A polycrystal cluster ZSM-5 molecular sieve, a preparation method and application thereof

Abstract

The present application relates to a kind of polycrystalline cluster ZSM-5 molecular sieve and its preparation method and application.The polycrystalline cluster ZSM-5 molecular sieve has at least two typical most probable pore diameters in the range of 5-50nm.During the preparation of the molecular sieve, two alkali sources (M1 and M2) are used, wherein the mass ratio of the two alkali sources M1 / M2 satisfies the following relationship: 0.1≤n(M1) / n(M2)≤10.0.The polycrystalline cluster ZSM-5 molecular sieve has higher propylene selectivity for large molecule naphthene ring-opening cracking.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst materials and relates to a polycrystalline cluster ZSM-5 molecular sieve and its preparation method and application. Background Art

[0002] Among the numerous factors influencing the catalytic cracking of hydrocarbons to produce low-carbon hydrocarbons, in addition to the cracking feedstock, reaction operating conditions, and reaction equipment, catalytic materials are considered a key factor in catalytic cracking technology. Research and development of catalytic materials with excellent performance has always been a hot topic in this field, but also a challenge. During catalytic cracking, cycloalkanes can undergo ring-opening decomposition to produce light olefins, as well as aromatic hydrocarbons through reactions such as hydrogen transfer and dehydrogenation. Therefore, enhancing the ring-opening decomposition reaction of cycloalkanes is a key design priority for cracking catalysts. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a catalytic material for strengthening the ring-opening decomposition reaction of cycloalkanes and improving the selectivity of propylene, as well as a preparation method and an application method thereof.

[0004] The room temperature of the present invention is 20-35°C.

[0005] In a first aspect, the present invention provides a polycrystalline cluster ZSM-5 molecular sieve having at least two most probable pore diameters within a pore diameter range of 1 to 100 nm, wherein the first most probable pore diameter has a smaller value, and the second most probable pore diameter has a greater value than the first probable pore diameter. Preferably, the first probable pore diameter is within a pore diameter range of 1 to less than 25 nm (referring to a pore diameter ≥1 nm and less than 25 nm), and the second probable pore diameter is within a range of 25 to 100 nm.

[0006] According to the polycrystalline cluster ZSM-5 molecular sieve described in the above technical solution, the polycrystalline cluster ZSM-5 molecular sieve has at least one most probable pore size in the range of 1 to less than 25 nm, for example, 8 to 20 nm, and at least one most probable pore size in the range of 25 to 100 nm, for example, 25 to 50 nm, where the pore size refers to the diameter.

[0007] The polycrystalline cluster ZSM-5 molecular sieve according to any of the above technical solutions, wherein:

[0008] Preferably, the polycrystalline cluster ZSM-5 molecular sieve has at least two most probable pore sizes in the range of 5 to 50 nm. For example, the pore size distribution diagram of the polycrystalline cluster ZSM-5 molecular sieve has one or more peaks at pore sizes of 5 to 20 nm and one or more peaks at pore sizes of 25 to 50 nm.

[0009] The polycrystalline cluster ZSM-5 molecular sieve according to any of the above technical solutions, wherein the polycrystalline cluster ZSM-5 molecular sieve is formed by stacking nanocrystals, the nanocrystals include nanocrystals of two different sizes, the two different sizes of nanocrystals include nanocrystals of a first size and nanocrystals of a second size, the nanocrystals of the first size are grains with a grain size between 1 and 50 nm, and the nanocrystals of the second size are grains with a grain size between 80 and 200 nm.

[0010] The grain size of a crystal 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 projected surface of the grain 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 their average value. Grains with a grain size of 1 to 50 nm are classified as first-size nanocrystals. Ten grains within this range are randomly selected and their arithmetic average is calculated as the average grain size of the first-size nanocrystals (also known as average first size, or nanocrystal size 1). Grains with a grain size of 80 to 200 nm are classified as second-size nanocrystals. Ten grains within this range are randomly selected and their arithmetic average is calculated as the average grain size of the second-size nanocrystals (also known as average second size, or nanocrystal size 2).

