MFI / FAU composite molecular sieve with cooperatively regulated micropore-mesopore-macropore structure and in-situ synthesis method of MFI / FAU composite molecular sieve

Abstract

The invention relates to an MFI / FAU composite molecular sieve with a cooperatively regulated micropore, mesopore and macropore structure and an in-situ synthesis method of the MFI / FAU composite molecular sieve. The molecular sieve is formed by premixing an MFI molecular sieve, an aluminum source, sodium hydroxide and water, introducing an FAU molecular sieve seed crystal, and crystallizing under a controlled hydrothermal condition, so as to finally obtain a composite material with a hierarchical porous structure. The prepared material has the advantage that the pore structure proportion is controllable (according to the pore volume, micropores account for 5-10%, mesopores account for 20-30% and macropores account for 60-80%), and the mass transfer efficiency and catalytic selectivity of macromolecular feeding are remarkably improved. The method does not need to use an organic structure-directing agent and a mesoporous template agent, and has the advantages of greenness, environmental protection, simple process and high yield. When a catalytic cracking catalyst prepared by taking the molecular sieve as an active component is applied to a crude oil catalytic cracking reaction, the catalytic relay capability of a complex parallel sequence reaction can be realized, the low-carbon olefin yield reaches 30% or above, the conversion rate reaches 86% or above, and the characteristics of high activity and high olefin yield are shown.

Description

Technical Field

[0001] This invention belongs to the technical field of preparing multi-level pore molecular sieve materials, specifically an MFI / FAU composite molecular sieve with coordinated microporous, mesoporous, and macroporous structures and its in situ synthesis method. It is suitable for catalytic conversion processes involving macromolecular reactants such as heavy oil and crude oil, and is particularly well-suited for demanding applications such as fluidized catalytic cracking and catalytic cracking. Background Art

[0002] Molecular sieve materials are crystalline aluminosilicates or aluminophosphates with a regular microporous structure. They play an important role in processes such as catalytic cracking, hydrocracking, isomerization, and molecular sieve membrane separation. The core characteristic of molecular sieves lies in their highly ordered pore structure. Based on their pore size, molecular sieve materials can be divided into microporous molecular sieves (pore size less than 2 nm), mesoporous materials (pore size 2-50 nm), and macroporous materials (pore size greater than 50 nm). Molecular sieves of different pore sizes can effectively separate molecules by size and provide a large number of active sites for catalytic reactions, thus achieving high selectivity and activity. However, traditional molecular sieves are primarily microporous structures, with pore sizes generally less than 2 nm. While this single microporous structure provides excellent sieving capabilities, it also introduces the problem of limited diffusion of substances. In particular, in catalytic processes involving large molecular reactants, the diffusion resistance of the micropores significantly affects the reaction rate and catalytic efficiency. Furthermore, although microporous molecular sieves have a high surface area, the catalytic reaction primarily occurs at the pore surface. The timely escape of product molecules is also restricted by the micropores, which can easily lead to catalyst deactivation and reduced reaction efficiency. It can be seen that molecular sieve materials with a single pore structure are gradually unable to meet actual needs. How to improve the transmission rate of reactants while maintaining a high specific surface area is an important direction of current molecular sieve research.

[0003] To address this problem, scientists have proposed introducing mesoporous and macroporous structures to construct multi-level pore structure molecular sieves. MFI-type molecular sieves (such as ZSM-5) and FAU-type molecular sieves (such as Y-type molecular sieves) have attracted widespread attention due to their good catalytic performance and thermal stability. Patent CN108745410A discloses a method for preparing a phosphorus-containing multi-level pore ZSM-5 / Y composite molecular sieve, which comprises mixing an alkali, an organic template, and deionized water, adding a NaY molecular sieve and a silicon source and a boron source, and then crystallizing. Subsequently, ammonium ion exchange and phosphide impregnation are performed to ultimately obtain a phosphorus-containing microporous-mesoporous ZSM-5 / Y composite molecular sieve. Patent CN115814848A discloses a ZSM-5 / Y composite molecular sieve, its preparation method, and application. The method comprises crystallizing a ZSM-5 molecular sieve mother liquor, mixing it with a NaY molecular sieve mother liquor, and then performing secondary crystallization to obtain a core-shell structure ZSM-5 / Y composite molecular sieve. Patents CN101767034A, CN115926833A, and CN117899810A all disclose ZSM-5 / Y molecular sieves. The literature (Journal of Petroleum (Petroleum Processing), 2015, 31(2): 535-541.) successfully prepared a core-shell structured ZSM-5 / Y zeolite catalytic material by using silicon and aluminum species formed by depolymerization of industrial NaY zeolite under alkaline conditions as raw materials. The literature (Journal of Materials Research, 2015, 30(16): 2434-2446) reported that a Y / ZSM-5 composite material was prepared by a two-step hydrothermal crystallization method. The literature (Chemical Engineering Journal, 2021, 417: 129-172) reported that a binder-free microporous-mesoporous Y / ZSM-5 zeolite composite material was prepared by a vapor phase transport (VPT) method and subsequent dealumination treatment. The literature (Materials Letters, 2024, 360: 135994) reported that a NaY zeolite shell was grown on a ZSM-5 core by hydrothermal crystallization to form a nanocrystalline core-shell structure.

