A method for rapidly preparing nano-Beta molecular sieve by microwave synthesis method

Abstract

The application relates to the technical field of Beta molecular sieve preparation, and discloses a method for rapidly preparing nano Beta molecular sieve by using a microwave synthesis method, which comprises the following steps: selecting appropriate silicon sources (such as silicon dioxide, white carbon black and the like) and aluminum sources (such as sodium metaaluminate, aluminum sulfate and the like), adding a template agent (such as tetraethylammonium hydroxide), an alkali source (such as sodium hydroxide) and deionized water, uniformly mixing and stirring according to a specific molar ratio to obtain an initial gel; then crystallizing the gel, and the crystallization can be carried out by using a conventional hydrothermal method or a microwave heating method; and after the crystallization is completed, the product is subjected to post-treatment such as filtering, washing, drying and high-temperature calcination, and finally, the Beta molecular sieve product is obtained. The method for rapidly preparing nano Beta molecular sieve by using the microwave synthesis method simplifies the synthesis steps, significantly shortens the crystallization time, improves the production efficiency, effectively controls the particle size of the nano Beta molecular sieve, and obtains the nano-level product with smaller particle size and more uniform distribution.

Description

Technical Field

[0001] This invention relates to the field of Beta molecular sieve preparation technology, and in particular to a method for rapidly preparing nano-Beta molecular sieves using microwave synthesis. Background Technology

[0002] Beta zeolite is a macroporous molecular sieve with a three-dimensional twelve-membered ring pore structure. Due to its unique pore structure, high specific surface area, excellent thermal stability, and acidity, it is widely used in petrochemical, fine chemical, and environmental protection fields. In industrial applications, Beta zeolite is mainly used as a catalyst or catalyst support, exhibiting excellent catalytic performance in reactions such as alkylation, isomerization, and cracking. Traditionally, Beta zeolite is mainly prepared via hydrothermal synthesis. This method typically requires high temperature and high pressure conditions, and the synthesis conditions (such as temperature, time, pH value, and type of template agent) significantly affect the crystal phase, particle size, morphology, and other properties of the final product.

[0003] However, traditional hydrothermal synthesis methods have some significant drawbacks. First, this method consumes a lot of energy, has low preparation efficiency, and crystallization time typically requires 2 to 3 days, which not only increases production costs but also limits product yield. Second, prolonged high-temperature reactions generate a large amount of chemical waste, which is inconsistent with the current development concept of green chemistry. Furthermore, traditional heating methods heat the reaction system through heat conduction and convection, resulting in low energy transfer efficiency and difficulty in achieving uniform heating, easily leading to unstable product quality. In contrast, microwave heating technology offers new possibilities for the synthesis of molecular sieves. Microwave heating directly acts on polar molecules in the reaction system, resulting in extremely high energy transfer efficiency and inducing high-frequency molecular vibrations, significantly increasing the reaction rate and shortening the synthesis time. This not only improves production efficiency but also reduces energy consumption. On the other hand, the performance of molecular sieves is closely related to their particle size and pore structure. Studies have shown that nanoscale molecular sieves, due to their larger specific surface area and shorter diffusion paths, often exhibit superior catalytic performance. By using surfactants, the crystallization process of molecular sieves can be controlled to prepare nanoscale molecular sieves with smaller particle sizes, thereby further improving the catalytic performance of molecular sieves. Therefore, developing a rapid, efficient, and controllable method for synthesizing nano-Beta molecular sieves is not only of great scientific significance but also of great application value.

[0004] To this end, patent application CN110065953A describes a method for rapidly synthesizing nano-Beta molecular sieves using microwave heating combined with a seed crystal method. However, this method requires the addition of Beta molecular sieve seeds and two stages: pre-crystallization and high-temperature crystallization. The synthesis steps are relatively complex and time-consuming.

[0005] Patent application CN110127715A describes a method for accelerating the synthesis of Beta molecular sieves using a promoter. However, this method requires the addition of a promoter and precise control of the ratio of promoter to silicon source. Dynamic crystallization at 95–145°C for 20–90 hours is time-consuming, and the particle size of the product is not controlled.

[0006] Patent application CN112939008A describes a method for rapidly synthesizing Beta molecular sieves of different particle sizes using a crystal particle size regulator, but this method requires 30 to 80 hours of crystallization, which is time-consuming.

