High-dispersity nano beta molecular sieve and preparation method thereof
By using a combination of polydiallyldialkylammonium salt and inorganic ammonium salt as flocculants, the problem of agglomeration and separation of nano-Beta molecular sieves was solved, and highly dispersed nano-β molecular sieves were prepared, thus improving their catalytic and adsorption performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- PETROCHINA CO LTD
- Filing Date
- 2024-11-08
- Publication Date
- 2026-05-08
AI Technical Summary
Existing technologies struggle to achieve high solids yield and rapid separation while maintaining the high specific surface area and mesoporous structure of nano-Beta molecular sieves, thus limiting their application in catalysis and adsorption.
A combination of highly efficient organic cationic flocculant polydiallyl dialkylammonium salt and inorganic ammonium salt was used as a flocculant to prepare highly dispersed nano-β molecular sieves through flocculation and calcination processes, avoiding agglomeration and achieving rapid separation.
The prepared nano-β molecular sieve has high dispersion, abundant external specific surface, high micropore exposure, and large intercrystalline pores, which enhances its application effect in catalysis and adsorption.
Smart Images
Figure CN121990593A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of molecular sieve preparation technology, specifically relating to a highly dispersed nano-β molecular sieve and its preparation method. Background Technology
[0002] Beta molecular sieves have a three-dimensional twelve-membered ring cross-channel structure, with straight channels in the
[100] and
[010] directions, and pore sizes of [missing information].
[001] The direction is a zigzag-shaped channel, and the orifice size is... Two straight channels intersect perpendicularly and are connected by zigzag channels, forming a three-dimensional cross-channel structure of macroporous molecular sieves. This unique channel structure of Beta molecular sieves, coupled with their strong acidity, has led to their widespread application not only in the traditional petrochemical industry but also in biomass conversion and environmental applications, demonstrating significant potential.
[0003] Currently, the synthesis of Beta zeolites mainly uses tetraethylammonium hydroxide (TEAOH) as a template agent, followed by hydrothermal crystallization at 100–160 °C for several days. The resulting crystals are typically large (>1 μm), which is detrimental to mass transfer and diffusion between reactants and products during the catalytic reaction. Years of application of Beta zeolites have fully demonstrated that nano-sized Beta zeolites, due to their larger specific surface area, more exposed active catalytic sites, and shorter diffusion paths, can further enhance their potential catalytic and adsorption performance. To obtain nano-sized Beta zeolites, novel template agents or additives are typically introduced into the synthesis system, or two-step crystallization and microwave-assisted synthesis methods are used to adjust the crystal size and morphology of nano-sized Beta zeolites. Corma et al. successfully prepared Beta zeolites with crystal sizes of 10–20 nm using a novel bifunctional quaternary ammonium salt cationic organic molecule containing short alkyl chains and cyclic alkyl chains as a template agent. Bein et al. synthesized Beta molecular sieves with a particle size of approximately 200 nm using a template agent containing a 4,4'-trimethylbis(N-methyl,N-benzylpiperidine) cation. While novel template agents can yield Beta nanomolecular sieves, their synthesis is complex and costly. Yu Jihong et al. reported an L-lysine-assisted two-step crystallization method to prepare nano-β molecular sieves with a wide silica-to-alumina ratio range (6-300) and particle sizes between 10-106 nm in a concentrated gel system. However, this two-step crystallization method suffers from complex synthesis processes, long synthesis cycles, and low production efficiency. Furthermore, current methods for preparing nano-Beta molecular sieves typically face problems such as low solid yields and difficulties in post-synthesis separation, limiting their large-scale industrial production and application.
[0004] To address the issues of low yield and difficulty in separation of nanocrystalline Beta solids due to their small size, inorganic ammonium salts can typically be added during the filtration process to neutralize the surface charge of the molecular sieve particles, reduce their potential, thereby reducing the electrostatic repulsion between particles and promoting particle aggregation to form flocs. Summary of the Invention
[0005] The inventors discovered in their experiments that during the process of using inorganic ammonium salts to promote particle aggregation and flocculent formation, the molecular sieves severely agglomerated into micron-sized particles, resulting in a loss of mesoporous structure. Incompletely crystallized silica also easily flocculated and blocked the pores, causing further loss of microporous structure. How to achieve high solids yield and rapid separation of nanocrystalline Beta molecular sieves while maintaining their high specific surface area and secondary mesoporous structure is a problem that urgently needs to be solved for the industrial application of nanocrystalline Beta molecular sieves.
[0006] To address the aforementioned technical problems, the present invention aims to provide a highly dispersed nano-β molecular sieve and its preparation method.
