High-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres and its preparation method

Abstract

The present invention provides a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres and a preparation method thereof. The preparation method includes: mixing kaolin, a binder, seeds and water, forming the mixture into kaolin microspheres, and then calcining to obtain activated kaolin microspheres. At least mixing the activated kaolin microspheres, a silicon source, transition metal ions and a hydroxyl radical initiator, carrying out crystallization, and then drying and calcining to obtain the high-silica ZSM-5 molecular sieve. The high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres provided by the present invention is prepared by this method. The present invention uses kaolin as a raw material, and under the synergistic action of transition metal ions and a hydroxyl radical initiator, a high-silica ZSM-5 molecular sieve is obtained by in-situ crystallization without using an organic template agent.

Description

Technical Field

[0001] The present invention relates to a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres and a preparation method thereof, belonging to the technical field of molecular sieves. Background Art

[0002] Due to its unique pore structure and good shape selectivity, ZSM-5 molecular sieve is widely used in the fields of petrochemical industry and fine chemical industry. Among them, the hydrophobic property, good stability and reasonable acid distribution of high-silica ZSM-5 molecular sieve have attracted more and more attention. For example, the isomerization performance of high-silica ZSM-5 molecular sieve is better. When used as a catalytic cracking (FCC) catalyst, it can not only improve the yield of light oil, but also increase the octane number of gasoline. However, when synthesizing high-silica ZSM-5 molecular sieve, organic amine template agents are usually required, which have the disadvantages of high raw material cost and serious pollution. Therefore, it has important theoretical significance and application value to obtain high-silica ZSM-5 molecular sieve by a template-free method.

[0003] CN101348263B discloses a microsphere-type high-silica ZSM-5 molecular sieve and a synthesis method thereof. This method uses a silicon source, an aluminum source, hydroxides of alkali metals or alkaline earth metals, tetrapropylammonium hydroxide or tetrapropylammonium bromide and water as raw materials, prepares a slurry, and obtains silicon-aluminum microspheres with a diameter of 30-200 microns by spray drying and forming. Then, the microspheres are placed in organic amine vapor and treated under hydrothermal conditions, and then calcined to obtain the product. This method does not require secondary forming and has better activity in application.

[0004] CN107282087B discloses a high-silica ZSM-5 molecular sieve, a preparation method thereof and an application. This method includes: sequentially and uniformly mixing a liquid alkaline silicon source, an aluminum source, ZSM-5 molecular sieve seeds, a template agent, an alkali, urea and water, and then carrying out aging and hydrothermal synthesis crystallization. Urea is added in the stage of uniform mixing of raw materials. The liquid alkaline silicon source is calculated as SiO2, and the aluminum source is calculated as Al2O3 to obtain a high-silica ZSM-5 molecular sieve. When the obtained high-silica ZSM-5 molecular sieve is used for catalyzing methanol to propylene, it has good selectivity. However, the addition of urea in this method increases the synthesis cost and pollution.

[0005] CN113044853A discloses a method for synthesizing nano high-silica aluminosilicate ZSM-5 molecular sieve. This method first carries out pseudo-solid phase activation on low-silica aluminosilicate minerals, and then mixes the activated minerals with an alkali, water and a template agent, and carries out a crystallization reaction under hydrothermal conditions to obtain a product nano high-silica aluminosilicate ZSM-5 molecular sieve. This invention adjusts the silicon-aluminum ratio of the product molecular sieve by adjusting the proportion of natural minerals in the raw materials, and synthesizes nano ZSM-5 molecular sieves with a silicon-aluminum ratio ranging from 130 to 2800. However, the dosage of the template agent in this method is too large and the crystallization time is too long.

[0006] CN110496595A discloses a preparation method of a high-silica ZSM-5 molecular sieve for degrading VOCs in a quasi-solid phase with controllable crystal grain size. The method includes: (1) mixing a silicon source, an alkali source, a template agent, ZSM-5 molecular sieve seeds and water to form a gel; (2) subjecting the gel in step (1) to hydrothermal treatment in a reaction kettle, and after the reaction ends, performing solid-liquid separation, washing, drying and calcination to obtain a molecular sieve raw material; (3) placing the molecular sieve raw material obtained in step (2) in an ammonium salt solution for ion exchange, and calcining to obtain an HZSM-5 molecular sieve. The ZSM-5 high-silica molecular sieve product prepared by this method has a special spherical appearance.

[0007] CN1429882A uses kaolin as a basic raw material, obtains kaolin microspheres through beating and spray drying forming, undergoes calcination activation, in-situ crystallization synthesizes a molecular sieve catalyst precursor, and then obtains a final Y-type catalytic cracking catalyst through final ion exchange and water washing and other operations.

[0008] CN110526259A discloses a method for in-situ synthesizing ZSM-5 molecular sieve from kaolin microspheres. This method adjusts the in-situ crystallization process, that is, first mixes the calcined kaolin microspheres with the sodium hydroxide solution used for crystallization, then directly adds seeds, an external silicon source and adjusts the alkalinity, and directly in-situ crystallizes to obtain a ZSM-5 molecular sieve with high crystallinity, large pore volume and large specific surface area, but its silicon-aluminum ratio is relatively low.

[0009] CN102895988A discloses a preparation method of an in-situ catalyst. This method uses kaolin as a raw material, adds water and a compound with a decomposition or boiling point temperature less than or equal to 150 °C to make a mixed slurry, obtains kaolin microspheres through spray drying, and then undergoes calcination, mixes and crystallizes with a silicon source, an alkali solution and a guiding agent, and the filter cake is filtered, washed and dried to obtain an in-situ crystallization catalyst. The catalytic cracking catalyst prepared by this method not only has high activity, but also has strong heavy oil conversion ability.

[0010] CN103253683A provides a method for directly in-situ crystallizing to prepare a ZSM-5 / mordenite composite without using a template agent. The method includes the following steps: pretreating high-temperature calcined kaolin microspheres with sodium silicate, then adding acid to make a reaction mixture, and performing hydrothermal crystallization to obtain an in-situ product containing a ZSM-5 / mordenite composite and a non-in-situ ZSM-5 / mordenite composite molecular sieve. The ZSM-5 and mordenite in the kaolin microsphere in-situ crystallized ZSM-5 / mordenite composite molecular sieve product prepared by this method have relatively high crystallinity and can be adjusted as needed, and have good abrasion resistance, and can be used to improve the propylene yield in the FCC process.