[0004] Although the existing methods have achieved the combination of MFI and FAU structures to a certain extent, they still face many technical bottlenecks in constructing multi-level pore structures. First, the existing processes generally rely on post-processing or physical mixing methods, and it is difficult to achieve the coordinated in-situ construction of micropores, mesopores and macropores in a single step, resulting in uneven spatial distribution of the pores and lack of effective coordination between the pores at each level, making it difficult to meet the needs of efficient conversion of macromolecular reactants. Secondly, there is currently a lack of precise control mechanisms for the pore volume distribution of the three types of pores. Most technologies can only confirm the "existence" of the pore structure, but cannot quantitatively control and optimize the ratio of micro-meso-macropores, which limits the further improvement of the diffusion performance and catalytic stability of molecular sieves. In addition, existing technologies mostly rely on organic structure-directing agents or multiple hydrothermal treatment processes, and the synthesis process is complex and energy-intensive, which not only increases the manufacturing cost, but also brings an environmental burden, which is not conducive to green and large-scale applications. Therefore, there is an urgent need to develop a new MFI / FAU composite molecular sieve material that does not require a template, can achieve precise coordinated regulation of multi-level pore structure under one-step hydrothermal conditions, and has both high catalytic activity and excellent mass transfer efficiency, so as to break through the limitations of the existing synthesis system and meet the actual needs of catalytic conversion of complex molecules. Summary of the Invention

[0005] The object of the present invention is to provide a kind of MFI / FAU composite molecular sieve and its in situ synthesis method of synergistically regulating micropore, mesopore and macropore structure, to solve the technical problems such as low efficiency of multi-level pore construction, uncontrollable pore structure, insufficient diffusion performance and poor adaptability to macromolecular reactants in existing molecular sieve materials. To achieve the above object, the present invention provides a kind of synthesis method of in situ construction MFI / FAU composite molecular sieve, which is characterized in that by regulating the raw material ratio, hydrothermal treatment conditions and FAU seed introduction amount, the synergistic regulation and synergistic construction of micropore (0.5-0.8nm), mesopore (5-50nm) and macropore (60-140nm) structures are achieved. While maintaining the excellent adsorption performance of the composite molecular sieve micropores, the diffusion efficiency of macromolecular guests is enhanced. This method does not require the use of an organic structure directing agent, has a low water consumption, and has a simple synthesis process, which is suitable for large-scale preparation.

[0006] The technical solution provided by the present invention is as follows: an in-situ synthesis method of an MFI / FAU composite molecular sieve with synergistically controlled microporous-mesoporous-macroporous structure, comprising the following steps:

[0007] (1) Mixing water, sodium hydroxide, MFI molecular sieve and aluminum source for 10-50 minutes to prepare mixture A;

[0008] (2) adding FAU structure molecular sieve seed crystals to the mixture A obtained in step (1), and mixing for 10 to 30 minutes to obtain a mixture B;

[0009] (3) hydrothermally treating the mixture B obtained in step (2) at 80-120° C. for 9-24 h;

[0010] (4) Washing and drying the mixture obtained in step (3) to obtain a microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve.

[0011] In step (1) of the present invention, the SiO2 / Al2O3 molar ratio of the MFI structure molecular sieve is not less than 18; the aluminum source is one or more of aluminum sulfate, sodium metaaluminate, aluminum hydroxide, pseudo-boehmite, and aluminum isopropoxide;

[0012] In step (1) of the present invention, the mixing is carried out by conventional stirring at room temperature; the conventional stirring is glass rod stirring or mechanical stirring.

[0013] In step (1) of the present invention, the aluminum source is calculated as equivalent oxide aluminum oxide, and the mass ratio is water: sodium hydroxide: MFI structure molecular sieve: Al2O3 = (10-14): (1-3): (10-15): 1; preferably 14:2:13:1.

[0014] In step (2) of the present invention, the mass ratio of FAU structure molecular sieve seed crystals to MFI structure molecular sieve crystals is (0.02-0.20):1.

[0015] In step (2) of the present invention, the mixing time is 10 to 30 minutes, and the mixing method is stirring or grinding, and is carried out at room temperature.

[0016] In step (3) of the present invention, the preferred temperature for the hydrothermal treatment is 100° C. and the time is 18 h.