[0011] According to the polycrystalline cluster ZSM-5 molecular sieve described in any of the above technical solutions, in one embodiment, the average grain size of the nanocrystals of the first size is 5 to 50 nm, for example, 10 to 48 nm or 20 to 45 nm.

[0012] According to the polycrystalline cluster ZSM-5 molecular sieve described in any of the above technical solutions, in one embodiment, the average grain size of the second-sized nanocrystals is 80 to 100 nm.

[0013] According to the polycrystalline cluster ZSM-5 molecular sieve described in any of the above technical solutions, in a specific embodiment, the relative crystallinity of the polycrystalline cluster ZSM-5 molecular sieve is 85-100%, such as 90-100%.

[0014] 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%.

[0015] According to the polycrystalline cluster ZSM-5 molecular sieve described in any of the above technical solutions, the mesoporous specific surface area of ​​the polycrystalline cluster ZSM-5 molecular sieve can account for 15-25% of the total specific surface area, such as 20-25%.

[0016] According to any of the above technical solutions, the polycrystalline cluster ZSM-5 molecular sieve has a mesopore volume of 35-45% of the total pore volume, for example, 38-42%.

[0017] In the present invention, the specific surface area, pore volume and pore size distribution are measured by nitrogen adsorption capacity method, and the pore size distribution is calculated by BJH method.

[0018] In a second aspect, the present invention provides a method for preparing a polycrystalline cluster ZSM-5 molecular sieve, the method comprising:

[0019] (1) dissolving two alkaline sources (M1 alkaline source and M2 alkaline source) in water to obtain an alkaline source solution, wherein the amount ratio of the two alkaline source substances n(M1) / n(M2) satisfies the following relationship: 0.1≤n(M1) / n(M2)≤10, for example, 0.5≤n(M1) / n(M2)≤5; wherein M1 is one or more of Li and Na, and M2 is one or more of K, Rb, and Cs; in one embodiment, M1 is Na and M2 is K;

[0020] (2) dissolving an aluminum source in water to obtain an aluminum source solution;

[0021] (3) dissolving the silicon source in the alkaline source solution of step (1) and stirring at room temperature for preferably 10 to 30 minutes;

[0022] (4) mixing the product of step (3) with water, then adding the aluminum source solution described in step (2) under stirring, and stirring at room temperature for 30 to 60 minutes; obtaining a mixed solution, referred to as a first mixed solution, wherein the molar ratio of the mixed solution is n(SiO2) / n(Al2O3)=20 to 200, n(M2O) / n(SiO2)=0.10 to 0.50, and n(H2O) / n(SiO2)=20 to 200; wherein M2O refers to an alkali metal oxide, which is the sum of M12O and M22O, M12O represents the oxide of the alkali metal in the M1 alkali source, and M22O represents the oxide of the alkali metal in the M2 alkali source;

[0023] (5) adding a certain amount of seed crystal dispersion to the mixed solution obtained in step (4), and stirring at a certain temperature for 10 to 48 hours; obtaining a mixed solution, referred to as a second mixed solution; wherein the amount of seed crystal added is 5 to 20% by mass of SiO2 in the silicon source;

[0024] (6) subjecting the mixed solution obtained in step (5) to hydrothermal dynamic crystallization at 140-180° C. for 6-48 hours;

[0025] (7) filtering, washing, drying, and calcining the product obtained in step (6) to obtain an alkali metal type polycrystalline cluster ZSM-5 molecular sieve; and

[0026] Optionally (8) the solid product obtained in step (7) is treated to obtain an H-type polycrystalline cluster ZSM-5 molecular sieve.

[0027] According to the method for preparing polycrystalline cluster ZSM-5 molecular sieve described in the above technical solution, the concentration of the alkali source solution in step (1) can be 5-40 mass %, such as 10-30 mass % or 15-25 mass % or 16-20 mass %.

[0028] The method for preparing a polycrystalline cluster ZSM-5 molecular sieve according to any of the above technical solutions, wherein the concentration of the aluminum source solution in step (2) 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.

