Micropore-mesopore composite molecular sieve, preparation method thereof and application of micropore-mesopore composite molecular sieve in direct catalytic cracking of waste plastics to produce low-carbon olefins

Abstract

The present application relates to the field of catalyst and the field of recycling of polymer materials, and discloses a micropore-mesopore composite molecular sieve, a preparation method thereof and application of the micropore-mesopore composite molecular sieve in a reaction of direct catalytic cracking of waste plastics to produce low-carbon olefins. 2 The micropore-mesopore composite molecular sieve comprises ZSM-23 molecular sieve and two-dimensional hexagonal all-silica mesoporous molecular sieve, the specific surface area of the two-dimensional hexagonal all-silica mesoporous molecular sieve is 500-800 m 2 / g, the pore volume is 0.8-1.5 mL / g, and the average pore size is 6-9 nm; and the content of the ZSM-23 molecular sieve is 40-80 wt%, and the content of the two-dimensional hexagonal all-silica mesoporous molecular sieve is 20-60 wt% based on the total weight of the micropore-mesopore composite molecular sieve. The novel catalyst of the present application not only solves the problem of recycling of waste plastics, but also increases the production of important chemical raw material low-carbon olefins.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalysts and the field of recycling of high molecular materials, in particular, to a microporous-mesoporous composite molecular sieve, a preparation method thereof and application of the microporous-mesoporous composite molecular sieve in a reaction of direct catalytic cracking of waste plastics to produce low-carbon olefins. BACKGROUND

[0002] Since the advent of plastic products in the 20th century, they have been widely used in various fields worldwide due to their light weight, high strength, corrosion resistance, good chemical stability, easy processing, and aesthetic and practical characteristics. However, plastics are difficult to degrade naturally, and conventional landfill technology, although it has low investment and simple operation, will occupy a large amount of land and cause land pollution. Incineration technology can achieve the requirements of reduction, and also recovers part of the energy, but this process easily releases a large amount of hydrocarbons, nitrogen compounds, sulfur compounds, and toxic substances, directly threatening human and ecological environmental health. Therefore, the recycling and high-value utilization of waste plastics, as a measure to save energy and protect the environment, have been widely valued by countries around the world. The main methods for recycling and utilizing waste plastics include classification recycling, production of monomer raw materials, production of clean fuel, and power generation.

[0003] China's plastic industry is one of the pillar industries of the national economy, and China has now entered the ranks of the world's major plastic producers. Under the background of new plastic restrictions, sharp reduction in imports, and garbage classification policies, China's waste plastic recycling enterprises are gradually moving away from the old way of extensive expansion and gradually examining the industrial layout with a green development perspective. Constantly cooperating with environmental protection and sanitation enterprises, the goal of green, low-carbon, and circular development is gradually achieved. Large-scale waste plastic recycling and utilization enterprises that operate in a standardized manner will gradually further classify the recycled waste plastics, continuously develop and apply new technologies and new products for waste plastics, gradually expand the application field of waste plastics, and improve the added value of recycled plastic products. In the existing technology, the main scheme for chemical recycling of waste plastics is waste plastic cracking technology. Waste plastic cracking includes three basic methods, namely, thermal cracking (one-stage method), catalytic cracking (one-stage method), and thermal cracking-catalytic modification (two-stage method). The earliest developed waste plastic cracking technology is thermal cracking technology. This technology refers to a thermal conversion process in which high-temperature anaerobic chemical decomposition reactions occur to convert large-molecular-weight organic matter in waste plastic products into small-molecular-weight liquid matter, fuel gas, and coke. The reaction temperature of this process is generally controlled at 350-900°C. If a catalyst is added during the thermal cracking process, it is a catalytic thermal cracking technology, which not only can reduce the cracking temperature, but also can improve the product performance. Thermal cracking-catalytic modification, as an improvement of catalytic cracking, uses a catalyst to catalytically modify the cracking gas after thermal cracking of waste plastics. This method has higher product quality, flexible operation, and low operating costs than thermal cracking and catalytic cracking methods, but the process is more complex.

[0004] The waste plastic treatment by cracking technology has wide flexibility, good energy recovery, and is one of the waste plastic treatment technologies with wide application prospect. In the prior art, the products produced by one-step thermal cracking method and one-step catalytic cracking method are mainly fuel oil, and only a small amount of low-carbon olefins (ethylene, propylene, butene) can be obtained. If a large amount of low-carbon olefins is needed, a two-stage method of thermal cracking-catalytic modification method needs to be used. Therefore, exploring a new chemical recycling process to produce pure and high-quality final products is an important research direction of plastic waste treatment. SUMMARY

[0005] The purpose of the present application is to solve the problem of less low-carbon olefins in the chemical recycling of waste plastics, and to provide a micropore-mesopore composite molecular sieve, a preparation method thereof and an application thereof in the reaction of directly catalytic cracking of waste plastics to produce low-carbon olefins. The new catalyst of the present application not only solves the problem of waste plastic recycling, but also increases the production of important chemical raw material low-carbon olefins.

[0006] In order to achieve the above purpose, the first aspect of the present application provides a micropore-mesopore composite molecular sieve, wherein the micropore-mesopore composite molecular sieve comprises a ZSM-23 molecular sieve and a two-dimensional hexagonal all-silicon mesoporous molecular sieve, wherein the specific surface area of the two-dimensional hexagonal all-silicon mesoporous molecular sieve is 500-800 m 2 / g, the pore volume is 0.8-1.5 mL / g, and the average pore size is 6-9 nm; and the content of the ZSM-23 molecular sieve is 40-80 wt% and the content of the two-dimensional hexagonal all-silicon mesoporous molecular sieve is 20-60 wt% based on the total weight of the micropore-mesopore composite molecular sieve.

[0007] The second aspect of the present application provides a preparation method of the aforementioned micropore-mesopore composite molecular sieve, wherein the preparation method comprises:

[0008] (1) hydrolyzing and gelatinizing a template agent, a silicon source and an acidic aqueous solution under hydrolysis and gelatinization conditions to obtain a gel mixture; crystallizing the gel mixture; and then filtering and first drying the product obtained by crystallization to obtain a mesoporous molecular sieve raw powder;

[0009] (2) mixing the mesoporous molecular sieve raw powder with a ZSM-23 molecular sieve and performing ball milling treatment, and second drying and calcining the solid powder obtained after ball milling to obtain a micropore-mesopore composite molecular sieve.

[0010] The third aspect of the present application provides an application of the aforementioned micropore-mesopore composite molecular sieve in the reaction of directly catalytic cracking of waste plastics to produce low-carbon olefins, wherein the application comprises: contacting the powder of the waste plastics with a catalyst for reaction, and the catalyst is the aforementioned micropore-mesopore composite molecular sieve.

[0011] By the technical scheme, the technical scheme has the following advantages:

[0012] 1、The micro-pore-mesopore composite molecular sieve provided by the application includes ZSM-23 micro-pore molecular sieve with appropriate acid centers on the surface and two-dimensional hexagonal all-silicon mesopore molecular sieve with a larger pore size, and has stable structure and good high-temperature resistance, which is helpful to the diffusion of raw material and product molecules in the cracking reaction process.

[0013] 2、In the preparation process of the micro-pore-mesopore composite molecular sieve, the ZSM-23 molecular sieve and the two-dimensional hexagonal all-silicon mesopore molecular sieve are mixed, ball milled and calcined to obtain the micro-pore-mesopore composite molecular sieve with uniform distribution of micro-pore channels and mesopore channels.

