its preparation method, and its application in the direct catalytic cracking of waste plastics to produce low-carbon olefins. The dual-pore composite catalyst comprises a modified ZSM-35 molecular sieve and a short rod-shaped mesoporous molecular sieve. The modified ZSM-35 molecular sieve includes ZSM-35 molecular sieve and boron oxide and metal oxide supported on the ZSM-35 molecular sieve. Based on the total weight of the dual-pore composite catalyst, the content of the modified ZSM-35 molecular sieve is 46-70% by weight, and the content of the short rod-shaped mesoporous molecular sieve is 30-54% by weight. This dual-pore composite catalyst, in the direct cracking of waste plastics to produce low-carbon olefins, not only solves the problem of waste plastic recycling but also increases the production of important chemical raw materials such as low-carbon olefins, representing a new one-step catalytic conversion and utilization pathway for waste plastics.

Description

Technical Field

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

[0002] Plastic products are characterized by their light weight, high strength, corrosion resistance, good chemical stability, ease of processing, and aesthetic appeal, making them widely used in various fields worldwide. 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. Currently, one-step thermal cracking and one-step catalytic cracking methods primarily produce fuel oil, yielding only small amounts of low-carbon olefins (ethylene, propylene, butene).

[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 recovery of low-carbon olefins in the chemical recycling of waste plastics is relatively low. This invention provides a dual-pore composite catalyst, its preparation method, and its application in the direct catalytic cracking of waste plastics to produce low-carbon olefins. This dual-pore composite catalyst, in the direct cracking of waste plastics to produce low-carbon olefins, not only solves the problem of waste plastic recycling but also increases the production of important chemical raw materials such as low-carbon olefins, representing a new one-step catalytic conversion and utilization pathway for waste plastics.

[0007] To achieve the above objectives, the first aspect of the present invention provides a dual-channel composite catalyst, wherein the dual-channel composite catalyst comprises a modified ZSM-35 molecular sieve and a short rod-shaped mesoporous molecular sieve, the modified ZSM-35 molecular sieve comprising a ZSM-35 molecular sieve and boron oxide and metal oxide supported on the ZSM-35 molecular sieve, and based on the total weight of the dual-channel composite catalyst, the content of the modified ZSM-35 molecular sieve is 46-70% by weight, and the content of the short rod-shaped mesoporous molecular sieve is 30-54% by weight.

[0008] The second aspect of the present invention provides a method for preparing a dual-channel composite catalyst, wherein the preparation method includes: mixing and ball-milling modified ZSM-35 molecular sieve and short rod-shaped mesoporous molecular sieve and then calcining them to obtain a dual-channel composite catalyst.

[0009] The third aspect of this invention provides an application of a dual-pore composite catalyst in the direct catalytic cracking of waste plastics to produce low-carbon olefins.

[0010] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0011] (1) The raw materials for the dual-pore composite catalyst provided by the present invention are readily available, the preparation method is simple, the conditions are easy to control, and the product has good repeatability.

[0012] (2) The dual-channel composite catalyst provided by the present invention includes modified zeolite molecular sieves with certain acidity on the surface and mesoporous materials with large pore size. It has a stable structure, good high temperature resistance, and helps the diffusion of raw material and product molecules during the pyrolysis reaction.

[0013] (3) The dual-pore composite catalyst provided by this invention can convert waste plastics into low-carbon olefins in one step when used in the direct catalytic cracking reaction of waste plastics to produce 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.

[0014] (4) The dual-pore composite catalyst provided by the present invention has mild process conditions, is easy to operate and has low requirements for reaction equipment when used for direct catalytic cracking of waste plastics to produce low-carbon olefins.

[0015] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0016] 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:

[0017] Figure 1 This is a scanning electron microscope (SEM) image of the short rod-shaped mesoporous molecular sieve A prepared in Example 1;

[0018] Figure 2 This is the small-angle X-ray diffraction (XRD) pattern of the dual-pore composite catalyst A prepared in Example 1;

[0019] Figure 3 This is the wide-angle X-ray diffraction (XRD) pattern of the dual-pore composite catalyst A prepared in Example 1;

[0020] Figure 4 This is a pore size distribution diagram of the dual-channel composite 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] In a first aspect, the present invention provides a dual-channel composite catalyst, wherein the dual-channel composite catalyst comprises a modified ZSM-35 molecular sieve and a short rod-shaped mesoporous molecular sieve, the modified ZSM-35 molecular sieve comprising a ZSM-35 molecular sieve and boron oxide and metal oxide supported on the ZSM-35 molecular sieve, and based on the total weight of the dual-channel composite catalyst, the content of the modified ZSM-35 molecular sieve is 46-70% by weight, and the content of the short rod-shaped mesoporous molecular sieve is 30-54% by weight.

[0023] The inventors of this invention discovered that, in the prior art, there is no process for the direct catalytic cracking of waste plastics to produce low-carbon olefins (including ethylene, propylene, and butene). One of the objectives of this invention is to solve this problem. Based on the inventors' understanding of the physicochemical properties of heterogeneous catalysts, catalysts used for the direct production of low-carbon olefins from waste plastics through catalytic cracking should possess a certain degree of acidity and good hydrothermal stability. Based on these requirements, ZSM-35 molecular sieves, which possess both a stable FER-type topological framework structure and a certain degree of acidity, are very suitable as the main component of a waste plastic cracking catalyst. However, because the ZSM-35 molecular sieve has a relatively small pore size (average pore diameter between 0.5-0.6 nm) and a small pore volume (generally not exceeding 0.3 cm³), it is problematic. 3 The molecular weight of waste plastics is relatively large, and the molecular chains are also relatively long. During the pyrolysis reaction of waste plastics, the larger reactant and product molecules have difficulty diffusing within the narrow channels, which not only affects the contact between reactants and active sites but also easily leads to side reactions such as deep dehydrogenation, thus causing a decline in catalyst performance. Compared with zeolite molecular sieves, short rod-shaped mesoporous molecular sieve materials have larger pore sizes (pore diameter greater than 10.0 nm, 20 times larger than the pore size of ZSM-35 molecular sieves) and larger pore volumes (up to 1.3 cm³). 3 Short rod-shaped mesoporous molecular sieves (with a surface area of ​​over 10 g) are highly suitable for catalytic reactions involving large molecules. However, as an all-silica material with extremely weak surface acidity, they are unsuitable as a standalone catalyst for the pyrolysis of waste plastics. During their research and development of catalysts for waste plastic pyrolysis, the inventors of this invention discovered that by combining the structural advantages of all-silica mesoporous inorganic materials with the surface acidic centers of zeolite molecular sieves, and mixing a certain amount of short rod-shaped mesoporous molecular sieves with ZSM-35 molecular sieves, the specific surface area and pore volume of the catalyst can be effectively increased, significantly improving the internal diffusion performance in the reaction. When used as a pyrolysis catalyst in the catalytic conversion reaction of waste plastics, it not only effectively improves the activity of the pyrolysis catalyst but also increases the selectivity for low-carbon olefins.