[0029] According to the method for preparing polycrystalline cluster ZSM-5 molecular sieve described in any of the above technical solutions, the silicon source in step (3) is silica sol, which can be ammonium silica sol and / or sodium silica sol, and the SiO2 content in the silica sol is 15 to 45 mass%, for example, 15 mass%, 25 mass%, 30 mass%, 45 mass% or a range formed by any two of these values ​​as boundary points.

[0030] A method for preparing a polycrystalline cluster ZSM-5 molecular sieve according to any of the above technical solutions, wherein the molar ratio of the mixed solution (first mixed solution) obtained in step (4) is n(SiO2) / n(Al2O3)=30~100 or 50-60, n(M2O) / n(SiO2)=0.15~0.3, and n(H2O) / n(SiO2)=20~200, for example, 40~120 or 70~95.

[0031] According to the method for preparing polycrystalline cluster ZSM-5 molecular sieve described in any of the above technical solutions, the seed crystal in step (5) is an MFI type molecular sieve, and the silicon-aluminum ratio (referring to the SiO2 / Al2O3 molar ratio) of the MFI type molecular sieve is 25~∞.

[0032] According to the method for preparing polycrystalline cluster ZSM-5 molecular sieve according to any of the above technical solutions, the concentration of the seeds in the seed dispersion in step (5) is 2-20 mass %, such as 4-10 mass % or 8-18 mass %.

[0033] According to the method for preparing polycrystalline cluster ZSM-5 molecular sieve described in any of the above technical solutions, the amount of seed crystals added in step (5) is 5-15% by mass of the silicon source calculated as SiO2.

[0034] According to the method for preparing polycrystalline cluster ZSM-5 molecular sieve described in any of the above technical solutions, the certain temperature described in step (5) is 60-90°C.

[0035] According to the method for preparing polycrystalline cluster ZSM-5 molecular sieves described in any of the above technical solutions, step (6) is to hydrothermally dynamically crystallize the mixed solution obtained in step (5) at 140-180° C. for 6-48 hours. The method of hydrothermal dynamic crystallization is known to those skilled in the art, for example, crystallization can be carried out in a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner under stirring.

[0036] According to the method for preparing a polycrystalline cluster ZSM-5 molecular sieve described in any of the above technical solutions, in step (7), the product obtained in step (6) is filtered, washed, dried, and calcined. These processes are well known in the art. For example, washing can be performed with water to remove the mother liquid attached to the molecular sieve. The calcination can be performed at 500-600° C. for 2-12 hours, for example, 2-6 hours.

[0037] According to the method for preparing a polycrystalline cluster ZSM-5 molecular sieve described in any of the above technical solutions, step (8) treats the solid product obtained in step (7) to obtain an H-type (also written as hydrogen-type) polycrystalline cluster ZSM-5 molecular sieve, for example, the solid product obtained in step (7) is subjected to ammonium exchange treatment, dried, and calcined to obtain an H-type polycrystalline cluster ZSM-5 molecular sieve. The ammonium exchange method can refer to the method for ammonium exchange of molecular sieves in the prior art, and generally comprises contacting the solid product of step (7) with an ammonium salt solution. In one embodiment, the ammonium exchange temperature is 50-95°C, the exchange time is 10-50 minutes, the concentration of the ammonium salt solution is 2-15% by mass, and the mass ratio of the ammonium salt solution to the solid product is 5-15:1, and the ammonium salt is, for example, one or more of ammonium sulfate, ammonium chloride, and ammonium nitrate. The solid product after ammonium exchange is filtered, optionally washed, dried, and calcined to obtain an H-type hollow ZSM-5 molecular sieve. For example, the calcination temperature can be 500-600°C, and the calcination time can be 1-5 hours.

[0038] The third aspect of the present invention provides an application of the polycrystalline cluster ZSM-5 molecular sieve provided by the present invention, wherein the application of the polycrystalline cluster ZSM-5 molecular sieve in the ring-opening cracking of macromolecular cycloalkanes can improve the selectivity of propylene in the macromolecular cycloalkanes ring-opening cracking products.

