Single-crystal hollow ZSM-5 molecular sieve as well as preparation method and application thereof

Abstract

The invention relates to a single-crystal hollow ZSM-5 molecular sieve and a preparation method and application thereof, the single-crystal hollow ZSM-5 molecular sieve has a double-layer closed hollow structure and a regular hexagonal morphology, the average grain size is 1.0-3.0 [mu] m, and the whole particle is a single-crystal structure. The synthesis method comprises the following steps: synthesizing a seed crystal solution; the preparation method comprises the following steps: dissolving a silicon source in alkali liquor, then mixing with an aluminum source solution to form a mixed solution with specific composition, adding the seed crystal solution, crystallizing, carrying out alkali treatment, and carrying out post-treatment. The molecular sieve has higher low-carbon olefin yield and higher propylene / ethylene ratio in hydrocarbon catalytic cracking reaction. The preparation method is simple, does not need to adopt a large amount of organic template agents, and is good in technical economy.

Description

Technical Field

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

[0002] At present, the main methods for producing ethylene and propylene include steam cracking, catalytic cracking and propane dehydrogenation. The catalytic cracking of hydrocarbons to produce low-carbon olefins is a typical high-temperature acid-catalyzed reaction. Its important core is the design of molecular sieve catalysts. In addition to adjusting the acid properties of the molecular sieve, its pore structure, grain size and other related physical and chemical properties also have an important influence on the product yield and selectivity. The pore structure of the molecular sieve plays a vital role in improving the cracking ability of large molecular hydrocarbons. By rationally designing the pore structure of the molecular sieve, the accessibility of the molecular sieve surface can be improved, the optimal utilization of the active center can be achieved, the pore volume can be increased, and the diffusion performance and catalytic cracking performance of the molecular sieve can be enhanced. Hollow materials have a special intracapsular microenvironment and a unique spatial confinement effect, and exhibit excellent performance in heterogeneous catalysis, biomedicine, adsorption separation and energy storage.

[0003] ZSM-5 molecular sieve has a unique pore structure, adjustable acidity and high thermal / hydrothermal stability, and is widely used in hydrocarbon catalytic cracking catalysts. Catalytic cracking often adjusts the target product according to market demand. However, the prior art does not provide a method for further improving the performance of ZSM-5 molecular sieve. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a new hollow ZSM-5 molecular sieve, which has a double-layer hollow structure. Another technical problem to be solved by the present invention is to provide a preparation method and application of the hollow ZSM-5 molecular sieve.

[0005] The first aspect of the present invention provides a single crystal hollow ZSM-5 molecular sieve, which has a double-layer closed hollow structure and a regular hexagonal morphology, an average grain size of 1.0 to 3.0 μm, and the entire particle is a single crystal structure.

[0006] The second aspect of the present invention provides a method for preparing a single-crystal hollow ZSM-5 molecular sieve, the method comprising (A) preparing a seed molecular sieve and (B) preparing a double-layer single-crystal hollow ZSM-5 molecular sieve:

[0007] A. Preparation of seed molecular sieve, including the following preparation steps:

[0008] (1) dissolving a silicon source (referred to as the first silicon source) and a template in water, and heating with stirring at 30 to 60° C. for 2 to 6 hours to obtain a solution;

[0009] (2) subjecting the solution obtained in step A(1) to hydrothermal dynamic crystallization at 140-180° C. for 8-24 hours;

[0010] (3) The reaction product obtained in step A(2) is recorded as the seed solution.

[0011] B. Preparation of single crystal hollow ZSM-5 molecular sieve, comprising the following preparation steps:

[0012] (1) dissolving an alkali source in water to obtain an alkali source solution;

[0013] (2) dissolving an aluminum source in water to obtain an aluminum source solution;

[0014] (3) dissolving a silicon source (referred to as the second silicon source) in the alkaline source solution obtained in step B (1), and stirring at room temperature for preferably 10 minutes or more, for example, 10 to 30 minutes; the obtained product is referred to as the first mixed solution;

[0015] (4) The product of step B(3) is optionally mixed with water, and then mixed with the aluminum source solution of step B(2), preferably under stirring, at room temperature, for example, for more than 30 minutes, for example, 30 to 60 minutes; the resulting mixed solution is referred to as a second mixed solution; the second mixed solution has the following molar ratio: n(SiO2) / n(Al2O3)=20 to 200, n(MB2O) / n(SiO2)=0.10 to 0.20, n(H2O) / n(SiO2)=20 to 60, wherein MB represents an alkali metal, which is one or more of K, Rb, and Cs;

