A small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres and a preparation method thereof

Abstract

The present invention provides a small-crystallite 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, seed crystals and water, shaping to obtain kaolin microspheres, and then calcining to obtain activated kaolin microspheres; at least mixing the activated kaolin microspheres, a silicon source treated with a weak acid, transition metal ions and a hydroxyl radical initiator, carrying out crystallization, and then drying and calcining to obtain the small-crystallite high-silica ZSM-5 molecular sieve. The small-crystallite 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 a silicon source treated with a weak acid, transition metal ions and a hydroxyl radical initiator, in-situ crystallization is carried out to obtain a small-crystallite high-silica ZSM-5 molecular sieve without using an organic template agent.

Description

Technical Field

[0001] The present invention relates to a small-crystallite 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] The crystal grain size of ZSM-5 molecular sieve has a direct relationship with the performance of the catalyst prepared therefrom. For example, small-crystallite ZSM-5 molecular sieve has better selectivity and service life. However, small-crystallite ZSM-5 molecular sieve has relatively high activity and thus is prone to agglomeration. It can be envisioned that in-situ crystallization and growth of small-crystallite molecular sieve on a mineral matrix can solve the problem of agglomeration. Among numerous mineral matrices, kaolin has become an ideal in-situ crystallization matrix due to its low price, rich resources, and abundant silicon and aluminum species. In addition, high-silica ZSM-5 molecular sieve also has many unique advantages. For example, it has good isomerization performance. When used in a fluid catalytic cracking (FCC) catalyst, it can not only increase the yield of light oil but also increase the octane number of gasoline. Therefore, in-situ synthesis of small-crystallite high-silica ZSM-5 molecular sieve on a kaolin matrix has important theoretical significance and application value.

[0003] CN113336240A discloses a method for preparing single / double-crystalline ZSM-5 zeolite by controlling kaolin minerals. This method uses natural minerals kaolin and quartz as raw materials, and realizes the morphology control of single / double-crystalline ZSM-5 zeolite by adjusting the addition amount of NH4F. The preparation method is simple and low-cost. However, the addition of fluoride makes this method have certain pollution.

[0004] CN108190912B discloses a method for synthesizing a solid waste bulk ZSM-5 zeolite molecular sieve. This method directly uses untreated solid waste silica fume as a silicon source and kaolin as an aluminum source to synthesize bulk ZSM-5 molecular sieve; no template agent needs to be added during the synthesis process, avoiding high energy consumption and environmental pollution during calcination. However, the operation of this method is relatively complex and cumbersome.

[0005] CN110526259A discloses a method for in-situ synthesizing ZSM-5 on kaolin microspheres. By adjusting the in-situ crystallization process, this method directly obtains ZSM-5 molecular sieve with high crystallinity, large pore volume, and large specific surface area. This method avoids adding special functional components to kaolin microspheres conventionally, improves the pore structure and increases the content of ZSM-5 molecular sieve, and the use of kaolin reduces the production cost of the in-situ crystallization product.

[0006] CN103848439A discloses a method for synthesizing ZSM-5 type molecular sieve. This method uses natural kaolin and diatomite as silicon source and aluminum source, mixes them in a certain proportion, and carries out crystallization under hydrothermal conditions to obtain the product ZSM-5 type molecular sieve. This method can not only greatly reduce the production cost of the molecular sieve, but also significantly improve the greenness of the molecular sieve material production process. The product obtained by this method has a relatively high crystallinity, but its silicon-aluminum ratio is relatively low and the crystal grain size is relatively large.

[0007] CN103253684A discloses a method for directly synthesizing small-crystalline ZSM-5 molecular sieve by in-situ crystallization. This method includes: pretreating high-temperature calcined kaolin microspheres containing five-membered ring characteristic structural units with water glass, then adding acid to make a reaction mixture, and carrying out hydrothermal crystallization to obtain an in-situ product and a non-in-situ product containing ZSM-5 molecular sieve. The relative crystallinity of the in-situ crystallized ZSM-5 molecular sieve product prepared by this method can be adjusted according to needs within 65%, the crystal grain size is 0.1 - 3 μm, and the abrasion resistance is good; the crystallinity of the non-in-situ ZSM-5 molecular sieve can reach more than 90%, and the crystal grain size is 0.1 - 3 μm.

[0008] CN110496595A discloses a preparation method of high-silicon ZSM-5 molecular sieve with controllable crystal grain size for VOCs degradation in quasi-solid phase. This method not only improves the single-pot yield of the product, reduces the production cost, but also reduces the discharge of mother liquor wastewater, realizing a green synthesis route for the molecular sieve.

[0009] Zhang Wei et al. (Guangzhou Chemical Industry, 2012, 40:20 - 23) reported that on the basis of the synthesis of conventional ZSM-5 molecular sieve, small-crystalline ZSM-5 molecular sieve was synthesized by methods such as adding template agent, alkali metal salt, and controlling the crystallization time, and the catalytic advantages of the small-crystalline molecular sieve were exerted.

[0010] CN101348263B discloses a microsphere-type high-silicon ZSM-5 molecular sieve and its synthesis method. 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, formulates a slurry, and obtains silicon-aluminum microspheres with a diameter of 30 - 200 microns by spray drying and forming. Then, they are placed in organic amine vapor, and after hydrothermal treatment and calcination, the microsphere-type high-silicon ZSM-5 molecular sieve is prepared. This method does not require secondary forming and has higher activity.

[0011] CN107282087B discloses a high-silica ZSM-5 molecular sieve, a preparation method thereof and an application thereof. The method includes: sequentially and uniformly mixing a liquid alkaline silicon source, an aluminum source, a ZSM-5 molecular sieve seed crystal, a template agent, an alkali, urea and water, and then performing aging and hydrothermal synthesis crystallization. Urea is added in the raw material uniform mixing stage. 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.