[0039] The polycrystalline cluster ZSM-5 molecular sieve provided by the present invention has at least two typical most probable pore sizes in the range of 1 to 100 nm, preferably in the range of 5 to 50 nm, which can provide diffusion paths for macromolecular cycloalkanes of different sizes and improve the conversion rate; the polycrystalline cluster ZSM-5 molecular sieve provided by the present invention also has two sizes of grains, which can have higher conversion rate and propylene selectivity.

[0040] The present invention provides a method for preparing a polycrystalline cluster ZSM-5 molecular sieve. Under the above-mentioned synthesis conditions of the present invention, M1 can cause the silicon-aluminum amorphous to gel into large, highly polymerized grains, and M2 can cause the silicon-aluminum amorphous to undergo weak gelation to generate small, oligomeric grains. In combination with other characteristics, the present invention provides a polycrystalline cluster ZSM-5 molecular sieve having the two grain sizes and the pore size distribution. The present invention provides a method for preparing a polycrystalline cluster ZSM-5 molecular sieve, which can synthesize the polycrystalline cluster ZSM-5 molecular sieve without the use of an organic template. The polycrystalline cluster ZSM-5 molecular sieve obtained by the method for preparing a polycrystalline cluster ZSM-5 molecular sieve provided by the present invention has a high degree of crystallinity, a special pore structure characteristic, and two most probable pore sizes. The obtained polycrystalline cluster ZSM-5 molecular sieve can be used for the ring-opening cracking of macromolecules containing cycloalkanes and cyclohydrocarbons to have a high conversion rate and propylene selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a scanning electron microscope image of the molecular sieve of Example 1.

[0042] Figure 2 This is a scanning electron microscope image of the molecular sieve of Example 2. DETAILED DESCRIPTION

[0043] The following describes the specific embodiments of the present invention 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 invention and are not intended to limit the present invention.

[0044] The present invention is further illustrated below by way of examples, but the present invention is not limited thereto.

[0045] Unless otherwise specified, the raw materials used in the following examples and comparative examples were commercially available.

[0046] Specific surface area and pore volume were analyzed using low-temperature nitrogen adsorption using an ASAP2420 physical adsorption instrument (Micromeritics Instruments, Inc., USA). The experimental method involved sample pretreatment in the first step: 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 involved 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. 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 of nitrogen from the purified sample at different pressure ratios were measured, and N2 adsorption-desorption isotherms were obtained.

[0047] In the examples and comparative examples, the room temperature was 26°C.

[0048] Example 1

[0049] (1) Add 1.94 g of potassium hydroxide and 2.80 g of sodium hydroxide to 24.86 g of deionized water and stir well;

[0050] (2) Add 3.45 g of aluminum sulfate 18hydrate to 27.91 g of deionized water and stir evenly;

[0051] (3) 59.70 g of silica sol (silicon oxide content 30% by mass, sodium type, sodium oxide content 0.08% by mass, pH 9.5) was slowly added to the alkaline source solution of step (1) and stirred at room temperature for 30 minutes;

[0052] (4) adding 402.93 g of deionized water to the product of step (3), and then adding the aluminum source solution obtained in step (2) under stirring, and stirring at room temperature for 30 minutes;

[0053] (5) 15.67 g of seed dispersion (seed is ZSM-5 molecular sieve, silicon-aluminum ratio is ∞ (pure silicon), sodium oxide content is 0.05 wt%, concentration is 8.0 wt%) was added to the product of step (4), and stirred at 60° C. for 1 hour to obtain a mixed solution;

[0054] (6) The mixed solution obtained in step (5) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjected to hydrothermal dynamic crystallization at 170° C. for 48 h;

[0055] (7) filtering, washing, drying, and calcining the product obtained in step (6) at 550° C. for 6 hours to obtain molecular sieve NM-1;

[0056] (8) Molecular sieve NM-1: ammonium chloride: deionized water were mixed in a mass ratio of 1:1:10, stirred 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, stirred in a water bath at 80°C for 30 min for a second ammonium exchange, filtered, washed, dried, and calcined at 550°C for 2 h to obtain ZSM-5 molecular sieve, recorded as NM-1-H. Figure 1 Its scanning electron microscope image.