[0016] (5) adding a certain amount of the seed solution described in step A(3) to the second mixed solution obtained in step B(4), and stirring at room temperature for preferably more than 1 hour, for example 1 to 6 hours; the obtained product is referred to as the third mixed solution;

[0017] (6) subjecting the product of step B(5), i.e., the third mixed solution, to hydrothermal dynamic crystallization at 140 to 180° C. for 6 to 48 hours;

[0018] (7) filtering, washing, drying and calcining the product obtained in step B (6) to obtain a parent molecular sieve;

[0019] (8) mixing the parent molecular sieve obtained in step B (7) with an alkali-containing solution, stirring at 60 to 90° C. for 20 to 60 min, wherein the alkali content in the alkali-containing solution is 0.4 to 1.0 mol / L;

[0020] and optionally (9) exchanging the solid product obtained in step B (8) to obtain an H-type single crystal hollow ZSM-5 molecular sieve.

[0021] The obtained H-type single-crystal hollow ZSM-5 molecular sieve has a double-layer closed hollow structure, and the molecular sieve particles are single-crystal particles with a regular hexagonal structure.

[0022] The room temperature of the present invention is 20-35°C.

[0023] The third aspect of the present invention provides the use of the single crystal hollow ZSM-5 molecular sieve in catalyst preparation, for example, in petrochemical and / or fine chemical industries.

[0024] A fourth aspect of the present invention provides a catalytic cracking method, comprising contacting hydrocarbon oil with the single crystal hollow ZSM-5 molecular sieve provided by the present invention.

[0025] The single crystal hollow ZSM-5 molecular sieve of the present invention has a double-layer closed hollow structure and a regular hexagonal morphology, has a rich pore structure, improves the accessibility of the active center of the molecular sieve, and has excellent catalytic performance. The molecular sieve can be used for catalyst preparation, such as petrochemical and / or fine chemical catalyst preparation, and has a higher light olefin yield and a higher propylene / ethylene ratio in hydrocarbon catalytic cracking reactions.

[0026] The method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention is simple, does not require the use of a large amount of organic template agents, has good technical and economic efficiency, and can prepare the single crystal hollow ZSM-5 molecular sieve provided by the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a transmission electron microscope image of the hydrogen-type double-layer single crystal hollow ZSM-5 molecular sieve obtained in Example 1.

[0028] Figure 2 This is the Fourier transform diffraction spectrum of the hydrogen-type double-layer single crystal hollow ZSM-5 molecular sieve prepared in Example 1. DETAILED DESCRIPTION

[0029] The following specific embodiments describe the specific embodiments of the present invention in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0030] The single crystal hollow ZSM-5 molecular sieve provided by the invention has a double-layer closed hollow structure.

[0031] The double-layer closed hollow structure has an external ZSM-5 molecular sieve wall and an internal structure closed by the external molecular sieve wall, the internal structure has an internal ZSM-5 molecular sieve wall and a space without ZSM-5 molecular sieve surrounded by the internal ZSM-5 molecular sieve wall, and there is a space without ZSM-5 molecular sieve between the internal molecular sieve wall and the external molecular sieve wall.

[0032] According to the present invention, the ZSM-5 molecular sieve grows along the ac axis direction.

[0033] According to the present invention, the growth orientation of the entire particle of the single crystal hollow ZSM-5 molecular sieve is consistent. The entire particle of the single crystal hollow ZSM-5 molecular sieve is a single crystal structure.

[0034] According to the present invention, the single crystal hollow ZSM-5 molecular sieve has a regular hexagonal morphology.

[0035] In a specific embodiment of the present invention, the average grain size of the single crystal hollow ZSM-5 molecular sieve is 1.0 to 3.0 μm, for example, 1.5 to 3.0 μm.

[0036] The grain size refers to the size of the widest part of the grain, which can be 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.

[0037] The single crystal hollow ZSM-5 molecular sieve has good hydrothermal stability, high crystal retention and good catalytic performance.

[0038] In the present invention, the relative crystallinity of the molecular sieve is based on the XRD standard ZSM-5 molecular sieve standard sample of the Petrochemical Science Research Institute, and the crystallinity of the standard sample is regarded as 100%.