[0012] CN113044853A discloses a method for synthesizing a nano high-silica-aluminum ratio ZSM-5 molecular sieve. The method is to first perform pseudo-solid phase activation on a low-silica-aluminum ratio mineral, and then mix the activated mineral with an alkali, water and a small amount of template agent, and crystallize under hydrothermal conditions to obtain a nano high-silica ZSM-5 molecular sieve. This method adjusts the silica-aluminum ratio of the product molecular sieve by adjusting the proportion of natural mineral in the raw materials, and synthesizes nano ZSM-5 molecular sieves with a silica-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, which is not conducive to its large-scale application.

[0013] In the prior art, ZSM-5 molecular sieve can be prepared by in-situ crystallization of kaolin, but the obtained ZSM-5 molecular sieve has a relatively low silica-aluminum ratio. The synthesis of high-silica ZSM-5 molecular sieve requires the use of organic template agents such as tetrapropylammonium bromide, etc., and the problems of high cost and large pollution are relatively serious. The small crystal ZSM-5 molecular sieve obtained by the above research is prone to agglomeration, which affects the exertion of its catalytic performance. Therefore, developing a method for preparing small crystal high-silica ZSM-5 molecular sieve by in-situ crystallization of kaolin without using organic template agents has become one of the problems to be solved urgently in this field. Summary of the Invention

[0014] To solve the above technical problems, the purpose of the present invention is to provide a small crystal high-silica 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 small crystal high-silica ZSM-5 molecular sieve without using an organic template agent.

[0015] To achieve the above purpose, the first aspect of the present invention provides a preparation method of a small crystal high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which includes the following steps:

[0016] (1) Mix kaolin, a binder, a seed crystal of ZSM-5 molecular sieve and water to obtain a slurry; form the slurry into kaolin microspheres, and then calcine the kaolin microspheres to obtain activated kaolin microspheres;

[0017] (2) Mix at least the activated kaolin microspheres, the weak acid-treated silicon source, the transition metal ions, and the hydroxyl radical initiator to obtain a gel system; after subjecting the gel system to crystallization, then subject it to at least drying and calcination to obtain the small-crystallite high-silica ZSM-5 molecular sieve.

[0018] In the above preparation method, preferably, in step (1), the kaolin includes soft kaolin and the like.

[0019] In the above preparation method, preferably, in step (1), the particle size of the kaolin is 3 - 10 μm.

[0020] In the above preparation method, preferably, 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 1.7% or less, and the sum of the sodium oxide and potassium oxide contents is 0.5% or less.

[0021] In the above preparation method, preferably, in step (1), the mixing mass ratio of the binder to the kaolin is 0.16 - 0.33.

[0022] In the above preparation method, preferably, in step (1), the binder includes one or a combination of several of water glass, sodium silicate, silica sol, etc. More preferably, the binder is water glass.

[0023] In the above preparation method, preferably, in step (1), the mixing mass ratio of the ZSM-5 molecular sieve seed crystals to the kaolin is (5 - 20) : 100.

[0024] In the above preparation method, preferably, in step (1), the ZSM-5 molecular sieve seed crystals are solid seed crystals of ZSM-5 molecular sieve, including Na-ZSM-5 molecular sieve and / or H-ZSM-5 molecular sieve; the crystal grain size of the ZSM-5 molecular sieve seed crystals is 0.1 - 1.0 μm, the relative crystallinity is 95% - 98%, and the silica-alumina ratio is 30 - 50. The seed crystals are pure-phase ZSM-5 without other impurity crystals.

[0025] In the above preparation method, preferably, in step (1), the solid content of the slurry is 25 - 65%.

[0026] In the above preparation method, preferably, in step (1), the particle size of the kaolin microspheres obtained after forming is 20 - 110 μm.

[0027] In the above preparation method, preferably, in step (1), the forming includes spray drying. The spray drying 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.

[0028] 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.

[0029] In the above preparation method, preferably, in step (2), the substances mixed with the activated kaolin microspheres, the silicon source treated with weak acid, 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.

[0030] In the above preparation method, preferably, in step (2), the pH value of the gel system is 10 - 14.

[0031] In the above preparation method, preferably, in step (2), the gel system is prepared by the following method: mixing the activated kaolin microspheres, the silicon source treated with weak acid, the alkali source that may or may not be added, and the water that may or may not be added to obtain a first mixture; mixing the transition metal ions and the hydroxyl radical initiator to obtain a first mixed solution; mixing the first mixture with the first mixed solution to obtain the gel system.

[0032] 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). Particularly preferably, the molar ratio of Na2O:Al2O3:SiO2:H2O in the first mixture is (10 - 50):1:(90 - 100):(800 - 1200).

[0033] In the above preparation method, those skilled in the art should understand that if the above sodium hydroxide and / or ammonium hydroxide are used as the base source in the form of a solution, and if the molar ratios of the components in the first mixture and the pH value of the gel system meet the above conditions, 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 as the base source in the form of a solution, in order to fully mix the activated kaolin microspheres and the silicon source treated with a weak acid and to make the molar ratios of the components in the first mixture meet the above conditions, water needs to be added during the preparation of the first mixture.

[0034] 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.

[0035] In the above preparation method, preferably, in step (2), the weak acid includes one or a combination of several of tartaric acid, 2-hydroxybutanedioic acid, citric acid, etc.

[0036] In the above preparation method, preferably, in step (2), the silicon source treated with a weak acid is obtained by the following method: mixing the silicon source and the weak acid evenly at a mass ratio of 1:(1.5 - 3), and then standing for 2 - 4 h to obtain the silicon source treated with a weak acid. More preferably, the temperature for mixing and standing is 35 - 70 °C. Both the mixing and standing processes can be carried out in a water bath.

[0037] In the above preparation method, preferably, in step (2), the addition amount of the transition metal ion 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.

