Hollow size controllable zsm-5 molecular sieve and preparation method and application thereof

Abstract

The present application relates to a kind of hollow size controllable ZSM-5 molecular sieve and its preparation method and application.The molecular sieve is synthesized by seed method, and is obtained by one-step alkali treatment, and the method does not use organic template agent.The hollow ZSM-5 molecular sieve grain length is 1.5-2.5 μm, grain width is 1.0-1.5 μm, shell wall thickness is 400-1000 nm, and the hollow size m (nm) and the seed grain size n (nm) used comply with the following relationship: 0.9≤m / n≤1.1.The molecular sieve has higher propylene yield and BTX yield in hydrocarbon cracking reaction.

Description

Technical Field

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

[0002] In recent years, research on hollow molecular sieves has become a hot topic in fields such as chemistry and new materials science. Due to their unique physicochemical properties, such as a multi-level structure and large specific surface area, hollow molecular sieves have shown promising applications in shape-selective adsorbents, catalysts, drug release agents, and microreactors, and have garnered increasing attention. The template method is a common method for preparing hollow molecular sieves. The principle is to use micro- / nanoparticles as templates. A precursor is deposited on their surface through chemical reaction deposition, electrostatic attraction, or in situ synthesis to form core-shell composite micro- / nanostructured particles of a certain thickness. The template is then removed by high-temperature calcination, heating, or dissolution, resulting in a hollow structure. Organic templates are expensive, significantly increasing the cost of molecular sieve synthesis. Therefore, their extensive use has limited the further application of molecular crystal materials from the perspectives of efficient energy utilization and environmental mitigation. Existing methods for preparing hollow molecular sieves suffer from issues such as high organic template dosage and uncontrollable hollow morphology. Summary of the Invention

[0003] The present invention provides a method for preparing a hollow ZSM-5 molecular sieve with controllable hollow size. Another technical problem to be solved by the present invention is to provide a hollow ZSM-5 molecular sieve obtained by the above method and its application.

[0004] A method for synthesizing size-controllable hollow ZSM-5 molecular sieve

[0005] The present invention provides a method for synthesizing a size-controllable hollow ZSM-5 molecular sieve, the method comprising:

[0006] (1) dissolving the silicon source in the alkaline source solution and stirring at room temperature for at least 10 minutes, for example, 10 to 30 minutes;

[0007] (2) mixing the product of step (1) with water, then adding an aluminum source solution under stirring, stirring at room temperature for 30 to 60 minutes, and obtaining a product recorded as a first mixed solution, wherein the molar ratio is: n(SiO2) / n(Al2O3)=50 to 200, n(MB2O) / n(SiO2)=0.10 to 0.40, and n(H2O) / n(SiO2)=20 to 100; wherein MB represents an alkali metal;

[0008] (3) hydrothermally dynamically crystallizing the product of step (2) at 80-140° C. for 4-12 hours, which is referred to as the first crystallization, to obtain a slurry after the first crystallization;

[0009] (4) adding the seed crystal dispersion to the first crystallized slurry obtained in step (3), and stirring at a certain temperature for at least 10 minutes, for example, 10 to 60 minutes; the obtained product is recorded as the second mixed solution; the certain temperature is 50 to 80° C.;

[0010] (5) subjecting the second mixed solution obtained in step (4) to hydrothermal dynamic crystallization at 140-180° C. for 8-48 hours, which is referred to as the second crystallization, to obtain a slurry after the second crystallization;

[0011] (6) filtering, washing, drying, and calcining the product obtained in step (5) to obtain a parent molecular sieve;

[0012] (7) mixing the parent molecular sieve obtained in step (6) with an alkaline solution, stirring at 60 to 90° C. for 20 to 60 minutes, wherein the alkaline solution has an alkali content of 0.4 to 2.0 mol / L; recovering a solid product; and

[0013] Optionally (8) the solid product obtained in step (7) is subjected to ammonium exchange to obtain an H-type hollow ZSM-5 molecular sieve.

[0014] In the present invention, the room temperature is 20-35°C.

