Double-layer single-crystal hollow ZSM-5 molecular sieve, and preparation method and application thereof

Abstract

The present application relates to a kind of double-layer single-crystal hollow ZSM-5 molecular sieve and its preparation method and application.The double-layer single-crystal hollow ZSM-5 molecular sieve has double-layer hollow structure, and has nanorod shell layer on the outer surface of the molecular sieve.It can be obtained by first synthesizing specific parent molecular sieve, and then being treated by alkali.The double-layer single-crystal hollow ZSM-5 molecular sieve of the present application has simple preparation method, does not need to use a large amount of organic template, and has good technical economy, and it is used for macromolecular catalytic reaction, such as in hydrocarbon catalytic cracking reaction, has higher low carbon olefin yield and BTX yield, and higher ethylene / propylene ratio.

Description

Technical Field

[0001] The invention belongs to the technical field of catalytic materials and relates to a double-layer single-crystal hollow ZSM-5 molecular sieve and a preparation method and application thereof. Background Art

[0002] Catalytic materials are the technological core of the petrochemical industry and the source of technological progress in the field. Catalytic cracking to produce light olefins is a typical high-temperature acid-catalyzed reaction, and the development and design of catalytic materials is crucial. ZSM-5 zeolite, with its unique pore structure, adjustable acidity, and high thermal and hydrothermal stability, is a preferred catalyst for hydrocarbon catalytic cracking. However, while its well-ordered microporous structure enhances the selectivity of specific products, it also restricts the diffusion of large-molecule hydrocarbon reactants and products, promotes the formation of carbon deposits, further covers active sites, and deactivates the catalyst. Constructing multi-level pores is an effective measure to address the diffusion limitations of molecular sieves. Hollow mesoporous ZSM-5 offers unique advantages: a special intracapsular microenvironment, a nanoscale multi-level pore shell, and a unique spatial confinement, which impart strong acidity, excellent diffusion properties, and outstanding encapsulation capabilities. However, existing hollow ZSM-5 zeolites have a monotonous morphology and are often synthesized using a large amount of organic templates.

[0003] Catalytic cracking of hydrocarbons is an important method for converting larger hydrocarbons into smaller hydrocarbons, such as ethylene and propylene. During the cracking process, hydrocarbons undergo numerous parallel and sequential reactions. In addition to cracking to produce smaller hydrocarbons, they may also aromatize to form aromatics. The resulting side-chain aromatics may further crack or dealkylate to form BTX light aromatics, or they may undergo hydrogen transfer to form heavier aromatics. In refineries, production may be optimized for ethylene or propylene, depending on the needs of the refinery. This necessitates the flexibility to adjust the product ratio. Summary of the Invention

[0004] The present invention aims to provide a hollow ZSM-5 molecular sieve having a single crystal structure, a double-layer closed hollow structure, and an epitaxially grown nanorod shell. Another technical problem to be solved by the present invention is to provide a preparation method and application method of the ZSM-5 molecular sieve.

[0005] The first aspect of the present invention provides a double-layer single-crystal hollow ZSM-5 molecular sieve, which has a double-layer closed hollow structure and an epitaxially grown nanorod shell, with an average grain size of 0.8 to 3.5 μm. The ZSM-5 molecular sieve grows along the ac axis direction, and the entire particle has a single crystal structure.

[0006] According to the present invention, the nanorod structure has an axial direction along the AC axis. The growth orientation of individual grains of the double-layer single-crystal hollow ZSM-5 molecular sieve is consistent, forming a single crystal structure. The crystal structure and growth orientation of the double-layer single-crystal hollow ZSM-5 molecular sieve can be observed using a high-power spherical aberration electron microscope.

[0007] The closed hollow structure refers to a space that does not contain ZSM-5 molecular sieve in the crystal grains of ZSM-5 molecular sieve, and the space is formed by enclosing a ZSM-5 molecular sieve wall with a certain thickness.

[0008] The double-layer single-crystal hollow ZSM-5 molecular sieve provided by the present invention, in one case, has a double-layer closed hollow structure and an epitaxially grown nanorod shell. The double-layer single-crystal hollow ZSM-5 molecular sieve has a grain length of 0.8 to 3.5 μm, a grain width of 0.5 to 2.0 μm, an inner hollow structure length of 0.5 to 2.0 μm, an inner hollow structure width of 0.3 to 1.0 μm, a distance between the inner hollow outer wall and the outer hollow inner wall of 200 to 400 nm, and the epitaxially grown nanorods have a length of 0.5 to 1.0 μm.

[0009] Grain size refers to the dimension at its widest point, which can be obtained by measuring the widest dimension of the grain projection in the SEM or TEM image of the sample. The average grain size is obtained by selecting 10 random molecular sieve grains from the SEM or TEM image and calculating the arithmetic mean of their grain sizes. Grain length refers to the length along the ac axis, width refers to the dimension perpendicular to the length, inner hollow structure length refers to the dimension at the longest point of the inner hollow structure projection, inner hollow structure width refers to the dimension perpendicular to the length of the inner hollow structure, and the distance from the inner hollow outer wall to the outer hollow inner wall refers to the randomly measured distance between the inner outer wall and the outer inner wall. From the SEM or TEM image, 10 randomly selected molecular sieve grains are measured for their grain length, grain width, hollow structure length, hollow structure width, and wall thickness. The arithmetic mean of these values ​​is calculated as the sample's grain length, grain width, hollow structure length, hollow structure width, and wall thickness.