[0017] In step (4) of the present invention, the solvent used for washing is deionized water, and the pH of the filtrate after washing is 6.5-7.5.

[0018] In step (4) of the present invention, the drying temperature is 80 to 120° C., and the drying time is 8 to 24 hours.

[0019] In the present invention, the MFI structure molecular sieve is selected from ZSM-5 molecular sieve, Silicalite-1 molecular sieve or TS-1 (titanium silicon molecular sieve), and the FAU structure molecular sieve is selected from Y-type molecular sieve, X-type molecular sieve or ultra-stable Y-type molecular sieve.

[0020] In step (1) of the present invention, water, sodium hydroxide, MFI structured molecular sieve and aluminum source are mixed in one step and then stirred, and the amount and stirring time of each component are controlled. Sodium hydroxide provides an alkaline environment, which can effectively promote the depolymerization and condensation reaction of the aluminum source, and at the same time has an etching effect on the silicon atoms of the MFI skeleton. The released silicon species further serve as a silicon source for the growth of the FAU crystal phase. This step is a key link in achieving the in-situ construction of a multi-level pore structure. When the ratio of NaOH to aluminum source is insufficient, the formation of mesopores and macropores is limited; if the amount is too much, it is easy to cause the skeleton to be destroyed. Controlling the stirring time to about 30 minutes can achieve a relatively uniform dispersion of the precursor. Insufficient or excessive stirring is not conducive to pore regulation. Then, FAU structured molecular sieve seed crystals are added to the mixture obtained in step (1). The introduction of FAU seed crystals can effectively provide nucleation sites, significantly shorten the formation cycle of the FAU crystal phase, and thus accelerate the growth process of the MFI / FAU composite structure. The amount of seed crystals should be controlled at 2-20% of the MFI mass. A lower amount will slow down the crystallization rate, while an excessive amount will easily form a FAU-rich phase, destroying the synergy of the pore structure. Then hydrothermal treatment is carried out. The temperature and time of hydrothermal treatment are crucial to the development of the pore structure. If the treatment time is too short (<9 hours) or the temperature is too low (<80°C), the mesopores and macropores will not be fully developed, the material will mainly be dominated by micropores, and the catalytic diffusion performance will be limited; if the time is too long or the temperature is too high, it may cause the macropore structure to collapse and reduce the specific surface area. The preferred condition is treatment at 100°C for 18 hours. Under this condition, an MFI / FAU composite molecular sieve with a reasonable pore structure distribution and coordinated proportions of the three types of pores can be obtained.

[0021] The present invention also provides the MFI / FAU composite molecular sieve prepared by the above method, which has a microporous-mesoporous-macroporous multi-level pore structure and a total specific surface area of ​​300m 2 ·g -1 ~400m 2 ·g -1 , micropore specific surface area is 200~300m 2 ·g -1 The micropore volume is 0.08~0.14cm 3 ·g -1 ; The mesopore specific surface area is 50~150m 2 ·g -1 The mesopore volume is 0.20~0.50cm 3 ·g -1 .

[0022] Among the pore volume contributions of micropores, mesopores, and macropores, micropores account for 5% to 10% of the pore volume, mesopores account for 20% to 30%, and macropores account for 60% to 80%. The presence of macropores provides a low-resistance channel for the rapid entry of macromolecular reactants and the exit of products, effectively reducing diffusion restrictions; mesopores serve as a relay pathway connecting micropores and macropores, improving overall mass transfer efficiency; and the microporous region maintains a high density of acidic sites, responsible for reaction activation. The three types of pores are spatially interconnected, synergistically realizing the integrated functionality of the molecular sieve: "rapid entry and exit - selective catalysis - efficient conversion."

[0023] The yield of the MFI / FAU composite molecular sieve described in the present invention is significantly increased to 92% to 97%, compared to only 60% to 80% using the conventional hydrothermal method. This yield is calculated based on the ratio of the mass of the synthesized molecular sieve to the mass of the solid raw materials (commercial MFI structure molecular sieve, aluminum source, NaOH, and FAU structure molecular sieve seed crystals). This invention effectively improves the efficiency of synthesizing MFI / FAU composite molecular sieves.

[0024] This invention significantly reduces the amount of water added during the synthesis process, allowing the preparation of a microporous-mesoporous-macroporous multi-level MFI / FAU composite molecular sieve using only a minimal amount of water. The in-situ introduction of the microporous-mesoporous-macroporous multi-level pore structure addresses the accessibility and diffusion restrictions of the acidic sites of the microporous molecular sieve to reactant molecules. Due to the reduced amount of water added, the synthesis yield of the composite molecular sieve is significantly improved. Furthermore, the reduced amount of water added reduces the load on production equipment, thereby reducing risks during the production process.

