Method for preparing aluminum-modulated MFI type zeolite molecular sieve by using acidic fluorine medium, product and application

Abstract

The invention discloses a method for preparing an aluminum-modulated MFI type zeolite molecular sieve from an acidic fluorine medium, a product and application, and belongs to the technical field of zeolite molecular sieve materials.The method comprises the steps that a silicon source, roasted nanoscale or micron-sized SAPO-34, a template agent and deionized water are mixed, and a mixed solution A is obtained; adding a solid fluorine source and a hydrofluoric acid aqueous solution with the concentration of 30-50wt.% into the mixed solution A to obtain a mixed solution B; transferring the mixed solution B into a closed stainless steel reaction kettle with a polytetrafluoroethylene lining, and carrying out hydrothermal reaction at 100-200 DEG C for 10-40 days; and after the reaction is finished, centrifuging, washing to be neutral, and drying to obtain the aluminum-modulated MFI type zeolite molecular sieve. Controllable adjustment of the silica-alumina ratio of the zeolite molecular sieve in the acidic fluorine medium is realized. By simply adjusting the adding amount of SAPO-34, the content of aluminum introduced into a framework can be flexibly regulated and controlled, the limitation that the silica-alumina ratio is too high in traditional fluorine medium synthesis is broken through, and the diversified requirements of different acid catalytic reactions for the acid site density can be met.

Description

Technical Field

[0001] This invention relates to the field of zeolite molecular sieve materials technology, specifically to methods, products, and applications for preparing aluminum modulated MFI type zeolite molecular sieves using acidic fluorine media. Background Technology

[0002] Zeolite molecular sieves are a class of aluminosilicate crystal materials with a regular microporous structure. Due to their high specific surface area, tunable acidity, and excellent thermal stability, they have been widely used in catalysis, adsorption, and separation. In acid-catalyzed reactions, their acidic sites mainly originate from the four-coordinated aluminum atoms in the framework.

[0003] To obtain zeolite molecular sieves with low defects and high hydrophobicity, existing processes generally use fluorine-containing systems as mineralizing agents, such as hydrofluoric acid or ammonium fluoride commonly used in the synthesis of MFI structures. However, this system has the following technical contradictions: Fluoride ions, while promoting crystal growth and reducing defects, will react with Al in the system. 3+ Rapid complexation to form AlF x Precipitation, typically AlF3, is a complex precipitation that is almost irreversible, preventing a large amount of aluminum from entering the framework. This directly results in a high silicon-to-aluminum ratio (usually >100) in the product, insufficient acid site density, and difficulty in meeting the high acid site requirements of reactions such as alkylation and cracking.

[0004] Furthermore, existing technologies commonly employ amorphous aluminum sources such as boehmite and aluminum sulfate. These aluminum sources have extremely low solubility in acidic fluorine media, further exacerbating the difficulty of aluminum entering the framework. As a result, the silicon-to-aluminum ratio remains too high, and the density of acidic sites is limited.

[0005] Therefore, there is an urgent need to develop a method for directly synthesizing low silica-to-alumina ratio zeolite molecular sieves in acidic fluorine media, while maintaining the low defect and high crystallinity characteristics imparted by fluorine media synthesis, so as to achieve a breakthrough in the performance of solid acid catalysts. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a method, product and application for preparing aluminum modulated MFI type zeolite molecular sieves using acidic fluorine media.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing aluminum-modulated MFI type zeolite molecular sieves using acidic fluorine media includes the following steps: S1: Mix silicon source, calcined nano- or micro-sized SAPO-34, template agent and deionized water, and stir at room temperature for 2-10 hours to obtain mixture A; S2: Add a solid fluoride source and a 30-50 wt.% hydrofluoric acid aqueous solution to mixture A, adjust the pH to 2-3, and continue stirring at room temperature for 0.5-1 h to obtain mixture B; S3: Transfer the mixture B into a closed stainless steel reactor lined with polytetrafluoroethylene and hydrothermally react at 100-200℃ for 10-40 days. S4: After the reaction is complete, the aluminum-modulated MFI type zeolite molecular sieve is obtained by centrifugation, washing until neutral, and drying. The molar ratios of the components, calculated as oxides, are as follows: SiO2:Al2O3:Solid fluorine source:Template agent:H2O:HF=1:0-0.05:0.1-0.2:0.1-0.5:10-100:0.2-1.0; The proportion of Al2O3 is controlled by the amount of SAPO-34 added (0 when SAPO-34 is not added, corresponding to pure silicon MFI molecular sieve).

[0008] Furthermore, the silicon source is one of silica sol, tetraethyl orthosilicate, silica, or silicic acid.