[0038] 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.

[0039] In the above preparation method, preferably, in step (2), the transition metal ion includes Fe 3+ , Cu 2+ , Mn 6 + , Mn 7+ and Ni 2+One or a combination of several of the above. 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 one or a combination of several of ferric chloride, copper chloride, nickel chloride, potassium manganate, potassium permanganate, etc.

[0040] In the above preparation method, preferably, in step (2), the hydroxyl radical initiator includes one or a combination of several of sodium persulfate, potassium persulfate, Fenton's reagent, etc.

[0041] In the above preparation method, preferably, in step (2), the temperature for mixing the activated kaolin microspheres, the silicon source treated with a weak acid, the transition metal ions and the hydroxyl radical initiator is 20 - 70 °C. More specifically, the temperature for mixing the first mixture with 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.

[0042] 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 - 24 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.

[0043] In the above preparation method, in step (2), before drying and calcining 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 conventionally adjusted by those skilled in the art.

[0044] In the above preparation method, preferably, in step (2), the drying temperature is 60 - 90 °C and the time is 12 - 18 h.

[0045] In the above preparation method, preferably, in step (2), the calcination temperature is 500 - 1000 °C and the time is 4 - 10 h.

[0046] The second aspect of the present invention provides a small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the preparation method of the small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres as described above.

[0047] According to the specific embodiments of the present invention, preferably, the silica-alumina ratio of the small-crystallite 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 small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is 60-100. Further preferably, the silica-alumina ratio of the small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is 80-100.

[0048] According to the specific embodiments of the present invention, preferably, the crystal size of the small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is 0.4-1.0 μm.

[0049] According to the specific embodiments of the present invention, preferably, the small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres has a mesoporous structure, and the mesopore volume of the small-crystallite high-silica ZSM-5 molecular sieve is 0.1-0.17 cm 3 / g.

[0050] According to the specific embodiments of the present invention, preferably, the relative crystallinity of the small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is 40%-60%.

[0051] According to the specific embodiments of the present invention, preferably, the small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is a small-crystallite high-silica ZSM-5 molecular sieve microsphere. Based on the total mass of the small-crystallite high-silica ZSM-5 molecular sieve microsphere being 100%, the content of the small-crystallite high-silica ZSM-5 molecular sieve therein is 38-56%.

[0052] According to the specific embodiments of the present invention, preferably, the small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres is a small-crystallite high-silica ZSM-5 molecular sieve microsphere, and the particle size of the small-crystallite high-silica ZSM-5 molecular sieve microsphere is 15-100 μm.

[0053] The present invention provides a small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres and a preparation method thereof. The preparation method of the present invention pre-introduces solid seeds of ZSM-5 into kaolin microspheres, realizing the in-situ growth of ZSM-5 molecular sieve on kaolin microspheres; and uses 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, and the synthesis process does not use an organic template agent at all; at the same time, after the present invention treats the silicon source with a weak acid, it reacts with free Na +Ions combine with each other and play a guiding role in crystallization to form small crystals. At the same time, they enter the zeolite unit cell and react to release CO2 during the subsequent calcination stage, resulting in a mesoporous structure. Finally, small-crystalline high-silica (silica-alumina ratio much greater than 30) ZSM-5 zeolite is prepared.

[0054] In the conventional preparation method of ZSM-5 zeolite, the silica-alumina ratio of ZSM-5 zeolite prepared using seed crystals is generally low. Usually, the silica-alumina ratio of ZSM-5 zeolite prepared using seed crystals does not exceed 30, and the crystal grain size is generally greater than 1 μm. This is because the dissolution rate of the active silica in kaolin microspheres in the synthesis system is slow, so it is not easy to form high-silica zeolite. In this invention, natural kaolin is used as the raw material, and under the synergistic action of a silicon source treated with weak acid, transition metal ions, and a hydroxyl radical initiator, without using an organic template agent, in-situ crystallization of kaolin microspheres to synthesize small-crystalline high-silica ZSM-5 zeolite is achieved. Therefore, the preparation method of this invention not only obtains small-crystalline high-silica ZSM-5 zeolite, but also greatly reduces the synthesis cost and pollution, has broad application prospects, and is of great significance for promoting the development of material synthesis and catalyst performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 Characteristic X-ray diffraction pattern of the small-crystalline high-silica ZSM-5 zeolite provided in Example 4.

[0056] Figure 2 Scanning electron micrograph of the small-crystalline high-silica ZSM-5 zeolite provided in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0057] 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.

[0058] According to the specific implementation manner of the present invention, preferably, the method for in-situ crystallization of kaolin microspheres to synthesize small-crystalline high-silica ZSM-5 zeolite of the present invention includes the following steps:

[0059] (1) Mix kaolin, binder, solid seed crystals of ZSM-5 zeolite, and water to obtain a slurry;

[0060] 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 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%; the mixing mass ratio of the binder to the kaolin is 0.16 - 0.33; the binder includes one or a combination of several of water glass, sodium silicate, and silica sol; the mixing mass ratio of the seed crystals of the ZSM-5 molecular sieve to the kaolin is (5 - 20):100; the solid seed crystals of the 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 the ZSM-5 molecular sieve is 0.1 - 1.0 μm, the relative crystallinity is 95% - 98%, and the silica-alumina ratio is 30 - 50; the solid seed crystals of the ZSM-5 molecular sieve are pure-phase ZSM-5 without other miscellaneous crystals; the solid content of the slurry is 25 - 65%;

[0061] The slurry is spray-dried and formed to obtain 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;

[0062] (2) Mix the activated kaolin microspheres, the silicon source treated with weak acid, the alkali source that can be optionally added or not added, and the water that can be optionally added or not added to obtain a first mixture; mix the transition metal ions and the hydroxyl radical initiator evenly (which can be carried out at room temperature) to obtain a first mixed solution; mix the first mixture and the first mixed solution at 20 - 70 °C and stir for 2 - 5 h (the stirring speed is more preferably 150 - 350 r / min) to obtain a gel system;