[0015] According to the method for synthesizing a size-controlled hollow ZSM-5 molecular sieve described in the above technical solution, the concentration of the alkaline source solution in step (1) can be 10 to 30% by mass, and the alkaline source is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide or cesium hydroxide.

[0016] According to the method for synthesizing a size-controlled hollow ZSM-5 molecular sieve described in any of the above schemes, the concentration of the aluminum source solution in step (2) can be 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.

[0017] According to the method for synthesizing a size-controlled hollow ZSM-5 molecular sieve as described in any of the above schemes, the silicon source in step (1) may be a silica sol, and the SiO2 content in the silica sol is 15% to 45% by mass, for example, the SiO2 content in the silica sol is 15% by mass, 25% by mass, 30% by mass, 45% by mass, or in a range formed by any two of the above values ​​as endpoints, and the silica sol may be an ammonium silica sol, a sodium silica sol, or a mixture thereof.

[0018] According to the method for synthesizing a size-controlled hollow ZSM-5 molecular sieve as described in any of the above schemes, the molar ratio of the first mixed solution in step (2) can be n(SiO2) / n(Al2O3)=50~100, n(MB2O) / n(SiO2)=0.10~0.30, for example, 0.15~0.25, and n(H2O) / n(SiO2)=40~90.

[0019] According to the method for synthesizing a size-controllable hollow ZSM-5 molecular sieve described in any of the above schemes, the seed crystal in step (4) is a pure silicon Silicate-1 molecular sieve, and the grain size of the seed crystal is preferably 200 to 1000 nm.

[0020] According to the method for synthesizing a size-controlled hollow ZSM-5 molecular sieve described in any of the above schemes, in step (4), seed crystals are added to a certain amount of water to obtain a seed crystal dispersion, and the concentration of the seed crystal dispersion can be 4 to 20 or 4 to 10% by mass.

[0021] According to the method for synthesizing a size-controlled hollow ZSM-5 molecular sieve described in any of the above schemes, in step (4), the amount of seed crystal added is 5 to 20% by mass of the silicon source calculated as SiO2 on a dry basis.

[0022] According to the method for synthesizing a size-controlled hollow ZSM-5 molecular sieve described in any of the above schemes, the silicon-to-aluminum ratio of the hollow ZSM-5 molecular sieve is preferably 20-50.

[0023] According to the method for synthesizing the size-controllable hollow ZSM-5 molecular sieve described in any of the above schemes, the silicon-to-aluminum ratio of the parent molecular sieve is preferably 30-80.

[0024] The hollow ZSM-5 molecular sieve obtained by any of the above schemes has an average grain length of 1.5 to 2.5 μm, an average grain width of 1.0 to 1.5 μm, and an average shell wall thickness of 400 to 1000 nm.

[0025] Preferably, the average hollow size m (nm) of the hollow ZSM-5 molecular sieve and the average grain size n (nm) of the seed crystals used meet the following relationship: 0.9≤m / n≤1.1.

[0026] The hollow ZSM-5 molecular sieve has a hollow structure and has a cavity inside the molecular sieve crystals.

[0027] The present invention also provides the use of the hollow ZSM-5 molecular sieve in a hydrocarbon catalytic cracking reaction, which can achieve higher propylene yields and BTX yields.

[0028] 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 sieves in the SEM or TEM image and calculating their average value.

[0029] The grain length is the dimension of the widest part of the grain in the SEM or TEM image, and the grain width is the dimension of the widest part of the grain perpendicular to the grain length. The grain length and grain width of 10 random grains were measured and the arithmetic mean was calculated as the average grain length and average grain width.

[0030] The hollow size refers to the size of the widest part of the hollow part in the TEM image. The hollow size values ​​of 10 particles are randomly selected and their arithmetic mean is taken as the average hollow size of the sample.

[0031] The shell wall thickness refers to the distance between the edge of the hollow portion of the grain in the TEM image and the outer surface of the grain. The shell wall thickness of a random grain parallel to the length of the grain is measured as the shell wall thickness of the grain. The wall thickness values ​​of 10 randomly selected grains are taken as the arithmetic mean of their values ​​as the average shell wall thickness of the sample.