[0024] According to the present invention, preferably, based on the total weight of the dual-channel composite catalyst, the content of the modified ZSM-35 molecular sieve is 50-64% by weight, and the content of the short rod-shaped mesoporous molecular sieve is 34-50% by weight; more preferably, based on the total weight of the dual-channel composite catalyst, the content of the modified ZSM-35 molecular sieve is 54-62% by weight, and the content of the short rod-shaped mesoporous molecular sieve is 38-46% by weight. In the present invention, by using the aforementioned specific content of each component, the prepared dual-channel composite catalyst can exhibit better catalytic activity and higher selectivity for low-carbon olefins when used in the direct catalytic cracking of waste plastics to produce low-carbon olefins.

[0025] The inventors of this invention also discovered that the relatively dense acid centers on the surface of ZSM-35 molecular sieves may lead to deep dehydrogenation during the pyrolysis reaction of waste plastic raw materials, resulting in catalyst deactivation and severe carbon deposition during the reaction. Therefore, it is necessary to modify the surface of ZSM-35 molecular sieves in an appropriate manner to reduce the density of surface acid centers to a certain extent, making it more suitable for the catalytic pyrolysis reaction of waste plastics. During catalyst development research, the inventors discovered that surface modification of ZSM-35 molecular sieves using specific oxides can effectively improve its surface properties. The dual-channel composite catalyst prepared by mixing the modified ZSM-35 molecular sieve with short rod-shaped mesoporous molecular sieves exhibits high catalytic activity and high selectivity for low-carbon olefins in the catalytic pyrolysis reaction of waste plastics.

[0026] According to the present invention, the modified ZSM-35 molecular sieve comprises ZSM-35 molecular sieve, boron oxide, and metal oxide, and based on the total weight of the modified ZSM-35 molecular sieve, the content of ZSM-35 molecular sieve is 92-98% by weight, the content of boron oxide is 0.4-1.6% by weight, and the content of metal oxide is 1.6-6.4% by weight; preferably, based on the total weight of the modified ZSM-35 molecular sieve, the content of ZSM-35 molecular sieve is 93-97% by weight, the content of boron oxide is 0.6-1.4% by weight, and the content of metal oxide is 2.4-5.6% by weight; more preferably, based on the total weight of the modified ZSM-35 molecular sieve, the content of ZSM-35 molecular sieve is 94-96% by weight, the content of boron oxide is 0.8-1.2% by weight, and the content of metal oxide is 3.2-4.8% by weight. In this invention, the modified ZSM-35 molecular sieve, using the aforementioned specific content of each component, enables the prepared dual-pore composite catalyst to exhibit better catalytic activity and higher low-carbon olefin selectivity when used in the direct catalytic cracking of waste plastics to produce low-carbon olefins.

[0027] The inventors of this invention use ZSM-35 molecular sieve with a SiO2 / Al2O3 molar ratio of 10-200 as the main basic component for modifying ZSM-35 molecular sieve, and introduce boron oxide and metal oxides as modifying components, which can improve both the activity of the dual-channel composite catalyst and the selectivity for low-carbon olefins. Preferably, when the SiO2 / Al2O3 molar ratio of the ZSM-35 zeolite molecular sieve is 20-90, both the catalyst activity and the selectivity for low-carbon olefins can be significantly improved.

[0028] According to the present invention, ZSM-35 molecular sieves can be obtained commercially. Specifically, the ZSM-35 molecular sieves are more preferably: ZSM-35 molecular sieves with a SiO2 / Al2O3 molar ratio of 20 were purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd.; ZSM-35 molecular sieves with a SiO2 / Al2O3 molar ratio of 30 were purchased from Tianjin Nanhua Catalyst Co., Ltd.; and ZSM-35 molecular sieves with a SiO2 / Al2O3 molar ratio of 90 were purchased from Nanjing Jicang Nanotechnology Co., Ltd.

[0029] According to the present invention, the metal oxide is selected from one or more of alkali metal oxides, alkaline earth metal oxides, and transition metal oxides; preferably, the metal oxide is selected from one or more of sodium oxide, potassium oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, and zinc oxide. In the present invention, the boron oxide and specific metal oxides selected from the present invention have the advantage of improving the surface electron distribution of ZSM-35 molecular sieves and selectively covering some of the overly dense acidic centers, making the surface characteristics of the dual-channel composite catalyst more suitable for the pyrolysis reaction of waste plastics.

[0030] According to the present invention, the preparation method of the modified ZSM-35 molecular sieve includes: mixing and contacting ZSM-35 molecular sieve with an aqueous solution containing boric acid and metal salt and reacting them; then subjecting it to dehydration, drying and calcination treatment to obtain the modified ZSM-35 molecular sieve.

[0031] According to the present invention, the metal salt is selected from one or more of carbonates, chlorides, sulfates and nitrates containing a metal component, preferably nitrates containing a metal component;

[0032] According to the present invention, the metal component is selected from one or more of alkali metals, alkaline earth metals and transition metals, preferably one or more of sodium, potassium, magnesium, calcium, strontium, barium and zinc;

[0033] According to the present invention, in the aqueous solution containing boric acid and metal salt, the mass concentration of boric acid is 0.05-0.60%, preferably 0.10-0.30%; and the mass concentration of metal salt is 0.3-3.0%, preferably 0.7-2.5%.

[0034] According to the present invention, the weight ratio of the ZSM-35 molecular sieve to the aqueous solution containing boric acid and metal salt is 1:(5-30), preferably 1:(8-20).

[0035] According to the present invention, the reaction conditions 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 ZSM-35 molecular sieve and the aqueous solution containing boric acid and metal salt.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] According to the present invention, the specific surface area of ​​the short rod-shaped mesoporous molecular sieve is 300-700 m². 2 / g, pore volume 1.3-1.8ml / g, average pore size 10-15nm, rod length 0.5-1μm.

[0040] According to the present invention, the preparation method of the short rod-shaped mesoporous molecular sieve includes the following steps: in the presence of a template agent, ammonium fluoride and heptane, tetraethyl orthosilicate is contacted with an acidic aqueous solution, and the resulting mixture is crystallized, washed, filtered, dried and the template agent is removed to obtain the short rod-shaped mesoporous molecular sieve.

[0041] According to the present invention, in the method for preparing short rod-shaped mesoporous molecular sieves, the template agent can be any of the triblock copolymer polyoxyethylene-polyoxypropylene-polyoxyethylene template agents conventionally used in the art, preferably P123.

[0042] According to the present invention, the heptane is preferably n-heptane.

[0043] According to the present invention, the acidic aqueous solution is preferably an aqueous solution of hydrochloric acid.

[0044] According to the present invention, in the method for preparing short rod-shaped mesoporous molecular sieves, the molar ratio of the template agent, ammonium fluoride, heptane, tetraethyl orthosilicate, water and hydrogen chloride is 1:(0.5-5):(10-200):(50-500):(3000-30000):(200-2000), preferably 1:(1-3):(20-100):(100-400):(4000-20000):(400-1600).