[0039] In a specific embodiment of the present invention, after the single crystal hollow ZSM-5 molecular sieve is modified under the condition of a phosphorus-aluminum molar ratio of 1, the crystal retention is greater than or equal to 90%, for example, 91-92%, under the condition of hydrothermal treatment at 800°C for 17 hours, and the atmosphere of the hydrothermal treatment is a 100 volume % water vapor atmosphere. The crystal retention is the ratio of the relative crystallinity of the molecular sieve obtained after the single crystal hollow ZSM-5 molecular sieve is modified under the condition of a phosphorus-aluminum molar ratio of 1 after the hydrothermal treatment to the relative crystallinity before the hydrothermal treatment.

[0040] In a specific embodiment of the present invention, after the single crystal hollow ZSM-5 molecular sieve is modified under the condition of a phosphorus-aluminum molar ratio of 1, and treated under 800°C hydrothermal treatment for 17 hours, the acid retention is greater than or equal to 30%, for example, 31-34%. The acid retention is the ratio of the acid content of the molecular sieve obtained after the single crystal hollow ZSM-5 molecular sieve is modified under the condition of a phosphorus-aluminum molar ratio of 1 after the hydrothermal treatment to the acid content before the hydrothermal treatment.

[0041] Acid content test method: weigh 0.2g of 20-40 mesh molecular sieve in a sample tube, place it in a heating furnace, use He as carrier gas at a flow rate of 25mL / min, heat to 600℃ at 20℃ / min, and purge for 90min to remove impurities adsorbed on the surface of the molecular sieve. Then cool to 150℃, keep constant temperature for 5min, pass NH3-He gas (10% NH3 and 90% He by mass fraction) into the system for 60min adsorption, then purge with He for 120min until the baseline is stable to desorb physically adsorbed ammonia. Program the temperature to 600℃ at a heating rate of 10℃ / min for desorption, keep for 60min, and the desorption is completed. Use TCD to detect changes in gas components, and the instrument automatically integrates to obtain the total acid content.

[0042] The modification is carried out under the condition that the phosphorus-aluminum molar ratio is 1, and phosphorus can be introduced into the single crystal hollow ZSM-5 molecular sieve according to the phosphorus-aluminum molar ratio of 1 by an equal volume impregnation method for modification. 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 then it is dried in an oven after being stirred evenly; then it is ground evenly and calcined at 550°C for 4 hours. Usually the mass ratio of the phosphorus-containing solution to the molecular sieve is 1 to 3. The phosphorus-containing solution is, for example, a phosphoric acid solution.

[0043] In a specific embodiment of the present invention, the mesoporous specific surface area of ​​the single crystal hollow ZSM-5 molecular sieve accounts for 5 to 15% of the total specific surface area, for example, 8 to 14%.

[0044] In a specific embodiment of the present invention, the mesopore volume of the single crystal hollow ZSM-5 molecular sieve accounts for 30 to 50% of the total pore volume, for example, 32 to 41%.

[0045] In the present invention, the total specific surface area, mesopore specific surface area and micropore specific surface area are obtained by BET analysis, and the BET analysis method is well known to those skilled in the art.

[0046] The single crystal hollow ZSM-5 molecular sieve provided by the present invention has a double-layer closed hollow structure. The molecular sieve pores are mainly microporous structures, and are rich in mesopores and macroporous structures between hollow walls. It can further provide multi-directional diffusion paths, expand the confined space, improve the accessibility of the active center, and have the ability to catalyze the conversion of large molecular hydrocarbons such as cracking.

[0047] The single crystal hollow ZSM-5 molecular sieve provided by the present invention, in one embodiment, is an H-type or phosphorus-containing single crystal hollow ZSM-5 molecular sieve, and the phosphorus content of the phosphorus-containing single crystal hollow ZSM-5 molecular sieve can be 0.5-10% by mass in terms of P2O5.

[0048] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, 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.

[0049] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, optionally, in step A(1), the R / SiO2 molar ratio is 0.05 to 0.50, for example, 0.1 to 0.4, and R represents a template.

[0050] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, optionally, in step A(1), the molar ratio of H2O / SiO2 is 10 to 80, for example, 30 to 55.

[0051] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, optionally, the grain size of the seed crystals in the seed solution (or seed liquid) in step A(3) is 200 to 800 nm, for example, 220 to 500 nm.

[0052] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, optionally, the mass concentration of the alkali source solution in step B(1) is preferably 10 to 30% such as 15 to 25% by mass.

[0053] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, the alkali source is one or more of potassium hydroxide, rubidium hydroxide or cesium hydroxide.

[0054] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, optionally, the mass concentration of the aluminum source solution in step B(2) is preferably 5 to 20% by mass, such as 8 to 12% by mass. The aluminum source can be one or more of aluminum sulfate, aluminum nitrate, aluminum isopropoxide, sodium aluminate or aluminum chloride.