[0007] Therefore, it can be seen that the existing technology still has the following problems in the preparation of Beta molecular sieves:

[0008] 1. Complex synthesis steps and long crystallization time: In existing technologies, even with methods such as microwave heating, seed crystal method, or accelerator, the synthesis of Beta molecular sieves still requires 4 to 20 hours, or even longer. Furthermore, some methods require two complex stages: pre-crystallization and high-temperature crystallization, or precise control of the ratio of accelerator to silicon source, or the addition of seed crystals to promote the crystallization process, increasing operational complexity.

[0009] 2. Limited particle size control and relatively large particle size: Current technologies have limited ability to control the particle size of nano-Beta molecular sieves, resulting in products with often relatively large particle sizes, or requiring the addition of crystal particle size modifiers to achieve particle size control. This limits the performance of molecular sieves in certain application areas.

[0010] Therefore, it is necessary to provide a method for rapidly preparing nano-Beta molecular sieves using microwave synthesis, aiming to simplify the synthesis steps, significantly shorten the crystallization time, improve production efficiency, and achieve effective control over the particle size of nano-Beta molecular sieves, thereby obtaining nanoscale products with smaller particle size and more uniform distribution. Summary of the Invention

[0011] The purpose of this invention is to provide a method for rapidly preparing nano-Beta molecular sieves using microwave synthesis, aiming to solve the problems of complex synthesis steps, long crystallization times, and limited control over nanoparticle size in existing technologies. This method, by optimizing the microwave heating process and reaction parameters, and combining them with surfactants, achieves a significant reduction in synthesis time and precise control of nanoparticle size. It eliminates the need for seed crystals or complex pretreatment processes, greatly simplifying the synthesis steps and significantly improving production efficiency, reducing energy consumption, and enhancing product performance.

[0012] The method for rapidly preparing nano Beta zeolite by microwave synthesis provided by the present invention includes adding a silicon source and an aluminum source into an alkaline solution respectively, and self-assembling into an ordered structure crystal nucleus under the action of a structure directing agent; subsequently adding a surfactant to regulate the growth process of the crystal nucleus, and evaporating the excess water to form a gel system; under the action of microwave, the crystal nucleus rapidly crystallizes to generate a nano-particle product with the structure of Beta zeolite; finally, the nano Beta zeolite is obtained through post-treatment such as centrifugation, filtration, washing, drying, grinding, and calcination.

[0013] It should be noted that the term "Beta" in the Beta zeolite involved in the present invention can be translated as the Greek letter "β" or the Chinese "Beta", etc.

[0014] The method for rapidly preparing nano Beta zeolite by microwave synthesis provided by the present invention comprises the following steps:

[0015] S1. Synthesize the initial gel: Mix an aluminum source, a silicon source, an alkali, a structure directing agent, a surfactant and deionized water. The silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, the template agent is calculated as TEA + calculated, the alkali metal source is calculated as A2O, the surfactant is calculated as R, and their original molar ratio is SiO2:Al2O3:TEA + :A2O:R:H2O = 40 - 50:1:15 - 30:2 - 5:2.5 - 8:200 - 500;

[0016] S2. Prepare a concentrated gel system: Heat and stir the initial gel obtained in step S1 to evaporate water, and control H2O / SiO2 to be 5 - 10;

[0017] S3. Microwave heating crystallization: Transfer the concentrated gel into a microwave reaction kettle and seal it, and use microwave to heat it to 150 - 180 °C and keep it for 3 - 6 h for crystallization;

[0018] S4. Centrifuge the crystallization product, wash it several times and then dry it to obtain a white solid product. Grind it and calcine it at 600 - 700 °C for 6 - 10 h to obtain the nano Beta zeolite product.

[0019] Preferably, the silicon source is one or more of fumed silica, tetraethyl orthosilicate, silica sol, precipitated silica, water glass, chromatography silica gel or coarse pore silica gel.

[0020] Preferably, the aluminum source is one or more of sodium aluminate, aluminum powder, pseudo-boehmite, aluminum sulfate, aluminum chloride, aluminum nitrate or aluminum acetate.

[0021] Preferably, the alkali is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate.

[0022] Preferably, the structure directing agent is one or more of tetraethylammonium hydroxide, tetraethylammonium bromide, or tetraethylammonium chloride.

[0023] Preferably, the surfactant is one or more of L-lysine or citric acid, and the molar ratio of silicon source to surfactant is 5 to 20.

[0024] Preferably, in the microwave heating crystallization step, the microwave heating temperature is 150-180°C and the crystallization time is 3-6 hours.

[0025] Preferably, the particle size of the obtained nano-Beta molecular sieve is 30-80 nm.