[0014] 3、The micro-pore-mesopore composite molecular sieve provided by the application can convert waste plastics into low-carbon olefins in one step in the reaction of waste plastic direct catalytic cracking for low-carbon olefins, and is a new method for chemical recycling of waste plastics, which solves the problem of waste plastic recycling and increases the production of important chemical raw material low-carbon olefins, and has good economic benefits.

[0015] 4、The micro-pore-mesopore composite molecular sieve provided by the application has mild process conditions, is easy to operate, and has low requirements for the reaction device in the reaction of waste plastic direct catalytic cracking for low-carbon olefins.

[0016] Other features and advantages of the application will be described in detail in the following specific embodiment part. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings are included to provide a further understanding of the application, and constitute a part of the specification, and are used together with the following specific embodiments to explain the application, but do not constitute a limitation on the application. In the drawings:

[0018] Figure 1 is the wide-angle X-ray diffraction (XRD) spectrum of ZSM-23 molecular sieve A prepared in Example 1 of the application;

[0019] Figure 2 is the small-angle X-ray diffraction (XRD) spectrum of the micro-pore-mesopore composite molecular sieve A prepared in Example 1 of the application;

[0020] Figure 3 is the pore size distribution graph of the micro-pore-mesopore composite molecular sieve A prepared in Example 1 of the application. DETAILED DESCRIPTION

[0021] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the invention. Any numeric range recited is intended to include all values from the lower value to the upper value, inclusive of both values, and to sub-ranges falling within the stated ranges. In this context, a sub-range can be expressed as from any one value in the stated range through another value in the same range, inclusive of the values.

[0022] As described above, the first aspect of the present application provides a micro-mesoporous composite molecular sieve, wherein the micro-mesoporous composite molecular sieve comprises a ZSM-23 molecular sieve and a two-dimensional hexagonal all-silica mesoporous molecular sieve, wherein the two-dimensional hexagonal all-silica mesoporous molecular sieve has a specific surface area of 500-800 m 2 / g, a pore volume of 0.8-1.5 mL / g, and an average pore size of 6-9 nm; and the content of the ZSM-23 molecular sieve is 40-80 wt%, and the content of the two-dimensional hexagonal all-silica mesoporous molecular sieve is 20-60 wt% based on the total weight of the micro-mesoporous composite molecular sieve.

[0023] The inventors of the present application found that there is no process for directly catalytic cracking of waste plastics to produce low-carbon olefins (including ethylene, propylene, butene) in the prior art, and the purpose of the present application is to solve this problem. According to the understanding of the physical and chemical properties of heterogeneous catalysts by the inventors, the catalyst for directly preparing low-carbon olefins by catalytic cracking of waste plastics should have a certain acidity. In addition, the waste plastic catalytic cracking catalyst needs to have good thermal stability. ZSM-23 molecular sieve not only has appropriate acidity, but also has good thermal stability (the crystal phase can still remain stable after high-temperature calcination at 650℃), and is a relatively suitable waste plastic catalytic cracking catalyst. However, ZSM-23 molecular sieve has MTT topology and has one-dimensional pores composed of ten-membered rings, and the pore size is only 0.56 nm x 0.45 nm. Since ZSM-23 is a microporous molecular sieve with small pore size, it seriously limits the improvement of the catalytic performance of ZSM-23 molecular sieve. The molecular weight of waste plastic products is large, and the molecular chain is also relatively long. During the cracking reaction of waste plastic products, the diffusion of reactant molecules and product molecules with large size in the narrow pore is difficult, which not only affects the contact between the reactants and the active centers, but also easily leads to the occurrence of deep dehydrogenation and other side reactions, thereby causing the performance of the catalyst to decrease. Compared with microporous molecular sieves, two-dimensional hexagonal all-silica mesoporous molecular sieve material has larger pore size (pore size between 6-9 nm) and larger pore volume (can reach 0.8 cm 3 / g or more, and is very suitable for catalytic reactions involving macromolecules. However, the two-dimensional hexagonal all-silica mesoporous molecular sieve is an all-silica material, and the surface thereof contains only a small amount of silanol groups, and the acidity is extremely weak, and is not suitable for catalyzing waste plastic cracking reactions alone as a catalyst. The inventors of the present application found, in the development and research of waste plastic cracking catalysts, that if the structural advantages of the all-silica mesoporous inorganic material and the surface acid center of the microporous molecular sieve are comprehensively utilized, a certain amount of two-dimensional hexagonal all-silica mesoporous molecular sieve and ZSM-23 molecular sieve are mixed, the specific surface area and pore volume of the catalyst can be effectively improved, and the internal diffusion performance in the reaction can be significantly improved. When applied to the catalytic conversion reaction of waste plastics as a cracking catalyst, the activity of the cracking catalyst can be effectively improved, and the selectivity of low-carbon olefins can be increased.

[0024] According to the present application, preferably, the content of the ZSM-23 molecular sieve is 50-70 wt%, and the content of the two-dimensional hexagonal all-silica mesoporous molecular sieve is 30-50 wt%, based on the total weight of the microporous-mesoporous composite molecular sieve; more preferably, the content of the ZSM-23 molecular sieve is 55-65 wt%, and the content of the two-dimensional hexagonal all-silica mesoporous molecular sieve is 35-45 wt%, based on the total weight of the microporous-mesoporous composite molecular sieve. In the present application, the use of the specific content of each component can make the microporous-mesoporous composite molecular sieve prepared in the present application have better catalytic activity and higher selectivity of low-carbon olefins when used in the reaction of preparing low-carbon olefins by direct catalytic cracking of waste plastics.

[0025] According to the present application, the specific surface area of the microporous-mesoporous composite molecular sieve is 290-440 m 2 / g, the pore volume is 0.8-1 mL / g, the pore size distribution is bimodal distribution, and the most probable pore diameters corresponding to the bimodal distribution are 0.4-0.7 nm and 5-10 nm, respectively; preferably, the specific surface area of the microporous-mesoporous composite molecular sieve is 320-400 m 2 / g, the pore volume is 0.85-0.93 mL / g, the pore size distribution is bimodal distribution, and the most probable pore diameters corresponding to the bimodal distribution are 0.5-0.6 nm and 6-9 nm, respectively; more preferably, the specific surface area of the microporous-mesoporous composite molecular sieve is 337-380 m 2 / g, the pore volume is 0.86-0.9 mL / g, the pore size distribution is bimodal distribution, and the most probable pore diameters corresponding to the bimodal distribution are 0.5-0.6 nm and 7-8 nm, respectively. In the present application, the microporous-mesoporous composite molecular sieve has the specific structural parameters described above, and can have better catalytic activity and higher selectivity of low-carbon olefins when used in the reaction of preparing low-carbon olefins by direct catalytic cracking of waste plastics.

[0026] According to the present application, the SiO2 / Al2O3 molar ratio of the ZSM-23 molecular sieve can be 90-130, preferably 100-120.

[0027] According to the present application, the ZSM-23 molecular sieve can be commercially available or laboratory prepared, in the present application, the ZSM-23 molecular sieve can be prepared by the following method:

[0028] At room temperature, dimethylamine and aluminum sulfate are dissolved in a certain amount of distilled water to prepare solution A; silica sol and aqueous alkali solution are mixed to prepare solution B. Solution A is slowly added to solution B, stirred for 5 h to obtain a gel mixture; the gel mixture is subjected to crystallization treatment, followed by filtration, washing, drying and calcination treatment to obtain the ZSM-23 molecular sieve.

[0029] According to the present application, in the preparation method of the ZSM-23 molecular sieve, the alkali is preferably sodium hydroxide or potassium hydroxide.