[0025] The present invention also provides the use of the microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve catalyst obtained by the above method in the catalytic cracking of crude oil. In this application, the total light olefin yield reached 30.51%, including 4.05% ethylene and 16.39% propylene, with a crude oil conversion rate of 86.07%.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) Realizing the coordinated regulation of the three types of pore structures: The present invention proposes a design concept in which micropores, mesopores and macropores are coordinated in proportion in the pore volume, breaking the limitation of the structural and functional separation of traditional micro / mesoporous materials, realizing the spatial interconnection and functional gradient collaboration of the three types of pores, and significantly improving the adaptability and diffusion efficiency of molecular sieves to macromolecular reactants.

[0028] (2) The material prepared by the present invention provides abundant acidic active centers in the micropore region, the mesopores serve as relay channels to improve the mass transfer efficiency, and the macropores provide low-resistance diffusion paths for macromolecular reactants, thereby realizing the synergistic function of multi-level pores.

[0029] (3) In-situ one-step method to construct a multi-level porous structure, which is simple and green: by in-situ introduction of FAU seeds in the alkaline etching-aluminum-silicon co-source system, combined with controlled hydrothermal treatment conditions, the multi-level porous structure can be simultaneously generated without the need for organic templates and additional mesoporous templates, which has industrial advantages such as short process, low energy consumption, and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 These are the X-ray diffraction patterns of the MFI / FAU composite molecular sieves obtained in Examples 1-3 and Comparative Examples 1-2 and 4.

[0031] Figure 2 This is a transmission electron microscope image of the microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve obtained in Example 1.

[0032] Figure 3 This is a transmission electron microscope image of the microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve obtained in Example 2.

[0033] Figure 4 This is a transmission electron microscope image of the microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve obtained in Example 3.

[0034] Figure 5 This is a scanning electron microscope image of the microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve obtained in Example 3.

[0035] Figure 6 This is a transmission electron microscope image of the MFI / FAU composite molecular sieve obtained in Comparative Example 1.

[0036] Figure 7 This is a transmission electron microscope image of the MFI / FAU composite molecular sieve obtained in Comparative Example 2.

[0037] Figure 8 This is a transmission electron microscope image of the mechanically mixed molecular sieve obtained in Comparative Example 3.

[0038] Figure 9 This is a transmission electron microscope image of Comparative Example 4.

[0039] Figure 10 The nitrogen physical adsorption and desorption isotherm of the microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve obtained in Example 3 is shown in FIG.

[0040] Figure 11 This is the pore size distribution diagram of the microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve obtained in Example 3. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below with reference to specific embodiments. It should be noted that the protection scope of the present invention is not limited to these specific embodiments.

[0042] Catalyst preparation: According to the mass ratio, the sample obtained in the embodiment or comparative example: 1 mol / L ammonium sulfate solution = 1:10, ion exchange is carried out at 80°C for 1 hour, washed and dried; the above operation is repeated once; finally, it is calcined at 550°C for 4 hours to obtain an ammonium-exchanged hydrogen sample; the obtained hydrogen sample is mixed with kaolin and silica sol in a mass ratio of 4:5:1, beaten and formed, and aged at 800°C and 100wt% water vapor for 4 hours to obtain a catalytic cracking catalyst.

[0043] The catalytic cracking experiments in the Examples and Comparative Examples were conducted in a micro-fixed-bed reactor. The reaction temperature was 590°C, the regeneration temperature was 650°C, 1.667 g of feedstock was added over 70 seconds, and the catalyst loading was 5 g. The gaseous and liquid products were analyzed using an Agilent 8890 gas chromatograph. The results of the catalytic cracking of Daqing crude oil are shown in Table 2.

[0044] Example 1

[0045] This embodiment provides a microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve, the preparation method of which includes the following steps:

[0046] 5.6g of deionized water, 0.7g of sodium hydroxide, 5g of ZSM-5 molecular sieve (MFI structure), and 0.625g of sodium metaaluminate were mixed and stirred for 30 minutes. 0.5g of NaY molecular sieve (FAU structure) seed crystals were added and stirred for another 30 minutes. The mixture was then transferred to a 100ml polytetrafluoroethylene-lined synthesis kettle, sealed, and placed in a 100°C oven for 24 hours. The mixture was then washed with deionized water until the filtrate had a pH of 7 and dried in a 100°C oven for 9 hours to obtain a microporous-mesoporous-macroporous multi-level MFI / FAU composite molecular sieve sample (designated S1). The yield of the composite molecular sieve S1 was 97%.

[0047] The XRD spectrum of the microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve sample (named S1) prepared in Example 1 is as follows: Figure 1 As shown in the transmission electron microscope (TEM) Figure 2 The pore structure data are shown in Table 1.