[0045] According to the present invention, the preferred contact conditions are: contact temperature 15-60℃ and contact time 5-40h; the contact can be carried out under stirring conditions, wherein the stirring conditions include: stirring rate 200-900 rpm.

[0046] According to the present invention, the crystallization process can be carried out in a hydrothermal reactor with a polytetrafluoroethylene liner, and the preferred crystallization conditions are: crystallization temperature 80-130℃ and crystallization time 10-40h.

[0047] According to the present invention, the washing method is not specifically defined and can be any method well known to those skilled in the art. Preferably, the separated solid is mixed with deionized water, stirred and pulped for 2 hours, allowed to stand for 3 hours, and then separated. The above washing process is repeated 6-10 times.

[0048] According to the present invention, the preferred drying conditions are: drying temperature 70-150℃ and drying time 3-20h.

[0049] According to the present invention, the preferred conditions for removing the template agent are: calcination treatment in air atmosphere, treatment temperature 400-600℃, and treatment time 6-50h.

[0050] According to the present invention, the specific surface area of ​​the dual-pore composite catalyst is 420-500 m². 2 / g, pore volume 0.5-1cm³ 3 / g; preferably, the specific surface area of ​​the dual-pore composite catalyst is 436-490m². 2 / g, pore volume 0.68-0.98cm³ 3 / g.

[0051] The second aspect of the present invention provides a method for preparing a dual-pore composite catalyst, wherein the preparation method includes: mixing and ball-milling modified ZSM-35 molecular sieve and short rod-shaped mesoporous molecular sieve, and then calcining them to obtain a dual-pore composite catalyst.

[0052] According to the present invention, the weight ratio of the modified ZSM-35 molecular sieve to the short rod-shaped mesoporous molecular sieve is 1:(0.4-1.2), preferably 1:(0.5-1.0);

[0053] According to the present invention, the ball milling is carried out in a ball mill, wherein the diameter of the grinding balls in the ball mill can be 2-3 mm; the number of grinding balls can be reasonably selected according to the size of the grinding jar, and for a grinding jar with a size of 100-300 mL, 2-8 grinding balls can usually be used; the grinding balls are made of agate or polytetrafluoroethylene, preferably agate. The ball milling conditions include: the rotational speed of the grinding balls can be 200-600 r / min, preferably 300-500 r / min; the temperature inside the grinding jar can be 30-90℃, preferably 40-80℃; and the ball milling time can be 5-50 h, preferably 8-24 h.

[0054] According to the present invention, the calcination conditions include: a temperature of 450-650℃, preferably 500-600℃; and a time of 3-20h, preferably 5-10h.

[0055] The third aspect of this invention provides an application of a dual-pore composite catalyst in the direct catalytic cracking of waste plastics to produce low-carbon olefins.

[0056] According to the present invention, the method of applying the catalyst includes: reacting waste plastic powder with a dual-pore composite catalyst under specific conditions.

[0057] According to the present invention, the contact conditions between the waste plastic powder and the dual-pore composite catalyst include: the contact temperature can be 420-580℃, preferably 450-540℃; the contact pressure can be 0.01-1 MPa, preferably 0.05-0.5 MPa; and the contact time can be 0.5-12 h, preferably 1-5 h.

[0058] According to the present invention, the weight ratio of the dual-channel composite catalyst to waste plastic powder can be 1:(0.5-50), preferably 1:(2-30).

[0059] The present invention will be described in detail below through embodiments.

[0060] In the following examples and comparative examples:

[0061] 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°.

[0062] 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°.

[0063] 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.

[0064] The scanning electron microscope (SEM) images of the samples were obtained using an XL-30 field emission environmental scanning electron microscope manufactured by FEI Corporation in the United States.

[0065] 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.

[0066] The drying oven was manufactured by Shanghai Yiheng Scientific Instruments Co., Ltd., model DHG-9030A.

[0067] The muffle furnace is manufactured by CARBOLITE, model CWF1100.

[0068] The P123 used in the examples and comparative examples was purchased from Aldrich. The ZSM-35 molecular sieve with a SiO2 / Al2O3 molar ratio of 20 used in the examples and comparative examples was purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd.; the ZSM-35 molecular sieve with a SiO2 / Al2O3 molar ratio of 30 was purchased from Tianjin Nanhua Catalyst Co., Ltd.; and the ZSM-35 molecular sieve with a SiO2 / Al2O3 molar ratio of 90 was purchased from Nanjing Jicang Nanotechnology Co., Ltd. All other reagents used in the examples and comparative examples were purchased from Sinopharm Chemical Reagent Co., Ltd., and were of analytical grade.

[0069] Example 1

[0070] This embodiment is intended to illustrate the dual-pore composite catalyst prepared according to the present invention.

[0071] (1) Preparation of short rod-shaped mesoporous molecular sieves

[0072] 58 g of P123 (0.01 mol) and 0.74 g (0.02 mol) of ammonium fluoride were mixed with 2165 g of hydrochloric acid aqueous solution (containing 10 mol of HCl) and stirred at 20 °C until P123 and ammonium fluoride were completely dissolved. 60 g of n-heptane (0.6 mol) and 582 g of tetraethyl orthosilicate (2.8 mol) were added to the above solution and stirred vigorously at 20 °C for 4 minutes, then allowed to stand for 1 hour. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor and crystallized at 100 °C for 24 hours. After filtration, the solid substance was washed with deionized water 8 times and then dried at 110 °C for 12 hours to obtain mesoporous molecular sieve powder. The mesoporous molecular sieve powder was calcined at 500 °C for 24 hours to remove the template agent, yielding short rod-shaped mesoporous molecular sieve A.

[0073] The specific surface area of ​​short rod-shaped mesoporous molecular sieve A is 594 m². 2 / g, pore volume is 1.6mL / g, and average pore size is 12nm.

[0074] Figure 1 This is a scanning electron microscope image of short rod-shaped mesoporous molecular sieve A. It can be seen that the microstructure of short rod-shaped mesoporous molecular sieve A is that of short rods, with rod lengths ranging from 0.5 to 1 μm.

[0075] (2) Preparation of modified ZSM-35 molecular sieve

[0076] 0.18 g of boric acid and 0.9 g of potassium nitrate were dissolved in 100 g of distilled water to prepare an aqueous solution. 9.5 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 30) was added to the above aqueous solution, and the mixture was stirred at 60 °C for 5 h. The water was removed using a rotary evaporator, and the solid product was dried at 110 °C for 8 h, and then calcined at 550 °C for 6 h to obtain modified ZSM-35 molecular sieve A.

[0077] Based on the total weight of modified ZSM-35 molecular sieve A, the content of ZSM-35 molecular sieve is 95.0% by weight, the content of boron oxide is 1.0% by weight, and the content of potassium oxide is 4.0% by weight.