[0030] According to the present application, in the preparation method of the ZSM-23 molecular sieve, the molar ratio of aluminum sulfate, dimethylamine, silica sol (calculated as SiO2), alkali (calculated as OH - ) and water is 1:(55-100):(90-130):(8-16):(2500-4500), preferably 1:(65-85):(100-120):(10-14):(3000-4000).

[0031] According to the present application, in the preparation method of the ZSM-23 molecular sieve, the crystallization process can be carried out in a hydrothermal reaction kettle equipped with a polytetrafluoroethylene lining, and the crystallization conditions are as follows: crystallization temperature 140-180℃, crystallization time 24-72h; preferably, the temperature is 150-170℃ and the time is 40-60h. Preferably, in order to achieve better crystallization effect, rapid stirring is required during the crystallization process.

[0032] According to the present application, in the preparation method of the ZSM-23 molecular sieve, the washing conditions are not particularly limited, for example, the washing process can include: after filtration, the solid product is repeatedly washed (the number of washing times can be 2-10) with distilled water, and then suction filtration is performed.

[0033] According to the present application, in the preparation method of the ZSM-23 molecular sieve, the drying conditions can be: drying temperature 60-150℃, drying time 3-20h; preferably, the temperature is 80-130℃ and the time is 5-16h.

[0034] According to the present application, the preparation method of the ZSM-23 molecular sieve, the calcination conditions can be: the calcination temperature is 450-650℃, the calcination time is 5-30h; preferably, the temperature is 500-600℃, and the time is 8-20h.

[0035] The second aspect of the present application provides a preparation method of the micropore-mesopore composite molecular sieve.

[0036] (1) under the hydrolysis gel preparation condition, the template agent, the silicon source and the acidic aqueous solution are hydrolyzed to prepare a gel mixture; the gel mixture is crystallized; then the product obtained by the crystallization is filtered and subjected to a first drying treatment to obtain a mesopore molecular sieve raw powder;

[0037] (2) the mesopore molecular sieve raw powder is mixed with the ZSM-23 molecular sieve and subjected to a ball milling treatment, and the solid powder obtained after the ball milling is subjected to a second drying and calcination treatment to obtain the micropore-mesopore composite molecular sieve.

[0038] The inventors of the present application find that: by mixing a certain amount of two-dimensional hexagonal all-silicon mesopore molecular sieve with ZSM-23 molecular sieve, the specific surface area and the pore volume of the catalyst can be effectively improved, and the internal diffusion performance in the reaction can be significantly improved. However, if the two prepared molecular sieves are mechanically mixed, the micropore channels and the mesopore channels in the mixed molecular sieve are not uniformly distributed, and the effect of improving the diffusion performance is not enough. In the present application, the mesopore molecular sieve raw powder (two-dimensional hexagonal all-silicon mesopore molecular sieve raw powder) is mixed with the ZSM-23 molecular sieve, and then subjected to a ball milling and calcination treatment to obtain the micropore-mesopore composite molecular sieve. The composite molecular sieve obtained by this method has uniform distribution of micropore channels and mesopore channels, and has high catalytic activity and high selectivity of low-carbon olefins when used in the catalytic cracking reaction of waste plastics.

[0039] According to the present application, in step (1), the template agent is a nonionic surfactant, preferably low, and the general formula of the template agent is EO a PO b EO a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer, and more preferably P123 (EO 20 PO 70 EO 20 ).

[0040] According to the present application, in step (1), the silicon source is an organic silicon ester or an inorganic silicon source, and is preferably one or more of methyl orthosilicate, ethyl orthosilicate, water glass and sodium metasilicate.

[0041] According to the present application, in step (1), the acidic aqueous solution is one or more of hydrochloric acid, aqueous sulfuric acid and aqueous nitric acid, preferably aqueous hydrochloric acid; the molar concentration of the solute in the acidic aqueous solution is 0.5-3 mol / L, preferably 1-2 mol / L.

[0042] According to the present application, in step (1), the molar ratio of the template agent, the silicon source, the acid in the acidic aqueous solution to the water in the acidic aqueous solution is 1:(40-100):(120-400):(6000-10000), preferably 1:(50-80):(150-300):(7000-9500).

[0043] According to the present application, in step (1), the hydrolysis and gelation conditions include: temperature of 20-60℃, preferably 30-50℃; time of 12-36h, preferably 18-30h.

[0044] According to the present application, in step (1), the crystallization conditions include: crystallization temperature of 70-150℃, preferably 80-120℃; crystallization time of 8-72h, preferably 20-30h. It is well known to those skilled in the art that the crystallization is generally carried out in a hydrothermal kettle, which will not be described here.

[0045] According to the present application, in step (1), there is no special requirement for the filtration process, which can be a filtration mode known in the art, including gravity filtration, pressure filtration, vacuum filtration or centrifugal filtration. Preferably, the filtration process specifically includes: using a suction filter bottle, vacuumizing the bottom side of the funnel or using a centrifugal filter to filter.

[0046] According to the present application, in step (1), the first drying temperature is 70-120℃, and the time is 3-10h.

[0047] According to the present application, in step (2), the weight ratio of the mesoporous molecular sieve raw powder to the ZSM-23 molecular sieve is 1:(0.3-5), preferably 1:(0.5-3).

[0048] According to the present application, in step (2), the ball milling is carried out in a ball mill, wherein the diameter of the milling balls in the ball mill can be 2-3mm; the number of the milling balls can be reasonably selected according to the size of the ball milling tank, and for a ball milling tank with a size of 100-300mL, 2-8 milling balls are usually used; the material of the milling balls is agate or polytetrafluoroethylene, preferably agate. The ball milling conditions include: the rotation speed of the milling balls can be 200-600r / min, preferably 300-500r / min; the temperature in the ball milling tank can be 30-90℃, preferably 40-80℃; the ball milling time can be 5-50h, preferably 8-24h.

[0049] According to the application, in step (2), the temperature of the second drying is 70-150℃, and the time is 3-20h.

[0050] According to the application, in step (2), the calcination conditions include: the calcination temperature is 450-650℃, preferably 500-600℃; and the calcination time is 5-30h, preferably 8-20h.

[0051] The third aspect of the application provides an application of the aforementioned micropore-mesopore composite molecular sieve in a reaction of direct catalytic cracking of waste plastics to produce low-carbon olefins, wherein the application includes: contacting the powder of the waste plastics with a catalyst to perform the reaction, and the catalyst is the aforementioned micropore-mesopore composite molecular sieve.

[0052] In the application, the conditions of contacting the waste plastic powder with the micropore-mesopore composite molecular sieve include: the temperature of the contacting can be 420-580℃, preferably 450-540℃; the pressure of the contacting can be 0.01-3MPa, preferably 0.01-1Mpa, and more preferably 0.05-0.5Mpa; the time of the contacting can be 0.5-12h, preferably 1-5h; and the weight ratio of the micropore-mesopore composite molecular sieve to the waste plastic powder can be 1:(0.5-50), preferably 1:(2-30).

[0053] The application will be described in detail below through examples.

[0054] In the following examples and comparative examples:

[0055] The small-angle XRD test of the sample was performed on a D8 ADVANCE high-power rotating target X-ray diffractometer of BRUKER AXS Company in Germany, and the scanning range was 0.5-10°.

[0056] The wide-angle XRD test of the sample was performed on an X'Pert MPD X-ray powder diffractometer of Philips Company in the Netherlands, Cu Kα target, and the scanning range 2θ=5-90°.