[0010] After the double-layer single-crystal hollow ZSM-5 molecular sieve is modified at a phosphorus-to-aluminum molar ratio of 1, the crystal retention rate is greater than or equal to 90%, such as 90-98% or 90.2-95%, and / or the acid retention rate is greater than or equal to 30%, such as 30-40% or 30.5-35%, after hydrothermal treatment at 800°C for 17 hours. This indicates that the phosphorus-modified hollow ZSM-5 molecular sieve has good hydrothermal stability. The crystallinity retention is the ratio of the relative crystallinity of the product obtained by hydrothermally treating the molecular sieve at a phosphorus-to-aluminum molar ratio of 1 at 800°C for 17 hours (referred to as the relative crystallinity after hydrothermal treatment) to the relative crystallinity of the product obtained by hydrothermally treating the molecular sieve at a phosphorus-to-aluminum molar ratio of 1 (referred to as the relative crystallinity before hydrothermal treatment). The acidity retention is the ratio of the acidity of the product obtained by hydrothermally treating the molecular sieve at a phosphorus-to-aluminum molar ratio of 1 at 800°C for 17 hours (referred to as the acidity after hydrothermal treatment) to the acidity of the product obtained by hydrothermally treating the molecular sieve at a phosphorus-to-aluminum molar ratio of 1 (referred to as the acidity before hydrothermal treatment). The hydrothermal treatment is carried out in a 100% by volume water vapor atmosphere.

[0011] The modification, performed at a phosphorus-aluminum molar ratio of 1, can be performed using an equal volume impregnation method. One method involves spreading the molecular sieve sample evenly on a watch glass or crucible, slowly pouring the phosphorus-containing solution onto the sample until it forms a slurry. Stirring the sample thoroughly and drying it in an oven is followed by grinding the sample until it is uniformly slurried and calcining it at 550°C for 4 hours. Typically, the mass ratio of phosphorus-containing solution to molecular sieve is 1-3. Examples of the phosphorus-containing solution include phosphoric acid solution, ammonium dihydrogen phosphate solution, or diammonium hydrogen phosphate solution.

[0012] In the present invention, the relative crystallinity of the molecular sieve is based on the XRD standard ZSM-5 molecular sieve standard sample of Sinopec Petrochemical Research Institute Co., Ltd., and the crystallinity of the standard sample is regarded as 100%.

[0013] Preferably, the mesoporous specific surface area of ​​the double-layer single crystal hollow ZSM-5 molecular sieve accounts for 15 to 25% of the total specific surface area.

[0014] Preferably, the mesopore volume of the double-layer single crystal hollow ZSM-5 molecular sieve accounts for 40 to 60% of the total pore volume.

[0015] The total specific surface area, mesopore specific surface area, micropore specific surface area, and pore volume in the present invention are measured using low-temperature nitrogen adsorption. The BET specific surface area is calculated using the BET formula, the micropore area is calculated using a t-plot, and the pore size distribution is calculated using the BJH method. The double-layer single-crystal hollow molecular sieve of the present invention has a predominantly microporous structure, while also being rich in mesopores and macropores. This further provides multi-directional diffusion pathways, expands confined space, improves accessibility to active centers, and possesses the ability to catalyze the cracking of large molecular hydrocarbons.

[0016] The double-layer single-crystal hollow ZSM-5 molecular sieve provided by the present invention can be an H-type double-layer single-crystal hollow ZSM-5 molecular sieve or a phosphorus-containing double-layer single-crystal hollow ZSM-5 molecular sieve, and the phosphorus content of the phosphorus-containing double-layer single-crystal hollow ZSM-5 molecular sieve can be 0.5-10% by mass in terms of P2O5.

[0017] The second aspect of the present invention provides a method for preparing the double-layer single-crystal hollow ZSM-5 molecular sieve, which comprises (A) preparing a seed molecular sieve and (B) preparing a double-layer single-crystal hollow ZSM-5 molecular sieve:

[0018] Wherein (A) preparing seed molecular sieve comprises:

[0019] (A1) mixing a silicon source (referred to as a first silicon source), a template, and water, and heating with stirring at 30 to 60° C. for 2 to 6 hours to obtain a mixed solution, referred to as a first mixed solution;

[0020] (A2) subjecting the mixed solution obtained in step (A1) to hydrothermal dynamic crystallization at 140-180° C. for 8-24 hours; for example, transferring the mixed solution to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and performing a hydrothermal crystallization reaction under stirring; the resulting crystallized product is referred to as the seed solution;

[0021] (B) preparing a double-layer single crystal hollow ZSM-5 molecular sieve, comprising the following steps:

[0022] (B1) dissolving an alkali source in water and stirring uniformly to obtain an alkali source solution;

[0023] (B2) mixing an aluminum source with water and stirring uniformly to obtain an aluminum source dispersion;

[0024] (B3) mixing a silicon source (referred to as the second silicon source) with the alkaline source solution of step (B1), and stirring at room temperature for more than 10 minutes, for example, 10 to 30 minutes;

[0025] (B4) the product of step (B3) is optionally mixed with a certain amount of dilution water, and mixed with the aluminum source dispersion under stirring, for example, by adding the aluminum source dispersion obtained in step (B2); and stirred at room temperature, for example, for 30 to 60 minutes to obtain a mixed solution, referred to as a second mixed solution;