[0011] In the prior art, ZSM-5 molecular sieves can be prepared by in-situ crystallization of kaolin, but the silicon-aluminum ratio of most ZSM-5 molecular sieves synthesized using seed crystals is relatively low, and the silicon-aluminum ratio of the prepared ZSM-5 molecular sieves usually does not exceed 30. The synthesis of high-silicon ZSM-5 molecular sieves requires the use of organic templates such as tetrapropylammonium bromide (TPABr), etc., which has serious problems such as high cost and large pollution. Therefore, developing a method for preparing high-silicon ZSM-5 molecular sieves without using organic templates has become one of the problems to be solved in the art. Summary of the invention

[0012] In order to solve the above technical problems, the purpose of the present invention is to provide a high-silicon ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres and a preparation method thereof. The method of the present invention can prepare a high-silicon ZSM-5 molecular sieve without using an organic template.

[0013] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a high-silicon ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which comprises the following steps:

[0014] (1) mixing kaolin, a binder, a seed crystal of ZSM-5 molecular sieve and water to obtain a slurry; molding the slurry to obtain kaolin microspheres, and then calcining the kaolin microspheres to obtain activated kaolin microspheres;

[0015] (2) at least the activated kaolin microspheres, silicon source, transition metal ions and hydroxyl radical initiator are mixed to obtain a gel system; the gel system is crystallized and then at least dried and calcined to obtain the high-silicon ZSM-5 molecular sieve.

[0016] In the above preparation method, preferably, in step (1), the kaolin includes soft kaolin and the like.

[0017] In the above preparation method, preferably, in step (1), the particle size of the kaolin is 3-10 μm.

[0018] In the above-mentioned preparation method, preferably, in step (1), based on the total mass of the kaolin being 100%, the aluminum oxide content is 40%-45%, the silicon oxide content is 52.8%-58%, the iron oxide content is less than 1.7%, and the sum of the sodium oxide and potassium oxide contents is less than 0.5%.

[0019] In the above preparation method, preferably, in step (1), the mixing mass ratio of the binder to the kaolin is 0.16-0.33.

[0020] In the above preparation method, preferably, in step (1), the binder includes one or a combination of several of sodium silicate, sodium metasilicate, silica sol, etc. More preferably, the binder is sodium silicate.

[0021] In the above preparation method, preferably, in step (1), the mixing mass ratio of the seed crystal of ZSM-5 zeolite to the kaolin is (5-20):100.

[0022] In the above preparation method, preferably, in step (1), the seed crystal of ZSM-5 zeolite is a solid seed crystal of ZSM-5 zeolite, including Na-ZSM-5 zeolite and / or H-ZSM-5 zeolite; the crystal grain size of the seed crystal of ZSM-5 zeolite is 0.5-1.5 μm, the relative crystallinity is 95%-98%, and the silica-alumina ratio is 30-50. The seed crystal is pure-phase ZSM-5 without other miscellaneous crystals.

[0023] In the above preparation method, preferably, in step (1), the solid content of the slurry is 25-65%.

[0024] In the above preparation method, preferably, in step (1), the particle size of the kaolin microspheres obtained by forming is 20-110 μm.

[0025] In the above preparation method, preferably, in step (1), the forming includes spray drying forming. The spray drying forming can be carried out in a spray dryer, and its operating conditions are preferably: the hot air inlet temperature is controlled at 115-125 °C, the sample injection flow rate is 15-25%, and the atomizing air flow rate is 450-550 L / h.

[0026] In the above preparation method, preferably, in step (1), the calcination temperature of the kaolin microspheres is 800-1000 °C, and the calcination time is 1-5 h.

[0027] In the above preparation method, preferably, in step (2), the components mixed with the activated kaolin microspheres, silicon source, transition metal ions, and hydroxyl radical initiator further include an alkali source and / or water. More preferably, sodium hydroxide, ammonium hydroxide, etc. can be used as the alkali source to adjust the pH value of the gel system.

[0028] In the above preparation method, preferably, in step (2), the pH value of the gel system is 10-14.

[0029] In the above preparation method, preferably, in step (2), the gel system is prepared by the following method: mixing the activated kaolin microspheres, a silicon source, an optional alkali source (which may or may not be added), and an optional water (which may or may not be added) to obtain a first mixture; mixing transition metal ions and a hydroxyl radical initiator to obtain a first mixed solution; and mixing the first mixture with the first mixed solution to obtain the gel system.

[0030] In the above preparation method, preferably, in step (2), the molar ratio of Na2O:Al2O3:SiO2:H2O in the first mixture is (10 - 50):1:(20 - 100):(800 - 1200); more preferably, the molar ratio of Na2O:Al2O3:SiO2:H2O in the first mixture is (10 - 50):1:(70 - 100):(800 - 1200); further preferably, the molar ratio of Na2O:Al2O3:SiO2:H2O in the first mixture is (10 - 50):1:(90 - 100):(800 - 1200).

[0031] In the above preparation method, those skilled in the art should understand that if the above sodium hydroxide and / or ammonium hydroxide are used in the form of a solution as the alkali source, and if the molar ratio of each component in the first mixture and the pH value of the gel system meet the above conditions, then water does not need to be additionally added during the preparation of the first mixture; if sodium hydroxide and / or ammonium hydroxide are not used in the form of a solution as the alkali source, then in order to fully mix the activated kaolin microspheres and the silicon source and make the molar ratio of each component in the first mixture meet the above conditions, water needs to be added during the preparation of the first mixture.

[0032] In the above preparation method, preferably, in step (2), the silicon source includes one or a combination of several of water glass, tetraethyl orthosilicate, silicon powder, silica sol, etc.

[0033] In the above preparation method, preferably, in step (2), the addition amount of the transition metal ions is 1% - 5% of the molar amount of Al2O3 in the gel system. Among them, the molar amount of Al2O3 in the gel system is the same as the molar amount of Al2O3 in the first mixture.