[0032] The method for preparing the hollow ZSM-5 molecular sieve provided by the present invention can adjust the hollow size of the obtained hollow molecular sieve by adjusting the grain size of the seed crystal.

[0033] The hollow ZSM-5 molecular sieve synthesis method provided by the present invention does not use an organic template during the synthesis process, is environmentally friendly, avoids organic amine emission pollution, and is conducive to industrial scale-up and application promotion. Seed crystals are added at the right time to prevent excessive seed dissolution, ensuring that the hollow structure is consistent with the seed crystal size. The size of the hollow structure can be controlled by controlling the seed crystal grain size.

[0034] The hollow ZSM-5 molecular sieve provided by the present invention has an adjustable hollow size, which is conducive to adapting to different reaction requirements. For example, by adjusting the cavity size, it can be used in catalytic cracking to achieve higher propylene yield and BTX yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a transmission electron microscope image of the molecular sieve of Example 1.

[0036] Figure 2 This is a scanning electron microscope image of the molecular sieve of Example 1.

[0037] Figure 3 This is a transmission electron microscope image of the molecular sieve of Example 2.

[0038] Figure 4 This is a scanning electron microscope image of the molecular sieve of Example 2. DETAILED DESCRIPTION

[0039] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the present application.

[0040] The synthesis method of the size-controllable hollow ZSM-5 molecular sieve provided by the present application, optionally, the concentration of the alkali source solution in step (1) is 10-30 mass%, for example, 15-25 mass%, and the alkali source is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, or cesium hydroxide.

[0041] The synthesis method of the size-controllable hollow ZSM-5 molecular sieve provided by the present application, optionally, the concentration of the aluminum source solution in step (2) is 5-20 mass%, for example, 8-18 mass%, and the aluminum source is one or more of aluminum sulfate, aluminum nitrate, aluminum isopropoxide, sodium aluminate, or aluminum chloride.

[0042] The synthesis method of the size-controllable hollow ZSM-5 molecular sieve provided by the present application, optionally, the silicon source in step (1) is silica sol, which can be ammonium-type silica sol and / or sodium-type silica sol. The SiO2 content in the silica sol is 15-45 mass%, for example, can be 15 mass%, 25 mass%, 30 mass%, 45 mass%, or a range formed by any two of the above values as endpoints.

[0043] The synthesis method of the size-controllable hollow ZSM-5 molecular sieve provided by the present application, optionally, the molar ratio of the first mixed solution in step (2) is n(SiO2) / n(Al2O3) = 50-200, for example, 50-100, for example, 55-70, or 62-70.

[0044] The synthesis method of the size-controllable hollow ZSM-5 molecular sieve provided by the present application, optionally, the molar ratio of the first mixed solution in step (2) is n(MB2O) / n(SiO2) = 0.10-0.40, for example, 0.10-0.30, or 0.15-0.25, or 0.18-0.21.

[0045] The synthesis method of the size-controllable hollow ZSM-5 molecular sieve provided by the present application, optionally, the molar ratio of the first mixed solution in step (2) is n(H2O) / n(SiO2) = 20-100, for example, 40-90, or 50-90.

[0046] The synthesis method of the size-controllable hollow ZSM-5 molecular sieve provided by the present application, optionally, the seed crystal in step (4) is a pure-silicon Silicate-1 molecular sieve, and the grain size of the seed crystal can be 200-1000 nm.

[0047] The method for synthesizing the size-controllable hollow ZSM-5 molecular sieve provided by the present invention, optionally, in step (4), seed crystals are added to a certain amount of water to prepare a seed crystal dispersion with a seed crystal concentration of 4 to 20% by mass, for example, 4 to 10% by mass.

[0048] The present invention provides a method for synthesizing a size-controlled hollow ZSM-5 molecular sieve. Optionally, in step (4), the amount of seed crystals added on a dry basis is 5 to 20% by mass of SiO2 in the silicon source, for example, 8 to 18% by mass.