[0009] Furthermore, the solid fluorine source is one of ammonium fluoride, sodium fluoride, or potassium fluoride.

[0010] Furthermore, the template agent is one of tetramethylammonium bromide, tetramethylammonium chloride, tetraethylammonium bromide, tetraethylammonium chloride, tetrapropylammonium bromide, tetrapropylammonium chloride, tetrabutylammonium bromide, or tetrabutylammonium chloride.

[0011] Furthermore, the amount of SAPO-34 added, based on the molar ratio of Al2O3 to SiO2 of 0–0.05, specifically represents 4.17–33.3% of the mass of SiO2.

[0012] An aluminum-modulated MFI type zeolite molecular sieve, prepared by any of the methods described above, has a silicon-to-aluminum ratio of 10-∞ and a crystal size of 14-22 μm.

[0013] Furthermore, the X-ray diffraction pattern of the molecular sieve is consistent with the typical characteristic diffraction peaks of MFI-type zeolite molecular sieves.

[0014] An application of the aforementioned aluminum-modulated MFI type zeolite molecular sieve in acid-catalyzed reactions, wherein the acid-catalyzed reaction is an alkylation reaction or a cracking reaction.

[0015] Compared with the prior art, the beneficial effects of this invention are as follows: 1. This invention effectively solves the technical problem of introducing aluminum into the framework of zeolite molecular sieves in acidic fluorine media. By using crystalline SAPO-34 as the aluminum source, it can retain some ordered structural fragments containing -Si-O-Al- during the dissolution process, enabling in-situ aluminum supply during molecular sieve crystallization, reducing the complexation and precipitation of aluminum and fluoride ions, promoting the smooth entry of aluminum into the framework to form a four-coordinate structure, thereby significantly improving the acidic site density of the molecular sieve.

[0016] 2. This invention achieves controllable adjustment of the silicon-to-aluminum ratio of zeolite molecular sieves in acidic fluorine media. By simply adjusting the amount of SAPO-34 added, the aluminum content introduced into the framework can be flexibly controlled, breaking through the limitation of a high silicon-to-aluminum ratio in traditional fluorine media synthesis, and meeting the diverse requirements of different acid-catalyzed reactions for acidic site density.

[0017] 3. This invention combines the advantages of fluorine-mediated synthesis with the characteristics of high acidity. While maintaining the low structural defects, high crystallinity, strong hydrophobicity, and excellent thermal / hydrothermal stability imparted by the fluorine medium to the molecular sieve, the acidity is enhanced by effectively introducing aluminum, enabling the product to exhibit superior potential performance in acid-catalyzed reactions.

[0018] 4. The process of this invention is simple and convenient to operate. It adopts a one-pot synthesis method, which does not require complicated steps, has low cost and energy consumption, and is easy to industrialize. It provides a feasible route for the preparation of high-performance zeolite molecular sieves in acidic fluorine media. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0020] Figure 1 X-ray diffraction patterns of MFI-type zeolite molecular sieves prepared at different crystallization times according to the present invention; Figure 2 Scanning electron microscope (SEM) images of MFI-type zeolite molecular sieves prepared at different crystallization times according to the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Example 1: Take 3g of silica sol (containing 0.9g of SiO2, calculated as SiO2), 0.3g of calcined micron-sized SAPO-34 (based on an Al2O3 to SiO2 molar ratio of 0.05, corresponding to 33.3% of SiO2 mass), 1.019g of tetrapropylammonium bromide, and 16.2g of deionized water, mix them, and stir at room temperature for 3 hours to form mixture A. Then add 0.1618g of ammonium fluoride (solid fluoride source to SiO2 molar ratio of 0.2) and 0.23g of 30wt.% hydrofluoric acid aqueous solution (HF to SiO2 molar ratio of 0.2, calculated as (0.23g×30%÷20g / mol)÷(0.9g÷60g / mol)=0.2). Adjust the pH to 2 and continue stirring at room temperature for 0.5 hours to form mixture B. Transfer mixture B into a 50 mL sealed stainless steel reactor lined with polytetrafluoroethylene and hydrothermally react at 160 °C for 20 days. After the reaction is completed, allow it to cool naturally, centrifuge at 10,000 rpm for 5 min, wash with deionized water until neutral, and dry in an oven at 80 °C for 8 hours. The resulting aluminum-modulated MFI type zeolite molecular sieve has a silica-alumina ratio of 18, a crystal size of 14 μm, and an X-ray diffraction pattern consistent with the characteristic peaks of the MFI type.