[0007] To achieve the above objectives, the present invention provides a method for preparing highly dispersed nano-β molecular sieves, comprising:
[0008] (1) Preparation of crystallization gel: Mix silicon source, aluminum source, alkali source, organic template agent and water to prepare crystallization gel;
[0009] (2) Crystallization: The crystallized gel is crystallized and then rapidly cooled to obtain a nano-molecular sieve slurry;
[0010] (3) Flocculation: A flocculant is added to the nano-molecular sieve slurry for flocculation, the flocculants are collected and calcined to obtain Na-type β-molecular sieve; wherein the flocculant comprises a combination of inorganic ammonium salt and polydiallyl dialkylammonium salt, the molar ratio of inorganic ammonium salt and polydiallyl dialkylammonium salt is 150-4000, and the molar ratio of the flocculant to the silicon source calculated as SiO2 is 0.01-0.2;
[0011] (4) Ammonium exchange and calcination: The Na-type β molecular sieve is subjected to ammonium exchange and calcination to obtain the nano β molecular sieve.
[0012] This invention utilizes a highly efficient organic cationic flocculant, polydiallyldialkylammonium salt, to replace a portion of the inorganic ammonium salt. Without altering the crystallization conditions of the Beta molecular sieve, it effectively alleviates the aggregation problem of nano-Beta molecular sieves, achieving rapid separation of nanocrystalline Beta. This solves the problem of easy aggregation and difficult separation of nano-sized molecular sieves in product processing. The Beta molecular sieve prepared by this method is a highly dispersed, loosely packed nanocrystal. The molecular sieve possesses abundant external surface area, high micropore exposure, and large intercrystalline pores, enhancing its application effects in catalysis, adsorption, and other fields.
[0013] In the flocculant of this invention, inorganic ammonium salts ensure sedimentation efficiency, while the organic cationic flocculant polydiallyldialkylammonium salt also promotes sedimentation. However, their main function is to disperse molecular sieve nanoparticles, preventing them from agglomerating and growing larger during processing, thus maintaining a high external specific surface area and mesoporous structure. Inorganic ammonium salts and polydiallyldialkylammonium salts exhibit a synergistic effect in the preparation of β-molecular sieves, promoting the synthesis of highly dispersed nano-Beta molecular sieves. Using either one alone as a flocculant cannot yield highly dispersed nano-β-molecular sieves.
[0014] Furthermore, this invention optimizes the dosage of organic cationic flocculant relative to inorganic ammonium salt. When the amount of cationic flocculant is too small, the molecular sieve nanoparticles rapidly settle and agglomerate severely; while when the amount of cationic flocculant is too large, the viscosity of the entire filtration system is too high, which not only leads to severe agglomeration but also makes it difficult to effectively separate the molecular sieves. In this invention, highly dispersed nanomolecular sieve products can only be prepared when two ammonium salts are added simultaneously in an appropriate ratio.
[0015] According to a specific embodiment of the present invention, preferably, the inorganic ammonium salt includes one or more of ammonium sulfate, ammonium bisulfate, ammonium chloride, and ammonium nitrate.
[0016] According to a specific embodiment of the present invention, preferably, the polydiallyldialkylammonium salt includes one or more of the following: polydiallyldimethylammonium chloride, polydiallyldimethylammonium bromide, polydiallyldimethylammonium nitrate, polydiallyldimethylammonium sulfate, polydiallyldiethylammonium chloride, polydiallyldiethylammonium bromide, polydiallyldiethylammonium nitrate, and polydiallyldiethylammonium sulfate.
[0017] According to a specific embodiment of the present invention, preferably, the weight-average molecular weight of the polydiallyl dialkylammonium salt is 10,000-800,000.
[0018] According to a specific embodiment of the present invention, preferably, the alkali source is calculated as alkali metal oxide M2O, the aluminum source is calculated as Al2O3, and the organic template agent is calculated as organic ammonium cation R. + Based on the silicon source being SiO2, the molar ratio of each component in the crystallized gel is: SiO2 / Al2O3 = 25-70, R + / SiO2=0.02-0.25, M2O / SiO2=0.03-0.20, H2O / SiO2=12-50.
[0019] According to a specific embodiment of the present invention, preferably, the organic template agent includes at least one of tetraethylammonium hydroxide, tetraethylammonium bromide, and tetraethylammonium chloride.
[0020] According to a specific embodiment of the present invention, preferably, the silicon source includes at least one of tetraethyl orthosilicate, silica sol, and coarse-porous silica gel.
[0021] According to a specific embodiment of the present invention, preferably, the aluminum source includes at least one of sodium aluminate, aluminum nitrate, and aluminum sulfate.
[0022] According to a specific embodiment of the present invention, preferably, the alkali source includes at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.