[0055] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, optionally, the silicon source in step B (3) is preferably silica sol, which can be ammonium silica sol, sodium silica sol or a combination thereof. The SiO2 content in the silica sol can be 10 to 45% by mass, for example, the SiO2 mass content of the silica sol is 15%, 25%, 30%, 45% or a range formed by any two of these data values ​​as endpoints.

[0056] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, optionally, the molar ratio of the mixed solution obtained in step B (4) is n(SiO2) / n(Al2O3)=20~200, for example, 45~65.

[0057] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, optionally, the molar ratio of the mixed solution obtained in step B (4) is n(K2O) / n(SiO2)=0.10-0.20, for example, 0.12-0.16.

[0058] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, optionally, the molar ratio of the mixed solution obtained in step B (4) is n(H2O) / n(SiO2)=20-60, for example, 40-60.

[0059] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, optionally, the SiO2 content in the seed solution in step B(5) accounts for 5 to 20% of the SiO2 content in the silicon source (second silicon source) in B(3), for example, 5 to 15% by mass.

[0060] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, in step B (6), the mixed solution obtained in step B (5) is subjected to hydrothermal dynamic crystallization at 140-180° C. for 6-48 hours. For example, the mixed solution obtained in step B (5) can be transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, and then subjected to hydrothermal dynamic crystallization. The dynamic crystallization is to perform a crystallization reaction on the mixed solution in a moving state, such as under stirring.

[0061] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, in step B (7), the product obtained in step B (6) 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, which can be washed with water, then dried, and then calcined. The calcination temperature is, for example, 450-600°C, for example, 500-600°C, and the calcination time is, for example, 2-12h or 2-6h. The mother molecular sieve is rich in silicon inside and rich in aluminum outside.

[0062] According to the preparation method of the single crystal hollow ZSM-5 molecular sieve provided by the present invention, in step B (8), 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. Then the solid product can be taken out, for example, filtered, washed, for example, with water to wash away the alkaline solution in the treated parent molecular sieve, and dried to obtain a solid. The alkaline solution is an aqueous solution containing alkali, and the alkali is, for example, one or more of sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide. The content of alkali in the alkaline solution is 0.4-2.0 mol / L, for example, 0.4-1 mol / L.

[0063] Step B (9) The solid product obtained in step B (8) is subjected to an exchange treatment to obtain an H-type double-layer single crystal hollow ZSM-5 molecular sieve. One embodiment includes the steps of exchanging the solid product of B (8), for example, performing ammonium exchange, filtering, optionally washing, drying, and roasting. The methods of ammonium exchange, filtering, washing, drying, and roasting are well known to those skilled in the art. For example, the roasting temperature can be 500 to 600° C., and the roasting time can be 1 to 5 hours.

[0064] Phosphorus can be introduced into the H-type single crystal hollow ZSM-5 molecular sieve to obtain a phosphorus-containing single crystal hollow ZSM-5 molecular sieve. The method of introducing phosphorus can refer to the existing method, for example, phosphorus can be introduced into the H-type single crystal hollow ZSM-5 molecular sieve by an impregnation method, which generally includes the steps of contacting the H-type single crystal 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, an ammonium monohydrogen phosphate solution, an ammonium dihydrogen phosphate solution, or a mixture of these solutions.

[0065] According to the present invention, the obtained single crystal hollow ZSM-5 molecular sieve has a double-layer closed hollow structure and a regular hexagonal morphology, the surface of the crystal grains is regular and smooth without attachments, and the average crystal grain size is 1.0 to 3.0 μm.

[0066] According to the method for preparing the single crystal hollow ZSM-5 molecular sieve provided by the present invention, a specific implementation method includes:

[0067] A Preparation of seed molecular sieve:

[0068] (1) Dissolve the silicon source and template in water, and heat with stirring at 30-60°C for 2-6 hours;

[0069] (2) transferring the solution of step A(1) into a high-pressure hydrothermal reactor, such as a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, and subjecting the solution to hydrothermal dynamic crystallization at 140 to 180° C. for 8 to 24 hours;

[0070] (3) The reaction product obtained in step A(2) is recorded as the seed solution.