[0026] (B5) adding a certain amount of the seed solution obtained in step (A2) to the mixed solution (second mixed solution) obtained in step (B4), and stirring at room temperature, for example, for 1 to 6 hours; obtaining a mixed solution, referred to as a third mixed solution; preferably, the mass ratio of the seed solution, calculated as SiO2, to the product obtained in (B4), calculated as SiO2, is 5 to 20:100;

[0027] (B6) subjecting the mixed solution obtained in step (B5) (the third mixed solution) to hydrothermal dynamic crystallization at 140-180° C. for 6-48 hours;

[0028] (B7) filtering, washing, drying, and calcining the product obtained in step (B6) to obtain a parent molecular sieve;

[0029] (B8) mixing the parent molecular sieve obtained in step (B7) with an alkaline solution, stirring at 60-90°C for, for example, 20-60 minutes, wherein the alkaline content in the alkaline solution is 0.4-2.0 mol / L; obtaining a solid product; and optionally (B9) treating the solid product obtained in step (B8) to obtain an H-type double-layer single crystal hollow ZSM-5 molecular sieve.

[0030] In the present invention, the room temperature is 20-35°C.

[0031] Optionally, in step A(1), the silicon source is one or more of methyl orthosilicate or ethyl orthosilicate, and the template is one or more of tetrapropylammonium hydroxide or tetrapropylammonium bromide.

[0032] Optionally, in step A(1), the ratio of template R / SiO2 is 0.05 to 0.50, such as 0.1 to 0.4, and the ratio of H2O / SiO2 is 10 to 80, such as 25 to 65. The ratios are molar ratios, wherein R represents the template.

[0033] Optionally, the grain size of the seed crystal in step (A2) is 200-800 nm.

[0034] In step (B1), the concentration of the alkali source solution may be 10 to 30% by mass. The alkali source is one or more of potassium hydroxide, rubidium hydroxide, or cesium hydroxide.

[0035] Optionally, the concentration of the aluminum source solution in step (B2) is 5 to 20% by mass, and the aluminum source is one or more of aluminum sulfate, aluminum nitrate, aluminum isopropoxide, sodium aluminate or aluminum chloride.

[0036] Optionally, the silicon source in step (B3) is silica sol, which can be ammonium silica sol, sodium silica sol or a mixture thereof, and the SiO2 content in the silica sol is 15 to 45% by mass, for example, it can be 15%, 25%, 30%, 45% or a content range formed by a combination of any two of these numbers as endpoints.

[0037] Optionally, the molar ratio of the mixed solution obtained in step (B4) is n(SiO2) / n(Al2O3)=20-200, for example, 30-100 or 40-80 or 45-65, n(M12O) / n(SiO2)=0.2-0.5, for example, 0.22-0.5 or 0.25-0.50 or 0.22-0.35, and n(H2O) / n(SiO2)=50-150, for example, 60-120 or 75-110. Wherein M1 represents an alkali metal, selected from one or more of K, Rb or Cs, preferably K.

[0038] Optionally, in step (B5), the SiO2 content in the seed solution accounts for 5 to 20% of the SiO2 content in the silicon source (referred to as the second silicon source) in step (B3), for example, 5 to 10% by weight.

[0039] In step (B6), the mixed solution obtained in step (B5) is subjected to hydrothermal dynamic crystallization at 140-180° C. for 6-48 hours. For example, the mixed solution obtained in step (B5) can be transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and then subjected to hydrothermal dynamic crystallization. The dynamic crystallization is performed by subjecting the mixed solution to a crystallization reaction while in motion, such as under stirring.

[0040] In step (B7), the product obtained in step (B6) is filtered to separate the crystallized molecular sieve from the mother liquor, and then washed to remove the mother liquor attached to the molecular sieve, such as with water, and then dried and calcined. The calcination temperature is, for example, 450-600° C., such as 500-600° C., and the calcination time is 2-12 hours, such as 2-6 hours.

[0041] Step (B7) produces a parent molecular sieve having solid crystals with a silicon-rich interior and an aluminum-rich exterior.

[0042] In step (B8), the parent molecular sieve is mixed with an alkaline solution and stirred at 60 to 90° C. for 20 to 60 minutes to form a hollow structure. The solid is then recovered, for example, by filtering, washing, for example, with water to remove the alkaline solution in the treated parent molecular sieve, and drying to obtain a solid. The alkaline solution is, for example, an alkaline solution containing one or more of sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide. The content of the alkali in the alkaline solution is 0.4-2.0 mol / L, for example, 0.4-1 mol / L.

[0043] Step (B9) processes the solid product obtained in step (B8) to obtain an H-type double-layer single-crystalline hollow ZSM-5 molecular sieve. One embodiment includes exchanging the solid product of step (B8), such as ammonium exchange, filtering, optionally washing, and then drying and calcining. The methods of ammonium exchange, drying, and calcining are well known to those skilled in the art. For example, the calcination temperature can be 500-600°C, and the calcination time can be 1-5 hours.

[0044] Phosphorus can be introduced into the H-type double-layer single-crystalline hollow ZSM-5 molecular sieve to obtain a phosphorus-containing double-layer single-crystalline hollow ZSM-5 molecular sieve. The method for introducing phosphorus can refer to existing methods. For example, phosphorus can be introduced into the H-type double-layer single-crystalline hollow ZSM-5 molecular sieve by impregnation, which generally includes the steps of contacting the H-type double-layer single-crystalline hollow ZSM-5 molecular sieve with an impregnation solution, drying, and calcining. The impregnation solution can be a phosphoric acid solution, an ammonium phosphate solution, a diammonium hydrogen phosphate solution, an ammonium dihydrogen phosphate solution, or a mixture of these solutions.