[0057] The pore structure parameter analysis of the sample was performed on an ASAP2020-M+C adsorptometer purchased from Micromeritics Company in the United States. The sample was vacuum degassed at 350℃ for 4h before determination, the specific surface area of the sample was calculated by BET method, and the pore volume was calculated by BJH model.

[0058] The elemental analysis experiment of the sample was performed on an Eagle III energy dispersive X-ray fluorescence spectrometer produced by EDAX Company in the United States.

[0059] The drying oven is produced by Shanghai Yiheng Scientific Instrument Co., Ltd., and the model number is DHG-9030A.

[0060] The muffle furnace is produced by CARBOLITE Co., Ltd., and the model number is CWF1100.

[0061] P123 used in the examples and comparative examples is purchased from Aldrich Co., Ltd., and other reagents used in the examples and comparative examples are purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., and the purity of the reagents is analytical pure.

[0062] Example 1

[0063] (1) Preparation of ZSM-23 molecular sieve

[0064] At room temperature, dimethylamine and aluminum sulfate were dissolved in distilled water, stirred for 24 h, and prepared into a clear solution A; silica sol and an aqueous solution of sodium hydroxide were mixed to prepare a mixed solution B. The molar ratio of the aluminum sulfate, dimethylamine, silica sol (calculated as SiO2), sodium hydroxide and water is 1:75:110:12:3500. Solution A was slowly added to solution B, and stirring was continued for 5 h to obtain a gel mixture; the gel mixture was transferred to a hydrothermal reaction kettle with a polytetrafluoroethylene liner, and crystallization treatment was carried out under stirring. The crystallization temperature was 160℃, and the crystallization time was 50 h. After the crystallization was completed, the solid material was filtered. The solid was washed with distilled water for 8 times, dried at 110℃ for 10 h, and then calcined at 550℃ for 12 h to obtain ZSM-23 molecular sieve A.

[0065] The specific surface area of ZSM-23 molecular sieve A is 234 m 2 / g, the pore volume is 0.75 cm 3 / g, and the most probable pore size is 0.55 nm.

[0066] Figure 1 is the wide-angle X-ray diffraction (XRD) spectrum of ZSM-23 molecular sieve A. The spectrum Figure 1 shows that the wide-angle x-ray diffraction angles of the sample are mainly: 2θ = 7.9°, 8.2°, 11.4°, 19.7°, 21.1°, 23.0°, 24.0°, 24.2° and 24.8°. The above diffraction signals are consistent with the ZSM-23 molecular sieve diffraction spectrum. This indicates that the synthesized ZSM-23 molecular sieve A has a typical MTT framework structure.

[0067] (2) Preparation of two-dimensional hexagonal all-silicon mesoporous molecular sieve raw powder

[0068] Put 120 g of non-ionic surfactant P123 into 3000 g of 2 M aqueous hydrochloric acid solution, stir at 40°C for 1 h; add 256 g of tetraethyl orthosilicate to the above solution, stir at 40°C for 24 h; transfer the above mixture to a hydrothermal kettle, hydrothermally crystallize at 100°C for 24 h. After the hydrothermal reaction is completed, separate the solid product from the mother liquor, wash with deionized water until neutral, and dry at 110°C for 5 h to obtain two-dimensional hexagonal all-silica mesoporous molecular sieve crude powder A.

[0069] (3) Preparation of microporous-mesoporous composite molecular sieve

[0070] Put 60 g of ZSM-23 molecular sieve A and 68 g of the above two-dimensional hexagonal all-silica mesoporous molecular sieve crude powder A into a 300 ml ball mill jar, wherein the material of the ball mill jar is polytetrafluoroethylene, the material of the grinding ball is agate, the diameter of the grinding ball is 2 mm, the number of the grinding ball is 5, and the rotation speed is 400 r / min. Close the ball mill jar, and ball mill at a temperature of 60°C in the ball mill jar for 12 h to obtain a solid powder; dry the solid powder at 110°C for 10 h, and then calcine at 550°C for 16 h to obtain microporous-mesoporous composite molecular sieve A.

[0071] The content of ZSM-23 molecular sieve A is 60% by weight, and the content of two-dimensional hexagonal all-silica mesoporous molecular sieve A is 40% by weight, based on the total weight of microporous-mesoporous composite molecular sieve A.

[0072] The specific surface area of microporous-mesoporous composite molecular sieve A is 367 m 2 / g, and the pore volume is 0.89 cm 3 / g.

[0073] Figure 2 is the small-angle XRD pattern of microporous-mesoporous composite molecular sieve A. The spectrum Figure 2 shows that there is a strong diffraction signal between 2θ = 0.6°-1°, corresponding to the (110) crystal face; there are two clear diffraction signals between 2θ = 1°-2°, indicating that the sample contains two-dimensional hexagonal mesoporous channels. In addition, the diffraction peak intensity of the (110) crystal face is high, and the peak shape is narrow, indicating that the mesoporous structure in the sample has good long-range order.

[0074] Figure 3 is the pore size distribution graph of microporous-mesoporous composite molecular sieve A. The spectrum Figure 3 shows that the sample has obvious dual-channel structure, and the most probable pore diameters of the dual pores are 0.55 nm and 7.5 nm, respectively. Among them, the microporous channel with a pore diameter of 0.55 nm is provided by ZSM-23 molecular sieve, and the mesoporous channel with a pore diameter of 7.5 nm is provided by two-dimensional hexagonal all-silica mesoporous molecular sieve.

[0075] (4) Performance evaluation of direct conversion of waste plastics to low-carbon olefins

[0076] The waste plastic catalytic cracking reaction performance evaluation of the microporous-mesoporous composite molecular sieve A was carried out on a fixed bed reaction device. The microporous-mesoporous composite molecular sieve A loading amount was 6 grams, the polyethylene waste plastic loading amount was 40g, the reaction temperature was 520℃, the reaction pressure was 0.1MPa, the reaction time was 2 hours, after the product was cooled and gas-liquid separation, the gas composition was analyzed by Agilent 6890 gas chromatograph equipped with Al2O3-S capillary chromatographic column and hydrogen flame detector (FID), and the quantitative analysis was carried out by using the programmed temperature and the correction factor; the liquid composition was analyzed by Agilent 6890 gas chromatograph equipped with PONA chromatographic column. The reaction results are shown in Table 1.

[0077] Example 2

[0078] (1) Preparation of ZSM-23 molecular sieve

[0079] At room temperature, dimethylamine and aluminum sulfate were dissolved in distilled water, stirred for 24h, and prepared into a clear solution A; silica sol and aqueous sodium hydroxide solution were mixed to prepare a mixed solution B. The molar ratio of the aluminum sulfate, dimethylamine, silica sol (calculated as SiO2), sodium hydroxide and water was 1:65:100:10:3000. Solution A was slowly added to solution B, and stirring was continued for 5h to obtain a gel mixture; the above gel mixture was transferred to a hydrothermal reaction kettle with a polytetrafluoroethylene liner, and crystallization treatment was carried out under stirring. The crystallization temperature was 150℃, and the crystallization time was 60h. After the crystallization was completed, the solid material was obtained by filtration. The solid was washed with distilled water for 5 times, dried at 80℃ for 16h, and then calcined at 500℃ for 20h to obtain ZSM-23 molecular sieve B.

[0080] The specific surface area of ZSM-23 molecular sieve B was 226m 2 / g, the pore volume was 0.73cm 3 / g, and the most probable pore diameter was 0.53nm.