[0071] B Preparation of single crystal hollow ZSM-5 molecular sieve:

[0072] (1) dissolving an alkali source in water and stirring uniformly to obtain an alkali source solution;

[0073] (2) dissolving an aluminum source in water and stirring uniformly to obtain an aluminum source solution;

[0074] (3) dissolving the silicon source in the alkaline source solution of step B (1) and stirring at room temperature for 10 to 30 minutes;

[0075] (4) adding the solution of step B (3) into a certain amount of water, then adding the aluminum source solution of step B (2) under stirring, and stirring at room temperature for 30 to 60 minutes to obtain a mixed solution;

[0076] (5) Slowly add a certain amount of the seed solution of step A (3) to the mixed solution obtained in step B (4), and stir at room temperature for 1 to 6 hours; obtain a mixed solution

[0077] (6) transferring the mixed solution obtained in step B (5) to a high-pressure hydrothermal reactor, such as a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, and subjecting the mixture to hydrothermal dynamic crystallization at 140 to 180° C. for 6 to 48 hours;

[0078] (7) filtering, washing, drying and calcining the product obtained in step B (6) to obtain a parent molecular sieve;

[0079] (8) mixing the parent molecular sieve obtained in step B (7) with an alkali-containing solution, stirring at 60 to 90° C. for 20 to 60 min, wherein the alkali content in the alkali-containing solution is 0.4 to 1.0 mol / L;

[0080] (9) The solid product obtained in step B (8) is subjected to ammonium exchange to obtain an H-type single crystal hollow ZSM-5 molecular sieve.

[0081] According to the application of the single crystal hollow ZSM-5 molecular sieve in catalyst preparation described in the present invention, in one embodiment, the single crystal hollow ZSM-5 molecular sieve is an H-type and / or phosphorus-containing single crystal hollow ZSM-5 molecular sieve, wherein the phosphorus content can be 0.5-10% by mass in terms of P2O5.

[0082] The catalytic cracking method provided by the present invention comprises contacting and reacting hydrocarbon oil with the single crystal hollow ZSM-5 molecular sieve provided by the present invention. The single crystal hollow ZSM-5 molecular sieve may be an H-type (hydrogen-type) single crystal hollow ZSM-5 molecular sieve and / or a phosphorus-containing single crystal hollow ZSM-5 molecular sieve.

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

[0084] Unless otherwise specified, the raw materials used in the following examples and comparative examples were commercially available.

[0085] The acid content of the molecular sieve can be determined using the Autochem II 2920 programmed temperature desorption instrument produced by Micromeritics, USA.

[0086] Low temperature nitrogen adsorption analysis, instrument: ASAP2420 physical adsorption instrument (American Mack Instruments). Experimental method: The first step is sample pretreatment: weigh a certain amount of sample and put it into the sample tube that has been measured by the blank, put it into the degassing treatment unit, and degas for 6 hours at a furnace temperature of 300℃ and a vacuum degree of less than 1.33Pa. The second step is sample measurement: put the pretreated sample tube into the measurement unit, fill the Dewar flask with liquid nitrogen, enter the analysis file to start the measurement, and the measurement process is to use the static volume method to measure the adsorption isotherm, calculate the pore size distribution according to the BJH method, and calculate the specific surface area using the BET formula.

[0087] Fourier transform diffraction spectrum, the measurement electron microscope model is JEM-ARM200F, and the electron diffraction mode of the electron microscope is directly photographed.

[0088] The room temperature of the following examples and comparative examples was 26°C.

[0089] Example 1

[0090] Prepare the seed solution:

[0091] (A1) 60.0 g of tetraethyl orthosilicate, 34.0 g of tetrapropylammonium hydroxide and 140.5 g of deionized water were mixed and heated at 40° C. with stirring for 4 h;

[0092] (A2) transferring the solution of step (A1) into a high pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it to dynamic crystallization at 170° C. for 12 h;

[0093] (A3) is taken out after the crystallization is completed and recorded as seed solution 1.

[0094] Preparation of double-layer single crystal hollow ZSM-5 molecular sieve:

[0095] (B1) adding 2.65 g of potassium hydroxide to 7.95 g of deionized water and stirring well to obtain an alkali source solution;

[0096] (B2) adding 2.10 g of aluminum sulfate 18hydrate to 18.9 g of deionized water and stirring well to obtain an aluminum source solution;

[0097] (B3) 29.70 g of silica sol (silicon oxide content 30%, pH 9.2, sodium type, sodium oxide content 0.22% by mass, the same below) was slowly added to the alkaline source solution of step (B1), and stirred at room temperature for 30 minutes;

[0098] (B4) adding 85.45 g of deionized water to the product obtained in step (B3), then adding the aluminum source solution in step (B2) under stirring, and stirring at room temperature for 30 minutes;