[0049] In one embodiment, in step (4), the seed crystal dispersion is added to the slurry after the first crystallization at a temperature of 50 to 80° C., and then stirred at a constant temperature of 50 to 80° C. for 10 to 60 minutes.

[0050] The present invention provides a method for synthesizing a size-controlled hollow ZSM-5 molecular sieve, wherein in step (5), the product obtained in step (4) is subjected to dynamic crystallization under hydrothermal conditions. The dynamic crystallization can be carried out under stirring, which is well known to those skilled in the art.

[0051] The present invention provides a method for synthesizing a size-controlled hollow ZSM-5 molecular sieve. In step (6), the product obtained in step (5) is filtered, washed, dried, and calcined. For example, the product can be washed with water to remove residual mother liquor attached to the molecular sieve. The calcination temperature is, for example, 450-600° C., for example, 500-600° C., and the calcination time is 2-12 hours, for example, 2-6 hours.

[0052] The present invention provides a method for synthesizing a size-controlled hollow ZSM-5 molecular sieve, wherein in step (7), the parent molecular sieve is mixed with an alkaline solution, stirred at 60 to 90° C. for 20 to 60 minutes to form a hollow structure, and then recovered to obtain a solid. The recovered solid product is, for example, filtered, washed, for example with water, to remove the alkaline solution in the treated parent molecular sieve, and dried to obtain a solid product. The alkali in the alkaline solution is, for example, 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 or 0.4 to 0.7 mol / L.

[0053] The present invention provides a method for synthesizing a size-controlled hollow ZSM-5 molecular sieve. In step (7), the silicon-aluminum ratio of the ZSM-5 molecular sieve before alkali treatment, i.e., the parent molecular sieve, is, for example, 30 to 80.

[0054] The present invention provides a method for synthesizing a size-controlled hollow ZSM-5 molecular sieve, wherein the solid product obtained in step (7) is subjected to ammonium exchange in step (8). 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. 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 (referred to as the second calcination) to obtain an H-type (hydrogen-type) hollow ZSM-5 molecular sieve; the calcination (second calcination) temperature can be, for example, 500-600°C, and the calcination time can be 1-5 hours.

[0055] The present invention provides a method for synthesizing a size-controllable hollow ZSM-5 molecular sieve. In one embodiment, the solid product obtained in step (7) has a silicon-to-aluminum ratio of 20 to 50. In the present invention, the silicon-to-aluminum ratio is the molar ratio of SiO2 / Al2O3.

[0056] In one embodiment, the hollow ZSM-5 molecular sieve of the present invention, for example, the H-type hollow ZSM-5 molecular sieve obtained in step (8), has a silicon-aluminum ratio of 20 to 50.

[0057] The synthesis method of the size-controlled hollow ZSM-5 molecular sieve provided by the present invention may further include step (9), introducing phosphorus into the H-type hollow ZSM-5 molecular sieve obtained in step (8) to obtain a phosphorus-containing hollow ZSM-5 molecular sieve. The method for introducing phosphorus can refer to the existing method, for example, phosphorus can be introduced into the H-type hollow ZSM-5 molecular sieve by an impregnation method, generally including the steps of contacting the H-type hollow ZSM-5 molecular sieve with an impregnation solution, drying, and roasting. The impregnation solution can be an aqueous phosphoric acid solution, an ammonium phosphate aqueous solution, an ammonium dihydrogen phosphate aqueous solution or an ammonium dihydrogen phosphate aqueous solution or a mixture of these solutions. The phosphorus content in the phosphorus-containing hollow ZSM-5 molecular sieve can be, for example, 0.5-10 weight %.