[0081] (2) Preparation of two-dimensional hexagonal all-silicon mesoporous molecular sieve raw powder

[0082] 153g of non-ionic surfactant P123 was added to 2000g of 1M hydrochloric acid aqueous solution, and stirred at 30℃ for 1h; 200g of methyl orthosilicate was added to the above solution, and stirred at 30℃ for 30h; the above mixture was transferred to a hydrothermal kettle, and hydrothermally crystallized at 110℃ for 20h. After the hydrothermal reaction was completed, the solid product was separated from the mother liquor, washed with deionized water until neutral, and dried at 120℃ for 3h to obtain two-dimensional hexagonal all-silicon mesoporous molecular sieve raw powder B.

[0083] (3) Preparation of microporous-mesoporous composite molecular sieve

[0084] Put 55 g of ZSM-23 molecular sieve B and 69 g of the above two-dimensional hexagonal all-silica mesoporous molecular sieve B raw powder into a 300 ml ball mill tank, wherein the material of the ball mill tank is polytetrafluoroethylene, the material of the grinding ball is agate, the diameter of the grinding ball is 2 mm, the number is 4, and the rotating speed is 500 r / min. Close the ball mill tank, and mill in the ball mill tank at a temperature of 40 ℃ for 24 h to obtain a solid powder; dry the solid powder at 70 ℃ for 20 h, and then calcine at 500 ℃ for 20 h to obtain the microporous-mesoporous composite molecular sieve B.

[0085] The content of the ZSM-23 molecular sieve B is 55% by weight, and the content of the two-dimensional hexagonal all-silica mesoporous molecular sieve B is 45% by weight, based on the total weight of the microporous-mesoporous composite molecular sieve B.

[0086] The specific surface area of the microporous-mesoporous composite molecular sieve B is 380 m 2 / g, and the pore volume is 0.90 cm 3 / g.

[0087] (4) Performance evaluation of the reaction of directly converting waste plastics into low-carbon olefins

[0088] The reaction performance of the microporous-mesoporous composite molecular sieve B was tested according to the performance evaluation method of the reaction of directly converting waste plastics into low-carbon olefins in step (4) in Example 1, and the evaluation results are listed in Table 1.

[0089] Example 3

[0090] (1) Preparation of ZSM-23 molecular sieve

[0091] At room temperature, dimethylamine and aluminum sulfate were dissolved in distilled water, stirred for 24 h, and prepared into a clear solution A; a silica sol and an aqueous solution of sodium hydroxide were mixed to prepare a mixed solution B. The molar ratio of the aluminum sulfate, dimethylamine, silica sol (calculated as SiO2), sodium hydroxide and water was 1:85:120:14:4000. Solution A was slowly added to solution B, and stirring was continued for 5 h to obtain a gel mixture; the gel mixture was transferred to a hydrothermal reaction kettle with a polytetrafluoroethylene liner, and a crystallization treatment was performed under stirring. The crystallization temperature was 170 ℃, and the crystallization time was 40 h. After the crystallization was completed, a solid material was obtained by filtration. The solid was washed with distilled water for 10 times, dried at 130 ℃ for 5 h, and then calcined at 600 ℃ for 8 h to obtain the ZSM-23 molecular sieve C.

[0092] The specific surface area of the ZSM-23 molecular sieve C was 238 m 2 / g, the pore volume was 0.79 cm 3 / g, and the most probable pore diameter was 0.57 nm.

[0093] (2) Preparation of two-dimensional hexagonal all-silica mesoporous molecular sieve raw powder

[0094] 80 g of non-ionic surfactant P123 was added into 4000 g of 1.5 M aqueous hydrochloric acid solution, and stirred at 50 ℃ for 1 h; 175 g of water glass with a concentration of 28.26% was added into the above solution, and stirred at 50 ℃ for 18 h; the above mixture was transferred into an autoclave, and hydrothermally crystallized at 90 ℃ for 30 h. After the hydrothermal reaction was completed, the solid product was separated from the mother liquor, washed with deionized water until neutral, and dried at 70 ℃ for 10 h to obtain two-dimensional hexagonal all-silica mesoporous molecular sieve powder C.

[0095] (3) Preparation of microporous-mesoporous composite molecular sieve

[0096] 65 g of ZSM-23 molecular sieve C and 52 g of the above two-dimensional hexagonal all-silica mesoporous molecular sieve powder C were mixed and placed into a 300 ml ball mill jar, wherein the material of the ball mill jar was polytetrafluoroethylene, the material of the grinding ball was agate, the diameter of the grinding ball was 2 mm, the number of the grinding ball was 8, and the rotation speed was 300 r / min. The ball mill jar was closed, and the solid powder was obtained by ball milling at 80 ℃ for 8 h in the ball mill jar; the solid powder was dried at 150 ℃ for 3 h, and then calcined at 600 ℃ for 8 h to obtain microporous-mesoporous composite molecular sieve C.

[0097] The content of ZSM-23 molecular sieve C was 65% by weight, and the content of two-dimensional hexagonal all-silica mesoporous molecular sieve C was 35% by weight, based on the total weight of microporous-mesoporous composite molecular sieve C.

[0098] The specific surface area of microporous-mesoporous composite molecular sieve C was 337 m 2 / g, and the pore volume was 0.86 cm 3 / g.

[0099] (4) Evaluation of the reaction performance of direct conversion of waste plastics to low-carbon olefins

[0100] The reaction performance of microporous-mesoporous composite molecular sieve C was tested according to the evaluation method of the reaction performance of direct conversion of waste plastics to low-carbon olefins in step (4) of Example 1, and the evaluation results are shown in Table 1.

[0101] Example 4

[0102] (1) Preparation of ZSM-23 molecular sieve

[0103] Dissolve dimethylamine and aluminum sulfate in distilled water under room temperature, stir for 24 h to prepare a clear solution A; mix silica sol and aqueous sodium hydroxide solution to prepare a mixed solution B. The molar ratio of aluminum sulfate, dimethylamine, silica sol (calculated as SiO2), sodium hydroxide and water is 1:75:90:12:3500. Slowly drop solution A into solution B, continue to stir for 5 h to obtain a gel mixture; transfer the gel mixture into a hydrothermal reactor with a polytetrafluoroethylene liner, and perform crystallization treatment under stirring. The crystallization temperature is 160°C, and the crystallization time is 50 h. After the crystallization is completed, filter to obtain a solid. Wash the solid with distilled water for 8 times, dry at 110°C for 10 h, and then calcine at 550°C for 12 h to obtain ZSM-23 molecular sieve D.

[0104] (2) Preparation of two-dimensional hexagonal all-silica mesoporous molecular sieve crude powder

[0105] Prepare two-dimensional hexagonal all-silica mesoporous molecular sieve crude powder A according to the method of step (2) in Example 1.

[0106] (3) Preparation of microporous-mesoporous composite molecular sieve

[0107] Put 50 g of ZSM-23 molecular sieve D and 85 g of the above two-dimensional hexagonal all-silica mesoporous molecular sieve crude powder A into a 300 ml ball mill jar, wherein the material of the ball mill jar is polytetrafluoroethylene, the material of the grinding ball is agate, the diameter of the grinding ball is 2 mm, the number of the grinding ball is 5, and the rotating speed is 400 r / min. Close the ball mill jar, and mill at a temperature of 60°C in the ball mill jar for 12 h to obtain a solid powder; dry the solid powder at 110°C for 10 h, and then calcine at 550°C for 16 h to obtain microporous-mesoporous composite molecular sieve D.

[0108] The content of ZSM-23 molecular sieve D is 50% by weight, and the content of two-dimensional hexagonal all-silica mesoporous molecular sieve A is 50% by weight, based on the total weight of microporous-mesoporous composite molecular sieve D.

[0109] The specific surface area of microporous-mesoporous composite molecular sieve D is 400 m 2 / g, and the pore volume is 0.93 cm 3 / g.