[0048] From Table 1, we can see that the total specific surface area of ​​the MFI / FAU composite molecular sieve S1 is 346m 2 ·g -1 , the micropore specific surface area is 268m 2 ·g -1 , the micropore volume is 0.1cm3 ·g -1 ; The mesopore specific surface area is 100m 2 ·g -1 , the mesopore volume is 0.38 cm 3 ·g -1 , the macropore volume is 1.22cm 3 ·g -1 The proportions of micropores, mesopores and macropores are 6%, 22% and 72% respectively.

[0049] Example 2

[0050] This embodiment provides a microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve, the preparation method of which includes the following steps:

[0051] 16.8g of deionized water, 2.1g of sodium hydroxide, 15g of ZSM-5 molecular sieve (MFI structure), and 1.875g of sodium metaaluminate were mixed and stirred for 30 minutes. 1.5g of NaY molecular sieve (FAU structure) seed crystals were added and stirred for another 30 minutes. The mixture was then transferred to a 100ml polytetrafluoroethylene-lined synthesis reactor, sealed, and placed in a 100°C oven for 12 hours. The mixture was then washed with deionized water until the filtrate had a pH of 7 and dried in a 100°C oven for 12 hours to obtain a microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve sample (designated S2). The yield of the composite molecular sieve S2 was 95%.

[0052] The XRD spectrum of the microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve sample (named S2) prepared in Example 2 is as follows: Figure 1 As shown in the transmission electron microscope (TEM) Figure 3 shown.

[0053] From Table 1, we can see that the total specific surface area of ​​the MFI / FAU composite molecular sieve S2 is 338m 2 ·g -1 , micropore specific surface area is 210m 2 ·g -1 , the micropore volume is 0.09cm 3 ·g -1 ; The mesopore specific surface area is 128m 2 ·g -1 , the mesopore volume is 0.37 cm 3 ·g -1 , the macropore volume is 0.72cm 3 ·g -1 The proportions of micropores, mesopores and macropores are 8%, 31% and 61% respectively.

[0054] Example 3

[0055] This embodiment provides a microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve, the preparation method of which includes the following steps:

[0056] 22.4 g of deionized water, 2.8 g of sodium hydroxide, 20 g of ZSM-5 molecular sieve (MFI structure), and 2.5 g of sodium metaaluminate were mixed and stirred for 30 minutes. 2.0 g of NaY molecular sieve (FAU structure) seed crystals were added and stirred for another 30 minutes. The mixture was then transferred to a 100 ml polytetrafluoroethylene-lined synthesis kettle, sealed, and placed in a 100° C. oven at a constant temperature for 18 hours. The mixture was then washed with deionized water until the filtrate had a pH of 7 and dried in a 100° C. oven for 12 hours to obtain a microporous-mesoporous-macroporous multi-level MFI / FAU composite molecular sieve sample (designated S3). The yield of this composite molecular sieve was 95%.

[0057] The XRD spectrum of the microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve sample (named S3) is as follows Figure 1 As shown in the transmission electron microscope (TEM) Figure 4 As shown in the scanning electron microscope (SEM) picture Figure 5 As shown in Figure 2, the physical adsorption-desorption isotherms are as follows: Figure 10 As shown, the pore size distribution diagram is as follows Figure 11 The evaluation results of catalytic cracking of Daqing crude oil are shown in Table 2.

[0058] From Table 1, we can see that the total specific surface area of ​​the MFI / FAU composite molecular sieve S3 is 340m 2 ·g -1 , the micropore specific surface area is 233m 2 ·g -1 , the micropore volume is 0.09cm 3 ·g -1 ; The mesopore specific surface area is 137m 2 ·g -1 , the mesopore volume is 0.43 cm 3 ·g -1 , the macropore volume is 1.35cm 3 ·g -1 Micropores, mesopores and macropores account for 5%, 23% and 72% respectively. Figure 10 It can be seen that the N2 adsorption-desorption isotherm of the MFI / FAU composite molecular sieve S3 belongs to the IV type isotherm, and there is a large hysteresis loop when the relative pressure is 0.45-0.9, indicating that the composite molecular sieve is a typical micro-mesocomposite material. No adsorption saturation platform appears at the relative pressure of 0.989, indicating that there is a macroporous structure in the composite molecular sieve. Figure 11 It can be seen that the pore size distribution of the MFI / FAU composite molecular sieve is 0.5-0.8 nm, 5-50 nm and 60-140 nm.