[0099] (B5) adding 6.24 g of the seed solution 1 of step (A3) to the product of step (B4), and stirring at room temperature for 4 hours; the obtained product is recorded as the third mixed solution;

[0100] (B6) transferring the third mixed solution of step (B5) into a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, and subjecting it to hydrothermal dynamic crystallization at 170° C. for 48 h;

[0101] (B7) filtering, washing, drying and calcining the product obtained in step (B6) (calcination temperature 550° C., calcination time 2 h, the same below) to obtain molecular sieve N-1;

[0102] (B8) mixing molecular sieve N-1 and a sodium hydroxide solution with a concentration of 0.6 mol / L, wherein the mass ratio of molecular sieve N-1 to sodium hydroxide solution is 1:10, heating the mixture to 80°C at a heating rate of 4°C / min, stirring the mixture at the same temperature for 30 min, filtering, washing and drying to obtain molecular sieve N-1-J;

[0103] (B9) Molecular sieve N-1-J, ammonium chloride and deionized water are mixed in a mass ratio of molecular sieve N-1-J: ammonium chloride: deionized water of 1:1:10, and stirred and heated in a water bath at 80°C for 30 min. The mixture is filtered, washed and dried. The dried solid, ammonium chloride and deionized water are then mixed in a mass ratio of 1:0.5:10, and the second ammonium exchange is performed. The mixture is filtered, washed, dried and calcined at 550°C for 2 h to obtain a hydrogen-type double-layer single crystal hollow ZSM-5 molecular sieve, which is designated as N-1-JH. Figure 1 The transmission electron microscope image shows a regular hexagonal morphology. Figure 2 Its Fourier transform diffraction spectrum.

[0104] Example 2

[0105] Prepare the seed solution:

[0106] (A1) 54.0 g of ethyl orthosilicate, 48.0 g of tetrapropylammonium hydroxide and 180.7 g of deionized water were mixed and heated at 40° C. with stirring for 4 h;

[0107] (A2) transferring the solution of step (A1) into a high pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it to dynamic crystallization at 170° C. for 12 h;

[0108] (A3) is taken out after the crystallization is completed and recorded as seed solution 2.

[0109] Preparation of double-layer single crystal hollow ZSM-5 molecular sieve:

[0110] (B1) adding 2.56 g of potassium hydroxide to 11.66 g of deionized water and stirring well to obtain an alkali source solution;

[0111] (B2) adding 1.35 g of aluminum isopropoxide to 15.53 g of deionized water and stirring to obtain an aluminum source solution;

[0112] (B3) slowly adding 30.60 g of silica sol (silicon oxide content 30%) to the alkali source solution of step (B1), and stirring at room temperature for 30 minutes;

[0113] (B4) adding 115.81 g of deionized water to the product obtained in step (B3), then adding the aluminum source solution in step (B2) under stirring, and stirring at room temperature for 30 minutes;

[0114] (B5) adding 9.18 g of the seed solution 2 of step (A3) to the product of step (B4) and stirring at room temperature for 4 hours;

[0115] (B6) transferring the product of 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;

[0116] (B7) filtering, washing, drying and calcining the product obtained in step (B6) to obtain molecular sieve N-2;

[0117] (B8) mixing molecular sieve N-2 and a sodium hydroxide solution having a concentration of 1.0 mol / L, wherein the mass ratio of molecular sieve N-2 to sodium hydroxide solution is 1:10, heating the mixture to 80°C at a heating rate of 4°C / min, stirring the mixture at the same temperature for 30 min, filtering, washing, and drying to obtain molecular sieve N-2-J;

[0118] (B9) The molecular sieve N-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 min, 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 h to obtain a hydrogen-type double-layer single crystal hollow ZSM-5 molecular sieve with a regular hexagonal morphology, denoted as N-2-JH.

[0119] Example 3

[0120] Prepare the seed solution:

[0121] (A1) 45.4 g of ethyl orthosilicate, 65.3 g of tetrapropylammonium hydroxide and 150.2 g of deionized water were mixed and heated at 40° C. with stirring for 4 h;

[0122] (A2) transferring the solution of step (A1) into a high pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it to dynamic crystallization at 170° C. for 12 h;

[0123] After the crystallization is completed, (A3) is taken out and recorded as seed solution 3.