[0057] Example 2

[0058] (1) Add 1.36 g of potassium hydroxide and 4.80 g of sodium hydroxide to 28.06 g of deionized water and stir evenly to obtain an alkaline source solution;

[0059] (2) adding 2.53 g of aluminum isopropoxide to 29.10 g of deionized water and stirring uniformly to obtain an aluminum source solution;

[0060] (3) 64.80 g of silica sol (silicon oxide content 30% by mass, the same as the silica sol used in Example 1) was slowly added to the alkali source solution in step (1) and stirred at room temperature for 30 minutes;

[0061] (4) 309.24 g of deionized water was added to the product of step (3), and then the aluminum source solution of step (2) was added under stirring, and stirred at room temperature for 30 minutes;

[0062] (5) Add 19.44 g of seed solution (ZSM-5 molecular sieve, concentration 10.0 mass %) to the product of step (4) and stir at 70°C for 1 hour;

[0063] (6) The product of step (5) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjected to hydrothermal dynamic crystallization at 170° C. for 48 h;

[0064] (7) filtering, washing, drying, and calcining the product obtained in step (6) at 550° C. for 6 hours to obtain molecular sieve NM-2;

[0065] (8) Molecular sieve NM-2: 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, stirred and heated in a water bath at 80°C for 30 minutes for the second ammonium exchange, filtered, washed, dried, and calcined at 550°C for 2 hours to obtain ZSM-5 molecular sieve, recorded as NM-2-H. Figure 2 Its scanning electron microscope image.

[0066] Example 3

[0067] (1) Add 7.20 g of potassium hydroxide and 2.80 g of sodium hydroxide to 40.0 g of deionized water and stir evenly to obtain an alkaline source solution;

[0068] (2) Add 1.32 g of sodium aluminate to 11.88 g of deionized water and stir evenly to obtain an aluminum source solution;

[0069] (3) 74.20 g of silica sol (silicon oxide content 30% by mass, same as in Example 1) was slowly added to the alkali source solution of step (1) and stirred at room temperature for 30 minutes;

[0070] (4) Add 404.42 g of deionized water to the product of step (3), then add the aluminum source solution of step (2) under stirring, and stir at room temperature for 30 minutes;

[0071] (5) adding 18.55 g of seed dispersion (ZSM-5 molecular sieve, concentration 18.0 mass %) to the product of step (4), stirring at 80° C. for 1 hour to obtain a mixed solution;

[0072] (6) The mixed solution of step (5) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally dynamic crystallized at 170° C. for 48 h;

[0073] (7) filtering, washing, drying, and calcining the product obtained in step (6) at 550° C. for 6 hours to obtain molecular sieve NM-3;

[0074] (8) Molecular sieve NM-3: 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. The dried solid: ammonium chloride: deionized water were then mixed in a mass ratio of 1:0.5:10, stirred and heated in a water bath at 80°C for 30 minutes for a second ammonium exchange, filtered, washed, dried, and calcined at 550°C for 2 hours to obtain ZSM-5 molecular sieve, which was designated as NM-3-H.

[0075] Comparative Example 1

[0076] (1) Add 4.18 g of sodium hydroxide to 21.95 g of deionized water and stir to obtain an alkaline source solution;

[0077] (2) Add 3.45 g of aluminum sulfate 18hydrate to 27.91 g of deionized water and stir evenly to obtain an aluminum source solution;

[0078] (3) 59.70 g of silica sol (silicon oxide content 30%) was slowly added to the alkali source solution in step (1) and stirred at room temperature for 30 minutes;

[0079] (4) Add 405.84 g of deionized water to the product of step (3), then add the aluminum source solution of step (2) under stirring, and stir at room temperature for 30 minutes;

[0080] (5) Add 15.67 g of seed dispersion (same as in Example 1, concentration 8.0 mass %) to the product of step (4) and stir at 60°C for 1 hour;

[0081] (6) The product of step (5) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjected to hydrothermal dynamic crystallization at 170° C. for 48 h;

[0082] (7) filtering, washing, drying, and calcining the product obtained in step (6) at 550° C. for 6 hours to obtain molecular sieve DNM-1;

[0083] (8) Molecular sieve DNM-1: 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. The dried solid: ammonium chloride: deionized water were then mixed in a mass ratio of 1:0.5:10, stirred and heated in a water bath at 80°C for 30 minutes for a second ammonium exchange, filtered, washed, dried, and calcined at 550°C for 2 hours to obtain ZSM-5 molecular sieve, which was recorded as DNM-1-H.

