A core-shell molecular sieve, its preparation method and application

Abstract

The present invention relates to a core-shell molecular sieve, a preparation method and an application thereof. The core-shell molecular sieve includes a SAPO-34 molecular sieve core and a ZSM-5 molecular sieve shell coated on the surface of the SAPO-34 molecular sieve core; the ratio of the peak height of the peak at 2θ = 9.5° to the peak height of the peak at 2θ = 23.02° in the X-ray diffraction pattern of the core-shell molecular sieve is (0.05-15):1. The core-shell molecular sieve of the present invention has a better conversion effect when used for catalytic conversion of hydrocarbon oil.

Description

Technical Field

[0001] The present invention relates to a core-shell molecular sieve, a preparation method thereof, and an application thereof. Background Art

[0002] The increasing social demand for high-value-added petroleum products has promoted the development of the refining industry towards deep processing, maximizing the conversion of petroleum fractions into more valuable products such as light olefins, BTX, etc. Zeolite molecular sieves are a class of microporous crystalline materials with a framework structure, having pore channels with specific sizes and shapes, a large specific surface area, and strong adjustable acidic properties, and are widely used in the processes of petroleum refining and processing, such as catalytic cracking, alkane isomerization, catalytic reforming, and toluene disproportionation and other catalytic reactions.

[0003] SAPO-34 has a unique small pore and large cage structure and suitable acidity. Among them, the small pores are beneficial to improving the selectivity of ethylene and propylene. ZSM-5 molecular sieve is a mesoporous molecular sieve with a high-silica three-dimensional straight channel of MFI structure, having good shape-selective catalysis and isomerization performance, high thermal and hydrothermal stability, a high specific surface area, a wide range of silica-alumina ratio changes, unique surface acidity, and a low carbon deposition amount.

[0004] In recent years, there has been research on forming a core-shell molecular sieve from two molecular sieves, generally composed of two molecular sieves with different crystal structures. One molecular sieve is the core, and the other molecular sieve is the shell layer wrapped on the surface of the core phase, in order to utilize the different advantages of the two types of core and shell molecular sieves and promote the catalytic reaction as a catalytic material. However, the existing technology's research on core-shell molecular sieves is in its infancy, and the research is not sufficient, making it difficult to prepare a core-shell molecular sieve with good performance. Summary of the Invention

[0005] The object of the present invention is to provide a core-shell molecular sieve, a preparation method thereof, and an application thereof, which has better catalytic performance when used for catalytic conversion of hydrocarbon oil.

[0006] To achieve the above object, in a first aspect of the present invention, a core-shell molecular sieve is provided. The core-shell molecular sieve includes a SAPO-34 molecular sieve core and a ZSM-5 molecular sieve shell covering the surface of the SAPO-34 molecular sieve core; the ratio of the peak height of the peak at 2θ = 9.5° to the peak height of the peak at 2θ = 23.02° in the X-ray diffraction pattern of the core-shell molecular sieve is (0.05 - 15):1.

[0007] Optionally, the ratio of the peak height of the peak at 2θ = 9.5° to the peak height of the peak at 2θ = 23.02° in the X-ray diffraction pattern of the core-shell molecular sieve is (0.1 - 10):1.

[0008] Optionally, the weight ratio of the SAPO-34 molecular sieve core to the ZSM-5 molecular sieve shell in the core-shell molecular sieve is (0.2 - 20):1, preferably (1 - 10):1.

[0009] Optionally, the total specific surface area of the core-shell molecular sieve is 300 m 2 / g or more, preferably 350 - 550 m 2 / g, more preferably 400 - 500 m 2 / g. The proportion of the mesoporous specific surface area in the total specific surface area is 5 - 30%, preferably 10 - 25%.

[0010] Optionally, the average thickness of the ZSM-5 molecular sieve shell is 50 - 2000 nm.

[0011] Optionally, the average crystal grain size of the ZSM-5 molecular sieve shell is 50 - 1000 nm, and the average crystal grain size of the SAPO-34 molecular sieve core is 1 - 10 μm.

[0012] Optionally, the silica-alumina molar ratio of the SAPO-34 molecular sieve core is 0.05 - 2 in terms of SiO2 / Al2O3, and the silica-alumina molar ratio of the ZSM-5 molecular sieve shell is 10 - 500 in terms of SiO2 / Al2O3.

[0013] Optionally, the average coverage of the ZSM-5 molecular sieve shell on the outer surface of the SAPO-34 molecular sieve core is 50 - 100%, preferably 80 - 100%.

[0014] Optionally, in the core-shell molecular sieve, the pore volume of pores with a pore diameter of 2 - 80 nm accounts for 10 - 30% of the total pore volume, and the pore volume of pores with a pore diameter of 20 - 80 nm accounts for 50 - 70% of the pore volume of pores with a pore diameter of 2 - 80 nm.

[0015] The second aspect of the present invention provides a method for preparing a core-shell molecular sieve, which includes:

[0016] S1. Making the SAPO-34 molecular sieve be in first contact and mixing with a first solution containing a surfactant, and separating a first solid from the resulting mixture;

[0017] S2. Making the first solid be in second contact and mixing with a slurry containing the ZSM-5 molecular sieve, and separating a second solid from the resulting mixture;

[0018] S3. Subjecting a second solution containing a silicon source, an aluminum source, a template agent, an alkali source, and a solvent to a first hydrothermal treatment at 30 - 300 °C for 3 - 100 h to obtain a ZSM-5 synthesis solution;

[0019] S4. Mix the second solid with the ZSM-5 synthesis solution and conduct a second hydrothermal treatment.

[0020] Optionally, in step S1, the content of the surfactant in the first solution is 0.05 - 20% by weight; the weight ratio of the first solution to the SAPO-34 molecular sieve based on dry weight is (10 - 200):1; the conditions for the first contact mixing include: temperature is 20 - 70°C, and time is 1 - 36 hours.

[0021] The surfactant is selected from one or more of polymethyl methacrylate, poly(diallyldimethylammonium chloride), pyridine dicarboxylic acid, ammonia water, ethylamine, n-butylamine, tetrapropylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium hydroxide.

[0022] The SAPO-34 molecular sieve is selected from one or more of sodium-type SAPO-34 molecular sieve, hydrogen-type SAPO-34 molecular sieve, and ion-exchanged SAPO-34 molecular sieve.

[0023] The silicon-aluminum molar ratio of the SAPO-34 molecular sieve, calculated as SiO2 / Al2O3, is 0.05 - 10, and the average crystal grain size is 1 - 10 μm.

