Core-shell structure zeolite containing ZSM-5 zeolite shell as well as preparation method and application of core-shell structure zeolite

Abstract

The invention relates to core-shell structure zeolite containing a ZSM-5 zeolite shell as well as a preparation method and application of the core-shell structure zeolite. The core-shell structure zeolite containing the ZSM-5 zeolite shell comprises spherical nuclear-phase zeolite and a shell layer wrapping the nuclear-phase zeolite, wherein the shell layer is continuous and compact ZSM-5 zeolite, and the ratio of the average particle size of the ZSM-5 zeolite to the average thickness of the shell layer is 9-32. The core-shell structure zeolite containing the ZSM-5 zeolite shell has a continuous and compact ZSM-5 zeolite shell layer, high pore channel smoothness exists between a nuclear phase and a shell phase, and when the core-shell structure zeolite containing the ZSM-5 zeolite shell is used in a catalytic cracking reaction, high reaction activity of nuclear-phase zeolite can be maintained, the selectivity of a target product low-carbon olefin can be improved, and the selectivity of side reactions such as hydrogen transfer can be reduced; meanwhile, a macromolecular aromatic hydrocarbon product generated by the nuclear-phase zeolite can be continuously cracked into a micromolecular BTX product in the shell ZSM-5 zeolite in the outward diffusion process, so that the BTX selectivity is improved.

Description

Technical Field

[0001] The present disclosure relates to the technical fields of material preparation and petrochemical engineering, and in particular to a core-shell zeolite containing a ZSM-5 zeolite shell, a preparation method thereof, and applications thereof. Background Art

[0002] Zeolites play a key role as catalysts in the conversion and refining of fossil fuels. Zeolites, with their regular microporous structure, large surface area, and controlled acidic sites, are widely used in catalytic cracking, light oil isomerization, olefin alkylation, catalytic reforming, hydrocracking, and separation processes. However, the simple pore structure of zeolites restricts the diffusion of reactants and products. Furthermore, surface defects hinder the hydrothermal stability of zeolites, limiting their application.

[0003] Growing a ZSM-5 shell coating on the surface of the core-phase zeolite can ensure that the mass transfer direction of the molecules follows a predetermined path and produce a synergistic effect of multiple pores, which is beneficial to improving the selectivity of the zeolite for specific reactions. It can also fill the defect sites on the outer surface of the core-phase zeolite and passivate the outer surface of the core-phase zeolite, thereby reducing the occurrence of side reactions and improving the hydrothermal stability of the zeolite.

[0004] Currently, the synthesis of core-shell zeolites containing a ZSM-5 zeolite shell cannot guarantee the formation of a dense shell of the shell ZSM-5 zeolite on the surface of the core phase zeolite. Hydrothermal synthesis is often used, but this method can result in some ZSM-5 nucleating and growing independently in the liquid phase. There are also reports of steam-assisted synthesis, but since it is impossible to ensure that the silicon and aluminum sources are tightly coated on the core phase zeolite surface, the shell ZSM-5 often accumulates as small crystallites on the surface of the core phase zeolite.

[0005] In summary, the pore structure of the products synthesized by the existing technology is not rich enough, and it is difficult to form a continuous and dense coating shell, which limits its application performance in different fields. In addition, there are shortcomings such as complex synthesis process, long synthesis cycle, and low single-pot yield, making it difficult to achieve industrial production. Summary of the Invention

[0006] The purpose of the present disclosure is to provide a core-shell structured zeolite containing a continuous and dense ZSM-5 zeolite shell, and a preparation method and application thereof.

[0007] In order to achieve the above-mentioned objectives, the present disclosure provides, in a first aspect, a core-shell structure zeolite containing a ZSM-5 zeolite shell, wherein the core-shell structure zeolite containing a ZSM-5 zeolite shell comprises a spherical core-phase zeolite and a shell layer encapsulating the core-phase zeolite; wherein the shell layer is a continuous and dense ZSM-5 zeolite, and the ratio of the average particle size of the ZSM-5 zeolite to the average thickness of the shell layer is 9 to 32.

[0008] Optionally, the average particle size of the ZSM-5 zeolite is 25 to 10,000 nm; the average thickness of the shell is 8 to 450 nm; and the particle size of the core phase zeolite is 20 to 2,500 nm.

[0009] Optionally, the total specific surface area of ​​the core-shell zeolite containing the ZSM-5 zeolite shell is 300 to 700 m 2 / g, external specific surface area is 20~300m 2 / g, micropore specific surface area is 200~600m 2 / g, the total pore volume is 0.3-0.6 ml / g, the micropore volume is 0.1-0.4 ml / g, and the mesopore volume is 0.1-0.3 ml / g.

[0010] Optionally, the core phase zeolite is at least one selected from aluminum silicate zeolite, aluminum phosphate zeolite, silicon phosphate aluminum zeolite, titanium silicalite and pure silicalite.

[0011] In a second aspect of the present disclosure, a method for preparing the core-shell zeolite containing a ZSM-5 zeolite shell according to the first aspect of the present disclosure is provided, the method comprising the following steps:

[0012] The core phase zeolite, the shell silicon source, the base catalyst, the cationic surfactant, the organic solvent, the water and the optional first aluminum source are mixed to carry out a self-assembly reaction, and the obtained solid product is subjected to a first drying and a first calcination to obtain a precursor;

[0013] Mixing the precursor with a template and an optional second aluminum source and performing a second drying to obtain a mixture to be crystallized;

[0014] The mixture to be crystallized is subjected to steam-assisted crystallization, and the obtained crystallized product is subjected to a third drying and a second calcination to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

[0015] Optionally, the weight ratio of the shell silicon source to the core phase zeolite calculated as SiO2 is (0.2-5):1;

[0016] The molar ratio of the total molar amount of the first aluminum source and the second aluminum source to the shell silicon source calculated as SiO2 is (0.001-0.5):1;

[0017] The weight ratio of the base catalyst to the shell silicon source is (0.01-30):1;

[0018] The weight ratio of the cationic surfactant, the organic solvent and the water is (0.001-0.1):1:(1-20);

[0019] The molar ratio of the precursor to the template calculated as SiO2 is 1:(0.03-0.5).

[0020] Optionally, the weight ratio of the shell silicon source to the core phase zeolite calculated as SiO2 is (0.2-1.2):1;

[0021] The molar ratio of the total molar amount of the first aluminum source and the second aluminum source to the shell silicon source calculated as SiO2 is (0.005-0.05):1;

[0022] The weight ratio of the base catalyst to the shell silicon source is (0.1-5):1;

[0023] The weight ratio of the cationic surfactant, the organic solvent and the water is (0.005-0.02):1:(1.2-4);

[0024] The molar ratio of the precursor to the template calculated as SiO2 is 1:(0.1-0.3).

[0025] Optionally, the shell silicon source is organic silane and / or inorganic silicate.