[0078] (3) Preparation of dual-pore composite catalyst

[0079] 29g of modified ZSM-35 molecular sieve A and 21g of short rod-shaped mesoporous molecular sieve A were added to a 300ml ball mill jar, along with six agate grinding balls with a diameter of 2mm. Ball milling was then initiated. The temperature inside the ball mill jar was controlled at 50℃, the grinding speed was 400r / min, and the milling time was 10h. The powder obtained after ball milling was calcined at 600℃ for 16h to obtain the dual-pore composite catalyst A.

[0080] Based on the total weight of catalyst A, the content of modified ZSM-35 molecular sieve is 58% by weight, and the content of short rod-shaped mesoporous molecular sieve is 42% by weight.

[0081] Catalyst A has a specific surface area of ​​462 m². 2 / g, pore volume is 0.83cm³ 3 / g.

[0082] Figure 2 This is the small-angle XRD pattern of catalyst A; from Figure 2 The spectrum shows three clearly visible diffraction peaks at small angles below 2°, proving that the mesoporous material in the catalyst has a typical two-dimensional hexagonal mesoporous structure. This indicates that the short rod-shaped mesoporous molecular sieve still retains a relatively regular mesoporous channel structure after being prepared into a catalyst, and the catalyst preparation process did not destroy the basic structure of the mesoporous molecular sieve.

[0083] Figure 3 This is the wide-angle XRD pattern of catalyst A; from Figure 3 The X-ray diffraction patterns show that the wide-angle X-ray diffraction angles of this sample are mainly: 2θ = 9.4°, 22.4°, 22.7°, 23.3°, 23.7°, 24.5°, and 25.3°. These diffraction signals are consistent with the diffraction patterns of ZSM-35 molecular sieves, indicating that the crystal phase of ZSM-35 molecular sieves did not undergo significant changes during catalyst preparation and maintained a good FER-type topological framework structure. Furthermore, no diffraction signals corresponding to boron oxide or metal oxides appeared in the wide-angle XRD pattern, indicating that the modified components are uniformly dispersed on the catalyst.

[0084] Figure 4 This is the pore size distribution diagram of catalyst A; from Figure 4 The spectrum shows that the sample has a distinct dual-channel structure with pore sizes of 0.5 nm and 12 nm, respectively. The 0.5 nm pore size is provided by modified ZSM-35 molecular sieve, while the 12 nm pore size is provided by short rod-shaped mesoporous molecular sieve.

[0085] (4) Evaluation of the reaction performance of direct conversion of waste plastics to low carbon olefins

[0086] The performance of the catalyst in the catalytic cracking of methyl tert-butyl ether was evaluated in a fixed-bed reactor. The catalyst loading was 10.0 g, the polyethylene waste plastic loading was 50.0 g, the reaction temperature was 480℃, the reaction pressure was 0.1 MPa, and the reaction time was 2 h. 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.

[0087] Example 2

[0088] This embodiment is intended to illustrate the dual-pore composite catalyst prepared according to the present invention.

[0089] (1) Preparation of short rod-shaped mesoporous molecular sieves

[0090] 58 g of P123 (0.01 mol) and 1.11 g (0.03 mol) of ammonium fluoride were mixed with 4184 g of hydrochloric acid aqueous solution (containing 16 mol of HCl) and stirred at 50 °C until P123 and ammonium fluoride were completely dissolved. 100 g of n-heptane (1.0 mol) and 832 g of tetraethyl orthosilicate (4.0 mol) were added to the above solution and stirred vigorously at 50 °C for 4 minutes, then allowed to stand for 2 hours. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor and crystallized at 80 °C for 40 hours. After filtration, the solid substance was washed with deionized water 8 times and then dried at 150 °C for 4 hours to obtain mesoporous molecular sieve powder. The mesoporous molecular sieve powder was calcined at 600 °C for 6 hours to remove the template agent, yielding short rod-shaped mesoporous molecular sieve B.

[0091] The specific surface area of ​​short rod-shaped mesoporous molecular sieve B is 609 m². 2 / g, pore volume is 1.7mL / g, and average pore size is 11nm.

[0092] (2) Preparation of modified ZSM-35 molecular sieve

[0093] 0.14 g of boric acid and 2.0 g of magnesium nitrate hexahydrate were dissolved in 80 g of distilled water to prepare an aqueous solution. 9.6 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 90) was 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 modified ZSM-35 molecular sieve B.

[0094] Based on the total weight of modified ZSM-35 molecular sieve B, the content of ZSM-35 molecular sieve is 96.0 wt%, the content of boron oxide is 0.8 wt%, and the content of magnesium oxide is 3.2 wt%.

[0095] (3) Preparation of dual-pore composite catalyst

[0096] 31g of modified ZSM-35 molecular sieve B and 19g of short rod-shaped mesoporous molecular sieve powder B were added to a 300ml ball mill jar, along with eight agate grinding balls with a diameter of 2mm. Ball milling was then initiated. The temperature inside the ball mill jar was controlled at 80℃, the grinding ball speed was 500r / min, and the milling time was 8h. The powder obtained after ball milling was calcined at 650℃ for 8h to obtain the dual-pore composite catalyst B.

[0097] Based on the total weight of catalyst B, the content of modified ZSM-35 molecular sieve is 62% by weight, and the content of short rod-shaped mesoporous molecular sieve is 38% by weight.

[0098] Catalyst B has a specific surface area of ​​452 m². 2 / g, pore volume is 0.78cm³ 3 / g.

[0099] 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 (4) of Example 1. The evaluation results are listed in Table 1.

[0100] Example 3

[0101] This embodiment is intended to illustrate the dual-pore composite catalyst prepared according to the present invention.

[0102] (1) Preparation of short rod-shaped mesoporous molecular sieves

[0103] 58 g of P123 (0.01 mol) and 0.37 g of ammonium fluoride (0.01 mol) were mixed with 1048 g of hydrochloric acid aqueous solution (containing 4 mol of HCl) and stirred at 15 °C until P123 and ammonium fluoride were completely dissolved. 20 g of n-heptane (0.2 mol) and 208 g of tetraethyl orthosilicate (1.0 mol) were added to the above solution and stirred vigorously at 15 °C for 20 minutes, then allowed to stand for 1 hour. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor and crystallized at 120 °C for 10 hours. After filtration, the solid substance was washed eight times with deionized water and then dried at 70 °C for 20 hours to obtain mesoporous molecular sieve powder. The mesoporous molecular sieve powder was calcined at 400 °C for 30 hours to remove the template agent, yielding short rod-shaped mesoporous molecular sieve C.

[0104] The specific surface area of ​​short rod-shaped mesoporous molecular sieve C is 571 m². 2 / g, pore volume is 1.5mL / g, and average pore size is 12nm.

[0105] (2) Preparation of modified ZSM-35 molecular sieve

[0106] 0.21 g of boric acid and 1.8 g of zinc nitrate hexahydrate were dissolved in 150 g of distilled water to prepare an aqueous solution. 9.4 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 20) was 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 modified ZSM-35 molecular sieve C.