[0045] The third aspect of the present invention provides an application of the double-layer single-crystal hollow ZSM-5 molecular sieve provided in the first aspect of the present invention, for example, in petrochemical and / or fine chemical industries. In one embodiment, the double-layer single-crystal hollow molecular sieve is used for catalytic cracking of hydrocarbon oil, which includes the step of contacting hydrocarbon with the double-layer single-crystal hollow ZSM-5 molecular sieve for catalytic cracking reaction. In one embodiment, the double-layer single-crystal hollow ZSM-5 molecular sieve is a hydrogen-type molecular sieve. In one embodiment, the double-layer single-crystal hollow ZSM-5 molecular sieve contains phosphorus, which is called a phosphorus-containing double-layer single-crystal hollow ZSM-5 molecular sieve, wherein the phosphorus content can be, for example, 0.5-10% by weight.

[0046] The double-layer single-crystal hollow ZSM-5 molecular sieve of the present invention has a double-layer enclosed hollow structure and an epitaxially grown nanorod shell. It has a rich pore structure and can provide multi-directional diffusion paths for macromolecular reactants, improving the accessibility of the molecular sieve's active centers and achieving excellent catalytic performance. The double-layer single-crystal hollow ZSM-5 molecular sieve can improve the accessibility of the molecular sieve's active sites and has the ability to catalyze macromolecular hydrocarbon reactions. For example, in hydrocarbon catalytic cracking reactions, it can achieve higher light olefin yields and BTX yields, as well as a higher ethylene / propylene ratio.

[0047] The method for synthesizing a double-layer single-crystal hollow ZSM-5 molecular sieve provided by the present invention can obtain the double-layer single-crystal hollow ZSM-5 molecular sieve without using a large amount of organic template during the synthesis process.

[0048] The double-layer single-crystal hollow ZSM-5 molecular sieve provided by the present invention can be applied in fields such as petrochemicals and fine chemicals, such as hydrocarbon adsorption separation and catalytic cracking / cracking, and has good industrial application value. For example, the double-layer single-crystal hollow ZSM-5 molecular sieve can be used in hydrocarbon catalytic cracking reactions to achieve higher light olefin (ethylene and propylene) yields and BTX yields, as well as a higher ethylene / propylene ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a transmission electron microscope image of the double-layer single crystal hollow ZSM-5 molecular sieve prepared in Example 1.

[0050] Figure 2 This is the Fourier transform diffraction spectrum of the double-layer single crystal hollow ZSM-5 molecular sieve prepared in Example 1, which shows that it has a single crystal structure. DETAILED DESCRIPTION

[0051] It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0052] Low-temperature nitrogen adsorption analysis was performed using an ASAP2420 physical adsorption instrument (Micromeritics Instruments, Inc., USA). Experimental method: The first step was sample pretreatment: a certain amount of sample was weighed and placed into a blank-tested sample tube. The tube was then placed in a degassing unit and degassed for 6 hours at a furnace temperature of 300°C and a vacuum of less than 1.33 Pa. The second step was sample measurement: the pretreated sample tube was placed into the measurement unit, the Dewar flask was filled with liquid nitrogen, and the analysis file was entered to begin the measurement. The measurement process involved determining the adsorption isotherm using the static volumetric method. The total pore volume was calculated based on the adsorption capacity of P / P0 = 0.98. The pore size distribution was calculated using the BJH method to obtain the mesopore volume. The specific surface area was calculated using the BET equation. Test conditions: The sample was vacuum degassed at 100°C and 300°C for 0.5 h and 6 h, respectively. N2 adsorption-desorption tests were then performed at 77.4 K. The adsorption and desorption amounts of nitrogen from the purified sample were measured under different pressure ratios, and N2 adsorption-desorption isotherms were obtained. The BET specific surface area was calculated using the BET formula, the micropore area was calculated using t-plot, and the pore size distribution was calculated using BJH.

[0053] The acid amount of the molecular sieve was determined using an Autochem II 2920 programmed temperature desorption instrument from Micromeritics. The test method was as follows: 0.2 g of the molecular sieve with a particle size of 20-40 was weighed into a sample tube, and was placed in a heating furnace, He with a flow rate of 25 mL / min was used as the carrier gas, the temperature was raised to 600 ℃ at a rate of 20 ℃ / min, and the molecular sieve was purged for 90 min to remove impurities adsorbed on the surface of the molecular sieve. Then the temperature was lowered to 150 ℃, and after constant temperature for 5 min, the system was connected to NH3-He gas (10% by mass NH3 and 90% by mass He) for adsorption for 60 min, and then He was used for purging for 120 min until the baseline was stable, so as to desorb the physically adsorbed ammonia. The temperature was programmed to rise to 600 ℃ at a rate of 10 ℃ / min for desorption, and the desorption was maintained for 60 min, and the desorption was completed. The change in the gas components was detected by TCD, and the total acid amount was obtained by automatic integration of the instrument.

[0054] Fourier transform diffraction spectrum, measuring instrument and method: the electron microscope model is JEM-ARM200F, and the electron diffraction mode of the electron microscope is directly photographed.

[0055] The raw materials used in the following examples and comparative examples were commercially available unless specifically stated otherwise. The room temperature of the examples and comparative examples was 26 ℃.