[0110] (4) Performance evaluation of direct conversion of waste plastics to low-carbon olefins

[0111] The reaction performance of catalyst D was tested according to the performance evaluation method of direct conversion of waste plastics to low-carbon olefins in step (4) of Example 1, and the evaluation results are shown in Table 1.

[0112] Example 5

[0113] (1) Preparation of ZSM-23 molecular sieve

[0114] At room temperature, dimethylamine and aluminum sulfate were dissolved in distilled water, stirred for 24 h to prepare a clear solution A; silica sol was mixed with an aqueous solution of sodium hydroxide to prepare a mixed solution B. The molar ratio of aluminum sulfate, dimethylamine, silica sol (calculated as SiO2), sodium hydroxide and water was 1:85:130:14:4000. Solution A was slowly added to solution B, and stirring was continued for 5 h to obtain a gel mixture; the gel mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner, and crystallization was carried out under stirring. The crystallization temperature was 170°C, and the crystallization time was 40 h. After crystallization, the solid was filtered. The solid was washed with distilled water for 10 times, dried at 130°C for 5 h, and then calcined at 600°C for 8 h to obtain ZSM-23 molecular sieve E.

[0115] (2) Preparation of two-dimensional hexagonal all-silica mesoporous molecular sieve raw powder

[0116] The two-dimensional hexagonal all-silica mesoporous molecular sieve C was prepared according to the method of step (2) in Example 3.

[0117] (3) Preparation of microporous-mesoporous composite molecular sieve

[0118] 70 g of ZSM-23 molecular sieve E and 45 g of the above two-dimensional hexagonal all-silica mesoporous molecular sieve raw powder C were mixed and placed in a 300 ml ball mill jar. The material of the ball mill jar was polytetrafluoroethylene, the material of the grinding ball was agate, the diameter of the grinding ball was 2 mm, the number of the grinding ball was 8, and the rotation speed was 300 r / min. The ball mill jar was closed, and the temperature in the ball mill jar was 80°C. The solid powder was obtained by ball milling for 8 h. The solid powder was dried at 150°C for 3 h, and then calcined at 600°C for 8 h to obtain the microporous-mesoporous composite molecular sieve E.

[0119] Based on the total weight of the microporous-mesoporous composite molecular sieve E, the content of ZSM-23 molecular sieve E was 70 wt%, and the content of two-dimensional hexagonal all-silica mesoporous molecular sieve C was 30 wt%.

[0120] The specific surface area of the microporous-mesoporous composite molecular sieve E was 323 m 2 / g, and the pore volume was 0.85 cm 3 / g.

[0121] (4) Evaluation of the reaction performance of the direct conversion of waste plastics to low-carbon olefins

[0122] The reaction performance of the microporous-mesoporous composite molecular sieve E was tested according to the method for evaluating the reaction performance of the direct conversion of waste plastics to low-carbon olefins in step (4) in Example 1, and the evaluation results are shown in Table 1.

[0123] Example 6

[0124] (1) Preparation of ZSM-23 molecular sieve

[0125] ZSM-23 molecular sieve D was prepared according to the method of step (1) in Example 4.

[0126] (2) Preparation of two-dimensional hexagonal all-silica mesoporous molecular sieve powder

[0127] Two-dimensional hexagonal all-silica mesoporous molecular sieve powder A was prepared according to the method of step (2) in Example 1.

[0128] (3) Preparation of microporous-mesoporous composite molecular sieve

[0129] 40 g of ZSM-23 molecular sieve D and 102 g of the above two-dimensional hexagonal all-silica mesoporous molecular sieve powder A were mixed and placed in a 300 ml ball mill tank, wherein the material of the ball mill tank was polytetrafluoroethylene, the material of the grinding ball was agate, the diameter of the grinding ball was 2 mm, the number was 5, and the rotation speed was 400 r / min. The ball mill tank was closed, and the solid powder was obtained by ball milling at a temperature of 60 ℃ in the ball mill tank for 12 h; the solid powder was dried at 110 ℃ for 10 h, and then calcined at 550 ℃ for 16 h to obtain microporous-mesoporous composite molecular sieve F.

[0130] Based on the total weight of the microporous-mesoporous composite molecular sieve F, the content of ZSM-23 molecular sieve D was 40 wt%, and the content of two-dimensional hexagonal all-silica mesoporous molecular sieve A was 60 wt%.

[0131] The specific surface area of the microporous-mesoporous composite molecular sieve F was 434 m 2 / g, and the pore volume was 0.96 cm 3 / g.

[0132] (4) Performance evaluation of direct conversion of waste plastics to low-carbon olefins

[0133] The reaction performance of catalyst F was tested according to the performance evaluation method of direct conversion of waste plastics to low-carbon olefins in step (4) in Example 1, and the evaluation results are shown in Table 1.

[0134] Example 7

[0135] (1) Preparation of ZSM-23 molecular sieve

[0136] ZSM-23 molecular sieve E was prepared according to the method of step (1) in Example 5.

[0137] (2) Preparation of two-dimensional hexagonal all-silica mesoporous molecular sieve powder

[0138] Two-dimensional hexagonal all-silica mesoporous molecular sieve C was prepared according to the method of step (2) in Example 3.

[0139] (3) Preparation of microporous-mesoporous composite molecular sieve

[0140] 80 g of ZSM-23 molecular sieve E was mixed with 30 g of the above two-dimensional hexagonal all-silica mesoporous molecular sieve powder C in a 300 ml ball mill tank, wherein the material of the ball mill tank was polytetrafluoroethylene, the material of the grinding ball was agate, the diameter of the grinding ball was 2 mm, the number was 8, and the rotating speed was 300 r / min. The ball mill tank was closed, and the solid powder was obtained by ball milling at 80 ℃ for 8 h in the ball mill tank; the solid powder was dried at 150 ℃ for 3 h, and then calcined at 600 ℃ for 8 h to obtain the microporous-mesoporous composite molecular sieve G.

[0141] The content of the ZSM-23 molecular sieve E was 80 wt%, and the content of the two-dimensional hexagonal all-silica mesoporous molecular sieve C was 20 wt% based on the total weight of the microporous-mesoporous composite molecular sieve G.

[0142] The specific surface area of the microporous-mesoporous composite molecular sieve G was 295 m 2 / g, and the pore volume was 0.83 cm 3 / g.

[0143] (4) Evaluation of the reaction performance of the direct conversion of waste plastics to low-carbon olefins

[0144] The reaction performance of the microporous-mesoporous composite molecular sieve G was tested according to the evaluation method of the reaction performance of the direct conversion of waste plastics to low-carbon olefins in step (4) of Example 1, and the evaluation results are shown in Table 1.

[0145] Comparative Example 1

[0146] (1) Preparation of ZSM-23 molecular sieve

[0147] The ZSM-23 molecular sieve A was prepared according to the method in step (1) of Example 1.

[0148] (2) Preparation of two-dimensional hexagonal all-silica mesoporous molecular sieve powder

[0149] The two-dimensional hexagonal all-silica mesoporous molecular sieve powder A was prepared according to the method in step (2) of Example 1.

[0150] (3) Preparation of microporous-mesoporous composite molecular sieve

[0151] 15 g of ZSM-23 molecular sieve A was mixed with 145 g of the above two-dimensional hexagonal all-silica mesoporous molecular sieve powder A in a 300 ml ball mill tank, wherein the material of the ball mill tank was polytetrafluoroethylene, the material of the grinding ball was agate, the diameter of the grinding ball was 2 mm, the number was 5, and the rotating speed was 400 r / min. The ball mill tank was closed, and the solid powder was obtained by ball milling at 60 ℃ for 12 h in the ball mill tank; the solid powder was dried at 110 ℃ for 10 h, and then calcined at 550 ℃ for 16 h to obtain the microporous-mesoporous composite molecular sieve D1.

