FAU molecular sieve and preparation method thereof
By directly crystallizing FAU molecular sieves from the reaction mixture, and using a target cation alkaline solution and a seed crystal directing agent, the lengthy and environmental problems of traditional synthesis processes are solved, achieving efficient and environmentally friendly preparation of FAU molecular sieves and improving product purity and performance consistency.
Patent Information
- Application Number
- CN202511716524.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-21
- Publication Date
- 2026-01-06
AI Technical Summary
The existing FAU molecular sieve synthesis process is lengthy, energy-intensive, environmentally unfriendly, and has poor product uniformity, especially affecting performance consistency when ion exchange is incomplete.
FAU molecular sieves that are not Na or K cations can be prepared by direct crystallization from the reaction mixture. By pre-constructing the microenvironment of the target product and using the alkaline solution of the target cation and FAU molecular sieve seed crystals as directing agents, the ion exchange step can be avoided, and the target cation-type FAU molecular sieve can be directly generated.
It simplifies the process, reduces energy consumption and costs, reduces wastewater discharge, and improves product purity and performance uniformity.
Smart Images
Figure CN121269746A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of inorganic microporous material synthesis technology, and relates to an FAU molecular sieve and its preparation method. Background Technology
[0002] FAU molecular sieves are functional materials with regular pore structures, high specific surface area, and good ion exchange performance, and are widely used in catalysis, adsorption separation, and ion conductors. Currently, the synthesis of these crystals typically employs hydrothermal synthesis, followed by a lengthy ion exchange step to replace sodium ions with target ions (such as Li). + Ca 2+ After processing (e.g., washing, drying, and calcination), the product still requires post-processing steps. This traditional method has drawbacks such as a long process flow, high time and energy consumption, large amounts of wastewater generation, and the potential impact on product performance uniformity due to incomplete ion exchange.
[0003] For example, the preparation process of copper-supported FAU molecular sieves disclosed in patent CN115672265A clearly embodies this traditional method: first, sodium-type FAU molecular sieves are synthesized, and then cation exchange is performed using a copper salt solution. While this approach is technically mature, it has significant drawbacks: firstly, the process is lengthy, with multiple exchanges and washings leading to low production efficiency and high energy consumption; secondly, it has poor environmental compatibility, as the ion exchange process generates large amounts of saline wastewater, increasing subsequent treatment costs and environmental pressure; and thirdly, product uniformity is difficult to guarantee, especially for Ca... 2+ Highly charged ions with slow diffusion rates are prone to forming concentration gradients within the crystal due to incomplete exchange, which directly affects their performance consistency in adsorption or catalytic applications.
[0004] To overcome these limitations, researchers have conducted numerous explorations, but none have fundamentally broken through the technological bottlenecks. For example, patent CN117923509A demonstrates a focus on resource recycling by recycling the mother liquor from FAU molecular sieve crystallization to synthesize type A molecular sieves, but its core is still based on a sodium-based synthesis system, failing to break free from dependence on sodium templates and essentially remaining within the exchange logic.
[0005] Therefore, developing a synthesis method that simplifies the process, saves energy and is environmentally friendly, and can directly obtain high-purity target ionic crystals has become an urgent problem to be solved in this field. Summary of the Invention
[0006] To address the shortcomings of existing technologies, the present invention aims to provide a FAU molecular sieve and its preparation method. The preparation method provided by the present invention eliminates the need for a traditional ion exchange step, enabling the direct crystallization of non-Na,K cation-dependent FAU molecular sieves from the reaction mixture, overcoming the defects of existing technologies that rely on ion exchange steps. Furthermore, this method features a short process flow, low cost, environmental friendliness, and high product purity.
[0007] To achieve this objective, the present invention adopts the following technical solution:
[0008] In a first aspect, the present invention provides a method for preparing FAU molecular sieves, wherein the cations in the FAU molecular sieves do not include Na. + and / or K + The preparation method includes: sequentially mixing an aluminum source, an alkaline solution of the target cation, an additive, and a silicon source to obtain a reaction gel, and then sequentially aging and crystallizing the reaction gel to obtain the FAU molecular sieve; the additive is a dispersion of the target FAU molecular sieve.