[0024] Optionally, in step S1, the first solution further contains a salt, the content of the salt is 0.05 - 10.0% by weight, and the salt is selected from one or more of sodium chloride, potassium chloride, ammonium chloride, and ammonium nitrate.

[0025] Optionally, in step S2, the content of the ZSM-5 molecular sieve in the slurry is 0.1 - 10% by weight, preferably 0.3 - 8% by weight; the weight ratio of the slurry to the SAPO-34 molecular sieve based on dry weight is (10 - 50):1; the conditions for the second contact mixing include: temperature is 20 - 60°C, and time is 1 - 24 hours.

[0026] The silicon-aluminum molar ratio of the ZSM-5 molecular sieve, calculated as SiO2 / Al2O3, is 10 - 200, and the average crystal grain size is 0.05 - 1.0 μm.

[0027] Optionally, in step S3, the conditions for the first hydrothermal treatment include: temperature is 75 - 250°C, and time is 10 - 80 hours; preferably, temperature is 80 - 180°C, and time is 18 - 50 hours.

[0028] There is a spectral peak at 2θ = 23.02° in the X-ray diffraction pattern of the ZSM-5 synthesis solution, and there is no spectral peak at 2θ = 23.87°.

[0029] The molar ratio of the amount of the template agent to the amount of the silicon source is (0.1-10):1, the molar ratio of the amount of the solvent to the amount of the silicon source is (2-150):1, and the molar ratio of the amount of the silicon source to the amount of the aluminum source is (10-800):1. Among them, the silicon source is calculated as SiO2, and the aluminum source is calculated as Al2O3;

[0030] The silicon source is selected from one or more of tetraethyl orthosilicate, water glass, macroporous silica gel, silica sol, white carbon black and activated clay; the aluminum source is selected from one or more of aluminum sulfate, aluminum isopropoxide, aluminum nitrate, aluminum sol, sodium metaaluminate and γ-aluminum oxide; the template agent is selected from one or more of tetrapropylammonium fluoride, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, polyvinyl alcohol, triethanolamine and sodium carboxymethylcellulose; the base source is sodium hydroxide; the solvent is water.

[0031] Optionally, in step S4, the conditions of the second hydrothermal treatment include: the temperature is 100-250 °C, and the time is 30-350 h. Preferably, the temperature is 100-200 °C, and the time is 50-120 hours;

[0032] The weight ratio of the ZSM-5 synthesis liquid to the amount of the second solid is (2-10):1.

[0033] The third aspect of the present invention provides a core-shell molecular sieve prepared by the method provided in the second aspect of the present invention.

[0034] The fourth aspect of the present invention provides an application of the core-shell molecular sieve provided in the first aspect and / or the third aspect of the present invention in catalytic cracking or catalytic pyrolysis of hydrocarbon oil.

[0035] Through the above technical solutions, the core-shell molecular sieve of the present invention has a SAPO-34 molecular sieve inner core and a ZSM-5 molecular sieve outer shell, and has high reaction activity. When it is used in the catalytic pyrolysis reaction of hydrocarbon oil, the yield of propylene and / or ethylene in the reaction product can be increased.

[0036] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation part. Description of the Drawings

[0037] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the following specific implementation, they are used to explain the present invention, but do not constitute a limitation to the present invention. In the drawings:

[0038] Figure 1 It is a SEM photograph of the core-shell molecular sieve prepared in Example 1 of the present invention.

[0039] Figure 2It is the SEM photograph of the SAPO-34 molecular sieve inner core in the core-shell molecular sieve prepared in Example 1 of the present invention.

[0040] Figure 3 It is the XRD patterns of the SAPO-34 molecular sieve, ZSM-5 molecular sieve and the prepared core-shell molecular sieve used in Example 1 of the present invention.

[0041] Figure 4 It is the SEM photograph of the core-shell molecular sieve prepared in Example 2 of the present invention. Detailed Embodiments

[0042] The following further describes the detailed embodiments of the present invention with reference to the accompanying drawings. It should be understood that the detailed embodiments described herein are only for explaining and illustrating the present invention, and are not used to limit the present invention.

[0043] The first aspect of the present invention provides a core-shell molecular sieve, which includes a SAPO-34 molecular sieve inner core and a ZSM-5 molecular sieve outer shell covering the surface of the SAPO-34 molecular sieve inner core; the ratio of the peak height of the peak at 2θ = 9.5° to the peak height of the peak at 2θ = 23.02° in the X-ray diffraction pattern of the core-shell molecular sieve is (0.05-15):1.

[0044] The core-shell molecular sieve of the present invention has a SAPO-34 molecular sieve inner core and a ZSM-5 molecular sieve outer shell, and has high reaction activity. When it is used in the catalytic cracking reaction of hydrocarbon oil, the yield of propylene and / or ethylene in the reaction products can be increased.

[0045] In the present invention, the peak at 2θ = 9.5° is the peak in the X-ray diffraction pattern within the range of 2θ angle of 9.5° ± 0.1°, and the peak at 2θ = 23.02° is the peak in the X-ray diffraction pattern within the range of 2θ angle of 23.02° ± 0.1°. The core-shell molecular sieve of the present invention has a SAPO-34 molecular sieve inner core and a ZSM-5 molecular sieve outer shell, and has better conversion effect when used in the catalytic conversion of hydrocarbon oil, and can increase the yield of propylene and / or ethylene.

[0046] In a specific embodiment of the present invention, the ratio of the peak height of the peak at 2θ = 9.5° to the peak height of the peak at 2θ = 23.02° in the X-ray diffraction pattern of the core-shell molecular sieve can be (0.1-10):1, or (0.1-8):1, or (0.12-4):1, or (0.8-8):1.

[0047] In a specific embodiment of the present invention, the weight ratio of the SAPO-34 molecular sieve core to the ZSM-5 molecular sieve shell in the core-shell molecular sieve can vary within a relatively wide range. For example, it can be (0.2 - 20):1, preferably (1 - 15):1, and more preferably (1 - 10):1. In the present invention, the weights of the SAPO-34 molecular sieve core and the ZSM-5 molecular sieve shell of the core-shell molecular sieve can be calculated by using the peak of the X-ray diffraction analysis spectrum to calculate the ratio of the core to the shell, and the fitting calculation is carried out by using the fitting function pseudo-voigt with JADE software.