[0107] Based on the total weight of modified ZSM-35 molecular sieve C, the content of ZSM-35 molecular sieve is 94 wt%, the content of boron oxide is 1.2 wt%, and the content of zinc oxide is 4.8 wt%.

[0108] (3) Preparation of dual-pore composite catalyst

[0109] 27g of modified ZSM-35 molecular sieve C and 23g of short rod-shaped mesoporous molecular sieve powder C were added to a 300ml ball mill jar, along with four 2mm diameter agate grinding balls, and ball milling was initiated. The temperature inside the ball mill jar was controlled at 40℃, the grinding ball speed was 300r / min, and the milling time was 24h. The powder obtained after ball milling was calcined at 550℃ for 20h to obtain the dual-pore composite catalyst C.

[0110] Based on the total weight of catalyst C, the content of modified ZSM-35 molecular sieve is 54% by weight, and the content of short rod-shaped mesoporous molecular sieve is 46% by weight.

[0111] Catalyst C has a specific surface area of ​​471 m². 2 / g, pore volume is 0.89cm³ 3 / g.

[0112] 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 (4) of Example 1. The evaluation results are listed in Table 1.

[0113] Example 4

[0114] This embodiment is intended to illustrate the dual-pore composite catalyst prepared according to the present invention.

[0115] Short rod-shaped mesoporous molecular sieve A was prepared according to the method in step (1) of Example 1.

[0116] (2) Preparation of modified ZSM-35 molecular sieve

[0117] 0.11 g of boric acid and 0.7 g of calcium nitrate were dissolved in 100 g of distilled water to prepare an aqueous solution. 9.5 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 90) was added to the above aqueous solution, and the mixture was stirred at 60 °C for 5 h. The water was removed using a rotary evaporator, and the solid product was dried at 110 °C for 8 h, and then calcined at 550 °C for 6 h to obtain modified ZSM-35 molecular sieve D.

[0118] Based on the total weight of modified ZSM-35 molecular sieve D, the content of ZSM-35 molecular sieve is 97% by weight, the content of boron oxide is 0.6% by weight, and the content of calcium oxide is 2.4% by weight.

[0119] (3) Preparation of dual-pore composite catalyst

[0120] 32g of modified ZSM-35 molecular sieve D and 18g of short rod-shaped mesoporous molecular sieve A were added to a 300ml ball mill jar, along with six agate grinding balls with a diameter of 2mm. Ball milling was then initiated. The temperature inside the ball mill jar was controlled at 50℃, the grinding ball speed was 400r / min, and the milling time was 10h. The powder obtained after ball milling was calcined at 600℃ for 16h to obtain the dual-pore composite catalyst D.

[0121] Based on the total weight of catalyst D, the content of modified ZSM-35 molecular sieve is 64% by weight, and the content of short rod-shaped mesoporous molecular sieve is 36% by weight.

[0122] The specific surface area of ​​catalyst D is 449 m². 2 / g, pore volume 0.75cm³ 3 / g.

[0123] 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 (4) of Example 1. The evaluation results are listed in Table 1.

[0124] Example 5

[0125] This embodiment is intended to illustrate the dual-pore composite catalyst prepared according to the present invention.

[0126] Short rod-shaped mesoporous molecular sieve B was prepared according to the method in step (1) of Example 2.

[0127] (2) Preparation of modified ZSM-35 molecular sieve

[0128] 0.25 g of boric acid and 1.0 g of barium nitrate were dissolved in 60 g of distilled water to prepare an aqueous solution. 9.3 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 30) 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 modified ZSM-35 molecular sieve E.

[0129] Based on the total weight of modified ZSM-35 molecular sieve E, the content of ZSM-35 molecular sieve is 93% by weight, the content of boron oxide is 1.4% by weight, and the content of barium oxide is 5.6% by weight.

[0130] (3) Preparation of dual-pore composite catalyst

[0131] 25g of modified ZSM-35 molecular sieve E and 25g of short rod-shaped mesoporous molecular sieve B were added to a 300ml ball mill jar, along with eight agate grinding balls with a diameter of 2mm. Ball milling was then initiated. The temperature inside the ball mill jar was controlled at 80℃, the grinding ball speed was 500r / min, and the milling time was 8h. The powder obtained after ball milling was calcined at 650℃ for 8h to obtain the dual-pore composite catalyst E.

[0132] Based on the total weight of catalyst E, the content of modified ZSM-35 molecular sieve is 50% by weight, and the content of short rod-shaped mesoporous molecular sieve is 50% by weight.

[0133] Catalyst E has a specific surface area of ​​480 m². 2 / g, pore volume is 0.94cm³ 3 / g.

[0134] 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 (4) of Example 1. The evaluation results are listed in Table 1.

[0135] Example 6

[0136] This embodiment is intended to illustrate the dual-pore composite catalyst prepared according to the present invention.

[0137] Short rod-shaped mesoporous molecular sieve A was prepared according to the method in step (1) of Example 1.

[0138] (2) Preparation of modified ZSM-35 molecular sieve

[0139] 0.07 g of boric acid and 0.4 g of sodium nitrate were dissolved in 120 g of distilled water to prepare an aqueous solution. 9.8 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 90) was 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 modified ZSM-35 molecular sieve F.

[0140] Based on the total weight of modified ZSM-35 molecular sieve F, the content of ZSM-35 molecular sieve is 98% by weight, the content of boron oxide is 0.4% by weight, and the content of sodium oxide is 1.6% by weight.

[0141] (3) Preparation of dual-pore composite catalyst

[0142] 35g of modified ZSM-35 molecular sieve F and 15g of short rod-shaped mesoporous molecular sieve A were added to a 300ml ball mill jar, along with six agate grinding balls with a diameter of 2mm. Ball milling was then initiated. The temperature inside the ball mill jar was controlled at 50℃, the grinding ball speed was 400r / min, and the milling time was 10h. The powder obtained after ball milling was calcined at 600℃ for 16h to obtain the dual-pore composite catalyst F.

[0143] Based on the total weight of catalyst F, the content of modified ZSM-35 molecular sieve is 70% by weight, and the content of short rod-shaped mesoporous molecular sieve is 30% by weight.

[0144] The specific surface area of ​​catalyst F is 436 m². 2 / g, pore volume is 0.68cm³ 3 / g.

[0145] 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 (4) of Example 1. The evaluation results are listed in Table 1.

[0146] Example 7

[0147] This embodiment is intended to illustrate the dual-pore composite catalyst prepared according to the present invention.

[0148] Short rod-shaped mesoporous molecular sieve B was prepared according to the method in step (1) of Example 2.

[0149] (2) Preparation of modified ZSM-35 molecular sieve

[0150] 0.28 g of boric acid and 1.3 g of strontium nitrate were dissolved in 50 g of distilled water to prepare an aqueous solution. 9.2 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 30) 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 modified ZSM-35 molecular sieve G.