[0009] In this invention, a complete microenvironment for the target product is pre-constructed by mixing an alkaline solution of an aluminum source and a target cation. The alkaline solution of the target cation not only provides the necessary alkaline conditions for crystallization but also serves as the sole charge balance source in the system. The pre-dispersed target FAU molecular sieve, with its surface already covered with target cations and possessing a complete FAU structure, acts as a seed crystal and a guiding agent, significantly reducing the nucleation energy barrier as an ideal template. During subsequent crystallization, the silicon source is guided to preferentially grow epitaxially on the seed crystal surface. Simultaneously, the target cations in the gel preferentially and in-situ balance the negative charge of the newly formed framework at the growth interface, ensuring that the chemical composition and structure of the seed crystal are perfectly replicated and continued in the newly formed portion. This process forms a self-catalytic virtuous cycle, ultimately generating the target cation-type FAU molecular sieve directly in one step during the crystallization stage, completely bypassing the dependence on sodium / potassium ions and the subsequent cumbersome ion exchange steps of traditional synthesis.
[0010] Furthermore, it must be emphasized that the raw materials must be mixed sequentially in a specific order in this invention. If all of them are mixed directly, the reactants will instantly aggregate and gel in a disorderly manner, triggering a large number of spontaneous nucleations in the bulk solution. This will not only generate impurities and reduce the purity of the product, but will also severely weaken the guiding effect of the target FAU molecular sieve seed crystals, ultimately leading to synthesis failure.
[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.
[0012] Preferably, the aluminum source includes aluminum sol.
[0013] Preferably, the mass content of Al2O3 in the aluminum sol is 10wt%~30wt%, for example, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, 27wt%, or 30wt%.
[0014] Preferably, the alkaline solution of the target cation includes any one or a combination of at least two of lithium hydroxide, calcium hydroxide, barium hydroxide, or strontium hydroxide.
[0015] In this invention, the hydroxides of the aforementioned metal ions are soluble in water and are moderately strong bases. They can not only provide the alkaline environment required for the reaction, but also serve as a direct source of the target ions, avoiding subsequent ion exchange steps. However, if hydroxides of other metal ions are used, on the one hand, their alkalinity is weak or they are amphoteric hydroxides, which cannot provide the required alkaline environment; on the other hand, their solubility in water may be poor, and both of these situations are not conducive to the reaction. In addition, other types of alkali metals have radioactivity and toxicity issues, which are not conducive to their application.
[0016] Preferably, the concentration of the alkaline solution is 1 mol / L to 2 mol / L, such as 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L or 2 mol / L.
[0017] Preferably, in the auxiliary agent, the mass fraction of the target FAU molecular sieve in the reaction gel is 1wt‰ to 5wt‰, for example, 1wt‰, 1.5wt‰, 2wt‰, 2.5wt‰, 3wt‰, 3.5wt‰, 4wt‰, 4.5wt‰ or 5wt‰, etc.
[0018] In this invention, the amount of additives added affects the purity of the product. By controlling it within the aforementioned preferred range, it is more beneficial to achieve a directional, efficient, and pure crystallization process. Too little additive will result in insufficient guiding effect and failure to suppress impurities; too much additive may lead to excessively small crystals or agglomeration.
[0019] Preferably, the silicon source includes silica sol.
[0020] In this invention, by using aluminum sol and silica sol as aluminum and silicon sources respectively, the introduction of impurity anions can be avoided, thus preventing them from forming precipitates or other impurity phases with the target cations.
[0021] Preferably, the mass content of SiO2 in the silica sol is 20wt%~40wt%, for example, 20wt%, 23wt%, 25wt%, 27wt%, 30wt%, 33wt%, 35wt%, 38wt%, or 40wt%.
[0022] Preferably, in the reactive gel, the molar ratio of SiO2 to Al2O3 is (2~3):1, for example 2:1, 2.2:1, 2.4:1, 2.5:1, 2.6:1, 2.8:1 or 3:1, and the molar ratio of the target cation to SiO2 is (0.2~0.4):1, for example 0.2:1, 0.22:1, 0.25:1, 0.27:1, 0.3:1, 0.32:1, 0.35:1, 0.38:1 or 0.4:1, etc.
[0023] In this invention, the molar ratio of SiO2 to Al2O3 determines the stability of the framework and the number of cation sites within it, while the molar ratio of the target cation to SiO2 ensures preferential nucleation and stable growth of the target FAU framework in a predetermined cation environment by providing the necessary structural guidance and charge balance. By controlling the molar ratios of SiO2 to Al2O3 and the target cation to SiO2 within the aforementioned preferred ranges, their synergy is more conducive to the synthesis of highly crystalline target FAU molecular sieves.
[0024] It should be noted that, in this invention, the reaction gel needs to be strongly alkaline.