[0048] In a specific embodiment of the present invention, the total specific surface area of the core-shell molecular sieve is above 300 m 2 / g, for example, 350 - 550 m 2 / g, preferably 350 - 520 m 2 / g, more preferably 380 - 400 m 2 / g, and further preferably 400 - 500 m 2 / g. The proportion of the mesoporous specific surface area in the total specific surface area is 5 - 30%, preferably 10 - 25%. Mesopores refer to pores with a pore diameter of 2 - 50 nm. In the present invention, the total specific surface area and the mesoporous specific surface area of the molecular sieve are measured by the low-temperature nitrogen adsorption capacity method, and the BET total specific surface area and the mesoporous specific surface area are calculated by using the BET formula.

[0049] According to the present invention, the average thickness of the ZSM-5 molecular sieve shell can vary within a relatively wide range. In a preferred specific embodiment, the average thickness of the ZSM-5 molecular sieve shell is 50 - 2000 nm, and more preferably 100 - 1000 nm. In the present invention, the thickness of the ZSM-5 molecular sieve shell is measured by the TEM method. The thickness of the shell layer at a certain position of a core-shell molecular sieve particle is randomly measured, and 10 particles are measured, and the average value is taken.

[0050] In a specific embodiment of the present invention, the average grain size of the ZSM-5 molecular sieve shell is 50-1000 nm, preferably 100-800 nm. The average grain size of the SAPO-34 molecular sieve particles is 1-10 μm, preferably 1.5-5 μm. In the present invention, the grain size refers to the size at the widest part of the grain, which can be obtained by measuring the size at the widest part of the grain projection surface in the SEM or TEM image of the sample. In the present invention, the average grain size is obtained by calculating the average value of the grain sizes measured for 10 randomly selected grains. The particle size refers to the size at the widest part of the particle, which can be obtained by measuring the size at the widest part of the particle projection surface in the SEM or TEM image of the sample. The average value of the particle sizes of multiple particles is the average particle size of the sample, and it can also be measured by a laser particle size analyzer. In the present invention, the average particle size is calculated by randomly measuring the particle sizes of 10 particles and calculating the average value. One particle may include one or more grains.

[0051] In a specific embodiment of the present invention, the silica-alumina molar ratio of the SAPO-34 molecular sieve core is 0.05-2 in terms of SiO2 / Al2O3, and the silica-alumina molar ratio of the ZSM-5 molecular sieve shell is 10-500 in terms of SiO2 / Al2O3, preferably 25-200. The silica-alumina molar ratio of the core-shell molecular sieve and the silica-alumina molar ratio of the SAPO-34 molecular sieve core are measured by the TEM-EDS method.

[0052] In a specific embodiment of the present invention, the average coverage of the ZSM-5 molecular sieve shell on the outer surface of the SAPO-34 molecular sieve core is 50-100%, preferably 80-100%. In the present invention, the coverage of the molecular sieve is measured by the SEM method. The ratio of the outer surface area of a molecular sieve core particle with a shell to the outer surface area of the core particle is calculated as the coverage of the particle. 10 particles are randomly measured, and the average value thereof is the average coverage.

[0053] In a specific embodiment of the present invention, the total pore volume of the core-shell molecular sieve is 0.28-0.42 mL / g, for example 0.3-0.4 mL / g or 0.32-0.38 mL / g.

[0054] In a specific embodiment of the present invention, in the core-shell molecular sieve, the pore volume of pores with a pore diameter of 2-80 nm accounts for 10-30% of the total pore volume, preferably 11-25%. The pore volume of pores with a pore diameter of 20-80 nm accounts for 50-70%, or 55-65%, or 58-64% of the pore volume of pores with a pore diameter of 2-80 nm.

[0055] The total pore volume and pore size distribution of the core-shell molecular sieve of the present invention can be measured by the low-temperature nitrogen adsorption capacity method. The BJH calculation method is used to calculate the pore size distribution, and the Ripp-151-90 method (Petrochemical Analysis Methods, RIPP Test Methods, published by Science Press in 1990) can be referred to. The core-shell molecular sieve of the present invention has an obvious hierarchical pore distribution of micropores-mesopores-macropores, with rich mesopore and macropore volumes at 20-80 nm, which is beneficial to the hierarchical cracking of naphthene macromolecules.

[0056] In a second aspect of the present invention, a method for preparing a core-shell molecular sieve is provided. The method includes: S1. First contacting and mixing the SAPO-34 molecular sieve with a first solution containing a surfactant, and separating a first solid from the resulting mixture; S2. Second contacting and mixing the first solid with a slurry containing ZSM-5 molecular sieve, and separating a second solid from the resulting mixture; S3. First hydrothermally treating a second solution containing a silicon source, an aluminum source, a template agent, an alkali source, and a solvent at 30-300 °C for 3-100 h to obtain a ZSM-5 synthesis solution; S4. Mixing the second solid with the ZSM-5 synthesis solution and performing a second hydrothermal treatment.

[0057] In a specific embodiment of the present invention, in step S1, the content of the surfactant in the first solution is 0.05-50 wt%; the weight ratio of the first solution to the SAPO-34 molecular sieve based on the dry weight can vary within a large range, for example, it can be (10-200):1. The conditions for the first contacting and mixing include: the temperature is 20-70 °C, and the time is more than 0.5 h, for example, 0.5-48 h or 1-36 h.

[0058] According to the present invention, the surfactant is conventionally used by those skilled in the art, and can be selected from one or more of polymethyl methacrylate, poly(diallyldimethylammonium chloride), pyridine dicarboxylic acid, ammonia water, ethylamine, n-butylamine, tetrapropylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium hydroxide; the SAPO-34 molecular sieve is selected from one or more of sodium-type SAPO-34 molecular sieve, hydrogen-type SAPO-34 molecular sieve, and ion-exchanged SAPO-34 molecular sieve. The ion-exchanged SAPO-34 molecular sieve refers to the SAPO-34 molecular sieve (such as Na-type SAPO-34 molecular sieve) after being exchanged with ions other than alkali metals, such as transition metal ions, ammonium ions, alkaline earth metal ions, Group IIIA metal ions, Group IVA metal ions, and Group VA metal ions; the silicon-aluminum molar ratio of the SAPO-34 molecular sieve is 0.05-10 in terms of SiO2 / Al2O3, preferably 0.05-2, and the average crystal grain size is 1-10 μm, preferably 1.5-5 μm.

[0059] In a specific embodiment of the present invention, in step S1, the first solution further contains a salt, and the content of the salt is 0.05-10.0% by weight. The salt is selected from one or more of sodium chloride, potassium chloride, ammonium chloride, and ammonium nitrate.