[0151] Based on the total weight of the modified ZSM-35 molecular sieve G, the content of ZSM-35 molecular sieve is 92 wt%, the content of boron oxide is 1.6 wt%, and the content of strontium oxide is 6.4 wt%.

[0152] (3) Preparation of dual-pore composite catalyst

[0153] 23g of modified ZSM-35 molecular sieve G and 27g of short rod-shaped mesoporous molecular sieve B were added to a 300ml ball mill jar, along with eight agate grinding balls with a diameter of 2mm. Ball milling was then initiated. The temperature inside the ball mill jar was controlled at 80℃, the grinding ball speed was 500r / min, and the milling time was 8h. The powder obtained after ball milling was calcined at 650℃ for 8h to obtain the dual-pore composite catalyst G.

[0154] Based on the total weight of catalyst G, the content of modified ZSM-35 molecular sieve is 46% by weight, and the content of short rod-shaped mesoporous molecular sieve is 54% by weight.

[0155] Catalyst G has a specific surface area of ​​490 m². 2 / g, pore volume is 0.98cm³ 3 / g.

[0156] 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 (4) of Example 1, and the evaluation results are listed in Table 1.

[0157] Comparative Example 1

[0158] Short rod-shaped mesoporous molecular sieve A was prepared according to the method in step (1) of Example 1.

[0159] (2) Preparation of modified ZSM-35 molecular sieve

[0160] 0.02 g of boric acid and 0.1 g of potassium nitrate were dissolved in 100 g of distilled water to prepare an aqueous solution. 9.5 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 30) was added to the above aqueous solution, and the mixture was stirred at 60 °C for 5 h. The water was removed using a rotary evaporator, and the solid product was dried at 110 °C for 8 h, and then calcined at 550 °C for 6 h to obtain modified ZSM-35 molecular sieve D1.

[0161] Based on the total weight of modified ZSM-35 molecular sieve D1, the content of ZSM-35 molecular sieve is 99.4% by weight, the content of boron oxide is 0.1% by weight, and the content of potassium oxide is 0.5% by weight.

[0162] (3) Preparation of dual-pore composite catalyst

[0163] 44g of modified ZSM-35 molecular sieve D1 and 6g of short rod-shaped mesoporous molecular sieve A were added to a 300ml ball mill jar, along with six 2mm diameter agate grinding balls, and ball milling was initiated. The temperature inside the ball mill jar was controlled at 50℃, the grinding ball speed was 400r / min, and the milling time was 10h. The powder obtained after ball milling was calcined at 700℃ for 2h to obtain the dual-pore composite catalyst D1.

[0164] Based on the total weight of catalyst D1, the content of modified ZSM-35 molecular sieve is 88% by weight, and the content of short rod-shaped mesoporous molecular sieve is 12% by weight.

[0165] The specific surface area of ​​catalyst D1 is 396 m². 2 / g, pore volume is 0.43cm³ 3 / g.

[0166] 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 (4) of Example 1. The evaluation results are listed in Table 1.

[0167] Comparative Example 2

[0168] Short rod-shaped mesoporous molecular sieve B was prepared according to the method in step (1) of Example 2.

[0169] (2) Preparation of modified ZSM-35 molecular sieve

[0170] 0.42 g of boric acid and 3.2 g of zinc nitrate hexahydrate were dissolved in 80 g of distilled water to prepare an aqueous solution. 8.9 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 30) was added to the above aqueous solution, and the mixture was stirred at 30 °C for 20 h. The water was removed using a rotary evaporator, and the solid product was dried at 80 °C for 20 h, and then calcined at 500 °C for 10 h to obtain modified ZSM-35 molecular sieve D2.

[0171] Based on the total weight of modified ZSM-35 molecular sieve D2, the content of ZSM-35 molecular sieve is 89% by weight, the content of boron oxide is 2.4% by weight, and the content of zinc oxide is 8.6% by weight.

[0172] (3) Preparation of dual-pore composite catalyst

[0173] 12g of modified ZSM-35 molecular sieve D2 and 38g of short rod-shaped mesoporous molecular sieve B were added to a 300ml ball mill jar, along with eight agate grinding balls with a diameter of 2mm. Ball milling was then initiated. The temperature inside the ball mill jar was controlled at 80℃, the grinding speed was 500r / min, and the milling time was 8h. The powder obtained after ball milling was calcined at 450℃ for 16h to obtain the dual-pore composite catalyst D2.

[0174] Based on the total weight of catalyst D2, the content of modified ZSM-35 molecular sieve is 24% by weight, and the content of short rod-shaped mesoporous molecular sieve is 76% by weight.

[0175] The specific surface area of ​​catalyst D2 is 537 m². 2 / g, pore volume is 1.28cm³ 3 / g.

[0176] 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 (4) of Example 1. The evaluation results are listed in Table 1.

[0177] Comparative Example 3

[0178] Cancel steps (1) and (3) in Example 1.

[0179] Modified ZSM-35 molecular sieve A was prepared according to the method in step (2) of Example 1.

[0180] The reaction performance of modified ZSM-35 molecular sieve A was tested according to the reaction performance evaluation method of waste plastic direct conversion to low carbon olefins in step (4) of Example 1. The evaluation results are listed in Table 1.

[0181] Comparative Example 4

[0182] Short rod-shaped mesoporous molecular sieve A was prepared according to the method in step (1) of Example 1.

[0183] Cancel steps (2) and (3) in Example 1.

[0184] The reaction performance of short rod-shaped mesoporous molecular sieve A was tested according to the reaction performance evaluation method for direct conversion of waste plastics to low carbon olefins in step (4) of Example 1. The evaluation results are listed in Table 1.

[0185] Comparative Example 5

[0186] Short rod-shaped mesoporous molecular sieve A was prepared according to the method in step (1) of Example 1.

[0187] Cancel step (2) in Example 1.

[0188] The dual-pore composite catalyst D3 was prepared according to step (3) of Example 1. The preparation conditions were changed; unmodified ZSM-35 molecular sieve was used instead of modified ZSM-35. The specific process is as follows:

[0189] 29g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 30) and 21g of short rod-shaped mesoporous molecular sieve A were added to a 300ml ball mill jar, along with six agate grinding balls with a diameter of 2mm. Ball milling was then initiated. The temperature inside the ball mill jar was controlled at 50℃, the grinding ball speed was 400r / min, and the milling time was 10h. The powder obtained after ball milling was calcined at 600℃ for 16h to obtain the dual-pore composite catalyst D3.

[0190] Based on the total weight of catalyst D3, the content of ZSM-35 molecular sieve is 58% by weight, and the content of short rod-shaped mesoporous molecular sieve is 42% by weight.

[0191] 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 (4) of Example 1. The evaluation results are listed in Table 1.

[0192] Comparative Example 6

[0193] Short rod-shaped mesoporous molecular sieve A was prepared according to the method in step (1) of Example 1.