[0023] According to a specific embodiment of the present invention, preferably, the crystallization conditions include crystallization at a temperature of 140-180°C for 20-96 hours.
[0024] According to a specific embodiment of the present invention, preferably, the crystallization is dynamic crystallization and is carried out under hydrothermal and closed conditions.
[0025] According to a specific embodiment of the present invention, preferably, the crystallized gel is further aged at a temperature of 20-60°C for a time of 1-6 hours.
[0026] According to a specific embodiment of the present invention, preferably, the preparation method of the above-mentioned highly dispersed nano-β molecular sieve includes the following steps:
[0027] (1) Preparation of crystallization gel: The silicon source, aluminum source, alkali source, organic template agent and water are mixed and aged to obtain the crystallization gel. The alkali source is calculated as alkali metal oxide M2O, the aluminum source is calculated as Al2O3, and the organic template agent is calculated as organic ammonium cation R. + Based on the silicon source being SiO2, the molar ratio of each component in the preparation of the crystallization gel is: SiO2 / Al2O3 = 25-70, R + / SiO2=0.02-0.25, M2O / SiO2=0.03-0.20, H2O / SiO2=12-50;
[0028] (2) Hydrothermal crystallization: The crystallized gel is dynamically crystallized under hydrothermal conditions, and then sealed and crystallized at 140-180℃ for 20-96 hours. After crystallization, it is rapidly cooled to obtain nano-molecular sieve slurry.
[0029] (3) Flocculation and post-treatment: Flocculant is added to the nano molecular sieve slurry, and the product is filtered, washed, dried and calcined to obtain a highly dispersed nano Na-type β molecular sieve.
[0030] (4) Preparation of H-type β molecular sieve: Naβ molecular sieve is obtained by ammonium exchange, filtration, washing, drying and calcination to obtain nano H-type β molecular sieve, namely the highly dispersed nano β molecular sieve.
[0031] The present invention also provides a highly dispersed nano-β molecular sieve, which is obtained by the above-described method for preparing highly dispersed nano-β molecular sieves.
[0032] According to a specific embodiment of the present invention, preferably, the above-mentioned nano-β molecular sieve satisfies one or more of the following conditions:
[0033] The grain size is 10-50 nm;
[0034] Total surface area is 650-900 m² 2 / g;
[0035] External specific surface area is 150-300m² 2 / g;
[0036] The average pore size is 25-50 nm;
[0037] The average pore size of the adsorption is 60-100 nm.
[0038] According to a specific embodiment of the present invention, preferably, the above-mentioned nano β molecular sieve has a *BEA topology, the central atoms of the molecular sieve framework are silicon and aluminum, and the micropore volume accounts for 20-40% of the total pore volume.
[0039] The technical solution provided by this invention has the following beneficial effects:
[0040] This invention utilizes a highly efficient organic cationic flocculant, polydiallyldialkylammonium salt, to replace a portion of the inorganic ammonium salt. Without altering the crystallization conditions of the Beta molecular sieve, this effectively alleviates the aggregation problem of nano-Beta molecular sieves, achieving rapid separation of nanocrystalline Beta. The Beta molecular sieve prepared by this method is a highly dispersed, loosely packed nanocrystal. The molecular sieve possesses abundant external surface area, high micropore exposure, and large intercrystalline pores, enhancing its application performance in catalysis, adsorption, and other fields. Attached Figure Description
[0041] Figure 1 The polycrystalline X-ray diffraction (PXRD) spectra of the nano-β molecular sieve products in Examples 1-3 are shown below.
[0042] Figure 2 The image shows a scanning electron microscope (SEM) image of the nano-β molecular sieve product from Example 1.
[0043] Figure 3 Here is a SEM image of the nano-β molecular sieve product from Example 2;
[0044] Figure 4 Here is a SEM image of the nano-β molecular sieve product from Example 2;
[0045] Figure 5The PXRD spectra of the nano-β molecular sieve products in Examples 4-7 are shown.
[0046] Figure 6 Here is a SEM image of the nano-β molecular sieve product from Example 4;
[0047] Figure 7 Here is a SEM image of the nano-β molecular sieve product from Example 5;
[0048] Figure 8 Here is a SEM image of the nano-β molecular sieve product from Example 6;
[0049] Figure 9 Here is a SEM image of the nano-β molecular sieve product from Example 7;
[0050] Figure 10 PXRD spectra of the nano-β molecular sieve products in Comparative Examples 1-3;
[0051] Figure 11 SEM image of the nano-β molecular sieve product of Comparative Example 1;
[0052] Figure 12 SEM image of the nano-β molecular sieve product of Comparative Example 2;
[0053] Figure 13 The image shows the SEM image of the nano-β molecular sieve product of Comparative Example 3. Detailed Implementation
[0054] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.