[0060] In a specific embodiment of the present invention, in step S1, the first contact mixing of the SAPO-34 molecular sieve with the first solution containing a surfactant and the separation of the first solid from the resulting mixture include: adding the SAPO-34 molecular sieve to a surfactant solution with a content of 0.05-50% by weight and contacting for at least 0.5 h, filtering, and drying to obtain the first solid. The present invention has no special requirements for drying. For example, it can be drying by baking, flash drying, or pneumatic drying. In one embodiment, the drying temperature is 50-150 °C, and the drying time is not limited as long as the sample is dried. For example, it can be 0.5-4 hours.

[0061] In a specific embodiment of the present invention, in step S2, the content of the ZSM-5 molecular sieve in the slurry is 0.1-10% by weight, preferably 0.3-8% by weight, or 0.2-1% by weight; the weight ratio of the slurry to the SAPO-34 molecular sieve based on the dry weight is (10-50):1; the conditions for the second contact mixing include: the temperature is 20-60 °C, and the time is 1-24 hours.

[0062] In a specific embodiment of the present invention, the silica-aluminum molar ratio of the ZSM-5 molecular sieve is 10-200 calculated as SiO2 / Al2O3, and the average crystal grain size is 0.05-1.0 μm. In one embodiment, the difference between the silica-aluminum molar ratio of the ZSM-5 molecular sieve in the slurry containing the ZSM-5 molecular sieve and the silica-aluminum molar ratio of the shell molecular sieve does not exceed ±10%. For example, the ZSM-5 zeolite has the same silica-aluminum molar ratio as the shell molecular sieve of the synthesized core-shell molecular sieve.

[0063] In a specific embodiment of the present invention, in step S2, the second contact mixing of the first solid with the slurry containing the ZSM-5 molecular sieve and the separation of the second solid from the resulting mixture include: adding the first solid to the slurry containing the ZSM-5 molecular sieve, stirring at 20-60 °C for more than 0.5 h, for example, 1-24 h, and then filtering and drying to obtain the second solid.

[0064] In a specific embodiment of the present invention, the average crystal grain size of the ZSM-5 molecular sieve is smaller than that of the SAPO-34 molecular sieve. In one embodiment, the average crystal grain size of the ZSM-5 molecular sieve in the slurry containing the ZSM-5 molecular sieve is 10-500 nm smaller than that of the SAPO-34 molecular sieve. For example, the average crystal grain size of the SAPO-34 molecular sieve is more than 1.5 times, such as 2-50 or 5-20 times, that of the ZSM-5 zeolite.

[0065] In a specific embodiment of the present invention, in step S3, the conditions of the first hydrothermal treatment include: the temperature is 50-300 °C, and the time is 4-100 hours; preferably, the temperature is 75-250 °C, and the time is 10-80 hours; preferably, the temperature is 80-180 °C, and the time is 18-50 hours.

[0066] In a specific embodiment of the present invention, in the present invention, in step S3, the crystallization state of the obtained ZSM-5 synthesis liquid is a state where the crystal grains are about to appear but have not yet appeared, close to the end of the crystallization induction period, and about to enter the rapid crystal nucleus growth stage. The obtained ZSM-5 synthesis liquid is subjected to XRD analysis, and there is a spectral peak at 2θ = 23.05°, and there is no spectral peak at 2θ = 23.87°. Preferably. The method for performing XRD analysis on the ZSM-5 synthesis liquid can be carried out according to the following method: After the ZSM-5 synthesis liquid is filtered, washed, dried, and calcined at 550 °C for 4 h, XRD analysis is then performed. The washing can be carried out with deionized water.

[0067] In a specific embodiment of the present invention, the molar ratio of the amount of the template agent to the amount of the silicon source is (0.1-10):1, preferably (0.1-3):1, more preferably (0.2-2.2):1, the molar ratio of the amount of the solvent to the amount of the silicon source is (2-150):1, preferably (10-120):1, and the molar ratio of the amount of the silicon source to the amount of the aluminum source is (10-800):1, preferably (20-800):1, where the silicon source is calculated as SiO2 and the aluminum source is calculated as Al2O3.

[0068] In a specific embodiment of the present invention, the silicon source is selected from one or more of tetraethyl orthosilicate, water glass, coarse pore silica gel, silica sol, white carbon black, and activated clay; the aluminum source is selected from one or more of aluminum sulfate, aluminum isopropoxide, aluminum nitrate, aluminum sol, sodium metaaluminate, and γ-aluminum oxide; the template agent is one or more of tetrapropylammonium fluoride, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, polyvinyl alcohol, triethanolamine, and sodium carboxymethyl cellulose, preferably one or more of tetrapropylammonium hydroxide, tetrapropylammonium chloride, and tetrapropylammonium bromide; the base source is sodium hydroxide.

[0069] In a specific embodiment of the present invention, in step S4, the conditions of the second hydrothermal treatment include: the temperature is 50 - 300 °C, and the time is 10 - 400 h; preferably, the temperature is 100 - 250 °C, and the time is 30 - 350 h; more preferably, the temperature is 100 - 200 °C, and the time is 50 - 120 hours.

[0070] In a specific embodiment of the present invention, the weight ratio of the ZSM-5 synthesis solution to the amount of the second solid is (2 - 10):1, preferably (4 - 10):1. Preferably, the weight ratio of the second solid on a dry basis to the ZSM-5 synthesis solution on a dry basis is greater than 0.2:1, for example (0.3 - 20):1 or (1 - 15):1 or (0.5 - 10):1 or (0.5 - 5):1 or (0.8 - 2):1 or (0.9 - 1.7):1.

[0071] In a specific embodiment of the present invention, the method further includes: after the second hydrothermal treatment, a process of recovering the core-shell molecular sieve may be included, and the recovery includes one or more steps of filtration, washing, and drying. The drying methods include, for example, air drying, oven drying, flash drying, and the drying conditions are, for example: the temperature is 50 - 150 °C, and the time is 0.5 - 4 h. The washing is a prior art, for example, water washing can be used, and the water can be deionized water. The weight ratio of the core-shell molecular sieve to water is 1:(5 - 20), and it can be washed once or multiple times until the pH value of the washed water is 8 - 9.

[0072] The dry basis referred to in the present invention means the solid product obtained after calcining the substance in air at 850 °C for 1 hour.