[0026] Preferably, by adjusting the raw material ratio and crystallization conditions, the rapid synthesis of nano-Beta molecular sieves is achieved, and hydrogen-form, ammonium-form, or Beta molecular sieves loaded with other metal cations are obtained through ion exchange technology.

[0027] Preferably, the centrifugation step is performed at a speed of 12,000-15,000 rpm and a centrifugation time of 10-30 min.

[0028] Compared with related technologies, the method for rapidly preparing nano-Beta molecular sieves using microwave synthesis provided by this invention has the following advantages:

[0029] This invention utilizes a microwave synthesis method to rapidly prepare nano-Beta molecular sieves. Microwave energy directly acts on reactant molecules, promoting molecular motion and collisions. Compared with the traditional hydrothermal method, microwave heating can achieve rapid and uniform heating, accelerate the formation and growth of crystal nuclei, and significantly shorten the crystallization time. This not only improves the synthesis efficiency but also helps to form a more uniform crystal structure.

[0030] This invention uses fumed silica, tetraethyl orthosilicate, or silica sol as the silicon source, sodium aluminate or aluminum powder as the aluminum source, tetraethylammonium hydroxide or tetraethylammonium bromide as the structure directing agent, and L-lysine or citric acid as the surfactant. These surfactants can interact with the crystal nuclei during the crystal nucleation stage, adsorb onto the crystal surface, and limit the further growth of the crystal, thereby achieving control over the particle size of nano-Beta molecular sieves.

[0031] The Beta molecular sieves synthesized by this method have a particle size of 30-80 nm, high specific surface area and abundant pore structure, exhibiting excellent catalytic performance and adsorption characteristics. Through the synergistic effect of microwave heating and surfactant, this method significantly shortens the synthesis time and achieves precise control of crystal size, providing a new technical approach for the large-scale production of high-performance nano Beta molecular sieves. Attached Figure Description

[0032] Figure 1Transmission electron microscope images of molecular sieve particles prepared in various embodiments and comparative examples of the present invention;

[0033] Figure 2 The XRD diffraction patterns and standard XRD data of the BEA (Beta molecular sieve structure code) structures of the various embodiments and comparative examples of the present invention are shown below.

[0034] Figure 3 The graph shows the nitrogen adsorption-desorption curves of the molecular sieve particles prepared in Example 1 of this invention. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0036] 1. Example 1

[0037] (1) At room temperature, 10.42 g of tetraethylammonium silicate (99%) was added to 16.2 g of tetraethylammonium hydroxide aqueous solution (25 wt%) and stirred until homogeneous. 0.22 g of sodium hydroxide (≥96%) was added and stirred to dissolve, followed by 5.4 g of deionized water. The solution was heated to 50 °C and stirred at a constant temperature for 6–10 h until the tetraethylammonium silicate was completely hydrolyzed, yielding synthetic solution A.

[0038] (2) Dissolve 0.205g of sodium aluminate (reagent grade) in 8mL of deionized water to obtain synthesis solution B.

[0039] (3) Dissolve 0.731 g L-lysine (98%) in 4.6 mL of deionized water to obtain synthesis solution C.

[0040] (4) At 50°C, the synthesis solutions B and C were slowly added dropwise to the synthesis solution A and stirred for 1 hour to obtain the initial synthesis gel.

[0041] (5) Place the initial synthetic gel under a heating lamp, stir slowly and evaporate the water until the mass decreases by 24g to obtain the synthetic concentrated gel.

[0042] (6) The synthesized concentrated gel was transferred to a microwave reactor and heated to 180°C by microwave. After reacting for 3 hours, a white liquid product was obtained.

[0043] (7) The white liquid product was separated by centrifugation at 14,000 rpm to obtain the solid product. The product was washed repeatedly by centrifugation with deionized water and ethanol until the washing solution was close to neutral.

[0044] (8) The product was dried in a 90°C oven overnight to obtain molecular sieve powder.

[0045] (9) The molecular sieve powder was ground and placed in a muffle furnace, heated to 650°C at a heating rate of 2°C / min, calcined for 6 hours, and then naturally cooled to obtain nano-Beta molecular sieves. The sample particle size was approximately 30 nm, and the BET specific surface area was 767.1 m². 2 / g, far exceeding that of ordinary commercial Beta molecular sieves (approximately 500m³ / g). 2 / g).