[0058] The present invention provides a method for synthesizing a size-controlled hollow ZSM-5 molecular sieve, in a specific embodiment, comprising:

[0059] (S1) dissolving an alkali source in water, stirring uniformly, and obtaining an alkali source solution after sufficient dissolution;

[0060] (S2) dissolving an aluminum source in water, stirring uniformly, and obtaining an aluminum source solution after the aluminum source is fully dissolved;

[0061] (S3) dissolving the silicon source in the alkaline source solution of step (S1) and stirring at room temperature for 10 to 30 minutes;

[0062] (S4) adding the solution of step (S3) to a certain amount of water, then adding the aluminum source solution of step (S2) under stirring, and stirring at room temperature for 30 to 60 minutes;

[0063] (S5) transferring the mixed solution of step (S4) into a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, and hydrothermally dynamically crystallizing at 80-140° C. for 4-12 hours, which is recorded as the first crystallization;

[0064] (S6) preparing a solution of a certain concentration by adding a certain amount of seed crystals to the slurry after the first crystallization in step (S5), and stirring at a temperature of 50-80° C. for 10-60 minutes;

[0065] (S7) transferring the mixed solution of step (S6) into a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, and performing hydrothermal dynamic crystallization at 140-180° C. for 8-48 hours, which is recorded as the second crystallization;

[0066] (S8) filtering, washing, drying, and calcining the product obtained in step (S7) to obtain a parent molecular sieve;

[0067] (S9) mixing the parent molecular sieve obtained in step (S8) with an alkaline solution, stirring at 60 to 90° C. for 20 to 60 minutes, wherein the alkaline solution has an alkali content of 0.4 to 2.0 mol / L;

[0068] (S10) exchanging the solid product obtained in step (S9) with ammonium to obtain an H-type hollow ZSM-5 molecular sieve.

[0069] The hollow size controllable ZSM-5 molecular sieve provided by the present invention is synthesized by the above method and then obtained by alkali treatment. This method does not require the use of a large amount of organic templates. In one embodiment, the average grain length of the molecular sieve is 1.5 to 2.5 μm, the average grain width is 1.0 to 1.5 μm, the average shell wall thickness is 400 to 1000 nm, and the hollow size can be adjusted. For example, the hollow size m (nm) and the seed crystal grain size n (nm) used meet the following relationship: 0.9≤m / n≤1.1. In a specific embodiment, the silicon-aluminum ratio of the hollow ZSM-5 molecular sieve is 20 to 50, and the silicon-aluminum ratio before alkali treatment is 30 to 80. Among them, the silicon-aluminum ratio is determined by the XRF method. The specific test method is well known to those skilled in the art and will not be repeated here.

[0070] The following examples further illustrate the present invention, but should not be construed as limiting the embodiments of the present invention.

[0071] The room temperature in the examples and comparative examples is 26°C.

[0072] Example 1

[0073] (1) Add 3.87 g of potassium hydroxide to 20.32 g of deionized water and stir to obtain an alkaline source solution;

[0074] (2) Add 1.75 g of aluminum sulfate 18hydrate to 14.16 g of deionized water and stir evenly to obtain an aluminum source solution;

[0075] (3) 42.10 g of silica sol (sodium silica sol, silicon oxide content 25% by mass, pH 9.5, sodium oxide content 0.22% by mass) was slowly added to the alkaline source solution of step (1) and stirred at room temperature for 30 minutes;

[0076] (4) adding 100.92 g of deionized water to the product of step (3), then adding the aluminum source solution of step (2) under stirring, and stirring at room temperature for 30 minutes;

[0077] (5) The mixed solution of step (4) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjected to hydrothermal dynamic crystallization at 120° C. for 6 h, which was recorded as the first crystallization;

[0078] (6) The product after the first crystallization in step (5) was cooled to 80°C, 13.16 g of seed crystal dispersion (Silicate-1 molecular sieve concentration 8.0 mass %) was added, and stirred at 80°C for 1 hour;

[0079] (7) The product of step (6) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjected to hydrothermal dynamic crystallization at 170°C for 48 hours, which was recorded as the second crystallization;

[0080] (8) The product obtained in step (7) was filtered, washed, dried, and calcined at 550° C. for 4 hours to obtain molecular sieve P-1;

[0081] (9) molecular sieve P-1 and a sodium hydroxide solution with a concentration of 0.4 mol / L were mixed uniformly, with the mass ratio of molecular sieve P-1 to the alkaline solution being 1:10, and the mixture was heated to 80°C at a heating rate of 4°C / min, and then stirred at the same temperature for 30 min, filtered, washed, and dried to obtain molecular sieve P-1-J;

[0082] (10) Molecular sieve P-1-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 hollow ZSM-5 molecular sieve, denoted as P-1-JH. Figure 1 The transmission electron microscope image is Figure 2A scanning electron microscope image thereof is shown in FIG. 1.