[0023] Example 2: 3g of silica sol, 0.15g of calcined nano-sized SAPO-34 (Al2O3 to SiO2 molar ratio 0.025), 1.019g of tetrapropylammonium bromide, and 16.2g of deionized water were mixed and stirred at room temperature for 3 hours to form mixture A. 0.13g of sodium fluoride (solid fluoride source to SiO2 molar ratio 0.15) and 0.46g of 40wt.% hydrofluoric acid aqueous solution (HF to SiO2 molar ratio 0.6) were added, and the pH was adjusted to 2.5. Stirring was continued at room temperature for 0.8 hours to form mixture B. The mixture was transferred to a polytetrafluoroethylene-lined reactor and hydrothermally reacted at 100℃ for 40 days. The post-treatment was the same as in Example 1. The resulting molecular sieve had a silica-to-alumina ratio of 37, a crystal size of 18μm, and XRD characteristics consistent with the MFI type.

[0024] Example 3: 3g of silica sol, 0.075g of calcined micron-sized SAPO-34 (Al2O3 to SiO2 molar ratio 0.0125), 1.019g of tetrapropylammonium bromide, and 16.2g of deionized water were mixed and stirred at room temperature for 3 hours to form mixture A. 0.15g of potassium fluoride (solid fluoride source to SiO2 molar ratio 0.1) and 0.76g of 50wt.% hydrofluoric acid aqueous solution (HF to SiO2 molar ratio 1.0, calculated as (0.76g×50%÷20g / mol)÷(0.9g÷60g / mol)=1.0) were added, and the pH was adjusted to 3. The mixture was stirred at room temperature for another hour to form mixture B, which was then transferred to a reactor and hydrothermally reacted at 200℃ for 10 days. The post-treatment was the same as in Example 1. The resulting molecular sieve had a silica-to-alumina ratio of 43, a crystal size of 22μm, and XRD and MFI characteristics consistent.

[0025] Example 4: Take 3g of silica sol, 0.0375g of calcined nano-sized SAPO-34 (Al2O3 to SiO2 molar ratio 0.005), 1.019g of tetrapropylammonium bromide and mix with 16.2g of deionized water; Another control group without SAPO-34 (Al2O3 to SiO2 molar ratio 0) was set up. All mixtures were stirred at room temperature for 3 hours to form mixture A. 0.18 g of ammonium fluoride (solid fluoride source to SiO2 molar ratio 0.15) and 0.3 g of 40 wt.% hydrofluoric acid aqueous solution (HF to SiO2 molar ratio 0.4) were added to adjust the pH to 2.3 and stirring was continued for 0.6 hours to form mixture B. After being transferred to a reactor, the sample was hydrothermally reacted at 160°C for 20 days. The post-treatment was the same as in Example 1. The sample with SAPO-34 added had a silicon-to-aluminum ratio of 63 and a crystal size of 20 μm. The silica-alumina ratio of the sample without SAPO-34 was ∞, and both samples exhibited typical characteristic peaks of MFI-type zeolite molecular sieves in their X-ray diffraction patterns.

[0026] like Figure 1 The X-ray diffraction patterns of the MFI-type zeolite molecular sieves prepared at different crystallization times in Example 1 are shown. It can be seen that the crystallinity of the MFI-type zeolite molecular sieve obtained in Example 1 gradually increases with the extension of crystallization time, and the detection results are consistent with the typical characteristic diffraction peaks of MFI-type zeolite molecular sieves, confirming that it is a high-purity MFI-type zeolite molecular sieve. like Figure 2 The scanning electron microscope images of the MFI-type zeolite molecular sieves prepared at different crystallization times in Example 1 are shown. It can be observed that the prepared MFI-type zeolite molecular sieves are all highly crystalline, with uniform large crystal morphology and crystal size distribution in the range of 14-22 μm.

[0027] It should be noted that in this invention, the silicon source is selected from silica sol, tetraethyl orthosilicate, silica, or silicic acid. All of the above silicon sources can stably provide silicon and can be gradually hydrolyzed or dissolved in an acidic fluorine medium, synergistically assembling with the aluminum species released from SAPO-34 to form the framework structure of an MFI-type zeolite molecular sieve. Whether it is colloidal silica sol, liquid tetraethyl orthosilicate, or solid silica or silicic acid, all can meet the silicon source requirements of the reaction system, ensuring that the final product has typical MFI-type structural characteristics.