[0059] Comparative Example 1

[0060] 5.6g of deionized water, 0.7g of sodium hydroxide, 5g of ZSM-5 molecular sieve (MFI structure) and 0.625g of sodium metaaluminate were stirred for 30 minutes, 0.5g of NaY molecular sieve (FAU structure) seed crystals were added and stirred for another 30 minutes, then transferred to a 100ml polytetrafluoroethylene-lined synthesis reactor, sealed and transferred to a 100°C oven for 1 hour; then washed with deionized water until the pH of the filtrate was 7, and dried in a 100°C oven for 9 hours to obtain a MFI / FAU composite molecular sieve sample without a macroporous structure (named D1). The XRD spectrum is shown in FIG. Figure 1 As shown in the transmission electron microscope (TEM) Figure 6 The evaluation results of catalytic cracking of Daqing crude oil are shown in Table 2.

[0061] Comparative Example 2

[0062] 5.6g of deionized water, 0.7g of sodium hydroxide, 5g of ZSM-5 molecular sieve (MFI structure) and 0.625g of sodium metaaluminate were stirred for 30 minutes, 0.5g of NaY molecular sieve (FAU structure) seed crystals were added and stirred for another 30 minutes, then transferred to a 100ml polytetrafluoroethylene-lined synthesis reactor, sealed and transferred to a 100°C oven for 3 hours; then washed with deionized water until the pH of the filtrate was 7, and dried in a 100°C oven for 9 hours to obtain a MFI / FAU composite molecular sieve sample without macroporous structure (named D2). The XRD spectrum is shown in FIG. Figure 1 As shown in the transmission electron microscope (TEM) Figure 7 The evaluation results of catalytic cracking of Daqing crude oil are shown in Table 2.

[0063] Comparative Example 3

[0064] The ZSM-5 molecular sieve (MFI structure) used in Example 1 and the NaY molecular sieve (FAU structure) seed crystals used were mechanically mixed in a mass ratio of 83%:17% to obtain a mechanically mixed molecular sieve sample (named D3). The XRD spectrum is shown in FIG. Figure 1 As shown in the transmission electron microscope (TEM) Figure 8 The evaluation results of catalytic cracking of Daqing crude oil are shown in Table 2.

[0065] Comparative Example 4

[0066] 22.4g deionized water, 2.8g sodium hydroxide, 20g ZSM-5 molecular sieve (MFI structure) were stirred for 30 minutes, then 2.5g sodium aluminate and 2.0g NaY molecular sieve (FAU structure) seed crystals were added and stirred for 30 minutes. The mixture was then transferred to a 100ml polytetrafluoroethylene-lined synthesis reactor, sealed, and transferred to a 100°C oven for 18 hours. The mixture was then washed with deionized water until the pH of the filtrate was 7, and dried in a 100°C oven for 12 hours to obtain an MFI / FAU composite molecular sieve sample (named D4). The XRD spectrum is shown in FIG. Figure 1 As shown in the transmission electron microscope (TEM) Figure 9 The evaluation results of catalytic cracking of Daqing crude oil are shown in Table 2. The only difference between the synthesis steps of Comparative Example D4 and Example S3 is that the addition order of the aluminum source (sodium metaaluminate) in Comparative Example D4 is postponed to step (2), that is, the aluminum source is added simultaneously with the introduction of FAU seeds. In Example S3, the aluminum source is mixed with water, NaOH, and ZSM-5 molecular sieve (MFI structure) in step (1).

[0067] Depend on Figure 1 It can be seen that the diffraction peaks observed at 2θ = 7.9°, 8.9°, 23.0°, 23.3° and 23.9° correspond to the orthorhombic MFI structure molecular sieve (PDF number: 00-044-0003), while the diffraction peaks observed at 2θ = 15.64°, 18.66°, 20.36°, 23.63°, 27.04°, 30.73°, 31.79° and 34.05° correspond to the cubic FAU structure molecular sieve (PDF number: 00-043-0168). The simultaneous appearance of characteristic diffraction peaks of MFI structure molecular sieve and FAU structure molecular sieve proves that the S1, S2 and S3 materials obtained in Examples 1-3 are all MFI / FAU composite materials, indicating that the MFI / FAU composite molecular sieve was successfully prepared. Figure 2-4 It can be seen that the MFI / FAU composite molecular sieves S1, S2 and S3 prepared in Examples 1-3 can be clearly observed to have a micropore-mesopore-macroporous structure.

[0068] Table 1 Pore structure data of Examples 1-3 and Comparative Examples 1-4

[0069]

[0070]

[0071] illustrate:

[0072] S BET : Total specific surface area calculated by BET method;

[0073] S micro: Micropore specific surface area calculated using the t-plot method;

[0074] S meso : mesopore specific surface area calculated by BJH method; V micro : Micropore volume calculated using the t-plot method;

[0075] V meso : mesopore volume calculated using the BJH method;

[0076] V macro : Macropore volume calculated by mercury intrusion method;

[0077] Micropore ratio:V micro / (V micro +V meso +V macro );

[0078] Mesopore ratio: V meso / (V micro +V meso +V macro );

[0079] Macropore ratio: V macro / (V micro +V meso +V macro );