[0063] Among them, 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); 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 weak acid includes one or a combination of several of tartaric acid, 2-hydroxybutanedioic acid, and citric acid; the silicon source treated with the weak acid is obtained by the following method: mixing the silicon source and the weak acid evenly at a mass ratio of 1:(1.5 - 3), and then standing for 2 - 4 h to obtain the silicon source treated with the weak acid; more preferably, the temperature for mixing and standing is 35 - 70°C; the base 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+ or a combination of several of them; the hydroxyl radical initiator includes one or a combination of several of sodium persulfate, potassium persulfate, and Fenton's reagent;

[0064] Transfer the gel system to a polytetrafluoroethylene reaction kettle, crystallize dynamically at 100 - 200°C for 12 - 48 h (more preferably crystallize dynamically at 120 - 180°C for 12 - 24 h), then filter and wash, dry at 60 - 90°C for 12 - 18 h, and then calcine at 500 - 1000°C for 4 - 10 h to obtain the small-crystallite high-silica ZSM-5 molecular sieve.

[0065] The small-crystallite high-silica ZSM-5 molecular sieve is a small-crystallite high-silica ZSM-5 molecular sieve microsphere, and the particle size of the small-crystallite high-silica ZSM-5 molecular sieve microsphere is 15 - 100 μm; based on the total mass of the small-crystallite high-silica ZSM-5 molecular sieve microsphere being 100%, the content of the small-crystallite high-silica ZSM-5 molecular sieve therein is 35 - 60%; the silicon-aluminum ratio of the small-crystallite high-silica ZSM-5 molecular sieve is 40 - 100, preferably 60 - 100, more preferably 80 - 100; the crystal size of the small-crystallite high-silica ZSM-5 molecular sieve is 0.4 - 1.0 μm; the relative crystallinity of the small-crystallite high-silica ZSM-5 molecular sieve is 40 - 60%; the small-crystallite high-silica ZSM-5 molecular sieve has a mesoporous structure, and its mesoporous volume is 0.1 - 0.17 cm 3 / g.

[0066] In the following examples, the experimental methods are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

[0067] Analysis method: For phase detection and confirmation, a Shimadzu XRD-7000 X-ray powder diffractometer was 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 of 5 - 40°, scanning speed of 8° / min. For X-ray fluorescence spectrometer (XRF) analysis, a Shimadzu XRF-1800 was used. Before testing, 200 mg of the powder was pressed into a tablet. For scanning electron microscope (SEM) analysis, a Hitachi S-4700 field emission scanning electron microscope was used. The test acceleration voltage was 20 kV. After the sample was ground finely, it was fixed on the test bench and photographed after sputtering with gold.

[0068] Preparation of kaolin microspheres A:

[0069] 3000 g (dry basis) of kaolin, 500 g of water glass, 150 g of Na-ZSM-5 seeds with a crystal grain size of 0.1 μm, relative crystallinity of 97%, and silicon-aluminum ratio of 40 were mixed with water to form a slurry with a solid content of 25%, and then spray-molded to obtain kaolin microspheres A with an average particle size of 20 μm.

[0070] Preparation of kaolin microspheres B:

[0071] 3000 g (dry basis) of kaolin, 1000 g of water glass, 300 g of H-ZSM-5 seeds with a crystal grain size of 0.4 μm, relative crystallinity of 97%, and silicon-aluminum ratio of 40 were mixed with water to form a slurry with a solid content of 45%, and then spray-molded to obtain kaolin microspheres B with an average particle size of 60 μm.

[0072] Preparation of kaolin microspheres C:

[0073] 3000 g (dry basis) of kaolin, 800 g of water glass, 600 g of H-ZSM-5 seeds with a crystal grain size of 1.0 μm, relative crystallinity of 97%, and silicon-aluminum ratio of 40 were mixed with water to form a slurry with a solid content of 65%, and then spray-molded to obtain kaolin microspheres C with a particle size of 110 μm.

[0074] Among them, in the preparation of kaolin microspheres A, kaolin microspheres B, and kaolin microspheres 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.

[0075] Example 1

[0076] This example provides a small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared through the following steps:

[0077] 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 treated with tartaric acid, water, and the activated microspheres B into a beaker in sequence according to the molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:800, mix them evenly, and then add an Fe 3+ solution (ferric chloride solution) and a mixed solution of 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. Among them, the tetraethyl orthosilicate treated with tartaric acid is obtained through the following method: Take an appropriate amount of tetraethyl orthosilicate and add it into a beaker, place it in a water bath at 40°C, add tartaric acid, mix them evenly and then let it stand for 3 h. Among them, the mass ratio of tetraethyl orthosilicate to tartaric acid is 1:1.5 to obtain the tetraethyl orthosilicate treated with tartaric acid; 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 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 it at 90°C for 12 h, and then calcine it at 500°C for 4 h to obtain small-crystallite high-silica ZSM-5 molecular sieve microspheres ZKM.

[0078] It is determined by an X-ray diffractometer that the ZKM in this example contains 50% ZSM-5 molecular sieve. Its silicon-aluminum ratio is 94 measured by an X-ray fluorescence spectrometer, and its crystal grain size is 0.6 μm measured by SEM.

