ZSM-5 molecular sieve with controllable hollow size as well as preparation method and application of ZSM-5 molecular sieve

Abstract

The invention relates to a ZSM-5 molecular sieve with a controllable hollow size and a preparation method and application thereof. The molecular sieve is synthesized by adopting a seed crystal method and is obtained through one-step alkali treatment, and an organic template agent is not used in the method. The hollow ZSM-5 molecular sieve has a crystal grain length of 1.5-2.5 [mu] m, a crystal grain width of 1.0-1.5 [mu] m, a shell wall thickness of 400-1000 nm, and a hollow size m (nm) and a used seed crystal grain size n (nm) meet the following relation: 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, the research on hollow molecular sieves has become a research hotspot in the fields of chemistry and new materials science. Hollow molecular sieves have shown broad application prospects in shape-selective adsorbents, catalysts, drug sustained-release agents and microreactors due to their unique physical and chemical properties such as multi-level structure and large specific surface area, and have received increasing attention. Template method is one of the common methods for preparing hollow molecular sieves. Its principle is to use micro / nanoparticles as templates, and form a certain thickness of precursors on their surface through chemical reaction deposition, electrostatic attraction or in-situ synthesis to form core-shell composite micro / nanostructure particles, and then remove the template by high-temperature calcination, heating or dissolution to obtain a hollow structure. Organic template agents are expensive and will greatly increase the synthesis cost of molecular sieves. Therefore, from the perspective of efficient use of energy and elimination of environmental pollution, the large-scale use of organic template agents has limited the further application of molecular crystal materials to a certain extent. The existing methods for preparing hollow molecular sieves have problems such as high use of organic template agents 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 method and its application.

[0004] A method for synthesizing a 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)=50-200, n(MB2O) / n(SiO2)=0.10-0.40, n(H2O) / n(SiO2)=20-100; wherein MB represents an alkali metal;

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

[0009] (4) adding the seed 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 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 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-controllable hollow ZSM-5 molecular sieve described in the above technical solution, the concentration of the alkali source solution in step (1) can be 10 to 30% by mass, and the alkali 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 as 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 type silica sol, a sodium type 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-controllable 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 as 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 as 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 a size-controlled 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 crystal.

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

[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 grains are randomly measured, and their arithmetic average is 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 part in the TEM image and the outer surface of the grain. The wall thickness of a grain parallel to the length of the grain is randomly measured as the shell wall thickness of the grain, and the wall thickness values ​​of 10 particles are randomly selected, and their arithmetic mean is taken 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 in the synthesis process, is environmentally friendly, avoids the emission pollution of organic amines, and is conducive to industrial scale-up and application promotion. Seed crystals are added at a certain time to avoid excessive dissolution of the seed crystals, which can ensure that the size of the hollow structure is consistent with the seed crystal size, and the size of the hollow structure can be controlled by controlling the grain size of the seed crystal.

[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 for catalytic cracking to have a 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 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 It is a scanning electron microscope image of the molecular sieve of Example 2. DETAILED DESCRIPTION

[0039] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

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

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

[0042] The method for synthesizing a size-controlled hollow ZSM-5 molecular sieve provided by the present invention, optionally, the silicon source in step (1) is a silica sol, which can be an ammonium silica sol and / or a sodium silica sol. The SiO2 content in the silica sol is 15 to 45% by mass, for example, 15% by mass, 25% by mass, 30% by mass, 45% by mass, or within a range formed by any two of the values ​​being endpoints.

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

[0044] The method for synthesizing a size-controllable hollow ZSM-5 molecular sieve provided by the present invention, 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 method for synthesizing a size-controllable hollow ZSM-5 molecular sieve provided by the present invention, 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 method for synthesizing a size-controllable hollow ZSM-5 molecular sieve provided by the present invention, optionally, the seed crystal described in step (4) is a pure silicon Silicate-1 molecular sieve, and the grain size of the seed crystal can be 200 to 1000 nm.

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

[0048] The method for synthesizing a size-controllable hollow ZSM-5 molecular sieve provided by the present invention, optionally, the amount of seed crystals added in step (4) on a dry basis is 5 to 20 mass % of SiO2 in the silicon source, for example 8 to 18 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 method for synthesizing a size-controllable hollow ZSM-5 molecular sieve provided by the present invention comprises the following steps: 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 method for synthesizing a size-controlled hollow ZSM-5 molecular sieve provided by the present invention comprises: in step (6), filtering, washing, drying and roasting the product obtained in step (5). For example, the product may be washed with water to wash away the residual mother liquid attached to the molecular sieve. The roasting, for example, is carried out at a roasting temperature of 450-600° C., for example, 500-600° C., and a roasting time of 2-12 hours, for example, 2 to 6 hours.