[0084] Comparative Example 2

[0085] (1) Add 3.87 g of potassium hydroxide to 20.32 g of deionized water and stir well;

[0086] (2) Add 3.45 g of aluminum sulfate 18hydrate to 27.91 g of deionized water and stir evenly;

[0087] (3) 59.70 g of silica sol (silicon oxide content 30%) was slowly added to the alkali source solution in step (1) and stirred at room temperature for 30 minutes;

[0088] (4) Add 407.47 g of deionized water to step (3), then add the aluminum source solution from step (2) under stirring, and stir at room temperature for 30 minutes;

[0089] (5) Add 15.67 g of seed dispersion (same as in Example 1, concentration 8.0 mass %) to the solution in step (4) and stir at 60°C for 1 hour;

[0090] (6) The mixed solution of step (5) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjected to hydrothermal dynamic crystallization at 170° C. for 48 h;

[0091] (7) filtering, washing, drying, and calcining the product obtained in step (6) at 550° C. for 6 hours to obtain molecular sieve DNM-2;

[0092] (8) Molecular sieve DNM-2: ammonium chloride: deionized water were mixed in a mass ratio of 1:1:10, stirred in a water bath at 80°C for 30 min, filtered, washed, and dried. The dried solid: ammonium chloride: deionized water were then mixed in a mass ratio of 1:0.5:10, stirred in a water bath at 80°C for 30 min for a second ammonium exchange, filtered, washed, dried, and calcined at 550°C for 2 h to obtain ZSM-5 molecular sieve, which was designated as DNM-2-H.

[0093] Table 1

[0094]

[0095] In Table 1, nanocrystal size 1 and nanocrystal size 2 refer to the average grain size of nanocrystals of a first size and the average grain size of nanocrystals of a second size, respectively.

[0096] Molecular sieve evaluation

[0097] The molecular sieves of the embodiments and comparative examples were aged and deactivated at 800°C and 100% steam for 4 hours, and 40-60 mesh particles were sieved out of the tablets. The evaluation was performed on a light oil microreactor. The model compound was a mixture of decahydronaphthalene and octahydrophenanthrene (mixed in a mass ratio of 1:1). The evaluation conditions were: reaction temperature 580°C, oil inlet time 70s, and agent-oil ratio 1.28 by weight. The results are listed in Table 2.

[0098] Table 2

[0099]

[0100] As can be seen from Table 2, compared with the comparative example, the ZSM-5 molecular sieve provided by the present invention has higher propylene yield and selectivity in the catalytic reaction of macromolecular cycloalkanes.

Claims

1. A polycrystalline cluster ZSM-5 molecular sieve, wherein the polycrystalline cluster ZSM-5 molecular sieve has at least two most probable pore diameters within a pore diameter range of 1 to 100 nm, wherein the value of the first most probable pore diameter is smaller and the value of the second probable pore diameter is greater than the value of the first probable pore diameter, the polycrystalline cluster ZSM-5 molecular sieve has at least one most probable pore diameter within a range of 8 to 20 nm and at least one most probable pore diameter within a range of 25 to 50 nm; the polycrystalline cluster ZSM-5 molecular sieve is formed by stacking nanocrystals, the nanocrystals containing nanocrystals of a first size and nanocrystals of a second size, the grain size of the nanocrystals of the first size being between 1 and 50 nm, and the grain size of the nanocrystals of the second size being between 80 and 200 nm, and the pore diameter refers to the diameter.

2. The polycrystalline cluster ZSM-5 molecular sieve according to claim 1, wherein The average grain size of the nanocrystals of the first size is 5-50 nm, and the average grain size of the nanocrystals of the second size is 80-100 nm.

3. The polycrystalline cluster ZSM-5 molecular sieve according to claim 2, wherein The average grain size of the nanocrystals of the first size is 20-45 nm.