[0083] Example 2

[0084] (1) 18.50 g of cesium hydroxide was added to 58.58 g of deionized water, and stirred to obtain an alkali source solution;

[0085] (2) 3.25 g of aluminum nitrate nonahydrate was added to 14.81 g of deionized water, and stirred to obtain an aluminum source solution;

[0086] (3) 114.80 g of silica sol (sodium type silica sol, silica content 15 mass%, pH value 9.2, sodium oxide content 0.25 mass%) was slowly added to the alkali source solution of step (1), and stirred at room temperature for 30 minutes;

[0087] (4) 273.71 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;

[0088] (5) The product of step (4) was transferred to a high-pressure hydrothermal reaction kettle with a polytetrafluoroethylene liner, and hydrothermally dynamically crystallized at 120°C for 6h, which is recorded as first crystallization;

[0089] (6) The product after the first crystallization of step (5) was cooled to 70°C, and then 55.10 g of a seed solution (Silicate-1 molecular sieve concentration 5.0 mass%) was added, and stirred at 70°C for 1 hour;

[0090] (7) The product of step (6) was transferred to a high-pressure hydrothermal reaction kettle with a polytetrafluoroethylene liner, and hydrothermally dynamically crystallized at 170°C for 48h, which is recorded as second crystallization;

[0091] (8) The product obtained in step (7) was filtered, washed, dried, and calcined at 550°C for 4 hours to obtain molecular sieve P-2;

[0092] (9) The molecular sieve P-2 was uniformly mixed with a sodium hydroxide solution with a concentration of 0.6 mol / L, and the mass ratio of the molecular sieve P-1 to the alkali solution was 1:10, and then the temperature was increased to 80°C at a temperature increasing rate of 4°C / min, and stirred at the temperature for 30 min, and then filtered, washed, and dried to obtain molecular sieve P-2-J;

[0093] (10) The molecular sieve P-2-J, ammonium chloride, and deionized water were uniformly mixed according to a mass ratio of 1:1:10, and stirred and heated at 80°C for 30 min, and then filtered, washed, and dried, and then the obtained solid, ammonium chloride, and deionized water were uniformly mixed according to a mass ratio of 1:0.5:10, and subjected to a second ammonium exchange, and then filtered, washed, and dried, and then calcined at 550°C for 2h to obtain a hydrogen type hollow ZSM-5 molecular sieve, which is recorded as P-2-J-H, Figure 3 The transmission electron microscope image is Figure 4 Its scanning electron microscope image.

[0094] Example 3

[0095] (1) Add 5.76 g of potassium hydroxide to 26.24 g of deionized water and stir to obtain an alkaline source solution;

[0096] (2) adding 1.97 g of aluminum isopropoxide to 22.66 g of deionized water and stirring uniformly to obtain an aluminum source solution;

[0097] (3) 55.60 g of silica sol (sodium silica sol, silicon oxide content 30% by mass, pH 9.5, sodium oxide content 0.22%) was slowly added to the alkaline source solution of step (1) and stirred at room temperature for 30 minutes;

[0098] (4) Add 115.81 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;

[0099] (5) The product of step (4) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjected to hydrothermal dynamic crystallization at 100° C. for 8 h, which was recorded as the first crystallization;

[0100] (6) adding 16.68 g of seed solution (10.0 mass % Silicate-1 molecular sieve concentration) to the product after the first crystallization in step (5) cooled to 60° C. and stirring at 60° C. for 1 hour;

[0101] (7) The product of step (6) was transferred to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjected to hydrothermal dynamic crystallization at 170°C for 48 hours, which was recorded as the second crystallization;

[0102] (8) The product obtained in step (7) was filtered, washed, dried, and calcined at 550° C. for 4 hours to obtain molecular sieve P-3;

[0103] (9) molecular sieve P-3 and a sodium hydroxide solution with a concentration of 0.8 mol / L were mixed evenly, with the mass ratio of molecular sieve P-3 to the alkaline solution being 1:10, and the mixture was heated to 80°C at a heating rate of 4°C / min, and then stirred at the same temperature for 30 min, filtered, washed, and dried to obtain molecular sieve P-3-J;

[0104] (10) Molecular sieve P-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 hollow ZSM-5 molecular sieve, which was recorded as P-3-JH.