[0079] Example 2

[0080] This embodiment provides a small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared through the following steps:

[0081] Take an appropriate amount of kaolin microspheres A and calcine them in a muffle furnace at 800 °C for 1 h to obtain activated kaolin microspheres A; add the water glass treated with citric acid, water, and activated kaolin microspheres A to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:800 in sequence and mix evenly, then add a Cu 2+ solution (copper 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 of 20 °C to obtain a gel system. Among them, the water glass treated with citric acid is obtained by the following method: take an appropriate amount of water glass and add it to a beaker, place it in a water bath at 50 °C, add citric acid, mix evenly and then stand for 3 h. The mass ratio of water glass to citric acid is 1:2 to obtain the water glass treated with citric acid; the addition amount of the Cu 2+ 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, carry out rotary dynamic crystallization at 100 °C for 12 h (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 small-crystallite high-silica ZSM-5 molecular sieve microspheres ZKM.

[0082] It is determined by an X-ray diffractometer that ZKM in this embodiment contains 38% of ZSM-5 molecular sieve. Its silicon-aluminum ratio is 90 measured by an X-ray fluorescence spectrometer, and its crystal grain size is 0.8 μm measured by SEM.

[0083] Example 3

[0084] This embodiment provides a small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared through the following steps:

[0085] Take an appropriate amount of kaolin microspheres C and calcine them in a muffle furnace at 800 °C for 1 h to obtain activated kaolin microspheres C; add the silicon powder treated with 2-hydroxybutanedioic acid, sodium hydroxide, water, and activated kaolin microspheres C to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:800 in sequence and mix evenly, then add Mn 6+A mixed solution of a solution (potassium manganate solution) and Fenton's reagent was stirred at 20 °C in a water bath for 4 h (stirring speed: 150 r / min) to obtain a gel system. Among them, the silica powder treated with 2-hydroxybutanedioic acid was obtained by the following method: An appropriate amount of silica powder was added to a beaker, placed in a water bath at 35 °C, 2-hydroxybutanedioic acid was added, and after mixing evenly, it was left standing for 3 h. The mass ratio of silica powder to 2-hydroxybutanedioic acid was 1:1.5 to obtain the silica powder treated with 2-hydroxybutanedioic acid; the Mn 6+ The addition amount of the solution was 5% of the molar amount of Al2O3 in the gel system, and the addition amount of Fenton's reagent (calculated as hydrogen peroxide) was 7% of the molar amount of Al2O3 in the gel system; then the gel system was transferred to a polytetrafluoroethylene reaction kettle and crystallized dynamically at 100 °C for 12 h (rotation speed: 15 rpm), and then after filtration and washing, it was dried at 60 °C for 18 h, and then calcined at 500 °C for 4 h to obtain small-crystalline high-silica ZSM-5 molecular sieve microspheres ZKM.

[0086] It was determined by an X-ray diffractometer that the ZKM in this example contained 44% ZSM-5 molecular sieve. The silicon-aluminum ratio was measured by an X-ray fluorescence spectrometer to be 90, and the crystal grain size was measured by SEM to be 0.9 μm.

[0087] Example 4

[0088] This example provides a small-crystalline high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0089] An appropriate amount of kaolin microspheres B was calcined in a muffle furnace at 900 °C for 4 h to obtain activated kaolin microspheres B; the water glass treated with tartaric acid, water and activated kaolin microspheres B were added to a beaker in sequence according to the molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O)=30:1:100:1000 and mixed evenly, and then Mn 7+ A mixed solution of a solution (potassium permanganate solution) and potassium persulfate was stirred at 50 °C in a water bath for 4 h (stirring speed: 150 r / min) to obtain a gel system. Among them, the water glass treated with tartaric acid was obtained by the following method: An appropriate amount of water glass was added to a beaker, placed in a water bath at 50 °C, tartaric acid was added, and after mixing evenly, it was left standing for 3 h. The mass ratio of water glass to tartaric acid was 1:1.5 to obtain the water glass treated with tartaric acid; 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 potassium persulfate is 7% of the molar amount of Al2O3 in the gel system; then the gel system is transferred to a polytetrafluoroethylene reactor and crystallized dynamically at 130 °C for 24 h (rotation speed is 15 rpm). After filtration and washing, it is dried at 80 °C for 12 h, and then calcined at 700 °C for 6 h to obtain small-crystallite high-silica ZSM-5 molecular sieve microspheres ZKM.

[0090] It is determined by an X-ray diffractometer that the ZKM in this example contains 56% ZSM-5 molecular sieve. The silicon-aluminum ratio is measured to be 100 by an X-ray fluorescence spectrometer, and the crystal grain size is measured to be 0.4 μm by SEM. Figure 1 It is the characteristic X-ray diffraction pattern of the small-crystallite high-silica ZSM-5 molecular sieve provided in this example. Figure 2 It is the scanning electron micrograph of the small-crystallite high-silica ZSM-5 molecular sieve provided in this example. The particle size of the small-crystallite high-silica ZSM-5 molecular sieve microspheres provided in this example is 50 μm; the relative crystallinity of the small-crystallite high-silica ZSM-5 molecular sieve is 60%; the small-crystallite high-silica ZSM-5 molecular sieve has a mesoporous structure, and its mesoporous volume is 0.16 cm 3 / g.

[0091] Example 5

[0092] This example provides a small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0093] 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 the silica sol treated with tartaric acid, water, and activated kaolin microspheres C to a beaker in sequence according to the molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 50:1:50:1200 and mix evenly. Then add Ni 2+ solution (nickel chloride solution) and a mixed solution of Fenton's reagent, and stir at 70 °C in a water bath for 4 h (stirring speed is 150 r / min) to obtain a gel system. Among them, the silica sol treated with tartaric acid is obtained by the following method: take an appropriate amount of silica sol and add it to a beaker, place it in a water bath at 70 °C, add tartaric acid, mix evenly and let it stand for 3 h. The mass ratio of silica sol to tartaric acid is 1:2.5 to obtain the silica sol treated with tartaric acid; the Ni 2+The addition amount of the solution is 5% of the molar amount of Al2O3 in the gel system, and the addition amount of the Fenton reagent (calculated as hydrogen peroxide) is 7% of the molar amount of Al2O3 in the gel system; then the gel system is transferred to a polytetrafluoroethylene reaction kettle and subjected to rotary dynamic crystallization at 170 °C for 24 h (rotation speed is 15 rpm), and then after filtration and washing, it is dried at 70 °C for 15 h, and then calcined at 900 °C for 10 h to obtain small-crystallite high-silica ZSM-5 molecular sieve microspheres ZKM.