[0026] Optionally, the first aluminum source is at least one selected from aluminum isopropoxide, triethylaluminum, sodium aluminate and potassium aluminate;

[0027] The second aluminum source is at least one selected from aluminum isopropoxide, sodium aluminate, aluminum isopropoxide, triethylaluminum, sodium aluminate and potassium aluminate.

[0028] Optionally, the base catalyst is at least one selected from ammonia water, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide.

[0029] Optionally, the cationic surfactant has the chemical formula C n H 2n+1 NR m X 4-m , wherein n is an integer of 8 to 22, m is an integer of 1 to 3, R is a C1 to C22 alkyl group, and X is Cl, Br or OH.

[0030] Optionally, the organic solvent is at least one selected from C1-C4 alcohol, benzene, toluene, tetrahydrofuran, chloroform, dichloromethane, acetonitrile and diethyl ether.

[0031] Optionally, the template is at least one selected from tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium bromide, tetrapropylammonium chloride, tetraethylammonium chloride, n-butylamine and triethanolamine.

[0032] Optionally, the self-assembly reaction conditions include: temperature of 0 to 75° C., time of 1 to 8 h;

[0033] The first drying conditions include: a temperature of 10 to 220° C. and a time of 1 to 24 hours;

[0034] The first calcination conditions include: a temperature of 400 to 850° C., an air atmosphere, and a calcination time of 2 to 10 hours;

[0035] The second drying conditions include: a temperature of 10 to 220° C. and a time of 1 to 24 hours;

[0036] The conditions of the third drying include: a temperature of 10 to 220° C. and a time of 1 to 24 hours;

[0037] The conditions for the second calcination include: a temperature of 400 to 850° C., an air atmosphere, and a calcination time of 2 to 10 hours.

[0038] Optionally, the steam-assisted crystallization conditions include: a temperature of 110 to 220° C. and a time of 1 to 100 hours.

[0039] The third aspect of the present disclosure provides use of the core-shell structured zeolite containing the ZSM-5 zeolite shell described in the first aspect of the present disclosure in catalytic cracking reaction to produce light olefins.

[0040] Through the above technical solution, the core-shell structured zeolite containing a ZSM-5 zeolite shell disclosed in the present invention has a continuous and dense ZSM-5 zeolite shell layer, and there is a high degree of pore patency between the core phase and the shell phase. When used in catalytic cracking reactions, it is beneficial to maintain the high reaction activity of the core phase zeolite and improve the selectivity of the target product light olefins, while reducing the selectivity of side reactions such as hydrogen transfer; at the same time, the large molecular aromatic hydrocarbon products produced by the core phase zeolite can continue to be cracked into small molecular BTX products in the shell layer ZSM-5 zeolite during the outward diffusion process, thereby improving the selectivity of BTX.

[0041] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0043] Figure 1 This is the XRD spectrum of the core-shell zeolite containing the ZSM-5 zeolite shell prepared in Example 1.

[0044] Figures 2 to 6 TEM images of the core-shell zeolites containing ZSM-5 zeolite shells prepared in Examples 1 to 5.

[0045] Figure 7This is the XRD spectrum of the core-shell structured zeolite containing a ZSM-5 zeolite shell prepared in Example 6.

[0046] Figure 8 This is a TEM image of the core-shell structured zeolite containing a ZSM-5 zeolite shell prepared in Example 6.

[0047] Figure 9 This is the XRD spectrum of the core-shell structured zeolite containing a ZSM-5 zeolite shell prepared in Example 7.

[0048] Figure 10 This is a TEM image of the core-shell structured zeolite containing a ZSM-5 zeolite shell prepared in Example 7.

[0049] Figure 11 This is the XRD spectrum of the zeolite prepared in Comparative Example 1. DETAILED DESCRIPTION

[0050] The following describes the specific embodiments of the present disclosure in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0051] In a first aspect of the present disclosure, a core-shell zeolite containing a ZSM-5 zeolite shell is provided, wherein the core-shell zeolite containing a ZSM-5 zeolite shell comprises a spherical core-phase zeolite and a shell layer encapsulating the core-phase zeolite; wherein the shell layer is a continuous and dense ZSM-5 zeolite, and the ratio of the average particle size of the ZSM-5 zeolite to the average thickness of the shell layer is 9 to 32.

[0052] The core-shell structure zeolite containing the ZSM-5 zeolite shell has an embedded core-shell structure, and the shell is a zeolite shell formed by continuous and dense ZSM-5 zeolite. In one embodiment, the ratio of the average particle size of the shell ZSM-5 zeolite to the average thickness of the shell is 9 to 32, specifically 8 to 30, 10 to 28 or 11 to 25, preferably 12 to 20. Among them, the average particle size of the shell ZSM-5 zeolite refers to the average value of the particle size of the ZSM-5 zeolite in the shell (the calculation method is to randomly measure the continuous ZSM-5 zeolite grain size of 100 lattice fringes in the TEM image and take the average value); the average thickness of the shell refers to the average value of the thickness of the ZSM-5 shell (the calculation method is to randomly measure the thickness of the ZSM-5 shell 100 times perpendicular to the crystal plane of the core phase zeolite in the TEM image and take the average value).

[0053] Furthermore, the particle size range of the shell ZSM-5 zeolite (range from minimum particle size to maximum particle size) can be 20 to 25,000 nm, and the average particle size can be 25 to 10,000 nm, preferably 130 to 350 nm; the thickness range of the shell (range from minimum thickness to maximum thickness) can be 2 to 1,000 nm, preferably 2 to 100 nm, and the average thickness of the shell can be 8 to 450 nm, preferably 5 to 30 nm; the particle size of the core phase zeolite can be 20 to 2,500 nm, preferably 20 to 600 nm.

[0054] The core-shell zeolite containing the ZSM-5 zeolite shell disclosed herein retains the microporous skeleton of the core phase zeolite, and the continuous and dense ZSM-5 zeolite shell is rich in micropores and mesopores, and the pores have strong openness, so that the core phase and the shell phase have a high degree of pore patency. Specifically, the total specific surface area of ​​the core-shell zeolite containing the ZSM-5 zeolite shell can be 300 to 700 m 2 / g, the external specific surface area can be 20 to 300m 2 / g, the micropore specific surface area can be 200~600m 2 / g, the total pore volume can be 0.3-0.6 ml / g, the micropore volume can be 0.1-0.4 ml / g, and the mesopore volume can be 0.1-0.3 ml / g.

[0055] The core phase zeolite can be various zeolites commonly used in the art that can be used for catalytic reactions. For example, the core phase zeolite can be at least one selected from aluminum silicate zeolite, aluminum phosphate zeolite, silicon phosphate aluminum zeolite, titanium silicalite and pure silicalite; further, the core phase zeolite can be at least one selected from FAU type zeolite, MFI type zeolite, BEA type zeolite, CHA type zeolite and FER type zeolite, preferably at least one selected from MFI type zeolite, BEA type zeolite and FAU type zeolite. The present disclosure can select core phase zeolites with different characteristics to meet actual application requirements. For the relevant characteristics of the core phase zeolite, the present disclosure has no special restrictions.