[0034] In the above preparation method, preferably, in step (2), the addition amount of the hydroxyl radical initiator is 1% - 7% of the molar amount of Al2O3 in the gel system. Among them, the molar amount of Al2O3 in the gel system is the same as the molar amount of Al2O3 in the first mixture.

[0035] In the above preparation method, preferably, in step (2), the transition metal ions include Fe 3+ , Cu 2+ , Mn 6 + , Mn 7+ and Ni 2+ or a combination of one or more of these. The transition metal ions can be mixed with other raw materials in the form of a transition metal ion salt solution. More preferably, the transition metal ion salt solution includes a combination of one or more of ferric chloride, copper chloride, nickel chloride, potassium manganate, and potassium permanganate, etc.

[0036] In the above preparation method, preferably, in step (2), the hydroxyl radical initiator includes a combination of one or more of sodium persulfate, potassium persulfate, and Fenton's reagent, etc.

[0037] In the above preparation method, preferably, in step (2), the temperature for mixing the activated kaolin microspheres, silicon source, transition metal ions, and hydroxyl radical initiator is 20 - 70°C. More specifically, the temperature for mixing the first mixture and the first mixed solution is 20 - 70°C. More preferably, the mixing is carried out under stirring conditions, and the stirring time is 2 - 5 h. The stirring speed is preferably 150 - 350 r / min.

[0038] In the above preparation method, preferably, in step (2), the crystallization temperature is 100 - 200°C, and the time is 12 - 48 h. More preferably, the crystallization temperature is 120 - 180°C, and the time is 12 - 36 h. The crystallization can be dynamic crystallization, such as rotary dynamic crystallization or stirring dynamic crystallization. More preferably, the crystallization is rotary dynamic crystallization, and the rotation speed is preferably 12 - 18 rpm.

[0039] In the above preparation method, in step (2), before drying and roasting the crystallized product, conventional steps such as filtration and washing can also be carried out. The present invention does not specifically limit it, and it can be adjusted conventionally by those skilled in the art.

[0040] In the above preparation method, preferably, in step (2), the drying temperature is 60 - 90°C, and the time is 12 - 18 h.

[0041] In the above preparation method, preferably, in step (2), the roasting temperature is 500 - 1000°C, and the time is 4 - 10 h.

[0042] In a second aspect of the present invention, there is provided a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the method for preparing a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres as described above.

[0043] According to a specific embodiment of the present invention, preferably, the silica-alumina ratio of the high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is 40-100. More preferably, the silica-alumina ratio of the high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is 60-100. Even more preferably, the silica-alumina ratio of the high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is 80-100.

[0044] According to a specific embodiment of the present invention, preferably, the crystal grain size of the high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is 1-3 μm; more preferably 1-2 μm.

[0045] According to a specific embodiment of the present invention, preferably, the relative crystallinity of the high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is 50-70%.

[0046] According to a specific embodiment of the present invention, preferably, the high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is a high-silica ZSM-5 molecular sieve microsphere. Based on the total mass of the high-silica ZSM-5 molecular sieve microsphere being 100%, the content of the high-silica ZSM-5 molecular sieve therein is 36-56%.

[0047] According to a specific embodiment of the present invention, preferably, the high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is a high-silica ZSM-5 molecular sieve microsphere, and the particle size of the high-silica ZSM-5 molecular sieve microsphere is 15-100 μm.

[0048] The present invention provides a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres and a preparation method thereof. In the preparation method of the present invention, solid seeds of ZSM-5 are pre-introduced into kaolin microspheres, realizing the in-situ growth of ZSM-5 molecular sieve on kaolin microspheres, and using transition metal ions to promote the generation of a large amount of hydroxyl radicals, thereby accelerating the formation of Si-O-Si bonds. The transition metal ions and hydroxyl radicals preferentially cooperate with each other to accelerate crystallization and promote the dissolution of active silicon in kaolin microspheres, increasing the silica-alumina ratio in the system. Moreover, no organic template is used in the synthesis process, and finally a high-silica (silica-alumina ratio much greater than 30) ZSM-5 molecular sieve is prepared.

[0049] In the conventional preparation method of ZSM-5 molecular sieve, the silica-alumina ratio of ZSM-5 molecular sieve prepared using seed crystals is generally low. Usually, the silica-alumina ratio of ZSM-5 molecular sieve prepared with seed crystals does not exceed 30. However, in the present invention, natural kaolin clay is used as the raw material, and under the synergistic action of transition metal ions and hydroxyl radical initiators, a high-silica ZSM-5 molecular sieve framework is obtained. Without using an organic template agent, the in-situ crystallization synthesis of high-silica ZSM-5 molecular sieve from kaolin microspheres is realized with the assistance of transition metal ions and hydroxyl radicals. Therefore, the preparation method of the present invention not only obtains high-silica ZSM-5 molecular sieve, but also greatly reduces the synthesis cost and reduces pollution, having broad application prospects and important significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Characteristic X-ray diffraction pattern of high-silica ZSM-5 molecular sieve microspheres ZKM provided for Example 4. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0052] According to the specific embodiments of the present invention, preferably, the method for synthesizing high-silica ZSM-5 molecular sieve by in-situ crystallization of kaolin microspheres of the present invention includes the following steps:

[0053] (1) Mix kaolin, binder, solid seed crystals of ZSM-5 molecular sieve, and water to obtain a slurry;

[0054] Among them, the kaolin includes soft kaolin, etc.; the particle size of the kaolin is 3-10 μm; based on the total mass of the kaolin being 100%, the alumina content is 40%-45%, the silica content is 52.8%-58%, the iron oxide content is below 1.7%, and the sum of the sodium oxide and potassium oxide contents is below 0.5%; the mixing mass ratio of the binder to the kaolin is 0.16-0.33; the binder includes one or a combination of water glass, sodium silicate, and silica sol; the mixing mass ratio of the seed crystals of ZSM-5 molecular sieve to the kaolin is (5-20):100; the solid seed crystals of ZSM-5 molecular sieve include Na-ZSM-5 molecular sieve and / or H-ZSM-5 molecular sieve; the crystal grain size of the solid seed crystals of ZSM-5 molecular sieve is 0.5-1.5 μm, the relative crystallinity is 95%-98%, and the silica-alumina ratio is 30-50; the solid seed crystals of ZSM-5 molecular sieve are pure-phase ZSM-5 without other miscellaneous crystals; the solid content of the slurry is 25%-65%;