[0073] The method for preparing the core-shell molecular sieve of the present invention may have at least one of the following beneficial effects, and preferably has multiple of the following beneficial effects: (1) rapid preparation; (2) it is possible to synthesize SAPO-34 molecular sieve with a lower amount of template; (3) it can improve the shell coverage; (4) it can increase the total specific surface area of the synthesized molecular sieve; (5) the synthesized molecular sieve has a higher proportion of mesoporous surface area; (6) it is possible to prepare the core-shell molecular sieve without adhering nano-ZSM-5 molecular sieve; (7) when the prepared core-shell molecular sieve material is used for light oil catalytic cracking, for example, for the conversion of naphtha containing cycloalkane rings, it has a higher conversion rate and a higher ethylene and / or propylene yield; (8) the synthesized molecular sieve has more pores with a diameter of 2 - 50 nm, and its pore size distribution has peaks at pore diameters of 2 - 4 nm and 40 - 80 nm, and has a rich mesoporous and macroporous pore volume.

[0074] The third aspect of the present invention provides a core-shell molecular sieve prepared by the method provided in the second aspect of the present invention.

[0075] In one embodiment, the core-shell molecular sieve includes a SAPO-34 molecular sieve core and a ZSM-5 molecular sieve shell covering the surface of the SAPO-34 molecular sieve core; the ratio of the peak height at 2θ = 9.5° to the peak height at 2θ = 23.02° in the X-ray diffraction pattern of the core-shell molecular sieve is (0.05 - 15):1.

[0076] The fourth aspect of the present invention provides an application of the core-shell molecular sieve provided in the first aspect or the third aspect of the present invention in hydrocarbon conversion. The hydrocarbon conversion reaction may include, for example, catalytic cracking reaction, alkylation reaction, and isomerization reaction. Preferably, the core-shell molecular sieve is used for catalytic cracking of hydrocarbon oil or catalytic pyrolysis of hydrocarbon oil.

[0077] In one embodiment, the ratio of the peak height at 2θ = 9.5° to the peak height at 2θ = 23.02° in its X-ray diffraction pattern is (0.05 - 15):1, the total specific surface area is greater than 300 m 2 / g, the proportion of the mesoporous surface area in the total specific surface area is preferably 5 - 30%, the average crystal grain size of the shell molecular sieve is 50 nm - 1000 nm, the shell thickness of the shell molecular sieve is 100 nm - 2000 nm, the average crystal grain size of the core-phase molecular sieve is 1 μm - 10 μm, the core-phase molecular sieve is an aggregate of single or multiple crystal grains, the silicon-aluminum molar ratio of the shell molecular sieve (calculated as SiO2 / Al2O3, i.e., the silicon-aluminum ratio) is 10 - 500, preferably 10 - 200, the silicon-aluminum molar ratio of the core-phase molecular sieve (calculated as SiO2 / Al2O3) is 0.05 - 10, preferably 0.05 - 2, and the ratio of the core phase to the shell of the core-shell molecular sieve is preferably (0.2 - 20):1, such as (1 - 15):1, preferably (1 - 10):1.

[0078] According to the synthesis method of the core-shell molecular sieve provided by the present invention, one embodiment includes the following steps:

[0079] S1. Add the SAPO-34 molecular sieve to a first solution containing a surfactant with a concentration of 0.05 - 50 wt%, stir at 20 - 70 °C for 0.5 - 48 h for treatment, wherein the weight ratio of the first solution to the SAPO-34 molecular sieve is preferably (10 - 200):1, filter and dry to obtain a first solid, and the silicon-aluminum molar ratio SiO2 / Al2O3 of the first solid is preferably 25 - 200;

[0080] S2. Add the first solid to a slurry containing ZSM-5 molecular sieve, the content of ZSM-5 zeolite in the slurry containing ZSM-5 molecular sieve is 0.2 - 8 wt%, the weight ratio of the slurry to the first solid is preferably (10 - 50):1, stir at 20 - 60 °C for at least 0.5 hour, such as 0.5 - 24 hours, and then filter and dry to obtain a second solid.

[0081] S3. Hydrothermally treat the mixed solution formed by mixing a silicon source, an aluminum source, a template (denoted as R), and water at 30 - 300 °C for 3 - 100 hours. Preferably, hydrothermally treat it at 75 - 250 °C for 10 - 80 hours to obtain a ZSM-5 synthesis solution; wherein, R / SiO2 = 0.1 - 10:1, H2O / SiO2 = 2 - 150:1, SiO2 / Al2O3 = 10 - 800:1, Na2O / SiO2 = 0 - 2:1, and the above ratios are molar ratios.

[0082] S4. Add the second solid to the ZSM-5 synthesis solution and hydrothermally treat it at 50 - 300 °C for 10 - 400 hours. Preferably, after adding the second solid to the ZSM-5 synthesis solution, hydrothermally treat it at 100 - 250 °C for 30 - 350 hours. After the hydrothermal treatment, filter, wash, and dry to obtain a core-shell molecular sieve material. Preferably, the amounts of the silicon source and the aluminum source are such that the silicon-aluminum molar ratio of the obtained shell-layer ZSM-5 molecular sieve is 25 - 200 in terms of SiO2 / Al2O3.

[0083] The present invention will be further illustrated by the following examples, but the present invention is not limited thereby.

[0084] In the examples and comparative examples, the instrument and test conditions for XRD analysis: Instrument: Empyrean. Test conditions: Tube voltage 40 kV, tube current 40 mA, Cu target Kα radiation, 2θ scanning range 5° - 35°, scanning rate 2 (°) / min. Calculate the ratio of the core phase to the shell layer from the X-ray diffraction analysis spectral peaks, and use the JADE software to perform fitting calculation with the fitting function pseudo-voigt.

[0085] Measure the crystal grain size and particle size of the molecular sieve by SEM. Randomly measure 10 crystal grain sizes and take their average value to obtain the average crystal grain size of the molecular sieve sample; randomly measure 10 particle sizes of the particles and take their average value to obtain the average particle size of the molecular sieve sample.

[0086] Measure the thickness of the molecular sieve outer shell by the TEM method. Randomly measure the thickness of the shell layer at a certain place of a core-shell molecular sieve particle, measure 10 particles, and take their average value.

[0087] Measure the coverage of the molecular sieve by the SEM method. Calculate the ratio of the outer surface area of a core-phase particle with a shell layer to the outer surface area of the core-phase particle as the coverage of the particle. Randomly measure 10 particles and take their average value.

[0088] The mesopore specific surface area, total specific surface area, total pore volume, and pore size distribution were measured by the low-temperature nitrogen adsorption capacity method using an ASAP 2420 adsorption instrument from Micromeritics, USA. The samples were vacuum degassed at 100 °C for 0.5 h and 300 °C for 6 h, and N2 adsorption and desorption tests were carried out at a temperature of 77.4 K. The adsorption and desorption amounts of nitrogen by the test samples under different specific pressure conditions were measured to obtain the N2 adsorption-desorption isotherm curve. The BET specific surface area (total specific surface area) was calculated using the BET formula, and the micropore area was calculated by the t-plot method.