[0056] The core-shell structure zeolite containing the ZSM-5 zeolite shell disclosed herein can cover the defect sites of the core-phase zeolite with the shell ZSM-5 zeolite, which is beneficial to improving the hydrothermal stability of the core-phase zeolite. The core-shell structure zeolite containing the ZSM-5 zeolite shell disclosed herein is particularly suitable for catalytic cracking reactions to produce light olefins. It can improve the selectivity of the target product light olefins while maintaining the high reaction activity of the core-phase zeolite and reduce the selectivity of side reactions such as hydrogen transfer; at the same time, the macromolecular aromatic hydrocarbon products produced by the core-phase zeolite can continue to crack into small molecular BTX products in the shell ZSM-5 zeolite during the outward diffusion process, thereby improving the selectivity of BTX.

[0057] In a second aspect of the present disclosure, a method for preparing the core-shell zeolite containing a ZSM-5 zeolite shell according to the first aspect of the present disclosure is provided, the method comprising the following steps S1 to S3:

[0058] S1, mixing a core phase zeolite, a shell silicon source, a base catalyst, a cationic surfactant, an organic solvent, water, and an optional first aluminum source to perform a self-assembly reaction, and performing a first drying and a first calcination on the obtained solid product to obtain a precursor;

[0059] S2, mixing the precursor with a template and an optional second aluminum source and performing a second drying to obtain a mixture to be crystallized;

[0060] S3, performing steam-assisted crystallization on the mixture to be crystallized, and performing a third drying and a second calcination on the obtained crystallized product to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

[0061] According to the present disclosure, the aluminum element in the core-shell zeolite containing the ZSM-5 zeolite shell can be deposited on the surface of the core phase zeolite together with SiO2 in step S1, or introduced into the synthesis system together with the template in step S2, or an aluminum source can be added in both steps S1 and S2. That is, at least one of the first aluminum source and the second aluminum source is present in the method. Specifically, in one embodiment, the method includes the following steps:

[0062] (1) mixing a core phase zeolite, a shell silicon source, an alkaline catalyst, a cationic surfactant, an organic solvent, water, and a first aluminum source to perform a self-assembly reaction, and performing a first drying and a first calcination on the obtained solid product to obtain a precursor;

[0063] (2) mixing the precursor with a template and performing a second drying to obtain a mixture to be crystallized;

[0064] (3) The mixture to be crystallized is subjected to steam-assisted crystallization, and the resulting crystallized product is subjected to a third drying and a second calcination to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

[0065] In another embodiment, the method comprises the following steps:

[0066] a. mixing a core phase zeolite, a shell silicon source, an alkali catalyst, a cationic surfactant, an organic solvent and water to perform a self-assembly reaction, and performing a first drying and a first calcination on the obtained solid product to obtain a precursor;

[0067] b. mixing the precursor with a template and a second aluminum source and performing a second drying to obtain a mixture to be crystallized;

[0068] c. The mixture to be crystallized is subjected to steam-assisted crystallization, and the resulting crystallized product is subjected to a third drying and a second calcination to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

[0069] The first aluminum source and the second aluminum source can be aluminum-containing compounds commonly found in the art. For example, the first aluminum source and the second aluminum source can each independently be at least one selected from aluminum isopropoxide, triethylaluminum, sodium aluminate, and potassium aluminate. Preferably, the first aluminum source and the second aluminum source can each independently be aluminum isopropoxide and / or sodium aluminate. The molar ratio of the first aluminum source and the second aluminum source to the shell silicon source calculated as SiO2 can be (0.001-0.5):1, preferably (0.005-0.05):1.

[0070] According to the present disclosure, in step S1, the state of the core phase zeolite can be a molecular sieve slurry dispersed by ultrasonic treatment, or a ground powder.

[0071] The shell silicon source can be an organic silicon source or an inorganic silicon source commonly used in the art. For example, the shell silicon source can be an organic silicon ester alkane and / or an inorganic silicate, wherein the organic silicon ester alkane can be, for example, ethyl orthosilicate, methyl orthosilicate, etc., and the inorganic silicate can be, for example, sodium silicate, etc.; preferably, the shell silicon source is ethyl orthosilicate and / or sodium silicate.

[0072] The base catalyst may be an organic base or an inorganic base. Specifically, the organic base may include a quaternary ammonium base such as at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide. The inorganic base may include at least one of ammonia water, sodium hydroxide, and potassium hydroxide. In one embodiment, the base catalyst may be at least one selected from ammonia water, sodium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide, preferably at least one selected from ammonia water, tetrapropylammonium hydroxide, and sodium hydroxide.

[0073] In one embodiment, the chemical formula of the cationic surfactant is C n H 2n+1 NR m X 4-m , wherein n is an integer of 8 to 22, m is an integer of 1 to 3, R is a C1 to C22 alkyl group, and X is Cl, Br or OH. Preferably, the cationic surfactant is selected from hexadecyltrimethylammonium bromide (chemical formula is C 16 H 33 N(CH3)3Br), tetradecyltrimethylammonium chloride (chemical formula is C 14 H 29N(CH3)3Cl), tetrapropylammonium hydroxide (chemical formula is C3H7N(C3H7)3OH).

[0074] The organic solvent may be any common organic solvent miscible with water. Specifically, the organic solvent may be at least one selected from C1 to C4 alcohols, benzene, toluene, tetrahydrofuran, chloroform, dichloromethane, acetonitrile and diethyl ether. Preferably, the organic solvent is at least one selected from methanol, ethanol and isopropanol.

[0075] The usage ratio of the core phase zeolite, shell silicon source, alkali catalyst, cationic surfactant, organic solvent and water can be adjusted within a certain range. Specifically, the weight ratio of the shell silicon source to the core phase zeolite calculated as SiO2 can be (0.2-5):1, preferably (0.2-1.2):1; the weight ratio of the alkali catalyst to the shell silicon source can be (0.01-30):1, preferably (0.1-5):1; the weight ratio of the cationic surfactant, the organic solvent and the water can be (0.001-0.1):1:(1-20), preferably (0.005-0.02):1:(1.2-4); the weight ratio of the cationic surfactant to the core phase zeolite can be (0.1-10):1, preferably (0.5-1.5):1.

[0076] The self-assembly reaction conditions may include: a temperature of 0-75°C and a time of 1-8 hours. After the self-assembly reaction is completed, the solid product can be obtained using common solid-liquid separation methods, such as filtration, suction filtration, centrifugation, etc. The first drying conditions may include: a temperature of 10-220°C and a time of 1-24 hours; the first calcination conditions may include: a temperature of 400-850°C, an air atmosphere, and a time of 2-10 hours.