[0055] The slurry is spray-dried to form kaolin microspheres with a particle size of 20-110 μm, and then the kaolin microspheres are calcined at 800-1000 °C for 1-5 h to obtain activated kaolin microspheres;

[0056] (2) The activated kaolin microspheres, a silicon source, an optionally added or non-added alkali source, and an optionally added or non-added water are mixed to obtain a first mixture; the transition metal ions and the hydroxyl radical initiator are mixed evenly (which can be carried out at room temperature) to obtain a first mixed solution; the first mixture and the first mixed solution are mixed and stirred at 20-70 °C for 2-5 h (the stirring speed is more preferably 150-350 r / min) to obtain a gel system; wherein, the molar ratio of Na2O:Al2O3:SiO2:H2O in the first mixture is (10-50):1:(20-100):(800-1200); more preferably, the molar ratio of Na2O:Al2O3:SiO2:H2O in the first mixture is (10-50):1:(70-100):(800-1200); further preferably, the molar ratio of Na2O:Al2O3:SiO2:H2O in the first mixture is (10-50):1:(90-100):(800-1200); the pH value of the gel system is 10-14; the silicon source includes one or a combination of several of water glass, tetraethyl orthosilicate, silicon powder, and silica sol; the alkali source includes sodium hydroxide and / or ammonium hydroxide; the addition amount of the transition metal ions is 1%-5% of the molar amount of Al2O3 in the gel system; the addition amount of the hydroxyl radical initiator is 1%-7% of the molar amount of Al2O3 in the gel system; the transition metal ions include Fe 3+ , Cu 2+ , Mn 6+ , Mn 7+ and Ni 2+ and a combination of one or several of them; the hydroxyl radical initiator includes one or a combination of several of sodium persulfate, potassium persulfate, and Fenton's reagent;

[0057] The gel system is transferred to a polytetrafluoroethylene reaction kettle and crystallized dynamically at 100-200 °C for 12-48 h (more preferably crystallized dynamically at 120-180 °C for 12-36 h), then after filtration and washing, dried at 60-90 °C for 12-18 h, and then calcined at 500-1000 °C for 4-10 h to obtain the high-silica ZSM-5 molecular sieve.

[0058] The high-silica ZSM-5 molecular sieve is a high-silica ZSM-5 molecular sieve microsphere, and the particle size of the high-silica ZSM-5 molecular sieve microsphere is 15 - 100 μm; based on the total mass of the high-silica ZSM-5 molecular sieve microsphere being 100%, the content of the high-silica ZSM-5 molecular sieve therein is 36 - 56%; the silica-alumina ratio of the high-silica ZSM-5 molecular sieve is 40 - 100, preferably 60 - 100, more preferably 80 - 100; the crystal grain size of the high-silica ZSM-5 molecular sieve is 1 - 3 μm (preferably 1 - 2 μm); the relative crystallinity of the high-silica ZSM-5 molecular sieve is 50 - 70%.

[0059] In the following examples, the experimental methods are all conventional methods unless otherwise specified; the reagents and materials can all be obtained from commercial sources unless otherwise specified.

[0060] Analysis method: For the detection and confirmation of the phase, a Shimadzu XRD-7000 type X-ray powder diffractometer is used; instrument parameters: Cu-Kα ray, wavelength of 0.1543 nm, tube voltage of 40 kV, tube current of 30 mA. Test conditions for the sample: scanning angle 5 - 40°, scanning speed 8° / min. For the analysis using an X-ray fluorescence spectrometer (XRF), a Shimadzu XRF-1800 is used, and 200 mg of the powder is pressed into a tablet before testing.

[0061] Preparation of kaolin microsphere A:

[0062] 3000 g (dry basis) of kaolin, 500 g of water glass, 150 g of Na-ZSM-5 seeds with a crystal grain size of 0.5 μm, a relative crystallinity of 97%, and a silica-alumina ratio of 40, and water are mixed to form a slurry with a solid content of 25%, and then spray formed to obtain kaolin microsphere A with an average particle size of 20 μm.

[0063] Preparation of kaolin microsphere B:

[0064] 3000 g (dry basis) of kaolin, 1000 g of water glass, 300 g of H-ZSM-5 seeds with a crystal grain size of 1.0 μm, a relative crystallinity of 97%, and a silica-alumina ratio of 40, and water are mixed to form a slurry with a solid content of 45%, and then spray formed to obtain kaolin microsphere B with an average particle size of 60 μm.

[0065] Preparation of kaolin microsphere C:

[0066] 3000 g (dry basis) of kaolin, 800 g of water glass, 600 g of H-ZSM-5 seeds with a crystal grain size of 1.5 μm, a relative crystallinity of 97%, and a silica-alumina ratio of 40, and water are mixed to form a slurry with a solid content of 65%, and then spray formed to obtain kaolin microsphere C with an average particle size of 110 μm.

[0067] Among them, in the preparation of kaolin microspheres A, B, and C, the kaolin used is soft kaolin with a particle size of 3 - 10 μm. Based on the total mass of the kaolin being 100%, the alumina content is 42.5%, the silica content is 55.3%, the iron oxide content is below 1.7%, and the sum of the sodium oxide and potassium oxide contents is below 0.5%. The spray drying and forming is carried out in a spray dryer, and its operating conditions are: the hot air inlet temperature is controlled at 120°C, the sample injection flow rate is 20%, and the atomizing air flow rate is 500 L / h.