[0055] Example 1
[0056] This embodiment provides a highly dispersed nano-β molecular sieve, the preparation method of which is as follows:
[0057] 600g of 30% silica sol, 22g of sodium aluminate, 17.4g of sodium hydroxide, 95g of tetraethylammonium hydroxide and 740g of deionized water were mixed thoroughly under vigorous stirring. The mixture was aged at room temperature for 4 hours to obtain a gel.
[0058] The gel was then transferred to a high-pressure stainless steel reactor and heated at 150°C for 56 hours to crystallize. After the reaction was completed, the temperature was quickly reduced to room temperature to obtain a nano-molecular sieve slurry.
[0059] 54.6 g of polydiallyldimethylammonium chloride with a molecular weight of 100,000 and 12.6 g of ammonium chloride were added to the nano-molecular sieve slurry and stirred thoroughly for 0.5 h to obtain a molecular sieve suspension. The molecular sieve suspension was filtered to obtain a filter cake and the filtration time was recorded. The filter cake was washed, dried and calcined at 550 °C for 6 h to obtain Na-type β-molecular sieve.
[0060] Na-type β molecular sieve was mixed with 0.5 mol / L (NH4)2SO4 aqueous solution at a solid-liquid ratio of 1:20 and subjected to ammonium exchange in a water bath at 80℃ for 2 hours. The precipitate was filtered, washed, dried, and then calcined at 550℃ for 6 hours to obtain nano-β molecular sieve (H-type β molecular sieve).
[0061] The XRD pattern of the nano-β molecular sieve product obtained in this embodiment is shown below. Figure 1 The product exhibits typical *BEA structural characteristic peaks. See SEM image below. Figure 2 The product is granular with a grain size of approximately 20 nm.
[0062] Example 2
[0063] This embodiment provides a highly dispersed nano-β molecular sieve, the preparation method of which is as follows:
[0064] 600g of 30% silica sol, 22g of sodium aluminate, 17.4g of sodium hydroxide, 95g of tetraethylammonium hydroxide and 740g of deionized water were mixed thoroughly under vigorous stirring. The mixture was aged at room temperature for 4 hours to obtain a gel.
[0065] The gel was then transferred to a high-pressure stainless steel reactor and heated at 150°C for 56 hours to crystallize. After the reaction was completed, the temperature was quickly reduced to room temperature to obtain a nano-molecular sieve slurry.
[0066] 36.4 g of polydiallyldimethylammonium chloride with a molecular weight of 100,000 and 12.6 g of ammonium chloride were added to the nano-molecular sieve slurry and stirred thoroughly for 0.5 h to obtain a molecular sieve suspension. The molecular sieve suspension was filtered to obtain a filter cake and the filtration time was recorded. The filter cake was washed, dried and calcined at 500 °C for 6 h to obtain the Na-type β-molecular sieve product.
[0067] Na-type β molecular sieve was mixed with 0.5 mol / L (NH4)2SO4 aqueous solution at a solid-liquid ratio of 1:20 and subjected to ammonium exchange in a water bath at 80℃ for 2 hours. The precipitate was filtered, washed, dried, and then calcined at 550℃ for 6 hours to obtain nano-β molecular sieve (H-type β molecular sieve).
[0068] The XRD pattern of the nano-β molecular sieve product obtained in this embodiment is shown below. Figure 1 The product exhibits typical *BEA structural characteristic peaks. See SEM image below. Figure 3The product is granular with a grain size of approximately 20 nm.
[0069] Example 3
[0070] This embodiment provides a highly dispersed nano-β molecular sieve, the preparation method of which is as follows:
[0071] 600g of 30% silica sol, 22g of sodium aluminate, 17.4g of sodium hydroxide, 95g of tetraethylammonium hydroxide and 740g of deionized water were mixed thoroughly under vigorous stirring. The mixture was aged at room temperature for 4 hours to obtain a gel.
[0072] The gel was then transferred to a high-pressure stainless steel reactor and heated at 150°C for 56 hours to crystallize. After the reaction was completed, the temperature was quickly reduced to room temperature to obtain a nano-molecular sieve slurry.
[0073] 24.2 g of polydiallyldimethylammonium chloride with a molecular weight of 100,000 and 12.6 g of ammonium chloride were added to the nano-molecular sieve slurry and stirred thoroughly for 0.5 h to obtain a molecular sieve suspension. The molecular sieve suspension was filtered to obtain a filter cake and the filtration time was recorded. The filter cake was washed, dried and calcined at 500 °C for 6 h to obtain the Na-type β-molecular sieve product.