[0056] Example 1

[0057] Preparation of seed crystal solution:

[0058] (A1) 30.0 g of tetraethyl orthosilicate, 34.0 g of tetrapropylammonium hydroxide and 44.2 g of deionized water were uniformly mixed, and heated and stirred at 40 ℃ for 4 h;

[0059] (A2) The solution of step (A1) was moved to a high-pressure hydrothermal reaction kettle with a polytetrafluoroethylene liner, and dynamically crystallized at 170 ℃ for 12 h;

[0060] (A3) After the crystallization was completed, the crystallization product was taken out of the reaction kettle, and was recorded as seed crystal solution 1.

[0061] Preparation of double-layer single-crystal hollow ZSM-5 molecular sieve:

[0062] (B1) 5.21 g of potassium hydroxide was added to 15.63 g of deionized water, and stirred uniformly;

[0063] (B2) 1.8 g of aluminum sulfate octadecahydrate was added to 16.2 g of deionized water, and stirred uniformly;

[0064] (B3) 30.20 g of silica sol (sodium type silica sol, silica content 30% by mass, sodium oxide content 0.22% by mass, pH value 9.2) was slowly added to the alkali source solution of step (B1), and stirred at room temperature for 30 min;

[0065] (B4) adding 214.47 g of deionized water to step (B3), then adding the aluminum source solution of step (B2) under stirring, and stirring at room temperature for 30 minutes to obtain a mixed solution;

[0066] (B5) adding 6.34 g of the seed solution 1 described in step (A3) to the mixed solution obtained in step (B4), and stirring at room temperature for 4 hours to obtain a mixed solution;

[0067] (B6) transferring the mixed solution obtained in step (B5) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it to hydrothermal dynamic crystallization at 170° C. for 48 h;

[0068] (B7) filtering, washing, drying, and calcining the product obtained in step (B6) at 550° C. for 2 h (the same below) to obtain molecular sieve M-1;

[0069] (B8) molecular sieve M-1 and a 0.6 mol / L sodium hydroxide solution were mixed uniformly, with the mass ratio of molecular sieve M-1 to sodium hydroxide solution being 1:10, and the mixture was heated to 80°C at a heating rate of 4°C / min, stirred at the same temperature for 30 min, filtered, washed, and dried to obtain molecular sieve M-1-J;

[0070] (B9) Mix molecular sieve M-1-J: ammonium chloride: deionized water in a mass ratio of 1:1:10, stir and heat in a water bath at 80°C for 30 minutes, filter, wash and dry, then mix the dried solid: ammonium chloride: deionized water in a mass ratio of 1:0.5:10, perform a second ammonium exchange, filter, wash, dry, and calcine at 550°C for 2 hours to obtain a hydrogen-type double-layer single crystal hollow ZSM-5 molecular sieve, recorded as M-1-JH. Figure 1 The transmission electron microscope image is Figure 2 Its Fourier transform diffraction spectrum.

[0071] Example 2

[0072] Prepare seed solution:

[0073] (A1) 54.8 g of ethyl orthosilicate, 29.7 g of tetrapropylammonium hydroxide, and 240.5 g of deionized water were mixed and heated with stirring at 40° C. for 4 h;

[0074] (A2) transferring the solution from step (A1) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it to dynamic crystallization at 170° C. for 12 h;

[0075] The obtained crystallized product is recorded as seed solution 2.

[0076] Preparation of double-layer single crystal hollow ZSM-5 molecular sieve:

[0077] (B1) adding 5.46 g of potassium hydroxide to 24.87 g of deionized water and stirring to obtain an alkaline source solution;

[0078] (B2) adding 1.24 g of aluminum isopropoxide to 14.26 g of deionized water and stirring to obtain an aluminum source solution;

[0079] (B3) 35.80 g of silica sol (silicon oxide content 30% by mass, same as Example 1) was slowly added to the alkali source solution of step (B1) and stirred at room temperature for 30 minutes;

[0080] (B4) adding 181.37 g of deionized water to step (B3), then adding the aluminum source solution from step (B2) with stirring, and stirring at room temperature for 30 minutes;

[0081] (B5) adding 10.74 g of seed solution 2 to the solution of step (B4) and stirring at room temperature for 4 hours;

[0082] (B6) transferring the mixed solution obtained in step (B5) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it to hydrothermal dynamic crystallization at 170° C. for 48 h;

[0083] (B7) filtering, washing, drying, and calcining the product obtained in step (B6) to obtain molecular sieve M-2;

[0084] (B8) molecular sieve M-2 and a 0.4 mol / L sodium hydroxide solution were mixed uniformly, with the mass ratio of molecular sieve M-2 to the alkaline solution being 1:10, and the mixture was heated to 80°C at a heating rate of 4°C / min, stirred at the same temperature for 30 min, filtered, washed, and dried to obtain molecular sieve M-2-J;

[0085] (B9) Molecular sieve M-2-J: ammonium chloride: deionized water were mixed in a mass ratio of 1:1:10, stirred and heated in a water bath at 80°C for 30 minutes, filtered, washed, and dried, and then the dried solid: ammonium chloride: deionized water were mixed in a mass ratio of 1:0.5:10, subjected to a second ammonium exchange, filtered, washed, dried, and calcined at 550°C for 2 hours to obtain a hydrogen-type double-layer single crystal hollow ZSM-5 molecular sieve, recorded as M-2-JH.