[0068] Example 1

[0069] This example provides a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared through the following steps:

[0070] Take an appropriate amount of kaolin microsphere A and calcine it in a muffle furnace at 800°C for 1 h to obtain activated kaolin microsphere A; add sodium silicate, water, and activated kaolin microsphere A into a beaker in the molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:800 in sequence, and then add a mixed solution of Fe 3+ solution (ferric chloride solution) and sodium persulfate, and stir for 4 h (the stirring speed is 150 r / min) under the water bath condition of 20°C to obtain a gel system; the addition amount of the Fe 3+ solution is 5% of the molar amount of Al2O3 in the gel system, and the addition amount of the sodium persulfate is 7% of the molar amount of Al2O3 in the gel system; then transfer the gel system to a polytetrafluoroethylene reaction kettle, carry out rotary dynamic crystallization at 100°C for 12 h (the rotation speed is 15 rpm), then after filtration and washing, dry at 70°C for 15 h, and then calcine at 500°C for 4 h to obtain high-silica ZSM-5 molecular sieve microspheres ZKM.

[0071] It is determined by an X-ray diffractometer that the ZKM in this example contains 36% of ZSM-5, and its silicon-aluminum ratio is 90 as determined by an X-ray fluorescence spectrometer.

[0072] Example 2

[0073] This example provides a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared through the following steps:

[0074] Take an appropriate amount of kaolin microsphere B and calcine it in a muffle furnace at 800°C for 1 h to obtain activated kaolin microsphere B; add tetraethyl orthosilicate, water, and activated kaolin microsphere B into a beaker in the molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:800 in sequence, and then add Cu2+ A mixed solution of a solution (copper chloride solution) and sodium persulfate is stirred for 4 h (the stirring speed is 150 r / min) under a water bath condition of 20 °C to obtain a gel system; the Cu 2+ The addition amount of the solution is 5% of the molar amount of Al2O3 in the gel system, and the addition amount of sodium persulfate is 7% of the molar amount of Al2O3 in the gel system; then the gel system is transferred to a polytetrafluoroethylene reaction kettle and crystallized dynamically by rotation at 100 °C for 12 h (the rotation speed is 15 rpm), and then after filtration and washing, it is dried at 80 °C for 12 h, and then calcined at 500 °C for 4 h to obtain high-silica ZSM-5 molecular sieve microspheres ZKM.

[0075] It is determined by an X-ray diffractometer that the ZKM in this example contains 55% of ZSM-5, and its silicon-aluminum ratio is 100 as determined by an X-ray fluorescence spectrometer.

[0076] Example 3

[0077] This example provides a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0078] An appropriate amount of kaolin microspheres C is calcined in a muffle furnace at 800 °C for 1 h to obtain activated kaolin microspheres C; silicon powder, sodium hydroxide, water and activated kaolin microspheres C are added to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:800 in sequence, and then Mn 6+ A mixed solution of a solution (potassium manganate solution) and potassium persulfate is stirred for 4 h (the stirring speed is 150 r / min) under a water bath condition of 20 °C to obtain a gel system; the Mn 6+ The addition amount of the solution is 5% of the molar amount of Al2O3 in the gel system, and the addition amount of potassium persulfate is 7% of the molar amount of Al2O3 in the gel system; then the gel system is transferred to a polytetrafluoroethylene reaction kettle and crystallized dynamically by rotation at 100 °C for 12 h (the rotation speed is 15 rpm), and then after filtration and washing, it is dried at 90 °C for 12 h, and then calcined at 500 °C for 4 h to obtain high-silica ZSM-5 molecular sieve microspheres ZKM.

[0079] It is determined by an X-ray diffractometer that the ZKM in this example contains 46% of ZSM-5, and its silicon-aluminum ratio is 97 as determined by an X-ray fluorescence spectrometer.

[0080] Example 4

[0081] This example provides a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0082] Take an appropriate amount of kaolin microspheres B and calcine them in a muffle furnace at 900 °C for 4 h to obtain activated kaolin microspheres B; add sodium silicate, water and activated kaolin microspheres B to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 30:1:20:1000 in sequence, and then add Ni 2+ solution (nickel chloride solution) and a mixed solution of Fenton's reagent, and stir for 4 h under a water bath condition of 50 °C (the stirring speed is 150 r / min) to obtain a gel system; the addition amount of the Ni 2+ solution is 5% of the molar amount of Al2O3 in the gel system, and the addition amount of the Fenton's reagent (calculated as hydrogen peroxide) is 7% of the molar amount of Al2O3 in the gel system; then transfer the gel system to a polytetrafluoroethylene reaction kettle, carry out rotary dynamic crystallization at 130 °C for 24 h (the rotation speed is 15 rpm), and then after filtration and washing, dry at 60 °C for 18 h, and then calcine at 700 °C for 6 h to obtain high-silica ZSM-5 molecular sieve microspheres ZKM.

[0083] It is determined by an X-ray diffractometer that the ZKM in this example contains 56% of ZSM-5, and its silicon-aluminum ratio is 40 as determined by an X-ray fluorescence spectrometer. Figure 1 This is the characteristic X-ray diffraction pattern of the high-silica ZSM-5 molecular sieve microspheres ZKM provided in this example. The average particle size of the high-silica ZSM-5 molecular sieve microspheres ZKM in this example is 52 μm, its crystal grain size is 1.7 μm, and the relative crystallinity is 65%.

[0084] Example 5

[0085] This example provides a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared through the following steps:

[0086] Take an appropriate amount of kaolin microspheres C and calcine them in a muffle furnace at 1000 °C for 5 h to obtain activated kaolin microspheres C; add silica sol, water and activated kaolin microspheres C to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 50:1:90:1200 in sequence, and then add Mn 7+ solution (potassium permanganate solution) and a mixed solution of sodium persulfate, and stir for 4 h under a water bath condition of 70 °C (the stirring speed is 150 r / min) to obtain a gel system; the Mn 7+The addition amount of the solution is 5% of the molar amount of Al2O3 in the gel system, and the addition amount of the sodium persulfate is 7% of the molar amount of Al2O3 in the gel system; then the gel system is transferred to a polytetrafluoroethylene reaction kettle, and undergoes rotary dynamic crystallization at 170 °C for 24 h (rotation speed is 15 rpm), and then after filtration and washing, it is dried at 80 °C for 12 h, and then calcined at 900 °C for 10 h to obtain high-silica ZSM-5 molecular sieve microspheres ZKM.