[0025] Preferably, the aging temperature is 20℃~30℃, such as 20℃, 22℃, 25℃, 27℃ or 30℃.
[0026] Preferably, the aging time is 2h to 24h, more preferably 4h to 10h, such as 2h, 4h, 5h, 6h, 7h, 8h, 10h, 15h, 20h or 24h.
[0027] Preferably, the crystallization temperature is 80℃~120℃, such as 80℃, 90℃, 100℃, 110℃ or 120℃.
[0028] Preferably, the crystallization time is 1h to 6h, more preferably 2h to 4h, for example 1h, 2h, 3h, 4h, 5h or 6h.
[0029] Preferably, after the crystallization is completed, the product is washed and dried sequentially.
[0030] In this invention, by optimizing the parameters of steps such as aging and crystallization, the particle size, morphology, and crystallinity of the crystals can be effectively controlled. A thorough aging process facilitates the complete hydrolysis, dissolution, and pre-assembly of each component, forming a precursor structure that is more conducive to the growth of the target crystal.
[0031] Preferably, the washing continues until the filtrate is neutral.
[0032] Preferably, the drying temperature is 100℃~120℃, for example 100℃, 105℃, 110℃, 115℃ or 120℃, and the time is 10h~15h, for example 10h, 11h, 12h, 13h, 14h or 15h.
[0033] Understandably, after crystallization, the product needs to be cooled and filtered to obtain a solid product, and then the solid product is washed and dried in sequence.
[0034] In a second aspect, the present invention provides an FAU molecular sieve prepared by the preparation method described in the first aspect.
[0035] Preferably, the crystallinity of the FAU molecular sieve is ≥90%, such as 90%, 91%, 92%, 93%, 94%, 95%, or 96%.
[0036] Preferably, the silica-alumina ratio of the FAU molecular sieve is 1 to 1.5, such as 1, 1.1, 1.2, 1.3, 1.4 or 1.5.
[0037] Preferably, the average particle size of the FAU molecular sieve is 0.5μm to 2μm, such as 0.5μm, 0.8μm, 1μm, 1.2μm, 1.5μm, 1.7μm or 2μm.
[0038] The numerical range described in this invention includes not only the point values listed above, but also any point values within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values included in the range.
[0039] Compared with the prior art, the present invention has the following beneficial effects:
[0040] 1. It eliminates the traditional ion exchange step and its subsequent extensive washing process, significantly shortening the production cycle and reducing energy consumption and costs.
[0041] 2. It reduces the discharge of saline wastewater generated by ion exchange, alleviating environmental pressure.
[0042] 3. Since the target ions directly participate in the nucleation and growth process of the crystal, their distribution in the crystal framework is more uniform, avoiding structural defects or incomplete exchange problems that may be caused by ion exchange, resulting in more uniform and stable product performance. Attached Figure Description
[0043] Figure 1 This is a SEM image of the LiX molecular sieve prepared in Example 1.
[0044] Figure 2 This is the XRD pattern of the LiX molecular sieve prepared in Example 1. Detailed Implementation
[0045] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.
[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.
[0047] Example 1
[0048] This embodiment provides a method for preparing LiX molecular sieves, as detailed below:
[0049] 1. Mix 128g of aluminum sol (Al2O3 content 20wt%) with 67mL of lithium hydroxide solution (1.5mol / L) and stir at 500rpm for 30min;
[0050] 2. Add LiX molecular sieve dispersion as an auxiliary agent to the above mixture (solvent is 10 mL of water, mass of LiX molecular sieve is 0.5 g), and continue stirring for 1 h until completely dissolved;
[0051] 3. Slowly add 100g of silica sol (SiO2 content is 30wt%), stir vigorously for 0.5h to form a uniform reaction gel (molar composition: SiO2 / Al2O3=2, LiOH / SiO2=0.2, LiX molecular sieve content is 1.6wt‰).
[0052] 4. Seal the reaction gel and allow it to age at room temperature for 6 hours;
[0053] 5. Transfer the aged gel into a stainless steel reactor lined with polytetrafluoroethylene and crystallize it in an oven at 100°C for 3 hours.
[0054] 6. After the reaction is complete, the product is cooled to room temperature, filtered, washed with deionized water until the filtrate is neutral, and dried at 110°C for 12 hours to obtain a white powder product.