[0086] Example 3

[0087] Prepare seed solution:

[0088] (A1) 47.6 g of ethyl orthosilicate, 70.4 g of tetrapropylammonium hydroxide, and 187.6 g of deionized water were mixed and heated with stirring at 40° C. for 4 h;

[0089] (A2) transferring the solution from step (A1) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it to dynamic crystallization at 170° C. for 12 h;

[0090] After the crystallization is completed, (A3) is taken out and recorded as seed solution 3.

[0091] Preparation of double-layer single crystal hollow ZSM-5 molecular sieve:

[0092] (B1) Add 6.70 g of potassium hydroxide to 26.80 g of deionized water and stir well;

[0093] (B2) Add 1.20 g of sodium aluminate to 10.80 g of deionized water and stir well;

[0094] (B3) 56.80 g of silica sol (silicon oxide content 30% by mass, same as Example 1) was slowly added to the alkali source solution of step (B1) and stirred at room temperature for 30 minutes;

[0095] (B4) adding 363.30 g of deionized water to step (B3), then adding the aluminum source solution from step (B2) while stirring, and stirring at room temperature for 30 minutes;

[0096] (B5) adding 6.34 g of the seed solution 3 from step (A3) to the mixture obtained in step (B4) and stirring at room temperature for 4 hours;

[0097] (B6) transferring the mixed solution obtained in step (B5) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it to hydrothermal dynamic crystallization at 170° C. for 48 h;

[0098] (B7) filtering, washing, drying, and calcining the product obtained in step (B6) to obtain molecular sieve M-3;

[0099] (B8) molecular sieve M-3 and a 1.0 mol / L sodium hydroxide solution were mixed uniformly, with the mass ratio of molecular sieve M-3 to the sodium hydroxide solution being 1:10, and the mixture was heated to 80°C at a heating rate of 4°C / min, stirred at the same temperature for 30 min, filtered, washed, and dried to obtain molecular sieve M-3-J;

[0100] (B9) Molecular sieve M-3-J: ammonium chloride: deionized water were mixed in a mass ratio of 1:1:10, stirred and heated in a water bath at 80°C for 30 minutes, filtered, washed, and dried, and then the dried solid: ammonium chloride: deionized water were mixed in a mass ratio of 1:0.5:10, subjected to a second ammonium exchange, filtered, washed, dried, and calcined at 550°C for 2 hours to obtain a hydrogen-type double-layer single crystal hollow ZSM-5 molecular sieve, recorded as M-3-JH.

[0101] Example 4

[0102] Prepare seed solution:

[0103] (A1) 43.5 g of ethyl orthosilicate, 35.9 g of tetrapropylammonium hydroxide, and 166.4 g of deionized water were mixed and heated with stirring at 40° C. for 4 h;

[0104] (A2) transferring the solution from step (A1) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it to dynamic crystallization at 170° C. for 12 h;

[0105] After the crystallization is completed, (A3) is taken out and recorded as seed solution 4.

[0106] Preparation of double-layer single crystal hollow ZSM-5 molecular sieve:

[0107] (B1) Add 6.50 g of potassium hydroxide to 15.17 g of deionized water and stir well;

[0108] (B2) Add 2.56 g of aluminum nitrate nonahydrate to 10.24 g of deionized water and stir well.

[0109] (B3) Slowly adding 64.9 g of silica sol (15% by mass of silica content) to the alkali source solution of step (B1) and stirring at room temperature for 30 minutes;

[0110] (B4) adding 225.39 g of deionized water to step (B3), then adding the aluminum source solution from step (B2) with stirring, and stirring at room temperature for 30 minutes;

[0111] (B5) Add 6.81 g of the seed solution 4 from step (A3) to the solution from step (B4) and stir at room temperature for 4 hours;

[0112] (B6) transferring the mixed solution from step (B5) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it to hydrothermal dynamic crystallization at 170° C. for 48 h;

[0113] (B7) filtering, washing, drying, and calcining the product obtained in step (B6) to obtain molecular sieve M-4;

[0114] (B8) molecular sieve M-4 and a 0.6 mol / L sodium hydroxide solution were mixed uniformly, with the mass ratio of molecular sieve M-4 to the sodium hydroxide solution being 1:10, and the mixture was heated to 80° C. at a heating rate of 4° C. / min, stirred at the same temperature for 30 min, filtered, washed, and dried to obtain molecular sieve M-4-J;

[0115] (B9) The molecular sieve M-4-J, ammonium chloride, and deionized water were mixed uniformly at a mass ratio of 1:1:10, stirred and heated under a water bath at 80°C for 30 min, filtered, washed, and dried. The obtained solid, ammonium chloride, and deionized water were mixed uniformly at a mass ratio of 1:0.5:10, subjected to a second ammonium exchange, filtered, washed, and dried, and calcined at 550°C for 2 h to obtain a hydrogen-type double-layer single-crystal hollow ZSM-5 molecular sieve, which was recorded as M-4-J-H.

[0116] Comparative Example 1

[0117] The conventional ZSM-5 molecular sieve was purchased from Sinopec Catalyst Company Qilu Branch, and had a silicon-aluminum molar ratio (SiO2 / Al2O3) of 25, which was recorded as DB1-H.

[0118] Comparative Example 2

[0119] (1) The conventional ZSM-5 molecular sieve (the same as the ZSM-5 molecular sieve in Comparative Example 1) and a sodium hydroxide solution with a concentration of 0.2 mol / L were mixed uniformly at a mass ratio of 1:10, heated and stirred at 80°C for 30 min, filtered, washed, and dried.