[0105] Comparative Example 1

[0106] (1) Add 3.87 g of potassium hydroxide to 20.32 g of deionized water and stir to obtain an alkaline source solution;

[0107] (2) Add 1.75 g of aluminum sulfate 18hydrate to 14.16 g of deionized water and stir evenly to obtain an aluminum source solution;

[0108] (3) 42.10 g of silica sol (sodium silica sol, silicon oxide content 25% by mass, same as Example 1) was slowly added to the alkali source solution of step (1) and stirred at room temperature for 30 minutes;

[0109] (4) 100.92 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;

[0110] (5) Add 13.16 g of seed solution (8.0% by mass of Silicate-1 molecular sieve) to the product of step (4) and stir at room temperature for 1 hour;

[0111] (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;

[0112] (7) filtering, washing, drying, and calcining the product obtained in step (6) at 550° C. for 4 hours to obtain molecular sieve DP-1;

[0113] (8) molecular sieve DP-1 and a sodium hydroxide solution with a concentration of 0.4 mol / L were mixed evenly, with the mass ratio of molecular sieve DP-1 to the alkaline solution being 1:10, and the mixture was heated to 80°C at a heating rate of 4°C / min and stirred at the same temperature for 30 min, filtered, washed, and dried to obtain molecular sieve DP-1-J;

[0114] (9) Molecular sieve DP-1-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 ZSM-5 molecular sieve, recorded as DP-1-JH.

[0115] Comparative Example 2

[0116] (1) Add 3.87 g of potassium hydroxide to 20.32 g of deionized water and stir to obtain an alkaline source solution;

[0117] (2) Add 1.75 g of aluminum sulfate 18hydrate to 14.16 g of deionized water and stir evenly to obtain an aluminum source solution;

[0118] (3) 42.10 g of silica sol (silicon oxide content 25% 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;

[0119] (4) adding 100.92 g of deionized water to the product of step (3), then adding the aluminum source solution of step (2) under stirring, and stirring at room temperature for 30 minutes;

[0120] (5) 13.16 g of seed solution (8.0% by mass of Silicate-1 molecular sieve) was added to the product of step (4) and stirred at 80°C for 48 hours;

[0121] (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;

[0122] (7) filtering, washing, drying, and calcining the product obtained in step (6) at 550° C. for 4 hours to obtain molecular sieve DP-2;

[0123] (8) molecular sieve DP-2 and a sodium hydroxide solution with a concentration of 0.4 mol / L were mixed uniformly, with the mass ratio of molecular sieve DP-2 to the alkaline solution being 1:10, and the mixture was heated to 80°C at a heating rate of 4°C / min and stirred at the same temperature for 30 min, filtered, washed, and dried to obtain molecular sieve DP-2-J;

[0124] (9) Molecular sieve DP-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 ZSM-5 molecular sieve, recorded as DP-2-JH.

[0125] Table 1

[0126]

[0127] Molecular sieve evaluation

[0128] 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 crucible, 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 compound was n-hexadecane, and the evaluation conditions were: reaction temperature 620°C, agent-oil ratio (weight) 0.75, oil feed rate 0.4 g / min, and oil feed time 300 s. The results are listed in Table 2.

[0129] Table 2

[0130]

[0131] As can be seen from Table 2, compared with the comparative example, the ZSM-5 molecular sieve provided by the present invention has a higher total yield of propylene and BTX in the catalytic reaction of long-chain alkane (n-hexadecane).