[0087] It is determined by an X-ray diffractometer that the ZKM in this example contains 49% of ZSM-5, and its silicon-aluminum ratio is 88 determined by an X-ray fluorescence spectrometer.

[0088] Example 6

[0089] This example provides a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0090] Take an appropriate amount of kaolin microspheres A and calcine them in a muffle furnace at 1000 °C for 5 h to obtain activated kaolin microspheres A; add tetraethyl orthosilicate, water and activated kaolin microspheres A into a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 50:1:100:1200 in sequence, and then add Fe 3+ solution (ferric chloride solution) and a mixed solution of potassium persulfate, and stir for 4 h (stirring speed is 150 r / min) under a water bath condition at 70 °C to obtain a gel system; the addition amount of the Fe 3+ solution is 5% of the molar amount of Al2O3 in the gel system, and the addition amount of the potassium persulfate is 7% of the molar amount of Al2O3 in the gel system; then the gel system is transferred to a polytetrafluoroethylene reaction kettle, and undergoes rotary dynamic crystallization at 200 °C for 48 h (rotation speed is 15 rpm), and then after filtration and washing, it is dried at 80 °C for 12 h, and then calcined at 1000 °C for 10 h to obtain high-silica ZSM-5 molecular sieve microspheres ZKM.

[0091] It is determined by an X-ray diffractometer that the ZKM in this example contains 38% of ZSM-5, and its silicon-aluminum ratio is 95 determined by an X-ray fluorescence spectrometer.

[0092] Example 7

[0093] This example provides a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0094] Take an appropriate amount of kaolin microspheres A and calcine them in a muffle furnace at 1000 °C for 2 h to obtain activated kaolin microspheres A; add silica sol, water and activated kaolin microspheres A to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:1200 in sequence, and then add Fe 3+ solution (iron chloride solution) and a mixed solution of Fenton's reagent, and stir for 4 h under a water bath condition of 70 °C (the stirring speed is 150 r / min) to obtain a gel system; the addition amount of the Fe 3+ solution is 5% of the molar amount of Al2O3 in the gel system, and the addition amount of the Fenton's reagent (calculated as hydrogen peroxide) is 7% of the molar amount of Al2O3 in the gel system; then transfer the gel system to a polytetrafluoroethylene reaction kettle, carry out rotary dynamic crystallization at 200 °C for 48 h (the rotation speed is 15 rpm), and then after filtration and washing, dry at 80 °C for 12 h, and then calcine at 1000 °C for 10 h to obtain high-silica ZSM-5 zeolite microspheres ZKM.

[0095] It is determined by an X-ray diffractometer that the ZKM in this example contains 40% of ZSM-5, and its silicon-aluminum ratio is 84 as determined by an X-ray fluorescence spectrometer.

[0096] Example 8

[0097] This example provides a high-silica ZSM-5 zeolite synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0098] Take an appropriate amount of kaolin microspheres B and calcine them in a muffle furnace at 800 °C for 4 h to obtain activated kaolin microspheres B; add water glass, water and activated kaolin microspheres B to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:900 in sequence, and then add Mn 6+ solution (potassium manganate solution) and a mixed solution of sodium persulfate, and stir for 4 h under a water bath condition of 30 °C (the stirring speed is 150 r / min) to obtain a gel system; the addition amount of the Mn 6+ solution is 5% of the molar amount of Al2O3 in the gel system, and the addition amount of the sodium persulfate is 7% of the molar amount of Al2O3 in the gel system; then transfer the gel system to a polytetrafluoroethylene reaction kettle, carry out rotary dynamic crystallization at 170 °C for 24 h (the rotation speed is 15 rpm), and then after filtration and washing, dry at 80 °C for 12 h, and then calcine at 800 °C for 10 h to obtain high-silica ZSM-5 zeolite microspheres ZKM.

[0099] It is determined by X-ray diffractometer that the ZKM in this example contains 54% ZSM-5, and its silica-alumina ratio is 98 determined by X-ray fluorescence spectrometer.

[0100] Example 9

[0101] This example provides a high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0102] Take an appropriate amount of kaolin microspheres C and calcine them in a muffle furnace at 800 °C for 4 h to obtain activated kaolin microspheres C; add sodium silicate, water and activated kaolin microspheres C into a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:70:1000 in sequence, and then add a mixed solution of Mn 7+ solution (potassium permanganate solution) and potassium persulfate, and stir for 4 h (stirring speed is 150 r / min) under the condition of a 50 °C water bath to obtain a gel system; the addition amount of the Mn 7+ solution is 5% of the molar amount of Al2O3 in the gel system, and the addition amount of potassium persulfate is 7% of the molar amount of Al2O3 in the gel system; then transfer the gel system to a polytetrafluoroethylene reaction kettle, perform rotary dynamic crystallization at 150 °C for 24 h (rotation speed is 15 rpm), and then after filtration and washing, dry at 80 °C for 12 h, and then calcine at 800 °C for 8 h to obtain high-silica ZSM-5 molecular sieve microspheres ZKM.

[0103] It is determined by X-ray diffractometer that the ZKM in this example contains 54% ZSM-5, and its silica-alumina ratio is 65 determined by X-ray fluorescence spectrometer.

[0104] Comparative Example 1

[0105] This comparative example provides a ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, and its preparation uses the same preparation conditions as in Example 2, except that sodium persulfate is not added during the synthesis process. The preparation process is as follows: Take an appropriate amount of kaolin microspheres B and calcine them in a muffle furnace at 800 °C for 1 h to obtain activated kaolin microspheres B; add tetraethyl orthosilicate, water and activated kaolin microspheres B into a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:800 in sequence, and then add Cu 2+ solution (copper chloride solution), mix evenly and stir for 4 h (stirring speed is 150 r / min) under the condition of a 20 °C water bath to obtain a gel system, and the Cu 2+The addition amount of the solution is 5% of the molar amount of Al2O3 in the gel system; then the gel system is transferred to a polytetrafluoroethylene reaction kettle and crystallized dynamically by rotation at 100 °C for 12 h (rotation speed is 15 rpm). After filtration and washing, it is dried at 80 °C for 12 h, and then calcined at 500 °C for 4 h to obtain ZSM-5 molecular sieve microspheres ZKM.