[0194] (2) Preparation of modified ZSM-35 molecular sieve

[0195] 0.9 g of potassium nitrate was dissolved in 100 g of distilled water to prepare an aqueous solution. 9.6 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 30) was 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 modified ZSM-35 molecular sieve D4.

[0196] Based on the total weight of modified ZSM-35 molecular sieve D4, the content of ZSM-35 molecular sieve is 96.0% by weight, and the content of potassium oxide is 4.0% by weight.

[0197] (3) Preparation of dual-pore composite catalyst

[0198] 29g of modified ZSM-35 molecular sieve D4 and 21g of short rod-shaped mesoporous molecular sieve A were added to a 300ml ball mill jar, along with six agate grinding balls with a diameter of 2mm. Ball milling was then initiated. The temperature inside the ball mill jar was controlled at 50℃, the grinding ball speed was 400r / min, and the milling time was 10h. The powder obtained after ball milling was calcined at 600℃ for 16h to obtain the dual-pore composite catalyst D4.

[0199] Based on the total weight of catalyst D4, the content of modified ZSM-35 molecular sieve is 58% by weight, and the content of short rod-shaped mesoporous molecular sieve is 42% by weight.

[0200] 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 (4) of Example 1. The evaluation results are listed in Table 1.

[0201] Comparative Example 7

[0202] Short rod-shaped mesoporous molecular sieve A was prepared according to the method in step (1) of Example 1.

[0203] (2) Preparation of modified ZSM-35 molecular sieve

[0204] 0.18 g of boric acid was dissolved in 100 g of distilled water to prepare an aqueous solution. 9.9 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 30) was added to the above aqueous solution, and the mixture was stirred at 60 °C for 5 h. The water was removed using a rotary evaporator, and the solid product was dried at 110 °C for 8 h, and then calcined at 550 °C for 6 h to obtain modified ZSM-35 molecular sieve D5.

[0205] Based on the total weight of modified ZSM-35 molecular sieve D5, the content of ZSM-35 molecular sieve is 99.0% by weight, and the content of boron oxide is 1.0% by weight.

[0206] (3) Preparation of dual-pore composite catalyst

[0207] 29g of modified ZSM-35 molecular sieve D5 and 21g of short rod-shaped mesoporous molecular sieve A were added to a 300ml ball mill jar, along with six agate grinding balls with a diameter of 2mm. Ball milling was then initiated. The temperature inside the ball mill jar was controlled at 50℃, the grinding ball speed was 400r / min, and the milling time was 10h. The powder obtained after ball milling was calcined at 600℃ for 16h to obtain the dual-pore composite catalyst D5.

[0208] Based on the total weight of catalyst D5, the content of modified ZSM-35 molecular sieve is 58% by weight, and the content of short rod-shaped mesoporous molecular sieve is 42% by weight.

[0209] 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 (4) of Example 1. The evaluation results are listed in Table 1.

[0210] Comparative Example 8

[0211] Short rod-shaped mesoporous molecular sieve A was prepared according to the method in step (1) of Example 1.

[0212] Modified ZSM-35 molecular sieve D6 was prepared according to step (2) in Example 1. The preparation conditions were changed, and the modified oxide was replaced with nickel oxide. The specific process is as follows:

[0213] 1.95 g of nickel nitrate hexahydrate was dissolved in 100 g of distilled water to prepare an aqueous solution. 9.5 g of ZSM-35 molecular sieve (SiO2 / Al2O3 = 30) was 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 modified ZSM-35 molecular sieve D6.

[0214] Based on the total weight of modified ZSM-35 molecular sieve D6, the content of ZSM-35 molecular sieve is 95.0% by weight, and the content of nickel oxide is 5.0% by weight.

[0215] (3) Preparation of dual-pore composite catalyst

[0216] 29g of modified ZSM-35 molecular sieve D6 and 21g of short rod-shaped mesoporous molecular sieve A were added to a 300ml ball mill jar, along with six 2mm diameter agate grinding balls, and ball milling was initiated. The temperature inside the ball mill jar was controlled at 50℃, the grinding ball speed was 400r / min, and the milling time was 10h. The powder obtained after ball milling was calcined at 600℃ for 16h to obtain the dual-pore composite catalyst D6.

[0217] Based on the total weight of catalyst D6, the content of modified ZSM-35 molecular sieve is 58% by weight, and the content of short rod-shaped mesoporous molecular sieve is 42% by weight.

[0218] 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 (4) of Example 1. The evaluation results are listed in Table 1.

[0219] Table 1

[0220] project catalyst Waste plastic conversion rate (%) Low-carbon olefin yield (%) Example 1 Catalyst A 100 43.7 Example 2 Catalyst B 100 43.5 Example 3 Catalyst C 100 43.2 Example 4 Catalyst D 100 41.8 Example 5 Catalyst E 100 41.4 Example 6 Catalyst F 100 40.9 Example 7 Catalyst G 100 40.6 Comparative Example 1 Catalyst D1 100 25.4 Comparative Example 2 Catalyst D2 90 16.3 Comparative Example 3 Modified ZSM-35 molecular sieve A 100 22.0 Comparative Example 4 Short rod-shaped mesoporous molecular sieve A 52 11.6 Comparative Example 5 Catalyst D3 100 27.3 Comparative Example 6 Catalyst D4 100 33.5 Comparative Example 7 Catalyst D5 100 31.8 Comparative Example 8 Catalyst D6 100 28.2

[0221] The results above demonstrate that the dual-pore composite 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.

[0222] In Comparative Example 1, the content of short rod-shaped mesoporous molecular sieve was too low, the content of modified ZSM-35 molecular sieve was too high, and the content of the modified component was not within the scope of the claims. Due to the limited number of mesoporous channels in the catalyst, the diffusion of reactant and product molecules was hindered during the reaction, resulting in a low yield of low-carbon olefins.

[0223] In Comparative Example 2, the content of short rod-shaped mesoporous molecular sieves was too high, the content of modified ZSM-35 molecular sieves was too low, and the content of the modified components was not within the scope of the claims. Due to the limited 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.

[0224] In Comparative Example 3, only modified ZSM-35 molecular sieve was used as the cracking catalyst, and no short rod-shaped mesoporous molecular sieve was added. Because the catalyst does not contain mesoporous channels, the diffusion of reactant and product molecules is hindered during the reaction, resulting in a low yield of low-carbon olefins.

[0225] In Comparative Example 4, only short rod-shaped mesoporous molecular sieves were used as cracking catalysts without the addition of modified ZSM-35 molecular sieves. Since there were almost no active acidic centers on the catalyst, the feed conversion rate was low and the yield of low-carbon olefins was low.

[0226] In Comparative Example 5, the ZSM-35 molecular sieve was not modified, resulting in a lower yield of low-carbon olefins.

[0227] In Comparative Example 6, modified ZSM-35 molecular sieves were prepared using only potassium oxide as the modifying component. The modification effect of ZSM-35 molecular sieves was poor, resulting in a low yield of low-carbon olefins.