[0094] It is determined by an X-ray diffractometer that the ZKM in this example contains 49% ZSM-5 molecular sieve. Its silica-alumina ratio is 42 determined by an X-ray fluorescence spectrometer, and its crystal grain size is 0.7 μm determined by SEM.

[0095] Example 6

[0096] This example provides a small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0097] 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 treated with citric acid, water and activated kaolin microspheres A to a beaker in sequence according to the molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O)=50:1:100:1200 and mix evenly, and then add Fe 3+ solution (a mixed solution of ferric chloride solution and Fenton reagent), stir at 70 °C in a water bath for 4 h (stirring speed is 150 r / min) to obtain a gel system. Among them, the tetraethyl orthosilicate treated with citric acid is obtained by the following method: take an appropriate amount of tetraethyl orthosilicate and add it to a beaker, place it in a water bath at 35 °C, add citric acid, mix evenly and then stand for 3 h. The mass ratio of tetraethyl orthosilicate to citric acid is 1:2 to obtain the tetraethyl orthosilicate treated with citric acid; 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 reagent (calculated as hydrogen peroxide) is 7% of the molar amount of Al2O3 in the gel system; then the gel system is transferred to a polytetrafluoroethylene reaction kettle and subjected to 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 small-crystallite high-silica ZSM-5 molecular sieve microspheres ZKM.

[0098] It is determined by an X-ray diffractometer that the ZKM in this example contains 38% ZSM-5 molecular sieve. Its silica-alumina ratio is 93 determined by an X-ray fluorescence spectrometer, and its crystal grain size is 1.0 μm determined by SEM.

[0099] Example 7

[0100] This example provides a small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0101] Take an appropriate amount of kaolin microsphere A and calcine it in a muffle furnace at 1000 °C for 2 h to obtain activated kaolin microsphere A; add the silica sol treated with tartaric acid, water, and activated kaolin microsphere A to a beaker in sequence according to the molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:1200 and mix evenly, then add Mn 7+ A mixed solution of a solution (potassium permanganate solution) and Fenton's reagent, and stir for 4 h (the stirring speed is 150 r / min) under the condition of a 70 °C water bath to obtain a gel system. Among them, the silica sol treated with tartaric acid is obtained by the following method: take an appropriate amount of silica sol and add it to a beaker, place it in a 50 °C water bath, add tartaric acid, mix evenly and then stand for 3 h. Among them, the mass ratio of silica sol to tartaric acid is 1:3 to obtain the silica sol treated with tartaric acid; 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 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), then after filtration and washing, dry at 80 °C for 12 h, and then calcine at 1000 °C for 10 h to obtain small-crystallite high-silica ZSM-5 molecular sieve microspheres ZKM.

[0102] It is determined by an X-ray diffractometer that the ZKM in this example contains 40% ZSM-5 molecular sieve. Its silicon-aluminum ratio is 89 determined by an X-ray fluorescence spectrometer, and its crystal grain size is 0.8 μm determined by SEM.

[0103] Example 8

[0104] This example provides a small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0105] Take an appropriate amount of kaolin microsphere B and calcine it in a muffle furnace at 800 °C for 4 h to obtain activated kaolin microsphere B; add the water glass treated with citric acid, water, and activated kaolin microsphere B to a beaker in sequence according to the molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 10:1:100:1200 and mix evenly, then add Cu 2+A mixed solution of a solution (copper chloride solution) and potassium persulfate is stirred at 30 °C in a water bath for 4 h (the stirring speed is 150 r / min) to obtain a gel system. Among them, the tartaric acid-treated sodium silicate is obtained by the following method: Take an appropriate amount of sodium silicate and add it to a beaker, place it in a water bath at 40 °C, add tartaric acid, mix evenly and let it stand for 3 h. Among them, the mass ratio of sodium silicate to tartaric acid is 1:1.5 to obtain the tartaric acid-treated sodium silicate; 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 potassium persulfate is 7% of the molar amount of Al2O3 in the gel system; then transfer the gel system to a polytetrafluoroethylene reaction kettle, and perform 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 small crystal high-silica ZSM-5 molecular sieve microspheres ZKM.

[0106] It is determined by an X-ray diffractometer that the ZKM in this example contains 54% ZSM-5 molecular sieve. The silicon-aluminum ratio is measured by an X-ray fluorescence spectrometer to be 95, and the crystal grain size is measured by SEM to be 1.0 μm.

[0107] Example 9

[0108] This example provides a small crystal high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres, which is prepared by the following steps:

[0109] 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 the tartaric acid-treated sodium silicate, water and activated kaolin microspheres C in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O)=10:1:70:1100 to a beaker in sequence and mix evenly, and then add Ni 2+ A mixed solution of a solution (nickel chloride solution) and a Fenton reagent is stirred at 50 °C in a water bath for 4 h (the stirring speed is 150 r / min) to obtain a gel system. Among them, the tartaric acid-treated sodium silicate is obtained by the following method: Take an appropriate amount of sodium silicate and add it to a beaker, place it in a water bath at 50 °C, add tartaric acid, mix evenly and let it stand for 3 h. Among them, the mass ratio of sodium silicate to tartaric acid is 1:2 to obtain the tartaric acid-treated sodium silicate; the Ni 2+The addition amount of the solution is 5% of the molar amount of Al2O3 in the gel system, and the addition amount of the Fenton reagent (calculated as hydrogen peroxide) 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 at 150 °C for 36 h (rotation speed is 15 rpm), and after filtration and washing, it is dried at 80 °C for 12 h, and then calcined at 800 °C for 8 h to obtain small-crystalline high-silica ZSM-5 molecular sieve microspheres ZKM.