[0055] Example 2
[0056] This embodiment provides a method for preparing LiX molecular sieves, as detailed below:
[0057] 1. Mix 170g of aluminum sol (Al2O3 content 10wt%) with 100mL of lithium hydroxide solution (1mol / L) and stir at 500rpm for 30min;
[0058] 2. Add the LiX molecular sieve dispersion to the above mixture as an auxiliary agent (the solvent is 10 mL of water, and the mass of LiX molecular sieve is 1.1 g), and continue stirring for 1 h until completely dissolved;
[0059] 3. Slowly add 100g of silica sol (SiO2 content is 20wt%), stir vigorously for 0.5h to form a uniform reaction gel (molar composition: SiO2 / Al2O3=2, LiOH / SiO2=0.3, LiX molecular sieve content is 3wt‰).
[0060] 4. Seal the reaction gel and allow it to age at room temperature for 4 hours;
[0061] 5. Transfer the aged gel into a stainless steel reactor lined with polytetrafluoroethylene and crystallize it in an oven at 100°C for 2 hours.
[0062] 6. After the reaction is complete, the product is cooled to room temperature, filtered, washed with deionized water until the filtrate is neutral, and dried at 100°C for 15 hours to obtain a white powder product.
[0063] Example 3
[0064] This embodiment provides a method for preparing LiX molecular sieves, as detailed below:
[0065] 1. Mix 150g of aluminum sol (30wt% Al2O3 content) with 133mL of lithium hydroxide solution (2mol / L) and stir at 500rpm for 30min;
[0066] 2. Add the LiX molecular sieve dispersion (solvent is 10 mL of water, mass of LiX molecular sieve is 2 g) to the above mixture, and continue stirring for 1 h until completely dissolved;
[0067] 3. Slowly add 100g of silica sol (SiO2 content is 40wt%), stir vigorously for 0.5h to form a uniform reaction gel (molar composition: SiO2 / Al2O3=1.5, LiOH / SiO2=0.4, additive ratio is 5wt‰).
[0068] 4. Seal the reaction gel and allow it to age at room temperature for 8 hours;
[0069] 5. Transfer the aged gel into a stainless steel reactor lined with polytetrafluoroethylene and crystallize it in an oven at 100°C for 4 hours.
[0070] 6. After the reaction is complete, the product is cooled to room temperature, filtered, washed with deionized water until the filtrate is neutral, and dried at 120°C for 10 hours to obtain a white powder product.
[0071] Example 4
[0072] The difference between this embodiment and Embodiment 1 is that lithium hydroxide in step 1 is replaced with an equimolar amount of calcium hydroxide, aging in step 4 is carried out for 10 hours, and crystallization in step 5 is carried out for 4 hours.
[0073] The remaining preparation methods and parameters are consistent with those in Example 1.
[0074] Example 5
[0075] The difference between this embodiment and Embodiment 1 is that lithium hydroxide in step 1 is replaced with an equimolar amount of barium hydroxide;
[0076] The remaining preparation methods and parameters are consistent with those in Example 1.
[0077] Example 6
[0078] The difference between this embodiment and Embodiment 1 is that lithium hydroxide in step 1 is replaced with an equimolar amount of strontium hydroxide;
[0079] The remaining preparation methods and parameters are consistent with those in Example 1.
[0080] Example 7
[0081] The difference between this embodiment and Embodiment 1 is that lithium hydroxide in step 1 is replaced with an equimolar amount of cerium hydroxide;
[0082] The remaining preparation methods and parameters are consistent with those in Example 1.
[0083] Example 8
[0084] The difference between this embodiment and Embodiment 1 is that the mass of LiX in the LiX molecular sieve dispersion added in step 2 is 0.2g.
[0085] The remaining preparation methods and parameters are consistent with those in Example 1.
[0086] Example 9
[0087] The difference between this embodiment and embodiment 1 is that the mass of LiX in the LiX molecular sieve dispersion added in step 2 is 2g.
[0088] The remaining preparation methods and parameters are consistent with those in Example 1.
[0089] Example 10
[0090] The difference between this embodiment and Embodiment 1 is that the aluminum source in step 1 is lithium sulfate;
[0091] The remaining preparation methods and parameters are consistent with those in Example 1.
[0092] Example 11
[0093] The difference between this embodiment and Embodiment 1 is that 40 mL of lithium hydroxide is added in step 1;
[0094] The remaining preparation methods and parameters are consistent with those in Example 1.
[0095] Example 12
[0096] The difference between this embodiment and Embodiment 1 is that in step 4, the device is left to stand for aging for 10 minutes.
[0097] The remaining preparation methods and parameters are consistent with those in Example 1.