[0124] Preparation of double-layer single crystal hollow ZSM-5 molecular sieve:

[0125] (B1) adding 6.80 g of rubidium hydroxide to 27.2 g of deionized water and stirring well to obtain an alkali source solution;

[0126] (B2) adding 1.08 g of sodium aluminate to 9.72 g of deionized water and stirring well to obtain an aluminum source solution;

[0127] (B3) slowly adding 62.3 g of silica sol (silicon oxide content 30%) to the alkali source solution of step (B1), and stirring at room temperature for 30 minutes;

[0128] (B4) adding 163.58 g of deionized water to the product obtained in step (B3), then adding the aluminum source solution in step (B2) under stirring, and stirring at room temperature for 30 minutes;

[0129] (B5) adding 22.43 g of the seed solution 3 of step (A3) to the product of step (B4), and stirring at room temperature for 4 hours;

[0130] (B6) transferring the product of 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;

[0131] (B7) filtering, washing, drying and calcining the product obtained in step (B6) to obtain molecular sieve N-3;

[0132] (B8) mixing molecular sieve N-3 and a sodium hydroxide solution with a concentration of 0.6 mol / L, wherein the mass ratio of molecular sieve N-3 to sodium hydroxide solution is 1:10, heating the mixture to 80°C at a heating rate of 4°C / min, stirring the mixture at the same temperature for 30 min, filtering, washing and drying the mixture to obtain molecular sieve N-3-J;

[0133] (B9) The molecular sieve N-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 min, 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 h to obtain a hydrogen-type double-layer single crystal hollow ZSM-5 molecular sieve having a regular hexagonal morphology, denoted as N-3-JH.

[0134] Comparative Example 1

[0135] Conventional ZSM-5 molecular sieve was purchased from Sinopec Catalyst Company Qilu Branch, with a silicon-aluminum molar ratio (SiO2 / Al2O3 of 25), and was denoted as DB1-H.

[0136] Comparative Example 2

[0137] (1) conventional ZSM-5 molecular sieve and 0.2 mol / L sodium hydroxide solution were uniformly mixed, the mass ratio of ZSM-5 molecular sieve to alkaline solution was 1:10, heated and stirred at 80° C. for 30 min, filtered, washed and dried;

[0138] (2) The conventional 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 DB2-H, which is not a hollow molecular sieve.

[0139] Comparative Example 3

[0140] Conventional ZSM-5 molecular sieve was purchased from Sinopec Catalyst Company Qilu Branch, with a silicon-aluminum molar ratio (SiO2 / Al2O3 of 25).

[0141] (1) conventional ZSM-5 molecular sieve and 1.0 mol / L sodium hydroxide solution were uniformly mixed, the mass ratio of ZSM-5 molecular sieve to alkaline solution was 1:10, heated and stirred at 80° C. for 30 min, filtered, washed and dried;

[0142] (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 is not a hollow molecular sieve.

[0143] Table 1

[0144]

[0145]

[0146] The molecular sieve synthesis ratio in Table 1 is the ratio of the product of step (B4). The seed size is the average size of the seed crystals, and the grain size is the average grain size of the final product.

[0147] Molecular sieve evaluation

[0148] The molecular sieves of the embodiments and comparative examples were modified and calcined under the condition of 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 then dried in an oven after stirring evenly; then ground evenly and calcined at 550°C for 4 hours.), and aged and deactivated at 800°C and 100% water vapor for 17 hours, and 40-60 mesh particles were sieved out of the tablets and evaluated on a fixed bed microreactor FB. The model compound was n-hexadecane, and the evaluation conditions were: reaction temperature 620°C, agent-oil ratio (weight) 0.75, and the results are listed in Table 2.

[0149] Table 2

[0150]

[0151] It can be seen from Table 2 that, compared with the comparative example, the single crystal hollow ZSM-5 molecular sieve provided by the present invention has a higher diene (ethylene and propylene) yield and a higher propylene / ethylene ratio.

Claims

1. A single crystal hollow ZSM-5 molecular sieve, wherein the single crystal hollow ZSM-5 molecular sieve has a double-layer closed hollow structure and a regular hexagonal morphology, an average grain size of 1.0 to 3.0 μm, and the entire particle is a single crystal structure.

2. The single crystal hollow ZSM-5 molecular sieve according to claim 1, wherein: The ZSM-5 molecular sieve grows along the ac axis direction, and the growth orientation of the entire particle is consistent.

3. The single crystal hollow ZSM-5 molecular sieve according to claim 1 or 2, wherein: After the single crystal hollow ZSM-5 molecular sieve is modified under the condition of a phosphorus-aluminum molar ratio of 1, the crystal retention degree is greater than or equal to 90% and the acid retention degree is greater than or equal to 30% under the condition of hydrothermal treatment at 800° C. for 17 hours.