[0106] It is determined by an X-ray diffractometer that the ZKM in this comparative example contains 40% of ZSM-5, and its silicon-aluminum ratio is 25 as determined by an X-ray fluorescence spectrometer.

[0107] Comparative Example 2

[0108] This comparative example provides a ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, and its preparation uses the same preparation conditions as in Example 2, except that transition metal ions are not added during the synthesis process. The preparation process is as follows: Take an appropriate amount of kaolin microspheres B and calcine them in a muffle furnace at 800 °C for 1 h to obtain activated kaolin microspheres B; Add tetraethyl orthosilicate, water, and activated kaolin microspheres B into a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:800 in sequence, then add sodium persulfate, mix evenly and stir for 4 h under a water bath condition at 20 °C (stirring speed is 150 r / min) to obtain a gel system. The addition amount of the sodium persulfate is 7% of the molar amount of Al2O3 in the gel system; then the gel system is transferred to a polytetrafluoroethylene reaction kettle and crystallized dynamically by rotation at 100 °C for 12 h (rotation speed is 15 rpm). After filtration and washing, it is dried at 80 °C for 12 h, and then calcined at 500 °C for 4 h to obtain ZSM-5 molecular sieve microspheres ZKM.

[0109] It is determined by an X-ray diffractometer that the ZKM in this comparative example contains 45% of ZSM-5, and its silicon-aluminum ratio is 30 as determined by an X-ray fluorescence spectrometer.

[0110] Comparative Example 3

[0111] This comparative example provides a ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres. Its preparation uses the same preparation conditions as in Example 2, except that no transition metal ions are added during the synthesis process, and an additional amount of sodium persulfate is added. The preparation process is as follows: Take an appropriate amount of kaolin microspheres B and calcine them in a muffle furnace at 800 °C for 1 h to obtain activated kaolin microspheres B; Add tetraethyl orthosilicate, water, and activated kaolin microspheres B to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:800 in sequence, then add sodium persulfate, mix evenly, and stir for 4 h under a water bath condition of 20 °C (the stirring speed is 150 r / min) to obtain a gel system. The added amount of sodium persulfate is 20% of the molar amount of Al2O3 in the gel system; Then transfer the gel system to a polytetrafluoroethylene reaction kettle, carry out rotary dynamic crystallization at 100 °C for 12 h (the rotation speed is 15 rpm), then after filtration and washing, dry at 80 °C for 12 h, and then calcine at 500 °C for 4 h to obtain ZSM-5 molecular sieve microspheres ZKM.

[0112] It was determined by an X-ray diffractometer that the ZKM in this comparative example contains 45% ZSM-5, and its silicon-aluminum ratio was determined by an X-ray fluorescence spectrometer to be 45.

[0113] Comparative Example 4

[0114] This comparative example provides a ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres. Its preparation uses the same preparation conditions as in Example 2, except that the Cu 2+ solution is replaced with a Co 2+ solution (cobalt chloride solution). The preparation process is as follows: Take an appropriate amount of kaolin microspheres B and calcine them in a muffle furnace at 800 °C for 1 h to obtain activated kaolin microspheres B; Add tetraethyl orthosilicate, water, and activated kaolin microspheres B to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:800 in sequence, then add a mixed solution of Co 2+ solution and sodium persulfate, and stir for 4 h under a water bath condition of 20 °C (the stirring speed is 150 r / min) to obtain a gel system; The added amount of Co 2+ solution is 5% of the molar amount of Al2O3 in the gel system, and the added amount of sodium persulfate is 7% of the molar amount of Al2O3 in the gel system; Then transfer the gel system to a polytetrafluoroethylene reaction kettle, carry out rotary dynamic crystallization at 100 °C for 12 h (the rotation speed is 15 rpm), then after filtration and washing, dry at 80 °C for 12 h, and then calcine at 500 °C for 4 h to obtain ZSM-5 molecular sieve microspheres ZKM.

[0115] It was determined by X-ray diffractometer that the ZKM of this comparative example contained 40% ZSM-5, and its silicon-aluminum ratio was 25 as determined by X-ray fluorescence spectrometer.

[0116] As can be seen from the above examples and comparative examples, the SAR of the molecular sieve product obtained in Example 2 was 100; compared with Example 2, no Na2S2O8 was introduced during the synthesis of Comparative Example 1, and the SAR of the obtained molecular sieve product was 25; compared with Example 2, no transition metal ions were introduced during the synthesis of Comparative Example 2, and the SAR of the obtained molecular sieve product was 30; compared with Example 2, no transition metal ions were introduced during the synthesis of Comparative Example 3, but more sodium persulfate was added, and the SAR of the obtained molecular sieve product was 45; compared with Example 2, Co 2+ was used as the transition metal ion during the synthesis of Comparative Example 4, and the SAR of the obtained molecular sieve product was 25. It can be seen that Co 2+ did not promote the large generation of hydroxyl radicals, so the silicon-aluminum ratio of the molecular sieve was not increased.

[0117] In summary, the present invention provides a method for in-situ crystallization synthesis of high-silica ZSM-5 molecular sieve from kaolin microspheres. This method uses kaolin microspheres, silicon source, transition metal ions, hydroxyl radical initiator and water as raw materials to in-situ crystallize and synthesize high-silica ZSM-5 molecular sieve. In the conventional method, the silicon-aluminum ratio of the ZSM-5 molecular sieve prepared using seed crystals is generally low. Usually, the silicon-aluminum ratio of the ZSM-5 molecular sieve prepared using seed crystals does not exceed 30. However, the present invention uses transition metal ions to promote the large generation of hydroxyl radicals, thereby accelerating the formation of Si-O-Si bonds and promoting the dissolution of active silicon in kaolin microspheres, increasing the silicon-aluminum ratio in the system, and obtaining a high-silica ZSM-5 molecular sieve framework. Therefore, the in-situ crystallization synthesis of high-silica ZSM-5 molecular sieve from kaolin microspheres is realized with the assistance of transition metal ions and hydroxyl radicals.