[0074] Na-type β molecular sieve was mixed with 0.5 mol / L (NH4)2SO4 aqueous solution at a solid-liquid ratio of 1:20 and subjected to ammonium exchange in a water bath at 80℃ for 2 hours. The precipitate was filtered, washed, dried, and then calcined at 550℃ for 6 hours to obtain nano-β molecular sieve (H-type β molecular sieve).
[0075] The XRD pattern of the nano-β molecular sieve product obtained in this embodiment is shown below. Figure 1 The product exhibits typical *BEA structural characteristic peaks. See SEM image below. Figure 4 The product is granular with a grain size of approximately 20 nm.
[0076] Example 4
[0077] This embodiment provides a highly dispersed nano-β molecular sieve, the preparation method of which is as follows:
[0078] 600g of 30% silica sol, 22g of sodium aluminate, 17.4g of sodium hydroxide, 95g of tetraethylammonium hydroxide and 740g of deionized water were mixed thoroughly under vigorous stirring. The mixture was aged at room temperature for 4 hours to obtain a gel.
[0079] The gel was then transferred to a high-pressure stainless steel reactor and heated at 150°C for 56 hours to crystallize. After the reaction was completed, the temperature was quickly reduced to room temperature to obtain a nano-molecular sieve slurry.
[0080] Add 6.3g of polydiallyldimethylammonium chloride with a molecular weight of 100,000 and 12.6g of ammonium chloride to the nano-molecular sieve slurry, and stir thoroughly for 0.5h to obtain a molecular sieve suspension; filter the molecular sieve suspension to obtain a filter cake and record the filtration time; wash and dry the filter cake and calcine it at 500℃ for 6h to obtain the Na-type β-molecular sieve product;
[0081] Na-type β molecular sieve was mixed with 0.5 mol / L (NH4)2SO4 aqueous solution at a solid-liquid ratio of 1:20 and subjected to ammonium exchange in a water bath at 80℃ for 2 hours. The precipitate was filtered, washed, dried, and then calcined at 550℃ for 6 hours to obtain nano-β molecular sieve (H-type β molecular sieve).
[0082] The XRD pattern of the nano-β molecular sieve product obtained in this embodiment is shown below. Figure 5 The product exhibits typical *BEA structural characteristic peaks. See SEM image below. Figure 6 The product is formed by the accumulation of 30-50nm particles.
[0083] Example 5
[0084] This embodiment provides a highly dispersed nano-β molecular sieve, the preparation method of which is as follows:
[0085] 600g of 30% silica sol, 22g of sodium aluminate, 17.4g of sodium hydroxide, 95g of tetraethylammonium hydroxide and 740g of deionized water were mixed thoroughly under vigorous stirring. The mixture was aged at room temperature for 4 hours to obtain a gel.
[0086] The gel was then transferred to a high-pressure stainless steel reactor and heated at 150°C for 56 hours to crystallize. After the reaction was completed, the temperature was quickly reduced to room temperature to obtain a nano-molecular sieve slurry.
[0087] 136.5 g of polydiallyldimethylammonium chloride with a molecular weight of 100,000 and 12.6 g of ammonium chloride were added to the nano-molecular sieve slurry and stirred thoroughly for 0.5 h to obtain a molecular sieve suspension. The molecular sieve suspension was filtered to obtain a filter cake and the filtration time was recorded. The filter cake was washed, dried and calcined at 500 °C for 6 h to obtain the Na-type β-molecular sieve product.
[0088] Na-type β molecular sieve was mixed with 0.5 mol / L (NH4)2SO4 aqueous solution at a solid-liquid ratio of 1:20 and subjected to ammonium exchange in a water bath at 80℃ for 2 hours. The precipitate was filtered, washed, dried, and then calcined at 550℃ for 6 hours to obtain nano-β molecular sieve (H-type β molecular sieve).
[0089] The XRD pattern of the nano-β molecular sieve product obtained in this embodiment is shown below. Figure 5 The product exhibits typical *BEA structural characteristic peaks. See SEM image below. Figure 7The product is formed by the accumulation of 30-50nm particles.
[0090] Example 6
[0091] This embodiment provides a highly dispersed nano-β molecular sieve, the preparation method of which is as follows:
[0092] 600g of 30% silica sol, 22g of sodium aluminate, 17.4g of sodium hydroxide, 95g of tetraethylammonium hydroxide and 740g of deionized water were mixed thoroughly under vigorous stirring. The mixture was aged at room temperature for 4 hours to obtain a gel.
[0093] The gel was then transferred to a high-pressure stainless steel reactor and heated at 150°C for 56 hours to crystallize. After the reaction was completed, the temperature was quickly reduced to room temperature to obtain a nano-molecular sieve slurry.