[0098] Comparative Example 1
[0099] The difference between this embodiment and Embodiment 1 is that step 2 is omitted;
[0100] The remaining preparation methods and parameters are consistent with those in Example 1.
[0101] Comparative Example 2
[0102] The difference between this embodiment and Embodiment 1 is that steps 1-3 are changed to: mixing all the aluminum sol, lithium hydroxide solution, LiX molecular sieve dispersion, and silica sol together at once;
[0103] The remaining preparation methods and parameters are consistent with those in Example 1.
[0104] Performance testing
[0105] The LiX molecular sieve prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown.
[0106] XRD tests were performed on the FAU molecular sieves prepared in Examples 1-12 and Comparative Examples 1-2. The relevant test results are as follows: Figure 2 As shown in Table 1.
[0107] Table 1
[0108]
[0109] Depend on Figure 1 It can be seen that the product prepared by the method provided by this invention has regular crystals, uniform particle size distribution, and an average particle size of approximately 0.6 μm. Figure 2It can be seen that the product prepared in Example 1 is a pure phase crystalline LiX, and its diffraction pattern matches the standard card.
[0110] As shown in Table 1, the FAU molecular sieve with the corresponding cation was successfully prepared using the preparation method provided by the present invention. The direct synthesis method provided by the present invention simplifies the process and effectively improves the overall performance of the product. The poor crystallinity of Comparative Example 1 and Comparative Example 2 is because the target FAU molecular sieve was not added as an auxiliary agent in Comparative Example 1. Therefore, the product prepared by Comparative Example 1 is amorphous silicate and aluminum oxide. In contrast, the product prepared by Comparative Example 2 was not mixed in the corresponding order, resulting in poor crystallinity and the presence of various impurities.
[0111] Furthermore, a comparison of the data from Example 1 and Examples 7-12 in Table 1 shows that in this invention, the types of alkali solution and aluminum source, the amount of target molecular sieve and alkali solution added, and the aging time all affect the crystallinity of the product. By controlling these within the preferred range of this invention, it is more beneficial to obtain a product with high crystallinity.
[0112] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.
Claims
1. A process for the preparation of a FAU molecular sieve characterized by, The cations in the FAU molecular sieve do not include Na + and / or K + The preparation method comprises the following steps: sequentially mixing an aluminum source, an alkali solution of target cations, an auxiliary agent and a silicon source to obtain a reaction gel, and then sequentially performing aging and crystallization on the reaction gel to obtain the FAU molecular sieve; the auxiliary agent is a dispersion liquid of the target FAU molecular sieve.
2. The production method according to claim 1, characterized by, The aluminum source comprises an aluminum sol; Preferably, the mass content of Al2O3 in the aluminum sol is 10wt%-30wt%.
3. The production method according to claim 1 or 2, characterized by, The alkali solution of the target cation comprises any one of lithium hydroxide, calcium hydroxide, barium hydroxide or strontium hydroxide or a combination of at least two of them; Preferably, the concentration of the alkali solution is 1mol / L-2mol / L.
4. The production method according to any one of claims 1 to 3, characterized by, In the additive, the mass fraction of the target FAU molecular sieve in the reaction gel is 1wt‰-5wt‰.
5. The method of any one of claims 1-4, wherein, The silicon source comprises a silicon sol; Preferably, the mass content of SiO2 in the silicon sol is 20wt%-40wt%.
6. The method of any one of claims 1-5, wherein, In the reaction gel, the molar ratio of SiO2 to Al2O3 is (2-3):1, and the molar ratio of the target cation to SiO2 is (0.2-0.4):
1.
7. The method of any one of claims 1-6, wherein, The aging temperature is 20°C-30°C; Preferably, the aging time is 2h-24h, and further preferably 4h-10h; Preferably, the crystallization temperature is 80°C-120°C; Preferably, the crystallization time is 1h-6h, and further preferably 2h-4h.
8. The method of any one of claims 1-7, wherein, After the crystallization is completed, the product is sequentially washed and dried; Preferably, the washing is performed until the filtrate is neutral; Preferably, the drying temperature is 100°C-120°C, and the time is 10h-15h.
9. A FAU molecular sieve prepared by the preparation method of any one of claims 1-8.
10. The FAU molecular sieve of Claim 9, wherein, The crystallinity of the FAU molecular sieve is ≥90%; Preferably, the silicon-aluminum ratio of the FAU molecular sieve is 1-1.5; Preferably, the average particle size of the FAU molecular sieve is 0.5μm-2μm.