[0080] From the pore structure data in Table 1, it can be seen that the MFI / FAU composite molecular sieves prepared in Examples 1-3 have a multi-level pore structure, mainly containing micropores, mesopores and macropores. In terms of pore volume, micropores account for 5% to 10%, mesopores account for 20% to 30%, and macropores account for 60% to 80%. The MFI / FAU composite molecular sieve has a large mesopore volume and a mesopore specific surface area of ​​50m 2 ·g -1 ~150m 2 ·g -1 The mesopore volume is between 0.20cm 3 ·g -1 ~0.50cm 3 ·g -1 Among them, the mesopore volume of S3 is 0.43cm 3 / g, macropore volume 1.35cm 3 This gradient pore structure results from the synergistic effect of the aluminum source premixing in step (1) and the 18-hour hydrothermal treatment in step (3). The microporous-mesoporous-macroporous multi-level pore structure of the MFI / FAU composite molecular sieve not only has excellent adsorption and shape-selective catalytic properties, but also enhances the diffusion efficiency of macromolecular guests and reduces the occurrence of side reactions during the catalytic process.

[0081] Comparative Examples 1-2 (D1, D2) failed to form a macroporous structure (the macropore ratio was 0%) due to insufficient hydrothermal treatment time (only 1 hour and 3 hours). D1 showed an extremely high mesopore ratio (71%) but lacked macropores; D2 also had a high mesopore ratio (77%) and a higher micropore ratio (23%) than the examples, but still had no macroporous structure. This severely limits its diffusion efficiency for macromolecular reactants. Comparative Example 3 (D3) is a mechanically mixed sample with significantly different pore structure characteristics: the highest total specific surface area (587m 2 ·g -1 ), but mainly contributed by micropores (S micro =554m 2 ·g -1 , V micro =0.22cm 3 ·g -1 The proportion of mesopores is extremely low (only 8%), and the mesopore volume is small (0.11cm 3 ·g -1 ), although the macropore ratio (75%) is high (due to the accumulation of pores in the mechanical mixture), it lacks in-situ connectivity and synergistic effects with the micropores / mesopores. In comparative example 4 (D4), the pore structure is seriously deteriorated due to the change in the order of aluminum source addition (delayed to step 2): the mesopore volume is sharply reduced to 0.20 cm 3 ·g -1 (Compared to S3's 0.43cm 3 ·g -1 decreased by about 53.5%), and the macropore volume collapsed to 0.31 cm 3 ·g -1 (Compared to S3's 1.35cm 3 ·g -1 The dramatic decrease in the volume of mesopores and macropores indicates that the aluminum source premixing step is crucial for constructing a well-developed and well-proportioned hierarchical pore structure.

[0082] Table 2 Evaluation results of Daqing crude oil catalytic cracking of examples and comparative examples

[0083]

[0084] The catalytic cracking evaluation results shown in Table 2 show that sample S3 prepared in Example 3 exhibited significant performance advantages in the catalytic cracking of Daqing crude oil. The total light olefins (ethylene + propylene + total butenes) yield of S3 reached 30.51%, significantly higher than that of comparative examples D1 (24.93%), D2 (24.69%), mechanically mixed sample D3 (24.15%), and comparative example D4 (27.89%) with delayed addition of the aluminum source. The crude oil conversion rate of S3 (86.07%) was also significantly higher than that of comparative examples D1 (82.48%), D2 (83.34%), mechanically mixed sample D3 (82.99%), and comparative example D4 (83.27%) with delayed addition of the aluminum source. This result fully demonstrates that the MFI / FAU composite molecular sieve catalyst S3, which has a microporous-mesoporous-macroporous multi-level pore structure, can effectively improve the yield of light olefins while maintaining high catalytic activity.

[0085] In Comparative Examples D1 and D2, the mesopore and macropore structures were not fully developed due to insufficient hydrothermal treatment time (only 1-3 hours), resulting in limited diffusion performance. In the mechanically mixed sample D3, the spatial coordination of multi-level channels could not be achieved due to physical mixing, resulting in low catalytic efficiency. In Comparative Example D4, although the same raw material ratio was used, the aluminum source was added later than step (2), which destroyed the synchronous process of alkaline etching of MFI molecular sieve and depolymerization of aluminum source in step (1), resulting in a sharp decrease of 53.5% (0.20 vs 0.43 cm) in the mesopore volume. 3 / g), macropore volume collapsed by 77% (0.31 vs 1.35 cm 3 / g), and the proportion of macropores dropped from 72% to 50%. This imbalance in pore structure directly resulted in the crude oil conversion rate and olefin yield of D4 being better than those of D1-D3, but still significantly lower than that of S3, confirming the necessity of premixing the aluminum source in step (1) to construct gradient pores. The excellent performance of S3 stems from its unique micropore (5%)-mesopore (23%)-macropore (72%) synergistic system: macropores provide fast diffusion channels for crude oil macromolecules, mesopores serve as intermediate product transmission hubs, and micropores ensure the efficient utilization of cracking active sites. This three-level pore relay mechanism ultimately achieved a conversion rate of 86.07% and a low-carbon olefin yield of 30.51%, breaking through the performance bottleneck of existing technologies.