[0046] 2. Example 2

[0047] In Example 1, the amount of L-lysine added in step (3) was changed to 1.462 g, while the other steps remained unchanged. After crystallization, a gel-like product was obtained. After centrifugation, washing, drying, grinding, and calcination, nano-Beta molecular sieves were obtained with a sample particle size of about 80 nm.

[0048] 3. Comparative Example 1

[0049] In Example 1, L-lysine was not added, other conditions remained unchanged, and synthesis solution C was not added. The synthesized concentrated gel was crystallized at 180°C under microwave heating for 3 hours to obtain a white liquid product. After centrifugation, washing, drying, grinding, and calcination, Beta molecular sieves were obtained with a sample particle size of approximately 200 nm.

[0050] 4. Comparative Example 2

[0051] In Example 1, L-lysine was not added, microwave heating was not used, other conditions remained unchanged, and synthesis solution C was not added. The concentrated gel was transferred to a reaction vessel, placed in a high-temperature oven, heated to 180°C, and crystallized for 3 hours to obtain a gel-like product. XRD analysis showed that the synthesis solution failed to crystallize successfully. After adjusting the heating temperature to 150°C and crystallizing for 48 hours, a white liquid product was obtained. After centrifugation, washing, drying, grinding, and calcination, Beta molecular sieves were obtained. The particle size of the obtained Beta molecular sieve sample was approximately 200 nm.

[0052] 5. Example 3

[0053] (1) Slowly add 3g of fumed silica to 14.336g of tetraethylammonium hydroxide aqueous solution (25wt%), place it in a water bath at 75℃ and heat and stir for 6-10h until the fumed silica reacts completely to obtain synthetic solution A.

[0054] (2) Add 0.179g sodium aluminate (reagent grade) and 0.13g sodium hydroxide (≥96%) to 8g deionized water respectively, stir to dissolve, and obtain synthesis solution B.

[0055] (3) Dissolve 0.96g of citric acid in 10mL of deionized water to obtain synthesis solution C.

[0056] (4) Under the condition of 75℃ water bath, the synthesis solutions B and C were slowly added dropwise to the synthesis solution A and stirred for 1 hour to obtain the initial synthesis gel.

[0057] (5) Place the initial synthetic gel under a heating lamp, stir slowly and evaporate the water until the mass decreases by 20g to obtain the synthetic concentrated gel.

[0058] (6) The synthesized concentrated gel was transferred to a microwave reactor and heated to 160°C by microwave. After reacting for 6 hours, a white liquid product was obtained.

[0059] (7) The subsequent steps are the same as in Example 1, and nano-Beta molecular sieves with a particle size of about 50 nm are obtained.

[0060] 6. Example 4

[0061] (1) Dissolve 10.24g of tetraethylammonium bromide (98%) in 21.51g of deionized water, then slowly add 3g of fumed silica, heat and stir in a 75°C water bath for 6-10 hours until the fumed silica has completely reacted to obtain synthetic solution A.

[0062] (2) Dissolve 0.066g sodium hydroxide (≥96%) in 8mL of deionized water, then add 0.059g aluminum powder, and stir at room temperature until the aluminum powder reacts fully to obtain synthetic solution B.

[0063] (3) The subsequent steps are the same as in Example 3, and nano-Beta molecular sieves with a particle size of about 80 nm are obtained.

[0064] 7. Comparative Example 3

[0065] In Example 4, without using microwave heating, and with other conditions unchanged, the synthesized concentrated gel was transferred to a reaction vessel, placed in a high-temperature oven and heated to 150°C for 48 hours to obtain a white liquid product. After centrifugation, washing, drying, grinding and calcination, nano-Beta molecular sieves were obtained with a sample particle size of approximately 100 nm.

[0066] In conjunction with the above embodiments and comparative examples, and referring to... Figure 1-3 , Figure 1 These are transmission electron microscope images of molecular sieve particles prepared in various embodiments and comparative examples of the present invention, mainly showing the particle size differences between different products.

[0067] Figure 2 The XRD diffraction patterns and standard XRD data of the BEA (Beta molecular sieve structure code) structures of the various embodiments and comparative examples of the present invention are shown to indicate that all prepared products are of the Beta molecular sieve structure.

[0068] Figure 3The graph shows the nitrogen adsorption-desorption curve of the molecular sieve particles prepared in Example 1 of this invention. Based on the curve data, the BET surface area is calculated to be 767.1 m². 2 / g, which is much higher than the BET surface area data of ordinary Beta molecular sieves in the literature (approximately 500m²). 2 / g), or you can supplement the nitrogen adsorption-desorption curve of ordinary Beta molecular sieve as a comparison.