[0120] (2) The alkali-treated conventional ZSM-5 molecular sieve, ammonium chloride, and deionized water were mixed uniformly at a mass ratio of 1:1:10, stirred and heated under a water bath at 80°C for 30 min, filtered, washed, and dried. The obtained solid, ammonium chloride, and deionized water were mixed uniformly at a mass ratio of 1:0.5:10, subjected to a second ammonium exchange, filtered, washed, and dried, and calcined at 550°C for 2 h to obtain a hydrogen-type molecular sieve DB2-H. The hydrogen-type molecular sieve DB2-H did not have a hollow structure and did not have a rod-like structure.

[0121] Comparative Example 3

[0122] The conventional ZSM-5 molecular sieve was purchased from Sinopec Catalyst Company Qilu Branch, and had a silicon-aluminum molar ratio (SiO2 / Al2O3) of 25, which was the same as the conventional ZSM-5 molecular sieve in Comparative Example 1.

[0123] (1) The conventional ZSM-5 molecular sieve and a sodium hydroxide solution with a concentration of 1.0 mol / L were mixed uniformly at a mass ratio of 1:10, heated and stirred at 80°C for 30 min, filtered, washed, and dried.

[0124] (2) The purchased ZSM-molecular sieve after alkali treatment: ammonium chloride: deionized water are mixed in a mass ratio of 1:1:10, stirred and heated in a water bath at 80°C for 30 minutes, filtered, washed, and dried, and then the dried solid: ammonium chloride: deionized water are mixed in a mass ratio of 1:0.5:10, subjected to a second ammonium exchange, filtered, washed, dried, and calcined at 550°C for 2 hours to obtain a hydrogen-type molecular sieve DB3-H, which does not have a rod-like structure or a hollow structure.

[0125] Table 1

[0126]

[0127]

[0128] Molecular sieve evaluation

[0129] The molecular sieves of the embodiments and comparative examples were modified and calcined under a phosphorus-aluminum molar ratio of 1:1 (the method is as follows: the molecular sieve sample is evenly spread on a watch glass or a crucible, and the phosphorus-containing solution is slowly poured onto the molecular sieve sample so that the molecular sieve sample finally presents a "slurry state", and after stirring evenly, it is dried in an oven; then it is ground evenly and calcined at 550°C for 4 hours.), after aging and deactivation at 800°C and 100% water vapor for 17 hours, the pellets were sieved to obtain 40-60 mesh particles, and evaluated on a fixed bed microreactor FB. The model compounds were n-hexadecane and 1,3,5-triisopropylbenzene. The evaluation conditions were: reaction temperature 620°C, agent-oil ratio (mass ratio) of 0.75, oil feed rate 0.4 g / min, and oil feed time 300 s. The results are listed in Tables 2 and 3.

[0130] Table 2 n-hexadecane conversion results

[0131]

[0132]

[0133] Table 3 1,3,5-triisopropylbenzene conversion results

[0134]

[0135] As can be seen from Tables 2 and 3, compared with the comparative example, the double-layer single crystal hollow ZSM-5 molecular sieve provided by the present invention has unique morphological characteristics and high diffusion performance, and has higher diene yield and BTX yield in the catalytic reaction of long-chain alkanes (n-hexadecane) and macromolecular cyclic hydrocarbons (1,3,5-triisopropylbenzene), as well as a higher ethylene / propylene ratio.

[0136] In Tables 2 and 3, diene refers to ethylene and propylene, and BTX refers to benzene, toluene, and xylene.

Claims

1. A double-layer single-crystal hollow ZSM-5 molecular sieve, the double-layer single-crystal hollow ZSM-5 molecular sieve having a double-layer closed hollow structure and an epitaxially grown nanorod shell, the average grain size of the double-layer single-crystal hollow ZSM-5 molecular sieve being 0.8 to 3.5 μm; the nanorods of the double-layer single-crystal hollow ZSM-5 molecular sieve growing along the ac axis, and the entire particle having a single crystal structure; The closed hollow structure refers to a space in the ZSM-5 molecular sieve grains that does not contain ZSM-5 molecular sieve, and the space is formed by a ZSM-5 molecular sieve wall having a certain thickness; The grain size refers to the size of the widest part of the grain, which is obtained by measuring the size of the widest part of the grain projection surface in the SEM or TEM image of the sample. The average grain size is obtained by selecting any 10 molecular sieve grains in the SEM or TEM image and calculating the arithmetic mean of their grain sizes.

2. The double-layer single crystal hollow ZSM-5 molecular sieve according to claim 1, wherein: The double-layer single-crystal hollow ZSM-5 molecular sieve has a double-layer closed hollow structure and an epitaxially grown nanorod shell. The double-layer single-crystal hollow ZSM-5 molecular sieve has a grain length of 0.8 to 3.5 μm, a grain width of 0.5 to 2.0 μm, an inner hollow structure length of 0.5 to 2.0 μm, an inner hollow structure width of 0.3 to 1.0 μm, a distance between the inner hollow outer wall and the outer hollow inner wall of 200 to 400 nm, and an epitaxially grown nanorod length of 0.5-1.0 μm. The grain length refers to the length along the ac axis, the width refers to the dimension perpendicular to the length direction, the inner hollow structure length refers to the dimension of the longest projection of the inner hollow structure, the inner hollow structure width refers to the dimension perpendicular to the length direction of the inner hollow structure, and the distance between the inner hollow outer wall and the outer hollow inner wall refers to the randomly measured distance between the inner outer wall and the outer inner wall; through SEM or TEM images, 10 molecular sieve grains are randomly selected, and their grain length, grain width, hollow structure length, hollow structure width, and wall thickness are measured, and their arithmetic average is calculated as the grain length, grain width, hollow structure length, hollow structure width, and wall thickness of the sample.