[0228] In Comparative Example 7, modified ZSM-35 molecular sieves were prepared using only boron oxide as the modifying component. The modification effect of ZSM-35 molecular sieves was poor, resulting in a low yield of low-carbon olefins.

[0229] In Comparative Example 8, instead of the modified oxide specifically defined in this invention, nickel oxide was used. Due to the lower modification effect of the same weight of nickel oxide, the yield of low-carbon olefins was lower.

[0230] 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 dual-pore composite catalyst in the direct catalytic cracking of waste plastics to produce low-carbon olefins, the application including: Waste plastic powder is reacted with a dual-channel composite catalyst, wherein the waste plastic powder is polyethylene waste plastic; characterized in that the dual-channel composite catalyst comprises a modified ZSM-35 molecular sieve and a short rod-shaped mesoporous molecular sieve, the modified ZSM-35 molecular sieve comprising a ZSM-35 molecular sieve and boron oxide and metal oxide supported on the ZSM-35 molecular sieve; the metal oxide is selected from one or more of sodium oxide, potassium oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide and zinc oxide; the total content of the modified ZSM-35 molecular sieve is... Based on weight, the ZSM-35 molecular sieve content is 92-98% by weight, the boron oxide content is 0.4-1.6% by weight, and the metal oxide content is 1.6-6.4% by weight; the dual-channel composite catalyst has a mesoporous-microporous dual-channel structure, with a micropore diameter of 0.5-0.6 nm and a mesopore diameter of 10-15 nm; and based on the total weight of the dual-channel composite catalyst, the modified ZSM-35 molecular sieve content is 50-64% by weight, and the short rod-shaped mesoporous molecular sieve content is 34-50% by weight.

2. The application according to claim 1, wherein, Based on the total weight of the dual-channel composite catalyst, the content of the modified ZSM-35 molecular sieve is 54-62% by weight, and the content of the short rod-shaped mesoporous molecular sieve is 38-46% by weight.

3. The application according to claim 1, wherein, Based on the total weight of the modified ZSM-35 molecular sieve, the content of the ZSM-35 molecular sieve is 93-97% by weight, the content of the boron oxide is 0.6-1.4% by weight, and the content of the metal oxide is 2.4-5.6% by weight.

4. The application according to claim 3, wherein, Based on the total weight of the modified ZSM-35 molecular sieve, the content of the ZSM-35 molecular sieve is 94-96% by weight, the content of the boron oxide is 0.8-1.2% by weight, and the content of the metal oxide is 3.2-4.8% by weight.

5. The application according to claim 1, wherein, The SiO2 / Al2O3 molar ratio of the ZSM-35 molecular sieve is 10-200.

6. The application according to claim 5, wherein, The SiO2 / Al2O3 molar ratio of the ZSM-35 molecular sieve is 20-90.

7. The application according to any one of claims 1-6, wherein, The preparation method of the modified ZSM-35 molecular sieve includes: ZSM-35 molecular sieve was mixed and reacted with an aqueous solution containing boric acid and metal salt; then, after dehydration, drying and calcination, modified ZSM-35 molecular sieve was obtained.

8. The application according to claim 7, wherein, The metal salt is selected from one or more of carbonates, chlorides, sulfates and nitrates containing a metal component; And / or, in the aqueous solution containing boric acid and metal salt, the mass concentration of boric acid is 0.05-0.60%, and the mass concentration of metal salt is 0.3-3.0%; And / or, the weight ratio of the ZSM-35 molecular sieve to the aqueous solution containing boric acid and metal salt is 1:(5-30). And / or, the reaction conditions include: a temperature of 10-100°C and a time of 0.5-50 h; And / or, the ZSM-35 molecular sieve is mixed and contacted with an aqueous solution containing boric acid and metal salt and reacted; then subjected to dehydration, drying and calcination treatment, wherein the calcination conditions include: temperature of 400-700℃ and time of 2-20h.

9. The application according to claim 8, wherein, The metal salt is a nitrate containing a metal component; And / or, the metal component is one or more of sodium, potassium, magnesium, calcium, strontium, barium and zinc.

10. The application according to claim 1, wherein, The specific surface area of ​​the short rod-shaped mesoporous molecular sieve is 300-700 m². 2 / g, pore volume is 1.3-1.8mL / g, rod length is 0.5-1µm; And / or, the specific surface area of ​​the dual-pore composite catalyst is 420-500 m². 2 / g, pore volume 0.5-1cm³ 3 / g.

11. The application according to claim 1 or 10, wherein, The preparation method of the short rod-shaped mesoporous molecular sieve includes: In the presence of a template agent, ammonium fluoride, and heptane, tetraethyl orthosilicate is contacted with an acidic aqueous solution, and the resulting mixture is crystallized, washed, filtered, dried, and the template agent is removed to obtain a short rod-shaped mesoporous molecular sieve. The template agent is a triblock copolymer polyoxyethylene-polyoxypropylene-polyoxyethylene template agent; The acidic aqueous solution is a hydrochloric acid aqueous solution; The molar ratio of the template agent, ammonium fluoride, heptane, tetraethyl orthosilicate, water, and hydrogen chloride is 1:(0.5-5):(10-200):(50-500):(3000-30000):(200-2000). The contact conditions include: a temperature of 15-60℃ and a time of 5-40h; The crystallization conditions include: a temperature of 80-130℃ and a time of 10-40h; The conditions for removing the template agent include: calcination in air atmosphere, treatment temperature 400-600℃, treatment time 6-50h.

12. The application according to claim 1 or 2, wherein, The preparation method of the dual-pore composite catalyst includes: Modified ZSM-35 molecular sieve and short rod-shaped mesoporous molecular sieve were mixed, ball-milled, and then calcined to obtain a dual-pore composite catalyst.

13. The application according to claim 12, wherein, The weight ratio of the modified ZSM-35 molecular sieve to the short rod-shaped mesoporous molecular sieve is 1:(0.4-1.2). And / or, the conditions for ball milling include: a ball rotation speed of 200-600 r / min, a temperature inside the ball mill jar of 30-90℃, and a milling time of 5-50 h; And / or, the modified ZSM-35 molecular sieve and the short rod-shaped mesoporous molecular sieve are mixed, ball-milled, and then calcined, wherein the calcination conditions include: a temperature of 450-650℃ and a time of 3-20h.

14. The application according to claim 13, wherein, The weight ratio of the modified ZSM-35 molecular sieve to the short rod-shaped mesoporous molecular sieve is 1:(0.5-1.0). And / or, the modified ZSM-35 molecular sieve and the short rod-shaped mesoporous molecular sieve are mixed, ball-milled, and then calcined, wherein the calcination conditions include: a temperature of 500-600℃ and a time of 5-10h.

15. The application according to claim 1, wherein, Waste plastic powder is reacted with a dual-pore composite catalyst under the following conditions: temperature 420-580℃, pressure 0.01-1MPa, and contact time 0.5-12h. And / or, the weight ratio of the dual-channel composite catalyst to the waste plastic powder is 1:(0.5-50).

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