[0094] Add 34.6g of polydiallyldimethylammonium chloride with a molecular weight of 100,000 and 4.2g of ammonium chloride to the nano-molecular sieve slurry, and stir thoroughly for 0.5h to obtain a molecular sieve suspension; filter the molecular sieve suspension to obtain a filter cake and record the filtration time; wash and dry the filter cake and calcine it at 500℃ for 6h to obtain the Na-type β-molecular sieve product;
[0095] Na-type β molecular sieve was mixed with 0.5 mol / L (NH4)2SO4 aqueous solution at a solid-liquid ratio of 1:20 and subjected to ammonium exchange in a water bath at 80℃ for 2 hours. The precipitate was filtered, washed, dried, and then calcined at 550℃ for 6 hours to obtain nano-β molecular sieve (H-type β molecular sieve).
[0096] The XRD pattern of the nano-β molecular sieve product obtained in this embodiment is shown below. Figure 5 The product exhibits typical *BEA structural characteristic peaks. See SEM image below. Figure 8 The product is formed by the accumulation of 20-40nm particles.
[0097] Example 7
[0098] This embodiment provides a highly dispersed nano-β molecular sieve, the preparation method of which is as follows:
[0099] 600g of 30% silica sol, 22g of sodium aluminate, 17.4g of sodium hydroxide, 95g of tetraethylammonium hydroxide and 740g of deionized water were mixed thoroughly under vigorous stirring. The mixture was aged at room temperature for 4 hours to obtain a gel.
[0100] The gel was then transferred to a high-pressure stainless steel reactor and heated at 150°C for 56 hours to crystallize. After the reaction was completed, the temperature was quickly reduced to room temperature to obtain a nano-molecular sieve slurry.
[0101] Add 36.4g of polydiallyldimethylammonium chloride with a molecular weight of 100,000 and 31.5g of ammonium chloride to the nano-molecular sieve slurry, and stir thoroughly for 0.5h to obtain a molecular sieve suspension; filter the molecular sieve suspension to obtain a filter cake and record the filtration time; wash and dry the filter cake and calcine it at 500℃ for 6h to obtain the Na-type β-molecular sieve product;
[0102] Na-type β molecular sieve was mixed with 0.5 mol / L (NH4)2SO4 aqueous solution at a solid-liquid ratio of 1:20 and subjected to ammonium exchange in a water bath at 80℃ for 2 hours. The precipitate was filtered, washed, dried, and then calcined at 550℃ for 6 hours to obtain nano-β molecular sieve (H-type β molecular sieve).
[0103] The XRD pattern of the nano-β molecular sieve product obtained in this embodiment is shown below. Figure 5 The product exhibits typical *BEA structural characteristic peaks. See SEM image below. Figure 9 The product is formed by the accumulation of 20-40nm particles.
[0104] Comparative Example 1
[0105] This comparative example provides a nano-β molecular sieve, the preparation method of which is as follows:
[0106] 600g of 30% silica sol, 22g of sodium aluminate, 17.4g of sodium hydroxide, 95g of tetraethylammonium hydroxide and 740g of deionized water were mixed thoroughly under vigorous stirring. The mixture was aged at room temperature for 4 hours to obtain a gel.
[0107] The gel was then transferred to a high-pressure stainless steel reactor and heated at 150°C for 56 hours to crystallize. After the reaction was completed, the temperature was quickly reduced to room temperature to obtain a nano-molecular sieve slurry.
[0108] 12.6 g of ammonium chloride was added to the nano-molecular sieve slurry and stirred thoroughly for 0.5 h to obtain a molecular sieve suspension; the molecular sieve suspension was filtered to obtain a filter cake and the filtration time was recorded; the filter cake was washed, dried and calcined at 500 °C for 6 h to obtain the Na-type β-molecular sieve product.
[0109] Na-type β molecular sieve was mixed with 0.5 mol / L (NH4)2SO4 aqueous solution at a solid-liquid ratio of 1:20 and subjected to ammonium exchange in a water bath at 80℃ for 2 hours. The precipitate was filtered, washed, dried, and then calcined at 550℃ for 6 hours to obtain nano-β molecular sieve (H-type β molecular sieve).
[0110] The XRD pattern of the nano-β molecular sieve product obtained in this comparative example is shown below. Figure 10 The product exhibits typical *BEA structural characteristic peaks. See SEM image below. Figure 11 The product is in block form with a grain size of approximately 100-200nm.
[0111] Comparative Example 2
[0112] This comparative example provides a nano-β molecular sieve, the preparation method of which is as follows:
[0113] 600g of 30% silica sol, 22g of sodium aluminate, 17.4g of sodium hydroxide, 95g of tetraethylammonium hydroxide and 740g of deionized water were mixed thoroughly under vigorous stirring. The mixture was aged at room temperature for 4 hours to obtain a gel.