[0052] The method for synthesizing a size-controlled hollow ZSM-5 molecular sieve provided by the present invention comprises the following steps: (7) mixing the parent molecular sieve with an alkali solution, stirring for 20 to 60 minutes at 60 to 90° C. to form a hollow structure, and then recovering the solid. The recovered solid product is, for example, filtered, washed, for example, with water to wash away the alkali solution in the treated parent molecular sieve, and dried to obtain a solid product. The alkali in the alkali solution is, for example, one or more of sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide. The content of the alkali in the alkali 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-controllable 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 synthesis method of the size-controlled hollow ZSM-5 molecular sieve provided by the present invention, step (8) is to perform ammonium exchange on the solid product obtained in step (7). The method of ammonium exchange can refer to the method of 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 temperature of ammonium exchange 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 roasted (referred to as the second roasting) to obtain an H-type (hydrogen-type) hollow ZSM-5 molecular sieve; the roasting (second roasting) temperature can be, for example, 500-600°C, and the roasting time can be 1-5 hours.

[0055] In one embodiment of the method for synthesizing a size-controllable hollow ZSM-5 molecular sieve provided by the present invention, the silicon-to-aluminum ratio of the solid product obtained in step (7) is 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 method for synthesizing a size-controlled hollow ZSM-5 molecular sieve provided by the present invention may further include step (9), wherein phosphorus is introduced 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 may refer to existing methods, for example, phosphorus may 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 may be an aqueous phosphoric acid solution, an ammonium phosphate aqueous solution, a diammonium hydrogen phosphate aqueous solution, or a diammonium dihydrogen phosphate aqueous solution, or a mixture of these solutions. The phosphorus content in the phosphorus-containing hollow ZSM-5 molecular sieve may be, for example, 0.5-10% by weight.

[0058] The method for synthesizing a size-controllable hollow ZSM-5 molecular sieve provided by the present invention, in a specific embodiment, comprises:

[0059] (S1) dissolving an alkali source in water, stirring evenly, and obtaining an alkali source solution after the alkali source is fully dissolved;

[0060] (S2) dissolving an aluminum source in water, stirring evenly, 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) into 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) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, and hydrothermally dynamically crystallizing at 80 to 140° C. for 4 to 12 hours, which is recorded as the first crystallization;

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

[0065] (S7) transferring the mixed solution of step (S6) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, and hydrothermally dynamically crystallizing 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 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 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) adding 3.87 g of potassium hydroxide to 20.32 g of deionized water and stirring well to obtain an alkaline source solution;

[0074] (2) adding 1.75 g of aluminum sulfate 18hydrate to 14.16 g of deionized water and stirring well 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) transferring the mixed solution of step (4) into a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner, and subjecting it to hydrothermal dynamic crystallization at 120° C. for 6 h, which is 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 dispersion (Silicate-1 molecular sieve concentration 8.0 mass %) was added, and stirred at 80° C. for 1 hour;

[0079] (7) transferring the product of step (6) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally crystallizing it at 170° C. for 48 h, which is recorded as the second crystallization;

[0080] (8) filtering, washing, drying, and calcining the product obtained in step (7) 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 evenly, with the mass ratio of molecular sieve P-1 to the alkaline solution being 1:10, the temperature was raised to 80°C at a heating rate of 4°C / min, and then stirred at this temperature for 30 min, filtered, washed, and dried to obtain molecular sieve P-1-J;

[0082] (10) The 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, and the second ammonium exchange was performed, 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 Here is the transmission electron microscopy image. Figure 2This is a scanning electron microscope image.

[0083] Example 2

[0084] (1) adding 18.50 g of cesium hydroxide to 58.58 g of deionized water and stirring well to obtain an alkali source solution;

[0085] (2) adding 3.25 g of aluminum nitrate nonahydrate to 14.81 g of deionized water and stirring well to obtain an aluminum source solution;

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

[0087] (4) adding 273.71 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;

[0088] (5) transferring the product of step (4) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it to hydrothermal dynamic crystallization at 120° C. for 6 h, which is recorded as the first crystallization;

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

[0090] (7) transferring the product of step (6) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally crystallizing it at 170° C. for 48 h, which is recorded as the second crystallization;

[0091] (8) filtering, washing, drying, and calcining the product obtained in step (7) at 550° C. for 4 hours to obtain molecular sieve P-2;

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

[0093] (10) The molecular sieve P-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, and the second ammonium exchange was performed, filtered, washed, dried, and calcined at 550°C for 2 h to obtain a hydrogen hollow ZSM-5 molecular sieve, denoted as P-2-JH. Figure 3 Here is the transmission electron microscopy image. Figure 4 This is a scanning electron microscope image.