3. The double-layer single crystal hollow ZSM-5 molecular sieve according to claim 1, wherein: The double-layer single crystal hollow ZSM-5 molecular sieve is modified under the condition of a phosphorus to aluminum molar ratio of 1, and after hydrothermal treatment at 800° C. for 17 hours, the crystal retention rate is greater than or equal to 90% and / or the acid retention rate is greater than or equal to 30%.

4. The double-layer single crystal hollow ZSM-5 molecular sieve according to claim 1, wherein The mesopore specific surface area of ​​the double-layer single crystal hollow ZSM-5 molecular sieve accounts for 15-25% of the total specific surface area, and the mesopore volume accounts for 40-60% of the total pore volume.

5. A method for preparing a double-layer single-crystal hollow ZSM-5 molecular sieve, the method comprising: A. Prepare seed solution, comprising the following preparation steps: (A1) mixing a first silicon source, a template, and water, and stirring at 30 to 60° C. for 2 to 6 hours; wherein the molar ratio of the template to the first silicon source, calculated as SiO2, is 0.05 to 0.50, and the molar ratio of water to the first silicon source, calculated as SiO2, is 10 to 80; (A2) hydrothermally crystallizing the product of step (A1) at 140 to 180° C. for 8 to 24 hours to obtain a seed solution; B. Preparation of double-layer single crystal hollow ZSM-5 molecular sieve, including the following preparation steps: (B1) dissolving an alkali source in water and stirring the water to obtain an alkali source solution; (B2) mixing an aluminum source with water and stirring uniformly to obtain an aluminum source dispersion; (B3) mixing the second silicon source solution with the alkaline source solution obtained in step (B1), and stirring at room temperature; (B4) The product of step (B3) is optionally mixed with a certain amount of dilution water, and mixed with the aluminum source dispersion obtained in step (B2) under stirring, and stirred at room temperature to obtain a mixed solution, wherein the mixed solution n (SiO2) / n (Al2O3) molar ratio = 20~200, n (H2O) / n (SiO2) molar ratio = 50~150; n (M12O) / n (SiO2) molar ratio = 0.20~0.50, wherein M1 represents an alkali metal; said M1 is one or more of K, Rb, and Cs; (B5) adding a certain amount of the seed solution obtained in step (A2) to the product of step (B4), stirring at room temperature, wherein the mass ratio of the seed solution (calculated as SiO2) to the product of (B4) (calculated as SiO2) is 5 to 20:100; (B6) hydrothermally crystallizing the product of step (B5) at 140 to 180° C. for 6 to 48 hours; (B7) filtering, washing, drying, and calcining the product obtained in step (B6) to obtain a parent molecular sieve; (B8) mixing the parent molecular sieve obtained in step (B7) with an alkali solution, stirring at 60 to 90°C for 20 to 60 minutes, wherein the alkali content in the alkali solution is 0.4-2.0 mol / L; and optionally (B9) treating the solid product obtained in step (B8) to obtain an H-type double-layer single-crystal hollow ZSM-5 molecular sieve; The room temperature is 20-35°C.

6. The method according to claim 5, wherein: In step (A1), the first silicon source is one or more of methyl orthosilicate or ethyl orthosilicate, the template is one or more of tetrapropylammonium hydroxide or tetrapropylammonium bromide, and the grain size of the seed crystal in step (A2) is 200-800 nm.

7. The method according to claim 5, wherein: In step (A1), the molar ratio of template R / SiO2 is 0.1 to 0.40, and the molar ratio of H2O / SiO2 is 25 to 65.

8. The method according to claim 5, wherein The concentration of the alkaline source solution in step (B1) is 10 to 30% by mass, and the alkaline source is one or more of potassium hydroxide, rubidium hydroxide or cesium hydroxide.

9. The method according to claim 5, wherein: The concentration of the aluminum source dispersion in step (B2) is 5 to 20% by mass, and the aluminum source is one or more of aluminum sulfate, aluminum nitrate, aluminum isopropoxide, sodium aluminate, or aluminum chloride.

10. The method according to claim 5, wherein In step (B3), the second silicon source is silica sol, and the silica sol is ammonium silica sol, sodium silica sol or a mixture thereof; the SiO2 content in the silica sol is 15-45% by mass.

11. The method according to claim 5, wherein: The stirring time of stirring at room temperature in the step (B3) is 10 to 30 minutes, the stirring time of stirring at room temperature in the step (B4) is 30 to 60 minutes, the stirring time of stirring at room temperature in the step (B6) is 1 to 6 hours, and the mass ratio of SiO2 in the seed solution to SiO2 in the second silicon source in the step (B5) is 5 to 20:

100.

12. The method according to claim 5, wherein: In step (B3), the stirring is carried out at room temperature for more than 10 minutes.

13. The method according to claim 11, wherein In step (B5), the mass ratio of SiO2 in the seed solution to SiO2 in the second silicon source is 5-10:

100.

14. Use of the double-layer single-crystal hollow ZSM-5 molecular sieve according to any one of claims 1 to 4 or the double-layer single-crystal hollow ZSM-5 molecular sieve obtained according to any one of claims 5 to 13 in catalytic cracking of hydrocarbons.

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