4. The polycrystalline cluster ZSM-5 molecular sieve according to claim 1, wherein The relative crystallinity of the polycrystalline cluster ZSM-5 molecular sieve is 85-100%.

5. The polycrystalline cluster ZSM-5 molecular sieve according to claim 1, wherein The mesopore specific surface area of ​​the polycrystalline cluster ZSM-5 molecular sieve accounts for 15-25% of the total specific surface area, and the mesopore volume accounts for 35-45% of the total pore volume.

6. A method for preparing a polycrystalline cluster ZSM-5 molecular sieve, the method comprising: (1) dissolving two alkaline sources in water to obtain an alkaline source solution; the two alkaline sources are M1 alkaline source and M2 alkaline source, and the ratio of the amount of the two alkaline sources is n (M1) / n (M2) satisfies the following relationship: 0.1≤ n (M1) / n (M2)≤10; wherein M1 is one or more of Li and Na, and M2 is one or more of K, Rb, and Cs; (2) dissolving an aluminum source in water to obtain an aluminum source solution; (3) Dissolve the silicon source in the alkaline source solution described in step (1) and stir at room temperature for 10 to 30 minutes; (4) Mixing the product of step (3) with water, then adding the aluminum source solution described in step (2) under stirring, and stirring at room temperature for 30 to 60 minutes; obtaining a first mixed solution, wherein the molar ratio of the first mixed solution is: n (SiO2) / n (Al2O3)=20~200, n (M2O) / n (SiO2)=0.10~0.50, n (H2O) / n (SiO2) = 20~200; M2O refers to alkali metal oxide, which is the sum of M12O and M22O; (5) adding a certain amount of seed crystal dispersion to the mixed solution obtained in step (4), and stirring at a certain temperature for 10 to 48 hours to obtain a second mixed solution; wherein the amount of seed crystal added is 5 to 20% by mass of SiO2 in the silicon source; the seed crystal is an MFI type molecular sieve, and the silicon-aluminum ratio SiO2 / Al2O3 of the MFI type molecular sieve is 25 to ∞; (6) subjecting the second mixed solution obtained in step (5) to hydrothermal dynamic crystallization at 140 to 180° C. for 6 to 48 hours; (7) filtering, washing, drying, and calcining the product obtained in step (6); Optionally (8) the solid product obtained in step (7) is treated to obtain an H-type polycrystalline cluster ZSM-5 molecular sieve.

7. The method according to claim 6, wherein: The concentration of the aluminum source solution in step (2) 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.

8. The method according to claim 6, wherein: In step (3), the silicon source is silica sol, and the silica sol is ammonium silica sol and / or sodium silica sol, and the SiO2 content in the silica sol is 15-45% by mass.

9. The method according to claim 6, wherein: The molar ratio of the first mixed solution obtained in step (4) is n (SiO2) / n (Al2O3)=30~100, n (M2O) / n (SiO2)=0.15~0.3, n (H2O) / n (SiO2)=20~200.

10. The method according to claim 6, wherein: The concentration of the seed crystals in the seed crystal dispersion in step (5) is 2 to 20% by mass.

11. The method according to claim 10, wherein: The concentration of the seed crystals in the seed crystal dispersion in step (5) is 8 to 18% by mass.

12. The method according to claim 6, wherein: In step (5), the amount of seed crystal added is 5-15% of the amount of silicon source calculated as SiO2.

13. The method according to claim 6, wherein: The certain temperature described in step (5) is 60~90℃.

14. The method according to claim 6, wherein 0.5≤ n (M1) / n (M2) ≤5。 15. The method according to claim 6, wherein In step (3), the stirring is carried out at room temperature for 10 to 30 minutes.

16. The method according to claim 9, wherein The molar ratio of the first mixed solution obtained in step (4) is n (H2O) / n (SiO2)=40~120.

17. Use of the polycrystalline cluster ZSM-5 molecular sieve according to any one of claims 1 to 5 or the polycrystalline cluster ZSM-5 molecular sieve obtained by the method according to any one of claims 6 to 16 in the ring-opening cracking of macromolecular cycloalkanes.

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