[0089] The silicon-aluminum molar ratio of the molecular sieve was measured by the TEM-EDS method.

[0090] The XRD analysis of the ZSM-5 synthesis solution was carried out as follows: The ZSM-5 synthesis solution was first filtered, then washed with deionized water 8 times the weight of the solid, dried at 120 °C for 4 h, calcined at 550 °C for 4 h, and after cooling, XRD measurement was carried out (the instrument and analysis method used for XRD measurement were as described above).

[0091] Example 1

[0092] S1. At room temperature (25 °C), the H-type SAPO-34 molecular sieve used as the core (with a silicon-aluminum molar ratio of 0.5, an average crystal grain size of 2.5 μm, and a crystallinity of 93.0%, whose SEM photograph is as Figure 2 shown, and the XRD pattern is as Figure 3 shown) was added to an aqueous solution containing methyl methacrylate and sodium chloride (where the concentration of methyl methacrylate was 0.2 wt%, and the concentration of sodium chloride was 5.0 wt%), stirred for 1 h, filtered, and dried in an air atmosphere at 50 °C to obtain the first solid;

[0093] S2. The first solid was put into a ZSM-5 molecular sieve suspension (a suspension formed by H-type ZSM-5 molecular sieve and water. In the ZSM-5 molecular sieve suspension, the concentration of ZSM-5 molecular sieve was 0.3 wt%, where the average crystal grain size of ZSM-5 molecular sieve was 0.5 μm, the silicon-aluminum molar ratio was 25, and the crystallinity was 93.2%. The ZSM-5 molecular sieve particles were single crystal grain particles, and its XRD pattern is as Figure 3 shown). The mass ratio of the first solid to the ZSM-5 molecular sieve suspension was 1:10, stirred at a temperature of 50 °C for 1 h, filtered, and the filter cake was dried in an air atmosphere at 90 °C to obtain the second solid;

[0094] S3. Dissolve aluminum isopropoxide in deionized water, add NaOH particles, and then successively add silica sol (SiO2 content 25.0 wt%, pH value 10.0, sodium oxide content 0.10 wt%) and tetrapropylammonium hydroxide solution (in the tetrapropylammonium hydroxide solution, the content of tetrapropylammonium hydroxide is 25 wt%). After stirring evenly, transfer it to a reaction kettle lined with polytetrafluoroethylene for crystallization, and carry out the first hydrothermal reaction at 80 °C for 48 h to obtain a ZSM-5 synthesis solution; after the ZSM-5 synthesis solution is filtered, washed, dried, and calcined, there is a peak at 2θ = 23.02° in the XRD pattern and no peak at 2θ = 23.87°.

[0095] S4. Add the second solid to the ZSM-5 synthesis solution (the weight ratio of the second solid to the ZSM-5 synthesis solution on a dry basis is 1:10), and carry out the second hydrothermal treatment at 120 °C for 60 h to obtain the core-shell molecular sieve, and its SEM photograph is as Figure 1 shown, and the XRD pattern is as Figure 3 shown.

[0096] Example 2

[0097] S1. At room temperature (25 °C), add 5.0 g of H-type SAPO-34 molecular sieve (silicon-aluminum ratio 0.3, average crystal grain size 2.0 μm, average particle size 10 μm, crystallinity 90.0%) to 50.0 g of an aqueous solution of polydiallyldimethylammonium chloride and sodium chloride (in this solution, the mass percentage of polydiallyldimethylammonium chloride is 0.2%, and the mass percentage of sodium chloride is 0.2%), stir for 2 h, filter, and dry the filter cake in an air atmosphere at 50 °C to obtain the first solid;

[0098] S2. Put the first solid into a suspension of H-type ZSM-5 molecular sieve (the weight percentage concentration of ZSM-5 molecular sieve in the ZSM-5 molecular sieve suspension is 2.5 wt%, the average crystal grain size of ZSM-5 molecular sieve is 0.1 μm, the silicon-aluminum ratio is 30.0, and the crystallinity is 92.0%); the mass ratio of SAPO-34 molecular sieve I to the ZSM-5 molecular sieve suspension is 1:45, stir at 50 °C for 2 hours, filter, and dry in an air atmosphere at 90 °C to obtain the second solid;

[0099] S3. Dissolve aluminum sol (concentration of Al2O3 is 25 wt%, molar ratio of aluminum to chlorine is 1.1) in deionized water, add NaOH particles, then successively add water glass (concentration of SiO2 is 251 g / L, modulus is 2.5) and tetrapropylammonium hydroxide solution (mass fraction of tetrapropylammonium hydroxide solution is 25%). After stirring evenly, transfer it to a reaction kettle lined with polytetrafluoroethylene for crystallization, and conduct the first hydrothermal treatment at 150 °C for 10 h to obtain a ZSM-5 synthesis solution. After the ZSM-5 synthesis solution is filtered, washed, dried, and calcined, there is a peak at 2θ = 23.02° in the XRD pattern and no peak at 2θ = 23.87°;

[0100] S4. Add the second solid to the ZSM-5 synthesis solution (the weight ratio of the second solid to the ZSM-5 synthesis solution on a dry basis is 1:10), and then conduct the second hydrothermal treatment at 130 °C for 80 h to obtain a core-shell molecular sieve, and its SEM photograph is as Figure 4 shown.

[0101] Example 3

[0102] S1. At room temperature of 25 °C, add H-type SAPO-34 molecular sieve used as the core phase (silicon-aluminum ratio is 0.4, average crystal grain size is 2000 nm, average particle size is 15.0 microns, crystallinity is 91.0%, dosage is 5.0 g) to 50.0 g of n-butylamine and sodium chloride aqueous solution (mass percentage of n-butylamine is 5.0%, mass fraction of sodium chloride is 2%). Stir for 24 h, filter, and dry in an air atmosphere at 70 °C to obtain the first solid;

[0103] S2. Put the first solid into the suspension of H-type ZSM-5 molecular sieve (the weight percentage concentration of ZSM-5 molecular sieve in the ZSM-5 molecular sieve suspension is: 5.0 wt%, the average crystal grain size of ZSM-5 molecular sieve is 50 nm, the silicon-aluminum ratio is 30.0, and the crystallinity is 95.0%). The mass ratio of SAPO-34 molecular sieve I to the ZSM-5 molecular sieve suspension is 1:20. Stir at a temperature of 50 °C for 10 h, filter, and then dry the filter cake in an air atmosphere at 120 °C to obtain the second solid;