[0110] It is determined by an X-ray diffractometer that the ZKM in this example contains 49% ZSM-5 molecular sieve. Its silicon-aluminum ratio is 65 measured by an X-ray fluorescence spectrometer, and its crystal grain size is 0.8 μm measured by SEM.

[0111] Comparative Example 1

[0112] 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 4, except that in the synthesis process, sodium silicate not treated with tartaric acid is directly used instead of sodium silicate treated with tartaric acid. The preparation process is as follows: 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 into a beaker in sequence according to the molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O)=30:1:100:1000 and mix them evenly, and then add Mn 7+ solution (potassium permanganate solution) and a mixed solution of potassium persulfate, and stir at 50 °C in a water bath for 4 h (stirring speed is 150 r / min) 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 the gel system is transferred to a polytetrafluoroethylene reaction kettle and crystallized dynamically at 130 °C for 24 h (rotation speed is 15 rpm), and after filtration and washing, it is dried at 80 °C for 12 h, and then calcined at 700 °C for 6 h to obtain ZSM-5 molecular sieve microspheres ZKM.

[0113] It is determined by an X-ray diffractometer that the ZKM in this comparative example contains 40% ZSM-5 molecular sieve. Its silicon-aluminum ratio is 85 measured by an X-ray fluorescence spectrometer, and its crystal grain size is 3.5 μm measured by SEM.

[0114] Comparative Example 2

[0115] 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 4, except that Mn 7+Solution. The preparation process is as follows: 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 the tartaric acid-treated sodium silicate, water, and activated kaolin microspheres B to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 30:1:100:1000 in sequence and mix them evenly. Then add potassium persulfate 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. Among them, the preparation method of the tartaric acid-treated sodium silicate is the same as that in Example 4, 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, carry out rotary dynamic crystallization at 130 °C for 24 h (the rotation speed is 15 rpm), then after filtration and washing, dry at 80 °C for 12 h, and then calcine at 700 °C for 6 h to obtain ZSM-5 zeolite microspheres ZKM.

[0116] It is determined by an X-ray diffractometer that the ZKM in this comparative example contains 49% ZSM-5 zeolite. Its silicon-aluminum ratio is 50 determined by an X-ray fluorescence spectrometer, and its crystal grain size is 0.5 μm determined by SEM.

[0117] Comparative Example 3

[0118] This comparative example provides a ZSM-5 zeolite synthesized by in-situ crystallization of kaolin microspheres, and its preparation uses the same preparation conditions as in Example 4, except that Mn is not added during the synthesis process. 7+ Solution, and add more potassium persulfate. The preparation process is as follows: 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 the tartaric acid-treated sodium silicate, water, and activated kaolin microspheres B to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 30:1:100:1000 in sequence and mix them evenly. Then add potassium persulfate 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. Among them, the preparation method of the tartaric acid-treated sodium silicate is the same as that in Example 4, 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, carry out rotary dynamic crystallization at 130 °C for 24 h (the rotation speed is 15 rpm), then after filtration and washing, dry at 80 °C for 12 h, and then calcine at 700 °C for 6 h to obtain ZSM-5 zeolite microspheres ZKM.

[0119] It is determined by an X-ray diffractometer that the ZKM in this comparative example contains 49% ZSM-5 zeolite. Its silicon-aluminum ratio is 65 determined by an X-ray fluorescence spectrometer, and its crystal grain size is 0.5 μm determined by SEM.

[0120] Comparative Example 4

[0121] 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 4, except that potassium persulfate is not added during the synthesis process. The preparation process is as follows: Take an appropriate amount of kaolin microsphere B and calcine it in a muffle furnace at 900 °C for 4 h to obtain activated kaolin microsphere B; Add the tartaric acid-treated sodium silicate, water, and activated kaolin microsphere B to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 30:1:100:1000 in sequence and mix evenly, then add Mn 7+ solution, and stir for 4 h (the stirring speed is 150 r / min) under a water bath condition of 50 °C to obtain a gel system. Among them, the preparation method of the tartaric acid-treated sodium silicate is the same as that in Example 4, and the addition amount of the Mn 7+ solution is 5% 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), then after filtration and washing, dry at 80 °C for 12 h, and then calcine at 700 °C for 6 h to obtain ZSM-5 molecular sieve microspheres ZKM.

[0122] It is determined by an X-ray diffractometer that the ZKM in this comparative example contains 40% ZSM-5 molecular sieve. Its silicon-aluminum ratio is measured to be 25 by an X-ray fluorescence spectrometer, and its crystal grain size is measured to be 0.6 μm by SEM.

[0123] Comparative Example 5

[0124] 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 4, except that the Mn 7+ solution is replaced with a Co 2+ solution (cobalt chloride solution) during the synthesis process. The preparation process is as follows: Take an appropriate amount of kaolin microsphere B and calcine it in a muffle furnace at 900 °C for 4 h to obtain activated kaolin microsphere B; Add the tartaric acid-treated sodium silicate, water, and activated kaolin microsphere B to a beaker in a molar ratio of n(Na2O):n(Al2O3):n(SiO2):n(H2O) = 30:1:100:1000 in sequence and mix evenly, then add a mixed solution of Co 2+ solution and potassium persulfate, and stir for 4 h (the stirring speed is 150 r / min) under a water bath condition of 50 °C to obtain a gel system. Among them, the preparation method of the tartaric acid-treated sodium silicate is the same as that in Example 4; the Co 2+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 130 °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 700 °C for 6 h to obtain ZSM-5 molecular sieve microspheres ZKM.