[0114] The gel was then transferred to a high-pressure stainless steel reactor and heated at 150°C for 56 hours to crystallize. After the reaction, the temperature was quickly reduced to room temperature to obtain a nano-molecular sieve slurry. The nano-molecular sieve slurry was then filtered to obtain a filter cake, and the filtration time was recorded. The filter cake was washed, dried, and then calcined at 500°C for 6 hours to obtain the Na-type β-molecular sieve product.
[0115] Na-type β molecular sieve was mixed with 0.5 mol / L (NH4)2SO4 aqueous solution at a solid-liquid ratio of 1:20 and subjected to ammonium exchange in a water bath at 80℃ for 2 hours. The precipitate was filtered, washed, dried, and then calcined at 550℃ for 6 hours to obtain nano-β molecular sieve (H-type β molecular sieve).
[0116] The XRD pattern of the nano-β molecular sieve product obtained in this comparative example is shown below. Figure 10 The product exhibits typical *BEA structural characteristic peaks. See SEM image below. Figure 12 The product is in block form with a grain size of approximately 100-250 nm.
[0117] Comparative Example 3
[0118] This comparative example provides a nano-β molecular sieve, the preparation method of which is as follows:
[0119] 600g of 30% silica sol, 22g of sodium aluminate, 17.4g of sodium hydroxide, 95g of tetraethylammonium hydroxide and 740g of deionized water were mixed thoroughly under vigorous stirring. The mixture was aged at room temperature for 4 hours to obtain a gel.
[0120] The gel was then transferred to a high-pressure stainless steel reactor and heated at 150°C for 56 hours to crystallize. After the reaction was completed, the temperature was quickly reduced to room temperature to obtain a nano-molecular sieve slurry.
[0121] Add 36.4g of polydiallyldimethylammonium chloride with a molecular weight of 100,000 to the nano-molecular sieve slurry and stir thoroughly for 0.5h to obtain a molecular sieve suspension; filter the molecular sieve suspension to obtain a filter cake and record the filtration time; wash and dry the filter cake and calcine it at 500℃ for 6h to obtain the Na-type β-molecular sieve product.
[0122] Na-type β molecular sieve was mixed with 0.5 mol / L (NH4)2SO4 aqueous solution at a solid-liquid ratio of 1:20 and subjected to ammonium exchange in a water bath at 80℃ for 2 hours. The precipitate was filtered, washed, dried, and then calcined at 550℃ for 6 hours to obtain nano-β molecular sieve (H-type β molecular sieve).
[0123] The XRD pattern of the nano-β molecular sieve product obtained in this comparative example is shown below. Figure 10 The product exhibits typical *BEA structural characteristic peaks. See SEM image below. Figure 13 The product is in block form with a grain size of approximately 100-250 nm.
[0124] The pore structure of the nano-β molecular sieve products obtained in the above examples and comparative examples was characterized, and the results are shown in Table 1. The filtrate treatment time in the preparation methods of the above examples and comparative examples was recorded, and the solid recovery rate was tested, and the results are shown in Table 2.
[0125] Table 1. Structural characterization results of molecular sieves
[0126]
[0127]
[0128] Table 2 Filtrate treatment time and solids recovery rate
[0129]
[0130] In Table 2:
[0131] The filtrate treatment time refers to the filtration time required for the molecular sieve suspension to stop dripping and form a filter cake. All examples and comparative examples were conducted under the same filtration conditions: an 18cm Buchner funnel equipped with slow-release qualitative filter paper, and a circulating water vacuum pump maintained at a flow rate of 60L / min and a vacuum level of 3kPa.
[0132] Solid recovery rate = x / [m(SiO2)+n(Al2O3)]×100% = x / 189.02×100%
[0133] Where x is the mass of the calcined nano-β molecular sieve (H-type β molecular sieve) product, m is the mass of SiO2 in the raw material = 600 × 0.3 = 180, n is the mass of Al2O3 in sodium aluminate = 22 × 0.41 = 9.02, and the Al2O3 content of the sodium aluminate raw material of this invention is 41%.
[0134] The specific surface area data and SEM images from Examples 2 and Comparative Examples 1-3 reveal that neither adding inorganic ammonium salts or polydiallyldialkylammonium salts as flocculants alone, nor adding any flocculant, can produce highly dispersed Beta molecular sieves. Only the simultaneous addition of both ammonium salts can prevent the agglomeration of nanocrystalline Beta molecular sieves, resulting in molecular sieves with smaller crystallites and higher specific surface areas. Furthermore, Example 2 exhibits a shorter molecular sieve recovery time and a higher recovery rate compared to Comparative Examples 1-3. This demonstrates a synergistic effect between inorganic ammonium salts and the organic cationic flocculant polydiallyldialkylammonium salt in the preparation of highly dispersed Beta molecular sieves.