[0104] S3. Dissolve sodium aluminate in 18.0 g of deionized water, add NaOH particles, then successively add coarse pore silica gel (SiO2 content is 98.0 wt%) and tetrapropylammonium bromide solution (mass fraction of tetrapropylammonium bromide solution is 25%). After stirring evenly, transfer it to a reaction kettle lined with polytetrafluoroethylene for crystallization, and conduct the first hydrothermal treatment at 130 °C for 30 h to obtain a ZSM-5 synthesis solution. After the ZSM-5 synthesis solution is filtered, washed, dried, and calcined, there is a peak at 2θ = 23.02° in the XRD pattern and no peak at 2θ = 23.87°;

[0105] S4. Add the second solid to the ZSM-5 synthesis solution (the weight ratio of the second solid to the ZSM-5 synthesis solution on a dry basis is 1:4), and conduct the second hydrothermal treatment at 80 °C for 100 h to obtain the core-shell molecular sieve.

[0106] Example 4

[0107] S1. At 25 °C, add the hydrogen-form SAPO-34 molecular sieve used as the core phase (silicon-aluminum ratio of 0.8, average crystal grain size of 5.0 μm, crystallinity of 92.0%, dosage of 5.0 g) to 50.0 g of a sodium chloride solution of pyridine dicarboxylic acid with a mass percentage of pyridine dicarboxylic acid of 1.0% (sodium chloride concentration of 1 wt%), stir for 10 h, filter, and dry the filter cake in an air atmosphere at 30 °C to obtain the first solid.

[0108] S2. Put the first solid into a ZSM-5 molecular sieve suspension (the weight percentage concentration of ZSM-5 molecular sieve in the ZSM-5 molecular sieve suspension is 4.0 wt%, hydrogen-form ZSM-5 molecular sieve, average crystal grain size of 0.5 μm, silicon-aluminum ratio of 30, crystallinity of 90.0%). The mass ratio of SAPO-34 molecular sieve I to the ZSM-5 molecular sieve suspension is 1:15. Stir at 50 °C for 24 hours, filter, and dry the filter cake in an air atmosphere at 140 °C to obtain the second solid.

[0109] S3. Dissolve aluminum sulfate in deionized water, add NaOH particles, then sequentially add white carbon black and sodium carboxymethylcellulose (CAS No.: 9004-32-4), stir evenly, transfer to a reaction kettle lined with polytetrafluoroethylene for crystallization, and conduct the first hydrothermal treatment at 150 °C for 12 h to obtain the ZSM-5 synthesis solution.

[0110] S4. Add the second solid to the ZSM-5 synthesis solution (the weight ratio of the second solid to the ZSM-5 synthesis solution on a dry basis is 1:8), and conduct the second hydrothermal treatment at 150 °C for 50 h to obtain the ZSM-5@SAPO-34 core-shell molecular sieve.

[0111] Example 5

[0112] The molecular sieve was prepared by the same method as in Example 1, except that in step S3, the temperature of the first hydrothermal treatment was 30 °C and the time was 3 h. After the crystallization product was filtered, washed, dried, and calcined, there was no peak at 2θ = 23.02° and no peak at 2θ = 23.87° in the XRD pattern.

[0113] Comparative Example 1

[0114] Mix 10.0 g of SAPO-34 and 20.0 g of ZSM-5 molecular sieve (the SAPO-34 and ZSM-5 molecular sieves used in steps 1 and 2) mechanically and then conduct characterization.

[0115] Table 1

[0116]

[0117] Table 1 shows the synthesis conditions and properties of the core-shell molecular sieve (in the table, the ratio of the peak height (D1) at 2θ = 9.5° to the peak height (D2) at 2θ = 23.02° is expressed as D1 / D2).

[0118] Test Example

[0119] The above molecular sieve was subjected to ammonium exchange to make the sodium oxide content less than 0.1 wt%, and an H-type molecular sieve was obtained. The ammonium exchange conditions were: molecular sieve: ammonium chloride: H2O = 1:0.5:10, ammonium exchange temperature 85 °C, ammonium exchange time 1 h. After ammonium exchange, it was filtered, washed, dried and calcined at 550 °C for 2 h. The obtained H-type molecular sieve sample was evaluated on a fixed-bed micro-reactor FB. The feedstock oil was the model compound n-octane, and the evaluation conditions were: reaction temperature 600 °C, catalyst-oil ratio (by weight) 0.15. The results are listed in Table 2.

[0120] Table 2

[0121] Sample Conversion rate, % Ethylene yield, % Propylene yield, % Example 1 58.80 7.07 10.15 Example 2 57.51 7.02 9.98 Example 3 56.94 6.84 9.16 Example 4 55.87 6.60 8.54 Example 5 52.86 5.89 7.87 Comparative Example 1 34.22 4.68 6.07

[0122] As can be seen from the above, the core-shell molecular sieve of the present invention has a SAPO-34 molecular sieve core and a ZSM-5 molecular sieve shell, and has high reaction activity. When it is used in the catalytic cracking reaction of hydrocarbon oil, the yields of propylene and ethylene in the reaction products can be increased

[0123] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0124] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. In order to avoid unnecessary repetition, the present invention will not describe various possible combination methods separately.

[0125] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A core-shell molecular sieve, the core-shell molecular sieve comprising a SAPO-34 molecular sieve core and a ZSM-5 molecular sieve shell covering the surface of the SAPO-34 molecular sieve core; the ratio of the peak height of the peak at 2θ = 9.5° to the peak height of the peak at 2θ = 23.02° in the X-ray diffraction pattern of the core-shell molecular sieve is (0.05 - 15):1; The core-shell molecular sieve is prepared by a method comprising the following steps: S1. First, bring the SAPO-34 molecular sieve into first contact and mixing with a first solution containing a surfactant, and separate a first solid from the resulting mixture; S2. Second, bring the first solid into second contact and mixing with a slurry containing a ZSM-5 molecular sieve, and separate a second solid from the resulting mixture; S3. First, hydrothermally treat a second solution containing a silicon source, an aluminum source, a template agent, an alkali source, and a solvent at 75 - 250 °C for 10 - 80 h to obtain a ZSM-5 synthesis solution; there is a spectral peak at 2θ = 23.02° in the X-ray diffraction pattern of the ZSM-5 synthesis solution, and there is no spectral peak at 2θ = 23.87°; S4. Mix the second solid with the ZSM-5 synthesis solution and conduct a second hydrothermal treatment.