Claims

1. A preparation method of high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which comprises the following steps: (1) Mix kaolin, a binder, seeds of ZSM-5 molecular sieve and water to obtain a slurry; Shape the slurry to obtain kaolin microspheres, and then calcine the kaolin microspheres to obtain activated kaolin microspheres; (2) Mix at least the activated kaolin microspheres, silicon source, transition metal ions, and hydroxyl radical initiator to obtain a gel system; the transition metal ions include Fe 3+ , Cu 2+ , Mn 6+ , Mn 7+ , and Ni 2+ or a combination of one or more of them, and the hydroxyl radical initiator includes one or more of sodium persulfate, potassium persulfate, and Fenton's reagent; after the gel system is crystallized, it is then dried and calcined at least to obtain the high-silica ZSM-5 molecular sieve.

2. The preparation method according to claim 1, wherein In step (1), the kaolin includes soft kaolin.

3. The preparation method according to claim 1, wherein In step (1), the particle size of the kaolin is 3-10 μm.

4. The preparation method according to claim 1, wherein, In step (1), based on the total mass of the kaolin being 100%, the alumina content therein is 40%-45%, the silica content is 52.8%-58%, the iron oxide content is below 1.7%, and the sum of the sodium oxide and potassium oxide contents is below 0.5%.

5. The preparation method according to claim 1, wherein, In step (1), the mixing mass ratio of the binder to the kaolin is 0.16-0.

33.

6. The preparation method according to claim 1, wherein, In step (1), the binder includes one or a combination of several of water glass, sodium silicate and silica sol.

7. The preparation method according to claim 1, wherein, In step (1), the mixing mass ratio of the seeds of ZSM-5 molecular sieve to the kaolin is (5-20):

100.

8. The preparation method according to claim 1, wherein, In step (1), the seeds of ZSM-5 molecular sieve are solid seeds of ZSM-5 molecular sieve, including Na-ZSM-5 molecular sieve and / or H-ZSM-5 molecular sieve; the crystal grain size of the seeds of ZSM-5 molecular sieve is 0.5-1.5 μm, the relative crystallinity is 95%-98%, and the silica-alumina ratio is 30-50.

9. The preparation method according to claim 1, wherein, In step (1), the solid content of the slurry is 25-65%.

10. The preparation method according to claim 1, wherein, In step (1), the particle size of the kaolin microspheres obtained by shaping is 20-110 μm.

11. According to the preparation method described in claim 10, wherein, In step (1), the shaping includes spray drying.

12. The preparation method according to claim 1, wherein In step (1), the calcination temperature of the kaolin microspheres is 800-1000 °C, and the calcination time is 1-5 h.

13. The preparation method according to claim 1, wherein, In step (2), also included in the mixing with the activated kaolin microspheres, a silicon source, transition metal ions and a hydroxyl radical initiator is an alkali source and / or water to obtain the gel system.

14. The preparation method according to claim 1 or 13, wherein, In step (2), the pH value of the gel system is 10-14.

15. The preparation method according to claim 1, wherein, In step (2), the gel system is prepared by the following method: mix the activated kaolin microspheres, a silicon source, an alkali source that can be optionally added or not added, and water that can be optionally added or not added to obtain a first mixture; mix the transition metal ions and the hydroxyl radical initiator to obtain a first mixed solution; mix the first mixture with the first mixed solution to obtain the gel system.

16. The preparation method according to claim 15, wherein, In step (2), the molar ratio of Na2O:Al2O3:SiO2:H2O in the first mixture is (10-50):1:(20-100):(800-1200).

17. The preparation method according to claim 16, wherein, In step (2), the molar ratio of Na2O:Al2O3:SiO2:H2O in the first mixture is (10-50):1:(70-100):(800-1200).

18. The preparation method according to claim 17, wherein, In step (2), the molar ratio of Na2O:Al2O3:SiO2:H2O in the first mixture is (10 - 50):1:(90 - 100):(800 - 1200).

19. The preparation method according to claim 1, wherein, In step (2), the silicon source includes one or a combination of several of water glass, tetraethyl orthosilicate, silicon powder, and silica sol.

20. The preparation method according to claim 1, wherein In step (2), the addition amount of the transition metal ions is 1% - 5% of the molar amount of Al2O3 in the gel system.

21. The preparation method according to claim 1, wherein, In step (2), the addition amount of the hydroxyl radical initiator is 1% - 7% of the molar amount of Al2O3 in the gel system.

22. The preparation method according to claim 1, wherein, In step (2), the temperature for mixing the activated kaolin microspheres, silicon source, transition metal ions, and hydroxyl radical initiator is 20 - 70°C.

23. The preparation method according to claim 22, wherein, In step (2), the mixing of the activated kaolin microspheres, silicon source, transition metal ions, and hydroxyl radical initiator is carried out under stirring conditions, and the stirring time is 2 - 5 h.

24. The preparation method according to claim 1, wherein, In step (2), the crystallization temperature is 100 - 200°C, and the time is 12 - 48 h.

25. The preparation method according to claim 24, wherein In step (2), the crystallization temperature is 120 - 180°C, and the time is 12 - 36 h.

26. The preparation method according to claim 1, wherein, In step (2), the calcination temperature is 500 - 1000°C, and the time is 4 - 10 h.

27. A high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the preparation method of the high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres according to any one of claims 1 - 26.

28. The high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres according to claim 27, wherein, The silica-alumina ratio of the high-silica ZSM-5 molecular sieve is 40 - 100.

29. The high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres according to claim 28, wherein, The silica-alumina ratio of the high-silica ZSM-5 molecular sieve is 60 - 100.

30. The high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres according to claim 29, wherein, The silica-alumina ratio of the high-silica ZSM-5 molecular sieve is 80 - 100.

31. The high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres according to claim 27, wherein, The high-silica ZSM-5 molecular sieve is a high-silica ZSM-5 molecular sieve microsphere. Based on the total mass of the high-silica ZSM-5 molecular sieve microsphere being 100%, the content of the high-silica ZSM-5 molecular sieve is 36 - 56%.

32. The high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres according to claim 31, wherein, The particle size of the high-silica ZSM-5 molecular sieve microsphere is 15 - 100 μm.

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