[0094] Example 3

[0095] (1) adding 5.76 g of potassium hydroxide to 26.24 g of deionized water and stirring well to obtain an alkali source solution;

[0096] (2) adding 1.97 g of aluminum isopropoxide to 22.66 g of deionized water and stirring well 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) adding 115.81 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;

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

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

[0101] (7) transferring the product of step (6) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally crystallizing it at 170° C. for 48 h, which is recorded as the second crystallization;

[0102] (8) filtering, washing, drying, and calcining the product obtained in step (7) 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 temperature was raised to 80°C at a heating rate of 4°C / min, and then stirred at this temperature for 30 min, filtered, washed, and dried to obtain molecular sieve P-3-J;

[0104] (10) The 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, denoted as P-3-JH.

[0105] Comparative Example 1

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

[0107] (2) adding 1.75 g of aluminum sulfate 18hydrate to 14.16 g of deionized water and stirring well 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 in Example 1) was slowly added to the alkali source solution of step (1) and stirred at room temperature for 30 minutes;

[0109] (4) Add 100.92 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;

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

[0111] (6) transferring the product of step (5) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it 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, the mass ratio of molecular sieve DP-1 to the alkaline solution was 1:10, the temperature was raised to 80°C at a heating rate of 4°C / min, and then stirred at this temperature for 30 minutes, 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 a ZSM-5 molecular sieve, denoted as DP-1-JH.

[0115] Comparative Example 2

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

[0117] (2) adding 1.75 g of aluminum sulfate 18hydrate to 14.16 g of deionized water and stirring well 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 alkaline 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) adding 13.16 g of seed solution (Silicate-1 molecular sieve concentration 8.0 mass %) to the product of step (4), and stirring at 80° C. for 48 hours;

[0121] (6) transferring the product of step (5) to a high-pressure hydrothermal reactor with a polytetrafluoroethylene liner and subjecting it 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 evenly, the mass ratio of molecular sieve DP-2 to the alkaline solution was 1:10, the temperature was raised to 80°C at a heating rate of 4°C / min, and then stirred at this temperature for 30 minutes, 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 a ZSM-5 molecular sieve, denoted 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 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.), 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, 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] It can be seen from Table 2 that, 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-controllable 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) 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)=50-200, n(MB2O) / n(SiO2)=0.10-0.40, n(H2O) / n(SiO2)=20-100; wherein MB represents an alkali metal; (3) hydrothermally dynamically crystallizing the product of step (2) at 80 to 140° C. for 4 to 12 hours, which is referred to as the first crystallization, to obtain a slurry after the first crystallization; (4) adding the seed dispersion to the slurry after the first crystallization in step (3), stirring at a certain temperature for at least 10 minutes; the obtained product is recorded as the second mixed solution; the certain temperature is 50 to 80° C.; (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; (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 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 2.0 mol / L; recovering a 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 alkaline source solution is 10 to 30% by mass, the alkaline 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, for example, 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 can be ammonium silica sol and / or sodium 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, for example 0.15~0.25, and n(H2O) / n(SiO2)=40~90.

6. The method according to claim 1, wherein: The seed crystal in step (4) is pure silicon Silicate-1 molecular sieve, and the grain size of the seed crystal is 200 to 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 weight, for example, 4 to 10% by weight; in step (4), the amount of seed crystals added is 5 to 20% by weight of the silicon source in terms of SiO2 on a dry basis, and the stirring time in step (4) is, for example, 10 to 60 minutes.

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. A hollow ZSM-5 molecular sieve with controllable hollow size, wherein the average grain length of the hollow ZSM-5 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, the average hollow size m (nm) and the average grain size n (nm) of the seed used meet the following relationship: 0.9≤m / n≤1.1, and the hollow ZSM-5 molecular sieve is synthesized according to the method described in any one of claims 1 to 8.

10. Use of the hollow ZSM-5 molecular sieve according to claim 9 in catalytic cracking reactions of hydrocarbons.

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