2. The core-shell molecular sieve according to claim 1, wherein, The ratio of the peak height of the peak at 2θ = 9.5° to the peak height of the peak at 2θ = 23.02° in the X-ray diffraction pattern of the core-shell molecular sieve is (0.1 - 10):

1.

3. The core-shell molecular sieve according to claim 1, wherein The weight ratio of the SAPO-34 molecular sieve core to the ZSM-5 molecular sieve shell in the core-shell molecular sieve is (0.2 - 20):

1.

4. The core-shell molecular sieve according to claim 3, wherein, The weight ratio of the SAPO-34 molecular sieve core to the ZSM-5 molecular sieve shell in the core-shell molecular sieve is (1 - 10):

1.

5. The core-shell molecular sieve according to claim 1, wherein, The total specific surface area of the core-shell molecular sieve is 300 m 2 / g or more.

6. The core-shell molecular sieve according to claim 5, wherein, The total specific surface area of the core-shell molecular sieve is 350-550 m 2 / g.

7. The core-shell molecular sieve according to claim 5, wherein, The total specific surface area of the core-shell molecular sieve is 400-500 m 2 / g.

8. The core-shell molecular sieve according to claim 5, wherein The proportion of the mesoporous specific surface area in the total specific surface area of the core-shell molecular sieve is 5 - 30%.

9. The core-shell molecular sieve according to claim 5, wherein, The proportion of the mesoporous specific surface area in the total specific surface area of the core-shell molecular sieve is 10 - 25%.

10. The core-shell molecular sieve according to claim 1, wherein, The average thickness of the ZSM-5 molecular sieve shell is 50 - 2000 nm.

11. The core-shell molecular sieve according to claim 1, wherein, The average crystal grain size of the ZSM-5 molecular sieve shell is 50 - 1000 nm, and the average crystal grain size of the SAPO-34 molecular sieve core is 1 - 10 μm.

12. The core-shell molecular sieve according to claim 1, wherein, The silicon-aluminum molar ratio of the SAPO-34 molecular sieve core is 0.05 - 2 in terms of SiO2 / Al2O3, and the silicon-aluminum molar ratio of the ZSM-5 molecular sieve shell is 10 - 500 in terms of SiO2 / Al2O3.

13. The core-shell molecular sieve according to claim 1, wherein, The average coverage of the ZSM-5 molecular sieve shell on the outer surface of the SAPO-34 molecular sieve core is 50 - 100%.

14. The core-shell molecular sieve according to claim 13, wherein, The average coverage of the ZSM-5 molecular sieve shell on the outer surface of the SAPO-34 molecular sieve core is 80 - 100%.

15. The core-shell molecular sieve according to claim 1, wherein, In the core-shell molecular sieve described above, the pore volume of pores with a pore diameter of 2 - 80 nm accounts for 10 - 30% of the total pore volume, and the pore volume of pores with a pore diameter of 20 - 80 nm accounts for 50 - 70% of the pore volume of pores with a pore diameter of 2 - 80 nm.

16. The core-shell molecular sieve according to claim 1, wherein, In step S1, the content of the surfactant in the first solution is 0.05 - 20% by weight; the weight ratio of the first solution to the SAPO-34 molecular sieve based on the dry weight is (10 - 200):1; the conditions for the first contact mixing include: temperature is 20 - 70°C, time is 1 - 36 hours; The surfactant is selected from one or more of polymethyl methacrylate, poly(diallyldimethylammonium chloride), pyridinedicarboxylic acid, ammonia water, ethylamine, n-butylamine, tetrapropylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium hydroxide; The SAPO-34 molecular sieve is selected from one or more of sodium-type SAPO-34 molecular sieve, hydrogen-type SAPO-34 molecular sieve, and ion-exchanged SAPO-34 molecular sieve; The silicon-aluminum molar ratio of the SAPO-34 molecular sieve, calculated as SiO2 / Al2O3, is 0.05 - 10, and the average crystal grain size is 1 - 10 μm.

17. The core-shell molecular sieve according to claim 1, wherein, In step S1, the first solution further contains salt, the content of the salt is 0.05 - 10.0% by weight, and the salt is selected from one or more of sodium chloride, potassium chloride, ammonium chloride, and ammonium nitrate.

18. The core-shell molecular sieve according to claim 1, wherein, In step S2, the content of the ZSM-5 molecular sieve in the slurry is 0.1 - 10% by weight; the weight ratio of the slurry to the SAPO-34 molecular sieve based on the dry weight is (10 - 50):1; the conditions for the second contact mixing include: temperature is 20 - 60°C, time is 1 - 24 hours; The silicon-aluminum molar ratio of the ZSM-5 molecular sieve, calculated as SiO2 / Al2O3, is 10 - 200, and the average crystal grain size is 0.05 - 1.0 μm.

19. The core-shell molecular sieve according to claim 18, wherein, In step S2, the content of the ZSM-5 molecular sieve in the slurry is 0.3 - 8% by weight.

20. The core-shell molecular sieve according to claim 1, wherein, In step S3, the conditions for the first hydrothermal treatment include: temperature is 80 - 180°C, time is 18 - 50 hours; The molar ratio of the amount of the template agent to the amount of the silicon source is (0.1 - 10):1, the molar ratio of the amount of the solvent to the amount of the silicon source is (2 - 150):1, and the molar ratio of the amount of the silicon source to the amount of the aluminum source is (10 - 800):1, where the silicon source is calculated as SiO2 and the aluminum source is calculated as Al2O3; The silicon source is selected from one or more of tetraethyl orthosilicate, water glass, macroporous silica gel, silica sol, white carbon black, and activated clay; the aluminum source is selected from one or more of aluminum sulfate, aluminum isopropoxide, aluminum nitrate, aluminum sol, sodium metaaluminate, and γ-aluminum oxide; the template agent is selected from one or more of tetrapropylammonium fluoride, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium chloride, polyvinyl alcohol, triethanolamine, and sodium carboxymethyl cellulose; the base source is sodium hydroxide; the solvent is water.

21. The core-shell molecular sieve according to claim 1, wherein, In step S4, the conditions for the second hydrothermal treatment include: temperature is 100 - 250°C, time is 30 - 350 h; The weight ratio of the ZSM-5 synthesis liquid to the amount of the second solid is (2 - 10):

1.

22. The core-shell molecular sieve according to claim 21, wherein, In step S4, the conditions for the second hydrothermal treatment include: temperature is 100 - 200°C, time is 50 - 120 hours.

23. Use of the core-shell molecular sieve according to any one of claims 1-22 in catalytic cracking or catalytic pyrolysis of hydrocarbon oil.

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