[0125] It is determined by an X-ray diffractometer that the ZKM of this comparative example contains 45% ZSM-5 molecular sieve. Its silicon-aluminum ratio is 45 determined by an X-ray fluorescence spectrometer, and its crystal grain size is 0.6 μm determined by SEM.

[0126] It can be seen from the above examples and comparative examples that the SAR of the molecular sieve product obtained in Example 4 is 100 and the crystal grain size is 0.4 μm. Compared with Example 4, tartaric acid was not used in the synthesis process of Comparative Example 1, and the SAR of the obtained molecular sieve product is 85 and the crystal grain size is 3.5 μm; compared with Example 4, no transition metal ions were introduced in the synthesis process of Comparative Example 2, and the SAR of the obtained molecular sieve product is 50 and the crystal grain size is 0.5 μm; compared with Example 4, no transition metal ions were added in the synthesis process of Comparative Example 3, but more potassium persulfate was added, and the SAR of the obtained molecular sieve product is 65 and the crystal grain size is 0.5 μm; compared with Example 4, no potassium persulfate was introduced in the synthesis process of Comparative Example 4, and the SAR of the obtained molecular sieve product is 25 and the crystal grain size is 0.6 μm; compared with Example 4, Co 2+ was used as the transition metal ion in the synthesis process of Comparative Example 5, and the SAR of the obtained molecular sieve product is 45. It can be seen that Co 2+ did not promote the generation of a large amount of hydroxyl radicals, so the silicon-aluminum ratio of the molecular sieve was not increased. Thus, it can be seen that the weak acid-treated silicon source, transition metal ions, and hydroxyl radical initiator adopted in the present invention play a synergistic role, and small-crystalline high-silicon ZSM-5 molecular sieves are synthesized by in-situ crystallization of kaolin microspheres.

[0127] In summary, the present invention provides a method for in-situ crystallization of small-crystallite high-silica ZSM-5 molecular sieve from kaolin microspheres. This method uses kaolin microspheres, a silicon source treated with a weak acid, transition metal ions, a hydroxyl radical initiator, and water as raw materials to in-situ crystallize a small-crystallite high-silica ZSM-5 molecular sieve. In conventional methods, 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 using seed crystals does not exceed 30, and the crystal grain size is generally greater than 1 μm. This may be because the dissolution rate of active silicon in kaolin microspheres in the synthesis system is slow, so it is not easy to form a high-silica molecular sieve. In the present invention, transition metal ions are used to promote the generation of a large amount of hydroxyl radicals, thereby accelerating the formation of Si-O-Si bonds and promoting the dissolution of active silicon in kaolin microspheres, increasing the silica-alumina ratio in the system, and obtaining a high-silica ZSM-5 molecular sieve framework. At the same time, after the silicon source is treated with a weak acid, it combines with free Na + ions, and during crystallization, it plays a guiding role to form small crystallites, enters the molecular sieve unit cell at the same time, and reacts to release CO2 during the subsequent calcination stage to obtain mesopores. Therefore, the present invention prepares a small-crystallite high-silica ZSM-5 molecular sieve.

Claims

1. A preparation method of small-crystallite 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, the silicon source treated with weak acid, transition metal ions and a hydroxyl radical initiator to obtain a gel system; the weak acid used for the silicon source treated with weak acid includes one or a combination of tartaric acid, 2-hydroxybutanedioic acid and citric acid, and the transition metal ions include Fe 3+ , Cu 2+ , Mn 6+ , Mn 7+ and Ni 2+ or a combination of several of them, and the hydroxyl radical initiator includes one or a combination of sodium persulfate, potassium persulfate and Fenton's reagent; after the gel system is crystallized, it is at least dried and calcined to obtain the small-crystallite 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 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 0.1 - 1.0 μm, the relative crystallinity is 95% - 98%, and the silica-alumina ratio is 30 - 50.

9. According to the preparation method described in 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), the alkali source and / or water are also mixed with the activated kaolin microspheres, the weak-acid-treated silicon source, transition metal ions, and hydroxyl radical initiator 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 in the following manner: Mix the activated kaolin microspheres, the weak-acid-treated silicon source, the alkali source that can be optionally added or not added, and the 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 1, wherein, In step (2), the silicon source treated with weak acid used for the silicon source includes one or a combination of several of water glass, tetraethyl orthosilicate, silicon powder, and silica sol.

19. The preparation method according to claim 1, wherein, In step (2), the silicon source treated with weak acid is obtained by the following method: mixing the silicon source and the weak acid evenly at a mass ratio of 1:(1.5 - 3), and then standing for 2 - 4 h to obtain the silicon source treated with weak acid.

20. The preparation method according to claim 19, wherein In step (2), the temperature for mixing and standing is 35 - 70 °C.

21. 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.

22. 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.

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

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

25. 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.

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

27. 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.

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

29. The small crystal high silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres according to claim 28, wherein, The silicon-aluminum ratio of the small-crystallite high-silica ZSM-5 molecular sieve is 40 - 100.

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

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

32. The small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres according to claim 28, wherein, The crystal size of the small-crystallite high-silica ZSM-5 molecular sieve is 0.4 - 1.0 μm.

33. The small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres according to claim 28, wherein, The small-crystallite high-silica ZSM-5 molecular sieve is a small-crystallite high-silica ZSM-5 molecular sieve microsphere. Based on the total mass of the small-crystallite high-silica ZSM-5 molecular sieve microsphere being 100%, the content of the small-crystallite high-silica ZSM-5 molecular sieve is 38 - 56%.

34. The small-crystallite high-silica ZSM-5 molecular sieve synthesized by in-situ crystallization of kaolin microspheres according to claim 33, wherein, The particle size of the small-crystallite high-silica ZSM-5 molecular sieve microsphere is 15 - 100 μm.

Images