[0077] In one embodiment, step S1 may include: adding the base catalyst and the cationic surfactant to a solution prepared in a certain proportion of the organic solvent and water, then adding the core phase zeolite, stirring evenly, adding the shell silicon source and the optional first aluminum source to carry out the self-assembly reaction, obtaining the solid product through solid-liquid separation, and then performing the first drying and first calcination on the solid product to obtain the precursor.

[0078] In step S2, the template agent can be a template agent commonly used in the art that can be directed to MFI structure zeolite. Specifically, the template agent can be at least one selected from tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium bromide, tetrapropylammonium chloride, tetraethylammonium chloride, n-butylamine and triethanolamine, preferably tetraethylammonium hydroxide and / or tetrapropylammonium hydroxide.

[0079] The molar ratio of the precursor to the template calculated as SiO2 can be 1:(0.03-0.5), preferably 1:(0.1-0.3). The precursor, template, and optional second aluminum source can be mixed by common mixing methods such as stirring, impregnation, and mechanical mixing.

[0080] The second drying conditions may include: a temperature of 10 to 220° C. and a time of 1 to 24 hours.

[0081] In step S3, the process of steam-assisted crystallization of the mixture to be crystallized can be carried out in a high-pressure closed container, using water as the liquid phase, and the water vapor is not in direct contact with the mixture to be crystallized. The conditions for the steam-assisted crystallization may include: a temperature of 110 to 220° C. and a time of 1 to 100 hours.

[0082] The conditions for the third drying may include: a temperature of 10 to 220° C. and a time of 1 to 24 hours; the conditions for the second calcination may include: a temperature of 400 to 850° C., an air atmosphere, and a time of 2 to 10 hours.

[0083] The preparation method of the core-shell zeolite containing the ZSM-5 zeolite shell disclosed in the present invention has the advantages of short synthesis process cycle, simple operation, low raw material cost, and low test equipment requirements, which is conducive to industrial production and application.

[0084] The third aspect of the present disclosure provides use of the core-shell structured zeolite containing the ZSM-5 zeolite shell described in the first aspect of the present disclosure in catalytic cracking reaction to produce light olefins.

[0085] Specifically, the application may include: catalytic cracking of cycloalkanes, chain alkanes or heavy oil to produce light olefins at 550°C to 700°C and a catalyst-to-oil ratio of 0.1 to 50.

[0086] The present disclosure is further described below with reference to examples, but the contents of the present disclosure are not limited thereby.

[0087] In the following examples, TEM detection was performed using an atomic resolution analytical transmission electron microscope JEM-ARM200F manufactured by JEOL Ltd. The test conditions were as follows: an accelerating voltage of 200 kV, and the sample suspension was dispersed onto a grating.

[0088] X-ray diffractometer (XRD) was performed using an Empyrean X-ray diffractometer from PANalytical (The Netherlands) using Cu Kα radiation (tube current 40 mA, voltage 40 kV). The relative crystallinity of the sample was calculated as the percentage of the characteristic peak area of ​​the zeolite in the XRD spectrum of the sample to the characteristic peak area of ​​the zeolite in the standard sample. The five peaks at 23.1°, 23.3°, 23.7°, 23.9°, and 24.4° are characteristic peaks of ZSM-5 zeolite; the two peaks at 21.3° and 22.4° are characteristic peaks of β zeolite; the three peaks at 16.21°, 18.18°, and 20.76° are characteristic peaks of SAPO-34 zeolite; and the three peaks at 22.7°, 23.6°, and 23.9° are characteristic peaks of Y zeolite. The calculation method of the core phase zeolite retention is as follows: the ratio of the relative crystallinity after hydrothermal aging of an embodiment or comparative example to the relative crystallinity before hydrothermal aging is the retention of the embodiment or comparative example, and the hydrothermal aging condition is 800°C for 17h.

[0089] BET measurements were performed using a Micromeritics Instruments ASAP2420 physical adsorption instrument. The contributions of micropores and mesopores were calculated using the t-plot and Barrett-Joyner-Halenda (BJH) model. The test conditions were: the sample was heated at 300°C, vacuumed at 1.33 Pa, and purged for 6 hours.

[0090] The ZSM-5 zeolite, β zeolite, SAPO-34 zeolite and Y zeolite used in the following examples were purchased from Sinopec Catalyst Qilu Branch.

[0091] Example 1

[0092] (1) Add 15 g of ammonia water (concentration 28-30 wt%) and 5 g of hexadecyltrimethylammonium bromide to a solution prepared by mixing 600 g of ethanol and 1050 g of distilled water, and stir evenly. Place 5 g of β-zeolite in 50 g of distilled water and ultrasonically disperse for 30 min. Pour the evenly dispersed β-zeolite slurry into the above solution, heat to 40°C, add 10 g of tetraethyl orthosilicate (SiO2 content 2.88 g), and stir at 40°C for 4 h to carry out self-assembly reaction. After the reaction is completed, centrifuge, dry at 105°C for 4 h, and calcine at 550°C for 5 h to obtain a precursor. Among them, the weight ratio of ethyl orthosilicate to beta zeolite calculated as SiO2 is 0.576:1; the weight ratio of ammonia water to ethyl orthosilicate is 1.5:1; the weight ratio of cetyltrimethylammonium bromide, ethanol and distilled water is 0.0083:1:1.83; and the weight ratio of cetyltrimethylammonium bromide to beta zeolite is 1:1.

[0093] (2) 8.43 g of tetrapropylammonium hydroxide solution (25 wt % concentration), 2 g of water, and 0.021 g of pseudoboehmite were placed in an autoclave and heated at 120°C for 12 h. The mixture was then mixed evenly with 6.31 g of the above-mentioned precursor and dried at 80°C for 4 h to obtain a mixture to be crystallized. The molar ratio of the precursor to tetrapropylammonium hydroxide, calculated as SiO2, was 1:0.27, and the molar ratio of the pseudoboehmite to ethyl orthosilicate, calculated as SiO2, was 0.0053:1.

[0094] (3) The mixture to be crystallized was subjected to steam-assisted crystallization at 170°C for 72 hours. The crystallized product was dried at 105°C for 6 hours and calcined at 600°C for 3 hours to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

[0095] The precursor and the final product, namely the core-shell zeolite containing the ZSM-5 zeolite shell, were characterized by XRD and the relative crystallinity was calculated. The relative crystallinity of the precursor ZSM-5 zeolite was 0, and the relative crystallinity of the final product ZSM-5 zeolite was 32.8%. The XRD spectrum of the core-shell zeolite containing the ZSM-5 zeolite shell is shown in FIG. Figure 1 , it can be seen that the spectrum has characteristic peaks of ZSM-5 zeolite and β zeolite; TEM photos are shown in Figure 2 , it can be seen that it has a core-shell structure, wherein the core phase zeolite is beta zeolite with a particle size of 20-100 nm; the thickness of the ZSM-5 zeolite shell ranges from 8-20 nm. The average particle size of the shell ZSM-5 zeolite, the average shell thickness, and the average particle size / average shell thickness of the shell ZSM-5 zeolite used in this example are listed in Table 1. The specific surface area and other data of the core phase zeolite and the core-shell zeolite containing the ZSM-5 zeolite shell used in this example are listed in Table 2.