[0135] Furthermore, in Examples 4 and 5, further reducing or increasing the amount of organic ammonium salt, and in Examples 6 and 7, further reducing or increasing the molar amount of flocculant relative to the silicon source, all resulted in an increase in the size and aggregation of molecular sieve crystals, and a decrease in both the total specific surface area and the external specific surface area. This demonstrates that the addition ratio of organic ammonium salt and the total amount of flocculant are equally important for the preparation of highly dispersed nanocrystalline Beta molecular sieves.
Claims
1. A method for preparing highly dispersed nano-β molecular sieves, comprising: (1) Preparation of crystallization gel: Mix silicon source, aluminum source, alkali source, organic template agent and water to prepare crystallization gel; (2) Crystallization: The crystallized gel is crystallized and then rapidly cooled to obtain a nano-molecular sieve slurry; (3) Flocculation: A flocculant is added to the nano-molecular sieve slurry for flocculation, the flocculants are collected and calcined to obtain Na-type β-molecular sieve; wherein the flocculant comprises a combination of inorganic ammonium salt and polydiallyl dialkylammonium salt, the molar ratio of inorganic ammonium salt to polydiallyl dialkylammonium salt is 150-4000:1, and the molar ratio of the flocculant to the silicon source calculated as SiO2 is 0.01-0.2:1; (4) Ammonium exchange and calcination: The Na-type β molecular sieve is subjected to ammonium exchange and calcination to obtain the nano β molecular sieve.
2. The method for preparing highly dispersed nano-β molecular sieves according to claim 1, wherein, The inorganic ammonium salt includes one or more of ammonium sulfate, ammonium bisulfate, ammonium chloride, and ammonium nitrate.
3. The method for preparing highly dispersed nano-β molecular sieves according to claim 1, wherein, The polydiallyl dialkylammonium salt includes one or more combinations of polydiallyl dimethylammonium chloride, polydiallyl dimethylammonium bromide, polydiallyl dimethylammonium nitrate, polydiallyl dimethylammonium sulfate, polydiallyl diethylammonium chloride, polydiallyl diethylammonium bromide, polydiallyl diethylammonium nitrate, and polydiallyl diethylammonium sulfate.
4. The method for preparing highly dispersed nano-β molecular sieves according to claim 1, wherein, The weight-average molecular weight of the polydiallyl dialkylammonium salt is 10,000-800,000.
5. The method for preparing highly dispersed nano-β molecular sieves according to claim 1, wherein, The alkali source is calculated as alkali metal oxide M2O, the aluminum source as Al2O3, and the organic template agent is calculated as organic ammonium cation R. + Based on the silicon source being SiO2, the molar ratio of each component in the crystallized gel is: SiO2 / Al2O3 = 25-70, R + / SiO2=0.02-0.25, M2O / SiO2=0.03-0.20, H2O / SiO2=12-50.
6. The method for preparing highly dispersed nano-β molecular sieves according to claim 1, wherein, The organic template agent includes at least one of tetraethylammonium hydroxide, tetraethylammonium bromide, and tetraethylammonium chloride.
7. The method for preparing highly dispersed nano-β molecular sieves according to claim 1, wherein, The silicon source includes at least one of tetraethyl orthosilicate, silica sol, and coarse-porous silica gel.
8. The method for preparing highly dispersed nano-β molecular sieves according to claim 1, wherein, The aluminum source includes at least one of sodium aluminate, aluminum nitrate, and aluminum sulfate.
9. The method for preparing highly dispersed nano-β molecular sieves according to claim 1, wherein, The alkaline source includes at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.
10. The method for preparing highly dispersed nano-β molecular sieves according to claim 1, wherein, Crystallization conditions include crystallization at 140-180℃ for 20-96 hours.
11. A highly dispersed nano-β molecular sieve, obtained by the preparation method of the highly dispersed nano-β molecular sieve according to any one of claims 1-10.
12. The highly dispersed nano-β molecular sieve according to claim 11, wherein, The nano-β molecular sieve satisfies one or more of the following conditions: The grain size is 10-50 nm; Total surface area is 650-900 m² 2 / g; External specific surface area is 150-300m² 2 / g; The average pore size is 25-50 nm; The average pore size of the adsorption is 60-100 nm.
13. The highly dispersed nano-β molecular sieve according to claim 11, wherein, The nano-β molecular sieve has a *BEA topology, with silicon and aluminum as the central atoms of the molecular sieve framework, and the micropore volume accounts for 20-40% of the total pore volume.