4. The single crystal hollow ZSM-5 molecular sieve according to claim 1, 2 or 3, wherein: The mesopore specific surface area of ​​the single crystal hollow ZSM-5 molecular sieve accounts for 5-15% of the total specific surface area, and the mesopore volume accounts for 30-50% of the total pore volume.

5. A method for preparing a single crystal hollow ZSM-5 molecular sieve, the method comprising: A. Preparation of seed molecular sieve, comprising the following steps: (1) dissolving a silicon source and a template in water, stirring at 30-60° C. for 2-6 hours, wherein the molar ratio of R / SiO2 is 0.05-0.50, and the molar ratio of H2O / SiO2 is 10-80; (2) subjecting the solution of step A(1) to hydrothermal dynamic crystallization at 140-180° C. for 8-24 hours; (3) The reaction product obtained in step A(2) is recorded as the seed solution. B. Preparation of single crystal hollow ZSM-5 molecular sieve, comprising the following steps: (1) dissolving an alkali source in water to obtain an alkali source solution; (2) dissolving an aluminum source in water to obtain an aluminum source solution; (3) dissolving the silicon source in the alkaline source solution described in step B (1), and stirring at room temperature, preferably for more than 10 minutes; (4) The product obtained in step B(3) is optionally mixed with water, and then mixed with the aluminum source solution in step B(2), and stirred at room temperature to obtain a mixed solution, wherein the mixed solution has the following molar ratio: n(SiO2) / n(Al2O3)=20-200, n(MB2O) / n(SiO2)=0.10-0.20, n(H2O) / n(SiO2)=20-60, wherein MB represents an alkali metal, which is one or more of K, Rb, and Cs; (5) adding a certain amount of the seed solution described in step A (3) to the mixed solution obtained in step B (4), and stirring at room temperature, for example, for 1 to 6 hours; (6) subjecting the product of step B(5) to hydrothermal dynamic crystallization at 140-180° C. for 6-48 hours; (7) filtering, washing, drying and calcining the product obtained in step B (6) to obtain a parent molecular sieve; (8) mixing the parent molecular sieve obtained in step B (7) with an alkali-containing solution, stirring at 60 to 90° C. for 20 to 60 min, wherein the alkali content in the alkali-containing solution is 0.4 to 1.0 mol / L; (9) The solid product obtained in step B (8) is subjected to exchange treatment to obtain an H-type single crystal hollow ZSM-5 molecular sieve.

6. The method according to claim 5, wherein: In step A(1), the 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 in step A(1), R / SiO2 is preferably 0.1 to 0.4, H2O / SiO2 is preferably 30 to 55, and R represents the template.

7. The method according to claim 5, wherein: The grain size of the seed crystals in the seed solution of step A(3) is 200 to 800 nm.

8. The method according to claim 5, wherein: The mass concentration of the alkaline source solution in step B(1) is 10-30%, and the alkaline source is one or more of potassium hydroxide, rubidium hydroxide or cesium hydroxide; In step B(2), the mass concentration of the aluminum source solution is 5-20%, and the aluminum source can be one or more of aluminum sulfate, aluminum nitrate, aluminum isopropoxide, sodium aluminate or aluminum chloride.

9. The method according to claim 5, wherein: The silicon source in step B (3) is silica sol, and the SiO2 content in the silica sol can be 10 to 45% by mass.

10. The method according to claim 5, wherein: The mixed solution obtained in step B (4) has the following molar ratios: n(SiO2) / n(Al2O3)=45-65, n(K2O) / n(SiO2)=0.12-0.16, n(H2O) / n(SiO2)=40-60. In step B(5), the SiO2 in the seed solution is 5 to 20% by mass, for example 5 to 15% by mass, of the SiO2 in the silicon source in step (3).

11. Use of the single crystal hollow ZSM-5 molecular sieve according to any one of claims 1 to 4 or the single crystal hollow ZSM-5 molecular sieve obtained by the method of any one of claims 5 to 10 in catalyst preparation.

12. A method for catalytic cracking of hydrocarbon oil, comprising contacting hydrocarbon oil with a single crystal hollow ZSM-5 molecular sieve as described in any one of claims 1 to 4 or a single crystal hollow ZSM-5 molecular sieve obtained by any one of claims 5 to 10, wherein in one embodiment, the single crystal hollow ZSM-5 molecular sieve is a phosphorus-containing single crystal hollow ZSM-5 molecular sieve and / or an H-type single crystal hollow ZSM-5 molecular sieve.

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