[0096] The core phase zeolite (β zeolite) and the final product (core-shell zeolite containing a ZSM-5 zeolite shell) used in this example were hydrothermally aged at 800°C for 17 h. The core phase zeolite retention of the aged core phase zeolite and the final product was calculated, and the results are listed in Table 3.

[0097] Example 2

[0098] (1) Add 15 g of ammonia water (concentration 28-30 wt%) and 5 g of hexadecyltrimethylammonium bromide to a solution prepared by mixing 600 g of ethanol and 1050 g of distilled water, and stir evenly. Place 5 g of β-zeolite in 50 g of distilled water and ultrasonically disperse for 30 min. Pour the evenly dispersed β-zeolite slurry into the above solution, heat to 40°C, add 7.5 g of tetraethyl orthosilicate (SiO2 content 2.16 g), and stir at 40°C for 4 h to carry out self-assembly reaction. After the reaction is completed, centrifuge, dry at 105°C for 12 h, and calcine at 550°C for 5 h to obtain a precursor. Among them, the weight ratio of ethyl orthosilicate to beta zeolite calculated as SiO2 is 0.432:1; the weight ratio of ammonia water to ethyl orthosilicate is 2:1; the weight ratio of cetyltrimethylammonium bromide, ethanol and distilled water is 0.0083:1:1.83; and the weight ratio of cetyltrimethylammonium bromide to beta zeolite is 1:1.

[0099] (2) 3.51 g of tetrapropylammonium hydroxide solution (25 wt %), 5 g of water, and 0.029 g of pseudoboehmite were placed in an autoclave and heated at 120°C for 12 h. The mixture was then mixed evenly with 5.73 g of the above-mentioned precursor and dried at 70°C for 4 h to obtain a mixture to be crystallized. The molar ratio of the precursor to tetrapropylammonium hydroxide, calculated as SiO2, was 1:0.15, and the molar ratio of the pseudoboehmite to ethyl orthosilicate, calculated as SiO2, was 0.01:1.

[0100] (3) The mixture to be crystallized was subjected to steam-assisted crystallization at 170°C for 72 hours. The crystallized product was dried at 120°C for 6 hours and calcined at 550°C for 3 hours to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

[0101] The XRD spectrum of the core-shell zeolite containing the ZSM-5 zeolite shell is similar to that of the Figure 1 Similar; TEM photos see Figure 3 , it can be seen that it has a core-shell structure, wherein the core phase zeolite is β zeolite with a particle size of 20-100 nm; the ZSM-5 zeolite shell thickness ranges from 5-20 nm. The average particle size of the shell ZSM-5 zeolite, the average shell thickness, and the average particle size / average shell thickness of the shell ZSM-5 zeolite used in this example are listed in Table 1. The specific surface area and other data of the core phase zeolite and the core-shell zeolite containing the ZSM-5 zeolite shell used in this example are listed in Table 2.

[0102] The core phase zeolite (β zeolite) and the final product (core-shell zeolite containing a ZSM-5 zeolite shell) used in this example were hydrothermally aged at 800°C for 17 h. The core phase zeolite retention of the aged core phase zeolite and the final product was calculated, and the results are listed in Table 3.

[0103] Example 3

[0104] (1) Add 15g of ammonia water (concentration 28-30% by weight) and 5g of hexadecyltrimethylammonium bromide to a solution prepared by mixing 600g of ethanol and 1050g of distilled water, and stir evenly. Place 5g of β-zeolite in 50g of distilled water and ultrasonically disperse for 30min. Pour the evenly dispersed β-zeolite slurry into the above solution, heat it to 40°C, add 10g of tetraethyl orthosilicate (SiO2 content is 2.88g) and 0.196g of aluminum isopropoxide, and stir at a constant temperature of 40°C for 4h to carry out self-assembly reaction. After the reaction is completed, centrifuge, dry at 105°C for 4h, and calcine at 550°C for 5h to obtain a precursor. Among them, the weight ratio of ethyl orthosilicate calculated as SiO2 to β-zeolite is 0.576:1; the weight ratio of ammonia water to ethyl orthosilicate is 1.5:1; the weight ratio of hexadecyltrimethylammonium bromide, ethanol and distilled water is 0.0083:1:1.83; the weight ratio of hexadecyltrimethylammonium bromide to β-zeolite is 1:1, and the molar ratio of aluminum isopropoxide to ethyl orthosilicate calculated as SiO2 is 0.02:1.

[0105] (2) 8.43 g of tetrapropylammonium hydroxide solution (25 wt %), 5 g of water, and 6.31 g of the above precursor were uniformly mixed and dried at 60° C. for 8 h to obtain a mixture to be crystallized. The molar ratio of the precursor to tetrapropylammonium hydroxide, calculated as SiO2, was 1:0.27.

[0106] (3) The mixture to be crystallized was subjected to steam-assisted crystallization at 160°C for 72 hours. The crystallized product was dried at 105°C for 6 hours and calcined at 600°C for 3 hours to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

[0107] The XRD spectrum of the core-shell zeolite containing the ZSM-5 zeolite shell is similar to that of the Figure 1 Similar; TEM photos see Figure 4 , it can be seen that it has a core-shell structure, wherein the core phase zeolite is β zeolite with a particle size of 20-100 nm; the ZSM-5 zeolite shell thickness ranges from 5-20 nm. The average particle size of the shell ZSM-5 zeolite, the average shell thickness, and the average particle size / average shell thickness of the shell ZSM-5 zeolite used in this example are listed in Table 1. The specific surface area and other data of the core phase zeolite and the core-shell zeolite containing the ZSM-5 zeolite shell used in this example are listed in Table 2.

[0108] The core phase zeolite (β zeolite) and the final product (core-shell zeolite containing a ZSM-5 zeolite shell) used in this example were hydrothermally aged at 800°C for 17 h. The core phase zeolite retention of the aged core phase zeolite and the final product was calculated, and the results are listed in Table 3.

[0109] Example 4

[0110] (1) Add 15g of ammonia water (concentration 28-30% by weight) and 5g of hexadecyltrimethylammonium bromide to a solution prepared by mixing 600g of ethanol and 1050g of distilled water, and stir evenly. Place 5g of β-zeolite in 50g of distilled water and ultrasonically disperse for 30min. Pour the evenly dispersed β-zeolite slurry into the above solution, add 20g of tetraethyl orthosilicate (SiO2 content is 5.76g) and 0.980g of aluminum isopropoxide, and stir at a constant temperature of 40℃ for 4h to carry out self-assembly reaction. After the reaction is completed, centrifuge, dry at 105℃ for 24h, and calcined at 550℃ for 5h to obtain a precursor. Among them, the weight ratio of ethyl orthosilicate to β zeolite calculated as SiO2 is 1.152:1; the weight ratio of ammonia water to ethyl orthosilicate is 0.75:1; the weight ratio of hexadecyltrimethylammonium bromide, ethanol and distilled water is 0.0083:1:1.83; the weight ratio of hexadecyltrimethylammonium bromide to β zeolite is 1:1, and the molar ratio of aluminum isopropoxide to ethyl orthosilicate calculated as SiO2 is 0.05:1.