[0152] The content of the ZSM-23 molecular sieve A was 15% by weight, and the content of the two-dimensional hexagonal all-silica mesoporous molecular sieve A was 85% by weight, based on the total weight of the microporous-mesoporous composite molecular sieve D1.

[0153] The specific surface area of the microporous-mesoporous composite molecular sieve D1 was 517 m2 / g, and the pore volume was 1.05 cm3 / g. 2 3 The specific surface area of the microporous-mesoporous composite molecular sieve D1 was 517 m2 / g, and the pore volume was 1.05 cm3 / g.

[0154] (4) Reaction performance evaluation of direct conversion of waste plastics to low-carbon olefins

[0155] The reaction performance of the microporous-mesoporous composite molecular sieve D1 was tested according to the method for evaluating the reaction performance of direct conversion of waste plastics to low-carbon olefins in step (4) in Example 1, and the evaluation results are listed in Table 1.

[0156] Comparative Example 2

[0157] (1) Preparation of ZSM-23 molecular sieve

[0158] The ZSM-23 molecular sieve C was prepared according to the method in step (1) in Example 3.

[0159] (2) Preparation of two-dimensional hexagonal all-silica mesoporous molecular sieve raw powder

[0160] The two-dimensional hexagonal all-silica mesoporous molecular sieve raw powder C was prepared according to the method in step (2) in Example 3.

[0161] (3) Preparation of microporous-mesoporous composite molecular sieve

[0162] 92 g of the ZSM-23 molecular sieve C and 12 g of the above two-dimensional hexagonal all-silica mesoporous molecular sieve raw powder C were mixed and placed in a 300 ml ball mill tank, wherein the material of the ball mill tank was polytetrafluoroethylene, the material of the grinding ball was agate, the diameter of the grinding ball was 2 mm, the number of the grinding ball was 8, and the rotation speed was 300 r / min. The ball mill tank was closed, and the solid powder was obtained by ball milling at 80 ℃ for 8 h in the ball mill tank; the solid powder was dried at 150 ℃ for 3 h, and then calcined at 600 ℃ for 8 h to obtain the microporous-mesoporous composite molecular sieve D2.

[0163] The content of the ZSM-23 molecular sieve C was 92% by weight, and the content of the two-dimensional hexagonal all-silica mesoporous molecular sieve C was 8% by weight, based on the total weight of the microporous-mesoporous composite molecular sieve D2.

[0164] The specific surface area of the microporous-mesoporous composite molecular sieve D2 was 261 m2 / g, and the pore volume was 0.79 cm3 / g. 2 3 The specific surface area of the microporous-mesoporous composite molecular sieve D2 was 261 m2 / g, and the pore volume was 0.79 cm3 / g.

[0165] (4) Reaction performance evaluation of direct conversion of waste plastics to low-carbon olefins​​

[0166] The reaction performance of the micro-mesopore composite molecular sieve D2 was tested according to the reaction performance evaluation method for direct conversion of waste plastics to light olefins in step (4) in Example 1, and the evaluation results are listed in Table 1.

[0167] Comparative Example 3

[0168] Step (1) in Example 1 was cancelled.

[0169] The two-dimensional hexagonal all-silica mesoporous molecular sieve A was prepared according to the method in step (2) in Example 1.

[0170] According to step (3) in Example 1.

[0171] The reaction performance of the two-dimensional hexagonal all-silica mesoporous molecular sieve A was tested according to the reaction performance evaluation method for direct conversion of waste plastics to light olefins in step (4) in Example 1, and the evaluation results are listed in Table 1.

[0172] Comparative Example 4

[0173] The ZSM-23 molecular sieve A was prepared according to the method in step (1) in Example 1.

[0174] Steps (2) and (3) in Example 1 were cancelled.

[0175] The reaction performance of the ZSM-23 molecular sieve A was tested according to the reaction performance evaluation method for direct conversion of waste plastics to light olefins in step (4) in Example 1, and the evaluation results are listed in Table 1.

[0176] Comparative Example 5

[0177] (1) Preparation of ZSM-23 molecular sieve

[0178] The ZSM-23 molecular sieve A was prepared according to the method in step (1) in Example 1.

[0179] (2) Preparation of two-dimensional hexagonal all-silica mesoporous molecular sieve raw powder

[0180] The two-dimensional hexagonal all-silica mesoporous molecular sieve raw powder A was prepared according to the method in step (2) in Example 1.

[0181] (3) Preparation of micro-mesopore composite molecular sieve

[0182] 60 g of the ZSM-23 molecular sieve A was mechanically mixed with 68 g of the above two-dimensional hexagonal all-silica mesoporous molecular sieve raw powder A, and then calcined at 550 ℃ for 16 h to obtain the micro-mesopore composite molecular sieve D3.

[0183] (4) Reaction performance evaluation for direct conversion of waste plastics to light olefins

[0184] The reaction performance of the microporous-mesoporous composite molecular sieve D3 was tested according to the reaction performance evaluation method of direct conversion of waste plastics to light olefins in step (4) in Example 1, and the evaluation results are listed in Table 1.

[0185] Comparative Example 6

[0186] The ZSM-23 molecular sieve A was prepared according to the method in step (1) in Example 1.

[0187] Step (2) in Example 1 was cancelled.

[0188] The microporous-mesoporous composite material D4 was prepared according to the method in step (3) in Example 1. The difference is that “40 g of silica powder (laboratory self-made, specific surface area of 274 m 2 / g, pore volume of 0.57 cm 3 / g)” was used instead of “68 g of the above two-dimensional hexagonal full-silica mesoporous molecular sieve raw powder A”.

[0189] The content of the ZSM-23 molecular sieve was 60% by weight, and the content of the silica was 40% by weight, based on the total weight of the microporous-mesoporous composite material D4.

[0190] The reaction performance of the composite material D4 was tested according to the reaction performance evaluation method of direct conversion of waste plastics to light olefins in step (4) in Example 1, and the evaluation results are listed in Table 1.

[0191] Comparative Example 7

[0192] The catalyst D5 was prepared according to the same method as in Example 1, except that step (2) of preparing the two-dimensional hexagonal full-silica mesoporous molecular sieve raw powder was cancelled, and in step (3), “68 g of the above two-dimensional hexagonal full-silica mesoporous molecular sieve raw powder A” was replaced with “40 g of a full-silica silicalite-1 zeolite molecular sieve carrier, and the specific surface area of the replaced carrier was 384 m 2 / g, pore volume of 0.29 ml / g, and most probable pore diameter of 0.55 nm”.

[0193] The reaction performance of the catalyst D5 was tested according to the reaction performance evaluation method of direct conversion of waste plastics to light olefins in step (4) in Example 1, and the evaluation results are listed in Table 1.

[0194] Table 1

[0195]

[0196]

[0197] It can be seen from the above results that the micropore-mesopore composite molecular sieve provided by the application can directly catalyze the conversion of waste plastics to produce low-carbon olefins. The conversion rate of waste plastics is 100%, and the yield of low-carbon olefins is high.

[0198] In Comparative Example 1, the content of the two-dimensional hexagonal all-silicon mesoporous molecular sieve is too high, and the content of the ZSM-23 molecular sieve is too low. Due to the small number of acid sites on the catalyst, the activation sites are insufficient during the reaction, resulting in low conversion of raw materials and low yield of low-carbon olefins.