[0028] The solid fluorine source is one of ammonium fluoride, sodium fluoride, or potassium fluoride. These fluorine sources release fluoride ions under acidic conditions, which, together with hydrofluoric acid, construct a high fluorine-to-silicon ratio synthesis environment. On the one hand, fluoride ions can participate in the structure guidance during the molecular sieve crystallization process, reducing framework defects; on the other hand, they synergistically maintain the system pH at 2-3 with hydrofluoric acid, preventing excessive complexation of aluminum ions to form AlFx precipitates, and ensuring that the aluminum released from SAPO-34 can smoothly enter the molecular sieve framework. Experiments show that high-crystallinity aluminum-modulated MFI-type zeolite molecular sieves can be prepared using any of the above solid fluorine sources.

[0029] Template agents include tetramethylammonium bromide, tetramethylammonium chloride, tetraethylammonium bromide, tetraethylammonium chloride, tetrapropylammonium bromide, tetrapropylammonium chloride, tetrabutylammonium bromide, or tetrabutylammonium chloride. The cations of these quaternary ammonium salt template agents can guide the formation of micropores in MFI-type zeolite molecular sieves through steric hindrance. The alkyl chain length matches the pore size of the MFI-type structure, ensuring that the product has an ordered microporous structure. Regardless of the template agent used, the controllable synthesis of MFI-type molecular sieves can be achieved by adjusting its dosage (0.1-0.5 molar ratio with SiO2).

[0030] Those skilled in the art can select appropriate types from the above-mentioned silicon source, solid fluorine source and template agent according to actual experimental conditions (such as raw material availability and reaction efficiency requirements), and can repeat the technical solution of the present invention without creative labor, and can obtain aluminum-modulated MFI type zeolite molecular sieves with expected acidity and structural characteristics.

[0031] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing aluminum-modulated MFI type zeolite molecular sieves using acidic fluorine media, characterized in that, Includes the following steps: S1: Mix silicon source, calcined nano- or micro-sized SAPO-34, template agent and deionized water, and stir at room temperature for 2-10 hours to obtain mixture A; S2: Add a solid fluoride source and a 30-50 wt.% hydrofluoric acid aqueous solution to mixture A, adjust the pH to 2-3, and continue stirring at room temperature for 0.5-1 h to obtain mixture B; S3: Transfer the mixture B into a closed stainless steel reactor lined with polytetrafluoroethylene and hydrothermally react at 100-200℃ for 10-40 days. S4: After the reaction is complete, the aluminum-modulated MFI type zeolite molecular sieve is obtained by centrifugation, washing until neutral, and drying. The molar ratios of the components, calculated as oxides, are as follows: SiO2:Al2O3:Solid fluorine source:Template agent:H2O:HF=1:0-0.05:0.1-0.2:0.1-0.5:10-100:0.2-1.0; The proportion of Al2O3 is controlled by the amount of SAPO-34 added (0 when SAPO-34 is not added, corresponding to pure silicon MFI molecular sieve).

2. The method for preparing aluminum-modulated MFI type zeolite molecular sieves using acidic fluorine media according to claim 1, characterized in that, The silicon source is one of silica sol, tetraethyl orthosilicate, silica, or silicic acid.

3. The method for preparing aluminum-modulated MFI type zeolite molecular sieves using acidic fluorine media according to claim 1, characterized in that, The solid fluorine source is one of ammonium fluoride, sodium fluoride, or potassium fluoride.

4. The method for preparing aluminum-modulated MFI type zeolite molecular sieves using acidic fluorine media according to claim 3, characterized in that, The template agent is one of tetramethylammonium bromide, tetramethylammonium chloride, tetraethylammonium bromide, tetraethylammonium chloride, tetrapropylammonium bromide, tetrapropylammonium chloride, tetrabutylammonium bromide, or tetrabutylammonium chloride.

5. The method for preparing aluminum-modulated MFI type zeolite molecular sieves using acidic fluorine media according to claim 1, characterized in that, The amount of SAPO-34 added, based on the molar ratio of Al2O3 to SiO2 of 0–0.05, specifically represents 4.17–33.3% of the mass of SiO2.

6. An aluminum-modulated MFI type zeolite molecular sieve, prepared by any one of claims 1-5, characterized in that, The silicon-to-aluminum ratio is 10–∞, and the crystal size is 14–22 μm.

7. The aluminum-modulated MFI type zeolite molecular sieve according to claim 6, characterized in that, The X-ray diffraction pattern of the molecular sieve is consistent with the typical characteristic diffraction peaks of MFI type zeolite molecular sieve.

8. The application of the aluminum-modulated MFI type zeolite molecular sieve according to claim 6 or 7 in acid-catalyzed reactions, characterized in that, The acid-catalyzed reaction is an alkylation reaction or a cracking reaction.

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