[0111] (2) 28.11 g of tetrapropylammonium hydroxide solution (25 wt %), 5 g of water, and 8.61 g of the above precursor were mixed uniformly and dried at 80° C. for 4 h to obtain a mixture to be crystallized. The molar ratio of the precursor to tetrapropylammonium hydroxide, calculated as SiO2, was 1:0.45.

[0112] (3) The mixture to be crystallized was subjected to steam-assisted crystallization at 170°C for 24 hours. The crystallized product was dried at 105°C for 6 hours and calcined at 600°C for 3 hours to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

[0113] The XRD spectrum of the core-shell zeolite containing the ZSM-5 zeolite shell is similar to that of the Figure 1 Similar; TEM photos see Figure 5 It can be seen that it has a core-shell structure, wherein the core phase zeolite is beta zeolite with a particle size of 20-100 nm; the thickness of the ZSM-5 zeolite shell ranges from 10-100 nm. The average particle size of the shell ZSM-5 zeolite, the average shell thickness, and the average particle size / average shell thickness of the shell ZSM-5 zeolite used in this example are listed in Table 1. The specific surface area and other data of the core phase zeolite and the core-shell zeolite containing the ZSM-5 zeolite shell used in this example are listed in Table 2.

[0114] The core phase zeolite (β zeolite) and the final product (core-shell zeolite containing a ZSM-5 zeolite shell) used in this example were hydrothermally aged at 800°C for 17 h. The core phase zeolite retention of the aged core phase zeolite and the final product was calculated, and the results are listed in Table 3.

[0115] Example 5

[0116] (1) Add 15 g of ammonia water (concentration 28-30 wt%) and 5 g of hexadecyltrimethylammonium bromide to a solution prepared by mixing 600 g of ethanol and 1050 g of distilled water, and stir evenly. Place 5 g of β-zeolite in 50 g of distilled water and ultrasonically disperse for 30 min. Pour the evenly dispersed β-zeolite slurry into the above solution, heat to 40°C, add 7.5 g of tetraethyl orthosilicate (SiO2 content 2.16 g), and stir at 40°C for 4 h to carry out self-assembly reaction. After the reaction is completed, centrifuge, dry at 105°C for 12 h, and calcine at 550°C for 5 h to obtain a precursor. Among them, the weight ratio of ethyl orthosilicate to beta zeolite calculated as SiO2 is 0.432:1; the weight ratio of ammonia water to ethyl orthosilicate is 2:1; the weight ratio of cetyltrimethylammonium bromide, ethanol and distilled water is 0.0083:1:1.83; and the weight ratio of cetyltrimethylammonium bromide to beta zeolite is 1:1.

[0117] (2) 3.51 g of tetrapropylammonium hydroxide solution (25 wt %), 5 g of water, and 0.030 g of sodium aluminate were stirred and dissolved, and then uniformly mixed with 5.73 g of the above-mentioned precursor, and dried at 70° C. for 4 h to obtain a mixture to be crystallized. The molar ratio of the precursor calculated as SiO2 to tetrapropylammonium hydroxide was 1:0.15, and the molar ratio of sodium aluminate to tetraethyl orthosilicate calculated as SiO2 was 0.0125:1.

[0118] (3) The mixture to be crystallized was subjected to steam-assisted crystallization at 180°C for 24 hours. The crystallized product was dried at 120°C for 4 hours and calcined at 550°C for 3 hours to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

[0119] The XRD spectrum of the core-shell zeolite containing the ZSM-5 zeolite shell is similar to that of the Figure 1 Similar; TEM photos see Figure 6 , it can be seen that it has a core-shell structure, wherein the core phase zeolite is β zeolite with a particle size of 20-100 nm; the ZSM-5 zeolite shell thickness ranges from 5-20 nm. The average particle size of the shell ZSM-5 zeolite, the average shell thickness, and the average particle size / average shell thickness of the shell ZSM-5 zeolite used in this example are listed in Table 1. The specific surface area and other data of the core phase zeolite and the core-shell zeolite containing the ZSM-5 zeolite shell used in this example are listed in Table 2.

[0120] The core phase zeolite (β zeolite) and the final product (core-shell zeolite containing a ZSM-5 zeolite shell) used in this example were hydrothermally aged at 800°C for 17 h. The core phase zeolite retention of the aged core phase zeolite and the final product was calculated, and the results are listed in Table 3.

[0121] Example 6

[0122] (1) Add 15 g of ammonia water (concentration 28-30 wt%) and 5 g of hexadecyltrimethylammonium bromide to a solution prepared by mixing 600 g of ethanol and 1050 g of distilled water, and stir evenly. Place 5 g of SAPO-34 zeolite in 50 g of distilled water and ultrasonically disperse for 30 min. Pour the evenly dispersed SAPO-34 zeolite slurry into the above solution, heat to 40°C, add 7.5 g of tetraethyl orthosilicate (SiO2 content 2.16 g), and stir at 40°C for 4 h to carry out self-assembly reaction. After the reaction is completed, centrifuge, dry at 105°C for 2 h, and calcine at 550°C for 5 h to obtain a precursor. Among them, the weight ratio of ethyl orthosilicate to SAPO-34 zeolite calculated as SiO2 is 0.432:1; the weight ratio of ammonia water to ethyl orthosilicate is 2:1; the weight ratio of hexadecyltrimethylammonium bromide, ethanol and distilled water is 0.0083:1:1.83; and the weight ratio of hexadecyltrimethylammonium bromide to SAPO-34 zeolite is 1:1.

[0123] (2) 7.63 g of tetrapropylammonium hydroxide solution (25 wt %), 5 g of water, and 0.030 g of sodium aluminate were stirred and dissolved, and then mixed evenly with 5.73 g of the above precursor, and dried at 70° C. for 4 h to obtain a mixture to be crystallized. The molar ratio of the precursor calculated as SiO2 to tetrapropylammonium hydroxide was 1:0.45, and the molar ratio of sodium aluminate to tetraethyl orthosilicate calculated as SiO2 was 0.0125:1.

[0124] (3) The mixture to be crystallized was subjected to steam-assisted crystallization at 180°C for 72 hours. The crystallized product was dried at 120°C for 4 hours and calcined at 550°C for 3 hours to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

[0125] The XRD spectrum of the core-shell zeolite containing the ZSM-5 zeolite shell is shown in Figure 7 , it can be seen that the spectrum has characteristic peaks of ZSM-5 zeolite and SAPO-34 zeolite; TEM photos are shown in Figure 8 , it can be seen that it has a core-shell structure, wherein the core phase zeolite is SAPO-34 zeolite with a particle size of 150-600 nm; the ZSM-5 zeolite shell thickness ranges from 5-30 nm. The average particle size, average shell thickness, and average particle size / average shell thickness of the ZSM-5 zeolite shell used in this example are listed in Table 1. The specific surface area and other data of the core phase zeolite and the core-shell zeolite containing the ZSM-5 zeolite shell used in this example are listed in Table 2.