[0069] Compared with related technologies, the method for rapidly preparing nano-Beta molecular sieves using microwave synthesis provided by this invention has the following advantages:

[0070] This method significantly shortens the synthesis time through microwave heating technology, solving the key problem of long synthesis cycles in traditional hydrothermal methods and significantly improving production efficiency. Secondly, microwave heating achieves rapid and uniform heating, effectively overcoming the product quality fluctuations caused by uneven temperature distribution in traditional methods, and improving product uniformity and synthesis stability.

[0071] By precisely controlling the synthesis parameters, this method can regulate the crystal size and morphology of nano-Beta molecular sieves, obtaining larger specific surface areas and optimized pore structures, thereby significantly improving the catalytic performance of the molecular sieves. This feature provides new possibilities for improving the efficiency of various catalytic reactions. Furthermore, this method aligns with green chemistry principles, significantly reducing chemical waste emissions and energy consumption, and providing a new pathway for environmentally friendly production.

[0072] The method of this invention is simple, easy to implement, low-cost, and highly scalable, laying the foundation for the large-scale industrial production of nano-Beta molecular sieves. This not only meets the demand for high-performance molecular sieves in traditional fields such as petrochemicals and fine chemicals, but also opens up broad prospects for applications in emerging fields such as new energy and environmental protection. In summary, this invention brings innovation to the preparation technology of nano-Beta molecular sieves and has significant practical and long-term value for promoting the development of related industries.

[0073] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for rapidly preparing nano-Beta molecular sieves using microwave synthesis, characterized in that, Includes the following steps: S1. Synthesis of initial gel: Mix aluminum source, silicon source, alkali, structure directing agent, surfactant, and deionized water. The silicon source is calculated as SiO2, the aluminum source as Al2O3, and the template agent as TEA. + The alkali metal source is represented by A2O, and the surfactant is represented by R. The original molar ratio is SiO2: Al2O3: TEA. + : A2O: R: H2O = 40~50: 1: 15~30: 2~5: 2.5~8: 200~500; S2. Preparation of concentrated gel system: The initial gel obtained in step S1 is heated and stirred to evaporate water, and the H2O / SiO2 ratio is controlled to be 5~10. S3. Microwave heating crystallization: Transfer the concentrated colloid into a microwave reactor and seal it. Use microwave heating to 150-180℃ and maintain it for 3-6 hours to crystallize. S4. Centrifuge the crystallized product, wash it several times and dry it to obtain a white solid product. Grind it and calcine it at 600-700℃ for 6-10 hours to obtain the nano Beta molecular sieve product. The surfactant is one or more of L-lysine or citric acid, and the molar ratio of silicon source to surfactant is 5 to 20.

2. The method for rapidly preparing nano-Beta molecular sieves using microwave synthesis as described in claim 1, characterized in that, The silicon source is one or more of fumed silica, tetraethyl orthosilicate, silica sol, silica gel, water glass, chromatography silica gel, or coarse-pore silica gel.

3. The method for rapidly preparing nano-Beta molecular sieves using microwave synthesis as described in claim 1, characterized in that, The aluminum source is one or more of sodium aluminate, aluminum powder, boehmite, aluminum sulfate, aluminum chloride, aluminum nitrate, or aluminum acetate.

4. The method for rapidly preparing nano-Beta molecular sieves using microwave synthesis as described in claim 1, characterized in that, The alkali is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, or potassium carbonate.

5. The method for rapidly preparing nano-Beta molecular sieves using microwave synthesis as described in claim 1, characterized in that, The structure directing agent is one or more of tetraethylammonium hydroxide, tetraethylammonium bromide, or tetraethylammonium chloride.

6. The method for rapidly preparing nano-Beta molecular sieves using microwave synthesis as described in claim 1, characterized in that, The resulting nano-Beta molecular sieves have a particle size of 50-80 nm.

7. The method for rapidly preparing nano-Beta molecular sieves using microwave synthesis as described in claim 1, characterized in that, By adjusting the raw material ratio and crystallization conditions, the rapid synthesis of nano-Beta molecular sieves can be achieved. Hydrogen-form, ammonium-form, or Beta molecular sieves loaded with other metal cations can be obtained through ion exchange technology.

8. The method for rapidly preparing nano-Beta molecular sieves using microwave synthesis as described in claim 1, characterized in that, The centrifugation step is performed at a speed of 12,000-15,000 rpm for a time of 10-30 minutes.

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