Claims

1. An in-situ synthesis method of MFI / FAU composite molecular sieve with coordinated regulation of microporous-mesoporous-macroporous structure, characterized in that: The method comprises the following specific steps: (1) Mixing water, sodium hydroxide, MFI molecular sieve and aluminum source for 10-50 minutes to prepare mixture A; (2) adding FAU structure molecular sieve seed crystals to the mixture A obtained in step (1), and mixing for 10 to 30 minutes to obtain a mixture B; (3) hydrothermally treating the mixture B obtained in step (2) at 80-120° C. for 9-24 h; (4) Washing and drying the mixture obtained in step (3) to obtain a microporous-mesoporous-macroporous multi-level pore MFI / FAU composite molecular sieve.

2. The in-situ synthesis method of an MFI / FAU composite molecular sieve with coordinated regulation of microporous-mesoporous-macroporous structure according to claim 1, characterized in that: In step (1), the SiO2 / Al2O3 molar ratio of the MFI structure molecular sieve is not less than 18; the aluminum source is one or more of aluminum sulfate, sodium aluminate, aluminum hydroxide, pseudo-boehmite, and aluminum isopropoxide; the aluminum source is calculated as equivalent oxide aluminum oxide, and the mass ratio is water: sodium hydroxide: MFI structure molecular sieve: Al2O3 = (10~14): (1~3): (10~15): 1; preferably 14:2:13:1; in step (2), the mass ratio is FAU structure molecular sieve seed: MFI structure molecular sieve = (0.02~0.20):

1.

3. The in-situ synthesis method of an MFI / FAU composite molecular sieve with coordinated regulation of microporous-mesoporous-macroporous structure according to claim 1, characterized in that: In step (1), the mixing time is 30 min.

4. The in-situ synthesis method of an MFI / FAU composite molecular sieve with coordinated regulation of microporous-mesoporous-macroporous structure according to claim 1, characterized in that: In step (3), the temperature of the hydrothermal treatment is 100° C. and the time is 18 h.

5. The in-situ synthesis method of an MFI / FAU composite molecular sieve with coordinated regulation of microporous-mesoporous-macroporous structure according to claim 1, characterized in that: In step (4), the solvent used for washing is deionized water, and the pH of the filtrate after washing is 6.5-7.5; the drying temperature is 80-120° C., and the drying time is 8-24 h.

6. The in-situ synthesis method of an MFI / FAU composite molecular sieve with coordinated regulation of microporous-mesoporous-macroporous structure according to claim 1, characterized in that: The yield of the MFI / FAU composite molecular sieve is 92-97%.

7. The in-situ synthesis method of an MFI / FAU composite molecular sieve with coordinated regulation of microporous-mesoporous-macroporous structure according to claim 1, characterized in that: The MFI structure molecular sieve is selected from ZSM-5 molecular sieve, Silicalite-1 molecular sieve or TS-1 (titanium silicon molecular sieve), and the FAU structure molecular sieve is selected from Y-type molecular sieve, X-type molecular sieve or ultra-stable Y-type molecular sieve.

8. The MFI / FAU composite molecular sieve with a coordinated microporous-mesoporous-macroporous structure prepared by the method according to any one of claims 1 to 7, characterized in that: The MFI / FAU composite molecular sieve has a multi-level pore structure, containing micropores, mesopores and macropores; based on pore volume, micropores account for 5% to 10%, mesopores account for 20% to 30%, and macropores account for 60% to 80%.

9. The MFI / FAU composite molecular sieve according to claim 8, characterized in that The pore size distribution range of the MFI / FAU composite molecular sieve is 0.5-0.8 nm, 5-50 nm and 60-140 nm, and the total specific surface area is 300 m 2 ·g -1 ~400m 2 ·g -1 , micropore specific surface area is 200~300m 2 ·g -1 The micropore volume is 0.08~0.14cm 3 ·g -1 ; The mesopore specific surface area is 50~150m 2 ·g -1 , the mesopore volume is 0.20~0.50cm 3 ·g -1 .

10. Use of the MFI / FAU composite molecular sieve according to any one of claims 8 to 9 in catalytic cracking of crude oil, characterized in that: The total light olefin yield is ≥30%, of which the ethylene yield is ≥4%, the propylene yield is ≥16%, the butene yield is ≥10%, and the crude oil conversion rate is ≥86%.

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