[0126] The core phase zeolite (SAPO-34 zeolite) used in this example and the final product (core-shell zeolite containing a ZSM-5 zeolite shell) were hydrothermally aged at 800°C for 17 h. The core phase zeolite retention of the aged core phase zeolite and the final product was calculated, and the results are listed in Table 3.

[0127] Example 7

[0128] (1) Add 15g of ammonia water (concentration 28-30% by weight) and 5g of hexadecyltrimethylammonium bromide to a solution prepared by mixing 600g of ethanol and 1050g of distilled water, and stir evenly. Place 5g of Y zeolite in 50g of distilled water and ultrasonically disperse for 30min. Pour the evenly dispersed Y zeolite slurry into the above solution, heat it to 40°C, add 10g of tetraethyl orthosilicate (SiO2 content is 2.88g) and 0.039g of aluminum isopropoxide, and stir at a constant temperature of 40°C for 4h to carry out self-assembly reaction. After the reaction is completed, centrifuge, dry at 105°C for 2h, and calcine at 550°C for 5h to obtain a precursor. Among them, the weight ratio of ethyl orthosilicate to Y zeolite calculated as SiO2 is 0.576:1; the weight ratio of ammonia water to ethyl orthosilicate is 1.5:1; the weight ratio of hexadecyltrimethylammonium bromide, ethanol and distilled water is 0.0083:1:1.83; the weight ratio of hexadecyltrimethylammonium bromide to Y zeolite is 1:1, and the molar ratio of aluminum isopropoxide to the shell silicon source calculated as SiO2 is 0.0053:1.

[0129] (2) 8.43 g of tetrapropylammonium hydroxide solution (25 wt %), 5 g of water, and 6.31 g of the above precursor were mixed uniformly and dried at 80° C. for 4 h to obtain a mixture to be crystallized. The molar ratio of the precursor to tetrapropylammonium hydroxide, calculated as SiO2, was 1:0.27.

[0130] (3) The mixture to be crystallized was subjected to steam-assisted crystallization at 150°C for 96 hours. The crystallized product was dried at 105°C for 6 hours and calcined at 600°C for 3 hours to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

[0131] The XRD spectrum of the core-shell zeolite containing the ZSM-5 zeolite shell is shown in Figure 9 , it can be seen that the spectrum has characteristic peaks of ZSM-5 zeolite and Y zeolite; TEM photos are shown in Figure 10 , it can be seen that it has a core-shell structure, wherein the core phase zeolite is Y zeolite with a particle size of 300-600 nm; the thickness of the ZSM-5 zeolite shell ranges from 8-30 nm. The average particle size of the shell ZSM-5 zeolite, the average shell thickness, and the average particle size / average shell thickness of the shell ZSM-5 zeolite used in this example are listed in Table 1. The specific surface area and other data of the core phase zeolite used in this example and the core-shell zeolite containing the ZSM-5 zeolite shell are listed in Table 2.

[0132] The core phase zeolite (Y zeolite) used in this example and the final product (core-shell zeolite containing a ZSM-5 zeolite shell) were hydrothermally aged at 800°C for 17 h. The core phase zeolite retention of the aged core phase zeolite and the final product was calculated, and the results are listed in Table 3.

[0133] Comparative Example 1

[0134] Zeolite was prepared according to the method of Example 1, except that, in step (3), steam-assisted crystallization was not used. Instead, the dried mixture to be crystallized was crystallized at 170°C for 72 h under anhydrous conditions, and the crystallized product was dried at 105°C for 6 h and calcined at 600°C for 3 h to obtain the zeolite prepared in this comparative example.

[0135] The XRD spectrum of the zeolite is shown in Figure 11 , it can be seen that the product does not show the characteristic peaks of ZSM-5 zeolite, indicating that it is impossible to obtain a core-shell zeolite containing a ZSM-5 zeolite shell in the absence of water in the synthesis system. The specific surface area and other data of this comparative example are listed in Table 2, and the core phase zeolite retention is listed in Table 3.

[0136] Comparative Example 2

[0137] SAPO-34 zeolite was ion-exchanged with a 1M TPABr propanol solution at 333K, filtered, and dried at 100°C for 12 hours, labeled TPA-SAPO-34. TEOS was dropwise added to a mixture of NaOH, TPAOH, and deionized water, then stirred continuously at 298K in a Teflon beaker for 10 hours to form a homogeneous solution. Al(OPri)3 was then slowly stirred at 298K for 24 hours and dispersed in a vacuum dish for solvent evaporation to obtain a ZSM-5 xerogel. TPA-SAPO-34 crystals were then added to the ZSM-5 xerogel (TPA-SAPO-34 crystal mass:ZSM-5 xerogel mass = 0.3:1), stirred continuously, and ground into a uniform mixture to be crystallized. The mixture was then subjected to steam-assisted crystallization at 135°C for 84 hours. The solid product was washed with deionized water, air-dried overnight, and finally calcined in air at 550°C for 5 hours.

[0138] The data of the average particle size of the shell ZSM-5 zeolite, the average shell thickness, and the average particle size / average shell thickness of the shell ZSM-5 zeolite of this comparative example are listed in Table 1, the specific surface area and other data of this comparative example are listed in Table 2, and the core phase zeolite retention is listed in Table 3.

[0139] As can be seen from Table 1, the zeolite product of this comparative example did not form a continuous and dense ZSM-5 shell layer (average particle size of the shell ZSM-5 zeolite / average thickness of the shell layer = 0.9).

[0140] Table 1

[0141]

[0142]

[0143] As can be seen from Table 1, the zeolite product prepared in Example has a continuous and dense ZSM-5 zeolite shell.

[0144] Table 2

[0145]

[0146] As can be seen from Table 2, in the core-shell structure zeolite containing a ZSM-5 zeolite shell prepared in the example, the total pore volume, micropore volume, and mesopore volume of the final product are similar to or slightly higher than those of the core-phase zeolite, indicating that the ZSM-5 zeolite shell is rich in micropores and mesopores, and the pores are highly open, resulting in a high degree of pore openness between the core phase and the shell phase.

[0147] Table 3

[0148]

[0149] As can be seen from Table 3, the core-shell structure zeolite containing the ZSM-5 zeolite shell prepared in the example has higher hydrothermal stability.

[0150] Test Case

[0151] The zeolite products prepared in the Examples and Comparative Examples were evaluated for their catalytic cracking of hexylcyclohexane. A 2g sample was placed in a stainless steel reaction tube, and 0.6g of hexylcyclohexane was injected via a syringe pump over a 140s period. The catalytic reaction was carried out at 650°C under atmospheric pressure. The product was analyzed using a gas fluorescence spectrometer, and the liquid product was analyzed by PONA using capillary column gas chromatography. The target product selectivity and hydrogen transfer coefficient were calculated according to the following formula. The evaluation data are shown in Table 4.