[0199] In Comparative Example 2, the content of the two-dimensional hexagonal all-silicon mesoporous molecular sieve is too low, and the content of the ZSM-23 molecular sieve is too high. Due to the small number of mesoporous channels in the catalyst, the diffusion of reactant and product molecules is hindered during the reaction, resulting in low yield of low-carbon olefins.

[0200] In Comparative Example 3, only the two-dimensional hexagonal all-silicon mesoporous molecular sieve is used as the cracking catalyst, and no ZSM-23 molecular sieve is added. Since there are almost no active acid sites on the catalyst, the conversion of raw materials is low, and the yield of low-carbon olefins is low.

[0201] In Comparative Example 4, only the ZSM-23 molecular sieve is used as the cracking catalyst, and no two-dimensional hexagonal all-silicon mesoporous molecular sieve is added. Since the catalyst does not contain mesoporous channels, the diffusion of reactant and product molecules is hindered during the reaction, resulting in low yield of low-carbon olefins.

[0202] In Comparative Example 5, the ball milling process is omitted in the preparation of the micropore-mesopore composite molecular sieve, resulting in uneven dispersion of the mesoporous molecular sieve and the microporous molecular sieve in the micropore-mesopore composite molecular sieve, affecting the diffusion effect, and resulting in low yield of low-carbon olefins.

[0203] In Comparative Example 6, silica powder is used instead of the two-dimensional hexagonal all-silicon mesoporous molecular sieve. Since the specific surface area of silica is low, the pore volume is small, and the pore structure is irregular, the dispersion effect is significantly lower than that of the two-dimensional hexagonal all-silicon mesoporous molecular sieve, resulting in low yield of low-carbon olefins in the composite material prepared.

[0204] In Comparative Example 7, the all-silicon silicalite-1 zeolite molecular sieve is used instead of the two-dimensional hexagonal all-silicon mesoporous molecular sieve. Although the main framework component of the all-silicon silicalite-1 zeolite molecular sieve and the two-dimensional hexagonal all-silicon mesoporous molecular sieve is silica, the pore of the all-silicon silicalite-1 zeolite molecular sieve belongs to the microporous category, which is not conducive to the diffusion of reactant and product molecules during the reaction, resulting in low yield of low-carbon olefins.

[0205] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A micropore-mesopore composite molecular sieve, characterized by, The micro-mesopore composite molecular sieve comprises ZSM-23 molecular sieve and two-dimensional hexagonal all-silica mesoporous molecular sieve, wherein the specific surface area of the two-dimensional hexagonal all-silica mesoporous molecular sieve is 500-800 m 2 / g, the average pore size is 6-9 nm; and the content of the ZSM-23 molecular sieve is 40-80% by weight, and the content of the two-dimensional hexagonal all-silica mesoporous molecular sieve is 20-60% by weight, based on the total weight of the micro-mesopore composite molecular sieve. The preparation method of the micropore-mesopore composite molecular sieve comprises the following steps: (1) under the hydrolysis gel preparation condition, a template agent, a silicon source and an acidic aqueous solution are subjected to hydrolysis gel preparation to obtain a gel mixture; the gel mixture is subjected to crystallization; then the product obtained by the crystallization is subjected to filtration and first drying treatment to obtain two-dimensional hexagonal all-silicon mesoporous molecular sieve raw powder; (2) the two-dimensional hexagonal all-silicon mesoporous molecular sieve raw powder is mixed with ZSM-23 molecular sieve and subjected to ball milling treatment, and the solid powder obtained after the ball milling is subjected to second drying and calcination treatment to obtain the micropore-mesopore composite molecular sieve.

2. The micro-mesoporous composite molecular sieve of claim 1, wherein, The content of the ZSM-23 molecular sieve is 50-70% by weight, and the content of the two-dimensional hexagonal all-silicon mesoporous molecular sieve is 30-50% by weight, based on the total weight of the micropore-mesopore composite molecular sieve.

3. The micro-mesoporous composite molecular sieve of claim 2, wherein, The content of the ZSM-23 molecular sieve is 55-65% by weight, and the content of the two-dimensional hexagonal all-silicon mesoporous molecular sieve is 35-45% by weight, based on the total weight of the micropore-mesopore composite molecular sieve.

4. The micro-mesoporous composite molecular sieve of any one of claims 1-3, wherein, The specific surface area of the micropore-mesopore composite molecular sieve is 290-440 m 2 / g, the pore volume is 0.8-1 mL / g, the pore size distribution is bimodal distribution, and the most probable pore sizes corresponding to the bimodal distribution are 0.4-0.7 nm and 5-10 nm, respectively.

5. The micro-mesoporous composite molecular sieve of claim 4, wherein, The specific surface area of the micropore-mesopore composite molecular sieve is 320-400 m 2 / g, the pore volume is 0.85-0.93 mL / g, the pore size distribution is bimodal distribution, and the most probable pore sizes corresponding to the bimodal distribution are 0.5-0.6 nm and 6-9 nm, respectively.

6. The micro-mesoporous composite molecular sieve of claim 5, wherein, The specific surface area of the micropore-mesopore composite molecular sieve is 337-380 m 2 / g, the pore volume is 0.86-0.9 mL / g, the pore size distribution is bimodal distribution, and the most probable pore sizes corresponding to the bimodal distribution are 0.5-0.6 nm and 7-8 nm, respectively.

7. The micro-mesoporous composite molecular sieve of any one of claims 1-3, wherein, The SiO2 / Al2O3 molar ratio of the ZSM-23 molecular sieve is 90-130.

8. The micro-mesoporous composite molecular sieve of claim 7, wherein, The SiO2 / Al2O3 molar ratio of the ZSM-23 molecular sieve is 100-120.

9. The micro-mesoporous composite molecular sieve of claim 1, wherein, In step (1), the template agent is a nonionic surfactant; the silicon source is an organic silicon ester or an inorganic silicon source; And / or, the molar concentration of the solute acid in the acidic aqueous solution is 0.5-3 mol / L; And / or, the molar ratio of the template agent, the silicon source, the acid in the acidic aqueous solution to water in the acidic aqueous solution is 1:(40-100):(120-400):(6000-10000).

10. The micro-mesoporous composite molecular sieve of claim 1, wherein, The hydrolysis gel preparation condition comprises a temperature of 20-60 ℃ and a time of 12-36 h; And / or, the crystallization condition comprises a temperature of 70-150 ℃ and a time of 8-72 h.

11. The micro-mesoporous composite molecular sieve of claim 1, wherein, In step (2), the weight ratio of the use amount of the two-dimensional hexagonal all-silicon mesoporous molecular sieve raw powder to the ZSM-23 molecular sieve is 1:(0.3-5); And / or, the calcination condition comprises a temperature of 450-650 ℃ and a time of 5-30 h.

12. The micro-mesoporous composite molecular sieve of claim 11, wherein, The calcination condition comprises a temperature of 500-600 ℃ and a time of 8-20 h.

13. Use of the micropore-mesopore composite molecular sieve according to any one of claims 1-12 in the direct catalytic cracking of waste plastics to produce light olefins, wherein, The application comprises: the powder of waste plastic is contacted with a catalyst to react, and the catalyst is the micropore-mesopore composite molecular sieve in any one of claims 1-12.

14. Use according to claim 13, wherein, The contact condition comprises a temperature of 420-580 ℃, a pressure of 0.01-3 MPa, and a contact time of 0.5-12 h; And / or, the weight ratio of the use amount of the catalyst to the waste plastic powder is 1:(0.5-50).

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