Claims

1. A method for synthesizing a size-controlled hollow ZSM-5 molecular sieve, the method comprising: (1) Dissolve the silicon source in the alkaline source solution and stir at room temperature for at least 10 minutes; (2) The product of step (1) is mixed with water, and then the aluminum source solution is added under stirring, and stirred at room temperature for 30 to 60 minutes to obtain a product, which is recorded as the first mixed solution. The molar ratio is: n (SiO2) / n (Al2O3)=50~200, n (MB2O) / n (SiO2)=0.10~0.40, n (H2O) / n (SiO2) = 20 ~ 100; MB represents alkali metal; (3) The product of step (2) is subjected to hydrothermal dynamic crystallization at 80-140°C for 4-12 h, which is recorded as the first crystallization; and a slurry after the first crystallization is obtained; (4) adding the seed crystal dispersion to the slurry after the first crystallization in step (3), and stirring at a certain temperature for at least 10 minutes; the obtained product is recorded as the second mixed liquid; the certain temperature is 50-80°C; the seed crystal is pure silicon Silicate-1 molecular sieve; (5) The second mixed solution obtained in step (4) is subjected to hydrothermal dynamic crystallization at 140-180°C for 8-48 h, which is recorded as the second crystallization; and a slurry after the second crystallization is obtained; (6) filtering, washing, drying, and calcining the product obtained in step (5) to obtain a parent molecular sieve; (7) mixing the parent molecular sieve obtained in step (6) with an alkaline solution, stirring at 60 to 90° C. for 20 to 60 min, wherein the alkaline content in the alkaline solution is 0.4 to 2.0 mol / L; recovering the solid product; and Optionally (8) the solid product obtained in step (7) is subjected to ammonium exchange to obtain an H-type hollow ZSM-5 molecular sieve.

2. The method according to claim 1, wherein In step (1), the concentration of the alkali source solution is 10 to 30% by mass, the alkali source is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide or cesium hydroxide, and the stirring time in step (1) is 10 to 30 minutes.

3. The method according to claim 1, 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.

4. The method according to claim 1, wherein In step (1), the silicon source is silica sol, the SiO2 content in the silica sol is 15% to 45% by mass, and the silica sol is ammonium-type silica sol and / or sodium-type silica sol.

5. The method according to claim 1, wherein The molar ratio of the first mixed solution in step (2) is: n (SiO2) / n (Al2O3)=50~100, n (MB2O) / n (SiO2)=0.10~0.30, n (H2O) / n (SiO2)=40~90.

6. The method according to claim 1, wherein The grain size of the seed crystal in step (4) is 200-1000 nm.

7. The method according to claim 1 or 6, wherein: In step (4), seed crystals are added to a certain amount of water to obtain a seed crystal dispersion, wherein the concentration of the seed crystal dispersion is 4 to 20% by mass; in step (4), the amount of seed crystals added is 5 to 20% by mass of the silicon source in terms of SiO2 on a dry basis, and the stirring time in step (4) is 10 to 60 min.

8. The method according to claim 1, wherein The silicon-aluminum ratio of the hollow ZSM-5 molecular sieve is 20-50, and the silicon-aluminum ratio of the parent molecular sieve is 30-80.

9. The method according to claim 5, wherein: The molar ratio of the first mixed solution in step (2) is n (MB2O) / n (SiO2)=0.15~0.

25.

10. The method according to claim 7, wherein: The concentration of the seed crystal dispersion is 4 to 10% by weight.

11. A hollow ZSM-5 molecular sieve with controllable hollow size, wherein the hollow ZSM-5 molecular sieve has an average crystallite length of 1.5 to 2.5 μm, an average crystallite width of 1.0 to 1.5 μm, an average shell wall thickness of 400 to 1000 nm, and an average hollow size m and an average crystallite size n of the seed crystals used satisfy the following relationship: 0.9 ≤ m / n ≤ 1.1, wherein m and n are expressed in nm. The hollow ZSM-5 molecular sieve is synthesized according to the method of any one of claims 1 to 10.

12. Use of the hollow ZSM-5 molecular sieve according to claim 11 in catalytic cracking reactions of hydrocarbons.

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