[0152] C2-C4 olefin selectivity = weight of C2-C4 olefins produced by the reaction / (weight of feed - weight of remaining hexylcyclohexane after reaction) × 100%

[0153] BTX selectivity = weight of BTX produced by the reaction / (weight of feed - weight of hexylcyclohexane remaining after the reaction) × 100%

[0154] Hydrogen transfer coefficient = weight of C4 alkanes in the product / weight of C4 olefins

[0155] Table 4

[0156] C2~C4 olefin selectivity (%) BTX selectivity (%) Hydrogen transfer coefficient Example 1 47.5 10.5 0.5 Example 2 46.3 11.8 0.5 Example 3 45.2 9.4 0.5 Example 4 41.5 8.2 0.5 Example 5 48.3 11.0 0.5 Example 6 43.7 6.9 0.5 Example 7 46.1 10.4 0.5 Comparative Example 1 37.2 5.8 0.7 Comparative Example 2 39.3 5.6 0.7

[0157] As can be seen from Table 4, the core-shell structured zeolite containing a ZSM-5 zeolite shell disclosed herein has high selectivity for light olefins and BTX for catalytic cracking reactions, indicating a high degree of pore openness between the core phase and the shell phase. The reduction in the product hydrogen transfer coefficient indicates that the ZSM-5 zeolite shell passivates the outer surface of the core phase zeolite, reducing the occurrence of side reactions.

[0158] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0159] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0160] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A core-shell zeolite containing a ZSM-5 zeolite shell, characterized in that: The core-shell structured zeolite containing a ZSM-5 zeolite shell comprises a spherical core phase zeolite and a shell layer encapsulating the core phase zeolite; wherein the shell layer is continuous and dense ZSM-5 zeolite, and the ratio of the average particle size of the ZSM-5 zeolite to the average thickness of the shell layer is 9 to 32.

2. The core-shell zeolite containing a ZSM-5 zeolite shell according to claim 1, wherein The average particle size of the ZSM-5 zeolite is 25 to 10,000 nm; the average thickness of the shell is 8 to 450 nm; and the particle size of the core phase zeolite is 20 to 2,500 nm.

3. The core-shell zeolite containing a ZSM-5 zeolite shell according to claim 1, wherein The total specific surface area of ​​the core-shell zeolite containing the ZSM-5 zeolite shell is 300 to 700 m 2 / g, external specific surface area is 20~300m 2 / g, micropore specific surface area is 200~600m 2 / g, the total pore volume is 0.3-0.6 ml / g, the micropore volume is 0.1-0.4 ml / g, and the mesopore volume is 0.1-0.3 ml / g.

4. The core-shell zeolite containing a ZSM-5 zeolite shell according to claim 1, wherein The core phase zeolite is at least one selected from aluminum silicate zeolite, aluminum phosphate zeolite, silicon phosphate aluminum zeolite, titanium silicalite and pure silicalite.

5. The method for preparing a core-shell zeolite containing a ZSM-5 zeolite shell according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: The core phase zeolite, the shell silicon source, the base catalyst, the cationic surfactant, the organic solvent, the water and the optional first aluminum source are mixed to carry out a self-assembly reaction, and the obtained solid product is subjected to a first drying and a first calcination to obtain a precursor; Mixing the precursor with a template and an optional second aluminum source and performing a second drying to obtain a mixture to be crystallized; The mixture to be crystallized is subjected to steam-assisted crystallization, and the obtained crystallized product is subjected to a third drying and a second calcination to obtain a core-shell structured zeolite containing a ZSM-5 zeolite shell.

6. The method according to claim 5, wherein: The weight ratio of the shell silicon source to the core phase zeolite calculated as SiO2 is (0.2-5):1; The molar ratio of the total molar amount of the first aluminum source and the second aluminum source to the shell silicon source calculated as SiO2 is (0.001-0.5):1; The weight ratio of the base catalyst to the shell silicon source is (0.01-30):1; The weight ratio of the cationic surfactant, the organic solvent and the water is (0.001-0.1):1:(1-20); The molar ratio of the precursor to the template calculated as SiO2 is 1:(0.03-0.5).

7. The method according to claim 6, wherein: The weight ratio of the shell silicon source to the core phase zeolite calculated as SiO2 is (0.2-1.2):1; The molar ratio of the total molar amount of the first aluminum source and the second aluminum source to the shell silicon source calculated as SiO2 is (0.005-0.05):1; The weight ratio of the base catalyst to the shell silicon source is (0.1-5):1; The weight ratio of the cationic surfactant, the organic solvent and the water is (0.005-0.02):1:(1.2-4); The molar ratio of the precursor to the template calculated as SiO2 is 1:(0.1-0.3).

8. The method according to claim 5, wherein The shell silicon source is organic silicon ester alkane and / or inorganic silicate; The first aluminum source is at least one selected from aluminum isopropoxide, triethylaluminum, sodium aluminate and potassium aluminate; The second aluminum source is at least one selected from aluminum isopropoxide, triethylaluminum, sodium aluminate and potassium aluminate.

9. The method according to claim 5, wherein: The alkaline catalyst is at least one selected from ammonia water, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide; The chemical formula of the cationic surfactant is C n H 2n+1 NR m X 4-m , wherein n is an integer of 8 to 22, m is an integer of 1 to 3, R is a C1 to C22 alkyl group, and X is Cl, Br or OH.

10. The method according to claim 5, wherein The organic solvent is at least one selected from C1-C4 alcohol, benzene, toluene, tetrahydrofuran, chloroform, dichloromethane, acetonitrile and diethyl ether; The template agent is at least one selected from tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium bromide, tetrapropylammonium chloride, tetraethylammonium chloride, n-butylamine and triethanolamine.

11. The method according to claim 5, wherein: The conditions of the self-assembly reaction include: temperature of 0 to 75° C., time of 1 to 8 hours; The first drying conditions include: a temperature of 10 to 220° C. and a time of 1 to 24 hours; The first calcination conditions include: a temperature of 400 to 850° C., an air atmosphere, and a calcination time of 2 to 10 hours; The second drying conditions include: a temperature of 10 to 220° C. and a time of 1 to 24 hours; The conditions of the third drying include: a temperature of 10 to 220° C. and a time of 1 to 24 hours; The conditions for the second calcination include: a temperature of 400 to 850° C., an air atmosphere, and a calcination time of 2 to 10 hours.

12. The method according to claim 5, wherein: The steam-assisted crystallization conditions include: a temperature of 110 to 220° C. and a time of 1 to 100 hours.

13. Use of the core-shell zeolite containing a ZSM-5 zeolite shell according to any one of claims 1 to 4 in the production of light olefins by catalytic cracking reaction.

Images